In Situ Surficial Polymerization of Ultrahigh-Nickel Cathode Material for Stable Solid-State Lithium Batteries

Ultrahigh-nickel cathode active materials (CAMs) suffer from detrimental side reactions when coupled with poly(ethylene oxide) (PEO)-based electrolytes in solid-state lithium-metal batteries (SLMBs). To circumvent this issue, here we propose a surface modification strategy for ultrahigh-nickel CAMs with a self-assembled nanoscale polymer coating. Without requiring additional initiators, the residual lithium compounds inherent on the surface of the ultrahigh-nickel CAMs are used as initiators to induce the in situ anionic polymerization of the monomer. Meanwhile, oxygen vacancies are generated on the surface through the coordination of -C = O and -C ≡ N with transition metal ions, which reduces the diffusion barrier for Li⁺ in their vicinity. Benefiting from the high voltage stability, rapid Li⁺ transfer, and elasticity of the coating layer, the coated LiNi_0.9Co_0.06Mn_0.04O₂ exhibits a capacity retention of 92% after 100 cycles when matched with PEO-based electrolytes. The pouch cell enables stable operation for 500 cycles at 1C. In addition, we propose to measure the M_W of recycled PEO after cycling by gel permeation chromatography, which is direct evidence that decomposition (cleavage of the ether linkages) of PEO is inhibited. As a vision, this efficient, high-yield, and simple nanoscale coating method is expected to promote the commercial application of SLMBs.