Understanding the Self-Healing Electrostatic Shield Mechanism at the Lithium–Metal Anode Surface

Lithium–metal anodes, with their impressive high specific capacity of approximately 3860 mAh/g, emerge as a promising alternative to Li-ion anodes. However, when subjected to higher recharge currents for accelerated battery charging, dendrites tend to form on the Li-metal surface. These dendrites can puncture the separator, leading to short circuits upon contact with the positive electrode. Such short circuits in a nonaqueous solvent can trigger runaway reactions, which raises safety concerns. In an effort to limit dendrite formation on the lithium–metal anode, the "self-healing" electrostatic shield mechanism (SHES) incorporates a small fraction of cesium salts in the electrolyte. These cesium ions remain charged on the surface, migrating toward the dendrites. The migration of Cs-ions to the dendrite surface creates a charged shield that compels lithium ions to deposit outside the dendrites, preventing the dendrite's undesirable growth. To delve deeper into the working of the SHES mechanism, this study specifically utilizes Li and Cs atoms in both solvated and non-solvated configurations. These atoms are employed to be adsorbed onto various sites of the Li slab surface. Density functional theory (DFT) calculations are employed to explore the adsorption energy of Cs ions on Li-metal and their relationship with dendrite formation. In the presence of the solid electrolyte interphase (SEI), Cs ions migrate to damaged areas, depositing over the exposed bare metal surface and grain boundaries. When the SEI breaks, Cs ions cover the exposed Li surface, creating a positively charged shield in the exposed area, thereby reducing the pathway for Li plating and subsequent dendrite growth.