Oxide Cathodes For Lithium-ion Batteries Research Articles

(Invited) High-Nickel Layered Oxide Cathodes: Crack Vs. Surface Reactivity

The appetite for long driving range and high energy density is pushing the nickel content in layered oxide cathodes for lithium-ion batteries. The lying of Ni3+/4+:3d band slightly above the Co3+/4+:3d band enables to extract more lithium during charge without encountering oxygen release from the lattice in high-nickel cathodes compared to that in LiCoO2. However, as the nickel content increases in the lattice, the cells suffer from cycle and thermal instability. The cycle instability has largely been attributed in the literature to the formation of cracks caused by the occurrence of H2-H3 phase transition with large lattice parameter changes during high degree of charge. Several approaches, such as doping with other cations and microstructural control of the primary and secondary particles, have been extensively pursued to overcome the challenges and improve the cycle life.With a systematic investigation of a number of cathode compositions and their characterization after extensive cycling, this presentation will illustrate that surface reactivity of high-nickel cathodes with electrolyte plays a dominant and decisive role on cycle life. Even cathodes like LiNiO2 with 100% Ni without any cation doping or surface coating could be cycled with high capacities over a large number of cycles with an appropriate choice of electrolyte that suppresses surface reactivity. Electrolytes that are stable to slightly higher voltages, even by as low as 100 mV, compared to the conventional electrolytes alter the surface reconstruction pathway on cathode surface in contact with electrolyte. Electrolytes with better high-voltage stability favor the formation of mildly reduced LiNi2O4 spinel on the surface without much oxygen release from the surface. In contrast, electrolytes that have inferior stability to higher voltages lead to a drastic reduction of the cathode surface to highly reduced Ni3O4 spinel and NiO rock salt phases with significant oxygen loss from and volume change on the surface, which could cause crack initiation on the surface, followed by their propagation into the bulk. Interestingly, the fast 3-dimensional lithium-ion and electron transport in spinel LiNi2O4 supports a facile charge transfer through the cathode-electrolyte interphase (CEI), resulting in better cycle life, in contrast to the poor lithium-ion transport in both spinel Ni3O4 and rock salt NiO phases, resulting in poor charge-transfer through the CEI and inferior cycle life. With robust electrolyte formulations with better high-voltage stability, long cycle life could be achieved even with the repeated occurrence of the H2-H3 phase transitions over a large number of cycles.

Deep-Learning Aided Atomic-Scale Phase Segmentation toward Diagnosing Complex Oxide Cathodes for Lithium-Ion Batteries.

Phase transformation─a universal phenomenon in materials─plays a key role in determining their properties. Resolving complex phase domains in materials is critical to fostering a new fundamental understanding that facilitates new material development. So far, although conventional classification strategies such as order-parameter methods have been developed to distinguish remarkably disparate phases, highly accurate and efficient phase segmentation for material systems composed of multiphases remains unavailable. Here, by coupling hard-attention-enhanced U-Net network and geometry simulation with atomic-resolution transmission electron microscopy, we successfully developed a deep-learning tool enabling automated atom-by-atom phase segmentation of intertwined phase domains in technologically important cathode materials for lithium-ion batteries. The new strategy outperforms traditional methods and quantitatively elucidates the correlation between the multiple phases formed during battery operation. Our work demonstrates how deep learning can be employed to foster an in-depth understanding of phase transformation-related key issues in complex materials.

Influence of Single-Crystalline Morphology on High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries

Single-crystal, high-nickel layered oxides have seen increasing interest due to their potential to address the surface reactivity and mechanical resilience issues inherent to these cathode compositions. Great strides have been made in methods for synthesizing single-crystal layered oxides, but much is still unknown about the impact of single-crystalline morphology on the electrochemical behavior of these materials.Here, we report a comparative study on the electrochemical operation of single- and polycrystalline LiNiO2, respectively termed SCLNO and PCLNO. SCLNO is synthesized with a molten-salt-assisted method, allowing the crystals to form at the same temperature as used for solid-state synthesis of PCLNO. As a result, the cathodes possess similar lattice structures with pure hexagonal layered phase and comparable levels of cation mixing (~1.5%), enabling a robust comparison of single-crystalline and polycrystalline morphology with minimal confounding variables. Charge/discharge performance, rate capability, and cycling stability reveal insights on the behavior single-crystal layered oxides and the performance tradeoffs they elicit. Particular attention is directed towards Li+ diffusion and phase evolution dynamics within the two morphologies, as characterized by in-situ and ex-situ X-ray diffraction, differential capacity analysis, and galvanostatic intermittent titration technique (GITT).As has been reported in other cathode systems,1 single-crystal LNO (SCLNO) delivers a lower initial capacity of about 200 mA h g-1, compared to nearly 230 mA h g-1 for polycrystalline LNO (PCLNO), most of which is lost in the low-voltage discharge region known to be particularly susceptible to kinetic hindrance.2 Indeed, GITT indicates a lower effective Li+ diffusivity in SCLNO. Interestingly, the single-crystal cathode exceeds the polycrystalline cathode in rate capability; SCLNO delivers 78% capacity at 10C discharge rate (158 mA h g-1) while PCLNO achieves only 25% capacity (57 mA h g-1). Analysis of the charge/discharge profiles of the materials reveals the H2-H3 transition is still present in SCLNO at high discharge rates, while it disappears completely in PCLNO. Despite the conflicting nature of the observed lower diffusivity, yet improved rate capability, further analysis suggests that the elimination of grain boundaries in single-crystalline cathodes may be responsible for both phenomena. Details of the experimental techniques, and results from the electrochemical analysis will be presented during the meeting. The findings from this study will contribute to understanding single-crystalline layered oxides and aid the design of higher-performance cathode materials.References Sun, X. Cao, H. Zhou, Advanced single-crystal layered Ni-rich cathode materials for next-generation high-energy-density and long-life Li-ion batteries, Phys. Rev. Mater. 6 (2022) 1–11Grenier, P.J. Reeves, H. Liu, I.D. Seymour, K. Märker, K.M. Wiaderek, P.J. Chupas, C.P. Grey, K.W. Chapman, Intrinsic Kinetic Limitations in Substituted Lithium-Layered Transition-Metal Oxide Electrodes, J. Am. Chem. Soc. 142 (2020) 7001–7011.

(Invited) Delineating the Intricacies Involved in the Synthesis of Cobalt-Free High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries

Improving the energy density and cost of lithium-ion batteries (LIBs) requires a rational compositional design of layered oxide LiNi1-x-yMnxCoyO2 (NMC) cathodes. The prevailing trend is to increase the nickel content in the cathode to maximize energy density, but high-nickel NMC generally suffers from surface and bulk instabilities that shorten battery life. Dopants, such as cobalt, can help mitigate these issues, but its supply shortage issue prohibits its usage especially in the massive electric vehicle market. Our recent finding suggests that a combination of manganese and aluminum in LiNi0.9Mn0.05Al0.05O2 (NMA-90) promotes attractive energy density, cycle life, rate capability and thermal stability, proving that cobalt can be eliminated in high-nickel cathodes. Post-mortem analysis further reveals that the Mn-Al combination provides synergistic improvements in structural and surface stabilities compared to LiNi0.9Mn0.05Co0.05O2 (NMC-90) and LiNi0.9Co0.05Al0.05O2 (NCA-90). A thorough understanding of the relationship between the synthesis condition and optimal materials properties of NMA-90 is necessary to enable its large-scale deployment. We will present findings from the calcination and coprecipitation study of several cobalt-free cathodes to elucidate this relationship. It is revealed that the cycle stability of LiNi0.9Mn0.1O2 (NM-90) is not dependent on Li/Ni mixing or primary particle size, but is dependent on the calcination temperature. Incorporating Al into NM-90 during coprecipitation reactions cause high internal porosity in the hydroxide precursor, which impacts the final morphology of the calcined cathodes and thus their electrochemical stability. The ongoing work in our lab provides insight on the synthesis sensitivity of NMA and strategizes methods to control its electrochemical properties.

