以溶膠凝膠法合成鋰電池具陽離子摻雜及碳材包覆之Li4Ti5O12負極材料與其電化學性質檢驗

SYNTHESIS BY SOL-GEL METHODE AND CHARACTERIZATION OF CATION DOPING AND CARBON COATING Li4Ti5O12 ANODE MATERIALS FOR LITHIUM ION BATTERIES

徐兆佳(Chao-chia Hsu)

指導教授 ： 林正裕

大同大學/工程學院/化學工程學系所/碩士(2012年)

摘要

在此研究中，利用溶膠凝膠法製備鋁摻雜與未摻雜之Li4Ti5O12。其結晶性、表面形貌與電化學特性，藉由X光繞射儀(XRD)、掃描式電子顯微鏡(SEM)、充放電測試、循環伏安法(CV)與電化學阻抗分析(EIS)進行分析。實驗結果顯示，在0.1C充放電速率下，未摻雜之Li4Ti5O12 (168.7 mAh g-1)與鋁摻雜之Li4Ti5O12 (162.6 mAh g-1)有著相近的放電電容量。當充放電速率提高到5C時，可以觀察出兩者在放電電容量上有明顯的差異，其放電電容量分別為73.0 mAh g-1(Li4Ti5O12)與107.4 mAh g-1 (Al-doped Li4Ti5O12)。當放電電壓從1伏降至0伏時，可以觀察出兩者在0.1C充放電速率下，其電電容量約增加了50 mAh g-1達到221 mAh g-1 (Li4Ti5O12)與228 mAh g-1 (Al-doped Li4Ti5O12)。當充放電速率為5C時，則放電電容分別為173.3 mAh g-1 (Li4Ti5O12)與190.0 mAh g-1 (Al-doped Li4Ti5O12)。藉由循環伏安法及電化學阻抗分析之量測，指出鋁離子之摻雜增加了電子導電性及鋰離子擴散的能力。同時也增加了在高速率充放電下之穩定性。另一方面，鋁離子之摻雜也降低了電荷轉移及溶液間之阻抗。
此外，在C/ Li4Ti5O12複合材料測試方面，選用了石墨稀(graphene)及PEDOT做為碳材來源進行初步測試。Li4Ti5O12與石墨稀的混合下，仍維持有不錯的電化學特性之表現。而Li4Ti5O12以PEDOT做混合，其所表現出之電容量並不理想，但仍有不錯的穩定性。

關鍵字

鋰離子電池 ； 負極材料 ； 鈦酸鋰 ； 鋁摻雜 ； 碳包覆

並列摘要

In this study, the samples of Li4Ti5O12 with or without Al-doping were synthesized by sol-gel method. The crystal structure and surface morphology were characterized by X-ray diffraction and scanning electronic microscopy, while the electrochemical performances including charge/discharge test, cyclic voltammetry, and electrode impedance spectroscopy were also investigated. The results revealed that the discharge capacity of Li4Ti5O12 and Al-doped Li4Ti5O12 at 0.1C were almost the same, which were 168.7 mAh g-1 and 162.6 mAh g-1, respectively. However, a large discrepancy in the discharge capacity between Li4Ti5O12 (73.0 mAh g-1) and Al-doped Li4Ti5O12 (107.4 mAh g-1) can be observed while the C rate was increased to 5 C. The capacities were further improved about 50 mAh/g when the charged and discharged between 0-2.5 V. The discharge capacity of Li4Ti5O12 and Al-doped Li4Ti5O12 at 0.1C were 221 mAh g-1 and 228 mAh g-1, respectively. When increasing the C rate to 5 C, a significant discrepancy in the discharge capacity between Li4Ti5O12 (173.3 mAh g-1) and Al-doped Li4Ti5O12 (190.0 mAh g-1) can be observed. Al3+ doping indeed enhanced the characteristics of lithium diffusion and electronic conductivity in the electrode; as indicated by cyclic voltammetry and AC impedance spectra. As a result, Al3+ doping does not change the electrochemical process, instead enhanced lithium diffusion, electronic conductivity, and high C-rate capability. On the other hand, the charge-transfer resistance and solution resistance also can be decreased.
Additionally, C/Li4Ti5O12 composites were prepared by using graphene and PEDOT. The Li4Ti5O12 mixed with graphene still maintain good electrochemical properties. The Li4Ti5O12 mixed with PEDOT exhibited poor capacity although it still retained good cycle stability.

並列關鍵字

Lithium-ion batteries ； Lithium titanate ； Al-doping ； anode material ； carbon coating

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