Cyanoethyl cellulose-based eutectogel electrolyte enabling high-voltage-tolerant and ion-conductive solid-state lithium metal batteries

Abstract

Solid-state polymer electrolytes are an important factor in the deployment of high-safety and high-energy-density solid-state lithium metal batteries. Nevertheless, use of the traditional polyethylene oxide-based solid-state polymer electrolyte is limited due to its inherently low ionic conductivity and narrow electrochemical stability window. Herein, for the first time, we specifically designed a cyanoethyl cellulose-in-deep eutectic solvent composite eutectogel as a promising candidate for hybrid solid-state polymer electrolytes. It is found that the proposed eutectogel electrolyte achieves high ionic conductivity (1.87 × 10−3 S cm−1 at 25°C), superior electrochemical stability (up to 4.8 V), and outstanding lithium plating/striping behavior (low overpotential of 0.04 V at 1 mA cm−2 and 1 mA h cm−2 over 300 h). With the eutectogel-based solid-state polymer electrolyte, a 4.45 V LiCoO2/Li metal battery delivers prominent long-term lifespan (capacity retention of 85% after 200 cycles) and high average Coulombic efficiency (99.5%) under ambient conditions, significantly outperforming the traditional carbonate-based liquid electrolyte. Our work demonstrates a promising strategy for designing eutectogel-based solid-state polymer electrolytes to realize high-voltage and high-energy lithium metal batteries.