Batteries with asymmetric solid-state electrolytes for sustainable energy storage

With the increased penetration of energy storage devices in daily life, safety hazard and energy density issues are attracting greater and greater interest. Conventional liquid electrolytes suffer from leakage, flammability, gasevolution, dendrite hazards and so on, especially when matching with high-energy-density metal anodes. Though solid-state electrolytes (SSEs) are promising candidates for the next-generation safe and high energy density energy storage system, individual SSE fails to meet the asynchronous demands of cathode and anode, because of their intrinsic solid chemistry properties. Among numerous modified approaches related to SSEs chemistry, asymmetric solid-state electrolytes (ASSEs) which have more than one SSE and multilayer structure take advantage of individual SSE layers and complement each other's disadvantages, showing Janus abilities. However, there are few reviews about ASSEs. Also, the problem of interface compatibility the between different electrolytes as well as the interface of electrodes and electrolytes is hindering the development of ASSEs. This review comprehensively outlines the state of the art of ASSEs. Additionally, it summarizes the advantages and functions of ASSEs with the unique structure for different energy storage. Furthermore, the interfacial compatibility and corresponding evaluation methods are discussed. Finally, an outlook on how ASSEs will develop in the future energy storage applications is proposed.