Electrolyte membrane, preparation method thereof, all-solid-state battery and electrical equipment

Abstract

The present application provides an electrolyte membrane, a preparation method thereof, an all-solid-state battery, and an electrical device, belonging to the technical field of batteries. The preparation method of the electrolyte membrane includes: mixing liquid succinonitrile with a lithium salt to obtain a lithium salt solution; adding the lithium salt solution to a skeleton membrane to obtain a modified skeleton membrane, wherein the skeleton membrane is a polymer-based porous material; mixing a sulfide electrolyte, a binder, and a solvent to obtain a slurry, adding the slurry to the modified skeleton membrane, and drying to obtain the electrolyte membrane. By using the lithium salt solution to treat the skeleton membrane, the method of the present application can improve the affinity between the skeleton membrane and the sulfide electrolyte. The method of the present application can solve the problem of poor affinity between the skeleton membrane and the sulfide electrolyte, improve the uniformity of the electrolyte membrane, and reduce the short-circuit probability of the battery. Moreover, the preparation method of the present application is simple in operation and low in production cost, which is conducive to large-scale popularization and application.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to an electrolyte membrane, a preparation method thereof, a all-solid-state battery, and an electrical device. Background Art

[0002] An all-solid-state battery is a battery that uses solid electrodes and a solid electrolyte, and has advantages such as high safety and high energy density. The all-solid-state battery is one of the important development directions of power batteries.

[0003] As an important component of an all-solid-state battery, the thickness of the electrolyte membrane is directly related to the energy density of the battery. In pursuit of high energy density, it is required that the thickness of the electrolyte membrane ≤ 20 μm.

[0004] As the part that isolates the positive and negative electrodes and efficiently transports lithium ions, the electrolyte membrane is required to have high ionic conductivity. Therefore, the amount of binder used in the preparation process of the electrolyte membrane needs to be as small as possible. However, a small amount of binder makes it difficult for the electrolyte membrane to have good mechanical properties. Therefore, a skeleton membrane is used to enhance the supportability to achieve a thickness ≤ 20 μm.

[0005] At present, some skeleton membrane samples have good mechanical properties enough to support rolling. However, since they do not start from the characteristics and application scenarios of the electrolyte membrane, there are many problems in the use process. The most important problem is that the uniformity of the electrolyte membrane is poor, which directly increases the short-circuit probability of the battery. Summary of the Invention

[0006] The purpose of the present application is to provide an electrolyte membrane, a preparation method thereof, an all-solid-state battery, and an electrical device to solve the above problems.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] A preparation method of an electrolyte membrane, comprising: mixing liquid succinonitrile with a lithium salt to obtain a lithium salt solution; adding the lithium salt solution to a skeleton membrane to obtain a modified skeleton membrane; wherein the skeleton membrane is a polymer-based porous material; mixing a sulfide electrolyte, a binder, and a solvent to obtain a slurry, adding the slurry to the modified skeleton membrane, and drying to obtain the electrolyte membrane.

[0009] According to an embodiment of the present application, the preparation method satisfies at least one of the following conditions:

[0010] (1) The lithium salt includes at least one of LiTFSI, LiFSI, LiODFB, LiPF2, and LiPF6;

[0011] (2) The concentration of the lithium salt solution is 0.5 - 2 mol / L;

[0012] (3) The lithium salt solution is prepared by the following method: mixing succinonitrile with a lithium salt and heating at a temperature of 50-70 °C to obtain the lithium salt solution.

[0013] According to an embodiment of the present application, the ratio of the mass of the lithium salt solution in the modified skeleton membrane to the mass of the modified skeleton membrane is (5x10 -4 ~2x10 -3 ):1.

[0014] According to an embodiment of the present application, the modified skeleton membrane is prepared by any one of the following methods:

[0015] Placing the skeleton membrane and the lithium salt solution in a vacuum environment, raising the temperature to make the lithium salt solution exist in the form of steam, loading the lithium salt solution on the skeleton membrane, and cooling to room temperature to obtain the modified skeleton membrane;

[0016] Or, adding the lithium salt solution to the skeleton membrane by means of spraying or dropping or soaking or coating, and the process of spraying or dropping or soaking or coating is carried out in an environment of 50-70 °C, loading the lithium salt solution on the skeleton membrane, and cooling to room temperature to obtain the modified skeleton membrane.

[0017] According to an embodiment of the present application, the skeleton membrane satisfies at least one of the following conditions:

[0018] A. The skeleton membrane includes polycarbonate, polyethylene terephthalate, polyamide, polypropylene, polyethylene or a composite of polypropylene and polyethylene;

[0019] B. The thickness of the skeleton membrane is 5-10 μm;

[0020] C. The porosity of the skeleton membrane is 70-92%.

