JP4660105B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

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

Currently, lithium ion secondary batteries are commercialized as non-aqueous electrolyte secondary batteries for portable devices such as mobile phones. In this battery, a lithium cobalt oxide (LiCoO ₂ ) is used for the positive electrode, a graphite material or a carbonaceous material is used for the negative electrode, an organic solvent in which a lithium salt is dissolved in a non-aqueous electrolyte, and a porous film is used for the separator. As the material of the separator, polyethylene (PE), polypropylene (PP), or a combination thereof is used.

  As a separator for a lithium ion secondary battery, a microporous film is more preferable than a nonwoven material. This is because it is difficult to make a thin film excellent in physical properties such as uniformity and puncture strength with a nonwoven fabric. The method for producing the microporous membrane is roughly divided into two processes, a wet process and a dry process.

  In the wet process, a hydrocarbon resin and polyolefin resin are mixed, heated and melted, processed into a sheet, then stretched uniaxially or biaxially, and finally the solvent is extracted and removed with a volatile solvent. It includes a process.

  On the other hand, the dry process includes a step of forming a microporous material by melting a polyolefin resin, extruding it into a film, and stretching the heat treated material at a low temperature and then stretching it again at a high temperature.

  A separator having a PP / PE / PP three-layer structure is known as a separator manufactured by the dry process. This separator is characterized in that a low melting point PE layer (melting point 135 ° C.) functions as a thermal fuse, and a high melting point PP layer (melting point 165 ° C.) is strong in mechanical strength.

  On the other hand, Patent Document 1 reports a method for producing a single-layer separator from a blend of PE / PP by a dry process.

  Patent Document 2 reports a method of forming a gel based on a polyethylene oxide (PEO) monomer having an acrylate end group in a microporous film. However, it is difficult for a gel-like substance or the like having adhesiveness at room temperature to provide uniform adhesion to the separator, and the battery reaction is uneven, and a long charge / discharge cycle life cannot be obtained. Furthermore, in the separator through the gel, since the hydrophilicity of PEO is high, moisture is likely to be mixed in the battery manufacturing process and the like, and the separator itself has adhesiveness, which makes it difficult to manufacture the battery. It was.

  In Patent Document 3, a porous separator made of a porous film containing polyethylene, polypropylene, cellulose, polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric is used, and the peel strength between the porous separator and the positive and negative electrodes is 10 gf / cm. When the following is established, the large current discharge characteristics and the charge / discharge cycle life are improved. When the peel strength exceeds 10 gf / cm, the interface resistance between the positive and negative electrodes and the separator increases, and the excellent large current discharge characteristics and the cycle life are obtained. There is a description that it will not be obtained.

However, if the peel strength between the separator and the positive and negative electrodes is reduced to 10 gf / cm or less as in Patent Document 3, a gap is easily generated in the electrode group due to gas generated during charging and discharging, and expansion / contraction of the electrode. In some cases, the lithium occlusion / release reaction is less likely to occur, so that the charge / discharge reaction spots increase, and a sufficient charge / discharge cycle life cannot be obtained.
US Patent No. 5,385,777 European Patent Publication 0651455A1 (Application No. 94307362.7) JP 2000-348776 A

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery having an improved charge / discharge cycle life.

A nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte,
The separator have a surface containing a resin component composed of at least one kind selected ethylene-vinyl acetate copolymer resins, ethylene-acrylate copolymer resins, polystyrene-butadiene block copolymer and the group consisting of nylon,
The positive electrode, the separator, and the negative electrode are integrated in a state where the surface containing the resin component of the separator is in contact with the negative electrode,
The peeling strength between the peeling strength and the separator and the negative electrode of the positive electrode and the separator is greater than 10 gf / cm, it is characterized in that not more than 30 gf / cm.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having an improved charge / discharge cycle life.

