CN103700800B - A kind of lithium ion battery separator manufacture method - Google Patents

Abstract

The invention relates to a lithium ion battery diaphragm and a preparation method thereof. The lithium ion battery diaphragm provided by the invention is divided into three layers, wherein the core layer is a cotton fiber film layer, and the upper and lower surface layers are polypropylene fiber film layers. Among them, the core layer of the diaphragm is made of cotton fiber after beating, and then mixed with antioxidants, flame retardants, etc., to form a film by wet papermaking process; the surface layer is made of polypropylene fiber after hydrophilic modification and then mixed with adhesive. The film is formed by the French paper-making process; then the lithium-ion battery separator is formed by heat-pressing with double hot-pressing rollers at 110°C to 150°C with cotton fiber film as the core layer and polypropylene fiber film as the upper and lower surface layers. The porosity of the lithium-ion battery separator is 40% to 80%, and the pore diameter is 0.01 micron to 0.2 micron; the longitudinal and transverse tensile strengths are basically the same, 120 to 300Mpa; the puncture strength is >20kg·mm ^-1 ; 1%; the thickness is 20 microns to 60 microns. The diaphragm has uniform pore distribution, high mechanical strength, low shrinkage rate, high thermal stability, good affinity/retaining performance, simple preparation, no pollution, and is suitable for industrial production.

Description

A kind of manufacturing method of lithium-ion battery diaphragm

technical field

The invention relates to the field of lithium-ion battery materials, in particular to a lithium-ion battery separator and a preparation method thereof.

Background technique

Separator is one of the key materials of lithium-ion batteries. It is used to block the positive and negative electrodes, prevent short circuit in the battery, and allow ions to pass through, so as to complete the transmission of lithium ions between the positive and negative electrodes during electrochemical charging and discharging. The performance of the separator determines the internal resistance of the battery, which directly affects the capacity, charge and discharge characteristics of the battery. As a lithium-ion battery separator, it must have good mechanical strength, especially puncture resistance, corrosion resistance of electrolyte, suitable porosity, high lyophilicity and liquid retention performance. Separators with excellent performance play an important role in improving the overall performance of lithium-ion batteries. Existing lithium quaternary ion battery separators mainly use polyethylene and polypropylene as raw materials, and the methods for preparing polyethylene films and polypropylene films mainly use dry and wet stretching processes. At present, dry methods are mainly used to produce separators. Polyolefin is melted, extruded, and blown into a crystalline polymer film, and then undergoes crystallization heat treatment and annealing to obtain a highly oriented multilayer structure, which is further stretched at high temperature to peel off the crystal interface to form a porous film. The dry method has a simple process, so the porosity and pore size cannot be well controlled. The current polyolefin separator produced by dry method has the disadvantages of uneven pore size distribution, low mechanical strength, poor thermal stability and poor affinity/retention of liquid.

Contents of the invention

The purpose of the present invention is to provide a lithium-ion battery separator with uniform pore size distribution, high mechanical strength and thermal stability, and good affinity/retention performance.

Simultaneously, the object of the present invention is also to provide a preparation method of a lithium-ion battery diaphragm.

In order to achieve the above object, the technical solution adopted in the present invention is: a lithium-ion battery separator, which is composed of a core layer made of cotton fibers and a total of three layers of upper and lower surface layers made of polypropylene fibers.

The lithium-ion battery separator has a porosity of 40% to 80%, a pore diameter of 0.01 micron to 0.2 micron; longitudinal and transverse tensile strengths of 120 to 300Mpa; puncture strength >20kg·mm ^-1 ; shrinkage at 90°C Rate <2%; thickness is 20 microns to 60 microns.

In the lithium-ion battery separator, the mass percentage of the antioxidant in the core layer is 0.01-1%, the mass percentage of the flame retardant is 0.01-1%, and the rest is cotton fiber with a beating degree of 50-75° .

In the lithium-ion battery separator, the mass percentage of the binder in the surface layer is 0.1-10%, and the rest is modified polypropylene fiber.

In the lithium-ion battery diaphragm, the percentage content of the modifier in the modified polypropylene fiber is 0.1-10%, and the percentage content of the additive is 0.01-1%.

The density of the modified polypropylene fiber of the lithium-ion battery diaphragm is 0.95-1.05 g·cm ^-3 .

