A diaphragm for improving polarization discharge of a lithium battery and a preparation method thereof

Abstract

The application discloses a kind of diaphragms, the diaphragm includes base film, and in the direction away from base film, in the at least one side of base film is sequentially provided with heat insulation coating and bonding coating, the slurry raw material of the heat insulation coating includes inorganic ceramic particles, the slurry raw material of the bonding coating includes conductive agent, PVDF.The application adds the mutual cooperation between conductive agent and PVDF in the slurry of bonding coating, to facilitate the improvement of the bonding force of bonding coating, while constructing ion transmission channel, it is favorable to the improvement of the electrical performance and safety performance of battery.The composite diaphragm of the application is favorable to improve the heat resistance of diaphragm, to improve the safety performance of battery.The cooperation between each substance in the slurry of heat insulation coating and bonding coating in the application, to obtain the slurry of uniform texture.And enhance the liquid retention and wettability of diaphragm, to prolong the cycle life of battery, in 3C charge and discharge field has greater effect.

Description

Technical Field

[0001] This invention relates to the field of battery separators, specifically to a separator that enhances the polarization discharge of lithium batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries have high energy density and high output power, can be repeatedly charged and discharged, and have no memory effect. They have become an ideal portable energy storage device and power source in people's lives.

[0003] In existing lithium battery technologies, the battery separator isolates the positive and negative electrodes, thereby reducing internal short circuits caused by contact between the positive and negative electrodes and improving battery safety. However, current technologies often use adhesives to bond the separator to the positive and negative electrodes. During battery cycling, rising temperatures can cause the separator to shrink, leading to contact between the positive and negative electrodes and causing an internal short circuit, thus reducing battery safety. Secondly, the use of adhesives hinders lithium-ion transport between the positive electrode and the separator, preventing the lithium-ion diffusion rate from matching the electrochemical reaction rate within the battery. This can lead to battery polarization, negatively impacting electrical performance. Thirdly, the adhesive strength of the adhesive decreases during battery cycling due to rising temperatures, directly contributing to a decline in battery safety. Summary of the Invention

[0004] In existing technologies, PVDF (polyvinylidene fluoride) is commonly used as a binder material for membranes due to its excellent chemical resistance and oxidation resistance. PVDF is a semi-crystalline polymer; its high crystallinity results in strong adhesion, but also leads to poor wettability with the electrolyte, resulting in lower lithium-ion transport capacity. Balancing the high adhesion of the membrane with lithium-ion conduction is a crucial issue that requires attention in current technologies.

[0005] This invention addresses the problems in the prior art by disclosing a separator for improving polarization discharge in lithium batteries and its preparation method. The battery separator of this invention constructs a lithium-ion transport channel between the positive electrode and the separator, which is beneficial to improving the migration speed of lithium ions and reducing the decline in electrical performance caused by battery polarization. Furthermore, the battery separator of this invention has better heat insulation performance and adhesion, thereby overcoming the decline in battery safety performance caused by separator shrinkage and detachment of the positive or negative electrode from the separator during battery cycling.

[0006] This invention is achieved through the following technical solution:

[0007] The present invention provides a diaphragm, the diaphragm comprising a base membrane, and in a direction away from the base membrane, a heat-insulating coating and an adhesive coating are sequentially disposed on at least one side of the base membrane, the slurry raw material of the heat-insulating coating comprising inorganic ceramic particles, and the slurry raw material of the adhesive coating comprising a conductive agent and PVDF.

[0008] The present invention features a heat-insulating coating and an adhesive coating on the base film of the battery separator. Firstly, the adhesive coating includes a conductive agent and PVDF. The conductive agent forms ion transport channels within the adhesive coating, while PVDF enhances the adhesion between the heat-insulating coating and the positive / negative electrode sheets, thereby improving the ion transport capacity of the battery separator while maintaining its adhesion. Secondly, the inorganic ceramic particles in the heat-insulating coating improve the battery's heat insulation performance, preventing shrinkage of the battery separator due to heat during battery cycling, thus improving the safety performance of the battery separator. Furthermore, the inorganic ceramic particles in the heat-insulating coating can also insulate the conductive properties of the conductive agent, reducing the occurrence of short circuits. The synergy between the heat-insulating coating and the adhesive coating not only improves the adhesion between the separator and the positive or negative electrode but also promotes lithium-ion transport, thereby enhancing the battery's safety and electrical performance.

[0009] As a further embodiment, the slurry raw materials for the heat-insulating coating also include a first wetting agent and a first binder. By mass, the ratio of the inorganic ceramic particles, the first wetting agent, and the first binder is (5-30 parts):(0.5-10 parts):(3-5 parts). The first wetting agent increases the wettability of the inorganic ceramic particles, thereby facilitating the dispersion of the inorganic ceramic particles in the slurry for the heat-insulating coating. The first binder can bind the inorganic ceramic particles in the slurry, thus improving the adhesion of the heat-insulating coating. Furthermore, it also improves the adhesion between the heat-insulating coating and the base film and the adhesive coating.

[0010] As a further embodiment, the slurry raw materials for the adhesive coating also include a second wetting agent and a second binder. By mass, the ratio of the conductive agent, the second wetting agent, the second binder, and PVDF is (0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts). The second wetting agent improves the wettability of the conductive agent, thereby facilitating its dispersion in the slurry to construct ion transport pathways. The synergistic effect of the second binder and PVDF increases the adhesion between the adhesive coatings and also enhances the adhesion between the adhesive coating and the heat insulation coating and the positive or negative electrode, thus helping to balance the technical problem of imbalance between adhesion and ion transport.

[0011] As a further embodiment, the first wetting agent and the second wetting agent include one or more of the following: acid ester wetting agents, ether wetting agents, monohydroxy alcohol wetting agents, polyhydroxy alcohol wetting agents, alkyl sulfate wetting agents, sulfone wetting agents, and sulfonate wetting agents. The first wetting agent and the second wetting agent may be the same or different.

[0012] As a further improvement, the first wetting agent includes a polyhydroxy alcohol wetting agent. The polyhydroxy structure in the polyhydroxy alcohol wetting agent can more easily adsorb onto the surface of the inorganic ceramic particles, thereby improving the wettability of the inorganic ceramic particles.

[0013] As a further improvement, the second wetting agent includes an alkyl sulfate wetting agent. Alkyl sulfate wetting agents can adsorb onto the surface of the conductive agent, thereby improving the wettability of the conductive agent; and the alkyl group can enhance the dispersion of the conductive agents. PVDF has lone pairs of electrons, while the sulfate ions in alkyl sulfate wetting agents are electron-deficient, promoting the interaction between PVDF and alkyl sulfate wetting agents, which is beneficial for improving the texture of the slurry.

[0014] As a further embodiment, the ester wetting agent includes methyl acrylate.

[0015] As a further embodiment, the ether wetting agent includes one or more of dodecylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

[0016] As a further embodiment, the monohydroxy alcohol wetting agent includes one or more of ethanol, n-butanol, and isobutanol.

[0017] As a further embodiment, the polyhydroxy alcohol wetting agent includes one or more of propylene glycol, glycerin, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and trimethylolpropane.

[0018] As a further embodiment, the alkyl sulfate wetting agent includes sodium dodecyl sulfate.

[0019] As a further embodiment, the sulfone-based wetting agent includes dimethyl sulfoxide.

[0020] As a further embodiment, the sulfonate wetting agent includes sodium dodecyl sulfonate.

[0021] As a further embodiment, the first adhesive and the second adhesive include one or more of the following: carboxymethylated cellulose derivative adhesives, polyester adhesives, rubber adhesives, polysaccharide adhesives, polyol adhesives, and amino ester adhesives. The first adhesive and the second adhesive may be the same or different.

[0022] As a further embodiment, the first adhesive comprises a polyester adhesive. Polyester adhesives have a more stable structure, allowing for better bonding of ceramic particles in the thermal insulation coating. Furthermore, the hydroxyl groups of the ester groups in the polyester adhesive better complement the fluorine in the PVDF of the adhesive coating, thereby improving the bond strength between the thermal insulation coating and the adhesive coating.

[0023] As a further improvement, the second adhesive includes a polysaccharide adhesive. Polysaccharide adhesives are substances with multiple hydroxyl and carboxyl groups, possessing strong electron-withdrawing capabilities, which is beneficial for the dispersion of conductive agents in the adhesive slurry; they also have good synergy with PVDF, thereby improving the adhesion of the adhesive coating.

[0024] As a further embodiment, the carboxymethylated derivative binder includes one or more of sodium carboxymethyl cellulose and carboxymethyl cellulose.

[0025] As a further embodiment, the polyester adhesive includes polymethyl methacrylate.

[0026] As a further embodiment, the rubber-based adhesive includes one or more of styrene-butadiene rubber, chloroprene rubber, and rosin ester.

[0027] As a further embodiment, the polysaccharide binder includes one or more of xanthan gum and sodium alginate.

[0028] As a further embodiment, the polyol adhesive includes one or more of polyacryl alcohol and polyvinyl alcohol.

[0029] As a further embodiment, the amino ester adhesive includes one or more of polyurethane and urea-formaldehyde resin adhesives.

[0030] As a further embodiment, the inorganic ceramic particles include one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), boehmite (AlO(OH)n), cesium dioxide (CeO2), titanium dioxide (TiO2), magnesium oxide (MgO), and zirconium dioxide (ZrO2).

[0031] As a further improvement, the inorganic ceramic particles have a D50 of 0.3 μm-1.2 μm and a D100 of 1.5 μm-3 μm. The selection of inorganic ceramic particles is beneficial in two ways: improving thermal insulation and promoting ion migration.

[0032] As a further improvement, the inorganic ceramic particles have a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm. The large particle size difference between the inorganic ceramic particles allows smaller particles to arrange themselves within the pores of larger particles, promoting a tighter arrangement of particles in the heat-insulating coating and improving its heat insulation effect. Furthermore, the small pores between the particles also facilitate ion migration, which is beneficial to the battery's electrical performance.

[0033] As a further embodiment, the conductive agent includes one or more of tubular conductive agents and particulate conductive agents.

[0034] As a further embodiment, the conductive agent includes a tubular conductive agent. The tubular conductive agent can form ion migration channels within its tubular structure, thereby facilitating the formation of ion transport channels in the adhesive coating, balancing adhesion and ion conductivity, and ultimately improving the battery's electrical performance.

[0035] As a further improvement, the tubular conductive agent includes carbon nanotubes.

[0036] As a further embodiment, the particulate conductive agent includes one or more of carbon black, graphite, and artificial graphite.

[0037] As a further embodiment, the PVDF particles have a D99 of 10μm-30μm and a D50 of 1μm-1.8μm. This particle size setting of PVDF is beneficial in two ways: firstly, it increases the packing density of the PVDF particles, thereby promoting improved adhesion; secondly, it also creates pores, which, in conjunction with the conductive agent, form ion migration channels.

[0038] As a further option, the PVDF particles have a D99 of 15 μm-20 μm and a D50 of 1.3 μm-1.5 μm. Particle sizes within this range create pores more suitable for ion migration.

[0039] As a further embodiment, the slurry raw materials for the heat-insulating coating include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, a polyhydroxy alcohol wetting agent, and a polyester binder. By mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent to the polyester binder is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts); the raw materials for the adhesive coating slurry... The material includes a tubular conductive agent, an alkyl sulfate wetting agent, a polysaccharide binder, and PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm. By weight, the ratio of the tubular conductive agent: alkyl sulfate wetting agent: polysaccharide binder: PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm is (0.05 parts-0.5 parts): (0.5 parts-10 parts): (3 parts-5 parts): (10 parts-15 parts). Building upon the above, we further discovered that: First, low-viscosity polysaccharide binders can penetrate between particles in the thermal insulation coating; second, polysaccharide binders, with their multi-hydroxyl structure, can also adsorb onto the surface of inorganic ceramic particles; third, the ester groups in polyester binders have electron-withdrawing capabilities, forming a bridge between the conductive agent and inorganic ceramic particles in the adhesive coating; fourth, multi-hydroxyl alcohol wetting agents possess strong polarity, promoting the dissolution of some PVDF at the interface between the adhesive coating and the thermal insulation coating into the thermal insulation coating. Furthermore, polyester binders may have a relatively large molecular weight, requiring the combination with substances of lower viscosity. Multi-hydroxyl wetting agents can also promote the dispersion of polyester binders in the slurry, thereby improving the adhesion of inorganic ceramic particles in the slurry and the adhesion of the thermal insulation coating. It is evident that the synergistic effect between the various substances in the thermal insulation coating and the adhesive coating enhances the bonding strength between them.

