KR20010084375A - Surface-treating composition of current collector for lithium secondary battery and surface-treating method using the same - Google Patents

Abstract

PURPOSE: A surface treatment composition of the collector for a lithium secondary battery and a surface treatment method using the composition are provided, to improve the ion conductivity, the lifetime of a battery, the energy density per weight and the volume energy density. CONSTITUTION: The composition comprises 0.5-2 wt% of an electrically conducting agent which is at least one metal oxide selected from the group consisting of tin oxide, tin oxide doped with indium, titanium oxide and antimony oxide; 1-5 wt% of a binder; 0.5-2 wt% of a dispersing agent; and a solvent. Preferably the binder is selected from the group consisting of Si(OR)4, Ti(OR)4, Sn(OR)4, Zr(OR)4 and their mixtures (wherein R is an alkyl group of C1-C4); the dispersing agent is acetyl acetone; and the solvent is alcohols, distilled water or their mixture. The method comprises the steps of washing a collector with an aqueous acid or base solution, washing it with distilled water and an organic solvent, and drying it; coating it with the composition; and heating it at a temperature of 100-200 deg.C.

Description

Surface treatment composition of current collector for lithium secondary battery and surface-treating method using the same

The present invention relates to a surface treatment composition of a current collector for a lithium secondary battery and a method of surface treatment using the same, and more particularly, the surface treatment of a current collector for a high capacity lithium secondary battery as well as improved high rate characteristics and lifetime. The present invention relates to a composition to be used and a surface treatment method of a current collector using the composition.

Lithium secondary batteries can be divided into lithium ion batteries using liquid electrolytes and lithium ion polymer batteries using solid electrolytes, depending on the type of electrolyte. As described above, since the lithium ion polymer battery uses a solid electrolyte, there is little risk of leakage of the electrolyte, and excellent workability can be obtained as a battery pack. It is light in weight, low in volume, and has a very small self-discharge rate. Due to these characteristics, lithium ion polymer batteries are not only safer than lithium ion batteries, but also easy to manufacture in square and large sized batteries.

On the other hand, a lithium secondary battery is usually made up including a cathode, a separator and an anode. In this case, the cathode and the anode are prepared by applying an active material composition on each current collector to form an active material layer. The cathodes, anodes and separators thus obtained are formed by laminating using heat or pressure.

According to the above method, the binding force of the active material layer to the current collector is weak, and the interface resistance between the current collector and the active material layer is increased, which causes various problems. In order to solve this problem, a method of forming a surface treatment film by coating a composition including a conventional binder and a conductive agent on both sides of the current collector, followed by drying and heat treatment.

As the conductive agent, a carbon material capable of forming a conductive network is used, and a conductive polymer is commonly used as a binder. By the way, according to this method, the electroconductive stain arises, the binding property of the binder in use decreases, and the electroconductivity partially falls, and the resistance polarization increases, causing the discharge capacity to fall at a predetermined discharge voltage. In addition, when the charge and discharge cycle is repeated, there is a problem that the initial irreversible capacity is large, so that the performance is degraded and the life is deteriorated. In particular, when a conductive polymer such as polyvinyl alcohol, polyvinylpyrrolidone, or the like is used as a binder, there is a problem in that the thickness of the surface treatment film is 10 to 30 μm, which is a limitation in increasing the capacity of the battery.

The technical problem to be solved by the present invention is to solve the above problems to improve the ion conductivity between the current collector and the active material layer to reduce the interface resistance, improve the binding force between the current collector and the active material layer to improve the battery life and at the same time surface treatment on the current collector It is to provide a surface treatment composition of an electrode current collector for a lithium secondary battery that can be reduced in thickness and high in capacity.

Another object of the present invention is to provide a method of surface treatment of a current collector using the surface treatment composition.

In order to achieve the first object, in the present invention, in the surface treatment composition of the electrode current collector for a lithium secondary battery comprising a conductive agent, a binder, a dispersant and a solvent,

The conductive agent is at least one metal oxide selected from the group consisting of tin oxide, indium tin oxide, titanium oxide and antimony oxide,

Provided is a surface treatment composition of an electrode current collector for a lithium secondary battery, the content of which is 0.5 to 2% by weight based on the total weight of the composition.

The second technical problem of the present invention, (a) washing the electrode current collector with an acid or base aqueous solution, washing with distilled water and an organic solvent, and then drying;

(b) coating on the cleaned current collector a surface treatment composition comprising at least one conductive agent, binder, dispersant and solvent selected from the group consisting of tin oxide, indium tin oxide, titanium oxide and antimony oxide Doing; And

(c) by the surface treatment method of the electrode current collector for a lithium secondary battery comprising the step of heat-treating the resultant at 100 to 200 ℃.

A feature of the present invention is to form a conductive layer containing a conductive agent such as tin oxide on the surface of the current collector to improve the binding force between the current collector and the active material layer and at the same time improve the electrical conductivity to reduce the interfacial resistance and lifespan of the battery To improve the characteristics.

The surface treatment composition of the electrode current collector of the present invention contains a tin oxide, titanium oxide, indium-doped tin oxide (ITO), a conductive agent selected from antimony oxide, a binder, a dispersant, and a solvent. The content of the conductive agent here is preferably 0.5 to 2% by weight based on the total weight of the composition.

Acetyl acetone, etc. are used as the dispersant, and the content thereof is a conventional level used in the surface treatment composition, and is preferably 0.5 to 2 wt% based on the total weight of the composition. And the binder is at least one selected from the group consisting of Si (OR) ₄ , Ti (OR) ₄ , Sn (OR) ₄ and Zr (OR) ₄ (wherein R is an alkyl group having 1 to 4 carbon atoms) In particular, it is preferable to use zirconium butoxide. And the content of the binder is preferably 1 to 5% by weight based on the total weight of the composition.

The solvent may be an alcohol solvent such as methanol, ethanol, isopropyl alcohol, distilled water, or a mixed solvent thereof.

Hereinafter, a method of surface treatment on an electrode current collector using the surface treatment composition according to the present invention will be described.

First, the current collector is washed with an acid or alkaline aqueous solution. In this case, when the current collector is an aluminum thin film which is a cathode current collector, it is washed with an aqueous alkali solution, for example, a 5% NaOH aqueous solution or a KOH aqueous solution, and when the current collector is a copper thin film as an anode current collector, an acid aqueous solution, for example For example, using 2M aqueous HCl solution. The current collector may be made of either a perforated metal foil or an extended metal foil.

Subsequently, the current collector washed with an acid or alkaline aqueous solution is washed with distilled water, and then further washed with an organic solvent such as acetone. The current collector thus washed is dried. At this time, the drying method is not particularly limited, but drying with air is common.

Separately, the surface treatment composition is prepared by mixing 0.5 to 2 wt% of a conductive agent, 1 to 5 wt% of a binder, 0.5 to 2 wt% of a dispersant, and the rest of the solvent based on the total weight of the surface treatment composition. do. Here, the mixing process of each of the above components is more effective in the ball mill (ball-mill).

Then, the obtained surface treatment composition is coated on both sides of the dried cathode current collector and the anode current collector, respectively, and then heat treated to complete the current collector having the surface treatment film formed on both surfaces. Here, the coating method of the surface treatment composition is not particularly limited, but a spray coating method is used.

The heat treatment process is to maintain a range of 100 to 200 ℃ using a hot air fan or lamp. At this time, when the heat treatment temperature exceeds 200 ° C., when the copper thin film is used as the current collector, the copper thin film is ductile, which is not preferable.

A cathode and an anode are manufactured by directly coating or casting each active material composition on the cathode current collector and the anode current collector obtained according to the above-described process. The separator and the anode thus obtained are interposed with a separator and then laminated with a silicon rubber material or a stainless hot roll. Subsequently, the resultant is subjected to an activation process, a tap welding process and a packaging process to complete a lithium ion battery or a lithium ion polymer battery.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

An aluminum foil surface having a thickness of 20 μm, which is a cathode current collector, was purified as follows. The aluminum foil was first immersed in 5% aqueous sodium hydroxide solution for 15 seconds and then washed with distilled water. It was then washed with acetone and then air dried.

