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Aging Of Lifepo_4 Upon Exposure To H_2o

机译:暴露于H_2o的Lifepo_4的老化

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The effect of H_2O on carbon-coated LiFePO_4 particles was investigated by chemical analysis, structural analysis (X-ray diffraction, SEM, TEM), optical spectroscopy (FTIR, Raman) and magnetic measurements. Upon immersion in water, part of the product floats while the main part sinks. Both the floating and the sinking part have been analyzed. We find that the floating and sinking part only differ by the amount of carbon that partly detaches from the particles upon immersion in water. Exposure to H_2O results in rapid attack, within minutes, of the surface layer of the particles, because the particles are no longer protected by carbon. The deterioration of the carbon coat is dependent on the synthesis process, either hydrothermal or solid-state reaction. In both cases, however, the carbon coat is permeable to water and fails to protect the surface of the LiFePO_4 particles. The consequence is that this immersion results in the chemical attack of LiFePO_4, but is restricted to the surface layer of the particles (few nanometers-thick). In case the particles are simply exposed to humid air, the carbon coat protects the particles more efficiently. In this case, the exposure to H_2O mainly results in the delithiation of the surface layer, due to the hydrophilic nature of Li, and only the surface layer is affected, at least for a reasonable time of exposure to humid air (weeks). In addition, within this timescale, the surface layer can be chemically lithiated again, and the samples can be dried to remove the moisture, restoring the reversible electrochemical properties.
机译:通过化学分析,结构分析(X射线衍射,SEM,TEM),光谱学(FTIR,拉曼)和磁学测量研究了H_2O对碳包覆的LiFePO_4颗粒的影响。浸入水中后,部分产品会漂浮而主要部分会下沉。浮动部分和下沉部分均已进行了分析。我们发现,漂浮和下沉的部分仅因浸入水中时部分从颗粒上脱离的碳含量不同而不同。暴露于H_2O会在几分钟之内迅速侵蚀颗粒的表面层,因为颗粒不再受到碳的保护。碳涂层的劣化取决于水热反应或固态反应的合成过程。然而,在两种情况下,碳涂层都可透水并且不能保护LiFePO_4颗粒的表面。结果是这种浸没会导致LiFePO_4发生化学侵蚀,但仅限于颗粒的表面层(几纳米厚)。如果仅将颗粒暴露在潮湿的空气中,则碳涂层可以更有效地保护颗粒。在这种情况下,由于Li的亲水性,暴露于H_2O主要导致表面层的脱锂,并且至少在合理的暴露于潮湿空气的时间(几周)内仅影响表面层。此外,在此时间范围内,可以再次对表面层进行化学锂化处理,并对样品进行干燥以去除水分,从而恢复可逆的电化学性能。

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