Institute of Applied Physics, University of Tsukuba, Tennodai, Tsukuba 305-8573, Japan.
Phys Chem Chem Phys. 2018 Jul 4;20(26):17615-17623. doi: 10.1039/c8cp02915f.
The migration behaviours of Li+ in three garnet- and one NASICON-type solid oxide electrolytes were studied on the micrometre scale by pulsed-gradient spin-echo (PGSE) 7Li NMR diffusion spectroscopy to clarify common and specific characteristics of each electrolyte. In these solid electrolytes, clear evidences of grain boundary effects in the diffusion of Li+ were not observed. The Li+ diffusion constants were dependent on parameters such as observation time (Δ) and pulsed field gradient (PFG) strength (g) for all the studied inorganic solid electrolytes. For low Δ values, Li+ ions underwent collisions and diffractions with diffraction distance Rdiffraction [μm]. The apparent Li+ diffusion constants (Dapparent [m2 s-1]) exhibited distributions in a wide range. In this paper, we introduced the apparent diffusion radius, rradius [μm], and compared it with Rdiffraction and mean square displacement (MSD) [μm]; the lengths of these distances were of the micrometre order (10-6 m). The relations between the values of rradius, Rdiffraction and MSD suggested that the migration behaviours of Li+ on the micrometre scale were complicated. Using high Δ and high g values, we obtained an equilibrated value of DLi. The temperature dependences of the number of carrier ions were estimated from the DLi values and ionic conductivities in the four solid oxide electrolytes. For simple comparison and reference, the data of DLi and ionic conductivity of LiPF6 in 1 M solution of propylene carbonate were added.
采用脉冲梯度自旋回波（PGSE）7Li NMR 扩散谱研究了 3 种石榴石型和 1 种 NASICON 型固体氧化物电解质中 Li+的迁移行为，以阐明每种电解质的共同和特定特征。在这些固体电解质中，没有观察到 Li+在扩散过程中明显的晶界效应。Li+扩散常数取决于观察时间（Δ）和脉冲磁场梯度（PFG）强度（g）等参数，所有研究的无机固体电解质均如此。对于低Δ值，Li+离子在与衍射距离 Rdiffraction [μm]发生碰撞和衍射。表观 Li+扩散常数（Dapparent [m2 s-1]）表现出广泛的分布。在本文中，我们引入了表观扩散半径 rradius [μm]，并将其与 Rdiffraction 和均方根位移（MSD）[μm]进行了比较；这些距离的长度为微米级（10-6 m）。rradius、Rdiffraction 和 MSD 值之间的关系表明，Li+在微米尺度上的迁移行为很复杂。通过使用高Δ和高 g 值，我们获得了 Li+的平衡扩散值 DLi。根据 DLi 值和四种固体氧化物电解质中的离子电导率，估算了载流子离子数随温度的变化。为了便于简单比较和参考，还添加了 LiPF6 在 1 M 碳酸丙烯酯溶液中的 DLi 值和离子电导率数据。
