Lunghammer S, Prutsch D, Breuer S, Rettenwander D, Hanzu I, Ma Q, Tietz F, Wilkening H M R
Institute for Chemistry and Technology of Materials (NAWI Graz), and Christian Doppler Laboratory for Batteries, Stremayrgasse 9, Graz University of Technology, A-8010, Graz, Austria.
ALISTORE-ERI European Research Institute, 33 Rue Saint Leu, F-80039, Amiens, France.
Sci Rep. 2018 Aug 10;8(1):11970. doi: 10.1038/s41598-018-30478-7.
The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of non-flammable ceramic electrolytes with very high conductivities. NaZr(SiO)PO-type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the µm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in NaScZr(SiO)PO that is characterized by an unprecedentedly high self-diffusion coefficient of 9 × 10 ms at -10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τ of only 2 ns. The underlying asymmetric diffusion-induced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely rapid Na jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.
绿色且经济友好型储能系统的实现需要具备优异性能的材料。未来基于钠这种储量丰富元素的电池，会利用具有非常高电导率的不可燃陶瓷电解质。NaZr(SiO)PO型超离子导体有望为本质安全且可持续的全固态电池铺平道路。到目前为止，从光谱测量中获取的信息很少，无法在原子长度尺度上阐明快速离子跳跃的起源。在此，我们结合宽带电导率光谱和核磁共振（NMR）弛豫，从微米到埃的长度尺度研究钠离子动力学。自旋晶格弛豫NMR揭示了NaScZr(SiO)PO中非常快速的钠离子交换过程，其特征是在-10°C时具有高达9×10 ms的前所未有的高自扩散系数。因此，在远低于环境温度的情况下，钠离子能够参与基本扩散过程，平均停留时间τ仅为2 ns。在兆赫兹范围内测量的潜在不对称扩散诱导NMR速率峰和相应的电导率等温线揭示了相关的离子运动。显然，局部但极其快速的钠跳跃，特别是涉及Sc-NZSP中的过渡位点，触发了长程离子传输，并在室温下将离子电导率提高到2 mS/cm。
