A separator, an electrode assembly, a power battery, and a vehicle

Abstract

The utility model provides a diaphragm for setting between positive pole piece and negative pole piece, include: base film and set up in the gel solid electrolyte layer of at least one surface of base film, the thickness of base film <5um. The utility model also provides an electrode assembly, a power battery and a vehicle. The diaphragm provided by the utility model takes <5um base film as a carrier, sets up the gel solid electrolyte layer through its surface, avoids positive pole and negative pole short circuit, solves the problem of diaphragm puncture caused by the decrease of base film mechanical strength, improves the yield of battery cell, and expands the application field of thickness <5um base film.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a separator, electrode assembly, power battery and vehicle. Background Technology

[0002] The separator is a key component of lithium-ion batteries, and it is one of the four main materials used in lithium-ion batteries. Under normal use, the separator separates the positive and negative electrodes of the lithium-ion battery, preventing them from coming into direct contact and thus avoiding short circuits during battery use.

[0003] Currently, the base film in separators is mainly ≥5μm thick, such as 5μm, 7μm, and 9μm. To improve the electrochemical performance of lithium-ion batteries, researchers have attempted to further reduce the thickness of the base film. However, further reduction in the thickness of the base film leads to a significant decrease in the mechanical strength of the separator, and problems such as hit-pot defects easily occur during the trial production process, thus hindering the application of base films with a thickness of less than 5μm. To broaden the application of 5μm base films and improve the mechanical properties of separators, researchers mainly improve the mechanical strength of separators by increasing the molecular weight of PE, adjusting the roller speed ratio, and reducing the porosity of the separator. However, these methods are currently immature and costly. Utility Model Content

[0004] The technical problem solved by this utility model is to provide a separator. The separator provided by this application can introduce a base film with a thickness of <5μm and improve the problem of low cell yield caused by the reduction of separator thickness.

[0005] In view of this, this application provides a separator for being disposed between a positive electrode and a negative electrode, comprising: a base film (1) and a gel solid electrolyte layer (2) disposed on at least one surface of the base film (1); the thickness of the base film (1) is <5 μm.

[0006] In some specific embodiments, the diaphragm further includes an adhesive layer (3) disposed on the surface of the gel solid electrolyte layer (2), or the adhesive layer (3) disposed on the surface of the base membrane (1).

[0007] In some specific embodiments, the thickness of the gel solid electrolyte layer (2) is 0.5 to 5 μm, and / or the thickness of the base film (1) is 1 to 4 μm.

[0008] In some specific embodiments, the thickness of the adhesive layer (3) is 0 to 10 μm and is not equal to 0.

[0009] In some specific embodiments, the puncture strength of the base membrane (1) is ≤300gf, and the tensile strength is ≤2000kgf / cm. 2 .

[0010] In some specific embodiments, the gel solid electrolyte layer (2) is obtained by curing a polymer monomer layer; the polymer monomer in the polymer monomer layer includes two or more of methyl methacrylate, acrylonitrile, methoxy polyethylene glycol methacrylate, 2-bromoethyl acrylate, hydroxypropyl acrylate and isostearyl acrylate.

[0011] In some specific embodiments, the thickness of the diaphragm is 1.5–15 μm.

[0012] This application also provides an electrode assembly, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator described in the above-mentioned embodiment.

[0013] This application also provides a power battery, including the electrode assembly described above.

[0014] This application also provides a vehicle including the power battery described above.

[0015] This application provides a separator comprising a base membrane and a gel solid electrolyte layer disposed on at least one surface of the base membrane, wherein the thickness of the base membrane is <5μm. The separator provided in this application avoids short circuits between the positive and negative electrodes by providing a gel solid electrolyte layer. At the same time, this application can use a base membrane with a thickness of <5μm. Since the gel solid electrolyte layer is disposed on the surface of the base membrane, it solves the problem of separator puncture caused by the decrease in mechanical strength due to the reduction in base membrane thickness, improves the yield of separators with reduced base membrane thickness, and broadens the application range of base membranes with a thickness of less than 5μm. Attached Figure Description

[0016] Figure 1 Schematic diagram of the diaphragm provided by this utility model Figure 1 ;

[0017] Figure 2 Schematic diagram of the diaphragm provided by this utility model Figure 2 ;

[0018] Figure 3 Schematic diagram of the diaphragm provided by this utility model Figure 3 ;

[0019] Figure 4 Schematic diagram of the diaphragm provided by this utility model Figure 4 ;

[0020] Figure 5 This is a schematic diagram of the diaphragm provided in Embodiment 1 of this utility model;

[0021] Figure 6 This is a schematic diagram of the diaphragm provided in Embodiment 2 of this utility model. Detailed Implementation

[0022] To further understand this utility model, preferred embodiments of this utility model are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this utility model, and not for limiting the scope of the claims of this utility model.

[0023] In view of the need to reduce the thickness of the separator base film and improve the yield of the battery cell in the prior art, this application provides a separator that improves the yield of the battery cell while reducing the thickness of the base film 1 by setting a gel solid electrolyte layer 2 on at least one surface of the base film 1, and further ensures the electrochemical performance of the battery. Specifically, this utility model discloses a separator for being disposed between the positive electrode and the negative electrode, comprising: a base film 1 and a gel solid electrolyte layer 2 disposed on at least one surface of the base film 1; the thickness of the base film 1 is <5μm.

[0024] In some specific embodiments, the separator consists of a base membrane 1 and a gel solid electrolyte layer 2 disposed on one surface of the base membrane 1, such as... Figure 1 As shown; in some specific embodiments, the diaphragm consists of a base membrane 1, a first gel solid electrolyte layer 2-1 disposed on the surface of the base membrane 1, and a second gel solid electrolyte layer 2-2, as shown. Figure 2 As shown; in this application, the first gel solid electrolyte layer 2-1 and the second gel solid electrolyte layer 2-2 may be the same or different, and this application does not impose any special restrictions on this.

[0025] In some specific embodiments, the separator further includes an adhesive layer 3, which is disposed on the surface of the base membrane 1 or on the surface of the gel solid electrolyte layer 2; in some specific embodiments, the separator is composed of a base membrane 1, a gel solid electrolyte layer 2 disposed on one surface of the base membrane 1, and an adhesive layer 3 disposed on the other surface of the base membrane 2, such as... Figure 3 As shown; in some specific embodiments, the diaphragm consists of a base membrane 1, a gel solid electrolyte layer 2 disposed on one surface of the base membrane 1, and an adhesive layer 3 disposed on the surface of the gel solid electrolyte layer 2, such as... Figure 4 As shown; in some specific embodiments, the diaphragm consists of a base membrane 1, a gel solid electrolyte layer 2 disposed on one surface of the base membrane 1, a first adhesive layer 3-1 disposed on the other surface of the base membrane 1, and a second adhesive layer 3-2 disposed on the surface of the gel solid electrolyte layer 2, as shown. Figure 5As shown; in some specific embodiments, the diaphragm is composed of a base membrane 1, a first gel solid electrolyte layer 2-1 and a second gel solid electrolyte layer 2-2 disposed on the surface of the base membrane 1, a first adhesive layer 3-1 disposed on the surface of the first gel solid electrolyte layer 2-1, and a second adhesive layer 3-2 disposed on the surface of the second gel solid electrolyte layer 2-2, as shown. Figure 6 As shown; in this application, the first adhesive layer 3-1 and the second adhesive layer 3-1 may be the same or different, and this application does not impose any special restrictions on this.

[0026] In some specific embodiments, the thickness of the base film 1 is <5μm. Specifically, the thickness of the base film 1 is 1-4μm, for example, the thickness of the base film 1 is 1μm, 2μm, 3μm, or 4μm. The base film 1 is a base film well known to those skilled in the art; for example, the base film 1 can be a PE base film or a PP base film. In this application, the thickness of the base film 1 is <5μm, and the puncture strength of a base film of this thickness is ≤300gf, and the tensile strength is ≤2000kgf / cm. 2 .