[0021] According to an embodiment of the present application, the preparation method satisfies at least one of the following conditions:

[0022] a. The sulfide electrolyte includes any one of Li6PS5Cl, Li3PS4, Li2S-P2S5;

[0023] b. The binder includes at least one of SBR, NBR, PVDF, PVDF-HFP, SBS, SEBS, SEPS;

[0024] c. The solvent includes at least one of n-heptane, methyl vinyl ketone, n-hexane, anisole, cyclopentyl methyl ether, butyl butyrate, xylene, toluene;

[0025] d. The mass ratio of the sulfide electrolyte to the binder is (90 - 99):(1 - 10);

[0026] e. The solid content of the slurry is 50 - 65 wt%;

[0027] f. The method of adding the slurry to the skeleton film includes coating, and the coating is carried out at a temperature of 40 - 50 °C;

[0028] g. The wet thickness of the coating is 15 - 30 μm;

[0029] h. The drying temperature is 35 - 45 °C;

[0030] i. The drying time is 23 - 25 h;

[0031] j. After the drying, the preparation method further includes a pressing step, and the pressure of the pressing is 280 - 320 MPa;

[0032] k. The pressing time is 1.8 - 2.2 min.

[0033] According to the embodiments of the present application, the thickness of the electrolyte film is less than or equal to 20 μm.

[0034] The present application also provides an electrolyte film, and the electrolyte film is prepared by the preparation method of the electrolyte film described above.

[0035] The present application also provides a all-solid-state battery, and the all-solid-state battery includes the electrolyte film described above.

[0036] The present application also provides an electrical device, and the electrical device includes the all-solid-state battery described above.

[0037] Compared with the prior art, the beneficial effects of the present application include:

[0038] By modifying the skeleton film with a lithium salt solution, the present application method can improve the affinity between the skeleton film and the sulfide electrolyte. Specifically, the lithium salt solution is prepared by a lithium salt and succinonitrile. The addition of the lithium salt is beneficial to promoting the transfer of lithium ions between the positive and negative electrodes, thereby improving the performance of the battery; succinonitrile has good affinity with the skeleton film, and succinonitrile can also interact with the slurry forming the electrolyte film when coating the slurry. That is to say, succinonitrile plays a connecting role between the skeleton film and the slurry forming the electrolyte film, so that the slurry has good wettability with the skeleton film. Generally speaking, the present application method can improve the problem of poor affinity between the skeleton film and the sulfide electrolyte, improve the uniformity of the electrolyte film, and reduce the short-circuit probability of the battery. Moreover, the preparation method of the present application is simple in operation and low in production cost, which is beneficial to large-scale popularization and application.

[0039] The electrolyte membrane of the present application has a low short - circuit rate.

[0040] The all - solid - state battery and the electrical equipment of the present application have a low short - circuit rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0042] Figure 1 It is a scanning electron microscope image of the front side of the electrolyte membrane in Example 1. The front side of the electrolyte membrane refers to the surface formed after the slurry is dried.

[0043] Figure 2 It is a scanning electron microscope image of the back side of the electrolyte membrane in Example 1. The back side of the electrolyte membrane refers to the surface of the modified skeleton membrane that is not coated with the slurry.

[0044] Figure 3 It is a scanning electron microscope image of the front side of the electrolyte membrane in Comparative Example 1.

[0045] Figure 4 It is a scanning electron microscope image of the back side of the electrolyte membrane in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] In order to better explain the technical solutions provided by the present application, before the embodiments, the technical solutions will be presented as a whole as follows:

[0047] The existing electrolyte membrane has a high short - circuit rate. The inventor believes that this problem is due to the poor affinity between the skeleton membrane and the sulfide electrolyte, resulting in poor infiltration of the electrolyte slurry and poor uniformity of the electrolyte membrane, directly increasing the short - circuit probability of the battery.

[0048] To solve the above - mentioned technical problems, the present application provides a method for preparing an electrolyte membrane, including:

[0049] Mix liquid succinonitrile with a lithium salt to obtain a lithium salt solution;

[0050] Add the lithium salt solution to the skeleton membrane to obtain a modified skeleton membrane; wherein, the skeleton membrane is a polymer - type porous material;

[0051] Mix a sulfide electrolyte, a binder, and a solvent to obtain a slurry, and add the slurry to the modified skeleton membrane. After drying, an electrolyte membrane is obtained.

[0052] The method of the present application can improve the affinity between the framework membrane and the sulfide electrolyte by treating the framework membrane with a lithium salt solution, solve the problem of poor affinity between the framework membrane and the sulfide electrolyte, improve the uniformity of the electrolyte membrane, and reduce the short-circuit probability of the battery. Specifically, the addition of the lithium salt is conducive to promoting the transfer of lithium ions between the positive and negative electrodes, thereby improving the performance of the battery; succinonitrile has good affinity with the framework membrane, and succinonitrile can also interact with the slurry when coating the slurry. That is to say, succinonitrile plays a connecting role between the framework membrane and the slurry, making the slurry have good wettability with the framework membrane.

[0053] According to the embodiments of the present application, the preparation method satisfies at least one of the following conditions:

[0054] (1) The lithium salt includes at least one of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), LiODFB (lithium difluorooxalate borate), LiPF2, and LiPF6; the lithium ions in the lithium salt can be complexed and dissociated with succinonitrile to achieve the transfer of lithium ions between the positive and negative electrodes. If the lithium salt is not added, succinonitrile is likely to complex some lithium ions, resulting in the loss of active lithium and affecting the structure of the sulfide electrolyte itself and the capacity of the active material.

[0055] (2) The concentration of the lithium salt solution is 0.5 - 2 mol / L; for example, the concentration of the lithium salt solution can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L. When the concentration of the lithium salt solution is within the above range, it is conducive to improving the affinity between the framework membrane and the sulfide electrolyte. If the concentration of the lithium salt solution is not within the above range, the performance of the electrolyte membrane will be poor. For example, if the content of succinonitrile is too high, succinonitrile is polar when in a liquid state, and excessive succinonitrile will react with P 5+ in the sulfide electrolyte, and in severe cases, it will cause the structure of the sulfide electrolyte to be damaged, thereby affecting the ion transport ability.

[0056] (3) The lithium salt solution is prepared by the following method: mixing succinonitrile and the lithium salt and heating at a temperature of 50 - 70 °C to obtain the lithium salt solution. For example, the heating temperature can be 50 °C, 55 °C, 60 °C, 65 °C, 70 °C. Since succinonitrile is solid at room temperature, it can be melted at the above temperature, and then the lithium salt can be completely dissolved and evenly dispersed to obtain the lithium salt solution.

[0057] According to the embodiments of the present application, the ratio of the mass of the lithium salt solution in the modified framework membrane to the mass of the modified framework membrane is (5x10 -4 ~2x10 -3 ):1. For example, the ratio of the mass of the lithium salt solution in the modified framework membrane to the mass of the modified framework membrane can be 5x10-4 : 1. 8x10 -4 : 1. 1x10 -3 : 1. 1.2x10 -3 : 1. 1.5x10 -3 : 1. 2x10 -3 : 1. At the above contents, the wettability between the skeleton film and the slurry can be effectively improved, and the short - circuit rate of the battery can be reduced. If the content of the lithium salt solution in the modified skeleton film is too small, the improvement in the wettability between the skeleton film and the slurry will be relatively small. If the content of the lithium salt solution in the modified skeleton film is too large, excessive succinonitrile will react with the sulfide electrolyte, affecting the ionic conductivity of the sulfide electrolyte, and thus leading to a reduction in battery performance.

[0058] Furthermore, the modified skeleton film includes a skeleton film and a lithium salt solution loaded on the skeleton film, and the lithium salt solution is uniformly dispersed in the skeleton film.

[0059] Furthermore, the content of the lithium salt solution in the modified skeleton film is tested by a gas chromatography - mass spectrometry (GC - MS).

[0060] According to an embodiment of the present application, the modified skeleton film is prepared by any one of the following methods:

[0061] Place the skeleton film and the lithium salt solution in a vacuum environment, raise the temperature to make the lithium salt solution exist in the form of vapor, load the lithium salt solution on the skeleton film, and cool to room temperature to obtain the modified skeleton film; furthermore, in this method, the temperature is greater than or equal to the boiling point of the lithium salt solution. By controlling the dosage of the lithium salt solution and the contact time between the lithium salt solution and the skeleton film, the content of the lithium salt solution in the modified skeleton film can be controlled until the content of the lithium salt solution in the modified skeleton film meets the usage requirements.

[0062] Alternatively, add the lithium salt solution to the skeleton film by means of spraying or dropping or soaking or coating, and the process of spraying or dropping or soaking or coating is carried out in an environment of 50 - 70 °C, load the lithium salt solution on the skeleton film, and cool to room temperature to obtain the modified skeleton film. In this method, by controlling the spraying amount and the contact time between the lithium salt solution and the skeleton film, the content of the lithium salt solution in the modified skeleton film can be controlled until the content of the lithium salt solution in the modified skeleton film meets the usage requirements.

[0063] Furthermore, after the loading amount meets the requirements, place the treated material at room temperature for 5 - 10 min (such as 5 min, 6 min, 7 min, 8 min, 9 min, 10 min), and then the modified skeleton film can be obtained.

[0064] According to an embodiment of the present application, the skeleton film satisfies at least one of the following conditions:

[0065] A. The skeletal membrane includes polycarbonate, polyethylene terephthalate, polyamide, polypropylene, polyethylene, or a composite of polypropylene and polyethylene; the skeletal membranes made of the above materials have good mechanical properties. At the same time, the skeletal membranes made of the above materials have good affinity with butanedinitrile, which is beneficial to improving the problem of poor affinity between the skeletal membrane and the slurry. For example, there are a large number of oxygen-containing functional groups on the surface of polyamide, so polyamide has good affinity with butanedinitrile.

[0066] B. The thickness of the skeletal membrane is 5 - 10 μm; for example, the thickness of the skeletal membrane can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm. When the thickness of the skeletal membrane is within the above range, the skeletal membrane can have excellent mechanical properties; if the thickness of the skeletal membrane is too large, it cannot significantly increase the mechanical properties of the skeletal membrane and will increase the thickness of the electrolyte membrane, resulting in a low energy density of the battery; if the thickness of the skeletal membrane is too small, its mechanical properties are poor, affecting the service life of the battery.

