Thermo-sensitive slurry for lithium battery diaphragm as well as preparation method and application of thermo-sensitive slurry

Abstract

The invention belongs to the technical field of lithium batteries, and particularly discloses thermosensitive slurry for a lithium battery diaphragm as well as a preparation method and application of the thermosensitive slurry. The thermosensitive slurry provided by the invention comprises the following components: a main agent, an additive, a dispersion stabilizer and a binder, the thermosensitive slurry comprises the following components in parts by weight: 80-120 parts of a main agent, 20-70 parts of an additive, 1-5 parts of a dispersion stabilizer and 1-4 parts of a binder, the main agent is selected from ethylene-acrylic acid copolymer and the like; the additive comprises tackifying resin and thermosensitive 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 thermosensitive wax. The thermosensitive slurry provided by the invention is coated on a base film to obtain a thermosensitive coating, when a battery breaks down, a thermosensitive protection layer can be formed, a positive electrode and a negative electrode are isolated, the thermal runaway reaction is avoided, and the safety of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a thermosensitive slurry for lithium battery separators, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries occupy an important position in the power supply market for portable electronic products such as electric vehicles and in the energy storage field due to their high energy density and long lifespan. Although significant progress has been made in the development of lithium-ion batteries, safety remains one of the key challenges for their further development. Lithium-ion batteries are highly susceptible to thermal runaway under the influence of electrical faults such as short circuits and overcharging, as well as heat sources, releasing large amounts of heat and explosive gases, leading to fires and explosions. Currently, many strategies exist to improve battery safety performance, such as flame-retardant electrolytes and PTC electrodes; however, these methods can affect the battery's electrochemical performance due to reduced electrolyte or electrode kinetics. In comparison, modification of the separator has the least impact on battery performance and has promising practical applications. High-safety separators with thermal shut-off functions are considered the most promising and attractive thermal protection strategy for lithium-ion batteries due to their reliability, simplicity, and low cost. Once the internal temperature of a lithium-ion battery reaches a certain value, the thermally shut-off separator can inhibit ion transfer, terminate the battery reaction, and prevent thermal runaway. Chinese patent CN114284640A discloses a lithium-ion battery separator with thermal shutdown function, comprising a porous base film and a thermal shutdown coating disposed on one or both sides of the porous base film; the thermal shutdown coating comprises the following components in parts by weight: 1-50 parts polymer particles, 0.1-5 parts aqueous binder, 0.1-5 parts dispersant, and 0.05-1 parts wetting agent. Although this solution blocks the porous channels of the base film by directly coating the surface of the base film with a high-adhesion thermal shutdown coating, thus blocking the transport of lithium ions, the pore-closing temperature of the separator is 120°C, which is close to the rupture temperature of the porous base film. Under thermal inertia, the separator is prone to damage, leading to a short circuit between the positive and negative electrodes.

[0003] Chinese patent CN114976487A discloses a boehmite-modified polyacrylonitrile reversible thermal shutdown lithium-ion battery separator, its manufacturing method, and its application. The method involves hydrothermal treatment of boehmite nanocrystals, water, and a crystal surface trap to obtain boehmite nanocrystals. Polyacrylonitrile, boehmite nanocrystals, and a solvent are then mixed and electrospun to form a composite membrane. This method introduces highly thermally stable boehmite and polyacrylonitrile, allowing the separator to maintain its dimensions at 200°C, exhibiting good thermal stability. However, this separator requires thermal shutdown above 150°C. At this temperature, the solid electrolyte interphase (SEI) membrane inside the battery decomposes, and the electrolyte reacts with the positive electrode, generating a large amount of heat and gas. This can breach the safety valve, ejecting a large amount of flammable electrolyte and fumes, which can easily lead to fire and explosion.

