JP2002110170A - Battery - Google Patents

Abstract

(57) [Problem] To provide a battery with improved safety in an external destruction test or the like without impairing battery performance. In a battery comprising a battery element (10) having a positive electrode, a negative electrode and an electrolyte layer laminated and housed in a flat case (40), a positive electrode current collector (1a) of a battery element located outside and a negative electrode A battery in which the current collector (3a) is thicker than the positive electrode current collector (1) and the negative electrode current collector (3) of the battery element located inside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery, and more particularly, to a battery having excellent battery characteristics and improved safety in heating, external destruction tests, and the like.

[0002]

2. Description of the Related Art A battery is usually formed on the basis of a unit battery element having a positive electrode, a negative electrode and an electrolyte layer. A battery element formed by stacking the unit battery elements is widely used, for example, in the field of lithium secondary batteries. These battery elements have a sufficient capacity by winding a long one and laminating a flat one. A flat battery in which battery elements formed into a flat shape by winding or lamination are housed in a flat case is known in the field of, for example, a lithium secondary battery. In particular, batteries using a laminate film as the flat case are expected to be used in the future because of their light weight.

In a battery, one of external destruction tests is a nail penetration test, that is, a battery of a predetermined size is penetrated in the thickness direction of a flat case to break the battery.
A test is performed to observe phenomena such as temperature rise, smoking, and ignition, and thereby evaluate the safety in the event that the battery is destroyed from the outside. As another test of the external destruction test, an external impact test, i.e., applying an external impact to the battery by dropping or dropping it, observing phenomena such as temperature rise, smoke and ignition, etc. An evaluation test is performed. Further, as one of the environmental tests, a heating test,
That is, the battery is heated to a predetermined temperature, and at that time, a phenomenon such as a temperature rise, smoking, or ignition is observed, and a test for evaluating the safety of the battery is also performed.

Hitherto, as a method for improving the safety in the above-described tests, proposals have been made such as devising a material of an electrolytic solution. However, such a method has a problem that battery performance is relatively poor. Another method is needed.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the safety in external destruction tests, environmental tests, and the like without impairing battery performance. Is to provide. Another object of the present invention is to provide a battery which is easy to manufacture and has excellent battery characteristics such as cycle characteristics and rate characteristics. Still another object of the present invention is to provide a battery that is small and lightweight, and has excellent volume energy density and weight energy density.

[0006]

SUMMARY OF THE INVENTION The present inventor has set the thickness of the current collector of the outermost electrode of a battery element formed by stacking unit battery elements to be smaller than the thickness of the current collector of the electrode located on the inner side. It has been found that when the electric conductor is formed thicker than at least one thickness, the heat capacity is increased and the mechanical strength is improved, and the above object can be achieved, and the present invention has been completed. That is, the gist of the present invention resides in the following (1) to (9). (1) In a battery in which a unit battery element having an electrode formed from a current collector and an electrode material layer and an electrolyte layer is stacked and housed in a case, the current collector of the outermost electrode is A battery having a thickness greater than at least one of the current collectors of the electrodes located further inside. (2) The thickness of the current collector of the outermost electrode and the electrode located on the innermost side thereof is greater than the thickness of at least one of the current collectors of the electrodes located on the innermost side. ). (3) The battery according to (1), wherein the thickness of the current collector of the outermost electrode is larger than the thickness of the current collector of any of the electrodes located inside. (4) The thickness of the current collector of the electrode located on the outermost side and one inner side thereof is larger than the thickness of the current collector of any electrode located on the inner side. A battery according to claim 1. (5) The current collector formed thickly is formed by laminating a plurality of conductive foils (1).
The battery according to any one of (1) to (4). (6) The unit battery element is stacked by being wound, and a terminal for taking out current to the outside of the case is connected to a thickly formed current collector portion. (1) The battery according to any one of (1) to (5). (7) The battery according to any one of (1) to (6), wherein the thick current collector has a thickness of 20 μm or more. (8) The battery according to any one of (1) to (7), wherein the electrolyte layer is formed of a non-fluid electrolyte. (9) The battery according to any one of (1) to (8), wherein the unit battery element is a lithium secondary battery.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of a main part of an example of the battery of the present invention, FIG. 2 is a schematic explanatory view of a main part of another example of the battery of the present invention, and FIG. FIG. 4 is an explanatory view of a tab structure of a stacked battery element, FIG. 5 is an explanatory view of a terminal structure of a stacked battery element housed in a flat case, and FIG. It is explanatory drawing of an example of an external appearance.

