JPH10241680A - Carbon material composition for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cycle property through high energy density, and enhance safety by using carbon material by carbonizing resin having such structure as a hydroxyl group in phenol resin is esterified for the negative electrode of a lithium ion secondary battery. SOLUTION: A formaldehyde aqueous solution and oxalic acid as a catalyst is added to phenol, so as to react to obtain phenol resin. Benzoic acid is mixed with the phenol so as to esterify. Hexamethylenetetramine is added to the obtained resin, and the same is pulverized and mixed, and is cured under the conditions of about 200 deg.C, for three hours. An obtained cured substance is pulverized, so that its particle size is made to be about 37μm or less. The temperature of the obtained cured substance is raised at the temperature rising speed of about 10 deg.C/minute in an argon atmosphere, and carbonizing treatment is conducted in conditions of about 1000 deg.C, and three hours so as to obtain negative electrode material. The mixture for cell containing obtained carbide of about 90 parts by weight and tetrafluoroethylene, as a binder, of about 10 parts by weight is compression molded, so as to form a negative electrode pellet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery using a carbon material for a negative electrode material.

[0002]

2. Description of the Related Art In recent years, the development of electronic technology has been remarkable. Among them, downsizing and weight reduction of electronic devices are mentioned as required items. Along with this, there is an increasing demand for smaller, lighter, and higher energy densities of batteries as mobile power supplies. Conventionally, aqueous secondary batteries such as lead batteries and Ni-Cd batteries have been mainly used as secondary batteries that are generally used. However, although these aqueous secondary batteries have no problem in cyclability,
It cannot be said that the battery weight and the energy density are sufficiently satisfactory.

Further, a lithium metal secondary battery using lithium or a lithium alloy as a negative electrode material has features of high energy density, low self-discharge, and light weight. However, this secondary battery has a high possibility that lithium will be deposited in the form of a negative electrode in the form of a dendrite during charging as the charge / discharge cycle progresses, and will eventually reach the positive electrode and cause an internal short circuit. Is said to be difficult.

Therefore, a non-aqueous electrolyte secondary battery using a carbon material as a negative electrode material has been proposed. This utilizes the fact that lithium is intercalated / deintercalated between carbon material layers,
Even when the charge / discharge cycle proceeds, no phenomenon such as precipitation of dendritic lithium on the negative electrode is observed, and the battery has a high energy density, is lightweight, and has excellent charge / discharge cycle characteristics.

As the carbon material for a negative electrode material for a lithium ion secondary battery described above, there is a carbon material using graphite described in Japanese Patent Application Laid-Open No. Hei 5-74457. Graphite is characterized by its very good cyclability,
Since the theoretical charge / discharge capacity is 372 mAh / g, there is a disadvantage that a charge / discharge capacity higher than this cannot be expected. In addition, other than the graphite material, JP-A-5-28996, 7-7
A negative electrode material using pitch coke disclosed in Japanese Patent No. 3868 is exemplified. This material is a graphitizable carbon material, but in the region where the firing temperature exceeds 2000 ° C., graphitization proceeds. When it becomes graphite, the charge / discharge capacity is determined. The temperature range before graphitization (1000 to 18)
(00 ° C.), a carbon material having a high charge / discharge capacity is obtained. However, the cyclability is poor, and the tar pitch contains many impurities, which adversely affects battery characteristics.

A carbon anode treated at a low temperature of about 500 ° C. to 700 ° C. is one of the promising candidates for the next generation high capacity carbon anode. 850mA reversible capacity
Exceeds graphite in terms of h / g and capacity per weight. Further, since the treatment is performed at a low temperature, the energy merit is also high. However, the drawback is that the potential is high and the hysteresis of the potential during charge and discharge is large.

Attention has been paid to lithium ion negative electrode materials other than carbon, such as metal oxides disclosed in JP-A-5-166536 and nitrogen compounds disclosed in JP-A-6-290782. However, although the metal oxide has a very large charge / discharge capacity of 8 Ah / g, its control is difficult because the instantaneous discharge amount is very high. In addition, tin oxide, niobium pentoxide, metal nitrogen compounds and the like have attracted attention as materials having extremely high lithium ion intercalation ability. However, since the charge / discharge capacity is extremely high, a large-capacity current flows instantaneously, which is practically dangerous. Some means of controlling it will be needed.

[0008] In order to increase the charge / discharge capacity of a carbon material and decrease the charge / discharge capacity of a metal oxide, a mixture of a carbon material and a metal compound is used. This is intended to reduce the apparent discharge amount by blending the metal oxide with the carbon material. However, simply blending with a carbon material using such a technique cannot control at a micro level, and cannot obtain a carbon material having desired characteristics.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion secondary battery electrode material having a high energy density, good cycleability and high safety. In order to achieve this object, the present inventor has conducted intensive studies, and as a result of using a carbon material obtained by carbonizing a resin having a structure in which hydroxyl groups in a phenol resin are esterified, as a negative electrode material. , High energy density and good cycle characteristics,
It has been found that a highly safe lithium ion secondary battery negative electrode material can be obtained.

[0010]

Means for Solving the Problems The present invention is characterized in that the carbonized material in the carbon material composition is obtained by carbonizing the esterified phenolic resin obtained by esterifying the hydroxyl group in the phenolic resin. The present invention relates to a carbon material composition for a lithium ion secondary battery.

The phenolic resin undergoes etherification between phenolic hydroxyl groups or polymerization between the phenolic hydroxyl group and hydrogen in the side chain of the phenolic resin during carbonization. Generally, the crystallinity is low when an ether bond is formed, while the crystallinity tends to be high in a dehydration reaction in which a carbon-carbon bond is formed. It becomes a low crystalline carbon material. However, the carbon-carbon bond formed by the dehydration-condensation reaction promotes partial crystallization in the carbon process from a micro viewpoint, and causes a reduction in charge / discharge capacity.

That is, by esterifying the hydroxyl group of the phenol resin, it is possible to prevent a condensation reaction between aromatics accompanied by generation of water during carbonization. As a result, the hydrocarbon group in the ester portion acts as a steric hindrance, so that partial crystallization is suppressed even when the heat treatment temperature is increased. Therefore, it has been confirmed that the charge / discharge amount of lithium ions is not limited to 372 mAh / g, which is the theoretical capacity of graphite, and a higher charge / discharge capacity can be achieved.

The carboxyls used in the present invention for esterification include aromatic carboxylic acids such as benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, naphthalenedicarboxylic acid, naphthoic acid and toluic acid, and acetic acid. And aliphatic carboxylic acids such as formic acid, propionic acid, adipic acid, maleic acid, malonic acid, succinic acid and tartaric acid, and anhydrides thereof, but not limited thereto. These may be used alone or in combination of two or more.

The phenols of the phenolic resin include, for example, phenol, orthocresol, metacresol,
Paracresol, 3,5-xylenol, 2,5-xylenol, 3,4-xylenol, 2,6-xylenol,
2,4-xylenol, 2,3-xylenol, bisphenol A, bisphenol F, biphenol, para-tert-butylphenol, paraoctylphenol,
Catechol, resorcin, hydroquinone, naphthol, melamine, etc., but not limited thereto.
These may be used alone or in combination of two or more. As the aldehydes, formaldehyde, paraformaldehyde, acetaldehyde, furfural, benzaldehyde and the like can be used, and they may be used alone or in combination of two or more.

[0015] The reaction catalyst used in the resin synthesis includes:
Acids such as hydrochloric acid, sulfuric acid, formic acid, acetic acid, oxalic acid, paratoluenesulfonic acid, and potassium hydroxide, sodium hydroxide,
Basic catalysts such as lithium hydroxide and barium hydroxide can be used. Further, a surfactant such as benzenesulfonic acid may be used for the purpose of promoting the reaction.

As a method for curing the obtained phenol resin, an acid such as formaldehyde, acetaldehyde, hexamethylenetetramine, epoxy resin or paratoluenesulfonic acid, and a compound having an isocyanate group are added, and the mixture is cured by heating or at room temperature. It can also be done.

The cured product obtained by the above method shall be fired in an atmosphere of an inert gas such as nitrogen, helium, argon or the like, or in a carbon monoxide atmosphere in coke. The firing temperature is 500 ° C. or higher, preferably 800 ° C. or higher, and is not particularly limited.

The thermosetting resin used in the present invention may be modified with aromatic hydrocarbon, metal or the like. Further, in the present invention, before firing, graphite, pitch and a material that can be a carbon material or the like is added and fired, or after firing,
A mixture of graphite, pitch, and a carbide of a material that can be a carbon material may be used.

[0019]

The present invention will be described below with reference to examples. However, the present invention is not limited by the examples. Further, “parts” and “%” shown in Examples and Comparative Examples are all “parts by weight” and “% by weight”.

Example 1 A reaction vessel equipped with a stirrer and a condenser was added with 100 parts by weight of phenol, 60 parts by weight of a 37% formaldehyde aqueous solution, and 1 part by weight of oxalic acid as a catalyst, and reacted to obtain 96 parts by weight of phenol resin A. . This phenolic resin A100
100 parts by weight of benzoic acid was added to 100 parts by weight to perform esterification. To 100 parts by weight of the obtained resin, 10 parts by weight of hexamethylenetetramine was added and pulverized and mixed.
The curing was carried out under the curing conditions of time until the acetone extraction rate became 10% or less. The cured product thus obtained was pulverized to a particle size of 37 μm or less. The obtained cured product was heated at a rate of 10 ° C./min in an argon atmosphere to 1000
C. for 3 hours to obtain a negative electrode material for a lithium ion secondary battery.

90 parts by weight of the carbide obtained by the above method,
A mixture containing 10 parts by weight of tetrafluoroethylene as a binder was compression-molded to a thickness of 20 mm to obtain negative electrode pellets. The cathode material used was a mixture of 84 parts by weight of Li _0.5 Co _0.5 V _0.5 O _2.5 , 10 parts by weight of acetylene black as a conductive agent, and 6 parts by weight of tetrafluoroethylene as a binder. The mixture obtained by mixing these was dried and compression-molded to prepare a positive electrode pellet (20 mmf). 1 as electrolyte
M LiBF ₄ was used, and microporous polypropylene was used as a separator. The separator was impregnated with the electrolyte.

Using the battery obtained in this manner, constant-current charging was performed for 2.5 V under the conditions of an upper limit voltage of 4.2 V and a current of 1 A.
After the time, a constant resistance discharge was performed under the conditions of a resistance of 5Ω and a termination current of 2.75 V, and the charge / discharge cycle was repeatedly performed.

Example 2 100 parts by weight of phthalic acid was mixed with phenolic resin A and esterified. Evaluation was carried out in the same manner as in Example 1 except that 10 parts by weight of hexamethylenetetramine was added to 100 parts by weight of the obtained resin and pulverized and mixed.

Example 3 100 parts by weight of propionic acid was mixed with phenolic resin A and esterified. Evaluation was carried out in the same manner as in Example 1 except that 10 parts by weight of hexamethylenetetramine was added to 100 parts by weight of the obtained resin and pulverized and mixed.

Example 4 Meta-cresol 100 was placed in a reactor equipped with a stirrer and a condenser.
Parts by weight, 37% formaldehyde (52 parts by weight), and oxalic acid (1 part by weight) as a catalyst, and the reaction was carried out.
2 parts by weight were obtained. Benzoic acid is added to this phenol resin B
00 parts by weight were mixed and esterification was performed. Obtained resin 1
To 00 parts by weight, 10 parts by weight of hexamethylenetetramine was added and pulverized and mixed. Thereafter, evaluation was performed in the same manner as in Example 1.

Example 5 Phenol resin B was mixed with 100 parts by weight of phthalic acid and esterified. To 100 parts by weight of the obtained resin, 10 parts by weight of hexamethylenetetramine was added and pulverized and mixed. Thereafter, evaluation was performed in the same manner as in Example 1.

Example 6 Evaluation was conducted in the same manner as in Example 1 except that 100 parts by weight of naphthoic acid was added to phenol resin A and esterification was performed.

Example 7 Bisphenol A10 was placed in a reactor equipped with a stirrer and a cooler.
0 parts by weight, 80 parts by weight of formaldehyde, and 1 part by weight of oxalic acid as a catalyst were reacted. 100 parts by weight of phthalic acid was mixed with the thermosetting resin and esterified.
To 100 parts by weight of the obtained resin, 10 parts by weight of hexamethylenetetramine was added and pulverized and mixed. Thereafter, evaluation was performed in the same manner as in Example 1.

Example 8 Evaluation was performed in the same manner as in Example 1 except that 100 parts by weight of maleic anhydride was added to phenol resin B and esterification was performed.

Example 9 Evaluation was performed in the same manner as in Example 1 except that 100 parts by weight of naphthalenedicarboxylic acid was added to phenol resin B and esterification was performed.

Example 10 In a reaction vessel equipped with a stirrer and a condenser, 100 parts by weight of phenol, 137 parts by weight of a 37% formaldehyde aqueous solution, and 1 part by weight of sodium hydroxide as a catalyst were mixed and reacted.
Phenol resin C was obtained. 100 parts by weight of acetic anhydride was blended with the phenol resin C to perform esterification. Evaluation was performed in the same manner as in Example 1 except that the obtained resin was cured under the curing conditions of 200 ° C. for 3 hours until the acetone extraction ratio became 10% or less.

Example 11 Evaluation was performed in the same manner as in Example 1 except that 100 parts by weight of maleic anhydride was added to phenol resin C and esterification was performed.

Comparative Example 1 100 parts by weight of phenolic resin A and 10 parts by weight of hexamethylenetetramine were added, pulverized and mixed, and cured under a curing condition of 200 ° C. for 3 hours until the acetone extraction ratio became 10% or less. Thereafter, the same procedure as in Example 1 was performed.

Comparative Example 2 A phenol resin C was cured in the same manner as in Example 1 except that the phenol resin C was cured under the conditions of 200 ° C. for 3 hours until the acetone extraction ratio became 10% or less.

[0035]

[Table 1] As can be seen from Table 1, the carbide of the thermosetting resin having a functional group as the carbon skeleton for the negative electrode material exhibited higher charge / discharge characteristic values than the phenol resin carbide having a simple skeleton.

[0036]

As can be seen from the above description, the carbon material obtained by the present invention is a carbon material having high energy density and high safety, and is therefore suitable for a carbon material for a lithium ion secondary battery electrode.

Claims (1)

[Claims] 1. A carbon material for a lithium ion secondary battery, wherein a carbonized material in a carbon material composition is obtained by carbonizing an esterified phenolic resin obtained by esterifying a hydroxyl group in a phenolic resin. Composition.