JPH09199177A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having a high filling factor, a high capacity, a good cycle characteristic, and high safety by changing the thickness of the current collector of at least one of a positive electrode sheet and a negative electrode sheet in the direction of the sheet length. SOLUTION: A current collector changed in thickness in the direction of the sheet length is used, and the thickness of the current collector at the thickest portion is 1.5-3 times the thickness at the thinnest portion. The resistance and heat generated by the current collector can be minimized. As the method for changing the thickness of the current collector, rolling is applied at the ordinary temperature or in the heated state, and the thickness of the current collector is preferably controlled by its strength.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a battery using an electrode body in which a positive electrode, a negative electrode and a separator are spirally wound.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras, mobile phones, and notebook computers, there is an increasing demand for small, lightweight, high-capacity secondary batteries. Most 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 risk that lithium will grow in a dendritic form due to repeated charging and discharging, causing a short circuit and 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 device that solves such a safety problem and enables high energy peculiar to lithium electrodes. This method utilizes the fact that during charging, lithium ions are occluded (doping) in the carbonaceous material to have the same potential as that of metallic lithium, which can be used for the negative electrode instead of metallic lithium. In addition, doped lithium ions are released from the negative electrode during discharge.
(Dedoping) is performed to return to the original positive electrode material. When such 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 has excellent safety. Is being done.

As a secondary battery using an electrode using the above-mentioned carbonaceous material doped with lithium ions,
JP-A-57-208079, JP-A-58-93176, JP-A-58-192266,
JP-A-62-90863, JP-A-62-122066, JP-A-2-66856 and the like are known, and as the shape of the electrode body used in the lithium-ion secondary battery, a positive electrode, a negative electrode, and a separator are spirally wound. The shape is generally common.

However, when the spiral electrode body is used, the current collectors near the lead terminals of the electrode sheets of the positive electrode and the negative electrode respectively have a larger current amount than the current collectors on the opposite side of the lead terminals. The current collector in the vicinity of the lead needs to have a certain thickness or more in order to reduce resistance and suppress heat generation. For this reason, the volume and weight of the current collector inside the battery cannot be ignored, which has been a constraint in manufacturing a battery having a high energy density.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a battery having a high filling rate, a high capacity and a high energy density.

[0007]

The present inventors have achieved the present invention as a result of studying a battery having a high filling rate, a high capacity, good cycle characteristics, and high safety.

That is, according to the present invention, in a battery using an electrode body formed by spirally winding a positive electrode sheet and a negative electrode sheet, the thickness of the collector of at least one of the positive electrode sheet and the negative electrode sheet is The present invention relates to a battery which changes in the sheet length direction.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of intensive studies by the present inventors, the thickness of the current collector is maximized at the lead portion where the current is concentrated, and the thickness of the current collector is reduced as the distance from the lead increases. It has been found that this makes it possible to minimize the resistance and heat generated in the current collector.

Further, as a result of intensive investigations by the present inventors,
In the spiral electrode body, it has been found that it is more desirable that the lead is attached to the end portion in the length direction of the electrode sheet, and the thickness of the current collector becomes thicker as it is closer to the lead.

That is, in order to prevent a step from occurring in the electrode in the process of spirally winding the electrode sheet and to eliminate the possibility of causing a short circuit and to improve the productivity, the electrode sheet length should be increased. Attach the lead to the end of the direction,
It is desirable that the shape of the current collector is thicker as it is closer to the lead.

In the present invention, as the current collector, a current collector whose thickness varies in the sheet length direction is used. Preferably, the thickness of the current collector at the thickest portion is 1 of the thickness at the thinnest portion. 5 times or more and 3 times or less. By setting the thickness of the current collector in the thickest part to 1.5 times or more the thickness of the thinnest part, it becomes possible to further minimize the resistance and heat generation in the current collector. On the other hand, if the thickness of the current collector in the thickest part is made thicker than three times the thickness of the thinnest part, it tends to be difficult to manufacture the current collector.

The method of changing the thickness of the current collector is not particularly limited, but it is preferable to carry out rolling at room temperature or in a heated state and control the thickness of the current collector by its strength.

The current collector of the present invention is preferably a metal, and the metal can be used in the form of foil, mesh, lath, etc., but is not particularly limited thereto.

Further, in the spiral electrode body, the respective electrode sheets of the positive electrode and the negative electrode are deformed into a spiral shape,
A tensile force is applied to the electrode material on the outer peripheral surface of both the positive electrode sheet and the negative electrode sheet, while a compressive force is applied to the inner peripheral surface.
Therefore, although the electrode material is applied in a flat plate state, the electrode material is stretched on the outer peripheral surface and the electrode material on the inner peripheral surface is contracted.

