| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 106 === Demand for high power and efficiency energy storage in this past half-century is tremendous high. Silicon, as a promising anode material for LIBs, has a various benefit, such as low working voltage, high theoretical specific capacity, low-cost, and earth abundance. Unfortunately, silicon anode has a big challenge in serious volume expansion during lithiation process, which affected in capacity fading and poor cycle performance. Thus, in order to control volume expansion in silicon, carbon coating and silicon particle size optimizing method lead to be promising ways.
During carbon coating process, the silicon powder mixed with glucose/coal tar at different ratios to reach 10 wt%, 20 wt%, and 30 wt% (40 wt% for coal tar) carbon contents after heat-treatment, respectively. It seems that glucose as a precursor has a better performance than coal tar. Furthermore, we got the best cycle performance at the optimum carbon content at 20 wt% (GL20 sample). GL20 sample shows high first charge capacity 2689.8 mAh/g with 31.4% in high rate retention and even after 200 cycles still stand in 1278.4 mAh/g. In addition, we investigated the particle size effect in carbon-coated silicon. Expectedly, we found that the smallest particle size (~100nm) with 20 wt% carbon coated silicon (SC100 sample) shown a breathtaking results with higher first cycle charge capacity (2838.1 mAh/g) than larger size of particle size (>400 nm) and it still can stand for 1751.5 mAh/g after 200 cycles. Moreover, additional KS6 graphite as a composite can be a good choice in increasing high rate retention and cycle performance. Based on the latest experiments of this study, it has proven that the addition of 45-60 wt% KS6 graphite can increase the high rate retention, and after 100 cycles the capacity still stand for more than 55% from its first charge capacity.
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