氧化亞錫鋰鈦氧複合材於高能鋰電池負極之應用

陳奕志(Yi-chih Chen)

指導教授 ： 諸柏仁

國立中央大學/理學院/化學系/碩士(2015年)

摘要

金屬氧化物(Metal oxide)負極材料視為新鋰電世代鋰電池的發展趨勢，本研究結合兩種不同鋰離子嵌入/脫嵌機制的金屬氧化物，形成一新穎複合材料，達成抑制粉末化、改善速率電容以及循環壽命表現之目標。氧化亞錫(SnO)屬於合金/去合金(Alloying/de-alloying)系統，可擁有高比電容量(875 mAh.g-1)以及電化學活性；然而，修飾用的鋰鈦氧 (Li4Ti5O12) 屬於嵌入/脫嵌機制(Intercalation / de-intercalation)，充放電過程中具有體積零應變(Zero-strain)，並且展現出優異的速率電容。本研究使用溶膠─凝膠法(Sol-gel)，並以75/25、50/50、25/75等不同SnO / LTO重量比例，合成出一系列複合材，結合兩材料特性，達成穩定氧化亞錫的體積變化問題，其中SnO-LTO(75/25)樣本的速率電容表現最為優異，於1C變速率充放電測試中仍保有466.2 mAh g-1放電容量，在0.2C下進行充放電30圈後，SnO-LTO(75/25)樣品仍有423.3 mAh g-1的電容量，電容保持率仍有約53.0%。此結果可看出鋰鈦氧有助於氧化亞錫結構穩定，並同時可改善速率電容以及循環壽命表現。藉循環伏安法測試以及搭配充放電圖，發現LTO可能於首圈充放電過程中，與分散於Li2O中，有如孔道一般，於高電位中短暫儲存鋰離子後將其轉移給SnO，然而LTO則成為在於充放電過程當中可
緩衝SnO所造成之劇烈體積膨脹現象，同時於高倍率操作條件下，此轉移鋰離子的行為表現使複合材於高倍率充放電下仍可保有較高的放電容量，以及優異的穩定性。

關鍵字

金屬氧化物 ； 負極材料 ； 氧化亞錫 ； 鋰鈦氧

並列摘要

Anode materials play a pivotal role for high power density lithium ion batteries applications. Graphite was the dominant materials of choice, but still fall short of the goal owing to low rate-capability and specific capacity (372 mAh g-1). Among other electrochemically active materials, Tin monoxide (SnO) appears promising to replace graphite and is widely explored due to its high specific capacity (875 mAh g-1).
However it suffered from pulverization problem and hampered its commercial implementation. In this study we have developed a novel composite anode material that combined two types of lithium ion insertion and exertion mechanisms with the purpose to reduce pulverization, improve rate capability and cycling performance. SnO is alloying/de-alloying system, which possess higher specific capability and electrochemical activity. On the other hand, Li4Ti5O12 (LTO) is an intercalation/de-intercalation system, which shows unique rate-capability and zero-strain ability. Combining the two features of the two materials we are able to stabilize the huge volume change of SnO. Pure SnO and the composite powder with SnO/LTO of 75/25, 50/50 and 25/75 wt% were successfully synthesized by sol-gel method. The decrease of capacity with increasing C-Rate was found to be slower in SnO-LTO (75/25) composite powders, and a high discharge capacity of 466.2 mAh.g-1 at 1Crate was observed, which is higher than that in commercial graphite anode materials. The presence of LTO appears to improve simultaneously the rate capability and cycle life through stabilizing the structure of whole active material. The observed cyclic voltammetry and galvanostatic cycling are reflected as lithium storage mechanism based on alloying-dealloying reaction of Sn in composite of Sn-LTO-Li2O, in which LTO acting as a buffer matrix, thus reducing pulverization. In addition, a flat plateau of LTO (1.55V) observed during charge cycle, but does not appear under discharge cycling of both samples, SnO-LTO (75/25) and SnO-LTO (50/50), represents that LTO could transport Li-ion to SnO from, accelerate alloying-dealloying reaction at higher C-Rate operation, and stabilize the pulverization during such reaction

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