An organic particle, a separator, and a secondary battery

Abstract

This application relates to organic particles, a separator, and a secondary battery, and is applied in the technical field of separator coating. The organic particles have a raised structure on their surface; the glass transition temperature of the organic particles is ≥120℃, the volume average particle size D50 of the organic particles is ≤1.0μm, and the roughness R of the organic particles is ≥1.1. The organic particles of this application have the effect of improving the electrolyte wettability and heat resistance while achieving a thinner battery separator.

Description

Technical Field

[0001] This application relates to the technical field of membrane coatings, and in particular to an organic particle, a membrane, and a secondary battery. Background Technology

[0002] Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. During charging, an external voltage is applied to the two electrodes of the battery, and the Li... + The electrode material is extracted from the positive electrode material, enters the electrolyte, passes through the separator, and reaches the negative electrode; the discharge path is reversed. When the battery is overcharged or punctured, thermal runaway can occur, posing a safety hazard of battery combustion and explosion. The separator is a key component in preventing these phenomena; its main function is to separate the positive and negative electrodes, preventing them from contacting and short-circuiting. It is also the Li... + The only channel for transmission.

[0003] Currently, lithium-ion battery separators are mostly powder ceramic coated separators. Ceramic separators not only possess the good mechanical properties of polyolefin separators but also combine the excellent high-temperature resistance of inorganic powders, significantly improving the dimensional stability of the separator under high-temperature conditions. Ceramic separators consist of four main components: ceramic particles, binder, solvent, and additives. The main preparation method involves dispersing ceramic particles and a ceramic binder uniformly in a solvent to form a ceramic slurry. After coating and drying, a separator coated with a ceramic layer is formed. Even if a large-area heat release occurs during charging and discharging, causing the organic base membrane to melt, the secondary battery prepared with a ceramic separator can still maintain the integrity of the separator, preventing instantaneous short circuits caused by significant separator shrinkage to a certain extent.

[0004] Commonly used ceramic particles include powder materials such as silicon dioxide, titanium dioxide, zirconium dioxide, and alumina. These particles are mostly in the μm range, and tend to agglomerate during ceramic slurry preparation, resulting in uneven dispersion and affecting coating uniformity. This, in turn, impacts the separator's electrolyte absorption and retention performance. With the pursuit of high energy density and ultra-thin batteries, thinner separators have become a major research focus. From the initial 20μm three-layer dry-process membrane to the 12μm wet-process membrane, the thickness of wet-process membranes has gradually decreased from 12μm to 9μm, 7μm, and even the extreme value of 5μm, with the trend towards thinner and thinner membranes. As the separator thickness decreases, the corresponding separator coating also becomes thinner; currently, the main ceramic coating thickness is 2~4μm, with 3μm thick ceramic coatings accounting for the majority. Reducing the ceramic coating thickness by 1μm can significantly improve battery performance and energy density. Therefore, nano-ceramic coatings have emerged on the market. The smaller the nano-ceramic particle size, the thinner the nano-ceramic coating thickness at the same areal density.

[0005] However, due to their high specific surface tension, nano-sized ceramic particles are more prone to agglomeration and sedimentation when used to prepare nano-ceramic slurries. This is because the small particle size and high density of nanoparticles result in uneven dispersion, affecting the coating uniformity and consequently the electrolyte absorption and retention performance of the diaphragm. Summary of the Invention

[0006] To address the issues of high density and poor electrolyte wettability of traditional inorganic nano-ceramic particles in coating slurry preparation, this application provides organic particles, a separator, and a secondary battery.

[0007] In a first aspect, this application provides an organic particle with a raised structure on its surface; the organic particle has a glass transition temperature ≥120℃, a volume average particle size D50 ≤1.0μm, and a roughness R ≥1.1.

[0008] Optionally, the organic particles have a glass transition temperature of 120~250℃, a volume average particle size D50 of 0.2~1.0μm, and a particle roughness R of 1.1~1.7.

[0009] Optionally, the organic particles include a first copolymer and a second copolymer, wherein the mass ratio of the first copolymer to the second copolymer is (20~80):(80~20).

[0010] Optionally, the first copolymer includes a first main structural unit, a carboxyl structural unit, and a first crosslinking structural unit, wherein the mass ratio of the first main structural unit, the carboxyl structural unit, and the first crosslinking structural unit is (140~160):(5~15):(5~15).

[0011] Optionally, the second copolymer includes a second main structural unit and a second crosslinked structural unit, wherein the mass ratio of the second main structural unit to the second crosslinked structural unit is (90~110):(5~10).

[0012] Optionally, the first main structural unit and the second main structural unit are each independently selected from any one or a combination of at least two of the following structural units: styrene structural unit, methylstyrene structural unit, sodium p-styrene sulfonate structural unit, acrylamide structural unit, methacrylamide structural unit, methacrylonitrile structural unit, methyl methacrylate structural unit, glycidyl methacrylate structural unit, isobornyl acrylate structural unit, and isobornyl methacrylate structural unit.

[0013] Optionally, the carboxyl structural unit includes any one or a combination of at least two of the following: acrylic acid structural unit, methacrylic acid structural unit, β-acryloyloxypropionic acid structural unit, maleic acid structural unit, itaconic acid structural unit, itaconic acid monobutyl ester structural unit, crotonic acid structural unit, methacryloyloxyethyl succinic acid monoester structural unit, and methacryloyloxyethyl maleic acid monoester structural unit.

[0014] Optionally, the first crosslinking structural unit and the second crosslinking structural unit are each independently selected from one or more combinations of 1,6-hexanediol diacrylate structural units, 1,3-butanediol dimethacrylate structural units, divinylbenzene structural units, methacrylic anhydride structural units, ethylene glycol dimethacrylate structural units, ethoxybisphenol A dimethacrylate structural units, trimethylolpropane trimethacrylate structural units, and pentaerythritol tetraacrylate structural units.

[0015] In a second aspect, this application provides a diaphragm, comprising a base membrane and an organic particle coating coated on the base membrane, the organic particle coating comprising an adhesive and organic particles as described in any one of the above, wherein the mass ratio of the organic particles to the adhesive is (55~160):(3~8).

[0016] Thirdly, this application provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and the separator described above.

[0017] In summary, this application includes at least one of the following beneficial technical effects:

[0018] The organic particles of this application have a raised surface structure with a roughness R of 1.1 or higher, a glass transition temperature ≥120℃, and a volume average particle size D50 ≤1.0μm. When a slurry containing these organic particles as heat-resistant particles is coated onto the surface of a base film, the resulting coating has numerous gaps, thus maintaining high electrolyte wettability and permeability. Furthermore, these organic particles exhibit high thermal stability, which is beneficial for improving the heat shrinkage resistance of the separator. Simultaneously, the density of these organic particles is lower than that of conventional inorganic heat-resistant particles, reducing the separator mass and consequently the battery mass. Compared to existing lithium-ion battery separators, at the same thickness, the separator using the organic particles provided by this invention exhibits excellent heat shrinkage resistance, better permeability and electrolyte wettability, and lower mass, aligning with the trend towards lightweight separators. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the organic particles provided in Example 1 of this application. Detailed Implementation

[0020] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the embodiments described herein are only some, not all, of the embodiments of this invention, and are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the protection scope of this invention.

[0021] It should be noted that, in this invention, as is known to those skilled in the art of chemical synthesis, each structural unit represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The mass ratio of each structural unit is the mass ratio of the monomers providing each structural unit.

[0022] In a first aspect, this application provides an organic particle with a raised structure on its surface; the organic particle has a glass transition temperature ≥120℃, a volume average particle size D50 ≤1.0μm, and a roughness R ≥1.1.

[0023] Optionally, the organic particles have a glass transition temperature of 120~250℃, a volume average particle size D50 of 0.2~1.0μm, and a particle roughness R of 1.1~1.7.

[0024] Optionally, the glass transition temperature of the organic particles can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.

[0025] The volume average particle size D50 of organic particles can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 0.25μm, 0.35μm, 0.45μm, 0.55μm, 0.65μm, 0.75μm, 0.85μm, 0.95μm, etc.

[0026] The particle roughness R of organic particles can be 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, etc.

[0027] By employing the above technical solution, the organic particles possess a core-shell structure with raspberry-like protrusions enveloping seed microspheres. The surface of the seed microspheres carries carboxyl groups. A second copolymer is then prepared, allowing it to nucleate and grow on the surface of the seed microspheres, ultimately forming the protruding structure. Compared to smooth particles, this protruding structure exhibits significantly higher roughness, more and wider gaps, resulting in better electrolyte wetting (a physical effect, similar to capillary action) and increased ion-conducting channels. The resulting organic particles not only possess high Tg and low density characteristics but also high roughness. The membrane prepared using these organic particles has higher porosity, thereby improving air permeability and electrolyte wettability. Furthermore, compared to traditional ceramic membranes, it has a smaller mass and can improve membrane thermal shrinkage, increasing the membrane's heat resistance temperature to at least greater than 130℃.

[0028] Optionally, the organic particles include a first copolymer and a second copolymer, wherein the mass ratio of the first copolymer to the second copolymer is (20~80):(80~20).

[0029] Optionally, the mass ratio of the first copolymer to the second copolymer is (30-80):(50-20).

[0030] Optionally, the mass ratio of the first copolymer to the second copolymer can be 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, etc.

[0031] Optionally, the first copolymer is a carboxyl-containing seed microsphere, and the second copolymer is formed by nucleation and growth on the surface of the seed microsphere.

