PBO coated diaphragm for lithium ion battery and preparation method of PBO coated diaphragm

Abstract

The invention provides a PBO (poly (p-phenylene benzobisoxazole)) coated diaphragm for a lithium ion battery and a preparation method of the PBO coated diaphragm. The PBO coated diaphragm comprises a lithium ion battery diaphragm substrate and a PBO (poly (p-phenylene benzobisoxazole)) pulp layer coated on the substrate. According to the coating layer, the thermal stability, the mechanical strength and the chemical stability of the lithium ion battery diaphragm can be remarkably improved, so that the comprehensive performance and the safety of a lithium ion battery are improved, and the coating method is simple, easy to implement, low in cost and suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, in particular to a PBO coated diaphragm for lithium ion batteries and a preparation method thereof. Background Art

[0002] With the widespread application of lithium-ion batteries in electric vehicles, energy storage and other fields, the requirements for their safety and performance are getting higher and higher. As a key component of lithium-ion batteries, the diaphragm plays the role of isolating the positive and negative electrodes, preventing short circuits and allowing lithium ions to pass through. Currently, the commonly used lithium-ion battery diaphragms are mainly polyolefin materials, but they have certain deficiencies in heat resistance, mechanical strength and chemical stability. They are prone to shrinkage and rupture under high temperature and external force, affecting the safety and performance of the battery. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a PBO coated diaphragm for a lithium ion battery and a preparation method thereof. By coating a PBO coating layer on a lithium ion battery diaphragm substrate, the composite diaphragm is endowed with excellent heat resistance, outstanding mechanical strength and good chemical stability.

[0004] The technical solution provided by the present invention is a PBO coated diaphragm for lithium ion batteries, characterized in that it comprises a lithium ion battery diaphragm substrate and a PBO (poly(p-phenylene benzobisoxazole)) pulp layer coated on the substrate.

[0005] Furthermore, the thickness of the PBO coating layer is 0.5-5 μm.

[0006] Furthermore, the PBO coating layer is a coating liquid, and the PBO coating liquid contains the following components by mass fraction: 10%-20% PBO pulp, 1%-5% dispersant, 1.5%-5% binder, 0.5%-1.5% wetting agent, and 0.5%-2% surfactant.

[0007] Furthermore, the dispersant is at least one of polyvinyl pyrrolidone and polyethylene glycol.

[0008] Furthermore, the binder is at least one of polyacrylic acid and polyurethane.

[0009] Furthermore, the wetting agent is at least one of sodium lauryl sulfate and polyethylene glycol.

[0010] Furthermore, the surfactant is sodium dodecyl sulfate.

[0011] Another technical solution provided by the present invention is a method for preparing a PBO-coated diaphragm for a lithium-ion battery, comprising the following steps:

[0012] (1) Preparing a PBO coating liquid: dispersing PBO pulp in a solvent, wherein the mass fraction of PBO pulp in the solvent is 10%-20%, adding a dispersant, a binder, a wetting agent and a surfactant, wherein the mass fraction of the dispersant in the coating liquid is 1%-5%, the mass fraction of the binder in the coating liquid is 1.5%-5%, the mass fraction of the wetting agent in the coating liquid is 0.5%-1.5%, and the mass fraction of the surfactant in the coating liquid is 0.5%-2%, and stirring to obtain a stable coating liquid;

[0013] (2) using a roller coating device to apply the coating liquid to the substrate: adjusting the equipment parameters so that the coating liquid is evenly coated on the surface of the lithium-ion battery separator substrate to avoid uneven thickness and missing coating;

[0014] (3) Drying the coated diaphragm: Drying at 100-120° C. for 1-5 min to form a stable composite diaphragm.

[0015] Furthermore, before step (1), the PBO pulp is pretreated and ground in a ball mill at a speed of 100-500 rpm for 1-2 hours to obtain PBO granular pulp with a particle size of 0.1-3 μm.

[0016] Furthermore, the solvent in step (1) is deionized water, the stirring speed is 600-800 rpm, the stirring time is 2-3 hours, and the line speed of the roller coating equipment in step (2) is 40-50 m / min.

[0017] Beneficial effects of the present invention:

[0018] 1. Excellent heat resistance: The PBO coating has high heat resistance, which can effectively prevent the diaphragm from shrinking and deforming at high temperatures, thereby improving the safety of the battery.

[0019] 2. Excellent mechanical strength: The PBO coating layer enhances the diaphragm’s ability to resist stretching and puncture, thus extending the battery’s service life.

