JPH11238527A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the internal resistance and realize high capacity of a battery by forming a positive electrode or a negative electrode from at least an active material and conductive fine metal powder and containing therein fine metal powder that forms a conductive network and has an mean particle diameter in a specific range. SOLUTION: A positive electrode 1 is composed by laminating an upper layer positive electrode film 2-1 and a lower layer positive electrode film 2-2 which contain fine metal powder and have a rectangular shape of a predetermined width interposing a positive electrode collector 4 made of metal foil. A negative electrode 5 is composed by laminating an upper layer negative electrode film 6-1 and a lower layer negative electrode film 6-2, which contain fine metal powder and have a rectangular shape of a predetermined width interposing a positive electrode collector 8 made of a metal foil. In addition, a cell body 10 is structured by laminating the positive electrode 1 and the negative electrode 5 interposing a separator 9. The conductivity of the positive electrode films 2-1, 2-2 and the negative electrode films 6-1, 6-2 can be improved and the resistance between the positive and negative collectors 4, 8 and these can be reduced by forming the positive electrode 1 or the negative electrode 5 from at least an active material and conductive fine metal powder and including therein fine metal powder that forms a conductive network and has a mean particle diameter in the range of 0.1-30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery having a high capacity, a light weight and a small internal resistance.

[0002]

2. Description of the Related Art In recent years, non-aqueous secondary batteries that can be expected to have high energy density have been actively researched and developed. For example, a lithium ion secondary battery having a positive electrode and a negative electrode containing an active material capable of inserting and releasing lithium ions. However, they have been widely used as power sources for mobile phones, notebook computers, and the like that require small size and light weight. However, in the conventional non-aqueous secondary battery described above, a sufficient capacity cannot be drawn out at a high current density (for example, 10 mA / cm ² or more), and one of the causes is insufficient reduction of the internal resistance of the battery. There is a problem that is.

[0003] The internal resistance of a secondary battery consists of the resistance of the electrodes, electrolyte and separator. Among them, the resistance of the electrolyte is determined by the type of the electrolyte used, and the resistance of the separator depends on the resistance of the electrolyte to be impregnated. Is
It is required to reduce the resistance of the electrode. Conventionally, an electrode is manufactured by applying a paste containing an active material to a current collector made of a metal foil, and is composed of an active material, an electrode layer containing a conductive carbon and a binder, and a current collector. . Therefore, in order to lower the resistance of the electrode, it is necessary to reduce the resistance of the electrode material layer or to form a physical or chemical unevenness on the surface of the current collector to improve the adhesion with the electrode material layer. It has been done.

[0004]

However, if the amount of conductive carbon added is increased in order to reduce the resistance of the electrode material layer, the volume of the electrode material layer increases, and the volume and the energy density by weight decrease. is there. In addition, the volume of the active material increases as charge and discharge are repeated, so that the adhesion between the electrode material layer and the current collector gradually decreases and the resistance of the electrode increases. Was enough.

Therefore, an object of the present invention is to provide a high-capacity non-aqueous secondary battery in which the internal resistance is reduced by lowering the resistance of the electrode in order to solve the above-mentioned problems.

[0006]

In order to achieve the above-mentioned object, the present invention solves the above-mentioned problems by forming a battery using a positive electrode or a negative electrode containing an active material and a metal fine powder for imparting conductivity. That is, the present invention has been completed, that is, the present invention relates to a nonaqueous secondary battery having a positive electrode and a negative electrode containing an active material capable of inserting and releasing lithium ions, wherein the positive electrode or the negative electrode has at least an active material and a conductive material. It is characterized by comprising the above-mentioned metal fine powder having an average particle size of 0.1 μm to 30 μm which is formed of conductive metal fine powder and forms a conductive network. Due to the high conductivity of the metal fine powder and the conductive network formed, higher conductivity is imparted to the positive electrode or the negative electrode as compared with the case where conductive carbon which is a conventional conductivity-imparting material is used.

[0007] The metal fine powder contained in the positive electrode may be:
Aluminum, titanium, a metal selected from stainless steel or an alloy containing the same, and the metal fine powder contained in the negative electrode, even when in contact with lithium metal selected from copper group and platinum group, significantly impairs the form It is desirable to use a metal or an alloy containing the same. By using the above metal or an alloy containing the same, a positive electrode or a negative electrode having excellent corrosion resistance and high conductivity can be obtained.

Preferably, the positive electrode contains 6 to 20% by volume of the metal fine powder, and the negative electrode contains 6 to 20% by volume of the metal fine powder. Without this, the conductivity of the positive electrode or the negative electrode can be increased.

Preferably, the positive electrode or the negative electrode comprises a plurality of stacked positive electrode films or negative electrode films containing an active material and metal fine powder. By stacking a positive electrode film or a negative electrode film containing fine metal powder, a highly conductive laminate can be manufactured.

Further, the positive electrode or the negative electrode may be composed of a positive electrode film or a negative electrode film laminated via a current collector made of a rectangular metal foil having a width smaller than that of the positive electrode film or the negative electrode film. The electrode can be reduced in weight, and the electrode can be provided with the mechanical strength required during battery production.

Further, the above-mentioned positive electrode film or negative electrode film comprises a paste obtained by adding a binder, conductive carbon, a solvent and a metal fine powder to a positive electrode active material or a negative electrode active material, and kneading the paste to form an olefin resin. It is desirably prepared by applying the composition on a flat plate, drying the applied paste, and peeling the obtained coating film from the flat plate.

A conductive thin film portion made of a conductive metal may be formed on one or both surfaces of the positive electrode film and / or the negative electrode film. By forming the conductive thin film portion, the resistance at the interface between the positive electrode films or the negative electrode films can be further reduced.

Further, the conductive thin film portion of the positive electrode film is made of a metal selected from aluminum, titanium, and stainless steel or an alloy containing the same, and the conductive thin film portion of the negative electrode film is made of a copper group and a platinum group. It is desirable to use a metal or an alloy containing the metal that does not significantly impair the form even when contacted with the selected lithium metal. Thereby, a thin film portion having high corrosion resistance and high conductivity can be obtained.

Further, the conductive thin film portion is formed on one or both surfaces of the positive electrode film or the negative electrode film by using any one method selected from a vapor deposition method, a sputtering method, an electrolytic plating method and an electroless plating method. Is desirable.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a schematic sectional view showing the structure of a non-aqueous secondary battery according to a first embodiment of the present invention. Upper layer positive electrode film 2 of rectangular shape having a predetermined width containing metal fine powder
Current collector 4 made of metal foil with -1 and lower positive electrode film 2-2
A negative electrode current collector 8 made of a metal foil is formed by stacking the upper negative electrode film 6-1 and the lower negative electrode film 6-2 having a predetermined width including a metal fine powder. The negative electrode 5 is produced by laminating the positive electrode 1 and the negative electrode 5 with the separator 9 interposed therebetween to form a unit cell body 10. The unit cell body 10 is further laminated with a new separator, wound in a spiral shape, housed in a cylindrical battery case, filled with an electrolytic solution, and then sealed to form a battery.

As described above, according to the first embodiment of the present invention, the inclusion of the fine metal powder not only improves the conductivity of the positive electrode film or the negative electrode film, but also improves the conductivity between the positive electrode film and the current collector. Alternatively, since the resistance between the negative electrode film and the current collector can be reduced, the resistance of the positive electrode or the negative electrode can be reduced. In addition, by using a rectangular current collector having a width smaller than that of the positive electrode film or the negative electrode film, the weight of the current collector can be reduced as compared with the related art, and mechanical strength can be imparted to the positive electrode or the negative electrode. Manufacturing becomes easier.

<Second Embodiment> FIG. 2 shows a second embodiment of the present invention.
It is a typical sectional view showing the structure of the nonaqueous system secondary battery in an embodiment. The conductive thin film layers 3-1 and 3-2 are formed on one side of the positive electrode films 2-1 and 2-2, and the conductive thin film layers 3-1 and 3-2 are formed.
And the positive electrode films 2-1 and 2-
2 to form a positive electrode 1 and a negative electrode film 6-1.
And 6-2 to form conductive thin film portions 7-1 and 7-2 on one side,
The conductive thin film portions 7-1 and 7-2 are opposed to each other, and the negative electrode current collector 8
A battery is manufactured in the same manner as in the first embodiment, except that the negative electrode 5 is prepared by laminating the negative electrode films 6-1 and 6-2 via.

