JP5233314B2 - Carbon material for secondary battery, electrode for secondary battery, and secondary battery - Google Patents

Description

  The present invention relates to a carbon material for a secondary battery, an electrode using the same, and a secondary battery.

  In recent years, with the remarkable development of electronic technology, there has been a demand for downsizing and weight reduction of electronic devices. Along with this, further miniaturization, weight reduction, and higher energy density have been demanded for mobile power sources or fixed power sources.

  Against this background, lithium ion secondary batteries have been proposed.

  Unlike a lead storage battery or a nickel-cadmium battery, a lithium ion secondary battery generates an electric current by moving lithium ions between the positive electrode and the negative electrode. Specifically, during the charging process, lithium ions are released from the positive electrode and occlude lithium ions on the negative electrode side. Conversely, in the discharge process, lithium ions are released from the negative electrode and occlude lithium ions on the positive electrode side. Therefore, to increase the capacity of the lithium ion secondary battery, it is essential to increase the amount of lithium ion occlusion on the negative electrode side.

At present, the material used for the negative electrode of the lithium ion secondary battery is a graphite-based material which is the mainstream of the negative electrode material for portable devices. The characteristics of this material include a high charge / discharge efficiency of 90% or higher and a high electrode density due to a high true density. However, since the theoretical charge / discharge capacity (372 mAh / g) exists, it is difficult to improve the capacity of the lithium ion secondary battery using the graphite-based material.

  As described above, in order to solve the problem that the theoretical charge / discharge capacity is 372 mAh / g, materials other than graphite-based materials have been studied. Specifically, an amorphous carbonaceous material, an alloy carbon composite material, a carbonaceous material carrying a metal element, a metal nitride, an alloy-based metal material, and the like are being studied. These materials are known for their very high discharge capacity. However, the initial charge / discharge efficiency is low and the deterioration of the cycle characteristics is difficult, and further improvement of characteristics is desired.

  Among the above-mentioned materials, the amorphous carbonaceous material has good cycle characteristics and has many very small pores, so it is easy to occlude Li ions and is used as a negative electrode of a lithium ion secondary battery. Is a material that is expected to have a large charge capacity, and has been studied in the past. For example, analysis of He adsorption amount, carbon material surface measured by butanol immersion method, internal pores and density, etc., with He having a molecular diameter similar to Li ion and butanol having a large molecular diameter as a probe molecule Thus, efforts are being made to analyze the correlation between the negative electrode capacity and the physical properties and improve the charge / discharge characteristics (see, for example, Patent Documents 1 and 2). However, it is not possible to improve both the negative electrode capacity and the charge / discharge efficiency only by the size, shape, volume, distribution, and density of the pores of the carbon material.

JP 2001-176512 A JP 08-115723 A

  The present invention relates to a carbon material for a secondary battery electrode that is excellent in cycleability and load characteristics as a lithium ion secondary battery, and exhibits a high charge capacity and high charge / discharge efficiency, an electrode for a secondary battery, and a lithium using the same An ion secondary battery is provided.

Such an object is achieved by the following present inventions (1) to (5).
(1) A carbon material having pores, wherein the carbon material is
A) 95 to 99 wt% of carbon and 1 to 5 wt% of at least one element of O, N, S, P and B as elements other than carbon,
B) The volume of the pores having a pore diameter of 0.25 to 0.45 nm is 30% by volume or more of the total pore volume,
C) The specific surface area is 15 m ² / g or less,
A carbon material for a secondary battery, characterized in that
(2) The carbon material for the secondary battery has a ratio (ρ _H / ρ _B ) of the density (ρ _H ) measured by the helium gas adsorption method to the density (ρ _B ) measured by the butanol immersion method is 0. The secondary battery according to (1), which has an average interplanar spacing (d) of 0.34 to 0.40 nm, which is 9 or more and is calculated from the X-ray diffraction spectrum method using the Bragg equation. Carbon material.
(3) A carbon material for a secondary battery, wherein the carbon material for a secondary battery according to (1) or (2) is non-crystalline.
(4) A secondary battery electrode using the carbon material for a secondary battery according to any one of (1) to (3) as an active material for an electrode.
(5) A secondary battery comprising the secondary battery electrode according to (4).

  ADVANTAGE OF THE INVENTION According to this invention, the carbon material for secondary battery electrodes which is excellent in cycling property and load characteristics as a lithium ion secondary battery, and expresses high charge capacity and high charge / discharge efficiency can be obtained. In addition, the lithium ion secondary battery using the secondary battery electrode obtained by using the carbon material for secondary battery electrode of the present invention as an electrode active material has excellent cycle characteristics and load characteristics, and has a high charge capacity. In addition, it has high charge / discharge efficiency.

  Hereinafter, the carbon material for a secondary battery, the electrode for a secondary battery, and the secondary battery of the present invention will be described in detail.

  The carbon material for a secondary battery of the present invention has pores, contains 95 to 99 wt% of carbon, and contains at least one of O, N, S, P and B as an element other than carbon. It contains 1 to 5 wt% of elements.

  Since the elements other than carbon are partially bonded to carbon in the carbon precursor in the production process of the carbon material, the carbon-carbon bond distance in the obtained carbon material changes. For example, in the case where the carbon precursor has a benzene ring, the carbon-carbon bond distance in the benzene ring is 1.337 mm, and the bond distance is 1.59 mm due to bonding of the B atom. To increase. Thus, when the bond distance is increased, the crystallite structure of the carbon material is broken, a random structure is formed, new pores are formed, and a lithium ion dope source is formed. In addition, since the elements other than carbon have high affinity with lithium ions, the doping amount of lithium ions is different from the doping amount based on the structure control accompanying the formation of new pores in addition to the elements other than carbon. The dope amount accompanying the affinity is increased, the dope amount of the carbon material is further increased, the cycle property and the load characteristic are excellent, and the charge / discharge capacity and the charge / discharge efficiency can be improved. When content of the said element is less than 1 wt%, it does not contribute to the improvement of charging / discharging capacity. On the other hand, if it exceeds 5 wt%, it contributes to the improvement of the charge / discharge capacity, but the charge / discharge efficiency is lowered.

  The carbon material for a secondary battery of the present invention can be obtained by carbonizing a carbon precursor. The carbon precursor is not particularly limited. For example, graphitization of natural pitches such as petroleum pitch and coal pitch, and thermoplastic resin such as polyethylene, polypropylene, acetylene-butadiene-styrene resin and acrylic resin, etc. Carbon precursors; non-graphitizable carbon precursors such as phenol resins, melamine resins, furan resins, epoxy resins and polyacrylonitrile; and mixtures of these graphitizable carbon precursors and non-graphitizable carbon precursors. One or more of these respective types of precursors can be used, but are not particularly limited.

  In the secondary battery carbon material of the present invention, in particular, when used as an active material for a negative electrode, an amorphous carbon material is more preferable in terms of cycleability and charge / discharge characteristics. As an amorphous carbonaceous material, it is easy to obtain as a carbon precursor from the above-mentioned naturally derived pitches such as petroleum pitch and coal pitch, and thermoplastic surname resins such as polyethylene, polypropylene, acetylene-butadiene-styrene resin and acrylic resin. Graphitized carbon; non-graphitizable carbon obtained from thermosetting resins such as the phenol resin, melamine resin, furan resin, and epoxy resin. Also, a carbon material in which a metal material such as aluminum, silver, tin and copper is supported on these amorphous carbons, an alloy-based carbon material in which the metal material is physically mixed and chemically mixed with the amorphous carbon material, etc. Is mentioned. These may be used alone or in combination.

  In the carbon material for a secondary battery according to the present invention, the elements other than carbon include an element in a resin (monomer), a catalyst during a resin reaction or an infusible treatment, a curing agent during a curing treatment, It can adjust with the element contained in a hardening accelerator and the carbonization accelerator at the time of a carbonization process.

A specific example of the carbon precursor will be described.
The phenol resin used as the carbon precursor is obtained, for example, by reacting phenols and aldehydes by a known method, more specifically, a novolak obtained by reacting in the presence of an acidic catalyst. And a resol type phenol resin obtained by reacting in the presence of a basic catalyst.
The melamine resin is obtained by reacting melamines and aldehydes by a known method, and these can be used alone or in combination, but are not particularly limited.

  When the novolac type phenol resin is used, a curing agent can be used together with the resin. The curing agent is not particularly limited as long as it is a curing agent for a novolak type phenol resin. For example, aldehyde sources such as hexamethylenetetramine, trioxane and paraformaldehyde; acid catalysts such as hydrochloric acid, sulfuric acid, phosphoric acid and succinic acid; amines Examples of the curing agent include imidazole curing agents such as imidazole, 1-methylimidazole, 2-imidazole, 1,2-dimethylimidazole, and 2-phenylimidazole; resol resin; epoxy resin and the like. Here, although the usage-amount of the hardening | curing agent in a novolak-type phenol resin is not specifically limited, Usually, 0.1-20 weight part can be used with respect to 100 weight part of phenol resins.

In addition to the curing agent, examples of curing accelerators include inorganic acids such as phosphoric acid; organic acids such as paratoluenesulfonic acid, benzenesulfonic acid and xylenesulfonic acid; benzyldimethylamine and 2,4 Tertiary amine compounds such as 1,6-trisdimethylaminomethylphenol; imidazole compounds such as 2-methylimidazole and 2-ethyl-4-methylimidazole; Lewis acids such as BF ₃ complex; organophosphorus compounds such as triphenylphosphine; Tetra-substituted phosphonium and tetra-substituted borates such as tetraphenyl phosphonium and tetraphenyl borate; Tetraphenyl boron salts such as 2-ethyl-4-methylimidazole and tetraphenyl borate; and the like are appropriately adjusted.

As a method for producing a carbon material for a secondary battery of the present invention, the carbon precursor, and in some cases, a curing agent, a curing accelerator or the like may be added to the carbon precursor (this may be subjected to a crosslinking treatment), and ordinary graphitization. It can manufacture by baking at temperature lower than process temperature (for example, 2800 degreeC or more). As a specific example, as an example using a phenol resin, the first heat treatment is performed at 400 to 800 ° C., and the carbon precursor subjected to the first heat treatment is pulverized to a predetermined particle diameter. Then, a carbon material can be obtained by carbonizing the carbon precursor grind | pulverized above at 800 to 1400 degreeC as 2nd heat processing. Although it does not specifically limit as time to perform 1st heat processing and 2nd heat processing, Usually, it heats up to the final heat processing temperature over 1 to 50 hours, and hold | maintains at the final heat processing temperature for 1 to 30 hours as needed.
In addition, the atmosphere in which the first heat treatment and the second heat treatment are performed is not particularly limited, and can be performed under any conditions such as in the air, in an inert gas atmosphere, and in a vacuum. Heat treatment conditions combined with more than one species may be used.

