TW202033447A - Method for manufacturing carbon conductive coating - Google Patents

Abstract

The present invention relates to a method for manufacturing carbon conductive coating for applying on a current collector used in a lithium ion battery. The method includes providing carbon material, an adhesive, a conductive agent and an additive dissolved and dispersed in a solvent, and then mixing the adhesive, the conductive agent and the additive sequentially via ball milling and a sonication method so as to form conductive slurry. A coupling agent is added and mixed with the conductive slurry. A conductive carbon-coated current collector is prepared by coating the conductive slurry on a copper foil.

Description

Preparation method of carbon conductive layer

The present invention relates to an electrochemical field, in particular to a carbon conductive layer and a preparation method thereof.

In order to reduce the internal resistance of the lithium battery and extend the life of the lithium battery, there are currently two current collector surface treatment methods used in lithium batteries. One is to etch the surface of the current collector chemically or physically to form uneven roughness. Surface, thereby increasing the contact area with the battery paste and the surface of the current collector and enhancing the adhesion, but this method requires higher process requirements and is expensive and is not conducive to mass production. Another method is to apply a conductive coating on the surface of the current collector. That is, the conductive slurry is uniformly coated on the surface of the aluminum foil or copper foil current collector to form a conductive coating, and then the battery slurry is coated on the conductive coating. The physical contact between the current collector and the conductive coating is The electrons generated by the scientific reaction are collected and exported to the external circuit to realize the process of converting chemical energy into electrical energy.

However, the contact between the current collector and the active material of the battery slurry is an important factor affecting the charge and discharge performance of lithium-ion batteries. During this process, the volume of the active material will change, and the expansion and contraction of the volume will cause the activity of the battery slurry. The adhesion between the material and the current collector becomes worse, and the contact resistance becomes larger, which causes a significant decrease in capacitance.

For example, a conductive coating coated on the copper foil of the current collector with a carbon-silicon composite material as the active material has a much higher expansion rate than graphite, and severe volume expansion and contraction will be active The material generates mechanical stress, which causes the battery paste to peel off from the current collector, causing the electrode capacitance to rapidly decline. And the existing conductive coating has poor adhesion. The conductive coating formed after the conductive slurry is coated on the surface of the current collector is easy to peel off, and the poor adhesion will increase the interface between the battery slurry and the current collector. Resistance, after being prepared into a battery, will affect the internal resistance of the battery. However, if the conductive coating material is selected from metal particles or metal-coated polymer particles, there will be disadvantages such as high cost, easy oxidation, easy delamination of the conductive coating slurry, and difficult construction.

The above-mentioned technologies are described in existing patents. For example, the Republic of China Patent No. I620372 discloses negative electrode materials for lithium ion batteries, negative electrodes for lithium ion batteries and lithium ion batteries. The negative electrode materials for lithium ion batteries contain carbon materials with the following characteristics: The average interplanar spacing calculated by the X-ray diffraction method is 0.335nm~0.340nm, the volume average particle size is 1μm~40μm, the maximum particle size is 74μm or less, and in the differential thermal analysis in air flow, it is at 300℃ There are at least two exothermic peaks in the temperature range below 1000°C. However, the carbon material provided by the conventional technology can only achieve the effects of improving the charging and discharging efficiency and thermal stability, and cannot solve the problem of easy peeling of the conductive coating.

Furthermore, the Republic of China Patent No. I569502 discloses a current collector that improves the use of the current collector by improving the adhesion between the surface of the conductive resin layer provided on the current collector and the active material. High-rate characteristics or electrode life of electric non-aqueous electrolyte batteries, electric double layer capacitors, or lithium ion capacitors. In the current collector of the previous proposal, a conductive resin layer is formed on at least one surface of a conductive base material. The conventional technology coats the surface of the current collector with a resin layer having uneven surfaces, and the active material can flow into the uneven parts to increase the adhesion between the battery slurry and the current collector. However, this conventional technology is a modified embodiment of the aforementioned chemical or physical surface etching on the surface of the current collector to form an uneven rough surface. The resin layer and the battery paste There are still doubts about the adhesion between the two.

