Ionic liquid-grafted MXene composite polymer electrolytes for high-performance solid-state batteries

All-solid-state batteries (ASSBs) have obtained much attention due to the high energy density and security. At present, PEO-based solid-state batteries are considered to be one of the most promising candidates for high-performance ASSBs due to the excellent processability and good interfacial stability. However, low ionic conductivity and Li + transference number seriously hinder their progress in practical applications. Here, a novel filler is developed by embedding ionic liquid (IL) grafted onto the surface of MXene to improve the electrochemical performance of PEO-based solid composite polymer electrolyte (MXene-IL-SPE) for ASSBs. The 2D MXene can significantly reduce the crystallinity of PEO, and the presence of IL not only enhances the dispersion of MXene in the polymer matrix, but also promotes the dissociation of lithium salts and anchors anions. As a result, the MXene-IL-SPE possesses high ionic conductivity (7.19 × 10 −4 S cm −1 ) and Li + transference number (0.51), together with wide electrochemical window (5.2 V) at 60 °C. The assembled LiFePO 4 |MXene-IL-SPE|Li full cell exhibits remarkable rate capability and exceptional capacity of 154.8 mAh g −1 over 120 cycles with an impressive 95.3 % capacity retention at 0.5 C. This design opens up a new way to prepare high performance CPEs for ASSBs.