As described above, the conductive thin film portion is formed on at least one side of the positive electrode film or the negative electrode film, and the positive electrode film or the negative electrode film is laminated with the current collector interposed therebetween. Alternatively, the resistance between the negative electrode film and the current collector can be further reduced.

Here, as the positive electrode material used as the positive electrode active material of the nonaqueous secondary batteries of the first and second embodiments of the present invention, any conventionally known materials can be used.
xCoO ₂ , LixNiO ₂ , MnO ₂ , LiMnO ₂ , Li
_{xMn 2 O 4, LixMn 2-} y O 4, α-V 2 O 5, TiS 2 and the like.

Further, as the negative electrode active material of the non-aqueous secondary batteries of the first and second embodiments of the present invention, known materials such as graphite, calcined carbonaceous material, silicon and silicon compound can be used.

Further, as the non-aqueous electrolyte used in the non-aqueous secondary batteries of the first and second embodiments of the present invention, a non-aqueous electrolyte obtained by dissolving a lithium compound in an organic solvent can be used. . The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery. As the organic solvent, for example, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2
-Diethoxyethane methyl formate, butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1-3 dioxofuran, 4-methyl-1,3-dioxofuran, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, butyronitrile, valeronitrile , Benzonitrile, 1,2-
Dichloroethane, 4-methyl-2-pentanone, 1,4
-Dioxane, anisole, diglyme, dimethylformamide, dimethylsulfoxide and the like. One of these solvents can be used alone, or two or more can be used in combination. As the electrolyte, for example, L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , Li
B (C ₆ H ₅ ) ₄ , LiCl, LiBr, LiI, LiC
H ₃ SO ₃ , LiCF ₃ SO ₃ , LiAlCl _4, etc., and one of these can be used alone.
More than one species may be used in combination.

As the separator of the first and second embodiments of the present invention, any of those used for non-aqueous secondary batteries can be used, but a porous insulating sheet such as porous polyethylene is used. It is desirable.

The positive and negative electrodes of the non-aqueous secondary batteries according to the first and second embodiments of the present invention are prepared by adding a binder and a solvent to a positive electrode active material or a negative electrode active material and kneading the paste. Then, the paste is applied to a flat plate of an olefin-based resin, and after drying, the obtained coating film is peeled off from the flat plate.
A positive electrode film and a negative electrode film can be obtained respectively. The thicknesses of the positive electrode film and the negative electrode film are respectively 20 μm to 500 μm,
It is desirable that it is from μm to 500 μm.

The flat plate used for producing the positive electrode film and the negative electrode film of the nonaqueous secondary batteries of the first and second embodiments of the present invention may be any olefin resin. Although it is possible, it is desirable to use one made of polypropylene.

The fine metal powder contained in the positive electrode film of the non-aqueous secondary batteries according to the first and second embodiments of the present invention has a high withstand voltage such as aluminum, titanium, and stainless steel, and has high conductivity. High metals can be used alone or in combination, but aluminum is preferred.

In addition, the metal fine powder contained in the negative electrode film of the non-aqueous secondary battery of the first and second embodiments of the present invention contains copper which does not react with lithium or does not decrease in conductivity even if it reacts. Metals such as copper, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, platinum and the like can be used alone or in combination, but copper or gold is preferably used.

Further, as the current collector of the non-aqueous secondary battery of the first and second embodiments of the present invention, any one usually used for the current collector of the non-aqueous secondary battery may be used. However, it is desirable to use, for example, an aluminum foil for the positive electrode current collector and, for example, a copper foil for the negative electrode current collector.

Further, the conductive thin film portion of the positive electrode film or the negative electrode film of the non-aqueous secondary battery according to the second embodiment of the present invention is formed by an evaporation method.
It can be formed by any one method selected from a sputtering method, an electrolytic plating method, and an electroless plating method. It is desirable to use an evaporation method for the positive electrode film.
The thickness of the formed conductive thin film portion is preferably 3 μm to 10 μm and 3 μm to 10 μm for the positive electrode film and the negative electrode film, respectively.

[0029]

The present invention will be described in more detail with reference to the following examples.

Example 1. 10 g of polyvinylidene fluoride (PVDF) was added to 100 g of natural carbon powder having an average particle size of 7 μm.
n-Methyl-2-pyrrolidone (NMP) is added and kneaded to prepare a paste, and this paste is 50 mm wide, 520 mm long and 20 μm thick copper foil (weight 4.29 g).
After drying, a calender press process was performed to obtain a negative electrode having a coating film having a thickness of 100 μm and a specific gravity of 1.2 on both sides. The weight of the negative electrode was 9.91 g.

For 88 g of lithium cobaltate, 6 g of acetylene black, 6 g of PVDF, and an average particle size of 1 μm
6 g of aluminum powder and NMP were added and kneaded to prepare a paste. The paste was applied on a polypropylene flat plate, dried, and calender-pressed. The width was 50 mm, the length was 480 mm, the thickness was 90 μm, and the specific gravity was specific. The positive electrode film of 2.5 was obtained by peeling off a polypropylene plate. This positive electrode film was placed in a vacuum deposition apparatus, and aluminum was deposited on one side. In the same manner, one more positive electrode film having aluminum deposited on one side was prepared, and the width was 20 m.
m, a length of 520 mm, and a thickness of 20 μm, an aluminum foil was interposed between the two positive electrode films to form a single positive electrode. The weight of this positive electrode was 11.00 g.

The separator has a width of 52 mm and a length of 540 m.
m, a thickness of 30 μm, and a weight of 0.84 g using two PET microporous membranes, winding while preventing short circuit between the positive electrode and the negative electrode,
During winding, the width of the negative electrode current collecting tab is 3 mm, the length is 60 mm,
A copper piece (0.08 g in weight) having a thickness of 50 μm was wound so as to be in contact with the negative electrode, and an aluminum piece (0.02 g in weight) having the same size as the positive electrode current collecting tab was brought into contact with the positive electrode. The negative electrode current collecting tab protruded on one side and the positive electrode current collecting tab protruded in the opposite direction to obtain a cylindrical wound battery body having a diameter of 17.4 mm and a length of 52 mm having a hole of 2 mm in the center. The weight of this cylindrical wound battery body is 20.
It was 48 g.

This cylindrical wound battery body was 17.4 m in diameter.
m, a stainless steel container (weight 8.90 g) with a bottom and a thickness of 0.25 mm and a length of 67 mm, with the negative electrode current collecting tab facing down, welding the negative electrode current collecting tab to the bottom of the can, and performing electrolysis. After injecting 4.00 g of the liquid, the positive electrode current collector tab was weighed 2.50 g.
And a can was caulked and sealed so as not to short-circuit the positive electrode and the negative electrode to obtain a battery having a diameter of 18 mm and a length of 65 mm. The weight of this battery was 38.09 g.

The electrolyte was mixed with a mixed solvent of ethylene carbonate and dimethyl carbonate (1: 1 by volume).
What added lithium hexafluorophosphate so that concentration might be 1 mol / l was used. The battery was charged to 4.2 V at a current density of ² mA / cm ² , discharged to 2.5 V, and the internal resistance was evaluated from the IR drop during charging and discharging. Table 1 shows the results
Shown in

Comparative Example 1. To 88 g of lithium cobaltate, 6 g of acetylene black, 6 g of PVDF and NMP were added and kneaded to prepare a paste.
After coating on both sides of an aluminum foil (weight: 1.40 g) having a length of 480 mm and a thickness of 20 μm, drying and calendering were performed to obtain a positive electrode having a coating having a thickness of 100 μm and a specific gravity of 2.4 on both sides. . The weight of this positive electrode was 11.77 g.
Met.

The negative electrode other than the positive electrode, the separator, the electrolytic solution, the container can, the positive and negative electrode current collecting tabs and the lid were formed in the same manner and in the same manner as in Example 1. A cylindrical wound battery body having a length of 0.4 mm and a length of 52 mm was obtained. The weight of this cylindrical wound battery body was 23.46 g. In the same manner as in Example 1, this cylindrically wound battery body was housed in a container, and an electrolytic solution was further injected to obtain a battery having a diameter of 18 mm and a length of 65 mm. The weight of this battery is 38.8
6 g. Table 1 shows the results.