[0032] By adopting the above technical solution, when the monomer mass ratio of the first copolymer and the second copolymer is in the range of (20~80):(80~20), as the proportion of the second copolymer in the polymerization system increases, the roughness of the resulting organic particles increases, enabling them to have better electrolyte wettability. When the mass proportion of the second copolymer exceeds this range, the roughness of the protruding structure may be too large, causing the particles to be easily broken; when the mass proportion of the second copolymer is below this range, the roughness of the protruding structure is too low, and the wettability decreases.

[0033] Optionally, the first copolymer includes a first main structural unit, a carboxyl structural unit, and a first crosslinking structural unit, wherein the mass ratio of the first main structural unit, the carboxyl structural unit, and the first crosslinking structural unit is (140~160):(5~15):(5~15).

[0034] In this invention, the mass ratio of the first main structural unit, the carboxyl structural unit, and the first crosslinking structural unit is within the above range, which can make the system more stable and less likely to cause excessive hydrophilicity and thus excessive moisture content in the membrane.

[0035] Optionally, the mass ratio of the first main structural unit, the carboxyl structural unit, and the first crosslinking structural unit can be 140:5:5, 142:6:6, 145:8:8, 148:10:10, 150:10:10, 152:12:12, 155:13:13, 158:14:14, 160:15:15, etc.

[0036] Optionally, the second copolymer includes a second main structural unit and a second crosslinked structural unit, wherein the mass ratio of the second main structural unit to the second crosslinked structural unit is (90~110):(5~10).

[0037] The mass ratio of the second main structural unit to the second crosslinking structural unit can be 90:5, 95:6, 100:7, 105:8, 110:9, 110:10, etc.

[0038] Optionally, the first main structural unit and the second main structural unit are each independently selected from any one or a combination of at least two of the following structural units: styrene structural unit, methylstyrene structural unit, sodium p-styrene sulfonate structural unit, acrylamide structural unit, methacrylamide structural unit, methacrylonitrile structural unit, methyl methacrylate structural unit, glycidyl methacrylate structural unit, isobornyl acrylate structural unit, and isobornyl methacrylate structural unit.

[0039] Optionally, the carboxyl structural unit includes any one or a combination of at least two of the following: acrylic acid structural unit, methacrylic acid structural unit, β-acryloyloxypropionic acid structural unit, maleic acid structural unit, itaconic acid structural unit, itaconic acid monobutyl ester structural unit, crotonic acid structural unit, methacryloyloxyethyl succinic acid monoester structural unit, and methacryloyloxyethyl maleic acid monoester structural unit.

[0040] Optionally, the first crosslinking structural unit and the second crosslinking structural unit are each independently selected from one or more combinations of 1,6-hexanediol diacrylate structural units, 1,3-butanediol dimethacrylate structural units, divinylbenzene structural units, methacrylic anhydride structural units, ethylene glycol dimethacrylate structural units, ethoxybisphenol A dimethacrylate structural units, trimethylolpropane trimethacrylate structural units, and pentaerythritol tetraacrylate structural units.

[0041] By adopting the above technical solution, the main structural unit provides high Tg for the organic particles, the carboxyl structural unit maintains the stability of the organic particles in the emulsion, and the crosslinking structural unit provides the structural framework of the organic particles.

[0042] It should be noted that in this invention, each structural unit in the first copolymer and the second copolymer originates from its corresponding monomer. For example, the carboxyl structural unit in the first copolymer originates from monomers such as acrylic acid, which become part of the first copolymer through polymerization. It is understood that the mass ratio between the structural units in the first copolymer and the second copolymer can be the mass ratio between the monomers corresponding to each structural unit.

[0043] In a second aspect, this application provides a diaphragm, the diaphragm comprising a base membrane and an organic particle coating coated on the base membrane, the organic particle coating comprising an adhesive and organic particles as described in any one of the above, wherein the mass ratio of the organic particles to the adhesive is (55~160):(3~8).

[0044] Optionally, the mass ratio of organic particles to binder can be 55:3, 65:3.5, 75:4, 85:4.5, 95:5, 105:5.5, 115:6, 125:6.5, 135:7, 145:7.5, 160:8, etc.

[0045] Optionally, the organic particulate slurry is prepared from the following raw materials in parts by weight:

[0046] 55-160 parts organic granules, 3-8 parts binder, 230-300 parts deionized water, 0.5-3 parts wetting agent, 0.5-1 part defoamer, and 0.5-3 parts anti-settling agent.

