JP3373751B2 - Secondary battery and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a large electric capacity,
The present invention relates to a secondary battery and its manufacturing method in which the electric capacity is less likely to decrease due to repeated charging / discharging, and particularly to a lithium ion secondary battery, a nickel hydrogen secondary battery, a nickel cadmium secondary battery, an alkaline manganese battery, a lead storage battery, etc. It is possible to remarkably extend the cycle life of charging / discharging and to increase the capacity thereof.

[0002]

2. Description of the Related Art In a secondary battery, as the charge and discharge are repeated, the electrode active materials of the positive electrode and the negative electrode repeatedly change in volume due to an electrochemical reaction. A gap is created in the battery, electrical connection is cut off, and the battery capacity is reduced. Conventionally, 30 to 40% of graphite having a particle size of about 5 micrometers was mixed for the purpose of ensuring the conduction between these electrode active materials and the current collector, but the reduction of electrical conduction due to charging and discharging was reduced. It was insufficient to prevent. Further, the space for filling the active material is sacrificed. Further, finer carbon black has also been added to help electrical contact between the active material and graphite. However, carbon black is a very bulky powder, and the density of the electrode active material layer tends to decrease by adding this,
Although measures such as pressing the electrode active material layer with a high pressure have been taken, if the pressure is increased to such a degree that the carbon black is crushed, the graphite will be deformed and there will be no gap for the electrolyte to seep out, and the predetermined characteristics There was a problem that I could not get it.

[0003]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention has found a battery structure that can be manufactured with a long life and at low cost and a manufacturing method thereof by investigating the mechanism of these conventional methods. A first object of the present invention is to extend the charge / discharge cycle life of a secondary battery.
The second object of the present invention is to increase the capacity of the secondary battery. A third object of the present invention is to reduce the internal resistance of the secondary battery. A fourth object of the present invention is to improve the rapid charging performance of the secondary battery. A fifth object of the present invention is to reduce the material cost of the secondary battery.

[0004]

According to the present invention, a conductive path is formed by depositing fine carbon particles, preferably soot pulverized, having a median diameter of 600 nm or less, preferably 300 nm or less, on the surface. Secondary battery using electrode active material, and soot or median diameter of 600
Nanometer or less carbon fine particles, preferably soot pulverized product, is mixed with an electrode active material, and a conductive path is formed by adhering the carbon particulate soot pulverized product to the surface of the electrode active material. This is a method for producing a secondary battery in which particles are formed and the composite particles are attached to a current collector. What is referred to as an electrode active material in the present invention is, for example, MnO ₂ , NiOO.
H, hydrogen storage alloy, LiMn ₂ O ₄ , Li-impregnated graphite, PbO ₂ , PbSO _4, etc., and as secondary batteries, lithium-ion secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, alkaline manganese batteries. , Lead-acid batteries, etc.

[0005]

[Function] The mechanism for extending the charge / discharge cycle life and increasing the battery capacity by using the electrode active material in which the conductive paths are formed by the pulverized soot, which is a fine particle of carbon, adhering to the surface of the electrode active material is It can be considered as follows. That is, taking a lithium ion battery as an example, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ which are positive electrode active materials of a secondary battery are described.
O ₄ always changes the valence of its metal atom as shown in ac below with charge and discharge, and the ionic radius of an atom with a large valence is 15 to 2 as compared with that of an atom with a small valence.
It is as small as 5%.

[0006]

[Chemical 1]

Therefore, the active material expands in volume when discharged and contracts in volume when charged. The cause of deterioration of the battery after repeated charging and discharging is largely due to insufficient contact between the active material and the carbon material or between the carbon materials due to repeated expansion and contraction, resulting in increase in internal resistance.

Further, with respect to a carbon-based material which absorbs and desorbs Li ions, which is used as an active material of a negative electrode of a lithium ion battery, conventionally, when Li ions are repeatedly occluded and desorbed, expansion and contraction occur, which causes Along with this, deterioration of conductivity between the carbon-based materials is unavoidable.

In the present invention, as shown in FIG. 1, the soot pulverized product 1 which is a fine particle of carbon is adsorbed on the surface of the particle 2 of the electrode active material or the particle 3 produced by the change of the electrode active material. A conductive mesh 4 is formed. Since the mesh 4 is composed of fine particles, it can freely deform while keeping contact with each other on the surface of the electrode active material as the electrode active material expands and contracts. Body 5
It is presumed that the charging current flows from the above to electrolyze the surface of the particle 3 which has been inactive until now to regenerate the active material.

Further, in MnO ₂ , as shown in FIG.
A battery having a porosity of 30 m ² / g is used for a battery. It has a very rugged surface and many fine pores, with over 95% of the electrode reaction occurring on the wall of this pore. With conventional coarse graphite and uncrushed carbon black, it was not possible to adhere to these dusty surfaces and pores, but with carbon particles of the order of 100 nanometers or less, they adhered to these surfaces and formed conductive paths. Since it can be formed, an ideal battery active material structure can be formed.

That is, in the case of particles obtained by crushing conventional graphite, the active material particles 12 and the graphite particles 11 having similar sizes have a stone wall-like structure in which they are intertwined with each other, as shown in FIG. In addition, while the contact between the graphite particles and the contact between the graphite particles and the active material particles were separated due to the expansion and contraction of the active material, in the structure of the present invention, the size of the conductive fine particles was 100 nm in diameter. And the diameter of the size of the active material is 1
Since it is much smaller than the order of 0000 nanometers, it is presumed that the conductive fine particles can change their arrangement relatively freely, and the conductive mesh is less likely to break even when the active material expands and contracts. .

The diameter of the carbon-based material that absorbs and desorbs Li ions, which is the electrode active material of the negative electrode, is 500
By adhering the conductive fine particles of the order of 100 nm of the present invention to the surface of the active material particles of 0 to 30,000 nanometers, the conductivity of the active material particle main body due to expansion and contraction accompanying the charging and discharging of the active material particles. Even if deterioration occurs, good conductivity is maintained as a whole by the conductive paths formed of conductive fine particles on the surface of the active material particles.

Since the inactive particles on the surface of the electrode are regenerated as the active material in this manner, the internal resistance of the battery is greatly reduced, the capacity is increased, and the battery can withstand rapid charging.

Furthermore, in the nickel-hydrogen secondary battery, the surface of the hydrogen-absorbing alloy powder can be obtained simply by immersing the hydrogen-absorbing alloy powder in a suspension obtained by mixing soot pulverized carbon fine particles and an organic polymer. A layer of soot pulverized carbon fine particles is formed on the surface of the carbon to facilitate the transfer of electrons to and from hydrogen ions. Thus, nickel using hydrogen storage alloy powder coated with soot pulverized carbon fine particles is used. In a hydrogen secondary battery, the internal resistance of the battery decreases.

Soot obtained by burning petroleum, natural gas, animal and vegetable oils, such as acetylene black, carbon black, ketjen black, etc., is formed by connecting fine particles of several tens of nanometers in a chain shape, as shown in FIG. ), It is a relatively large lump with a diameter of 10,000 to 50,000 nanometers and is very bulky as it is, and the bulk density becomes small to adhere to the surface of the electrode active material to form a conductive path. Too inappropriate. However, if this is pulverized to have an order of 100 nanometers as shown in FIG. 3B, it becomes possible to adhere to the surface of the electrode active material and form a conductive path without lowering the bulk density. It is suitable as fine particles to be used. To this, a polymer having a hydrophilic group and a hydrophobic group in the same molecule, for example, an organic polymer dispersion aid (protective colloid) such as glue, gum arabic, polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose, and casein is added. The India ink forms a stable colloid and can be easily attached to the surface of the active material particles by mixing with the electrode active material. Further, a surfactant may be added in order to promote the dispersion of the pulverized soot, which is carbon fine particles, in water.

As a method for pulverizing soot, a highly viscous fluid or a plastic mass, which is a mixture of water, an organic liquid, or a solution containing a polymer, is subjected to a strong shearing force to shorten the chain-like structure. A method of cutting is particularly preferable, and for example, a triroll mill, hand kneading, attrition mill, etc. used for producing printing ink, ink, etc. are suitably used.

The amount of the conductive fine particles added may be smaller as the particle size of the conductive fine particles is smaller. In particular, if soot, which is fine particles with a chain-like microstructure, is used, the mesh-shaped conductive paths formed by the chain-like fine particles expand and contract as the active material expands and contracts during charging and discharging. It is presumed that the substance is not electrically isolated. Thus, the effect that the electrical conductivity is maintained by the loose bonding of the chain-like fine particles is an effect that could not be expected at all in the case of mixing the conventional coarse graphite particles with the electrode active material. It was achieved for the first time by using a pulverized product of soot, which is a carbon particle of.

Further, when the pulverized soot which is the fine carbon particles of the present invention is used, even if the addition amount thereof is much smaller than that of the conventional coarse graphite, sufficient conductivity can be obtained. Therefore, it is possible to reduce the amount of carbon per certain volume of the battery and increase the amount of active material,
It is possible to increase the energy density of the battery.

