Multivalent Cation Additives for Building Dendrite-Free and Stable Electrode-Electrolyte Interface on Lithium-Metal Anodes

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Li-metal anodes are ideal anode materials for Li-based batteries owing to high theoretical capacity and low redox potential. However, the practical application of Li-metal anodes face challenges, such as uneven deposition morphology and progressive electrolyte decomposition during repeated Li deposition and dissolution. To improve the reversibility, high-concentration electrolytes (HCEs), such as 4 M Li[FSI] in DME,[1] have been reported to effectively flatten the deposition morphology and improve the Coulombic efficiency. Nevertheless, HCEs have several limitations, including poor oxidation stability, high viscosity, and high production costs.[2] Therefore, technologies for creating the HCEs’ features in lower concentration ranges are expected to be developed.In this presentation, we introduce an effective approach to utilize multivalent cations (e.g. Ca2+, Ba2+) as electrolyte additives to construct dual-cation electrolytes (DCEs) for Li-metal anodes. Because multivalent cations have much stronger coordination with anions and solvent molecules than Li+, it is usually difficult to reduce multivalent cations to metal state in organic electrolytes. When multivalent cations are mixed with Li+ in electrolytes, the Coulomb interaction among different cations would modify the solvation structure. Anions are promoted to directly coordinate with cations increasing the ratio of the contact-ion pairs (CIPs) to diminish the free energy of the electrolyte system.[3] This phenomenon creates the solvation environment similar to HCEs, which contributes to maintaining a dendritic-free deposition morphology. Furthermore, as a unique feature of DCEs, multivalent cations are prone to be involved in the formation of solid-electrolyte interphase (SEI) in addition to Li+. The chemical bonds between multivalent cations and the other SEI compositions (e.g., F, O, S, C and N) can enhance the structural stability and functionality of SEI, as an effective controlling factor for the reaction behavior of Li-metal anodes.[4][1] J. Qian, J-G. Zhang et al, Nat. Commun. 6, 6362 (2015)[2] Y. Yamada, A. Yamada et al, Nat. Energy 4, 269 (2019)[3] H. Li, T. Ichitsubo et al, Cell Rep. Phys. Sci. 3, 100907 (2022)[4] H. Li, T. Ichitsubo et al, submitted.