Binder, ceramic separator, and secondary battery

Abstract

The application discloses a kind of binder, ceramic diaphragm and its secondary battery.The binder includes first polymer and second polymer, the first polymer and the second polymer are connected by chemical bond;The first polymer is polyacrylate polymer or SBR polymer containing first self-crosslinking structural unit, the Tg of the first polymer is ≤20 ℃, the second polymer is polyacrylic acid polymer or polyacrylamide polymer containing second self-crosslinking structural unit, the Tg of the second polymer is ≥80 ℃.The first polymer of low Tg is resistant to water and oil, but the heat resistance is generally, mainly plays the role of bonding, high Tg second polymer is resistant to oil and not resistant to water, mainly plays the role of heat resistance and improves electrolyte wettability, and by the interaction of first crosslinking structure and second crosslinking structure, so that binder simultaneously has excellent water and solvent resistance and heat resistance, and the affinity of electrolyte is better.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to an adhesive, a ceramic separator, and a secondary battery thereof. Background Technology

[0002] Lithium-ion secondary batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. Among these, the separator, as one of the key components affecting battery performance, is crucial for the overall performance of the lithium-ion battery. + The only channel for transmission, its main function is to separate the positive and negative terminals of the battery to prevent them from coming into contact and causing a short circuit.

[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. With the development of the smart era, thinning has become the main development direction of lithium-ion batteries, thus requiring ceramic separators to be correspondingly thinner while maintaining good air permeability, heat resistance, and adhesion.

[0004] To improve cell strength, an adhesive material is typically sprayed onto the ceramic-coated separator, and then hot-pressed to bond the electrodes to the separator, improving the separator's adhesion and simultaneously enhancing the electrolyte's wettability. The adhesive plays a crucial role in bonding ceramic particles during separator fabrication; its adhesion, electrochemical stability, and thermal stability all affect the electrochemical and thermal shrinkage properties of the ceramic separator.

[0005] Traditional binders such as polyvinylidene fluoride (PVDF) and PVDF-hexafluoropropylene copolymer possess good mechanical and adhesive properties, but their application requires the addition of organic solvents, causing environmental pollution. Furthermore, while oil-based PVDF-coated ceramic separators offer a good balance of thinness, heat resistance, and hot-press bonding of electrodes, and superior hot-press bonding and separator uniformity compared to water-based PVDF coatings, the subsequent water washing process after applying oil-based PVDF to the ceramic coating imposes requirements on the ceramic coating's resistance to water and solvents (DMAC / NMP). Otherwise, ceramic particles may detach during the water washing or oil-based PVDF coating process, affecting the overall performance of the lithium-ion battery separator.

[0006] However, water-soluble polymers, such as polyacrylic acid and polyvinyl alcohol, which have environmental advantages, have limited adhesive strength. Furthermore, when used in oil-coated PVDF membranes, the ceramic coating fails to function properly during washing or extraction due to the water solubility of the binder, leading to coating peeling and powdering on the base membrane surface. While acrylate and SBR binders have good water resistance, their heat resistance is inferior to that of water-soluble binders. Summary of the Invention

[0007] To address the problems of existing adhesives used for ceramic separators, this invention provides a water- and solvent-resistant adhesive, a ceramic separator, and a secondary battery thereof.

[0008] In a first aspect, the adhesive provided by the present invention includes a first polymer and a second polymer, wherein the first polymer and the second polymer are connected by chemical bonds; the first polymer is a polyacrylate polymer or an SBR polymer containing a first self-crosslinking structural unit, wherein the glass transition temperature Tg of the first polymer is ≤20℃; and the second polymer is a polyacrylic acid polymer or a polyacrylamide polymer containing a second self-crosslinking structural unit, wherein the glass transition temperature Tg of the second polymer is ≥80℃.

[0009] Furthermore, the glass transition temperature (Tg) of the first polymer is -70 to 20°C, and the glass transition temperature (Tg) of the second polymer is 80 to 150°C.

[0010] Furthermore, the swelling degree of the adhesive is <3%.

[0011] Furthermore, the mass ratio of the first polymer to the second polymer is (5~9):(1~5).

[0012] Furthermore, the mass ratio of the first self-crosslinking structural unit in the first polymer to the polyacrylate polymer or SBR polymer in the first polymer is (3~15):(113~265); and / or, the mass ratio of the second self-crosslinking structural unit in the second polymer to the polyacrylic acid polymer or polyacrylamide polymer in the second polymer is (3~10):(25~115).

