WO2016110111A1

WO2016110111A1 - Manufacturing method of carbon fiber fabric used as cathode sheet of lithium ion battery

Info

Publication number: WO2016110111A1
Application number: PCT/CN2015/088136
Authority: WO
Inventors: 田东
Original assignee: 田东
Priority date: 2015-01-08
Filing date: 2015-08-26
Publication date: 2016-07-14
Also published as: CN104538590B; CN104538590A

Abstract

A manufacturing method of a carbon fiber fabric used as a cathode sheet of a lithium ion battery. The method employs a carbon fiber spinnable pitch as a raw material, and comprises preparing a precursor, pre-oxidizing the precursor, and stretch-breaking, spinning and weaving the same to obtain a pre-oxidized fiber, then performing carbonization, graphitization, cutting, and electrode lug welding thereon to obtain a cathode sheet of a lithium ion battery, wherein said manufacturing processes differ completely from current manufacturing processes. The cathode sheet manufactured by the method changes a traditional manufacturing process, and conserves auxiliary materials and the use of manufacturing devices, thus greatly reducing manufacturing costs. In the invention, interwoven carbon fiber filaments form an advantageous electrically conducting network with good electrical conductivity, thereby greatly reducing an internal resistance of a manufactured battery, and meeting the need for a high current of the lithium ion battery upon charging and discharging.

Description

Method for preparing carbon fiber cloth as negative electrode sheet for lithium ion battery

Technical field

The invention relates to a method for preparing a negative electrode sheet for a lithium ion battery. Specifically, the negative electrode sheet according to the present invention uses a carbon fiber cloth.

Background technique

With the development of the automotive industry, the depletion of non-renewable fossil fuels such as oil and natural gas has received increasing attention, and air pollution and room temperature effects have become global problems. In order to solve the energy problem and achieve low-carbon environmental protection, based on the current development level of energy technology, electric vehicle technology has gradually become the focus of global economic development. The United States, Japan, Germany, China and other countries have successively restricted the use of fuel vehicles and vigorously developed electric vehicles. As the core component of electric vehicles, the power battery has also ushered in a great development opportunity. Power battery refers to the battery used in electric vehicles, including lithium ion batteries, lead acid batteries, fuel cells, etc. Among them, lithium ion batteries have higher specific energy, higher specific power, less self-discharge, long service life and good safety. Other advantages have become the focus of current development in various countries.

The negative electrode material is one of the four major raw materials (positive electrode, negative electrode, electrolyte, and separator) of the lithium ion battery. At present, the commercial lithium ion battery anode material is made of graphite carbon material, which has a low lithium insertion/deintercalation potential and is suitable. It has the advantages of reversible capacity, abundant resources and low price, and is an ideal anode material for lithium ion batteries. When graphite is used as a negative electrode material, it is necessary to obtain a negative electrode sheet by a process of slurrying, coating, tableting, baking, etc., and then assembly with the positive electrode sheet and other subsequent work, and finally only a lithium ion finished product.

Carbon fiber has a wide range of applications and is a carbon material with excellent properties. It has many advantages such as high strength, small coefficient of thermal expansion, good thermal conductivity and excellent electrical conductivity. Chinese patent CN 102623704A, by adding carbon fiber, utilizes its high conductivity and strength. Adsorption to prepare lithium carbonate-carbon fiber composite anode materials to solve the problem of material large-rate charge and discharge performance and improve conductivity, to meet the requirements of modern society for lithium-ion battery applications. Chinese patent CN 102290582A, by adding nano-long carbon fiber VGCF, improves battery conductivity and reduces internal resistance.

A preparation method of a tin/graphene/carbon fiber composite lithium battery anode material disclosed in Chinese patent CN 104037393A, a network structure composed of a mixture of graphene and carbon fiber, provides a large number of smooth transport channels for lithium ion in and out electrodes, so that it can be fully Contact with the anode material improves the utilization efficiency of the anode material. Improve the effective position of lithium storage in the negative electrode material and the transport speed of lithium during charge and discharge. The high electrical conductivity of graphene and carbon fiber can quickly achieve carrier migration, improve output power and effectively reduce battery Internal resistance of the body.

Chinese patent CN 102560744A discloses a preparation method of general-purpose pitch-based carbon fiber, which successfully applies the spinning equipment of chemical fiber industry to the spinning production process of petroleum and coal-based isotropic spinnable asphalt, in the pre-oxidation process. The gas phase oxidation method is adopted, and the pre-oxidation treatment is carried out by using the gas oxidant which is easy to operate and polluted. In the pre-oxidation treatment and the carbonization treatment process, an excellent process parameter optimization scheme is adopted, and the excellent production performance is successfully produced. General purpose pitch based carbon fiber.

None of the above patents disclose the use of carbon fiber as a negative electrode for lithium ion batteries, and a method for preparing carbon fiber cloth negative electrode sheets using carbon fibers.

Summary of the invention

The invention is to provide a novel preparation method of a negative electrode sheet for a lithium ion battery, and to change a conventional method for obtaining a negative electrode sheet by using a graphite particle as a raw material, and finally obtaining a negative electrode sheet by a process of slurrying, coating, tableting, baking, and the like. It saves copper foil base, binder (CMC, SBR), conductive agent (SP) and other ingredients and accessories, as well as supporting production equipment. At the same time, the negative electrode sheet prepared by the invention combines the advantages of the carbon fiber, especially after the treatment by the graphitization step, further improves the conductivity and the gram capacity, and can meet the requirements of high rate charge and discharge.

The technical problem solved by the present invention is achieved by the following technical solution. A carbon fiber cloth is used as a preparation method of a negative electrode sheet for a lithium ion battery, and the preparation steps are as follows:

(1) Preparation of raw silk: heating and melting carbon fiber spinnable asphalt, and obtaining raw asphalt fiber by spinning mechanism;

(2) pre-oxidation of raw silk: the asphalt fiber raw material is heated in air to a temperature higher than the softening point of the asphalt by 10 to 50 ° C for 3 to 24 hours;

(3) Preparation of pre-oxidized silk cloth: the oxidized raw yarn is subjected to strip cutting, spinning and weaving to obtain a pre-oxidized silk cloth;

(4) Carbonization treatment: the pre-oxidized wire cloth is heated under the protection of an inert gas at a temperature increase rate of 1 to 20 ° C / min to 700 ° C to 1300 ° C, maintained at a high temperature for 0.5 to 5 hours, and then cooled to room temperature;

(5) Graphitization treatment: the carbonized pre-oxidized silk cloth is further subjected to high temperature graphitization treatment;

(6) slitting and slicing: the graphitized carbon fiber cloth is cut into small pieces;

(7) Tab Bonding: The tabs are bonded to the slit pieces to finally obtain the carbon fiber cloth negative electrode sheets which can be used as the lithium ion battery of the present invention.

Further, the softening point of carbon fiber spinnable asphalt is 150-300 ° C, the amount of residual carbon is ≥ 60%, and quinoline is not The solution (QI) ≤ 3.0%. If the amount of residual carbon in the asphalt is too high, the production cost of the asphalt will increase, and the amount of residual carbon will be too low, indicating that the volatile content in the asphalt is high, which will reduce the strength and yield of the carbon fiber produced.

Further, the diameter of the asphalt fiber strand is between 4 and 30 μm, and the diameter is too small, which increases the difficulty of spinning, and the spun yarn is easily broken, resulting in the fiber cloth produced in the later stage having too low strength and too large diameter, which will increase. The channel resistance of lithium ion in and out, while reducing the rate of charge and discharge of the battery.

Further, the heating rate of the pre-oxidation of the raw silk is controlled to 0.5 to 5 ° C / min, and the heating rate is too high, which may cause the raw silk to melt, and the temperature is too low to achieve the effect of oxidation. If the temperature is too high, the carbonization treatment will be lowered. rate.

Further, the thickness of the pre-oxidized silk cloth is 50 to 200 μm, and the thickness is too small, which causes the unit volume capacity of the negative electrode sheet to decrease, and the thickness is too large, which may affect the transfer of the later battery core.

Further, the temperature of the high temperature graphitization treatment is 2600 ° C or higher.

Further, the size of the small piece is determined according to different lithium ion battery models, and the specific process requirements are well known to those skilled in the art, and are not described herein.

The commonly used method of tab welding is to directly solder the nickel tab of the metal material to the base of the negative electrode-copper foil by ultrasonic or laser. However, the negative electrode sheet of the present invention is a non-metal material, and the conventional soldering method cannot be used. The present invention bonds nickel tabs and carbon fiber cloth by means of conductive adhesive or soldering having adhesive properties. At the same time, the position of the tab can be bonded to any position of the pole piece according to the actual process requirements.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) Changed the traditional lithium ion battery negative electrode preparation process, saving some auxiliary materials and production equipment, greatly reducing production costs;

(2) The negative electrode sheet prepared by the invention has better flexibility and toughness than the conventional negative electrode sheet because the whole negative electrode sheet is a whole, and the safety performance of the battery is improved;

(3) The negative electrode sheet of the invention is intricately interlaced with carbon fiber filaments to form a good conductive network, and has excellent electrical conductivity, can greatly reduce the internal resistance of the final finished battery, and meet the requirements of large current charge and discharge of the lithium ion power battery;

(4) The carbon fiber itself has more microporous structure, can ensure the absorption and retention of the electrolyte, meets the rapid ingress and egress of lithium ions, and has excellent cycle performance, and is an ideal anode material.

