Engineering in situ heterometallic layer for robust Zn electrochemistry in extreme Zn(BF₄)₂ electrolyte environment

The performance of zinc metal batteries is critically affected by the electrolyte environment originating from various zinc salt formulations. Zn(BF₄)₂, in particular, offers a notable cost advantage and its fluoride-containing groups facilitate the formation of a beneficial ZnF₂ interfacial layer, thereby making it a promising candidate for application. Nonetheless, the strong acidity of the Zn(BF₄)₂-based electrolyte exacerbates the dendrite formation and promotes parasitic reactions, leading to rapid battery failure. Herein, M(BF₄)_n (M: Cu, Sn, In) salts were adopted as additives in Zn(BF₄)₂ electrolyte to in situ construct the heterometallic layers. Through comparison, the In(BF₄)₃-derived ZnIn interface demonstrates superior corrosion-resistance capability and the strongest zinc affinity, protecting the anode from acidic erosion and accelerating the Zn²⁺ transportation kinetics. The symmetric cell with the optimized electrolyte exhibits a long lifespan of 2500 cycles while the full cell involving the polyaniline cathode also presents a high capacity retention of 81.3 % after 1500 cycles, outperforming the cell with the original Zn(BF₄)₂ electrolyte. The strategy of generating an interface layer within the battery through electrolyte additives can be readily applied to other metal battery technologies.