JP2009181833A - Non-aqueous secondary battery and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery capable of inhibiting rupture of an electrode plate and dropping of an electrode mix, reduced in unevenness of its capacity and having high reliability, by adapted to have such a configuration that the density of an active material of at least one of a positive electrode plate and a negative electrode plate is partly reduced at the inner circumferential surface and the outer circumferential surface of an electrode group. <P>SOLUTION: The non-aqueous secondary battery is configured such that the density of the active material of the electrode plate is partly reduced at the inner circumferential surface and the outer circumferential surface of the electrode group through a first step of applying a coating of a positive electrode mix and a coating of a negative electrode mix so as to form at least one portion 3 of a current collector 1 where the thickness of the coating is reduced, and a second step of drying the coating of the positive electrode mix or the negative electrode mix, and then applying pressing so as to provide a portion 7 where the density of the active material of the electrode plate is reduced in at least one portion of the positive electrode plate or the negative electrode plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous secondary battery represented by a lithium ion secondary battery and a method for producing the same.

In recent years, lithium ion secondary batteries, which are widely used as power sources for portable electronic devices, use a carbonaceous material capable of occluding and releasing lithium for the negative electrode plate, and a transition metal such as LiCoO ₂ and lithium for the positive electrode plate. As a result, a secondary battery with a high potential and a high discharge capacity has been realized. However, with the recent increase in functionality of electronic and communication devices, the capacity has further increased. Is desired. Here, as an electrode plate for realizing a high-capacity non-aqueous secondary battery, a mixture paint obtained by coating each constituent material for both the positive electrode plate and the negative electrode plate is applied and dried on a current collector, and then pressed. Thus, a method of compressing to a specified thickness is used. At this time, the active material density is increased by filling and pressing a larger amount of the active material, and the capacity can be further increased.

  However, when the active material density of the electrode plate is increased, the flexibility of the electrode plate is insufficient, and there is a problem that the electrode plate is broken when the electrode plate is wound. As a factor that causes breakage during winding, the mixture on the inner peripheral side of the winding is compressed by the compressive stress of the winding, and the current that cannot be absorbed by the mixture reaches the current collector, and the limit of the breaking stress of the current collector Cutting occurs when the value exceeds. Therefore, in order to relieve the compressive stress of the electrode plate, a method of reducing the density of the inner peripheral surface of the winding can be considered. For example, as shown in FIG. As shown in FIG. 6 (b), an electrode mixture layer in which the active material density continuously decreases or increases is formed by applying the coating material while continuously decreasing or increasing the coating amount, and then drying and pressing. A method has been proposed (see, for example, Patent Document 1).

Moreover, in order to suppress the cutting | disconnection of the electrode plate in the process of pressing, as shown, for example in FIG. 7, the method of changing continuously the thickness of the mixture layer of the electrode plate of a coating end is proposed. (For example, refer to Patent Document 2).
Japanese Patent No. 3614984 JP 2004-303622 A

  However, the above-described prior art of Patent Document 1 aims to stabilize the battery capacity by preventing the mixture from falling off, and does not consider the breakage of the electrode plate. Lowering the density has an effect on cutting at the time of winding. In this case as well, it is possible to absorb the compressive stress on the inner circumference side of the winding, but the density is continuously changed on both sides of the electrode plate. However, it is necessary to continuously control the coating weight precisely, and it is difficult to stably manufacture the electrode plate.

  Moreover, the prior art of patent document 2 suppresses the cutting | disconnection at the time of rolling, and does not consider the cutting | disconnection of the electrode plate at the time of winding. In general, if the thickness is reduced, an effect can be seen in cutting during winding. In this case as well, it is possible to absorb the compressive stress on the inner periphery of the winding, but the effect on cutting the electrode plate compared to the density On the other hand, in coating coating, it is necessary to continuously and accurately control the coating thickness, and it is difficult to stably produce an electrode plate.

The present invention has been made in view of the above-described conventional problems, and in the electrode group formed by winding the positive electrode plate and the negative electrode plate, the active material density of at least a part of the inner peripheral side at the time of winding is the outer peripheral side at the time of winding. By forming a portion smaller than the active material density, it is possible to suppress the breakage of the electrode plates, and to provide a production method capable of stably producing these electrode plates, thereby reducing battery capacity variation and good It aims at providing the non-aqueous secondary battery which shows a lifetime characteristic.

