Lithium ion capacitors (LICs), with their high power density and medium energy density have become a popular energy storage device on the market. Among various electrode materials of lithium ion batteries (LIBs), LiNi_0.5Co_0.2Mn_0.3O₂ (NCM), which has both high capacity and good cycle performance, has been widely used to improve the energy density of power devices. Unfortunately, the short cycle life and low power density of NCM have become new challenges for LICs. This work deeply analyzes the capacity failure mechanism of NCM in LICs during cycling, and finds that in the cycling process, the transition metal (TM) in NCM will dissolve and produce a shuttle effect, which eventually accumulates on the anode surface. Comfortingly, the precise Al₂O₃ coating on the NCM surface obtained by atomic layer deposition (ALD) successfully restrains the dissolution of TM in NCM during cycling, thus preventing the shuttle effect of TM. An additional benefit of the Al₂O₃ coating is to reduce internal stress changes of NCM secondary particles during long-time charging and discharging, thereby ensuring a close contact inside NCM particles after multiple cycles. As a result, the LICs assembled by the Al₂O₃ coated NCM composite cathode exhibit an excellent cycle capability and rate performance. This work paves a way for improving the electrochemical performance of LICs with the NCM cathode, and provides a reference for the further research on the performance attenuation mechanism of other composite electrodes in LICs.

锂离子电容器（LICs）具有高功率密度和中等能量密度，已成为市场上流行的能量存储设备。在锂离子电池（LIB）的各种电极材料中，LiNi _0.5 Co _0.2 Mn _0.3 O ₂（NCM）具有高容量和良好的循环性能，已被广泛用于提高功率器件的能量密度。不幸的是，NCM的短循环寿命和低功率密度已成为LIC的新挑战。这项工作深入分析了LIC中NCM在循环过程中的容量破坏机理，发现在循环过程中，NCM中的过渡金属（TM）会溶解并产生穿梭效应，最终累积在阳极表面。令人欣慰的是，通过原子层沉积（ALD）获得的NCM表面上的精确Al ₂ O ₃涂层成功地抑制了循环过程中TM在NCM中的溶解，从而防止了TM的穿梭效应。Al ₂ O ₃的另一个好处涂层是为了减少NCM二次颗粒在长时间充电和放电期间的内部应力变化，从而确保多个循环后NCM颗粒内部紧密接触。结果，由Al ₂ O ₃涂覆的NCM复合阴极组装的LIC显示出优异的循环能力和倍率性能。这项工作为改进带有NCM阴极的LIC的电化学性能铺平了道路，为进一步研究LIC中其他复合电极的性能衰减机理提供了参考。