JP5017897B2 - Carbon material, secondary battery negative electrode material, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a carbon material, a negative electrode material for a secondary battery, and a nonaqueous electrolyte secondary battery.

Carbon materials are used in a wide range of applications such as negative electrodes for lithium ion secondary batteries, capacitor electrodes, electrodes for electrolysis and activated carbon, and further development is expected in the future.
These carbon materials are conventionally made from coconut husk, coal coke, coal or petroleum pitch, furan resin, phenol resin, or the like (see, for example, Patent Document 1).
However, the conventional carbon materials obtained from these raw materials are not sufficient in charge / discharge characteristics such as charge / discharge capacity and cycle characteristics, particularly when used as a negative electrode material for a non-aqueous electrolyte secondary battery. There was no case.

JP 05-043345 A

  The present invention relates to a carbon material capable of producing a negative electrode material for a non-aqueous electrolyte secondary battery excellent in charge / discharge characteristics, particularly low irreversible capacity and charge / discharge cycle performance, and a negative electrode material for a secondary battery using the same. And a non-aqueous electrolyte secondary battery.

Such an object is achieved by the following present inventions (1) to (5).
(1) A granular carbon material obtained by carbonizing a resin composition, wherein the carbon content in the carbon material is 99.9% or more and the ratio of the carbon material particles having a diameter of 1 μm or less is A carbon material characterized by being 1% or less of the total carbon material.
(2) The carbon material according to (1), wherein the resin composition includes a phenol resin obtained by reacting a phenol and an aldehyde.
(3) The carbon material according to (1) or (2), wherein the carbon material has a specific surface area of 1.0 m ² / g or less by a BET three-point method by nitrogen adsorption.
(4) A negative electrode material for a secondary battery comprising the carbon material described in any one of (1) to (3).
(5) A non-aqueous electrolyte secondary battery using the secondary battery negative electrode material according to (4).

  By using the carbon material of the present invention, a negative electrode material for a non-aqueous electrolyte secondary battery excellent in charge / discharge characteristics, in particular, low irreversible capacity and charge / discharge cycle performance can be obtained.

Below, the carbon material of this invention, the negative electrode material for secondary batteries using the same, and a nonaqueous electrolyte secondary battery are demonstrated in detail.
The carbon material of the present invention is a granular carbon material obtained by carbonizing a resin composition, the carbon material particles having a carbon content in the carbon material of 99.9% or more and a diameter of 1 μm or less. The ratio is 1% or less of the entire carbon material.
Moreover, the negative electrode material for secondary batteries of this invention contains the carbon material of the said this invention, It is characterized by the above-mentioned.
And the nonaqueous electrolyte secondary battery of this invention uses the said secondary battery negative electrode material of this invention, It is characterized by the above-mentioned.

First, the carbon material of the present invention will be described.
The resin composition used for the carbon material of the present invention is, for example, one selected from a thermosetting resin, a thermoplastic resin, or other polymer materials (hereinafter, these may be simply referred to as “main component resins”). ) Can be contained. The main component resins can be used alone or in combination of two or more. Moreover, a hardening agent, an additive, etc. can be suitably contained together with the said main component resin.

  In the carbon material of the present invention, the above resin composition may contain only one kind of resin as the main component resin, but this is also referred to as a resin composition for convenience.

  It is preferable that the said resin composition contains the phenol resin formed by making phenols and aldehydes react. Although it does not specifically limit as said phenol resin, For example, phenol resins, such as a novolak type phenol resin and a resol type phenol resin, epoxy resins, such as a bisphenol type epoxy resin and a novolak type epoxy resin, melamine resin, urea resin, aniline resin, cyanate Examples thereof include resins, furan resins, ketone resins, unsaturated polyester resins, urethane resins and the like. In addition, modified resins in which these are modified with various components can also be used.

When a thermosetting resin is used as the main component resin, the curing agent can usually be used in combination.
Although it does not specifically limit as a hardening | curing agent used here, For example, in the case of a novolak-type phenol resin, a hexamethylenetetramine, paraform, etc. can be used. In the case of an epoxy resin, for example, polyamine compounds such as aliphatic polyamines and aromatic polyamines, acid anhydrides, imidazole compounds, dicyandiamide, novolac type phenol resins and the like can be used.
In addition, even if the thermosetting resin is usually used in combination with a predetermined amount of curing agent, the resin composition used in the present invention is synthesized with a smaller amount than usual or without using a curing agent in combination. You can also.

  As said main component resin used for the carbon material of this invention, a thermosetting resin is preferable. Thereby, the remaining carbon rate of a carbon material can be raised more.

In addition to the above, an additive can be blended in the resin composition used in the carbon material of the present invention.
Although it does not specifically limit as an additive used here, For example, the carbon material precursor carbonized at 200-800 degreeC, a graphite and a graphite modifier, an organic acid, an inorganic acid, a nitrogen-containing compound, an oxygen-containing compound, an oxygen-containing compound, Sulfur, an aromatic compound, a nonferrous metal element, etc. can be mentioned.
The above additives may be used alone or in combination of two or more depending on the type and properties of the main component resins used.

Although it does not specifically limit in carbonization process conditions, For example, it heats up from normal temperature at 1-200 degreeC / hour, and it hold | maintains at 800-3000 degreeC for 0.1 to 50 hours, Preferably it carries out for 0.5 to 10 hours. be able to. As the atmosphere during the carbonization treatment, for example, it can be performed under an inert atmosphere such as nitrogen or helium gas, or under a substantially inert atmosphere such that a trace amount of oxygen is present in the inert gas.
Conditions such as temperature and time during the carbonization can be adjusted as appropriate in order to optimize the characteristics of the carbon material.

In addition, before performing the said carbonization process, a pre carbonization process can be performed.
Although it does not specifically limit as conditions for pre carbonization here, For example, it heats up from 1 degreeC / hour from normal temperature, and is 0.1 to 50 hours at 500 to 1000 degreeC, Preferably it is 0.5 to 10 hours Can be held.

Further, when a thermosetting resin or a polymerizable polymer compound is used as the main component resin of the resin composition, the resin composition can be cured before the pre-carbonization treatment.
Although it does not specifically limit as a hardening processing method, For example, it can carry out by the method of giving the calorie | heat amount which can perform hardening reaction to a resin composition, the method of thermosetting, or the method of using together main component resin and a hardening | curing agent. .

  In addition, when performing the said carbonization process or a pre carbonization process, a metal, a pigment, a lubricant, an antistatic agent, antioxidant etc. can also be added to the said resin composition.

  When the said hardening process and / or pre carbonization process are performed, it is preferable to grind | pulverize a processed material before the said carbonization process after that. Thereby, the uniformity of the heat history and the surface state during carbonization can be improved, and the handleability of the processed product can be improved.

The carbon material of the present invention is characterized in that the carbon content in the carbon material is 99.9% or more and the ratio of carbon material particles having a diameter of 1 μm or less is 1% or less of the whole carbon material.
By doing so, the charge / discharge efficiency can be increased and the irreversible capacity can be greatly reduced.
Further, when used in a secondary battery, the effect of improving charge / discharge cycle characteristics can be enhanced.

The reason why the charge / discharge characteristics can be improved as described above is presumed as follows.
First, since the heteroatom content is low, it is possible to prevent deterioration of cycle characteristics caused by adsorption with lithium ions, and by using a carbon material having a carbon content of 99.9% or more, good cycleability is achieved. It is thought that the carbon material which has can be obtained.
Second, because the carbon material structure has three-dimensional crosslinkability, even when the number of cycles is increased compared to graphite materials, physical loss such as delamination between carbon layers is unlikely to occur, improving cycleability. Can be considered.
Third, by using a carbon material in which the ratio of the carbon material particle diameter is 1 μm or less is 1% or less of the total carbon material, the decomposition area of the electrolyte solution is reduced by reducing the contact area between the carbon material and the electrolyte solution. It is thought that it becomes possible to suppress this. Here, the proportion of the carbon material particles having a diameter of 1 μm or less is more preferably 0.5% or less, and particularly preferably 0.1% or less. By doing so, the effect of improving the characteristics can be enhanced.

It is preferable that the specific surface area by the BET three point method by nitrogen adsorption of the carbon material of the present invention is 1.0 m ² / g or less. More preferably, it is 0.5 m < ² > / g or less, Most preferably, it is 0.1 m < ² > / g or less. By doing so, the effect of improving the characteristics can be enhanced.

  Here, the shape of the carbon material of the present invention is preferably substantially spherical. By using a substantially spherical one, the contact area with the electrolytic solution can be further reduced.

  The standard for this carbonization condition varies depending on the type of resin used and the amount used, as described above, but generally the rate of temperature increase is preferably about 10 ° C. to 100 ° C./hour. If it is slower than this, the carbonization process takes a long time, so that an oxidation reaction due to oxygen or the like in the atmosphere tends to occur. The discharge efficiency may decrease. If it is earlier than this, it becomes difficult to sufficiently control the resin skeleton by the thermal history, and it may not be possible to fully utilize the merit of the characteristics of the material.

Next, the negative electrode material for secondary batteries of the present invention will be described.
The negative electrode material for secondary batteries of the present invention is characterized by containing the carbon material of the present invention.

  The negative electrode material for a secondary battery of the present invention is not particularly limited. For example, a fluorine-based polymer containing polyethylene, polypropylene, etc., a rubbery polymer such as butyl rubber, butadiene rubber, etc. with respect to 100 parts by weight of the carbon material of the present invention. 1 to 30 parts by weight of an organic polymer binder and an appropriate amount of a viscosity adjusting solvent such as N-methyl-2-pyrrolidone and dimethylformamide are added and kneaded to form a paste-like mixture by compression molding, roll molding, etc. Can be obtained by molding into a sheet shape, a pellet shape or the like. Moreover, it can also obtain by apply | coating shaping | molding the mixture made into the slurry form with the solvent for viscosity adjustments on collectors, such as copper foil and nickel foil.

Next, the nonaqueous electrolyte secondary battery of the present invention will be described.
The nonaqueous electrolyte secondary battery of the present invention is characterized by using the secondary battery negative electrode material of the present invention.

When the above-mentioned negative electrode material for a secondary battery is applied to the nonaqueous electrolyte secondary battery of the present invention, it is not particularly limited.For example, the negative electrode material for a secondary battery is disposed to face the positive electrode material via a separator, A nonaqueous electrolyte secondary battery can be obtained by using the electrolytic solution.
Although it does not specifically limit as a positive electrode material, For example, conductive polymers, such as complex oxides, such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, polyaniline, polypyrrole, etc. can be used. Although it does not specifically limit as a separator, For example, microporous films, such as polyethylene and a polypropylene, a nonwoven fabric, etc. can be used. Although it does not specifically limit as electrolyte solution, For example, what melt | dissolved lithium salt used as electrolyte in a non-aqueous solvent can be used. As the electrolyte, for example, lithium metal salts such as LiClO ₄ and LiPF ₆ , tetraalkylammonium salts, and the like can be used. As the non-aqueous solvent, for example, cyclic esters such as propylene carbonate, ethylene carbonate, and γ-butyrolactone, chain esters such as diethyl carbonate, ethers such as dimethoxyethane, and the like can be used. Moreover, the solid electrolyte which mixed the said salts with polyethylene oxide, polyacrylonitrile, etc. can also be used, for example.

  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, “part” indicates “part by weight”, and “%” indicates “% by weight”.

1. Production of carbon material <Example 1>
(1) Preparation of Resin Composition A resin was prepared by reacting 1000 parts by weight of phenol, 829 parts by weight of 50% aqueous formaldehyde solution, and 10 parts by weight of 30% aqueous ammonia at 100 ° C. for 3 hours. Thereafter, the temperature was raised from 100 ° C. over 5 hours, reached 200 ° C., held for 1 hour, cured, and then pulverized with a vibration ball mill to obtain a resin composition A.
(2) Production of carbon material The cured resin composition A obtained above was heated at 10 ° C./hour between room temperature and 2500 ° C., and after reaching 2500 ° C., held for another 10 hours for carbonization. The carbon material A1 was obtained by processing.
The obtained carbon material A1 was classified and cut using a cross jet mill KJ50 manufactured by Kurimoto Steel Works, thereby obtaining a carbon material A2 having a predetermined particle size distribution.

<Example 2>
(1) Production of carbon material A carbon material A3 having a predetermined particle size distribution is obtained by classifying and cutting the carbon material A1 obtained in Example 1 using a cross jet mill KJ50 manufactured by Kurimoto Steel Works. Got.

<Example 3>
(1) Preparation of composition 1000 parts by weight of phenol, 829 parts by weight of 50% formaldehyde aqueous solution, 10 parts by weight of 30% aqueous ammonia, 100 parts by weight of polyvinyl alcohol, and 1000 parts by weight of water were prepared after an emulsion was prepared by a flask reaction. By curing in a spherical resin cured product. Thereafter, the temperature was raised from 100 ° C. over 5 hours, and after reaching 200 ° C., the resin was further cured for 1 hour to obtain a resin composition B.
(2) Production of carbon material The cured resin composition B obtained above was heated from room temperature to 2500 ° C. at a rate of 10 ° C./hour, and after reaching 2500 ° C., it was kept for another 10 hours and carbonized. Processing was performed to obtain a carbon material B1.

<Comparative Example 1>
(1) Production of carbon material Carbon material A1 was obtained in Example 1.

<Comparative example 2>
(1) Production of carbon material The resin composition A was heated from room temperature to 1000 ° C. at 10 ° C./hour, and after reaching 1000 ° C., the resin composition A was further carbonized by holding for 10 hours. Got.

<Comparative Example 3>
(1) Manufacture of carbon material The carbon material A4 obtained in Comparative Example 2 is classified and cut using a cross jet mill KJ50 manufactured by Kurimoto Steel Works and has a predetermined particle size distribution. A5 was obtained.

2. Evaluation of Resin Composition and Carbon Material The following evaluation was performed on the resin compositions and carbon materials obtained in Examples and Comparative Examples.

(1) Evaluation of carbon content of carbon material The carbon content was measured by a thermal conductivity method using an elemental analysis measuring device “PE2400” manufactured by PerkinElmer.

(2) Evaluation of particle size distribution of carbon material The particle size distribution was measured by a wet method using LA-920 manufactured by Horiba. In the ratio of 1 μm or less, calculation was performed based on the frequency of each particle size.

(3) Measurement of specific surface area of carbon material The specific surface area was measured based on a BET three-point measurement method using nitrogen gas using a specific surface area measuring device “NOVA1200” manufactured by Yuasa Ionics.

3. Evaluation as negative electrode material for secondary battery (1) Production of bipolar coin cell for secondary battery evaluation 10 parts of polyvinylidene fluoride as a binder with respect to 100 parts of carbon material obtained in Examples and Comparative Examples, diluted An appropriate amount of N-methyl-2-pyrrolidone as a solvent was added and mixed to prepare a slurry-like negative electrode mixture. The prepared negative electrode slurry-like mixture was applied to both sides of 18 μm copper foil, and then vacuum-dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut out as a circle having a diameter of 16.156 mm to produce a negative electrode.
The positive electrode was evaluated with a bipolar coin cell using lithium metal. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of lithium perchlorate in a mixed solution of ethylene carbonate and diethylene carbonate having a volume ratio of 1: 1 was used.

(2) Evaluation of charge capacity and discharge capacity Charge conditions were maintained at a constant current of 25 mAh / g until 1 mV and then held for 20 hours, and discharge conditions were set until the current decayed to 1.25 mAh / g or less. . The cut-off potential in the discharge conditions was 2.5 V, and the charge / discharge cycle was repeated up to 100 cycles.

(3) Evaluation of charge / discharge efficiency Based on the value obtained in the above (2), the charge / discharge efficiency was calculated by the following formula.
Charge / discharge efficiency (%) = [discharge capacity / charge capacity] × 100

(4) Irreversible capacity Based on the value obtained in (2) above, the irreversible capacity was calculated by the following formula.
Irreversible capacity (mAh / g) = charge capacity-discharge capacity

(5) Evaluation of charge / discharge cycle Based on the value obtained in the above (2), calculation was performed according to the following formula.
Capacity retention rate (%) = [100th discharge capacity / 10th discharge capacity] × 100

The results of the evaluation are shown in Table 1.

Examples 1 to 3 all have a carbon content in the carbon material of 99.9% or more, and the ratio of carbon material particles having a diameter of 1 μm or less is 1% or less of the entire carbon material. , A negative electrode material for a secondary battery containing the same, and a non-aqueous electrolyte secondary battery using the same, as compared with a comparative example using a carbon material not in this range, has excellent charge / discharge efficiency and irreversible capacity. It became low and showed favorable charge / discharge cycle property.

Claims (3)

A granular carbon material obtained by carbonizing a resin composition , wherein the resin composition contains a phenol resin obtained by reacting a phenol and an aldehyde, and the carbon content in the carbon material There is at least 99.9%, and the ratio of the diameter 1μm or less of the carbon material particles Ri 1% der less of the total carbon material, 0.1 m specific surface area by BET3-point method by nitrogen adsorption of the carbon material carbon material, characterized in der Rukoto below ² / g. A negative electrode material for a secondary battery comprising the carbon material according to claim 1 . A nonaqueous electrolyte secondary battery using the negative electrode material for a secondary battery according to claim 2 .