JP4772289B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, electronic devices such as mobile communication devices, notebook computers, palmtop computers, integrated video cameras, portable CD (MD) players, cordless telephones, etc. have been reduced in size and weight. As a power source, a battery having a small size and a large capacity is particularly demanded.

  Examples of batteries that are widely used as power sources for these electronic devices include primary batteries such as alkaline manganese batteries, and secondary batteries such as nickel cadmium batteries and lead storage batteries. Among these, non-aqueous electrolyte secondary batteries that use lithium composite oxide for the positive electrode and carbonaceous materials that can occlude and release lithium ions for the negative electrode are small and light, have high unit cell voltage, and have high energy density. Is attracting attention.

  In this non-aqueous electrolyte secondary battery, gas is generated and the internal pressure of the battery rises during abnormal use, especially when it is overcharged or left at an abnormally high temperature, but a safety valve is provided to avoid rupture. ing.

  For example, in Patent Document 1, a part having a low peel strength is provided in a part of a heat-sealed portion of a film container, and a gas having a low peel strength is peeled off when the internal pressure is increased, thereby releasing the gas in the container to the outside. , Preventing bursting.

  However, when a portion having a low fusion strength is provided in the heat fusion portion as in Patent Document 1, moisture easily enters from there, so that sufficient battery performance may not be obtained.

  As a method for solving this problem, Patent Document 2 discloses a safety valve made of a heat-welded resin sheet having a melting point lower than that of a laminate sheet, in a part of a seal portion of a bag-like outer case formed of a laminate sheet mainly composed of a resin film. It is described that a member is incorporated, and the heat-welded resin sheet is softened and melted by an increase in temperature during abnormal use, and is deformed by the pressure in the battery, and gas is released to the outside from the gap generated thereby.

In patent document 2, since the width | variety of a heat welding resin sheet is made wider than a seal | sticker part in order to make the heat transfer to a heat welding resin sheet favorable, the polymer-made separator (patent document 2 which hold | maintains the electrolyte of patent document 2 ( When a liquid non-aqueous electrolyte is used instead of a gel electrolyte, the liquid non-aqueous electrolyte that has oozed out on the surface of the electrode group due to expansion and contraction due to charge and discharge adheres to the heat-welded resin sheet, and is normally left at a high temperature. In the case of (such as on the dashboard in the summer), the heat-welded resin sheet melts, the seal part peels off, and the electrode comes into contact with moisture in the air, resulting in a problem that the performance deteriorates.
JP 11-97070 A JP 2001-93489 A

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that is highly safe when the internal pressure is increased due to overcharging or the like and that keeps its sealing property when left at a high temperature that can normally occur.

The non-aqueous electrolyte secondary battery according to the present invention comprises a container having at least a portion of the inner surface is formed from a casing film is a sealant layer, and a side portion Ru sealed by thermal fusion, and a cup portion, said cup an electrode assembly and a nonaqueous electrolyte containing a positive electrode and a negative electrode Ru housed in part, a non-aqueous electrolyte secondary battery comprising a
Than the sealant layer in a portion of the side portion is disposed so as thermoplastic films of low melting point end of the cup portion located at the edge portion side than the boundary between the cup portion and the side portion The side portion is sealed .

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery which is excellent in the safety at the time of the internal pressure rise by overcharge etc., and has a high capacity | capacitance recovery rate at the time of high temperature storage can be provided.

  An embodiment of a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a thin nonaqueous electrolyte secondary battery which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 shows the thin nonaqueous electrolyte secondary battery of FIG. 3 is a partial cross-sectional view taken along a line, FIG. 3 is a plan view of the thin non-aqueous electrolyte secondary battery of FIG. 1, and FIG. 4 is a view of the heat of the container sealing portion of the thin non-aqueous electrolyte secondary battery of FIG. It is sectional drawing which showed typically the location where the plastic film was interposed.

