JP2002042886A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery free from the problem of generating a large short circuit current due to the temperature rise of the battery caused by internal short circuit or the like, which leads to further rise of battery temperature by the heating to increase the short circuit current. SOLUTION: This battery is provided with an electrode containing an electron conductive material wherein resistance rises following the rise of temperature, and a conductive assistant. The electron conductive material of the electrode is composed of a conductive filler and crystalline resin, and the fusing point of the crystalline resin is set within a range of 90-160 deg.C. The conductive assistant contains a plurality of assistants of different grain diameters. The ratio of the conductive filler included in the electron conductive material is set to 40-70 pts.wt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery, and more particularly, to a battery using an electrode whose resistance increases with an increase in temperature.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, batteries used as power supplies have been increasing in capacity and output density. As a battery satisfying these requirements, a lithium ion secondary battery has attracted attention. This lithium ion secondary battery has the advantage of high energy density, but requires sufficient measures for safety due to the use of a non-aqueous electrolyte.

[0003] As a countermeasure against the above-mentioned safety, for example, Japanese Patent Application Laid-Open No. 4-328278 discloses a method in which a safety valve is provided at a positive electrode cap portion of a cylindrical battery, and a rise in internal pressure is released by the safety valve. In Japanese Patent Application Laid-Open No. 7-220755, when an external short circuit occurs, the resistance rises in response to the heat generated by the short circuit and the current is cut off.
TC (Positive Temperature C)
A method of incorporating an effective device into a battery is disclosed. For example, by designing the PTC element to operate when the temperature of the battery reaches 90 ° C. or more due to an external short circuit, the PTC element can be used as a safety component that operates first when the battery is abnormal.

Also, when a short circuit occurs inside the lithium secondary battery and the temperature rises, the polyethylene or polypropylene separator disposed between the positive electrode and the negative electrode softens or melts, thereby blocking the pores of the separator. As a result, there is a method in which the non-aqueous electrolyte contained in the separator is extruded or sealed to lower the ionic conductivity of the separator portion and attenuate the short-circuit current.

[0005] Further, the step of manufacturing the above-mentioned lithium ion secondary battery includes, for example, forming a substrate such as a copper foil serving as a current collector on a base material.
A step of applying a negative electrode active material such as graphite, a slurry containing a binder such as PVDF (polyvinylidene fluoride) and a solvent, and drying to form a thin film to produce a negative electrode. Similarly, aluminum as a current collector It comprises a step of forming a thin film on a base material such as a foil to produce a positive electrode, and a step of assembling them. Here, the positive electrode includes, for example, a positive electrode active material such as LiCoO 2, a binder, and a conductive auxiliary. The conductive additive is used to increase the electron conductivity of the positive electrode when the electron conductivity of the positive electrode active material is poor. For example, carbon black (eg, acetylene black) and graphite (eg, artificial graphite KS-6: Lonza).

[0006]

However, these conventional lithium secondary batteries have the following problems. (1) When the safety valve operates, moisture in the atmosphere enters the inside of the battery, and if lithium exists in the negative electrode, an exothermic reaction may occur. (2) Although the PTC element has no adverse effect due to the operation of shutting off the external short circuit, when the short circuit occurs and the temperature rises, the increase in the short circuit current cannot be suppressed. (3) When the separator is separated from the heat generating portion, the separator does not always melt. In addition, when the temperature becomes higher than the melting temperature of the separator, the separator flows and the function of electrically insulating the positive and negative electrodes is lost, resulting in a short circuit. (4) In the conventional configuration of the positive electrode and the negative electrode, when the temperature rises due to an internal short circuit or the like, a large short-circuit current is generated. Therefore, the heat generated further increases the battery temperature and further increases the short-circuit current.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. In the case of using an electrode whose resistance rises with a rise in temperature, the temperature rises due to an internal short-circuit and a large short-circuit current is generated. It is another object of the present invention to provide a highly safe and high-performance battery capable of suppressing an increase in short-circuit current even if the temperature of the battery further rises due to this heat generation.

[0008]

A first battery according to the present invention comprises an electrode comprising an active material layer containing an active material, an electron conductive material and a conductive auxiliary in contact with the active material, The electronic conductive material has a conductive filler and a crystalline resin, and the melting point of the crystalline resin is in a range of 90 ° C to 160 ° C.

In a second battery according to the present invention, the electrode of the battery according to the first invention contains a plurality of conductive additives having different particle diameters.

In a third battery according to the present invention, the electrode of the battery according to the first invention is composed of a positive electrode and a negative electrode, and at least one of the electrodes is provided with a conductive auxiliary agent substantially equivalent to the solid component of the active material layer. It is contained at a ratio of 0.1 to 10% of the total weight.

A fourth battery according to the present invention is the battery according to the first invention, wherein the proportion of the conductive filler contained in the electronic conductive material of the electrode of the battery of the first invention is 40 parts by weight to 70 parts by weight.

In a fifth battery according to the present invention, the conductive filler of the electrode of the battery of the first invention is made of a carbon material or a conductive non-oxide.

In a sixth battery according to the present invention, the average particle size of the conductive auxiliary of the electrode of the battery of the first invention is set to 1/1000 to 1/10 of the average particle size of the electronic conductive material. Things.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a schematic cross-sectional view of a main part of a battery according to a first embodiment for carrying out the present invention. In the drawing, 1 is a positive electrode, 2 is a negative electrode, and 3 is provided between the positive electrode 1 and the negative electrode 2. Separator, 4 is a positive electrode current collector, 5 is a negative electrode current collector, 6 is a positive electrode active material layer, 7 is a negative electrode active material layer, 8 is a positive electrode active material, 9 is an electron conductive material,
0 is a conductive additive, and 11 is a binder.

In this battery, the electrode comprises a positive electrode 1 and a negative electrode 2. The positive electrode 1 has a positive electrode active material layer 6 formed on the surface of a positive electrode current collector 4 made of a metal film such as aluminum. Is formed by forming a negative electrode active material layer 7 formed by molding a negative electrode active material such as carbon particles with a binder on the surface of a negative electrode current collector 5 made of a metal film such as copper. The separator 3 holds, for example, an electrolytic solution containing lithium ions. For the solid electrolyte type lithium battery, an ion conductive solid polymer is used. For the gel electrolyte lithium battery, an ion conductive gel solid solid is used. Use molecules. Further, the positive electrode active material layer 6 of this battery
Is formed by bonding a positive electrode active material 8, an electron conductive material 9, and a conductive auxiliary agent 10 with a binder 11, and the total amount of the electron conductive material 9 and the conductive auxiliary agent 10 is It is in the range of 1 to 20 parts by weight per 100 parts by weight of substance 8.

The positive electrode active material 8 has low conductivity,
The positive electrode active material 8 is formed by the electron conductive material 9 and the conductive auxiliary agent 10.
And the current collector 4 is electrically connected. The electron conductive material 9 having a large particle size forms a fundamental path of electron conduction, and the conductive auxiliary agent 10 having a small particle size is dispersed throughout the periphery of the positive electrode active material 8 and collected from every corner of the positive electrode active material 8. It is charging.

Further, the electronic conductive material 9 contains a conductive filler and a crystalline resin, and has a temperature of 90.degree.
It has a so-called PTC characteristic in which the positive rate of change of the resistance value becomes large near the 60 ° C. range.

Examples of the conductive filler include a carbon material,
Materials such as conductive non-oxides can be used.
As the carbon material, for example, carbon black, graphite, carbon fiber, metal carbide, and the like can be used. Examples of the carbon black include acetylene black, furnace black, lamp black, and the like. Further, as the conductive non-oxide, for example, a metal carbide, a metal nitride, a metal silicide, a metal boride, and the like can be used. As the metal carbide, for example, TiC, Z
rC, VC, NbC, TaC, Mo ₂ C, WC, B ₄ C,
Cr ₃ C _{2 and the} like. Metal nitrides include, for example, TiN, Z
There are rN, VN, NbN, TaN, Cr ₂ N and the like, and metal borides include, for example, TiB ₂ , ZrB ₂ , NbB ₂ , Tb
aB ₂ , CrB, MoB, WB and the like.

The crystalline resin includes, for example, high density polyethylene (melting point: 130 ° C. to 140 ° C.), low density polyethylene (melting point: 110 ° C. to 112 ° C.), polyurethane elastomer (melting point: 140 ° C. to 160 ° C.), Polymers such as polyvinyl chloride (melting point: about 145 ° C.), which have melting points in the range of 90 ° C. to 160 ° C.

In the electron conductive material 9, the temperature at which the function of the PTC is exhibited depends on the melting point of the crystalline resin contained in the electron conductive material 9. Therefore, by changing the material of the crystalline resin, the function of the PTC is improved. The developing temperature is 90 ° C. to 16
It is possible to adjust the temperature to between 0 ° C.

The PTC characteristic may be a reversible material that returns to the original resistance value when the temperature is lowered after the function of the PTC has been developed once, or may have no reversibility.

The temperature at which the function of the PTC is developed is 90 ° C.
Although the following is preferable from the viewpoint of ensuring safety, the resistance value of the electrode increases in a temperature range where the battery can be normally stored or used. Performance degradation occurs.
If the temperature at which this PTC function is developed exceeds 160 ° C., the internal temperature of the battery will rise to this temperature, which is not preferable from the viewpoint of safety. Therefore, in the electronic conductive material 9, the temperature at which the function of PTC is developed is 90.
Design to be in the range of ° C to 160 ° C. Since the temperature at which the function of the PTC is developed depends on the melting point of the crystalline resin, a crystalline resin having a melting point in the range of 90 ° C to 160 ° C is selected.

In the electron conductive material 9, the magnitude of the resistance of the electrode in a normal state, that is, before the PTC function is developed, depends on the electron conductive material 9 and the conductive auxiliary agent 10 with respect to the entire positive electrode active material layer 6. Can be adjusted by changing the ratio. In the electronic conductive material 9, the crystalline resin contained therein softens, melts, and expands in volume, thereby increasing its own resistance value, thereby exhibiting the function of PTC.

In the positive electrode 1 shown in FIG. 1, since the electron conductive material 9 itself contained in the positive electrode active material layer 6 has PTC characteristics, the temperature of the positive electrode 1 is lower than the PTC temperature in the electron conductive material 9.
When the temperature is higher than the temperature at which the function of (1) is developed, the resistance value of the positive electrode active material layer 6 increases. In addition, current collection in small details, which is difficult only with the electronic conductive material, is performed by the added conductive assistant 10. Thereby, the electronic resistance of the electrode is reduced, and the battery characteristics such as charge and discharge characteristics are improved.

In the present embodiment, the positive electrode active material layer 6 is composed of the positive electrode active material 8, the electron conductive material 9, and the conductive auxiliary agent 10.
The example having the binder and the binder 11 has been described as an example, but the invention is not limited to this.

Although the electron conductive material 9 is a particle,
The shape may be a fiber-like or scale-like small piece. The point is that the electron conductive material 9 can be located between the adjacent positive electrode active materials 8 and the conductive auxiliary can be present around the electron conductive material 9 and the positive electrode active material 8. Any shape may be used as long as it has a size.

In the present embodiment, in particular, the positive electrode 1
The structure of the electron conductive material and the conductive auxiliary agent including the conductive filler and the crystalline resin in the positive electrode active material layer 6 is shown,
This is not limited to the positive electrode, and the same effect can be obtained by applying the configuration of the present embodiment to the negative electrode 2 and configuring a battery using the same.

Next, an example of a method of manufacturing the positive electrode 1, an example of a method of manufacturing the negative electrode 2, and an example of a method of manufacturing a battery using the positive electrode 1 and the negative electrode 2 will be described. (Method of Manufacturing Positive Electrode) An electronic conductive material having a sufficiently low volume resistivity at room temperature and a large volume resistivity at a temperature higher than a predetermined temperature between 90 ° C and 160 ° C (for example, a conductive filler and a crystalline resin). Are kneaded at a predetermined ratio) to obtain fine particles of an electronic conductive material.

As a method for pulverizing the electronic conductive material, it is preferable to use compressed air or compressed inert gas such as nitrogen or argon. In particular, when the particle size is reduced, a supersonic airflow is generated in the above-described one, and in this airflow, powders of the electronic conductive material collide with each other or the powders are applied to a wall surface (not shown). Thus, fine particles of an electron conductive material having a small particle diameter can be obtained (the method of obtaining fine particles by this method is called a jet mill method).

If it is not necessary to reduce the particle size of the fine particles of the electronically conductive material more than necessary, instead of using compressed air, the electronically conductive material is put into a ball mill and rotated to grind. (A method of obtaining fine particles by this method is called a ball mill method).

Next, the fine particles of the electron conductive material, the positive electrode active material (eg, LiCoO 2), and the binder (eg, P
VDF) and a conductive additive (for example, acetylene black) were dispersed in a dispersion medium (for example, N-methylpyrrolidone (hereinafter abbreviated as NMP)) to prepare a positive electrode active material paste.

Next, the above-mentioned positive electrode active material paste was applied on a current collector base material (for example, a metal film having a predetermined thickness) to be the positive electrode current collector 4.

Further, after drying this, it was pressed at a predetermined temperature and a predetermined surface pressure to form a positive electrode active material layer 6 having a desired thickness, and a positive electrode 1 was obtained.

In the manufacturing method of the electrode (specifically, the positive electrode 1) shown here, since the pressing is performed at a predetermined temperature and a predetermined surface pressure, the electronic conductive material 9 and the active material (here, the positive electrode active material) are pressed. Of the electrode can be improved, and the resistance of the electrode in a normal state can be reduced. That is, the resistance of the manufactured electrode can be adjusted by adjusting the temperature and the pressure (here, the surface pressure) when the electrode is pressed.

Here, an example in which the positive electrode active material paste is pressed at a predetermined temperature and a predetermined surface pressure has been described. However, after the positive electrode active material paste is pressed at a predetermined surface pressure, a predetermined temperature (preferably a melting point) is used. Alternatively, the positive electrode 1 may be obtained by heating the positive electrode active material paste at a temperature close to the melting point.

Next, a method for manufacturing the negative electrode 2 will be described. (Method of Manufacturing Negative Electrode) Mesophase carbon microbeads (hereinafter abbreviated as MCMB) and a negative electrode active material paste prepared by dispersing PVDF in NMP are used as a negative electrode current collector base material (for example, a predetermined thickness). The negative electrode 2 can be obtained by applying the negative electrode active material layer 7 on a metal film having a negative electrode active material layer 7).

Next, a method for manufacturing a battery will be described. (Battery manufacturing method) For example, a porous polypropylene sheet is sandwiched between two electrodes obtained by the above-described method, that is, a positive electrode and a negative electrode, and both electrodes are attached to each other to form a pair of batteries having a positive electrode and a negative electrode. Can be obtained. Since the battery obtained by such a method has a characteristic in which the resistance of the positive electrode increases as the temperature increases, a short-circuit accident occurs outside or inside the battery, and even if the temperature of the battery increases, In order to suppress an increase in short-circuit current, the safety of the battery itself is ensured.

Embodiment 2 A battery was prepared by mixing a plurality of types of the conductive assistants 10 contained in the electrode in the first embodiment. In the battery according to the present embodiment, since the conductive additives having different particle diameters are contained in the electrodes, the electrodes can be easily formed with the conductive aids having a large particle diameter, and the current collecting effect can be obtained with the conductive aids having a small particle diameter. Can be improved.

Embodiment 3 In the first embodiment, the conductive auxiliary agent 10 contained in the electrode is 0.1% of substantially the total weight of all solid components excluding volatile components in the active material layer.
A battery was prepared by containing the battery in a ratio of 10% to 10%. The battery in the present embodiment contains 0.1% or more of the conductive additive, so that the current collection efficiency of the electrode is increased, so that a battery having good cycle characteristics can be obtained. In addition, since the ratio of the conductive assistant is 10% or less, the PTC function works efficiently, and the short-circuit current can be reduced. Therefore, both battery characteristics and safety are ensured.

Embodiment 4 FIG. In the first embodiment, the ratio of the conductive filler contained in the electronic conductive material is set to 4
A battery was prepared with 0 to 70 parts by weight. In the battery according to the present embodiment, since the proportion of the conductive filler contained in the electronic conductive material is 40 parts by weight or more, the electronic resistance of the electronic conductive material itself can be reduced. Therefore, the electronic resistance of the electrode is low, and the discharge capacity value of the battery can be increased. In addition, since it is 70 parts by weight or less, the PTC function works satisfactorily, and the short-circuit current value during the short-circuit test can be reduced.

Embodiment 5 FIG. In the first embodiment, the battery was manufactured such that the average particle size of the conductive auxiliary agent 10 contained in the electrode was 1/1000 to 1/10 of the average particle size of the electronic conductive material. In the battery of the present embodiment, the average particle size of the conductive additive is 1/1000 to 1/10 of the average particle size of the electronic conductive material. In this case, the current can be efficiently collected in the gap between the active material and the gap between the active materials, so that a safe battery having a low short-circuit current value and good battery characteristics can be obtained.

[0042]

[Embodiment 1] Hereinafter, more specific examples of the present invention will be described. Note that the present invention is not limited to these examples. (Method of manufacturing positive electrode) Volume resistivity at room temperature is 0.2
(Ω · cm) Volume resistivity at 135 ° C. is 20
An electronic conductive material having characteristics of (Ω · cm) (for example, a mixture of 60 parts by weight of carbon black and 40 parts by weight of polyethylene) is finely pulverized by a jet mill method.

Next, 12 parts by weight of these fine particles, 83.5 parts by weight of a positive electrode active material (eg, LiCoO 2), and 0.1% of carbon (eg, acetylene black) as a conductive aid.
5 parts by weight and 4 parts by weight of a binder (for example, PVDF) are adjusted by dispersing them in NMP as a dispersion medium to obtain a positive electrode active material paste.

Next, the above-mentioned positive electrode active material paste was applied by a doctor blade method on a 20 μm-thick metal film (here, aluminum foil) serving as the positive electrode current collector 4. Further, after drying at 80 ° C., pressing is performed at a predetermined temperature (for example, room temperature) and a predetermined surface pressure (for example, 2 ton / cm 2) to form a positive electrode active material layer 6 having a thickness of about 70 μm.
I got

(Method of manufacturing negative electrode) 90 parts by weight of MCMB
A negative electrode active material paste prepared by dispersing 10 parts by weight of PVDF in NMP was coated on a negative electrode current collector made of a copper foil having a thickness of 16 μm by a doctor blade method to form a negative electrode active material layer 7. Was prepared. (Battery manufacturing method) A porous polypropylene sheet (trade name; Celgard # 2400, manufactured by Hoechst) is sandwiched between the positive electrode and the negative electrode obtained by the above-described method, and the positive electrode and the negative electrode are bonded. Having a pair of batteries.

(Evaluation of Battery) In order to evaluate the battery of the present invention, evaluation was performed using the following method. (Capacity test) The positive electrode of the prepared electrode is 65 mm x 38 m
m, the negative electrode was cut into a size of 71 mm × 44 mm, and a porous polypropylene sheet (manufactured by Hoechst, trade name: Celgard # 2400) used as the separator 3 was
A unit cell was obtained by sandwiching both electrodes between the positive electrode and the negative electrode. The current collecting terminals of the positive electrode and the negative electrode of this unit cell were respectively attached by spot welding, and these were put into a bag made of an aluminum laminate sheet, and mixed with a mixed solvent of ethylene carbonate and diethyl carbonate (molar ratio: 1: 1). After injecting an electrolytic solution in which lithium fluorophosphate was dissolved at a concentration of 1.0 (mol / dm ³ ), the battery was sealed by heat sealing to obtain a battery. A charge / discharge test at room temperature of this battery was performed. (Short Circuit Test) Also, a battery prepared in the same manner as in the above capacity test was charged at room temperature until the voltage became 4.2 V at 80 mA. After completion of charging, the temperature of the battery was gradually raised from room temperature, the positive electrode and the negative electrode were short-circuited at a predetermined temperature, and the current value at that time was measured.

Comparative Example 1 For comparison, a conductive auxiliary was not added, and only an electronic conductive material was added. In this comparative example, the method for manufacturing the positive electrode, the method for manufacturing the negative electrode, the method for manufacturing the battery, and the method for evaluating the battery were the same as those shown in Example 1 except that no conductive auxiliary was added.

Comparative Example 2 For further comparison, Example 1
In the method for producing a positive electrode of the above, the production was carried out by adding only a conductive auxiliary without adding an electron conductive material. In this comparative example, the method for manufacturing a positive electrode, the method for manufacturing a negative electrode, the method for manufacturing a battery, and the method for evaluating a battery are the same as those shown in Example 1, except that the electrode does not contain an electronic conductive material.

