An anode-free aqueous hybrid batteries enabled by in-situ Cu/Sn/Zn alloy formation on pure Cu substrate

Zn-based rechargeable aqueous battery attracts attention due to its simplicity and benignity. Here, we propose an anode-free aqueous hybrid system with 4 M ZnSO4 and 2 M Li2SO4 in 10% DME. Since the electrolyte is the only source of Zn, the capacity ratio between Zn salts and the cathode is also evaluated to achieve a suitable formulation of the electrolyte composition. To improve the Zn nucleation and densify the deposition, we include an additive SnBr2 to initiate the in-situ formation of Cu/Sn/Zn alloy on the surface of the Cu current collector. The effects of the SnBr2 additive on the Zn deposition, stripping, and the Cu/Sn/Zn alloy formation was investigated and characterized. SEM, cross-sectional analysis by Focused ion beam (FIB), and in-situ transmission X-ray microscope (TXM) all confirm the more uniform and dense deposition of Zn on Cu under the assistance of SnBr2. The anode-free hybrid aqueous Cu||LFP full cell achieves 99.1% average coulombic efficiency with relatively good capacity retention (35.2%) after 100 cycles by adding SnBr2 in the hybrid electrolyte with an optimized electrolyte/cathode capacity ratio of 9.45. The proposed anode-free approach is hoped to help the sustainable development of an aqueous battery system with high energy density and environmental benignity.