  In the electrode group 1, the positive electrode 2, the negative electrode 3, and the separator 4 are wound in a spiral shape, and further formed into a flat and rectangular shape. The positive electrode tab 5 electrically connected to the positive electrode 2 and the negative electrode tab 6 electrically connected to the negative electrode 3 protrude from the same surface of the electrode group 1 to the outside. The liquid non-aqueous electrolyte is held in the electrode group 1.

  Such an electrode group 1 is accommodated in the cup part 7 of the exterior film folded in half. Further, the positive and negative electrode tabs 5 and 6 are drawn out from the opposite side of the bent portion of the exterior film and serve as a positive electrode terminal and a negative electrode terminal. For example, as shown in FIG. 2, the exterior film has a sealant layer 8 constituting an inner surface, a resin layer 9 constituting an outer surface, a sealant layer 8, and a barrier layer 10 disposed between the resin layers 9. No)). Further, the cup portion 7 of the exterior film is formed by, for example, overhanging or drawing.

  Three sides excluding the bent portion of the exterior film are sealed by heat sealing. Among them, in one of the sealing portions 11b and 11c orthogonal to the sealing portion 11a from which the positive and negative electrode tabs 5 and 6 extend (for example, 11b), as illustrated in FIG. Thermal fusion is performed in a state where a thermoplastic film 12 having a melting point lower than that of the sealant layer 8 is disposed between the sealant layer 8 and the sealant layer 8 of the other exterior film. At this time, the inner end portion 12a of the thermoplastic film 12 is positioned outside the boundary of the sealing portion 11b. The shortest distance d between the boundary of the sealing portion 11b and the inner end portion 12a of the thermoplastic film 12 is preferably in the range of 0.5 to 2 mm.

  According to the secondary battery configured as described above, the thermoplastic film 12 having a melting point lower than that of the sealant layer 8 is interposed such that the inner end 12a is not sandwiched between the boundaries of the sealing portion 11b. When the liquid nonaqueous electrolyte oozes out on the surface of the electrode group 1 due to expansion and contraction associated with charging / discharging, it is possible to reduce the nonaqueous electrolyte from adhering to the thermoplastic film 12. Accordingly, when the thermoplastic film 12 is partially melted in a high temperature environment where the secondary battery can normally occur, it is possible to suppress the thermoplastic film 12 from being deteriorated by the nonaqueous electrolyte. It can suppress that the sealing strength of an exterior film container falls in the high temperature environment within the tolerance of a grade.

  In addition, when the nonaqueous electrolyte secondary battery generates gas due to overcharge or the like and falls into an abnormally high temperature state, because the thermoplastic film 12 melts and flows earlier than the sealant layer 8 of the exterior film, Thus, gas can be discharged to the outside through the gap generated. For this reason, explosion can be prevented, and ignition can be avoided because the temperature rise can be suppressed by heat release by gas discharge.

  In this secondary battery, by setting the shortest distance d between the boundary of the sealing portion 11b and the inner end portion 12a of the thermoplastic film 12 within a range of 0.5 to 2 mm, safety when the internal pressure is increased due to overcharge or the like. The secondary battery can be made high and has little capacity deterioration due to high-temperature storage. That is, when the shortest distance d is less than 0.5 mm, the non-aqueous electrolyte tends to adhere to the thermoplastic film 12, and thus the capacity deterioration during high-temperature storage may increase. On the other hand, if the shortest distance d exceeds 2 mm, the heat transfer to the thermoplastic film 12 is deteriorated when the internal pressure is increased due to overcharge or the like, and the operation of the safety valve mechanism is delayed, which may lead to rupture or ignition.

  A more preferable range of the shortest distance d is 0.5 to 1.0 mm.

  In addition, in FIG. 1-4 mentioned above, although the example which made the shape of the thermoplastic film rectangular was demonstrated, the shape of a thermoplastic film is not limited to this, For example, a circle, an ellipse, a triangle, a polygon, a wedge shape It is possible to make various shapes such as.

