Large-scale fabrication of re duce d graphene oxide-sulfur composite films for flexible lithium-sulfur batteries

The rapid development of flexible electronic devices requires the design of flexible energy-storage devices. Lithium-sulfur(Li-S) batteries are attracting much interest due to their high energy density. Therefore, flexible Li-S batteries with high areal capacity are desired. Herein, we fabricated freestanding reduced graphene oxide-sulfur(RGO@S) composite films with a cross-linked structure using a blade coating technique, followed by a subsequent chemical reduction. The porous cross-linked structure endows the composite films with excellent electrochemical performance. The batteries based on RGO@S composite films could exhibit a high discharge capacity of 1381 m Ah/g at 0.1 C and excellent cycle stability. Furthermore, the freestanding composite film possesses excellent conductivity and high mechanical strength. Therefore, they can be used as the cathodes of flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled and remained stable electrochemical performance under different bending states.

Sulfur nanoparticles encapsulated in reduced graphene oxide nanotubes for flexible lithium-sulfur batteries

Rapid development of flexible electronic devices is promoting the design of flexible energy-storage devices. Lithium-sulfur （Li-S） batteries are considered as promising candidates for high energy density energy-storage devices. Therefore, flexible Li-S batteries are desired. In this study, we fabricated composite films of freestanding reduced graphene oxide nanotubes wrapped sulfur nanoparticles （RGONTs@S） by pressing RGONTs@S composite foams, which were synthesized by combining cold quenching with freeze-drying and a subsequent reduction process. These RGONTs@S composite films can serve as self-supporting cathodes for Li-S batteries without additional binders and conductive agents. Their interconnected tubular structure allows easy electron transport throughout the network and helps to confine the polysulfides produced during the charge/ discharge process. As a result, the RGONTs@S composite films exhibited a high initial specific capacity, remarkable cycling stabilit36 and excellent rate capability. More importantly, the RGONTs@S composite films can serve as electrodes in flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled using these electrodes and they displayed stable electrochemical performance at different bending states.

Application and structure of carbon nanotube and graphene-based flexible electrode materials and assembly modes of flexible lithium-ion batteries toward different functions

In recent years,the rapid development of portable/wearable electronics has created an urgent need for the development of flexible energy storage devices.Flexible lithium-ion batteries(FLIBs)have emerged as the most attractive and versatile flexible electronic storage devices available.Carbon nanotubes(CNTs)are hollow-structured tubular nanomaterials with high electrical conductivity,large specific surface area,and excellent mechanical properties.Graphene(G)is to some extent comparable to CNTs,because both have unlimited value in flexible electrodes.Herein,a systematic summary of the application of CNT and G in FLIBs electrodes is presented,including different functional applications and services at different temperatures.Furthermore,the effects of electrode structures,including powder,wire-shaped,and film-shaped structures,on electrochemical properties is highlighted.The assembly structures of the FLIBs consisting of CNT and G-based flexible electrodes to realize different functions,including bendability,stretchability,foldability,self-healing,and self-detecting,are systematically reviewed.The current challenges and development prospects of flexible CNT and G-based flexible electrodes and corresponding FLIBs are discussed.

sp^(3)-like defect structure of hetero graphene-carbon nanotubes for promoting carrier transfer and stability

Three-dimensional(3 D) hybrid of nanocarbons is a very promising way to the high-performance design of electrocatalysis materials.However,sp^(3)-like defect structure,a combination of high strength and conduction of graphene and carbon nanotubes(CNTs) is rarely reported.Herein,3 D neural-like hybrids of graphene(from reduced graphene oxide) and carbon nanotubes(CNTs) have been integrated via sp^(3)-like defect structure by a hydrothermal approach.The sp^(3)-like defect structure endows 3 D nanocarbon hybrids with an enhanced carrier transfer,high structural stability,and electrocatalytic durability.The neural-like structure is shown to demonstrate a cascade effect of charges and significant performances regarding bio-electrocatalysis and lithium-sulfur energy storage.The concept and mechanism of "sp^(3)-like defect structure" are proposed at an atomic/nanoscale to clarify the generation of rational structure as well as the cascade electron transfer.

Current collectors based on multiwalled carbon-nanotubes and fewlayer graphene for enhancing the conversion process in scalable lithium-sulfur battery

We investigated herein the morphological,structural,and electrochemical features of electrodes using a sulfur(S)-super P carbon(SPC)composite(i.e.,S@SPC-73),and including few-layer graphene(FLG),multiwalled carbon nanotubes(MWCNTs),or a mixture of them within the current collector design.Furthermore,we studied the effect of two different electron-conducting agents,that is,SPC and FLG,used in the slurry for the electrode preparation.The supports have high structural crystallinity,while their morphologies are dependent on the type of material used.Cyclic voltammetry(CV)shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization.This activation process is verified by electrochemical impedance spectroscopy(EIS)with a decrease of the resistance after the first CV scan.Furthermore,CV at increasing scan rates indicates a Li+diffusion coefficient(D)ranging between 10^(−9) and 10^(−7) cm^(2)·s^(−1)in the various states of charge of the cell,and the highest D value for the electrodes using FLG as electron-conducting agent.Galvanostatic tests performed at constant current of C/5(1 C=1675 mA·g_(s)^(−1))show high initial specific capacity values,which decrease during the initial cycles due to a partial loss of the active material,and subsequently increase due to the activation process.All the electrodes show a Coulombic efficiency higher than 97%upon the initial cycles,and a retention strongly dependent on the electrode formulation.Therefore,this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology,mechanical stability,and promising electrochemical performance in practical Li-S cells.

柔性锂离子电池负极材料研究进展

柔性锂离子电池越来越受到人们的关注,本文主要介绍了柔性锂离子电池负极材料的研究进展。柔性负极材料主要包括碳纳米管基、石墨烯基、纳米炭纤维基及炭布基等几类,本文对这几类柔性负极材料的特点及研究方法作了介绍。最后,对目前柔性锂离子电池负极材料存在的问题进行了总结,对于这些问题的克服即是将来的研究方向。

碳基柔性电极的结构设计、制备和组装

柔性电子器件日益流行,给人们的日常生活带来了巨大的变革,同时也激发了柔性储能器件的设计和研制,其中,柔性锂离子电池引起了广泛的关注.为了获得柔性储能器件,首先需要制备柔性电极,即要求在反复变形状态下,电极能够保持优异的力学和电学性能.碳材料具有优异的力学性能和导电性,不仅能够直接制备柔性电极,还能够与活性材料复合,作为基底提供自支撑的导电网络.但是"刚性"的活性材料与"柔性"基底从力学和形态本质上均不匹配,二者的复合、组装、制备方法及其结合强度直接影响电池的电化学性能.本文综述了近年来碳纳米管、碳纳米线、石墨烯、石墨炔及碳布等碳基柔性电极的发展情况,着重分析了自支撑柔性电极的制备方法、结构特征与电化学性能的关系,同时简要总结了目前几种典型结构的柔性锂离子电池,探讨了碳材料柔性电极面临的挑战,并对其未来发展方向进行了展望.