JP5348720B2 - Flat non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat nonaqueous secondary battery superior in safety at high temperatures. <P>SOLUTION: In a space formed by caulking and sealing an outer case and a sealing case via an insulating gasket, the flat nonaqueous secondary battery has an electrode group in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, and has a nonaqueous solution. The positive electrode has the main body and a current collecting tab which is protruded from the main body and narrower in width than the main body. On both faces of the positive electrode of which the both sides opposes to the negative electrode, the separator having the main body to cover the main body of the positive electrode and a flared part to cover a part of the current collecting tab of the positive electrode is arranged. At least in a part of a peripheral portion of the main body, two sheets of the separators have a joined part adhered via a layer constituted of a resin of the same kind as a constituting resin of the separator. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a flat non-aqueous secondary battery with good safety.

  In a flat non-aqueous secondary battery generally called a coin-type battery or a button-type battery, an electrode body in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween, and a non-aqueous electrolyte are used as an outer case. And a structure accommodated in a space formed by a sealing case and a gasket.

  In the flat non-aqueous secondary battery as described above, a positive electrode mixture layer or a negative electrode mixture layer is formed on one side or both sides of the current collector on the positive electrode and the negative electrode, and a part of the current collector is mixed with the positive electrode mixture. It is exposed without forming a material layer or negative electrode mixture layer, and this is used as a current collecting tab, and this current collecting tab is used for electrical connection with an outer case or sealing case that also serves as a terminal by bending it. There is something.

  A flat non-aqueous secondary battery having an electrode group in which the positive electrode as described above is inserted into a bag-shaped separator and laminated with the negative electrode is also known (Patent Document 1). In this battery, when forming a bag-shaped separator, an insulating polymer film such as a polyester resin film is disposed between two separators, and the film and the separator are separated by an adhesive component provided on the surface of the film. Glued.

JP-T-2004-509443

  By the way, it is common to use a microporous film (microporous film) made of polyolefin such as polyethylene as a separator for non-aqueous secondary batteries. Such a microporous membrane is usually manufactured through a process of performing uniaxial stretching or biaxial stretching, but since distortion occurs due to stretching, the microporous film is likely to shrink when exposed to high temperatures. When the inside of the non-aqueous secondary battery is in a high temperature state and the separator contracts, the positive electrode and the negative electrode may be in direct contact with each other, causing a short circuit.

  On the other hand, in the case of a battery using the bag-shaped separator, since the two separators enclosing the positive electrode are joined to each other, the separator is unlikely to contract even at high temperatures. However, in some cases, the inventor's investigation has revealed that the short-circuit suppressing effect at high temperatures is not necessarily good.

  This invention is made | formed in view of the said situation, The objective is to provide the flat type non-aqueous secondary battery with favorable safety | security under high temperature.

  The flat non-aqueous secondary battery of the present invention that has achieved the above-described object has a plurality of positive electrodes and a plurality of negative electrodes in a space formed by caulking and sealing an outer case and a sealing case via an insulating gasket. Is a flat non-aqueous secondary battery having electrode groups and non-aqueous electrolytes alternately stacked via separators, and the positive electrode protrudes from the main body portion in a plan view. A positive electrode mixture layer including a positive electrode active material on one or both sides of the current collector is formed on the main body portion of the positive electrode. In the current collector tab portion of the positive electrode, a positive electrode mixture layer is not formed on the current collector, and the negative electrode protrudes from the main body portion and the main body portion in plan view. And a current collector tab portion having a narrow width, and the main body portion of the negative electrode has one surface of the current collector or A negative electrode agent layer containing a negative electrode active material is formed on the surface, and in the current collecting tab portion of the negative electrode, the negative electrode agent layer is not formed on the current collector, and at least both sides face the negative electrode Separators made of a microporous film made of a thermoplastic resin are disposed on both surfaces of the positive electrode, and the two separators protrude from the main body, a main body covering the entire main body of the positive electrode, and the positive electrode Of the current collecting tab portion, and a projecting portion that covers at least a portion including the boundary portion with the main body portion, and at least a part of the peripheral portion of the main portion of the two separators, It has the junction part welded through the layer comprised with the same kind of resin as the thermoplastic resin which comprises the separator of a sheet | seat, It is characterized by the above-mentioned.

