Solid electrolyte, method for the same, and all-solid-state secondary battery comprising the same

Abstract

The solid electrolyte according to the present invention is represented by the following chemical formula 1 and has a trigonal crystal structure. [Chemical Formula 1] Na3.2+xZr2-xNxSi2.2P1.2O12 In the above chemical formula 1, N is a p-block element, and x is 0.01 to 0.3.

Description

Technology Field

[0001] The present invention relates to a solid electrolyte, a method for manufacturing the same, and an all-solid-state secondary battery comprising the same, and more specifically, to a solid electrolyte comprising a p-block element, a method for manufacturing the same, and an all-solid-state secondary battery comprising the same. Background Technology

[0003] Recently, driven by industrial demands, the development of batteries with high energy density and safety is actively underway. For example, lithium-ion batteries are being commercialized not only in the fields of information and communication devices but also in the automotive sector. In the automotive sector, safety is considered particularly important because it is directly related to human life.

[0004] All-solid-state batteries in which liquid electrolyte is replaced with a solid electrolyte are being proposed. By not using flammable organic dispersion media, all-solid-state batteries can significantly reduce the likelihood of fire or explosion even in the event of a short circuit. The problem to be solved

[0006] The problem that the present invention aims to solve is to provide a solid electrolyte with improved electrochemical properties and an all-solid-state secondary battery containing the same. means of solving the problem

[0008] The solid electrolyte according to the embodiments of the present invention is represented by the following chemical formula 1 and may have a trigonal crystal structure.

[0009] [Chemical Formula 1]

[0010] Na 3+x Zr 2-x N x Si 2.2 P 0.8 O 12

[0011] In the above chemical formula 1, N is a p-block element, and x can be 0.01 to 0.3.

[0012] A solid-state secondary battery according to some embodiments of the present invention comprises: a first electrode comprising sodium; a second electrode spaced apart from the first electrode and comprising a negative electrode active material; and an electrolyte layer provided between the first electrode and the second electrode, wherein the electrolyte layer may comprise a solid electrolyte having a trigonal crystal structure represented by the following chemical formula 1.

[0013] [Chemical Formula 1]

[0014] Na 3+x Zr 2-x N x Si 2.2 P 0.8 O 12

[0015] In the above chemical formula 1, N is a p-block element, and x can be 0.01 to 0.3.

[0016] A solid electrolyte according to some embodiments of the present invention is represented by the following chemical formula 2 and may have a monoclinic crystal structure.

[0017] [Chemical Formula 2]

[0018] Na 3+x Zr 2-x N x Si2PO 12

[0019] In the above chemical formula 2, N is a p-block element, and x is 0.01 to 0.3.

[0020] A solid-state secondary battery according to some embodiments of the present invention comprises: a first electrode comprising sodium; a second electrode spaced apart from the first electrode and comprising a negative active material; and an electrolyte layer provided between the first electrode and the second electrode, wherein the electrolyte layer may comprise a solid electrolyte having a monoclinic crystal structure represented by the following chemical formula 2.

[0021] [Chemical Formula 2]

[0022] Na 3+x Zr2-x N x Si2PO 12

[0023] In the above chemical formula 2, N is a p-block element, and x is 0.01 to 0.3. Effects of the invention

[0025] The solid electrolyte according to the present invention may include a p-block element, thereby expanding the ion channels of sodium ions in a solid sodium secondary battery. Accordingly, improved sodium ion conductivity can be exhibited at room temperature. Brief explanation of the drawing

[0027] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment of the present invention. FIG. 2 is an SEM image of embodiments and comparative examples according to the present invention. Figure 3 shows the analysis results based on X-ray diffraction (XRD) of embodiments and comparative examples according to the present invention. Figure 4 shows the results of measuring the ionic conductivity of the embodiments and comparative examples according to the present invention. Figure 5 is a Nyquist plot according to temperature of the embodiments and comparative examples according to the present invention. Figure 6 shows the results of measuring the ion conductivity according to temperature of the embodiments and comparative examples according to the present invention. Figure 7 shows the results of the reaction stability evaluation of an all-solid-state secondary battery using a solid electrolyte according to the embodiments and comparative examples of the present invention. Figure 8 shows the results of measuring the current density of an all-solid-state secondary battery using a solid electrolyte according to the embodiments and comparative examples of the present invention. FIG. 9 is a graph showing the cycle performance of an all-solid-state secondary battery using a solid electrolyte according to the embodiments and comparative examples of the present invention. FIG. 10 is a graph showing the results of measuring the rate characteristics of an all-solid-state secondary battery using a solid electrolyte according to the embodiments and comparative examples of the present invention. Specific details for implementing the invention

[0028] The present invention will be described in detail below by explaining embodiments of the present invention with reference to the attached drawings.

