Buildinga Protective Layer on Medium-Nickel and Low-CobaltCathodes for High-Voltage Lithium-Ion Batteries

The layered oxide is considered a promising high-voltage cathode for its high specific capacity. However, its inherent structural instability and capacity decay limit commercial applications. Here, we propose a W–Al–B (WAB) coating layer on the surface of a LiNi_0.65Co_0.07Mn_0.28O₂ (NCM) cathode to improve structural stability and reduce side reactions. The WAB protective layer can accelerate lithium-ion (Li⁺) diffusion at the interface and suppress side reactions between the cathode and the electrolyte at high voltages. After introducing the WAB layer, the reversible discharge capacity of the NCM cathode is increased from 186 to 192 mAh/g at 0.1 C. The WAB@NCM cathode shows better cyclic stability with a capacity retention of 95.2% at 1 C after 150 cycles, in comparison to 91.9% for the bare NCM cathode. According to systematic characterizations, the improved electrochemical performance is ascribed to the formation of LiAlO₂, LiWO₃, and Li₂B₄O₇ species at the interface. Our functional coating layer design can provide some understanding of long-cycle and high-voltage cathode materials.