In-situ solidification of plastic interlayers enabling high-voltage solid lithium batteries with poly(ethylene oxide) based polymer electrolytes

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes play an important role in the next-generation solid batteries owing to their distinct advantages of low cost, light weight, and easy large-scale production. However, the oxidative decomposition potential lower than 3.8 V (vs Li/Li+) of pure PEO severely hinders its coupling with high-voltage cathodes, directly leading to the limited energy density. Herein, the succinonitrile (SN) plastic crystal interlayers are in-situ solidified between high-voltage cathodes and PEO electrolytes in order to address the critical issue of interfacial incompatibility of PEO against high-voltage cathodes. On the one hand, the liquid SN fully penetrates the porous cathode and spreads out on cathode surface at the temperature higher than its melting point, followed by in-situ solidification forming ion-conducting networks inside the cathode and at cathodic interface after cooling to room temperature. On the other hand, the solidified SN acts as a physical shield to isolate PEO from high-voltage cathodes, avoiding PEO decomposition at high charging potentials. Consequently, PEO can be coupled with a high-voltage LiNi0.6Co0.2Mn0.2O2 cathode, endowing the resultant solid cell with a remarkable cycling stability under cutoff voltages of 4.2, 4.25, and 4.3 V after 100 cycles. Furthermore, a high cathode loading of 10.3 mg cm-2 with initial discharge capacity of 152.4 mAh g-1 (corresponding to 1.57 mAh cm-2) is achieved along with the capacity retention of 80.8% over 50 cycles. This work provides a promising strategy to improve the compatibility of PEO-based electrolytes against high-voltage cathodes via facile in-situ solidification of plastic interlayers.