[0047] Optionally, the organic granules can be 55 parts, 65 parts, 75 parts, 85 parts, 90 parts, 95 parts, 100 parts, 110 parts, 120 parts, 130 parts, 140 parts, 150 parts, 160 parts, etc.; the binder can be 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, etc.; and the deionized water can be 230 parts, 240 parts, 250 parts, 260 parts, 270 parts, 280 parts, 290 parts, 300 parts, 235 parts, 245 parts, 255 parts, 265 parts, 275 parts, 285 parts, 295 parts, etc.

[0048] The wetting agent can be 0.5 parts, 0.7 parts, 0.9 parts, 1.1 parts, 1.3 parts, 1.5 parts, 1.8 parts, 2.1 parts, 2.4 parts, 2.7 parts, 3.0 parts, etc.; the defoamer can be 0.5 parts, 0.55 parts, 0.6 parts, 0.65 parts, 0.7 parts, 0.75 parts, 0.8 parts, 0.85 parts, 0.9 parts, 0.95 parts, 1.0 parts, etc.; and the anti-settling agent can be 0.5 parts, 0.7 parts, 0.9 parts, 1.1 parts, 1.3 parts, 1.5 parts, 1.8 parts, 2.1 parts, 2.4 parts, 2.7 parts, 3.0 parts, etc.

[0049] The diaphragm provided by the present invention can be prepared by the following example preparation method, specifically including the following steps:

[0050] Preparation of organic particle emulsion: (1) Add 90-110 parts of water to the reactor, purge with nitrogen for 20-40 minutes, heat the sealed container to 80-90°C, add an initiator aqueous solution containing 0.4-0.6 parts of ammonium persulfate and 15-25 parts of water, and then add a pre-emulsion of 138-158 parts of styrene, 5-15 parts of methacrylic acid, 5-15 parts of 1,6-hexanediol diacrylate, 2 parts of sodium dodecylbenzene sulfonate, 2 parts of sodium p-styrene sulfonate and 150 parts of water at 85°C at a uniform rate to the reactor. The total addition time is 4 hours. After the addition is completed, keep warm for 4 hours and then cool down to obtain the organic particle seed emulsion.

[0051] (2) Styrene 90-110 parts, 1,6-hexanediol diacrylate 5-10 parts, and swelling aid 2-butanone 0.5-1.5 parts are stirred evenly and then slowly added dropwise to the seed emulsion. At the same time, an initiator aqueous solution of ammonium persulfate 0.3-0.8 parts and water 5-15 parts is added. The reaction is continued at 85°C for 4 hours and then cooled to room temperature to obtain an organic particulate emulsion with a raspberry-like structure.

[0052] Preparation of organic granular slurry: Add 230-300 parts of water and 0.5-3 parts of anti-settling agent to a high-speed mixer and disperse at low speed for 25-35 minutes. Then add 55-160 parts of organic granular emulsion (added according to solids content), stir, and then add 0.5-3 parts of wetting agent. After stirring for 30 minutes, add 3-8 parts of binder (added according to solids content) and 0.5-1 part of defoamer. Stir at low speed for 25-35 minutes and then discharge to obtain organic granular slurry.

[0053] Preparation of the diaphragm: The obtained organic particle slurry is coated onto the base membrane and then wound up to obtain a composite diaphragm with an organic particle coating.

[0054] It should be noted that the specific substances used in the above preparation method do not mean that only the above substances can be used in this invention, but should be selected according to the description of each raw material and monomer in the specific embodiments section of this invention.

[0055] By adopting the above technical solution, this application incorporates organic particles into the organic particle coating to replace traditional inorganic ceramic particles. Through a seed-interface polymerization process, seed microspheres with carboxyl groups on their surface are first synthesized. Then, a second copolymer is introduced, allowing the second copolymer to nucleate and grow on the surface of the seed microspheres, ultimately forming a raised structure. The organic particles not only possess high Tg and low density characteristics but also high roughness, resulting in a membrane with higher porosity, thereby improving air permeability and electrolyte wettability. Furthermore, compared to traditional ceramic membranes, it has a smaller mass and can improve membrane thermal shrinkage, increasing the membrane's heat resistance temperature to at least greater than 130°C.

[0056] Thirdly, this application provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator as described above.

[0057] The organic particles of this application have a raised surface structure with a roughness R of 1.1 or higher, a glass transition temperature ≥120℃, and a volume average particle size D50 ≤1.0μm. When a slurry containing these organic particles as heat-resistant particles is coated onto the surface of a base film, the resulting coating has numerous gaps, thus maintaining high electrolyte wettability and permeability. Furthermore, these organic particles exhibit high thermal stability, which is beneficial for improving the heat shrinkage resistance of the separator. Simultaneously, the density of these organic particles is lower than that of conventional inorganic heat-resistant particles, reducing the separator mass and consequently the battery mass. Compared to existing lithium-ion battery separators, at the same thickness, the separator using the organic particles provided by this invention exhibits excellent heat shrinkage resistance, better permeability and electrolyte wettability, and lower mass, aligning with the trend towards lightweight separators.

