Investigating the Effects of Electrolytes on Li Deposition By Electrochemical Quartz Crystal Microbalance
Authors: Ge Shiyu , Lopez Jeffrey 
Published: December 2024

Batteries for EVs and grid-scale energy storage are necessary to meet the increasing energy demands in modern society and support the creation of a net-zero emission world. Among various kinds of batteries, lithium metal batteries (LMBs) using lithium metal anodes (LMAs) are one of the most promising candidates. They provide high theoretical specific capacity (3,860 mAh g-1) and high specific energy (>500 Wh kg-1), improving performance beyond what is possible with lithium-ion batteries1,2. However, the high reactivity of LMAs brings problems like low Coulombic efficiency and poor cycling stability to the LMBs. Electrolyte engineering is one approach to solve these problems since it can enable smooth, compact, and uniform Li deposition with large particles. Considering the strong size effect on mechanical properties of Li, desired Li deposits exhibit different mechanical properties, such as shear modulus, compared with smaller Li particles3. Therefore, studying mechanical properties of Li at micrometer scale is also important for forming desired Li deposition and can guide the design of next-generation electrolytes. To investigate the mechanical properties of favored Li deposits, an in situ characterization technology of electrochemical quartz crystal microbalance (EQCM) is employed.

In this presentation, we will discuss the mechanisms of Li deposition in LMBs studied by EQCM. This technique allows the in situ monitoring of mass changes, as well as the measurements of mechanical properties detected by EQCM-dissipation (EQCM-D) mode4. We used it to investigate the Li film formed by different electrolytes, especially focusing on localized high concentration electrolytes (LHCEs), which are the state-of-the-art electrolytes in LMBs5. The effects of different diluents including 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE), tris(2,2,2-trifluoroethyl)orthoformate (TFEO), and bis(2,2,2-trifluoroethyl) ether (BTFE) were studied. The measurements of mass change and modulus of Li film can give new insights into the mechanisms of Li deposition, supporting the other characterization techniques such as SEM. Ultimately, this study provides new insights into the subtle mechanical differences of Li metal deposited in different electrolytes. This will guide the next-generation electrolyte design for achieving high Coulombic efficiency, excellent cycling stability, and practical application for LMBs.

References:

[1] Liu, Bin, Ji-Guang Zhang, and Wu Xu. "Advancing lithium metal batteries." Joule 2.5 (2018): 833-845.

[2] Liu, Jun, et al. "Pathways for practical high-energy long-cycling lithium metal batteries." Nature Energy 4.3 (2019): 180-186.

[3] Xu, Chen, et al. "Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes." Proceedings of the National Academy of Sciences 114.1 (2017): 57-61.

[4] Ji, Yuchen, et al. "From bulk to interface: electrochemical phenomena and mechanism studies in batteries via electrochemical quartz crystal microbalance." Chemical Society Reviews 50.19 (2021): 10743-10763.

[5] Cao, Xia, et al. "Effects of fluorinated solvents on electrolyte solvation structures and electrode/electrolyte interphases for lithium metal batteries." Proceedings of the National Academy of Sciences 118.9 (2021): e2020357118.