Ion conductor for sodium ion battery, secondary battery comprising same, and method for manufacturing ion conductor for sodium ion battery

Abstract

The present invention relates to a solid ion conductor which has a high ion conductivity and can be used for an all-solid-state sodium ion battery. The ion conductor for a sodium ion battery according to the present invention has a composition represented by chemical formula 1. [Chemical formula 1] Na3-XGd1-XZrXCl6 (here, x=0.1-0.9)

Description

Ionic conductor for sodium ion battery, secondary battery including same, method for manufacturing ionic conductor for sodium ion battery

[0001] This invention was supported by the following national research and development project.

[0002] [Project ID] 1415184637

[0003] [Assignment Number] 20012196

[0004] Ministry of Trade, Industry and Energy

[0005] [Name of Project Management (Specialist) Institution] Korea Institute of Industrial Technology Planning and Evaluation

[0006] [Research Project Name] Industrial Technology Alchemist Project

[0007] [Research Project Name] AI-Based Supercritical Materials

[0008] The present invention relates to an ion conductor for a sodium ion battery having high ion conductivity and usable for an all-solid-state sodium ion battery, and a secondary battery including the same, and a method for manufacturing the ion conductor for a sodium ion battery.

[0009] All-solid-state batteries are attracting attention as a promising solution that can overcome the limitations of existing lithium-ion battery technology and meet the growing demand for high energy density and safe storage systems.

[0010] Among the ionic conductors developed for all-solid-state batteries to date, some exhibit conductivity comparable to liquid electrolytes. However, issues related to interfacial decomposition reactions remain unresolved. Furthermore, another challenge facing lithium-ion battery technology is the need for alternatives due to the shortage of lithium metal.

[0011] Because sodium is abundant on Earth, if a sodium-containing solid electrolyte can be realized with performance comparable to that of lithium-based electrolytes, it could become a cost-effective alternative to lithium. Furthermore, all-solid-state sodium-ion batteries could offer improved safety and higher energy density through the use of higher-voltage cathodes, metal anodes, and a layered architecture.

[0012] Solid electrolytes for halide-based sodium-ion batteries, which are currently being developed, are known to have high electrochemical stability compared to sulfide-based solid electrolytes, and in particular, good stability with high-voltage cathode materials.

[0013] Among the solid electrolytes for sodium halide ion batteries, Na 2.4 Er 0.4 Zr 0.6 Cl6 and Na 2.25 Y 0.25 Zr 0.75 Cl6 has the highest ionic conductivity (0.04 mS / cm) among sodium halide electrolytes to date, but does not achieve the ionic conductivity (approximately 1 mS / cm) considered essential from a commercial perspective.

[0014] The purpose of the present invention is to provide an ionic conductor for a sodium ion battery having a commercially applicable level of ionic conductivity, which is a halide-based material having high electrochemical stability and good stability with a high-voltage cathode material, and a secondary battery including the same.

[0015] One aspect of the present invention is to provide an ion conductor for a sodium ion battery, represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Na 3-x Gd 1-x Zr x Cl6

[0018] (where x = 0.1 ~ 1.0)

[0019] Another aspect of the present invention provides a secondary battery comprising a positive electrode, a negative electrode disposed opposite the positive electrode with a predetermined gap therebetween, and an electrolyte disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, or the electrolyte comprises an ion conductor for a sodium ion battery.

[0020] The ion conductor for a sodium ion battery according to the present invention is a halide-based material having high electrochemical stability and good stability with a high-voltage cathode material, while exhibiting high ion conductivity that is commercially applicable.

[0021] Figure 1 shows Na synthesized at 480°C. 3-x Gd 1-x Zr x This is the XRD pattern of Cl6.

[0022] Figure 2 shows Na synthesized at 460°C. 3-x Gd 1-x Zr x This is the XRD pattern of Cl6.

[0023] Figure 3 is a schematic diagram of the structure of an EIS cell for measuring Nyquist plots.

[0024] Figure 4 shows Na synthesized at 480°C. 3-x Gd 1-x Zr x This is the Nyquist plot of Cl6.

[0025] Figure 5 shows Na synthesized at 460°C. 3-x Gd 1-x Zr x This is the Nyquist plot of Cl6.

[0026] Figure 6 is Na 2.5 Gd 0.5 Zr 0.5 This is the Nyquist plot of the Cl6 pellet.

[0027] Figure 7 is Na 2.5 Gd 0.5 Zr 0.5 This is the result of Rietveld analysis of Cl6.

[0028] The terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her own invention.

[0029] Hereinafter, the present invention will be described in detail based on preferred embodiments thereof with reference to the attached drawings. The embodiments described in this specification and the configurations depicted in the drawings are merely preferred embodiments of the present invention and do not fully represent the technical ideas of the present invention. Therefore, various equivalents and modified examples may exist that can replace them at the time of this application, and the scope of the present invention is not limited to the embodiments described below.

[0030]

[0031] [Embodiment 1]

[0032] The first embodiment of the present invention is an ion conductor for a sodium ion battery represented by the following chemical formula 1.

[0033] [Chemical Formula 1]

[0034] Na 3-x Gd 1-x Zr x Cl6

[0035] (where x = 0.1 ~ 0.9)

[0036] In terms of ionic conductivity, it is preferable that the above x includes Zr in the range of 0.1 to 0.9. More preferably, x may be 0.3 to 0.8, and most preferably, x may be 0.4 to 0.6.

[0037] The ion conductor for a sodium ion battery according to the present invention may have a main phase having a crystal structure of space group P21 / n. It is preferable that the composition have a crystal structure of space group P21 / n to obtain good ion conductivity.

[0038] In the present invention, the main phase means a phase that is mainly included and may include other phases other than the main phase, and may have a volume fraction of 70% or more, 80% or more, preferably 90% or more, and more preferably 95% or more.

[0039]

[0040] [Embodiment 2]

[0041] A second embodiment of the present invention is a secondary battery including an ion conductor for a sodium ion battery.

[0042] A secondary battery according to a second embodiment comprises a positive electrode, a negative electrode disposed opposite the positive electrode with a predetermined gap therebetween, and an electrolyte disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, or the electrolyte comprises an ion conductor according to the first embodiment.

[0043] The above positive electrode, negative electrode and electrolyte may be applied in any possible form known in the secondary battery field, and may preferably be configured as an all-solid-state battery.

[0044]

[0045] [Embodiment 3]

[0046] A third embodiment of the present invention is a method for manufacturing an ion conductor for a sodium ion battery, comprising the following steps (a) to (d).

[0047] (a) a step of preparing a precursor of a material constituting an ion conductor for a sodium ion battery as described in any one of claims 1 to 3;

[0048] (b) a step of crushing the precursor;

[0049] (c) A step of synthesizing by heating the pulverized precursor at a temperature of 470°C to 900°C for 6 to 48 hours.

[0050] (d) a step of quenching the synthesized material;

[0051] In the above step (a), the precursor is a material containing sodium (Na), gadolinium (Gd), zirconium (Zr), and chlorine (Cl), and may be, for example, sodium (Na) chloride, gadolinium (Gd) chloride, and zirconium (Zr) chloride.

[0052] In the above step (c), if the synthesis temperature is less than 470°C, it is difficult to obtain a compound having a crystal structure with excellent ion conductivity, and if it is more than 900°C, contamination may occur from the synthesis vessel (e.g., crucible).

[0053] In the above step (c), if the synthesis time is less than 6 hours, sufficient synthesis is difficult to achieve, and if it exceeds 48 hours, energy costs become excessive. Therefore, 6 to 48 hours is preferable, 8 to 48 hours is more preferable, 10 to 48 hours is more preferable, and 12 to 48 hours is most preferable.

[0054] In the above step (d), the quenching may be gas quenching, and the gas quenching may be, for example, air quenching.

[0055] The ion conductor for a sodium ion battery synthesized in the above step (d) may have a crystal structure of a space group P21 / n.

[0056]

[0057] <Example 1>

[0058] Sodium chloride (NaCl, 99.99% purity) powder, gadolinium chloride (GdCl3, 99.99% purity) powder, and zirconium chloride (ZrCl4, 99.99% purity) powder were used as precursors for synthesizing ion conductors for sodium ion batteries.