  As pores in the carbon material for a secondary battery of the present invention obtained above, a pore diameter between 0.25 nm and 0.45 nm is preferable as a range of reversible pores that occlude / desorb lithium ions, If the pore diameter is smaller than 0.25 nm, the reversible pores capable of inserting / extracting lithium ions are decreased, and the charge / discharge capacity tends to be reduced. On the other hand, if it is larger than 0.45 nm, the irreversible pores increase, and the charge / discharge efficiency tends to decrease.

The pore volume having a pore diameter of 0.25 nm to 0.45 nm in the secondary battery carbon material of the present invention is 30% by volume or more of the total pore volume, and more preferably 50% or more. If it is 30% by volume or less, the above-described irreversible capacity increases or the capacity decreases.
As a method for measuring the pore volume, a nitrogen gas adsorption method can be used and the pore volume can be calculated by a micropore method.

Moreover, the specific surface area of the carbon material for secondary batteries of this invention is 15 m < ² > / g or less. Moreover, it is preferable that it is 1 m < ² > / g as a lower limit. When the specific surface area is larger than 15 m ² , the reaction with the electrolytic solution increases, the irreversible capacity increases, and the charge / discharge efficiency tends to decrease. On the other hand, if the specific surface area is less than 1 m ² / g, the pore volume in the carbon material becomes small and the capacity tends to decrease.
As a method for measuring the specific surface area, a nitrogen gas adsorption method is used, and the BET three-point method is also used.

Further, the carbon material for a secondary battery of the present invention has a ratio (ρ _H / ρ _B ) of the density (ρ _H ) measured by the helium gas adsorption method to the density (ρ _B ) measured by the butanol immersion method. .9 or more is preferable. More preferably, the density ratio (ρ _H / ρ _B ) is in the range of 0.9 to 1.5, and more preferably 0.9 to 1.375. By setting it as this range, it will be excellent in charge capacity and charging / discharging efficiency. Although it can be used outside the above range, if the density ratio (ρ _H / ρ _B ) is smaller than 0.9, the number of large pores into which butanol can be immersed increases and the charge capacity is improved, but the charge / discharge efficiency may be reduced. There is. On the other hand, if the density ratio is too large, there is no problem in charge / discharge efficiency, but the charge capacity tends to be small.

  The carbon material for a secondary battery of the present invention preferably has an average interplanar spacing (d) of 0.34 to 0.40 nm calculated from the X-ray diffraction spectrum method using the Bragg equation. By setting it as this range, it will be excellent in charge capacity and charging / discharging efficiency. It can also be used outside the above range, but if the average interplanar spacing (d) is less than 0.34, it may be close to a crystal structure and the charge capacity may be reduced, and if it is greater than 0.40, the electrolyte will permeate. Although the number of pores increases and the charge capacity increases, on the other hand, the reaction with the electrolyte increases and the charge / discharge efficiency may be lowered.

In the present invention, since the density ratio (ρ _H / ρ _B ) is 0.9 or more and the average spacing (d) is 0.34 to 0.40 nm, the charge capacity and charge / discharge are further increased. It will be excellent in efficiency. Even if only the density ratio satisfies 0.9 or more, as described above, if the average interplanar spacing is smaller than 0.34, the charge capacity may be reduced because it approaches the crystal structure, and if larger than 0.40, the charging capacity becomes large. However, the charge / discharge efficiency may be reduced.

Next, the secondary battery electrode of the present invention will be described.
The electrode for a secondary battery of the present invention contains the carbon material described above as an electrode active material.

The said carbon material used for the electrode for secondary batteries of this invention is generally used for the active material for negative electrodes as an active material for electrodes.
The negative electrode active material is not limited as long as it is a material capable of inserting and releasing lithium ions, but among the carbon materials of the present invention, an amorphous carbon material is more preferable.

Moreover, when using the said carbon material in the active material for positive electrodes, it can also be used as a electrically conductive agent with respect to the active material for positive electrodes.
As the positive electrode active material, a transition metal oxide containing lithium having a high energy density and excellent in reversible desorption / insertion of lithium ions is preferable. For example, a cobalt composite oxide such as LiCoO ₂ , LiMn ₂ O _4, etc. Manganese composite oxides, nickel composite oxides such as LiNiO ₂ , mixtures of these oxides, and LiNiO ₂ in which part of nickel is replaced with cobalt or manganese, iron composite oxides such as LiFeVO ₄ and LiFePO _4, etc. Can be mentioned. The carbon material is used as a conductive agent with respect to the positive electrode active material. Specifically, in order to provide conductivity to the positive electrode active material, an electrode active material is added to form an electrode. In some cases, the resistance of the electrode can be lowered.

The method for producing an electrode for a secondary battery of the present invention can be produced using the electrode active material, a binder, and an appropriate amount of a conductive agent.
Examples of the binder include polyethylene, polypropylene, polyethylene terephthalate, polyacrylonitrile, aromatic polyamide, cellulose, carboxymethyl cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene rubber, isoprene rubber, butadiene rubber, and ethylene.・ Propylene rubber, ethylene-propylene-diene copolymer, styrene / butadiene / styrene block copolymer, styrene / isoprene / styrene block copolymer, polyvinyl alcohol, polyvinyl propynal, polyvinyl butyral, polyacrylamide, polyethylene glycol, polypropylene Glycol and polybutylene glycol; polyvinylidene fluoride resin, polytetrafluoroethylene, tetrafluoroethylene-he Fluorine such as safluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer and polyvinyl fluoride Resin: Vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber, vinylidene fluoride-pentafluoropropylene fluororubber, vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluoro rubber, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber, and vinylidene fluoride - vinylidene fluoride-based fluororubber such as chlorotrifluoroethylene-based fluorine rubber.

  Although the amount of the binder used is not particularly limited, it can be generally used in an amount of 1 to 20 wt% with respect to the electrode active material. In particular, it is preferably 1 to 15 wt%, more preferably 3 to 7 wt% for the negative electrode. Although it can be used even outside these ranges, if the amount of the binder is too large, the amount of the active material present in the electrode is relatively reduced, which may reduce the capacity of the electrode. If the amount of the binder is too small, it may be difficult to bind the active material to the current collector of the electrode.

  Examples of the conductive agent include carbon fibers such as graphite and acetylene black, but the amount of the conductive agent used is not particularly limited, but it is usually 1 to 15 wt% with respect to the electrode active material. More specifically, it is preferably 2 to 10 wt%, more preferably 3 to 7 wt% in the negative electrode. In the positive electrode, 5 to 15 wt% is preferable, and 5 to 10 wt% is more preferable. Although it can be used outside these ranges, if the amount of the conductive agent is too large, the amount of the active material present in the electrode may be reduced more than necessary, and the volume capacity of the electrode may be reduced.

As a method for producing an electrode for a secondary battery of the present invention, for example, an appropriate amount of the binder, the electrode active material, and a conductive agent are weighed and mixed for each of the positive electrode and the negative electrode. The slurry is adjusted to a predetermined viscosity in a solvent (N-methyl-2-pyrrolidone, acrylonitrile, etc.), and then applied onto the current collector metal foil to form a coating film. Subsequently, in order to fix the active material for electrodes in the coating film on the current collector, it is obtained by performing a heat treatment at about 50 to 200 ° C. as a step of removing the polar solvent. The temperature and time of the heat treatment are not particularly limited, but it is preferable to perform the heat treatment at a temperature and time at which the electrode active material is not oxidized and the polar solvent can be removed.
Examples of the current collector metal foil include an aluminum foil for the positive electrode and a copper foil for the negative electrode.

Further, as a specific example of the method for manufacturing the secondary battery electrode, in the case of the positive electrode, the slurry for the secondary battery electrode is used as a metal foil for a current collector using a doctor blade or an applicator. The film is uniformly coated at the position to form a coating film, and then the coating film is dried and compression-molded with a roll press to obtain the smoothness of the electrode.
In the case of a negative electrode, the slurry for the secondary battery electrode is uniformly applied to a predetermined position on both sides of the copper foil as a current collector metal foil using a doctor blade or an applicator to form a coating film, Subsequently, after drying the said coating film and adjusting the smoothness of an electrode surface with a roll press machine, it is obtained by compression-molding to a density preferable as an electrode with a press machine.

Next, the secondary battery of the present invention will be described.
The secondary battery of the present invention is characterized by using the secondary battery electrode of the present invention. More specifically, it includes a positive electrode, a negative electrode, and an electrolyte. Further, the secondary battery includes a separator for preventing the positive electrode and the negative electrode from being short-circuited.

  In the secondary battery of the present invention, for example, a negative electrode obtained by using the carbon material for a secondary battery as a negative electrode material is disposed to face the positive electrode with a separator interposed therebetween, and an electrolyte is used between the electrodes. Thus, a secondary battery is obtained.

  Although it does not specifically limit as a separator, The microporous film, nonwoven fabric, etc. which consist of polyethylene, a polypropylene, etc. can be used.

  As the electrolyte, a known electrolytic solution, a room temperature molten salt (ionic liquid), an organic or inorganic solid electrolyte, and the like can be used. Examples of the known electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. Examples of the room temperature molten salt (ionic liquid) include imidazolium salts, pyrrolidinium salts, pyridinium salts, aliphatic salts, ammonium salts, phosphonium salts, sulfonium salts, and the like. Examples of the solid electrolyte include polyether polymers, polyester polymers, polyimine polymers, polyvinyl acetal polymers, polyacrylonitrile polymers, polyfluorinated alkene polymers, polyvinyl chloride polymers, poly (vinyl chloride-fluoride). Vinylidene) -based polymers, poly (styrene-acrylonitrile) -based polymers, and organic polymer gels represented by linear polymers such as nitrile rubber; inorganic ceramics such as zirconia; silver iodide, silver iodide sulfur compounds, iodine And inorganic electrolytes such as silver rubidium compounds. Moreover, in order to reduce ionic conductivity, what melt | dissolved lithium salt in the said electrolyte can be used as an electrolyte for secondary batteries.

Examples of the lithium salt dissolved in the electrolyte include LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC ( CF ₃ SO ₂ ) _{3 and the} like. You may use these individually or in combination of 2 or more types. Can be used.