[0004] Chinese patent CN114597579A discloses a composite diaphragm, its preparation method, and its application, comprising a diaphragm substrate and a composite coating disposed on at least one surface of the diaphragm substrate; the composite coating comprises a ceramic material, a low-melting-point polymer material, and a polymer binder, wherein the ceramic material comprises 54%–90% by mass, and the low-melting-point polymer material comprises 8%–45% by mass; wherein the ceramic material serves as the skeleton material, and the low-melting-point polymer material fills the spaces between the ceramic materials. This composite diaphragm exhibits excellent heat shrinkage resistance and a low thermal shutdown temperature while maintaining air permeability. However, the method of filling the low-melting-point polymer material within a high-temperature resistant material can affect the efficiency of the diaphragm's thermal shutdown pore closure, easily leading to increased local internal resistance and heat generation due to inconsistent pore closure, thus triggering thermal runaway.

[0005] The safety mechanism of the above-mentioned membrane solutions is "to use heat-sensitive polymer materials to melt and flow into the pores of the base membrane, thereby closing the pores and blocking lithium-ion transport". The effectiveness of this approach depends on the structure of the original base membrane and coating, which has problems such as high pore-closing temperature and low membrane rupture temperature. More importantly, the speed, degree and uniformity of "blocking" are difficult to control. Under thermal inertia, before complete pore closure can be achieved, the membrane has already shrunk and decomposed, resulting in a short circuit between the positive and negative electrodes.

[0006] Therefore, there is an urgent need to develop new thermally sensitive coatings and safety separators for lithium batteries to better solve the problem of thermal runaway in lithium batteries, while overcoming problems such as poor pore-closing effect of separators and easy thermal inertial shrinkage. Summary of the Invention

[0007] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a thermosensitive slurry for lithium-ion battery separators. The thermosensitive slurry of this invention is coated onto the battery separator to form a thermosensitive coating. When the battery malfunctions, the molten / softened polymer in the thermosensitive slurry triggers a step-melting effect, fusing together to form a continuous, non-conductive thin-film structure—a thermosensitive protective layer—at the interface between the electrode and the separator. This protective layer blocks ion transport within the battery by forming independent separators between the positive and negative electrodes, while preventing short circuits between the positive and negative electrodes and the occurrence of exothermic runaway reactions between the electrodes and the electrolyte, thus terminating the exothermic reaction of the battery and improving its intrinsic safety. Furthermore, this thermosensitive slurry can strengthen the interfacial mechanical strength and prevent lithium dendrite penetration, thereby improving the high-temperature safety and interfacial stability of the battery.

[0008] The present invention also provides a method for preparing a heat-sensitive slurry.

[0009] The present invention also provides a lithium-ion battery separator.

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

[0011] In a first aspect, the present invention provides a heat-sensitive slurry for lithium-ion battery separators, comprising the following components: a main agent, additives, a dispersing stabilizer, and a binder;

[0012] The components of the thermosensitive slurry, by weight, include: 80-120 parts of main agent, 20-70 parts of additive, 1-5 parts of dispersant stabilizer and 1-4 parts of 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 composition of tackifying resin and heat-sensitive wax in a mass ratio of 1 to 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 thermosensitive wax.

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

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

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

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

[0020] According to some embodiments of the present invention, the components of the thermosensitive slurry, by weight, include: 90-110 parts of main agent, 30-60 parts of additive, 1.5-4 parts of dispersant stabilizer and 1.5-3.5 parts of binder.

[0021] According to some embodiments of the present invention, the components of the thermosensitive slurry, by weight, include: 90-110 parts of main agent, 30-50 parts of additive, 1.5-4 parts of dispersant stabilizer and 1.5-3.5 parts of binder.

[0022] According to some embodiments of the present invention, the components of the thermosensitive slurry also include water. The present invention does not have special requirements on the amount of water used; it is only necessary to add an appropriate amount of water so that the solid content of the thermosensitive slurry is 25wt%~40wt%.

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

[0024] Preliminary explorations of this invention have revealed that, under this preferred embodiment, when the thermosensitive slurry obtained by this invention is applied to a battery, in the event of overcharging, short circuits, or other faults, the thermosensitive protective coating formed by the melting of the thermosensitive slurry is denser and can adhere to the surface of the electrode, becoming a non-porous isolation layer that avoids contact between the positive and negative electrodes. This successfully blocks ion transport between the positive and negative electrodes, blocks the battery's thermal runaway reaction, and prevents the battery from opening valves, leaking liquid, generating gas, catching fire, or exploding, thus ensuring high safety.

