Designing carbonate–ether polymer electrolytes to overcome the conductivity–stability trade-off in high-voltage lithium batteries

Abstract

The growing use of electric vehicles and portable electronic devices has increased the demand for lithium batteries with both high energy density and enhanced safety. Solid polymer electrolytes (SPEs) offer a safer alternative to liquid electrolytes, which are associated with leakage and flammability risks. Research has primarily focused on ether-based polymers, particularly polyethylene oxide (PEO); however, their limited oxidative stability restricts their use with high-voltage cathode materials operating above 4 V. In contrast, carbonate-based polymers exhibit excellent oxidative stability due to the presence of electron-withdrawing C[dbnd]O functional groups, but their low chain flexibility results in reduced ionic conductivity. To address this trade-off between conductivity and stability, we synthesized carbonate-functionalized polymers—poly(trimethylene carbonate) propionate anhydride (PTMC-PA) and poly(carbonate diol) propionate anhydride (PCDL-PA)—and blended them with polyethylene glycol dimethyl ether (PEGDME) to design a balanced carbonate–ether-based SPE. The SPE containing 20 wt% PCDL-PA achieved an ionic conductivity of up to 1.49 × 10−4 S cm−1 at 25 °C, thereby effectively mitigating the poor conductivity issue of conventional carbonate-based polymer electrolytes. Furthermore, electrochemical testing demonstrated excellent oxidative stability, with the cells maintaining 76 % capacity retention after 100 cycles at 0.5C up to 4.4 V. Overall, the proposed carbonate–ether-based SPE successfully balances ionic conductivity and voltage stability, highlighting its potential for next-generation safe and high-energy lithium metal batteries. © 2024