JPH11144762A - Spiral lithium ion battery electrode and spiral lithium ion battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery with good energy density and efficiency in which the reduction in capacity through peeling or falling of an active material from an electrode accompanying the charge and discharge cycle is suppressed by providing an electrode having a current collector wound so that a rough surface is situated on the outside, and a smooth other surface is situated on the inside. SOLUTION: A current collector 1 has a roughed surface 1 on one side and a smooth surface 3 on the other side. Active material layers 4, consisting of an active material and a binder having a conductive agent added thereto, are provided on both sides thereof. As a current collector, an aluminum foil the only one side of which is roughened by sand blasting is used, a paste mixture of polyvinylidene fluoride powder, LiNiO2 , and n-methyl-2-pyrolidone is applied to both the sides in a thickness of 0.09 mm as one side and 0.2 mm including both the sides of the foil, and the pyrolidone is then dried and removed, whereby an electrode can be provided. The one side of the current surface is a roughened surface of 3<R<20 by a value of 10-point average roughness R (μm), the other side is a smooth surface of 0.5<R<7, and the difference in roughness between the roughened surface and the smooth surface is set to 1 or more and 8 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used in a so-called spiral lithium ion battery in which an electrode and a separator are wound together and accommodated in a battery case, and a spiral lithium ion battery using the electrode. .

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more portable and cordless, expectations for secondary batteries having a high energy density have increased. Against this background, lithium secondary batteries have been developed as power supplies for various devices. Among the alkaline secondary batteries, lithium-ion batteries are expected to have high reliability and can be reduced in size and weight, and thus have been mounted on mobile phones, video cameras, and the like.

In a lithium ion battery, for example, lithium cobalt oxide (LiCoO ₂ ) is usually used for a positive electrode, carbon is used for a negative electrode, and an organic solvent in which a lithium salt is dissolved is used for an electrolyte.

[0004] The charging reaction of this battery is such that at the time of charging, lithium ions held on the positive electrode are de-incalated,
On the other hand, lithium ions are occluded in the carbon of the negative electrode. In addition, lithium ions occluded during discharge are released in the form of ions, while the lithium ions proceed to the positive electrode by incorporation. The battery reaction is as follows.

[0005]

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In the formula, e- represents an electron, and C represents carbon.

Such a lithium ion battery has a high voltage of 3 to 4 V in a single cell, has a high energy density and a high energy efficiency, and has a higher safety than a case where lithium metal is used for the negative electrode. And high cycle life.

[0008] In addition to the above cobalt, oxides such as manganese, molybdenum, and vanadium, sulfides, selenides, and the like have been studied for the positive electrode of this type of secondary battery. On the other hand, carbon materials that occlude and release lithium ions, such as coke, fired resin, carbon fiber, pyrolytic carbon, natural graphite, and mesophase microspheres, are used for the negative electrode. By using this kind of carbon material, the reaction between lithium and the electrolytic solution and the precipitation in the form of dendrites can be suppressed as compared with the case where metallic lithium is used, so that the negative electrode characteristics can be improved.

The electrolyte may be an organic solvent such as propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, tetrahydrafuran, or the like, for example, LiClO ₄ , LiBF ₄ , L
iPF _6, which was dissolved LiAsF ₆ lithium ion and lithium ion conductive solid electrolyte such as or the like is utilized.

[0010]

However, in this type of conventional battery, the active material peels off from the electrode and further drops off as the active material expands and contracts during charging and discharging. There is a problem that the battery capacity is reduced when the charge / discharge cycle is repeated for a long time.

The above problem is particularly remarkable in a so-called spiral lithium-ion battery such as a cylindrical or square battery in which a positive electrode and a negative electrode and a separator are stacked, spirally wound and stored in a battery case. there were.

In order to solve this problem, there has been proposed an electrode for bonding the active material to the current collector by using an adhesive portion generated by a concentration gradient of the binder as an electrode for binding the active material with the binder ( JP-A-4-82156). According to this proposal, since the active material is pressed against the current collector using the adhesive portion generated by the concentration gradient of the binder, it is possible to prevent the active material from falling off the current collector to some extent.

