Brookhaven National Laboratory , Upton, New York 11973, United States.
Department of Chemical Engineering, Columbia University , New York, New York 10027, United States.
ACS Appl Mater Interfaces. 2016 May 11;8(18):11418-30. doi: 10.1021/acsami.6b01134. Epub 2016 Apr 27.
Aggregation of nanosized materials in composite lithium-ion-battery electrodes can be a significant factor influencing electrochemical behavior. In this study, aggregation was controlled in magnetite, Fe3O4, composite electrodes via oleic acid capping and subsequent dispersion in a carbon black matrix. A heat treatment process was effective in the removal of the oleic acid capping agent while preserving a high degree of Fe3O4 dispersion. Electrochemical testing showed that Fe3O4 dispersion is initially beneficial in delivering a higher functional capacity, in agreement with continuum model simulations. However, increased capacity fade upon extended cycling was observed for the dispersed Fe3O4 composites relative to the aggregated Fe3O4 composites. X-ray absorption spectroscopy measurements of electrodes post cycling indicated that the dispersed Fe3O4 electrodes are more oxidized in the discharged state, consistent with reduced reversibility compared with the aggregated sample. Higher charge-transfer resistance for the dispersed sample after cycling suggests increased surface-film formation on the dispersed, high-surface-area nanocrystalline Fe3O4 compared to the aggregated materials. This study provides insight into the specific effects of aggregation on electrochemistry through a multiscale view of mechanisms for magnetite composite electrodes.
纳米材料在复合锂离子电池电极中的聚集可能是影响电化学行为的一个重要因素。在这项研究中，通过油酸包覆和随后在炭黑基质中的分散来控制四氧化三铁（Fe3O4）复合材料中的聚集。热处理过程有效地去除了油酸包覆剂，同时保持了高度的 Fe3O4 分散性。电化学测试表明，Fe3O4 的分散在最初提供更高的功能容量方面是有益的，这与连续体模型模拟结果一致。然而，与聚集的 Fe3O4 复合材料相比，分散的 Fe3O4 复合材料在延长循环后表现出更大的容量衰减。循环后电极的 X 射线吸收光谱测量表明，在放电状态下分散的 Fe3O4 电极更氧化，与聚集样品相比，可逆性降低。循环后分散样品的电荷转移电阻较高表明，与聚集材料相比，分散的高表面积纳米晶 Fe3O4 上形成了更多的表面膜。这项研究通过对磁铁矿复合材料电极的机制进行多尺度分析，深入了解了聚集对电化学的具体影响。
