Calcium-Pillar Boosting Smooth Phase Transition in Potassium Vanadate Nanobelts toward Superior Cycling Performance in Potassium-Ion Batteries.

The depletion of lithium resources has prompted exploration into alternative rechargeable energy storage systems, and potassium-ion batteries (PIBs) have emerged as promising candidates. As an active cathode material for PIBs, potassium vanadate (K x V 2 O 5 ) usually suffers from structural damage during electrochemical K-ion insertion/extraction and hence leading to unsatisfactory cycling performance. Here, we introduce Ca 2+ ions as pillars into the potassium vanadate to enhance its structural stability and smooth its phase transition behavior. The additional Ca 2+ not only stabilizes the layered structure but also promotes the rearrangement of interlayer ions and leads to a smooth solid-solution phase transition. The optimal composition K 0.36 Ca 0.05 V 2 O 5 (KCVO) exhibits outstanding cyclic stability, delivering a capacity of ∼90 mA h g -1 at 20 mA g -1 with negligible capacity decay even after 700 cycles at 500 mA g -1 . Theoretical calculations indicate lower energy barriers for K + diffusion, promoting rapid reaction kinetics. The excellent performances and detailed investigations offer insights into the structural regulation of layered vanadium cathodes.