[0013] Furthermore, the first polymer further includes a first vinyl structural unit, an acrylate structural unit, and a first functional structural unit, wherein the mass ratio of the first vinyl structural unit to the acrylate structural unit to the first functional structural unit to the first self-crosslinking structural unit is (10~50):(100~200):(3~15):(3~15); and / or, the second polymer further includes a second vinyl structural unit and a second functional structural unit, wherein the mass ratio of the second vinyl structural unit to the second functional structural unit to the second self-crosslinking structural unit is (10~50):(15~65):(3~10).

[0014] Furthermore, the first functional structural unit and the second functional structural unit are each independently derived from functional monomers containing carboxyl or hydroxyl groups, wherein the functional monomers are selected from any one or a combination of at least two of acrylic acid, methacrylic acid, vinylacrylic acid, β-acryloyloxypropionic acid, maleic acid, itaconic acid, monobutyl itaconic acid, crotonic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

[0015] In a second aspect, the present invention provides a ceramic diaphragm, comprising a base membrane and a ceramic coating, wherein the ceramic coating comprises an adhesive as described in the first aspect, and the electrolyte wettability of the ceramic diaphragm is >2.0 cm / min.

[0016] Furthermore, the ceramic diaphragm exhibits less than 3% longitudinal and transverse thermal shrinkage at 130°C.

[0017] Thirdly, the present invention provides a secondary battery, which is a lithium-ion battery or a sodium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a ceramic separator as described in the second aspect.

[0018] Compared with the prior art, the present invention has the following beneficial effects.

[0019] The adhesive of the present invention is formed by two polymers linked by chemical bonds. The first polymer contains a first self-crosslinking structural unit, and the second polymer contains a second self-crosslinking structural unit. The first polymer and the second polymer have different Tg values. The first polymer with a low Tg is resistant to water and oil, but has relatively poor heat resistance and mainly plays a bonding role. The second polymer with a high Tg is resistant to oil but not to water and mainly plays a role in heat resistance and improving electrolyte wettability. Through the interaction between the first crosslinking structure and the second crosslinking structure, the adhesive simultaneously possesses excellent water and solvent resistance and heat resistance, and has better affinity with the electrolyte.

[0020] The ceramic diaphragm prepared by the binder of the present invention has excellent adhesion, air permeability, better wettability with electrolyte and high heat shrinkage resistance, and also has excellent water and solvent resistance.

[0021] This invention solves the problem of degumming or powdering caused by binder failure during the oil coating, water washing, and extraction processes of PVdF separators, ensuring the overall performance of lithium-ion PVdF oil-coated separators, thereby improving battery performance and safety reliability. Detailed Implementation

[0022] 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.

[0023] In this invention, as is known to those skilled in the art of chemical synthesis, each structural unit represents a structural portion of the 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.

[0024] In a first aspect, the adhesive provided by the present invention includes a first polymer and a second polymer, wherein the first polymer and the second polymer are connected by chemical bonds; the first polymer is a polyacrylate polymer or an SBR polymer containing a first self-crosslinking structural unit, wherein the glass transition temperature Tg of the first polymer is ≤20℃; and the second polymer is a polyacrylic acid polymer or a polyacrylamide polymer containing a second self-crosslinking structural unit, wherein the glass transition temperature Tg of the second polymer is ≥80℃.

[0025] In some specific embodiments, the glass transition temperature (Tg) of the first polymer is -70 to 20°C, and the glass transition temperature (Tg) of the second polymer is 80 to 150°C.

[0026] The first polymer has a relatively low glass transition temperature (Tg) and good water and oil resistance, but its heat resistance is relatively average, and it mainly serves as an adhesive. The second polymer has a relatively high glass transition temperature (Tg) and mainly serves as a heat-resistant agent and improves the wettability of the electrolyte, so that the adhesive has excellent water and solvent resistance and heat resistance, and has better affinity with the electrolyte.

[0027] In some specific embodiments, the swelling degree of the adhesive in water or organic solvents is <3%. The smaller the swelling degree value, the better the water / solvent resistance of the adhesive, and the ceramic diaphragm will not delaminate or shed powder during the oil coating PVdF or water washing process.

[0028] In some specific embodiments, the mass ratio of the first polymer to the second polymer is (5~9):(1~5); specifically, the mass ratio can be 5:1, 6.1:2, 7:2, 7.5:2.5, 8:3, 8:3.5, 8.5:4, 9:5, etc.

[0029] In some specific embodiments, the mass ratio of the first self-crosslinking structural unit in the first polymer to the polyacrylate polymer or SBR polymer in the first polymer is (3~15):(113~265); specifically, the mass ratio can be 3:113, 4:125, 5:131, 6:137, 7:150, 8:185, 9:200, 10:211, 12:235, 13:247, 15:264.9, etc.

[0030] In some specific embodiments, the mass ratio of the second self-crosslinking structural unit in the second polymer to the polyacrylic acid polymer or polyacrylamide polymer in the second polymer is (3~10):(25~115); specifically, the mass ratio can be 3:25, 4:31, 5:37, 6:49, 7:66, 8:79, 8.4:87, 9:98, 9.5:109, 10:114.8, etc.

