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

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.