Preparation method of polymer adhesive for diaphragm coating, polymer adhesive, diaphragm and battery

Abstract

The present invention belongs to the technical field of battery diaphragms, and particularly relates to a preparation method of a polymer glue for diaphragm coating, the polymer glue, a diaphragm and a battery. The polymer glue comprises polymer particles, and the polymer particles comprise a core and a shell. The core comprises a base core and an elastic structure. The base core has pores at least on the surface, and the elastic structure penetrates at least through the pores on the surface of the base core. The shell covers the surface of the core. The PDI of the polymer particles is <1 and the D50 is 1 μm to 11 μm. The glass transition temperature of the material of the base core is not less than 50 °C, the elastic modulus of the material of the elastic structure is 10 MPa to 80 MPa, and the material of the shell has a hot pressing adhesion to the electrode sheet of not less than 5 N / m under the conditions of 55 °C and 4 MPa. The polymer glue does not fill the ceramic particles and the diaphragm pores, can improve the rate and cycle performance of the battery, and the ceramic coating prepared from the polymer glue can fully release stress and is not easy to shed powder.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators. Specifically, it relates to a preparation method of a polymer adhesive for separator coatings, the polymer adhesive, the separator, and the battery. Background Art

[0002] Currently, the commercially used lithium-ion battery separators are mainly polyolefin-based separators with good acid and alkali resistance, high tensile strength, and pores. However, such separators are prone to shrinkage at high temperatures, which may cause the positive and negative electrodes of the battery to come into direct contact, resulting in internal short circuits and causing spontaneous combustion or explosion, posing a great safety hazard. In addition, the surface energy tension of polyolefin-based separators is low, making it difficult to be wetted by the electrolyte, which hinders the penetration of lithium ions to a certain extent, resulting in a low battery capacity and seriously affecting its performance.

[0003] It has been proposed to coat one or both sides of the separator with a ceramic heat-resistant coating. On the one hand, it can effectively reduce the thermal shrinkage of the separator and prevent fire and explosion caused by short circuits between the positive and negative electrodes at high battery temperatures. At the same time, the ceramic coating can also improve the wettability of the separator to the electrolyte. However, the coating of ceramic inorganic particles must rely on a binder to have good adhesion, and the existing binders are prone to filling the gaps between the ceramics and the pores of the separator, resulting in an increase in the internal resistance of lithium ions and affecting the rate and cycle performance of the battery. In addition, the existing ceramic coatings are difficult to release stress when the volume changes during the lithium deintercalation and intercalation processes of the battery, and the ceramic coatings are prone to powdering.

[0004] It should be noted that this part of the content of the present invention only provides the background technology related to the present invention, and does not necessarily constitute the prior art or the well-known technology. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects that the existing ceramic coatings are difficult to release stress, the ceramic coatings are prone to powdering, and the ceramic coating binders are prone to filling the gaps between the ceramics and the pores of the separator, affecting the rate and cycle performance of the battery. The present invention provides a preparation method of a polymer adhesive for separator coatings, the polymer adhesive, the separator, and the battery. This polymer adhesive does not fill the ceramic particles and the pores of the separator, can improve the rate and cycle performance of the battery, and the ceramic coating prepared from the polymer adhesive can fully release stress and is not prone to powdering.

[0006] To achieve the above object, in a first aspect, the present invention provides a polymer glue for diaphragm coating, which comprises polymer particles. The polymer particles comprise a core and a shell. The core comprises a base core and an elastic structure. The base core has pores at least on its surface. The elastic structure penetrates at least through the pores on the surface of the base core. The shell coats the surface of the core. The PDI of the polymer particles is < 1 and the D50 is 1 μm to 11 μm. The glass transition temperature of the material of the base core is not less than 50 °C. The elastic modulus of the material of the elastic structure is 10 MPa to 80 MPa. The material of the shell has a bonding force to the pole piece of not less than 5 N / m under the conditions of 55 °C and 4 MPa.

[0007] In some preferred embodiments, the base core is a porous base core, and the elastic structure penetrates through the pores inside the porous base core.

[0008] In some preferred embodiments, in the core, the volume ratio of the elastic structure to the base core is 1:2.5 to 9.

[0009] In some preferred embodiments, in the polymer particles, the volume ratio of the shell to the base core is 1:1.5 to 6.

[0010] In some preferred embodiments, the base core comprises a polymer formed by polymerizing base core monomers. The base core monomers include at least one monomer selected from acrylic monomers and vinyl monomers.

[0011] Preferably, the base core comprises polymethyl methacrylate.

[0012] In some preferred embodiments, the shell comprises a copolymer, which is formed by copolymerizing a mixed monomer comprising a first shell monomer, a second shell monomer, and a third shell monomer. The first shell monomer is selected from at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, vinyl acetate; the second shell monomer is selected from at least one of trifluoroethyl methacrylate, 2-hydroxypropyl methacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, ethylene glycol diacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, glycidyl methacrylate, N-hydroxymethyl acrylamide, N-butoxymethyl acrylamide, divinylbenzene, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane; the third shell monomer is selected from at least one of methyl methacrylate, ethyl methacrylate, methacrylic acid, acrylic acid, acrylonitrile, styrene, isobornyl methacrylate, acrylamide.

[0013] In a second aspect, the present invention provides a method for preparing the polymer glue described in the first aspect, including: preparing a spherical core precursor, the glass transition temperature of the material of the core precursor is not less than 50 °C, making pores at least on the surface of the core precursor to obtain a core, the core has pores at least on the surface, so that the elastic material penetrates at least through the pores on the surface of the core to obtain a core, the elastic modulus of the elastic material is 10 MPa to 80 MPa, coating a viscous material on the surface of the core, and formulating it into a stable emulsion to obtain the polymer glue, the viscous material is hot-pressed under the conditions of 55 °C and 4 MPa, and the adhesive force to the pole piece is not less than 5 N / m.