Alternatively, a battery has been proposed in which the carbon filling density of the carbon layer on the inner surface side of the spiral negative electrode is 5 to 20% lower than that of the outer carbon layer (Japanese Patent Application Laid-Open No. 6-290774).
With these attempts, the amount of carbon dropped off can be reduced by reducing the amount of carbon on the inner surface side in particular, and a decrease in battery capacity due to charge / discharge cycles can be suppressed to some extent.

However, if a binder is used to prevent the active material from falling off, the binder will rather increase the internal resistance of the battery, lower the energy density of the battery, and improve the original excellent characteristics of the lithium ion battery. There was a problem that the characteristics could not be fully exhibited.

Even if the carbon packing density on the inner surface side of the negative electrode is relatively smaller than that on the outer surface side, the carbon packing density on the inner surface side needs to secure a certain amount of electricity. There was a limit in providing For this reason, the above-described conventional technology is required to suppress a decrease in battery capacity in further charge / discharge cycles, but cannot achieve a high energy density that satisfies this requirement.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a current collector having a specific form is used as an electrode and that the current collector is formed into an electrode by specific processing. Could solve the above problem.

[0017]

SUMMARY OF THE INVENTION The present invention is to provide a lithium ion battery which suppresses a decrease in capacity due to peeling or falling off of an active material from an electrode due to a charge / discharge cycle, and is more excellent in energy density and energy efficiency. A current collector made of a metal substrate having a rough surface on one side and a smoother surface on the other side as a current collector used for the electrode, and lithium on both surfaces of the current collector. An electrode formed by coating an active material layer capable of inserting and extracting ions, wherein the current collector is wound so that one side of the current collector is rough and the other side of the current collector is smooth. Electrodes.

By using this electrode in a spiral-wound lithium-ion battery, it is possible to remarkably suppress a decrease in capacity due to a charge / discharge cycle of the battery, and to dramatically improve the life of the battery.

In the present invention, as an active material of the positive electrode, for example, transition metal oxides such as vanadium pentoxide, manganese dioxide, and molybdenum trioxide capable of absorbing and releasing lithium ions, and transition metal chalcogen compounds such as iron sulfide are used. ,
Further, a composite compound of these and lithium can be used. In particular, LiCoO ₂ , LiNiO ₂ , LiMn
₂ O ₄ , LiMnO ₂ , LiAl ₀ . ₂₅ Ni ₀ . ₇₅ O ₂ , Li
FeO ₂ is preferable because a high energy density can be obtained, that is, a high electromotive force can be obtained.

As the negative electrode active material, for example, tin-based oxides and carbons capable of occluding and releasing lithium ions are used, and coke, fired resin, carbon fiber, pyrolytic carbon, natural graphite, and mesophase spherules are used. preferable. In particular, if the shape is scaly natural graphite, high energy
It is more preferable because the density can be obtained.

In the present invention, as the current collector, for example,
A metal foil such as Al, Cu, Ni, Ti, Fe, and stainless steel can be used, or a metal foil formed by, for example, electrochemically reducing and depositing a metal may be used.

In order to make one side rougher than the other side, one side is punched by a sandplast method, an electroplating method, an etching method, or a hole is made from one side with a needle or the like. The surface on which the tip protrudes is roughened by burrs). The current collector is also a metal foil having a rough surface on the deposition surface side composed of polycrystalline surfaces and a smooth surface on the substrate surface side by electrochemically reducing and depositing a metal on a smooth substrate surface. Can be obtained.

As the binder used for applying and fixing the active material to the current collector, for example, polyvinylidene fluoride, polytetrafluoroethylene, fluororubber and the like are used.

[0024]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a spiral-type lithium-ion battery electrode of the present invention before winding. One surface 2 of a current collector 1 is a rough surface (hereinafter referred to as “roughened surface”), and the other surface 3 is It is a smooth surface. An active material layer 4 made of an active material and a binder to which a conductive agent is added is provided on both surfaces.