  As a method for producing the secondary battery of the present invention, a known method can be applied. For example, first, the positive electrode and the negative electrode obtained above are prepared by cutting into a predetermined shape and size, and then bonded together via the separator so that the positive electrode and the negative electrode are not in direct contact with each other. A layer cell is used. Next, the electrolyte is injected between the electrodes of the single-layer cell by a method such as injection. Thus, the obtained cell is inserted and sealed in the exterior body which consists of a laminated film of the three-layer structure of a polyester film-aluminum film-modified polyolefin film, for example, and a secondary battery is obtained. Depending on the application, these may be used as a single cell or as a module connecting a plurality of cells.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the examples. In the examples and comparative examples, “parts” indicates “parts by weight” and “%” indicates “% by weight”.

1. Production of carbon material <Example 1>
100 parts of phenol, 64.5 parts of 37% formaldehyde aqueous solution, and 3 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, dehydrated at elevated temperature, and 90 parts of phenolic resin were added. Obtained. After pulverizing and mixing 10 parts of hexamethylenetetramine added to 100 parts of the phenol resin obtained by repeating the above operation, curing treatment was performed at 200 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after the carbonization treatment for 3 hours after reaching 450 ° C., the grinding treatment was performed until the average particle size became 13 μm. The carbon material obtained by the pulverization was further heated, and carbonized for 10 hours after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The carbon content of the obtained carbon material was 97.5%, and contained 1.2% oxygen and 1.1% nitrogen as elements other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.38 nm, ρ _H = 1.426, ρ _B = 1.517, ρ _H / ρ _B = 0.94, and 0.25- The pore volume of 0.45 nm was 55% by volume with respect to the total pore volume. Further, the specific surface area in the BET method was 8.0 m ² / g.

<Example 2>
100 parts of phenol, 60 parts of a 37% aqueous formaldehyde solution, and 3 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a cooling tube, reacted at 100 ° C. for 3 hours, dehydrated by heating, and 90 parts of phenol resin were obtained. . After pulverizing and mixing 10 parts of hexamethylenetetramine with respect to 100 parts of the phenol resin obtained by repeating the above operation, a curing treatment was performed at 150 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after a carbonization treatment for 1 hour after reaching 500 ° C., a pulverization treatment was performed until the average particle size became 14 μm. The carbon material obtained by the pulverization was further heated, and carbonized for 4 hours after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 96.8% and contained 1.2% oxygen and 1.9% nitrogen as elements other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum was 0.383 nm, ρ _H = 1.623, ρ _B = 1.52, ρ _H / ρ _B = 1.07, and 0.25 to 0.25 The pore volume of 0.45 nm was 51% by volume with respect to the total pore volume. Moreover, the specific surface area in the BET method was 8.1 m ² / g.

<Example 3>
20 parts of hexamethylenetetramine was added to 100 parts of the phenol resin obtained by the same operation as in Example 1 and pulverized and mixed, followed by curing at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after carbonization treatment for 6 hours after reaching 500 ° C., pulverization treatment was performed until the average particle size became 12 μm. The carbon material obtained by the pulverization treatment was further heated up and carbonized for 1 hour after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 96.2% and contained 1.5% oxygen and 2.1% nitrogen as elements other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.373 nm, ρ _H = 1.547, ρ _B = 1.498, ρ _H / ρ _B = 1.03, and 0.25 to 0.25 The pore volume at 0.45 nm was 45% by volume with respect to the total pore volume. The specific surface area in the BET method was 9.4 m ² / g.

<Example 4>
10 parts of hexamethylenetetramine and 5 parts of paratoluenesulfonic acid were added to 100 parts of phenol resin obtained by the same operation as in Example 1 and pulverized and mixed, followed by curing at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after carbonization treatment for 3 hours after reaching 500 ° C., pulverization treatment was performed until the average particle size became 12 μm. The carbon material obtained by the pulverization treatment was further heated up and carbonized for 12 hours after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 97.9%, and contained 0.5% oxygen, 0.6% nitrogen, and 0.9% sulfur as elements other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.382 nm, ρ _H = 1.688, ρ _B = 1.521, ρ _H / ρ _B = 1.11. The pore volume of 0.45 nm was 48% by volume with respect to the total pore volume. Moreover, the specific surface area in the BET method was 6.8 m ² / g.

<Example 5>
10 parts of hexamethylenetetramine and 2 parts of phosphoric acid were added to 100 parts of the phenol resin obtained by the same operation as in Example 1 and pulverized and mixed, followed by curing at 150 ° C. for 1 hour. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after the carbonization treatment for 9 hours after reaching 450 ° C., the grinding treatment was performed until the average particle size became 13 μm. The carbon material obtained by the pulverization treatment was further heated up and carbonized for 12 hours after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The carbon content of the obtained carbon material was 96.9%, and contained 0.5% oxygen, 0.9% nitrogen, and 1.4% phosphorus as elements other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.381 nm, ρ _H = 1.711, ρ _B = 1.601, ρ _H / ρ _B = 1.069, and 0.25 to 0.25 The pore volume of 0.45 nm was 43% by volume with respect to the total pore volume. The specific surface area in the BET method was 5.2 m ² / g.

