Rechargeable magnesium batteries are identified as a promising next‐generation energy storage system, but their development is hindered by the anode−electrolyte−cathode incompatibilities and passivation of magnesium metal anode. To avoid or alleviate these problems, the exploitation of alternative anode materials is a promising choice. Herein, we present titanium pyrophosphate (TiP2O7) as anode materials for magnesium‐ion batteries (MIBs) and investigate the effect of the crystal phase on its magnesium storage performance. Compared with the metastable layered TiP2O7, the thermodynamically stable cubic TiP2O7 displays a better rate capability of 72 mAh g−1 at 5000 mA g−1. Moreover, cubic TiP2O7 exhibits excellent cycling stability with the capacity of 60 mAh g−1 after 5000 cycles at 1000 mA g−1, which are better than previously reported Ti‐based anode materials for MIBs. In situ X‐ray diffraction technology confirms the single‐phase magnesium‐ion intercalation/deintercalation reaction mechanism of cubic TiP2O7 with a low volume change of 3.2%. In addition, the density functional theory calculation results demonstrate that three‐dimensional magnesium‐ion diffusion can be allowed in cubic TiP2O7 with a low migration energy barrier of 0.62 eV. Our work demonstrates the promise of TiP2O7 as high‐rate and long‐life anode materials for MIBs and may pave the way for further development of MIBs.

The rechargeable aqueous zinc-ion battery is a promising candidate for energy storage demands owing to its low cost, intrinsic safety, and ecofriendliness. However, existing aqueous zinc-ion batteries are far from achieving the exploration of appreciable cathode materials because multivalent ions have the strong charge repulsion with the host material and inherent sluggish kinetics during the charge and discharge process. Herein, we introduce a novel urchin-like magnesium vanadate as the cathode material for aqueous zinc-ion batteries. Specifically, the battery delivers a high capacity of 272 mA h g–1 at 0.2 A g–1 and an excellent long-term cycling stability with a reversible capacity of 128.9 mA h g–1 even after 500 cycles at 4.0 A g–1. Additionally, the calculated energy density for the MgV2O4 cathode is 171.5 W h kg–1 at 140.6 W kg–1 power density. These remarkable electrochemical performances are attributed to the crystal structure of urchin-like MgV2O4 with low-valence vanadium, transforming from the order to disorder and producing a new phase during the electrochemical cycling process. This work may open an avenue for the application of low-valent vanadium-based materials for aqueous zinc-ion storage.

VO2 generally has a higher theoretical capacity and layered structure suitable for the intercalation/extraction of zinc ions. However, Zn2+ ions with high charge density interact with the crystal lattice and limit further improvement in electrochemical performance. Defect engineering is a potential modification method with very promising application prospects, but the established procedures for preparing defects are complicated. In this study, VO2–x(B) with oxygen deficiency is prepared by a simple solution reaction with NaBH4. The presence of oxygen deficiencies is confirmed by positron annihilation lifetime spectroscopy, UV/Vis absorbance spectroscopy and others. Owing to the presence of oxygen defects, the aqueous Zn/VO2–x(B) battery exhibits improved specific capacity, excellent reversibility, and structural stability. Ex situ characterization techniques are employed to demonstrate the reversible insertion‐extraction mechanism of Zn2+ ions from and into the host material. In addition, the Zn/VO2–x(B) batteries still exhibit considerable electrochemical performance, even with high‐loading electrodes (about 4 mg cm−2).

In recent years, zinc‐ion batteries (ZIBs) with near neutral (pH ≈ 4–6) Zn2+‐containing aqueous electrolyte have received extensive research due to their advantages of high safety, low production cost, suitable anode zinc, and environmental friendliness, etc. At present, one of the key challenges of aqueous ZIBs is the development of cathode materials with stable structure, rapid kinetics, and high capacity, etc. Compared with other cathode materials, V2O5 has an important potential application because of its high theoretical specific capacity (589 mA h g−1) based on two electron transfers, relatively low production cost, and suitable layered structure that facilitates zinc ion insertion/extraction. Herein, the following sections are proposed: 1) An understanding of the structure and energy storage mechanism of V2O5; 2) The recent development on the aqueous Zn/V2O5 battery from properties of V2O5 cathode and composition optimization of battery structure; 3) The application of V2O5 cathode in flexible ZIBs; and 4) The outlook and development trends in the future.

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