Diaphragm and preparation method thereof, battery and electric device

Abstract

The invention relates to a diaphragm and a preparation method thereof, a battery and a power utilization device, the diaphragm comprises a base membrane, a titanium aluminum lithium phosphate layer and a lithium supplementing layer, one side of the base membrane is coated with the titanium aluminum lithium phosphate layer, and the other side of the base membrane is coated with the lithium supplementing layer; the lithium supplementing layer comprises the following components in percentage by mass: 30%-80% of a lithium supplementing agent, 10%-60% of ceramic particles, 0.1%-2% of a dispersing agent, 0.5%-5% of a conductive agent and 5%-15% of a binder. The diaphragm structure is optimized, one side of the base membrane is coated with the titanium aluminum lithium phosphate layer, and the other side of the base membrane is coated with the lithium supplementing layer, so that the first efficiency and the capacity of the battery are improved, and the safety performance of the battery is also ensured.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly to a separator and its preparation method, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage fields due to their advantages such as high energy density, long cycle life, light weight, environmental protection, and low self-discharge rate. During the cyclic charge and discharge process of a lithium-ion battery, when charging, lithium continuously deintercalates from the positive electrode, passes through the electrolyte, and embeds into the negative electrode, and then during discharge, it deintercalates from the negative electrode and returns to the positive electrode. However, in each cycle, a small amount of lithium is lost due to various reasons (such as side reactions, formation of lithium dendrites, etc.). As the number of cycles increases, the loss of lithium gradually accumulates, resulting in a decrease in battery capacity.

[0003] Traditional technologies usually take lithium supplementation measures for the positive electrode or the negative electrode, and perform a lithium supplementation process. The lithium supplementation process is also called "pre-lithiation", which is to add a lithium source to the inside of the battery before the lithium-ion battery works to supplement lithium ions. By pre-lithiation, lithium is supplemented inside the battery to offset irreversible lithium loss, so as to improve the initial efficiency, capacity, and energy density of the battery. For example, electrochemical method is used for positive electrode lithium supplementation. By adding a lithium supplementation material to the positive electrode of the lithium-ion battery, the lithium supplementation material decomposes and releases active lithium during the battery charging process to make up for the irreversible active lithium loss. However, this method will reduce the amount of active substances in the positive electrode, and the lithium supplementation additive for the positive electrode usually has a very low reversible capacity and will not contribute to the battery capacity after the first charge and discharge. It belongs to an inert and ineffective substance, which is not conducive to improving the battery energy density and capacity. The research and development of negative electrode lithium supplementation technology started earlier, including various lithium supplementation methods such as physical mixing lithium supplementation based on metallic lithium and electrochemical lithiation. However, negative electrode lithium supplementation is still limited by several major problems in battery manufacturing processes, that is, the use of metallic lithium is incompatible with the production environment, conventional solvents, binders, air, and heat treatment processes, etc., which increases the difficulty of lithium supplementation for the negative electrode. Summary of the Invention

[0004] Based on this, it is necessary to provide a separator and its preparation method, a battery, and an electrical device to improve the capacity and initial efficiency of the battery.

[0005] In one aspect of the present application, a separator is provided, which includes a base film, a lithium titanium aluminum phosphate layer, and a lithium supplementation layer. The lithium titanium aluminum phosphate layer is coated on one side of the base film, and the lithium supplementation layer is coated on the other side of the base film;

[0006] The lithium supplementation layer includes components with the following mass percentages: 30% - 80% of a lithium supplementation agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder.

[0007] In this application, by optimizing the separator structure, a layer of lithium titanium aluminum phosphate is coated on one side of the base film. Lithium titanium aluminum phosphate has good ionic conductivity, which can not only improve the ionic conductivity of the separator, but also enhance the tensile strength and thermal shrinkage performance of the separator, preventing the separator from shrinking along the puncture holes and causing separator failure. This lithium titanium aluminum phosphate layer can reduce the short-circuit risk and avoid problems such as battery fire or explosion, effectively improving the safety of the battery. Moreover, a lithium supplement layer is coated on the other side of the base film. By properly designing the composition of the lithium supplement layer, an effective and safe lithium supplement pathway is obtained. The lithium supplement layer adds a lithium source to supplement lithium ions, offsetting the irreversible lithium loss, and ultimately improving the initial efficiency and capacity of the battery on the premise of improving the battery safety performance.

