JPH10112323A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighter battery, by producing a current collector as layer construction of thin films P containing specific resin and electronic conductive thin films E in the inner electrode, and by making the thin films E include a junction layer having high adhesive strength with the thin film P and an electric conductive layer with resistance less than that of the junction layer. SOLUTION: Thin films P consist of thermoplastic resin such as polyethylene, polyethylene terephthalate, or polypropylene, which has a thermal transformation temperature less than the ignition temperature of organic electrolyte in a battery. Thin films E used in the current collector of a negative electrode 4 contain mainly Ni and Cu in junction layers and electric conductive layers, and thin films P containing resin constitute two or three layers structure with thin films E. Thin films E used in the current collector of a positive electrode 3 is composed of aluminum Al and SUS for example. Thus, a lighter battery is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such a requirement is an active material such as lithium metal or lithium alloy, or a host material containing lithium ions (here, a host material refers to a material that can occlude and release lithium ions). Lithium intercalation compound occluded in a certain carbon is used as a negative electrode material, and LiC
This is a lithium secondary battery using an aprotic organic solvent in which a lithium salt such as IO ₄ and LiPF ₆ is dissolved as an electrolyte.

A lithium secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held by a negative electrode current collector as a support, and reversibly electrochemically reacts with lithium ions like a lithium cobalt composite oxide. It consists of a positive electrode plate holding the positive electrode active material on a positive electrode current collector as its support, and a separator that holds an electrolytic solution and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between both electrodes. .

In the case of a rectangular or cylindrical battery, the positive electrode plate, the separator and the negative electrode plate are each formed by laminating thin sheets or foils in order, and spirally wound into a battery container. Is stored. Therefore, the plates are
Generally, an active material or a host material is mixed with an organic binder, a conductive agent and a solvent to form a paste, which is applied to the surface of the support, dried, and then pressure-formed together with the support in the thickness direction. You. Conventionally, as the current collector of the electrode plate,
Since it is necessary to have its own conductivity, a metal foil such as copper or aluminum has been used.

[0005]

In the case of equipment using a battery as a power source, not limited to a lithium battery, the demand for weight reduction and safety of the entire equipment has not been exhausted. Therefore, if the battery performance is the same, the lighter and safer the battery, the more favorable the user.

[0006] However, there are limitations in production and handling in reducing the thickness of the metal foil of the current collector. In addition, PTC elements, protection circuits, current cutoff mechanisms, and the like are provided as countermeasures against device damage, but there are few measures to secure the electrodes themselves, which are energy storage sources. Therefore, an object of the present invention is to provide a lightweight and safe battery by deviating from the concept of the conventional current collector and making the structure of the current collector completely different from the conventional one.

[0007]

In order to achieve the object, a battery of the present invention comprises an internal electrode comprising a mixture containing an active material or a host material and a film-like current collector holding the mixture. The current collector comprises a thin film P containing a resin;
It is a layered body with the electron conductive thin film E, and the thin film E is characterized by including a bonding layer having excellent adhesion to the thin film P and a conductive layer having a lower resistivity than the bonding layer.

[0008] The battery of the present invention is lighter than a battery having a metal foil of the same thickness as the current collector because the current collector has a thin film P containing a resin as a core. The thin film P may be a composition of a resin and another material in addition to the one composed of only the resin. In addition, since most of the resins have a heat deformation temperature lower than the ignition point of the organic electrolyte, even if heat is generated by short-circuiting, the thin film P containing the resin is formed before the organic electrolyte such as the organic electrolyte or the polymer electrolyte ignites. Heat shrinks or melts, interrupting the current. In this regard, in the case of metal foil, since its melting point is higher than the ignition point of the organic electrolyte, if heat is generated due to short-circuit, the organic electrolyte will ignite before the electrode temperature reaches the melting point of the metal foil, resulting in a dangerous state. Differently, the current collector applied to the present invention also has a current interruption function. Although most of the resin is insulative, the current flows through the thin film E of the current collector because the electron conductive thin film E is in close contact with the surface of the thin film P containing the resin.

However, if the portion of the thin film E is too thin, the resistance of the thin film E becomes too high to allow a current to flow easily, so that sufficient discharge capacity cannot be obtained. On the other hand, it is technically difficult to form a plated film directly in contact with the thin film P containing resin, and increasing the thickness by vapor deposition requires a great deal of cost. Further, even if the thin film E is made of a metal foil, there is a case where some metals are not commercially available in a foil form.