  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 non-aqueous 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 non-aqueous secondary battery with good safety at high temperatures.

It is a longitudinal cross-sectional view which represents typically an example of the flat non-aqueous secondary battery of this invention. It is a principal part cross-sectional enlarged view of FIG. It is a top view which represents typically an example of the positive electrode which concerns on the flat nonaqueous secondary battery of this invention. It is a top view which represents typically an example of the separator which concerns on the flat nonaqueous secondary battery of this invention. It is a top view of the separator used for the flat nonaqueous secondary battery of an Example.

  1 and 2 schematically show an example of the flat non-aqueous secondary battery of the present invention. FIG. 1 is a longitudinal sectional view showing a cross section of a battery case (outer case 2 and sealing case 3) and an insulating gasket 4 part of a flat non-aqueous secondary battery. FIG. 2 is an enlarged view of the main part of FIG. Furthermore, the electrode group is shown in cross section. As shown in FIGS. 1 and 2, the flat non-aqueous secondary battery 1 is formed by laminating a positive electrode 5 and a negative electrode 6 so that their planes are substantially parallel (including parallel) to the flat plane of the battery. A mold type electrode group and a non-aqueous electrolyte (not shown) are accommodated in a space (sealed space) formed by the outer case 2, the sealing case 3, and the insulating gasket 4. The sealing case 3 is fitted to the opening of the outer case 2 via an insulating gasket 4, and the opening end of the outer case 2 is tightened inward, whereby the insulating gasket 4 contacts the sealing case 3. Thereby, the opening part of the exterior case 2 is sealed, and the inside of the battery has a sealed structure. The outer case 2 and the sealing case 3 are made of a metal such as stainless steel, and the insulating gasket 4 is made of an insulating resin such as polypropylene.

  FIG. 3 schematically shows a plan view of the positive electrode 5. The positive electrode 5 has a main body 5a and a width larger than that of the main body 5a projecting from the main body 5a in plan view (in the vertical direction in FIG. 3). And a current collecting tab portion 5b having a narrow length.

  As for the main-body part 5a of the positive electrode 5, the positive mix layer 51 is formed in the single side | surface or both surfaces of a collector (52 in FIG. 2). In the current collecting tab portion 5b of the positive electrode 5, the positive electrode mixture layer is not formed on the surface of the current collector 52, and the current collector 52 is exposed.

  The negative electrode also has a main body portion and a current collecting tab that protrudes from the main body portion in a plan view and is narrower than the main body portion, as in the positive electrode 5, and is shown in FIGS. 1 and 2. As described above, the negative electrode agent layer 61 is formed on one or both surfaces of the current collector 62 in the main body 6 a of the negative electrode 6. Further, in the current collecting tab portion 6 b of the negative electrode 6, the negative electrode agent layer is not formed on the surface of the current collector 62, and the current collector 62 is exposed.

  In the battery shown in FIG. 1 and FIG. 2, the upper and lower ends of the electrode group are negative electrodes 6B and 6B, and these negative electrodes 6B and 6B are provided on only one side of the current collector 62 (the inner surface of the battery). A layer 61 is provided. In addition, the exposed surface of the current collector 62 of the negative electrode 6B on the upper side in the drawing in the electrode group is welded to the inner surface of the sealing case 3 or is directly connected without being welded. That is, in the battery shown in FIGS. 1 and 2, the sealing case 3 also serves as the negative electrode terminal.

  And all the negative electrodes 6 (the negative electrode 6A in which the negative electrode agent layer 61 is formed on both surfaces of the current collector 62 and the negative electrode 6B in which the negative electrode agent layer 61 is formed on one surface of the current collector 62) included in the electrode group, Are electrically connected to each other through the current collecting tab portion 6b. In addition, the connection of the current collection tab part 6b of each negative electrode 6 can be performed by welding, for example.

  Further, in the battery shown in FIGS. 1 and 2, the current collecting tab portions 5b of the respective positive electrodes 5 are electrically connected to each other, and are welded to the inner surface of the outer case 2 or directly contacted without being welded. Are electrically connected. That is, in the battery shown in FIGS. 1 and 2, the outer case 2 also serves as a positive electrode terminal. In the battery shown in FIGS. 1 and 2, for the purpose of insulating the negative electrode 6B located at the lowermost part of the electrode group from the outer case 2 also serving as the positive electrode terminal, polyethylene terephthalate (PET), polyimide, etc. An insulating seal 8 made of tape or the like is disposed.

