A heat-sensitive slurry for lithium battery separators, and a preparation method and applications thereof

Abstract

The application belongs to the technical field of lithium batteries, and specifically discloses a heat-sensitive slurry for a lithium battery diaphragm, a preparation method and application thereof. The heat-sensitive slurry comprises the following components: a main agent, an additive, a dispersion stabilizer and a binder. The components of the heat-sensitive slurry comprise 80-120 parts of the main agent, 20-70 parts of the additive, 1-5 parts of the dispersion stabilizer and 1-4 parts of the binder. The main agent is selected from ethylene-acrylic acid copolymer and the like. The additive comprises tackifying resin and heat-sensitive wax. The melting temperature of the main agent is 5-20 DEG C higher than the softening point or melting point of the tackifying resin and / or the heat-sensitive wax. The heat-sensitive slurry provided by the application is coated on a base film to obtain a heat-sensitive coating layer. When a battery fails, a heat-sensitive protective layer is formed to isolate the positive electrode and the negative electrode, thereby avoiding the occurrence of thermal runaway reaction and improving the safety of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery, in particular to a heat-sensitive slurry for lithium battery separator, its preparation method and application. BACKGROUND

[0002] Lithium ion batteries have occupied an important position in the power market of portable electronic products and energy storage fields such as electric vehicles due to their high energy density and long life. Although the development of lithium ion batteries has made remarkable achievements, safety is still one of the key challenges for further development; lithium ion batteries are prone to thermal runaway under the action of electrical faults such as short circuit, overcharge and heat source, releasing a large amount of heat and flammable gas, and causing fire and explosion. At present, there are many strategies to improve the safety performance of batteries, such as flame-retardant electrolyte and PTC electrode, however, due to the reduction of electrolyte or electrode dynamics, these methods will affect the electrochemical performance of the battery. In contrast, the modification of the separator has the least impact on the performance of the battery and has practical application prospects. High-safety separators with thermal shutdown function are considered to be the most promising and attractive thermal protection strategy in lithium ion batteries due to their reliability, simplicity and low cost. Once the internal temperature of the lithium ion battery reaches a certain value, the thermal closing separator can inhibit ion transfer, terminate battery reaction and prevent thermal runaway. Chinese patent CN114284640A discloses a lithium ion battery separator with thermal shutdown function, which comprises a porous base film and a thermal shutdown coating layer arranged on one side or both sides of the porous base film; the thermal shutdown coating layer comprises the following components by mass fraction: polymer particles 1-50 parts, aqueous binder 0.1-5 parts, dispersant 0.1-5 parts and wetting agent 0.05-1 part. Although this scheme directly coats a high-adhesion thermal shutdown coating layer on the surface of the base film to block the porous channels of the porous base film and block the transmission of lithium ions, the closing temperature of the separator is 120℃, which is close to the breaking temperature of the porous base film. Under thermal inertia, the separator is prone to breakage, causing short circuit between the positive and negative electrodes.

[0003] Chinese patent CN114976487A discloses a boehmite modified polyacrylonitrile reversible thermal shutdown type lithium battery separator, manufacturing method and application. Pseudoboehmite, water and crystal face capturing agent are subjected to hydrothermal treatment to obtain boehmite nanocrystals; polyacrylonitrile, boehmite nanocrystals and solvent are mixed and then electrospun to form a composite film. This scheme introduces boehmite and polyacrylonitrile with high thermal stability to make the separator maintain its size and have good thermal stability at 200℃, but the separator needs to be closed at 150℃ or above, at which time the solid electrolyte interface film (SEI film) in the battery decomposes, the electrolyte reacts with the positive electrode, generating a large amount of heat and gas, which bursts the safety valve and sprays a large amount of flammable electrolyte and smoke, which is prone to cause fire and explosion.

[0004] Chinese patent CN114597579A discloses a composite diaphragm and its preparation method and application, which comprises a diaphragm substrate and a composite coating provided on at least one side surface of the diaphragm substrate; the composite coating comprises ceramic material, low-melting-point high polymer material and polymer binder, the mass percentage of the ceramic material is 54% to 90%, and the mass percentage of the low-melting-point high polymer material is 8% to 45%; wherein the ceramic material is a skeleton material, and the low-melting-point high polymer material is filled between the ceramic materials. The composite diaphragm has excellent heat shrinkage resistance and a low thermal shutdown temperature under the condition of ensuring the air permeability, but the way of filling the low-melting-point high polymer material in the high-temperature-resistant material will affect the efficiency of the diaphragm heat shutdown and close the pores, and easily cause local resistance increase and heat generation due to inconsistent close pores, thereby causing thermal runaway.

[0005] The safety mechanism of the above-mentioned diaphragm is to make the heat-sensitive polymer material melt and flow into the pores of the base film to close the pores and block the transmission of lithium ions. The effect of this idea depends on the structure of the original base film and coating, and there are problems such as high diaphragm closing temperature, low diaphragm breaking temperature, etc. More importantly, the speed, degree and uniformity of "plugging" are difficult to control. Before the complete closing of the pores is realized, the diaphragm has already shrunk and decomposed, resulting in short circuit between the positive and negative electrodes.

