K+ pre-intercalated hydrate vanadium pentoxide as cathode for enhanced stability and kinetics in sodium ion batteries

Hydrate vanadium pentoxide (V 2 O 5 · n H 2 O, VOH) is a promising cathode material for rechargeable batteries, due to its high theoretical capacity, adjustable interlayer spacing, and the inherent multivalency of vanadium. However, the simultaneous intercalation and redox reactions during Na + storage poses challenges for structural stability during cycling. This work chemically pre-inserts potassium ions (K + ) to VOH, forming KVOH during hydrothermal synthesis. The pre-intercalated K + partially replaces weakly bound interlayer water, reducing the interlayer spacing and stabilizing the layered framework by mitigating the stress from repeated Na + insertion/extraction. X-ray absorption revealed the partial reduction of V 5+ to V 4+ to compensate the insertion of K + to maintain the electroneutrality. XPS analyses and DFT calculations corroborate the K + insertion. The resulting KVOH demonstrated enhanced rate capability with an energy efficiency of 76 % at 0.05 A g −1 , along with improved kinetics evidenced by lower electrochemical impedance, diminished polarization, and accelerated Na + diffusion. • K + partially replaces interlayer water in VOH, reducing the interlayer spacing. • Reduced spacing boosts electrostatic forces, improving stability and kinetics. • Increased V 4+ in KVOH enhances electron hopping and improving conductivity. • KVOH delivers superior rate capability and enhanced energy efficiency.