Bilayer Artificial Solid Electrolyte Interphase with 75 GPa Young's Modulus Enable High Energy Density Lithium Metal Pouch Cells

Abstract The artificial solid electrolyte interphase (SEI) layer is capable of protecting lithium anodes and preventing side reactions with electrolytes. The development of inorganic/organic composite hybrid SEI can be considered as an efficient strategy to combine the merits of high lithium ion conductivity, high mechanical modulus, and high flexibility. However, it still poses a great challenge to solve the agglomeration problem in these composite SEI to maintain the strong interaction between SEI and lithium metal. Herein, an inorganic/organic bilayer ultra‐thin SEI (P‐FEM@Li) derivative from reactive fluorinated copolymer (P‐FEM) is prepared and shows ultra‐large Young's modulus (> 75 GPa). The robust inorganic LiF‐rich layer provides superior ionic conductivity and large modulus, while the flexible organic polymer layer regulates lithium ions transport and interphase compatibility. The lithium anodes with P‐FEM induced bilayer SEI demonstrate stable cycles for more than 4400 h at 1 mA cm ⁻² and the average coulombic efficiency (CE) of Li||P‐FEM@Cu is 99.78% after 100 cycles. Moreover, the P‐FEM@Li||NCM811 punch cell with 428 Wh kg ⁻¹ exhibits a high‐capacity retention of 73% after 175 cycles. This work provides a new way to prepare practical SEI for lithium anodes.