Salt‐in‐Salt Reinforced Carbonate Electrolyte for Li Metal Batteries

The instability of carbonate electrolyte with metallic Li greatly limits its application in high‐voltage Li metal batteries. Here, a “salt‐in‐salt” strategy is applied to boost the LiNO(3) solubility in the carbonate electrolyte with Mg(TFSI)(2) carrier, which enables the inorganic‐rich solid electrolyte interphase (SEI) for excellent Li metal anode performance and also maintains the cathode stability. In the designed electrolyte, both NO(3) (−) and PF(6) (−) anions participate in the Li(+)‐solvent complexes, thus promoting the formation of inorganic‐rich SEI. Our designed electrolyte has achieved a superior Li CE of 99.7 %, enabling the high‐loading NCM811||Li (4.5 mAh cm(−2)) full cell with N/P ratio of 1.92 to achieve 84.6 % capacity retention after 200 cycles. The enhancement of LiNO(3) solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries.