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.