[0006] Therefore, it is urgent to develop new heat-sensitive coating and safety diaphragm for lithium batteries to better solve the problem of lithium battery thermal runaway and overcome the problems of poor diaphragm closing effect and easy thermal inertia shrinkage. SUMMARY

[0007] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a heat-sensitive slurry for lithium ion battery diaphragm. The heat-sensitive slurry of the present application is coated on the battery diaphragm to obtain a heat-sensitive coating. When the battery fails, the molten / softened polymer in the heat-sensitive slurry will trigger a step melting effect to fuse with each other, forming a continuous, adhesive and flexible non-conductive thin film structure, i.e. a heat-sensitive protective layer, at the interface between the electrode and the diaphragm. This protective layer forms independent isolation bodies for the positive and negative electrodes, blocks the ion transmission inside the battery, avoids the short circuit between the positive and negative electrodes, and prevents the occurrence of heat runaway reaction between the electrode and the electrolyte, thereby terminating the battery reaction and heat release, and improving the intrinsic safety of the battery. In addition, the heat-sensitive slurry can strengthen the mechanical strength of the interface, prevent lithium dendrites from penetrating, and improve the high-temperature safety and interface stability of the battery.

[0008] The present application also provides a preparation method of the heat-sensitive slurry.

[0009] The present application also provides a lithium ion battery diaphragm.

[0010] The present application also provides a lithium ion battery.

[0011] In a first aspect of the present application, a heat-sensitive paste for a lithium-ion battery separator is provided, comprising the following components: a main agent, an additive, a dispersion stabilizer, and a binder;

[0012] In some embodiments of the present application, the components of the heat-sensitive paste include, by mass fraction: 80-120 parts of the main agent, 20-70 parts of the additive, 1-5 parts of the dispersion stabilizer, and 1-4 parts of the binder.

[0013] The main agent is selected from at least one of ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, polyolefin, ethylene-butyl acrylate copolymer, polymethyl methacrylate, polyurethane, ethylene-acrylic acid resin ionomer, or methyl acrylate / ethyl acrylate / methyl methacrylate copolymer.

[0014] The additive is a combination of tackifying resin and heat-sensitive wax in a mass ratio of 1-4:1.

[0015] The melting temperature of the main agent is 5-20°C higher than the softening point or melting point of the tackifying resin and / or the heat-sensitive wax.

[0016] The softening point of the tackifying resin is lower than the melting point of the heat-sensitive wax.

[0017] According to some embodiments of the present application, the main agent is ethylene-acrylic acid copolymer.

[0018] According to some embodiments of the present application, the tackifying resin is selected from at least one of rosin resin, terpene resin, hydrocarbon petroleum resin, phenol resin, methyl styrene tackifying resin, polyhexamethylene adipate, coumarone-indene resin, and epoxy resin.

[0019] According to some embodiments of the present application, the heat-sensitive wax is selected from at least one of Fischer-Tropsch wax, vegetable wax, vinyl bis-stearyl amide, microcrystalline wax, paraffin wax, mineral wax, oxidized Fischer-Tropsch wax, and oxidized polyolefin wax.

[0020] According to some embodiments of the present application, the components of the heat-sensitive paste include, by mass fraction: 90-110 parts of the main agent, 30-60 parts of the additive, 1.5-4 parts of the dispersion stabilizer, and 1.5-3.5 parts of the binder.

[0021] According to some embodiments of the present application, the components of the heat-sensitive paste include, by mass fraction: 90-110 parts of the main agent, 30-50 parts of the additive, 1.5-4 parts of the dispersion stabilizer, and 1.5-3.5 parts of the binder.

[0022] According to some embodiments of the present application, the components of the heat-sensitive slurry further include water, and the present application does not have a specific requirement for the amount of water, only that an appropriate amount of water is added so that the solid content of the heat-sensitive slurry is 25wt%-40wt%.

[0023] According to some embodiments of the present application, the additive is a combination of tackifying resin and heat-sensitive wax in a mass ratio of 1.5-3:1.

[0024] The present application has found that, in this preferred embodiment, when the heat-sensitive slurry obtained by the present application is applied to a battery, if overcharging, short circuit or other faults occur, the heat-sensitive protective coating formed by the melting of the heat-sensitive slurry is more dense and can adhere to the surface of the electrode sheet, becoming a non-porous isolation layer that prevents the positive and negative electrodes from contacting, successfully blocking the ion transmission between the positive and negative electrodes, blocking the thermal runaway reaction of the battery, and making the battery not valve, not leaking, not gas production, not fire and explosion, and highly safe.

[0025] According to some embodiments of the present application, the dispersion stabilizer is selected from at least two of sodium succinate, acrylic block copolymer, polyether-modified siloxane, polyoxyethylene sorbitan monolaurate, sodium carboxymethyl cellulose, acrylic polymer, and sodium alginate.

[0026] According to some embodiments of the present application, the dispersion stabilizer includes sodium carboxymethyl cellulose, sodium succinate, and acrylic block copolymer.

[0027] According to some embodiments of the present application, the dispersion stabilizer is a combination of sodium carboxymethyl cellulose, sodium succinate, and acrylic block copolymer in a mass ratio of 1:1-2:5-8.

[0028] The present application has found that, in this preferred embodiment, the heat-sensitive slurry obtained by the present application is uniformly dispersed and stable, and is more uniformly coated on the surface of the separator, and when applied to a battery, the thermal response of the fault is faster, the heat-sensitive protective layer formed is more uniform, and the safety of the battery is higher.

[0029] According to some embodiments of the present application, the binder is selected from at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, polyacrylate, and polymethyl methacrylate.

[0030] According to some embodiments of the present application, the melting temperature of the main agent is 10-15°C higher than the softening point or melting point of the tackifying resin and / or the heat-sensitive wax.

