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The V2O5·nH2O xerogel composed of thin acicular interconnected nanowire networks has been synthesized via a facile freeze-drying process and exhibits superior sodium storage capacity.

Li-S) batteries is seriously restricted by their low sulfur loading and utilization, sluggish reaction kinetics, and poor cycling stability. [4,5] So far, appropriate active adsorption [6,7] and catalytic centers, such as metal sulfides, [8][9][10] oxides, [11][12][13] nitrides, [14] and vanadium compounds, [15] have been introduced to enhance the sulfur utilization and accelerate the reversible conversion between lithium polysulfides (LiPSs) and Li 2 S. [16,17] However, high weight percentages of these additives sacrifice the overall energy density of Li-S batteries. Single-atom metal catalysts (SACs) comprising monodispersed metal atoms on appropriate substrates have a theoretical 100% atom utilization efficiency, and therefore have a much higher activity than conventional bulk metal and nanoparticle catalysts. [18,19] Various SACs have been introduced into Li-S batteries to improve their electrochemical performance. [20][21][22] Generally, the effects of SACs have been attributed to their good adsorption ability to LiPSs and their high catalytic activity. However, the lack of a fundamental understanding of the catalysis mechanism and the material properties that govern catalytic activity have hindered the selection and rational design of SACs for Li-S batteries. In previous studies, the SACs were usually Single-atom metal catalysts (SACs) are used as sulfur cathode additives to promote battery performance, although the material selection and mechanism that govern the catalytic activity remain unclear. It is shown that d-p orbital hybridization between the single-atom metal and the sulfur species can be used as a descriptor for understanding the catalytic activity of SACs in Li-S batteries. Transition metals with a lower atomic number are found, like Ti, to have fewer filled anti-bonding states, which effectively bind lithium polysulfides (LiPSs) and catalyze their electrochemical reaction. A series of single-atom metal catalysts (Me = Mn, Cu, Cr, Ti) embedded in threedimensional (3D) electrodes are prepared by a controllable nitrogen coordination approach. Among them, the single-atom Ti-embedded electrode has the lowest electrochemical barrier to LiPSs reduction/Li 2 S oxidation and the highest catalytic activity, matching well with the theoretical calculations. By virtue of the highly active catalytic center of single-atom Ti on the conductive transport network, high sulfur utilization is achieved with a low catalyst loading (1 wt.%) and a high area-sulfur loading (8 mg cm −2 ). With good mechanical stability for bending, these 3D electrodes are suitable for fabricating bendable/foldable Li-S batteries for wearable electronics.

Developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. In order to realize the fast and efficient transport of ions/electrons and the stable structure during the charge/discharge process, hierarchical porous Fe3O4/graphene nanowires supported by amorphous vanadium oxide matrixes have been rationally synthesized through a facile phase separation process. The porous structure is directly in situ constructed from the FeVO4·1.1H2O@graphene nanowires along with the crystallization of Fe3O4 and the amorphization of vanadium oxide without using any hard templates. The hierarchical porous Fe3O4/VOx/graphene nanowires exhibit a high Coulombic efficiency and outstanding reversible specific capacity (1146 mAh g(-1)). Even at the high current density of 5 A g(-1), the porous nanowires maintain a reversible capacity of ∼500 mAh g(-1). Moreover, the amorphization and conversion reactions between Fe and Fe3O4 of the hierarchical porous Fe3O4/VOx/graphene nanowires were also investigated by in situ X-ray diffraction and X-ray photoelectron spectroscopy. Our work demonstrates that the amorphous vanadium oxides matrixes supporting hierarchical porous Fe3O4/graphene nanowires are one of the most attractive anodes in energy storage applications.