  Moreover, in FIG. 1-4 mentioned above, since the shape of the thermoplastic film was made into the rectangle, although the distance of the inner edge part of a thermoplastic film and the boundary of a sealing part was constant, the distance was not uniform. Also good. For example, when the shape of the thermoplastic film is made circular, the shortest distance (the distance between the most protruding portion of the thermoplastic film and the boundary of the sealing portion facing this portion) is 0.5 to 2 mm. Although it is good, a higher effect can be obtained when the distance from the boundary of the sealing portion is in the range of 0.5 to 2 mm in other locations.

  Hereinafter, the exterior film, the thermoplastic film, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte will be described.

1) Exterior film The exterior film is preferably a laminate film including a sealant layer constituting the inner surface, a resin layer constituting the outer surface, and a barrier layer. In addition, this exterior film accept | permits including the adhesive agent used in order to bond each layer together. Each layer may be formed of one type of material or two or more types of materials.

The melting point of the sealant layer is preferably 120 ° C to 170 ° C. Examples of the thermoplastic resin forming the sealant layer include polypropylene resins (eg, homopolymers, block copolymers, random copolymers, etc.), polyethylene resins (eg, high density polyethylene, linear low density polyethylene, ethylene / butene). And ethylene / α-olefin (C ₃ -C ₈ ) copolymer such as 1 copolymer, crosslinked polyethylene, acid-modified polyethylene, and the like. Among these, a polyethylene resin is preferable. When polyethylene-based resin is used for the sealant layer, even if heat fusion is performed under low temperature and low pressure conditions that do not cause thermal deterioration of the barrier layer, it is sufficient that liquid leakage does not occur from the joint between the positive and negative electrode leads and the outer film. The sealing strength can be ensured.

  The barrier layer can be formed from, for example, an aluminum alloy, aluminum, stainless steel, iron, copper, nickel, or the like.

  The resin layer constituting the outer surface is for protecting the barrier layer. The resin layer can be formed from, for example, a polyamide resin.

  The thickness of the exterior film is desirably 0.3 mm or less. A more preferable range is 0.05 to 0.3 mm.

2) Thermoplastic film The melting point of the thermoplastic film is preferably 70 ° C to 110 ° C. This is due to the reason explained below. When the melting point is lower than 70 ° C., the thermoplastic film may be melted by a natural temperature increase (about 40 to 50 ° C.) due to charging / discharging of the secondary battery and the sealing strength may be lowered. On the other hand, if the melting point exceeds 110 ° C., the valve operation when the internal pressure increases due to overcharge or the like may be delayed, and the ignition rate may increase. A more preferable range is 80 ° C to 100 ° C.

  Examples of the resin constituting the thermoplastic film include ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-methyl acrylate copolymers, ethylene-methacrylic acid copolymers, and ethylene-methacrylic acid. Examples thereof include a methyl copolymer. The type of the constituent resin can be one type or two or more types. Among these, ionomers and ethylene-vinyl acetate copolymers are preferable because they are excellent in compatibility with polyethylene resins.

  The thickness of the thermoplastic film is desirably in the range of 10 to 100 μm. This is due to the reason explained below. If the thickness is less than 10 μm, since the thermoplastic film is thin, the thermoplastic film may be broken or fused with the sealant layer at the time of sealing, and a portion without the thermoplastic film may be formed. There is a possibility that the valve operation at the time of rising will be delayed and the firing rate will be increased. On the other hand, if the thickness exceeds 100 μm, the difference in thickness from the portion where the thermoplastic film is not interposed becomes large, so that the heat and pressure for heat fusion becomes non-uniform and sufficient sealing strength is obtained. There is a risk that it will not be obtained. A more preferable range of the thickness is 30 to 70 μm.

  The area of the thermoplastic film is desirably 0.5 to 30% (more preferably 5 to 15%) when the total area of the sealing portion is 100%.

  The position of the thermoplastic film is not limited to any position on the long side or the short side as long as it is in a part of the sealing part, but the long side is more quickly outgassing when the internal pressure rises, preferable.