[0014] In some preferred embodiments, the preparation of the core includes: emulsifying and mixing evenly a mixture including the core precursor, a pore-forming agent, a water-soluble monomer, an initiator, an emulsifier, and water, reacting under stirring conditions, washing with water, and performing solid-liquid separation to obtain the core, the pore-forming agent is selected from at least one of cyclohexanol, toluene, xylene, benzene, acetone, isopropanol, ethyl acetate, and halogenated hydrocarbons, the water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, and allyl ether, the reaction temperature is 55 °C to 100 °C, the reaction time is 2 h to 10 h, and the mass ratio of the core precursor, the pore-forming agent, and the water-soluble monomer in the mixture is 1:0.01 to 0.27:0.01 to 0.45;

[0015] The preparation of the core includes: emulsifying and mixing evenly a mixture including the core, an elastic material, an emulsifier, and water to obtain the core, and the mass ratio of the elastic material and the core in the mixture is 1∶1.5 to 12.

[0016] In some preferred embodiments, the preparation of the core includes: emulsifying and mixing evenly a mixture including the core, an elastic material, an emulsifier, and water to obtain the core, and the mass ratio of the elastic material and the core in the mixture is 1∶2.5 to 9.

[0017] In some preferred embodiments, the coating of the viscous material includes: mixing evenly a mixture including the core, an initiator, and a viscous material monomer, and performing a polymerization reaction to coat the viscous material on the surface of the core, and the mass ratio of the viscous material monomer and the core is 1∶1.5 to 6.

[0018] In some preferred embodiments, the preparation of the base core precursor includes: in water, uniformly mixing a mixture including a dispersant, an emulsifier, a base core monomer, an initiator, and a crosslinking agent, and after the reaction, performing solid-liquid separation to obtain the base core precursor. The crosslinking agent is selected from at least one of acrylamide, hydroxymethyl acrylamide, bifunctional acrylate, trifunctional acrylate, and divinyl compounds. The reaction temperature is 50°C to 100°C, and the ratio of the mass of the crosslinking agent to the mass of the base core monomer in the mixture is 0.01 to 0.1.

[0019] In a third aspect, the present invention provides a battery separator. A polymer glue as described in the first aspect and / or a polymer glue prepared by the preparation method as described in the second aspect is mixed uniformly with ceramic particles to obtain a mixed membrane liquid, and the mixed membrane liquid is coated on the surface of a separator substrate to obtain the battery separator.

[0020] In a fourth aspect, the present invention provides a battery, including a positive electrode, a negative electrode, and the battery separator as described in the third aspect located between the positive electrode and the negative electrode.

[0021] The polymer glue for the separator coating of the present invention, the polymer glue includes polymer particles, the polymer particles include a core and a shell coated on the surface of the core. The core includes at least a base core with pores on the surface and at least an elastic structure penetrating through the pores on the surface of the base core. The PDI of the polymer particles < 1, the particle size is uniform and the D50 is 1 μm to 11 μm, which can avoid the polymer glue from filling the gaps such as ceramic particles and the pores of the separator, reduce the internal resistance of conductive ions, and thus improve the rate and cycle performance of the battery. The material of the shell, under the conditions of hot pressing at 55°C and 4 MPa, has an adhesive force to the electrode sheet of not less than 5 N / m, which can improve the adhesive strength of the polymer glue and promote the firm adhesion of the coating to the electrode sheet. The elastic modulus of the material of the elastic structure is 10 MPa to 80 MPa, so that when the volume changes during the process of ion de-insertion and insertion of the ceramic coating, etc., the stress can be fully released, which can ensure that the ceramic coating, etc. has a lasting adhesive strength to the electrode sheet and prevent the ceramic coating, etc. from falling off powder. The glass transition temperature of the material of the base core is not less than 50°C, providing rigidity for the polymer glue, which can ensure the structural stability of the separator, withstand a certain pressure during the battery manufacturing process without deformation, and ensure the support and isolation of the electrode sheet and the separator.

[0022] Compared with the case where the elastic structure is directly coated on the surface of the base core to form the core, in the present invention, the elastic structure penetrates through the pores on the surface of the base core, which can avoid the generation of a sliding layer between the base core material and the elastic material during hot pressing and the volume expansion and contraction and temperature cycling during the use of the battery, which may affect the battery performance. The elastic structure penetrates through the pores on the surface of the base core, forming elastic protrusions on the surface of the core, which can also lock the viscous material of the shell and avoid the generation of a sliding layer between the core and the viscous material of the shell, which may affect the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a process flow chart of the preparation method of the polymer glue of the present invention.

[0025] Figure 2 It is a schematic diagram of the product molding of the polymer glue of the present invention.

[0026] Figure 3 It is a scanning electron microscope photo of the core precursor of Example 1 of the present invention.

[0027] Figure 4 It is a scanning electron microscope photo of the porous core of Example 1 of the present invention.

[0028] Figure 5 It is a scanning electron microscope photo of the polymer particles of Example 1 of the present invention.

[0029] Figure 6 It is a scanning electron microscope photo of the film formation of the polymer glue of Example 1 of the present invention.

[0030] Figure 7 It is a particle size distribution diagram of the polymer particles of the polymer glue of Example 1 of the present invention.

[0031] Figure 8 It is a schematic diagram of the battery separator of the present invention. Detailed implementation manners

[0032] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0033] The inventors of the present application have found through research that existing ceramic coatings are difficult to release stress, the ceramic coatings are prone to powder falling, and the ceramic coating binders are prone to filling the gaps between ceramic particles and the pores of the separator, affecting the rate and cycle performance of the battery.

