Speaker
Ms
Gugulethu Nkala
(Molecular Science Institute, School of Chemistry, University of the Witwatersrand, private bag X3, Johannesburg, 2050, South Africa)
Description
NASICON-type materials such as rhombohedral LiTi2(PO4)3 (LTP), belonging to the R-3c space group, have been studied as potential solid-state electrolytes because of their thermal and chemical stability, as well high ionic diffusion attributed to their 3D framework consisting of TiO6 octahedra, corner-linked to PO4 tetrahedra, allowing for fast transportation of Li+ cations. [1] However, the room-temperature conductivity of LTP is not practical for use in Lithium ion batteries (LIBs) as it is approximately 4×10-7 S cm-1. [2] Research around this class of materials has been focused on ways to increase their conductivities, including tuning the bottleneck size by substituting Ti4+ with other cations such as Zr4+ and Hf4+, and increasing Li+ concentration by lattice site substitution with M3+ cations as in Al-doped LTP. [3, 4] In the former case, substitutions in the framework with cations of larger ionic radii increase the lattice constants a and c, resulting in a bigger bottleneck size, thus higher conductivity of the mobile cations, Li+.
In this work, we explore the possibility of lattice substitution as well as investigate if Sn4+-doped LTP formulations exhibit an improved ionic conductivity compared to LTP. Materials of the general formula Li〖Ti〗_(2-x) 〖Sn〗_x (〖PO〗_4 )_3 (for 0, 2, 4, 6, 8, 10, 50 mole % Sn) have been synthesized following the conventional solid-state method. Room-temperature X-ray diffraction was employed as the primary characterization technique, giving insight into the phase compositions and relative phase purities of the products. Room-temperature Raman spectroscopy was used to further establish the structural properties of LTP as a function of dopant percentage. Information about the phase stabilities of the aforementioned materials was obtained by differential thermal analysis, establishing whether or not there was any temperature-dependent polymorphism exhibited by the said products. The room-temperature conductivities were determined using electrochemical impedance spectroscopy.
References:
1. Anantharamulu, N., Rao, K.K., Rambabu, G., Kumar, B.V., Radha, V. and Vithal, M., 2011. A wide-ranging review on Nasicon type materials. Journal of materials science, 46(9), pp.2821-2837.
2. Bachman, J.C., Muy, S., Grimaud, A., Chang, H.H., Pour, N., Lux, S.F., Paschos, O., Maglia, F., Lupart, S., Lamp, P. and Giordano, L., 2015. Inorganic solid-state electrolytes for lithium batteries: mechanisms and properties governing ion conduction. Chemical reviews, 116(1), pp.140-162.
3. Aono, H., Sugimoto, E., Sadaoka, Y., Imanaka, N. and Adachi, G.Y., 1993. The Electrical Properties of Ceramic Electrolytes for LiM x Ti2− x (PO 4) 3+ yLi2 O, M= Ge, Sn, Hf, and Zr Systems. Journal of the Electrochemical Society, 140(7), pp.1827-1833.
4. Wang, S., Ben, L., Li, H. and Chen, L., 2014. Identifying Li+ ion transport properties of aluminum doped lithium titanium phosphate solid electrolyte at wide temperature range. Solid State Ionics, 268, pp.110-116.
Primary author
Ms
Gugulethu Nkala
(Molecular Science Institute, School of Chemistry, University of the Witwatersrand, private bag X3, Johannesburg, 2050, South Africa)
Co-authors
Dr
Caren Billing
(Molecular Science Institute, School of Chemistry, University of the Witwatersrand, private bag X3, Johannesburg, 2050, South Africa)
Prof.
David Billing
(Molecular Science Institute, School of Chemistry, University of the Witwatersrand, private bag X3, Johannesburg, 2050, South Africa)
Dr
Roy Forbes
(Molecular Science Institute, School of Chemistry, University of the Witwatersrand, private bag X3, Johannesburg, 2050, South Africa)