FIG. 2 is a diagram showing the maximum short-circuit current at the time of the short-circuit test at each temperature of the batteries shown in Example 1, Comparative Example 1, and Comparative Example 2. FIG. 3 is a diagram showing a discharge capacity value with respect to a discharge current value of the batteries shown in Example 1, Comparative Example 1, and Comparative Example 2. Here, each discharge capacity value is a discharge at each discharge current value when the discharge capacity at (1/4) C (1C is a current value required to discharge the battery capacity in unit time) is 100%. Shows the capacitance value.

As shown in FIG. 3, in Comparative Example 1, the electronic resistance of the battery was high because it did not contain a conductive additive other than the electronic conductive material, and the discharge capacity value at a high discharge current such as 2C was low. Further, in FIG. 2, when Example 1 and Comparative Example 2 are compared, in Comparative Example 2, the electrodes do not contain an electronic conductive material having a characteristic of increasing the resistance as the temperature increases. Even so, the electrode short-circuit current hardly decreases because the electrode resistance does not increase. On the other hand, since the active material, the electron conductive material, the conductive additive, and the binder are mixed at a predetermined ratio in the electrode of Example 1, when a battery is configured using this electrode, the temperature of the battery is reduced. Is 160 ° C
Since the increase in short-circuit current is suppressed before the time exceeds, the safety and reliability of the battery are further improved. Further, in addition to the electronic conductive material, the function of the conductive auxiliary agent enables the current to be collected in detail, thereby reducing the resistance of the electrode and improving the battery characteristics.

Here, acetylene black (Denka Black, manufactured by Denki Kagaku Co., Ltd.) was used as the conductive auxiliary agent, but there is no need to be limited to this, and carbon black such as Ketjen black and lamp black, and graphite such as KS6 and MCMB. Any conductive auxiliary agent may be used as long as it does not have a PTC function and has a function of enhancing the conductivity of the positive electrode active material layer, such as high-quality carbon. As described above, the electrodes contain a predetermined amount of both an electronic conductive material having a characteristic of increasing resistance with a rise in temperature and a conductive additive, so that the short-circuit current value at high temperatures is low, and the discharge capacity and cycle characteristics are reduced. A battery having good battery characteristics such as the above can be obtained.

Comparative Example 3 Further, for comparison, Example 1 was used.
, An electrode was formed by using a kneading material of carbon black and a polypropylene resin (melting point: 168 ° C.) as the electronic conductive material 9, and a battery was formed by using the electrode. In Comparative Example 3, the method for manufacturing the negative electrode and the method for manufacturing the battery are the same as those in Example 1. FIG. 4 is a diagram showing the relationship between the battery temperature and the maximum short-circuit current when a short-circuit test was performed on the batteries of Example 1 and Comparative Example 3. As shown in the figure, in Comparative Example 3, a polypropylene resin having a melting point of 168 ° C. was used as the crystalline resin. Therefore, when an electrode containing this crystalline resin was applied to a battery, the temperature at which the function of PTC was exhibited was 160 ° C. Is considered to be exceeded. In contrast, in Example 1, polyethylene having a melting point lower than 160 ° C. was used as the crystalline resin, so that an increase in short-circuit current before the battery temperature exceeded 160 ° C. was suppressed, so that the safety and reliability of the battery were improved. The properties are further improved. As described above, the crystalline resin contained in the electronic conductive material 9 has a melting point of 90 ° C. to 160 ° C.
If the temperature is within the range of ° C., the temperature at which the performance of the PTC is exhibited is maintained at 160 ° C. without lowering the performance of the battery.
Can be smaller than

Comparative Example 4 For comparison, in Example 1, a positive electrode was manufactured using a material obtained by kneading 38 parts by weight of carbon black and 62 parts by weight of polyethylene as an electronic conductive material, and a battery was formed using the positive electrode. Manufactured. In Comparative Example 4, the method for manufacturing the negative electrode and the method for manufacturing the battery were the same as those in Example 1.

Comparative Example 5 For comparison, a positive electrode was manufactured using a material obtained by kneading 71 parts by weight of carbon black and 29 parts by weight of polyethylene as an electronic conductive material, and a battery was manufactured using the positive electrode. In Comparative Example 5, the method for manufacturing the negative electrode and the method for manufacturing the battery were the same as those in Example 1.

Table 1 shows the discharge capacity values at 2 C for each of the batteries of Example 1, Comparative Examples 4 and 5, and 14
It shows the maximum short-circuit current at 0 ° C. As shown in Table 1, Comparative Example 4 has a higher electrode electronic resistance and lower discharge capacity value than Example 1. In Comparative Example 5, the discharge capacity value was higher than that in Example 1. However, since the ratio of carbon black was too large and the function of the PTC function was insufficient, the short-circuit test showed almost no decrease in the short-circuit current value. I couldn't.

[0056]

[Table 1]

Therefore, by changing the ratio of the conductive filler contained in the electronic conductive material, the maximum short-circuit current during the short-circuit test and the discharge capacity of the battery can be set to appropriate values. In particular, by setting the ratio of the conductive filler contained in the electronic conductive material to 40 to 70 parts by weight, the maximum short-circuit current during the short-circuit test can be reduced and the discharge capacity value of the battery can be increased. .

Embodiment 2 FIG. (Manufacturing Method of Positive Electrode) As in the first embodiment, the electronic conductive material is finely pulverized.

