Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev Lett. 2013 Jul 5;111(1):018301. doi: 10.1103/PhysRevLett.111.018301. Epub 2013 Jul 3.
The dynamics of Li(+) transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) and dielectric spectroscopy with molecular dynamics (MD) simulations. The results are summarized in a relaxation time map covering wide ranges of temperature and time. The temperature dependence of the dc conductivity and the dielectric α relaxation time is found to be identical, indicating a strong coupling between both. The relaxation times obtained from the NSE measurements at 0.05 Å(-1)<q<0.2 Å(-1) are of similar magnitude as the relaxation time of Li(+) predicted by MD simulation. Our results suggest that the characteristic live times of the ions within the oxygen cages are mainly determined by the α relaxation that corresponds to local segmental motions of polymers, to a much lesser extent by the main chain relaxation, and not at all by the β relaxation or other faster processes. It is the first time decisive experimental evidence for a microscopic picture of the Li ion transportation process is shown in which the PEO chain forms EO cages over several monomer units and the Li ion "jump" from cage to cage. The role of the backbone of the polymer is discussed and contributes signifcantly to the Li ion transportation process. Moreover, detailed characteristic length and time scales of the Li(+) transport process in this polymer electrolyte are identified and interpreted.
通过将中子自旋回波（NSE）和介电光谱与分子动力学（MD）模拟相结合，研究了聚乙烯氧化物（PEO）和双（三氟甲烷磺酰）亚胺锂（LiTFSI）混合物中 Li(+)传输的动力学。结果总结在一个涵盖宽温度和时间范围的弛豫时间图中。发现直流电导率和介电 α 松弛时间的温度依赖性相同，表明两者之间存在强烈耦合。从 0.05 Å(-1)<q<0.2 Å(-1)的 NSE 测量中获得的弛豫时间与 MD 模拟预测的 Li(+)弛豫时间具有相似的大小。我们的结果表明，离子在氧笼内的特征寿命主要由对应于聚合物局部段运动的 α 松弛决定，在较小程度上由主链松弛决定，而与 β 松弛或其他更快的过程无关。这是首次在微观层面上展示 Li 离子输运过程的决定性实验证据，其中 PEO 链在几个单体单元上形成 EO 笼，Li 离子“跳跃”从笼到笼。讨论了聚合物主链的作用，并对 Li 离子输运过程有重要贡献。此外，还确定并解释了这种聚合物电解质中 Li(+)传输过程的详细特征长度和时间尺度。
