Magnesium ion batteries (MIBs) have attracted much attention due to their low cost and high safety properties. However, the intense charge repulsion effect and sluggish diffusion dynamics of Mg2+ ions result in unsatisfactory electrochemical performance of conventional cathode materials in MIBs. This work reports water‐lubricated aluminum vanadate (HAlVO) as high‐performance cathode material for Mg2+ ions storage and investigates the capacity fade mechanism of water‐free aluminum vanadate (AlVO). The charge density difference based on density functional theory calculation is performed to analyze the charge transfer process of water‐lubricated/free aluminum vanadates (HAlVO/AlVO). The different charge transfer phenomena of two materials and the charge shielding effect of water molecule in HAlVO are revealed. Moreover, the single‐phase structural evolution process and the Mg2+ ions storage mechanism of HAlVO are further investigated deeply by different in situ and ex situ characterization methods. This work proves that HAlVO is a potential candidate cathode material to satisfy the high‐performance reversible Mg2+ ions storage, and the water‐lubricated method is an effective strategy to improve the electrochemical performance of vanadium oxides cathode.

Aqueous zinc‐ion batteries (AZIBs) attract much attention owing to their high safety, environmentally friendliness and low cost. However, the unsatisfactory performance of cathode materials is one of the unsolved important factors for their widespread application. Herein, we report NH4V4O10 nanorods with Mg2+ ion preinsertion (Mg‐NHVO) as a high‐performance cathode material for AZIBs. The preinserted Mg2+ ions effectively improve the reaction kinetics and structural stability of NH4V4O10 (NHVO), which are confirmed by electrochemical analysis and density functional theory calculations. Compared with pristine NHVO, the intrinsic conductivity of Mg‐NHVO is improved by 5 times based on the test results of a single nanorod device. Besides, Mg‐NHVO could maintain a high specific capacity of 152.3 mAh g−1 after 6000 cycles at the current density of 5 A g−1, which is larger than that of NHVO (only exhibits a low specific capacity of 30.5 mAh g−1 at the same condition). Moreover, the two‐phase crystal structure evolution process of Mg‐NHVO in AZIBs is revealed. This work provides a simple and efficient method to improve the electrochemical performance of ammonium vanadates and enhances the understanding about the reaction mechanism of layered vanadium‐based materials in AZIBs.

Rechargeable Ca‐ion batteries (CIBs) have attracted great interest due to potentially high output voltage and abundant calcium resources. Among various cathode materials, manganese oxides with high theoretical capacity and low cost are suitable as strong candidates for rechargeable CIBs. However, the dissolution of manganese and the strong electrostatic interactions between Ca2+ and host materials result in inferior cycle stability and poor rate performance. Herein, a MnO2‐polyaniline (PANI) hybrid cathode with both PANI intercalation and coating is developed to solve the above problems. The intercalation of PANI can expand the interlayer spacing and effectively buffer the local electrostatic interaction for facile Ca2+ diffusion. Meanwhile, the density functional theory (DFT) calculations prove that the PANI coating inhibits manganese dissolution by forming strong Mn‐N bonds to enhance the structural integrity of MnO2. Benefitting from the above, the MnO2‐PANI (MnO2‐P) cathode delivers high capacity (150 mAh g⁻1 at 0.1 A g⁻1), excellent rate performance (120 mAh g⁻1 at 1 A g⁻1) and long‐term cycling stability (5000 cycles). The organic‐inorganic hybrid desig provides a new strategy for developing high performance CIBs cathode materials.

Lithium supply shortages have prompted the search for alternatives to widespread grid system applications. Potassium-ion batteries (PIBs) have emerged to promising candidates for this purpose. Nonetheless, the large radius of K (1.38 Å) impedes the march of satisfactory cathode materials. Here, we used solid-phase synthesis to prepare a layered K MnO ·0.25H O (KMO) cathode, comprising alternately connected MnO octahedra with a large interlayer spacing (0.64 nm) to accommodate the migration and transport of K ions. The cathode material achieved initial specific capacities of 102.3 and 88.1 mA h g at current densities of 60 mA g and 1 A g , respectively. The storage mechanism of K ions in PIBs was demonstrated ex situ using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy measurements. Overall, our proposed KMO was confirmed as an auspicious cathode material for potential use in PIBs.

Lithium supply shortages have prompted the search for alternatives to widespread grid system applications. Potassium-ion batteries (PIBs) have emerged to promising candidates for this purpose. Nonetheless, the large radius of K+ (1.38 Å) impedes the march of satisfactory cathode materials. Here, we used solid-phase synthesis to prepare a layered K0.37MnO2·0.25H2O (KMO) cathode, comprising alternately connected MnO6 octahedra with a large interlayer spacing (0.64 nm) to accommodate the migration and transport of K+ ions. The cathode material achieved initial specific capacities of 102.3 and 88.1 mA h g-1 at current densities of 60 mA g-1 and 1 A g-1, respectively. The storage mechanism of K+ ions in PIBs was demonstrated ex situ using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy measurements. Overall, our proposed KMO was confirmed as an auspicious cathode material for potential use in PIBs.