JPH1131501A - Method of manufacturing electrode for secondary battery, electrode for secondary battery, and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a secondary battery and a secondary battery which recovers a decrease in discharge capacity caused by being left in the air and makes full use of the charge / discharge capacity inherent in an amorphous carbon material. The purpose is to: SOLUTION: A step of preparing an amorphous carbon material and a heat treatment for removing the hydrophilic functional group of the amorphous carbon material in an inert atmosphere or in a vacuum to perform a secondary process of the amorphous carbon material. A method for producing a secondary battery electrode having a process of obtaining a battery electrode material, and an electrode forming process of forming a secondary battery electrode using the secondary battery electrode material; An electrode and a secondary battery using the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode for a secondary battery, an electrode for a secondary battery, and a secondary battery using the same, and more particularly to a method for generating an electromotive force by the entry and exit of ions such as lithium ions. .

[0002]

2. Description of the Related Art In recent years, the use of secondary batteries has been increasingly widespread, and accordingly, demands for higher capacity have been increasing.

[0003] In response to such demands, Ni-C
The measures have been taken by means of increasing the capacity of the secondary battery. As a result, the capacity has been improved to about 175 mAh / g at present.

On the other hand, non-aqueous electrolyte batteries using an alkali metal such as lithium for the negative electrode are widely used as power sources for electronic devices and the like because of their high energy density.

[0005] Recently, research and development of a secondary battery have been particularly advanced. In the case of a secondary battery using lithium as a negative electrode, metal is deposited in a dendrite shape on the negative electrode during overcharging. May affect properties.

Therefore, a non-aqueous electrolyte secondary battery using a carbonaceous material, a doped compound or an alloyed material as a negative electrode instead of using lithium metal for the negative electrode has been proposed.

In this secondary battery, the possibility of dendrite formation is low as compared with a case where lithium metal is used as the negative electrode as it is, and it is considerably improved.

Among these, when graphite is used, lithium is held in the graphite in an ionic state instead of a metallic state by taking a form of a lithium-graphite intercalation compound peculiar to graphite.

As a result, in terms of energy density, a capacity of 372 mAh / g is obtained in the case of the first stage in which lithium ions are held between the layers of graphite.

[0010] This is about 1/10 compared to 3700 mAh / g, which is the value when lithium metal is used as the negative electrode.
However, there is no problem of dendrite when metallic lithium is used for the negative electrode, and the conventional Ni-Cd2
Compared with the secondary battery, the capacity is approximately doubled.

[0011] Recently, attempts have been made to use amorphous carbon obtained by treating an organic substance at a relatively low heat treatment temperature of around 1000 ° C among carbon materials for a negative electrode.

In this case, the capacity varies greatly depending on the organic material used as a raw material, but when a specific starting material is used, a material having a higher capacity of 500 mAh / g or more than that of graphite is obtained. ing.

[0013]

However, when graphite is used, there are the following manufacturing problems.

First, graphite includes natural graphite and artificial graphite. Of these, graphite excavated from a mine is used as natural graphite, but this natural graphite contains impurities such as iron considerably.

For this reason, a treatment for removing impurities is required, but it is still difficult to completely remove the impurities, which is advantageous in terms of cost. However, natural graphite is used for the negative electrode of the secondary battery. In such a case, the characteristics of the electrodes vary.

On the other hand, in the case of artificial graphite, there is not much problem of impurities as found in natural graphite, but at the time of production, a heat treatment temperature of at least about 2800 ° C. is required, so that energy cost is low. It is disadvantageous.

Also, no matter how the starting material is selected,
Obtaining something close to a graphite structure is often difficult.

Further, in both cases of natural graphite and artificial graphite, since they take the form of a lithium-graphite intercalation compound, the composition is limited to C ₆ Li and the energy density is limited to 372 mAh / g. It is.

In the case of an amorphous carbon material, an energy density of 372 mAh / g or more, which is the upper limit of the graphitic material, is obtained, although the reason is not always clear.

However, the amorphous carbon material is 100
Since the treatment is performed at a low temperature of about 0 ° C., the surface and the inside contain many atoms such as hydrogen and nitrogen.

In particular, hydrophilic surface functional groups such as a carboxyl group and a hydroxyl group are formed by the reaction of water with water when carbon is exposed to the air.

As a practical matter, in the manufacturing process, the period from the raw material production to the battery production is exposed to air,
This will cause deterioration of the amorphous carbon material.

Further, the surface functional groups thus formed on the carbon surface cannot be removed by vacuum drying at about 200 ° C., and when used as an electrode of a lithium secondary battery, the migration of lithium in the electrolyte is prevented. And the charge / discharge capacity is reduced.

The present invention has been made in order to solve such a problem of the amorphous carbon material. The present invention has been made in consideration of the secondary battery electrode and the electrode utilizing the inherent capacity of the carbon powder of the amorphous carbon material. An object is to provide a secondary battery.

[0025]

The present invention comprises a step of preparing an amorphous carbon material and a heat treatment for removing the hydrophilic functional group of the amorphous carbon material in an inert atmosphere or in a vacuum. Producing a secondary battery electrode material of an amorphous carbon material; and forming an electrode for forming a secondary battery electrode using the secondary battery electrode material. An electrode for a secondary battery according to such a method and a secondary battery using the same are provided.

With such a configuration, an electrode for a secondary battery and a secondary battery utilizing the inherent capacity of the amorphous carbon material are provided.

[0027]

According to the present invention, there is provided a process for preparing an amorphous carbon material, and removing the hydrophilic functional group of the amorphous carbon material in an inert atmosphere or vacuum. Performing a heat treatment to obtain a secondary battery electrode material of an amorphous carbon material, and an electrode forming process of forming a secondary battery electrode using the secondary battery electrode material. It is a manufacturing method.

With such a configuration, hydrophilic functional groups such as a carboxyl group and a hydroxyl group which may be present on the surface of the carbon of the amorphous carbon material are effectively eliminated, and the reduced charge / discharge capacity of the secondary battery is reduced. Has the effect of restoring.

More specifically, the heat treatment of the amorphous carbon material may be performed in a temperature range of 400 ° C. to 700 ° C. in an inert atmosphere or vacuum. Performing a heat treatment is preferable because the above-mentioned effect can be surely exhibited.

Here, it is preferable that the heat treatment of the amorphous carbon material is performed a plurality of times so that the hydrophilic functional group can be more effectively eliminated.

According to a fourth aspect of the present invention, in the step of preparing the amorphous carbon material, a non-magnetic material obtained by performing a heat treatment at 600 ° C. or more and 1500 ° C. or less in an inert atmosphere or in a vacuum in an inert atmosphere. It is preferable to use a crystalline carbon material.

This is because the amorphous carbon material can be surely obtained by such a treatment. Here, it is preferable that the organic matter contains petroleum pitch, coal pitch or an organic polymer as described in claim 5, and the organic polymer is a phenol resin or an aromatic polyamide as described in claim 6. , An aromatic polyimide or a furfuryl alcohol resin.

This is because such a starting material can surely obtain an amorphous carbon material. Further, as described in claim 7, after the heat treatment in the temperature range of 400 ° C. or more and 700 ° C. or less, it is preferable to further have a step of maintaining the amorphous carbon material in an atmosphere or a vacuum having a dew point of −20 ° C. or less. It is.

This prevents the effect of the reheat treatment from being lost without being exposed to moisture or the like.

In the electrode forming step, the amorphous carbon material may be applied on the metal member.

Further, the present invention described in claim 9 is based on claim 1.
A secondary battery electrode obtained by the method for producing a secondary battery electrode according to any one of Items 1 to 8, and capable of occluding and releasing alkali metal ions.

With such a configuration, an electrode is obtained in which hydrophilic functional groups such as carboxyl groups and hydroxyl groups which may be present on the carbon surface of the amorphous carbon material are removed.

According to a tenth aspect of the present invention, there is provided an electrode for a secondary battery according to the ninth aspect, the other electrode, and the electrode disposed between the one electrode and the other electrode. And a negative electrode, which is an electrode for a secondary battery according to claim 9, comprising:
A secondary battery includes a positive electrode and an electrolyte containing a lithium compound disposed between the negative electrode and the positive electrode.

With such a configuration, an energy density of 372 mAh / g or more, which is the upper limit of the graphite material, can be reliably obtained.

The present invention relates to the use of an amorphous carbon material which can be suitably obtained by subjecting an organic substance to a heat treatment in an inert atmosphere or in a vacuum in a temperature range of 600 ° C. to 1500 ° C. for an electrode of a secondary battery. During storage, atoms such as carbon dioxide, hydrogen, and nitrogen present on the surface and inside are exposed to air and react with oxygen and moisture during storage. This is based on the finding that it is caused by the formation of a group.

According to the study of the present inventors, among these surface functional groups, hydrophilic functional groups such as carboxyl groups and hydroxyl groups existing on the surface are particularly important.

In a secondary battery such as lithium, lithium or the like enters and exits the carbon from the end face of the hexagonal mesh surface of the carbon as the battery is charged and discharged. These functional groups are suitable for closing the entrance. As a result, a phenomenon of charge / discharge capacity is caused.
This is probably because these surface functional groups have a high electron-withdrawing property and easily trap lithium and the like.

The presence of these surface functional groups was confirmed by a neutralization titration or a technique of separating a carbon peak or an oxygen peak by XPS. Further, in the measurement of the thermogravimetric loss and the mass spectrometry, the release of carbon dioxide gas considered to accompany the decomposition of the surface functional group was observed from 200 ° C. to 600 ° C.

Hereinafter, each embodiment of the present invention will be described in detail. (Embodiment 1) In this embodiment, coal pitch, petroleum pitch, novolak type phenol resin, aromatic polyamide (trade name: Kevlar), aromatic polyimide (trade name:
Kapton) and furfuryl alcohol resin were each used as a starting material, and the heat treatment was again confirmed to eliminate surface functional groups.

First, each of the above starting materials was heated to 800 ° C. at a rate of 5 ° C./min in a nitrogen atmosphere, where it was held for 1 hour to obtain an amorphous carbon material.

Next, these amorphous carbon materials were pulverized in an argon atmosphere using alumina balls to obtain powders.

Then, using these powders,
Five cylindrical batteries were manufactured in an atmosphere having a dew point of −30 ° C., and the discharge capacity was measured.

The production of this cylindrical battery is as follows. (1) A powder of an amorphous carbon material is mixed with 10% by weight of ethylene tetrafluoride (PTFE) as a binder to a thickness of 0.1 wt.
It was applied on a 2 mm copper foil to obtain a negative electrode. (2) LiCoO ₂ was applied on a copper foil having a thickness of 0.2 mm to obtain a positive electrode. (3) LiPF was added to an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 1: 1.
₆ was dissolved at 1 mol / l to obtain an electrolytic solution. (4) A porous polypropylene impregnated with an electrolytic solution was sandwiched between the positive electrode and the negative electrode thus obtained, and five roll-in type cylindrical batteries were produced.

Then, after leaving these powders in the air for 2 weeks, five cylindrical batteries were prepared in an atmosphere having a dew point of -30 ° C., and the discharge capacity was measured.

After leaving these powders in the air for 2 weeks, they were subjected to another heat treatment at 600 ° C. for 1 hour in an argon atmosphere. Five batteries were prepared and the discharge capacity was measured.

The average value obtained by measuring the discharge capacity of each battery immediately after the above production is shown in the column immediately after the production in Table 1 below (Table 1). Is shown in the column of the same table after being left for two weeks, and the average value of the discharge capacity of each battery that was left to heat for two weeks was measured again in the column of the same table after the reheat treatment.

[0052]

[Table 1]

From the results of Table 1, it was found that in the present embodiment, the discharge capacity of the secondary battery could be recovered by the heat treatment again.

(Embodiment 2) In this embodiment, a suitable temperature condition for producing an amorphous carbon material was examined.

First, a novolak-type phenol resin was heated at 600 ° C. and 80 ° C. in a nitrogen atmosphere at a rate of 5 ° C./min.
0 ° C, 1000 ° C, 1200 ° C, 1400 ° C, 1500
° C or 1800 ° C, and kept at each temperature for 1 hour to obtain a carbon material.

A powder was prepared using each of these carbon materials in the same manner as in Embodiment 1, a battery was prepared using each powder, and the same discharge capacity was measured.

In the following (Table 2), the average value obtained by measuring the discharge capacity of each battery immediately after production is shown in the column immediately after production. The column after standing for two weeks and the average value of the discharge capacity of each battery which was heat-treated again after standing for two weeks are shown in the column after re-heating in the same table, respectively.

[0058]

[Table 2]

From the results shown in Table 2, it can be seen that in the present embodiment, the discharge capacity of the secondary battery is recovered at 1500 ° C. or less by the second heat treatment. The effect of the recovery is that the heat treatment temperature for obtaining the carbon material is 600 ° C.
It can be seen that the expression occurs even when the amount is reduced to the maximum. In addition,
When the heat treatment temperature for obtaining a carbon material is lower than 600 ° C., a large variation in measured values is considered, which is considered to be caused by the fact that an amorphous carbon material may not be obtained, making evaluation impossible.

Therefore, it can be determined that the discharge capacity of the secondary battery can be recovered by the heat treatment suitably again when the heat treatment temperature for obtaining the carbon material is between 600 ° C. and 1500 ° C.

The same confirmation was performed for coal pitch, petroleum pitch, aromatic polyamide (trade name: Kevlar), aromatic polyimide (trade name: Kapton), and furfuryl alcohol resin. If the heat treatment temperature for obtaining is between 600 ° C. and 1500 ° C., the result that the effect of the heat treatment again can be obtained was obtained.

(Embodiment 3) In this embodiment, a suitable temperature condition for the second heat treatment was examined.

First, a coal pitch was placed in a nitrogen atmosphere at 5 ° C. /
The temperature was raised to 1000 ° C. at a rate of temperature increase of 1 min and maintained for 1 hour to obtain a carbon material.

Next, a powder was prepared using each of the carbon materials in the same manner as in Embodiment 1, a battery was prepared using the powder, and the same discharge capacity was measured.

The discharge capacity of the battery immediately after fabrication was 462 mAh / g on average, and 265 mAh / g after standing in air for 2 weeks.

Then, the carbon material after standing was treated at a treatment temperature of 300 ° C., 400 ° C., 500 ° C., 600 ° C., 700 ° C.
The temperature was set at 800 ° C. or 800 ° C., and another heat treatment was performed in the same manner as in Embodiment 1, and the average value of the discharge capacity of the battery was measured.

The following Table 3 shows the ratio of the average value obtained by measuring the discharge capacity of each battery obtained by heat-treating the battery left for 2 weeks to the average value obtained by measuring the discharge capacity of each battery immediately after fabrication. Shown as a percentage of capacity.

[0068]

[Table 3]

From the results shown in Table 3, in the present embodiment, the recovery ratio of the discharge capacity of the secondary battery by the second heat treatment is preferably restored when the heat treatment temperature is between 400 ° C. and 700 ° C. It can be determined that it can be done.

The same confirmation was conducted for petroleum pitch, novolak type phenol resin, aromatic polyamide (trade name: Kevlar), aromatic polyimide (trade name: Kapton), and furfuryl alcohol resin. When the heat treatment temperature was between 400 ° C. and 700 ° C., the same effect could be obtained.

Further, for the above-mentioned starting materials, when the first heat treatment temperature was changed from 600 ° C. to 1500 ° C. and the heat treatment temperature was again changed from 400 ° C. to 700 ° C., the same capacity recovery effect was confirmed. Was.

The heating rate and time in the above embodiment are merely examples, and in the first heat treatment, it is sufficient to select an appropriate heating rate and the like at which an amorphous carbon material can be obtained. In the second heat treatment step, an appropriate temperature rising rate or the like that can eliminate the functional group may be selected.

In the above, an example in which lithium ions are applied to a cylindrical battery has been described. However, the present invention is also applicable to other alkali metal ions, and variously applicable to other coin-shaped or square batteries. Things.

The temperature at which the carbon material is held before or during the electrode formation after the second heat treatment may be at room temperature as long as the electrode can be formed immediately after the second heat treatment, and the dew point temperature is theoretically the same. -30 ° C, although lower is better
However, the temperature is not limited to −20 ° C., and if the temperature is −20 ° C. or less, even after a certain period of time until the electrodes are formed after the heat treatment again,
This is a level at which the discharge capacity can be practically maintained.

The atmosphere during the heat treatment is not limited to the exemplified inert gas, but may be a vacuum.

[0076]

As described above, according to the structure of the present invention, it is possible to effectively reduce the discharge capacity of the secondary battery due to the fact that the amorphous carbon material as the electrode material is left in the air. It is possible to provide a secondary battery electrode and a secondary battery that are recovered and do not impair the discharge capacity of the secondary battery that the amorphous carbon material can originally carry.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 H01M 10/40 Z (72) Inventor Souji Tsuchiya Matsushita 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Giken Co., Ltd.

Claims (11)

[Claims] 1. A step of preparing an amorphous carbon material, and performing a heat treatment for removing the hydrophilic functional group of the amorphous carbon material in an inert atmosphere or in a vacuum. A method for producing an electrode for a secondary battery, comprising: a step of obtaining an electrode material for a secondary battery; and an electrode forming step of forming an electrode for a secondary battery using the electrode material for a secondary battery. 2. The heat treatment of the amorphous carbon material according to claim 1, wherein the heat treatment is performed on the amorphous carbon material in an inert atmosphere or in a vacuum in a temperature range of 400 ° C. to 700 ° C. A method for manufacturing an electrode for a secondary battery. 3. The method according to claim 1, wherein the heat treatment of the amorphous carbon material is performed a plurality of times. 4. In the step of preparing an amorphous carbon material, an organic substance is heated to 600 ° C. or more in an inert atmosphere or vacuum.
The method for manufacturing an electrode for a secondary battery according to claim 1, wherein an amorphous carbon material obtained by performing a heat treatment at a temperature of 00 ° C. or less is used. 5. The method according to claim 4, wherein the organic substance contains petroleum pitch, coal pitch or an organic polymer. 6. The method according to claim 5, wherein the organic polymer comprises a phenol resin, an aromatic polyamide, an aromatic polyimide or a furfuryl alcohol resin. 7. The method according to claim 2, further comprising, after the heat treatment in a temperature range of 400 ° C. or more and 700 ° C. or less, further holding the amorphous carbon material in an atmosphere having a dew point of −20 ° C. or less or in a vacuum. 2. The method for producing an electrode for a secondary battery according to item 1. 8. The method according to claim 7, wherein in the electrode forming step, an amorphous carbon material is applied on the metal member. 9. A secondary battery electrode obtained by the method for producing a secondary battery electrode according to claim 1 and capable of occluding and releasing alkali metal ions. 10. A secondary battery comprising one of the electrodes for a secondary battery according to claim 9, an other electrode, and an electrolyte disposed between the one electrode and the other electrode. 11. A secondary battery comprising a negative electrode as the electrode for a secondary battery according to claim 9, a positive electrode, and an electrolyte containing a lithium compound disposed between the negative electrode and the positive electrode.