[0031] According to some embodiments of the present application, the softening point of the tackifying resin is 3-10°C lower than the melting point of the heat-sensitive wax.

[0032] The whole thermal sensitive coating is designed to keep stable during normal operation of the battery and to form an isolation layer when the battery is overheated. The two temperature characteristics are to precisely control the "response sequence" and "synergy" of different components during temperature rise, so as to achieve rapid, effective and firm shutdown protection.

[0033] During normal operation (temperature is lower than the softening point of the additive), the coating is a solid skeleton composed of high-melting main agent, in which solid tackifying resin and thermal sensitive wax particles are uniformly dispersed. At this time, the coating has high mechanical strength and does not affect the normal transmission of ions, and the battery performance is stable. During the initial overheating (temperature reaches the softening point / melting point of the additive, but does not reach the melting temperature of the main agent), the tackifying resin softens first and becomes sticky; the thermal sensitive wax melts and becomes a low-viscosity liquid; at this time, the main agent still remains in a solid state as a supporting skeleton to prevent the overall coating from collapsing or flowing excessively. The melted wax and softened resin begin to wet and wrap the main agent particles and flow in the gaps between the particles, initially producing a bonding effect, ensuring that the additive system is in an optimal state of suitable viscosity and easy spreading before the main agent melts, laying a solid foundation for the final formation of a high-quality protective layer. When the temperature continues to rise to the melting temperature of the main agent, the main agent polymer as the "skeleton" begins to melt and changes from a solid particle to a viscous flow state. The additive, which has been in a molten / softened state, rapidly and uniformly merges with the molten main agent to form a continuous, dense and well-bonded film.

[0034] If the melting point of the main agent is too low (too close to or lower than the additive), all components may melt at the same time, causing the coating to lose skeletal support and flow excessively, or even be absorbed by the separator or electrode, and thus unable to form a uniform and effective isolation layer; if the melting point of the main agent is too high (more than 20°C higher than the additive), when the additive has melted, the main agent is still too hard, which hinders the flow and fusion of the additive, resulting in a discontinuous, porous or poorly adhered protective layer, which also cannot effectively block ion transmission.

[0035] If the temperature difference between the tackifying resin and the thermal sensitive wax of the additive is not properly designed (the temperature of the thermal sensitive wax is lower than that of the tackifying resin), the wax melts first while the resin has not softened, and the liquid wax may not mix effectively with the still solid resin, which is prone to phase separation, or the wax may flow alone first, resulting in uneven film formation and affecting the integrity and adhesion of the protective layer. If the melting temperatures of the two are exactly the same, although they will respond at the same time, there is a lack of the above-mentioned "sticky first and then flow" synergy effect, and the optimal fluidity and spreading effect cannot be achieved.

[0036] The temperature difference design of the main agent and the additive mainly ensures the timing of the thermal response and the structural integrity of the protective layer, and the temperature difference design of the additive is mainly to optimize the melting fluidity and film forming quality inside the additive system. Based on this, the application significantly improves the thermal safety performance of the battery by improving the response reliability, film forming quality and blocking efficiency of the heat-sensitive coating.

[0037] In a second aspect, the application provides a preparation method of the heat-sensitive slurry according to the first aspect of the application, comprising the following steps:

[0038] S1, first mixing water, a main agent and an additive to obtain a mixture I;

[0039] S2, second mixing a dispersion stabilizer with the mixture I to obtain a mixture II;

[0040] S3, third mixing water, a binder and the mixture II to obtain the heat-sensitive slurry.

[0041] According to some embodiments of the application, the application does not have special requirements for the amount of water used in step S1, which can be exemplarily 45wt%-55wt% of the total water amount, and the amount of water used in step S3 is the remaining water amount.

[0042] According to some embodiments of the application, the first mixing, the second mixing and the third mixing are each independently carried out under stirring conditions.

[0043] According to some embodiments of the application, the conditions of the first mixing include a stirring speed of 200-500rpm, a time of 30-60min and a temperature of 25-35℃.

[0044] According to some embodiments of the application, the conditions of the second mixing include a stirring speed of 400-800rpm, a time of 25-50min and a temperature of 20-30℃.

[0045] According to some embodiments of the application, the conditions of the third mixing include a stirring speed of 200-400rpm, a time of 15-30min and a temperature of 20-25℃.

[0046] In a third aspect, the application provides a lithium ion battery separator, which comprises a base film and a heat-sensitive slurry coated on at least one side of the base film; the heat-sensitive slurry is the heat-sensitive slurry according to the first aspect of the application; the base film comprises a polyolefin separator; the thickness of the polyolefin separator is 7-12μm, and the thickness of the heat-sensitive slurry coating on the base film is 1-15μm.

[0047] According to some embodiments of the present application, the polyolefin separator is a temperature-resistant polyolefin separator; the temperature-resistant treatment is coating a temperature-resistant coating on the separator, and the coating slurry of the temperature-resistant coating comprises a coating main agent I, a coating main agent II, a coating improving agent, a coating binder and a solvent.

[0048] According to some embodiments of the present application, the coating slurry of the temperature-resistant coating contains 20wt%-38wt% of the coating main agent I, 5wt%-13wt% of the coating main agent II, 1wt%-3wt% of the coating improving agent, 1wt%-3wt% of the coating binder and 55wt%-70wt% of the solvent.

