JPH0864201A - Negative electrode for lithium battery and method for manufacturing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a negative electrode for a lithium battery, which can suppress side reactions on the surface of a current collector, has a simple structure, and has a high electricity quantity density. A lithium battery negative electrode according to the present invention is a negative electrode obtained by crimping a metal foil 1 having a maximum surface roughness Rmax of 3 μm or more and a centerline average roughness Ra of 0.2 μm or more onto a carbon fiber 2. And a positive electrode 4 made of a lithium aluminum alloy, a diaphragm 5 containing an electrolytic solution is sandwiched therebetween.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery negative electrode and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the spread of portable electronic devices, the development of lithium batteries featuring high energy density has become active. So far, coin type batteries used for watches, calculators, etc. or cylindrical type batteries for mobile phones have been developed and commercialized.

Among these lithium batteries, there has been announced one in which a carbonaceous material capable of inserting and extracting lithium ions is used for the negative electrode to greatly improve the characteristics of the battery (see, for example, Japanese Patent Application Laid-Open No. Hei 10 (1999) -135242). No. 1-279578).

In such a battery, the negative electrode is a sheet made by kneading a carbonaceous powder material with a conductive agent such as acetylene black and a binder such as polytetrafluoroethylene, nitrile rubber or polyvinylidene fluoride, and kneading. And is carried on a conductive substrate.

As carbonaceous powder materials capable of inserting and extracting lithium ions, commercially available powders of pitch type, PAN type, needle coke, peak coke, etc., cellulose resins, phenol resins, acrylic resins, vinyl halide resins, A material obtained by firing and carbonizing an organic polymer such as a polyamide-imide resin, a furan resin, a polyimide resin, or a polyamide resin may be used. However, materials other than the above may be used as long as they can store and release lithium ions.

On the other hand, similarly to the negative electrode, the positive electrode also has a structure in which a conductive material and a binder are added to the positive electrode material, and the mixture is kneaded into a sheet and carried on a conductive substrate.

As the positive electrode material, polypyrrole or polyacrole
Anion dopants such as niline, polyacene, and polythiophene
Pingable conductive polymer or MnO₂, V
₂O_Five, TiO₂, Cr₃O₇, V₃O₆, MoO₃,
CoO₂, LiCoO₂, LiMn ₂O_Four, LiNiO
₂, LiFeO₂Oxides such as TiS₂, VS₂, Fe
S, MoS₃Sulfides such as NbSe₃Selenium, etc.
Compounds and the like can be used.

In a lithium battery, since a high voltage (at least 3 V or more) is applied between the positive and negative electrodes, the conductive substrate may have a considerably high potential. Therefore, the conductive substrate used for the negative electrode or the positive electrode is formed of a material that does not dissolve even when a high voltage is applied between the positive and negative electrodes and that does not react with the electrolytic solution component such as lithium ion.

The electrolyte solvent used in the battery includes propylene carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate, 1,2-dimethoxyethane, sulfolane,
1,3-dioxolane, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, 3-methylsulfolane and the like, and mixed solvents thereof have been investigated.

The electrolyte solute, that is, the electrolyte is LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiS.
bF ₆ , LiCF ₃ SO ₃ , LiPF ₆ , LiN (CF
Lithium salts such as ₃ SO ₃ ) ₂ and LiAlClO ₄ and mixtures thereof have been studied.

As the diaphragm material for preventing a short circuit between the positive and negative electrodes, a polymer non-woven fabric such as polyethylene, polypropylene or polytetrafluoroethylene is used.

In the above-mentioned lithium battery (also referred to as a lithium ion battery), a conductive material and a binder are added as auxiliary materials in addition to the carbonaceous powder material as a constituent element of the negative electrode. However, since the conductive agent or the binder itself does not participate in the charging and discharging of the battery, the addition of the conductive agent and the binder has been a cause of limiting the capacity density of the battery.

Further, when the conductive agent and the binder are present,
Since the diffusion of lithium ions is likely to be adversely affected inside the battery, it has also been a cause of deterioration of battery characteristics.

From the above, in order to manufacture a lithium battery having a higher capacity density and excellent battery characteristics,
It was necessary to fundamentally remove the conductive agent and the binder from the electrodes.

Therefore, it has been studied to use a carbon fiber as an electrode member, which has sufficient electric conductivity and can retain its shape without using any conductive agent or binder.

However, carbon fibers have an electric resistance of 10 to 10 as compared with metal materials such as silver, copper and aluminum.
Since it is large on the order of 100 times or more, as shown in FIG. 3, when the current collecting terminal A is taken out from one end of the carbon fiber 12 to collect current, a portion where a current flows well (area near the current collecting terminal A: B Point) and a portion where current does not easily flow (region far from the current collecting terminal A: point C). Since most of the current flows concentratedly in a certain area near the current collecting terminal A, the utilization factor of the entire electrode is lowered and the electrode is locally deteriorated.

