A study of lithium deposition-dissolution processes in a few selected electrolyte solutions by electrochemical quartz crystal microbalance

In this work, the electrochemical quartz crystal microbalance (EQCM) technique was applied to the study of the charge-discharge cycling of lithium electrodes in a few important Li battery electrolyte solutions. These included ethylene and dimethyl carbonates (EC-DMC) mixtures containing LiAsF₆ or LiPF₆ as the electrolyte, tetrahydrofuran (THF)-EC/LiAsF₆ solutions of two different solvent ratios, and 1-3-dioxolane/LiAsF₆ solutions. The substrate electrode was nickel plated on the quartz crystal. All the experiments were conducted in potentiostatic mode. After an initial step in which the electrode was polarized from open-circuit potential to 0 V (Li/Li⁺), repeated deposition-dissolution steps were conducted within predetermined potential limits. These experiments proved the superiority of 1-3-dioxolane/LiAsF₆ solutions as a selected electrolyte system for rechargeable Li batteries with Li metal anode. The EQCM studies revealed that in both EC-DMC or EC-THF solutions, Li deposition is accompanied by a pronounced corrosion and accumulation of surface species that further partially dissolve during the anodic steps. These studies also reflected the difference in the surface chemistry developed on lithium in EC-THF solutions of different EC concentrations. At low EC concentration the Li passivity is better, and thus cycling efficiency is higher. This correlates well with previous studies which revealed that at low EC concentrations in ethereal solutions, Li₂CO₃ is an important component in the Li surface films.