[0058] Source of raw materials

[0059] Styrene (CAS: 100-42-5), Methylstyrene (CAS: 98-83-9), Sodium p-styrenesulfonate (CAS: 2695-37-6), Acrylamide (CAS: 79-06-1), Methacrylamide (CAS: 79-39-0), Methacrylonitrile (CAS: 126-98-7), Methyl methacrylate (CAS: 80-62-6), Glycidyl methacrylate (CAS: 106-91-2), Isoborneol acrylate (CAS: 5888-33-5), Isoborneol methacrylate (CAS: 7534-94-3).

[0060] Acrylic acid (CAS: 79-10-7), methacrylic acid (CAS: 79-41-4), β-acryloyloxypropionic acid (CAS: 24615-84-7), maleic acid (CAS: 110-16-7), itaconic acid (CAS: 97-65-4), monobutyl itaconic acid (CAS: 6439-57-2), crotonic acid (CAS: 107-93-7), methacryloyloxyethyl succinate monoester (CAS: 20882-04-6), methacryloyloxyethyl maleic acid monoester (CAS: 51978-15-5).

[0061] 1,6-Hexanediol diacrylate (CAS: 13048-33-4), 1,3-Butanediol dimethacrylate (CAS: 1189-08-8), Divinylbenzene (CAS: 66657-91-8), Methacrylamide (CAS: 760-93-0), Ethylene glycol dimethacrylate (CAS: 97-90-5), Ethoxybisphenol A dimethacrylate (CAS: 41637-38-1), Trimethylolpropane trimethacrylate (CAS: 3290-92-4), Pentaerythritol tetraacrylate (CAS: 4986-89-4).

[0062] Acrylic ester adhesives, SBR adhesives, acrylamide adhesives, acrylic adhesives, or acrylonitrile adhesives are all commercially available. The adhesive used in this embodiment was purchased from Shenzhen Haodian Technology Co., Ltd.

[0063] Example 1

[0064] (1) Preparation of organic particulate emulsion

[0065] Prepare the main raw materials for the organic particulate emulsion according to the following mass proportions:

[0066] First copolymer: 150 parts styrene, 10 parts methacrylic acid, 10 parts 1,6-hexanediol diacrylate, 2 parts sodium dodecylbenzenesulfonate, 2 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0067] Second copolymer: 100 parts styrene, 6 parts 1,6-hexanediol diacrylate and 1 part 2-butanone.

[0068] Its preparation method includes the following steps:

[0069] S1. Add 100 parts of water to the reactor, purge with nitrogen for 30 minutes, heat the sealed container to 85°C, add an initiator aqueous solution containing 0.5 parts of ammonium persulfate and 20 parts of water, then prepare a first mixed monomer preemulsion by adding 150 parts of styrene, 10 parts of methacrylic acid, 10 parts of 1,6-hexanediol diacrylate, 2 parts of sodium dodecylbenzenesulfonate, 2 parts of sodium p-styrenesulfonate and 150 parts of water at a uniform rate to the reactor at 85°C for a total dropping time of 4 hours. After the dropping is completed, keep warm for 4 hours, and then cool to obtain the organic particle seed emulsion, which contains seed microspheres with carboxyl groups.

[0070] S2. Styrene 100 parts, 1,6-hexanediol diacrylate 6 parts and 2-butanone 1 part are stirred evenly to prepare a second mixed monomer. The mixture is slowly added dropwise to the above organic particle seed emulsion. At the same time, an initiator aqueous solution containing 0.5 parts ammonium persulfate and 10 parts water is added. The reaction is continued at 85°C for 4 hours. After cooling to room temperature, an emulsion with organic particles and a solid content of 30% is obtained.

[0071] The obtained organic particles had a glass transition temperature of 153℃, a volume average particle size D50 of 0.356 μm, a particle roughness R of 1.52, and a swelling ratio of 1.1%. Their scanning electron microscope (SEM) images are shown below. Figure 1 As shown.

[0072] (2) Preparation of the diaphragm

[0073] A separator includes a base membrane and an organic particle coating fixed on the base membrane, the organic particle coating being prepared from the following raw materials in parts by weight:

[0074] The ingredients include 100 parts organic granules, 5 parts binder, 250 parts deionized water, and 4 parts additives, including 1 part wetting agent, 1 part defoamer, and 2 parts anti-settling agent.

[0075] The adhesive is an acrylic adhesive, the wetting agent is BYK-346, the defoamer is BYK-093, and the anti-settling agent is CMC1220.