Therefore, as shown in FIG.
An electrode having a structure in which a current collector 11 made of a metal material is pressure bonded to the back surface of the electrode has been proposed. In this electrode, a current collecting terminal A ′ is taken out from one end of the current collector 11 to collect current, so that the current collecting body 11 causes the current collecting terminal A ′ to point B (a region near the current collecting terminal A ′). And the electric resistance from the current collecting terminal A'to the point C (region far from the current collecting terminal A ') are substantially equal to each other.

[0018]

In the electrode manufactured as described above, the current often flows to the side of the current collector 11, but it is difficult for the current to flow from the current collector 11 to the side of the carbon fiber 12. Therefore, in a lithium battery using such an electrode as a negative electrode, a surplus electron transfer reaction occurs at the interface between the current collector 11 and the electrolytic solution, and metallic lithium is deposited on the surface of the current collector 11, or γ -Side reactions such as decomposition of electrolytic solution components such as butyrolactone and propylene carbonate were likely to occur.

For this reason, the battery characteristics are deteriorated with time, and a sudden voltage drop occurs at the time of charging / discharging switching of the battery, and an electromotive force is greatly reduced.

An object of the present invention is to provide a negative electrode for a lithium battery, which can suppress side reactions on the electrode surface as described above and has a simple structure and a high capacity density.

[0021]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have used a metal foil having a roughened surface as a current collector to obtain a current collector. The inventors have found that a side reaction such as precipitation of lithium on the surface can be significantly suppressed, and have completed a negative electrode for a lithium battery having excellent electrode characteristics.

The negative electrode for a lithium battery according to the first invention is
It has a structure in which a metal foil is pressure-bonded to carbon fibers, and the surface of the metal foil pressure-bonded to the carbon fibers has a maximum height Rmax of 3
It is characterized by having a surface roughness of not less than μm and not less than 0.2 μm with respect to the centerline average roughness Ra.

The term "surface roughness" as used herein means the surface roughness (JIS B) specified in Japanese Industrial Standards (JIS).
-0601), and in particular, the maximum height Rmax and the center line average roughness Ra are used as the index indicating the surface roughness in the present invention.

In the first invention, the maximum height Rmax is 6 μm or more and the center line average roughness Ra is 0.
More preferably, it has a surface roughness of 6 μm or more.

As the surface roughness, the maximum height Rmax is 3 μm.
If the average line roughness Ra is 0.2 μm or more,
Adhesion with general-purpose carbon fiber is excellent.

In the present invention, the metal foil used for the negative electrode for a lithium battery is made of a material which, when used as a negative electrode, does not form an alloy with lithium in the potential range indicated by the negative electrode and does not dissolve in the electrolytic solution. Required. When a negative electrode made of carbon fiber is used as a lithium battery, it is 0 to 2 in a noble direction with respect to the deposition potential of lithium.
It is preferable that stable operation can be performed within the range of V. Here, the stable operation means that lithium ions (Li ⁺ ) which are electrolyte solution components are deposited on the surface of the metal foil or BF ₄ ⁻ , BF ₆ ⁻ , ClO ₄ ⁻ , CF which are counter ions of lithium ions.
₃ SO ₃ ⁻ , N (CF ₃ SO ₃ ) ₂ ^{− and} other negative ions are not decomposed, propylene carbonate, γ-butyrolactone and other non-aqueous solvents are not decomposed, and a metal foil current collector is a solution. React with ingredients to form compounds,
Indicates that a dissolution reaction does not occur. Preferred examples of the metal material that does not cause a dissolution reaction within the range of 0 to 2 V in the noble direction from the lithium deposition potential include copper and nickel.

In the present invention, the carbon fiber used for the negative electrode for a lithium battery is a carbon fiber capable of absorbing and desorbing lithium ions, having a high electric conductivity, and being capable of retaining its shape by itself. Any of a system, a PAN system, a rayon system, and a vapor phase growth system may be used. The electric conductivity is preferably 10 ³ s / m or more, and more preferably 10 ⁴ s / m or more.

The carbon fiber preferably has an interlayer distance d ₀₀₂ of 0.33 nm or more and 0.38 nm or less as a crystal state calculated by (002) plane diffraction analysis. The crystallite size in the C-axis direction of a carbon crystal is 30.
The thickness is preferably nm or less, and more preferably 20 nm or less.

