JPH08138676A - Negative electrode material and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte secondary battery with which a high-energy density can be obtained and at the same time which excels in quick charging by obtaining a carbonaceous material having a large negative electrode capacity. CONSTITUTION: A carbonaceous material produced by heating a high-molecular compound having an amide linkage and an aromatic ring is used for a negative electrode material. Particularly, when the carbonaceous material produced by heating the high-molecular compound having constitution in which the amide linkage is connected to the para position of the aromatic ringe, a large negative electrode capacity is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon-based negative electrode material and a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art Recent remarkable advances in electronic technology have made electronic devices smaller and lighter one after another. Along with this, batteries, which are portable power sources, are required to be smaller and lighter and have higher energy density.

Conventionally, an aqueous solution type battery such as a lead battery or a nickel-cadmium battery has been mainly used as a secondary battery for general use. However, although these aqueous solution type batteries can satisfy the cycle characteristics to some extent, they cannot be said to be satisfactory in terms of battery weight and energy density.

Recently, non-aqueous electrolyte secondary batteries using lithium or a lithium alloy as a negative electrode have been actively researched and developed. This battery has the excellent characteristics of high energy density, low self-discharge, and light weight. However, as the charge / discharge cycle progresses, during charging, lithium has a dendrite-like crystal growth from the negative electrode and reaches the positive electrode, resulting in an internal short circuit, which is a major obstacle to practical use. .

On the other hand, a non-aqueous electrolyte secondary battery (so-called lithium ion secondary battery) has been proposed in which a carbon material is used for the negative electrode instead of lithium metal or lithium alloy. This battery utilizes doping / dedoping of lithium between carbon layers for the negative electrode reaction, and even if the charging / discharging cycle proceeds, lithium is not seen to be deposited as dendrites during charging, which is favorable. Exhibits charge / discharge cycle characteristics.

[0006] Carbon materials are roughly classified into graphite with a developed crystal structure and non-graphite with an undeveloped crystal structure. Further, non-graphite is divided into graphitizable carbon material and non-graphitizable carbon material. Among them, as the negative electrode material, the 33rd Battery Symposium Summary P. 83 (1992), the non-graphitizable carbon material is excellent and suitable for practical battery characteristics. Also,
Japanese Unexamined Patent Publication (Kokai) No. 2-66856 describes that among non-graphitizable carbon materials, a carbonaceous material having a specific crystal structure parameter is suitable as a negative electrode material.

[0007]

As described above, the non-aqueous electrolyte secondary battery using the carbonaceous material as the negative electrode greatly exceeds the conventional lead battery and nickel-cadmium battery in terms of energy density. Further, it is superior to the secondary battery using lithium metal or lithium alloy for the negative electrode in terms of cycle characteristics and safety.

However, the so-called Walkman and 8
In many cases, a secondary battery used in a mm video camera or the like is rapidly charged, and it is also necessary to be able to withstand such rapid charging. From the viewpoint of this rapid charging performance, it is hard to say that the non-aqueous electrolyte secondary battery is superior to the nickel-cadmium battery.

Therefore, the present invention has been proposed in view of the above conventional circumstances, provides a negative electrode material having a large negative electrode capacity, and has a high energy density and a non-aqueous electrolysis excellent in rapid charging performance. An object is to provide a liquid secondary battery.

[0010]

[Means for Solving the Problems] In order to achieve the above-mentioned object, as a result of intensive investigations by the present inventors, a carbonaceous material obtained by heat-treating a polymer compound having an amide bond and an aromatic ring was obtained. It has been found that a large negative electrode capacity can be obtained and that the rapid charging performance of the battery can be improved by using it.

The negative electrode material of the present invention has been completed based on these findings, and is a carbonaceous material produced by heat-treating a polymer compound having an amide bond and an aromatic ring. It is characterized by.

Further, the present invention is characterized in that it is a carbonaceous material produced by heat treating raw material fibers obtained by spinning a polymer compound having an amide bond and an aromatic ring.

Further, the polymer compound is characterized in that it has a structure in which an amide bond is bonded to the para position of an aromatic ring.

Further, the polymer compound is characterized in that it comprises only a structure in which the amide bond is bonded to the para position of the aromatic ring.

Further, the non-aqueous electrolyte secondary battery of the present invention is an electrolysis system comprising a negative electrode made of the above carbonaceous material, a positive electrode made of a transition metal complex oxide containing lithium, and an electrolyte dissolved in a non-aqueous solvent. It is characterized by having a liquid.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of the present invention will be described below.

The present invention is applied to a non-aqueous electrolyte secondary battery (lithium ion secondary battery) using a carbonaceous material for the negative electrode.

