Enhancing the electrochemical performance of high-capacity anodes via material modification in next-generation Li-ion batteries

Abstract

Nowadays, the attention on the electric vehicle and energy storage system increases and Li-ion battery is a promising system because of its high energy density and power density to store the renewable energy such as tidal, wind, solar, bio and geothermal energy. However, the typical anodes used in commercial Li-ion batteries are the carbon-based materials based on the graphite, which has a limited specific capacity of 372 mAh g-1.2 For a further increase in the capacity, the use of new anode materials with a high specific capacities is necessary. Among various candidates, SnS2 based anode has a much higher specific capacity (1231 mAh g-1)3 than graphite, but it has a large irreversible capacity. As the other promising anode, silicon (Si) is widely proposed due to its large capacity (4400 mAh g-1), but the cyclic stability of Si based anode is very poor because of a large volume expansion exceeding 300%. To improve the electrochemical performances and stability of both SnS2 and Si anodes, in this thesis, I studied two techniques including the facile phosphorus embedding and a preparation of 3D current collector for SnS2 and Si anodes, respectively. Specifically, this study focuses on improving the electrochemical performances such as rate capability, cyclic stability using these two methods. Phosphorus embedding into SnS2 can be easily fabricated by a high-energy ball mill, and it achieves 404 mAh g-1 at 200 cycles at a current density of 0.5 A g-1. The 3D Cu can be easily prepared by a combination of chemical oxidation and thermal reduction, and the silicon anode to use the developed 3D Cu as a current collector exhibits a large discharge capacity of 841 mAh g-1 (= 0.90 mAh cm-2) even after 300 cycles at a current density of 1 A g-1. In addition, to elucidate the improved electrochemical performances by these two techniques, the microstructural and electrochemical analyses using XRD, Raman spectroscopy, XPS, SEM, TEM, CV, GITT are conducted.