**4. Conclusions**

In summary, highly densified LAGP pellets were fabricated by using SPS technique and exhibited high ionic conductivity at room temperature. The influence of SPS sintering temperatures (600–750 ◦C) and times (1–10 min) on the microstructure, density, and ionic conductivity of the LAGP pellets were studied in detail. It can be concluded that the optimal SPS condition for LAGP pellets was 650 ◦C and 10 min, and the synthesized LAGP pellets were dense with minimal visible porosity. The density of the LAGP pellets was as high as 3.477 g cm<sup>−</sup>3, a relative density of 97.6% and the ionic conductivity was 3.29 × 10−<sup>4</sup> S cm<sup>−</sup>1, with a activation energy of 0.239 eV at RT. Sintering temperatures higher than 650 ◦C caused the formation of voids and microcracks in the LAGP pellets, negatively a ffecting the density and ionic conductivity. These results clearly demonstrate the potential of the SPS approach to synthesize solid electrolytes used in ASSLIBs, owing to the drastically reduced sintering temperature and time compared with that used in conventional sintering processes.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/9/8/1086/s1, Figure S1: Low-magnification SEM images of SPS pellets sintered for 2 min at different temperatures of (a) 650 ◦C, (b) 700 ◦C, and (c) 750 ◦C.

**Author Contributions:** Conceptualization, H.Z. and J.L.; Funding acquisition, J.L.; Investigation, H.Z.; Methodology, A.P. and S.D.; Project administration, J.L.; Resources, L.B.; Supervision, J.L.; Writing – original draft, H.Z.; Writing – review & editing, A.P., S.D., L.B. and J.L.

**Acknowledgments:** This work was supported by the Nature Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), B.C. Knowledge Development Fund (BCKDF), and the University of British Columbia (UBC). Hongzheng Zhu is grateful for financial support from Chinese Scholarship Council (CSC).

**Conflicts of Interest:** The authors declare no conflict of interest.
