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 LiNi0.9Co0.06Mn0.04O2 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 MW 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.