In addition, US Patent No. 9,437,344 discloses graphite or graphite-carbon particles used as a negative electrode material for lithium secondary batteries with high conductivity. The carbon particles are formed by core carbon or graphite particles and a plurality of satellite carbon or graphite particles respectively combined with the core particles, wherein the core particles are spherical, the shape is slightly elongated, and the satellite particles are disc-shaped, flake-shaped or flake-shaped particles. Each particle contains graphite crystallites with a crystal axis size and a lateral size, but it cannot solve the problem of easy peeling of the conductive coating.

Therefore, in order to meet the needs of the industry, it is necessary to develop a highly conductive, which can be coated between the battery slurry of lithium ion batteries and the copper foil current collector and can avoid the battery slurry of lithium ion batteries and the copper foil current collector Carbon conductive layer in case of body peeling.

The adhesion between the current collector of the conventional lithium ion battery and the battery slurry is not good. In addition, the conductive coating formed after the current conductive slurry is coated on the surface of the current collector is easy to peel off from the surface of the current collector, resulting in Disadvantages of large capacity attenuation. In addition, the poor adhesion between the existing conductive coating and the current collector will also increase the interface resistance between the subsequent battery slurry and the current collector, thereby increasing the battery pack of the lithium-ion battery and causing the performance of the lithium-ion battery to decrease.

In order to solve the above problems, the present invention provides a method for preparing a carbon conductive layer, including: providing a carbon material, an adhesive, a guiding agent and an additive; the carbon material, the adhesive, the guiding agent and the additive Stir and disperse in a solvent; use a ball milling process and an ultrasonic vibration process to sequentially grind and mix the carbon material, the adhesive, the promoter, and the additives dispersed in the solvent to obtain a conductive paste Adding a coupling agent to the conductive paste; and coating the conductive paste on a surface of a current collector for the current collector A carbon conductive layer is formed on the surface.

In an embodiment of the present invention, the carbon conductive layer has a thickness of 0.1 μm to 2 μm.

In an embodiment of the present invention, the current collector coated with the carbon conductive layer has a tensile strength greater than 7.0 Kg _f .

In an embodiment of the present invention, the coupling agent is 3-aminopropyltriethoxysilane (APTES).

In an embodiment of the present invention, the coupling agent is selected from alkyl silane coupling agents, amino silane coupling agents, alkenyl silane coupling agents, epoxy alkyl silane coupling agents, and alkyl acryloyloxy Group consisting of silane coupling agents.

In an embodiment of the present invention, relative to 100 parts by weight of the solid content in the conductive paste, the carbon material content is 5 to 85 parts by weight, the adhesive content is 5 to 50 parts by weight, and the guide agent The content is 1 part to 40 parts by weight, and the additive content is 1 part to 30 parts by weight.

In an embodiment of the present invention, the carbon material may be selected from graphite or graphene.

In an embodiment of the present invention, the guiding agent may be selected from the group consisting of carbon nanofibers, carbon nanotubes, acetylene black, conductive carbon black, and flake graphite.

In an embodiment of the present invention, the adhesive may be selected from the group consisting of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) and polyacrylic acid ( PAA), and the additive is selected from the group consisting of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium stearate.

In an embodiment of the present invention, the solvent is selected from the group consisting of: Water, ethanol, N-methylpyrrolidone (NMP), toluene and acetone.

In order to solve the above problems, the present invention provides a carbon conductive layer for coating on a surface of a current collector. The carbon conductive layer includes a conductive paste composed of a carbon dispersed in a solvent. It is composed of materials, an adhesive, a conductive agent and an additive; wherein the current collector coated with the carbon conductive layer has a tensile strength greater than 7.0 Kg _f .

In an embodiment of the present invention, the solvent, the carbon material, the adhesive, the promoter, and the additive are sequentially ball milled and shaken to form the conductive paste.

In an embodiment of the present invention, the carbon conductive layer has a thickness of 0.1 μm to 2 μm.

In an embodiment of the present invention, the carbon conductive layer further includes a coupling agent.