  The non-aqueous electrolyte of the non-aqueous electrolyte secondary battery basically exists centering on the separator, and the electrode reaction can be uniformly performed as the separator and the electrode are in close contact with each other. For this reason, although it is desirable that the adhesion between the electrode and the separator is higher, the separator is made of polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF) as described in Patent Document 3. In order to increase the adhesion of the electrode, it is necessary to apply a high-temperature and high-pressure heating press to the electrode and the separator to bond them together. Therefore, sufficient charge / discharge cycle life could not be obtained.

  The separator used in the present invention includes at least one resin selected from the group consisting of ethylene vinyl acetate copolymer resin (EVA), ethylene / acrylate copolymer resin (EEA), polystyrene / butadiene block copolymer, and nylon. Since the component is contained, hot melt adhesiveness can be exhibited at a relatively low temperature of 50 ° C to 100 ° C. Therefore, the peeling strength between at least one of the positive and negative electrodes and the separator can be made larger than 10 gf / cm and 30 gf / cm or less without applying an excessive heating press to the electrode and the separator. Adhesiveness with the electrode can be increased without impairing ion permeability. As a result, it is possible to reduce the occurrence of gaps in the electrode group due to the gas generated during charging and discharging and the expansion and contraction of the electrode, so that the unevenness of occlusion / release of lithium ions on the electrode surface can be reduced, Charge / discharge cycle characteristics can be improved. Moreover, this separator is excellent also in solvent resistance.

  The upper limit of the peel strength is 30 gf / cm. If the peel strength is higher than 30 gf / cm, the lithium ion permeability of the separator is impaired even when the separator containing the resin component described above is used. This is because the cycle life is shortened. A more desirable range is 13 to 26 gf / cm.

  As for the peel strength, if either the peel strength of the positive electrode and the separator or the peel strength of the negative electrode and the separator is within the above-mentioned range, sufficient charge / discharge cycle characteristics can be obtained, but a more excellent charge / discharge cycle. In order to obtain characteristics, it is desirable that both the peel strength between the positive electrode and the separator and the peel strength between the negative electrode and the separator are within the ranges described above.

  In addition, it is not preferable that the temperature indicating the hot melt adhesiveness is lower. In the separator exhibiting the hot melt property at 50 ° C. or lower, the lithium ion permeability is reduced when the battery temperature is 50 ° C. or higher. May be reduced. Since 40 ° C. to 50 ° C. is a temperature that can be increased even under natural conditions, the above resin component that provides hot melt properties at 50 to 100 ° C. is contained.

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

1) Separator The separator can be formed from a porous sheet, for example. As a porous sheet, a porous film and a nonwoven fabric can be mentioned, for example.

  The separator is combined with at least one resin component selected from the group consisting of ethylene vinyl acetate copolymer resin (EVA), ethylene / acrylate copolymer resin (EEA), polystyrene / butadiene block copolymer and nylon. It is desirable that other resins are contained.

  The other resin is preferably at least one material selected from polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Of these, polyethylene and polypropylene are preferable. Separator using at least one of polyethylene and polypropylene as other resin can reduce clogging due to melting at the time of heat bonding with electrode, and also at abnormal temperature because shutdown function works at proper temperature The safety is also excellent.

  The content of at least one resin component selected from the group consisting of EVA, EEA, polystyrene / butadiene block copolymer, and nylon in the separator is preferably in the range of 0.1 to 10% by weight. This is due to the reason explained below. If the content is less than 0.1% by weight, the effect of adding the resin component may not be sufficiently obtained. On the other hand, if the content exceeds 10% by weight, the separator tends to be clogged when bonded to the electrode by a hot press, so that the internal resistance of the battery may be increased. The more preferable range of the content is 0.5 to 10% by weight, and the most preferable range is 1 to 5% by weight.

  The separator containing the resin component is, for example, a film composed of the resin component and another component film stacked to form a laminated structure of two or more layers, and these are integrated using a stretching process, or a base material film It is also possible to obtain a separator by adding the resin component particles therein and uniformly dispersing in the stretching step.

  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 separator preferably has a heat shrinkage rate of 120% or less at 120 ° C. for 1 hour. The heat shrinkage rate is more preferably 15% or less.

  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 separator preferably has an air permeability of 600 seconds / 100 cm ³ or less. The air permeability means time (seconds) required for 100 cm ³ of air to pass through the porous sheet. The upper limit value of the air permeability is more preferably 500 seconds / 100 cm ³ . The lower limit value of the air permeability is preferably 50 seconds / 100 cm ^3, and a more preferable lower limit value is 80 seconds / 100 cm ³ .

2) 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.

  The positive electrode layer preferably further includes a binder and a conductive agent.

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.

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethersulfone, ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). be able to.

  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.

3) Negative electrode The negative electrode includes a current collector and a negative electrode layer supported on one side 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. The electrode density after pressing is preferably 1.25 to 1.55 g / cm ³ .

  The negative electrode is selected from a metal such as aluminum, magnesium, tin, and silicon, a metal oxide, a metal sulfide, or a metal nitride instead of the above-described carbon material that occludes / releases lithium ions. A metal compound containing a lithium compound or a lithium alloy can be used.

  Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.

  Examples of the metal sulfide include tin sulfide and titanium sulfide.

  Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.

  Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.

4) Nonaqueous electrolyte The nonaqueous electrolyte contains a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent. As the non-aqueous electrolyte, a gel-like non-aqueous electrolyte in which a liquid non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent is used, and an organic polymer compound or a crosslinked polymer is dissolved in the liquid non-aqueous electrolyte to form a gel. May be used.

  Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, sultone compounds (sultone compounds having at least one double bond in the ring, 1,3-propane sultone (PS), etc.), vinylene carbonate (VC), Vinylethylene carbonate (VEC), phenylethylene carbonate (phEC), γ-butyrolactone (GBL), γ-valerolactone (VL), methyl propionate (MP), ethyl propionate (EP), 2-methylfuran (2Me- F), furan (F), thiophene (TIOP), catechol carbonate (CATC), ethylene sulfite (ES), 12-crown-4 (Crown), tetraethylene glycol dimethyl ether (Ether), cyclohexylbenzene (CHB), 2 , 4-Diff Examples include Luoloanisole (DFA). The type of the non-aqueous solvent can be one type or two or more types.

  Examples of the composition of the non-aqueous solvent include those containing a cyclic carbonate and a chain carbonate, and those containing a cyclic carbonate and GBL. Examples of the cyclic carbonate include ethylene carbonate (EC) and propylene carbonate (PC). The chain carbonate preferably contains methyl ethyl carbonate (MEC), and only MEC may be used as the chain carbonate, or another chain carbonate may be used in combination with MEC. The other chain carbonate is preferably at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC).

Examples of the lithium salt include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), trifluoro Examples include lithium salts such as lithium metasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [(LiN (CF ₃ SO ₂ ) ₂ ], LiN (C ₂ F ₅ SO ₂ ) ₂ . The type of electrolyte to be used can be one type or two or more types, and among them, those containing LiPF ₆ or LiBF ₄ are preferable.

  The lithium salt concentration in the non-aqueous solvent is desirably 0.5 to 2.5 mol / L. A more preferable range is 0.8 to 2.0 mol / L.

  The liquid non-aqueous electrolyte preferably contains a surfactant such as trioctyl phosphate (TOP) in order to improve the wettability with the separator. The addition amount of the surfactant is preferably 3% or less, and more preferably in the range of 0.1 to 1%.

  The amount of the liquid non-aqueous electrolyte is preferably 1.5 to 5.5 g per battery unit capacity 1 Ah. A more preferable range of the liquid nonaqueous electrolytic mass is 2 to 5 g / Ah.

  Integration of an electrode and a separator is performed by the method demonstrated below, for example.

  The positive electrode and the negative electrode are wound so as to form a flat spiral with a separator interposed therebetween, or the positive electrode and the negative electrode are wound in a spiral with a separator interposed therebetween, and then compressed in the radial direction to be flattened. The electrode group is obtained by forming a shape or bending the positive electrode and the negative electrode one or more times with a separator interposed therebetween.

