Synthesis Method for Long Cycle Life Lithium-Ion Cathode Material: Nickel-Rich Core-Shell LiNi0.8Co0.1Mn0.1O2

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

Millions of electric vehicles (EVs) on the road are powered by lithium-ion batteries (LIBs) based on nickel-rich layered oxide (NRLO) cathodes, and they suffer from a limited driving range and safety concerns. Increasing the Ni content is a key way to boost the energy densities of LIBs and alleviate the EV range anxiety, which are, however, compromised by the rapid performance fading. One unique challenge lies in the worsening of the microstructural stability with a rising Ni-content in the cathode. In this review, we focus on the latest advances in the understanding of NLRO microstructures, particularly the microstructural degradation mechanisms, state-of-the-art stabilization strategies, and advanced characterization methods. We first elaborate on the fundamental mechanisms underlying the microstructural failures of NRLOs, including anisotropic lattice evolution, microcracking, and surface degradation, as a result of which other degradation processes, such as electrolyte decomposition and transition metal dissolution, can be severely aggravated. Afterwards, we discuss representative stabilization strategies, including the surface treatment and construction of radial concentration gradients in polycrystalline secondary particles, the fabrication of rod-shaped primary particles, and the development of single-crystal NRLO cathodes. We then introduce emerging microstructural characterization techniques, especially for identification of the particle orientation, dynamic changes, and elemental distributions in NRLO microstructures. Finally, we provide perspectives on the remaining challenges and opportunities for the development of stable NRLO cathodes for the zero-carbon future.

Heterogeneous Degradation in Thick Nickel-Rich Cathodes During High-Temperature Storage and Mitigation of Thermal Instability by Regulating Cationic Disordering

The thermal instability is a major problem in high-energy nickel-rich layered cathode materials for large-scale battery application. Due to the scarce investigation of thick electrodes at the practical full-cell level, the understanding of thermal failure mechanism is still insufficient. Herein, an intrinsic origin of thermal instability in fully charged industrial pouch cells during high-temperature storage is discovered. Through the investigation from crystals to particles, and from electrodes to cells, it is shown that serious top-down heterogeneous degradation occurs along the depth direction of the thick electrode, including phase transition, cationic disordering, intergranular/intragranular cracks, and side reactions. Such degradation originates from the abundant oxygen vacancies and reduced catalytic Ni²⁺ at cathode surface, causing microstructural defects and directly leading to the thermal instability. Nonmagnetic elements doping and surface modification are suggested to be effective in mitigating the thermal instability through modulating cationic disordering.

NCA, NCM811, and the Route to Ni-Richer Lithium-Ion Batteries

The aim of this article is to examine the progress achieved in the recent years on two advanced cathode materials for EV Li-ion batteries, namely Ni-rich layered oxides LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Co0.1Mn0.1O2 (NCM811). Both materials have the common layered (two-dimensional) crystal network isostructural with LiCoO2. The performance of these electrode materials are examined, the mitigation of their drawbacks (i.e., antisite defects, microcracks, surface side reactions) are discussed, together with the prospect on a next generation of Li-ion batteries with Co-free Ni-rich Li-ion batteries.

Research Progress on the Surface of High-Nickel Nickel-Cobalt-Manganese Ternary Cathode Materials: A Mini Review

To address increasingly prominent energy problems, lithium-ion batteries have been widely developed. The high-nickel type nickel–cobalt–manganese (NCM) ternary cathode material has attracted attention because of its high energy density, but it has problems such as cation mixing. To address these issues, it is necessary to start from the surface and interface of the cathode material, explore the mechanism underlying the material's structural change and the occurrence of side reactions, and propose corresponding optimization schemes. This article reviews the defects caused by cation mixing and energy bands in high-nickel NCM ternary cathode materials. This review discusses the reasons why the core-shell structure has become an optimized high-nickel ternary cathode material in recent years and the research progress of core-shell materials. The synthesis method of high-nickel NCM ternary cathode material is summarized. A good theoretical basis for future experimental exploration is provided.

A comprehensive study of the multiple effects of Y/Al substitution on O3-type NaNi0.33Mn0.33Fe0.33O2 with improved cycling stability and rate capability for Na-ion battery applications

