No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Revealing Gliding-Induced Structural Distortion in High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries
... 58 Yu et al. discussed that the structural essence of the H3 phase is an O3-O1 intergrowth structure, in which the O1 slabs originate from the gliding of original O3 slabs in high-nickel layered oxide cathodes. 59 During the transformation from the O3 phase to the O1 phase, the oxygen stacking sequence changes from cubic close packing (ABCABC) in the O3 phase to hexagonal close packing (ABAB) in the O1 phase, accompanied by pronounced TM migration. 59,60 This is due to the different migration pathways in the O1 and O3 phases, resulting in a lower energy barrier for Ni ion migration into the Li layer in the O1 phase. ...
... 59 During the transformation from the O3 phase to the O1 phase, the oxygen stacking sequence changes from cubic close packing (ABCABC) in the O3 phase to hexagonal close packing (ABAB) in the O1 phase, accompanied by pronounced TM migration. 59,60 This is due to the different migration pathways in the O1 and O3 phases, resulting in a lower energy barrier for Ni ion migration into the Li layer in the O1 phase. 60 For the NCM333 cathode, Ni 2+ in the pristine state is prone to mixing and migration, while in NCM811, Ni is also easy to migrate, but both without vacancies within the Li layer. ...
Efforts to improve the specific capacity and energy density of lithium nickel-cobalt-manganese oxide (NCM) cathodes focus on operating at high voltages or increasing nickel content. However, both approaches necessitate a...
... At the end stage of delithiation, a rapid drop of D Li + for all the cathodes can be inspected, for which the contraction of lattice along c-axis should be responsible. [37,38] However, NM91 displays significantly dropped voltage decay compared to EL-N9-3 after the 200 th cycles ( Figure S15), accompanied by the pronouncedly reduced D Li + values, which is almost one orders of magnitude smaller than that of EL-N9-3 during the H2-H3 phase transition process. These findings powerfully demonstrate that NM91 undergoes more severe structural degradation to form surface Li-insulative rock-salt phase and thicker detrimental by-products layers, whereas EL-N9-3 maintains a more stable layered structure that enables better conduction of Li + while reducing detrimental side reactions. ...
Recently, Co‐free Ni‐rich cathodes have received extensive concerns as a competitive candidate for next‐generation sustainable lithium‐ion batteries (LIBs) due to their high‐capacity/operation voltage merits and elimination of expensive Co component. However, it is extremely challenging to solve the issues involving their intrinsic chemo‐mechanical instabilities triggered by anisotropic lattice stress and short cycle life. Herein, we rationally incorporate tiny quintuple high‐valence cations to engineer an entropy‐assisted LiNi0.9Mn0.085Nb0.003W0.003Sb0.003Ta0.003Mo0.003O2 (denoted as EL‐N9‐3) as a competitive cathode for LIBs. Thanks to such multi‐component synergistic superiorities, the five‐cations modulated EL‐N9‐3 is endowed with a robust lattice structure and optimized crystallographic texture, thereby significantly strengthening lattice oxygen framework, mitigating surface side‐reactions and irreversible phase transitions, and further prohibiting the microcracks formation and reproduction. The well‐designed EL‐N9‐3 cathode demonstrates exceptional long‐cycle duration, showing a competitive capacity retention of 86.7 % after 200 cycles at an elevated cut‐off potential of 4.5 V. Besides, the EL‐N9‐3‐based pouch‐type full cell can steadily sustain 500 cycles within a wide voltage window of 2.8–4.4 V at 1 C rate, with 70.8 % capacity retention. This work proves that the entropy‐assisted complex doping strategy is an effective avenue to achieve advanced Co‐free ultrahigh‐Ni layered cathodes, definitely expediting their extensive utilization in next‐generation LIBs.
The low specific capacity and the poor capacity retention at extreme fast charging/discharging limit the nickel-rich layered cathode commercialization in electric vehicles, and the root causes are interface instability and capacity loss induced by birth defects and irreversible phase transition. In this work, we propose a lattice reconstruction strategy combining polyvinylpyrrolidone-assisted wet chemistry and calcination to prepare the aluminum-modified LiNi0.83Co0.11Mn0.06O2 (ANCM). Our method offers distinct advantages in tailoring birth defects (residual alkali and rocksalt phase), reducing Li vacancies and oxygen vacancies, exhibiting gradient Ni concentration distribution, suppressing the Li/Ni intermixing defects, lowering the lattice strain before and after recycling, and inhibiting the microcracks. The ANCM constructs robust crystal lattices and delivers an initial discharge capacity of 155.3 mAh/g with 89.2% capacity retention after 200 cycles at 5 C. This work highlights the importance of synthesis design and structural modification for cathode materials.
Surface reconstruction and the associated severe strain propagation have long been reported as the major cause of cathode failure during fast charging and long-term cycling. Despite tremendous attempts, no known strategies can simultaneously address the electro-chemomechanical instability without sacrificing energy and power density. Here we report an epitaxial entropy-assisted coating strategy for ultrahigh-Ni LiNixCoyMn1−x−yO2 (x ≥ 0.9) cathodes via an oriented attachment-driven reaction between Wadsley–Roth phase-based oxides and the layered-oxide cathodes. The high anti-cracking and anti-corrosion tolerances as well as the fast ionic transport of the entropy-assisted surface effectively improved the fast charging/discharging capability, wide temperature tolerance and thermal stability of the ultrahigh-Ni cathodes. Comprehensive analysis from the primary and secondary particle level to the electrode level using multi-scale in situ synchrotron X-ray probes reveals greatly reduced lattice dislocations, anisotropic lattice strain and oxygen release as well as improved bulk/local structural stability, even when charging beyond the threshold state of charge (75%) of layered cathodes.
