Sodium ion halide solid electrolyte and preparation method and application thereof

Abstract

The invention discloses a sodium ion halide solid electrolyte as well as a preparation method and application thereof, and belongs to the technical field of batteries, the sodium ion halide solid electrolyte realizes optimization of a sodium ion transmission path and a microstructure by doping BH4 anions and O anions into a structure and regulating and controlling the doping amount; the sodium ion migration activation energy is reduced, the ionic conductivity of the product is effectively improved, and meanwhile, the product has oxidation resistance and high electrochemical stability and can be compatible with a high-voltage positive electrode material during application.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a sodium ion halide solid electrolyte and a preparation method and application thereof. Background Art

[0002] Sodium ion solid electrolytes are generally divided into sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes and polymer solid electrolytes. Among them, sulfide solid electrolytes have high ionic conductivity, but their electrochemical window is narrow, their compatibility with positive electrode materials is poor, and their sensitivity to water and oxygen is high; oxide solid electrolytes have good electrochemical stability, but poor air stability and insufficient interface compatibility, and high energy consumption for processing; polymer solid electrolytes have the advantage of good interface compatibility, but insufficient ionic conductivity at room temperature, a narrow electrochemical window, and poor thermal stability.

[0003] In contrast, halide solid electrolytes have the characteristics of high ionic conductivity, high interfacial compatibility, high electrochemical stability and excellent mechanical properties. However, in the field of sodium solid-state batteries, the ionic conductivity and high-voltage resistance of existing sodium ion halide solid electrolytes still cannot meet the rapid development of technology. Summary of the invention

[0004] Based on the defects of the prior art, the purpose of the present invention is to provide a sodium ion halide solid electrolyte, which optimizes the sodium ion transmission path and microstructure by doping BH4 anions and O anions into the structure and regulating the doping amount, thereby reducing the activation energy of sodium ion migration and effectively improving the ionic conductivity of the product. At the same time, the product has oxidation resistance and high electrochemical stability, and is compatible with high-voltage positive electrode materials when used.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A sodium ion halide solid electrolyte, the chemical formula of which is as follows:

[0007] Na 2+2x MO 1+x (BH4) y X 4-y , wherein M is at least one of Zr, Hf, Ti, and Mo, X is a halogen, 0≤x≤1, 0≤y≤1.

[0008] The sodium ion halide solid electrolyte of the present invention has specific BH4 anions and O anions doped in the molecular structure. These two anions can adjust the amorphization degree of the overall solid electrolyte, thereby optimizing the transmission path of sodium ions when applied to solid-state batteries, reducing the migration activation energy of sodium ions, and improving the ionic conductivity of the product. At the same time, it can make the MO bond strength in the solid electrolyte higher, improve the oxidation resistance of the solid electrolyte, make it compatible with positive electrode materials such as layered oxides or polyanion types, so that the energy density of the solid-state battery can be controlled and improved; in addition, the product has a certain deformability, so it can achieve close contact with the positive electrode material and maintain good interface stability.

[0009] However, since the simultaneous doping of the two anions will also affect the microstructure and component composition of the product, if an excessive amount is introduced, it may cause a large amount of NaCl and Na2O impurities to be generated outside the amorphous phase, which in turn will reduce the degree of amorphization of the entire sodium ion halide solid electrolyte and fail to achieve the expected high ionic conductivity. Therefore, it is necessary to optimize and limit the doping amount.

[0010] Preferably, the M is at least one of Zr and Hf.

[0011] When the above metals are used to construct the sodium ion halide solid electrolyte of the present invention, the metal oxygen bond strength formed is higher, and the product can achieve better ionic conductivity and oxidation resistance.

[0012] Preferably, the ionic conductivity of the sodium ion halide solid electrolyte at 25-30°C is ≥ 0.1 mS·cm -1 .

[0013] Preferably, the sodium ion halide solid electrolyte is Na 2+2x ZrO 1+x (BH4) y Cl 4-y , where 0.25≤x≤2, 0.3≤y≤0.5;

[0014] More preferably, the sodium ion halide solid electrolyte is Na 2+2x ZrO 1+x (BH4) y Cl 4-y , where 0.375≤x≤0.5, 0.3≤y≤0.4.

[0015] By preference, when the doping ratio of the above BH4 anion and O anion is selected, the obtained sodium ion halide solid electrolyte has higher ion conductivity and better performance. At the same time, the actual production cost-effectiveness of the central metal ion with Zr having high abundance and low cost is higher.

[0016] Another object of the present invention is to provide a method for preparing the sodium ion halide solid electrolyte, comprising the following steps:

[0017] The prepared raw materials are mixed and ball-milled to obtain the sodium ion halide solid electrolyte.

[0018] Preferably, the preparation raw materials include a sodium source, an oxygen source, NaBH4, a M source and a halogen source;

[0019] More preferably, the sodium source and the oxygen source may be the same, and more preferably, the sodium source and the oxygen source are at least one of NaOH and Na2O.

[0020] More preferably, the M source and the halogen source may be the same, and more preferably, the M source and the halogen source are halides of metal M.

[0021] Preferably, the rotation speed during ball milling is ≥300 rpm, the ball milling time is ≥1 h, and the ball-to-material ratio during ball milling is (40-85):1.

[0022] More preferably, the rotation speed during ball milling is 300-650 rpm, the ball milling time is 1-10 h, and the ball-to-material ratio during ball milling is (75-85):1.

[0023] Another object of the present invention is to provide another method for preparing the sodium ion halide solid electrolyte, comprising the following steps:

[0024] The prepared raw materials are mixed, heated and melted under a protective atmosphere, and cooled to obtain the sodium ion halide solid electrolyte.

[0025] Preferably, the preparation raw materials include NaBH4, an oxygen source, an M source and a halogen source;

[0026] More preferably, the M source, the oxygen source and the halogen source may be the same;

[0027] More preferably, the oxygen source is an oxide of metal M, and the halogen source is a halide of metal M.

[0028] Preferably, the temperature during the heating and melting is 120 to 500° C., and the time is 0.5 to 20 hours.

[0029] Another object of the present invention is to provide another method for preparing the sodium ion halide solid electrolyte, comprising the following steps:

[0030] The raw materials are mixed and ball-milled, and the obtained powder is tableted and then sintered to obtain the sodium ion halide solid electrolyte.

[0031] Preferably, the preparation raw materials include a sodium source, an oxygen source, NaBH4, a M source and a halogen source;

[0032] More preferably, the sodium source and the oxygen source may be the same, and more preferably, the sodium source and the oxygen source are at least one of NaOH and Na2O.

[0033] More preferably, the M source and the halogen source may be the same, and more preferably, the M source and the halogen source are halides of metal M.

[0034] Preferably, the rotation speed during ball milling is ≥300 rpm, the ball milling time is ≥1 h, and the ball-to-material ratio during ball milling is (40-85):1.

[0035] More preferably, the rotation speed during ball milling is 300-650 rpm, the ball milling time is 1-10 h, and the ball-to-material ratio during ball milling is (75-85):1.

[0036] Preferably, the sintering temperature is 150-600° C. and the sintering time is 1-100 h.

[0037] It should be noted that the preparation method of the sodium ion halide solid electrolyte described in the present invention includes but is not limited to the above method. Those skilled in the art know that the existing preparation process of the sodium ion halide solid electrolyte is mature. In addition to the above process, conventional synthesis methods such as chemical vapor spray method and hydrothermal method can also be used to synthesize the product. It can also be prepared by doping with commercially available solid electrolytes. As long as its chemical composition and chemical structure meet the limitations of the scheme described in the present invention and can obtain similar technical effects, it is acceptable.

[0038] Another object of the present invention is to provide an application of the sodium ion halide solid electrolyte in the preparation of a secondary battery.

[0039] Another object of the present invention is to provide a secondary battery comprising the sodium ion halide solid electrolyte of the present invention.

[0040] Preferably, the secondary battery is an all-solid-state sodium ion secondary battery.

[0041] The sodium ion halide solid electrolyte of the present invention regulates the position and transmission path of sodium ions in the structure by doping with specific anions, effectively improving the ionic conductivity, which can reach a maximum of 0.35mS·cm at room temperature. -1 At the same time, the product has an ideal high oxidation resistance potential and interface compatibility, small interface resistance, and low degree of interface side reactions. When used in secondary batteries, especially all-solid-state sodium ion secondary batteries, it can show excellent electrochemical properties of high safety and high cycle stability. The secondary battery can be used as a power supply device in large-scale energy storage equipment such as solar power generation, wind power generation, smart grid peak regulation, distributed power stations, backup power supplies or communication base stations.

[0042] Preferably, the secondary battery comprises a positive electrode sheet and a negative electrode sheet.

[0043] Preferably, the oxidation resistance potential of the secondary battery is ≥4V.

[0044] The beneficial effect of the present invention is that the present invention provides a sodium ion halide solid electrolyte, which optimizes the sodium ion transmission path and microstructure by doping BH4 anions and O anions into the structure and regulating the doping amount, reduces the activation energy of sodium ion migration, and effectively improves the ion conductivity of the product. At the same time, the product has oxidation resistance and high electrochemical stability, and is compatible with high-voltage positive electrode materials when used. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is an AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 1;

[0046] Figure 2 is an AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 2;

[0047] Figure 3 is an AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 3;

[0048] Figure 4 is an AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 4;

[0049] Figure 5 This is the AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 5;

[0050] Figure 6 is an AC impedance diagram of the sodium ion halide solid electrolyte obtained in Example 6;

[0051] Figure 7 The AC impedance diagram of the sodium ion halide solid electrolyte obtained in Comparative Example 2;

[0052] Figure 8 This is the AC impedance diagram of the sodium ion halide solid electrolyte obtained in Comparative Example 5;

[0053] Fig. 9 is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 1;

[0054] Fig.10 is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 2;

[0055] Fig.11 is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 3;

[0056] Fig.12is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 4;

[0057] Fig.13 is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 5;

[0058] Fig.14 is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Example 6;

[0059] Fig.15 This is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Comparative Example 2;

[0060] Fig.16 This is the XRD spectrum of the sodium ion halide solid electrolyte obtained in Comparative Example 2. DETAILED DESCRIPTION

[0061] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, the purpose of which is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention, unless otherwise specified, are all commonly used common reagents and instruments.

[0062] Example 1

[0063] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof according to the present invention, wherein the preparation method of the sodium ion halide solid electrolyte comprises the following steps:

[0064] (1) in an inert gas environment with a water and oxygen content of ≤0.01 ppm, mixing the raw materials, then grinding and mixing them evenly in a mortar to obtain a mixed powder; the raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.25:1:0.3;

[0065] (2) The mixed powder is ball-milled in a sealed ball milling jar equipped with an inert atmosphere at a ball-to-material ratio of 75:1 at a rotation speed of 500 rpm for 2 hours, and then the ball-to-material is separated using a molecular sieve to obtain the sodium ion halide solid electrolyte. The chemical formula of the product is shown in Table 1.

[0066] Example 2

[0067] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.375:1:0.3.

[0068] Example 3

[0069] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.5:1:0.3.

[0070] Example 4

[0071] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.75:1:0.3.

[0072] Example 5

[0073] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 2:1:0.3.

[0074] Example 6

[0075] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.375:1:0.4.

[0076] Example 7

[0077] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.5:1:0.4.

[0078] Example 8

[0079] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.75:1:0.4.

[0080] Example 9

[0081] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.375:1:0.5.

[0082] Example 10

[0083] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.5:1:0.5.

[0084] Embodiment 11

[0085] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 1.75:1:0.5.

[0086] Example 12

[0087] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, HfCl4 and NaBH4 in a molar ratio of 1.375:1:0.3.

[0088] Embodiment 13

[0089] An embodiment of a sodium ion halide solid electrolyte and a preparation method and application thereof described in the present invention is different from the embodiment only in that the preparation raw materials are Na2O, ZrBr4 and NaBH4 in a molar ratio of 1.375:1:0.3.

