Uncovering the Crucial Role of Chelating Structures in Cyano-Alkyl-Phosphate Electrolytes for High-Voltage Lithium Metal Batteries.

Abstract

The inferior oxidative stability of commercial carbonate electrolytes and overgrowth of the electrode-electrolyte interphase (EEI) have largely hindered the development of high-voltage lithium metal batteries. In this study, these challenges are addressed by designing Li+-solvent chelating solvation structures to inhibit solvent decomposition using cyano-alkyl-phosphate as a demonstration. Theoretical and experimental studies confirm that the -P═O and -C≡N groups within diethyl (2-cyanethyl) phosphonate exhibit a comparable ability to coordinate with Li+, facilitating the formation of seven-membered chelating structures. This unique solvation structure contributes to the formation of anion-derived inorganic-rich EEI with high stability and robustness, hindering the further decomposition of the electrolyte. Additionally, the cyano group has a strong complexation with the transition metal (TM) in the cathode to inhibit TM dissolution, thereby ensuring the structural stability of the cathode particle. Utilizing this special chelating structure, the designed electrolyte demonstrates favorable Li plating/stripping reversibility and promising oxidative stability in high-voltage batteries. Consequently, the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode exhibits a high capacity retention (90%) after operating 300 cycles. Under harsh testing conditions, the 4.6 V Li||NCM811 pouch cell with a capacity of 1.4 Ah (∼295 Wh kg-1 based on the total mass of the cell) retains 70% capacity after 80 cycles. This work provides new insights into the correlation between the solvation structure and oxidative stability of electrolytes, contributing significantly to the advancement of high-voltage lithium metal batteries.