Layered oxide cathodes with a high‐nickel (Ni ≥ 0.9) content exhibit great potential for enabling high‐energy‐density lithium‐ion batteries. However, their practical feasibility and cycle life are hampered by severe surface reactivity with the electrolyte. A LiNi0.90Co0.05Al0.05O2 cathode is presented enriched with Al on the surface (S‐NCA) and benchmark it against a LiNi0.90Co0.05Al0.05O2 cathode obtained by a conventional co‐precipitation method that has a uniform Al distribution throughout the bulk (B‐NCA). The S‐NCA cathode greatly outperform with an impressive capacity retention of 84% after 1000 cycles in pouch full cells with graphite anode compared to 62% retention for B‐NCA. Advanced surface characterization methodologies, including time‐of‐flight secondary‐ion mass spectrometry, reveal that the Al‐enriched surface morphology facilitates the formation of a robust, thin electrode‐electrolyte interphase (EEI), effectively suppressing the oxidative decomposition of the electrolyte, gas generation, and metallic dead lithium formation on graphite anode. The results illustrate that surface reactivity with the electrolyte is the primary factor limiting the cycle of cells with high‐Ni cathodes. The work provides valuable insights toward the practical viability of ultrahigh‐Ni cathodes in lithium‐ion batteries.
Raising the charging cut‐off voltage of layered oxide cathodes can improve their energy density. However, it inevitably introduces instabilities regarding both bulk structure and surface/interface. Herein, exploiting the unique characteristics of high‐valance Nb ⁵⁺ element, we achieved a synchronous surface‐to‐bulk modified LiCoO 2 featuring Li 3 NbO 4 surface coating layer, Nb‐doped bulk, and the desired concentration gradient architecture through one‐step calcination. Such a multifunctional structure facilitates the construction of high‐quality cathode/electrolyte interface, enhances Li ⁺ diffusion, and restrains lattice‐O loss, Co migration and associated layer‐to‐spinel phase distortion. Therefore, a stable operation of Nb‐modified LiCoO 2 half‐cell is achieved at 4.6 V (90.9% capacity retention after 200 cycles). Long‐life 250 Wh/kg and 4.7 V‐class 550 Wh/kg pouch‐cells assembled with graphite and thin Li anodes are harvested (both beyond 87% after 1600 and 200 cycles). This multifunctional one‐step modification strategy establishes a technological paradigm to pave the way for high‐energy density and long‐life lithium‐ion cathode materials.
This article is protected by copyright. All rights reserved
Further commercialization of Ni‐rich layered cathodes is hindered by severe structure/interface degradation and kinetic hindrance that occur during electrochemical operation, which leads to safety risks and reduced range in electric vehicles (EVs). Herein, by selecting elements with different solubility properties, a multifunctional strategy that synchronously fabricates perovskite‐type SrZrO3 coating and Sr/Zr co‐doping is employed to strengthen the structure/interface stability and the Li⁺ transport mobility of LiNi0.85Co0.10Mn0.05O2 (NCM). Perovskite‐type SrZrO3 protective layers formed on the particle surface can substantially mitigate the unexpected interfacial side reactions and surface phase transitions. In addition, a robust crystal framework is constructed by optimizing local O coordination through the introduction of strong Zr−O bonds. Notably, Li⁺ diffusion kinetics is effectively improved due to expanded cell parameters and O‐Li‐O slab spacing with the incorporation of large‐diameter Sr pillar ions, as revealed by X‐ray diffraction. As a result, the Sr/Zr‐modified NCM achieves a remarkable capacity retention of 99.4% after 200 cycles at 1 C, and a high rate capacity of 168.9 mAh g⁻¹ at 10 C. This work opens new avenues to develop high‐performance NCM cathodes with high energy and high power for EVs with long calendar life.
In order to reduce cost and increase energy density, it is critical to eliminate cobalt and increase nickel content in practical LiNi1−x−yMnxCoyO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) cathodes. However, the implementation of cobalt‐free, high‐nickel layered oxide cathodes in lithium‐ion batteries (LIBs) is hindered by the inherent issue of high surface reactivity with the electrolyte and microcrack formation during cycling. Herein, the origin of key parameters for microstructural engineering in cobalt‐free LiNiO2 (LNO) is comprehensively investigated with two representative dopants, B and Al. A notable difference in the segregation energy between B and Al results in different morphologies of LNO particles. The low solubility of B into the host structure leads to a surface‐confined distribution of B, inhibiting the growth of primary particles, whereas the highly soluble Al facilitates primary particle growth. Recognition of this key parameter can help improve the cycle life of cobalt‐free LIBs via microstructural engineering by increasing the aspect ratio inside the cathode particle. It is demonstrated that boron‐doping in LNO (B‐LNO) is the most effective dopant strategy for microstructural engineering of the primary particles. The B‐LNO exhibits an excellent capacity retention of 81% in full cells after 300 cycles compared to both LNO and Al‐doped LNO (Al‐LNO).
Ni‐rich layered oxides are promising cathode material for high‐energy‐density lithium‐ion batteries (LIBs). However, they suffer from poor capacity retention due to unstable structures. Herein, a strategy of high‐valence W doping is put forward to tune the nanometer‐sized crystal domains and reshape the primary particle textures, which can stabilize the structure against the formation of microcracks to improve the electrochemical performance. The Ni‐rich layered oxide with 0.5 mol% doped W delivers a high‐capacity retention of 91.6% up to 300 cycles under 1 C. Such an improved performance is ascribed to the pre‐introduced nanometer‐sized spinel and rock‐salt crystal domains, which remarkably improve the structure stability, and the radially alignment of primary particles, and effectively reduce the anisotropic mechanical strain in deep charge states. This study sheds light on the design of high‐performance Co‐less Ni‐rich cathode materials through the adjustment of microstructures via a small amount of suitable dopants.
Lithiated oxides like Li[NixCoyMnz]O2 (x+y+z=1) with high nickel content (x≥0.8) can possess high specific capacity ≥ 200 mAhg-1 and have attracted extensive attention as perspective cathode materials for advanced lithium-ion batteries. In this work, we synthesized LiNi0.9Co0.1O2 (NC90) materials and studied their structural characteristics, electrochemical performance, and thermal behavior in Li-cells. We developed modified cationic-doped NC90 samples with greatly improved properties due to doping with Mo6+ and B3+ and dual doping via simultaneous modification with these dopants. The main results of the current study are significantly higher capacity retention, greatly reduced voltage hysteresis, and considerably decreased charge-transfer resistance of the Mo and Mo-B doped electrodes compared to the undoped ones upon prolonged cycling. We also revealed remarkable microstructural stability of the Mo-doped electrodes, whereas the undoped samples were unstable and exhibited networks of cracks developed upon cycling. Using density functional theory, we modeled the electronic structure of the undoped, Mo, B single-doped, and Mo-B dual-doped samples and established that the Ni-site is preferred over Co and Li sites. Additionally, density functional theory-based bonding strength calculations suggest that the dopants form strong bonds with oxygen, possibly reducing oxygen release from the cathode. An important finding is that B-dopant tends to segregate to the surface of NC90 similarly to that in NCM85 materials, as shown in our previous reports. In conclusion, this study presents a general approach for effectively stabilizing high-energy Ni-rich layered cathodes charged up to 4.3 V.
High-Ni-content layered materials are promising cathodes for next-generation lithium-ion batteries. However, investigating the atomic configurations of the delithiation-induced complex phase boundaries and their transitions remains challenging. Here, by using deep-learning-aided super-resolution electron microscopy, we resolve the intralayer transition motifs at complex phase boundaries in high-Ni cathodes. We reveal that an O3 → O1 transformation driven by delithiation leads to the formation of two types of O1–O3 interface, the continuous- and abrupt-transition interfaces. The interfacial misfit is accommodated by a continuous shear-transition zone and an abrupt structural unit, respectively. Atomic-scale simulations show that uneven in-plane Li+ distribution contributes to the formation of both types of interface, and the abrupt transition is energetically more favourable in a delithiated state where O1 is dominant, or when there is an uneven in-plane Li+ distribution in a delithiated O3 lattice. Moreover, a twin-like motif that introduces structural units analogous to the abrupt-type O1–O3 interface is also uncovered. The structural transition motifs resolved in this study provide further understanding of shear-induced phase transformations and phase boundaries in high-Ni layered cathodes. High-Ni-content layered cathodes are promising for lithium-ion batteries, but investigating their delithiation-induced phase boundaries is challenging. Intralayer transition motifs at complex phase boundaries in these high-Ni electrodes are now resolved using deep-learning-aided super-resolution electron microscopy.
With continuous improvement of batteries in energy density, enhancing their safety is becoming increasingly urgent. Herein, practical high energy density LiNi0.8Mn0.1Co0.1O2|graphite‐SiO pouch cell with nonflammable localized high concentration electrolyte (LHCE) is proposed that presents unique self‐discharge characteristic before thermal runaway (TR), thus effectively reducing safety hazards. Compared with the reference electrolyte, pouch cell with nonflammable LHCE can increase self‐generated heat temperature by 4.4 °C, increase TR triggering temperature by 47.3 °C, decrease the TR highest temperature by 71.8 °C, and extend the time from self‐generated heat to triggering TR by ≈8 h. In addition, the cell with nonflammable LHCE presents superior high voltage cycle stability, attributed to the formation of robust inorganic‐rich electrode–electrolyte interphase. The strategy represents a pivotal step forward for practical high energy and high safety batteries.
The elimination of Co from Ni-rich layered cathodes is considered a priority to reduce their material cost and for sustainable development of Li-ion batteries (LIBs) as Co is becoming increasingly scarce. The introduction of 1 mol% Mo into Li(Ni0.9Mn0.1)O2 delivers 234 mAh g−1 at 4.4 V. The cycling stability of a full cell featuring the Li(Ni0.89Mn0.1Mo0.01)O2 (Mo–NM90) cathode is enhanced with a modified electrolyte; retaining 86% of its initial capacity after 1,000 cycles while providing 880 Wh kgcathode−1. The grain size refinement achieved by Mo doping dissipates the deleterious strain from abrupt lattice contraction through fracture toughening and the removal of local compositional inhomogeneities. Enhanced cation ordering induced by the presence of Mo6+ also stabilizes the delithiated structure through a pillar effect. The Mo–NM90 cathode is able to deliver a high capacity with cycling stability suitable for the long service life for electric vehicles at a reduced material cost, furthering the realization of a commercially viable Co-free cathode for LIBs. Cobalt-free cathodes are highly desirable for the sustainable development of rechargeable batteries. Here the authors report a high-performance cathode by introducing a small amount of Mo into a layered Li(Ni0.9Mn0.1)O2 material that enables a long-term, high-voltage Li-ion battery.
Li‐rich layered oxides (LLOs) suffer from rapid voltage decay and capacity fading, greatly hindering their applications as high‐energy cathode materials for Li‐ion batteries (LIBs), which are closely associated with irreversible structural transformation and lattice oxygen loss upon electrochemical cycling. A strategy of Al/Ti synergistic bulk doping is proposed to stabilize LLOs against structural degradations, yielding remarkable electrochemical performance including a minor voltage decay of 0.34 mV cycle⁻¹ and a superior capacity retention of 89.7% over 500 cycles at 1C. The improved structural stability of Al/Ti codoped LLOs is well maintained after not only initial but also long cycles. This effect can be attributed to the cooperation of Al and Ti, with the former stabilizing the lattice oxygen by strong Al–O bonds and the latter improving the Li⁺ conductivity by expanding the lattice. The facile bulk synergistic doping of LLOs paves avenues toward their application for high‐energy LIBs.
