JP2005190912A - Lithium secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery with high safety even at vibration and shock given. <P>SOLUTION: The manufacturing method of the lithium secondary battery having an electrode plate group laminating or winding round cathodes and anodes includes a process of adhering and forming a porous layer consisting of an inorganic oxide filler and a binder on an anode, winding round or laminating the cathode and the anode to make up an electrode plate group, and dipping a top and bottom end faces of the electrode group in solution consisting of an insulator and the binder to harden them. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery excellent in safety such as short circuit resistance and heat resistance.

In a chemical battery such as a lithium secondary battery, there is a separator between the positive electrode and the negative electrode that electrically insulates each electrode plate and holds an electrolyte solution. In lithium secondary batteries, microporous thin film sheets mainly made of polyethylene are currently used.
However, sheet-like separators made of these resins generally tend to shrink at low temperatures, so that when a sharply shaped protrusion such as an internal short circuit or a nail penetrates the battery, the short circuit part is caused by a short circuit reaction heat that is instantaneously generated. It had the problem of expanding and generating much more heat of reaction and promoting abnormal overheating.
Therefore, as a technique for improving the safety including the above-mentioned problems, there is a technique for arranging a high heat-resistant non-shrinkable insulating layer on the electrode, and the purpose is different. A technique for forming a porous layer made of a polymer binder (see Patent Document 1) has been proposed.
Japanese Patent Laid-Open No. 10-106530

  However, when the above conventional technology is applied to a lithium secondary battery, the length in the width direction of the negative electrode is generally longer than that of the positive electrode, so when a porous layer is formed only on the positive electrode, an internal short circuit at the upper and lower end surfaces There is a risk of occurrence. In addition, when a porous layer is formed on the negative electrode or on both the positive electrode and the negative electrode, the upper and lower end surfaces of the positive electrode (if the porous layer is formed on both the positive electrode and the negative electrode, the porous formed on the positive electrode The upper and lower end face portions of the layer are in contact with the porous layer on the opposing negative electrode, and there is a risk that the porous layer will be peeled off or cracked particularly due to vibration or impact, causing an internal short circuit.

  In addition, since there is no insulating layer on the end face of the electrode plate, there is a risk that an internal short circuit may occur due to vibration or impact.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a lithium secondary battery having high safety even when subjected to vibration or impact.

  The lithium secondary battery of the present invention is a lithium secondary battery having an electrode plate group in which a positive electrode and a negative electrode are laminated or wound, and the negative electrode has a porous layer made of an inorganic oxide filler and a binder on the electrode plate. The end face of the electrode plate group is protected by an insulator. By protecting the end face of the electrode plate group with an insulator, the movement of the electrode plate due to vibration or impact is suppressed, so that the above problem can be avoided.

  Here, when the porous layer is bonded and formed on the negative electrode as a separator, and the space generated by the difference in length in the width direction between the positive electrode and the negative electrode is filled with an insulator, the effect of the present invention is achieved. Becomes remarkable and is preferable.

  In addition, since the insulator is made of insulating fine particles and an adhesive, the insulator becomes porous, so that the electrolyte can be injected, the gas emitted from the battery can be released, and the mechanical strength can be secured. it can.

Further, a lithium secondary battery is manufactured by winding or laminating the positive electrode and the negative electrode to produce an electrode plate group, and immersing and curing the upper and lower end surfaces of the electrode plate group in a solution comprising an insulator and an adhesive. As a result, not only can the end of the electrode plate group be protected by an insulator, but also the positive electrode and the negative electrode at the end of the electrode plate group can be firmly bonded via the insulator to further move the electrode. Since it can suppress, the said subject can be avoided.

  As described above, according to the present invention, it is possible to provide a highly safe lithium secondary battery in which the occurrence of an internal short circuit is unlikely to occur because the movement of the electrode plate is suppressed even when there is vibration or impact. It becomes.

  Preferred embodiments of the present invention are shown below.

  FIG. 1 shows a schematic diagram of the structure of a lithium secondary battery according to the present invention. 1 is a porous layer formed on the electrode plate, 2 is a negative electrode, 3 is an insulator, and 4 is a positive electrode. FIG. 1 is a schematic view when a porous layer is formed only on the negative electrode. Since the width of the negative electrode 2 is longer than that of the positive electrode 4 due to the design of the lithium secondary battery, the upper and lower end surface portions of the positive electrode 4 are in contact with the porous layer 1 on the opposite negative electrode 2, and the porous layer is particularly affected by vibration or impact. There is a risk of peeling or cracking of 1 and causing an internal short circuit. However, since the upper and lower end surfaces of the electrode plate group are protected by the insulator 3, the movement of the electrode plate is suppressed even when there is vibration or impact, and therefore the occurrence of an internal short circuit can be suppressed.

  The insulator is preferably a porous material in consideration of the pouring property of the electrolytic solution and the release property of the gas generated in the battery. Moreover, it must have high heat resistance and high mechanical strength. As a material having the above properties, a mixture of insulating fine particles and an adhesive may be mentioned.

  For the method of applying an insulator, a step of producing a plate group in which a positive electrode and a negative electrode formed by bonding a porous layer are overlapped and wound or laminated, and the end surface of the electrode plate group is formed of insulating fine particles and an adhesive. A step of immersing in a mixed solution of

  The insulating fine particles are preferably inorganic oxides such as alumina, titanium oxide and silica having high heat resistance, solid electrolytes having lithium ion conductivity, or mixtures thereof.

  The adhesive used for the insulator is a binder having a strong adhesive force, and is preferably a thermoplastic resin, a UV curable resin, a synthetic rubber adhesive, or the like.

  The porous layer formed on the negative electrode must be bonded and formed on at least the negative electrode described in detail below. When formed only on the positive electrode, contact between the positive electrode end and the negative electrode tends to occur at the end in the width direction, which is not preferable.

  Also, it is desirable that the porous layer is used as a binder because it has high heat resistance and is non-crystalline. When an internal short circuit occurs in a lithium secondary battery, the heat generation temperature may locally exceed several hundred degrees Celsius. For this reason, those that are crystalline and have a low crystal melting point, and those that are non-crystalline but have a low decomposition start temperature, may cause the internal short circuit to expand as the porous layer is deformed due to softening or burning of the resin. Accompanied by. From this point of view, the polymer is preferably a rubbery polymer containing a polyacrylonitrile group that is non-crystalline, has high heat resistance, and has rubber elasticity.

Furthermore, an inorganic oxide is preferably used as a filler in the porous layer. Various resin fine particles are also commonly used as fillers. However, as described above, they need heat resistance and must be electrochemically stable within the range of use of lithium secondary batteries. However, inorganic materials are most preferable as materials suitable for coating. The inorganic oxide is alumina from the viewpoint of electrochemical stability, and the content of the inorganic oxide in the porous layer is 50 parts by weight or more and 9
More preferably, it is 9 parts by weight or less. When the amount of the binder is less than 50 parts by weight, it is difficult to control the pore structure formed by the gaps between the alumina, and when the amount of the binder is more than 99 parts by weight, the adhesion of the porous layer is low. This is because the function may be lost due to dropout due to the decrease. This inorganic oxide may be used as a mixture of a plurality of types or in multiple layers.

  For the positive electrode, lithium cobaltate and its modified products (such as those obtained by eutectic aluminum and magnesium), lithium nickelate and its modified products (such as those in which nickel has been partially substituted with cobalt), and lithium manganate And composite oxides such as modified products thereof. As a binder, polytetrafluoroethylene (PTFE), modified acrylonitrile rubber particle binder (BM-500B manufactured by Nippon Zeon Co., Ltd.) and the like are used for thickening carboxymethylcellulose (CMC), polyethylene oxide (PEO), soluble modification It may be combined with acrylonitrile rubber (BM-720H manufactured by Nippon Zeon Co., Ltd.), etc., and a single polyvinylidene fluoride (PVDF) having both binding properties and thickening properties and a modified product thereof are used alone or in combination. May be. As the conductive agent, acetylene black, ketjen black, and various graphites may be used alone or in combination.

  For the negative electrode, various natural graphites, silicon-based composite materials such as artificial graphite and silicide, lithium metal, and various alloy composition materials can be used as the active material. Various binders such as PVDF and modified products thereof can be used as the binder. From the viewpoint of improving the lithium ion acceptability as described above, styrene butadiene rubber (SBR) and modified products thereof including CMC are used. It can be said that it is more preferable to add a small amount together with the cellulose resin.

 Further, in the present invention, as a material for electrically insulating the positive electrode and the negative electrode, in addition to the porous layer formed on the negative electrode, a microporous polymer film conventionally used for lithium secondary batteries may be used together. . The polymer film used in this case preferably has a single-layer or multi-layer structure made of a microporous film of polyolefin resin such as polyethylene resin or polypropylene resin or a nonwoven fabric.

