"In situ integrated design of composite SEI-gel electrolytes boosting high-safety and wide-temperature lithium metal batteries."

Neither single electrolyte design nor solid electrolyte interface (SEI) engineering alone can effectively resolve the dual challenges of sluggish reaction kinetics and unstable interfaces in polymer-based lithium metal batteries (LMBs). Herein, a rational integrated design strategy is adopted to simultaneously fabricate poly(trifluoroethyl methacrylate-co-4-oxo-5,8,11-trioxa-3-azatridec-12-en-1-yl acrylate)-based gel polymer electrolyte (PTDA-GPE) and stable composite SEI during the thermal-induced in situ polymerization process. The resulting PTDA-GPE demonstrates superior Li⁺ transport kinetics (1.34 mS cm^-1 at 30 °C), enhanced mechanical strength and flame retardancy, and an expanded electrochemical window of up to 4.8 V (vs. Li⁺/Li). Notably, the SEI constructed using the differentiated adsorption forces and redox kinetics between various components and lithium metal has a unique organic-inorganic composite structure. Ultimately, Li/PTDA-GPE/LiFePO₄ batteries can achieve over 1000 stable cycles at -20 °C and 60 °C (capacity retention of 95 % and 80 %, respectively)，and Li/PTDA-GPE/LiCoO₂ demonstrates high capacity retention of 98 % after 200 cycles. In addition, the 1.2 Ah Li/PTDA-GPE/LiFePO₄ pouch cell can guarantee enhanced safety features and constant output voltage under abuse conditions. This work demonstrates a facile and universal strategy for in situ integrated fabrication of composite SEI/GPE.