Additives Capable of Stably Supplying Anions/Cations for Homogeneous Lithium Deposition/Stripping

Abstract

One of the important factors leading to lithium dendrites is a slow lithium-ion mass transport and imbalanced distribution of the Li⁺ concentration and nuclei sites on the anode surface. To achieve uniform lithium deposition during the charge and discharge process, we introduce a homemade new copolymer (with the quaternary ammonium group N₃R⁺I^- on its side chain as the main functional group), named P35, as a functional electrolyte additive to regulate the lithium deposition. Theoretical calculations show that under the strong coordinating interaction between I^- and N₃R⁺, P35 preferentially adsorbs onto the lithium foil surface, effectively countering the adsorption of lithium salt anions such as PF₆^-. Moreover, the positive charge carried by the quaternary ammonium salt group of P35 could interact with PF₆^- to limit their mobility. Consequently, the dipole interaction on lithium ions is diminished, leading to an enhancement in the transport rate and a decrease in the concentration gradient of lithium ions. Furthermore, a more efficient SEI was formed due to the dual charges electrostatic shield formed by N₃R⁺I^-. Li-Li symmetric cells and Li-LiFePO₄ full cells assembled with electrolytes with P35 exhibit better rate performance, smaller polarization, and smoother deposition morphology in comparison to the cells without the P35 additive.