| With more and more energy and environmental concerning,society need higherdemands of batteries.Lithium-ion batteries are widely commercial application fortheir distinctive advantages of high voltage and specific capacity,long cycle life,nomemory effect and environmentally friendly. Lithium oxide with high insertionpotential are general selected as cathode material of Lithium-ion battery.The maincathode materials contain layered struc-ture LiCoO2,LiNiO2,spinel LiMn2O4andOlivine type LiFePO4. Spinel LiMn2O4is recognized as one of the most promisingcathode materials for its high voltage,low cost and environmentally friendly.However, the fast attenuation capacity and poor cycle performance especially in hightemperature requiring improv-ed as cathode material for Li-ion battery.In this article,the author modified with Whisker MWCNTs as carbon sourcecoated on the surface of LiMn2O4to improve the fast attenuation capacity and poorcycle performance,which w ith high crystallinty and excellent dispersibility.Theconductivity of LiMn2O4particles improved because of doping the high conductivityof CNTs,the nano pore structure and length-diameter lead to able to adsorption ofelectrolyte effictively,as a result,isolated electrolyte to corrode LiMn2O4,reducedissolution of Mn and inhibition Jahn-teller effect.CNTs preparated by CVD method usually with structure defect and impuritieslike carbon nano particles,amorphous carbon,nanometer metal catalyst particles,andthe CNTs usually hard to dispersed for entangled between the carbon tubes.thereforeit cannot show its real electrochemical properties，the author take up purification anddispersion to pretreat CNTs before modified with Whisker MWCNTs as carbonsource coated on the surface of LiMn2O4.（1）In this experiment,the author took use of4mol/L HNO3and microwaveoxidation to eliminate impurities in CNTs,compared with the SEM and TEM ofCNTs,we found that carbon tubes after purification get shorter, a lot of active ports ondefect were opened and most impurities were oxidized.besides,the author took use ofhigh temperature graphitization to purify CNTs,compared with the SEM and TEM,we found that amorphous carbon graphitized on the surface of carbon tubes and internalstructure became ordered after graphitization.compared with TG-DTA and XRD ofCNTs,we know that the structure of CNTs became more steady,and the purity ofCNTs achieve more than99.9%.（2）For the dispersion of carbon nanotubes,the author took measures asfollows,ultrasonic dispersion,ball-milling dispersion,added nano dispersing agent andseveral methods together to dispersion.We observed and analyzed the SEM of CNTsand the precipitation conditions of CNTs in alcohol.The experimental results showthat the best dispersion effect of CNTs when the ultrasonic time gets six hours,theball-milling time and speed should be two hours at150r/min,and added1%nanodispersing agent show the best dispersion effect.The author set the best effectdispersion scheme as follows that ball-millig,ultrasonic and add nano dispersingagent.The author took use of ball-milling to mix powder with CNTs doped LiMn2O4inthis article.Through change the different ball-milling time and speed,compared withdry-milling and wet-milling.we observed SEM of the powder and the electrochemicalperformance of battery. We found that the phase of powder were morewell-distributed,the coat effect shows better,and the ball-milling time and speedshould be mid-low and short.At the end of the article,we explored the electrochemical performance,cycleperformance and C-rate performance of battery which doped different quantity ofCNTs.The result shows that compared to the sample which doped non-CNTs,thebattery doped CNTs show higer initial charge-discharge efficiency,higer cycleefficiency and better C-rate performance,though the initial discharge capacitydeclined.The sample which doped nothing its initial discharge capacity get117.27mAh/g,the initial charge-discharge efficiency get93.89%and the capacityretention rate is88.5%after20cycles,compared it,the sample which doped1%wtCNTs show better performance,its initial discharge capacity is116.43mAh/g,theinitial charge-discharge efficiency get96.51%and the capacity retention rate is93.4%after20cycles.besides,the author also modified with SP and CNTs as compositecarbon source coated on the surface of LiMn2O4,then test its electrochemical performance and cycle performance.The results show that the sample which doped2%wtCNTs get better effect than the sample which doped2%wtSP,and the best effectappeared when the ratio of the CNTs to SP is1to2,the initial charge-dischargeefficiency get96.68%and the capacity retention rate is96.8%after20cycles. Inconclusion the sample which doped CNTs or composite conductor able to improvethe electrochemical performance,cycle performance and C-rate performance. |
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