Cyano-Functionalized Lithium Sulfonimide Salt for High-Voltage Lithium Metal Batteries

Lithium metal batteries are considered one of the most promising technological routes for next-generation energy storage systems with high energy density. However, when paired with high-voltage cathodes such as NCM811, conventional lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based electrolytes face severe corrosion of the aluminum current collector when the operating voltage exceeds 3.8 V vs. Li+/Li, leading to rapid capacity decay and even cell failure. In this work, we designed and synthesized a cyano-containing lithium salt, lithium cyano(trifluoromethanesulfonyl)imide (LiCTFSI), to address this issue. The electrochemical performance of 1 M LiCTFSI and 1 M LiTFSI in the same carbonate solvent was systematically compared in NCM811/Li cells. The results demonstrate that LiCTFSI effectively suppresses aluminum corrosion at high potentials and forms a thinner and more compact cathode electrolyte interphase to protect NCM811 cathodes. With the LiCTFSI electrolyte, NCM811/Li cells (mass loading = 19.55 mg cm−2) achieve a capacity retention of 81.7% after 200 cycles at a high cutoff voltage of 4.6 V vs. Li+/Li. This work provides a new strategy for developing advanced electrolyte salts for high-voltage, high-energy-density lithium metal batteries.