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couple high-capacity sulfur positive electrodes with earth-abundant sodium negative electrodes are unsurprisingly considered as a promising candidate. [8][9][10][11] In the process of cycle, the elemental sulfur of the cathode is dissolvated, reduced to form various soluble polysulfides, that is, S x 2− ions and radicals (1 ≤ x ≤ 8), and eventually the insoluble Na 2 S 2 and Na 2 S. [8,10,12] However, the practical applications are seriously hindered by several obstacles, in which the fundamental challenges are originated from the insulating properties of elemental sulfur and sodium sulfides, the volume changes at the cathode on cycling and the dissolution of sodium poly sulfides in the electrolyte. [9,[13][14][15] To date, extensive efforts have been made toward the enhancement of RT-Na/S batteries, including Na 2 S cathodes, [16,17] carbonaceous buffer matrixes, [12,18,19] a class of sodium polysulfides, [20,21] and the functional carbon-coated Nafion separator. [22] These approaches, while are validated to improve the cyclability of the RT Na-S batteries, tend to result in complicated synthetic processes and decreased theoretical capacity. In addition, it was suggested that the polar-polar interaction is a strong chemical interaction between polar sodium polysulfides and polar host materials. [23,24] Although there is no universal conclusion on the exact configuration of the interactions due to the complexity of carbon matrix, their similar effect in suppressing the polysulfide shuttle has also been reported in Li-S battery systems. [25][26][27] Instead of relying on polar-polar interactions, the suitably tailored hosts can bind sodium polysulfides through metal-sulfur bonding. Examples of such materials are sub-stoichiometric metal chalcogenides, MXene phases and metal-organic frameworks (MOFs). [28][29][30][31] In practice, these oxide and sulfide materials are able to bridge sodium polysulfides through both polar-polar Na-S(O) interaction and Lewis acid-base bonding, depending on the exposed facets to some extent. [25,32] However, to simply increase metal and/or binder content only neutralizes the advantageous energy density of the overall cell. Moreover, most of the sulfur-carbon electrode materials are directly prepared using elemental S and various carbon matrixes as started materials through vapor-infiltration or meltinfusion method. [8,10] As a result, the aggregated particles are Room temperature sodium-sulfur batteries have emerged as promising candidate for application in energy storage. However, the electrodes are usually obtained through infusing elemental sulfur into various carbon sources, and the precipitation of insoluble and irreversible sulfide species on the surface of carbon and sodium readily leads to continuous capacity degradation. Here, a novel strategy is demonstrated to prepare a covalent sulfur-carbon complex (SC-BDSA) with high covalent-sulfur concentration (40.1%) that relies on SO 3 H (Benzenedisulfonic acid, BDSA) and SO 4 2− as the sulfur source rather than elemental sulfur. M...

Low crystal MoS2 nanoflakes embedded on N-doping CNT has been prepared via alternating current and hydrothermal technique, demonstrating superior rate behavior for LIBs and SIBs.

Heteroatom modification represents one of the major areas of carbon materials' research in electrical energy storage. However, the influence of heteroatomic state evolution on electrochemical properties remains an elusive topic. Herein, thiophene-2,5-dicarboxylic acid is chemically activated to prepare O,S-diatomic hybrid carbon material (OS-C). The heteroatoms and carbon matrix coexist in the form of CO/CO and CS/SS bonds, which introduce porous networks to the partially graphitized carbon skeleton and provide abundant active sites for better ion absorption. Moreover, the heteroatoms and carbon matrix are bridged to establish stable pseudocapacitive functional groups like quinoid unit and disulfide bonds, which can be electrochemically converted into benzenoid units and mercaptan anions through Faradaic reactions to further improve the reversible capacity. Combined with the detailed kinetic exploration and in situ investigation of the electrochemical impedance spectra, the energy storage mechanism for lithium/sodium is proposed in the following steps: Faradaic reactions at a higher potential range, energy storage at active sites, and ions intercalation on the graphitized parts in the low-voltage states. Greatly, the electrode can store lithium up to the capacity of ≈700 mAh g −1 , while also delivering ≈330 mAh g −1 of sodium storage, providing lifetimes in excess of thousands of cycles.

Transition metal–nitrogen–carbon (TM–N–C) nanomaterials are promising platinum-based substitutes for the oxygen reduction reaction (ORR). However, large-scale commercial production of high-efficiency, durable TM–N–C catalysts remains a formidable challenge. In this work, a facile ″ZIF-on-ZIF″ strategy is first adopted to design ZIF-8@ZIF-67 core–shell polyhedral nanocages, and then, ferrocene (Fc) is added to form ZIF-8@ZIF-67@Fc double-layer encapsulating polyhedral nanocages. Finally, Zn, Co, and Fe tridoped N–C nanocages (ZnCoFe–N–C) as the high-efficiency ORR electrocatalyst are prepared through high-temperature annealing. Benefiting from the trimetal, nitrogen and carbon species bond to each other to form highly efficient active sites, and the material exhibits outstanding performance in 0.1 M KOH, onset potential and half-wave potential of up to 0.95 and 0.878 V (vs RHE), respectively, and long-term durability and methanol tolerance. Furthermore, when utilizing as a zinc–air battery (ZAB) air electrode, it exhibits wonderful indicators, reflected in an open circuit voltage of 1.525 V, power density of 350.2 mW cm–2, and specific capacity of 794.7 mAh gzn –1, which outperforms the benchmark Pt/C catalyst. This work provides a facile and effective strategy to obtain a highly efficient and stable TM–N–C electrocatalyst for the ORR in ZABs.