Deposition and etching of (101)Zn facet exposed zinc electrode induced by trace COS achieving ultra-long cycle stability in zinc batteries

Rechargeable aqueous zinc-based batteries (RZBs) often suffer from poor cycling stability due to the instability of zinc deposition and etching processes. This work achieves dendrite-free zinc deposition with a smaller nucleation radius and rapid completion of the nucleation stage by a “triple regulation strategy” with trace chitosan oligosaccharide (COS) in ZnSO₄ electrolyte (2 g L⁻¹ COS). Theoretical and experimental results indicate that COS, with hydroxyl and amino functional groups, exhibits a high affinity for the (002)_Zn and (100)_Zn facets. Under the influence of a small amount of COS, the selective exposure of the (101)_Zn facet is facilitated. The extensively exposed (101)_Zn facet is protected by COS, which inhibits the occurrence of side reactions. Moreover, the presence of trace COS-02 changes the etching mode from three-dimensional (3D) to two-dimensional (2D), ensuring a uniform distribution of Zn²⁺ in the electric field during the deposition process. The unique 3D deposition and 2D etching mechanism induced by the COS additive result in exceptional cycling stability, exceeding 3800 h (1 mA cm⁻²) and 430 h (5 mA cm⁻²) in zinc symmetrical cells. Additionally, COS acts as a “molecular pillar” to stabilize VS₂, enabling the Zn||VS₂ full cell to achieve 1000 stable cycles with 89.6% capacity retention and an average coulombic efficiency of 99.95%. This work reveals a novel multiple regulation mechanism by using trace COS in RZBs, and provides a new approach for the development of long-term stable RZBs with preferential exposure facets.