Armoring lithium metal anode with soft–rigid gradient interphase toward high-capacity and long-life all-solid-state battery

Solid polymer electrolytes (SPEs) are highly promising for realizing high-capacity, low-cost, and safe Li metal batteries. However, the Li dendritic growth and side reactions between Li and SPEs also plague these systems. Herein, a fluorinated lithium salt coating (FC) with organic-inorganic gradient and soft–rigid feature is introduced on Li surface as an artificial protective layer by the in-situ reaction between Li metal and fluorinated carboxylic acid. The FC layer can improve the interface stability and wettability between Li and SPEs, assist the transport of Li ions, and guide Li nucleation, contributing to a dendrite-free Li deposition and long-lifespan Li metal batteries. The symmetric cell with FC-Li anodes exhibits a high areal capacity of 1 mAh cm−2 at 0.5 mA cm−2, and an ultra-long lifespan of 2000 h at a current density of 0.1 mA cm−2. Moreover, the full cell paired with the LiFePO4 cathode exhibits improved cycling stability, remaining 83.7% capacity after 500 cycles at 1 C. When matching with the S cathode, the FC layer can prevent the shuttle effect, contributing to stable and high-capacity Li–S battery. This work provided a promising way for the construction of stable all-solid-state lithium metal batteries with prolonged lifespan.