Investigation on Electrochemical Properties and Degradation Mechanism of Silicon Oxide-Containing Negative Electrode for Li-Ion Rechargeable Battery

Abstract

Recently Li-ion rechargeable battery (LIB) has been widely used as power source for not only portable device but also electric vehicle (EV). For EVs, a high-performance LIB with a high energy density is strongly required to increase the mileage. Si-containing materials are promising negative electrode materials for LIB because of large theoretical capacity compared with that of conventional carbon materials. Therefore, a great deal of effort has been made to put Si-containing materials into practical use. However, there are still some problems to be solved. In this paper, we investigated electrochemical properties of the Si or SiO-containing negative electrodes. We selected the ketjen black as a conductive enhancer and the polyimide-based binder as a binder material, and then tried to fabricate the negative electrode with an excellent cycle property and long life. However, the electrodes where only Si or SiO-containing material was used as the active material showed a rapid decrease in capacity with cycles. Therefore, we fabricated the composite electrode where SiO was composed with graphite in weight ratio of 1:2, 1:1 and 2:1, and checked electrochemical properties using various electrolytes. For the electrode where the weight ratio of SiO and graphite was 1:2, the initial discharge capacities of ca. 596 and 614 mAh/g were observed using 1M LiPF6 in EC:DMC (= 1:2) with and without 5wt% FEC, respectively, for the voltage range of 0.02 and 1.0 V. On the other hands, the reversible discharge capacities of ca. 542 and 244 mAh/g were observed using 1M LiPF6 in EC:DMC (= 1:2) with and without 5wt% FEC, respectively, after 200 cycles. Therefore, it is important to clarify the degradation mechanism due to the difference of the electrolyte for improving cycle proeprty and life. In the presentation, we will clarify the degradation mechanism of SiO-containing negative electrode by the combination of Li MAS NMR and XPS measurements. Acknowledgement This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO).