Diaphragm capable of bonding pole piece at normal temperature and high pressure and preparation method thereof

Abstract

The invention provides a diaphragm capable of bonding a pole piece at normal temperature and high pressure and a preparation method thereof, the diaphragm comprises a base material and a finished product slurry, the base material is a polyolefin lithium battery diaphragm, and the finished product slurry is coated on at least one side of the polyolefin lithium battery diaphragm; the finished product slurry comprises the following components in parts by mass: 83-94 parts of PAA, 5-16 parts of PMMA and 0.1-1 part of a wetting agent. The finished slurry coated on at least one side of the polyolefin lithium battery diaphragm comprises the PAA core-shell material, the coated diaphragm has relatively small coating gram weight and thickness, pressure can be applied at a conventional temperature in a battery cell preparation process, the diaphragm and a pole piece are relatively firmly bonded and attached, a battery cell shaping effect is achieved, and the service life of the battery cell is prolonged. The energy consumption cost caused by hot pressing in the battery cell manufacturing process can be reduced, and the situation that the battery cell is fluffy and cannot enter a shell due to poor bonding caused by hot pressing can be reduced, so that the shell entering efficiency of the battery cell and the energy density of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a diaphragm capable of bonding pole pieces at room temperature and under high pressure, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are superior to other types of batteries in terms of high capacity, high cycle and cost-effectiveness. They are increasingly used in 3C, power and energy storage. Among them, the diaphragm is one of the most critical components in the structure of lithium batteries. The main function of the diaphragm is to separate the positive and negative electrodes to prevent internal short circuits in the battery and allow lithium ions to shuttle normally during normal charging and discharging to achieve charging and discharging. The performance of the diaphragm directly affects the safety performance of the battery.

[0003] The most commonly used porous polyolefin separator in lithium-ion batteries is polyethylene (PE) and polypropylene (PP). The future development direction of lithium batteries is to improve safety and energy density. The current mainstream solution is to coat the separator base film. Coating is essentially a modification method. Specific materials are coated on the polyolefin base film to meet more diversified needs, especially the dry and wet separators are becoming thinner and lighter. The melting points of polyethylene and polypropylene are about 130°C and 170°C respectively. If the temperature exceeds this, the separator will melt and cause a short circuit in the battery; while the coating material can withstand high temperatures up to 180°C, and the separator shrinkage rate is less than 5%. After adding a coating layer on the surface of the separator, it can not only improve the thermal stability of the separator, but also increase the wettability of the separator to the electrolyte, and also prevent and reduce the oxidation of the separator.

[0004] At present, the bonding of PVDF coating and pole piece requires hot pressing for 60-150s at 80-100℃ and 1-3MPa pressure to shape and harden the battery cell for easy insertion into the shell. Moreover, the hot pressing energy consumption in the battery cell preparation process is high, which increases the cost of battery cell preparation. In addition, the heat is transferred to the middle layer of the battery cell during the hot pressing process, resulting in poor hot pressing opening and a high defective rate of battery cell preparation. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the present invention provides a diaphragm capable of bonding pole pieces at room temperature and high pressure, and a preparation method thereof, thereby reducing the hot pressing energy consumption in the battery cell preparation process, which not only reduces the cost of battery cell preparation, but also prevents poor hot pressing openings caused by heat transfer to the middle layer of the battery cell during the hot pressing process of the battery cell, thereby improving the yield rate of battery cell preparation.

[0006] The technical solution provided by the present invention is: a diaphragm capable of bonding pole pieces at room temperature and high pressure, the diaphragm comprising a substrate and a finished slurry, the substrate being a polyolefin lithium battery diaphragm, the finished slurry being coated on at least one side of the polyolefin lithium battery diaphragm, the finished slurry comprising the following components in mass fractions: 83-94 parts of PAA, 5-16 parts of PMMA, and 0.1-1 part of a wetting agent.

[0007] Furthermore, the wetting agent is a polyether siloxane copolymer.

[0008] Furthermore, the coating thickness of the finished slurry is between 0.5-2um, and the coating weight is between 0.2-0.4g / m 2 between.

[0009] Furthermore, the PAA material is a polyacrylate dual-core structure, with a Tg temperature of <40° C. and a particle size D50 of 0.5-7 um; and the porosity of the substrate is 30-70%.

[0010] Another technical solution provided by the present invention is a method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure, comprising the following steps:

[0011] S1: using polyolefin lithium battery separator as substrate;

[0012] S2: Evenly stir PAA, PMMA, wetting agent and water to prepare a finished slurry;

[0013] S3: coating the finished slurry on at least one side of the polyolefin lithium battery separator by micro-gravure roller transfer coating technology to obtain a semi-finished film;

[0014] S4: Drying the semi-finished film to obtain a finished film.

[0015] Furthermore, before step S1, the surface of the substrate is treated to remove surface impurities and then dried.

[0016] Furthermore, in step S2, the solid content of the finished slurry is controlled to be 3-15%.

[0017] Furthermore, in step S3, a micro-gravure roller or wire rod is used for transfer, the temperature of the slurry on the machine is controlled to be 20-40°C, the coating speed ratio is controlled to be 0.85-1.5, the coating speed is ≥15m / min, and the finished slurry is coated on at least one side of the polyolefin lithium battery separator to obtain a semi-finished film.

[0018] Furthermore, in step S3, the thickness of the finished slurry coating on one side is controlled to be 0.3-2 um.

[0019] Furthermore, in step S4, the semi-finished film is fed into the oven step by step, and the drying temperature is controlled to be less than 70° C., and the drying time is controlled to be ≥ 2 min.

[0020] The beneficial effects of the present invention are:

[0021] 1. The finished product coated on at least one side of the polyolefin lithium battery separator of the present invention includes PAA, which reduces the thickness and gram weight and provides better bonding strength, so that more separators are used per unit volume of the battery, thereby improving the energy density of the battery.

[0022] 2. The finished product coated on at least one side of the polyolefin lithium battery separator of the present invention includes PAA. When manufacturing the battery cell, under a pressure of 1-3 MPa, the typical shaping and hardening effect can be achieved by applying pressure at room temperature for 60-150 seconds, thereby reducing the hot pressing energy consumption in the battery cell preparation process and reducing the cost of battery cell preparation.

[0023] 3. The finished product coated on at least one side of the polyolefin lithium battery separator of the present invention includes PAA, which not only reduces the energy consumption of the battery cell and plays a role in bonding the separator and the electrode, but also reduces the material cost of the battery separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0025] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0026] Embodiment 1

[0027] according to Figure 1 As shown, this embodiment provides a method for preparing a diaphragm capable of bonding a pole piece at room temperature and high pressure, comprising the following steps:

[0028] A polyolefin lithium battery separator is used as a substrate; specifically: a polyolefin lithium battery separator with a porosity of 30% is selected as the substrate; the surface of the substrate is treated to remove surface impurities, and then dried;

[0029] Prepare the liquefied treatment material of PAA, PMMA and wetting agent finished products; add 88 parts of PAA, 11.5 parts of PMMA and 0.5 parts of wetting agent into water for stirring, the wetting agent is polyether siloxane copolymer, mix to obtain the finished slurry, and control the solid content of the finished slurry to be 5%; in the process of shaping the battery cell, the PAA material with core-shell structure, the polyacrylate of the outer core is well bonded to the pole piece under a certain pressure at room temperature, and the battery cell is shaped without the need for a hot press plate, which facilitates the battery cell to enter the shell and improves the energy density of the battery cell;

[0030] The finished slurry is coated on both sides of the polyolefin lithium battery separator by micro-gravure roller transfer coating technology to obtain a semi-finished film; specifically: a Φ100mm micro-gravure roller is used, the slurry temperature is controlled to 30°C; the coating speed ratio is controlled to 0.9, the coating speed is 80m / min, and the finished slurry is coated on at least one side of the polyolefin lithium battery separator; a semi-finished film is obtained; the thickness of the finished slurry coating on one side is controlled to be 1.0um;

[0031] The semi-finished film was dried at an oven drying temperature of 50°C and a drying time of 3 min to obtain a finished film.

[0032] Embodiment 2

[0033] according to Figure 1 As shown, this embodiment provides a method for preparing a diaphragm capable of bonding a pole piece at room temperature and high pressure, comprising the following steps:

[0034] A polyolefin lithium battery separator is used as a substrate; specifically: a polyolefin lithium battery separator with a porosity of 70% is selected as the substrate; the surface of the substrate is treated to remove surface impurities, and then dried;

[0035] Prepare the liquefied treatment material of PAA, PMMA and wetting agent finished products; add 91.2 parts of PAA, 8.6 parts of PMMA and 0.2 parts of wetting agent into water and stir to obtain the finished slurry, and control the solid content of the finished slurry to be 11%; in the process of shaping the battery cell, the PAA material with core-shell structure, the polyacrylate of the outer core is well bonded to the pole piece under a certain pressure at room temperature, and the battery cell is shaped without the need for a hot press plate, so that the battery cell is convenient to be put into the shell and the energy density of the battery cell is improved;

[0036] The finished slurry is coated on at least one side of the polyolefin lithium battery separator by micro-gravure roller transfer coating technology to obtain a semi-finished film; specifically: using a Φ120mm micro-gravure roller, the slurry temperature is controlled to 25°C; controlling the coating speed ratio to 1.2 and the coating speed to 60m / min, the finished slurry is coated on both sides of the polyolefin lithium battery separator; obtaining a semi-finished film; the thickness of the finished slurry coating on one side is controlled to be 2um;

[0037] The semi-finished film is dried to obtain a finished film; specifically, the semi-finished film is fed into an oven step by step; the drying temperature is 40° C., and the drying time is controlled to be 5 minutes.

[0038] Embodiment 3

[0039] according to Figure 1 As shown, this embodiment provides a method for preparing a diaphragm capable of bonding a pole piece at room temperature and high pressure, comprising the following steps:

[0040] A polyolefin lithium battery separator is used as a substrate; specifically: a polyolefin lithium battery separator with a porosity of 50% is selected as the substrate; the surface of the substrate is treated to remove surface impurities, and then dried;

[0041] Prepare the liquefied treatment material of PAA, PMMA and wetting agent finished products; add 93 parts of PAA, 6.2 parts of PMMA and 0.8 parts of wetting agent into water and stir to obtain the finished slurry, and control the solid content of the finished slurry to be 15%; in the process of shaping the battery cell, the PAA material with core-shell structure, the polyacrylate of the outer core is well bonded to the pole piece under a certain pressure at room temperature, and the battery cell is shaped without the need for a hot press plate, so that the battery cell is convenient to be put into the shell and the energy density of the battery cell is improved;

[0042] The finished slurry is coated on at least one side of the polyolefin lithium battery separator by micro-gravure roller transfer coating technology to obtain a semi-finished film; specifically: using a Φ150mm micro-gravure roller, the slurry temperature is controlled to 35°C; controlling the coating speed ratio to 1.3 and the coating speed to 50m / min, the finished slurry is coated on both sides of the polyolefin lithium battery separator; obtaining a semi-finished film; the thickness of the finished slurry coating on one side is controlled to be 0.8um;

[0043] The semi-finished film is dried to obtain a finished film; specifically, the semi-finished film is fed into an oven step by step; the drying temperature is 45° C., and the drying time is controlled to be 4 minutes.

