Xiangzhong Kong

Rational design of multi-shelled CoO/Co9S8 hollow microspheres for high-performance hybrid supercapacitors

Hollow structures with complex interiors are promising to endow electroactive materials with fascinating physical properties, such as low mass density, large surface area and high permeability. Meanwhile, the construction of hollow structures with binary chemical compositions could further enhance the resultant electrochemical properties. Herein, we reported a designed synthesis of multi-shelled CoO/Co9S8 hollow microspheres by calcining a hollow microsphere precursor with S powder in argon gas (Ar). The inherent characteristic of cobalt(II) mono-oxide can benefit the electrochemical activity, while the cobalt sulfide component could improve the electrical conductivity of this cobalt-based composite material. These multi-shelled hollow structures are proved to possess a porous texture with a relatively large specific surface area (SSA = 43.1 m2 g−1), which could provide more active sites for electrochemical reactions. As a result, the as-prepared multi-shelled CoO/Co9S8 hollow microspheres exhibit an enhanced specific capacitance and excellent rate performance when evaluated as electrode materials for hybrid supercapacitors.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo2O4 porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo2O4 dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m2 g-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo2O4 dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g-1 can be maintained after 180 cycles at 200 mA g-1. Even at a high current density of 2000 mA g-1, the electrode can still deliver a specific capacity of 423.3 mA h g-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo2O4 porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm-2 and a Tafel slope of 93 mV dec-1.

Self-templating synthesis of double-wall shelled vanadium oxide hollow microspheres for high-performance lithium ion batteries

Hollow structured vanadium pentoxide microspheres with multiple double-walled shells were fabricated from solid vanadium oxide precursors through ascorbic acid-assisted solvothermal growth. The interiors of the vanadium oxide microspheres and number of the novel double-walled shells can be readily controlled by adjusting the combustion of solid vanadium oxide precursors. The formation mechanism of the unique structures is elucidated and attributed to the diffusion controlled oxidation process in air. The obtained V2O5 hollow spheres with triple double-walled shells show improved electrochemical performance compared to single-shelled V2O5 hollow microspheres as electrode materials for lithium-ion batteries.

Facile fabrication of interconnected-mesoporous T-Nb2O5 nanofibers as anodes for lithium-ion batteries

Niobium pentoxide (Nb2O5) has been extensively studied as anode materials for lithium ion batteries (LIBs) due to its good rate performance and safety advantages. However, the intrinsic low electronic conductivity has largely restricted its practical application. In this work, we report the construction of mesoporous T-Nb2O5 nanofibers by electrospinning followed by heat treatment in air. The interconnected mesoporous structure ensures a high surface area with easy electrolyte penetration. When used as anodes for LIBs, the mesoporous Nb2O5 electrode delivers a high reversible specific capacity of 238 mA h g−1 after 1,000 cycles at a current density of 1 A g−1 within a voltage range of 0.01–3.0 V. Even at a higher discharge cut-off voltage window of 1.0–3.0 V, it still possesses a high reversible capacity of 166 mA h g−1 after 200 cycles. Moreover, the porous Nb2O5 electrode also exhibits excellent rate capability. The enhanced electrochemical performances are attributed to the synergistic effects of porous nanofiber structure and unique crystal structure of T-Nb2O5, which has endowed this material a large electrode-electrolyte contact area with improved electronic conductivity.摘要五氧化二铌Nb2O5由于其良好的倍率性能和安全性, 作为锂离子电池负极材料被广泛研究. 但是其固有的低电子电导率在很大程度上限制了其电化学性能的发挥. 在本论文中, 我们通过静电纺丝和后续空气热处理构建了具有连续介孔结构的T-Nb2O5纳米纤维. 介孔结构彼此互连, 确保高表面积的同时也促进了电解液的渗透. 当用作锂离子电池负极时在电压窗口为0.01–3.0 V, 电流密度为1 A g−1的条件下, 循环1000圈后可逆比容量达到238 mA h g−1. 即使提高电压窗口到1.0–3.0 V, 在循环200圈后仍然有166 mA h g−1的可逆比容量. 此外, 电极材料还表现出优异的倍率性能. 多孔纳米纤维结构和T-Nb2O5独特晶体结构的协同效应, 增大了电极和电解质的接触面积, 改善了电子传导性, 从而使电化学性能得到提高.

In situ formation of porous graphitic carbon wrapped MnO/Ni microsphere networks as binder-free anodes for high-performance lithium-ion batteries

Flexible hybrid electrodes with high electronic conductivity and porosity have attracted great attention for energy storage and conversion systems. Herein, we report the fabrication of a porous graphitic carbon wrapped MnO/Ni microsphere network (MnO/Ni/CNF) by a combined solvothermal and electrospinning method followed by stabilization and carbonization processes. Carbon nanofibers which link porous MnO/Ni/C microspheres function as both a 3D conductive network and a current collector for the flexible composite electrode. Meanwhile, the porous MnO/Ni microspheres are coated with porous graphene-like carbon layers, further improving the electronic conductivity and facilitating the electrolyte penetration. When directly utilized as an anode material for LIBs, the MnO/Ni/CNF electrode exhibits excellent electrochemical performances, including high reversible capacity, good cycle stability and rate capability. The as-prepared flexible electrode delivers a capacity of 534.5 mA h g−1 at 200 mA g−1 after 100 cycles (based on the whole electrode mass) and possesses a capacity retention of 95.7% even after long-term 600 cycles at 1 A g−1, suggesting its promising applicability in lithium ion batteries as a flexible binder-free anode.

Three-Dimensional Carbon-Coated Treelike Ni3S2 Superstructures on a Nickel Foam as Binder-Free Bifunctional Electrodes

Three-dimensional (3D) nanostructures are commonly endowed with numerous active sites, large specific surface area, and good mechanical strength, which make them as an efficient candidate for energy storage and conversion. Herein, by considering the advantages of 3D nanostructures, we successfully fabricated carbon-coated nickel sulfide on a nickel foam (C@NS@NF) with a unique 3D treelike superstructure via a two-step hydrothermal process. By virtue of its hierarchical superstructures, 3D treelike architecture, and carbon shell encapsulation, the as-fabricated carbon-coated Ni3S2 can be directly served as binder-free bifunctional electrodes for supercapacitor and hydrogen evolution reaction, where high specific areal capacitance (6.086 F cm-2 at 10 mA cm-2) for supercapacitors and low overpotential (92 mV at 10 mA cm-2) for the electrocatalyst have been demonstrated. These inspiring results of this material make it as a potential candidate for energy storage and conversion.