Investgation On Carbonaceous Nanomaterials As Conductive Additives For Lithium Ion Batteries

Lithium ion batteries are playing an increasingly important role in the worldmarket of energy storage and conversion devices due to their relatively high energydensity and good cycle stability. In the field of lithium ion batteries, conductiveadditives as an important part of electrode dramatically influence the performance oflithium ion batteries. A certain amount of conductor is usually added to the electrodeactive particles to enhance the electronic conductivity and to reduce the ohmicresistance of electrode, as well as improving the utilization ratio of the active materials.At the same time, the microstructure and distribution of conductors can influenceelectrolyte diffusion.To improve electrochemical reaction activity of electrode materials，in this paper,we used carbon black(0D), carbon nanotubes(1D) and graphene nanosheets (2D) asconductive additives for lithium ion batteries, configuring a point, line, surfacecomposite. Here will come to investigate the corresponding conductive network ofelectrodes, presenting the interface structure model. We investigated the influence ofcarbonaceous nanomaterials with different microstrcture on electrochemical reactionactivity of electrodes. The main research contents are as follows:A comparative investigation was carried out on three kind of carbonaceousconducting additives in different dimensions, such as carbon black, multiwalledcarbon nanotubes and graphene nanosheets, combining with spherical naturalgraphite/LiFePO4as an anode/cathode material for lithium ion batteries. Microstructureof the carbon conductors and the corresponding conductive network of electrodes wereinvestigated by XRD, nitrogen adsorption, TEM, and SEM. The SEM images showedthat carbon black, carbon nanotubes, graphene nanosheets connected with the activeparticles, composing a three dimensional network with point, line, sheet structure,respectively. The anodic/cathodic performance was tested by cyclic voltammetry andgalvanostatic charge-discharge experiments and AC impedance spectra. We foundedthat graphene could effectively reduce the AC impedance and polarization phenomenonof electrodes and improve the reversible capacity and rate performance. The reversiblecapacity of electrode, which prepared by graphene and graphite composite was up to366mAh/g and without attenuation after20cycles at0.1C rate. The discharge capacityof electrode fabricated by graphene and lithium iron phosphate composite was124 mAh/g at1C rate. Which was increased9mAh/g and21mAh/g for carbon and carbonnanotubes as conductive additives, respectively.We investigated the preparetion method of graphene nanosheets and carbonnanobelts. An investgation was carried out on Carbon nanobelts as anode material forlithium ion batteries. Graphene nanosheets were prepared via a modified Hummers’method. Carbon nanobelts were synthesized by chemical method, using carbonnanotubes prepared by chemical vapor deposition and hydrogen-arc discharge,respectively. The thickness of graphene was about10layers. Its specific surface areawas up to575.3m2/g. The prepared carbon naobelts formed a porous network structure.Carbon nanobelts as the anode of lithium ion battery had excellent electrochemicalperformance. Even in the current density of200mA/g, the reversible capacity of carbonnanobelts was as high as503mAh/g. While the multiwalled carbon nanotubes as anodematerial, the corresponding capacity was only about200mAh/g.