JPH10188950A - Electrode for battery, and secondary battery using the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a battery excellent in safety, and provide a secondary battery using this electrode by laminating a resin layer on at least one part of an electrode material layer, which contains the active material. SOLUTION: An electrode for battery is formed by providing an electrode material layer, which contains an active material, on one surface or both surfaces of a collector. It is necessary for safety to laminate a resin layer on a part or the whole of the electrode material layer. As a resin, any resin, for example polyvinylidene fluoride, can be used. As a method for laminating the resin layer, any method for coating the electrode material layer with a resin solution and for drying it can be used. In this case, the electrode material and the resin layer are desirably adhered to each other so as to secure the higher safety. With this structure, even in the case where it is stung by a nail, the electrode material layer and the controller are hard to be exposed, and since the sudden generation of internal short-circuit between the electrode material layer or the collector and a battery can through the nail is hard to be generated, the safety is further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery electrode and a secondary battery using the battery electrode.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras, mobile phones, and notebook computers, demand for small, lightweight, high-capacity secondary batteries has been increasing. Many of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but it is difficult to increase the energy density because the average battery voltage is as low as 1.2V. Therefore, research on high energy secondary batteries using metallic lithium for the negative electrode has been conducted.

However, in a secondary battery using metallic lithium as a negative electrode, there is a danger that lithium may grow in dendrites by repeated charging and discharging, causing an internal short circuit and causing ignition. In addition, since highly active metal lithium is used, the risk is inherently high, and there are many problems in using it for consumer use. In recent years, lithium ion secondary batteries using various carbonaceous materials have been devised as a solution to such a safety problem and attaining high energy unique to a lithium electrode. This method utilizes that lithium ions are occluded (doped) in the carbonaceous material during charging and have the same potential as metallic lithium, and can be used as a negative electrode instead of metallic lithium. Further, at the time of discharging, the doped lithium ions are released (undoped) from the negative electrode and return to the original positive electrode material. like this,
When a carbonaceous material that can be doped with lithium ions is used as the negative electrode, the problem of dendrite formation is small, and since there is no metallic lithium, it is also excellent in safety, and active research is currently being conducted. .

[0004] Secondary batteries using battery electrodes utilizing lithium ion doping of the carbonaceous material described in JP-A-57-208079, JP-A-58-93176, and JP-A-58-93176.
No. 8-192266, JP-A-62-90863, JP-A-62-122066,
It is described in each gazette such as JP-A-2-66856.

Conventionally, battery electrodes used in these batteries generally include a positive electrode active material or a negative electrode active material and a binder,
An electrode material paste prepared by dissolving and dispersing an electrode material made of a conductive material or the like in a solvent is applied to one or both surfaces of a current collector and dried.

[0006]

On the other hand, in recent years, with the widespread use of secondary batteries having a high energy density, the demand for safety has been increasing. For example, as a safety test of a lithium ion secondary battery, a guideline for lithium secondary battery safety evaluation standards (Japanese Society of Storage Battery Association guideline SBAG11)
As described in 01), there are various tests such as electrical test, mechanical test and environmental test. In addition, various tests such as nail penetration, crushing, heating, and dropping in water are described as misuse tests in mechanical tests and environmental tests. Since batteries are in the hands of ordinary consumers, it is essential to pass these misuse tests. One of the most severe tests is the nail penetration test. However, with the battery electrode manufactured by the above method, the safety at the time of the nail penetration test was insufficient.

An object of the present invention is to provide a battery electrode having excellent safety and a secondary battery using the battery electrode.

[0008]

In order to achieve the above object, the present invention has the following arrangement.

"(1) In a battery electrode having an electrode material layer containing an active material provided on one or both surfaces of a current collector, a resin layer is laminated on at least a part of the electrode material layer. Characteristic electrode for batteries.

(2) A secondary battery using the battery electrode according to the above (1). "

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The battery electrode of the present invention is manufactured by providing an electrode material layer containing an active material on one or both surfaces of a current collector.

The current collector in the present invention is preferably a metal,
The metal can be used in the form of a foil, a net, a lath, or the like, but these are not particularly limited.

The battery electrode according to the present invention can be used for any kind of battery. In particular, when used for a lithium ion secondary battery, a carbonaceous material is preferably used as a part or all of the negative electrode active material. You.

