JP2002117838A - Fabrication method of carbonaceous thin film electrode, carbonaceous negative electrode for nonaqueous electrolytic solution secondary battery and nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fabrication method of a carbonaceous thin film electrode, a negative electrode material for a nonaqueous electrolytic solution secondary battery and a nonaqueous electrolytic solution secondary battery wherein charge- discharge cycle characteristics are superior and a large capacity can be realized by a low temperature heat treatment process of a low cost without relying on a binder molding method to bring about a reduction of actuation reliability. SOLUTION: The carbon film electrode fabricated by coating/heat-treating a coating solution on a current collector wherein a nonvolatile carbon containing compound is dissolved or dispersed in an organic solvent is used as the negative electrode of the nonaqueous electrolytic solution secondary battery, thereby the secondary battery is superior in the charge-discharge cycle characteristics and the high capacity can be realized because the electrode does not contain a binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved negative electrode and a method for producing the negative electrode.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries with a high energy density using a carbon material negative electrode that occludes and releases lithium ions by a reversible electrochemical reaction have been put into practical use.
It is widely used as a power source for various portable electronic devices. As these carbon materials, in addition to natural graphite, petroleum pitch, coal tar pitch, needle coke, condensed polycyclic aromatic hydrocarbon compounds, mesophase carbon microbeads, mesophase carbon fibers, and other easily graphitizable carbon materials are used at 2500 ° C or higher. , Preferably 3000 ° C
The artificial graphite-based carbon heat-treated at the above-mentioned high temperature is excellent in charge-discharge cycle characteristics, effective utilization rate of occluded lithium ions, flatness of discharge voltage, and the like, and is preferably used. Among them, the mesophase carbon material is known as an optimal carbon anode material because it exhibits excellent charge / discharge characteristics under a large current. However, these carbon materials having a developed graphite structure can only provide a discharge capacity of 300 to 370 mAh / g corresponding to the first-stage graphite intercalation compound C ₆ Li. Further, since a heat treatment near 3000 ° C. is required, it is an industrially disadvantageous material in terms of processing equipment cost, energy cost, and productivity.

On the other hand, among the above graphitizable carbon materials or non-graphitizable carbon materials which have been heat-treated at a relatively low temperature of 1000 to 2000 ° C., there are 37 amorphous carbon materials.
Materials exhibiting a large capacity of 0 mAh / g or more and up to about 700 mAh / g have been found. However, although the capacity is large, the electrochemical reversibility is poor and the utilization rate of the stored lithium ions is low. Low is an issue.