Atomic-Scale Understanding of New Phase Transition Pathway and Phase Boundary Structures in Layered Oxide Cathodes for Lithium-Ion Batteries.

Atomic-Scale Understanding of New Phase Transition Pathway and Phase Boundary Structures in Layered Oxide Cathodes for Lithium-Ion Batteries.

High-voltage electrolyte design for a Ni-rich layered oxide cathode for lithium-ion batteries

LiNi0.8Co0.1Mn0.1O2 (NCM811) is one of the most promising cathode materials in high-energy-density Li-ion batteries (LIBs) because of its high capacity and low cost. However, it still suffers from irreversible capacity fading at high cut-off voltages. This is mainly because high voltage accelerates the hydrolysis reaction of lithium hexafluorophosphate with trace water to generate byproducts such as highly corrosive hydrogen fluoride (HF) resulting in an unstable cathode–electrolyte interface and continuous irreversible phase transitions. Here, we modify a conventional electrolyte by adding the dual additives of tetrabutyl titanate (TBT) and lithium difluoroxalate borate (LiDFOB) to form a stable Ti-, B-, and F-rich interfacial layer to eliminate the unfavorable cathode-electrolyte side reactions and suppress deleterious phase transitions. Additionally, TBT can stabilize the electrolyte by removing H2O/HF. With the synergistic effect of the dual additives, the cycling stability of NCM811 at high voltages is enhanced considerably. The Li∣NCM811 cell with dual additives exhibits a high capacity retention rate of 86% after 200 cycles at 1 C and a high cut-off voltage of 4.5 V. This strategy provides a reference for designing high-voltage electrolytes for LIBs.

Controlling the Microstructure of Cobalt-Free, High-Nickel Cathode Materials with Dopant Solubility for Lithium-Ion Batteries.

Microstructural engineering is becoming notably important in the realization of cobalt-free, high-nickel layered oxide cathodes for lithium-ion batteries since it is one of the most effective ways to improve the overall performance by enhancing the mechanical and electrochemical properties of cathodes. In this regard, various dopants have been investigated to improve the structural and interfacial stabilities of cathodes with doping. Yet, there is a lack of a systematic understanding of the effects of dopants on microstructural engineering and cell performances. Herein, we show controlling the primary particle size by adopting dopants with different oxidation states and solubilities in the host structure as an effective way for tuning the cathode microstructure and performance. The reduction in the primary particle size of cobalt-free high-nickel layered oxide cathode materials, e.g., LiNi0.95Mn0.05O2 (NM955), with high-valent dopants, such as Mo6+ and W6+, gives a more homogeneous distribution of Li during cycling with suppressed microcracking, cell resistance, and transition-metal dissolution compared to lower-valent dopants, such as Sn4+ and Zr4+. Accordingly, this approach offers promising electrochemical performance with cobalt-free high-nickel layered oxide cathodes.

Synergistic Strategy Using Doping and Polymeric Coating Enables High-Performance High-Nickel Layered Cathodes for Lithium-Ion Batteries

As one of the most promising cathode materials for lithium-ion batteries, nickel-rich layered oxide LiNi0.83Co0.11Mn0.06O2 (NCM83) has an inherent issue with rapid capacity decay caused by phase change and interface side reactions during the charge/discharge cycling. Herein, an effectively synergistic strategy for improving the structural stability and electrochemical performance of NCM83 cathodes has been proposed, combining surface polymeric coating with bulk doping by the high-temperature solid-phase method. The comprehensive results demonstrate that the niobium (Nb) element can be successfully bulk-doped into the crystal lattice, which could increase the layer spacing, thus stabilizing the crystal structure and minimizing the Li+/Ni2+ mixing in the as-prepared NCM83 cathode. Meanwhile, a small amount of Nb in the form of oxide and a layer of polyaniline (PANI) was coated on the NCM83 cathode’s surface. This not only can prevent electrolyte erosion and inhibit side reactions but also can effectively improve the transport coefficient of Li+ during the charge and discharge process. The optimized NCM83 cathode exhibited outstanding discharge-specific capacity (236.79 mAh g–1 at 0.2 C rate and 215.67 mAh g–1 at 2 C rate), stable cycling performance (capacity retention of 84.4% after 100 cycles at 2 C), and excellent rate performance (150.58 mAh g–1 at 10 C) by taking advantage of the synergistic effects. The synergistic strategy using Nb doping in combination with a surface polymeric coating can enhance the fundamental understanding of the high-nickel layered oxide cathodes for lithium-ion batteries.

