Improving Carbon Anodes Of Lithium-ion Battery By Combined Methods

Lithium-ion battery has mushroomed the most rapidly during the past few years, because it meets the development requirements of modem information technology such as high capacity and small volume. There is great potential in improving disordered carbon anodes, in order to improve the properties of lithium- ion battery. The paper reviewed a lot of literature about lithium storage mechanism in carbon and methods improving carbon anodes. It was found that the role of surface played in Li storage was not exsert sufficiently and the improving methods were singleness, due to the mechanism limitation that the more surface area of carbon is, the more the irreversible capacity of carbon is. We firstly used the combined methods to improve anodes of petroleum coke, starting with activation to form sufficient surface area and then deposition to reduce apparent surface area, in order to exsert sufficiently the role of surface played in Li storage, and to improve properties of lithium-ion battery. The activation includes gas and chemical activation, and the deposition includes chemical vapor deposition of benzene and resin deposition of bakelite. The electrochemical properties of the carbon anodes were investigated using a there- electrode cell in an argon dry-box. The electrolyte was 1M LiClO4 dissolved in a mixture of propylene carbonate and ethylene glycol dimethylether. The conclusions were as follow: Carbon anodes improved by combined methods of activation and deposition have better properties than those by single activation or deposition do. Especially, the discharge capacity and efficiency grow greatly when petroleum coke anode was improved by benzene deposition after chemical activation (KOH). Its discharge capacity reached 4O7mAhIg, exceeding the theoretic upper limit ofcapacity of graphite. Chemical activated carbon has Iarge sudece area (2532m'/g)and which was not generally thought to fit tO store lithium. Deposition makes itpossible to be used as carbon anode with high capacity. The influences ofdeposition conditions on the carbon activated fOr 90 min were investigated. It wasindicated that the discharge capacity increases with deposition time, benzenevolume concentration, fiow-rate of deposition gas and paticular size. And theoptimum condition was also determined.The edge strUctUre of carbon layer of graPhitic crystallite (GC) plays animportant roIe in properties of carbon anodes. With the initial growth of carbonlayers, a new side surface fOrmed by edgc of carbon layers changescorrespondingly, which is not only beneficial fOr Li to go in and out the carbonlayers within GC, but also for Li tO store on the new sndce. The initial growth ofcarbon layer also goes with the decreases in content of unorganized carbon orstrUctUre flaw within carbon layer. A new formed side suffece and decrease incontent of unorganized carbon or smictore flaw within carbon layer makeproperties of carbon anode increase greatly. The improvement of edge strUcture ofcarbon lnyer of GC is precondition of activation, deposition and deposition afteractivation.A new model of graPhite crystallite including H atoms was established.Through this model, we can ca1culated many parameters such as surface area, sidesurface area and plane suthee area fOrmed by carbon layers, surface area betWeencarbon layers and H cont6nt. Using X-ray dibotion analyses (XRD), we can alsocalcuIate those parameters of carbon mentioned above, even fOr carbon with no002 peak in XRD patterns. It aIso provided an ideaI method to cstimate the reIativevalue of suffoce area of carbon material. Unlike other methods, for example, N2adsorption can't be applied to estimate sudsce area when POre diameter is toosmall, or surface are...