JP3465864B2 - Lithium secondary battery and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to improvement of its electrode plate.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic equipment such as AV equipment and personal computers have been rapidly developed, and a demand for a small, lightweight secondary battery having a high energy density as a power source for driving these equipment. Is increasing. Among them, lithium secondary batteries are particularly highly expected as batteries having a high voltage and a high energy density. Conventionally, in such a lithium secondary battery, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O is used as a positive electrode active material.
_{For example} , a lithium-containing metal oxide showing a voltage of 4 V class with respect to lithium such as ₄ is used, and a carbon material capable of intercalating and deintercalating lithium is used for the negative electrode.

However, since these lithium secondary batteries use an organic electrolytic solution having a low conductivity, they carry out a large current discharge as compared with an aqueous solution secondary battery such as a nickel-cadmium battery or a lead storage battery. If you do, the capacity will drop significantly. Therefore, by increasing the electrode area, the discharge characteristic at a large current is secured. Specifically, the mixture is applied to a metal foil to form a thin positive electrode plate and a negative electrode plate in a film shape, and these are opposed to each other through a separator made of a nonwoven fabric made of a polyolefin resin such as polypropylene to form a spiral shape. It is wound and used.

[0004]

In the process of working the electrode plate of a lithium secondary battery, rolling is applied in order to increase the packing density of the positive and negative electrode mixture. Therefore, particularly, the positive electrode active material particles or the negative electrode carbon material particles on the surface of the electrode plate facing the counter electrode are deflected in the rolling direction. Since a lithium secondary battery uses an organic electrolytic solution having a low conductivity, it is necessary to smoothly move ions in order to obtain excellent discharge characteristics. However, these particles deflected on the surface of the electrode plate reduce the air permeability and hinder the movement of ions. Therefore, such an electrode plate has a high internal resistance and cannot take out a large current. The present invention solves such a problem, and provides a lithium secondary battery having a low internal resistance and capable of charging and discharging a large current.

[0005]

The lithium secondary battery of the present invention comprises a current collector whose surface is coated with a positive electrode mixture containing an active material composed of a lithium-containing composite oxide, and a roller surface having a high pitch and a high peak. A positive electrode plate is obtained by rolling with a roller having continuous undulations whose average particle size is 2 to 10 times the average particle size of the active material, and similarly, a current collector having a surface coated with a carbon material that absorbs and releases lithium. Is rolled using a roller having continuous undulations in which the pitch and the height of peaks are 2 to 10 times the average particle diameter of the carbon material to obtain a negative electrode plate.
After rolling with a conventional roller having a smooth roller surface, the surface of the electrode plate is roughened by polishing. In this way, the current collector coated with the mixture is rolled with a roller having continuous undulations, or by polishing after rolling, ions can be moved smoothly.
A lithium secondary battery having a low internal resistance and capable of extracting a large current can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A lithium secondary battery of the present invention comprises a positive electrode containing an active material composed of a lithium-containing composite oxide, a negative electrode containing a carbon material that absorbs and releases lithium, and a non-aqueous electrolyte. The positive electrode has continuous undulations in which the pitch and the height of peaks are 2 to 10 times the average particle size of the active material on the surface. Further, another lithium secondary battery of the present invention comprises a positive electrode containing an active material made of a lithium-containing composite oxide, a negative electrode containing a carbon material that occludes and releases lithium, and a non-aqueous electrolyte solution. Both the pitch and the height of peaks on the surface are 2 to 10 of the average particle diameter of the carbon material.
It has doubled continuous undulations.

The method for producing a lithium secondary battery of the present invention comprises the steps of applying a positive electrode mixture containing an active material composed of a lithium-containing composite oxide to a current collector and drying the mixture, and the pitch and peak height on the roller surface. Includes a step of rolling the current collector coated with the positive electrode mixture using a roller having continuous undulations having an average particle diameter of 2 to 10 times the active material. Another method for manufacturing a lithium secondary battery of the present invention is a step of applying a carbon material that absorbs and releases lithium to a current collector and drying, and the pitch and peak height on the roller surface are the average particle diameter of the carbon material. It includes a step of rolling the current collector coated with the carbon material using a roller having continuous undulations of 2 to 10 times. The undulations formed on the roller surface of these rollers require the pitch and the height of the peaks to be twice or more the diameter of these particles in order to disperse the orientation of the particles of the active material or carbon material on the surface of the electrode plate. . Further, if the pitch of the undulations and the height of the peaks exceed 10 times the particle diameter, the packing density becomes rather low and uneven rolling occurs.

Further, a step of applying a positive electrode mixture containing an active material composed of a lithium-containing composite oxide to the current collector, drying it, and rolling it with a roller, and a surface of the positive electrode mixture covering the current collector The method includes a step of roughening the surface by polishing. In addition, a step of applying a carbon material that absorbs and releases lithium to the current collector, drying it, and rolling it with a roller, and a step of roughening the surface of the carbon material that covers the current collector by polishing are included. It is a waste.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. Example 1 A cylindrical lithium secondary battery was manufactured as follows.