<Example 6>
100 parts of phenol, 146.6 parts of 37% formaldehyde aqueous solution and 3 parts of sodium hydroxide were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, dehydrated at elevated temperature, and 95 parts of phenol resin. Got. 100 parts of the phenol resin obtained by repeating the above operation was cured at 130 ° C. for 1 hour, then heated in a nitrogen atmosphere, and after carbonization for 3 hours after reaching 500 ° C., the average particle size was 11 μm. Grinding was performed until. The carbon material obtained by the pulverization treatment was further heated up and carbonized for 12 hours after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 97.9% and contained 1.7% of oxygen as an element other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.373 nm, ρ _H = 1.482, ρ _B = 1.501, ρ _H / ρ _B = 0.99, and 0.25 to 0.25 The pore volume of 0.45 nm was 53% by volume with respect to the total pore volume. Moreover, the specific surface area in the BET method was 6.2 m ² / g.

<Example 7>
100 parts of phenol resin obtained by the same operation as in Example 6 was subjected to curing treatment at 150 ° C. for 1 hour, and then held at 300 ° C. for 1 h in an oxygen atmosphere to perform infusibilization treatment. Next, the temperature was raised in a nitrogen atmosphere, and after calcination for 3 hours after reaching 500 ° C., pulverization was performed until the average particle size became 13 μm. The carbon material obtained by the pulverization was further heated, and carbonized for 6 hours after reaching 1150 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 97.1% and contained 2.4% oxygen as an element other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.373 nm, ρ _H = 1.472, ρ _B = 1.521, ρ _H / ρ _B = 0.97, and 0.25- The pore volume of 0.45 nm was 49% by volume with respect to the total pore volume. The specific surface area in the BET method was 7.5 m ² / g.

<Comparative Example 1>
100 parts of urea, 135 parts of 37% formaldehyde aqueous solution, and 3 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a cooling tube, reacted at 100 ° C. for 6 hours, dehydrated at elevated temperature, and 95 parts of ketone resin was obtained. . The obtained ketone resin was heated in a nitrogen atmosphere, and after calcination treatment for 2 hours after reaching 500 ° C., pulverization treatment was performed until the average particle size became 13 μm. The carbon material obtained by the pulverization was further heated, and carbonized for 10 hours after reaching 1000 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 97.9% and contained 0.5% oxygen as an element other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.397 nm, ρ _H = 1.84, ρ _B = 1.322, ρ _H / ρ _B = 1.392, and 0.25- The pore volume of 0.45 nm was 25% by volume with respect to the total pore volume. Moreover, the specific surface area in the BET method was 18.2 m ² / g.

<Comparative example 2>
100 parts of phenol, 115 parts of 43% formaldehyde aqueous solution and 3 parts of sodium hydroxide were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, dehydrated by heating, and 90 parts of phenol resin were obtained. It was. Curing treatment was performed at 150 ° C. for 3 hours on 100 parts of the phenol resin obtained by repeating the above operation. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and after carbonization treatment for 3 hours after reaching 500 ° C., pulverization treatment was performed until the average particle size became 11 μm. The carbon material obtained by the pulverization treatment was further heated up and carbonized for 1 hour after reaching 1100 ° C. to obtain a carbon material for a secondary battery. The obtained carbon material had a carbon content of 96.2% and contained 0.4% oxygen as an element other than carbon. The interplanar spacing measured from the X-ray diffraction spectrum is 0.41 nm, ρ _H = 1.40, ρ _B = 1.58, ρ _H / ρ _B = 0.88, and 0.25- The pore volume of 0.45 nm was 26% by volume with respect to the total pore volume. Further, the specific surface area in the BET method was 17.3 m ² / g.

Evaluation of carbon material (1) Measurement of carbon material composition a) Carbon content The obtained carbon material was dried at 110 ° C./vacuum for 3 hours, and then an elemental analysis measuring device (2400IICHNS / O) manufactured by Perkin Elner Co., Ltd. was used. The carbon composition ratio was measured.
B) Oxygen, nitrogen, and sulfur content The obtained carbon material was dried at 110 ° C./vacuum for 3 hours, and then the composition of each element was measured using an elemental analyzer (2400IICHNS / O) manufactured by Perkin Elner. did.
C) Boron content The obtained carbon material was dried at 110 ° C./vacuum for 3 hours, then weighed 1 g, and qualitatively determined boron using a JEOL fluorescent X-ray analyzer (JSX-3201M). For quantitative determination, a calibration curve was drawn with boron oxide (B2O3) to determine the boron content contained in the carbon material.

(2) Measurement of pore volume and pore distribution Using a Shimadzu Corporation pore distribution measuring device “ASAP2010”, the sample was vacuum-heated and pretreated at 623 K, and the adsorbed gas was desorbed. ₂ is used to measure the adsorption isotherm at 77.3 K in the range of an absolute pressure of 760 mmHg and a relative pressure of 0.005 to 0.86, and the thickness t of the adsorption layer is determined from the specific surface area and adsorption amount of the obtained adsorption medium. The mean pore hydraulic radius was calculated based on the thickness formula of Halsey and Halsey and Jura, and the pore volume was calculated based on the following formula.
The thickness formulas of Halsey and Halsey and Jura are as described below.
t = (M × Vsp / 22414) × (Va / S)
[Wherein, t: statistical thickness of the adsorption layer, M: molecular weight of the adsorbate, Va: adsorption amount per unit weight of the adsorbent, Vsp: specific volume of the adsorbate gas, S: specific surface area of the adsorbent]
t _I = HP1 × [HP2 / ln (Prel _I )] HP3
[Where, t _I : thickness of I ^th point, HP1: Halsey parameter # 1, HP2: Halsey parameter # 2, HP3: Halsey parameter # 3, Prel _I : relative pressure (mmHg) of I ^th point]
Average hydraulic radius (nm): R _I = (t _I + t _I-1 ) / 20
Increment of pore surface area blocked at the Ith point ΔS: ΔS = S _I-1 −S _I
Integrated pore surface area (m ² / g) blocked at the Ith point S: S = S ₁ + S ₂ + S ₃ +... Sn
Pore volume increment ΔV blocked at the Ith point:
ΔV = (S × 10 ⁴ cm ² / m ² ) × (R _I × 10 ⁻⁸ cm / Å)
Ith point pore volume ΔV / ΔR _I (cm ³ / g): ΔV / ΔR _I = ΔV / t _I −t _I−1
The Ith point refers to an individual measurement point by each relative pressure.
Pore volume blocked at the Ith point (cm ³ / g): V = V ₁ + V ₂ + V ₃ +... Vn.

