Electrolyte film and preparation method thereof

Abstract

The invention provides an electrolyte film and a preparation method thereof, the electrolyte film comprises a sulfide solid electrolyte and a binder, and the molecular weight of the binder is 0.5-7 million; the porosity of the electrolyte film is smaller than or equal to 10%. According to the electrolyte film and the preparation method thereof provided by the invention, the electrolyte film is prepared by adopting the binder with the molecular weight of 50-7,000,000, and the porosity of the electrolyte film is less than or equal to 10%, so that not only is the mechanical strength of the electrolyte film increased, but also the stability of the ionic conductivity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to an electrolyte film and a preparation method thereof. Background Art

[0002] With the rapid development of electric vehicles and portable electronic products, lithium batteries with higher energy density have become one of the research hotspots in the field of power batteries and energy storage.

[0003] There are still some problems with the electrolyte film in existing lithium batteries. For example, the electrolyte film has a high porosity, which leads to a decrease in mechanical strength and affects the stability of the electrolyte film. Summary of the invention

[0004] The object of the present invention is to provide an electrolyte film and a preparation method thereof, which reduces the porosity of the electrolyte film, increases the mechanical strength of the electrolyte film, and improves the stability of ion conductivity.

[0005] To achieve the above-mentioned object, in a first aspect, the present invention provides an electrolyte film, comprising: a sulfide solid electrolyte and a binder, wherein the molecular weight of the binder is 500,000-7,000,000; The porosity of the electrolyte film is less than or equal to 10%. The beneficial effect of the electrolyte film provided by the present invention is that the electrolyte film is prepared by using a binder with a molecular weight of 500,000-7,000,000 and making its porosity less than or equal to 10%, which not only increases the mechanical strength of the electrolyte film, but also improves the stability of ionic conductivity.

[0006] In some embodiments, the tensile strength of the electrolyte film is 0.3-1 MPa, and the bending radius of the electrolyte film is less than or equal to 5 mm.

[0007] In some embodiments, the elongation at break of the electrolyte film is 0.5-1.5%.

[0008] In some embodiments, the weight percentage of the sulfide solid electrolyte is 94-96wt%, and the weight percentage of the binder is 4-6wt%.

[0009] In some embodiments, the ionic conductivity of the electrolyte film is greater than or equal to 1.5 mS / cm, and the electronic conductivity of the electrolyte film is greater than or equal to 2.4*10 -10 -6.1*10 -10 S / cm.

[0010] In some embodiments, the thickness of the electrolyte film is less than or equal to 65 μm.

[0011] In some embodiments, the binder includes at least one of a thermoplastic elastomer, styrene-butadiene rubber, polyvinylidene fluoride, thermoplastic styrene-butadiene rubber, synthetic rubber, hydrogenated nitrile rubber, polyethylene-vinyl acetate, polymethyl methacrylate, polyacrylic acid, polyisobutylene, cis-1,4-polybutadiene rubber, and nitrile rubber.

[0012] In a second aspect, an embodiment of the present invention provides a method for preparing an electrolyte film for preparing the electrolyte film. The preparation method includes: Stirring and mixing a solution containing a binder with a sulfide solid electrolyte to obtain a slurry; Coating the slurry on a release film and performing a heat treatment on the release film to form an electrolyte film on the release film; Separating the electrolyte film from the release film and performing a heat and pressure treatment on the electrolyte film.

[0013] The beneficial effect of the method for preparing the electrolyte film provided by the present invention is that after the slurry is coated on the release film, a heat treatment is performed on it, and after the electrolyte film is separated from the release film, a heat and pressure treatment is performed on the electrolyte film, so that the porosity of the electrolyte film is less than or equal to 10%. This not only increases the mechanical strength of the electrolyte film but also improves the stability of the ionic conductivity.

[0014] In some embodiments, the transferring the release film to a heating device for heat treatment includes: Transferring the release film to a vacuum transition chamber at 50 - 100 °C and heating for 2 - 12 hours; Transferring the release film to a heating table at 50 - 100 °C and heating for 2 - 12 hours.

[0015] In some embodiments, the separating the electrolyte film from the release film includes: Applying a pressure of 30 - 80 MPa to the electrolyte film until the electrolyte film is separated from the release film.

[0016] In some embodiments, the performing a heat and pressure treatment on the electrolyte film includes: Placing the electrolyte film in an environment at 50 - 100 °C and applying a pressure of 30 - 80 MPa to the electrolyte film and maintaining for 2 - 12 hours.

[0017] In some embodiments, the sulfide solid electrolyte is in a powder state, and the D50 of the sulfide solid electrolyte is 3 - 15 μm. Description of the Drawings

[0018] Figure 1The present invention provides a flow chart of a method for preparing an electrolyte membrane according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the usual meanings understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Unless otherwise specified, the "connection" described in this article can be a direct connection or an indirect connection, that is, connected through an intermediate.

[0020] In addition, it should be understood that the orientations or positional relationships indicated by "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. in this document are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The "first" and "second" in this document are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0021] In view of the problems existing in the prior art, an embodiment of the present invention provides an electrolyte film, a sulfide solid electrolyte and a binder, wherein the molecular weight of the binder is 500,000-7,000,000, and the porosity of the electrolyte film is less than or equal to 10%.

[0022] In this embodiment, the electrolyte membrane is prepared by using a binder with a molecular weight of 500,000-7 million and by heating and pressurizing, and its porosity is less than or equal to 10%, which not only increases the mechanical strength of the electrolyte membrane, but also improves the stability of ionic conductivity.

[0023] In some specific embodiments, the molecular weight of the binder can be 500,000, 1,000,000, 1,500,000, 1,800,000, 2,000,000, 2,300,000, 2,500,000, 2,800,000, 3,000,000, 4,000,000, 5,000,000, 6,000,000 or 7,000,000, etc. The porosity of the electrolyte film can be 1%, 3%, 4%, 5%, 9% or 10%, etc. Wherein, the binder includes at least one of thermoplastic elastomer, styrene-butadiene rubber, polyvinylidene fluoride, thermoplastic styrene-butadiene rubber, synthetic rubber, hydrogenated nitrile rubber, polyethylene-vinyl acetate, polymethyl methacrylate, polyacrylic acid, polyisobutylene, butadiene rubber and nitrile rubber. More preferably, the binder is polyisobutylene, and the mechanism of action of polyisobutylene is based on physical adsorption theory. Since polyisobutylene and sulfide electrolyte are physically adsorbed and do not react, when the binder is polyisobutylene, the ionic conductivity of the membrane is higher and the transport speed of lithium ions is faster.

[0024] It is understandable that improving the mechanical strength of the electrolyte membrane is also conducive to achieving continuous coating of the electrolyte film, accelerating the large-scale production process of the electrolyte film, and improving the energy density and safety of the battery.

[0025] In some embodiments, the tensile strength of the electrolyte film is 0.3-1 MPa, and the bending radius of the electrolyte film is less than or equal to 5 mm.

[0026] In some specific embodiments, the tensile strength of the electrolyte film is 0.3 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa or 1 MPa, etc. The bending radius of the electrolyte film is 1 mm, 2 mm, 3 mm, 4 mm or 5 mm, etc.

[0027] In some embodiments, the weight percentage of the sulfide solid electrolyte is 94-96wt%, and the weight percentage of the binder is 4-6wt%.

[0028] In some specific embodiments, when the weight percentage of the sulfide solid electrolyte is 94wt%, the weight percentage of the binder is 6wt%. When the weight percentage of the sulfide solid electrolyte is 95wt%, the weight percentage of the binder is 5wt%. When the weight percentage of the sulfide solid electrolyte is 96wt%, the weight percentage of the binder is 4wt%.

[0029] In some embodiments, the ionic conductivity of the electrolyte film is greater than or equal to 1.5 mS / cm, and the electronic conductivity of the electrolyte film is 2.4*10-10-6.1*10-10 S / cm.

[0030] In some embodiments, the thickness of the electrolyte film is less than or equal to 65 μm.

[0031] In another embodiment of the present invention, a method for preparing an electrolyte film is provided, which is used to prepare the electrolyte film in the above embodiment, and the preparation method comprises: S101: stirring and mixing a solution containing a binder and a sulfide solid electrolyte to obtain a slurry.

[0032] Prior to this step, a solution containing a binder is prepared in advance. Specifically, the binder is mixed with an ester or benzene solvent and heated at 80-90° C. for 24 hours to fully dissolve the binder and the solvent. Finally, the solution is allowed to stand for defoaming to obtain the solution containing the binder.

[0033] In this step, specifically, the sulfide solid electrolyte and the solution containing the binder are placed in a degassing machine in a certain ratio and mixed, and then filtered to defoam, so as to finally obtain the slurry.

[0034] The rotation speed of the degassing machine is 1200-3200 rpm, and the stirring time is 10-60 min. The sulfide solid electrolyte is in the form of powder, and the D50 of the sulfide solid electrolyte is 3-15 μm.

[0035] S102: coating the slurry on a release film, and heating the release film to form an electrolyte film on the release film.