  A thermoplastic film may be interposed between at least one of the positive electrode lead and the negative electrode lead and the sealant layer of the laminate film, but the thermoplastic film is provided in another part, and a protective film is interposed instead. You may let them. The protective film can be formed from, for example, a polyethylene resin. Among these, acid-modified polyethylene is preferable. When this film is used, the electrode lead can be sufficiently covered, so that the thickness of the sealant layer can be reduced. Moreover, since the usage-amount of acid-modified polyethylene can be decreased compared with the case where a sealant layer is formed with acid-modified polyethylene, manufacturing cost can be reduced.

3) Positive electrode The positive electrode includes a current collector and a positive electrode layer that is supported on one or both surfaces of the current collector and includes an active material.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and lithium. Examples thereof include vanadium oxide and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, when a lithium-containing cobalt oxide (for example, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ) is used. This is preferable because a high voltage can be obtained. In addition, the kind of positive electrode active material to be used can be made into 1 type or 2 types or more.

  The positive electrode layer can contain a conductive agent. Examples of the conductive agent include acetylene black, carbon black, and graphite.

  The positive electrode layer may contain a binder. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyether sulfone, ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Can be used.

  The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 85 to 98% by weight of the positive electrode active material, 1 to 10% by weight of the conductive agent, and 1 to 5% by weight of the binder.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel.

  The positive electrode is produced, for example, by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, drying it, and pressing it.

4) Negative electrode The negative electrode includes a current collector and a negative electrode layer supported on one or both sides of the current collector.

  The negative electrode layer preferably contains a carbonaceous material that absorbs and releases lithium ions and a binder.

Examples of the carbonaceous material include graphite materials, carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic vapor phase carbonaceous material, and resin fired body; thermosetting resin, isotropic pitch, mesophase pitch, and the like. Graphite material or carbonaceous material obtained by heat-treating carbon-based carbon, mesophase pitch-based carbon fiber, mesophase microspheres, etc. at 500 to 3000 ° C .; a carbon layer having a surface of the graphite material particles having lower crystallinity than the particles Can be mentioned. Among them, it is preferable to use a graphite material having a graphite crystal having a (002) plane spacing _d002 of 0.34 nm or less. A nonaqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can greatly improve battery capacity and large current discharge characteristics. More preferably, the surface interval _d002 is 0.337 nm or less.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Can be used.

  The blending ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 10% by weight of the binder.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel.

  The negative electrode is, for example, kneaded with a carbonaceous material that occludes / releases lithium ions and a binder in the presence of a solvent, and the resulting suspension is applied to a current collector and dried, followed by a desired pressure. It is produced by pressing once or multistage pressing 2-5 times.

5) Separator As this separator, a microporous film, a woven fabric, a non-woven fabric, a laminate of the same material or different materials among these can be used. In particular, the microporous membrane causes a so-called shutdown phenomenon in which the resin constituting the separator plastically deforms and closes the fine pores when the temperature of the electrode group rises abnormally due to heat generated by overcharging, etc., and the flow of lithium ions Is prevented, and further overheating is prevented, and the overcharge state can be safely terminated, which is preferable. Examples of the material for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-butene copolymer. As a material for forming the separator, one type or two or more types selected from the types described above can be used.

The separator preferably has an air permeability of 200 to 600 seconds / 100 cm ³ . The air permeability means the time (seconds) required for 100 cm ³ of air to pass through the separator, and can be measured by a method defined in JIS (Japanese Industrial Standard) P8117. The value of the air permeability is more preferably 250 to 500 seconds / 100 cm ³ , and further preferably 300 to 450 seconds / 100 cm ³ .

The temperature at which the separator causes a shutdown phenomenon, so-called shutdown temperature, is preferably in the range of 100 to 160 ° C. The shutdown temperature can be measured as a temperature at which the air permeability after the separator is heated to a certain temperature is measured and the value of the air permeability becomes 100,000 seconds / 100 cm ³ or more. The shutdown temperature of the separator is more preferably 110 to 150 ° C.

