Hayamizu Kikuko, Seki Shiro
Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573, Japan.
Department of Environmental Chemistry and Chemical Engineering, Kogakuin University, Hachioji, Tokyo 192-0015, Japan and Material Science Laboratory, Central Research Institute of Electric Power Industry, Yokosuka 240-0196, Japan.
Phys Chem Chem Phys. 2017 Aug 30;19(34):23483-23491. doi: 10.1039/c7cp03647g.
The long-range Li ion diffusion in LiAlGe(PO) (LAGP), a NASICON-type glass ceramic conductor with high ionic conductivity, was studied using pulsed-gradient spin-echo (PGSE) Li NMR. LAGP is stable in air and water, and can be used for all-solid Li batteries as well as next generation Li-air batteries. The Li ion conduction mechanisms in the micrometer space are important for the design of Li batteries and development of new materials. Our previous studies on sulfide-based and garnet-type solid conductors showed that uniform Li ion diffusion is hampered by narrow pathways surrounded by stationary anions. The Li ions are engaged in parameter-dependent diffusion with the parameters being observation time (Δ) and pulsed-field gradient (PFG) strength (g); this is completely different from the Li diffusion in solution and polymer electrolytes, and also from molecular diffusion in neutral porous media. In this study, we observed apparent diffusion constant (D) values for the LAGP, that were almost continuously distributed within a limited range at a certain Δ. At very long observation times (above 300 ms) and large g (∼13 Tm), an equilibrated diffusion constant (close to the tracer diffusion constant) could be observed. The apparent activation energy of Li ion diffusion was about 16 kJ mol, which was smaller than the activation energy for the ionic conductivity. The temperature-dependent carrier ion numbers were estimated.
利用脉冲梯度自旋回波（PGSE）锂核磁共振研究了具有高离子电导率的NASICON型玻璃陶瓷导体LiAlGe(PO)（LAGP）中的长程锂离子扩散。LAGP在空气和水中稳定，可用于全固态锂电池以及下一代锂空气电池。微米空间中的锂离子传导机制对于锂电池设计和新材料开发很重要。我们之前对硫化物基和石榴石型固体导体的研究表明，均匀的锂离子扩散受到固定阴离子包围的狭窄通道的阻碍。锂离子参与与参数相关的扩散，参数为观测时间（Δ）和脉冲场梯度（PFG）强度（g）；这与溶液和聚合物电解质中的锂扩散以及中性多孔介质中的分子扩散完全不同。在本研究中，我们观察到LAGP的表观扩散常数（D）值，在特定的Δ下，这些值在有限范围内几乎连续分布。在非常长的观测时间（超过300毫秒）和大g（约13 Tm）时，可以观察到平衡扩散常数（接近示踪扩散常数）。锂离子扩散的表观活化能约为16 kJ/mol，低于离子电导率的活化能。估计了温度依赖的载流子离子数。
