JP2003288863A - Electrochemical devices - Google Patents

Abstract

(57) [Problem] To provide an electrochemical device that efficiently dissipates heat generated inside, has higher safety, and has a high volumetric energy density. SOLUTION: The thickness is 4 mm or less and the energy density is 250.
Electricity having a power generation element that is greater than or equal to wh / l and an exterior body that accommodates the power generation element, and having a plurality of concavo-convex structures formed on at least one of the planar portions that are the maximum area of the exterior body Chemical device.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a power generating element,
The present invention relates to an electrochemical device using a laminate film as an outer package, and more particularly to a structure for improving the heat dissipation efficiency of the electrochemical device.

[0002]

2. Description of the Related Art Due to the remarkable development of mobile devices in recent years,
The importance of electrochemical devices used as power sources for portable devices, especially lithium-ion batteries, is rapidly increasing. Furthermore, as the functions of mobile devices have increased, higher energy has been achieved, and battery characteristics have been improved. There is an attempt to solidify the electrolyte as a measure for that, but it has not been put to practical use because of a fundamental technical problem in battery characteristics, for example, that it cannot be used at room temperature.

Therefore, in recent years, the center of development has shifted to batteries using a gelled electrolyte, which can obtain the characteristics close to those of liquid type batteries while improving the defects of the liquid type. In the case of this gelled battery, there is no electrolytic solution liberated at room temperature and the amount of the solution is smaller than that of the liquid type battery, and therefore, the effect on safety is obtained.

Therefore, lithium-ion batteries are currently classified into the following three types. (1) A liquid battery using an electrolytic solution. (2) A solid electrolyte battery that uses a solid electrolyte in the form of a gel formed by an electrolytic solution and a polymer. (3) Inorganic material A solid electrolyte battery using an electrolyte that utilizes lithium ion conduction in the solid of an organic material.

Here, the battery using the gelled electrolyte corresponding to the above (2) can contribute to the safety as described above. However, in order to differentiate such a battery from a battery using a conventional metal case, weight reduction and thickness reduction are attempted at the same time, and in particular, an outer casing using an aluminum foil has been used. It has become possible to make it even thinner.

As an exterior body using such an aluminum foil, there is one disclosed in the following patent as an already disclosed example, and it is mainly classified by the bonding place of the aluminum foil. (1) Deep-drawing type: Japanese Patent Laid-Open No. 2000-138040 (2) Gassho type: Japanese Patent Laid-Open No. 2000-149885

With respect to the above (1), an aluminum foil is molded in advance, a battery is inserted into the molded portion, and the aluminum foil is bonded after the insertion. In this case, the bonded portion extends in three directions of the battery. Regarding (2) above,
Aluminum foil is bonded from both sides at the center of the side of the battery. That is, the bonded portion is formed along the center of the side surface of the battery.

However, when such a thin battery is used, heat generation due to charging / discharging, in particular, abnormal heat generation phenomenon due to overcharge or rise in outside air temperature may occur. If such an abnormal heating phenomenon is left as it is, the gas generated by the decomposition of the electrolytic solution causes the exterior body to swell or burst.
In addition, thermal runaway may eventually lead to ignition.

In order to prevent such abnormal heat generation and thermal runaway, measures such as provision of a heat-sensitive protective element have been taken, but in order to keep the battery safer, heat dissipation from the battery structure should be improved. Had to do.

[0010]

DISCLOSURE OF THE INVENTION An object of the present invention is to efficiently dissipate the heat generated inside and to improve safety.
Moreover, it is to provide an electrochemical device having a high volume energy density.

