JP2006302553A - Manufacturing method of lithium secondary battery cathode plate, and lithium secondary battery using the cathode plate manufactured by the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a cathode plate is cut at neighboring area of innermost circumference of an electrode plate group where radius of curvature becomes small because flexibility of the cathode plate is sharply reduced, in the case of using LiNi<SB>x</SB>Mn<SB>y</SB>Co<SB>(1-x-y)</SB>O<SB>2</SB>as a cathode activator in exchange for LiCoO<SB>2</SB>. <P>SOLUTION: The manufacturing method of the lithium secondary battery cathode plate formed by painting a paste for the cathode plate prepared by kneading and dispersing a lithium-containing nickel complex oxide as a cathode activator, a binder, and a carboxymethyl cellulose having ammonium salt as functional group on a current collector, and by drying and rolling the paste comprises a process of forming a cathode plate precursor by applying the paste for cathode plate on the current collector, a process of drying the cathode plate precursor, and a process of rolling the cathode plate precursor after drying. The cathode plate precursor is dried at a temperature of 300 to 500°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in a lithium secondary battery, particularly its positive electrode plate.

  In recent years, as batteries used in portable electronic / communication equipment such as mobile phones and laptop computers, carbon materials capable of occluding and releasing lithium ions are used as negative electrode active materials, and lithium-containing cobalt is used as a lithium transition metal composite oxide. From the oxide, a lithium secondary battery using a positive electrode active material such as lithium-containing nickel oxide as a positive electrode active material has been put into practical use for the purpose of higher capacity.

_{LiNi x Mn y Co (1-} xy) O 2 as the lithium-containing nickel oxide, a conductive material acetylene black, and an aqueous solution of carboxymethyl cellulose sodium salt was a functional group, and the binder is added, a paste. The positive electrode plate paste is applied to an aluminum foil serving as a current collector, dried, and then rolled to a predetermined density. In this way, a positive electrode plate is produced. The positive electrode plate and the negative electrode plate are wound in a spiral shape through a separator to produce an electrode plate group. The electrode plate group thus produced is placed in a bottomed case, and a non-aqueous electrolyte is injected. The opening of the bottomed case and the sealing plate are sealed by caulking through an insulating gasket to form a lithium secondary battery.

Regarding the improvement of the thickening material in the paste for the negative electrode plate of the lithium secondary battery, it has been proposed to improve the adhesion by using carboxymethylcellulose having an ammonium salt as a functional group as the thickening material. In addition, it is proposed that lithium-containing cobalt oxide is used as a positive electrode active material, carboxymethyl cellulose having an ammonium salt as a functional group is used as a thickener for a positive electrode plate paste, and the positive electrode plate is dried at 200 to 300 ° C. (For example, refer to Patent Document 1).
JP-A-11-162451

However, a conventional positive electrode plate uses lithium-containing cobalt oxide (hereinafter abbreviated as LiCoO ₂ ) as a positive electrode active material, and carboxymethyl cellulose (hereinafter referred to as a functional group) having an ammonium salt as a functional group as a thickener for a positive electrode plate paste. , NH ₃ -CMC), and the positive electrode plate is dried at 200 to 300 ° C. Under these drying conditions, NH ₃ -CMC remains as a residue. Thus, even if NH ₃ —CMC remained as a residue, there was no problem in the flexibility of the positive electrode plate when LiCoO ₂ was used as the positive electrode active material.

However, when using _{LiNi x Mn y Co (1-} xy) O 2 as a positive electrode active material with the high capacity, may become hard and positive electrode plate due to the shape of the active material, the positive electrode plate high Due to the densification, voids inside the positive electrode plate are reduced, and there is a problem that the flexibility of the positive electrode plate is remarkably lowered as compared with LiCoO ₂ .

  Therefore, there is a problem that the positive electrode plate is cut near the innermost periphery of the electrode plate group having a small radius of curvature.

Even if a lithium secondary battery is manufactured using a plate group in which the positive electrode plate was not cut, the radius of curvature decreases near the innermost circumference of the plate group during the winding process of the lithium secondary battery. There was a problem in that the production yield was significantly reduced.

  Further, there is a problem that even after the battery is constructed, the positive electrode plate is cut near the innermost periphery of the electrode plate group in which the radius of curvature decreases due to expansion and contraction of the positive electrode plate due to charge and discharge. Accordingly, there is a problem that the function of the lithium secondary battery is lost.

