Investigation of the effects of CO₂ annealing of polymer matrix composite anode electrodes used in Li-ion batteries

Recently, silicon with a high specific capacity (similar to 4000 mAh.g(-1)) is widely used as the anode material in Li-ion battery cells. However, it is known that due to changes in the structure of silicon particles during charge-discharge, they cause a decrease in the capacity of the system. CO2 annealing is applied on polymer matrix composite anode electrodes of Li-ion batteries to develop cell capacity and energy efficiency. The rearranged polymer structure and polymer Si particle interactions are effective in battery performance after annealing with CO2. In this study, Si/C/PVDF and LiCoO2 was preferred as the anode and the cathode, respectively. SEM, AFM and water contact angle measurements are applied to samples. With results, water repellence and surface roughness increased with increasing CO2 pressure. Samples annealed under CO2 shows better electrochemical performance and higher discharge capacities. The first charge capacity after CO2 is found to be 189 mAhg(-1), and an improvement of 37% is achieved compared to the classical cell. The decrease of the surface energy of the electrode delays the diffusion of the electrolyte and thus the degradation of the structure of the polymeric electrode, thus improving the charge-discharge initial capacities. Besides, it is seen in the battery performance test results that the active surface area of the electrode increases thanks to the increasing surface roughness, and thus the capacity is positively affected.