JP2002063894A - Production method of carbon material film, and nonaqueous secondary battery using the carbon material film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a carbon material film with reduced volume of binder. SOLUTION: In the production method of the carbon material film, in which a carbon material is deposited on the surface of a conductive substrate through electrophoretic migration electrodeposition, a conductive substrate as a negative electrode and an opposite electrode as a positive electrode are dipped in a liquid, in which at least iodine is dissolved in non-protic solvent and a carbon material is dispersed, and direct current electric field is applied between them, or conductive substrate as a positive electrode and a counter electrode as a negative electrode are dipped in a liquid, in which a carbon material is dispersed in the non-protic solvent, and direct current electric field is applied, to deposit a carbon material film on the surface of the conductive substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a carbon material film and a non-aqueous electrolyte secondary battery using the carbon material film for a negative electrode. More specifically, the present invention relates to a method for producing a carbon material film by electrophoretic electrodeposition and a non-aqueous electrolyte secondary battery using the carbon material film for a negative electrode and not necessarily requiring a binder.

[0002]

2. Description of the Related Art In recent years, high-capacity secondary batteries have been required as electronic devices have become smaller. Among them, non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, have a light weight and a high energy density, and thus are regarded as promising power sources for driving portable devices, and are being actively researched and developed. Metal materials, carbon materials, and the like are being studied as the negative electrode active material. Among these, when lithium metal is used as the negative electrode active material, dendrite is generated and grows on the lithium electrode when charge and discharge are repeated, which may eventually cause an internal short circuit. Lithium alloys such as lithium aluminum alloys have been proposed instead of lithium metal,
If the charge / discharge cycle is long or the depth of charge / discharge is deep, segregation of the alloy or the like occurs, so that it is difficult to obtain sufficient characteristics.

[0003] Therefore, a lithium secondary battery using a carbon material as a host material for a negative electrode and utilizing an electrochemical insertion / desorption reaction of lithium ions, that is, a lithium ion battery, has been proposed and partially put into practical use. A lithium ion battery using a carbon material for the negative electrode has excellent cycle characteristics and safety. Carbon materials have a wide range of structures and forms from graphite to amorphous carbon, and their physical property values or the fine structure formed by the hexagonal mesh of carbon greatly affect the performance of the electrode. Various carbon materials have been proposed. For example, JP-A-60-182670, JP-A-60-221964
Japanese Patent Application Laid-Open No. 4-155776, a graphite-based carbon material disclosed in Japanese Patent Application Laid-Open No. 61-111907, a relatively amorphous carbon material disclosed in Japanese Patent Application Laid-Open No. 62-90863, and the like. Japanese Patent Application Laid-Open No. 4-280068 using carbon fiber as disclosed in JP-A-61-214417.
And Japanese Patent Application Laid-Open No. 4-342958, which focus on the fine structure of the carbon material instead of the crystallinity of the carbon material.

At present, carbon materials used for negative electrodes of lithium ion batteries are roughly classified into carbon materials fired at about 1000 ° C. and graphite materials fired at about 2800 ° C. When the former is used, there is an advantage that the reaction with the electrolytic solution is small and decomposition of the electrolytic solution does not easily occur, but there is a disadvantage that a change in potential due to release of lithium ions is large.

[0005] On the other hand, when the latter is used, it has the advantage that the change in potential due to the release of lithium ions is small, but it reacts with the electrolytic solution to cause decomposition of the electrolytic solution and further destroys the carbon material. There are disadvantages (J. Electrochem.
Soc., Vo.117, p.222 (1970)). As a result, problems such as a decrease in charge / discharge efficiency, a decrease in cycle characteristics, and a decrease in battery safety occur. It has been reported that a graphite-based material can be used when a specific electrolyte is used (J. Electroc.
hem.Soc., Vo.137, p.2009 (1990)), but the problem is that the improvement in battery temperature characteristics and cycle characteristics is considerably limited by the type of electrolyte because the electrolyte is limited. Remains. Therefore, in the development of a lithium ion battery, it can be said that it is important to pay attention to the combination of an electrolyte and a carbon material that does not cause decomposition of the electrolyte and destruction of the carbon material.

For a negative electrode of a lithium-ion battery, a powdery or fibrous carbon material and a binder are mixed to prepare a paste-like electrode mixture to which a dispersion medium is added. And then drying the dispersion medium. At this time, it is general to provide a step of compression molding or pressing for the purpose of pressing the electrode mixture onto the current collector, making the electrode thickness uniform, and improving the electrode capacity. This compression step increases the bulk density (apparent density or packing density) of the electrode and increases the energy density per unit deposition of the battery. However, in this conventional process, even if the performance of the carbon material itself is excellent, a problem may remain in the cycle characteristics, the amount of the active material charged per unit volume, and the like.

On the other hand, as an electrode provided with a carbon material film without using a binder, Japanese Patent Application Laid-Open Nos. 60-36315, 63-13282, and 63-2
No. 4555 proposes a method of directly depositing a carbon material on the surface of a metal substrate which can be a current collector, that is, a method of obtaining a carbon material by gas phase carbonization. In this method, since the carbon material is directly deposited on the substrate surface, a binder is not required, and at the same time, since the carbon material is deposited on the substrate surface with good adhesion, an electrode having high capacity and excellent cycle characteristics is obtained. Can be In addition to the above, in JP-A-4-92364, JP-A-5-347155, etc., a carbon material is deposited on a porous metal substrate by impregnating the porous metal substrate with a solid or liquid organic compound, followed by firing. That is, an electrode manufacturing method by solid-phase carbonization or liquid-phase carbonization has been proposed.

On the other hand, electrophoretic electrodeposition is described in, for example, “Wet Process Handbook, p. 124, Nikkan Kogyo Shimbun (1.
996) ”is widely applied as a coating method for metals, metal compounds, oxides, phosphors, organic and inorganic paints, rubbers, dielectrics, glass, etc. using aqueous and non-aqueous electrodeposition baths. For example, the electrophoretic electrodeposition of oxide particles is described in “Wet Process Handbook, pp. 146-64”. 128-132, Nikkan Kogyo Shimbun (199
6) ". The deposition by this method is considered to be due to the following mechanism: First, a small amount of water and iodine react quickly with acetone to generate protons, and the protons are dispersed. The oxide particles are positively charged by being adsorbed on the surface of the oxide particles.When a direct current is applied in this state, the positively charged oxide particles move toward the discharging electrode, and the working electrode (cathode) It is believed to be deposited on the surface.

Further, the scale is increased in a general manufacturing process, and the product is applied to rubber products and coating in the automobile industry. Since the introduction of electrodeposition technology for painting metal articles in the early 1960's, this method has been widely applied throughout the world as a technique for coating a variety of products in the automotive and appliance industries. This method is described in detail in the following article. (1) Percy E. Pierce, Journal of Coatings Technol
ogy, Vol. 53, p. 52 (1981). (2) Fritz Beck and Harald Guder, J. Electrochem.
Soc., Vol. 134, p. 2416 (1987). (3) Fritz Beck, Electrochimica Acta, Vol. 33, p.
839 (1988).

Japanese Patent Application Laid-Open No. 5-94821 discloses an example in which electrophoretic electrodeposition is applied to a method for manufacturing an electrode for a secondary battery.
Japanese Patent Application Laid-Open No. 5-110666 discloses a method in which a direct current electric field is applied between a conductive substrate as a negative electrode (cathode) and a counter electrode to deposit an active material directly on a current collector.
It has been proposed for use in lead-acid batteries. Examples of application of electrophoretic electrodeposition to a method for producing a carbon material film include:
In JP-A-9-74052, etc., activated carbon, a conductivity-imparting material, a binder, and a binder are dispersed in a solvent such as water or ethanol, and a conductive substrate is used as a positive electrode (anode) to form a positive electrode (anode). It has been proposed to apply a direct current electric field between them and use the deposited one for an electric double layer capacitor.
Carbon black, acetylene black, Ketjen black, graphite powder, carbon fiber, or ruthenium oxide, a binder selected from polysaccharides are used as the conductivity-imparting material, and water and alcohol are used as solvents. And those selected from strong polar solvents.

[0011]

The above-mentioned electrode using the carbon material, its production method and electrophoretic electrodeposition have some problems. In the case of gas-phase carbonization, the cost is generally high, and it is difficult to control the crystallinity and deposition amount of the carbon material which affects the electrode characteristics. That is, the crystallinity is increased by increasing the deposition temperature of the carbon material, but the deposition amount of carbon is hardly increased. For this, for example,
"Michio Inagaki, Carbon Materials Engineering, pp. 66-68, Nikkan Kogyo Shimbun (1985)" states that in the gas phase pyrolysis process, carbon particles similar to carbon black in the gas phase (called soot-like particles). However, the substance is not always clear.), As described above, the generated carbon particles always enter the pyrolysis carbon, so that new growth cones are generated, and as a result, the carbon material is This is because it is considered that they cannot grow significantly.

When a carbon material film is formed directly on the surface of a substrate by gasification, liquid phase and solidification, there is a disadvantage that the carbon material film is formed on the entire substrate. For example, when manufacturing a battery using an electrode in which a carbon material is directly deposited on a substrate surface, a step of welding the electrode and the battery can requires a step of peeling off the carbon material deposited on the welded portion. .

Therefore, as a countermeasure against this, it is conceivable to perform masking in order to form a portion where no carbon material is deposited. However, the carbon generation temperature must be set to be equal to or lower than the melting point of the masking constituent material, and the masking effect is significantly reduced in consideration of the adhesion between the masking constituent material and the substrate. In addition, even if the deposited carbon material is removed in order to form a welded portion, when a conductive substrate having a catalytic action is used, the adhesion between the carbon material and the substrate is improved. Will be very difficult.

This is because the substrate itself acts as a catalyst, so that when depositing carbon, catalyst atoms are incorporated into carbon, and the current collector becomes thinner or thinner. In addition, as the demand for higher capacity batteries increases, it becomes necessary to reduce the thickness of a metal plate serving as a current collector (conductive substrate) as one means of reducing battery weight. However, as described above, even when the current collecting function for the active material is sufficient, it is difficult to separate carbon only from the welded portion when welding with a battery can or the like, or welding is performed without separating. However, there are problems that the internal resistance of the battery is increased, the production yield is reduced, and the reliability is greatly affected, because problems remain in the welding resistance and strength.

In addition to the above, JP-A-4-92364 and JP-A-5-347155 disclose that a three-dimensional structure such as a porous metal substrate is impregnated with a precursor of a powdery or liquid carbon material. It describes a carbon electrode that is solidified after it has been cured. In these production methods, since the yield from the precursor of the carbon material to the carbon material is low, it is difficult to obtain a high-density carbon electrode. When a three-dimensional structure having a high porosity is used in order to reduce the weight of the battery, it is not possible to sufficiently receive the catalytic action of carbonizing the carbon material.
Furthermore, the heat treatment temperature must be lower than the melting point of the metal constituting the metal current collector. From the above, there is a limitation in increasing the crystallinity of the carbon material, and there remains a problem that a sufficient capacity cannot be obtained.

On the other hand, producing a carbon electrode using a powdery or fibrous carbon material requires a complicated process and includes a binder for binding the carbon material. It is difficult to sufficiently increase the energy density of the portion corresponding to. In increasing the energy density of a lithium ion battery, it is an important point to increase the filling amount per volume of the carbon material used for the negative electrode. Therefore, the use of a binder does not lead to a fundamental solution in consideration of increasing the energy density of a battery.

Next, the problems of the method for producing a carbon material film using electrophoretic electrodeposition include the fact that a film forming technique for forming only a carbon material has not been established and that the electrodeposition bath has a polarity. Is used. Regarding the former, Japanese Patent Application Laid-Open No. 9-74052 proposes to obtain a carbon material film by co-depositing activated carbon, a conductivity-imparting substance, and a binder on the anode, but the binder is included. Therefore, it is difficult for the energy density of at least the corresponding portion to be sufficiently high. If no binder is used, the binding properties between the carbon material particles and the adhesive strength between the carbon material film and the substrate are reduced, so that the electrode characteristics, particularly the cycle characteristics, are significantly reduced.

One of the causes is considered to be a solvent for dispersing particles to be deposited during electrophoretic electrodeposition. When a solvent having a strong polarity is used, for example, “Hideyuki Negishi et al., Surface Technology, Vol. 49, p. 25, (1998)”
It is described that reduction of water or a protic solvent other than water occurs at a potential required for electrophoretic electrodeposition. For example, Japanese Unexamined Patent Publication
In JP-A-94821, JP-A-9-74052 and the like, a solvent selected from strong polar solvents such as water and alcohol is used. Therefore, since gas is generated by the reduction reaction of the solvent in the vicinity of the electrode during the electrophoretic electrodeposition, the uniformity of the obtained film is likely to be adversely affected.

From the above, in order to solve the problem, it was necessary to examine the electrode (anode or cathode) to be deposited, including the combination of the particles to be deposited, the solvent for dispersing the particles, the additives, and the like. For example, as a preparation of various oxide superconducting films and a superconductor magnetic shield by depositing oxide superconducting powder on a tubular substrate, production of a YBCO film from an acetone-iodine bath (Nobuyuki Koura et al. Surface technology, Vol. 40, p. 819 (1989)), Preparation of BSCCO film from toluene-based bath (N. Koura, etal, Ph.
ysica C, Vol. 200, p. 50 (1992)), preparation of a TBCCO film from a cyclohexanone-iodine bath (N. Koura, et al.
al, Jpn. J. Appl. Phys.,), as a technique for thinning a solid electrolyte in a solid oxide fuel cell, deposition of YSZ particles from an acetylacetone bath (T. Ishihara, et al,
Chem. Lett., 1992, p. 947 (1992)) etc. are reported to deposit on the cathode.

In an acetone bath containing nitrocellulose instead of iodine, the conductivity is increased by adding a trace amount of a strong base, and the particles are negatively charged by the addition of a strong acid to deposit the particles on the anode side. (J. Mizuguchi et al, J. Electrochem. Soc., Vol.
130, p.1819 (1983)). Therefore, it can be said that it is extremely important to find optimum deposition conditions such as a solvent, an additive, an electrode, etc., which are compatible with the particles to be deposited.

[0021]

SUMMARY OF THE INVENTION In view of the above, it is possible to form a carbon material film on the surface of a conductive substrate without being restricted by the crystallinity of a carbon material as an active material, and to increase the energy density of a lithium ion battery. From the viewpoint of the present invention, the present inventors have conducted various studies for the purpose of reducing the weight corresponding to the binder not participating in the electrode reaction in order to increase the active material density of the electrode, and as a result, have reached the present invention. That is, when electrophoretic electrodeposition is used as a method for forming a carbon material film, the carbon material can be directly deposited on a substrate without being restricted by the crystallinity of the carbon material, and the unit volume of the active material is not necessarily required because a binder is not necessarily required. It has been found that the per-packing amount, that is, the active material density is dramatically increased, so that the conventional problems have been solved.

More specifically, a carbon material film not necessarily requiring a binder is prepared by electrophoretic electrodeposition using an aprotic solvent instead of a strong polar solvent as a solvent, and the carbon material film is prepared. Is used as a negative electrode to manufacture a secondary battery. Further, in the conventional manufacturing method, preparation of the electrode mixture, application, drying of the dispersant, and the like were complicated, but according to the present invention, each process time can be shortened, and in addition, continuous production of the electrode is facilitated. .

The bulk density (apparent density or packing density) of an electrode in the present invention means the total mass of an active material, a conductive agent, a binder, and the like, which are substances other than the active material, occupied by the electrode mixture. It is divided by volume. That is, it can be expressed by the formula of bulk density = total mass of electrode mixture / volume occupied by electrode mixture. The packing structure of the particles depends on the size and shape of the particles, the interaction between the particles, and the like, and the bulk density and the packing ratio are used as one of the indexes for quantitatively discussing the packing structure. On the other hand, the active material density is the weight of the active material in a unit volume of the electrode. The active material density does not exceed the true density of the active material, and the difference from the true density is due to a change in the volume of a material other than the active material, such as a binder, and a void in the electrode.

Thus, according to the present invention, in a method for producing a carbon material film in which a carbon material is deposited on the surface of a conductive substrate by electrophoretic electrodeposition, at least iodine is dissolved in an aprotic solvent and the carbon material is dispersed therein. In the solution thus obtained, a conductive substrate as a negative electrode and a counter electrode as a positive electrode are immersed, and a DC electric field is applied between the two to deposit a carbon material film on the surface of the conductive substrate. A method for manufacturing a first carbon material film is provided. Further, according to the present invention, in a method for producing a carbon material film for depositing a carbon material on the surface of a conductive substrate by electrophoretic electrodeposition,
In a liquid in which a carbon material is dispersed in an aprotic solvent, a conductive substrate as a positive electrode and a counter electrode as a negative electrode are immersed,
A second method for manufacturing a carbon material film is provided, wherein a carbon material film is deposited on the surface of the conductive substrate by applying a DC electric field between the two.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The first method for producing a carbon material film is as follows.
By dissolving at least iodine in an aprotic solvent and using a liquid in which a carbon material is dispersed, by applying a DC electric field between the conductive substrate and the counter electrode as a negative electrode,
A carbon material is deposited on the surface of the conductive substrate. More specifically, iodine is dissolved in an aprotic solvent to form a state in which a carbon material is suspended and dispersed, and at least two electrodes are immersed in the dispersion solution to form a non-aqueous electrolyte secondary battery. A conductive substrate used as a current collector is provided as a negative electrode, that is, a working electrode (cathode). On one side, for example, platinum is provided as a counter electrode (anode, positive electrode), and when a direct current is applied, the charged carbon material becomes a working electrode. The carbon material moves toward the surface of the working electrode, and is deposited on the surface of the working electrode to form a film.

As the counter electrode of the present invention, chemically and electrochemically stable platinum, graphite and the like are preferably used. The aprotic solvent of the present invention is not particularly limited as long as it has the property. Specifically, acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone,
Ketones such as 2-hexanone, methyl isobutyl ketone, 2-heptanone, 4-heptanone, acetonylacetone, and acetylacetone; ethers such as diethyl ether; hydrocarbons such as toluene and n-hexane; and nitrogen compounds such as acetonitrile. And one or more of these are used as a mixed solvent. In particular, acetone and acetylacetone are preferably used.

Further, a small amount of a protic solvent may be added to the aprotic solvent of the present invention. Although depending on the amount of dispersion of the carbon material, the carbon material particles can be positively charged by adsorbing on the surface of the carbon material particles in which the protic solvent is dispersed. When direct current is applied in this state,
It is considered that the positively charged carbon material particles move toward the discharging electrode and are deposited on the working electrode surface. But,
If the protic solvent is excessively added, gas generation due to a reduction reaction of water or a protic solvent other than water is likely to occur in the vicinity of the electrode during electrophoretic electrodeposition, depending on various conditions such as electrolysis voltage. It is conceivable that the uniformity of the resulting film tends to be adversely affected.

As the protic solvent, water or a lower alcohol having 4 or less carbon atoms, for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, t
Ert-butyl alcohol and the like are preferably used. Among them, water is particularly preferably used. During continuous production, it is desirable to supplement water or lower alcohol to compensate for the decrease in the concentration of the protic solvent.

The method for dispersing and suspending the carbon material of the present invention is preferably carried out sufficiently by ultrasonic irradiation or stirring, but is not particularly limited. As a method of electrophoretic electrodeposition in the first method, any of electrodeposition using a constant voltage, electrodeposition using a constant current, electrodeposition using a pulse, and the like can be suitably used.

The conductive substrate of the present invention is not particularly limited.
Any known substrate can be used. further,
The conductive substrate of the present invention also includes a substrate in which a metal or a conductive oxide is plated or coated on the surface of an insulator such as plastic or glass. The surface state, thickness, size, shape, and the like of the substrate are not particularly limited. The shape of the conductive substrate of the present invention is preferably a foil shape or a plate shape. Further, a porous metal substrate such as a foam, a nonwoven fabric, a mesh, a felt, and an expanded shape may also be used.

The deposition amount of the carbon material can be controlled by the above-described electrolysis method, electrolysis time, particle diameter of the carbon material, dispersion amount of the carbon material, electrolysis voltage and the like. For example, when the electrolytic voltage is set higher, the thickness of the deposited film tends to be larger. During continuous production, it is desirable to supplement the carbon material to compensate for the decrease in concentration.

It is preferable that 1 mg to 5 g of iodine is added to 1 L of the aprotic solvent. If the amount of iodine added is less than 1 mg, it is considered that the amount of protons adsorbed on the carbon material is reduced, and the amount of iodine is likely to be reduced. When the amount of iodine added is more than 5 g, the conductivity of the aprotic solvent tends to increase. This causes an increase in the electrolysis current during electrophoretic electrodeposition, which increases the possibility of ignition of the electrodeposition bath and generates bubbles due to the electrode reaction, thereby inhibiting electrodeposition. Is thought to decrease.

The second method for producing a carbon material film is to apply a DC electric field between the conductive substrate and the counter electrode using a liquid in which the carbon material is dispersed in an aprotic solvent. By doing so, a carbon material is deposited on the surface of the conductive substrate. More specifically, no iodine is required, and a carbon material is suspended and dispersed in an aprotic solvent, at least two electrodes are immersed in the dispersion solution, and a non-aqueous electrolyte secondary battery is prepared. A conductive substrate used as a current collector is installed as a positive electrode, that is, a working electrode (anode), and a counter electrode (anode, positive electrode) is provided on one side.
For example, when platinum is provided and a direct current is applied, the carbon material moves toward the working electrode, and the carbon material is deposited on the surface of the working electrode to form a film.

In most electrophoretic electrodepositions, an additive such as iodine is added to a solvent in which particles to be deposited are dispersed. However, when the addition of iodine is small, the amount of protons adsorbed on the particles decreases, so that the deposition amount does not increase. Conversely, as the amount of iodine added increases, the conductivity of the solution increases, which causes an increase in the electrolytic current during electrophoretic electrodeposition, causing the formation of bubbles due to the electrode reaction, etc., thereby causing the deposition to be hindered. It is difficult to control such as reducing the amount. Further, a step of washing the additive or the like when the deposited film is pulled up from the electrodeposition bath may be provided. Therefore, it is more preferable not to add the additive in terms of manufacturing. Therefore, as a result of diligent studies, the present invention has not necessarily required an additive such as iodine.

As the counter electrode in the second method, chemically and electrochemically safe platinum, graphite and the like are preferably used. As the method of dispersing and suspending the carbon material in the second method, it is preferable to sufficiently perform ultrasonic irradiation, stirring, or the like, but there is no particular limitation. As the electrophoretic electrodeposition method of the second method, any of constant voltage electrodeposition, electrodeposition with a constant current, electrodeposition with a pulse, and the like can be suitably used.

The conductive substrate of the present invention is not particularly limited.
Any known substrate can be used. further,
The conductive substrate of the present invention also includes a substrate in which a metal, a conductive oxide, or the like is plated or coated on the surface of an insulator such as plastic or glass. The surface state, thickness, size, shape, and the like of the substrate are not particularly limited. The shape of the conductive substrate of the present invention is preferably a foil shape or a plate shape. Further, a porous metal substrate such as a foam, a nonwoven fabric, a mesh, a felt, and an expanded shape may also be used.

The deposition amount of the carbon material can be controlled by the electrolysis method, the electrolysis time, the particle size of the carbon material, the dispersion amount of the carbon material, the electrolysis voltage and the like. For example, when the electrodeposition voltage is set higher, the thickness of the deposited film tends to be larger. During continuous production, it is desirable to supplement the carbon material to compensate for the decrease in concentration.

As the aprotic solvent used in the second method, any of the above aprotic solvents can be used.
Of these, acetonitrile is most preferably used. As a material constituting the conductive substrate used in the first and second methods, for example, in consideration of use as a current collector of a lithium ion secondary battery, a material that does not alloy with lithium, that is, copper, nickel , Stainless steel, brass,
Molybdenum and tungsten are preferably used. For example, metals such as aluminum, tin, and lead can form solid solutions or intermetallic compounds with lithium. Therefore, if it precipitates during charging or lithium forms a solid solution with the above-mentioned metal, the volume may swell, further deform, or the like, which may cause problems such as adversely affecting cycle characteristics. The shape of the conductive substrate is preferably a foil or plate. Further, a porous metal substrate such as a foam, a nonwoven fabric, a mesh, a felt, and an expanded shape may also be used.

As the carbon material used in the first and second methods, for example, considering use as a negative electrode material of a lithium ion secondary battery, artificial graphite, natural graphite,
From the group consisting of graphite material with low-crystalline carbon material attached to the surface of highly crystalline graphite (hereinafter referred to as surface amorphous graphite), mesocarbon microbeads, mesophase pitch, isotropic pitch, carbon fiber, and coke At least one or more can be selected. In addition to the above, known negative electrode materials for lithium ion batteries, such as a carbon material to which boron or phosphorus is added, can also be used.

The surface amorphous graphite in the present invention is:
It can be obtained by using a highly crystalline graphite material as a core material and attaching low-crystalline carbon to the surface of the graphite material by a method such as a vapor phase method or a solid phase method. The highly crystalline graphite used for the core material is natural graphite, artificial graphite, or mesocarbon microbeads, mesophase pitch powder, etc. in the form of particles (flaky to massive, fibrous, whisker-like, spherical, crushed, etc.). Of graphitized products such as conductive pitch powder
Species or two or more can be used.

The particle size distribution of the carbon material of the present invention is 0.1 to 1
It is preferably about 50 μm. When the particle size of the carbon material is smaller than 0.1 μm, the risk of causing an internal short circuit through the pores of the battery separator increases, whereas when the particle size is larger than 150 μm, the uniformity of the electrode and the active material Any of these is not preferred because the handling properties and the like in the process of producing an electrode having a high packing density are reduced.

After the electrophoretic electrodeposition, the carbon material film of the present invention
It is desirable to wash with an aprotic organic solvent and dry before use. As an aprotic organic solvent for washing, acetone,
Acetonitrile is particularly preferably used.

The carbon material films obtained by the first and second methods are preferably used as a negative electrode of a non-aqueous electrolytic secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode may contain, for example, an oxide containing lithium as a positive electrode active material. LiCo as a positive electrode active material
_{O 2, LiNiO 2, LiMnO 2} , LiFeO 2 and, LiA _1-x TxO ₂ (wherein A is Fe of this series, Co, N
i is either M or Mn, and T represents a transition metal, a 4B group metal or a 5B group metal. 0 ≦ X ≦ 1), LiMn
₂ O ₄ , and LiMn _2-z T _z O ₄ (where T is a transition metal,
It represents a Group 4B or Group 5B metal. 0 ≦ Z ≦ 2),
LiVO _{2 and the} like. The positive electrode has a conductive agent as an active material,
It can be formed by mixing a binder and, in some cases, a solid electrolyte or the like.

As the conductive agent, carbons such as carbon black (acetylene black, Ketjen black, thermal black, and channel black), graphite powder, metal powder and the like can be used, but are not limited thereto. . As the binder, fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride, polyolefin-based polymers such as polyethylene and polypropylene, and synthetic rubbers can be used, but are not limited thereto.

The mixing ratio is based on 100 parts by weight of the active material.
It is preferable that the conductive agent is 1 to 50 parts by weight and the binder is 1 to 30 parts by weight. When the amount of the conductive agent is less than 1 part by weight, the resistance of the electrode increases the polarization and the like, and the charge / discharge capacity decreases, which is not practical. If the amount of the conductive agent is more than 50 parts by weight (the weight part changes depending on the type of the conductive agent to be mixed), the ratio of the active material contained in the electrode is reduced, and the discharge capacity as a positive electrode is undesirably reduced. If the amount of the binder is less than 1 part by weight, the binding ability is lost, and the amount of the binder is 3 parts by weight.
If the amount is larger than 0 parts by weight, as in the case of the conductive agent, the amount of the active material contained in the electrode decreases, the resistance or polarization of the electrode increases, and the discharge capacity decreases, which is not practical.
It is preferable to perform heat treatment at a temperature around the melting point (T _m ) of each binder in order to improve the binding property in producing the positive electrode.

As the non-aqueous electrolyte (ionic conductor) of the present invention, an organic solvent-based electrolyte or a solid electrolyte can be suitably used. As a solvent for the organic solvent-based electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, esters such as γ-butyrolactone, tetrahydrofuran, substituted tetrahydrofuran such as 2-methyltetrahydrofuran, dioxolane, Ethers such as diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, dimethylsulfoxide, sulfolane, methylsulfolane,
Acetonitrile, methyl formate, methyl acetate and the like can be mentioned, and these can be used as one kind or a mixed solvent of two or more kinds.

As the supporting electrolyte salt, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium arsenide hexafluoride, lithium trifluoromethanesulfonate, lithium halide, lithium chloride aluminate And the like, and these can be used alone or in combination of two or more.

An organic solvent-based electrolyte can be prepared by dissolving the supporting electrolyte salt in the organic solvent selected above. The organic solvent and the supporting electrolyte used when preparing the organic solvent-based electrolyte are not limited to those listed above, and any known one can be used.

Further, as a method for forming a solid electrolyte,
A monomer or the like can be mixed with the same organic solvent as used for the organic solvent-based electrolyte solution, and a polymerization reaction including a crosslinking reaction can be performed to solidify the mixture. These monomers include ethylene oxide, propylene oxide, glycidyl methacrylate and the like. These monomers may be used alone or in combination of two or more. If the amount of the monomer with respect to the solvent is too small, solidification is difficult, and if the amount is too large, lithium ion conductivity is impaired.
0% is preferred.

Further, an initiator for accelerating a crosslinking reaction or a polymerization reaction may be added. Examples of the polymerization initiator include azoisobutyronitrile and benzoyl peroxide. These initiators may be used alone or in combination of two or more. Alternatively, one or two or more polymers such as polyvinylidene fluoride, hexafluoropropylene, polymethyl methacrylate, and polyvinyl chloride are mixed, dissolved in a solvent such as tetrahydrofuran, N-methyl-2-pyrrolidone, cast and dried. It can also be prepared by impregnating the solvent from which the solvent has been removed with the above solvent. Alternatively, acrylonitrile, methyl acrylate, vinyl acetate, or the like as a vinyl monomer may be mixed with the organic solvent and heated to be polymerized and solidified.

