Organic Mixed Ionic‐Electronic Conductors as Multi‐Functional Binders for Energy‐Dense Carbon‐Free Solid‐State Batteries

Abstract Solid‐state lithium‐metal batteries are considered as one of the most promising candidates for next‐generation energy storage devices with high energy density and enhanced safety. Great efforts have been made to design solid‐state electrolytes with enhanced ionic conductivity and to protect the electrochemical interface of the lithium anode. However, the obstruction of ionic‐electronic transport within the cathode remains as another key challenge that needs to be addressed for the practical application of solid‐state batteries. Here, we prepared organic mixed ionic‐electronic conductors (OMIECs) by in‐situ co‐polymerization of three organic monomers (boron‐type crosslinker, ionic liquid, and sulfolene) in the network of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate). The as‐prepared OMIECs show an electronic conductivity up to 33.6 S cm −1 and ionic conductivity of 1.7×10 −4 S cm −1 at 30 °C, and also binder functionality, providing a combined path for Li + /e − transport in cathodes and maintaining mechanical/(electro−)chemical stability. As a result, solid‐state cathodes composed of 90.0 wt % active materials and only 10.0 wt % OMIECs display exceptional electrochemical characteristics at 30 °C, including high C‐rate capabilities and prolonged cycle life. This novel design of all‐in‐one OMIECs for carbon‐free cathodes demonstrates a promising strategy for developing multifunctional additives for high‐performance solid‐state batteries.