Decoupling the mechanical strength and ionic conductivity of an ionogel polymer electrolyte for realizing thermally stable lithium-ion batteries

Gel electrolytes are promising candidates for fulfilling the performance and safety requirements of a new generation of lithium-ion battery technologies owing to their quasi-solid-state and ameliorated mechanical strength. However, there is a dilemma that requires the sacrifice of the ionic conductivity in exchange for mechanical strength. Here, a mechanically robust ionogel polymer electrolyte (IGPE) is explored to overcome this plight. The IGPE film is prepared by the nonsolvent induced phase separation method, and the obtained optimal flexible IGPE-5 sample exhibits robust mechanical strength with 178% elongation at break and 6.65 MPa breaking strength. In addition, the IGPE-5 presents a high ionic conductivity of 0.80 mS cm−1 at 25 °C, a wide electrochemical stability window of 4.7 V and high thermal stability up to 220 °C. The LiFePO4/IGPE-5/Li cell displays initial discharge capacity of 161.9 mAh g−1 and a capacity retention of 94.5% after 200 cycles at 0.5C at 55 °C. The IGPE-5-based flexible battery can withstand bending and cutting tests, indicating that the excellent flexibility and interface compatibility of IGPE-5.