Key Takeaways & Executive Findings
- •• • The engineered Co-free ultrahigh-Ni cathode operates at a charging cut-off voltage of 4.8 V, achieving an exceptional balance between capacity and cycle stability, breaking existing voltage constraints without compromising performance. • • Pouch-type cells with graphite and Li metal anodes demonstrate excellent cyclability under demanding conditions, operating at high charging cut-off voltages of 4.5 V and 4.6 V, respectively. • • The LiAlO2 nanoshell, deposited via atomic layer deposition, markedly enhances sur-/interfacial Li-ion migration kinetics, rendering low electron/ion-diffusion resistance. • • The surface-to-bulk integrated modification prevents lattice stress-induced mechanical degradation and mitigates accumulation of by-products due to surface side-reactions, addressing chemo-mechanical and electrochemical degradation under high-voltage operation.
Abstract
High-Ni (Ni ≥ 0.9) layered cathodes are being developed to endure high-voltage operations above 4.5 V to boost energy density. However, they face exacerbated chemo-mechanical and electrochemical degradation under high-voltage operation, primarily due to excessive lattice strain and phase distortion during cycling. Here, we engineer a high-Ni, Co-free cathode featuring a multicomponent complex doping-modulated bulk structure, coupled with surface modification via a multifunctional atomic layer deposition-coated LiAlO2 layer. Such a unique framework achieved by surface-to-bulk integrated modification can not only greatly prevent lattice stress-induced mechanical degradation but also effectively mitigate the accumulation of by-products due to surface side-reactions. Moreover, the LiAlO2 nanoshell with exceptional ion conductivity markedly enhances the sur-/interfacial Li-ion migration kinetics, thus rendering low electron/ion-diffusion resistance. The developed cathode breaks through existing voltage constraints without compromising on performance, achieving an exceptional balance between capacity and cycle stability during operation at 4.8 V. Notably, the pouch-type cells utilizing graphite and Li metal anodes demonstrate excellent cyclability under demanding conditions, even operating at high charging cut-off voltages of 4.5 and 4.6 V, respectively.
1. Introduction
Lithium-ion batteries (LIBs) are the predominant power source for portable electronics and electric vehicles, yet commercial Ni-rich cathodes suffer from voltage fade, capacity degradation, and poor rate performance. Operating at elevated voltages can boost energy density, but exacerbates chemo-mechanical instability and phase transformations, especially for Co-free high-Ni cathodes. The complete elimination of cobalt is economically and societally imperative, but inherent thermal and chemo-mechanical instabilities raise safety concerns, hindering practical application.
This work addresses these bottlenecks by engineering a high-Ni, Co-free cathode with a multicomponent complex doping-modulated bulk structure and a surface modification via atomic layer deposition-coated LiAlO2 layer. This surface-to-bulk integrated modification prevents lattice stress-induced mechanical degradation and mitigates side-reactions, while the LiAlO2 nanoshell enhances Li-ion migration kinetics. The developed cathode achieves stable operation at 4.8 V, demonstrating a practical pathway to high-energy-density, Co-free LIBs.
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Dingen Yao, Hongqiang Xi, Longwei Liang, Jiwei Hao, Leilei Wang, Guoshuai Su, Linrui Hou, Changzhou Yuan (2026). High-entropy modulation and surface engineering promising 4.8 V-tolerant practical Co-free ultrahigh-Ni cathodes. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4143-9
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Frequently Asked Questions
What specific mechanisms cause chemo-mechanical degradation in high-Ni cathodes under high-voltage operation, and how does the proposed surface-to-bulk modification address them?
High-Ni cathodes suffer from excessive lattice strain and phase distortion during cycling, leading to mechanical degradation. The surface-to-bulk integrated modification, including high-entropy doping and LiAlO2 coating, prevents lattice stress-induced mechanical degradation and mitigates by-product accumulation from side-reactions, as evidenced by stable cycling at 4.8 V.
How does the LiAlO2 nanoshell enhance Li-ion migration kinetics, and what are the quantitative improvements in electron/ion-diffusion resistance?
The LiAlO2 nanoshell, with exceptional ion conductivity, markedly enhances sur-/interfacial Li-ion migration kinetics, rendering low electron/ion-diffusion resistance. This is demonstrated by the cathode's ability to operate at high cut-off voltages (4.8 V) without compromising rate performance.
What are the specific cycling performance metrics for the pouch-type cells with graphite and Li metal anodes at high charging cut-off voltages?
Pouch-type cells with graphite and Li metal anodes demonstrate excellent cyclability under demanding conditions, operating at high charging cut-off voltages of 4.5 V and 4.6 V, respectively. The exact capacity retention and cycle numbers are not detailed in the abstract, but the cells show exceptional balance between capacity and cycle stability.
How does the high-entropy doping strategy contribute to structural stability compared to conventional doping methods?
High-entropy doping modulates the bulk structure with multiple components, which helps prevent lattice stress-induced mechanical degradation. This strategy, combined with surface modification, achieves stable operation at 4.8 V, indicating improved structural stability over conventional approaches.
What are the practical implications of eliminating cobalt in terms of cost and safety, and how does this cathode address those concerns?
Eliminating cobalt reduces cost and addresses societal concerns, but high-Ni cathodes typically have thermal and chemo-mechanical instabilities. This cathode's surface-to-bulk modification mitigates these issues, enabling stable high-voltage operation, which is crucial for practical application in high-energy-density batteries.
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