  The positive electrode and the negative electrode are bonded to the separator by heat forming in the thickness direction of the obtained electrode group.

  The thermoforming may be performed after the electrode group is stored in a container, or may be performed before the electrode group is stored in the container.

  The atmosphere in which the heat forming is performed is preferably a reduced pressure atmosphere including a vacuum or a normal pressure atmosphere.

  The molding can be performed by, for example, press molding or insertion into a molding die.

  The temperature of the thermoforming is preferably in the range of 40 to 120 ° C. A more preferable range is 60 to 90 ° C.

The molding pressure for the heat molding is preferably in the range of 0.01 to 30 kg / cm ² . A more preferable range is 8 to 20 kg / cm ² .

  A container for accommodating the electrode group and the non-aqueous electrolyte described above will be described.

  The shape of the container may be, for example, a bottomed rectangular tube shape, a bag shape, or a cup shape.

  This container can be formed from, for example, a sheet including a resin layer, a metal plate, a metal film, or the like.

  The resin layer contained in the sheet can be formed from, for example, polyolefin (for example, polyethylene, polypropylene), polyamide or the like. The sheet may be composed of only one type or two or more types of resin layers, but may include a metal layer. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel.

  The metal plate and the metal film can be formed of, for example, iron, stainless steel, or aluminum.

  The nonaqueous electrolyte secondary battery according to the present invention can have various forms such as a cylindrical shape, a rectangular shape, and a thin shape. Among them, a thin lithium ion secondary battery and a prismatic lithium ion secondary battery will be described in detail with reference to FIGS.

  First, a thin lithium ion secondary battery will be described with reference to FIGS.

  As shown in FIG. 1, an electrode group 2 is accommodated in a container body 1 having a long box-like cup shape. The electrode group 2 has a structure in which a laminate including a positive electrode 3, a negative electrode 4, and a separator 5 disposed between the positive electrode 3 and the negative electrode 4 is wound into a flat shape. The nonaqueous electrolyte is held in the electrode group 2. A lid plate 6 is integrated with the container body 1. The container body 1 and the cover plate 6 are each composed of a laminate film. The laminate film includes an external protective layer 7, an internal protective layer 8 containing a thermoplastic resin, and a metal layer 9 disposed between the external protective layer 7 and the internal protective layer 8. A lid 6 is fixed to the container body 1 by heat sealing using a thermoplastic resin of the inner protective layer 8, whereby the electrode group 2 is sealed in the container. A positive electrode tab 10 is connected to the positive electrode 3, and a negative electrode tab 11 is connected to the negative electrode 4, and each is pulled out of the container and serves as a positive electrode terminal and a negative electrode terminal.

  Next, the prismatic nonaqueous electrolyte secondary battery will be described.

  As shown in FIG. 3, an electrode group 13 is accommodated in a bottomed rectangular cylindrical container 12 made of metal such as aluminum. In the electrode group 13, a positive electrode 14, a separator 15 and a negative electrode 16 are laminated in this order and wound in a flat shape. A spacer 17 having an opening near the center is disposed above the electrode group 13.

  The nonaqueous electrolyte is held in the electrode group 13. A sealing plate 18 b having a liquid injection port 18 a and having a circular hole opened near the center is laser welded to the opening of the container 12. The liquid injection port 18a is covered with a sealing lid (not shown). The negative electrode terminal 19 is disposed in a circular hole of the sealing plate 18b via a hermetic seal. The negative electrode tab 20 drawn out from the negative electrode 16 is welded to the lower end of the negative electrode terminal 19. On the other hand, a positive electrode tab (not shown) is connected to a container 12 that also serves as a positive electrode terminal.

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

Example 1
<Preparation of positive electrode>
First, 91% by weight of lithium cobalt oxide (Li _x CoO _2, where X is 0 <X ≦ 1) powder is used as 3% by weight of acetylene black, 3% by weight of graphite, and polyvinylidene fluoride (PVdF) as a binder. 3% by weight and N-methyl-2-pyrrolidone (NMP) as a solvent were 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, and then dried and pressed, whereby the electrode density was 3 g / cm ³ and the positive electrode layer was supported on both sides of the current collector. A positive electrode having a structure was prepared.

<Production of negative electrode>
93% by weight of powder of mesophase pitch carbon fiber (fiber diameter 8 μm, average fiber length 20 μm, average interplanar spacing (d ₀₀₂ ) 0.3360 nm) heat treated at 3000 ° C. as a carbonaceous material, as a binder A slurry was prepared by mixing 7% by weight of polyvinylidene fluoride (PVdF). A structure in which the slurry is applied to both surfaces of a current collector made of a copper foil having a thickness of 12 μm, dried and pressed to have an electrode density of 1.4 g / cm ³ and a negative electrode layer supported on the current collector A negative electrode was prepared.

<Separator>
A two-layer structure in which an ethylene vinyl acetate copolymer (EVA) film is laminated on a polyethylene (PE) base film is integrated in a stretching process, and the heat shrinkage is 20 μm at 120 ° C. in a thickness of 25 μm. %, And a separator with a porosity of 50% was obtained. The EVA content in the separator was 2% by weight.

<Preparation of liquid nonaqueous electrolyte>
Ethylene carbonate (EC) and γ-butyrolactone (GBL) are mixed so that the volume ratio (EC: GBL) is 1: 2, and 0.5% by weight of vinylene carbonate (VC) is added to the mixed solvent. A non-aqueous solvent was prepared. Further, lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained nonaqueous solvent so as to have a concentration of 1.5 mol / L to prepare a liquid nonaqueous electrolyte.

<Production of electrode group>
A belt-like positive electrode lead was welded to the positive electrode current collector, and a belt-like negative electrode lead was welded to the negative electrode current collector, and then the positive electrode and the negative electrode were spirally wound through the separator therebetween. Then, it shape | molded in flat shape and produced the electrode group.

While this electrode group was heated to 80 ° C., press molding was performed at a pressure of 20 kg / cm ² for 30 seconds to integrate the positive electrode, the negative electrode, and the separator.

  A laminate film having a thickness of 100 μm in which both surfaces of an aluminum foil were covered with polypropylene was formed into a bag shape, and the electrode group was accommodated in the bag.

  Next, the electrode group in the laminate film was vacuum dried at 80 ° C. for 12 hours to remove moisture contained in the electrode group and the laminate film.

  A liquid non-aqueous electrolyte is injected into the electrode group in the laminate film so that the amount per battery capacity 1Ah is 4.8 g, and has the structure shown in FIGS. A thin nonaqueous electrolyte secondary battery having a width of 35 mm and a height of 62 mm was assembled.

  The following treatment was applied to the non-aqueous electrolyte secondary battery as an initial charge / discharge process. First, after being left in a high temperature environment of 45 ° C. for 2 hours, constant current / constant voltage charging was performed for 15 hours at 0.2 C to 4.2 V in that environment. Thereafter, it was left at 20 ° C. for 7 days. Furthermore, it discharged to 3.0V at 0.2C in a 20 degreeC environment, and the nonaqueous electrolyte secondary battery was manufactured.

(Comparative Example 1)
The separator is thin as in Example 1 except that a polyethylene (PE) porous film having a thickness of 25 μm, a thermal shrinkage at 120 ° C. of 1 hour of 20%, and a porosity of 50% is used. A non-aqueous electrolyte secondary battery was manufactured.

(Examples 2 to 5, Comparative Examples 2 and 3)
A thin nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the EVA content in the separator was changed as shown in Table 1 below.

(Examples 6 to 10, Comparative Examples 4 and 5)
A thin non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the resin added to the separator was ethylene / acrylate copolymer resin (EEA) and the content was changed as shown in Table 2. Manufactured.

(Examples 11 to 15, Comparative Examples 6 and 7)
A thin nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the type of resin added to the separator was a polystyrene / butadiene block copolymer and the content was changed as shown in Table 3. .