In an embodiment of the present invention, the coupling agent is 3-aminopropyltriethoxysilane (APTES).

In an embodiment of the present invention, the coupling agent is selected from alkyl silane coupling agents, amino silane coupling agents, alkenyl silane coupling agents, epoxy alkyl silane coupling agents, and alkyl acryloyloxy Group consisting of silane coupling agents.

In an embodiment of the present invention, relative to 100 parts by weight of the solid content in the conductive paste, the carbon material content is 5 to 85 parts by weight, and the adhesive content is 5 to 50 parts by weight, which helps guide The content of the agent is 1 part to 40 parts by weight, and the content of the additive is 1 part to 30 parts by weight.

In an embodiment of the present invention, the carbon material may be selected from graphite or graphene, and the guiding agent may be selected from the group consisting of carbon nanofiber, carbon nanotube, acetylene black, conductive carbon black And flake graphite.

In an embodiment of the present invention, the adhesive may be selected from the group consisting of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) and polyacrylic acid ( PAA), and the additive is selected from the group consisting of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium stearate.

In order to solve the above-mentioned problems, the present invention further provides a current collector, the current collector is formed with a carbon conductive layer as described above on at least one surface.

Compared with the conductive coating used in the current collector of the conventional lithium ion battery, the carbon conductive layer and the preparation method thereof provided by the present invention disperse the carbon material, the adhesive, the conductive agent and the additive formula in a solvent, according to The sequence is mixed and dispersed by means of ball milling and ultrasonic vibration to obtain a conductive slurry that is stably dispersed in a solvent. The conductive paste can be coated on the surface of the current collector to obtain the current collector formed with the carbon conductive layer. When applied to a lithium-ion battery, a battery slurry layer is coated on the surface of the carbon conductive layer. The carbon conductive layer can increase the adhesion between the battery slurry layer and the current collector and reduce shedding In this case, it can also effectively reduce the internal resistance of the battery and improve the battery performance.

S01~S04‧‧‧Step

10‧‧‧Current collector

101‧‧‧surface

20‧‧‧Carbon conductive layer

40‧‧‧Battery paste layer

Figure 1 is a schematic diagram of the process of the method for preparing a carbon conductive layer of the present invention; Figure 2 is a schematic diagram of the structure of a carbon conductive layer coated on a current collector prepared by the method of preparing a carbon conductive layer of the present invention; Figure 3 is the present invention The carbon conductive layer prepared by the carbon conductive layer preparation method is coated on the current collector and then coated with the battery slurry; Figure 4 is a schematic diagram of the conductive slurry constituting the carbon conductive layer of the present invention; Figure 5 is the present invention The carbon conductive layer is formed on the current collector and magnified by electron microscope Schematic diagram; Figure 6 is a schematic diagram of the tensile test results of the carbon conductive layer formed on the current collector of the present invention; and Figure 7 is a schematic diagram of the conductivity test results of the current collector of the present invention and a conventional current collector.

With regard to the technical content and detailed description of the present invention, the description is as follows in conjunction with the drawings: Please refer to Fig. 1, which is a schematic flow chart of the method for preparing a carbon conductive layer of the present invention. The present invention provides a method for preparing a carbon conductive layer, including: Step S01: providing a carbon material, an adhesive, a guiding agent and an additive; Step S02: the carbon material, the adhesive, the guiding agent and the Additives are dispersed in a solvent; Step S03: provide a ball milling procedure and an ultrasonic vibration procedure, sequentially grind and mix the carbon material, the adhesive, the promoter and the additive dispersed in the solvent to obtain a Conductive paste; step S04: adding a coupling agent to the conductive paste; and step S05: coating the conductive paste on a surface of a current collector so as to be on the surface of the current collector A carbon conductive layer is formed.

In an embodiment of the present invention, the solvent, the carbon material, the adhesive, the promoter, and the additive are mixed and dispersed successively through a wet ball milling process and an ultrasonic vibration process to form the conductive paste. The following is a detailed preparation method of the carbon conductive layer of the present invention.