  FIG. 4 schematically shows a plan view of the separator according to the battery of the present invention. In FIG. 4, assuming the case of a stacked electrode group in which the positive electrode, the negative electrode, and the separator are stacked together with the separator 7, the positive electrode 5 disposed below the separator 7 is indicated by a dotted line, A current collecting tab portion 6b related to the negative electrode disposed on the lower side is indicated by a one-dot chain line, and a binding tape 9 for suppressing positional deviation of each component related to the electrode group is indicated by a two-dot chain line. Further, the positive electrode 5 shown in FIG. 4 has an electrode group in which both sides (both sides) face the negative electrode. Although not shown in FIG. 4, when the electrode group is used, the upper side of the separator 7 (in the drawing) In the forward direction), at least a negative electrode is arranged.

  As shown in FIG. 4, the separator 7 and the other separator disposed below (in the depth direction in the drawing) via the positive electrode 5 (indicated by a dotted line in the drawing) are joined at the peripheral edge thereof. It has a joint 7c (indicated by a lattice pattern in the figure). In other words, the separator 7 and the separator disposed below the separator 7 are joined at the peripheral edge to form a bag shape, and the positive electrode 5 is accommodated therein.

  The separator 7 protrudes from the main body part 7a (that is, the main body part 7a having a larger area in plan view than the main body part 5a of the positive electrode 5) covering the entire surface of the main body part 5a of the positive electrode 5 and the main body part 7a. A protruding portion 7b that covers at least a portion of the electric tab portion 5b including a boundary portion with the main body portion 5a. And the junction part which joined two separators (Separator 7 and the separator arrange | positioned under the positive electrode 5) arrange | positioned at both surfaces of the positive electrode 5 to at least one part of the peripheral part of the main-body part 7a of the separator 7 7c is provided.

  The separator joining portion 7c is formed by welding the peripheral portions of the two separators with a layer made of the same kind of resin as the thermoplastic resin constituting the separator interposed therebetween. For example, a layer made of a resin different from the separator resin is interposed between the separators, and this layer and two separators are welded together, or an adhesive is applied to both sides of this layer. When the bonded portion is formed by bonding with two separators via this adhesive, the strength of the bonded portion is likely to be smaller than other portions of the separator. Thus, when the separator contracts, the bonded portion may peel off and the positive electrode and the negative electrode may be in direct contact with each other.

  On the other hand, in the battery of the present invention, as described above, the peripheral portion of the two separators is welded while interposing a layer made of the same kind of resin as the constituent resin of the separator to form a joint portion. In addition, the strength of the joined portion is substantially equal to the strength of the separator itself. For this reason, even if the temperature inside the battery is high enough to cause the separator to shrink, the separation of the joint is suppressed well, the separator is prevented from shrinking, and the contact between the positive electrode and the negative electrode is prevented. It becomes a battery having high safety.

  The layer interposed between the two separators can also serve as a guide for the positive electrode. The presence of such a layer joins the two separators and arranges the positive electrode between them. Since the displacement of the positive electrode during the process can be prevented, the productivity of the electrode group, and hence the productivity of the battery using the same can be improved.

  In addition, although all the peripheral parts which concern on the main part of a separator may be a junction part, as shown in FIG. 4, for example, as shown in FIG. You may leave as 7d and 7d. After the two separators are welded to form a bag, the positive electrode is accommodated therein, the positive electrode is disposed on one separator, and the separator is further disposed on the positive electrode. When the positive electrode is housed in a separator that is welded to form a bag, air may remain in the separator. However, when manufacturing a battery using such a positive electrode, when the outer case and the sealing case are caulked, the residual air is well discharged outside the separator through the non-welded portions 7d and 7d. Occurrence of problems due to residual air in the separator (problems such as non-uniform reaction during power generation and reduced capacity) can be prevented.