In the method for producing a negative electrode for a lithium battery according to the second invention, the surface roughness is 3 with respect to the maximum height Rmax.
a step of roughening at least one surface of the metal foil so that the center line average roughness Ra is 0.2 μm or more, and a metal is used so that the roughened surface contacts the electrode member made of carbon fiber. And a step of pressing the foil onto the carbon fiber.

In the method for producing a negative electrode for a lithium battery according to the second aspect of the present invention, when roughening at least one surface of the metal foil, (1) the degree of unevenness of the metal foil surface itself is increased. When roughening,
(2) The case of roughening the surface of the metal foil by forming a substance having a composition different from that of the material forming the metal foil in various shapes, and (3) combining (1) and (2) above. Therefore, it is considered that the surface is roughened.

(1) As the roughening means for roughening by increasing the degree of unevenness of the metal foil surface itself, the metal material forming the metal foil or the required roughening is used. Various means can be appropriately selected according to the degree.

First, as a very effective means in such a case, the metal foil is immersed in an electrolytic solution containing the same type of metal ion as the main constituent element constituting the surface of the metal foil to form the metal foil as an electrode. As a method, a method of electrochemically depositing metal ions in the electrolytic solution on the surface of the metal foil by energizing, that is, a so-called electrodeposition method can be mentioned. In this method, the degree of unevenness on the surface of the metal foil can be increased by depositing metal ions.

The electrodeposition method has an advantage that the amount and form of the metal deposited on the surface of the metal foil can be easily controlled by appropriately adjusting the amount of electricity and the potential of the metal foil during electrodeposition. .

For example, when it is desired to deposit copper in a granular form on the surface of a metal foil containing copper as a main component by the above electrodeposition method to roughen the surface, the surface is immersed in a copper sulfate (CuSO ₄ ) solution. The potential of the metal foil is 0.5 ± 0.1 V vs NH
This can be achieved by setting E. Also, nickel can be supported in an island shape on the surface of the metal foil containing nickel as a main component by the same means.

Further, as another means for roughening at least one surface of the metal foil, etching treatment of the metal foil surface with a chemical can be mentioned. In this method, the degree of unevenness on the surface of the metal foil can be increased by scraping metal atoms from the surface of the metal foil.

As a typical etching process,
Examples include etching with ferric chloride (FeCl ₂ ). For example, when it is desired to roughen the surface of a metal foil containing nickel as a main component, the metal foil may be dipped in an aqueous solution containing ferric chloride (FeCl ₂ ), and the immersion time and the solution temperature may be roughened. It is preferable to set appropriately according to the degree to be converted. Japanese Industrial Standard (JIS K-1447)
Describes a detailed description of the concentration of the aqueous solution. This etching treatment using an aqueous solution containing ferric chloride can be applied not only to a metal foil containing nickel as a main component, but also to roughening the surface of a metal foil containing iron or copper as a main component.

Although the mechanism of etching with ferric chloride has not been completely clarified so far, it is considered that the reaction proceeds in the following steps. For example,
In the etching treatment of the surface of the metal foil containing nickel as a main component, as a first step, diffusion of Fe ₃ ⁺ ions in the solution to the surface of the metal foil containing nickel as a main component occurs, and as a second step, It is considered that the nickel atoms of the metal foil and the Fe ₃ ⁺ ions in the solution undergo electron exchange (see Chemical formula 1).

[0038]

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Furthermore, as the third step, it is considered that the newly generated nickel ions Ni ^{2 +} are released from the surface of the metal foil.

(2) A typical surface roughening means for roughening the surface of the metal foil by forming a substance having a composition different from that of the material forming the metal foil in various shapes. , Alkaline oxidation treatment with chemicals can be mentioned. For example, if you want to roughen the surface of a metal foil containing copper as the main component by using an alkali oxidation treatment, warm the alkaline treatment solution and immerse the metal foil in the treatment solution. In addition, a film made of an oxide having a composition different from that of the metal material is formed. By forming the coating film made of this oxide, the degree of unevenness on the surface of the metal foil can be increased.

In the alkaline oxidation treatment, it is preferable to use a water-soluble treatment chemical in which the pH value (pH) of the solution, which is an index showing the hydrogen ion concentration, is 7 or more, and more preferably, the pH is greater than 9. It is desirable to use treatment chemicals.

The pH value of the treatment solution means that when the hydrogen ion concentration in the solution is [H ⁺ ] (mol / l),

[0043]

Embedded image

This value can be easily obtained by using litmus test paper, various test agents such as BET solution, and a pH meter.

