JPH09204936A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a battery with high filling ratio and high battery capacity by increasing the application quantity of a positive electrode material and a negative electrode material within a specified range. SOLUTION: When the application quantity of an electrode material is increased, the charge and discharge capacity of a battery is increased because the substantial charging quantity is increased. With an application thickness less than 250μm, the filling ratio is largely reduced by the reduction in application thickness, and in order to provide a higher filling ratio, thus, the application thickness must be set to 250μm or more. When the application thickness is larger than 400μm, the probability of cracking in winding is increased. Thus, in both a positive electrode sheet and a negative electrode sheet which are spirally wound, the total application thickness in both the sheets is set to 250μm or more and 400μm or less, whereby a battery with high filling ratio and high battery capacity can be manufactured.

Description

Detailed Description of the Invention

[0001]

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

[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 in which metallic lithium is used 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.
It is (de-doped) and returns to the original carbonaceous material. When such a carbonaceous material doped with lithium ions is used as a negative electrode, the problem of dendrite formation is small, and since there is no metallic lithium, the safety is also excellent. Has been done.

As a secondary battery using an electrode utilizing the above-described carbonaceous material doped with lithium ions, Japanese Patent Laid-Open Nos. 57-208079, 58-93176, 58-192266, and 58-192266 are known. JP-A-62-90863, JP-A-62-122066 and JP-A-2-66856 are known, and the shape of the electrode body used in the lithium-ion secondary battery is a shape in which a positive electrode, a negative electrode, and a separator are spirally wound. Is common.

[0005]

In the spiral electrode body, the positive electrode current collector, the negative electrode current collector, and the separator are used for the battery can in addition to the positive electrode material and the negative electrode material having essential functions as a battery. Occupies the volume inside. for that reason,
The filling amount of the positive electrode material and the negative electrode material in the battery can is limited,
There was a limit to increasing the capacity of batteries.

An object of the present invention is to provide means for further increasing the capacity of a battery.

[0007]

The present inventors have achieved the present invention as a result of extensive studies on a battery having a high capacity.

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 coating thickness of both the inner peripheral surface and the outer peripheral surface of both the positive electrode sheet and the negative electrode sheet is adjusted. Is more than 250 μm and
It relates to a battery having a thickness of 400 μm or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION That is, according to the present invention, by increasing the coating amount of the positive electrode material and the negative electrode material, the filling amount in the battery can be increased, and a high performance battery having a substantially large charge / discharge capacity can be obtained. Obtainable.

Further, when the coating amount of the electrode material is increased, the length of the electrode sheet is shortened, that is, the length of the current collector and the separator is shortened, so that the positive electrode material and the negative electrode material can be increased. Therefore, it was found that the charging / discharging capacity of the battery is increased because the coating amount of the electrode material is increased to increase the substantial filling amount. As a result of further diligent study by the present inventors regarding this effect, the coating thickness was 250 μm.
If it is less than 1, the decrease in the filling rate due to the decrease in the coating thickness is large,
It was found that the coating thickness needs to be 250 μm or more in order to obtain a higher filling rate.

As described above, in order to increase the filling amount of the positive electrode material and the negative electrode material, the lengths of the positive electrode current collector, the negative electrode current collector, and the separator are shortened, and further, the thickness is reduced, and The volume occupied by the electric body and the separator may be reduced. However, since the positive electrode current collector, the negative electrode current collector, and the separator are required to have portions facing each other, the length of the positive electrode current collector corresponds to the length of the negative electrode current collector and the separator. . It is theoretically possible to shorten these lengths as much as possible to increase the coating amount of the electrode material per unit area of the current collector and increase the film thickness. However, in the spirally shaped electrode body, expansion and contraction occur on the outer and inner peripheral surfaces of the positive and negative electrode sheets, which may cause cracks in the electrode material when spirally wound and eventually cause short circuits. Come on. Therefore, as a result of intensive investigations by the present inventors, it was found that when the coating thickness is greater than 400 μm, the probability of cracking during winding increases.

When a spiral electrode body is used, a tensile force is applied to the electrode material on the outer peripheral surfaces of both the positive electrode sheet and the negative electrode sheet, and the basis weight (application amount per unit area) of the electrode material is substantially reduced. Since compression force is applied to the peripheral surface, the basis weight of the electrode material is substantially increased. Therefore, in order to achieve balance in the spiral state, it is desirable that the amount of active material on the outer peripheral surface be larger than that on the inner peripheral surface. However,
If the amount of active material on the outer peripheral surface is excessively larger than that on the inner peripheral surface, it may cause warpage during drying or pressing of the electrode sheet after coating, which may cause misalignment when spirally wound or electrode cracks. , It is easy to cause a short circuit. In particular, when the coating thickness of the electrode material is 250 μm or more as in the present invention, it is easily affected by the influence.

Therefore, as a result of a more precise examination of the coating amount of the electrode material on the outer peripheral surface and the coating amount of the electrode material on the inner peripheral surface, in order to balance in the spiral state and prevent cracking of the electrode, coating of the outer peripheral surface is performed. It was found that it is more preferable to make the amount 1.03 times to 1.20 times the inner peripheral surface. Varying the ratio of the coating amount of the outer peripheral surface and the coating amount of the inner peripheral surface between the outer peripheral surface and the inner peripheral surface can be carried out on either one of the positive electrode sheet and the negative electrode sheet, , Both electrode sheets can also be implemented. When the operation is performed on one of the positive electrode sheet and the negative electrode sheet, the coating amount on the outer peripheral surface is more preferably 1.08 to 1.20 times that on the inner peripheral surface, although it varies slightly depending on the size of the battery. Further, when both electrode sheets, the positive electrode sheet and the negative electrode sheet, are used, it is more preferable that the ratio is 1.03 to 1.10 times.

These batteries can be applied to non-aqueous electrolyte secondary batteries containing an alkali metal salt, and preferably,
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.

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 kind of alkali or alkaline earth metal element, and B is at least one kind of transition metal element) is most preferably used since it has a 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, A,
When B consists of two or more elements, x is the total number of moles of alkali or alkaline earth metals excluding Li, and y is N.
It is the total number of moles of all transition metal elements excluding i, and when y = 0, A contains at least one alkaline earth metal). Also, in this case, changing the type, number, and composition of A and B,
It is very suitable to use active materials having different characteristics, which is the gist of the present invention, by using positive electrode materials having different x, y, a, and b.

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.

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 and the like are used. Can be used.

In the present invention, carbon fiber is preferably used as the electrode material applied to the negative electrode. in this case,
The carbon fiber is not particularly limited, but a fibrous organic material is generally used. The carbon fiber used in the present invention, for example, PAN-based carbon fiber obtained from polyacrylonitrile (PAN), pitch-based carbon fiber obtained from pitch such as coal or petroleum, cellulose-based carbon fiber obtained from cellulose, low molecular weight Vapor grown carbon fibers obtained from organic gas, polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenolic resin, carbon fibers obtained by firing furfuryl alcohol and the like, and the characteristics of electrodes and batteries In accordance with the above, a carbon fiber satisfying the characteristics is appropriately selected. Furthermore, among these carbon fibers, PA
N-based carbon fibers and pitch-based carbon fibers are more preferably used. Especially when used for the negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt such as lithium, PA
N-based carbon fibers are particularly preferred.

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 More preferred is 20 μm carbon fiber. It is also possible to use several kinds of carbon fibers having different diameters, if necessary.

Furthermore, 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 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 of the binder added is usually 0.01 wt% to 40 wt% in the electrode material. 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.

Examples of the conductive material that can be used in the battery of the present invention include carbon materials and metal powders. For the purpose of improving conductivity by adding a conductive material, the material of the positive electrode, the negative electrode active material,
Shape, particle size, and the type of binder, the optimum particle size and addition amount is determined by the blending amount, etc., usually 1 nm to 100 μm in primary particle size, more preferably 5 nm to 20 μm fine particles are used, The addition amount is 0.5 to 30 wt%, more preferably 0.7 to 20 wt%. Those having a primary particle size of less than 1 nm tend to be difficult to produce stably, and those having a primary particle size of more than 100 μm tend to have a small effect of addition. On the other hand, 0.5 wt
If the amount added is less than%, the effect of addition is poor, and if it exceeds 20 wt%, the capacity per unit weight of the electrode tends to decrease.

The electrode material thus obtained can be used as an electrode for various batteries, and the type of battery is not particularly limited, but it is preferably used for 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 solvent used in the electrolytic solution used in the present invention is not particularly limited, and a conventional solvent may be used, and examples thereof include an acid or alkali aqueous solution or a non-aqueous 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.

As the electrolyte contained in the electrolytic solution used in the battery of the present invention, an alkali metal halide, perchlorate, thiocyanate, borofluoride, phosphorofluoride,
Arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate, etc. are preferably used. Lithium salt, in particular, has the lowest standard electrode potential, and therefore a large potential difference can be obtained. Therefore, as the electrolyte contained in the electrolytic solution,
More preferably, a lithium salt is used.

The method of applying the positive electrode material and the negative electrode material to the current collector to prepare an electrode sheet is not particularly limited, but in view of the characteristics of the present invention, a solution dispersed in a solvent together with a binder, a conductive material, etc. is applied. After that, a general method is to dry or attach the active material to the current collector using a conductive binder or a mixture of a conductive material and a binder.

The current collector of the present invention may be made of metal in the form of foil, mesh, lath or the like, but these are not particularly limited.

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, as the porous membrane, a symmetric membrane and an asymmetric membrane are generally used, but 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, Porosity 30-80% is desirable. Further, 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 battery 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 material. A battery using an alkali metal or a secondary battery is effective.

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

Further, the battery can loaded with the spiral electrode body is not particularly limited, but a battery can plated with iron for corrosion resistance, a stainless steel battery can, 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.

Further, the shape of the spiral in the present invention does not necessarily have to be a true cylindrical shape, and may be a long 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.

[0034]

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 a positive electrode active material, and polyvinylidene fluoride was used as a binder (Kureha Chemical Co., Ltd., PVDF KF11
5% by weight of 00) and 15% by weight of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., SP-20) as a conductive material were mixed to obtain an electrode material for a positive electrode. Using an aluminum foil with a thickness of 20 μm as a current collector,
A positive electrode (amount of active material: outer peripheral side 320 g / m ² , outer peripheral side 320 g / m ² (total coating thickness 256 μm, coating length 144 mm)) was applied to obtain a positive electrode sheet.

Subsequently, as an electrode material for the negative electrode, PAN-based carbon fiber (Toray Industries, Inc., Torayca T300) was shortened to about 20 μm and then fired in a vacuum at 1500 ° C. for 4 hours to obtain the same binder as the positive electrode. A conductive material was used and kneaded at the same ratio as the positive electrode. An electrode material for the negative electrode to copper foil having a thickness of 10μm as a current collector, the applied negative electrode (active material content: outer circumferential side 115 g / m ² (coating thickness 105
μm), 115 g / m ² on the inner circumference side (total coating thickness 255 μm, coating length 171 m
m)) was prepared. These positive electrode and negative electrode sheets were superposed on each other with a porous polypropylene film (Daicel Chemical Co., Ltd., Celguard # 2500) separator interposed therebetween and wound to obtain 30 cylindrical electrode bodies. No internal short circuit occurred in these electrode bodies. Any 10 of these electrode bodies were loaded into battery cans with an internal volume of 5 cc, and a 1: 1 mixture of propylene carbonate and dimethyl carbonate containing 1M lithium borofluoride was used as the electrolyte. Was produced. This battery, charging current 400mA,
A constant current constant voltage charge was performed at a constant voltage value of 4.2V and a charging time of 2.5 hours, and a capacity test was performed at a discharge current of 200mA and a discharge end voltage of 2.5V.The average battery capacity was 378mAh for the first time, and the capacity after 100 cycles had elapsed. The average retention rate was 80%.

[0037] Example 2 positive electrode active material weight outer periphery 337 g / m ² to the inner circumferential side 303 g / m ² (total coating thickness 256 .mu.m, coated length 144 mm) and the outer circumferential side 118 g / m ² of the negative electrode active material weight, A battery similar to that of Example 1 was prepared except that the inner peripheral side was 112 g / m ² (total coating thickness 255 μm, coating length 171 mm), and the test was conducted under the same conditions. The average battery capacity was initially 383 mAh.
The average capacity retention rate after 100 cycles was 84%.

[0038] Comparative Example 1 a positive electrode active material weight outer peripheral side 210g / m ² to the inner circumferential side 210g / m ² (total coating thickness 168Myuemu, application length 203 mm) and the outer peripheral side 79 g / m ² of the negative electrode active material weight, Inner circumference 79g / m ² (total coating thickness 175μm, coating length 2
(30 mm) except that the same battery as in Example 1 was prepared and tested under the same conditions. The average battery capacity was 354 mAh for the first time.
The average capacity retention rate after 100 cycles was 80%.

[0039]

EFFECTS OF THE INVENTION In the battery of the present invention, both the positive electrode sheet and the negative electrode sheet which are spirally wound have a coating thickness of 25 on both the positive electrode sheet and the negative electrode sheet.
By setting the thickness to 0 μm or more and 400 μm or less, it becomes possible to manufacture a battery having a high filling rate and a high battery capacity.

Claims (11)

[Claims] 1. A battery using an electrode body formed by spirally winding a positive electrode sheet and a negative electrode sheet, wherein the total coating thickness of both the outer peripheral surface and the inner peripheral surface of the positive electrode sheet is 250 μm or more and 400 μm or less. A battery characterized in that the total coating thickness on both the outer peripheral surface and the inner peripheral surface of the negative electrode sheet is 250 μm or more and 400 μm or less. 2. The battery according to claim 1, wherein the amount of active material applied per area of the current collector in the positive electrode sheet is larger on the outer peripheral surface than on the inner peripheral surface. 3. The battery according to claim 1, wherein the amount of active material applied per area of the current collector in the negative electrode sheet is larger on the outer peripheral surface than on the inner peripheral surface. 4. The ratio of the coating amount of the active material per area of the outer peripheral surface to the inner peripheral surface of at least one of the positive electrode sheet and the negative electrode sheet is 1.03 or more and 1.20 or less. The battery according to claim 1. 5. The battery according to claim 1, wherein a lithium salt is used as an electrolyte. 6. The battery according to claim 1, wherein the electrode material applied to the positive electrode contains a transition metal compound. 7. The battery according to claim 1, wherein the electrode material applied to the negative electrode contains a carbonaceous material. 8. The battery according to claim 8, wherein the carbonaceous material is carbon fiber. 9. The battery according to claim 8, wherein the carbon fiber is a polyacrylonitrile-based carbon fiber. 10. The carbon fiber has a diameter of 1 μm to 100 μm,
The length is 100 μm or less, and the length is less than 100 μm.
The battery according to 1. 11. The battery according to claim 10, wherein the length of the carbon fiber is not less than the diameter of the carbon fiber.