| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 104 === Unlike the conventional milling method of preparing glasses and glass-ceramic, we implement a different way to make the sulfite glasses. In this study, we use propylamine as a solvent to dissolve the starting materials of Na2S and P2S5. Through the dissolution process, the obtained powder achieves composition homogeneity at the molecular level. Then we press the powder with uniaxial force(469 MPa) to form glass.
The X-ray diffraction patterns of xNa2S-(100-x)P2S5 (x=75,80) show two broad background diffractions at low angle and a few unknown peaks of low intensity which indicate they are amorphous. After heating the glassy sample of 75Na2S-25P2S5 at 270 oC, the sharp peaks in X-ray diffraction pattern emerge, matching the pattern of cubic Na3PS4 crystal. It seems that crystallization of sulfide glass is easy at such a high sodium content. In addition to glasses and glass-ceramic electrolyte, we also use solid-state reaction to synthesize NaFe(SO4)2 and NaCrO2. They are candidate compositions of sodium battery cathode.
After measuring electrical impedance of xNa2S-(100-x)P2S5
(x=75,80) and 75Na2S-25P2S5 which has been heated at 270 oC, we compare the sodium ion conductivity of the three solid electrolytes at different temperature. The ion conductivity of 75Na2S-25P2S5 is measured 4.8 x 10-7 S cm-1 at 30 oC and 1.9 x 10-3 S cm-1 at 200 oC in the heating ramp at a 20 oC interval. In the cooling ramp at a 10 oC interval, the ion conductivity is slight higher, measured 2.0 x 10-6 S cm-1 at 30 oC and 1.3 x 10-3 S cm-1 at 200 oC. For the composition of high sodium content, 80Na2S-20P2S5, the ion conductivity is measured 1.2 x 10-7 S cm-1 at 33 oC and 1.6 x 10-3 S cm-1 at 200 oC in the heating ramp. And the ion conductivity is 4.3 x 10-7 S cm-1 at 33 oC and 1.5 x 10-3 S cm-1 at 200 oC in the cooling ramp.
On the ion conductivity of Na3PS4, the ion conductivity is 7.3 x 10-6 S cm-1 at 33 oC and 2.1 x 10-3 S cm-1 at 200 oC in the heating ramp. And the ion conductivity is 2.3 x 10-6 S cm-1 at 33 oC and 8.4 x 10-4 S cm-1 at 200 oC in the cooling ramp.
On the ion conductivity of NaCrO2, the ion conductivity is 3.8 x 10-9 S cm-1 at 35 oC and 1.8 x 10-7 S cm-1 at 140 oC in the heating ramp. And the ion conductivity of NaFe(SO4)2 is 2 x 10-9 S cm-1 at 100 oC and 3.6 x 10-8 S cm-1 at 160 oC in the heating ramp.
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