[0036] In this step, the slurry is evenly coated on the release film using a transfer coater or a flat plate coater. The release film is then transferred to a vacuum transition chamber or a heating table for heating and drying. The heating temperature of the vacuum transition chamber or the heating table is controlled at 50-100°C, and the heating time is 2-12 hours.

[0037] S103: separating the electrolyte film from the release film, and performing a heating and pressurizing treatment on the electrolyte film.

[0038] In this step, a roller press is used to apply a pressure of 30-80 MPa to the electrolyte film until the electrolyte film is separated from the release film. Then, the electrolyte film is placed on a hot press, which provides a temperature environment of 50-100° C. to the electrolyte film and applies a pressure of 30-80 MPa to the electrolyte film for 2-12 hours to finally obtain the electrolyte film.

[0039] The binders used in the following examples and comparative examples are all polyisobutylene.

[0040] Embodiment 1 The present invention provides a method for preparing an electrolyte film, and the preparation method specifically comprises the following steps: (1) A binder having a weight percentage of 6 wt% and an ester or benzene solvent are mixed at a temperature of 80° C. and maintained for 24 hours to prepare a solution containing the binder, wherein the molecular weight of the binder is 2 million.

[0041] (2) A solution of a sulfide solid electrolyte and a binder with a weight percentage of 94 wt % was placed in a degassing machine, the speed of the degassing machine was controlled to be 1200 rpm, and the stirring time was 60 min to obtain a slurry.

[0042] (3) Use a transfer coater to evenly coat the slurry on the release film.

[0043] (4) The release film coated with the slurry was transferred to a heating platform, and the temperature of the heating platform was controlled at 50° C. for 12 h to form an electrolyte thin film on the release film.

[0044] (5) The electrolyte film is pressurized using a roller press at a pressure of 30 MPa to separate the electrolyte film from the release film.

[0045] (6) The electrolyte film is placed on a hot press, which heats the electrolyte film to 50°C and applies a pressure of 80 MPa to the electrolyte film for 2 hours to obtain an electrolyte film.

[0046] Embodiment 2 The present invention provides a method for preparing an electrolyte film, and the preparation method specifically comprises the following steps: (1) A binder having a weight percentage of 5 wt% and an ester or benzene solvent are mixed at a temperature of 85° C. and maintained for 24 hours to prepare a solution containing the binder, wherein the molecular weight of the binder is 3 million.

[0047] (2) A solution of a sulfide solid electrolyte and a binder with a weight percentage of 95 wt % was placed in a degassing machine, the speed of the degassing machine was controlled to be 2000 rpm, and the stirring time was 30 min to obtain a slurry.

[0048] (3) Use a transfer coater to evenly coat the slurry on the release film.

[0049] (4) The release film coated with the slurry was transferred to a heating platform, and the temperature of the heating platform was controlled at 75° C. for 7 h to form an electrolyte thin film on the release film.

[0050] (5) The electrolyte film is pressurized using a roller press at a pressure of 55 MPa to separate the electrolyte film from the release film.

[0051] (6) The electrolyte film is placed on a hot press, which heats the electrolyte film to 75°C and applies a pressure of 55 MPa to the electrolyte film for 7 hours to obtain an electrolyte film.

[0052] Embodiment 3 The present invention provides a method for preparing an electrolyte film, and the preparation method specifically comprises the following steps: (1) A binder having a weight percentage of 4 wt% is mixed with an ester or benzene solvent at a temperature of 90° C. and maintained for 24 hours to prepare a solution containing the binder, wherein the molecular weight of the binder is 4 million.

[0053] (2) A solution of a sulfide solid electrolyte and a binder with a weight percentage of 96 wt % was placed in a degassing machine, the speed of the degassing machine was controlled to be 3200 rpm, and the stirring time was 10 min to obtain a slurry.

[0054] (3) Use a transfer coater to evenly coat the slurry on the release film.

[0055] (4) The release film coated with the slurry was transferred to a heating platform, and the temperature of the heating platform was controlled at 100° C. for 12 h to form an electrolyte thin film on the release film.

[0056] (5) The electrolyte film is pressurized using a roller press at a pressure of 80 MPa to separate the electrolyte film from the release film.

[0057] (6) The electrolyte film is placed on a hot press, which heats the electrolyte film to 100°C and applies a pressure of 30 MPa to the electrolyte film for 12 hours to obtain an electrolyte film.

[0058] Embodiment 4 The present invention provides a method for preparing an electrolyte film, and the preparation method specifically comprises the following steps: (1) A binder having a weight percentage of 6 wt% and an ester or benzene solvent are mixed at a temperature of 80° C. and maintained for 24 hours to prepare a solution containing the binder, wherein the molecular weight of the binder is 1 million.