DRAWINGS

1 is a schematic view showing the structure of a carbon fiber cloth negative electrode sheet of the present invention.

Figure 2 is a graph showing the charge and discharge curves of the negative electrode sheet of Example 1.

Figure 3 is a graph showing the rate discharge of the battery in Example 2.

detailed description

In order to make the technical means, the creative features, the workflow, and the method of use of the present invention easy to understand and understand, the present invention is further explained below.

Example 1

The carbon fiber spinnable pitch having a softening point of 250 ° C is heated to 280 ° C to melt into a liquid having a flowing state, and the spinneret of the melt spinning machine is adjusted to obtain a pitch fiber strand having a diameter of 20 ± 1 μm, and the raw yarn is The air was heated to 230 ° C at a heating rate of 2 ° C / min, and oxidized for 12 hours. The oxidized raw yarn was passed through a slitting and spinning fabric to obtain a pre-oxidized silk cloth, and the thickness was controlled at 140 ± 3 μm. The surface density was controlled at 31.3±0.5 mg/cm2, and the pre-oxidized wire was heated under the protection of an inert gas at a heating rate of 10 ° C/min to 900 ° C, maintained at a high temperature for 2 hours, and then cooled to room temperature. The carbonized pre-oxidized silk cloth is further graphitized at a high temperature, and the finally obtained carbon fiber cloth has a thickness of 130±3 μm and an areal density of 18.8±0.5 mg/cm 2 .

According to the design process requirements, the carbon fiber was cut into a negative electrode piece having a length of 735±2 mm and a width of 57.5±0.1, and a nickel electrode was bonded to the end by a conductive adhesive.

In order to examine the gram capacity of the negative electrode sheet of Example 1, the test was carried out by the half-cell test method. The negative electrode sheet prepared in Example 1 was used as the counter electrode with the lithium metal sheet as the counter electrode, and the electrolyte was 1 mol/L LiPF6/EC+DEC+DMC. =1:1:1, the polypropylene microporous membrane is a membrane and assembled into a battery. The charge-discharge voltage is 0-2.0V, and the charge-discharge rate is 0.2C. The battery performance can be tested. The initial discharge capacity of the electrode material is 345.3mAh/g. See Figure 2, the first efficiency is 95.2%.

In order to test the performance of the negative electrode sheet in Example 1, LiCoO2 powder: SP: KS-6: PVDF = 94:2.5:1.5:2 (weight ratio), uniformly mixed with NMP as a solvent, and then applied to aluminum foil. Vacuum drying at 100 ° C; the dried positive electrode sheet was rolled and cut into pieces to obtain a thickness of 119 ± 3 μm, the dressing surface density was controlled at 40 ± 0.5 mg / cm 2 , and the length was 683 ± 2 mm. For the positive electrode piece of 56±0.1mm, the positive and negative electrode pieces are wound, injected, sealed, and formed into a 18650 cylindrical battery. The separator is Celgard 2400, and the electrolyte is 1M LiPF6/DMC: EC: DEC. The battery detection device performs electrical performance test, and the test results are shown in Table 1.

Example 2

The carbon fiber spinnable pitch with a softening point of 200 ° C is heated to 250 ° C to melt into a liquid with a flowing state, and the spinneret of the melt spinning machine is adjusted to receive a pitch fiber strand having a diameter of 5 ± 1 μm, and the raw yarn is The air was heated to 200 ° C at a heating rate of 1.5 ° C / min, and oxidized for 10 hours. The oxidized raw yarn was passed through a stripping and spinning fabric to obtain a pre-oxidized silk cloth, and the thickness was controlled at 105 ± 3 μm. The surface density was controlled at 23.5±0.5 mg/cm2, and the pre-oxidized wire cloth was heated under the protection of an inert gas at a temperature increase rate of 5 ° C/min to 850 ° C, maintained at a high temperature for 1 hour, and then cooled to room temperature. The carbonized pre-oxidized silk cloth was further graphitized at a high temperature, and the finally obtained carbon fiber cloth had a thickness of 98 ± 3 μm and an areal density of 13.4 ± 0.5 mg/cm 2 .

According to the design process requirements, the carbon fiber was cut into a negative electrode piece having a length of 717±2 mm and a width of 57.5±0.1, and a nickel electrode was bonded to the end by a conductive adhesive.

In order to examine the gram capacity of the negative electrode sheet of Example 1, the battery performance was tested by the half-cell method of Example 1, and the initial discharge capacity of the electrode material was 341.1 mAh/g, and the first efficiency was 94.2%.

