Effect of Doping and Preparation Methods in Solid Electrolyte for Lithium Batteries

 

Recently, solid electrolytes with reasonable room temperature lithium ionic conductivity are being examined for high energy density batteries with safe operation. Several solid state electrolytes based on sulfides and oxides have been investigated [1]. Among them, Garnet phase materials have shown significant improvement in conductivity [2]. Garnet has cubic and tetragonal phases of which the cubic is high temperature with a high ionic conductivity value of 10^-4 S/cm [3]. Several doped compositions have also been reported in order to improve the cubic phase ionic conductivity [4]. LLTO Perovskite system has also been reported for high ionic conductivity value of 10^-4 S/cm [5,6]. Currently, we have synthesized a Ti, Cr, Ta doped Li₇La₃Zr₂O₁₂and LLTO by a simple Pechini process to investigate their ionic conductivities.

A Pechini method was used to synthesize these compounds using nitrate salts, ethylene glycol and citric acid in a 38:36:26 ratio respectively in de-ionized water. The samples were dried in an oven overnight at 120°C and then heat-treated at different temperatures to achieve the desired phases. The optimized product was heat treated at 1000°C for six hours, pelletized and then sintered again at higher temperatures (1200°C) to perform the ionic conductivity measurements using impedance spectroscopy.

Samples were characterized by XRD for phase analysis and electrochemical impedance performance has been investigated under varying temperatures and voltages. The effect of doping on the phase transition in LLZO and LLTO will be presented. Figure 1 shows the impedance plot for the Ta doped garnet (Li₇La₃Zr_1.5Ta_.0.5O₁₂) at room temperature. Ionic conductivity value of 1.27(x10^-4) S/cm has been obtained.

Detailed impedance measurements on systematic doping of Ti, Cr, Ta etc. in LLZO and LLTO phases using various sample preparation conditions, various ohmic contacts for the pellets will be discussed.

Figure. 1 Impedance plot for Li₇La₃Zr_1.5Ta_0.5O₁₂ at room temperature.

Acknowledgements

 

This work has been supported by the US Dept. of Energy/NETL, EERE program. FRB acknowledges Oak Ridge Institute for Science and Education (ORISE) fellowship.

References

 

 

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[2] E. Rangasamy, J. Wolfenstine, J. Sakamoto, Solid State Ionics 206 (2012) 28-32.

[3] I. Kokal, M. Somer, P.H.L. Notten, H.T. Hintzen, Solid State Ionics 185 (2011) 42-46.

[4] Y. Jin, P.J. McGinn, Journal of Power Sources 196 (2011) 8683-8687.

[5] B. Antoniassi, A. H. M Gonzalez, S. L. Fernades, C. F. O. Graeff, Materials Chemistry and Physics 2011, 127, 51.

[6] O. Bohnke, Q.N. Pham, A. Boulant, J. Emery, T. Salkus, M. Barre, Solid State Ionics 2011, 188, 144.