Diaphragm, electrochemical device, and electronic device

Abstract

The application relates to the technical field of electrochemical energy storage devices, in particular to a diaphragm, an electrochemical device and an electronic device, which mainly comprises: a diaphragm for an electrochemical device, the diaphragm comprising a porous base material and a porous coating arranged on at least one surface of the porous base material, the porosity of the porous coating being 60% to 80%; and the porous coating comprising a polymer; the specific strength at break of the polymer being a cN / dtex, the bulk density of the polymer being b g / m 3 , and the elastic modulus of the polymer being c GPa, a, b and c satisfying: c=0.1*a*b; wherein 60<=a<=120, 0.9<=b<=1.3. The diaphragm provided by the application has appropriate elastic properties, and effectively improves the problem that the diaphragm is extruded in the battery cycle process.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage device technology, and particularly to diaphragms, electrochemical devices and electronic devices. Background Technology

[0002] The separator is one of the key materials in lithium-ion batteries. However, during battery cycling, the electrode volume expands significantly due to the extraction and insertion of lithium ions, which compresses the separator and causes a series of problems such as lifespan, safety, and cell deformation.

[0003] Therefore, there is an urgent need to improve the problem of separator compression during battery cycling. Summary of the Invention

[0004] Based on the shortcomings of the prior art, this application provides a separator, an electrochemical device, and an electronic device, which aim to improve the problem of separator compression during battery cycling.

[0005] To achieve the above objectives, this application provides a diaphragm for an electrochemical device, the diaphragm comprising a porous substrate and a porous coating disposed on at least one surface of the porous substrate, the porous coating having a porosity of 60% to 80%.

[0006] Furthermore, the porous coating comprises a polymer with a tensile strength of a cN / dtex and a bulk density of bg / m³. 3 The elastic modulus of the polymer is c GPa, and a, b, and c satisfy: c = 0.1 * a * b;

[0007] Where 60≤a≤120, 0.9≤b≤1.3.

[0008] In some embodiments, the elastic modulus of the polymer is between 6 GPa and 12 GPa.

[0009] In some embodiments, the swelling degree of the polymer is 5% to 40%.

[0010] In some embodiments, the number-average molecular weight of the polymer is from 60,000 g / mol to 120,000 g / mol.

[0011] In some embodiments, the glass transition temperature of the polymer is 260°C to 300°C.

[0012] In some embodiments, the polymer includes at least one of aromatic polyamide, polyimide, and semi-aromatic polyamide.

[0013] In some embodiments, the porous coating includes an adhesive, wherein the mass ratio of the polymer to the adhesive is (5-9):(1-5).

[0014] In some embodiments, the adhesive includes at least one of polyacrylic acid, polymethyl methacrylate, polyacrylonitrile, polyamide, polycarboxylic acid, polyacrylate, polyvinyl alcohol, polyvinyl acetate, cellulose acetate, cellulose acetate propionate, carboxymethyl cellulose, nitrile rubber, styrene-butadiene rubber, and latex.

[0015] This application also provides an electrochemical device, the electrochemical device including the diaphragm.

[0016] This application also provides an electronic device, which includes any of the electrochemical devices described herein.

[0017] The beneficial effects of this application are as follows:

[0018] This application controls the porosity and tensile strength of the porous coating on the separator, which helps improve the structural stability of the porous coating, coordinates its bulk density, and regulates the elastic properties of the polymer, further improving the elastic properties of the separator coating. During battery charging, the separator coating deforms under the stress of electrode expansion, absorbing the corresponding stress and preventing the electrode from cracking and deforming due to excessive reverse force of the separator on the electrode. During battery discharging, the stress decreases, the deformation of the separator recovers, and it can re-support the electrode structure, maintaining the stability of the lithium-ion channel, thereby improving the cycle expansion of the battery. Detailed Implementation

[0019] The term "coating" refers to one or more layers applied to one or both sides of a porous substrate material. Functional coatings can be single-layer, double-layer, or multi-layer structures.

[0020] The term "fracture strength" refers to the tensile force that a material can withstand when its thickness is 1 tex.

[0021] The term "volume density" refers to the ratio of a material's mass to its volume.

[0022] The term "swelling degree" refers to the degree to which a material, such as a polymer, expands in volume after adsorbing solvent molecules. Swelling degree can be expressed as the change in mass or volume of the material before and after adsorbing solvent molecules.

[0023] The term "glass transition temperature" refers to the critical temperature at which a material transitions from a rigid glassy state to a soft, elastic state.

[0024] The term "binder" refers to a substance used for interfacial interactions to firmly bond two or more materials together. This document may use any organic binder that can bond polymers to porous substrate materials or to each other.

[0025] The term "pore" refers to the tiny voids within a porous medium.

[0026] The term "porosity" refers to the ratio of pore volume to total volume in a porous medium, expressed as a percentage (%).

[0027] The term "elastic modulus" refers to the physical quantity that represents the ratio of stress to strain within the elastic deformation range of a material.

[0028] The term "specific logarithmic viscosity" refers to the natural logarithm of the ratio of a material's viscosity to its solvent viscosity, divided by the mass concentration of the material. Specific logarithmic viscosity describes the flow behavior of a material solution; the higher the specific logarithmic viscosity, the higher the viscosity of the material.

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0030] In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features. In this application, numerical ranges are involved; unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value, or with other lower or upper limits, to form an unspecified range.

[0031] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0032] The separator is one of the key materials in lithium-ion batteries. However, during battery cycling, the electrode volume expands significantly due to the extraction and insertion of lithium ions, which compresses the separator and causes a series of problems such as lifespan, safety, and cell deformation.

[0033] Therefore, there is an urgent need to improve the problem of separator compression during battery cycling.

[0034] Based on the shortcomings of existing technologies, this solution provides a separator, an electrochemical device, and an electronic device, aiming to improve the problem of separator compression during battery cycling.

[0035] To achieve the above objectives, this solution provides a diaphragm for an electrochemical device, the diaphragm comprising a porous substrate and a porous coating disposed on at least one surface of the porous substrate, the porous coating having a porosity of 60% to 80%.

[0036] Furthermore, the porous coating includes a polymer with a specific tensile strength of a cN / dtex, a bulk density of b g / m3, and an elastic modulus of c GPa. a, b, and c satisfy: c = 0.1 * a * b.

[0037] Among them, 60 <a<120,0.9≤b≤1.3。

[0038] The porosity of the porous coating on the separator is set between 60% and 80%. This increases the number of lithium-ion channels while improving the separator's liquid retention, thereby promoting lithium-ion shuttle movement, reducing the risk of lithium-ion aggregation, and meeting the requirements of high-rate charge and discharge. The lower limit of the porous coating's porosity is greater than or equal to 60%, which helps increase the pore structure on the separator and improves its elasticity. During battery charging, the separator coating deforms under the stress of electrode expansion, absorbing the corresponding stress and avoiding defects such as electrode cracking and deformation caused by excessive reverse force from the separator on the electrodes. Simultaneously, the upper limit of the porous coating's porosity (80%) helps improve the rigidity of the porous coating's framework structure. During battery discharge, as stress decreases, the separator's deformation recovers, allowing it to re-support the electrode structure and maintain the stability of the lithium-ion channels, thus improving the battery's cycle expansion.

