Ni-rich Cathode Materials Research Articles

Self-induced corrosion of Ni-rich cathode materials by fluor-lithium salts

Self-induced corrosion of Ni-rich cathode materials by fluor-lithium salts

Restraining Planar Gliding in Single-Crystalline LiNi0.9Co0.05Mn0.05O2 Cathodes by Combining Bulk and Surface Modification Strategies.

The delamination cracking from planar gliding along the (003) facets and anisotropic lattice strain perpendicular to the (003) facets inevitable lead to degradation of Ni-rich single-crystal cathode materials, adversely affecting their cyclability. Herein, we rationally design a single-crystal LiNi0.9Co0.05Mn0.05O2 (SC90) cathode with robust chemo-mechanical properties, in which coherently grown MgO6 octahedra and BO4 tetrahedra are incorporated into the lattice, and a stabilizing Mg3(BO3)2 layer is concurrently formed on the particle surface. Multiscale in/ex situ characterizations and theoretical calculations indicate that introducing the MgO6 and BO4 units leads to a "pinning effect" within the layered structure. This in turn strongly mitigates mechanical degradation by reducing planar gliding and delamination cracking over extended cycling. Moreover, the Mg3(BO3)2 coating maintains fast lithium diffusion by suppressing parasitic reactions at the cathode|electrolyte interface. The tailored SC90 cathode exhibits a capacity retention of ~88% after 300 cycles at 5C rate, significantly outperforming the pristine counterpart (~60%). Additionally, a pouch-type full cell with a graphite anode sustains a specific discharge capacity of 177 mAh g-1 after 500 cycles, with 90% capacity retention. This work highlights the "pining effect" in preventing unfavorable slab sliding and structural deterioration, offering new insights for designing advanced ultrahigh Ni single-crystal cathodes.

Surface Reconstruction Reduces Internal Stress of Ni-Rich Cathode Particles.

High-voltage Ni-rich layered cathode materials are undoubtedly a powerful driving force for high-energy density lithium batteries. However, residual lithium impurities on the surface of Ni-rich materials can cause more severe side reactions under high-voltage, leading to rapid decay. There is still no reliable mechanistic explanation for this phenomenon. It has been detected that residual alkali on the cathode surface under high voltage can cause obvious side reactions. This side reaction will affect the capacity retention of the material and increase the internal stress of the particles. In addition, the surface reconstruction of Ni-rich cathodes is achieved through simple chemical reactions, turning waste into treasure. The newly generated Ti-based layer not only repairs the structure of the nickel-rich material but also optimizes the material from a dynamic perspective. Removing residual lithium components on the cathode surface effectively reduces the hydrolysis and self-catalytic side reactions of PF6 - at the electrolyte cathode interface and suppresses gas generation during cycling, promoting the application of the next generation of high-energy density Ni-rich layered cathode-based lithium batteries with high-voltage.

Tuning Molten-Salt-Mediated Calcination in Promoting Single-Crystal Synthesis of Ni-Rich LiNixMnyCozO2 Cathode Materials

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.

Dual Modification Strategy for Enhanced Cycling and Rate Performance of Ni-Rich Cathode Materials in Lithium-Ion Batteries.

A great challenge in the commercialization process of layered Ni-rich cathode material LiNixCoyMn1-x-yO2 (NCM, x ≥ 80%) for lithium-ion batteries is the surface instability, which is exacerbated by the increase in nickel content. The high surface alkalinity and unavoidable cathode/electrolyte interface side reactions result in significant decrease for the capacity of NCM material. Surface coating and doping are common and effective ways to improve the electrochemical performance of Ni-rich cathode material. In this study, an in situ reaction is induced on the surface of secondary particles of NCM material to construct a stable lithium sulfate coating, while achieving sulfur doping in the near surface region. The synergistic modification of lithium sulfate coating and lattice sulfur doping significantly reduced the content of harmful residual lithium compounds (RLCs) on the surface of NCM material, suppressed the side reactions between the cathode material surface and electrolyte and the degradation of surface structure of the NCM material, effectively improved the rate capability and cycling stability of the NCM material.