  The present invention solves such a conventional problem, and the positive electrode plate is not cut in the vicinity of the innermost periphery of the electrode plate group having a small radius of curvature, and the lithium secondary battery is excellent in productivity and battery characteristics. A method for producing a positive electrode plate for use is provided.

In order to solve the conventional problem, a method for producing a positive electrode plate for a lithium secondary battery according to the present invention includes:
A paste for a positive electrode plate in which a lithium-containing nickel composite oxide as a positive electrode active material, a binder, and carboxymethyl cellulose having an ammonium salt as a functional group as a thickener are kneaded and dispersed in a dispersion medium, In the method for producing a positive electrode plate for a lithium secondary battery obtained by coating, drying and rolling on
A positive electrode plate paste obtained by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and carboxymethyl cellulose having the ammonium salt as a functional group as a thickener in the dispersion medium. Manufacturing process;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
A method for producing a positive electrode plate for a lithium secondary battery comprising a step of rolling the positive electrode plate precursor, followed by rolling,
It is a manufacturing method of the positive electrode plate for lithium secondary batteries which performs the said drying at the temperature of 300 to 500 degreeC.

The method for producing a positive electrode plate for a lithium secondary battery in another invention is as follows:
A positive electrode plate paste obtained by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and carboxymethyl cellulose having the ammonium salt as a functional group as a thickener in the dispersion medium. Manufacturing process;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
After drying the positive electrode plate precursor,
In the method for producing a positive electrode plate for a lithium secondary battery, the drying is performed at a temperature equal to or higher than a gasification temperature of a functional group of carboxymethylcellulose having the ammonium salt as a functional group and equal to or lower than an oxidative decomposition temperature of a thickener skeleton. .

  By using an aqueous solution of carboxyl methyl cellulose having an ammonium salt as a functional group as a thickener, the ammonium salt, which is a functional group, disappears as ammonia gas by drying, so that the positive electrode plate remains flexible without becoming locally hard. Therefore, the productivity of the electrode plate group and the lithium secondary battery can be drastically improved.

  According to the present invention, the positive electrode plate is not cut in the vicinity of the innermost circumference of the electrode plate group having a small radius of curvature, and the deterioration of the charge / discharge capacity and the deterioration of the load characteristics can be suppressed to a very low level even after repeated charge / discharge. it can. Further, since the flexibility of the positive electrode plate can be maintained, the positive electrode plate is not cut during the assembly process of the lithium secondary battery, and the productivity can be improved.

The method for producing a positive electrode plate for a lithium secondary battery according to the present invention includes a lithium-containing nickel composite oxide as a positive electrode active material, a binder, and a carboxymethyl cellulose having an ammonium salt as a functional group (hereinafter referred to as NH _3). In the method for producing a positive electrode plate for a lithium secondary battery, the paste for positive electrode plate obtained by kneading and dispersing in a dispersion medium is applied to a current collector, dried and rolled.
A step of preparing a positive electrode plate paste by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and the NH ₃ —CMC as the thickener in the dispersion medium;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
A method for producing a positive electrode plate for a lithium secondary battery comprising a step of rolling the positive electrode plate precursor, followed by rolling,
It is a manufacturing method of the positive electrode plate for lithium secondary batteries which performs the said drying at the temperature of 300 to 500 degreeC.

A lithium-containing nickel composite oxide as a positive electrode active material, a conductive material, a binder, and an aqueous solution in which NH ₃ -CMC is dissolved as a thickener are simultaneously blended, mixed and dispersed to prepare a positive electrode plate paste. .

The binder is not particularly limited as long as it can be mixed and dispersed in the dispersion medium. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber, acrylic polymer, vinyl A polymer or the like can be used alone or as a mixture or copolymer of two or more. As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, and a dispersion of polytetrafluoroethylene resin are preferable.

The application method is not particularly limited. Mixed and dispersed positive electrode plate paste,
For example, using a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc.
Can be painted.

The current collector is preferably, for example, an aluminum foil or a foil subjected to lath processing or etching.

  The drying conditions will be described below.

NH ₃ group which is a functional group of thickeners NH _3-CMC has remained remained as positive electrode residues in the plate, positive electrode plate can no longer be maintained firmly becomes flexibility locally. Further, when a battery is produced using the positive electrode plate, ammonium gas resulting from NH ₃ groups is generated when the charge / discharge cycle is repeated or stored at a high temperature. As a result, the charge / discharge cycle and high-temperature storage characteristics deteriorate. Therefore, the NH ₃ group which is a functional group of thickeners NH _3-CMC is gasified in the drying step, the positive electrode must be such not to leave as a residue in the plate.

It is necessary to dry at 300 ° C. or higher as a temperature for gasifying the NH ₃ group that is a functional group of the thickener NH ₃ -CMC. When the drying temperature is higher than 500 ° C., the skeleton portion of the thickener is oxidatively decomposed, and part of it is carbonized and hardened, so the flexibility in the positive electrode plate decreases, and as a result, the positive electrode plate becomes brittle. It becomes. From the above, the drying temperature is preferably 300 to 500 ° C.

By doing so, the productivity of the electrode plate group and the battery can be drastically improved.

  The drying time is preferably 5 to 10 minutes.

As a rolling method, it is preferable to perform rolling several times with a roll press until a predetermined thickness is reached, or to change the pressing pressure.

  The positive electrode plate preferably has a thickness of 0.11 to 0.20 mm and is flexible.

In another embodiment of the present invention, a method for producing a positive electrode plate for a lithium secondary battery,
A step of preparing a positive electrode plate paste by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and NH ₃ -CMC as the thickener in the dispersion medium;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
After drying the positive electrode plate precursor,
In the method for producing a positive electrode plate for a lithium secondary battery, the drying is performed at a temperature not lower than the gasification temperature of the functional group of NH ₃ -CMC and not higher than the oxidative decomposition temperature of the thickener skeleton.

NH ₃ group which is a functional group of thickeners NH _3-CMC has remained remained as positive electrode residues in the plate, positive electrode plate can no longer be maintained firmly becomes flexibility locally. for that reason,
The NH ₃ group which is a functional group of thickeners NH _3-CMC is gasified in the drying step, the positive electrode must be such not to leave as a residue in the plate. Therefore, by drying at a temperature higher than the temperature at which the functional group portion of NH ₃ —CMC that is a thickener can be eliminated, the NH ₃ group that is a functional machine is not left as a residue in the positive electrode plate. it can.

Further, when the skeleton of the thickener is dried at a temperature that causes oxidative decomposition, a portion of the thickener hardens due to carbonization, and as a result, the positive electrode plate becomes brittle. Therefore, it must be dried at a temperature below the temperature at which the skeleton of the thickener is oxidatively decomposed.

From the above, the drying temperature must be dried at a temperature equal to or higher than the disappearance temperature at which the functional group portion of NH ₃ -CMC, which is a thickening material, can be lost, and lower than the oxidative decomposition temperature of the skeleton portion. .

By doing so, the productivity of the electrode plate group and the battery can be drastically improved.

The lithium secondary battery using this positive electrode plate can suppress deterioration of charge / discharge capacity and load characteristics when using repeated charge / discharge.

The electrode plate group is produced by winding the positive electrode plate 5 and the negative electrode plate 6 in a spiral shape with a separator 7 interposed therebetween. Such an electrode plate group is inserted into the bottomed battery case. A non-aqueous electrolyte is injected into the electrode plate group inserted into the bottomed electric case.

The positive electrode lead 3 is connected to the positive electrode plate 5 by welding, and the negative electrode lead 9 is connected to the negative electrode plate 6 by welding. An upper insulating plate 4 is disposed at the upper end of the electrode plate group, and a lower insulating plate 10 is disposed at the lower end of the electrode plate group. The opening of the bottomed battery case 8 and the sealing plate 1 are sealed by caulking through an insulating gasket 2. In this way, a cylindrical lithium secondary battery having a diameter of 17 mm and a height of 50 mm is produced.

This negative electrode plate paste was applied to both sides of a 15 μm thick copper foil as a current collector using a die coater. Then, after drying at a predetermined temperature, the sheet was rolled to a thickness of 0.2 mm, cut to a predetermined dimension, and a sheet-like negative electrode plate 6 was produced.

The non-aqueous electrolytic solution was prepared by mixing 1 mol / liter of lithium hexafluorophosphate (hereinafter abbreviated as LiPF ₆ ) as an electrolyte salt in a non-aqueous solvent obtained by mixing 30 vol% ethylene carbonate, 50 vol% diethyl carbonate, and 20 vol% methyl propionate. It is dissolved so as to have a concentration of L.

The bottomed battery case 8 is made of a stainless steel plate having an electrolytic solution resistance, and this stainless steel plate is formed by deep drawing.

Example 1
_{LiNi x Mn y Co (1-} xy) O 2 powder (X = Y = 0.33) 50 parts by weight as a positive electrode active material, acetylene black as a conductive material (hereinafter, referred to as AB) and 1.5 parts by weight, 7 parts by weight of a dispersion solution containing 50 parts by weight of polytetrafluoroethylene (hereinafter abbreviated as PTFE) as a binder and 41.5 parts by weight of an aqueous solution containing 1 part by weight of NH ₃ -CMC are mixed and dispersed. Thus, a positive electrode plate paste was prepared.

This positive electrode plate paste was used as a current collector for aluminum having a thickness of 20 μm (hereinafter referred to as Al
It was applied on both sides of the foil using a die coater.

Then, after drying at a predetermined temperature, the positive electrode plate was dried at 300 ° C., which is a temperature at which the functional group portion of NH ₃ —CMC gasifies and disappears, for 10 minutes.

Then, it rolled so that it might become thickness 0.17mm, and cut | disconnected to the predetermined dimension, and the sheet-like positive electrode plate 5 was produced.

The positive electrode plate 5 produced in this manner was used as an example positive electrode plate 1, and a battery using the positive electrode plate 5 was used as an example battery 1.

(Example 2)
In the production of the positive electrode plate, the positive electrode plate obtained by the same production method as in Example 1 was used as Example positive electrode plate 2 except that the drying temperature after coating was set to 400 ° C., and a battery using the same was used. Example battery 2
It was.

(Example 3)
In the production of the positive electrode plate, the positive electrode plate obtained by the same production method as in Example 1 was used as Example positive electrode plate 3 except that the drying temperature after coating was 500 ° C. Example battery 3
It was.

(Comparative Example 1)
In the production of the positive electrode plate, the positive electrode plate obtained by the same production method as in Example 1 was compared except that carboxymethyl cellulose having a sodium salt as a functional group (hereinafter abbreviated as Na-CMC) was used as a thickener. An example positive electrode plate 1 was used, and a battery using the same was used as a comparative example battery 1.

(Comparative Example 2)
In the production of the positive electrode plate, a positive electrode plate obtained by the same production method as in Example 1 was used as a comparative positive electrode plate 2 except that the drying temperature after coating was 200 ° C., and a battery using this was compared. An example battery 2 was obtained.

(Comparative Example 3)
In the production of the positive electrode plate, a positive electrode plate obtained by the same production method as in Example 1 was used as a comparative positive electrode plate 3 except that the drying temperature after coating was set to 600 ° C., and a battery using this was compared. Example battery 3
It was.

A bending test was performed on the positive electrode plates 1 to 3 and the positive electrode plates 1 to 3 of the comparative example thus obtained.

  The method of the bending test is as follows.

A positive electrode plate having a width of 30 mm and a length of 100 mm was used for the test. A round bar having a diameter of 2 mm was disposed along the width direction of the positive electrode plate. The bending was repeated 100 times in the length direction of the positive electrode plate.

Then, the length of the crack generated in the width direction of the positive electrode plate brought into contact with the round bar was visually observed. The crack rate was calculated from the following formula, and the results are shown in Table 1.

Crack rate [%] = (Length with crack [mm] ÷ Length of electrode plate width [mm]) ×
100
In addition, the cycle life characteristics and high-temperature storage characteristics of Example batteries 1 to 3 and Comparative example batteries 1 to 3 were tested.

  The test method for cycle life characteristics is as follows.

Charging was performed at a constant current of 500 mA, and charging was performed at a constant voltage of 4.1 V when the voltage of the cylindrical lithium secondary battery reached 4.1 V. Such charging was performed for a total of 2 hours. Discharge at 20 ° C
Then, the discharge was terminated when the voltage of the cylindrical lithium secondary battery became 3.0 V at a constant current of 720 mA. The results are shown in FIG.

  The test method for the high temperature storage characteristics is as follows.

Charging was performed at a constant current of 500 mA, and charging was performed at a constant voltage of 4.1 V when the voltage of the cylindrical lithium secondary battery reached 4.1 V. The cylindrical lithium secondary battery charged in this way
C. Stored for 20 days. Then, charge and discharge several times at room temperature (the voltage of the cylindrical lithium secondary battery is 4
. When the voltage reached 1V, the battery was charged at a constant voltage of 4.1V. Such charging was performed for a total of 2 hours. The discharge was performed at 20 ° C. with a constant current of 720 mA, and the discharge was terminated when the voltage of the cylindrical lithium secondary battery reached 3.0V. ), The battery capacity until the voltage of the cylindrical lithium secondary battery reached 3.0 V at a constant current of 720 mA was determined. The ratio to the battery capacity before storage is shown in Table 2.

