JP2002075455A - Lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary cell with excellent safety and volume efficiency, with a structure capable of reducing cost, enabled to obtain an optional voltage according to the number of lamination units. SOLUTION: A structure successively laminating an aluminum current collector 1a, a positive pole binder 1b, a polymer electrolyte layer 3, a negative pole binder layer 2b, and a copper current collector 2a, is formed as one lamination unit. For the cell, enclosing a plurality of the unit lamination units formed by making non-coated surfaces 1c, 2c of the current collectors of the positive pole 1 and negative pole 2 contact with each other inside an outer case, an optional cell voltage is obtained by laminating the lamination units, further, safety is improved and manufacturing cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery having a laminated structure, and more particularly to a battery capable of obtaining an arbitrary voltage depending on the number of units to be laminated.

[0002]

2. Description of the Related Art In recent years, small batteries as power sources for driving various electronic devices, and large batteries for electric vehicles or nighttime power storage have been actively developed from the viewpoint of environmental and energy problems. There is a strong demand for the realization of secondary batteries that are higher in voltage, higher in energy density and more economical.

As the most promising battery system satisfying these demands, a lithium-containing composite oxide such as a lithium-cobalt composite oxide or a lithium-manganese composite oxide is used for a positive electrode, and a carbon material capable of inserting and extracting lithium ions is used for a negative electrode. Cylindrical, oval and square lithium secondary batteries have already been put into practical use. However, since these lithium ion secondary batteries use a flammable solvent as an electrolyte, there is a problem in safety at the time of malfunction or abnormal use of equipment, and it is necessary to equip various safety protection circuits. In addition, since high voltage of several hundred volts is required for electric vehicle applications, a large number of cells are required, and material costs are increased because the cells are used as current collectors of assembled batteries connected in series or in parallel. There is a problem. In addition, in the case of an aggregate, there is a problem that the resistance of the battery becomes large, and the energy that can be taken out decreases. Further, in the case of a cylindrical shape, the volume efficiency is not good, which is disadvantageous for increasing the size.

On the other hand, a battery having a rectangular structure has a good volumetric efficiency and is suitable for a battery pack.
61775, JP-A-9-320636, JP-A-9-32
No. 0637 discloses a battery having a laminated structure in which electrode plates sandwiched between bag-like separators are sequentially laminated.
55 also proposes a battery having a plate-shaped laminated structure in which a plurality of electrode laminates are laminated.

[0005] However, although these batteries have improved volumetric efficiency as compared with the cylindrical type, there is a problem that the single cell voltage does not change and is not satisfactory for high voltage applications.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a battery which is excellent in safety and volumetric efficiency, can be manufactured at a low cost, and can obtain an arbitrary voltage depending on the number of lamination units. Is what you do.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, a first constitution of the present invention is to laminate a positive electrode current collector, a positive electrode mixture, a polymer electrolyte, a negative electrode mixture, and a negative electrode current collector in this order. Are stacked in a single outer case, and the uncoated surfaces of the positive electrode current collector and the negative electrode current collector are brought into contact with each other.

In a second aspect of the present invention, a metal foil comprising a clad plate is used as a current collector for a positive electrode and a negative electrode. The positive electrode current collector of the clad plate, the positive electrode mixture, the polymer electrolyte, and another clad plate The negative electrode mixture on the surface and the negative electrode current collector of the same clad plate were stacked in this order, and one unit was laminated in order and sealed in a single outer case. In this case, since a solid polymer electrolyte containing a lithium salt or a polymer electrolyte containing a lithium salt and an organic solvent is used as the electrolyte, the electrolyte itself has no fluidity, and each unit has no common electrolyte.
Even in a single outer case, they are independent, and an arbitrary battery voltage can be obtained by laminating a plurality of units in the above configuration.

With the above structure, the manufacturing process can be simplified, and despite the cell comprising one outer case,
Since a voltage in which several cells are connected in series can be obtained, the number of outer cases can be reduced, and as a result, cost can be reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing the structure of a power generating element which is an embodiment of the electrode for a lithium secondary battery of the present invention, in which a positive electrode mixture layer 1b applied to one surface of an aluminum current collector 1a of a positive electrode 1 and a negative electrode The polymer electrolyte layer 3 is sandwiched between the negative electrode mixture layers 2b applied to one surface of the second copper current collector 2a to form the power generation element 4.

FIG. 2 shows an aluminum laminate film pack comprising a plurality of laminates 5 in which the power generating elements of FIG. 1 are sequentially laminated with the uncoated surface 1c of the positive electrode current collector and the uncoated surface 2c of the negative electrode current collector. FIG. 3 is a schematic view of a battery inserted in FIG. 6
Is a positive electrode lead mounting terminal provided on the positive electrode of the multilayer body 5, to which an aluminum positive electrode lead 7 is welded. Reference numeral 8 denotes a negative electrode lead mounting terminal provided on the negative electrode of the multilayer body 5, to which a copper negative electrode lead 9 is welded. Reference numeral 10 denotes an outer case formed of a laminated film obtained by laminating an aluminum foil as an intermediate layer, a polypropylene film on the inner side thereof, and a polyethylene terephthalate film and a nylon film on the outer side. The multilayer body 5 accommodated in the outer case 10 is sealed in a state where the positive electrode lead 7 and the negative electrode lead 9 are led out of the outer case 10 and heat-sealed the opening of the outer case 10. It is sealed with clothes.

In the battery of this embodiment, since a plurality of power generating elements 4 connected in series and stacked are housed in a single exterior case 10, an arbitrary battery voltage corresponding to the number of the stacked power generating elements 4 is applied. Obtainable. Also, compared to the conventional case where batteries are connected in series, the number of cases, sealing plates, current collecting tabs and the like of the unit cells can be reduced, so that the number of steps and material cost can be significantly reduced.

FIG. 3 is a schematic view showing an electrode of a laminated structure using a clad plate as a current collector according to another embodiment of the lithium ion battery of the present invention. The positive electrode mixture layer 1b is provided on the surface of the aluminum foil 12 of the clad plate 11,
The negative electrode mixture layer 2b is applied to the surface of the first copper foil 13 to form a positive electrode and negative electrode clad plate. The polymer electrolyte layer 3 is sandwiched between the two sets of clad plates to form a power generating element 14.

FIG. 4 is a schematic sectional view of a plurality of laminated bodies in which the power generating elements of FIG. 3 are sequentially laminated. Both ends of the laminated body, that is, the positive end 15 and the negative end 16 may be clad plates, or may be one obtained by applying a positive electrode mixture and a negative electrode mixture to one surface of an aluminum foil or a copper foil, respectively. In the case of a clad plate, the positive electrode lead is taken from the copper foil portion 13 not coated with the negative electrode mixture, and the negative electrode lead is taken from the aluminum foil portion 12 not coated with the positive electrode mixture. When an aluminum foil current collector or a copper foil current collector is used at the end, the positive electrode lead 7 is the uncoated portion 1 of the aluminum foil shown in FIG.
From c, the negative electrode lead 9 is taken from the uncoated portion 2c of the copper foil. As the outer case 10, a laminated film pack shown in FIG. 2 or a cylindrical tube can be used.

The batteries stacked in the other embodiments have the same effects as described above, and the man-hour and cost can be significantly reduced because the cathode and the anode are connected by the clad plate.

In any of the embodiments, when the exterior body is made of metal, a terminal may be formed by exposing a part of the positive electrode or negative electrode current collector of the laminate with the metal and bringing the current collector into contact therewith. However, the present invention is not limited to the structure, components, and materials described in the above configuration.

The material of the positive electrode current collector is preferably aluminum foil, and the material of the negative electrode current collector is preferably copper or nickel metal foil. However, the present invention is not limited thereto, and a net may be used. .

The clad plate is not particularly limited, and various methods used for joining aluminum and dissimilar materials, such as a melting method and a pressure welding method, can be considered. The method is preferred.