[0020] 3. Good chemical stability: PBO is stable in the electrolyte environment, reducing side reactions and improving the cycle performance of the battery.

[0021] 4. Excellent insulation performance: ensure good insulation between positive and negative electrodes, reduce battery self-discharge rate, and improve energy storage efficiency.

[0022] A PBO-coated diaphragm for lithium-ion batteries optimizes battery performance in many aspects, including thermal, mechanical, chemical and electrochemical properties, which significantly improves the safety, reliability, charge and discharge performance of the battery. Whether in high-energy demand fields such as electric vehicles or in application scenarios with high battery performance requirements such as portable electronic devices, PBO-coated diaphragms can provide better performance support for batteries to meet the needs of different users. DETAILED DESCRIPTION

[0023] In order to make the objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific embodiments.

[0024] Example 1

[0025] Preparation of PBO coating liquid: PBO pulp was put into a ball mill and ground at a speed of 150 rpm for 1.8 hours to obtain PBO granular pulp with a particle size of 2 μm. The pretreated PBO pulp was dispersed in deionized water, and dispersant polyvinyl pyrrolidone and binder polyacrylic acid, wetting agent sodium dodecyl sulfate, and surfactant sodium dodecyl sulfate were added and stirred evenly. Among them, the mass fraction of PBO pulp was 10%, the dispersant was 1%, the binder was 2%, the wetting agent was 0.5%, and the surfactant was 0.5%. During the stirring process, the stirring speed was controlled to 600 rpm and the stirring time was 3 hours to ensure that the PBO particles were fully dispersed in the solvent to form a uniform coating liquid.

[0026] Roller coating: Use roller coating equipment to apply the coating liquid to the lithium-ion battery separator substrate. Adjust the line speed to 50 meters / minute to ensure that the coating liquid is evenly coated on the substrate surface, and the coating thickness is about 1.5μm.

[0027] Drying: The coated diaphragm was placed in an oven and dried at 100°C for 5 minutes to obtain a composite diaphragm.

[0028] Example 2

[0029] Preparation of PBO coating liquid: PBO pulp was put into a ball mill and ground at a speed of 500 rpm for 1 hour to obtain PBO granular pulp with a particle size of 0.8 μm. The treated PBO pulp was dispersed in deionized water, and dispersant polyvinyl pyrrolidone and binder polyacrylic acid, wetting agent sodium lauryl sulfate, and surfactant sodium lauryl sulfate were added and stirred evenly. The mass fraction of PBO pulp was 15%, the dispersant was 2%, the binder was 3%, the wetting agent was 0.5%, and the surfactant was 1.5%. A uniform and stable coating liquid was prepared by combining high-speed stirring and ultrasonic dispersion at a stirring speed of 700 rpm and a stirring time of 2.4 hours.

[0030] Roller coating: Adjust the roller coating equipment parameters, the line speed is 45 m / min, ensure that the coating liquid is evenly coated on the substrate surface, and the coating thickness is about 2 μm.

[0031] Drying: Dry at 110°C for 4 min.

[0032] Example 3

[0033] Preparation of PBO coating liquid: PBO pulp is put into a ball mill and ground at a speed of 300 rpm for 2 hours to obtain PBO granular pulp with a particle size of 1 μm. The pretreated PBO pulp is dispersed in deionized water, and the additives are adjusted to be dispersant polyethylene glycol, binder polyurethane, wetting agent sodium dodecyl sulfate, and surfactant sodium dodecyl sulfate. The mass fraction of PBO pulp is 20%, dispersant is 3%, binder is 4%, wetting agent is 1%, and surfactant is 1.5%. The coating liquid is prepared by combining mechanical stirring and ultrasonic dispersion, with a stirring speed of 800 rpm and a stirring time of 2 hours.

[0034] Roller coating: Optimize the roller coating process and adjust the line speed to 40 m / min to ensure that the coating liquid is evenly coated on the substrate surface with a coating thickness of approximately 2.5 μm.

[0035] Drying: Dry at 120°C for 3 min.

[0036] Comparative Example

[0037] A common lithium-ion battery separator without PBO coating was used as a comparative example. The separator was only a polyolefin separator without any special treatment.

[0038] Performance Testing:

[0039] (1) Heat resistance test: The separators of the comparative example, example 1, example 2 and example 3 were placed in a high temperature environment (150° C. / 1 h) and their shrinkage force was tested.

[0040] (2) Mechanical property test: The tensile strength and puncture strength of the separators of the comparative example, example 1, example 2 and example 3 were measured by tensile test and puncture test.