Preparation of conductive paste

In an exemplary embodiment, the carbon material (KS6), the adhesive (CMC), the promoter (Super p), the additive (such as the surfactant (Sodium dodecyl sulfate, SDS)) and the solvent (water) are mixed Together, they are dispersed by high-speed stirring, and then put into a ball mill container to be ball milled by the wet ball mill, and then the semi-finished slurry is taken out and processed by ultrasonic vibration. Preparation is complete.

Among them, the solid content of the conductive paste is 1-40 weight percent, the content of carbon material (KS6) is 5 to 85 weight percent, the content of adhesive (CMC) is 5 to 50 weight percent, and the content of super p is 1 to 40 weight percent, and the content of the surface active agent (SDS) is 1 to 30 weight percent.

Preparation of current collector with the carbon conductive layer

In addition, a coupling agent (such as 3-aminopropyltriethoxysilane (APTES)) can be added to the conductive slurry prepared above, and then the conductive slurry can be coated on the conductive slurry by knife coating. On the surface of clean aluminum foil current collector or copper foil current collector, by adjusting the blade gap and coating speed, the thickness of the conductive paste formed is 1 micron to 100 micrometers, and then the aluminum foil current collector coated with conductive paste Or the copper foil current collector is placed in an oven for a drying process, and the drying temperature is 100° C., to prepare an aluminum foil current collector or a copper foil current collector with the carbon conductive layer.

In addition, the types of coupling agents may include, but are not limited to, alkyl silane coupling agents, amino silane coupling agents, alkenyl silane coupling agents, epoxy alkyl silane coupling agents, and alkyl acryloxy silanes. Coupling agent. Among them, the coupling agent (APTES) can simultaneously bond with the inorganic functional groups on the surface of the current collector and the carbon conductive layer, effectively improving the interfacial interaction between the carbon conductive layer and the current collector, and making the carbon conductive layer and the collector The bonding strength of the interface between the electrical bodies has been significantly improved, and the detailed test results will be described later.

Please refer to FIG. 2. FIG. 2 is a schematic diagram of the structure of a carbon conductive layer coated on a current collector of the present invention. The present invention provides a carbon conductive layer 20 for coating on a surface 101 of a current collector 10. The carbon conductive layer 20 includes a conductive paste composed of a carbon material dispersed in a solvent, The current collector 10 coated with the carbon conductive layer 20 has a tensile strength greater than 7.0 Kg _f .

The current collector 10 can be an aluminum foil or a copper foil, which is used as a positive and negative electrode material in a lithium battery. The solvent, the carbon material, the adhesive, the conductive agent, and the additives are ball milled and shaken to form the conductive paste. The conductive paste can be stably dispersed in a solvent (such as water) for up to three months. The slurry is coated on one surface 101 or both surfaces 101 of the aluminum foil or the copper foil to form the carbon conductive layer, and the formed carbon conductive layer has a thickness of 0.1 μm to 2 μm.

Wherein, the carbon material can be selected from graphite or graphene. The guiding agent can be selected from the group consisting of carbon nanofibers, carbon nanotubes, acetylene black, conductive carbon black, and flake graphite. The adhesive can be selected from the group consisting of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and polyacrylic acid (PAA). The additives can be selected from sodium polyacrylate, sodium alkylbenzene sulfonate, and sodium stearate. The solvent can be in the group consisting of water, ethanol, N-methylpyrrolidone (NMP), toluene, and acetone. But not limited to this.

In an embodiment of the present invention, the solvent, the carbon material, the adhesive, the promoter and the additive are mixed and dispersed sequentially through a wet ball milling process and an ultrasonic vibration process to form the conductive paste . That is, the solvent, the carbon material, the adhesive, the promoter, and the additive are first obtained by a wet ball milling process to obtain a semi-finished product, and then the semi-finished product is dispersed in the solvent, the carbon material, and the adhesive through an ultrasonic vibration process. Agent, the assistant and the additive form the conductive paste.

