JP2009043424A - Flat shape nonaqueous electrolytic liquid secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat-shape nonaqueous electrolytic liquid secondary battery having superior load characteristics and charge and discharge cycle characteristics for a long period. <P>SOLUTION: The flat-shape nonaqueous electrolytic liquid secondary battery has: an electrode body that has a positive electrode, a negative electrode, and a separator in a sealed space in which a sealing plate is inserted and engaged with an opening part of an outer package can through a gasket and the opening end part of the outer package can is formed by being tightened inward; and a non-aqueous electrolytic liquid. The reaction area of the electrode body is larger than the area of the battery in a plan view, and at least the portion in which the positive electrode and the negative electrode are not facing each other in the sealed space has a non-woven fabric. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a flat nonaqueous electrolyte secondary battery excellent in long-term charge / discharge cycle characteristics.

  In a flat nonaqueous electrolyte secondary battery generally called a coin-type battery or a button-type battery, for example, as shown in FIG. 1, an electrode body in which a positive electrode 3 and a negative electrode 5 are opposed to each other with a separator 4 therebetween. And the non-aqueous electrolyte are housed in a space formed by the sealing plate 1, the outer can 2, and the gasket 6. The sealing plate 1 is fitted to the opening of the outer can 2 via the gasket 6, and the opening end of the outer can 2 is tightened inward, whereby the gasket 6 comes into contact with the sealing plate 1. The opening of the outer can 2 is sealed so that the inside of the battery has a sealed structure.

  By the way, the flat non-aqueous electrolyte secondary battery as described above may be applied to a power supply application such as a portable device, for example. Therefore, it is required to improve the load characteristics so that the discharge can be performed.

  For example, in Patent Document 1 and Patent Document 2, the electrode body used in the flat nonaqueous electrolyte secondary battery has a wound structure (that is, a wound electrode body), so that the opposing area between the positive electrode and the negative electrode is increased. A technique for increasing the load characteristics of the battery has been proposed.

JP 2000-164259 A JP 2001-68143 A

  However, since the above-described wound electrode body needs to use a current collector that does not participate in the power generation reaction for the positive electrode and the negative electrode, the use of the wound electrode body may lead to a decrease in battery capacity. For this reason, in a flat non-aqueous electrolyte secondary battery, the volume of the battery is made more effective in order to suppress the decrease in capacity as much as possible while improving the load characteristics using the wound electrode body. It is necessary to use and make the volume of the wound electrode body as large as possible. On the other hand, in order to ensure good battery characteristics, it is also necessary to increase the injection amount of the non-aqueous electrolyte as much as possible.

  However, as described above, in the flat nonaqueous electrolyte secondary battery in which the volume occupied by the electrode body is increased, the sealing plate is inserted after the electrode body is inserted into the outer can and the nonaqueous electrolyte solution is injected during the production. Since the pressure is applied to the inside of the battery when the opening of the outer can is sealed using the gasket and the gasket, a part of the non-aqueous electrolyte may overflow from the outer can. When such a battery is used over a long period of time and repeatedly charged and discharged, the inventors have clarified that the discharge characteristics are greatly deteriorated due to a shortage of the non-aqueous electrolyte.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a flat non-aqueous electrolyte secondary battery excellent in load characteristics and long-term charge / discharge cycle characteristics.

  The flat non-aqueous electrolyte secondary battery of the present invention that has achieved the above object has a sealing plate fitted to the opening of the outer can through a gasket, and the opening end of the outer can is inward A flat nonaqueous electrolyte secondary battery having an electrode body having a positive electrode, a negative electrode, and a separator, and a nonaqueous electrolyte solution in a sealed space formed by tightening, wherein the reaction area of the electrode body However, it is larger than the area of the battery in plan view, and has a non-woven fabric at least at a location where the positive electrode and the negative electrode are not opposed to each other in the sealed space.

  In the flat nonaqueous electrolyte secondary battery of the present invention, the reaction area of the electrode body, that is, the facing area between the positive electrode and the negative electrode related to the electrode body is made larger than the area of the battery in plan view, Increases the characteristics.