Synthesis of nano cubic microstructure LiNi0.8Co0.1Mn0.1O2 cathode materials via rapid precipitation assisted with hydrothermal treatment

In this work, a modified Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 with a unique nano cubic microstructure is successfully synthesized via a rapid precipitation assisted with hydrothermal treatment. The formation of this distinctive microstructure is attributed to the homogeneous rapid precipitation in microreactor, which predominantly generates uniform crystal nuclei. The as-prepared material with nano-/microstructure shows superior initial reversible capacity (205.3 mAh·g−1 at 2.7–4.3 V) and rate capability (163.9 mAh·g−1 at 5 C). Additionally, it maintains a high capacity (188.2 mAh·g−1) with a retention of 87.2 % at 1 C after 200 cycles, demonstrating outstanding cycling stability. Our work presents a straightforward and efficient approach for producing nano-cubic microstructure layered cathode materials.

Synergistically regulating the structural tolerance of Co-free Ni-rich cathode materials at high-rate through multi-heteroatoms substitution

Cobalt-free, nickel-rich layered oxides are attracting extensive interest as cathodes to construct high-energy and sustainable lithium-ion batteries, but the intrinsic structure instability and weakened reaction kinetics deteriorate their application. Nowadays, doping engineering, especially multielement doping, has become an effective modification method for obtaining high-performance Ni-rich materials. Herein, the designed doping strategy with high oxidation states element (Zr4+, Mo6+) substituting transition metal element and Mg2+ replacing Li+ in LiNi0.9Mn0.1O2 (NM-ZMM) has been designed to enhance its electrochemical properties. The introduced doping elements with high oxidation states can generate the strong metal-O bond, which contributes to suppress the structural collapse induced by internal stress, and then maintain unblock ion channels for NM-ZMM. Meanwhile, the presence of Mg2+ can also be employed as the pillar ions to reinforce the structure stability, and occupy the Li-sites to inhibit lattice distortion during charging/discharging process. Thus, benefitting from the synergistic reinforcement of co-doping strategy, as-prepared NM-ZMM materials exhibit the prominent capacity retention (87.5 %, 210 cycles, 1C; 85.5 %, 2C, 150 cycles). Thereof, this creative strategy is crucial in strengthening the electrochemical performance of Ni-rich Co-free materials, which contributes to promote the development of high-performance and cost-effective Li-ion storage technology.

Machine learning descriptors for crystal materials: applications in Ni-rich layered cathode and lithium anode materials for high-energy-density lithium batteries

Lithium batteries have revolutionized energy storage with their high energy density and long lifespan, but challenges such as energy density limitations, safety, and cost still need to be addressed. Crystalline materials, including Ni-rich cathodes and lithium anodes, play pivotal roles in the performance of high-energy-density lithium batteries. Understanding the micro-scale behavior and degradation mechanisms of these materials is crucial for improving macro-scale battery performance. Simulation methods, particularly machine learning (ML) techniques, have become indispensable tools in elucidating these intricate processes because of great efficiency and acceptable accuracy. ML methods depend on descriptors, which bridge the gap between crystal structures and input matrices of models. These descriptors encode essential atomic-level details in crystal structures, enabling predictions of material properties and behaviors relevant to lithium batteries. This paper reviews and discusses the diverse array of descriptors employed in the simulation of crystalline materials for lithium batteries with high energy density. Case studies highlight the effectiveness of different descriptors in simulating cathode behaviors such as Li/Ni disordering, screening of stable LiNi0.8Co0.1Mn0.1O2 (NMC811) configurations, and lithium deposition behaviors at the anode interface. The discussed descriptors can also be applied to other crystalline cathode, anode, and electrolyte materials in lithium batteries and advance the development of lithium batteries with superior energy density.

Constructing electrochemically stable single crystal Ni-rich cathode material via modification with high valence metal oxides

Single crystal Ni-rich cathode materials (SCNCM) are a good supplement in the market of nickel-based materials due to their safety and excellent electrochemical performance. However, the challenges of cation mixing, phase change during charge/discharge, and low thermal stability remain unresolved in single crystal particles. To address these issues, SCNCM are rationally modified by incorporating transition metal (TM) oxides, and the influence of metal ions with different valence states on the electrochemical properties of SCNCM is methodically explored through experimental results and theoretical calculations. Enhanced structural stability is demonstrated in SCNCM after the modifications, and the degree of improvement in the matrix materials varies depending on the valence state of doped TM ions. The highest structural stability is found in WO3-modified SCNCM, due to the smaller effective ion radii, higher electro-negativity, stronger W–O bond, and efficient suppression of oxygen vacancy generation. As a result, WO3-modified SCNCM have outstanding cycle performance, with a capacity retention rate of 90.2% after 200 cycles. This study provides an insight into the design of advanced SCNCM with enhanced reversibility and cyclability.

