WO2016110113A1

WO2016110113A1 - Method of preparing lithium ion battery negative electrode sheet using carbon fiber cloth as matrix

Info

Publication number: WO2016110113A1
Application number: PCT/CN2015/088159
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: CN104577041A; CN104577041B

Abstract

Provided is a method of preparing lithium ion battery negative electrode sheet using a carbon fiber cloth as a matrix, the method comprising: using a carbon fiber cloth as a substitution of a traditional negative electrode sheet matrix such as copper foil, and using a carbon fiber spinnable pitch as a starting material; preparing and pre-oxidizing filaments, performing a stretch breaking process, spinning and weaving to obtain a pre-oxidized fiber cloth; and carbonizing and graphitizing, coating negative electrode slurry, rolling, cutting into small pieces, and tab welding the pre-oxidized fiber cloth to obtain a lithium ion negative electrode sheet. The lithium ion negative electrode sheet produced by the embodiment of the invention is completely different from a lithium ion negative electrode sheet produced by a conventional preparation process. Thus the carbon fiber produced after a graphitization process provides an increased electrical conductivity and heat dissipation performance in comparison to copper foil.

Description

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

Technical field

The invention relates to a preparation method of a negative electrode sheet for a lithium ion battery, in particular to a method for preparing a negative electrode sheet by replacing a conventional negative electrode sheet base copper foil with a carbon fiber cloth.

Background technique

Carbon fiber cloth is a new type of carbon fiber derivative, which is made by using carbon fiber raw silk through the process of cutting, spinning and weaving. According to the raw materials, there are mainly PAN-based carbon fiber cloths (more than 90% of the carbon fiber cloths on the market), viscose-based carbon fiber cloths, and pitch-based carbon fiber cloths. According to the weaving method, the main organic woven carbon fiber cloth, knitted carbon fiber cloth, woven carbon fiber cloth, carbon fiber prepreg, carbon fiber non-woven fabric and the like. It is mainly used for reinforcement and repair of various structural types and structural shapes such as building bridges and tunnels, and structural reinforcement of joints. Applicable to various structural types, reinforcement of various structural parts, such as beams, slabs, columns, roof trusses, piers, bridges, cylinders, shells and other structures. It is suitable for reinforcement and seismic strengthening of concrete structures, masonry structures and wood structures in port engineering and water conservancy and hydropower projects. It is especially suitable for structural reinforcement of complex forms such as curved surfaces and joints. The principle of carbon fiber cloth reinforcement is: the high-performance carbon fiber supporting resin impregnating glue is bonded to the surface of the concrete member, and the good tensile strength of the carbon fiber material is used to enhance the bearing capacity and strength of the member. The utility model has the advantages of convenient construction, no need for large-scale machine equipment, no wet operation, no need for hot fire, no need for on-site fixed facilities, less construction occupied space and high construction efficiency. High durability, because it does not rust, it is very suitable for use in high acid, alkali, salt and atmospheric corrosive environments.

Lithium-ion batteries consist of a positive electrode, a negative electrode, an electrolyte, a separator, and other ancillary materials. The positive and negative electrodes of lithium-ion battery are composed of two different lithium ion intercalation compounds. When charging, lithium ions are deintercalated from the positive electrode and inserted into the negative electrode through the electrolyte. The negative electrode is in a lithium-rich state, and the positive electrode is in a depleted state. On discharge, the opposite is true. Deintercalation from the negative electrode, the electrolyte is embedded in the positive electrode, and the positive electrode is in a lithium-rich state, which is what people call a "rocking chair battery." The preparation process of the lithium ion battery is that the positive and negative active materials are respectively coated on the aluminum foil and the copper foil substrate by pulping, and finally obtained by rolling, tableting, assembling, injecting, forming and the like.

At present, a copper foil is generally used for a negative electrode substrate, and is coated on a copper foil by mixing a negative electrode material with a conductive agent and a binder, but since the negative electrode material is generally a non-metallic graphite-based carbon material, A common problem in the industry is that the negative active material and the copper foil have problems such as loosening of the material due to poor adhesion, powder removal, and poor overall flexibility of the negative electrode sheet. In order to solve the problems of material loss, powder removal, etc., only through Increase the proportion of binder component (CMC, SBR or PVDF) to enhance the adhesion between the anode material and the copper foil, but the binder component is too high, which will inevitably lead to the flexibility of the pole piece as a whole. The energy density per unit volume of the sheet is not conducive to the performance of the final finished battery.

Summary of the invention

The present invention is directed to solving the above technical problems, and a method for preparing a negative electrode tab of a lithium ion battery using a carbon fiber cloth as a negative electrode substrate.

A method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth, 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) slurry coating: coating the negative electrode slurry on the graphitized carbon fiber cloth;

(7) roll-pressed sheet: the coated negative electrode sheet is rolled and slit into small pieces;

(8) Tab Bonding: The tabs were bonded to the slit pieces to finally obtain a negative electrode sheet of the present invention using a carbon fiber cloth as a substrate for a lithium ion battery.

Further, the softening point of the carbon fiber spinnable asphalt is 150 to 300 ° C, the amount of residual carbon is ≥ 60%, and the quinoline insoluble matter (QI) is ≤ 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 temperature is raised to 10 to 50 ° C above the softening point of the asphalt. If the heating rate is too high, the raw silk will be melted, and the temperature will be too low to achieve the effect of oxidation. If the temperature is too high, the yield of the carbonization treatment will be lowered.