[0040] As a further embodiment, the slurry of the heat-insulating coating comprises alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, propylene glycol, and polymethyl methacrylate. By mass, the ratio of alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to propylene glycol to polymethyl methacrylate is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts); the raw material package of the adhesive coating slurry... The battery comprises carbon nanotubes, sodium dodecyl sulfate, sodium alginate, and PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm. By mass, the ratio of carbon nanotubes:sodium dodecyl sulfate:sodium alginate:PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm is (0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts). The volume expansion of alumina helps to interrupt battery operation and improves battery safety. The two hydroxyl groups in propylene glycol reduce the probability of hydrogen bonding between molecules due to excessive hydroxyl groups, which promotes both the wettability and dispersibility of alumina. The carbon-carbon double bonds in polymethyl acrylate (PMMA) promote the electron-withdrawing effect of the ester groups, which is beneficial for improving the adhesion of conductive agents. PMMA interacts with the lone pairs of electrons in alumina, causing PMMA to adhere to the alumina particles in the separator coating. The long-chain structure of sodium dodecyl sulfate (SLS) improves the dispersibility of carbon nanotubes, forming uniform ion transport channels in the adhesive coating. Furthermore, SLS's weak alkaline properties promote the dissolution of sodium alginate in the adhesive coating, which is beneficial for the bonding strength between the various substances in the adhesive coating. In addition, with the combination of sodium alginate and PVDF, the adhesive coating expands under high current without cracking, thus improving battery safety. Both sodium alginate and PMMA contain abundant carboxyl groups, making them easier to combine and improving the adhesion between the heat insulation coating and the adhesive coating.

[0041] As a further embodiment, the raw materials of the heat-insulating coating slurry also include a first dispersant and a first thickener; the raw materials of the adhesive coating slurry also include a second dispersant and a second thickener. By mass, the ratio of the inorganic ceramic particles, the first wetting agent, the first binder, the first dispersant, and the first thickener is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts); by mass, the ratio of the conductive agent, the second wetting agent, the second binder, PVDF, the second dispersant, and the second thickener is (0.05 parts-0.5 parts):(0.5 parts-10 parts):(3 parts-5 parts):(10 parts-15 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts). The first and second dispersants promote the dispersion of substances in the slurry, while the first and second thickeners improve the texture of the slurry, which is beneficial for uniform slurry coating and thus enables the slurry to function as both a heat-insulating coating and an adhesive coating.

[0042] As a further embodiment, the first dispersant and the second dispersant include one or more of the following: modified polyether polymer dispersant, fatty alcohol dispersant, phenyl sulfonate dispersant, alkyl polyether dispersant, phosphate dispersant, ammonium acid dispersant, and citrate dispersant.

[0043] As a further embodiment, the first dispersant comprises an ammonium acid dispersant. The carboxyl groups in the ammonium acid dispersant can reduce the surface tension of the solution, and the carboxylic acid groups and ammonium groups in the ammonium acid dispersant have good wettability. When adsorbed on the surface of inorganic ceramic particles, the inorganic ceramic particles are kept dispersed stably by electrostatic repulsion and spatial positioning.

[0044] As a further embodiment, the second dispersant comprises a sulfonate dispersant having a phenyl group. The sulfonate group in the sulfonate dispersant having a phenyl group is an electron-withdrawing group, which is beneficial for the dispersion of the conductive agent in the adhesive coating.

[0045] As a further embodiment, the modified polyether polymer dispersant includes a modified polyether amide resin.

[0046] As a further embodiment, the fatty alcohol dispersant includes fatty alcohol polyoxyethylene ether.

[0047] As a further embodiment, the sulfonate dispersant having phenyl groups includes one or more of sodium dodecylbenzenesulfonate and sodium benzenesulfonate.

[0048] As a further embodiment, the phosphate dispersant includes one or more of sodium hexametaphosphate and sodium polyphosphate.

[0049] As a further embodiment, the ammonium dispersant includes ammonium polyacrylate.

[0050] As a further embodiment, the citrate dispersant includes sodium citrate.

[0051] As a further embodiment, the first thickener and the second thickener include one or more of polyol thickeners, pyrrole thickeners, and carboxymethylated derivative thickeners.

[0052] As a further improvement, the first thickener includes a pyrrole-based thickener.

[0053] As a further option, the second thickener includes a carboxymethylated derivative thickener.

[0054] As a further embodiment, the polyol thickener includes one or more of polyvinyl alcohol and polyethylene glycol.

[0055] As a further embodiment, the pyrrole thickener includes polyvinylpyrrolidone.

[0056] As a further embodiment, the carboxymethylated derivative thickener includes sodium carboxymethyl cellulose.

[0057] As a further embodiment, the slurry raw materials of the heat-insulating coating include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, polyhydroxy alcohol wetting agents, polyester binders, ammonium acid dispersants, and pyrrole thickeners. By mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent to the polyester binder to the ammonium acid dispersant to the pyrrole thickener is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts). The raw materials of the adhesive coating slurry include tubular conductive materials. The tubular conductive agent, alkyl sulfate wetting agent, polysaccharide binder, PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm, phenyl sulfonate dispersant, and carboxymethylated derivative thickener are present in the following proportions by weight: (0.05-0.5 parts): (0.5-10 parts): (3-5 parts): (10-15 parts): (0.05-0.1 parts): (0.5-10 parts). Building upon the previous findings, we further discovered that the ammonium group in ammonium acid dispersants is an electron-donating group, capable of interacting with the electron-withdrawing groups in polyhydroxy alcohol wetting agents and polyester binders. This promotes uniform dispersion of inorganic ceramic particles and, consequently, more uniform dispersion of all substances in the slurry. In pyrrole thickeners, the nitrogen atom in the pyrrole ring provides a pair of electrons to form a five-center, six-electron conjugated π bond, exhibiting an electron-donating effect. This, combined with polyhydroxy alcohol wetting agents, improves the texture of the heat-insulating coating slurry. The interaction between carboxymethylated derivative thickeners and pyrrole thickeners enhances the interaction between the heat-insulating coating and the adhesive layer, thereby improving the adhesion between the coatings. Phenyl sulfonate dispersants possess strong electron-withdrawing capabilities, further improving the dispersibility of conductive agents.

