Low-cost, low-strain and lattice-water-rich Mn0.25(VO)0.75PO4·2.25H2O as high-rate and stable cathodes for aqueous Zn-ion batteries

Abstract

Aqueous zinc‐ion batteries (ZIBs) have become a promising alternative to lithium-ion batteries (LIBs) for grid‐scale energy storage. However, the bivalent nature and large radius of zinc hydrated ions commonly lead to a strong electrostatic interaction with the host lattice and a huge strain feature during zinc-ion insertion, which results in slow diffusion kinetics and poor cycling stability. Herein, a lattice-water-rich V-based polyanionic cathode, named Mn0.25(VO)0.75PO4·2.25H2O (MnVP), is mass-producible and in which the sufficient lattice water weakens the electrostatic interactions and facilitates the rapid Zn2+ migration kinetics. The introduced Mn3+ ions partially replaced the V elements, which made the crystal structure more stable during the cycle. Besides, the doping of inactive Mn3+ can introduce the crystal water, which lower the stress and strain of the host lattice during zinc-ion insertion. Thus, the MnVP cathode delivers a high specific capacity (207.7 mAh g−1 at 0.1 A g−1), excellent rate capability (93.5% retention at 5 A g−1) and long cycle durability (after 700 cycles with a capacity retention of 88.4 %). Furthermore, the simple preparation and low cost make this cathode expect to be used in large‐scale energy storage systems.