[0025] According to some embodiments of the present invention, the dispersing 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 invention, the dispersion stabilizer includes sodium carboxymethyl cellulose, sodium succinate, and acrylic block copolymer.

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

[0028] The present invention has discovered that, under the preferred embodiment, the thermosensitive slurry obtained by the present invention is uniformly and stably dispersed, and is more evenly coated on the surface of the separator. When applied to the battery, it results in a faster fault thermal response, a more uniform thermosensitive protective layer, and higher battery safety.

[0029] According to some embodiments of the present invention, the adhesive 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 invention, 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 thermosensitive wax.

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

[0032] The design intent of the entire thermal coating in this invention is to maintain stability during normal battery operation and to rapidly respond and form an insulating layer when the battery overheats. The two temperature characteristics mentioned are intended to precisely control the "response sequence" and "synergistic effect" of different components during the heating process, thereby achieving rapid, effective, and robust shutdown protection.

[0033] Under normal operating conditions (temperature below the additive softening point), the coating is a robust framework composed of a high-melting-point main agent, with solid tackifying resin and thermosensitive wax particles uniformly dispersed within. At this stage, the coating exhibits high mechanical strength, does not impede normal ion transport, and ensures stable battery performance. In the initial overheating phase (temperature reaches the additive softening / melting point but not the main agent melting temperature), the tackifying resin softens first, becoming viscous; the thermosensitive wax then melts, becoming a low-viscosity liquid. At this point, the main agent remains solid, acting as a supporting framework to prevent the coating from collapsing or excessively flowing. The molten wax and softened resin begin to wet and encapsulate the main agent particles, flowing between the particles and initially creating adhesion. This ensures that the additive system is in an optimal state of suitable viscosity and easy spreadability before the main agent melts, laying a solid foundation for the final formation of a high-quality protective layer. As the temperature continues to rise to the main agent melting temperature, the main agent polymer, acting as the "framework," begins to melt, transforming from solid particles into a viscous flow state. The additives, which are already in a molten / softened state, rapidly and uniformly fuse with the molten main agent to form a continuous, dense film with good adhesion.

[0034] If the melting point of the main agent is too low (too close to or lower than that of the additive), all components may melt simultaneously, causing the coating to lose its skeletal support prematurely and flow excessively, or even be absorbed by the diaphragm or electrode, failing 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 that of the additive), when the additive has melted, the main agent is still too hard, which will hinder the flow and fusion of the additive, resulting in a discontinuous, porous or poorly adhered protective layer, which also fails to effectively block ion transport.

[0035] If the temperature difference between the tackifying resin and the thermosensitive wax is not properly designed (the thermosensitive wax temperature is lower than that of the tackifying resin), the wax will melt first while the resin has not yet softened. The liquid wax may not be able to mix effectively with the still-solid resin, easily leading to phase separation. Alternatively, the wax may flow separately first, resulting in uneven film formation and affecting the integrity and adhesion of the protective layer. If both melt at the same temperature, although they will respond simultaneously, the aforementioned synergistic effect of "tack first, then flow" is lacking, failing to achieve optimal flowability and spreading effect.

[0036] The temperature difference design between the main agent and the additives primarily ensures the timing of the thermal response and the structural integrity of the protective layer, while the temperature difference design of the additives mainly optimizes the melt flowability and film quality within the additive system. Based on this, the present invention significantly improves the thermal safety performance of the battery by enhancing the response reliability, film quality, and blocking efficiency of the thermosensitive coating.

[0037] A second aspect of the present invention provides a method for preparing a thermosensitive slurry as described in the first aspect of the present invention, comprising the following steps:

[0038] S1. Mix water, main agent and additives to obtain mixture I;

[0039] S2. The dispersant stabilizer is mixed with mixture I for the second time to obtain mixture II;

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

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

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

[0043] According to some embodiments of the present invention, the conditions for the first mixing include: a stirring speed of 200-500 rpm, a time of 30-60 min, and a temperature of 25-35°C.

[0044] According to some embodiments of the present invention, the conditions for the second mixing include: a stirring speed of 400-800 rpm, a time of 25-50 min, and a temperature of 20-30°C.

