Modulating non-electrochemical (de)intercalation processes in layered vanadium oxides for enhanced calcium-ion storage

Calcium-ion batteries (CIBs) are promising candidates for post-lithium-ion batteries but face challenges including unsuitable cathodes and unclear failure mechanisms. Herein, a reconstructed vanadium oxide (Li@MgVO) is employed to investigate interlayer ion evolution during Ca 2+ -storage. Experiments and theory reveal that the previously overlooked non-electrochemical (de)intercalation processes of interlayer ions critically impact Ca 2+ -storage. Specifically, although Ca 2+ can intercalate into host materials without an applied electrochemical driving force, they do not contribute to the discharge capacity and, more seriously, hinders complete Ca 2+ deintercalation. Encouragingly, pre-intercalated Mg 2+ and Li + in Li@MgVO interlayers can exchange with Ca 2+ during cycling, and this “pre-intercalation-exchange” mechanism effectively minimizes the undesirable Ca 2+ intercalated via non-electrochemical processes. Consequently, the assembled Ca-ion hybrid capacitor exhibits a high capacity of 60 mAh g −1 at 500 mA g −1 with a capacity retention of 97.13% after 300 cycles, significantly higher than that of unmodified vanadium oxide (18 mAh g −1 and 80.45% capacity retention).