[0044] The experimental results of the bonding strength of the diaphragm prepared by the present invention are as follows:

[0045] project Bonding strength N / m Embodiment 1 13 Embodiment 2 18 Embodiment 3 24

[0046] The micron-scale core-shell material prepared by the present invention through a special formula and process design has an "egg-shaped" latex particle structure. The shell layer is as hard and thin as an eggshell, which can effectively shield the bonding effect of the core layer and prevent the diaphragm from becoming sticky after coating. At the same time, it is easier to break after pressure is applied, and can adapt to a wide range of temperature and pressure conditions; a thicker core layer means more adhesive substances, and thus has a higher bonding force. The thickness of the coating can be controlled between 0.5-2um, which can be thinner than the coating thickness of PVDF, and the coating weight can be controlled between 0.2-0.4g / m 2 , 0.4-0.8g / m heavier than conventional PVDF coating 2Lower, by reducing the thickness and gram weight, better bonding strength, more battery internal diaphragm is used per unit volume, and the energy density of the battery is improved; the bonding of PVDF coating and pole piece requires 80-100℃, 1-3mpa pressure, and hot pressing for 60-150s, so that the battery cell can be shaped and hardened for easy shell insertion. The PAA material used in the present invention does not require high temperature. It only needs to be pressed at room temperature for 60-150s under a pressure of 1-3mpa, to achieve the typical shaping and hardening effect, reduce the hot pressing energy consumption in the battery cell preparation process, not only reduce the cost of battery cell preparation, but also prevent the hot pressing opening caused by the loss of heat transferred to the middle layer of the battery cell during the hot pressing process of the battery cell, and improve the yield rate of battery cell preparation.

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A diaphragm capable of bonding pole pieces at room temperature and high pressure, characterized in that: The diaphragm includes a substrate and a finished slurry, wherein the substrate is a polyolefin lithium battery diaphragm, the finished slurry is coated on at least one side of the polyolefin lithium battery diaphragm, and the finished slurry includes the following components in parts by weight: 83-94 parts of PAA, 5-16 parts of PMMA, and 0.1-1 part of a wetting agent.

2. A diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 1, characterized in that: The wetting agent is a polyether siloxane copolymer.

3. The diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 1, characterized in that: The coating thickness of the finished slurry is between 0.5-2um, and the coating weight is between 0.2-0.4g / m 2 between.

4. The diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 1, characterized in that: The PAA material is a polyacrylate dual-core structure, with a Tg temperature of less than 40° C. and a particle size D50 of 0.5-7 μm; and the porosity of the substrate is 30-70%.

5. A method for preparing a diaphragm capable of bonding pole pieces at room temperature and under high pressure according to any one of claims 1 to 4, characterized in that: The steps include: S1: using polyolefin lithium battery separator as substrate; S2: Evenly stir PAA, PMMA, wetting agent and water to prepare a finished slurry; S3: coating the finished slurry on at least one side of the polyolefin lithium battery separator by micro-gravure roller transfer coating technology to obtain a semi-finished film; S4: Drying the semi-finished film to obtain a finished film.

6. The method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 5, characterized in that: Before step S1, the surface of the substrate is treated to remove surface impurities and then dried.

7. The method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 5, characterized in that: In step S2, the solid content of the finished slurry is controlled to be 3-15%.

8. The method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 5, characterized in that: In step S3, a micro-gravure roller or wire rod is used for transfer, the temperature of the slurry on the machine is controlled to be 20-40° C., the coating speed ratio is controlled to be 0.85-1.5, the coating speed is ≥15 m / min, and the finished slurry is coated on at least one side of the polyolefin lithium battery separator to obtain a semi-finished film.

9. The method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 5, characterized in that: The thickness of the finished slurry coating on one side in step S3 is controlled to be 0.3-2 um.

10. The method for preparing a diaphragm capable of bonding pole pieces at room temperature and high pressure according to claim 5, characterized in that: In step S4, the semi-finished film is fed into the oven step by step, and the drying temperature is controlled to be less than 70° C. and the drying time is controlled to be ≥ 2 min.

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