Molecular design of non-fluorinated linear ethereal solvent for high-voltage Li metal batteries

Stable cycling of 4.5 V LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) based Li metal batteries is a great challenge as both electrodes work at the extreme voltage. Ethereal electrolytes have been demonstrated to exhibit better stability towards Li metal anode. Unfortunately, their limited electrochemical windows hinder their application in high-voltage Li metal batteries. Herein, we take 1,2-dimethoxyethane molecules as a starting point to design a series of non-fluorinated linear ethereal solvents via either extending the ethylene glycol (EG) units in the backbones or the terminal alkyl group. Further theoretical calculation suggests that with the extension of the EG unit in the backbone, the Li + solvation energy increases, leading to the formation of solvent-separated ion pairs, while the extension of the terminal alkyl chain results in an ion-pair solvation structure due to the steric effect. Consequently, 1,2-dibutoxyethane (EDB) is selected as the solvent for high-voltage Li metal batteries. The 4.5 V Li || NCM811 cells can stably operate over 600 cycles with EDB electrolyte. Notably 1 Ah-level Li || NCM811 pouch cell demonstrates a long cycle life over 100 times, even with a low negative-to-positive capacity ratio of 1.2 and an electrolyte-to-cathode capacity of 2.8 g Ah −1 .