The positive electrode mixture layer is made of a polymer containing a positive electrode active material, a conductive agent, a lithium salt or a non-aqueous electrolyte in which a lithium salt is dissolved. As the positive electrode active material, LiM
a lithium-containing composite oxide in which n ₂ O ₄ , LiCoO ₂ , LiNiO ₂ or a part of the transition metal in the formula is replaced by another transition metal such as Ni, Fe, Cr, Ti, V, or B, Al, A lithium-containing composite oxide represented by a compound substituted with a compound of a metal other than a transition metal such as P, Sn, or Si or a metalloid can be used, but is not particularly limited thereto. Carbon materials such as artificial graphite and acetylene black are used as the conductive agent. As the electrolyte,
A non-aqueous solvent and an electrolyte salt containing lithium used in a conventional battery are used. Specifically, cyclic esters such as ethylene carbonate, propylene carbonate, and vinylene carbonate, dimethyl carbonate,
One or more solvents selected from the group consisting of linear esters such as diethyl carbonate and ethyl methyl carbonate, and ethers such as 1,2-dimethoxyethane and 2-methyltetrahydrofuran are used. As the electrolyte salt, an inorganic salt such as LiPF ₆ and LiBF ₄ is used. As the polymer holding the electrolyte, for example, polyethylene oxide (hereinafter, referred to as PEO) is used as a matrix.

The negative electrode mixture layer is made of a polymer containing a negative electrode active material, a conductive agent, a lithium salt or a non-aqueous electrolyte in which a lithium salt is dissolved. Examples of the negative electrode active material include lithium metal, lithium alloys, oxides that occlude and release lithium, compounds such as nitrides, carbon materials, and the like.
Lithium alloys and the like are not preferred, and compounds such as oxides and nitrides, or carbon materials, and among them, carbon materials are most preferred. As the conductive agent, the electrolytic solution, and the polymer holding the electrolytic solution, those used for the positive electrode can be used.

As the polymer electrolyte, a solid polymer electrolyte containing only a lithium salt or a gel electrolyte containing an electrolyte is used. As a material of the polymer electrolyte, a matrix of a composite such as PEO, polypropylene oxide (hereinafter, referred to as PPO), polyacrylonitrile, polyvinylpyrrolidone, polyvinyl chloride, polyvinylidene fluoride, or a crosslinked isocyanate thereof, or a low molecular weight PEO Polymer electrolytes in which an ion dissociating group such as PPO and PPO is grafted to the polymer main chain, and polymers such as phenin oxide and phenin sulfide polymers can be used.

As the outer case, a composite in which a heat-fusible resin is laminated on a metal or a metal can is used. Aluminum is used for the exterior metal of the laminate composite,
Metals such as iron, copper, nickel and titanium, and alloys such as stainless steel and aluminum alloys can be used. As the heat-fusible resin of the laminate composite, a polymer film such as polyethylene, polypropylene, or polyvinyl chloride can be used.
Aluminum, iron, stainless steel and the like can be used as the metal can.

[0023]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited by these Examples.

Example 1 First, lithium hexafluorophosphate was dissolved in a mixed solvent of polyethylene oxide and ethylene carbonate and propylene carbonate at a volume ratio of 1: 1 to contain an electrolyte having a concentration of 1.5 M. Thus, a polymer gel electrolyte was prepared. A powder of lithium manganese composite oxide (LiMn ₂ O ₄ ) and acetylene black as carbon black were added thereto in a weight ratio of 10: 80: 1.
The mixture was mixed at a ratio of 0 to prepare a positive electrode mixture paste, which was applied to one surface of an aluminum foil having a thickness of 20 μm and dried to prepare a positive electrode sheet.

Next, the above-mentioned polymer gel electrolyte and artificial graphite were mixed at a weight ratio of 22:78 to prepare a negative electrode mixture paste, which was applied to one surface of a copper foil having a thickness of 18 μm.
It dried and the negative electrode sheet was produced.

Subsequently, for the polymer gel electrolyte,
A film was formed by coating, and left to dry at room temperature to prepare a sheet-like polymer electrolyte layer.

Next, a 15 cm square sheet piece was taken out from the sheet-shaped positive electrode, sheet-shaped negative electrode, and sheet-shaped gel polymer electrolyte layer. A power generation element was manufactured by laminating a polymer electrolyte layer sheet piece between the positive electrode sheet piece and the negative electrode sheet piece. Two of these power generating elements were stacked in series to form a two-layered laminated body, and current collecting leads were attached by spot welding to the respective ends of the positive electrode and the negative electrode of the laminated body. Further, the respective power generating elements were electrically connected by caulking.

Then, the laminate is inserted into a bag-shaped aluminum laminate film, and the terminals are respectively led out to the outside from the positive electrode and the negative electrode. Obtained.

This battery was charged and discharged with a current density of 0.5 mA / c.
m ² , charge end voltage 8.6 V, discharge end voltage 6.0
And discharged for 10 cycles. The average voltage at the 10th cycle was 7.6 V, and the positive electrode capacity density was 110 mAh /
g was obtained.

(Example 2) A clad plate piece of 0.05 mm thick aluminum and 0.05 mm thick copper joined by a cold pressure welding method was cut out into a disk shape having a diameter of 15 mm. It was a conductor.

First, the positive electrode mixture of Example 1 was applied to the aluminum surface of the clad plate piece, and the negative electrode mixture was applied to the copper surface.
A clad bipolar plate electrode having a mixture layer having different polarities on both sides was produced. Next, the positive electrode mixture of Example 1 was applied only to the aluminum foil surface of the clad plate to prepare a clad positive electrode plate in which the copper surface opposite to the coated surface was exposed. Conversely, the negative electrode mixture of Example 1 was applied only to the copper foil surface of the clad plate, thereby producing a clad negative electrode plate having the aluminum surface opposite to the coated surface exposed.

Subsequently, the sheet-shaped polymer electrolyte is applied between the clad cathode plate and the first clad bipolar plate, between the first and second clad bipolar plates, and between the second clad bipolar plate and the clad anode plate. This was inserted into a three-layer structure laminate. A positive electrode sealing plate made of aluminum is attached to the copper surface of the clad positive electrode plate of this laminate, and a negative electrode sealing plate made of copper is attached to the aluminum surface of the negative electrode clad plate. Was inserted into a stainless steel cylinder, and the opening was sealed to obtain a cylindrical battery. In the present embodiment, aluminum and copper used in a non-aqueous electrolyte secondary battery are usually used as a material of the positive electrode sealing plate and the negative electrode sealing plate. In this case, since neither of them is in contact with the electrolyte, It is not limited to aluminum and copper, and various metals such as nickel, iron, titanium, stainless steel and the like can be used, and they do not need to be metals as long as they have conductivity. This battery was charged and discharged at a current density of 0.1.
5 mA / cm ² , discharging to a charging end voltage of 12.9 V and a discharging end voltage of 9.0 V, and performing this for 10 cycles,
Average voltage is 11.4 V, positive electrode capacity density 110 mAh / g
I got

Example 3 Between the sheet-shaped positive electrode of Example 1 and the first clad bipolar plate of Example 2, between the first, second and third clad bipolar plates, and between the third clad bipolar plate and Example 1 The sheet-like polymer electrolyte was inserted between the sheet-like negative electrodes to obtain a four-layer laminate. The current collecting terminals of the positive electrode and the negative electrode were attached in the same manner as in Example 1, inserted into an aluminum laminated film pack, and sealed to obtain a battery having a four-layer laminated structure.

When the charge / discharge current density of this battery was set to 0.5 mA / cm ² , the charge end voltage was 17.2.
V, the battery was discharged to a discharge end voltage of 12 V, and this was repeated for 10 cycles to obtain an average voltage of 15.2 V.

Example 4 15 μm thick negative electrode current collector
A laminated battery having a five-layer structure was obtained in the same manner as in Example 1 except that a nickel foil of m was used.

When the charge / discharge current density of this battery was set to 0.5 mA / cm ² , the charge end voltage was 21.5.
V, when the battery was discharged to a discharge end voltage of 15 V, an average voltage of 19.0 V was obtained.

In the first, third and fourth embodiments, an aluminum laminate film was used as the outer case. However, the same characteristics as those of the first embodiment can be obtained by using a laminate film of another metal.

Although the stainless steel can was used in the second embodiment, the same characteristics as those of the above embodiment can be obtained by using another metal can.

In the second embodiment, aluminum and copper, which are usually used in a non-aqueous electrolyte secondary battery, are used as the material of the positive electrode sealing plate and the negative electrode sealing plate, respectively.
Since none of them are in contact with the electrolyte, they are not particularly limited to aluminum and copper, and various metals such as nickel, iron, titanium, and stainless steel can be used. You may.

[0040]

As described above, the positive electrode current collector, the positive electrode mixture,
A multi-unit laminate in which the non-coated surface of the positive electrode current collector and the non-coated surface of the negative electrode current collector are brought into contact with each other as one unit in which a laminate of the polymer electrolyte, the negative electrode mixture, and the negative electrode current collector A battery enclosed in an outer case, or a metal foil made of a clad plate as a current collector using a positive electrode active material on one surface thereof,
A battery in which a plurality of unit laminates in which a negative electrode active material is coated on the other surface and one unit is interposed with a polymer electrolyte interposed therebetween is sealed in a single outer case. Obtainable. Further, since the process can be simplified, the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a power generating element according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the multi-layer structure battery.

FIG. 3 is a schematic cross-sectional view of a power generating element according to another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of the multi-layer structure battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Aluminum current collector 1b Positive electrode mixture layer 1c Positive electrode collector uncoated surface 2 Negative electrode 2a Copper current collector 2b Negative electrode mixture layer 2c Negative electrode current collector uncoated surface 3 Polymer electrolyte layer 4,14 Power generation element 5 Plural laminates 6 Positive electrode lead terminal 7 Positive electrode lead 8 Negative electrode lead terminal 9 Negative electrode lead 10 Outer case 11 Cladding plate 12 Aluminum foil 13 Copper foil 15 Positive end 16 Negative end

Continuation of front page (72) Inventor Akikatsu Morita 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. AM04 AM05 AM07 AM16 BJ06 BJ12 DJ02 DJ07 EJ01 5H050 AA19 BA17 CA07 CA08 CA09 CB01 CB02 CB07 CB08 CB12 DA06 DA07 DA08 FA02 FA03

Claims (7)

[Claims] 1. An uncoated surface of a positive electrode current collector and an uncoated surface of a negative electrode current collector, in which a unit in which a positive electrode current collector, a positive electrode mixture, a polymer electrolyte, a negative electrode mixture, and a negative electrode current collector are sequentially laminated is defined as one unit. A plurality of units are sequentially laminated by bringing the surfaces into contact with each other, and the plurality of unit laminates are sealed in a single outer case so that an arbitrary battery voltage corresponding to the number of the plurality of unit laminates can be obtained. Next battery. 2. A metal foil comprising a clad plate is used as a current collector for a positive electrode and a negative electrode, and a positive electrode current collector, a positive electrode mixture, a polymer electrolyte, and a negative electrode mixture on another clad plate surface of the clad plate are used. By enclosing a multi-unit laminate in which a negative electrode current collector of a clad plate is laminated as one unit with a polymer electrolyte interposed in a single outer case, an arbitrary battery voltage corresponding to the number of the plurality of unit laminations can be obtained. Lithium secondary battery. 3. The cathode active material is LiMn ₂ O ₄ or LiCoO.
_2, LiNiO ₂ or lithium secondary battery according to claim 1 or 2, a portion of the transition metal in the formula is a lithium-containing composite oxide represented by those substituted with other metals. 4. The lithium secondary battery according to claim 1, wherein the negative electrode active material is a carbon material capable of inserting and extracting lithium. 5. The lithium secondary battery according to claim 1, wherein the outer case is made of a metal or a metal laminated resin. 6. The lithium secondary battery according to claim 1, wherein the aluminum, copper or nickel current collector is a metal foil. 7. The lithium secondary battery according to claim 1, wherein the positive electrode mixture, the negative electrode mixture, and the polymer electrolyte contain a lithium salt or a polymer material containing a lithium salt and an organic solvent.