Ultra‐High Capacity and Cyclability of β‐phase Ca_0.14V₂O₅as a Promising Cathode in Calcium‐Ion Batteries

Abstract

Crystalline water-free β-phase Ca 0.14 V 2 O 5 is reported for the first time as a viable cathode material for calcium-ion batteries (CIBs). In contrast to layered α-V 2 O 5 and δ-Ca x V 2 O 5 •nH 2 O, which have limited capacity, the β-phase delivers a reversible capacity of ≈247 mAh g −1 , which corresponds to the insertion/extraction of Ca 2+ between Ca 0.14 V 2 O 5 and Ca 1.0 V 2 O 5 . The process of Ca 2+ insertion process and the accompanying structural relaxation are theoretically and experimentally verified. The initial insertion of Ca 2+ into Ca 0.14 V 2 O 5 causes a slight shift of oxygen atoms surrounding hepta-coordination sites, creating penta-coordinated sites that are then partially filled up to Ca 0.33 V 2 O 5 . Further insertion occurs through the stepwise occupation of up to 50% of neighboring hexa-and tetra-coordination sites to form Ca 0.67 V 2 O 5 and Ca 1.0 V 2 O 5 , respectively. The rearrangement of oxygen atoms in Ca 0.14 V 2 O 5 also minimizes dimensional changes, leading to high cyclic stability during repeated charge/discharge cycles. The remarkable electrochemical performance of full cells containing a Ca 0.14 V 2 O 5 cathode and a K metal anode in Ca 2+ /K + hybrid electrolytes, is also demonstrated, thanks to the inertness of K + insertion into Ca 0.14 V 2 O 5 and the absence of calcium plating/stripping. The cyclic stability and high capacity of Ca 0.14 V 2 O 5 is not compromised in hybrid electrolytes, making it a viable CIB cathode.

Sodium ion pre-intercalation regulates the electron density and structural stability of vanadium oxide nanowires for Ca–ion batteries

“…6,7 In a single redox reaction, multivalent ions demonstrate the capacity to furnish a larger quantity of electrons compared to monovalent ions such as Li + , Na + , and K + , which results in a superior volumetric energy density. 8,9 Recently, zinc-ion batteries (ZIBs), [10][11][12] magnesium-ion batteries (MIBs), [13][14][15] calcium-ion batteries (CIBs), [16][17][18][19] and aluminum-ion batteries (AIBs) [20][21][22] have garnered extensive attention from scientists and achieved significant advancements. Among these various candidates, CIBs are the most favored by researchers as the standard reduction potential of calcium (−2.87 V vs. the standard hydrogen electrode (SHE)) is in proximity to the reduction potential of lithium (−3.04 V vs. SHE), which is in contrast to zinc (−0.76 V vs. SHE), aluminum (−1.66 V vs. SHE), and magnesium (−2.37 V vs. SHE).…”

Fluoride frameworks as potential calcium battery cathodes

“…Previous studies have employed both experimental and computational techniques that have explored select chemistries as possible CB cathodes. The set of inorganic cathodes that have been reported with Ca so far include CaMo 6 X 8 (X = S, Se, or Te), 21 VOPO 4 ·2H 2 O, 22 Ca x V 2 O 5 , 23–27 CaV 2 O 4 , 28,29 CaMn 2 O 4 , 30 MoO 3 , 31–33 NH 4 V 4 O 10 , 34 CaCo 2 O 4 , 35,36 NaFePO 4 F, 37 TiS 2 , 38 CaV 6 O 16 ·2.8H 2 O, 39 Prussian-blue analogues (PBAs), 40–44 and other polyanionic frameworks. 45–48 However, only a select few of these compounds show reasonable electrochemical performance, with most suffering from inadequate cycling stability, poor Ca-ion diffusion, and large volume changes during charge/discharge.…”

“…Recently, Chando et al 30 explored the post-spinel phase of CaMn 2 O 4 as a CB-cathode candidate using both experiments and density functional theory (DFT 50,51 ) calculations and reported a low cycling capacity of 52 mA h g −1 at a rate of C/33. Prabakar et al 26 used a water-free β-phase Ca 0.14 V 2 O 5 as a Ca-cathode and reported a reversible capacity of ∼247 mA h g −1 . The authors stated that unlike conventional layered β-V 2 O 5 and δ-Ca x V 2 O 5 · n H 2 O cathodes, the β-phase facilitates efficient insertion/extraction of Ca ions, contributing to improved cycling stability and minimal dimensional changes during charge/discharge cycles.…”

“…The authors stated that unlike conventional layered β-V 2 O 5 and δ-Ca x V 2 O 5 · n H 2 O cathodes, the β-phase facilitates efficient insertion/extraction of Ca ions, contributing to improved cycling stability and minimal dimensional changes during charge/discharge cycles. 26…”