Hydrogen bonding enhanced SiO2/PEO composite electrolytes for solid-state lithium batteries

The use of solid electrolytes can fundamentally change energy storage systems due to their higher safety and energy density. Herein, we design hydrogen-bonded polyethylene oxide (PEO) composite solid electrolytes (CSEs), which are hydrolyzed by tetraethyl orthosilicate (TEOS) in alkaline solution to form SiO2 with rich hydroxyl groups on its surface. This in situ formed SiO2 can not only reduce the crystallinity of PEO and increase the ionic conductivity (1.8 × 10−4 S cm−1 at 30 °C), but also adsorb anions so as to increase the lithium-ion transference number (tLi+ = 0.42). More importantly, hydrogen bonding can be formed with PEO, LITFSI and succinonitrile to form an interconnected network to improve the mechanical strength (Young's modulus = 0.72 GPa). In addition, we avoid the poor film formability and low mechanical strength by adjusting the ratio of EO : Li to 30 : 1 to reduce the content of lithium salt in the CSEs. Due to the high mechanical strength, the critical current density of lithium symmetrical batteries is as high as 1.4 mA cm−2. Using this CSE, a solid state LiFePO4‖Li battery delivers a high discharge capacity of 161.2 mA h g−1 at 0.5C with a capacity retention of 88% after 400 cycles at 30 °C. The in situ formed highly dispersed SiO2 reinforced PEO with abundant hydrogen bonds enables high performance of solid-state lithium batteries at room temperature.