Tunable Layered (Na,Mn)V₈O₂₀·nH₂O Cathode Material for High-Performance Aqueous Zinc Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) show promise for use in energy storage. However, the development of ZIBs has been plagued by the limited cathode candidates, which usually show low capacity or poor cycling performance. Here, a reversible Zn//(Na,Mn)V₈O₂₀·nH₂O system is reported, the introduction of manganese (Mn) ions in NaV₈O₂₀ to form (Na,Mn)V₈O₂₀ exhibits an outstanding electrochemical performance with a capacity of 377 mA h g^-1 at a current density of 0.1 A g^-1. Through experimental and theoretical results, it is discovered that the outstanding performance of (Na,Mn)V₈O₂₀·nH₂O is ascribed to the Mn²⁺/Mn³⁺-induced high electrical conductivity and Na⁺-induced fast migration of Zn²⁺. Other cathode materials derived from (Na,Mn)V₈O₂₀·nH₂O by substituting Mn with Fe, Co, Ni, Ca, and K are explored to confirm the unique advantages of transition metal ions. With an increase in Mn content in NaV₈O₂₀, (Na_0.33,Mn_0.65)V₈O₂₀ ·nH₂O can deliver a reversible capacity of 150 mA h g^-1 and a capacity retention of 99% after 1000 cycles, which may open new opportunities for the development of high-performance aqueous ZIBs.