Study On The Preparation Of Activated Carbon/nano-carbon Hybrid Material By Chemical Activation

Activated carbon has abundant porous structure, and nano-carbon suchas carbon nanowalls and carbon nanotubes has special physical and chemicalproperties. Attempt has been made to prepare new types of carbon materialwith hierarchical structure and to make sure it can share the advantages ofcarbon material and nano-carbon material by controlling the experimentconditions. In this thesis, activated carbon/carbon nanowalls hybrid materialand activated carbon/carbon nanotubes hybrid material were successfullysynthesised in-situ by chemical activation with KOH from pitch by mixingcobalt compound. It is the first time to prepare carbon nanowalls by chemicalactivation. The effect of the experiment conditions on the morphologiestructure and properties of activated carbon was investigated. The growthmechanics of the activated carbon/nanocarbon hybrid material was discussedin the thesis. These activated carbon/nanocarbon hybrid material were used aselectrode materials for electric double-layer capacitor(EDLC)and lithium ionbatteries, and the energy storage mechanism was explained. Main work is summarized as following:1. The effect of pretreatment (preoxidized, precarbonized andpreoxidized-precarbonized) the kind and ratio of boron compound theration of KOH the kind and ratio of cobalt compound activation temperatureon the nano-carbon structure were investigated systematically. The resultsshows:(1) Precarbonized-activated method and prexidized-activated methodprepared lots of carbon nanowalls and carbon nanotubes;(2) The reason forthe formation of nano-carbon structure is not boron. Carbon nanowallsgrowed by mixing NaBH4with pitch attributing to H2produced by NaBH4during activation. Too much NaBH4was bad for the formation of carbonnanostructure;(3) Best ratio of KOH to prepare nano-carbon corresponded tothe ratio of cobalt. When the ratio of cobalt was not invariant, the content ofcarbon nonawalls increased first and then decreased with the increasing of theratio of KOH. When the ratio of cobalt changed, the ratio of KOH also had tochange to prepare nanocarbon;(4) Compared to the cobalt acetate, Co(OH)2nanoparticles was better for the growth of nano-carbon;(5)900℃was thebest activation temperature for the formation of nano-carbon structure.2. Activated carbon/carbon nanotubes hybrid material (AC/CNTs) andactivated carbon/carbon nanowalls hybrid material (AC/CNWs) weresuccessfully synthesized. Activated carbon/carbon nanotubes hybrid materialhad a lot of carbon nanotubes (CNTs), the diameter of CNWs was in therange of100~350nm, the length of CNTs was in the range of10~25m. Activated carbon/carbon nanowalls hybrid material had a lot of carbonnanowalls(CNWs), the thickness of CNWs was in the range of15~20nm, thewidth of CNWs was in the range of15~20nm3. Nano-carbon can growed by chemical activation with KOH frompitch, and in this thesis the growth mechanics of the new scientificphenomenon was discussed after lots of experiments: graphitic crystallitesand fragmented graphitic layers with different dimensions were formedduring chemical activation by KOH, and then the adjacent fragmentedgraphitic layers tend to connect together by cobalt nanoparticles catalyst.When fragmented graphitic layers were large and the cobalt nanoparticleswere large, carbon nanowalls growed. When fragmented graphitic layers weresmall and cobalt nanoparticles were small, carbon nanotubes growed.4. The AC/CNWs was used as electrode materials for electricdouble-layer capacitor (EDLC) and lithium ion batteries for the first time.When it was used in EDLC, the results showed that at a current density of0.02A/g and5A/g, discharge specific capacitance was143F/g and116F/grespectively. AC/CNWs also showed good cycling performance. When it wasdischarged at the current density of0.1A/g for100cycles, its specificcapacitance was up to140F/g. When AC/CNWs used in lithium ion batteries,the percentage of irreversible capacity at the first cycle was large. Reversiblecapacity was up to91mAh/g at2C after100cycles.5. The AC/CNTs was used as electrode materials for EDLC. It was found that when the current density was0.02A/g and2A/g, the specificcapacitance was184F/g and140F/g respectively. AC/CNTs showed goodcycling stability performance. The specific capacitance was158F/g at thecurrent density of0.1A/g for100cycles.6. Two series of carbon/nanotubes/graphite hybrid material wereprepared. They were used as electrode materials for lithium ion batteries. Thecycling behaviour and rate capability of the carbon/nanotubes/graphite hybridmaterial and graphite were compared. It was found that both of the two seriesof carbon/nanotubes/graphite hybrid material showed better electrochemicalperformance than graphite. The sample of using graphite and Co/pitch as rawmaterial improved remarkably rate capability. It exhibited an excellent ratecapability with a reversible capacity of274mAh/g at2C after100cycles.