[0004] The above-mentioned carbon anode material is usually in the form of powder or fiber, and must be molded together with an appropriate binder in order to be used as a battery electrode. In the case of a small coin-type battery, it is usually formed into a pellet shape, and in the case of a cylindrical battery for a large current, a metal current collector foil is formed as a coating film together with a binder. At this time, since the binder is usually an electrically insulating organic polymer such as a polyolefin, a fluorine-containing polymer, or a polyimide, the electric resistance in the electrode body after the molding increases, which hinders the output of the battery in a large current discharge. Had contributed. Also, in terms of long-term reliability, peeling, chipping, desorption, etc. of some carbon materials due to swelling or dissolving phenomena of the binder material in the electrolytic solution and deterioration due to electrochemical reaction have progressed over a long period of use. However, there is a problem that the performance of the battery is deteriorated. Therefore, a high-performance negative electrode and a method for producing the same, which sufficiently extract characteristics of the carbon material from a carbon material useful as a battery active material, have been eagerly desired.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a non-volatile semiconductor device that can exhibit excellent charge-discharge cycle characteristics and achieve a large capacity by a low-cost low-temperature heat treatment process without relying on a binder molding method that causes a reduction in operation reliability. It is intended to provide a method for producing a carbon thin film negative electrode for an aqueous electrolyte secondary battery, a carbonaceous negative electrode material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have repeated studies focusing on a method for producing a negative electrode which requires the use of a binder. As a result, (1) a non-aqueous electrolyte secondary solution characterized by being prepared by applying and heating a coating solution obtained by dissolving or dispersing a nonvolatile carbon-containing compound in an organic solvent on a current collector. (2) Non-aqueous electrolyte secondary according to (1), wherein a method for producing a carbon thin film negative electrode for a battery, (2) a coating liquid containing a nonvolatile carbon-containing compound but not containing a binder is used. (3) The carbon for a non-aqueous electrolyte secondary battery according to (1) or (2), wherein (3) the nonvolatile carbon-containing compound is a graphitizable carbon. Method for producing a porous thin film negative electrode,
(4) The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to (3), wherein the graphitizable carbon is mesophase pitch carbon, and (5) the organic solvent is pyridine or quinoline. , Pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide,
(1) The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to any one of (1) to (4), wherein the negative electrode contains cyclohexanone; (6) The heat treatment temperature is in the range of 500 to 2000 ° C. The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to any one of (1) to (5),
(7) The method for producing a carbon thin film negative electrode for a nonaqueous electrolyte secondary battery according to any one of (1) to (6), wherein the heat treatment atmosphere is an inert atmosphere; A negative electrode for a non-aqueous electrolyte secondary battery, comprising a carbonaceous film capable of electrochemically storing and releasing lithium ions without a binder, and (9) a binder A coating liquid in which a non-volatile carbon-containing compound is dissolved or dispersed in an organic solvent by applying a carbonaceous film capable of electrochemically occluding and releasing lithium ions to a current collector without coating and heating. (8) The negative electrode for a non-aqueous electrolyte secondary battery according to (8), wherein the nonvolatile carbon-containing compound is a graphitizable carbon body (9). The negative electrode for a non-aqueous electrolyte secondary battery according to item 1, wherein (11) the graphitizable carbon is mesophase pitch carbon The negative electrode for a nonaqueous secondary battery according to (10) that there, (12) the organic solvent is pyridine, quinoline, pyrrolidone, dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide,
(13) The negative electrode for a non-aqueous electrolyte secondary battery according to any one of (9) to (11), which comprises cyclohexanone.
(9) The negative electrode for a non-aqueous electrolyte secondary battery according to (9) to (12), wherein the heat treatment temperature is in a range of 500 to 2000 ° C., (14) The heat treatment atmosphere is an inert atmosphere. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of (9) to (13), wherein (15) an organic solvent containing a nonvolatile carbon-containing compound but not containing a binder is made of an electronically conductive foil. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of (9) to (14), which is obtained by applying the composition on a current collecting zone and then sintering, comprising (16) a nonvolatile carbon-containing compound. The nonaqueous electrolysis according to any one of (9) to (15), wherein the nonaqueous electrolysis is obtained by impregnating and coating an organic solvent containing no binder into a current collector made of an electron conductive porous body, followed by firing. A negative electrode for a liquid secondary battery, (17) wherein the current collector is stainless steel A negative electrode for a non-aqueous electrolyte secondary battery according to 16), (18) a positive electrode, and a carbonaceous film capable of electrochemically absorbing and releasing lithium ions without a binder on a current collector. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte and a non-aqueous electrolyte; (19) a non-aqueous electrolyte provided with a binder-free carbonaceous film; The non-aqueous electrolyte solution according to (18), which is obtained by applying and heating a coating solution obtained by dissolving or dispersing the contained compound in an organic solvent on a current collector. Secondary battery, (20) the organic solvent is pyridine, quinoline, pyrrolidone, dimethylformamide, dimethylacetamide,
(18) The nonaqueous electrolyte secondary battery according to any one of (18) to (19), which contains dimethyl sulfoxide and cyclohexanone, (21) a heat treatment temperature of 500 to 2000 ° C.
The nonaqueous electrolyte secondary battery according to any one of (18) to (20), wherein the heat treatment atmosphere is an inert atmosphere (18) to (2).
The nonaqueous electrolyte secondary battery according to 1), (23) a negative electrode obtained by applying an organic solvent solution containing a nonvolatile carbon-containing compound on an electron-conductive foil-like current collector and then firing the resultant. (18) The non-aqueous electrolyte secondary battery according to any one of (18) to (22), wherein (24) an organic solvent containing a nonvolatile carbon-containing compound is contained in a current collector made of an electron conductive porous material. The nonaqueous electrolyte secondary battery according to any one of (18) to (23), wherein the negative electrode obtained by impregnation coating and firing is used, and (25) the current collector is stainless steel. Non-aqueous electrolyte secondary batteries according to (18) to (24),
As described above, the inventors have found that the above-mentioned problems can be solved, and have completed the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The non-volatile carbon-containing compound of the present invention includes coal-based heavy oil such as coal tar pitch from soft pitch to hard pitch, dry distillation liquefied oil, etc .; Heavy oil such as ethylene tar and other heavy oils which are by-produced during thermal cracking of crude oil, naphtha and the like. Further, aromatic hydrocarbons such as acenaphthylene, decacyclene, and anthracene; N-ring compounds such as phenazine and acridine; S-ring compounds such as thiophene; alicyclic rings such as adamantane, biphenyl and terphenyl; Polymers such as polyphenylene, polyvinyl chloride and polyvinyl alcohol. Further, natural polymers such as cellulose and saccharides, thermoplastic resins such as polyphenylene sulfide, and polyphenylene oxide, and thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin can also be used. In particular, an easily graphitizable carbon body is suitably used as such a non-volatile carbon-containing compound. Mesophase pitch carbon is most preferably used as a non-volatile carbon-containing compound.

