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All-solid-state lithium batteries have gained more attention as the next-generation batteries with high energy density, high safety and long life. Recently, cubic-phase lithium-rich anti-perovskite (LiRAP: Li3-x OH x X (X = Cl, Br), including x = 0) compounds have been actively investigated due to their certain advantages to overcome the problems faced by other solid electrolytes [1]. In this work, we investigated the ionic conductivity of Li2OHBr by chemical doping. Li2OHBr was mechanochemically synthesized using LiOH and LiBr [2]. Powder X-ray diffraction (PXRD) pattern of the synthesized sample well agreed with cubic Li2OHBr with a lattice constant of 4.046 Å and no impurities were observed as shown in Fig. 1(a). In the Nyquist plot of Au/Li2OHBr/Au symmetrical cell measured at 25 ºC, one semicircular arc was observed (Fig. 1(b)). The total ionic conductivity of Li2OHBr evaluated based on this semicircular arc was 1.1 × 10–6 S cm–1 at 25 ˚C. In an attempt to improve the ionic conductivity, Li2OHBr1-x Cl x , Li1.8M0.1OHBr (M = Mg, Ca, Sr, Ba) and Li2+x OH1-x Br were synthesized by the same manner as Li2OHBr. The PXRD measurements revealed that most of the modified Li2OHBr formed cubic phase without impurities and the lattice constant slightly changed by chemical doping (Fig. 1(a)). The total ionic conductivity of Li2OHBr0.75Cl0.25, Li1.8Ca0.1OHBr and Li2.2OH0.8Br were 9.3 × 10–7, 4.9 × 10–7 and 3.6 × 10–6 S cm–1 at 25 ºC, respectively. It has been reported that grain-boundary resistance is generally larger than bulk resistance in LiRAPs[3] and also, the LiRAPs have a tendency to form Li vacancy around the grain boundary [4]. Thus, the reason why Li2.2OH0.8Br has larger ionic conductivity than Li2OHBr is because, the Li concentration around grain boundary is increased. So, it can be one of the strategies to improve ionic conductivity of LiRAPs. Acknowledgement: This work was supported by JSPS KAKENHI Grant Number JP18K14318 and in part JP19H05813 (Grant-in-Aid for Scientific Research on Innovative Areas “Interface IONICS”). One of the authors Manoj Krishna Sugumar thankfully acknowledges the financial assistance from Yoshida Scholarship Foundation. References: [1] Y. Zhao, L. L. Daemen, J. Am. Chem. Soc. 134 (2012) 15042. [2] M. K. Sugumar, T. Yamamoto, M. Motoyama, and Y. Iriyama, Solid State Ionics 349 (2020) 15298. [3] J. A. Dawson, P. Canepa, T. Famprikis, C. Masquelier, and M. S. Islam, J. Am. Chem. Soc. 140 (2018) 362. [4] K. Shen, Y. Wang, J. Zhang, Y. Zong, G. Li, C. Zhao, and H. Chen, Phys. Chem. Chem. Phys. 22 (2020) 3030. Figure 1 |
