A solid-like succinonitrile-based polymer electrolyte with superior mechanical strength for high performance lithium metal batteries

Succinonitrile (SN)-based electrolytes provide an attractive candidate for solid electrolytes because of their high room-temperature ionic conductivity and favorable interfacial contact with electrodes. However, the mechanical strength of SN will suffer from a significant decrease when complexing with lithium salts, which results in excessive plastic and even liquid-like behavior and hence impedes its further application as a self-supporting electrolyte film in solid lithium metal batteries (LMBs). Here, a robust solid-like succinonitrile (SN)-based polymer electrolyte (SNPE) is proposed to address this issue through a facile film casting strategy, which is fabricated by mixing PVDF with SN and introducing dual-salt (LiTFSI-LiBOB) and FEC to suppress the side reactions of SN. By adjusting the weight ratio of SN to PVDF, the optimized SNPE (SN PVDF = 3:5) not only exhibited comparable ionic conductivity (0.97 mS cm−1) at room temperature but also exhibited superior mechanical robustness (15.7 MPa). As a result, the Li symmetric cell using the SNPE prevents itself from short-circuiting for >1500 h under a current density of 0.1 mA cm−2. Moreover, the LiFePO4 (LFP)|Li cell assembled with SNPE delivers long-term cycling stability under 2C at room temperature, with a high capacity retention of 87.8 % over 1000 cycles. This design proves to be an effective approach for enhancing the mechanical strength of SN-based electrolytes, broadening their application in LMBs.