[0058] As a further embodiment, the slurry of the heat-insulating coating comprises alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, propylene glycol, polymethyl acrylate, ammonium polyacrylate, and polyvinylpyrrolidone. By mass, the ratio of the alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to propylene glycol to polymethyl acrylate to ammonium polyacrylate to polyvinylpyrrolidone is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts); the raw material of the adhesive coating slurry includes sodium carbon. The composition of the carbon nanotubes, sodium dodecyl sulfate, sodium alginate, PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm, sodium dodecylbenzenesulfonate, and sodium carboxymethyl cellulose, by mass, is (0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts):(0.05-0.1 parts):(0.5-10 parts). The shorter main chains of polyacrylic acid and polyvinylpyrrolidone result in better flexibility and stable presence in the slurry, thus improving the dispersibility and wettability of the inorganic ceramic particles. Sodium dodecylbenzenesulfonate and sodium carboxymethyl cellulose are both sodium salts, making them easier to dissolve together in the adhesive coating slurry.

[0059] As a further embodiment, the slurry of the heat-insulating coating further includes a first solution, and the slurry of the adhesive coating further includes a second solution. By mass, the ratio of the first solvent, inorganic ceramic particles, first wetting agent, first binder, first dispersant, and first thickener is (90-110 parts):(5-30 parts):(0.5-10 parts):(3-5 parts):(0.05-0.1 parts):(0.5-10 parts). By mass, the ratio of the second solvent, conductive agent, second wetting agent, second binder, PVDF, second dispersant, and second thickener is (90-110 parts):(0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts):(0.05-0.1 parts):(0.5-10 parts). The first solution is not limited to deionized water.

[0060] As a further embodiment, the base film includes one of polypropylene (PP), polyethylene (PE), PP / PE / PE composite film, polyethylene terephthalate (PET), polyimide (PI), cellulose film, polyamide film (PA), spandex, and aramid film.

[0061] The present invention also provides a method for preparing the diaphragm, the method comprising:

[0062] S1: According to the mass ratio, add the first dispersant, the first thickener, the first wetting agent, the inorganic ceramic particles, and the first binder to the first solution, and mix them evenly for the first time to obtain the slurry of the heat insulation coating.

[0063] S2: According to the mass ratio, add the second dispersant, the second thickener, and PVDF to the second solution, mix them evenly for the second time, then refine the particles in the slurry, add the second wetting agent, the conductive agent, and the second binder, and mix them evenly for the third time to obtain the slurry for the adhesive coating.

[0064] S3: The heat insulation coating slurry and the adhesive coating slurry are sequentially coated on one or both sides of the base membrane, and then dried to obtain a composite diaphragm, namely the diaphragm of the present invention.

[0065] As a best example of the present invention, each substance can be dispersed evenly after being added, which is beneficial to improving the dispersibility of the slurry.

[0066] As a further embodiment, the conditions for the first mixing in S1 are stirring and mixing at a speed of 1000 r / min-2000 r / min for 20 min-60 min; the conditions for the first mixing in S2 are stirring and mixing at a speed of 800 r / min-2000 r / min for 10 min-40 min; the conditions for the completion of particle refinement in S2 are that the particle size of PVDF in the adhesive coating slurry is D99 of 10 μm-30 μm and D50 of 1 μm-1.8 μm; the conditions for the third mixing in S2 are stirring and mixing at a speed of 500 r / min-1800 r / min for 20 min-30 min; the coating method in S3 includes electrostatic spraying; and the drying temperature in S3 is 40℃-120℃. The electrostatic spraying method in this invention facilitates a more suitable particle distribution density in the slurry for both the heat-insulating and adhesive coatings. The denser packing of particles in the edge regions enhances adhesion between coatings, between the coating and the positive or negative electrode, and between the coating and the base film. Furthermore, it facilitates the formation of ion migration channels in the internal regions. This, in turn, improves both the adhesion of the separator and the electrical performance of the battery.

[0067] The features and beneficial effects of this invention are as follows:

[0068] (1) In this invention, a conductive agent is added to the slurry of the adhesive coating to cooperate with PVDF, which helps to improve the adhesion of the adhesive coating and at the same time builds an ion transport channel, which is beneficial to the improvement of the battery's electrical performance and safety performance.

[0069] (2) The composite separator of the present invention is beneficial to improving the heat resistance of the separator, thereby improving the safety performance of the battery.

[0070] (3) The combination of various substances in the slurry of the heat insulation coating and the adhesive coating in this invention results in a slurry with uniform texture. Furthermore, it enhances the liquid retention and wettability of the separator, thereby extending the battery cycle life and playing a greater role in the 3C charging and discharging field.

[0071] (4) The composite coating slurry of the present invention can use water as a solvent, which is low in cost, environmentally friendly, and has controllable viscosity, good wettability and dispersibility. The preparation process of the present invention is simple, low in cost, and suitable for large-scale production. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 An image of the diaphragm provided in Embodiment 1 of the present invention. Detailed Implementation

[0074] To facilitate understanding of the separator for improving polarization discharge in lithium batteries and its preparation method, a more comprehensive description of the separator of the present invention will be provided below, along with embodiments of the invention. However, these embodiments are not intended to limit the scope of the invention. It should be understood that these embodiments are for more detailed description only and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention. Relational terms such as "first" and "second" are merely used to distinguish one component from another with the same name, and do not necessarily require or imply any such actual relationship or order between these components.

[0075] The preparation method of the diaphragm of the present invention will be described using the preparation process of Example 1 as an example:

[0076] Example 1:

[0077] S1: According to the mass ratio, add the first dispersant, the first thickener, the first wetting agent, alumina particles, and the first binder to deionized water, mix them evenly for the first time, and obtain the slurry of the heat insulation coating.

[0078] S2: According to the mass ratio, add the second dispersant, the second thickener, and PVDF to the second solution, mix them evenly for the second time, then refine the particles in the slurry, add the second wetting agent, the conductive agent, and the second binder, and mix them evenly for the third time to obtain the slurry for the adhesive coating.

[0079] S3: The heat insulation coating slurry and the adhesive coating slurry are sequentially coated on one or both sides of the base membrane, and then dried to obtain a composite diaphragm, namely the diaphragm of the present invention.

[0080] As a best example of the present invention, each substance can be dispersed evenly after being added, which is beneficial to improving the dispersibility of the slurry.

[0081] As a further embodiment, the conditions for the first mixing in S1 are stirring and mixing at a speed of 1000 r / min-2000 r / min for 20 min-60 min; the conditions for the first mixing in S2 are stirring and mixing at a speed of 800 r / min-2000 r / min for 10 min-40 min; the conditions for the completion of particle refinement in S2 are that the particle size of PVDF in the adhesive coating slurry is D99 of 10 μm-30 μm and D50 of 1 μm-1.8 μm; the conditions for the third mixing in S2 are stirring and mixing at a speed of 500 r / min-1800 r / min for 20 min-30 min; the coating method in S3 includes electrostatic spraying; and the drying temperature in S3 is 40℃-120℃.

[0082] Best example:

[0083] S1: Add dispersant, thickener, and wetting agent to deionized water, stir evenly, then add alumina powder and stir at high speed until homogeneous; stirring time is 20-60 minutes, stirring speed is 1000-2000 rpm, to obtain an alumina slurry. Add binder and stir using a disperser for 20-30 minutes, stirring speed is 500-800 rpm, to obtain a slurry with an alumina heat-insulating coating.

[0084] S2: Add dispersant and thickener to deionized water and stir until homogeneous. Use a double planetary mixer, a mixing system with a dispersion disc. Internally, it consists of a stirring paddle and a dispersion slurry. Rotation speed: 800 rpm - 2000 rpm. Add PVDF powder and stir until homogeneous. Use a disperser to stir for 10-40 minutes at a speed of 800 rpm - 2000 rpm to obtain the slurry for the adhesive coating.

[0085] S3: Use a sand mill to grind the PVDF slurry. After the particle size decreases (D99 is 10μm-30μm, D50 is 1μm-1.8μm), add a wetting agent and stir using a disperser for 20-30 minutes at a speed of 500-800 r / min.

[0086] S4: After stirring evenly, add the conductive agent and stir for 20-30 minutes at a speed of 800-1800 r / min. Add the binder and stir using a disperser for 20-30 minutes at a speed of 500-800 r / min to obtain the PVDF membrane coating slurry.

[0087] In this invention, the amounts of substances added in Examples 1-20 are the same, wherein the amount of inorganic ceramic added is 20g, the amount of the first wetting agent added is 5g, the amount of the first binder added is 4g, the amount of the first thickener added is 6g, the amount of the first dispersant added is 0.08g, the amount of conductive agent added is 3g, the amount of the second wetting agent added is 5g, the amount of the second binder added is 4g, the amount of the second thickener added is 5g, the amount of the second dispersant added is 0.08g, and the amount of PVDF added is 12.5g.

[0088] We will also obtain the battery separator for testing, including adhesion, etc. The battery separator of this invention was used in a battery, and electrical performance tests were also conducted. The testing process included:

[0089] (1) Battery preparation: The positive electrode is a ternary material (nickel-cobalt-manganese), the negative electrode is graphite, and the electrolyte is a standard electrolyte with EC (ethylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) = 1:1:1 and lithium hexafluorophosphate concentration of 1 mol / L.

[0090] (2) Adhesion test: The 180-degree peel test was used.

[0091] Validation Result Analysis

[0092] Table 1. Formulation of raw materials for the heat-insulating coatings of the embodiments and comparative examples of the present invention.

[0093]

[0094] Table 2 Formulation of the adhesive coatings in the embodiments and comparative examples of the present invention.

[0095] Example 1 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 2 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 25μm-30μm, and D50 is 1μm-1.2μm. carbon nanotubes Example 3 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 10μm-24μm, and D50 is 1.6μm-1.8μm. carbon nanotubes Example 4 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 5 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 6 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 7 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 8 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 9 Sodium dodecyl sulfate Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 10 dimethyl sulfoxide polymethyl acrylate polyethylene glycol ammonium polyacrylate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 11 n-Butanol Xanthan Gum Polyvinylpyrrolidone Fatty alcohol polyoxyethylene ether D99 is 25μm-30μm, and D50 is 1μm-1.2μm. carbon black Example 12 Methyl acrylate Styrene-butadiene rubber Polyvinyl alcohol Polyvinylpyrrolidone D99 is 10μm-24μm, and D50 is 1.6μm-1.8μm. graphene Example 13 Propylene glycol Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 14 Dodecylphenol polyoxyethylene ether Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 15 ethanol Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 16 dimethyl sulfoxide Sodium alginate Sodium carboxymethyl cellulose Sodium dodecylbenzenesulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 17 Sodium dodecyl sulfate polymethyl acrylate polyethylene glycol Acetamide D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 18 Sodium dodecyl sulfate Polyvinyl alcohol Sodium carboxymethyl cellulose Sodium polyacrylate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 19 Sodium dodecyl sulfate Styrene-butadiene rubber polyethylene glycol ammonium polyacrylate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes Example 20 Sodium dodecyl sulfate polyurethane Polyvinylpyrrolidone Sodium polyethylene glycol alkyl aryl ether sulfonate D99 is 15μm-20μm, and D50 is 1.3μm-1.5μm. carbon nanotubes

[0096] Table 3 Test results of embodiments and comparative examples of the present invention

[0097]

[0098]

[0099] The coating of the composite diaphragm was obtained by the method of the present invention, such as... Figure 1 As shown, a heat-insulating coating and an adhesive coating are sequentially coated on the surface of the base film. The heat-insulating coating improves the heat insulation performance of the separator during battery cycling, thereby reducing the decrease in adhesion between the adhesive coating and the positive or negative electrode due to temperature rise. A conductive agent and PVDF are added to the adhesive coating. The conductive agent forms ion transport channels in the adhesive coating, reducing electrode polarization caused by impeded lithium-ion migration. PVDF improves the adhesion between the heat-insulating coating and the positive / negative electrode. The heat-insulating coating isolates the adhesive coating from heat and also isolates the electron transport effect of the conductive agent in the adhesive coating from the separator. Therefore, in this invention, the synergy between the heat-insulating coating and the adhesive coating not only improves the adhesion between the separator and the positive or negative electrode but also promotes lithium-ion transport, thus improving the battery's safety and electrical performance. By comparing Examples 1-20 with Comparative Examples 1-2 in Tables 1-3, we found that the separators of Examples 1-20 of the present invention have better electrical performance and adhesion when used in batteries than those of Comparative Examples 1-2, where Comparative Example 1 is a separator obtained by conventional methods. Therefore, the separator of the present invention is beneficial for improving the electrical performance of batteries.

[0100] Based on this, we further optimized the optimal system among the diaphragm coating and the adhesive coating, as well as the best matching system between the diaphragm coating and the adhesive coating.

[0101] Comparing Examples 1-3, we found that the battery in Example 1 exhibits superior electrical performance compared to those in Examples 2-3. We believe this is because the particle size of the ceramic particles in the heat-insulating coating and the PVDF particles in the adhesive coating in Example 1, when matched, creates suitable ion transport channels within the separator, thereby improving the battery's electrical performance. We also found that the peel adhesion and hot-press adhesion of Example 1 are significantly higher than those of Examples 2 and 3. We believe this is likely due to the denser packing of the PVDF particles in Example 1, which enhances the adhesion. Further optimization yielded inorganic ceramic particles with a D50 of 0.6 μm-0.9 μm and a D100 of 2 μm-3 μm, and PVDF with a D99 of 15 μm-20 μm and a D50 of 1.3 μm-1.5 μm.

[0102] We further optimized the first wetting agent. Comparing Examples 1 and 4-5, we found that Example 1 yielded superior battery electrical performance and separator adhesion compared to Examples 4 and 5. We believe that Example 1 uses a polyhydroxy alcohol wetting agent, where the polyhydroxy structure makes it easier to adsorb onto the surface of inorganic ceramic particles, thus improving the wettability of the inorganic ceramic particles, promoting uniform dispersion of the particles in the slurry, facilitating the formation of ion transport channels, and increasing battery cycle performance. We further optimized the use of a polyhydroxy alcohol wetting agent.

[0103] Based on this, we further optimized the first binder, as in Examples 1 and 6-9. We found that although the electrical performance of the batteries in Examples 1 and 6-9 did not differ significantly, the difference in the adhesion strength of the separator was more significant, with Example 1 showing better adhesion. Firstly, we believe that polyester binders, with their superior structure, offer greater stability during battery cycling, which is more conducive to bonding ceramic particles in the heat-insulating coating, thus promoting improved adhesion within the heat-insulating coating. Secondly, the better combination of the hydroxyl groups in the polyester binder and the fluorine in the PVDF in the adhesive coating enhances the bonding strength between the heat-insulating coating and the adhesive coating. Therefore, polyester binders not only improve the adhesion strength within the heat-insulating coating but also enhance the adhesion strength between the heat-insulating coating and the adhesive coating. We further optimized the first binder to be a polyester binder.

[0104] We further optimized the second wetting agent in the adhesive coating. Comparing Examples 1 and 13-16, we found that Example 1 exhibited superior electrical properties and adhesion compared to Examples 13-16. The second wetting agent is used to impregnate the conductive agent, promoting its uniform dispersion in the adhesive coating slurry. Example 1 selected an alkyl sulfate wetting agent, which, on one hand, adsorbs onto the surface of the conductive agent, improving its wettability; on the other hand, the sulfate ions in the alkyl sulfate wetting agent are electron-deficient, allowing for better compatibility with the PVDF in the adhesive coating, thereby improving the slurry's texture and fluidity, facilitating coating, and promoting more uniform dispersion of the adhesive coating's adhesion. We further optimized the second wetting agent to be an alkyl sulfate wetting agent.

[0105] Based on this, we further investigated the second binder in the adhesive coating. Comparing Examples 1 and 17-20, we found that Example 1 exhibited the best peel adhesion and hot-press adhesion. We believe that polysaccharide binders, on the one hand, work in conjunction with PVDF to further enhance the adhesion of the adhesive coating, thereby improving the adhesion between the positive / negative electrodes and the separator, reducing the occurrence of separator detachment from the positive and negative electrodes due to decreased adhesion during battery cycling; on the other hand, polysaccharide binders, with their multiple hydroxyl and carboxyl groups, possess strong electron-withdrawing capabilities, which facilitates the bonding of conductive agents in the slurry, thus promoting the formation of ion channels. We further preferred a polysaccharide binder as the second binder.

[0106] We found that the interaction between the adhesive coating and the heat-insulating coating more easily improves the performance of the separator, thereby enhancing the battery's electrical performance. Building on the above, we also found that the tubular conductive agent selected in Example 1 more readily establishes ion transport channels in the slurry. The interaction between the tubular conductive agent and PVDF achieves a balance between adhesion and ion conductivity in the adhesive coating, which is beneficial for improving the battery's electrical performance. Furthermore, we found that polysaccharide binders, due to their low viscosity, can penetrate between the particles in the heat-insulating coating slurry. Therefore, the polyhydroxy structure of the polysaccharide binder in Example 1 can further adsorb onto the surface of the inorganic ceramic particles in the heat-insulating coating, thereby increasing the interaction between the heat-insulating coating and the adhesive coating. Based on this, polyester binders may have relatively large molecular weights, so they need to be combined with substances with lower viscosity. Polyhydroxyl wetting agents can further promote the dispersion of polyester binders in the slurry, thereby improving the adhesion of inorganic ceramic particles and the thermal insulation coating. Furthermore, the ester groups in the polyester binder of the thermal insulation coating have electron-withdrawing capabilities, which can be adsorbed into the conductive agent of the adhesive coating, further promoting the adhesion between the thermal insulation coating and the adhesive coating. Polyhydroxyl alcohol wetting agents in the thermal insulation coating have strong polarity, which can promote the dissolution of some PVDF at the interface between the thermal insulation coating and the adhesive coating, further enhancing the adhesion between the adhesive coating and the thermal insulation coating of the diaphragm. Through a comparison of Examples 1 and Examples 10-12, we can see that the synergy between the substances in the thermal insulation coating and the adhesive coating promotes the bonding strength between them. We further specify that the slurry raw materials for the heat-insulating coating include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, a polyhydroxy alcohol wetting agent, and a polyester binder. By mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent to the polyester binder is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts); the raw materials for the adhesive coating slurry... The material includes a tubular conductive agent, an alkyl sulfate wetting agent, a polysaccharide binder, and PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm. By weight, the ratio of the tubular conductive agent: alkyl sulfate wetting agent: polysaccharide binder: PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm is (0.05 parts-0.5 parts): (0.5 parts-10 parts): (3 parts-5 parts): (10 parts-15 parts).

[0107] Building upon this, in Example 1, we further combined a first dispersant, a second dispersant, a first thickener, and a second thickener to complement the heat-insulating coating and the adhesive coating of the present invention. We further discovered that the ammonium group in the ammonium acid dispersant of the first dispersant is an electron-donating group, which can interact with the electron-withdrawing groups in the polyhydroxy alcohol wetting agent and the polyester binder, promoting uniform dispersion of inorganic ceramic particles and further uniform dispersion of the various substances in the slurry. In the pyrrole thickener of the first thickener, the nitrogen atom in the pyrrole ring provides a pair of electrons to form a five-center, six-electron conjugated π bond, exhibiting an electron-donating effect and interacting with the polyhydroxy alcohol wetting agent to improve the texture of the heat-insulating coating slurry. The carboxymethylated derivative thickener and the pyrrole thickener in the second thickener interact to increase the interaction between the adhesives of the heat-insulating coating and the adhesive coating, thereby improving the adhesion between the coatings. The phenyl sulfonate dispersant in the second dispersant has a strong electron-withdrawing ability, further improving the dispersibility of the conductive agent. We verified through comparison between Example 1 and Examples 10-12 that Example 1 exhibits the best electrical properties and adhesion. We further preferred that the slurry raw materials for the heat-insulating coating include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, a polyhydroxy alcohol wetting agent, a polyester binder, an ammonium acid dispersant, and a pyrrole thickener. By mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent, the polyester binder, the ammonium acid dispersant, and the pyrrole thickener is (5-30 parts):(0.5-10 parts):(3-5 parts):(0.05-0.1 parts):(0.5-10 parts). The raw materials for the adhesive coating slurry include tubular conductive materials. The tubular conductive agent, alkyl sulfate wetting agent, polysaccharide binder, PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm, phenyl sulfonate dispersant, and carboxymethylated derivative thickener are present in the following proportions by weight: (0.05-0.5 parts): (0.5-10 parts): (3-5 parts): (10-15 parts): (0.05-0.1 parts): (0.5-10 parts).

[0108] Building upon this, we further discovered that in this invention, the plate-like alumina used in Example 1 allows for volume expansion of the alumina in the heat-insulating coating when the current in the battery is too high, which can block the battery's operation and thus improve battery safety. Propylene glycol enhances the wettability of alumina, which we believe is likely due to the alumina surface cooperating with the hydroxyl groups in propylene glycol via van der Waals forces, thereby improving wettability. While multiple hydroxyl groups can increase adsorption on the alumina surface, the two hydroxyl groups of propylene glycol selected in this invention reduce the probability of hydrogen bonding between molecules due to excessive hydroxyl groups, thus promoting alumina wettability and dispersibility. The carbon-carbon double bonds in polymethyl acrylate (PMMA) promote the electron-withdrawing effect of the ester groups. On one hand, PMMA can more stably bond the conductive carbon in the adhesive coating, which is beneficial to the adhesion between the heat-insulating coating and the adhesive coating; on the other hand, PMMA is soluble in solution, which is beneficial for dispersion in the slurry, and thus generates an electronic effect with the lone pairs of electrons in the alumina, causing the PMMA to adhere to the alumina particles in the separator coating. The long-chain structure of sodium dodecyl sulfate (SOS) can adsorb onto the surface of carbon nanotubes, creating steric hindrance that improves the wettability and dispersibility of carbon nanotubes, forming uniform ion transport channels in the adhesive coating. SOS's weak alkaline properties promote the dissolution of sodium alginate in the adhesive coating, thus enhancing the bonding strength between substances in the coating. Furthermore, the combination of SOS and PVDF allows the adhesive coating to expand under high current without cracking, improving battery safety. Both SOS and polymethyl acrylate (PMMA) contain abundant carboxyl groups, making them easier to combine and improving the adhesion between the thermal insulation and adhesive coatings. Additionally, the shorter main chains of polyacrylic acid and polyvinylpyrrolidone (PVDF) provide better flexibility and stability in the slurry, improving the dispersibility and wettability of inorganic ceramic particles. Sodium dodecylbenzenesulfonate (SDF) and sodium carboxymethyl cellulose (CMC) are both sodium salts, making them more easily dissolved together in the adhesive coating slurry. We verified by comparing Example 1 with Examples 10-12 that Example 1 has the best electrical properties and adhesion.We further specify that the slurry for the heat-insulating coating comprises alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, propylene glycol, polymethyl acrylate, ammonium polyacrylate, and polyvinylpyrrolidone. By mass, the ratio of alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to propylene glycol to polymethyl acrylate to ammonium polyacrylate to polyvinylpyrrolidone is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts); the raw materials for the adhesive coating slurry include sodium carbon. Carbon nanotubes, sodium dodecyl sulfate, sodium alginate, PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm, sodium dodecylbenzenesulfonate, sodium carboxymethyl cellulose, by weight, the ratio of carbon nanotubes: sodium dodecyl sulfate: sodium alginate: PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm: sodium dodecylbenzenesulfonate: sodium carboxymethyl cellulose is (0.05-0.5 parts): (0.5-10 parts): (3-5 parts): (10-15 parts): (0.05-0.1 parts): (0.5-10 parts).

[0109] In summary, the synergy between the heat-insulating coating and the adhesive coating of the present invention not only improves the adhesion between the separator and the positive or negative electrode, but also promotes the transport of lithium ions, thereby improving the safety and electrical performance of the battery.

[0110] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base membrane, and in a direction away from the base membrane, a heat-insulating coating and an adhesive coating are sequentially disposed on at least one side of the base membrane; The slurry raw materials for the heat insulation coating include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, a polyhydroxy alcohol wetting agent, and a polyester binder; by mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent to the polyester binder is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts); the raw materials for the adhesive coating slurry include pipe The product comprises a tubular conductive agent, an alkyl sulfate wetting agent, a polysaccharide binder, and PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm; by weight, the ratio of the tubular conductive agent, alkyl sulfate wetting agent, polysaccharide binder, and PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm is (0.05-0.5 parts): (0.5-10 parts): (3-5 parts): (10-15 parts).

2. The diaphragm according to claim 1, characterized in that, The polyhydroxy alcohol wetting agent includes one or more of propylene glycol, glycerin, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and trimethylolpropane; The alkyl sulfate wetting agent includes sodium dodecyl sulfate.

3. The diaphragm according to claim 1, characterized in that, The polyester adhesive includes polymethyl methacrylate; The polysaccharide binder includes one or more of xanthan gum and sodium alginate.

4. A diaphragm according to claim 1, characterized in that, The inorganic ceramic particles include one or more of the following: silicon dioxide, aluminum oxide, boehmite, cesium dioxide, titanium dioxide, magnesium oxide, and zirconium dioxide. The tubular conductive agent includes carbon nanotubes.

5. A diaphragm according to claim 1, characterized in that, The slurry for the heat-insulating coating comprises alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, propylene glycol, and polymethyl methacrylate; by mass, the ratio of alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to propylene glycol to polymethyl methacrylate is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts); the raw material for the adhesive coating slurry includes carbon nanotubes. The carbon nanotubes, sodium dodecyl sulfate, sodium alginate, and PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm are used. The ratio of carbon nanotubes, sodium dodecyl sulfate, sodium alginate, and PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm by mass is (0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts).