[0031] In some specific embodiments, the first polymer further includes a first vinyl structural unit, an acrylate structural unit, and a first functional structural unit, wherein the mass ratio of the first vinyl structural unit: acrylate structural unit: first functional structural unit: first self-crosslinking structural unit is (10~50):(100~200):(3~15):(3~15); specifically, the mass ratio can be 10:100:3:3, 15:120:4:4, 19:130:5:5, 25:140:6:6, 30:148:7:8, 36:155:8:9, 40:160:10:9, 43:168:12:11, 47:180:14:13, 50:200:15:14, etc.

[0032] In some specific embodiments, the second polymer further includes a second vinyl structural unit and a second functional structural unit, wherein the mass ratio of the second vinyl structural unit to the second functional structural unit to the second self-crosslinking structural unit is (10~50):(15~65):(3~10); specifically, the mass ratio can be 10:15:3, 11:20:4, 12:26:5, 12.6:32:6, 13:40:7, 13.2:47:8, 14:55:9, 14.3:60:9.2, 15:65:10, etc.

[0033] In this invention, the mass ratio between each structural unit is the mass ratio of the individual units providing each structural unit.

[0034] The first vinyl structural unit and the second vinyl structural unit are each independently derived from vinyl monomers. The vinyl monomers are selected from any one or a combination of at least two of styrene, acrylonitrile, methylstyrene, ethylstyrene, divinylbenzene, 1,4-butadiene, isoprene, vinyl acetate, N-vinylpyrrolidone, acrylamide, and methacrylamide, preferably at least one of styrene, 1,4-butadiene, and acrylamide.

[0035] The acrylate structural unit is derived from acrylate monomers, which are selected from any one or a combination of at least two of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, 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. Preferably, at least one of the following: n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and tert-butyl methacrylate.

[0036] The first functional structural unit and the second functional structural unit are each independently derived from functional monomers containing carboxyl or hydroxyl groups. The functional monomers are selected from any one or a combination of at least two of acrylic acid, methacrylic acid, vinylacrylic acid, β-acryloyloxypropionic acid, maleic acid, itaconic acid, monobutyl itaconic acid, crotonic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; preferably at least one of acrylic acid, methacrylic acid, and hydroxyethyl acrylate.

[0037] The first and second self-crosslinking structural units are each independently derived from self-crosslinking monomers, and can be selected from one or a combination of at least two of hydroxymethylacrylamide, hydroxyethylacrylamide, N-n-butoxymethylacrylamide, N-isobutoxymethylacrylamide, and hydroxyethylacrylamide.

[0038] The preparation method of the adhesive of the present invention:

[0039] 1) Add water to the reactor, heat to 80-85℃ and purge with nitrogen, then add an aqueous solution containing the first initiator; then, mix the vinyl monomers, acrylate monomers, functional monomers, self-crosslinking monomers, emulsifier and water for preparing the first polymer in a certain proportion, stir thoroughly to emulsify into a first pre-emulsion, and add the first pre-emulsion dropwise to the reactor at a uniform rate for a total dropwise time of 3-12 hours; after the dropwise addition is completed, add an aqueous solution containing the first initiator, keep warm and mature for 3-6 hours, and then cool to obtain the first polymer;

[0040] 2) After mixing the vinyl monomers, functional monomers, self-crosslinking monomers, emulsifiers and water in a certain proportion to prepare the second polymer, the mixture is thoroughly stirred and emulsified into a second pre-emulsion. The second pre-emulsion and the aqueous solution containing the second initiator are simultaneously added dropwise to the first polymer at room temperature, and the addition is controlled to be completed within 2 hours. Stirring is continued for 3 to 6 hours to allow the monomers in the second pre-emulsion to completely swell in the network structure of the first polymer. Then the temperature is raised to 80 to 85°C and reacted for 6 hours. After polymerization and crosslinking, an adhesive with an interpenetrating network structure is obtained.

[0041] The monomers used to prepare the first polymer and the second polymer can be the same or different, as long as the selected monomers and their corresponding mass ratios satisfy the requirement that the glass transition temperature (Tg) of the first polymer is ≤20℃ and the glass transition temperature (Tg) of the second polymer is ≥80℃. The emulsifier can be sodium dodecylbenzenesulfonate, and both the first and second initiators can be selected from ammonium persulfate.

[0042] The preparation methods and glass transition temperature control methods of the aforementioned polymers are well known to those skilled in the art, or can be known by those skilled in the art based on existing technology. For example, the glass transition temperature can be controlled by controlling the composition and ratio of the polymer monomers.

