Xiangdong Zhu,Caiyan Shen,Tian Qiu,Yu Zhang,Wei Xu,Guorong Hu,Yanbing Cao,Zhongdong Peng,Ke Du
Driven by the growing demand for energy density of lithium-ion batteries, ultra-nickel- rich layered oxides LiNi x Co y Mn z O 2 (x > 0.9) (ultra-Ni-rich NCM) cathodes attract considerable attention. However, these cathode materials suffer from severe structural degradation during cycling, primarily due to phase transitions, which significantly hinders their long-term application. In this work, ultra-Ni-rich NCM cathode materials with Co- and Mn-rich surface architectures are synthesized using Co/Mn-rich shell precursors and are systematically investigated to evaluate the suitability of different surface chemistries under various electrochemical conditions. The results reveal that the Co-rich surface significantly enhances the electrochemical kinetics by mitigating the Li + concentration gradient between the surface and bulk, thereby effectively suppressing structural degradation. In contrast, the Mn-rich surface, due to the presence of electrochemically inert Mn 4+ , leads to sluggish kinetics and incomplete phase transitions within the voltage window of 2.8–4.3 V. This results in a lower capacity but notably improved structural integrity. Upon increasing the upper cutoff voltage to 4.4V, the Mn-rich shell cathode undergoes more complete phase transitions, leading to a substantial improvement in capacity while maintaining superior structural stability.
Steven Hu,Xinghui Liang,Huimin Yuan,Zhenning Xu,Jun Wang,Hai Liu,Kaihua Xu,Xing Ou
The development of Co-free ultrahigh-Ni (Ni > 0.9) layered oxide cathode materials holds immense promise for addressing electric vehicle range limitations and cost efficiency, though substantial obstacles persist in structural durability, thermal stability, and safety. To concurrently enhance the structural integrity and interfacial stability of LiNi 0.95 Mn 0.05 O 2 , a dual-functional co-regulation strategy integrating Zr/Al bulk doping with Li 6 Zr 2 O 7 surface coating is implemented. Controlled Zr 4+ /Al 3+ co-incorporation expands interlayer spacing, strengthens transition metal–oxygen bonding, and stabilizes the oxygen framework, thereby improving Li + diffusion kinetics while suppressing cation disorder. Concurrently, the epitaxially Li 6 Zr 2 O 7 coating effectively passivates the surface by eliminating residual lithium species, inhibiting grain coarsening, and suppressing interfacial side reactions. These coupled bulk-surface modifications synergistically inhibit mechanical stress-induced crack propagation and deleterious phase transformations. Therefore, the optimized cathode achieves 96.9% capacity retention after 100 cycles at 1 C, while maintaining stable operation under extreme electrochemical conditions (4.5 V cutoff voltage) and thermal extremes (−10 °C/60 °C). This work demonstrates a synergistic modification paradigm for designing robust ultrahigh-Ni cathodes, thereby propelling the advancement of next-generation high-energy density lithium-ion batteries.
Lifan Wang,Guicheng Liu,Rui Wang,Xindong Wang,Liguang Wang,Zhenpeng Yao,Chun Zhan,Jun Lu
Ultrahigh-Ni layered oxides are proposed as promising cathodes to fulfill the range demand of electric vehicles; yet, they are still haunted by compromised cyclability and thermal robustness. State-of-the-art surface coating has been applied to solve the instability via blocking the physical contact between the electrolyte and the highly active Ni 4+ ions on the cathode surface, but it falls short in handling the chemo–physical mobility of the oxidized lattice oxygen ions in the cathode. Herein, a direct regulation strategy is proposed to accommodate the highly active anionic redox within the solid phase. By leveraging the stable oxygen vacancies/interstitials in a lithium and oxygen dual-ion conductor (layered perovskite La 4 NiLiO 8 ) coating layer, the reactivity of the surface lattice oxygen ion is dramatically restrained. As a result, the oxygen release from the lattice is suppressed, as well as the undesired irreversible phase transition and intergranular mechanical cracking. Meanwhile, the introduced dual-ion conductor can also facilitate lithium-ion diffusion kinetics and electronic conductivity on the particle surface. This work demonstrates that accommodating the anionic redox chemistry by dual-ion conductors is an effective strategy for capacity versus stability juggling of the high-energy cathodes.
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