A microcapsule, a lithium ion battery separator containing the microcapsule, and a lithium ion battery

Abstract

The application discloses a kind of microcapsules, by inside hollow mesoporous microspheres loaded with inactivator and the polymer layer of coating in the surface of the hollow mesoporous microspheres constitute;The D50 of the hollow mesoporous microspheres is ≤3um, D90≤8um, pore volume is 0.2-0.3cm 3 / g, pore size is 100-300nm;The inactivator is organic acid;The melting point of the polymer is 100-250 DEG C.The application also discloses lithium ion battery separator and lithium ion battery containing the microcapsule.The microcapsule of the application is loaded on the separator, can release inactivator at high temperature, and react with negative direction high active material, reduce negative active, improve the thermal safety of lithium ion battery, and have important value to energy type lithium ion battery safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a microcapsule, a lithium ion battery separator containing the microcapsule and a lithium ion battery. BACKGROUND

[0002] Lithium ion power batteries gradually establish a broad market with the advantages of high working voltage, long cycle life and fast charging and discharging speed, and play an important role in small electronic products such as mobile phones, computers and electric tools. With the development of electric vehicles and energy storage fields, the use conditions of lithium ion batteries are more demanding, especially in extreme conditions (high temperature), to ensure the cycle performance and safety performance of the battery. However, with the continuous improvement of energy density, the stability of lithium ion batteries is greatly challenged, especially at high temperature. At present, the common ways to improve the thermal safety of the battery are positive material modification, separator coating, module design, BMS management, etc., which have high requirements for material preparation and design.

[0003] Invention CN105932200A invention patent provides a kind of lithium ion battery composite separator and its preparation method and lithium ion battery, and the patent has a layer of microcapsule protective layer on the surface of base film, and phase change material and fire retardant are contained in capsule;The microcapsule inside described in CN105932200A and CN113181589A invention patent coats liquid fire extinguishing agent and coolant, which can play a role in extinguishing fire when the battery is on fire;CN112029343A and CN112018445A invention patent propose a kind of microsphere structure of self-destruction structure, when the battery thermal runaway, microcapsule breaks and releases chemical inhibitor to block the redox reaction of battery, thereby improving the safety of battery. However, the microcapsule microsphere structure described above has the problem of slow reaction speed, which is only a fire extinguishing protection measure taken when the battery has thermal runaway, and cannot eliminate the risk of battery thermal runaway from the root. SUMMARY

[0004] Based on the technical problems existing in the background art, the present application proposes a kind of microcapsule, a lithium ion battery separator containing the microcapsule and a lithium ion battery.

[0005] The microcapsule proposed by the present application is composed of mesoporous microspheres loaded with inactivator inside and polymer layer coated on the surface of the mesoporous microspheres.

[0006] The D50 of the mesoporous microspheres is ≤3um, the D90 is ≤8um, the total pore volume is 0.2-0.3cm 3 / g, and the pore size is 100-300nm.

[0007] The inactivator is an organic acid.

[0008] The melting point of the polymer is 100-250℃.

[0009] Preferably, the organic acid is at least one of citric acid, oxalic acid, iso-octanoic acid.

[0010] The mechanism of action of the present application is:

[0011] At high temperature (≥120℃), the inactivator coated in the mesoporous microspheres is released, reacts with LiC x to reduce the activity in the negative direction, and avoid thermal runaway when the positive and negative electrodes are in contact. The specific inactivation reaction is as follows:

[0012] 2LiC x +2H+=H2↑+2Li++2C x

[0013] Preferably, the mesoporous microspheres are at least one of SiO2 mesoporous microspheres, polystyrene mesoporous microspheres, and graphite mesoporous microspheres; and the polymer is at least one of polypropylene, polyethylene terephthalate, polyethylene, melamine formaldehyde resin, polyvinyl fluoride carbonate, polyvinyl chloride, polycarbonate, and polyvinylidene fluoride.

[0014] A method for preparing the microcapsule comprises the following steps:

[0015] S1, first adsorb the inactivator in the mesoporous microspheres by vacuum impregnation, then heat treat to recrystallize and solidify the inactivator, to obtain mesoporous microspheres loaded with inactivator inside;

[0016] S2, coat a polymer layer on the surface of the mesoporous microspheres loaded with inactivator inside to seal the mesopores, to obtain the microcapsule.

[0017] Preferably, in S1, the inactivator is dissolved in a solvent to obtain an inactivator solution, then the mesoporous microspheres are added to the inactivator solution, stirred thoroughly, then filtered, and the filtered microspheres are heat treated under vacuum to recrystallize and solidify the inactivator, to obtain mesoporous microspheres loaded with inactivator inside.

[0018] Preferably, in S1, the mass ratio of inactivator to mesoporous microspheres is 1:(1-3).

[0019] Preferably, in S1, the heat treatment temperature is 85-95℃, and the time is 20-30h.

[0020] Preferably, in S2, the polymer and emulsifier are added to a good solvent of the polymer, stirred thoroughly to dissolve, then the mesoporous microspheres loaded with inactivator inside are added and stirred uniformly, then heated and stirred to solidify the polymer on the surface of the mesoporous microspheres, after solidification, a poor solvent of the polymer is added until the solid is analyzed out, filtered and dried to obtain the microcapsule.

[0021] In S2, the mesoporous microspheres are insoluble in any one of a good solvent of the polymer, a poor solvent of the polymer.

[0022] Preferably, in S2, the good solvent of the polymer is at least one of 1, 2, 3-trichlorobenzene, xylene, DMF, DMSO, dichloromethane, n-octane, pentane, and amyl acetate.

[0023] Preferably, in S2, the poor solvent of the polymer is anhydrous ethanol.

[0024] Preferably, in S2, the mass ratio of the polymer, the emulsifier, and the good solvent of the polymer is (15-25):(6-15):100.

[0025] Preferably, in S2, the mass ratio of the mesoporous microspheres loaded with the inactivator and the polymer is 300:(15-20).

[0026] Preferably, in S2, the heating and stirring temperature is 70-140℃, and the time is 20-30h.

[0027] A lithium ion battery separator includes a separator substrate and microcapsules loaded on at least one surface of the separator substrate, and the microcapsules are prepared by the preparation method.

[0028] Preferably, the polymer layer of the microcapsules can stably exist below 100℃ and does not react with other components inside the battery.

[0029] Preferably, the material of the separator substrate is at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0030] A lithium ion battery includes a positive electrode sheet, a negative electrode sheet, and the lithium ion battery separator, and the lithium ion battery separator is located between the positive electrode sheet and the negative electrode sheet.

[0031] Preferably, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is at least one of lithium cobaltate, lithium nickelate, lithium manganese oxide, lithium manganate, lithium nickel manganate, lithium-rich manganese-based, manganese iron lithium phosphate, lithium nickel cobalt aluminum manganate, lithium nickel cobalt manganate, lithium iron phosphate, and lithium vanadium phosphate.

[0032] Preferably, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material is at least one of metallic lithium, metallic lithium alloy, graphite, hard carbon, lithium metal nitride, antimony oxide, carbon germanium composite material, carbon silicon composite material, lithium titanate, and lithium titanium oxide.

[0033] The beneficial effects of the present application are as follows:

[0034] 1.The microcapsule provided by the present application is coated on the separator, and the core material of the microcapsule is an inactivator, which can release the inactivator at high temperature to react with the negative active material, completely or partially inactivating the negative active material, reducing the negative active, and reducing the risk of delayed internal short circuit fire of the battery, so that the risk of battery thermal runaway can be fundamentally eliminated at the beginning stage of battery thermal runaway, thereby improving the thermal safety of the lithium ion battery and providing safety protection for the battery. The microcapsule structure provided by the present application is easy to prepare, has high technical maturity, and is easy to expand production, so whether it is a rapid verification sample in the laboratory or further expansion, it has good application value.

[0035] 2.The shell material of the microcapsule provided by the present application has good compatibility with the separator, and has little or no effect on the performance of the battery.

[0036] 3.The microcapsule provided by the present application is cheap, easy to obtain and mass-produced, and can reduce the cost of the battery while improving the battery. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 SEM image of the microcapsule prepared in Example 1 of the present application.

[0038] Figure 2 TG curve of the microcapsule prepared in Example 1 of the present application.

[0039] Figure 3 Battery cell charge-discharge curve of the battery of Example 1-3 and Comparative Example 1 of the present application.

[0040] Figure 4 Voltage change curve of the separator of Example 1-3 and Comparative Example 1 of the present application at high temperature. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described in detail below through specific examples.

[0042] Example 1

[0043] Preparation of microcapsule:

[0044] S1, under magnetic stirring, 300g PS mesoporous microspheres were added to a saturated oxalic acid solution (containing 100g oxalic acid), stirred for 1h, then filtered, and the filtered microspheres were transferred to a 90℃ oven and placed under vacuum for 24h to obtain PS mesoporous microspheres loaded with oxalic acid inside; wherein the D50 of the PS mesoporous microspheres is ≤3um, the D90 is ≤8um, the total pore volume is 0.2-0.3cm 3 / g, and the pore size is 100-300nm;

[0045] S2, 15 g of polyethylene powder, 6.9 g of Span80 were added into 100 g of xylene and stirred at a rotation speed of 1000 rpm for 30 min to fully dissolve, then 300 g of the PS mesoporous microspheres loaded with oxalic acid prepared in S1 were added, and stirring was continued at a rotation speed of 500 rpm for 1 h, then the temperature was increased to 90℃, and constant temperature stirring was performed for 20-30 h, anhydrous ethanol was slowly added, and after the solid precipitated, it was filtered and dried to obtain microcapsules.

[0046] Preparation of the separator:

[0047] 40 parts of the microcapsules prepared above, 8 parts of a water-based binder, 0.5 parts of a dispersant, 0.5 parts of a thickening agent and 51 parts of water were mixed, and high-speed stirring and dispersion were performed at 800 rpm for 30 min to obtain a slurry;

[0048] The slurry was uniformly coated on a PE base film at a coating speed of 30 m / min, and then dried at 60℃ for 2 min to obtain a lithium ion battery separator with a coating layer on the surface, wherein the thickness of the coating layer was 2 μm, and the areal density was 4 g / m 2 .

[0049] Assembly of the battery:

[0050] The test battery was a soft-pack battery, the positive electrode was NMC (811), and the negative electrode was graphite. NMC (811), a binder PVDF and a conductive agent superP were mixed in a mass ratio of 95:3:2 with an organic solvent NMP to form a paste, which was uniformly coated on a 15 μm aluminum foil, and then subjected to drying, rolling and slicing processes to obtain a positive electrode sheet, which was cut into a size of 5×5 cm for use. Graphite, a binder (CMC) and deionized water were mixed in a mass ratio of 8:1:1 to form a slurry, which was coated on a copper foil to obtain a negative electrode sheet. The positive electrode sheet, the negative electrode sheet, the separator and a commercially available electrolyte (lmol / L LiPF6 / EC+DMC+DEC+EMC) were assembled into a battery.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is only that the preparation method of the separator is different, and the specific method is as follows:

[0053] Preparation of the separator:

[0054] 40 parts of the microcapsules prepared above, 8 parts of a water-based binder, 0.5 parts of a dispersant, 0.5 parts of a thickening agent and 51 parts of water were mixed, and high-speed stirring and dispersion were performed at 800 rpm for 30 min to obtain a slurry;

[0055] The slurry is uniformly coated on the PE base film at a coating speed of 20 m / min, and then dried at 60℃ for 3 min to obtain a lithium ion battery separator with a coating layer on the surface, wherein the thickness of the coating layer is 4 μm, and the area density is 10 g / m 2 .

[0056] Example 3

[0057] Example 3 is different from Example 1 only in that the preparation method of the separator is different, specifically as follows:

[0058] Preparation of the separator:

[0059] 40 parts of the microcapsules prepared in Example 1, 8 parts of a water-based binder, 0.5 parts of a dispersing agent, 0.5 parts of a thickening agent, and 51 parts of water are mixed, and high-speed stirring and dispersion are carried out at 800 rpm for 30 min to obtain a slurry;

[0060] The slurry is uniformly coated on the PE base film at a coating speed of 10 m / min, and then dried at 60℃ for 5 min to obtain a lithium ion battery separator with a coating layer on the surface, wherein the thickness of the coating layer is 6 μm, and the area density is 16 g / m 2 .

[0061] Comparative Example 1

[0062] Comparative Example 1 is different from Example 1 only in that a common PE base film is used as the separator.

[0063] Test Example

[0064] The microcapsules prepared in Example 1 are subjected to SEM test, and the test results are shown in Figure 1 From Figure 1 it can be seen that the surface of the ball is completely covered by the polymer, and there is no obvious hole leakage.

[0065] The microcapsules prepared in Example 1 are subjected to TG test, and the test results are shown in Figure 2 From Figure 2 it can be seen that the TG curve of the microcapsules starts to lose weight at 94℃, and the weight loss reaches 20% at 120℃, 40% at 220℃, and tends to be stable until the temperature reaches 620℃, at which time the inactivator and the polymer for sealing the holes have basically completely released and decomposed, and only the microsphere shell remains. The weight loss starts at 94℃, which meets the design requirements, indicating that the inactivator starts to release and starts to inactivate.