The positive electrode was manufactured as follows. Li
₂ CO ₃ and Co ₃ O ₄ were mixed at a molar ratio of 3: 2, and the mixture was baked at 900 ° C. for 10 hours to obtain LiCo.
O ₂ was synthesized. LiCoO ₂ 100 thus obtained
3 parts by weight of acetylene black is used as a conductive material based on parts by weight.
Parts by weight and 7 parts by weight of polytetrafluoroethylene as a binder were mixed. This mixture is then treated with LiCo
Carboxymethyl cellulose equivalent to O ₂ (hereinafter CM
It was suspended in an aqueous solution (referred to as C) to obtain a positive electrode mixture paste. The obtained positive electrode mixture paste was applied to both surfaces of an aluminum foil having a thickness of 30 μm, and then dried. Then, the pair of rollers 9 shown in FIG. 1 was used to roll the aluminum foil coated with the positive electrode mixture. On the roller surface 9b of the roller 9, peaks 9a having a height of 50 μm extending in the rotation axis direction of the roller 9 are continuously formed in the circumferential direction at a pitch of 50 μm. This rolled aluminum foil has a width of 37 mm and a length of 39
It was cut into 0 mm to obtain a positive electrode plate.

The negative electrode was manufactured as follows. As the negative electrode material, mesophase graphite having an average particle size of 6.0 μm obtained by graphitizing mesophase spheres at a high temperature of 2800 ° C. was used. 3.5 parts by weight of styrene-butadiene rubber as a binder was mixed with 95 parts by weight of this mesophase graphite, and the mixture was suspended in a 1 wt% CMC aqueous solution in an amount equal to that of mesophase graphite to form a paste. Apply this paste to a thickness of 20
It was applied to both sides of a copper foil of μm and dried. Next, the copper foil coated with the negative electrode material was rolled using a roller similar to that used in the production of the positive electrode plate. This was cut into a width of 39 mm and a length of 420 mm to obtain a negative electrode plate.

Using these, a cylindrical lithium secondary battery shown in FIG. 2 was produced. An electrode plate group 4 in which a positive electrode plate 5 and a negative electrode plate 6 are spirally wound via a separator 7 is housed inside a battery case 1 made of stainless steel whose inner wall surface is treated with an organic electrolytic solution. ing. The opening of the battery case 1 is fitted with a sealing plate 2 provided with a safety valve via an insulating packing 3 so that the battery is sealed. A positive electrode lead 5a is pulled out from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6a is also discharged from the negative electrode plate 6.
Are drawn out and connected to the bottom of the battery case 1.
An insulating ring 8 is provided on each of the upper and lower portions of the electrode plate group 4. The positive electrode lead 5a made of aluminum on the positive electrode plate 5,
The negative electrode lead 6a made of nickel was attached to the negative electrode plate 6, respectively. The positive electrode plate 5 and the negative electrode plate 6 were spirally wound through a polypropylene separator 7 having a predetermined size to form an electrode plate group 4, which was housed in the cylindrical battery case 1.
Then, an electrolyte solution was prepared by dissolving 1 mol / liter of LiPF ₆ in a solvent in which ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 1: 1 and the electrolyte solution was injected into the battery case 1. After that, the opening of the battery case 1 was sealed with the sealing plate 2 to obtain a lithium secondary battery.

Example 2 Example 1 was used in which flake artificial graphite having an average particle size of 20 μm was used in place of mesophase graphite.
A negative electrode plate similar to that was prepared. A battery similar to that in Example 1 was constructed using this negative electrode plate.

Example 3 Similar to Example 1, the current collector coated with the positive electrode mixture and the negative electrode material was rolled using a conventional rolling roller having a smooth roller surface, and then,
The surface was polished using # 600 sandpaper to obtain a roughened positive electrode plate and negative electrode plate. Using the positive electrode plate and the negative electrode plate, a battery similar to that in Example 1 was manufactured.

Example 4 Example 3 was used in which scale-like artificial graphite having an average particle size of 20 μm was used instead of mesophase graphite.
A negative electrode plate similar to that was prepared. A battery similar to that in Example 3 was produced using this negative electrode plate.

Comparative Example 1 For rolling the positive electrode plate and the negative electrode plate, the same conventional rolling roller as used in Examples 3 and 4 was used to prepare a negative electrode plate. A similar battery was made.

Comparative Example 2 Comparative Example 1 was used in which scale-like artificial graphite having an average particle size of 20 μm was used in place of mesophase graphite.
A negative electrode plate similar to the above was prepared, and using this, a battery similar to the comparative example 1 was prepared.

Using the batteries of Examples 1 to 4 thus produced and 5 cells of each of the batteries of Comparative Examples 1 and 2, at an ambient temperature of 20 ° C., a constant voltage of 4.1 V and a limiting current of 500 mA. Charging was carried out for 2 hours. These charged batteries are
Discharge with constant current of 0.2A, 1A and 2A,
The discharge capacity was measured. Also, 10 mV at a frequency of 1 kHz
Was applied to measure the internal resistance. The results are shown in Table 1. However, the discharge capacity is the ratio of the discharge capacity when discharged at a constant current of 1 A and 2 A, with the discharge capacity at a constant current of 0.2 A being 100%.