In FIGS. 1 to 3, each element is shown separately from the actual one for convenience of viewing. 1 and 2 show only one of the lower side of the battery,
The upper side is omitted. FIG. 3 shows only one upper side of the battery and omits the lower side.

The basic structure of a battery according to the present invention is the same as that of a conventional battery, and includes a unit battery element having a positive electrode, a negative electrode, and an electrolyte layer housed in a case. A typical example of such a battery is a lithium secondary battery. Therefore, the following description will be made based on the above-described lithium secondary battery.

[0010] The battery element defined in the present invention has a positive electrode, a negative electrode and an electrolyte layer. At least one of the positive electrode and the negative electrode is formed by forming an electrode material layer on a current collector. In the case of a lithium secondary battery, the electrode material layer is mainly composed of an active material and a binder. The electrolyte layer is provided between the positive electrode and the negative electrode. The electrolyte layer is roughly divided into a liquid electrolyte layer and a non-fluid electrolyte layer. The former is mainly composed of an electrolytic solution mainly composed of a lithium salt and a non-aqueous solvent (such as carbonates), and the latter is a gel of the electrolytic solution. And a solid electrolyte. The gel of the electrolytic solution is usually formed by gelling the electrolytic solution with a polymer. The electrolyte layer may be formed by impregnating a separator such as a polyethylene porous membrane with the above components. The use of a non-fluid electrolyte is preferred from the viewpoint of preventing electrolyte leakage. In particular, when a case made of a laminated film described later is used together, not only can the battery be further reduced in size and weight while improving safety, but also the effect of thickening the outermost current collector described later. Will also be noticeable. In terms of ionic conductivity,
Among the non-fluid electrolytes, the gel of the electrolyte is preferable.

In the present invention, the constituent material of each of the above-mentioned elements can be arbitrarily selected from materials known in conventional batteries. Further, various conditions can be appropriately selected. For example, as a material of the current collector, a conductive foil using a metal such as aluminum, nickel, copper, and SUS (stainless steel) may be used. The thickness of the current collector is usually 0.1 to 100 μm. In particular, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector.

In a lithium secondary battery, the electrode material layer is usually composed of an active material and a binder, and may contain a conductive agent as required. Examples of the positive electrode active material include a composite oxide of lithium and one or more metals selected from the group consisting of cobalt, nickel, and manganese. Examples of the negative electrode active material include carbonaceous materials such as graphite and coke. These are usually used in a particle size of 1 to 30 μm. Examples of the binder include a fluorine resin such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene, and a CN group-containing polymer such as polyacrylonitrile and polyvinylidene cyanide. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. The electrodes can be formed by mixing these materials with a mortar or the like and then pressing the materials on a current collector. Further, an electrode material layer can also be formed by applying and drying a paint in which these materials are dissolved on a current collector. In this case, as the solvent used, for example,
N-methylpyrrolidone, dimethylformamide and the like can be mentioned. The amount of the binder is usually 0.1 to 30 parts by weight based on 100 parts by weight of the active material, and the amount of the solvent is usually 10 to 90% by weight as the concentration in the coating material.

Examples of the lithium salt (supporting electrolyte) constituting the electrolyte include LiPF ₆ and LiClO ₄ .
Examples of the solvent include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and lactones such as gamma butyrolactone. Among these, it is preferable to use ethylene carbonate, propylene carbonate, and gamma-butyrolactone. The concentration of the supporting electrolyte in the electrolyte is usually 0.5 to
2 mol / L.

As the polymerizable monomer used for preparing the gel electrolyte (polymer electrolyte), a monomer polymerizable by heat, ultraviolet rays, an electron beam, etc., that is, for example,
Various monomers having a functional group such as an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group are exemplified.
In addition to N-group-containing polymers, acrylic derivative-based polymers such as polymethacrylic acid, polyvinyl alcohol-based polymers such as polyvinyl acetate, and halogen-containing polymers such as polyvinyl chloride are exemplified.

As a material of the case for housing the battery element, for example, a flexible film such as a laminate film composed of a metal layer and a synthetic resin layer disposed on both sides thereof can be mentioned. In the case of a laminate film, the metal is preferably aluminum, the outer layer synthetic resin is preferably polyamide or polyester, and the inner layer synthetic resin is preferably polyethylene or polypropylene. The laminated film has good gas barrier properties and can be reduced in weight and thickness, and thus is suitable for improving the energy density of the battery. Furthermore, compared to metal cans that have been most commonly used in the past, the above-mentioned laminated film tends to have a lower strength against nail penetration and the like, and the effect of the present invention when a laminated film is used is particularly remarkable. is there.

The battery of the present invention may be of a flat plate type in which flat unit battery elements are stacked. In addition, the unit battery element formed in a long length was wound and laminated so as to have a flat plate shape,
A flat wound battery may be used. Furthermore, a cylindrical wound battery in which long unit battery elements are wound and laminated in a cylindrical shape may be used. The examples shown in this specification are a flat plate type battery (FIGS. 1 and 2) and a flat wound type battery (FIG. 3). In the present invention, a flat plate type battery is preferably used.

When the battery of the present invention is of a flat-plate type,
For example, as shown in FIGS. 4 and 5, a battery element (10) in which unit battery elements each having a positive electrode, a negative electrode, and an electrolyte layer are stacked in a thickness direction is accommodated in a flat case (40). And it has an appearance as shown in FIG. 6, for example.
4 to 6, reference numerals (6) and (7) denote electrode tabs assembled together, and (20) and (30) denote extraction terminals joined to the electrode tabs for extracting current to the outside of the case. is there. When using a flat plate type battery, it is preferable that the unit battery element has a structure in which three or more sets are stacked, more preferably, five or more sets are stacked, and more than ten sets are stacked. Is particularly preferable, and a structure in which 20 or more sets are stacked is most preferable. When three or more sets are stacked, the calorific value increases in a nail penetration test or the like, so that the effects of the present invention become remarkable.

In the battery of the present invention, the unit battery elements are stacked and housed in the battery case, and the current collector of the electrode of the outermost unit battery element is located inside the unit battery element. Characterized in that the thickness is greater than at least one thickness of the current collector of the electrode. Preferably, the thickness of the current collectors of the outermost and innermost electrodes is greater than the thickness of at least one of the current collectors of the innermost electrodes. In short, for example, in a flat plate battery, it is necessary to increase the thickness of one or both outermost current collectors, and usually,
Preferably, both outermost current collectors are thickened. Further, for example, in the case of a flat wound battery, it is necessary to increase the thickness of at least a part of the outermost periphery, and it is usually preferable to increase the thickness of the outermost periphery area by half or more, particularly, substantially the entirety. Note that the current collector of the electrode of the unit battery element located on the outermost side may be thicker than at least one of the current collectors of the electrode of the unit battery element located on the inner side. Some of the current collectors of the electrodes of the unit battery elements located may have a thickness equal to or greater than that of the current collector of the electrodes of the unit battery elements located outermost.

A specific example of such a battery is shown below in FIGS.
Description will be made using the battery illustrated in FIG.

The battery exemplified in FIG. 1 is a flat plate type battery, and the unit located inside the positive / negative current collector of the unit battery element located on the outermost side (lower side in FIG. 1) in the thickness direction. This is an example in which a metal foil thicker than the current collector of the battery element is used. In FIG. 1, reference numeral (1) denotes a positive electrode current collector, (1a) denotes a positive electrode current collector thicker than (1), and (2) denotes a positive electrode material layer mainly composed of a positive electrode active material, a conductive material, and a binder. Reference numeral (3) denotes a negative electrode current collector, reference numeral (3a) denotes a negative electrode current collector thicker than (3), (4) denotes a negative electrode material layer mainly composed of a negative electrode active material and a binder, and (5) denotes: (41) is a metal layer of a flat case (40) made of a laminated film, and (42) is a metal layer (4).
1) synthetic resin layers arranged on both sides, (10a), (1)
0b) and (10c) are unit battery elements.

In FIG. 1, the positive electrode current collector (1a) and the negative electrode current collector (3a) in the outermost unit battery element (10a) are the outermost electrode of the battery element (10) and one of the outermost electrodes. Each of the current collectors of the inner electrodes is configured,
These current collectors are formed to be thicker than any of the other positive electrode current collectors (1) and (3) existing inside. In the case of the battery illustrated in FIG. 1, a positive electrode is positioned as a battery element on the lower side illustrated, but a negative electrode may be positioned. Further, it is preferable that the battery element in which the current collector is formed thick is formed also on the upper side (not shown). The uppermost surface and the lowermost surface of the battery element (10) may have the same polarity or different polarities. These are the same in the batteries exemplified in FIGS.

The battery illustrated in FIG. 2 is a flat plate type battery, and includes a current collector of unit battery elements located on the outermost side (lower side in the figure) in a thickness direction and a current collector of unit battery elements located inside. Although the thickness of the current collector is the same as that of the current collector, the current collector is formed thick by stacking another metal foil on the current collector of the outermost unit battery element. In FIG. 2, reference numeral (11)
Is a metal foil stacked in contact with the positive electrode current collector. FIG.
In (2), a metal foil (11) is laminated in contact with the positive electrode current collector (1) to form a current collector (1a) of the outermost electrode of the battery element (10). (1a)
Is thicker than any of the other positive electrode current collectors (1) and (3) present inside. The battery illustrated in FIG. 2 has the same current collector thickness as that of the battery illustrated in FIG. 1, so that the unit battery elements on the outermost and inner sides of the stacked battery elements are equal. It has a common shape, and has an advantage that management in manufacturing is easy.

In the above embodiment, it is preferable that the additionally laminated metal foil (11) is made of the same material as the positive electrode current collector (1) on which the active material is formed, since no contact potential difference occurs.

The battery illustrated in FIG. 3 is a flat wound type battery in which the thickness of the wound current collector is the same, but the current collector located on the outermost side in the thickness direction (upper side in the figure). This is an example in which the outermost current collector is formed thick by stacking a metal foil on the body. In FIG. 3, reference numeral (11) is
It is a metal foil in which a plurality of (two in this case) sheets are stacked on the positive electrode current collector via the thin film members (60a) and (60b). The metal foil (11) is formed by extending the positive electrode current collector (1) and is made of the same material as the positive electrode current collector (1). The metal foil (11) is formed by forming an unformed portion of the positive electrode material layer (2) at an end portion of the positive electrode current collector (1), and folding (turning around) the portion to overlap. You. Thin film member (60b)
Is formed by extending the electrolyte layer (5) and is the same material as the electrolyte layer. The thin film members (60) and (60a) are formed by folding (turning around) the separator used for the electrolyte layer and overlapping. FIG.
In the above, the end portion of the positive electrode current collector (1) is extended and folded, so that the outermost current collector portion of the battery element (10) is thicker than other current collector portions existing inside it. are doing. In FIG. 3, a plurality of metal foils (11) are laminated, but only one may be laminated. In addition, as long as the metal foil (11) is electrically connected, the positive electrode current collector (1) can be separated from the metal foil (11). Further, in FIG. 3, the thin film members (60a) and (60b) are provided between the positive electrode current collector (1) and the metal foil (11), and between the metal foils. You can also.

In the battery of FIG. 3, a thin film member (60a),
When (60b) is omitted, the metal foil (11) is formed in contact with the positive electrode current collector (1) to be overlapped, and the current extracting terminal (2)
0) produces the following effects. That is, in the wound type battery, as a result of winding and laminating the battery element formed on a series of metal foils, the current concentration to the current extraction part outside the battery becomes remarkable,
In such a battery, by providing the current take-out portion to the outside of the battery in a portion where the current collector is formed thick, the electric resistance of this portion can be reduced, and current concentration can be reduced. As a result, there is also an effect that the rate characteristics and the power characteristics are improved. FIG. 1 configured as above
3, the fact that the current collector of the battery element located outside is thicker than the current collector of the battery element located inside operates as follows.

For example, in a nail penetration test, when a nail of a predetermined size is inserted in the thickness direction of the flat case (40), the battery element (10) in the flat case (40) is deformed and broken, and And the negative electrode are short-circuited, and heat is generated at that location. At this time, in the conventional battery, the active material present in the short-circuited electrode generates reaction heat in a chain, resulting in intense heat generation, leading to smoke and ignition.

On the other hand, in the battery of the present invention, at the time of the above-mentioned external destruction, the battery element having a thick current collector is first destroyed. The broken battery element causes a short circuit between the positive electrode and the negative electrode, and heat is generated at that point.However, the current collector has a large thickness, so it has a larger heat capacity and excellent thermal conductivity compared to conventional batteries. ing. Therefore, the heat generated by the short circuit is quickly absorbed and diffused, so that the temperature rise of the short circuit portion is suppressed. If the temperature is controlled below the decomposition temperature of the active material, no chain reaction will occur, and no violent smoke or ignition will occur.

As a further effect, for example, in a case where a metal piece collides against the flat case (40) in an external impact test, when the metal piece collides with the collision portion or the internal battery element (1).
0) may be deformed or broken, causing a short circuit between the positive electrode and the negative electrode, and heat may be generated at that location. At this time, in the conventional battery, the active material present in the short-circuited electrode generates reaction heat in a chain, resulting in intense heat generation, leading to smoke and ignition.

On the other hand, in the battery of the present invention, when the metal piece collides with and penetrates the flat portion of the flat case,
A mechanism similar to the above operates to suppress smoke and ignition of the battery. In addition, by increasing the thickness of the current collector located on the outside of the current collector of the battery element, the thickness of the current collector subjected to the impact is increased and the probability of penetration into the battery is reduced. Can be. Further, even when the metal piece collides with the side surface of the flat case, the reinforced current collector positioned outside serves as a protective wall, and receives an impact, thereby reducing damage to the inside of the battery.

Another effect is that, for example, when the temperature of the cylindrical wound type battery rises in the heating test and the overcharge test, the conventional battery does not sufficiently radiate heat, resulting in a slight occurrence. The generated heat accumulates and causes a rise in temperature, resulting in the generation of reaction heat in a chain, resulting in intense heat generation, leading to smoke and ignition.

On the other hand, in the battery of the present invention, since the thickness of the outer collector is large, the battery has an excellent heat conduction characteristic and easily dissipates internal heat to the outside. For this reason, the temperature rise of the battery can be reduced, and the start of a thermal runaway reaction due to heat storage can be reduced.

To increase the thickness of the positive electrode current collector, a thick current collector may be used simply as described above, or a plurality of conductive foils may be laminated to increase the thickness. The configuration of the positive electrode current collector when laminating the conductive foil is not particularly limited as long as the thickness satisfies the following conditions, but usually, a metal foil or an alloy foil is used. Specifically, the same material as that of the positive electrode current collector is preferably used, and aluminum is particularly preferable. The width of increase in the thickness with respect to the internal current collector is usually 1 μm or more, preferably 10 μm or more, usually 200 μm or less, preferably 100 μm or less. In particular, it is preferable to set it to 2 times or more and 5 times or less with respect to the internal current collector. In the present invention, the total thickness of the current collector to be thickened is preferably 20 μm or more, particularly preferably 30 μm or more, and most preferably 50 μm or more.
It is preferably at most 250 μm, particularly preferably at most 100 μm, most preferably at most 80 μm. If the increase in the thickness is too large, the thickness of the electrode material layer becomes relatively too thin, so that the capacity of the whole battery is reduced. If the thickness is too small, the effect of the present invention tends to be insufficient.

When the thickness of the negative electrode current collector is increased, the method and the increase in the thickness may be the same as those of the positive electrode current collector. That is, when the thickness is increased by laminating metal foils, it is preferable to use the same material as the negative electrode current collector, and it is most preferable to use copper.

In the present invention, it is preferable that the thickness of the current collector of the outermost electrode is larger than the thickness of the current collector of any electrode located inside. For example, in a flat plate type battery, it is preferable to make the current collector of the outermost electrode thicker. Specifically, it can be realized by thickening only the current collector of the outermost electrode among the two electrodes of the outermost unit battery element. For example, for a wound type battery, it is preferable that the current collector of the battery element is formed thick at least for one round of the outermost circumference. Specifically, it can be realized by forming an uncoated portion on the current collector in advance and winding it extra. It can also be realized by co-winding a metal foil of a predetermined length only in the outer peripheral portion. Further, in the present invention, it is also preferable that the thickness of the current collector of the outermost electrode and the electrode located one inner side than the outermost electrode is larger than the thickness of the current collector of any electrode located further inside. .
For example, in a flat plate type battery, it can be realized by increasing both the current collectors of the two electrodes (positive electrode and negative electrode) of the outermost unit battery element.

In the present invention, the thickly provided current collector may be provided not only on the outermost side or the outermost side and one inside thereof but also inside the battery element. If the area for increasing the thickness of the current collector is provided in the inner battery element, the heat capacity and the mechanical strength are increased by that amount, so that the effect of the present invention becomes remarkable. Since the thickness of the electrode material layer is relatively reduced, the capacity of the battery is reduced. For this reason, when the thickly provided current collector is provided inside the battery element, it is preferable that the thickness be approximately half of the number of stacked current collectors. The thickly provided current collector may be one of the positive electrode and the negative electrode, or may be provided on both. It is preferable to provide them on both sides in terms of improving safety and characteristics.

As described with reference to FIG. 3, the thickness increasing portion of the current collector may use a thin film member (60) other than the metal foil in addition to increasing the thickness of the current collector with the metal foil. . Therefore, in the present invention, "thickening the current collector" means not only increasing the thickness of the current collector itself, or increasing the thickness by laminating a metal foil or the like on the current collector,
Increasing the thickness by laminating the thin film member and the metal foil as described above is also included. Organic as a thin film member,
An inorganic thin film can be used, and as a form, an independent thin film or a thin film formed on a substrate by, for example, coating, vapor deposition, sputtering, or the like, or a thin film formed directly on a current collector can be used. These thin film members may be electronically conductive or electronically insulating. Among these, an electronically insulating flat member is particularly preferable. The constituent material of the electronically insulating plate member is not particularly limited as long as it has electronic insulating properties. Usually, synthetic resins such as polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, vinyl chloride, and vinylidene chloride are used. .
The thickness is usually 0.1 μm or more, preferably 1 μm or more.
0 μm or more, usually 200 μm or less, preferably 100 μm
m or less. These may be laminated as independent thin films, or may be laminated by an adhesive or the like.

The constituent material of the thin film member (60) may be a porous member. In the case of a porous member, the voids are preferably filled with a liquid, particularly preferably an electrolytic solution. If the liquid is filled, the heat capacity is increased by that amount, and the effect of the present invention becomes remarkable. It is particularly preferable that such an electronic insulating member has excellent heat capacity and heat conductivity.

[0038]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the present invention. In the following examples, the following evaluations and tests were performed.

(1) Battery capacity: at a current density of C / 2.
After constant current charging to 1 V, C / 25 at a voltage of 4.1 V
The battery charged by charging at a constant voltage to a current density of 0.2 V is discharged at a constant current of 0.2 C at a constant current of 2.7 V and measured. Here, 1C means a current value at which the rated capacity of the battery can be discharged in one hour.

(2) External destruction test: A battery with a diameter of 2.5 mm is penetrated in the thickness direction of the flat case to break the battery, and the behavior at that time is observed. Then, there was no change (only the nail penetrated), smoke and fire were evaluated.

Example 1 First, according to the composition shown in Tables 1 and 2 below, each component was treated with a kneader for 2 hours to prepare a positive electrode paint and a negative electrode paint. Further, according to the composition shown in Table 3 below, each component was mixed with stirring and dissolved to prepare an electrolyte paint.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

Next, a positive electrode paint was applied on a 20 μm-thick aluminum tab-equipped positive electrode current collector and a 20 μm-thick copper tab-equipped negative electrode current collector with a tab, and then dried by an extrusion die coater. Then, a porous film in which the active material was bound to one surface of the current collector by a binder was obtained. Next, after performing the consolidation treatment on each of the above porous membranes by a roll press (calender), the porous membranes were cut into a predetermined size to obtain a plate-shaped positive electrode and a plate-shaped negative electrode.

Next, an electrolyte paint is applied to the positive electrode and the negative electrode, and a separately prepared electrolyte paint impregnated polymer porous film is interposed therebetween, and the resultant is heated at 90 ° C. for 30 minutes to form an electrolyte. Fluidized. Then, a flat unit battery element having a positive electrode, a negative electrode, and a non-fluid electrolyte layer was obtained.

Next, the obtained 20 unit battery elements were alternately laminated in the order in which the negative electrode current collectors were the upper and lower outermost surfaces.
The unit battery elements thus stacked are referred to as "unit battery element 1", "unit battery element 2", "unit battery element 19", and "unit battery element 20" in this order from the bottom. On the lower surface of the unit battery element 1, a copper foil having a thickness of 20 μm was laminated. An aluminum foil having a thickness of 20 μm was laminated between the unit battery elements 1 and 2. On the upper surface of the unit battery element 20, a copper foil having a thickness of 20 μm was laminated. The thickness between the unit battery elements 19 and 20 is 2
An aluminum foil of 0 μm was laminated. Next, a terminal for extracting a current was connected to the laminate to obtain a battery element.

Thereafter, the above-mentioned assembly was housed in a flat case in which a laminate film composed of an aluminum layer and a synthetic resin layer disposed on both sides thereof was preformed, and vacuum-sealed to obtain a flat battery. . Then, outside the flat case, the terminal of the positive electrode and the aluminum layer in the laminate film were connected by a conductive wire.
Table 4 shows the evaluation and test results of the obtained batteries.

Comparative Example 1 A flat battery was obtained in the same manner as in Example 1, except that the lamination of the aluminum foil and the copper foil was omitted.
Table 4 shows the evaluation and test results of the obtained batteries.

Example 2 In Example 1, the unit battery elements were alternately stacked in the order in which the positive electrode was the upper and lower outermost surfaces. Two aluminum foils each having a thickness of 20 μm were laminated on the lower surface of the unit battery element 1. A copper foil having a thickness of 35 μm was laminated between the unit battery elements 1 and 2. 20 μm thick on the upper surface of the unit battery element 20
Were laminated. Unit battery element 19
A copper foil having a thickness of 35 μm was laminated between and. Otherwise, in the same manner as in Example 1, a flat battery was obtained.

Example 3 In Example 1, a 20 μm-thick aluminum tabbed positive electrode current collector was replaced with a 40 μm-thick aluminum tabbed positive electrode current collector, and a 20 μm-thick copper tabbed negative electrode current collector was used. It was changed to a 35 μm-thick copper tabbed negative electrode current collector. Lamination of aluminum foil and copper foil was omitted. Otherwise, in the same manner as in Example 1, a flat battery was obtained.

[0052]

[Table 4]

[0053]

According to the present invention described above, a battery having improved safety in an external destruction test or the like is provided without impairing the battery performance.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a main part of an example of a battery of the present invention.

FIG. 2 is a schematic explanatory view of a main part of another example of the battery of the present invention.

FIG. 3 is a schematic explanatory view of a main part of another example of the battery of the present invention.

FIG. 4 is an explanatory diagram of a tab structure of stacked battery elements.

FIG. 5 is an explanatory view of a terminal structure of battery elements stacked and housed in a flat case.

FIG. 6 is a diagram illustrating an example of the appearance of a battery.

[Explanation of symbols]

 1: positive electrode current collector 1a: thickened positive electrode current collector 2: positive electrode material layer 3: negative electrode current collector 3a: thickened negative electrode current collector 4: negative electrode material layer 5: electrolyte layer 6: electrode tab 7: electrode tab 10: Battery element 11: Metal foil 20: Extract terminal 30: Extract terminal 40: Flat case 41: Metal layer 42: Synthetic resin layer 60: Thin film member

Claims (9)

[Claims] 1. A battery in which unit cells having an electrode formed of a current collector and an electrode material layer and an electrolyte layer are stacked and housed in a case, current collection of an outermost electrode is performed. A battery, wherein the thickness of the body is greater than the thickness of at least one of the current collectors of the inner electrodes. 2. The method according to claim 1, wherein the thickness of the current collector of the outermost electrode and the innermost electrode is greater than the thickness of at least one of the current collectors of the innermost electrode. The battery according to claim 1. 3. The battery according to claim 1, wherein the thickness of the current collector of the outermost electrode is greater than the thickness of the current collector of any of the innermost electrodes. . 4. The method according to claim 1, wherein the thickness of the current collector of the outermost electrode and the current collector of the innermost electrode is larger than the thickness of the current collector of any of the electrodes located further inside. Item 3. The battery according to Item 2. 5. The battery according to claim 1, wherein the thickly formed current collector is formed by laminating a plurality of conductive foils. 6. The unit battery element, wherein the unit battery elements are stacked by being wound, and a terminal for taking out current to the outside of the case is connected to a thickly formed current collector portion. Item 6. The battery according to any one of Items 1 to 5. 7. A thick current collector having a thickness of 20 μm
The battery according to any one of claims 1 to 6, wherein: 8. The battery according to claim 1, wherein the electrolyte layer is formed from a non-flowable electrolyte. 9. The battery according to claim 1, wherein the unit battery element is a lithium secondary battery.