(Examples 16 to 20, Comparative Examples 8 and 9)
A thin non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the type of resin added to the separator was nylon (nylon 12-based copolymer) and the content was changed as shown in Table 4. .

(Examples 21 to 25, Comparative Examples 10, 11, and 12)
Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed so that the volume ratio (EC: MEC) is 1: 2, and 0.5% by weight of vinylene carbonate (VC) is added to the mixed solvent. Further, 1 mol / L of lithium hexafluorophosphate (LiPF ₆ ) was dissolved as an electrolyte to obtain a liquid nonaqueous electrolyte. A thin nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this liquid nonaqueous electrolyte was used and the amount of EVA added to the separator was changed as shown in Table 5.

(Examples 26 to 30, Comparative Examples 13 and 14)
A thin nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 21 except that the type of resin added to the separator was ethylene / acrylate copolymer resin (EEA) and the content was changed as shown in Table 6. Manufactured.

(Examples 31 to 35, Comparative Examples 15 and 16)
A thin nonaqueous electrolyte secondary battery was produced in the same manner as in Example 21 except that the type of resin added to the separator was a polystyrene / butadiene block copolymer and the content was changed as shown in Table 7. .

(Examples 36 to 40, Comparative Examples 17 and 18)
A thin nonaqueous electrolyte secondary battery was produced in the same manner as in Example 21 except that the type of resin added to the separator was nylon (nylon 12-based copolymer) and the content thereof was changed as shown in Table 8. .

(Examples 41 to 44, Comparative Example 19)
As a container, an aluminum alloy (AA symbol 3003) rectangular parallelepiped case (thickness 4.1 mm, width 34 mm, height 41 mm) having a thickness of 0.25 mm was prepared.

  Five types of separators were obtained in the same manner as described in Example 1 except that the types and amounts of resins added to the separators were as shown in Table 9 below. An electrode group was produced from the obtained separators in the same manner as described in Example 1 above. Subsequently, the electrode group was press-molded in the same manner as described in Example 1 to integrate the positive electrode, the negative electrode, and the separator.

  After the electrode group is stored in the container, it is dried at 80 ° C. for 12 hours, so that the liquid non-aqueous electrolyte having the same composition as described in Example 21 is 3.5 g per 1 Ah of battery capacity. A rectangular non-aqueous electrolyte secondary battery having a structure shown in FIG. 3 having a thickness of 4.1 mm, a width of 34 mm, and a height of 43 mm was manufactured by covering with a cap-shaped aluminum material.

  The non-aqueous electrolyte secondary batteries of Examples 41 to 44 and Comparative Example 19 were subjected to the following treatment as the initial charge / discharge process. First, after the injection, the solution was accumulated and allowed to stand for 24 hours, and under that environment, constant current / constant voltage charging was performed at 0.2 C to 4.2 V for 15 hours. Thereafter, it was left at 20 ° C. for 7 days. Furthermore, it discharged to 3.0V at 0.2C in a 20 degreeC environment, and the nonaqueous electrolyte secondary battery was manufactured.

  About the obtained secondary battery of Examples 1-44 and Comparative Examples 1-19, the battery characteristic was evaluated by the method demonstrated below.

<Charge / discharge cycle test>
In an environment of 25 ° C, the battery is charged with a constant current of 4.2V and a constant voltage for 3 hours at a current of 1.0C. The operation was repeated for 500 cycles. The discharge capacity at the 500th cycle is expressed by setting the discharge capacity at the first cycle to 100%, and the result is also shown in Tables 1 to 9 below as the capacity retention ratio after 500 cycles.

<Measurement of peel strength>
Apart from the battery that performs the charge / discharge cycle, after the initial charge / discharge, a cell whose initial capacity was confirmed was prepared, and the peel strength was measured. Hereafter, the measuring method of peeling strength is described.

