JP2002151355A - Laminated electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated electric double-layer capacitor with high reliability at a low cost. SOLUTION: In a laminated electric double-layer capacitor, having a plurality of electric double-layer capacitor cells connected in series, the laminated electric double-layer capacitor of the present invention is characterized with the electric double-layer capacitor cells respectively having discharge leveling resistors (rc) connected in parallel. Namely, the laminated electric double-layer capacitor of the present invention makes it possible to reduce irregularities in insulating resistors (rp) of the electric double-layer capacitor cells, that is, the irregularities in applied voltage, by connecting the discharge leveling resistors in parallel with the electric double-layer capacitor cells. Hence, it is possible to achieve a laminated electric double-layer capacitor, having high reliability at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multilayer electric double layer capacitor having a plurality of electric double layer capacitor cells connected in series.

[0002]

2. Description of the Related Art An electric double layer capacitor is used as a backup power supply for an electronic device or the like, and has an advantage that not only has a large electric capacity but also a charge / discharge speed can be made faster than that of a secondary battery. is there. Because of these advantages, the electric double layer capacitor is expected to be applied to electric vehicles because it can be used effectively for regenerative energy and the like.

[0003] A general electric double layer capacitor uses a thin film of activated carbon or the like formed on a metal foil as an electrode.
The electrodes are stacked with a separator interposed therebetween and impregnated with an electrolytic solution to form one cell of the electric double layer capacitor (electric double layer capacitor cell). Since each electric double layer capacitor cell has a voltage tolerance of several volts or less, when used at a higher voltage, the electric double layer capacitor cells are connected in series so that the required voltage can be obtained, and a high charge / discharge capacity is required. In order to obtain it, it is used as an assembly in which electric double layer capacitor cells are connected in parallel.

[0004] When the electric double layer capacitor is left in a charged state, it consumes energy due to minute internal conduction, chemical change, and the like, and a self-discharge phenomenon in which the amount of charge is reduced appears. The self-discharge rate is a dependent value by an electric double layer insulation resistance shown in the equivalent circuit of a capacitor (r _p) shown in FIG. 9, the value of this r _p is attached somewhat rose by product Is the current situation.

Therefore, the voltage applied to each electric double layer capacitor cell connected in series greatly varies as charging and discharging are repeated, and eventually exceeds the withstand voltage of the electric double layer capacitor cell and exceeds the withstand voltage. It can also destroy the capacitor cell.

Conventionally, as disclosed in Japanese Utility Model Publication No. 5-10349 and Japanese Patent No. 716339, when a plurality of electric double layer capacitor cells are connected in series, an external electronic device using a Zener diode or the like is used. In general, a circuit is provided to average the variation and / or protect it from overvoltage.

[0007]

However, one protection circuit using an expensive semiconductor or the like is required for one electric double layer capacitor cell, which causes an increase in cost.

Accordingly, an object of the present invention is to provide a highly reliable multilayer electric double layer capacitor at a lower cost.

[0009]

According to the present invention, there is provided a multilayer electric double layer capacitor having a plurality of electric double layer capacitor cells connected in series. The electric double layer capacitor cell has a discharge leveling resistor connected in parallel.

That is, in the multilayer electric double layer capacitor of the present invention, by connecting a discharge leveling resistor in parallel with each electric double layer capacitor cell, the insulation resistance of each electric double layer capacitor cell, that is, the applied voltage Variation can be reduced, and a highly reliable and low-cost multilayer electric double layer capacitor can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A multilayer electric double layer capacitor according to the present invention will be described based on the following embodiments. The multilayer electric double layer capacitor of the present embodiment is obtained by connecting a plurality of electric double layer capacitor cells in series. The required voltage is obtained by connecting the electric double layer capacitor cells in series.

Each electric double layer capacitor cell has a discharge leveling resistor connected in parallel. The amount of self-discharge can be leveled by connecting a discharge leveling resistor in parallel to each electric double layer capacitor cell.

Here, dQ (Q: amount of electricity charged in the electric double layer capacitor cell) / dt, which is the amount of self-discharge per unit time, is -V (V: terminal voltage of the electric double layer capacitor cell). ) / R (R: insulation resistance of electric double layer capacitor cell). Therefore, for two electric double layer capacitor cells having the same terminal voltage and the insulation resistance of r ₁ and r ₂ respectively, the ratio of the self-discharge rate is r ₂ / r ₁ . For example, when r ₂ is 3 times the r _1, rather than the electric double layer capacitor cell self-discharge rate insulation resistance is r ₂ of the electric double layer capacitor cell insulation resistance is r ₁ 3 Twice as fast (arriving at an arbitrary voltage Vx three times faster). In addition, when the change with time of the value of V is obtained, V = V ₀ e ^{−t / CR} (V ₀ : initial value of terminal voltage,
C: capacitance of the electric double layer capacitor cell).

Here, as is clear from the equivalent circuit of the electric double layer capacitor cell of the multilayer electric double layer capacitor of the present invention shown in FIG. 1, the discharge leveling resistor and the electric double layer capacitor cell are connected in parallel. the combined resistance value in the case of connection (r) is derived by _{r = r p · r c /} (r p + r c) to. Thus, the same resistance value ratio of the self-discharge speed when the discharge leveling resistors (r _c) were connected to each of the electric double layer capacitor cell _{(r 1 r 2 + r 2} r c) /
(R ₁ r ₂ + r ₁ r _c ), which is (r ₁ + r _c ) / (r ₂ ) as compared with the case where the discharge leveling resistors are not connected in parallel.
+ R _c ) times.

Therefore, when the value of r _c is a finite value, that is, when the discharge leveling resistors are connected in parallel,
The difference in the self-discharge speed can be reduced as compared with the case where a discharge leveling resistor is connected. Also, as the value of r _c is small, self-discharge rate of the two electric double layer capacitor cell becomes closer (equal eventually). Therefore, it is desirable that the resistance value (r _c ) of the discharge leveling resistor be low. Furthermore, it is preferable that the resistance value (r _c ) is lower than the insulation resistance (r _p ) of each electric double layer capacitor cell. However, if too r _c is small, the self-discharge rate is too large, a value corresponding to the intended use. For example, in a usage method in which charging and discharging are repeated in a short time, a small value of r _c has little effect. On the contrary, when it is necessary to leave the battery for a long time after charging, r _c
By increasing the value of _c to some extent, waste due to self-discharge is reduced.

As the discharge leveling resistor, a resistor used for general electronic / electric equipment may be connected between the positive and negative terminals of each electric double layer capacitor cell, or between the positive and negative electrodes. Any configuration may be used as long as it can impart conductivity to the substrate.

As a preferable configuration, a method of imparting conductivity having a predetermined resistance value to an electrode fixing portion for fixing a positive electrode terminal and a negative electrode terminal of each electric double layer capacitor cell, a case of each electric double layer capacitor cell, A method of imparting conductivity at a predetermined resistance value to a portion where the positive electrode and the negative electrode come into contact with each other. In this way, the cost can be reduced by sharing the discharge leveling resistor with an indispensable part such as the case of the electric double layer capacitor cell.

As a method for imparting conductivity to the case,
A method in which part or all of the case is made of a conductive resin can be exemplified. The resistance value of the conductive resin can be freely controlled by the type and amount of the conductive material (carbon fiber, metal powder, metal fiber) to be mixed. Note that the case can also serve as the electrode fixing portion.

The amount of self-discharge is increased by connecting a discharge leveling resistor in parallel with the electric double layer capacitor cell, but the resistance of the discharge leveling resistor is 100 to 100000 times the resistance of the load. The power that is wasted by setting the power to a high level is practically negligible.

Further, the insulation resistance is from 1 time to 1/1000 of the insulation resistance.
By determining the value of the leveling resistance between the times, the variation in the amount of self-discharge can be reduced. The effect increases as the resistance value of the leveling resistor decreases, but the power loss at the leveling resistor increases. More preferably, when the leveling resistance is about 1/10 of the insulation resistance, the SOC loss per time is about 2.4%, and there is no practical problem.

The electric double layer capacitor cell is not particularly limited, but is exemplified by a structure comprising a positive electrode, a negative electrode, an electrolytic solution impregnated in the electrodes, and a case for storing the electrodes and the electrolytic solution. it can.

A general positive electrode includes a current collector made of a conductive thin film and a positive electrode active material layer formed on the current collector and containing a positive electrode active material having a large specific surface area.

The material of the current collector is not particularly limited, but it is preferable to use a metal material having excellent conductivity such as aluminum, nickel, and copper. The shape is not particularly limited, but is preferably plate-shaped, and particularly preferably has a certain thickness. When the current collector has a plate shape, the plate thickness is not particularly limited, and is appropriately selected so as to obtain a desired current collection performance.

