JP6749804B2 - Electrochemical cell - Google Patents

Description

The present invention relates to a reflow solderable and reliable electrochemical cell.

There is known an electrochemical cell such as an electric double layer capacitor that is used for supporting data writing to a memory when a momentary power failure occurs and smoothing a circuit voltage, and has a low resistance due to winding and stacking. In addition, as a package of these electrochemical cells, a laminate type package has been conventionally known.
In this type of electrochemical cell package, there has been proposed a ceramic package that has excellent sealing properties, improves long-term reliability, and is compatible with reflow soldering (see Patent Document 1).
As the electrodes of this type of electrochemical cell, various electrode sheet configurations are known in addition to an electrode sheet obtained by applying a slurry containing an active material to a collector made of aluminum foil or the like. For example, the electrode described in Patent Document 2 below has a structure that can improve the adhesion between the active material and the current collector and suppress the surface resistance value.

JP, 2013-30750, A JP 2006-100477A

Conventionally, in a ceramic package used in this type of electrochemical cell, a constant container wall thickness has been required due to manufacturing and durability requirements. Further, since the lead of the element internally connected to the pad film of the container has a certain thickness, there is a problem that the size of the element that can be accommodated in the container is further restricted.
For this reason, it is necessary to have higher conductivity and capacity density than the conventional configuration in order to place an electrochemical cell equipped with a ceramic package in the same mounting space as the conventional laminate type. It was
Further, in order to further reduce the mounting space, it is necessary to provide an element which has improved heat resistance and withstand voltage and is required to be used in a single cell.
Further, in an electrochemical cell using a ceramic package, when reflow soldering is performed, problems such as an increase in internal resistance due to the heat of the solder occur and there is a problem that the electrochemical cell deteriorates in characteristics due to the reflow soldering process. It was

The present invention has been made in view of the conventional circumstances, and to provide an electrochemical cell having high conductivity, high capacity density, high reliability even with a small element shape, and less characteristic deterioration due to reflow soldering. To aim.

In order to solve the above-mentioned problems, the present invention is formed on a base container, a cell element housed in the base container, a plurality of cell leads that are extensions of the cell element, and an inner bottom surface of the base container. An electrochemical cell having at least a pad film made of a valve metal, an intra-base wiring connected to the pad film and formed from an inner bottom surface to a lower surface of the base container, and a lid that hermetically closes the base container. In the cell element, the positive electrode and the negative electrode are arranged with a separator interposed therebetween, and further, a nonaqueous electrolytic solution is contained, and at least one of the positive electrode and the negative electrode is an aluminum current collector, and on the aluminum current collector. A layer of a carbon material fixed by a compound of aluminum and carbon, and an active material layer formed on the layer of the carbon material and containing activated carbon, a conductive additive and a binder , wherein the non-aqueous electrolytic solution is a supporting salt. : 13 to 43% by mass and the balance solvent, and the composition has a composition of sulfolane: 60 to 90% by mass and ethylmethylsulfone: 10 to 40% by mass in the balance solvent mass ratio.
Since the cell element and the electrolytic solution are housed in the airtight base container and the supporting salt, sulfolane and ethyl methyl sulfone are used as the proper ratio of the electrolytic solution, the supporting salt has high solubility and receives the heat of the reflow solder. In addition, it is possible to provide an electrochemical cell having a low internal resistance increase rate and a small decrease in capacity and improved heat resistance.
Further, since the interface between the layer of carbon material and the aluminum current collector is fixed by the compound of aluminum and carbon, the adhesion of the carbon particles on the surface of the aluminum current collector does not easily deteriorate even when the heat of the reflow solder is received. Therefore, an electrochemical cell having high heat resistance can be obtained.
Further, the non-aqueous electrolytic solution is a supporting salt of a spiro compound 15 to 40 mass%, the balance solvent, in the balance solvent mass ratio, sulfolane: 64-88 mass%, ethyl methyl sulfone: 12-36 mass% composition. May have.

In the present invention, an intervening layer containing the compound of aluminum and carbon is formed on a surface portion of the aluminum current collector, and a second surface portion extending outward from the intervening layer is formed. It is possible to adopt a structure in which a layer of the carbon material having a conductive layer in which a plurality of carbon particles are fixed is formed on the surface portion of.
By adopting a structure having a conductive layer having a plurality of carbon particles fixed on a second surface portion extending from an intervening layer containing a compound of aluminum and carbon formed on the surface portion of the aluminum current collector, An electrode structure can be formed in which the carbon particles do not separate from the aluminum current collector even when subjected to the above. Therefore, even if the heat of the reflow solder is received, the adhesion of the carbon particles on the surface of the aluminum current collector is unlikely to be lowered, so that an electrochemical cell having high heat resistance can be provided.
In the present invention, it is possible to adopt a configuration in which the conductive layer contains an active material.
The capacity of the cell can be increased by including the active material in the conductive layer.

In the present invention, the supporting salt may be a quaternary ammonium salt or a quaternary phosphonium salt.
With these supporting salts, high solubility of the supporting salt in the electrolytic solution can be obtained, and the solvent can have high electric conductivity.
In the present invention, it is possible to employ a configuration in which the positive electrode, the negative electrode, and the separator of the cell element housed in the base container are impregnated with the nonaqueous electrolytic solution.
When impregnating the positive electrode, the negative electrode of the cell element, and the periphery of the separator with the non-aqueous electrolytic solution, the size was reduced by using an electrolytic solution composed of a solvent containing sulfolane and ethylmethylsulfone in the above composition ratio and a supporting salt in the above composition ratio. It is possible to provide an electrochemical cell in which the cell element is sufficiently impregnated with the electrolytic solution.

The electrochemical cell of the present invention has a structure in which a layer of a carbon material is fixed by a compound of aluminum and carbon on an aluminum current collector of a cell element, and an active material layer containing activated carbon, a conductive additive and a binder is provided thereon. Since the above electrode is provided, it has good adhesion between the aluminum current collector and the carbon material layer, and can suppress an increase in interface resistance between the aluminum current collector and the carbon material layer. Therefore, it is possible to provide an electrochemical cell having higher conductivity and higher capacity density than an electrochemical cell having a conventional structure in which a slurry containing an active material, a conductive auxiliary agent, and a binder is directly coated on an aluminum current collector. In addition, since good adhesion between the aluminum current collector and the carbon material layer is less likely to be deteriorated even when receiving heat of the reflow solder, the cell element is housed in the base container, and wiring is provided in the base container. It is possible to provide an electrochemical cell capable of highly reliable reflow soldering with a small element shape.
Since the electrochemical cell of the present invention has sulfolane: 60 to 90% by mass and ethylmethylsulfone: 10 to 40% by mass as a solvent in addition to 13 to 43% by mass of the supporting salt, the conductivity and the capacity density are It is possible to provide an electrochemical cell having high chargeability and excellent charging characteristics. Further, when the base container accommodating the cell element is sealed with the lid, the heat of welding for sealing is transferred to the non-aqueous electrolytic solution, the non-aqueous electrolytic solution is difficult to evaporate, and the quality of the non-aqueous electrolytic solution deteriorates. It is possible to provide an electrochemical cell in which resistance is unlikely to increase.