[0019]

[Table 1]

From Table 1, all of the batteries of Examples 1 to 4 show excellent discharge characteristics as compared with the batteries of Comparative Examples 1 and 2. Further, in Comparative Examples 1 and 2 in which rolling is performed using a conventional roller, the battery of Comparative Example 2 using artificial graphite in which particles are easily deflected during rolling is a spherical grain-shaped mesophase graphite that is difficult to deflect. The large current discharge characteristics are significantly inferior to those of the battery of Comparative Example 1 in which Example 1 is used, whereas the characteristics of Examples 1 and 2 are almost the same. As described above, the battery of Example 2 using the flake-shaped artificial graphite as the negative electrode material has a greater effect due to the surface roughening than the battery of Example 1 using mesophase graphite. It is presumed that this is because the surface area was increased and the orientation of the particles on the surface was improved by providing the undulations on the electrode surface. Further, the batteries of Examples 3 and 4 in which the surface was roughened by polishing after the conventional rolling process were slightly inferior to the batteries of Examples 1 and 2, respectively, but the large current discharge characteristics were large. It can be seen that it will be improved.
The batteries of Examples 1 and 3 using mesophase graphite were also
The roughening of the surface improves the discharge characteristics. Since the mesophase graphite particles are spherical, it is considered that the deviation of the orientation is small even if the conventional rolling is performed. Therefore, it is considered that the improvement of the discharge characteristics is due to the effect of improving the particle orientation of the active material material in the positive electrode is larger than the effect of improving the orientation of the graphite particles in the negative electrode. From this, it is understood that the large current discharge characteristics of the battery are improved by roughening the surface of the electrode plate during rolling or after rolling. On the other hand, regarding the internal resistance, when mesophase graphite is used, no significant improvement is observed,
When artificial graphite is used, it is greatly reduced.

In Examples 1 and 2, the rolling roller itself was provided with undulations. However, the same effect can be obtained by rolling the undulating pattern sheet on both sides of the electrode plate. Further, in the first and second embodiments, the direction of the ridges formed on the roller surface is made to coincide with the rotation axis direction of the roller 9, but it may be formed in a direction perpendicular to the rotation axis or in another direction. good. Furthermore, in Examples 3 and 4, the surface was roughened using sandpaper,
The same effect can be obtained by using a wire brush or a file.

[0022]

According to the present invention, by roughening the surface of the electrode plate, it is possible to provide a lithium secondary battery in which the capacity is small even when charged and discharged at a high current density.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a rolling roller used in an example of the present invention.

FIG. 2 is a longitudinal sectional view of the lithium secondary battery.

[Explanation of symbols]

1 battery case 2 Seal plate 3 insulating packing 4 electrode group 5 Positive plate 5a Positive lead 6 Negative plate 6a Negative electrode lead 7 separator 8 insulating ring 9 rollers 9a mountain 9b Roller surface

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hide Koshina 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-5-242888 (JP, A) JP-A-7 -122262 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/00-4/62 H01M 10/36-10/40

Claims (6)

(57) [Claims] 1. A positive electrode including an active material made of a lithium-containing composite oxide, a negative electrode including a carbon material that absorbs and releases lithium, and a non-aqueous electrolyte solution, wherein the positive electrode has a high pitch and a high peak. A lithium secondary battery having continuous undulations, each having a size of 2 to 10 times the average particle size of the active material. 2. A positive electrode containing an active material made of a lithium-containing composite oxide, a negative electrode containing a carbon material that occludes and releases lithium, and a non-aqueous electrolyte solution, wherein the negative electrode has a high pitch and a high peak. A lithium secondary battery having continuous undulations, each having an average particle size of 2 to 10 times the average particle size of the carbon material. 3. A step of applying a positive electrode mixture containing an active material composed of a lithium-containing composite oxide to a current collector and drying, and a pitch and a peak height on the roller surface are equal to the average particle diameter of the active material. A method for manufacturing a lithium secondary battery, which comprises a step of rolling the current collector coated with the positive electrode mixture using a roller having continuous undulations of 10 times. 4. A process in which a carbon material that absorbs and releases lithium is applied to a current collector and dried, and the pitch and the height of peaks on the roller surface are 2 to 10 times the average particle diameter of the carbon material. A method for manufacturing a lithium secondary battery, comprising the step of rolling the current collector coated with the carbon material using a roller having the undulations. 5. A step of applying a positive electrode mixture containing an active material composed of a lithium-containing composite oxide to a current collector, drying the mixture, and rolling it with a roller, and a surface of the positive electrode mixture covering the current collector. A method of manufacturing a lithium secondary battery, including the step of roughening the surface by polishing. 6. A step of applying a carbon material that absorbs and releases lithium to a current collector, drying it, and rolling it with a roller, and roughening the surface of the carbon material that covers the current collector by polishing. A method of manufacturing a lithium secondary battery, including the steps of: