Effects of surrounding confinements of Si nanoparticles on Si-based anode performance for lithium ion batteries

A Review of Recent Advancements in Electrospun Anode Materials to Improve Rechargeable Lithium Battery Performance

Although lithium-ion batteries have already had a considerable impact on making our lives smarter, healthier, and cleaner by powering smartphones, wearable devices, and electric vehicles, demands for significant improvement in battery performance have grown with the continuous development of electronic devices. Developing novel anode materials offers one of the most promising routes to meet these demands and to resolve issues present in existing graphite anodes, such as a low theoretical capacity and poor rate capabilities. Significant improvements over current commercial batteries have been identified using the electrospinning process, owing to a simple processing technique and a wide variety of electrospinnable materials. It is important to understand previous work on nanofiber anode materials to establish strategies that encourage the implementation of current technological developments into commercial lithium-ion battery production, and to advance the design of novel nanofiber anode materials that will be used in the next-generation of batteries. This review identifies previous research into electrospun nanofiber anode materials based on the type of electrochemical reactions present and provides insights that can be used to improve conventional lithium-ion battery performances and to pioneer novel manufacturing routes that can successfully produce the next generation of batteries.

SiO2-confined silicon/carbon nanofiber composites as an anode for lithium-ion batteries

A nanoscale silica coating of silicon/carbon nanofibers enabled stable solid electrolyte interphase formation on an electrode surface and improved cycling performance.

Conversion of silica nanoparticles into Si nanocrystals through electrochemical reduction

The precise design of Si-based materials at the nanometer scale is a quite complex issue but of utmost importance for their present and potential applications. This paper reports the first attempt to address the electrochemical reduction of SiO₂ at the nanometer scale. SiO₂ nanoparticles are first covered with a uniform carbon layer with controlled thickness at an accuracy of a few nanometers, by pressure-pulsed chemical vapor deposition. With appropriate thickness, the carbon layer plays significant roles as a current path and also as a physical barrier against Si-crystal growth, and the SiO₂ nanoparticles are successfully converted into extremely small Si nanocrystals (<20 nm) inside the shell-like carbon layer whose morphology is derived from the original SiO₂ nanoparticles. Thus, the proposed electroreduction method offers a new synthesis strategy of Si-C nanocomposites utilizing the morphology of SiO₂ nanomaterials, which are well known for a wide variety of defined and regular nanostructures. Owing to the volume difference of SiO₂ and the corresponding Si, nanopores are generated around the Si nanocrystals. It has been demonstrated that the nanopores around the Si nanocrystals are effective to improve cycle performance of Si as a negative electrode for lithium-ion batteries. The present method is in principle applicable to various SiO₂ nanomaterials, and thus, offers production of a variety of Si-C composites whose carbon nanostructures can be defined by their parent SiO₂ nanomaterials.

Sandwich-lithiation and longitudinal crack in amorphous silicon coated on carbon nanofibers

Silicon-carbon nanofibers coaxial sponge, with strong mechanical integrity and improved electronic conductivity, is a promising anode structure to apply into commercial high-capacity lithium ion batteries. We characterized the electrochemical and mechanical behaviors of amorphous silicon-coated carbon nanofibers (a-Si/CNFs) with in situ transmission electron microscopy (TEM). It was found that lithiation of the a-Si coating layer occurred from the surface and the a-Si/CNF interface concurrently, and propagated toward the center of the a-Si layer. Such a process leads to a sandwiched Li(x)Si/Si/Li(x)Si structure, indicating fast Li transport through the a-Si/CNF interface. Nanocracks and sponge-like structures developed in the a-Si layer during the lithiation-delithiation cycles. Lithiation of the a-Si layer sealed in the hollow CNF was also observed, but at a much lower speed than the counterpart of the a-Si layer coated on the CNF surface. An analytical solution of the stress field was formulated based on the continuum theory of finite deformation, explaining the experimental observation of longitudinal crack formation and general mechanical degradation mechanism in a-Si/CNF electrode.

Green synthesis and stable li-storage performance of FeSi(2)/Si@C nanocomposite for lithium-ion batteries

Si-based alloy materials have received great attention as an alternative anode for high capacity and safe Li-ion batteries, but practical implementation of these materials is hindered by their poor electrochemical utilization and cyclability. To tackle this problem, we developed a core-shelled FeSi2/Si@C nanocomposite by a direct ball-milling of Fe and Si powders. Such a nanostructured composite can effectively buffer the volumetric change by alloying active Si phase with inactive FeSi2 matrix in its inner cores and prevent the aggregation of the active Si particles by outer graphite shells, so as to improve the cycling stability of the composite material. As a result, the FeSi2/Si@C composite exhibits a high Li-storage capacity of ∼1010 mA g(-1) and an excellent cyclability with 94% capacity retention after 200 cycles, showing a great promise for battery applications. More significantly, the synthetic method developed in this work possesses several advantages of low cost, zero emission, and operational simplicity, possibly to be extended for making other Li-storage alloys for large-scale applications in Li-ion batteries.

Carbon nanofibers prepared via electrospinning

Carbon nanofibers prepared via electrospinning and following carbonization are summarized by focusing on the structure and properties in relation to their applications, after a brief review of electrospinning of some polymers. Carbon precursors, pore structure control, improvement in electrical conductivity,and metal loading into carbon nanofibers via electrospinning are discussed from the viewpoint of structure and texture control of carbon.

Preparation and electrochemical performance of hyper-networked Li4Ti5O12/carbon hybrid nanofiber sheets for a battery-supercapacitor hybrid system

Hyper-networked Li(4)Ti(5)O(12)/carbon hybrid nanofiber sheets that contain both a faradaically rechargeable battery-type component, namely Li(4)Ti(5)O(12), and a non-faradaically rechargeable supercapacitor-type component, namely N-enriched carbon, are prepared by electrospinning and their dual function as a negative electrode of lithium-ion batteries (LIBs) and a capacitor is tested for a new class of hybrid energy storage (denoted BatCap). An aqueous solution composed of polyvinylpyrrolidone, lithium hydroxide, titanium(IV) bis(ammonium-lactato)dihydroxide and ammonium persulfate is electrospun to obtain hyper-networked nanofiber sheets. Next, the sheets are exposed to pyrrole monomer vapor to prepare the polypyrrole-coated nanofiber sheets (PPy-HNS). The hyper-networked Li(4)Ti(5)O(12)/N-enriched carbon hybrid nanofiber sheets (LTO/C-HNS) are then obtained by a stepwise heat treatment of the PPy-HNS. The LTO/C-HNS deliver a specific capacity of 135 mAh g(-1) at 4000 mA g(-1) as a negative electrode for LIBs. In addition, potentiodynamic experiments are performed using a full cell with activated carbon (AC) as the positive electrode and LTO/C-HNS as the negative electrode to estimate the capacitance properties. This new asymmetric electrode system exhibits a high energy density of 91 W kg(-1) and 22 W kg(-1) at power densities of 50 W kg(-1) and 4000 W kg(-1), respectively, which are superior to the values observed for the AC [symbol: see text] AC symmetric electrode system.