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 LiNO₃ 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 NO₃ ^- and PF₆ ^- 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 LiNO₃ solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries.