Stable Zn metal deposition/stripping in Zn-Li dual-ion batteries achieved by acetonitrile-water co-solvent enhanced acetamide-based deep eutectic electrolytes

Abstract

Zinc batteries have emerged as potential candidates for next-generation energy storage due to their high safety, environmental friendliness, and abundant raw material. However, zinc dendrite formation and water-related parasitic reaction occurred during zinc metal deposition/stripping, resulting in limited batteries cycle life. To address these challenges, this study developed an acetamide-based deep eutectic electrolytes (DEEs) with acetonitrile and water as co-solvents to improve the cyclability of Zn metal deposition/stripping. The co-solvents optimized DEEs is being examined first with Zn//Cu asymmetric cell, delivering high Zn deposition/stripping average coulombic efficiency (CE) of 99.79 % for over 2800 cycles. The addition of co-solvents effectively increases the exchange current density and decrease charge transfer resistance for Zn deposition/stripping. The dual ion batteries using LiMn₂O₄ (LMO) as cathode and Zn metal anode were assembled and subject to electrochemical evaluation. The battery delivers an initial capacity of 53 mAh g⁻¹ and > 30 mAh g⁻¹ after 1200 cycles, stably operating for over 2400 cycles with average CE > 99 % and 24.7 mAh g⁻¹ capacity. An organic/inorganic hybrid interfacial layer composed of Zn-N and amide-related structures is found on the surface of cycled LMO cathode. The layer could effectively suppress parasitic oxidative reactions between the solvent and active materials, leading to high CE and maintaining high Mn³⁺ /Mn⁴⁺ ratio. This study demonstrates that co-solvents design in DEEs offers a promising strategy for high-performance Zn-based hybrid batteries.