Preparation Of Carbon Based Composites And Their Applications As Anode Material For Lithium/sodium Ion Batteries

Rechargeable lithium ion batteries(LIBs)have been widely used in electric vehicles,portable electronics and stationary energy storage due to their advantages of high energy,long lifespan,and environmental friendliness.However,considering the limited and unevenly distributed availability of Li deposits on the earth,LIBs have not been able to meet tremendous demand for large-scale storage systems for future.Rechargeable sodium ion batteries(SIBs),as an alternative to LIBs,have received increasing attention in recent years,owning to the natural abundance of sodium resources ubiquitous around the world and potential low cost.Nevertheless,fundamental problems still remain that severely hinder its practical application both LIBs and SIBs,including low electronic conductivity and large volume expansion during the Li+/Na+ insertion/extraction process.Hence,it is more challenging and urgent to develop efficient anode materials with higher discharge/charge capacities and better cycling behavior for application in LIBs and SIBs.Herein,in this paper,carbon-based composite electrode materials are designed and synthesized by adjusting the corresponding composition,morphology and structure.The electrochemical performance both LIBs and SIBs of carbon-based composite electrode materials are tested and analyzed.The contents of this paper as follows:(1)We used a thermal decomposition method to fill CNTs channels with Fe3O4 nanoparticles.SEM and TEM results confirm that the Fe3O4 nanoparticles in the CNTs channels(Fe3O4@CNT)were clearly observed to be cube-shaped and without any agglomeration.This nanostructure displayed voids that apparently effectively prevented active material from aggregating and helped to accommodate their volumetric expansion during the cycling process.As an anode material for LIBs,Fe3O4@CNT composite displays a stable cycling performance with a reversible capacity(720 mAh g-1)of after 200 discharge/charge cycles at the current density of 1 A g-1;As for the SIBs,a specific capacity of 377 mAh g-1 at 0.1 A g-1 was achieved after 300 cycles.The facile synthetic route and unique nanostructure design may be extended to high-performance anode materials for LIBs and SIBs.In addition,we assembled an LIB full cell with the Fe3O4@CNT nanocomposite as the anode and commercially available LiCoO2 as the cathode,and exhibited excellent electrochemical performance.(2)A 3D GR encapsulated with a hollow FeP@carbon nanocomposite(H-FeP@C@GR)was successfully synthesized via a combination of hydrothermal reaction,carbon coating process,phosphidation treatment,and carbothermic reaction.This 3D network structure can not only naturally accommodate the lithiation/sodiation-induced volume change but also offer more active sites for lithium/sodiumion insertion.As a result,when tested in LIBs and SIBs,the H-FeP@C@GR electrode yielded an excellent electrochemical performance in terms of reversibility,rate capacity,and cycling performance.Then,hierarchical FeP nanosheets internally wired by N-doped hollow carbon nanofibers(HCNFs@FeP)is rationally designed and synthesized via a combination of hydrothermal route and phosphidation treatment.And the electrochemical performance of the as-prepared HCNFs@FeP composite as an anode material for LIBs and SIBs were also studied.(3)3D-Si/GR composite was synthesized by a magnesiothermic reductionprocess using silica particles as the starting material.SEM and TEM characterization indicate the presence of the three-dimensional interconnected macroporous network in 3D-Si/GR composite,where the macropores are formed due to the removal of the unreacted silica particles by HF etching.When evaluated an anode material for LIBs,the as-synthesized 3D-Si/GR composite displays a discharge capacity of 888 mAh g-1 after 100 discharge/charge cycles at the current density of 0.2 A g-1.The excellent electrochemical performance of 3D-Si/GR composite can be attributed to the synergetic effects between Si network and grapheme.(4)3D interconnected NiS-GNS-CNT aerogels have been synthesized successfully by a simple hydrothermal method.SEM and TEM results confirm that NiS particles ranging from 150 nm to 250 nm uniformly and closely attached on the 3D network structure of GNS-CNT.In this unique 3D interconnected network structure,the hierarchical GNS-CNT architecture with good electrical conductivity and relatively large surface area can enhance the conductivity of NiS particles and effectively hinder the agglomeration of NiS particles during Li+ insertion and extraction process.Therefore,when used as anode material for half LIBs,NiS-GNS-CNT aerogels still have the reversible specific capacity of 732 mAh g-1 in the 350 th cycle at 0.5 A g-1.Most important of all,a new NiS-GNS-CNT//LiCoO2 full cell was successfully assembled,and exhibits excellent electrochemical performance.