The prepared carbon conductive layer has good hydrophilicity, conductivity, high specific surface area, corrosion resistance and oxidation resistance, thereby reducing the interface resistance between the battery slurry of the subsequent lithium battery and the current collector 10. As shown in Figure 3, the carbon conductive layer of the present invention is coated on the current collector and then the battery slurry is coated. The current collector 10 in the figure is coated with the carbon conductive layer 20 of the above embodiment, and then Carbon conductive layer 20 The surface is applied to a battery slurry layer 40 of the above-mentioned lithium battery. The carbon conductive layer 20 increases the contact area between the battery slurry layer 40 formed on the surface 101 of the current collector 10 and the current collector 10, and increases The interaction force between the battery paste layer 40 and the current collector 10 prevents the battery paste layer 40 from easily peeling off or dissolving from the current collector 10. In the subsequent use of the current collector 10 in the process of charging and discharging the lithium battery, the battery slurry layer 40 and the current collector 10 will not peel off or dissolve.

Experimental example

0.025 grams of adhesive (CMC) and solvent (water) are mixed at room temperature. The adhesive is made of a hydrophilic material, but it is not limited to this. After mixing, stir at room temperature for 1 hour, add 0.01 g of additives (such as surfactant (SDS)) and 0.015 g of promoter (Super p), stir at room temperature for 20 minutes, and pour the resulting intermediate solution into a A carbon source (ie carbon material) was added to the ball mill container. The carbon source was 0.05 grams of KS6. The intermediate solution of the carbon source was added to perform wet ball milling at a speed of 500 rpm for 3 hours, and then ultrasonic vibration 3 Hours, the conductive paste is obtained. Add 0.1 ml of coupling agent before coating on the surface of the current collector to form the carbon conductive layer on the surface of the current collector.

Identification and testing

As shown in Figure 4, it is a schematic diagram of the conductive paste constituting the carbon conductive layer of the present invention. The conductive paste prepared by the above-mentioned preparation method does not exhibit delamination after being allowed to stand for three months, indicating that the conductive paste is uniformly mixed and has good stability.

As shown in Figure 5, it is a schematic diagram of the carbon conductive layer of the present invention after being formed on the current collector and magnified and observed by an electron microscope. Part (A) is the carbon conductive layer magnified and observed by a low magnification electron microscope, and part (B) It is a carbon conductive layer magnified by a high-magnification electron microscope. The conductive slurry is coated on the copper foil current collector to prepare a carbon-coated copper foil. It can be observed that the copper foil collector is covered with a layer Uniform and dense carbon conductive layer, and the coverage of the carbon conductive layer is good. There is no exposed copper foil current collector. The sheet-shaped carbon conductive layer is closely attached to the copper foil current collector. After the tape stripping test of the copper foil current collector with the carbon conductive layer, the tape did not stick the carbon conductive layer from the copper foil current collector. The carbon conductive layer was still completely attached to the surface of the copper foil current collector. The force test level is 0, which means that the carbon conductive layer has excellent adhesion to the copper foil current collector.

As shown in Figure 6, it is a schematic diagram of the tensile test results of the carbon conductive layer formed on the current collector of the present invention. The tensile test results show that the tensile strength of the copper foil current collector with the carbon conductive layer is about 7.0 Kg _f , which is better than the 6.8 Kg _f of the copper foil without the carbon conductive layer. When the copper foil current collector of the conductive layer was bent at 180°, the carbon conductive layer did not peel off and no powder fell, indicating that the carbon conductive layer was tightly attached to the copper foil current collector. Afterwards, during the rolling process of the lithium battery electrode sheet, there will be no cracking or falling off.

In addition, the carbon-coated copper foil was immersed in polar and non-polar solvents and treated with ultrasonic vibration for 20 minutes. The results showed that there was no peeling in each solvent, and it remained the same after standing for eight months. The effect of solvent resistance is good. The adhesion performance of the carbon conductive layer on the copper foil current collector is good and there is no dissolution. Therefore, the type of battery slurry used for lithium batteries will not be selected because the carbon conductive layer is in the solvent. It will be stripped and limited.

