KR20010001828A - Preparation of electrodes for secondary lithium batteries - Google Patents

Abstract

PURPOSE: An electrode manufacturing method for a lithium secondary cell is provided to enhance adhering force between a current collecting layer and an activating layer while protecting a deposited metal layer from damage. CONSTITUTION: An electrode for a lithium secondary cell is manufacture by compounding a current collecting material with an electrode active material. A carbon or plastic fiber mesh deposited with a conductive metal is used. The carbon or plastic fiber mesh is used as coated with a conductive metal. The surface of the current collecting material is coated for a pretreatment with a slurry in which a binder resin and conductive particles are dispersed into an organic solvent. The plastic fiber includes polyethylene, polypropylene and polyester. The conductive metal includes copper, aluminium, nickel or stainless steel. The conductive metal coating can be performed via a vacuum deposition.

Description

Manufacturing method of electrode for lithium secondary battery {Preparation of electrodes for secondary lithium batteries}

The present invention relates to a method for manufacturing an electrode for a lithium secondary battery, and more particularly, using a conductive metal deposited on a surface of carbon fiber or plastic fiber as a current collector for an electrode, and before the active material is bonded to the current collector, It relates to a method characterized in that the coating with an organic solvent slurry containing a binder resin and conductive particles.

Lithium secondary batteries are roughly classified into lithium ion batteries and lithium polymer batteries. Lithium ion batteries are porous polyethylene and polypropylene which are placed between two electrodes as separators and filled with a liquid electrolyte, and lithium polymer batteries are used as separators. The polymer membrane is in the form of absorbing liquid electrolyte or having ionic conductivity on its own.

Electrodes used in the lithium battery are usually manufactured by bonding an active material to a current collector made of a conductive metal such as nickel, aluminum, copper, or stainless steel foil or a mesh, and they are disposed between the active material layer and the current collector due to the weight of the metallic current collector. As the charge and discharge cycle of the battery is low due to low adhesive strength, there is a problem that the active material layer is gradually peeled from the current collector layer by the expansion and contraction of the active material layer, thereby losing the characteristics of the battery. In particular, in the case of a prismatic lithium ion battery and a polymer battery that do not receive relatively uniform pressure from the case of the battery, such adhesion is very important.

In order to solve the above problem, a method of using a metal coated carbon or graphite fiber net as a current collector has been proposed (see US Pat. No. 5,747,195). However, this method also did not provide satisfactory adhesion between the current collector and the active material.

On the other hand, in order to improve the adhesive force of the metal current collector with the electrode active material layer, a method of etching using the current collector surface as an acid or an alkaline solution has been used. However, applying this method to the metal-coated carbon fiber net is undesirable since the deposited metal film may be damaged.

Therefore, the present inventors have studied diligently to improve the adhesion between the current collector layer and the active material layer, and as a current collector layer of the electrode, a carbon fiber or plastic fiber deposited with metal is used, but before the current collector and the active material are combined, The present invention was completed by finding that the entire surface was pretreated with conductive particles and a binder resin-containing slurry to improve adhesion between the current collector layer and the active material layer, thereby improving battery characteristics.

Accordingly, it is an object of the present invention to provide a method of manufacturing an electrode which is particularly useful for use in a lithium secondary battery because the adhesion between the current collector layer and the active material layer is light and improved.

1 is a graph comparing discharge characteristics according to the number of cycles of a lithium polymer secondary battery including an electrode manufactured by using a pretreated current collector and an unpretreated current collector according to the present invention.

Figure 2 is a graph comparing the discharge characteristics according to the discharge ratio of the lithium polymer secondary battery including an electrode prepared using a pre-treated current collector and a pre-treated current collector according to the present invention.

In order to achieve the object of the present invention, in the present invention, in the manufacture of an electrode for a lithium secondary battery by bonding the electrode active material to the current collector, as the current collector, a carbon fiber or a plastic fiber mesh coated with a conductive metal is coated. And pretreating the current collector surface with a slurry in which binder resin and conductive particles are dispersed in an organic solvent before bonding with the active material.

Hereinafter, the present invention will be described in more detail.

According to the present invention, the current collector is used by coating a carbon fiber or plastic fiber mesh with a conductive metal. Specific examples of plastic fibers include polyethylene, polypropylene, polyester, and the like, and examples of conductive metals include copper, aluminum, nickel, or stainless steel, with copper and aluminum being preferred. Coating of the metal component can be carried out by vacuum deposition.

According to the present invention, the pretreatment is performed before the current collector is combined with the active material, which is carried out by coating the surface of the current collector using a slurry in the organic solvent of the conductive particles and the binder resin.

The conductive particles used in the present invention may be aluminum powder, copper powder and conductive carbon powder having an electrical conductivity of about 10 ⁻² S / cm or more, for example, acetylene black and graphite. In addition, the binder resin used in the slurry is fluorinated alkanes such as polyvinylidene fluoride (PVDF), copolymers of PVDF and polytetrafluoroethylene (PTFE), and polyalkanes and polyalkenes having excellent adhesion to metals. , Polyacrylates, styrene-butadiene copolymers or copolymers thereof.

The slurry for pretreatment according to the present invention is prepared by dispersing the conductive particles and the binder resin in an organic solvent, and N-methylpyrrolidone (NMP) is most preferable as the organic solvent. The concentration of the conductive particles and the binder resin in the slurry is preferably 10 to 70 g / l and 20 to 150 g / l, respectively.

