In Situ Optical Investigations of Lithium Depositions on Pristine and Aged Lithium Metal Electrodes

A custom-designed in situ optical cell is used to investigate the behavior of lithium (Li0) deposition in a symmetrical face-to-face setup. The experiment aims at monitoring the lithium deposition on both pristine and aged lithium foils, as a function of the waiting time between the lithium electrodes and the electrolyte (LP30: 1.0 M LiPF6 in EC: DMC (50/50 (v/v))). Constant current and electrochemical impedance spectroscopy measurements are applied at ∼28 °C. The experiments show that lithium metal deposits in a wide range of morphologies, which are cataloged in terms of forms, structures, textures and colors for better visualization and improved analysis. Pristine lithium electrodes show tree-like deposition morphologies over the entire range of applied waiting times, but aged samples provided fibrous, and spheroidal forms as dominant lithium deposition morphologies at waiting times ≥ 24 h. Gas-treated metal foils (artificially aged by exposing pristine lithium to N2 at 25 °C for 1 h) showed a similar deposition behavior as the aged-over-time foils. The storage of lithium has a measurable influence on the deposition behavior on lithium foils. The obtained results help to further understand the lithium deposition behavior under different realistic conditions, which is for instance applicable to rechargeable lithium metal batteries

In Situ Optical and Electrochemical Investigations of Lithium Depositions as a Function of Current Densities

The electrodeposition behavior of lithium metal as a function of the current density at room temperature was investigated in a symmetrical face‑to‑face in‑situ optical cell. After a defined initial contact time between electrode and electrolyte, various current densities in the range of 0.05 mA cm−2 to 10 mA cm−2 were tested. Constant current phases, electrochemical impedance spectroscopy measurements and in situ images of the working electrode were recorded and results were compared. Two regimes of lithium deposition with different optical and electrochemical characteristics were identified as a function of current density. The first regime, at low current densities (0.05 mA cm−2–0.5 mA cm−2), showed none to tiny lithium depositions with sporadic large lithium structures at the higher end of this range. The second regime, at high current densities (2 mA cm−2–10 mA cm−2), showed many smaller, deposited lithium structures. The experimental results are discussed in the context of the formation and presence of metal-electrolyte interphases presumably by chemical reactions between lithium and electrolyte, current density and their interactions with each other. The correlation of fundamental parameters of lithium metal deposition with current density must be taken into account for the development of lithium metal-based energy storage devices