High-entropy metal oxide containing hybrid electrolyte for long-life Li-metal batteries

Solid-state electrolytes are responsible for transporting lithium ions between electrodes in solid-state batteries and are essential for high-safety and high-energy lithium-metal batteries. Developing novel solid-state electrolytes with high ionic conductivity and good interfacial contact is an urgent need. Here, to this end, a solid-state hybrid electrolyte is developed by mixing high-entropy lithium-containing metal oxide (Lix(Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)1-xO, HEOLi) matrix and poly(ethylene oxide)-lithium salt binder and casting on PTFE substrate. By virtue of the low lithium-ion migration energy barrier of the HEOLi (0.36 eV) and the strong interaction between the oxygen vacancies of the HEOLi and the lithium salt anions, a biphasic transport of lithium ions in both inorganic and polymeric phases of the hybrid electrolyte is achieved, yielding a high ionic conductivity of 3 × 10−4 S cm−1 at 30 °C. The Li/Li symmetric cells with the hybrid electrolyte show a low overpotential of 45 mV and a long cycle life of more than 2500 h. Furthermore, coupled with the LiFePO4 cathodes and metallic lithium anodes, solid-state full cells with the hybrid electrolyte deliver a high capacity of 150 mAh g−1, stable cycle performance, and high safety. Consequently, hybrid electrolytes based on high-entropy metal oxides have broad application prospects in solid-state electrochemical energy storage and are expected to achieve lithium-metal batteries with high safety, high energy density, and long life.