Renzhong Chen

Controlled Synthesis of Carbon Nanofibers Anchored with ZnxCo3–xO4 Nanocubes as Binder-Free Anode Materials for Lithium-Ion Batteries

The direct growth of complex ternary metal oxides on three-dimensional conductive substrates is highly desirable for improving the electrochemical performance of lithium-ion batteries (LIBs). We herein report a facile and scalable strategy for the preparation of carbon nanofibers (CNFs) anchored with ZnxCo3-xO4 (ZCO) nanocubes, involving a hydrothermal process and thermal treatment. Moreover, the size of the ZCO nanocubes was adjusted by the quantity of urea used in the hydrothermal process. Serving as a binder-free anode material for LIBs, the ZnCo2O4/CNFs composite prepared using 1.0 mmol of urea (ZCO/CNFs-10) exhibited excellent electrochemical performance with high reversible capacity, excellent cycling stability, and good rate capability. More specifically, a high reversible capacity of ∼600 mAh g(-1) was obtained at a current density of 0.5 C following 300 charge-discharge cycles. The excellent electrochemical performance could be associated with the controllable size of the ZCO nanocubes and synergistic effects between ZCO and the CNFs.

Facile fabrication of foldable electrospun polyacrylonitrile-based carbon nanofibers for flexible lithium-ion batteries

To enable electrospun polyacrylonitrile-based C nanofibers (CNFs) to be employed as anode materials in flexible Li-ion batteries, it is essential to overcome their frangibility and enhance their flexibility. Here, we report a simple method for fabricating free-standing, pure, and foldable CNFs (FCNFs) that involves a novel Zn(Ac)2-assisted electrospinning–peroxidation–carbonization process. Zn(Ac)2 was demonstrated to enhance the uniformity of the peroxidation process by relieving the stress concentration and thereby reducing the fracture of the resulting FCNFs. It also created a porous structure that improved the mechanical strength and flexibility of the FCNFs. Both flexible FCNFs and strong FCNFs, called FCNF-3/4 and FCNF-1/2, respectively, which were fabricated by adjusting the stirring temperature of the spinning solution, exhibited novel multi-folding capacity and excellent elastic-recovery properties and outperformed most state-of-the-art electrospun polyacrylonitrile-based CNFs. In addition, a systematic FCNF flexibility mechanism in which the fabric texture, fiber structure, and microstructure are considered was proposed. When used as a self-supported anode for half-cells, FCNF-3/4 exhibited a discharge capacity of 630 mA h g−1 over 100 cycles with good stability and a high coulombic efficiency, while FCNF-1/2 yielded a better rate performance than FCNF-3/4. Furthermore, a metal-conductor-free foldable full cell consisting of a commercial flexible LiCoO2/CNT cathode and a FCNF-3/4 anode was assembled and was able to light an LED even when it was folded twice. More importantly, the FCNFs proved to be applicable as foldable conductive substrates that are used to load high-capacity active materials (e.g., Si and ZnxCo3−xO4), indicating their high potential to be applied in flexible energy storage devices.

Excimer Ultraviolet-Irradiated Carbon Nanofibers as Advanced Anodes for Long Cycle Life Lithium-Ion Batteries

Carbon nanofibers (CNFs) bearing oxygen-containing functional groups and inhomogeneous nanopores are successfully prepared by excimer UV radiation. The CNFs demonstrate potential for use as an anodic material in rechargeable Li-ion batteries. Their improved electrochemical performances are attributed to the chemically bonded solid-electrolyte interface films on the CNF surface. This approach is also applicable to other carbonaceous electrode materials.

Highly efficient and green fabrication of a modified C nanofiber interlayer for high-performance Li–S batteries

Rechargeable Li–S batteries hold great promise for energy storage applications because they exhibit high theoretical capacity, low cost, and non-toxicity. However, the practical applications of these batteries are hindered by their low electronic conductivity and short cycling lifetime. Herein, we present a simple and efficient strategy for improving the performance of Li–S batteries, utilizing excimer ultraviolet radiation to produce a functional C nanofiber (EUV-CNF) interlayer. In the presence of water and oxygen, the above irradiation results in the formation of oxygenated functional groups (e.g., OH and CO) and nanopores on the interlayer surface. Compared to the sulfur cathode with a pristine C nanofiber (CNF) interlayer, that with the EUV-CNF interlayer exhibits a higher capacity of 917 mA h g−1 after 200 cycles at 0.2C and a lower average capacity fading per cycle (0.16%). This excellent cycling performance is attributed to the functionalization of the CNF interlayer, which not only improves cathode conductivity but also allows effective trapping of polysulfides within the cathode without hampering Li-ion conductivity. Thus, this work presents a simple, efficient, and environmentally friendly approach to improving the performance of Li–S batteries and thus paves the way to expanding their application scope.

Highly mesoporous C nanofibers with graphitized pore walls fabricated via ZnCo2O4-induced activating-catalyzed-graphitization for long-lifespan lithium-ion batteries

Transition metals (TMs), e.g. Fe, Co, and Ni, are normally unsuitable for the fabrication of highly porous C materials with graphitized C layers since in situ formed carbides on the surface of the TMs impede their catalytic graphitization effect. In this paper, we report on highly mesoporous sponge-like C nanofibers (SLCNFs) with graphitized pore-walls fabricated through novel activating-catalyzed-graphitization using ZnCo2O4 as a source of ZnO and metallic Co. During the carbonization, the ZnO functions as an in situ activating agent to provide O species to oxidize the inert Co3C to active Co; the original transient “amorphous C/Co–graphite/Co3C” process induced by the metallic Co can be translated into a cyclic “amorphous C/Co–graphite/Co3C–COx/Co” system, to fabricate a sponge-like well-interconnected mesoporous structure. This gives SLCNFs a high reversible capacity (900 mA h g−1 at 0.1 A g−1 after 100 cycles), good rate performance, and excellent super-long-term cycle stability (460 mA h g−1 at 1.67 A g−1 after 2000 cycles) when used as the anode of a lithium-ion battery. The usability of SLCNFs as a conductive substrate for sulfur is also demonstrated, indicating their excellent potential for application to energy storage and conversion.