JP2000100471A - Sheet battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent self-discharging between a positive electrode active material layer and a negative electrode active material layer by providing a bipolar electrode unit having the positive electrode active material layer on a current collector layer for a positive electrode of a composite current collector and having the negative electrode active material layer on a current collector layer for a negative electrode and a solid electrolyte. SOLUTION: In a composite current collector P having one surface being a current collector layer for the positive electrode and the other surface being a current collector layer for the negative electrode, a positive electrode active material layer CP1 is arranged on the current collector layer for the positive electrode, and a negative electrode active material layer AP1 is arranged on the current collector layer for the negative electrode to constitute a bipolar electrode unit BU. In respective sets of two sets by connecting, for example, this bipolar electrode unit BU in series by two units, a solid electrolyte ES is interposed between the two bipolar electrode units BU. A positive electrode terminal CT of a battery is positioned between two positive electrode active material layers CP1 existing on both sides so that the surface for dividing the positive electrode terminal CT into two parts along an X-X line at a right angle to a space becomes the reference surface of the mirror image relationship.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sheet battery such as a lithium secondary sheet battery.

[0002]

2. Description of the Related Art A lithium secondary battery having a large discharge capacity has been spotlighted as a battery for electronic equipment such as a portable telephone and a personal computer. Conventionally, as such a lithium secondary battery, a three-dimensional battery such as a columnar or box-shaped battery has been mainly used, but recently, attention has been paid to a lithium secondary sheet battery in view of a space factor and a light weight.

In a conventional lithium secondary sheet battery, a sheet-like power generating element having a structure in which a negative electrode sheet and a positive electrode sheet are stacked with a separator interposed therebetween is accommodated in a bag made of a suitable waterproof sheet. It has a structure filled with electrolyte and sealed. The liquid electrolyte functions in a state where the separator is impregnated, as in the case of the three-dimensional battery.

The advantage of a lithium secondary sheet battery is that, unlike a three-dimensional battery, it is thin, and because of its good heat dissipation, the degree of heat trapped in the battery is low. Even if a current flows or a penetrating scratch is caused by a nail or the like, an explosion accident due to burning of lithium inside the battery is unlikely to occur, which is extremely safe.

In order to increase the capacity of not only lithium secondary sheet batteries but also sheet batteries, a plurality of combinations (hereinafter, unit cells) of a pair of a negative electrode sheet and a positive electrode sheet are connected in series, and those connected in series are connected in parallel. To increase the effective reaction area. At that time, in view of the problem that the connection resistance between the unit cells increases, Japanese Patent Application Laid-Open No. H8-7926 adopts a bipolar electrode unit as the unit cell,
In addition, proposals have been made to use a liquid electrolyte as an electrolyte.

As shown in FIG. 3 (indicated by reference numeral BU), the bipolar electrode unit has a positive electrode current collector layer CP on one side and a negative electrode current collector layer AP on the other side.
The composite current collector P has a structure in which the positive electrode active material layer CP1 is provided on the positive electrode current collector layer CP, and the negative electrode active material layer AP1 is provided on the negative electrode current collector layer AP. FIG. 4 shows an example of a sectional view of a sheet battery using one bipolar electrode unit BU having such a structure.
A cross-sectional view of a sheet battery in which a negative electrode sheet AS is stacked with a separator U interposed therebetween with a separator S interposed therebetween, while a positive electrode sheet CS is stacked with a separator S interposed therebetween under U.
LE is a liquid electrolyte.

When the bipolar electrode unit BU is used, the positive electrode active material layer CP1 and the negative electrode active material layer A
Since the liquid electrolyte LE, which is a conductive material, is in communication between P1 and each tip, there is a problem that self-discharge occurs between the two tips as shown by the arrow Y. FIG. 5 is a cross-sectional view of a battery that can prevent such self-discharge, and shows a portion between the current collector layer AS1 of the negative electrode sheet AS and the positive electrode current collector layer CP of the bipolar electrode unit BU, and a diagram of the positive electrode sheet CS. An electric insulator EI is provided between the current collector layer CS1 and the negative electrode current collector layer AP of the bipolar electrode unit BU to interrupt communication of the liquid electrolyte and prevent self-discharge.

However, if the interruption of the communication of the liquid electrolyte by the electric insulator EI is insufficient, self-discharge cannot be prevented, so that the interruption must be surely performed. In many applications of the sheet battery, a large number of bipolar electrode units BU are often stacked, and an electrical insulator EI is required for each stack. Therefore, the installation of the electric insulator EI has a problem of increasing the number of manufacturing steps of the sheet battery, but also complicates the structure of the battery, increases the thickness of the battery, reduces the area of the positive and negative active material layers, And other problems.

[0009]

SUMMARY OF THE INVENTION In view of the above, the present invention provides
It is an object to provide a sheet battery in which self-discharge between a positive electrode active material layer and a negative electrode active material layer of a bipolar electrode unit is prevented.

[0010]

The above object can be solved by the following sheet battery. (1) having a positive electrode active material layer on the positive electrode current collector layer of a composite current collector in which one surface is a positive electrode current collector layer and the other surface is a negative electrode current collector layer; A sheet battery comprising: a bipolar electrode unit having a negative electrode active material layer on a current collector layer for use; and a solid electrolyte. (2) The composite current collector is formed by plating one side of a metal foil serving as a current collector layer of one pole with a metal serving as a current collector layer of the other pole and forming the same (1). A sheet battery as described. (3) The composite current collector is formed by rolling a clad material of a metal to be a current collector layer for a negative electrode and a metal to be a current collector layer for a positive electrode, (1) or (2). A sheet battery as described. (4) The sheet battery according to any one of the above (1) to (3), wherein the positive electrode current collector layer is an aluminum layer, and the negative electrode current collector layer is a copper layer. (5) a first set having one or a plurality of serially connected bipolar electrode units and a second set having one or a plurality of serially connected bipolar electrode units are connected in parallel; Set the discharge capacity of the first set to 10
The sheet battery according to any one of (1) to (4), wherein the discharge capacity of the second set is within a range of 100 ± 10 when 0 is set. (6) The sheet battery according to any one of the above (1) to (5), which is a lithium secondary battery.

[0011]

The solid electrolyte, unlike the liquid electrolyte, is basically provided only between the surfaces where the positive electrode active material layer and the negative electrode active material layer directly face each other. Alternatively, the solid electrolyte may exceed both ends between the surfaces, but the solid electrolyte does not reach the vicinity indicated by the arrow Y in FIG. 4 described above, and a vacuum or a gas usually exists in the vicinity. Therefore, in the present invention, since the front ends of the positive electrode active material layer CP1 and the negative electrode active material layer AP1 (see FIG. 3) of the bipolar electrode unit BU are electrically insulated by vacuum or gas, the space between the two layers is maintained. Self-discharge is prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The bipolar electrode unit used in the present invention may be basically the same as the conventional structure shown in FIG. 3 described above. Continued with FIG.
The constituent material of each part of the bipolar electrode unit BU may be a conventionally known material. Therefore, in the following, some examples of well-known materials of each layer will be given taking the case of a lithium secondary sheet battery as an example.

Examples of the material of the positive electrode current collector layer CP include conductive metals such as aluminum, aluminum alloy, and titanium. Of these, aluminum is particularly preferred. On the other hand, examples of the material of the negative electrode current collector layer AP include conductive metals such as copper, nickel, silver, and SUS. Above all,
Copper is particularly preferred. The thickness of each of the positive electrode current collector layer CP and the negative electrode current collector layer AP in the composite current collector P may be as usual, and both layers are, for example, about 1 to 100 μm.

In the composite current collector P, the positive electrode current collector layer CP and the negative electrode current collector layer AP are directly connected to each other or via an intermediate layer (not shown in FIG. 3) made of a third material. And are electrically conductive. The purpose of employing the bipolar electrode unit is to reduce the increase in connection resistance between the conventional unit cells as described above, but also to reduce the thickness of the entire sheet battery. In the latter case, it is preferable to directly join the positive electrode current collector layer CP and the negative electrode current collector layer AP by removing the above-mentioned intermediate layer. Further, in order to further improve the electrical continuity between the positive electrode current collector layer CP and the negative electrode current collector layer AP, it is preferable that both layers are metal-bonded rather than simply being in close physical contact. . The composite current collector P in which both layers are metal-bonded is formed by, for example, electroplating or soaking plating on one surface of a metal foil to be a current collector layer of one electrode and a metal to be a current collector layer of the other electrode. And a method of rolling a clad material of a metal serving as a current collector layer for a negative electrode and a metal serving as a current collector layer for a positive electrode, and the like.

When a composite current collector P in which the positive electrode current collector layer CP is aluminum and the negative electrode current collector layer AP is copper is produced by a plating method, copper is coated on one side of an aluminum foil in a usual manner. When electroplating by this method, a thin copper layer of about 2 μm can be easily formed.

[0016] As the positive electrode active material, Li · Co-based composite oxides such as LiCoO _2, such as LiNiO ₂ Li · N
Examples thereof include i-based composite oxides and Li / Mn-based composite oxides such as LiMn ₂ O ₄ . Polytetrafluoroethylene, polyvinylidene fluoride, as a binder for the positive electrode active material,
Examples include polyethylene and ethylene-propylene-diene-based polymers, and examples of the conductive agent include various conductive graphites and conductive carbon blacks. The amount of the positive electrode active material used is about 80 to 95 parts by weight per 100 parts by weight of the total amount of the positive electrode active material, the binder, and the conductive agent, and the amount of the binder used is 1 to 100 parts by weight of the positive electrode active material. About 10 parts by weight, and the amount of conductive agent used is
It is about 3 to 15 parts by weight per 0 parts by weight. The positive electrode active material layer CP1 can be formed by applying a mixed composition including a positive electrode active material, a binder, and a conductive agent on the positive electrode current collector layer CP, drying the resultant sufficiently, and then rolling. , Its thickness is 2
It is about 0 to 500 μm, especially about 50 to 200 μm.

Examples of the negative electrode active material include various natural graphites and artificial graphites, for example, graphites such as fibrous graphite, flaky graphite and spherical graphite, and various lithium alloys. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, ethylene-propylene-diene-based polymer, and the like. The amount of the negative electrode active material used is the total amount of the negative electrode active material and the binder. It is about 80 to 96 parts by weight per 100 parts by weight. Negative electrode active material layer A
P1 can be formed by applying a mixed composition composed of a negative electrode active material and a binder on the negative electrode current collector layer AP, drying it sufficiently, and rolling it. It is about 500 μm, especially about 50 to 200 μm.

In the example of the solid electrolyte, Li_ThreeN, Li_TwoO
-B_TwoO_Three-SiO_TwoSystem, B_TwoS_Three−Li_TwoS-LiI
System, P_TwoS_Five−Li_TwoS-LiI system, GeS_Two−Li_Two
S-LiI system, SiS_Two−Li_TwoNo S-LiI system
The solid electrolyte is exemplified. In another example of a solid electrolyte,
LiI, LiClO_Four, LiCF_ThreeSO_Three, LiBF _Four
There is a mixture of such lithium compounds and organic polymers,
For example, ethylene carbonate and propylene carbonate
And polyacrylonitrile and poly-tetraethyleneglyco
-Di-acrylate and LiClO_FourMixture with
Lopylene carbonate, polyacrylonitrile and LiC
10_FourMixtures with ethylene carbonate and propylene
Carbonate, polyacrylonitrile and poly-tetraet
Tylene glycol diacrylate and LiBF_FourWith
Mixture, propylene carbonate and polyacrylonitrile
And LiCF_ThreeSO_ThreeAnd the like.

A sheet battery generally comprises a sheet-like power generating element. In a lithium secondary sheet battery which does not like contact with moisture, the sheet-like power generating element is accommodated in a bag made of a waterproof film. . The sheet battery of the present invention is no exception. However, the sheet-like power generating element has the above-mentioned bipolar electrode unit as a power generating element unit, and is mainly used with a sheet-like solid electrolyte. The power generating element used in the present invention may be composed of only bipolar electrode units, and the number of bipolar electrode units may be one or more. Further, the power generating element includes a bipolar electrode unit and a normal positive electrode sheet (having a positive electrode active material layer on only one side or both sides of a positive electrode current collector) and / or a negative electrode sheet (only one side or both sides of a negative electrode current collector). (Having a negative electrode active material layer).

FIG. 1 conceptually shows various connection examples of a power generating element unit forming a power generating element in the present invention. FIG.
, The short solid line represents the negative electrode active material layer AP1, the long middle solid line represents the positive electrode active material layer CP1, the two dotted lines represent the composite current collector P, and the one dotted line represents the ordinary current collector. , Respectively. Therefore, a set of a short thick solid line, two dotted lines and a long middle solid line represents one bipolar electrode unit BU, and a set of a short thick solid line and one dotted line represents a normal negative electrode sheet AS.
And a set of a long solid line and a single dotted line means an ordinary positive electrode sheet CS. Further, in FIG. 1, a thin solid line indicates the state of electrical connection, CT indicates the positive terminal of the battery, and AT indicates the negative terminal of the battery. In FIG. 1, the illustration of the solid electrolyte layer is all omitted, but the positive electrode active material layer CP1 and the negative electrode active material layer AP1 do not directly contact each other, and the solid electrolyte layer always intervenes between them. ing.

In FIG. 1A, the positive electrode sheet CS, one bipolar electrode unit BU, and the negative electrode sheet AS are connected in series from the top of the figure, and the current collector of the positive electrode sheet CS is The current collector of the negative electrode sheet AS is connected to the positive electrode terminal CT, and the current collector of the negative electrode sheet AS is connected to the negative electrode terminal AT of the battery.

In FIG. 1B, five bipolar electrode units BU are connected in series. In FIG. 1B, the negative electrode active material layer AP1 of the uppermost bipolar electrode unit BU is shown.
Is connected to the negative electrode terminal AT, while the positive electrode active material layer CP1 of the lowermost bipolar electrode unit BU is connected to the positive electrode terminal CT.

In FIG. 1C, a first pair G1 and G2 in which two bipolar electrode units BU are connected in series is shown.
Of two bipolar electrode units BU connected in series
The two sets (the number of bipolar electrode units: a total of four) with the second set G2 are connected in parallel so as to be in a mirror image relationship with each other at the XX line (hereinafter referred to as a reference line or reference plane) in FIG. Each positive electrode active material layer CP1 of the two bipolar electrode units BU closest to the reference line is connected to the positive terminal CT,
Each of the negative electrode active material layers AP1 of the two bipolar electrode units BU located far from the reference line is connected to the negative electrode terminal AT.

FIG. 2 is a cross-sectional view of the embodiment of the sheet battery of the present invention corresponding to FIG. 1C, and the reference numerals of the respective parts in FIG. 2 correspond to the corresponding parts in FIG. To match that of. In each of the two sets of two bipolar electrode units BU connected in series, a solid electrolyte sheet ES is interposed between the two bipolar electrode units BU. The positive electrode terminal CT is located between the two positive electrode active material layers CP1 existing on both sides of the positive electrode terminal CT, and a plane that divides the positive electrode terminal CT into two along the XX line perpendicular to the paper surface is a mirror image reference plane. . That is, 2
Two sets of two bipolar electrode units BU connected in series are located in a mirror image relationship with respect to the reference plane.

Each bipolar electrode unit produced in the factory has its own positive electrode active material layer CP when the production lot is different.
1 and the composition of the negative electrode active material layer AP1, the thickness of each part, the amount of the active material, the density of the active material, and the like, may be varied.
Such variations cause variations in the discharge capacity and discharge life of the bipolar electrode unit. Such variations are generally small within the same manufacturing lot, but may be large in some cases.

In any case, one or a plurality of serially connected bipolar electrode units having a large variation
When the two sets are connected in parallel as a set, the charge / discharge cycle characteristics of the battery may deteriorate due to the difference in the discharge capacity between the two sets. To reduce this decrease, the difference in discharge capacity between the two sets may be reduced as much as possible. Specifically, the above 2
When the discharge capacity of the first set in the set is 100,
The discharge capacity of the second set is in the range of 100 ± 10, especially 1
Within the range of 00 ± 5. When comparing the discharge capacity of the first set with that of the second set, a charge-discharge cycle in which the battery was charged to 4.2 V at room temperature and then discharged until the battery voltage dropped to 2.75 V was performed. It is better to compare the discharge capacities measured in the first charge / discharge cycle. If the first set of discharge capacities measured by this method is, for example, 1000 mA · H per gram of the positive electrode active material, the corresponding discharge capacity of the second set is 900 to 1 / g of the positive electrode active material.
What is necessary is just to select and use the bipolar electrode unit BU with uniform performance so as to be within the range of 100 mA · H. If bipolar electrode units BU in the same production lot are used, the above conditions can often be satisfied.

The method of connecting the two sets in parallel, the positions of the individual bipolar electrode units, the positive electrode terminal, the negative electrode terminal, and the like may be arbitrary. The two sets are, as shown in FIG. When they are positioned so as to have a mirror image relationship with each other with respect to the surface, it is more effective in reducing deterioration of the charge / discharge cycle characteristics of the battery. The mirror image relationship here is a mirror image relationship in a strict sense (one-to-one symmetry of each part)
It is not always necessary to arrange the same number of bipolar electrode units having the same or substantially similar performance, shape, dimensions, etc. on both sides of the reference surface, and each bipolar electrode unit corresponding to the reference surface is substantially a mirror image. It only has to exist at the relevant position or in the vicinity thereof.

[0028]

Even if a bipolar electrode unit is used,
Since there is no problem of self-discharge between the positive electrode active material layer and the negative electrode active material layer seen in a conventional sheet battery using a liquid electrolyte, it is necessary to provide the electric insulator EI as shown in FIG. The structure and manufacturing method of the sheet battery are simplified, and the area of the positive and negative active material layers can be increased, so that the battery capacity is increased, and the safety of the battery is also improved.
And so on.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a connection example of a power generating element unit forming a power generating element in the present invention.

FIG. 2 is a cross-sectional view of the embodiment of the sheet battery of the present invention corresponding to FIG. 1C.

FIG. 3 is a cross-sectional view of a general bipolar electrode unit used in the related art or the present invention.

FIG. 4 is a cross-sectional view of a conventional sheet battery using a bipolar electrode unit.

FIG. 5 is a cross-sectional view of another conventional sheet battery using a bipolar electrode unit.

[Explanation of symbols]

 AP1 Negative active material layer CP1 Positive active material layer P Composite current collector BU Bipolar electrode unit CT Positive terminal of battery AT Negative terminal of battery ES Solid electrolyte

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference)

Claims (6)

[Claims] 1. A composite current collector in which one surface is a positive electrode current collector layer and the other surface is a negative electrode current collector layer has a positive electrode active material layer on the positive electrode current collector layer. A sheet battery comprising: a bipolar electrode unit having a negative electrode active material layer on a negative electrode current collector layer; and a solid electrolyte. 2. The composite current collector is formed by plating one surface of a metal foil serving as a current collector layer of one electrode with a metal serving as a current collector layer of the other electrode. 2. The sheet battery according to 1. 3. The composite current collector is formed by rolling a metal clad material of a negative electrode current collector layer and a metal of a positive electrode current collector layer. Sheet battery. 4. The sheet battery according to claim 1, wherein the positive electrode current collector layer is an aluminum layer, and the negative electrode current collector layer is a copper layer. 5. A first set having one or a plurality of serially connected bipolar electrode units and a second set having one or a plurality of serially connected bipolar electrode units are connected in parallel. When the discharge capacity of the first set is 100, the discharge capacity of the second set is 10
The sheet battery according to any one of claims 1 to 4, which is within a range of 0 ± 10. 6. The sheet battery according to claim 1, which is a lithium secondary battery.