JP2001313035A - Nonaqeuos cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conduction promoting agent which can improve adhesion of an electrode without increasing the volume of binder or decreasing the volume of conduction promoting agent, and to provide a nonaqueous cell using the same. SOLUTION: The conduction promoting agent includes the same volume of fine carbon particles with functional group which dislocates and ionizes in nonaqueous solvent, and fine carbon particles practically without functional group on their surface. A cathode electrode and/or an anode electrode of the nonaqueous cell includes the conduction promoting agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous battery provided with a conductive auxiliary and a positive electrode and / or a negative electrode using the conductive auxiliary.

[0002]

2. Description of the Related Art Electrodes of a lithium secondary battery and a lithium ion secondary battery are usually made of an electrode active material, a conductive auxiliary material for improving the conductivity of the electrode, and a metal foil as a current collector. And a binder bound thereon. When manufacturing an electrode, the adhesion between the electrode material and the current collector is an important factor that affects the performance of the electrode. If the adhesion of the electrode is poor, the durability of repeated charge / discharge is reduced, or the capacity is reduced due to the drop of the electrode material, which causes a micro short circuit.

[0003] The adhesion between the electrode material and the current collector can be improved by increasing the amount of the binder, which is a binder, but the binder does not directly participate in the reaction of the battery and has conductivity itself. Therefore, when the amount of the binder in the entire electrode increases, as a result, the capacity of the battery decreases and the resistance of the electrode increases. Also, it is common practice to add a conductive auxiliary to the electrode material in order to reduce the resistance of the electrode,
For example, as shown in Japanese Patent Application Laid-Open No. 10-306193, when general acetylene black is used as a conductive additive, acetylene black absorbs a binder. Therefore, when the amount of acetylene black increases, the adhesion of the electrode increases. Is reduced.

Recently, lithium secondary batteries using a polymer electrolyte instead of a non-aqueous electrolyte have been developed. By polymerizing the electrolyte, it is expected that the battery can be freely shaped and compact. However, the ionic conductivity of the current polymer electrolyte is at most about 10 ⁻⁴ S / cm, which is about two orders of magnitude smaller than that of the non-aqueous electrolyte. Therefore, a gel electrolyte in which an electrolyte is impregnated in a polymer has been studied. It has been reported that even when the electrolyte is gelled, the conductivity at room temperature exceeds 10 ^-3 S / cm. For example, JY Song et al. Have published a review on this [J. Power Sources, 77 (1999) 183. Patent publications include, for example, JP-A-8-264205. As a gel electrolyte, polyethylene oxide-based,
There have been proposed polyacrylonitrile-based, polymethylmethacrylic-based, polyfukkavinylidene-based copolymers, and copolymers containing these.

[0005] However, the conventional gel polymer electrolyte is characterized in that the polymer matrix contains an electrolytic solution. Although the ionic conductivity is improved as compared with the all solid type polymer electrolyte, the level of the electrolytic solution is still low. When a battery is formed using this electrolyte, the internal resistance of the electrode is large due to the low ionic conductivity of the electrolyte phase, the output is reduced, and it becomes difficult to flow current. We cannot pull out enough. In order to be able to extract the capacitance, it is necessary to improve the ionic conductivity in the electrode and lower the internal resistance.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive auxiliary material capable of improving the adhesion of an electrode without increasing the amount of a binder or reducing the amount of a conductive auxiliary material. A nonaqueous battery provided with a positive electrode and / or a negative electrode using the conductive auxiliary material is provided.

[0007]

The non-aqueous battery according to the present invention is characterized in that the non-aqueous battery contains carbon having a functional group capable of dissociating ions in a non-aqueous solution on its surface.

[0008] A non-aqueous battery according to a second aspect is characterized in that the functional group capable of dissociating ions in a non-aqueous solution is a salt of a sulfonic acid group.

The non-aqueous battery according to claim 3 is characterized in that the salt of the sulfonic acid group is a lithium sulfonate.

A non-aqueous battery according to a fourth aspect is characterized in that the non-aqueous battery contains both carbon having an ion-dissociable functional group on the surface and carbon having no functional group.

