The Role of the SEI in Lithium and Calcium Metal Batteries


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Due to their high energy density and theoretical specific capacity, alkali and alkaline earth metal anodes are gaining increasing attention. Lithium metal is the most investigated anode candidate for next generation batteries. However, the commercialization of lithium metal anodes is still delayed by several drawbacks. Lithium metal reacts with the electrolyte, forming an inhomogeneous solid electrolyte interphase (SEI). Electrodissolution/-deposition of lithium is favored where the SEI is less resistive or cracked, leading to protrusions and dendrite growth. This does not only lower the coulombic efficiency (CE) and cell specific capacity but also raises safety risks. [1-2] Therefore, an effective SEI is required to enable safe high energy batteries with lithium metal anodes by limiting lithium protrusions. There are different approaches to grow an effective SEI, such as the use of electrolyte additives, mechanical methods and chemical modification. [3-6]
In contrast to this, alkaline earth metal anodes, such as magnesium or calcium, are less prone to dendrite formation, while still offering high theoretical specific capacities. However, their oxide passivation layer does not allow significant mobility for their divalent ions, leading to large overvoltage and slow reaction kinetics, which hinders the cycling. Therefore, electrolytes which limit passivation layer formation have to be applied and additives are investigated regarding their ability to remove the oxide layers. [7,8]
Herein, we present a novel mechanochemical approach to form an effective SEI on the lithium metal surface by combining mechanical and chemical modification utilizing ionic liquids (ILs) prior to cell assembly. It limits dendrite growth even at high current densities of 10 mA cm-2 in low temperature lithium metal batteries using liquid electrolytes. To further highlight the importance of surface treatment, we investigate different salts, salt mixtures and additives in electrolytes for calcium metal batteries as well as mechanical modification of calcium metal anodes.

Acknowledgements: The authors would like to acknowledge financial support from the European Union through the Horizon 2020 framework program for research and innovation within the projects “SPIDER” (814389) and “VIDICAT” (829145).

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[2] Bieker, G.; Winter, M.; Bieker, P., Physical Chemistry Chemical Physics 2015, 17 (14), 8670-8679.
[3] Peled, E., Journal of The Electrochemical Society 1979, 126 (12), 2047-2051.
[4] Josef, E.; Yan, Y.; Stan, M. C.; Wellmann, J.; Vizintin, A.; Winter, M.; Johansson, P.; Dominko, R.; Guterman, R., Israel Journal of Chemistry 2019.
[5] Basile, A.; Bhatt, A. I.; O’Mullane, A. P., Nature Communications 2016, 7, 11794.
[6] Becking, J.; Gröbmeyer, A.; Kolek, M.; Rodehorst, U.; Schulze, S.; Winter, M.; Bieker, P.; Stan, M. C., Advanced Materials Interfaces 2017, 4 (16), 1700166.
[7] Shterenberg, I.; Salama, M.; Yoo, H. D.; Gofer, Y.; Park, J.-B.; Sun, Y.-K.; Aurbach, D., Journal of The Electrochemical Society 2015, 162 (13), A7118-A7128.
[8] Stievano, L.; de Meatza, I.; Bitenc, J.; Cavallo, C.; Brutti, S.; Navarra, M. A., Journal of Power Sources 2021, 482, 228875.

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