JPH1050294A - Power storage element with thermosensitive resistor layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage element with no fear of rupture or fire of the power storage element even if high current caused by accidental short circuit of the power storage element flows, high safety, and high energy density. SOLUTION: By using conductive microbeads obtained by covering Ni or Cu on the surface of a hollow balloon formed with the partition of thermoplastic resin having a melting point of 120-170 deg.C as a thermosensitive resistor 3, even if a power storage element is accidentally short-circuited, high current flows, and temperature is raised, the resin partition of the conductive microbeads is melted, and the conductive microbeads are electrically separated each other. Resistance value of a thermosensitive resistor layer mainly comprising the thermosensitive resistors is sharply increased, resistance value between an electrode current collector and an electrode layer is increased, and energy in the electrode layer is instantaneously released.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power storage device, and more particularly to an improvement in safety of a power storage device.

[0002]

2. Description of the Related Art In recent years, in the development of high-performance electronic devices and electric vehicles, there has been an increasing demand for higher energy storage elements mounted thereon. For these energy storage devices, conventional Ni-Cd batteries, lead batteries, Ni-MH batteries, electric double layer capacitors, or a negative electrode active material using metallic lithium, a lithium alloy, or a carbon material capable of inserting and extracting lithium ions, Development of lithium batteries and the like using transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganese spinel, and manganese dioxide and sulfides such as thionyl chloride and SO _{2 as the} positive electrode active material has been made.

[0003] These high-performance batteries have a high energy density and are expected to meet the demands for higher energy and smaller and lighter batteries. However, on the other hand, there is a problem of safety such that if a short circuit occurs accidentally, a very large amount of heat is generated, and in the worst case, the battery explodes and burns. In response to conventional safety, a mechanism that melts and closes the micropores of the separator that separates the positive electrode and the negative electrode when the temperature exceeds a certain temperature, a method of connecting a safety mechanism such as a thermistor or thermal fuse in series with the power storage element, or a power storage element A method of electrically connecting a battery terminal in the inside and an electrode for storing electric energy via the above-described safety element has been used. However, these conventional methods can effectively suppress the short-circuit current when, for example, the electrodes are directly in contact with each other inside the power storage element due to displacement due to fusing of the separator, swelling of the electrodes, and vibration, causing an internal short circuit. Did not.
For this reason, those having a high energy density are very difficult to take safety measures, and especially, it is extremely difficult to increase the size.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-energy-density energy storage device having a high safety without a risk of the energy storage device exploding or burning even if a large current flows due to an erroneous short circuit of the energy storage device. Is to provide.

[0005]

According to the present invention, there is provided a conductive balloon in which the surface of a hollow balloon formed of a thermoplastic resin having a melting point in the range of 120 to 170 ° C. is coated with Ni or Cu. By using conductive micro beads,
When a short circuit occurs accidentally in the storage element, a large current flows and the temperature rises, the resin partition walls of the conductive microbeads melt,
When the conductive microbeads that have been in contact with the conductive microbeads are separated from each other, the resistance value of the thermosensitive resistor layer mainly composed of the thermosensitive resistor rapidly increases, and the electrode current collector ( It has been found that the resistance between the positive electrode active material layer and the negative electrode active material layer) and the electrode layer (the positive electrode and the negative electrode) increases, and as a result, the energy of the electrode layer can be prevented from being released at once. It was completed in.