Impacts of Mg doping on the structural properties and degradation mechanisms of a Li and Mn rich layered oxide cathode for lithium-ion batteries

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.

Revealing the effect of Nb5+ on the electrochemical performance of nickel-rich layered LiNi0.83Co0.11Mn0.06O2 oxide cathode for lithium-ion batteries

The layered Nb5+-doped LiNi0.83Co0.11Mn0.06O2 (NCM) oxide cathode materials are successfully synthesized through introducing Nb2O5 into the precursor Ni0.83Co0.11Mn0.06(OH)2 during the lithiation process. The results refined by GSAS software present that the Nb5+-doped samples possess the perfect crystal structure with broader Li+ diffusion pathways. Moreover, the morphology characterized by scanning electron microscope displays the compact secondary particles packed by smaller primary particles under the effect of Nb5+. The excellent electrochemical properties are also acquired from the Nb5+-doped samples, in which the optimal rate performance and cycling stability are performed for NCM-1.0 when up to 1.0 mol % of Nb2O5 (based on the precursor) is added. Benefited from the introduction of Nb5+, the cell assembled with the NCM-1.0 electrode retains higher capacity retention of 86.6 % at 1.0 C and 25 °C, and 71.7 % at 1.0 C and 60 °C after 200cycles. Moreover, it also delivers higher discharge specific capacity of 154.6 mAh g−1 at 5.0 C. Therefore, the Nb5+-doping strategy may open an effective route for optimizing nickel-rich oxide cathode materials, which is worth popularizing for the enhancement of the electrochemical performance of nickel-rich cathodes for lithium-ion batteries.

Oxide Cathodes: Functions, Instabilities, Self Healing, and Degradation Mitigations.

Recent progress in high-energy-density oxide cathodes for lithium-ion batteries has pushed the limits of lithium usage and accessible redox couples. It often invokes hybrid anion- and cation-redox (HACR), with exotic valence states such as oxidized oxygen ions under high voltages. Electrochemical cycling under such extreme conditions over an extended period can trigger various forms of chemical, electrochemical, mechanical, and microstructural degradations, which shorten the battery life and cause safety issues. Mitigation strategies require an in-depth understanding of the underlying mechanisms. Here we offer a systematic overview of the functions, instabilities, and peculiar materials behaviors of the oxide cathodes. We note unusual anion and cation mobilities caused by high-voltage charging and exotic valences. It explains the extensive lattice reconstructions at room temperature in both good (plasticity and self-healing) and bad (phase change, corrosion, and damage) senses, with intriguing electrochemomechanical coupling. The insights are critical to the understanding of the unusual self-healing phenomena in ceramics (e.g., grain boundary sliding and lattice microcrack healing) and to novel cathode designs and degradation mitigations (e.g., suppressing stress-corrosion cracking and constructing reactively wetted cathode coating). Such mixed ionic-electronic conducting, electrochemically active oxides can be thought of as almost "metalized" if at voltages far from the open-circuit voltage, thus differing significantly from the highly insulating ionic materials in electronic transport and mechanical behaviors. These characteristics should be better understood and exploited for high-performance energy storage, electrocatalysis, and other emerging applications.