[0011] In the nonaqueous battery according to the fifth aspect, the carbon having an ion-dissociable functional group on the surface is fine particles having an average particle diameter of 1 µm or less and / or having an aspect ratio of 50 or less.
It is a fibrous shape having a diameter of 0 or less and a diameter of 20 μm or less.

A non-aqueous battery according to a sixth aspect is characterized in that the content of carbon having ion-dissociable functional groups on the surface is 1 to 30% by weight of the electrode active material.

The non-aqueous battery according to the present invention is characterized in that the electrolyte is a gel-like polymer electrolyte comprising an organic electrolyte solution in which a polymer and a lithium salt are dissolved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive auxiliary used for the electrode for a non-aqueous battery of the present invention contains carbon having on its surface a functional group capable of dissociating ions in a non-aqueous solution in all or a part of the conductive auxiliary. It is characterized by the following.

First, the conductive additive used in the non-aqueous battery of the present invention contains carbon having a surface having a functional group capable of dissociating ions in a non-aqueous solution. Here, the non-aqueous solution means propylene carbonate (PC), ethylene carbonate (E
C), dimethyl carbonate (DMC), diethyl carbonate (DEC), etimemethyl carbonate (EM
C), dimethoxyethane DME) or a simple or mixed solution, as a supporting salt, LiPF ₆ , LiBF ₄ , Li
It is obtained by dissolving ClO ₄ , LiAsF _{6 and the} like. In order to obtain a non-aqueous battery with a higher capacity, it is preferable to use a gel polymer electrolyte composed of an organic electrolyte solution in which a polymer and a lithium salt are dissolved as the electrolyte, and the charge / discharge capacity of the lithium ion polymer secondary battery can be increased.

The ion-dissociable functional groups include, for example, salts of sulfonic acid groups, salts of carboxyl groups, salts of imide groups, and salts of meside groups. In particular, when used for an electrode of a lithium secondary battery or a lithium ion secondary battery, a lithium salt of a sulfonic acid group is desirable. Examples of the carbon having a functional group capable of dissociating ions on the surface include carbon black produced by various methods, natural graphite, various carbons produced by carbonizing organic substances, and the like.

The conductive additive of the present invention contains, in addition to the carbon having the ion-dissociable functional group on the surface thereof, carbon having substantially no functional group on the surface. The proportion of carbon having a functional group capable of ion dissociation on the surface in the conductive additive is 10 to 80% by weight. By setting the content in such a range, the adhesion can be improved while maintaining the conductivity of the electrode. The phrase "having virtually no functional group on the surface" refers to a state in which acetylene black or the like produced by an ordinary synthesis method does not exceed the amount of ion dissociable groups on the surface.

When carbon fine particles are used, the size thereof is preferably 1 nm to 10 μm from the viewpoint of durability and adhesion of the electrode. By setting the size within this range, a network of carbon fine particles is formed between the electrode active materials. And the conductivity of the electrode can be improved. The carbon usable for this purpose does not necessarily need to be fine particles, and may be a fibrous carbon having an ion dissociable group in the surface region. A fibrous carbon having an aspect ratio of 500 or less and a diameter of 20 μm or less may be used. It is preferably used. Further, the content of carbon as a conductive additive is particularly preferably 1 to 30% by weight of the electrode active material.

FIG. 1 shows the concept of another effect other than the adhesion of the present invention for simultaneously solving the improvement of the electron conductivity and the ion conductivity in the electrode. Electrons schematically move on the carbon skeleton and move in the surrounding ionic region. It is considered that the creation of an ionic region around the carbon facilitates the passage of ions, resulting in an improvement in ionic conductivity.

As described above, in the conductive aid used in the non-aqueous battery of the present invention, carbon black having a functional group that dissociates in a non-aqueous solution on the surface is formed by dissociating the salt of the functional group in the electrode material slurry. By doing so, they repel each other and disperse in smaller units.

