Layer cell, assembled battery including layer cell, and method for assembling layer cell

Layer cell includes an outer casing, positive electrode, negative electrode, separator disposed between the positive electrode and the negative electrode, and electrically conductive current collector passing through the positive electrode, the negative electrode and the separator in an axial direction of the outer casing. The positive electrode, the negative electrode and the separator are stacked in the axial direction of the outer casing. First electrode which is one of the positive electrode and the negative electrode is in contact with an inner surface of the outer casing, but is not in contact with the current collector. Second electrode which is the other electrode is not in contact with the outer casing, but is in contact with the current collector. An outer edge of the second electrode is covered with the separator. Peripheral edge of a hole, in the first electrode is covered with the separator.

TECHNICAL FIELD

The present invention relates to a layer cell. Specifically, the present invention relates to a layer cell with improved cooling performance, an assembled battery including the layer cell, and a method for assembling the layer cell.

BACKGROUND ART

Electrode structures of a secondary cell are mainly classified into two types, i.e., a spiral-wound type and a layer type. In a cell having the spiral-wound type electrode structure (a spiral-wound cell; refer to, for example, Patent Literature 1), a positive electrode and a negative electrode which are spirally wound with a separator interposed therebetween are housed in a cell case. In a cell having the layer type electrode structure (a layer cell), an electrode group including a positive electrode and a negative electrode which are alternately stacked with a separator interposed therebetween is housed in a cell case. Patent Literature 2 discloses a cylindrical-type cell in which disc-shaped electrodes are stacked. Patent Literature 3 discloses a rectangular-type cell in which rectangular sheet-shaped electrodes are stacked.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

With regard to the spiral-wound cell, the separator with low thermal conductivity is provided in a multilayered manner between the surface and center of the cell. As the result, even when a surface temperature of the cell case is close to an ambient temperature, a temperature of a portion around the center of the spiral-wound cell becomes considerably high.

The cylindrical-type layer cell disclosed in Patent Literature 2 has a structure to collect electricity in such a manner that the stacked electrodes come into contact with terminals, respectively. In the course of assembling the cylindrical-type layer cell, consequently, there is a possibility of infant failures due to a short circuit between the positive electrode and the negative electrode. Further, the electrode repeatedly contracts and expands by the repetition of charge and discharge. As the result, there is a possibility of secular failures due to the deformation and displacement of the electrode and the short circuit between the positive electrode and the negative electrode.

The present invention has been devised to solve the problems described above, and an object thereof is to restrain temperature rise inside a cell and to prevent a short circuit between electrodes.

Solution to Problem

In order to achieve the object described above, a layer cell according to the present invention includes: a tubular outer casing; a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrically conductive current collector passing through the positive electrode, the negative electrode and the separator in an axial direction of the outer casing. Herein, the positive electrode, the negative electrode and the separator are stacked in the axial direction of the outer casing. A first electrode which is one of the positive electrode and the negative electrode comes into contact with an inner surface of the outer casing so as to be electrically connected to the inner surface of the outer casing, but is not in contact with the current collector. A second electrode which is the other one of the positive electrode and the negative electrode is not in contact with the inner surface of the outer casing, but comes into contact with the current collector so as to be electrically connected to the current collector. An outer edge of the second electrode is covered with the separator. A peripheral edge of a hole, through which the current collector passes, in the first electrode is covered with the separator.

According to this configuration, the outer casing is made of a metal, and serves as a current collector terminal of the first electrode. An outward dimension of the first electrode is slightly larger than an inward dimension of the tubular outer casing, so that the entire outer periphery of the first electrode or a part of the outer periphery is in contact with the inner surface of the outer casing. When the first electrode is put into the outer casing under pressure, the first electrode firmly comes into contact with the outer casing. Thus, the first electrode is connected to the outer casing with thermally small resistance. Therefore, this configuration effectively acts on the cooling of the first electrode.

Herein, the outward dimension of the electrode refers a dimension from a graphic center to an outer periphery of a sheet-shaped electrode. In a case of a disc-shaped electrode, an outward dimension is referred to as an outer diameter. Likewise, the inward dimension of the outer casing refers a dimension between a graphic center at a vertical section of the tubular outer casing in the axial direction and the inner surface of the outer casing. In a case of a cylindrical outer casing, an inward dimension is referred to as an inner diameter.

The outward dimension of the second electrode is smaller than the inward dimension of the tubular outer casing, so that the second electrode does not come into contact with the outer casing. Accordingly, the second electrode is isolated from the outer casing.

Heat generated from the first electrode is directly transferred to the outer casing. Heat generated from the second electrode is transferred to the first electrode through the separator.

An overall heat transfer coefficient (U1) of a spiral-wound cell is represented by Mathematical Formula 1 as will be described later. On the other hand, an overall heat transfer coefficient (U2) of the layer cell according to the present invention is represented by Mathematical Formula 2. It is apparent from a comparison between the two coefficients that there is a large difference with regard to the term of a winding number n. In the spiral-wound cell, as the winding number n becomes larger, the overall heat transfer coefficient becomes smaller. Detailed description using substitution of specific numerical values will be given in the following embodiments.

In the layer cell according to the present invention, as described above, there is no necessity of a pipe or a heatsink for feeding a coolant into the cell in order to restrain the temperature inside the cell. Accordingly, the structure of the layer cell according to the present invention is compact. In the layer cell according to the present invention, moreover, it is possible to restrain temperature rise inside the cell easily by cooling the surface of the outer casing.

Each of the positive electrode, the negative electrode and the separator has a hole formed on the center thereof, for allowing the current collector to pass therethrough. The rod-shaped current collector passes through the holes. A diameter of the hole of the first electrode is larger than an outward dimension of the rod-shaped current collector. Therefore, the first electrode does not come into contact with the current collector. A diameter of the hole of the second electrode is smaller than the outward dimension of the rod-shaped current collector. Therefore, the second electrode comes into contact with the current collector and is electrically connected to the current collector. The current collector is made of a metal and serves as a current collector terminal of the second electrode. Moreover, the current collector is preferably a round rod, but may be a rectangular rod.

With regard to the layer cell according to the present invention, further, in the state that the electrodes and the separator are stacked, the outer edge of the second electrode is covered with the separator, and the peripheral edge of the hole, through which the current collector passes, in the first electrode is covered with the separator. Therefore, the first electrode and the second electrode are separated from each other by the separator with reliability at the outer edge of the second electrode and the peripheral edge of the hole in the first electrode. Accordingly, the electrodes do not come into contact with each other at the outer edge of one of the electrodes and the peripheral edge of the hole in the other electrode because of the deformation of the electrodes. In the case of the disc-shaped electrode, the outer diameter of the separator is larger than the outer diameter of the second electrode. In the case where the current collector is a round rod, moreover, the hole diameter of the separator is smaller than the hole diameter of the first electrode.

In the layer cell according to the present invention, the first electrode is enclosed with a bag-shaped first separator in a state that an outer edge of the first electrode is exposed at the outside of the first separator, and the second electrode is enclosed with a bag-shaped second separator in a state that a peripheral edge of a hole, through which the current collector passes, in the second electrode is exposed at the outside of the second separator. According to this configuration, since the separators have the bag shape, the separators prevent a short circuit between the electrodes from occurring because of dust or foreign matters derived from the electrodes.

In the layer cell according to the present invention, the current collector has a side surface on which a groove is formed, a diameter of the narrowest portion of the current collector is larger than the diameter of the hole, through which the current collector passes, in the second electrode, and a diameter of the thickest portion of the current collector is smaller than the diameter of the hole, through which the current collector passes, in the first electrode.

There is a possibility that, at the time of assembly of the electrodes, the coupling between the current collector and the electrode is loosened and the tight contact between the current collector and the electrode is hampered. In order to solve this problem, the layer cell according to the present invention includes the current collector on which a screw groove is formed. According to this configuration, it becomes possible to maintain the state that the second electrode is firmly fitted into the current collector by the screw groove formed on the current collector. This configuration prevents the coupling between the electrode and the current collector from being loosened at the time of layer cell assembling work.

In the layer cell according to the present invention, the negative electrode contains a hydrogen storage alloy. In the layer cell according to the present invention, further, each of the positive electrode and the negative electrode is an electrode that is charged and discharged, and is also an electrode that applies electrolysis to an electrolyte retained in the layer cell with an electric current fed from the outside. According to this configuration, each of the positive and negative electrodes plays a role of an electrode that is charged and discharged in a secondary cell and a role of an electrode that generates hydrogen gas.

In the layer cell according to the present invention, preferably, a charge-capacity of the negative electrode is smaller than a charge-capacity of the positive electrode. The layer cell is a so-called negative electrode regulation-type cell. Herein, these charge-capacities are simply referred to as a positive electrode capacity and a negative electrode capacity, respectively, in some cases.

The layer cell according to the present invention further includes a hydrogen storage chamber disposed inside the outer casing, for storing hydrogen gas generated from the negative electrode. Herein, the hydrogen storage chamber may be an independent space. Moreover, the hydrogen storage chamber is not an independent space, but may be formed on a clearance in the electrode and a clearance in the separator.

In the negative electrode regulation-type layer cell, as the charge progresses, the negative electrode is fully charged before the positive electrode is fully charged. At the overcharge in which the charge is continued from the full charge state, hydrogen gas is generated from the negative electrode (see Reaction Formula (1)).
H++e−→½H2(1)

The hydrogen gas generated from the negative electrode is stored in the hydrogen storage alloy of the negative electrode to serve as an energy source at the time of discharge. In a case of a positive electrode made of nickel oxyhydroxide, a reaction formula at the time of discharge is Reaction Formula (2).
Negative electrode ½H→H++e−
Positive electrode NiOOH+e−+H+→Ni(OH)2
Whole NiOOH+½H2→Ni(OH)2(2)

Since the hydrogen storage alloy is expensive, the negative electrode significantly affects on a price of the cell. In a normal positive electrode regulation-type secondary cell, an amount of materials for a negative electrode is 1.5 to 2 times as large as that for a positive electrode. However, the layer cell according to the present invention is allowed to reduce the amount of expensive materials for the negative electrode. Therefore, it is possible to obtain an inexpensive layer cell.

In the layer cell according to the present invention, the negative electrode is charged in such a manner that the hydrogen storage alloy contained in the negative electrode stores the hydrogen gas stored in the hydrogen storage chamber. According to this configuration, the negative electrode is charged with the hydrogen gas generated by the overcharge. Accordingly, the hydrogen gas is effectively utilized. The hydrogen storage alloy contained in the negative electrode acts as a so-called catalyst.

In the layer cell according to the present invention, preferably, the positive electrode contains manganese dioxide. Heretofore, a manganese dioxide positive electrode has been used for a primary cell to be known as a manganese dioxide-zinc cell, but has not been used for a secondary cell. The reason therefor is as follows. That is, when the manganese dioxide positive electrode is discharged until manganese hydroxide, trimanganese tetraoxide Mn3O4is generated, which is not able to charge again. However, the inventors of the present invention have found that irreversible trimanganese tetraoxide is not generated by contacting the positive electrode with oxygen. The inventors of the present invention have succeeded in adopting manganese dioxide as a material for a positive electrode of a secondary cell by supplying oxygen to the circumference of the positive electrode.

In the layer cell according to the present invention, the outer casing has a side portion formed into a cylindrical shape. Moreover, the outer casing has bulging portions that have a dome shape at axial two ends thereof, and the hydrogen storage chamber is provided in each of the bulging portions.

When the charge is continued after the negative electrode is fully charged, hydrogen gas is generated from the negative electrode. The generated hydrogen gas is stored in the hydrogen storage chamber, is stored in the negative electrode at the time of discharge, and is effectively utilized. Thus, it becomes possible to reduce an amount of expensive materials for a negative electrode. Therefore, it is possible to manufacture an inexpensive layer cell. The structure that each of the two ends of the cylindrical can bulges in a dome shape is suitable for storage of high-pressure hydrogen gas.

An assembled battery includes a plurality of layer cells according to the present invention, and the layer cells are connected to each other via a columnar metal fitting. Herein, in each of the layer cells, the outer casing has a cylindrical body portion made of a metal, and lid portions for covering openings formed at axial two ends of the body portion, and the current collector passes through the lid portions. The metal fitting has a top surface and a bottom surface each having a connection cavity formed thereon. The end of the current collector in one of the layer cells is fittable into the connection cavity formed on the top surface of the metal fitting. The end of the current collector in the different one of the layer cells adjoining the layer cell is fittable into the connection cavity formed on the bottom surface of the metal fitting, with an insulator interposed between the end and the connection cavity. The bottom surface of the metal fitting is electrically connected to the outer casing in the different layer cell.

The bottom surface and top surface of the metal fitting are capable of coming into surface contact with the lid portions of the adjoining layer cells. The insulator is interposed between the cavity formed on the bottom surface of the metal fitting and the current collector. In the two layer cells adjoining each other, therefore, the current collectors are isolated from each other. The current collector in one of the layer cells and the outer casing in the adjacent layer cell are connected to each other via the metal fitting. As the result, the adjoining layer cells are connected in series via the metal fitting.

An assembled battery includes a plurality of layer cells according to the present invention. Herein, the outer casing in each of the layer cells has a one-end closed container having a rectangular section, and a lid member for covering an opening of the container. The layer cells are connected to each other such that the container in one of the layer cells and the lid member in the different one of the layer cells adjoining the layer cell are in surface contact with each other.

According to this configuration, the lid member in one layer cell and the bottom of the container in the adjacent layer cell come into contact with each other, so that the two layer cells are stacked and electrically connected in series. It is possible to raise an output voltage from an assembled battery by connecting a large number of layer cells as described above.

A method for assembling the layer cell according to the present invention includes: a first step of previously preparing a current collector having a side surface on which a screw groove is formed, and a round rod having the same outer diameter as a diameter of a root of the screw groove on the current collector; a second step of assembling an electrode group in such a manner as to sequentially insert a positive electrode and a negative electrode into the round rod with a separator interposed between the positive electrode and the negative electrode and stack the electrodes; a third step, to be carried out subsequent to the second step, of disposing presser plates on two ends of the electrode group to hold the electrode group and applying pressure to the presser plates to compress the electrode group: a fourth step of pulling out the round rod while maintaining the compressed state; a fifth step of pushing the current collector instead of the round rod into the electrode group while rotating the current collector and, then, screwing the current collector into a screw hole formed on the center of the presser plate to assemble an electrode assembly while maintaining the compressed state of the electrode group; a sixth step of putting the electrode assembly into the outer casing under pressure; a seventh step of deaerating the outer casing; an eighth step of injecting an electrolyte into the outer casing; and a ninth step, to be carried out subsequent to the eighth step, of attaching a lid to the outer casing to seal the outer casing.

Advantageous Effects of Invention

According to the present invention, temperature rise inside a cell is restrained without a necessity of redundant space for cooling. Further, the layer cell according to the present invention allows the prevention of a short circuit between electrodes.

DESCRIPTION OF EMBODIMENTS

With reference to the drawings, hereinafter, description will be given of embodiments of the present invention; however, the present invention is not intended to be limited to these embodiments.

Prior to the description of the respective embodiments of the present invention, first, description will be given of an example of a secondary cell to which the present invention is applied. The secondary cell is not limited to types to be described in the respective embodiments, and may be secondary cells such as a nickel-iron cell, a zinc-manganese cell and a nickel-cadmium cell.

A negative electrode contains, as a principal material, a hydrogen storage alloy, e.g. lanthanum-nickel. Nickel oxyhydroxide was used as an active material of a positive electrode. An alkaline aqueous solution such as a KOH aqueous solution, which is typically used in a nickel-metal hydride cell, was used as an electrolyte to be retained in a separator.

The negative electrode to be used herein is obtained as follows. That is, a paste obtained by adding a solvent to a hydrogen storage alloy, an electrically conductive filler and a binder was applied onto a substrate so as to be formed into a sheet shape, and then was cured. Likewise, the positive electrode to be used herein is obtained as follows. That is, a paste obtained by adding a solvent to a positive electrode active material, an electrically conductive filler and a binder was applied onto a substrate so as to be formed into a sheet shape, and then was cured.

The electrically conductive filler to be used herein was a carbon particle. The binder to be used herein was a thermoplastic resin which dissolves in a water-soluble solvent. The substrate to be used herein was a foamable nickel sheet. The separator to be used herein was a polypropylene fiber.

A negative electrode contains a hydrogen storage alloy. A positive electrode contains manganese dioxide as an active material. The positive electrode and negative electrode to be used herein were obtained as follows. That is, a paste obtained by adding a solvent to an active material, an electrically conductive filler and a binder was applied onto a nickel substrate so as to be formed into a sheet shape, and then was cured. The electrically conductive filler, binder, separator and electrolyte to be used herein were the same as those in the nickel-metal hydride cell.

In the positive electrode of the manganese dioxide cell, manganese dioxide MnO2is changed to manganese oxyhydroxide MnOOH, and then is changed to manganese hydroxide Mn(OH)2in the course of discharge. When the positive electrode is discharged until manganese hydroxide, trimanganese tetraoxide Mn3O4is generated, which is not able to charge again. However, even when manganese dioxide is subjected to the oxidation by the discharge, the contact with oxygen allows manganese oxyhydroxide to be returned to manganese dioxide. Thus, manganese dioxide is not changed until manganese hydroxide, so that irreversible trimanganese tetraoxide is not generated. Hence, the positive electrode contains no trimanganese tetraoxide or contains trimanganese tetraoxide of less than 5% at the most. Oxygen gas generated from the positive electrode at the time of overcharge is stored in the cell and is used.

With regard to a negative electrode, first, lithium titanate, carboxymethylcellulose (CMC) and Ketjen Black (KB) were mixed, so that a slurry mixture was prepared. Next, this mixture was applied onto a stainless steel foil, was temporarily dried, and then was subjected to heat treatment. Thus, the negative electrode was obtained.

With regard to a positive electrode, first, lithium iron phosphate, CMC, active carbon and KB were mixed, so that a slimy mixture was prepared. Next, this mixture was applied onto a stainless steel foil, was temporally dried, and then was subjected to heat treatment. Thus, the positive electrode was obtained.

A separator to be used herein was a microporous film made of polypropylene. An electrolyte to be used herein was 1 mol/L LiPF6/EC:DEC. An electroconductive agent to be used herein was KB.

A binder to be used herein was CMC. A current collector to be used herein was stainless steel.

A nickel-zinc cell includes: a negative electrode containing zinc or a zinc compound, a positive electrode containing nickel oxide, nickel hydroxide or nickel oxyhydroxide; and an electrolyte containing phosphate in a range from 0.025 M to 0.25 M and free alkali in a range from 4 M to 9 M.

First Embodiment

FIG. 1is a section view schematically illustrating, in an axial direction, a cylindrical-type layer cell (hereinafter, simply referred to as a layer cell) according to a first embodiment of the present invention. As illustrated inFIG. 1, the layer cell11includes, as main constituent elements, an outer casing15, a current collector17, and electrode units13each housed in the outer casing. The outer casing15is configured with a one-end closed cylindrical can12, and a disc-shaped lid member16attached to an opening12cof the cylindrical can. Each of the cylindrical can12and the lid member16is made of iron, but may be made of a different metal. An outer diameter of the lid member16is slightly larger than an inner diameter of the opening12cof the cylindrical can. After the electrode units13are housed in the outer casing15, the lid member16is tightly fitted at the opening12cof the cylindrical can.

Each of the electrode units13is configured with a positive electrode13acontaining a positive electrode active material, a negative electrode13bcontaining a hydrogen storage alloy, and a separator13cdisposed between the positive electrode13aand the negative electrode13b, for allowing ions to pass therethrough, but preventing electrons from passing therethrough. The electrode units13are stacked in an axial direction (a direction X inFIG. 1) of the cylindrical can12and are housed in the outer casing15. Herein, an electrolyte (not illustrated) is retained in the separator13c. Each of the positive electrode13a, the negative electrode13band the separator13chas a disc shape with a hole formed at the center. An outer diameter of the negative electrode13bis smaller than an inner diameter of the cylindrical can12, so that an outer edge13bbof the negative electrode is not in contact with an inner surface12aof the cylindrical can. On the other hand, an outer diameter of the positive electrode13ais larger than the inner diameter of the cylindrical can12, so that an outer edge13abof the positive electrode is in contact with the inner surface12aof the cylindrical can, and the positive electrode13ais electrically connected to the cylindrical can12. Preferably, the outer diameter of the positive electrode13ais larger by 100 μm than the inner diameter of the cylindrical can12.

The current collector17is made of nickel-plated iron, and has a rod-shaped shaft portion17aand a hold portion17bformed at one end of the shaft portion17a. The nickel plating treatment prevents the current collector17from being corroded by the electrolyte contained in the separator13c. The shaft portion17aof the current collector passes through the center of the electrode unit13including the positive electrode13a, the negative electrode13band the separator13c, in the axial direction (the direction X inFIG. 1) of the outer casing15. A diameter of the hole formed on the center of the negative electrode13bis smaller than an outer diameter of the shaft portion17a. Accordingly, a peripheral edge13baof the hole of the negative electrode comes into contact with the shaft portion17a, so that the negative electrode13bis electrically connected to the current collector17. On the other hand, a diameter of the hole formed on the center of the positive electrode13ais larger than the outer diameter of the shaft portion17a. Accordingly, a peripheral edge13aaof the hole of the positive electrode does not come into contact with the shaft portion17a, so that the positive electrode13ais electrically isolated from the current collector17.

The electrode units13are disposed to be sequentially stacked on the hold portion17bof the current collector. The hold portion17bprevents the electrode unit13from being disengaged from the end of the current collector17during assembly. The hold portion17bhas a disc shape. The hold portion17bis disposed on a bottom12bof the cylindrical can with an insulating plate14interposed between the hold portion17band the bottom12b. The insulating plate14prevents an electrical short circuit due to direct contact of the current collector17with the cylindrical can12. The opposite end of the shaft portion17ato the hold portion17bis supported by a shaft support18provided on the center of the lid member16. The shaft support18is made of an insulative material in order to prevent an electrical short circuit between the lid member16and the shaft portion17a. The shaft portion protruding from the lid member16serves as a positive electrode terminal17c. The cylindrical can12serves as a negative electrode terminal.

Next, description will be given of a relation between the sizes of the positive electrode13a, negative electrode13band separator13cand the sizes of the outer casing15and current collector17. An outer edge of the separator13cis covered with the positive electrode13a(first electrode), and the outer edge of the negative electrode13b(second electrode) is covered with the separator13c. Moreover, the peripheral edge of the hole, through which the current collector17passes, in the positive electrode13ais covered with the separator13c, and the peripheral edge of the hole, through which the current collector17passes, in the separator13cis covered with the negative electrode13b.

In other words, the outer diameter of the separator13cis larger than the outer diameter of the negative electrode13b(second electrode). Therefore, the positive electrode13aand the negative electrode13bare completely separated from each other by the separator13cin the vicinity of an inner circumferential surface of the outer casing15. Thus, the electrodes do not come into contact with each other even when becoming deformed. Further, the diameter of the hole formed on the center of the separator13cis smaller than the diameter of the hole formed on the center of the positive electrode13a. Therefore, the positive electrode13aand the negative electrode13bare completely separated from each other by the separator13cin the vicinity of an outer circumferential surface of the current collector17. Thus, the electrodes do not come into contact with each other even when becoming deformed. Moreover, the outer diameter of the separator13cis smaller than the outer diameter of the positive electrode13a(first electrode). Therefore, the separator13cis not interposed between the positive electrode13aand the cylindrical can12. Further, the diameter of the hole formed on the center of the separator13cis larger than the diameter of the hole formed on the center of the negative electrode13b. Therefore, the separator13cis not interposed between the negative electrode13band the current collector17.

The outer edge of the positive electrode13ais brought into contact with the inner surface, which serves as a current collector terminal, of the outer casing15, so that electricity and heat generated from the positive electrode13acan be transmitted to the outer casing15with good efficiency. Likewise, the peripheral edge of the hole, through which the current collector passes, in the negative electrode13bis brought into contact with the current collector17serving as a current collector terminal, so that electricity generated from the negative electrode13bcan be transmitted to the current collector17with good efficiency.

The inventors of the present invention have adopted a cylindrical cell having a stacked structure as an electrode structure. Thus, the inventors of the present invention have allowed to transmit electricity and heat generated from electrodes to an outer casing and a current collector with good efficiency. Thereby, the inventors of the present invention have realized a layer cell with improved cooling performance and current collecting performance.

Next, description will be given of functions and effects of a cooling structure in the first embodiment.

The outer edge13abof the positive electrode is firmly pressed against the inner surface12aof the cylindrical can and is in tight contact with the inner surface12aof the cylindrical can. Heat generated from the positive electrode13ais directly transferred to the cylindrical can12. Moreover, heat generated from the negative electrode13bis transferred to the positive electrode13avia the separator13c. The thin and single separator13cdoes not hinder the heat transfer so much. As described above, heat generated from each of the electrodes13aand13bis transferred to the cylindrical can12at low heat resistance, so that temperature rise inside the layer cell is restrained.

Herein, description will be given of a difference in temperature rise between the layer cell according to the embodiment of the present invention and a conventional spiral-wound cell, on the basis of a calculation example. In the spiral-wound cell, an overall heat transfer coefficient (U1) is expressed by Mathematical Formula 1. In the layer cell, on the other hand, an overall heat transfer coefficient (U2) is expressed by Mathematical Formula 2.

Herein, calculation is made with regard to a 18650-type cell used as an example. The spiral-wound cell has the following specifications.

Mathematical Formula 1 into which these values are substituted results in U1=0.0011 Wm−2deg−1.

On the other hand, the layer cell according to this embodiment has the following specifications.

Therefore, Mathematical Formula 2 into which these values are substituted results in U2=100 Wm−2deg−1.

A comparison between the two examples indicates that the layer cell according to the embodiment of the present invention is more excellent in heat transfer by about 100000 times than the conventional spiral-wound cell.

Next, description will be given of a modification example of the first embodiment. Specifically, this modification example adopts bag-shaped separators.

FIG. 2Ais a section view illustrating the electrodes enclosed with the bag-shaped separators. For the sake of simplification,FIG. 2Aillustrates one positive electrode13aand one negative electrode13b. The positive electrode13ais enclosed with the bag-shaped separator13caexcept the outer edge. Moreover, the negative electrode13bis enclosed with the bag-shaped separator13cbexcept the peripheral edge of the hole through which the current collector passes.

FIG. 2Bis a plan view illustrating the positive electrode13a(first electrode) enclosed with the bag-shaped separator.FIG. 2Cis a plan view illustrating the negative electrode13b(second electrode) enclosed with the bag-shaped separator.

The positive electrode13ais sandwiched between two separators each having an outer diameter which is smaller than the outer diameter of the positive electrode13aand a hole diameter which is larger than the hole diameter of the positive electrode13a, and the overlapping portions in the two separators (the edges of the holes) are bonded together by thermal welding. Thus, the positive electrode13aenclosed with the bag-shaped separator13cais formed. The negative electrode13bis sandwiched between two separators each having an outer diameter which is larger than the outer diameter of the negative electrode13band a hole diameter which is smaller than the hole diameter of the negative electrode13b, and the overlapping portions in the two separators (the outer peripheral portions) are bonded together by thermal welding. Thus, the negative electrode13benclosed with the bag-shaped separator13cbis formed.

Dust or foreign matters derived from the electrodes in the course of transporting the cell and the course of assembling the cell are trapped inside the bag-shaped separator. The bag-shaped separators prevent the dust or foreign matters derived from the electrodes from being interposed between the electrodes and between the electrode and the current collector terminal. Therefore, an internal short circuit does not occur. Further, the bag-shaped separators are prevented from being interposed between the positive electrode13aand the cylindrical can12and between the negative electrode13band the current collector17because the separators are disposed out of the right place.

Second Embodiment

FIG. 3is a section view schematically illustrating, in an axial direction, a pipe-type layer cell (hereinafter, simply referred to as a layer cell) according to a second embodiment of the present invention. As illustrated inFIG. 3, the layer cell21has almost the same structure as that of the layer cell11illustrated inFIG. 1except part of an outer casing and part of a current collector. Specifically, the outer casing25is configured with a round pipe22and disc-shaped lid members26attached to openings22bformed at two ends of the round pipe22. The current collector27passes through the lid member26and is supported by the lid member26.

Hereinafter, description will be mainly given of a difference between the layer cell21and the layer cell11.

Electrode units23each of which is configured with a positive electrode23a, a negative electrode23band a separator23care sequentially stacked in such a state that a shaft portion27aof the current collector passes therethrough. The current collector27is supported by shaft supports28formed on the centers of the lid members26, respectively, at two ends27bthereof. Each of the shaft supports28is made of an insulative material in order to prevent an electrical short circuit between the lid member26and the current collector27. Each of the ends27bof the current collector protruding from the lid members26serves as a negative electrode terminal. The round pipe22serves as a positive electrode terminal.

Next, description will be given of an assembled battery including the layer cell21.FIG. 4Aillustrates a state that a metal fitting29is attached to the layer cell21. The metal fitting29is disposed between the layer cell21and the adjacent layer cell21′ so as to be brought into surface contact with the lid member26of the layer cell21. The metal fitting29is made of a column-shaped metal, but may be made of a prism-shaped metal. An axial direction of the metal fitting29corresponds with an axial direction (a direction X inFIG. 4A) of the current collector27. The metal fitting29has a top surface29a(the left side in the figure), and a cavity29aais formed on the center of the top surface29ain a vertical direction to the top surface29a. The cavity29aaallows the current collector27′ of the adjacent layer cell21′ to be fitted thereinto. The metal fitting29also has a bottom surface29b(the right side in the figure), and a cavity29bais formed on the center of the bottom surface29bin a vertical direction to the bottom surface29b. The cavity29baallows an insulating member24to be fitted thereinto. Moreover, a cavity24ais formed on the center of the insulating member24in the vertical direction to the bottom surface29b. The cavity29aallows the shaft portion27bof the current collector in the layer cell21to be fitted thereinto. The bottom surface29bof the metal fitting comes into surface contact with the lid member26of the layer cell, so that the layer cell21and the adjacent layer cell21′ are electrically connected to each other via the metal fitting29. Herein, the insulating member24prevents an electrical short circuit due to the contact of the current collector27with the outer casing25.

As illustrated inFIG. 4B, it is possible to obtain the assembled battery20in which the layer cells are connected in series, by coupling the adjoining layer cells21to each other using the metal fitting29.

Third Embodiment

FIG. 5is a section view schematically illustrating, in an axial direction, a capsule-type layer cell (hereinafter, simply referred to as a layer cell) according to a third embodiment of the present invention. The layer cell31includes, as main constituent elements, an outer casing35, a current collector37, and electrode units33each housed in the outer casing. The outer casing35is configured with a one end-closed cylindrical outer structural unit32and a lid member36attached to an opening32cof the outer structural unit32. Each of the outer structural unit32and the lid member36is made of nickel-plated iron, but may be made of a metal such as aluminum or titanium.

The outer structural unit32has a tubular side portion32aand a bulging portion32bthat bulges in a dome shape at the bottom thereof, and the lid member36also has a tubular side portion36aand a bulging portion36bthat bulges in a dome shape at the bottom thereof. An outer diameter of the side portion36aof the lid member is smaller than an inner diameter of the opening32cof the outer structural unit32. The opening32cis covered with the lid member36in such a direction that the bulging portion36bbulges outward the opening32cof the outer structural unit. The lid member36is bonded to the outer structural unit32by an insulating seal member38. The insulating seal member38plays a role to electrically insulate the outer structural unit32from the lid member36, and also plays a role to form a sealed space inside the outer casing35by the seal of the bonded portion. The insulating seal member38is made of a material having an insulating property and a sealing property, such as asphalt pitch.

Each of the electrode units33is configured with a positive electrode33acontaining a positive electrode active material, a negative electrode33bcontaining a hydrogen storage alloy, and a separator33cdisposed between the positive electrode33aand the negative electrode33b, for allowing ions to pass therethrough, but preventing electrons from passing therethrough. Moreover, the electrode units33are stacked in an axial direction (a direction X inFIG. 5) of the outer structural unit32and are housed in the outer casing35. Herein, an electrolyte is retained in the separator33c. Each of the positive electrode33a, the negative electrode33band the separator33chas a disc shape with a hole formed at the center. Moreover, an outer diameter of the positive electrode33ais smaller than an inner diameter of the outer structural unit32, so that an outer edge33aaof the positive electrode is not in contact with an inner surface32aaof the outer structural unit. On the other hand, an outer diameter of the negative electrode33bis larger than the inner diameter of the outer structural unit32, so that an outer edge33baof the negative electrode is in contact with the inner surface32aaof the outer structural unit32, and thus the negative electrode33bis electrically connected to the outer structural unit32. Preferably, the outer diameter of the negative electrode33bis larger by 100 μm than the inner diameter of the outer structural unit32.

The current collector37is made of electrically conductive nickel-plated iron, and has a rod-shaped shaft portion37aand a hold portion37battached to one end of the shaft portion37a. The shaft portion37aof the current collector37passes through the center of the electrode unit33configured with the positive electrode33a, the negative electrode33band the separator33c, in the axial direction (the direction X inFIG. 5) of the outer casing35. A diameter of the hole formed on the center of the positive electrode33ais smaller than an outer diameter of the shaft portion37a. Accordingly, a peripheral edge33abof the hole of the positive electrode comes into contact with the shaft portion37a, so that the positive electrode33ais electrically connected to the current collector37. On the other hand, a diameter of the hole formed on the center of the negative electrode33bis larger than the outer diameter of the shaft portion37a. Accordingly, a peripheral edge33bbof the hole of the negative electrode is not in contact with the shaft portion37a.

The electrode units33are disposed to be sequentially stacked on the hold portion37bof the current collector. Herein, the hold portion37bprevents the electrode unit33from being disengaged from the end of the current collector37. Presser plates34aeach made of an insulating material are disposed at two ends of the stacked electrode units33, and prevent the electrode units33from being damaged when the electrode units33are stacked and pressed. The presser plate34ais preferably made of a material which is appropriately used as an insulating material and a structural material, and is made of polypropylene. The hold portion37bhas a disc shape. The hold portion37bis not in contact with the bulging portion32bat the bottom of the outer structural unit. Therefore, the hold portion37band the outer structural unit32aare electrically isolated from each other. An opposite end37cof the shaft portion to the hold portion37bpasses through a hole36cformed on the center of the lid member36, and protrudes outward (the right direction in the figure) the lid member36. The end37cprotruding from the lid member36serves as a positive electrode terminal. The outer structural unit32serves as a negative electrode terminal.

Hydrogen storage chambers39are provided in inward spaces of the bulging portions32band36b. More specifically, the hydrogen storage chamber39is disposed on the space, which is formed by the inner surface32ba,36baof the bulging portion and the electrode unit33, in the outer casing.

The negative electrode33bcontains a hydrogen storage alloy. A charge-capacity of the negative electrode33bis smaller than a charge-capacity of the positive electrode33a. Hydrogen gas generated from the negative electrode because of overcharge is stored in the hydrogen storage chamber39. The hydrogen gas stored in the hydrogen storage chamber39is stored by the hydrogen storage alloy, so that the negative electrode33bis charged.

<Amount of Active Material>

In the layer cell according to the embodiment of the present invention, the positive electrode capacity is 1000 mAh. The negative electrode capacity corresponds to 80% of the positive electrode capacity.

In a negative electrode regulation-type cell, hydrogen gas is generated from a negative electrode in an overcharged state. In other words, charge to 800 mAh or more causes generation of hydrogen gas from the negative electrode (see Reaction Formula (1)). The generated hydrogen gas is stored in the negative electrode. Hydrogen gas which is not stored in the negative electrode is stored in a clearance formed inside the cell. Provision of a hydrogen gas storage chamber in a cell allows the cell to store and accumulate hydrogen gas in a larger amount. When the hydrogen gas to be generated is large in amount, a pressure in the cell rises. Each of the layer cells according to the first to third embodiments adopts a hermetic structure. Therefore, the stored hydrogen gas is not leaked from the cell.

With regard to discharge of the layer cell, hydrogen stored in the negative electrode is discharged as hydrogen ions and electrons from the hydrogen storage alloy. However, the hydrogen gas stored and accumulated in the layer cell is stored in the hydrogen storage alloy, so that the charged state of the negative electrode is maintained (see Reaction Formula (2) at the time of discharge). As described above, the hydrogen gas is not useless because the hydrogen gas is utilized as an energy source at the time of discharge. The hydrogen storage alloy acts as a so-called catalyst. Therefore, a volume change of the negative electrode is small in charge and discharge. This leads to preventing degradation of the negative electrode, and prolonging the lifetime of the cell.

Herein, the electrode plays a role of an electrode that is charged and discharged in a conventional secondary cell. In addition, the electrode also plays a role of an electrode that applies electrolysis to water contained in an electrolyte to generate hydrogen gas.

The price of the negative electrode occupies 80% of the total price of the electrodes, which is expensive. A positive electrode regulation-type cell requires negative electrodes which are 1.7 times as much as positive electrodes. According to the present invention, however, the amount of negative electrodes is reduced to 80% relative to the amount of positive electrodes. Thus, it becomes possible to reduce the price of the electrodes to one-half. Even when the amount of negative electrodes is reduced, a cell capacity is not reduced by using hydrogen gas stored by overcharge.

Fourth Embodiment

With reference to an axial section view ofFIG. 6A, description will be given of a rectangular-type layer cell (hereinafter, simply referred to as a layer cell) according to a fourth embodiment of the present invention. The layer cell71includes, as main constituent elements, an outer casing75, current collectors77, and electrode units74each housed in the outer casing. The outer casing75is configured with a body member72and a lid member73. The body member72is a one end-closed rectangular container. An opening72cof the body member72is covered with the lid member73, so that a sealed space can be formed inside the body member72. Each of the body member72and the lid member73is made of iron. As illustrated in a plan view ofFIG. 6B, the layer cell71has a rectangular shape as a whole.

Each of the electrode units74is configured with a positive electrode74acontaining a positive electrode active material, a negative electrode74bcontaining a hydrogen storage alloy, and a separator74cdisposed between the positive electrode74aand the negative electrode74b, for allowing ions to pass therethrough, but preventing electrons from passing therethrough. The separator74cplays a role to prevent a short circuit between the positive electrode74aand the negative electrode74b, and a role to retain an electrolyte. The positive electrode74aand the negative electrode74bare stacked in an axial direction (a direction Y inFIG. 6A) of the body member72with the separator74cinterposed therebetween, and are housed in the outer casing75. Each of the positive electrode74a, the negative electrode74band the separator74chas a sheet shape. An outward dimension of the negative electrode74bis smaller than an inward dimension of the body member72, so that an outer edge74bbof the negative electrode is not in contact with an inner surface72aof the body member. On the other hand, an outward dimension of the positive electrode74ais larger than the inward dimension of the body member72, so that an outer edge74abof the positive electrode is in contact with the inner surface72aof the body member72under pressure, and thus the positive electrode74ais electrically connected to the body member72. Therefore, since heat generated from the electrode unit74is transferred to the body member72with a small temperature gradient, rise in temperature of the electrode unit74is restrained. Preferably, the outward dimension of the positive electrode74ais larger by 100 μm than the inward dimension of the body member72.

Each of the current collectors77is made of electrically conductive nickel-plated iron. Moreover, the current collector77has an inverted conical-shaped countersunk portion77band a shaft portion77afollowing the countersunk portion77b, and takes a form of a countersunk screw as a whole.

The electrodes74band74ahave holes74baand74aathrough which the shaft portion77aof the current collector77passes, respectively. A diameter of the hole74baformed on the negative electrode74bis smaller than an outer diameter of the shaft portion77a, so that the negative electrode74bcomes into contact with the shaft portion77aand thus the negative electrode74bis electrically connected to the current collector77. On the other hand, a diameter of the hole74aaformed on the positive electrode74ais larger than the outer diameter of the shaft portion77a, so that the positive electrode74adoes not come into contact with the shaft portion77a.

The four current collectors77(seeFIG. 6B) are coupled to one another via a coupling plate77dlocated under the electrode units74. In other words, a screw portion77cformed at a lower end77caof the current collector is screwed into a screw hole77daformed on the coupling plate77d, so that the current collector77is coupled to the coupling plate77d. The electrode units74are disposed to be sequentially superposed on the coupling plate77d, and the coupling plate77dprevents the electrode units74from being disengaged from the end of the current collector77. An insulating plate76bis disposed between the bottom72bof the body member and the coupling plate77dto prevent an electrical short circuit between the current collector77and the body member72because of the contact of the coupling plate77dwith the bottom72bof the body member. Specifically, the coupling plate77dis surrounded with the insulating plate76bmade of polypropylene.

The lid member73has a flat plate portion73aand a bent portion73bwhich is bent at a right angle from the flat plate portion. An insulating plate76ais disposed inward the bent portion73band on the opening72cof the body member. The insulating plate76aprevents an electrical short circuit between the uppermost electrode unit74and the lid member73. A groove76aais formed on the opposite surface of the insulating plate76ato the lid member73such that an outer edge of the opening of the body member72is fitted thereinto. A seal member80made of asphalt pitch is disposed between the groove76aaand the outer edge of the opening of the body member72so as to keep the hermeticity inside the outer casing75. For the similar purpose, the seal member80made of asphalt pitch is also disposed on the hole, through which the shaft portion77aof the current collector passes, in the insulating plate76a.

The lid member73is connected to the coupling plate77dby the current collector77acting as a countersunk screw. The body member72serves as a positive electrode terminal, and the lid member73serves as a negative electrode terminal.

FIG. 7is a diagram illustrating a schematic configuration in a case where an assembled battery70is configured with a plurality of layer cells71. These layer cells71are connected in series in such a manner that the flat plate portion73aof the lid member in one of the layer cells71is opposed to and is brought into surface contact with the bottom72bof the body member in the adjacent layer cell. The layer cells71connected in series are sandwiched between a positive electrode terminal board78aand a negative electrode terminal board78bto form the assembled battery70. More specifically, the positive electrode terminal board78athat comes into surface contact with the body member72and the negative electrode terminal board78bthat comes into surface contact with the lid member73are disposed inside a housing70a. Then, the plurality of layer cells71is housed between the positive electrode terminal board78aand the negative electrode terminal board78bto form the assembled battery70. External cool air is supplied into the housing70aby a suction fan79aand a forced draft fan79bto cool the assembled battery70. An output from the assembled battery70is extracted from the positive electrode terminal board78aand the negative electrode terminal board78bto the outside through a cable (not illustrated).

Fifth Embodiment

FIG. 8is a section view schematically illustrating, in an axial direction, a cylindrical-type layer cell (hereinafter, simply referred to as a layer cell) according to a fifth embodiment. The layer cell90includes, as main constituent elements, a cylindrical can92, a current collector17, and electrode units93each housed in the cylindrical can. Each of the electrode units93is configured with a positive electrode93a, a negative electrode93b, and a separator93cdisposed between the positive electrode93aand the negative electrode93b.

The electrode units93are disposed to be sequentially superposed on a presser plate98blocated under the current collector97, and the presser plate98bprevents the electrode units93from being disengaged from an end of the current collector97. The presser plate98bis a nickel-plated steel plate having a disc shape. A presser plate98ais disposed on the uppermost one of the stacked electrode units93, and the electrode units93can be compressed by the presser plates98aand98b.

The electrode units93are inserted into the cylindrical can92in an axial direction (a direction X inFIG. 8) of the cylindrical can92. An outer diameter of the positive electrode93ais smaller than an inner diameter of the cylindrical can92, so that an outer edge93abof the positive electrode does not come into contact with an inner surface92aof the cylindrical can. On the other hand, an outer diameter of the negative electrode93bis larger than the inner diameter of the cylindrical can92, so that an outer periphery93bbof the negative electrode comes into contact with the inner surface92aof the cylindrical can92and the negative electrode93bis electrically connected to the cylindrical can92. An upper opening of the cylindrical can92is covered with a lid member96. An insulating member99is disposed between the lid member96and the cylindrical can92to prevent an electrical short circuit due to the contact of the lid member96with the cylindrical can92.

An insulating sheet94is disposed on the bottom92bof the cylindrical can to prevent an electrical short circuit between the current collector97and the cylindrical can92from occurring because one end97bof the current collector directly comes into contact with the bottom92bof the cylindrical can. A connecting plate91which has a shape of a plate bowed downward and is made of an elastic material is attached to the other end97aof the current collector. An end91aof the connecting plate comes into contact with a bottom surface96bof the lid member, and is forced downward by the lid member96. Thus, the current collector97and the lid member96are electrically connected to each other via the connecting plate91.

A projection96aformed on the center of the lid member96serves as a positive electrode terminal. Moreover, the cylindrical can92serves as a negative electrode terminal.

This embodiment is different from each of the foregoing embodiments with regard to part of the structure of the current collector. Hereinafter, description will be given of the point of difference.

FIG. 9is a partial section view schematically illustrating a relation between the current collector97and the electrode unit93. As illustrated inFIG. 9, the current collector97has a side surface formed as a screw portion97cthat includes screw grooves in which the root has a diameter d and the crest has a diameter D (d<D).

As illustrated inFIG. 9, a diameter of a hole93aaformed on the positive electrode93ais smaller than the diameter (d) of the root of the screw portion97c, so that the positive electrode93ais screwed into the shaft portion97aof the current collector and firmly comes into contact with the current collector97. Thus, the positive electrode93ais electrically connected to the current collector97. On the other hand, a diameter of a hole93baformed on the negative electrode93bis larger than the diameter (D) of the crest of the screw portion97c, so that the negative electrode93bdoes not come into contact with the shaft portion97aof the current collector. Thus, the negative electrode93bis electrically isolated from the current collector97.

It becomes possible to satisfactorily ensure the contact between the positive electrode93aand the current collector97in such a manner that the diameter of the hole formed on the positive electrode93ais made smaller than the outer diameter of the root of the screw portion of the current collector97. The screw grooves formed on the current collector97prevent the coupling between the current collector and the electrode from being loosened at the time of assembly of the electrode, and ensure the tight contact between the current collector and the electrode. That is, a firmly fitted state is maintained in such a manner that the positive electrode93ais fitted along the screw portion formed on the current collector97. Thus, it becomes possible to ensure the contact state of the electrode with the current collector even when the electrode becomes deformed by charge and discharge. Herein, the current collector having the screw grooves is also applicable to the first to fourth embodiments in addition to this embodiment.

FIG. 10is a plan view (the left side inFIG. 10) and a side view (the right side inFIG. 10) illustrating a current collector according to another embodiment. The current collector97′ has a side surface on which V-shaped grooves are entirely and circumferentially formed in an axial direction, and a section thereof has a sawtooth shape. Since the section of the current collector has the sawtooth shape, a contact area of the current collector with the electrode becomes large. When the electrode is brought into tight contact with the current collector in the axial direction under pressure, then, the electrode slides along the grooves formed on the current collector. As the result, a contact failure between the electrode and the current collector is less prone to occur. Even when the electrode becomes deformed in the course of charge and discharge, the electrode is not damaged because the electrode slides along the grooves of the current collector.

With reference toFIG. 11, next, description will be given of a method for assembling the layer cell according to the present invention. The electrode units93are stacked in such a manner that the positive electrode93aand the negative electrode93bare sequentially inserted, with the separator93cinterposed therebetween, into a round rod95having an outer diameter (d′) which is slightly smaller than the root of each of the screw grooves formed on the side surface of the current collector97. Next, the electrode units93are stacked in predetermined sets, and the presser plates98aand98bare disposed beside the two ends of the electrode units93, respectively, to hold the electrode group, so that an electrode current collector A is assembled (see the left side inFIG. 11).

Next, the electrode group is compressed with the presser plates98aand98b, and the round rod95is pulled out while the compressed state is maintained. In place of the round rod95, the current collector97is pushed into the electrode group, which is held by the presser plates98aand98band to which pressure is applied, while being rotated. Next, the presser plates98aand98bare screwed into the current collector97, and an electrode assembly B is assembled in a state that the electrode group is continuously compressed (the right side inFIG. 11).

Next, the electrode assembly B is put into the cylindrical can92under pressure, the cylindrical can92is subjected to deaeration, and the electrolyte is injected into the cylindrical can92. After the injection of the electrolyte, the lid member96is attached onto the opening of the cylindrical can92and the opening of the cylindrical can92is caulked, so that the layer cell is hermetically sealed.

The layer cell according to the fifth embodiment of the present invention was charged in a rate of 0.5 C to 8 C and, after the full charge, the internal temperature and surface temperature of the layer cell were measured. With regard to a temperature measurement method, the internal temperature was measured in such a manner that a thermocouple is attached to the center of the current collector. Moreover, the surface temperature was measured in such a manner that a thermocouple is attached to a surface of the outer casing of the layer cell. Herein, the measurement was performed in a state that a room temperature is set at 15° C. and 1 m/s air is blown on the layer cell by a fan.

Table 1 shows results of measurement of a cell temperature after the layer cell is charged such that the SOC is 100% at each charge rate (0.5 C, 1 C, 2 C, 5 C, 8 C). In Table 1, the left column shows the largest value of a difference between the cell surface temperature and the room temperature (=measured temperature−room temperature), and the right column shows the largest value of a difference between the cell internal temperature and the room temperature (=core temperature−room temperature). At each of the charge rates, the difference between the cell temperature and the room temperature rapidly rose when the SOC exceeds 80%. At the charge rate of 2 C or less, each of the differences in temperature of the cell (measured temperature−room temperature, core temperature−room temperature) was less than 5° C. At the charge rate of 8 C, each of these differences in temperature was less than 30° C.

FIG. 12is a graph illustrating the difference between the cell internal temperature after the charge and the room temperature with the values of the respective charge rates taken as parameters. InFIG. 12, the vertical axis indicates a temperature difference scaled on a Celsius basis, and the horizontal axis indicates an elapsed time scaled on a minute basis. It is apparent from the graph that the difference between the cell internal temperature and the room temperature (temperature rise) at the charge rate of 2 C or less is 4° C. or less, which is considerably small. The reason therefor is considered to be as follows. That is, heat is not accumulated in the cell because the heat generation by the charge and the heat dissipation are well balanced.

It is understood that there is a difference between the cell internal temperature and the room temperature at the charge rate of 5 C and the charge rate of 8 C. However, the difference between the cell internal temperature and the room temperature decreases to less than 5° C. in less than 20 minutes. It is apparent from this result that the cell is considerably excellent in heat dissipating property.

It was apparent from the test results that the layer cell according to the present invention is large in internal thermal conductivity and the cell internal temperature is lowered in a short time even when the temperature rises because of the charge.

INDUSTRIAL APPLICABILITY

The layer cell according to the present invention can be suitably used as a consumer power storage apparatus in addition to an industrial power storage apparatus.

REFERENCE SIGNS LIST