As the third electrolyte layer disposed between the positive electrode side and the negative electrode side, a material soaked in a support such as porous polyethylene, porous polypropylene, or non-woven fabric may be used as necessary. In this case, it can be prepared by impregnating the support with a liquid electrolyte and then polymerizing the vinyl monomer in the electrolyte with light or heat, or removing the solvent. In addition, examples of the inorganic solid electrolyte include lithium nitride, halide, oxyacid salt, and the like. More specifically, Li ₃ N, Li
_{I, LiSiO 4 -LiI-LiOH,} Li 3 PO 4 -L
i ₄ SiO _{4 and the} like. In addition to the above, a molten salt or the like can be applied instead of the organic solvent-based electrolyte.

Examples of the separator for holding the electrolytic solution include non-woven fabrics or woven fabrics of synthetic resin fibers, glass fibers, and natural fibers having electrical insulation properties, and molded articles of powder such as alumina. Among them, nonwoven fabrics such as polyvinylidene chloride, polyethylene, and polypropylene are preferable from the viewpoint of quality stability and the like. Some of these synthetic resin non-woven fabrics have a function of isolating the positive and negative electrodes when the battery is abnormally heated by the heat of the separator, and these can be suitably used from the viewpoint of safety. The thickness of the separator is not particularly limited, but it is sufficient that the separator can hold a required amount of electrolyte solution and has a thickness that prevents a short circuit between the positive electrode and the negative electrode, and usually a thickness of about 0.01 to 1 mm is used. And it is preferably about 0.02 to 0.05 mm. The carbon material film obtained by the first and second methods can be used for any known battery in addition to the lithium ion battery.

[0053]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be outlined. First, an outline of an apparatus used for electrophoretic electrodeposition will be described. FIGS. 1 to 3 show a case where the conductive substrate is used as a negative electrode. The carbon material 2 is put into the aprotic solvent 1 to which a small amount of iodine has been added, and the suspension is sufficiently stirred and stirred under ultrasonic irradiation. In the liquid, a conductive substrate used as a current collector of a non-aqueous electrolyte secondary battery is used as a working electrode (cathode) 31, and a counter electrode (anode) 41 is arranged on one side. Using the DC power supply 5, a DC current is applied between the two electrodes to deposit the carbon material 2 on the surface of the working electrode 31. Although the shape of the counter electrode in FIG. 1 is plate-shaped, the shape is not particularly limited. For example, as shown in FIG. 2, the working electrode 31 and the spiral electrode (anode) 4
2 or a plate-like electrode (anode) 43 in parallel with the working electrode 31 as shown in FIG.

Next, the case where the conductive substrate is used as the positive electrode is shown in FIG.
To # 6. The carbon material 2 is put into the aprotic solvent 1 and sufficiently stirred under ultrasonic irradiation to be suspended. In the solution, a conductive substrate used as a current collector of a non-aqueous electrolyte secondary battery is used as a working electrode (anode) 32, and a counter electrode (cathode) 44 is arranged on one side. A direct current is applied between the two electrodes using a direct current power source 5, and the carbon material 2 is applied to the surface of the working electrode 32.
Is deposited. Although the shape of the counter electrode in FIG. 4 is plate-shaped, the shape is not particularly limited. For example, as shown in FIG. 5, a working electrode 31 and a spiral electrode (cathode)
45, or a plate-shaped electrode (cathode) 46 can be provided in parallel with the working electrode 32 as shown in FIG.

After the electrophoretic electrodeposition, the working electrode 31 or 32
Is taken out, washed with a solvent or the like, and temporarily dried at 40 to 100 ° C. Thereafter, heat treatment is performed at about 150 ° C., and compression molding is performed. Roller press machines are usually used for compression molding, and when these press machines are used, the material of the press surface,
The rotation method, temperature, atmosphere, and the like are not particularly limited. afterwards,
Weld the lead to the electrodeposited part of the electrode, and remove
A material dried in vacuum at about 50 ° C. is used as a negative electrode. As the drying and dehydrating methods, general methods can be used. For example, there is a method using hot air, vacuum, far-infrared rays, electron beam, low-humidity air, etc., alone or in combination.

On the other hand, a general method for producing a negative electrode using a binder will be described below. The binder is dissolved in a solvent in a mortar to disperse the negative electrode active material. For the dispersion treatment, a kneader, a ball mill, a paint shaker, a dynamill or the like is used, and the paste is prepared so that the negative electrode active material and the binder are uniformly dispersed. This paste is applied to a metal foil of a current collector, and this is temporarily dried at 40 to 100 ° C. Then 150
Heat treatment at about ° C and compression molding. Roller presses are usually used for compression molding, and when these presses are applied, the material of the press surface, the rotation method, the temperature, the atmosphere, and the like are not particularly limited. Thereafter, a lead is welded to the electrodeposited portion of the electrode, and vacuum-dried at about 150 ° C. to remove moisture is used as a negative electrode.

For evaluation of electrochemical characteristics, a three-electrode cell was applied, and the negative electrode prepared by the above-described method was used as a test electrode, and metallic lithium was used as a counter electrode and a reference electrode. The cell is configured so that the surface area of the counter electrode is sufficiently larger than that of the test electrode and is regulated by the potential of the test electrode. As the electrolyte, a mixed solvent mainly composed of ethylene carbonate (hereinafter referred to as EC) is used, but is not particularly limited. A solution in which 0.5 to ³ mol / dm ³ of a lithium salt is dissolved in this mixed solvent is used. The charge / discharge operation test is performed by constant current charge / discharge, and the charge termination potential is 0 to 0.01 Vv
s. Li / Li ⁺ , discharge end potential of 2.0 to 3.0 Vv
s. Li / Li ⁺ .

The characteristic evaluation of the non-aqueous secondary battery using the negative electrode of the present invention can be applied to various shapes such as a cylindrical shape, a square shape, a coin shape, a button shape, a sheet shape, a paper shape, and a card shape. For example, in a cylindrical or prismatic battery, a sheet electrode is mainly inserted into a can, and the can and the sheet electrode are electrically connected. An electrolyte is injected and the sealing plate is sealed via an insulating packing, or the sealing plate and the can are insulated and hermetically sealed by hermetic sealing to produce a battery. At this time, a safety valve provided with a safety element can be used as a sealing plate. Examples of the safety element include a fuse, a bimetal, a PTC element, and the like as an overcurrent prevention element. In addition to the safety valve, as a countermeasure against a rise in the internal pressure of the battery can, a method of making a crack in the gasket, a method of making a crack in the sealing plate, a method of making a cut in the battery can, and the like are used. Further, an external circuit incorporating measures for overcharging and overdischarging may be used.

In the case of a coin-type or button-type battery,
The positive and negative electrodes are formed into pellets, which are put into a can,
A method of caulking the lid via an insulating packing is common. As the electrolyte, a mixed solvent mainly composed of EC is used.
There is no particular limitation. 0.5-3.0 mo in this mixed solvent
A solution in which 1 / dm ³ of a lithium salt is dissolved is used. As the separator, a synthetic resin nonwoven fabric was used. The charge / discharge operation test was performed at a constant current, and the charge end voltage was set to 2.7 to 2.9.
V, and the discharge end voltage is 4.1 to 4.3 V. Then
The cycle characteristics of the fabricated battery are examined. In addition, all the electrode and battery evaluations are performed in a glove box under an inert gas atmosphere. In general, argon, nitrogen, and the like are preferably used as the inert gas. EXAMPLES Hereinafter, the effects of the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

EXAMPLES The present invention will be described in more detail with reference to the following examples.
The example is a method of forming a carbon material film of the present invention, and the comparative example is a method of manufacturing a conventional negative electrode using a binder.