Enhanced high-rate performance and cyclic stability of LiNi0.8Co0.1Mn0.1O2 through LiAlO2 and polyaniline double-layer coating

LiNi0.8Co0.1Mn0.1O2 (NCM811) is widely utilized in electric vehicle batteries due to its high capacity and low cost, but its poor high-rate performance and cyclic stability restrict its applications. In this study, the NCM811 was surface coated both with ionic conductor LiAlO2 and electrical conductor polyaniline to simultaneously improve its high-rate performance and cyclic stability. Results show that the coated NCM811 has excellent capacity retention rate, namely 93.6% (25 ℃) and 83.9% (50 ℃) at 10C after 100 cycles. These results demonstrate that prepared double-layer coating is effective way to improve high-rate performance of Ni-rich cathode materials.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Modulating Grain Boundary Networks to Achieve Superior Chemomechanical Coupling Properties in Nickel-Rich Cathode Materials.

To forge ahead with the next generation of power batteries boasting superior energy density, nickel-rich layered oxides are regarded as some of the most promising cathode materials. However, challenges such as microcracks, which are attributed to the elevated nickel content of the materials, have posed impediments to their further development and application. Consequently, this article focuses on the understanding of the materials in the deep delithiation state, dissecting their degradation mechanisms through a dual lens of electrochemical and mechanical properties. The comprehensive analysis reveals that microcracks within the particles exhibit a degree of reversibility. However, with repeated Li+ de-/intercalation, these microcracks progressively propagate and permeate the entire particle, ultimately leading to particle fragmentation. Therefore, this study employs Dy2O3 as an inducer to facilitate the growth of primary crystal grains, reducing the internal porosity of the particles. This effectively enhances the conductivity and lithium-ion diffusion kinetics in deep lithium-ion deintercalation states of nickel-rich cathode materials. The modified material exhibits significant suppression of microcrack formation and growth during cycling, leading to notable improvements in its chemical-mechanical properties. These degradation mechanisms and modification strategies of Ni-rich cathodes offer valuable insights into the development of Ni-rich cathode materials tailored for electric vehicles.

Beyond dopant selection: The critical grain size window as a key performance dictator for Co-free, Ni-rich cathode materials

Despite the immense potential of cobalt-free, nickel-rich cathode materials to replace their cobalt-containing counterparts in lithium-ion batteries (LIBs), their widespread adoption remains hindered by performance limitations. While extensive research has explored various doping strategies to address this challenge, the reported benefits vary significantly, suggesting an incomplete understanding of dopant influence and thus hindering the full potential of these additives. Our investigation into the effect of various dopants on Li(Ni0.95Mn0.05)O2 performance yielded a surprising discovery: the LIB performance of transition metal-doped Li(Ni0.95Mn0.05)O2 becomes remarkably consistent across different dopant types, provided the calcination conditions are optimized. Regardless of dopant type, a critical grain size window is identified as a key factor influencing the performance of the doped Li(Ni0.95Mn0.05)O2. Calcination within a specific temperature range is paramount to control this previously overlooked performance determinant, which significantly impacts grain growth, primary particle morphology, and lattice structure. This novel insight allows us to demonstrate that cost-effective dopants such as Ti can achieve performance in stabilizing Li(Ni0.95Mn0.05)O2 comparable to that of more expensive, higher-valence alternatives (e.g., Nb, Ta, W, and Mo). This discovery paves the way for developing practical material design processes that meet the stringent requirements of the LIB industry.

Impact of high-temperature storage on capacity fading of Ni-rich cathodes in sulfide-based all-solid-state batteries

Despite the extensive research efforts focused on enhancing the lifespan and energy density of all-solid-state batteries, the calendar aging behavior of cathodes within the all-solid-state batteries system continues to be underexplored. In this study, we elucidate the capacity fading of Ni-rich cathodes in sulfide-based all-solid-state batteries after high-temperature storage using electrochemical techniques, synchrotron X-ray-based characterization tools, and electron microscopy. High-temperature storage negatively affects the electrochemical performance of Ni-rich cathodes, limiting their charge and discharge capacities, notably charge fading. The underlying cause of capacity fading lies in interfacial side reactions between Ni-rich cathode materials and solid electrolytes. The LiNbO3 coating layer is found to be effective in preventing interfacial degradation, which virtually eliminates charge and discharge fading. These findings offer a deeper understanding of the capacity fading of Ni-rich cathodes in sulfide-based all-solid-state battery systems during high-temperature storage. Furthermore, they provide insights for achieving all-solid-state batteries with high thermal durability and energy density.

In-situ Ti4+-doped modification of layer-structured Ni-rich LiNi0.83Co0.11Mn0.06O2 cathode materials for high-energy lithium-ion batteries

The further commercialization of layer-structured Ni-rich LiNi0.83Co0.11Mn0.06O2 (NCM83) cathode for high-energy lithium-ion batteries (LIBs) has been challenged by severe capacity decay and thermal instability owing to the microcracks and harmful phase transitions. Herein, Ti4+-doped NCM83 cathode materials are rationally designed via a simple and low-cost in-situ modification method to improve the crystal structure and electrode–electrolyte interface stability by inhibiting irreversible polarizations and harmful phase transitions of the NCM83 cathode materials due to Ti4+-doped forms stronger metal-O bonds and a stable bulk structural. In addition, the optimal doping amount of the composite cathode material is also determined through the results of physical characterization and electrochemical performance testing. The optimized Ti4+-doped NCM83 cathode material presents wider Li+ ions diffusion channels (c = 14.1687 Å), lower Li+/Ni2+ mixing degree (2.68 %), and compact bulk structure. The cell assembled with the optimized Ti4+-doped NCM83 cathode material exhibits remarkable capacity retention ratio of 95.4 % after 100cycles at 2.0C and room temperature, and outstanding reversible discharge specific capacity of 148.2 mAh g−1 at 5.0C. Even under elevated temperature of 60 °C, it delivers excellent capacity retention ratio of 92.2 % after 100cycles at 2.0C, which is significantly superior to the 47.9 % of the unmodified cathode material. Thus, the in-situ Ti4+-doped strategy presents superior advantages in enhancing the structural stability of Ni-rich cathode materials for LIBs.

Analyzing the Doping Mechanism of High-Valence Element in Ni-Rich Cathode Materials

Layered cathode materials, LiMO2 (M=Ni, Co,Mn, or Al), with a high nickel content are promising cathode materials owing to their near-theoretical specific capacity. However, the inherent chemical and structural instabilities of Ni-rich cathodes lead to several problems, including rapid capacity fading, thermal instability, gas evolution, and safety concerns.1 Introducing additional elements into Ni-rich cathodes is an essential strategy for addressing the instability of the cathode material. Conventionally, this doping strategy considers only the incorporation of additional elements into the bulk structure of the cathode in terms of fortifying the crystal structure.2 However, high-valence elements are likely to be insoluble in the crystal structure, resulting in accumulation along the interparticle boundaries.3 Herein, a new mechanism for doping high-valence elements into Ni-rich cathodes and their effects on the morphology and crystal structure are investigated by calcining LiNiO2 (LNO) and X-doped LNO cathodes (X=Al, Nb, Ta, and Mo) at various temperatures. Operando X-ray diffraction analysis reveals that the temperature at which the content of Li-X-O compounds declines is higher for the dopants with high oxidation states, reinforcing segregation at the grain boundary. Thus, the highly aligned microstructure and high crystallinity of the LNO cathode are maintained over a wide calcination temperature range after doping with high-valence elements, enhancing the electrochemical performance.

Understanding Ni-Rich Layered Cathode Materials for Fast-Charging Li-Ion Batteries

The market for electric vehicles (EVs) has experienced significant growth, and this trend is expected to continue in the coming years. While the lithium-ion battery (LIB) technologies for EVs have made significant progress so far, they still face several disadvantages compared to the internal combustion engines. A predominate challenge is reducing battery charging time. [1] Traditional LIBs typically use Li[Ni1-x-yCox(Mn and/or Al)y]O2 as cathode materials. To improve the driving range of EVs, energy density has been the focus of research and development in the past decade, which led to the wide adoption of Ni-rich (Ni content > 80%) layered oxide cathodes in LIBs.[2] With increasing Ni content, however, the structural changes that the cathode material undergoes during electrochemical reactions also become more severe, which negatively impact their fast-charging performances.[3-5] It is evident that addressing the fast charging limitations requires a deep understanding of the active materials. In this presentation, we show our recent effort in improving fast charging performances of Ni-rich layered cathodes. As the reactivity of Li[Ni1-x-yCox(Mn and/or Al)y]O2 cathodes vary with the states of dis/charges, their fast charging performances are directly linked to the charging/discharging protocol. In addition, we report how various physical properties of the cathode materials, such as microstructures and facets, can affect kinetics and charging rates. Our perspectives on future development strategies for fast charging Ni-rich layered cathode materials will also be discussed.[1] X. Wang, Y.-L. Ding, Y.-P. Deng, Z. Chen, Adv. Energy Mater. 2020, 10, 1903864.[2] S.-T. Myung; F. Maglia; K.-J. Park; C. S. Yoon; P. Lamp; S.-J. Kim; Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.[3] F. Schipper; E. M. Erickson; C. Erk; J.-Y. Shin; F. F. Chesneau; D. Aurbach, J. Electrochem. Soc. 2017, 164, A6220.[4] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155.[5] J. Park, H. Zhao, S. D. Kang, K. Lim, C.-C. Chen, Y.-S. Yu, R. D. Braatz, D. A. Shapiro, J. Hong, M. F. Toney, M. Z. Bazant, W. C. Chueh, Nat. Mater. 2021, 20, 991.