[0049] According to some embodiments of the present application, the coating main agent I is selected from at least one of ultra-fine alumina, ultra-fine boehmite, aramid, polyimide, nanofiber, lithium aluminum titanium phosphate, zirconium oxide, and silicon dioxide; the coating main agent II is selected from at least one of aluminum hydroxide, magnesium hydroxide, decabromodiphenyl ethane, ammonium polyphosphate, and borate; the coating stabilizer is selected from at least one of ammonium polyacrylate, phosphate ester polymer, hydroxyethyl cellulose, polyethylene glycol, and carboxymethyl cellulose; the coating binder is selected from at least one of polyacrylic acid, polyacrylate, polyacrylamide, polyvinyl alcohol, acrylic acid-butyl acrylate copolymer, styrene acrylate, and aliphatic water-based polyurethane; and the solvent is selected from at least one of deionized water, N-methyl pyrrolidone, dimethylacetamide, dimethylformamide and dimethyl sulfoxide.

[0050] It should be noted that, in the present application, the method for preparing the coating slurry is not particularly required, and the components can be mixed uniformly, and the coating process and the coating thickness of the coating slurry on the base film are not particularly required, and the conventional method in the art can be used, which will not be described herein again, and the person skilled in the art should not understand it as a limitation of the present application.

[0051] According to some embodiments of the present application, the separator comprises a base film and a heat-sensitive slurry A coated on the positive electrode side of the base film and a heat-sensitive slurry B coated on the negative electrode side of the base film.

[0052] The heat-sensitive slurry A is the heat-sensitive slurry according to the first aspect of the present application.

[0053] The heat-sensitive slurry B is a heat-sensitive slurry obtained by adding 10-20 parts of an additive to the heat-sensitive slurry A.

[0054] According to a fourth aspect of the present application, the heat-sensitive slurry according to the first aspect of the present application or the separator according to the third aspect of the present application is applied in a lithium ion battery.

[0055] In a fifth aspect, the present application provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the separator is the lithium ion battery separator according to the third aspect of the present application.

[0056] A schematic diagram of the separator coating structure in the lithium ion battery of the present application is shown in the left side of FIG. 1, and a schematic diagram of the function of the separator coating is shown in the right side of FIG. 1. Figure 1 Figure 1

[0057] Advantages of the present application:

[0058] When the battery fails, the molten / softened polymer in the heat-sensitive paste on the positive electrode and / or negative electrode side will trigger the step melting effect and fuse with each other under the combined action of the internal pressure and temperature of the battery, forming a continuous, adhesive and flexible non-conductive thin film structure at the interface between the electrode (positive electrode and negative electrode) and the separator, isolating the positive electrode and the negative electrode, blocking the ion transmission in the battery, avoiding the occurrence of short circuit between the positive electrode and the negative electrode and the heat runaway reaction induced between the electrode sheet and the electrolyte, terminating the battery reaction and heat release, and improving the intrinsic safety of the battery. At the same time, the mechanical strength of the interface is strengthened to prevent lithium dendrite penetration, thereby improving the high-temperature safety and interface stability of the battery.

[0059] The heat-sensitive paste provided by the present application has simple preparation process, environmental protection and low cost, can improve the high-temperature safety and interface stability of the battery, and does not affect the electrical performance of the battery during normal operation, and is suitable for large-scale popularization and application.

[0060] Other features and advantages of the present application will be described in the following description, and some will become apparent from the description, or will be understood by those skilled in the art through implementation of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0061] The present application will be further described below in conjunction with the drawings and examples, wherein:

[0062] Figure 1 A schematic diagram of the structure of the lithium ion battery provided by the present application is shown in FIG. 1, wherein the left side of the figure is a schematic diagram of the battery and the separator coating structure, and the right side of the figure is a schematic diagram of the function of the separator coating;

[0063] Figure 2 A SEM image of the separator S1 of Example 1 of the present application is shown in FIG. 2, wherein A is a SEM image of the temperature-resistant coating, B is a SEM image of the heat-sensitive protective layer, and C is a SEM image of the heat-sensitive protective layer formed on the surface of the separator under the critical condition;

[0064] Figure 3 ​​The battery performance test results of the battery prepared by the separator of the present application example 1 and the comparative example 1, wherein, A figure is the ACIR test result, B figure is the DCR test result under different SOC conditions;

[0065] Figure 4 The battery cycle performance test results of the battery prepared by the separator of the present application example 1 and the comparative example 1, wherein, A figure is the charge cycle capacity retention rate test result, B figure is the discharge cycle capacity retention rate test result;

[0066] Figure 5 The battery needle puncture test process phenomenon diagram of the present application, wherein, A figure is the battery needle puncture test process phenomenon diagram of the present application example 1, B figure is the battery needle puncture test process phenomenon diagram of the present application example 3, C figure is the battery needle puncture test process phenomenon diagram of the present application comparative example 1;

[0067] The figure mark: 1-base film; 2-temperature resistant coating; 3-heat sensitive coating; 4-positive electrode; 5-negative electrode; 6-heat sensitive protective layer. DETAILED DESCRIPTION

[0068] The concept and the technical effects of the present application will be described below in combination with the examples, so as to fully understand the purpose, features and effects of the present application. Obviously, the described examples are only a part of the examples of the present application, but not all the examples, and other examples obtained by the person skilled in the art without creative labor based on the examples of the present application, all belong to the protection scope of the present application.

[0069] The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased in the market, and the reagents are all analytical pure products.

