| The artificial graphite wastes with different resources of raw materials and initialgraphitization degrees were selected as the research objects. They were graphitized atdifferent temperatures. The structural transformation laws of graphite microcrystallitein the further graphitization process were investigated. The relationships between themicrostructures and the charge and discharge performances of artificial graphite werediscussed. And the influences of the heat treatment temperature, holding time andvacuum technology on the microstructure and the true density were also researched.The working principle and the structure characteristics of the Acheson andLengthwise graphitization furnaces were compared. The imagination of theapplication of lengthwise graphitization furnace to the graphitization treatment of theartificial graphite anode for lithium ion batteries was put forwarded. The artificialgraphite powders after surface shaping, classification and carbon coated were furthergraphitized by using a industrial lengthwise graphitization furnace. The influences ofthe materials, sizes of container, distribution of temperature and the graphitizationtechnologies on the properties of products were researched. The negative pressuretransformation system was applied to decrease the energy consumption and avoid thesecondary pollution.The main experimental results were given as follows:Two artificial graphite scraps PCG (petroleum coke) and NCG (needle coke) withlow initial graphitization degrees of75.93%and83.14%were further graphitized inthe temperature range of2400℃~3000℃. The structural transformation laws ofgraphite microcrystallite in the heat treatment process were investigated. Therelationships between the microstructures and the charge and discharge performancesof artificial graphite were discussed. Results show that different graphite scrapspossess similar behaviors of structural transformation. The graphitization degree Gand the sizes of microcrystallite Lc, Laand V increase with the increasing of heattreatment temperature and d002drops at the same time. The graphite crystallite growsfaster in the base plane direction than in the vertical direction. The increasing speedsof Lc, Laand V of the artificial graphite microcrystallite and their initialgraphitization degree are close contact. The increasing rates of graphite materials withlow initial graphitization degree are a bit higher than those of samples with high value of G. The difficulty levels of the aggregates places great influences on the structuralparameters and electrochemical performances of artificial graphite scraps. Thedischarge capacities of artificial graphite scarps samples with same aggregate are welllinear fitted with their crystallite parameters. However, the correlation coefficientdecrease when the discharge capacities and structural parameters of artificial graphitescraps are fitted together. It can be seen the improvement of the graphitization degreeand the discharge capacity of graphite scarps anode can be achieved by increase theheat treatment temperature of further graphitization.Two artificial graphite scraps CGM and HAG with high initial graphitizationdegrees of92.79%and88.72%were further graphitized in the temperature range of2400℃~3000℃. The influences of the heat treatment temperature, holding timeand the vacuum technology on the microcrystallite and true density of artificialgraphite were investigated. The charge and discharge performances of graphite withwell developed structure at large current were discussed. Experimental results showthat the graphitization degree of the artificial graphite with high initial value ofdegree can also be improved after the further graphitization. Measures, such asincrease heat treatment temperature, prolong the holding time and treat it undervacuum conditions, can improve the growth of the graphite microcrystallite insamples and make the graphene planes pack more regular. The true density of sampleCGM-3000-0reach2.226g/cm3and the graphitization degree increase to94.19%,which are very close to those of the theoretical graphite. And the graphitizationdegree of sample HAG-3000-0increase from88.72%to90.00%and its true densityis2.178g/cm3. The relationships between the charge and discharge capacity and thegraphitization degree of samples CGM and HAG with high degree value still conformto the supposed linearity regression equation. The differences between the actualdetermination value and the predict data according to the equation are very small.Sample CGM-3000-0possesses excellent charge and discharge performancesespecially at large current density. Its discharge capacities at15mA/g and350mA/gare as high as344.2mAh/g and273.2mAh/g respectively.The artificial graphite powders after surface shaped, classified and carbon coatedwere further graphitized by using a industrial lengthwise graphitization furnace. Theinfluences of the materials, sizes of container, distribution of temperature and thegraphitization technologies on the properties of products were researched. Thefeasibility of the application of the lengthwise furnace to the graphitized treatment ofgraphite anode for lithium ion batteries was discussed. Results show that the lengthwise technology can be applied to the high temperature heat treatment of theartificial graphite powders. The temperature distributions of the lengthwise furnaceare uniform. The ideal products can be manufactured by using appropriate assemblyfurnace method and power transmission project. The heating rate at the earlier stageplays little effect the properties of products. However, prolonging the time of highpower can effectively improve the properties and the homogeneity of products. Thecylindrical multi holes crucible can heat the powders effectively, which possessesbetter distribution of temperature and the uniformity of products than those of singleholes crucible. However, the properties of products in the core part of crucible dropsevidently. It is difficult to be removed even by prolong the holding time at high power.The usage of negative pressure system can realize the effective transportation ofpowders and decrease the possibilities of secondary pollution. |
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