[0045] According to some embodiments of the present invention, the conditions for the third mixing include: a stirring speed of 200-400 rpm, a time of 15-30 min, and a temperature of 20-25°C.

[0046] In a third aspect, the present invention provides a lithium-ion battery separator, the separator comprising a base film and a thermosensitive paste coated on at least one side of the base film; the thermosensitive paste is the thermosensitive paste described in the first aspect of the present invention; the base film comprises a polyolefin separator; the thickness of the polyolefin separator is 7-12 μm, and the thickness of the thermosensitive paste coating on the base film is 1-15 μm.

[0047] According to some embodiments of the present invention, the polyolefin separator is a polyolefin separator that has undergone heat resistance treatment; the heat resistance treatment is to coat the separator with a heat resistance coating, wherein the coating slurry of the heat resistance coating includes coating agent I, coating agent II, coating improver, coating binder and solvent.

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

[0049] According to some embodiments of the present invention, the coating agent I is selected from at least one of ultrafine alumina, ultrafine boehmite, aramid, polyimide, nanofiber, lithium titanium aluminum phosphate, zirconium oxide, and silica; the coating 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 polymers, hydroxyethyl cellulose, polyethylene glycol, and sodium carboxymethyl cellulose; the coating binder is selected from at least one of polyacrylic acid, polyacrylate, polyacrylamide, polyvinyl alcohol, acrylate-butyl acrylate copolymer, styrene acrylate, and aliphatic waterborne polyurethane; and the solvent is selected from at least one of deionized water, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide.

[0050] It should be noted that in this invention, there are no special requirements for the method of preparing the coating slurry, as long as the components are mixed evenly. This invention also does not have special requirements for the coating process and coating thickness of the coating slurry on the base film, which can be carried out in accordance with conventional methods in the art. This invention will not be described in detail here, and those skilled in the art should not understand it as a limitation of this invention.

[0051] According to some embodiments of the present invention, the separator includes a base membrane and a thermosensitive paste A coated on the positive electrode side of the base membrane and a thermosensitive paste B coated on the negative electrode side of the base membrane;

[0052] The thermal slurry A is the thermal slurry described in the first aspect of the present invention;

[0053] The thermosensitive paste B is a thermosensitive paste with 10-20 parts of additives added to the thermosensitive paste A.

[0054] A fourth aspect of the present invention provides the application of the thermosensitive slurry as described in the first aspect of the present invention or the separator as described in the third aspect of the present invention in a lithium-ion battery.

[0055] A fifth aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the lithium-ion battery separator described in the third aspect of the present invention.

[0056] A schematic diagram of the separator coating structure in the lithium-ion battery of the present invention is shown below. Figure 1 The diagram on the left shows a schematic representation of the membrane coating's function. Figure 1 As shown in the right-hand diagram.

[0057] The beneficial effects of this invention are:

[0058] When the thermosensitive slurry provided by this invention is applied to a battery, in the event of a battery malfunction, the molten / softened polymers in the thermosensitive slurry on the positive and / or negative electrode sides will trigger a step-melting effect and fuse together under the combined action of internal pressure and temperature. This forms a continuous, non-conductive thin film structure with certain adhesion and flexibility at the interface between the electrodes (positive and negative electrodes) and the separator, isolating the positive and negative electrodes, blocking ion transport inside the battery, and preventing short circuits between the positive and negative electrodes and the occurrence of thermal runaway reactions induced between the electrode sheets and the electrolyte. This terminates the exothermic reaction of the battery and improves the intrinsic safety of the battery. At the same time, it strengthens the mechanical strength of the interface and prevents lithium dendrite penetration, thereby improving the high-temperature safety and interface stability of the battery.

[0059] The thermal slurry preparation process provided by this invention is simple, environmentally friendly, and low in cost. It can improve the high-temperature safety and interface stability of the battery, while not affecting the electrical performance of the battery during normal operation, making it suitable for large-scale application.

[0060] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0061] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0062] Figure 1 The diagram shows the structure of the lithium-ion battery provided by the present invention, wherein the left diagram is a schematic diagram of the battery and the separator coating structure, and the right diagram is a schematic diagram of the function of the separator coating.