[0043] Secondly, the present invention provides a ceramic diaphragm, comprising a base membrane and a ceramic coating, wherein the ceramic coating is obtained by coating and drying a ceramic slurry containing the binder described in the first aspect, and the electrolyte wettability of the ceramic diaphragm is >2.0 cm / min. The ceramic diaphragm has a low areal density, high heat shrinkage resistance, and suitable air permeability time, while also possessing water and solvent resistance.

[0044] The ceramic slurry includes ceramic particles, a binder as described in the first aspect, an additive, and a solvent, wherein the mass ratio of the ceramic particles to the binder is (50~150):(3~10).

[0045] In some specific embodiments, the additives are wetting agents, defoamers, and anti-settling agents, and the solvent is deionized water. Adding wetting agents and defoamers facilitates coating. In the ceramic slurry, the mass ratio of the ceramic particles, binder, deionized water, wetting agent, defoamer, and anti-settling agent is (50~150):(3~10):(200~300):(0.5~2):(0.5~2):(0.5~2); specifically, the mass ratio can be 50:3:200:0.5:0.5:0.5, 55:3:212:0.6:0.6:0.6, or 60:4:223:0.8:0.9. :1, 65:5:237:1.3:1.2:1.3, 72:6:249:1.4:1.3:1.4, 85:7.5:258:1.5:1.5:1.5, 65:8.3:266:1.7:1.7:1.6, 130:8.7:275:1.8:1.8:1.7, 140:9.2:285:1.9:1.8:1.9, 150:10:300:2:2:2, etc.

[0046] The method for preparing ceramic diaphragms using the binder of the first aspect is well known in the prior art. For example: in a high-speed mixer, deionized water and an anti-settling agent are added and dispersed at low speed for 30-60 minutes. After dispersion, ceramic particles are added, stirred, and then dispersed by sand milling for 0.5-2 hours. The mixture is then transferred back to the mixer, a wetting agent is added, and stirred for 30-60 minutes. The binder of the first aspect and a defoamer are then added, and the mixture is stirred at low speed for 30-60 minutes before being discharged to obtain a ceramic slurry. The prepared ceramic slurry is coated onto the surface of a diaphragm substrate, dried, and then wound up to obtain a ceramic diaphragm.

[0047] In some specific embodiments, the coating adhesion of the ceramic diaphragm is >40 N / m, and the longitudinal and transverse thermal shrinkage of the ceramic diaphragm at 130°C are both <3%.

[0048] In some specific embodiments, the electrolyte wettability of the ceramic diaphragm is >2 cm / min.

[0049] A secondary coating of PVdF / PMMA diaphragm adhesive is applied to the prepared ceramic diaphragm using either water-based or oil-based coating methods, such as spraying, rolling, or dot application. No adhesive peeling or powder shedding occurs during this secondary coating process.

[0050] Thirdly, the present invention provides a secondary battery, which is a lithium-ion battery or a sodium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a ceramic separator as described in the second aspect. The battery is prepared by assembling the negative electrode, the positive electrode, the electrolyte, and the ceramic separator into a battery.

[0051] The specific embodiments of the present invention will be further explained and described below through examples and comparative examples.

[0052] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art. Monomers conforming to this invention are commercially available.

[0053] Example 1

[0054] 1) Preparation of adhesive

[0055] 100 parts of water were added to the reactor, heated to 80°C, and nitrogen was purged for 30 minutes. An initiator aqueous solution of 0.4 parts ammonium persulfate and 10 parts water was added. Then, 35 parts styrene, 130 parts isooctyl acrylate, 3 parts acrylic acid, 3 parts hydroxyethyl acrylate, 5 parts hydroxymethyl acrylamide, 1 part sodium dodecylbenzenesulfonate, and 150 parts water were mixed and thoroughly emulsified to form a first pre-emulsion. This first pre-emulsion was added dropwise to the reactor at 80°C over a total dropping time of 5 hours. After the dropping was completed, an initiator aqueous solution of 0.2 parts ammonium persulfate and 6 parts water was added, and the mixture was kept at this temperature for 5 hours. After cooling, the first polymer was obtained. The glass transition temperature (Tg) of the first polymer was -22°C.

[0056] 15 parts styrene, 35 parts acrylamide, 40 parts methacrylic acid, 5 parts hydroxymethylacrylamide, 0.5 parts sodium dodecylbenzenesulfonate, and 150 parts water were mixed and emulsified thoroughly to form a second pre-emulsion. The second pre-emulsion, along with an initiator aqueous solution of 0.3 parts ammonium persulfate and 10 parts water, was simultaneously added dropwise to the first polymer at room temperature, controlled to be completed within 2 hours. Stirring continued for 3–6 hours to allow the monomers in the second pre-emulsion to completely swell in the network structure of the first polymer. The temperature was then raised to 85°C and reacted for 6 hours. After polymerization and crosslinking, an adhesive with an interpenetrating network structure was obtained. The glass transition temperature (Tg) of the second polymer in the obtained adhesive was 140°C.