The present invention can be carried out in the following modes by combining the above-described current collectors and active materials. An aluminum foil having only one surface roughened by a sandplast method was used as a current collector, and a paste-like mixture of polyvinylidene fluoride powder, LiNiO ₂ and n-methyl-2-pyrrolidone was used on both surfaces at 0.09 mm on one surface, and a double-sided foil was used on both surfaces. In addition, it can be applied to a thickness of 0.2 mm, and the pyrrolidone can be dried and removed to form an electrode.

In another embodiment of the present invention, the current collector is an aluminum foil obtained by etching one surface of an aluminum foil. The untreated surface side is a smooth surface, and the opposite side is a rough surface.
Be fluororubber and the active material in which LiCoO ₂ powder and conductive auxiliary agent a mixture of acetylene black to a thickness of, for example, 0.01~0.4mm by coating deposited electrode as a binder to both surfaces of the aluminum foil it can.

The present invention further provides a collector having a porous titanium substrate coated with a titanium foil so that the surface of the porous titanium substrate is roughened and the surface of the titanium foil is smoothed. It is also possible to use a mixture of LiCoO ₂ powder as an active material and polyvinylidene fluoride to form an electrode.

According to the present invention, an electrode is obtained by applying a paste-like mixture of natural graphite powder and polyvinylidene fluoride on both surfaces of a copper foil whose one surface has been roughened by electroplating at a high current density, and drying it. be able to.

The current collector having a smooth surface and a rough surface formed by the various methods described above has one surface having a ten-point average roughness R (μm).
Of 3 <R <20, and 0.5 <R <on the other surface.
7 and the difference between the roughness of the rough surface and the roughness of the smooth surface is 1 or more and 1
When it is 8 or less, the cycle life of the battery is improved when the battery is housed with the rough surface on the outside and the smooth surface on the inside.

When the electrode of the present invention is incorporated into a spiral-wound lithium-ion battery, A
When 1 or Ti is used, a positive electrode is used, and a laminate obtained through a diaphragm and a negative electrode is wound in accordance with the shape of the battery case, and is stored in the battery case. On the other hand, as a current collector, N
When i, Fe, Cu, stainless steel, or the like is used, it can be used as a negative electrode. The current collector is wound so that the rough surface side is inside the smooth surface.

A positive electrode lead is pulled out from the positive electrode and connected to the positive terminal of the sealing plate. On the other hand, a negative electrode lead is pulled out from the negative electrode and connected to the negative electrode terminal of the sealing plate. An insulating ring is provided at each end edge of the electrode plate group formed by laminating and winding the electrode, the diaphragm, and the negative electrode of the present invention that is a positive electrode,
A positive electrode terminal separated from each other by an insulating seal is provided on a sealing plate provided thereon.

[0032]

Next, a spiral lithium ion battery incorporating the electrode according to the present invention will be described in detail. First, the positive electrode and the negative electrode were manufactured under the following conditions.

(Positive electrode 1) LiCoO as a positive electrode active material
₍₂₎ 100 parts by weight of powder, 10 parts by weight of graphite and 10 parts by weight of polyvinylidene fluoride were mixed, and N-methyl-2 was added.
-Dissolved in pyrrolidone and made into a paste. next,
This paste was applied to both sides (both sides R = 0.7) of an aluminum foil having a thickness of 20 μm, dried and roll-pressed. Thus, the thickness is 0.20 mm, the width is 50 mm, and the length is 25.
A 0 mm electrode plate was produced.

(Positive electrode 2) An electrode plate was manufactured in the same manner as in the positive electrode 1, except that an aluminum foil etched on one side was used as a current collector. The ten-point average roughness R (μm) of the etched surface of the aluminum foil is 7, and the R of the untreated surface is 1.

(Negative electrode 1) 20 parts by weight of polyvinylidene fluoride was mixed with 100 parts by weight of flaky natural graphite powder, dissolved in N-methyl-2-pyrrolidone, and then made into a paste. This paste was applied to both sides (both sides R = 1.1) of a rolled copper foil having a thickness of 20 μm, dried, and roll-pressed. Thus, a thickness of 0.20 mm, a width of 55 mm,
An electrode plate having a length of 280 mm was produced.

(Negative electrode 2) High current density (10 A / dm ² )
A copper foil (rough surface R = 5.6 on the copper deposition side, smooth surface R = 1.1 on the substrate surface side) obtained by electrolytic reduction deposition treatment without adding a brightener as a current collector Other than that used, negative electrode 1
A negative electrode plate was produced in the same manner as described above.