From the results in Table 1, when Na-CMC is used as the thickener as in Comparative Example 1, the Na group that is a functional group is not gasified in the positive electrode plate after drying, and remains as a residue. The flexibility of the positive electrode plate was reduced and cracks were generated.

In addition, when the drying temperature is as low as 200 ° C. as in Comparative Example 2, NH ₃ -CMC is not sufficiently decomposed as NH 3 groups as ammonium gas, so that the flexibility of the positive electrode plate is reduced and cracks are generated. did.

  Moreover, since gasification was inadequate, the capacity | capacitance deterioration after storage became large as shown in Table 2.

Further, when the drying temperature is as high as 600 ° C. as in Comparative Example 3, it is considered that the positive electrode plate becomes brittle and cracks occur because the thickener self-degradation is oxidatively decomposed.

In Examples 2 and 3, the drying temperatures are 400 ° C. and 500 ° C. and the disappearance temperature of NH ₃ -CMC, but since it is not the decomposition temperature of the skeleton, the flexibility of the positive electrode plate is maintained and the occurrence rate of cracks Is also low.

From this, it can be said that the drying temperature is preferably 300 to 500 ° C., and is preferably higher than the disappearance temperature of the thickener NH ₃ -CMC and lower than the oxidative decomposition temperature of the skeleton portion of the thickener.

From the results of FIG. 2, it was found that Examples 1 to 3 were superior to Comparative Examples 1 to 3 in that the capacity was less deteriorated even when the charge / discharge cycle was repeated, and the cycle characteristics were excellent.

From this result, it can be said that there is a correlation between the crack generation rate of the positive electrode plate and the cycle characteristics.

Thus, the positive electrode plate using NH ₃ -CMC as the thickener is rich in flexibility and has a space that can follow the expansion and contraction of the positive electrode active material accompanying the charge / discharge cycle. It is done.

According to the present invention, since the positive electrode plate has good flexibility and does not break, it is useful as a power source for small electronic devices and a power source for industrial applications.

Schematic longitudinal sectional view of a cylindrical lithium secondary battery used in an example of the present invention Cycle life characteristic diagram of cylindrical lithium secondary battery

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Insulating gasket 3 Positive electrode lead 4 Upper insulating plate 5 Positive electrode plate 6 Negative electrode plate 7 Separator 8 Bottomed battery case 9 Negative electrode lead 10 Lower insulating plate

Claims (3)

A paste for a positive electrode plate in which a lithium-containing nickel composite oxide as a positive electrode active material, a binder, and carboxymethyl cellulose having an ammonium salt as a functional group as a thickener are kneaded and dispersed in a dispersion medium, In the method for producing a positive electrode plate for a lithium secondary battery obtained by coating, drying and rolling on
A positive electrode plate paste obtained by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and carboxymethyl cellulose having the ammonium salt as a functional group as a thickener in the dispersion medium. Manufacturing process;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
A method for producing a positive electrode plate for a lithium secondary battery comprising a step of rolling the positive electrode plate precursor, followed by rolling,
The manufacturing method of the positive electrode plate for lithium secondary batteries which performs the said drying at the temperature of 300 to 500 degreeC. A paste for a positive electrode plate in which a lithium-containing nickel composite oxide as a positive electrode active material, a binder, and carboxymethyl cellulose having a functional group of an ammonium salt as a thickener is kneaded and dispersed in a dispersion medium is used as a current collector. In the method for producing a positive electrode plate for a lithium secondary battery obtained by coating, drying and rolling,
A positive electrode plate paste obtained by kneading and dispersing the lithium-containing nickel composite oxide as the positive electrode active material, the binder, and carboxymethyl cellulose having the ammonium salt as a functional group as a thickener in the dispersion medium. Manufacturing process;
Applying the positive electrode plate paste to the current collector to form a positive electrode plate precursor;
Drying the positive electrode plate precursor;
After drying the positive electrode plate precursor,
A method for producing a positive electrode plate for a lithium secondary battery, wherein the drying is performed at a temperature not lower than the gasification temperature of the functional group portion of carboxymethyl cellulose having the ammonium salt as a functional group and not higher than the oxidative decomposition temperature of the skeleton portion of the thickener. . A lithium secondary battery comprising: a positive electrode plate produced by the production method according to claim 1; a negative electrode plate made of a carbon material as an active material; a separator; and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent.