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a) Layered crystal structure of NCM. Reproduced with permission.61 Copyright 2017, American Chemical Society. b) Layered crystal structure of Li2MnO3 with C2/m space group symmetry. [100]m, [−1−10]m, and [−110]m crystallographic orientations with transition metal and Li columns within the TM layer aligned along the projection direction.
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In order to satisfy the energy demands of the electromobility market, both Ni‐rich and Li‐rich layered oxides of NCM type are receiving much attention as high‐energy‐density cathode materials for application in Li‐ion batteries. However, due to different stability issues, their longevity is limited. During formation and continuous cycling, especial...
Citations
... However, Ni-rich NMC suffers from structural and interfacial instability, causing degradation of the electrode and significantly affecting the overall electrochemical performance [9,10]. The polycrystalline structure of NMC exacerbates these degradations due to its weak grain boundaries, which are prone to cracking, exposing new surfaces for parasitic side reactions with the electrolyte [11][12][13][14][15]. ...
High Ni-content LiNixMnyCozO2 (NMC) cathodes (with x ≥ 0.8, x + y + z = 1) have gained attention recently for their high energy density in electric vehicle (EV) Li-ion batteries. However, Ni-rich cathodes pose challenges in capacity retention due to inherent structural and surface redox instabilities. One promising strategy is to make the Ni-rich NMC material in the form of single-crystal micron-sized particles, as they resist intergranular and surface degradation during cycling. Among various methods to synthesize single-crystal NMC (SC-NMC) particles, molten-salt-assisted calcination offers distinct processing advantages but at present, is not yet optimized or mechanistically clarified to yield the desired control over crystal growth and morphology. In this project, molten-salt-mediated transformation of Ni0.85Mn0.05Co0.15(OH)2 precursor (P-NMC) particles to LiNi0.85Mn0.05Co0.15O2 particles is investigated in terms of the crystal growth mechanism and its electrochemical response. Unlike previous studies that involved large volumes of molten salt, using a smaller volume of molten KCl is found to result in larger primary particles with improved cycling performance achieved via partial reactive dissolution and heterogeneous nucleation growth, suggesting that the ratio of molten salt volume to NMC mass is an important parameter in the synthesis of single-crystal Ni-rich NMC materials.
... The obtained discharge capacities at different C-rates are shown in Figure 6b. All samples exhibit a typical drop in the initial charge capacity, which is related to the loss of active lithium, [51] structural rearrangements, and contact loss. [52] The post processing that affects the microstructure and ionic partial transport affects the overall capacities, leading to higher attainable capacitites compared to using the pristine solid electrolyte. ...
While post‐synthesis processing steps are frequently applied in the preparation of cathode composites for solid‐state batteries to ensure homogeneous mixing and good contact with the cathode active material, little is known about the processes that occur during milling and how they influence structure and transport of solid electrolytes. Here, an extensive set of experimental methods and simulations are used to study the effects of post‐synthesis milling by a frequency and planetary ball mill on the highly conducting chloride‐rich argyrodite Li5.5PS4.5Cl1.5. Structural analyses show that processing can reduce the coherence length and increase the disorder. The reduced crystallite size correlates with a decrease in ionic conductivity in the post‐processed solid electrolytes. Simulating the ball milling processes by the discrete element method provides fundamental understanding and reveals the correlation of the loss in coherence with the specific energy input and the numbers of stressing events during the milling process. An observed decrease in particle size in ball milled samples leads to lower tortuosity in the cathode composites. As the loss in coherence and decrease in particle size have opposite effects on the performance, optimizing these processing conditions will play a significant role on the road to highly performing solid‐state batteries.
... At a highly delithiated state, the active Ni 4+ ions are unstable and have a tendency to form an NiO-like rocksalt phase on the cathode surface that increases the resistance, leading to capacity decay. 52,53 The apparent morphological evolution of the TiO 2 -coated NCM622 particles before and after cycling can be observed in Figures S19, S20, and S26. Second, as discussed in the section ''mechanism behind high-voltage stability,'' an in situ formed N and F-rich interphase is detected between cathode and ceramic-based CSE in the ASSBs, which is attributed to the decomposition of the infiltrated PVDF-LiTFSI during the initial cycles in analogy of the solid electrolyte interphase that forms in LE-based LIBs. ...
