K₃v₂(Po₄)₃/C as a New High‐Voltage Cathode Material for Calcium‐Ion Batteries with a Water‐In‐Salt Electrolyte

Abstract

Aqueous Ca‐ion batteries (ACIBs) attract immense attention due to its high safety and the high abundance of calcium. However, the development of ACIBs is hindered by the lack of high voltage cathode materials to host the large radius and divalent Ca2+. Herein, polyanionic phosphate K3V2(PO4)3/C (KVP/C) is provided as a new cathode material for ACIBs. Due to the robust structure of polyanion material and the wide electrochemical window of water‐in‐salt electrolyte, KVP/C delivers a high working voltage of 3.74 V versus Ca2+/Ca with a specific capacity of 102.4 mAh g−1 and a long‐life of 6000 cycles at 500 mA g−1. Furthermore, the calcium storage mechanism of KVP/C is shown to be the coexistence of solid solution and two‐phase reaction by in situ X‐ray diffraction, ex situ transmission electron microscope, and X‐ray photoelectron spectroscopy. Finally, an aqueous calcium‐ion full cell, based on an organic compound as anode and KVP/C as cathode, is constructed and it shows good stability for 200 cycles and a specific capacity of 80.2 mAh g−1. This work demonstrates that vanadium‐based phosphate materials are promising high‐voltage cathode materials for ACIBs and renew the prospects for ACIBs.

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), 10–12 magnesium–ion batteries (MIBs), 13–15 calcium–ion batteries (CIBs), 16–19 and aluminum–ion batteries (AIBs) 20–22 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 .…”