[0090] Comparative Example 1

[0091] A sodium ion halide solid electrolyte and a preparation method and application thereof, the difference from the embodiment is only that the preparation raw materials are Na2O and ZrCl4 in a molar ratio of 1.25:1.

[0092] Comparative Example 2

[0093] A sodium ion halide solid electrolyte and a preparation method and application thereof, the difference from the embodiment is only that the preparation raw materials are Na2O and ZrCl4 with a molar ratio of 1.375:1.

[0094] Comparative Example 3

[0095] A sodium ion halide solid electrolyte and a preparation method and application thereof, the difference from the embodiment is only that the preparation raw materials are Na2O and ZrCl4 in a molar ratio of 1.5:1.

[0096] Comparative Example 4

[0097] A sodium ion halide solid electrolyte and a preparation method and application thereof, the only difference from the embodiment is that the preparation raw materials are Na2O and ZrCl4 in a molar ratio of 1:1, and the ball milling time is 6 hours.

[0098] Comparative Example 5

[0099] A sodium ion halide solid electrolyte and a preparation method and application thereof, the only difference from the embodiment is that the preparation raw materials are Na2O and ZrCl4 in a molar ratio of 2:1, and the ball milling time is 8 hours.

[0100] Comparative Example 6

[0101] A sodium ion halide solid electrolyte and its preparation method and application, the only difference from the embodiment is that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 2:1:0.3, the ball milling speed is 400rpm, and the ball milling time is 4h.

[0102] Comparative Example 7

[0103] A sodium ion halide solid electrolyte and its preparation method and application, the only difference from the embodiment is that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 2:1:0.4, the ball milling speed is 400rpm, and the ball milling time is 4h.

[0104] Comparative Example 8

[0105] A sodium ion halide solid electrolyte and its preparation method and application, the only difference from the embodiment is that the preparation raw materials are Na2O, ZrCl4 and NaBH4 in a molar ratio of 2:1:0.5, the ball milling speed is 400rpm, and the ball milling time is 4h.

[0106] Effect Example 1

[0107] In order to verify the ionic conductivity of the sodium ion halide solid electrolyte of the present invention, each embodiment and comparative example was cut into membranes of the same size, and then an AC impedance test was performed. The AC impedance test was performed on a Biologic electrochemical workstation, and the ionic conductivity was calculated according to the obtained AC impedance spectrum and the formula: σ = L / R; wherein σ is the ionic conductivity (S / cm), L is the thickness of the electrolyte membrane (cm), R is the measured impedance (Ω), and S is the area of ​​the electrolyte membrane (cm 2 ).

[0108] The test results are shown in Table 1 and Figures 1 to 8 shown.

[0109] Table 1

[0110]

[0111]

[0112] It can be seen from the test results that the sodium ion halide solid electrolyte of the present invention optimizes the ion transmission channel and significantly improves the transmission efficiency due to the incorporation of BH4 and O anions. Compared with the products of Comparative Examples 1 to 8 in which no anion is incorporated or only O anions are incorporated or only BH4 anions are incorporated, the ion conductivity is significantly improved, and the ion conductivity is between 0.16 and 0.35 mS·cm -1 At the same time, it can be seen that the amount of the two anions added also has an effect on the ionic conductivity of the product. When the sodium ion halide solid electrolyte Na 2+2x ZrO 1+x (BH4) y Cl 4-y When the ionic conductivity of the product is within the range of 0.375≤x≤0.5 and 0.3≤y≤0.4, the ionic conductivity of the product is higher.