... [21][22][23][24][25][26] It has been found that the significant expansion and contraction of the c-lattice parameter during cycling induces stress on the cathode secondary particles, potentially leading to the development of micro-cracks along the grain boundaries of primary particles. 27 This phenomenon primarily occurs during highvoltage cycling and is associated with pronounced and abrupt anisotropic volume changes, specifically related to the H2-H3 phase transition. 28,29 The subsequent intergranular fracture can lead to the formation of microcracks, exposing the interior of the particle to electrolyte penetration. ...
Nickel-rich layered oxides, crucial for high-energy-density Li-ion batteries, face challenges in cycle life due to intricate chemo-mechanical degradation. This study pioneers a comprehensive approach, integrating nano X-ray computed tomography and advanced electrochemical methods, to untangle the interplay of degradation mechanisms in complex composite electrodes. The evolution of cracking in Nickel-rich cathodes is meticulously quantified under diverse operating conditions. Surprisingly, our findings unveil that, contrary to conventional wisdom, crack formation is not the primary driver of capacity decay in Nickel-rich cathodes. Instead, the limiting factor emerges from the interplay between cycling-induced cracks and a progressively growing resistivity. Cracks, amplifying electrochemically active surfaces, foster side reactions, elevating resistance, and consequently diminishing capacity and current rate capability. This novel insight redirects attention to the dynamic resistivity growth, pinpointing operating conditions as a critical contributor. This work not only advances our understanding of Nickel-rich cathode degradation but also provides a framework for strategic mitigation strategies.
... In addition to the cobalt-free strategy, reducing the nickel content in Li[Ni x Mn y ]O 2 can further reduce the production costs of batteries. However, compared to high-nickel NCM cathodes, reducing the nickel content in Li[Ni x Mn y ]O 2 (x, y > 0.2) results in a lower effective energy density under the same charge/discharge voltage window [20,21]. To address this issue, Liu et al. [22] proposed that manganese substitution for cobalt in ternary cathode materials can be suitable for high-voltage operation. ...
Medium-nickel cobalt-free cathode materials have attracted much attention in recent years for their low cost and high energy density. However, the structural stability of nickel-based cathode materials becomes compromised when accompanied by the increasing of voltage, leading to poor cycling performance and, thus, hindering their widespread industrial application. In this work, we investigated the optimal charge cut-off voltage for the nickel-based cathode material LiNi0.6Mn0.4O2 (NM64). Within the voltage range of 3.0 to 4.5 V, the electrode energy density reached 784.08 Wh/kg, with an initial Coulombic efficiency of 84.49%. The reversible specific capacity at 0.1 C reached 197.84 mAh/g, and it still maintained a high reversible specific capacity of nearly 150 mAh/g, with a capacity retention rate of 86% after 150 cycles at 1 C. Furthermore, NM64 exhibited an intact morphological structure without noticeable cracking after 150 cycles, indicating excellent structural stability. This study emphasizes the relationship between the stability of NM64 cathodes and different operating voltage ranges, thereby promoting the development of high-voltage layered nickel-based cathode materials.
... For instance, positive electrode materials like layered oxides based on Nickel, Manganese, and Cobalt (NMC's) and the spinel LiMn 2 O 4 experience notable volume alterations, in particular, when charged to high voltages [1][2][3][4][5]. The mismatch between the lithiated and delithiated structures, differing in volume and shape, induces an important source of strain leading to mechanical stresses, which are at the origin of electrode material degradation and battery performance deterioration after repeated cycles [6][7][8][9][10][11]. More precisely, these changes affect the general morphology of electrode materials, a well-known cause of capacity loss [7]. ...