Ni‐rich LiNi1−x−yMnxCoyO2 (NMC) layered oxides are promising cathode materials for high‐energy density lithium ion batteries but suffer from severe capacity fading upon cycling. Elemental substitution (= doping) with Mg has repeatedly attracted attention in NMC materials to overcome instability problems at reasonable cost, yet rational compositional tuning is needed to guarantee sufficient cycle life without compromising energy density on the material level. Herein, a series of Mg‐substituted NMC materials with 90 mol% Ni are investigated regarding key performance metrics in NMC || graphite full‐cells benchmarked against LiNi0.80Mn0.10Co0.10O2 and LiNi0.90Mn0.05Co0.05O2 synthetized using the same co‐precipitation route. A linear correlation between cycle life and attainable gravimetric capacities is demonstrated, which are directly influenced by the degree of Mg substitution and the amount of Li⁺ cycled upon (de‐)lithiation processes. A Mg content <2 mol% should be considered to take notable benefit from the increase in Ni content from 80 to 90 mol% to achieve a higher energy density. The present study highlights the importance of evaluating the true implications of elemental substitution on cell performance and is expected to be an insightful guideline for the future development of NMC‐type cathode materials in particular with high Ni and low Co content.
Single‐crystalline Ni‐rich cathodes are promising candidates for the next‐generation high‐energy Li‐ion batteries. However, they still suffer from poor rate capability and low specific capacity due to the severe kinetic hindrance at the nondilute state during Li⁺ intercalation. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that this obstacle can be tackled by regulating the oxidation state of nickel via injecting high‐valence foreign Ta⁵⁺. The as‐obtained single‐crystalline LiNi0.8Co0.1Mn0.1O2 delivers a high specific capacity (211.2 mAh g⁻¹ at 0.1 C), high initial Coulombic efficiency (93.8 %), excellent rate capability (157 mAh g⁻¹ at 4 C), and good durability (90.4 % after 100 cycles under 0.5 C). This work provides a strategy to mitigate the Li⁺ kinetic hindrance of the appealing single‐crystalline Ni‐rich cathodes and will inspire peers to conduct an intensive study.
The implementation of high‐nickel layered oxide cathodes in lithium‐ion batteries is hampered by the inherent issues of formation of NiO‐like rock‐salt phase as well as residual lithium (e.g., LiOH, LiHCO3, and Li2CO3) on the surface. To overcome the challenges, here a rational strategy is presented of interdiffusion‐based surface reconstruction via dry coating and the design principles for identifying the optimum coating ions on a LiNi0.91Mn0.03Co0.06O2 (NMC91) cathode. Notably, the combined approach of theoretical screening, which involves the consideration of superexchange interactions among different oxidation states and density functional theory calculations, along with experimental analyses, which involve the characterization of the decrease in Ni content and residual lithium on the surface of NMC91, demonstrate the effective reduction in rock‐salt phase and residual lithium. Among the four ions investigated (Al, Co, Fe, and Ti), cobalt‐coated NMC91 is the most effective at reducing the rock‐salt phase and residual lithium by successfully reconstructing the surface of NMC91 and exhibits an excellent capacity retention of 85% in a full cell after 300 cycles at 30 °C.
A series of single-crystal, Ni-rich Li[NixCoyMn1–x–y]O2 (NCM) cathodes (x = 0.7, 0.8, and 0.9) with particle diameters of ∼3 μm are systematically compared with polycrystalline cathodes with corresponding Ni contents. Despite their high resistance to microcracking, the electrochemical performances of single-crystal NCM cathodes, in terms of capacity and cycling stability, are inferior to those of polycrystalline NCM cathodes. In situ XRD and TEM analyses reveal that the lithium concentrations in single-crystal NCM cathodes become spatially inhomogeneous during cycling; this phenomenon is exacerbated by high C rates and Ni contents, resulting in the coexistence of phases with widely different unit cell dimensions within a single cathode particle. This coexistence of two phases induces nonuniform stress that generates structural defects, impairing the diffusion of lithium ions and, eventually, leading to rapid capacity fading.
The compositional phase diagram of LiNiO 2 as a function of lithium content has been the object of numerous experimental and computational studies over the last two decades. Even between experimental...
Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes.We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.
The fast capacity/voltage fading with a low rate capability has challenged the commercialization of layer‐structured Ni‐rich cathodes in lithium‐ion batteries. In this study, an ultrathin and stable interface of LiNi0.8Mn0.1Co0.1O2 (NCM) is designed via a passivation strategy, dramatically enhancing the capacity retention and operating voltage stability of cathode at a high cut‐off voltage of 4.5 V. The rebuilt interface as a stable path for Li⁺ transport, would strengthen the cathode–electrolyte interface stability, and restrain the detrimental factors for cathode–electrolyte interfacial reactions, intergranular cracking and irreversible phase transformation from layered to spinel, even salt‐rock phase. The as‐optimized NCM displays a higher cyclability (i.e., 206.6 mA h g⁻¹ at 0.25 C (50 mA g⁻¹) with 92.0% capacity retention over 100 cycles) and a better rate capability (141.0 and 112.6 mA h g⁻¹ at 12.5 and 25 C, respectively) than pristine NCM (205.0 mA h g⁻¹ with 73.0% capacity retention at 0.25 C; 120.9 and 93.1 mA h g⁻¹ at 12.5 and 25 C, respectively).