[0067] C. The porosity of the skeletal membrane is 70 - 92%; for example, the porosity of the skeletal membrane can be 70%, 75%, 80%, 85%, 90%, 92%.

[0068] According to the embodiments of the present application, the preparation method satisfies at least one of the following conditions:

[0069] a. The sulfide electrolyte includes any one of Li6PS5Cl, Li3PS4, and Li2S - P2S5;

[0070] b. The binder includes at least one of SBR (styrene - butadiene rubber), NBR (nitrile - butadiene rubber), PVDF (polyvinylidene fluoride), PVDF - HFP (poly(vinylidene fluoride - co - hexafluoropropylene)), SBS (styrene - butadiene - styrene block copolymer), SEBS (hydrogenated styrene - butadiene block copolymer), and SEPS (hydrogenated styrene - isoprene - styrene block copolymer);

[0071] c. The solvent includes at least one of n - heptane, methyl vinyl ketone, n - hexane, anisole, cyclopentyl methyl ether, butyl butyrate, xylene, and toluene; at the coating temperature, butanedinitrile in the modified skeletal membrane has a certain fluidity, and the above solvents have similar polarity to butanedinitrile. Therefore, the slurry and butanedinitrile show a tendency of similar - phase solubility. Using the above solvents is beneficial to enhancing the infiltration of the slurry on the modified skeletal membrane, achieving the uniformity of the electrolyte membrane, and further reducing the short - circuit rate.

[0072] d. The mass ratio of the sulfide electrolyte to the binder is (90 - 99):(1 - 10); for example, the mass ratio of the sulfide electrolyte to the binder can be 90:10, 95:5, 98:2, 99:1.

[0073] e. The solid content of the slurry is 50 - 65 wt%; for example, the solid content of the slurry can be 50 wt%, 55 wt%, 60 wt%, 62 wt%, 65 wt%.

[0074] According to the embodiments of the present application, after the sulfide electrolyte, the binder and the solvent are mixed, the slurry can be obtained by mixing the slurry at a rotation speed of 800 - 1200 rpm (for example, it can be 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm) for 20 - 40 min (20 min, 30 min, 40 min); further, the mixing of the slurry can be carried out in a high - speed homogenizer.

[0075] f. The method of adding the slurry to the skeleton film includes coating, and the coating is carried out at a temperature of 40 - 50 °C; for example, the coating can be carried out at a temperature of 40 °C, 45 °C or 50 °C.

[0076] Further, a coating device is used to coat the slurry on the modified skeleton film, and the coating device can be flat coating, transfer coating, extrusion spraying or gravure coating.

[0077] g. The wet thickness of the coating is 15 - 30 μm; for example, the wet thickness of the coating can be 15 μm, 20 μm, 25 μm, 30 μm; the wet thickness of the coating will affect the thickness of the final electrolyte membrane. When the wet thickness of the coating is within the above range, the battery can have excellent electrical properties and excellent mechanical properties at the same time. If the wet thickness of the coating is too small, it is easy to cause a large porosity of the electrolyte membrane, which is easy to grow dendrites, and then the battery is prone to short - circuit problems; if the wet thickness of the coating is too large, the thickness of the final electrolyte membrane is too large, resulting in a low energy density of the battery.

[0078] h. The drying temperature is 35 - 45 °C; for example, the drying temperature can be 35 °C, 40 °C, 45 °C.

[0079] i. The drying time is 23 - 25 h; for example, the drying time can be 23 h, 24 h, 25 h;

[0080] j. After the drying, the preparation method further includes a pressing step, and the pressing pressure is 280 - 320 MPa; for example, the pressing pressure can be 280 MPa, 300 MPa, 320 MPa.

[0081] k. The pressing time is 1.8 to 2.2 min. For example, the pressing time can be 1.8 min, 2 min, or 2.2 min.

[0082] According to an embodiment of the present application, the thickness of the electrolyte membrane is less than or equal to 20 μm, preferably less than or equal to 19 μm, more preferably 15 to 19 μm, and even more preferably 18 to 19 μm. The electrolyte membrane of the present application has a small thickness, which is beneficial to improving the energy density of the battery.

[0083] The present application also provides an electrolyte membrane, which is prepared by the preparation method of the electrolyte membrane described above. Thus, this electrolyte membrane has the same structure as the electrolyte membrane prepared by the method described above, so this electrolyte membrane has a low battery short-circuit rate.

[0084] The present application also provides a all-solid-state battery, which includes the electrolyte membrane described above. Thus, this battery has a low battery short-circuit rate.

[0085] Further, the all-solid-state battery further includes a positive electrode and a negative electrode, and the electrolyte membrane is located between the positive electrode and the negative electrode.

[0086] The present application also provides an electrical device, which includes the all-solid-state battery described above. Thus, this electrical device has a low battery short-circuit rate.

[0087] The following will describe the implementation scheme of the present application in detail with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0088] Example 1

[0089] Modification treatment of the skeleton membrane:

[0090] (1) Prepare a lithium salt solution: Weigh succinonitrile and a lithium salt in a certain proportion, and then heat-treat them at 55 °C to completely dissolve and disperse them evenly to obtain a lithium salt solution. The concentration of the lithium salt in succinonitrile is 1 mol / L, and the lithium salt is LiTFSI.

[0091] (2) Modification treatment: When the operating environment temperature is 60 °C, spray the prepared lithium salt solution onto the skeleton membrane (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, and a grammage of 3 g / m 2, the MD tensile strength is 0.8 N / 15 mm, and the CD tensile strength is 0.3 N / 15 mm), so that the ratio of the mass of the lithium salt solution in the modified skeleton film to the mass of the modified skeleton film is 1×10 -3 :1, thus obtaining the modified skeleton film.

[0092] Preparation of the electrolyte membrane:

[0093] Weigh the sulfide electrolyte, binder and solvent in a certain proportion, then mix the slurry at a speed of 1000 rpm for 30 min in a high-speed homogenizer to obtain the slurry. Then, coat the slurry on the modified skeleton film with a gravure coater at 45 °C. Among them, the modified skeleton film is placed on the base film, and the base film is aluminum foil. The wet thickness of the coating is 30 μm. Subsequently, dry it at 40 °C for 24 h, and after drying, press it at a pressure of 300 MPa for 2 min. After pressing, remove the base film to obtain the electrolyte membrane. Among them, the sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0094] From Figure 1 and Figure 2 it can be seen that there is electrolyte on both the front and the back of the electrolyte membrane, indicating that after the skeleton film is modified, the slurry can wet the modified skeleton film well, enabling the electrolyte to migrate to the surface of the uncoated side of the modified skeleton film, thereby forming a uniform electrolyte membrane on the front and back of the modified skeleton film.

[0095] Example 2

[0096] Modification treatment of the skeleton film:

[0097] (1) Prepare the lithium salt solution: Weigh succinonitrile and the lithium salt in a certain proportion, then heat-treat it at 55 °C to completely dissolve and disperse it evenly to obtain the lithium salt solution. Among them, the concentration of the lithium salt in succinonitrile is 1 mol / L. The lithium salt is LiTFSI.

[0098] (2) Modification treatment: When the operating environment temperature is 60 °C, spray the prepared lithium salt solution on the skeleton film (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, and a grammage of 3 g / m 2 , the MD tensile strength is 0.8 N / 15 mm, and the CD tensile strength is 0.3 N / 15 mm), so that the ratio of the mass of the lithium salt solution in the modified skeleton film to the mass of the modified skeleton film is 5×10 -4 :1, thus obtaining the modified skeleton film.

[0099] Preparation of the electrolyte membrane:

[0100] Weigh the sulfide electrolyte, binder, and solvent in a certain proportion, then mix the slurry at a speed of 1000 rpm in a high-speed homogenizer for 30 min to obtain the slurry. Then, coat the slurry on the modified skeleton membrane with a gravure coater at 45 °C. Among them, the modified skeleton membrane is placed on the base film, and the base film is aluminum foil. The wet coating thickness is 30 μm. Subsequently, dry it at 40 °C for 24 h. After drying, press it at a pressure of 300 MPa for 2 min. After pressing, remove the base film to obtain the electrolyte membrane. The sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0101] Example 3

[0102] Modification treatment of the skeleton membrane:

[0103] (1) Prepare the lithium salt solution: Weigh succinonitrile and the lithium salt in a certain proportion, then heat-treat it at 55 °C to completely dissolve and disperse it evenly to obtain the lithium salt solution. The concentration of the lithium salt in succinonitrile is 1 mol / L. The lithium salt is LiTFSI.

[0104] (2) Modification treatment: When the operating environment temperature is 60 °C, spray the prepared lithium salt solution on the skeleton membrane (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, a grammage of 3 g / m 2 , the MD tensile strength is 0.8 N / 15 mm, and the CD tensile strength is 0.3 N / 15 mm) in a spraying form, so that the mass ratio of the lithium salt solution in the modified skeleton membrane to the mass of the modified skeleton membrane is 2×10 -3 :1, that is, the modified skeleton membrane is obtained.

[0105] Preparation of the electrolyte membrane:

[0106] Weigh the sulfide electrolyte, binder, and solvent in a certain proportion, then mix the slurry at a speed of 1000 rpm in a high-speed homogenizer for 30 min to obtain the slurry. Then, coat the slurry on the modified skeleton membrane with a gravure coater at 45 °C. Among them, the modified skeleton membrane is placed on the base film, and the base film is aluminum foil. The wet coating thickness is 30 μm. Subsequently, dry it at 40 °C for 24 h. After drying, press it at a pressure of 300 MPa for 2 min. After pressing, remove the base film to obtain the electrolyte membrane. The sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0107] Example 4

[0108] Modification treatment of the skeleton membrane:

[0109] (1) Prepare the lithium salt solution: Weigh succinonitrile and the lithium salt in a certain proportion, and then heat-treat them at 55 °C to completely dissolve and disperse them evenly, obtaining the lithium salt solution. The concentration of the lithium salt in succinonitrile is 1 mol / L, and the lithium salt is LiTFSI.

