Regulation of Hydrogen Evolution Reaction and Dendrite Growth by Multifunctional Additive for Zn-Ion Batteries
Aqueous zinc-ion batteries (ZIBs) are a low-cost, high-safety alternative to lithium-ion batteries for grid-scale energy storage, but their commercial viability is constrained by zinc dendrite growth and the hydrogen evolution reaction (HER) on the Zn anode, which cause low Coulombic efficiency (CE), short cycle life, and capacity fade. This study introduces polyquaternium-7 (PQ-7), a cationic surfactant, as a multifunctional electrolyte additive. Experimental and theoretical analyses reveal that PQ-7 adsorbs at initial tip sites on the Zn anode, shielding H2O molecules and inhibiting HER. Competitive adsorption with Zn2+ mitigates the tip effect, promoting uniform Zn deposition over dendritic growth. Consequently, symmetric Zn||Zn cells with PQ-7 achieve stable cycling for over 2117 h at 5 mA cm−2 and 1 mAh cm−2, a 15-fold increase over additive-free cells. Zn||Ti cells exhibit a CE exceeding 98% after 240 cycles. Zn||MnO2 full batteries retain 92.1% capacity after 1000 cycles at 1 C and 80% after 1000 cycles at 5 C. These results demonstrate that PQ-7 effectively regulates Zn deposition and suppresses parasitic reactions, offering a straightforward, low-cost strategy for long-life aqueous ZIBs.