[0029] FIG. 1 is a cross-sectional view of an all-solid-state battery (10) according to an embodiment of the present invention.

[0030] Referring to FIG. 1, the all-solid-state battery (10) may include a positive electrode layer (100), a negative electrode layer (200) spaced apart from the positive electrode layer (100), and a solid electrolyte layer (300) disposed between the positive electrode layer (100) and the negative electrode layer (200).

[0031] The anode layer (100) may include an anode active layer (120) and an anode current collector (110) stacked on one side of the anode active layer (120). The cathode layer (200) may include a cathode active layer (220) and a cathode current collector (210) stacked on one side of the cathode active layer (220). Sodium ions move through the solid electrolyte layer (300) through electrochemical behavior and may be exchanged between the anode active layer (120) and the cathode active layer (210). The anode current collector (110) may transfer electrons to the anode active layer (120). The cathode current collector (220) may transfer electrons to the cathode active layer (210).

[0032] The above positive active layer (120) may include a positive active material, a solid electrolyte composite, a composite of the positive active material and the solid electrolyte, a conductive material, and a binder. The above positive current collector (110) may mainly use aluminum (Al), stainless steel, titanium (Ti), a plate, or a foil.

[0033] The above-mentioned negative active layer (220) may include a negative active material, a conductive material, and a binder. The above-mentioned negative current collector (210) may mainly use aluminum (Al), copper (Cu), stainless steel, titanium (Ti), a plate, or a foil.

[0034] The solid electrolyte layer (300) above contains sodium ions (Na₂S) between the anode layer (100) and the cathode layer (200). + It may be a medium for delivering ). The solid electrolyte layer (300) may include a p-block element. According to embodiments of the present invention, the solid electrolyte layer may be represented by the following chemical formula 1 and may have a rhombohedral crystal structure.

[0035] [Chemical Formula 1]

[0036] Na 3+x Zr 2-x N x Si 2.2 P 0.8 O 12

[0037] In the above chemical formula 1, N may be a p-block element. N may be, for example, Sb or Sn, and preferably, N may be Sn. x may be, for example, 0.01 to 0.3 or 0.05 to 0.15. x may be, for example, 0.1. Since the solid electrolyte has a trigonal crystal structure, the electrochemical properties and stability of the all-solid-state secondary battery can be improved.

[0038] According to other embodiments of the present invention, the solid electrolyte layer may be represented by the following chemical formula 2 and may have a monoclinic crystal structure.

[0039] [Chemical Formula 2]

[0040] Na 3+x Zr 2-x N xSi2PO 12

[0041] In the above chemical formula 2, N may be a p-block element. N may be, for example, Sb or Sn, and preferably, N may be Sb. x may be, for example, 0.01 to 0.3 or 0.04 to 0.11. x may be, for example, 0.1.

[0043] According to embodiments of the present invention, the solid electrolyte (300) can be prepared using Si(OC2H5)4, ZrO(NO3)2, NH4H2PO4, NaNO3, and Sb(CH3CO2)3 through a sol-gel synthesis method. According to other embodiments of the present invention, the solid electrolyte (300) can be prepared using Si(OC2H5)4, ZrO(NO3)2, NH4H2PO4, NaNO3, and Sn(CH3CO2)4 through a sol-gel synthesis method.

[0045] Examples and Comparative Examples

[0046] Synthetic composition ratio NaNO3 ZrO(NO3)2 Si(OC2H5)4 NH4H2PO4 Sb(CH3CO2)3 Sn(CH3CO2)4 Molar ratio Example 1 Na 3.1 Zr 1.9 Sb 0.1 Si2PO 12 3.1 1.9 2 1 0.1 - Example 2 Na 3.1 Zr 1.9 Sn 0.1 Yes 2.2 P 0.8 About 12 3.1 1.9 2.2 0.8 - 0.1 Comparative Example 1 Na3Zr2Si2PO 12 3 2 2 1 - - Comparative Example 2 Na3Zr2Si 2.2 P 0.8 O 12 3 2 2.2 0.8 - -

[0048] Examples 1 and 2 correspond to solid electrolytes doped with p-block elements, respectively. Example 1 corresponds to a solid electrolyte doped with antimony (Sb). Example 2 corresponds to a solid electrolyte doped with tin (Sn). Comparative Examples 1 and 2 correspond to solid electrolytes not doped with p-block elements, respectively. Examples 1, 2, 1, and 2 were prepared by a conventional sol-gel synthesis method based on the molar ratios of the metals listed in Table 1.

[0049] Experimental Example 1: Scanning Transmission Microscope Analysis

[0050] Figure 2 is the result of analyzing solid electrolytes according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2 using a scanning electron microscope.