Normally, acetylene black used as a conductive additive forms secondary particles of about several hundred nm.
Although the binder is absorbed in the pores, the carbon black having a functional group does not absorb the binder because it has good dispersibility and is difficult to form large secondary particles. Therefore, when carbon black having a functional group is used as the conductive additive, the adhesion of the electrode is improved as compared with the case where acetylene black is used in the same amount as the conductive additive.

Although the internal resistance and the polarization phenomenon of an electrode coated with fine particles, such as an electrode of a lithium ion battery, are not well understood, the thickness of the electrode is reduced in order to form an electrode having good response. In addition to controlling shape factors such as (1) speeding up the charge transfer process of the electrode active material, (2)
It is considered important to improve the electron conductivity in the electrode and (3) to improve the ion conductivity in the electrode. In order to reduce the electron conduction resistance, a conductive additive such as acetylene black is usually added even in a solution-based battery. In order to reduce the ion conduction resistance, it is thought that electron conductivity and ionic conductivity can be improved simultaneously by using carbon in which fine particles or fibrous carbon is provided with an ion dissociable group such as lithium sulfonate. investigated.

The conductive auxiliary material of the present invention can be used for a non-aqueous battery and / or a negative electrode to constitute a non-aqueous battery. This will be described with reference to FIG. In a nonaqueous battery, a thin film of a positive electrode (1) and a negative electrode (2), and a separator (3) sandwiched between them, a rolled body is inserted into a battery can (7), and a positive electrode lead ( 4) is welded to the positive electrode side cover (6), the negative electrode lead (5) is welded to the bottom of the battery can, and the inside of the can is filled with a non-aqueous electrolyte.

As the electrolyte of the present invention, a gel polymer electrolyte comprising an organic electrolytic solution in which a polymer and a lithium salt are dissolved can be preferably used. The present invention intends to constitute a novel and high-capacity lithium-ion polymer secondary battery by incorporating fine particles having a lithium-ion dissociable group and / or fibrous carbon into a battery electrode of a gel-like polymer electrolyte. It is. The positive electrode of the lithium ion polymer secondary battery has a configuration in which the gel polymer electrolyte fills the voids of the mixture of the positive electrode active material fine particles and the carbon provided with the ion dissociating group, and the negative electrode has the positive electrode active material as the negative electrode. It is manufactured in the same manner in place of the active material. A thin battery was constructed by sandwiching a separately manufactured gel polymer electrolyte membrane between these positive and negative electrodes. FIG. 3 shows a schematic diagram of the cross section.

[0025]

The present invention will be described with reference to the following examples and comparative examples. Example 1 One embodiment of the present invention will be described by selecting carbon black having a sulfonic acid group on its surface as carbon in the form of fine particles and / or fibrous or both having ion-dissociable groups formed thereon. Note that carbon black having a sulfonic acid group on the surface is obtained by sulfonating carbon black with concentrated sulfuric acid or the like. In the present invention, a sulfonic acid group bonded to carbon is neutralized with lithium hydroxide or the like, and a sufficiently dried lithium sulfonic acid salt is used. Thereafter, this was added with 5% by weight of sulfonated carbon black, 85% by weight of LiCoO ₂ , 10% by weight of polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent. Then, a positive electrode was obtained. Li metal was used for the negative electrode. A quartz glass filter paper impregnated with a 1 M LiPF ₆ propylene carbonate dimethyl carbonate solution (mixing ratio 1: 1) as an electrolytic solution was sandwiched therebetween to form a coin-containing cell. This electrode is shown in Table 1.
As shown in Table 2, the conductivity was almost the same as that of Comparative Example 2, and the adhesion was further improved. The evaluation of electrode adhesion was 1
A 5mm square adhesive tape is stuck on the electrode surface and 200mm /
The measurement was performed by measuring the breaking load when peeled perpendicularly to the electrode surface at a speed of min (FIG. 4). The conductivity was evaluated by pressing a mirror-polished SUS electrode against the electrode surface and measuring the resistance between the SUS electrode and the current collector can. Table 1 shows the results of the evaluation as electrode breaking loads.
It was shown to.