As the water-soluble treatment chemical, specifically, an alkaline aqueous solution containing potassium chlorate, potassium hydroxide, sodium persulfate, potassium persulfate or the like as an oxidizing agent can be preferably used. Although the solution temperature during the alkaline oxidation treatment is slightly affected by the treatment time, it is generally preferably 50 ° C. or higher and 100 ° C. or lower, and more preferably 60 ° C. or higher and 80 ° C. or lower.

Although the treatment time is slightly affected by the solution temperature, it is preferably in the range of 1 minute to 30 minutes, more preferably 2 minutes to 15 minutes.

The larger the pH value of the aqueous treatment chemical, the treatment temperature, and the treatment time, the higher the growth rate of the oxide coating on the surface of the metal foil, but any of the pH value of the treatment solution, the treatment temperature, and the treatment time value. However, if it exceeds the setting range mentioned above, the copper foil surface will be covered with a thick oxide coating, and the electrical insulation of the metal foil surface will be high, and the current collection function originally required for the metal foil will be significantly reduced. Will be done.
Further, even if any of the pH value of the treatment solution, the treatment temperature, and the treatment time value is significantly lower than the above-mentioned set range, a portion where the oxide coating grows and a portion where the oxide coating does not grow are mixedly obtained on the surface of the metal foil. Therefore, when this is used as an electrode constituent member, a locally low electric resistance portion and a high electric resistance portion locally occur, which causes local deterioration of the electrode. Therefore, in the alkaline oxidation treatment, by performing the oxidation treatment under the treatment conditions in which the pH value of the treatment solution, the treatment temperature, and the treatment time are appropriately set, the thickness is not thick enough to lose the current collecting function and the surface is entirely covered. It is possible to reproducibly form an oxide film that is not thin enough to cover.

In the case of a metal foil to be roughened, particularly a copper foil,
Prior to the alkali oxidation treatment, it is preferable to thoroughly boil in ketones or alcohols such as methyl ethyl ketone, acetone, ethanol, methanol, etc. in advance to thoroughly remove stains attributable to the organic components on the surface before the treatment.

After the alkaline oxidation treatment, the metal foil is thoroughly washed with water and then with ethers or alcohols, and then stored in an inert gas atmosphere such as nitrogen or argon until the electrode is assembled. Is desirable.

Furthermore, when roughening the metal foil,
Although the roughening treatment as described above may be performed alone,
It is also possible to use a plurality of roughening means in combination.

(3) When the metal foil is roughened by combining different roughening means, for example, first, the surface of the metal foil is once roughened by the electrodeposition method, and then the alkali oxidation treatment is further performed. By applying it, a film made of an oxide can be formed on the surface of the metal foil, and the surface can be roughened more effectively. In addition, the surface of the metal foil is first roughened by etching with a chemical agent, and then alkali oxidation is further applied to form a film made of an oxide on the surface of the metal foil to further effectively roughen the surface. You can also do it.

[0052]

As a result of repeated experiments, the present inventors have found that by using the negative electrode for a lithium battery according to the present invention, it is possible to further suppress deterioration of characteristics of the lithium battery over time. The mechanism of action has not yet been clarified so far, and it is thought that it is due to the following reasons.

In the negative electrode for a lithium battery according to the present invention, the surface crimped to the carbon fiber is 3 μm or more with respect to the maximum height Rmax and the center line average roughness Ra due to the roughening of the surface of the metal foil involved in the current collection. Since the surface roughness is 0.2 μm or more, the adhesion between the electrode member made of carbon fiber and the metal foil at the time of pressure bonding is further improved as compared with the conventional case, and the interface between the metal foil and the electrode member made of carbon fiber is increased. It is considered that the area of the portion where the surface of the metal foil comes into contact with the electrolytic solution is further reduced. For this reason, an electric current smoothly flows between the metal foil and the carbon fiber, and metal lithium deposition based on the transfer of excess electrons on the surface of the metal foil in contact with the electrolytic solution or lithium fluoride, etc. that occurs with it Side reactions such as formation of a high electric resistance composition are less likely to occur. Therefore, when such a negative electrode is used, the internal resistance of the lithium battery, which is inherent to the lithium battery, can be suppressed to a small value, and a sudden drop in voltage from the charging voltage to the discharging voltage does not occur at the time of charging switching of the battery.

In particular, as a negative electrode for a lithium battery according to the present invention, even if a negative electrode in which a metal foil whose surface is roughened by forming a film made of an oxide is pressure-bonded to one side of carbon fiber is used, The mechanism of action that can more effectively suppress the deterioration of the characteristics of the above with time has not yet been clarified yet, but it is considered to be as follows.

