Recent developments and progress of halogen elements in enhancing the performance of all-solid-state lithium metal batteries

Rechargeable Li-ion batteries (LIBs) have found wide applications in portable electronics, electric vehicles, large-scale smart grids and so on. However, traditional LIBs are unable to meet the growing energy-storage demand due to rapid growth of electric vehicles and increased demand for grid energy storages. Furthermore, the LIBs containing flammable liquid electrolytes are limited by potential safety risks. In view of this, all-solid-state lithium metal batteries (ASSLMBs) with high energy density and ensured safety are considered to be promising battery systems. As a key component in the ASSLMBs, solid-state electrolytes (SSEs) have a profound impact on the performance of the ASSLMBs. However, key issues remain unsolved, such as poor room-temperature ionic conductivity of the SSEs and incompatible electrode/electrolyte interface. It is found that halogen elements exhibit a prominent role in the solid batteries, such as improvement of the conductivity for the inorganic SSEs via halogen doping, modification based on halogen materials to create a conformal electrode/SSE interface and promising halide electrolytes. In the current review, we first give an overview of the inorganic SSEs and discuss the tailoring effect of ionic conductivity via halogen doping. Then, the dilemma at the electrode/electrolyte interface is introduced followed by the effect of halogen elements in stabilizing the interface will be commented. At last, recent progress of the promising halide electrolytes are summarized, including their advanced synthesis technique, structure, ionic conductivity, and electrochemical performance. This review aims to arouse the interest of halogen elements to be applied in ASSLMBs for high-performance energy storage systems.