[0034] In this regard, in a first aspect, the present invention provides a polymer adhesive for a separator coating, which comprises polymer particles. The polymer particles comprise a core and a shell. The core comprises a base core and an elastic structure. The base core has pores at least on its surface. The elastic structure penetrates at least through the pores on the surface of the base core. The shell coats the surface of the core. The PDI of the polymer particles is < 1 and the D50 is 1 μm to 11 μm. The glass transition temperature of the material of the base core is not less than 50 °C. The elastic modulus of the material of the elastic structure is 10 MPa to 80 MPa. The material of the shell has a bonding force to the electrode sheet of not less than 5 N / m under the conditions of 55 °C and 4 MPa hot pressing.

[0035] For the polymer adhesive for a separator coating of the present invention, the polymer adhesive comprises polymer particles. The polymer particles comprise a core and a shell coated on the surface of the core. The core comprises a base core with pores at least on its surface and an elastic structure penetrating at least through the pores on the surface of the base core. In the present invention, the elastic structure penetrates through the pores on the surface of the base core. On the one hand, the elastic material is embedded in the base core material, which can avoid the generation of a sliding layer between the base core material and the elastic material. On the other hand, elastic protrusions are formed on the surface of the core, which can lock the shell material and avoid the generation of a sliding layer between the core and the shell material. The elastic structure of the present invention penetrates through the pores on the surface of the base core. During hot pressing and battery use, no sliding layer will be generated between the rigid base core, the elastic material and the shell adhesive material, and they are closely combined, which can maintain the stable performance of the battery.

[0036] For the polymer particles of the polymer adhesive of the present invention, the glass transition temperature of the material of the base core is not less than 50 °C, which provides rigidity for the polymer adhesive, can ensure the structural stability of the separator, can withstand a certain pressure without deformation during battery manufacturing, and ensure the support and isolation of the electrode sheet and the separator. The material of the shell has a bonding force to the electrode sheet of not less than 5 N / m under the conditions of 55 °C and 4 MPa hot pressing, which can improve the bonding strength of the polymer adhesive and promote the firm bonding of the coating and the electrode sheet. The elastic modulus of the material of the elastic structure is 10 MPa to 80 MPa, which improves the rebound characteristics and flexibility of the ceramic coating, etc., so that the ceramic coating, etc. can fully release stress when the volume changes during the ion de-insertion / insertion process of the battery, can ensure that the ceramic coating, etc. has a lasting bonding strength to the electrode sheet, and prevent the ceramic coating, etc. from falling powder.

[0037] The present invention is achieved through the synergistic effect among a base core with a glass transition temperature of not less than 50 °C, an elastic structure with an elastic modulus of 10 MPa to 80 MPa, and a casing material with an adhesive force to the electrode sheet of not less than 5 N / m under the conditions of hot pressing at 55 °C and 4 MPa. While ensuring that ceramic coatings and the like have a lasting bonding strength to the electrode sheet and preventing powder shedding of ceramic coatings and the like, the structural stability of the separator is guaranteed, and the support and isolation of the electrode sheet and the separator are ensured. By passing the elastic structure through the pores on the surface of the base core, the rigid base core, the elastic material, and the casing adhesive material are kept tightly bonded, the battery performance is kept stable, and the function of ensuring lasting bonding strength and guaranteeing structural stability is maximally exerted.

[0038] The PDI of the polymer particles of the polymer glue of the present invention is < 1, the particle size is uniform, and the D50 is 1 μm to 11 μm, which can avoid the polymer glue from filling the gaps between ceramic particles and the pores of the separator, reduce the internal resistance of conductive ions, and thus improve the rate and cycle performance of the battery.

[0039] If the elastic structure directly coats the surface of the base core to form an inner core in the present invention, during hot pressing and when the battery expands and contracts in volume and the temperature cycles up and down during battery use, it is easy to cause delamination between the base core, the elastic material layer, and the casing, resulting in the loss of adhesive force and affecting the stable performance of the battery. If the PDI of the polymer particles is ≥ 1 and the D50 < 1 μm in the present invention, it is easy to have the problem that the polymer glue fills the gaps between ceramic particles and the pores of the separator. If the D50 of the polymer particles > 11 μm, it is easy to have the problem that the distance between the separator and the electrode sheet is too large. When conductive ions are transported in the electrolyte, the ion conduction path becomes longer. According to the resistance law, the increase in path length leads to an increase in resistance, thereby increasing the internal resistance of the battery. The increase in battery internal resistance further causes an increase in energy loss during the charge and discharge process of the battery, reducing the charge and discharge efficiency of the battery and resulting in a reduction in the actual available capacity of the battery. If the elastic modulus of the elastic material of the elastic structure > 80 MPa, it is easy to have the problem that ceramic coatings and the like cannot fully release stress when the volume changes during the ion de-insertion process of the battery, resulting in powder shedding of ceramic coatings and the like. If the elastic modulus of the elastic material of the elastic structure < 10 MPa, it is easy to have the problem that the supporting force and binding force of the polymer glue on ceramic particles are insufficient, making it difficult to resist the stress generated by the volume change of the electrode material and unable to return to its original state after being stressed. As the charge and discharge cycle progresses, the electrode material is likely to fall off from the electrode sheet, resulting in a reduction in the active material of the electrode and a decrease in the capacity of the battery, and the charge and discharge performance deteriorates. If the adhesive force of the casing material to the electrode sheet is less than 5 N / m, it is easy to have the problem that the bonding force between the coating and the electrode sheet deteriorates and powder shedding of ceramic coatings and the like occurs.

[0040] The PDI of the polymer particles is preferably < 0.3, more preferably < 0.1, and even more preferably < 0.05. The D50 is, for example, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, and 11 μm. The elastic modulus of the material of the elastic structure is, for example, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, and 80 MPa.