  In order to achieve the above object, the non-aqueous secondary battery of the present invention is a positive electrode in which an active material composed of at least a lithium-containing composite oxide, a conductive material, and a water-insoluble polymer binder are kneaded and dispersed in a dispersion medium. A negative electrode mixture in which a positive electrode plate obtained by applying a mixture paint on a positive electrode current collector, an active material made of a material capable of holding at least lithium, and a water-insoluble polymer binder are kneaded and dispersed in a dispersion medium. A non-aqueous secondary battery comprising an electrode group formed by winding a negative electrode plate and a separator spirally coated with a paint on a negative electrode current collector and a non-aqueous solvent, The active material density on the inner peripheral side of at least one of the positive electrode plate and the negative electrode plate is partially smaller than the active material density on the outer peripheral side.

  According to the nonaqueous secondary battery of the present invention, the active material density of at least one of the positive electrode plate and the negative electrode plate is partially reduced on the inner peripheral side and the outer peripheral side of the electrode group, so that the flexibility of the electrode plate is increased. Since the cutting of the electrode plate when the electrode plate is processed into a sheet shape and when the electrode plate is wound can be suppressed, a highly reliable non-aqueous secondary battery can be obtained.

  In the first invention of the present invention, a positive electrode mixture paint obtained by kneading and dispersing at least an active material composed of a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium is applied onto a positive electrode current collector. A negative electrode plate constituted by applying a negative electrode mixture paint obtained by kneading and dispersing an active material made of a material capable of holding lithium and a binder in a dispersion medium onto a negative electrode current collector; A non-aqueous secondary battery comprising an electrode group formed by winding a separator in a spiral shape and an electrolyte solution comprising a non-aqueous solvent, wherein the active material density of at least one of a positive electrode plate and a negative electrode plate is By making the active material density on the inner peripheral side of the electrode group smaller than the active material density on the outer peripheral side, when the positive electrode plate, the negative electrode plate, and the separator are spirally wound, the active material density of the positive electrode plate or the negative electrode plate Bending to the electrode plate at a small area Stress relieve, it is possible to suppress the cutting of the electrode plate, it is possible to provide a highly reliable non-aqueous secondary battery.

  In the second aspect of the present invention, at least one portion of the positive electrode plate and the negative electrode plate having a small active material density includes a coating end portion at the innermost circumference when the electrode group is wound. By adopting the configuration, it is possible to relieve the compressive stress at a portion having a large curvature at the time of winding and further suppress the breakage of the electrode plate.

  In the third aspect of the present invention, the portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is at least from the innermost coating end with respect to the longitudinal direction of the electrode plate. By setting the range up to one turn, it is possible to include a portion having a large curvature at the time of winding over a wide range, and it is possible to further suppress the breakage of the electrode plate.

  In the fourth aspect of the present invention, the thickness of the portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is the same as the other portions, so that the electrode at the time of winding is obtained. It is possible to relieve the bending stress to the plate and suppress the breakage of the electrode plate.

  In the fifth aspect of the present invention, the electrode at the time of winding is configured by differently forming the thickness of the portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate from the other portions. The bending stress to the plate is further relaxed, and it is possible to further suppress the breakage of the electrode plate.

  In a sixth aspect of the present invention, a positive electrode mixture paint obtained by kneading and dispersing at least an active material composed of a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium is applied onto a positive electrode current collector. A negative electrode plate constituted by applying a negative electrode mixture paint obtained by kneading and dispersing an active material made of a material capable of holding lithium and a binder in a dispersion medium onto a negative electrode current collector; A method for producing a non-aqueous secondary battery comprising an electrode group formed by winding a separator in a spiral shape and an electrolyte comprising a non-aqueous solvent, the positive electrode being at least one of a positive electrode plate and a negative electrode plate The first step of applying and forming the coating amount of the mixture paint or the negative electrode mixture paint so as to be partially different between the inner peripheral side and the outer peripheral side of the electrode group, and predetermined after drying the positive electrode mixture paint or the negative electrode mixture paint Second process pressed to thickness By using the electrode group, it is possible to suppress the breakage of the electrode plate when processing the electrode plate into a sheet shape and when the electrode plate is wound, and to obtain a highly reliable non-aqueous secondary battery. .

  In the seventh invention of the present invention, by controlling the coating amount of the positive electrode mixture paint or the negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector, By making the active material density on the inner peripheral side of at least one of the positive electrode plate and the negative electrode plate smaller than the active material density on the outer peripheral side, the flexibility of the electrode plate is increased, the compressive stress during winding is reduced, and the electrode By suppressing the breakage of the plate, a more reliable non-aqueous secondary battery can be obtained.

