Water activity and electrocrystallization modulated by a high-Lewis-basicity co-solvent for reversible Zn anodes

Abstract

Aqueous rechargeable zinc metal batteries exhibit significant potential for large-scale energy storage due to their environmental friendliness, high safety and low cost. However, the severe hydrogen evolution reaction, uncontrollable dendrite growth and low coulombic efficiency of the Zn metal anode hinders their further application. Herein, high-basicity N-methylacetamide (NMA), which can anchor water molecules via strong hydrogen bonds, is introduced as a co-solvent into a 1 M ZnSO₄ electrolyte, thus reducing the decomposition activity of water molecules. Additionally, the NMA molecules and SO₄²⁻ interact with the Zn²⁺ solvation sheath to release water molecules around Zn²⁺ and further reduce the HER. Moreover, the NMA-based electrolyte promotes Zn (002) deposition, improving the intrinsic corrosion resistance and uniform deposition of the zinc anode. At 1 mA cm⁻², the Zn//Cu battery achieves a high average coulombic efficiency of 99.85% for 1200 cycles. The Zn//Zn symmetric battery delivers a long lifespan of more than 900 h even at high areal capacity (6 mA h cm⁻²) and high depth of discharge (DOD ≈ 50%) conditions. The Zn//NaV₃O₈ full battery undergoes 300 cycles with a capacity retention of 82.7% at 0.1 A g⁻¹ under a low negative/positive capacity (N/P) ratio of 3.24 and high discharge depth of the zinc metal anode (DOD ≈ 30.8%).