[0070] Preparation example 1: this preparation example is used to illustrate the temperature resistant coating treated base film used in the present application and its preparation method:

[0071] Raw materials:

[0072] Coating main agent I: ultrafine alumina, D 50 0.2-0.6 μm, model HJA-400, purchased from Anhui Yishitong Material Science and Technology Co., Ltd.; coating main agent II: aluminum hydroxide, D 50 ≤2.5 μm, model JATH-01FD, purchased from Anhui Yishitong Material Science and Technology Co., Ltd.;

[0073] Coating improver: ammonium polyacrylate, CAS No. 9003-03-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium carboxymethyl cellulose, model WY-2800, purchased from Changshu Wei Yi Technology Co., Ltd.

[0074] Coating binder: polyacrylate emulsion, model GR-401, solid content 29%, purchased from Hunan Gaorui Power Source Material Co., Ltd.; polyacrylamide solution, model GR-508GII, solid content 20%, purchased from Hunan Gaorui Power Source Material Co., Ltd.

[0075] Base film preparation method:

[0076] Mix 0.84 kg of coating main agent I, 0.3 kg of coating main agent II, 0.09 kg of stabilizer ammonium polyacrylate, 0.015 kg of sodium carboxymethyl cellulose, and 1.665 kg of water, and stir at high speed for 30 min (stirring speed 1200 rpm); grind with a sand mill for 20 min (speed 500 rpm), add coating binder polyacrylate 0.056 kg, polyacrylamide 0.034 kg, and stir at low speed for 60 min (stirring speed 300 rpm); use gravure coating process to coat 1.5 μm thick coating slurry on both sides of a 7 μm polyethylene base film, then dry at 45°C to obtain a temperature-resistant coating-treated base film, named base film Z1.

[0077] Example 1

[0078] This example provides a heat-sensitive slurry for lithium battery separators, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0079] Prepare each raw material according to Table 1, wherein:

[0080] Ethylene-acrylic acid copolymer: aqueous emulsion, melting temperature 105°C, solid content 30%, model LW-290, purchased from Nanjing Tenshi New Material Technology Co., Ltd.;

[0081] Tackifying resin: rosin resin, aqueous emulsion, softening point 90°C, model SBR-939, solid content 55%, purchased from Guangzhou Songbao Chemical Co., Ltd.;

[0082] Heat-sensitive wax: Fischer-Tropsch wax, aqueous emulsion, melting point 95°C, solid content 33.5%, model 5351, purchased from Shanghai Xinnuo Chemical Co., Ltd.;

[0083] Sodium succinate: yellowish to yellow liquid, solid content 75±2%, model Comwet® 0057, purchased from Shanghai Yingcheng Chemical Co., Ltd.;

[0084] Acrylic block copolymer: yellow liquid, solid content 60%, model HH2021, purchased from Guangzhou Huhuan Chemical Auxiliary Co., Ltd.

[0085] Sodium carboxymethyl cellulose: powder, model WY-2800, purchased from Changshu Wei Yi Technology Co., Ltd., configured into a 2% solid content aqueous solution for use;

[0086] Styrene butadiene rubber: aqueous emulsion, solid content 40%, model A-100, purchased from Wuxi Sigma New Energy Technology Co., Ltd.

[0087] Polyvinylidene fluoride: powder, model TLF7002, purchased from Ningxia Tianlin New Material Technology Co., Ltd.

[0088]

[0089] Preparation of heat-sensitive slurry:

[0090] 1) The first material containing 10.33 g of water, main agent, and additive was subjected to first mixing to obtain mixture I, and the first mixing conditions were as follows: stirring speed 200 rpm, time 30 min, and temperature 25℃;

[0091] 2) The second material containing the dispersion stabilizer and mixture I was subjected to second mixing to obtain mixture II, and the second mixing conditions were as follows: stirring speed 400 rpm, time 25 min, and temperature 25℃;

[0092] 3) The third material containing 10 g of water, binder, and mixture II was subjected to third mixing to obtain heat-sensitive slurry, and the solid content of the heat-sensitive slurry was about 30%.

[0093] Preparation of separator:

[0094] The heat-sensitive slurry was coated on the A side of the base film Z1 prepared in Preparation Example 1, and after drying at 30℃, the thickness of the heat-sensitive coating obtained was 2 μm. Then, the heat-sensitive slurry was coated on the B side of the base film Z1, and after drying at 35℃, the thickness of the heat-sensitive coating obtained was 2 μm. Then, the separator was left to stand overnight in a drying room (25℃, humidity <1% RH) to obtain the separator S1.

[0095] Example 2

[0096] This example provides a heat-sensitive slurry for a lithium battery separator, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0097] The preparation method of this example is basically the same as that of Example 1, except that the heat-sensitive slurry formula of this example is different from that of Example 1, and the specific formula is shown in Table 2.

[0098]

[0099] The separator S2 is finally prepared in this example.

[0100] Example 3

[0101] This example provides a heat-sensitive slurry for lithium battery separators, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0102] The preparation method of this example is basically the same as that of Example 1, except that in this example, the additive used is rosin resin and Fischer-Tropsch wax in a mass ratio of 1:1.

[0103] The separator S3 is finally prepared in this example.

[0104] Example 4

[0105] This example provides a heat-sensitive slurry for lithium battery separators, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0106] The preparation method of this example is basically the same as that of Example 1, except that in this example, the additive used is rosin resin and Fischer-Tropsch wax in a mass ratio of 2:1, and the total mass of the additive is 55g.

[0107] The separator S4 is finally prepared in this example.

[0108] Example 5

[0109] This example provides a heat-sensitive slurry for lithium battery separators, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0110] The preparation method of this example is basically the same as that of Example 1, except that in this example, the total amount of the dispersion stabilizer used is the same as in Example 1, but the mass ratio of sodium carboxymethyl cellulose, sodium succinate, and acrylic block copolymer is 1:1.48:1.48.

