KR20030047462A - Method for preparing electrode for battery - Google Patents

Abstract

PURPOSE: A method for preparing an electrode for a battery and a battery containing the electrode prepared by the method are provided, to improve the adhesive strength of an electrode and to reduce the amount of moisture and remaining solvent remarkably, thereby enhancing the properties of a battery. CONSTITUTION: The method comprises the steps of coating an electrode slurry comprising an active material, an electrode binder and an organic solvent onto a metal foil; and drying the coated one by irradiating a near infrared ray to the coated metal foil. Preferably the near infrared ray has a wavelength of 0.76-2.5 micrometers.

Description

Method for producing a battery electrode {METHOD FOR PREPARING ELECTRODE FOR BATTERY}

The present invention relates to a method for manufacturing a battery electrode, and more particularly, to an electrode having excellent adhesion, and to a method for manufacturing a battery electrode that can improve battery characteristics by dramatically reducing the moisture and residual solvent of the electrode.

Typical electrode coating processes for batteries include a binder, water, or an organic solvent such as NMP (N-methyl pyrrolidinone), acetone, DMA (dimethylacetamide), DMF (mimethylformaldehyde), or the like in a carbon or oxide active material. The mixed slurry is used. The slurry is applied onto the thin metal foil in an appropriate amount or thickness as it flows through the gap between the comma and the coating roll during die gap or roll coating. The applied slurry contains a solvent or a medium as described above, the solvent is evaporated during the drying (Drying) process.

In the electrode in the solid form in which the solvent is evaporated and left, residual moisture or residual solvent, which is contained in a solvent or an intermediate and remains after drying, remains. In general, a large amount of residual moisture or residual solvent in the electrode causes two major problems in the electrode.

First, the adhesion between the electrode and the foil is reduced. As the solvent evaporates, the binder component remaining in the solvent solidifies in a solid form and is positioned between the powder and the metal foil, and adhesion is generated as the residual solvent increases. The decrease in adhesion is one of the main reasons for the decrease in cell performance after assembling the cell.

Second, the residual moisture remaining in the electrode reacts with the electrolyte that is added while assembling the electrode to produce hydrofluoric acid. More hydrofluoric acid leads to unwanted electrode surface reactions, reducing cell performance.

Due to this problem, the drying process of the slurry is considered very important.

As a general method of drying the battery electrode, the following method is mainly used.

Hot air at an appropriate speed is blown up and down the coating electrode at an appropriate air volume. When hot air is introduced, the solvent in the slurry applied on the foil is evaporated due to the effect of reducing the volatilization point of the solvent and the heat applied.

However, since the drying method dried by hot air is caused by conduction of heat by heated guide rolls in the drying furnace and convection by heated air, drying proceeds from the surface of the slurry which is in contact with the hot air. The solvent inside the slurry evaporates as heat is introduced into the inside of the slurry. In practice, however, solvent evaporation on the surface occurs first, and the slurry viscosity on the surface increases as the solid content increases. As a result, when the solidification is completed, the internal solvent molecules are difficult to escape to the surface. Adhesion and residual moisture are increased.

Because of this problem, the general drying process is largely divided into two regions. The slurry-coated metal foil is led to a drying furnace maintained at about 100 to 120 ° C. This suppresses the rapid evaporation of solvent on the surface, allowing the internal solvent molecules to vaporize and flow out to the surface. Next, it is passed to a drying furnace which is maintained at 130 to 160 degrees. The reason why the temperature is increased is to evaporate the residual solvent inside the electrode by injecting high-speed hot air to allow heat to propagate to the inside. There is a disadvantage that the drying process becomes difficult depending on the solids content and the total volatilization amount of the slurry used. In addition, due to the internal solvent molecules that are quickly released, problems such as pinholes on the surface of the electrode and a crater shape defect (Deffect) are generated.

In view of the problems of the prior art, it is an object of the present invention to provide a method for manufacturing a battery electrode that can produce an electrode with excellent adhesion.

Another object of the present invention is to provide a method for producing a battery electrode that can improve battery characteristics by dramatically reducing the moisture and residual solvent of the electrode.

Still another object of the present invention is to provide a method for manufacturing a battery electrode, in which the drying time can be reduced in the method for manufacturing a battery electrode for producing an electrode by slurry coating.

In the present invention, in order to achieve the above object, in the method for manufacturing a battery electrode comprising the step of coating an electrode slurry containing an active material, an electrode binder, and an organic solvent on a metal foil and then drying,

The drying provides a method for manufacturing a battery electrode which is carried out by irradiating near infrared rays on a metal foil coated with an electrode slurry.

Hereinafter, the present invention will be described in detail.

The present invention is a method of manufacturing a battery electrode for producing an electrode by slurry coating, by applying a new drying method, to improve the adhesion of the electrode, and significantly reduce the residual amount of water and solvent after drying to ultimately improve the performance of the battery will be. That is, unlike the conventional method requiring a long drying time using conduction or radiation, the light penetrates deep into the slurry using light having high thermal energy. In this case, light with high thermal energy collides directly with the solvent molecules inside to vaporize the solvent molecules in an instant. Therefore, the evaporation is simultaneously performed on the surface and the inside, thereby increasing the adhesion between the binder and the metal foil.

This light energy is generated when using a near infrared (Near Infrared) of the wavelength of 30 ㎛ or less, more preferably 0.76 to 2.5 ㎛. The maximum temperature of the blackbody that can be reached in this wavelength range is 3811 K. In the present invention, when the near-infrared rays generated in the black body are irradiated with the solvent with a certain amount of visible light according to the kind of dry material and the total amount of volatilization, the solvent molecules are instantaneously vaporized.

The manufacturing method of the present invention is drying in the process of coating a battery electrode slurry containing an organic solvent, for example, N-Methyl-Pyrrolidinone (NMP) or water, as a solvent, when preparing a battery electrode. ) The effect is greatly improved.

The battery applied to the present invention

a) a carbon negative electrode such as graphite capable of inhaling and discharging lithium;

b) a positive electrode comprising a transition metal composite oxide such as lithium, manganese and cobalt capable of inhaling and discharging lithium;

c) binders such as PVDF (polyvinylidene fluoride), NBR (acrylonitrilebutadiene rubber), SBR (styrenebutadiene rubber) which provide a binding force between the active material of the positive electrode and the negative electrode;

d) conductive materials such as acetylene black and graphite for the purpose of improving conductivity; And

e) organic solvents such as NMP, acetone, DMA, DMF and inorganic solvents such as water

The electrode component of the lithium ion secondary battery.

The electrolyte of the lithium ion secondary battery uses an organic solvent having an aprotic in which lithium salts such as LiClO ₄ and LiPF ₆ are dissolved.

The active material used for the negative electrode capable of inhaling and discharging lithium is a carbon-based material selected from the group consisting of graphite, carbon fiber, and activated carbon. At this time, the negative electrode includes a binder, preferably PVDF, SBR in addition to the negative electrode active material.

As the active material of the positive electrode, a lithium transition metal composite oxide represented by Chemical Formula 1 may be used.

[Formula 1]

Li _x MO ₂

In Chemical Formula 1, M is Ni, Co, or Mn, and x is 0.05 ≦ x ≦ 1.10.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

(Manufacture of Cathode)

SBR and CMC were mixed with a carbon powder, a binder, and a thickener in a weight ratio of 95: 4: 1, and then dispersed in water to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was uniformly coated with a comma gap of 200 μm on a cross section of a Cu foil having a thickness of 10 μm using a negative electrode current collector, and then injected into a module generating near infrared rays. The length of the module was 15 cm and the coating speed was 3 m / min. The content of near infrared ray was 20%, and the surface temperature of the electrode measured by the infrared sensor was 60 ° C.

The dried electrode was sampled to measure moisture with a Metroohm Karl Fischer moisture meter. In the moisture measurement conditions, an electrode sample was placed in an oven set to 150 ° C on a Karl Fischer measuring instrument, and the measurement time was 2 hours.

Adhesion was measured using an adhesion tester manufactured by the method of ASTM D4541. The electrode was cut into an area of 25 cm 2, and the result of measuring adhesion by the method of ASTM D4541 is shown in Table 1 below.

(Manufacture of Anode)

A positive electrode mixture slurry was prepared by adding 92 wt% of lithium cobalt composite oxide, 4 wt% of carbon as a conductive material, and 4 wt% of PVDF as a binder to NMP as a solvent. The positive electrode mixture slurry was applied to an Al thin film of a positive electrode current collector having a thickness of 20 μm. NMP was dried by setting the near infrared ray to 20% and the visible ray to 80%.

Residual moisture and adhesion were measured as with the negative electrode.

Residual NMP measured the amount of NMP, raising the temperature to 200 degreeC.

Thereafter, compression molding was performed using a roll press to prepare a strip-shaped anode.

