JPH1197067A - Battery and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery of high capacity and high safety, and a manufacturing method thereof. SOLUTION: In this battery, an electrode body obtained by placing an positive electrode sheet and a negative electrode sheet respectively prepared by coating one or both faces of collectors with a positive electrode material and a negative electrode material respectively comprising at least an electrode active material and a binding material, in opposition to each other, is used. On this occasion, a blending ratio of the binding material of one or both of the positive electrode material and the negative electrode material is not less than 25% and not more than 40% by volume ratio to the total electrode material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a positive electrode sheet and a negative electrode sheet which are produced by applying at least one of a positive electrode material and a negative electrode material composed of an electrode active material and a binder to one or both surfaces of a current collector. The present invention relates to a battery using an electrode body having sheets facing each other and a method for manufacturing the same.

[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. For this reason, research on high energy secondary batteries has been conducted using lithium metal, which is the most basic metal for the negative electrode.

However, in a secondary battery using lithium metal for the negative electrode, there is a risk of lithium growing in a dendritic form (dendrites) due to repeated charging and discharging, causing a 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, such safety problems have been solved.
In addition, lithium ion secondary batteries using various carbonaceous materials have been devised as those capable of high energy peculiar to lithium electrodes. This method utilizes that lithium ions are occluded (doped) in the carbonaceous material during charging, have the same potential as metallic lithium, and can be used as a negative electrode instead of metallic lithium. Further, at the time of discharge, the doped lithium ions are released (dedoped) from the negative electrode and return to the original carbonaceous material. When such a carbonaceous material doped with lithium ions is used as the negative electrode, the problem of dendrite generation is small, and since there is no metallic lithium, there is a feature that the safety is excellent, Currently, active research is being conducted.

[0005] As a secondary battery using an electrode utilizing lithium ion doping of the above carbonaceous material,
JP-A-57-20807, JP-A-58-931
No. 76, JP-A-58-192266, JP-A-62-90863, JP-A-62-12266, JP-A-2-66656, and the like.

At present, LiCoO ₂ is most popular as a positive electrode active material used for a positive electrode of a lithium ion secondary battery, and LiNiO ₂ , LiNiO ₂
Mn ₂ O ₄ , LiMnO _{2 and the} like.
Since the amount of lithium ions that can be inserted into and released from a positive electrode active material using is larger than others, research and development have been promoted as a very promising material. The present inventors have also conducted intensive studies on the development of a positive electrode active material having a large amount of lithium ion occlusion and release.

[0007]

However, lithium ion secondary batteries use a non-aqueous electrolyte, and therefore have the danger that the electrolyte will burn in the event of an accident. In addition, the risk is increased by increasing the capacity. In particular, a dangerous situation for the battery is a so-called internal short circuit in which the positive electrode and the negative electrode come into direct contact inside the battery due to external mechanical force or the like. When an internal short-circuit occurs, the energy held by the battery is concentrated at the short-circuit location, and there is a danger of causing the worst case in which smoke, fire, and eventually the battery explodes due to abnormal heating.

Accordingly, an object of the present invention is to provide a battery capable of ensuring high safety in a battery having a high capacity, that is, a high energy density, and a method of manufacturing the battery.

[0009]

According to the present invention, there is provided a positive electrode sheet comprising at least one of a positive electrode material composed of an electrode active material and a binder, and a negative electrode material coated on one or both surfaces of a current collector. In a battery using an electrode body in which a sheet is opposed, the mixing ratio of one or both of the positive electrode material and the negative electrode material is 25% or more and 40% by volume ratio with respect to the entire electrode material. This is basically achieved by a battery characterized by the following.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies, and have obtained the following findings when the battery internal temperature rises due to the occurrence of a short circuit inside a lithium ion secondary battery.
Inside the battery, the lithium-containing transition metal oxide, which is the positive electrode active material, and the carbon material, which is the negative electrode active material, generate heat mainly depending on the constituent materials, as described above. In particular, since the positive electrode active material releases oxygen as a result of thermal decomposition, it induces combustion inside the battery, resulting in a very dangerous state. In addition, it has been found that the more the carbon material absorbs lithium ions, the more the calorific value during decomposition increases dramatically. Therefore, if a short circuit occurs inside the battery in the charged state, a large amount of heat is generated, and there is a high risk of thermal runaway.