[0111] The separator S5 is finally prepared in this example.

[0112] Example 6

[0113] This example provides a heat-sensitive slurry for lithium battery separators, and uses the heat-sensitive slurry to prepare a lithium battery separator.

[0114] The preparation method of this example is basically the same as that of Example 1, except that in this example, ethylene-vinyl acetate copolymer (model ET2805, melting point 110°C, purchased from Jiangsu Sipernat Petrochemical Co., Ltd.) is used instead of ethylene-acrylic acid copolymer in Example 1.

[0115] The separator S6 is finally prepared in this example.

[0116] Example 7

[0117] The present embodiment provides a heat-sensitive slurry for a lithium battery separator, and a lithium battery separator prepared using the heat-sensitive slurry.

[0118] The preparation method of the present embodiment is basically the same as that of Embodiment 1, except that, in the present embodiment, only the heat-sensitive slurry on the negative side of the separator is coated, and the heat-sensitive slurry on the positive side is not coated.

[0119] The present embodiment finally prepares a separator S7.

[0120] Embodiment 8

[0121] The present embodiment provides a heat-sensitive slurry for a lithium battery separator, and a lithium battery separator prepared using the heat-sensitive slurry.

[0122] The preparation method of the present embodiment is basically the same as that of Embodiment 1, except that, in the present embodiment, two heat-sensitive slurries, heat-sensitive slurry A and heat-sensitive slurry B, are prepared, and the preparation methods of the two are the same as that of Embodiment 1, wherein heat-sensitive slurry A, which is the same as that of Embodiment 1, is coated on the negative side, and heat-sensitive slurry B, which is different from heat-sensitive slurry A in composition, is coated on the positive side, as shown in Table 3 below.

[0123]

[0124] The present embodiment finally prepares a separator S8.

[0125] Embodiment 9

[0126] The present embodiment provides a heat-sensitive slurry for a lithium battery separator, and a lithium battery separator prepared using the heat-sensitive slurry.

[0127] The preparation method of the present embodiment is basically the same as that of Embodiment 1, except that, in the present embodiment, the amounts of each raw material and water are adjusted so that the solid content of the prepared heat-sensitive slurry A is 35 wt%, as shown in Table 4 below.

[0128]

[0129] The present embodiment finally prepares a separator S9.

[0130] Embodiment 10

[0131] The present embodiment provides a heat-sensitive slurry for a lithium battery separator, and a lithium battery separator prepared using the heat-sensitive slurry.

[0132] The preparation method of the present embodiment is basically the same as that of Embodiment 1, except that, in the present embodiment, the base film Z1 is not used, and the heat-sensitive slurry A is directly coated on both sides of a 7 μm polyethylene-based film, and the rest of the preparation process is the same as that of Embodiment 1.

[0133] The present example finally prepared the separator S10.

[0134] Comparative Example 1

[0135] The present comparative example used the same base film Z1 as in Example 1 as a lithium battery separator to prepare a separator DS1.

[0136] Comparative Example 2

[0137] The present comparative example provided a heat-sensitive sizing for a lithium battery separator and used the heat-sensitive sizing to prepare a lithium battery separator.

[0138] The preparation method of the present comparative example was basically the same as that of Example 1, except that in the present comparative example, an equal amount of ethylene acrylic acid copolymer (type 90A, melting point 95°C, Shanghai Xinuo Chemical Co., Ltd.) was used to replace the main agent in Example 1.

[0139] The present comparative example finally prepared the separator DS2.

[0140] Comparative Example 3

[0141] The present comparative example provided a heat-sensitive sizing for a lithium battery separator and used the heat-sensitive sizing to prepare a lithium battery separator.

[0142] The preparation method of the present comparative example was basically the same as that of Example 1, except that in the present comparative example, an equal amount of terpene-modified phenolic resin (type E-200NT, softening point 130°C, Jining Sun Never Sets Biological Science and Technology Co., Ltd.) was used to replace the tackifying resin in Example 1.

[0143] The present comparative example finally prepared the separator DS3.

[0144] Comparative Example 4

[0145] The present comparative example provided a heat-sensitive sizing for a lithium battery separator and used the heat-sensitive sizing to prepare a lithium battery separator.

[0146] The preparation method of the present comparative example was basically the same as that of Example 1, except that in the present comparative example, an equal amount of polyethylene wax (type 90A, melting point 85°C, Shanghai Xinuo Chemical Co., Ltd.) was used to replace the heat-sensitive wax in Example 1.

[0147] The present comparative example finally prepared the separator DS4.

[0148] Comparative Example 5

[0149] The present comparative example provided a heat-sensitive sizing for a lithium battery separator and used the heat-sensitive sizing to prepare a lithium battery separator.

[0150] The preparation method of the present comparative example is basically the same as that of example 1, except that the total amount of the additive in the present comparative example is 15 g, and the mass ratio of the rosin resin and the Fischer-Tropsch wax is the same as that of example 1.

[0151] The present comparative example finally prepared a separator DS5.

[0152] Comparative example 6

[0153] The present comparative example provides a heat-sensitive slurry for a lithium battery separator, and a lithium battery separator prepared using the heat-sensitive slurry.

[0154] The preparation method of the present comparative example is basically the same as that of example 1, except that no additive is used in the present comparative example, and the amount of the main agent is increased to keep the solid content of the heat-sensitive slurry A unchanged.