Separately, 4 g of zirconium n-butoxide and 2 g of tin oxide were added to 2 g of acetyl acetone and 272 g of ethanol, and then mixed for 1 hour to prepare a surface treatment composition. The surface treatment composition was spray-coated to a thickness of 1-2 μm on the above-described aluminum thin film, and then dried at about 150 ° C. using a hot air blower to perform a surface treatment of the cathode current collector.

On the other hand, the anode current collector copper thin film was immersed in 2M HCl aqueous solution for 5 seconds, and then washed with distilled water. It was then washed with acetone and then air dried.

Thereafter, the surface treatment composition was spray-coated to a thickness of 1-2 μm on the copper thin film as in the case of the cathode, and then dried at about 150 ° C. using a hot air blower to perform surface treatment of the anode current collector.

The cathode active material composition and the anode active material composition were cast on the surface-treated aluminum thin film and the copper thin film, respectively, and dried to prepare a cathode and an anode. Here, the cathode active material composition was prepared by mixing 1000 g of LiMn ₂ O ₄ and 50 g of carbon black, and then adding a mixture of 123 g of polyvinylidene fluoride, 500 g of NMP, 700 g of acetone, and 230 g of dibutylphthalic acid to sufficiently mix the mixture. The anode active material composition was prepared by sufficiently mixing graphite 1000g, polyvinylidene fluoride 120g, NMP 500g, and acetone 700g.

Thereafter, the obtained cathode, anode and polymer electrolyte were laminated using a stainless hot roll. Subsequently, a lithium ion polymer battery was completed by impregnating the resultant with an organic electrolyte solution and going through an activation process, a tap welding process, and a packaging process.

Example 2

The preparation was carried out according to the same method as Example 1, except that ITO was used instead of tin oxide in preparing the surface treatment composition.

Comparative example

An aluminum thin film having a thickness of 20 μm was cut to an appropriate size, and the surface thereof was washed. Here, the method of cleaning the surface of the aluminum thin film is to first immerse the aluminum thin film in 5% NaOH aqueous solution for 15 seconds and then sequentially wash with distilled water and acetone. Then, it was dried using air.

The surface treatment composition was spray coated to a thickness of 10 to 15 μm on the cleaned aluminum thin film. Here, the surface treatment composition was prepared by mixing 10 g of polyvinyl alcohol, 5 g of SP black, and 0.2 g of a surfactant (triton, Aldrich) in a ball mill for 1 hour, and then adding 50 g of methanol and 50 g of distilled water thereto.

Separately, a copper thin film having a thickness of 20 μm was cut to an appropriate size, and the surface thereof was washed. Here, the method for cleaning the surface of the copper thin film is to first immerse the aluminum thin film in 2M HCl aqueous solution for 5 seconds and then sequentially wash with distilled water and acetone. Then, it was dried using air.

The surface treatment composition was spray-coated to a thickness of 10 to 15 mu m to the thin copper film cleaned according to the above-described method.

The cathode active material composition and the anode active material composition were cast on the surface-treated aluminum thin film and the copper thin film, respectively, and dried to prepare a cathode and an anode. Here, the cathode active material composition was prepared by mixing 1000 g of LiMn ₂ O ₄ and 50 g of carbon black, and then adding a mixture of 123 g of polyvinylene fluoride, 500 g of NMP, 700 g of acetone, and 230 g of dibutylphthalic acid to sufficiently mix the same. And the anode active material composition was prepared by sufficiently mixing graphite 1000g, polyvinylene fluoride 120g, NMP 500g, acetone 700g.

The resulting cathode, anode and polymer solid electrolyte were then laminated using a stainless hot roll. Subsequently, a lithium ion polymer battery was completed by impregnating the resultant with an organic electrolyte solution and going through an activation process, a tap welding process, and a packaging process.

Ion conductivity, high rate characteristics, and lifetime characteristics of the lithium ion polymer batteries prepared according to Examples 1-2 and Comparative Examples were measured.

