A battery separator, preparation method thereof and application in lithium-ion batteries

Abstract

The present invention relates to the technical field of battery separators, and discloses a battery separator, a preparation method thereof, and its application in lithium-ion batteries. The battery separator comprises a base membrane and a coating provided on at least one surface of the base membrane; the raw materials of the coating include inorganic particles and core-shell structured particles; in the core-shell structured particles, the core layer comprises a copolymer formed by emulsion polymerization of monomers a and b, and n-heptane dispersed in the copolymer; the core layer has a glass transition temperature and a shell layer viscosity flow temperature both higher than the battery hot pressing temperature, while the shell layer has a glass transition temperature lower than the battery hot pressing temperature; the monomer a is methyl methacrylate and / or acrylonitrile, and the monomer b is at least one of hydroxyethyl methacrylate, acrylamide, and hydroxypropyl acrylate. The present invention can provide the separator coating with a plurality of pore structures, thereby enabling the battery separator to have a high liquid absorption rate and ionic conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a battery separator, a preparation method thereof, and application in lithium-ion batteries. Background Art

[0002] As a key component of lithium-ion batteries, the separator prevents contact between the positive and negative electrodes and facilitates the movement of lithium ions between them, ultimately determining battery performance and safety. The diverse use cases of lithium batteries place higher demands on separators, which influence battery cycle performance, rate capability, and safety.

[0003] To improve battery separator performance, current approaches focus on applying ceramic coatings (such as alumina and boehmite) to polyolefin separators to enhance their thermal stability and puncture resistance. However, while ceramic coatings can partially compensate for the drawbacks of thinner separators, they can also significantly reduce the separator's liquid absorption and ionic conductivity, thereby impacting the battery's rate capability and cycling performance.

[0004] Patent CN119833881A discloses a battery separator, a preparation method thereof, and a secondary battery. By embedding polymethyl methacrylate sticky microspheres in the ceramic coating of the separator, and making these sticky microspheres partially protrude on the outer surface of the ceramic coating and partially completely buried in the ceramic coating, the sticky microspheres can enhance the viscosity of the separator while forming an electrolyte channel between the separator and the electrode by utilizing the protruding sticky microsphere particles, which is beneficial to electrolyte infiltration. However, this method makes it difficult to form more ion diffusion paths inside the ceramic coating, and therefore has limited effect in improving the liquid absorption rate and ionic conductivity of the separator. Summary of the Invention

[0005] To address the technical problem that existing ceramic coatings can easily reduce the liquid absorption and ionic conductivity of battery separators, the present invention provides a battery separator, a preparation method, and its use in lithium-ion batteries. This invention enables the separator coating to have a more porous structure, thereby achieving higher liquid absorption and ionic conductivity.

[0006] The specific technical solutions of the present invention are:

[0007] In a first aspect, the present invention provides a battery separator comprising a base film and a coating provided on at least one surface of the base film; the raw materials of the coating comprise inorganic particles and core-shell structured particles; in the core-shell structured particles, the core layer comprises a copolymer formed by emulsion polymerization of monomer a and monomer b and n-heptane dispersed in the copolymer, the glass transition temperature of the core layer and the viscosity flow temperature of the shell layer are both higher than the battery hot pressing temperature, and the glass transition temperature of the shell layer is lower than the battery hot pressing temperature; the monomer a is methyl methacrylate and / or acrylonitrile, and the monomer b is at least one of hydroxyethyl methacrylate, acrylamide and hydroxypropyl acrylate.

[0008] The present invention adds core-shell structured particles to the coating, and the glass transition temperature of the shell layer is lower than the battery hot pressing temperature. Therefore, during the hot pressing process when preparing the battery, the shell layer changes from a glassy state to a highly elastic state, which can play a bonding role between the inorganic particles and between the inorganic particles and the base membrane; at the same time, since the glass transition temperature of the core layer is higher than the battery hot pressing temperature, it can maintain its shape during hot pressing, giving the core-shell structured particles a certain rigidity, enabling them to maintain a spherical structure, and making the ceramic coating have more pores, thereby improving the liquid absorption rate and ionic conductivity of the battery separator.