The positive electrode active material is not particularly limited, and a known positive electrode active material can be used. However, it is necessary to use a positive electrode active material that has a large specific surface area and does not cause a chemical reaction with the electrolytic solution as described above, and does not cause an electrochemical reaction with the electrolytic solution even if polarization due to charging occurs. . Therefore, it is necessary to select an appropriate one according to the electrolytic solution used. Activated carbon and the like are mentioned as a positive electrode active material satisfying such requirements.

The activated carbon may be in the form of powder, granules, or fibrous. Therefore, it can be appropriately selected from known activated carbons such as coconut shell activated carbon, wood-based activated carbon, coal-based activated carbon, and activated carbon using resin as a raw material. . The specific surface area per gram of the positive electrode active material such as activated carbon can be appropriately selected according to the type of the electric double layer capacitor, and may be, for example, 1000 to 3000 m ² / g, and more preferably 1 to 3000 m ² / g.
500 to 3000 m ² / g can be adopted. However, it is not limited to these.

As a material constituting the positive electrode active material layer, a binder or a conductive agent can be used in addition to the positive electrode active material, if necessary. The binder binds between the positive electrode active materials and between the positive electrode active material and the current collector, and the type thereof is not particularly limited. However, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, carboxyethyl cellulose, and polytetrafluorocarbon are used. Examples include ethylene. Further, the conductive material is to improve the conductivity between the positive electrode active material and between the positive electrode active material and the current collector,
The type is not particularly limited, but, for example, carbon black can be used.

The method for forming the positive electrode active material layer is not particularly limited either, and it can be formed by a known forming method. For example, the positive electrode active material layer can be formed as follows.

First, a powdery positive electrode active material, a conductive material, and a binder are prepared, and they are added to an appropriate dispersion medium, mixed well, and dispersed to prepare a paste-like positive electrode mixture. This positive electrode mixture is uniformly applied on the surface of the sheet-shaped current collector by a predetermined application method to form a mixture application layer. As the coating method, a known coating method such as a doctor blade method, a screen printing method, and a spin coating method can be employed.

Thereafter, the mixture coating layer is dried to remove the dispersion medium, thereby forming a positive electrode active material layer. If necessary, it is press-formed by an appropriate press-forming method to adjust the shape and density. The positive electrode active material layer may be formed on one surface of the current collector, or may be formed on both surfaces of the current collector.

The material of the negative electrode is not particularly limited by the composition of the material, but it is preferable to use a material in which a negative electrode active material layer containing a negative electrode active material is formed on a current collector similarly to the positive electrode. .

In this case, the type of the negative electrode active material is not particularly limited, and a known negative electrode active material can be used. It is necessary to use a negative electrode active material that does not cause a chemical reaction with the electrolytic solution, and particularly does not cause an electrochemical reaction with the electrolytic solution even when polarization occurs during charging. Therefore, it is necessary to select an appropriate one according to the electrolytic solution used. It is preferable to use a material having a large specific surface area as the negative electrode active material, and the same active material as the positive electrode such as activated carbon can be used.

As a material constituting the negative electrode active material layer, it is preferable to use a binder or a conductive agent in addition to the negative electrode active material. The types of the binder and the conductive agent are not particularly limited, and the same materials as those for the positive electrode can be used.

Also, the method for forming the negative electrode active material layer is not particularly limited, and it can be formed by a known forming method, and the negative electrode active material layer can be formed by the same forming method as the positive electrode. .

Further, the arrangement of the positive electrode and the negative electrode is not particularly limited, and can be applied to any known arrangement. For example, a laminated electrode or a wound electrode may be used. Can be applied to In addition to the electrode bodies, a positive electrode plate and a negative electrode plate each having a sheet-like shape are configured to face each other, and cylindrical positive electrodes and negative electrodes having different diameters are alternately concentric with each other. The present invention can also be applied to arrangements such as those provided.

In the above arrangement of the electrodes, a separator is generally provided between the positive electrode and the negative electrode. In the present invention, such a separator is preferably provided. As the separator, a known separator can be used. For example, a separator made of polyethylene, Japanese paper, or the like can be used.

The electrolytic solution is not particularly limited, and a known electrolytic solution, that is, a solution obtained by dissolving an electrolyte in a solvent can be used. In the present invention, water may be used as the solvent, or a non-aqueous electrolyte using an organic solvent may be used.
When the latter nonaqueous electrolyte is used, it is preferable to use a carbonate-based organic solvent such as propylene carbonate or ethylene carbonate, tetrahydrofuran, dimethoxyethane, or the like as the solvent.

The electrolyte is not particularly limited and may be a known electrolyte.
Of cations and anions
Salt can be given. As the electrolyte, for example, L
iBF_Four, LiPF₆, LiClO_Four, (C_TwoH_Five)_FourNBF
_Four, (CH_Three)_FourNBF_Four, CH _Three(C_TwoH_Five)_ThreeNBF_FourEtc.
can give.

The case is a member for holding the above-mentioned electrode body and electrolyte. The shape and material are not particularly limited, but may be made of a known shape and material, for example, a metal or resin having a cylindrical or square shape and in which an undesired reaction with the electrolytic solution does not proceed. As described above, when the function of the discharge leveling resistor also functions as the case, it is preferable that the connection between the positive electrode and the negative electrode and the case does not change the resistance value due to the contact resistance. For example, when connecting the positive and negative terminals to the case lid, the problem of contact resistance is reduced by molding the case lid with the positive and negative terminals present by injection molding or the like. .

It should be noted that one case is not always required for each electric double layer capacitor cell, and a plurality of electric double layer capacitor cells may share the case. In the case where the case is shared, a partition member may be provided for each electric double layer capacitor cell, and in the case of parallel connection, the electrolytic solution may be freely moved without providing the partition member.

Then, the electric double layer capacitor cell includes:
Other elements can be added as needed.
For example, there is a safety valve or the like that adjusts the internal pressure when the inside of the case becomes high pressure for some reason.

[0041]

The multilayer electric double layer capacitor of the present embodiment has the following features.
With the above-mentioned configuration, even if the insulation resistance of each electric double layer capacitor cell constituting this multilayer electric double layer capacitor varies, the overall resistance value can be reduced by the discharge leveling resistors connected in parallel. Variations are reduced.
As a result, the variation in the self-discharge speed of the electric double layer capacitor cell can be reduced, and the difference in voltage change between the electric double layer capacitor cells can be reduced.

Therefore, even if the present multilayer electric double layer capacitor is charged for a certain amount and left for a while, the amount of electricity remaining in each electric double layer capacitor cell, that is, the voltage value of each electric double layer capacitor cell is substantially equal. Become. Therefore, voltage application is not concentrated on the electric double layer capacitor cell having a relatively high insulation resistance, and the risk of breakdown is reduced.

Further, since the discharge leveling resistor can be realized at low cost, even if the discharge leveling resistor is connected to each electric double layer capacitor cell constituting the multilayer electric double layer capacitor, the overall cost is low. Can be

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Electric Double Layer Capacitor Cell) An electric double layer capacitor cell in which a case lid also serves as a discharge leveling resistor will be described.

As shown in FIGS. 2 and 3, the electric double layer capacitor cell 10 of the present embodiment comprises an electrode body in which a positive electrode 1 and a negative electrode 2 are laminated with a separator (not shown) interposed therebetween in an electrolytic solution (not shown). Together with the case 3. The positive electrode 1 is electrically connected to the positive terminal 4, and the negative electrode 2 is electrically connected to the negative terminal 5. The positive terminal 4 and the negative terminal 5 are fixed to the case lid 6. The case lid 6 also functions as a discharge leveling resistor, and is formed by molding a conductive resin mixed with a carbon filler in a resin (PPS, phenol or the like) matrix. The conductivity (resistance value) of the discharge leveling resistor is adjusted by the amount of the carbon filler mixed therein.

(Comparative Example) Among the electric double layer capacitor cells 10 described above, an electric double layer capacitor cell in which the case lid 6 was not provided with conductivity (no carbon filler was mixed) was manufactured. And 2 electric double layer capacitor cells. The electric double layer capacitor cell of Comparative Example 1 had an insulation resistance of 3 kΩ, and the electric double layer capacitor cell of Comparative Example 2 had an insulation resistance of 1 kΩ.

(Examples 1 to 3) Positive terminal 4 and negative terminal 5
The electric double layer capacitor cell employing the case lid 6 having a resistance value between 1 kΩ, 500Ω and 100Ω was manufactured, and the electric double layer capacitor cells of Examples 1 to 3 were obtained.
In each embodiment, the electric double layer capacitor cell having the branch number 1 has an insulation resistance of 3 k before being fixed to the case lid 6.
The electric resistance of the electric double layer capacitor cell having the resistance number of Ω and the branch number of 2 was 1 kΩ before being fixed to the case lid 6.

(Time-dependent change in open-circuit voltage of electric double-layer capacitor cell) The electric-double-layer capacitor cells of Comparative Example and Examples 1 to 3 were each charged to 2.5 V, and thereafter, the time-dependent change in open-circuit voltage was measured. .

(Results) Comparative Example (FIG. 4), Example 1-1,
-2 (FIG. 5), 2-1 and -2 (FIG. 6), 3-1 and -2
The results for FIGS. 7 and 8 are shown respectively. As is apparent from these figures, the variation in the open-circuit voltage value decreases as the resistance value of the resistor connected in parallel between the terminals decreases.

Also, in Example 3 in which the resistance value of the resistor is relatively small (100Ω), as is apparent from FIG. 8, it takes about 5 hours for the voltage value to decrease by 20%, and in practice, It turned out to be no problem at all. Therefore, when the width of the insulation resistance variation of the electric double layer capacitor cell is about 1 kΩ to 3 kΩ, the resistance value of the discharge leveling resistor may be 1 kΩ or less, preferably 500 Ω or less, more preferably 100 Ω or less. it can.

[0051]

The multilayer electric double layer capacitor of the present invention is a multilayer electric double layer capacitor having a plurality of electric double layer capacitor cells connected in series, wherein each of the electric double layer capacitor cells is connected in parallel. With the connected discharge leveling resistor, the insulation resistance of each electric double layer capacitor cell, that is, the variation in applied voltage can be reduced. Therefore, a highly reliable low-cost multilayer electric double layer capacitor can be obtained.

Further, a low-cost member (such as a case lid) can be used as the discharge leveling resistor.

As described above, the multilayer electric double layer capacitor of the present invention has an effect that a highly reliable multilayer electric double layer capacitor can be provided at lower cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit of an electric double layer capacitor cell in a multilayer electric double layer capacitor of the present invention.

FIG. 2 is a plan view of the electric double layer capacitor cell of the present embodiment.

FIG. 3 is a cross-sectional view of the electric double layer capacitor cell of the present embodiment.

FIG. 4 is a graph showing the change over time of the open-circuit voltage of the electric double layer capacitor cell of the comparative example.

FIG. 5 is a graph showing the change over time of the open-circuit voltage of the electric double layer capacitor cell of Example 1.

FIG. 6 is a graph showing the change over time of the open-circuit voltage of the electric double layer capacitor cell of Example 2.

FIG. 7 is a graph showing the change over time of the open-circuit voltage of the electric double layer capacitor cell of Example 3.

FIG. 8 is a graph showing the change over time of the open-circuit voltage of the electric double layer capacitor cell of FIG.

FIG. 9 is a diagram showing an equivalent circuit of a conventional electric double layer capacitor cell.

[Description of Signs] 10 ... Electric double layer capacitor cell 1 ... Positive electrode 2 ... Negative electrode 3 ... Case 4 ... Positive terminal 5 ... Negative terminal 6 ... Case lid

Claims (4)

[Claims] 1. A multilayer electric double layer capacitor having a plurality of electric double layer capacitor cells connected in series, wherein each of said electric double layer capacitor cells has a discharge leveling resistor connected in parallel. A multilayer electric double layer capacitor characterized by the following. 2. Each of the electric double layer capacitor cells has a positive electrode terminal and a negative electrode terminal, and an electrode fixing portion for fixing the positive electrode terminal and the negative electrode terminal, wherein the electrode fixing portion includes the positive electrode terminal and the negative electrode terminal. 2. The multilayer electric double layer capacitor according to claim 1, wherein a current can flow between the negative electrode terminals and also functions as the discharge leveling resistor. 3. The electric double layer capacitor cell has a positive electrode, a negative electrode, and a case for holding the positive electrode and the negative electrode, wherein the case is capable of conducting electricity between the positive electrode and the negative electrode and the discharge leveling. The multilayer electric double-layer capacitor according to claim 1, which also functions as a resistor. 4. The multilayer electric double layer capacitor according to claim 1, wherein a resistance value of said resistor is smaller than an insulation resistance value of each of said electric double layer capacitor cells.