High Potassium Storage Capability of H2V3O8 in a Non‐Aqueous Electrolyte

Abstract Potassium‐ion batteries (KIBs) are one of the potential candidates for large‐scale energy storage devices with low cost due to the abundance of potassium resources. However, the development of cathode materials with high capacity and structural stability has been a challenge due to the difficulties of intercalation of the large size of K‐ions into host materials. In this work, H 2 V 3 O 8 (or V 3 O 7 ⋅H 2 O) is reported as a new cathode material for KIBs. It shows reversible potassium‐intercalation behavior with the first discharge capacity of 168 mAh g −1 at 5 mA g −1 and an average discharge voltage of ∼2.5 V (vs. K/K + ) in 0.5 M KPF 6 in EC/DEC (1:1 v/v). The specific capacity increases up to 181 mAh g −1 for the third cycle and gradually decreases with 75% of the capacity retention after 100 cycles. The chemical formula of the potassiated phase is K 1.77 H 2 V 3 O 8 . However, scan‐rate dependent cyclic voltammetry and elemental analyses suggest that ∼28% of the capacity comes from the surface K ions on the H 2 V 3 O 8 particles; thus, the bulk‐intercalated phase can be formulated as K 1.27 H 2 V 3 O 8 . The crystal structure is stable during the electrochemical cycling, keeping the structural water, confirming that H 2 V 3 O 8 can be considered as one of the high‐capacity cathode materials for KIBs.