[0063] Figure 2 The images shown are SEM images of the diaphragm S1 in Embodiment 1 of the present invention, wherein: A is a SEM image of the heat-resistant coating, B is a SEM image of the thermosensitive protective layer, and C is a SEM image of the thermosensitive protective layer that forms a film on the diaphragm surface when the critical conditions are met.

[0064] Figure 3The figures show the battery performance test results prepared with the separators of Example 1 and Comparative Example 1 of the present invention, wherein Figure A shows the ACIR test results and Figure B shows the DCR test results under different SOC conditions.

[0065] Figure 4 The figures show the battery cycle performance test results prepared with the separators of Example 1 and Comparative Example 1 of the present invention, wherein Figure A shows the test results of the capacity retention rate during charging cycle and Figure B shows the test results of the capacity retention rate during discharging cycle.

[0066] Figure 5 The following are diagrams illustrating the battery needle penetration test process of the present invention: Figure A shows the battery needle penetration test process of the separator prepared in Example 1 of the present invention; Figure B shows the battery needle penetration test process of the separator prepared in Example 3 of the present invention; and Figure C shows the battery needle penetration test process of the separator prepared in Comparative Example 1 of the present invention.

[0067] Figure reference numerals: 1-Base film; 2-Temperature resistant coating; 3-Thermosensitive coating; 4-Positive electrode; 5-Negative electrode; 6-Thermosensitive protective layer. Detailed Implementation

[0068] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0069] Unless otherwise specified in the examples, the procedures were performed under standard conditions or conditions recommended by the manufacturer. All reagents and instruments used, unless otherwise specified by the manufacturer, were commercially available standard products, and all reagents were analytical grade products.

[0070] Preparation Example 1: This preparation example is used to exemplify the heat-resistant coating treatment of the base film used in this invention and its preparation method:

[0071] raw material:

[0072] Coating agent I: Ultrafine alumina, D 50 The coating thickness is 0.2-0.6μm, model number HJA-400, purchased from Anhui Yishitong Materials Technology Co., Ltd.; Coating main agent II: aluminum hydroxide, D 50 ≤2.5μm, model JATH-01FD, purchased from Anhui Yishitong Materials Technology Co., Ltd.;

[0073] Coating improvers: Ammonium polyacrylate, CAS No. 9003-03-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; Sodium carboxymethyl cellulose, model WY-2800, purchased from Changshu Weiyi Technology Co., Ltd.

[0074] Coating adhesive: Polyacrylate emulsion, model GR-401, solid content 29%, purchased from Hunan Gaorui Power Materials Co., Ltd.; Polyacrylamide solution, model GR-508GⅡ, solid content 20%, purchased from Hunan Gaorui Power Materials Co., Ltd.

[0075] Base film preparation method:

[0076] Mix 0.84 kg of coating agent I, 0.3 kg of coating 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 in a sand mill for 20 min (speed 500 rpm), add coating binder polyacrylate 0.056 kg and polyacrylamide 0.034 kg, and stir at low speed for 60 min (stirring speed 300 rpm); apply a 1.5 μm thick coating slurry to both sides of a 7 μm polyethylene base film using a gravure coating process, and then dry at 45℃ to obtain a heat-resistant coating base film, named base film Z1.

[0077] Example 1

[0078] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0079] Prepare the raw materials according to Table 1, including:

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

[0081] Tackifying resin: Rosin resin, water-based emulsion, softening point 90℃, model SBR-939, solid content 55%, purchased from Guangzhou Songbao Chemical Co., Ltd.

[0082] Thermosensitive wax: Fischer-Tropsch wax, water-based emulsion, melting point 95℃, solid content 33.5%, model 5351, purchased from Shanghai Xinnuo Chemical Co., Ltd.;

[0083] Sodium succinate: a pale yellow to yellow liquid with a solid content of 75±2%, product name Comwet® 0057, purchased from Shanghai Yingcheng Chemical Co., Ltd.;

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

[0085] Sodium carboxymethyl cellulose: powder, model WY-2800, purchased from Changshu Weiyi Technology Co., Ltd., and prepared as an aqueous solution with a solid content of 2% for use;

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

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

[0088] Preparation of thermosensitive slurry:

[0089] 1) The first material containing 10.33g of water, main agent and additive is mixed for the first time to obtain mixture I. The conditions for the first mixing are: stirring speed of 200rpm, time of 30min and temperature of 25℃.