  Further, in the flat non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte is retained in the non-woven fabric disposed in the battery, thereby preventing the non-aqueous electrolyte from overflowing during battery manufacture. The amount of the non-aqueous electrolyte solution is increased as much as possible. Since the non-aqueous electrolyte retained in the nonwoven fabric can also contribute to the discharge reaction of the battery, in the battery of the present invention, charging and discharging that may occur due to a shortage of the non-aqueous electrolyte due to the above-described action of the nonwoven fabric was repeated over a long period of time. The deterioration of the discharge characteristics is suppressed.

  In the battery industry, a flat battery with a diameter larger than the height is called a coin-type battery or a button-type battery, but there is a clear gap between the coin-type battery and the button-type battery. There is no difference, and the flat nonaqueous electrolyte secondary battery of the present invention includes both coin-type batteries and button-type batteries.

  According to the present invention, it is possible to provide a flat nonaqueous electrolyte secondary battery excellent in load characteristics and long-term charge / discharge cycle characteristics.

  FIG. 2 shows an example of the flat nonaqueous electrolyte secondary battery of the present invention. FIG. 2 is a schematic view of a cross-section of the main part of a flat nonaqueous electrolyte secondary battery. The battery shown in FIG. 2 includes a positive electrode 3 having positive electrode mixture layers 31 and 31 on both sides of a positive electrode current collector 32, and a negative electrode 5 having negative electrode mixture layers 51 and 51 on both sides of a negative electrode current collector 52. It has a spirally wound electrode body 10 that is stacked via a separator 4 and wound in a spiral shape, and is further flattened, and the electrode body 10 has a non-aqueous electrolyte (not shown), It is accommodated in a space (sealed space) formed by the sealing plate 1, the outer can 2 and the gasket 6. The sealing plate 1 is fitted to the opening of the outer can 2 via the gasket 6, and the opening end of the outer can 2 is tightened inward, whereby the gasket 6 comes into contact with the sealing plate 1. The opening of the outer can 2 is sealed so that the inside of the battery has a sealed structure.

  The sealing plate 1 also serves as a negative electrode terminal, and the exposed portion of the current collector 52 (the portion where the negative electrode mixture layer 51 is not formed) in the negative electrode 5 associated with the wound electrode body 10 is in contact with the inner surface of the sealing plate 1. Or is welded to the inner surface of the sealing plate 1. The sealing plate 1 can be made of a clad material of iron, stainless steel, aluminum or aluminum alloy and stainless steel or iron.

  The outer can 2 also serves as a positive electrode terminal. In the positive electrode 3 of the spirally wound electrode body 10, an exposed portion (a positive electrode mixture layer 31 is formed on the current collector 32 at a portion on the left side as shown in FIG. 2. The exposed portion of the positive electrode current collector 32 is in contact with the inner surface of the outer can 2 or is welded to the inner surface of the outer can 2. The outer can 2 can be made of stainless steel, aluminum, or a clad material of aluminum alloy and stainless steel.

  2 is a nonwoven fabric. In the battery shown in FIG. 2, the nonwoven fabric 7 is in contact with the inner surface of the sealing plate 1 or inside the exposed portion of the negative electrode current collector 52 welded to the inner surface of the sealing plate 1 (negative electrode current collector). 52 and the separator 4). In the battery of the present invention, the non-aqueous electrolyte is held in the nonwoven fabric 7 to prevent overflow of the non-aqueous electrolyte during battery manufacture, and the amount of non-aqueous electrolyte held by the battery is made as much as possible. It is increasing.

  Next, an example of the arrangement method of the nonwoven fabric 7 in the case of manufacturing the flat nonaqueous electrolyte secondary battery having the structure shown in FIG. 2 will be described with reference to FIGS. FIG. 3 to FIG. 5 show the appearance of the flat non-aqueous electrolyte secondary battery from obliquely above the front in each manufacturing process.

  First, as shown in FIG. 3, the negative electrode current collector 52 relating to the negative electrode of the wound electrode body 10 is brought into contact with or welded to the inner surface of the sealing plate 1.

  Next, as shown in FIG. 4, the nonwoven fabric 7 is disposed on the upper side of the negative electrode current collector 52. In FIG. 4, a nonwoven fabric 7 having a length in the lateral direction in the drawing is longer than the bottom surface portion (bottom surface portion in FIG. 4) of the sealing plate 1. However, for example, a nonwoven fabric having a shorter lateral length than the bottom surface of the sealing plate 1 may be used for the nonwoven fabric 7 and the left and right ends may be disposed without folding. Further, the nonwoven fabric 7 is made of a nonwoven fabric having a lateral length shorter than the bottom surface portion of the sealing plate and having a lower length in the figure longer than the bottom surface portion of the sealing plate 1, and the right and left ends are not folded. Only the lower side in the figure may be arranged while being folded upward along the side wall of the sealing plate 1. Furthermore, the nonwoven fabric 7 is made of a nonwoven fabric having a lateral length longer than the bottom surface portion of the sealing plate 1 and a lower length in the figure than the bottom surface portion of the sealing plate 1. The three sides may be arranged while being folded upward along the side wall of the sealing plate 1.

  Next, as shown in FIG. 5, the wound electrode body 10 is placed on the nonwoven fabric 7. Thereafter, a nonaqueous electrolytic solution is added, and subsequently, a gasket is disposed on the outer periphery of the sealing plate 1, covered with an outer can, and then sealed to produce a battery. As described above, the exposed portion of the positive electrode current collector 32 of the wound electrode body 10 may be brought into contact with the inner surface of the outer can or welded to the inner surface of the outer can.

  3 to 5 show an example in which the wound electrode body 10 and the nonwoven fabric 7 are disposed in the sealing plate 1 to produce a battery. However, the wound electrode body and the nonwoven fabric are disposed in an outer can so that the battery is It may be produced.

  2 to 5 show an example in which the nonwoven fabric 7 is arranged inside the exposed portion of the negative electrode current collector 52 on the sealing plate 1 side, the place where the nonwoven fabric 7 is arranged is the positive electrode in the battery. There is no particular limitation as long as it is other than a portion where the negative electrode and the negative electrode face each other.

  In addition, it is preferable to arrange | position a nonwoven fabric inside the battery side wall from which a pressure is comparatively hard to apply from a viewpoint of exhibiting the nonaqueous electrolyte retention function by a nonwoven fabric more effectively. When arranging a nonwoven fabric inside the battery side wall, for example, as shown in FIGS. 3 to 5, the size of the nonwoven fabric 7 is made larger than the bottom surface of the sealing plate 1, A method of folding three sides along the side wall of the sealing plate 1 may be adopted, and the non-woven fabric may not be arranged on the bottom surface of the sealing plate, but the non-woven fabric may be arranged only on the inner surface of the battery side wall. .

  On the other hand, for example, when the exposed portion of the negative electrode current collector or the exposed portion of the positive electrode current collector in the wound electrode body is merely contacted without being welded to the inner surface of the sealing plate or the inner surface of the outer can, When gas is generated in the battery during use and the thickness of the battery expands slightly, the contact between the negative electrode and positive electrode of the wound electrode body and the sealing plate that also functions as the negative electrode terminal and the outer can that also functions as the positive electrode terminal is insufficient. Thus, the electrical connection may be lost. In such a case, as shown in FIGS. 3 to 5, the non-woven fabric 7 may be disposed so as to be sandwiched between the exposed portions of the negative electrode current collector 52 in parallel or substantially parallel to the bottom surface of the sealing plate 1. In addition, it is preferable to dispose them so as to be sandwiched inside the exposed portion of the positive electrode current collector in parallel or substantially parallel to the bottom surface of the outer can.

  When the battery is sealed, the nonwoven fabric arranged in this way is sandwiched between the sealing electrode and the outer can together with the wound electrode body and compressed, but the battery expands due to gas generation in the battery, and the bottom surface of the sealing plate- When the distance between the outer can bottoms increases, the nonwoven fabric swells and tries to return to its original size. The exposed portion of the negative electrode current collector is pressed against the inner surface of the sealing plate by the swollen nonwoven fabric, or the exposed portion of the positive electrode current collector is pressed against the inner surface of the outer can. The electrical connection between the negative electrode and the sealing plate and the electrical connection between the positive electrode and the outer can can be maintained well.

  There is no restriction | limiting in particular as a raw material of the nonwoven fabric arrange | positioned in a battery, For example, polyolefin, such as polyethylene (PE), polypropylene (PP), and polymethylpentene (TPX); Polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. Various known resins can be used as the material for the battery inner member (for example, separator) of the non-aqueous electrolyte secondary battery.

  Further, the porosity of the nonwoven fabric is preferably 50% or more, and more preferably 70% or more, from the viewpoint of making the holding function of the non-aqueous electrolyte better. In addition, if the porosity of the nonwoven fabric is too large, for example, the degree of swelling (recovery of size) of the nonwoven fabric when the battery is swollen may be reduced. In this case, the exposure of the negative electrode current collector may be reduced. The porosity of the nonwoven fabric is preferably 95% or less, and more preferably 90% or less, because the action of pressing the exposed portion of the portion and the positive electrode current collector against the inner surface of the sealing plate or the inner surface of the outer can is reduced. .

  In addition, the porosity of the nonwoven fabric referred to in the present specification is a value representing the ratio of the apparent volume of the nonwoven fabric and the volume of the nonwoven fabric constituent fiber obtained from the mass of the nonwoven fabric and the specific gravity of the constituent fiber of the nonwoven fabric as a percentage. It is.

  In addition, the thickness of the nonwoven fabric is preferably 100 μm or more, and more preferably 150 μm or more, from the viewpoint of making the nonaqueous electrolyte holding function better. If the nonwoven fabric is too thick, the occupied volume of the nonwoven fabric in the battery becomes too large, which may cause a decrease in battery capacity. Therefore, the thickness of the nonwoven fabric is preferably 500 μm or less, and is 400 μm or less. It is more preferable.

  The positive electrode according to the flat nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and is a positive electrode used in a conventionally known nonaqueous electrolyte secondary battery, that is, for example, a positive electrode active material, a conductive additive. In addition, a positive electrode mixture containing a binder or the like can be used.

Examples of the positive electrode active material include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O ₂ , and Li _x Ni _1-y M 2. _{y O 2, Li x Mn y} Ni z Co 1-y-z O 2, Li x Mn 2 O 4, etc. _{Li x Mn} lithium transition metal composite oxides, such as _2-y M _{y O 4} and the like (provided that In the above lithium transition metal composite oxides, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al and Cr, and 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 ≦ z ≦ 2.2.) These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  Examples of the conductive assistant include carbon black, scaly graphite, ketjen black, acetylene black, and fibrous carbon. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), carboxymethyl cellulose, and styrene butadiene rubber.

  For the positive electrode, for example, a positive electrode mixture obtained by mixing a positive electrode active material, a conductive additive, and a binder is dispersed in water or an organic solvent to prepare a positive electrode mixture-containing paste (in this case, the binder is preliminarily mixed with water or It may be dissolved or dispersed in a solvent and mixed with a positive electrode active material to prepare a positive electrode mixture-containing paste), and the positive electrode mixture-containing paste is made of metal foil, expanded metal, plain weave metal mesh, etc. It is manufactured by forming a positive electrode mixture layer by applying it to one or both sides of a current collector, drying it, and then press-molding it. However, the method for manufacturing the positive electrode is not limited to the above-described method, and may be another method.

  As a composition of the positive electrode, for example, in 100% by mass of the positive electrode mixture constituting the positive electrode, the positive electrode active material is 75 to 90% by mass, the conductive additive is 5 to 20% by mass, and the binder is 3 to 15% by mass. Is preferred. Moreover, it is preferable that the thickness of a positive mix layer is 30-200 micrometers, for example.

  The material for the current collector of the positive electrode is preferably aluminum or an aluminum alloy. Moreover, it is preferable that the thickness of a collector is 8-20 micrometers, for example.

  Examples of the negative electrode according to the battery of the present invention include a negative electrode having lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, lithium titanate, and the like as an active material.

  Examples of the lithium alloy that can be used for the negative electrode active material include lithium alloys that reversibly alloy with lithium, such as lithium-aluminum and lithium-gallium, and the lithium content is, for example, 1 to 15 atomic%. Is preferred. Examples of the carbon material that can be used for the negative electrode active material include artificial graphite, natural graphite, low crystalline carbon, coke, and anthracite.

The lithium titanate that can be used for the negative electrode active material is represented by the general formula Li _x Ti _y O ₄ , and x and y are 0.8 ≦ x ≦ 1.4 and 1.6 ≦ y ≦ 2.2, respectively. Lithium titanate having a stoichiometric number is preferable, and lithium titanate having a stoichiometric number of x = 1.33 and y = 1.67 is particularly preferable. The lithium titanate represented by the general formula Li _x Ti _y O ₄ can be obtained, for example, by heat-treating titanium oxide and a lithium compound at 760 to 1100 ° C. As the titanium oxide, either anatase type or rutile type can be used, and examples of the lithium compound include lithium hydroxide, lithium carbonate, and lithium oxide.