(Invited, Digital Presentation) Pushing the Limits of High Nickel NMC Cathodes

Lithium-ion batteries now dominate electrochemical energy storage for vehicle propulsion and grid storage in addition to portable electronics. In 2022, they celebrate their 50th anniversary, and yet still achieve only 25% of their theoretical energy density. The dominant anode and cathode today are graphitic carbon and the layered NMC oxides, LI[NiMnCoAl]O2. Both need improving. Most of the carbon in the anode must go, and the NMCs need pushing to their limit and at the same time eliminating cobalt. I will today discuss the challenges faced as we push the limits of the NMCs to their limits, > 80% lithium cycling, and Ni>0.8 and Co <<0.1. The higher the Ni content the lower the charging voltage needed for a given cycling capacity, but the greater its surface and bulk reactivity. The issues discussed will include 1stcycle loss [1], high rate capability [2], cathode stability [3], and surface/bulk reactivity and the impact of surface/bulk modification [4,5] and the micron-size single crystals vs meatballs on these [6]. This work is being supported by DOE-EERE-BMR-Battery500 consortium.[1]. Hui Zhou, Fengxia Xin, Ben Pei, M. Stanley Whittingham, “What Limits the Capacity of Layered Oxide Cathodes in Lithium Batteries?”, ACS Energy Lett. 2019, 4: 1902−1906.[2]. Chunmei Ban, Zheng Li, Zhuangchun Wu, Melanie J. Kirkham, Le Chen, Yoon Seok Jung, E. Andrew Payzant, Yanfa Yan, M. Stanley Whittingham, and Anne C. Dillon “Extremely Durable High-Rate Capability of a LiNi0.4Mn0.4Co0.2O2 Cathode Enabled by Single–Wall Carbon Nanotubes”, Advanced Energy Materials, 2011, 1: 58-62.[3]. Hyung-Joo Noh, Sungjune Youn, Chong Seung Yoon, Yang-Kook Sun “Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 (x = ¼ 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries”, J. Power Sources, 2013, 233: 121-130.[4]. Fengxia Xin, Hui Zhou, Yanxu Zong, Mateusz Zuba, Yan Chen, Natasha A. Chernova, Jianming Bai, Ben Pei, Anshika Goel, Jatinkumar Rana, Feng Wang, Ke An, Louis F. J. Piper, Guangwen Zhou, and M. Stanley Whittingham, “What is the Role of Nb in Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries?”, ACS Energy Letters, 2021, 6: 1377-1382.[5]. Ben Pei, Hui Zhou, Anshika Goel, Mateusz Zuba, Hao Liu, Fengxia Xin, and M. Stanley Whittingham, “Al Substitution for Mn during Co-Precipitation Boosts the Electrochemical Performance of LiNi0.8Mn0.1Co0.1O2”, J. Electrochemical Society, 2021, 68: 050532.[6]. Yujing Bi, Jinhui Tao, Yuqin Wu, Linze Li, Yaobin Xu, Enyuan Hu, Bingbin Wu, Jiangtao Hu, Chongmin Wang, JiGuang Zhang, Yue Qi and Jie Xiao, “Reversible planar gliding and microcracking in a single-crystalline Ni-rich cathode”, Science, 2020, 370: 1313-1317.