[0009] In addition, the present invention disperses n-heptane in the core layer of the core-shell structured particles. During the hot pressing process when preparing the battery, the n-heptane can evaporate rapidly, forming pores in the core layer. At the same time, because the shell layer softens (transforms into a highly elastic state) but does not reach a viscous flow state during hot pressing, the volatilized n-heptane can form pores in the shell layer. In this way, the core-shell structured particles can have a through-hole structure connected to the outside world, which is conducive to forming more ion diffusion paths in the coating, giving the separator a higher liquid absorption rate and ionic conductivity.

[0010] On this basis, in combination with n-heptane, the present invention uses a copolymer formed by emulsion polymerization of monomer a and monomer b in the core layer. The specific combination of monomer a and monomer b can make the copolymer have a non-polar main chain and polar side chain groups. These polar side chain groups produce a certain degree of microphase repulsion with the non-polar n-heptane, which can enable the n-heptane to form a more uniform nanoscale dispersion during emulsion polymerization, and make the diffusion of n-heptane in the core layer to the surface of the core-shell structure particles more uniform during battery hot pressing. Furthermore, after the battery is hot pressed, pores with smaller pore size and higher distribution density are formed in the core-shell structure particles, which helps to improve the liquid absorption rate and ionic conductivity of the diaphragm.

[0011] Preferably, the molar ratio of monomer a to monomer b is 1:0.05-0.09.

[0012] Within a certain range, increasing the proportion of monomer a and monomer b can result in more polar side chain groups in the core layer copolymer, which is beneficial for using the polar side chain groups to produce a certain degree of microphase repulsion of n-heptane, thereby improving the membrane's liquid absorption rate and ionic conductivity. However, when the proportion of monomer b is too high, the compatibility between the copolymer and n-heptane will be poor, which will adversely affect the dispersion of n-heptane in the core layer and is not conducive to improving the membrane's liquid absorption rate and ionic conductivity. Based on this, the present invention controls the molar ratio of monomer a to monomer b to 1:0.05-0.09, which can further improve the membrane's liquid absorption rate and ionic conductivity.

[0013] Preferably, in the core-shell structured particles, the thickness of the core layer accounts for 60-90%, the glass transition temperatures of the core layer and the shell layer are 120-150°C and 40-90°C respectively, and the viscous flow temperature of the shell layer is 160-200°C.

[0014] Preferably, the particle size of the core-shell structured particles is greater than the thickness of the coating.

[0015] Through the above design, the core-shell structure particles can be protruded from the coating surface, forming better adhesion between the diaphragm and the electrode during hot pressing of the battery, while improving the electrolyte wettability. In addition, it can also alleviate the expansion of the electrode during charging and discharging, and improve the battery's cycle and safety performance.

[0016] Furthermore, the core-shell structured particles are spherical particles with a particle size of 3 to 10 μm; the single layer thickness of the coating (ie, the thickness of the coating on each surface of the base film) is 1 to 3 μm.

[0017] Preferably, in the core-shell structured particles, the shell layer is formed by polymerization of at least one monomer selected from the group consisting of methyl methacrylate, butyl acrylate, methyl butyl acrylate and acrylonitrile.

[0018] Preferably, the raw materials of the coating further include porous binder microspheres; the porous binder microspheres are a copolymer formed by 4-styrenesulfonic acid lithium salt, butadiene and styrene, and have a glass transition temperature of 30-55°C.

[0019] Lithium 4-styrenesulfonate can give the porous binder microspheres better lithium ion conductivity, thereby reducing the internal resistance of the lithium ion battery and improving the rate performance of the lithium ion battery.

[0020] By controlling the glass transition temperature of the porous binder microspheres at 30-55°C, they can maintain their spherical structure to a certain extent while playing the role of a binder, reducing the deformation and minimizing the hindrance to the embedding of lithium ions into the active material.

[0021] Furthermore, the molar ratio of the lithium 4-styrenesulfonate, butadiene and styrene is (1-2): (4-6): (2-5).

[0022] Furthermore, the porous binder microspheres have a particle size of 5 to 100 nm and a pore size of 0.5 to 1.5 nm.

[0023] Preferably, the raw materials of the coating further include a dispersant; the dispersant includes at least one of sodium lauryl sulfate, sodium oleate, and sodium polyacrylate.

[0024] Preferably, the raw materials of the coating include, by weight: 55-60 parts of inorganic particles, 25-40 parts of core-shell structure particles, 10-18 parts of porous binder microspheres, and 2-6 parts of dispersant.

[0025] Preferably, the inorganic particles are porous inorganic microspheres with a particle size of 0.9-2 μm and a pore size of 2-50 nm, and the material includes at least one of alumina, boehmite, silica and barium sulfate.

[0026] Preferably, the base film has a thickness of 5 to 35 μm.

[0027] Preferably, the base membrane is a polyolefin microporous membrane.

[0028] Furthermore, the polyolefin microporous membrane is a polyethylene single-layer microporous membrane, a polypropylene single-layer microporous membrane, a polypropylene / polyethylene / polypropylene multi-layer microporous membrane or a polypropylene multi-layer microporous membrane.

[0029] In a second aspect, the present invention provides a method for preparing the battery separator, comprising the following steps:

[0030] S1: Monomer a, monomer b and n-heptane are mixed and added dropwise to an aqueous solution of a dispersant. After emulsification, an oil-phase initiator is added to carry out a core-layer polymerization reaction. An emulsion containing a shell-layer monomer, an emulsifier and water is then added dropwise to carry out a shell-layer polymerization reaction. An aqueous-phase initiator is added to carry out a shell-layer polymerization reaction, and the product is separated to obtain core-shell structured particles.

[0031] S2: Mix coating raw materials including core-shell structure particles and inorganic particles to form a slurry, apply it to the surface of the base film, and dry it to obtain a battery separator.

[0032] Preferably, in step S1, the mass of the n-heptane is 10-25% of the total mass of monomer a and monomer b.

[0033] Preferably, in step S1, the mass of water in the dispersant aqueous solution is 3 to 5 times the total mass of monomer a and monomer b, and the concentration of the dispersant aqueous solution is 1 to 2%; the dispersant comprises at least one of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and glycerol.

[0034] Preferably, in step S1, the emulsification is carried out by stirring at a rotation speed of 1000-1600 rpm for 30-50 min.

[0035] Preferably, in step S1, the oil phase initiator includes azobisisobutyronitrile and / or benzoyl peroxide, and the amount used is 0.5-1% of the total mass of monomer a and monomer b; the temperature of the core layer polymerization reaction is 75-80°C, and the time is 2-3 hours.

[0036] Preferably, in step S1, the aqueous phase initiator includes potassium persulfate, and the amount used is 0.3-0.5% of the mass of the shell monomer; the temperature of the shell polymerization reaction is 60-70° C., and the time is 1.5-2 h.

[0037] Preferably, in step S2, the solid content of the slurry is 35-50%, and the speed of coating the slurry on the surface of the base film is 40-60 m / min.

[0038] In a third aspect, the present invention provides application of the battery separator in a lithium-ion battery.

[0039] Preferably, the preparation method of the lithium-ion battery comprises the following steps: winding or stacking the positive electrode sheet, battery separator and negative electrode sheet to form the basic structure of the battery core, placing them in a battery shell, welding the tabs, and hot pressing at 95-115°C to obtain a lithium-ion battery.

[0040] Furthermore, the hot pressing pressure is 1.5-2.5 MPa.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) In the diaphragm coating of the present invention, core-shell structured particles are used, wherein the glass transition temperature of the shell layer is lower than the hot pressing temperature of the battery and the glass transition temperature of the core layer is higher than the hot pressing temperature of the battery. This can maintain more pores in the diaphragm coating while exerting a bonding effect, thereby making the diaphragm have a higher liquid absorption rate and ionic conductivity.

[0043] (2) The present invention adds n-heptane as a porogen in the core layer of the core-shell structured particles, and adopts a copolymer formed by emulsion polymerization of monomer a and monomer b as the core layer matrix, and combines it with a shell layer whose glass transition temperature is lower than the battery hot pressing temperature and whose viscosity flow temperature is higher than the battery hot pressing temperature. After the battery is hot pressed, a large number of nano-scale through-holes can be formed in the core-shell structured particles, thereby improving the liquid absorption rate and ionic conductivity of the diaphragm. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the embodiments.

[0045] First, the present invention relates to a battery separator, comprising a base film and a coating provided on at least one surface of the base film; the raw materials of the coating include inorganic particles and core-shell structured particles; in the core-shell structured particles, the core layer includes a copolymer formed by emulsion polymerization of monomer a and monomer b and n-heptane dispersed in the copolymer, the core layer glass transition temperature and the shell layer viscosity flow temperature are both higher than the battery hot pressing temperature, and the shell layer glass transition temperature is lower than the battery hot pressing temperature; the monomer a is methyl methacrylate and / or acrylonitrile, and the monomer b is at least one of hydroxyethyl methacrylate, acrylamide and hydroxypropyl acrylate.