  When the negative electrode active material is lithium or a lithium alloy, the negative electrode is formed by bonding the lithium or lithium alloy to a current collector such as a metal network to form a negative electrode layer made of lithium or lithium alloy on the surface of the current collector. Can be obtained. On the other hand, when a carbon material or lithium titanate is used as the negative electrode active material, for example, a negative electrode composite obtained by mixing a carbon material or lithium titanate with a binder as the negative electrode active material and, if necessary, a conductive additive. The negative electrode mixture-containing paste is prepared by dispersing the agent in water or an organic solvent (in this case, the binder is previously dissolved or dispersed in water or solvent, and mixed with the negative electrode active material or the like to contain the negative electrode mixture) A paste may be prepared), and the negative electrode mixture-containing paste is applied to a current collector made of metal foil, expanded metal, plain woven wire mesh, etc., dried, and then pressed to form a negative electrode mixture layer Thus, a negative electrode can be manufactured. However, the manufacturing method of the negative electrode is not limited to the above-described method, and other methods may be used.

  In addition, as a binder and conductive support agent which concern on a negative electrode, the various binders and conductive support agent which were illustrated previously as what can be used for a positive electrode can be used.

  The composition of the negative electrode when a carbon material is used as the negative electrode active material is, for example, that the carbon material is 80 to 95% by mass and the binder is 3 to 15% by mass in 100% by mass of the negative electrode mixture constituting the negative electrode. Moreover, when using together a conductive support agent, it is preferable that a conductive support agent shall be 5-20 mass%. On the other hand, the composition of the negative electrode when lithium titanate is used as the negative electrode active material is, for example, 75 to 90% by mass of lithium titanate and 3 to 15% by mass of the binder in 100% by mass of the negative electrode mixture constituting the negative electrode. In addition, when a conductive auxiliary is used in combination, the conductive auxiliary is preferably 5 to 20% by mass.

  The thickness of the negative electrode agent layer or the negative electrode mixture layer in the negative electrode is preferably 40 to 200 μm, for example.

  The material for the current collector of the negative electrode is preferably copper or a copper alloy. Moreover, it is preferable that the thickness of a collector is 5-25 micrometers, for example.

  As the separator, either a microporous resin film or a resin nonwoven fabric can be used. Examples of the material include polyolefins such as PE, PP and TPX, and fluorine resins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) for heat resistance; polyphenylene sulfide (PPS); polyether ether Ketone (PEEK); PBT etc. are mentioned. Moreover, you may comprise a separator by laminating | stacking two or more microporous resin films and resin nonwoven fabrics of the said material, or laminating | stacking two or more microporous resin films or resin nonwoven fabrics. The thickness of the separator is preferably, for example, 5 to 25 μm, and the porosity is preferably, for example, 30 to 70%.

  The flat nonaqueous electrolyte secondary battery of the present invention has a reaction area of an electrode body constituted by the positive electrode, the negative electrode, and the separator, that is, an area where the positive electrode and the negative electrode face each other, as viewed from above the battery. It is larger than the area (projected area in plan view). In a conventional flat battery, for example, as shown in FIG. 1, it is mainstream to use an electrode body in which a positive electrode consisting of only one layer and a negative electrode consisting of only one layer are stacked via a separator. The reaction area of the electrode body is smaller than the area of the battery in plan view. In contrast, in the flat non-aqueous electrolyte secondary battery of the present invention, as described above, the reaction area of the electrode body is made larger than the area of the battery in plan view to improve the load characteristics of the battery. Yes.

  As a method for making the reaction area of the electrode body larger than the area in the plan view of the battery, a method using a laminated electrode body in which two or more positive electrodes and two or more negative electrodes are laminated via a separator, As shown in FIG. 2, a method of using a spirally wound electrode body in which a laminated body in which a positive electrode and a negative electrode are laminated via a separator is spirally wound and crushed as necessary is used. . Among these, it is more preferable to use a wound electrode body (flat wound electrode body) because the production of the electrode body is easier and the productivity of the battery can be further increased.