The carbonaceous material is not particularly limited, and generally, a material obtained by firing an organic substance is used.
In addition, either crystalline or non-crystalline may be used. The form is not particularly limited, such as a powder form and a fibrous form. Specific examples include carbon fiber, artificial or natural graphite powder, and carbon fluoride.

In the present invention, carbon fibers are more preferably used. The carbon fiber used here is not particularly limited, but generally is obtained by firing an organic substance. Specifically, polyacrylonitrile (PA
N) PAN-based carbon fiber, pitch-based carbon fiber obtained from pitch such as coal or petroleum, cellulosic carbon fiber obtained from cellulose, vapor-grown carbon fiber obtained from gas of low molecular weight organic matter, and the like. However, in addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, and the like are also preferably used. Among these carbon fibers, carbon fibers satisfying the characteristics are appropriately selected and used according to the characteristics of the electrode and the battery in which the carbon fibers are used. Among the carbon fibers, when used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt such as lithium, PAN
-Based carbon fibers and pitch-based carbon fibers are preferred. Among them, PAN-based carbon fibers are preferably used because alkali metal ions, particularly lithium ions, are preferably doped.

The diameter and length of the carbon fiber are not particularly limited, but it is preferable to use milled carbon fiber from the viewpoint of easy application by a coater. The milled carbon fibers have a diameter of preferably 0.1 to 1000 μm, more preferably 3 to 10 μm, and an average length of preferably 5 μm or more and less than 1 mm, more preferably 7 μm or more and less than 100 μm. When milled carbon fibers are used, it is more preferable to perform high-temperature heat treatment in advance to improve cycle characteristics.

In the present invention, the amount of the carbonaceous material used is not particularly limited, but is preferably 70% by weight in the electrode material.
As described above, the content is preferably 99% by weight or less. If it is less than 70% by weight or more than 99% by weight, the battery capacity tends to decrease. More preferably, the content is 75% by weight or more and 90% by weight or less.

In the present invention, when a carbonaceous material is used as the negative electrode active material, a Li composite oxide is preferably used as the positive electrode active material. Especially LiCoO ₂ , LiNiO ₂ , LiMn ₂ O
₄ , Li _y Ni _1-x Me _x O ₂ (Me: Ti, V, Mn, or Fe), Li _1-xa
A _x Ni _1-yb B _y O ₂ (where A is at least one kind of alkali or alkaline earth metal element and B is at least one kind of transition metal element) has a high voltage and a large energy density, Most preferably used. In particular, Li
_{In 1-xa} A _x Ni _1-yb B _y O ₂ , 0 <x ≦ 0.1, 0 ≦ y ≦ 0.
3, -0.1 ≤ a ≤ 0.1, -0.15 ≤ b ≤ 0.15 (However, when A and B are composed of two or more elements, x is an alkali or alkaline earth metal excluding Li, and y is excluding Ni When y is equal to the total number of moles of all transition metal elements, A includes at least one or more alkaline earth metal elements.) By doing so, a positive electrode material having excellent characteristics can be obtained. Especially preferred
A includes Mg, Sr, and B includes Co and Fe.

As the positive electrode active material, in addition to the Li composite oxide, a transition metal oxide containing an alkali metal, an inorganic compound such as a transition metal chalcogen, polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, polythiophene Conjugated polymers such as
Examples include a crosslinked polymer having a disulfide bond, thionyl chloride, and the like. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt as an electrolyte, cobalt, nickel, manganese, molybdenum, vanadium,
Transition metal oxides such as chromium, iron, copper and titanium and transition metal compounds such as transition metal chalcogens are preferably used.

In the present invention, the binder is not particularly limited. Specifically, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride
/ Propylene hexafluoride copolymer, tetrafluoroethylene / propylene hexafluoro copolymer, polyethylene, polypropylene, styrene / propylene copolymer (SBR), polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyacetic acid Vinyl, polyacrylic acid, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyacrylamide, polyvinyl acetal, polyurethane, polyethylene oxide, polypropylene oxide, polydimethylsiloxane, epoxy resin, melamine resin, phenolic resin, lignin, alginic acid,
Examples include pectin, gelatin, cellulose and / or a cellulose salt. These can be used alone,
It can be used as a mixture of more than one species.

When the above-mentioned binder is added to the solvent, the form may be a powder, a solution or a dispersion (dispersion,
Emulsion).

The amount of the binder used is not particularly limited, but may be 0.1% by weight or more and 30% by weight or less in the electrode material.
The following is preferred. If it is less than 0.1% by weight, the coating properties may be insufficient, and if it exceeds 30% by weight, the battery capacity tends to decrease. 0.5% by weight or more, 20% by weight
It is more preferred that:

The conductive material used in the present invention is not particularly limited, such as a carbon material and a metal powder. Particularly preferred conductive materials include various carbon blacks.

Specific examples of carbon black include gas black, oil black, acetylene black, and the like. Creosote oil, petroleum heavy oil, natural gas, naphthalene, pitch oil, acetylene gas, etc. are used as raw materials.
Those manufactured by a furnace method, a contact method, a thermal method, or the like can be used.

Among carbon blacks, acetylene black or Ketjen black having a significantly low hydrogen content and a high carbon content is preferably used from the viewpoint of conductivity. In addition, from the viewpoints of further improving conductivity and improving electrode characteristics, it is also possible to use natural graphite, artificial graphite and the like in combination.

In order to improve the conductivity by adding a conductive material, the optimum particle size and the amount of addition should be determined experimentally according to the material, shape, and particle size of the active material, and the type and amount of the binder. Usually, fine particles having a primary particle diameter of 0.001 μm to 100 μm, more preferably 0.005 μm to 20 μm are used,
The addition amount is 0.1 to 20% by weight, more preferably 0.5 to 10% by weight in the electrode material. Primary particle size 0.00
If it is less than 1 μm, stable production is difficult, and
Thicknesses exceeding 100 μm are not preferred because of the problem that the effect of addition is small. On the other hand, if the addition amount is less than 0.1 wt%, the effect of addition is small, and if it exceeds 20 wt%, the capacity per unit weight of the electrode decreases.

The method for producing an electrode for a battery by providing an electrode material layer on a current collector is not particularly limited.
An electrode material paste prepared by dissolving and dispersing an electrode material composed of a binder, a conductive material, or the like in a solvent is applied to one or both surfaces of the current collector, and then dried.

The solvent is not particularly limited, and any one of water and an organic solvent can be appropriately selected and used depending on the solubility of the binder and the like.

The method for dispersing the electrode material in the solvent is not particularly limited, and it can be carried out using a known disperser.

Examples of the dispersing machine include a ribbon mixer, a screw mixer, a homogenizer, a homomixer, a pin mixer, a kneader, a ball mill, a bead mill, and a mill. These dispersers may be used alone or in combination.

Further, at the time of dispersion, various dispersants,
It is also preferable to add a stabilizer and a surfactant.

As a method of applying the electrode material paste to the current collector, a general method can be used. Specifically, reverse roll method, direct roll method, blade method, knife method, extrusion method, curtain method,
A gravure method, a bar method, a dip method, a squeeze method, a spray method and the like can be mentioned.

Further, if necessary, it is preferable to subject the electrode for a battery after application and drying to a treatment such as a heat treatment or a press.

The electrode material layers are preferably provided on both sides of the current collector. When a battery electrode is manufactured by providing an electrode material layer on one side of the current collector, the battery electrode is likely to be warped during heat treatment or pressing, so the two uncoated surfaces should be overlapped. Therefore, it is preferable to take the same form as when applied to both surfaces.

In the present invention, in order to improve safety,
It is indispensable to laminate a resin layer on a part or entire range of the electrode material layer.

The resin is not particularly limited, and the same resin as the binder described above can be used. The form is not particularly limited, such as liquid, solution, dispersion (dispersion, emulsion, etc.), film, mesh, and fiber. It is also preferable that the resin layer contains various conductive materials, stabilizers, dispersants, surfactants, and the like, if necessary.

The method for laminating the resin layer is not particularly limited, and examples thereof include a method of applying and drying a resin solution or the like on the electrode material layer, and a method of attaching a film on the electrode material layer. When the resin layer is laminated by the former method, it is preferable that the solvent contained in the resin solution does not dissolve the binder contained in the electrode material layer.

As long as the effect of improving the safety of the resin layer can be ensured, there is no problem in laminating the entire electrode material layer or only a part of the electrode material layer. Specific examples include a method of applying in a stripe form, a method of applying a resin solution by spraying, and a method of attaching a porous film. In addition, it is not always necessary to laminate the electrode material layers on both sides of the electrode for the electrode, and there is no particular problem if only one side is used. In addition, there is no need to laminate both the positive electrode and the negative electrode.

The thickness of the resin layer is not particularly limited, but is preferably 100 μm or less. 100μ
If m is exceeded, battery performance such as battery capacity may be adversely affected. Further, the thickness is preferably 50 μm or less.

In the present invention, it is sufficient that a resin layer is laminated on at least a part of the electrode material layer. However, in order to ensure higher safety, it is necessary that the electrode material and the resin layer are bonded to each other. preferable. By doing so, for example, even when a nail is pierced, the electrode material layer or the current collector is less likely to be exposed, and a sharp internal short circuit with the battery can is less likely to occur via the nail, thereby further improving safety. .

The form of the battery using the battery electrode manufactured in the present invention is not particularly limited, but a battery using an electrode body in which a positive electrode, a negative electrode, and a separator are spirally wound is used as an electrode unit. This is preferable because the current per area is small and the battery can be used under heavy load. Also, the form is not particularly limited, such as a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

The separator in the present invention is not particularly limited as long as it can prevent a short circuit between the positive electrode and the negative electrode. In addition, the electrolyte has good permeability,
It is desirable not to cause electron and ion migration resistance, and typical materials include polyolefin, polyester,
Polyamide, polyacrylate, polymethacrylate,
Polysulfone, polycarbonate, polytetrafluoroethylene and the like can be mentioned. Among them, polyethylene, polypropylene, polysulfone and the like are particularly preferred because of their excellent strength and safety. Examples of the shape of the separator generally include a porous film and a nonwoven fabric, but a porous film is preferable because the filling rate in the battery can is easily increased. Further, the porous membrane is generally a symmetric membrane or an asymmetric membrane, but may be a composite membrane in which a plurality of types of membranes are laminated in order to improve strength and safety. The porosity of the porous film is preferably as high as possible in order to increase the permeability of electrons and ions, but there is a risk of causing a decrease in the strength of the film, so it should be determined according to the material and the film thickness. is there. Generally, it is desirable that the film thickness is 20 to 100 μm and the porosity is 30 to 80%.
Further, the diameter of the pores is desirably within a range in which the active material, the binder, and the conductive material detached from the electrode sheet do not penetrate.

In the present invention, the shape of the spirally wound electrode body does not necessarily have to be a true cylindrical shape.
A long cylindrical shape having an elliptical spiral cross section or a prism having a rectangular cross section such as a rectangle may be used. In this case, the battery can can also take a shape corresponding to the shape of the electrode body. Typical usage patterns include:
The most common form is a spiral-shaped electrode body and electrolyte loaded in a cylindrical bottom battery can, and the lead taken out of the electrode sheet is sealed with the cap and the battery can welded together. However, the present invention is not particularly limited to this mode.

In the present invention, the battery can in which the spiral electrode body is loaded is not particularly limited.
Battery cans, stainless steel battery cans, and the like, which are plated with a metal such as, are preferred because of their excellent strength, corrosion resistance, and workability. Further, it is possible to reduce the weight by using an aluminum alloy or various engineering plastics, and it is also possible to use various engineering plastics and metals in combination.

The solvent used for the electrolyte in the present invention is not particularly limited, and a conventional solvent can be used. For example, an acid or alkali aqueous solution, a non-aqueous solvent and the like can be mentioned. Among them, as the solvent of the electrolyte of the secondary battery comprising the non-aqueous electrolyte containing the above-described alkali metal salt, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, γ
-Butyrolactone, N-methyl-2-pyrrolidone, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolan, methyl formate, sulfolane, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate And their derivatives and mixtures are preferably used.

The electrolyte contained in the electrolytic solution of the present invention includes alkali metal, especially lithium halide,
Perchlorate, thiocyanate, borofluoride, phosphorous fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate and the like are preferably used. Particularly, lithium salt has the lowest standard electrode potential and can obtain a large potential difference, and thus is more preferably used as an electrolyte contained in an electrolytic solution.

According to the present invention, it is possible to provide a battery electrode having excellent safety and a secondary battery using the battery electrode.

[0048]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to these examples. Note that the nail penetration test is based on the guidelines for lithium secondary battery safety evaluation standards (guideline of the Japan Storage Battery Association, SBAG
1101).

Example 1 90 wt% of LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride: 5 wt% of “KF polymer” # 1000 (manufactured by Kureha Chemical Industry Co., Ltd.) as a binder, and acetylene black as a conductive material:
5 wt% of "DENKA BLACK" (manufactured by Denki Kagaku Kogyo KK) was mixed, and this mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode material paste. Then, the positive electrode material paste was uniformly applied to both surfaces of a 20 μm-thick aluminum foil as a current collector, dried, and then roll-pressed to obtain a positive electrode.

Next, a PAN-based carbon fiber “Treca” T-300 (manufactured by Toray Industries, Inc.) as a negative electrode active material was shortened to 80 watts.
t%, polyvinylidene fluoride as binder: 15 wt% of “KF Polymer” # 1000 (Kureha Chemical Industry Co., Ltd.), and acetylene black as conductive material: 5 wt% of “Denka Black” (Denki Chemical Industry Co., Ltd.) And mix this mixture with N-methyl-2.
-Dispersed in pyrrolidone to prepare a negative electrode material paste.
Then, the negative electrode material paste is applied with a thickness of 16 μm as a current collector.
After being uniformly applied to both sides of a copper foil having a thickness of m and dried, the roll was pressed to obtain a negative electrode.

Next, sodium carboxymethylcellulose: “CMC Daicel” was added to the electrode material layers of the positive electrode and the negative electrode.
An aqueous solution of # 1290 (manufactured by Daicel Chemical Industries, Ltd.) was applied and dried to laminate a resin layer having a thickness of 10 μm.

Next, an aluminum plate having a thickness of 100 μm and a width of 3 mm was welded to the positive electrode and a nickel plate having a thickness of 100 μm was welded to the negative electrode, and then a porous polyethylene film “SETELA” E25MMO (Tonen Chemical Co., Ltd.) was used as a separator. )), The positive electrode was overlapped so as to be on the inside, and wound, thereby obtaining a spiral electrode body. Similarly,
A total of 100 electrode bodies were produced. The filling rate of the electrode body in the battery can was 98%.

Next, the electrode body was loaded into a cylindrical battery can having a diameter of 18 mm and a length of 65 mm, and propylene carbonate and dimethyl carbonate containing 1M-lithium phosphofluoride as an electrolyte were used.
A battery using a 1: 1 mixture was prepared. The battery was charged at a constant current and a constant voltage with a charging current of 1 A, a constant voltage value of 4.2 V, and a charging time of 2.5 hours, and a capacity test was performed at a discharge current of 200 mA and a discharge end voltage of 2.5 V.

Next, the battery was subjected to a nail penetration test. The results are shown in Table 1.

Example 2 In Example 1, sodium carboxymethylcellulose: “CMC Daicel” was added to the electrode material layers of the positive electrode and the negative electrode.
An aqueous solution of # 1290 (manufactured by Daicel Chemical Industries, Ltd.) 80 wt% and alkali lignin (special grade of reagent manufactured by Wako Pure Chemical Industries, Ltd.) 20 wt% was applied and dried to form a 10 μm-thick resin layer. Except for the above, the production of the battery
A capacity test and a nail penetration test were performed. The results are shown in Table 1.

Comparative Example 1 A battery was prepared, a capacity test and a nail penetration test were performed in the same manner as in Example 1 except that the resin layer was not laminated. The results are shown in Table 1.

Comparative Example 2 In Comparative Example 1, the filling rate of the electrode body to the battery can was changed to 8
A battery was prepared, a capacity test, and a nail penetration test were performed in the same manner as in Comparative Example 1 except that 0% was set. The results are shown in Table 1.

[0058]

【table 1】

[0059]

According to the present invention, it is possible to provide a battery electrode excellent in safety and a secondary battery using the battery electrode.

Claims (8)

[Claims] 1. A battery electrode comprising an electrode material layer containing an active material provided on one or both surfaces of a current collector, wherein a resin layer is laminated on at least a part of the electrode material layer. Electrode for the battery. 2. The battery electrode according to claim 1, wherein the electrode material layer and the resin layer are bonded to each other. 3. The battery electrode according to claim 1, wherein a part or all of the active material is a carbonaceous material. 4. The battery electrode according to claim 1, wherein a part or all of the carbonaceous material is carbon fiber. 5. The battery electrode according to claim 4, wherein the carbon fiber is a carbon fiber obtained from polyacrylonitrile. 6. The battery electrode according to claim 4, wherein the carbon fibers are milled carbon fibers. 7. The battery electrode according to claim 1, wherein part or all of the active material is a Li composite oxide. 8. A secondary battery using the battery electrode according to any one of claims 1 to 7.