| Lithium ion battery cathode material olivine-type lithium iron phosphate has advantages of environment friendly,low price,rich source of raw materials,the characteristics of high specific energy and safety performance.It is one of the most potential lithium ion battery cathode material.But lithium ion battery cathode material olivine-type LiFePO4 has its disadvantages.First,because it has the smaller bulk density and low specific capacity,the volume of the lithium ion battery is relatively larger.Second,it has smaller ion diffusion coefficient and lower conductivity.Electrical conductivity of the materials is related to magnetic and hole-type polaron.On the one hand,there is a related law between the spin of hole in olivine-type lithium iron phosphate and ferric iron cation(Fe3+)electronic structure of the(tg↑)3(eg↑)2.On the other hand,because bivalent iron cation(Fe2+)electronic structure of the(tg↑)3(eg↑)2 tg has double exchange mechanism of ferromagnetic coupling,lost electronics will cause extremely sub-type distortion.Then it can produce the spin polarization charge cloud.In this article,the method with which composite materials were synthesised is the sol-gel method that its operation is simple and we can more easily control the synthesis conditions and get smaller particle.Lithium iron phosphate carbon composite material was synthesised by one step sol-gel method.The metal elemental copper and lithium iron phosphate carbon composite material was synthesised by two step sol-gel method.AxOy type metal oxide(manganese dioxide,oxidation aluminium)and olivine type lithium iron phosphate carbon composite material was synthesised by two step sol-gel method.We studied the thermal characteristics from synthetic process of samples,phase structure,functional group and chemical bonds,microscopic surface morphology and magnetic properties of composite material by using TG,XRD,FTIR,SEM and VSM methods.The main research results and innovation points are as follows:1.LiFePO4/C composite materials that were prepared through using five different carbon sources which were ethylene glycol,polyethylene glycol(4000),polyvinyl alcohol(PVA-124),monohydrate citric acid and glucose,by sol gel method,were researched to reveal the effects of different carbon sources on the lithium iron phosphate composite materials.XRD showed that the samples were olivine lithium iron phosphate.SEM showed that the sample that its carbon source was ethylene glycol had porous structure,and another sample that its carbon source was glucose had the size of 40 microns.VSM research revealed that,on the one hand,relative saturation magnetization intensity of samples with polyvinyl alcohol(PVA-124)as the carbon source were largest and it was 2.01 emu/g,on the other hand,coercive force of samples with ethylene glycol as the carbon source were largest and it was 170.67 Oe.2.The effects of Cu and lithium iron phosphate composite materials were studied.First,Cu and lithium iron phosphate composite materials of different mass ratio were prepared by two-step sol-gel.Second,thermal characteristics,phase structure,functional group and chemical bonds,microscopic surface morphology and magnetic properties of Cu and lithium iron phosphate composite materials samples were studied,by TG,XRD,FTIR,SEM and VSM method.The TG showed that composite precursor transformed into Cu and lithium iron phosphate composite materials samples after heating 400℃.Composite materials phase structure analysis appeared the lithium iron phosphate and Cu main peaks and no obvious impurity peaks.Microstructure SEM analysis indicated that the composite materials granularity,good dispersivity was obvious and the main particle size was 400 nm.Hysteresis loop test at room temperature showed that the introduction of the Cu made the Ms(emu/g),Mr(emu/g)and the Area of hysteresis loop(kOe·emu/g)of the composite materials were tiny decreased.3.The effects of manganese dioxide and lithium iron phosphate composite materials were studied.First,Manganese dioxide and lithium iron phosphate composite materials of different mass ratio were prepared by two-step sol-gel.Second,thermal characteristics,phase structure,functional group and chemical bonds,microscopic surface morphology and magnetic properties of manganese dioxide and lithium iron phosphate composite materials samples were studied.by TG,XRD,FTIR,SEM and VSM method.The TG showed that composite precursor transformed into manganese dioxide and lithium iron phosphate composite materials samples after heating 400℃.Composite materials phase structure analysis appeared the lithium iron phosphate and manganese dioxide main peaks and no obvious impurity peaks.Microstructure SEM analysis indicated that the composite materials granularity,good dispersivity was obvious and the main particle size was 168 nm.Hysteresis loop test at room temperature showed that the introduction of the manganese dioxide made the Ms(emu/g),Mr(emu/g)and the Area of hysteresis loop(kOe·emu/g)of the composite materials were basically increased with the increase of manganese dioxide.4.The effects of Al2O3 and lithium iron phosphate composite materials were studied.First,Al2O3 and lithium iron phosphate composite materials of different mass ratio were prepared by two-step sol-gel.Second,thermal characteristics,phase structure,functional group and chemical bonds,microscopic surface morphology and magnetic properties of Al2O3 and lithium iron phosphate composite materials samples were studied.by TG,XRD,FTIR,SEM and VSM method.The TG showed that composite precursor transformed into Al2O3 and lithium iron phosphate composite materials samples after heating 450℃.Composite materials phase structure analysis appeared the lithium iron phosphate and Al2O3 main peaks and no obvious impurity peaks.Microstructure SEM analysis indicated that the composite materials granularity,good dispersivity was obvious and the main particle size was 350 nm.Hysteresis loop test at room temperature showed that the introduction of the Al2O3 made the Ms(emu/g),Mr(emu/g)and the Area of hysteresis loop(kOe·emu/g)of the composite materials were tiny change. |
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