That is, the state will be described by taking a lithium ion battery as an example. The positive electrode of the lithium ion battery is LiCoO 2.
A positive electrode mixture prepared by mixing graphite powder and a binder such as polyvinylidene fluoride with the powder of ₂ is applied to the surface of the aluminum foil of the electrode current collector to a thickness of about 200 micrometers. In this case, if LiCoO ₂ powder covered with a soot pulverized product which is the carbon fine particles of the present invention is used, not only more LiCoO ₂ can be applied with the same thickness, but also the electric resistance of the active material layer Since it is small, the active material layer is 40
Even if the thickness is 0 μm, the internal resistance of the battery is not adversely affected. Therefore, the aluminum foil that is shorter by that amount can be used, and the copper foil of the separator and the current collector of the negative electrode also becomes shorter, resulting in a 30-40% material savings.
Manufacturing costs can be reduced.

As the method for producing the composite particles of the present invention, the particles of the electrode active material and the pulverized product of soot which is fine carbon particles may be pulverized and mixed in water or an organic solvent. Further, at this time, it helps disperse the soot pulverized carbon fine particles and the adhesion of the electrode active material to the particle surface, and further assists the pulverization by the shearing force to improve the affinity between the pulverized soot carbon fine particles and the dispersion medium. It is desirable to add a suitable organic polymer, for example, a dispersion aid such as polyvinyl alcohol, glue, gum arabic, polyvinylpyrrolidone, carboxymethylcellulose, casein or the like in order to enhance the viscosity. In addition, the surface of the particles of the electrode active material is coated by impregnating the positive electrode coated with the particles of the electrode active material by the conventional method with a slurry of finely divided carbon particles of soot and water or an organic solvent. Fine carbon particles may be attached to.

Further, in the case of using the electrode active material covered with the pulverized soot which is the carbon fine particles of the present invention, if a small amount of organic germanium is added to the electrolytic solution, the electroconductivity of the surface of the electrode active material is further improved, and the charge and discharge is improved. It is effective in extending the cycle life.

[0022]

[Reference example]

[Reference Example 1] 5 ml of a suspension consisting of 1% by weight of carbon black having a median diameter of 140 nm, 0.6% by weight of polyvinyl alcohol and the balance of water, and 5 g of LiCoO ₂ powder were mixed and pulverized in a ball mill. Dried. This dried product was crushed, and 0.3 g of polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent were added and mixed to form a slurry, which was applied on an aluminum foil and dried to obtain a positive electrode. For the negative electrode, a coke layer was applied on a copper foil and dried. This was wound through a porous polypropylene separator, a 1 M solution of LiPF ₆ in ethylmethyl carbonate-ethylene carbonate (mixing ratio 3: 1) was added as an electrolytic solution, and the mixture was sealed in a battery container. Charge end voltage 4.2V, discharge end voltage 3.0V,
A charge / discharge cycle test was performed at a charge of 0.25C and a discharge of 0.5C. As a result, 2 grams of conventional graphite is added to the positive electrode,
As shown in Table 1, as compared with the case of using 3.3 grams of LiCoO ₂ powder, the charge / discharge cycle life more than twice as long was obtained,
Moreover, the electric capacity was about 50% higher. FIG. 3 shows the results of measuring the particle size distribution of the suspension used in this test with a laser diffraction / scattering particle size distribution analyzer LA-910W manufactured by Horiba Ltd., and the median diameter thereof is about 140 nanometers (0.14 nm).
μm), and the distribution range of particles is approximately 70 to 300.
It is in the nanometer range, and 90% or more is 90
Concentrated in a narrow range of ~ 250 nanometers.

[0023]

[Table 1]

[0024]

[Reference Example 2] Particles of electrolytic manganese dioxide having a particle diameter of 20 micrometers were mixed with 6% by weight of carbon black having a median diameter of 100 nanometers, 3% by weight of glue, and the balance consisting of water to obtain manganese dioxide. A fine particle layer of carbon was formed on the surface of the particles. This mixture was filtered, dried and crushed. This powder was packed in an insulating container, electrodes were placed at both ends, and pressure was applied at 50 kg / cm ² , and the relationship between the coating amount and the electrical resistance was determined. As a result, as shown in Table 2, Test Nos. 2 to 4 in which a carbon fine particle layer was formed on the surface showed good electrical conductivity.

[0025]

[Table 2]

[0026]

As is apparent from the above description, in the secondary battery of the present invention, there is little decrease in battery capacity due to repeated charging / discharging, and it has a long life. It can be extended, and as its raw material, it is possible to use carbon black, acetylene black, etc., which are produced in large quantities for automobile tires, etc., so that they can be manufactured at extremely low cost. For example, electric vehicles, uninterruptible power supplies. It is possible to provide an electrode structure suitable for a battery of an apparatus or the like and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a reaction on an electrode surface of a battery of the present invention.