[0110] (2) Modification treatment: When the operating environment temperature is 60 °C, spray the prepared lithium salt solution onto the skeleton membrane (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, a grammage of 3 g / m 2 , MD tensile strength of 0.8 N / 15 mm, CD tensile strength of 0.3 N / 15 mm) in the form of spraying, so that the ratio of the mass of the lithium salt solution in the modified skeleton membrane to the mass of the modified skeleton membrane is 1x10 -3 :1, that is, the modified skeleton membrane is obtained.

[0111] Preparation of the electrolyte membrane:

[0112] Weigh the sulfide electrolyte, binder and solvent in a certain proportion, and then mix the slurry in a high-speed homogenizer at a speed of 1000 rpm for 30 min to obtain the slurry. Then, coat the slurry on the modified skeleton membrane with a gravure coater in an environment of 45 °C. Among them, the modified skeleton membrane is placed on the base film, and the base film is aluminum foil. The wet coating thickness is 25 μm. Subsequently, dry it at a temperature of 40 °C for 24 h. After drying, press it at a pressure of 300 MPa for 2 min. After pressing, remove the base film to obtain the electrolyte membrane. Among them, the sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0113] Example 5

[0114] Refer to the method of Example 1 to prepare the modified skeleton membrane, and use the modified skeleton membrane to prepare the electrolyte membrane. Other parameters are the same as those in Example 1, except that: the material of the skeleton membrane in Example 5 is polyamide, with a thickness of 9 μm, a porosity of 74.5%, a grammage of 3.07 g / m 2 , MD tensile strength of 0.6 N / 15 mm, CD tensile strength of 0.4 N / 15 mm.

[0115] Example 6

[0116] Refer to the method of Example 1 to prepare the modified skeleton membrane, and use the modified skeleton membrane to prepare the electrolyte membrane. Other parameters are the same as those in Example 1, except that: the sulfide electrolyte in Example 6 is Li3PS4.

[0117] Example 7

[0118] Prepare the modified framework membrane according to the method of Example 1, and prepare the electrolyte membrane using the modified framework membrane. Other parameters are the same as those in Example 1, except that: the lithium salt in Example 7 is LiFSI.

[0119] Comparative Example 1

[0120] The framework membrane used in Comparative Example 1 was not modified.

[0121] Preparation of the electrolyte membrane:

[0122] Weigh the sulfide electrolyte, binder and solvent in a certain proportion, then mix the slurry at a speed of 1000 rpm in a high-speed homogenizer for 30 min to obtain a slurry, and then coat the slurry on the framework membrane (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, and a grammage of 3 g / m 2 , the MD tensile strength is 0.8 N / 15 mm, and the CD tensile strength is 0.3 N / 15 mm) with a gravure coater at 45 °C. The framework membrane is placed on the base film, and the base film is aluminum foil. The wet coating thickness is 100 μm. Subsequently, it is dried at 40 °C for 24 h, and after drying, it is pressed at a pressure of 300 MPa for 2 min. After pressing, the base film is peeled off to obtain the electrolyte membrane. Among them, the sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0123] From Figure 3 and Figure 4 it can be seen that there is electrolyte on the front side of the electrolyte membrane, and part of the framework membrane is exposed on the back side of the electrolyte membrane, indicating that the slurry fails to fully infiltrate the framework membrane, and the uniformity of the electrolyte membrane is poor. The position where part of the framework membrane is exposed cannot transfer lithium ions, which will directly lose part of the active lithium and is also prone to forming lithium dendrites, ultimately leading to battery short circuit.

[0124] Comparative Example 2

[0125] The framework membrane used in Comparative Example 2 was not modified.

[0126] Preparation of the electrolyte membrane:

[0127] Weigh the sulfide electrolyte, binder and solvent in a certain proportion, then mix the slurry at a speed of 1000 rpm in a high-speed homogenizer for 30 min to obtain a slurry, and then coat the slurry on the framework membrane (made of polycarbonate, with a thickness of 8 μm, a porosity of 71.5%, and a grammage of 3 g / m 2, the MD tensile strength is 0.8 N / 15 mm and the CD tensile strength is 0.3 N / 15 mm). Among them, the skeleton film is placed on the base film, the base film is aluminum foil, the wet coating thickness is 30 μm, and then it is dried at a temperature of 40 °C for 24 h. After drying, it is pressed at a pressure of 300 MPa for 2 min. After pressing, the base film is peeled off to obtain the electrolyte membrane. Among them, the sulfide electrolyte is Li6PS5Cl, the binder is PVDF-HFP, the mass ratio of Li6PS5Cl to PVDF-HFP is 98:2, the solvent is butyl butyrate, and the solid content of the slurry is 62 wt%.

[0128] Comparative Example 3

[0129] The skeleton film used in Comparative Example 3 was not modified.

