Dendrite-less aluminum anodes enabled with in-situ gallium alloying for molten salt aluminum batteries

Molten salt aluminum batteries (MSABs) are promising for next-generation grid-scale energy storage owing to the high capacity and cost-effectiveness. However, the dendrite formation induces safety risks and rapid performance degradation, particularly under high-rate and high-loading conditions. Here, we present a simple and efficient strategy to in-situ construct an aluminum-gallium (Al-Ga) alloy anode by introducing GaCl₃ to the chloroaluminate melt electrolyte. The GaCl₃ spontaneously reacts with Al at the electrolyte/anode interface through a displacement reaction, yielding metallic Ga that subsequently interdiffuses with Al to form a homogeneous Al-Ga alloy anode, owed to its liquid nature at the temperature of operation. The Al-Ga alloy anode reduces nucleation barriers, homogenizes the interfacial electric field and enhances interfacial charge transport, thereby enabling uniform aluminum deposition and stable dendrite-less cycling. As a result, the in-situ gallium alloying strategy enables symmetric cells to cycle stably for over 1,100 h at 5.0 mA cm^-2. The aluminum-sulfur cell using Al-Ga alloy anode maintains 5000 cycles with a capacity decay of only 0.0012% per cycle at 5.83 mA cm^-2. Our work highlights the advantage of in-situ alloying strategy with rationally designed alloying elements for a simple, low-cost and scalable approach for practical deployment.