Constructing a gradient soft-coupled SEI film using a dilute ternary electrolyte system towards high-performance zinc-ion batteries with wide temperature stability†

Abstract

The electrolyte concentration plays a pivotal role in determining the efficacy of rechargeable batteries. While prior research has primarily focused on high electrolyte concentrations, the potential of dilute electrolytes remains largely unexplored. This investigation introduces a ternary electrolyte system for zinc-ion batteries, comprising water, acetonitrile (AN), and dimethyl sulfoxide (DMSO), with a remarkably low concentration of 0.3 M Zn(OTf)₂. This innovative electrolyte exhibits a compelling suite of advantages, including environmental benignity, enhanced safety, cost-effectiveness, an expanded electrochemical window, high ionic conductivity, and a broad operating temperature range. The solvated structure of the ultra-low concentration electrolyte is primarily in the form of contact ion pairs (CIPs), which are made up of AN, DMSO, H₂O, and OTf⁻. This interplay results in the formation of a unique rigid-soft coupled electrolyte interface that promotes ordered zinc plating, concurrently reducing viscosity and accelerating the migration rate of zinc ions, thereby significantly enhancing the rate performance of the battery. The symmetric cell, utilizing this electrolyte, demonstrates exceptional durability, characterized by a negligible hysteresis voltage of 32 mV after 3000 hours of cycling at a current density of 1 mA cm⁻² and 1 mA h cm⁻². Furthermore, the cell exhibits an impressive cycle life exceeding 8000 hours. The Zn‖W–VO₂ full cell, utilizing this TSIS-0.3 electrolyte, not only maintains a capacity comparable to that achieved with a 3 M Zn(OTf)₂ electrolyte, but also showcases superior cycle life and capacity retention. Notably, it retains over 92% of its capacity after 540 cycles at a current density of 0.5 A g⁻¹. Concurrently, it can sustain the high-voltage positive ZnHCF cycle for 200 cycles at 0.2 A g⁻¹, exhibiting a capacity retention rate above 100%. Furthermore, TSIS-0.3 facilitates the effective operation of Zn batteries across an extensive temperature range from −30 to 40 °C. Investigating low-concentration electrolytes is crucial as it enhances more selectivity for zinc salts and significantly increases the economic feasibility of zinc-ion batteries due to their low cost.