[0057] 2) Ceramic diaphragm

[0058] In a high-speed mixer, 250 parts of deionized water and 1 part of anti-settling agent are added and dispersed at low speed for 30 minutes. Then, 100 parts of ceramic particles are added and stirred. After stirring, the mixture is dispersed by sand milling for 2 hours. Then, it is transferred back to the mixer and 1 part of wetting agent is added. After stirring for 30 minutes, 5 parts of the binder prepared in this invention and 1 part of defoamer are added. After stirring at low speed for 30 minutes, the mixture is discharged to obtain a ceramic slurry. The prepared ceramic slurry is coated on the surface of a diaphragm substrate, dried, and then wound up to obtain a ceramic diaphragm.

[0059] 3) Secondary batteries

[0060] The negative electrode, positive electrode, electrolyte, etc. of the lithium-ion secondary battery prepared according to conventional methods in the art are stacked in sequence with the positive electrode, the ceramic separator of the present invention, and the negative electrode, and then wound to obtain the cell. The cell is placed in an aluminum-plastic film, and the electrolyte is injected into the bare cell. After vacuum sealing, standing, formation, shaping, and capacity testing, the lithium-ion secondary battery is obtained.

[0061] Example 2

[0062] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the binder preparation was carried out by adjusting the types and amounts of monomers used in the polymer, so that the glass transition temperature (Tg) of the first polymer was 18°C ​​and the glass transition temperature (Tg) of the resulting second polymer was 82°C. Specifically, the monomers used in the first polymer were 40 parts styrene, 100 parts n-butyl acrylate, 12 parts acrylic acid, and 3 parts hydroxyethyl acrylamide; the monomers used in the second polymer were 40 parts styrene, 40 parts methacrylic acid, 15 parts hydroxyethyl acrylate, and 3 parts hydroxyethyl acrylamide. The rest was the same as in Example 1.

[0063] Example 3

[0064] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the binder preparation was carried out by adjusting the types and amounts of monomers used in the polymer, so that the glass transition temperature (Tg) of the first polymer was -30°C, and the glass transition temperature (Tg) of the resulting second polymer was 160°C. Specifically, the monomers used in the first polymer were 35 parts styrene, 160 parts isooctyl acrylate, 10 parts acrylic acid, and 6 parts hydroxyethyl acryloyl urea, while the monomers used in the second polymer were 10 parts styrene, 65 parts methacrylic acid, and 6 parts hydroxyethyl acryloyl urea. The rest was the same as in Example 1.

[0065] Example 4

[0066] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the binder was prepared by adjusting the types and amounts of monomers used in the polymer to achieve a glass transition temperature (Tg) of -33°C for the first polymer. The monomers used in the first polymer were 35 parts styrene, 160 parts isooctyl acrylate, 10 parts acrylic acid, and 5 parts N-butoxymethacrylamide. The rest was the same as in Example 1.

[0067] Example 5

[0068] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the binder was prepared by adjusting the type and amount of monomers used in the polymer to achieve a glass transition temperature (Tg) of 147°C for the second polymer. The monomers used in the second polymer were 10 parts styrene, 65 parts methacrylic acid, and 5 parts N-isobutoxymethacrylamide. The rest was the same as in Example 1.

[0069] Example 6

[0070] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the binder preparation was carried out by adjusting the types and amounts of monomers used in the polymer, so that the glass transition temperature (Tg) of the first polymer was -20°C, and the glass transition temperature (Tg) of the resulting second polymer was 126°C. Specifically, the monomers used in the first polymer were 35 parts styrene, 160 parts isooctyl acrylate, 10 parts acrylic acid, and 15 parts hydroxymethylacrylamide, while the monomers used in the second polymer were 30 parts styrene, 45 parts methacrylic acid, and 10 parts hydroxymethylacrylamide. The rest was the same as in Example 1.

[0071] Example 7

[0072] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the ceramic separator was prepared with 150 parts of ceramic particles and 10 parts of binder.

[0073] Example 8

[0074] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this example and Example 1 is that the ceramic separator was prepared with 50 parts of ceramic particles and 3 parts of binder.

[0075] Comparative Example 1

[0076] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the binder includes a first polymer and a second polymer, but the second polymer does not contain self-crosslinking structural units. The second polymer coats the outer layer of the first polymer to form a core-shell structure binder. The rest is the same as in Example 1.

