An oxide solid electrolyte, a preparation method thereof, and a solid-state battery

Abstract

The present invention belongs to the technical field of solid-state battery preparation, and discloses an oxide solid electrolyte, a preparation method thereof, and a solid-state battery. The oxide solid electrolyte is a mixed solid electrolyte, and its chemical formula is A2MF, where A is any one of Li, Na, and K elements; M is BO3 3‑ , CO3 2‑ , NO3 ‑ , NO2 ‑ , SiO4 4‑ , SiO3 2‑ , PO3 3‑ , PO4 3‑ , SO4 2‑ , SO3 2‑ , ClO4 ‑ , ClO3 ‑ , CrO4 2‑ , MnO4 2‑ and TeO4 2‑ Any one or more of them, while ensuring the valence balance of the chemical formula.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state battery preparation, and specifically relates to an oxide solid electrolyte, a preparation method thereof, and a solid-state battery. Background Art

[0002] Lithium-ion batteries have been widely used in new energy vehicles, data centers, communication base stations, major equipment, energy storage power stations and other fields due to their excellent energy density. In the past two centuries, the academic community has mainly focused on the research of lithium-ion batteries based on liquid electrolytes. Although traditional liquid electrolytes have high ionic conductivity, organic electrolytes are flammable and prone to combustion or even explosion accidents during battery thermal runaway. In contrast, all-solid-state lithium batteries use solid electrolytes (SSEs) to replace liquid electrolytes and separators, avoiding the use of organic solvents and improving the safety of lithium-ion batteries. Generally, solid electrolytes can be divided into three categories: polymer solid electrolytes, composite solid electrolytes, and inorganic solid electrolytes. Among them, inorganic solid electrolytes can be specifically divided into sulfide solid electrolytes, oxohalide solid electrolytes, and oxide solid electrolytes. Sulfide solid electrolytes have received extensive attention due to their excellent ionic conductivity and excellent low-temperature performance. However, sulfide solid electrolytes have strict manufacturing processes, poor chemical stability, are extremely sensitive to air humidity, and can react with water vapor to produce highly toxic H2S gas. Oxohalide solid electrolytes have both high ionic conductivity and strong stability, and have a higher room-temperature conductivity and lower humidity sensitivity than sulfides. However, the raw materials required for oxohalide solid electrolytes involve transition metal elements such as Ta and Y, and the high raw material cost limits the large-scale application of oxohalide solid electrolytes. Oxide solid electrolytes have the advantages of sulfide and oxohalide solid electrolytes and are compatible with high-voltage cathodes. The ionic conductivity of some doped and modified oxide solid electrolytes can also reach the order of 10 -3 S / cm at room temperature. However, the preparation process of oxide solid electrolytes is relatively complex and requires a high sintering temperature to densify them. Summary of the Invention

[0003] In order to overcome the disadvantages and deficiencies in the prior art, the primary object of the present invention is to provide an oxide solid electrolyte; this oxide solid electrolyte has a unique polyanion cluster structure, and the lattice distortion brought about by this structure is beneficial to constructing a high-entropy environment, providing multiple possible ion transport channels, thereby reducing the energy barrier of ion migration; in addition, by adjusting the doping ratio of the two polyanions, the degree of lattice distortion can be affected, which can further promote ion transport.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned oxide solid electrolyte; this method integrates a variety of technical means to improve the ionic conductivity of the solid electrolyte, and through the mechanism of the synergistic action of electrons and ions, that is, fluoride ions and polyanions can reduce the degree of electron-ion coupling through the local field effect, reducing the Coulomb interaction between the anion skeleton in the lattice and lithium ions, which is beneficial to the rapid migration of lithium ions in the lattice, and finally significantly improves the ionic conductivity of the electrolyte.

[0005] Another object of the present invention is to provide an application of the above-mentioned oxide solid electrolyte; the solid electrolyte material prepared by the present invention not only has low cost, but also has high ionic conductivity and good stability, is suitable for large-scale production, and is suitable for the wide application of the next-generation solid-state battery, and is a new technical path for developing low-cost and high-performance solid-state batteries.