Therefore, the electron conductive thin film E itself has a laminated structure including a bonding layer having excellent adhesion to the thin film P and a conductive layer having a lower resistivity than the bonding layer. Since the bonding layer is interposed between the thin film P and the conductive layer for the purpose of bringing the entire thin film E into close contact with the thin film P, the resistivity may be low as long as it has electronic conductivity. Therefore, forming means such as (1) applying a conductive powder such as carbon or metal mixed with an organic binder and (2) evaporating a metal can be applied. Since the conductive layer is formed on the bonding layer containing a conductive material, it can be formed thick by plating, and lowers the electric resistance of the entire thin film E. In this way, the current collector has the thin film E having a low electric resistance adhered to the thin film P containing the resin. The thickness of the entire thin film E is 0.1 to
5 μm is preferred.

As described above, the battery of the present invention is light and safe because its current collector is light and has a current interrupting function when a short circuit occurs. Of course, it is not limited to an organic electrolyte battery, and there is no distinction between a primary battery and a secondary battery.
It goes without saying that weight reduction and safety can be expected in all batteries such as d batteries, Ni-HM batteries, and lead batteries.
Further, when a conventional current collector made of a metal foil is cut into a predetermined size, burrs may be generated on the cut surface, which may cause a short circuit. Since the thin film P containing a resin is used as a core, the cutting property is excellent and burrs do not occur.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In order to ensure the above current interruption function, in the case of an organic electrolyte battery, the resin of the thin film P is preferably one having a heat distortion temperature lower than the ignition point of the organic electrolyte of the battery. . As a method for measuring the ignition point, there are known two methods, a constant-speed heating method and a constant-temperature heating method. If you are not sure which one is more realistic, it is safer to choose a lower measurement. Examples of the material of the resin constituting the thin film P include polyethylene (PE) and polyethylene terephthalate (PE).
T) and thermoplastic resins such as polypropylene (PP).

As the thin film E applied to the current collector of the positive electrode, Al and SUS are preferable because of their excellent corrosion resistance. As the thin film E applied to the current collector of the negative electrode, it is preferable that both the bonding layer and the conductive layer mainly include Ni and Cu. In particular, since Ni does not dissolve up to 4.0 to 4.2 V vs. Li / Li ⁺ , the usable potential region is wide.

The layer structure of the layered body may be two layers of a thin film P containing a resin and a thin film E, or three layers of a thin film E, a thin film P containing a resin and a thin film E in this order. The electron conductive thin film E
The third layer other than the bonding layer and the conductive layer may be interposed between the bonding layer and the conductive layer, or the third layer may be provided on the conductive layer. For example, it is conceivable to provide a third layer having excellent adhesion to the mixture layer on the conductive layer. As a means for forming a layer, various known means including vapor deposition and plating can be applied. The thin film P and the thin film E may be in close contact with each other, or may be in close contact with each other. The shape of the entire electrode is not limited to a spiral shape.

[0015]

【Example】

-Example 1-An example of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view of the organic electrolyte battery of the embodiment. The organic electrolyte battery 1 is a prismatic lithium secondary battery in which an electrode group 2 including a positive electrode plate 3, a negative electrode plate 4, and a separator 5 is housed in a battery case 6 together with a non-aqueous electrolyte (not shown).

The positive electrode plate 3 is a current collector in which a lithium-cobalt composite oxide is held as an active material. The current collector was obtained by laminating a 1 μm-thick aluminum foil on both sides of a 15 μm-thick PP film and bonding them with an adhesive. The positive electrode plate 3 is prepared by mixing 8 parts of polyvinylidene fluoride as a binder and 5 parts of acetylene black as a conductive agent together with 87 parts of an active material to prepare a paste, and then applying the paste to both surfaces of the current collector material , Made by drying.

The current collector of the negative electrode plate 4 is a 15 μm thick PP.
First, a mixture of 90% by weight of nickel Ni powder having an average particle diameter of 0.3 μm and 10% by weight of polyamideimide powder is applied to both sides of the film to a thickness of 5 μm, and then electrolessly plated with nickel having a thickness of 1 μm. Obtained by. FIG. 2 shows a cross-sectional view of the current collector. The obtained current collector 41 is a PP film 4
2 and a thin film E composed of a bonding layer 43 in close contact with the PP film 42 and a conductive layer 44 thereon. The bonding layer 43 has a relatively high electric resistance since the nickel content is 80% by weight, but is strongly adhered to the PP film 42 by the binder. Since the conductive layer 44 is 99% by weight or more of nickel, it has a low electric resistance and is chemically bonded to nickel in the bonding layer 43. The negative electrode plate 4 is prepared by mixing 86 parts of graphite (graphite) as a host material and 14 parts of polyvinylidene fluoride as a binder and forming a paste on both surfaces of the current collector 41, and then drying the mixture. It was produced by.

The separator 5 is a polyethylene microporous membrane. The electrolyte was ethylene carbonate: diethyl carbonate = 4: 6 containing 1 mol / l of LiPF6.
(Volume ratio).

Each dimension is such that the positive electrode plate 3 has a thickness of 180 μm.
m, width 29 mm, separator 5 thickness 25 μm, width 3
3 mm, the negative electrode plate 4 has a thickness of 170 μm and a width of 31 mm. The negative electrode plate 4 is superposed in order and wound around the polyethylene core in an elliptical shape around the core.
It is stored in. The battery case 6 has a thickness of 0.3 mm,
The surface of an iron main body having an inner size of 33.1 × 46.5 × 7.5 mm is nickel-plated with a thickness of 5 μm, and a hole 12 for injecting an electrolyte is provided at an upper side portion.

The positive electrode plate 3 includes a safety valve 8 and a positive electrode terminal 1.
0 is connected via a positive electrode lead 11 to a terminal 10 of a case lid 7 provided with a zero. The negative electrode plate 4 is connected to a negative electrode lead (not shown) welded to the lower surface of the lid 7. Then, the battery is sealed by laser welding the lid 7 to the case 6.

The weight of the completed battery was 16 g.
This battery was charged at a constant current of 1 CmA to a final charge voltage of 4.1 V, and then 2.5 m in diameter from the side of the case 6 of the battery 1.
m was passed through an iron nail and observed for a while, but the electrolyte did not ignite.

Example 2 Same as Example 1 except that the current collector of the negative electrode plate 4 was made of copper having a thickness of about 2000 angstroms by vacuum evaporation instead of applying nickel powder to the PP film. The battery was manufactured under the conditions.

The weight of the completed battery was 16 g.
This battery was charged at a constant current of 1 CmA to a final charge voltage of 4.1 V, and then 2.5 m in diameter from the side of the case 6 of the battery 1.
m was passed through an iron nail and observed for a while, but the electrolyte did not ignite.

Comparative Example A comparison was made under the same conditions as in Example 1 except that a 20 μm thick aluminum foil was used as the current collector of the positive electrode plate 3 and a 20 μm thick copper foil was used as the current collector of the negative electrode plate 4. Batteries were manufactured. The weight of this battery was 20 g. When an iron nail having a diameter of 2.5 mm was passed through the side of the case 6 of the battery 1, smoke was emitted 30 seconds later.

[0025]

As described above, according to the present invention, the battery can be made light and safe, which is useful as a component of a portable electronic device.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an organic electrolyte battery of an example.

FIG. 2 is a cross-sectional view showing a current collector applied to an electrode of an organic electrolyte battery of an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic electrolyte battery 2 Electrode group 3 Positive electrode plate 4 Negative electrode plate 5 Separator 6 Battery case 7 Case cover 41 Current collector 42 PP film (thin film P) 43 Bonding layer 44 Conductive layer

Claims (9)

[Claims] 1. A battery in which an internal electrode comprises a mixture containing an active material or a host material and a film-like current collector holding the same, wherein the current collector comprises a thin film P containing a resin, A battery comprising a layered body with a conductive thin film E, wherein the thin film E includes a bonding layer having excellent adhesion to the thin film P and a conductive layer having a lower resistivity than the bonding layer. 2. The battery according to claim 1, wherein the battery is an organic electrolyte battery such as an organic electrolyte battery or a polymer electrolyte battery. 3. The battery according to claim 2, wherein the resin of the thin film P has a heat distortion temperature lower than the ignition point of the organic electrolyte. 4. The resin of the thin film P is made of polyethylene (P
The battery according to claim 2, comprising a thermoplastic resin such as E), polyethylene terephthalate (PET), or polypropylene (PP). 5. The bonding layer according to claim 1, wherein said bonding layer comprises a mixture of a conductive powder such as Al, Ni, Cu, Fe and a binder.
The battery according to any one of the above. 6. The battery according to claim 1, wherein said bonding layer is made of a vapor-deposited metal. 7. The battery according to claim 6, wherein the metal deposited is aluminum Al, nickel Ni or copper Cu. 8. The battery according to claim 1, wherein said conductive layer is made of a plated metal. 9. The plated metal is nickel Ni or copper C.
The battery according to claim 8, which is u.