Enhanced Utilization Rate and Dendrite Suppression of Zn Powder Anode for High-Performance Zinc-Ion Battery

Lithium-ion batteries (LIBs) have become the popular rechargeable energy supply in many fields from portable electronic devices to electric vehicles in recent years. However, the escalating price of lithium resources and the recurrent occurrence of safety issues serve to impede the demand for and application of batteries. Rechargeable aqueous zinc-ion batteries have received significant research interest due to their low cost, high safety, non-flammability, and environmental friendliness. However, Zn-based batteries using Zn metal as the anode suffer from a significant issue of side reactions like dendrite and low utilization rate, causing a decrease in energy density and N/P ratio. Among various strategies to overcome the drawbacks of zinc metal, the zinc powder-based anode has attracted attention for its potential industrial application, especially for flexible energy-storage devices. However, the large surface area of zinc powder in an aqueous electrolyte accelerates side reactions such as hydrogen evolution and passivation, increasing the internal pressure and triggering seal failure, eventually resulting in cell failure. Continuous repeating of the Zn dissolution/deposition process results in a loose connection between Zn powders and conductive materials, leading to dead Zn formation during cycling. In addition, the high hydrophobicity of zinc powder and conductive material hinders the infiltration of the aqueous electrolyte into the interior of the anode, thereby restricting its utilization rate.<br/>In this study, we designed a Zn anode using spontaneously reduced graphene oxide (rGO)-coated zinc powders and a polyacrylic acid (PAA) hydrophilic binder. The high tensile strength of rGO and its scaffold structure effectively suppress dendrite growth in zinc and reduce the hydrophobicity of zinc powder. Additionally, the high hydrophilicity of PAA can improve the wettability between the zinc powder-based anode and the electrolyte. Hydrogen bonding between the -COOH groups of PAA and residual functional groups of rGO mitigates the risk of PAA dissolution in the aqueous electrolyte, preventing the loss of its function as a binder. This ensures that the binder remains stable and maintains electrode integrity within the electrolyte.<br/>Various analyses confirmed that the coated rGO coating layer effectively suppressed side reactions and dendrite growth on the zinc powder-based electrode. Additionally, the PAA binder increased the electrolyte permeability due to enhanced aqueous electrolyte wettability of the electrode. The combination of these two materials resulted in enhanced surface stability of the active material and hydrophilicity of the anode, leading to a significant increase in the cycle stability and utilization rate of the powder-based zinc-ion battery.