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.