JP2005259621A - Laminated film sheathed battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated film sheathed battery in which a force loaded on electrode groups and heat conduction when heated and sealed can be suppressed, and in which inside short-circuit is reduced. <P>SOLUTION: In the laminated film sheathed battery 1, the outer rim of the sheathed body of the laminated film 2 is thermally fused. In the sheathed body, the electrode groups 10 in which the positive electrodes and the negative electrodes are laminated via a separator and a framed state resin frame 5 to protect the electrode groups 10 are sealed. In the one side of the resin frame 5, a groove part of a roughly U-shaped cross-section is formed in the one face side in the height direction, and into the groove, the electrode terminal is fitted. The electrode terminal is fixed to the outer rim part of the laminated film 2, and taken out to the outside of the laminated film sheathed battery 1. The height h of the resin frame 5 is in the range of 90-110% of the thickness a of the electrode groups. Even if external force is applied, the resin frame 5 protects the electrode groups 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated film-clad battery, and more particularly to a laminated film-clad battery in which an electrode group in which a positive electrode and a negative electrode are laminated via a separator is enclosed in a laminated film.

  In recent years, with the development of electronic devices, there has been a demand for development of a non-aqueous electrolyte secondary battery that is small and lightweight, has high energy density, and can be repeatedly charged and discharged. Such a nonaqueous electrolyte secondary battery includes a negative electrode using lithium or a lithium alloy as a negative electrode active material, and an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as a positive electrode active material. A lithium secondary battery including a positive electrode in which a turbid liquid is applied to a current collector and a non-aqueous electrolyte is known. Recently, as a negative electrode active material, for example, a negative electrode including a carbonaceous material capable of occluding and releasing lithium ions such as coke, graphite, carbon fiber, a resin fired body, pyrolytic vapor phase carbon, and lithium cobalt as a positive electrode active material. Development and commercialization of lithium ion secondary batteries using a positive electrode containing a double oxide or a lithium manganese double oxide are being actively carried out.

  Conventionally, in these nonaqueous electrolyte secondary batteries, coin-shaped and cylindrical shapes have been mainstream, but with the diversification of applications, there is a demand for those having excellent volume-efficiency shapes such as square and oval. It is growing. In addition, for the purpose of further reducing the weight and size, it has been studied to change the electrode body and the exterior body containing the nonaqueous electrolyte from a conventional metal exterior can to a film material. As this film material, in order to prevent gas such as water vapor and oxygen from entering and exiting the inside and outside of the film, a metal foil such as an aluminum foil is arranged in the center, and the outermost layer protects the metal foil from physical impact. A multilayer film (hereinafter referred to as a laminate film) in which a resin layer such as a resin is formed and a heat-fusible resin layer such as a polypropylene resin is formed in the innermost layer is generally used.

  In a laminate film package battery using a laminate film as an exterior body, the electrode group and the heat-fusible resin layer are disposed between two laminate films so that the four sides (periphery) of the two laminate films are in contact with each other. Is sealed in the exterior together with the non-aqueous electrolyte. At this time, the electrode terminal connected to the electrode group is sandwiched between the fused portions of the laminate film. Therefore, since the power generation element is enclosed in the lightweight laminate film, the weight of the battery can be reduced. In addition, by performing thermocompression bonding in a reduced-pressure atmosphere, the laminate film exterior is in a reduced-pressure state, so the laminate-film exterior battery is exposed to atmospheric pressure from the outside, and the positive and negative electrodes are appropriately pressurized via the separator ( The battery output can be improved.

  On the other hand, the laminate film is not as strong as the conventional metal outer can. For this reason, for example, when the battery internal pressure rises due to the vapor of the non-aqueous electrolyte component, the battery expands and easily changes its shape. In order to avoid this, a technique is disclosed that includes an insulating adhesive layer between a power generation element and a laminate film (see, for example, Patent Document 1).

JP 2003-151512 A

  However, when the inside of the battery is in a reduced pressure state when the battery is manufactured, the laminate film is deformed along the power generation element (electrode group), so that the laminate film is pressed against the outer peripheral portion of the power generation element. For this reason, since a large force is applied to the outer peripheral portion of the power generation element, the power generation element is easily damaged and the active material layer is easily separated. In addition, since the laminate film is heated and sealed when the power generation element is sealed, the heat may be conducted to the power generation element and the separator between the positive electrode and the negative electrode may contract or melt. When these phenomena occur, an internal short circuit is likely to occur, resulting in poor battery yield and markedly reduced battery productivity. Further, when a plurality of laminated film-clad batteries are used in combination, force may be applied from the outside of the battery, which may cause damage to the power generation element.

  An object of the present invention is to provide a laminated film-clad battery in which the force applied to the electrode group and the heat conduction at the time of heat sealing can be suppressed and the internal short circuit is reduced.

  In order to solve the above problems, the present invention provides a laminated film-clad battery in which an electrode group in which a positive electrode and a negative electrode are laminated via a separator is enclosed in a laminate film outer package, and the electrode group is disposed around the electrode group. A frame-shaped protective member for protecting the frame is provided.

  In the present invention, since the frame-shaped protective member for protecting the electrode group is provided around the electrode group in which the positive electrode and the negative electrode are laminated via the separator in the laminate film outer package, the electrode group can be applied even if force is applied from the outside. Is protected by a frame-shaped protective member, so that damage to the electrode group is prevented, and heat conduction to the electrode group at the time of heat sealing of the laminate film is interrupted, so that melting and shrinkage of the separator are suppressed. Internal short circuit can be reduced.

  In this case, if the height of the protective member is smaller than 90% of the thickness of the electrode group, an external force acts on the electrode group at a portion exceeding the height of the protective member, and the height of the protective member is the thickness of the electrode group. If it is larger than 110%, the binding force between the positive electrode and the negative electrode is reduced, and the output is reduced. Therefore, the height of the protective member is preferably 90% to 110% of the thickness of the electrode group. In addition, if the protective member has a groove for supporting the electrode terminal connected to the electrode group, the electrode terminal is supported by the groove even if an external force is applied to the electrode terminal. Therefore, the fatigue of the electrode terminal due to external force and the force applied to the fused portion of the laminate film in which the electrode terminal is sandwiched can be suppressed.

  According to the present invention, since the protective member for protecting the electrode group is provided around the electrode group in the laminate body of the laminate film, the electrode group is prevented from being damaged even when an external force is applied, and the laminate film is heated. Since heat conduction to the electrode group at the time of sealing is interrupted and the melting and shrinkage of the separator are suppressed, an effect that the internal short circuit can be reduced can be obtained.

  Hereinafter, an embodiment of a laminated film-clad battery according to the present invention will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1, the laminated film-clad battery 1 of the present embodiment has a shape in which one surface side (lower side in FIG. 1) is substantially flat and the other surface side (upper side) is convex. In the laminated film-clad battery 1, the four sides of the outer edge portion of the laminated film 2 of the outer package are sealed by heat sealing. Positive and negative electrode terminals 3 are led out from one side of the outer edge portion of the laminated film-clad battery 1, and the electrode terminals 3 are fixed (supported) at the fusion part of the laminated film 2. As shown in FIG. 2, an electrode group 10 in which positive and negative electrodes are laminated via a separator, a frame-shaped resin frame 5 as a protective member for protecting the electrode group 10, and illustration are omitted in the exterior of the laminate film 2. The non-aqueous electrolyte solution is enclosed. The resin frame 5 is disposed on the four side surfaces (entire circumference) of the electrode group 10.

  For the laminate film 2, a multilayer film having a three-layer structure including a metal foil serving as a base material, a protective resin layer protecting the metal foil, and a heat-sealing resin layer is used. In the laminate film 2, a protective resin layer, a metal foil, and a heat-sealing resin layer are laminated in this order via an adhesive and are formed by press working. As the metal foil, an aluminum foil having a thickness of 40 μm is used. Since this aluminum foil prevents the entry and exit of gases such as water vapor and oxygen, the laminate film 2 has gas barrier properties. A 25 μm-thick nylon film is used for the protective resin layer, and a polypropylene (hereinafter abbreviated as PP) film is used for the heat-sealing resin layer.

  As shown in FIG. 3, the electrode group 10 has a structure in which a plurality of positive electrodes 11 and negative electrodes 12 are stacked in the vertical direction via separators 13. The positive electrode 11 and the negative electrode 12 are alternately stacked one by one so that the upper and lower ends become the negative electrode 12, and one separator 13 is stacked between each of the positive electrode 11 and the negative electrode 12. At this time, the positive electrode lead piece (not shown) connected to each positive electrode 11 is laminated on one side of the electrode group 10 and the negative lead piece (not shown) connected to each negative electrode 12 is laminated on the other side. ing. In the laminated film exterior battery 1, the positive electrode 11 is cut to a size slightly smaller than the negative electrode 12 in order to prevent an internal short circuit between the positive electrode 11 and the negative electrode 12. The separator 13 is made of a microporous PP film cut to the same size as the negative electrode 12 in order to achieve insulation between the positive and negative electrodes and to reduce the size of the electrode group 10 and insert it inside the resin frame 5. It is used. The thickness a of the electrode group 10 indicates the distance between the upper and lower ends in the stacking direction of the electrode group 10. In FIG. 3, the thicknesses of the positive electrode 11, the negative electrode 12, and the separator 13 are shown to be thicker than the actual thickness for easy understanding of the configuration of the electrode group 10.

  All of the positive electrode lead piece and the negative electrode lead piece are assembled and connected to the positive and negative electrode terminals 3, respectively. An aluminum plate is used for the positive electrode terminal 3 and a nickel plate is used for the negative electrode terminal 3. The positive and negative electrode terminals 3 have a rectangular cross section with a thickness of 0.3 mm and a width of 15 mm. A PP tape having a thickness of 100 μm and a width of 10 mm is attached to the outer periphery of the positive and negative electrode terminals 3 as a seal tape.

  The positive electrode 11 uses a lithium manganese composite oxide as a positive electrode active material. The positive electrode 11 has a positive electrode mixture coated on both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 20 μm, and has a thin plate shape with a thickness of 90 μm and a rectangular shape. A band-like positive electrode lead piece made of aluminum is connected to one side of one side of the positive electrode current collector by ultrasonic welding. In the positive electrode mixture, 10 parts by weight of flaky graphite as a conductive agent and 5 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) are blended as a conductive agent with respect to 100 parts by weight of the positive electrode active material. ing. The positive electrode 11 is formed by adding N-methylpyrrolidone (hereinafter abbreviated as NMP) as a dispersion solvent to the components of the positive electrode mixture, applying the kneaded slurry to an aluminum foil, and then drying and pressing. Yes.

  On the other hand, graphite powder is used for the negative electrode 12 as a negative electrode active material. The negative electrode 12 has a negative electrode mixture coated on both sides of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm, and has a thin plate shape of 70 μm and a square shape. A copper strip-like negative electrode lead piece is connected to one side of one side of the negative electrode current collector by ultrasonic welding. In the negative electrode mixture, 10 parts by weight of PVDF as a binder is blended with 90 parts by weight of the negative electrode active material. The negative electrode 12 is formed by adding NMP as a dispersion solvent to the components of the negative electrode mixture and applying a kneaded slurry to the rolled copper foil, followed by drying and pressing.

  As shown in FIG. 4, the resin frame 5 is made of PP resin and has a frame shape into which the electrode group 10 can be inserted. On one side of the resin frame 5, two grooves 6 having a substantially U-shaped cross section for supporting the positive and negative electrode terminals 3 are formed on one side in the stacking direction (thickness a direction) of the electrode group 10 to be inserted. . The groove 6 is formed in a size that allows the electrode terminal 3 having the above-described size to be fitted therein. The height h of the resin frame 5 is set in the range of 90 to 110% with respect to the thickness a of the electrode group 10 (see FIG. 3).

In addition, 1 mol / liter (1M) of lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt (electrolyte) is dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in the non-aqueous electrolyte. Is used.

(Battery assembly)
In assembling the laminated film-clad battery 1, first, the electrode group 10 is inserted inside the resin frame 5. At this time, the positive and negative electrode terminals 3 are fitted into the two grooves 6 of the resin frame 5, respectively. Next, the laminate film 2 is placed on a cradle made of silicon rubber having a recess formed in accordance with the shape of the resin frame 5, and the resin frame 5 with the electrode group 10 inserted therein is aligned with the recess of the cradle. Place on the laminate film 2. Thereby, the laminate film 2 is deformed along the recess of the cradle, and the electrode group 10 and the resin frame 5 enter the recess.

  Next, after injecting the non-aqueous electrolyte into the concave portion of the deformed laminate film 2, another laminate film 2 is covered and the outer edges of the two laminate films are overlapped. At this time, the tips of the positive and negative electrode terminals 3 are projected outward from the outer edge of the laminate film 2. Subsequently, a metal plate heated to about 170 to 190 ° C., which is the melting temperature of the PP film, is pressed on the upper side of the laminated laminate film 2, and the outer edge portion of the laminate film 2 is thermocompression-bonded under a reduced pressure atmosphere. The laminated film 2 is heat-sealed. As a result, the softened PP resin is brought into close contact with the periphery of the electrode terminal 3 in the heat-sealed portion, and the gap is filled, and the assembly of the laminated film-clad battery 1 having a sealed structure is completed.

(Action etc.)
As shown in FIG. 5, in the conventional laminated film-clad battery 20 in which only the electrode group 10 is enclosed in the outer package of the laminate film 2 without the resin frame 5, the inside of the battery is in a reduced pressure state. A large force is applied to the outer peripheral portion of the electrode group 10 by being pressed from the outside at atmospheric pressure. For this reason, damage to the electrode group 10 such as bending of the outer peripheral portions of the positive electrode and the negative electrode and accompanying peeling of the active material layer is caused, and defects such as an internal short circuit occur at the outer peripheral portion of the electrode group 10. In addition, since the thermocompression bonding of the outer edge portion of the laminate film 2 is performed at about 170 to 190 ° C., this heat is conducted to the separator 13 constituting the electrode group 10, and the separator 13 contracts and melts, Similarly, a defect such as an internal short circuit may occur.

  In the laminated film exterior battery 1 of the present embodiment, the electrode group 10 is inserted into the resin frame 5 and enclosed in the exterior body of the laminate film 2 together with the resin frame 5 when the battery is manufactured. For this reason, when the electrode group 10 is sealed, the laminate film 2 is deformed along the shape of the resin frame 5, so that even if the inside of the battery is in a reduced pressure state and is pressed from the outside at atmospheric pressure, No force is applied, and damage such as bending of the outer peripheral portion of the electrode group 10 and peeling of the active material layer can be prevented (see FIG. 2). Moreover, since the heat conduction to the electrode group 10 is blocked by the resin frame 5 when the laminate film 2 is thermocompression bonded, the separator 13 can be prevented from melting and shrinking. Therefore, since the laminated film-clad battery 1 according to the present embodiment can be produced without causing an internal short circuit, the defective rate during battery production can be reduced.

  Further, in the laminated film-clad battery 1 of the present embodiment, even when in use, the resin frame 5 protects the electrode group 10, so that the force applied to the electrode group 10 is suppressed even when a force is applied from the outside. It is possible to prevent damage to the electrode group 10 and use the laminated film-clad battery 1 for a long period of time. Furthermore, when using as an assembled battery in which a plurality of laminated film-clad batteries 1 are combined, the force applied to the electrode group 10 of each battery is suppressed by the resin frame 5 even when a force is applied from the outside. The assembled battery can be used without causing damage to the group 10.

  Furthermore, when the resin frame 5 is disposed outside the laminated film-clad battery 1, since the resin frame larger than the battery is used, the entire battery becomes large. In particular, the assembled battery has a considerable size. In the laminated film-clad battery 1 of the present embodiment, since the resin frame 5 is enclosed in the laminated body of the laminated film 2, the laminated film-clad battery 1 can be made compact.

  Furthermore, an external force such as wiring connection is likely to be applied to the tip of the electrode terminal 3 protruding outward. For this reason, in the conventional laminated film-clad battery 20, force is applied to the fused portion of the laminated film 2 to which the electrode terminal 3 is fixed and the electrode group 10 connected to the electrode terminal 3. The electrode group 10 is damaged). In the laminated film-clad battery 1 of this embodiment, the electrode terminal 3 is supported by a groove 6 formed on one side of the resin frame 5. For this reason, even if an external force is applied to the electrode terminal 3, the movement of the electrode terminal 3 is prevented by the groove 6. Therefore, fatigue of the electrode terminal 3 due to the external force is suppressed, and the fusion part is damaged or the electrode group 10 is damaged. Can be suppressed.

  Next, examples of the laminated film-clad battery 1 manufactured according to this embodiment will be described. In addition, it describes together about the battery of the comparative example produced for the comparison.

(Example 1)
As shown in Table 1 below, in Example 1, the laminated film-clad battery 1 was manufactured with the ratio of the height h of the resin frame 5 to the thickness a of the electrode group 10 being 85%.

(Example 2 to Example 5)
As shown in Table 1, Example 2 to Example 5 were the same as Example 1 except that the ratio of the height h of the resin frame 5 to the thickness a of the electrode group 10 was changed. The ratio of the height h to the thickness a was 90% in Example 2, 100% in Example 3, 110% in Example 4, and 115% in Example 5.

(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, the resin frame 5 was not disposed, and only the electrode group 10 was enclosed in the laminate film 2. That is, the battery of Comparative Example 1 is a conventional laminated film-clad battery.

<Test and evaluation>
The following tests were performed and evaluated for each of the 20 batteries of Examples and Comparative Examples produced as described above.

  Before injecting the non-aqueous electrolyte, a short check was performed in which the resistance between the positive and negative terminals of each battery was measured with a digital multimeter, and a battery having a resistance value of 50 MΩ or higher was determined as a good product. From this result, the ratio of defective products with respect to the number of test batteries was calculated as a percentage to obtain the defective rate at the time of manufacturing each battery. Next, each battery of the example and the comparative example was initialized after being charged and discharged in an atmosphere having an environmental temperature of 25 ± 2 ° C. Charging conditions were 4.1V constant voltage, limiting current 5A, 2.5 hours, and discharging conditions were 1A constant current, final voltage 2.7V. Furthermore, after each battery was charged under the above-mentioned charging conditions (fully charged state), the output was measured in an atmosphere having an environmental temperature of 25 ± 2 ° C. In the measurement, discharge was performed at current values of 10A, 30A, and 90A for 10 seconds each, and the battery voltage value at each 5 seconds was plotted on the vertical axis with respect to the horizontal axis current value. A current value at a point where a straight line obtained by approximating three points intersected with 2.7 V, which is the end voltage, was read, and the product of this current value and 2.7 V was used as the output of the battery. Based on the measured defect rate and output results, a comprehensive evaluation of each battery was performed. In the overall evaluation, a battery having no defect and excellent output was indicated by 、, a battery having a slight defect was indicated by ◯, a battery having a slightly reduced output was indicated by Δ, and a battery having a markedly increased defect was indicated by ×. Table 2 below shows the failure rate, output, and comprehensive evaluation results for each battery.

  As shown in Table 2, in the battery of Comparative Example 1 manufactured without arranging the resin frame 5, the defect rate was 50%, and sufficient productivity could not be obtained. On the other hand, in the batteries of Examples 1 to 5 in which the periphery of the electrode group 10 is protected by the resin frame 5 and the height h of the resin frame 5 is in the range of 85 to 115% of the thickness a of the electrode group 10, The defective rate was significantly reduced, and good results could be obtained. From this, it was found that the height h of the resin frame 5 is preferably 85% or more and 115% or less of the thickness a of the electrode group 10.

  Further, in the battery of Example 1 in which the height h of the resin frame 5 was 85% of the thickness a of the electrode group 10, the defect rate was improved as compared with the battery of Comparative Example 1, but the defect rate was 5%. A good product was generated. On the contrary, in the battery of Example 5 in which the height h of the resin frame 5 is 115% of the thickness a of the electrode group 10, the defective rate was 0%, but no defective product was generated, but the output was different from that of other batteries. As a result, the result decreased by about 15%. In the batteries of Examples 2 to 4 in which the height h of the resin frame 5 is in the range of 90 to 110% of the thickness a of the electrode group 10, there is no generation of defective products, and the output is excellent. showed that. This is because when the height h of the resin frame 5 is smaller than 90% of the thickness a of the electrode group, a force is applied to the electrode group 10 exceeding the height of the resin frame 5, so that the electrode group 10 is protected. When the height h of the resin frame 5 is greater than 110% of the thickness a of the electrode group, an appropriate pressure is not applied between the stacked positive and negative electrodes (restraint). Therefore, it is conceivable that the electrical conductivity is lowered and the output of the battery is lowered. Therefore, when using a plurality of laminated film-clad batteries 1 as an assembled battery or considering the mass production system of the batteries, the height h of the resin frame 5 should be 90% to 110% of the thickness a of the electrode group. Was found to be more preferred.

  In the present embodiment, polypropylene resin is exemplified as the material of the resin frame 5, but the present invention is not limited to this. The material of the resin frame 5 that can be used in other than the present embodiment may be an electrically insulating resin without being dissolved in the non-aqueous electrolyte used, and examples thereof include polyolefin resins such as polyethylene. be able to.

  In the present embodiment, the electrode group 10 in which the positive electrode 11, the negative electrode 12, and the separator 13 are cut into a rectangular shape and stacked is illustrated, but the present invention is not limited to the shape of the battery. It can also be applied to other batteries. Further, the size of the battery is not particularly limited. Similar effects can be obtained by using the resin frame 5 that matches the shape and size of the electrode group 10. Further, the laminate film-covered battery 1 of the present embodiment can be used as a card-type secondary battery by further accommodating it in an outer case such as a card-type, for example.

  Furthermore, in this embodiment, although the example which formed the two groove parts 6 in 1 side of the resin frame 5 was shown, this invention is not limited to this. For example, three or more groove portions 6 may be formed, and the groove portions 6 may be formed on two opposite sides. In this way, the common resin frame 5 can be applied to a battery or the like in which the electrode terminals 3 are arranged on the opposite sides of the electrode group 10 in addition to arranging the positive and negative electrode terminals 3 side by side. It becomes possible.

  Furthermore, in the present embodiment, the laminated film-clad battery 1 is illustrated, but the present invention is not limited to this, and the same effect can be obtained even when applied to other secondary batteries and primary batteries. it can. Moreover, according to the kind etc. of the battery to which this invention is applied, components, such as an active material which comprises the positive electrode 11 and the negative electrode 12, and the material of the separator 13 can be changed arbitrarily.

  According to the laminated film-clad battery according to the present invention, the force applied to the electrode group and the heat conduction at the time of heat sealing can be suppressed and the internal short circuit is reduced, so that it contributes to manufacturing and sales and can be used industrially.

It is a perspective view which shows the external appearance of the laminated film exterior battery of embodiment which concerns on this invention. It is sectional drawing which shows the outline of the laminated film exterior battery of embodiment. It is sectional drawing which shows the outline of the electrode group of the laminate film exterior battery of embodiment. It is a perspective view which shows the external appearance of the resin frame which protects the electrode group of the laminate film exterior battery of embodiment. It is sectional drawing which shows the outline of the conventional laminated film exterior battery.

Explanation of symbols

1 Laminated film exterior battery 2 Laminated film 5 Resin frame (protective member)
6 Groove (groove)
10 Electrode group

Claims (3)

  In a laminated film-clad battery in which an electrode group in which a positive electrode and a negative electrode are laminated via a separator is enclosed in a laminate film outer package, a frame-shaped protective member that protects the electrode group is provided around the electrode group A laminated film exterior battery characterized by.   2. The laminated film-clad battery according to claim 1, wherein a height of the protective member is 90% to 110% of a thickness of the electrode group.   The laminated film-clad battery according to claim 1, wherein a groove for supporting an electrode terminal connected to the electrode group is formed in the protective member.