Title Page
Contents
Abstract 9
Chapter 1. Introduction 10
1.1. Secondary battery 10
1.2. Cathode 11
1.3. Anode 12
1.4. Electrolyte 13
1.5. Li ion battery 14
1.6. Na ion battery 15
Chapter 2. Vacancy-controlled quaternary sulfide Na₃₋xZn₁₋xGa₁₊xS₄ with improved ionic conductivity and aqueous stability[이미지참조] 16
2.1. Introduction 16
2.2. Experiment 18
2.3. Results and Discussion 20
Chapter 3. Conclusion 43
Chapter 4. Reference 44
초록 51
Table 1. Rietveld refinement results of Na₃ZnGaS₄. 30
Table 2. Rietveld refinement results of Na₂.₉₅Zn₀.₉₅Ga₁.₀₅S₄. 30
Table 3. Rietveld refinement results of Na₂.₉₀Zn₀.₉₀Ga₁.₁₀S₄. 31
Table 4. Rietveld refinement results of Na₂.₈₅Zn₀.₈₅Ga₁.₁₅S₄. 31
Table 5. Rietveld refinement results of Na₂.₈₀Zn₀.₈₀Ga₁.₂₀S₄. 32
Table 6. Rietveld refinement results of Na₂.₇₀Zn₀.₇₀Ga₁.₃₀S₄. 32
Table 7. Rietveld refinement results of Na₂.₆₀Zn₀.₆₀Ga₁.₄₀S₄. Due to the presence of NaGaS₂ impurities, the total amount of Na was assumed to be 2.70 and all the vacancies were placed on Na(2) sites. 33
Table 8. Rietveld refinement results of Na₂.₅₀Zn₀.₅₀Ga₁.₅₀S₄. Due to the presence of NaGaS₂ impurities, the total amount of Na was assumed to be 2.70 and all the vacancies were placed on Na(2) sites. 33
Figure 1. Calculated equilibrium voltages for the decomposition reactions of (A) Na₃ZnGaS₄ and (B) Na₃ZnGaSe₄. The green shaded area denotes the thermodynamic ESW. (C) Driving force for the decompositions of Na₃ZnGaS₄... 21
Figure 1.1. The most stable Zn/Ga distribution, determined via Coulomb energy and DFT formation energy calculations. The fractional coordinates of Zn: (0.07860, 0.12750, 0.81190), (0.42140, 0.87250, 0.31190),... 22
Figure 1.2. LSV at a scan rate of 0.1 mV s¯¹. Open circles indicate open-circuit voltages, from which the voltage was scanned in either negative or positive directions. 22
Figure 2. (A) Structural features of Na₃ZnGaS₄; highlighting two interpenetrating chains consisting of corner-shared T2 supertetrahedra. (B) Connectivity of Na ions with interatomic distances of less than 4.2 Å. (C) Evolution of... 25
Figure 2.1. Polyhedron connectivity (A) Na(1)S₆ and (B) Na(2)S₆. Due to corner-shared nature between Na(1) octahedra in (A), Na(1)-Na(1) conduction is expected to be low. 26
Figure 2.2. Iso-energy surfaces of -1.1 eV with Emin=-1.81 eV. Percolation threshold was +0.66 eV (E=-1.15 eV) along a-axis and b-axis, and +0.58 eV (E=-1.23 eV) to c-axis direction. It is obvious that Na(1) sites have no...[이미지참조] 26
Figure 3. (A) XRD patterns of Na₃₋xZn₁₋xGa₁₊xS₄ (x=0, 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, and 0.50). (B) Change in the axis lengths and unit cell volumes with 'x'. (C) Change in the SOF and Uiso values for Na(1) and Na(2) with...[이미지참조] 28
Figure 3.1. Full-pattern Rietveld refinement of XRD patterns for Na₃₋xZn₁₋xGa₁₊xS₄ using the I4₁/acd structure. Red dots, black line, and blue line represent the experimental, calculated, and difference profiles, respectively. The...[이미지참조] 29
Figure 4. (A) EIS spectra of Na₃₋xZn₁₋xGa₁₊xS₄ (x=0~0.50) under AC voltage modulation of ±10 mV at RT (2 MHz~0.1 Hz). The inset shows the EIS spectrum of Na₃ZnGaS₄. (B) Arrhenius plot of бion in Na₃₋xZn₁₋xGa₁₊xS₄ (x=...[이미지참조] 36
Figure 4.1. Comparison of XRD patterns of Na₃₋xZnxGa₁₊xS₄.[이미지참조] 37
Figure 4.2. EIS spectra of Na₃₋xZnxGa₁₊xS₄. In contrast to the conspicuous enhancement of бion upon incorporating vacancies in Na₃₋xZnxGa₁₊xS₄, the бion was increased only by two-fold due to the pre-existing vacancies in Na₃ZnGaS₄.[이미지참조] 37
Figure 4.3. (A) EIS spectrum and (B) Arrhenius plot for a hot-pressed (200℃, 5T, 10 min) pellet of Na₂.₈Zn₀.₈Ga₁.₂S₄. 38
Figure 4.4. Difference in MSD plots along the axis directions in 3 vac (Na₂.₈₁Zn₀.₈₁Ga₁.₁₉S₄). 38
Figure 5. (A) Concentration changes in H₂S gas liberated from Na₂.₈Zn₀.₈Ga₁.₂S₄ during exposure to humid N₂. The behaviors in Na₃PS₄ and Na₃SbS₄ also are included for comparison. XRD patterns of pristine/wet (B)... 40
Figure 5.1. EIS spectrum for Na₂.₈Zn₀.₈Ga₁.₂S₄ after drying at 80℃. The resistance of 0.57 kW was quite close to 0.55 kW measured with as-made Na₂.₈Zn₀.₈Ga₁.₂S₄ (Figure 4A). 41
Figure 5.2. (A) Recovery of XRD patterns of Na₃SbSe₄ after vacuum-drying at 150℃. (B) Comparison of EIS spectra before and after soaking in water. Despite the sign of reactions in water (possibly, excessive hydration... 41