  The temperature at which the separator melts to form a film breakage, so-called melting temperature, is preferably 160 ° C. or higher and 15 ° C. or higher than the shutdown temperature.

  The separator preferably has a porosity in the range of 30 to 60%. A more preferable range of the porosity is 35 to 50%.

  The thickness of the separator is preferably 30 μm or less, and more preferably 25 μm or less. Moreover, it is preferable that the lower limit of thickness is 5 micrometers, and a more preferable lower limit is 8 micrometers.

  The width of the separator is desirably wider than the width of the positive electrode and the negative electrode. By adopting such a configuration, it is possible to prevent the positive electrode and the negative electrode from coming into direct contact without a separator.

6) Nonaqueous electrolyte A nonaqueous electrolyte contains a nonaqueous solvent and an electrolyte (for example, lithium salt) dissolved in the nonaqueous solvent. The form of the non-aqueous electrolyte is not limited to a liquid form, and a gel or solid form can also be used.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), and trifluoromethanesulfonic acid. Lithium (LiCF ₃ SO ₃ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ or the like can be used, and two or more kinds may be mixed and used.

  Examples of the non-aqueous solvent include γ-butyrolactone, ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, methylsulfolane. , Acetonitrile, propyl nitrile, anisole, acetate ester, propionate ester and the like can be used, and two or more kinds may be mixed and used.

  It is preferable to add a surfactant such as trioctyl phosphate (TOP) to the non-aqueous solvent. By adding such a surfactant, it becomes possible to improve the wettability of the nonaqueous electrolyte with respect to the separator.

  The concentration of the electrolyte in the non-aqueous solvent is preferably 0.5 mol / L or more.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
<Preparation of positive electrode>
First, 90% by weight of lithium cobalt oxide (Li _x CoO ₂ ; X is 0 <X ≦ 1) powder, 5% by weight of acetylene black, and 5% by weight of polyvinylidene fluoride (PVdF) dimethylformamide (DMF) solution was added and mixed to prepare a slurry. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, then dried and pressed to produce a positive electrode having a structure in which the positive electrode layer was supported on both sides of the current collector. The thickness of the positive electrode layer was 60 μm per side.

<Production of negative electrode>
As a carbonaceous material, 95% by weight of powder of mesophase pitch-based carbon fiber (having a (002) plane interval (d ₀₀₂ ) of 0.336 nm determined by powder X-ray diffraction) heat-treated at 3000 ° C. and polyvinylidene fluoride ( (PVdF) 5% by weight dimethylformamide (DMF) solution was mixed to prepare a slurry. The slurry was applied to both surfaces of a current collector made of a copper foil having a thickness of 12 μm, dried, and pressed to prepare a negative electrode having a structure in which the negative electrode layer was supported on the current collector. The thickness of the negative electrode layer was 55 μm per side.

The surface spacing d ₀₀₂ of (002) plane of the carbonaceous material were respectively determined by the powder X-ray diffraction spectrum half width midpoint method. At this time, scattering correction such as Lorentz scattering was not performed.

<Separator>
A separator made of a microporous polyethylene film having a thickness of 25 μm was prepared.

<Preparation of liquid nonaqueous electrolyte (nonaqueous electrolyte)>
A non-aqueous solvent was prepared by mixing ethylene carbonate (EC) and γ-butyrolactone (GBL) so that the volume ratio was 1: 2. 1.5 mol / L of lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained nonaqueous solvent to prepare a liquid nonaqueous electrolyte.

<Production of electrode group>
A positive electrode lead 5 made of a strip-shaped aluminum foil having a thickness of 100 μm was ultrasonically welded to the positive electrode current collector, and a negative electrode lead 6 made of a strip-shaped nickel foil having a thickness of 100 μm was ultrasonically welded to the negative electrode current collector. Next, the positive electrode 2 and the negative electrode 3 were spirally wound through the separator 4 therebetween, and then formed into a flat shape to produce an electrode group 1.

