為因應未來幾年動力電源和儲能市場的快速成長，鋰離子二次電池在勢必需要往更大的能量密度、更快速充放電以及較長的循環壽命三個方向來發展。本研究將針對此一趨势設計開發能符合此一目地的新穎負極材料。 鋰鈦氧(Li4Ti5O12，簡稱LTO)具有鋰離子嵌入嵌出時體積不易變化的優點，展現較長的循環壽命，因此普遍應用在動力型電池的負極端;不過較低的理論電容量以及較差的快速充放電表現，讓LTO的發展備受考驗。本實驗使用LTO複合過渡金屬氧化物- Co3O4，希望藉由LTO的結構穩定性的優點以及Co3O4在充放電時還原出部分不可逆的高導電度Co金屬與高理論電容的優點，使鋰離子嵌入嵌出過程中第一層先經過外層體積零應變的LTO，Li4Ti5O12 + 3Li+ +3e- ↔ Li7Ti5O12，再經過能夠提供大量電容量的Co3O4，Co3O4 + 8Li+ + 8e- ↔ 3Co0 + 4Li2O，從FE-SEM、HRTEM結構的檢測配合電性測試證實以LTO包覆在外層能夠抑制Co3O4體積膨脹，有效延長電池循環壽命。 本研究中探討不同LTO及Co3O4比例的複合樣品:LC(75/25)、LC(50/50)與LC(25/75)，並且以為主體為LTO的LC(75/25)-6以及主體為Co3O4的LC(25/75)-6樣品展現優良的電性表現。比較同樣在0.1C下放電電容量，純的鋰鈦氧電容量為140.4mAh/g，LC(75/25) 與LC(25/75)放電電容量表現為363.6mAh.g與682.2mAh/g，若將充放電速度提高到1C及2C，LC(75/25) 與LC(25/75)也有239.1 、 198.6 mAh/g與397.9 mAh/g 、 312 mAh/g的表現，經過以0.1C與1C充放電循環150圈後電性依然有很好的穩定性足證明此一結構設計可以製作符合未來趨勢的鋰電池負極材料。 ;To meet the emerging growth of power and energy storage market, new generation of lithium-ion batteries (LIBs) must meet the reqirements such as high energy density、high power、fast charge/discharge and long cycle life. The purpose of this research is to design high performance electrode active materials so as to meet those requirements. Spinel lithium titanate LTO(Li4Ti5O12)-based anode has attracted great interest in high power lithium ion batteries due to its zero-strain character during lithiation and a very flat potential plateau at about 1.55V (vs. Li/Li+), which served as a safe electrode. Due to its low conductivity (~10-13 S cm-1) 、 low lithium ion diffusivity (~10-12 cm2 s-1) and poor specific capacity, LTO suffers from poor capacity and lower power density at high charge/discharge rates. Present research proposed to incorporate transition metal oxide (TMO) into the LTO in order to mitigate these drawbacks. Because TMO have been envisaged as alternate anode materials for LIBs which has high specific capacity and could reduce a part of high conductivity transition metal irreversibly and remain as the electrical conduction enhancer. Moreover, it contributes in promoting electron transfer in the redox reaction of LTO and thus improving the rate capability of LTO. For the synthesis of the composite anode materials, Co3O4 was incorporated into LTO with three different composition, LTO:Co3O4=75:25、50:50 and 25:75 of weight percentage. Furthermore, it was found that by reducing calcination time from 12h to 6h, the capacity could be enhanced. Compared to 140.4 mAh/g in single LTO anode, the result shows that LC(75/25)-6 and LC(25/75)-6 could enhance the lithium charge capacity to about 363.5 and 682.2 mAh/g under 0.1C. The charge/discharge rate could be improved to 1C and 2C, with the capacity around 239.1 and 198.6 mAh/g for LC(75/25)-6 、 397.9 mAh/g and 312 mAh/g for LC(25/75)-6. It also performs good cycling stability, in which after 150 cycles under0.1C and 1C remain stable for LC(75/25)-6 and LC(25/75)-6. The Coulombice efficiency of capacity、rate capacity and long-term cycle is almost 100%.
