A capsule binder, a binder composition, a separator, and a battery

Abstract

To overcome the problems of easy powder shedding and poor thermal safety of existing separator adhesives, this invention provides a capsule adhesive, an adhesive composition, a separator, and a battery. The capsule adhesive includes a core and a polymer layer disposed on the outer surface of the core and at least partially covering the core. The core includes a phase change material; the polymer layer includes a polymer comprising acrylate structural units, hydrophilic functional structural units, and crosslinked structural units; the mass ratio of the phase change material, acrylate structural units, hydrophilic functional structural units, and crosslinked structural units is (40~60):(20~40):(1~5):(5~20). The capsule adhesive provided by this invention introduces a phase change material into the core. When the internal temperature of the battery rapidly rises to the phase change temperature of the core, the phase change material absorbs heat, slowing down the temperature rise, reducing the possibility of thermal runaway accidents, and improving the safety performance of the secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a capsule binder, binder composition, separator, and 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-ion electrolyte... + The lithium ions are extracted from the positive electrode material, enter the electrolyte, pass through the separator, and reach the negative electrode; the discharge path is reversed. As a crucial component of lithium-ion batteries, the separator separates the positive and negative electrodes to prevent short circuits while allowing lithium ions to freely move between them during charging and discharging to achieve energy storage and release. The performance of the separator directly affects battery internal resistance, cycle life, and battery safety. Currently, separators for lithium-ion power batteries are mostly made of polyolefins, such as polypropylene / polyethylene double-layer composite separators or polypropylene / polyethylene / polypropylene triple-layer composite separators. However, these separators have low high-temperature resistance. Lithium-ion batteries generate heat during charging and discharging, especially at high rates or under extreme ambient temperatures. Abnormal heat release can cause thermal shrinkage of the separator, leading to short circuits at the positive and negative electrode contacts and potential safety hazards such as thermal runaway. Uneven temperature distribution or continuous temperature rise during charging and discharging accelerates electrode material aging and SEI film thickening, easily resulting in capacity decay and shortened battery life.

[0003] In existing technologies, to improve the heat resistance of the separator, a heat-resistant coating is applied to one or both sides of the polyolefin separator to enhance its heat resistance, thereby improving the safety performance of the lithium-ion battery. However, the binder in the heat-resistant coating suffers from problems such as easy powdering and poor heat resistance. Secondly, phase change materials (PCMs), due to their unique latent heat storage and isothermal regulation characteristics, have become ideal materials for battery thermal management. During the phase change process, PCMs absorb or release a large amount of latent heat without causing changes in the ambient temperature. They can achieve passive temperature control without external energy and can absorb a large amount of heat in the early stages of thermal runaway in lithium-ion batteries, buying time for the safety system to respond.

[0004] Therefore, there is an urgent need to provide an adhesive with good heat resistance, strong adhesion, and high latent heat of phase change to improve the thermal safety performance of the diaphragm. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that existing membrane adhesives are prone to powdering and have poor thermal safety. The present invention provides a capsule adhesive, an adhesive composition, a membrane, and a battery.

[0006] To solve the above-mentioned technical problems, the present invention provides a capsule binder, the capsule binder comprising a core and a polymer layer disposed on the outer surface of the core and at least partially covering the core, the core comprising a phase change material; the polymer layer comprising a polymer comprising acrylate structural units, hydrophilic functional structural units and crosslinked structural units; the mass ratio of the phase change material, acrylate structural units, hydrophilic functional structural units and crosslinked structural units is (40~60):(20~40):(1~5):(5~20).

[0007] Preferably, the phase transition temperature of the capsule binder is 25~90℃; the latent heat of phase transition of the capsule binder is greater than 150KJ / kg.

[0008] Preferably, the electrolyte swelling rate of the capsule binder is less than 40%.

[0009] Preferably, the glass transition temperature of the polymer is -40 to 20°C.

[0010] Preferably, the phase change material includes one or more of C18-C50 straight-chain alkanes, C12-C20 fatty acids, and C12-C30 fatty alcohols; the hydrophilic functional structural unit includes one or more of acrylic structural units or hydroxy acrylate structural units.