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 preparation of the negative electrode slurry and the size of the slit into small pieces are 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. The use of non-metallic carbon fiber cloth instead of metal copper foil is technically a bold innovation and breakthrough. The carbon fiber conductive and heat dissipation performance after graphitization is more advantageous than copper foil, and because of the copper as the matrix. The thickness of the foil is only about 10μm, and the strength is extremely poor. The carbon fiber cloth is used as the base body, and it is not easy to have broken pieces and no curling;

2. The carbon fiber cloth and the negative electrode active material belong to the same graphite. In addition to being a matrix, it can also participate as a part of the active material, participate in the insertion and extraction of lithium ions, and increase the volumetric energy density of the pole piece;

3. The carbon fiber cloth is a non-metal material, and has good bonding performance with graphite. In the process of configuring the negative electrode slurry, the proportion of the binder component can be reduced, and the content of the active material can be further increased;

4. The carbon fiber filaments in the carbon fiber cloth are intricately interlaced to form a good conductive network, and the electrical conductivity is excellent. The conductive paste may be added during the configuration of the negative electrode slurry or added less than normal, and the resulting negative electrode sheet still has good. Conductivity, the battery has a lower internal resistance;

5. The invention solves the technical problem of bonding the polar ear and the pole piece. The advantage is that the conductive ear or the soldering method can be placed at any position of the pole piece to meet the lithium ion battery with special process requirements.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the structure of a negative electrode sheet using a carbon fiber cloth as a substrate.

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 Empty The gas was heated to 240 ° C at a heating rate of 2 ° C / min, and oxidized for 3 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 100 ± 3 μm. The areal density was controlled at 19.6±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 90±3 μm and an areal density of 11.8±0.5 mg/cm 2 .

The anode active material was prepared in a ratio of CMC:SBR=96.5:1.5:2, and coated on a carbon fiber cloth by a coater, and the coated areal density was controlled at 18.8±0.5 mg/cm2, and the thickness was 180. After ±3μm, the coated pole piece is then rolled, and the thickness of the rolled roll is 130±3μm. According to the design process requirements, the carbon fiber is divided into negative electrode pieces with a length of 735±2mm and a width of 57.5±0.1 while using conductive The glue is bonded to the nickel tab at the end.

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 having a flowing state, and the spinneret of the melt spinning machine is adjusted to receive a pitch fiber strand having a diameter of 6 ± 1 μm, and the raw yarn is The temperature was raised to 230 ° C in the air at a heating rate of 1.5 ° C / min, and the oxidation treatment was carried out for 14 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 85 ± 3 μm. The areal density was controlled at 16.7±0.5 mg/cm2, and the pre-oxidized wire 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 75 ± 3 μm and an areal density of 9.4 ± 0.5 mg/cm 2 .

The anode active material was prepared in a ratio of CMC:SBR=96.5:1.5:2, and coated on a carbon fiber cloth by a coater, and the coated areal density was controlled at 13.4±0.5 mg/cm2, and the thickness was 115. ±3 μm and then rolling the coated pole piece to a thickness of 98 ± 3 μm, according to the design process It is required to divide the carbon fiber into a negative electrode piece having a length of 735±2 mm and a width of 57.5±0.1, and at the same time, a nickel tab is bonded to the end by a conductive adhesive.

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, and the test results are shown in Table 1.

Comparative example 1

A copper foil was used as the substrate, and other conditions were the same as those in Example 1. The negative electrode tab was prepared, and the test method and the positive electrode tab were the same as in Example 1. The test results are shown in Table 1.

Comparative example 2

A copper foil was used as the substrate, and other conditions were the same as those in Example 2. The negative electrode tab was prepared, and 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 carbon fiber cloth of the present invention is used as the negative electrode pole piece base, and the battery obtained by using the copper foil-based negative electrode pole piece has a cycle, a charge rate charging, and a battery internal resistance. Better performance.

The basic principles, main features, and advantages of the present invention are shown and described above. The bank 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 described in the foregoing description and the description of the present invention. Such changes and modifications are intended to fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

A method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth, 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) slurry coating: coating the negative electrode slurry on the graphitized carbon fiber cloth;

(7) roll-pressed sheet: the coated negative electrode sheet is rolled and slit into small pieces;

(8) Tab Bonding: The tabs were bonded to the slit pieces to finally obtain a negative electrode sheet of the present invention using a carbon fiber cloth as a substrate for a lithium ion battery.
The method for preparing a negative electrode sheet for a lithium ion battery based on carbon fiber cloth according to claim 1, wherein the softening point of the carbon fiber spinnable asphalt in the step (1) is 150 to 300 ° C, and the amount of carbon residue is ≥ 60%. , quinoline insoluble matter (QI) ≤ 3.0%.
The method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth according to claim 1, wherein the diameter of the asphalt fiber strand in the step (1) is between 4 and 30 μm.
The method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth according to claim 1, wherein the heating rate of the pre-oxidation of the strand in the step (2) is controlled to 0.5 to 5 ° C / min.
The method for preparing a negative electrode sheet for a lithium ion battery using a carbon fiber cloth as a base according to claim 1, wherein the thickness of the pre-oxygen wire cloth in the step (3) is 50 to 200 μm.
The method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth according to claim 1, wherein the temperature of the graphitization treatment in the step (5) is 2600 ° C or higher.
The method for preparing a negative electrode sheet for a lithium ion battery based on a carbon fiber cloth according to claim 1, wherein the step (7) is performed by using a conductive adhesive or a soldering method.