[0090] 2) The second material containing the dispersant stabilizer and mixture I is mixed a second time to obtain mixture II; the conditions for the second mixing are: stirring speed of 400 rpm, time of 25 min, and temperature of 25℃;

[0091] 3) The third material containing 10g of water, binder, and mixture II is mixed in a third batch to obtain a heat-sensitive slurry; the solid content of the heat-sensitive slurry is about 30%.

[0092] Preparation of the diaphragm:

[0093] Thermosensitive slurry was coated on side A of the base membrane Z1 prepared in Preparation Example 1. After drying at 30°C, the thickness of the thermosensitive coating was 2 μm. Then, the thermosensitive slurry was coated on side B of the base membrane Z1. After drying at 35°C, the thickness of the thermosensitive coating was 2 μm. The membrane was then left to stand overnight in a drying room (25°C, humidity <1% RH) to obtain membrane S1.

[0094] Example 2

[0095] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0096] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the thermosensitive slurry formulation of this embodiment is different from that of Example 1, as shown in Table 2.

[0097] In this embodiment, the diaphragm S2 was finally obtained.

[0098] Example 3

[0099] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0100] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the additives used in this embodiment are rosin resin and Fischer-Tropsch wax in a mass ratio of 1:1.

[0101] In this embodiment, the final prepared membrane S3 is obtained.

[0102] Example 4

[0103] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0104] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the additives used in this embodiment are rosin resin and Fischer-Tropsch wax in a mass ratio of 2:1, and the total mass of the additives is 55g.

[0105] In this embodiment, the final prepared membrane S4 is obtained.

[0106] Example 5

[0107] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0108] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that the total amount of dispersant stabilizer used in this embodiment is the same as that in Example 1, but the mass ratio of sodium carboxymethyl cellulose, sodium succinate and acrylic block copolymer is 1:1.48:1.48.

[0109] In this embodiment, the final prepared membrane S5 is obtained.

[0110] Example 6

[0111] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0112] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in this embodiment, ethylene-vinyl acetate copolymer (model ET2805, melting point 110℃, purchased from Jiangsu Sirbang Petrochemical Co., Ltd.) is used to replace the ethylene-acrylic acid copolymer in Example 1.

[0113] In this embodiment, the final prepared membrane S6 is obtained.

[0114] Example 7

[0115] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0116] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in this embodiment, only the thermal slurry on the negative electrode side of the diaphragm is coated, and the thermal slurry on the positive electrode side is not coated.

[0117] In this embodiment, the final prepared membrane S7 is obtained.

[0118] Example 8

[0119] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0120] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in this embodiment, two kinds of thermosensitive pastes are prepared: thermosensitive paste A and thermosensitive paste B. The preparation methods of the two are the same as those of Example 1. The thermosensitive paste A, which is the same as that of Example 1, is coated on the negative electrode side, and the thermosensitive paste B, which has a different composition from that of thermosensitive paste A, is coated on the positive electrode side, as shown in Table 3 below.

[0121] In this embodiment, the final prepared membrane S8 is obtained.

[0122] Example 9

[0123] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0124] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in this embodiment, the amount of each raw material and water is adjusted so that the solid content of the prepared heat-sensitive slurry A is 35wt%, as shown in Table 4 below.

[0125] In this embodiment, the final prepared membrane S9 is obtained.

[0126] Example 10

[0127] This embodiment provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0128] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in this embodiment, the base film Z1 is not used, and the thermosensitive slurry A is directly coated on both sides of the 7μm polyethylene base film. The rest of the preparation process is the same as that of Example 1.

[0129] In this embodiment, the final prepared membrane S10 is obtained.

[0130] Comparative Example 1

[0131] This comparative example uses the same base film Z1 as in Example 1 as the lithium battery separator, namely separator DS1.

[0132] Comparative Example 2

[0133] This comparative example provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0134] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in this comparative example, an equal mass of ethylene-acrylic acid copolymer (model 90A, melting point 95℃, Shanghai Xinnuo Chemical Co., Ltd.) is used to replace the main agent in Example 1.