Mechanical degradation in electrode materials during successive electrochemical cycling is critical for battery lifetime and aging properties. A common strategy to mitigate electrode mechanical degradation is to suppress the volume variation induced by Li/Na intercalation/deintercalation, thereby designing strain-less electrodes. In this study, we investigate the electrochemically-induced volume variation in layered and spinel compounds used in Li-ion and Na-ion battery electrode materials through density functional theory computations. Specifically, we propose to decompose the volume variation into electronic, ionic, and structural contributions. Based on this analysis, we suggest methods to separately influence each contribution through strategies such as chemical substitution, doping, and polymorphism. Altogether, we conclude that volume variations can be controlled by designing either mechanically hard or compact electrode materials.
... The peaks in the pristine sample correspond to the known xLiMnO 2 -(1-x) LiNi x Mn y Co z O 2 monoclinic and rhombohedral bulk structure. 28,33,34 Treated samples spectra mirror the diffraction pattern of pristine sample and show no meaningful change, indicating that the bulk structure remains unchanged in all tested temperatures. ...
... It is well known that temperature combined with changes to surface oxygen could lead to restructuring similar to electrochemical activation. 3,33 The Mn 3s XPS shows an increase in energy split, values which are presented in Table S3. Values at low temperatures, 50 & 80°C seems close to pristine value. ...
Most next-generation electrode materials are prone to interfacial degradation, which eventually spreads to the bulk and impairs electrochemical performance. One promising method for reducing interfacial degradation is to surface engineer the electrode materials to form an artificial cathode electrolyte interphase as a protective layer. Nevertheless, the majority of coating techniques entail wet processes, high temperatures, or exposure to ambient conditions. These experimental conditions are only sometimes conducive and can adversely affect the material structure or composition. Therefore, we investigate the efficacy of a low-temperature, facile atomic surface reduction (ASR) using trimethylaluminum vapors as a surface modification strategy for Li and Mn-rich NCM (LMR-NCM). The results presented herein manifest that the extent of TMA-assisted ASR is temperature-dependent. All tested temperatures demonstrated improved electrochemical performance. However, ASR carried out at temperatures >100 °C was more effective in preserving the structural integrity and improving the electrochemical performance. Electrochemical testing revealed improved rate capabilities, cycling stability, and capacity retention of ASR-treated LMR-NCM. Additionally, post-cycling high-resolution scanning electron microscopy analysis verified that after extended cycling, ASR carried out at T > 100 °C showed no cracks or cleavage, demonstrating the efficiency of this method in preventing surface degradation.
... In case of layered oxides, this type of structure is often referred to as H 1 -type structure. [140][141][142][143] The structure is stable for various compositions of NCM oxides. 144 The atomic models of crystal structure for NCM811 in different planes are depicted in Fig. 1b and c. ...
This review provides an overview of recent advances in the utilization of Ni-rich nickel–cobalt–manganese (NCM) oxides as cathode materials for Li-ion rechargeable batteries (LIBs). In the past decade, Ni-rich NCM cathodes have been extensively investigated because of their rational capacity and easy accessibility of constituent elements. However, huge capacity fading and irreversible structural disorder, associated with oxygen release, are the major limitations which hinder the desired electrochemical performance of these cathodes. The LIB performance can be improved through several strategies such as doping, coating, composite formation, microstructure manipulation and replacing the Mn ions. Attempts are also made to amend the crystal orientation and achieve additive-induced surface engineering of NCM cathodes. However, the practical application of high-performance LIBs demand an effective modification of the intrinsic properties of NCMs. Substandard thermal stability is another safety aspect to be resolved in the Ni-rich NCMs. However, efforts in this context are not enough. Apart from designing NCM cathodes, there are major issues such as cost-effectiveness, supply and demand for constituent elements, and the reuse of spent batteries, which hinder the realisation of LIBs with high electrochemical performance. Keeping in mind the current research interests, this review article presents concise and in-depth strategies to design NCM cathodes for future energy demands of mankind by considering the cost and Co abundance-related issues.
... This issue arises mainly from the surface degradation of the cathode particles, especially those with high Ni concentrations, such as NCM and NCA. [4,5,[45][46][47] The primary concern is the transformation of Ni 4þ into a more stable yet electrically insulating Ni─O phase. This transformation occurs alongside the breakdown of the electrolyte on the cathode surface and the formation of microcracks owing to repeated charging and discharging. ...