The electrochemical cell of 1st Embodiment which concerns on this invention is shown, (a) is a perspective view, (b) is a partial cross section figure. The relationship between the pad film, the via wiring, and the connection terminal of the same electrochemical cell is shown, (a) is a view seen from the pad film side, and (b) is a view seen from the connection terminal side. FIG. 3A is a plan view of the connection portion, and FIG. 6B is a cross-sectional view showing an example of a state in which a welding tip is used to weld the cell lead and the pad film of the same electrochemical cell. The cell element accommodated in the same electrochemical cell is shown, (a) is a block diagram of a cell element, (b) is a partial expanded sectional view of a collector and a conductive layer. The block diagram which shows the electrochemical cell of 2nd Embodiment which concerns on this invention. The block diagram which shows the electrochemical cell of 3rd Embodiment which concerns on this invention. The electrochemical cell of 4th Embodiment which concerns on this invention is shown, (a) is a perspective view of a base container, (b) is sectional drawing of the electrochemical cell provided with the said base container, (c) is another. Sectional drawing which shows the electrochemical cell of an example. 6 is a graph showing the internal resistance before and after the reflow soldering test for the electrochemical cells of Examples 1 and 2 and the electrochemical cell of Comparative Example 1. 6 is a graph showing the discharge time before and after the reflow soldering test for the electrochemical cells of Examples 1 and 2 and the electrochemical cell of Comparative Example 1. The internal resistance before and after the reflow soldering test was determined for the electrochemical cell of Comparative Example 2 obtained by changing the solvent for the electrochemical cell of Example 1, and compared with the internal resistance measurement result of the electrochemical cell of Example 1. The graph shown. 6 is a graph showing the discharge time before and after the reflow soldering test for the electrochemical cell of Example 1 and the electrochemical cell of Comparative Example 2. The graph which shows the capacity retention rate according to the elapsed days when it sets 60 degreeC and the charging voltage 3.0V about the electrochemical cell of Example 1, and the electrochemical cell of Comparative Example 2. The graph which shows the internal resistance increase rate according to the elapsed days when 60 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Example 1, and the electrochemical cell of Comparative Example 2. The graph which shows the capacity retention rate according to the elapsed days when 85 degreeC and the charging voltage are set to 3.0V about the electrochemical cell of Example 1, and the electrochemical cell of Comparative Example 2. The graph which shows the internal resistance increase rate according to the elapsed days when it set to 85 degreeC and the charging voltage 2.5V about the electrochemical cell of Example 1, and the electrochemical cell of Comparative Example 2. The graph which shows the internal resistance before and behind a reflow soldering test about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the discharge time before and after a reflow soldering test about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the capacity retention rate according to the preservation days when 70 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the internal resistance increase rate according to the preservation days when 70 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the capacity retention rate according to the preservation days when 85 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the internal resistance increase rate according to the preservation|save days at the time of setting to 85 degreeC and the charging voltage 2.5V about the electrochemical cell of Examples 3 and 4 and the electrochemical cell of Comparative Examples 3 and 4. The graph which shows the internal resistance before and behind a reflow soldering test about the electrochemical cell of Examples 5, 6, and 7 and the electrochemical cell of Comparative Examples 5 and 6. The graph which shows the discharge time before and after a reflow soldering test about the electrochemical cell of Examples 5, 6, and 7 and the electrochemical cell of Comparative Examples 5 and 6. 7 is a graph showing the capacity retention rate according to the number of days of storage when the electrochemical cell of Example 5 and the electrochemical cells of Comparative Examples 5 and 6 are set to 70° C. and a charging voltage of 2.5V. The graph which shows the internal resistance increase rate according to the preservation|save days when 70 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Example 5, and the electrochemical cells of Comparative Examples 5 and 6. The graph which shows the capacity retention rate according to the preservation|save days when 85 degreeC and the charging voltage are set to 2.5V about the electrochemical cell of Example 5, and the electrochemical cells of Comparative Examples 5 and 6. The graph which shows the internal resistance increase rate according to the preservation days when 85 degreeC and the charging voltage of 2.5V are set about the electrochemical cell of Example 5, and the electrochemical cells of Comparative Examples 5 and 6.

Hereinafter, the electrochemical cell according to the first embodiment of the present invention will be described with reference to the drawings.
The electrochemical cell 1 of the first embodiment is mainly used by being mounted on a substrate inside a personal computer or a small portable device.
(Electrochemical cell 1)
FIG. 1A is an external view (perspective view) of the electrochemical cell 1 of this embodiment.
As shown in FIG. 1, the electrochemical cell 1 is shown in the shape of a rectangular parallelepiped as an example, but it may be in the shape of a track or a cylinder. The electrochemical cell 1 of the present embodiment stores a cell element 6 which is a power generation element and functions as a container, and a lid (lid) 10 that functions as a sealing plate for hermetically closing the opening. Is equipped as an exterior part. The outer container of the electrochemical cell 1 is composed of this base container 2 and a lid 10 that seals the opening of the base container 2.

FIG. 1B is a sectional view taken along the line AA of FIG. The cell element 6 is housed in the concave base container 2, the electrolyte solution 7 is further filled therein, and the base 10 is provided by a lid 10 pressed against a seal ring 9 provided around the upper surface of the opening of the base container 2. The container 2 is hermetically sealed. On the bottom surface 2c of the base of the base container 2, a pair of current collector metal films, which are pad films 5, are juxtaposed. Further, a plurality of via wirings 3 are formed on the bottom surface side of the pad film 5 from the inner bottom surface 2c of the base to the bottom surface 2d of the base so as to penetrate the bottom wall of the base container. These via wirings 3 electrically connect the pad film 5 and the connection terminals 4 formed on the base lower surface 2d.

On the other hand, the cell element 6 is housed in the base container 2. The cell element 6 has a set of electrode sheets made of a current collector of a metal sheet carrying a layer of a carbon material such as carbon particles and formed by a winding method or a laminating method with an insulating separator inserted. Is. A cell lead 8 made of a metal plate is connected to each end of the positive and negative electrode current collectors. The cell lead 8 of each of the positive electrode and the negative electrode is fixed to each of the pair of pad films 5 by, for example, welding. The positive electrode and the negative electrode of the cell element 6 are electrically connected to the mounting pattern of the substrate mounted by the connection terminal 4.

(Base container 2)
The base container 2 is a container made of a box-shaped ceramic having an opening at the top, and has a rectangular base bottom portion 2a and a rectangular frame-shaped base peripheral wall portion 2b standing on the outer edge of the base bottom portion 2a. doing. The size of the base container 2 may be about 5 to 20 mm on each side and about 1 to 3 mm in height. 2(a) and 2(b) are diagrams showing a base inner bottom surface 2c and a base lower surface 2d of the base container 2, respectively. A pair of pad films 5 made of a conductive material are arranged on the inner bottom surface 2c of the base shown in FIG. 2(a). Four via wirings 3 indicated by broken lines are provided adjacent to each other on the lower surface of the pad film 5, and these via wirings 3 are connected to connection terminals 4 (also indicated by broken lines) arranged on the lower surface 2d of the base. ing.

The constituent material of the base container 2 includes ceramics containing at least one selected from the group consisting of alumina, silicon nitride, zirconia, silicon carbide, aluminum nitride, mullite, and composite materials thereof. Is not limited to this. Soda lime glass or heat resistant glass can also be used. Since a long glass can be used as a material, a large number of glass can be set for one glass in the case of a small package, and cost reduction of the base member can be expected.
In the base container 2 of the present embodiment, for example, after the ceramic green sheet corresponding to the base bottom portion 2a punched in a rectangular shape is bonded to the ceramic green sheet corresponding to the base peripheral wall portion 2b punched in a rectangular frame shape, Formed by firing. A through hole can be formed by punching a hole in the ceramic green sheet corresponding to the base bottom portion 2b in advance, and the via wiring 3 can be formed using this through hole.

(Via wiring 3)
The via wiring 3 is a wiring formed from the inner bottom surface 2c of the base container 2 to the lower surface 2d of the base. In the via wiring 3, first, a through hole is formed in the base bottom portion 2a for penetrating the inner bottom surface 2c of the base and the lower surface 2d of the base substantially vertically, and the wiring hole is filled with a wiring paste of metal such as tungsten. It is formed by In addition, by forming the via wiring 3, the airtightness of the through hole is satisfied.
As the conductive paste used for the via wiring 3, a paste in which carbon and a resin are mixed, a paste in which tungsten, molybdenum, nickel, gold, or a composite material of these metals and a resin are mixed can be used.

The paste filled in the through holes becomes the via wiring 3 by firing together with the ceramic green sheet that becomes the base container 2.
As described above, when the base container 2 is formed of a glass material such as soda lime glass or heat-resistant glass, the means for forming recesses or through holes in these glasses is a chemical etching method or sandblasting. The recess and the through hole can be formed at the same time by a physical method or by using a mold in a high temperature atmosphere. Then, after forming an aluminum film on the inner surface of the through hole, a glass paste having a matched thermal expansion coefficient is filled into the through hole, and debinding and firing are performed to form the airtight and conductive via wiring 3. Can be formed. In such a case, there is no concern that the via wiring 3 will be dissolved by the electrolytic solution 7 described later. The film forming the inner surface of the via wiring 3 is not limited to aluminum and may be a film containing other valve metal such as titanium.

(Connection terminal 4)
A pair of connection terminals 4 are provided on the lower surface 2d of the base shown in FIG. 2B so as to face the pad film 5. The connection terminal 4 is fixed to the board by a reflow process or the like with cream solder or the like provided on the pattern of the mounting board.
In the present embodiment, the connection terminal 4 can be formed by printing an electrode pattern made of tungsten in advance on the ceramic green sheet that will be the base container 2 and firing the ceramic green sheet. Further, it is preferable that the connection terminal 4 has a pattern of tungsten formed by a printing method and a plating film made of nickel and gold. Further, tungsten and these plating materials are patterned also in the concave portion of the base side surface 2e, and these function as a part of the connection terminal.

(Pad film 5)
The pad film 5 is a substantially rectangular film made of a conductive material and arranged at two locations on the inner bottom surface 2c of the base. The pad film 5 has a welded portion for preventing direct contact between the upper end portion of the via wiring 3 and the electrolytic solution 7 and for connecting the cell lead 8 by welding.
In addition, although the pad films 5 of the present embodiment are juxtaposed in the longitudinal direction of the base container 2, it is also possible to juxtapose them in the short side direction or in the diagonal direction of the longitudinal direction.
The pad film 5 is a film made of a chemically stable valve metal such as aluminum or titanium, and is made of a material that is difficult to dissolve in the electrolytic solution 7. These films can be provided by a known film forming method such as vapor deposition, ion plating or sputtering. In the case of using these methods, first, a metal such as tungsten is filled in the through holes by a printing method or the like and baked to finish the airtight via wiring 3 and then formed. When the film is formed in a vacuum, for example, a mask made of metal or the like, which is patterned to have two openings spatially separated from each other so as to configure the positive electrode pad film 5 and the negative electrode pad film 5, is prepared. The valve metal material is housed in the chamber of the film forming apparatus and is evacuated to a predetermined degree of vacuum by a vacuum exhaust system, and then the valve metal material is vapor-deposited or the target made of the valve metal material is physically hit with ions to remove the valve metal material. It is skipped and a film is formed on the inner bottom surface 2c of the base. In these film forming methods, the film forming conditions are easily controlled, so that the formed film has a low resistivity and can be formed as a high density film in which a liquid hardly penetrates.

The aluminum film can also be formed by a screen printing method. A technique has been developed that can form a wiring pattern at a temperature of 150° C. or lower even for aluminum that is easily oxidized at high temperatures. Since this method is a printing method, a thicker film can be formed as compared with a thin film forming technique such as a vapor deposition method, and a thick film of several tens of μm can be easily obtained. Further, the aluminum film can be produced by an electroplating method. If the film is formed to a thickness of about 40 μm using a plating solution composed of dimethyl sulfone and aluminum chloride, a film having a smooth surface and a uniform inside can be obtained.

Then, the film thickness of the pad film 5 is preferably 5 μm or more and 100 μm or less. Preferably, the range of 10 μm or more and 30 μm or less is more desirable. If the film thickness is thin, fine pores existing inside the film are connected, and the electrolytic solution 7 easily penetrates into the tungsten via wiring 3 under the pad film to easily cause electrolytic corrosion of tungsten. This is because when the cell lead 8 is connected by welding, the welding conditions are extremely limited and it becomes difficult to realize reliable joining. Here, an experiment of forming an aluminum film having a thickness of 5 μm as the pad film 5 on the soda lime glass plate having a thickness of about 1.3 mm by the ion plating method and then welding a thin plate of aluminum having a thickness of 80 μm by ultrasonic welding was conducted. Carried out.
As a result, it was confirmed that minute cracks were generated in the glass plate in one sample out of five cell leads. Therefore, it can be estimated that 5 μm is the practically lower limit of the thickness of the pad film 5. Practically, it is desirable that the thickness of the pad film 5 is 10 μm or more.

(Cell element 6)
Next, the cell element 6 will be described. The cell element 6 includes an aluminum foil having a thickness of 5 μm to 100 μm as a current collector, and a pair of positive and negative electrode sheets provided with a layer of a carbon material containing an active material on the surface thereof is wound with a separator made of an insulator interposed therebetween. It is a power generation element that is integrated by methods such as stacking and folding.
In the cell element 6 of this embodiment, an intervening layer containing a compound of aluminum and carbon is formed on a surface portion of an aluminum current collector as described later, and a second surface portion extending outward from the intervening layer. The electrode sheet is provided with a special structure in which a conductive layer having a plurality of carbon particles fixed thereto is provided in a carbon material layer. Further, in this electrode sheet, it is preferable that the active material layer is formed on the conductive layer. Further, the conductive layer may include an active material. When the conductive layer contains an active material, it preferably contains activated carbon. The capacity of the electrochemical cell can be increased by forming the electrode sheet having the conductive layer containing the active material. Even in this case, the adhesiveness of the carbon particles on the surface of the aluminum current collector does not easily deteriorate even when the heat of the reflow solder is applied, so that the electrochemical cell having high heat resistance can be obtained.
This electrode sheet can be manufactured with reference to, for example, WO2004/087984. Specifically, it can be obtained by applying carbon particles to the surface of the aluminum foil and then heating the carbon foil in a hydrocarbon atmosphere to about 300 to 650°C.
By this heat treatment, a compound of aluminum and carbon can be generated on the surface of the aluminum foil, and the carbon particles can be fixed on the surface of the aluminum foil by the compound of aluminum and carbon. More specifically, TOYAL CARBO (registered trademark) manufactured by Toyo Aluminum Co., Ltd. can be used. As the compound of aluminum and carbon, aluminum carbide (Al ₄ C ₃ ) is particularly preferable.

FIG. 4 shows a schematic structure of an example in which the cell element 6 has a wound structure.
As shown in FIG. 4A, the cell element 6 includes a film-shaped positive electrode body (positive electrode) 32 including a conductive layer 30 including a carbon particle aggregate and a positive electrode current collector 31 of an aluminum foil, and an aggregate of carbon particles. A film-shaped negative electrode body (negative electrode) 42 including a conductive layer 40 including a body and a negative electrode current collector 41 of aluminum foil, and a film-shaped separator 35 provided between the positive electrode body 32 and the negative electrode body 42 are laminated. Has a laminated structure. That is, the cell element 6 has a spiral structure in which a film-shaped positive electrode body 32 and a negative electrode body 42 are laminated so as to face each other with a separator 35 in between, and the laminated body is wound in the same direction. ing.
Further, the cell lead 8 for the positive electrode is joined to a part of the positive electrode current collector 31, the cell lead 8 for the negative electrode is joined to a part of the negative electrode current collector 41, and these are drawn out of the spiral structure. The cell element 6 shown in FIG. 4(a) is configured.

Aluminum used as the aluminum foil is not particularly limited, and pure aluminum or aluminum alloy can be widely used. Aluminum used in the present embodiment has a composition of lead (Pb), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc ( Zn), titanium (Ti), vanadium (V), gallium (Ga), aluminum alloy in which at least one alloy element of nickel (Ni) and boron (B) is added within a necessary range, or an unavoidable impurity element. It also includes aluminum containing.

The thickness of the aluminum foil is not particularly limited, but may be in the range of 5 μm or more and 100 μm or less, for example, in the range of 5 μm or more and 20 μm or less.
The thickness of the carbon material layer can be set in the range of 0.01 μm or more and 200 μm or less, for example, in the range of 0.3 μm or more and 50 μm or less.
The relationship between the positive electrode current collector 31 and the conductive layer 30 has a structure shown in an enlarged manner in FIG. That is, the conductive layer 30 including the aggregate of carbon particles is formed on the surface portion of the positive electrode current collector 31, and the intervening layer 33 is formed between the positive electrode current collector 31 and the conductive layer 30. The intervening layer 33 forms a first surface portion containing a compound of aluminum and carbon, which is formed on at least a part of the surface of the positive electrode current collector 31 made of aluminum. Conductive layer 30 includes a second surface portion 34 that includes an aluminum and carbon compound extending outwardly from the aluminum and carbon compound of intervening layer 33. A plurality of carbon particles 36 are fixed to the second surface portion 34 to form the conductive layer 30. The conductive layer 30 may be formed on one surface of the positive electrode current collector 31 as shown in FIG. 4A, or may be formed on both surfaces.
Further, in the present embodiment, it is preferable that an active material layer made of activated carbon, a conductive auxiliary agent, and a binder is formed to a required thickness (for example, about 30 μm) on the conductive layer 30 having the carbon particles 36 formed on the surface thereof.
Similarly, the relationship between the negative electrode current collector 41 and the conductive layer 40 is such that the intermediate layer (first surface portion) 33 is formed on the surface of the negative electrode current collector 41, and the second surface portion 34 is formed thereon. The plurality of carbon particles 36 are fixed to the second surface portion 34 to form the conductive layer 40. It is preferable that an active material layer made of activated carbon, a conductive auxiliary agent, and a binder is formed on the conductive layer 40 to a required thickness (for example, about 30 μm). Further, the conductive layer 40 may be formed on one surface of the negative electrode current collector 41 as shown in FIG. 4A, or may be formed on both surfaces.

The separator 35 regulates the direct contact between the positive electrode body 32 and the negative electrode body 42, and an insulating film having a large ion permeability and a predetermined mechanical strength is used. For example, in an environment where heat resistance is required, in addition to glass fiber, resins such as polytetrafluoroethylene, polyphenylene sulfide, polyethylene terephthalate, polyamide and polyimide can be used. The pore diameter and thickness of the separator are not particularly limited, but are determined based on the current value of the equipment used and the internal resistance of the electrochemical cell 1. It is also possible to use a ceramic porous body as the separator.
The configuration of the cell element 6 shown in FIG. 4A is a general example of a wound cell element, but the cell element may have any configuration such as a laminated type or a foldable type.

(Electrolyte 7)
As the electrolytic solution 7, it is preferable to use a mixed electrolytic solution in which a supporting salt is dissolved in a mixed solvent containing sulfolane (SL) and ethylmethylsulfone (EMS).
Sulfolane (SL) is one of cyclic sulfones, and has a high dielectric constant and can dissolve a large amount of supporting salt to form an electrolytic solution having good conductivity. Since SL has a high boiling point and strong oxidation resistance, it can be used as the main solvent of the electrolytic solution of the electrochemical cell. In addition, ethyl methyl sulfone (EMS) is one of chain sulfones. By mixing this EMS with sulfolane (SL) having a high melting point and using it as the solvent of the electrolytic solution, the viscosity can be lowered as compared with the solvent containing only sulfolane (SL).
Examples of the supporting salt include a quaternary ammonium salt and a quaternary phosphonium salt. More specifically, of the quaternary ammonium salts, examples of compounds having only a fatty chain include triethylmethylammonium (TEMA) salts and tetraethylammonium (TEA) salts. Examples of the spiro compound include 5-azoniaspiro[4,4]nonanetetrafluoroborate (spiro-(1,1′)-bipyrrolidinium:SBP-BF4), 6-azoniaspiro[5,5]undecanetetrafluoroborate, 3 -Azoniaspiro[2,6]nonanetetrafluoroborate, 4-azoniaspiro[3,5]nonanetetrafluoroborate and the like can be mentioned. Examples of the quaternary phosphonium salt include 5-phosphonylspiro[4,4]nonanetetrafluoroborate.
As the supporting salt, a quaternary ammonium salt is preferable, a spiro compound is more preferable, and 5-azoniaspiro[4,4]nonanetetrafluoroborate is further preferable. Since the spiro compound of the quaternary ammonium salt has high electric conductivity, the discharge capacity can be increased.

The electrolytic solution 7 has, for example, a composition of a supporting salt of 13 to 43% by mass and a balance solvent, and in a balance solvent mass ratio, sulfolane (SL): 60 to 90% by mass, ethylmethylsulfone (EMS): 10 to 40% by mass. It is preferable that the electrolytic solution has a composition of 10%. In the present embodiment, when the upper limit and the lower limit of mass% are expressed as 13 to 43 mass%, the upper limit and the lower limit are included unless otherwise noted. Therefore, 13 to 43 mass% means 13 mass% or more and 43 mass% or less.
For example, it is possible to use an electrolytic solution in which a mass ratio (%) of the supporting electrolyte is 25 mass% and SL:EMS=80 mass%:20 mass% with respect to the mass of the entire electrolytic solution.
Further, the mass of the supporting salt is more preferably in the range of 20 to 30% by mass and further preferably in the range of 22 to 27% by mass with respect to the mass of the entire electrolytic solution.
The mass ratio of each component to the entire solvent is more preferably SL: 75 to 85 mass% and EMS: 15 to 25 mass%.

(Cell lead 8)
The cell lead 8 is a terminal for extracting electric power from the cell element 6. As the cell lead 8, an extension part in which the current collector itself is thinly extended, or another thin and thin plate or wire-like lead which is mechanically connected to form the extension part is used. It is desirable that the cell lead 8 of the present embodiment be an extension of the current collector itself, and the welding region 8a that is a part of the cell lead 8 is fixed to the welding portion 5a of the pad film 5 by welding.
As shown in FIGS. 3( a) and 3 (b ), the cell lead 8 of this embodiment has a length that allows the cell 6 to be placed outside the base container 2, and when the cell lead 8 is welded to the pad film 5. Further, it is desirable that the length is such that it does not hinder the movement of the welding tip 20. This is because if it is excessively long, the internal resistance increases. The cell element 6 is housed in the base container 2 after welding the cell lead 8 and the pad film 5, but at this time, the cell lead 8 is folded inside the base container 2. Further, when the cell lead 8 is folded, it is necessary to take care so that the cell lead 8 does not touch the seal ring 9 in order to avoid a short circuit of the cell element 6.

(Seal ring 9)
As shown in FIG. 1, the seal ring 9 has a rectangular frame-shaped cross section that matches the shape of the upper end surface of the base wall portion 2b of the base container 2, and the brazing material is attached to the upper end surface of the base wall portion 2b. Are joined through. The seal ring 9 may be made of a material having a thermal expansion coefficient close to that of ceramics, such as Kovar (trade name of Westinghouse Co.) which is an iron-cobalt-nickel alloy. The brazing material is made of Ag-Cu alloy, Au-Cu alloy, or the like.

(Lid 10)
As shown in FIG. 1, the lid 10 is joined to the upper surface of the seal ring 9 and seals the base container 2. For the lid 10, an alloy such as Kovar or 42 alloy having a thermal expansion coefficient close to that of ceramics, which is plated with nickel, is used. Specifically, a Kovar thin plate having a thickness of about 0.1 mm to 0.2 mm and having a surface plated with electrolytic nickel or electroless nickel with a thickness of about 2 μm to 4 μm is used. The lid 10 using such a material can be welded to the seal ring 9 by, for example, resistance seam welding or laser seam welding, and improves the airtightness of the inside of the base container 2 in the closed state.

In the resistance seam welding used as a method of welding the lid 10 and the seal ring 9, after the lid 10 is brought into contact with the seal ring 9, two trapezoidal shapes facing each other are formed at two points on the long side of the lid 10 substantially at the center. The roller electrode is arranged and a low-voltage large-current is passed for a short time, and the lid 10 is temporarily welded (spot welding). In this way, the lid 10 is temporarily fixed, and its position does not shift due to vibration or the like during welding work.
Subsequently, for example, the base container 2 and the lid 10 are moved and welded so that the long side is traced by the roller electrode from the end of the long side. Next, the base container 2 and the lid 10 are rotated 90 degrees, and the short sides are similarly welded. In this way, welding is performed over the entire circumference of the lid 10. In both the temporary fixing and the resistance seam welding described above, diffusion of gold and nickel occurs at the interface between the lid 10 and the seal ring 9, and an airtight and strong diffusion bonding layer is formed. Thereby, the lid 10 seals the base container 2 with high airtightness.

Welding of the lid 10 and the seal ring 9 can also be performed by using laser scanning irradiation. After the temporary welding is carried out in the same manner as described above, the laser is scanned and irradiated so as to make one round around the lid 10. As a result, a diffusion bonding layer is formed at the interface between the lid 10 and the seal ring 9. In this case, the melting temperature can be lowered to the temperature of the brazing material by sticking a sheet of brazing material made of silver and copper on the surface of the lid 10 on the joining side.
When the electrolytic solution 7 is composed of a solvent or a supporting salt that is liquid at room temperature and the step of filling the electrolytic solution 7 before sealing the lid 10 is adopted, the liquid may be present at the interface between the lid 10 and the seal ring 9. There can be a location. Even in such a case, joining using seam welding is possible.
Seam welding may use roller electrodes or laser scanning irradiation.
It is considered that the reason why the airtight welding is possible even if liquid is present at the interface is that the liquid present at the interface evaporates and scatters because the temperature in the vicinity rapidly rises during welding. The upper end surface of the base container 2 and the lid 10 may be joined via a brazing material without using the seal ring 9.

