JP2005032671A - Coin-form nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coin form nonaqueous secondary battery with a high capacity and superior load characteristics. <P>SOLUTION: In the coin form nonaqueous secondary battery in which, in an enclosed space formed out of a positive electrode can, a negative electrode can, and an annular insulative gasket, a positive electrode of forming a positive electrode mix paint film to a positive electrode collector, a negative electrode of forming a negative electrode mix paint film to a negative electrode collector, an electrode with a winding structure spirally winding via a separator, and a nonaqueous electrolytic solution, is housed, the exposed part of the positive electrode collector, having no positive electrode mix paint film, is arranged on the outermost circumference of the positive electrode; the exposed part of the negative electrode collector, having no negative electrode mix paint film is arranged on the outermost circumference of the negative electrode; the shortage parts with short width are arranged on the exposure parts of the electrode collectors in the width direction of the electrode having the winding structure; the electrodes having the winding structure are retained, by winding insulative retaining tapes to the positions of the shortage parts of the exposed parts of these electrode collectors; and therewith the exposure part of the positive electrode collector is welded to the positive electrode can, and the exposure part of the negative electrode collector is welded to the negative electrode can. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coin-type non-aqueous secondary battery, and more particularly to a coin-type non-aqueous secondary battery having high capacity and excellent load characteristics.

  Currently, lithium ion secondary batteries are mainly used as power sources for portable electronic devices such as mobile phones and notebook computers. The reason for this is that it has become possible to reduce the weight and increase the voltage compared to conventional secondary batteries such as nickel-cadmium secondary batteries and metal hydride secondary batteries. Can be mentioned.

Currently used lithium ion secondary batteries use a metal oxide such as LiCoO ₂ as the positive electrode and graphite as the negative electrode. In commercially available cylindrical or prismatic lithium ion secondary batteries, the electrodes In general, a coating electrode in which a mixture coating film containing an active material is formed on a metal foil is used.

On the other hand, in the conventional coin-type battery, the above-described coated electrode is not used, and a pellet-shaped molded body of an electrode mixture is generally used as an electrode (for example, a patent Reference 1).
JP 2001-266953 A (first page)

  However, the recent development of small portable devices is progressing, and with the development of smaller mobile devices besides mobile phones, particularly wireless technologies represented by Bluetooth, small batteries such as coin-type batteries, There is a demand for a non-aqueous secondary battery of a lithium ion secondary battery system having a high capacity and excellent load characteristics.

  However, since the conventional coin-type battery uses the electrode-molded pellet-shaped molded body as described above, there is a problem that the thickness is large and the load characteristics are remarkably deteriorated. Therefore, in order to obtain excellent load characteristics, it is necessary to increase the electrode area, and even in a coin-type battery, a metal foil that becomes a current collector used in a cylindrical battery or a square battery is used. A method in which a mixture coating film containing an active material is formed as a positive electrode and a negative electrode, and these are wound through a separator to form a wound structure electrode body.

  However, in the case of an electrode body with a normal winding structure, both the positive electrode and the negative electrode are welded to a positive electrode current collector and a negative electrode current collector made of metal foil, respectively, and then welded to the positive electrode can and the negative electrode can, respectively. Since this lead has a thickness of several hundred microns, in a small battery, the thickness and volume occupied by the lead are increased, causing a reduction in capacity. Recently, a coin-type lithium ion secondary battery made in China is commercially available. In this battery, the aluminum foil and copper foil of the current collector are exposed at the outermost periphery of the wound electrode body. However, there is a problem in that the load characteristics deteriorate because a liquid layer of the electrolytic solution is formed between the can and the metal foil.

  An object of the present invention is to solve the problems of the coin-type non-aqueous secondary battery as described above, and to provide a coin-type non-aqueous secondary battery having high capacity and excellent load characteristics.

  The present invention provides a positive electrode mixture coating film containing a positive electrode active material in at least a part of a positive electrode current collector made of metal foil in a sealed space formed by a positive electrode can, a negative electrode can and an annular insulating gasket. A positive electrode formed and a negative electrode formed by forming a negative electrode mixture coating film containing a negative electrode active material on at least a part of a negative electrode current collector made of a metal foil, are spirally wound through a separator. In a coin-type non-aqueous secondary battery containing a wound structure electrode body and a non-aqueous electrolyte solution, a positive electrode collection in which a positive electrode mixture coating film is not formed on the outermost periphery of the positive electrode. An exposed portion of the current collector is provided, and the negative electrode is provided with an exposed portion of the negative electrode current collector in which the negative electrode mixture coating film is not formed at the outermost peripheral portion, and the exposed portion of the positive electrode current collector and the negative electrode The exposed part of the current collector has a short width with respect to the width direction of the wound electrode body. An insulating holding tape is wound around the position where the exposed portion of the positive electrode current collector lacks the exposed portion and the exposed portion of the negative electrode current collector lacks the exposed portion of the negative electrode current collector. The above-mentioned problem is solved by welding the exposed portion of the current collector to the inner surface of the positive electrode can and welding the exposed portion of the negative electrode current collector to the inner surface of the negative electrode can.

  The coin-type non-aqueous secondary battery of the present invention has a high capacity and excellent load characteristics.

  The present invention is configured as described above, and does not employ a conventional method of collecting current through a current collector made of metal foil and a lead, and a positive current collector made of metal foil and a positive electrode. It is characterized in that current collection is performed by directly welding the inner surface of the can and directly welding the negative electrode current collector made of metal foil and the inner surface of the negative electrode can. The welding method between the positive electrode current collector made of the metal foil and the inner surface of the positive electrode can and the welding method between the negative electrode current collector made of the metal foil and the inner surface of the negative electrode can include ultrasonic welding, resistance welding, and the like. Any method may be used as long as no liquid layer is formed between the two. Further, in the conventional case, a method of winding an outer peripheral tape made of polypropylene or the like over almost the entire width of the outer peripheral portion of the electrode body is used as a holder for the electrode body having a wound structure. Since the outermost peripheral part of the body is insulated and it is impossible to collect current between each electrode and each can, in the present invention, an insulating holding body wound around the outer peripheral part of the electrode body of the wound structure is used. An electrode having a short width with respect to the width direction of the electrode body, provided with a lacking portion in each of the exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector, and an electrode having a winding structure with the holding tape at the lacking portion The electrode body having a winding structure is held in a part of the width direction of the body, and the exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector other than the lacked portion are respectively attached to the inner surface of the positive electrode can and the inner surface of the negative electrode can. Positive by welding The electrolytic solution liquid layer is not formed between the exposed part of the current collector and the inner surface of the positive electrode can or between the exposed part of the negative electrode current collector and the inner surface of the negative electrode can. An excellent coin-type non-aqueous secondary battery is obtained.

  The position of the holding tape for holding the electrode body having the winding structure may be anywhere in the width direction of the electrode body having the winding structure because the width of the holding tape is narrow, and may be not only one place but also two or more places. However, in consideration of production simplicity and retention, it is preferable to provide one at the center in the width direction.

  When holding a normal rectangular electrode with a holding tape, the exposed portion of the electrode current collector is fixed by the tape, making it difficult to weld the can. However, as in the present invention, the portion where the holding tape is wound Since the exposed portion of the electrode current collector can be moved freely even after being held by the holding tape, welding with the can is facilitated. The welding of the exposed portion of the positive electrode current collector and the inner surface of the positive electrode can and the welding of the exposed portion of the negative electrode current collector and the inner surface of the negative electrode can be performed only once, respectively. In order to prevent the movement, it is preferable to weld at two or more locations. As a result, the lead used for the electrode body of the conventional winding structure can be removed, so that the capacity reduction due to the lead is suppressed, and the exposed portion of the electrode current collector is directly welded to the inner surface of the can. It is possible to prevent the load characteristics from being lowered.

  The shape of the coin-type non-aqueous secondary battery of the present invention is so thin as compared to the flat area, that is, if it has a so-called coin shape, the planar shape is circular, square, rectangular, elliptical, those shapes Any shape may be used, such as a shape in which is mixed.

In the present invention, the active material of the positive electrode is not particularly limited in the production of the positive electrode. For example, LiCoO ₂ , LiNiO ₂ , LiNi _x Co _1-x O ₂ , LiMnO ₂ , LiMn ₂ O _4, etc. A lithium-containing composite oxide capable of inserting / extracting lithium ions is preferably used.

  In the production of the positive electrode, the positive electrode active material, if necessary, for example, carbon black, graphite, ketjen black, acetylene black, carbon nanotubes, fullerene, vapor grown carbon fiber and other carbonaceous materials, Al, A positive electrode mixture is prepared by adding and mixing a conductive additive such as a metal powder such as Pt, and a binder such as polyvinylidene fluoride, fluorine rubber, styrene butadiene rubber, polytetrafluoroethylene, and the like. Is dispersed in a solvent to prepare a slurry-like positive electrode mixture-containing paste (the binder may be dissolved or dispersed in a solvent in advance, and then a positive electrode active material, a conductive additive, etc. may be mixed), and the positive electrode The mixture-containing paste is applied to a positive electrode current collector made of a metal foil such as an aluminum foil and dried to form a positive electrode mixture coating film. And pressurizes optionally be made by way of the step of adjusting the thickness of the positive electrode mixture coating film. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

  In the present invention, for production of the negative electrode, as the negative electrode active material, for example, a carbonaceous material such as carbon black or graphite is preferably used. In preparing the negative electrode, if necessary, for example, the same binder as in the case of the positive electrode is added to the negative electrode active material, and if necessary, the same conductive assistant as in the case of the positive electrode is added. In addition, a negative electrode mixture is prepared by mixing, and the negative electrode mixture is dispersed in a solvent to prepare a slurry-like negative electrode mixture-containing paste (the binder is dissolved or dispersed in the solvent in advance, The negative electrode mixture-containing paste may be applied to a negative electrode current collector made of a metal foil such as copper foil and dried to form a negative electrode mixture coating film. It is produced by pressing and adjusting the thickness of the negative electrode mixture coating film. However, the manufacturing method of the negative electrode is not limited to the above-described examples, and other methods may be used.

  The non-aqueous electrolyte is prepared by dissolving an electrolyte salt such as a lithium salt in a non-aqueous solvent such as an organic solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, methyl ethyl carbonate, Tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,2-dimethoxyethane and the like can be mentioned, and these solvents may be used alone or in combination of two or more.

Examples of the electrolyte salt dissolved in the non-aqueous solvent include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , (C _n F _{2n + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ). NLi (m, n ≧ 1) and the like can be mentioned, and these can be used alone or in combination of two or more. And as a density | concentration in electrolyte solution of these electrolyte salts, about 0.3-1.7 mol / l is preferable.

  Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples. In the following examples and the like, “parts” means parts by mass.

Example 1
Example 1 will be described in the order of production of a positive electrode, production of a negative electrode, preparation of an electrolytic solution, and assembly of a coin-type non-aqueous secondary battery.

Production of positive electrode:
LiCoO ₂ is used as the positive electrode active material, carbon black is used as the conductive auxiliary agent, and polyvinylidene fluoride is used as the binder. First, 93 parts of LiCoO ₂ and 3 parts of carbon black are mixed, and the resulting mixture and polyvinylidene fluoride are mixed. A positive electrode mixture-containing paste was prepared by mixing 4 parts with a binder solution that had been previously dissolved in N-methyl-2-pyrrolidone, and the obtained positive electrode mixture-containing paste was made of an aluminum foil having a thickness of 15 μm. Applying to both sides of the positive electrode current collector with an applicator (however, when the completed positive electrode is overlapped with the negative electrode through a separator and wound into a spiral structure to form a wound structure electrode body, The positive electrode mixture-containing paste was not applied to the part, and the exposed part of the positive electrode current collector was left on both sides of the positive electrode current collector) Then, a positive electrode mixture coating film was formed, and then roll-pressed and cut into a predetermined size to obtain a belt-like positive electrode. The width of the positive electrode is 15 mm, the length of the exposed portion of the positive electrode current collector that is the outermost peripheral portion when wound is 20 mm, and the central portion in the width direction is 8 mm wide. The missing part was provided by cutting off.

Production of negative electrode:
Using graphite as a negative electrode active material, using polyvinylidene fluoride as a binder, mixing 94 parts of the graphite and 6 parts of polyvinylidene fluoride with a binder solution in which N-methyl-2-pyrrolidone was previously dissolved, A negative electrode mixture-containing paste was prepared. The obtained negative electrode mixture-containing paste was applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm by an applicator (however, the completed negative electrode was overlapped with the positive electrode via a separator to form a spiral shape. No electrode-containing paste is applied to the outermost portion when the electrode body is wound to form a wound structure so that the exposed portions of the negative electrode current collector remain on both sides of the negative electrode current collector. And dried to form a negative electrode mixture coating film, and then roll-pressed and cut into a predetermined size to obtain a sheet-like negative electrode. The width of the negative electrode is 16 mm, the length of the exposed portion of the negative electrode current collector that is the outermost periphery when wound is 20 mm, and the central portion in the width direction is 8 mm wide. The missing part was provided by cutting off.

Electrolyte preparation:
LiPF ₆ was prepared by dissolving at a concentration of 1.2 mol / l in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1: 2.

Assembling the coin-type non-aqueous secondary battery:
The positive electrode and the negative electrode were wound in a spiral shape with a separator made of a microporous polypropylene film interposed between them, and pressed flatly so that it could be easily finished into a coin-type battery. Next, a polyethylene holding tape having a thickness of 0.05 mm and a width of 3 mm was wound around the lacking portion of the positive electrode current collector and the lacking portion of the negative electrode current collector at the outer peripheral portion of the electrode body having the winding structure. This state is shown in FIG.

  In FIG. 1, 1 is an electrode body having a winding structure, and the electrode body 1 having this winding structure is obtained by winding the positive electrode and the negative electrode in a spiral shape with a separator interposed therebetween, and pressing flatly. 2 is a holding tape wound around the outer periphery of the electrode body 1 to hold the wound structure, 3 is an exposed portion of the positive electrode current collector, and 4 is an exposed portion of the negative electrode current collector. . The holding tape 2 is wound around the outer peripheral portion of the electrode body 1 having a winding structure at a portion lacking the exposed portion 3 of the positive electrode current collector and a portion lacking the exposed portion 4 of the negative electrode current collector. 1 is wound around the outer peripheral portion of 1 and holds the electrode body 1 having a wound structure. The exposed portion 3 of the positive electrode current collector is connected to the inner surface of a stainless steel positive electrode can (not shown) by welding, and the exposed portion 4 of the negative electrode current collector is a stainless steel negative electrode can (not shown). ) To the inner surface by welding.

  And after inject | pouring the said electrolyte solution into the negative electrode can in which the electrode body of the winding structure hold | maintained with the holding tape as mentioned above was accommodated, and confirming that the electrolyte solution infiltrated the electrode body of the winding structure, it is a conventional method The coin type non-aqueous secondary battery of type 2025 (thickness 2.5 mm, diameter 20 mm) was assembled. That is, when sealing the above, a polypropylene annular insulating gasket is attached to the periphery of the negative electrode can in advance, and the positive electrode can is covered with the negative electrode can containing the wound electrode body or electrolyte, The open end of the positive electrode can was clamped inward. As a result, as described above, the wound electrode body and the non-aqueous electrolyte solution whose outer periphery is held by the holding tape are a sealed space formed by the positive electrode can, the negative electrode can and the annular insulating gasket. The coin-shaped non-aqueous secondary battery is assembled by being housed therein.

Example 2
A 2025 type coin-type non-aqueous secondary battery was produced in the same manner as in Example 1 except that the width of the lacking portion of the exposed portion of the positive electrode current collector and the lacking portion of the exposed portion of the negative electrode current collector was 4 mm.

Comparative Example 1
A wound electrode body was produced in the same manner as in Example 1 except that the exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector were not provided with the lack of the central portion in the width direction. The holding tape for holding the wound electrode body is not wrapped around the outer periphery of the wound electrode body, and the holding tape is wound in the width direction of the wound electrode body to expose the positive electrode current collector. 2025-type coin-shaped non-water is almost the same as in Example 1, except that the welding of the portion and the inner surface of the positive electrode can is not performed, and the exposed portion of the negative electrode current collector and the inner surface of the negative electrode can are not welded. A secondary battery was produced. However, the inner surface of the positive electrode can is preliminarily welded with an aluminum mesh, and the inner surface of the negative electrode can is preliminarily welded with a stainless steel mesh and welded to the exposed portion of the positive electrode current collector and the inner surface of the positive electrode can. The exposed aluminum net was brought into contact, and the exposed portion of the negative electrode current collector was contacted with the stainless steel net welded to the inner surface of the negative electrode can.

Comparative Example 2
One end of a 0.3 mm thick aluminum lead is welded to the exposed portion of the positive electrode current collector, and one end of a 0.3 mm thick nickel lead is welded to the exposed portion of the negative electrode current collector. An electrode body having a structure was prepared, and the other end of the aluminum lead was welded to the inner surface of the positive electrode can, and the other end of the nickel lead was welded to the inner surface of the negative electrode can. A 2025 type coin-type non-aqueous secondary battery was produced. However, the lengths of the positive electrode mixture coating film and the negative electrode mixture coating film in the positive electrode and the negative electrode were each reduced by 10 mm in consideration of the lead thickness.

About the battery of the said Examples 1-2 and Comparative Examples 1-2, it charged / discharged between the charge end voltage 4.2V and the discharge end voltage 3.0V on the following conditions, and measured discharge capacity. That is, the charge current density was fixed at 1.5 mA / cm ^2, the initial discharge capacity at a discharge current density of 1.5 mA / cm ² was measured, followed by a discharge current density of ^{3mA / cm 2, 6mA / cm} 2, The discharge capacity at 9 mA / cm ² was measured. The results are shown in Table 1.

As shown in Table 1, the batteries of Examples 1 and ² have a large initial discharge capacity at a discharge current density of 1.5 mA / cm ² , a high capacity, and a large discharge capacity even in a high current density region. The load characteristics were excellent.

  In contrast, the battery of Comparative Example 1 has a large capacity drop in the high current density region and the load characteristics are inferior, and the battery of Comparative Example 2 has the initial discharge capacity of Examples 1-2. In comparison with the batteries of Examples 1 and 2, the discharge capacity was small even in the high current density region, and the capacity was not high.

It is a perspective view which shows typically an example of the electrode body of the winding structure used for the coin type non-aqueous secondary battery which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode body of winding structure 2 Holding tape 3 Exposed part of positive electrode current collector 4 Exposed part of negative electrode current collector

Claims (3)

A positive electrode mixture coating film containing a positive electrode active material is formed on at least a part of a positive electrode current collector made of a metal foil in a sealed space formed by a positive electrode can, a negative electrode can and an annular insulating gasket. A winding structure in which a positive electrode and a negative electrode formed by forming a negative electrode mixture coating film containing a negative electrode active material on at least a part of a negative electrode current collector made of a metal foil are spirally wound through a separator. A coin-type non-aqueous secondary battery containing a non-aqueous electrolyte solution, wherein the positive electrode is a positive electrode current collector in which a positive electrode mixture coating film is not formed on the outermost periphery thereof. The negative electrode has an exposed portion of a negative electrode current collector in which the negative electrode mixture coating film is not formed at the outermost peripheral portion, and the exposed portion of the positive electrode current collector and the negative electrode current collector The exposed part of the body is provided with a part lacking a short width in the width direction of the wound electrode body. In addition, an insulating holding tape is wound around the position where the exposed portion of the positive electrode current collector is absent and the exposed portion of the negative electrode current collector is absent to hold the wound electrode body, and the positive electrode current collector A coin-type non-aqueous secondary battery, wherein an exposed portion is welded to an inner surface of a positive electrode can and an exposed portion of a negative electrode current collector is welded to the inner surface of the negative electrode can. 2. The coin-type non-aqueous secondary battery according to claim 1, wherein the positive electrode current collector has one or more exposed portions and the negative electrode current collector has one or more exposed portions. 2. The welded portion between the exposed portion of the positive electrode current collector and the inner surface of the positive electrode can and the welded portion between the exposed portion of the negative electrode current collector and the inner surface of the negative electrode can are each one or more. The coin-shaped non-aqueous secondary battery described.

Images