The next generation of automotive lithium‐ion batteries may employ NMC811 materials; however, defective particles are of significant interest due to their links to performance loss. Here, it is demonstrated that even before operation, on average, one‐third of NMC811 particles experience some form of defect, increasing in severity near the separator interface. It is determined that defective particles can be detected and quantified using low resolution imaging, presenting a significant improvement for material statistics. Fluorescence and diffraction data reveal that the variation of Mn content within the NMC particles may correlate to crystallographic disordering, indicating that the mobility and dissolution of Mn may be a key aspect of degradation during initial cycling. This, however, does not appear to correlate with the severity of particle cracking, which when analyzed at high spatial resolutions, reveals cracking structures similar to lower Ni content NMC, suggesting that the disconnection and separation of neighboring primary particles may be due to electrochemical expansion/contraction, exacerbated by other factors such as grain orientation that are inherent in such polycrystalline materials. These findings can guide research directions toward mitigating degradation at each respective length‐scale: electrode sheets, secondary and primary particles, and individual crystals, ultimately leading to improved automotive ranges and lifetimes.
High‐Ni layered oxide cathodes are considered to be one of the most promising cathodes for high‐energy‐density lithium‐ion batteries due to their high capacity and low cost. However, surfice residues, such as NiO‐type rock‐salt phase and Li2CO3, are often formed at the particle surface due to the high reactivity of Ni³⁺, and inevitably result in an inferior electrochemical performance, hindering the practical application. Herein, unprecedentedly clean surfaces without any surfice residues are obtained in a representative LiNi0.8Co0.2O2 cathode by Ti‐gradient doping. High‐resolution transmission electron microscopy (TEM) reveals that the particle surface is composed of a disordered layered phase (≈6 nm in thickness) with the same rhombohedra structure as its interior. The formation of this disordered layered phase at the particle surface is electrochemically favored. It leads to the highest rate capacity ever reported and a superior cycling stability. First‐principles calculations further confirm that the excellent electrochemical performance has roots in the excellent chemical/structural stability of such a disordered layered structure, mainly arising from the improved robustness of the oxygen framework by Ti doping. This strategy of constructing the disordered layered phase at the particle surface could be extended to other high‐Ni layered transition metal oxides, which will contribute to the enhancement of their electrochemical performance.
Nickel-rich layered transition metal oxides are attractive cathode materials for rechargeable lithium-ion batteries but suffer from inherent structural and thermal instabilities that limit the deliverable capacity and cycling performance on charging to a cutoff voltage above 4.3 V. Here we report LiNi0.90Co0.07Mg0.03O2 as a new stable cathode material. The obtained LiNi0.90Co0.07Mg0.03O2 microspheres exhibit a high capacity (228.3 mAh g-1 at 0.1 C) and remarkable cyclability (84.3% capacity retention after 300 cycles). Combined X-ray diffraction and Cs-corrected microscopy reveal that Mg doping stabilizes the layered structure by suppressing Li/Ni cation mixing and Ni migration to interlayer Li slabs. Because of the pillar effect of Mg in Li sites, LiNi0.90Co0.07Mg0.03O2 shows decent thermal stability and small lattice variation until charging to 4.7 V, undergoing a H1–H2 phase transition without discernable formation of unstable H3 phase. The results indicate that moderate Mg doping is a facile yet effective strategy to develop high-performance Ni-rich cathode materials.
The FAULTS program is a powerful tool for the refinement of diffraction patterns of materials with planar defects. A new release of the FAULTS program is herein presented, together with a number of new capabilities, aimed at improving the refinement process and evolving towards a more user-friendly approach. These include the possibility to refine multiple sets of single-crystal profiles of diffuse streaks, the visualization of the model structures, the possibility to add the diffracted intensities from secondary phases as background and the new DIFFaX2FAULTS converter, among others. Three examples related to battery materials are shown to illustrate the capabilities of the program.
The computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) enables chemical-bonding analysis based on periodic plane-wave (PAW) density-functional theory (DFT) output and is applicable to a wide range of first-principles simulations in solid-state and materials chemistry. LOBSTER incorporates analytic projection routines described previously in this very journal [J. Comput. Chem. 2013, 34, 2557] and offers improved functionality. It calculates, among others, atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the recently introduced bond-weighted distribution function (BWDF). The software is offered free-of-charge for non-commercial research. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.
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.
Several improvements of the tetrahedron method for Brillouin-zone integrations are presented. (1) A translational grid of k points and tetrahedra is suggested that renders the results for insulators identical to those obtained with special-point methods with the same number of k points. (2) A simple correction formula goes beyond the linear approximation of matrix elements within the tetrahedra and also improves the results for metals significantly. For a required accuracy this reduces the number of k points by orders of magnitude. (3) Irreducible k points and tetrahedra are selected by a fully automated procedure, requiring as input only the space-group operations. (4) The integration is formulated as a weighted sum over irreducible k points with integration weights calculated using the tetrahedron method once for a given band structure. This allows an efficient use of the tetrahedron method also in plane-wave-based electronic-structure methods.
In this research, we systematically examine the impact of atomic cation dopants and metal oxides coatings, including their respective oxidation states, on the electrochemical performance of Ni-rich NCA90 cathode materials....
