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Scanning Tunneling Microscopy Study on Surface Reactions of Carbon Negative Electrodes in Rechargeable Lithium Batteries

可充电锂电池碳负极表面反应的扫描隧道显微镜研究

基本信息

批准号：
09650903
负责人：
ABE Takeshi
金额：
$ 2.11万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

Graphite is now widely used as negative electrode in rechargeable lithium batteries. It is generally recognized that a kind of passivating film, called solid electrolyte interface (SEI), is formed on carbon negative electrode during the first charging. Effective SET layer prevents further solvent decomposition and improves the safety and the cycleability of Li-ion cells. Solvent choice is very important to obtain excellent SEI.For example, propylene carbonate (PC) is a poor solvent for graphite anode because it decomposes at ca. 1 V vs. Li/Li^+, and thereby no intercalation takes place. However, the addition of 12-crown-4 to PC solution or the use of partially fluorinated PC suppresses solvent decomposition and enables lithium intercalation, in the present work, we observed the morphology changes of graphite surface in 12-crown-4/PC and 3-trifluoromethyl-2,5-dioxa- cyclopentan-1-one (TFPC) using electrochemical STM, and elucidated the mechanism of SEI formation on graphite negative ele … More ctrode in these electrolyte systems.In 1 M LiC1O_4/TFPC, exfoliation of graphite layers was observed at potentials around 0.9 V ; however, the exfoliation was not so severe as that observed in 1 M LiC1O_4/PC.Below 0.8 V, especially below around 0.5 V, such exfoliation was terminated by the formation of SEI along the newly formed step edges. In this case, the instability of TFPC against reduction enables rapid SEI formation and suppresses further exfoliation.The addition of 12-crown-4 into PC greatly suppressed the exfoliation. After potential was kept at 0.9 V, atomically flat, island-like structures with an enhanced height of 1 nm (referred to as "hills".) appeared on the surface. When the potential was kept below 0.8 V, part of the hills was swelled and changed to irregular-shaped structures with an enhanced height of 20-30 nm (referred to as "blisters"). Blister formation became more significant as the potential was lowered. The observed morphology changes were very similar to those observed in ethylene carbonate (EC)-based solutions in previous studies. These hills and blisters are considered to have been formed by the intercalation of Li^+/12- crown-4 complexes and their decomposition followed by accumulation of the decomposed products, respectively. Selective coordination of 12-crown-4 to Li^+ prevents PC from being co-intercalated within graphite, and thereby suppresses the exfoliation of graphite layers. Less

石墨现在被广泛用作可充电锂电池的负极。一般认为，碳负极在首次充电过程中会形成一种钝化膜，称为固体电解质界面（SEI）。有效的SET层可防止溶剂进一步分解，并提高锂离子电池的安全性和可循环性。溶剂的选择对获得良好的SEI膜非常重要，例如碳酸丙烯酯（PC）是石墨阳极的不良溶剂，因为它在约100 ℃时分解。1 V vs. Li/Li^+，因此不发生嵌入。然而，在PC溶液中加入12-冠-4或使用部分氟化的PC抑制了溶剂的分解，并使嵌锂成为可能。本工作利用电化学扫描隧道显微镜观察了12-冠-4/PC和3-三氟甲基-2，5-二氧杂环戊-1-酮（TFPC）中石墨表面形貌的变化，并阐明了在石墨负极上形成SEI的机理。 ...更多信息在1 M LiClO_4/TFPC中，在约0.9 V的电势下观察到石墨层的剥离;然而，剥离不像在1 M LiClO_4/PC中观察到的那样严重。低于0.8 V，特别是低于约0.5 V，这种剥离通过沿新形成的台阶边缘沿着形成SEI而终止。在这种情况下，TFPC对还原的不稳定性使得快速形成SEI并抑制进一步的剥离。在电势保持在0.9V之后，原子级平坦的岛状结构具有Inm的增强高度（称为“丘”）。出现在表面上。当电位保持在0.8V以下时，部分山丘膨胀并变成高度增加20-30 nm的不规则形状结构（称为“气泡”）。随着电位降低，泡罩形成变得更加显著。观察到的形态变化与先前研究中在碳酸亚乙酯（EC）基溶液中观察到的形态变化非常相似。这些丘和泡被认为分别是由Li^+/12-冠-4络合物的插入和它们的分解以及随后的分解产物的积累形成的。12-冠-4与Li^+的选择性配位阻止了PC在石墨中的共插层，从而抑制了石墨层的剥离。少