[0041] (3) Chemical stability test: The comparative example, Example 1, Example 2 and Example 3 diaphragms were immersed in electrolyte for 72 hours and the conductivity change rate was measured.

[0042] The performance tests were conducted on the composite membranes prepared in Examples 1, 2, and 3 and the comparative example, and the results are shown in the following table:

[0043] Performance Indicators Example 1 Example 2 Example 3 Comparative Example 1 Thickness(μm) 12 13.5 14 14.5 Shrinkage rate (%) 1.3 1.1 0.8 3.9 Tensile strength(MPa) 427 445 458 203 Puncture strength (gf) 411 424 440 240 Conductivity change rate (%) 8 5 3 20

[0044] The composite diaphragm of the present invention has excellent heat resistance. At a high temperature of 150-300°C, the shrinkage rate of the diaphragm is less than 2%, which effectively prevents deformation and short circuit caused by high temperature, improves battery safety, and has excellent mechanical strength. The tensile strength and puncture strength are at least 2 times higher than those of uncoated diaphragms, and can withstand the mechanical stress inside the battery, prolong the service life, and have good chemical stability. The structure and performance are kept stable in the electrolyte environment, and the electrolyte does not react, which reduces side reactions and improves cycle performance. It can be applied to various types of lithium-ion batteries to meet the needs of different application scenarios.

[0045] Based on the above performance test results, it is shown that the PBO coated diaphragm for lithium ion batteries prepared by the present invention is significantly superior to traditional common diaphragms in terms of heat resistance, mechanical properties and chemical stability, and can effectively improve the safety performance and service life of the battery.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A PBO coated diaphragm for lithium ion battery, characterized in that: The invention comprises a lithium-ion battery separator substrate and a PBO pulp layer coated on the substrate.

2. The PBO coated separator for lithium ion battery according to claim 1, characterized in that: The thickness of the PBO coating layer is 0.5-5 μm.

3. The PBO coated separator for lithium ion battery according to claim 1, characterized in that: The PBO coating layer is a coating liquid, which contains the following components by mass fraction: 10%-20% PBO pulp, 1%-5% dispersant, 1.5%-5% binder, 0.5%-1.5% wetting agent, and 0.5%-2% surfactant.

4. The PBO coated separator for lithium ion battery according to claim 3, characterized in that: The dispersant is at least one of polyvinyl pyrrolidone and polyethylene glycol.

5. The PBO coated separator for lithium ion battery according to claim 3, characterized in that: The binder is at least one of polyacrylic acid and polyurethane.

6. The PBO coated separator for lithium ion battery according to claim 3, characterized in that: The wetting agent is at least one of sodium lauryl sulfate and polyethylene glycol.

7. The PBO coated separator for lithium ion battery according to claim 3, characterized in that: The surfactant is sodium lauryl sulfate.

8. A method for preparing a PBO coated diaphragm for a lithium ion battery according to any one of claims 1 to 7, characterized in that: The steps include: (1) Preparing a PBO coating liquid: dispersing PBO pulp in a solvent, wherein the mass fraction of PBO pulp in the solvent is 10%-20%, adding a dispersant, a binder, a wetting agent and a surfactant, wherein the mass fraction of the dispersant in the coating liquid is 1%-5%, the mass fraction of the binder in the coating liquid is 1.5%-5%, the mass fraction of the wetting agent in the coating liquid is 0.5%-1.5%, and the mass fraction of the surfactant in the coating liquid is 0.5%-2%, and stirring to obtain a stable coating liquid; (2) using a roller coating device to apply the coating liquid to the substrate: adjusting the equipment parameters so that the coating liquid is evenly coated on the surface of the lithium-ion battery separator substrate to avoid uneven thickness and missing coating; (3) Drying the coated diaphragm: Drying at 100-120° C. for 1-5 min to form a stable composite diaphragm.

9. The method for preparing a PBO coated diaphragm for a lithium ion battery according to claim 8, characterized in that: Before step (1), the PBO pulp is pretreated and ground in a ball mill at a speed of 100-500 rpm for 1-2 hours to obtain PBO granular pulp with a particle size of 0.1-3 μm.

10. The method for preparing a PBO coated diaphragm for a lithium ion battery according to claim 8, characterized in that: The solvent in step (1) is deionized water, the stirring speed is 600-800 rpm, the stirring time is 2-3 hours, and the line speed of the roller coating equipment in step (2) is 40-50 m / min.