Salt particle suspension electrolyte with trace-water for improving ionic concentrations at interfaces in zinc-based dual-ion batteries†

Dual-ion batteries (DIBs) have garnered significant interest due to their cost-effectiveness, high operating voltage, and eco-friendly nature. The electrolyte, serving as the provider of active ions during the charge/discharge cycles, is pivotal to the performance metrics of DIBs, such as capacity, energy density, and lifespan. Despite this, the high-concentration electrolytes that rely heavily on main salts often compromise the cost-effectiveness of DIBs. Therefore, a salt particle suspension electrolyte (SPSE) system has been successfully developed based on a linear carbonate solvent with a trace amount of water and applied in graphite‖zinc and graphite‖graphite DIBs. This innovative SPSE offers a high surface anion concentration that reduces concentration polarization, improves anion utilization efficiency at the electrode surface, and ensures a sufficient anion supply even at relatively low electrolyte concentrations. The prototype DIB, based on a zinc metal-free anode concept utilizing a graphite anode, an expanded graphite cathode, and a SPSE with a zinc trifluoromethylsulfonate [Zn(OTf)₂] salt has demonstrated a remarkable discharge capacity of 178.66 mA h g⁻¹ at a current rate of 10 mA g⁻¹, and an impressive 84.7% capacity retention after 240 cycles at 100 mA g⁻¹. The energy density of the battery with respect to the cathode mass soared to 304.8 W h kg⁻¹. Our results provide novel insight into the rational design and construction of superior suspension electrolytes for DIBs, demonstrating a groundbreaking electrolyte formulation strategy that can improve battery performance as well as lower production costs.