Therefore, in the spiral electrode body in which the outer peripheral surface and the inner peripheral surface are coated with the same coating amount in a flat plate state,
Since the electrode material is stretched on the outer peripheral surface, the coating amount per unit area in the spiral state is reduced, so that the load on the positive electrode on the outer peripheral surface of the positive electrode is increased and the positive electrode potential is increased. There is a risk of liquid decomposition. Further, since the electrode material is contracted on the inner peripheral surface, the coating amount per unit area in the spiral state increases, and the positive electrode active material amount becomes excessive on the inner peripheral surface of the positive electrode. Will not be occluded in the negative electrode and lithium ions will become dendritic metal (dendrites) and precipitate, causing a short circuit.

That is, the spiral curvature is larger toward the portion closer to the central portion. For example, since the curvature is larger on the innermost peripheral surface, the ratio of contraction of the electrode material is large. In addition, since the outermost circumference has a relatively small curvature, the extent to which the electrode material is extended is small. Therefore, in order to obtain the optimum balance according to the curvature of the spiral, it was found that the optimum balance is obtained by changing the coating amount of the electrode material in the length direction of the electrode sheet.

In the present invention, the coating amount of the electrode material is thin on the outer peripheral side when the thickness of the electrode material on the inner peripheral surface is changed,
It is preferable to use a current collector whose thickness increases toward the inner peripheral side, that is, toward the center side, and to form the leads on the inner peripheral side, as shown in FIG. In this case, it is possible to apply the electrode material to the inner peripheral surface first and then apply the outer peripheral surface with the simplest knife coater with a constant clearance. On the other hand, when changing the thickness of the electrode material on the outer peripheral surface, a current collector that is thicker on the outer peripheral side and thinner toward the inner peripheral side is used, and the lead is mounted on the outer peripheral side in the shape shown in FIG. Preferably.

As described above, by changing the thickness of the current collector in the length direction, the coating amount can be easily changed in the length direction of the electrode sheet. On at least one of the inner and outer peripheral surfaces of the positive and negative electrode sheets, the outer peripheral surface of the sheet is closer to the outer peripheral side, and the inner peripheral surface is closer to the inner peripheral side (center side). It is desirable to increase the coating amount.

The battery used in the present invention is not particularly limited as long as it uses a spirally wound electrode body, but as a battery for mounting on portable equipment requiring high energy density, a negative electrode is used. A battery using an alkali metal as a material and a secondary battery using cation or anion doping to a carbonaceous material are effective.

In the present invention, as the electrode material applied to the positive electrode, carbon fiber, carbonaceous material such as artificial or natural graphite powder, carbon fluoride, inorganic compound such as metal or metal oxide, organic polymer compound and the like are used. Can be used.

Further, in the present invention, as an electrode material applied to the positive electrode, a positive electrode active material used in a usual secondary battery can be mentioned. Examples of such a positive electrode active material include inorganic compounds such as transition metal oxides and transition metal chalcogens containing an alkali metal, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyaniline,
Examples thereof include conjugated polymers such as polypyrrole and polythiophene, crosslinked polymers having a disulfide bond, and thionyl chloride. In the present invention, a lithium salt is preferably used as the electrolyte, but in this case, cobalt, nickel, manganese, molybdenum, vanadium, chromium, iron,
Transition metal oxides such as copper and titanium and transition metal compounds such as transition metal chalcogens are preferably used. In particular, L
iCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li _y Ni _1-x
M _x O ₂ (M: Ti, V, Mn, or Fe), L
_{i 1-xa A x Ni 1} -yb B y O 2 ( however, A is at least,
One alkali or alkaline earth metal element, in particular B is at least one transition metal element),
It is most preferably used because of its large energy density. Especially _{wherein, Li 1-xa A x Ni} 1-yb B y O 2 is 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 metal except Li, and y is the total number of moles of all transition metal elements except Ni, When y = 0, A contains at least one kind of alkaline earth metal), and a positive electrode material having excellent characteristics can be obtained.

In the present invention, as the electrode material applied to the negative electrode, carbon fiber, artificial or natural graphite powder, carbonaceous material such as fluorocarbon, inorganic compound such as metal or metal oxide, organic polymer compound, etc. Can be used.

In the present invention, the electrode material applied to the negative electrode is preferably a carbonaceous material, more preferably carbon fiber. In this case, the carbon fiber is not particularly limited, but a carbon fiber obtained by firing an organic material into a fibrous state is generally used. Examples of the carbon fiber used in the present invention include P obtained from polyacrylonitrile (PAN).
AN-based carbon fiber, pitch-based carbon fiber obtained from pitch of coal or petroleum, cellulose-based carbon fiber obtained from cellulose, vapor-grown carbon fiber obtained from gas of low molecular weight organic substance, polyvinyl alcohol, lignin, polyvinyl chloride , Polyamide, polyimide, phenolic resin, carbon fibers obtained by firing furfuryl alcohol and the like, depending on the characteristics of the electrode and the battery,
A carbon fiber that satisfies the characteristics is appropriately selected. further,
Among these carbon fibers, PAN-based carbon fibers and pitch-based carbon fibers are more preferably used. Particularly, when used in the negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt such as lithium, PAN-based carbon fiber is particularly preferable.

Further, the length of the carbon fiber preferably used in the present invention is not particularly limited, but it is usually preferably 10
The thickness is 0 μm or less, more preferably 50 μm or less. When the length of the carbon fiber exceeds 100 μm, it is difficult to apply the carbon fiber uniformly using a coater, which is not preferable. If the length of the carbon fiber is shorter than the diameter of the carbon fiber, there is a risk of breaking in the fiber direction. Therefore, the length of the carbon fiber is more preferably the carbon fiber diameter or more.

The diameter of the carbon fiber preferably used in the present invention is appropriately determined depending on the form of each electrode or battery, but generally, carbon fiber having a diameter of 1 to 100 μm is preferably used, and a diameter of 3 to 3 is used. More preferred is 20 μm carbon fiber. It is also possible to use several kinds of carbon fibers having different diameters, if necessary.

Examples of the conductive material that can be used in the battery of the present invention include carbon materials and metal powders, and particularly preferable conductive materials include various carbon blacks and artificial graphite. Furthermore, in the case of a lithium ion battery, a carbon material is particularly preferable as the conductive material of the negative electrode.

When controlling the balance between the positive and negative electrodes by occluding lithium ions, a preferable method for controlling the characteristics of the conductive material is to bake the conductive material. The firing temperature, time, atmosphere conditions, etc. This makes it possible to obtain a conductive material exhibiting optimum characteristics. Further, the amount of the conductive material added is preferably 0.5 to 30 wt%, more preferably 0.7 to 20 wt%. The particle size of the conductive material is preferably
Primary particle size is 1nm ~ 100μm, more preferably 5nm ~ 20μ
m particles are used.

The binder used in the battery of the present invention may be either a thermoplastic resin or a thermosetting resin, and is not particularly limited. It is also possible to use the binder in the form of a solution or emulsion. The amount added as a binder is usually 0.01 wt% to 40 wt% in the electrode material,
Used. Examples of the binder include various epoxy resins, cellulose resins, organic fluorine-based polymers, and copolymers, acrylic resins, organic chloro-based resins, polyimides,
Examples thereof include polyamide and polycarbonate. In particular, organic fluorine-based polymers and copolymers are preferable from the viewpoint of stability, and among them, polytetrafluoroethylene, polyvinylidene fluoride, propylene hexafluoride polymer and copolymers are preferable binders.

The separator used in the present invention is not particularly limited as long as it prevents short circuit between the positive electrode and the negative electrode. It is desirable that the electrolyte has good permeability and does not become a resistance to transfer of electrons and ions. Typical materials include polyester, polyamide, polyolefin, polyacrylate, polymethacrylate, polysulfone, polycarbonate, and polytetrafluoroethylene. To be Among these, polypropylene, polyethylene, polysulfone and the like are particularly preferable because they are excellent in strength and safety. The shape of the separator is generally a porous film or a non-woven 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 the strength,
In order to improve safety, it is also possible to use a composite membrane in which a plurality of types of membranes are laminated. The porosity of the porous film should be as high as possible in order to enhance the permeability of electrons and ions, but there is a risk of reducing the strength of the film, so it should be determined according to the material and film thickness. . Generally, the film thickness is 20
〜100 μm, and porosity 30-80% is desirable. The pore diameter is preferably in a range in which the active material, the binder, and the conductive material detached from the electrode sheet do not permeate, and specifically, the average pore diameter is preferably 0.01 to 1 μm.

The method for applying the positive electrode material and the negative electrode material to the current collector to prepare the electrode sheet is not particularly limited, and it can be obtained by applying the electrode material to one side or both sides of the current collector. When the electrode material is applied to one surface of the current collector, it is preferable to take the same form as when applying the electrode material to both surfaces by stacking two current collectors. However, it is desirable to apply the electrode material to both surfaces of the current collector because it is difficult to heat or press the electrode sheet in the case of single-sided application, and winding deviation easily occurs when the electrode sheet is spirally wound.

When the positive electrode active material is an inorganic compound such as a metal or a metal oxide, a charge / discharge reaction occurs due to cation doping and dedoping, and when it is an organic polymer compound,
A charge / discharge reaction occurs due to anion doping and dedoping, but these are appropriately selected according to the required positive electrode characteristics of the battery and are not particularly limited.

Further, these electrode materials can be used as the active electrodes of various batteries, such as primary batteries and secondary batteries.
What kind of battery is used is not particularly limited.

When used in a non-aqueous electrolyte secondary battery containing an alkali metal salt, a carbonaceous material doped with an alkali metal or a cation is used for the negative electrode and a material doped with an anion is used for the positive electrode.

The electrode material thus obtained can be used as an electrode of various batteries, and the type of the battery is not particularly limited, but it is preferably used as an electrode of a secondary battery. Particularly preferable secondary batteries include secondary batteries using a non-aqueous electrolyte solution containing an alkali metal salt such as lithium perchlorate, lithium borofluoride, and phosphorus hexafluoride / lithium.

The electrolyte contained in the electrolytic solution used in the battery of the present invention includes alkali metal halides, perchlorates, thiocyanates, borofluorides, and phosphorus fluorides.
Arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate, etc. are preferably used. In particular, a lithium salt has the lowest standard electrode potential and a large potential difference can be obtained, so it is more preferable to use a lithium salt as the electrolyte contained in the electrolytic solution.

The solvent used in the electrolytic solution used in the present invention is not particularly limited, and a conventional solvent is used, and examples thereof include an acid or alkaline aqueous solution, or a nonaqueous solvent. Among them, as the solvent of the electrolytic solution of the secondary battery comprising a non-aqueous electrolytic solution containing an alkali metal salt, propylene carbonate, ethylene carbonate, dimethyl carbonate, γ-butyrolactone, N- methylpyrrolidone, acetonitrile, N, N- Dimethylformamide, dimethylsulfoxide, tetrahydrofuran, 1,3-dioxolane,
Methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate,
And derivatives and mixtures of these are preferably used.

Further, the shape of the spiral in the present invention does not necessarily have to be a true cylindrical shape, and may be an oblong cylindrical shape having an elliptical spiral cross section or a prismatic shape such as a rectangular spiral cross section. . In this case, the battery can can also take a shape corresponding to the shape of the electrode body. As a typical use form, a spirally-shaped electrode body and an electrolytic solution are loaded into a cylindrical battery can having a bottom, and leads taken out from the electrode sheet are sealed in a state of being welded to the cap and the battery can. The form is mentioned as the most common form, but is not particularly limited to this form.

The battery used in the present invention is not particularly limited as long as it is a battery using an electrode body wound in a spiral shape, but as a battery for mounting on portable equipment requiring high energy density, a negative electrode is used. A battery using an alkali metal as a material and a secondary battery using cation or anion doping to a carbonaceous material are effective.

The battery can loaded with the spiral electrode body is not particularly limited, but a battery can plated with iron for corrosion resistance, a battery can made of stainless steel, and the like have strength, corrosion resistance, It is preferable because it is excellent in 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 a metal together.

[0041]

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 80 wt% of LiCoO ₂ was used as the positive electrode active material, and polyvinylidene fluoride (KF1100 manufactured by Kureha Chemical Co., Ltd.) was used as the binder.
5 wt% and 10 wt% artificial graphite (SP-20, manufactured by Nippon Graphite Industry Co., Ltd.) were mixed as a conductive material to obtain an electrode material for a positive electrode.

Aluminum foil (thickness 20 μm) was stretched while increasing the pressure in the lengthwise direction, one end 20 μm, the other end 10 μm.
I got a collector. The positive electrode material was applied to this current collector with a knife coater at a constant clearance and dried, and the coating thickness was 120 μm at one end and at the other end.
It was 125 μm. Further, the opposite surface was similarly coated so that the coating thickness was 130 μm, heat-treated at 150 ° C., and then pressed at a pressure of 500 kgf / cm to obtain a positive electrode sheet. At this time, the average coating amount of the positive electrode active material is
It was 221 g / m ² , and the inner surface averaged 207 g / m ² .