[0039] For example, the porosity of the porous coating is 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or within the range of any two of the above values.

[0040] The lower limit of the polymer's tensile strength is set at 60 cN / dtex. This maintains the structural stability of the separator while improving its elastic properties, allowing the separator to undergo recoverable deformation during battery cycling and thus mitigating the problem of the separator being squeezed during battery cycling. The upper limit of the polymer's tensile strength is set at 120 cN / dtex. This reduces the reverse force exerted by the separator on the electrode when absorbing the stress from the electrode expansion, thereby reducing the risk of cracking and deformation of the electrode due to internal stress.

[0041] For example, the polymers have specific tensile strengths of 60 cN / dtex, 62 cN / dtex, 64 cN / dtex, 66 cN / dtex, 68 cN / dtex, 70 cN / dtex, 72 cN / dtex, 74 cN / dtex, 76 cN / dtex, 78 cN / dtex, 80 cN / dtex, 82 cN / dtex, 84 cN / dtex, 86 cN / dtex, 88 cN / dtex, 90 cN / dtex, and 92 cN / dtex. N / dtex, 94cN / dtex, 96cN / dtex, 98cN / dtex, 100cN / dtex, 102cN / dtex, 104cN / dtex, 106cN / dtex, 108cN / dtex, 110cN / dtex, 112cN / dtex, 114cN / dtex, 116cN / dtex, 118cN / dtex, 120cN / dtex, or within the range of any two of the above values.

[0042] The bulk density of the polymer was set at 0.9 g / m³. 3 Up to 1.3g / m 3 This facilitates the stacking and entanglement of molecular chains in the polymer, thereby improving the polymer's structural stability and elastic properties, and further enhancing the elastic properties of the membrane. Furthermore, the lower limit of the polymer's bulk density is controlled at 0.9 g / m³. 3 This helps improve the structural stability of the porous coating on the diaphragm, reducing the risk of the diaphragm being difficult to recover after deformation, while the upper limit of the polymer's bulk density is controlled at 1.3 g / m³. 3 It not only improves the ion transport effect of the membrane by controlling the stacking and entanglement effect of polymer molecular chains, thereby meeting the requirements of high-rate charging and discharging, but also improves the elastic properties of the porous coating, further alleviating the squeezing of the membrane caused by the expansion of the electrode.

[0043] For example, the bulk density of the polymer is 0.90 g / m³. 3 0.92g / m 3 0.94g / m 3 0.96g / m 3 0.98g / m 3 1.00g / m 3 1.02g / m 3 1.04g / m 3 1.06g / m 3 1.08g / m 3 1.10g / m 3 1.12g / m 3 1.14g / m 3 1.16g / m 31.18g / m 3 1.20g / m 3 1.22g / m 3 1.24g / m 3 1.26g / m 3 1.28g / m 3 1.30g / m 3 Or it falls within the range of any two of the above values.

[0044] In some embodiments, the polymer has a specific tensile strength of a cN / dtex and a bulk density of b g / m³. 3 The polymer has an elastic modulus of c GPa, and a, b, and c satisfy: c = 0.1 * a * b. This scheme controls the elastic modulus of the polymer by setting its breaking strength and bulk density, thereby improving the elastic performance of the separator. During battery charging, the separator coating deforms under the stress of electrode expansion, absorbing the corresponding stress and avoiding defects such as electrode cracking and deformation caused by excessive reverse force of the separator on the electrode. Moreover, during battery discharge, the stress decreases, and the deformation of the separator recovers, enabling it to support the electrode structure again, maintain good lithium-ion channels, and ensure the stability of the lithium-ion channels, thus improving the battery's cycle expansion problem. At the same time, after the deformation recovers, the porosity of the porous coating further promotes the reabsorption of electrolyte by the separator, providing good lithium-ion channels and ensuring their stability.

[0045] This solution controls the porosity and tensile strength of the porous coating on the separator, which helps improve the structural stability of the porous coating, and, in conjunction with its bulk density, regulates the elastic properties of the polymer, further improving the elastic properties of the separator coating. During battery charging, the separator coating deforms under the stress of electrode expansion, absorbing the corresponding stress and preventing the electrode from cracking and deforming due to excessive reverse force exerted by the separator on the electrode. During battery discharging, the stress decreases, the deformation of the separator recovers, and it can re-support the electrode structure, maintaining good lithium-ion channels and ensuring the stability of the lithium-ion channels, thereby improving the cycle expansion of the battery.

[0046] In some embodiments, the elastic modulus of the polymer is between 6 GPa and 12 GPa.

[0047] Setting the lower limit of the polymer's elastic modulus to 6 GPa helps improve the elastic properties of the separator, causing it to absorb the stress from the expansion of the electrode and deform. During battery discharge, as the stress decreases, the separator's deformation recovers, maintaining good lithium-ion channels and thus buffering the pressure of the electrode expansion on the separator. Meanwhile, controlling the upper limit of the polymer's elastic modulus to 12 GPa reduces the reverse force of the separator on the electrode, thereby reducing defects such as electrode cracking and deformation due to internal stress, and thus improving the battery's cycle expansion problem.

[0048] For example, the elastic modulus of the polymer is 6 GPa, 6.2 GPa, 6.4 GPa, 6.6 GPa, 6.8 GPa, 7.0 GPa, 7.2 GPa, 7.4 GPa, 7.6 GPa, 7.8 GPa, 8.0 GPa, 8.2 GPa, 8.4 GPa, 8.6 GPa, 8.8 GPa, 9.0 GPa, 9.2 GPa, 9.4 GPa, 9.6 GPa, 9.8 GPa, 10.0 GPa, 10.2 GPa, 10.4 GPa, 10.6 GPa, 10.8 GPa, 11.0 GPa, 11.2 GPa, 11.4 GPa, 11.6 GPa, 11.8 GPa, 12.0 GPa, or falls within the range of any two of the above values.

[0049] In some embodiments, the elastic modulus of the polymer is any one of 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, 11 GPa, and 12 GPa.

[0050] In some embodiments, the swelling degree of the polymer is 5% to 40%.

[0051] This method does not impose any particular restrictions on the polymer swelling degree test method. Any swelling degree test method known in the prior art can be used, as long as it can achieve the purpose of this method. For example, it can include soaking in a test electrolyte at 60°C for 7 days. This method does not impose any particular restrictions on the test electrolyte. Any test electrolyte known in the prior art can be used, as long as it can test the swelling degree of the polymer.

