An integrate and ultra-flexible solid-state lithium battery enabled by in situ polymerized solid electrolyte

Searching for ultra-safe flexible electrolytes is crucial to the exploitation of flexible solid-state batteries and wearable devices. However, it is very challenging to simultaneously conquer the issues of the elastic electrolyte, including low ionic conductivity, inferior electrolyte/electrode interface compatibility, and unsatisfying cycling stability of the assembled cell. Herein, we developed an elastic PEL electrolyte using poly(butyl acrylate) cross-linked polyethylene glycol and EMIMTFSI with an ultrahigh elongation of 1000%. The PEL-0.1 electrolyte delivers an ionic conductivity of 1.19 × 10−4 S cm−1 and good flame resistance. The superior interface compatibility between electrodes and electrolyte is realized by the in situ polymerized PEL on cathode and contact stability towards metallic lithium, which facilitates the ion conduction in the solid-state cell and accommodate the electrode volume changes during the charge/discharge processes. The Li/PEL-0.1/Li cell can stable cycle for 300 h at 50 mV. The little difference in the impedance of the tabulate and wire-shaped solid-state batteries at various deformation states demonstrates the good shape conformability and feasibility of flexible PEL electrolyte. The integrated LiFePO4/PEL-0.1/Li batteries show excellent cycling stability at all the temperatures of 25 °C, 40 °C and 60 °C. A series of destructive operations on the working pouch cell confirms the superior safety and practicability of the designed electrolyte. The study proposed a promising ultrasafe and flexible electrolyte with outstanding electrochemical performance in the applications of the next-generation flexible solid-state lithium batteries and wearable devices.