Benefited from its high process feasibility and controllable costs, binary-metal layered structured LiNi0.8Mn0.2O2 (NM) can effectively alleviate the cobalt supply crisis under the surge of global electric vehicles (EVs) sales, which is considered as the most promising next-generation cathode material for lithium-ion batteries (LIBs). However, the lack of deep understanding on the failure mechanism of NM has seriously hindered its application, especially under the harsh condition of high-voltage without sacrifices of reversible capacity. Herein, single-crystal LiNi0.8Mn0.2O2 is selected and compared with traditional LiNi0.8Co0.1Mn0.1O2 (NCM), mainly focusing on the failure mechanism of Co-free cathode and illuminating the significant effect of Co element on the Li/Ni antisite defect and dynamic characteristic. Specifically, the presence of high Li/Ni antisite defect in NM cathode easily results in the extremely dramatic H2/H3 phase transition, which exacerbates the distortion of the lattice, mechanical strain changes and exhibits poor electrochemical performance, especially under the high cutoff voltage. Furthermore, the reaction kinetic of NM is impaired due to the absence of Co element, especially at the single-crystal architecture. Whereas, the negative influence of Li/Ni antisite defect is controllable at low current densities, owing to the attenuated polarization. Notably, Co-free NM can exhibit better safety performance than that of NCM cathode. These findings are beneficial for understanding the fundamental reaction mechanism of single-crystal Ni-rich Co-free cathode materials, providing new insights and great encouragements to design and develop the next generation of LIBs with low-cost and high-safety performances.
Single-crystal Ni-rich Li[NixMnyCo1-x-y]O2 (SC-NMC) cathodes represent a promising approach to mitigate the cracking issue of conventional polycrystalline cathodes. However, many reported SC-NMC cathodes still suffer from unsatisfactory cycling stability, particularly under high charge cutoff voltage and/or elevated temperature. Herein, we report an ultraconformal and durable poly(3,4-ethylenedioxythiophene) (PEDOT) coating for SC-NMC cathodes using an oxidative chemical vapor deposition (oCVD) technique, which significantly improves their high-voltage (4.6 V) and high-temperature operation resiliency. The PEDOT coated SC LiNi0.83Mn0.1Co0.07O2 (SC-NMC83) delivers an impressive capacity retention rate of 96.7% and 89.5% after 100 and 200 cycles, respectively. Significantly, even after calendar aging at 45 °C and 4.6 V, the coated cathode can still retain 85.3% (in comparison with 59.6% for the bare one) of the initial capacity after 100 cycles at a 0.5 C rate. Synchrotron X-ray experiments and interface characterization collectively reveal that the conformal PEDOT coating not only effectively stabilizes the crystallographic structure and maintains the integrity of the particles but also significantly suppresses the electrolyte's corrosion, resulting in improved electrochemical/thermal stability. Our findings highlight the promise of an oCVD PEDOT coating for single-crystal Ni-rich cathodes to meet the grand challenge of high-energy batteries under extreme conditions.
Ni-rich layered oxide is a promising cathode material for future advanced lithium-ion batteries (LIBs). However, the nickel-rich layered cathode material exhibits insufficient high-voltage cycling stability ascribing to the phase transformation, surface side reactions, and lattice oxygen evolution. This work developed an effective inorganic coating strategy to construct LiNiO2/Na1-xNi1-yPO4 surface hybrid coating layer and Na bulk doping simultaneously by a simple wet-chemical method, improving the high-voltage performance of LiNi0.8Co0.1Mn0.1O2 (NCM) effectively. It is found that the surface oxygen vacancy and surface residual lithium on NCM reacts with NaNiPO4 precursors at 500 °C to form LiNiO2 inner layer in addition to the Na1-xNi1-yPO4 outer layer, which is structurally coherent to the layered lattice of NCM. In the constructed hybrid layer, layered phase LiNiO2 firmly fixes on the NCM surface. At the same time, highly chemical stable Na1-xNi1-yPO4 with lattice tunnels can enable lithium-ion transport and act as a protecting layer to inhibit surface side reactions. In addition, Na bulk doping could enlarge lithium-ion diffusion channels and stabilize lattice structure. All these advantages contribute to improving the electrochemical performance of NCM. The results show that the surface treatment NCM cathode exhibit excellent cycling stability with a higher capacity retention of 88% after 200 cycles under 25 °C and 86% after 100 cycles under 55 °C, both at 1 C. This method provides a feasible strategy to promote the high-voltage cycling performance of electrode material, thus improving the service life, energy density, and safety performance of Li-ion batteries.
Herein, a systematic investigation is conducted to unveil the role of phosphorus (P) or boron (B) doping on the development of radially aligned textured microstructure during the synthesis of LiNi0.92Co0.04Mn0.04O2...
The pressing demand in electrical vehicle (EV) markets for high-energy-density lithium-ion batteries (LIBs) requires further increasing the Ni content in high-Ni and low-Co cathodes. However, the commercialization of high-Ni cathodes is hindered by their intrinsic chemomechanical instabilities and fast capacity fade. The emerging single-crystalline strategy offers a promising solution, yet the operation and degradation mechanism of single-crystalline cathodes remain elusive, especially in the extremely challenging ultrahigh-Ni (Ni > 90%) regime whereby the phase transformation, oxygen loss, and mechanical instability are exacerbated with increased Ni content. Herein, we decipher the atomic-scale stabilization mechanism controlling the enhanced cycling performance of an ultrahigh-Ni single-crystalline cathode. We find that the charge/discharge inhomogeneity, the intergranular cracking, and oxygen-loss-related phase degradations that are prominent in ultrahigh-Ni polycrystalline cathodes are considerably suppressed in their single-crystalline counterparts, leading to improved chemomechanical and cycling stabilities of the single-crystalline cathodes. Our work offers important guidance for designing next-generation single-crystalline cathodes for high-capacity, long-life LIBs.