[0052] The upper limit of polymer swelling is controlled at 40%, which can promote the formation of a "gel-like" surface of the separator. After shaping, formation and other processes, as well as external pressure during use, it forms a mechanical riveting effect with the electrode, which enhances the adhesion and reduces the risk of separator failure caused by separation from the electrode. Furthermore, the lower limit of polymer swelling is controlled at 5%, which helps to maintain the porosity of the porous coating structure of the separator while ensuring the liquid retention of the separator. This alleviates the volume expansion caused by separator swelling and ensures the stability of the lithium-ion channel.

[0053] For example, the swelling degree of the polymer is 5%, 6%, 7%, 8%, 9%, 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%, or within the range of any two of the above values.

[0054] In some embodiments, the number-average molecular weight of the polymer is from 60,000 g / mol to 120,000 g / mol.

[0055] A lower limit of the polymer's number-average molecular weight of 60,000 g / mol not only helps improve the rigidity of the porous coating on the separator and enhance its deformation recovery ability, but also facilitates achieving a higher glass transition temperature, further ensuring the separator's elastic properties, mechanical strength, and thermal stability. An upper limit of the polymer's number-average molecular weight of 120,000 g / mol helps control the separator's hardness, preventing excessive hardness from failing to buffer the expansion stress of the electrode sheets.

[0056] For example, the number average molecular weight of the polymers is 60000 g / mol, 62000 g / mol, 64000 g / mol, 66000 g / mol, 68000 g / mol, 70000 g / mol, 72000 g / mol, 74000 g / mol, 76000 g / mol, 78000 g / mol, 80000 g / mol, 82000 g / mol, 84000 g / mol, 86000 g / mol, 88000 g / mol, 90000 g / mol, 92 000g / mol, 94000g / mol, 96000g / mol, 98000g / mol, 100000g / mol, 102000g / mol, 104000g / mol, 106000g / mol, 108000g / mol, 110000g / mol, 112000g / mol, 114000g / mol, 116000g / mol, 118000g / mol, 120000g / mol, or within the range of any two of the above values.

[0057] In some embodiments, the glass transition temperature of the polymer is 260°C to 300°C.

[0058] The lower limit of the polymer's glass transition temperature is 260℃. Controlling the polymer's number-average molecular weight helps ensure its mechanical strength and thermal stability, further guaranteeing the membrane's elasticity and improving its mechanical strength, thus reducing the risk of internal short circuits caused by lithium dendrites. The upper limit of the polymer's glass transition temperature is 300℃. When the battery experiences abnormal temperature rise due to internal short circuits or other issues, the polymer can rapidly melt or soften, blocking the pores in the membrane and thus blocking ion transport, improving battery safety.

[0059] For example, the glass transition temperature of the polymer is 260°C, 261°C, 262°C, 263°C, 264°C, 265°C, 266°C, 267°C, 268°C, 269°C, 270°C, 271°C, 272°C, 273°C, 274°C, 275°C, 276°C, 277°C, 278°C, 279°C, 280°C, 281°C, 282°C, 283°C, 284°C, 285°C, 286°C, 287°C, 288°C, 289°C, 290°C, 291°C, 292°C, 293°C, 294°C, 295°C, 296°C, 297°C, 298°C, 299°C, 300°C, or falls within the range of any two of the above values.

[0060] In some embodiments, the polymer includes at least one of aromatic polyamide, polyimide, and semi-aromatic polyamide.

[0061] Aromatic polyamides possess excellent elastic properties, effectively improving the elasticity of the separator. This buffers the stress caused by electrode expansion during battery cycling, effectively mitigating battery cycling expansion. Furthermore, aromatic polyamides exhibit excellent thermal stability and mechanical strength, further enhancing the thermal stability and mechanical strength of the separator. This reduces the risk of cathode-cathode overlap and the risk of internal short circuits caused by lithium dendrites during battery cycling, thereby improving the safety of the electrochemical device. Simultaneously, the amide bonds in aromatic polyamides can increase the electrolyte affinity of the separator, further ensuring the stability of the lithium-ion channel.

[0062] Polyimide possesses excellent high-temperature resistance and shrinkage resistance, which can improve the thermal stability of the separator. Furthermore, the imide groups in its molecules can impart a certain flame-retardant effect to the separator, thereby reducing the risk of battery thermal runaway. At the same time, polyimide can regulate the pore structure of the porous coating, promoting the formation of a porous coating with uniform channels on the separator. This, combined with the increased affinity of the imide groups for the electrolyte, effectively improves the lithium-ion channels.

[0063] Semi-aromatic polyamides contain aromatic rings and aliphatic segments in their molecular backbone, exhibiting excellent thermal stability and mechanical properties. This effectively improves the thermal stability and mechanical strength of the separator, thereby reducing the risk of cathode-cathode overlap during battery cycling and the risk of internal short circuits caused by lithium dendrites. Simultaneously, semi-aromatic polyamides have low water absorption, reducing the risk of separator swelling due to water absorption.

[0064] In some embodiments, the mass ratio of polymer to binder is (5-9):(1-5).

[0065] Maintaining a polymer-to-binder mass ratio of 9:1 not only helps regulate the elastic properties of the porous coating on the separator but also improves the adhesion between the porous coating and the electrode, further reducing the risk of separator detachment from the electrode. Conversely, maintaining a polymer-to-binder mass ratio of 5:5, with increased polymer content, helps improve the separator's elastic properties and alleviates the problem of separator compression during battery cycling.

[0066] Controlling the mass ratio of polymer to binder not only helps to adjust the elastic properties of the porous coating on the diaphragm, but also helps to improve the adhesion between the porous coating on the diaphragm and the electrode, further reducing the separation of the diaphragm from the electrode.

[0067] For example, the mass ratio of polymer to binder is 5:1, 5:2, 5:3, 5:4, 5:5, 6:1, 6:2, 6:3, 6:4, 6:5, 7:1, 7:2, 7:3, 7:4, 7:5, 8:1, 8:2, 8:3, 8:4, 8:5, 9:1, 9:2, 9:3, 9:4, 9:5, or within any range of two of the above values.

[0068] In some embodiments, the glass transition temperature of the adhesive is 45°C to 115°C.

[0069] The lower limit of the glass transition temperature of the binder is 45°C. This not only improves the adhesive strength of the binder and addresses the problem of insufficient adhesion of the separator during winding and other processes, thus improving processing accuracy, but also enhances the adhesion between the separator and the electrode based on the polymer, reducing the risk of separator detachment from the electrode and thereby improving the cycle performance of the battery. Simultaneously, the polymer helps to regulate the elastic properties of the separator, alleviating the problem of separator compression during battery cycling. Furthermore, the upper limit of the glass transition temperature of the binder is 115°C, which helps to reduce the difference in glass transition temperatures between the polymer and the binder, thereby improving the compatibility between the polymer and the binder and further ensuring the improving effect of the binder.

[0070] For example, the glass transition temperature of the adhesive is 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 111°C, 112°C, 113°C, 114°C, or 115°C, or falls within a range of any two of the above values. In some embodiments, the glass transition temperature of the adhesive is 45°C to 60°C; or,

[0071] The glass transition temperature of the adhesive is 80°C to 115°C.

