Improved stability of solid polymer electrolyte using an additive for a 4 V lithium-ion battery operated at room temperature

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are potential candidates for developing next-generation batteries owing to their enhanced energy densities and improved safety. However, the application of PEO-based SPEs to Li-ion batteries with 4 V cathodes and graphite anodes at room temperature remains limited because of the low ionic conductivity, decomposition of PEO at high voltages (∼4 V), and co-intercalation of PEO-based SPE into graphite electrodes. In this study, a semi-interpenetrating polymer network (semi-IPN) PEO-based SPE that includes a lithium salt, thiol-ene cross-linkers, and poly(ethylene glycol) dimethyl ether (PEGDME) plasticizer is developed. On introducing fluoroethylene carbonate (FEC) as an additive, we find that the ionic conductivity of the prepared SPE increases to 4.45 × 10 −4 S cm −1 , and the electrochemical stability improves to 5.3 V. The FEC forms stable electrode/electrolyte interfaces on LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) and graphite surfaces, suppressing graphite exfoliation and cracking of NMC811 particles. At 25 °C, the NMC811||graphite cell based on the prepared SPE presents cycling stability up to 100 cycles with a high coulombic efficiency of 99.5% and capacity retention of 77%. The resulting battery performance suggests a potential approach for enhancing the energy density and safety of Li-ion polymer batteries operating at room temperature. • The PEO-based SPEs were prepared using thiol-ene “click reaction”. • The prepared SPE was successfully applied to lithium-ion batteries. • The fluoroethylene carbonate was effective to form stable interfacial layers. • The NMC811||graphite cell using the SPE achieved long-term cycling.