In the present invention, in order to improve the rapid charging performance of such a non-aqueous electrolyte secondary battery, it is produced by heat-treating a polymer compound having an amide bond and an aromatic ring as a negative electrode material. A carbonaceous material will be used.

Examples of the polymer compound having an amide bond and an aromatic ring include aromatic polyamide compounds such as polymetaphenylene isophthalamide, polyparaphenylene terephthalamide and polyparabenzamide, and substituted compounds thereof. Preference is given to homopolymers, copolymers or mixtures of the compounds. Among them, those having a structure in which the amide bond is bonded to the para position of the aromatic ring are preferable, and those having only a structure in which the amide bond is bonded to the para position of the aromatic ring are more preferable, such as polyparaphenylene terephthalamide. . Also,
A polymer compound having an amide bond bonded to the para position of an aromatic ring and a polymer compound having an amide bond bonded to the meta position of an aromatic ring may be mixed and used. Commercial products of such polymer compounds include Nomex, Kevlar (manufactured by DuPont), Conex, Technora (manufactured by Teijin).

The above-mentioned polymer compound has different properties as a polymer, that is, crystallinity and orientation, depending on its synthesis method, which affects the negative electrode performance of the finally obtained carbonaceous material. Examples of methods for synthesizing the polymer material include low temperature solution polymerization and interfacial polymerization.

In addition to the fibrous form obtained by the spinning process, the polymer compound has various forms such as a paper form, a molded body, a pulp form and a thread form, and any form can be used. However, when a fibrous material is used, a carbonaceous material having a large negative electrode capacity can be obtained.

As the carbonaceous material as the negative electrode material, such a polymer compound is used, for example, in a nitrogen stream at a temperature of 300 to 7.
After the carbonization operation at 00 ° C, the temperature is raised in a nitrogen stream at a rate of 1 to 20 ° C / min, and the maximum temperature is 900 to 1500.
It is generated by heat treatment under the conditions of 0 ° C. and a holding temperature of 0 to 5 hours. At this time, the carbonization operation may be omitted depending on the case.

The carbonaceous material (non-graphitizable carbon material) thus produced has a large negative electrode capacity and can impart a high energy density to the battery and improve the rapid charging performance of the battery.

It is considered that such a carbonaceous material having excellent negative electrode characteristics can be obtained by heat-treating a polymer compound having an amide bond and an aromatic ring for the following reason.

First, the above-mentioned polymer compound has characteristics that it has high heat resistance and flame retardancy because of its high decomposition temperature. Therefore, in such a heat treatment step,
Most of them adopt a so-called solid-phase carbonization process in which carbonization proceeds without melting. It is speculated that this is one of the reasons why a carbonaceous material having a large negative electrode capacity is produced.

In particular, a polymer compound having an amide bond only in the para position of an aromatic ring has higher heat resistance than a polymer compound having an amide bond only in the meta position of an aromatic ring. Since a more ideal solid-phase carbonization process is adopted, a carbonaceous material having excellent negative electrode characteristics can be produced.

Incidentally, the copolymer having both the structure in which the amide bond is bonded to the para position of the aromatic ring and the structure in which the amide bond is bonded to the meta position of the aromatic ring are only the structure in which the amide bond is bonded to the para position of the aromatic ring. It shows intermediate properties between a polymer compound consisting of and a polymer compound consisting of a structure in which an amide bond is bonded to the meta position of an aromatic ring.

Further, when such a polymer compound has a fibrous shape, it is carbonized while maintaining its form, and during carbonization, the volatilized organic components are likely to escape to the outside. Micropores from which organic components have been removed
Since it becomes a micro reaction site that can be dedoped, a carbonaceous material having a larger negative electrode capacity can be obtained.

In order to obtain a carbonaceous material having excellent negative electrode characteristics, it is important that the maximum temperature reached in the heat treatment step is 900 to 1500 ° C. as described above. If the maximum temperature reached by the heat treatment is lower than this range, a carbonaceous material having a large irreversible capacity that is not discharged even if charged is generated. Moreover, when the maximum temperature is set higher than this range, the characteristic structure for the non-graphitizable carbon material to exhibit a high capacity is impaired.

The carbonaceous materials produced by heat-treating the above-described polymer compounds all have a high capacity, but among them, as described in JP-A-2-66856, the powder X-ray diffraction method is used. Those satisfying the conditions that the required (002) plane spacing is 0.37 nm or more, the true density is 1.70 g / cc or less, and that there is no oxidation exothermic peak at 700 ° C. or higher in DTA (differential thermal analysis) It is suitable.

The above carbonaceous material is actually crushed.
After the classification, the material is used as a negative electrode material for a battery, and this pulverization operation may be performed at any time before or after the carbonization operation, the high temperature heat treatment, or during the temperature rising process.

However, the carbonaceous material powder used for the negative electrode material preferably has a particle diameter of 1 μm or more. When a carbonaceous material containing a large amount of particles having a particle size of less than 1 μm is used, the irreversible capacity that is not discharged even when charged at the beginning of the charge / discharge cycle increases. The reason for this is not clear,
It is considered that particles having a particle diameter of less than 1 μm have a large specific surface area, and thus have a large reaction area for causing a side reaction with the electrolytic solution.

The upper limit of the particle diameter of the carbonaceous material varies depending on the size and structure of the battery to which it is applied, and is set appropriately. For example, in a cylindrical battery, a spiral electrode structure in which strip electrodes are wound in multiple layers is adopted. In this case, in order to reduce the size of the battery, a separator that is as thin as possible is used, and the carbonaceous material preferably has a particle size that does not exceed the thickness of the separator. Also, in the case of a large battery, there is not much restriction on the large particle size side,
The choice of particle size is wide.

The non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode made of the above carbonaceous material, a positive electrode made of a transition metal composite oxide containing lithium, and an electrolyte dissolved in a non-aqueous solvent. It is configured to have an electrolytic solution.

Since the negative electrode has a high capacity, the positive electrode preferably contains a sufficient amount of Li corresponding thereto, for example, the general formula LiMO ₂ (where M is Co, N
represents at least one of i. A lithium-transition metal composite oxide composed of lithium and a transition metal represented by the formula (1) or an intercalation compound containing Li is suitable.

Specifically, in a steady state (for example, after repeating charging / discharging about 5 times), 2 g / g of the negative electrode carbonaceous material is used.
It is necessary to contain Li corresponding to a charge / discharge capacity of 50 mAh or more, preferably Li corresponding to a charge / discharge capacity of 300 mAh or more, and more preferably Li corresponding to a charge / discharge capacity of 330 mAh or more. preferable.

However, it is not always necessary to supply all the Li from the positive electrode material, and the important point is that the carbonaceous material 1 is contained in the battery system.
It suffices that Li corresponding to a charge / discharge capacity of 250 mAh or more per g is present. The amount of Li in the battery system is measured by examining the discharge capacity of the battery. On the other hand, the non-aqueous electrolytic solution is prepared by appropriately combining an organic solvent and an electrolyte. As the organic solvent and the electrolyte, any of those usually used in this type of non-aqueous electrolyte secondary battery can be used.

For example, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4- Methyl-1,3-
Dioxolane, sulfolane, methylsulfolane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and the like can be used.

The electrolyte is LiClO ₄ , LiAs.
F ₆ , LiPF ₆ , LiBF ₄ , LiB (C
₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, L
iN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ ,
LiCl, LiBr, etc.

In a battery, the positive electrode made of the positive electrode active material, the negative electrode made of the negative electrode active material and the non-aqueous electrolyte are housed in, for example, an iron battery can, and the battery can and the battery lid are caulked and hermetically sealed. Consists of The positive electrode and the negative electrode are connected to the battery lid and the battery can by a lead member, respectively, and are energized from the outside through the battery lid and the battery can and the lead member. Note that such a battery may be provided with a current interrupting mechanism that interrupts the current in the battery system in response to an increase in the internal pressure of the battery when an abnormality such as overcharging occurs, thereby improving safety.

[0041]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 A carbonaceous material as a negative electrode material was synthesized as follows.

Dry spinning was performed from a liquid crystal solution in which a polymer of polyparaphenylene terephthalamide was dissolved in concentrated sulfuric acid to obtain a raw material fiber. A carbonaceous material was produced by filling 10 g of this raw material fiber in a crucible, holding it at a temperature of 500 ° C. for 5 hours in a nitrogen stream, and further raising the temperature to 1200 ° C. and heat-treating it for 1 hour. Then, this carbonaceous material was crushed into a powder.

Example 2 A carbonaceous material as a negative electrode material was synthesized as follows.

A raw material fiber was obtained by dry spinning from a liquid crystal solution prepared by dissolving a copolymer of polyparaphenylene terephthalamide and polymetaphenylene isophthalamide in concentrated sulfuric acid. 10 g of this raw material fiber was filled in a crucible and kept at a temperature of 500 ° C. for 5 hours in a nitrogen gas stream.
A carbonaceous material was produced by heating to 0 ° C. and heat-treating for 1 hour. Then, this carbonaceous material was crushed into a powder.

Example 3 A carbonaceous material as a negative electrode material was synthesized as follows.

Dry spinning was carried out from a liquid crystal solution in which a polymer of polymetaphenylene isophthalamide was dissolved in concentrated sulfuric acid to obtain a raw material fiber. A carbonaceous material was produced by filling 10 g of this raw material fiber in a crucible, holding it at a temperature of 500 ° C. for 5 hours in a nitrogen stream, and further raising the temperature to 1200 ° C. and heat-treating it for 1 hour. Then, this carbonaceous material was crushed into a powder.

Example 4 A carbonaceous material as a negative electrode material was synthesized as follows.

A 10 g crucible was filled with a polymer of polyparaphenylene terephthalamide, and the temperature was 50 in a nitrogen stream.
The carbonaceous material was produced by maintaining the temperature at 0 ° C. for 5 hours, further raising the temperature to 1200 ° C. and heat-treating for 1 hour. Then, this carbonaceous material was crushed into a powder.

Example 5 A carbonaceous material as a negative electrode material was synthesized as follows.

10 g of a polymer of polymetaphenylene isophthalamide was charged into a crucible, and the temperature was adjusted to 50 at a nitrogen stream.
The carbonaceous material was produced by maintaining the temperature at 0 ° C. for 5 hours, further raising the temperature to 1200 ° C. and heat-treating for 1 hour. Then, this carbonaceous material was crushed into a powder.

Comparative Example 1 A carbonaceous material as a negative electrode material was synthesized as follows.

0.5 parts by weight of 85% phosphoric acid and 10 parts by weight of water were mixed with 100 parts by weight of furfuryl alcohol,
A viscous polymer [furfuryl alcohol resin (PFA)] was obtained by heating on a hot water bath for 5 hours. The polymer solution was adjusted to pH 5 with 1N sodium hydroxide, and residual water and unreacted alcohol were removed by vacuum distillation.

The furfuryl alcohol resin thus obtained was carbonized in a nitrogen stream at a temperature of 500 ° C. for 5 hours, and then at a temperature of 1
A carbonaceous material was produced by heating to 200 ° C. and heat-treating for 1 hour. Then, this carbonaceous material was crushed into a powder.

With respect to the carbonaceous materials thus produced in Examples 1 to 5 and Comparative Example 1, the negative electrode capacity, capacity loss and rapid charging performance were measured as follows.

First, a working electrode was made of the produced carbonaceous material.

Immediately before the preparation of the negative electrode mix in the next step, the carbonaceous material was heated in an Ar atmosphere at a heating rate of about 30 ° C. /
Pre-heat treatment was performed under the conditions that the temperature reached, the temperature reached 600 ° C., and the temperature reached was held for 1 hour. Then, to this carbonaceous material, polyvinylidene fluoride in an amount equivalent to 10% by weight as a binder and dimethylformamide as a solvent were mixed and dried to prepare a negative electrode mix. 3 out of this negative mix
Diameter of 7 mg with Ni mesh as the current collector is 1
A working electrode was prepared by molding into a pellet of 5.5 mm.

As shown in FIG. 1, the working electrode thus prepared was used as an upper electrode can 4 containing the working electrode 1.
And a lower electrode can 5 accommodating the counter electrode 2 into a separator 3
It was incorporated into the evaluation cell in the form of being laminated via. The material of each member is as follows.

Cell configuration of evaluation cell Cell type: coin-type cell (diameter 20 mm, thickness 2.5)
mm) Counter electrode: Li metal Separator: Polypropylene porous membrane Electrolyte solution: LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent in which propylene carbonate (PC) and dimethoxyethane (DME) were mixed at a volume ratio of 1: 1. Then, the evaluation cell was intermittently charged and discharged, and the capacity and capacity loss were measured. The charging and discharging conditions are as follows. In this test method, strictly speaking, the process of doping the carbonaceous material with lithium is discharging, not charging, and the process of dedoping lithium is charging. However, here, for convenience, the doping process is called charging and the dedoping process is called discharging in accordance with the actual state of the actual battery.

[0060] Charging (doping process of the lithium): After 1 hour charging at a constant current of 1mA per cell, the charging / pause cycle such pause 2 hours, the potential change at the time of rest (time) ^-1/2 Until the equilibrium potential estimated by plotting is 3 mV (Li / Li ⁺ ),
I went repeatedly.

Discharge (lithium dedoping process): A discharge / pause cycle in which a constant current of 1 mA per cell is discharged for 1 hour and then a rest is carried out for 2 hours, when the terminal voltage is 1.
This was repeated until it reached 5V.

Table 1 shows the amount of discharged electricity measured in this manner as capacity, and the value obtained by subtracting the amount of discharged electricity from the amount of charged electricity as capacity loss.

It is known that the amount of discharged electricity obtained by this test method is smaller than the amount of charged electricity obtained by using any negative electrode material. The value obtained by subtracting the amount of discharged electricity from the amount of charged electricity, that is, the capacity loss that is not discharged even when charged is an important value for evaluating the negative electrode material in a practical battery.

Next, with respect to the evaluation cell, 10 mV (Li
/ Li ⁺ ) was charged for 1 hour and then discharged at a constant current of 1 mA per cell until the terminal voltage became 1.5V.

The quick charge performance was evaluated by obtaining the ratio of the discharged electricity quantity measured after this rapid charge to the discharged electricity quantity measured after the above intermittent charge.

Table 1 shows the measurement results of the quick charge performance together with the measurement results of the capacity and the capacity loss.

[0067]

[Table 1]

As can be seen from Table 1, the carbonaceous materials of Examples 1 to 5 produced by heat-treating a polymer compound having an amide bond and an aromatic ring were obtained by heat-treating a furfuryl alcohol resin. The capacity is larger than that of the produced carbonaceous material of Comparative Example 1.

In particular, the carbonaceous materials of Examples 1 to 3 produced by heat-treating raw material fibers obtained by dry spinning a polymer compound having an amide bond and an aromatic ring were dry-spun. As compared with the carbonaceous materials of Examples 4 and 5 produced by directly heat-treating a polymer compound that is not present, the capacity is large and the rapid charging performance is excellent.

Further, among the carbonaceous materials of Examples 1 to 3, Example 1 produced by heat-treating fibers of a polymer compound having a structure in which an amide bond is bonded to the para position of an aromatic ring The carbonaceous material of Example 2 has a higher capacity than the carbonaceous material of Example 3 produced by heat-treating fibers of a polymer compound having an amide bond bonded to the meta position of an aromatic ring. Is big.

Further, comparing the carbonaceous materials of Example 1 and Example 2, the carbonaceous material produced by heat-treating a polymer compound fiber having only a structure in which an amide bond is bonded to the para position of an aromatic ring is produced. The carbonaceous material of Example 1 was produced by heat treating a fiber of a polymer compound having both a structure in which an amide bond was bonded to a para position of an aromatic ring and a structure in which an amide bond was bonded to a meta position of an aromatic ring. The capacity is larger than that of the carbonaceous material of Example 2.

From the above, a carbonaceous material produced by heat-treating a polymer compound having an amide bond and an aromatic ring, particularly a polymer compound having a structure in which the amide bond is bonded to the para position of the aromatic ring It was found that the carbonaceous material produced by heat-treating the raw material fiber obtained by dry spinning is suitable as the negative electrode material of the non-aqueous electrolyte secondary battery.

[0073]

As is apparent from the above description, the carbonaceous material produced by heat-treating a polymer compound having an amide bond and an aromatic ring has a large negative electrode capacity. In particular, a carbonaceous material produced by heat-treating a raw material fiber obtained by dry-spinning a polymer compound having a structure in which an amide bond is bonded to the para position of an aromatic ring has a particularly large negative electrode capacity. Therefore, by using such a carbonaceous material, it is possible to obtain a high energy density and to obtain a non-aqueous electrolyte secondary battery excellent in rapid charging performance. Therefore, the present invention greatly contributes to the improvement of the practicality of various electronic devices in which a battery is required to have a quick charge performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an evaluation cell used for characteristic evaluation of a negative electrode material of the present invention.

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Claims (5)

[Claims] 1. A negative electrode material, which is a carbonaceous material produced by heat-treating a polymer compound having an amide bond and an aromatic ring. 2. The negative electrode material according to claim 1, wherein the raw material fiber obtained by spinning a polymer compound having an amide bond and an aromatic ring is a carbonaceous material produced by heat treatment. . 3. The negative electrode material according to claim 1, wherein the polymer compound has a structure in which an amide bond is bonded to a para position of an aromatic ring. 4. The negative electrode material according to claim 3, wherein the polymer compound has only a structure in which an amide bond is bonded to a para position of an aromatic ring. 5. A negative electrode made of a carbonaceous material produced by heat-treating a polymer compound having an amide bond and an aromatic ring, a positive electrode made of a transition metal composite oxide containing lithium, and an electrolyte in a non-aqueous solvent. A non-aqueous electrolyte secondary battery, which is configured to have a dissolved electrolyte solution.