(Invited) Single Crystal Ni-Rich Cathode Materials: Synthesis, Scaleup and Validation

Synthesis of high-performance single crystal Ni-rich NMC, especially when Ni≥0.8, poses a challenge. A conflict exists because as Ni content increase in NMC811, a lower calcination temperature is preferred due to Ni reduction at elevated temperatures, while high temperatures favour single crystal growth.Therefore, molten salt is sometimes employed as the reaction media to promote growth of single crystal NMC811. In general, four approaches for synthesizing of Ni-rich NMC single crystals: molten salt, hydrothermal, direct solid-state synthesis and multi-step lithiation. Molten salt and hydrothermal approaches result in the formation of well-segregated large crystals, but they also increase manufacturing cost. Direct solid-state synthesis, which involves ball milling all precursors together followed by calcination, is a time-saving approach. However, it poses challenge for impurity control due to contamination from milling media, and it can damage the material structure. The calcination of TM(OH)2 precursor with LiOH at very high sintering temperatures forms micron-sized primary particles which, however, still exhibit significantly agglomerated. A post-synthesis milling process is required to break down those NMC811 crystal clusters.This talk will discuss an innovative nanoscale phase separation approach for synthesis of high-performance single crystal NMC811 that is readily adaptable for industry manufacturing. The reaction mechanism of single crystal growth is investigated to understand the synthesis-morphology-performance relationship in growing single crystal NMC811 in the absence of molten salts. The scaled single crystal NMC811 is then further validated in a 2Ah Li-ion pouch cells, demonstrating 1000 stable cycling, confirming the feasibility of this new synthesis approach. This work provides new insights that are broadly applicable for cost-efficient large-scale synthesis of single crystals for different advanced battery technologies to accelerate deep decarbonization process.

Revealing the Impact of Dual Site Modification on the Phase Transformation and Ion Transport Mechanism of Ni-Rich Cathode Materials.

Ni-rich cathode materials have garnered significant attention attributable to the high reversible capacity and superior rate performance, particularly in the electric vehicle industry. However, the structural degradation experienced during cycling results in rapid capacity decay and deterioration of the rate performance, thereby impeding the widespread application of Ni-rich cathodes. Herein, a Mg/Ti co-doping strategy was developed to boost the structure stability and Li-ion transport kinetics of the Ni-rich cathode material LiNi0.90Co0.05Mn0.05O2 (NCM9055) under long cycle. It is demonstrated that the Mg2+ ions inserted into the lithium layer could serve as pillars, enhancing the stability of the delithiated layer structure. The introduction of robust Ti-O bonding mitigated the detrimental H2-H3 phase transition (∼4.2 V) during cycling. In addition, despite the fact that Mg/Ti co-doping slightly reduces Li+ diffusion coefficient in the modified cathode material (NCM9055-MT), it effectively stabilized the robustness of the layered structure and maintained the Li+ diffusion channel while charging and discharging, thereby improving the Li+ diffusion coefficient after a long cycle. Therefore, the Mg/Ti co-doped cathode materials exhibited an exceptional capacity retention rate of 99.9% (100 cycles, 1 C). Additionally, the Li+ diffusion coefficient of the co-doped NCM9055-MT (2.924 × 10-10 cm2 s-1) after 100 cycles was effectively enhanced compared with the case of undoped NCM9055 (4.806 × 10-11 cm2 s-1). This work demonstrates that the Mg/Ti co-doping approach effectively enhanced the stability of layered Ni-rich cathode materials.

Regulating the Charge Distribution of Oxygen by High-Entropy Doping to Stabilize Single-Crystal Ni-Rich Cathode Materials

Regulating the Charge Distribution of Oxygen by High-Entropy Doping to Stabilize Single-Crystal Ni-Rich Cathode Materials