[0051] Figure 2a shows the results of analyzing a solid electrolyte according to Comparative Example 1. Figure 2b shows the results of analyzing a solid electrolyte according to Example 1. Referring to Figures 2a and 2b, it can be seen that the solid electrolyte according to Example 1, which is doped with p-block elements, forms a closer interface between the metals constituting the solid electrolyte than Comparative Example 1, which is not doped with p-block elements.

[0052] Figure 2c shows the results of analyzing the solid electrolyte according to Comparative Example 2. Figure 2d shows the results of analyzing the solid electrolyte according to Example 2. Referring to Figures 2c and 2d, it can be seen that the solid electrolyte according to Example 1, which is doped with p-block elements, forms a closer interface between the metals constituting the solid electrolyte than Comparative Example 1, which is not doped with p-block elements.

[0054] Experimental Example 2: X-ray Diffraction (XRD) Analysis

[0055] Figure 3 shows the X-ray diffraction analysis results of solid electrolytes according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2. Referring to Figure 3, it can be confirmed that Example 1 has a monoclinic crystal structure, identical to Comparative Example 1. Furthermore, in the case of Example 1, Zr 4+ It can be confirmed through Figure 3 that antimony (Sb) is doped at the location.

[0056] Comparing the XRDs of Example 2 and Comparative Example 2, it can be confirmed that Example 2 has a composite crystal structure of monoclinic and trigonal systems, unlike Comparative Example 2, which consists solely of monoclinic systems. Furthermore, in the case of Example 2, Zr 4+ It can be confirmed through Figure 3 that tin (Sn) is doped at the location.

[0058] Experimental Example 3: Measurement of Ionic Conductivity at Room Temperature

[0059] Figure 4 shows the results of measuring the ionic conductivity at room temperature of solid electrolytes according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2. Referring to Figure 4, it can be seen that the resistance of the solid electrolyte is 672 ohms in the case of Comparative Example 1 and decreased to 423 ohms in the case of Example 1.

[0060] When comparing Example 2 and Example 2, it can be seen that the resistance of the solid electrolyte decreased to 2080.09 ohm in Comparative Example 2 and 278.89 ohm in Example 2.

[0061] That is, referring to FIG. 4, it can be seen that Examples 1 and 2, which are doped with p-block elements, have lower resistance and higher ionic conductivity compared to Comparative Examples 1 and 2, which are not doped with p-block elements.

[0063] Experimental Example 4: Measurement of Ionic Conductivity According to Temperature

[0064] To measure the activation energies of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, a symmetric cell was fabricated using a solid electrolyte (300) and a sodium electrode. Nyquist plots of the symmetric cell at different temperatures are shown in FIG. 5. Through FIG. 5, the respective activation energies of Examples 1 and 2 and Comparative Examples 1 and 2 can be determined, and the activation energies of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2 below.

[0065] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Activation energy (eV) 0.181 0.10 0.191 0.19

[0066] Referring to FIG. 5 and Table 2, it can be seen that the activation energy of Example 1 is lower than that of Comparative Example 1. Additionally, it can be seen that the activation energy of Example 2 is lower than that of Comparative Example 2. Referring to FIG. 6, it can be seen that the ionic conductivity of Example 1 is greater than that of Comparative Example 1. Likewise, it can be seen that the ionic conductivity of Example 2 is greater than that of Comparative Example 2.

[0067] That is, through FIG. 6, it can be confirmed that Examples 1 and 2, which are doped with p-block elements, have superior ionic conductivity compared to Comparative Examples 1 and 1, which are not doped with p-block elements.

[0069] Experimental Example 5: Evaluation of Reaction Stability 1

[0070] To evaluate the reaction stability of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, a symmetric cell was fabricated using a solid electrolyte (300) and a sodium electrode. The symmetric cell had a current density of 0.1 mA / cm² at 25°C. 2 Tested under the conditions of.

[0071] Referring to FIG. 7, it can be seen that in the case of Example 1, stable reaction behavior without overvoltage is maintained for about 465 hours, and in the case of Comparative Example 1, stable reaction behavior without overvoltage is maintained for about 147 hours, which is lower than that of Example 1. In the case of Example 2, stable reaction behavior without overvoltage is maintained for about 1673 hours, and in the case of Comparative Example 2, stable reaction behavior without overvoltage is maintained for about 55 hours, which is lower than that of Example 2.

[0072] That is, through FIG. 7, it can be confirmed that Examples 1 and 2, which are doped with p-block elements, have superior reaction stability compared to Comparative Examples 1 and 1, which are not doped with p-block elements.

[0074] Experimental Example 6: Reaction Stability Evaluation 2

[0075] To evaluate the reaction stability of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, a symmetric cell was fabricated using a solid electrolyte (300) and a sodium electrode. The symmetric cell had a current density of 0.1 mA / cm² at 25°C. 2 , 0.2mA / cm 2 ,0.3mA / cm 2 Tested by increasing it.

[0076] Referring to FIG. 8, in the case of Comparative Example 1, 0.1 mA / cm 2 At 0.2 mA / cm 2 It can be confirmed that overvoltage occurs when increased. In the case of Example 1, 0.3 mA / cm 2 It can be confirmed that stable reaction behavior is maintained even in the case of .

[0077] In the case of Comparative Example 2, 0.2 mA / cm 2 At 0.3 mA / cm 2 It can be confirmed that overvoltage occurs when increased. In the case of Example 2, 0.3 mA / cm 2 It can be confirmed that stable reaction behavior is maintained even in the case of .

[0078] That is, through FIG. 8, it can be confirmed that Examples 1 and 2, which are doped with p-block elements, have superior reaction stability compared to Comparative Examples 1 and 1, which are not doped with p-block elements.

[0080] Experimental Example 7: Evaluation of Cycle Performance of All-Solid State Secondary Battery

[0081] Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were subjected to a half-cell test at a current rate of 0.1C, a voltage range of 2.0V to 4.0V, and a temperature of 25°C.

[0082] Referring to FIG. 9, in the case of Example 1 and Comparative Example 1, it can be seen that after 50 cycles, the capacity retention rate of Example 1 is 93.7%, and the capacity retention rate of Comparative Example 1 is 84.97%.

[0083] In the case of Example 2 and Comparative Example 2, it can be seen that after 300 cycles, the capacity retention rate of Example 2 is 65.89%, and the capacity retention rate of Comparative Example 2 is 56.16%.

[0084] That is, through FIG. 9, it can be confirmed that Examples 1 and 2, which are doped with p-block elements, have a superior capacity retention rate compared to Comparative Examples 1 and 1, which are not doped with p-block elements.

[0086] Experimental Example 8: Evaluation of Rate Characteristics of All-Solid State Secondary Battery

[0087] Half-cell tests were conducted on Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at 25°C with different charge-discharge rates. Example 1 and Comparative Example 1 were conducted with charge-discharge rates of 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, and 0.3C. Example 2 and Comparative Example 2 were conducted with charge-discharge rates of 0.05C, 0.1C, 0.3C, 0.5C, and 0.1C.

[0088] Referring to FIG. 10, it can be seen that Example 1 has superior rate characteristics compared to Comparative Example 1, and Example 2 has superior rate characteristics compared to Comparative Example 2.

[0089] That is, through FIG. 10, it can be confirmed that Examples 1 and 2, which are doped with p-block elements, have superior rate characteristics compared to Comparative Examples 1 and 1, which are not doped with p-block elements.

[0091] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 Solid electrolyte represented by the following chemical formula 1 and having a trigonal crystal structure: [Chemical Formula 1]Na 3+x Zr 2-x N x Si 2.2 P 1.2 O 12 In the above chemical formula 1, N is a p-block element and is Sn, and x is 0.01 to 0.

3. Claim 2 delete Claim 3 The solid electrolyte of claim 1, wherein x is 0.05 to 0.

15. Claim 4 A solid electrolyte according to claim 1, wherein x is 0.

1. Claim 5 An all-solid-state secondary battery comprising: a first electrode comprising sodium; a second electrode spaced apart from the first electrode and comprising a negative active material; and an electrolyte layer provided between the first electrode and the second electrode, wherein the electrolyte layer is represented by the following chemical formula 1 and comprises a solid electrolyte having a trigonal crystal structure. [Chemical Formula 1] Na 3+x Zr 2-x N x Si 2.2 P 0.8 O 12 In the above chemical formula 1, N is a p-block element and is Sn, and x is 0.01 to 0.

3. Claim 6 Solid electrolyte represented by the following chemical formula 2 and having a monoclinic crystal structure: [Chemical Formula 2]Na 3+x Zr 2-x N x Si2PO 12 In the above chemical formula 2, N is a p-block element and is Sb, and x is 0.01 to 0.

3. Claim 7 delete Claim 8 In claim 6, the solid electrolyte is such that x is 0.04 to 0.

11. Claim 9 In claim 6, the solid electrolyte is such that x is 0.

1. Claim 10 An all-solid-state secondary battery comprising: a first electrode comprising sodium; a second electrode spaced apart from the first electrode and comprising a negative electrode active material; and an electrolyte layer provided between the first electrode and the second electrode, wherein the electrolyte layer is represented by the following chemical formula 2 and comprises a solid electrolyte having a monoclinic crystal structure: [Chemical Formula 2]Na 3+x Zr 2-x N x Si2PO 12 In the above chemical formula 2, N is a p-block element and is Sb, and x is 0.01 to 0.3.

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