Insights into the Energy Storage Differences of Zinc and Calcium Ions with Layered Vanadium Oxide as a Model Material

Abstract Multivalent ion batteries (e.g., Zn 2+ , Ca 2+ ) are gaining great attention owing to their potentially high capacity, cheap cost, and good safety. However, significant disparities exist in achieved capacity, voltage, and kinetic performance within zinc and calcium ion electrolytes. Herein, the electrochemical and kinetic properties of Zn 2+ and Ca 2+ in aqueous electrolytes are investigated using a single‐crystal V 2 O 5 (V 2 O 5 ·Pyridine, PVO) model material with stable large interlayer spacing. It is found that the discharge‐specific capacity in 1 m Zn(ClO 4 ) 2 aqueous solution is 247.3 mAh g −1 at 0.3 A g −1 , which is remarkably higher than 158.4 mAh g −1 in 1 m Ca(ClO 4 ) 2 . Mechanistic studies show that in aqueous ZIB, H + is intercalated first, followed by the generation of Zn 4 (OH) 7 ClO 4 , and finally H + and Zn 2+ are co‐intercalated. But in aqueous CIB, H + dominates the intercalation process. It is found that six times more Zn 2+ than Ca 2+ is intercalated into PVO, owing to its smaller radii and its relative higher intercalation potential (Zn 2+ @‐0.34 V, Ca 2+ @‐0.65 V vs .. Ag/AgCl), giving it a higher specific capacity. Furthermore, density functional theory calculations demonstrate lower intercalation energies for Ca 2+ (−6.67 eV) compared to Zn 2+ (−1.85 eV), explaining the lower intercalation potential of Ca 2+ .