[0135] The final diaphragm DS2 was prepared in this comparative example.

[0136] Comparative Example 3

[0137] This comparative example provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0138] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in this comparative example, an equal mass of terpene-modified phenolic resin (model E-200NT, softening point 130℃, Jining Ribuluo Biotechnology Co., Ltd.) is used to replace the tackifying resin in Example 1.

[0139] The final diaphragm prepared in this comparative example is DS3.

[0140] Comparative Example 4

[0141] This comparative example provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0142] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in this comparative example, the thermosensitive wax in Example 1 is replaced with an equal mass of polyethylene wax (model 90A, melting point 85℃, Shanghai Xinnuo Chemical Co., Ltd.).

[0143] The final diaphragm prepared in this comparative example is DS4.

[0144] Comparative Example 5

[0145] This comparative example provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0146] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that the total amount of additives used in this comparative example is 15g, and the mass ratio of rosin resin and Fischer-Tropsch wax is the same as that in Example 1.

[0147] The final diaphragm prepared in this comparative example is DS5.

[0148] Comparative Example 6

[0149] This comparative example provides a thermosensitive slurry for lithium battery separators, and uses the thermosensitive slurry to prepare lithium battery separators.

[0150] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that no additives are used in this comparative example, and the amount of main agent is increased to keep the solid content of the heat-sensitive slurry A unchanged.

[0151] The final diaphragm prepared in this comparative example is DS6.

[0152] Comparative Example 7

[0153] This comparative example provides a lithium battery separator.

[0154] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in this comparative example, the heat-resistant coating agent for preparing the base film Z1 is mixed with the heat-sensitive slurry A to obtain the functional slurry, which is then coated on both sides of a 7μm polyethylene base film using a process similar to that of Example 1. The rest of the preparation process is the same as that of Example 1.

[0155] The final diaphragm prepared in this comparative example is DS7.

[0156] Test Example 1:

[0157] The membrane S1 prepared in Example 1 was observed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown in the figure, Figure A shows the temperature-resistant coating of the Z1 diaphragm, Figure B shows the thermosensitive protective layer of the Z1 diaphragm, and Figure C shows the thermosensitive protective layer formed on the surface of the Z1 diaphragm when the critical conditions are met.

[0158] Test Example 2:

[0159] In accordance with the requirements of GB / T36363-2018 Polyolefin Separators for Lithium-ion Batteries, the separators prepared in the examples and comparative examples were tested for air permeability and heat shrinkage performance.

[0160] The air permeability of the samples was tested using a Gurley 4110 air permeability tester, following the method specified in 6.5.4 of GB / T36363-2018. The transverse (TD) and longitudinal (MD) heat shrinkage of the diaphragm were tested according to the method specified in 6.5.2 of GB / T36363-2018, with the holding temperature set at 150℃ and the holding time at 30 min. The test results are shown in Table 5 below.

[0161] Real-time impedance testing was conducted using a simulated battery (stainless steel sheet / / separator / / stainless steel sheet) and a CHI660e electrochemical workstation to evaluate the high-temperature blocking effect of the separator: the simulated battery was placed in a forced-air drying oven and heated to 115°C at a rate of 5°C / min and held for 10 min, while continuously monitoring the change in AC impedance of the battery during the heating process.

[0162] The test results are shown in Table 6 below:

[0163] The results above show that the thermosensitive slurry provided by the present invention can form a fixed structure during the high-temperature melting and film formation process, which can block ion transport and inhibit the shrinkage of the base film. The prepared separator has fast and efficient film formation, good high-temperature dimensional stability, and excellent air permeability, making it suitable for lithium-ion batteries.

[0164] Test Example 3:

[0165] Battery fabrication: The separator (side A) is brought into contact with the positive electrode (lithium iron phosphate), and the separator (side B) is brought into contact with the negative electrode (graphite). Cells are fabricated using winding or stacking processes. After assembly, baking at 85°C, electrolyte injection, and formation and capacity testing, the cells are shipped out. To evaluate the impact of the separator on battery electrical performance, AC internal resistance (ACIR) and DC internal resistance (DCR) tests are conducted, as detailed below:

[0166] ACIR testing: The ACIR of the battery is tested using an AC internal resistance meter. The ACIR test includes tests after battery formation (ACIR1), after aging (ACIR2), after 24 hours of capacity grading (ACIR3), and after 96 hours (ACIR4). Test conditions: frequency 1kHz, current 10mA, accuracy ±0.1%.

