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

Layered VSe2 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 V3+/V4+ redox pair, VSe2 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 V4+ to V5+. In this light, a simple in-situ electrochemical oxidation strategy was used to raise the valence state of V atoms in VSe2 to boost its Zn-storage performance. Experimental results and material characterization indicate that the initial VSe2 cathode undergoes an in-situ electrochemical oxidation-induced irreversible phase transformation process from VSe2 to amorphous V2O5 at a high potential (1.35–1.8 V vs. Zn/Zn2+) during the first charge. In the subsequent cycles, the resulting amorphous V2O5 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 VSe2 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 VSe2 cathode, but also provides a new insight into the design of high-performance cathode materials for large voltage ranges.