That is, a heat-sensitive resistor layer mainly composed of a heat-sensitive resistor whose resistance value increases irreversibly when the temperature exceeds a certain temperature is formed on the surface of the electrode current collector, and electric energy is formed thereon. Is a power storage element with a heat-sensitive resistor layer formed by laminating an electrode layer that accumulates, more preferably, the heat-sensitive resistor layer comprises at least the heat-sensitive resistor and a matrix resin, The heat-sensitive resistor layer contains a conductive auxiliary, and the heat-sensitive resistor is conductive microbeads in which the surface of a hollow balloon made of a resin partition is coated with a conductive metal. But 1
Selected from thermoplastic resins having a melting point in the range of 20 to 170 ° C., wherein the coating metal of the hollow balloon is Ni or C;
u is a power storage element with a heat-sensitive resistor layer.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the heat-sensitive resistor used in the present invention will be described in detail. The heat sensitive resistor used is 12
Ni or Cu was coated on the surface of a hollow balloon having a particle size of 0.5 to 20 μm formed by a partition wall of a thermoplastic resin having a melting point in the range of 0 to 170 ° C. by a conventionally known method such as plating and vapor deposition. It consists of conductive microbeads. Hollow balloons are prepared by a conventionally known method for producing microcapsules, in which a low-boiling lipophilic solvent is O / W-emulsified in water using an appropriate surfactant, and then a resin partition is formed by a submerged polymerization method. After the produced product is classified and dried, it is obtained by removing the internal low boiling point solvent by an appropriate method.

[0008] As the resin partition wall component, PMMA resin,
Polyacrylonitrile, vinylidene chloride-polyacrylonitrile copolymer resin or the like is preferably used, but it is necessary to use a resin having a melting point in the range of 120 to 170 ° C. Particularly preferred among these are those having a melting point of 120 to
PMMA relatively easy to set in the range of 170 ° C
Resin and vinylidene chloride-polyacrylonitrile copolymer resin.

It is preferable to use a hollow balloon having a melting point of less than 120 ° C. since the resistance value of the heat-sensitive resistor layer may increase even at a low temperature at which there is no possibility that the power storage element will burst or burn. Absent. Further, when a hollow balloon having a resin partition wall having a melting point of 170 ° C. or more is used, the matrix resin is melted first, so that the resistance value does not increase, or the electrolyte component in the battery boils first. It is not preferable because the power storage element may evaporate and burst or burn. The particle diameter of the hollow balloon is preferably about 0.5 to 20 μm, more preferably about 1 to 10 μm. It is difficult to actually produce a hollow balloon having a particle diameter of 0.5 μm or less, and if it is 20 μm or more, it is not preferable because the thickness of the heat-sensitive resistor layer is too large in consideration of the thickness.

The surface of the hollow balloon obtained as described above is coated with Ni or Cu by a conventionally known method such as an electroless plating method or a vapor deposition method to produce conductive microbeads. The resistance value of the obtained conductive microbeads is preferably 10 to 1 × 10 ⁻⁴ Ω · cm, and can be adjusted by the coating thickness of the conductive metal. When the resistance value of the conductive microbeads is 10 Ω · cm or more, the resistance value of the heat-sensitive resistor layer becomes unnecessarily high, and there is a practical problem.
Further, it is not preferable to set the resistance value to 1 × 10 ⁻⁴ Ω · cm or less, since an excessive property is given.

Next, a method for manufacturing the heat-sensitive resistor layer of the present invention will be described. As a method of forming the heat-sensitive resistor layer, a paste obtained by mixing conductive microbeads of a heat-sensitive resistor, a matrix resin, and a suitable solvent into a slurry is applied onto a current collector by a conventionally known method and dried. Is most preferable. The thickness of the layer is preferably about 3 to 30 μm, particularly preferably about 5 to 20 μm. Layer thickness 3
If the thickness is less than μm, when the resistance value increases, the film may be broken and the effect of controlling the resistance value may be lost, which is not preferable. On the other hand, if the thickness is 30 μm or more, the volume and the weight are excessively increased, which is not preferable in view of the demand for reducing the size and weight of the battery.

The matrix resin used is polyvinylidene fluoride (PVD) which has excellent adhesion to a current collector such as a copper foil or an aluminum foil and is preferably used as a binder for an electrode layer.
Those excellent in adhesion to F) are preferable. In particular,
Thermoplastic resins such as PVDF, fluorocarbon resins such as fluororubber, polyimide resins, polyamide imide resins, and polyamide resins, and thermosetting resins such as phenol resins and epoxy resins. Among them, the use of the same fluororesin, PVDF or fluororubber, is particularly preferable in consideration of the resistance to the electrolytic solution and the adhesion of the electrode layer binder to PVDF.

