Cation-driven phase transition and anion-enhanced kinetics for high energy efficiency zinc-interhalide complex batteries

Aqueous Zn-halogen batteries, valued for high safety, large capacity, and low cost, suffer from the polyhalide shuttle effect and chaotic zinc electrodeposition, reducing energy efficiency and lifespan. Here we show a cation-driven positive electrode phase transition to suppress the shuttle effect and achieve uniform zinc electrodeposition, along with an anion kinetic enhancement strategy to improve energy efficiency and lifespan. Taking tetramethylammonium halide (TMAX, X = F, Cl, Br) as a subject, TMA⁺ promotes oriented zinc (101) deposition on the negative electrode through electrostatic shielding, significantly extending cycling life. Concurrently, it captures I₃^- on the positive electrode, forming a stable solid-phase interhalide complex that enhances coulombic efficiency. Compared to I₃^- and TMAI₃, X^- anions lower the Gibbs free energy differences of I^- → I₂X^- and I₂X^- → TMAI₂X, accelerating I^-/I₂X^-/TMAI₂X conversions and improving voltage efficiency. In TMAF-modified electrolytes, zinc interhalide complex batteries achieve a high energy efficiency of 95.2% at 0.2 A g^-1 with good reversibility, showing only 0.1% capacity decay per cycle over 1000 cycles. At 1 A g^-1, they show a low decay rate of 0.1‰ per cycle across 10,000 cycles. This study provides insights into enhancing energy efficiency and long-term stability for sustainable energy storage.