[0059] (2) A solution of a sulfide solid electrolyte and a binder with a weight percentage of 94 wt % was placed in a degassing machine, the speed of the degassing machine was controlled to be 1200 rpm, and the stirring time was 60 min to obtain a slurry.

[0060] (3) Use a transfer coater to evenly coat the slurry on the release film.

[0061] (4) The release film coated with the slurry was transferred to a heating platform, and the temperature of the heating platform was controlled at 50° C. for 12 h to form an electrolyte thin film on the release film.

[0062] (5) The electrolyte film is pressurized using a roller press at a pressure of 30 MPa to separate the electrolyte film from the release film.

[0063] (6) The electrolyte film is placed on a hot press, which heats the electrolyte film to 50°C and applies a pressure of 80 MPa to the electrolyte film for 2 hours to obtain an electrolyte film.

[0064] Embodiment 5 The present invention provides a method for preparing an electrolyte film, and the preparation method specifically comprises the following steps: (1) A binder having a weight percentage of 6 wt% is mixed with an ester or benzene solvent at a temperature of 80° C. and maintained at the temperature for 24 hours to prepare a solution containing the binder, wherein the molecular weight of the binder is 6.5 million.

[0065] (2) A solution of a sulfide solid electrolyte and a binder with a weight percentage of 94 wt % was placed in a degassing machine, the speed of the degassing machine was controlled to be 1200 rpm, and the stirring time was 60 min to obtain a slurry.

[0066] (3) Use a transfer coater to evenly coat the slurry on the release film.

[0067] (4) The release film coated with the slurry was transferred to a heating platform, and the temperature of the heating platform was controlled at 50° C. for 12 h to form an electrolyte thin film on the release film.

[0068] (5) The electrolyte film is pressurized using a roller press at a pressure of 30 MPa to separate the electrolyte film from the release film.

[0069] (6) The electrolyte film is placed on a hot press, which heats the electrolyte film to 50°C and applies a pressure of 80 MPa to the electrolyte film for 2 hours to obtain an electrolyte film.

[0070] Comparative Example 1 S1: Add 93wt% solid electrolyte and 7wt% binder to The dispersion liquid is fully mixed to obtain a uniformly dispersed electrolyte slurry; wherein the molecular weight of the binder is 300,000.

[0071] S2: Apply the electrolyte slurry on the skeleton, heat to 50°C for 12 hours, and then pressurize to 30MPa. An electrolyte film is obtained.

[0072] Comparative Example 2 S1: Add 97wt% solid electrolyte and 3wt% binder to The dispersion is fully mixed to obtain a uniformly dispersed electrolyte slurry, wherein the molecular weight of the binder is 8 million.

[0073] S2: Apply the electrolyte slurry on the skeleton, heat to 50°C for 12 hours, and then pressurize to 30MPa. An electrolyte film is obtained.

[0074] Comparative Example 3 S1: Add 94wt% solid electrolyte and 6wt% binder to The dispersion is fully mixed to obtain a uniformly dispersed electrolyte slurry, wherein the molecular weight of the binder is 2 million.

[0075] S2: Apply the electrolyte slurry on the skeleton, heat to 50°C for 12 hours, and then pressurize to 30MPa. An electrolyte film is obtained.

[0076] Examples 1 to 5, the prior art The comparative examples 1 to 3 prepared by the method for preparing the electrolyte film by using the above method are compared to obtain the following table 1:

[0077] Table 1 The porosity, ionic conductivity, electronic conductivity, tensile strength and thickness of the electrolyte films in Examples 1 to 5 and Comparative Examples 1 to 3 were tested by mercury intrusion method (the porosity was calculated by measuring the pressure change of mercury in the pores of the material), AC impedance spectroscopy (the instrument used was Gamry Reference 620 electrochemical workstation), DC polarization method (the instrument used was Gamry Reference 620 electrochemical workstation, calculated by Hebb-Wagner DC polarization method), universal mechanical testing machine (produced by Shanghai Xiangjie Instrument Technology Co., Ltd.), bending testing machine (the instrument used was QTY-32 paint film cylindrical bending tester), and optical microscope (produced by Yuescope) to prepare the following Table 2 after testing the porosity, ionic conductivity, electronic conductivity, tensile strength and thickness of the electrolyte films in Examples 1 to 5 and Comparative Examples 1 to 3:

[0078] Table 2 According to Table 2, the porosity of the electrolyte membranes in Examples 1 to 5 is less than 10%, the porosity of the electrolyte membranes in Comparative Examples 1, 2, and 3 is higher than 10%, the ionic conductivity of the electrolyte membranes in Examples 1 to 5 is greater than or equal to 1.5 mS / cm, and the ionic conductivity of the electrolyte membranes in Comparative Examples 1, 2, and 3 is less than 1.5 mS / cm. The electronic conductivity of the electrolyte membranes in Examples 1 to 5 is 2.4*10 -10 -6.1*10 -10 S / cm, the electronic conductivity of the electrolyte films of Comparative Examples 1, 2, and 3 is less than 2.4*10 -10 S / cm. The tensile strength of the electrolyte film in Examples 1 to 5 is in the range of 0.3-1MPa, the tensile strength of Comparative Examples 1 and 2 is in the range of 0.3-1MPa, and the tensile strength of the electrolyte film in Comparative Example 3 is less than 0.3MPa. The bending radius of the electrolyte film in Examples 1 to 5 is less than 5mm, and the bending radius of the electrolyte film in Comparative Examples 1, 2, and 3 is 7mm, 6mm, and 7mm, respectively. The thickness of the electrolyte film in Examples 1 to 5 and Comparative Examples 1, 2, and 3 is 50μm. According to Table 2, the electrolyte film provided in the present application has higher mechanical strength than the existing electrolyte films on the market, and the stability of ionic conductivity is also higher.

[0079] The above is only a specific implementation of the embodiment of the present application, but the protection scope of the embodiment of the present application is not limited thereto, and any changes or replacements within the technical scope disclosed in the embodiment of the present application should be included in the protection scope of the embodiment of the present application. Therefore, the protection scope of the embodiment of the present application should be based on the protection scope of the claims.

Claims

1. An electrolyte membrane, characterized in that: include: Sulfide solid electrolyte and binder, wherein the molecular weight of the binder is 500,000-7,000,000; The porosity of the electrolyte film is less than or equal to 10%.

2. The electrolyte membrane according to claim 1, characterized in that The tensile strength of the electrolyte film is 0.3-1 MPa, and the bending radius of the electrolyte film is less than or equal to 5 mm.

3. The electrolyte membrane according to claim 1, characterized in that The elongation at break of the electrolyte film is 0.5-1.5%.

4. The electrolyte membrane according to claim 1, characterized in that The weight percentage of the sulfide solid electrolyte is 94-96wt%, and the weight percentage of the binder is 4-6wt%.

5. The electrolyte membrane according to claim 1, characterized in that The ionic conductivity of the electrolyte film is greater than or equal to 1.5 mS / cm, and the electronic conductivity of the electrolyte film is greater than or equal to 2.4*10 -10 -6.1*10 -10 S / cm.

6. The electrolyte membrane according to claim 1, characterized in that The thickness of the electrolyte film is less than or equal to 65 μm.

7. The electrolyte membrane according to claim 1, characterized in that The binder includes at least one of thermoplastic elastomer, styrene-butadiene rubber, polyvinylidene fluoride, thermoplastic styrene-butadiene rubber, synthetic rubber, hydrogenated nitrile rubber, polyethylene-vinyl acetate, polymethyl methacrylate, polyacrylic acid, polyisobutylene, butadiene rubber, and nitrile rubber.

8. A method for preparing an electrolyte film, characterized in that: For preparing the electrolyte film according to any one of claims 1 to 6, the preparation method comprising: A solution containing a binder and a sulfide solid electrolyte are stirred and mixed to obtain a slurry; coating the slurry on a release film, and heating the release film to form an electrolyte film on the release film; The electrolyte film is separated from the release film, and the electrolyte film is subjected to a heating and pressurizing treatment.

9. The preparation method according to claim 8, characterized in that: The step of transferring the release film to a heating device for heating treatment comprises: Transfer the release film to a vacuum transition chamber at 50-100° C. and heat for 2-12 hours; The release film is transferred to a heating table at 50-100° C. and heated for 2-12 hours.

10. The preparation method according to claim 8, characterized in that: The step of separating the electrolyte film from the release film comprises: A pressure of 30-80 MPa is applied to the electrolyte film until the electrolyte film is separated from the release film.

11. The preparation method according to claim 8, characterized in that: The step of heating and pressurizing the electrolyte film comprises: The electrolyte film is placed in an environment of 50-100° C., and a pressure of 30-80 MPa is applied to the electrolyte film for 2-12 hours.

12. The preparation method according to claim 8, characterized in that: The sulfide solid electrolyte is in the state of powder, and the D50 of the sulfide solid electrolyte is 3-15 μm.

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