王必恒同学于Polymers发表文章

《Probing the Dynamics of Li + Ions on the Crystal Surface: A Solid-State NMR Study》

https://www.mdpi.com/2073-4360/12/2/391, Published: 9 February 2020, https://doi.org/10.3390/polym12020391。

Abstract: Polyethylene oxide-based solid polymer electrolytes (SPEs) are of research interest because of their potential applications in all-solid-state Li⁺ batteries. However, despite their advantages in terms of compatibility with the electrodes and easy processing, polyethylene oxide (PEO)/Li⁺ complexes often suffer from low conductivity at room temperature. Understanding the conduction mechanism and, in turn, developing strategies to improve the conductivity have long been the main objectives underlying research into PEO/Li⁺ complex electrolytes. Here, we prepared several special PEO/Li⁺ complex samples where the PEO/Li⁺ complex structures were located on the surfaces of PEO crystals and consisted of high content chain ends. We found two different Li⁺ species in the PEO/Li⁺ complex structures via solid-state nuclear magnetic resonance (NMR). The 2D ⁷Li exchange NMR showed the exchange process between the different Li⁺ species. The exchange dynamics of the Li⁺ ions provide a molecular mechanism of the Li⁺ transportation in the surface of PEO crystal lamella, which is further correlated with the ionic conduction mechanism of the PEO/Li⁺ complex structure.

本研究通过浸泡方法将Li⁺富集在PEO结晶表面，证明了PEO晶片表面存在两种化学环境的Li⁺。通过⁷Li NMR和¹³C NMR发现这两种 Li⁺分别与PEO结晶表面的链端和链段进行配位。2D ⁷Li exchange NMR进行Li⁺动力学研究发现两种Li⁺存在快速交换运动，305 K时交换速率为38 s^-1，高于大部分的半晶型PEO/Li⁺；且交换运动所需活化能约为28.7 kJ/mol，低于大部分半晶PEO/Li⁺的活化能。这些结果从分子层面上揭示了Li⁺在PEO结晶表面的离子传输机制，即链端的高运动性促进锂离子的运动，在导电过程中起到重要作用。