| Because lithium ion battery has large energy density, high working voltage, longcycle life and also is environmental friendly, now it has become the best performancebattery system. Because of its excellent characteristics, graphite is widely used aslithium ion battery anodes material, but there are still problems such as poorcompatibility with solvent, low reversible capacity for the first charge and discharge,and short cycle life. According to the above defects, combined with the previousmethods, the modification of graphite anode materials is studied in this paper.Graphite oxide was prepared by the method of the improved hummers method,introducing oxygen containing functional groups to the graphite layers. The respectiveeffect of oxidant on the microstructure of the graphite oxide was determined includingconcentrated sulfuric acid, potassium permanganate and hydrogen peroxid through thesingle factor experiment. Combined with XRD and FTIR analysis results, the bestadding quantities of three kinds of oxidants were determined as follows:200ml H2SO4,KMnO420g, H2O225ml. The SEM image of the graphite oxide showed that it wasgathered by the transparent sheet with fold structure loose of overlap. The XRD spectrashowed that the characteristic peak of graphite oxide appeared near11°, and the layerspacing was0.8036nm. Ir spectra proved that there were a lot of polarityoxygen-containing groups on the surface of graphite oxide. Laser particle size test resultshowed that D50was13.67um and D90was5.09um. Graphite oxide had a narrowparticle size distribution and basic standard normal distribution.Under the action of ultrasonic, citric acid iron was introduced into the graphiteoxide layer to prepared graphite oxide/ferric citrate precursor material. The r–GO/Fe3O4composite materials was prepared by heat treatment in the nitrogen atmospheretube furnace. The influence of citric acid iron content, calcination temperature andthermal insulation time on the microstructure and battery performance of the materialwas studied. The experiment results showed that: when the citric acid iron content was1.0g, calcination temperature was650℃, and thermal insulation time for preparationwas2h, r-GO/Fe3O4composite battery performance was the best. The charge anddischarge specific capacity were respectively418.905mAh/g and519.817mAh/g, andthe coulomb efficiency for the first time was up to80.7%. After20cycles, the charge and discharge specific capacity of the sample changed from the original418.905mAh/gto393.316mAh/g, and after20cycles the capacity retention rate was as high as72.7%.Polyaniline was prepared on graphite/citric acid iron oxide precursor materials byin situ polymerization method. The amount of polyaniline coated was changed bychanging the dosage of aniline, and the influence of polyaniline coating treatment on thematerial structure and the battery performance was indirectly explored. XRD resultsshowed that polyaniline was coated in the surface of r-GO/Fe3O4composite materialwith amorphous type. By comparing the material charge and discharge curves for thefirst time, and it can be known that after polyaniline coated, charge and dischargespecific capacity and coulomb efficiency of the material had the been obviouslyimproved. When the dosage of aniline was0.15mol, the first charge and dischargespecific capacity reached569.332mAh/g and655.720mAh/g, the reversible capacity ofmaterial for the first time reached the largest and the first charge and dischargeefficiency reached86.8%. After20cycles, material circulation efficiency was above96%and capacity retention rate reached91.2%.Compared with pure graphite anode, r-GO/Fe3O4composite material coated withpolyaniline shows higher specific capacity and more excellent cycle performance andcan be used as potential lithium ion battery anode materials. |
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