  In the eighth aspect of the present invention, the coating amount at the start or end of the application of the positive electrode mixture paint or the negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector is determined. By changing the shape, a portion having a low active material density formed on at least one of the positive electrode plate and the negative electrode plate is formed on the inner peripheral side, and the portion having the low active material density is at least the most when the electrode group is wound. By including the coating edge on the inner circumference, it is possible to change the coating amount at the start of coating or at the end of coating on the same surface, alleviating the compressive stress during winding, and cutting the electrode plate This makes it possible to obtain a highly reliable non-aqueous secondary battery.

  In the ninth aspect of the present invention, the application amount of the positive electrode mixture paint or the negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector is applied for a certain period of time. By changing after the elapse of time, the portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is separated from the coating end portion at least on the innermost circumference with respect to the longitudinal direction of the electrode group. By forming in the range up to, it is possible to include a portion having a large curvature at the time of winding, and it is possible to manufacture a more flexible electrode plate, and it is more reliable by suppressing the breakage of the electrode plate An aqueous secondary battery can be obtained.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a non-aqueous secondary battery of the present invention. After preparing the electrode group 14 which wound the positive electrode plate 5 which uses a composite lithium oxide as an active material, and the negative electrode plate 9 which uses the material which can hold | maintain lithium as an active material through the separator 10, it produces electrode group 14 is housed in the bottomed cylindrical battery case 11 together with the insulating plate 15, the negative electrode lead 16 led out from the lower part of the electrode group 14 is welded to the bottom part of the battery case 11, and then led out from the upper part of the electrode group 14. After the positive electrode lead 17 is welded to the sealing plate 12 and a predetermined amount of an electrolyte solution (not shown) made of a nonaqueous solvent is injected into the battery case 11, the sealing gasket 13 is attached to the periphery of the opening of the battery case 11. The sealing plate 12 is inserted, and the opening of the battery case 11 is bent inward to be caulked and sealed.

Next, with reference to FIG. 4, the state of the electrode plate breakage that occurs when the electrode plate and the separator are actually wound to form the electrode group will be described. FIG. 4 is a schematic view of a winding device that forms a group of electrodes by winding the positive electrode plate 5, the negative electrode plate 9, and the separator 10. In FIG. 4, a positive plate transport unit 25 having a plurality of roller units for transporting the positive electrode plate 5, a negative plate transport unit 26 having a plurality of roller units for transporting the negative electrode plate 9, the positive plate 5 and the negative plate 9. And a separator 27 for winding the separator 10 together. Winding is performed by applying tension while rotating and pulling the winding portion 27 so that the positive electrode plate 5, the negative electrode plate 9, and the separator 10 are not bent.

  Factors of electrode plate breakage that occur when the electrode group 14 is configured using the winding device described above are roughly divided into the following two. First, when the positive electrode plate 5 is wound around a plurality of roller portions of the conveyance unit 25 and conveyed, the negative electrode plate 9 receives a bending stress due to the curvature of the roller unit, or the negative electrode plate 9 has a plurality of rollers of the conveyance unit 26. The electrode plate is cut by receiving bending stress due to the curvature of the roller portion when being wound around the portion. Second, the electrode plate breaks due to the bending stress caused by the curvature at the winding portion 27 and the tensile stress caused by the tension applied to the positive electrode plate 5 or the negative electrode plate 9.

  Further, the cause of the breakage of the electrode plate at the winding part of the winding device will be described in more detail with reference to FIG. FIG. 3 shows a cross-sectional view of the cylindrical electrode group 14, in which the positive electrode plate 5, the negative electrode plate 9, and the separator 10 are wound. Further, the portion from the innermost coating end portion 5a to the first winding 5b in the positive electrode plate 5 and the portion from the innermost coating end portion 9a to the first winding 9b in the negative electrode plate 9 are the positive electrode plate. 5 and the negative electrode plate 9 have the largest curvature, and the tensile stress at the time of winding is concentrated, so that the electrode plate is easily cut. Hereinafter, the number of turns in the positive electrode plate 5 and the negative electrode plate 9 when the electrode group 14 is configured starts from the innermost coating end portion 5a, and the first round 5b, and the innermost circumference A place where the winding starts from the coating end portion 9a and makes one turn is defined as a first turn 9b.

  In order to suppress the breakage of the electrode plate that occurs when the electrode group 14 is configured as described above, the bending stress applied to the electrode plate can be relaxed at the winding portion where the radius of curvature of the electrode group 14 is reduced. As a result of intensive studies from this viewpoint, the electrode plate of the nonaqueous secondary battery of the present invention has the largest curvature of the positive electrode plate 5 when the spiral electrode group 14 is formed as shown in FIG. Intermittently or continuously within a range from the coating end portion 5a to the first winding 5b, which is a portion, and a range from the coating end portion 9a to the first winding 9b, which is a portion where the curvature of the negative electrode plate 9 is the largest. In particular, the present inventors have newly found that it is possible to suppress breakage of the electrode plate by forming a portion having a low active material density.