First, the cell to be measured is disassembled, and the center part of the electrode group 2 (half the length when the spirally wound sheet is spread into a sheet and half the height) ), An electrode bundle having a width (x) of 40 mm and a length (y) of 20 mm (a bundle in which the positive electrode 3-separator 5 and the negative electrode 4-separator 5 overlapped) was cut out. Only the portion of the negative electrode 4-separator 5 is selected from the electrode bundle, peeled to half (20 mm × 20 mm) as shown by hatching in FIG. 4, the peeled negative electrode portion is fixed, and the other peeled separator portion is fixed. The peel strength (gf / cm) was determined from the load when the remaining half (20 mm × 20 mm) was peeled off over the apparatus (RHEO METER; NRM-2010J-CW manufactured by Fudo Kogyo Co., Ltd.). The results are also shown in Tables 1 to 9 below as the peel strength between the negative electrode and the separator. Note that when the peel strength between the positive electrode and the separator was measured in the same manner as in the case of the negative electrode, results similar to those in the case of the negative electrode were obtained.

As is clear from Table 1, the secondary batteries of Examples 1 to 5 in which the peel strength between the positive electrode and the separator and the peel strength between the negative electrode and the separator are greater than 10 gf / cm and 30 gf / cm or less have the peel strength described above. It can be understood that the capacity retention rate after 500 cycles is high as compared with the secondary batteries of Comparative Examples 1 to 3 outside the range.

From the results of Tables 2 to 4, it is also possible to use ethylene / acrylate copolymer resin (EEA), polystyrene / butadiene block copolymer or nylon (nylon 12 copolymer) instead of EVA as a resin to be added to the separator. It was confirmed that the capacity retention rate after 500 cycles could be improved by setting the peel strength between the positive electrode and the separator and the peel strength between the negative electrode and the separator to be greater than 10 gf / cm and 30 gf / cm or less.

From the results of Tables 5 to 8, in the secondary batteries of Examples 21 to 40 and Comparative Examples 10 to 18 in which the electrolytic solution was changed from the EC / GBL system to the EC / MEC system, the peel strength between the positive electrode and the separator and the negative electrode and the separator It was confirmed that the capacity retention rate after 500 cycles could be improved by setting the peel strength of the resin to greater than 10 gf / cm and not more than 30 gf / cm.

  As is clear from Table 9, even in the secondary batteries of Examples 41 to 44 and Comparative Example 19 in which a metal container was used instead of the laminate film container, the peel strength between the positive electrode and the separator and the peel strength between the negative electrode and the separator were It was confirmed that the capacity retention rate after 500 cycles could be improved by setting it to be larger than 10 gf / cm and not more than 30 gf / cm.

  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 which concerns on 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 partial notch perspective view which shows the square nonaqueous electrolyte secondary battery which is one Embodiment of the nonaqueous electrolyte secondary battery which concerns on this invention. The schematic diagram for demonstrating the measuring method of the peeling strength of the negative electrode and separator in the nonaqueous electrolyte secondary battery of Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Container main body, 2 ... Electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Separator, 6 ... Cover plate, 7 ... External protective layer, 8 ... Internal protective layer, 9 ... Metal layer, 10 ... Positive electrode terminal, 11 DESCRIPTION OF SYMBOLS ... Negative electrode terminal, 12 ... Bottomed cylindrical container, 13 ... Electrode group, 14 ... Positive electrode, 15 ... Separator, 16 ... Negative electrode, 17 ... Spacer,
18a ... liquid injection port, 18b ... sealing plate, 19 ... negative electrode terminal, 20 ... negative electrode tab.

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,
The separator have a surface containing a resin component composed of at least one kind selected ethylene-vinyl acetate copolymer resins, ethylene-acrylate copolymer resins, polystyrene-butadiene block copolymer and the group consisting of nylon,
The positive electrode, the separator, and the negative electrode are integrated in a state where the surface containing the resin component of the separator is in contact with the negative electrode,
A nonaqueous electrolyte secondary battery , wherein a peel strength between the positive electrode and the separator and a peel strength between the negative electrode and the separator are greater than 10 gf / cm and 30 gf / cm or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator further contains at least one of polyethylene and polypropylene.   3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the resin component in the separator is in the range of 0.1 to 10% by weight.

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