Enhanced Zn2+ Transport in Ionic Liquid Electrolyte by Hydrofluoroether Dilution for High‐Power and Long‐Life Zn/Graphite Cells

Higher Zn²⁺ mobility: A hydrofluoroether diluent is introduced into Zn-based ionic liquid electrolyte to break down the larger ionic aggregates into smaller ones with enhanced Zn²⁺ mobility, which improves the rate capability and cycling performance of Zn/graphite dual ion batteries.

Abstract

Ionic liquid (IL) electrolytes have been widely used in high-voltage Li-based dual ion batteries (DIBs) due to their strong resistance against oxidation. However, their applications in Zn-based DIBs are restricted because the high charge density of divalent Zn²⁺ aggravates the ionic interactions in ionic networks and leads to insufficient Zn²⁺ mobility. Herein, we introduce a hydrofluoroether diluent into a Zn-based IL electrolyte to break down the larger ionic aggregates into smaller ones with weakened ionic interactions. This unique solvation structure reduces the Stokes radius of Zn²⁺ from 1.3 nm to 0.97 nm and increases its diffusion coefficient by ∼30 times while retaining the high oxidation stability, enabling the charge/discharge cycling of Zn/graphite DIBs at a high rate of 20 C. Moreover, the enhanced mobility of Zn²⁺ also promotes compact Zn deposition, which allows the operation of anode-free Zn/graphite DIBs with 90 % capacity retention after 100 cycles.

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