  In the case of using a wound electrode body, as described above, in the positive electrode on the outermost peripheral side, the end portion of the current collector and the vicinity thereof are exposed without forming a positive electrode mixture layer. The positive electrode and the outer can can be electrically connected by welding or contacting the exposed portion of the electric body with the outer can serving also as the positive electrode terminal. Also, when using a wound electrode body, in the negative electrode on the outermost peripheral side, the end portion of the current collector and the vicinity thereof are exposed so as not to form a negative electrode agent layer or a negative electrode mixture layer. The negative electrode and the sealing plate can be electrically connected by welding or contacting the exposed portion of the electric body with the sealing plate also serving as the negative electrode terminal.

  On the other hand, when using a laminated electrode body, the outermost electrode on the outer can side that also serves as the positive electrode terminal is used as the positive electrode, and the current collector is exposed without forming a positive electrode mixture layer on the outer can side of the positive electrode. In addition, the positive electrode and the outer can can be electrically connected by welding or bringing the exposed portion of the current collector into contact with the outer can. When a laminated electrode body is used, the outermost electrode on the side of the sealing plate that also serves as the negative electrode terminal is used as the negative electrode, and the negative electrode layer or the negative electrode mixture layer is not formed on the sealing plate side of the negative electrode. The negative electrode and the sealing plate can be electrically connected by exposing the electric body and welding or contacting the exposed portion of the current collector and the sealing plate.

  In addition to the above, the current collecting tab electrically connected to the current collector of the electrode is welded to the inner surface of the outer can and the sealing plate, thereby electrically connecting the outer can and the sealing plate serving both as the electrode and the external terminal. It is also possible to connect them.

  As a material of the gasket, for example, PP; nylon (nylon 6, nylon 66, etc.); etc., for heat resistance, fluorine resin such as PFA; polyphenylene ether (PPE); polysulfone (PSF); polyarylate (PAR) ); Polyethersulfone (PES); PPS; PEEK;

  Examples of the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate; Ethers such as 2-dimethoxyethane, diglyme (diethylene glycol methyl ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), 1,2-dimethoxyethane, 1,2-diethoxymethane, tetrahydrofuran; An electrolytic solution prepared by dissolving an electrolyte (lithium salt) in a concentration of about 0.3 to 2.0 mol / L in the organic solvent can be used. The above organic solvents may be used alone or in combination of two or more.

Examples of the electrolyte include LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) Lithium salts such as ₂ are mentioned.

In addition, fluorine atom content such as LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, etc. When a non-aqueous electrolyte prepared using a lithium salt is used in a battery, as described above, hydrogen fluoride is generated by moisture inevitably mixed during battery manufacture, and this impairs the leakage resistance of the battery. Therefore, the peripheral edge of the sealing plate has a shoulder portion that is stepped down from the upper surface of the sealing plate, and further has a wall portion that extends downward from the shoulder portion and ends at the lower edge. It is preferable to constitute a battery by using.

  The flat shape of the flat non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and may be a polygonal shape such as a square (quadrangle) in addition to a circular shape that is the mainstream of conventionally known flat batteries, but is particularly flat. In the case of using a wound electrode body that has been crushed into a shape, the internal volume of the battery can be used more effectively, and the capacity per battery volume can be increased more easily, so that it is preferably rectangular. In addition, the polygon such as a square as the planar shape of the battery in this specification includes a shape in which the corner is cut off and a shape in which the corner is curved.

  Although the flat nonaqueous electrolyte secondary battery of the present invention has been described with reference to FIGS. 2 to 5, FIGS. 2 to 5 show only an example of the battery of the present invention. The batteries are not limited to those shown in these drawings. Further, FIGS. 2 to 5 are only schematic views showing the structure of the battery of the present invention, and the size of each component is not necessarily accurate.

  The flat nonaqueous electrolyte secondary battery of the present invention maintains good discharge characteristics even after repeated charge and discharge over a long period of time, and also has excellent load characteristics. For example, for a watch (communication type) or mobile phone Suitable for various applications where conventional flat type non-aqueous electrolyte secondary batteries are applied, including applications that require continuous discharge over a long period of time, such as power supplies for headsets, and that require a relatively large current discharge Can be applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In the following examples and the like, “parts” means parts by mass.

Example 1
Example 1 will be described in the order of positive electrode preparation, negative electrode preparation, electrolyte solution preparation, and battery assembly.

<Preparation of positive electrode>
A positive electrode was prepared using LiCoO ₂ as a positive electrode active material, carbon black as a conductive additive, and PVDF as a binder. First, 93 parts of LiCoO ₂ and 3 parts of carbon black were mixed, and the resulting mixture was mixed with a binder solution in which 4 parts of PVDF were previously dissolved in N-methyl-2-pyrrolidone (NMP). Thus, a positive electrode mixture-containing paste was prepared. The obtained positive electrode mixture-containing paste was applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm by an applicator (however, the completed positive electrode was superposed on the negative electrode via a separator and wound in a spiral shape). Do not apply the positive electrode mixture-containing paste to the part that will be the outermost periphery when turning into an electrode body with a wound structure, so that the exposed portion of the positive electrode current collector remains on both sides of the positive electrode current collector And dried to form a positive electrode mixture layer, and then roll-pressed and cut into a predetermined size to obtain a strip-shaped positive electrode. The positive electrode has a width of 15 mm and a thickness of 120 μm, and the length of the exposed portion of the positive electrode current collector that is the outermost peripheral portion when wound is 20 mm.

<Production of negative electrode>
A negative electrode was prepared using graphite as the negative electrode active material and PVDF as the binder. The graphite: 94 parts, PVDF: 6 parts, and a binder solution previously dissolved in NMP were mixed to prepare a negative electrode mixture-containing paste. The obtained negative electrode mixture-containing paste was applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 10 μm by an applicator (however, the completed negative electrode was overlapped with the positive electrode via a separator to form a spiral shape) No negative electrode mixture-containing paste is applied to the outermost portion when the electrode body is wound to form an electrode body with a wound structure, so that exposed portions of the negative electrode current collector remain on both sides of the negative electrode current collector And dried to form a negative electrode mixture layer, and then roll-pressed and cut into a predetermined size to obtain a sheet-like negative electrode. The negative electrode has a width of 16 mm and a thickness of 140 μm, and the length of the exposed portion of the negative electrode current collector at the outermost peripheral portion when wound is 20 mm.

<Preparation of electrolyte>
An electrolytic solution was prepared by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1: 2 at a concentration of 1.2 mol / l.

<Battery assembly>
The positive electrode and the negative electrode are spirally wound so that a separator made of a microporous PE film having a thickness of 16 μm is interposed between the positive electrode and the negative electrode, and pressed into a flat shape so that a coin-type battery can be easily finished. Thus, a wound electrode body was produced. The wound electrode body, 300 μl of non-aqueous electrolyte, and non-woven fabric are accommodated in a sealed space composed of a sealing plate, an outer can, and a gasket according to the procedure shown in FIGS. Thus, a rectangular flat nonaqueous electrolyte secondary battery having a length of 24.5 mm and a thickness of 3 mm was produced.

  Specifically, first, as shown in FIG. 3, the negative electrode current collector 52 related to the negative electrode of the wound electrode body 10 was welded to the inner surface of the sealing plate 1. Next, as shown in FIG. 4, a PP nonwoven fabric having a length of 22 mm, a width of 20 mm, a porosity of 80%, and a thickness of 350 μm was placed on the upper side of the negative electrode current collector 52. Here, as shown in FIG. 4, the non-woven fabric is arranged by folding the left and right sides in the width direction upward by 2 mm along the side wall of the sealing plate 1. Next, as shown in FIG. 5, the wound electrode body 10 was placed on the nonwoven fabric 7, and then the positive electrode current collector 32 was welded to the inner surface of the outer can 2. Thereafter, a non-aqueous electrolyte was added, and subsequently, a PP gasket was disposed on the outer periphery of the sealing plate 1 and covered with an outer can, and then sealed to prepare a battery.

Here, the flat nonaqueous electrolyte secondary battery of Example 1 will be described with reference to FIG. 2. The positive electrode 3 is a sheet obtained by applying a positive electrode mixture containing LiCoO ₂ as a positive electrode active material to a current collector. The negative electrode 5 is formed by applying a negative electrode mixture containing graphite as a negative electrode active material to a current collector to form a sheet. Between these positive electrodes 3 and 5, there are micropores. A separator 4 made of a conductive PE film is interposed to constitute an electrode body, and a nonwoven fabric 7 is disposed between the upper side of the exposed portion of the negative electrode current collector and the separator, and this electrode body and a non-aqueous electrolyte (illustrated) Is not accommodated in the sealed space formed by the sealing plate 1, the outer can 2, and the gasket 6. The battery seals the opening of the outer can 2 by tightening the opening end of the outer can 2 inward and pressing the gasket 6 against the sealing plate 1 and the outer can 2 at the time of assembly. The inside of the battery is sealed.

Comparative Example 1
A flat nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the non-woven fabric was not used. In the flat type nonaqueous electrolyte secondary battery of Comparative Example 1, a part of the nonaqueous electrolyte leaked during sealing.

Comparative Example 2
A flat nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the amount of the nonaqueous electrolyte placed in the battery was changed to 250 μl without using a non-woven fabric.

For the batteries of Example 1 and Comparative Examples 1 and 2, the capacity retention rate at the 500th charge / discharge cycle was measured. The results are shown in Table 1. In the charging / discharging of the battery, a series of operations in which charging was performed at a constant current of 100 mA until the voltage reached 4.2 V, and then discharging was performed at a constant current of 100 mA to a final voltage of 3.0 V was defined as one cycle. The capacity maintenance rate at the 500th cycle was calculated by the following formula.
Capacity maintenance rate (%) = (discharge capacity at 500th cycle / discharge capacity at the first cycle)
× 100

  As shown in Table 1, it was confirmed that the flat nonaqueous electrolyte secondary battery of Example 1 had a capacity retention rate at the 500th cycle superior to that of the flat nonaqueous electrolyte secondary battery of Comparative Example 1. did it. This result is considered to be due to the fact that in the battery of the example, the electrolyte solution could be held by the nonwoven fabric, so that the amount of the electrolyte solution into the battery could be increased.

For the flat nonaqueous electrolyte secondary battery of Example 1 (not used for the capacity retention rate measurement), a continuous discharge of 10 mA at 20 ° C. and a continuous discharge of 1 mA at 20 ° C. were performed. The discharge capacity when the final voltage was 3.0 V was measured, and the load characteristics of the battery of Example 1 were evaluated by “the ratio of the discharge capacity at 10 mA to the discharge capacity at 1 mA” obtained by the following formula. In addition, the charging of the battery at the time of load characteristic evaluation is constant current charging until reaching 4.2V at a current of 5 mA at 20 ° C. in both cases of continuous discharge at 10 mA and continuous discharge at 1 mA, and thereafter The constant voltage charging at 4.2 V was performed under the condition that the total charging time was 48 hours.
Load characteristics (%) = 100 × (discharge capacity at 10 mA) / (discharge capacity at 1 mA)

  As a result of the test, the load characteristic of the battery of Example 1 was 98%, and it was confirmed that the battery had excellent load characteristics.

It is a principal part cross-sectional schematic diagram of the conventional flat nonaqueous electrolyte secondary battery. It is a principal part cross-section schematic diagram which shows an example of the flat nonaqueous electrolyte secondary battery of this invention. It is a schematic diagram for demonstrating an example of the manufacturing process of the flat nonaqueous electrolyte secondary battery of this invention. It is a schematic diagram for demonstrating the next process of the process shown in FIG. It is a schematic diagram for demonstrating the next process of the process shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Exterior can 3 Positive electrode 4 Separator 5 Negative electrode 6 Gasket 7 Non-woven fabric 10 Winding electrode body

Claims (4)

An electrode having a positive electrode, a negative electrode, and a separator in a sealed space formed by fitting a sealing plate to the opening of the outer can through a gasket and tightening the opening end of the outer can inward. A flat non-aqueous electrolyte secondary battery having a body and a non-aqueous electrolyte,
The reaction area of the electrode body is larger than the area of the battery in plan view,
A flat nonaqueous electrolyte secondary battery comprising a non-woven fabric at least at a location where the positive electrode and the negative electrode are not opposed to each other in the sealed space.   The flat non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode body is a wound electrode body obtained by winding a laminated body in which a positive electrode and a negative electrode are laminated via a separator in a spiral shape.   The flat nonaqueous electrolyte secondary battery according to claim 1, which is square in a plan view. The flat nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the non-woven fabric has a porosity of 50 to 95%.

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