[0008] The above-mentioned lithium supplement layer includes components with the following mass percentages: 30% - 80% of lithium supplement agent, 10% - 60% of ceramic particles, 0.1% - 2% of dispersant, 0.5% - 5% of conductive agent, and 5% - 15% of binder. Through the interaction of the lithium supplement agent, ceramic particles, dispersant, conductive agent, and binder with specific mass ratios, the lithium supplement layer can synergistically release active lithium evenly, ensuring the safety of lithium supplementation. Moreover, this lithium supplement layer has high conductivity and good cycle stability, and its structure is stable and not prone to change during the cycle.

[0009] In some embodiments, in the lithium supplement layer by mass percentage, the lithium supplement agent is 40% - 70%, the ceramic particles are 20% - 50%, the dispersant is 0.5% - 2%, the conductive agent is 1.0% - 5%, and the binder is 5% - 12%.

[0010] In some embodiments, the thickness of the lithium supplement layer is 2μm - 7μm.

[0011] In some embodiments, the thickness of the lithium titanium aluminum phosphate layer is 1μm - 5μm.

[0012] In some embodiments, the separator satisfies at least one of the following conditions:

[0013] (1) The lithium supplement agent includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate;

[0014] (2) The ceramic particles include at least one of alumina, boehmite, silica, and calcium hydroxide;

[0015] (3) The dispersant includes at least one of polyvinylpyrrolidone, silicone rubber dispersant, and carboxymethyl cellulose dispersant;

[0016] (4) The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene;

[0017] (5) The binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0018] In some embodiments, the lithium titanium aluminum phosphate layer comprises components with the following mass percentages: 80% - 95% of lithium titanium aluminum phosphate particles, 0.1% - 3% of a dispersant, and 4% - 15% of a binder.

[0019] In a second aspect of the present application, a method for preparing a separator is provided, comprising the following steps:

[0020] By mass percentage, 30% - 80% of a lithium supplement agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder are mixed in a solvent to form a lithium supplement slurry, and the lithium supplement slurry is coated on one side of a base film to form a lithium supplement layer; a lithium titanium aluminum phosphate layer is coated on the other side of the base film.

[0021] In some embodiments, coating the lithium titanium aluminum phosphate layer on the other side of the base film comprises the following steps:

[0022] By mass percentage, 80% - 95% of lithium titanium aluminum phosphate particles, 0.1% - 3% of a dispersant, and 4% - 15% of a binder are homogenized in a solvent and then coated on the other side of the base film to form a lithium titanium aluminum phosphate layer.

[0023] In a third aspect of the present application, a battery is provided, comprising a positive electrode sheet, a negative electrode sheet, and the separator as described in the first aspect and a separator prepared by the preparation method as described in the second aspect. The separator is located between the positive electrode sheet and the negative electrode sheet, the lithium supplement layer is located between the separator and the positive electrode sheet, and the lithium titanium aluminum phosphate layer is located between the separator and the negative electrode sheet.

[0024] In a fourth aspect of the present application, an electrical device is provided, comprising the battery as described in the third aspect. Description of the Drawings

[0025] Figure 1 Schematic diagram of the separator structure for Example 1.

[0026] Description of the reference numerals:

[0027] 1. Lithium supplement layer; 2. Base film; 3. Lithium titanium aluminum phosphate layer. Detailed Description of the Embodiments

[0028] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0030] During the cyclic charge and discharge process of a lithium-ion battery, lithium loss will occur, and the lithium loss will gradually accumulate, resulting in a decrease in battery capacity. However, the existing lithium replenishment measures for the positive or negative electrode are not very effective, which is not conducive to the improvement of battery capacity, initial efficiency, and energy density. In view of the foregoing problems, how to improve battery safety, capacity, and initial efficiency without reducing the battery energy density. This application takes a different approach and conducts the lithium replenishment process by redesiging the separator structure.