Next, 6 parts by weight of these fine particles, 87 parts by weight of a positive electrode active material (for example, LiCoO2), and 0.75% of acetylene black having a particle size of about 42 nm as a conductive aid.
Ketjen black having a particle size of about 30 nm by weight and 0.1 part by weight.
75 parts by weight and 5.5 parts by weight of a binder (for example, PVDF) are adjusted by dispersing in NMP which is a dispersion medium,
A positive electrode active material paste is obtained.

Next, the above-mentioned positive electrode active material paste was applied on the positive electrode current collector 4 in the same manner as in the first embodiment.
After drying in, apply on the back side, after drying, at room temperature,
Pressing was performed at ² ton / cm ² , and a positive electrode active material layer having a thickness of about 70 μm was formed on both sides of the aluminum foil to obtain a positive electrode.

(Production Method of Negative Electrode) 90 parts by weight of MCMB,
A negative electrode active material paste prepared by dispersing 10 parts by weight of PVDF in NMP is coated on a negative electrode current collector made of a copper foil having a thickness of 16 μm by a doctor blade method, dried at 80 ° C., and the back surface is also similar. And dried. Further, the resultant was pressed at ² ton / cm ² at room temperature to produce a negative electrode having a negative electrode active material layer having a thickness of about 90 μm. (Battery production method) The positive electrode of the produced double-sided coated electrode was 24
The electrode was cut into a size of 8 mm × 46 mm and the negative electrode in a size of 342 mm × 50 mm, and the current collecting terminals of the positive electrode and the negative electrode were attached to the ends of each electrode by ultrasonic welding. Furthermore, a negative electrode is sandwiched between bag-like porous polypropylene sheets (trade name: Celgard # 2400, manufactured by Hoechst) used as a separator, and the positive electrode is stacked on the negative electrode and spirally wound a predetermined number of times. Then, a flat spiral laminated body was produced.
This was put in a bag made of an aluminum laminate sheet, and an electrolyte obtained by dissolving lithium hexafluorophosphate at a concentration of 1.0 mol / dm ³ in a mixed solvent of ethylene carbonate and diethyl carbonate (molar ratio 1: 1) was used. After injecting the liquid, it was sealed by heat sealing to obtain a battery.

(Evaluation of Battery) In order to evaluate the battery of the present invention, evaluation was performed using the following method. (Capacity test) In the same manner as in Example 1, a charge / discharge test at room temperature of the produced battery was performed. (Overcharge test) After pre-charging the above battery at 230 mA for 30 minutes, discharge it to 2.75 V, charge it to 10 V at 3 C, and check for short-circuit, ignition, smoke, etc. of the battery to evaluate safety. Was done.

Comparative Example 6 For comparison, in the manufacture of the positive electrode, 6 parts by weight of the electronic conductive material, 1.5 parts by weight of acetylene black, 5.5 parts by weight of the binder, and the dispersion were dispersed in NMP which is a dispersion medium. An active material paste was obtained. In this comparative example, except that the conductive auxiliary was only acetylene black, the method of manufacturing a positive electrode,
The method for manufacturing the negative electrode, the method for manufacturing the battery, and the method for evaluating the battery are the same as those described in Example 2.

Comparative Example 7 For comparison, in the manufacture of the positive electrode, 6 parts by weight of the electronic conductive material, 1.5 parts by weight of Ketjen black, 5.5 parts by weight of the binder were adjusted by dispersing in NMP as a dispersion medium, A positive electrode active material paste was obtained. In this comparative example, except that the conductive auxiliary was only Ketjen black, the method of manufacturing the positive electrode,
The method for manufacturing the negative electrode, the method for manufacturing the battery, and the method for evaluating the battery are the same as those described in Example 2.

Table 2 shows the discharge capacity value at 2C, the discharge capacity value at the 100th cycle, and the results of the overcharge test for each of the batteries of Example 2, Comparative Example 6, and Comparative Example 7. The discharge capacity value at 2C is shown as a percentage (%) when the discharge capacity value at 1 / 4C is 100%, and the discharge capacity value at the 100th cycle is the discharge capacity at the first cycle when discharging at 1C. The values are shown as percentages (%) when the value is set to 100%.

[0066]

[Table 2]

As shown in Table 2, the battery of Comparative Example 6 was 2C
Has a high discharge capacity value, but the discharge capacity value at the 100th cycle is low, and the cycle characteristics are poor. In the overcharge test,
After the battery reached 10 V, a short circuit occurred and the battery generated heat. The battery of Comparative Example 7 has a low discharge capacity value of 2C but a high discharge capacity value at the 100th cycle. The overcharge test was also good. Even when the voltage reached 10 V, no short circuit occurred and the battery generated almost no heat. Compared to these, the battery of Example 2 in which two kinds of conductive assistants were added was excellent in both the discharge capacity value of 2C, the discharge capacity value at the 100th cycle, and the overcharge test, and was a battery with good battery characteristics and high safety. You can see that it is.

Embodiment 3 FIG. In the third embodiment, the content ratio of the electron conductive material in the positive electrode active material in the first embodiment is set to about 6% with respect to substantially the total weight of all solid components excluding volatile components such as a solvent in the active material layer. %, The content of the conductive additive was changed variously, and the other conditions were the same as in Example 1.