In a negative electrode using a metal foil whose surface is covered with a thin film made of an oxide, compared with the case of using a metal foil having no surface coating made of an oxide, the electrolytic solution and the metal foil are particularly used. It is expected that the current density at the interface with and will be kept low. As described above, it is considered that the rate of electron exchange between the metal foil and the lithium ions in the electrolytic solution becomes extremely slow by suppressing the amount of electricity passed between the metal foil and the electrolytic solution to a lower level. Therefore, in a negative electrode using a metal foil whose surface is covered with a thin film made of an oxide, almost no charge transfer occurs between the surface of the metal foil and the electrolytic solution, and lithium ions in the electrolytic solution are reduced to reduce the metal. The possibility that metallic lithium is deposited on the foil surface can be further suppressed.

On the other hand, if a coating film made of an oxide is present at the interface between the electrode member usually made of carbon fiber and the metal foil, the oxide is an insulating substance and the flow of the electrode is obstructed to increase the internal resistance of the battery. I fear that I will do it.

However, in the method for producing a negative electrode for a lithium battery according to the present invention, since the metal foil is pressure-bonded to the electrode member made of carbon fiber, the thin coating made of oxide collapses at the pressure-bonded portion and the metal foil is partially exposed. However, since direct bonding occurs between the exposed metal foil and the carbon fiber, it is considered that the current is smoothly supplied.

Therefore, a negative electrode for a lithium battery, which can suppress the deposition of metallic lithium on the surface of the metal foil and the accompanying side reactions such as the formation of a high electric resistance composition, very efficiently without causing an increase in the internal resistance of the battery. Provided.

[0059]

EXAMPLES Examples according to the present invention will be described below. However, the present invention is not limited to the examples shown below. In addition, in this example, a carbon fiber / LiAl battery was manufactured in order to evaluate the characteristics of the negative electrode.

Example 1 As a carbon material, plain weave pitch-based carbon fiber XN-40 (product name of Nippon Oil Co., Ltd., Granoc cloth 300 g /
m ² ) was used. This was cut into a size of 5 cm × 5 cm and exposed to a vapor of methyl ethyl ketone for 10 minutes to remove the sizing agent adhering to the surface. The carbon fiber prepared in this way is further cut into a size of 2.5 cm × 1.5 cm, and the end surface is sewn with a thread to prevent fraying,
Used as an electrode material.

A rolled copper foil having a thickness of 18 μm was used as the metal foil. This was cut into 2.5 cm × 1.5 cm and boiled in ethanol for 10 minutes to remove surface stains.

As the copper foil treating chemical, an inner layer copper foil oxide treating agent Enplate MB-438 aqueous solution manufactured by Meltex was used. The pH value of the solution after preparation was measured with a litmus test paper and found to be 14. This treatment solution was placed in a glass beaker and adjusted with a hot water bath so that the liquid temperature was 71 ± 5 ° C.

Then, the copper foil was dipped in this treatment solution for 2 minutes for oxidation treatment, and then rinsed well with pure water. The rinsing was repeated until the pH value of the rinsing solution became less than 8. Then, the copper foil was sandwiched between paper towels to remove all the water adhering to the surface. A soot-like oxide film was formed on the surface of the copper foil which was thus oxidized. The thickness of this oxide film was such that it could be easily removed by rubbing it with the tip of the tweezers. Further, the surface roughness of the copper foil has a maximum height Rmax of 3.6 μm,
The center line average roughness Ra was 0.35 μm.

Next, a laminate of carbon fibers and copper foils subjected to alkali oxidation treatment was sandwiched between two Teflon plates, and the carbon fiber resistivity was measured using a carbon fiber resistivity measuring device. The copper foil was pressure-bonded onto the carbon fiber at a pressure of 2.0 Ωcm ² or less.

Using the carbon fiber pressure-bonded with the copper foil as described above, a single cell carbon fiber / Li as shown in FIG.
An Al battery was produced.

As shown in FIG. 1, carbon fibers 2 to which a copper foil 1 having a roughened surface was pressure bonded, and a lithium aluminum alloy electrode 4 containing 20% by weight of aluminum on a stainless lath plate were prepared. , And a diaphragm 5 containing an electrolytic solution are laminated, and two sheets of insulation treatment are performed so as to be in contact with one surface of each of the copper foil 1 and the lithium aluminum alloy electrode 4.
These were sandwiched between US plates 3 and fixed with Teflon tape.

A non-woven fabric containing polypropylene and polyethylene was used for the diaphragm, and 1 mol / l LiBF was used for the electrolytic solution.
A propylene carbonate solution containing ₄ (Mitsubishi Yuka Battery Grade) was used.