LiCoO2, as a domain cathode material of Li-ion batteries, faces a great deal of challenges due to the limited cycling stability at high voltage (>4.35 V vs. Li/Li⁺). These issues are tentatively addressed here by a multifunctional self-stabilization modification strategy, involving trace Mg bulk doping, surface gradient Ti doping and BaTiO3 dot coating in LiCoO2. The multifunctional synergy is verified to overcome the detrimental irreversible phase transition and the growth of impedance of LiCoO2 cycling at 4.6 V. By using soft X-ray absorption spectroscopy (sXAS) and electron paramagnetic resonance (EPR) techniques, we also elucidate that Ti surface gradient doping can reinforce the structure rigidity of the particles while significantly attenuates the irreversible oxygen redox at high voltage. All these strategies promote the prolonged cyclic performance of LiCoO2 under 4.6 V high-voltage through different mechanism. This elaborate investigation provides an instructive contribution in the advancement of high-voltage LiCoO2.
LiNiO2 and cobalt-free ultrahigh-Ni content cathodes suffer from rapid capacity loss and severe chemomechanical degradation, especially when operated at high voltages. Here, by cycling LiNiO2 up to 4.7 V, we report the atomic-scale observation of O1 faulted phase-induced deactivation of LiNiO2. We find that, although a thin layer of the O3 phase forms on the particle surface by reversible O3 → O1 transformation during discharge, the bulk
interior still maintains the O1 faulted phase, leading to rapid capacity loss of LiNiO2. Moreover, the atomic configuration of the O1/O3 interface is investigated comprehensively. We reveal that the misfit along the c axes of the O1 and O3 phases results in the formation of misfit dislocations, whereby cation mixing is promoted at the dislocation cores. A transition zone with continuous shear along the a−b plane is uncovered between the O1 and O3 phases for the first time. Besides, severe oxygen loss-induced pore formation and concurrent rock salt transformation are also identified.
Battery safety is critical to the application of lithium-ion batteries, especially for high energy density battery applied in electric vehicles. In this paper, the thermal runaway mechanism of LiNi0.8Co0.1Mn0.1O2 based lithium-ion battery is illustrated. And the reaction between cathode and flammable electrolyte is proved as the trigger of the thermal runaway accident. In detail, with differential scanning calorimeter tests for battery components, the material combination contributing to thermal runaway was decoupled. Characterization with synchrotron X-ray diffraction and transmission electron microscopy with in-situ heating proved that the vigorous exothermic reaction is initiated by the liberated oxygen species. The pulse of highly active oxygen species reacted quickly with the electrolyte, accompanied with tremendous heat release, which accelerated the phase transformation of charged cathode. Also, the mechanism is verified by a confirmatory experiment when the highly active oxygen species were trapped by anion receptor, the phase transformation of the charged cathode was inhibited. Clarifying the thermal runaway mechanism of LiNi0.8Co0.1Mn0.1 based lithium-ion battery may light the way to battery chemistries of both high energy density and high safety.
The high-nickel layered oxides are potential candidate cathode materials of next-generation high energy lithium-ion batteries, in which higher nickel/lower cobalt strategy is effective for increasing specific capacity and reducing cost of cathode. Unfortunately, the fast decay of capacity/potential, and serious thermal concern are critical obstacles for the commercialization of high-nickel oxides due to structural instability. Herein, in order to improve the structure and thermal stability of high-nickel layered oxides, we demonstrate a feasible and simple strategy of the surface gradient doping with yttrium, without forming the hard interface between coating layer and bulk. As expected, after introducing yttrium, the surface gradient doping layer is formed tightly based on the oxidation induced segregation, leading to improved structure and thermal stability. Correspondingly, the good capacity retention and potential stability are obtained for the yttrium-doped sample, together with the superior thermal behavior. The excellent electrochemical performance of the yttrium-doped sample is primarily attributed to the strong yttrium-oxygen bonding and stable oxygen framework on the surface layer. Therefore, the surface manipulating strategy with the surface gradient doping is feasible and effective for improving the structure and thermal stability, as well as the capacity/potential stability during cycling for the high-Ni layered oxides.
To boost the use of electronic devices and driving mileage of electric vehicles, it is urgent to develop lithium-ion batteries (LIBs) with higher energy density and longer life. High-voltage and high-capacity cathode materials, such as LiCoO2, LiNi0.5Mn1.5O4, Ni-rich layered oxides, and lithium-rich layered oxides, are critically important for LIBs to obtain high energy density. Among various forms of these materials, “single-crystal” cathodes (SCCs) have shown many advantages over other forms for industrial applications, including good crystallinity, high mechanical strength, high reaction homogeneity, small specific surface area, excellent structural stability, and high thermal stability, which can noticeably improve the cycling performance and safety of SCC-based batteries. Therefore, SCCs have received wide attention from academic to industrial communities and have been applied to the liquid-based and solid-state batteries in recent years. In this paper, the advantages, progress, and challenges of SCCs for high-voltage cathode materials are reviewed. Moreover, we summarize the efforts for improving the electrochemical performance of SCCs, intending to provide insights into the development of high-performance cathodes for practical LIBs.
Ni-rich cathode materials show great potential of applying in high-energy lithium ion batteries, but their inferior cycling stability hinders this process. Study on the electrode/electrolyte interfacial reaction is indispensable to understand the capacity failure mechanism of Ni-rich cathode materials and further address this issue. This work demonstrates the domain size effects on interfacial side reactions firstly, and further analyzes the inherent mechanism of side reaction induced capacity decay through comparing the interfacial behaviors before and after MgO coating. It has been determined that LiF deposition caused thicker SEI films may not increase the surface film resistance, while HF erosion induced surface phase transition will increase the charge transfer resistance, and the later plays the dominant factor to declined capacity of Ni-rich cathode materials. This work suggests strategies to suppress the capacity decay of layered cathode materials and provides a guidance for the domain size control to match the various applications under different current rates.