[0155] The present comparative example finally prepared a separator DS6.

[0156] Comparative example 7

[0157] The present comparative example provides a lithium battery separator.

[0158] The preparation method of the present comparative example is basically the same as that of example 1, except that in the present comparative example, the temperature-resistant coating main agent for preparing the base film Z1 is mixed with the heat-sensitive slurry A to obtain a functional slurry, which is coated on both sides of a 7 μm polyethylene-based film using a similar process as that of example 1, and the remaining preparation process is the same as that of example 1.

[0159] The present comparative example finally prepared a separator DS7.

[0160] Test example 1:

[0161] The separator S1 prepared in example 1 was observed by scanning electron microscope (SEM), and the results are shown in FIG. 1, wherein FIG. A shows the temperature-resistant coating layer of the Z1 separator, FIG. B shows the heat-sensitive protective layer of the Z1 separator, and FIG. C shows the heat-sensitive protective layer formed on the surface of the Z1 separator under the critical condition. Figure 2

[0162] Test example 2:

[0163] According to the requirements of GB / T36363-2018 Polyolefin Separator for Lithium Ion Battery, the separators prepared in the examples and comparative examples were tested for air permeability and thermal shrinkage performance.

[0164] ​The air permeability of the sample was tested by using a Gurley 4110 type air permeability tester according to the method specified in 6.5.4 of GB / T36363-2018; the transverse (TD) and longitudinal (MD) thermal shrinkage of the separator was tested according to the method specified in 6.5.2 of GB / T36363-2018, and the temperature was set to 150℃ and the holding time was 30 min; the test results are shown in Table 5 below:

[0165]

[0166] A simulated battery (stainless steel sheet / / separator / / stainless steel sheet) and a CHI660e electrochemical workstation were used to carry out real-time impedance tests to evaluate the high-temperature blocking effect of the separator: the simulated battery was placed in a blast drying oven, and the temperature was raised to 115℃ at a rate of 5℃ / min and then maintained for 10 min, and the change in the AC impedance of the battery during the temperature rise was continuously monitored.

[0167] The test results are shown in Table 6 below:

[0168]

[0169] From the above results, it can be seen that the heat-sensitive slurry provided by the application can form a fixed structure during the high-temperature melting and film-forming process, which can block ion transmission and also inhibit the shrinkage of the base film. The prepared separator has the advantages of rapid and efficient film formation, good high-temperature dimensional stability, excellent air permeability, and is suitable for lithium ion batteries.

[0170] Test Example 3:

[0171] Preparation of the battery: the side of the separator A was in contact with the positive electrode (lithium iron phosphate) of the battery, and the side of the separator B was in contact with the negative electrode (graphite) of the battery, and the battery was prepared into a cell by winding or stacking process; after assembly, high-temperature baking at 85℃, liquid injection, formation and capacity distribution, the battery was delivered. To evaluate the effect of the separator on the electrical performance of the battery, AC internal resistance (ACIR) and DC internal resistance (DCR) tests were carried out, as follows:

[0172] ACIR test: ACIR of the battery was tested by using an AC internal resistance tester. The ACIR test included after battery formation (ACIR1), after aging (ACIR2), after 24 h of capacity distribution (ACIR3) and after 96 h of capacity distribution (ACIR4). Test conditions: frequency 1 kHz, current 10 mA, accuracy ±0.1%.

[0173] DCR Test: The battery cells were placed in an environmental chamber at 25°C and DCR tests were performed at different SOCs (0-100%). Test conditions: (1) The 100% SOC battery was left to stand for 30 minutes to eliminate polarization effect; (2) A 280A DC pulse was applied between the positive and negative terminals using a DC internal resistance tester for 10ms, and the voltage drop ΔV was recorded; (3) DCR was calculated: R = ΔV / I. The test results are as follows. Figure 3 As shown in Figure A (ACIR test results) and Figure B (DCR test results), compared with Comparative Example 1, the ACR and DCR of Example 1 are both within the normal range and are lower than those of Comparative Example 1 without a thermal protective layer. This indicates that the thermal slurry of Example 1 does not have an adverse effect on the battery internal resistance, and the lower internal resistance is beneficial to the improvement of the battery's electrical performance and safety performance.

[0174] Cyclic testing: The test shall be conducted according to the method specified in Appendix A, Test Method A.2.11 of GB / T 36276-2018. Figure 4 It can be seen that after 478 cycles, the charging capacity retention rate of the battery in Example 1 ( Figure 4 Figure A in the figure), discharge capacity retention rate ( Figure 4 The results (Figure B) are significantly better than those of Comparative Example 1, indicating that the thermosensitive slurry of the present invention does not have an adverse effect on the battery's electrical performance and has excellent interface stability, which improves the battery's cycle life.

[0175] Test Example 4:

[0176] According to national standards, the separators prepared in the examples and comparative examples were applied to energy storage lithium-ion batteries for safety performance testing.

[0177] The overcharge test is conducted according to the method specified in Appendix A, Test Method A.2.12 of GB / T 36276-2018. The test battery sample is placed in a stainless steel clamp and the battery is observed to see if it opens the valve, leaks, produces gas, smokes, catches fire or explodes.

[0178] The short circuit test shall be conducted in accordance with the method specified in Appendix A, Test Method A.2.14 of GB / T 36276-2018. The test battery sample shall be placed in a stainless steel clamp and clamped. Observe whether the battery opens the valve, leaks, produces gas, smokes, catches fire or explodes.