[0072] Controlling the glass transition temperature of the binder to 45°C to 60°C, or 80°C to 115°C, further improves the adhesive strength of the binder. This not only improves the adhesion between the separator and the electrode, reducing the risk of separation between the separator and the electrode, but also improves the adhesion during separator processing, thereby improving the assembly accuracy of the battery.

[0073] In some embodiments, the adhesive includes at least one of polyacrylic acid, polymethyl methacrylate, polyacrylonitrile, polyamide, polycarboxylic acid, polyacrylate, polyvinyl alcohol, polyvinyl acetate, cellulose acetate, cellulose acetate propionate, carboxymethyl cellulose, nitrile rubber, styrene-butadiene rubber, and latex.

[0074] Adding a binder, which combines with the polymer, helps to regulate the elastic properties of the porous coating. This alleviates the problem of the separator being squeezed, while reducing the problem of the electrode cracking and deformation caused by excessive elasticity and excessive reverse force on the electrode, thus ensuring the safety of the battery. Furthermore, the binder, based on the polymer, can further improve the adhesion between the separator and the electrode, thereby reducing the risk of the separator and the electrode detaching. At the same time, the binder helps to improve the problem of insufficient adhesion of the separator in processes such as winding, thereby improving the processing accuracy.

[0075] In some embodiments, the binder used in this scheme is crosslinkable. During the preparation of the diaphragm, the binder is crosslinked under the action of the crosslinking agent, forming a more stable crosslinked network on the porous coating skeleton of the polymer, thereby further improving the elastic properties and structural stability of the diaphragm.

[0076] In some embodiments, the thickness of the porous coating is from 0.5 μm to 4 μm.

[0077] The lower limit of the porous coating thickness is 0.5μm, which effectively improves the liquid retention of the separator, thereby improving the lithium ion channel and reducing the risk of lithium ion aggregation. The upper limit of the porous coating thickness is 4μm. Combined with the porosity of the porous coating, the rigidity of the separator is guaranteed, avoiding the separator's inability to recover from deformation, thus alleviating the problem of the separator being squeezed.

[0078] For example, the thickness of the porous coating is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3.0μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, or 4μm, or falls within the range of any two of the above values.

[0079] In some embodiments, the average pore size of the porous coating is from 0.01 μm to 0.5 μm.

[0080] The lower limit of the average pore size of the porous coating is controlled at 0.01 μm. Based on the polymer and binder, the synergistic effect of porosity and thickness not only helps to improve the structural stability of the porous coating, thus ensuring the elastic performance of the membrane, but also promotes the uniform shuttle of lithium ions through the membrane, thereby reducing the risk of lithium ion aggregation. At the same time, the upper limit of the average pore size of the porous coating is controlled at 0.5 μm, which is conducive to the rapid shuttle of ions through the membrane and improves the liquid retention of the membrane, thereby improving the lithium ion channel.

[0081] For example, the average pore size of the porous coating is 0.01μm, 0.02μm, 0.03μm, 0.04μm, 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.10μm, 0.12μm, 0.14μm, 0.16μm, 0.18μm, 0.20μm, 0.24μm, 0.26μm, 0.28μm, 0.30μm, 0.32μm, 0.34μm, 0.36μm, 0.38μm, 0.40μm, 0.42μm, 0.44μm, 0.46μm, 0.48μm, or 0.50μm, or falls within the range of any two of the above values.

[0082] In some embodiments, the pore size of the porous substrate is from 10 nm to 60 nm.

[0083] The lower limit of the pore size of the porous substrate is set to 10nm to avoid pore blockage caused by excessively small pore size, thereby ensuring the stability of lithium-ion channels and preventing conductive particles from passing through the separator, thus reducing the risk of short circuits in the battery. The upper limit of the pore size of the porous substrate is set to work in conjunction with the porous coating to increase the number of lithium-ion channels on the basis of polymer and binder, thereby improving the ion transport efficiency of the separator and reducing the risk of lithium-ion aggregation.

[0084] For example, the pore size of the porous substrate is 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm, 50nm, 52nm, 54nm, 56nm, 58nm, 60nm, or within any two of the above values.

[0085] In some embodiments, the thickness of the diaphragm is from 3 μm to 20 μm.

[0086] The lower limit of the separator thickness is set at 3μm. Combined with the porous coating, the separator's liquid retention is ensured while maintaining its mechanical strength, thereby reducing the risk of lithium dendrites piercing the separator and thus reducing the risk of anode-cathode overlap. Meanwhile, the upper limit of the separator thickness is set at 20μm, which is beneficial to improving the lithium-ion conduction speed and thus improving the battery's charge and discharge efficiency.

[0087] For example, the thickness of the diaphragm is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or within any two of the above values.

[0088] In some embodiments, the porous substrate includes: a base film, and / or a ceramic layer disposed on at least one surface of the base film.

[0089] In some embodiments, the base film includes at least one of polyolefin base film, polyester base film, polyamide base film, cellulose base film, polyester base film, and halogenated polymer base film.

[0090] In some embodiments, the base film includes at least one of polyethylene, polypropylene, polyethylene-polypropylene copolymer, polyethylene-polypropylene-polyethylene copolymer, cellulose, polyamide, polyimide, polyester, polyacetal, polyethylene terephthalate, polycarbonate, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate.

[0091] This solution does not impose any particular restrictions on the base film, which can be any base film known in the prior art, as long as it can achieve the purpose of this solution. For example, it can include, but is not limited to, at least one of the base films mentioned above.

[0092] In some embodiments, the ceramic layer includes at least one of alumina, zirconium oxide, silicon dioxide, boehmite, and titanium dioxide.

[0093] This solution does not impose any particular restrictions on the ceramic layer, which can be any ceramic layer known in the prior art, as long as it can achieve the purpose of this solution. For example, it can include, but is not limited to, at least one of the ceramic layers mentioned above.

[0094] This solution does not impose any particular restrictions on the preparation method of the diaphragm. It can be any diaphragm preparation method known in the prior art, as long as it can achieve the purpose of this solution. For example, the diaphragm prepared by this solution can be obtained by using pore-forming agents, phase separation, etc.

[0095] In some embodiments, the method for preparing the diaphragm includes the following steps:

[0096] The polymer, binder, and solvent are mixed to obtain a coating slurry;

[0097] A diaphragm is obtained by coating at least one side of a porous substrate with a coating slurry, followed by coagulation bath and drying.

[0098] This method involves applying a coating slurry, followed by a coagulation bath to allow aromatic polyamides and binders to precipitate and solidify, thereby stably forming a porous coating on a porous substrate and obtaining the diaphragm provided by this method.

[0099] This solution does not impose any particular restrictions on the coating method of the coating slurry. It can be any coating method known in the prior art, as long as it can achieve the purpose of this solution. For example, it can include, but is not limited to, brushing, spraying, dipping and coating methods.

