JPH09306477A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold high capacity despite of efficiency discharge and reduce the cost by orientating a hexagonal surface of a particle of a scaly black lead for a negative electrode or a material coated with a carbon material having crystallinity lower than the black lead, in relation to a positive electrode by a prescribed angle. SOLUTION: A hexagonal surface of a carbon of scaly black lead used for a negative carbon material possible of occlusion/emission of lithium is orientated to an opposed positive electrode vertically or ±45 deg. from the vertical. It is all right that a material coated with a carbon material having cystallinity lower than the black lead is used as substitute for the scaly black lead. The particle side part, where the lithium ion can be inserted/released, is thus oriented in the counter electrode side so that a shielding rate by other particles is reduced and the route length of the lithium ion can be shortened. A particle having the ratio T/D of the particle side part T to the mean particle size D, 1/3 or less is preferable. For example, when a negative electrode mix paste is squeezed out from the tip projecting port 7 of a rectangular coated nozzle of a coater, the plane side of the particles is aligned in parallel by projecting pressure so as to be oriented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to high energy density and improvement of charge / discharge characteristics thereof.

[0002]

2. Description of the Related Art Conventionally, in non-aqueous electrolyte secondary batteries, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ), molybdenum disulfide are used as positive electrode active materials. (Mo
S ₂ ), titanium disulfide (TiS ₂ ), manganese dioxide (M
Transition metal sulfides or oxides such as nO ₂ ) and vanadium pentoxide (V ₂ O ₅ ) are used. On the other hand, for the negative electrode active material, metallic lithium, a metal material such as a lithium-aluminum alloy or a lithium-wood alloy, and a non-metallic material capable of absorbing and releasing lithium ions in recent years,
For example, carbon materials such as natural graphite, artificial graphite and amorphous carbon having a lower crystallinity than these are used. Furthermore, as novel non-metallic materials capable of inserting and extracting lithium ions, metal compounds such as iron oxide (FeO ₂ etc.) and tungsten oxide (WO ₂ ) or various inorganic layered compounds (LiN ₃ , BC _2). N, etc.), polymer compounds (polythiophene, polyacetylene, etc.), and other negative electrode active materials have been proposed.

Also, as the electrolyte, propylene carbonate (PC), ethylene carbonate (EC), gamma butyrolactone (GBL), diethyl carbonate (DEC), 2-methyltetrahydrofuran (MTHF), etc. in which a lithium salt is dissolved are often used. ing.

In recent years, among non-aqueous electrolyte secondary batteries using these positive and negative electrodes and electrolyte, the average discharge voltage is about 3.6V.
The battery system having high voltage and high energy density has been attracting attention as a power source for various electronic devices. The positive electrode active materials of these battery systems include LiCoO ₂ , LiNiO ₂ and LiM.
A lithium composite oxide such as n ₂ O ₄ is used, and a graphite or amorphous carbon material is used as the negative electrode active material.

However, the discharge voltage curve of a battery using an amorphous carbon material as a negative electrode becomes more oblique than that of a graphitic carbon material as a negative electrode, which is suitable for a motor drive power source of a portable electronic device or the like and a constant output. It doesn't.

The graphite carbon material can maintain the battery voltage at a high voltage, but the characteristics of the negative electrode plate change depending on the crystal arrangement and shape. In particular, the magnitude of charge / discharge current is affected. For example, mesophase spherules and graphitized mesophase fibers have a graphite-structured array oriented at the central point, and a hexagonal carbon end face where lithium ions can be inserted and desorbed is formed on the entire particle surface, which is extremely Easy to get the charge / discharge current of the battery. However, since these materials are expensive and have a point orientation, they have a volume disorder due to the disordered crystal structure, which is about 20% of lithium compared with natural graphite in which crystals are very developed. There is little ion capacity. On the other hand, most of the inexpensive materials, natural graphite and artificial graphite, are scaly due to pulverization.
The scaly particles are composed of a flat surface portion and side surface portions, the flat surface portion is formed of a carbon hexagonal net, and the crystal arrangement is arranged in parallel with the flat surface portion. It is only on the side surface of the scale-like particles that lithium ions can be inserted and desorbed. And when the electrode plate is a conventional negative electrode mixture paste when applied to a metal core material by a doctor blade method, for example, since the plane portion of the particles is oriented parallel to the core material when the paste contacts the core material, The plane portion of the particles on the core material faces the opposite electrode. Therefore, it has a particle shape that makes it difficult for the electric current itself to be taken out, and becomes an electrode plate.

[0007]

As shown in the above conventional examples, natural graphite and artificial graphite, which are inexpensive and have a large capacity for lithium ion insertion / desorption, are promising materials for the negative electrode carbon material of lithium ion batteries. However, most of natural graphite and artificial graphite are scaly due to pulverization. The scaly particles are composed of a flat surface portion and side surface portions, the flat surface portion is formed of a carbon hexagonal net, and the crystal arrangement is arranged in parallel with the flat surface portion. Lithium ions can be inserted / desorbed only on the side surface of the scale-like particle, and when formed into an electrode plate, the flat surface of the particle has a shape that easily faces the counter electrode. Therefore, it has a particle shape that makes it difficult for the electric current itself to be taken out, and serves as an electrode plate.

[0008]

Means for Solving the Problems In order to solve the above problems in a non-aqueous electrolyte secondary battery using scaly natural graphite or artificial graphite particles as a negative electrode, the present invention uses a scaly graphite or scaly carbonaceous material for the negative electrode. The surface of graphite is coated with a carbon material having a lower crystallinity than graphite, and the hexagonal plane of carbon of the flake graphite is perpendicular to the facing positive electrode or ± 45 degrees from the perpendicular. The electrode plate in which the particles are oriented so that the angle is within the angle is used as the negative electrode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, natural graphite or artificial graphite, which is inexpensive and has a large capacity for insertion / desorption of lithium ions, can be used, and conventional amorphous carbon materials or mesophase microsphere graphitized products, It is possible to provide a non-aqueous electrolyte secondary battery that is cheaper and has a higher capacity than a battery that uses a negative electrode of mesophase fiber graphitized material.

[0010]

【Example】

(Example 1) In order to produce a negative electrode for a lithium secondary battery of the present invention, a negative electrode mixture paste coating machine as shown in Fig. 1 was used. The negative electrode mixture paste is sucked up and pressurized by the pump 2 from the negative electrode mixture paste tank 3, is applied from the quenching iron coating nozzle 1 to one surface of the copper foil hoop 4 of the negative electrode core material, and is dried in the drying furnace 6. The paste dehydrated and dried is wound up as the negative electrode-coated hoop 5. The hoop coated on one side is attached again to 4 and is coated on the surface of the uncoated core material in the same manner as described above to form a negative electrode coated on both sides.

FIG. 2 shows an enlarged view of the coating nozzle 1 of the negative electrode mixture paste coating machine of FIG. The tip protrusion port 7 of the nozzle 1 has a rectangular shape, and the negative electrode paste is pushed out from the tip protrusion port 7 from the paste reservoir 8 inside the nozzle. When the negative electrode paste is extruded from the inside of the nozzle, the carbon hexagonal plane side of the scale-like particles in the negative electrode mixture paste is aligned in parallel with the long side of the rectangular projecting opening by the projecting pressure.

The negative electrode mixture paste is flake graphite particles, and here, 10 of KS15 (average particle size 6 μm) manufactured by Lonza Co., Ltd. is used.
3 parts by weight of styrene-butadiene rubber, 1 part by weight of carboxymethyl cellulose (CMC), and 0% by weight of the paste had a water content of 30%. For comparison, a negative electrode mixture paste using mesophase graphite microspheres (MCMB manufactured by Osaka Gas Co., average particle size 6 μm, graphitized 2800 ° C.) instead of the flaky graphite particles was also prepared with the same component composition as above.

The coating thickness is adjusted by the length of the long side of the rectangular paste projecting opening, and the thickness of the mixture on one side after drying is 100 μm.
Became. The content density of the graphite particles was about 1.4 g / cc per unit volume regardless of the shape such as scaly or spherical. The drying temperature of the drying furnace 6 was 140 ° C.

(Embodiment 2) The negative electrode mixture paste coating machine of FIG. 1 was used, but the shape of the projecting port at the tip of the nozzle shown in FIG. 75
A parallelogram-shaped nozzle was prepared, and the negative electrode mixture paste of scaly graphite particles and mesophase graphite microspheres was applied in the same manner as in Example 1. Further, coating was also performed using a nozzle in which the angle θ was set to 0 degree and the lattice of the projecting ports was removed. As a result of observing the cross section of the negative electrode mixture after the coating and drying of the scale-like graphite particle mixture paste with a scanning electron microscope, the angle of the scale-like particles was almost the same as the angle of the parallelogram of the nozzle protruding port that was set. It was The above Examples 1 and 2 are summarized in the following (Table 1), and the symbols of the electrode plates are respectively attached.

[0015]

[Table 1]

(Example 3) A cylindrical battery was experimentally manufactured using the negative electrode plates produced in Examples 1 and 2. FIG. 3 is a vertical sectional view of the cylindrical battery. Battery size is 17 in diameter
mm and height is 50 mm.

The negative electrode plate 1 is spirally wound with the positive electrode plate 3 via the polyethylene separator 2, and is welded and fixed to the bottom surface of the nickel-plated iron case 5 by the nickel negative electrode lead 4. Similarly, the positive electrode plate 3 is connected to the positive electrode terminal 8 by the aluminum positive electrode lead 7.

The positive electrode is lithium cobalt oxide (LiCo
The composition is 3 parts by weight of carbon black and 7 parts by weight of tetrafluoroethylene resin (PTFE) with respect to 100 parts by weight of O ₂ ). The positive electrode has a width of 38 mm, a length of 350 mm, and a thickness of A to L, and the negative electrode plate and the separator are actually wound,
The thickness of the electrode plate allows it to be inserted into the battery case.

The electrolytic solution is lithium hexafluorophosphate (LiPF
₆ ) was dissolved at a concentration of 1 mol / liter in a mixed solvent of an organic solvent ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 3.

