Novel design of high elastic solid polymer electrolyte for stable lithium metal batteries

Li metal anodes have high specific capacity and low electrode potential, and have always been considered as one of the most promising anode materials. However, the growth of Li dendrites, unstable solid electrolyte interface layer (SEI), severe side reactions at the Li/electrolyte interface, and infinite volume expansion of the Li anode seriously hinder the practical application of solid-state Li metal batteries (LMBs). Herein, we report a polyurethane elastomer (TPU) material with high elasticity and interfacial stability as a solid polymer electrolyte (SPE) for LMBs. The synergistic effects of its designed soft chain forging (PEO) and hard chain segments (IPDI) can enhance Li ion conductivity, elastic modulus and flexibility of the SPE to settle the challenges of the Li metal anodes. Moreover, Li₂S, as a solid-state electrolyte additive, is able to effectively inhibit the occurrence of side reactions at the interface between Li metal and SPE, promote the decomposition of N(CF₃SO₂)₂^- and in-situ generation of LiF with low Li⁺ diffusion barrier and excellent electronic insulation, achieving rapid Li ion transport and uniform Li deposition. As a result, stable cycle of up to 1400 h has been achieved for a Li||TPU-Li₂S||Li battery at 0.1 mA/cm² at 50 ℃, accompanied with a stable cycling performance of 350 h at a higher current density of 0.5 mA/cm². Finally, the LiFePO₄||TPU-Li₂S||Li full battery exhibits an excellent cycling performance with a capacity retention rate of 80 % after 500 cycles at 1C. This simple and low-cost strategy provides novel design thoughts for practical application of high-performance SPEs in stable and long-life LMBs.