[0031] Based on this, an embodiment of the present application provides a separator, which includes a base film, a lithium titanium aluminum phosphate layer, and a lithium replenishment layer. The lithium titanium aluminum phosphate layer is coated on one side of the base film, and the lithium replenishment layer is coated on the other side of the base film.

[0032] The lithium replenishment layer includes the following components in mass percentage: 30% - 80% of a lithium replenishment agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder.

[0033] Lithium titanium aluminum phosphate, as a solid electrolyte, has high ionic conductivity. Ions move in the lithium titanium aluminum phosphate lattice by occupying vacancies, thereby forming an ion transport channel. This structure enables ions to be transported in the solid electrolyte at a relatively fast speed, thus improving the rate performance of the battery. Moreover, the lithium titanium aluminum phosphate solid electrolyte also has good chemical stability and mechanical properties. However, since lithium titanium aluminum phosphate is prone to chemical reaction with the negative electrode, consuming lithium ions and resulting in a decrease in active lithium, the irreversible capacity of the battery increases. In this application, by optimizing the separator structure, a lithium titanium aluminum phosphate layer is coated on one side of the base film, and a specific lithium replenishment layer is coated on the other side. On the premise of improving battery safety, the initial efficiency and capacity of the battery are improved, achieving unexpected effects.

[0034] Different from the traditional method of improving battery capacity by lithium supplementation at the positive electrode or the negative electrode, in this application, by optimizing the separator structure, a layer of lithium titanium aluminum phosphate is coated on one side of the base film. Lithium titanium aluminum phosphate has good ionic conductivity, which can not only improve the ionic conductivity of the separator, but also improve the tensile strength and thermal shrinkage performance of the separator, avoiding the shrinkage of the separator along the puncture holes and causing the failure of the separator; this lithium titanium aluminum phosphate layer can reduce the risk of short circuit and avoid the problems of battery fire or explosion, effectively improving the safety of the battery; moreover, a lithium supplementation layer is coated on the other side of the base film. By properly designing the composition of the lithium supplementation layer, an effective and safe lithium supplementation path is obtained. The lithium supplementation layer increases the lithium source to supplement lithium ions, offsetting the irreversible lithium loss, and finally improving the first efficiency and capacity of the battery on the premise of improving the battery safety performance.

[0035] The above-mentioned lithium supplementation layer includes components with the following mass percentages: 30% - 80% of lithium supplementation agent, 10% - 60% of ceramic particles, 0.1% - 2% of dispersant, 0.5% - 5% of conductive agent, and 5% - 15% of binder. Through the interaction of the lithium supplementation agent, ceramic particles, dispersant, conductive agent, and binder with specific mass ratios, the lithium supplementation layer can synergistically enhance the effect, enabling the lithium supplementation layer to uniformly release active lithium and ensuring the safety of lithium supplementation; moreover, the lithium supplementation layer has high conductivity and good cycle stability, and the structure of the lithium supplementation layer is stable and not prone to change during the cycle.

[0036] As an example, the mass percentage of the lithium supplementation agent in the lithium supplementation layer can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, and 80%, or it can also be within the range formed by any two of the above point values as the end values. The mass percentage of the lithium supplementation agent in the lithium supplementation layer is preferably 40% - 70%.

[0037] As an example, the mass percentage of ceramic particles in the lithium supplement layer can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% and 60%, or within the range formed by any two of the above point values as the end values. The mass percentage of ceramic particles is preferably 20% - 50%.

[0038] As an example, the mass percentage of the dispersant in the lithium supplement layer can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% and 2.0%, or within the range formed by any two of the above point values as the end values. The mass percentage of the dispersant is preferably 0.5% - 2%.

[0039] As an example, the mass percentage of the conductive agent in the lithium supplement layer can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9% and 5.0%, or within the range formed by any two of the above point values as the end values. The mass percentage of the conductive agent is preferably 1.0% - 5%.