According to the present invention, the slurry is coated on the surface of the current collector so as to have a dry thickness of 0.1 to 20 μm, preferably 0.5 to 2 μm.

The current collector pretreatment process according to the present invention can be usefully applied even when the conductive metal fiber mesh is used as the current collector substrate, not the carbon fiber or plastic fiber on which the conductive metal is deposited.

A battery electrode may be manufactured by coating or laminating an electrode active material on a pretreated current collector in a conventional manner, and may fabricate a lithium secondary battery by laminating these electrodes with a separator. .

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Pretreatment of current collector

Example 1

Both sides of the carbon fiber mesh sheet were coated to a thickness of 3500 kPa of copper by vacuum deposition or sputtering. On the other hand, the dispersion which disperse | distributed 5 g of acetylene black (50% compression | made by Chevron company) in the solution which melt | dissolved 20 g of PVDF (Kynar 461 by Elf Atochem) in 180 g of NMP was prepared. The dispersion prepared above was coated on the coated carbon fiber mesh sheet and dried under vacuum at 80 ° C. for about 2 hours to prepare a carbon fiber current collector pretreated with a coating thickness of 1 μm.

Example 2

A carbon fiber current collector pretreated with a coating thickness of 1 μm was prepared using a solution in which styrene-butadiene copolymer (manufactured by Zeon, Japan) was dissolved in 207 g of NMP instead of PVDF. It was.

Preparation of the electrode

Example 3

250 g of dibutyl phthalate (DBP) (Aldrich), 900 g of lithium cobalt oxide (LiCoO ₂ ) (Similar C012, Japan) and a solution of 167 g of PVDF copolymer (Solef 21216) dissolved in 2,500 g of acetone A positive electrode paste was prepared by dispersing 5 g of acetylene black (50% compression, manufactured by Chevron). The obtained paste was cast on one side of the pretreated current collector obtained in Example 2, dried at 100 ° C. for 20 minutes, then cast again on the other side of the current collector and dried, and then pressed using a roller. By cutting, a positive electrode for a lithium ion battery having a final paste thickness of 135 μm was prepared.

In addition, 1,000 g of graphite (MCMB 25-28, manufactured by Osaka Gas, Japan) with a grain size of 25 μm and heat treated at 2800 ° C. was combined with 40 g of acetylene black (50% compression made by Chevron) and 300 g of DBP. (Solef 21216) 250 g was added to a solution dissolved in 2,500 g of acetone and mixed, which was cast on one side of the pretreated current collector obtained in Example 2, dried at 100 ° C. for 20 minutes, and then the other one of the current collector. After casting back to the cotton, dried, and then compressed using a roller and cut to prepare a negative electrode for a lithium ion battery with a final paste thickness of 155 μm.

Comparative Example 1

In the same manner as in Example 3, instead of the carbon fiber current collector obtained in Example 2, + and-electrodes were prepared using a carbon fiber current collector that was not pretreated.

Manufacture of lithium battery

150 g of silica (Aldrich) and 430 g of DBP were added to 3,000 g of acetone in which 300 g of PVDF copolymer (Solef 21216) was dissolved, mixed, and then coated on a polyester film (SKC) to form a membrane having a thickness of 75 μm. Prepared.

The + and − electrodes prepared according to Example 3 or Comparative Example 1 were laminated with the separator, the DBP was extracted with methanol, dried and placed in a plastic battery case, and the electrolyte [ethyl carbonate (EC) / dimethyl carbonate was placed in the battery case. A lithium secondary battery was manufactured by injecting and sealing 1M-LiPF ₆ ] in a 1/1 mixture of (DMC).

Discharge characteristics change according to the cycle number and discharge ratio (c-rate) of the two lithium secondary batteries thus prepared were measured and shown in FIGS. 1 and 2, respectively (in FIGS. 1 and 2, a is a pretreatment according to the present invention). And b is the result of using an unpretreated current collector).

1 and 2 it can be seen that the battery characteristics of the lithium secondary battery is significantly improved when the current collector is used in accordance with the present invention.

According to the present invention, a carbon fiber or a plastic fiber mesh coated with a conductive metal is deposited as a current collector of an electrode used in a battery, and a binder and conductive particles are dispersed on the surface of the current collector before bonding the current collector and the active material. It is possible to provide a lithium secondary battery having improved battery characteristics by coating and pre-treated with the slurry.

Claims (6)

In a method of manufacturing an electrode for a lithium secondary battery by bonding an electrode active material to a current collector, a carbon fiber or plastic fiber mesh coated with a conductive metal is deposited as a current collector, and the surface of the current collector is binder before bonding with the active material. Resin and conductive particles are coated with a slurry dispersed in an organic solvent to be pretreated. The method of claim 1, The conductive metal is copper or aluminum. The method of claim 1, The conductive particles are aluminum powder, copper powder, acetylene black powder or graphite powder. The method of claim 1, Characterized in that the binder resin is polyvinylidene fluoride (PVDF), copolymer of PVDF and polytetrafluoroethylene (PTFE), polyalkane, polyalkene, polyacrylate, styrene-butadiene copolymer or a combination thereof Way. The method of claim 1, And the concentration of the conductive particles and the binder resin in the slurry is 10 to 70 g / l and 20 to 150 g / l, respectively. The method of claim 1, The slurry is coated with a dry coating thickness in the range of 0.1 to 20 μm.