(3) Specific surface area measurement The specific surface area measurement of the carbon material was measured by the BET 3 point method (0.05 <P / Po <0.30) using Nova-1200 made from Yuasa. A specific measuring method is shown below.
From the following formula (1), the total surface area S _total was calculated from the monomolecular adsorption amount W _m and the following formula (2), and the specific surface area S was calculated from the following formula (3).
_{1 / [W (P o /} P-1) = (C-1) / W m C (P / P o) / W m C ····· (1)
Wherein (1), P: gas pressure of adsorbate in the adsorption equilibrium, P _o: saturated vapor pressure of the adsorbate in the adsorption temperature, W: adsorption amount in the adsorption equilibrium pressure P, W _m: monolayer adsorption amount,
C: constant related to the magnitude of the interaction between the solid surface and the adsorbate (C = exp {(E1-E2) RT}) [wherein E1: heat of adsorption of the first layer (kJ / mol), E2 : Heat of liquefaction at measurement temperature of adsorbate (kJ / mol)]]
S _total = (W _m NA _cs ) M (2)
[In formula (2), N: Avogadro number, M: molecular weight, A _cs : adsorption cross section]
S = S _total / w (3)
[In formula (3), w: sample weight (g)]

(4) Measurement of average spacing The measurement method of the average spacing in the carbon material is as follows. Here, the X-ray diffraction image obtained by the X-ray diffraction spectrum method can grasp the crystal structure of the carbon material to some extent. The X-ray diffraction spectrum of the carbon material of the present invention was measured by an X-ray diffraction apparatus “XRD-7000” manufactured by Shimadzu Corporation. From the spectrum obtained from the X-ray diffraction measurement of the carbon material of the present invention, the average interplanar spacing d (nm) was calculated from the following Bragg equation.
λ = 2d _hkl sin θ Bragg equation (d _hkl = d ₀₀₂ )
[Where: λ: wavelength of characteristic X-ray Kα ₁ output from the cathode, θ: reflection angle of spectrum]

(5) Measurement of density ρ _B by butanol immersion method The butanol immersion method was measured according to the following.
A specific gravity bottle used for the butanol immersion method was prepared, and the mass and volume of the specific gravity bottle were accurately measured. Next, 40% by volume of a carbon material to be measured with respect to the specific gravity bottle was added, and the weight was measured. Then, after filling the specific gravity bottle with butanol, it is placed in a thermostatic layer at 25 ° C. and left to stand for 30 minutes. When butanol enters the pores inside the carbon material, the volume of butanol apparently decreases, so the reduced butanol content is added to the specific gravity bottle. Then, the above was repeated until the butanol did not decrease (until saturation), and the total weight was measured.
Ρ _B by the butanol immersion method was calculated by the following formula.
ρ _B = carbon material weight / [specific gravity bottle volume− (saturated specific gravity bottle weight) / butanol specific gravity]
Here, the butanol specific gravity is 0.810 g / mL.

(6) Measurement of density ρ _H by helium gas adsorption method The density “ρ _H ” measurement by helium gas adsorption method is measured using a high-precision automatic volume meter (Estech VM-100) based on JIS-Z-8901. went. As a pretreatment, the carbon material was measured after being dried at 150 ° C. for 2 hours in a vacuum. Measurement was performed at an ambient temperature of 25 ° C.
The measuring device has a sample chamber and an expansion chamber, the sample chamber and the expansion chamber have pressure gauges for measuring the pressure in the chamber, and the sample chamber and the expansion chamber are connected by a connecting pipe. Each was equipped with a gas discharge valve and an introduction valve.
For the measurement, carbon material was put in the sample chamber, helium gas was passed through the helium gas introduction valve, the connecting pipe in the sample chamber, and the helium gas discharge valve in the expansion chamber, and the inside of the apparatus was completely replaced with helium gas. Next, the valve between the sample chamber and the expansion chamber and the valve of the helium gas discharge pipe from the expansion chamber are closed and helium gas is introduced from the helium gas introduction pipe in the sample chamber to 134 kPa, and then the helium gas introduction pipe is stopped. The valve was closed. Subsequently, the pressure in the sample chamber 5 minutes after the stop valve was closed was measured. Next, the valve between the sample chamber and the expansion chamber was opened, helium gas was transferred to the expansion chamber, and the pressure at that time was measured.
The density ρ _H was calculated by the following formula.
Sample volume = volume of sample chamber−volume of expansion chamber / [(sample chamber pressure / expansion chamber pressure) −1]
Since the weight of the sample is the weight of the sample introduced into the sample chamber, ρ _H = the weight of the sample introduced into the sample chamber / the volume of the sample.