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

  3 kg of lithium cobaltate was stirred in a double-arm kneader together with 1 kg of PVDF # 1320 (N-methylpyrrolidone (NMP) solution with a solid content of 12 parts by weight), 90 g of acetylene black and an appropriate amount of NMP. A positive electrode paste was prepared. This paste was applied and dried on a 15 μm thick aluminum foil, rolled to a total thickness of 160 μm, and then slit to a width that could be inserted into a cylindrical mold 18650 to obtain a positive electrode hoop.

  On the other hand, 3 kg of artificial graphite was mixed with Nippon Zeon Co., Ltd. styrene-butadiene copolymer rubber particle binder BM-400B (solid content 40 parts by weight) 75 g, CMC 30 g and an appropriate amount of water in a double arm kneader. Stirring to prepare a negative electrode paste. This paste was applied to and dried on a 10 μm thick copper foil, rolled to a total thickness of 180 μm, and then slit into a width that could be inserted into a cylindrical mold 18650 to obtain a negative electrode hoop.

  On the other hand, 970 g of alumina having a median diameter of 0.3 μm was stirred with a double arm kneader together with 375 g of polyacrylonitrile modified rubber binder BM-720H (solid content 8 parts by weight) manufactured by Nippon Zeon Co., Ltd. and an appropriate amount of NMP. Thus, a porous film paste was produced. This paste was applied and dried on the above negative electrode hoop by 20 μm on each side.

These positive and negative electrodes were overlapped to form a winding, and were cut at a predetermined length to produce an electrode plate group. On the other hand, 1000 g of alumina and 1000 g of hot melt adhesive were mixed, and the upper and lower end surfaces of the electrode plate group were immersed in a heated solution and cooled to prepare an electrode plate group in which the end surfaces of the electrode plate group were filled with an insulator. Next, the electrode plate group is inserted into a battery case, and 5.5 g of an electrolytic solution in which 1% of LiPF ₆ and 3% by weight of VC are dissolved in an EC / DMC / EMC mixed solvent is added and sealed. 1,000 18650 lithium secondary batteries were produced. This is Example 1.

On the other hand, in the same manner as in Example 1, the positive electrode and the negative electrode coated with the porous film paste were overlapped to form a wound, and the electrode plate group produced by cutting at a predetermined length was inserted into the battery case. Then, 5.5 g of an electrolytic solution in which 1 part of LiPF ₆ and 3 parts by weight of VC were dissolved in an EC / DMC / EMC mixed solvent was added and sealed to prepare 1000 cylindrical 18650 lithium secondary batteries. This is referred to as Comparative Example 1.

These batteries were evaluated by the following method.
(Drop test)
After charging the above-mentioned 2000 batteries at a constant current of 1400 mA until the charging voltage is 4.2 V, the battery is charged at a constant voltage of 4.2 V until the charging current is 100 mA, and then 1.5 m high from the ground. Then, the OCV after dropping 5 times was measured, and the occurrence frequency of internal short circuit was evaluated.

  The results are shown in (Table 1).

  As shown in Table 1, in Comparative Example 1 in which the end face of the electrode plate group was not protected, there was an internal short circuit caused by an impact caused by dropping. On the other hand, in Example 1 in which the end face of the electrode plate group was protected, an internal short circuit due to dropping did not occur.

  This is considered to be because the movement of the electrode plate due to the impact of dropping is suppressed by protecting the end face of the electrode plate group with an insulator.

  As in this example, using a method of immersing and curing the electrode group in a solution composed of insulating fine particles and an adhesive, not only can the end surface of the electrode group be protected by an insulator, but also through the insulator. Thus, the positive electrode and the negative electrode at the end of the electrode plate group can be firmly bonded, and the movement of the electrode plate can be further suppressed.

The lithium secondary battery according to the present invention has excellent safety and is useful as a power source for portable electronic devices and the like.

Schematic diagram of the structure of the lithium secondary battery in the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous layer apply | coated on electrode 2 Negative electrode 3 Insulator 4 Positive electrode

Claims (3)

In a lithium secondary battery having an electrode plate group in which a positive electrode and a negative electrode are laminated or wound,
A lithium secondary battery, wherein the negative electrode has a porous layer made of an inorganic oxide filler and a binder adhered on an electrode plate, and an end face of the electrode plate group is protected by an insulator. . The lithium secondary battery according to claim 1, wherein the insulator includes insulating fine particles and an adhesive. In a method for producing a lithium secondary battery having an electrode plate group in which a positive electrode and a negative electrode are laminated or wound, a porous layer comprising an inorganic oxide filler and a binder is formed on the negative electrode, and the positive electrode and the negative electrode A method for producing a lithium secondary battery, comprising: producing a plate group by winding or laminating and laminating the upper and lower end surfaces of the plate group in a solution comprising an insulator and an adhesive.