[0100] In some embodiments, the solvent includes at least one selected from dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylacetamide, dimethyl sulfoxide, and dichloromethane.

[0101] This solution does not have any particular restrictions on solvents, as long as they can achieve the purpose of this solution. For example, it may include, but is not limited to, at least one of the solvents mentioned above.

[0102] In some embodiments, the coagulation bath is carried out in a mixture of water and solvent; the mass concentration of the solvent is greater than 0% and less than or equal to 20% based on the mass of water.

[0103] A solvent mass concentration greater than 0% facilitates rapid exchange between the solvent in the coating slurry and the mixture in the coagulation bath, thereby improving preparation efficiency. Furthermore, a solvent mass concentration less than or equal to 20% helps to form a porous coating with uniform and numerous pores on the diaphragm and ensures the structural stability of the porous coating, thus guaranteeing the elastic properties of the diaphragm.

[0104] For example, the mass concentration of the solvent is 0.01%, 0.10%, 0.20%, 0.40%, 0.60%, 0.80%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%, 5.5%, 6.00%, 6.50%, 7.00%, 7.50%, 8.00%, 8.50%, 9.00%, 9.50%, or 10.00%. 10.50%, 11.00%, 11.50%, 12.00%, 12.50%, 13.00%, 13.50%, 14.00%, 14.50%, 15.00%, 15.50%, 16.00%, 16.50%, 17.00%, 17.50%, 18.00%, 18.50%, 19.00%, 19.50%, 20.00%, or within the range of any two of the above values.

[0105] This method does not impose any particular restrictions on the concentration of the solvent in the coagulation bath, as long as the purpose of this method can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned solvent concentrations.

[0106] This solution also provides an electrochemical device, which includes a diaphragm.

[0107] The electrochemical devices provided in this solution include any device that performs an electrochemical reaction to convert chemical energy into electrical energy, including but not limited to all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors.

[0108] In some embodiments, the electrochemical device includes a lithium secondary battery;

[0109] Lithium secondary batteries include lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0110] In some embodiments, the electrochemical device includes an electrolyte, a positive electrode, and a negative electrode.

[0111] In some embodiments, the electrolyte includes at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0112] In some embodiments, the liquid electrolyte includes a non-aqueous solvent;

[0113] Non-aqueous solvents include at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0114] In some embodiments, the carbonate compound may include at least one of diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butyl carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0115] This scheme does not have any particular restrictions on carbonate compounds, as long as they can achieve the purpose of this scheme, such as including but not limited to at least one of the carbonate compounds mentioned above.

[0116] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0117] This scheme does not have any particular restrictions on carboxylic acid ester compounds, as long as they can achieve the purpose of this scheme, such as including but not limited to at least one of the above-mentioned carboxylic acid ester compounds.

[0118] In some embodiments, the ether compound may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0119] This scheme does not have any particular restrictions on ether compounds, as long as they can achieve the purpose of this scheme, such as including but not limited to at least one of the above-mentioned ether compounds.

[0120] In some embodiments, the non-aqueous solvent includes at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0121] This method does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this method. For example, it may include, but is not limited to, at least one of the non-aqueous solvents mentioned above. The use of non-aqueous solvents is unrestricted, as long as they can serve as a medium to facilitate the movement of ions participating in the electrochemical reaction of the battery.

[0122] In some embodiments, the liquid electrolyte includes lithium salts;

[0123] Lithium salts may include at least one of LiPF6, LiBF4, LiBOB, LiB(C6H5)4, LiB(C2O4)2, LiAsF6, LiCl, LiClO4, LiCH3SO3, LiCF3SO3, LiC4F9SO3, LiC(SO2CF3)3, LiN(SO2CF3)2, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiSiF6, LiSbF6, LiAlO4, LiAlCl4, LiI, and lithium difluoroborate.

[0124] This scheme does not impose any particular restrictions on lithium salts, as long as they can achieve the purpose of this scheme. For example, it may include, but is not limited to, at least one of the lithium salts mentioned above. The use of lithium salts is unrestricted, as long as they can participate in the ion movement of the battery electrochemical reaction.

[0125] This solution does not impose any particular restrictions on the electrolyte; it can be any electrolyte known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the electrolytes mentioned above.

[0126] In some embodiments, the positive electrode includes a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0127] In some implementations, the positive current collector includes a positive metal foil or a composite positive current collector.

[0128] In some implementations, the positive electrode metal foil includes aluminum foil.

[0129] This solution does not impose any particular restrictions on the positive electrode metal foil, which can be any positive electrode metal foil known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the above-mentioned positive electrode metal foils.

[0130] In some embodiments, the composite positive current collector includes a metal foil and a conductive layer disposed on at least one side of the metal foil;

[0131] The conductive layer includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0132] This solution does not impose any particular limitation on the conductive layer, which can be any conductive layer known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the conductive layers mentioned above.

[0133] This solution does not impose any particular restrictions on the composite positive electrode current collector, which can be any composite positive electrode current collector known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, the composite positive electrode current collector mentioned above.

[0134] This solution does not impose any particular restrictions on the positive electrode current collector, which can be any positive electrode current collector known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, the positive electrode current collector mentioned above.

[0135] In some embodiments, the positive electrode active material layer includes a positive electrode active material;

[0136] The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminate.

[0137] This solution does not impose any particular restrictions on the positive electrode active material. It can be any positive electrode active material known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the above-mentioned positive electrode active materials.

[0138] In some embodiments, the positive electrode active material includes a dopant;

[0139] The dopant includes at least one of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, and Ge.

[0140] This solution does not impose any particular restrictions on the dopant, which can be any dopant known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the dopants mentioned above.

[0141] In some embodiments, the positive electrode active material layer includes a positive electrode binder;

[0142] The positive electrode binder includes at least one of polyvinylidene fluoride, poly(vinylidene fluoride)-hexafluoropropylene, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone, acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer.

[0143] This solution does not impose any particular restrictions on the positive electrode binder, which can be any positive electrode binder known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the positive electrode binders mentioned above.

[0144] In some embodiments, the positive electrode active material layer includes a conductive agent;

[0145] The positive electrode conductive agent includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0146] This solution does not impose any particular restrictions on the positive electrode conductive agent, which can be any positive electrode conductive agent known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the positive electrode conductive agents mentioned above.

[0147] In some embodiments, the positive electrode active material layer includes additives.

[0148] In some implementations, the additives include thickeners;

[0149] Thickeners include at least one of cellulose thickeners, acrylate thickeners, and polyurethane thickeners.

[0150] In some embodiments, the thickener includes at least one of sodium carboxymethyl cellulose, sodium hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylpyrrolidone.

[0151] This solution does not impose any particular restrictions on the thickener, which can be any thickener known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the thickeners mentioned above.

[0152] In some implementations, the additives include dispersants;

[0153] Dispersants include surfactant dispersants and / or polymeric dispersants.