Here, it is a major point not to cause thermal runaway, but in essence, reducing the short-circuit current and reducing the amount of heat generated per time is the best way to prevent thermal runaway. Is the way. In consideration of this point, when examining the material configurations of the positive electrode and the negative electrode, it was found that the amount of heat generated by the short circuit of the battery greatly changed depending on the content ratio of the binder. That is, it has been found that it is possible to suppress heat generation due to a short-circuit current at the time of an internal short-circuit by increasing the content ratio of the binder. on the other hand,
Since the substance used for the binder has low conductivity, an excessively large ratio of the binder increases the electric resistance, and undesirably impairs the load characteristics of the battery. However, the characteristics can be maintained to some extent by adjusting the amount of a conductive material added for maintaining the conductivity.
Also, increasing the mixing ratio of the binder and the conductive material is
The content of the active material is substantially reduced, which leads to a reduction in the capacity of the battery.

From the above, after all, at least one of the positive electrode material and the negative electrode material present in the battery is made into a volume ratio of 25% or more and 40% or less, thereby maintaining the battery characteristics. Thus, a highly safe battery can be supplied even when an internal short circuit occurs.

Here, the effective binder compounding ratio for achieving the object of the present invention in the positive electrode and the negative electrode was examined.
In the positive electrode, the volume ratio is 30% of the whole positive electrode material.
It has been found that it is preferable to set the above to 40% or less. On the other hand, in the case of the negative electrode material, the effect is exhibited even if the amount is less than that of the positive electrode material.
It has been found that high safety can be maintained by setting the content to 5% or more and 30% or less.

Incidentally, the binder used in the present invention may be either a thermoplastic resin or a thermosetting resin, and is not particularly limited. However, the binder is deformed or changes its properties due to heat generation inside the battery. In view of the fact that they are preferred, those that exhibit plasticity by heat are preferred. When used as a part of the positive and negative electrode materials, they can be used in the form of a solution or an emulsion. Specifically, examples of the binder include various epoxy resins, cellulose resins, organic fluorine-based polymers, copolymers, acrylic resins, organic chlorinated resins, polyimides, polyamides, and polycarbonates. In particular, organic fluoropolymers and copolymers are preferable from the viewpoint of chemical stability, but considering that they should be softened and melted at the start of heat generation due to an internal short circuit, heat generation causes the active material of the positive and negative electrodes to undergo thermal runaway. Those whose properties are easily changed are preferable, and among them, polyvinylidene fluoride, propylene hexafluoride polymer and copolymer are mentioned as preferable examples.

There is no particular limitation on the battery used in the present invention. However, as a battery mounted on a portable device requiring a high energy density, a battery using an alkali metal as a negative electrode material, a carbonaceous material, or the like can be used. A secondary battery utilizing doping of a cation or an anion into a metal is effective.

In the case of these batteries, that is, when used for a non-aqueous electrolyte secondary battery containing an alkali metal salt, a carbonaceous material doped with an alkali metal or a cation is used as a negative electrode and a material doped with an anion is used as a negative electrode. Will be used for the positive electrode.

As a positive electrode active material, as a carbonaceous material,
Carbon fiber, artificial or natural graphite powder, carbon fluoride, inorganic compounds such as metals or metal oxides, and organic polymer compounds can be used. In this case, a charge / discharge reaction occurs using cation doping and undoping using an inorganic compound such as a metal or a metal oxide as a positive electrode. In the case of an organic polymer compound, a charge / discharge reaction occurs by doping and undoping of an anion. As described above, various charge / discharge reaction modes are adopted depending on the substance, and these are appropriately selected according to the required positive electrode characteristics of the battery.