The negative electrodes A to F in Examples 1 and 2 had a width of 40 m so that the capacity of MCMB was 300 mAh / g.
m, length 400 mm, thickness 0.21 mm. The negative electrodes G to L of Examples 1 and 2 are KS.
Width of 40 mm so that the capacity of 15 is 340 mAh / g,
The length is adjusted to 400 mm and the thickness is adjusted to 0.17 mm.

The symbols of the batteries using these various negative electrodes were changed from A'to L ', similarly to the symbols of the negative electrodes. The charging conditions of the batteries A'to L'were set to 4.1V constant voltage / current (maximum current 500 mA) and charged for 2 hours. In order to see the effect of the present invention, the discharge is performed with a battery capacity of about 700 mAh.
On the other hand, the current was 1.4 A, and the current was passed until the battery voltage became 3V. The result is shown in FIG. By the way, when discharged at a low current of 100 mA which does not depend on the discharge rate characteristic, that is, the nominal capacity of the batteries is 7 for batteries A'-F '.
00 mAh, batteries G'-L 'were 850 mAh.

In FIG. 4, when MCMB is used as the negative electrode carbon material and the parallelogram of the projecting mouth shape at the time of coating has an angle of 0 to 90 degrees A'to F ', the discharge voltage curve changes regardless of the angle. No discharge was observed, indicating good discharge characteristics. On the other hand, it was found that in the case of using the flake graphite particles KS15, the discharge characteristics were significantly changed by G'-L 'in which the angle of the parallelogram of the projecting opening shape during coating was changed. By the way, what is defined as the present invention is I'-L 'in which the discharge characteristic shows the same discharge curve shape as MCMB and the discharge capacity of the battery is large. These batteries G '
As described above, the discharge characteristics of L'to L'change because the hexagonal carbon mesh plane of the flake graphite particles is an angle close to parallel to the positive electrode of the counter electrode. It is considered that the side surface of the detached scale is shielded from the flow of lithium ions by other scale-like particles. In other words, the length of the path when lithium ions move from the counter electrode is long due to the scale-like shape of other particles. However, in the batteries I ′ to L ′ using the same scaly graphite particles, since the scaly side surface portion, which is the reaction surface of the particles themselves, is oriented to the counter electrode side, the degree of shielding of other scaly graphite particles is small, and the lithium flake graphite particles are We believe that this is the effect of shortening the ion path length.

The same effect can be obtained with natural graphite particles having a similar shape, artificial graphite particles other than KS, and scaly graphite particles whose surface is coated with a carbon material having a lower crystallinity than graphite. . From the tendency of the particle shape, the effect can be obtained when the ratio T / D of the average particle diameter D measured by the particle size distribution and the particle side surface (particle thickness) T obtained by the electron microscope is 1/3 or less. I understood.

Since the MCMB of the comparative example has a crystal arrangement in which the reaction surfaces for insertion / desorption of lithium ions are arranged almost all over the surface and the particle shape is spherical or lumpy, such an electrode plate is used. Particle orientation is not seen when set to
It is possible to discharge 90% of the battery capacity. However,
The capacity of lithium ion insertion / desorption of the carbon material itself is more than that of scaly graphite particles such as natural graphite (NG-7) or KS.
0-20% smaller and expensive.

[0025]

As is apparent from the above description, in the present invention, the ratio T / of the average particle diameter D of the negative electrode carbon material measured by the particle size distribution and the side surface portion (particle thickness) T of the particle obtained by the electron microscope T / D
Is 1/3 or less of scaly graphite or particles in which the surface of scaly graphite is coated with a carbon material having a lower crystallinity than graphite, and the hexagonal planes of carbon of these scaly graphite particles face each other. A non-aqueous electrolyte secondary battery using a negative electrode in which particles are oriented vertically or within ± 45 degrees from the vertical with respect to the positive electrode maintains high capacity even at high rate discharge, and is manufactured at a lower cost than before. It has high industrial value.

[Brief description of drawings]

FIG. 1 is a schematic view of a negative electrode mixture paste coating machine.

[Fig. 2] Enlarged view of the coating nozzle

[Fig. 3] Vertical sectional view of the battery

FIG. 4 is a diagram showing a discharge curve of a battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coating nozzle 2 Pump 3 Paste tank 4 Negative electrode core material hoop 5 Negative electrode coated hoop 6 Drying furnace 7 Negative electrode paste protruding port 8 Negative electrode paste reservoir 9 Negative electrode plate 10 Separator 11 Positive electrode plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Takeuchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masaya Okochi, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary using a non-aqueous electrolyte, comprising a rechargeable positive electrode and a negative electrode plate group containing a carbon material as a main component capable of inserting and extracting lithium through a separator. In the battery, the negative electrode carbon material is composed of scaly graphite or a scaly graphite surface coated with a carbon material having a lower crystallinity than graphite, and the negative electrode has a hexagonal plane of carbon of those scaly graphite particles. , A non-aqueous electrolyte secondary battery in which particles are oriented perpendicularly or within an angle of ± 45 degrees from the perpendicular to the facing positive electrode.