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New Insight into Li/Ni Disorder in Layered Cathode Materials for Lithium ion Battery: A Joint Study of Neutron Diffraction, Electrochemical Kinetics Analysis and First-principles Calculations
Abstract
Although layered cathode materials LiNixMnyCo1-x-yO2 have attracted much attention due to their number of advantages, the issue of Li/Ni disorder seriously restricts their electrochemical properties. It is very important and pivotal for the better optimization of layered cathode materials to clearly explain the detailed relationships among the Li/Ni disorder, Li⁺ migration resistance, electrochemical kinetics and electrochemical properties. Here we focus on the LiNixMnyCo1-x-yO2 cathode material and report relationships among the crystal structures, Li⁺ migration resistance, electrochemical kinetics and electrochemical properties by combining neutron diffraction techniques, electrochemical kinetic analysis techniques and first-principles calculation methods. The results suggest that more Li⁺/Ni²⁺ ion exchange will shrink the inter-slab space thickness, causing a higher Li⁺ ion migration barrier and inferior electrochemical kinetics, all of which should be responsible for the limited electrochemical properties.
... Lithium-ion batteries are currently used as energy-storage technology and contain Li x -Ni y -Oz in different proportions in the city. They are widely used in transportation, including hybrid and electric vehicles (EVs) [91]. It has been observed that EVs influence the content of Ni in PM [92]. ...
... Additionally, public transportation in Santiago has incorporated nearly 2000 electric buses [95] since 2017, underscoring the importance of understanding the environmental implications of such technologies [93,94] use, e-waste, and disposal. This finding could prompt further investigations into the study of the elemental composition of PM to track changes in the vehicle market [91]. For example, the presence of Ba, Pb, Cr, and Fe-rich particles [96] on the leaf surface could indicate the popularity of the use of cars with combustion engines, while the presence of Ni-rich and rare earth elements (REEs)-rich particles could be linked to the use of EVs. ...
Green infrastructure, such as street trees, can help improve air quality, but the role of rainfall in cleaning total particulate matter (TPM) from tree leaves is not well understood, especially in cities like Santiago, Chile. This study measured TPM deposited on leaves and its elemental composition of two native tree species, Quillaja saponaria and Schinus molle, by five independent rainfall episodes. The results showed significant differences in how each tree species responded to rainfall. The total amount of TPM finally removed or retained at the leaf level in the five rainfall events studied was 4.72 and 8.43 mg/gldw for Q. saponaria and S. molle, respectively. Q. saponaria decreased TPM levels after rainfall, while S. molle exhibited mixed responses, increasing or decreasing TPM accumulation on leaves after different intensities of rainfalls. Elemental analysis revealed metals such as lithium and nickel—potentially linked to electric vehicle batteries—and tin and antimony– potentially linked to industrial processes. Rainfall benefited air quality by removing heavy metals from the atmosphere and aiding plant recovery from TPM accumulation. However, further research is needed on metal speciation in TPM and its foliar uptake by plants. This study provides some insights into the complex interactions between trees leaves, TPM deposition, and rainfall.
... Besides, Rietveld refinement of neutron diffraction pattern is also widely used to probe order and disorder quantitatively among cathode particles. For exaxmple, Zhao et al. [167]. successfully captured lower extent of Li-Ni mixng among NMC materials synthesised through co-precipitation (NMC(A)) compared with that obtained by solid-state reaction (NMC(B)) ( Fig. 10c) by this method. ...
... This effect disrupts the path of migration of lithium ions, increasing the impedance of the cell. 15 In addition, highly oxidized Ni species will react with the electrolyte, forming a surface film over the cathode and dissolving Ni 2+ into the electrolyte, causing the decomposition of the cathode and loss of electrolyte. 12 Moreover, during a high state of charge, the oxidation of oxygen ions can take place leading to loss of lattice oxygen, which results in transition metal (TM) dissolution. ...
We conducted a qualitative comparison between two methods for detecting side reactions, the voltage hold and voltage decay methods using a high-precision coulometry (HPC) tester. The measurements were conducted with Si-G/NMC811 commercial cells for three different temperatures and four different states of charge (SoC) to determine the voltage and the temperature dependency of side reactions. Here, we show that the voltage hold and the voltage decay methods deliver comparable results when determining the differential capacity with an incremental capacity analysis (ICA) instead of a single pulse for the voltage decay method. Both methods presented a good agreement for high temperatures and high SoC cases. Only at 90% SoC was there a discrepancy of 15% on the leakage capacities, which was attributed to the peak shape of the ICA curve. Therefore, it was found advantageous to analyse the ICA shape of the respective cells when performing such measurements. In addition, with the end of charge point and end of discharge point slippage evaluation, it was possible to observe that couple side reactions dominate the leakage currents at higher SoCs and lead to reversible losses. The irreversible losses remain almost constant for SoCs higher than 50%.
... 24 The D TMO and D Li values are calculated using the following equations (1) and (2), respectively, where "c" denotes the lattice parameter and "z" is the oxygen position. 25 The narrow D Li for Li due to the Li + /Ni 2+ ion exchange is not desirable because of increasing Li + migration resistance. 16 ...
The mixed hydroxide precipitate (MHP), an intermediate product derived from the laterite ores, is the most abundant Ni source on the earth's crust. Herein, the potential use of MHP without purification for cathode synthesis is explored. The characteristics of NMC111 with 0 to 51% wt. MHP addition are compared in terms of crystal structure, morphology, and electrochemical properties. The typical layered cathode structure is preserved up to the 12.7 wt. % MHP addition. Rietveld refinement results confirm that the lattice parameters and Li‐slabs were expanded as the amount of the MHP increased. The electrochemical results show that the first discharge capacity does not decrease until the 5.1 wt. % MHP addition. Furthermore, the long‐term stability is improved by increasing MHP addition. While the pristine NMC keeps its 81% of first discharge capacity after 100 cycles, 5.1 wt. % MHP added sample retained 88%. Although the MHP addition tends to lower the rate capability of the cathode, the addition of MHP up to 2.6 wt. % does not compromise fast charge and discharge properties. EIS analyses show that the MHP addition reduces the charge transfer resistance of the cathode, which is a clue to enhanced Li‐ion diffusivity. MHP derived Li(Ni0.333Co0.333Mn0.333)O2 as a cathode material for Li‐ion batteries investigate the effect of MHP in the range between (0 and 51%) as a Ni Mn and Co source for NMC111 cathode synthesis using sol‐gel technique. The change in crystallographic structure, chemistry, and electrochemical performance is discussed. The MHP addition up to the 5.1 wt. % improves capacity retention of 88% after 100 cycle.
... The D/r 2 for Ca-NMC is consistently smaller than SX-NMC, which seems to suggest a decrease in the bulk Li-ion diffusion in Ca-NMC. However, the reaction with CaI 2 does not lead to any appreciable irreversible change in the bulk structure, specifically the Li-Ni anti-site defect concentration, which is relevant to the bulk Li-ion diffusion 34,35 and remains 1.8(7)% in Ca-NMC (full structural data available in Table S3), as 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 22 opposed to 2.5(1)% in SX-NMC. Hence, the Li-ion diffusivity in the bulk crystal lattice is not expected to be affected by the surface modification. ...
The surface of the layered transition metal oxide cathode plays an important role in its function and degradation. Modification of the surface structure and chemistry is often necessary to overcome the debilitating effect of the native surface. Here, we employ a chemical reduction method using CaI2 to modify the native surface of single-crystalline layered transition metal oxide cathode particles. High-resolution transmission electron microscopy shows the formation of a conformal cubic phase at the particle surface, where the outmost layer is enriched with Ca. The modified surface significantly improves the long-term capacity retention at low rates of cycling, yet the rate capability is compromised by the impeded interfacial kinetics at high voltages. The lack of oxygen vacancy generation in the chemically induced surface phase transformation likely results in a dense surface layer that accounts for the improved electrochemical stability and impeded Li-ion diffusion. This work highlights the strong dependence of the electrode’s (electro)chemical stability and intercalation kinetics on the surface structure and chemistry, which can be further tailored by the chemical reduction method.
... To determine the degree of disorder in the layered structure, the R-factor (=intensity ratio of [I (006) + I (012) /I (101) ]) has been evaluated based on the XRD peaks. The R-factor is known as a good indicator to represent the hexagonal ordering with layered structure [28,[57][58][59]. A lower R-factor implies a well-ordered structure. ...
The well-defined layered structure for Li⁺ (de)intercalation of transition metal oxide cathodes plays a crucial role in delivering high capacity for lithium-ion batteries. Therefore, structural deformations of the layered structure are often considered as the evidence of deterioration in the battery performance and stability. In this study, the surface degradation mechanism of the layered LiNi1/3Co1/3Mn1/3O2 cathode is examined on charge–discharge using an operando Raman cell. We revealed the surface degradation process of the cathode with the A1g Raman spectral window (∼600 cm⁻¹) in the voltage range of 2.8–4.35 V, and proposed the nucleation-merging mechanism. The spectral shifts and mappings have been compared between the early-stage and later-stage cycles (≥15 cycles). It has been identified that the degradation process not only involves the structural changes (i.e., nucleation of the degenerated layers), but also the growth/merging between the degenerated layers during charge and discharge. This observation provides key information on how the reconstructed surface can expand during cycling.
... This provides a possible explanation for why Mn 3+ increases the Li/Ni disordering. As previous literature reported, Ni existing in the lithium layer reduce the thickness of the lithium layer [47]. In our case, LLO-V with larger Li/Ni disordering exhibits the expansion of the thickness of Li-layer. ...
The degree of electrochemical activation of Li2MnO3 component has a vital role in achieving high capacity in Co-free Li-rich layered cathodes. However, due to the segregation of Li2MnO3 component in these cathodes sintering at high temperature, it is difficult to be fully activated. Herein, a strategy is proposed to alleviate segregation of Li2MnO3 component by reducing the oxidation state of partial Mn with tailoring oxygen partial pressure during heat treatment. Combined with X-ray photoelectron spectroscopy, electron energy loss spectrum and soft X-ray absorption spectroscopy, some slight Mn³⁺ have been confirmed to be introduced into the bulk lattice. Monte Carlo simulation is applied to identify the Mn³⁺ positive effect on alleviating LiMn6 segregation. As a result, the material sintered in the O2-deficient environment exhibits an accelerated activation of Li2MnO3 component at the pre-cycles and delivers a high capacity over 250 mAh g⁻¹ with the capacity retention about 92% over 100 cycle. This strategy provides a simple but effective method to exploit the electrochemical activity in Co-free Li-rich layered oxides.
... The presence of Ni 2 + in the Li layer inhibits the diffusion of Li + ions and decreases the reversible capacity. If Li + ions occupy the transition metal (TM) layers, the crystal lattice will be hard to deintercalate, resulting in poor electrochemical performance [14][15][16][17] . Nevertheless, an appropriate content of excess Li and cation mixing can stabilize the crystal structure of the Li transition metal oxide electrodes at high states of charge [18][19][20][21] . ...
In this study we investigated the effect of the Li-excess on electrochemical properties of LixNi0.6Co0.2Mn0.2O2 cathode materials, which was obtained by sintering Ni0.6Co0.2Mn0.2(OH)2 with a various amounts of LiOH (samples with Li-excesses of 5, 10, 20, and 25 mol % are denoted herein as NCM-5, NCM-10, NCM-20, and NCM-25, respectively). The LixNi0.6Co0.2Mn0.2O2 samples retained their excellent crystalline ordering in the rhombohedral layered structure, with the space group R3-m. When the Li-excess increased, Rietveld refinement revealed that cation mixing occurred, the lattice parameters decreased, the transition metal slab thickness increased, and the inter-slab Li space thickness decreased. Nevertheless, an appropriate degree of cation mixing could retain the structural stability and improve the rate capability of the electrodes. It was found that the sample containing the 20 mol % Li-excess (NCM-20) achieved the best cyclic stability, with a capacity retention of 90% at a current rate of 1C/1C for 200 cycles between 2.8 and 4.5 V at room temperature. In situ X-ray diffraction confirmed the greater stability of the crystal phase and physical structure of NCM-20 upon initial cycling. In operando microcalorimetry revealed that the thermal stability of NCM-20 was greater than that of the other cathode materials; it exhibited markedly less heat-generated flux and prevented thermal runaway.
Failure of the active particles is inherently electrochemo‐mechanics dominated. This review comprehensively examines the electrochemo‐mechanical degradation and failure mechanisms of active particles in high‐energy density lithium‐ion batteries. The study delves into the growth of passivating layers, such as the solid electrolyte interphase (SEI), and their impact on battery performance. It highlights the role of elevated temperatures in accelerating degradation reactions, such as the dissolution of transition metals and the formation of new SEI layers, leading to capacity fade and increased internal resistance. The review also discusses the mechanical degradation of electrode materials, including the fracture of active particles and the impact of stress on electrode performance. Advanced characterization techniques, such as cryogenic scanning transmission electron microscopy and 3D tomography, are explored to provide insights into the structural and chemical evolution of battery materials. By addressing the interplay between chemical, mechanical, and thermal factors, this review aims to provide guidelines for the chemistry development, material selection, structural design as well as recycling of next‐generation batteries with high safety, durability, and high energy density.
The desire to obtain higher energy densities in lithium–ion batteries (LIBs) to meet the growing demands of emerging technologies is faced with challenges related to poor capacity retention during cycling caused by structural and interfacial instability of the battery materials. Since the electrode–electrolyte interface plays a decisive role in achieving remarkable electrochemical performance, it must be suitably engineered to address the aforementioned issues. The development of coatings, particularly on the surface of cathode materials, has been proven to be effective in resolving interfacial issues in LIBs. The use of atomic layer deposition (ALD) over other surface coating techniques is advantageous in terms of coating uniformity, conformity, and thickness control. This review article provides a summary of the impact of various ALD-engineered surface coatings to the cycling performance of different intercalation cathode materials in LIBs. Since ALD allows coating development on complex substrates, this article provides a comprehensive discussion of coatings formed directly on a powder active material and composite electrode. Additionally, a perspective regarding the fundamental deposition parameters and electrochemical testing data to be reported in future research is provided.
The Detroit Big Three General Motors (GMs), Ford, and Stellantis predict that electric vehicle (EV) sales will comprise 40–50% of the annual vehicle sales by 2030. Among the key components of LIBs, the LiNixMnyCo1−x−yO2 cathode, which comprises nickel, manganese, and cobalt (NMC) in various stoichiometric ratios, is widely used in EV batteries. This review reveals NMC cathodes from laboratory research. Furthermore, this study examines the environmental effect of NMC cathode production for EV batteries (including coating technologies), encompassing aspects such as energy consumption, water usage, and air emissions. Although gaps persist in NMC cathode environmental assessments (NMC111, NMC532, NMC622, and NMC811), limited life cycle assessments “(LCA)” have been conducted. Most available data originate from Asia (primarily China), accounting for 85% of the production of EV LIB cathode materials. The concept of battery passports for data collection on LIB components has been proposed to facilitate material traceability as a system for ensuring a sustainable supply chain for critical minerals. The automotive industry’s shift to electrification necessitates a sustainable supply chain from mine to vehicle end-of-life. As the critical mineral supply moves from Asia to North America, environmentally friendly industrial methods must be studied to provide this supply chain direction.
Due to their stable crystal framework, promising energy density, and structural versatility, layered 3d transition metal oxides have emerged as the preferred cathodes for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). While extensive research has individually addressed the lithium and sodium 3d transition metal layered oxides, the differences and interconnections between the two types of materials have largely been overlooked. Effectively utilizing these summaries is essential for driving innovative structural designs and inspiring new insights into the structure‐property relationships. This review comprehensively bridges this gap by meticulously examining the disparities and links in the behavior of the layered oxides upon Li⁺ and Na⁺ storage and transfer. Key aspects, including atomic and electronic structure, phase transition mechanisms, charge compensation mechanisms and electrochemical kinetics, are carefully summarized. The implications of these aspects on the battery cycle life, energy density, and rate capability are thoroughly discussed. Additionally, by leveraging the unique characteristics of each oxide structure, this review explores the interconnection between lithium and sodium layered oxides in depth. Finally, a concise perspective on future targets and direction of 3d layered oxides is deduced and proposed.
First-principles calculations are employed to investigate the structural, electronic, magnetic, thermoelectric, and electrochemical characteristics of Nickel-rich layered cathodes by substitution of Zn and Cr such as LiNi1-x-yZnyCrxO2 (with x= 0.00, 0.16 and 0.32, y = 0.00 and 0.16). The structure of pure LiNiO2 and substituted are organized in a trigonal arrangement inside the P3m1 space group. Using PBE-GGA approximation, the spin-polarized calculation of pure LiNiO2 in a spin-down channel exhibits a band gap of 0.48 eV. Whereas Zn and Cr substitution results in the band gap reduction to zero, and metallic behavior is observed. Electronic charge density calculation Ni(Zn, Cr)-O reveals covalent bonding. In electrochemical investigation, by the increasing substitution concentration of Zn and Cr in LiNi1-x-yZnyCrxO2 significant improvements are observed at 4.65-3.89 V potential with a good theoretical discharge capacity of 48-246 mAhg-1. The exchange constants N∘α and N∘β demonstrate negative values that validate the ferromagnetic nature of substituted material. The thermoelectric parameters have been determined using the BoltzTraP code and the highest ZT value of 0.35 is obtained for LiNi0.52Zn0.16Cr0.32O2. These results offer a new perspective of doping techniques for nickel-rich cathode materials, providing helpful insight for the development of high-performance cathodes for lithium-ion battery applications
Ni‐rich layered oxides are considered as promising cathodes for next‐generation lithium‐ion batteries. However, they still suffer microstructure and surface instability particularly under high operating voltage, leading to rapid capacity fading and battery failure. In this context, Ni‐rich layered cathodes (LiNi x Co y Mn 1− x − y O 2 ; LNCM) with aluminum and indium co‐modified crystal and surface structures are developed by a simple one‐pot calcination approach. Battery tests show that the Al and In co‐modified LNCM electrodes demonstrate remarkably enhanced rate capability and cycling stability compared with the pristine LNCM, Al‐doped LNCM, and In‐modified LNCM counterparts. Further characterizations reveal a simultaneous suppression of cracking and resistive film growth. The improved microstructural and surface stability originate from the synergistic functions of Al and In co‐modification. The incorporation of Al ³⁺ into transition metal slab significantly reduces the Li ⁺ /Ni ²⁺ antisite, which noticeably mitigates the undesired layer to rock‐salt phase transformation. The In ³⁺ dopant dispersed in Li interslab can dissipate the anisotropic lattice strain, enabling greatly improved reversibility of H2↔H3 phase transition occurred in delithiation‐lithiation processes. Meanwhile, the synchronously formed LiInO 2 adherent coatings deplete lithium residues, facilitate lithium‐ion transfer, and resist electrolyte corrosion. Microstructure and surface engineering through Al and In co‐modification offer a promising design strategy for Ni‐rich layered cathodes.
Ni-rich layered oxides have been widely studied as cathodes because of their high energy density. However, the gradual structural transformation during the cycle will lead to the capacity degradation and potential decay of the cathode materials. In this paper, first-principle calculations were used to investigate the formation energy, and geometric and electronic structure of Mg-doped LiNiO2 cathode for Li-ion batteries. The results show that Mg doping has little effect on the geometric structure of LiNiO2 but has great effect on its electronic structure. Our data give an insight into the microscopic mechanism of Mg-doped LiNiO2 and provide a theoretical reference for experimental research, which is helpful to the design of safer and higher energy density Ni-rich cathodes.
In this work, all calculations were performed by the VASP package; the PBE functional in the generalized gradient approximation (GGA) was employed to describe the exchange–correlation interactions. An energy cutoff of 520 eV and a 5 × 5 × 3 Monkhorst–Pack mesh of k-point sampling in the Brillouin zone were chosen for all calculations. All atoms were relaxed until the convergences of 10−5 eV/f.u in energy and 0.01 eV/Å in force were reached.
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Abstract
The Lithium and Manganese-rich layered oxides with the formula Li1.2Ni0.1Mn0.6Co0.1O2 (LMR-NMC) are considered the most promising cathode materials for next-generation lithium-ion batteries due to their high energy densities, low cost, high thermal stability, and environmental safety. This paper reports the synthesis of LMR-NMC oxides in the presence of glycine-urea or citric acid-urea as surface modifiers for LMR-NMC-A and LMR-NMC-B, respectively using the solution combustion technique. The crystal structures of LMR-NMC-A and LMR-NMC-B samples were confirmed to have Hexagonal α-NaFeO2 structures in the R-3m space group. The HRSEM images reveal two different morphologies of the samples; Nano platelet (LMR-NMC-A) and Cubic-like (LMR-NMC-B). The cyclic voltammetric studies (CV) performed at a low scan rate value of 0.1 mV s−1 and a potential window of 2.0 - 5.0 V confirm the formation of the irreversible Li2MnO3 phase above 4.8V in the first cycle and the presence of three redox peaks corresponding to Ni2+/Ni4+, Co2+/Co3+, and Mn3+/Mn in the subsequent cycles. The electrochemical properties of LMR-NMC-A and LMR-NMC-B electrodes demonstrated an initial discharge-specific capacity of 325.21 mAh g−1 and 300 mAh g−1, respectively, in a potential range between 2.0-5.0V at a 0.1C rate. A comparison of the electrochemical properties of both morphologies of LMR-NMC revealed that the Nanoplatelet-like (LMR-NMC-A) sample performs better than the cubic-like (LMR-NMC-B) sample. The Nanoplatelet-like layered oxide demonstrated a high specific capacity of 180mAh g−1 at a 1C rate and a high Coulombic efficiency of 86% after 200 cycles. BET indicates that LMR-NMC-A has a significantly higher surface area and substantial pore volume than LMR-NMC-B, addressing high voltage working capability, low voltage fading, and high specific capacitance values to a greater extent. These findings confirm the suitability of LMR-NMC-A as a cathode material for lithium-ion batteries used in high-load appliances and heavy vehicles.
Ni‐rich layered oxides are one of the most attractive cathode materials in high‐energy‐density lithium‐ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long‐range cationic disordering of Co‐free Ni‐rich Li1−m(Ni0.94Al0.06)1+mO2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near‐surface region of NA particles with very low cation disorder (NA‐LCD, m≤0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a “core–shell” structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA‐HCD, 0.06≤m≤0.15) that lead to a slow capacity decay upon cycling.
Ni‐rich layered oxides are one of the most attractive cathode materials in high‐energy‐density lithium‐ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long‐range cationic disordering of Co‐free Ni‐rich Li1‐m(Ni0.94Al0.06)1+mO2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near‐surface region of NA particles with very low cation disorder (NA‐LCD, m ≤ 0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a “core‐shell” structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA‐HCD, 0.06 ≤ m ≤ 0.15) that lead to a slow capacity decay upon cycling.
The ion-intercalation-based rechargeable batteries are emerging as the most efficient energy storage technology for electronic vehicles, grids, and portable devices. These devices require rechargeable batteries with higher energy-density than commercial Li-ion batteries, which are intrinsically limited by specific capacities and electrochemical potentials of transition-metal (M) electrode materials. Over the past decades, a significant number of studies have focused on exploring coordination environments and electronic origins of these materials based on ligand field theory (LFT). However, studies to understand and manipulate the relationship between their local-structural characteristics and electrochemical properties are limited. In this review, we comprehensively discussed how the combining of LFT and first-principles calculations can be used to derive Fermi levels that determine electrochemical potential, crystal field stabilization energy, and anionic redox activity. Based on this, a series of strategies are proposed to improve the phase-stability and energy-density of intercalation-type electrode materials, such as ion-intercalation potential tuning of rigid-band systems and electrode phase stability regulations with different M periods. Two high energy-density cathode materials, M-free LiBCF2 and Li-free group-VB/VIB MX2 (X = S, Se), are successfully designed from the aforementioned principles derived. Finally, we also highlight further directions for designing better intercalation-type materials based on LFT and their opportunities/challenges.
Ni-rich layered lithium transition metal oxides have been considered as one of the most promising cathodes for next-generation lithium-ion batteries (LIBs) because of their high capacities and affordable costs. However, they still suffer bulk and surface structural instability, leading to rapid performance decay and subsequent cathode failure. In this context, Ni-rich layered cathodes with indium modified crystal and surface structures are developed by a simple one-pot calcination approach. Battery tests manifest that the indium modified LiNi0.8Co0.1Mn0.1O2 electrodes exhibit remarkably enhanced rate capability and cycling stability compared to the pristine one, including under high operating voltage condition. Further studies evidence a simultaneous mitigation of intra/inter-granular mechanical cracks and resistive surface films growth, which directly embodied in a dramatically suppressed ohmic loss after long-term cycling. The improved microstructural and surface stability are attributed by the synergistic functions of indium modification. On the one hand, trace amount of In³⁺ occupy crystalline Li⁺-site, which not only dissipate the intrinsic lattice strain during cycling, but also reduce Li⁺/Ni²⁺ antisite to avoid the undesired layer to rock-salt phase transformation. On the other hand, the rest of indium deplete lithium residues, and form conductive LiInO2 adherent coatings to protect the cathode from side reactions with electrolyte. The present work demonstrates that microstructure and surface engineering through indium modification offers a promising design strategy for further improvements of Ni-rich layered cathodes.
The rapid industrial advances in portable electronics and electric vehicles are strongly influencing the development of electrochemical energy sources, especially lithium-ion batteries. Research is being actively pursued to improve the performance of lithium-ion batteries in areas relating to higher energy density and capacity, longer service life, increased safety, etc. In order to address such issues a thorough understanding of the behavior of battery materials under realistic operating conditions is required, which forms the base necessary for a targeted material engineering. Diffraction methods based on X-ray, synchrotron and neutron radiation are powerful tools for studies of battery materials, allowing a deep understanding of structural evolution, redox processes and transport properties under real operating conditions. The current review presents and discusses X-ray, synchrotron and neutron diffraction techniques and their role in battery material research. In addition, the types of in situ/in operando cell design and materials, the role and application of neutron scattering and imaging techniques for battery research are briefly discussed, along with modern trends in diffraction-based methods for studies of electrochemical energy systems.
Layered LiNi0.8Mn0.1Co0.1O2 (NMC811) has received considerable attention as a high-energy density cathode for next generation lithium-ion batteries (LiBs). The charge compensation process underlying the achievement of high capacity is generally described by a two-stage redox reaction between Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺. However, the increase of the Ni for the high battery capacity often leads to a significant degradation of the NMC811 material. In this study, the magnetic property of the NMC811 battery system has been compared at low (4.3 V) and high (4.7 V) cut-off voltages. There has been a notable drop in the magnetic moment from 2.33 μB (pristine) to 2.11 μB and 2.07 μB for the cathodes cycled at 4.3 V and 4.7 V, respectively. The amount of low-spin Ni⁴⁺ increased in the cathode material after the high voltage cycling. A density-functional theory (DFT) simulation has been adopted to further understand the discrepancy in the magnetic moment upon the different voltages. The local magnetic moment (μB) of the transition metals are evaluated with different atomic environments including the Li/Ni exchange. Also, the corresponding density of states (DOS) are provided. It is shown that the electrochemical performance will significantly deteriorate when a high antiferromagnetic interaction occurs with the Li/Ni exchange.
LiNi0.80Co0.15Al0.05O2 (NCA) is widely used in Li-ion batteries due to its high reversible capacity and energy density. However, residual Li on the exterior of NCA suffers severe side reactions with air during preparation process, which destroy the surface of cathode material and cause irreversible capacity loss. This performance degradation has remained an issue that needs to be solved. Herein, a bifunctional modification strategy consisting of V doping and coating with Li3VO4 is reported to address this issue. V-doped and Li3VO4-coated NCA (VNCA) cathode materials were obtained using solid-phase method through one-step sintering. External Li3VO4 coating layer formed from the consumption of surface residual Li prevents the occurrence of interfacial adverse reactions. Furthermore, V doping stabilizes lattice structure. Obtained cathode material can improve the stability and rate capability of Li-ion batteries. 100-cycle cycle retention rate of VNCA coated with 2-M% Li3VO4 at 1 C is 89.32%, which is significantly higher than that of NCA (67%). Additionally, specific discharge capacity of VNCA at 10 C (145.6 mAh·g⁻¹) is considerably higher than that of NCA (129.8 mAh·g⁻¹).
Lithium-ion batteries (LIBs) are remarkable electrochemical energy storage systems, which play a critical role in modern society. Demanding new applications have been pushing for further battery advancements, such as developments of all-solid-state and sodium-ion batteries. However, both the LIBs and these new technologies still face challenges that limit their full realization. These include irreversible electrochemical reactions, electrode structure degradations, and surface/interface side reactions. Solving them requires comprehensive characterizations of battery systems over multiple length and time scales. Among the advanced probing techniques, neutron-based ones have unique advantages in exploring battery material structures, ionic diffusions, electrochemical reactions, and cell failure mechanisms, information that will aid the development of next-generation high-performance battery systems. In this Perspective, we briefly review the principles and characteristics of various neutron techniques and their recent applications in battery system studies. Operando neutron characterizations of batteries on spatiotemporal scales and prospects of their future designs and applications are discussed.
The surface of the layered transition metal oxide cathode plays an important role in its function and degradation. Modification of the surface structure and chemistry is often necessary to overcome the debilitating effect of the native surface. Here, we employ a chemical reduction method using CaI2 to modify the native surface of single-crystalline layered transition metal oxide cathode particles. High-resolution transmission electron microscopy shows the formation of a conformal cubic phase at the particle surface, where the outmost layer is enriched with Ca. The modified surface significantly improves the long-term capacity retention at low rates of cycling, yet the rate capability is compromised by the impeded interfacial kinetics at high voltages. The lack of oxygen vacancy generation in the chemically induced surface phase transformation likely results in a dense surface layer that accounts for the improved electrochemical stability and impeded Li-ion diffusion. This work highlights the strong dependence of the electrode's (electro)chemical stability and intercalation kinetics on the surface structure and chemistry, which can be further tailored by the chemical reduction method.
Controlling Li/Ni disordering has always been a priority in designing Co‐free layered oxide cathodes. The Li/Ni disordering is an atomic‐scale structural defect that has been extensively studied by macroscopic statistical characterizations. Significantly less is known about its microstructure in the layered structure and correlations with electrochemical performance. In this work, combining multiscale structural characterizations, it is found that Li/Ni disordering surprisingly takes various microstructural forms in Co‐free layered cathodes. Li/Ni disordering at insufficient calcination temperature tends to manifest as localized rock salt nanodomain in the layered structure. However, an excessively high calcination temperature causes Li/Ni disordering as a massive rock salt phase inside the particles. Only at an appropriate calcination temperature, the Li/Ni disordering is present in the layered structure as the form of well‐known anti‐site defects. These microstructural differences lead to widely varying electrochemical performance, and an in‐depth structure‐performance connection is built. Besides, the above results also reflect that more careful and precise control of experimental conditions is required to synthesize Co‐free layered cathodes. These findings may inspire the design of novel Co‐free cathodes and light the way forward.
Cobalt‐free LiNixMn1−xO2 (NM, x ≥ 0.5) layered oxides are considered to be promising cathode materials for next‐generation lithium‐ion batteries because of exceptionally high capacity and low cost, yet the fundamental role of manganese ions in the NM layered structure and rate performance has not been fully addressed to date. Herein, a series of Ni‐fixed LiNi0.6Co0.4−xMnxO2 (x = 0, 0.1, 0.2, 0.3, and 0.4) systems are employed as cathode materials to investigate the functionality of Mn ions on their structures and electrochemical properties. It is found that contrary to prior reports, the change in the c‐axis lattice parameter is not in close connection with the rate performance of NM cathodes. In particular, superconducting quantum interference device (SQUID) measurements are performed to verify the fact that Mn³⁺ and Mn⁴⁺ ions with high spin states cause severe magnetic frustration in the structures of cathode materials, which profoundly aggravates the Li/Ni ionic disorder and blocks Li⁺ migration, contributing to inferior rate performance. In addition, Li⁺ migration hindered by Li/Ni disorder, is theoretically demonstrated by ab initio calculation. This work not only provides fresh insight into the role of Mn in NM layered oxide cathodes but also proposes an effective strategy to resolve their inferior rate performance.
Understanding the nature of and controlling the cation disorder in kesterite-based absorber materials remain a crucial challenge for improving their photovoltaic (PV) performances. Herein, the combination of neutron diffraction and synchrotron-based X-ray absorption techniques was implemented to investigate the relationships among cation disorder, defect concentration, overall long-range crystallographic order, and local atomic-scale structure for (AgxCu1-x)2ZnSnSe4(ACZTSe) material. The joint Rietveld refinement technique was used to directly reveal the effect of cation substitution and quantify the concentration of defects in Ag-alloyed stoichiometric and nonstoichiometric Cu2ZnSnSe4(CZTSe). The results showed that 10%-Ag-alloyed nonstoichiometric ACZTSe had the lowest concentration of detrimental antisite CuZndefects (∼8 × 10¹⁹defects per cm⁻³), which was two times lower than pristine and five times lower than the stoichiometric compositions. Moreover, Ag incorporation maintained the concentrations of beneficial Cu vacancies (VCu) and antisite ZnCudefects to >2 × 10²⁰defects per cm⁻³. X-ray absorption measurements were performed to verify the degree of disorder through the changes in bond length and coordination number. Therefore, the incorporation of Ag into the CZTSe lattice could control the distribution of antisite defects, in the form of short- and long-range site disorder. This study paves the way to systematically understand and further improve the properties of kesterite-based materials for different energy applications.
Nickel-rich NMC (LiNixMnyCo1−x−yO2, x ⩾ 0.8) electrode materials are known for their great potential as lithium battery cathode active materials due to their high capacities, low cost, and environment friendliness. However, these materials confront some technical challenges such as structural, surface, and electrochemical instability while different synthesis methods have large influences on NMC morphology, structure, and electrochemical performance. This review summarizes the most common synthesis techniques which have been employed to prepare high-quality Ni-rich positive electrode materials. Besides, recently reported and widely recognized studies on the degradation and mitigation mechanisms of Ni-rich electrodes are outlined in this paper. This review summarizes different studies on doping of Ni-rich materials which are useful for enhancing the capacity and performance and mitigating structural decay of the electrodes. Moreover, surface modifications by thin coatings with metal oxides and Li containing metal oxide layers are also reviewed as those overlayers can enhance stability of NMCs during the long-term cycling. Therefore, the focus of this paper is on fabrication of Ni rich NMC material, as well as reviewing the effect of doping, surface coating and synergistic effect of both for enhancing Ni-rich electrode material performance.
Nickel‐rich layered oxides are one of the most promising cathode candidates for next‐generation high‐energy‐density lithium‐ion batteries. However, due to similar ion radius between Li⁺ and Ni²⁺(0.76 and 0.69 Å), the Li⁺/Ni²⁺ mixing phenomenon seriously hinders the migration of Li⁺ and increases kinetic barrier of Li⁺ diffusion, resulting in limited rate capability. In this work, the introduction of Ce⁴⁺ to effectively improve electrochemical properties of Ni‐rich cathode materials is proposed. The LiNi0.8Co0.15Al0.05O2 (LNCA) is modified with an additional precursor oxidization process using an appropriate amount of (NH4)2Ce(NO3)6. The Ce(NO3)6²⁻ easily obtains electrons and generates reduction reactions, while Ni(OH)2 is prone to electron loss and oxidation reaction. The participation of (NH4)2Ce(NO3)6 can promote the oxidation of Ni²⁺ to Ni³⁺, thereby reducing the Li⁺/Ni²⁺ mixing and increasing the structural stability of LNCA samples. Ce⁴⁺ cation doping can impede Li⁺/Ni²⁺ mixing of LNCA cathode materials upon the long‐term cycles. Both rate performance and long‐term cyclability of Li[Ni0.8Co0.15Al0.05]0.97Ce0.03O2 (LNCA‐Ce0.03) sample are significantly improved. Besides, a practical pouch cell based on the cathode presents sufficient gravimetric energy density (≈300 Wh kg⁻¹) and cycling stability (capacity retention of 81.3% after 500 cycles at 1 C).
One of the bottlenecks limiting the cycling stability of high voltage lithium metal batteries (LMBs) is the lack of suitable electrolytes. Herein, phenyl vinyl sulfone (PVS) is proposed as a multifunctional additive to stabilize both cathode and anode interfaces as it can be preferentially oxidized/reduced on the electrode surfaces. The PVS derived solid electrolyte interphase films can not only reduce the transition metal dissolution on the cathode side, but also suppress the Li dendrite spread on the lithium anode side. The Li||Li symmetric battery with PVS addition delivers longer cycle life and a higher critical current density of over 3.0 mAh cm⁻². The LiNi0.8Co0.1Mn0.1O2 (NCM811)||Li full cell exhibits excellent capacity retention of 80.8% or 80.0% after 400 cycles at 0.5 C or 1 C rate with the voltage range of 3.0–4.3 V. In particular, the NCM811|||Li cell under constrained conditions remains operation over 150 cycles. This work offers new insights on the electrolyte formulations for the next generation of LMBs.
Ni-rich transition metal oxide cathodes (Ni-rich NMC), which can be represented as the formular of LiNixCoyMn1-x-y (x ≧ 0.5, y < 0.5), have emerged as the promising electrode material for high-energy density lithium-ion batteries. This battery type can achieve high capacities due to the high amount of Ni as it can provide a large number of electrons by two-stage redox reaction between Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺. However, the increase of the Ni content in the NMC cathodes often results in a capacity fading and poor cycle life of the batteries because of the cathode degradation. Herein, the origin of the active involvements of the Ni element in the degradation process has been studied. The degradation of the Ni-rich NMC is likely to be triggered by NiO on the surface with the cathode-electrolyte interphase (CEI) formation, followed by the disorder in the layered structure both at surface and bulk after the initial cycle. The difference in the Ni content of the active material leads to the discrepancy of the surface environment. To gain deep insights into the aggressive deterioration of the Ni-rich NMC material, a density functional theory (DFT) simulation has been adopted for the cathodes with different Ni concentrations (Ni: 10%, 33%, 50%, 80%, and 100%). Also, the electronic structure of LiNi0.5Co0.2Mn0.3O2, and LiNi1/3Co1/3Mn1/3O2 are examined at 50% Li⁺ (de)intercalation. The findings deduced from the DFT study suggest that the Ni(d)-O(p) character with high oxidation Ni (Ni³⁺ and/or Ni⁴⁺) is the key to understand the (electro)chemical process involved with the degradation mechanism of the cathode.
Ni-rich layered cathode LiNi0.8Mn0.1Co0.1O2 (NMC811) have been facing serious structural issues including high degree of Li/Ni mixing and poor surface stability, which lead to poor electrochemical cycling performances compared to other layered cathode with lower Ni content. Various surface coatings have been investigated to enhance the electrochemical performances of Ni-rich cathode. While, most work focus on the materials and methods of coating, and few has explored the subtle structural variations of cathode particles after coating. In this work, Li2ZrO3 coating induced structural variations of NMC811 have been carefully investigated. Ordered occupancy of Ni in Li slab with reduced Li/Ni mixing degree is firstly discovered after Li2ZrO3 coating. Moreover, the O–O distance becomes longer with less active O on surface, which can greatly suppress surface side reactions at high potentials. The obtained large reversible capacity and excellent capacity retention can be ascribed to the subtle structural variations of NMC811 after Li2ZrO3 coating.
With the development of high energy density battery technology, layered transition metal oxide cathode materials, particularly Ni-rich layered cathodes of Li-ion batteries are urgently required due to its high energy density. However, Li/Ni intermixing inevitably occurs in Ni-rich cathode materials and affects the materials in terms of structure and performance. This review comprehensively summarizes the causes of Li/Ni intermixing and analyzes its inevitability due to ionic radius, Ni migration, magnetic interactions, and thermal stability. In addition, the effect of Li/Ni intermixing on materials is summarized, particularly its benefits, which have not yet been comprehensively examined. Finally, the methods for regulating Li/Ni intermixing that corresponds to its causes are presented in detail. This review can help researchers fully understand Li/Ni intermixing and propose solutions for the current shortcomings of Li/Ni intermixing research and directions for future studies.
Factors affecting the cycling life of cylindrical lithium-ion batteries of LiNi0.8Co0.15Al0.05O2 (NCA) with graphite were examined in terms of the rechargeable capacity and polarization of NCA derivatives of LizNi0.8Co0.15Al0.05O2-δ (0.8 ≤ z ≤ 1.05). NCA derivatives with rock-salt domains in the structure were prepared by a co-precipitation method and the structures of [Li1-yNiy]3(b)[Ni,Co,Al]3(a)O26(c) based on a space group of R3m were refined by a Rietveld method of the XRD patterns. The electrochemical reactivity of the NCA derivatives with rock-salt domains was examined in non-aqueous lithium cells, and it was found that the rechargeable capacities (Q) of the samples decrease linearly as the amount of rock-salt domain (y) increases. An empirical relation is obtained to be Q = 181.4 - 725.5y in which Q reaches zero at y = 0.25, which is derived from not only the capacity loss owing to inactive rock-salt domains but also the polarization increase. The galvanostatic intermittent titration technique (GITT) measurement told us that polarization of NCA derivatives increases when the amount of rock-salt domains is above 2%, i.e., y > 0.02, and such a relation is remarkable in the lithium insertion direction into the structure, which is ascribed to slow lithium ion mobility due to nickel ions in the lithium layers. The NCA derivatives with increased rock-salt domains of above 2% deteriorate rapidly in non-aqueous lithium cells upon charge and discharge cycles, which is ascribed to the cumulative increase in polarization during charge and discharge. An extended cycling test for cylindrical lithium-ion batteries of the NCA derivatives with a graphite negative electrode at elevated temperature was performed and the quantitative relation is discussed thereof.
High crystallinity Li-rich porous materials integrating with an in situ formed surface containing carbonaceous compounds are synthesized through a facile approach. The rationally designed procedure involves the formation of a specific morphology of a hydroxide precursor assisted by a self-made template and subsequent high temperature treatment to obtain Li1.2Mn0.56Ni0.16Co0.08O2 target product. The porous morphology is investigated using field-emission scanning electron microscopy and its surface area quantitatively examined by gas sorption analysis couple with the Brunauer-Emmett–Teller method. The crystallinity is characterized by X-ray diffraction and high-resolution transmission elec-tron microscopy. X-ray photoelectron spectroscopy, CHN element analysis and small angle neutron scattering confirm the presence of the carbonaceous compounds in the surface composition. The prepared material exhibits superior dis-charge rate capability and excellent cycling stability. It shows minor capacity loss after 100 cycles at 0.5 C and main-tains 94.9% of its initial capacity after 500 cycles at 2 C. Even more notably, the “voltage decay” during cycling is also significantly decreased. It has been found that carbonaceous compounds play a critical role for reducing the layered to spinel structural transformation during cycling. Therefore, the present porous Li-rich material with surface modified a carbonaceous compounds represents an attractive material for advanced Lithium-ion batteries.
This work provides a convenient, effective and highly versatile coating strategy for the layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3). Here, layered oxide LiMO2 (M = Ni0.5Mn0.5 and Ni1/3Mn1/3Co1/3) have been successfully coated with ion conductor of Li2SiO3 by in situ hydrolysis of tetraethyl orthosilicate (TEOS) followed by the lithiation process. The discharge capacity, cycle stability, rate capability and some other electrochemical performances of layered cathode materials LiMO2 can be highly enhanced through surface-modification by coating appropriate content of Li2SiO3. Particularly, the 3mol% Li2SiO3 coated LiNi1/3Mn1/3Co1/3O2 exhibits approximately a discharge capacity of 111 mAh/g after 300 cycles at the current density of 800 mA/g (5 C). Potentiostatic intermittent titration technique (PITT) test was carried out to investigate the mechanism of the improvement in the electrochemical properties. The diffusion coefficient of Li+-ion (DLi) of Li2SiO3 coated layered oxide materials has been greatly increased. We believe our methodology provides a convenient, effective and highly versatile coating strategy, which can be expected to open the way to ameliorate the electrochemical properties of electrode materials for lithium ion batteries.
Li-ion battery technology has become very important in recent years as these batteries show great
promise as power sources that can lead us to the electric vehicle (EV) revolution. The development of
new materials for Li-ion batteries is the focus of research in prominent groups in the field of materials
science throughout the world. Li-ion batteries can be considered to be the most impressive success story
of modern electrochemistry in the last two decades. They power most of today’s portable devices, and
seem to overcome the psychological barriers against the use of such high energy density devices on
a larger scale for more demanding applications, such as EV. Since this field is advancing rapidly and
attracting an increasing number of researchers, it is important to provide current and timely updates of
this constantly changing technology. In this review, we describe the key aspects of Li-ion batteries: the
basic science behind their operation, the most relevant components, anodes, cathodes, electrolyte
solutions, as well as important future directions for R&D of advanced Li-ion batteries for demanding
use, such as EV and load-leveling applications.
The effect of Cr-doping on the structural, physical and electrochemical properties of Li2MnO3 and LiNi0.5Mn0.5O2 is reported. The formation of the solid solution and local distortion of the structure with the increase in Cr doping (0.7Li(2)MnO(3)- 0.3LiNi(0.5)Mn(0.5)O(2)) was confirmed respectively, by X-Ray diffraction and Raman spectroscopy. Morphological investigations and elemental mapping showed the formation of primary particles in the range 0.5-1.0 mu m and homogeneity, respectively. Electrochemical measurements on the materials were carried out in different voltage ranges and temperatures. Structural transformation of the material from layered to spinel symmetry has been observed with cycling in case of the samples with low Li2MnO3 content (0.3Li(2)MnO(3)-0.7LiNi(0.5)Mn(0.5)O(2)). Cr acted as a catalyst to enhance the activation of the material with high Li2MnO3 content.
Mix transition metal layered oxide materials are much attractive for cathode materials in lithium ion batteries. However, the disordered arrangement between lithium and transition metal ions in local regions of these materials always occurs, and seriously affects their electrochemical performance. Here we report experimental and first-principles calculations of Li+/Ni2+ ion exchange in the LiNi0.42Mn0.42Co0.16O2 materials prepared by solid state reaction and co-precipitation methods. The impact of Li+/Ni2+ ions exchange on crystal/electronic structure, electrochemical performance and stress are investigated in detail. Results show that there are obvious anisotropic stress and smaller inter-slab space of the unit cell associating with more Li+/Ni2+ ion exchange. During delithiation process, the distortion force in the unit cell of the material with large Li+/Ni2+ ion exchange increases sharply and presents strong spin-flip transition of Ni ions (magnetic moment direction change). These issues are closel
About phase: The coexistence of rhombohedral LiTMO2 (TM=Ni, Co, or Mn) and monoclinic Li2 MnO3 -like structures inside Li1.2 Mn0.567 Ni0.166 Co0.067 O2 is revealed directly at atomic resolution. The hetero-interface along the [001]rh /[103]mon zone axis direction is demonstrated, indicating the two-phase nature of these lithium-rich cathode materials (green Li, blue Mn, red O, cyan TM).
An unresolved question for the layered oxides is: what is the optimum value of y in the formula LiNiyMnyCo1–2yO2 for energy storage at moderate reaction rates? Here we report a systematic study of the specific capacity, rate capability
and cycle life of LixNiyMnyCo1–2yO2 (y = 0.5, 0.45, 0.4, and 0.333). The voltage of the Li/y = 0.333 couple crosses over those of lower cobalt content for x < 0.55,
as the Co redox begins to get involved. This early involvement of cobalt, rather than just Ni, leads to a slightly smaller
specific capacity for y = 0.333 than for LiNiyMnyCo1–2yO2 with y > 0.333 when charging above 4 V. Overall the y = 0.4 material has the optimum properties, having the highest theoretical
capacity, less of the expensive cobalt and yet rate capabilities and capacity retention comparable to the y = 0.333 material.
We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order N-atoms(3) operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ''metric'' and a special ''preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order N-atoms(2) scaling is found for systems up to 100 electrons. If we take into account that the number of k points can be implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
An improved way of estimating the local tangent in the nudged elastic band method for finding minimum energy paths is presented. In systems where the force along the minimum energy path is large compared to the restoring force perpendicular to the path and when many images of the system are included in the elastic band, kinks can develop and prevent the band from converging to the minimum energy path. We show how the kinks arise and present an improved way of estimating the local tangent which solves the problem. The task of finding an accurate energy and configuration for the saddle point is also discussed and examples given where a complementary method, the dimer method, is used to efficiently converge to the saddle point. Both methods only require the first derivative of the energy and can, therefore, easily be applied in plane wave based density-functional theory calculations. Examples are given from studies of the exchange diffusion mechanism in a Si crystal, Al addimer formation on the Al(100) surface, and dissociative adsorption of CH4 on an Ir(111) surface. (C) 2000 American Institute of Physics. [S0021-9606(00)70546-0].
A modification of the nudged elastic band method for finding minimum energy paths is presented. One of the images is made to climb up along the elastic band to converge rigorously on the highest saddle point. Also, variable spring constants are used to increase the density of images near the top of the energy barrier to get an improved estimate of the reaction coordinate near the saddle point. Applications to CH4 dissociative adsorption on Ir(111) and H-2 on Si(100) using plane wave based density functional theory are presented. (C) 2000 American Institute of Physics. [S0021-9606(00)71246-3].
The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Blöchl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules (H2, H2O, Li2, N2, F2, BF3, SiF4) and several bulk systems (diamond, Si, V, Li, Ca, CaF2, Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
A one-step synthesis method was used, with LiF or NiF2 as fluorine precursor, to prepare Li1.1(Ni0.425Mn0.425Co0.15)0.9O1.8F0.2 materials. 7Li and 19F magic angle spinning NMR analyses revealed the presence of fluorine as LiF at the surface of the Li(Ni0.425Mn0.425Co0.15)O2 particles, rejecting the formation of fluorine-substituted Li1.1(Ni0.425Mn0.425Co0.15)0.9O1.8F0.2 materials. These results highlighted that change in cell parameters with increasing fluorine content is not by itself proof for effective fluorine substitution for oxygen in layered oxides and that heterogeneity in the transition metal and fluoride-ion distribution at the crystallite scale can be at the origin of these modifications. LiF was shown to be present as small particles in some grain boundaries but not as a continuous layer covering the particles surface. Improved cycling stability was observed for these LiF-coated materials, showing that effective fluorine substitution for oxygen is not required for improvement of the cyclability of these layered oxides; a surface modification can be sufficient and can also have a huge impact.
Technological improvements in rechargeable solid-state batteries are being driven by an ever-increasing demand for portable electronic devices. Lithium-ion batteries are the systems of choice, offering high energy density, flexible and lightweight design, and longer lifespan than comparable battery technologies. We present a brief historical review of the development of lithium-based rechargeable batteries, highlight ongoing research strategies, and discuss the challenges that remain regarding the synthesis, characterization, electrochemical performance and safety of these systems.
Researchers must find a sustainable way of providing the power our modern lifestyles demand.
Li-rich layered oxides have attracted attention as promising positive electrode materials for next-generation lithium-ion secondary batteries because of their high energy storage capacity. The participation of the oxygen anion has been hypothesized to contribute to these oxides' high capacity. In the present study, we used O K-edge and Mn L-edge X-ray absorption spectroscopy (XAS) to study the reversible redox reactions that occur in single-phase Li-rich layered manganese oxide, Li2MnO3. We semiquantitatively analyzed the oxygen and manganese reactions by dividing the charge/discharge voltage region into two parts. The O K-edge XAS indicated that the electrons at the oxygen site reversibly contributed to the charge compensation throughout the charge/discharge processes at operating voltages between 2.0 and 4.8 V vs. Li+/Li0. The Mn L-edge XAS spectra indicated that the Mn redox reaction occurred only in the lower-voltage region. Thus, at higher potentials, the electrons, mainly at the oxygen site, contributed to the charge compensation. Peaks whose energies were similar to peroxide appeared in and then disappeared from the O K-edge spectra obtained during the reversible redox cycles. These results indicate that the reorganization of the oxygen network in the crystal structure affects the redox components. By using two kinds of detection modes with different probing depths in XAS measurements, it was found that these redox reactions are bulk phenomena in the electrode.
Decoupling the relevant parameters determining the electrochemical performance of spinel-type LiNi0.5Mn1.5O4 would contribute to promote its commercialization as cathode material for Li-ion batteries with high energy density. These parameters mainly comprise Ni/Mn ordering and non-stoichiometry, but their drivers and individual contribution to electrochemical performance remain to be fully ascertained. A series of samples annealed at different temperatures in the vicinity of an ordering transition have been thoroughly characterized by means of neutron powder diffraction to accurately establish composition-structure-property relationships in this material. The analysis revealed that deviations from a perfectly ordered crystal are possible through two different types of defects with significantly different effects on properties. These structural defects are in addition to previously described compositional defects, involving the creation of Mn3+ in the spinel lattice and Ni-rich rock salt secondary phases. Among the two types, the formation of antiphase boundaries is detrimental to transport, leading to poor rate performance of the electrode. In contrast, Ni/Mn mixing in an ordered framework can lead to behavior competitive with fully disordered samples, even at much lower Mn3+ contents that theoretically impart enhanced electronic conductivity. This work establishes design guidelines for fast transport in materials close to full stoichiometry, avoiding deleterious effects of rock salt impurities and Mn3+ dissolution.
A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.