Compared to the fossil-fuelled cars, developing a high-safety, low-cost, long-life lithium ion battery with higher energy density is critical important to enhance the market acceptance of electric vehicles. Herein, a novel quaternary low-cobalt LiNi0.88Co0.06Mn0.03Al0.03O2 cathode material (NCMA-ZB) is rationally designed and synthesized by a two-step modification of Zr-doping and LiBO2-coating for the first time. Impressively, the two-step modified NCMA-ZB cathode exhibits greatly improved long-term cycling performance, voltage fading, high-temperature performance and safety performance. Further studies demonstrate that the two-step modification of Zr-doping and LiBO2-coating can remarkably strengthen the structural stability during the cell cycling. In addition, the thermal decomposition temperature of the modified NCMA-ZB cathode is increased by ∼8 ℃. Finally, the coin cells assembled by the as-prepared NCMA-ZB cathodes show a discharge specific capacity of 211.7 mAh g⁻¹ and an initial coulombic efficiency of 89.0% at 0.1 C and 25 ℃ with a cut-off voltage range of 3.0-4.3 V. The corresponding capacity retention reaches 98.1% after 50 cycles at 1C. It additionally provides significantly improved high-temperature electrochemical performance of capacity retention of 97.8% after 50 cycles at 45 ℃. Moreover, the 18650-type cylindrical full cell configured with NCMA-ZB as the cathode obtains capacity retention of 95.8% after 1000 cycles at 1C at 2.75-4.2 V.
LiCoO2 is a dominant cathode material for lithium-ion (Li-ion) batteries due to its high volumetric energy density, which could potentially be further improved by charging to high voltages. However, practical adoption of high-voltage charging is hindered by LiCoO2’s structural instability at the deeply delithiated state and the associated safety concerns. Here, we achieve stable cycling of LiCoO2 at 4.6 V (versus Li/Li+) through trace Ti–Mg–Al co-doping. Using state-of-the-art synchrotron X-ray imaging and spectroscopic techniques, we report the incorporation of Mg and Al into the LiCoO2 lattice, which inhibits the undesired phase transition at voltages above 4.5 V. We also show that, even in trace amounts, Ti segregates significantly at grain boundaries and on the surface, modifying the microstructure of the particles while stabilizing the surface oxygen at high voltages. These dopants contribute through different mechanisms and synergistically promote the cycle stability of LiCoO2 at 4.6 V.
The influence of the initial Li/Co stoichiometry in LiCoO2 (LCO) (1.00 ≤ Li/Co ≤ 1.05) on the phase transition mechanisms occurring at high voltage during lithium de-intercalation (V > 4.5 vs. Li+/Li) was investigated by in situ X-ray diffraction. Even if the excess Li+ in Li1.024Co0.976O1.976 doesn’t hinder the formation of the H1 3 and O1 phases, the latter are obtained at higher voltages and exhibit larger c parameters compared to their analogues formed from Li1.00CoO2. We also showed that for the stoichiometric Li1.00CoO2, the de-intercalation process is more complex than already reported, with the formation of an intermediate structure between H1 3 and O1.
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.
A new density functional (DF) of the generalized gradient approximation (GGA) type for general chemistry applications termed B97-D is proposed. It is based on Becke's power-series ansatz from 1997 and is explicitly parameterized by including damped atom-pairwise dispersion corrections of the form C(6) x R(-6). A general computational scheme for the parameters used in this correction has been established and parameters for elements up to xenon and a scaling factor for the dispersion part for several common density functionals (BLYP, PBE, TPSS, B3LYP) are reported. The new functional is tested in comparison with other GGAs and the B3LYP hybrid functional on standard thermochemical benchmark sets, for 40 noncovalently bound complexes, including large stacked aromatic molecules and group II element clusters, and for the computation of molecular geometries. Further cross-validation tests were performed for organometallic reactions and other difficult problems for standard functionals. In summary, it is found that B97-D belongs to one of the most accurate general purpose GGAs, reaching, for example for the G97/2 set of heat of formations, a mean absolute deviation of only 3.8 kcal mol(-1). The performance for noncovalently bound systems including many pure van der Waals complexes is exceptionally good, reaching on the average CCSD(T) accuracy. The basic strategy in the development to restrict the density functional description to shorter electron correlation lengths scales and to describe situations with medium to large interatomic distances by damped C(6) x R(-6) terms seems to be very successful, as demonstrated for some notoriously difficult reactions. As an example, for the isomerization of larger branched to linear alkanes, B97-D is the only DF available that yields the right sign for the energy difference. From a practical point of view, the new functional seems to be quite robust and it is thus suggested as an efficient and accurate quantum chemical method for large systems where dispersion forces are of general importance.
Single-Crystal" Cathode Materials for Lithium-Ion Batteries
- Y Wang
- E Wang
- X Zhang
- H Yu
- High-Voltage
Wang, Y.; Wang, E.; Zhang, X.; Yu, H. High-Voltage "Single-Crystal" Cathode Materials for Lithium-Ion Batteries. Energy Fuels
2021, 35 (3), 1918−1932.
- Z Wu
- G Zeng
- J Yin
- C.-L Chiang
- Q Zhang
- B Zhang
- J Chen
- Y Yan
- Y Tang
- H Zhang
Wu, Z.; Zeng, G.; Yin, J.; Chiang, C.-L.; Zhang, Q.; Zhang, B.;
Chen, J.; Yan, Y.; Tang, Y.; Zhang, H.; et al. Unveiling the Evolution
of LiCoO2 beyond 4.6 V. ACS Energy Lett. 2023, 8 (11), 4806−4817.