Sodium‐ion batteries (SIBs), which are an alternative to lithium‐ion batteries (LIBs), have attracted increasing attention due to their low cost of Na resources and similar Na storage mechanism to LIBs. Compared with anode materials and electrolytes, the development of cathode materials lags behind. Therefore, the key to improving the specific energy and promoting the application of SIBs is to develop high‐performance sodium intercalation cathode materials. Transition‐metal oxides are one of the most promising cathode materials for SIBs owing to their excellent energy density, high specific discharge capacity, and environmentally friendly nature. In the present work, the latest progress in the research of transition‐metal oxides is summarized. Moreover, the existing challenges are discussed, and a series of strategies are proposed to overcome these drawbacks. This review aims at providing guidance for the development of metal oxides in the next stage.

Aqueous rechargeable zinc-ion hybrid supercapacitors are considered to be a promising candidate for large-scale energy storage devices owing to their high safety, long life, and low price. In this paper, a nitrogen doped hierarchical porous carbon is evaluated as the cathode for aqueous rechargeable zinc-ion hybrid supercapacitors. Benefiting from the synergistic merits of excellent structural features of N-HPC and tiny zinc dendrite of Zn anode in ZnSO₄ electrolyte, the zinc-ion hybrid supercapacitor exhibits excellent energy storage performance including high capacity of 136.8 mAh·g⁻¹ at 0.1·Ag⁻¹, high energy density of 191 Wh·kg⁻¹, large power density of 3,633.4 W·kg⁻¹, and satisfactory cycling stability of up to 5,000 cycles with a capacity retention of 90.9%. This work presents a new prospect of developing high-performance aqueous rechargeable zinc ion energy storage devices.

Currently, emerging battery technologies are being studied intensively. The lack of ideal electrode materials remains a key hindrance to further development of new batteries. The novel MXene material, due to its unique structural characteristics and physicochemical properties, shows the ability to enhance the electrochemical performance of the electrode. In addition to the adjustable layer spacing, because of excellent electrical conductivity, rich chemical composition, and controllable surface chemistry, MXene has the potential for use in diverse applications as an ideal electrode material in various battery systems. This review covers the recent progress achieved in research of the zinc‐ion energy storage of MXenes, including MXene‐based cathodes, MXene‐derived cathodes, MXene‐modified zinc anodes, and electrolyte additives. Moreover, further structural design and reaction mechanisms of MXenes in zinc‐ion storage are explored.

The lack of high-performance cathode materials is a great challenge for the development of large-scale energy storage sodium ion batteries. Here, a new resource-rich P2-type Na_0.44Mn_0.6Ni_0.4−xCu_xO₂ (0 ≤ x ≤ 0.3) sodium-ion battery (NIBs) cathode material was designed and synthesized by a sol–gel method. Na ions occupy the Na_f sites and the Na_e sites in a proportion of 1 : 1, which maintains the high symmetry and stability of the P2-type structure. The charging/discharging tests show that Na_0.44Mn_0.6Ni_0.3Cu_0.1O₂ has a high initial capacity of 149 mA h g⁻¹ and 80% capacity retention after 50 cycles at 0.1C, showing a high energy density of 469 W h kg⁻¹. The addition of inactive copper enhances the lattice spacing, obviously reducing the irreversible reaction resistance (R_f) during the intercalation and deintercalation of Na⁺, thereby reducing the internal resistance of the battery and improving the cycle performance. In order to maintain the P2-type structure, the voltage is controlled at 1.5–4.0 V during charging and discharging, which inhibits the phase transition of P2-O2, leading to the improvement of cycling performance. Therefore, the Cu-substituted Na_0.44Mn_0.6Ni_0.3Cu_0.1O₂ possibly serves as a promising high capacity, high energy density and stable cathode for sodium ion battery applications.