Fabrication Of Self-supporting Nanocomposite High-capacity Electrode Materials And Their Electrochemical Energy Storage Properties

The thorough transformation of the energy structure has proceeded at a furious pace in response to the global energy crisis and environment degradation. People constantly pursue portable, entertaining and health-oriented electronic equipment, miniaturized precision electronic devices plus comfortable and pollution-free electric automobile with enhanced development of science and technology. Traditional rechargeable batteries cannot meet the demand of new generation of electronic devices because of their shortcomings like low specific capacities, slow charge/discharge rates, short lifespans, heaviness, inflexibility, high price and so on. Hence, it is of utmost urgency to develop neotype energy storage devices in the directions of ultrahigh specific energy, super long cycle life, fast charge/discharge rates, lightweight, softness, hygiene, safety, etc.New-style self-supporteding electrode materials as well as their composite materials can avoid utilizing conventional binderas and conductive additives, not only saving the resources and lowering the cost but also reducing multiple processing steps. The removal of current collectors reduces the weight and volumes of full batteries to a largeextent. The combinative capability of electrode material and self-supported materials endows excellent conductivity, which is superior to that of those materials prepared by traditional coating methods by far. thus self-supporting materials are prominent in the aspects of structure stability and conductivity. Suitable self-supporting materials can also produce flexible electrode materials that possess favorable flexibility and mechanical properties, laying a foundation for the new generation of flexible energy storage devices. This dissertation focuses on the fabrication and properties of high-capacity self-supporting nanocomposite electrode materials. The main contents are as follows:(1) Fabrication of hierarchical Sb@C composite materials:a hierarchically porous Sb@C composite material has been obtained by a facile "impregnation-ripening-calcination" method using cotton fabric as self-supporting substrates and templates. ultrafine Sb nanoparticles are uniformly embedded in the carbon matrices, throught a low-concentration precursor solution layer-by-layer impregnation synthesis route. Our method avoid the formation of large particles are normally obtained by high-concentration precursors soaking. The resulting composite materials have replicated the frame of intertwined carbon fabric that is structurally integrated, so they could be directly applied as electrode materials for assembling batteries without using binders, conductive additives or current collectors. Sb@C composite materials can gain a high capacity of about660mAh g-1and have a capacity retention of nearly100%after300charge/discharge cycles. Compared with traditional coating method, this present route is simple, low-cost and scalable.(2) Flexible lithium-ion batteries based on flexible MnO-rGO thin films:flexible and self-supporting MnO-rGO thin films have synthesized by a simple "complexation-film-reduction" route. Ultrathin graphene layers and ultrafine MnO nanoparticles are formed as a layer-by-layer three-dimensional hierarchical architeture. This compact structure with fine mechanical properties and flexibility can be straightly utilized as the anodes for lithium-ion batteries. The combination of ultrafine nanoparticles and graphene leads to a interconnected network that is beneficial to the transport of electrons and ions. The unique layer-by-layer structure effectively restrains structural damage caused by volume effect in charge/discharge cycles. Therefore, this flexible MnO-rGO thin films shows extraordinary electrochemical properties. A flexible lithium-ion battery assembled with a commercial lithium colbalt oxides material and a flexible MnO-rGO thin film displays discharge specific capacity as high as1000mAh g-1during deep charge/discharge cycles, and the specific capacity keeps stable after200charge/discharge cycles. This battery could lighten over one hundred commercial LED lights with ease, and the LED lights are not affected during the bending test of the battery.(3) Flexible MOx-rGO (M=Co, Mo, Sn) thin film materials synthesized by a general method:several flexible MOx-rGO thin films materials have been prepared by controlling polar solutions, reduction atmospheres and calcination temperatures according the precursor’s properties based on a "complexation-film-reduction" route. This route is designable, general and maneuverable. We have explored the dependence of the particle size of the product on the polarity of the precursor solution. The layer-by-layer three-dimensional porous thin film offers the active matericals of CoO, MoO2and Sn with a huge clinging space and a buffering space to relieve volume change during charge/discharge cycles.(4) Flexible Sb-rGO//NVP-rGO sodium-ion full battery:Flexible power sources have shown great promise in next-generation bendable, implantable, and wearable electronic systems. Here we report on flexible and binder-free electrodes of Na3V2(PO4)3/reduced graphene oxide (NVP/rGO) and Sb/reduced graphene oxide (Sb/rGO) nanocomposites for sodium-ion batteries. The Sb/rGO and NVP/rGO paper electrodes with high flexibility and tailorability can be easily fabricated. Sb and NVP nanoparticles are embedded homogenously in the inter-connected framework of rGO nanosheets, which provides structurally stable hosts for Na-ion intercalation and deintercalation. The NVP/rGO paper-like cathode delivers a reversible capacity of113mAh g-1at100mA g-1and high capacity retention of-96.6%after120cycles. The Sb/rGO paper-like anode gives a highly reversible capacity of612mAh g-1at100mA g-1, an excellent rate capacity up to30C, and a good cycle performance. Moreover, the sodium-ion full cell of NVP/rGO//Sb/rGO has been fabricated, delivering a highly reversible capacity of～400mAh g-1at a current density of100mA g-1after100charge/discharge cycles. This work may provide promising electrode candidates for developing next-generation energy-storage devices with high capacity and long cycle life.