Study on the Application of Ailicon-Cobalt Oxide Anode Material in Lithium-Ion Batteries

Silicon (Si)-based materials have the highest capacity among the investigated anode materials and have been recognized as one of the most promising materials for lithium-ion batteries. However, it is still a significant challenge to obtain good performance for practical applications due to the huge volume change during the electrochemical process. To date, the most successful strategy is to introduce other components into Si to form composite or alloy materials.

     In this paper, using the etching technology, porous silicon was prepared, and the silicon and porous silicon were modified by chemical precipitation method. The surface morphology of the obtained material was analyzed by SEM and TEM, the crystalline was characterized by XRD, BET was used to measure the specific surface area and pore size distribution. The charge-discharge properties of the battery, in which lithium as the anode and the prepared materials as the cathode, were analyzed. Then the electrical characteristics were studied by cyclic voltammetry and AC impedance analysis method.

     In the program of charge and discharge experiments of the Li (without modified)/Si battery, the discharge capacity was 2281 mAh g^-1 in the first circle, and it will decreased to 555 mAh g^-1 in the second circle, indicating the rate of decline up to 75.7%. The results show that the discharge capacitance of the prepared lithium battery using silica, which modified by 12% CoO, as the cathode materials were 3269 mAh g^-1 and 2021 mAh g^-1 in the first and second circle, respectively, the rate of decline was 38.18%, which is superior than other sample. Using porous silicon modified by variety of weight percentage as cathode materials for lithium batteries, the charge and discharge results showed that when the weight percentage of cobalt oxide fixed at 12% showed the best results, and the first and second discharge capacity was 3590 mAh g^-1 and 2679 mAh g^-1, respectively, the rate of the discharge capacity decrease was only 25.4%.

      The cyclic voltammetry results showed that the peak current density of Li/Si-CoO (12%) battery was corresponding to the Li/Si system. According to the AC impedance analysis, we inferred the main reason for the decline in silicon battery in the process of continuous charge-discharge is the increase of impedance capacitance of charge transfer (R_ct). The R_ct of the Li/Si battery increased from 9.02 to 13.98 Ω at the end of first and fifth charge and discharge, however, the R_ct of the Li/Si-CoO(12.0%) was 4.52Ω, which is lower than that of the Li/Si battery. The reason may be the volume of expansion and contraction of silicon can be effectively slow down due to the addition of the cobalt oxide. On the other hand, the conductivity may be increased because of the formation of cobalt metal in the process of charge and discharge, which will improve the utilization rate of silicon materials and slow its capacity decline.