[0006] Another object of the present invention is to provide a solid-state battery made of the above-mentioned oxide solid electrolyte.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] An oxide solid electrolyte, the chemical formula of the oxide solid electrolyte is A2MF, where A is any one of Li, Na, and K elements; M is BO3 3- , CO3 2- , NO3 - , NO2 - , SiO4 4- , SiO3 2- , PO3 3- , PO4 3- , SO4 2- , SO3 2- , ClO4 - , ClO3 - , CrO4 2- , MnO4 2- , TeO4 2- any one or more of them, while ensuring the valence balance of the chemical formula.

[0009] The oxide solid electrolyte is a mixture solid electrolyte, and the raw materials used do not have the characteristics of ionic conductors, while the solid electrolyte obtained through this design has the properties of ionic conductors; this oxide solid electrolyte presents irregular particles, and the particle size is in the range of 10nm~100μm; the room-temperature ionic conductivity of the oxide solid electrolyte reaches 10 -5 Scm -1 or more.

[0010] Specifically, for the Li-based oxide solid electrolyte, its chemical composition is Li2MF (M is BO33- 、 CO3 2- 、 NO3 - 、 NO2 - 、 SiO4 4- 、 SiO3 2- 、 PO3 3- 、 PO4 3- 、 SO4 2- 、 SO3 2- 、 ClO4 - 、 ClO3 - 、 CrO4 2- 、 MnO4 2- and TeO4 2- (one or more of them, while ensuring the valence balance of the chemical formula).

[0011] For the Na-based oxide solid electrolyte, its chemical composition is Na2MF (M is BO3 3- 、 CO3 2- 、 NO3 - 、 NO2 - 、 SiO4 4- 、 SiO3 2- 、 PO3 3- 、 PO4 3- 、 SO4 2- 、 SO3 2- 、 ClO4 - 、 ClO3 - 、 CrO4 2- 、 MnO4 2- and TeO4 2- (one or more of them, while ensuring the valence balance of the chemical formula).

[0012] For the K-based oxide solid electrolyte, its chemical composition is K2MF (M is BO3 3- 、 CO3 2- 、 NO3 - 、 NO2 - 、 SiO4 4- 、 SiO3 2- 、 PO3 3- 、 PO4 3- 、 SO4 2- 、 SO3 2- 、 ClO4 - 、 ClO3 - 、 CrO4 2- 、 MnO4 2- and TeO4 2- (one or more of them, while ensuring the valence balance of the chemical formula).

[0013] The above-mentioned method for preparing an oxide solid electrolyte comprises the following steps:

[0014] Under a dry environment, alkali metal fluoride AF and alkali metal salt AM are weighed as starting raw materials, put into a homogenizer and mix them thoroughly, the mixture is transferred into a container, placed in a high-temperature furnace and heated to 100-300°C at a heating rate of 10-20°C / min for pre-sintering; the pre-sintered product is placed in a ball mill, and a wet grinding solvent is added for ball milling, the ball milling parameters are set to a rotation speed of 200rpm-600rpm, and the ball milling time is 6-12 hours; the material obtained after ball milling is loaded into a mold and a pressure of 2t-8t is applied; then the pressurized material is transferred to a high-temperature furnace and sintered at 300°C-700°C, and the obtained solid is crushed and ground after cooling to finally obtain an oxide solid electrolyte.

[0015] The molar ratio of the alkali metal fluoride AF to the alkali metal salt AM is 1:1; A in both AF and AM is any one of Li, Na and K; AM is A3BO3 3- 、A2CO3 2- 、ANO3 - 、ANO2 - 、A4SiO4 4- 、A2SiO3 2- 、A3PO3 3- 、A3PO4 3- 、A2SO4 2- 、A2SO3 2- 、AClO4 - 、AC1O3 - 、A2CrO4 2- 、A2MnO4 2- and A2TeO4 2- When AM is a plurality of the above alkali metal salts, the amount of each alkali metal salt is used to ensure the valence balance of the chemical formula of the final oxide solid electrolyte.

