JP2010040466A - Laminated nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated nonaqueous electrolyte secondary battery which is hardly deformed with cycle characteristics improved. <P>SOLUTION: This battery has pass structure as a diffusion route of an electrolyte in a porous sheet 5 disposed outside power generating elements and the projecting parts 1 of a separator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a laminated laminate non-aqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are widely used as power sources for small devices, and greatly contribute to the development of today's mobile devices. In addition to small-sized portable electronic devices in recent years, due to consideration for environmental issues and increased awareness of energy savings, applications that require high capacity and high lifespan characteristics and reliability such as electric vehicles and power storage are required. Demand is growing.

  As the life characteristics of the battery, it is particularly required that the deterioration of the discharge capacity due to repeated charge / discharge is small. Such a cycle characteristic is considered to be sufficient if a capacity of about 60 to 70% of the initial capacity is maintained after 500 cycles, for example, in a conventional small electronic device application. However, it is considered that the above-described lithium ion secondary battery for applications such as electric vehicles and power storage needs high life characteristics at several thousand cycles or more.

  On the other hand, in a lithium ion secondary battery, the non-aqueous electrolyte is decomposed inside the electrode due to repeated charge and discharge, resulting in insufficient electrolyte, resulting in characteristics such as increased battery resistance and capacity degradation. It has been pointed out. This phenomenon is called liquid withering. As a result of volume expansion of the electrode active material layer due to charge and discharge, and electrolyte solution undergoing reductive decomposition or oxidative decomposition at the negative electrode or the positive electrode, the electrolyte solution becomes insufficient and the separator and electrode A region where the electrolyte solution is not sufficiently filled is formed inside the material layer. In such a region, the diffusion of lithium ions is hindered, so that the resistance increases, and lithium ions cannot be smoothly inserted into and extracted from the active material, causing capacity deterioration. In particular, for lithium ion secondary batteries that require a long life, it is important to suppress such deterioration of characteristics due to liquid drainage.

  As a method for suppressing the influence of the liquid withering, for example, a method in which a sufficient amount of the electrolytic solution is accommodated in the cell in advance so as not to cause deterioration of characteristics due to shortage of the electrolytic solution is conceivable.

  The electrolyte in the battery is present in the void portion of the power generation element body composed of the positive electrode, the negative electrode, and the separator, and in the dead space between the exterior body and the power generation element.

  In a cylindrical or prismatic battery, even if there is a large amount of electrolyte in the dead space, the battery can hardly be deformed because a metal can that is hard and difficult to deform is used as the exterior body.

  On the other hand, in recent years, in the case of a laminated structure in which a plurality of positive electrodes and negative electrodes are laminated via a separator and the respective negative electrode current collectors and positive electrode current collectors are connected to each other, the outer body generally has a mass higher than that of a metal can. A laminated film in which a metal foil layer such as light aluminum and a resin layer are joined is used. Since the laminate film has lower strength than a metal can, when a large amount of electrolyte is injected, the laminate film is easily deformed as a battery by the electrolyte in the dead space.

  As described above, in a battery using a laminate film, it is necessary to take appropriate measures to prevent deformation even when a large amount of electrolyte is injected in order to prevent liquid drainage, and a power generation element composed of a positive electrode, a negative electrode, and a separator. In addition to the above, it is possible to use a structure including an electrolyte solution holding member.

  Patent Document 1 describes that a tape that swells and absorbs an electrolytic solution is fixed to the outermost periphery of a power generation element to improve leakage resistance and improve cycle characteristics.

JP 2003-151634 A

  When the above-described means is used as a method for absorbing the electrolytic solution, the process of fixing the tape to the power generation element has difficulty in manufacturability such as sticking of the tape, and the tape on the outermost periphery and the inside of the power generation element The reliability of the path structure as the electrolyte diffusion path is low, and it may not be efficient to supply the electrolyte from the tape part that holds the liquid inside the power generation element where the electrolyte was consumed in the cycle test. .

  In order to solve this problem, the laminated liquid non-aqueous electrolyte secondary battery can be manufactured while reliably connecting the liquid retaining part of the electrolytic solution and the separator, and improving the reliability of the path structure as a diffusion path of the electrolytic solution. It is necessary to make it difficult to deform.

  That is, the technical problem of the present invention is to provide a laminated laminated non-aqueous electrolyte secondary battery that has improved cycle characteristics and is difficult to deform.

  The laminated laminated nonaqueous electrolyte secondary battery of the present invention is a laminated laminated nonaqueous electrolyte secondary battery in which a positive electrode and a negative electrode are laminated via a separator, and a laminate having a porous sheet as an outermost layer is packaged with a laminated film. The separator has a convex portion, and the convex portion of the separator is in contact with the porous sheet.

  The laminated laminate nonaqueous electrolyte secondary battery of the present invention is characterized in that the convex portions of the separator do not overlap on the side surface of the laminated body.

  According to the present invention, by providing a path structure with the convex portions of the separator and the porous sheet, cycle characteristics are improved, and a laminated laminated nonaqueous electrolyte secondary battery that is difficult to deform is obtained.

  A laminated laminate nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described below.

(Battery configuration in the present invention)
FIG. 3 is a diagram of a separator showing an example of an embodiment of the present invention. The separator convex part 1 is a part other than the electrode insulating part 2 of the separator which is a quadrangle of the same size as the negative electrode in the separator.

  FIG. 1 is a plan perspective view of a laminated laminated nonaqueous electrolyte secondary battery according to Example 1 of the present invention. A positive electrode active material layer containing a positive electrode current collector 6 and a positive electrode active material capable of occluding and releasing lithium ions, and a negative electrode current collector 4 and a negative electrode active material layer containing a negative electrode active material capable of occluding and releasing lithium ions However, the power generation element body which is laminated so as to face each other through the separator having the separator convex portion 1 and the electrode insulating portion of the separator, and the porous sheet 5 are laminated outside thereof.

  The aluminum tab 7 is welded to the positive electrode current collector 6 and the nickel tab 9 is welded to the negative electrode current collector 4, and the tab, the current collector, and the current collector are integrated so as to be electrically connected. The convex portions 1 of the folded separators are fixed to the porous sheet 5 with a tape 8. The power generation element body and the electrolytic solution are housed in an aluminum laminate film folded in two, and the outer peripheral three sides are heat welded to form the heat welded portion 10, thereby producing a laminated laminate battery.

  The porous sheet and the folded convex portion of the separator can be fixed with a tape to have a pass structure. The convex part of a separator should just be long enough to be fixed to a porous sheet by folding. In order to prevent the battery from becoming thick, it is preferable that the convex portions of the separators in each layer are shifted so as not to overlap each other.

  FIG. 2 is a view showing other than the aluminum laminate film in the AA cross section of FIG. 1. The convex portions 1 of the separators of the respective layers are fixed by the porous sheet 5 and the tape 8 which are the outermost parts, and the electrode insulating portions 2 of the separators of the respective layers each have a path structure with the porous sheet 5.

  When the porous sheets are arranged above and below the power generation element, it is preferable in terms of characteristics that the convex portion of the separator has a path structure with the porous sheet on the near side.

  Examples of means for producing the pass structure include fixing with a tape, partial thermocompression bonding, partial compression bonding, and partial ultrasonic fusion.

  A laminated body including a power generation element is accommodated in an aluminum laminate film together with a non-aqueous electrolyte solution in which a lithium salt is dissolved to constitute a laminated laminate battery.

  In the power generation element body in which the positive electrode and the negative electrode are laminated via the separator, the separator has a convex portion of the separator, and the porous sheet outside the power generation element and the convex portion of the separator have a path structure, The electrolyte solution retained in the porous sheet is characterized in that the electrolyte solution is supplied into the power generation element by diffusing into the power generation element consumed with the use of the secondary battery.

(Current collector)
As the positive electrode current collector, aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used. As the negative electrode current collector, copper, stainless steel, nickel, titanium, or an alloy thereof can be used.

(Separator)
As the separator, a polyolefin film such as polypropylene or polyethylene, or a porous film such as a fluororesin is used.

(Porous sheet)
The material used for the porous sheet is not particularly limited, but polyolefin, polyamide resin, polyvinyl acetate, polyvinyl alcohol, sulfonic acid group-containing resin, fluorine-containing resin, cellulose and the like can be used.

(Positive electrode)
As the positive electrode active material, a lithium-containing composite oxide is usually used. Specifically, LiMO ₂ (M is one kind selected from Mn, Fe, Co, Ni, or a mixture of two or more kinds, May be substituted with other cations such as Mg, Al, Ti), and general-purpose materials such as LiMn ₂ O ₄ can be used. An olivine type material represented by LiFePO ₄ can also be used. A positive electrode active material selected from these and a conductive auxiliary agent such as carbon black, together with a binder such as polyvinylidene fluoride (hereinafter referred to as PVdF), N-methyl-2-pyrrolidone (hereinafter referred to as NMP) and the like. A positive electrode active material layer can be obtained by a method of dispersing and kneading in a solvent, applying the slurry to a positive electrode current collector such as an aluminum foil with a coating apparatus, and then drying the solvent. For example, by performing this coating on both surfaces of the positive electrode current collector, a positive electrode having a positive electrode active material layer formed on both surfaces can be obtained. The obtained positive electrode is compressed and adjusted to an appropriate density by pressing.

(Negative electrode)
Examples of the negative electrode active material include carbon materials such as graphite and amorphous carbon, materials that form an alloy with Li such as Li metal, Si, Sn, and Al, Si oxide, and multimetallic elements other than Si and Si. Si composite oxide containing, Sn oxide, Sn composite oxide containing multimetallic elements other than Sn and Sn, Li ₄ Ti ₅ O ₁₂ , or the like can be used alone or in combination. Using a slurry obtained by dispersing and kneading a negative electrode active material selected from these materials and, if necessary, a conductive additive in a solvent such as NMP together with a binder such as PVdF, and a negative electrode current collector such as a copper foil A negative electrode in which a negative electrode active material layer is formed on both surfaces of the negative electrode current collector can be obtained by the same method as for the positive electrode.

  As the conductive assistant, carbonaceous powder such as carbon black and acetylene black can be used.

  As the binder, fluorine resins such as PVdF and polytetrafluoroethylene, polyolefin resins, styrene resins, acrylic resins, polyimide resins and the like can be used.

(Electrolyte)
As the electrolytic solution, a nonaqueous solvent in which an electrolyte is dissolved can be used. In the case of a lithium ion secondary battery, the electrolyte uses a lithium salt, which is dissolved in a non-aqueous solvent. The lithium salt, lithium imide _{salt, LiPF 6, LiAsF 6, LiAlCl} 4, LiClO 4, LiBF 4, etc. LiSbF ₆ and the like. Of these, LiPF ₆ and LiBF ₄ are particularly preferable. Examples of the lithium imide salt include LiN (C _k Fn _{2k + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (k and m are each independently 1 or 2). These can be used alone or in combination of two or more.

  The non-aqueous solvent is at least selected from organic solvents such as cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers and their fluorinated derivatives. One kind of organic solvent is used. More specifically, cyclic carbonates: propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and derivatives thereof, chain carbonates: dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and derivatives thereof, aliphatic carboxylic acid esters: methyl formate, methyl acetate, ethyl propionate, and derivatives thereof, γ-lactones: γ-butyrolactone, And derivatives thereof, cyclic ethers: tetrahydrofuran, 2-methyltetrahydrofuran, chain ethers: 1, 2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, and derivatives thereof, Other: dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylic acid ester, 1 type (s) or 2 or more types can be mixed and used.

  Furthermore, it is also possible to use common, for example, vinylene carbonate (VC) as the electrolyte solution additive.

  Examples of the present invention are described in detail below. The present invention is not limited only to the following examples.

Example 1
(Preparation of negative electrode)
An artificial graphite powder having an average particle size of 30 μm as a negative electrode active material and PVdF as a binder were uniformly dispersed and kneaded in NMP at a weight ratio of 95: 5 to prepare a slurry. After applying this slurry on a 10 μm thick copper foil serving as a negative electrode current collector, NMP was evaporated at 125 ° C. for 10 minutes to form a negative electrode active material layer. Similarly, a negative electrode active material layer was formed on the other surface and pressed to prepare a negative electrode having an active material layer on both surfaces. The electrode density was adjusted so that the thickness excluding the negative electrode current collector was 135 μm, and the porosity of the active material layer was 30%.

(Preparation of positive electrode)
A slurry is obtained by uniformly dispersing and kneading a LiMn ₂ O ₄ powder having an average particle diameter of 10 μm as a positive electrode active material, PVdF as a binder, and carbon black as a conductive auxiliary agent in a weight ratio of 92: 4: 4 in NMP. Produced. The slurry was applied on a 20 μm thick aluminum foil serving as a positive electrode current collector, and then NMP was evaporated at 125 ° C. for 10 minutes to form a positive electrode active material layer. Similarly, a positive electrode active material layer was formed on the other surface and pressed to produce a positive electrode having an active material layer on both surfaces. The electrode density was adjusted so that the thickness excluding the positive electrode current collector was 245 μm, and the porosity of the active material layer was 30%.

The electrolyte used was a solvent in which 1 mol / L LiPF ₆ was dissolved as an electrolyte in ethylene carbonate: diethyl carbonate = 30: 70 (volume%) as a solvent. The separator was made of polyethylene and polypropylene and had a thickness of 25 μm and a porosity of 40%.

(Cut electrode)
The negative electrode produced as described above was cut into a shape in which a negative electrode active material layer having a size of 30 mm × 14 mm and an uncoated portion of a negative electrode active material layer having a size of 5 mm × 5 mm were extended to the short side portion. Similarly, the positive electrode produced as described above was cut into a shape in which a positive electrode active material layer of 28 mm × 13 mm and an uncoated portion of a positive electrode active material layer of 5 mm × 5 mm were extended.

(Cut out the separator)
The separator was cut into a shape of 4 mm × 3 mm on the long side of the separator as a convex part of 32 mm × 16 mm and the separator. Ten separators are used in total, and five of them are cut out at 2 mm, 8 mm, 14 mm, 20 mm, and 26 mm from the end of one long side of the separator so that the convex portions of the separators of each layer do not overlap. It was. The remaining 5 sheets were cut out at 2 mm, 8 mm, 14 mm, 20 mm, and 26 mm from the end of the other long side portion of the separator.

(Cut out porous sheet)
A porous sheet made of polyethylene and having a thickness of 270 μm and a porosity of 55% was cut into a shape of 32 mm × 16 mm.

(Production of laminated battery)
FIG. 4 is a plan view of a power generation element in which the convex portions of the separator of the present invention do not overlap on the side surface of the laminate. The negative electrode, the positive electrode, the separator, and the porous sheet 5 were each prepared in 6 sheets, 5 sheets, 10 sheets, and 2 sheets, and the porous sheet 5 was disposed on the upper and lower outermost layers of the laminate one by one. The negative electrode and the positive electrode were sequentially laminated via a separator so that the outermost periphery excluding the negative electrode was removed (porous sheet 5 / separator / negative electrode / separator / positive electrode / separator /.../ separator / positive electrode / separator / negative electrode / Separator / porous sheet 5). In that case, the convex part 1 of the separator was laminated | stacked so that it might arrange | position five each on either side and may not overlap. Further, the positive electrode current collectors 6 and the negative electrode current collectors 4 overlap each other, and the active material layer uncoated portions of both electrodes are disposed on the left and right sides of the laminate. In these operations, lamination was performed while determining the position of each laminate using a jig dug into the shape of the negative electrode current collector 4, the shape of the positive electrode current collector 6, and the shape of the separator. The convex portions 1 of the separator were folded up and down by 5 sheets, and the porous sheet 5 and the convex portions 1 of the separator were fixed with a PPS tape (polyphenylene sulfide tape) having a thickness of 15 μm.

  A tab with an aluminum sealant having a width of 5 mm, a length of 20 mm, and a thickness of 0.1 mm is used as a positive electrode current collector, a tab with a nickel sealant of the same size is used as a negative electrode current collector, a tab, a current collector, and a current collector. They were integrated by ultrasonic welding so that they were electrically connected to each other. Next, an aluminum laminate film made of 70 mm × 70 mm polypropylene and aluminum foil with a thickness of 125 μm is folded in two as the battery outer package, the laminated body is accommodated, and the sides excluding one side where the electrolyte solution is injected are bonded by thermal welding. did. After impregnating under reduced pressure by injecting the same amount of electrolytic solution as the total pore volume of the laminate obtained by multiplying the volume of each laminate excluding the convex portion of the separator by its porosity, A laminated laminate battery was produced by thermally welding the opening.

(Conditioning of laminated laminate batteries)
The battery was conditioned at a constant temperature of 20 ° C. in the first cycle with a charge of 0.2 C, 4.2 V constant current and constant voltage for 10 hours, and then discharged to a constant potential of 3.0 V at 0.2 C constant current. It was.

(Measurement method of battery thickness)
The maximum battery thickness after conditioning was measured with calipers.

(Measurement method for cycle test)
After measuring the maximum thickness of the battery, charge it for 1 hour at 1C, 4.2V constant current and constant voltage in a constant temperature bath at 60 ° C, then discharge it to a constant potential of 3.0V at 1C constant current. As a result, 500 cycles were performed. Based on the discharge capacity of one cycle, the discharge capacity after 500 cycles was defined as the post-cycle capacity retention rate, and the post-cycle capacity retention rate was measured.

(Example 2)
FIG. 5 is a plan view of the power generation element in which the convex portions of the separator of the present invention overlap on the side surface of the laminate. The lamination method was performed in the same manner as the lamination according to FIG. At that time, five convex portions 1 of the separator were arranged on the left and right sides and laminated so as to overlap each other. FIG. 6 is a plan perspective view of the laminated laminated nonaqueous electrolyte secondary battery of Example 2 of the present invention. A laminated laminate battery was produced in the same manner as in Example 1 except that the convex portions of the separator overlapped with the convex portions of the other separators.

  The maximum cell thickness after conditioning was measured, and the capacity retention rate after cycling was measured.

(Comparative Example 1)
7 is a perspective plan view of the laminated laminate nonaqueous electrolyte secondary battery of Comparative Example 1. FIG. The power generation element was laminated by the same method as that of FIG. FIG. 8 is a view showing a portion other than the aluminum laminate film in the BB cross section of FIG. 7. A laminated laminate battery was produced in the same manner as in Example 1 except that the porous sheet 5 and the separator did not have a pass structure and there were no separator protrusions.

  The maximum cell thickness after conditioning was measured, and the capacity retention rate after cycling was measured.

(Comparative Example 2)
FIG. 9 is a plan perspective view of the laminated laminate nonaqueous electrolyte secondary battery of Comparative Example 2. FIG. 10 is a diagram illustrating a portion other than the aluminum laminate film in the cross section taken along the line CC in FIG. 9. There is no convex part of the separator, and the electrode insulating part 2 of one separator is punched in a shape of 32 mm × 160 mm, the electrode insulating part 2 of the separator is folded in a zigzag shape, and the upper and lower parts of the separator electrode insulating part 2 are porous A laminated laminate battery was produced in the same manner as in Example 1 except that the sheet 5 was in contact with each other.

  The maximum cell thickness after conditioning was measured, and the capacity retention rate after cycling was measured.

  Table 1 shows the battery thicknesses of Examples 1 and 2 and Comparative Examples 1 and 2, and the capacity retention ratio after cycling.

  From the results of the post-cycle capacity retention ratios of Examples 1 and 2 and Comparative Example 1, it was confirmed that the post-cycle capacity retention ratio was improved because the convex portions of the porous sheet and the separator had a pass structure. In addition, from the results of the capacity retention ratio after cycles of Examples 1 and 2 and Comparative Example 2, the porous sheet has a convex portion and a path structure of the separator of each layer, and the porous sheet is located above and below the electrode insulating portion of the separator. It was confirmed that the post-cycle capacity retention rate was better than that having a partial and path structure. Further, when Example 1 was compared with Example 2, it was confirmed that in Example 2, the battery thickness was increased due to the overlapping of the convex portions of the separator, but the capacity retention rate after cycling was good without much difference.

  In the laminated laminate battery of the present invention, an electrolytic solution is retained in a porous sheet, which diffuses into the power generation element consumed as a result of the use of the secondary battery. It was confirmed that the capacity maintenance rate after the cycle was improved because of the supply structure. In addition, since the porous sheet retains the electrolytic solution, it was confirmed that the battery was consumed and was not easily deformed even when diffused inside the power generation element.

  Considering the results of the examples in total, a cycle structure is improved by providing a path structure with the convex portion of the separator and the porous sheet, and a multilayer laminated non-aqueous electrolyte secondary battery that is difficult to deform is obtained. I understood it.

  The embodiments of the present invention have been described above using the embodiments. However, the present invention is not limited to these embodiments, and the present invention is not limited to the scope of the present invention. Included in the invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

1 is a plan perspective view of a laminated laminate nonaqueous electrolyte secondary battery according to Example 1 of the present invention. FIG. The figure which shows things other than an aluminum laminate film among the AA cross sections of FIG. The figure of the separator which shows an example of embodiment of this invention. The top view of the electric power generation element with which the convex parts of the separator of this invention do not overlap on the side surface of a laminated body. The top view of the electric power generation element with which the convex parts of the separator of this invention overlap on the side surface of a laminated body. The plane perspective view of the lamination type lamination nonaqueous electrolyte secondary battery of Example 2 of the present invention. FIG. 3 is a plan perspective view of a laminated laminate nonaqueous electrolyte secondary battery of Comparative Example 1. The figure which shows things other than an aluminum laminate film among the BB cross sections of FIG. FIG. 6 is a plan perspective view of a laminated laminate nonaqueous electrolyte secondary battery of Comparative Example 2. The figure which shows other than an aluminum laminate film among the cross sections of CC of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separator convex part 2 Separator electrode insulation part 3 Negative electrode 4 Negative electrode current collector 5 Porous sheet 6 Positive electrode current collector 7 Aluminum tab 8 Tape 9 Nickel tab 10 Thermal welding part 11 Positive electrode

Claims (2)

  In a laminated laminated nonaqueous electrolyte secondary battery in which a positive electrode and a negative electrode are laminated via a separator, and a laminate having a porous sheet as an outermost layer is packaged with a laminate film, the separator has a convex portion, A laminated laminated non-aqueous electrolyte secondary battery, characterized in that a portion is in contact with the porous sheet.   The multilayer laminated nonaqueous electrolyte secondary battery according to claim 1, wherein the convex portions of the separator do not overlap each other on a side surface of the multilayer body.

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