O3-NaNi0.33Mn0.33Fe0.33O2 layered oxide has attracted increasing attention as one of the most promising materials for Na-ion battery applications due to air stability and environmental friendliness, but the complex phase transitions and inferior cycling stability are extremely challenging to overcome. Cation substitution has been widely used to stabilize crystal structures and improve electrochemical performance for SIBs. Based on past experimental results, it was discovered that the transition metal-oxygen bond energy of the introduced dopant is an important factor for optimizing electrochemical performance. In this study, we validated our hypothesis that yttrium (Y)-which possesses high bond energy for oxygen-is most likely to be an ideal doping element by conducting a comparative study of substituting Mn in O3-NaNi0.33Mn0.33Fe0.33O2 layered oxide with aluminum (Al) and Y through elemental doping. As hypothesized, the electrochemical properties of NaNi0.33Mn0.33Fe0.33O2 have increased markedly by introducing a small amount of Y and Al, and the Y-doped materials showed superior rate performance and cycling stability due to enhanced Na+ diffusion reaction kinetics and layered structure stability. Furthermore, the substitution of Y for Mn can improve thermal stability and alleviate phase transformations. The improvement mechanism of Y substitution can be attributed to a larger d-spacing and stronger metal-oxygen bond. These results suggest that structural modulation is an effective strategy to reinforce electrochemical properties of layered oxides and provides some guidance about designing promising electrode materials.

In situ synthesis of a nickel concentration gradient structure of Ni-rich LiNi0.8Co0.15Al0.05O2 with promising superior electrochemical properties at high cut-off voltage

Nickel-rich layered cathode materials have aroused widespread interest due to their high discharge capacity, which is a basic requirement for next-generation high energy density lithium batteries. However, with the increase of nickel content, cathode materials face the serious challenge of capacity degradation, which is attributed to the formation of rock salt-type oxides such as NiO on the surface of cathode particles. To overcome this shortcoming, a novel Ni concentration gradient LiNi0.8Co0.15Al0.05O2 (NCG-NCA) cathode material was successfully synthesized using the characteristic reaction of Ni2+ and dimethylglyoxime. The final synthesized nickel concentration gradient material combines the advantages of high discharge capacity and excellent stability, which are attributed to the high nickel content in the core and high cobalt content on the surface of the material particles. The cycling stability of the NCG material is remarkably improved, exhibiting an excellent capacity retention of 75% after 200 cycles at a current density of 10C (1C = 160 mA g-1) under a high cut-off voltage of 4.5 V, much higher than that of a pristine NCA (P-NCA) cathode without NCG (50%). The excellent cycling stability of NCG-NCA is due to formation of a stable surface, which is not prone to serious atomic rearrangement on the surface. More importantly, with the structural analysis of NCA materials by neutron diffraction, we find that the proportion of Li/Ni mixing of NCA is reduced by utilizing the NCG structure; in turn, the rate performance of NCG-NCA cathode materials is improved greatly.

Multifunctional Integration of Double-Shell Hybrid Nanostructure for Alleviating Surface Degradation of LiNi0.8Co0.1Mn0.1O2 Cathode for Advanced Lithium-Ion Batteries at High Cutoff Voltage

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode is considered to be among the most promising candidates for high-energy-density lithium-ion batteries (LIBs). However, both capacity fading and structural degradation occur during long-term cycling, which extremely limit the commercial applications of NCM811, especially at a high cutoff voltage (>4.3 V). Here, we design a double-shell hybrid nanostructure consisting of a Li₂SiO₃ coating layer and a cation-mixed layer (Fm3̅m phase) to improve its electrochemical performance. Consequently, the Si-modified NCM811 electrode shows outstanding cycling stability with a 95.2% capacity retention at 4.3 V after 100 cycles and 87.3% at a 4.5 V high cutoff voltage after 100 cycles. This designed double-shell hybrid nanostructure alleviates side reactions, structural degradation, and internal cracking, effectively enhancing the surface structural stability. This efficient strategy provides a valuable step toward further commercial applications of the LiNi_0.8Co_0.1Mn_0.1O₂ cathode and enriches the fundamental understanding of layered cathode materials.

Controllable TiO2 coating on the nickel-rich layered cathode through TiCl4 hydrolysis via fluidized bed chemical vapor deposition

Surface coating of metal oxides is an effective approach for enhancing the capacity retention of a nickel-rich layered cathode. Current conventional coating techniques including wet chemistry methods and atomic layer deposition are restricted by the difficulty in perfectly balancing the coating quality and scale-up production. Herein, a highly efficient TiO₂ coating route through fluidized bed chemical vapor deposition (FBCVD) was proposed to enable scalable and high yield synthesis of a TiO₂ coated nickel-rich cathode. The technological parameters including coating time and TiCl₄ supply rate were systematically studied, and thus a utility TiO₂ deposition rate model was deduced, promoting the controllable TiO₂ coating. The FBCVD TiO₂ deposition mechanism was fundamentally analyzed based on the TiCl₄ hydrolysis principle. The amorphous and uniform TiO₂ coating layer is compactly attached on the particle surface, forming a classical core-shell structure. Electrochemical evaluations reveal that the TiO₂ coating by FBCVD route indeed improves the capacity retention from 89.08% to 95.89% after 50 cycles.