o-Phenylenediamine-modulated vanadium pentoxide cathode for enhanced capacity in calcium-ion batteries

Calcium-ion batteries (CIBs) emerge as promising electrochemical energy storage technology due to the natural abundance of calcium and its low redox potential (−2.87 V vs. SHE). However, developing high-performance CIBs cathodes remains hindered by large ionic radius and strong electrostatic interactions with host. Herein, an organic intercalation strategy is proposed to enhance the calcium storage capability of vanadium pentoxide. This study demonstrates that different molecular configurations critically influence the structure of the host material and determine intercalation success. Insertion of ortho-phenylenediamine (oPD) extends the layer spacing; meanwhile, oPD provides reversible C=N/C–N redox sites coordinating Ca 2+ ions, delivering extra capacity. The optimized VO-oPD (V 2 O 5 ·0.3oPD·0.48H 2 O) exhibits higher specific capacity and accelerated Ca 2+ diffusion, delivering a high capacity of 174.77 mA h g −1 at 0.1 A g −1 with exceptional rate capability. Remarkably, it retains 75 mA h g −1 after 10,000 long cycles at 0.5 A g −1 and with about 99 % capacity retention. This opens up a promising avenue for organic-inorganic cathode materials. • oPD can successfully be embedded between V 2 O 5 layers, while mPD and pPD induce destructive VO 2 transformation. • oPD provides reversible C=N/C–N redox sites coordinating Ca 2+ ions, delivering extra capacity compared to mPD and pPD. • VO-oPD retains 75 mA h g −1 after 10,000 long cycles at 0.5 A g −1 and with about 99 % capacity retention.