Boosting the Zn-storage performance of layered VSe2 cathodes via an in situ electrochemical oxidation strategy

Layered VSe ₂ with high electronic conductivity, low ion migration barriers and large interlayer spacing is a potential cathode material for Zn-ion batteries (ZIBs). However, relying only on the V ³⁺/V ⁴⁺ redox pair, VSe ₂ exhibits unsatisfactory Zn-storage performance. Considering the multiple electron transfer of V atoms, it is expected that the specific capacity will be enhanced by raising V ⁴⁺ to V ⁵⁺ . In this light, a simple in-situ electrochemical oxidation strategy was used to raise the valence state of V atoms in VSe ₂ to boost its Zn-storage performance. Experimental results and material characterization indicate that the initial VSe ₂ cathode undergoes an in-situ electrochemical oxidation-induced irreversible phase transformation process from VSe ₂ to amorphous V ₂O ₅ at a high potential (1.35–1.8 V vs. Zn/Zn ²⁺) during the first charge. In the subsequent cycles, the resulting amorphous V ₂O ₅ cathode with high valence state and abundant active sites become the new host for Zn-storage, it can deliver a high specific capacity of 302.5 mAh g ⁻¹ at 0.1 A g ⁻¹ (3 times higher than that of the initial VSe ₂ cathode), a satisfactory rate performance of 116.1 mAh g ⁻¹ at 2 A g ⁻¹, and a long cycle life of 4000 cycles at 2 A g ⁻¹ . This work not only investigates the electrochemical oxidation mechanism of the VSe ₂ cathode, but also provides a new insight into the design of high-performance cathode materials for large voltage ranges.