[0016] The wet grinding solvent is one of ethanol, isopropanol, n-hexane, acetone, methanol, ethylene glycol, cyclohexane, dichloromethane and n-heptane;

[0017] The "dry environment" refers to an environment where the relative humidity is less than 30% or the dew point is less than -2°C.

[0018] The above-mentioned application of an oxide solid electrolyte in the preparation of a solid-state battery.

[0019] A solid-state battery comprising the above-mentioned oxide solid-state electrolyte.

[0020] The present invention has the following advantages and beneficial effects compared with the prior art:

[0021] (1) The present invention innovatively integrates a variety of means to improve the ionic conductivity of solid electrolytes to prepare a class of mixed oxide solid electrolytes; and a regulation scheme is given to enable its room temperature ionic conductivity to reach 10 -5 Scm -1 or above.

[0022] (2) Fluoride ions with high electronegativity are introduced during the preparation process of the present invention. The high electronegativity of fluoride ions can induce the polarization of adjacent cations and weaken the strong bonding between lithium ions and the lattice. Fluoride ions are single-charge anions with a relatively small ionic radius (≈1.33 Å) and a low charge density, which can further weaken the binding effect on lithium ions. In addition, a stable LiF layer can be formed at the electrolyte / electrode interface, reducing side reactions and promoting the uniform deposition of lithium ions.

[0023] (3) The present invention adopts an innovative design of a polyanion cluster structure. The electrolyte material prepared by the present invention has a unique polyanion cluster structure. The polyanion has a large volume and dispersed negative charges, which can reduce the charge density in the local area of the lattice. This dispersion effect weakens the Coulomb attraction between lithium ions and the lattice and reduces the migration energy barrier of lithium ions. In addition, the mixed structure of polyanions with different sizes can induce lattice distortion. Such a high-entropy environment brings rich lithium ion hopping sites, which can effectively reduce the migration energy barrier of lithium ions. In addition, by adjusting the addition ratio of various polyanions, the degree of lattice distortion can be flexibly regulated, and the ion migration path can be further optimized.

[0024] (4) The present invention designs an electron-ion synergy mechanism, that is, fluoride ions and polyanions can reduce the degree of electron-ion coupling through the local field effect, reducing the Coulomb interaction between the anion skeleton in the lattice and lithium ions. This is conducive to the rapid migration of lithium ions in the lattice and finally significantly improves the ionic conductivity of the electrolyte.

[0025] (5) The difference between the solid electrolyte designed by the method of the present invention and the solid electrolyte prepared by the existing method is that the composition of the solid electrolyte designed by this method is a mixture of several substances that do not have the properties of ionic conductors. This mixed solid electrolyte has low preparation cost, high efficiency in process and excellent performance, and has great application potential.

[0026] (6) The raw materials used in the present invention are cheap and easily available, significantly reducing the production cost and providing economic feasibility for large-scale commercial applications. At the same time, the synthesis process conditions of the present invention are mild and suitable for large-scale production. Description of the Drawings

[0027] Figure 1AC impedance spectra of the raw materials and products prepared according to the solution of the present invention in Example 1. The left figure shows the AC impedance spectrum of the raw materials LiF and Li2SO4, and the right figure shows the product Li2(SO4) 0.5 F and Li2(SO4) 0.3 (CO3) 0.2 AC impedance spectrum of F

[0028] Figure 2 AC impedance spectrum of the product prepared by the mechanical mixing method in Example 1. The left figure shows the AC impedance spectrum of the product LiF•Li2SO4, and the right figure shows the AC impedance spectrum of the product LiF•Li2SO4•Li2CO3