[0027] This application does not impose any particular limitation on the preparation method of the gel solid electrolyte layer 2; it can be prepared according to methods well known to those skilled in the art. In some specific embodiments, the gel solid electrolyte layer 2 is obtained by high-temperature curing of a polymer monomer layer. The polymer monomers in the polymer monomer layer are polymer monomers capable of initiating in-situ reactions. Specifically, the polymer monomers in the polymer monomer layer include two or more of methyl methacrylate, acrylonitrile, methoxy polyethylene glycol methacrylate, 2-bromoethyl acrylate, hydroxypropyl acrylate, and isostearyl acrylate. In some specific embodiments, the polymer monomers are selected from a mixture of methyl methacrylate and hydroxypropyl acrylate or a mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate. Further, the specific preparation method of the gel solid electrolyte layer 2 is as follows:

[0028] The polymer monomer is dissolved in an organic solvent to obtain a casting solution;

[0029] The casting solution is prepared on the surface of the base membrane, and then subjected to the first stage coagulation bath and the second stage coagulation bath in sequence. After washing with water and drying, the initial diaphragm is obtained.

[0030] The initial separator was prepared into a battery cell, and after high-temperature curing, a gel solid electrolyte layer was obtained.

[0031] In the above-mentioned process of preparing the gel solid electrolyte layer, the polymer monomer in the casting solution has a mass fraction of 5-60 wt%, specifically, the polymer monomer in the casting solution has a mass fraction of 10-45 wt%; the slurry viscosity of the casting solution is 2000-8000 mPa, specifically, the slurry viscosity of the casting solution is 3000-6000 mPa.

[0032] The coagulation bath is mainly used for oil-based coatings, primarily for solvent exchange, promoting rapid solvent precipitation in the coating to form a uniform porous structure. It also controls the pore size and porosity of the coating. In the above preparation process, the first coagulation bath is for preliminary phase separation and solvent extraction, while the second coagulation bath is for fine-tuning the structure and complete extraction. In some specific embodiments, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 10–30% and a temperature of 10–40°C; the second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 5–20% and a temperature of 20–30°C. In other specific embodiments, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 15–20% and a temperature of 15–30°C; the second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 10–15% and a temperature of 23–27°C. After the above two-stage coagulation bath, the water washing time is 10-60 seconds, and the drying temperature is 30-60°C.

[0033] The above process forms an initial separator with a polymer monomer layer on its surface, which is then used to prepare a battery cell. High-temperature curing yields a gel solid electrolyte layer. During this process, under the initiation of the initiator in the electrolyte within the battery cell, the polymer monomers in the polymer monomer layer undergo in-situ polymerization, resulting in the gel solid electrolyte layer. The high-temperature curing temperature is 50–100°C, and the time is 3–10 hours; specifically, the high-temperature curing temperature is 60–80°C, and the time is 6–8 hours. The initiator can be any initiator known to those skilled in the art for initiating free radical polymer and copolymerization reactions of olefins and dienes. For example, the initiator may be selected from one or more of azobisisobutyronitrile, azobisisobutyronitrile, azobisisobutyronitrile, potassium persulfate, ammonium persulfate, lauroyl peroxide, benzoyl peroxide, and dodecyl peroxide. In some specific embodiments, the initiator is selected from azobisisobutyronitrile.

[0034] In some specific embodiments, the adhesive layer is prepared after drying, specifically as follows:

[0035] The adhesive material and water are mixed to obtain a mixed solution;

[0036] The mixed solution is prepared on the surface of the polymer monomer layer or base film and then dried.

[0037] In some specific embodiments, the thickness of the gel solid electrolyte layer 2 is 0.5 to 5 μm, specifically, the thickness of the gel solid electrolyte layer 2 is 1 to 4.5 μm.

[0038] For those skilled in the art, base films with a thickness <5μm have low strength, for example, puncture strength ≤300gf and tensile strength ≤2000kgf / cm. 2 Such a thin and low-strength base film would not be used in the actual battery cell manufacturing process in the prior art because the low mechanical strength would lead to a high hit-pot yield. However, this application has a gel solid electrolyte layer on the surface of the base film of this thickness. The base film only serves as a carrier. By introducing the gel solid electrolyte layer, the positive and negative electrodes are separated, thereby improving the yield of the base film with a thickness of <5μm in the finished battery cell.

[0039] In some specific embodiments, the thickness of the adhesive layer 3 is 0 to 10 μm and is not equal to 0. Specifically, the thickness of the adhesive layer 3 is 3 to 8 μm.