Example 2 2.5% by weight of sulfonated carbon black, 2.5% by weight of acetylene black, 85% by weight of LiCoO ₂ , 10% by weight of polyvinylidene fluoride as a binder, N-methylpyrrolidone as a solvent, and a homogenizer. A coin-shaped cell was formed in the same configuration as in Example 1 by using this positive electrode, which was mixed to form a slurry, applied and dried on an aluminum foil, and used as a positive electrode. Evaluation of adhesion and conductivity was performed by the same method as in Example 1. As shown in Table 1, the conductivity of the electrode was greatly improved as compared with Example 1, and the adhesion of the electrode was almost the same as that of Example 1. In addition, as shown in FIG. 5, charging and discharging could be performed without any problem, and the electrode had satisfactory performance as an electrode.

Comparative Example 1 5% by weight of acetylene black, 85% by weight of LiCoO ₂ , 10% by weight of polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent were mixed with a homogenizer to form a slurry, which was coated on an aluminum foil. It dried and was set as the positive electrode. Li metal was used for the negative electrode. A quartz glass filter paper impregnated with a 1 M LiPF ₆ propylene carbonate-dimethyl carbonate solution (mixing ratio 1: 1) was sandwiched between them to form a coin cell. As shown in Table 1, this electrode had no problem in conductivity, but had poor adhesion. Example 1 above
The resistance and adhesion of the electrodes using the conductive aids obtained in Comparative Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below (electrode breaking load).

[0028]

[Table 1] In the table, the resistance 電極 of the electrode indicates that the resistance is very small. ○ indicates that it can be used as an electrode. The adhesion ◎ of the electrode indicates that the adhesion is very good. ○
Indicates that it can be used as an electrode. Δ indicates that the adhesion is poor.

Example 3 A polymer-electrolyte composite positive electrode containing sulfonated carbon black was prepared by the following method. LiM as positive electrode active material
n204, 60% by weight, sulfonated carbon black 1
0% by weight, 7% by weight of polyethylene glycol diacrylate, 23% by weight of an electrolyte solution, and 0.2% by weight of azoisobutyronitrile were added as high molecular weight monomers and mixed well with stirring. It was applied to an electric conductor and polymerized by heating at 80 ° C. for 1 hour to obtain a positive electrode.
The electrolyte solution used was 1 mol / mol in a mixed solvent of propylene carbonate and ethylene carbonate in a volume ratio of 1: 1.
One liter of LiPF ₆ salt is dissolved. A negative electrode was similarly manufactured using hard carbon as the negative electrode active material instead of the positive electrode active material. The weight ratio of polyethylene glycol diacrylate and the electrolyte solution was prepared in the same manner as described above, and a polymerization initiator benzyldimethyl ketal having a weight ratio of 0.5 was added, followed by ultraviolet polymerization to produce a gel polymer electrolyte membrane. The produced gel electrolyte polymer membrane was sandwiched between the positive electrode and the negative electrode produced earlier, so that the lead could be taken out from each current collector, stored in an aluminum laminate pack, and then sealed to form a thin battery.

Example 4 A positive electrode was prepared in the same manner as in Example 3, except that the positive electrode active material LiMn204 was changed to 60% by weight and the sulfonated carbon black was changed to 5% by weight. A thin battery having substantially the same size as that of Example 3 was manufactured.

Comparative Example 2 A positive electrode, a negative electrode, and a gel electrolyte polymer membrane were prepared in the same manner as in Example 3 except that the sulfonated carbon black was replaced with ordinary acetylene black. Was prepared.

FIG. 6 shows the charge / discharge characteristics of the batteries produced in Examples 3, 4 and Comparative Example 2. After charging 5mA constant current up to 4.2V, constant voltage charging at 4.2V,
The total charging time was 4 hours. This is a summary of the results of the discharge capacity when a constant current discharge is performed from 2 mA to 2 V in the range of 1 mA to 8 mA. As is apparent from the figure, the battery capacity that can be passed at a high current density is greatly increased by replacing acetylene black in the electrode with sulfonated carbon black. As can be seen from Example 3, the amount of sulfonated carbon black is further improved by increasing the amount. However, if the amount is excessively increased, the amount of active material in the electrode is relatively reduced, so that the amount of electricity that can be taken out decreases. Therefore, the amount of carbon having a lithium ion dissociable group molded therein is preferably 5 to 15% by weight.

[0033]

According to the present invention, both a carbon fine particle having a functional group capable of dissociating ions in a non-aqueous solution and a carbon fine particle having substantially no ordinary functional group are mixed, preferably in a ratio of 1: 1. By mixing at a ratio and using it as a conductive aid for electrodes for non-aqueous batteries, the adhesion of the electrodes can be significantly improved without reducing the capacity of the battery or the conductivity of the electrodes. Furthermore, a battery using a gel polymer electrolyte can be used to obtain a high-capacity nonaqueous battery by adopting the configuration of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic view of carbon used in the present invention.

FIG. 2 is a schematic sectional view showing a configuration example of a non-aqueous electrolyte secondary battery.

FIG. 3 is a cross-sectional view of the thin lithium ion polymer secondary battery of the present invention.

FIG. 4 is a conceptual diagram of an adhesion evaluation test.

FIG. 5 is a charge / discharge curve diagram of an electrode (Example 2) produced using the sulfonate-introduced carbon black and acetylene black of the present invention. The evaluation conditions were the same as in Examples 1 and 2.
The current density of 0.28 mA / cm ²
The battery was charged and discharged at a constant current of 4.2 V and a discharge termination voltage of 3.5 V at a constant current.

FIG. 6 is a diagram showing the discharge current density dependence of the discharge capacity of the lithium ion polymer secondary batteries of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Positive side cover 7 Battery can 8 Jig 9 Double-sided tape 10 Electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Mikio Kawai, Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Yuji Tangami, 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa, Nissan Motor Co., Ltd. (72) Inventor Hideaki Horie 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. (72) Inventor Takaaki Abe 2 Takaracho, Kanagawa-ku, Yokohama City, Kanagawa Prefecture Nissan Motor Co., Ltd. (72) Inventor Osamu Shimamura Kanagawa 2 in Takaracho, Kanagawa-ku, Yokohama, Nissan Motor Co., Ltd. (72) Inventor Toshihiro Takekawa 2 in Takaracho, Kanagawa-ku, Yokohama-shi Nissan Motor Co., Ltd. (72) Ryuzo Uemura 2, Takaracho in Kanagawa-ku, Kanagawa Prefecture F-term (reference) in Nissan Motor Co., Ltd. 5H029 AJ03 AK03 AL12 AM03 AM04 AM05 AM07 AM16 BJ02 BJ14 CJ11 CJ22 DJ08 DJ12 DJ15 DJ16 EJ12 HJ00 HJ05 5H050 AA08 BA17 BA18 CA08 CB12 DA02 DA03 DA10 EA24 FA12 FA16 FA17 GA14 GA21 GA22 HA05

Claims (7)

[Claims] 1. A non-aqueous battery, wherein at least one of the positive electrode and the negative electrode contains, as a conductive additive, carbon having on its surface a functional group capable of dissociating ions in a non-aqueous solution. 2. The functional group capable of dissociating ions in a non-aqueous solution is a salt of a sulfonic acid group.
The non-aqueous battery as described. 3. The non-aqueous battery according to claim 2, wherein the salt of the sulfonic acid group is a lithium sulfonate. 4. The non-aqueous battery according to claim 1, wherein the non-aqueous battery contains both carbon having an ion-dissociable functional group on the surface and carbon having no ion-dissociable functional group. 5. The method according to claim 1, wherein the carbon having an ion-dissociable functional group on its surface is in the form of fine particles having an average particle diameter of 1 μm or less and / or fibrous particles having an aspect ratio of 500 or less and a diameter of 20 μm or less. The non-aqueous battery according to claim 1, wherein: 6. The non-aqueous battery according to claim 1, wherein the content of carbon having a functional group capable of dissociating ions on the surface is 1 to 30% by weight of the electrode active material. 7. The non-aqueous battery according to claim 5, wherein the electrolyte is a gel polymer electrolyte composed of an organic electrolyte in which a polymer and a lithium salt are dissolved.