Evaluation of battery characteristics (1) Production of negative electrode Using the carbon material obtained above, the binder was blended in a ratio of 10% polyvinylidene fluoride and 3% acetylene black, respectively, and further diluted solvent A suitable amount of N-methyl-2-pyrrolidone was added and mixed to prepare a slurry-like negative electrode mixture.
This negative electrode slurry mixture was applied to both sides of a 10 μm copper foil, and then vacuum dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed to 100 μm by a roll press. This was cut into a size of 40 mm in width and 290 mm in length to produce a negative electrode. Using this negative electrode, a negative electrode was punched out with a diameter of 13 mm as an electrode for a lithium ion secondary battery.

(2) Production of lithium ion secondary battery In the order of the negative electrode, separator (polypropylene porous film: width 45 mm, thickness 25 μm), and lithium metal (thickness 1 mm) as the working electrode, in the Bipolar cell made by Hosen. Arranged in a predetermined position. Further, an electrolytic solution in which lithium perchlorate is dissolved at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio is 1: 1) is injected into a lithium ion secondary solution. A battery was produced.

(3) Evaluation of battery characteristics <Evaluation of initial charge / discharge characteristics>
Regarding the charging capacity, constant current charging is performed with the current density at the time of charging being 25 mA / g, and from the time when the potential reaches 0 V, constant voltage charging is performed at 0 V until the current density reaches 1.25 mA / g. The amount of electricity charged was taken as the charge capacity.
On the other hand, with respect to the discharge capacity, constant current discharge was performed with a current density at the time of discharge of 25 mA / g, and constant voltage discharge was performed at 2.5 V from the time when the potential reached 2.5 V, and the current density was 1.25 mA. The amount of electricity discharged up to / g was taken as the discharge capacity.
In addition, evaluation of the charging / discharging characteristic was performed using the charging / discharging characteristic evaluation apparatus (Hokuto Denko Co., Ltd. product: HJR-1010mSM8).
The initial charge / discharge efficiency was defined by the following equation.
Initial charge / discharge efficiency (%) = initial discharge capacity (mAh / g) / initial charge capacity (mAh / g) × 100

<Cycle evaluation>
The discharge capacity obtained after the initial charge / discharge characteristic evaluation conditions were repeatedly measured 200 times was defined as the discharge capacity at the 200th cycle. Moreover, the cycle property (200 cycle capacity maintenance rate) was defined by the following formula.
Cycle performance (%, 200 cycle capacity retention rate) = 200th cycle discharge capacity (mAh / g) / initial discharge capacity (mAh / g) × 100

<Evaluation of load characteristics>
The discharge capacity obtained by the initial charge / discharge characteristic evaluation is defined as the reference capacity (C ₀ ), and after charging the reference capacity, discharging is performed at a current density that discharges the charged amount in 1 hour. The capacity. Similarly, after charging the reference capacity, discharging was performed at a current density that discharges the charged amount in 2 minutes, and the obtained discharge capacity was set to 30 C capacity. Moreover, the load characteristic (capacity maintenance rate at 30 C vs. 1 C) was defined by the following equation.
Load characteristics (%, capacity retention rate at 30 C vs. 1 C) = 30 C capacity (mAh / g) / 1 C capacity (mAh / g) × 100

  Regarding the above evaluation results, the evaluation results of carbon materials are shown in Table 1, and the evaluation results of battery characteristics are shown in Table 2.

  From the results of Tables 1 and 2, Examples 1 to 7 were secondary in which the carbon content, the content of elements other than carbon were controlled, and the pore volume, average interplanar spacing, ρH, ρB, ρH / ρB were controlled. It was a lithium ion secondary battery provided with a carbon material for batteries, and was superior in charge / discharge characteristics, cycle performance, and load characteristics as compared with Comparative Examples 1 and 2 in which the above parameters were not controlled.

Claims (5)

A carbon material having pores, the carbon material,
A) 95 to 99 wt% of carbon and 1 to 5 wt% of at least one element of O, N, S, P and B as elements other than carbon,
B) The volume of the pores having a pore diameter of 0.25 to 0.45 nm is 30% by volume or more of the total pore volume,
C) The specific surface area is 15 m ² / g or less,
A carbon material for a secondary battery, characterized in that
(However, carbon materials for secondary batteries made of β-naphthol resin are excluded.) The carbon material for a secondary battery has a ratio (ρ _H / ρ _B ) of a density (ρ _H ) measured by a helium gas adsorption method to a density (ρ _B ) measured by a butanol immersion method of 0.9 or more. 2. The carbon material for a secondary battery according to claim 1, wherein an average interplanar spacing (d) of the carbon material calculated from the X-ray diffraction spectrum method using the Bragg equation is 0.34 to 0.40 nm.   A carbon material for a secondary battery, wherein the carbon material for a secondary battery according to claim 1 or 2 is non-crystalline.   The carbon material for secondary batteries of any one of the said Claims 1-3 is used for the active material for electrodes, The electrode for secondary batteries characterized by the above-mentioned.   A secondary battery comprising the secondary battery electrode according to claim 4.