[0076] The preparation method includes the following steps: 250 parts of deionized water and 2 parts of anti-settling agent are added to a high-speed mixer and dispersed at low speed for 30 minutes. After dispersion, 100 parts of organic particles (added according to solid content) are added and stirred. Then, 1 part of wetting agent is added and stirred for 30 minutes. After stirring, 5 parts of binder (added according to solid content) and 1 part of defoamer are added and stirred at low speed for 30 minutes. The mixture is then discharged to obtain an organic particle slurry. The obtained organic particle slurry is coated onto a 7μm membrane with a thickness of 2μm and then wound up to obtain a composite membrane with an organic particle coating.

[0077] (3) Preparation of secondary batteries

[0078] The separator prepared above is stacked sequentially with the positive and negative electrode sheets. In this embodiment, the positive electrode active material is lithium iron phosphate, the negative electrode active material is graphite, and the electrolyte is EC:DMC:EMC=1:1:1 (LiPF6, 1.0 ~ 1.2 mol / L). The separator acts as a separator between the positive and negative electrodes, forming an electrode assembly. The electrode assembly is placed in an outer package, injected with commercially available electrolyte, and sealed. After processes such as electrolyte injection, formation, and degassing, a lithium-ion secondary battery is obtained.

[0079] Example 2

[0080] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, separators, and secondary batteries. The main difference from Example 1 is that the preparation of the organic particle emulsion is achieved by adjusting the type and amount of monomers used in the polymer, so that the glass transition temperature of the organic particles is 130°C, the volume average particle size D50 is 0.373 μm, the particle roughness R is 1.48, and the swelling is 1.8%.

[0081] Specifically:

[0082] First copolymer: 140 parts styrene, 5 parts methacrylic acid, 4 parts 1,6-hexanediol diacrylate, 4 parts sodium dodecylbenzenesulfonate, 4 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0083] Second copolymer: 90 parts styrene, 4 parts 1,6-hexanediol diacrylate and 1 part 2-butanone.

[0084] The rest is the same as in Example 1.

[0085] Example 3

[0086] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, a separator, and a secondary battery. The main difference from Example 1 is that the preparation of the organic particle emulsion is achieved by adjusting the type and amount of monomers used in the polymer, so that the glass transition temperature of the organic particles is 142°C, the volume average particle size D50 is 0.502 μm, the particle roughness R is 1.73, and the swelling is 0.9%.

[0087] Specifically:

[0088] First copolymer: 140 parts styrene, 5 parts methacrylic acid, 5 parts 1,6-hexanediol diacrylate, 1.0 part sodium dodecylbenzenesulfonate, 2 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0089] Second copolymer: 130 parts styrene, 12 parts 1,6-hexanediol diacrylate and 1 part 2-butanone.

[0090] The rest is the same as in Example 1.

[0091] Example 4

[0092] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, a separator, and a secondary battery. The main difference from Example 1 is that the preparation of the organic particle emulsion is achieved by adjusting the type and amount of monomers used in the polymer, so that the glass transition temperature of the organic particles is 240°C, the volume average particle size D50 is 0.803 μm, the particle roughness R is 1.15, and the swelling is 0.6%.

[0093] Specifically:

[0094] First copolymer: 150 parts methylstyrene, 10 parts methacrylic acid, 10 parts divinylbenzene, 0.6 parts sodium dodecylbenzenesulfonate, 1.2 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0095] Second copolymer: 50 parts methylstyrene, 2 parts divinylbenzene and 1 part 2-butanone.

[0096] The rest is the same as in Example 1.

[0097] Example 5

[0098] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, a separator, and a secondary battery. The main difference from Example 1 is that the preparation of the organic particle emulsion is achieved by adjusting the type and amount of monomers used in the polymer, so that the glass transition temperature of the organic particles is 260°C, the volume average particle size D50 is 0.986 μm, the particle roughness R is 1.89, and the swelling is 0.5%.

[0099] Specifically:

[0100] First copolymer: 70 parts methylstyrene, 8 parts methacrylic acid, 8 parts divinylbenzene, 3 parts sodium dodecylbenzenesulfonate, 3 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0101] Second copolymer: 170 parts methylstyrene, 15 parts divinylbenzene and 1 part 2-butanone.

[0102] Comparative Example 1

[0103] An organic particulate emulsion, differing from Example 1 in that it includes only the first copolymer and excludes the second copolymer, and its preparation method does not include step S2, as follows:

[0104] 100 parts of water were added to the reactor, nitrogen gas was purged for 30 minutes, and the sealed container was heated to 85°C. An initiator aqueous solution containing 0.5 parts of ammonium persulfate and 20 parts of water was added. Then, 150 parts of styrene, 10 parts of methacrylic acid, 10 parts of 1,6-hexanediol diacrylate, 2 parts of sodium dodecylbenzenesulfonate, 2 parts of sodium p-styrenesulfonate, and 150 parts of water were prepared to form a first mixed monomer pre-emulsion. This pre-emulsion was added dropwise to the reactor at 85°C at a uniform rate for a total dropping time of 4 hours. After the dropping was completed, the mixture was kept at the same temperature for 4 hours. After cooling, the organic particle seed emulsion was obtained. The organic particle seed emulsion contained seed microspheres with carboxyl groups.

