Preparation And Modification Of Lower-temperature-carbonized Microsphere For Lithium Ion Battery Anode Material

As a new type of chemical power source, Lithium ion battery has a lot ofadvantages, such as high working voltage, high specific energy, discharge voltagesteady, low self discharge, long cycle life, low temperature performance, no memoryand no pollution, etc. It can meet the need for portable electrical battery. Small,lightweight and environmental friendly is conducive to the dual requirements, it iswidely used in mobile, laptop and other small electronic devices, and also it wouldbe the ideal power supply for electric vehicles in the future. Anode material is amajor component of the lithium ion batteries, which affects the battery performancedirectly, so high-capacity, reliable cyclic performances of anode materials become aresearch focus. Graphite is the mainstream of commercial anode material, but due tothe structural characteristics of graphite, the development of graphite anode materialshave encountered limitation, such as it cannot meet the requirement of specificcapacity and the continuous high-current discharge capacity for large-scale powerbattery, etc., so hard carbon and non-carbon material attract attention. The hardcarbon material shows better performance in terms of cycle life and safety, andinexpensive, non-toxic, so it has a strong significance.Lower-Temperature-Carbonized Microsphere is a kind of amorphous, hardcarbon sphere. The preparation is as follows:(1) polyacrylonitrile (PAN) spheresprepared by emulsion polymerization;(2)Lower-Temperature-CarbonizedMicrosphere prepared by dealing PAN spheres across pre-oxidation andcarbonization at low temperature. As the size of material is uniform and controllable,the method is low-cost, environmental friendly and sustainable large-scaleproduction. In the paper, Lower-Temperature-Carbonized Microspheres were used aslithium ion battery anode material, and study the effects on electrochemicalperformance about carbonization temperature, performance of conductive agent,pore-forming by calcium carbonate (CaCO3), doping lithium carbonate (Li2CO3) anddoping silicon powder (Si).The main work is as follows:1. The effects of carbonization temperature (from500℃to900℃) on theelectrochemical performance were studied. The results revealed that, thedegree of graphitization increased with carbonization temperature increasing, electrical conductivity is also improved. And the capacitydecreased gradually, cycle stability increased. When the carbonizationtemperature is600℃, the cycle performance was greatly improved, theinitial charging capacity reached383.62mAh/g, and still remained310mAh/g after50cycles.2. The effects of the shape and dispersion of conductive agent on theelectrochemical performance of carbon microspheres was studied, and theconductive agent are conductive carbon black, dispersive carbon nanotubesand carbon nanotube powder. Results showed that, carbon nanotubes isbetter to the form the space network structure, the initial charging capacityreached410mAh/g, which was better than383mAh/g of conductivecarbon black, and the initial charging capacity of dispersive carbonnanotubes reached455mAh/g, and it still remained360mAh/g after50cycles.3. The effects of morphology, specific surface area and the percents of pore incarbon spheres on the electrochemical properties were studied, and thecarbon microspheres dealt with pore-forming when Calcium carbonate(CaCO3) used as template agent. Results revealed that it has obvious effectbefore or after carbonization to etch template agent, especially thepercentage of microporous in carbon microspheres. Carbon microsphereswhich etched after carbonizing, the initial charging capacity reached620mAh/g, it still remained520mAh/g after50cycles, has obviousimprovement comparing with untreated carbon microspheres.4. The effects of the mounts of lithium carbonate on the electrochemicalperformance of carbon microspheres was studied, and lithium carbonatedoped by direct method and emulsion polymerization. The result showedthat lithium carbonate doped into carbon spheres by direct method,carbonic acid lithium would form on surface and micropore, it is benefit toforming of the SEI film, when the amount of lithium carbonate was4%, theelectrochemical properties is better, the initial charging capacity reached505mAh/g. while carbonate lithium doped by emulsion polymerization,the micropore would not be covered, the SEI film still formed on thesurface. When the amount of lithium carbonate was2%(lithium carbonatein carbon microspheres was3.4%), the electrochemical performance is the best, the initial charging capacity reached530mAh/g, it remained440mAh/g after50cycles.5. The effects of the content of silicon in silicon carbon composite on theelectrochemical performance was studied, and C-Si composite prepared asfollows: PAN-Si composite was prepared by seed emulsion polymerizationwhile silicon powder as seeds and acrylonitrile as monomer, andsilicon-carbon composite prepared after carbonizing PAN-Si composite,The results showed that the initial capacity increased with the increasing ofthe content of silicon composites, cycle performance decreased, it wasmore obvious under different current density. When the content of siliconwas5%(the content of silicon in silicon-carbon composite was7.5%), theelectrochemical performance is the best, it still remained570mA/g after50cycles, indicating excellent cycle performance and high specific capacity.