[0029] Figure 3 The product Li2(SO4) prepared according to the solution of the present invention in Example 1 0.5 XRD patterns (left) of the product Li2(SO4) 0.5 F and the raw materials, and FTIR patterns (right) of the product LiF•Li2SO4 prepared by the mechanical mixing method and the product Li2(SO4)

[0030] Figure 4 The product Li2(SO4) prepared according to the solution of the present invention in Example 1 0.5 F and Li2(SO4) 0.3 (CO3) 0.2 Cycling test results of the lithium metal symmetric battery with F

[0031] Figure 5 AC impedance spectra of the raw materials and products prepared according to the solution of the present invention in Example 2. The left figure shows the AC impedance spectra of the raw materials NaF, Na4SiO4 and NaNO3, and the right figure shows the product Na2(SiO4) 0.1 (NO3) 0.6 F and Na2(SiO4) 0.2 (NO3) 0.2 AC impedance spectrum of F

[0032] Figure 6 AC impedance spectra of the products prepared by the mechanical mixing method in Example 2. The left figure shows the AC impedance spectrum of the product NaF•Na4SiO4•NaNO3-1, and the right figure shows the AC impedance spectrum of the product NaF•Na4SiO4•NaNO3-2 Detailed implementation manners

[0033] The present invention will be further described in detail below in conjunction with examples and the accompanying drawings, but the implementation manners of the present invention are not limited thereto

[0034] Example 1:

[0035] In a dry environment (relative humidity less than 30%), weigh 1 mol LiF and 0.5 mol Li2SO4 as raw materials to prepare Li2(SO4) 0.5 F, weigh 1 mol LiF, 0.3 mol Li2SO4 and 0.2 mol Li2CO3 as raw materials to prepare Li2(SO4) 0.3 (CO3) 0.2 F. The specific steps of the preparation method are as follows: put the raw materials into a homogenizer and mix them thoroughly, then transfer the mixture into a container, place it in a high-temperature furnace and heat it to 300°C at a heating rate of 10°C / min for pre-sintering; put the product obtained after pre-sintering into a ball mill, add ethanol as a wet grinding solvent, and perform ball milling at a speed of 500rpm for 12 hours, and put the material obtained after ball milling into a mold and apply a pressure of 2t; then transfer the pressurized material to a high-temperature furnace and sinter it at a temperature of 600°C, and after cooling, crush and grind the obtained solid to finally obtain the following product: oxide solid electrolyte Li2(SO4) 0.5 F and Li2(SO4) 0.3 (CO3) 0.2 F.

[0036] The raw materials and products used in the preparation were subjected to impedance tests respectively. The AC impedance spectra were as follows: Figure 1 shown; from Figure 1 It can be seen that the raw materials LiF and Li2SO4 themselves have no conductivity, and Li2CO3 is also known to have no conductivity. However, the product Li2(SO4) prepared by the scheme of the present invention has 0.5 F and Li2(SO4) 0.3 (CO3) 0.2 F has the property of conducting electricity, indicating that the target product is successfully synthesized and is a mixture. Figure 1 It can also be seen from the right figure that the double polyanion solid electrolyte (Li2(SO4) 0.3 (CO3) 0.2 F) Compared with the single polyanion solid electrolyte (Li2(SO4) 0.5 F) shows lower impedance, indicating that anion CO3 2- Doping can effectively improve lithium ion conductivity.

[0037] To demonstrate that the mixed oxide solid electrolyte prepared by the present invention has more excellent performance, a comparative experiment was carried out by using the existing mechanical mixing method to prepare the product; the specific steps of the mechanical mixing method are as follows: first, the weighed raw materials are put into an agate mortar for premixing, and then the sample obtained by premixing is put into a ball mill jar for ball milling, and the product is obtained by ball milling and mixing evenly. The product prepared by the mechanical mixing method with 1 mol LiF and 0.5 mol Li2SO4 as raw materials is denoted as LiF•Li2SO4; the product prepared by the mechanical mixing method with 1 mol LiF, 0.3 mol Li2SO4 and 0.2 mol Li2CO3 as raw materials is denoted as LiF•Li2SO4•Li2CO3; the impedance tests were carried out on the products LiF•Li2SO4 and LiF•Li2SO4•Li2CO3 prepared by this mechanical mixing method, and the results are as Figure 2 shown. Figure 2 And Figure 1 By comparison, it can be seen that the performance of the product prepared by the existing mechanical mixing method is worse in conductivity than the product prepared by the scheme of the present invention, with almost no impedance value and no commercial value.