(Negative electrode 3) A copper foil having a thickness of 20 μm was pierced from one side with a needle having a diameter of 0.5 mm, and the other side where the tip of the needle came out had a burr height of 10 to 300 μm and a puncture density of 100 to 1000.
A negative electrode plate was prepared in the same manner as in the negative electrode 1 except that a copper foil having a rough surface of pieces / cm ² was used as a current collector.

(Negative electrode 4) A negative electrode plate was prepared in the same manner as the negative electrode 1 except that a current collector was a copper foil (rough surface R = 10, flat scene R = 1.1) which had been subjected to sand plast treatment on one side. did.

Example 1 Leads were attached to the electrode plates of the positive electrode 2 and the negative electrode 2, respectively, and the positive and negative electrode plates were laminated with a polyethylene membrane having a thickness of 0.025 mm, a width of 57 mm and a length of 290 mm. Thus, an electrode plate group wound 15 times was formed, and housed in a battery case having a diameter of 4 mm and a height of 80 mm. As an electrolyte, a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 and a solution of lithium hexafluorophosphate dissolved at 1 mol / l were injected, and then sealed and tested. Battery.

(Examples 2 to 7) In each example, a test battery similar to that of Example 1 was produced by combining the positive electrode and the negative electrode shown in Table 1.

Comparative Example 1 A test battery similar to that of Example 1 was prepared except that the positive electrode 1 was used instead of the positive electrode 2 used in Example 1, and the negative electrode 1 was used instead of the negative electrode 2.

In Examples 1 to 7 and Comparative Example 1, the positive electrode lead and the negative electrode lead were connected to an external charge / discharge power supply, and the current 2
After charging to 4.2 V at 50 mA for 2 hours, a current of 250
A cycle test was performed under the condition of discharging to 3.0 V at mV, and the cycle life was evaluated based on a change in discharge capacity accompanying the cycle. Table 1 shows the results.

[0043]

[Table 1]

[0044]

As described above, an active material layer capable of inserting and extracting lithium ions is provided on both sides of a current collector having one surface rougher than the other surface, and the active material layer is laminated with a diaphragm so that the rough surface side is outward. When the electrode according to the present invention wound so as to be used in a spiral lithium-ion battery, a long-life battery with a small capacity reduction can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electrode plate showing a state before winding of an electrode of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current collector 2 Roughened surface 3 Smooth surface 4 Active material layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eriko Yagasaki 3-2-2, Nakanoshima, Kita-ku, Osaka City Inside Kansai Electric Power Co., Inc. (72) Toshiharu Tada 3-2-2, Nakanoshima, Kita-ku, Osaka Kansai Inside Electric Power Company

Claims (5)

[Claims] 1. A current collector comprising a metal substrate having one surface rough and the other surface smoother than the one surface, and an active material layer coated on both surfaces of the current collector and capable of inserting and extracting lithium ions. Wherein the current collector is wound such that one side of the current collector is rough and the other side is smooth and the other side is inside. 2. The current collector according to claim 1, wherein one surface of the current collector has a roughness of 3 or more in terms of ten-point average roughness R (μm), and the other surface has a roughness of 0.5 <.
It forms a smooth surface of R <7, and the difference in roughness between the rough surface and the smooth surface is 1.
The spiral lithium ion battery electrode according to claim 1, wherein the number is 5 or more. 3. An electrode for a spiral-wound lithium-ion battery, wherein the active material layer according to claim 1 comprises an aggregate of flaky active materials. 4. An electrode in which an active material layer capable of storing and releasing lithium ions is provided on both sides of a current collector, and a separator attached to at least one side of the electrode are wound together and housed in a battery case. Wherein the current collector has a rough surface on one side and is smoother on the other surface than the other surface, and the other surface has a smooth surface on one side, which is a rough surface of the current collector. A spiral lithium-ion battery, which is wound so as to be more outward. 5. The spiral-wound lithium-ion battery according to claim 4, wherein the electrodes using the current collector are a positive electrode and a negative electrode.