Multi-Level Regulation of Electrostatic Microenvironment With Anion Vacancies for Low-Lithium-Gradient Polymer Electrolyte

Abstract

Solid-state lithium-metal batteries based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVH) are frequently proposed to address the detrimental safety issue of conventional lithium-ion batteries by eliminating the use of flammable solvents, but still face a key challenge: low capacity and sluggish charge/discharge rate due to the intrinsic large-gradient Li⁺ distribution across the ionically-inert PVH matrix. Herein, Te vacancies in form of Bi₂Te_3−x are proposed to polarize the PVH unit to realize efficient decoupling of lithium salts at the atomic level in PVH-based solid polymeric electrolyte. Te vacancies in the PVH electrolyte doped with Bi₂Te_3−x (PVBT) induce a high-throughput and homogenous Li⁺ flow within the PVH matrices and near the Li metal. Theoretical calculations show that Te vacancies own high adsorption energy with bis(trifluoromethanesulfonyl)imide anions (TFSI⁻), repulsive effect on Li⁺, and localized electron distribution, giving rise to a lithium-ion concentration gradient of 30 mol m⁻³, the smallest among the PVH-based inorganic/organic composite electrolytes. Consequently, the polarized electrolyte owns an unprecedented high-rate battery capacity of 114 mAh g⁻¹ at ∼700 mA g⁻¹ and also superior capacity performances with a cathode loading of 12 mg cm⁻², outperforming the state-of-art PVH-based inorganic/organic composite electrolytes in Li||LiFePO₄ battery. The work demonstrates an efficient strategy for achieving fast Li⁺ diffusion dynamics across polymeric matrices of classic solid-state electrolytes.