Synergistic effects of salt concentration and working temperature towards dendrite-free lithium deposition

Fig1. Corresponding in situ optical images of Li deposition morphologies under different conditions

A research team led by Yongyao Xia's research group at Fudan University employed an in situ optical microscope to investigate the effect of the electrolyte concentration and the working temperature on the Li-plating/-stripping process. The paper entitled “Synergistic Effects of Salt Concentration and Working Temperature towards Dendrite-Free Lithium Deposition” was recently published in Research (Research 2019 Article ID: 7481319 DOI: 10.34133/2019/7481319). https://spj.sciencemag.org/research/2019/7481319/.

Li metal is the most promising anode for high-energy chemical batteries due to its high theoretical specific capacity (3860 mAh g-1) and the low electrochemical potential (-3.04 V versus SHE.) for rechargeable batteries. However, the practical application of Li anode is much hindered by the dendrites growth (leading to the issue of short circuit) and side reactions between Li metal and liquid electrolytes (resulting in poor Coulombic efficiency). Recently, many reports have well demonstrated two effective methods towards practical lithium metal anode. The highly concentrated electrolyte can effectively reduce the side reactions of Li metal with solvents. And rising working temperature can heal lithium dendrites. However, high salt concentration can’t eliminate lithium dendrites drastically. And elevated temperature will aggravate side reactions so to lead irreversible capacity loss.

In this work, we achieve high-Coulombic-efficiency and high-capacity deposited-Li on copper foil without dendrites through synergistic effects of salt concentration and working temperature. Highly concentrated electrolytes can effectively increase the Coulombic efficiency of Li-plating/-stripping while rising temperature helps to homogenize the distribution of ions to eliminate lithium dendrites. For another, rising working temperature and increasing salt concentration induce the LiF-rich solid electrolyte interphase (SEI) layer to suppress the lithium dendrites.

Operando optical microscopy, XPS and ex-situ SEM characterization are applied to evaluate the effect of these two factors. Explosive growth of Li dendrites is observed and recorded in real time in the low concentration of 1m electrolyte at 27oC. With the rise of the working temperature, the merging process of Li dendrites can be directly observed (as shown in this journal). In spite of the merging behavior at elevated temperature, Li dendrites still grow up in low-salt concentration electrolyte. With the synergistic effect of high concentration and rising temperature, dendrite-free Li deposition behavior can be detected with Operando optical microscopy. Under the optimized condition (3 m electrolyte at 60oC), high average Coulombic efficiency of 99.2% over 150 cycles is achieved with a high areal capacity of 2 mAh cm-2 on copper foil, which offers a promising pathway towards practical application of Li-anode.

Tag: Emerging materials research