[0113] The sodium ion halide solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 2 and 5 were subjected to XRD testing. The results are as follows: Figures 9 to 16 As shown, by comparing the products of Comparative Examples 2 and 5 without doping and only with oxygen anion doping, it can be seen that when the doping amount of O anions is relatively low, the product obtained in Example 1, in addition to the amorphous main phase, is basically the diffraction peaks of Na2O, NaCl and Na2ZrCl6, and the impurity peak of Na2ZrCl6 has a strong crystallinity. As the doping amount increases, the intensity of each characteristic peak in the spectrum of the product of Example 2 is reduced, indicating that O anions can regulate the amorphization degree of the product at this doping amount. Corresponding characteristic peaks also appear in the spectrum of the product of Example 3, and the crystallinity is relatively stable; as the doping amount of O anions further increases, the amorphous products of Examples 4 and 5 The degree of calcination is reduced and the ion conduction efficiency is reduced. The main reason is that the Cl ions close to the Zr ions are gradually replaced by a large amount of O anions, and more impurities such as NaCl are generated. Therefore, the intensity of the corresponding characteristic peak is also improved, which ultimately affects the ionic conductivity of the product. As shown in Table 1, after fixing the amount of Na2O added and thus the amount of O anion doping, the product of Example 6 increases the doping amount of BH4 anions compared to the product of Example 2. It can be seen that the intensity of the characteristic peak corresponding to the impurity of the product is reduced, while the intensity of the amorphous main phase is increased, indicating that the product can achieve better structural regulation at this doping amount, so the ionic conductivity is improved, which corresponds to the results in Table 1.

[0114] Furthermore, the sodium ion halide solid electrolyte obtained in Example 2 is used to prepare an all-solid-state battery: the sodium ion halide solid electrolyte obtained in Example 2 and conductive carbon black are mixed in a mass ratio of 7:3 and pressed into sheets to obtain a positive electrode sheet, a commercial sodium tin alloy is cut into a negative electrode sheet, and the sodium ion halide solid electrolyte obtained in Example 2 is cut and pressed into a solid electrolyte membrane to be assembled into an all-solid-state battery.

[0115] Subsequently, the oxidation potential of the all-solid-state battery was tested by cyclic voltammetry, with the scanning voltage range being from open circuit voltage to 5 V and the scanning rate being 0.1 mV / s. The tested oxidation potential was 4.1 V, indicating that the sodium ion halide solid electrolyte of the present invention has high oxidation resistance.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the present invention.

Claims

1. A sodium ion halide solid electrolyte, characterized in that: Its chemical formula is as follows: Na 2+2x MO 1+x (BH4) y X 4-y , wherein M is at least one of Zr, Hf, Ti, and Mo, X is a halogen, 0≤x≤1, 0≤y≤1.

2. The sodium ion halide solid electrolyte according to claim 1, characterized in that: The M is at least one of Zr and Hf.

3. The sodium ion halide solid electrolyte according to claim 1, characterized in that: The ionic conductivity of the sodium ion halide solid electrolyte at 25-30° C. is ≥0.1 mS·cm -1 .

4. The sodium ion halide solid electrolyte according to claim 2, characterized in that: The sodium ion halide solid electrolyte is Na 2+2x ZrO 1+x (BH4) y Cl 4-y , where 0.25≤x≤2, 0.3≤y≤0.

5.

5. The sodium ion halide solid electrolyte according to claim 4, characterized in that: The sodium ion halide solid electrolyte is Na 2+2x ZrO 1+x (BH4) y Cl 4-y , where 0.375≤x≤0.5, 0.3≤y≤0.

4.

6. The method for preparing the sodium ion halide solid electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: The prepared raw materials are mixed and ball-milled to obtain the sodium ion halide solid electrolyte.

7. The method for preparing the sodium ion halide solid electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: The prepared raw materials are mixed, heated and melted under a protective atmosphere, and cooled to obtain the sodium ion halide solid electrolyte.

8. The method for preparing the sodium ion halide solid electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials are mixed and ball-milled, and the obtained powder is tableted and then sintered to obtain the sodium ion halide solid electrolyte.

9. Use of the sodium ion halide solid electrolyte according to any one of claims 1 to 5 in the preparation of a secondary battery.

10. A secondary battery, characterized in that: It comprises the sodium ion halide solid electrolyte according to any one of claims 1 to 5; preferably, the secondary battery is an all-solid-state sodium ion secondary battery.

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