KV3O8 with a large interlayer as a viable cathode material for zinc-ion batteries

We demonstrate the feasibility of using KV3O8 with an interlayer distance of ~7.7 Å as a cathode material for zinc-ion batteries. Its electrochemical inactivity is circumvented through particle size reduction with an increase in the surface area to 33.2 m2 g−1 from 2.6 m2 g−1. The shortened diffusion path results in significant improvement of the capacity to 249 mAh (g-oxide)−1 (25 mA g−1: 0.1C) despite almost no capacity being delivered by the as-received KV3O8 particles. Structural investigation using ex situ X-ray diffraction and ex situ X-ray absorption near edge structure spectroscopy reveals that KV3O8 undergoes a single-phase reaction assisted by the V5+/4+ redox pair. This monotonous structural change results in capacity retention of approximately 85.1% for 200 cycles. The size effect also affects the rate capability. Namely, the electrode delivers a discharge capacity of 182 mAh g−1 at a rate of 7C (1.75 A g−1), with ~82.8% retention of the initial capacity for 500 cycles in a continuous cycling test at 5C (1.25 A g−1). This work presents a facile approach that enables the use of materials with large interlayer distance as cathode materials for zinc-ion batteries.