A lead terminal is taken out from the copper foil 1 pressed onto the carbon fiber to form a carbon fiber electrode. Although not shown in the drawing, the lead-out portion of the copper foil 1 is shielded with an insulating material that is insoluble in a non-aqueous solvent such as a silicone adhesive. The voltage applied to the carbon fiber electrode is 0 to 1 for the lithium aluminum alloy electrode.
It was set to V. Further, in the lithium aluminum alloy electrode 4, the lead terminal is taken out from the current collector stainless steel lath plate to form the positive electrode.

Using the lithium battery having the above structure, charging / discharging was performed at an electric current of 1.13 mA, and the average current efficiency from the second cycle to the 100th cycle was measured. The current efficiency here means the discharge capacity (mAH) when discharging from 1 V to 0 V in a carbon fiber / LiAl battery.
Charge capacity (mA from 0V to 1V)
H) means the ratio. The average current efficiency means the average of the current efficiencies measured in each cycle.

As a result, the average current efficiency obtained in the battery according to Example 1 was almost 100%. From the obtained charge / discharge data, it is considered that the exchange of electrons between the copper foil and the electrolytic solution did not substantially occur.

Further, after the charge and discharge characteristics were evaluated, the battery according to Example 1 was disassembled and E of the surface of the copper foil on the side pressed against the carbon fiber was pressed.
DX analysis was performed to examine whether or not lithium dendrite and lithium fluoride, which is a product of the side reaction with lithium dendrite, were produced.

As a result, almost no side reaction products such as lithium dendrite and lithium fluoride were observed on the surface of the copper foil.

Further, surface analysis was carried out by X-ray photoelectron spectroscopy, and the abundance ratio of lithium atoms on the surface of the copper foil on the side pressed to the carbon fiber was examined. As a result, the abundance ratio of lithium atoms to all the atoms on the surface of the copper foil on the side of pressure bonding to the carbon fiber was 1.3%.

Example 2 Plain weave pitch-based carbon fiber XN-40 (trade name: Granoc cloth 300 g / manufactured by Nippon Oil Co., Ltd.) as a carbon raw material
m ² ) was used. This was pretreated in the same manner as in Example 1 to obtain an electrode material.

As the metal foil, electrolytic copper foil CF-T9-LP-18 manufactured by Fukuda Metal Foil & Powder Co. was used. This electrolytic copper foil is one in which granular copper is electrochemically supported on only one side, and the surface roughness is based on Japanese Industrial Standards (JIS), the maximum height Rmax is 6 to 8 μm, and the center line is The average roughness Ra is 0.6 to 0.8 μm. The average thickness of this electrolytic copper foil was 18 μm. This electrolytic copper foil was cut into a size of 5 cm × 5 cm, boiled in ethanol to remove dirt on the surface, and the surface on which the granular copper was carried was pressed to carbon fiber in the same manner as in Example 1. did.

A single-cell carbon fiber battery having a structure as shown in FIG. 1 was produced by using the carbon fiber to which the electrolytic copper foil was pressure bonded as described above.

Using the obtained battery, the amount of electricity passed was 1.13 mA.
The charging / discharging was carried out and the average current efficiency from the second cycle to the 100th cycle was measured.

As a result, the average current efficiency obtained in the battery according to Example 2 was 96.2%.

After the charge and discharge characteristics were evaluated, the lithium battery according to Example 2 was disassembled and surface analysis was performed by X-ray photoelectron spectroscopy to determine the abundance ratio of lithium atoms on the surface of the electro-deposited copper foil that was crimped to the carbon fibers. Examined. As a result, the abundance ratio of lithium atoms in all the atoms on the surface of the electro-deposited copper foil that was pressure bonded to the carbon fibers was 1.6%.

Example 3 As a carbon raw material, plain weave pitch-based carbon fiber XN-40 (product name of Nippon Oil Co., Ltd., Granoc cloth 300 g /
m ² ) was used. This was subjected to the same pretreatment as in Example 1 to obtain an electrode material.

For the metal foil, as in Example 2, Fukuda Metal Foil
An electrolytic copper foil CF-T9-LP-18 manufactured by Kofu Co., Ltd. was used. This
Cut the electro-deposited copper foil into a size of 5 cm x 5 cm and
After removing the dirt on the surface by boiling in
The foil was subjected to the same alkali oxidation treatment as in Example 1.
gave. After the oxidation treatment, the granular copper of this electrolytic copper foil is supported.
When the surface on the side where is analyzed by X-ray photoelectron spectroscopy,
Copper oxide (CuO, Cu ₂O) coating formation was observed.
The surface of the electrolytic copper foil on which granular copper is supported is carbon fiber.
I crimped onto the fiber.