When a thermoplastic resin is used as the matrix resin, it is preferable to select a resin having a melting point higher than that of the partition resin of the conductive microbeads. If a resin with a melting point lower than the melting point of the conductive microbead partition resin is used, the matrix resin will melt before the conductive microbead resin partition melts and fluidity will develop, and on the contrary, the heat-sensitive resistor layer resistance This is not preferable because the value may decrease. The matrix resin is 3 parts per 100 parts by weight of the conductive microbeads as the heat-sensitive resistor.
-20 parts by weight, particularly preferably 5-15 parts by weight. Addition of less than 3 parts by weight is not preferred because adhesion to the current collector is poor. Addition of more than 20 parts by weight is not preferable because the resistance value becomes too high.

Incidentally, a conductive agent such as graphite, carbon, metal particles or the like can be added to the heat-sensitive resistor layer as a conductive assistant. The amount of addition may be selected in consideration of the required conductivity. An electrode layer for accumulating electric energy is formed on the thus obtained heat-sensitive resistor layer by a conventionally known method, whereby the electric storage element of the present invention can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in which the electric storage element of the present invention is a lithium battery will be described below, but the present invention is not limited to these, and lead batteries, Ni-Cd batteries, Ni-MH batteries And an electric double layer capacitor.

Example 1 <Formation of Heat-Sensitive Resistor Layer of Example 1> As a heat-sensitive resistor, a vinylidene chloride-polyacrylonitrile copolymer resin partition wall having a particle size of 2 to 8 μm (resin partition softening point) 130
° C) was coated with Ni by electroless plating to obtain conductive microbeads having a resistance value of 1 × 10 ⁻³ Ω · cm. A paste obtained by mixing and slurrying 100 parts by weight of the conductive microbeads and 10 parts by weight of PVDF powder as a matrix resin in N-methylpyrrolidone was used as a 20 μm-thick aluminum foil used for a current collector of a positive electrode and a negative electrode. Each of the 12 μm copper foils used for the current collector was dried on one side and dried on both sides so that the thickness became 10 μm to form a heat-sensitive resistor layer.

<Preparation of Positive Electrode of Example 1> As a positive electrode active material, 88 parts by weight of lithium manganese spinel having an average particle diameter of 5 μm, 2 parts by weight of Ketjen black as a conductive additive, and 10 parts by weight of PVDF powder as a binder were used. A paste obtained by mixing and slurrying in N-methylpyrrolidone is coated on the heat-sensitive resistor layer for the current collector of the positive electrode and dried on both sides such that the thickness on one side after drying is 100 μm, and the positive electrode active material layer is dried. Was formed and then rolled with a roll press to adjust the density to obtain a positive electrode.

<Preparation of Negative Electrode of Example 1> 90 parts by weight of artificial graphite having an average particle size of 25 μm as a negative electrode active material and P of a binder were used.
A paste obtained by mixing and slurrying 10 parts by weight of VDF in N-methylpyrrolidone is applied on a heat-sensitive resistor layer for a current collector of a negative electrode and dried on both sides so that the thickness on one side after drying becomes 100 μm. After forming the negative electrode active material layer, the negative electrode was obtained by adjusting the density by rolling with a roll press.

Example 2 <Formation of Heat-Sensitive Resistor Layer of Example 2> A hollow balloon having a particle size of 5 to 15 μm and a PMMA-based resin partition wall (softening point of resin partition wall: 160 ° C.) was used as the heat-sensitive resistor. Was coated with Cu by electroless plating to obtain conductive microbeads having a resistance value of 1 × 10 ⁻² Ω · cm. A paste obtained by mixing and slurrying 100 parts by weight of the conductive microbeads and 10 parts by weight of PVDF powder as a matrix resin in N-methylpyrrolidone was used as a 20 μm-thick aluminum foil used for a current collector of a positive electrode and a negative electrode. Each of the 12 μm copper foils used for the current collector was dried on one side and dried on both sides so that the thickness became 20 μm to form a heat-sensitive resistor layer. About the positive electrode and the negative electrode, the positive electrode and the negative electrode were produced in the same manner as in Example 1.

Example 3 <Formation of Heat-Sensitive Resistor Layer of Example 3> As a heat-sensitive resistor, a hollow balloon having a particle diameter of 3 to 10 μm and a PMMA-based resin partition wall (softening point of resin partition wall: 140 ° C.) Was coated with Cu by electroless plating to obtain conductive microbeads having a resistance value of 1 × 10 ⁻² Ω · cm. A paste obtained by mixing and slurrying 100 parts by weight of the conductive microbeads, 10 parts by weight of PVDF powder as a matrix resin, and 2 parts by weight of Ketjen black as a conductive aid in N-methylpyrrolidone was used as a current collector for a positive electrode. A 20 μm thick aluminum foil to be used and a 12 μm copper foil to be used as a current collector for the negative electrode were coated on both sides so that the thickness became 15 μm after drying on one side, and then dried to form a heat-sensitive resistor layer. . About the positive electrode and the negative electrode, the positive electrode and the negative electrode were produced in the same manner as in Example 1.

Comparative Example 1 <Preparation of Positive Electrode of Comparative Example 1>
A paste obtained by mixing and slurrying 88 parts by weight of lithium manganese spinel having a thickness of 2 μm, 2 parts by weight of Ketjen black as a conductive additive, and 10 parts by weight of PVDF powder as a binder in N-methylpyrrolidone was used as a current collector. A positive electrode active material layer was formed by coating and drying both sides of a 20-μm-thick aluminum foil so that the single-sided thickness after drying was 100 μm to form a positive electrode active material layer, and then rolling by a roll press to adjust the density to obtain a positive electrode.

<Preparation of Negative Electrode of Comparative Example 1> 90 parts by weight of artificial graphite having an average particle size of 25 μm as a negative electrode active material and P
A paste obtained by mixing and slurrying 10 parts by weight of VDF in N-methylpyrrolidone was coated on a 12 μm thick copper foil of a current collector, dried and coated on both sides such that the thickness on one side was 100 μm, and then dried. After the layer was formed, the density was adjusted by rolling with a roll press to obtain a negative electrode.

Comparative Example 2 <Formation of Heat-Sensitive Resistor Layer of Comparative Example 2> As the heat-sensitive resistor, a vinylidene chloride-polyacrylonitrile copolymer resin partition wall having a particle size of 2 to 8 μm (softening point of resin partition wall) 90 ° C)
Was coated with Ni by electroless plating to obtain conductive microbeads having a resistance value of 1 × 10 ⁻³ Ω · cm. A paste obtained by mixing and slurrying 100 parts by weight of the conductive microbeads and 10 parts by weight of PVDF powder as a matrix resin in N-methylpyrrolidone was used as a 20 μm-thick aluminum foil used for a current collector of a positive electrode and a negative electrode. Each of the 12 μm copper foils used for the current collector was dried on one side and dried on both sides so that the thickness became 20 μm to form a heat-sensitive resistor layer. For the positive electrode and the negative electrode, see Example 1
In the same manner as in the above, a positive electrode and a negative electrode were produced.

<Comparative Example 3><Formation of Heat-Sensitive Resistor Layer of Comparative Example 3> As a heat-sensitive resistor, a hollow balloon having a particle diameter of 3 to 10 μm and a PMMA-based resin partition wall (softening point of resin partition wall: 190 ° C.) Was coated with Cu by electroless plating to obtain conductive microbeads having a resistance value of 1 × 10 ⁻² Ω · cm. A paste obtained by mixing and slurrying 100 parts by weight of the conductive microbeads and 10 parts by weight of PVDF powder as a matrix resin in N-methylpyrrolidone was used as a 20 μm-thick aluminum foil used for a current collector of a positive electrode and a negative electrode. Each of the 12 μm copper foils used for the current collector was dried on one side and then dried on both sides to a thickness of 15 μm to form a heat-sensitive resistor layer. About the positive electrode and the negative electrode, the positive electrode and the negative electrode were produced in the same manner as in Example 1.

<< Preparation of Battery >> The electrodes prepared in Examples and Comparative Examples were wound into a cylindrical shape via a microporous polypropylene film separator to form an electrode group shown in FIG. After inserting this electrode group into a battery can made of steel plate, 1 mol / l of lithium hexafluorophosphate was dissolved in a solvent in which ethylene carbonate, dimethyl carbonate and diethyl carbonate were mixed at a volume ratio of 2: 2: 1. After injecting the electrolytic solution, the battery was sealed by caulking to produce a battery.

<< Confirmation of Safety >> The prepared battery was put into an oven, and the change in resistance value when the temperature was raised from room temperature to 200 ° C. was measured. The result is shown in FIG. In all of the batteries of the examples, the resistance value sharply increased from around the melting point of the partition resin of the heat-sensitive resistor, but the batteries of Comparative Examples 1 and 3 showed almost no change in the resistance value even at around 200 ° C. .
The resistance of the battery of Comparative Example 2 is already high even at room temperature. The reason is that the melting point of the partition resin of the heat-sensitive resistor is 90 ° C.
This is considered to be because the hollow balloon was already deformed at the drying temperature at the time of forming the layer, and good conduction was not achieved.

Next, FIG. 3 shows the result of intentionally causing an internal short circuit in the manufactured battery and measuring the temperature change of the electrolytic solution. In each of the batteries of the examples, the temperature of the electrolytic solution rises up to around the melting point of the partition resin of the heat-sensitive resistor, but thereafter the temperature gradually falls. On the other hand, since the batteries of Comparative Examples 1 and 3 continued to heat up even when the temperature exceeded 200 ° C., the measurement was stopped halfway. The temperature of the battery of Comparative Example 2 rose slowly and did not rise sharply. The reason for this may be a conduction failure from the beginning as described above.

[0028]

According to the power storage device of the present invention, the resistance value between the current collector and the electrode layer sharply increases at the time of short-circuit, and the short-circuit current is suppressed.
It is possible to provide a high-energy-density power storage element that can prevent burning and has high safety.

[Brief description of the drawings]

FIG. 1 shows an electrode group when a power storage element of the present invention is a lithium secondary battery.

FIG. 2 shows a change in resistance value when the batteries prepared in Examples and Comparative Examples were put into an oven and heated from room temperature to 200 ° C.

FIG. 3 shows a change in temperature of an electrolytic solution when an internal short circuit is intentionally generated in the batteries prepared in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode 2 ... Negative electrode 3 ... Heat sensitive resistor layer 4 ... Positive electrode active material layer 5 ... Negative electrode active material layer 6 ... Microporous separator 7 ... Electrode group 8 ... electrode terminal

Claims (6)

[Claims] 1. A heat-sensitive resistor layer mainly composed of a heat-sensitive resistor whose resistance value increases irreversibly when the temperature exceeds a certain temperature is formed on the surface of the electrode current collector, and electric energy is formed thereon. An energy storage device with a heat-sensitive resistor layer, wherein an electrode layer that accumulates heat is laminated. 2. The power storage element with a heat-sensitive resistor layer according to claim 1, wherein the heat-sensitive resistor layer comprises at least the heat-sensitive resistor and a matrix resin. 3. The storage element with a heat-sensitive resistor layer according to claim 1, wherein the heat-sensitive resistor layer contains a conductive auxiliary. 4. The heat-sensitive resistor according to claim 1, wherein the heat-sensitive resistor is a conductive microbead having a surface of a hollow balloon formed of a resin partition wall coated with a conductive metal. Storage element with resistive resistive layer. 5. The hollow balloon having a resin partition wall having a thickness of 120 to 120.
5. The storage element with a heat-sensitive resistor layer according to claim 1, wherein the storage element is selected from a thermoplastic resin having a melting point in a range of 170 [deg.] C. 6. The method according to claim 1, wherein the coating metal of the hollow balloon is Ni or Cu.
Or a power storage element with a heat-sensitive resistor layer according to item 5.