As a result of the measurement, it was found that the lithium ion polymer battery prepared according to Example 1-2 has superior ion conductivity and high rate characteristics as compared with the case of the comparative example. This is because the interfacial resistance between the electrode plates is reduced by forming a tin oxide layer having excellent conductivity on both surfaces of the current collector. In addition, in the lithium ion polymer battery of Example 1-2, battery life was improved by improving the bonding strength of the active material layer to the current collector.

Meanwhile, the energy density per weight of the lithium ion polymer battery prepared according to Example 1-2 and Comparative Example was investigated.

As a result, the lithium ion polymer battery prepared according to Example 1-2 improved the weight energy density by 30% or more as compared with the case of the comparative example. As described above, the thickness of the surface treatment film according to Example 1-2 is 1-2 μm, which is greatly reduced compared to the comparative example (the thickness of the surface treatment film: 10-15 μm), thereby relatively having the cathode and anode plates. This is because the capacity increases.

According to the present invention, by coating a metal oxide having excellent conductivity on the surface of the current collector, the interface resistance between the current collector and the active material layer is reduced, thereby improving the ion conductivity and the high rate characteristic, and the binding force between the current collector and the active material layer is increased, thereby increasing the battery life. Is improved. In addition, the thickness of the conductive film formed on the surface of the current collector is reduced, so that the capacity of the cathode and anode plates is relatively increased, thereby improving the energy density per weight and the volume energy density.

Claims (9)

In the surface treatment composition of the electrode current collector for lithium secondary batteries containing a conductive agent, a binder, a dispersant and a solvent, The conductive agent is at least one metal oxide selected from the group consisting of tin oxide, indium-doped tin oxide, titanium oxide and antimony oxide, The content of the surface treatment composition of the electrode current collector for a lithium secondary battery, characterized in that 0.5 to 2% by weight based on the total weight of the composition. The method of claim 1, wherein the binder is selected from the group consisting of Si (OR) ₄ , Ti (OR) ₄ , Sn (OR) ₄ and Zr (OR) ₄ (where R is an alkyl group having 1 to 4 carbon atoms) One or more, The content of the surface treatment composition of the electrode current collector for a lithium secondary battery, characterized in that 1 to 5% by weight based on the total weight of the composition. The method of claim 1 wherein the dispersant is acetyl acetone, The content of the surface treatment composition of the electrode current collector for a lithium secondary battery, characterized in that 0.5 to 2% by weight based on the total weight of the composition. The surface treatment composition of an electrode current collector for a lithium secondary battery according to claim 1, wherein the solvent is alcohol, distilled water or a mixture thereof. (a) washing the electrode current collector with an acid or base aqueous solution, washing with distilled water and an organic solvent, and then drying; (b) coating on the cleaned current collector a surface treatment composition comprising at least one conductive agent, binder, dispersant and solvent selected from the group consisting of tin oxide, indium tin oxide, titanium oxide and antimony oxide Doing; And (c) a surface treatment method of an electrode current collector for a lithium secondary battery, comprising the step of heat-treating the resultant at 100 to 200 ° C. The surface treatment method of an electrode current collector for a lithium secondary battery according to claim 5, wherein the content of the conductive agent is 0.5 to 2% by weight based on the total weight of the composition. The method of claim 5 wherein the dispersant is acetyl acetone, The content is 0.5 to 2% by weight based on the total weight of the composition, the surface treatment method for an electrode current collector for a lithium secondary battery. The method of claim 5, wherein the binder is selected from the group consisting of Si (OR) ₄ , Ti (OR) ₄ , Sn (OR) ₄ and Zr (OR) ₄ (where R is an alkyl group having 1 to 4 carbon atoms) At least one or more, the content is 1 to 5% by weight based on the total weight of the composition, the surface treatment method for an electrode current collector for a lithium secondary battery. The surface treatment method for an electrode current collector for a lithium secondary battery according to claim 5, wherein the solvent is alcohol, distilled water or a mixture thereof.