Reciprocal Salt Flux Growth of LiFePO4 Single Crystals with Controlled Defect Concentrations
Reciprocal Salt Flux Growth of LiFePO4 Single Crystals with Controlled Defect Concentrations
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DOI：
10.1021/cm4027682
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发表时间：
2013-11-26
影响因子：
8.6
通讯作者：
Khalifah, Peter G.
中科院分区：
文献类型：
--
作者：
Janssen, Yuri;Santhanagopalan, Dhamodaran;Khalifah, Peter G.
已经开发了用于重要电池材料LiFePO 4的单晶的助熔剂生长的改进方法，允许在相对较低的温度下容易地制备具有发育良好的小面的高达1 cm的单晶。通过粉末X射线衍射和单晶衍射（X射线和中子中的α）对这些样品的结构表征表明，样品通常是化学计量的，在Li位点上具有非常低浓度的Fe缺陷，尽管具有较大浓度缺陷的晶体可以使用富Fe熔剂来具体生长。这些缺陷通过形成富铁（Li 1 -2xFex）FePO 4部分固溶体而发生，与文献中更常见的反位缺陷相反，反位缺陷将保持理想的LiFePO 4化学计量。LiFePO 4缺陷被示出为肉蟹石状（2 Li+ -> Fe 2 + +空位）的基础上从单晶衍射数据，观察到的缺陷浓度上的晶胞参数的依赖性，和它们观察到的相行为（缺陷只出现在从相对于化学计量LiFePO 4富Fe的熔剂的生长）的组合物精制。通过像差校正扫描透射电子显微镜研究了缺陷的分布，发现其高度不均匀，表明含缺陷的晶体可能由橄榄石LiFePO 4和肉松苷Fe-3（PO 4）（2）的内轴共生体组成，其方式使Fe-Li缺陷对微晶内Li离子传输速率的不利影响最小化。
Improved methods for the flux growth of single crystals of the important battery material LiFePO4 have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and a in neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li1-2xFex)FePO4 partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO4 stoichiometry. The LiFePO4 defects are shown to be sarcopside-like (2 Li+ -> Fe2+ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO4). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO4 and sarcopside Fe-3(PO4)(2) in a manner that minimizes the detrimental influence of Fe-Li defects on the rate of Li-ion transport within crystallites.