[0066] The batteries of Examples 1-3 and Comparative Example 1 are subjected to charge-discharge test, and the test method is 0.1C charge-discharge, and the test results are shown in Figure 3 From Figure 3It can be seen from the above that the battery cell using the separator coated with the microcapsule of the application has no obvious difference in the charge-discharge curve from the battery cell using the PE-based separator as the separator in the comparative example, indicating that the state of the coated separator has not changed greatly, and also indicating that the coating does not leak at room temperature, resulting in a great change in the electrical performance.

[0067] The batteries of Examples 1-3 and Comparative Example 1 were subjected to high-temperature voltage change test, and the test method was to place the batteries in a 130°C oven, externally connected to a test cabinet, and the test cabinet was set to rest for 10h, and the recording conditions were voltage recording: 0.001V, and time recording: 10s. The test results are shown in Table 2. Figure 4 Figure 4 It can be seen from the above that the separator coated with the microcapsule of the inactivation agent has an obvious pressure drop change at about 120S under high temperature, indicating that the inactivation agent acts, inactivates the negative electrode, reduces the activity of the negative electrode, and achieves the effect of protecting the battery cell, while the voltage of the comparative sample does not change greatly, thereby indicating that coating the microcapsule containing the inactivation agent on the separator has a good effect of thermally triggering the inactivation of the battery cell and protecting the battery cell.

[0068] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the application within the technical range disclosed by the application, which should be covered within the protection scope of the application.​

Claims

1. A method for preparing microcapsules, characterized in that, Includes the following steps: S1. First, the inactivating agent is adsorbed into the mesoporous microspheres by vacuum impregnation, and then the inactivating agent is recrystallized and solidified by heat treatment to obtain mesoporous microspheres loaded with inactivating agent. S2. A polymer layer is coated on the surface of the mesoporous microspheres loaded with inactivating agent inside to seal the mesopores and obtain the microcapsules. The microcapsule is composed of mesoporous microspheres loaded with an inactivating agent inside and a polymer layer covering the surface of the mesoporous microspheres; The mesoporous microspheres have a D50 ≤ 3 μm, a D90 ≤ 8 μm, and a total pore volume of 0.2-0.3 cm³. 3 / g, pore size 100-300nm; The inactivating agent is an organic acid; the organic acid is at least one of citric acid, oxalic acid, and isooctanoic acid. The polymer has a melting point of 100-250℃.

2. The method for preparing microcapsules according to claim 1, characterized in that, In step S1, the inactivating agent is dissolved in a solvent to obtain an inactivating agent solution. Then, mesoporous microspheres are added to the inactivating agent solution, stirred thoroughly, and then filtered. The filtered microspheres are then heated under vacuum conditions to recrystallize and solidify the inactivating agent, resulting in mesoporous microspheres loaded with the inactivating agent.

3. The method for preparing microcapsules according to claim 1, characterized in that, In step S2, the polymer and emulsifier are added to a good solvent for the polymer and stirred thoroughly to dissolve. Then, mesoporous microspheres loaded with an inactivating agent are added and stirred evenly. The mixture is then heated and stirred to solidify the polymer on the surface of the mesoporous microspheres. After solidification, a poor solvent for the polymer is added until the solid is fully precipitated. The mixture is then filtered and dried to obtain the microcapsules.

4. The method for preparing microcapsules according to claim 1, characterized in that, The mesoporous microspheres are at least one of SiO2 mesoporous microspheres, polystyrene mesoporous microspheres, and graphite mesoporous microspheres; the polymer is at least one of polypropylene, polyethylene terephthalate, polyethylene, melamine-formaldehyde resin, polyfluoroethylene carbonate, polyvinyl chloride, polycarbonate, and polyvinylidene fluoride.

5. A lithium-ion battery separator, characterized in that, It includes a diaphragm substrate and microcapsules loaded on at least one surface of the diaphragm substrate, wherein the microcapsules are prepared by the preparation method according to any one of claims 1-4.

6. The lithium-ion battery separator according to claim 5, characterized in that, The membrane substrate is made of at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and the lithium-ion battery separator as described in claim 5, wherein the lithium-ion battery separator is located between the positive electrode and the negative electrode.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode sheet includes a positive electrode active material, which is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based oxide, lithium manganese iron phosphate, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium vanadium phosphate. The negative electrode sheet includes a negative electrode active material, which is at least one of lithium metal, lithium metal alloy, graphite, hard carbon, lithium metal nitride, antimony oxide, carbon-germanium composite material, carbon-silicon composite material, lithium titanate, and lithium titanium oxide.

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