Reversible Mn ²⁺ Ion Storage in a Layered VSe ₂ Cathode: Insights into Storage Kinetics and Structural Reversibility in Aqueous Manganese-Ion Batteries

Aqueous manganese-ion batteries (MIBs) have emerged as a potential candidate for large-scale energy storage systems due to the intrinsic advantages of the multivalent Mn 2+ charge carrier, which include high safety, environmental benignity, and low cost. However, the development of stable and high-performance cathode materials capable of reversibly hosting Mn 2+ ions remains a critical challenge. Layered vanadium-based chalcogenides offer a promising solution due to their expanded interlayer spacing that accommodates large, solvated Mn 2+ ionic clusters and the multivalent redox activity of vanadium that promotes the charge compensation. In this work, we investigated VSe 2, a graphene-like 2D layered structure, as a potential cathode for aqueous MIBs. The VSe 2 cathode could reversibly store Mn ions by intercalation, delivering a capacity of 210 mAh g –1 at 0.5 A g –1 and retaining 61 mAh g –1 at 10 A g –1 along with good stability over 1500 cycles. The Mn-ion storage kinetics and structural stability in the VSe 2 cathode are also studied using ex situ characterization tools. It is revealed that Mn 2+ induces reversible lattice expansion accompanied by transient stacking disorder without causing an irreversible phase transformation and structural collapse. This work highlights the viability of rationally designed transition metal dichalcogenide composites as next-generation cathodes for safe, cost-effective, and sustainable aqueous MIB systems.