6. A diaphragm according to claim 1, characterized in that, The raw materials of the heat insulation coating slurry also include a first dispersant and a first thickener; the raw materials of the adhesive coating slurry also include a second dispersant and a second thickener; by mass, the ratio of the inorganic ceramic particles, polyhydroxy alcohol wetting agent, polyester binder, first dispersant, and first thickener is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts); by mass, the ratio of the conductive agent, alkyl sulfate wetting agent, polysaccharide binder, PVDF, second dispersant, and second thickener is (0.05 parts-0.5 parts):(0.5 parts-10 parts):(3 parts-5 parts):(10 parts-15 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts).

7. A diaphragm according to claim 6, characterized in that, The first dispersant and the second dispersant include one or more of the following: modified polyether polymer dispersant, fatty alcohol dispersant, phenyl sulfonate dispersant, alkyl polyether dispersant, phosphate dispersant, ammonium acid dispersant, and citrate dispersant; the first thickener and the second thickener include one or more of the following: polyol thickener, pyrrole thickener, and carboxymethylated derivative thickener.

8. A diaphragm according to claim 7, characterized in that, The modified polyether polymer dispersant includes a modified polyether amide resin; The fatty alcohol dispersant includes fatty alcohol polyoxyethylene ether; The phenyl sulfonate dispersant includes one or more of sodium dodecylbenzenesulfonate and sodium benzenesulfonate; The phosphate dispersant includes one or more of sodium hexametaphosphate and sodium polyphosphate; The ammonium acid dispersant includes ammonium polyacrylate; The citrate dispersant includes sodium citrate; The polyol thickener includes one or more of polyvinyl alcohol and polyethylene glycol; The pyrrole thickener includes polyvinylpyrrolidone; The carboxymethylated derivative thickener includes sodium carboxymethyl cellulose.

9. A diaphragm according to claim 1, characterized in that, The raw materials for the heat-insulating coating slurry include inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, polyhydroxy alcohol wetting agents, polyester binders, ammonium acid dispersants, and pyrrole thickeners. By mass, the ratio of the inorganic ceramic particles with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to the polyhydroxy alcohol wetting agent, polyester binder, ammonium acid dispersant, and pyrrole thickener is (5-30 parts):(0.5-10 parts):(3-5 parts):(0.05-0.1 parts):(0.5-10 parts). The raw materials for the adhesive coating slurry include tubular conductive agents and alkyl groups. The product comprises a sulfate wetting agent, a polysaccharide binder, PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm, a phenyl sulfonate dispersant, and a carboxymethylated derivative thickener. The ratio, by mass, of the tubular conductive agent: alkyl sulfate wetting agent: polysaccharide binder: PVDF with a D99 of 15μm-20μm and a D50 of 1.3μm-1.5μm: phenyl sulfonate dispersant: carboxymethylated derivative thickener is (0.05-0.5 parts): (0.5-10 parts): (3-5 parts): (10-15 parts): (0.05-0.1 parts): (0.5-10 parts).

10. A diaphragm according to claim 1, characterized in that, The raw materials for the heat-insulating coating slurry include alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm, propylene glycol, polymethyl acrylate, ammonium polyacrylate, and polyvinylpyrrolidone; by mass, the ratio of alumina with a D50 of 0.6μm-0.9μm and a D100 of 2μm-3μm to propylene glycol to polymethyl acrylate to ammonium polyacrylate to polyvinylpyrrolidone is (5 parts-30 parts):(0.5 parts-10 parts):(3 parts-5 parts):(0.05 parts-0.1 parts):(0.5 parts-10 parts); the raw materials for the adhesive coating slurry include carbon nanotubes. Sodium dodecyl sulfate, sodium alginate, PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm, sodium dodecylbenzene sulfonate, sodium carboxymethyl cellulose; by mass, the ratio of carbon nanotubes: sodium dodecyl sulfate: sodium alginate: PVDF with D99 ​​of 15μm-20μm and D50 of 1.3μm-1.5μm: sodium dodecylbenzene sulfonate: sodium carboxymethyl cellulose is (0.05 parts-0.5 parts): (0.5 parts-10 parts): (3 parts-5 parts): (10 parts-15 parts): (0.05 parts-0.1 parts): (0.5 parts-10 parts).

11. A diaphragm according to claim 6, characterized in that, The heat-insulating coating slurry further includes a first solvent, and the adhesive coating slurry further includes a second solvent; by mass, the ratio of the first solvent, inorganic ceramic particles, polyhydroxy alcohol wetting agent, polyester binder, first dispersant, and first thickener is (90-110 parts):(5-30 parts):(0.5-10 parts):(3-5 parts):(0.05-0.1 parts):(0.5-10 parts); by mass, the ratio of the second solvent, conductive agent, alkyl sulfate wetting agent, polysaccharide binder, PVDF, second dispersant, and second thickener is (90-110 parts):(0.05-0.5 parts):(0.5-10 parts):(3-5 parts):(10-15 parts):(0.05-0.1 parts):(0.5-10 parts).

12. A method for preparing a diaphragm according to any one of claims 1-11, characterized in that, The preparation method includes: S1: According to the mass ratio, add the first dispersant, the first thickener, the polyhydroxy alcohol wetting agent, the inorganic ceramic particles, and the polyester binder to the first solvent respectively, mix them evenly for the first time, and obtain the slurry of the heat insulation coating. S2: According to the mass ratio, add the second dispersant, the second thickener, and PVDF to the second solvent, mix them evenly for the second time, then refine the particles in the slurry, add alkyl sulfate wetting agent, conductive agent, and polysaccharide binder, and mix them evenly for the third time to obtain the slurry for the adhesive coating. S3: The heat insulation coating slurry and the adhesive coating slurry are sequentially coated on one or both sides of the base membrane, and then dried to obtain a composite membrane.

13. The preparation method according to claim 12, characterized in that, The first mixing condition in S1 is stirring at a speed of 1000-2000 r / min for 20-60 min; the second mixing condition in S2 is stirring at a speed of 800-2000 r / min for 10-40 min; the particle refinement in S2 ends when the particle size of PVDF in the adhesive coating slurry is D99 of 10μm-30μm and D50 of 1μm-1.8μm; the third mixing condition in S2 is stirring at a speed of 500-1800 r / min for 20-30 min; the coating method in S3 includes electrostatic spraying; the drying temperature in S3 is 40℃-120℃.

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