[0038] The product prepared by this scheme was subjected to XRD test, and the data are shown in Figure 3 (left); It can be seen from Figure 3 (left) that the diffraction peak positions of the product Li2(SO4) 0.5 F and the raw materials LiF and Li2SO4 are basically unchanged, indicating that the lattice structure of the synthesized product has not changed significantly, and the product Li2(SO4) 0.5 F is just a mixture. To further determine whether the product is synthesized, the raw materials, LiF•Li2SO4 prepared by the mechanical mixing method and the product Li2(SO4) 0.5 F prepared by this scheme were subjected to FTIR test, and the data are shown in Figure 3 (right). The results prove that the product prepared by this scheme has new peaks in the range of 2000 - 4000 cm -1 compared with the product prepared by the mechanical mixing method, which is speculated to be the F-N-O oscillation peak, indicating that the product prepared by this scheme forms a new coordination, which may be the reason why the ionic conductivity of the sample prepared by the scheme of the present invention is better than that of the sample prepared by the mechanical preparation method.

[0039] Finally, the products Li2(SO4) 0.5 F and Li2(SO4) 0.3 (CO3) 0.2 F solid electrolytes prepared by the scheme of the present invention were assembled into lithium metal symmetric batteries. The test results show that Li2(SO4) 0.3 (CO3) 0.2The lithium metal symmetric battery assembled with F solid electrolyte has low polarization voltage, higher limiting current density and lithium cycling stability. Figure 4 .

[0040] Embodiment 2:

[0041] In a dry environment (relative humidity less than 30%), weigh 1 mol NaF, 0.1 mol Na4SiO4 and 0.6 mol NaNO3 to prepare Na2(SiO4) 0.1 (NO3) 0.6 F, weigh 1 mol NaF, 0.2 mol Na4SiO4 and 0.2 mol NaNO3 to prepare Na2(SiO4) 0.2 (NO3) 0.2 F. Put the raw materials into a homogenizer and mix them thoroughly; transfer the mixture into a container, place it in a high-temperature furnace and heat it to 200℃ at a heating rate of 10℃ / min for pre-sintering; put the product obtained after pre-sintering into a ball mill, add ethanol as a wet grinding solvent, and perform ball milling at a speed of 500rpm for 8 hours, and put the material obtained after ball milling into a mold and apply a pressure of 2t; then transfer the material after applying pressure to a high-temperature furnace and sinter it at a temperature of 700℃, and after cooling, crush and grind the obtained solid to finally obtain the following product: oxide solid electrolyte Na2(SiO4) 0.1 (NO3) 0.6 F. Na2(SiO4) 0.2 (NO3) 0.2 F.

[0042] The raw materials and products used in this example were subjected to AC impedance tests, and the AC impedance spectra were as follows: Figure 5 As shown. Figure 5 It can be seen that the raw materials NaF, Na4SiO4 and NaNO3 themselves do not have conductivity, and the product Na2(SiO4) prepared by the scheme of the present invention 0.1 (NO3) 0.6 F and Na2(SiO4) 0.2 (NO3) 0.2 F has a certain ionic conductivity, indicating that the synthesis is successful. Compared with Na2(SiO4) 0.1 (NO3) 0.6 F and Na2(SiO4) 0.2 (NO3) 0.2 It can be seen from the impedance data of F that the ionic conductivity of the sample can be effectively changed by adjusting the ratio of the two polyanions.