The above materials may be formed on a current collector by a vacuum thin film manufacturing method such as a vacuum vapor adsorption method, a sputtering method, a chemical vapor deposition (CVD) method, or may be dissolved or dispersed in an organic solvent. Alternatively, a target carbon thin film electrode may be prepared by preparing a coating liquid, applying the coating liquid on a current collector, and performing a heat treatment. However, it is needless to mention that the latter method is suitable for mass production in industrial terms.

Although all known organic solvents can be used,
In particular, when an organic solvent containing at least pyridine, quinoline, pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and cyclohexanone is used, a coating liquid in which the nonvolatile carbon-containing compound is suitably dissolved or dispersed can be prepared. Organic solvents that may be used in combination with these organic solvents include alcohols represented by methanol, ethanol, ketones represented by acetone, 2-butanone, esters represented by ethyl acetate, butyl acetate, and diethyl. Ethers such as ether, tetrahydrofuran and dioxane, amines such as triethylamine and ethylenediamine, and the like are used.

The desired coating liquid can be obtained by mixing, stirring or dispersing the above-mentioned nonvolatile carbon-containing compound with the above-mentioned organic solvent. When mixing both, heating and stirring may be performed, or mixing and dispersion may be performed using a dispersing device represented by a ball mill, an attritor, and a planetary mill.

The coating liquid is preferably a solution containing no dispersed particles, and is most suitable for obtaining a suitable film. However, even if the coating liquid contains dispersed particles, if there is a dissolved component, the dissolution component is formed between the particles when the film is formed. A uniform film can be obtained by supplementing the carbonaceous material based on.
As a method for removing the dispersed particles from the dispersion, known means such as filtration and centrifugation can be used. Also,
Means for extracting a component soluble in a solvent from a material such as Soxhlet extraction is also useful and effective.

The coating solution thus prepared is applied to the current collector by a known coating method such as blade coating, wire bar coating, spin coating, spray coating, dip coating, or bead coating. Can be applied. An electrostatic spray deposition (ESD) method in which an electric field is applied between a heated current collector and a nozzle containing a coating liquid to simultaneously perform film formation and heat treatment is preferably used.

The liquid applied on the current collector is subjected to a heat treatment to form a carbonaceous film capable of electrochemically absorbing and releasing lithium ions. The heat treatment temperature at this time is 5
Good results are obtained when the temperature is in the range of 00 to 2000 ° C,
When the temperature is in the range of 700 to 1200 ° C., even better results can be obtained. The heat treatment may be performed in an air atmosphere, but better results can be obtained by performing the heat treatment in an inert gas atmosphere represented by nitrogen, argon, helium, or the like.

As the current collector, any known materials having electron conductivity can be used, but non-corrosive materials are particularly preferable. Examples of such a material include conductive carbon, gold, platinum, and stainless steel, and stainless steel is preferably used. The shape of the current collector is practically a foil or a porous body.

The thus prepared negative electrode, the electrolytic solution and the positive electrode plate described below are combined with other battery components such as a separator, a gasket, a current collector, a sealing plate, a cell case, and the like to form a lithium ion secondary battery. Construct a secondary battery.
The battery that can be manufactured is not particularly limited, such as a cylindrical type, a square type, a coin type, but basically, a current collector and a negative electrode material are placed on a cell floor plate, and an electrolyte and a separator are further placed thereon. A positive electrode is placed so as to face the negative electrode, and caulked together with a gasket and a sealing plate to form a secondary battery.

Non-aqueous solvents that can be used for the electrolyte include:
Propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, 1,
A single organic solvent such as 3-dioxolane or a mixture of two or more organic solvents can be used.