[0154] In some embodiments, the dispersant includes at least one of polyvinylpyrrolidone, polyoxyethylene ether, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium lignosulfonate, polyacrylic acid, polymethacrylic acid, sodium polystyrene sulfonate, and sodium carboxymethyl cellulose.

[0155] This solution does not impose any particular limitation on the dispersant, which can be any dispersant known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the dispersants mentioned above.

[0156] This solution does not impose any particular restrictions on additives, which can be any additives known in the prior art, as long as they can achieve the purpose of this application. For example, they can include, but are not limited to, at least one of the additives mentioned above.

[0157] This solution does not impose any particular restrictions on the positive electrode active material layer. It can be any positive electrode active material layer known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the above-mentioned positive electrode active material layers.

[0158] This solution does not impose any particular restrictions on the positive electrode, which can be any positive electrode known in the prior art, as long as it can achieve the purpose of this application, such as including but not limited to the positive electrode mentioned above.

[0159] In some embodiments, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on at least one side of the negative electrode current collector.

[0160] In some embodiments, the negative electrode current collector includes a negative electrode metal foil or a composite negative electrode current collector.

[0161] In some implementations, the negative electrode metal foil includes copper foil.

[0162] In some embodiments, the composite negative electrode current collector includes a negative electrode metal foil and a negative electrode conductive layer disposed on at least one side of the negative electrode metal foil.

[0163] This solution does not impose any particular limitation on the metal foil; it can be any metal foil known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, the metal foils mentioned above. This solution also does not impose any particular limitation on the conductive layer of the composite negative electrode current collector; it can be any conductive layer known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the conductive layers mentioned above.

[0164] This solution does not impose any particular restrictions on the negative electrode current collector, which can be any negative electrode current collector known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrode current collectors mentioned above.

[0165] In some embodiments, the negative electrode active material layer includes a negative electrode active material;

[0166] The negative electrode active material includes at least one of the following: natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres, Sn, SnO2, SnO, Li4Ti5O12, Si materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon-oxygen composite materials.

[0167] This solution does not impose any particular restrictions on the negative electrode active material. It can be any negative electrode active material known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrode active materials mentioned above.

[0168] In some embodiments, the negative electrode active material layer includes a negative electrode binder;

[0169] The negative electrode binder includes at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene.

[0170] This solution does not impose any particular restrictions on the negative electrode binder, which can be any negative electrode binder known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrode binders mentioned above.

[0171] In some embodiments, the negative electrode active material layer includes a negative electrode conductive agent.

[0172] This solution does not impose any particular limitation on the negative electrode conductive agent, which can be any negative electrode conductive agent known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrode conductive agents mentioned above.

[0173] In some embodiments, the negative electrode active material layer includes additives.

[0174] In some embodiments, the additives include thickeners; the additives include dispersants.

[0175] This solution does not impose any particular restrictions on the additives used in the negative electrode active material layer. Any additive known in the prior art can be used, as long as it achieves the purpose of this application. For example, it may include, but is not limited to, at least one of the additives mentioned above. Similarly, this solution does not impose any particular restrictions on the thickeners used in the negative electrode active material layer. Any thickener known in the prior art can be used, as long as it achieves the purpose of this application. For example, it may include, but is not limited to, at least one of the thickeners mentioned above. Finally, this solution does not impose any particular restrictions on the dispersants used in the negative electrode active material layer. Any dispersant known in the prior art can be used, as long as it achieves the purpose of this application. For example, it may include, but is not limited to, at least one of the dispersants mentioned above.

[0176] This solution does not impose any particular restrictions on the negative electrode active material layer. It can be any negative electrode active material layer known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrode active material layers mentioned above.

[0177] This solution does not impose any particular restrictions on the negative electrode, which can be any negative electrode known in the prior art, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of the negative electrodes mentioned above.

[0178] This solution also provides an electronic device, which includes any of the electrochemical devices described herein.

[0179] The electronic device in this solution is not particularly limited and can be any electronic device known in the prior art. The electrochemical device in this solution is not particularly limited in its application and can be used with any electronic device known in the prior art. According to some embodiments of this solution, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, and android robots.

[0180] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the reagents used, unless otherwise specified, are commercially available reagents and materials. The source information of the raw materials used in the following examples and comparative examples is for illustrative purposes only and does not constitute any restriction on the procurement of raw materials. Those skilled in the art will know that the relevant raw materials can be obtained through other commercial channels or prepared by conventional methods in the art.

[0181] Example 1

[0182] 1. Preparation of the diaphragm:

[0183] Preparation of polymer and binder: The aromatic polyamide has a breaking strength of 97 cN / dtex and a bulk density of 1.02 g / m³. 3 The elastic modulus is 9.9 GPa, the swelling degree is 8%, the number average molecular weight is 100,000 g / mol, and the glass transition temperature is 279℃; the glass transition temperature of acrylic acid is 45℃; the porous substrate is a porous polyethylene film with an alumina ceramic layer on one side, and the thickness of the porous substrate is 7 μm and the pore size is 30 nm.

[0184] Aromatic polyamide and acrylic acid were mixed at a mass ratio of 7:3 and dispersed in N-methyl-2-pyrrolidone to obtain a coating slurry with a solid content of 5%. The coating slurry was coated on one side of the ceramic layer of a porous substrate, and then coagulated in a coagulation bath with a mass concentration of greater than 0% and less than or equal to 20% N-methyl-2-pyrrolidone. The coagulation bath temperature was set at 20-40°C and the time was 10-30s. Then it was dried at 85°C to obtain a diaphragm.

[0185] The porosity of the porous coating on the diaphragm was tested using the following method: The apparent volume of both the diaphragm and the porous substrate was measured and denoted as V. 隔膜 V 基材 Then, the true volume of the diaphragm and the porous substrate of the diaphragm was measured sequentially using an HX-TD type true density meter, and recorded as V. 真隔膜 and V 真基材 ; via V 涂层 =V 隔膜 -V 基材 V 真涂层 =V 真隔膜 -V 真基材 Then, through porosity (%) = (1-V) 真涂层 / V 涂层 )*100, calculate the porosity of the porous coating.

[0186] 2. Preparation of the positive electrode:

[0187] Lithium cobalt oxide, conductive agent SuperP, and binder polyvinylidene fluoride, with a mass ratio of 96:2:2, were thoroughly mixed in N-methylpyrrolidone to obtain a positive electrode slurry. The positive electrode slurry was coated onto a current collector aluminum foil and then dried at 85°C. Subsequently, it was cold-pressed, trimmed, and slit in sequence, and then dried under vacuum at 85°C for 6 hours. The tabs were then welded to obtain the positive electrode.

[0188] 3. Preparation of the negative electrode:

[0189] A negative electrode slurry was prepared by thoroughly mixing artificial graphite (anode active material), SuperP (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) in deionized water at a mass ratio of 98:0.5:1:0.5. The negative electrode slurry was coated onto copper foil (anode current collector), dried, cold-pressed, slit, and dried under vacuum at 85°C for 6 hours. The tabs were then welded to obtain the negative electrode.