[0041] In some preferred embodiments, the base core is a porous base core, and the elastic structure penetrates through the pores inside the porous base core. Under this preferred scheme, the base core is a porous base core. Since the porous structure provides additional support, it is more conducive to improving the mechanical strength and puncture resistance of the separator, avoiding physical damage to the separator during battery assembly and use. Also, because the porous structure helps to disperse heat, reducing the risk of thermal runaway, it is more conducive to improving the thermal stability of the separator and enhancing safety. Moreover, since the porous structure increases the specific surface area of the separator, it is more conducive to improving the adsorption and retention capacity of the separator for the electrolyte. Additionally, because the porous structure improves the wettability between the separator and the electrolyte, it is more conducive to the uniform distribution of the electrolyte in the battery, improving battery performance. Furthermore, since the porous structure provides more ion transport channels, it is more conducive to improving the ion conductivity of the separator, reducing the internal resistance of the battery, and improving battery performance. When the base core is a porous base core and the elastic structure penetrates through the pores inside the porous base core, it is more conducive to avoiding the generation of a sliding layer between the base core material and the elastic material during hot pressing and the volume expansion and contraction and temperature cycling during battery use, which may affect the stable performance of the battery.

[0042] In some preferred embodiments, in the inner core, the volume ratio of the elastic structure to the base core is 1:2.5 to 9. Under this preferred scheme, it is more conducive to ensuring that the rigid base core effectively supports the electrode sheet so that it does not collapse during hot pressing, ensuring the structural stability of the separator, ensuring the support and isolation of the electrode sheet and the separator, ensuring that the ceramic coating and the like fully release stress when the volume changes during the ion de-insertion and insertion process of the battery, ensuring that the ceramic coating and the like have a lasting bonding strength to the electrode sheet. At the same time, it is more conducive to effectively locking the viscous material of the outer shell through the elastic protrusions on the surface of the inner core, avoiding the generation of a sliding layer between the inner core and the viscous material of the outer shell, and maintaining the stable performance of the battery. In the inner core, the volume ratio of the elastic structure to the base core is, for example, 1:2.5, 1:4, 1:7, and 1:9.

[0043] In some preferred embodiments, in the polymer particles, the volume ratio of the outer shell to the base core is 1:1.5 to 6. Under this preferred scheme, it is more conducive to ensuring that the rigid base core effectively supports the electrode sheet so that it does not collapse during hot pressing, ensuring the structural stability of the separator, ensuring the support and isolation of the electrode sheet and the separator, and more conducive to improving the bonding strength of the polymer glue, promoting the firm bonding of the coating to the electrode sheet. In the polymer particles, the volume ratio of the outer shell to the base core is, for example, 1:1.5, 1:2, 1:3, 1:4, 1:5, and 1:6.

[0044] In some preferred embodiments, the base core comprises a polymer formed by polymerizing base core monomers, and the base core monomers include at least one monomer selected from acrylic monomers and vinyl monomers. Specifically, the acrylic monomers may include, for example, methacrylic monomers.

[0045] Preferably, the base core comprises polymethyl methacrylate (PMMA). In this preferred embodiment, PMMA does not contain a benzene structure, conforms to the environmental protection concept of battery development, and ensures a more environmentally friendly and healthy ecological environment in battery production and subsequent recycling.

[0046] In some preferred embodiments, the outer shell comprises a copolymer formed by copolymerizing a mixed monomer including a first outer shell monomer, a second outer shell monomer, and a third outer shell monomer. The first outer shell monomer is selected from at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and vinyl acetate. The second outer shell monomer is selected from at least one of trifluoroethyl methacrylate, 2-hydroxypropyl methacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, ethylene glycol diacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, glycidyl methacrylate, N-hydroxymethyl acrylamide, N-butoxymethyl acrylamide, divinylbenzene, vinyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. The third outer shell monomer is selected from at least one of methyl methacrylate, ethyl methacrylate, methacrylic acid, acrylic acid, acrylonitrile, styrene, isobornyl methacrylate, and acrylamide. In this preferred embodiment, the copolymer of the outer shell is formed by copolymerizing the above-mentioned first outer shell monomer, second outer shell monomer, and third outer shell monomer. The first outer shell monomer mainly provides viscosity, the second outer shell monomer mainly provides a cross-linked structure and functional groups, and the third outer shell monomer mainly improves the viscosity strength, which is more conducive to improving the bonding strength of the polymer glue and promoting the firm bonding of the coating to the electrode. The participation of the second outer shell monomer in copolymerization can also improve the electrolyte resistance and bonding performance of ceramic coatings, etc. Further preferably, the mass ratio of the first outer shell monomer, the second outer shell monomer, and the third outer shell monomer is 1:0.06 - 2:0.3 - 4, which is more conducive to improving the bonding strength of the polymer glue and promoting the firm bonding of the coating to the electrode.

[0047] In some preferred embodiments, the material of the elastic structure is a monofunctional acrylate oligomer.

[0048] In some preferred embodiments, the viscosity of the polymer glue is preferably 10 cps - 1000 cps, and the solid content is preferably 1 wt% - 80 wt%.

[0049] In a second aspect, the present invention provides a method for preparing the polymer glue described in the first aspect, with reference to Figure 1 , which includes: preparing a spherical core precursor, the glass transition temperature of the material of the core precursor is not less than 50 °C, creating pores at least on the surface of the core precursor to obtain a core, the core has pores at least on the surface, so that an elastic material penetrates at least through the pores on the surface of the core to obtain a core, the elastic modulus of the elastic material is 10 MPa to 80 MPa, coating a viscous material on the surface of the core, and formulating it into a stable emulsion to obtain the polymer glue, the viscous material is hot-pressed under the conditions of 55 °C and 4 MPa, and the adhesive force to the pole piece is not less than 5 N / m.

[0050] In some preferred embodiments, the preparation of the core includes: emulsifying and mixing evenly a mixture including the core precursor, a pore-forming agent, a water-soluble monomer, an initiator, an emulsifier, and water, reacting under stirring conditions, washing with water, and performing solid-liquid separation to obtain the core, the pore-forming agent is selected from at least one of cyclohexanol, toluene, xylene, benzene, acetone, isopropanol, ethyl acetate, and halogenated hydrocarbons, the water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, and allyl ether, the reaction temperature is 55 °C to 100 °C, the reaction time is 2 h to 10 h, and the mass ratio of the core precursor, the pore-forming agent, and the water-soluble monomer in the mixture is 1:0.01 to 0.27:0.01 to 0.45;

[0051] The preparation of the core includes: emulsifying and mixing evenly a mixture including the core, an elastic material, an emulsifier, and water to obtain the core, and the mass ratio of the elastic material and the core in the mixture is 1∶1.5 to 12.

[0052] Under this preferred solution, the porogen introduces the water-soluble monomer into the core precursor, and the water-soluble monomer is separated during the water washing process to obtain the core. The porogen is selected from at least one of cyclohexanol, toluene, xylene, benzene, acetone, isopropanol, ethyl acetate, and halogenated hydrocarbons. The water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, and allyl ether. The reaction temperature is 55°C to 100°C, and the reaction time is 2h to 10h. The mass ratio of the core precursor, porogen, and water-soluble monomer is 1:0.01 to 0.27:0.01 to 0.45, which is more conducive to creating pores in the core precursor to obtain a porous core. Further, during the process of emulsifying and mixing evenly the mixture including the core, elastic material, emulsifier, and water, the elastic material penetrates into the pores of the core. The mass ratio of the elastic material to the porous core is 1∶1.5 to 12, which is more conducive to the elastic material penetrating into the pores inside the porous core. The mass ratio of the elastic material to the core in the mixture is, for example, 1∶1.5, 1∶3.5, 1∶6, 1∶8, 1∶10, and 1∶12.

[0053] For the preparation of the core, the initiator is, for example, one or more of benzoyl peroxide, dilauroyl peroxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, azobisisoheptonitrile, potassium persulfate, sodium persulfate, and ammonium persulfate. The emulsifier is, for example, one or more of nonionic surfactants and anionic surfactants. Excluding the effective components other than water, the mass fraction of the core precursor is preferably 56wt% to 96.85wt%, the mass fraction of the porogen is preferably 1wt% to 15wt%, the mass fraction of the water-soluble monomer is preferably 1wt% to 25wt%, the mass fraction of the initiator is preferably 0.15wt% to 1wt%, and the mass fraction of the emulsifier is preferably 1wt% to 3wt%. For the preparation of the inner core, the emulsifier is, for example, one or more of nonionic surfactants and anionic surfactants.

[0054] In some preferred embodiments, the preparation of the inner core includes: emulsifying and mixing evenly the mixture including the core, elastic material, emulsifier, and water to obtain the inner core. The mass ratio of the elastic material to the core in the mixture is 1∶2.5 to 9. Under this preferred solution, it is more conducive to making the volume ratio of the elastic structure to the core in the inner core be 1∶2.5 to 9. The emulsifier is, for example, one or more of nonionic surfactants and anionic surfactants. The mass ratio of the elastic material to the core in the mixture is, for example, 1∶2.5, 1∶4, 1∶7, and 1∶9.

[0055] In some preferred embodiments, the preparation of the coated adhesive material comprises: emulsifying and uniformly mixing a mixture including the core, an initiator, an emulsifier, and an adhesive material monomer, and performing a polymerization reaction to coat the adhesive material on the surface of the core. The mass ratio of the adhesive material monomer to the base core is 1:1.5 to 6. Under this preferred scheme, with the mass ratio of the adhesive material monomer to the base core being 1:1.5 to 6, it is more conducive to the volume ratio of the outer shell to the base core in the polymer particles being 1:1.5 to 6. The initiator is, for example, one or more of organic peroxides, inorganic peroxides, azo compounds, or redox initiators. The reaction temperature is preferably 50°C to 120°C, and the reaction time is preferably 0.5 h to 24 h. The mass ratio of the adhesive material monomer to the base core is, for example, 1:1.5, 1:2, 1:3, 1:4, 1:5, and 1:6.

[0056] In some preferred embodiments, the preparation of the base core precursor comprises: uniformly mixing a mixture including a dispersant, an emulsifier, a base core monomer, an initiator, and a crosslinking agent in water, and performing solid-liquid separation after the reaction to obtain the base core precursor. The crosslinking agent is selected from at least one of acrylamide, hydroxymethyl acrylamide, bifunctional acrylate, trifunctional acrylate, and divinyl compounds. The reaction temperature is 50°C to 100°C, and the ratio of the mass of the crosslinking agent to the mass of the base core monomer in the mixture is 0.01 to 0.1.

[0057] Under this preferred scheme, for the preparation of the base core precursor, with the crosslinking agent selected from at least one of acrylamide, hydroxymethyl acrylamide, bifunctional acrylate, trifunctional acrylate, and divinyl compounds, the reaction temperature being 50°C to 100°C, and the ratio of the mass of the crosslinking agent to the mass of the base core monomer being 0.01 to 0.1, it is more conducive to ensuring that the base core monomer forms a uniform network structure during the polymerization process, maintaining the integrity of the spherical shape, preventing the base core precursor from cracking or deforming during the polymerization process, improving the structural stability of the base core precursor, preventing the spherical structure from collapsing during the process of creating pores in the base core precursor to prepare the base core, preventing the pore structure from collapsing or deforming during the use as a battery separator coating adhesive, ensuring the long-term stability of the pore structure, and improving the pore creation effect of preparing the base core from the base core precursor. The ratio of the mass of the crosslinking agent to the mass of the base core monomer in the mixture is, for example, 0.01, 0.03, 0.05, 0.07, 0.09, and 1.

[0058] The dispersant is selected from one or more of polyacrylic acid, carboxymethyl cellulose and its salts, polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylamide. The emulsifier is selected from one or more of polyoxyethylene ethers, copolymers of ethylene oxide and propylene oxide, polyhydric fatty acid esters, alkyl sulfates, alkyl benzene sulfonates, and quaternary ammonium salts. The core monomer is selected from one or more of acrylic acid-based, methacrylic acid-based, and vinyl-based monomers, preferably methyl methacrylate (MMA) monomer. The initiator is one or more of benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, azobisisoheptonitrile, potassium persulfate, sodium persulfate, and ammonium persulfate. The reaction time is, for example, 1 h to 12 h. Excluding the active ingredients other than water, the mass ratio of the dispersant is preferably 1 wt% to 15 wt%, the mass ratio of the emulsifier is preferably 1 wt% to 3 wt%, the mass ratio of the initiator is preferably 0.3 wt% to 1 wt%, the mass ratio of the crosslinking agent is preferably 1 wt% to 6 wt%, and the mass ratio of the core monomer is preferably 75 wt% to 96.7 wt%. When the core monomer is an acrylic acid-based monomer and a vinyl-based monomer, the polymerization reaction rate and the degree of polymerization are more easily controlled, which is more conducive to precisely controlling the process of the polymerization reaction and obtaining spherical particles with uniform particle size and regular morphology. When the core monomer is methyl methacrylate (MMA) monomer, it has more suitable reaction activity, which is more conducive to smoothly occurring free radical polymerization reaction under the action of the initiator, precisely controlling the polymerization process, and obtaining spherical particles with uniform particle size and regular morphology.

[0059] In a third aspect, the present invention provides a battery separator. Referring to Figure 8 , the polymer glue described in the first aspect and / or the polymer glue prepared by the preparation method described in the second aspect is mixed uniformly with ceramic particles to obtain a mixed membrane liquid, and the mixed membrane liquid is coated on the surface of the separator substrate to obtain the battery separator. The battery separator of the present invention has a ceramic heat-resistant coating. The polymer glue is not easy to fill the gaps between ceramic particles and the pores of the separator. The battery has high rate and cycle performance, can fully release stress when volume changes occur during the ion de-insertion / insertion process of the battery, has a lasting bonding strength to the electrode plate, and is not easy to shed powder.

[0060] In a fourth aspect, the present invention provides a battery, including a positive electrode, a negative electrode, and the battery separator described in the third aspect located between the positive electrode and the negative electrode.

[0061] The present invention will be further elaborated in detail below with specific examples.

[0062] Example 1

[0063] A preparation method of a polymer glue for a separator coating, referring to Figure 2 , the steps are as follows:

[0064] Step 1: Add 200 parts of deionized water, 6 parts of polyvinyl alcohol (dispersant), and 1 part of OP-10 (dodecylphenol polyoxyethylene ether, emulsifier) into a reaction kettle, stir evenly, then add 90 parts of methyl methacrylate (core monomer), 0.5 part of azobisisobutyronitrile (initiator), and 3 parts of 1,6-ethyleneglycol diacrylate (crosslinker, bifunctional acrylate), mix evenly, heat up to 70 °C, react for 8 h, and filter (solid-liquid separation) to obtain a core precursor. Herein, the aforesaid "parts" refer to mass. Among the effective components except deionized water, the mass ratio of the dispersant is 5.97 wt%, the mass ratio of the emulsifier is 1 wt%, the mass ratio of the core monomer is 89.6 wt%, the mass ratio of the initiator is 0.5 wt%, the mass ratio of the crosslinker is 2.99 wt%, and the ratio of the mass of the crosslinker to the mass of the core monomer is 0.033; The scanning electron microscope photograph of the core precursor is referred to Figure 3 ;

[0065] Step 2: Emulsify and mix 75 parts of the core precursor prepared in Step 1, 15 parts of cyclohexanol (pore-forming agent), 10 parts of acrylamide (water-soluble monomer), 0.15 part of ammonium persulfate (initiator), and 2 parts of polyvinylpyrrolidone (emulsifier) evenly in 200 parts of deionized water, then, under stirring conditions, heat up to 65 °C and react for 5 h, discharge the material, wash it with water, and perform solid-liquid separation to obtain a core. Herein, the aforesaid "parts" refer to mass. Among the effective components except deionized water, the mass ratio of the core precursor is 73.4 wt%, the mass ratio of the pore-forming agent is 14.68 wt%, the mass ratio of the water-soluble monomer is 9.79 wt%, the mass ratio of the initiator is 0.15 wt%, the mass ratio of the emulsifier is 1.96 wt%, and the mass ratio of the core precursor, the pore-forming agent, and the water-soluble monomer is 1:0.2:0.13. The core is a porous core; The scanning electron microscope photograph of the porous core is referred to Figure 4 ;

[0066] Step 3: Emulsify and mix 50 parts of the core prepared in Step 2, 20 parts of a monofunctional acrylate oligomer with an elastic modulus E = 40 MPa (elastic material), 0.5 part of potassium persulfate (initiator), and 2.5 parts of polyoxyethylene polyoxypropylene ether (emulsifier) evenly in 200 parts of deionized water, then heat up to 75 °C, and dropwise add a pre-emulsified emulsion mixed with 10 parts of n-butyl acrylate (first shell monomer), 4 parts of 2-hydroxyethyl methacrylate (second shell monomer), and 16 parts of methyl methacrylate (third shell monomer) into the reaction kettle, mix evenly, end the reaction after reacting for 8 h, and adjust the viscosity and solid content to form a stable emulsion, namely a polymer glue. The mass ratio of the elastic material to the core is 1∶2.5. The first shell monomer, the second shell monomer, and the third shell monomer are used as sticky material monomers, and the mass ratio of the sticky material monomers to the core is 1∶1.67.

[0067] A polymer adhesive for diaphragm coating, prepared by the aforementioned preparation method. The polymer adhesive includes polymer particles, and the polymer particles include a core and a shell coated on the surface of the core. The core includes a base core and an elastic structure. The base core is a porous base core, and the elastic structure penetrates through the pores on the surface and inside the pores of the porous base core. The material of the elastic structure is a monofunctional acrylate oligomer, and the elastic modulus of the material of the elastic structure is 40 MPa. The material of the base core is polymethyl methacrylate (PMMA), and the glass transition temperature of the material of the base core is 105 °C. The material of the shell is a copolymer of n-butyl acrylate - 2-hydroxyethyl methacrylate - methyl methacrylate. The material of the shell is hot-pressed under the conditions of 55 °C and 4 MPa, and the adhesion force to the electrode sheet is 8 N / m. The PDI of the polymer particles < 1 and the D50 is about 5 μm. For the particle size distribution diagram of the polymer particles, see Figure 7 , in the core, the volume ratio of the elastic structure to the porous base core is 1:2.5. In the polymer particles, the volume ratio of the shell to the base core is 1:1.67. For the scanning electron microscope photograph of the polymer particles, refer to Figure 5 .

[0068] Example 2

[0069] It was carried out with reference to the preparation method of Example 1. The difference is that in Step 1, the base core monomer is styrene. For the polymer adhesive for diaphragm coating with reference to Example 1, the material of the base core is polystyrene (glass transition temperature is 100 °C).

[0070] Example 3

[0071] It was carried out with reference to the preparation method of Example 1. The difference is that in Step 1, the base core monomer is an equal amount of styrene and methyl methacrylate. For the polymer adhesive for diaphragm coating with reference to Example 1, the material of the base core is a copolymer of styrene and methyl methacrylate (glass transition temperature is 102.5 °C).

[0072] Example 4

[0073] It was carried out with reference to the preparation method of Example 1. The difference is that in Step 2, the cyclohexanol porogen is replaced with a n-heptane porogen; for the polymer adhesive for diaphragm coating with reference to Example 1, the base core is a base core with pores on the surface, and the elastic structure penetrates through the pores on the surface of the base core.

[0074] Example 5

[0075] It was carried out with reference to the preparation method of Example 1. The difference is that in Step 3, the addition amount of the elastic material is 4 parts, and the mass ratio of the elastic material to the base core is 1:12.5; for the polymer adhesive for diaphragm coating with reference to Example 1, the elastic structure penetrates through the pores on the surface of the porous base core. In the core, the volume ratio of the elastic structure to the porous base core is 1:12.5.

[0076] Example 6

[0077] The preparation method of Reference Example 1 was followed, except that in Step 3, the addition amount of the elastic material was 5 parts, and the mass ratio of the elastic material to the mass of the base nucleus was 1:10; referring to the polymer glue for the diaphragm coating of Reference Example 1, in the inner core, the volume ratio of the elastic structure to the porous base nucleus was 1:10.

[0078] Comparative Example 1

[0079] The preparation method of Reference Example 1 was followed, except that Step 2 was not carried out; referring to the polymer glue for the diaphragm coating of Reference Example 1, the polymer glue included polymer particles, the polymer particles included a poly(methyl methacrylate) (PMMA) inner core, a first coating layer coated on the outside of the inner core, and a second coating layer coated on the outside of the first coating layer. The elastic modulus of the first coating layer was 40 MPa, the material of the first coating layer was a monofunctional acrylate oligomer, and the material of the second coating layer was a copolymer of n-butyl acrylate - methacrylic acid - 2-hydroxyethyl methacrylate - methyl methacrylate.

[0080] Test Example

[0081] The polymer glues of Examples 1 to 6 and Comparative Example 1 were respectively mixed evenly with ceramic particles to obtain a mixed film solution. The ceramic particles were alumina particles. The mixed film solution was coated on the surface of a PE-based diaphragm substrate (single-sided coating, coating thickness was 5 μm) to obtain a battery diaphragm. The surface of the battery diaphragm had a ceramic coating. The scanning electron micrograph of the film formation of the polymer glue of Example 1 is shown in Figure 6 . The initial bonding strength between the ceramic coating and the electrode was tested. The electrode was made of aluminum foil coated with ternary material. The test method was to thermally press the battery diaphragm and the electrode into one body for 60 s at 4 MPa and 55 °C to prepare a test plate. The free end of the electrode was folded 180° at the tensile testing machine. The free end of the electrode and the test plate were respectively clamped on the upper and lower holders, and the tensile testing machine was used to continuously peel at a certain tensile speed until the electrode and the ceramic coating were completely separated. The peeling strength test result was read as the initial bonding strength (GB / T 2790-1995). The results are shown in Table 1. The performance stability of the lithium-ion battery was tested. The battery diaphragm was assembled into a lithium-ion battery and charged and discharged 400 times, and the battery capacity retention rate was measured (GB / T 31484-2015). The results are shown in Table 1. For the lithium-ion battery, the change in the bonding strength between the ceramic coating and the electrode after 400 cycles was tested (GB / T 2790-1995). The results are shown in Table 1.

[0082] Table 1

[0083]

[0084] Comparing with the comparative example and Comparative Example 1, the elastic structure penetrates through the pores on the surface of the base core, which can improve the battery capacity retention rate and enhance the performance stability of the lithium-ion battery.

[0085] Comparing Comparative Example 1 to Example 3, the base core includes polymethyl methacrylate (PMMA), which is more conducive to improving the battery capacity retention rate and enhancing the performance stability of the lithium-ion battery. When the base core is polymethyl methacrylate (PMMA), it is further more conducive to improving the battery capacity retention rate and enhancing the performance stability of the lithium-ion battery. Comparing Comparative Example 1, Example 4 and Example 5, the base core is a porous base core, and the elastic structure penetrates through the pores inside the porous base core, which is more conducive to improving the battery capacity retention rate and enhancing the performance stability of the lithium-ion battery. Comparing Comparative Example 1 and Example 6, in the inner core, the volume ratio of the elastic structure to the base core is 1:2.5 to 9, which is more conducive to the ceramic coating having a lasting bonding strength to the electrode sheet, improving the battery capacity retention rate and enhancing the performance stability of the lithium-ion battery.

