JP5327249B2 - battery - Google Patents

Description

  The present invention relates to a battery, and more particularly, to a battery manufactured using a laminate film as an exterior material.

  In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape recorder), a mobile phone, or a laptop computer have appeared, and their size and weight have been reduced. Along with this, the demand for batteries used as power sources for portable electronic devices is growing rapidly, and the battery design is lighter, thinner, and more efficient in the storage space in devices to realize smaller and lighter devices. It is required to use. As a battery satisfying such requirements, a lithium ion battery having a large energy density and output density is most suitable.

  Among them, a battery having a high degree of freedom of shape, a thin and large area sheet type battery, a thin and small area card type battery, and the like are desired. However, in the conventional method using a metal can as an exterior, it is thin. It is difficult to produce a battery.

  In order to solve such problems, a battery using a substance having an adhesive action in an electrolytic solution or a gel electrolyte using a polymer has been studied. In these batteries, the electrode and the electrolyte are in close contact with each other, and the contact state can be maintained. This makes it possible to produce a thin battery using a film-like exterior material such as an aluminum laminate film.

  Conventionally, laminated films have mainly been used for foods, pharmaceuticals, films, and the like, and these have expiration dates, expiration dates, etc., and long-term reliability is not always necessary. On the other hand, long-term reliability is required because secondary batteries are repeatedly used for charging and discharging.

  FIG. 1 shows a configuration of a battery using a laminate film as an exterior material. Reference numeral 1 indicates a battery covered with a laminate film. Since the laminate film has no conductivity, it is necessary to lead out the lead 2 so as to be sandwiched between the bonded portions of the film. In this state, the inner resin films of the laminate film face each other, and the battery element peripheral portion is heat-sealed to be hermetically sealed. At this time, by narrowing the seal width by heat sealing, the internal battery element can be designed to be large, and the capacity of the battery can be increased.

  In FIG. 2, an example of the main structures of the laminate film 10 is shown. The metal foil indicated by reference numeral 11 is composed of a multilayer film having moisture resistance and insulation sandwiched between the resin film 12 and the resin film 13. Nylon or polyethylene terephthalate (PET) is used for the outer resin film 12 because of its beautiful appearance, toughness, and flexibility. The metal foil 11 plays the most important role of preventing moisture, oxygen and light from entering and protecting the contents, and aluminum (Al) is most often used because of its lightness, extensibility, price and ease of processing. Since the inner resin film 13 is a part that melts and fuses with heat or ultrasonic waves, polyolefin is suitable, and unstretched polypropylene (CPP) is often used. If necessary, an adhesive layer 14 may be provided between the metal foil 11 and the resin films 12 and 13.

  When the battery element is packaged with the laminate film 10 and heat-sealed, the inner CPP layer is melted and bonded. However, the metal of the lead 2 derived from the battery element and the CPP have poor adhesion. Therefore, as shown in FIGS. 1 and 3, a resin material is bonded to both surfaces of the lead 2 in order to improve adhesion to the CPP. This is called sealant 3.

  Problems when using an aluminum laminate film as an exterior material include a problem that moisture easily enters inside, and that the infiltrated moisture causes an undesirable electrochemical reaction inside the battery, resulting in deterioration of battery characteristics. . Since moisture cannot pass through the Al layer, it penetrates from the inner resin film (CPP) portion.

  The amount of moisture intrusion is proportional to the intrusion path cross-sectional area (cross-sectional area of the CPP layer) and inversely proportional to the intrusion path length (seal width). Therefore, it is necessary to make the CPP layer thin to reduce the cross-sectional area, or to increase the seal width and to increase the path length to prevent moisture from entering. From the viewpoint of increasing the capacity of the battery, the CPP layer It is preferable to make the path narrower by reducing the thickness and to suppress the amount of intrusion moisture. In this case, since the laminate film itself becomes thin, it is possible to design a large battery as a whole and increase the capacity.

  Here, by narrowing the seal width, there arises a problem that it becomes difficult to ensure the strength of the seal portion. In order to solve this, it is necessary to perform heat fusion using a metal block heater having a large heat capacity. When a conventional laminate film is used, the inner resin film 13 has a certain thickness, and the resin film 13 can absorb the pressure of the metal block heater even if the lead 2 is bitten during heat sealing. . However, when the inner resin film 13 is thin, a large pressure is locally applied to the portion where the lead 2 is sandwiched, and the lead 2 is sheared, or the lead 2 breaks through the resin film 13 and the metal foil 11. There is a risk of short circuit.

Therefore, as described in Patent Document 1 below, the recess 21 is formed in the portion corresponding to the lead 2 of the metal block heater 20, and the above-described problems are caused by heat fusion while performing alignment. Can be solved (FIG. 4).
JP 2000-348695 A

  However, in addition to the above problems, there is a problem that may be caused by making the CPP layer thin. For example, as shown in FIG. 5, there is a problem that an Al cut burr (hereinafter referred to as burr) 30 generated when the laminate film 10 is cut breaks through the CPP layer and is short-circuited to the lead 2 and the positive and negative terminals of the battery are short-circuited. It is.

  Even if the burr 30 faces the outside of the battery or there is no burr, a short circuit occurs when the head portion of the metal block heater 20 applies pressure to the end of the laminate film 10 at the time of heat fusion. Probability is high.

  In view of the above problems, an object of the present invention is to provide a highly safe battery that does not cause a short circuit due to pressurization of a burr and a heat fusion heater and a decrease in cycle characteristics due to moisture intrusion.

In order to solve the problem, the battery of the present invention comprises a battery element having a positive electrode and a negative electrode provided with reaction layers on both sides of a strip-shaped metal foil, and an electrolyte, and an outer surface and an inner surface of the metal layer sandwiched between resin layers. A lead electrically connected to the battery element is led out from the opening of the laminate film with both surfaces facing the laminate film covered with a resin material. A battery sealed by heat sealing,
Thickness t of heat-sealed part sandwiching the lead _Four However, the thickness t of the heat-sealed part that does not sandwich the lead _Three Thicker than
When the thickness of the laminate film is t, the thickness of the resin layer on the inner surface of the laminate film is p, the thickness of the lead is L, and the thickness of one side of the resin material covering the lead is S,
The thickness p of the resin layer on the inner surface of the laminate film is 20 to 40 (μm),
Thickness t of heat-sealed part that does not sandwich the lead _Three Is t × 2−p × 2 + 5 <t _Three <T × 2-5 (μm),
Thickness t of heat-sealed part sandwiching the lead _Four T * 2-p * 2 + 5 + (L + S) <t _Four <T × 2-5 + (L + S) (μm)

According to the present invention, when heat fusion is performed on the lead lead-out side, a large pressure is locally applied to the lead by using the heater head having a notch in the portion facing the lead, as described above. To prevent it from being applied.

  According to the present invention, it is possible to solve the problems in using a thin laminate film exterior that can improve the battery capacity, and to obtain a high-performance battery that does not cause a short circuit and moisture intrusion.

  Below, the detail of the battery which can apply this invention is demonstrated.

  FIG. 6 shows an example of a battery element constituting a battery to which the present invention is applied. This battery has a battery element 40 formed by laminating a belt-like positive electrode 41, a separator 43a, a belt-like negative electrode 42 arranged to face the positive electrode 41, and a separator 43b, and being wound in the longitudinal direction. The gel electrolyte 44 is applied to both surfaces of the positive electrode 41 and the negative electrode 42.

[Positive electrode]
The positive electrode 41 is formed by forming positive electrode active material layers containing a positive electrode active material on both surfaces of a positive electrode current collector. The positive electrode current collector is made of a metal foil such as an Al foil, a nickel (Ni) foil, or a stainless steel foil.

  The positive electrode active material layer includes, for example, a positive electrode active material, a conductive agent, and a binder. These are uniformly mixed to form a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent to form a slurry. Next, the slurry is uniformly applied on the positive electrode current collector by a doctor blade method or the like, dried at a high temperature, and the solvent is removed. Here, the positive electrode active material, the conductive agent, the binder, and the solvent only have to be uniformly dispersed, and the mixing ratio is not limited.

As the positive electrode active material, a composite oxide of lithium and a transition metal is used. _{Specifically, LiCoO 2, LiNiO 2, LiMn} 2 O 4 and the like. A solid solution in which a part of the transition metal element is substituted with another element can also be used. Examples thereof include LiNi _0.5 Co _0.5 O ₂ and LiNi _0.8 Co _0.2 O ₂ .

  As the conductive agent, for example, a carbon material such as carbon black or graphite is used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene or the like is used. Moreover, as a solvent, N-methylpyrrolidone etc. are used, for example.

  The positive electrode 41 has a positive electrode terminal (indicated by a lead 45 in FIG. 6) connected to the electrode end by spot welding or ultrasonic welding. The positive electrode terminal is preferably a metal foil or a mesh-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material for the positive electrode terminal include Al.

[Negative electrode]
The negative electrode 42 is formed by forming a negative electrode active material layer containing a negative electrode active material on both surfaces of a negative electrode current collector. The negative electrode current collector is made of a metal foil such as copper foil, Ni foil, or stainless steel foil.

  The negative electrode active material layer includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. These are uniformly mixed to form a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent to form a slurry. Next, this slurry is uniformly applied on the negative electrode current collector by a doctor blade method or the like, dried at a high temperature, and the solvent is blown off. Here, the negative electrode active material, the conductive agent, the binder, and the solvent only have to be uniformly dispersed, and the mixing ratio is not limited.

  As the negative electrode active material, lithium metal, a lithium alloy, a carbon material that can be doped / undoped with lithium, or a composite material of a metal material and a carbon material is used. Specifically, examples of the carbon material that can be doped / dedoped with lithium include graphite, non-graphitizable carbon, and graphitizable carbon. Examples of graphite include artificial graphite such as mesophase carbon microbeads, carbon fiber, and coke. Natural graphite can be used. Various types of metals can be used as materials capable of alloying lithium, but tin (Sn), cobalt (Co), indium (In), Al, silicon (Si) and alloys thereof are often used. It is done. When metal lithium is used, it is not always necessary to use powder as a coating film with a binder, and a rolled Li metal plate may be used.

  As the binder, for example, polyvinylidene fluoride, styrene butadiene rubber or the like is used. Moreover, as a solvent, N-methylpyrrolidone, methyl ethyl ketone, etc. are used, for example.

  Similarly to the positive electrode 41, the negative electrode 42 also has a negative electrode terminal (indicated by a lead 45 in FIG. 6) connected to the electrode end by spot welding or ultrasonic welding. The negative electrode terminal is preferably a metal foil or a mesh-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material for the negative electrode terminal include copper and Ni.

  In addition, although it is preferable that the positive electrode terminal and the negative electrode terminal are derived | led-out from the same direction, there is no problem even if it derive | leads out from which direction as long as a short circuit etc. do not occur and there is no problem in battery performance. Moreover, the connection place of a positive electrode terminal and a negative electrode terminal will not be restricted to said example, if the electrical contact has taken place and the attachment method.

[Electrolytes]
As the electrolyte, an electrolyte salt and an organic solvent that are generally used in lithium ion batteries can be used, and the electrolyte may be a gel electrolyte or an electrolyte solution.

  Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, or hydrogen of these carbonic acid esters to halogen. Examples include substituted solvents. One of these solvents may be used alone, or a plurality of these solvents may be mixed with a predetermined composition.

As electrolyte salt, what melt | dissolves in the said nonaqueous solvent can be used. For example _{LiPF 6, LiBF 4, LiN (} CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiClO 4 and the like. The electrolyte salt concentration is not a problem as long as it can be dissolved in the above solvent, but the lithium ion concentration is in the range of 0.4 mol / kg or more and 2.0 mol / kg or less with respect to the non-aqueous solvent. Is preferred.

  In the case of a gel electrolyte, the above electrolyte is gelled with a matrix polymer. The matrix polymer is not particularly limited as long as it is compatible with a non-aqueous electrolyte obtained by dissolving the electrolyte salt in the non-aqueous solvent and can be gelled. Examples of such matrix polymers include polymers containing repeating units such as polyvinylidene fluoride, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polymethacrylonitrile and the like. Such a polymer may be used individually by 1 type, and may mix and use 2 or more types.

Among them, particularly preferred as the matrix polymer is polyvinylidene fluoride or a copolymer in which hexafluoropropylene is introduced at a ratio of 7.5% or less to polyvinylidene fluoride. Such polymers have a number average molecular weight in the range of 5.0 × 10 ⁵ to 7.0 × 10 ⁵ (500,000 to 700,000) or a weight average molecular weight of 2.1 × 10 ⁵ to 3. The range is 1 × 10 ⁵ (210,000-310,000), and the intrinsic viscosity is in the range of 1.7 to 2.1.

[Separator]
The separator is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric, and these two or more kinds of porous films are laminated. It may be a structure. Among these, polyethylene and polypropylene porous films are the most effective.

  In general, the thickness of the separator is preferably 5 to 50 μm, more preferably 7 to 30 μm. If the separator is too thick, the amount of the active material filled decreases, the battery capacity decreases, and the ionic conductivity decreases and the current characteristics deteriorate. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

  Such a laminated film for packaging the battery element 40 has a structure as shown in FIG. 2, and the battery element 40 is covered and sealed with a laminate film having moisture resistance and insulation. The lead 2 is connected to each of the positive electrode 41 and the negative electrode 42 and is led out by being sandwiched between sealing portions of the laminate film.

  This time, Nylon or PET 15 ± 5μm on the exterior and Al foil 35 ± 5μm as a laminate film suitable for the characteristics of enabling the production of a highly safe battery even if the laminate film is thin and the heat-sealed part is narrow It was found that a structure with CPP of 30 ± 10 μm is suitable for the interior. An adhesive layer of 2 to 3 μm may be present between the Al foil and the inner / outer resin film.

  In the present invention, as shown in FIG. 7, the end of the laminate film is avoided at the lead take-out side and heat-sealed by the heater head so that the thickness of the end of the laminate film is larger than the thickness of the seal portion. By manufacturing the battery, a short circuit due to burrs can be prevented. This method can also prevent a short circuit that occurs when the head steps on the end of the laminate film. FIG. 7 is a top view of the lead-out side of the battery element, and a portion A indicated by hatching is a seal portion.

  FIG. 8 shows a state in which heat welding is performed by the heater head 56 so as to avoid the end portion of the laminate film 50. The laminate film 50 has a structure including an Al layer 51, an outermost nylon layer or PET layer 52, and an interior CPP layer 53, and has moisture resistance and insulating properties. Note that the thickness of the laminate film 50 is t, and the thickness of the CPP layer 53 is p.

  FIG. 9 shows a cross-sectional view (a ′ ′ in FIG. 7) of the lead portion at the lead extraction side of the battery manufactured in this way. Reference numeral 54 denotes a lead, which is coated with a sealant 55 to improve adhesion with the CPP layer.

  A portion indicated by A is a portion heat-sealed by the heater head, and B is an end portion of the laminate film that has not been heat-sealed by the heater head. Since the A part is heated and pressurized by the heater head, the CPP melts and flows to the non-pressurized part (B part). For this reason, B part becomes thick gradually as it approaches the laminate film end from A part. The B part is not directly heated by the heater head, but the CPP is melted by the residual heat generated during the heating of the A part, and the CPP layer and the lead or the CPP layer are often bonded to each other. Further, there is no problem even if the portion B is not bonded.

  On the other hand, FIG. 10 shows a cross-sectional view (bb ′ in FIG. 7) of the heat-sealed portion where the leads are not sandwiched. A portion indicated by A is a portion heated and pressed by the heater head, and a portion indicated by B is a portion not heated and pressed by the heater head. Similarly to FIG. 7, since the CPP in which the CPP is melted flows, the B part gradually becomes thicker from the A part toward the end of the laminate film.

At this time, when the thickness of the heat-sealed portion is t ₁ , the thickness of the laminate film end is t ₂ , the thickness of the laminate film 50 is t, and the thickness of the CPP layer is p as shown in FIG. The thickness t ₁ of the heat fusion part is
t × 2−p × 2 + 5 <t ₁ <t × 2-5 [μm]
And the thickness t ₂ at the end of the laminate film is
t ₁ <t × 2 ≦ t ₂ [μm]
There is a relationship that satisfies. By avoiding the short-circuit by preventing the end portion from being heat-sealed, the thickness of the end portion becomes thicker than the heat-sealed portion inside the end portion.

The thickness t ₁ of the heat-sealed portion is heated and pressed by the heater head, so that the melted CPP flows to the end of the laminated film, and after heat-sealing, the original thickness (thickness of two laminated films stacked) Smaller than that). However, if a too strong pressure is applied at the time of thermal fusion, the CPP flows and the resin for thermal fusion becomes insufficient, sealing performance is impaired and moisture enters. In this case, water is reduced inside the battery to generate gas and the battery expands. If the thickness of the CPP layer after heat fusion is larger than 5 μm, that is, if the thickness t ₁ of the heat fusion portion is larger than [t × 2−p × 2 + 5] μm, the CPP layer is not insufficient, Can be sufficiently suppressed.

Further, when the thickness t ₁ of the heat fusion part is too thick, there is a possibility that the sealing is not sufficiently performed. In this case as well, moisture permeates, water is reduced inside the battery to generate gas, and the battery expands. If the thickness of the CPP layer after heat fusion is less than 5 μm compared to the thickness of the original CPP layer (corresponding to the thickness of two stacked CPP layers), the CPP will not melt. It is sufficient and the sealing performance is not so good. That is, if the thickness t ₁ of the heat-sealed portion is smaller than [t × 2-5] μm, the CPP is sufficiently melted and sealed, and high cycle characteristics can be maintained.

Further, by heating and pressurizing with the heater head while avoiding the laminate film end portion, the thickness t ₂ of the laminate film end portion becomes larger than the thickness t ₁ of the heat welded portion. As a result, it is possible to prevent burrs generated at the end of the laminate film from penetrating through the sealant and short-circuiting, and at the time of heat welding, the heater head steps on the end of the laminate film and the lead and the Al layer contact to cause a short circuit. Can be prevented.

At this time, since the end of the laminate film is not pressurized with the heater head, the thickness t ₂ is not thinner than the original thickness [t × 2] μm (the thickness of the two laminated films stacked), Moreover, it becomes thick by CPP extruded from the heat welding part. However, when the portion of the laminated film where the heater head is not stepped is large, the CPP is not pushed out to the end of the film and has a cross section as shown in FIG. In such a case, the thickness t ₂ of the end portion of the laminate film is measured by using a caliper or the like by overlapping the end portions of the laminate film extending vertically with fingers or the like. The thickness t ₁ of the heat welded portion is smaller than t × 2 because it is pressurized, and the thickness t ₂ of the laminate film end portion is t × 2, so that t ₁ <t ₂ , thus avoiding a short circuit. be able to.

  By using such a method, it is possible to manufacture a battery that is blocked by a thick CPP layer even when burrs 30 are generated as shown in FIG.

  In addition to the above-described method, a safer battery can be manufactured by using the following method.

  As in the prior art, the lead portion is heated and pressurized with a metal heater, so that a large pressure is locally applied to the lead portion as compared with other heat fusion portions. Therefore, heat fusion was performed using a heater head provided with a notch at a position where the lead was sandwiched.

In this case, since a heater head provided with a notch is used, the laminate film thickness of the lead portion is thicker than the laminate film thickness of the heat-sealed portion where the lead is not sandwiched. When the thickness of the laminate film is t, the thickness of the CPP layer is p, the thickness of the lead is L, and the thickness of one side of the sealant covering the lead is S, as shown in FIG.
The thickness t _{3 of the} heat-sealed part that does not sandwich the lead when the battery is covered with a film is:
t × 2-p × 2 + 5 <t ₃ <t × 2-5 [μm]
And the thickness t _{4 of the} heat-sealed part sandwiching the lead is
t × 2−p × 2 + 5 + (L + S) <t ₄ <t × 2-5 + (L + S) [μm]
It is characterized by being.

The thickness t _{3 of the} heat-sealed part where the lead is not sandwiched and the thickness t ₄ of the heat-sealed part where the lead is sandwiched are heated and pressurized by the heater head, so the CPP layer melts and flows at the time of heat welding. It becomes smaller than the thickness. If the thickness of the CPP layer after heat sealing is larger than 5 μm, that is, if the thickness t _{3 of the} heat-sealed part not sandwiching the leads is larger than [t × 2−p × 2 + 5] μm, the CPP layer is insufficient. Without intruding, the intrusion of moisture can be sufficiently suppressed. Further, if the thickness of the CPP layer after heat fusion is reduced within 5 μm compared to the thickness of the original CPP layer, the melting of the CPP is insufficient and the sealing performance is not very good. That is, if the thickness t _{3 of the} heat-sealed portion that does not sandwich the lead is smaller than [t × 2-5] μm, the CPP is sufficiently melted and sealed, and high cycle characteristics can be maintained.

  Further, the heat-sealed portion sandwiching the leads melts and thins the sealant covering the leads in addition to the CPP layer. Resin flows through the sealant by heat welding and becomes about half the thickness. If the sealant is thinner than this, it becomes difficult to prevent a short circuit between the lead and the laminate film. Moreover, when the sealant is not so much melted, heat welding between the laminate film and the lead is insufficient, and moisture easily enters.

  However, even when a large amount of sealant flows, it is sufficient that the thickness combined with the CPP is within a predetermined range, and even when the sealant is only slightly dissolved, a large amount of CPP is dissolved and sealed. If the combined thickness of the sealant and the CPP is within a predetermined range, there is no problem.

Similarly to the thickness t ₃ of the heat-sealed portion where the lead is not sandwiched, when the thickness of the CPP layer after the heat-sealing is larger than 5 μm, that is, the thickness t _{4 of the} heat-sealed portion sandwiching the lead is [ When it is larger than t × 2−p × 2 + 5 + (L + S)], moisture intrusion can be sufficiently suppressed. Moreover, when the reduction in thickness is less than 5 μm, the sealing performance is insufficient. That is, if the thickness t _{4 of the} heat-sealed portion sandwiching the leads is smaller than [t × 2-5 + (L + S)], the CPP is sufficiently melted and sealed.

  Here, since the conventional CPP layer was about 45-50 micrometers in the laminate film used this time, the CPP layer was 20-40 micrometers. The thinner the CPP layer is, the better the battery capacity is. However, since the melted CPP flows to the non-pressurized portion at the time of heat fusion, the sealing performance is impaired even if the CPP layer is too thin. In consideration of these, the CPP layer is preferably 20 to 40 μm.

  By manufacturing the battery in this way, pressure is locally applied to the lead, the lead is not cut, the lead does not break through the CPP layer, and the necessary CPP does not flow, thereby preventing a short circuit. .

  Note that the heater head used for heat fusion is not limited to the above, and any material and shape of the heater head may be used as long as it can be sealed so as to satisfy the above conditions.

  Hereinafter, the present invention will be specifically described by way of examples.

[Production of positive electrode]
92% by weight of lithium cobaltate (LiCoO ₂ ), 3% by weight of powdered polyvinylidene fluoride, and 5% by weight of powdered graphite were uniformly mixed and dispersed in N-methylpyrrolidone to form a slurry-like positive electrode composite. An agent was prepared. This positive electrode mixture was uniformly applied to both surfaces of an Al foil serving as a positive electrode current collector, and dried under reduced pressure at 100 ° C. for 24 hours to form a positive electrode active material layer.

  Next, this was pressure-formed by a roll press machine to obtain a positive electrode sheet. This positive electrode sheet was cut into a strip of 50 mm × 300 mm to form a positive electrode, and an Al ribbon lead was welded to the non-coated portion of the active material. In addition, polypropylene pieces were bonded to both sides of the portion of the lead sandwiched between the aluminum laminate films.

[Production of negative electrode]
Artificial graphite (91% by weight) and powdery polyvinylidene fluoride (9% by weight) were uniformly mixed and dispersed in N-methylpyrrolidone to prepare a slurry-like negative electrode mixture. Next, this negative electrode mixture was uniformly applied to both surfaces of a copper foil serving as a negative electrode current collector, and dried under reduced pressure at 120 ° C. for 24 hours to form a negative electrode active material layer.

  Next, this was subjected to pressure molding with a roll press machine to obtain a negative electrode sheet. This negative electrode sheet was cut into a strip of 52 mm × 320 mm to form a negative electrode, and Ni ribbon leads were welded to uncoated portions of the substance. In addition, a piece of polypropylene was bonded to both sides of the lead between the aluminum laminate films.

[Preparation of gel electrolyte]
A polyvinylidene fluoride copolymerized with 6.9% of hexafluoropropylene, a non-aqueous electrolyte, and dimethyl carbonate (DMC) as a diluting solvent are mixed, stirred and dissolved to obtain a sol electrolyte solution. Obtained. The electrolyte was prepared by mixing ethylene carbonate and propylene carbonate in a weight ratio of 6: 4 and dissolving 0.8 mol / kg LiPF ₆ and 0.2 mol / kg LiBF ₄ . The mixing ratio was a weight ratio of polyvinylidene fluoride: electrolyte: DMC = 1: 6: 12. Next, the obtained sol-form electrolyte solution was uniformly applied to both surfaces of the positive electrode and the negative electrode. Then, it was made to dry at 50 degreeC for 3 minute (s), the solvent was removed, and the gel electrolyte layer was formed on both surfaces of the positive electrode and the negative electrode.

[Production of test battery]
A belt-like positive electrode having a gel electrolyte layer formed on both sides and a belt-like negative electrode having a gel electrolyte layer formed on both sides, produced as described above, are wound in a longitudinal direction via a separator. Thus, a battery element was obtained. As the separator, a porous polyethylene film having a thickness of 10 μm and a porosity of 33% was used.

  Finally, as shown in FIG. 14, the battery element 60 is sandwiched between an aluminum laminate film 61 in which an Al foil is sandwiched between a pair of resin films, and the outer peripheral edge of the aluminum laminate film 61 is thermally fused under reduced pressure. Sealed by. In addition, it produced so that the width | variety (A + B of FIG.7, FIG.9 and FIG.10) of the terrace part of a battery might be about 2.5 mm.

  The following points were examined using such a test battery.

<Example 1>
The batteries of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-7 were produced by changing the heater head width, and the temperature of the heater head and the pressure at the time of heat fusion were changed, respectively. The thickness t ₁ of the attaching portion and the thickness t _{2 of the} end portion of the laminate film were changed. The batteries of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are 2.0 mm wide heater heads, and the batteries of Comparative Examples 1-3 to 1-7 are 3.0 mm wide heaters. A head was used, and an aluminum laminate film having a nylon layer of 15 μm, an adhesive layer of 3 μm, an aluminum layer of 35 μm, an adhesive layer of 2 μm, a CPP layer of 30 μm and a thickness of 85 μm was used for the exterior of each battery. In addition, an Al ribbon having a width of 4 mm and a thickness of 70 μm was used for the lead, and a piece of polypropylene having a width of 6 mm and a thickness of 50 μm was adhered to both sides of the portion sandwiched between the aluminum laminate films.

  When such a laminate film is used, the thickness when all of the CPP disappears is 110 μm, the thickness when the laminate film is not crushed at all is 170 μm, and if the resin from other parts flows, Become thicker.

When the thickness of the heat fusion part is t ₁ , the thickness of the laminate film end part is t ₂ , the thickness of the laminate film is t, and the thickness of the CPP layer is p, the thickness t _{1 of the} heat fusion part But,
t × 2−p × 2 + 5 <t ₁ <t × 2-5 [μm]
The thickness t ₂ at the end of the laminate film is
t ₁ <t × 2 ≦ t ₂ [μm]
If the relationship satisfies the above, it is possible to prevent short-circuit due to burrs, short-circuit between the laminate film Al layer and the lead due to pressurization of the heater head, and gas generation due to moisture intrusion. Therefore, in the case of the laminate film used this time, a battery that can withstand practical use can be obtained if 115 μm <t ₁ <165 μm and t ₂ ≧ 170 μm.

Table 1 below shows the thickness t ₁ of the heat-sealed portion and the thickness t _{2 of the} end portion of the laminate film and the heaters of the batteries of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-7. Indicates the head width. In addition, Table 1 also shows the lower and upper limits of the thickness range of the heat-sealed portion described above. In addition, the shaded part in the table indicates a part out of an appropriate range among the thickness t ₁ of the heat-sealed part and the thickness t ₂ of the laminate film end part.

  Ten such test batteries were produced, and the number of short-circuited batteries among the ten test batteries was examined. For the batteries that did not cause any short circuit, the battery swelling (thickness increase) [mm] and cycle characteristics [%] due to gas generation inside the battery were further measured.

  For the presence or absence of a short circuit, the resistance between both positive and negative leads was measured. The battery immediately after assembly has a sufficiently large DC resistance, but if it is short-circuited, it has a small resistance value on the order of mΩ. As a cause of the short circuit, there is a case where a large pressure is applied to the lead portion and the lead is passed through the innermost layer CCP of the aluminum laminate film exterior or the lead burr penetrates and reaches the Al foil layer.

  On the other hand, when a strong pressure is applied to the portion where the lead is not sandwiched during heat fusion, the CPP flows to impair the sealing performance, and moisture enters. In that case, water is reduced inside the battery to generate gas, and the battery expands. The battery may swell even with moisture in the electrolyte, but the amount is small. The thickness of the battery after the initial assembly charge was measured. If the thickness increased by 0.1 mm or more, it was judged as defective, and if it was less than 0.1 mm, it was regarded as good.

  Further, regardless of whether or not the lead is sandwiched, if the heat-sealed portion is too thick, there is a possibility that the sealing is not sufficiently performed. Even in this case, moisture permeates, the water is reduced inside the battery to generate gas, and the battery expands. As before, the thickness of the battery after initial assembly was measured, and if there was an increase in thickness of 0.1 mm or more, it was judged as defective, and if it was less than 0.1 mm, it was regarded as good.

  For the cycle characteristics, standard charge and 1C-3V cut-off constant current discharge were performed, and the change in discharge capacity for each cycle was measured. Here, the capacity retention rate after 500 cycles was examined, and 80% or more was regarded as non-defective. The 80% capacity retention rate after 500 cycles is a value that is generally necessary and sufficient in the specifications of portable electronic devices. If moisture penetrates, the cycle characteristics are impaired by side reactions. The cycle characteristics are calculated by the following formula.

  Cycle characteristics = (discharge capacity at 500th cycle) / (discharge capacity at the first cycle) × 100 [%]

Below, the structure of the battery of each Example and the result of the above-mentioned test are shown. In addition, the shaded part in the table indicates a part out of an appropriate range among the thickness t ₁ of the heat-sealed part and the thickness t ₂ of the laminate film end part.

As is clear from the above table, heat fusion is performed using a heater head having a width of 2.0 mm smaller than the width of the terrace portion so as to avoid the end portion of the laminate film, and the thickness t of the heat fusion portion. Examples 1-1 to _{1 in} which ₁ is in a predetermined range (115 <t ₁ <165 [μm]) and the thickness t ₂ of the laminate film end is larger than the thickness t _{1 of the} heat-sealed portion Each battery of No. 3 has no short circuit and no swelling due to gas, and has high cycle characteristics.

On the other hand, even if the end portion is avoided by using a head having a width smaller than the width of the terrace portion, it cannot be used as a battery if the thickness t ₁ of the heat fusion portion is not within a predetermined range. In Comparative Example 1-1, a heater head having a width of 2.0 mm was used and the thickness t ₁ of the heat-sealed portion was made as thin as 110 μm. Yes. In Comparative Example 1-2, a heater head with a width of 2.0 mm was used and the thickness t ₁ of the heat-sealed portion was made as thick as 168 μm. However, the sealing performance was insufficient because the seal was too weak. Yes, gas intrusion occurs due to moisture intrusion.

Furthermore, when a 3.0 mm wide heater head is used as in Comparative Examples 1-3 to 1-6, the end of the laminate film is pressed by the heater head, and the lead and the Al layer are short-circuited or burrs are not generated. It breaks through the CPP layer and shorts with the lead, causing a short circuit. Also, as in Comparative Example 1-7, when a 3.0 mm wide heater head is used to seal weakly, a short circuit does not occur, but the thickness t ₁ of the heat-sealed portion and the thickness t of the laminate film end portion. _{Since 2} is large, moisture enters and gas is generated, the battery swells and the cycle characteristics deteriorate.

  Thus, by making the thickness of the end portion larger than the thickness of the heat-sealed portion, it is possible to create a battery that avoids short-circuiting and gas swelling.

<Example 2>
The battery for test by changing the thickness t _{3 of} the heat-sealed part and the thickness t ₄ of the lead part by changing the structure of the laminate film for covering the battery element and the temperature and pressure of the heater head at the time of heat-sealing. Was made. The laminate film used for the exterior is an outermost nylon layer of 15 μm, an adhesive layer of 3 μm, an aluminum foil of 35 μm, an adhesive layer of 2 μm, a CPP layer of 30 μm, and a total thickness of 85 μm. Only an aluminum laminate film having a total thickness of 75 μm was used (the nylon layer was 15 μm, the adhesive layer was 3 μm, the aluminum foil was 35 μm, the adhesive layer was 2 μm, and the CPP layer was 20 μm). Further, a heater head having a width of 2.0 mm was used at the time of heat-bonding the lead-out side, and the seal width was set to 2.2 mm including a portion bonded to the lead or the like due to residual heat.

  In each of the batteries of Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-12, an Al ribbon having a width of 4 mm and a thickness of 70 μm was used, and a portion sandwiched between the aluminum laminate films had a width of 6 mm. A 50 μm thick polypropylene piece was bonded to both sides. Further, in each of the batteries of Examples 2-15 and 2-16 and Comparative Examples 2-13 to 2-16, an Al ribbon having a width of 4 mm and a thickness of 100 μm was used as the lead, and the portion sandwiched between the aluminum laminate films was A polypropylene piece having a width of 6 mm and a thickness of 60 μm was adhered to both sides.

