Electrochemical Characterization of Phosphorous-doped Soft Carbon using Single Particle for Lithium Battery Anode

The electrochemical properties of single particles of pristine and P-doped soft carbon (18, 12um in diameter, respectively, provided by GS Energy Co.) were investigated using a microelectrode technique. A finely manipulated Ni-plated platinum filament (diameter:15um) was used to maintain electrical contact with a soft carbon single particle in the organic electrolyte under optical microscope observation and the galvanostatic charge-discharge tests were carried out. This single particle technique using microelectrode gives intrinsic information on the material, itself, without mixing effect with electrode parameters such as compositions (binder and conductive agent), density (porosity) and loading amounts on the unit area. The discharge capacity of pristine and P-doped soft carbon single particle were 1.4 nAh and 0.6 nAh, respectively, in the potential range of 0.005-2.5 V vs Li/Li+, which shows fairly agreement with the results of coin type half cell. The discharge rate capability of the single soft carbon particle was excellent, and the single particle exhibited the discharge retention of about 80% at a high rate of 70 C (100 nA). The delithiation process of the soft carbon single particle was not controlled only by Li ion diffusion, but by the charge transfer reaction at a rate up to 70 C. The charge transfer resistances of soft carbon, which were estimated by Tafel plot of single particle, increased remarkably by P-doping. The kinetic properties, including charge transfer and film resistances of soft carbon with P-doping will be discussed.