"Li-1.04(Ni0.40Mn0.40Co0.20-zAlz)(0.96)O-2" (z = 0; 0.05 and 0.10) samples were synthesized using a coprecipitation method followed by calcinations at 500 degrees C for 5 h and then at 950 degrees C for 2 h. Structural and physico-chemical characterizations have shown that these materials were obtained pure with a small overlithiation ratio (Li/M 1.01-1.03) and thus a significant exchange between the divalent nickel ions from the slabs and the lithium ions from the interslab spaces (between 4% for the non substituted material and 8% for the aluminum substituted ones). Aluminum substitution induces a decrease of the reversible capacity, but also a major improvement of the thermal stability in the deintercalated state (corresponding to the charge state of the battery). These results have thus shown that the composition Li-1.01(Ni0.39Mn0.40Co0.15Al0.06)(0.99)O-2 is very attractive for large scale lithium-ion batteries to be developed for EV and HEV applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3571479]
LiCoO2 is a commercial cathode material for Li ion batteries; however, due to the structural instability with more Li+ deintercalation, only half of Li ions in LiCoO2 can be utilized in practical batteries. Therefore, there is still considerable room to improve its capacity if the stability of deliathiated layered structure is enhanced. In this work, we stabilize the delithiated structure by utilizing Li/Ni disorder to introduce Ni into Li layer. Our results demonstrate that, when charged to 4.5 V (vs. Li/Li+) at 1 C, the capacity retention of Ni-containing LiCoO2 after 100 cycles is twice that of pristine LiCoO2. In addition, density functional theory computations and ab initio molecular dynamics simulations reveal that Ni in Li layer is immobile in the lattice, and acts as pillars to support the layered structure. Furthermore, the computed diffusion coefficient of Ni-pillared LiCoO2 at 300 K is comparable to that of pristine LiCoO2, indicating that a small amount of Ni in the Li layer do not severely block Li diffusion. The pillar effect of Ni in Li layer is confirmed both experimentally and computationally, and the strategy can be generalized to the improvement and design of layered materials for high-voltage Li ion batteries.
0.3Li2MnO3•0.7LiNi0.5-xMn0.5-xM2xO2 (M=Mg or Al, x=0-0.08) samples have been synthesized by a combination of Co-precipitation (CP) and solid-state reaction. Electrochemical measurements show that not only the charge/discharge capacity of lithium-rich materials can be enhanced, what more important, its rate capacity can be greatly improved by doping magnesium and aluminum. At the current density of 400mAg-1, the 0.3Li2MnO3•0.7LiNi0.46Mn0.46Mg0.08O2 and 0.3Li2MnO3•0.7LiNi0.49Mn0.49Al0.02O2 electrodes deliver discharge capacities of 135mAhg-1 and 127mAhg-1, respectively, while the pristine electrode delivers a discharge capacity of only 10mAhg-1. Through studying the structure of lithium-rich materials, we find that the Li/Ni mixing of lithium-rich materials is reduced by doping magnesium and aluminum, in turn, the performance of doped lithium-rich materials is improved greatly. Furthermore, compared with Al-doped lithium-rich materials, the Li/Ni mixing of Mg-doped materials is further reduced. So the performance improvement of Mg-doped lithium-rich materials is more obvious than that of Al-doped materials.
The defect chemistry in a series of layered lithium transition-metal oxides, LiMO2 (M = Co, Ni, Mn, and Li1/3Mn2/3), is investigated by systematic first-principles calculations. The calculations clearly show that Ni3+ ions in LiNiO2 are easily reduced, whereas Mn3+ ions in LiMnO2 are easily oxidized under ordinary high-temperature synthesis conditions. It is expected that LiCoO2 and Li(Li1/3Mn2/3)O2 with low defect concentrations are easily synthesized. These results are highly consistent with the characteristics and conductive properties of the oxides observed in experiments. The calculations also suggest that the surfaces of the oxides are reduced at a nanometer scale by immersion of the samples in organic electrolytes of lithium-ion batteries, and the tendency of the surface reduction is consistent with the defect chemistry at high temperatures. The formation of the lithium vacancy and interstitial are elementary reactions of electrode active materials in the charging and discharging processes of lithium-ion batteries, respectively. The defect formation energies in conjunction with the electrode potentials can quantitatively describe the electrode behavior.
Neutron diffraction is a unique technique to study Li-ion batteries because of its high sensitivity toward detecting lithium ions and ability to differentiate between different cations. This information is essential for understanding the subtle structure/property relationships of active electrode materials. In this study, neutron diffraction was utilized to probe the cation disorder in LiNiO2 with and without Al3+ substitution by different synthesis processes. The powder neutron diffraction revealed that a strong oxidizer rather than Al3+-doping greatly reduces Li+ and Ni2+ mixing. The amount of Ni2+ at Li-site is 6% for Li1-x(Ni0.75Al0.25)(1+x)O-2 synthesized from excess LiOH, while it is only 0.6% for Li1-x(Ni0.75Al0.25)(1+x)O-2 which was synthesized from excess Li2O2. The reduction of Ni2+ at Li-sites greatly improves electrochemical performance. The substitution of Al3+ stabilizes the hexagonal lattice of Li1-xNi1+x-yAlyO2 even for highly lithium-deficient phases.
A series of the mixed transition metal compounds, Li[(Ni1/3Co1/3Mn1/3)1–x-y
Alx
By
]O2-z
Fz
(x = 0, 0.02, y = 0, 0.02, z = 0, 0.02), were synthesized via coprecipitation followed by a high-temperature heat-treatment. XRD patterns revealed that this material has a typical α-NaFeO2 type layered structure with R3-m space group. Rietveld refinement explained that cation mixing within the Li(Ni1/3Co1/3Mn1/3)O2 could be absolutely diminished by Al-doping. Al, B and F doped compounds showed both improved physical and electrochemical properties, high tap-density, and delivered a reversible capacity of 190 mAh/g with excellent capacity retention even when the electrodes were cycled between 3.0 and 4.7 V.
In this study we report the effects of the Ni content on the electrochemical properties and the structural and thermal stabilities of Li[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) synthesized via a coprecipitation method. The electrochemical and thermal properties of Li[NixCoyMnz]O2 are strongly dependent on its composition. An increase of the Ni content results in an increase of specific discharge capacity and total residual lithium content but the corresponding capacity retention and safety characteristics gradually decreased. The structural stability is related to the thermal and electrochemical stabilities, as confirmed by X-ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. Developing an ideal cathode material with both high capacity and safety will be a challenging task that requires precise control of microstructure and physico-chemical properties of the electrode.
LiNi0.5Mn0.5O2, LiNi0.475Al0.05Mn0.475O2, and LiNi0.5Mn0.45Ti0.05O2 were prepared via the emulsion drying method. The as-prepared materials showed different degrees of cation mixing. Rietveld refinement of X-ray diffraction data revealed that Al and Ti doping in LiNi0.5Mn0.5O2 was significantly effective to decrease the cation mixing in the octahedral Li layers. The cation mixing consequently affected to the charge and discharge capacities. The irreversible capacity was the smallest for the Al doped LiNi0.5Mn0.5O2, which showed the smallest cation mixing. Al and Ti doped LiNi0.5Mn0.5O2 delivered a stable capacity of about 175mAhg−1 with high reversibility. Such higher capacities were possible to be obtained by the achievement of structural stabilization and enhancement of structural integrity by Al and Ti doping in LiNi0.5Mn0.5O2.
Prospective positive-electrode (cathode) materials for a lithium secondary battery, viz., Li[Li0.2Ni0.2−x/2Mn0.6−x/2Crx]O2 (x=0, 0.02, 0.04, 0.06, 0.08), were synthesized using a solid-state pyrolysis method. The structural and electrochemical properties were examined by means of X-ray diffraction, cyclic voltammetry, SEM and charge–discharge tests. The results demonstrated that the powders maintain the α-NaFeO2-type layered structure regardless of the chromium content in the range x≤0.08. The Cr doping of x=0.04 showed improved capacity and rate capability comparing to undoped Li[Li0.2Ni0.2Mn0.6]O2. ac impedance measurement showed that Cr-doped electrode has the lower impedance value during cycling. It is considered that the higher capacity and superior rate capability of Cr-doping samples would be ascribed to the reduced resistance of the electrode during cycling.
This paper deals with the ground state of an interacting electron gas in an external potential v(r). It is proved that there exists a universal functional of the density, Fn(r), independent of v(r), such that the expression Ev(r)n(r)dr+Fn(r) has as its minimum value the correct ground-state energy associated with v(r). The functional Fn(r) is then discussed for two situations: (1) n(r)=n0+n(r), n/n01, and (2) n(r)= (r/r0) with arbitrary and r0. In both cases F can be expressed entirely in terms of the correlation energy and linear and higher order electronic polarizabilities of a uniform electron gas. This approach also sheds some light on generalized Thomas-Fermi methods and their limitations. Some new extensions of these methods are presented.
Layered LiCo1/3Ni1/3Mn1/3O2 was prepared by a solid state reaction at 1000 °C in air and examined in nonaqueous lithium cells. LiCo1/3Ni1/3Mn1/3O2 showed a rechargeable capacity of 150 mAh g−1 in 3.5–4.2 V or 200 mAh g−1 in 3.5–5.0 V. Operating voltage of Li / LiCo1/3Ni1/3Mn1/3O2 was by 0.2–0.25 V lower than that of a cell with LiCoO2 or LiMn2O4 and by 0.15–0.3 V higher than that with LiNiO2 or LiCo1/2Ni1/2O2 due to a complex solid solution mechanism.
Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, the density of energy that can be stored at a specific power input and retrieved at a specific power output, the cycle and shelf life, the storage efficiency, and the cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid-solution range. The solid-solution range, which is reduced at higher current by the rate of transfer of the working ion across electrode/electrolyte interfaces and within a host, limits the amount of charge per electrode formula unit that can be transferred over the time Δt = Δt(I). Moreover, the difference between the energies of the LUMO and the HOMO of the electrolyte, i.e. the electrolyte window, determines the maximum voltage for a long shelf and cycle life. The maximum stable voltage with an aqueous electrolyte is 1.5 V; the Li-ion rechargeable battery uses an organic electrolyte with a larger window, which increase the density of stored energy for a given Δt. Anode or cathode electrochemical potentials outside the electrolyte window can increase V, but they require formation of a passivating surface layer that must be permeable to Li+ and capable of adapting rapidly to the changing electrode surface area as the electrode changes volume during cycling. A passivating surface layer adds to the impedance of the Li+ transfer across the electrode/electrolyte interface and lowers the cycle life of a battery cell. Moreover, formation of a passivation layer on the anode robs Li from the cathode irreversibly on an initial charge, further lowering the reversible Δt. These problems plus the cost of quality control of manufacturing plague development of Li-ion rechargeable batteries that can compete with the internal combustion engine for powering electric cars and that can provide the needed low-cost storage of electrical energy generated by renewable wind and/or solar energy. Chemists are contributing to incremental improvements of the conventional strategy by (1) investigating and controlling electrode passivation layers, (2) improving the rate of Li+ transfer across electrode/electrolyte interfaces, (3) identifying electrolytes with larger windows while retaining a Li+ conductivity σLi > 10-3 S cm-1, (4) synthesizing electrode morphologies that reduce the size of the active particles while pinning them on current collectors of large surface area accessible by the electrolyte, (5) lowering the cost of cell fabrication, (6) designing displacement-reaction anodes of higher capacity that allow a safe, fast charge, (7) designing alternative cathode hosts. However, new strategies are needed for batteries that go beyond powering hand-held devices. These strategies include (1) the use of electrode hosts with two-electron redox centers, (2) replacing the cathode hosts (a) by materials undergoing displacement reactions, e.g. sulfur, (b) by liquid cathodes that may contain flow-through redox molecules, (c) by catalysts for air cathodes, and /or (3) by the development of a Li+ solid electrolyte separator membrane that allows an organic and aqueous liquid electrolyte on the anode and cathode sides, respectively. Opportunities exist for the chemist to bring together oxide and polymer or graphene chemistry in imaginative morphologies.
An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.
A cathode material (see figure) is shown to give a performance and cycle life comparable to that obtained with the LiCoO2 cathode now used in cellular phones and laptop computers. These performance features have been accomplished without the use of the expensive and toxic element cobalt and without compromising the volume energy density desired for hand-held devices.
In order to address power and energy demands of mobile electronics and electric cars, Li-ion technology is urgently being optimized by using alternative materials. This article presents a review of our recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Size effects revealed in the storage of lithium through micropores (hard carbon spheres), alloys (Si, SnSb), and conversion reactions (Cr2O3, MnO) are studied. The formation of nano/micro core–shell, dispersed composite, and surface pinning structures can improve their cycling performance. Surface coating on LiCoO2 and LiMn2O4 was found to be an effective way to enhance their thermal and chemical stability and the mechanisms are discussed. Theoretical simulations and experiments on LiFePO4 reveal that alkali metal ions and nitrogen doping into the LiFePO4 lattice are possible approaches to increase its electronic conductivity and does not block transport of lithium ion along the 1D channel.
The challenges for further development of Li rechargeable batteries for electric vehicles are reviewed. Most important is safety, which requires development of a nonflammable electrolyte with either a larger window between its lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) or a constituent (or additive) that can develop rapidly a solid/electrolyte-interface (SEI) layer to prevent plating of Li on a carbon anode during a fast charge of the battery. A high Li(+)-ion conductivity (sigma(Li) > 10(-4) S/cm) in the electrolyte and across the electrode/ electrolyte interface is needed for a power battery. Important also is ail increase in the density of the stored energy, which is the product of the voltage and capacity of reversible Li insertion/extraction into/from the electrodes. It will be difficult to design a better anode than carbon, but carbon requires formation of an SEI layer, which involves an irreversible capacity loss. The design of a cathode composed of environmentally benign, low-cost materials that has its electrochemical potential pc well-matched to the HOMO of the electrolyte and allows access to two Li atoms per transition-metal cation would increase the energy density, but it is a daunting challenge. Two redox couples can be accessed where the cation redox couples are "pinned" at the top of the 0 2p bands, but to take advantage of this possibility, it must be realized in a framework structure that can accept more than one Li atom per transition-metal cation, Moreover, such a situation represents an intrinsic voltage limit of the cathode, and matching this limit to the HOMO of the electrolyte requires the ability to tune the intrinsic voltage limit. Finally, the chemical compatibility in the battery must allow a long service life.
Layered Li(Ni0.5−xMn0.5−xM2x′)O2 materials (M′=Co, Al, Ti; x=0, 0.025) were synthesized using a manganese-nickel hydroxide precursor, and the effect of dopants on the electrochemical properties was investigated. Li(Ni0.5Mn0.5)O2 exhibited a discharge capacity of 120 mAh/g in the voltage range of 2.8–4.3 V with a slight capacity fade up to 40 cycles (0.09% per cycle); by doping of 5 mol% Co, Al, and Ti, the discharge capacities increased to 140, 142, and 132 mAh/g, respectively, and almost no capacity fading was observed. The cathode material containing 5 mol% Co had the lowest impedance, 47 Ω cm2, while undoped, Ti-doped, and Al-doped materials had impedance of 64, 62, and 99 Ω cm2, respectively. Unlike the other dopants, cobalt was found to improve the electronic conductivity of the material. Further improvement in the impedance of these materials is needed to meet the requirement for powering hybrid electric vehicle (HEV, <35 Ω cm2). In all materials, structural transformation from a layered to a spinel structure was not observed during electrochemical cycling. Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) data suggested that Ni and Mn exist as Ni2+ and Mn4+ in the layered structure. Differential scanning calorimetry (DSC) data showed that exothermic peaks of fully charged Li1−y(Ni0.5−xMn0.5−xM2x′)O2 appeared at higher temperature (270–290 °C) than LiNiO2-based cathode materials, which indicates that the thermal stability of Li(Ni0.5−xMn0.5−xM2x′)O2 is better than those of LiNiO2-based cathode materials.
We present a detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set. We will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temperature density-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N-atoms(2) scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge density including a new special 'preconditioning' optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. We have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio molecular-dynamics package), The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}
For Abstract see ChemInform Abstract in Full Text.
The local environments and short-range ordering of LiNi 0.5Mn0.5O2, a potential Li-ion battery positive electrode material, were investigated by using a combination of X-ray and neutron diffraction and isotopic substitution (NDIS) techniques, 6Li Magic Angle Spinning (MAS) NMR spectroscopy, and for the first time, X-ray and neutron Pair Distribution Function (PDF) analysis, associated with Reverse Monte Carlo (RMC) calculations. Three samples were studied: 6Li(NiMn) 0.5O2,7Li(NiMn)0.5O2, and 7Li(NiMn)0.5O2 enriched with 62Ni (denoted as 7LiZERONi0.5Mn0.5O 2), so that the resulting scattering length of Ni atoms is null. LiNi0.5Mn0.5O2 adopts the LiCoO2 structure (space group R3m) and comprises separate lithium layers, transition metal layers (Ni, Mn), and oxygen layers. NMR experiments and Rietveld refinements show that there is approximately 10% of Ni/Li site exchange between the Li and transition metal layers. PDF analysis of the neutron data revealed considerable local distortions in the layers that were not captured in the Rietveld refinements performed using the Bragg diffraction data and the LiCoO2 structure, resulting in different M-O bond lengths of 1.93 and 2.07 Å for Mn-O and Ni/Li-O, respectively. Large clusters of 2400-3456 atoms were built to investigate cation ordering. The RMC method was then used to improve the fit between the calculated model and experimental PDF data. Both NMR and RMC results were consistent with a nonrandom distribution of Ni, Mn, and Li cations in the transition metal layers; both the Ni and Li atoms are, on average, close to more Mn ions than predicted based on a random distribution of these ions in the transition metal layers. Constraints from both experimental methods showed the presence of short-range order in the transition metal layers comprising LiMn6 and LiMn5Ni clusters combined with Ni and Mn contacts resembling those found in the so-called "flower structure" or structures derived from ordered honeycomb arrays.
New applications such as hybrid electric vehicles and power backup require rechargeable batteries that combine high energy density with high charge and discharge rate capability. Using ab initio computational modeling, we identified useful strategies to design higher rate battery electrodes and tested them on lithium nickel manganese oxide [Li(Ni(0.5)Mn(0.5))O2], a safe, inexpensive material that has been thought to have poor intrinsic rate capability. By modifying its crystal structure, we obtained unexpectedly high rate-capability, considerably better than lithium cobalt oxide (LiCoO2), the current battery electrode material of choice.
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