Hosted by: Feng Wang (SET) and Dong Su (CFN)

All-solid-state Li-ion batteries (LIBs) are promising candidates to solve some problems of conventional LIBs with liquid electrolytes. However, large interfacial resistance of Li-ion transfer at the electrode/solid-electrolyte interface causes low power density and prevents practical use. One effective idea to reduce the resistance is in situ fabrication of electrode active materials from parent solid electrolytes. Such in situ formed electrodes were discovered in Li2O-Al2O3-TiO2-P2O5-based solid electrolytes (LATP) [1]. The electrodes are irreversibly formed by decomposing the negative-side electrolytes with the excess Li-ion insertion reaction. However, it was not clear how the electrodes were formed in nanometer scale during the charge-discharge processes. Here, we used electron holography to visualize the electric potential distribution [2,3] and spatially-resolved electron energy loss spectroscopy (SR-EELS) to directly observe the Li distribution and electronic structure changes of Ti and O in the formed electrodes [3-5]. We succeeded in observing the potential changes during the fabrication processes of the in situ formed electrode. We also found from SR-EELS that the inserted Li-ions were distributed in 400 - 700 nm around the negative-side electrolytes, and the Ti was reduced from Ti4+ to Ti3+. Pico-meter scale expansion of O-O distance due to the Li insertion reaction was also visualized. The author will report the detail of those microscopy techniques and their results in the presentation. References [1] Y. Iriyama, C. Yada, T. Abe, Z. Ogumi, K. Kikuchi, Electrochem. Commun., 8 (2006) 1287-1291. [2] K. Yamamoto, Y. Iriyama, T. Asaka, T. Hirayama, H. Fujita, K. Nonaka, K. Miyahara, Y. Sugita, Z. Ogumi, Electorochem. Commun., 20 (2012) 113-116. [3] K. Yamamoto, Y. Iriyama, T. Hirayama, Microscopy 66 (2017) 50-61. (Special issue: Challenges for lithium detection), https://doi.org/10.1093/jmicro/dfw043. (open acce