[0086] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A polymer glue for diaphragm coating, characterized in that: It comprises polymer particles, the polymer particles comprise a core and a shell, the core comprises a base core and an elastic material, the base core at least has holes on its surface, the elastic material at least penetrates through the holes on the surface of the base core, the shell is coated on the surface of the core, the PDI of the polymer particles is less than 1 and the D50 is 1 μm to 11 μm, the glass transition temperature of the material of the base core is not less than 50° C., the elastic modulus of the elastic material is 10 MPa to 80 MPa, the material of the shell is hot pressed under the conditions of 55° C. and 4 MPa, and the bonding force to the pole piece is not less than 5 N / m; The preparation of the inner core comprises: emulsifying and mixing a mixture comprising the base core, an elastic material, an emulsifier and water uniformly to obtain the inner core.

2. The polymer glue according to claim 1, characterized in that The base core includes a polymer formed by polymerizing a base core monomer, and the base core monomer includes a vinyl monomer.

3. The polymer glue according to claim 2, characterized in that The base core includes polymethyl methacrylate.

4. The polymer glue according to claim 1, characterized in that The shell comprises a copolymer, and the copolymer is formed by copolymerization of shell monomers including a first shell monomer, a second shell monomer, and a third shell monomer, wherein the first shell monomer is selected from at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and vinyl acetate, and the second shell monomer is selected from at least one of trifluoroethyl methacrylate, 2-hydroxypropyl methacrylate, 1, At least one of 6-hexanediol diacrylate, tripropylene glycol diacrylate, ethylene glycol diacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, glycidyl methacrylate, N-hydroxymethyl acrylamide, N-butoxymethyl acrylamide, divinylbenzene, vinyl trimethoxy silane, and γ-methacryloxypropyl trimethoxy silane; and the third shell monomer is selected from at least one of methyl methacrylate, ethyl methacrylate, methacrylic acid, acrylic acid, acrylonitrile, styrene, isobornyl methacrylate, and acrylamide.

5. A method for preparing the polymer glue according to any one of claims 1 to 4, characterized in that: include: A spherical base core precursor is prepared, wherein the glass transition temperature of the material of the base core precursor is not less than 50°C, holes are formed at least on the surface of the base core precursor to obtain a base core, wherein the base core has holes on at least the surface, so that an elastic material at least penetrates through the holes on the surface of the base core to obtain an inner core, wherein the elastic modulus of the elastic material is 10MPa~80MPa, and an outer shell is coated on the surface of the inner core to prepare a stable emulsion to obtain the polymer glue, wherein the material of the outer shell is hot pressed under the conditions of 55°C and 4MPa, and the bonding force to the electrode is not less than 5N / m.

6. The preparation method according to claim 5, characterized in that: The preparation of the base core comprises: emulsifying and mixing a mixture including the base core precursor, a porogen, a water-soluble monomer, an initiator, an emulsifier and water, reacting under stirring conditions, washing with water, and performing solid-liquid separation to obtain the base core, wherein the porogen is selected from at least one of cyclohexanol, toluene, xylene, benzene, acetone, isopropanol, ethyl acetate and halogenated hydrocarbons, and the water-soluble monomer is selected from at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N,N-dimethylacrylamide and propenyl ether, the reaction temperature is 55° C. to 100° C., the reaction time is 2 h to 10 h, and the mass ratio of the base core precursor, the porogen and the water-soluble monomer in the mixture is 1:0.01-0.27:0.01-0.45; The preparation of the inner core comprises: emulsifying and mixing a mixture comprising the base core, an elastic material, an emulsifier and water uniformly to obtain the inner core, wherein the mass ratio of the elastic material to the base core in the mixture is 1:1.5-12.

7. The preparation method according to claim 5, characterized in that: The preparation of the inner core comprises: emulsifying and mixing a mixture comprising the base core, an elastic material, an emulsifier and water uniformly to obtain the inner core, wherein the mass ratio of the elastic material to the base core in the mixture is 1:2.5-9.

8. The preparation method according to claim 5, characterized in that: The step of coating the shell includes: uniformly mixing a mixture including the core, an initiator, and a shell monomer, polymerizing, and coating the shell on the surface of the core, wherein the mass ratio of the shell monomer to the base core is 1:1.5-6.

9. The preparation method according to claim 5, characterized in that: The preparation of the base core precursor comprises: uniformly mixing a mixture including a dispersant, an emulsifier, a base core monomer, an initiator, and a crosslinking agent in water, and performing solid-liquid separation after the reaction to obtain the base core precursor, wherein the crosslinking agent is selected from at least one of a trifunctional acrylate and a divinyl compound, the reaction temperature is 50° C. to 100° C., and the ratio of the mass of the crosslinking agent in the mixture to the mass of the base core monomer is 0.01 to 0.

1.

10. A battery separator, characterized in that: The polymer glue described in any one of claims 1 to 4 is uniformly mixed with ceramic particles to obtain a mixed membrane liquid, and the mixed membrane liquid is applied to the surface of the diaphragm substrate to obtain the battery diaphragm.

11. A battery separator, characterized in that: The polymer glue prepared by the preparation method of the polymer glue according to any one of claims 5 to 9 is uniformly mixed with ceramic particles to obtain a mixed membrane liquid, and the mixed membrane liquid is applied to the surface of the diaphragm substrate to obtain the battery diaphragm.

12. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the battery separator according to claim 10 or 11 located between the positive electrode and the negative electrode.

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