FIG. 5 shows the relationship between the content of the conductive additive to the total solid content and the maximum short-circuit current in the short circuit test, and the relationship between the content of the conductive additive to the total solid content and the discharge capacity value at the 100th cycle. FIG. When the ratio of the conductive auxiliary agent is less than 0.1%, the resistance of the electrode itself is high in a normal state (when the temperature of the battery is sufficiently low), so that the current collection from the active material is deteriorated. Cycle characteristics deteriorate. If the ratio of the conductive additive exceeds 10%, the ratio of the active material in the electrode decreases, and the cycle characteristics deteriorate. If the ratio of the active material is not changed, the thickness of the electrode becomes large (in this case, the cycle characteristics are deteriorated due to the thick electrode). A large amount of short-circuit current flows through the conductive additive, so that heat generation of the battery cannot be prevented and there is a problem in safety.
Therefore, the ratio of the conductive assistant in the electrode is set to 0.1 to 1 of the total solids.
By setting it to 0%, the discharge capacity of the battery can be increased, and a short-circuit current does not increase, so that a battery excellent in both battery characteristics and safety can be obtained. When the ratio of the conductive additive is within this range, the resistance of the electrode in a normal state is preferably low.

Embodiment 4 FIG. In the present Example 4, the content ratio of the combined amount of the electron conductive material and the conductive auxiliary was changed variously, and other methods for manufacturing the positive electrode and the negative electrode, the method for manufacturing the battery, and the like were the same as those in Example 1. It is. FIG. 6 shows the active material 10
FIG. 6 is a diagram showing the relationship between the ratio of the total amount of the electronic conductive material and the conductive additive to 0 parts by weight, the maximum short-circuit current in a short-circuit test, and the discharge capacity value at 2 C, and specifically examined the positive electrode. Here, the conductive assistant is set to a fixed amount of 0.5 part by weight, and the amount of the electronic conductive material is changed.

When the ratio of the total amount of the electronic conductive material and the conductive additive is less than 1 part by weight, the resistance value of the electrode itself under normal conditions is too high, the discharge capacity is low, and there is a problem in terms of battery performance. .
As shown in FIG. 6, when the ratio of the total amount of the electronic conductive material and the conductive additive is less than 1 part by weight, the PTC function is reduced, the short circuit current is increased, and the safety of the battery is reduced. On the other hand, if the amount exceeds 20 parts by weight, the amount of active material in the electrode decreases, so that the discharge capacity decreases. Therefore, the ratio of the total amount of the electron conductive material and the conductive auxiliary agent contained in the electrode is 1 part by weight to 20 parts by weight.
By using parts by weight, the resistance of the electrode under normal conditions can be reduced, and the discharge capacity of a battery using this electrode can be increased, whereby a battery with more desirable characteristics can be obtained.

Embodiment 5 FIG. The fifth embodiment is different from the first embodiment in that the average particle size of the conductive auxiliary agent with respect to the average particle size of the electronic conductive material is variously changed.

FIG. 7 is a diagram showing the relationship between (average particle size of conductive auxiliary agent / average particle size of electronic conductive material), maximum short-circuit current in a short-circuit test at 140 ° C., and discharge capacity value. As shown in the figure, when (average particle size of the conductive auxiliary agent / average particle size of the electronic conductive material) exceeds 1/10, the current collection efficiency of the details inside the active material layer is reduced, and the current collection is insufficient. Therefore, the discharge capacity decreases and the maximum short-circuit current increases. Also,
If it is less than 1/1000, the maximum short-circuit current increases.

Originally, the electrode has a current collection path formed of an electron conductive material. However, the current collection of details is insufficient with only the electron conductive material. Therefore, by adding a conductive aid having a fine particle diameter, the active material and the electronic conductive material are connected by the conductive aid that has entered the gap between the active material and the electronic conductive material, thereby enabling current collection in detail. However, when the particle size of the conductive aid becomes large and it is not necessary to enter the gap between the active material and the electronic conductive material, it becomes impossible to collect current in details,
The current collection efficiency decreases, and the discharge capacity decreases. Furthermore, a current collecting path by the conductive auxiliary is formed separately from the current collecting path by the electronic conductive material, and when the temperature rises, the resistance of the electronic conductive material increases, and the current collecting path of the electronic conductive material is cut off. Also, a current flows through the current collecting path by the conductive additive, and the short-circuit current increases. Also, when the particle size of the conductive auxiliary becomes small,
The number of particles of the conductive aid increases, and the conductive aid not only enters the gap between the active material and the electronic conductive material, but also overflows from the gap,
The overflowing conductive auxiliary particles form a thin current collecting path, and the maximum short-circuit current increases. On the other hand, if the particle size of the conductive additive is too small, the moldability of the electrode will be poor and the mechanical strength will be low. In the electrode of the present invention, since (average particle size of the conductive additive) / (average particle size of the electronic conductive material) was 1/1000 to 1/10, a battery having a low maximum short-circuit current and a high discharge capacity was obtained. Can be made.

The first to fifth embodiments and examples 1 to 5
In particular, the configuration and evaluation results for the positive electrode are shown, but the same description can be given for the negative electrode.

The first to fifth embodiments and the first to fifth embodiments are also described.
The electrodes and batteries shown in 5 are not only organic electrolyte type, solid electrolyte type, and gel electrolyte type lithium ion secondary batteries, but also primary batteries such as lithium / manganese dioxide batteries,
In addition, it can be used in a secondary battery.

Further, the present invention is also effective for an aqueous primary battery and a secondary battery. In addition, regardless of the battery shape,
It can also be used for primary and secondary batteries such as wound type and button type.

