Heteroatom-doped carbon materials (HDCMs) have been widely studied as one of the most prominent material candidates for a wide range of applications, such as batteries, supercapacitors (SCs) and ORR. In...

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.

A new class of oxygen reduction reaction (ORR) catalysts based on graphene quantum dots (GQDs) supported by graphene nanoribbons (GNRs) has been developed through a one-step simultaneous reduction reaction, leading to ultrahigh performance for O reduction with an excellent electrocatalytic activity (higher limiting current density and lower overpotential than those of platinum) and high selectivity and stability in alkaline media comparable to the best C-based ORR catalysts reported so far. Electron microscopy revealed numerous surface/edge defects on the GQD/GNR surfaces and at their interface to act as the active sites. This, coupled with efficient charge transfer between the intimately contacted GQDs and GNRs, rationalized the observed ultrahigh electrocatalytic performance for the resultant GQD-GNR hybrids. Thus, this study opens a new direction for developing low-cost, highly efficient, C-based ORR electrocatalysts.

The design of carbon‐based materials with a high mass density and large porosity has always been a challenging goal, since they fulfill the demands of next‐generation supercapacitors and other electrochemical devices. We report a new class of high‐density heteroatom‐doped porous carbon that can be used as an aqueous‐based supercapacitor material. The material was synthesized by an in situ dehalogenation reaction between a halogenated conjugated diene and nitrogen‐containing nucleophiles. Under the given conditions, pyridinium salts can only continue to perform the dehalogenation if there is residue water remaining from the starting materials. The obtained carbon materials are highly doped by various heteroatoms, leading to high densities, abundant multimodal pores, and an excellent volumetric capacitive performance. Porous carbon tri‐doped with nitrogen, phosphorous, and oxygen exhibits a high packing density (2.13 g cm−3) and an exceptional volumetric energy density (36.8 Wh L−1) in alkaline electrolytes, making it competitive to even some Ni‐MH cells.

Nevertheless, the research on SIBs was barely conducted after the successful commercialization of LIBs in 1990s, and this situation continued until the end of the 20th century. An obstacle toward the development of SIBs is the lack of suitable anode materials with acceptable performance. The early work conducted by Dahn et al. [5] suggested that hard carbon (HC) has a reversible capacity of 300 mAh g −1 for sodium, approaching the lithium storage capacity in graphite. Extensive attention has been focused on the development of SIBs recently, with a variety of materials being considered as potential anodes for SIBs, which includes alloys, [6-8] organic materials, [9-11] and carbonaceous materials. [12-14] Because of high sodium-ion storage capacity, appropriate working potential, excellent cycling stability, and natural abundance, HC represents the most promising anode for SIBs. Nowadays, increasing interests have been concentrated on revealing sodium intercalation process in HC, [15-19] but the steady state of sodium stored in HC still remains unexplored, which leads us to investigate the steady state of sodium ions in HC from thermodynamic and kinetic aspects. Heretofore, the steady state of sodium in HC has been incidentally proposed, but remains a controversial issue. Specifically, Stevens and Dahn [20] originally revealed the metallic nature of sodium absorbed in nanopores at the voltage plateau as the adsorption potential approaching the deposition potential of sodium metal. Meanwhile, the formation of metallic sodium was also confirmed with operando 23 Na solid-state nuclear magnetic resonance (NMR) and in situ Raman at the plateau region. [21,22] Moreover, Ji and co-workers [23] suggested that sodium adsorbed onto the pore surface is atomic even close to the cutoff potential (0.05-0 V). On the other hand, Liu et al. [19] demonstrated that neither metallic nor quasi-metallic sodium is presented in the whole discharge region over 0 V, based on the results of ex situ 23 Na NMR and electron paramagnetic resonance (EPR). Recently, Guo et al. [13] claimed that sodium stored in the HC is in the ionic state above 0.1 V, whereas metallic sodium clusters form in the nanopores at the plateau voltage, with the methods of EPR, XRD, and Raman. Apparently, scattered efforts have been devoted to uncover the state of sodium stored in hard carbon recently, nevertheless, systematic investigations are Hard carbon (HC) is the most promising anode material for sodium-ion batteries (SIBs), nevertheless, the understanding of sodium storage mechanism in HC is very limited. As an important aspect of storage mechanism, the steady state of sodium stored in HC has not been revealed clearly to date. Herein, the formation mechanism of quasi-metallic sodium and the quasi-ionic bond between sodium and carbon within the electrochemical reaction on the basis of theoretical calculations are disclosed. The presence of quasi-metallic sodium is further confirmed with the assistance of a specific reaction between the sodiated HC electrode and eth...

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Supercapacitors with fast charge/discharge rate and long cycling stability (>50 000 cycles) are attractive for energy storage and mobile power supply. In this paper, a facile strategy is developed to fabricate an Fe2O3/FeS‐decorated N, S‐codoped hierarchical porous carbon hybrid. Its microstructure and compositions can be readily controlled through adjusting the hydrothermal reaction between waxberry and iron sulfate. The constructed supercapacitors with the as‐prepared carbon materials from this reaction are able to exhibit outstanding capacitive performance with a superfast charge/discharge rate (<1 s), ultralong cycle life (>50 000 cycles, 80 A g−1), ultrahigh volumetric capacitance (1320.4 F cm−3, 0.1 A g−1), and high energy density (100.9 W h kg−1, 221.9 W h L−1). The outstanding performance makes it one of the best biomass‐derived supercapacitors. The superior capacitive behavior is likely to arise from the N and S codoping on the surface/edge/skeleton of the carbon microspheres and nanosheet composites coupled with the fast redox reaction of Fe2O3/FeS. Overall, this research presents a new avenue for developing the next generation of sustainable high‐performance energy storage device.

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