[0046] In some specific embodiments, the molar ratio of monomer a to monomer b is 1:0.05-0.09.

[0047] In some specific embodiments, in the core-shell structured particles, the thickness of the core layer accounts for 60-90%, the glass transition temperatures of the core layer and the shell layer are 120-150°C and 40-90°C respectively, and the viscous flow temperature of the shell layer is 160-200°C.

[0048] In some embodiments, the core-shell particles have a particle size greater than the thickness of the coating. Optionally or preferably, the core-shell particles are spherical particles with a particle size of 3 to 10 μm, and the single layer thickness of the coating (i.e., the thickness of the coating on each surface of the base film) is 1 to 3 μm.

[0049] In some specific embodiments, in the core-shell structured particles, the shell layer is formed by polymerization of at least one monomer selected from the group consisting of methyl methacrylate, butyl acrylate, methyl butyl acrylate, and acrylonitrile.

[0050] In some specific embodiments, the inorganic particles are porous inorganic microspheres with a particle size of 0.9-2 μm and a pore size of 2-50 nm, and the material includes at least one of alumina, boehmite, silica, and barium sulfate.

[0051] In some specific embodiments, the raw materials of the coating further include porous binder microspheres with a particle size of 5 to 100 nm and a pore size of 0.5 to 1.5 nm; the porous binder microspheres are a copolymer formed by 4-styrenesulfonic acid lithium salt, butadiene and styrene in a molar ratio of (1 to 2): (4 to 6): (2 to 5), and have a glass transition temperature of 30 to 55°C.

[0052] In some specific embodiments, the raw materials of the coating further include a dispersant; the dispersant includes at least one of sodium lauryl sulfate, sodium oleate, and sodium polyacrylate.

[0053] In some specific embodiments, the raw materials of the coating include, by weight: 55-60 parts of inorganic particles, 25-40 parts of core-shell structure particles, 10-18 parts of porous binder microspheres, and 2-6 parts of dispersant.

[0054] In some specific embodiments, the base film has a thickness of 5 to 35 μm.

[0055] In some specific embodiments, the base film is a polyolefin microporous film. Optionally or preferably, the polyolefin microporous film is a polyethylene single-layer microporous film, a polypropylene single-layer microporous film, a polypropylene / polyethylene / polypropylene multi-layer microporous film, or a polypropylene multi-layer microporous film.

[0056] Second, the present invention relates to a method for preparing the above-mentioned battery separator, comprising the following steps:

[0057] S1: Monomer a, monomer b and n-heptane are mixed and added dropwise to an aqueous solution of a dispersant. After emulsification, an oil-phase initiator is added to carry out a core-layer polymerization reaction. An emulsion containing a shell-layer monomer, an emulsifier and water is then added dropwise to carry out a shell-layer polymerization reaction. An aqueous-phase initiator is added to carry out a shell-layer polymerization reaction, and the product is separated to obtain core-shell structured particles.

[0058] S2: Mix coating raw materials including core-shell structure particles and inorganic particles to form a slurry, apply it to the surface of the base film, and dry it to obtain a battery separator.

[0059] In some specific embodiments, in step S1, the mass of n-heptane is 10-25% of the total mass of monomer a and monomer b.

[0060] In some specific embodiments, in step S1, the mass of water in the dispersant aqueous solution is 3 to 5 times the total mass of monomer a and monomer b, and the concentration of the dispersant aqueous solution is 1 to 2%; the dispersant includes at least one of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and glycerol.

[0061] In some specific embodiments, in step S1, the emulsification is carried out by stirring at a rotation speed of 1000-1600 rpm for 30-50 min.

[0062] In some specific embodiments, in step S1, the oil phase initiator includes azobisisobutyronitrile and / or benzoyl peroxide, and the amount used is 0.5-1% of the total mass of monomer a and monomer b; the temperature of the core layer polymerization reaction is 75-80°C, and the time is 2-3 hours.

[0063] In some specific embodiments, in step S1, the aqueous phase initiator includes potassium persulfate, and the amount used is 0.3-0.5% of the mass of the shell monomer; the temperature of the shell polymerization reaction is 60-70°C, and the time is 1.5-2 hours.

