A production method of dry-process lithium battery separator and application thereof

Abstract

The application discloses a production method of dry-process lithium battery diaphragm and application thereof, and belongs to the technical field of lithium battery diaphragm. The production method of the dry-process lithium battery diaphragm is disclosed, polybutene-1 is blended with polypropylene to improve the mechanical property and heat resistance of the diaphragm, high-frequency high-voltage corona discharge is used on the surface of the treated plastic to generate low-temperature plasma, free radical reaction is generated on the surface of the diaphragm to make the polymer crosslink, the surface becomes rough and the wettability of the diaphragm to electrolyte is increased, the surface molecules of the treated surface are oxidized and polarized, ion electric shock erodes the surface, and the surface properties are changed to improve the hydrophilic ability, thereby the liquid absorption rate of the diaphragm is improved, the affinity to organic electrolyte is strong, and the liquid affinity performance is good. The production method disclosed by the application is simple and convenient, environment-friendly, low in cost, high in added value and free of environmental pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery separator, and particularly relates to a production method of dry-process lithium battery separator and application thereof. BACKGROUND

[0002] A lithium battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte. The separator is a thin film with a microporous structure and is a key link in a lithium ion battery. It is the most technically challenging key inner component in the lithium ion battery industry chain, and its cost accounts for about 10%-20%. The separator material is not conductive, and its physical and chemical properties have a great influence on the performance of the battery. Since the electrolyte is an organic solvent system, a separator material resistant to organic solvents is needed, and a high-strength thin polyolefin porous film is generally used. The lithium battery separator is immersed in the electrolyte, and the surface has a large number of micropores that allow lithium ions to pass through. The material, number and thickness of the micropores will affect the speed of lithium ions passing through the separator, and thus affect the discharge rate, cycle life and other properties of the battery. Because the mainstream lithium battery separator on the market in the past is a dry-process separator, it accounts for about 70% of the market share. Dry-process separators are mainly used in lithium iron phosphate batteries. The current mainstream preparation method of battery separators is divided into three types: dry-process unidirectional stretching, dry-process bidirectional stretching and wet-process bidirectional stretching. The dry-process separator process is the most commonly used method in the preparation process of lithium ion battery separators, but the corresponding wet-process can better control the pore size, distribution and porosity. The dry-process bidirectional stretching process is a unique separator manufacturing process in China. This process adds nucleating agents to PP, and uses the difference in density between different phases of PP to form micropores during the stretching process. On August 23, 2019, CN201910450957.9 disclosed a high-puncture-strength dry-process separator and a preparation method thereof, which used ceramic nano-enhanced particles and plasticizers. In fact, the application effect is not good, and the ceramic particles are prone to stress concentration and breakage. Compared with wet-process separators, the dry-process unidirectional stretching preparation method has lower cost and better long-term stability. The main raw material of the dry-process stretched separator is polypropylene, which has high mechanical properties at room temperature. However, the battery separator prepared therefrom has the disadvantages of low porosity, poor solvent wettability, poor thermal stability and low electrolyte absorption rate, which hinders the further improvement of the performance of lithium batteries. The polarity of polyolefin is low, the compatibility of the lithium ion battery electrolyte and the separator interface is poor, the affinity for organic electrolyte is weak, and the liquid affinity performance is poor, which is not conducive to the rapid migration of lithium ions, and thus affects the performance of the battery. Therefore, the low liquid absorption rate of the polyolefin separator makes the electrochemical performance of the lithium ion battery poor. Therefore, there is an urgent need for a production method of dry-process lithium battery separator and application thereof to meet the existing application market and performance requirements. SUMMARY

[0003] Therefore, the application provides a production method of dry-process lithium battery separator and application thereof.

[0004] A dry method for producing lithium battery diaphragm, comprising the following steps: first, the main resin and polybutene-1 resin with a melt index of 0.6-0.65 are uniformly mixed at high speed to obtain a mixed resin; the mixed resin is put into the feeding hopper of an extruder, and the mixed resin is processed into a uniform melt, extruded and cast to obtain a cast base film, and then a retreating annealing is performed after a corona treatment to prepare an annealed base film; second, stretching: the annealed base film is subjected to a cold drawing at a temperature of 75-85 DEG C and a hot drawing ratio of 1.1-1.2; and then a hot drawing treatment is performed; the drawing temperature of the hot drawing is 135-145 DEG C, and the hot drawing ratio is 1.2-1.4; third, heat setting: the product of the hot drawing treatment is subjected to a heat setting treatment, and the lithium battery diaphragm is obtained.