In these solvents, L of about 0.5 to 2.0 M is added.
iClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃
An electrolyte such as LiAsF ₆ is dissolved to form an electrolyte.
Alternatively, a solid polymer electrolyte which is a conductor of an alkali metal cation such as lithium ion can be used. The material of the positive electrode body is not particularly limited, but is preferably made of a metal chalcogen compound that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Such metal chalcogen compounds include vanadium oxide, vanadium sulfide, molybdenum oxide, molybdenum sulfide, manganese oxide, chromium oxide, titanium oxide, titanium sulfide and the like. Composite oxides and composite sulfides. Preferably, Cr
₃ O ₈ , V ₂ O ₅ , V ₅ O ₁₃ , VO ₂ , Cr ₂ O ₅ , MnO ₂ , T
iO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , MoS ₂ , Mo
S ₃ , VS ₂ , Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _{2 and the} like. LiMY ₂ (M is a transition metal such as Co or Ni; Y is a chalcogen compound such as O or S); LiM ₂ Y ₄
(M is Mn, Y is O), oxides such as WO ₃ , CuS, F
e Sulfides such as _0.25 V _0.75 S ₂ , Na _0.1 CrS ₂ , NiP
Phosphorus, sulfur compounds such as S ₃ and FePS ₃ , VSe ₂ , Nb
A selenium compound such as Se ₃ can also be used. These are mixed with a binder described below and applied on a current collector to form a positive electrode.

Examples of the binder that can be used for the above purpose include:
Solvent-stable, polyethylene, polypropylene,
Polyethylene terephthalate, aromatic polyamide, resin-based polymers such as cellulose, styrene-butadiene rubber,
Rubbery polymers such as isoprene rubber, butadiene rubber, and ethylene / propylene rubber, styrene / butadiene / styrene block copolymers, their hydrogenated products, styrene / isoprene / styrene block copolymers, and their thermoplasticity such as their hydrogenated products Elastomeric polymers, soft resinous polymers such as syndiotactic 12-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (2 to 12 carbon atoms) copolymer, polyvinylidene fluoride,
Fluoropolymers such as polytetrafluoroethylene and polytetrafluoroethylene / ethylene copolymers; and polymer compositions having ion conductivity of alkali metal ions, particularly lithium ions, may be mentioned.

Examples of the above polymers having ion conductivity include polyether polymer compounds such as polyethylene oxide and polypropylene oxide, crosslinked polymers of polyether compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinylpyrrolidone, and the like. Polyvinylidene carbonate, a system in which a lithium salt, or a lithium-based alkali metal salt is composited with a polymer compound such as polyacrylonitrile, or a high dielectric constant such as propylene carbonate, ethylene carbonate, and γ-butyrolactone A system containing an organic compound can be used. The ionic conductivity of such an ion-conductive polymer composition at room temperature is preferably 10 ^-5 S / cm or more, and more preferably 10 ^-3 S / cm or more.

The separator holding the electrolyte is generally a material having excellent liquid retention properties. For example, the separator is impregnated with the above electrolyte using a nonwoven fabric or a porous film of a polyolefin resin. Is expressed.

[0021]

Next, the present invention will be described in detail with reference to examples. However, the examples are for describing the present invention in detail, and it is refused that the present invention is not limited by these examples. Not even. All parts mentioned here are parts by weight.

Example 1 Mesophase pitch carbon (manufactured by Petka Corporation) was pulverized well in a mortar, and
The mixture was filled in a cylindrical filter paper for Soxhlet and extracted by a Soxhlet continuous extraction device for a total of 36 hours using 30 parts of quinoline as an extraction solvent. The extract was taken out, put into a syringe, and sprayed on a stainless steel foil heated to 1000 ° C. by an ESD (electrostatic spray deposition) method. At this time, a DC applied voltage between the syringe and the stainless steel was 12 kV, and the film was formed in a nitrogen gas. The thickness of the carbon thin film thus obtained was 30 μm.

The thus obtained electrode (negative electrode) was sandwiched with a separator made of polypropylene impregnated with an electrolytic solution, and a cell facing the lithium metal electrode was prepared, and subjected to a charge / discharge test. As the electrolytic solution, a solution in which lithium perchlorate was dissolved at a ratio of 1 mol / L in a solvent in which ethylene carbonate and propylene carbonate were mixed at a weight ratio of 1: 1 was used.

The charge / discharge test was performed by a constant current charge / discharge method. Current density of 0.1 mA / cm ² and potential difference between electrodes is 0 V
, And then undoped until the potential difference between the electrodes reached 1.5 V. The charge and discharge were repeated 5 cycles, and the doping capacity and the undoping capacity were measured. Table 1 shows the measurement results.