[0064] In some specific embodiments, in step S2, the solid content of the slurry is 35-50%, and the speed of coating the slurry on the surface of the base film is 40-60 m / min.

[0065] Third, the present invention relates to the application of the above battery separator in lithium-ion batteries.

[0066] In some specific embodiments, the preparation method of the lithium-ion battery includes the following steps: winding or stacking the positive electrode sheet, the battery separator and the negative electrode sheet to form the basic structure of the battery core, placing them in a battery shell, welding the tabs, and hot pressing at 95~115°C and 1.5~2.5MPa to obtain a lithium-ion battery.

[0067] The present invention is described below by way of specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, any changes and advantages that can be imagined by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0068] Example 1

[0069] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0070] S1: Preparation of core-shell structured particles

[0071] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 47:47:6 as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase. The n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0072] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0073] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0074] S2: Preparation of battery separator

[0075] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 57:25:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0076] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0077] S3: Preparation of lithium-ion batteries

[0078] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0079] Example 2

[0080] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0081] S1: Preparation of core-shell structured particles

[0082] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 47:47:6 as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase. The n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0083] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0084] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0085] S2: Preparation of battery separator

[0086] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 47:35:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0087] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0088] S3: Preparation of lithium-ion batteries

[0089] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0090] Example 3

[0091] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0092] S1: Preparation of core-shell structured particles

[0093] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 47:47:6 as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase. The n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0094] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0095] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0096] S2: Preparation of battery separator

[0097] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 42:40:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0098] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0099] S3: Preparation of lithium-ion batteries

[0100] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0101] Example 4

[0102] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0103] S1: Preparation of core-shell structured particles

[0104] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 46:46:8 as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase. The n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0105] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0106] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0107] S2: Preparation of battery separator

[0108] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 42:45:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0109] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0110] S3: Preparation of lithium-ion batteries

[0111] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0112] Example 5

[0113] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0114] S1: Preparation of core-shell structured particles

[0115] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 43:43:14 as core layer monomers. The mixture was stirred at 600 rpm for 15 minutes to form an oil phase, where the n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0116] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0117] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0118] S2: Preparation of battery separator

[0119] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water. Then, add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 42:45:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, have a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0120] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0121] S3: Preparation of lithium-ion batteries

[0122] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0123] Example 6

[0124] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0125] S1: Preparation of core-shell structured particles

[0126] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 49:49:2 as core layer monomers. The mixture was stirred at 600 rpm for 15 minutes to form an oil phase, where the n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0127] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0128] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0129] S2: Preparation of battery separator

[0130] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water. Then, add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 42:45:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, have a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0131] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0132] S3: Preparation of lithium-ion batteries

[0133] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0134] Comparative Example 1

[0135] The only difference between this comparative example and Example 1 is that no core-shell structured particles are used in the coating; the remaining steps are the same as those in Example 1. Specifically, this comparative example prepares a battery separator and manufactures a lithium-ion battery cell by the following steps:

[0136] S1: Preparation of battery separator

[0137] S1.1: First, mix the inorganic particles, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, porous binder microspheres, and dispersant is 82:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0138] S1.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0139] S2: Preparation of lithium-ion batteries

[0140] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0141] Comparative Example 2

[0142] The only difference between this comparative example and Example 1 is that no inorganic particles are used in the coating; the remaining steps are the same as those in Example 1. Specifically, this comparative example prepares a battery separator and manufactures a lithium-ion battery cell by the following steps:

[0143] S1: Preparation of core-shell structured particles

[0144] S1.1: Methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate were mixed in a molar ratio of 47:47:6 as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase. The n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0145] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0146] S1.3: Filter the core-shell structured particle dispersion and dry it at 35°C to obtain spherical core-shell structured particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscous flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0147] S2: Preparation of battery separator

[0148] S2.1: First, mix the core-shell particles, dispersant sodium lauryl sulfate, and water. Then, add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the core-shell particles, porous binder microspheres, and dispersant is 82:14:4. The porous binder microspheres are formed by copolymerizing lithium 4-styrenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5. They have a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0149] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0150] S3: Preparation of lithium-ion batteries

[0151] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0152] Comparative Example 3

[0153] The only difference between this comparative example and Example 1 is that the core-shell structure particles in the coating are replaced with acrylic acid water-soluble glue; the remaining steps are the same as Example 1. Specifically, this comparative example prepares a battery separator and manufactures a lithium-ion battery cell by the following steps:

[0154] S1: Preparation of battery separator

[0155] S1.1: First, mix the inorganic particles, acrylic water-soluble glue, dispersant sodium lauryl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, acrylic water-soluble glue, porous binder microspheres, and dispersant is 57:25:14:4; the inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm; the porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0156] S1.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0157] S2: Preparation of lithium-ion batteries

[0158] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0159] Comparative Example 4

[0160] The only difference between this comparative example and Example 1 is that n-heptane was not added to the core layer during the preparation of the core-shell structured particles; the remaining steps were the same as those in Example 1. Specifically, this comparative example prepared a battery separator and made it into a lithium-ion battery cell by the following steps:

[0161] S1: Preparation of core-shell structured particles

[0162] S1.1: Mix methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate in a molar ratio of 47:47:6 as core layer monomers. Stir at 600 rpm for 15 minutes to form an oil phase. Heat deionized water (4 times the mass of the core layer monomers) to 75°C with stirring. Add glycerol as a dispersant and dissolve thoroughly to form an aqueous phase with a 1% dispersant content. Slowly add the oil phase dropwise to the aqueous phase while stirring at 1200 rpm. Emulsify for 40 minutes to form a stable emulsion. Then, heat the mixture to 75°C and add azobisisobutyronitrile (0.7% by mass of the core layer monomers). React at 75°C for 3 hours. Then cool the mixture to 60°C and adjust the pH of the system to neutral to obtain a core layer particle dispersion.

[0163] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present in an amount of 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0164] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0165] S2: Preparation of battery separator

[0166] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium lauryl sulfate, and water. Then, add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 57:25:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, have a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0167] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0168] S3: Preparation of lithium-ion batteries

[0169] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0170] Comparative Example 5

[0171] The battery separator is prepared and made into a lithium-ion battery cell through the following steps:

[0172] S1: Preparation of core-shell structured particles

[0173] S1.1: Methyl methacrylate and acrylonitrile were mixed in a 1:1 molar ratio as core layer monomers. This mixture was mixed with n-heptane and stirred at 600 rpm for 15 minutes to form an oil phase, where the n-heptane content was 15% of the core layer monomer weight. Deionized water (4 times the weight of the core layer monomer weight) was heated to 75°C with stirring. Glycerol, a dispersant, was added and dissolved thoroughly to form an aqueous phase containing 1% dispersant. The oil phase was slowly added dropwise to the aqueous phase while stirring at 1200 rpm. After emulsification for 40 minutes to form a stable emulsion, the mixture was heated to 75°C and azobisisobutyronitrile (0.7% by weight of the core layer monomer weight) was added. The mixture was allowed to react at 75°C for 3 hours. The temperature was then lowered to 60°C and the pH of the system was adjusted to neutral to obtain a core layer particle dispersion.

[0174] S1.2: Butyl acrylate and methyl butyl acrylate were mixed in a molar ratio of 1:3 as the shell monomers. This was pre-emulsified with water and an emulsifier, sodium alkylbenzene sulfonate, to obtain a pre-emulsion. The shell monomers were present at 50% by weight of the core monomers, and the amounts of water and emulsifier were 2.5 times and 2% of the core monomers, respectively. The pre-emulsion was slowly dripped into the core particle dispersion while stirring continuously at 300 rpm. Potassium persulfate (0.4% by weight, based on the weight of the shell monomers) was then added. The mixture was reacted at 60°C for 2 h to obtain a dispersion of core-shell particles.

[0175] S1.3: Filter the core-shell structure particle dispersion and dry it at 35°C to obtain spherical core-shell structure particles with an average particle size of 5 μm, wherein the glass transition temperature of the shell layer polymer is 50°C, the viscosity flow temperature is 170°C, the glass transition temperature of the core layer polymer is 130°C, and the core-shell thickness ratio is 8:2.

[0176] S2: Preparation of battery separator

[0177] S2.1: First, mix the inorganic particles, core-shell particles, dispersant sodium dialkyl sulfate, and water, then add the porous binder microspheres and mix thoroughly to obtain a coating slurry with a solid content of 45%. The mass ratio of the inorganic particles, core-shell particles, porous binder microspheres, and dispersant is 57:25:14:4. The inorganic particles are porous alumina microspheres with an average particle size of 1 μm and an average pore size of 30 nm. The porous binder microspheres are formed by copolymerizing lithium 4-phenylenesulfonate, butadiene, and styrene in a molar ratio of 1:4:5, with a glass transition temperature of 45°C, an average particle size of 30 nm, and an average pore size of 1 nm.