[0190] 4. Electrolyte:

[0191] It is composed of an organic solvent and lithium hexafluorophosphate; the organic solvent is a mixture of ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate in a mass ratio of 1:1:1; the concentration of lithium hexafluorophosphate is 1 mol / L.

[0192] 5. Preparation of lithium-ion secondary batteries:

[0193] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound to form the final electrode assembly. This assembly is placed in a packaging shell, infused with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0194] Example 2

[0195] The difference between Example 2 and Example 1 is:

[0196] The aromatic polyamide has a breaking specific strength of 60 cN / dtex and an elastic modulus of 6.1 GPa;

[0197] The rest are as described in Example 1.

[0198] Example 3

[0199] The difference between Example 3 and Example 1 is:

[0200] The aromatic polyamide has a breaking specific strength of 120 cN / dtex and an elastic modulus of 12.2 GPa;

[0201] The rest are as described in Example 1.

[0202] Example 4

[0203] The difference between Example 4 and Example 1 is:

[0204] The bulk density of aromatic polyamide is 0.9 g / m³. 3 The elastic modulus is 8.7 GPa;

[0205] The rest are as described in Example 1.

[0206] Example 5

[0207] The difference between Example 5 and Example 1 is:

[0208] The bulk density of aromatic polyamide is 1.3 g / m³. 3 The elastic modulus is 12.6 GPa;

[0209] The rest are as described in Example 1.

[0210] Example 6

[0211] The difference between Example 6 and Example 1 is:

[0212] The porosity of the porous coating is 60%;

[0213] The rest are as described in Example 1.

[0214] Example 7

[0215] The difference between Example 7 and Example 1 is:

[0216] The porosity of the porous coating is 80%;

[0217] The rest are as described in Example 1.

[0218] Example 8

[0219] The difference between Example 8 and Example 1 is:

[0220] The swelling degree of aromatic polyamide is 5%;

[0221] The rest are as described in Example 1.

[0222] Example 9

[0223] The difference between Example 9 and Example 1 is:

[0224] The swelling degree of aromatic polyamide is 40%;

[0225] The rest are as described in Example 1.

[0226] Example 10

[0227] The difference between Example 10 and Example 1 is:

[0228] The number-average molecular weight of aromatic polyamides is 60,000 g / mol;

[0229] The rest are as described in Example 1.

[0230] Example 11

[0231] The difference between Example 11 and Example 1 is:

[0232] The molecular weight of aromatic polyamide is 120,000 g / mol;

[0233] The rest are as described in Example 1.

[0234] Example 12

[0235] The difference between Example 12 and Example 1 is:

[0236] The glass transition temperature of aromatic polyamides is 260℃;

[0237] The rest are as described in Example 1.

[0238] Example 13

[0239] The difference between Example 13 and Example 1 is:

[0240] The glass transition temperature of aromatic polyamides is 300℃;

[0241] The rest are as described in Example 1.

[0242] Example 14

[0243] The difference between Example 14 and Example 1 is:

[0244] The mass ratio of aromatic polyamide to acrylic acid is 5:5;

[0245] The rest are as described in Example 1.

[0246] Example 15

[0247] The difference between Example 15 and Example 1 is:

[0248] The mass ratio of aromatic polyamide to acrylic acid is 9:1;

[0249] The rest are as described in Example 1.

[0250] Example 16

[0251] The difference between Example 16 and Example 1 is:

[0252] The glass transition temperature of acrylic acid is 60°C.

[0253] The rest are as described in Example 1.

[0254] Example 17

[0255] The difference between Example 17 and Example 1 is:

[0256] Replace acrylic acid with nitrile rubber, which has a glass transition temperature of 115°C;

[0257] The rest are as described in Example 1.

[0258] Comparative Example 1

[0259] The difference between Comparative Example 1 and Example 1 is as follows:

[0260] The aromatic polyamide has a breaking strength of 50 cN / dtex and an elastic modulus of 5.1 GPa;

[0261] The rest are as described in Example 1.

[0262] Comparative Example 2

[0263] The difference between Comparative Example 2 and Example 1 is as follows:

[0264] The aromatic polyamide has a breaking strength of 135 cN / dtex and an elastic modulus of 13.8 GPa;

[0265] The rest are as described in Example 1.

[0266] Comparative Example 3

[0267] The difference between Comparative Example 3 and Example 1 is as follows:

[0268] The aromatic polyamide has a tensile strength of 60 cN / dtex and a bulk density of 0.8 g / m³. 3 The elastic modulus is 4.8 GPa;

[0269] The rest are as described in Example 1.

[0270] Comparative Example 4

[0271] The difference between Comparative Example 4 and Example 1 is as follows:

[0272] The bulk density of aromatic polyamide is 1.5 g / m³. 3 The elastic modulus is 14.6 GPa;

[0273] The rest are as described in Example 1.

[0274] Comparative Example 5

[0275] The difference between Comparative Example 5 and Example 1 is as follows:

[0276] The porosity of the porous coating is 50%;

[0277] The rest are as described in Example 1.

[0278] Comparative Example 6

[0279] The difference between Comparative Example 6 and Example 1 is as follows:

[0280] The porosity of the porous coating is 86%;

[0281] The rest are as described in Example 1.

[0282] Test method:

[0283] 1. Liquid retention coefficient: Record the mass of the separator membrane, denoted as W. 初After assembling the separator into a battery, it was subjected to constant current discharge at a rate of 0.7C and a cutoff voltage of 3V, followed by full charging. The battery was then disassembled, and the separator and electrodes were removed. The separator was centrifuged at 3000 rpm for 10 minutes to remove free electrolyte, and the mass of the separator was recorded as W. 保液 According to the formula: Liquid retention coefficient = W 保液 *100% / W 初 Calculate the liquid retention coefficient of the separating membrane.

[0284] 2. Battery expansion rate: After assembling the separator into a battery, the thickness change before and after 500 battery cycles is measured and recorded as H. 初 and H 后 According to the formula: Battery expansion rate = 100% * (H 后 -H 初 ) / H 初 The battery expansion rate is calculated. The thickness test steps include: placing the battery with the pitted side facing up in the center of the PPG-10083MD thickness gauge, with the top edge of the battery flush with the edge of the lower pressure plate of the PPG-10083MD thickness gauge, inputting the set pressure (600g in this case), and then testing the battery thickness.

[0285] 3. Cycle capacity retention: After assembling the separator into a battery, it is charged at 0.1C rate in an environment of 25℃ until the upper limit voltage is 4.3V, and then discharged at constant current rate of 1C until the final voltage is 3V. The discharge capacity of the first cycle is recorded as C1; after repeating the charge-discharge cycle 500 times, the discharge capacity of the 500th cycle is recorded as C. 500 Repeat the test on C1 and C of five batteries respectively. 500 And calculate C respectively 500 *100% / C1, take the average value as the battery's cycle capacity retention rate.

