JPH09161847A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a lithium ion from being trapped by a surplus negative electrode by a charging/discharging cycle to improve safety, by removing the electrode material in the innermost peripheral side surface portion of a positive electrode sheet, and in the outermost peripheral port portion of a negative electrode sheet. SOLUTION: Electrode material for a possitive electrode; obtained by kneading positive electrode active material containing a transition metallic compound, a binding agent, and conductive material; is coated on both surfaces of a sheet-like current collector except a side surface portion, and then is heat- treated to obtain a positive electrode sheet. Electrode material for a negative electrode; obtained by kneading negative electrode active material containing carbonaceous material, a binding agent, and conductive material; is coated on both surfaces of a sheet-like current collector except a side surface portion, to be heat-treated and pressed to obtain a negative electrode sheet. The positive and negative sheets are laminated via a separator, to be wound so that the positive and negative electrode sheets can be placed on the innermost and outermost peripheral sides respectively, to remove the electrode material from the innermost and outermost peripheral surface portions respectively.

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.

Thus, the lithium ion secondary battery is
Lithium ions released from the positive electrode are charged by being absorbed in the carbon material of the negative electrode to develop a potential difference. Therefore, if there is a positive electrode that does not face the negative electrode, the destination of lithium ions released from the positive electrode disappears, and metal lithium is deposited on the surface of the current collector or the electrode material of the negative electrode as metallic lithium. Lithium metal is dangerous because it reacts violently with heat due to the presence of water, and it is necessary to prevent the deposition of lithium metal to enhance the safety of the battery. Therefore, it is known that in a lithium-ion secondary battery, the positive electrode always faces the negative electrode, and the positive electrode that does not face the negative electrode does not exist (JP-A-1-128371). In the case of a lithium ion secondary battery using a spiral electrode body, it is often the case that a negative electrode is present at both the outermost circumference and the innermost circumference to improve safety.

Conventionally, it has been thought that such an excess negative electrode without a counter positive electrode is not related to the transfer of lithium ions, but recently, as the number of charge / discharge cycles has increased, the presence of the counter positive electrode with lithium ions has increased. A problem was found that lithium ions in the electrolyte were reduced by being trapped in the excess negative electrode. This phenomenon was particularly noticeable from the beginning of the charge / discharge cycle when an electrolytic solution having a high conductivity was used, and a countermeasure was indispensable. In addition, when there is a negative electrode in which lithium ions are difficult to be occluded, the negative electrode apparently does not reach the full charge potential. Therefore, the positive electrode potential is likely to be high, which deteriorates cycle characteristics and safety.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a battery which is highly safe and easy to manufacture, without lithium ions being trapped in an excess negative electrode during charge / discharge cycles.

[0007]

Means for Solving the Problems The inventors of the present invention have earnestly studied a battery which can be easily manufactured and has high safety in which lithium ions are not trapped in an excess negative electrode during a charge / discharge cycle. Achieved the invention.

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 positive electrode sheet is located on the innermost peripheral side and the negative electrode sheet is located on the outermost peripheral side. The present invention relates to a battery in which the electrode material is removed from the innermost peripheral surface portion of the sheet and the outermost peripheral surface portion of the negative electrode sheet.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the battery of the present invention, the positive electrode sheet is located on the innermost peripheral side and the negative electrode sheet is located on the outermost peripheral side. The outermost circumference is
Since the electrode sheet may come into direct contact with the battery can, the outermost periphery is preferably the negative electrode having the same pole as the battery can. Furthermore, it is customary to equip the cap (projection), which is the positive electrode, with a safety mechanism such as a battery overcurrent prevention mechanism and an internal pressure release mechanism, and it is desirable to attach the positive electrode lead to the innermost circumference for safety reasons. It is preferable that the innermost periphery is the positive electrode.

In the battery of the present invention, the innermost peripheral surface portion of the positive electrode sheet and the negative electrode are formed so that the counter electrode does not exist at the outermost peripheral surface portion and the innermost peripheral surface portion of the spiral electrode body. The electrode material on the outermost peripheral surface portion of the sheet is removed.
If the electrode materials on the innermost peripheral surface of the positive electrode sheet and the outermost peripheral surface of the negative electrode sheet are not removed, there is a risk that lithium ions will be trapped in the excess negative electrode during the charge / discharge cycle. An example of the spiral electrode body in the battery of the present invention is shown in FIG.

Further, in the present invention, it is more preferable that the negative electrode sheet is made slightly longer so that the negative electrode material coated surface always faces the positive electrode material coated surface. This is because if the surface coated with the negative electrode material is shorter than the surface coated with the positive electrode material, there is a negative electrode that does not oppose the positive electrode, and metallic lithium tends to precipitate on the surface of the electrode material or the like.

Further, two kinds of electrode sheets having different lengths are prepared by coating an electrode material on one surface of the current collector, and the exposed surfaces of the current collector are overlapped with each other, whereby a portion where no counter electrode exists is formed. Although it is possible to provide an electrode sheet in which the electrode material is not applied to the present invention, the thickness of the current collector is doubled to reduce the effective volume in the battery.
It is preferable to apply the electrode material to both surfaces of the current collector as the electrode sheet, because winding deviation tends to occur when the stacked electrode sheets are spirally circulated.

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

Furthermore, 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-ax A x Ni} 1-yb B y O 2 is, 0 <x ≦ 0.1,0 ≦ y
X is the total number of moles of alkali or alkaline earth metal excluding Li, y is the total number of moles of all transition metal elements excluding Ni, and when y = 0, A is at least one or more. (Including the alkaline earth metal), a positive electrode material having excellent properties can be obtained. In this case, A, B
Since it is possible to obtain active materials having different characteristics, which is the gist of the present invention, by changing the type, number, composition, or using positive electrode materials with different x, y, a, and b, it is very possible. It is suitable.

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, 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 such as coal or petroleum, cellulose-based carbon fiber obtained from cellulose, vapor-grown carbon fiber obtained from gas of low molecular weight organic matter, livinyl alcohol, lignin, polychlorination Examples thereof include carbon fibers obtained by firing vinyl, polyamide, polyimide, phenol resin, furfuryl alcohol, etc., and carbon fibers satisfying the characteristics are appropriately selected according to the characteristics of the battery. 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.

The diameter of the carbon fibers preferably used in the present invention is appropriately determined depending on the form of each electrode or battery, but generally, carbon fibers having a diameter of 1 to 100 μm are 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.

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. If the length of the carbon fiber exceeds 100 μm, it will be difficult to apply it uniformly using a coater. Further, if the length of the carbon fiber is shorter than the diameter of the carbon fiber, the carbon fiber may be broken 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,
The optimum particle size and addition amount should be determined depending on the shape, particle size, and type of binder, compounding amount, etc., but usually the primary particle size is 1 nm to 100 μm, more preferably 5 nm to 20 μm.
Fine particles of m are used, and the addition amount is 0.5 to 30 wt.
%, More preferably 0.7 to 20 wt% is used. If the primary particle size is less than 1 nm, stable production is difficult, and if the primary particle size exceeds 100 μm, the effect of addition may be small. On the other hand, if the addition amount is less than 0.5 wt%, 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 can be used, and examples thereof include an acid or alkaline aqueous solution or a non-aqueous solvent. Among these, 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.

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. 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 for producing the electrode sheet by applying the positive electrode material and the negative electrode material to the current collector is not particularly limited, but in view of the properties of the present invention, a solution dispersed in a solvent is applied together with a binder, a conductive material and the like. 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, 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 is preferably as high as possible in order to enhance the permeability of electrons and ions, but it may cause a decrease in the strength of the film and is therefore determined according to the material and film thickness. Generally, film thickness is 20-100μ
m and porosity of 30-80% are desirable. Further, the diameter of the pores is preferably in a range in which the active material detached from the electrode sheet, the binder, and the conductive material do not permeate. Specifically, the average pore diameter is
It 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.

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, and It is preferable because it is excellent in workability. Further, it is possible to reduce the weight by using various engineering plastics, and it is also possible to use various engineering plastics and metal together.

Furthermore, the shape of the spiral in the present invention does not necessarily have to be a true cylindrical shape, and may be a long cylinder 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 limited to this form.

[0033]

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 was used as the binder (PVDF KF11 manufactured by Kureha Chemical Co., Ltd.).
00) 5 wt% and artificial graphite (Nippon Graphite Industry Co., Ltd., SP-20) 15% as a conductive material were mixed to obtain an electrode material for a positive electrode. An aluminum foil having a thickness of 20 μm was used as a current collector, and the positive electrode material was applied as shown in FIG. 2 at a density of 220 g / m ^{2 on} both the outer peripheral surface and the inner peripheral surface. 500kg after heat treatment at 150 ℃
Pressing was performed at a pressure of f / cm to obtain a positive electrode sheet.

Subsequently, as an electrode material for the negative electrode, PAN-based carbon fiber (Toray Industries, Inc., trading card T300) was used, and the average length was 30 μm.
The short fiber was kneaded in the same ratio as the positive electrode using the same binder and conductive material as the positive electrode. As shown in Fig. 3, the electrode material for the negative electrode was applied to a current collector copper foil with a thickness of 10 μm at a density of 80 g / m ^{2 on} both the outer and inner peripheral surfaces, and heat treatment and pressing were performed in the same manner as the positive electrode. A negative electrode sheet was obtained.

These positive electrode and negative electrode sheets were superposed on each other with a porous polypropylene film (Daicel Chemical Co., Ltd., Celgard # 2500) separator interposed therebetween and wound to obtain a cylindrical electrode body. This electrode body was loaded into a battery can having an internal volume of 5 cc, and a battery was prepared using dimethyl carbonate containing 1M6 lithium phosphorus fluoride as an electrolytic solution.

This battery was charged with a charging current of 400 mA and a constant voltage of 4.2
V, charging time 2.5 hours, constant current constant voltage charge, discharge current 20
When a capacity test was performed at 0 mA and a discharge end voltage of 2.5 V, the battery capacity was 395 mAh for the first time and the capacity retention rate after 100 cycles was 88%.

Example 2 As shown in FIGS. 4 and 5, Example 1 was repeated except that the length of each of the positive electrode sheet and the negative electrode sheet was increased by 10 mm.
A battery was produced in the same manner as in 1. and a capacity test was performed under the same conditions as in Example 1. As a result, the battery capacity was 408 mAh for the first time, and the capacity retention rate after 100 cycles was 88%.

Comparative Example 1 A battery similar to that of Example 1 except that the electrode material was applied so that the length of the positive electrode and the negative electrode was 260 mm and the length of the negative electrode was 290 mm. Was produced. Example 1
When the capacity test was performed under the same conditions as above, the battery capacity was 37
At 5 mAh, the capacity retention rate after 100 cycles was 83%.

Comparative Example 2 A battery similar to Example 2 except that the electrode material was applied so that the positive electrode and the negative electrode had the same length on both the outer peripheral surface and the inner peripheral surface with a length of 270 mm for the positive electrode and 300 mm for the negative electrode. When I made
The battery could not be manufactured because it could not be loaded into the battery can.

[0041]

According to the battery of the present invention, the positive electrode sheet is located on the innermost peripheral side and the negative electrode sheet is located on the outermost peripheral side, and the innermost peripheral surface portion of the positive electrode sheet and the outermost peripheral surface portion of the negative electrode sheet are made of an electrode material. Is removed, the lithium ion is prevented from being trapped in the excess negative electrode due to the charge / discharge cycle, and the battery has high safety and is easy to manufacture.

In the battery of the present invention, since the negative electrode sheet is located on the outermost peripheral side, even if the electrode sheet is in direct contact with the battery can, it is the same electrode as the battery can, so it is safe. Furthermore, since the positive electrode sheet of the battery of the present invention is efficiently connected to the positive electrode cap (protrusion) equipped with a safety mechanism such as an overcurrent prevention mechanism and an internal pressure release mechanism, it is on the innermost peripheral side and It is highly likely.

[Brief description of the drawings]

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

FIG. 2 is a side sectional view of the positive electrode sheet used in Example 1.

3 is a side sectional view of the negative electrode sheet used in Example 1. FIG.

FIG. 4 is a side sectional view of a positive electrode sheet used in Example 2.

5 is a side sectional view of the negative electrode sheet used in Example 2. FIG.

[Explanation of symbols]

 1: outer peripheral surface of positive electrode sheet 2: inner peripheral surface of positive electrode sheet 3: outer peripheral surface of negative electrode sheet 4: inner peripheral surface of negative electrode sheet 5: separator 6: outer peripheral surface of electrode 7: inner peripheral surface of electrode 8: current collector ( Outer side) 9: Current collector (inner side)

Claims (10)

[Claims] 1. A battery using an electrode body formed by spirally winding a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is located on the innermost peripheral side and the negative electrode sheet is located on the outermost peripheral side. A battery characterized in that the electrode material is removed from the peripheral surface portion and the outermost peripheral surface portion of the negative electrode sheet. 2. The battery according to claim 1, wherein the negative electrode sheet is longer than the positive electrode sheet. 3. The battery according to claim 1, wherein the surface coated with the positive electrode material faces the surface coated with the negative electrode material. 4. The battery according to claim 1, wherein a lithium salt is used as an electrolyte. 5. The battery according to claim 1, wherein the electrode material applied to the positive electrode contains a transition metal compound. 6. The battery according to claim 1, wherein the electrode material applied to the negative electrode contains a carbonaceous material. 7. The battery according to claim 6, wherein the carbonaceous material is carbon fiber. 8. The battery according to claim 7, wherein the carbon fiber is a polyacrylonitrile-based carbon fiber. 9. The battery according to claim 7, wherein the carbon fiber has a diameter of 1 μm to 100 μm and a length of 100 μm or less. 10. The battery according to claim 9, wherein the length of the carbon fiber is not less than the diameter of the carbon fiber.