[0178] S2.2: The coating slurry is applied to both sides of a polyethylene monolayer microporous membrane at a speed of 50 m / min, and dried at 80°C for 35 min to obtain a battery separator, wherein the thickness of the polyethylene monolayer microporous membrane is 12 μm, and the thickness of the coating formed on each surface thereof is 2 μm.

[0179] S3: Preparation of lithium-ion batteries

[0180] The positive electrode sheet, separator and negative electrode sheet are stacked to form the basic structure of the battery cell. The stacked battery cell is placed in the battery shell and the tabs are welded. Then, the stacked battery cell is hot pressed for 150 seconds at a temperature of 95°C and a pressure of 2MPa to shape the stacked battery cell. Then, liquid injection, sealing, formation and aging are carried out to obtain a lithium-ion battery.

[0181] Test Case

[0182] The lithium-ion batteries prepared in the examples and comparative examples were tested for the liquid absorption rate, air permeability, and ionic conductivity of the separators therein using the following method:

[0183] (1) Liquid absorption rate: The liquid absorption rate of the diaphragm is tested by weighing method;

[0184] (2) Air permeability: Use an air permeability tester to test the air permeability of the diaphragm;

[0185] (3) Ionic conductivity: An electrochemical workstation was used to measure the ionic conductivity of the diaphragm.

[0186] The test results are shown in Table 1.

[0187] Table 1 Diaphragm performance test results

[0188]

[0189] Analyzing the diaphragm performance test results in Table 1, it can be seen that:

[0190] (1) Compared with Comparative Examples 1 and 3, the membranes of Examples 1 to 6 have higher liquid absorption and ionic conductivity. This shows that compared with conventional binders (such as acrylic water-soluble glue), the use of the core-shell structured particles of the present invention as a binder in the coating can improve the liquid absorption and ionic conductivity of the battery separator. The reason for this is that: in the core-shell structured particles used in the present invention, the glass transition temperature of the shell layer is lower than the battery hot pressing temperature, so it can play the role of an adhesive after hot pressing. At the same time, since the glass transition temperature of the core layer is higher than the battery hot pressing temperature, it can maintain its shape during hot pressing, giving the core-shell structured particles a certain rigidity, enabling them to maintain a spherical structure, and making the ceramic coating have more pores, thereby improving the liquid absorption and ionic conductivity of the battery separator; in addition, the use of n-heptane in the core layer can form pores in the core-shell structured particles, further improving the liquid absorption and ionic conductivity of the separator.

[0191] (2) Compared with Comparative Example 2, the ionic conductivity of Examples 1 to 6 is higher. This indicates that in the system of the present invention, the ionic conductivity of the battery separator can be improved by adding inorganic particles to the coating.

[0192] (3) Compared with Comparative Example 4, the liquid absorption rate and ion conductivity of the separators of Examples 1 to 6 are higher. This shows that by adding n-heptane to the core layer of the core-shell structured particles, the liquid absorption rate and ion conductivity of the battery separator can be improved. The reason for this is that during the hot pressing process when preparing the battery, n-heptane can evaporate quickly, forming channels in the core layer. At the same time, since the shell layer softens (transforms into a highly elastic state) but does not reach a viscous flow state during hot pressing, the volatilized n-heptane can form channels in the shell layer. In this way, the core-shell structured particles can have a through-hole structure connected to the outside world, which is conducive to the formation of more ion diffusion paths in the coating.

[0193] (4) Compared with Comparative Example 5, the liquid absorption rate and ionic conductivity of the separators of Examples 1 to 6 are higher. This shows that when preparing core-shell structured particles, by introducing polar monomers into the core layer, the liquid absorption rate and ionic conductivity of the battery separator can be improved. The reason for this is that when a specific monomer a (methyl methacrylate and / or acrylonitrile) is used in combination with monomer b (at least one of hydroxyethyl methacrylate, acrylamide and hydroxypropyl acrylate), the core layer copolymer obtained can have a non-polar main chain and polar side chain groups. These polar side chain groups produce a certain degree of microphase repulsion with the non-polar n-heptane, which can make the n-heptane form a more uniform nano-scale dispersion during emulsion polymerization, and make the diffusion of n-heptane in the core layer to the surface of the core-shell structured particles more uniform during battery hot pressing, thereby forming pores with smaller pore size and higher distribution density in the core-shell structured particles after battery hot pressing.