[0179] The heating test shall be conducted in accordance with the method specified in Appendix A, Test Method A.2.18 of GB / T 36276-2018, and the battery shall be observed to see if the valve opens, leaks, produces gas, smokes, catches fire or explodes;

[0180] The needle puncture test (simulating internal short circuit of the battery) is tested according to the method specified in GB / T 31485 2015: the full battery monomer is placed in the needle puncture tester and clamped with a stainless steel clamp, and the needle puncture test is carried out, the test conditions are: 6mm steel needle (tungsten steel needle, smooth and clean surface without rust, the conical angle of the needle tip is 45°), the needle puncture speed is 25mm / s, the needle completely penetrates the battery, and is taken out after staying in the battery for 1h, and whether the battery is valve opening, liquid leakage, gas production, smoke emission, fire and explosion is observed.

[0181] Part of the needle puncture test process phenomenon diagram is shown in Figure 5 The test results are shown in Table 7 as follows:

[0182]

[0183]

[0184] From the above results, it can be seen that the heat-sensitive slurry provided by the present application, when the battery fails, the step melting effect is fused with each other, a continuous, certain adhesion and flexibility non-conductive thin film structure is formed at the interface between the electrode (positive and negative) and the separator, which isolates the positive and negative electrodes, blocks the ion transmission in the battery, terminates the battery reaction and heat release, improves the intrinsic safety of the battery, and does not affect the electrical performance, and is suitable for application in the field of electric power energy storage.

[0185] The above has made a detailed description of the embodiments of the present application, but the present application is not limited to the above embodiments, within the knowledge range of ordinary skilled in the art, various changes can be made without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A heat-sensitive slurry for a lithium-ion battery separator, characterized in that, The heat-sensitive slurry comprises the following components: a main agent, an additive, a dispersion stabilizer, and a binder. The components of the heat-sensitive slurry comprise, in terms of mass fraction, 80-120 parts of the main agent, 20-70 parts of the additive, 1-5 parts of the dispersion stabilizer, and 1-4 parts of the binder. The main agent is at least one selected from ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, polyolefin, ethylene-butyl acrylate copolymer, polymethyl methacrylate, polyurethane, ethylene-acrylic acid resin ionomer, or methyl acrylate / ethyl acrylate / methyl methacrylate copolymer. The additive is a combination of tackifying resin and heat-sensitive wax at a mass ratio of 1-4:

1. The melting temperature of the main agent is 5-20℃ higher than the softening point or melting point of the tackifying resin and the heat-sensitive wax. The softening point of the tackifying resin is lower than the melting point of the heat-sensitive wax.

2. The heat sensitive paste of claim 1, wherein, The components of the heat-sensitive slurry comprise, in terms of mass fraction, 90-110 parts of the main agent, 30-60 parts of the additive, 1.5-4 parts of the dispersion stabilizer, and 1.5-3.5 parts of the binder; the additive is a combination of tackifying resin and heat-sensitive wax at a mass ratio of 1.5-3:

1.

3. The heat sensitive paste of claim 1, wherein, The dispersion stabilizer is at least two selected from sodium succinate, polyether-modified siloxane, polyoxyethylene sorbitan monolaurate, sodium carboxymethyl cellulose, acrylic acid polymer, and sodium alginate; the binder is at least one selected from styrene-butadiene rubber, polyvinylidene fluoride, polyacrylamide, polyacrylic acid, polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, and polyacrylate.

4. The heat sensitive paste of claim 1, wherein, The melting temperature of the main agent is 10-15℃ higher than the softening point or melting point of the tackifying resin and the heat-sensitive wax; the softening point of the tackifying resin is 3-10℃ lower than the melting point of the heat-sensitive wax.

5. A method of preparing a heat sensitive paste as claimed in any one of claims 1 to 4, characterised in that, The heat-sensitive slurry comprises the following steps: S1, first mixing water, a main agent, and an additive to obtain a mixture I; S2, second mixing a dispersion stabilizer with the mixture I to obtain a mixture II; S3, third mixing water, a binder, and the mixture II to obtain the heat-sensitive slurry.

6. The preparation method according to claim 5, characterized in that, The first mixing conditions include a stirring speed of 200-500 rpm, a time of 30-60 min, and a temperature of 25-35℃; and / or, the second mixing conditions include a stirring speed of 400-800 rpm, a time of 25-50 min, and a temperature of 20-30℃; and / or, the third mixing conditions include a stirring speed of 200-400 rpm, a time of 15-30 min, and a temperature of 20-25℃.

7. A lithium-ion battery separator, characterized by, The separator comprises a base film and a heat-sensitive slurry coated on at least one side of the base film; the heat-sensitive slurry is the heat-sensitive slurry according to any one of claims 1-4; the base film comprises a polyolefin separator; the thickness of the polyolefin separator is 7-12 μm, and the thickness of the heat-sensitive slurry coating on the base film is 1-15 μm.

8. The lithium-ion battery separator of claim 7, wherein, The separator comprises a base film and a heat-sensitive slurry A coated on the positive electrode side of the base film and a heat-sensitive slurry B coated on the negative electrode side of the base film; The heat-sensitive slurry A is the heat-sensitive slurry according to any one of claims 1-4. The heat-sensitive paste B is a heat-sensitive paste to which 10 to 20 parts of an additive are added to the heat-sensitive paste A.

9. Use of the heat-sensitive paste according to any one of claims 1 to 4 or the separator according to claim 7, claim 8 in a lithium-ion battery.

10. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, characterized by, The separator is the lithium-ion battery separator according to claim 7 or 8.

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