[0040] In some specific embodiments, the thickness of the diaphragm is 1.5 to 15 μm, and further, the thickness of the diaphragm is 3 to 10 μm.

[0041] This application also provides an electrode assembly, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator described in the above-described scheme.

[0042] In this application, the positive electrode is a positive electrode known to those skilled in the art, and the negative electrode is a negative electrode known to those skilled in the art. There are no particular limitations on the positive electrode and the negative electrode.

[0043] This application also provides a power battery including the aforementioned electrode assembly. For the power battery provided in this application, apart from the electrode assembly, the other components are well-known to those skilled in the art, and this application does not impose any special limitations on them. In some specific embodiments, the power battery is a lithium-ion battery.

[0044] This application also provides a vehicle including the aforementioned power battery; for the vehicle provided by this application, apart from the battery, other devices in the vehicle are devices well known to those skilled in the art, and this application does not impose any special restrictions on them, that is, in some specific embodiments, the battery of the vehicle is the aforementioned power battery.

[0045] To further understand this utility model, the diaphragm provided by this utility model will be described in detail below with reference to the embodiments. The scope of protection of this utility model is not limited by the following embodiments.

[0046] Example 1

[0047] The structural schematic diagram of the diaphragm provided in this embodiment is as follows: Figure 5 As shown, specifically, the diaphragm consists of a base membrane 1, a gel solid electrolyte layer 2, a first adhesive layer 3-1, and a second adhesive layer 3-2. The gel solid electrolyte layer 2 is disposed on one surface of the base membrane 1, the first adhesive layer 3-1 is disposed on the other surface of the base membrane 1, and the second adhesive layer 3-2 is disposed on the surface of the gel solid electrolyte layer 2. The base membrane 1 is a 3μm PE base membrane, the gel solid electrolyte layer 2 is obtained by high-temperature curing of a mixture of methyl methacrylate and hydroxypropyl acrylate, and the materials of the first adhesive layer 3-1 and the second adhesive layer 3-2 are polyvinylidene fluoride.

[0048] The preparation method of the above-mentioned diaphragm specifically includes the following steps:

[0049] A mixture of methyl methacrylate and hydroxypropyl acrylate is dissolved in N,N-dimethylacetamide to obtain a casting solution; the mass fraction of the mixture of methyl methacrylate and hydroxypropyl acrylate in the casting solution is 30 wt%, and the slurry viscosity of the casting solution is 4800 mPas.

[0050] The casting solution was coated onto one side of a 3μm PE base film using a micro-grooving roller to form a polymer monomer layer. Then, the film underwent a first-stage coagulation bath and a second-stage coagulation bath sequentially. After washing with water for 60 seconds, it was dried in a drying oven at 60℃ and then wound up. The first-stage coagulation bath consisted of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30℃. The second-stage coagulation bath also consisted of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30℃.

[0051] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 60 minutes to fully dissolve the powder mixture and obtain a mixed solution, wherein the mass fraction of polyvinylidene fluoride in the mixed solution was 30 wt%. The mixed solution was then sprayed onto both sides of the semi-finished diaphragm and dried in an oven at 60°C for 30 minutes to obtain the initial diaphragm with a coating thickness of 5 μm.

[0052] The initial separator was prepared into a battery cell, and the battery cell was cured at 60°C for 6 hours to allow the polymer monomer layer to polymerize in situ into a gel electrolyte layer under the action of the electrolyte. The initiator contained in the electrolyte was azobisisoheptanenitrile.

[0053] Example 2

[0054] The structural schematic diagram of the diaphragm provided in this embodiment is as follows: Figure 6 As shown, specifically, the diaphragm consists of a base membrane 1, a first gel solid electrolyte layer 2-1, a second gel solid electrolyte layer 2-2, a first adhesive layer 3-1, and a second adhesive layer 3-2. The first gel solid electrolyte layer 2-1 is disposed on one surface of the base membrane 1, and the second gel solid electrolyte layer 2-2 is disposed on the other surface of the base membrane 1. The first adhesive layer 3-1 is disposed on the surface of the first gel solid electrolyte layer 2-1, and the second adhesive layer 3-2 is disposed on the surface of the second gel solid electrolyte layer 2-2. The base membrane 1 is a 4μm PE base membrane. The first gel solid electrolyte layer 2-1 and the second gel solid electrolyte layer 2-2 are both obtained by high-temperature curing of a mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate. The materials of the first adhesive layer 3-1 and the second adhesive layer 3-2 are both polyvinylidene fluoride.

