Solid-state lithium batteries (SSLiBs) has been extensively studied in the past five years. The widely studied solid-state electrolytes (SSEs) includes LiSICON [1], NASICON-type Li conductors [2], perovskites [3] and garnets [4]. It is realized that garnet electrolyte is the most promising oxide electrolyte, due to its high Li-ion conductivity, stability with high voltage Li cathodes and Li anode. However, recently there has been reports [5, 6] on metal element reduction in certain garnet composition. Metal element reduction can lead to electronic conductivity, which is detrimental to cell performance. The reduction reaction is mostly likely to occur at grain boundaries. Since grain boundary is very thin and Li element is hard to detect, limited techniques can characterize the reduction reaction. Fudong and co-workers [5] applied neutron depth profiling technique to study Li content variation. Yisi and co-workers [6] conducted advanced XPS technique to study reduction on garnet grain surface.

TOF-SIMS is surface sensitive technique with nano scale resolution. Herein, we will present our TOF-SIMS study on garnet dopant stability against Li metal. It is found that Nb dopant is not stable to Li metal. Nb doped garnet changes color upon contacting Li metal. This color change progress through the whole ceramic sample. EIS results show that resistance continues increase while the reaction progress. TOF-SIMS results indicate Nb element segregates to grain boundary and presents a different coordination at grain boundary than in bulk garnet.

Reference:

[1] Xu, X. et al. Chem. Mater. 23, 3798-3804 (2011).

[2] Feng, J. K. et al. Mater. Technol. 28, 276-279 (2013).

[3] Ihlefeld, J. F. et al. Adv. Mater. 23, 5663-5667 (2011).

[4] Thangadurai, V. et al. Chem. Soc. Rev. 43, 4714-4727 (2014).

[5] Han, F. et al. Nature Energy 4, 187-196 (2019).

[6] Zhu, Y. et al. Adv. Energy Mater. 9, 1803440 (2019).