Operando Photonic Stopband Monitoring of Lithium-Ion Battery Electrodes

Research in lithium-ion batteries is often focused on optimising the electrode performance of either the anode1 or cathode2. One common research strategy is to explore alternative electrode material candidates for use as both the anode3 and cathode4. Another approach involves optimising the performance of existing electrode materials through structured electrode architectures with nano-sized features. Incorporating nanostructure into electrode design has reported advantages of shorter ion diffusion lengths and improved rate capability during cycling5. A common and simple technique for introducing nanostructure to electrodes is the use of a photonic crystal template, particularly inverse opal photonic crystals. The porous geometry, highly interconnected material and nano-sized features of the pore walls are all believed to contribute to improved electrochemical performance in inverse opal electrodes6 7.Photonic crystal materials are more than just a structural template and are renowned for their ability to tune the wavelengths of light propagating in the structure8 9. The repeating dielectric material comprising the structure reflects specific wavelengths, known as the photonic bandgap or stopband, depending on the size of the repeating lattice and the refractive index contrast between the composite materials. Tuning the photonic stopband of various inverse opal materials has been extensively studied10 11. Inverse opal battery electrodes have yet to exploit the optical potential of the photonic stopband.Here, we showcase a fundamentally new operando analysis technique for lithium-ion battery electrodes adopting a photonic crystal structure. Visible spectroscopy is used to monitor the presence and position of the photonic stopband of the electrode material during battery cycling, see Figure 1. Capitalizing on the sensitivity of the photonic stopband to lattice size and refractive index contrast, shifts or changes in the optical spectrum can be correlated to the electrode environment and material performance. Several optical effects are observed throughout the cycling process and linked back to the battery performance of the anode. A TiO2 inverse opal anode is reported on here, yet the technique is versatile and should be applicable to a wide range of electrode materials possessing a photonic crystal structure. References Kim, H.; Choi, W.; Yoon, J.; Um, J. H.; Lee, W.; Kim, J.; Cabana, J.; Yoon, W.-S., Exploring Anomalous Charge Storage in Anode Materials for Next-Generation Li Rechargeable Batteries. Chemical Reviews 2020, 120 (14), 6934-6976.Xu, J.; Dou, S.; Liu, H.; Dai, L., Cathode materials for next generation lithium ion batteries. Nano Energy 2013, 2 (4), 439-442.Liang, B.; Liu, Y.; Xu, Y., Silicon-based materials as high capacity anodes for next generation lithium ion batteries. Journal of Power Sources 2014, 267, 469-490.Manthiram, A.; Song, B.; Li, W., A perspective on nickel-rich layered oxide cathodes for lithium-ion batteries. Energy Storage Materials 2017, 6, 125-139.Mahmood, N.; Tang, T.; Hou, Y., Nanostructured Anode Materials for Lithium Ion Batteries: Progress, Challenge and Perspective. Advanced Energy Materials 2016, 6 (17), 1600374.McNulty, D.; Carroll, E.; O'Dwyer, C., Rutile TiO2 Inverse Opal Anodes for Li-Ion Batteries with Long Cycle Life, High-Rate Capability, and High Structural Stability. Advanced Energy Materials 2017, 7 (12), 1602291.McNulty, D.; Geaney, H.; Buckley, D.; O'Dwyer, C., High capacity binder-free nanocrystalline GeO2 inverse opal anodes for Li-ion batteries with long cycle life and stable cell voltage. Nano Energy 2018, 43, 11-21.John, S., Strong localization of photons in certain disordered dielectric superlattices. Phys. Rev. Lett. 1987, 58 (23), 2486-2489.Yablonovitch, E., Inhibited spontaneous emission in solid-state physics and electronics. Phys. Rev. Lett. 1987, 58 (20), 2059-2062.Schroden, R. C.; Al-Daous, M.; Blanford, C. F.; Stein, A., Optical Properties of Inverse Opal Photonic Crystals. Chemistry of Materials 2002, 14 (8), 3305-3315.Lonergan, A.; Hu, C.; O’Dwyer, C., Filling in the gaps: The nature of light transmission through solvent-filled inverse opal photonic crystals. Physical Review Materials 2020, 4 (6), 065201. Figure 1 (a) Schematic diagram of simultaneous electrochemical and optical characterisation techniques for photonic crystal electrodes. (b) Galvanostatic charge/discharge data for a TiO2 inverse opal electrode. (c) Optical spectrum for a TiO2 inverse opal submerged in LiPF6 electrolyte. (d) SEM image showing the ordered structure of a pristine TiO2 inverse opal. (e) Operando optical spectra obtained at 0.5 V intervals during discharge of the TiO2 inverse opal electrode. Figure 1

Correction to “Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries”

Correction to “Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries”

Understanding the nucleation and growth of the degenerated surface structure of the layered transition metal oxide cathodes for lithium-ion batteries by operando Raman spectroscopy

• The surface degradation process of the lithium-layered transition metal oxide cathode is revealed by an operando Raman spectroscopy study. • The degradation process is visualized by Raman mapping with the spectral window of ∼600 cm −1 . • The degradation process not only involves the structural changes, but also the growth and merging between the degenerated layers on charge–discharge. • The present study offers crucial information to counter the capacity decay of the NMC batteries. 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 LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode is examined on charge–discharge using an operando Raman cell. We revealed the surface degradation process of the cathode with the A 1g 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.

Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries

Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries

Introducing 4s-2p Orbital Hybridization to Stabilize Spinel Oxide Cathodes for Lithium-Ion Batteries.

Oxides composed of an oxygen framework and interstitial cations are promising cathode materials for lithium‐ion batteries. However, the instability of the oxygen framework under harsh operating conditions results in fast battery capacity decay, due to the weak orbital interactions between cations and oxygen (mainly 3d–2p interaction). Here, a robust and endurable oxygen framework is created by introducing strong 4s–2p orbital hybridization into the structure using LiNi0.5Mn1.5O4 oxide as an example. The modified oxide delivers extraordinarily stable battery performance, achieving 71.4 % capacity retention after 2000 cycles at 1 C. This work shows that an orbital‐level understanding can be leveraged to engineer high structural stability of the anion oxygen framework of oxides. Moreover, the similarity of the oxygen lattice between oxide electrodes makes this approach extendable to other electrodes, with orbital‐focused engineering a new avenue for the fundamental modification of battery materials.

Investigation of Lithium Polyacrylate Binders for Aqueous Processing of Ni-Rich Lithium Layered Oxide Cathodes for Lithium-Ion Batteries.

Ni‐rich layered oxide cathodes are promising candidates to satisfy the increasing energy demand of lithium‐ion batteries for automotive applications. Aqueous processing of such materials, although desirable to reduce costs and improve sustainability, remains challenging due to the Li+/H+ exchange upon contact with water, resulting in a pH increase and corrosion of the aluminum current collector. Herein, an example was given for tuning the properties of aqueous LiNi0.83Co0.12Mn0.05O2 electrode pastes using a lithium polyacrylate‐based binder to find the “sweet spot” for processing parameters and electrochemical performance. Polyacrylic acid was partially neutralized to balance high initial capacity, good cycling stability, and the prevention of aluminum corrosion. Optimized LiOH/polyacrylic acid ratios in water were identified, showing comparable cycling performance to electrodes processed with polyvinylidene difluoride requiring toxic N‐methyl‐2‐pyrrolidone as solvent. This work gives an exemplary study for tuning aqueous electrode pastes properties aiming towards a more environmentally friendly processing of Ni‐rich cathodes.

Accelerated Degradation in a Quasi-Single-Crystalline Layered Oxide Cathode for Lithium-Ion Batteries Caused by Residual Grain Boundaries.

The rapidly growing demand of electrical vehicles (EVs) requires high-energy-density lithium-ion batteries (LIBs) with excellent cycling stability and safety performance. However, conventional polycrystalline high-Ni cathodes severely suffer from intrinsic chemomechanical degradation and fast capacity fade. The emerging single-crystallization strategy offers a promising pathway to improve the cathode's chemomechanical stability; however, the single-crystallinity of the cathode is not always guaranteed, and residual grain boundaries (GBs) could persist in nonideal synthesis conditions, leading to the formation of "quasi-single-crystalline" (QSC) cathodes. So far, there has been a lack of understanding of the influence of these residual GBs on the electrochemical performance and structural stability. Herein, we investigate the degradation pathway of a QSC high-Ni cathode through transmission electron microscopy and X-ray techniques. The residual GBs caused by insufficient calcination time dramatically exacerbate the cathode's chemomechanical instability and cycling performance. Our work offers important guidance for next-generation cathodes for long-life LIBs.

Influences of Enhanced Entropy in Layered Rocksalt Oxide Cathodes for Lithium-Ion Batteries

Influences of Enhanced Entropy in Layered Rocksalt Oxide Cathodes for Lithium-Ion Batteries