(Production of battery)

Porous polyethylene film was used as a separator, and the strip-shaped cathode and the strip-shaped anode were laminated and wound several times to prepare a jelly roll. The length and width were adjusted so that it was properly embedded in a battery can having an outer diameter of 18 mm and a height of 65 mm. The manufactured jelly roll was accommodated in a battery can, and the insulating plate was arrange | positioned on the upper and lower surfaces of the electrode element. Then, a negative electrode lead made of nickel was drawn from the current collector and welded to the battery can, and a positive electrode lead made of aluminum was drawn from the positive electrode current collector, and welded to an aluminum pressure release valve mounted on the battery cover to manufacture a battery. The electrolyte solution impregnated into this battery was injected. LiPF ₆ solution was used as a solvent and electrolyte in which EC and EMC were mixed in a volume ratio of 1: 2.

The battery thus prepared was charged to 4.2 V at a constant current of 0.4 mA / cm 2. The standard capacity of the electrolyte secondary battery was 1000 mAh, and a charge and discharge cycle was conducted at a rate of 1 C (1000 mA / h) with constant current from 4.2 V to 3 V.

Example 2

A battery was manufactured in the same manner as in Example 1, except that the near-infrared content was 30% and the surface temperature was 70 ° C. when the negative electrode and the positive electrode were manufactured.

Example 3

A battery was manufactured in the same manner as in Example 1, except that the near-infrared content was 60% and the surface temperature was 80 ° C. when the negative electrode and the positive electrode were manufactured.

Comparative Example 1

(Manufacture of Cathode)

A negative electrode was manufactured in the same manner as in Example 1, but the drying method was hot air. The temperature of the drying furnace is set at 40 ℃ in the first drying section of 3 m length for each section, and 70 ℃ for the second drying section at 3 m, and the wind speed is 10 m / min for the first drying section and 20 m for the second drying section. The speed was set at / min.

At this time, the dried electrode was sampled to measure moisture with a Metro Ohm Karl Fischer moisture meter. In the moisture measurement conditions, an electrode sample was placed in an oven set at 250 ° C. on a Karl Fischer measuring instrument, and the measurement time was 2 hours.

Adhesion was measured using an adhesion tester manufactured by the method of ASTM D4541. The electrode was cut into an area of 25 cm 2, and the result of measuring adhesion by the method of ASTM D4541 is shown in Table 1 below.

(Manufacture of Anode)

A positive electrode was prepared in the same manner as in Example 1, but drying was performed by setting the drying conditions of the negative electrode.

Measurement of physical properties also measured the residual moisture, residual NMP and adhesion as in the negative electrode.

(Production of battery)

The battery was manufactured in the same manner as in Example 1, using the negative electrode and the positive electrode prepared above.

Comparative Example 2

In the same manner as in Comparative Example 1, the drying conditions of the negative electrode and the positive electrode was set to 50 ℃ in the primary drying section, the secondary drying section of 3 m to 80 ℃.

Comparative Example 3

In the same manner as in Comparative Example 1, the drying conditions of the negative electrode and the positive electrode was set to a secondary drying section of 70 ℃, 3 m in the primary drying section to 100 ℃.

Comparative Example 4

In the same manner as in Comparative Example 1, but the drying conditions of the negative electrode and the positive electrode was set to a secondary drying section of 90 ℃, 3 m in the first drying section to 120 ℃.

Comparative Example 5

In the same manner as in Comparative Example 1, but the drying conditions of the negative electrode and the positive electrode was set to 110 ℃, the secondary drying section of 3 m in the primary drying section to 140 ℃.

Table 1 below compares the electrode moisture and the amount of change in electrode moisture and residual solvent according to the content of near-infrared rays used with the comparative example using a conventional hot air drying method.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Drying condition NIR 20% Near Infrared NIR 30% Near Infrared NIR 60% Hot air 40/70 ℃ Hot air 50/80 ℃ Hot air 70/100 ℃ Hot air 90/120 ℃ Hot air 110/140 ℃ Cathode Residual Water (ppm) 405 207 105 1537 1510 1305 1210 1265 Anode Residual NMP (ppm) 60 52 40 250 227 170 130 90 Adhesive strength (g) 800 860 900 50 150 380 350 400

In the electrode manufacturing method of the present invention, the slurry is dried using near-infrared rays, so that the adhesion of the electrode is excellent, and the moisture and residual solvent of the electrode can be drastically reduced, so that the battery characteristics of the battery are greatly improved.

Claims (4)

In the method of manufacturing a battery electrode comprising the step of coating an electrode slurry containing an active material, an electrode binder, and an organic solvent on a metal foil and then drying, The drying is a method of manufacturing a battery electrode that is carried out by irradiating near infrared rays on a metal foil coated with an electrode slurry. The method of claim 1, The near infrared ray has a wavelength of up to 30 ㎛ method for producing a battery electrode. The method of claim 1, The near-infrared ray has a wavelength of 0.76 to 2.5 μm. A battery comprising an electrode produced by the method of claim 1.