<Preparation of exterior film>
A stretched nylon film 9 having a thickness of 25 μm, an aluminum alloy foil (JIS H 4160 A8079 material) 10 having a thickness of 40 μm, and a linear low density polyethylene film (sealant film) 8 having a thickness of 30 μm and a melting point of 122 ° C. A laminate film was produced by laminating and bonding in this order via a urethane-based adhesive. The laminate film was stretched or deep-drawn from the sealant film side to form a cup-shaped electrode group housing, and then bent 180 ° with the sealant film inside to obtain a container.

<Preparation of nonaqueous electrolyte secondary battery>
While accommodating the electrode group 1 in the cup part 7 of the container, the positive electrode lead terminal 5 and the negative electrode lead terminal 6 were pulled out of the container. The positive electrode lead terminal 5 and the negative electrode lead terminal 6 were covered with a protective film made of polyethylene resin so as to straddle the two lead terminals, and the other surface was covered with a similar protective film so as to straddle the two lead terminals. The positive and negative electrode lead terminals sandwiched between the two protective films were further sandwiched between exterior films, and a top seal 11a having a width of 4 mm was applied.

  Next, a rectangular ionomer film having a melting point of 90 ° C., a thickness of 30 μm and a length of 10 mm is formed as a thermoplastic film 12 at the center of the long side perpendicular to the top seal 11a portion. (In this case, the inner long side) 12a is interposed so that the shortest distance d between the boundary of the sealing portion is 0.5 mm, and a side seal 11b having a width of 4 mm is applied to one end portion on the longitudinal direction side. .

  Subsequently, the electrode group in the container was vacuum-dried at 80 ° C. for 12 hours. Subsequently, a liquid non-aqueous electrolyte is injected into the electrode group in the container so that the amount per battery capacity 1Ah is 4.8 g, and a side seal 11c having a width of 4 mm is applied to the end portion on the other side in the longitudinal direction. A thin nonaqueous electrolyte secondary battery having a structure of 4.5 mm, a width of 35 mm, and a height of 60 mm and having the structure shown in FIGS. The area of the ionomer film was 6% of the total area of the sealing portion (the total area of the top seal 11a and the side seals 11b and 11c).

  The following treatment was applied to the non-aqueous electrolyte secondary battery as an initial charge / discharge process. First, constant current / constant voltage charging was performed for 15 hours at room temperature to 4.2 V at 0.2C. Then, it discharged to 3.0V at 0.2C at room temperature, and produced the nonaqueous electrolyte secondary battery.

  Here, 1C is a current value necessary for discharging the nominal capacity (Ah) in one hour. Therefore, 0.2 C is a current value necessary for discharging the nominal capacity (Ah) in 5 hours.

(Examples 2 to 4)
Except for changing the vertical and horizontal dimensions so as not to change the area of the thermoplastic film and changing the shortest distance d between the inner end of the thermoplastic film and the boundary of the sealing portion as shown in Table 1 below. In the same manner as described in Example 1, a nonaqueous electrolyte secondary battery was produced.

(Example 5)
A nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that an ethylene-vinyl acetate copolymer film having a melting point of 70 ° C. was used as the thermoplastic film.

(Example 6)
A nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that a low-density polyethylene film having a melting point of 110 ° C. was used as the thermoplastic film.

(Comparative Example 1)
Except for sandwiching the inner end of the thermoplastic film between the boundaries of the sealing part (the distance between the inner end of the thermoplastic film and the boundary of the sealing part is 0 mm), as described in Example 1 above. Similarly, a nonaqueous electrolyte secondary battery was manufactured.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that a linear low density polyethylene film having a melting point of 122 ° C. was used as the thermoplastic film.

  About the obtained secondary battery of Examples 1-6 and Comparative Examples 1-2, it evaluated by the method demonstrated below.

