A sodium-ion halide solid electrolyte, its preparation method and application

Abstract

The present invention discloses a sodium-ion halide solid electrolyte, a preparation method thereof and an application thereof, belonging to the technical field of batteries. The sodium-ion halide solid electrolyte of the present invention realizes the optimization of the sodium-ion transmission path and microstructure by doping BH4 anions and O anions in the structure and regulating the doping amount, reduces the activation energy of sodium-ion migration, effectively improves the ionic conductivity of the product, and at the same time, the product has oxidation resistance and high electrochemical stability, and can be compatible with high-voltage cathode materials during application.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a sodium ion halide solid electrolyte, a preparation method thereof, and an 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 they have a narrow electrochemical window, poor compatibility with positive electrode materials, and high sensitivity to water and oxygen; oxide solid electrolytes have good electrochemical stability, but poor air stability and insufficient interfacial compatibility, and at the same time, the energy consumption required for processing is high; polymer solid electrolytes have the advantage of good interfacial 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 performance of existing sodium ion halide solid electrolytes still cannot meet the high-speed development of technology. Summary of the Invention

[0004] Based on the defects existing in the prior art, the purpose of the present invention is to provide a sodium ion halide solid electrolyte, which optimizes the sodium ion transport path and microstructure by incorporating BH4 anions and O anions into the structure and regulating the doping amount, reduces the activation energy of sodium ion migration, effectively improves the ionic conductivity of the product, and at the same time, the product has oxidation resistance, high electrochemical stability, and can be compatible with high-voltage positive electrode materials during application.

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

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

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

[0008] In the sodium-ion halide solid electrolyte of the present invention, specific BH4 anions and O anions are incorporated into the molecular structure. These two anions can regulate the degree of amorphization of the overall solid electrolyte, thereby optimizing the sodium-ion transport path when it is applied to solid-state batteries, reducing the migration activation energy of sodium ions, improving the ionic conductivity of the product. At the same time, it can make the M-O bond strength in the solid electrolyte higher, enhancing the oxidation resistance of the solid electrolyte, enabling it to be compatible with cathode materials such as layered oxides or polyanion types, and allowing the energy density of the solid-state battery to be controllably increased; in addition, this product has a certain deformability, so it can achieve close contact with the cathode material and maintain good interfacial stability.

[0009] However, since the synchronous doping of the two anions will also affect the microstructure and 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, instead resulting in a decrease in the degree of amorphization of the entire sodium-ion halide solid electrolyte and being unable to achieve the expected high ionic conductivity. Therefore, it is necessary to preferably limit the doping amount.

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

[0011] When using the above metals to construct the sodium-ion halide solid electrolyte of the present invention, the formed metal-oxygen bond has a higher strength, and the product can achieve more excellent 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 ≤ 1 and 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 and 0.3 ≤ y ≤ 0.4.

[0015] After optimization, when the doping ratio of the above BH4 anions and O anions is selected, the obtained sodium-ion halide solid electrolyte has a higher ionic conductivity and better performance. At the same time, using Zr with a higher abundance and lower cost as the central metal ion has a higher practical production cost performance.

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

[0017] After the preparation raw materials are mixed and ball-milled, the sodium halide solid electrolyte is obtained.

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

[0019] More preferably, the sodium source and the oxygen source can 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 can 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 halide solid electrolyte, comprising the following steps:

[0024] The preparation raw materials are mixed and heated and melted under a protective atmosphere, and then cooled to obtain the sodium 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 can 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 heating and melting is 120 - 500 °C, and the time is 0.5 - 20 h.

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

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

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

[0032] More preferably, the sodium source and the oxygen source can be the same. 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 can be the same. 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 time is 1 - 100 h.

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

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

[0039] Another object of the present invention is to provide a secondary battery including 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 sites and transport paths of sodium ions in the structure by doping specific anions, effectively improving the ionic conductivity, which can reach up to 0.35 mS·cm at room temperature. -1 . At the same time, this product has an ideal high oxidation resistance potential and interfacial compatibility, with a small interfacial resistance and a low degree of interfacial side reactions. When applied in secondary batteries, especially all-solid-state sodium ion secondary batteries, it can exhibit excellent electrochemical properties of high safety and high cycle stability. This secondary battery can be used as a power supply device in large-scale energy storage devices such as solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

[0042] Preferably, the secondary battery includes a positive electrode plate and a negative electrode plate.

