The Synthesis Of MTiS₃(M=Pb,Sn)/Graphene Oxide Compounds And The Research In Lithium Storage Performance

In the past three decades,the performance of secondary lithium-ion batteries(LIBs)have been significantly improved.However,the energy density of LIBs is still not sufficient for the mobile energy.In order to meet these needs,it is necessary to develop new electrode materials with higher rate capability and longer cycle life.In recent years,two-dimensional(2D)van der Waals(vd W)heterostructures have attracted attention in energy storage.A functional vd W heterojunction can be formed by stacking different 2D layers,which provides an excellent opportunity to construct high performance electrode materials.Misfit layer compound(MLC)is a unique 2D vd W heterojunction material.Nevertheless,the research of MLC as an electrode material is in its infancy.In this paper,two kinds of MLC materials,Pb Ti S₃(PTS)and Sn Ti S₃(STS)were prepared by chemical vapor transport method.Then PTS(or STS)and graphene oxide(GO)were used as raw materials,with the help of physical grinding to initiate the exfoliation of the bulk material,PTS(STS)/GO composite materials were successfully obtained.In addition,we also prepared a highly flexible STS-x%/GO free standing membrane by ultrasonic vacuum filtration method.On the basis of this,the electrochemical performance of the above three materials as an anode material for LIBs was systematically investigated.The specific research results are as follows:1?The PTS/GO composite with a larger specific surface area was obtained by physical grinding.The strong binding between GO and metal ions can promote the exfoliation of PTS bulk crystals and improve the stability of the electrode.Moreover,the PTS/GO composite can combine the advantages of soften Pb S layer and structural stability of Ti S₂layer,which is beneficial for the better electrochemical performance.Additionally,the in-situ electrochemical reduction of GO can improve the conductivity of the electrode.Therefore,the PTS/GO could deliver a high lithium storage capacity of 569 m A h g^-1 at the1000 cycles at 2.0 A g^-1.The assembled PTS/GO/Li(Ni_0.5Co_0.2Mn_0.3)O₂ full battery proves its practical application.It can deliver an initial discharge specific capacity of 218 m A h g^-1(at 0.1 A g^-1).Besides,there is 70%capacity retention after 100 cycles.At last,the full battery can successfully light up 85 light-emitting diodes.The results of in-situ X-ray diffraction indicate the reversible conversion-alloying reaction mechanism of PTS.2?Green chemistry requires eco-friendly and non-toxic.Similarly,lead-free STS/GO was synthesized by physical grinding.The strong binding between STS and GO can help to significantly reduce the crystal domain size of STS,therefore the synthesized STS/GO has a larger specific area.Meanwhile,the heterostructure Sn S/Ti S₂ has the advantages of the metal conductivity of Ti S₂and the high theoretical specific capacity of Sn S,which is conducive to achieving higher lithium storage performance.Futhermore,GO will undergo electrochemical reduction during the cycle,which can improve the conductivity of the framework.Thus,the STS/GO electrode exhibits stable cycling(at 2.0 A g^-1,the lithium storage capacity after 1000^th is 614 m A h g^-1),and excellent rate performance(The rate capacity at 3.0 A g^-1 is 534 m A h g^-1.)In-situ and ex-situ X-ray diffractions revealed the conversion-alloying mechanism of STS as LIBs anode.3?The highly flexible free-standing membrane STS-x%/GO was prepared by ultrasonic and vacuum filtration method.In the title membrane,the GO layer serves as a framework to support the membrane,buffering the volume expansion of STS.Additionally,the GO membrane will be reduced to r GO during the first cycle,which could improve the conductivity and enhance the electron transport capability.The STS can prevent the GO layer from being stacked tightly,which facilitate the infiltration of the electrolyte.Benefiting from the synergy effect between STS and GO,when the content of STS is 45%,the STS/GO membrane shows the best lithium storage performance.STS-45%/GO can deliver the specific capacity of 239 m A h g^-1 after 500 cycles at 1.0 A g^-1.After adding lithium salt(or surfactant)to the system,the GO layer can be further loosened.Thus,the electron transport and the diffusion of lithium ions can be improved.Among them,the addition of lithium carbonate can obviously improve the electrochemical performance.STS-45%/GO-Li₂CO₃ can deliver the the specific capacity of 635 m A h g^-1 after 500 cycles at 1.0 A g^-1,which is much higher than the specific capacity of the STS-45%/GO electrode.