  In order to form a portion having a low active material density on the electrode plate for a non-aqueous secondary battery as described above, first, the positive electrode plate 5 or the negative electrode plate 9 is formed of the current collector 1 as shown in FIG. It is produced through a first step of applying and forming a portion 3 where the thickness of the electrode mixture paint 2 is reduced in at least one place. In this first step, as a method of applying and forming the portion 3 where the thickness of the electrode mixture paint 2 becomes thin, a collector is intermittently provided in the longitudinal direction of the positive electrode plate 5 or the negative electrode plate 9 using a die coater or the like. An intermittent coating system can be used to form the film. In this intermittent system, the electrode mixture paint 2 discharged from the tip of the die can be stopped by adjusting the pressure inside the die manifold to a negative pressure, but the electrode as shown in FIG. In order to apply and form the portion 3 where the thickness of the mixture paint 2 is reduced, the timing at which the pressure is released after the inside of the die manifold is made negative and the electrode mixture paint 2 is re-discharged is important. When the width of the portion where the thickness of the electrode mixture paint 2 becomes thin is W, the portion 3 where the thickness of the electrode mixture paint 2 becomes thin can be formed with the width W by adjusting the timing accurately. Here, the width W corresponds to the length of one turn in the winding, and is a portion from the coating end 5a to the first turn 5b or a portion from the coating end 9a to the first turn 9b in FIG. .

Next, after the electrode mixture paint 2 is dried, a second step of pressing to a predetermined thickness is performed to form a portion having a low active material density in at least one portion of the positive electrode plate 5 or the negative electrode plate 9. As shown in FIG. 5A, when the thickness of the portion 3 where the thickness of the electrode mixture paint 2 is reduced as T is T, as shown in FIG. The method of forming the portion 7 where the active material density of the electrode mixture layer 6 is small, and the active material density remains after coating and drying by pressing to a thickness T or more as shown in FIG. Although it is possible to form the portion 7 and the recessed portion 8 having a low active material density on the positive electrode plate 5 or the negative electrode plate 9 by the method of forming the recessed portion 8 on the electrode plate, it is not limited to these.

  Hereinafter, an example of a method for producing an electrode plate according to the present invention will be described. When the electrode plate applied to the present invention is wound to form an electrode group, it is necessary to have toughness that does not cause cracking or dropping of the electrode mixture layer. The prescription of the electrode plate is not limited to the following method as long as this toughness can be exhibited. First, a positive electrode active material, a conductive material, and a binder are placed in an appropriate dispersion medium, mixed and dispersed by a dispersing machine such as a planetary mixer, and adjusted to an optimum viscosity for application to a current collector. The positive electrode mixture paint was prepared.

  Examples of the positive electrode active material include lithium cobaltate and modified products thereof (such as lithium cobaltate in which aluminum or magnesium is dissolved), lithium nickelate and modified products thereof (such as nickel partially substituted with cobalt). And composite oxides such as lithium manganate and modified products thereof.

  As the conductive material type at this time, for example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and various graphites may be used alone or in combination.

  As the binder for the positive electrode at this time, for example, polyvinylidene fluoride (PVdF), a modified polyvinylidene fluoride, polytetrafluoroethylene (PTFE), a rubber particle binder having an acrylate unit, and the like can be used. At this time, an acrylate monomer or an acrylate oligomer into which a reactive functional group is introduced can be mixed in the binder.

  Using the die coater, the positive electrode mixture paint prepared as described above is applied to form a portion where the thickness of the positive electrode mixture paint is reduced on the aluminum foil by adjusting the pressure inside the manifold of the die coater to a negative pressure, then After drying, it was compressed to a predetermined thickness with a press.

  Next, the negative electrode active material and the binder are placed in an appropriate dispersion medium, mixed and dispersed by a dispersing machine such as a planetary mixer, and adjusted to an optimum viscosity for application to the current collector, and then kneaded. A negative electrode mixture paint was prepared. As the negative electrode active material, various natural graphites, silicon-based composite materials such as artificial graphite and silicide, and various alloy composition materials can be used.

  Various binders such as PVdF and modified products thereof can be used as the negative electrode binder at this time. From the viewpoint of improving lithium ion acceptability, styrene-butadiene copolymer rubber particles (SBR) and modified products thereof are used. In addition, it can be said that it is more preferable to use a cellulose resin such as carboxymethyl cellulose (CMC) in combination or to add a small amount.

For the electrolytic solution, it is possible to use various lithium compounds such as LiPF ₆ and LiBF ₄ as an electrolyte salt. Further, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) can be used alone or in combination as a solvent. It is also preferable to use vinylene carbonate (VC), cyclohexylbenzene (CHB), and modified products thereof in order to form a good film on the positive and negative electrodes and to ensure stability during overcharge.

Using the die coater, the negative electrode mixture paint prepared as described above is adjusted to a negative pressure inside the die coater manifold, thereby applying and forming a portion where the thickness of the negative electrode mixture paint is thin on the copper foil. After drying, it was compressed to a predetermined thickness with a press.

  The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium ion secondary battery, but a microporous film of an olefin-based resin such as polyethylene or polypropylene is generally used singly or in combination. Also preferred as an embodiment. The thickness of the separator is not particularly limited, but may be 10 to 25 μm.

  An embodiment of the present invention will be described with reference to the drawings and tables. First, 100 parts by weight of lithium cobaltate as an active material, 2 parts by weight of acetylene black as a conductive material with respect to 100 parts by weight of the active material, and 2 parts by weight of polyvinylidene fluoride as a binder with respect to 100 parts by weight of the active material Was mixed with an appropriate amount of N-methyl-2-pyrrolidone in a double-arm kneader to prepare a positive electrode mixture paint.

  Next, as shown in FIG. 5 (a), the positive electrode mixture paint is applied to the current collector 1 of aluminum foil having a thickness of 15 μm so that the width W of the portion 3 where the thickness is reduced becomes the length of one turn. After coating and drying, a positive electrode plate was prepared in which the thickness of the positive electrode mixture layer on one side was 100 μm and the thickness T of the portion 3 where the thickness of the positive electrode mixture layer was reduced was 75 μm.

  Further, as shown in FIG. 5B, the positive electrode plate is pressed so that the total thickness becomes 180 μm, whereby the active material density of the positive electrode mixture layer having a mixture single-sided thickness of 82.5 μm is small. 7 was formed. Thereafter, slitting was performed, and the positive electrode plate 5 was produced.

  Further, separately from the positive electrode plate, the positive electrode mixture paint is applied to a current collector 1 made of 15 μm thick aluminum foil so that the thickness of the positive electrode mixture layer is 100 μm after drying. Pressing was performed so that the total thickness was 180 μm, and slit processing was performed to a prescribed width of the cylindrical battery, to produce a positive electrode plate having a constant active material density.

  On the other hand, 100 parts by weight of artificial graphite as an active material for the negative electrode plate, and 2.5 parts by weight of styrene-butadiene copolymer rubber particle dispersion (solid content 40% by weight) as a binder for 100 parts by weight of the active material. (1 part by weight in terms of solid content of the binder), 1 part by weight of carboxymethylcellulose as a thickener with respect to 100 parts by weight of the active material, and an appropriate amount of water are stirred in a double-arm kneader, and the negative electrode A mixture paint was prepared.

  Next, as shown in FIG. 5A, the negative electrode mixture paint is applied to the copper foil current collector 1 having a thickness of 10 μm so that the width W of the portion 3 where the thickness is reduced becomes the length of one turn. After coating and drying, a negative electrode plate was prepared in which the thickness of the negative electrode mixture layer on one side was 110 μm, and the thickness T of the portion where the mixture thickness was reduced was 80 μm. Further, this negative electrode plate was pressed to a total thickness of 170 μm, and then slitted to a specified width of the cylindrical battery to produce a negative electrode plate.

  Separately from the negative electrode plate, the negative electrode paint is applied to a copper foil current collector 1 having a thickness of 10 μm so that the mixture thickness becomes 110 μm after drying, and the total thickness of the negative electrode plate is 170 μm. And slitting into a specified width of the cylindrical battery to prepare a negative electrode plate having a constant active material density.

The positive electrode plate and the negative electrode plate are wound as shown in FIG. 2 using a polyethylene microporous film having a thickness of 20 μm as shown in FIG. 2, inserted into the battery case, and 1M of LiPF ₆ and 3% of VC are mixed in an EC / DMC / MEC mixed solvent. An electrolytic solution in which parts by weight were dissolved was added and sealed to prepare a cylindrical lithium ion secondary battery.

  In the above-described cylindrical lithium ion secondary battery, an example of a lithium ion secondary battery manufactured using a positive electrode plate provided with a portion having a small active material density in the electrode mixture layer and a negative electrode plate having a constant active material density A, a lithium ion secondary battery produced using a positive electrode plate 5 having a constant active material density of the electrode mixture layer and a negative electrode plate provided with a portion having a low active material density of the electrode mixture layer. Example B, positive electrode plate Example C was a lithium ion secondary battery prepared by providing a portion where the active material density of the electrode mixture layer was low in both the negative electrode plate and the negative electrode plate.