[0059] Precursor powders were weighed to have stoichiometric ratios of 3-x NaCl, 1-x GdCl3, and x ZrCl4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0). The weighed raw material powders were mixed and ground using an agate mortar for 10 minutes.

[0060] The mixed powder prepared in this way was placed in a quartz tube and sealed under vacuum conditions.

[0061] The sealed quartz tube was placed in a box furnace, heated to 480°C at a heating rate of 40°C / h, maintained for 1 hour, and then quenched in air.

[0062]

[0063] <Example 2>

[0064] A raw material mixture powder was prepared in the same manner as in Example 1.

[0065] The prepared mixed powder was placed in a quartz tube, sealed under vacuum conditions, the sealed quartz tube was placed in a box furnace, heated to 460°C at a heating rate of 40°C / h, maintained for 12 hours, and then slowly cooled at a rate of 5°C / h.

[0066]

[0067] Crystal structure analysis

[0068] To confirm the crystal structure of the compounds synthesized according to Examples 1 and 2, X-ray diffraction (XRD) patterns were obtained within the 2θ range of 10 to 90° at a scan rate of 5° per minute using a device equipped with Cu Kα radiation.

[0069] Figure 1 shows Na synthesized at 480°C. 3-xGd 1-x Zr x This is the XRD pattern of Cl6.

[0070] Na synthesized at 480℃ 3-x Gd 1-x Zr x For Cl6, it was found that the crystal structure has space group P21 / n when x is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, and 1.0.

[0071] Figure 2 shows Na synthesized at 460°C. 3-x Gd 1-x Zr x This is the XRD pattern of Cl6.

[0072] Na synthesized at 460℃ 3-x Gd 1-x Zr x For Cl6, Na3GdCl6 and Na 2.9 Gd 0.9 Zr 0.1 Cl6 exhibited a crystal structure in space group R-3. Na 2.1 Gd 0.1 Zr 0.9 Cl6 and Na2ZrCl6 showed crystal structures of space group P-3m1. When x was 0.2, 0.3, 0.4, 0.5, 0.6, and 0.8, the crystal structures of space groups R-3 and P-3m1 appeared as mixed phases.

[0073] That is, the crystal structures of the compound synthesized at a relatively high temperature and then quenched according to Example 1 were found to be different from those of the compound synthesized at a relatively low temperature and then slowly cooled according to Example 2.

[0074]

[0075] Cell fabrication and impedance measurement

[0076] As shown in Fig. 3, a compound pellet having a diameter of 13Φ was sandwiched between two indium (In) foils, and two stainless steel (SUS) disks were placed on both sides of the pellet, and then pressed with a press at a load of 4 tons for 2 minutes to manufacture a solid electrolyte (SSE) pellet.

[0077] Then, it was placed in the center of the POM mold, and indium foil (50 μm thick) was placed on the top and bottom of the solid electrolyte pellet to reduce the resistance of the stainless steel surface. Finally, the cell was assembled, and impedance was measured after applying 4 tons of pressure using a torque wrench.

[0078] EIS measurements were performed at room temperature by applying a sine wave with an amplitude of ±10 m V over a frequency range of 105 Hz, and the results were as shown in Figs. 4 and 5, and the results are summarized in Table 1 below.

[0079] Example 1Na 3-x Gd 1-x Zr x Cl6x=0x=0.1x=0.2x=0.3x=0.4x=0.5x=0.6x=0.7x=0.8x=0.9x=1.0σ(mS / cm)0 .000030.001330.01830.1020.1860.3380.1370.1200.0880.0310.0004 Example 2 Na 3-x Gd 1-x Zr x Cl6x=0x=0.1x=0.2x=0.3x=0.4x=0.5x=0.6x=0.7x=0.8x=0.9x=1.0σ(μS / cm)0.01450.5070.8651.0091.3933.4127.0242.8352.8070.5710.218

[0080] As confirmed in Table 1, Na 3-x Gd 1-x Zr x In Cl6, the ionic conductivity increases with increasing Zr content, peaks at a Zr content of 0.5 to 0.6, and then decreases again.