[0194] (5) Compared with Example 5 and Example 6, the membrane liquid absorption rate and ion conductivity of Example 1 and Example 4 are higher. This shows that when preparing core-shell structure particles, the ratio between the two types of monomers will affect the liquid absorption rate and ion conductivity of the battery membrane. The reason for this is that within a certain range, by increasing the proportion of monomer a (methyl methacrylate and / or acrylonitrile) and monomer b (at least one of hydroxyethyl methacrylate, acrylamide and hydroxypropyl acrylate), the core layer copolymer can be provided with more polar side chain groups, which is beneficial to utilize the polar side chain groups to produce a certain degree of microphase repulsion of n-heptane, thereby improving the membrane liquid absorption rate and ion conductivity; however, when the proportion of monomer b is too high, the compatibility between the copolymer and n-heptane will be poor, which will have an adverse effect on the dispersion of n-heptane in the core layer, and is not conducive to improving the membrane liquid absorption rate and ion conductivity.

[0195] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used herein are conventional in the art and can be obtained from conventional commercial sources. The methods used herein are conventional in the art, unless otherwise specified.

[0196] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A battery separator, characterized in that: The invention comprises a base film and a coating provided on at least one surface of the base film; the raw materials of the coating include inorganic particles and core-shell structured particles; in the core-shell structured particles, the core layer includes a copolymer formed by emulsion polymerization of monomers a and b in a molar ratio of 1:0.05-0.09, and n-heptane dispersed in the copolymer; the glass transition temperature of the core layer and the viscosity flow temperature of the shell layer are both higher than the battery hot pressing temperature, and the glass transition temperature of the shell layer is lower than the battery hot pressing temperature; the monomer a is methyl methacrylate and / or acrylonitrile, and the monomer b is at least one of hydroxyethyl methacrylate, acrylamide and hydroxypropyl acrylate; the n-heptane volatilizes rapidly during the hot pressing process when preparing the battery, forming channels in the core layer and the shell layer.

2. The battery separator according to claim 1, characterized in that In the core-shell structure particles, the thickness of the core layer accounts for 60-90%, the glass transition temperatures of the core layer and the shell layer are 120-150°C and 40-90°C respectively, and the viscous flow temperature of the shell layer is 160-200°C.

3. The battery separator according to claim 1 or 2, characterized in that The particle size of the core-shell structured particles is greater than the thickness of the coating.

4. The battery separator according to claim 3, characterized in that The core-shell structure particles are spherical particles with a particle size of 3 to 10 μm; the single layer thickness of the coating is 1 to 3 μm.

5. The battery separator according to claim 1, characterized in that The raw materials of the coating also include porous binder microspheres; the porous binder microspheres are a copolymer formed by 4-styrenesulfonic acid lithium salt, butadiene and styrene, and have a glass transition temperature of 30-55°C.

6. The battery separator according to claim 1, characterized in that The inorganic particles are porous inorganic microspheres with a particle size of 0.9 to 2 μm and a pore size of 2 to 50 nm, and the material includes at least one of aluminum oxide, boehmite, silicon dioxide and barium sulfate.

7. A method for preparing a battery separator according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: Monomer a, monomer b and n-heptane are mixed and added dropwise to an aqueous solution of a dispersant. After emulsification, an oil-phase initiator is added to carry out a core-layer polymerization reaction. An emulsion containing a shell-layer monomer, an emulsifier and water is then added dropwise to carry out a shell-layer polymerization reaction. An aqueous-phase initiator is added to carry out a shell-layer polymerization reaction, and the product is separated to obtain core-shell structured particles. S2: Mix coating raw materials including core-shell structure particles and inorganic particles to form a slurry, apply it to the surface of the base film, and dry it to obtain a battery separator.

8. The preparation method according to claim 7, characterized in that In step S1, the mass of the n-heptane is 10-25% of the total mass of monomer a and monomer b.

9. Use of the battery separator according to any one of claims 1 to 6 in a lithium-ion battery.

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