[0286] 4. Degree of Lithium Plaque: After assembling the separator into a battery, charge it at 1.5C rate in an environment of 25℃ until the upper limit voltage is 4.3V, and then discharge it at a constant current rate of 1C until the final voltage is 3V. After repeating the charge-discharge cycle 500 times, disassemble the battery and observe the condition of the negative electrode interface to determine the degree of lithium plaque. Excellent: No lithium deposition at the negative electrode interface; Good: Lithium deposition area greater than 0 and less than 10% at the negative electrode interface; Significant lithium plaque: Lithium deposition area between 10% and 30% at the negative electrode interface; Severe lithium plaque: Lithium deposition area greater than 30% at the negative electrode interface.

[0287] Some process parameters of Examples 1 to 17 and Comparative Examples 1 to 6 are shown in Table 1.

[0288] Table 1. Partial process parameters of Examples 1-17 and Comparative Examples 1-6

[0289]

[0290]

[0291]

[0292] According to the above test methods, the performance of the membranes prepared in Examples 1 to 17 and Comparative Examples 1 to 6 were tested respectively; the performance data of Examples 1 to 17 and Comparative Examples 1 to 6 are shown in Table 2.

[0293] Table 2. Performance data of Examples 1-17 and Comparative Examples 1-6

[0294]

[0295]

[0296] From Table 1 and Table 2, we can see that:

[0297] The separator prepared in Example 1 exhibited the best performance, with a liquid retention coefficient of 1.34, a battery expansion rate of 7.0%, a cycle retention rate of 92.4%, and excellent battery performance after cycling, without lithium plating.

[0298] Based on Examples 1 to 5, when the elastic modulus of the polymer was altered by controlling its fracture specific strength and bulk density, the cycle capacity retention was 91.2%–92.4%, and the battery expansion rate was 5.7%–9.3%. In contrast, Comparative Examples 1 to 4 showed a cycle capacity retention of 85.3%–86.9%, a battery expansion rate of 10.8%–15.8%, and severe lithium plating, resulting in poor performance. This verifies that a polymer with a suitable elastic modulus is beneficial for buffering the stress of electrode expansion and supporting the electrode, maintaining the stability of ion channels, thereby reducing the risk of battery cycle expansion and lithium plating.

[0299] Referring to Examples 6, 7, and 1, increasing the porosity of the porous coating on the separator improved the liquid retention coefficient from 1.34 to 1.27 and 1.36, indicating that it helps improve the liquid retention of the separator, with a cycle capacity retention rate of 91.3%–92.4% and a battery expansion rate of 7.0%–8.4%. In contrast, Comparative Examples 5 and 6, with porosities adjusted to 50% and 86%, respectively, saw their liquid retention coefficients decrease to 1.14 and 1.25, respectively, their cycle capacity retention rates drop to 84.2% and 85.6%, respectively, and their battery expansion rates increase to 11.4% and 13.5%, respectively, with severe lithium plating also occurring. This verifies that a porous coating with suitable porosity helps improve the elastic properties of the separator and maintains its pore rigidity, allowing the separator to buffer the pressure of electrode expansion during battery charging and recover its deformation during battery discharge, supporting the electrode structure, thereby improving the stability of the lithium-ion channel and effectively improving battery cycle expansion, cycle life, and lithium plating issues.

[0300] Referring to Examples 8, 9, and 1, the polymer swelling degree was reduced from 40% to 5%, and the liquid retention coefficient was increased slightly from 1.26 to 1.33. This demonstrates that the polymer with low swelling degree helps improve the liquid retention of the separator. Furthermore, the battery swelling rate decreased from 9.1% to 6.1%, the cycle capacity retention rate increased slightly from 89.7% to 91.9%, and the degree of lithium plating improved from good to excellent. This further verifies that the polymer with low swelling degree helps improve the structural stability of the porous coating of the separator, maintain the stability of the lithium-ion channels, thereby suppressing battery cycle swelling, reducing the risk of lithium plating, and improving the cycle life of the battery.

[0301] Referring to Examples 10, 11, and 1, the number-average molecular weight of the polymer was adjusted from 60,000 g / mol and 120,000 g / mol to 100,000 g / mol. The battery expansion rate changed from 9.3% and 7.8% to 7.0%, the cycle capacity retention rate slightly increased from 91.6% and 90.2% to 92.4%, and the degree of lithium plating after cycling improved from good to excellent. This indicates that a polymer with a suitable number-average molecular weight helps to improve the elastic properties of the separator, buffer the expansion stress of the electrode, and improve the stability of the lithium-ion channel, thereby reducing the risk of battery expansion and improving the cycle life of the battery.

[0302] Based on Examples 12 to 17 and Example 1, the battery expansion rate was 6.2% to 8.3%, and the cycle capacity retention rate was 89.9% to 92.4%. This demonstrates that appropriately controlling the glass transition temperature of the polymer and binder, as well as the ratio of the polymer and binder, allows the polymer and binder to work together to improve the elasticity and adhesion of the porous coating of the separator. This can alleviate and suppress the expansion of the electrode, effectively reduce the battery expansion rate, and improve the battery cycle life.

[0303] The above description is only a part or preferred embodiment of this application. Those skilled in the art should understand that the above embodiments should not be construed as limiting the scope of protection of this application. All equivalent structural transformations made using the content of this application specification under the overall concept of this application, or direct / indirect applications in other related technical fields, are included within the scope of protection of this application.

Claims

1. A diaphragm for use in an electrochemical device, characterized in that, The diaphragm includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate, wherein the porosity of the porous coating is 60% to 80%. Furthermore, the porous coating comprises a polymer with a tensile strength of a cN / dtex and a bulk density of bg / m³. 3 The polymer has an elastic modulus of c GPa, and a, b, and c satisfy: c = 0.1 a b; Where 60≤a≤120, 0.9≤b≤1.3; The elastic modulus of the polymer is 6 GPa to 12 GPa; The polymer includes at least one of aromatic polyamide, polyimide, and semi-aromatic polyamide.

2. The diaphragm according to claim 1, characterized in that, The swelling degree of the polymer is 5% to 40%.

3. The diaphragm according to claim 1, characterized in that, The number-average molecular weight of the polymer is between 60,000 g / mol and 120,000 g / mol.

4. The diaphragm according to claim 3, characterized in that, The polymer has a glass transition temperature of 260°C to 300°C.

5. The diaphragm according to claim 1, characterized in that, The porous coating includes an adhesive, wherein the mass ratio of the polymer to the adhesive is (5~9):(1~5).

6. The diaphragm according to claim 5, characterized in that, The glass transition temperature of the adhesive is 45℃~115℃.

7. An electrochemical device, characterized in that, The electrochemical device includes a diaphragm according to any one of claims 1 to 6.

8. An electronic device, characterized in that, The electronic device includes the electrochemical device according to claim 7.

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