Next, as a negative electrode active material, PAN-based carbon fiber
(Toray Co., Ltd., trading card T300) was made into short fibers with an average length of about 20 μm and then fired at 1200 ° C. for 4 hours in a nitrogen atmosphere, using the same binder and conductive material as the positive electrode. After kneading in the same ratio as above, it was applied to a copper foil (thickness 10 μm) having a constant thickness as a current collector so that the active material active material amount was 70 g / m ² on both the outer and inner circumference sides. A negative electrode sheet was produced.

A porous polypropylene film (manufactured by Daicel Chemical Industries, Celgard # 25
A cylindrical electrode body was obtained by stacking with a separator of (00) and winding. At this time, in the positive electrode sheet, the lead is attached to the thickest side of the current collector, and this side, that is, the lead becomes the inner peripheral part (center), and the surface coated later (constant coating thickness is constant) becomes the outer peripheral surface. It is.

This electrode body was loaded into a battery can having an internal volume of 5 cc, and a battery using a 1: 1 mixed solution of dimethyl carbonate containing 1M lithium hexafluorofluoride and ethylene carbonate was prepared as an electrolytic solution. The charging current of this battery is 40
A constant current constant voltage charge was performed at 0 mA, 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.The battery capacity was 392 mAh for the first time, and the capacity after 100 cycles The retention rate was 86%.

Example 2 A battery was prepared in the same manner as in Example 1 except that the positive electrode active material was applied in a uniform thickness such that the outer peripheral surface was 221 g / m ² and the inner peripheral surface was 207 g / m ² . When a capacity test was performed under the same conditions as in Example 1, the battery capacity was 390 mAh for the first time, and the capacity retention rate after 100 cycles was 84%.

Comparative Example 1 A capacity test was conducted under the same conditions as in Example 2 except that an aluminum foil having a thickness of 20 μm was used as the collector of the positive electrode. The battery capacity was 377 mAh for the first time, and after 100 cycles had elapsed. The capacity retention rate was 84%, and the initial electric capacity was low.

[0049]

EFFECT OF THE INVENTION By changing the thickness of the current collector of at least one of the positive electrode sheet and the negative electrode sheet in the sheet length direction, the resistance and heat generated in the current collector can be minimized. By reducing the volume and weight occupied by the current collector inside the battery, it is possible to manufacture a battery having a high filling rate, a high capacity, a high energy density, and high safety.

[Brief description of drawings]

FIG. 1 is an example of a cross-sectional view of an electrode sheet.

FIG. 2 is an example of a cross-sectional view of an electrode sheet.

[Explanation of symbols]

 1: Current collector 2: Electrode material (inner peripheral direction of inner peripheral surface) 3: Electrode material (outer peripheral direction of inner peripheral surface) 4: Electrode material (inner peripheral direction of outer peripheral surface) 5: Electrode material (of outer peripheral surface) Peripheral direction) 6: Lead

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01M 10/36 H01M 10/36 A

Claims (12)

[Claims] 1. In a battery using an electrode body formed by spirally winding a positive electrode sheet and a negative electrode sheet, at least one of the positive electrode sheet and the negative electrode sheet has a current collector whose thickness is in a sheet length direction. A battery characterized by changing with. 2. The battery according to claim 1, wherein the thickness of the current collector becomes thicker as the current collector is closer to the terminal connection lead. 3. The battery according to claim 1, wherein the thickness of the current collector changes continuously. 4. The battery according to claim 1, wherein the thickness of the current collector in the thickest part is 1.5 times or more and 3 times or less the thickness of the current collector in the thinnest part. 5. The battery according to claim 1, wherein the current collector is a metal. 6. The battery according to claim 1, wherein a lithium salt is used as an electrolyte. 7. The battery according to claim 1, wherein the electrode material applied to the positive electrode contains a transition metal compound. 8. The battery according to claim 1, wherein the electrode material applied to the negative electrode contains a carbonaceous material. 9. The battery according to claim 8, wherein the carbonaceous material is carbon fiber. 10. The battery according to claim 9, wherein the carbon fiber is a polyacrylonitrile-based carbon fiber. 11. The carbon fiber has a diameter of 1 μm to 100 μm,
A length of 100 μm or less, characterized in that
The battery according to 0. 12. The battery according to claim 11, wherein the length of the carbon fiber is not less than the diameter of the carbon fiber.