JP5099789B2 - Flat non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a flat non-aqueous electrolyte secondary battery, and more particularly to a flat non-aqueous electrolyte secondary battery that prevents damage to a separator and electrodes during lead terminal welding.

A metal oxide such as MnO ₂ or V ₂ O ₅ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or polyacene structure is used as the positive electrode active material, and metal lithium, lithium alloy, or polyacene structure is used as the negative electrode. Organic compounds such as lithium, carbonaceous materials that can occlude and release lithium, or oxides such as lithium titanate and lithium-containing silicon oxide, and the electrolyte is propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _{2 in} a non-aqueous solvent such as methyl ethyl carbonate, dimethoxyethane, and γ-butyrolactone. Dissolve supporting salt such as Coin-type and button-type flat non-aqueous electrolyte secondary batteries using non-aqueous electrolytes have already been commercialized, and SRAMs and RTCs that discharge at light loads with discharge currents of several to several tens of μA are already available. It is applied to applications such as backup power supplies and main power supplies for wristwatches that do not require battery replacement.

  On the other hand, as main power sources for small information terminals such as mobile phones and PDAs, larger rectangular and cylindrical lithium ion secondary batteries and nickel hydride storage batteries are used. However, in recent years, downsizing of devices used has been accelerated, and it is required to reduce the size of the secondary battery as the main power source. On the other hand, a metal negative electrode case also serving as a negative electrode terminal as shown in Patent Document 1 and Patent Document 2 and a metal positive electrode case also serving as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or A flat non-aqueous electrolyte secondary battery having a sealing structure in which a negative electrode case is crimped by caulking and includes a non-aqueous electrolyte and a power generation element including at least a positive electrode, a separator, and a negative electrode. When a cross section in a direction perpendicular to the flat surface of the battery is viewed, an electrode group having positive and negative electrode facing surfaces in which at least three or more positive and negative electrodes are opposed to each other via a separator is housed, and within the electrode group A flat nonaqueous electrolyte secondary battery has been proposed in which the sum of the positive and negative electrode facing areas is larger than the opening area of the insulating gasket.

  Next, when incorporating these flat non-aqueous electrolyte secondary batteries into equipment, the lead terminals are welded to the outside of the positive electrode case and / or the negative electrode case in the same manner as conventional flat batteries, and the lead terminal ends are connected to the inside of the equipment. A method of soldering and incorporating the circuit board is considered. However, in the battery, since it is necessary to store an electrode group having a large electrode area in the battery in a compact manner, the thickness of the electrode layer including the positive electrode active substance-containing layer, the negative electrode active substance-containing layer, and the separator is approximately 1.0 mm. A current collecting mechanism is adopted that suppresses the following, further stacks or winds, and makes the upper and lower surfaces of the electrode group contact the positive electrode case and the negative electrode case. Therefore, there is no problem as long as the electrode layer is thick. However, in a battery configuration having an electrode layer thickness of 1.0 mm or less, the heat generated when welding the lead terminal to the case outer surface of the flat battery is reduced. It is easy to be transferred to the inside of the electrode group through the battery case and the electrode group current collector, and as a result, the generated heat reaches the separator, causing the separator to perforate and shrink, leading to an internal short circuit and capacity deterioration. It was. In addition, there is a problem that the electrode leading to the welded part is peeled off from the current collector, which is considered to be a cause of the capacity reduction.

JP 2001-68160 A JP 2001-68143 A

  The present invention has been made in view of the above situation, and its purpose is to block the transfer of heat generated when welding the lead terminal to the battery case to the inside of the electrode group, and prevent the occurrence of capacity deterioration and internal short circuit. The object is to provide a flat nonaqueous electrolyte secondary battery.

  As a result of intensive studies, the present inventors have found that in a flat non-aqueous electrolyte secondary battery, a non-metallic heat insulating material is provided between the positive electrode and / or the negative electrode case and the thin film separator, whereby the positive electrode and the negative electrode case are provided. It has been found that the heat generated when welding the lead terminal from the outside of the battery can be blocked from being transmitted to the inside of the electrode group, and the destruction of the electrode and separator in the battery can be suppressed. In addition, with regard to the method of installing the heat insulating material, the current collecting part of the electrode group in contact with the battery case is processed into a U shape, and the heat insulating material is held inside the U shape so that the structure is not complicated and the productivity is excellent. It was found that the electrode and the thin film separator in the battery can be prevented from being destroyed while maintaining the above, and because the battery is compact, a high capacity can be obtained.

  According to the present invention, it is possible to eliminate the problems of perforation and shrinkage of the separator after the lead terminal is welded to the battery while maintaining the high capacity of the battery, so that the industrial value is very large. An excellent flat nonaqueous electrolyte secondary battery can be provided.

1 is a cross-sectional view of a flat nonaqueous electrolyte secondary battery of Example 1. FIG. FIG. 2 is a partially enlarged view of the flat nonaqueous electrolyte secondary battery in FIG. 1.

  Hereinafter, how the present inventors have realized the flat nonaqueous electrolyte secondary battery (hereinafter simply referred to as a battery) of the present invention will be described. In order to prevent the heat generated during lead terminal welding from being transmitted to the inside of the electrode, a non-metallic material is inserted between the battery case and the electrode group. However, nonmetallic materials with low thermal conductivity are generally poor in electrical conductivity.

  Therefore, it is possible to energize the electrode group and the positive electrode case or the negative electrode case by making the current collecting part of the electrode group long and forming a U shape, and inserting a heat insulating material therein, and only performing heat insulation It becomes possible. Nonmetallic materials with low thermal conductivity include glassy materials, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). , Fluoropolymers such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and polyvinylidene fluoride (PVDF), polyimide, liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), polyethylene terephthalate A resin selected from (PET), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and acetate resin is preferably stable with respect to the electrolyte and lithium ions, and heat generated during terminal welding. Therefore, in order to prevent the heat insulating material from melting and affecting the battery performance, a heat insulating material having a heat resistance of 150 ° C. or higher is more preferable. A glassy material and a fluororesin such as PTFE, FEP, ETFE, PFA, PVDF, polyimide, etc. A resin selected from LCP, PPS and PBT is more preferable.

  Moreover, about the form, flexible materials, such as a film, a woven fabric, a nonwoven fabric, and a fiber, have good adhesiveness with an electrode current collection member, and a heat insulation effect is high and preferable. Further, a tape-like material made of these materials as a base material and coated with an adhesive on one side or both sides is excellent in preventing displacement of the electrode current collecting member and the heat insulating material, and is more effective. Further, the shape of the heat insulating material is not particularly limited, but it is more preferable to make the area larger than the area of the current collecting portion of the electrode group for the purpose of giving flexibility to the position and direction of the terminal during terminal welding.

  Regarding the thickness of the heat insulating material, if the thickness is small, the heat insulating effect is insufficient, and if it is thick, the amount of active substance that can be incorporated in the battery decreases, leading to a decrease in battery capacity. Considering these, the thickness of the heat insulating material is suitably 0.05 mm or more and 0.20 mm or less.

Next, the present battery has a main structure in the structure of the battery including the electrode, and the positive electrode active substance is not limited. MnO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , LiTi ₂ Metal oxides such as O ₄ , Li ₄ Ti ₅ O ₁₂ , LiFe ₂ O ₄ , lithium cobaltate, lithium nickelate and lithium manganate, or inorganic compounds such as graphite fluoride and FeS ₂ , or polyaniline and polyacene structures Any organic compounds such as can be applied. However, lithium-containing oxides in which lithium cobaltate, lithium nickelate, lithium manganate, mixtures thereof, or some of these elements are substituted with other metal elements are high in terms of operating potential and excellent cycle characteristics. Lithium cobaltate is a flat type non-aqueous electrolyte secondary battery that is more preferable and may be used for a long period of time because it has a high capacity, is low in reactivity with electrolytes and moisture, and is chemically stable. Is more preferable.

Next, the negative electrode active material of the battery is not limited, and is lithium metal, Li-Al, Li-In, Li-Sn, Li-Si, Li-Ge, Li-Bi, Li-Pb, or the like. Lithium alloys, organic compounds such as polyacene structures, carbonaceous materials capable of occluding and releasing lithium, Nb ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, and Li-containing silicon oxides All kinds of oxides can be used, but carbonaceous materials that can occlude and release Li are preferable in terms of excellent cycle characteristics, low operating potential, and high capacity. natural graphite and artificial graphite in that the voltage drop is small, expanded graphite, mesophase pitch fired body, d ₀₀₂ surface, such as mesophase pitch fiber sintered body Carbonaceous material surface interval following graphite structure 0.338nm has developed is more preferable.

  As for the electrodes, both the positive and negative electrodes may be formed by pressure forming a granular mixture as found in conventional flat batteries or by filling the metal net with a mixture. From the standpoint of ease, a slurry obtained by applying a slurry mixture to a metal foil and drying it is preferable, and a rolled product thereof can also be used. When using an electrode in which a mixture layer containing an active substance is applied to the metal foil as described above, the electrode used inside the electrode group is one in which an active substance-containing layer is formed on both sides of the metal foil. From the viewpoint of efficiency, the metal negative electrode case that also serves as the negative electrode terminal, and both ends of the electrode component material that contacts the metal positive electrode case that also serves as the positive electrode terminal, in order to reduce contact resistance, It is particularly preferable to expose the metal foil. In this regard, an electrode in which an active substance-containing layer is formed only on one side may be used only in this portion, or after an active substance-containing layer is once formed on both sides, the active substance-containing layer may be removed only on one side.

  Moreover, the material of the lead terminal welded to the battery is not particularly limited as long as conductivity is obtained, and a stainless material is preferable in terms of excellent terminal strength and workability. Further, the thickness and shape of the terminal are not particularly limited.

  Hereinafter, examples and comparative examples of the present invention will be described in detail.

Example 1
1 is a cross-sectional view of a flat nonaqueous electrolyte secondary battery according to Example 1 of the present invention, and FIG. 2 is a partially enlarged view of FIG. In the figure, the battery case of the flat non-aqueous electrolyte secondary battery of Example 1 has a negative electrode case 7 in which an insulating gasket 6 is integrated with a positive electrode case 8 made of stainless steel. Contains a power generating element wound in a spiral shape between a positive electrode active substance-containing layer 1a and a negative electrode active substance-containing layer 3a with a separator 5 made of a polyethylene microporous film interposed therebetween. 1b is a positive electrode current collector, 2 is a positive electrode side heat insulating material, 3 is a negative electrode plate, 3b is a negative electrode current collector, and 4 is a negative electrode side heat insulating material.

Next, a method for manufacturing the flat nonaqueous electrolyte secondary battery of Example 1 will be described. First, 5 parts by mass of acetylene black and 5 parts by mass of graphite powder are added as conductive materials to 100 parts by mass of LiCoO ₂ , 5 parts by mass of polyvinylidene fluoride (PVDF) is added as a binder, and diluted and mixed with N-methylpyrrolidone. As a result, a slurry-like positive electrode mixture was obtained. This positive electrode mixture was applied to one side of a 0.02 mm thick aluminum foil as the positive electrode current collector 1b by a doctor blade method and dried to form the positive electrode active substance-containing layer 1a on the aluminum foil surface. Thereafter, coating and drying were performed in the same manner on the other side to prepare a double-sided coated positive electrode having a positive electrode active material-containing layer 1a having a coating thickness of 0.15 mm on both sides. Next, this double-side coated positive electrode was cut out to a width of 15 mm and a length of 120 mm, the portion from the end of one side of the electrode to 10 mm was used as the current-carrying part, the positive-electrode active substance-containing layer 1a was removed, The layer 1a was removed to an area of 22 mm from the end to obtain a positive electrode plate 1. As the heat insulating material 2, a glass cloth having a length of 11 mm and a width of 16 mm is used as a base material, and a glass tape having a thickness of 0.03 mm coated with an adhesive is applied to the positive electrode active material containing layer 1 a from the end of the positive electrode plate. It was affixed at a position 10 mm from the end of the surface that was removed from the end to a region 22 mm away.

  Next, 2.5 parts by mass of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders are added to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, diluted with ion-exchanged water, mixed, and slurry A negative electrode mixture was obtained. The obtained negative electrode mixture was applied to a 0.02 mm thick copper foil, which is the negative electrode current collector 3b, so that the thickness of the negative electrode active material-containing layer 3a was 0.15 mm, and dried in the same manner as in the case of the positive electrode. And a double-sided coated negative electrode body was produced. Next, this negative electrode body is cut out to have a width of 15 mm and a length of 120 mm, and the portion from the end of one side of the electrode to 10 mm is used as a current-carrying part, the negative electrode active substance-containing layer 3a is removed, and the negative electrode active substance-containing layer 3a on the back side. Was removed to an area of 22 mm from the end to form a negative electrode plate 3. A glass cloth having a length of 11 mm and a width of 16 mm is used as a base material at a position 10 mm from the end of the surface obtained by removing the negative electrode active material-containing layer 3 a from the end of the negative electrode plate 3 to an area of 22 mm from the end. A glass tape having a thickness of 0.03 mm with a pressure-sensitive adhesive applied on one side was attached.

  Next, the positive and negative electrode energizing portions were finished, and the positive electrode 1 and the negative electrode 3 were wound between the positive electrode plate 1 and the negative electrode plate 3 with a separator 5 made of a polyethylene microporous film having a thickness of 25 μm. A space in the center of the wound electrode in a certain direction so that the uncoated portions of the positive electrode plate and the negative electrode plate are bent in opposite directions in the winding direction and have a positive and negative electrode facing portion in the horizontal direction with respect to the flat surface of the flat battery. Pressurized until no more.

After the produced electrode group was dried at 85 ° C. for 12 hours, the uncoated portion on the negative electrode side of the electrode group was in contact with the inner bottom surface of the negative electrode case 7 having a thickness of 0.25 mm integrated with the insulating gasket 6. Then, a non-aqueous electrolyte in which LiPF ₆ was dissolved as a supporting salt in a ratio of 1 mol / l was poured into a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1, and the positive electrode was not coated. The positive electrode case 8 having a thickness of 0.25 mm is fitted so as to be in contact with the upper surface, and after being turned upside down, the positive electrode case 8 is crimped, sealed, and flattened as in Example 1 having a thickness of 3 mm and a diameter of 24.5 mm. A nonaqueous electrolyte secondary battery was fabricated.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that a glass tape having a thickness of 0.05 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 3)
A battery was fabricated in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.14 mm, and a glass tape having a thickness of 0.10 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

Example 4
A battery was prepared in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.13 mm, and a glass tape having a thickness of 0.15 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 5)
A battery was fabricated in the same manner as in Example 1 except that the active substance-containing layer of the positive electrode and the negative electrode had a thickness of 0.12 mm, and a glass tape having a thickness of 0.20 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 6)
A battery was fabricated in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.10 mm and a glass tape having a thickness of 0.30 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 7)
A battery was fabricated in the same manner as in Example 1, except that a PTFE film having a base material and a PTFE tape having a thickness of 0.03 mm coated with an adhesive on one side was attached as a heat insulating material to the positive electrode plate and the negative electrode plate.

(Example 8)
A battery was fabricated in the same manner as in Example 1 except that a PTFE tape having a thickness of 0.05 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

Example 9
A battery was fabricated in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.14 mm, and a PTFE tape having a thickness of 0.10 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 10)
A battery was prepared in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.13 mm and a PTFE tape having a thickness of 0.15 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 11)
A battery was fabricated in the same manner as in Example 1 except that the active substance containing layer of the positive electrode and the negative electrode had a thickness of 0.12 mm, and a PTFE tape having a thickness of 0.20 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Example 12)
A battery was fabricated in the same manner as in Example 1 except that the active substance-containing layer of the positive electrode and the negative electrode had a thickness of 0.10 mm, and a PTFE tape having a thickness of 0.30 mm was attached to the positive electrode plate and the negative electrode plate as a heat insulating material.

(Comparative Example 1)
A battery was produced in the same manner as in Example 1 except that the heat insulating material was not attached to the positive electrode plate and the negative electrode plate.

  For each of the 300 batteries of this example and the comparative example produced as described above, a lead terminal made of stainless steel with a thickness of 0.2 mm was further added to both the positive and negative battery cases, and the output voltage of the resistance welding machine was set to 480 ± 10 V. Set and welded. Fifty of these batteries were extracted at random, the batteries were disassembled, and the positive and negative separators were perforated, contracted, and the electrodes were peeled off. Next, 50 pieces were further extracted from the remaining batteries, and the initial charge was performed at a constant current and a constant voltage of 4.2 V and 3 mA for 48 hours. After leaving at room temperature for 3 days, the open circuit voltage was measured. Thereafter, only the batteries having the open circuit voltage of 4.0 V or higher were selected, and further discharged to 3.0 V at a constant current of 1 mA to obtain the discharge capacity.

  The separator of the battery of this example and the comparative example, perforation, shrinkage, electrode peeling rate, the number of batteries whose open circuit voltage after standing for 3 days was 4.0 V or more, and the average of the discharge capacity thereafter The values are shown in Table 1.

  As is apparent from Table 1, the batteries of the respective examples of the present invention were made by punching, shrinking, and peeling off the electrodes on the positive and negative electrode sides after resistance welding of the lead terminals to the battery as compared with the battery of Comparative Example 1. Is greatly improved, the internal short circuit of the battery is suppressed, and the rate of occurrence of the battery in which the open circuit voltage is reduced is reduced. Regarding the batteries of Examples 1 and 7, there was some shrinkage of the positive electrode and negative electrode side separators after resistance welding, but the internal short circuit within the battery did not occur. In particular, regarding the batteries of Examples 2 to 6 and Examples 8 to 12 in which the thickness of the glass tape that is a heat insulating material or the PTFE tape that is a fluororesin is 0.05 mm or more, after resistance welding the lead terminal to the battery The separators on the positive and negative electrode sides are hardly perforated, contracted, peeled off from the electrodes, and the open circuit voltage is hardly lowered. Furthermore, since the batteries of Examples 2 to 5 and Examples 8 to 11 have an appropriate thickness of the heat insulating material, many active substances can be packed in the battery, and a high capacity battery can be obtained.

  In the examples of the present invention, the case where glass and PTFE are used as the base material of the non-metallic heat insulating material has been described. However, the base material is FEP, ETFE, PFA, PVDF, polyimide, LCP, PPS, PBT. The same effect can be obtained when using. In the embodiments of the present invention, a flat nonaqueous solvent secondary battery using a nonaqueous solvent as a nonaqueous electrolyte has been described. However, the present invention is a polymer secondary battery using a polymer electrolyte as a nonaqueous electrolyte. It can also be applied to solid electrolyte secondary batteries using solid electrolytes, and it is also effective for batteries using polymer thin films and solid electrolyte films that may be damaged by heat when welding instead of resin separators. It is. The battery shape has been described based on a coin-type non-aqueous electrolyte secondary battery that is sealed by crimping the positive electrode case, but it is also possible to replace the positive and negative electrodes and seal the negative electrode case by crimping. . Further, the battery shape does not have to be a perfect circle, and can be applied to a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape or a square shape.

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 1a Positive electrode active material content layer 1b Positive electrode collector 2 Heat insulation material (positive electrode side)
DESCRIPTION OF SYMBOLS 3 Negative electrode plate 3a Negative electrode active material content layer 3b Negative electrode collector 4 Heat insulating material (negative electrode side)
5 Separator 6 Insulating gasket 7 Negative electrode case 8 Positive electrode case

Claims (4)

A metal negative electrode case that also serves as a negative electrode terminal and a metal positive electrode case that also serves as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or the negative electrode case is further crimped by caulking. In the flat non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte and an electrode group in which at least a positive-electrode active substance-containing layer, a negative-electrode active substance-containing layer, a thin film separator are combined,
A flat nonaqueous electrolyte secondary battery comprising a non-metallic film, a woven fabric, a non-woven fabric, or a heat insulating material provided between the positive electrode and / or negative electrode case and the thin film separator.   A positive electrode component having conductivity is exposed from one electrode group including at least a positive electrode, a separator, and a negative electrode to one outside in a direction horizontal to the flat surface of the flat battery, and the positive electrode component is directly or electrically applied to the positive electrode case. A structure in which a negative electrode component having conductivity is exposed to the other outside in the direction parallel to the flat surface of the flat battery of the electrode group, and the negative electrode component is directly or electrically connected to the negative electrode case. And the constituent exposed portions of the positive electrode and / or the negative electrode form a U-shape having a flat portion in a direction horizontal to the flat surface of the flat battery, and the heat insulating material is disposed inside the U-shape. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the battery is held.   The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the heat insulating material is made of glass and has a thickness of 0.05 mm or more and 0.20 mm or less.   2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein a constituent material of the heat insulating material is made of a resin, and a thickness thereof is 0.05 mm or more and 0.20 mm or less.

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