[0105] Comparative Example 2

[0106] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, separators and secondary batteries. The main difference from Example 1 is that the preparation of the organic particle emulsion is achieved by adjusting the type and amount of monomers used in the polymer, so that the glass transition temperature of the organic particles is 153°C, the volume average particle size D50 is 0.104 μm and the particle roughness R is 1.00.

[0107] Specifically:

[0108] First copolymer: 180 parts styrene, 5 parts methacrylic acid, 6 parts 1,6-hexanediol diacrylate, 6 parts sodium dodecylbenzenesulfonate, 6 parts sodium p-styrenesulfonate, and an initiator aqueous solution containing 0.5 parts ammonium persulfate and 20 parts water.

[0109] Second copolymer: 20 parts styrene, 0.5 parts 1,6-hexanediol diacrylate and 1 part 2-butanone.

[0110] The rest is the same as in Example 1.

[0111] Comparative Example 3

[0112] A ceramic-coated diaphragm differs from Example 1 in that an equal amount of inorganic particles, specifically alumina particles, are used to replace the organic particles, resulting in a ceramic coating with a thickness of 2 μm. All other aspects remain the same.

[0113] Comparative Example 4

[0114] This embodiment uses most of the operating steps in Example 1 to prepare organic particles, a separator, and a secondary battery. The main difference from Example 1 is that in the preparation of the organic particle emulsion, the amount of swelling agent (i.e., 2-butanone) in the second copolymer is 0.

[0115] Performance testing

[0116] (1) Glass transition temperature Tg test method: The organic particulate emulsion obtained by the scheme described in this invention is dried and then tested for glass transition temperature using a simultaneous thermal analyzer DSC 3500 Sirius. The first heating range is room temperature to 320℃, and the heating rate is 5 to 20K / min. The second heating range is 70 to 320℃, and the heating rate is 5 to 20K / min.

[0117] (2) Roughness test method: Take organic particulate emulsion and coat it on the base film (according to a surface density of 0.5 g / m). 2 The microspheres were coated and then scanned using SEM (magnification 5000x). The unevenness was quantitatively characterized using SEM image contour analysis, defined as the ratio of the actual perimeter of the microsphere's contour to the equivalent circumference of a circle with equal projected area. ImageJ was used to perform threshold segmentation and contour extraction on the single-particle SEM image to obtain the particle's projected area and actual perimeter. These values ​​were then substituted into the formula to calculate the unevenness of a single particle. More than 30 isolated, non-overlapping microspheres were randomly selected for statistical analysis, and the mean ± standard deviation was used as the overall unevenness characterization result for the sample.

[0118] R=L real / L eq

[0119] L real : Actual perimeter of the microsphere's edge contour as measured by SEM; L eq : The circumference of a perfect circle with an equal projected area.

[0120] (3) Swelling test method: The organic particle emulsion prepared by the scheme described in this invention is mixed with NMP solvent at a ratio of 1:1, and baked at 100℃ for 24h, 160℃ for 24h, and 200℃ for 6h to form a film. After cutting into pieces, the film is immersed in electrolyte (electrolyte composition: EC:EMC:DEC=3:5:2, 1mol / L LiPF6), and the initial mass is recorded. The mass swelling under the condition of 60℃ for 72h is tested respectively.

[0121] Mass swelling: Mass swelling rate = (W after swelling - W initial swelling) / W initial swelling * 100%

[0122] (4) Volume average particle size D50 test method: The emulsions prepared in each example and comparative example were tested using a laser particle size analyzer (Zhuhai Omec Instrument Co., Ltd., model: LS-909E) to obtain the volume average particle size Dv50 based on the volume standard.

[0123] (5) Diaphragm surface density: Ten diaphragms of 100×100mm size prepared using the method described in this invention were weighed on an analytical balance, and the weight was recorded. The surface density was calculated using the following formula.

[0124] Surface density = mass (g) / area (10 * 100 * 100 / 10) 6 m)

[0125] (6) Electrolyte wettability: The 100×100mm membrane prepared by the scheme described in this invention is suspended and laid flat. 10μL of electrolyte droplets (electrolyte composition: EC:EMC:DEC=3:5:2, 1mol / LLiPF6) are dropped into the central area of ​​the membrane, and the electrolyte diffusion diameter is tested after 1min.

[0126] (7) The test method for heat shrinkage resistance is as follows: the diaphragm prepared by the scheme described in this invention is cut into 100×100mm specifications, placed between two A4 sheets of paper, placed on an iron tray, and transferred to an oven at 130℃ for baking for 1 hour. The change rate of longitudinal width (MD) and transverse width (TD) before and after the test is then tested.