  When providing a non-welding part in the peripheral part of a separator, it is preferable that the number shall be about 1-5 from a viewpoint of suppressing the productivity fall of a battery. Moreover, when providing a non-welding part in the peripheral part of a separator, the length of the outer edge of the non-welding part related to the main part of the separator is the total length of the outer edge related to the main part of the separator (the total length of the outer edge excluding the overhanging part) Is preferably about 15 to 60%. That is, in the main part of the separator, it is preferable that 40% or more (preferably 70% or more) of the entire length of the outer edge is a joined part, thereby ensuring good joining strength between the separators. Can do.

  In order to form a joint portion at the peripheral edge of two separators and accommodate the positive electrode between these separators, for example, the layer is placed at a place where it is planned to be a joint portion on one separator. A film is placed, a positive electrode is disposed on the separator, and a separator is further stacked thereon, and then a peripheral portion of these separators is welded. In addition, a film to be the layer is placed in a place where it is planned to become a joint portion on one separator, and the separator and the film are previously welded. Adopting a method of laminating the peripheral portion by overlapping, or a method of inserting a positive electrode between these separators after forming a joined portion by interposing a film serving as the layer between two separators. You can also.

  For example, the peripheral edge of the separator can be welded by a hot press. In this case, the heating temperature may be a temperature higher than the melting point of the thermoplastic resin constituting the separator, but for example, the heating temperature is preferably 10 to 50 ° C. higher than the melting point. Moreover, about the time of a hot press, if a junction part can be formed satisfactorily, there will be no restriction | limiting, However, Usually, it shall be about 1 to 10 second.

  As described above, the microporous membrane constituting the separator is usually produced through a stretching process, but generally, the strain in the production direction (MD direction) is perpendicular to the production direction (TD direction). Larger than Therefore, in such a microporous film, the thermal shrinkage rate is anisotropic, and the thermal shrinkage rate in the direction corresponding to the MD direction is large, while the thermal shrinkage rate is small in the TD direction.

Therefore, for example, the heat shrinkage ratio Ca at 100 ° C. in an arbitrary direction A (usually corresponding to the MD direction of the microporous film) is 1 to 20%, and a direction B (usually fine) when the thermal shrinkage at 100 ° C. in corresponding to the TD direction of the porous film) was Cb (%), the ratio Ca / C b of the thermal shrinkage Ca and thermal shrinkage Cb is preferably 1.5 or more In the case where the electrode group is configured by using a separator made of a microporous membrane that is more preferably 2 or more, it is preferable to arrange the separator so that the direction A and the direction B are in a specific direction. . In addition, it is preferable that the thermal contraction rate Cb of a separator (microporous film which comprises a separator) is 0 to 10%.

  In FIG. 4, the direction A in the microporous membrane constituting the separator 7 is indicated by a dotted arrow, and the direction B is indicated by a solid arrow. Specifically, as shown in FIG. In the separators 7 existing on both sides, the direction B is substantially parallel to the direction in which the current collecting tab portion 5b of the positive electrode 5 protrudes from the main body portion 5a (in the horizontal direction in the figure). It is preferable to arrange in such a manner.

  As shown in FIG. 4, in the battery of the present invention, the two separators 7 arranged on both surfaces of the positive electrode 5 have at least a part of the peripheral portion of the main portion 7a as the joint portion 7c. Of the peripheral portion of 7b, at least a portion where the current collecting tab portion 5b of the positive electrode 5 protrudes cannot be a joint portion. Therefore, for example, when the separator 7 is arranged so that the direction in which the thermal contraction rate of the separator 7 is large (the direction A) is substantially parallel to the direction in which the current collecting tab portion 5b of the positive electrode 5 protrudes from the main body portion 5a. When the inside of the battery becomes high temperature, large contraction occurs in the protruding portion 7b, and the vicinity of the boundary portion with the main body portion 5a in the current collecting tab portion 5b of the positive electrode 5 (that is, the vicinity of the negative electrode adjacent to the positive electrode 5). May be exposed, and such a portion may come into contact with the negative electrode to cause a short circuit.

  However, when the direction B in the separator 7 is substantially parallel to the direction in which the current collecting tab portion 5b of the positive electrode 5 protrudes from the main body portion 5a, even when the temperature inside the battery becomes high, the overhanging portion 7b Since the shrinkage is suppressed, the contact between the current collecting tab portion 5b of the positive electrode 5 and the negative electrode can be prevented, and the occurrence of a short circuit can be suppressed.