[0011] The present invention also provides an adhesive composition comprising a heat-resistant adhesive and a capsule adhesive as described in any one of the above, wherein the mass ratio of the heat-resistant adhesive to the capsule adhesive is (30~50):(50~70).

[0012] Preferably, the adhesive composition has a tensile strength of 0.5~40MPa, an elongation at break of 50%~500%, and an electrolyte mass swelling rate of less than 30%.

[0013] Preferably, the glass transition temperature of the heat-resistant adhesive is greater than 100°C.

[0014] The present invention also provides a diaphragm comprising a base membrane and a functional layer disposed on at least one side of the base membrane, the functional layer comprising ceramic particles and an adhesive composition as described above.

[0015] The present invention also provides a battery comprising the separator as described above.

[0016] The capsule binder provided in this application introduces a phase change material into the core. When the internal temperature of the battery rises rapidly to the phase change temperature of the core, the phase change material absorbs heat and slows down the temperature rise, reducing the possibility of thermal runaway accidents and improving the safety performance of the secondary battery. The adhesiveness of the capsule binder is improved by introducing acrylate structural units, hydrophilic functional structural units, and cross-linking structural units into the polymer layer.

[0017] In particular, the combined use of the capsule binder and the heat-resistant binder gives the functional layer of the prepared separator high adhesion while improving the separator's heat shrinkage resistance. Furthermore, the binder composition, through the introduction of the capsule binder, also possesses heat buffering properties, absorbing heat during battery charging and discharging, reducing the possibility of thermal runaway accidents, and improving battery safety. Moreover, no organic solvents are added during the separator preparation process, making the binder composition environmentally friendly and harmless. Detailed Implementation

[0018] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] One embodiment of this application provides a capsule binder, the capsule binder comprising a core and a polymer layer disposed on the outer surface of the core and at least partially covering the core, the core comprising a phase change material; the polymer layer comprising a polymer, the polymer comprising acrylate structural units, hydrophilic functional structural units and crosslinked structural units; the mass ratio of the phase change material, acrylate structural units, hydrophilic functional structural units and crosslinked structural units is (40~60):(20~40):(1~5):(5~20).

[0020] The capsule binder provided in this application introduces a phase change material (PCM) into the core. When the internal temperature of the battery rises rapidly to the PCM's phase change temperature, the PCM absorbs heat, slowing down the temperature rise and reducing the possibility of thermal runaway accidents, thus improving the safety performance of the secondary battery. The adhesiveness of the capsule binder is improved by introducing acrylate structural units, hydrophilic functional structural units, and cross-linking structural units into the polymer layer. The heat absorption capacity of the capsule binder is increased by limiting the mass ratio of the PCM to the polymer layer structural units. The adhesive performance of the capsule binder is improved by limiting the mass ratio of each structural unit in the polymer layer.

[0021] Specifically, the mass ratio of phase change material, acrylate structural unit, hydrophilic functional structural unit and cross-linked structural unit includes, but is not limited to, 40:20:1:5, 60:40:5:20, 40:40:5:20, 40:40:5:20, 40:20:5:20, 40:40:1:20, 40:40:5:5, 50:30:3:10, 40:30:5:20, 40:40:3:10, 40:30:3:20 or 40:40:3:20.

[0022] In some embodiments, the phase transition temperature of the capsule binder is 25~90℃; the latent heat of phase transition of the capsule binder is greater than 150KJ / kg.

[0023] Specifically, the phase transition temperature of the capsule binder includes, but is not limited to, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C. The latent heat of phase transition of the capsule binder is 150~250 KJ / kg.

[0024] In some embodiments, the electrolyte swelling rate of the capsule binder is less than 40%.

[0025] In some embodiments, the phase change temperature of the phase change material is 25~90℃; and / or, the latent heat of phase change of the phase change material is greater than 150KJ / kg. By limiting the phase change temperature within the above range, the binder has a wider temperature buffering and control capability, improving the reliability of the capsule binder in complex temperature environments. By limiting the latent heat of phase change of the phase change material within the above range, the capsule binder can achieve a significant heat buffering effect with a smaller dosage.

