Reversible and rapid calcium intercalation into molybdenum vanadium oxides

Abstract

Looming concerns regarding scarcity, high prices, and safety threaten the long-term use of lithium in energy storage devices. Calcium has been explored in batteries because of its abundance and low cost, but the larger size and higher charge density of calcium ions relative to lithium impairs diffusion kinetics and cyclic stability. In this work, an aqueous calcium–ion battery is demonstrated using orthorhombic, trigonal, and tetragonal polymorphs of molybdenum vanadium oxide (MoVO) as a host for calcium ions. Orthorhombic and trigonal MoVOs outperform the tetragonal structure because large hexagonal and heptagonal tunnels are ubiquitous in such crystals, providing facile pathways for calcium–ion diffusion. For trigonal MoVO, a specific capacity of ∼203 mAh g −1 was obtained at 0.2C and at a 100 times faster rate of 20C, an ∼60 mAh g −1 capacity was achieved. The open-tunnel trigonal and orthorhombic polymorphs also promoted cyclic stability and reversibility. A review of the literature indicates that MoVO provides one of the best performances reported to date for the storage of calcium ions.

Intercalation Hosts for Multivalent‐Ion Batteries

“…Reproduced with under the terms of CC‐BY license. [ 23 ] Copyright 2022 the Author(s). Published by PNAS.…”

“…[19][20][21] Recent work has shown that open-tunnels are also ubiquitous in certain complex oxide materials [22] such as molybdenum vanadium oxides (Mo 3 VO x ) that exhibit pentagonal-, hexagonal-, and heptagonal-shaped tunnels. [22][23][24] Such open tunnels with large pores enable facile diffusion of multivalent ions. Especially, in an aqueous battery, ions along with its solvation sheath can get inserted.…”

“…In addition to large pores, structural subunits within the unit cell need to be edge-or corner-shared (Figure 2e) to prevent undesirable phase changes and maintain mechanical stability. So far, only a small set of open-tunnel oxides with large pore tunnels and edge/corner sharing have been discovered, [22][23][24][25][26][27][28] and synthesis processes to produce such materials are not well developed.…”

“…This data has been derived from the information listed in Table 1 (taken from Refs. 15,[17][18][19][20][21][22][23]. The regions for different materials in Figure 3 When considering power density, organic materials displayed the best overall performance.…”

Highly Reversible Intercalation of Calcium Ions in Layered Vanadium Compounds Enabled by Acetonitrile–Water Hybrid Electrolyte

“…Compared with other types of batteries, the development of CIBs is still in its primary stage due to a variety of challenges. − First and most importantly, the search for cathode candidates that can store Ca 2+ ions in large capacity is a challenging task. , To date, only a limited choice of cathode materials have been identified to show feasible intercalation of Ca 2+ ions, including the open framework structure (i.e., Prussian blue, metal–organic compounds (MOCs), hexacyanoferrate , ), layered compounds (i.e., TiS 2 , α-MoO 3 , , α-V 2 O 5 , trigonal MoVO, Mg 0.25 V 2 O 5 ·H 2 O, Ca 0.28 V 2 O 5 ·H 2 O, CaV 6 O 16 ·2.8H 2 O), transitional metal oxides (i.e., CaMn 2 O 4 , CaCo 2 O 4 , Ca 0.4 MnO 2 ), polyanions (i.e., Na 1.5 VPO 4.8 F 0.7 ), and organic cathode material (PTCDA). The authors explored the calcium storage mechanism of these materials.…”