According to the Japanese Industrial Standards (JIS), the maximum surface roughness Rmax is 7 to 9 μm and the center line average roughness Ra is 0.5 to 0.5. It was 0.9 μm.

A single-cell carbon fiber battery having a structure as shown in FIG. 1 was produced by using the carbon fiber to which the electrolytic copper foil subjected to the oxidation treatment as described above was pressure bonded.

Using the obtained lithium battery, the energization amount was 1.
Charge and discharge at 13mA, from the second cycle to the 100th
The average current efficiency up to the cycle was measured.

As a result, the average current efficiency obtained in the lithium battery according to Example 3 was 97.6%.

After the evaluation of charge / discharge characteristics, the lithium battery according to Example 3 was disassembled and surface analysis was performed by X-ray photoelectron spectroscopy to determine the abundance ratio of lithium atoms on the surface of the electrolytic copper foil that was crimped to the carbon fiber. Examined. As a result, the abundance ratio of lithium atoms in all the atoms on the surface of the copper foil that was pressed to the carbon fiber was 2.1%.

Comparative Example 1 As a carbon raw material, plain weave pitch-based carbon fiber XN-40 (product name of Nippon Oil Co., Ltd., Granoc cloth 300 g /
m ² ) was a rolled copper foil having a thickness of 18 μm as a metal foil.

In Comparative Example 1, the copper foil was pressed onto the carbon fiber in the same manner as in Example 1 except that the surface of the copper foil was not subjected to any alkali oxidation treatment. At this time, regarding the surface roughness of the copper foil, the maximum height Rmax was 1.2 μm and the center line average roughness Ra was 0.1 μm.

A carbon fiber battery of a single cell having a structure as shown in FIG. 2 was prepared by using the carbon fiber to which the copper foil was pressure bonded as described above.

As shown in FIG. 2, a carbon fiber 2 to which a rolled copper foil 11 having a flat surface was pressure-bonded, a lithium aluminum alloy electrode 4 containing 20% by weight of aluminum in a stainless lath plate, and an electrolytic solution And a diaphragm 5 including
Two sheets of SUS that have been insulated so as to contact one surface of each of the copper foil 1 and the lithium aluminum alloy electrode 4
These were sandwiched between the plates 3 and fixed with Teflon tape.

Charging and discharging were performed using the carbon fiber battery having the above structure, and the average current efficiency from the second cycle to the 100th cycle was measured.

As a result, the average current efficiency obtained in the battery of Comparative Example 1 was 83.5%.

After the charge and discharge characteristics were evaluated, the lithium battery of Comparative Example 1 was disassembled, and EDX analysis was performed on the surface of the copper foil that was pressed against the carbon fiber to check whether lithium dendrite and lithium fluoride were produced. It was

As a result, the presence of by-products such as lithium dendrite and lithium fluoride was clearly observed on the surface of the copper foil.

Further, surface analysis was carried out by X-ray photoelectron spectroscopy, and the abundance ratio of lithium atoms on the surface of the copper foil on the side pressed to the carbon fiber was examined. As a result, the abundance ratio of lithium atoms in all atoms on the copper foil surface was 76.4%.

Example 4 As a carbon raw material, plain weave pitch-based carbon fiber XN-40 (Nippon Petroleum product name Granoc cloth 300 g /
m ² ) was used. This was subjected to the same pretreatment as in Example 1 to obtain an electrode material.

A rolled nickel foil having a thickness of 20 μm was used as the metal foil. This nickel foil is cut into a size of 5 cm x 5 cm, exposed to methyl ethyl ketone vapor for 10 minutes,
The dirt on the surface was removed. After that, Japanese Industrial Standards (JI
Using a treatment solution satisfying the condition of "type 1 ferric chloride solution" defined in S-K1447), a nickel foil was immersed in the treatment solution heated to a temperature of 30 ° C for 10 seconds to perform etching treatment. After the etching treatment, the nickel foil was subjected to ultrasonic cleaning in pure water to remove stains on its surface, and then vacuum dried. At this time, the surface roughness of the nickel foil has a maximum height Rmax of 6.5 μm and a center line average roughness Ra of 0.
It was 38 μm.

The nickel foil whose surface was roughened as described above was pressed onto carbon fibers in the same manner as in Example 1.

A single-cell lithium battery having a structure as shown in FIG. 1 was prepared by using the carbon fibers to which the nickel foil roughened as described above was pressed.

Using the lithium battery thus obtained, the energization amount was 1.
Charging / discharging was performed at 13 mA, and the average current efficiency from the 2nd cycle to the 50th cycle was measured.

As a result, the average current efficiency obtained in the battery according to Example 4 was 92%.