[0026] In some embodiments, the phase change material includes one or more of C18-C50 straight-chain alkanes, C12-C20 fatty acids, and C12-C30 fatty alcohols; the hydrophilic functional structural unit includes one or more of acrylic structural units or hydroxy acrylate structural units.

[0027] Specifically, the phase change material includes at least one of phase change wax, palmitic acid, stearic acid, and n-tetradecyl alcohol.

[0028] In some embodiments, the hydrophilic functional structural unit includes one or more of acrylic structural units or hydroxy acrylate structural units. The hydrophilic functional structural unit is a structural unit obtained by polymerization of hydrophilic monomers. Specifically, the hydrophilic monomer includes at least one of acrylic acid, methacrylic acid, vinylacrylic acid, β-acryloyloxypropionic acid, maleic acid, itaconic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate. By selecting the above-mentioned hydrophilic monomers in the polymer layer, the bonding strength between the polymer layer and the metal oxide or ceramic particles is enhanced, while simultaneously promoting the dispersion and dissolution of the capsule binder in water.

[0029] In a preferred embodiment, the hydrophilic monomer is selected from at least one of acrylic acid, maleic acid, and hydroxyethyl acrylate.

[0030] In some embodiments, the glass transition temperature (Tg) of the polymer is -40 to 20°C. By limiting the glass transition temperature of the polymer, the adhesive strength of the capsule binder is controlled. When the glass transition temperature of the polymer is higher than 20°C, the adhesive properties of the capsule binder decrease.

[0031] In some embodiments, the acrylate structural unit is a structural unit obtained by polymerization of acrylate monomers, and the acrylate monomers include at least one selected from n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isobornyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate. By selecting the above-mentioned acrylate monomers, the adhesion properties of the polymer layer are improved, the peel strength of the membrane is further enhanced, and the flexibility of the polymer layer is adjusted.

[0032] In a preferred embodiment, the acrylate monomer is selected from at least one of isooctyl acrylate, n-butyl acrylate, isooctyl methacrylate, and isobornyl acrylate.

[0033] In some embodiments, the cross-linked structural unit is a structural unit obtained by polymerization of cross-linked monomers. Specifically, the cross-linked monomers have at least two functionalities.

[0034] The crosslinking monomers include at least one of divinyl aromatic hydrocarbon compounds, diol diacrylate compounds, bisphenol A diacrylate, heterocycloalkane diacrylate compounds, diol dimethacrylate compounds, bisphenol A dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and pentaerythritol tetraacrylate. By selecting the above crosslinking monomers, a three-dimensional network structure is formed in the polymer layer, which improves the tensile strength of the capsule binder, reduces the electrolyte swelling rate of the capsule binder, and enhances solvent resistance.

[0035] Furthermore, the divinyl aromatic hydrocarbon compounds include at least one of divinylbenzene, divinyltoluene, and divinylxylene.

[0036] Diol diacrylate compounds include at least one of ethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, polyethylene glycol monomethyl ether acrylate, ethylene glycol dicyclopentenyl ether acrylate, and 1,4-butanediol diacrylate.

[0037] Bisphenol A diacrylates include ethoxylated bisphenol A diacrylates.

[0038] Heteroazocycloalkanes diacrylates include 1,4-disacryloylpiperazine.

[0039] Diol dimethacrylate compounds include at least one of polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, and dipropylene glycol dimethacrylate.

[0040] In a preferred embodiment, the crosslinking monomer is selected from divinylbenzene.

[0041] An embodiment of the present invention also provides a method for preparing a capsule binder, comprising the following steps:

[0042] The phase change material, vinyl monomers, acrylate monomers, hydrophilic monomers, crosslinking monomers, and initiator are added to a reactor and heated. The heating temperature is greater than 5°C compared with the phase change temperature of the phase change material. The mixture is stirred until the phase change wax is completely dissolved, resulting in an oil phase mixture.

[0043] Polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP) dispersant is added to a reactor with water and heated and stirred at 85°C until completely dissolved to obtain an aqueous phase mixture.

[0044] The oil phase mixture is mixed with the aqueous phase mixture and then dispersed into a suspension by a high-speed homogenizer.

[0045] The suspension was heated to 80°C under a nitrogen atmosphere and subjected to a polymerization reaction for 6 hours to obtain the capsule binder.

[0046] As those skilled in the art know, the reactions in the above steps are conventional free radical polymerization, and the specific methods and reaction conditions are common free radical polymerization methods in the prior art, which will not be described in detail in this invention.

[0047] Initiators include one or more of the following: sodium persulfate, ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, azobisisobutyronitrile, benzoyl peroxide (BPO), benzoyl peroxide / sucrose, tert-butyl hydroperoxide / sodium sodium metabisulfite, tert-butyl hydroperoxide / sodium metabisulfite, benzoyl peroxide / N,N-dimethylaniline, ammonium persulfate / sodium bisulfite, potassium persulfate / sodium bisulfite, hydrogen peroxide / tartaric acid, hydrogen peroxide / sodium formaldehyde sulfoxylate, ammonium persulfate / ferrous sulfate, hydrogen peroxide / ferrous sulfate, benzoyl peroxide / N,N-diethylaniline, benzoyl peroxide / ferrous pyrophosphate, potassium persulfate / silver nitrate, persulfate / thiol, cumene hydroperoxide / ferrous chloride, potassium persulfate / ferrous chloride, hydrogen peroxide / ferrous chloride, and cumene hydroperoxide / tetraethyleneimine.

[0048] An embodiment of the present invention also provides an adhesive composition comprising a heat-resistant adhesive and a capsule adhesive as described in any one of the above embodiments, wherein the mass ratio of the heat-resistant adhesive to the capsule adhesive is (30-50):(50-70). The heat-resistant adhesive comprises one or more of polyacrylic acid, polyacrylonitrile, polyacrylamide, and polyvinyl alcohol. By limiting the mass ratio of the heat-resistant adhesive to the capsule adhesive within the above range, the adhesive composition exhibits high adhesion, high temperature resistance, and good thermal buffering properties.

[0049] In some embodiments, the adhesive composition has a tensile strength of 0.5 to 40 MPa, an elongation at break of 50% to 500%, and an electrolyte mass swelling rate of less than 30%.

[0050] The combined use of capsule binder and heat-resistant binder gives the prepared separator functional layer high adhesion while improving the separator's heat shrinkage resistance. Furthermore, the binder composition, through the introduction of the capsule binder, also possesses heat buffering properties, absorbing heat during battery charging and discharging, reducing the possibility of thermal runaway accidents, and improving battery safety. Moreover, no organic solvents are added during the separator preparation process, making the binder composition environmentally friendly and harmless.

[0051] Furthermore, the glass transition temperature of the heat-resistant adhesive is greater than 100°C.

[0052] It is understandable that, based on the content of the adhesive composition being 100%, the mass content of the heat-resistant adhesive is 30% to 50%, and the mass content of the capsule adhesive is 50% to 70%.

[0053] An embodiment of the present invention also provides a diaphragm, comprising a base membrane and a functional layer disposed on at least one side of the base membrane, the functional layer comprising ceramic particles and the binder composition described above. Specifically, the base membrane is a polyolefin membrane.

[0054] Furthermore, the slurry for preparing the functional layer includes ceramic particles, a binder composition, additives, and a solvent, wherein the solvent is water, and the additives include at least one of a wetting agent, a defoamer, and an anti-settling agent.

[0055] The wetting agent includes one of the following: sulfate ester salts, sulfonates, or alkynyldiol wetting agents, preferably the alkynyldiol wetting agent Surfdol 610.

[0056] The defoamer includes one of the following: polyether, silicone, or mineral oil defoamers, with mineral oil defoamer DF691 being the preferred choice.

[0057] Anti-settling agents include sodium hydroxymethyl cellulose, preferably CMC1220.

[0058] Specifically, by weight, the slurry for preparing the functional layer includes 800-100 parts ceramic particles, 5-10 parts binder composition, 0.5-3 parts wetting agent, 0.5-1 part defoamer, 0.5-3 parts anti-settling agent and 230-300 parts water.

[0059] An embodiment of the present invention also provides a battery, including the separator as described above.

[0060] The present invention will be further illustrated by the following examples.

[0061] Specifically, the capsule binder, binder composition, and diaphragm disclosed in this invention are described.

[0062] Example 1

[0063] 1) Capsule binder

[0064] Add 50 parts of phase change wax (Zhongjia, ZJ-PCM-A-62), 30 parts of isooctyl acrylate, 10 parts of divinylbenzene, 3 parts of acrylic acid, and 1 part of BPO initiator to a reactor, and stir at 65°C until the phase change wax is completely dissolved to obtain an oil phase mixture.

[0065] Add 15 parts of PVA1788 dispersant and water to a reactor, heat and stir at 85°C until completely dissolved to obtain an aqueous mixture;

[0066] The oil phase mixture and the aqueous phase mixture were dispersed into a suspension at high speed using a homogenizer;

[0067] The suspension was heated to 80°C under a nitrogen atmosphere and subjected to a polymerization reaction for 6 hours to obtain the capsule binder.

[0068] The mass ratio of phase change material, acrylate structural unit, hydrophilic functional structural unit and cross-linked structural unit in the capsule binder is m1:m2:m3:m4.

[0069] 2) Adhesive composition

[0070] The mass ratio of capsule binder to polyacrylic acid in the adhesive composition is 1:1.

[0071] 3) Diaphragm

[0072] Add 100 parts of ceramic particles, 250 parts of deionized water, 2 parts of anti-settling agent CMC1220, 1 part of wetting agent Surfdol 610, and 1 part of defoamer DF 691 to a high-speed mixer. After stirring for 30 minutes, add 8 parts of binder composition in proportion. After 30 minutes, discharge the material, coat the resulting slurry onto a polyolefin-based membrane, and wind it up to obtain a separator.

[0073] Examples 2 to 12

[0074] Examples 2 to 12 are largely the same as Example 1, except that the components of the capsule binder are different, as shown in Table 1.

[0075] Table 1

[0076]

[0077] Examples 13-15

[0078] Examples 13-15 are largely the same as Example 1, except that the components of the adhesive composition are different, as shown in Table 2. The heat-resistant adhesive can be obtained by purchasing or synthesizing.

[0079] Table 2

[0080]

[0081] Comparative Examples 1 to 12

[0082] The steps of Comparative Examples 1 to 12 are mostly the same as those of Example 1, except that the composition of the capsule binder is different, as shown in Table 1.

[0083] Comparative Examples 13 to 16

[0084] The steps of Comparative Examples 13 to 16 are mostly the same as those of Example 1, except that the adhesive compositions are different, as detailed in Table 2.

[0085] Performance testing:

[0086] The capsule binder, binder composition, and diaphragm prepared in the above examples and comparative examples were tested as follows.

[0087] 1) Tensile strength:

[0088] The capsule binders and binder compositions obtained in the examples and comparative examples were prepared according to the national standard GB / T 528 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber". After drying, they were cut into type 1A dumbbell-shaped specimens (test length 20.0±0.5mm, thickness 2.0±0.2mm). The tensile strength was tested using an electronic tensile testing machine at a speed of 50mm / min (Dongguan Dazhong Instrument Co., Ltd., model DZ 101).

[0089] 2) Electrolyte swelling rate: The capsule binder and binder composition obtained in the examples and comparative examples were respectively made into films, cut into pieces, weighed and recorded as m1, and soaked in electrolyte (EC:EMC:DEC=3:5:2, 1mol / L LiPF6) at 60°C for 72h. After removing the films, the residual electrolyte on the surface of the films was wiped with a wiping cloth and weighed again and recorded as m2. The swelling rate was calculated.

[0090] Swelling degree = [(m2-m1) / m1]*100%.

[0091] 3) Test method for phase change temperature and latent heat of phase change: After drying the capsule binder obtained in the examples and comparative examples, the phase change temperature and latent heat of phase change were tested using a simultaneous thermal analyzer DSC 3500 Sirius.

[0092] 4) Heat resistance cycle test: The capsule binders obtained in the examples and comparative examples were sealed and heated in cycles of 25°C for 30 min, 90°C for 30 min, and 25°C for 30 min. After 300 cycles, samples were dried and the latent heat of phase change was tested using a DSC 3500 Sirius synchronous thermal analyzer.

[0093] 5) The test method for adhesion is as follows: the diaphragms prepared in the examples and comparative examples are cut into 30×100mm specifications, 30mm wide 3M tape is selected, and the adhesion strength is tested using an electronic tensile testing machine (Dongguan Dazhong Instrument Co., Ltd., model DZ 101).

[0094] 6) The test method for heat shrinkage resistance is as follows: cut the diaphragm prepared in the example and comparative example into 100×100mm size, place it between two A4 sheets of paper, and then place them together on an iron tray. Transfer them to an oven at 150℃ and bake for 1 hour. Test the change rate of longitudinal width (MD) and transverse width (TD) before and after.

[0095] 7) The test method for breathability time is: use a Gurley breathability meter for testing.

[0096] The test results obtained from the examples and comparative examples are shown in Table 3 and Table 3 (continued).

[0097] Table 3

[0098]

[0099] Continued from Table 3

[0100]

[0101] As can be seen from the test results in Table 3, the capsule binder prepared by the present invention from phase change material, acrylate structural unit, hydrophilic functional structural unit and cross-linking structural unit has the characteristics of low swelling, high adhesion and high latent heat (>150J / g). When combined with heat-resistant binder as a binder composition, it has a lower swelling rate and higher tensile strength. When used for ceramic membrane coating, it can not only effectively bond ceramic and base membrane (strong adhesion >40N / m), but also improve the heat shrinkage resistance of the membrane under high temperature conditions of 150℃ (<3%), and does not affect the air permeability of the membrane. The air permeability time is kept within 210s / 100ml. Without affecting the lithium ion transport of the membrane, the introduction of phase change material and heat-resistant binder greatly improves the thermal safety performance of the membrane.

[0102] As can be seen from the test results in Table 3, the latent heat of phase change of the capsule binder is not only related to the type of phase change material, but also has a significant impact on the latent heat of phase change due to changes in the ratio between monomers. Comparing Examples 2, 3, 5, and 6 with Examples 1 and 1, it can be seen that when the proportion of phase change material decreases, the latent heat of phase change of the capsule binder drops below 150 J / g, leading to a decrease in the passive temperature control effect. Conversely, when the proportion of phase change material is too high and the proportion of polymer shell is too low, although the material has a high latent heat value, the low shell proportion results in poor capsule tensile strength, leading to a high risk of shell rupture and phase change material leakage. Furthermore, the prepared binder composition has poor adhesion performance, posing a risk of material shedding when used for ceramic diaphragm coating.

[0103] As can be seen from Examples 4, 5, 7, 8, 1, and 2, acrylate structural units are mainly used to adjust the Tg and adhesion of the capsule material. If the amount of acrylate structural units is too low, the capsule Tg will be too high, the adhesion performance will be reduced, and the thermal shrinkage performance of the separator at 150°C will be deviated. If the amount of acrylate structural units is too high, the latent heat value of the capsule binder will be reduced, and the swelling will increase, resulting in additional electrolyte consumption and affecting the long-term cycle life of the battery.

[0104] As can be seen from Examples 6, 7, 9, 10, 1, 3, and 4, the introduction of hydrophilic functional structural units can improve the reaction and storage stability of capsule binders. If the amount is too low, the reaction system will be unstable and gelation may occur during storage. If the amount is too high, it may lead to excessive viscosity and agglomeration during the synthesis process.