  When the direction B in the separator 7 is substantially parallel to the direction in which the current collecting tab portion 5b of the positive electrode protrudes from the main body portion 5a, the direction A that is more likely to be thermally contracted is indicated by a dotted arrow in FIG. In this direction, shrinkage at high temperatures is suppressed by the joint 7c formed at the peripheral edge of the separator 7.

  Therefore, the safety of the battery at high temperatures can be further enhanced by using the electrode group configured by arranging the separator as described above.

In addition, the thermal contraction rate Ca and Cb of the separator (microporous film constituting the separator) referred to in the present specification is determined by placing the separator in a constant temperature bath at 100 ° C. for 1 hour, and measuring the dimensions of the separator before and after that with a projector. Measure and calculate by the following formula.
Thermal shrinkage (%) = 100 x (dimension before throwing-dimension after throwing) / (dimension before throwing)

  In the battery shown in FIG. 1 and FIG. 2, both the upper and lower electrodes (the two outermost electrodes) in the electrode group are negative electrodes. In the battery of the present invention, the embodiment shown in FIG. 1 and FIG. In contrast, one or both of the upper and lower electrodes (the two outermost electrodes) in the electrode group may be used as a positive electrode. In addition, when the electrode on the side close to the battery case (for example, the outer case) that also serves as the positive electrode terminal is used as the positive electrode among the outermost electrodes of the electrode group, this positive electrode has a positive electrode mixture layer on both sides of the current collector. However, it may be in contact with a battery case (for example, an exterior case) that also serves as a positive electrode terminal only at the current collecting tab portion, and has a positive electrode mixture layer only on one side of the current collector (the surface inside the battery). The exposed surface of the body may be electrically connected by being welded to the inner surface of a battery case (for example, an exterior case) that also serves as the positive electrode terminal, or by direct contact without being welded.

  When both the upper and lower electrodes (the two outermost electrodes) in the electrode group are positive electrodes, the connection between the negative electrode terminal and the battery case (for example, a sealing case) and the negative electrode is connected to the current collecting tab of each negative electrode. The parts can be electrically connected to each other, and these can be welded to the inner surface of a battery case (for example, a sealing case) that also serves as the negative electrode terminal, or directly contacted without welding.

  Further, in the battery of the present invention, separators are disposed on both surfaces of the positive electrode at least on both sides facing the negative electrode, but only the positive electrode disposed on the outermost part of the electrode group, that is, one side (one surface) is opposed to the negative electrode. With respect to the positive electrode, separators may be disposed on both surfaces thereof (joint portions may be formed on these two separators), or the separator may be disposed only on the surface facing the negative electrode. Absent. Furthermore, when both the outermost electrodes related to the electrode group are positive electrodes, and separators are not arranged on both surfaces of these positive electrodes, the battery case serving also as the negative electrode terminal and the outermost positive electrode of the electrode group, An insulator such as an insulating seal made of a tape formed of polyethylene terephthalate (PET) or polyimide is disposed.

  Also, for the electrical connection between the current collecting tab portion of each positive electrode and the battery case that also serves as the positive electrode terminal, and the electrical connection between the current collecting tab portion of each negative electrode and the battery case that also serves as the negative electrode terminal, You may perform via a separate lead body (lead body comprised with metal foil etc.).

  The positive electrode mixture layer of the positive electrode according to the battery of the present invention is a layer containing a positive electrode active material, a conductive additive, a binder and the like.

Examples of the positive electrode active material according to the battery of the present invention include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _2. lithium transition metal composite such as _{Li x Ni 1-y M y} O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 (However, in each of the above lithium transition metal composite oxides, M is at least one selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, and Cr.) It is a metal element, and 0 ≦ x ≦ 1.1, 0 <y <1.0, and 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.

  Moreover, as a conductive support agent of a positive electrode, carbon black, scale-like graphite, ketjen black, acetylene black, fibrous carbon etc. are mentioned, for example. Furthermore, examples of the binder for the positive electrode 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 or the like 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 other methods may be used.

