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

Abstract

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 (t_Li⁺ = 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.