[0130] Refer to the method of Comparative Example 1 to prepare the electrolyte membrane. Other parameters are the same as those in Comparative Example 1, except that: the skeleton film material in Comparative Example 3 is polyamide, the thickness is 9 μm, the porosity is 74.5%, and the grammage is 3.07 g / m 2 , the MD tensile strength is 0.6 N / 15 mm and the CD tensile strength is 0.4 N / 15 mm.

[0131] Comparative Example 4

[0132] The skeleton film used in Comparative Example 4 was not modified.

[0133] Refer to the method of Comparative Example 2 to prepare the electrolyte membrane. Other parameters are the same as those in Comparative Example 2, except that: the skeleton film material in Comparative Example 4 is polyamide, the thickness is 9 μm, the porosity is 74.5%, and the grammage is 3.07 g / m 2 , the MD tensile strength is 0.6 N / 15 mm and the CD tensile strength is 0.4 N / 15 mm.

[0134] Perform performance tests on the electrolyte membranes of Examples 1-7 and Comparative Examples 1-4. For the reliability of the data, 3 parallel experimental groups are set for the tests of each example or comparative example, and the test results are shown in Tables 1 and 2.

[0135] The thickness of the electrolyte membrane is measured using a CHY-CA thickness gauge.

[0136] The ionic conductivity is calculated by the following formula: б = L / (RS). Where L is the thickness of the electrolyte membrane, R is the resistance of the electrolyte membrane, obtained by EIS; S is the cross-sectional area of the test sample.

[0137] The porosity is calculated by the following formula:

[0138] The porosity ρ = 1 - bulk density ÷ true density.

[0139] Among them, the total volume at this ratio is calculated through the mass and true density of each component of the electrolyte membrane. The true density of this component ratio is obtained by dividing the total mass by the total volume. The compaction density is obtained by dividing the mass of the electrolyte membrane by the volume of the electrolyte membrane (the product of the area of the electrolyte membrane and the thickness of the electrolyte membrane).

[0140] Evaluation of electrical properties: The obtained electrolyte membrane is cut into a rectangle of 4 cm * 6 cm, and a single-piece soft package is assembled by matching a negative electrode plate of 4 cm * 6 cm and a positive electrode plate of 3.8 cm * 5.8 cm. The pressing pressure of the soft package is 500 Mpa. The assembled soft package is subjected to a charge-discharge test at 0.1 C at 45 °C, and the voltage range is 2 - 4.2 V.

[0141] Table 1 Relevant parameter table of electrolyte membranes in Examples 1 - 7 and Comparative Examples 1 - 4

[0142]

[0143]

[0144] As can be seen from Table 1, compared with Comparative Examples 1 - 4, the electrolyte membranes in Examples 1 - 7 have simultaneously smaller thickness, smaller porosity, and higher ionic conductivity, indicating that the comprehensive performance of the electrolyte membranes in Examples 1 - 7 is superior to that of the electrolyte membranes in Comparative Examples 1 - 4. Specifically, during the preparation of the electrolyte membrane, the wet thickness of the slurry coating in Example 2 and Comparative Example 2 is the same, both being 30 μm. As can be seen from Table 1, in the finally formed electrolyte membrane, the thickness of the electrolyte membrane in Example 2 is smaller than that of the electrolyte membrane in Comparative Example 2, and the porosity of the electrolyte membrane in Example 2 is smaller than that of the electrolyte membrane in Comparative Example 2. That is to say, after the skeleton membrane is modified, the uniformity of the electrolyte membrane can be significantly improved from the thickness of the electrolyte membrane. Due to the good wettability of the slurry and the modified skeleton membrane, a denser electrolyte membrane will be obtained. In addition, during the preparation of the electrolyte membrane, the wet thickness of the slurry coating in Example 2, Example 1, and Example 3 is the same, and the content of the lithium salt solution in the modified skeleton membrane gradually increases (500 ppm, 1000 ppm, 2000 ppm respectively). The ionic conductivities of the electrolyte membranes in Example 2, Example 1, and Example 3 gradually decrease. That is to say, the content of the lithium salt solution in the modified skeleton membrane will affect the ionic conductivity of the electrolyte membrane, but the ionic conductivities of the above examples are sufficient to support the 1C charge-discharge of the battery. During the preparation of the electrolyte membrane, the content of the lithium salt solution in the modified skeleton membranes of Example 1 and Example 4 is the same, and the wet thickness of the slurry coating decreases (30 μm and 25 μm respectively), and the porosity of the electrolyte membrane significantly increases, indicating that the wet thickness of the slurry coating will affect the porosity of the electrolyte membrane.

