In situ construction of an ultra-thin and flexible polymer electrolyte for stable all-solid-state lithium-metal batteries

Solid polymer electrolytes (SPEs) with low density, high flexibility and excellent processability have been attracting broad interest in constructing high energy density and safe all-solid-state batteries. However, the poor lithium-ion (Li + ) migration kinetics should be addressed before their large-scale applications. Reducing the thickness can efficiently shorten the Li + diffusion distance and time, making the low ionic conductivity of electrolytes still applicable for practical applications. Herein, by integrating polyethylene fiber (PEF) with an in situ polymerized network, i.e ., poly[(poly(ethylene glycol) methyl ether methacrylate)- r -(vinyl ethylene carbonate)- r -(dimethyl aminopropyl methacrylamide)- r -(polyethylene glycol dimethacrylate)] (PPVD), an ultra-thin, flexible and mechanically robust SPE with a thickness of ≈5 μm was developed. With an ionic conductivity of 2.0 × 10 −2 mS cm −1 , such an in situ constructed ultra-thin SPE still exhibits a high ionic conductance of 0.1 S, providing sufficient Li + conductance for operable batteries at room temperature. As a result, the assembled Li|PPVD@PEF|Li symmetric cell delivers stable cycling performance over 800 h. The Li|PPVD@PEF|LiFePO 4 full cell exhibits excellent cycling stability with a capacity retention of 85.7% over 500 cycles. The current design of the in situ constructed ultra-thin SPE not only decreases the electrolyte/electrode interfacial resistance but also sheds light on breaking the bottleneck of ionic conductivity for SPEs towards high energy density batteries.