Department of NanoEngineering, Program of Materials Science and Engineering, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0448, United States.
Chemical and Engineering Materials Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37830, United States.
ACS Appl Mater Interfaces. 2017 Oct 25;9(42):36745-36754. doi: 10.1021/acsami.7b09903. Epub 2017 Oct 16.
Spontaneous and anisotropic surface segregation of W cations in LiMnNiO particles can alter the Wulff shape and improve surface stability, thereby significantly improving the electrochemical performance. An Auger electron nanoprobe was employed to identify the anisotropic surface segregation, whereby W cations prefer to segregate to {110} surface facets to decrease its relative surface energy according to Gibbs adsorption theory and subsequently increase its surface area according to Wulff theory. Consequently, the rate performance is improved (e.g., by ∼5-fold at a high rate of 25C) because the {110} facets have more open channels for fast lithium ion diffusion. Furthermore, X-ray photoelectron spectroscopy (XPS) depth profiling suggested that the surface segregation and partial reduction of W cation inhibit the formation of Mn on surfaces to improve cycling stability via enhancing the cathode electrolyte interphase (CEI) stability at high charging voltages. This is the first report of using anisotropic surface segregation to thermodynamically control the particle morphology as well as enhancing CEI stability as a facile, and potentially general, method to significantly improve the electrochemical performance of battery electrodes. Combining neutron diffraction, an Auger electron nanoprobe, XPS, and other characterizations, we depict the underlying mechanisms of improved ionic transport and CEI stability in high-voltage LiMnNiO spinel materials.
在 LiMnNiO 颗粒中，W 阳离子的自发各向异性表面偏析可以改变 Wulff 形状并提高表面稳定性，从而显著改善电化学性能。我们采用俄歇电子纳米探针来识别各向异性表面偏析，根据吉布斯吸附理论，W 阳离子优先偏析到 {110} 表面面来降低其相对表面能，进而根据 Wulff 理论增加其表面积。因此，提高了倍率性能（例如，在 25°C 的高倍率下提高约 5 倍），因为 {110} 面具有更多的开放通道，有利于锂离子快速扩散。此外，X 射线光电子能谱（XPS）深度剖析表明，表面偏析和部分还原的 W 阳离子抑制了 Mn 在表面上的形成，通过提高高充电电压下的阴极电解质界面（CEI）稳定性来提高循环稳定性。这是首次报道采用各向异性表面偏析来控制颗粒形态，以及增强 CEI 稳定性的方法，这是一种简单且具有普遍适用性的方法，可以显著提高电池电极的电化学性能。我们结合中子衍射、俄歇电子纳米探针、XPS 和其他特性描述了在高压 LiMnNiO 尖晶石材料中改善离子传输和 CEI 稳定性的潜在机制。