This review explores the challenges and advancements in the development of high‐energy lithium‐ion batteries (LIBs), particularly focusing on the electrochemical and structural stability of Ni‐rich cathode materials. Despite their potential to increase the energy density of LIBs, these cathode materials encounter issues such as irreversible phase transitions and structural degradation during cycling, which ultimately affect their electrochemical performance. Elemental doping/substitution has emerged as promising strategies to address these challenges. However, the precise mechanisms underlying their performance enhancement remain unclear. The objective is to elucidate the complex reaction mechanisms triggered by doping and substitution in Ni‐rich cathode materials by employing in situ operando analyses to uncover their effects on electrochemical behavior and structural integrity during cycling. This comprehensive investigation aims to clarify the roles of elemental dopants or substituents in the crystal structures of Ni‐rich cathode materials, thereby offering valuable insights for the structural engineering of cathode materials in high‐energy LIBs. By elucidating these intricate mechanisms, this review provides a practical roadmap for future research and significantly contributes to LIB technology by guiding material design and optimization strategies in the development of advanced LIBs.
... Current efforts to improve performance and capacity involve reducing the Co content of cathode materials by replacing Co with less toxic and less expensive Mn and Ni, resulting in the lithium nickel manganese cobalt oxides (NMC), which also show increased practical capacities particularly for Ni-rich stoichiometries. [5][6][7][8] . The increased complexity of these materials warrants further consideration of how their charge compensation mechanisms vary with composition, including the extent to which different transition metal (TM) centres and oxygen participate during cycling. ...
... Improved understanding of oxygen's role in charge compensation could inform approaches to increase capacity 9,10 or mitigate degradation of cathode active materials. 5,11 The dominant experimental techniques for understanding oxygen redox activity in Li-ion battery cathode materials are O K-edge core loss spectroscopies, which involve probing transitions from the O 1s to unoccupied states, and include X-ray absorption spectroscopy(XAS) 12,13 , electron energy loss spectroscopy (EELS) 12,14 , X-ray Raman spectroscopy, and resonant inelastic X-ray scattering (RIXS) 15,16 . Although RIXS can potentially give the most detailed insight into the nature of O redox, 17,18 interpreting RIXS is challenging, even when first-principles calculations are available for comparison. ...
Core loss spectroscopies can provide powerful element-specific insight into the redox processes occurring in Li-ion battery cathodes, but this requires accurate interpretation of the spectral features. Here, we systematically interpret oxygen K-edge core loss spectra of layered lithium transition-metal (TM) oxides (LiMO 2 where M=Co, Ni ,Mn) from first principles using density-functional theory (DFT). Spectra are simulated using three exchange-correlation functionals, comprising the GGA functional PBE, the DFT-PBE + Hubbard U method and the meta-GGA functional rSCAN. In general, rSCAN provides a better match to experimentally observed excitation energies of spectral features compared to both PBE and PBE+U, especially at energies close to the main edge. Projected density of states of core-hole calculations show that the O orbitals are better described by rSCAN. Hybridisation, structural distortions, chemical composition , and magnetism significantly influence the spectra. The O K-edge spectrum of LiNiO 2 obtained using rSCAN shows a closer match to the experimental XAS when derived from a simulation cell which includes a Jahn-Teller distortion, showing that the DFT-calculated pre-edge feature contains information about not only chemical species but also geometric distortion. Core loss spectra derived from DFT can also differentiate between materials with the same structure and magnetic configuration but comprising different TMs; these differences are comparable to those observed in experimental XAS from the same materials. This foundational work helps establish the extent to which DFT can be used to bridge the interpretation gap between experimental spectroscopic signatures and ab initio methods describing complex battery materials, such as lithium nickel manganese cobalt oxides. 2 https://doi.org/10.26434/chemrxiv-2024-tmh4h ORCID: https://orcid.org/0009-0009-9676-7487 Content not peer-reviewed by ChemRxiv.