Effects of cesium cations in lithium deposition via self-healing electrostatic shield mechanism

Lithium (Li) dendrite formation is one of the critical challenges for rechargeable Li metal batteries. The traditional method of suppressing Li dendrites, by using high-quality solid electrolyte interphase films, cannot effectively solve this problem. Recently, we proposed a novel self-healing electrostatic shield (SHES) mechanism to achieve dendrite-free Li deposition by adding so-called non-Li⁺ SHES additives in electrolytes, which adsorb but do not deposit on the active sites of Li electrodes and thus force Li to be deposited in the region away from protuberant tips. In this paper, the electrochemical behavior of the cesium cation (Cs⁺) as the typical non-Li cation suitable for the SHES mechanism is further investigated in detail to reveal its effects on preventing the growth of Li dendrites. Typical adsorption behavior rather than chemical reaction is observed. The existence of Cs⁺ cations in the electrolyte does not change the components or structure of the Li surface film, which is consistent with what the SHES mechanism predicts. Various factors affecting the effectiveness of the SHES mechanism are also discussed. The morphologies of the deposited Li films are smooth and uniform during the repeated deposition-stripping cycles and at various current densities (from 0.1 to 1.0 mA cm^-2) by adding just a small amount (0.05 M) of Cs⁺ additive in the electrolyte.