Speaker
Description
Lithium-ion (Li-ion) batteries are commonly used as energy storage device for both mobile and stationary applications. Even though the Li-ion technology is clearly a huge success story for modern electrochemistry, lately, there has been serious concerns regarding several aspects, e.g., availability and price of lithium raw material [1]. Consequently, the industry is currently and actively looking for alternatives to the Li-ion technology. Here one option might be to simply replace lithium with its neighbour in the periodic table i.e. sodium (Na) [2], which is a more abundant, accessible and less expensive element. A famous group of such compounds is the so-called Na Super Ionic Conductors (NaSICON). One of the materials within the NaSICON family that is known to have highly mobile sodium ions is Na$_{1+x}$Ti$_{2-x}$Fe$_{x}$(PO$_{4}$)$_{3}$ [3]. Electrochemical measurements have suggested that substitution of Fe for Ti results in higher capacity and better retention. Finally, our own studies [4,5] have revealed enhancements of the battery performance by introducing a nano-scale coating of carbon onto the submicron-sized NaSICON particles. However, the underlying mechanism for such effect is still partly unknown. In this study we have investigated the microscopic Na-ion self-diffusion in Na$_{1+x}$Ti$_{2-x}$Fe$_{x}$(PO$_{4}$)$_{3}$ using the muon spin rotation ($\mu^+$SR) technique [6,7]. We present values of both activation energy of the diffusion process as well as temperature dependent Na-ion self-diffusion coefficients ($D_{\rm Na}$).
[1] G. Alexander, J.B. Goodenough, M. Månsson, et al., Physica Scripta 95, 062501 (2020)
[2] Kubota & Komaba, J. Electrochem. Soc. 162, A2538 (2015)
[3] M.J. Aragón et al., J. Power Sources 252, 208 (2014)
[4] S. Difi et al., J. Phys. Chem. C 119, 25220 (2015)
[5] S. Difi et al., Hyperfine Interact 237, 61 (2016)
[6] Sugiyama, Månsson, Phys. Rev. Lett. 103, 147601 (2009)
[7] M. Månsson & J. Sugiyama, Phys. Scr. 88, 068509 (2013)