[0040] As an example, the mass percentage of the binder in the lithium supplement layer can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% and 15%, or within the range formed by any two of the above point values as the end values. The mass percentage of the binder is preferably 5% - 12%.

[0041] In some of these embodiments, in the lithium supplement layer by mass percentage, the lithium supplement agent is 40% - 70%, the ceramic particles are 20% - 50%, the dispersant is 0.5% - 2%, the conductive agent is 1.0% - 5%, and the binder is 5% - 12%. Under this mass ratio, the lithium supplement effect of the lithium supplement layer is better, further improving the first efficiency and capacity of the battery.

[0042] In some of these embodiments, the thickness of the lithium supplement layer is 2μm - 7μm. The thickness of the lithium supplement layer is preferably 3μm - 5μm. When the thickness of the lithium supplement layer is 3μm - 5μm, the comprehensive performance of the battery is better, well balancing the lithium supplement stability and battery safety, making the battery have a higher capacity and first efficiency.

[0043] As an example, the thickness of the lithium supplement layer can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, and 7μm, or within the range formed by any two of the above point values as the end values.

[0044] In some of these embodiments, the thickness of the lithium titanium aluminum phosphate layer is 1μm - 5μm.

[0045] As an example, the thickness of the lithium titanium aluminum phosphate layer is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, and 5μm, or within the range formed by any two of the above point values as the end values. The thickness of the lithium titanium aluminum phosphate layer is preferably 2μm - 5μm. When the thickness of the lithium titanium aluminum phosphate layer is 2μm - 5μm, the separator has a higher separator puncture strength, the comprehensive performance of the battery is better, and it can more fully ensure the safety of the battery.

[0046] In some of these embodiments, the lithium supplement agent includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate.

[0047] In some of these embodiments, the ceramic particles include at least one of alumina, boehmite, silica, and calcium hydroxide.

[0048] In some of these embodiments, the dispersant includes at least one of polyvinylpyrrolidone, silicone rubber dispersant, and carboxymethyl cellulose dispersant.

[0049] In some of these embodiments, the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

[0050] In some of these embodiments, the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0051] In some embodiments, the lithium titanium aluminum phosphate layer includes the following components in percentage by weight: 80% to 95% of lithium titanium aluminum phosphate particles, 0.1% to 3% of a dispersant, and 4% to 15% of a binder.

[0052] As an example, the mass percentage of the lithium aluminum titanium phosphate particles in the lithium aluminum titanium phosphate layer can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, and 95%, or can be within a range consisting of any two of the above values as end values. The mass percentage of the lithium aluminum titanium phosphate particles is preferably 85% to 90%.

[0053] As an example, the mass percentage of the dispersant in the lithium titanium aluminum phosphate layer can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% and 3.0%, or can be within the range formed by any two of the above points as end values. The mass percentage of the dispersant is preferably 1.5% to 2%.

[0054] As an example, the binder content in the lithium aluminum titanium phosphate layer can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%, or can be within a range consisting of any two of the above values. The binder content is preferably 10% to 15%.

[0055] In some embodiments, the dispersant in the lithium titanium aluminum phosphate layer includes at least one of polyvinyl pyrrolidone, silicone rubber dispersant, carboxymethyl cellulose, and polyacrylic acid dispersant.

[0056] In some embodiments, the binder in the lithium aluminum titanium phosphate layer includes polyvinylidene fluoride, butadiene

[0057] At least one of styrene rubber and sodium carboxymethyl cellulose.

[0058] In some embodiments, the base film is made of one or both of polyethylene (PE) and polypropylene (PP).

[0059] Furthermore, the base film is a PE base film, a PP base film or a PP / PE / PP composite base film. The PP / PE / PP composite base film is a three-layer composite film in which both sides of a polyethylene film are composited with a polypropylene film.

[0060] The second aspect of the present application provides a method for preparing a separator, comprising the following steps:

[0061] Taking mass percentage content, 30% - 80% of a lithium supplement agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder are mixed in a solvent to form a lithium supplement slurry, and the lithium supplement slurry is coated on one side of a base film to form a lithium supplement layer; a lithium titanium aluminum phosphate layer is coated on the other side of the base film.

[0062] The method for preparing this separator is simple and easy to operate; the lithium supplement layer has good process compatibility and does not require significant adjustment to the existing battery manufacturing process.

[0063] Understood, by controlling the content of the lithium supplement agent in the lithium supplement layer, the lithium supplement amount per unit area can be quantitatively controlled. It is possible to first prepare the lithium supplement layer and then prepare the lithium titanium aluminum phosphate layer, first prepare the lithium titanium aluminum phosphate layer and then prepare the lithium supplement layer, or prepare the lithium supplement layer and the lithium titanium aluminum phosphate layer simultaneously.

[0064] Further, the solvent used in the homogenization process is at least one of alkanes, ethers, esters, and ketones. Even further, the mass of the solvent accounts for 20% - 80% of the mass of the lithium supplement slurry, wherein the lithium supplement slurry includes the solvent, the lithium supplement agent, ceramic particles, a dispersant, a conductive agent, and a binder.

[0065] In some of the embodiments, coating the lithium titanium aluminum phosphate layer on the other side of the base film includes the following steps: taking mass percentage content, 80% - 95% of lithium titanium aluminum phosphate particles, 0.1% - 3% of a dispersant, and 4% - 15% of a binder are mixed in a solvent to form a lithium supplement slurry, and the lithium supplement slurry is coated on the other side of the base film, and after drying to remove the solvent, a lithium titanium aluminum phosphate layer is formed.

[0066] Further, the solvent used in the homogenization process is at least one of alkanes, ethers, esters, and ketones.

[0067] Even further, the mass of the solvent accounts for 20% - 80% of the mass of the lithium titanium aluminum phosphate coating slurry, wherein the lithium titanium aluminum phosphate coating slurry includes the solvent, lithium titanium aluminum phosphate particles, a dispersant, and a binder.

[0068] The third aspect of the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator as described in the first aspect or a separator prepared by the preparation method described in the second aspect, the separator is located between the positive electrode sheet and the negative electrode sheet, the lithium supplement layer is located between the separator and the positive electrode sheet, and the lithium titanium aluminum phosphate layer is located between the separator and the negative electrode sheet.

[0069] The fourth aspect of the present application provides an electrical device, comprising the battery as described in the third aspect.

[0070] The following are specific embodiments.

[0071] Embodiment 1

[0072] A separator: By mass percentage, 60% of lithium cobaltate, 30% of ceramic particles (boehmite), 0.5% of a dispersant (polyvinylpyrrolidone), 4.5% of a conductive agent (conductive carbon black), and 5% of a binder (polyvinylidene fluoride) are mixed to obtain a mixture. Then, a solvent (N-methylpyrrolidone) is added to the mixture and mixed thoroughly to obtain a lithium supplement slurry; the mass ratio of the solvent to the mixture is 50%. The lithium supplement slurry is sprayed on one side of the base film 2, and after drying to remove the solvent, a lithium supplement layer 1 with a thickness of 4 μm is formed; the base film 2 uses a 9-μm-thick PE base film;

[0073] By mass percentage, 85% of lithium titanium aluminum phosphate particles, 2% of a dispersant (polyacrylic acid), and 13% of a binder (polyvinylidene fluoride) are mixed. Then, a solvent is added to the mixture and mixed thoroughly to obtain a slurry. The mass ratio of the solvent (N-methylpyrrolidone) to the mixture is 50%. The aforementioned slurry is sprayed on the other side of the base film 2, and after drying to remove the solvent, a lithium titanium aluminum phosphate layer 3 (LATP layer) with a thickness of 3 μm is formed; the separator is prepared, and the structure of the separator is as Figure 1 shown.

[0074] By winding the positive electrode sheet, the above-mentioned separator, and the negative electrode sheet in a winding manner to form an electric core, the side where the lithium supplement layer 1 of the above-mentioned separator is located corresponds to the positive electrode sheet, and the side where the lithium titanium aluminum phosphate layer 3 is located corresponds to the negative electrode sheet. Then, through methods such as liquid injection, encapsulation, formation, and grading, the final lithium-ion battery is obtained.

[0075] Embodiment 2

[0076] Embodiment 2 is basically the same as Embodiment 1, the difference being that: the lithium supplement layer includes components with the following mass percentages: 30% of lithium nickelate, 60% of ceramic particles, 2% of a dispersant, 1% of a conductive agent, and 7% of a binder.

[0077] Embodiment 3

[0078] Embodiment 3 is basically the same as Embodiment 1, the difference being that: the lithium supplement layer includes components with the following mass percentages: 80% of lithium manganate, 10% of ceramic particles, 1% of a dispersant, 4% of a conductive agent, and 5% of a binder.

[0079] Embodiment 4

[0080] Embodiment 4 is basically the same as Embodiment 1, the difference being that: the coating surface weight of the lithium supplement slurry is adjusted so that the thickness of the lithium supplement layer is 7 μm.

[0081] Embodiment 5

[0082] Example 5 is basically the same as Example 1, except that the thickness of the lithium titanium aluminum phosphate layer is 1 μm.

[0083] Example 6

[0084] Example 6 is basically the same as Example 1, except that the lithium cobaltate is replaced with an equal mass of lithium iron phosphate.

[0085] Comparative Example 1

[0086] Comparative Example 1 is basically the same as Example 1, except that the lithium supplement layer is omitted and the lithium titanium aluminum phosphate layer is replaced with a ceramic layer of the same thickness. Among them, the ceramic layer includes the following components in mass percentage: 75% ceramic, 10% conductive agent, and 15% binder.

[0087] Comparative Example 2

[0088] Comparative Example 2 is basically the same as Example 1, except that the lithium titanium aluminum phosphate layer is omitted.

[0089] Comparative Example 3

[0090] Comparative Example 3 is basically the same as Example 1, except that the lithium supplement layer is omitted.

[0091] Comparative Example 4

[0092] Comparative Example 4 is basically the same as Example 1, except that the lithium supplement layer includes the following components in mass percentage: 20% lithium cobaltate, 70% ceramic particles, 2% dispersant, 2% conductive agent, and 6% binder.

[0093] The batteries prepared in Examples 1-6 and Comparative Examples 1-4 were tested for capacity, initial efficiency, and diaphragm puncture strength, and the test results are shown in Table 1 below.

[0094] Among them, the test conditions for capacity, initial efficiency, and diaphragm puncture strength are as follows:

[0095] Capacity:

[0096] 1. The temperature for capacity equalization is kept constant at 25 °C;

[0097] 2. Constant current and constant voltage charging at 2 A until 3.65 V, cutoff at 0.1 A;

[0098] 3. Constant current discharge at 2 A until 2.5 V;

[0099] 4. The capacity in step 3 is taken as the test capacity.

[0100] Initial efficiency:

[0101] Formation conditions:

[0102] 1. The formation temperature is maintained at a constant 45°C.

[0103] 2. Constant current charging at 0.2 A for 240 min.

[0104] Formation conditions:

[0105] 1. The formation temperature is maintained at a constant 25°C.

[0106] 2. Constant current and constant voltage charging at 2 A until 3.65 V, and cutoff at 0.1 A.

[0107] 3. Constant current discharging at 2 A until 2.5 V.

[0108] The first efficiency = (the first formation discharge capacity / (the first formation charging capacity + the first formation discharge capacity)) * 100%.

[0109] Puncture strength: Cut a sample strip about 4.5 cm wide in the MD direction. The initial distance between the needle tip (needle length 60 mm, needle tip is a spherical ball with a diameter of 1 mm) and the film is 10 mm. Lower it at a speed of 50 mm / min until it penetrates. Test 3 points on 1 sample strip, and take the arithmetic mean as the result.

[0110] Table 1

[0111]

[0112] As can be seen from Table 1 above, the batteries made with the separators of Examples 1 to 6 improve the battery safety while increasing the battery capacity and the first efficiency. By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that by optimizing the separator structure, with a lithium - supplementing coating on one side and a lithium titanium aluminum phosphate layer on the other side, the capacity can be increased by about 15%, the first efficiency can be increased by about 6%, and the separator puncture strength can be increased by about 20%. The batteries produced not only have good safety, but also have higher capacity and first efficiency.

[0113] By comparing Example 1 with Examples 2 to 3, it can be seen that when the lithium - supplementing agent is 40% - 70%, the ceramic particles are 20% - 50%, the dispersant is 0.5% - 2%, the conductive agent is 1.0% - 5%, and the binder is 5% - 12% by mass percentage in the lithium - supplementing layer, the battery performance is better, with higher capacity and first efficiency.

[0114] By comparing Example 1 with Example 4, it can be seen that when the thickness of the lithium - supplementing layer is 3 μm - 5 μm, the comprehensive performance of the battery is better, with higher capacity and first efficiency.

[0115] By comparing Example 1 with Example 5, it can be seen that when the thickness of the lithium titanium aluminum phosphate layer is 2 μm - 5 μm, the comprehensive performance of the battery is better, with higher safety.

[0116] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0117] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A diaphragm, characterized in that, It includes a base film, a lithium titanium aluminum phosphate layer, and a lithium supplement layer. The lithium titanium aluminum phosphate layer is coated on one side of the base film, and the lithium supplement layer is coated on the other side of the base film; The lithium supplement layer includes components with the following mass percentages: 30% - 80% of a lithium supplement agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder.

2. The diaphragm according to claim 1, characterized in that, In the lithium supplement layer, by mass percentage, the lithium supplement agent is 40% - 70%, the ceramic particles are 20% - 50%, the dispersant is 0.5% - 2%, the conductive agent is 1.0% - 5%, and the binder is 5% - 12%.

3. The diaphragm according to claim 1, characterized in that, The thickness of the lithium supplement layer is 2μm - 7μm.

4. The diaphragm according to claim 1, wherein, The thickness of the lithium titanium aluminum phosphate layer is 1μm - 5μm.

5. The diaphragm according to any one of claims 1 to 4, characterized in that, Meet at least one of the following conditions: (1) The lithium supplement agent includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate; (2) The ceramic particles include at least one of alumina, boehmite, silica, and calcium hydroxide; (3) The dispersant includes at least one of polyvinylpyrrolidone, silicone rubber dispersant, and carboxymethyl cellulose dispersant; (4) The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene; (5) The binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

6. The diaphragm according to any one of claims 1 to 4, characterized in that, The lithium titanium aluminum phosphate layer includes components with the following mass percentages: 80% - 95% of lithium titanium aluminum phosphate particles, 0.1% - 3% of a dispersant, and 4% - 15% of a binder.

7. A method for preparing a diaphragm, characterized in that: It includes the following steps: By mass percentage, mix 30% - 80% of a lithium supplement agent, 10% - 60% of ceramic particles, 0.1% - 2% of a dispersant, 0.5% - 5% of a conductive agent, and 5% - 15% of a binder in a solvent to form a lithium supplement slurry. Coat the lithium supplement slurry on one side of the base film to form a lithium supplement layer; coat a lithium titanium aluminum phosphate layer on the other side of the base film.

8. The method for preparing a diaphragm according to claim 7, characterized in that: The step of coating a lithium titanium aluminum phosphate layer on the other side of the base film includes the following steps: By mass percentage, homogenize 80% - 95% of lithium titanium aluminum phosphate particles, 0.1% - 3% of a dispersant, and 4% - 15% of a binder in a solvent and then coat it on the other side of the base film to form a lithium titanium aluminum phosphate layer.

9. A battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, and the separator as described in any one of claims 1 to 6 and the separator prepared by the preparation method as described in claim 7 or 8. The separator is located between the positive electrode sheet and the negative electrode sheet. The lithium supplement layer is located between the separator and the positive electrode sheet, and the lithium titanium aluminum phosphate layer is located between the separator and the negative electrode sheet.

10. An electrical device, characterized in that, It includes the battery as described in claim 9.

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