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.

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Titanium based oxides are pomising electrode materials due to the appropriate operating voltage, small strain expansion, fast rate capability, safety, and low cost. Carbon materials exhibit a high cyclic stability...

Selenium exhibits smaller volume expansion and much higher electrical conductivity compared with sulfur, which makes it considered as a potential cathode material. In order to improve electrochemical performance of potassium-selenium (KÀ Se) batteries, we prepared porous carbon/Se (PC/Se) composite via carbonization, KOH activation and melt diffusion and synthesized a novel porous carbon/Se/graphene oxide (PC/Se/GO) composite with the Se content of~40 % via controlling the ionic strength of the solution as cathode material in the work. The combination of porous carbon structure and graphene can effectively relieve the volume expansion of selenium during the charge and discharge process, and provide excellent conductivity. The one-step conversion without polyselenides between the PC/Se/GO composite and metal potassium further improves the capacity and cycling stability. Therefore, the PC/Se/GO delivers high discharge capacities of 426.3 and 316.8 mAh g À 1 in the 2nd and 150th cycles at 0.5 C. This work plays an important reference role for the exploration of advanced potassiumselenium batteries.

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Long cycle-life, low cost, and rechargeable aqueous zinc batteries are marketable energy storage systems for scalable applications. The graphene is a potential cathode, but it tends to strongly achieve effective zinc-ion storage because of surface texture properties. Herein, we synthesize a functional holey graphene electrode via a facile diazotization method. The functional groups (−NH– and −SO4H groups) are used as the redox centers of the internal ion reservoir to ensure the high performance of the reversible and efficient zinc-ion batteries. The unique surface structure of graphene serves as the ion carrier to provide electrochemical double-layer adsorption with SO4 2–. The hybrid mechanism endows the batteries with superior electrochemical performance. The highly conductive and holey graphene acts as the matrix to facilitate the excellent electron and proton transport. The battery possesses an excellent performance with a high capacity, high rate performance (234 mA h g–1 at 0.1 A g–1 and 101 mA h g–1 even at 10 A g–1), and long-cycle lifetime (maintaining 98% at a large current density of 10 A g–1 after 4000 cycles). Furthermore, the quasi-solid-state soft zinc-ion battery displays stable electrochemical performance. A new door is opened about graphene-based materials as the cathode for high-performance rechargeable zinc energy storage.

The application of sodium ion batteries (SIBs) in future large-scale energy storage equipment is facing great challenges due to its unstable cathode materials. Herein, monocrystalline orthorhombic Na0.44Mn0.9Li0.1O2 with high crystallinity...

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