Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
Guilin Electrical Equipment Scientific Research Institute Co. Ltd., Guilin 541004, Guangxi, China.
ACS Appl Mater Interfaces. 2022 Dec 21;14(50):55491-55502. doi: 10.1021/acsami.2c14235. Epub 2022 Dec 12.
Developments in electric vehicles and mobile electronic devices are promoting the demand for lithium-ion batteries with higher capacity and longer lifetime. The performances of lithium-ion batteries are crucially affected by cathode materials, among which ternary cathode materials are the most competitive option with the advantages of high capacity, safety, and cost-effectiveness. However, although high-nickel ternary cathode materials can achieve relatively high specific capacity, they generally have unsatisfactory stability during long-term cycling. In this study, the microscopic mechanisms of the cathode failure and the principle of coating modification in lithium-ion batteries have been comprehensively examined. It has been revealed that the irreversible capacity fading is mainly attributed to the interface chemical reaction, which reduces the transition-metal valence states and generates undesired disordered rock-salt phases. This structural phase transformation at the interface induces the dissolution of transition metals and results in irreversible capacity loss of the cathode. To restrain the occurrence of this process, a LiNbO coating-modified single-crystal LiNiCoMnO (NCM811) cathode material has been prepared. The electrochemical properties as well as the microstructural evolution of the cathode-electrolyte interface during cycling of both the uncoated and coated samples have been comprehensively characterized and compared through impedance spectroscopy testing, SEM-EDX, STEM, and EELS characterization. Additionally, molecular dynamics simulation results confirmed that LiNbO coating can effectively inhibit the dissolution of transition metals while providing stable lithium-ion channels. The experimental results also indicate that the coating modification can effectively improve the cycling stability of the NCM811, with the capacity retention rate for 500 cycles increasing from 19% to 70%. This study is helpful to deepen the understanding of the capacity fading mechanisms, and the coating method is effective at maintaining the structural stability and improving the cycle life of lithium-ion batteries.
电动汽车和移动电子设备的发展推动了对具有更高容量和更长寿命的锂离子电池的需求。锂离子电池的性能主要受阴极材料的影响，其中三元阴极材料是最具竞争力的选择，具有高容量、安全性和成本效益高的优点。然而，尽管高镍三元阴极材料可以实现相对较高的比容量，但它们在长期循环中通常稳定性不佳。在这项研究中，全面研究了锂离子电池中阴极失效的微观机制和涂层改性原理。研究表明，不可逆容量衰减主要归因于界面化学反应，该反应降低了过渡金属的价态并生成了不理想的无序岩盐相。这种界面结构相变导致过渡金属的溶解，并导致阴极不可逆容量损失。为了抑制这种过程的发生，制备了一种 LiNbO 涂层修饰的单晶 LiNiCoMnO（NCM811）阴极材料。通过阻抗谱测试、SEM-EDX、STEM 和 EELS 表征，综合比较了未涂层和涂层样品在循环过程中的电化学性能以及阴极-电解质界面的微观结构演变。此外，分子动力学模拟结果证实，LiNbO 涂层可以有效抑制过渡金属的溶解，同时提供稳定的锂离子通道。实验结果还表明，涂层修饰可以有效提高 NCM811 的循环稳定性，容量保持率从 500 次循环的 19%提高到 70%。这项研究有助于深化对容量衰减机制的理解，并且涂层方法可以有效保持锂离子电池的结构稳定性并提高其循环寿命。
