Current collector containing heat-sensitive flame-retardant microcapsule coating, preparation method of current collector and application of current collector in lithium battery

Abstract

The invention relates to a current collector containing a heat-sensitive flame-retardant microcapsule coating, a preparation method of the current collector and application of the current collector in a lithium battery, firstly, a heat-sensitive flame-retardant microcapsule wrapped with a fire extinguishing agent core material is prepared and mixed in conductive slurry, and the current collector is coated with the heat-sensitive flame-retardant microcapsule; after the current collector coated with the heat-sensitive flame-retardant microcapsule coating is further prepared into a lithium battery, an active fireproof function can be realized, and when the temperature of the battery exceeds a set threshold value, a fire extinguishing agent is automatically released, so that millisecond-level active protection is realized; the fire extinguishing unit is integrated on the current collector in situ, so that the purpose of efficiently inhibiting thermal runaway is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a current collector containing a thermosensitive flame-retardant microcapsule coating and a preparation method and application thereof in lithium batteries. BACKGROUND

[0002] Lithium ion batteries have been widely used in consumer electronics, electric vehicles and large-scale energy storage due to their high energy density and long cycle life. However, lithium ion batteries are prone to thermal runaway under abuse conditions (such as overcharge, short circuit, extrusion, etc.), which can cause fire, explosion and other serious safety accidents, thereby restricting their further development and application.

[0003] Thermal runaway is the result of a series of exothermic side reactions in the battery. Once triggered, the battery temperature will rise sharply, up to 800℃ or more, accompanied by flammable gas injection and flame. Existing external safety measures, such as battery management system (BMS), thermal management system, reinforced shell, etc., can delay or control thermal runaway to some extent, but often respond with a lag and cannot intervene fundamentally from the core area of the battery internal electrochemical reaction - the electrode layer.

[0004] With the rapid development of new energy vehicles and energy storage industry, the safety problem of lithium ion battery thermal runaway has become increasingly prominent. The existing safety technology has significant limitations: electrolyte additives are continuously consumed during the cycle process; the thermal response of the fireproof separator is lagging; the external fire extinguishing system cannot timely block the chain reaction in the battery. Especially for high energy density batteries, traditional methods are difficult to balance safety and electrochemical performance.

[0005] Thermal runaway is essentially an energy feedback process. Local overheating triggers electrolyte decomposition, heat production leads to temperature rise in adjacent areas, and active material phase change releases heat, resulting in exponential temperature growth. The key to prevention and control is to interrupt the energy accumulation in the initial stage in time. Current research focuses on the application of fire extinguishing agents, but there are implementation bottlenecks: gas fire extinguishing agents need high-pressure containers for storage; dry powder fire extinguishing agents corrode electrodes; liquid fire extinguishing agents cause internal short circuit of the battery.

[0006] Therefore, there is an urgent need in the art for a technical solution that can quickly and actively respond from the core area of the battery reaction, and effectively inhibit the early development of thermal runaway through multiple mechanisms. SUMMARY

[0007] To solve the above technical problems, the application provides a current collector containing a thermosensitive flame-retardant microcapsule coating and a preparation method and application thereof in lithium batteries.

[0008] The technical solution adopted by the application is: a preparation method of a current collector containing a thermosensitive flame-retardant microcapsule coating, comprising the following steps:

[0009] S1: Preparation of MUF prepolymer, a resin solution for the shell layer of thermosensitive flame-retardant microcapsules;

[0010] S2: Preparation of emulsion for the core of the heat-sensitive flame-retardant microcapsule;

[0011] S3: The emulsion is added to the resin solution MUF prepolymer to prepare heat-sensitive flame-retardant microcapsules;

[0012] S4: Add conductive agent and binder to solvent to make conductive paste;

[0013] S5: Disperse the heat-sensitive flame-retardant microcapsules in the conductive slurry;

[0014] S6: A conductive slurry containing thermosensitive flame-retardant microcapsules is coated onto a metal foil substrate and dried to obtain a current collector containing a thermosensitive flame-retardant microcapsule coating.

[0015] Preferably, in step S1, the prepolymer is prepolymerized from melamine, urea and formaldehyde solution (37%), and the input ratio is 57:0:100~43:13:100 by mass.

[0016] Preferably, in step S1, the pH value of the prepolymer reaction process is controlled at 8~10, and the reaction temperature is controlled at 25℃~80℃.

[0017] Preferably, in step S2, the emulsion includes a fire-retardant core material, which is composed of one or more of perfluorohexanone, heptafluorocyclopentane, 2-BTP, perfluorotributylamine and perfluorooctane.

[0018] Preferably, in the conductive slurry, the conductive agent is at least one of conductive carbon black, carbon nanotubes, intermediate carbon phase microspheres, graphite, graphene and carbon fiber; the binder is at least one of polyvinylidene fluoride and polyacrylate; and the conductive agent is 1% to 10% by mass, the binder is 1% to 40%, and the thermosensitive flame retardant microcapsules are 25% to 35%.

[0019] Preferably, the metal foil substrate is aluminum foil, copper foil, composite aluminum foil, or composite copper foil with a thickness of 3 to 20 μm.

[0020] Preferably, the coated conductive functional layer is subjected to gradient drying, followed by step drying at corresponding times and temperatures: the first stage is drying at 70℃~80℃ for 3~8 minutes; the second stage is drying at 100℃~110℃ for 6~10 minutes; and the third stage is drying at 80℃~90℃ for 3~5 minutes.

[0021] Preferably, the dry thickness of the composite coating is 3–50 μm.

[0022] A current collector containing a thermosensitive flame-retardant microcapsule coating is prepared by a method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating.

[0023] An electrode sheet includes a current collector containing a thermosensitive flame-retardant microcapsule coating.

[0024] A lithium battery includes a current collector containing a thermosensitive flame-retardant microcapsule coating.

[0025] The advantages and positive effects of this invention are: it provides a thermosensitive flame-retardant microcapsule that can rupture in response to a set temperature, containing a fire extinguishing agent. Upon rupture due to heat, the fire extinguishing agent is released, effectively suppressing thermal runaway; when used in the conductive materials of lithium batteries, it can significantly improve the safety performance of lithium batteries; when thermal runaway occurs in the battery, the microcapsule shell ruptures at a trigger temperature of 120°C, and the released fire extinguishing agent effectively suppresses the thermal chain reaction through the synergistic effect of gas phase cooling, free radical capture, and inert gas isolation, greatly improving the overall safety performance of the lithium-ion battery system. Attached Figure Description

[0026] Figure 1 This is a thermogravimetric curve of the thermosensitive flame-retardant microcapsules of the present invention. Detailed Implementation

[0027] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0028] This invention relates to a current collector containing a thermosensitive flame-retardant microcapsule coating, its preparation method, and its application in lithium batteries. First, a thermosensitive flame-retardant microcapsule encapsulating a fire extinguishing agent core material is prepared. This microcapsule can be mixed into a conductive slurry and coated onto the current collector. After the current collector coated with the thermosensitive flame-retardant microcapsule coating is further manufactured into a lithium battery, it can achieve active fire protection. When the battery temperature exceeds a set threshold, it automatically releases the fire extinguishing agent, achieving millisecond-level active protection. By integrating the fire extinguishing unit in situ into the current collector, the purpose of efficiently suppressing thermal runaway is achieved.

[0029] The core material of the thermosensitive flame-retardant microcapsule is a fire-retardant material with fire-extinguishing properties, coated with melamine-urea-formaldehyde resin. This thermosensitive flame-retardant microcapsule can rupture under certain temperature conditions, releasing the internal core material components (fire extinguishing agent), thereby suppressing battery thermal runaway. During preparation, an emulsion capable of forming the core material and a prepolymer capable of forming the coating material are prepared separately. The fire-retardant core material is formed from one or more of perfluorohexanone, heptafluorocyclopentane, 2-BTP, perfluorotributylamine, and perfluorooctane. The prepolymer is formed from a mixture of melamine, urea, and formaldehyde. The core material emulsion is added to the prepolymer, and after in-situ polymerization, curing, washing, and drying, microcapsules with an average particle size of 1–15 μm are obtained. These microcapsules are thermosensitive and can rupture at an ambient temperature of 120°C, releasing the fire extinguishing agent, thereby achieving rapid temperature control.

[0030] The microcapsule preparation method is as follows:

[0031] S1: Preparation of MFU prepolymer of resin solution for the shell layer of thermosensitive flame retardant microcapsules: Melamine, urea, formaldehyde solution and deionized water are added to a reaction vessel and stirred rapidly until the monomers are completely dissolved. The pH of the solution is adjusted to weak alkalinity and heated to 25~80℃ for 1~5 hours. After that, the solution is rapidly cooled to room temperature and diluted with water to obtain the MUF prepolymer. In some embodiments of the present invention, the pH value is 8~10.

[0032] S2: Prepare a partial emulsion of the fireproof core of a heat-sensitive flame-retardant microcapsule; add one or more of perfluorohexanone, heptafluorocyclopentane, 2-BTP, perfluorotributylamine and perfluorooctane to a beaker, add an appropriate amount of emulsifier and methyl perfluorobutyl ether, stir at high speed for initial reaction, then adjust the speed for emulsification, and add defoamer and sodium chloride solution during the process to stabilize the emulsion;

[0033] S3: Adjust the pH of the emulsion to weakly acidic, add it slowly through multiple channels to the MUF prepolymer prepared in step S1, stir and disperse quickly for coating, heat and react for a period of time, filter and wash the product, and finally freeze dry to obtain thermosensitive flame retardant microcapsules with an average particle size of 1-15 μm.

[0034] Furthermore, the preparation of current collectors containing microcapsules also includes the following steps:

[0035] Conductive agent and binder are added to solvent to prepare conductive slurry; S3 thermosensitive flame retardant microcapsules are added to conductive slurry and dispersed, then coated onto metal foil substrate, and dried to obtain current collector containing thermosensitive flame retardant microcapsule coating.

[0036] S4: Conductive paste preparation: Composed of conductive carbon material (particle size 30-50 nm) and polyvinylidene fluoride (molecular weight 500,000), the conductive agent and binder are dispersed in NMP in a certain proportion, and the solid content is controlled at 40%-65%. The conductive functional layer contains at least one conductive agent selected from conductive carbon black, carbon nanotubes, intermediate carbon phase microspheres, graphite, graphene, and carbon fiber, and at least one binder selected from polyvinylidene fluoride and polyacrylate; wherein, calculated by mass percentage, the conductive agent is 1%-10% and the binder is 1%-40%.

[0037] S5: Microcapsule blending: Add dried microcapsules to the conductive slurry at a mass ratio of 30±10%; stir at 500-1000 rpm for 30-60 min; the conductive slurry adopts a three-stage dispersion process, and the viscosity of the slurry after blending is controlled at 2000-8000 cp.

[0038] S6: Coating and forming: The mixed slurry is coated onto the metal foil using a slit coating method. The metal foil substrate is aluminum foil, copper foil, composite aluminum foil, or composite copper foil with a thickness of 3 to 20 μm. The tension during the coating process is kept constant at 15 ± 1 N to prevent mechanical damage to the microcapsules. The coating speed is 0.5 to 5 m / min. The coating gap accuracy is controlled at ± 2 μm.

[0039] S7: Step drying: The coated conductive functional layer is subjected to gradient drying. First, it is pre-cured at room temperature and humidity ≤10% for 1-3 hours, then subjected to step drying. The first stage is drying at 70℃-80℃ for 3-8 minutes; the second stage is drying at 100℃-110℃ for 6-10 minutes; and the third stage is drying at 80℃-90℃ for 3-5 minutes. The resulting current collector containing microcapsules has a dry coating thickness of 3-50 μm.

[0040] The adaptive current collector of the integrated thermosensitive flame-retardant microcapsules prepared above can support the lithium battery electrode sheet, or the thermosensitive flame-retardant microcapsules prepared in the above process can be added to the active material layer on the surface of the electrode sheet and then assembled to form a lithium battery.

[0041] By integrating thermosensitive flame-retardant microcapsules into the conductive functional layer, the shell material (melamine-urea-formaldehyde resin) has a precise rupture temperature of approximately 120°C to 150°C. Within the normal operating temperature range of the battery, the functional layer maintains excellent conductivity and structural stability, with negligible impact on the battery's internal resistance and cycle performance. Once the battery's internal temperature rises sharply to the microcapsule rupture point due to thermal runaway, the microcapsule ruptures instantly, releasing a composite fire extinguishing agent that responds rapidly through a multi-mechanism synergistic effect: perfluorohexanone and heptafluorocyclopentane exert efficient physical cooling (gas-phase cooling) while simultaneously diluting the oxygen concentration to form an isolation barrier. 2-BTP and perfluorotributylamine not only have the effects of gas phase cooling and oxygen dilution, but can also capture free radicals in the combustion chain reaction at high temperatures, blocking the chemical process of flame propagation; perfluorooctane is characterized by its excellent chemical stability and gas phase diffusion ability, and achieves flame retardancy by filling the combustion space after vaporization and reducing the concentration of combustible gases. This method of rapidly releasing extinguishing agents from the current collector / electrode source can significantly reduce the peak temperature and heating rate of thermal runaway of individual cells, and effectively block the spread of heat to adjacent cells in the module, thereby greatly improving the overall safety performance of lithium-ion battery systems.

[0042] This functional layer remains stable under normal battery conditions, and its impact on the battery's electrochemical performance is controllable. When the battery experiences thermal runaway, the microcapsule shell begins to rupture at 120°C. The released extinguishing agent, through the synergistic effect of gas-phase cooling, free radical capture, and inert gas isolation, reduces the peak temperature of thermal runaway in a single cell, slows down the rate of temperature rise, and effectively suppresses thermal chain reactions.

[0043] The present invention will be described below with reference to the embodiments. Experimental methods that do not specify the operation steps are performed in accordance with the corresponding product instructions. Unless otherwise specified, the instruments, reagents and consumables used in the embodiments can be purchased from commercial companies.

[0044] Example 1: Current collector coated with functional layer using aluminum foil as substrate

[0045] 1. Microcapsule preparation: Add 640g of melamine, 200g of urea, and 1.6L of formaldehyde solution (37%) to the reactor. Stir at 2000r / min for 15 minutes to rapidly dissolve the monomers. Adjust the pH to 8.8 with sodium hydroxide and adjust the temperature to 70℃. After reacting for 1 hour, cool to room temperature to form a prepolymer. Add 2L of deionized water to dilute. Take 10g of perfluorohexanone, 10g of heptafluorocyclopentane, 10g of 2-BTP, 0.2g of sodium dodecylbenzenesulfonate, 0.2g of methyl perfluorobutyl ether, and 100g of deionized water. Adjust the stirring speed to 500r / min. After the solution is initially mixed, adjust the stirring speed to 200r / min and stir rapidly to emulsify. Add 2mL of 1-octanol to defoam, and mix to form a core material emulsion. Then reduce the stirring speed to 500r / min and add 5mL of 5% sodium chloride to stabilize the emulsion. Add citric acid solution to adjust the pH of the emulsion to 4.5. Disperse the emulsion in the prepolymer aqueous solution at a flow rate of 1mL / min. After stirring at 70℃ for 2 hours, filter and wash, and freeze-dry at -40℃ for 24 hours to obtain thermosensitive flame-retardant microcapsules with an average particle size of 4μm and a rupture temperature of approximately 120℃~150℃. The thermogravimetric curve of the thermosensitive flame-retardant microcapsules is shown in the figure. Figure 1 .

[0046] 2. Preparation of conductive paste: Accurately weigh 540g of conductive agent SuperP, 90g of binder PVDF, and 2370g of solvent NMP into a homogenizing tank, and stir at 1200r / min for 2h to form a uniform and stable conductive paste.

[0047] 3. Microcapsule blending: Weigh 270g of the heat-sensitive flame-retardant microcapsules prepared in step 1 and slowly add them to the conductive slurry in step 2. Then stir at a low speed of 400 rpm for 15 minutes to ensure that the microcapsules are uniformly dispersed in the slurry. The viscosity of the slurry is tested to be 4500±500cp.

[0048] 4. Coating and Forming: Using a transfer coater, the above-mentioned mixed slurry is coated onto an aluminum foil substrate with a thickness of 12 μm. The coating speed is set to 1.2 m / min, and the coating gap is controlled to 10 μm ± 2 μm to form a uniform wet film.

[0049] 5. Step drying: The coated wet film is placed in a three-stage drying oven for drying: the first stage is drying at 80°C for 3 minutes; the second stage is drying at 100°C for 7 minutes; and the third stage is drying at 85°C for 3 minutes. After the solvent has completely evaporated, a conductive functional layer with a dry thickness of about 10 μm is obtained, and the microcapsules are uniformly distributed on the surface of the aluminum foil.

[0050] Example 2: Current collector coated with a functional layer of copper foil substrate

[0051] 1. Microcapsule preparation: Microcapsules prepared in Example 1 were used.

[0052] 2. Preparation of conductive paste: Accurately weigh 250g of acetylene black, 750g of SBR binder, 250g of CMC binder, and 1050g of water. In a homogenizing tank, stir at 1500 rpm for 2 hours to form a uniform and stable conductive paste, and then stir at 1500 rpm for 1.5 hours to form a uniformly dispersed conductive paste.

[0053] 3. Microcapsule blending: Weigh 250g of the heat-sensitive flame-retardant microcapsules prepared in step 1 and slowly add them to the conductive slurry in step 2. Stir at a low speed of 350 rpm for 30 minutes to ensure uniform dispersion. The slurry viscosity should be controlled at 3000±500 cp.

[0054] 4. Coating and Forming: Using a slot coater, the mixed slurry is coated onto a 6µm copper foil substrate. The coating speed is set to 1m / min, and the coating gap is controlled to 10μm±2μm to form a uniform wet film.

[0055] 5. Step drying: The coated wet film is placed in a three-stage drying oven: the first stage is drying at 80°C for 4 minutes, the second stage is drying at 110°C for 6 minutes, and the third stage is drying at 80°C for 3 minutes. After the solvent has completely evaporated, a conductive functional layer with a dry thickness of approximately 8 μm is obtained.

[0056] Example 3: Preparation of Lithium-ion Batteries

[0057] The conductive agent CNT and the binder PVDF were first mixed evenly in NMP solution, and then LiCoO2 material was added. The total mass was mixed according to the ratio of positive electrode material: conductive agent: binder = 96.5:1.5:2. The mixture was then stirred at high speed at 2500 rpm for 3 hours to obtain a positive electrode slurry. The positive electrode slurry was coated on the conductive aluminum foil prepared in Example 1 and dried to obtain a positive electrode sheet.

[0058] The conductive agent SP and the binder CMC were first mixed evenly in an aqueous solution, and then artificial graphite material was added. The total mass of the mixture was 96:1.5:2.5 (graphite:conductive agent:binder). The mixture was then stirred at high speed for 3 hours at 1500 rpm to obtain a negative electrode slurry. The negative electrode slurry was coated onto the conductive copper foil prepared in Example 2 and dried to obtain a negative electrode sheet.

[0059] The positive and negative electrodes and separators were stacked, packaged, baked, injected with electrolyte, packaged again, left to stand, formed, and tested to produce a 3Ah-level battery. The test results are shown in Table 1.

[0060] Comparative Example 1: Preparation of Lithium-ion Batteries

[0061] The difference from Example 3 is that the positive electrode is coated on a 12µm aluminum foil, and the negative electrode is coated on a 6µm copper foil, while the coating density, compaction density, and liquid injection volume are all the same. Tests were conducted, and the results are shown in Table 1.

[0062] Table 1

[0063]

[0064] As shown in Table 1, the thermosensitive flame-retardant microcapsules introduced into the lithium-ion battery current collector in Example 3 will reduce the conductivity of the electrode and the specific energy of the battery to a certain extent, but will not have a significant adverse effect on the basic electrochemical performance of the battery, and will improve the safety performance of the battery and increase the probability of the battery passing through a needle puncture.

[0065] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating, characterized in that: Includes the following steps: S1: Preparation of MUF prepolymer, a resin solution for the shell layer of thermosensitive flame-retardant microcapsules; S2: Preparation of emulsion for the core of the heat-sensitive flame-retardant microcapsule; S3: Add the emulsion to the resin solution MUF prepolymer to prepare heat-sensitive flame-retardant microcapsules; S4: Add conductive agent and binder to solvent to make conductive paste; S5: Disperse the heat-sensitive flame-retardant microcapsules in the conductive slurry; S6: A conductive slurry containing thermosensitive flame-retardant microcapsules is coated onto a metal foil substrate and dried to obtain a current collector containing a thermosensitive flame-retardant microcapsule coating.

2. The preparation method of the thermosensitive flame-retardant microcapsules according to claim 1, characterized in that: In step S1, the prepolymer is prepolymerized from melamine, urea and formaldehyde, with the input ratio being 57:0:100 to 43:13:100 by mass.

3. The preparation method of the heat-sensitive flame-retardant microcapsules according to claim 2, characterized in that: In step S1, the pH value of the prepolymer reaction is controlled at 8~10, and the reaction temperature is controlled at 25℃~80℃.

4. The preparation method of the thermosensitive flame-retardant microcapsules according to claim 3, characterized in that: In step S2, the emulsion includes a fire-retardant core material, which is composed of one or more of perfluorohexanone, heptafluorocyclopentane, 2-BTP, perfluorotributylamine, and perfluorooctane.

5. The method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating according to any one of claims 1-4, characterized in that: In the conductive paste, the conductive agent is at least one of conductive carbon black, carbon nanotubes, intermediate carbon phase microspheres, graphite, graphene and carbon fiber; the binder is at least one of polyvinylidene fluoride and polyacrylate; calculated by mass percentage, the conductive agent is 1%~10%, the binder is 1%~40%, and the heat-sensitive flame-retardant microcapsules are 25-35%.

6. The method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating according to claim 5, characterized in that: The metal foil substrate is aluminum foil, copper foil, composite aluminum foil, or composite copper foil with a thickness of 3 to 20 μm.

7. The method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating according to claim 5, characterized in that: The coated conductive functional layer is subjected to gradient drying, followed by step drying at corresponding times and temperatures: the first stage is drying at 70℃~80℃ for 3~8 minutes; the second stage is drying at 100℃~110℃ for 6~10 minutes; and the third stage is drying at 80℃~90℃ for 3~5 minutes. Preferably, the dry thickness of the composite coating is 3–50 μm.

8. A current collector containing a thermosensitive flame-retardant microcapsule coating prepared by the method for preparing a current collector containing a thermosensitive flame-retardant microcapsule coating as described in any one of claims 1-7.

9. An electrode sheet, characterized in that: The current collector includes the thermosensitive flame-retardant microcapsule coating as described in claim 8.

10. A lithium battery, characterized in that: The current collector includes the thermosensitive flame-retardant microcapsule coating as described in claim 8.

Images