[0145] Table 2 Application of electrolyte membranes in Examples 1 - 7 and Comparative Examples 1 - 4 to soft packages

[0146]

[0147]

[0148] As can be seen from Table 2, the OCVs of Examples 1-7 are all within the normal range, indicating that no short circuits occurred in the soft packs assembled with the electrolyte membranes of Examples 1-7. No short circuit problems occurred during the cycle tests of Examples 1-3 and Examples 5-7. This is mainly because the skeleton membrane was modified to improve the wettability of the slurry on the skeleton membrane, enabling good contact between the electrolyte and the skeleton membrane, and finally obtaining an electrolyte membrane with good uniformity and low porosity. In the three parallel experiments of Example 4, a short circuit occurred during one cycle. This is mainly because the thickness of the electrolyte membrane in Example 4 is about 15 μm. The lower the thickness of the electrolyte membrane, the fewer the number of stacked particles, resulting in a relatively large porosity of the electrolyte membrane. During the charge and discharge process, dendrites are likely to grow in the pores, thus causing a short circuit phenomenon during the cycle. The OCVs of Comparative Example 2 and Comparative Example 4 are 0, indicating that short circuits occurred after the soft packs were assembled with the electrolyte membranes of Comparative Example 2 and Comparative Example 4. This is mainly because the affinity between the skeleton membrane and the slurry is poor when the skeleton membrane is not modified, resulting in an extremely uneven electrolyte membrane, large porosity, and easy dendrite growth. The skeleton membranes of Comparative Example 1 and Comparative Example 2 were not modified. Compared with Comparative Example 2, the thickness of the electrolyte membrane in Comparative Example 1 increased. The soft pack assembled in Comparative Example 1 did not short circuit, but due to the poor affinity between the skeleton membrane and the slurry, a large number of pores were formed in the electrolyte membrane, and dendrites were generated during the charge and discharge process, thus causing a short circuit problem during the cycle.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing an electrolyte membrane, characterized in that: include: mixing liquid succinonitrile with a lithium salt to obtain a lithium salt solution; Adding the lithium salt solution to a skeleton membrane to obtain a modified skeleton membrane; wherein the skeleton membrane is a polymer porous material; Mixing a sulfide electrolyte, a binder and a solvent to obtain a slurry, adding the slurry to the modified skeleton membrane, and drying to obtain an electrolyte membrane; Wherein, the concentration of the lithium salt solution is 0.5~2 mol / L; The modified skeleton membrane is prepared by any one of the following methods: placing the skeleton membrane and the lithium salt solution in a vacuum environment, raising the temperature so that the lithium salt solution exists in the form of steam, allowing the lithium salt solution to be loaded on the skeleton membrane, and cooling to room temperature to obtain the modified skeleton membrane; Alternatively, the lithium salt solution is added to the skeleton membrane by spraying, dripping, soaking or coating, and the spraying, dripping, soaking or coating process is carried out in an environment of 50-70° C., so that the lithium salt solution is loaded on the skeleton membrane, and cooled to room temperature to obtain the modified skeleton membrane; The method of adding the slurry to the skeleton membrane includes coating, and the coating is performed at a temperature of 40-50°C.

2. The method for preparing an electrolyte membrane according to claim 1, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The lithium salt includes at least one of LiTFSI, LiFSI, LiODFB, LiPF2 and LiPF6; (2) The lithium salt solution is prepared by the following method: succinonitrile and lithium salt are mixed, and heated at a temperature of 50 to 70° C. to obtain a lithium salt solution.

3. The method for preparing an electrolyte membrane according to claim 2, characterized in that: The ratio of the mass of the lithium salt solution in the modified skeleton membrane to the mass of the modified skeleton membrane is (5x10 -4 ~2x10 -3 ):

1.

4. The method for preparing an electrolyte membrane according to claim 1, characterized in that: The skeleton membrane satisfies at least one of the following conditions: A. The skeleton membrane comprises polycarbonate, polyethylene terephthalate, polyamide, polypropylene, polyethylene or a composite of polypropylene and polyethylene; B. The thickness of the skeleton membrane is 5-10 μm; C. The porosity of the skeleton membrane is 70-92%.

5. The method for preparing an electrolyte membrane according to claim 4, characterized in that: The preparation method satisfies at least one of the following conditions: a. The sulfide electrolyte includes any one of Li6PS5Cl, Li3PS4, and Li2S-P2S5; b. The binder includes at least one of SBR, NBR, PVDF, PVDF-HFP, SBS, SEBS, and SEPS; c. The solvent comprises at least one of n-heptane, methyl vinyl ketone, n-hexane, anisole, cyclopentyl methyl ether, butyl butyrate, xylene and toluene; d. The mass ratio of the sulfide electrolyte to the binder is (90-99): (1-10); e. The solid content of the slurry is 50~65wt%; g. The wet thickness of the coating is 15 to 30 μm; h. The drying temperature is 35 to 45 ° C; i. The drying time is 23 to 25 hours; j. After the drying, the preparation method further comprises a pressing step, wherein the pressing pressure is 280 to 320 MPa; k. The pressing time is 1.8 to 2.2 minutes.

6. The method for preparing an electrolyte membrane according to any one of claims 1 to 5, characterized in that: The thickness of the electrolyte membrane is less than or equal to 20 μm.

7. An electrolyte membrane, characterized in that: The electrolyte membrane is prepared by the method for preparing the electrolyte membrane according to any one of claims 1 to 6.

8. An all-solid-state battery, characterized in that: The all-solid-state battery comprises the electrolyte membrane according to claim 7.

9. An electrical device, characterized in that: The electrical equipment includes the all-solid-state battery according to claim 8.

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