Examples of the positive electrode containing no carbonaceous material include inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals, and conjugated polymers such as polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, and polythiophene. And positive electrode active materials used in ordinary secondary batteries, such as a crosslinked polymer having a disulfide bond and thionyl chloride. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, transition metal oxides and transition metals such as cobalt, nickel, manganese, molybdenum, vanadium, chromium, iron, copper, and titanium are used. Chalcogens are preferably used. In particular, LiCoO ₂ , LiNiO ₂ , L
iMn ₂ O ₄ , Li _y Ni _{1 -x} Me _x O ₂ (Me: T
i, V, Mn, or Fe), Li _{1 -xa} A _x Ni
_{1 -yb} B _y O ₂ (however, A is at least one alkali or alkaline earth metal element, B is at least one transition metal element) has a high voltage, the energy density is also large, and most preferably used. In particular, L
In _{i 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 the total number of moles of alkali or alkaline earth metals excluding Li, and y is all transition metals excluding Ni. The total number of moles of elements, if y = 0, A is at least 1
Or more kinds of alkaline earth metals), it is possible to obtain a positive electrode active material having excellent characteristics. Particularly preferred A is Mg, Sr, B is Co, F
e.

The carbon material used as the negative electrode active material has various shapes and is not particularly limited, such as a sphere, a scale, and a fibrous shape. Examples of the carbon material include artificial or natural graphite, carbon fluoride, metal, and metal oxide. Inorganic compounds and organic high molecular compounds can be used, and generally those obtained by firing organic substances are often used. Specifically, polyacrylonitrile (PAN) -based carbon material, pitch-based carbon material obtained from pitch such as coal or petroleum, cellulose-based carbon material obtained from cellulose, polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, A carbon material obtained by baking phenol resin, furfuryl alcohol, or the like is also preferably used.

The size of the carbon material to be used is not limited, but in particular, the equivalent diameter should be set to 100 μm or less from the viewpoint that it can be uniformly applied using a coater at the time of producing an electrode sheet. It is preferable that the thickness be 1 μm or more in view of handling properties and ease of kneading when preparing the positive and negative electrode materials. Further, in consideration of the size at which occlusion and release of alkali metal ions, particularly lithium ions, can be favorably performed, the equivalent diameter is more preferably 1 μm or more and 50 μm or less.

When a fibrous carbon material, that is, carbon fiber is used, and when used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, a PAN-based carbon fiber and a pitch-based carbon fiber are used. Is preferred. In particular, PAN-based carbon fibers are preferably used in that the doping of alkali metal ions, particularly lithium ions, is good.

The diameter of the carbon fiber should be determined so that it can easily take each form, but preferably 1 to 1
A carbon fiber having a diameter of 00 μm is used, and 3 to 20 μm is more preferable. It is also possible to use several types of carbon fibers of different diameters. The length is not particularly limited, but is preferably less than 100 μm, more preferably 50 μm or less, and shortened to a length of not less than the diameter of the carbon fiber, because it can be uniformly applied using a coater.

When a positive electrode material and a negative electrode material are applied to a current collector to form an electrode sheet, any form may be used. However, due to the properties of the present invention, the electrode sheet may be used together with a binder and a conductive material. Dissolved in a solvent, after applying the liquid dispersed, dried or, the method of attaching the active material to the current collector using a conductive binder or a mixture of the conductive material and the binder is generally, There is no particular limitation.

Examples of the conductive material usable in the present invention include carbon materials and metal powders. Particularly preferred conductive materials include various carbon blacks. For the purpose of improving conductivity by adding a conductive material, the optimal particle size and the amount of addition should be determined experimentally according to the material, shape, and particle size of the positive electrode and the negative electrode active material, and the type and amount of the binder. Is usually 1 nm to 100 μm in primary particle diameter,
More preferably, fine particles of 5 nm to 20 μm are used, and the addition amount is 0.5 to 30 wt%, more preferably 0.7 to 20 wt%. If the primary particle diameter is less than 1 nm, it is difficult to produce the particles stably, and if the primary particle diameter exceeds 100 μm, the effect of addition becomes small. On the other hand, if the amount is less than 0.5 wt%, the effect of the addition is poor, and if it exceeds 20 wt%, the capacity per unit weight of the electrode decreases.

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

Further, the electrode can be used as an active electrode of various batteries, and there is no particular limitation on what kind of battery such as a primary battery or a secondary battery is used. Among them, it is preferably used for an electrode of a secondary battery. As a particularly preferred secondary battery, a secondary battery using a nonaqueous electrolyte containing an alkali metal salt such as lithium perchlorate, lithium borofluoride, or lithium lithium hexafluoride can be given.

As the electrolyte for the above battery, a conventional electrolyte is used without any particular limitation, and examples thereof include an acid or alkali aqueous solution and a non-aqueous solvent.
Among these, propylene carbonate, ethylene carbonate, dimethyl carbonate, and γ are used as electrolytes for secondary batteries composed of the non-aqueous electrolyte containing the alkali metal salt described above.
-Butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolan, methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate, And their derivatives and mixtures are preferably used. Examples of the electrolyte contained in the electrolyte include alkali metal, particularly lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride,
Aluminum fluoride, trifluoromethyl sulfate and the like are preferably used.

Further, the separator used in the present invention is for preventing a short circuit between the positive electrode and the negative electrode, and is not particularly limited.
It is desirable not to cause electron and ion transfer resistance, and typical materials include polyester, polyamide, polyolefin, polyacrylate, polymethacrylate,
Polysulfone, polycarbonate, polytetrafluoroethylene and the like can be mentioned. Among them, in particular, polypropylene, polyethylene, polysulfone and the like, strength,
Excellent in safety and preferred. The shape is generally a porous film or 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,
In order to improve strength and safety, a composite film in which a plurality of types of films are laminated can be used. 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. Therefore, the porosity should be determined according to the material and the film thickness. . In general,
The film thickness is preferably 20 to 100 μm, and the porosity is preferably 30 to 80%. In addition, the diameter of the hole is the active material detached from the electrode sheet,
It is preferable that the binder and the conductive material do not pass through, and specifically, those having an average pore diameter of 0.01 to 1 μm are preferable.

[0029]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited by this.

Example 1 LiCoO ₂ was 60 vol% as a positive electrode active material, and PVDF KF1100 was used as a binder (manufactured by Kureha Chemical Industry Co., Ltd.).
30 vol%, Denka Black (manufactured by Denki Kagaku Kogyo Co., Ltd.) 10 vol% as a conductive material, and a paste using N methyl 2-pyrrolidone as a solvent was prepared.
Using aluminum foil (thickness 20μm) as current collector,
198 g / m ² on the outer peripheral surface, the active material of 180 g / m ² on the inner peripheral surface is coated, after the drying process of 100 ° C., the total thickness is carried out pressing to be 180 [mu] m, to obtain a positive electrode sheet Was. Then, artificial graphite LB-BG was used as the negative electrode active material.
After preparing a paste in the same manner as the positive electrode at a ratio of 75 vol% (manufactured by Nippon Graphite Industry Co., Ltd.) and the same binder as the positive electrode at a ratio of 25 vol%, a copper foil (16 μm thick) was used as a current collector.
The active material was applied so that the applied amount was 85 g / m ^{2 on} both the outer peripheral surface and the inner peripheral surface, and was dried in the same manner as in the positive electrode, and pressed so that the total thickness was 170 μm, to obtain a negative electrode sheet. These positive / negative electrode sheets are converted to a porous three-layer film (polypropylene / polyethylene / polypropylene)
(UPORE / UP-3015, manufactured by Ube Industries, Ltd.)
And a spiral electrode was obtained to obtain a cylindrical electrode body.

Further, the electrode body was loaded into a battery can having an outer diameter of 18 mm and a height of 65 mm, and a mixture of ethylene carbonate and dimethyl carbonate containing 1 M lithium borofluoride in a ratio of 30 wt%: 70 wt% was injected as an electrolytic solution. After that, a sealed battery was manufactured using a sealing body. This battery was charged at a charging current of 1 A, a constant voltage of 4.2 V, and a charging time of 2.5 V.
The battery was charged for 1 hour at a constant current and a constant voltage, and a capacity test was performed at a discharge current of 0.2 A and a discharge end voltage of 2.5 V. The battery capacity was 1340 mAh for the first time, and the capacity retention after 100 cycles passed was 85%. . Further, after charging 10 batteries manufactured under the same conditions as the above battery under the above conditions,
When the battery was crushed by applying pressure from the vicinity of the center of the side surface of the battery using a round rod of 10 mm, the appearance of the battery was not particularly changed except that the electrolyte of all 10 batteries leaked to the outside. The maximum surface temperature of the ten batteries was as low as about 90 ° C. on average.

Example 2 The composition of the positive electrode was 60 vol% of the active material, 30 vol% of the binder,
Conductive material 10vol%, the negative electrode composition is 90vol% active material,
A battery similar to that of Example 1 was prepared except that the binder was 10 vol%, and a capacity test was performed on this battery under the same conditions as in Example 1.
The capacity retention after 0 cycles was 87%. Further, after charging 10 batteries manufactured under the same conditions as the above battery under the above conditions, the battery was crushed by applying pressure from near the center of the side surface of the battery using a round bar having a diameter of 25 mm.
White smoke grew milder than the sealed part. Also, 10
The maximum surface temperature of each battery was about 120 ° C. on average.

Example 3 The composition of the positive electrode was 80 vol% of the active material, 15 vol% of the binder,
A battery similar to that of Example 1 was prepared except that the conductive material was 5 vol%, the negative electrode composition was 65 vol% of the active material, and the binder was 35 vol%, and a capacity test was performed on this battery under the same conditions as in Example 1. However, the battery capacity was initially 1345 mAh,
The capacity retention after the elapse of the cycle was 90%. Further, after charging 10 batteries produced under the same conditions as the above battery under the above conditions, the battery was crushed by applying pressure from near the center of the side surface of the battery using a round bar having a diameter of 25 mm.
White smoke grew milder than the sealed part. Also, 10
The maximum surface temperature of each battery was about 130 ° C. on average.

Comparative Example 1 The composition of the positive electrode was 80 vol% of the active material, 15 vol% of the binder,
A battery similar to that of Example 1 was prepared except that the conductive material was 5 vol%, the negative electrode composition was 90 vol% of the active material, and the binder was 10 vol%, and a capacity test was performed on the battery under the same conditions as in Example 1. However, the battery capacity was 1351 mAh for the first time,
The capacity retention after the elapse of the cycle was 90%. Further, after charging 10 batteries manufactured under the same conditions as the above battery under the above conditions, the battery was crushed by applying pressure from near the center of the side of the battery using a round bar having a diameter of 25 mm. Erupted violently. The maximum surface temperature of the ten batteries reached about 180 ° C. on average.

[0035]

According to the present invention, a positive electrode sheet and a negative electrode sheet prepared by applying at least one of a positive electrode material and a negative electrode material composed of an electrode active material and a binder to one or both surfaces of a current collector are opposed to each other. In the method for manufacturing a battery using the electrode body, the mixing ratio of at least one of the positive electrode material and the negative electrode material is at least 25% by volume and 40% with respect to the entire electrode material.
% Or less, a battery with high capacity and high safety can be manufactured.

Claims (8)

[Claims] An electrode comprising a positive electrode sheet and a negative electrode sheet each having at least one of a positive electrode material composed of an electrode active material and a binder and a negative electrode material applied to one or both surfaces of a current collector. In a battery using a body, the mixing ratio of either or both of the positive electrode material and the negative electrode material is 25% by volume with respect to the entirety of each electrode material.
% Or more and 40% or less. 2. The battery according to claim 1, wherein the mixing ratio of the binder of the positive electrode material is 30% or more and 40% or less by volume relative to the whole positive electrode material. 3. The battery according to claim 1, wherein the binder compounding ratio of the negative electrode material is at least 25% and at most 30% by volume relative to the whole negative electrode material. 4. The battery according to claim 1, wherein the electrolyte of the battery uses a lithium salt as an electrolyte. 5. The battery according to claim 1, wherein the positive electrode of the battery contains a transition metal compound capable of inserting and extracting lithium ions. 6. The battery according to claim 1, wherein the positive electrode of the battery contains at least a nickel-containing metal oxide capable of inserting and extracting lithium ions. 7. The battery according to claim 1, wherein the negative electrode of the battery contains a carbon material capable of occluding and releasing lithium ions. 8. A positive electrode sheet and a negative electrode sheet formed by applying a positive electrode material comprising at least an electrode active material and a binder, and a negative electrode material to one or both surfaces of a current collector, respectively. In the method for manufacturing a battery using the electrode body, the mixing ratio of one or both of the positive electrode material and the negative electrode material is 25% or more and 40% or less by volume ratio with respect to the entire electrode material. A method for producing a battery.