Example 1 Iodine 2 was added to 100 mL of special grade acetone (manufactured by Kishida Chemical).
0.0 mg (hereinafter referred to as 0.20 g / L) was dissolved. 1.0 g of artificial graphite (trade name: KS-25; manufactured by Lonza) was added thereto and suspended for 10 minutes using an ultrasonic irradiator. By this operation, the artificial graphite particles were sufficiently dispersed in the acetone bath, and this was used for the electrodeposition bath.
Copper foil (thickness: 20 μm, electrode size: 3.5 cm × 3.0 c) used as a working electrode 31 for a current collector of a nonaqueous electrolyte secondary battery
m), a platinum plate was arranged on one side as the counter electrode 41, and was set as shown in FIG. After stopping the ultrasonic of the electrodeposition bath,
Using a DC power supply 5, 1000 V was applied for 5 minutes to turn off the power. When the copper foil was pulled out from the electrodeposition bath, a carbon material film of artificial graphite particles was formed on the copper foil.

Thereafter, washing was performed using acetone, and this was preliminarily dried at 50 to 70 ° C. A part (3.0 × 0.5 c
m) is removed and the carbon material is deposited (deposition area: 3.0 c).
mx 3.0 cm). Then, at about 150 ° C, 1
Heat treatment was performed for 2 hours and compression molding was performed. A roller press was used for compression molding. Next, a lead of nickel foil (50 μm) was welded to the non-deposited portion. After that, what was vacuum-dried at about 150 ° C. for 12 hours to remove water was used as a negative electrode.

Example 2 Except that 100 mL of special grade acetylacetone (manufactured by Kishida Chemical), 2.5 g / L of iodine was used as an aprotic solvent, and artificial graphite (trade name: KS-15; manufactured by Lonza) was used as a carbon material. Produced a carbon material film in the same manner as in Example 1. A part (3.0 × 0.5 cm) of the carbon material film is removed, and the amount of carbon material deposited (deposition area: 3.0 cm × 3.0 cm).
0 cm).

Example 3 The amount of iodine added was 5.0 g / L, and natural graphite was used as a carbon material.
A carbon material film was produced in the same manner as in Example 1 except that a nickel foil was used as the conductive substrate. In order to form a welded part of the lead, a part (3.0 × 0.
5 cm), and the amount of carbon material deposited (deposition area: 3.
(0 cm × 3.0 cm). Then about 150 ° C
For 12 hours and compression molded. A roller press was used for compression molding. Next, a lead of nickel foil (50 μm) was welded to the non-deposited portion. After that, what was vacuum-dried at about 150 ° C. for 12 hours to remove water was used as a negative electrode.

Example 4 The procedure of Example 1 was repeated except that the amount of iodine added was 4.0 g / L, artificial graphite (trade name: KS-6, manufactured by Lonza) as a carbon material, and stainless steel as a conductive substrate. Thus, a carbon material film was produced. Part of the carbon material film (3.0 ×
0.5 cm) and the amount of carbon material deposited (deposition area:
(3.0 cm × 3.0 cm) was measured.

Example 5 Iodine was added in an amount of 3.0 g / L, and natural graphite was used as a carbon material.
A carbon material film was produced in the same manner as in Example 1 except that brass casting was used as the conductive substrate. A part (3.0 × 0.5 cm) of the carbon material film was removed, and the deposition amount of the carbon material (deposition area: 3.0 cm × 3.0 cm) was measured.

Example 6 The same procedure as in Example 1 was carried out except that the amount of iodine added was 2.0 g / L, artificial graphite (trade name: KS-25; manufactured by Lonza) as a carbon material, and molybdenum as a conductive substrate. A carbon material film was produced. Part of the carbon material film (3.0 ×
0.5 cm) and the amount of carbon material deposited (deposition area:
(3.0 cm × 3.0 cm) was measured.

Example 7 Artificial graphite (trade name: KS-
25; manufactured by Lonza), and a carbon material film was produced in the same manner as in Example 1 except that molybdenum was used as the conductive substrate. A part (3.0 × 0.5 cm) of the carbon material film is removed, and the amount of carbon material deposited (deposition area: 3.0 cm × 3.0)
cm).

Example 8 A graphite material in which the amount of iodine was 0.5 g / L and a low-crystalline carbon material was adhered to the surface of a highly crystalline graphite as a carbon material (hereinafter referred to as surface amorphous graphite) 12 μm, d ₀₀₂ =
A carbon material film was produced in the same manner as in Example 1 except that 0.336 nm and an R value of 0.35) were used. A part (3.0 × 0.5 cm) of the carbon material was removed, and the amount of the carbon material deposited (deposition area: 3.0 cm × 3.0 cm) was measured.

As a method for measuring the average interplanar spacing (d ₀₀₂ ) and the crystallite size (Lc, La) by the X-ray wide-angle diffraction method, a known method, for example, “Carbon Material Experiment Technique 1p. 63 Carbon Materials Society of Japan (Science and Technology) "
And the method described in JP-A-61-111907. The form factor K (=
Lc · β · cos θ / λ; β: half width, θ: angle of d ₀₀₂ , λ: wavelength of X-ray) used 0.9. The particle size was measured using a laser diffraction particle size distribution analyzer (SALD110 manufactured by Shimadzu Corporation).
The measurement was carried out using 0) to obtain a particle size having a peak in the particle size distribution.

Example 9 A carbon material was prepared in the same manner as in Example 1 except that 2.0 g / L of iodine was added, mesocarbon microbeads (hereinafter referred to as MCMB) as a carbon material, and nickel foil as a conductive substrate. A film was prepared. Part of the carbon material film (3.0 x 0.5 cm) to make the welded part of the lead
Is removed, and the amount of carbon material deposited (deposition area: 3.0 cm ×
3.0 cm). Thereafter, heat treatment was performed at about 150 ° C. for 12 hours, and compression molding was performed. Next, a lead of nickel foil (50 μm) was welded to the non-deposited portion. After that, what was vacuum-dried at about 150 ° C. for 12 hours to remove water was used as a negative electrode.

Example 10 Example 1 was the same as Example 1 except that 100 mL of special grade acetylacetone (manufactured by Kishida Chemical) was used as the aprotic solvent, the amount of iodine added was 0.25 g / L, mesophase pitch was used as the carbon material, and stainless steel was used as the conductive substrate. Similarly, a carbon material film was produced. Part of the carbon material film (3.0 × 0.5c)
m) is removed and the carbon material is deposited (deposition area: 3.0 c).
mx 3.0 cm).

Example 11 A carbon material film was produced in the same manner as in Example 1, except that the amount of iodine added was 0.15 g / L, the carbon material was an isotropic pitch, and the conductive substrate was brass. A part (3.0 × 0.5 cm) of the carbon material film was removed, and the deposition amount of the carbon material (deposition area: 3.0 cm × 3.0 cm) was measured.

Example 12 A carbon material film was produced in the same manner as in Example 1 except that the amount of iodine added was 0.10 g / L, coke was used as a carbon raw material, and molybdenum was used as a conductive substrate. A part (3.0 × 0.5 cm) of the carbon material film was removed, and the deposition amount of the carbon material (deposition area: 3.0 cm × 3.0 cm) was measured.

Example 13 A carbon material film was produced in the same manner as in Example 1 except that the amount of iodine added was 9.5 g / L, and artificial graphite (trade name: KS-15; manufactured by Lonza) was used as a carbon raw material. . A part (3.0 × 0.5 cm) of the carbon material film was removed, and the deposition amount of the carbon material (deposition area: 3.0 cm × 3.0 cm) was measured.

Example 14 A carbon material was prepared in the same manner as in Example 1 except that the amount of iodine added was 0 g / L, artificial graphite (trade name: KS-25; manufactured by Lonza) as a carbon raw material, and nickel as a conductive substrate. A film was prepared. Part of the carbon material film (3.0 × 0.5c)
m) is removed and the carbon material is deposited (deposition area: 3.0 c).
mx 3.0 cm).

Example 15 100 g of artificial graphite (trade name: KS-25; manufactured by Lonza) was placed in 100 mL of special grade acetonitrile (manufactured by Kishida Chemical) and suspended for 10 minutes using an ultrasonic irradiator. By this operation, the artificial graphite particles were sufficiently dispersed in the acetonitrile bath, and were used for the electrodeposition bath. Copper foil (thickness 2) used as a working electrode 32 for a current collector of a non-aqueous electrolyte secondary battery
0 μm, electrode size 3.5 cm × 3.0 cm), and a platinum plate was arranged on one side as a counter electrode 44, and set as shown in FIG. After the ultrasonic wave in the electrodeposition bath was stopped, 1000 V was applied for 5 minutes using the DC power supply 5 to turn off the power. When the copper foil was pulled out from the electrodeposition bath, a carbon material film of artificial graphite particles was formed on the copper foil.

Thereafter, washing was performed using acetonitrile, and this was provisionally dried at 50 to 70 ° C. In order to form a welded part of the lead, a part (3.0 × 0.
5 cm), and the amount of carbon material deposited (deposition area: 3.
(0 cm × 3.0 cm). Then about 150 ° C
For 12 hours and compression molded. A roller press was used for compression molding. Next, a lead of nickel foil (50 μm) was welded to the non-deposited portion. After that, what was vacuum-dried at about 150 ° C. for 12 hours to remove water was used as a negative electrode.

Comparative Example 1 The binder PVdF was dissolved in a solvent N-methyl-2-pyrrolidone (hereinafter referred to as NMP) in a mortar, and artificial graphite (trade name: KS-25; manufactured by Lonza) was dispersed as a carbon material. I let it. For dispersion processing, use a twin-screw planetary mixing and kneading machine,
The paste was adjusted so that the carbon material and the binder were uniformly dispersed. The composition of the negative electrode was 100 parts by weight of a carbon material, PVd
F10 parts by weight, and the weight of the active material was 8.5 mg / cm ^2.
(Active material weight per unit area of current collector).
This paste was applied to a copper foil of about 20 μm,
Preliminarily dried at ７０70 ° C. Thereafter, heat treatment was performed at about 150 ° C. for 12 hours, and compression molding was performed. A roller press was used for compression molding. The electrode size was 3.5 × 3.0 cm (coated portion 3.0 × 3.0 cm), and a nickel foil (50 μm) lead was welded to the uncoated portion. After that, what was vacuum-dried at about 150 ° C. for 12 hours to remove water was used as a negative electrode.

Comparative Example 2 A negative electrode was produced in the same manner as in Comparative Example 1, except that the composition of the negative electrode was 100 parts by weight of the carbon material and 5 parts by weight of PVdF.

Comparative Example 3 A negative electrode was produced in the same manner as in Comparative Example 1, except that the composition of the negative electrode was 100 parts by weight of the carbon material and 3 parts by weight of PVdF.

Comparative Example 4 Natural graphite was used as the carbon material, and the composition of the negative electrode was 100 carbon material.
A negative electrode was produced in the same manner as in Comparative Example 1 except that the weight parts were changed to 3 parts by weight of PVdF.

Comparative Example 5 MCMB was used as the carbon material, and the composition of the negative electrode was 100 carbon material.
A negative electrode was produced in the same manner as in Comparative Example 1 except that the weight parts were changed to 3 parts by weight of PVdF. First, Table 1 shows the weight of the carbon material films obtained in Examples 1 to 15.

[0084]

[Table 1]

In Examples 1 to 12 and 15, the deposition amount was 70%.
It was found that ８０80 mg of the carbon material film was obtained. The thickness of the deposited carbon material film was uniform on the order of several microns. On the other hand, in Example 13, although a carbon material film made of artificial graphite was obtained, the film thickness was uneven. The reason for this is that the amount of iodine added is too large, the conductivity of acetone increases, which affects the increase in electrolysis current during electrophoretic electrodeposition, and the generation of bubbles due to electrode reactions, resulting in the formation of carbon material films. It is considered that the thickness became non-uniform. In Example 14, since iodine was not added, the amount of protons to be adsorbed on the carbon material was extremely small, and it was considered that this had an effect on the reduction in the amount of deposition. From the above, it was found that the carbon deposition amount and the film thickness uniformity depended on the iodine addition amount.

Next, the electrode characteristics of the negative electrodes made of the carbon material films obtained in Examples and Comparative Examples were examined. To evaluate the electrochemical characteristics of the negative electrode, a three-electrode cell was used, and the negative electrode was used as a test electrode, and lithium metal was used as a counter electrode and a reference electrode. The cell was configured so that the surface area of the counter electrode was sufficiently larger than that of the test electrode, and was regulated by the potential of the test electrode. As the electrolytic solution, a solution prepared by dissolving 1.0 mol / dm ³ of lithium perchlorate LiClO ₄ in a mixed solvent of EC and diethyl carbonate (hereinafter referred to as DEC) at a volume ratio of 1: 1 was used. Charge / discharge operation test is 30 mA · g
^-1 constant current charge / discharge, charge termination potential 0 V vs. Li / Li
⁺ , Discharge end potential 2.5 V vs. This was performed at 20 ° C. in a glove box under an atmosphere of Li / Li ⁺ and argon.

Table 2 shows the initial discharge results of the negative electrodes obtained in the examples and comparative examples. The discharge capacity in Table 2 is
It was calculated by the formula of {discharge current value (mA) × discharge time (h) / weight of carbon material (g)} = discharge capacity (mAh / g). The actual discharge capacity is: discharge current value (mA) × discharge time (h) / (weight of carbon material + weight of binder)
(G)｝ = discharge capacity (mAh / g).

[0088]

[Table 2]

As shown in Table 2, it was found that the carbon material film of the present invention can be used as a negative electrode. Also, a discharge capacity almost equivalent to that of a conventional negative electrode using a binder is obtained,
Since the negative electrode of the present invention does not use a binder, it has been found that the discharge capacity is substantially increased by reflecting the weight reduction.

Next, the cycle characteristics of the negative electrodes obtained in Examples and Comparative Examples were examined. The discharge capacity retention rate in this example was calculated by the formula of (discharge capacity in each cycle / discharge capacity in the first cycle) × 100 = discharge capacity retention rate (%). FIG. 7 shows the discharge capacity retention ratios of the negative electrodes obtained in Examples and Comparative Examples. Examples 1, 3, 9, 15 of the present invention
The cycle characteristics of the negative electrode were as good as Comparative Example 1 corresponding to the conventional negative electrode. From the results of these cycle tests, it was clarified that the carbon material film was formed to have such strength that it could be used as a negative electrode.

Comparative Example 2 using 5 parts by weight of a binder
The discharge capacity retention rate of the negative electrode rapidly decreased at around 60 cycles, and in the negative electrodes of Comparative Examples 3 to 5 using 3 parts by weight of the binder, respectively, at around 20 cycles. After the end of the cycle test, when observing each negative electrode, the electrode mixture was almost peeled off from the current collector and barely adhered. From the above, there is a limit in reducing the weight corresponding to the binder in the conventional negative electrode, and therefore, considering the weight reduction and the compactness of the battery, the carbon material film by the electrophoretic electrodeposition of the present invention is used as the negative electrode. Was found to be effective.