FIG. 2 is a particle size distribution chart of a carbon additive used in the present invention.

FIG. 3 is a schematic diagram showing a microstructure of soot particles used in the present invention, where A is before pulverization and B is after pulverization.

FIG. 4 is a schematic diagram showing a microstructure of manganese dioxide particles having carbon fine particles adsorbed on the surface used in the present invention.

FIG. 5 is a schematic view showing a mixed state of a conventional electrode active material and graphite.

[Explanation of symbols]

1, 11 ... Conductive fine particles 2, 12 ... Particles of electrode active material 3 ... Particles with changed electrode active material 4 ... Conductive mesh 5, 13 ... Current collector

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-225761 (JP, A) JP-A-62-188167 (JP, A) JP-A-4-345760 (JP, A) JP-A-4- 162357 (JP, A) JP 10-228922 (JP, A) JP 4-12454 (JP, A) JP 7-130369 (JP, A) W. h. smyrl, et. al. , KITHIUM ION INSERT ION ELECTRODES: CAT HODE MORPHOLOGY AND D PERFORMANCE, AD R ep, AD-A-281443, 252-253 Christine A. Frys z, et. al, Carbon fillments and carbon black as a conductive live additive to the manganese dioxide ER, 58, 41 of the United States, 58, 41 of the United States. .Cl. ⁷ , DB name) H01M 4/62 H01M 10/06 H01M 10/24 H01M 10/40

Claims (15)

(57) [Claims] 1. A pulverized soot median diameter is 600 nm or less fine particles of carbon by adheres,
A secondary battery comprising electrode active material particles having a conductive path formed on the surface thereof. 2. The method of claim 1, are fine particles of carbon
A secondary battery having a median diameter of crushed soot of 300 nanometers or less. 3. An apparatus according to claim 1 or claim 2, secondary battery, wherein the ground product of soot is fine particles of carbon and has a microstructure finer particles led to chain form. 4. The method according to any one of claims 1 to 3.
Therefore, the soot crushed as fine particles of carbon and the organic polymer coexist.
Secondary battery which is characterized that you have to exist. 5. The organic polymer according to claim 4, wherein the organic polymer has the same content.
A secondary battery having a hydrophilic group and a hydrophobic group in its child . 6. The organic polymer according to claim 5, wherein the organic polymer is glue or
Labia gum, polyvinyl alcohol, polyvinylpyrroli
Low in Don, Carboxymethylcellulose and Casein
Secondary battery, wherein a call, including one with. 7. The carbon fine particles according to claim 4.
Rechargeable battery pulverized product with an organic polymer of soot, characterized in that it is a component of India ink. 8. The method according to any one of claims 1 to 7.
The secondary battery is a lithium-ion battery or nickel cadmium.
Um battery, nickel hydrogen battery, alkaline manganese battery,
Secondary battery which is characterized and this is one of the lead-acid battery. 9. A median diameter of 600 nanometers or less
A conductive path is formed on the surface due to the adhesion of fine particles of carbon.
Using the electrode active material particles formed,
/ Or secondary battery comprising it to contain organic germanium electrode active material particles. 10. The median diameter is 600 nanometers or less.
Crushed soot, which is a fine particle of carbon, as electrode active material particles
Mixing, in the fine particles of the carbon on the surface of the electrode active material particles
Form a conductive path by adhering a crushed soot
Composite particles, and attach the composite particles on the electrode collector.
A method of manufacturing a secondary battery, which is characterized by wearing. 11. The carbon fine particles according to claim 10,
The median diameter of crushed soot is less than 300 nanometers
Preparation of a secondary battery, wherein the Dearuko. 12. The odor according to claim 10 or claim 11.
The pulverized soot, which is a fine particle of carbon, has finer particles.
Preparation of a secondary battery, wherein the this and has a microstructure that led to chain form. 13. Any of claims 10 to 12.
In this, pulverized soot, which is a fine particle of carbon, and electrode active material
Upon mixing with the quality manufacturing process of the secondary battery characterized that you add an organic polymer. 14. The median diameter is 600 nanometers or less.
The suspension containing the pulverized soot, which is a fine particle of carbon, is collected.
Apply or contact with the electrode active material particle layer applied on the body.
By squeezing, the carbon on the surface of the electrode active material particles
To form a conductive path by adhering pulverized soot, which is a fine particle of
Preparation of a secondary battery, wherein the Turkey. 15. A crushed soot carbon black and a liquid.
By applying a shearing force to the mixture with the body,
Characterized by milling the ann diameter to 600 nanometers or less
And carbon fine particles for batteries.