[0077] Comparative Example 2

[0078] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the binder includes a first polymer and a second polymer, but the first polymer does not contain self-crosslinking structural units, and the second polymer coats the outer layer of the first polymer to form a core-shell structure binder. The rest is the same as in Example 1.

[0079] Comparative Example 3

[0080] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the binder includes a first polymer and a second polymer, but neither the first polymer nor the second polymer contains self-crosslinking structural units. The second polymer coats the outer layer of the first polymer to form a core-shell structure binder. The rest is the same as in Example 1.

[0081] Comparative Example 4

[0082] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the self-crosslinking monomer used in the first polymer of the binder is 20 parts, and the self-crosslinking monomer used in the second polymer is 15 parts.

[0083] Comparative Example 5

[0084] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the preparation of the binder was carried out by adjusting the type and amount of monomers used in the polymer so that the glass transition temperature Tg of the first polymer was 25°C and the glass transition temperature Tg of the second polymer of the resulting binder was 100°C; the rest was the same as in Example 1.

[0085] Comparative Example 6

[0086] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the preparation of the binder was carried out by adjusting the type and amount of monomers used in the polymer so that the glass transition temperature Tg of the first polymer was -25°C and the glass transition temperature Tg of the second polymer of the binder was 75°C; the rest was the same as in Example 1.

[0087] Comparative Example 7

[0088] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the preparation of the binder was carried out by adjusting the type and amount of monomers used in the polymer so that the glass transition temperature Tg of the first polymer was 25°C and the glass transition temperature Tg of the second polymer of the resulting binder was 75°C; the rest was the same as in Example 1.

[0089] Comparative Example 8

[0090] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the ceramic separator was prepared with 50 parts of ceramic particles and 1 part of binder. The rest is the same as in Example 1.

[0091] Comparative Example 9

[0092] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the ceramic separator was prepared with 150 parts of ceramic particles and 15 parts of binder. The rest is the same as in Example 1.

[0093] Comparative Example 10

[0094] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the binder contains a first polymer but does not contain a second polymer.

[0095] Comparative Example 11

[0096] The binder, ceramic separator, and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that the binder contains a second polymer but does not contain a first polymer.

[0097] Performance testing

[0098] The adhesives prepared in Examples 1-8 and Comparative Examples 1-11 were characterized and their performance was tested. The test results are shown in Table 1.

[0099] [Swelling Degree] After the adhesive was baked at 100℃ for 24 hours to form a film, it was cut into pieces and immersed in different solvents (water / DMAC / NMP). The swelling degree was then tested at room temperature and at 60℃ for 72 hours. The smaller the swelling degree value, the better the water / solvent resistance of the adhesive.

[0100] [Glass Transition Temperature Tg] After the adhesive is dried, the glass transition temperature is tested using a simultaneous thermal analyzer DSC 3500 Sirius. The heating range is -70~150℃, and the heating rate is 5~20K / min. The glass transition temperatures of the first polymer and the second polymer during the preparation of the adhesive are tested.

[0101] Table 1 Test results of the adhesive

[0102] ;

[0103] The ceramic diaphragms prepared in Examples 1-8 and Comparative Examples 1-11 were subjected to performance tests, and the test results are shown in Tables 2-1 and 2-2.

[0104] [Electrolyte wettability]: The ceramic diaphragm was cut into 100×100mm pieces, suspended and laid flat. 10μL of electrolyte droplet (electrolyte composition: EC:EMC:DEC=3:5:2, 1mol / L LiPF6) was dropped into the center area of ​​the ceramic diaphragm. The diffusion diameter of the electrolyte was tested after 1 minute to evaluate the wettability of the ceramic diaphragm and the electrolyte. The longer the diffusion diameter, the better the electrolyte wettability.

[0105] [Liquid Resistance]: The ceramic diaphragm was cut into 100×100mm sizes and immersed in different solvents (water / DMAC / NMP) for 4 hours at room temperature and 60℃ respectively. The coating peeling was observed to evaluate the water / oil resistance of the ceramic diaphragm.

[0106] [Coating Adhesion]: The ceramic diaphragm was cut into 20×100mm sizes and the coating adhesion was tested using an electronic tensile testing machine (Dongguan Dazhong Instrument Co., Ltd., model DZ 101) to evaluate the bonding ability between the coating on the ceramic diaphragm and the diaphragm substrate.

[0107] [Heat Shrinkage]: The ceramic diaphragm was cut into 100×100mm sizes, placed between two A4 sheets of paper, placed on an iron tray, and baked in a 130℃ oven for 1 hour. The change rate of longitudinal width (MD) and transverse width (TD) before and after the test was measured, i.e., longitudinal heat shrinkage and transverse heat shrinkage, to evaluate the heat resistance of the ceramic diaphragm.

[0108] [Air Permeability]: The ceramic diaphragm was cut into 100×400mm pieces, and its air permeability was tested using a Gurley air permeability meter. Under a pressure of 1.21kPa, the area through which 100ml of air passed was 6.45cm². 2 The time required for the diaphragm to be in place is measured in seconds per 100 mL.

[0109] [Separator-Electrode Peel Strength]: The ceramic separator is cut into 40×300mm specifications and bonded with a 30*200mm positive / negative electrode. After bonding, it is hot-pressed at 85℃ and 1MPa for 1~10min. After removal, it is fixed to a stainless steel plate with 3M double-sided tape and then fixed on the fixture of the peel force tester. A 180-degree peel test is performed at a speed of 10mm / min and a load of 10N to evaluate the peel strength between the ceramic separator and the electrode.

[0110] Table 2-1 Test results of ceramic diaphragms

[0111] ;

[0112] Table 2-2 Test Results of Ceramic Diaphragms

[0113] ;

[0114] The lithium-ion secondary batteries prepared in Examples 1-8 and Comparative Examples 1-11 were subjected to electrical performance tests, including 0.5C discharge specific capacity, DCIR at 50% SOC discharge, and capacity retention after 500 cycles at 1C. The test results are shown in Table 3.

[0115] 【0.5C Discharge Capacity Test】① The battery was placed in a constant temperature chamber at 25℃ for 2 hours; ② Charging: Constant current and constant voltage charging was used (0.5C CC to 3.65V, 0.05C cutoff), and the battery was left to stand for 30 minutes after being fully charged; ③ Discharging: The battery was discharged at 0.5C to 2.5V, and left to stand for 30 minutes after being completely discharged; ④ Calculation of 0.5C discharge capacity: The battery was charged and discharged at 0.5C for 3 cycles, and the average discharge capacity of the 3 cycles was taken as the reference capacity. 0.5C discharge capacity = reference capacity / mass of positive electrode active material.

[0116]

Cell DCIR Test

[0117]

Cyclic Test

[0118] Table 3 Electrical performance test results

[0119] ;

[0120] As can be seen from the performance test results in Tables 1, 2-1, 2-2, and 3, the use of the water- and solvent-resistant binder of this invention and the ceramic diaphragm and secondary battery prepared by the binder can effectively improve the water and solvent resistance of the binder, improve the water / oil resistance, heat resistance, air permeability, coating adhesion, electrolyte wettability, and battery performance of the ceramic diaphragm.

[0121] Comparing the test results of Examples 1-8 with those of Comparative Examples 1-3, it can be seen that when the first polymer and / or the second polymer do not contain self-crosslinking structural units and the binder has a core-shell structure, the binder has a large degree of swelling in water or solvent, resulting in poor water / solvent resistance. Although the prepared separator can maintain good air permeability, heat resistance, and electrolyte wettability, it will exhibit varying degrees of powder and adhesive shedding during the secondary coating of oil-coated PVdF. This leads to a decrease in the peel strength between the secondary coated PVdF separator and the electrode, which cannot suppress the deformation stress generated by the electrode rebound during cell cycling, thereby affecting the cycle performance of the battery.

[0122] Comparing the test results of Examples 1-6 with Comparative Example 4, it can be seen that as the content of self-crosslinking structural units in the polymer increases, the crosslinking degree of the binder itself increases, resulting in better water and solvent resistance. The coated separator does not exhibit powder or adhesive loss during the secondary oil coating PVdF process, and the adhesion performance between the separator and the electrode is stable, leading to good battery cycle stability. However, when the content of self-crosslinking structural units in the polymer exceeds the range disclosed in this invention, the crosslinking monomer concentration is too high during the binder synthesis process, causing agglomeration and excessive slag discharge, making it impossible to produce a ceramic separator.

[0123] Comparing the test results of Examples 1-6 with those of Comparative Examples 5-7, it can be seen that when the glass transition temperatures of the first and second polymers selected as binders are not within the range disclosed in this invention, the bonding performance of the binder to the ceramic and the base membrane or the heat resistance of the separator decreases. When the Tg of the first polymer in the binder is higher than 20°C, the coating on the separator will exhibit varying degrees of powder shedding, leading to poor uniformity or detachment of the secondary adhesive coating and PVdF coating, and a decrease in the peel strength between the separator and the electrode, thereby affecting cycle performance. When the Tg of the second polymer in the binder is lower than 80°C, the heat resistance of the prepared ceramic separator decreases by more than 3% at 130°C, posing a thermal safety risk after being made into a secondary battery. When the glass transition temperature Tg of the first polymer in the binder is -70 to 20°C and the glass transition temperature Tg of the second polymer is 80 to 150°C, the performance is better.