[Overcharge test]
About 10 each of the secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2, a constant current / constant voltage overcharge test was performed up to 10 V at 1.0 C at 20 ° C. At that time, the number of batteries that ignited was recorded, the ignition rate (%) was calculated, and the results are shown in Table 1 below.

[High temperature storage test]
For each of the 10 secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2, constant current / constant voltage charging was performed at room temperature to 4.2 V at 1.0 C for 3 hours. Then, it discharged to 3.0V at 1.0C at room temperature, the discharge capacity at this time was measured, and it recorded as a reference capacity. Further, constant current / constant voltage charging was performed at room temperature to 4.2 V at 1.0 C for 3 hours and left at 100 ° C. for 4 hours. After cooling, discharge to 3.0V at 1.0C at room temperature, and further charge for 3 hours at 1.0C to 4.2V at room temperature, then charge to 3.0V at 1.0C at room temperature. After discharging, the discharge capacity at this time was measured and recorded as the recovery capacity. At that time, capacity recovery rate (%) = (recovery capacity) / (reference capacity) × 100 was calculated, and the average value of the results is shown in Table 1 below.

  As is clear from Table 1, the secondary batteries of Examples 1 to 6 in which the thermoplastic film was interposed in the sealing portion of the exterior film so that the end portion was not sandwiched between the boundaries of the sealing portion were excessive. The ignition rate during charging was small, and the capacity recovery rate after the high-temperature storage test was also good.

  On the other hand, in the secondary battery of Comparative Example 1 in which the thermoplastic film is sandwiched between the boundaries of the sealing portion, the thermoplastic film is melted in the high-temperature storage test, the sealing performance is lowered, and moisture in the air reaches the inside. Since it penetrate | invaded, the capacity | capacitance recovery rate at the time of high temperature storage became low compared with Examples 1-6. Further, in Comparative Example 2 in which the melting point of the thermoplastic film is the same as that of the sealant layer, the gas generated in the overcharge test does not escape to the outside and cannot be dissipated. There were many compared.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view which shows the thin nonaqueous electrolyte secondary battery which is one Embodiment of the nonaqueous electrolyte secondary battery concerning this invention. FIG. 2 is a partial cross-sectional view of the nonaqueous electrolyte secondary battery in FIG. 1 cut along the line II-II. The top view of the thin nonaqueous electrolyte secondary battery of FIG. Sectional drawing which showed typically the location where the thermoplastic film was interposed among the container sealing parts of the thin nonaqueous electrolyte secondary battery of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrode group, 2 ... Positive electrode, 3 ... Negative electrode, 4 ... Separator, 5 ... Positive electrode lead, 6 ... Negative electrode lead, 7 ... Cup part, 8 ... Sealant layer, 9 ... Resin layer, 10 ... Barrier layer, 11a-11c ... Sealing part, 12 ... Thermoplastic film, 12a ... Inside end part.

Claims (3)

At least a portion of the inner surface is formed from a casing film is a sealant layer, the electrode comprising a side portion Ru sealed by thermal fusion, a container having a cup portion, the positive electrode and the negative electrode Ru housed in the cup portion a non-aqueous electrolyte secondary battery comprising the group and a non-aqueous electrolyte, a,
Than the sealant layer in a portion of the side portion is disposed so as thermoplastic films of low melting point end of the cup portion located at the edge portion side than the boundary between the cup portion and the side portion A non-aqueous electrolyte secondary battery , wherein the side portion is sealed . 2. The nonaqueous electrolyte according to claim 1, wherein a shortest distance between a boundary between the side portion and the cup portion and an end portion on the cup portion side of the thermoplastic film is in a range of 0.5 mm to 2 mm. Secondary battery.   The non-aqueous electrolyte secondary according to claim 1 or 2, wherein the sealant layer contains a polyethylene-based resin, and the thermoplastic film contains at least one of an ionomer and an ethylene-vinyl acetate copolymer. battery.

Images