Next, batteries were prepared using the negative electrodes obtained in Examples and Comparative Examples and evaluated. Lithium cobaltate LiCoO ₂ was used as the positive electrode active material. Binder PV
dF was dissolved in a solvent NMP in a mortar to disperse the positive electrode active material and the conductive agent acetylene black. For the dispersion treatment, a biaxial planetary mixing and kneading machine was used, and the paste was adjusted so that the positive electrode active material, the conductive agent, and the binder were uniformly dispersed. The composition of the positive electrode was 100 parts by weight of LiCoO ₂ , 5 parts by weight of acetylene black, and 10 parts by weight of PVdF, and the weight of the active material was about 15.0 mg / cm ² (weight of the active material per unit area of the current collector).

This paste was applied on an aluminum foil having a thickness of 50 μm, and was temporarily dried at 50 to 70 ° C.
After heat treatment at ℃, compression molding was performed. For the compression molding, using a roller press machine in the air, the active material density is 2.8 to 3.0 g.
/ Cm ³ . Furthermore, what was dried under reduced pressure at about 150 ° C. for removing water was used as a positive electrode.

In the battery, the negative electrode and the positive electrode produced as described above were each separated by a separator (polyethylene porous body, 25 μm thick).
m), covered with a laminate film containing aluminum foil, and sealed on three sides with heat.
1 mol / d in a mixed solvent of C and DEC at a volume ratio of 1: 1
A solution prepared by dissolving m ³ LiClO ₄ was injected, and the other was sealed with heat to produce the product. In the charging / discharging operation test, the charging current was set to a constant current of 1.0 mA.
Time. The discharge end voltage was set to 2.75 V, and the discharge current was set to 0.2 mA. All battery evaluations were performed at 20 ° C. in a glove box under an argon atmosphere. Table 3 shows the results of battery characteristics using the carbon material films obtained in Examples and Comparative Examples as negative electrodes.

[0095]

[Table 3]

As shown in Table 3, it was found that when the carbon material film of the present invention was used for the negative electrode, the effect of increasing the capacity was observed as compared with the conventional negative electrode. The reason for this is that the negative electrodes of Examples 1, 3, 9, and 15 of the present invention did not contain a binder, so that a negative electrode having a high filling amount of the carbon material, that is, a high active material density could be produced. It is thought that this was reflected. In addition, the active material densities of the negative electrodes of Comparative Examples 1 to 5 were increased to values shown in Table 3 or more, and the active material densities of the negative electrodes of Examples 1 to 3 were 1.
The production was attempted to be 60 g / cm ³ . However, during the pressing, the yield was sharply reduced, for example, the electrode mixture was peeled off from the copper foil as the current collector, or adhered to the pressing side, and the production was difficult.

Next, the results of the cycle characteristics of the negative electrodes obtained in Examples and Comparative Examples shown in Table 3 are shown in FIG. The cycle characteristics of the negative electrodes of Examples 1, 3, and 9 of the present invention were as good as Comparative Example 1 corresponding to the conventional negative electrode. From the results of these cycle tests, it was clarified that the carbon material film was formed to have such strength that it could be used as a negative electrode. But,
The negative electrode of Comparative Example 2 using 5 parts by weight of the binder gradually discharged from the vicinity of 60 cycles, and the negative electrodes of Comparative Examples 3 to 5 using 3 parts by weight of the binder gradually discharged from around 20 to 40 cycles. Decreased. After the completion of the cycle test, the battery was disassembled and each negative electrode was observed. As a result, it was confirmed that the electrode mixture had poor binding properties with the current collector. From the above, there is a limit in reducing the weight equivalent to the binder in the conventional negative electrode,
It has been found that it is effective to use the carbon material film formed by electrophoretic electrodeposition of the present invention for the negative electrode as one means for solving the weight reduction and compactness of the battery.

[0098]

As is apparent from the above, the use of electrophoretic electrodeposition does not limit the crystallinity of the carbon material, and the carbon material film is directly deposited on the surface of the conductive substrate by a simple manufacturing process and control. It became clear that we could do that. further,
This carbon material film can reduce the weight corresponding to the binder not participating in the electrode reaction and increase the active material density of the electrode, that is, increase the filling amount per unit volume of the carbon material as the active material. This is effective in increasing the energy density of a non-aqueous electrolyte secondary battery, particularly a lithium ion battery. Therefore, the industrial significance of the present invention is very large.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 2 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 3 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 4 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 5 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 6 is a schematic explanatory view of a method for producing a carbon material film of the present invention.

FIG. 7 is a graph showing the discharge capacity retention ratio of the negative electrodes obtained in Examples and Comparative Examples.

FIG. 8 is a graph showing cycle characteristics of batteries obtained in Examples and Comparative Examples.

[Explanation of symbols]

 Reference Signs List 1 aprotic solvent 2 carbon material 5 DC power supply 31 working electrode (cathode) 32 working electrode (anode) 41 counter electrode (anode) 42 spiral electrode (anode) 43 plate electrode (anode) 44 counter electrode (cathode) 45 Spiral electrode (cathode) 46 Plate electrode (cathode)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01M 4/66 H01M 4/66 A 10/40 10/40 Z (72) Inventor Kazuo Yamada Osaka-shi, Osaka 22-22 Nagaike-cho, Abeno-ku, Sharp Corporation (72) Inventor Takehito Mitate 22-22-22, Nagaike-cho, Abeno-ku, Osaka, Osaka Prefecture (72) Inventor Nobuyuki Koura 2-Satsukidaira, Misato-shi, Saitama 2-1-110 (72) Inventor Yasushi Idemoto 479 Yamazaki, Noda-shi, Chiba (Mizuki 43-10) (72) Inventor Futa Matsumoto 1-5 Toyocho, Kuroiso-shi, Tochigi Pref. F-term (reference) 5J301 BA01 BA02 BE10 5H017 AA03 AS10 BB00 BB16 EE01 EE04 5H029 AJ03 AK03 AL06 AM03 AM04 AM05 AM07 CJ11 CJ28 DJ07 HJ01 5H050 AA08 BA17 CA08 CB07 EA07 4 FA04 GA11 GA27 HA01

Claims (8)

[Claims] 1. A method for producing a carbon material film in which a carbon material is deposited on the surface of a conductive substrate by electrophoretic electrodeposition, comprising: dissolving at least iodine in an aprotic solvent; By immersing a conductive substrate as a negative electrode and a counter electrode as a positive electrode and applying a DC electric field between the two, a carbon material film is deposited on the surface of the conductive substrate. Production method. 2. An amount of 1 m of iodine per liter of aprotic solvent
The method for producing a carbon material film according to claim 1, wherein g to 5 g is added. 3. The method for producing a carbon material film according to claim 1, wherein the aprotic solvent is acetone or acetylacetone. 4. A method for producing a carbon material film in which a carbon material is deposited on the surface of a conductive substrate by electrophoretic electrodeposition, wherein a conductive material as a positive electrode is added to a liquid in which a carbon material is dispersed in an aprotic solvent. , Soak the counter electrode as a negative electrode,
A method for producing a carbon material film, wherein a carbon material film is deposited on the surface of the conductive substrate by applying a DC electric field between the two. 5. The method according to claim 4, wherein the aprotic solvent is acetonitrile. 6. The conductive substrate according to claim 1, wherein the conductive substrate is made of a material selected from the group consisting of copper, nickel, stainless steel, brass, molybdenum and tungsten. 3. The method for producing a carbon material film according to item 1. 7. The carbon material is composed of artificial graphite, natural graphite, graphite material having a low crystalline carbon material adhered to the surface of highly crystalline graphite, mesocarbon microbeads, mesophase pitch, isotropic pitch and coke. The method for producing a carbon material film according to any one of claims 1 to 6, wherein at least one kind is selected from a group. 8. A non-aqueous electrolyte secondary battery comprising at least a positive electrode, a non-aqueous electrolyte, and a negative electrode, wherein the negative electrode is
7. A non-aqueous electrolyte secondary battery comprising a carbon material film produced by any one of the methods of item 7.