Flexible, stable, fast-ion-conducting composite electrolyte composed of nanostructured Na-super-ion-conductor framework and continuous Poly(ethylene oxide) for all-solid-state Na battery

Abstract

Solid-state electrolytes have attracted increasing attentions, as they can solve the safety issues related to the use of flammable liquid electrolytes. However, it is still challenging to achieve high ionic conductivity of solid-state electrolytes and to create low interface impedance between solid electrolyte and solid electrode at room temperature. Herein, we report the development of high-performance NASICON/Poly(ethylene oxide) composite electrolytes (CEs) for all-solid-state Na batteries that can be used at room temperature (23.8 °C). With the novel combination of nanostructured NASICON framework and continuous poly(ethylene oxide) filler, an outstanding room-temperature ionic conductivity of 1.4×10−4 S cm−1 is obtained. The fast Na-ion diffusion pathways at the 3D inter-connected NASICON-Poly(ethylene oxide) interfaces are visually observed for the first time via scanning probe microscopy, contributing to the superior ionic conductivity in CEs. The NASICON framework further strengthens the mechanical structure of CEs and effectively suppresses Na dendrites. Intimate and stable contact is achieved between the solid-state CEs and solid ceramic electrodes at room temperature, along with low electrolyte-electrode interface impedance and good durability, due to the high flexibility of CEs. Prototypes of all-solid-state Na batteries using the CEs are developed, demonstrating excellent electrochemical performance, which verifies that the present solid-state CEs are promising alternatives to the conventional liquid electrolytes.