Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM, 87185, USA.
Adv Mater. 2017 Jul;29(26). doi: 10.1002/adma.201700236. Epub 2017 May 5.
Many lithium-storage materials operate via first-order phase transformations with slow kinetics largely restricted by the nucleation and growth of a new phase. Due to the energy penalties associated with interfaces between coexisting phases, the tendency for a single-phase solid-solution pathway with exceptional reaction kinetics has been predicted to increase with decreasing particle size. Unfortunately, phase evolutions inside such small particles (tens of nanometers) are often shrouded by electrode-scale inhomogeneous reactions containing millions of particles, leading to intensive debate over the size-dependent microscopic reaction mechanisms. This study provides a generally applicable methodology capable of tracking lithiation pathways in individual nanoparticles and unambiguously reveals that lithiation of anatase TiO , previously long believed to be biphasic, converts to a single-phase reaction when particle size reaches ≈25 nm. These results imply the prevalence of such a size-dependent transition in lithiation mechanism among intercalation compounds and provide important guidelines for designing high-power electrodes, especially cathodes.
许多储能材料通过一级相变来工作，动力学过程受到很大限制，主要是由于新相的成核和生长。由于共存相之间的界面会带来能量损耗，因此人们预测，具有特殊反应动力学的单相固溶途径的趋势会随着粒径的减小而增加。不幸的是，如此小的颗粒（几十纳米）内部的相演变通常被包含数百万个颗粒的电极尺度不均匀反应所掩盖，这导致了关于尺寸依赖性微观反应机制的激烈争论。本研究提供了一种通用的方法，能够跟踪单个纳米颗粒中的嵌锂途径，并明确表明，当粒径达到约 25nm 时，锐钛矿 TiO2 的嵌锂过程，以前被认为是两相的，会转化为单相反应。这些结果表明，在插层化合物中，这种尺寸相关的转变在嵌锂机制中非常普遍，并为设计高功率电极，特别是阴极，提供了重要的指导。