[0043] To demonstrate that the mixed oxide solid electrolyte prepared by the present invention has more excellent performance, a comparative experiment was carried out using the existing mechanical mixing method to prepare the product; the specific steps of the mechanical mixing method are as follows: first, the weighed raw materials are put into an agate mortar for premixing, and then the sample obtained by premixing is put into a ball mill jar for ball milling, and the product is obtained after uniform ball milling. The product prepared by the mechanical mixing method using 1 mol of NaF, 0.1 mol of Na4SiO4 and 0.6 mol of NaNO3 as raw materials is denoted as NaF•Na4SiO4•NaNO3-1, and the product prepared by the mechanical mixing method using 1 mol of NaF, 0.2 mol of Na4SiO4 and 0.2 mol of NaNO3 as raw materials is denoted as NaF•Na4SiO4•NaNO3-2. Impedance tests were carried out on NaF•Na4SiO4•NaNO3-1 and NaF•Na4SiO4•NaNO3-2 prepared by this mechanical mixing method, and the results are as Figure 6 shown. Comparing Figure 5 and Figure 6 it can be seen that the products prepared by the existing mechanical mixing method have no impedance value or unstable impedance, and their performance is far lower than that of the products prepared by the present invention.

[0044] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A solid oxide electrolyte, characterized in that: The chemical formula of the oxide solid electrolyte is Li2(SO4) 0.5 F, Li2(SO4) 0.3 (CO3) 0.2 F, Na2(SiO4) 0.1 (NO3) 0.6 F or Na2(SiO4) 0.2 (NO3) 0.2 F; The oxide solid electrolyte is a mixture of several substances that do not have the properties of ion conductors, and the mixture has the properties of ion conductors.

2. An oxide solid electrolyte according to claim 1, characterized in that: The oxide solid electrolyte presents irregular particles with a particle size ranging from 10 nm to 100 μm; the room-temperature ionic conductivity of the oxide solid electrolyte reaches 10 -5 S cm -1 or more.

3. A method for preparing the oxide solid electrolyte according to claim 1, characterized in that The steps include: Under a dry environment, alkali metal fluoride AF and alkali metal salt AM are weighed as starting raw materials, put into a homogenizer and mix them thoroughly, transfer the mixture into a container, place it into a high-temperature furnace and heat it to 100-300°C at a heating rate of 10-20°C / min for pre-sintering; put the pre-sintered product into a ball mill, add a wet grinding solvent for ball milling, set the ball milling parameters to a speed of 200rpm-600rpm, and the ball milling time is 6-12 hours; put the material obtained after ball milling into a mold and apply a pressure of 2t-8t; then transfer the pressurized material to a high-temperature furnace and sinter it at 300°C-700°C, and crush the obtained solid after cooling, Grind and finally obtain the oxide solid electrolyte.

4. The preparation method of an oxide solid electrolyte according to claim 3, wherein: The molar ratio of the alkali metal fluoride AF to the alkali metal salt AM is 1:1; When the AF is LiF, the AM is Li2SO4, or a mixture of Li2SO4 and A2CO3; When the AF is NaF, the AM is a mixture of Na4SiO4 and NaNO3; The amount of each alkali metal salt used ensures that the chemical formula of the final oxide solid electrolyte is valence balanced.

5. The preparation method of an oxide solid electrolyte according to claim 3, characterized in that: The wet grinding solvent is one of ethanol, isopropanol, n-hexane, acetone, methanol, ethylene glycol, cyclohexane, dichloromethane and n-heptane.

6. The preparation method of an oxide solid electrolyte according to claim 3, wherein: The dry environment refers to an environment with a relative humidity of less than 30% or a dew point of less than -2°C.

7. An application of the oxide solid electrolyte according to claim 1, characterized in that: This application uses the oxide solid electrolyte to prepare a solid-state battery.

8. A solid-state battery, characterized in that The solid-state battery comprises an oxide solid-state electrolyte as claimed in claim 1.

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