Flexible all-solid-state electrolytes with ordered fast Li-ion-conductive nano-pathways for rechargeable lithium batteries

Abstract

Battery separator and polymer host mixed with lithium salt and volatile plasticizer are simultaneously utilized in conventional lithium batteries, resulting in some inevitable disadvantages for the end products such as poor thermal stability, flammability, even explosibility. Herein, all-solid-state electrolytes (SSEs) composed of flexible poly(ethylene oxide) (PEO) and novel lithium bis(modified imidazole)borate (LiBMB) based thermotropic ionic liquid-crystal with highly ordered fast ion-conductive nano-pathways are prepared for potential application in safe lithium batteries without separator and any volatile plasticizer. Molecular structure and thermotropic liquid-crystal behavior of the prepared LiBMB are confirmed. The influence of PEO content on the crystalline structure, thermal stability, ion-conductive performance, and electrochemical stability of the produced LiBMB/PEO SSEs are extensively assessed. The maximum ionic conductivity, Li-ion transference number, and diffusion coefficient of the developed SSEs reach 0.45 × 10−3 S cm−1, 0.54, and 2.33 × 10−7 cm2 s−1 at 30 °C, respectively, benefiting from the maintenance of the ordered fast ion-conductive nano-pathways. The optimum LiFePO4/SSEs/Li cell delivers an initial discharge capacity of about 145.5 mA h g−1 at the discharge rate of 0.1 C, showing a promising application in new generation of all-solid-state safe Li-ion batteries.