After the charge and discharge characteristics were evaluated, the battery according to Example 4 was disassembled and surface analysis was carried out by X-ray photoelectron spectroscopy to examine the abundance ratio of lithium atoms on the surface of the nickel foil which was crimped to the carbon fibers. . As a result, the abundance ratio of lithium atoms among all the atoms on the nickel foil surface was 1.8%.
Met.

Comparative Example 2 As in Example 4, plain weave pitch-based carbon fiber was used as the carbon raw material, and rolled nickel foil having a thickness of 20 μm was used as the metal foil.

In Comparative Example 2, the nickel foil was pressure-bonded to the carbon fiber in the same manner as in Example 4, except that the surface of the nickel foil was not etched with the ferric chloride solution. At this time, regarding the surface roughness of the nickel foil, the maximum height Rmax is 1.2 μm and the center line average roughness Ra is 0.
It was 2 μm.

A single-cell lithium battery having a structure as shown in FIG. 2 was produced by using the carbon fiber to which the nickel foil was pressure-bonded as described above.

Using the obtained lithium battery, the energization amount was 1.
Charging / discharging was performed at 13 mA, and the average current efficiency from the 2nd cycle to the 50th cycle was measured.

As a result, the average current efficiency obtained in the lithium battery of Comparative Example 2 was 62.1%.

After the charge and discharge characteristics were evaluated, the lithium battery of Comparative Example 2 was disassembled and surface analysis was carried out by X-ray photoelectron spectroscopy to examine the abundance ratio of lithium atoms on the surface of the nickel foil that was crimped to the carbon fiber. It was As a result, the abundance ratio of lithium atoms in all atoms on the nickel foil surface was 3
It was 2.4%.

As is clear from the above-mentioned embodiment, not the electrode in which the metal foil having the flat surface is pressure-bonded to the carbon fiber is used.
It was shown that the cycle characteristics of the lithium battery can be significantly improved by using the electrode in which the metal foil having the roughened surface is pressure bonded to the carbon fiber as the negative electrode.

This is because the surface of the metal foil is roughened so that the pressure-bonding property between the metal foil and the carbon fiber is enhanced and a sufficient current flows between the metal foil and the carbon fiber. ,
In addition, due to this, the area where the metal foil is in direct contact with the electrolytic solution is further reduced, so that the surplus electron transfer reaction at the interface between the metal foil and the electrolytic solution is suppressed, and the surface of the metal foil caused by this is suppressed. It is considered that the side reaction was suppressed to be smaller.

In this example, the example using the plain weave carbon fiber was shown, but it has been confirmed that the same effect can be obtained by using the non-woven carbon fiber.

[0112]

The negative electrode for a lithium battery according to the present invention comprises:
Since side reactions such as precipitation and decomposition of the electrolyte solution component on the surface of the metal foil can be suppressed to a small level, an increase in electric resistance at the negative electrode can be suppressed to a small level. Therefore, by using this negative electrode, a lithium battery having a simple structure and a high capacity density can be obtained. In the lithium battery obtained in this manner, deterioration of characteristics over time is suppressed, so that a long battery life can be secured.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of a lithium battery according to an embodiment of the present invention.

2 is a schematic diagram showing the structure of a lithium battery manufactured in Comparative Example 1. FIG.

FIG. 3 is a schematic diagram showing a current flow in an electrode made of only carbon fibers.

FIG. 4 is a schematic diagram showing a current flow in an electrode in which a current collector is pressure-bonded to carbon fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal foil 2 Carbon fiber 3 SUS plate 4 Lithium aluminum alloy electrode 5 Separating film In addition, the same code | symbol shows the same or corresponding part in each figure.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoshi Miyai, 3-22 Nakanoshima, Kita-ku, Osaka, Osaka Prefecture 3-22 Kansai Electric Power Co., Inc. (72) Toshiharu Tada 3--3, Nakanoshima, Kita-ku, Osaka, Osaka No.22 inside Kansai Electric Power Co., Inc.

Claims (2)

[Claims] 1. A negative electrode for a lithium battery, in which a metal foil is pressure-bonded to carbon fiber, wherein a surface of the metal foil pressure-bonded to the carbon fiber has a maximum height Rmax of 3 μm or more and a center line average roughness Ra. The negative electrode for a lithium battery is characterized by having a surface roughness of 0.2 μm or more. 2. The surface roughness is 3 μm or more for the maximum height Rmax and 0.2 μm for the center line average roughness Ra.
As described above, a step of roughening at least one surface of the metal foil, and a step of pressure-bonding the metal foil to the electrode member such that the roughened surface is in contact with an electrode member made of carbon fiber. A method of manufacturing a negative electrode for a lithium battery, comprising: