Heteroatom-doped carbon materials (HDCMs) have been widely studied as some of the most prominent material candidates for use in a wide range of applications, such as batteries, supercapacitors (SCs), and the oxygen reduction reaction (ORR). Over the past few years, various metal-free heteroatom-doped carbon composites have been developed via integrating different heteroatoms into carbon with different nanostructures, from single-atom doping (N, P, B, S, etc.) to multiple heteroatom doping (N/P/S, N/S/B, etc.). For the first time, this review comprehensively analyzes the relevant features of HDCMs used in batteries, SCs, and the ORR, and provides guidance for the design of more efficient materials. By controlling the content and types of heteroatom-containing reagents, not only the physical and chemical properties of the material can be adjusted, but also the specific surface area and pore volume can be increased via controlling the morphology, thereby enhancing the electrochemical performance of the material. Subsequently, this review summarizes the developments and the history of HDCMs, including synthesis methods, the relationship between doping (doping position and content) and performance, reaction mechanisms, and evaluations of systems. In addition, the important role of oxygen doping is raised and discussed, to remind researchers not to ignore the role of oxygen in improving material properties. Finally, future developments and challenges relating to key technologies in this thriving field are also discussed in this report.

This review summarizes the development history, basic characteristics, special co-intercalation mechanism, origin of the superior performance of ether-based electrolytes in sodium-ion batteries and their advancements in other batteries.

Sodium‐ion batteries, representative members of the post‐lithium‐battery club, are very attractive and promising for large‐scale energy storage applications. The increasing technological improvements in sodium‐ion batteries (Na‐ion batteries) are being driven by the demand for Na‐based electrode materials that are resource‐abundant, cost‐effective, and long lasting. Polyanion‐type compounds are among the most promising electrode materials for Na‐ion batteries due to their stability, safety, and suitable operating voltages. The most representative polyanion‐type electrode materials are Na₃V₂(PO₄)₃ and NaTi₂(PO₄)₃ for Na‐based cathode and anode materials, respectively. Both show superior electrochemical properties and attractive prospects in terms of their development and application in Na‐ion batteries. Carbonophosphate Na₃MnCO₃PO₄ and amorphous FePO₄ have also recently emerged and are contributing to further developing the research scope of polyanion‐type Na‐ion batteries. However, the typical low conductivity and relatively low capacity performance of such materials still restrict their development. This paper presents a brief review of the research progress of polyanion‐type electrode materials for Na‐ion batteries, summarizing recent accomplishments, highlighting emerging strategies, and discussing the remaining challenges of such systems.

Aluminum is a naturally abundant, trivalent charge carrier with high theoretical specific capacity and volumetric energy density, rendering aluminum-ion batteries a technology of choice for future large-scale energy storage. However, the frequent collapse of the host structure of the cathode materials and sluggish kinetics of aluminum ion diffusion have thus far hampered the realization of practical battery devices. Here, we synthesize Al_xMnO₂·nH₂O by an in-situ electrochemical transformation reaction to be used as a cathode material for an aluminum-ion battery with a configuration of Al/Al(OTF)₃-H₂O/Al_xMnO₂·nH₂O. This cell is not only based on aqueous electrolyte chemistry but also delivers a high specific capacity of 467 mAh g⁻¹ and a record high energy density of 481 Wh kg⁻¹. The high safety of aqueous electrolyte, facile cell assembly and the low cost of materials suggest that this aqueous aluminum-ion battery holds promise for large-scale energy applications.

Clarifying the microstructure of hard carbon is essential to reveal its sodium storage mechanism and to develop hard carbon negative electrodes for high-performance sodium ion batteries. Currently, although various sodium storage mechanisms for hard carbon models are proposed, they are still controversial. Besides, the puzzling and abnormal variation of a Na⁺ diffusion coefficient during the discharge process cannot be well explained. Inspired by amorphous alloys, we propose and confirm the dispersion region at the junction between amorphous structures and graphite microcrystals, which is closely related to the structure of graphite microcrystals. The special dispersion region plays a buffer role in the sodium ion diffusion process and provides satisfactory storage capacity. Therefore, the effect of synthesis conditions on the local structure in the dispersion region should be considered when designing hard carbon. In this work, a specific graphite microcrystalline structure of hard carbon is precisely synthesized by screening organic molecules, and the constraint relationship between the parameters of the graphite microcrystalline structure is revealed. Importantly, this work is of great significance for resolving the current controversy about the sodium storage mechanism and making clear the anomalies of sodium ion diffusion in the low-voltage interval (<0.1 V) in hard carbon.