Cellulose-based eutectogel electrolyte with high ionic conductivity for solid-state lithium-ion batteries

It is known that the low ionic conductivity of solid-state polymer electrolytes at room temperature (RT) has severely restricted their practical application in lithium-ion batteries. Although eutectogel (ETG) electrolytes could solve this problem to some extent, highly compatible deep eutectic solvent (DES)/polymer systems are desirable to further enhance ion conduction. Herein, we designed cellulose-based ETG (CETG) with dual channels through "hopping" and "vehicle" mechanisms by hydroxyethyl cellulose (HEC) molecular chains and N-methylacetamide (NMA)/LiTFSI-derived DES, respectively. Thanks to the strong molecular interactions between HEC and DES, the highest DES content in the ETG could achieve 90 %, which endowed the CETG with an excellent ionic conductivity of 2.04 × 10–3 S cm−1 at 30 °C. Additionally, our designed CETG displayed good self-healing and fire retardant properties. The assembled Li/LiFePO4 cell showed a capacity retention of 91.8 % after 200 cycles at 0.2 C under RT with an initial discharge capacity of 156.2 mAh g−1. In particular, the capacity retention rates of the assembled batteries reached 95.2 % and 92.1 %, respectively, after 100 cycles at 0.2 C under 60 °C and 50 cycles at 0.2 C under 100 °C. Our fabrication strategy would provide a novel idea for the design of green, safe and efficient solid-state polymer electrolytes for lithium-ion batteries.