Synthesis Of Transition Metal Compounds And Research Of Energy Storage Properties

Benefiting from the high energy density,high safety,long lifespan and no memory effect,lithium ion batteries(LIBs)are regarded as most promising energy storage device and dominate the market of portable electronic products.However,the rapid updating of the electronic products and the rapid development of the electric vehicles provide higher demands to the LIBs.Thus,it is necessary to develop new generation LIBs with high energy density and high-power density to meet the market demands.Besides,the cost-effectively sodium ion batteries(NIBs)have enormous potential in the large-scale energy storage systems,which arouse the interests to develop high performance NIBs as well.In general,anode materials have great influence on the property of the battery.So it is important to explore alternative anode to improve the properties of LIBs/NIBs.Transition metal dichalacodenides(TMDs)have typical layer structure,which is benefiting for the fast insertion and diffusion of the lithium/sodium ions.Usually,TMDs can provide higher capacity than commercial graphite.Besides,transition metal phosphide(TMP)have higher capacity and low intercalation potential.As a consequence,TMDs and TMP are considered as the potential anode materials.However,the electrochemically-induced volume expansion and low conductivity hinder the development of the TMDs and TMP.This thesis has modified the energy storage properties of TMDs and TMP though various methods.Chapter 1 introduces the backgrounds and principles of the LIBs/NIBs.Various anode materials with different energy storage mechanisms are described.And the development of TMDs and TMP are described in detail.The research backgrounds and contents are presented in the last part of this chapter.Chapter 2 describes the reagents,instruments and characterization methods applied in the thesis.Chapter 3 introduces the reduced graphene oxide-coated NbSe3 nanobelts(NbSe3@rGO),which are synthesized by the solid-state reaction and PDDA-assisted method.The rGO not only increase the conductivity,but also accommodate the volume expansion.As a result,the lithium storage property of NbSe3@rGO is enhanced.Besides,the influence of the graphene content on the electrochemical performance is investigated.In the chapter 4,we synthesize the free-standing WSe2/C hybrid nanofiber by the means of electrospinning and selenization process.The peculiar structure with three-dimensional cross-linked network provides stable structure and multichannels for ions diffusion.The application of the C increases the electronic conductivity and suppress the aggregation and restack of WSe2,leading to the improvement of the structure stability.As a consequence,the lithium/sodium storage properties of WSe2/C are enhanced obviously.Especially in lithium-ion batteries,the WSe2/C delivers larger capacity/superior rate capability/ultra-long lifespan(257mAh/g after 10000 cycles at the high rate of 25 A/g).The in situ TEM is utilized to monitor the structure change of the WSe2/C single nanofiber during lithiation-delithiation process.And the result clarifies that the volume expansion of the WSe2/C during electrochemical process is small.In the chapter 5,two types of transition metal phosphides,Cu3P and Co2P,are hybridized with N-doped carbon(demoted as Cu3P-Co2P/N-C)via electrospinning and phosphorization methods.The free-standing Cu3P-Co2P/N-C can work as anode electrode in LIBs/NIBs directively,which avoid the exfoliation of the active material from the collector.Combining with the advantages of various components and their synergistic effect,the energy storage performances are enhanced.In the LIBs,the specific capacity around 316.9 mAh/g is kept after 2000 cycles at 5 A/g.Chapter 6 summarizes the contents of this thesis and provides the prospective.