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

[0044] The beneficial effects of the present invention are as follows: The present invention provides a sodium ion halide solid electrolyte. By incorporating BH4 anions and O anions into the structure and regulating the doping amount, the sodium ion transport path and microstructure are optimized, the activation energy of sodium ion migration is reduced, the ionic conductivity of the product is effectively improved. At the same time, the product has oxidation resistance and high electrochemical stability, and can be compatible with high-voltage cathode materials during application. Description of the Drawings

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

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

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

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

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

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

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

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

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

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

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

[0056] Figure 12XRD pattern of the sodium halide solid electrolyte obtained in Example 4;

[0057] Figure 13 XRD pattern of the sodium halide solid electrolyte obtained in Example 5;

[0058] Figure 14 XRD pattern of the sodium halide solid electrolyte obtained in Example 6;

[0059] Figure 15 XRD pattern of the sodium halide solid electrolyte obtained in Comparative Example 2;

[0060] Figure 16 XRD pattern of the sodium halide solid electrolyte obtained in Comparative Example 2. Detailed implementation manners

[0061] To better illustrate the objectives, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific examples and comparative examples. The purpose is to understand the content of the present invention in detail, rather than a limitation to the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention are all common ordinary reagents and instruments unless otherwise specified.

[0062] Example 1

[0063] An embodiment of a sodium halide solid electrolyte and its preparation method and application according to the present invention. The preparation method of the sodium halide solid electrolyte includes the following steps:

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

[0065] (2) The mixed powder is ball-milled in a sealed ball mill tank with an inert atmosphere protection at a rotation speed of 500 rpm for 2 h according to a ball-to-material ratio of 75:1, and then the ball and the material are separated by molecular sieve to obtain the sodium halide solid electrolyte. The chemical formula of this product is shown in Table 1.

[0066] Example 2

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

[0068] Example 3

[0069] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.5:1:0.3.

[0070] Example 4

[0071] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.75:1:0.3.

[0072] Example 5

[0073] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 2:1:0.3.

[0074] Example 6

[0075] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.375:1:0.4.

[0076] Example 7

[0077] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.5:1:0.4.

[0078] Example 8

[0079] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.75:1:0.4.

[0080] Example 9

[0081] An example of the sodium-ion halide solid electrolyte, its preparation method and application according to the present invention, the difference from the example is only that the preparation raw materials are Na2O, ZrCl4 and NaBH4 with a molar ratio of 1.375:1:0.5.

[0082] Example 10

[0083] An embodiment of a sodium ion halide solid electrolyte, a preparation method thereof, and an application thereof described in the present invention differs 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] Example 11

[0085] An embodiment of a sodium ion halide solid electrolyte, a preparation method thereof, and an application thereof described in the present invention differs 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, a preparation method thereof, and an application thereof described in the present invention differs 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] Example 13

[0089] An embodiment of a sodium ion halide solid electrolyte, a preparation method thereof, and an application thereof described in the present invention differs 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, a preparation method thereof, and an application thereof, the only difference from the embodiment being 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, a preparation method thereof, and an application thereof, the only difference from the embodiment being that the preparation raw materials are Na2O and ZrCl4 in a molar ratio of 1.375:1.

[0094] Comparative Example 3

[0095] A sodium ion halide solid electrolyte, a preparation method thereof, and an application thereof, the only difference from the embodiment being 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, a preparation method thereof, and an application thereof, which differs from the embodiment only in 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, its preparation method and application. The difference from the example is only that the preparation raw materials are Na2O and ZrCl4 with a molar ratio of 2:1, and the ball milling time is 8 h.

[0100] Comparative Example 6

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

[0102] Comparative Example 7

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

[0104] Comparative Example 8

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

[0106] Effect Example 1

[0107] To verify the ionic conductivity of the sodium ion halide solid electrolyte of the present invention, the examples and comparative examples were cut into membrane sheets of the same size, and then an alternating current impedance test was carried out. The alternating current impedance test was carried out on a Biologic electrochemical workstation, and the ionic conductivity was calculated according to the obtained alternating current impedance spectrum and the formula: σ = L / R; where 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 - 8 as follows.

