First‐Order Phase Transformation in Highly Concentrated Electrolyte for High‐Rate and Long‐Cycle Aqueous Zn‐Ion Battery

Abstract Concentrated electrolyte offers a promising approach to enhance aqueous batteries, yet its influence on electrode phase transformations and mechanical properties remains largely unknown. This work shows that salt‐concentrated electrolyte induces a first‐order phase transformation, rather than the conventional conversion reaction of VS 4 cathode typically observed in dilute electrolyte. This transformation results in a semi‐coherent phase boundary, reducing strain and improving energy efficiency. As a result, capacity doubles and cycle life increase sixty‐fold compared to regular dilute electrolyte. The first‐order phase transformation is attributed to reduced de‐solvation energy and charge transfer energy barrier due to different Zn 2+ solvation structure in the concentrated electrolyte. Our findings offer groundbreaking insights into the microstructure evolution of electrode in concentrated electrolyte and pave the way to further develop batteries with excellent performance.