High-Performance Single-Ion Polymer Conductors for Solid-State Lithium Metal Batteries

Solid-state lithium (Li) metal batteries (SSLMBs) have attracted much research interest due to safety and high energy density. It is necessary to develop solid electrolytes with large ionic conductivity, high Li-ion transference number, and good compatibility with electrodes for SSLMBs. One drawback of the traditional dual-ion polymer conductors is the low Li-ion transference number, which causes unwanted polarization in SSLMBs. In this work, we developed a single-ion polymer conductor (SIPC) with carbonyl and cyano groups. When the ion–dipole interactions between Li ions and carbonyl/cyano groups were precisely tuned, the SIPC possessed an excellent selectivity for Li-ion conduction (the Li-ion transference number was more than 0.9), a high room-temperature ionic conductivity of about 10^-4 S cm^-1, a wide electrochemical stability window (>4.5 V, vs Li/Li⁺), and a good electrochemical stability with Li metal during long-term cycling at 26 and 60 °C. With the optimized SIPC, LiFePO₄-based SSLMBs showed good rate and cycle performance in a wide temperature range from -20 to 90 °C. Using the same method, we also prepared sodium- and potassium-based SIPCs with high ionic conductivity and high cationic transference numbers. Thus, tuning the ion–dipole interactions in SIPCs is an effective way to enhance the electrochemical properties of solid polymer electrolytes.