[0124] Comparing the test results of Examples 1 and 7-8 with those of Comparative Examples 8-9, it can be seen that when the binder content in the ceramic separator is too low, it cannot effectively bond the ceramic and the base membrane, resulting in a ceramic separator prone to powder shedding, poor thermal safety performance, and unsuitability for secondary batteries. When the binder content in the ceramic separator is too high, the gas permeability of the resulting ceramic separator increases excessively, affecting the lithium-ion transport efficiency of the battery and causing a high DC internal resistance during discharge, thus affecting the cycle performance of the battery. The best performance is achieved when the mass ratio of ceramic particles to binder is (50-150):(3-10).

[0125] Comparing the test results of Examples 1-8 with those of Comparative Examples 10-11, it can be seen that when the binder does not contain the second polymer, although the binder and its diaphragm have good water / solvent resistance, the heat resistance of the prepared diaphragm decreases significantly at 130°C and its wettability with the electrolyte is also poor. When the binder does not contain the first polymer, the binder has a particularly large swelling degree in water, and its water resistance deteriorates. Although the prepared diaphragm can maintain good heat resistance and electrolyte wettability, its water resistance is very poor. The coating of the ceramic diaphragm completely falls off after being soaked in water, resulting in a significant decrease in the peel strength between the diaphragm and the electrode, which seriously affects the cycle performance.

[0126] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. An adhesive, characterized in that, The adhesive comprises a first polymer and a second polymer, which are connected by chemical bonds; the first polymer is a polyacrylate polymer or an SBR polymer containing a first self-crosslinking structural unit, and the glass transition temperature Tg of the first polymer is ≤20℃; the second polymer is a polyacrylic acid polymer or a polyacrylamide polymer containing a second self-crosslinking structural unit, and the glass transition temperature Tg of the second polymer is ≥80℃. The first polymer further includes a first vinyl structural unit, an acrylate structural unit, and a first functional structural unit, wherein the mass ratio of the first vinyl structural unit to the acrylate structural unit to the first functional structural unit to the first self-crosslinking structural unit is (10~50):(100~200):(3~15):(3~15). The second polymer further includes a second vinyl structural unit and a second functional structural unit, wherein the mass ratio of the second vinyl structural unit to the second functional structural unit to the second self-crosslinking structural unit is (10~50):(15~65):(3~10). The first vinyl structural unit and the second vinyl structural unit are each independently derived from vinyl monomers, which are selected from any one or a combination of at least two of styrene, acrylonitrile, methylstyrene, ethylstyrene, divinylbenzene, 1,4-butadiene, isoprene, vinyl acetate, N-vinylpyrrolidone, acrylamide, and methacrylamide. The acrylate structural unit is derived from acrylate monomers, which are selected from any one or a combination of at least two of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, 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. The first functional structural unit and the second functional structural unit are each independently derived from functional monomers containing carboxyl or hydroxyl groups. The functional monomers are selected from any one or a combination of at least two of the following: acrylic acid, methacrylic acid, vinylacrylic acid, β-acryloyloxypropionic acid, maleic acid, itaconic acid, monobutyl itaconic acid, crotonic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. The first self-crosslinking structural unit and the second self-crosslinking structural unit are each independently derived from self-crosslinking monomers, selected from one or at least two combinations of hydroxymethylacrylamide, hydroxyethylacrylamide, N-n-butoxymethylacrylamide, N-isobutoxymethylacrylamide, and hydroxyethylacrylurea.

2. The adhesive according to claim 1, characterized in that, The glass transition temperature (Tg) of the first polymer is -70 to 20°C, and the glass transition temperature (Tg) of the binder of the second polymer is 80 to 150°C.

3. The adhesive according to claim 1, characterized in that, The swelling degree of the adhesive is <3%.

4. The adhesive according to claim 2, characterized in that, The mass ratio of the first polymer to the second polymer is (5~9):(1~5).

5. The adhesive according to claim 4, characterized in that, The mass ratio of the first self-crosslinking structural unit in the first polymer to the polyacrylate polymer or SBR polymer in the first polymer is (3~15):(113~265). And / or, the mass ratio of the second self-crosslinking structural unit in the second polymer to the polyacrylic acid polymer or polyacrylamide polymer in the second polymer is (3~10):(25~115).

6. A ceramic diaphragm, characterized in that, It includes a base membrane and a ceramic coating, wherein the ceramic coating includes the binder as described in any one of claims 1 to 5, and the electrolyte wettability of the ceramic membrane is >2.0 cm / min.

7. The ceramic diaphragm according to claim 6, characterized in that, The ceramic diaphragm exhibits less than 3% longitudinal and transverse thermal shrinkage at 130°C.

8. A secondary battery, characterized in that, The secondary battery is a lithium-ion battery or a sodium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a ceramic separator as described in any one of claims 6 to 7.