[0005] Further, the setting temperature of the heat setting treatment of the third step is 125-145 DEG C, and the setting shrinkage is 12%-18%.

[0006] Further, the main resin of the first step comprises one or more of polypropylene and polyethylene.

[0007] Further, the mixed mass ratio of the main resin with a melt index of 2.0-3.0 and the polybutene-1 resin with a melt index of 0.6-0.65 in the first step is 90-95:10-15.

[0008] Further, the extrusion casting process of the first step is that the casting roller temperature is 80-100 DEG C, the die gap is 1.2-1.25 mm, the die head temperature is 235-240 DEG C, and the production line speed is 80-100 mm / min.

[0009] Further, the corona process of the first step is that the output voltage is 10-15 kV, the corona frequency is 28-35 kHz, and the corona time is 0.2-0.5 s.

[0010] Further, the annealing step of the first step is that the cast base film is annealed at a temperature of 130-155 DEG C for 70-100 min.

[0011] The present application has the following beneficial effects:

[0012] The production method of the dry-process lithium battery diaphragm disclosed by the application uses polybutene-1 and polypropylene blending to improve the mechanical property and heat resistance of the diaphragm, and uses high-frequency high-voltage corona discharge on the surface of the treated plastic to generate low-temperature plasma, so that the surface of the diaphragm generates free radical reaction to crosslink the polymer, the surface becomes rough and the wettability to electrolyte is increased, the surface molecules are oxidized and polarized, the surface is eroded by ion electric shock, and the surface properties are changed, the hydrophilic ability is improved, the liquid absorption rate of the diaphragm is improved, the affinity to organic electrolyte is strong, the liquid affinity performance is good, the production method disclosed by the application is simple and convenient, no organic solvent is used, the environment is friendly, the cost is low, the added value is high, and there is no environmental pollution. DETAILED DESCRIPTION

[0013] The application can be better understood according to the following examples, however, those skilled in the art will easily understand that the content described in the examples is only used to illustrate the application, and should not and will not limit the application described in detail in the claims. Example 1

[0014] The production method of the dry-process lithium battery diaphragm comprises the following steps: first step, the mass ratio of 190℃, 2.16kg under the melt index of 2.8g / 10min main body 802 polypropylene resin and 190℃, 2.16kg under the melt index of 0.65g / 10min HY-ED050 polybutene-1 resin is 90:10, the main body 802 polypropylene resin with a melt index of 2.8g / 10min and the HY-ED050 polybutene-1 resin with a melt index of 0.65 from Dongfanghongye are uniformly mixed at high speed to obtain mixed resin; the mixed resin is put into the feeding hopper of the extruder, the mixed resin is processed into uniform melt, extrusion casting, the extrusion casting process is that the casting roller temperature is 100℃, the die gap is 1.25mm, the casting die temperature is 240℃, and the production line speed is 100mm / min, the casting base film is obtained, then the annealing base film is prepared after corona discharge, the corona discharge process is that the output voltage of Nantong Sansheng Plastic CW-4030 corona machine is 15kV, the corona frequency is 28kHz, the corona time is 0.2s, and the annealing is carried out at 130℃ for 100min; the second step of stretching: the annealing base film is cold-drawn again, the cold-drawing temperature is 75℃, and the hot-drawing ratio is 1.1; then the hot-drawing treatment is carried out; the stretching temperature of the hot-drawing is 135℃, and the hot-drawing ratio is 1.4; the third step of heat setting: the product after the hot-drawing treatment is subjected to heat setting treatment, the setting temperature of the heat setting treatment is 145℃, and the setting shrinkage rate is 18%, and the diaphragm is obtained.

[0015] The performance of the diaphragm product: thickness 25.2 μm, puncture strength 405 gf, permeability 4.32 s / mL, porosity 40.9%, tensile strength MD 139.6 MPa, TD 24.2 MPa, elongation at break MD 32.4%, TD 128.96%, average pore size 1.0 μm, liquid absorption rate 159%. Example 2

[0016] The production method of the dry method lithium battery diaphragm comprises the following steps: first step, the mixing mass ratio of the main body FS3028 polypropylene resin with a melt index of 2.4 g / 10 min and the D600 polybutene-1 resin with a melt index of 0.6 at 190 ℃ and 2.16 kg is 95:15, the melt index of the main body FS3028 polypropylene resin with a melt index of 2.4 g / 10 min and the D600 polybutene-1 resin with a melt index of 0.6 at 190 ℃ and 2.16 kg is 2.4, the mixed resin is uniformly mixed at high speed, the mixed resin is put into the feeding hopper of the extruder, the mixed resin is processed into a uniform melt, extrusion casting is carried out, the extrusion casting process is that the casting roller temperature is 80 ℃, the die port is 1.2 mm, the casting die temperature is 235 ℃, and the production line speed is 80 mm / min, the casting base film is obtained, then the annealing base film is prepared through corona and annealing, the corona process is that the output voltage is 10 kV, the corona frequency is 35 kHz, the corona time is 0.5 s, and the annealing is carried out at 155 ℃ for 70 min; the second step of stretching: the annealing base film is cold-drawn again, the cold-drawing temperature is 85 ℃, and the hot-drawing ratio is 1.2; then the hot-drawing treatment is carried out; the stretching temperature of the hot-drawing is 145 ℃, and the hot-drawing ratio is 1.2; the third step of heat setting: the product subjected to the hot-drawing treatment is subjected to heat setting treatment, the setting temperature of the heat setting treatment is 125 ℃, and the setting shrinkage rate is 12%, and the dry method lithium battery diaphragm is obtained.

[0017] The performance of the diaphragm product: thickness 25.1 μm, puncture strength 412 gf, permeability 4.32 s / mL, porosity 40.1%, tensile strength MD 139.8 MPa, TD 24.5 MPa, elongation at break MD 31.8%, TD 131.35%, average pore size 1.0 μm, liquid absorption rate 168%.

[0018] Note: refer to GB / T 36363-2018 Polyolefin Diaphragm for Lithium Ion Battery; liquid absorption rate refers to QB / T2303.1-2008 Battery Layer Paper Part 11: Determination of Liquid Absorption Rate; puncture strength is tested according to the requirements of ASTM D4833-00e1. The needle shape is Ф=1.0 mm hemisphere, and the needle running speed is 1 mm / s.

[0019] The above merely describes the preferred embodiments of the present application, but not for limiting the protection scope of the present application. Any equivalent changes and modifications made according to the content of the present application are included in the patent scope of the present application.

Claims

1. A method for producing a dry-process lithium battery separator, characterized in that, Includes the following steps: Step 1: Polypropylene with a melt index of 2.0-3.0 and polybutene-1 resin with a melt index of 0.6-0.65 are mixed at high speed to obtain a mixed resin; the mass ratio of the main resin and the polybutene-1 resin with a melt index of 0.6-0.65 is (90-95):(10-15); the mixed resin is fed into the feed hopper of an extruder, processed into a uniform melt, extruded and cast to obtain a cast base film, and then corona-treated and annealed to prepare an annealed base film; the corona treatment in step 1 is characterized by an output voltage of 10-15kV, a corona frequency of 28-35kHz, and a corona time of [missing information]. 0.2–0.5 s; The first step of annealing involves annealing the cast base film at a temperature of 130–155°C for 70–100 min; The second step, stretching: The annealed base film is then subjected to a cold stretch at a temperature of 75–85°C, with a stretching ratio of 1.1–1.2; followed by hot stretching treatment at a temperature of 135–145°C, with a stretching ratio of 1.2–1.4; The third step, heat setting: The product of the hot stretching treatment is heat set to obtain the final product; The heat setting temperature in the third step is 125–145°C, and the heat setting shrinkage rate is 12%–18%.

2. The method for producing a dry-process lithium battery separator according to claim 1, characterized in that, The first step of the extrusion casting process has the following parameters: casting roller temperature 80~100℃, die opening 1.2~1.25mm, casting die head temperature 235~240℃, and production line speed 80~100mm / min.

3. The application of a dry-process lithium battery separator produced by the method of producing a dry-process lithium battery separator as described in any one of claims 1-2 in lithium batteries.