Department of Materials Science & NanoEngineering, Rice University, Houston, TX, 77005, USA.
Department of Chemistry, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Nat Commun. 2017 Oct 30;8(1):1194. doi: 10.1038/s41467-017-01315-8.
Olivine lithium iron phosphate is a technologically important electrode material for lithium-ion batteries and a model system for studying electrochemically driven phase transformations. Despite extensive studies, many aspects of the phase transformation and lithium transport in this material are still not well understood. Here we combine operando hard X-ray spectroscopic imaging and phase-field modeling to elucidate the delithiation dynamics of single-crystal lithium iron phosphate microrods with long-axis along the [010] direction. Lithium diffusivity is found to be two-dimensional in microsized particles containing ~3% lithium-iron anti-site defects. Our study provides direct evidence for the previously predicted surface reaction-limited phase-boundary migration mechanism and the potential operation of a hybrid mode of phase growth, in which phase-boundary movement is controlled by surface reaction or lithium diffusion in different crystallographic directions. These findings uncover the rich phase-transformation behaviors in lithium iron phosphate and intercalation compounds in general and can help guide the design of better electrodes.
橄榄石型磷酸铁锂是锂离子电池中一种重要的电极材料，也是研究电化学驱动相转变的模型体系。尽管已经进行了广泛的研究，但该材料的相转变和锂离子输运的许多方面仍未得到很好的理解。在这里，我们结合在位硬 X 射线光谱成像和相场模拟，阐明了[010]方向长轴的单晶磷酸铁锂微棒的脱锂动力学。在含有~3%锂-铁反位缺陷的微颗粒中，发现锂离子扩散具有二维特性。我们的研究为先前预测的表面反应控制的相界迁移机制以及相生长混合模式的潜在运行提供了直接证据，在这种混合模式中，相界的移动受到表面反应或不同晶向锂离子扩散的控制。这些发现揭示了磷酸铁锂和插层化合物中丰富的相转变行为，有助于指导更好的电极设计。
