本論文主要研究以天然農作廢棄物製備之碳材，合成磷酸亞鐵鋰/碳(LiFePO4/C)複合陰極材料。以天然廢棄物製備之碳材優點，在於原料來源便宜，又兼具資源回收及環保概念，經本實驗室特殊製孔劑處理後，更具備高表面積(>2000 m2/g)之特性，並利用此諸多優點之碳粉，進行LiFePO4/C之複合材料合成。 利用高溫固態法，以高表面積碳材製備LiFePO4/C之最佳製程條件為320 ℃煆燒起始物10小時後，以球磨方式混入8 wt.%花生殼碳材，壓錠後以600 ℃煆燒12小時。LiFePO4/C在充放電速率0.2 C及充放電截止電壓分別為4.3和2.5 V時，其初次放電電容量為140 mAh/g，至電荷維持率80 %時，循環壽命為456次，於特徵曲線硬幣型電池測試中，最大充放電速率可承受至2.0 C充放電，放電電容量為60 mAh/g以上。 在合成LiFePO4的過程中加入高表面積碳材，可抑制LiFePO4晶粒成長並提升電池性能，由TEM/EDS分析LiFePO4/C，發現碳包覆在LiFePO4周圍，可有效增進電子導電率；並得到四點探針導電度計及總有機碳測定儀之佐證；由拉曼光譜測試結果，以最佳製程條件600 ℃下合成LiFePO4/C可得到較高比例的石墨化碳；添加稻殼碳、甘蔗皮碳與花生殼碳此三種高表面積碳材，合成LiFePO4/C陰極材料之比表面積，仍具有高表面積之特性，並有不錯之電容量；微分掃描熱卡儀分析測試不同循環次數之LiFePO4/C，經100次循環後其放熱量僅較一次循環者增加0.6 J/g，結構相當穩定，以高表面積碳材製備之LiFePO4/C具有良好之熱安全性。 In this thesis, we prepared carbon materials by pyrolysis of agriculture crop residues and used to synthesize LiFePO4/C composites. The advantages of pyrolytic carbons from above are low cost and environmentally benign. Furthermore, the pyrolytic carbons treated with poregenic agent gave both high surface area (>2000 m2/g) and high porosity. Hence, we adopted a solid state method to obtain olivine structural LiFePO4 fine powders and mixed small amount of high surface area carbon into the product to improve the electronic conductivity. The electrochemical studies concluded the optimum calcination process for the synthesized LiFePO4/C composites were 600oC for 12 h in Ar/H2 (vol. 95:5) gas with addition of 8.0 wt.% high surface area carbon. The LiFePO4/C composite delivered a discharge capacity of 140 mAhg-1 in the first cycle at a 0.2C-rate between 4.3 to 2.5 V, and he number of cycles sustained was 456 cycles at a preset cut-off value of 80% capacity retention. In the cyclability tests of LiFePO4 electrodes at different charging and discharging rates, the specific capacity decreases with increasing charge/discharge rate, and the capacity retention remains very good for all the different rates. Therefore, the high surface area carbon coated LiFePO4 electrodes demonstrated high capacity and good cyclability.
