An artificial protection layer for Zn electrode enabling uniform Zn deposition and stable cycling of Zn-MnO2 full cells under limited anode condition

Abstract

Aqueous rechargeable zinc batteries are promising candidates for grid-level energy storage systems. However, critical challenges of dendrite growth and side reactions occur on Zn metal anode, which leads to unsatisfactory electrochemical performance. Herein, we fabricate an artificial protection layer of carrageenan on Zn electrode. The sulfonic acid groups on carrageenan act as active sites for interacting with Zn2+, which facilitates Zn2+ transport and enhances Zn2+ desolvation. Carrageenan also blocks the diffusion of sulfate anions from the electrolyte. It ensures enlarged Zn2+ transference number and reduced cation concentration gradient, so that uniform Zn deposition under the protection layer is realized. Meanwhile, the carrageenan layer also inhibits side reactions with the electrolyte. As a result, the protected Zn electrode presents stable cycle life of over 1500 h (750 cycles) in symmetric cells and realizes 99.4 % stripping/plating coulombic efficiency. More importantly, the full cell assembled with protected Zn anode and MnO2 cathode at N/P = 1 condition (based on theoretical capacities of anode and cathode) delivers 80.9 % capacity retention after 100 cycles, superior to 26.0 % with bare Zn. Our work presents an effective protection path for Zn metal anode toward practical aqueous zinc batteries.