The antioxidant is at least one of dibutyl hydroxytoluene, dibutyl hydroxyanisole, dibutyl phthalate and dioctyl phthalate.

The flame retardant is at least one of chloroethyl phosphate polymer, ammonium polyphosphate, aluminum hydroxide and magnesium hydroxide.

The adhesive is at least one of PVA and PVDF.

The modifier is fresh light calcium carbonate, and the additive is sodium acrylate.

A preparation method of a lithium-ion battery diaphragm, comprising the following steps:

(1) Put the cotton fiber in water, make a mixture with a pulp concentration of 2% to 5%, and beat it in the beater until the beating degree (or knocking degree) is 50-75°;

(2) Put the 50-75° cotton fiber slurry in water, make a suspension with a slurry concentration of 0.5%-2%, add antioxidants and flame retardants, stir evenly, dehydrate it on a copper grid, and squeeze it. Dried into a film, ready to use;

(3) Degrease and swell polypropylene fibers in boiling water, add modified light calcium carbonate and additive sodium acrylate, and stir to obtain hydrophilic modified polypropylene fibers;

(4) Put the modified polypropylene fiber in the water with a concentration of 1% to 3%, add the adhesive, mix it evenly, dehydrate it on the copper grid, and dry it to form a film;

(5) Put two polypropylene films between one cotton fiber film and introduce it into double hot pressing rollers, and heat press it into a three-layer structure at a temperature of 110°C-150°C and a pressure of 100-200kgf·cm ^-2 Lithium-ion battery separator.

The lithium ion battery diaphragm provided by the invention is divided into three layers, wherein the core layer is a cotton fiber film layer, and the upper and lower surface layers are polypropylene fiber film layers. Each layer of film directly uses fiber as raw material, and is formed into a film through a wet papermaking process. The preparation method provided by the invention can make the arrangement of fiber chains in the film layer more regular, and the mechanical strength in the longitudinal and transverse directions is more uniform, and has higher durability. Piercing, tension resistance and other properties, more importantly, the high-temperature shrinkage of the prepared lithium-ion battery separator is significantly reduced (shrinkage at 900C < 1%), which makes the thermal stability of the separator better, thus greatly improving The safety performance of the lithium-ion battery using the separator is guaranteed.

The core layer of the lithium-ion battery diaphragm provided by the present invention is directly made of cotton fiber to form a film. Due to the excellent affinity/liquid retention performance of the cotton fiber to the electrolyte, lithium ions can quickly pass through the diaphragm, ensuring the electrolyte/diaphragm system High conductivity effectively improves the capacity and charge-discharge performance of lithium-ion batteries.

The lithium-ion battery diaphragm prepared by the present invention has a porosity of 40% to 80%, a pore diameter of 0.01 micron to 0.2 micron; longitudinal and transverse tensile strengths of 120 to 300Mpa; puncture strength > 20kg·mm ^-1 ; 90 Shrinkage rate <1% at ℃; thickness is 20 microns to 60 microns. The diaphragm has uniform pore distribution, high mechanical strength, low shrinkage rate, high thermal stability, good affinity/retaining performance, simple preparation, no pollution, and is suitable for industrial production.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Among them: 1—the cotton fiber core layer of the diaphragm, 2—the polypropylene surface layer of the diaphragm

detailed description

Example 1

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 60°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of the cotton pulp obtained in step (1) and water at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 90°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 110°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 110°C and a pressure of 100kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 2

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 60°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into the double hot pressing roller at a temperature of 130°C and a pressure of 160kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 3

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 60°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into the double hot pressing roller at a temperature of 150°C and a pressure of 200kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 4

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain a cotton pulp with a beating degree of 65°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 110°C and a pressure of 130kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 5

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain a cotton pulp with a beating degree of 65°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 130°C and a pressure of 200kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 6

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 70°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 110°C and a pressure of 160kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 7

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 70°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 130°C and a pressure of 110kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 8

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 70°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into the double hot pressing roller at a temperature of 120°C and a pressure of 160kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 9

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 75°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3)

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into the double hot pressing roller at a temperature of 130°C and a pressure of 130kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

Example 10

The original formula of the Li-ion battery diaphragm of this embodiment is shown in Table 1.

The preparation method of the lithium-ion battery separator of the present embodiment comprises the following steps:

(1) Weigh each raw material according to the ratio of raw materials shown in Table 1, make a mixture of cotton fiber and water at a ratio of 4:100, put it in a beater, and obtain cotton pulp with a beating degree of 75°, and dehydrate it. , measure its moisture content;

(2) Make a mixture of cotton pulp and water obtained in step (1) at a ratio of 1:100, add antioxidants and flame retardants, stir and disperse, dehydrate and form on a copper grid, and then press and dry at 110°C to form a film ,stand-by;

(3) Make a suspension of modified polypropylene fiber and water at a ratio of 1:100, add an adhesive, stir, and evenly disperse it on a copper grid for dehydration to form, and dry at 90°C to form a film;

(4) Repeat step (3);

(5) The polypropylene film obtained in step (3) and step (4) is used as the upper and lower surface layers, and the cotton fiber film obtained in step (2) is used as the core layer to be combined and introduced into double hot pressing rollers at a temperature of 130°C and a pressure of 200kgf· cm ^-2 under the condition of hot pressing to obtain a lithium-ion battery separator with a three-layer structure.

The ratio of raw materials of each embodiment of table 1 ion battery separator

The detection data of the Li-ion battery diaphragm that each embodiment of table 2 makes

Claims (9)

1. A lithium-ion battery diaphragm, characterized in that: the diaphragm is made up of a core layer made of cotton fibers and a total of three layers of upper and lower surface layers prepared by polypropylene fibers; the porosity of the lithium-ion battery diaphragm is 40% to 80%. %, the pore size is 0.01 micron to 0.2 micron; the longitudinal and transverse tensile strength is consistent, 120 to 300 Mpa; the puncture strength is >20kg·mm ^-1 ; the shrinkage rate at 90°C is <1%; the thickness is 20 micron to 60 micron. 2. Lithium-ion battery diaphragm as claimed in claim 1, is characterized in that: the mass percentage of antioxidant in the core layer is 0.01～1%, the mass percentage of flame retardant is 0.01～1%, and the rest is Cotton fibers with a beating degree of 50-75°. 3. Lithium-ion battery diaphragm as claimed in claim 1, is characterized in that: the mass percentage of adhesive in the surface layer is 0.1～10%, and the rest is modified polypropylene fiber, and described modified polypropylene fiber is Degreasing and swelling polypropylene fibers in boiling water, adding modified light calcium carbonate and additive sodium acrylate, and stirring to obtain hydrophilic modified polypropylene fibers. 4 . The lithium-ion battery separator according to claim 3 , wherein the percentage content of the modifier in the modified polypropylene fiber is 0.1-10%, and the percentage content of the additive is 0.01-1%. 5. Lithium-ion battery diaphragm as claimed in claim 2, is characterized in that: antioxidant is dibutyl hydroxytoluene, dibutyl hydroxyanisole, dibutyl phthalate and dioctyl phthalate at least one. 6. The lithium-ion battery separator according to claim 2, wherein the flame retardant is at least one of chloroethyl phosphate polymer, ammonium polyphosphate, aluminum hydroxide, and magnesium hydroxide. 7. The lithium-ion battery separator according to claim 3, wherein the adhesive is at least one of PVA and PVDF. 8. The lithium-ion battery diaphragm as claimed in claim 4, characterized in that: the modifying agent is newly modified light calcium carbonate. 9. The preparation method of lithium-ion battery diaphragm as claimed in claim 1, is characterized in that: comprises the following steps: (1) Put the cotton fiber in water, make a mixture with a pulp concentration of 2% to 5%, and put it in a beater to beat until the beating degree (or knocking degree) is 50-75°; (2) Put cotton fiber pulp at 50-75° in water to prepare a suspension with a slurry concentration of 0.5%-2%, add antioxidants and flame retardants, stir evenly, dehydrate and form on a copper grid, press, Dried into a film, ready to use; (3) Degreasing and swelling polypropylene fibers in boiling water, adding modified light calcium carbonate and additive sodium acrylate, and stirring to obtain hydrophilic modified polypropylene fibers; (4) Put the modified polypropylene fiber in water at a concentration of 1% to 3%, add an adhesive, mix evenly, dehydrate and form on a copper grid, and dry to form a film; (5) Put two polypropylene films sandwiched by a cotton fiber film into double heat press rollers, and heat press it into a three-layer structure at a temperature of 110°C to 150°C and a pressure of 100-200kgf·cm-2 Lithium-ion battery separator.