[0167] 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.

[0168] 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.

[0169] Test Example 4:

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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;

[0174] The needle penetration test (simulating an internal short circuit in a battery) is conducted according to the method specified in GB / T 31485 2015: a fully charged battery cell is placed in the needle penetration test machine and clamped in a stainless steel fixture. The test conditions are: 6mm steel needle (tungsten steel needle, smooth, clean and rust-free surface, cone angle of the needle tip 45°), needle penetration speed 25mm / s, the needle completely penetrates the battery, and the battery is removed after 1 hour. The battery is then observed to see if it opens the valve, leaks, produces gas, smokes, catches fire or explodes.

[0175] Some of the phenomena observed during the acupuncture test are shown in the following diagrams. Figure 5 As shown in Table 7 below:

[0176] The results above show that the thermosensitive slurry provided by the present invention, when the battery fails, fuses with each other through a step-melting effect, forming a continuous, non-conductive thin film structure with certain adhesion and flexibility at the interface between the electrodes (positive and negative electrodes) and the separator. This isolates the positive and negative electrodes, blocks the internal ion transport of the battery, terminates the exothermic reaction of the battery, improves the intrinsic safety of the battery, and does not affect the electrical performance. It is suitable for application in the field of power energy storage.

[0177] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A thermally sensitive slurry for lithium-ion battery separators, characterized in that, It includes the following components: main agent, additives, dispersant stabilizer and binder; The components of the thermosensitive slurry, by weight, include: 80-120 parts of main agent, 20-70 parts of additive, 1-5 parts of dispersant stabilizer and 1-4 parts of binder; 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; The additive is a composition of tackifying resin and heat-sensitive wax in a mass ratio of 1 to 4:1; 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 thermosensitive wax. The softening point of the tackifying resin is lower than the melting point of the thermosensitive wax.

2. The thermosensitive slurry according to claim 1, characterized in that, The components of the thermosensitive slurry, by weight, include: 90-110 parts of main agent, 30-60 parts of additive, 1.5-4 parts of dispersant stabilizer and 1.5-3.5 parts of binder; the additive is a composition of tackifying resin and thermosensitive wax in a weight ratio of 1.5-3:

1.

3. The thermosensitive slurry according to claim 1, characterized in that, The dispersant and 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; 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.

4. The thermosensitive slurry according to claim 1, characterized in that, 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 thermosensitive wax; the softening point of the tackifying resin is 3-10°C lower than the melting point of the thermosensitive wax.

5. A method for preparing a thermosensitive slurry as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mix water, main agent and additives to obtain mixture I; S2. The dispersant stabilizer is mixed with mixture I for the second time to obtain mixture II; S3. Mix water, binder and mixture II in a third mixing process to obtain the heat-sensitive slurry.

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

7. A lithium-ion battery separator, characterized in that, The separator includes a base membrane and a thermosensitive paste coated on at least one side of the base membrane; the thermosensitive paste is the thermosensitive paste according to any one of claims 1 to 4; the base membrane includes a polyolefin separator; the thickness of the polyolefin separator is 7 to 12 μm, and the thickness of the thermosensitive paste coating on the base membrane is 1 to 15 μm.

8. The lithium-ion battery separator according to claim 7, characterized in that, The diaphragm includes a base membrane and a thermosensitive paste A coated on the positive electrode side of the base membrane and a thermosensitive paste B coated on the negative electrode side of the base membrane; The thermosensitive paste A is the thermosensitive paste according to any one of claims 1 to 4; The thermosensitive paste B is a thermosensitive paste with 10-20 parts of additives added to the thermosensitive paste A.

9. The application of the thermosensitive slurry as described in any one of claims 1 to 4 or the separator as described in claim 7 or claim 8 in lithium-ion batteries.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The separator is the lithium-ion battery separator as described in claim 7 or 8.

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