[0011]

That is, the above object is achieved by the following constitution of the present invention. (1) Thickness less than 4mm, energy density is 250wh / l
An electrochemical device having the power generation element as described above and an exterior body accommodating the power generation element, wherein a plurality of concavo-convex structures are formed on at least one of the plane portions having the maximum area of the exterior body. (2) The electrochemical device according to (1) above, wherein the exterior body plane portion on which the plurality of concave-convex structures are formed is a lid member for a deep-drawing exterior body. (3) The electrochemical device according to the above (1) or (2), wherein the material for the flat surface portion of the exterior body on which the plurality of uneven structures are formed is aluminum. (4) The electrochemical device according to the above (1) or (2), wherein the material for the flat surface portion of the exterior body on which the plurality of concavo-convex structures are formed is a heat conductive rubber. (5) The uneven structure has a height of 0.05 to
The electrochemical device according to any one of (1) to (4) above, which has a range of 1 mm. (6) The electrochemical device according to any one of (1) to (5), wherein the exterior body material is a laminate film having a metal foil and a heat-fusible resin.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The electrochemical device of the present invention has a power generating element having a thickness of 4 mm or less and an energy density of 250 wh / l or more, and an outer casing for housing this power generating element.
A plurality of concavo-convex structures are formed on at least one of the flat surface portions that have the maximum area of the exterior body.

As described above, by forming a plurality of concavo-convex structures on at least one of the flat surfaces which is the maximum area of the outer package, the heat dissipation efficiency of the battery is improved and the safety factor against internal heat generation is improved. It can be a high battery and can operate at higher voltage.

As described above, as the exterior member of the electrochemical device, a deep drawing type exterior member is usually used in many cases.
However, although this metal deep-drawing case is excellent in strength, assembling property, etc., it is difficult to make the case shape complicated due to manufacturing restrictions. For this reason,
In order to further enhance the heat dissipation effect in the deep-drawing type case, it is preferable to form an uneven structure on the lid member of the deep-drawing case. For this lid member, a flat plate-shaped metal material is usually processed and used according to the shape of the deep drawing case. Therefore, by using a lid member that has been subjected to an unevenness process in advance, it is possible to easily introduce the uneven structure into a device having a deep-drawing type exterior member. Further, since only the lid member needs to be changed, the conventional manufacturing process and parts can be used as they are, which is advantageous in manufacturing.

Further, since the electrochemical device is in the form of a flat block or plate, the contact area with the heat-radiating outer package occupying a large volume is large, and heat can be efficiently transferred to the heat-radiating outer package. You can

FIG. 1 shows an example of the constitution of the electrochemical device of the present invention.
Shown in. FIG. 1 is a schematic sectional view of an electrochemical device.
In the figure, the electrochemical device has a power generation element 2, a deep-drawing type outer casing 1, and a lid member 3 of the deep-drawing type outer casing 1.

The electrochemical device 2 is a flat rectangular parallelepiped or a plate, as shown in FIGS. 1 and 2, and has a flat surface portion 21 having a maximum area and a side surface portion 22 which is a thickness portion. Here, FIG. 2 shows a state in which the power generating element 2 of the electrochemical device is housed in the deep-drawing type outer casing. In FIG. 2, the lead 4 of the power generating element 2 housed inside is pulled out from the bonded portion of the outer casing 1.

The lid member of the exterior body is provided with a concavo-convex structure for enhancing the heat radiation effect. The height of the unevenness in the uneven structure has a thickness of 4 mm or less and an energy density of 250.
The height may be such that the heat generation of the power generation element of wh / l can be effectively dissipated. On the other hand, if the height is too high, the volume of the electrochemical device that does not contribute to power generation increases, and the volume energy density of the entire device decreases.

Therefore, the height h of the uneven structure most suitable for a flat electrochemical device is preferably 0.05 to 1 m.
m, more preferably 0.2 to 0.8 mm.

Further, the concavo-convex structure may have any shape and the number of concavities and convexes that can obtain the surface area required for heat dissipation. Therefore, the shape of the concavities and convexities is not particularly limited, and may be a rib, fin structure, or the like that is generally adopted in a heat dissipation plate or a heat dissipation member, or conversely, a dimple structure. Further, it may be shaped like a boss. The surface area required for heat dissipation is about 1.5 to 5 times, especially about 3 to 5 times the flat surface.

The lid member is preferably formed of a heat conductive member in order to enhance the heat radiation effect. As the heat conductive member, for example, a metal material having good heat conductivity such as aluminum, copper, stainless steel, or having corrosion resistance and strength can be used.

Further, in order to improve the thermal conductivity, a matrix resin filled with metal, ceramics, carbon fiber or the like having a high thermal conductivity can be used. For example, as described in JP-A-2-166755, a heat transfer sheet in which a metal oxide or boron nitride is mixed in a silicone gel and a groove is further provided on the surface can be used.

Further, as described in JP-A-2-196453, in order to impart strength and improve workability, a silicone rubber mixed with a heat conductive filler is used as a strength retaining layer, and the heat conductivity is improved. A heat conductive sheet in which a flexible silicone gel mixed with a filler is combined as a deformable layer can also be used.

Furthermore, as described in JP-A-6-155517 and JP-A-7-14950, a low hardness silicone having a reinforcing layer selected from a mesh, a resin film or a non-woven fabric. A rubber sheet or the like may be used.

The thermal conductivity of the thermal conductive member must be at least higher than that of the outer casing of the electrochemical device. Specifically, a metal material is preferably 100 to 500.
W / m · k, preferably 0.8-for the above resin-based materials
It is about 1.5 W / m · k.

Further, the heat conducting member may contain a flame retardant. The flame retardant may be coated on the surface of the metal with a binder or the like, or may be dispersed in the resin material.

By including the flame retardant in this way, even if the electrochemical device is in thermal runaway and ignites, it is possible to prevent the spread of fire and ensure safety.

Examples of such flame retardants include halogenated phosphoric acid esters, halogenated compounds such as brominated epoxy resins, organic compounds such as phosphoric acid ester amides, and the like.
Inorganic materials such as antimony trioxide and aluminum hydride can be used.

Further, the heat-sensitive protective element may be arranged so as to be in contact with the heat conductive member. By arranging the heat-sensitive protective element in contact with the heat-conductive member in this way, it is possible to operate at a temperature closer to the internal temperature, the sensitivity of the heat-sensitive protective element is improved, and the safety is improved. To do.

Specific examples of the heat-sensitive protective element for an electrochemical device include a thermal fuse and a PTC element.

The heat-sensitive protective element can be attached by mechanical means, but is preferably attached by adhesion. In addition, the sensitivity can be further improved by using a heat conductive adhesive.

In order to thermally stabilize the battery, it is more desirable to use a thermally stabilized compound as the active material inside the battery in addition to the above structure. Taking a lithium ion secondary battery system as an example of such a compound, lithium manganate having a spinel structure as a positive electrode active material can be mentioned. Further, among the compounds having a layered structure capable of inserting and releasing lithium, compounds having the same structure as lithium cobalt oxide to which manganese, cobalt and nickel are added are preferable.

[Electrochemical Device] The electrochemical device of the present invention comprises a unit including a power generation element. The power generation element has, for example, a structure in which positive and negative electrodes made of metal foil such as aluminum foil or copper foil, a separator, a polymer solid electrolyte, and the like are alternately laminated. Lead-out electrodes (lead-out terminals) are provided for the positive and negative electrodes.
Are connected. The lead-out terminal, that is, the lead-out electrode,
It is made of metal foil such as aluminum, copper, nickel, and stainless steel.

The exterior body is formed by laminating a polyolefin resin layer such as polypropylene or polyethylene as a heat-adhesive resin layer on one surface of a metal layer such as aluminum and a heat-resistant polyester resin or nylon layer on the other surface. It is composed of a laminated film. The outer package is formed in a bag shape in which one side is opened by previously heat-bonding two laminated films to each other on the heat-adhesive resin layers on the end faces of the three sides to form a seal portion. Alternatively, a single laminated film may be folded back and the end faces of both sides may be heat-bonded to form a seal portion to form a bag shape.

Examples of the metal-resin adhesive include acid-modified polyethylene such as carboxylic acid, acid-modified polypropylene, epoxy resin and modified isocyanate. Since the metal-resin adhesive is provided between the metal and the polyolefin resin to improve the adhesion between them, a size sufficient to cover the sealing portion of the extraction electrode is sufficient.

The element used in the electrochemical device of the present invention is not limited to the secondary battery having a laminated structure,
A wound secondary battery or a capacitor having a structure similar to these is used.

The electrochemical device of the present invention can be used as the following lithium secondary battery and electric double layer capacitor.

[Lithium Secondary Battery] Although the structure of the lithium secondary battery in the present invention is not particularly limited, it is usually composed of a positive electrode, a negative electrode and a polymer solid electrolyte, and is applied to a laminated battery, a prismatic battery or the like. .

The electrode to be combined with the solid polymer electrolyte may be appropriately selected from those known as electrodes for lithium secondary batteries and used, preferably an electrode active material and a gel electrolyte, and optionally a conductive auxiliary agent. Is used.

A negative electrode active material such as a carbon material, a lithium metal, a lithium alloy or an oxide material is used for the negative electrode, and an oxide or a carbon material capable of intercalating / deintercalating lithium ions is used for the positive electrode. It is preferable to use a positive electrode active material such as By using such an electrode, a lithium secondary battery having good characteristics can be obtained.

The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin-fired carbon material, carbon black, carbon fiber and the like. These are used as powder. Of these, graphite is preferable, and its average particle diameter is preferably 1 to 30 μm, and particularly preferably 5 to 25 μm. If the average particle size is too small, the charge / discharge cycle life tends to be short, and the capacity variation (individual difference) tends to increase. If the average particle size is too large, the variation in capacity becomes extremely large and the average capacity becomes small. When the average particle diameter is large, the variation in capacity is considered to be due to the variation in the contact between graphite and the current collector and the contact between graphite.

Lithium ion is an intercalating day
Intercalatable oxides include lithium
Complex oxides are preferred, for example LiCoO 2.₂, LiM
n₂O _Four, LiNiO₂, LiV₂O_FourAnd so on.
Further, among these, Mn, Ni, and Co are particularly added.
Li (Mn, Ni, Co) O₂ Compound represented by
However, it is more preferable because it has excellent thermal stability. These acids
The average particle size of the compound powder is about 1 to 40 μm
Is preferred.

A conductive auxiliary agent is added to the electrode, if necessary. Examples of the conductive aid include graphite, carbon black, carbon fibers, metals such as nickel, aluminum, copper, silver and the like, and graphite and carbon black are particularly preferable.

The electrode composition of the positive electrode is, by weight ratio, active material: conducting auxiliary agent: gel electrolyte = 30 to 90: 3 to 10: 1.
The range of 0 to 70 is preferable, and in the negative electrode, by weight ratio, active material: conducting auxiliary agent: gel electrolyte = 30 to 90: 0 to 10: 1.
The range of 0 to 70 is preferable. The gel electrolyte is not particularly limited, and a commonly used one may be used. Also,
An electrode containing no gel electrolyte is also preferably used. In this case, fluororesin, fluororubber or the like can be used as the binder, and the amount of the binder is about 3 to 30% by mass.

In the production of electrodes, first, an active material and, if necessary, a conductive auxiliary agent are dispersed in a gel electrolyte solution or a binder solution to prepare a coating solution.

Then, this electrode coating solution is applied to the current collector. The means for applying is not particularly limited and may be appropriately determined depending on the material and shape of the current collector. Generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method and the like are used.
Then, if necessary, rolling treatment is performed by a flat plate press, a calendar roll, or the like.

The current collector may be appropriately selected from ordinary current collectors depending on the shape of the device used by the battery, the method of disposing the current collector in the case, and the like. Generally, aluminum or the like is used for the positive electrode and copper, nickel or the like is used for the negative electrode.
A metal foil, a metal mesh or the like is usually used as the current collector. Although the metal mesh has a smaller contact resistance with the electrode than the metal foil, the metal foil can also obtain a sufficiently small contact resistance.

Then, the solvent is evaporated to produce an electrode. The coating thickness is preferably about 50 to 400 μm.

The polymer film is, for example, PEO (polyethylene oxide) type, PAN (polyacrylonitrile)
It is possible to use a polymer microporous membrane such as a PVDF (polyvinylidene fluoride) -based polymer.

Such a positive electrode, a polymer film and a negative electrode are laminated in this order and pressure-bonded to obtain a battery body.

The electrolytic solution with which the polymer membrane is impregnated generally comprises an electrolyte salt and a solvent. As the electrolyte salt, for example, Li
BF ₄ , LiPF ₆ , LiAsF ₆ , LiSO ₃ C
Lithium salts such as F ₃ , LiClO ₄ , and LiN (SO ₂ CF ₃ ) ₂ can be applied.

The solvent of the electrolytic solution is not particularly limited as long as it has good compatibility with the above-mentioned polymer solid electrolyte and electrolyte salt, but it is a polar organic solvent which does not decompose even at a high operating voltage in a lithium battery or the like. Solvents such as ethylene carbonate (EC), propylene carbonate (P
C), butylene carbonate, dimethyl carbonate (DMC), carbonates such as diethyl carbonate and ethyl methyl carbonate, tetrahydrofuran (T
HF), cyclic ethers such as 2-methyltetrahydrofuran, cyclic ethers such as 1,3-dioxolane and 4-methyldioxolane, lactones such as γ-butyrolactone, and sulfolane are preferably used. 3-Methylsulfolane, dimethoxyethane, diethoxyethane, ethoxymethoxyethane, ethyl diglyme and the like may be used.

The concentration of the electrolyte salt when considering that the solvent and the electrolyte salt constitute an electrolyte solution is preferably 0.3 to 5 mol.
l / l. Usually, it shows the highest ionic conductivity around 1 mol / l.

When a microporous polymer film is dipped in such an electrolyte solution, the polymer film absorbs the electrolyte solution and gels to become a polymer solid electrolyte.

When the composition of the polymer solid electrolyte is represented by the copolymer / electrolyte solution, the ratio of the electrolyte solution is preferably 40 to 90 mass% from the viewpoint of the strength of the membrane and the ionic conductivity.

[Electric Double Layer Capacitor] The structure of the electric double layer capacitor in the present invention is not particularly limited, but usually, a pair of polarizable electrodes are arranged through a polymer solid electrolyte, and the polarizable electrode and the polymer are arranged. An insulating gasket is arranged around the solid electrolyte. Such an electric double layer capacitor may be of what is called a paper type, a laminated type or the like.

For the polarizable electrode, activated carbon, activated carbon fiber or the like is used as a conductive active material, and a fluororesin, fluororubber or the like is added as a binder thereto. And it is preferable to use what formed this mixture in the sheet-like electrode. The amount of the binder is about 5 to 15% by mass. A gel electrolyte may be used as the binder.

The collector used for the polarizable electrode is platinum,
It may be conductive rubber such as conductive butyl rubber, may be formed by thermal spraying of a metal such as aluminum or nickel, and a metal mesh may be attached to one surface of the electrode layer.

In the electric double layer capacitor, the polarizable electrode as described above and the solid polymer electrolyte are combined.

The polymer film is, for example, PEO (polyethylene oxide) type, PAN (polyacrylonitrile) type,
A polymer microporous film such as a PVDF (polyvinylidene fluoride) system can be used.

As the electrolyte salt, (C ₂ H ₅ ) ₄ NB is used.
F ₄ , (C ₂ H ₅ ) ₃ CH ₃ NBF ₄ , (C ₂ H ₅ ) ₄ PB
F _4, and the like.

The non-aqueous solvent used in the electrolytic solution may be any of various known ones, such as propylene carbonate, ethylene carbonate, γ-, which are electrochemically stable non-aqueous solvents.
Butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane alone or a mixed solvent is preferable.

The concentration of the electrolyte in such a non-aqueous solvent-based electrolyte solution may be 0.1 to 3 mol / l.

When a microporous polymer film is dipped in such an electrolyte solution, the polymer film absorbs the electrolyte solution and gels to become a polymer solid electrolyte.

When the composition of the solid polymer electrolyte is represented by the copolymer / electrolyte solution, the ratio of the electrolyte solution is preferably 40 to 90 mass% from the viewpoint of the strength of the membrane and the ionic conductivity.

As the insulating gasket, an insulator such as polypropylene or butyl rubber may be used.

[0067]

Embodiments will be described in detail below with reference to embodiments. [Example 1] (1) Battery structure As shown in Fig. 1, a battery was produced in which a lithium secondary battery unit as a power generating element was enclosed in an outer package. This battery element is formed of a positive electrode and a current collector material thereof, a negative electrode and a current collector material thereof, and a gelled solid electrolyte membrane.

The power generating element has a thickness of 3.0 mm and a capacity of 20.
The energy density was 00 mAh and the energy density was 280 wh / l.

The height of the concave and convex portions of the battery thus manufactured was sample 1: 0.03 mm, sample 2: 0.1 mm, sample 3: 0.6 mm, sample 4: 1.
mm (the ratio of the height of the uneven portion to the thickness of the outer casing is 1%, 3.3%, 20%, 33%, respectively), and the lid member (specifically, aluminum, thermal conductivity 237 W / mk) Using it, it was enclosed in a deep-drawing type exterior body as shown in FIG. 2 to obtain an electrochemical device. A sample 5 having no unevenness as shown in FIG. 3 was also manufactured.

Each of the batteries obtained was subjected to an overcharge test at room temperature under the same environment.

The overcharge test was conducted as follows.
First, using a 12V constant-voltage constant-current device, a predetermined current was applied to confirm whether each sample to be tested had thermal runaway or ignition. Specifically, 2000 mA was applied as a standard current to a battery having a capacity of 2000 mAh. Further, the same evaluation was performed by applying 3000 mA at 6V.

As a result, samples 2, 3 and 4 did not cause thermal runaway. Also, Sample 5 ignited. In sample 1, the heat dissipation was insufficient and the temperature increased to 140 ° C. due to heat generation, and then the thermal runaway mode was reached.

[0073]

As described above, according to the present invention, the heat generated between the electrochemical device units can be efficiently radiated when the thin electrochemical device is layered, so that it is safer and has high volume energy density. It becomes possible to provide a chemical device module.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic configuration of an electrochemical device of the present invention.

FIG. 2 is a schematic perspective view showing a deep-drawing type outer casing of the electrochemical device of the present invention.

FIG. 3 is a schematic cross-sectional view showing a configuration example of an electrochemical device having a conventional structure.

[Explanation of symbols]

1 exterior body 2 power generation element 3 Lid member

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Claims (6)

[Claims] 1. A thickness of 4 mm or less and an energy density of 250
An electric power generation device having a power generation element of wh / l or more and an exterior body accommodating the power generation element, and having a plurality of concavo-convex structures formed on at least one of the plane portions having the maximum area of the exterior body Chemical device. 2. The outer surface of the exterior body on which the plurality of concavo-convex structures are formed is a lid member of a deep-drawing exterior body.
Electrochemical device. 3. The electrochemical device according to claim 1, wherein the material for the flat surface portion of the exterior body on which the plurality of concavo-convex structures are formed is aluminum. 4. The electrochemical device according to claim 1 or 2, wherein the material for the flat surface portion of the exterior body on which the plurality of concavo-convex structures are formed is a heat conductive rubber. 5. The concavo-convex structure has a concavo-convex height of 0.
The electrochemical device according to any one of claims 1 to 4, which has a range of 05 to 1 mm. 6. The electrochemical device according to claim 1, wherein the outer casing material is a laminate film having a metal foil and a heat-fusible resin.