In order to test the performance of the negative electrode sheet in Example 1, LiFePO4 powder: SP: KS-6: PVDF = 92: 3.5: 2: 2.5 (weight ratio), uniformly mixed with NMP as a solvent, and then applied to an aluminum foil. Vacuum drying at 95 ° C; the dried positive electrode sheet was rolled and cut into pieces to obtain a thickness of 172 ± 3 μm, the dressing surface density was controlled at 33 ± 0.5 mg / cm 2 , and the length was 662 ± 2 mm. For the positive electrode piece of 56±0.1mm, the positive and negative electrode pieces are wound, injected, sealed, and formed into a 18650 cylindrical battery. The separator is Celgard 2400, and the electrolyte is 1M LiPF6/DMC: EC: DEC. The power battery detection device performs electrical performance detection. The rate discharge curve is shown in Figure 3. The test results are shown in Table 1.

Comparative example 1

Using the conventional artificial graphite particles (particle diameter D50=15±2μm, specific surface area 3.2m2/g) as the negative electrode material, the same negative electrode piece which meets the requirements of the process in the first embodiment is prepared, and the test method and the positive electrode piece are the same as the embodiment. 1. The test results are shown in Table 1.

Comparative example 2

Using the artificial graphite in Comparative Example 1 as the negative electrode material, the same negative electrode tab which meets the requirements of the process in Example 2 was prepared. The test method and the positive electrode tab were the same as in Example 2. The test results are shown in Table 1.

Table 1 compares the performance of negative electrode materials in different examples and comparative examples.

As can be seen from the above table, the use of the carbon fiber cloth of the present invention as the negative electrode sheet is lower in the specific capacity than the commercial negative electrode material, but the difference is not large. In terms of circulation, rate charging and discharging, and internal resistance of the battery, they all have stronger advantages than graphite particle-based anode materials.

The basic principles, main features, and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing description and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to be included within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

A carbon fiber cloth is used as a preparation method of a negative electrode sheet for a lithium ion battery, and the preparation steps are as follows:

(1) Preparation of raw silk: heating and melting carbon fiber spinnable asphalt, and obtaining raw asphalt fiber by spinning mechanism;

(2) pre-oxidation of raw silk: the asphalt fiber raw material is heated in air to a temperature higher than the softening point of the asphalt by 10 to 50 ° C for 3 to 24 hours;

(3) Preparation of pre-oxidized silk cloth: the oxidized raw yarn is subjected to strip cutting, spinning and weaving to obtain a pre-oxidized silk cloth;

(4) Carbonization treatment: the pre-oxidized wire cloth is heated under the protection of an inert gas at a temperature increase rate of 1 to 20 ° C / min to 700 ° C to 1300 ° C, maintained at a high temperature for 0.5 to 5 hours, and then cooled to room temperature;

(5) Graphitization treatment: the carbonized pre-oxidized silk cloth is further subjected to high temperature graphitization treatment;

(6) slitting and slicing: the graphitized carbon fiber cloth is cut into small pieces;

(7) Tab Bonding: The tabs are bonded to the slit pieces to finally obtain the carbon fiber cloth negative electrode sheets which can be used as the lithium ion battery of the present invention.
The carbon fiber cloth according to claim 1 is used as a method for preparing a negative electrode sheet for a lithium ion battery, characterized in that in the step (1), the softening point of the carbon fiber spinnable asphalt is 150 to 300 ° C, and the amount of residual carbon is ≥ 60%. Quinoline insolubles (QI) ≤ 3.0%.
The carbon fiber cloth according to claim 1 is used as a method for preparing a negative electrode sheet for a lithium ion battery, characterized in that the diameter of the pitch fiber strand in the step (1) is between 5 and 30 μm.
The carbon fiber cloth according to claim 1 is used as a method for preparing a negative electrode sheet for a lithium ion battery, characterized in that the heating rate of the pre-oxidation of the strand in the step (2) is controlled to 0.5 to 5 ° C / min.
The carbon fiber cloth according to claim 1 is used as a method for preparing a negative electrode sheet for a lithium ion battery, characterized in that the thickness of the pre-oxygen wire cloth in the step (3) is 50 to 200 μm.
A carbon fiber cloth according to claim 1, which is used as a method for producing a negative electrode sheet for a lithium ion battery, characterized in that the temperature of the graphitization treatment in the step (5) is 2600 ° C or higher.
A carbon fiber cloth according to claim 1 is used as a method for preparing a negative electrode sheet for a lithium ion battery, characterized in that the step (7) is performed by using a conductive adhesive or a soldering method.