[0127] (8) The test method for air permeability time is as follows: the diaphragm prepared by the scheme described in this invention is cut into 100×400mm specifications and tested using a Gurley air permeability meter.

[0128] The properties of the organic particles in Examples 1-5 and Comparative Examples 1-4 are shown in the table below.

[0129] Table 1

[0130]

[0131] The above-mentioned diaphragms were subjected to the diaphragm performance tests described above, and the test results are shown in Table 2.

[0132] Table 2

[0133]

[0134] As can be seen from Examples 1-4 and Table 1-2, the greater the surface roughness of the prepared organic particles, the more gaps the coated membrane has, which helps to maintain high electrolyte wettability and air permeability.

[0135] As can be seen from Examples 1 and 5, Comparative Example 2, and Tables 1-2, when the mass ratio of the second copolymer to the first copolymer is too large, it easily leads to excessive roughness. The organic particles are prone to breakage after being used to prepare the diaphragm, resulting in the diaphragm failing to maintain good electrolyte wetting and air permeability. When the proportion of the second copolymer is too small, the roughness decreases, making it difficult to guarantee its electrolyte wettability.

[0136] Based on Example 1, Comparative Examples 1 and 3, and in conjunction with Tables 1-2, it can be seen that the organic particles of Example 1, when made into a separator, have a lower areal density, which can reduce the separator mass and thus reduce the battery mass. Furthermore, the separator has good air permeability, and the heat resistance of the polymer particle material is used to improve the thermal shrinkage of the separator and increase the heat resistance temperature.

[0137] As can be seen from Example 1, Comparative Example 4 and Tables 1-2, no swelling agent was added when preparing the second copolymer, so organic particles with a raised structure could not be formed, resulting in poor electrolyte wettability.

[0138] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing application concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions claimed in this application.

Claims

1. An organic particle, characterized in that, The organic particles have a raised structure on their surface; the glass transition temperature of the organic particles is ≥120℃, the volume average particle size D50 of the organic particles is ≤1.0μm, and the roughness R of the organic particles is ≥1.

1. The organic particles include a first copolymer and a second copolymer, wherein the mass ratio of the first copolymer to the second copolymer is (20~80):(80~20).

2. The organic particles according to claim 1, characterized in that, The organic particles have a glass transition temperature of 120~250℃, a volume average particle size D50 of 0.2~1.0μm, and a particle roughness R of 1.1~1.

7.

3. The organic particles according to claim 1, characterized in that, The first copolymer comprises a first main structural unit, a carboxyl structural unit and a first crosslinking structural unit, wherein the mass ratio of the first main structural unit, the carboxyl structural unit and the first crosslinking structural unit is (140~160):(5~15):(5~15).

4. The organic particles according to claim 3, characterized in that, The second copolymer comprises a second main structural unit and a second crosslinked structural unit, wherein the mass ratio of the second main structural unit to the second crosslinked structural unit is (90~110):(5~10).

5. The organic particles according to claim 4, characterized in that, The first main structural unit and the second main structural unit are each independently selected from any one or a combination of at least two of the following structural units: styrene structural unit, methylstyrene structural unit, sodium p-styrene sulfonate structural unit, acrylamide structural unit, methacrylamide structural unit, methacrylonitrile structural unit, methyl methacrylate structural unit, glycidyl methacrylate structural unit, isobornyl acrylate structural unit, and isobornyl methacrylate structural unit.

6. The organic particles according to claim 3, characterized in that, The carboxyl structural unit includes any one or a combination of at least two of the following: acrylic acid structural unit, methacrylic acid structural unit, β-acryloyloxypropionic acid structural unit, maleic acid structural unit, itaconic acid structural unit, itaconic acid monobutyl ester structural unit, crotonic acid structural unit, methacryloyloxyethyl succinic acid monoester structural unit, and methacryloyloxyethyl maleic acid monoester structural unit.

7. The organic particles according to claim 4, characterized in that, The first crosslinking structural unit and the second crosslinking structural unit are each independently selected from one or more combinations of 1,6-hexanediol diacrylate structural units, 1,3-butanediol dimethacrylate structural units, divinylbenzene structural units, methacrylic anhydride structural units, ethylene glycol dimethacrylate structural units, ethoxybisphenol A dimethacrylate structural units, trimethylolpropane trimethacrylate structural units, and pentaerythritol tetraacrylate structural units.

8. A diaphragm, characterized in that, The coating includes a base film and an organic particle coating applied to the base film, the organic particle coating comprising an adhesive and organic particles as described in any one of claims 1 to 7, wherein the mass ratio of the organic particles to the adhesive is (55 to 160): (3 to 8).

9. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator as described in claim 8.

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