Ultra-low cost and high Coulombic efficiency aqueous zinc-ion battery

Deposition/dissolution-type cathodes can enable aqueous batteries to achieve high volumetric energy density, making them promising for large-scale energy storage systems (ESSs). However, developing low-cost materials with high deposition/dissolution efficiency remains challenging. Iron (Fe), the fourth most abundant element in the Earth’s crust, offers a cost-effective solution. Designing a battery system based on deposition/dissolution-type Fe cathode could significantly reduce EES costs. Inspired by this, a battery system with 1 M ZnSO₄ + 1 M FeSO₄ + 0.01 M H₂SO₄ (ZFH) electrolyte, graphite felt (GF) collector, and zinc anode is designed. As a result, the constructed half-cell exhibits a high cathode deposition/dissolution efficiency of about 100% and a flat discharge platform of 0.34 V vs. Ag/AgCl. Coupled with the zinc (Zn) anode, the Zn//GF full-cell stable cycling for over 2300 times with nearly 100% efficiency in the ZFH electrolyte. The discharging voltage reaches approximately 1.0 V at 5 mA·cm⁻². The electrochemical quartz crystal microbalance (EQCM) measurement combined with other technologies reveals the transformation mechanism between the Fe²⁺ and FeOOH·0.5H₂O on the GF cathode during electrochemical cycling. This strategy further reduces cost by adopting cheap elements, giving new insights into the cost-effective large-scale electrochemical energy storage systems.