Finally, as shown in Figure 7, it is a schematic diagram of the comparison of the conductivity test results between the current collector of the present invention and the conventional current collector. The conventional current collector (ie bare copper foil) and the current collector of the present invention (ie, a carbon conductive layer is formed on the surface of the current collector) were used to prepare pure carbon lithium ion batteries, and the two prepared The AC impedance of the lithium ion battery after 40 cycles at the initial and 1C rate. It can be seen from Figure 7 that the lithium ion battery made of the current collector of the present invention is compared with the lithium ion battery made of the conventional current collector. The battery has low battery internal resistance.

In summary, the carbon conductive layer and the preparation method thereof provided by the present invention disperse the carbon material, adhesive, guide agent and additive formula in a solvent, and mix and disperse by wet ball milling and ultrasonic vibration to obtain Conductive paste dispersed stably in solvent. The conductive paste is applied to the surface of the current collector to obtain the current collector formed with the carbon conductive layer. Applying the current collector to a lithium-ion battery can increase the adhesion between the subsequent battery slurry layer and the current collector to reduce shedding, and can also effectively reduce the internal resistance of the battery and improve the battery performance. In addition, the carbon conductive layer prepared by the preparation method of the carbon conductive layer provided by the present invention has good hydrophilicity, conductivity, high specific surface area, corrosion resistance and oxidation, thereby reducing the interface between the subsequent battery slurry layer and the current collector resistance. The carbon conductive layer will increase the contact area between the battery paste layer and the current collector on the surface of the current collector, so that the interaction between the battery paste layer and the current collector is strong, and avoid the battery paste layer from the current collector surface Falling off, during the charging and discharging process of the lithium battery, the battery slurry layer and the current collector will not be peeled off or the battery slurry layer will be dissolved.

Those skilled in the art should understand the various changes that can be made according to the embodiments of the present invention without departing from the spirit of the present invention. Therefore, it is obvious that the listed implementation modes are not intended to limit the present invention, but are intended to cover the modifications made in the spirit and scope of the present invention under the definition of the scope of the appended application.

S01~S05‧‧‧Step

Claims (10)

A method for preparing a carbon conductive layer includes: providing a carbon material, an adhesive, a promoter, and an additive; dispersing the carbon material, the adhesive, the promoter, and the additive in a solvent; sequentially Provide a ball milling process and an ultrasonic vibration process, grind and mix the carbon material, the adhesive, the promoter, and the additive dispersed in the solvent to obtain a conductive slurry; add a coupling agent to the conductive slurry And the conductive paste is coated on a surface of a current collector to form a carbon conductive layer on the surface of the current collector. The method for preparing a carbon conductive layer as described in the first item of the patent application, wherein the carbon conductive layer has a thickness of 0.1 micrometer to 2 micrometers. According to the method for preparing a carbon conductive layer described in item 1 of the scope of patent application, the current collector coated with the carbon conductive layer has a tensile strength greater than 7.0 Kg _f . The method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, wherein the coupling agent is 3-aminopropyltriethoxysilane. The method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, wherein the coupling agent is selected from the group consisting of: alkyl silane coupling agent, amino silane coupling agent, alkenyl group Silane coupling agent, alkylene oxide silane coupling agent and alkyl acryloxy silane coupling agent. The method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, wherein relative to 100 parts by weight of the solid content in the conductive paste, the carbon material content is 5 to 85 parts by weight, and the adhesive content is 5 Parts to 50 parts by weight, the content of the guide agent is 1 part to 40 parts by weight, and the additive content is 1 part to 30 parts by weight. According to the method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, the carbon material can be selected from graphite or graphene. The method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, wherein the promoter can be selected from the group consisting of carbon nanofibers, carbon nanotubes, acetylene black, conductive carbon black and Flake graphite. The method for preparing a carbon conductive layer as described in item 1 of the patent application, wherein the adhesive can be selected from the group consisting of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), Styrene-butadiene rubber (SBR) and polyacrylic acid (PAA), and the additive is selected from the group consisting of sodium polyacrylate, sodium alkylbenzene sulfonate and sodium stearate. The method for preparing a carbon conductive layer as described in item 1 of the scope of patent application, wherein the solvent is selected from the group consisting of water, ethanol, N-methylpyrrolidone (NMP), toluene, and acetone.

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