[0081] For Example 1, the highest ionic conductivity was Na 2.5 Gd 0.5 Zr 0.5 It is Cl6 and reached 0.338 mS / cm.

[0082] In comparison, the trend of change in ionic conductivity according to the content of Zr in Example 2 is similar to that in Example 1, Na 2.4 Gd 0.4 Zr 0.6 Cl6 showed the highest ionic conductivity, but the value was 7.024 μS / cm, which was significantly lower than that of Example 1.

[0083] This difference in ionic conductivity appears to be due to the difference in that the space group of the crystal structure of Example 1 is P21 / n, whereas the space group of the crystal structure of Example 2 is a mixed phase of R-3 and P-3m1.

[0084] From this, Zr can improve ionic conductivity, but its effect is limited when R-3 and P-3m1 phases are mixed, so Na 3-x Gd 1-x Zr x It can be said that it is desirable to synthesize Cl6 by proceeding at high temperature as in Example 1 and then quenching it so that it becomes a phase with a space group of P21 / n.

[0085]

[0086] EIS measurement

[0087] Na synthesized according to Example 1, which showed the highest ionic conductivity in EIS measurements 2.5 Gd 0.5 Zr 0.5 After polishing the Cl6 pellets with abrasive paper to make the surface smooth, cells were made in the same manner as the cell manufacturing process described above, and EIS measurements were performed.

[0088] Figure 6 shows Na applied to an electrochemical cell. 2.5 Gd 0.5 Zr 0.5This is the Nyquist plot of the Cl6 pellet. Through the measurements in Fig. 6, Na 2.5 Gd 0.5 Zr 0.5 The ionic conductivity of the Cl6 pellet was measured to be 0.98 mS / cm.

[0089] Meanwhile, Na 2.5 Gd 0.5 Zr 0.5 As confirmed through Rietveld refinement of the XRD pattern obtained from the Cl6 sample, as shown in Fig. 7, Na 2.5 Gd 0.5 Zr 0.5 The Cl6 sample consists entirely of the P21 / n phase.

[0090] Na 2.5 Gd 0.5 Zr 0.5 The ionic conductivity of the Cl6 sample achieved the highest level of ionic conductivity among the halide-based solid electrolytes for all-solid-state sodium-ion batteries.

Claims

1. An ion conductor for a sodium ion battery, represented by the following chemical formula 1. [Chemical Formula 1] On 3-x Mr. 1-x Zr x Cl 6 (where x = 0.1 ~ 0.9) 2. In paragraph 1, An ionic conductor for a sodium ion battery, wherein the above x is 0.3 to 0.

8.

3. In paragraph 1, An ionic conductor for a sodium ion battery, wherein the above x is 0.4 to 0.

6.

4. In any one of paragraphs 1 to 3, The above ion conductor for sodium ion batteries has a main phase in space group P2. 1 An ionic conductor for a sodium ion battery having a crystal structure of / n.

5. Bipolar, A cathode and a positive electrode are positioned opposite each other at a predetermined distance from each other. Containing an electrolyte disposed between the positive and negative electrodes, A secondary battery, wherein at least one of the positive electrode, negative electrode or electrolyte comprises a solid ion conductor as described in any one of claims 1 to 3. 6.(a) A step of preparing a precursor of a material constituting an ion conductor for a sodium ion battery according to any one of claims 1 to 3; (b) a step of crushing the precursor; (c) a step of synthesizing by heating the pulverized precursor at a temperature of 470°C to 900°C for 6 to 48 hours; and (d) a step of quenching the synthesized material; A method for producing an ion conductor for a sodium ion battery.

7. In paragraph 6, A method for producing an ion conductor for a sodium ion battery, wherein the above precursors are Na chloride, Gd chloride, and Zr chloride.

8. In paragraph 6, The above quenching is a method for manufacturing an ion conductor for a sodium ion battery, wherein the quenching is gas quenching.

9. In paragraph 6, The ion conductor for a sodium ion battery synthesized in the above step (d) has a space group P2 of the main phase. 1 A method for manufacturing an ion conductor for a sodium ion battery having a crystal structure of / n.

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