  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. From the viewpoint of reducing the total thickness of the positive electrode and increasing the number of layers of the positive electrode and the negative electrode in the battery to increase the facing area between the positive electrode mixture layer and the negative electrode agent layer and improving the load characteristics of the battery, It is preferable to use a metal foil for the current collector. 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) The paste containing the negative electrode mixture may be applied to a current collector made of metal foil, expanded metal, plain weave metal mesh, etc., dried, and then pressed to form a negative electrode layer (negative electrode composite). The negative electrode can be produced by forming an agent layer. 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 layer (including 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. From the viewpoint of reducing the total thickness of the negative electrode and increasing the number of layers of the positive electrode and negative electrode in the battery to increase the facing area between the positive electrode mixture layer and the negative electrode agent layer, and improving the load characteristics of the battery, It is preferable to use a metal foil for the current collector. Moreover, it is preferable that the thickness of a collector is 5-30 micrometers, for example.

  A separator made of a microporous film made of a thermoplastic resin is used. As the thermoplastic resin constituting the separator, for example, polyolefins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, polymethylpentene, and the like are preferable. From the viewpoint of arranging and welding the same type of resin as the constituent resin, the melting point, that is, the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K 7121 is 100. A polyolefin of ˜180 ° C. is more preferable.

  As the form of the microporous film made of the thermoplastic resin constituting the separator, any form may be used as long as it has an ionic conductivity sufficient to obtain the required battery characteristics. Or the ion-permeable microporous film (microporous film currently used widely as a battery separator) which has many holes formed by the wet extending | stretching method etc. is preferable.

  The thickness of the separator is preferably, for example, 5 to 25 μm, and the porosity is preferably, for example, 30 to 70%.

  Moreover, the layer for interposing between the two separators arranged on both surfaces of the positive electrode to form a joint portion is composed of the same kind of resin as the constituent resin of the separator. A film made of the same kind of resin can be used. The thickness of the film is preferably 5 to 25 μm, for example.

  The positive electrode, the negative electrode, and the separator are stacked and used as a stacked electrode group as shown in FIG. 1 and FIG. 2, and the current collecting tab portion of each positive electrode is the same in a plan view of the electrode group. It is preferable that the current collecting tabs of the negative electrodes are arranged so as to face in the same direction in the plan view of the electrode group. Thereby, current collection of the positive electrode and the negative electrode becomes easier.

  Furthermore, the current collecting tab portion of each positive electrode and the current collecting tab portion of each negative electrode only need to be arranged so as not to contact each other in a plan view of the electrode group, but these contacts are better suppressed, And from the viewpoint of making the production of the battery better, as shown in FIG. 4, the current collecting tab portion 5b of each positive electrode and the current collecting tab portion 6b of each negative electrode face each other in a plan view of the electrode group. More preferably, it is arranged at a position where

  In addition, as shown in FIG. 4, the electrode group formed by laminating the positive electrode, the negative electrode, and the separator is bound to the outer periphery with a binding tape 9 made of polypropylene having chemical resistance, etc. It is preferable to suppress misalignment of the positive electrode and the negative electrode wrapped in the separator.

  There are a plurality of positive electrodes and negative electrodes in the electrode group, and the total number of layers of the electrode is at least 4, but it is also possible to make it more (5 layers, 6 layers, 7 layers, 8 layers, etc.) It is. However, if the number of stacked positive and negative electrodes is increased too much, the merit as a flat battery may be reduced. Therefore, it is usually preferable to have 40 layers or less.

  Examples of non-aqueous electrolytes for batteries include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonate esters such as dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate. 1,2-dimethoxyethane, diglyme (diethylene glycol methyl ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), 1,2-dimethoxyethane, 1,2-diethoxymethane, tetrahydrofuran, etc. It is possible to use an electrolytic solution prepared by dissolving an electrolyte (lithium salt) in a concentration of about 0.3 to 2.0 mol / L in an organic solvent such as ether; That. 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.

  The planar shape of the flat non-aqueous secondary battery of the present invention is not particularly limited, and may be a polygonal shape such as a square (quadrangle) in addition to the circular shape that is the mainstream of conventionally known flat batteries. 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. Moreover, the planar shape of the main body part of the positive electrode and the negative electrode may be a shape corresponding to the planar shape of the battery, and may be a substantially circular shape or a polygon such as a rectangle such as a rectangle or a square. In the case of a substantially circular shape, the portion corresponding to the location where the current collecting tab portion of the counter electrode is disposed is cut off as shown in FIG. 3 in order to prevent contact with the current collecting tab portion of the counter electrode. It is preferable to keep it.

  In FIG. 1 and FIG. 2, an example in which the outer case is a positive electrode case and the sealing case is a negative electrode case is shown, but the battery of the present invention is not limited to this, and if necessary, the outer case is a negative electrode case. The sealing case may be a positive electrode case.

  The flat non-aqueous secondary battery of the present invention can be applied to the same use as a conventionally known flat non-aqueous secondary battery.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<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. When applying the positive electrode mixture-containing paste, the application part and the non-application part were continuously arranged every 5 cm, and the part that was the application part on the front surface was also the application part on the back surface. Subsequently, the applied positive electrode mixture-containing paste was dried to form a positive electrode mixture layer, and then roll-pressed and cut into a predetermined size to obtain a belt-like positive electrode. The positive electrode had a width of 40 mm, and the positive electrode mixture layer forming portion had a thickness of 140 μm.

  The shape of the belt-like positive electrode shown in FIG. 3 is such that the positive electrode mixture layer forming portion is the main body portion (arc portion diameter 15.1 mm) and the positive electrode mixture layer non-forming portion is the current collecting tab portion. The battery positive electrode was obtained.

<Integration of battery positive electrode and separator>
A PE microporous membrane separator (thickness 16 μm, heat shrinkage ratio Ca in direction A is 4%, heat shrinkage ratio Cb in direction B is 2%, Ca / Cb = 2) is shown in FIGS. 4 and 5 ( In FIG. 5, the length of i was 5 mm and the length of ii was 0.8 mm), and the direction B was cut out so that it was parallel to the direction in which the overhanging portion protruded from the main portion.

  The separator is disposed on both surfaces of the battery positive electrode, and a film (thickness: 100 μm) composed of the same PE as the constituent resin of the separator is disposed in the two separators illustrated in FIG. The place where this film is arranged is welded by a hot press (temperature 170 ° C., press time 2 seconds), and a joining portion is formed via a PE layer on a part of the peripheral portion of the main body according to the two separators, The battery positive electrode and the separator were integrated. In addition, the width | variety of the junction part concerning two separators was 0.3 mm. Of the outer edges of the main parts of the two separators, 90% of the length was used as the joint.

<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 one or both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm by an applicator. In addition, when applying the negative electrode mixture-containing paste, when the coated part and the non-coated part are continuously applied every 5 cm and are applied to both sides of the current collector, the place where the coated part is the surface is the back side However, it was made to become an application part. Subsequently, the applied negative electrode mixture-containing paste was dried to form a negative electrode mixture layer, and then roll-pressed and cut into a predetermined size to obtain a strip-shaped negative electrode. The negative electrode had a width of 40 mm, and the negative electrode mixture layer forming portion had a thickness of 190 μm when formed on both sides of the current collector and 100 μm when formed on one side of the current collector.

  The strip-shaped negative electrode has the same shape as the positive electrode so that the negative electrode mixture layer forming portion is the main body portion (arc portion diameter 16.3 mm) and the negative electrode mixture layer non-forming portion is the current collecting tab portion. The negative electrode for a battery having a negative electrode mixture layer on one side of the current collector and the negative electrode for a battery having a negative electrode mixture layer on both sides of the current collector were obtained. A part of the negative electrode for a battery having the negative electrode mixture layer on one side of the current collector was punched after a PET film having a thickness of 100 μm was attached to the exposed surface of the current collector of the strip-shaped negative electrode. .

<Battery assembly>
7 positive electrodes for a battery integrated with the separator, 6 negative electrodes for a battery in which a negative electrode mixture layer is formed on both sides of the current collector, and a negative electrode for a battery in which a negative electrode mixture layer is formed on one side of the current collector The battery negative electrode with a negative electrode mixture layer formed on one side of the current collector was used as the outermost electrode using two sheets (one of which was a PET film affixed to the exposed surface of the current collector) The battery positive electrode and the battery negative electrode were alternately stacked. And the current collection tab part of each battery positive electrode was welded collectively, and the current collection tab part of each battery negative electrode was welded collectively, and the electrode group was formed. The electrode group was placed in the outer case so that the PET film faced the inner surface of the outer case, and the collected current collecting tab portion of the positive electrode was welded to the inner surface of the outer case. In addition, an insulating gasket was attached to the sealing case, and a non-aqueous electrolyte (LiPF ₆ dissolved 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) 200 mg After putting, the outer case containing the electrode group was covered and the periphery was caulked to obtain a flat non-aqueous secondary battery having a diameter of 20 mm and a thickness of 3.2 mm. The flat non-aqueous secondary battery is designed to discharge at a current value of 14 mA and a discharge capacity of 70 mAh.

Comparative Example 1
A PET film having an ethylene vinyl acrylate as an adhesive resin on both sides, instead of a PE film, instead of a PE film instead of a film that is interposed between two separators arranged on both sides of the positive electrode (PET film thickness is 100 μm) A flat nonaqueous secondary battery was produced in the same manner as in Example 1 except that.

  The batteries of Example 1 and Comparative Example 1 (20 batteries each) were charged at a current value of 35 mAh until the voltage reached 4.2 V, and then charged at a constant current of 4.2 V—constant current-constant voltage charging For 3 days and then stored in an 80 ° C. environment for 50 days. Each battery after storage was dropped 10 times from a height of 1.9 m, and then the presence or absence of heat generation was confirmed.

  As a result of the test, in all of the 20 batteries of Example 1, no heat was generated, but in the battery of Comparative Example 1, 3 out of 20 batteries had two separators arranged on both sides of the positive electrode, and these separators. Heat was generated due to peeling between the PET film and the PET film.

DESCRIPTION OF SYMBOLS 1 Flat type non-aqueous secondary battery 2 Exterior case 3 Sealing case 4 Insulating gasket 5 Positive electrode 5a Positive electrode main body 5b Positive electrode current collecting tab 6 Negative electrode 6a Negative electrode main body 6b Negative electrode current collecting tab 7 Separator 7a Main body 7b Separator overhang 7c Joint

Claims (3)

In a space formed by caulking and sealing the outer case and the sealing case via an insulating gasket, there is an electrode group in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked via a separator and a non-aqueous electrolyte. A flat non-aqueous secondary battery,
The positive electrode has a main body portion and a current collecting tab portion that protrudes from the main body portion in a plan view and is narrower than the main body portion. The main body portion of the positive electrode includes a current collector. A positive electrode mixture layer containing a positive electrode active material is formed on one side or both sides, and in the current collector tab portion of the positive electrode, a positive electrode mixture layer is not formed on the current collector,
The negative electrode has a main body portion and a current collecting tab portion that protrudes from the main body portion in a plan view and is narrower than the main body portion. The main body portion of the negative electrode includes a current collector. A negative electrode agent layer containing a negative electrode active material is formed on one side or both sides, and in the current collector tab portion of the negative electrode, the negative electrode agent layer is not formed on the current collector,
At least a separator made of a microporous film made of a thermoplastic resin is disposed on both sides of the positive electrode facing both sides of the negative electrode,
The two separators include a main body that covers the entire surface of the main body of the positive electrode, and an overhang that protrudes from the main body and covers at least a portion of the current collecting tab of the positive electrode that includes a boundary with the main body. Have
In addition, the two separators have a joining portion welded via a layer made of the same type of resin as the thermoplastic resin constituting the two separators in at least a part of the peripheral portion of the main portion. and it is,
Said two separators, flat-shaped nonaqueous secondary battery, wherein the junction der Rukoto 40% or more of the outer edges total length in the main portion. The two separators arranged on both sides of the positive electrode have a heat shrinkage ratio Ca at 100 ° C. in an arbitrary direction A of 1 to 20%, and heat shrinkage at 100 ° C. in a direction B orthogonal to the direction A. when rates were as Cb (%) protruding, the ratio Ca / C b of the thermal shrinkage Ca and thermal shrinkage Cb is not less than 1.5, the direction B is, from the collector tab portion main body portion of the positive electrode flat-shaped nonaqueous secondary battery according to claim 1 which is arranged to be flat line in the direction of. The flat non-aqueous secondary battery according to claim 1 or 2 , wherein the thermoplastic resin constituting the separator is polyolefin.

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