[0109] Table 1

[0110]

[0111] It can be seen from the test results that due to the incorporation of BH4 and O anions in the sodium halide solid electrolyte of the present invention, the ion transport channels are optimized and the transport efficiency is significantly improved. Compared with the products of Comparative Examples 1-8 without anion incorporation or only O anion incorporation or only BH4 anion incorporation, the ionic conductivity is significantly increased, and the ionic conductivity is in the range of 0.16-0.35 mS·cm -1 -1. At the same time, it can be seen that the incorporation amounts of the two anions also have an impact on the ionic conductivity of the product. When in the sodium halide solid electrolyte Na 2+2x ZrO 1+x (BH4) y Cl 4-y , when 0.375 ≤ x ≤ 0.5 and 0.3 ≤ y ≤ 0.4, the ionic conductivity of the product is higher.

[0112] The sodium halide solid electrolytes prepared in Examples 1-6 and Comparative Examples 2 and 5 were subjected to XRD tests, and the results are as Figures 9 - 16 shown. Comparing with the products of Comparative Examples 2 and 5 without incorporation and only oxygen anion incorporation, it can be seen that when the incorporation amount of O anions is relatively low, the product obtained in Example 1, in addition to the amorphous main phase, basically has diffraction peaks of Na2O, NaCl and Na2ZrCl6, and the impurity peak of Na2ZrCl6 has relatively strong crystallinity. As the incorporation amount increases, the intensities of the characteristic peaks in the spectrum of the product in Example 2 all decrease, indicating that the O anions can regulate the degree of amorphization of the product at this incorporation amount. The corresponding characteristic peaks also appear in the spectrum of the product in Example 3, and the crystallinity is relatively stable; as the incorporation amount of O anions further increases, the degree of amorphization of the products in Examples 4 and 5 decreases and the ion conduction efficiency decreases. The main reason is that the Cl ions close to the Zr ions are gradually replaced by a large number of O anions, and at the same time, more impurities such as NaCl are generated. Therefore, the intensities of the corresponding characteristic peaks also increase, ultimately affecting the ionic conductivity of the product. As corresponding to the results in Table 1, after fixing the addition amount of Na2O and thus fixing the incorporation amount of O anions, the product in Example 6 increased the incorporation amount of BH4 anions compared with the product in Example 2. It can be seen that the intensity of the characteristic peak corresponding to the impurity of the product decreases, and the intensity of the amorphous main phase increases, indicating that the product can achieve better structural regulation at this incorporation amount. Therefore, the ionic conductivity is increased, corresponding to the results in Table 1.

[0113] Furthermore, the sodium halide solid electrolyte obtained in Example 2 was used to prepare a all-solid-state battery: the sodium halide solid electrolyte obtained in Example 2 and conductive carbon black were mixed at a mass ratio of 7:3 and pressed into a positive electrode sheet. A commercial sodium-tin alloy was cut into a negative electrode sheet, and the sodium halide solid electrolyte obtained in Example 2 was cut and pressed into a solid electrolyte membrane to assemble a all-solid-state battery.

[0114] Subsequently, the oxidation potential of the all-solid-state battery was tested by cyclic voltammetry. The scanning voltage range was from the open-circuit voltage to 5 V, and the scanning rate was 0.1 mV / s. The test result showed that the oxidation potential was 4.1 V, indicating that the sodium ion halide solid electrolyte described in the present invention has high oxidation resistance performance.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit of 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 , where M is at least one of Zr, Hf, Ti, and Mo, X is a halogen, 0 ≤ x ≤ 1, and 0 < y ≤ 1.

2. The sodium halide solid electrolyte according to claim 1, wherein The M is at least one of Zr and Hf.

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

5.

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

4.

6. The preparation method of the sodium ion halide solid electrolyte according to any one of claims 1 to 5, characterized in that, It includes the following steps: After the preparation raw materials are mixed and ball-milled, the sodium ion halide solid electrolyte is obtained.

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

8. The preparation method of the sodium ion halide solid electrolyte according to any one of claims 1 to 5, characterized in that, It includes the following steps: The preparation raw materials are mixed and ball-milled, and the obtained powder is pressed 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 includes the sodium ion halide solid electrolyte according to any one of claims 1 to 5.

11. The secondary battery according to claim 10, characterized in that, The secondary battery is an all-solid-state sodium ion secondary battery.

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