JP5128900B2 - Lithium secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a lithium secondary battery and a manufacturing method thereof.

  Conventionally, a lithium secondary battery has a transition metal contained in lithium manganate, which is a positive electrode material, dissolved with charge and discharge, and deposited on the negative electrode surface in a dendrite (dendritic) shape, penetrating the separator. It is known that a voltage failure occurs.

  In the technique described in Patent Document 1, the above-described micro short circuit is prevented by winding the positive electrode and the negative electrode through a separator having a thickness in consideration of the amount of copper contained in lithium manganate. .

JP 2002-203531 A

  However, recently, it has been known that minute particles or foil pieces of nickel, which is a transition metal, enter an end portion of a wound group of an element, thereby causing an internal short circuit. If an internal short circuit occurs, the battery itself may burn out due to the heat generated by the rapid self-discharge of the battery.

  A lithium secondary battery is manufactured by inserting a wound group into a metal battery can whose inner and outer surfaces are plated with nickel, and then fixing the wound group with a disk on the outer periphery on the opening side of the battery can. To provide a groove. Next, it is common to inject an electrolytic solution and crimp the metal battery lid to perform sealing.

  The origin of the nickel microparticles that cause the above problems is not completely clear, but one of them is the process in which the nickel plating layer applied to the inner surface of the metal battery can forms a groove in the upper part of the battery can. There is a possibility that it peels off and becomes a small piece and is mixed with the electrolyte inside the battery.

  Further, in the step of forming a groove in the upper portion of the can, a crack (crack) may occur in the nickel plating layer applied to the battery can. The cracked portion is easily corroded because the steel can base is not protected by the plating layer.

  Then, an object of this invention is to provide the technique which can prevent mixing of the nickel microparticles to the inside by the process of a battery can, maintaining a corrosion resistance.

  In order to solve the above problems, in the present invention, after the battery can is sealed, the outer surface of the battery is plated so that the peeling of the plating on both the inner and outer surfaces can be eliminated.

  For example, the method for manufacturing a lithium secondary battery according to the present invention includes a step of inserting a wound group consisting of a positive electrode, a negative electrode, and a separator into a battery can having a bottom portion, a side wall portion, and a top opening. A step of injecting an electrolytic solution into the battery can, a step of forming a groove in the outer peripheral surface of the side wall of the battery can, a step of sealing the upper opening of the battery can with a battery lid, Forming a plating layer on the outer surface of the sealed battery.

  First, in order to clarify the present invention, a cylindrical lithium secondary battery 200 produced by a conventional manufacturing method will be described with reference to FIGS. 5 and 6A to 6E. FIG. 5 is a flowchart showing a manufacturing process of a conventional cylindrical lithium secondary battery 200, and FIGS. 6A to 6E are schematic views showing a manufacturing process of the conventional cylindrical lithium secondary battery 200. FIG.

  First, as shown in FIG. 6A, nickel plating 120 is applied to both the inner and outer surfaces of a steel battery can 107 (S21). Next, as shown in FIG. 6 (b), the winding group 102 that has been produced in advance and wound with the positive electrode and the negative electrode through a separator is inserted into a battery can 107 with nickel plating 120 applied thereto. (S22). Further, as shown in FIG. 6C, a groove 109 for fixing the inserted wound group 102 inside the battery can 107 is formed on the upper opening side of the battery can 107 (S23). After injecting the electrolytic solution 115 (S24, FIG. 6D), the opening of the battery can 107 is sealed with the battery lid 110 (S25), and a cylindrical lithium secondary battery as shown in FIG. 200 is manufactured.

  However, in such a conventional method, the nickel plating 120 on both the inner and outer surfaces of the groove portion 109 is peeled off by the groove processing in step 23, and the nickel fine pieces on the inner surface are removed from the battery can 170 at the time of electrolyte injection in step 24. There was an inconvenience of getting inside. In addition, cracks on the external surface can lead to corrosion.

  Therefore, in the present invention, a safer cylindrical lithium secondary battery 100 is manufactured by a novel manufacturing method. Hereinafter, description will be made with reference to FIG. 1 and FIGS. 2 (a) to 2 (e). FIG. 1 is a flowchart showing a manufacturing process of a cylindrical lithium secondary battery 100 according to the present invention, and FIGS. 2A to 2E show the manufacturing of the cylindrical lithium secondary battery 100 according to the present invention. It is the schematic showing a process.

  First, as shown in FIG. 2 (a), a wound group 102 prepared by winding a positive electrode and a negative electrode through a separator is inserted into the battery can 107 (S11). At this time, the battery can 107 is not subjected to plating with nickel or the like in advance. Next, as shown in FIG. 2B, a groove 109 for fixing the inserted wound group 102 inside the battery can 107 is formed on the upper opening side of the battery can 107 (S12). Further, an electrolytic solution 115 is injected (S13, FIG. 2 (c)), and the opening of the battery can 107 is sealed by the battery lid 110 (S14, see FIG. 2 (d)). Thereafter, nickel plating 120 is applied only to the outer surface of the battery (S15, see FIG. 2 (e)) to manufacture a cylindrical lithium secondary battery 100.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. However, the present invention is not limited to these examples. FIG. 3 is a cross-sectional view of a cylindrical lithium secondary battery 100 according to the present invention.

<Step 1> Preparation of positive electrode First, lithium manganate (LiMn ₂ O ₄ ) as a lithium transition metal complex oxide of a positive electrode active material, graphite powder and acetylene black as a conductive material, and a binder (binder) Polyvinylidene fluoride (hereinafter referred to as PVdF) was mixed at a mass ratio of 85: 8: 2: 5 to obtain a positive electrode mixture. The slurry obtained by adding N-methyl-2-pyrrolidone (hereinafter referred to as NMP) as a dispersion solvent and kneading the mixture as necessary is applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 20 μm. Applied. At this time, an uncoated portion with a width of 30 mm was left on one side edge in the longitudinal direction.

  The positive electrode active material is not limited to the above. As long as it is a lithium transition metal double oxide, nickel, cobalt, or the like may be used. The binder is not limited to the above, and other polymers such as polyethylene, polystyrene, polybutadiene, nitrocellulose, latex, acrylonitrile and the like may be used. Furthermore, similarly, other conductive materials may be used as long as they are normally used.

This was dried and then pressed and cut to obtain a positive electrode having a width of 82 mm, an arbitrary length, and a positive electrode mixed material application part having an arbitrary thickness. Here, the bulk density of the positive electrode mixture layer is 2.65 g / cm ³ , but the present invention is not limited to this, as long as it has a size suitable for the positive electrode and a bulk density.

  Furthermore, a notch was made in the slurry uncoated portion left on one side edge of the positive electrode obtained by the above treatment. The remaining part of the notch was the positive electrode lead piece 103, the interval between the adjacent positive electrode lead pieces 103 was 50 mm, and the width of the positive electrode lead piece 103 was 5 mm.

<Step 2> Production of negative electrode Lump graphite as a negative electrode active material, vapor-grown carbon fiber as a conductive material, PVdF as a binder, a thermosetting plasticized polyvinyl alcohol resin composition (hereinafter referred to as PVA) described later, The NMP solution of the mixture was mixed at a mass ratio of 87.62: 4.76: 7.62 to obtain a negative electrode mixture. A slurry obtained by adding NMP as a dispersion solvent and kneading as needed was applied to both surfaces of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm. At this time, an uncoated portion having a width of 30 mm was left on one side edge in the longitudinal direction.

  In addition, the negative electrode active material should just be a carbonaceous material, and is not restricted to said thing. Furthermore, similarly, other conductive materials may be used as long as they are normally used.

  In the above treatment, the PVA is prepared by mixing and dissolving a first resin component made of a thermosetting polyvinyl alcohol resin and a second resin component made of an acrylic resin plasticizer in NMP. Using. The thermosetting polyvinyl alcohol resin as the first resin component is obtained by adding a cyclic acid anhydride such as succinic acid anhydride to an polyvinyl alcohol resin having an average degree of polymerization of about 2000 in an organic solvent such as NMP. , And obtained in a substantially anhydrous state in the presence of a catalyst such as triethylamine. The reaction ratio between the polyvinyl alcohol resin and the cyclic acid anhydride is preferably about 0.1 equivalent of the anhydride group of the cyclic acid anhydride with respect to 1 equivalent of the alcoholic hydroxyl group of the polyvinyl alcohol resin. The acrylic resin plasticizer as the second resin component is preferably a reaction product of a lauryl acrylate / acrylic acid copolymer and a bifunctional epoxy resin.

  This was dried and then pressed and cut to obtain a negative electrode having a width of 86 mm, an arbitrary length, and a negative electrode mixed material application part having an arbitrary thickness. Here, in this example, the negative electrode was compressed so that the porosity of the negative electrode mixture layer was about 35%, but the present invention is not limited to this, and has a size suitable for the negative electrode and a porosity. If so, other configurations may be used.

  Furthermore, the not-applied part left on one side edge of the negative electrode obtained by the above-described treatment was notched in the same manner as the positive electrode. The remainder of the notch was a negative electrode lead piece 106, the interval between adjacent negative electrode lead pieces 106 was 50 mm, and the width of the negative electrode lead piece 106 was 5 mm.

<Step 3> Production of wound group The produced positive electrode and the negative electrode were wound together with a polyethylene separator having a width of 90 mm and a thickness of 40 μm so that the two electrodes do not directly contact each other. A hollow cylindrical shaft core 101 made of polypropylene was used at the center of winding. At this time, the positive electrode lead piece 103 and the negative electrode lead piece 106 were respectively positioned on opposite end surfaces of the wound group 102 (electrode group). Further, the lengths of the positive electrode, the negative electrode, and the separator were adjusted, and the diameter of the wound group 102 was 38 ± 0.1 mm. Of course, the length and thickness of the separator are not limited to the above.

<Step 4> Assembly of Battery The positive electrode lead piece 103 was deformed, and all of the positive electrode lead pieces 103 were assembled and brought into contact with the flange extending from the positive electrode current collecting ring 104 substantially on the extension line of the axis 101 of the wound group 102. Then, the positive electrode lead piece 103 and the collar outer peripheral surface of the positive electrode current collection ring 104 were connected by ultrasonic welding.

  On the other hand, the negative electrode current collector ring 105 and the negative electrode lead piece 106 are similarly ultrasonically welded to the outer peripheral surface of the flange portion extending from the negative electrode current collector ring 105 and the negative electrode lead piece 106. Was connected to the outer peripheral surface of the flange portion of the negative electrode current collecting ring 105.

  Thereafter, an insulating coating was applied to the entire circumference of the outer peripheral surface of the flange portion of the positive electrode current collecting ring 104. For this insulation coating, an adhesive tape in which the base material was polyimide and an adhesive made of hexamethacrylate was applied on one side thereof was used. This adhesive tape was wound one or more times from the outer peripheral surface of the collar portion of the positive electrode current collecting ring 104 to the outer peripheral surface of the wound group to form an insulating coating, and the wound group 102 was inserted into the battery can 107.

  As the battery can 107, a steel container having an outer diameter of 40 mm and an inner diameter of 39 mm was used. Of course, other materials or the like may be used for the material of the battery can 107.

  Subsequently, a negative electrode lead plate 108 for electrical conduction, which was previously welded to the negative electrode current collecting ring 105, was welded to the bottom of the battery can 107. Next, in order to fix the wound group 102 inserted into the battery can 107, a groove process was performed on the opening-side outer peripheral surface of the battery can 107 to form a groove portion 109.

  On the other hand, the positive electrode current collector ring 104 is preliminarily welded with a positive electrode lead 112 formed by overlapping a plurality of aluminum ribbons, and the other end of the positive electrode lead 112 is sealed with a battery for sealing the battery can 107. Welded to the lower surface of the lid 110.

  Next, the nonaqueous electrolyte was poured into the battery can 107, and then the battery can 107 was covered with the battery cover 110 so that the positive electrode lead 112 was folded.

Here, the non-aqueous electrolyte is 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) in a solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate are mixed at a volume ratio of 1: 1: 1. Although what was melt | dissolved was used, of course, it is not limited to this, You may use another electrolyte solution.

The battery lid 110 is provided with a cleavage valve 113 as an internal pressure release mechanism that cleaves as the internal pressure of the cylindrical lithium secondary battery 100 increases. The cleavage pressure of the cleavage valve 113 was set to about 9 × 10 ⁵ Pa. The battery lid 110 was sealed by laminating components such as a cleavage valve 113 (internal gas exhaust valve) and crimping the periphery of the battery lid 110 via a gasket 111 made of EPDM resin.

<Step 5> Nickel plating The sealed cylindrical lithium secondary battery 100 obtained by the above manufacturing process is plated with nickel on the outside of the cylindrical lithium secondary battery 100 in the following plating process. gave.

The sealed cylindrical lithium secondary battery 100 was immersed in a catalyst solution having the composition shown below for 5-10 minutes to form a Pd catalyst layer on the surface of the cylindrical lithium secondary battery 100. Thereafter, the substrate was rinsed with pure water for 5 minutes, and then immersed in an electroless nickel plating solution shown below for about 20 minutes to form a nickel plating layer having a thickness of about 3 μm.
(Composition of catalyst solution for plating and working conditions)
Palladium chloride 0.2g / liter Concentrated hydrochloric acid 2ml / liter Working temperature Room temperature Immersion time 5-10 minutes (Electroless nickel plating solution composition and working conditions)
Nickel sulfate 25 g / liter Sodium hypophosphite 25 g / liter Organic acid sodium 25 g / liter Plating solution pH 4-5
Working temperature 90 ℃
Plating deposition rate: about 10 μm / hour Immersion time: about 20 minutes In this way, only the outer surface of the cylindrical lithium secondary battery 100 was plated with nickel. The electroless nickel film contains approximately 10% phosphorus derived from sodium hypophosphite contained in the electroless nickel plating solution, and the film composition is an alloy of nickel and phosphorus. By plating this alloy, the cylindrical lithium secondary battery 100 has practically sufficient corrosion resistance.

  Since the steps 1 to 4 are the same as those in the first embodiment, detailed description thereof is omitted. Hereinafter, step 5 will be described.

<Step 5> Nickel plating As in Example 1, the sealed cylindrical lithium secondary battery 100 was immersed in a catalyst solution having the composition shown below for 5-10 minutes to form a Pd catalyst layer on the surface. Thereafter, it is rinsed with pure water for 5 minutes, and then immersed in the electroless nickel plating solution shown below for about 30 minutes, and a nickel plating layer having a thickness of about 3 μm is formed on the outer surface of the cylindrical lithium secondary battery 100. Only formed.
(Composition of catalyst solution for plating and working conditions)
Palladium chloride 0.2g / liter Concentrated hydrochloric acid 2ml / liter Working temperature Room temperature Immersion time 5-10 minutes (Electroless nickel plating solution composition and working conditions)
Nickel sulfate 30 g / liter Dimethylamine borane 3.5 g / liter Boric acid 30 g / liter Rochelle salt 60 g / liter Plating solution pH 5-7
Working temperature 50 ℃
Plating deposition rate: about 5 μm / hour Immersion time: about 30 minutes The electroless nickel film applied by the method of Example 2 includes dimethylamine borane contained in the electroless nickel plating solution and approximately 1% boron derived from boric acid. The film composition is an alloy of nickel and boron. By plating this alloy, the cylindrical lithium secondary battery 100 has practically sufficient corrosion resistance.

  Since the steps 1 to 4 are the same as those in the first embodiment, detailed description of the first embodiment will be omitted. Hereinafter, step 5 will be described.

<Step 5> Nickel plating Here, only the electrolytic nickel plating solution is used without using the catalyst solution. Therefore, unlike the case of the electroless nickel as described above, the plating cannot be performed only by being immersed in the plating solution. Therefore, the cylindrical lithium secondary battery 100 is made conductive by using a contact electrode and maintained at a negative potential, and the cylindrical lithium secondary battery 100 is used as a cathode and electrolysis is performed in an electrolytic nickel plating solution shown below, about 3 μm. The nickel plating layer of thickness was formed on the surface.
(Electrolytic nickel plating solution composition and working conditions)
Nickel sulfate 240 g / liter Nickel chloride 45 g / liter Boric acid 30 g / liter Rochelle salt 60 g / liter Sodium naphthalene sulfonate 1 g / liter Plating solution pH 4
Working temperature 30 ℃
Plating current density about 2-10 A / dm ²
Immersion time: about 3 minutes The composition of the electrolytic nickel film applied by the method of Example 3 is almost pure nickel. Therefore, the nickel-plated cylindrical lithium secondary battery 100 has practically sufficient corrosion resistance.

  Further, in the case of plating using such an electrolytic method, the working temperature is low, and the influence on a material having relatively low heat resistance such as a separator in the cylindrical lithium secondary battery 100 can be reduced. .

  FIG. 4 shows a chart comparing the cylindrical lithium secondary battery 100 manufactured according to this example and the lithium secondary battery manufactured by the conventional method. In the conventional example, the battery can having a plating layer is used for both the inner surface and the outer surface of the battery can, and the lithium secondary battery is manufactured through the process of processing the groove. There was a possibility of causing peeling. As a result, there is a possibility of causing a short circuit caused by plating fine pieces mixed inside and corrosion at an external peeling portion.

  However, according to the cylindrical lithium secondary battery 100 manufactured according to the present embodiment, the plating is performed after both the grooving process and the sealing process, so that the plating layer is not peeled off due to the stress at the time of processing. It is possible to prevent short-circuiting due to mixing of small pieces and external corrosion.

It is a flowchart which shows the manufacturing process of the cylindrical lithium secondary battery which concerns on this invention. It is the schematic showing the manufacturing process of the cylindrical lithium secondary battery which concerns on this invention. It is sectional drawing of the cylindrical lithium secondary battery which concerns on this invention. It is the chart which compared the cylindrical lithium secondary battery manufactured by the present Example with the battery manufactured by the conventional method. It is a flowchart which shows the manufacturing process of the conventional cylindrical lithium secondary battery. It is the schematic showing the manufacturing process of the conventional cylindrical lithium secondary battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 200 ... Cylindrical lithium secondary battery, 101 ... Axle, 102 ... Winding group, 103 ... Positive electrode lead piece, 104 ... Positive electrode current collection ring, 105 ... Negative electrode current collection ring, 106 ... Negative electrode lead piece, 107 ... Battery can, 108 ... Negative electrode lead plate, 109 ... Groove, 110 ... Battery cover, 111 ... Gasket, 112 ... Positive electrode lead, 113 ... Cleavage valve

Claims (7)

Inserting a wound group consisting of a positive electrode, a negative electrode, and a separator into a battery can comprising a bottom portion, a side wall portion, and an upper opening;
Injecting an electrolyte into the battery can;
Forming a groove on the outer peripheral surface of the side wall of the battery can;
Sealing the upper opening of the battery can with a battery lid;
Forming a plating layer on the outer surface of the sealed battery;
A method for producing a lithium secondary battery, comprising: It is a manufacturing method of the lithium secondary battery according to claim 1,
The step of forming the plating layer includes
A method for producing a lithium secondary battery, comprising forming a palladium catalyst layer on the battery and then immersing it in an electroless plating solution. It is a manufacturing method of the lithium secondary battery according to claim 1,
The step of forming the plating layer includes
A method for producing a lithium secondary battery, comprising the step of performing electrolysis in a plating solution using the battery as a cathode. A method for producing a lithium secondary battery according to any one of claims 1 to 3,
The said plating layer is comprised with either Ni, a Ni-P alloy, and a Ni-B alloy by the composition of the said plating solution. The manufacturing method of a lithium secondary battery characterized by the above-mentioned.   The lithium secondary battery manufactured with the manufacturing method of the lithium secondary battery of any one of Claim 1 to 4. The lithium secondary battery according to claim 5,
The lithium secondary battery is characterized in that the battery can is made of steel. The lithium secondary battery according to claim 5 or 6,
A lithium secondary battery characterized by being used in an electric vehicle.

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