  In Example 2, when a laminate film having a total thickness of 85 μm was used, the thickness when all of the CPP disappeared was 110 μm, and the thickness when the laminate film was not crushed at all was 170 μm. If it flows, it becomes thicker.

  When a laminate film with a total thickness of 75 μm is used, the thickness when the CPP is completely removed is 110 μm, and when the laminate film is not crushed at all, the thickness is 150 μm. If it becomes thicker.

The thickness of the heat-sealed part that does not sandwich the lead is t ₃ , the thickness of the heat-sealed part that sandwiches the lead is t ₄ , the thickness of the laminate film is t, the thickness of the CPP layer is p, and the thickness of the lead Is L, and the thickness of one side of the sealant covering the lead is S,
The thickness t _{3 of the} heat-sealed part that does not sandwich the lead when the battery is covered with a film is:
t × 2-p × 2 + 5 <t ₃ <t × 2-5 [μm]
And the thickness t _{4 of the} heat-sealed part sandwiching the lead is
t × 2−p × 2 + 5 + (L + S) <t ₄ <t × 2-5 + (L + S) [μm]
If the relationship is satisfied, it is possible to prevent a short circuit due to burrs, a short circuit between the laminate film Al layer and the lead due to pressurization by the heater head, and gas generation due to moisture intrusion. Therefore, a battery that can withstand practical use can be obtained by setting each example and comparative example within the following ranges.

(1) In the case of a laminate film having a total thickness of 85 μm, a lead thickness of 70 μm, and a sealant thickness (single side) of 50 μm (Examples 2-1 to 2-12 and Comparative Examples 2-1 to 2-8), 115 μm <t ₃ < 165 μm, 235 μm <t ₄ <285 μm.
(2) In the case of a laminate film having a total thickness of 75 μm, a lead thickness of 70 μm, and a sealant thickness (one side) of 50 μm (Examples 2-13 and 2-14 and Comparative Examples 2-9 to 2-12), 115 μm <t ₃ < 145 μm, 235 μm <t ₄ <265 μm.
(3) In the case of a laminate film having a total thickness of 85 μm and a lead thickness of 100 μm and a sealant thickness (single side) of 60 μm (Examples 2-15 and 2-16 and Comparative Examples 2-13 to 2-16), 115 μm <t ₃ < 165 μm, 275 μm <t ₄ <325 μm.

Table 3 below shows the thickness of the laminate film and the thickness of the CPP layer of each battery of Examples 2-1 to 2-16 and Comparative Examples 2-1 to 2-16, and the heat-sealed portion that does not sandwich the leads. It shows the thickness t ₄ of the heat-sealed portions sandwiching a thickness t ₃ and the lead of the. The hatched portion in the table indicates the thickness t _{3 of the} heat-sealed portion that does not sandwich the lead and the thickness t ₄ of the heat-sealed portion that sandwiches the lead that are out of range. Further, in Table 3, the thickness of the heat-sealed portion where the lead is not sandwiched is defined as the heat-welded portion, and the thickness of the heat-sealed portion where the lead is sandwiched is defined as the lead portion. lower and upper limit of the thickness of the heat-sealed portions sandwiching the t ₃ and the lead are also shown, respectively.

  Ten such test batteries were produced, and the number of short-circuited batteries among the ten test batteries was examined. For the batteries that did not cause any short circuit, the battery swelling (thickness increase) [mm] and cycle characteristics [%] due to gas generation inside the battery were further measured. The measurement method of each test is the same as each measurement method of Example 1.

Table 4 below shows the configuration of the battery of each example and the results of the above test. The hatched portion in the table indicates the thickness t _{3 of the} heat-sealed portion that does not sandwich the lead and the thickness t ₄ of the heat-sealed portion that sandwiches the lead that are out of range. Further, in Table 4, the thickness of the heat-sealed portion where the lead is not sandwiched is the heat-welded portion t ₃ , and the thickness of the heat-sealed portion where the lead is sandwiched is the lead portion t ₄ .

  As is clear from the above table, a battery with good performance can be obtained when the portion sandwiching the leads is appropriately thicker than the fusion portion not sandwiching the leads. Each example is an example.

  An example of a defective product is a battery having a thick heat-sealed portion that does not sandwich the lead. In this case, the cross-sectional area of the moisture intrusion path becomes large, and the infiltrated moisture becomes gas inside, so that the battery swells and the cycle becomes worse. For example, it is a case like Comparative Examples 2-2, 2-4, and 2-14. In the heat-sealed portion where the leads are not sandwiched, the laminate film is 170 μm when the two upper and lower layers are overlapped, but in Comparative Examples 2-2, 2-4 and 2-14, it is 168 μm after the heat-sealing, and the CPP layer Is not sufficiently sealed. For this reason, moisture enters the inside and gas is generated, and the gas bulges are successively large values of 0.18 mm, 0.17 mm, and 0.21 mm.

In addition, when the heat-sealed portion where the lead is not sandwiched is too thin, a defective battery is obtained. For example, in Comparative Example 2-1 and Comparative Example 2-3, the thickness t _{3 of the} heat-sealed portion that does not sandwich the lead is 112 μm. Since the laminate films are 170 μm in the upper and lower two layers and have the CPP layers of 30 μm in the upper and lower sides, the thickness should be 110 μm even when all the CPP layers melt and flow. That is, the CPP layers of Comparative Example 2-1 and Comparative Example 2-3 are very thin as 2 μm, and the resin responsible for adhesion is insufficient, so that moisture penetrates and battery performance is impaired.

Furthermore, as in Comparative Example 2-5 and Comparative Example 2-7, if the thickness t _{4 of the} heat-sealed portion sandwiching the leads is too thin, the leads are short-circuited and the battery is not formed. Further, for example, as in Comparative Example 2-6 and Comparative Example 2-7, even if the thickness t _{4 of the} heat-sealed part sandwiching the leads is too thick, the cycle characteristics are deteriorated due to moisture penetration.

  In this way, in consideration of short-circuits and insufficient sealing properties that are problematic when using a thin laminate film for improving battery capacity, it is possible to produce a battery using the above-described method. Thus, a battery having high performance can be obtained.

  Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible.

  For example, in the above-described embodiment, a case where an electrode winding body in which a strip-like positive electrode and a strip-like negative electrode are stacked via a separator and wound in the longitudinal direction is used as an example will be described. However, the present invention is not limited to this, and a case where a laminated electrode body formed by laminating a positive electrode and a negative electrode is used, or a so-called zigzag folded electrode body that is not wound is used. It is also applicable to cases.

  In addition, the battery according to the embodiment as described above is not particularly limited with respect to its shape, such as a cylindrical shape or a rectangular shape, and can be various sizes such as a thin shape and a large size.

It is a perspective view which shows the battery which used the laminate film as an exterior material. It is sectional drawing which shows an example of the main structures of a laminate film. It is sectional drawing which shows the battery produced using the lead which adhere | attached the sealant for preventing a contact with a laminate film. It is a basic diagram which shows the heat sealing | fusion method which prevents that a big pressure is applied to a lead | read | reed. It is a basic diagram which shows a mode that the Al cut burr produced at the time of the cutting of a laminate film pierces a resin layer, and is short-circuited with a lead | read | reed. It is a basic diagram which shows an example of the battery element which comprises the battery to which this invention is applied. It is a basic diagram which shows the contact position of the heater head in the case of heat-seal | fusing except the edge part of a laminate film. It is a schematic diagram which shows a mode that it heat-seal | fuses except the edge part of a laminate film. It is sectional drawing of the lead part in the battery heat-sealed except the edge part of the laminate film. It is sectional drawing of the part which does not pinch | pin the lead in the battery heat-fused except the edge part of the laminate film. It is sectional drawing which shows the heat sealing | fusion part in case the part which the heater head of a laminate film does not step on is large. It is sectional drawing which shows the state when a burr | flash generate | occur | produces in the battery heat-fused except the edge part of the laminate film. FIG. 4 is a schematic diagram showing a thickness t _{3 of a} heat-sealed portion that does not sandwich a lead, a thickness t _{4 of a} heat-sealed portion that sandwiches a lead, a thickness L of a lead, and a thickness S of a sealant (one side). It is a basic diagram which shows a mode that a battery element is pinched | interposed with an aluminum laminate film.

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Lead 3 ... Sealant 10 ... Laminate film 11 ... Metal foil 12 ... Resin film 13 ... Resin film 14 ... Adhesive layer 20 ... Metal block heater 30 ... Burr 40 ... Battery element 41 ... Positive electrode 42 ... Negative electrode 43a, 43b ... Separator 44 ... Gel electrolyte 45 ... Lead 50 ... Laminate film 51 ... Al layer 52 ... Nylon or PET layer 53 ... CPP layer 54 ... Lead 55 ... Sealant 60 ... Battery element 61 ... Aluminum laminate film

Claims (7)

A battery element having a positive electrode and a negative electrode provided with reaction layers on both sides of a strip-shaped metal foil, and an electrolyte is covered with a laminate film in which an outer surface and an inner surface of a metal layer are sandwiched between resin layers. Battery in which the connected lead is led out from the opening of the laminate film with both surfaces of the lead facing the laminate film covered with a resin material, and the opening is sealed by heat sealing Because
The thickness t ₄ of the heat-sealed portions sandwiching the lead, rather thick than the thickness t ₃ of heat-sealing portion not pinch the lead,
When the thickness of the laminate film is t, the thickness of the resin layer on the inner surface of the laminate film is p, the thickness of the lead is L, and the thickness of one surface of the resin material covering the lead is S,
The thickness p of the resin layer on the inner surface of the laminate film is 20 to 40 (μm),
The thickness t _{3 of the} heat-sealed portion that does not sandwich the lead is t × 2-p × 2 + 5 <t ₃ <t × 2-5 (μm),
The thickness t ₄ of the heat-sealed portions sandwiching the lead is a t × 2-p × 2 + 5 + (L + S) <t 4 <t × 2-5 + (L + S) (μm) <br /> cell. The laminate film includes the metal layer having a thickness of 35 ± 5 (μm), the resin layer on the outer surface of the laminate film having a thickness of 15 ± 5 (μm), and the laminate having a thickness of 30 ± 10 (μm). The resin layer on the inner surface of the film
With
The thickness t of the laminate film is 60 to 100 (μm).
The battery according to claim 1. The laminate film includes the metal layer having a thickness of 35 ± 5 (μm), the resin layer on the outer surface of the laminate film having a thickness of 15 ± 5 (μm), and the laminate having a thickness of 30 ± 10 (μm). An adhesive layer having a thickness of 2 to 3 (μm) formed between the resin layer on the inner surface of the film and the metal layer and the resin layer on the outer surface of the laminate film, and the inner surface of the metal layer and the laminate film And at least one of an adhesive layer having a thickness of 2 to 3 (μm) formed between the resin layer and
With
The thickness t of the laminate film is 60 to 106 (μm).
The battery according to claim 1. The thickness t of the laminate film is 75 to 85 (μm).
The battery according to claim 3. The total thickness of the resin layer on the outer surface of the metal layer of the laminate film, the metal layer, and the resin layer on the inner surface of the metal layer is 70 to 80 (μm).
The battery according to claim 4. The lead thickness L is 70 to 100 (μm).
The battery according to claim 1. Thickness t of heat-sealed part that does not sandwich the lead _Three But 115 <t ₁ <165 (μm),
Thickness t of heat-sealed part sandwiching the lead _Four 235 <t _Four <325 (μm)
The battery according to any one of claims 4 to 6.

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