[0055] The preparation method of the above-mentioned diaphragm specifically includes the following steps:

[0056] A mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate was dissolved in N,N-dimethylacetamide to obtain a casting solution; the mass fraction of the mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate in the casting solution was 30 wt%, and the slurry viscosity of the casting solution was 4000 mPas.

[0057] The casting solution is simultaneously coated onto both sides of the base film using a micro-grooving roller to form a polymer monomer layer. Then, it undergoes a first-stage coagulation bath and a second-stage coagulation bath sequentially. After washing with water for 60 seconds, it is dried in a drying oven at 60°C and then wound up. The first-stage coagulation bath consists of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30°C. The second-stage coagulation bath also consists of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30°C.

[0058] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 70 minutes to fully dissolve the powder mixture and obtain a mixed solution, wherein the mass fraction of polyvinylidene fluoride in the mixed solution was 30 wt%. The mixed solution was then sprayed onto the surface of the polymer monomer layer and dried in an oven at 60°C for 30 minutes to obtain an initial diaphragm with a coating thickness of 5 μm.

[0059] The separator was prepared into a battery cell, and the battery cell was cured at 60°C for 6 hours to allow the polymer monomer layer to polymerize in situ into a gel electrolyte layer under the action of the electrolyte. The initiator contained in the electrolyte was azobisisoheptanenitrile.

[0060] Comparative Example 1

[0061] In this comparative example, the diaphragm consists of a base membrane, a ceramic layer, a first adhesive layer, and a second adhesive layer. The ceramic layer is disposed on one surface of the base membrane, the first adhesive layer is disposed on the other surface of the base membrane, and the second adhesive layer is disposed on the surface of the ceramic layer. The base membrane is a 3μm PE base membrane, the ceramic layer is made of conventional boehmite, and the adhesive layer is made of polyvinylidene fluoride.

[0062] The preparation method of the above-mentioned diaphragm specifically includes the following steps:

[0063] Thickener, binder and wetting agent are added to deionized water and stirred until completely dissolved. Then boehmite particles with a particle size of 600-1000 nm are added, stirred evenly and ground for 3 hours. Then surfactant is added and ground for 10 hours to obtain water-based ceramic slurry. The slurry contains 30 wt% deionized water and 40 wt% boehmite particles.

[0064] The above slurry was coated on one side of the base membrane and dried in an oven at 60°C for 80 minutes to obtain a semi-finished diaphragm with a ceramic layer coating thickness of 3 μm.

[0065] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 60 minutes to fully dissolve the powder mixture and obtain a mixed solution, wherein the mass fraction of polyvinylidene fluoride in the mixed solution was 30 wt%. The mixed solution was then sprayed onto both sides of the semi-finished diaphragm and dried in an oven at 60°C for 30 minutes to obtain the finished diaphragm with a coating thickness of 5 μm.

[0066] Comparative Example 2

[0067] The diaphragm in this comparative example consists of a base membrane, a first ceramic layer, a second ceramic layer, a first adhesive layer, and a second adhesive layer. The first ceramic layer is disposed on one surface of the base membrane, the second ceramic layer is disposed on the other surface of the base membrane, the first adhesive layer is disposed on the surface of the first ceramic layer, and the second adhesive layer is disposed on the surface of the second ceramic layer. The base membrane is a 4μm PE base membrane, the first and second ceramic layers are both made of conventional alumina, and the first and second adhesive layers are both made of polyvinylidene fluoride.

[0068] The preparation method of the above-mentioned diaphragm specifically includes the following steps:

[0069] Thickener, binder and wetting agent are added to deionized water and stirred until completely dissolved. Then alumina particles with a particle size of 300-500 nm are added, stirred evenly and ground for 8 hours. Then surfactant is added and ground for 12 hours to obtain water-based ceramic slurry. The slurry contains 20 wt% deionized water and 60 wt% alumina particles.