[0105] As can be seen from Examples 8, 9, Comparative Examples 11, 12, Comparative Examples 1 and 4, the crosslinked monomer structural unit has a significant impact on the swelling and tensile strength of the capsule binder. If the amount of crosslinked monomer structural unit is too low, the tensile strength of the capsule binder decreases, the swelling increases, the capsule structure is at risk of breakage, and the Tg is too low, resulting in a decrease in the heat resistance of the capsule binder itself, which leads to an increase in the air permeability time of the diaphragm and a decrease in the heat shrinkage performance at 150℃. If the amount is too high, the crosslinking is too high, the capsule bonding performance decreases, and the overall performance of the diaphragm deteriorates.

[0106] As can be seen from Examples 13-15, Comparative Example 1, and Comparative Examples 13-16, the binder composition formed by compounding the heat-resistant binder and the capsule binder in a certain proportion results in a lower thermal shrinkage rate of the prepared ceramic separator at 150°C when the proportion of heat-resistant binder increases. When the amount of heat-resistant binder is too high, the adhesion performance of the ceramic coating decreases, posing a risk of powder shedding, and the air permeability time of the prepared ceramic separator increases significantly, affecting the lithium-ion transmission efficiency of the battery. When the amount of heat-resistant binder is too low, the thermal shrinkage rate of the prepared ceramic separator at 150°C is high, and the heat resistance of the separator decreases.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A capsule binder, characterized in that, The capsule binder includes a core and a polymer layer disposed on the outer surface of the core and at least partially covering the core. The core includes a phase change material. The polymer layer includes a polymer, which includes acrylate structural units, hydrophilic functional structural units, and crosslinked structural units. The mass ratio of the phase change material, acrylate structural units, hydrophilic functional structural units, and crosslinked structural units is (40~60):30:(1~5):(5~20). The acrylate structural unit is a structural unit obtained by polymerization of acrylate monomers, and the acrylate monomers include at least one of the following: n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, and lauryl methacrylate. The hydrophilic functional structural unit includes one or more of acrylic structural units or hydroxy acrylate structural units; The cross-linked structural unit is a structural unit obtained by polymerization of cross-linked monomers, and the cross-linked monomers include at least one of divinyl aromatic hydrocarbons, bisphenol A diacrylate, heterocycloalkane diacrylates, bisphenol A dimethacrylate, and pentaerythritol tetraacrylate. The glass transition temperature of the polymer is -40~20℃; The phase transition temperature of the capsule binder is 25~90℃; the latent heat of phase transition of the capsule binder is greater than 150KJ / kg.

2. The capsule binder according to claim 1, characterized in that, The electrolyte swelling rate of the capsule binder is less than 40%.

3. The capsule binder according to claim 1, characterized in that, The phase change material includes one or more of the following: C18-C50 straight-chain alkanes, C12-C20 fatty acids, and C12-C30 fatty alcohols.

4. The capsule binder according to claim 1, characterized in that, The acrylate monomers also include at least one of cyclohexyl methacrylate, isobornyl acrylate, and isobornyl methacrylate.

5. An adhesive composition, characterized in that, It includes a heat-resistant adhesive and a capsule adhesive as described in any one of claims 1 to 4, wherein the mass ratio of the heat-resistant adhesive to the capsule adhesive is (30 to 50): (50 to 70).

6. The adhesive composition according to claim 5, characterized in that, The adhesive composition has a tensile strength of 0.5~40MPa, an elongation at break of 50%~500%, and an electrolyte mass swelling rate of less than 30%.

7. The adhesive composition according to claim 5, characterized in that, The glass transition temperature of the heat-resistant adhesive is greater than 100°C.

8. A diaphragm, characterized in that, It includes a base film and a functional layer disposed on at least one side of the base film, the functional layer comprising ceramic particles and the adhesive composition according to any one of claims 5-7.

9. A battery, characterized in that, Includes the diaphragm as described in claim 8.

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