Example 2. To 100 g of natural carbon powder having an average particle size of 7 μm, 54 g of oxygen-free copper powder having an average particle size of 20 μm, 10 g of PVDF, and NMP were added and kneaded to prepare a paste. It was applied to a copper foil having a thickness of 520 mm and a thickness of 20 μm, dried, and then subjected to calendar press processing to obtain a negative electrode having a coating film having a thickness of 100 μm on both sides. The weight of the negative electrode was 13.65 g. A battery was obtained in the same manner as in Example 1 except for the negative electrode. The total weight of this battery was 42.61 g.

Embodiment 3 FIG. For 88 g of lithium cobaltate, 6.4 g of aluminum powder having an average particle size of 5 μm and PVDF6
g, and NMP are added and kneaded to produce a paste,
This is applied to an aluminum foil having a width of 50 mm, a length of 480 mm, and a thickness of 20 μm, and after drying, calendering is performed.
A positive electrode having a coating film having a thickness of 100 μm on both surfaces was obtained. The weight of this positive electrode was 11.90 g. A battery was obtained in the same manner as in Example 1, except for the positive electrode. The total weight of this battery was 39.00 g.

Embodiment 4 FIG. 12.8 g of aluminum powder having an average particle size of 5 μm and PVDF were added to 88 g of lithium cobalt oxide.
6 g and NMP were added and kneaded to prepare a paste, which was 50 mm in width, 480 mm in length, and 20 μm in thickness.
And dried and then calendered to obtain a positive electrode having a coating film having a thickness of 100 μm on both surfaces.
The weight of this positive electrode was 12.02 g. A battery was obtained in the same manner as in Example 1, except for the positive electrode. The total weight of this battery was 39.11 g.

[0040]

Table 1 Internal resistance (mΩ) Positive electrode weight (g) Negative electrode weight (g) Battery weight (g) Example 1 50 11.00 9.91 38.09 Comparative Example 1 100 11.77 9.91 38.86 Example 2 40 11.77 13.65 42.61 Example 3 40 11.90 9.91 39.00 Example 4 30 12.02 9.91 39.11

[0041]

As described above, according to the present invention, the resistance of the positive electrode film or the negative electrode film can be reduced by adding the fine metal powder, and the positive electrode film or the negative electrode film can be laminated to form the positive electrode film or the negative electrode film. Since the electrical resistance at the interface between the films or between the negative electrode films is reduced, the resistance of the electrodes can be reduced, and the internal resistance of the battery can be reduced. Further, by adopting a configuration in which a rectangular current collector having a width smaller than that of the positive electrode film or the negative electrode film is interposed between the positive electrode film or the negative electrode film, the battery can be reduced in weight, and the positive electrode and the negative electrode are required at the time of battery production. Mechanical strength can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of a non-aqueous secondary battery according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a non-aqueous secondary battery according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode, 2-1 Upper layer positive electrode film, 2-2 Lower layer positive electrode film, 3-1 Upper layer positive electrode film conductive thin film section, 3-2 Lower layer positive electrode film conductive thin film section, 4 Positive electrode collector 5 Negative electrode; 6-1 Upper negative electrode film; 6-2 Lower negative electrode film; 7-1 Upper conductive thin film portion of negative electrode film; 7-2 Lower conductive thin film portion of negative electrode film; Body, 9 separator, 10 unit cell body.

Claims (3)

[Claims] 1. A non-aqueous secondary battery having a positive electrode and a negative electrode containing an active material capable of inserting and releasing lithium ions,
A non-aqueous secondary battery, wherein the positive electrode or the negative electrode comprises at least an active material and conductive metal fine powder, and includes the metal fine powder having an average particle size of 0.1 μm to 30 μm forming a conductive network. 2. The non-aqueous secondary battery according to claim 1, wherein the fine metal powder contained in the positive electrode is made of a metal selected from aluminum, titanium, and stainless steel, or an alloy containing the same. 3. The method according to claim 1, wherein the fine metal powder contained in the negative electrode is made of a metal which does not significantly impair the form even when it comes into contact with lithium metal selected from a copper group and a platinum group, or an alloy containing the metal. The non-aqueous secondary battery according to claim 1.