[0070] The above slurry was coated on both sides of the base membrane and dried in an oven at 90°C for 120 minutes to obtain a diaphragm semi-finished product with a ceramic layer coating thickness of 3 μm.

[0071] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 120 minutes to fully dissolve the powder mixture and obtain a mixed solution, wherein the mass fraction of polyvinylidene fluoride in the mixed solution was 50 wt%. The mixed solution was then sprayed onto both sides of the diaphragm semi-finished product and dried in an oven at 80°C for 30 minutes to obtain the finished diaphragm with a coating thickness of 5 μm.

[0072] Comparative Example 3

[0073] In this comparative example, the diaphragm consists of a base membrane 1, a gel solid electrolyte layer 2, a first adhesive layer 3-1, and a second adhesive layer 3-2. The gel solid electrolyte layer 2 is disposed on one surface of the base membrane 1, the first adhesive layer 3-1 is disposed on the other surface of the base membrane 1, and the second adhesive layer 3-2 is disposed on the surface of the gel solid electrolyte layer 2. The base membrane 1 is a 7μm PE base membrane, the gel solid electrolyte layer 2 is obtained by high-temperature curing of a mixture of methyl methacrylate and hydroxypropyl acrylate, and the materials of the first adhesive layer 3-1 and the second adhesive layer 3-2 are both polyvinylidene fluoride.

[0074] The method for preparing the above-mentioned diaphragm includes the following steps:

[0075] A mixture of methyl methacrylate and hydroxypropyl acrylate is dissolved in N,N-dimethylacetamide to obtain a casting solution; the mass fraction of the mixture of methyl methacrylate and hydroxypropyl acrylate in the casting solution is 30 wt%, and the slurry viscosity of the casting solution is 4800 mPas.

[0076] The casting solution was coated onto one side of a 3μm PE base film using a micro-grooving roller to form a polymer monomer layer. Then, the film underwent a first-stage coagulation bath and a second-stage coagulation bath sequentially. After washing with water for 60 seconds, it was dried in a drying oven at 60℃ and then wound up. The first-stage coagulation bath consisted of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30℃. The second-stage coagulation bath also consisted of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30℃.

[0077] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 60 minutes to fully dissolve the powder mixture and obtain a mixed solution. The mass fraction of polyvinylidene fluoride in the mixed solution was 30 wt%. The mixed solution was then sprayed onto both sides of the semi-finished diaphragm and dried in an oven at 60°C for 30 minutes to obtain the initial diaphragm with a coating thickness of 5 μm.

[0078] The separator was prepared into a battery cell, and the battery cell was cured at 60°C for 6 hours to allow the polymer monomer layer to polymerize in situ into a gel electrolyte layer under the action of the electrolyte. The initiator contained in the electrolyte was azobisisoheptanenitrile.

[0079] Comparative Example 4

[0080] The diaphragm in this comparative example consists of a base membrane 1, a first gel solid electrolyte layer 2-1, a second gel solid electrolyte layer 2-2, a first adhesive layer 3-1, and a second adhesive layer 3-2. The first gel solid electrolyte layer 2-1 is disposed on one surface of the base membrane 1, and the second gel solid electrolyte layer 2-2 is disposed on the other surface of the base membrane 1. The first adhesive layer 3-1 is disposed on the surface of the first gel solid electrolyte layer 2-1, and the second adhesive layer 3-2 is disposed on the surface of the second gel solid electrolyte layer 2-2. The base membrane 1 is a 7μm PE base membrane. The first gel solid electrolyte layer 2-1 and the second gel solid electrolyte layer 2-2 are both obtained by high-temperature curing of a mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate. The materials of the first adhesive layer 3-1 and the second adhesive layer 3-2 are both polyvinylidene fluoride.

[0081] The preparation method of the above-mentioned diaphragm specifically includes the following steps:

[0082] A mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate was dissolved in N,N-dimethylacetamide to obtain a casting solution; the mass fraction of the mixture of methoxy polyethylene glycol methacrylate and 2-bromoethyl acrylate in the casting solution was 30 wt%, and the slurry viscosity of the casting solution was 4000 mPas.