(Comparative Example 1)
In Example 1 above, a lithium ion secondary battery manufactured using the positive electrode plate 5 having a constant active material density of the electrode mixture layer and the negative electrode plate having a constant active material density of the electrode mixture layer was compared with Comparative Example 1. It was.

  As shown in FIG. 2, the lithium ion secondary battery manufactured under the above conditions is wound around the positive electrode plate 5, the negative electrode plate 9, and the separator 10 to form the electrode group 14, and then the electrode group 14 is disassembled. Evaluation was made on whether the positive electrode plate 5 and the negative electrode plate 9 were cut and the mixture was removed. 100 pieces were evaluated for each example, and the occurrence rate of electrode plate breakage and the occurrence rate of mixture dropout at that time are shown in Table 1.

  As shown in (Table 1), the electrode plates of Examples A to C in which a portion having a low active material density was formed as compared with the electrode plate of Comparative Example 1 in which a portion having a low active material density was not formed on the electrode plate. Was found to be able to suppress electrode plate breakage and mixture dropping during electrode group construction.

  Further, in the electrode plate of Comparative Example 1, when the electrode group was disassembled after being configured, the electrode plate was cut mostly because of the positive electrode plate, and the portion having the smallest curvature when the electrode group was formed. The fracture | rupture in (5a-5b shown in FIG. 3) was confirmed. On the other hand, the mixture drop occurred mostly in the negative electrode plate, and it was confirmed that the mixture was dropped at the portion with the smallest curvature (9a to 9b shown in FIG. 3) when the electrode group was formed. It was.

  Next, the lithium ion secondary battery manufactured under the above conditions was evaluated as follows. First, regarding the battery capacity variation, the battery after being sealed for 7 days in a 45 ° C environment was subjected to initial charge / discharge twice for a finished battery after sealing (a non-defective product without electrode plate breakage and active material removal). 20 battery capacities were measured, and the battery capacity variation in 20 batteries was measured.

  Moreover, as 500 cycle capacity | capacitance maintenance factor, initial charge / discharge was performed twice about the completed battery after sealing, and after storing for 7 days in a 45 degreeC environment, the following charge / discharge cycles were repeated 500 times. For charging, charging is performed at a constant voltage of 4.2 V and 1400 mA. When charging current is reduced to 100 mA, charging is terminated, and discharging is performed at a constant current of 2000 mA and discharging to a final voltage of 3 V as one cycle. The discharge capacity ratio of the 500th cycle with respect to the eyes was measured as a 500 cycle capacity retention rate. The contents evaluated for the above items are shown in (Table 2).

  From the results of (Table 2), it was found that Examples A to C had little variation in battery capacity and improved the capacity maintenance rate of 500 cycles of charge / discharge. This is because the current collection performance is good and the variation in the initial capacity is small because there are few cuts during the winding and the mixture dropout. Further, it was found that even if the electrode plate expands and contracts during the charge / discharge cycle, the balance between the positive electrode plate and the negative electrode plate does not collapse locally, so that the cycle deterioration is small. On the other hand, in Comparative Example 1, since there are many cuts and droppings of the mixture during winding, the current collection performance is poor, and the variation in capacity is large. Further, it has been found that the balance between the positive electrode plate and the negative electrode plate may be locally broken due to the expansion and contraction of the electrode plate that occurs during the charge / discharge cycle, and as a result, the capacity retention rate decreases.

  As in Example 1, first, 100 parts by weight of lithium cobaltate as an active material, 2 parts by weight of acetylene black as a conductive material with respect to 100 parts by weight of the active material, and 100 parts by weight of polyvinylidene fluoride as a binder A positive electrode mixture paint was prepared by stirring and kneading 2 parts by weight with an appropriate amount of N-methyl-2-pyrrolidone in a double-arm kneader. Next, as shown in FIG. 5 (a), this positive electrode mixture paint is applied to a 15 μm thick aluminum foil current collector 1 with a thinned portion 3 applied, and after drying, a single-side positive electrode mixture layer A positive electrode plate with a thickness of 100 μm, a thickness T of the portion where the thickness of the positive electrode mixture layer is reduced to 75 μm, and a width W of 3 mm was produced. The width W of 3 mm corresponds to a quarter turn in the winding.

  Further, as shown in FIG. 5B, the positive electrode plate is pressed so that the total thickness becomes 180 μm, whereby the active material of the positive electrode mixture layer with the thickness of the positive electrode mixture layer on one side being 82.5 μm. A portion 7 having a low density was formed. Thereafter, slitting was performed to produce a positive electrode plate.

Apart from the positive electrode plate, a negative electrode plate was prepared in the same manner as in Example 1. These positive electrode plate and negative electrode plate are wound as shown in FIG. 2 using a 20 μm thick polyethylene microporous film as a separator, inserted into the battery case, and 1M and VC of LiPF ₆ in an EC / DMC / MEC mixed solvent. An electrolytic solution in which 3 parts by weight of the electrolyte was dissolved was added and sealed to prepare a cylindrical lithium ion secondary battery, and Example D was obtained.

  In the same manner, a positive electrode plate provided with a portion where the width W of the portion where the active material density of the electrode mixture layer is small is 6 mm (corresponding to a half turn) and a negative electrode plate having a constant active material density were prepared. Example E, positive electrode plate provided with a portion where the width W of the portion where the active material density of the electrode mixture layer is small is 9 mm (equivalent to three quarter turns) and a negative electrode having a constant active material density Example F, a positive electrode plate provided with a portion where the width W of the portion where the active material density of the electrode mixture layer is small is equivalent to 12 mm (corresponding to one turn) and the active material density of the lithium ion secondary battery produced using the plate A lithium ion secondary battery manufactured using a certain negative electrode plate was manufactured in Example G. A positive electrode plate provided with a portion where the width W of the portion where the active material density of the electrode mixture layer was small was 24 mm (corresponding to two turns) and the active plate Lithium ion secondary battery fabricated using negative electrode plate with constant material density Was as in Example H.

With respect to the lithium battery manufactured under the above conditions, as shown in FIG. 2, after the positive electrode plate 5, the negative electrode plate 9, and the separator 10 are wound to form the electrode group 14, the electrode group 14 is disassembled, and the positive electrode plate 5. Evaluation was made on whether the negative electrode plate 9 was broken and the mixture was removed. 100 pieces were evaluated for each example, and the occurrence rate of electrode plate breakage and the occurrence rate of mixture dropping at that time are shown in Table 3.

  As shown in (Table 3), even if the electrode plate of Comparative Example 1 in which a portion having a low active material density is not formed on the electrode plate or a portion having a low active material density is formed, the range is wound. The electrode plates in Examples D to F of less than one turn cannot be said to have a suppressing effect when the rate of occurrence of electrode plate breakage and the rate of mixture dropout are the same or slightly lower when constituting the electrode group. .

  On the other hand, it was found that Examples G and H in which the portion having a low active material density is one or more turns of the winding can suppress the breakage of the electrode plate and the dropping of the mixture.

  Next, for the lithium ion secondary battery fabricated under the above conditions, the battery capacity variation of 20 batteries and the capacity retention rate of 500 cycles were measured in the same manner as in Example 1.

  The contents evaluated for the above items are shown in (Table 4).

From the results of (Table 4), even if Comparative Example 1 in which a portion having a low active material density is not formed on the electrode plate or a portion having a low active material density is formed, the range is less than one turn of winding. In DF, since the electrode plate was frequently cut and the mixture dropped during winding, the current collection performance was poor, and the capacity variation was large. Further, it has been found that the balance between the positive electrode plate and the negative electrode plate may be locally broken due to the expansion and contraction of the electrode plate that occurs during the charge / discharge cycle, and as a result, the capacity retention rate decreases. On the other hand, it was found that in Examples G to H where the active material density is small in one or more turns, there is little variation in battery capacity, and the capacity retention rate of 500 cycles of charge / discharge is improved. This was because the electrode plate was not cut and the mixture was not dropped during winding, so the current collection performance was good and the initial capacity variation was small. Further, it was found that even when the electrode plate expands or contracts during the charge / discharge cycle, the balance between the positive electrode plate and the negative electrode plate does not collapse locally, so that the cycle deterioration is small.

  In Example 2, a portion having a low density was formed only on the positive electrode plate, but it goes without saying that the same effect can be obtained even if a portion having a low density is formed on the negative electrode plate. Moreover, although the location with a low density was formed continuously, it cannot be overemphasized that the same effect is acquired even if it forms intermittently.

  From the above results, by using the present invention, it is possible to suppress the breakage of the electrode plate when configuring the electrode group, to realize a non-aqueous secondary battery with less capacity variation and excellent cycle characteristics. Is possible.

  When the non-aqueous secondary battery according to the present invention forms a portion having a low active material density on at least one of the positive electrode plate and the negative electrode plate compressed to a specified thickness, By making the location where the curvature is the largest, there is less capacity variation and better charge / discharge cycle characteristics than conventional non-aqueous secondary batteries. It is useful as a portable power source and the like for which capacity is desired.

1 is a partially cutaway perspective view of a cylindrical non-aqueous secondary battery according to an embodiment of the present invention. Schematic showing a positive electrode plate and a negative electrode plate according to the same embodiment Sectional drawing which shows the winding state of the electrode group which concerns on the Example Sectional drawing which shows the outline of the winding apparatus of the electrode group which concerns on the Example (A) Cross-sectional view after coating of electrode plate in the present invention, (b) Cross-sectional view of electrode plate having a portion with low active material density in the present invention, (c) Recessed portion with low active material density in the present invention. Cross section of electrode plate (A) Cross-sectional view of electrode plate with continuously changing coating amount in conventional example, (b) Cross-sectional view after pressing electrode plate of conventional example Partial sectional view of an electrode plate in which the coating amount is continuously changed at the coating end in the conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2 Electrode mixture coating 3 Thickness reduction place 5 Positive electrode plate 5a Coating end part 5b First roll 6 Electrode mixture layer 7 Location where the active material density is low 8 Recessed part 9 Negative electrode plate 9a Coating end part 9b First roll 10 Separator 11 Battery case 12 Sealing plate 13 Sealing gasket 14 Electrode group 15 Insulating plate 16 Negative electrode lead 17 Positive electrode lead 25 Conveying unit 26 Conveying unit 27 Winding unit T Thickness W Width

Claims (9)

  A positive electrode plate formed by applying a positive electrode mixture paint obtained by kneading and dispersing an active material composed of at least a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium on a positive electrode current collector, and at least holding lithium A negative electrode plate composed of an active material and a binder mixed with a dispersion medium and dispersed on a negative electrode current collector and a separator are wound in a spiral shape. A non-aqueous secondary battery comprising an electrode group and an electrolyte solution comprising a non-aqueous solvent, wherein the active material density on the inner circumference side of at least one of the positive electrode plate and the negative electrode plate is A non-aqueous secondary battery characterized in that it is partially smaller than the active material density on the side.   The portion having a low active material density formed on at least one of the positive electrode plate and the negative electrode plate is configured to include at least an innermost coating end portion when the electrode group is wound. The non-aqueous secondary battery according to claim 1.   The portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is at least in the range from the coating end of the innermost circumference to one turn with respect to the longitudinal direction of the electrode plate. The non-aqueous secondary battery according to claim 1.   2. The non-aqueous secondary battery according to claim 1, wherein a thickness of the portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is the same as that of other portions.   2. The non-aqueous secondary according to claim 1, wherein a thickness of a portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is different from other portions. battery.   A positive electrode plate formed by applying a positive electrode mixture paint obtained by kneading and dispersing an active material composed of at least a lithium-containing composite oxide, a conductive material, and a binder in a dispersion medium on a positive electrode current collector, and at least holding lithium A negative electrode plate composed of an active material and a binder mixed with a dispersion medium and dispersed on a negative electrode current collector and a separator are wound in a spiral shape. A method for producing a non-aqueous secondary battery comprising an electrolyte solution comprising an electrode group and a non-aqueous solvent, wherein the positive electrode mixture paint or the negative electrode mixture paint of at least one of the positive electrode plate and the negative electrode plate A first step of coating and forming the coating so that the coating amount is partially smaller than the inner peripheral side and the outer peripheral side of the electrode group, and the positive electrode mixture paint or the negative electrode mixture paint is dried and then pressed to a predetermined thickness Before going through the second step Method for producing a nonaqueous secondary battery, which comprises an electrode group.   By controlling the amount of the positive electrode mixture paint or negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector, at least the positive electrode plate and the negative electrode plate of the electrode group The method for manufacturing a non-aqueous secondary battery according to claim 6, wherein the active material density on the inner peripheral side in either one is made smaller than the active material density on the outer peripheral side.   By changing the coating amount at the start or end of application of the positive electrode mixture paint or negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector, the positive electrode plate and A portion having a low active material density formed on at least one of the negative electrode plates is formed on the inner peripheral side, and the portion having the low active material density is at least the innermost coating end when the electrode group is wound. The method for manufacturing a non-aqueous secondary battery according to claim 6, wherein: By changing the coating amount of the positive electrode mixture paint or the negative electrode mixture paint applied on at least one of the positive electrode current collector and the negative electrode current collector after a predetermined time has elapsed since the start of application, The portion having a small active material density formed on at least one of the positive electrode plate and the negative electrode plate is formed in a range from at least the innermost coating end to one turn with respect to the longitudinal direction of the electrode plate. The method for producing a non-aqueous secondary battery according to claim 6.

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