리튬 이차 전지용 실리콘산화물-흑연 복합체 음극의 전기화학적 특성

Abstract

High energy density batteries are in demand for light weight portable electronics equipments. To meet such requirements, recently lithium based anode alloys such as Li22Si5 and Li22Sn5, with theoretical capacities 4190 and 990 mAhg^(-1) respectively, were identified as the possible alternatives to graphite which has only 372 mAhg^(-1) as energy density. However, the application of these materials was hampered as they inherit wide volume variations which results in loss of electrical contact between the active materials and current collector causing cell failure. In order to absorb the volume changes during cycling process the silicon in the electrode materials were modified as intermetallic alloys, compounds, nanosized active materials or composite materials so as to provide high cycle capacity. Although several Silicon based materials have been synthesized and explored , the SiO based anodes have shown promising results. X. Yang et al reported nanosized silicon from mechanical reduction of SiO with lithium to deliver an initial and 50th cycle capacity as 770 and 762mAhg^(-1) respectively. In this study we report a simple method involving a single step for the production of Si/SiO/Graphite and SiO/Graphite composite anode with high energy density. And also present the physical and electrochemical characterization of the anode materials. A new anode composition material comprising of SiO and graphite has been prepared by adopting ball milling technique. SiO-Graphite composite shows initial discharge and charge capacity values of 1738 and 693 mAhg^(-1), respectively. The electrode sustains reversible charge capacity value of 318 mAhg^(-1) at 100th cycle. The repetitive volume changes during cycling causes anode particle fracture which leads to the loss of electrical contact between the particles limiting cycle life performance of the cell. So we made in the form of a slurry using a simple solution mixture consisting of propylene carbonate (PC) and acetone(Ac) and then heat treated to order improve the cycle performance. The heat treated organic slurry composite has initial discharge and charge capacity values of 1346 and 612 mAhg^(-1), respectively. The reversible charge capacity value of 500 mAhg^(-1) at 100th cycle with a high coulombic efficiency ~99%. The study shows the achieved significant improvement in cycle performance of SiO-Graphite composite. And In this study, we tried electrochemical pretreatment to remove the initial charge capacity recovery though cc-cv (constant current-constant voltage) technique. we can resolved the present state that discharge capacity increase in initial cycle by 24 constant -voltage process.