The electrochemical cell 1 configured as described above has the positive electrode including the conductive layers 30 and 40 in which carbon particles are fixed by the compound of aluminum and carbon on the current collectors 31 and 41 made of aluminum forming the cell element 6. Since the body 32 and the negative electrode body 42 are provided, the aluminum current collectors 31 and 41 have good adhesion to the conductive layers 30 and 40 of the carbon material layer, and the aluminum current collectors 31 and 41 are It is possible to suppress an increase in interface resistance between the carbon material layer and the conductive layers 30 and 40. Therefore, the electrochemical cell 1 having higher conductivity and higher capacity density than the electrochemical cell having the conventional structure in which the slurry containing the active material, the conductive auxiliary agent, the binder and the like is directly coated on the aluminum current collector 1. Can be provided. Further, the good adhesion between the current collectors 31 and 41 of aluminum and the conductive layers 30 and 40 of the carbon material layer is less likely to be deteriorated even when the heat of the reflow solder is received. It is possible to provide the electrochemical cell 1 that can be reflow-soldered with high reliability even if it is housed in the base container 2 and has a small element shape having wiring in the base container 2.

The electrochemical cell of the present embodiment has a composition of a supporting salt of 13 to 43 mass% and a balance solvent, and a composition of sulfolane: 60 to 90 mass% and ethylmethylsulfone: 10 to 40 mass% in a balance solvent mass ratio. Since the electrolytic solution 7 is provided, the electrochemical cell 1 having high conductivity and high capacity density and excellent charging characteristics can be provided. The electrolytic solution having the above composition is desirable as an electrolytic solution for achieving a withstand voltage of 2.5 V, and has characteristics that it can withstand higher voltage charging and has excellent long-term storage stability. Regarding long-term storage stability, it has a feature of being excellent in high temperature stability at 70°C and 85°C.
When the base container 2 containing the cell element 6 is sealed with the lid 10 by a method such as laser welding, seam welding or brazing, even if heat for sealing is transferred to the non-aqueous electrolyte near the lid, It is possible to provide the electrochemical cell 1 in which the non-aqueous electrolyte is less likely to evaporate and the resistance is less likely to increase due to the alteration of the non-aqueous electrolyte.
In addition, since it is possible to secure a withstand voltage of 3V in the case of the above-mentioned electrolytic solution, the conventional method of using two electrochemical cells with a withstand voltage of 2.5V in series is replaced with a single booster circuit. It can be a cell. This has the effect of reducing the mounting space.

A second embodiment of the electrochemical cell according to the present invention will be described with reference to FIG.
In the electrochemical cell 15 shown in FIG. 5, the via wiring 3 is not directly penetrated from the inner bottom surface 2c of the base to the lower surface 2d of the base, but the via wiring 3 is the two base plates that form the base bottom portion 2a. The structure is such that it is stopped at the interface between the bottom portion 2f and the base second bottom portion 2g. A wiring pattern 18 is provided on this interface. The wiring pattern 18 is connected to the via wiring 3, extends horizontally, is exposed on the outer surface, and is further connected to the connection terminal 4.
The pad film 5 is formed of an aluminum film with a thickness of 5 μm to 100 μm, as in the first embodiment. The pair of cell leads 8 connected to the cell element 6 are connected to the pad film 5 by welding. Further, after the electrolytic solution 7 is filled, the base container 2 is hermetically sealed by the lid 10 to form an outer container.

Other configurations of the electrochemical cell 15 shown in FIG. 5 are the same as those of the electrochemical cell 1 of the first embodiment.
Also in the electrochemical cell 15 having the configuration shown in FIG. 5, similar to the electrochemical cell 1 described above, it is possible to provide the electrochemical cell 15 having high conductivity and high capacity density and high reliability even with a small element shape. Further, it is possible to provide the electrochemical cell 15 having high conductivity and high capacity density and excellent charging characteristics, and having a hermetically sealed structure in which resistance increase hardly occurs due to alteration of the non-aqueous electrolyte. Furthermore, it is possible to provide an electrochemical cell that can withstand high voltage charging and has excellent long-term storage stability.

A third embodiment of the electrochemical cell according to the present invention will be described with reference to FIG.
In the electrochemical cell 16 shown in FIG. 6, the outer container is composed of a base container 2 made of only a ceramic flat plate and a cavity-shaped lid 10a made of a metal having a concave shape. The cross section of FIG. As in the previous embodiment, the cell element 6, the pair of cell leads 8 and the electrolytic solution 7 are housed inside the outer container, and the cell lead 8 and the pad film 5 formed on the base container 2 are welded together. Connected by.

As shown in FIG. 6, the cavity-type lid 10a is welded so as to cover the cell element 6 and the like, with its opening abutting on a seal ring 9 provided around the base container 2. Laser seam welding is preferred for this welding. Further, when seam welding is performed, laser is scanned and irradiated from the direction of the arrow in FIG. In resistance seam welding using a roller electrode, the roller electrode is likely to come into contact with the step of the cavity type lid 10a, and it is difficult to bring the roller electrode into proper contact with the joint.
In the cavity-type lid 10a, a small hole is provided in the bottom surface portion (upper end portion in the figure) of the cavity-type lid 10a. This is intended to be able to fill the electrolytic solution 7 through this small hole after welding the base container 2 and the cavity type lid 10a, and then to hermetically seal using the sealing plug 10b.
As a result, it is possible to prevent the efficiency of the sealing operation from being lowered due to the presence of the electrolytic solution 7 between the seal ring 9 and the bonding surface of the cavity lid 10a. The material and the thickness range of the pad film 5 formed on the inner surface of the base container 2, the structure and the number of the via wiring 3, and the bonding means between the cell lead 8 and the pad film 5 are the same as those described above. Omit it.

Other configurations of the electrochemical cell 16 shown in FIG. 6 are the same as those of the electrochemical cell 1 of the first embodiment.
Also in the electrochemical cell 16 having the configuration shown in FIG. 6, similar to the electrochemical cell 1 described above, it is possible to provide the electrochemical cell 16 having high conductivity and high capacity density and high reliability even with a small element shape. In addition, it is possible to provide the electrochemical cell 16 having high conductivity and high capacity density, excellent charging characteristics, and having a hermetically sealed structure in which resistance increase hardly occurs due to alteration of the non-aqueous electrolyte. In addition, it is possible to provide the electrochemical cell 16 having high conductivity and high capacity density, excellent charging characteristics, and having a hermetically sealed structure in which resistance increase hardly occurs due to alteration of the non-aqueous electrolyte. Further, it is possible to provide the electrochemical cell 16 that can withstand high voltage charging and has excellent long-term storage stability.

A fourth embodiment of the electrochemical cell according to the present invention will be described with reference to FIG.
FIG. 7A shows the base container 2 used in the fourth embodiment. In the present embodiment, the base container 2 is composed of a ceramic flat plate and a metal cylindrical metal side wall 12 joined to the flat plate, thereby forming a concave container. A via wiring 3 that directly penetrates the base bottom portion 2a is provided on the inner bottom surface 2c of the base container 2, and a pair of pad films 5 are arranged thereon. The metal side wall 12 made of metal is selected so that its coefficient of thermal expansion matches that of the base container 2, and is joined to the flat plate with a brazing material.
On the other hand, the opening on the opposite side of the base container 2 forms the joint surface of the lid 10. In this modification, the seal ring 9 of the first embodiment for sealing the lid 10 is unnecessary, and the metal side wall 12 itself also serves as the seal ring 9. Therefore, at least the surface of the metal side wall 12 that is joined to the lid 10 is plated with nickel and gold, and the lid 10 is brought into contact with the plated surface and is subjected to resistance seam welding or laser seam welding. It is configured so that it can be joined.

FIG. 7B shows a cross-sectional view of the electrochemical cell 17 using the flat base container 2. A pair of cell leads 8 connected to the cell element 6 are connected to the pad film 5 by welding means, and are connected to the connection terminal 4 by the via wiring 3. The electrolytic solution 7 is filled in the outer container and is hermetically sealed by the lid 10. The material and thickness of the pad film are the same as those described above. Since the metal side wall 12 is made of metal, it can be processed into various shapes. The shape can be selected from corners, track shapes, ellipses, circles, and the like. In particular, when a standard hollow pipe is used after being cut to an arbitrary length, the height of the electrochemical cell 17 can be freely determined and the manufacturing cost can be reduced.
In the electrochemical cell 17 shown in FIG. 7C, the metal side wall 12 is used as in FIG. 7B, but the pad film 5 is formed only on the positive electrode side. The positive electrode cell lead 8b is connected to the pad film 5 by ultrasonic welding, while the negative electrode cell lead 8c is connected to the inside of the metal side wall 12 by welding. Since the metal side wall 12 is made of metal and the path through which the current flows is large, the wiring resistance value on the negative electrode side can be suppressed low. Therefore, the electrochemical cell 17 of the present embodiment can discharge a large current.

In the electrochemical cell 17 shown in FIG. 7, other configurations are the same as those of the electrochemical cell 1 of the first embodiment.
Also in the electrochemical cell 17 having the configuration shown in FIG. 7, similar to the electrochemical cell 1 described above, the electrochemical cell having high conductivity and capacity density and capable of highly reliable reflow soldering even with a small element shape. A cell 17 can be provided. Further, it is possible to provide the electrochemical cell 17 which has high conductivity and high capacity density, is excellent in charging characteristics, and is resistant to an increase in resistance due to the alteration of the non-aqueous electrolyte even with the hermetically sealed structure. Furthermore, it is possible to provide the electrochemical cell 17 that can withstand high voltage charging and has excellent long-term storage stability.

A concave base container 2 and a lid 10 shown in FIGS. 1A and 1B were prepared. As the base container 2, a box-shaped container made of alumina having a long side of 10 mm, a short side of 8 mm, a height of 1.8 mm, and a bottom wall thickness of 0.38 mm was used.
The base container 2 was formed by adhering a ceramic green sheet corresponding to the wall portion 2b punched out in a rectangular frame shape to a ceramic green sheet and firing it at about 1500°C. Four via wirings having an outer diameter of 0.2 mm were provided on each of the positive electrode side and the negative electrode side so as to directly penetrate the inner bottom surface 2c of the base and the lower surface 2d of the base. The surface of the via wiring 3 was plated with nickel and gold. A pair of connection terminals 4 were arranged on the bottom surface 2d of the base and connected to the via wiring 3. The connection terminal 4 was plated with gold using nickel as a base.

Next, a pair of pad films 5 made of a vapor deposited film of aluminum were formed on the inner bottom surface 2c of the base. The pad film 5 has a short side of 2.4 mm, a long side of 3 mm and a thickness of about 15 μm. On the other hand, as the lid 10, a Kovar plate having a long side of 9 mm, a short side of 7 mm, and a thickness of 0.125 mm was prepared, and the surface thereof was subjected to electrolytic nickel plating.
Subsequently, the cell element 6 is prepared.
In Example 1, TOYAL CARBON (registered trademark) manufactured by Toyo Aluminum Co., Ltd. in which carbon particles were fixed to the surface of a collector made of an aluminum foil having a thickness of 20 μm with aluminum carbide (Al ₄ C ₃ ) was used as the surface layer. 85% by mass of activated carbon having a particle size of 6 μm, a conductive auxiliary agent (Ketjen black, 8% by mass), a binder (polytetrafluoroethylene, 7% by mass) and a 30 μm thick active material layer consisting of a thickener are applied on one side. The prepared sheet electrode was produced. In Example 2, an electrode sheet was prepared in which a 10 μm-thick active material layer containing activated carbon having a particle diameter of 6 μm was fixed to one surface of a current collector made of an aluminum foil having a thickness of 20 μm with aluminum carbide (Al ₄ C ₃ ). ..
After these sheet electrodes were cut to an appropriate length, a thin aluminum plate having a thickness of 80 μm, a width of 1.5 mm and a length of 4 mm was attached to one end of the sheet electrode by ultrasonic welding to form a cell lead 8. PTFE/glass/PPA/nylon/PEEK/PBT (PTFE: polytetrafluoroethylene, PPA: polyphthalamide, PEEK: polyether ether ketone, PBT: poly Butylene terephthalate) was sandwiched between separators, and then a core was inserted and wound in a track shape. Then, the winding core was taken out and the gap was lightly crushed to obtain a winding type cell element 6.

Then, ultrasonic welding is performed. The cell lead 8 was brought into close contact with the surface of the pad film 5 of the base container 2 prepared previously and positioned. The ultrasonic welding was performed for each of the cell leads 8. The oscillation frequency of the ultrasonic melter was 40 kHz. The welding horn is made of iron, and the ultrasonic welding tip 20 made of the same material is integrally provided at the tip of the horn. On the surface of the tip 20 for ultrasonic welding, a zigzag lattice-shaped concavo-convex pattern (narl) having a pitch of 0.2 mm was provided in an area of 2.0×1.5 mm. The difference between the height of the mountain and the bottom of the valley is 0.2 mm. The welding mode was a mode in which the energy supplied to the cell lead 8 during welding was controlled, the set value of the welding energy was in the range of 0.5 to 100 J, and the welding time was in the range of 50 to 2000 msec. After the ultrasonic welding tip 20 descends to the surface of the cell lead 8 made of aluminum by an air mechanism, it bites into the surface of the cell lead 8 and vibrates between the interface between the cell lead 8 and the pad film 5 to perform welding. ..

After the ultrasonic welding was completed, the cell element 6 was housed in the base container 2 by folding the cell lead 8. At this time, care was taken so that the cell lead 8 did not come into contact with the seal ring 9. This is to avoid a short circuit in the electrochemical cell.
Next, the base container 2 accommodating the cell element 6 was immersed in the liquid electrolyte solution 7 and vacuum degassed for 1 minute. Here, SBP·BF4 (5-azoniaspiro[4.4]nonane tetrafluforoborate) was used as the supporting salt of the electrolytic solution 7, and a mixed solution of sulfolane (SL) and ethyl methyl sulfone (EMS) was used as the non-aqueous solvent. Was prepared at the following ratio and used as a mixed electrolytic solution. The mixing ratio is 25% by mass of the supporting salt in the mass ratio with respect to the mass of the entire electrolytic solution and the composition of the balance solvent, and SL: 80% by mass and EMS: 20% by mass as the electrolytic solution contained in the solvent. There is.

Then, after returning to atmospheric pressure and taking out the base container 2 accommodating the cell element 6 from the electrolytic solution 7, the lid 10 is brought into contact with the seal ring 9 under a nitrogen atmosphere, and two points on the long side are attached. Temporary welding was performed, and then resistance seam welding was continuously performed on the long side and the short side in this order to hermetically seal the base container 2. Thus, the electrochemical cell of this example was produced.
The electrical characteristic test of the produced electrochemical cell was performed.

For comparison, when a sheet electrode is manufactured in the manufacturing process, 85% by mass of activated carbon having a particle size of 6 μm and a conductive auxiliary is applied to the surface of a current collector made of aluminum having a thickness of 20 μm as in Example 1. A sheet electrode for comparison having a 30 μm-thick active material layer consisting of an agent (Ketjen black, 8% by mass), a binder (polytetrafluoroethylene, 7% by mass) and a thickener was applied on one side to prepare a sheet electrode for comparison. An electrochemical cell of Comparative Example 1 which was housed in the base container 2 by the same method as described above and sealed with the lid 10 was produced.
In order to evaluate the resistance to the reflow solder for each of the obtained electrochemical cells, a reflow solder test in which the whole is kept at 260° C. for 5 seconds is performed, and the internal resistance (Ω) before and after the reflow solder test is measured. The change rate (change rate before and after reflow) was calculated.
The internal resistance was obtained by measuring the impedance at an alternating current of 1 kHz (the same applies to the measurement of the internal resistance shown below). The results are shown in Table 1 below and FIG.

As is clear from the results shown in Table 1 and FIG. 8, an electrochemical cell (electric double layer capacitor) equipped with a sheet electrode having a structure in which a layer of a carbon material is supported by aluminum carbide (Al ₄ C ₃ ) according to the present invention. It was found that even when exposed to the heating environment of the reflow solder, the internal resistance did not increase much and the deterioration was extremely small compared to the conventional structure shown in Comparative Example 1. Therefore, it can be seen that the electrochemical cell according to the present invention can withstand the process of reflow soldering and can suppress an increase in internal resistance as an electrochemical cell.

Next, the electrochemical cell having the same structure as those of Examples 1 and 2 and the electrochemical cell having the same structure as Comparative Example 1 were charged at a charging voltage of 3.0 V/charging current of 10 mA for 10 minutes, and then discharged. The discharge time (sec) was measured under the conditions of 1 mA and a discharge end voltage of 2.0V. Further, the same reflow soldering test as in the previous example was carried out, the discharge time (sec) before and after the reflow soldering test was measured, and the change rate before and after that (change rate before and after reflow) was calculated. The results are shown in Table 2 below and FIG.

As is clear from the results shown in Table 2 and FIG. 9, even when the electrochemical cell having the sheet electrode of the present invention structure is exposed to the heating environment of the reflow solder, the discharge time is reduced less and the capacity is less reduced. It has been found. Therefore, it can be seen that the electrochemical cell according to the present invention can withstand the process of reflow soldering and can suppress the decrease in capacity of the electrochemical cell.

Next, for comparison, 25% by mass of the supporting salt, the mass ratio of the remaining solvent in the solvent, PC (propylene carbonate):EC (ethylene carbonate):DMC (dimethyl carbonate)=39% by mass:32% by mass: Comparative Example 2 was prepared in the same manner as in Example 1 except that the electrolytic solution mixed in the proportion of 29% by mass was used.
With respect to each electrochemical cell having the same structure as that of the above-described Example 1 and Comparative Example 2, the same reflow soldering test as in the previous example was performed, the internal resistance (Ω) before and after the reflow soldering test was measured, and the change before and after that was measured. The rate (change rate before and after reflow) was evaluated. Further, the discharge time (sec) before and after the reflow soldering test and the change rate before and after that (change rate before and after reflow) were evaluated. The results are shown in Tables 3 and 4 below and FIGS. 10 and 11.

From the results shown in Table 3 and FIG. 10, with respect to the change rate of the internal resistance before and after the reflow soldering test (change rate before and after reflow), Example 1 in which SL is the main solvent is Comparative Example 2 in which PC and EC are the main solvents. Although the internal resistance was higher than that, the rate of change before and after reflow was slightly smaller. Further, from the results shown in Table 4 and FIG. 11, with respect to the rate of change of the discharge time before and after the reflow soldering test at 3.0-2.0 V, the SL-based electrolytic solution having high withstand voltage was used in Example 1 Then, the decrease in discharge time due to reflow was smaller than that in Comparative Example 2. As described above, regarding the initial electrical characteristics (internal resistance, capacity), it was found that when the SL-based electrolytic solution was used, the characteristics were particularly excellent in the high voltage band.

<Evaluation of storage characteristics>
Next, using an electrochemical cell having the same structure as that of Example 1 and Comparative Example 2, using a charging voltage of 3.0 V at 60° C. and a charging voltage of 2.5 V at 85° C. Table 5, Table 7, FIG. 12 and FIG. 14 show the capacity retention rate according to the number of days (HTV (storage characteristic), internal resistance increase rate (internal resistance increase rate in HTV (storage characteristic)). ) Are shown in Table 6, Table 8, FIG. 13 and FIG. These tests correspond to floating tests in which voltage is applied under high temperature storage.

In the electrochemical cell of Comparative Example 2, the internal resistance increased significantly and the capacity retention rate decreased significantly with the passage of storage days. On the other hand, the electrochemical cell of Example 1 has a small internal resistance increase rate at a storage temperature of 60° C./charging voltage of 3.0 V and a storage temperature of 85° C./charging voltage of 2.5 V, and maintains the capacity. Almost no decrease in the rate has occurred.
Therefore, it can be seen that the electrochemical cell of Example 1 has a low internal resistance increase rate even after the elapse of days and a high capacity retention rate even after the elapse of days.
From the above results, the cell element is provided with a sheet electrode having a structure in which a carbon material layer is supported by aluminum carbide (Al ₄ C ₃ ), and a mixed solvent of sulfolane (SL) and ethyl methyl sulfone (EMS) in a desired ratio. Electrochemical cell using electrolyte solution is superior to conventional electrochemical cell equipped with coating type electrode and electrochemical cell using mixed solvent of propylene carbonate, ethylene carbonate and dimethyl carbonate became. That is, the electrochemical cells of Examples 3 and 4 can be charged at 3 V, have excellent withstand voltage characteristics, can obtain high capacity, and have excellent heat resistance characteristics.
Further, an electrochemical cell equipped with a sheet electrode having a structure in which a carbon material layer is supported by aluminum carbide (Al ₄ C ₃ ) has an internal structure different from that of a conventional electrode structure of a coating type even when exposed to a heating environment of reflow solder. It was found that the increase in resistance was small.

<Supported salt ratio change test>
Next, when preparing the electrochemical cell of Example 1, the electrochemical cell of Example 3 using the electrolytic solution in which the mass ratio of the supporting salt in the applied electrolytic solution was set to 15 mass%, and 40 mass % Of the electrochemical cell using the electrolytic solution set to 100%, Comparative Example 3 using the electrolytic solution of 10% by mass, and Comparative Example 3 using the electrolytic solution of 45% by mass The electrochemical cell of Example 4 was prepared and subjected to the following impedance measurement test.
In the impedance measurement test, taking into consideration the resistance to reflow solder, a reflow solder test in which the entire electrochemical cell is held at 260°C for 5 seconds is performed, the internal resistance before and after the reflow solder test is measured, and the change rate of the internal resistance before and after that is measured. (Rate before and after reflow) was calculated. The results are shown in Table 9 below and FIG.

As is clear from the results shown in Table 9 and FIG. 16, the electrochemical cell having the electrolytic solution in which the mass ratio of the supporting salt was set in the range of 13 to 43 mass% exhibited low internal resistance even after the reflow soldering.
In the electrochemical cell of Comparative Example 3 in which the mass ratio of the supporting salt was less than the desirable range (13 to 43 mass%) of the present invention, the conductivity was decreased and the internal resistance was increased. In the electrochemical cell of Comparative Example 4 in which the mass ratio of the supporting salt was excessively larger than the above range, since the ratio of the solvent to the supporting salt was small, the influence of decomposition or deterioration of the solvent due to heating became large, and the reflow soldering was performed. This increased the internal resistance.

Using the electrochemical cells having the same structures as those in Examples 3 and 4 and Comparative Examples 3 and 4, the same reflow solder test as in the previous example was performed, and the discharge time (sec) after the reflow solder test was measured. The change rate before and after that (change rate before and after reflow) was evaluated. The results are shown in Table 10 below and FIG.
As charging conditions, the electrochemical cells of Examples 3 and 4 and Comparative Examples 3 and 4 were set to have a charging voltage of 3.0 V, a charging current of 10 mA, and a charging time of 10 minutes. As the discharge conditions, the discharge current was set to 1 mA and the discharge end voltage was set to 2.0V.

From the results shown in Table 10 and FIG. 17, the supporting salt (SBP/BF4) was exposed to the heating environment of the reflow solder by setting the range of 13 mass% to 43 mass% in which the increase in internal resistance due to the reflow solder was small. Even if it does, it can be seen that it is possible to provide an electrochemical cell with a small decrease in discharge time and a small decrease in capacity.

<Evaluation of storage characteristics by changing the ratio of supporting salt>
Using electrochemical cells having the same structure as those in Examples 3 and 4 and Comparative Examples 3 and 4, a test for evaluating storage characteristics was performed.

Table 11 and FIG. 18 below show the capacity retention rate (the capacity retention rate in HTV (storage characteristics)) according to the elapsed (storage) days when the charging voltage is set to 2.5 V at 70° C. The rate (internal resistance increase rate in HTV (storage characteristic)) is shown in Table 12 and FIG. 19 below.
Table 13 and FIG. 20 below show the capacity retention rate (the capacity retention rate in HTV (storage characteristics)) according to the elapsed (storage) days when the charging voltage is set to 2.5 V at 85° C. The rate (internal resistance increase rate in HTV (storage characteristic)) is shown in Table 14 and FIG. 21 below.

From the above results, from the data at 70° C. in Tables 11 and 12, Comparative Example 3 in which the content of the supporting salt was reduced showed a large decrease in the capacity retention rate as compared with Examples 3 and 4. This is because by reducing the content of the supporting salt, the ratio of the solvent to the supporting salt was increased, and the influence of decomposition or deterioration of the supporting salt due to heating was increased. On the other hand, in Comparative Example 4 in which the content of the supporting salt was increased, the increase in internal resistance was larger than that in Examples 3 and 4. This is because the amount of the supporting salt was too large and the ratio of the solvent in the electrolytic solution was small, and the influence of the decomposition and deterioration of the solvent became large. From this, the electrochemical cell having the electrolytic solution in which the mass ratio of the supporting salt is set in the range of 13 to 43 mass% has an internal resistance of 70°C at a voltage of 2.5 V even after a lapse of days. It can be seen that the storage characteristics are excellent because the increase and the capacity retention rate are suppressed.
Further, from the data of 85° C. in Tables 13 and 14, Comparative Example 3 in which the content of the supporting salt was reduced showed a large decrease in the capacity retention rate as compared with Examples 3 and 4. In Comparative Example 4 in which the content of the supporting salt was increased, the increase in internal resistance was larger than that in Examples 3 and 4. From these results, the electrochemical cell having the electrolytic solution in which the mass ratio of the supporting salt was set in the range of 13 to 43% by mass showed that the internal resistance was maintained even when the number of days passed while the voltage of 2.5 V was applied at the temperature of 85°C. It can be seen that the storage characteristics are excellent because the increase and the capacity retention rate are suppressed.

<Solvent ratio change test>
When preparing the electrochemical cell having the above-mentioned structure, 25 mass% of SBP.BF4 (5-azoniaspiro[4.4]nonane tetrafluforoborate) was used as the supporting salt, and sulfolane (SL) and ethyl were used as the non-aqueous solvent. A mixed solution of methyl sulfone (EMS) was prepared in the following proportions and used as a mixed electrolytic solution. The other structure is the same as that of the first embodiment.
The mixture ratio of SL and EMS used as a solvent was SL:EMS=80 mass%:20 mass% in Example 5, SL:EMS=88 mass%:12 mass% in Example 6, SL: EMS=64% by mass: 36% by mass for Example 7, SL:EMS=93% by mass: 7% by mass for Comparative example 5, SL:EMS=53% by mass: 47% by mass Was used as Comparative Example 6.

Similar to the evaluations carried out previously for the electrochemical cells having the same structure as Examples 5 to 7 and Comparative Examples 5 and 6, the internal resistance and the change rate before and after it (change rate before and after reflow) were compared. The results are shown in Table 15 below and FIG.

As shown in Table 15 and FIG. 22, it is considered that Comparative Example 5 having a small EMS had an increased viscosity and an impaired impregnation property with an electrolytic solution when a cell element was produced, and thus an internal resistance increased. On the contrary, it is considered that Comparative Example 6 containing a large amount of EMS has a reduced viscosity and a reduced internal resistance.

The discharge time (sec) after the reflow soldering test and the change rate before and after it (change rate before and after reflow) were measured using the electrochemical cells having the same structures as those in Examples 5 to 7 and Comparative Examples 5 and 6 described above. The results are shown in Table 16 below and FIG.
As the charging conditions, the electrochemical voltage of each Example and Comparative Example was set to 3.0 V, the charging current was 10 mA, and the charging time was 10 minutes. As the discharge conditions, the discharge current was set to 1 mA and the final voltage was set to 2.0V.

As shown in Table 16 and FIG. 23, in Comparative Example 6 in which EMS was large and SL was small, the capacity was a small value. This is because the dielectric constant of the electrolytic solution decreased due to the small amount of SL. On the other hand, the electrochemical cells of Examples 5 to 7 and Comparative Example 5 exhibited high capacity even after reflow.

<EMS ratio change preservation characteristic evaluation>
Using an electrochemical cell having the same structure as that of Example 5 and Comparative Examples 5 and 6 described above, a test for evaluating storage characteristics was performed.
Table 17 and FIG. 24 below show the capacity retention rate (the capacity retention rate in HTV (storage characteristics)) according to the elapsed (storage) days when the charging voltage is set to 2.5 V at 70° C. The rate (internal resistance increase rate in HTV (storage characteristic)) is shown in Table 18 and FIG. 25 below.
Table 19 and FIG. 26 below show the capacity retention rate (the capacity retention rate in HTV (storage characteristics)) according to the elapsed (storage) days when the charging voltage is set to 2.5 V at 85° C. The rate (internal resistance increase rate in HTV (storage characteristic)) is shown in Table 20 and FIG. 27 below.

As shown in Tables 17 and 18 and FIGS. 24 and 25, both Comparative Example 5 in which the EMS is less than the preferable range (10 to 40 mass%) of the present application and Comparative Example 6 in which the EMS is more than the preferable range of the present application, maintain the capacity. The rate decreased and the internal resistance increased. This is because in Comparative Example 5 where the EMS is small, since the viscosity is high and the impregnation property of the electrolytic solution when manufacturing the cell element is poor, the electrolytic solution that is not impregnated when sealing the cell during assembly overflows to the outside of the cell, This is because the lack of the electrolytic solution in the inside causes the electrolytic solution to easily deteriorate with time. On the contrary, in Comparative Example 6 in which EMS is large, the withstand voltage is lowered due to the decrease in SL.
Further, as shown in Tables 19 and 20 and FIGS. 26 and 27, in Comparative Example 5 in which the EMS is less than the preferable range of the present application and Comparative Example 6 in which the EMS is more than that in the present invention, the capacity retention ratio decreases and the internal resistance increases. It was seen.
As shown in Tables 15 to 20 above, by using a solvent mixed in the range of SL: 60 to 90% by mass and EMS: 10 to 40% by mass, a cell having excellent storage characteristics can be obtained.

DESCRIPTION OF SYMBOLS 1... Electrochemical cell, 2... Base container, 2a... Base bottom part, 2b... Base wall part, 2c... Base inner bottom surface, 2d... Base lower surface, 2e... Base side surface, 2f... Base 1st bottom part, 2g... Base second Bottom part, 3... Via wiring, 4... Connection terminal, 5... Pad film, 5a... Welding part, 6... Cell element, 7... Electrolyte, 8... Cell lead, 8a... Welding area, 8b... Positive cell lead, 8c... Negative cell lead , 9... Seal ring, 10... Lid, 10a... Cavity type lid, 10b... Sealing plug, 15, 16, 17... Electrochemical cell, 18... Wiring pattern, 20... Ultrasonic tip, 20a... Tip of tip, 30... Conductive layer, 31... Positive electrode current collector, 32... Positive electrode body (positive electrode), 33... Intervening layer (first surface portion), 34... Second surface portion, 35... Separator, 36... Carbon particles, 40... Conductivity Layer, 41... Negative electrode collector, 42... Negative electrode body (negative electrode).

Claims (7)

A base container, a cell element accommodated in the base container, a plurality of cell leads that are extensions of the cell element, a pad film made of a valve metal formed on an inner bottom surface of the base container, and the pad An electrochemical cell having at least a lid connected to a film and formed from an inner bottom surface to a lower surface of the base container, and a lid that hermetically closes the base container,
In the cell element, the positive electrode and the negative electrode are arranged with a separator interposed therebetween, and further, a nonaqueous electrolytic solution is contained, and at least one of the positive electrode and the negative electrode is an aluminum current collector, and aluminum is provided on the aluminum current collector. A layer of a carbon material fixed by a carbon compound, and an active material layer containing activated carbon, a conductive auxiliary agent and a binder formed on the carbon material layer ,
The non-aqueous electrolyte is a supporting salt: 13 to 43% by mass, the balance solvent, and has a composition of sulfolane: 60 to 90% by mass and ethylmethylsulfone: 10 to 40% by mass in the balance solvent ratio. And an electrochemical cell. The non-aqueous electrolyte is a supporting salt of a spiro compound in an amount of 15 to 40 mass% and a balance solvent, and has a composition of sulfolane: 64-88 mass% and ethylmethylsulfone: 12 to 36 mass% in a balance solvent mass ratio. The electrochemical cell according to claim 1, wherein: The electrochemical cell according to claim 1 or claim 2, wherein the lid is welded to the base container. An intervening layer containing the compound of aluminum and carbon is formed on a surface portion of the aluminum current collector, a second surface portion extending outward from the intervening layer is formed, and the second surface portion is formed on the second surface portion. The electrochemical cell according to claim 1, wherein a layer of the carbon material having a conductive layer to which a plurality of carbon particles are fixed is formed. The electrochemical cell according to claim 4 , wherein the conductive layer contains an active material. The electrochemical cell according to claim 1, wherein the supporting salt is a quaternary ammonium salt or a quaternary phosphonium salt. The electrochemical cell according to any one of claims 1 to 6 , wherein the positive electrode, the negative electrode, and the separator of the cell element housed in the base container are impregnated with the nonaqueous electrolytic solution. ..

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