Synthesis of K^sub 0.25^V^sub 2^O^sub 5^ hierarchical microspheres as a high-rate and long-cycle cathode for lithium metal batteries

Hierarchical potassium vanadate (K0.25V2O5) microspheres are synthesized via a facile hydrothermal reaction followed by annealing process. The K0.25V2O5 microspheres with an average diameter of ∼1–2 μm, are composed of interconnected nanosheets, exhibiting the hierarchical structures. This novel architecture exhibits excellent lithium storage performance, including a discharge specific capacity of 249 mA h g−1 at the current density of 100 mA g−1, good cyclic stability up to 500 cycles and a satisfactory rate capacity of 161.2 mA h g−1 at 1.5 A g−1. The good performance of K0.25V2O5 microspheres may be ascribed to the hierarchical spherical morphology and its stable structure. Importantly, a quantitative analysis method was first used to calculate the contribution of capacitive charge storage for potassium vanadates. The dominant capacitive charge storage mechanism enables the high rate capability of K0.25V2O5 microspheres. However, the volumetric energy density of this material is tiny (897 Wh/L), which limits the practical application.