A Lithiophilic–Lithiophobic Gradient Solid Electrolyte Interface Toward a Highly Stable Solid‐State Polymer Lithium Metal Batteries

Abstract The functional lithiophilic−lithiophobic gradient solid electrolyte interphase (SEI) between Li‐metal anode and solid‐state polymer electrolytes may be effective in addressing the long‐standing issue of side reactions and Li‐dendrite growth during repeated deposition or dissolution in solid‐state polymer‐based high‐energy‐density batteries. Herein, a reliable lithiophilic–lithiophobic gradient SEI (G‐SEI) of LiAg‐LiF/Li 3 N is in situ formed by AgTFSI, used as an additive for polyethylene oxide‐based electrolyte (PEO‐Ag). The upper layer consists of a lithiophobic LiF/Li 3 N‐rich layer, wherein LiF possesses a high interfacial energy, while Li 3 N enables fast Li + diffusion, which synergistically facilitates the uniform deposition of Li + . Lithiophilic Li–Ag alloy can effectively reduce the nucleation overpotential and promote more planar growth of lithium. Furthermore, such G‐SEI possesses a high mechanical modulus, mitigating the penetration of dendrites through the SEI and thereby preventing the continuous degradation of the PEO‐based electrolyte. As a result, an over three times improvement in the lifespan of Li | PEO‐Ag | LFP cell is achieved, demonstrating an 81.4% capacity retention rate after 500 cycles at 1C, as compared to Li | PEO | LFP cell with common SEI. Thus, the developments of the lithiophilic‐lithiophobic gradient SEI provide a substantial path toward high‐performance solid‐state lithium batteries.