We prepare hollow N-doped carbon spheres (HNCSs) with a high specific surface and sufficient internal space. The rich space within the hollow carbon spheres relieves structural stress during long-term battery cycling. The N functional groups enhance Zn adsorption, thus inhibiting the nucleation and growth of Zn at the highly active sites on the electrode surface and achieving uniform deposition.

Abstract

Severe dendrite growth on Zn anodes poses a significant challenge to the development of Zn-based batteries. An effective strategy for inhibiting the formation of Zn dendrites involves electrode modification. In this study, hollow nitrogen-doped carbon spheres (HNCS) are synthesized and used as electrodes to regulate Zn deposition in Zn-based flow batteries. The electrochemical performance of HNCS reveals that the pyrrole nitrogen of HNCS changes the electrode surface state. Therefore, HNCS can inhibit the hydrogen evolution reaction and achieve uniform Zn deposition. HNCS can effectively inhibit dendrite growth and improve the reversibility of the Zn plating/stripping process to regulate the reversibility of Zn-based batteries. The zinc-bromine redox flow battery assembled with HNCS significantly reduces the hydrogen evolution reaction and exhibits a coulombic efficiency of 90 % and energy efficiency of 73 % at a current density of 60 mA cm⁻². Similarly, an alkaline zinc-iron flow battery can maintain high Coulombic efficiency and energy efficiency of 83 %.