[0083] The casting solution is simultaneously coated onto both sides of the base film using a micro-grooving roller to form a polymer monomer layer. Then, it undergoes a first-stage coagulation bath and a second-stage coagulation bath sequentially. After washing with water for 60 seconds, it is dried in a drying oven at 60°C and then wound up. The first-stage coagulation bath consists of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30°C. The second-stage coagulation bath also consists of an aqueous solution of N,N-dimethylformamide with a mass concentration of 20% and a temperature of 30°C.

[0084] Polyvinylidene fluoride and water were added to a double planetary mixer and stirred for 70 minutes to fully dissolve the powder mixture and obtain a mixed solution. The mass fraction of polyvinylidene fluoride in the mixed solution was 30 wt%. The mixed solution was then sprayed onto both sides of the semi-finished diaphragm and dried in a 60°C oven for 30 minutes to obtain the initial diaphragm with a coating thickness of 5 μm.

[0085] The separator was prepared into a battery cell, and the battery cell was cured at 60°C for 6 hours to allow the polymer monomer layer to polymerize in situ into a gel electrolyte layer under the action of the electrolyte. The initiator contained in the electrolyte was azobisisoheptanenitrile.

[0086] The battery cells prepared in the above embodiments and comparative examples were formed at 45°C, aged at room temperature for 24 hours, and then subjected to capacity testing to obtain finished battery cells. The finished battery cells were then subjected to performance testing, and the results are shown in Table 1.

[0087] Table 1 Performance data of the battery cells prepared in the examples and comparative examples.

[0088]

[0089] Note: The yield rate of battery cells is calculated as the number of cells that have been normally formed / the total number of battery cells;

[0090] The 80% SOC cycle count refers to the number of charge-discharge cycles when the battery capacity retention rate reaches 80% SOC.

[0091] The 80% storage days refers to the number of days the battery can be stored when its capacity recovery rate reaches 80% of its SOC.

[0092] As shown in Table 1, compared with Examples 1 and 2, the thickness of the base film in Comparative Examples 1 and 2 is <5μm. Although a conventional ceramic layer is set on the surface, the yield of the finished cells is extremely low. In Comparative Examples 3 and 4, a gel solid electrolyte layer is set on the surface of the base film, and the thickness of the base film is >5μm. The yield of the finished cells is relatively high. However, due to the thicker base film, the volumetric energy density of the cells is reduced, and the electrochemical performance of the batteries is also deteriorated.

[0093] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made to this utility model without departing from the principle of this utility model, and these improvements and modifications also fall within the protection scope of the claims of this utility model.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A diaphragm for being disposed between a positive electrode and a negative electrode, characterized in that, include: A base film (1) and a gel solid electrolyte layer (2) disposed on at least one surface of the base film (1); The thickness of the base film (1) is <5 μm.

2. The diaphragm according to claim 1, characterized in that, The diaphragm further includes an adhesive layer (3), which is disposed on the surface of the gel solid electrolyte layer (2), or the adhesive layer (3) is disposed on the surface of the base membrane (1).

3. The diaphragm according to claim 1, characterized in that, The thickness of the gel solid electrolyte layer (2) is 0.5 to 5 μm, and / or the thickness of the base film (1) is 1 to 4 μm.

4. The diaphragm according to claim 2, characterized in that, The thickness of the adhesive layer (3) is 0 to 10 μm and is not equal to 0.

5. The diaphragm according to claim 1, characterized in that, The base membrane (1) has a puncture strength ≤300gf and a tensile strength ≤2000kgf / cm. 2 .

6. The diaphragm according to claim 1, characterized in that, The gel solid electrolyte layer (2) is obtained by curing the polymer monomer layer; the polymer monomer in the polymer monomer layer includes two or more of methyl methacrylate, acrylonitrile, methoxy polyethylene glycol methacrylate, 2-bromoethyl acrylate, hydroxypropyl acrylate and isostearyl acrylate.

7. The diaphragm according to claim 1, characterized in that, The thickness of the diaphragm is 1.5 to 15 μm.

8. An electrode assembly, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The diaphragm is the diaphragm according to any one of claims 1 to 7.

9. A power battery, characterized in that, Includes the electrode assembly as described in claim 8.

10. A vehicle, characterized in that, Includes the power battery as described in claim 9.

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