(Comparative Example 1) One part of mesophase pitch carbon (manufactured by Petka Corporation) ground in a mortar was mixed with 10 parts of a solvent obtained by mixing dimethylformamide and 2-butanone at a weight ratio of 1: 1. 3 using a mill
Time-dispersed. Thus, a dispersion of mesophase pitch carbon was obtained. The size of the fine particles contained in the coating liquid was found to be an average particle size of 0.25 μm by particle size distribution measurement. Polyvinylidene fluoride (P
VdF) 1 part of this dispersion was added to and dissolved, and the resulting mixture was stirred to obtain a slurry-like coating liquid. This slurry was spin-coated on a nickel foil and pre-dried at 80 ° C. After further pressurizing and pressing, vacuum drying was performed at 110 ° C. to form an electrode (negative electrode). The thickness of the carbon thin film thus obtained was 31 μm. After producing a cell in the same manner as in Example 1 using this negative electrode, a test was performed in exactly the same manner as in Example 1. Table 1 shows the results.

Example 2 A planetary mill was used together with 1 part of mesophase pitch carbon (made by Petka Corporation) ground in a mortar and 10 parts of a solvent obtained by mixing quinoline and cyclohexanone at a weight ratio of 1: 1. For 3 hours. Thus, a dispersion liquid in which the mesophase pitch carbon was partially dissolved was obtained, and this was used as a coating liquid. Particle size distribution measurement revealed that the size of the fine particles contained in the coating liquid was 0.2 μm or less. This dispersion coating solution was spin-coated on a nickel foil and preliminarily dried at 100 ° C. 1000 ° C in a nitrogen gas atmosphere
To form an electrode (negative electrode). The thickness of the carbon thin film thus obtained was 28 μm. After producing a cell in the same manner as in Example 1 using this negative electrode, a test was performed in the same manner as in Example 1. Table 1 shows the results.

(Comparative Example 2) In Comparative Example 1, the pre-dried electrode was heated and fired at 1000 ° C.
Two negative electrodes were obtained. After producing a cell in the same manner as in Example 1 using this negative electrode, a test was performed in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 A test was performed in the same manner as in Example 1 except that high-temperature calcined carbon (Mitsubishi Gas: 2800 ° C.) was used instead of mesophase pitch carbon. Table 1 shows the results.

[0029]

[Table 1]

[0030]

The method for producing a carbon thin film electrode (negative electrode) of the present invention is to provide a carbon thin film electrode having excellent charge / discharge cycle characteristics and capable of exhibiting a large capacity by a low-cost low-temperature heat treatment process. Such a non-aqueous electrolyte secondary battery negative electrode material has only a carbon thin film on the current collector and does not contain a binder that causes a decrease in operation reliability. It has an excellent effect of being excellent in charge / discharge cycle characteristics and realizing a large capacity.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5H029 AJ03 AJ05 AK02 AK03 AK05 AL06 AL07 AL08 AM02 AM03 AM04 AM05 AM07 AM16 CJ02 CJ22 DJ08 5H050 AA07 AA08 BA17 CA01 CA02 CA07 CA08 CA09 CA11 CB07 CB08 CB09 DA03 GA04 GA11 FA

Claims (8)

[Claims] 1. A non-aqueous electrolyte secondary battery prepared by applying and heating a coating solution obtained by dissolving or dispersing a nonvolatile carbon-containing compound in an organic solvent on a current collector. Of carbonaceous thin film negative electrode for use. 2. A coating liquid containing a nonvolatile carbon-containing compound but not containing a binder is used.
3. The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to item 1. 3. The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-volatile carbon-containing compound is a graphitizable carbon. 4. The method for producing a carbon thin film negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the graphitizable carbon is mesophase pitch carbon. 5. A negative electrode for a non-aqueous electrolyte secondary battery, comprising a current collector and a carbonaceous film capable of electrochemically occluding and releasing lithium ions without a binder. . 6. A coating liquid in which a non-volatile carbon-containing compound is dissolved or dispersed in an organic solvent in a carbonaceous film containing no binder capable of electrochemically storing and releasing lithium ions,
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 5, wherein the negative electrode is obtained by coating and heating on a current collector. 7. A positive electrode, a negative electrode comprising a current collector and a carbonaceous film capable of electrochemically occluding and releasing lithium ions without a binder, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery comprising: 8. A negative electrode provided with a carbonaceous film containing no binder is coated with a coating liquid obtained by dissolving or dispersing a nonvolatile carbon-containing compound in an organic solvent on a current collector and heat-treated. The non-aqueous electrolyte secondary battery according to claim 7, wherein the non-aqueous electrolyte secondary battery is obtained.