FIG. 8 is a schematic sectional view showing the structure of a cylindrical lithium ion secondary battery. In the figure, reference numeral 200 denotes an outer can made of stainless steel or the like also serving as a negative electrode terminal, and 100 denotes a battery body housed inside the outer can. The battery body has a structure in which a positive electrode 1, a separator 3 and a negative electrode 2 are spirally wound. Has become. The positive electrode 1 of the battery body 100 is the first embodiment.
5. It has the configuration of the electrode described in any one of Examples 1 to 5.

[0079]

As described above, according to the battery of the present invention, there is provided an electrode containing an active material, an electronic conductive material and a conductive auxiliary in contact with the active material, and the above-mentioned electronic conductive material is provided. Since it is composed of a conductive filler and a crystalline resin, and the melting point of the crystalline resin is in a range of 90 ° C to 160 ° C,
Even if the battery temperature rises due to heat generated by a short circuit or the like, it is possible to suppress an increase in short circuit current. Therefore, a highly safe battery can be obtained.

Further, since the conductive additives having different particle diameters are contained in the electrodes, the electrodes can be easily formed by the conductive aids having a large particle diameter, and the current collecting effect can be improved by the conductive aids having a small particle diameter. Can be.

Further, in at least one of the positive electrode and the negative electrode, the conductive auxiliary agent is contained at a ratio of 0.1 to 10% of the total weight of the solid components of the active material layer, so that the current collection efficiency is increased. And the PTC function can work efficiently. Therefore, a battery having good cycle characteristics and high safety can be obtained.

Further, since the ratio of the conductive filler contained in the electronic conductive material is set to 40 parts by weight to 70 parts by weight, the electronic resistance of the electrode is low, and the discharge capacity value of the battery can be increased. The PTC function operates sufficiently, and the short-circuit current value during the short-circuit test can be reduced.

Further, since the conductive filler is a carbon material or a conductive non-oxide, it can be easily dispersed in the crystalline resin and can have a PTC function.

Since the average particle size of the conductive additive is set to be 1/1000 to 1/10 of the average particle size of the electronically conductive material, the conductive auxiliary agent having an appropriate number of particles can be mixed with the active material and the electron conductive material. The gap between the conductive material and the gap between the active materials can be effectively collected in the gap between the active materials.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of a battery according to a first embodiment.

FIG. 2 is a diagram showing the relationship between the maximum short-circuit current and the temperature of the batteries according to Example 1, Comparative Examples 1 and 2.

FIG. 3 is a diagram showing a relationship between a discharge capacity value and a discharge current value of batteries according to Example 1, Comparative Examples 1 and 2.

FIG. 4 is a diagram showing the relationship between the maximum short-circuit current and the temperature of the batteries according to Example 1 and Comparative Example 3.

FIG. 5 is a diagram showing the relationship between the maximum short-circuit current, the discharge capacity value at the 100th cycle, and the ratio of the conductive additive according to Example 3.

FIG. 6 is a graph showing the relationship between the maximum short-circuit current and the discharge capacity value at 2 C according to Example 4 and the ratio of the total amount of the electronic conductive material and the conductive auxiliary to the active material.

FIG. 7 is a diagram showing the relationship between the maximum short-circuit current and the discharge capacity value according to Example 5 and (average particle size of conductive additive / average particle size of electronic conductive material).

FIG. 8 is a cross-sectional view showing a cylindrical lithium ion secondary battery.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 positive electrode, 2 negative electrode, 3 separator, 4 positive electrode current collector, 5 negative electrode current collector, 6 positive electrode active material layer, 7 negative electrode active material layer, 8 positive electrode active material, 9 electron conductive material, 10 conductive auxiliary, 11 Binder, 100 battery body, 200 outer can

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hironori Kuriki 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Hiroaki Urushiba 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Within Rishi Electric Co., Ltd. (72) Hisashi Shioda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsui Electric Co., Ltd. (72) Atsushi Arakane 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Mitsubishi Inside (72) Inventor Takashi Nishimura 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Shigeru Aihara 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Daigo Takemura 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Akira Shirakami Marunouchi, Chiyoda-ku, Tokyo 2-3-2 F-term in Mitsubishi Electric Co., Ltd. (Reference) EA01 EA08 FA02 FA05 HA01 HA05 HA14

Claims (6)

[Claims] 1. An electrode comprising an active material layer containing an active material and an electronic conductive material and a conductive auxiliary in contact with the active material, wherein the electronic conductive material comprises a conductive filler and a crystalline resin. The crystalline resin has a melting point of 90 ° C.
A battery characterized by being in the range of 160 ° C. 2. The battery according to claim 1, wherein the electrode contains a plurality of conductive assistants having different particle sizes. 3. An electrode comprising a positive electrode and a negative electrode, wherein in at least one of the electrodes, a conductive auxiliary is contained in a ratio of 0.1 to 10% of a total weight of solid components of the active material layer. The battery according to claim 1, wherein: 4. The battery according to claim 1, wherein the ratio of the conductive filler contained in the electronic conductive material is 40 parts by weight to 70 parts by weight. 5. The battery according to claim 1, wherein the conductive filler is a carbon material or a conductive non-oxide. 6. The battery according to claim 1, wherein the average particle size of the conductive auxiliary agent is 1/1000 to 1/10 of the average particle size of the electronic conductive material.