JP4238099B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

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

  Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are light weight, high voltage, high energy density, and high output, so the demand is increasing year by year, such as mobile phones and video cameras. Installed in the most advanced portable electronic devices. Recently, the performance of these electronic devices has been remarkably improved, and accordingly, the performance of the non-aqueous secondary batteries mounted on them has been demanded. Particularly, the demand for high capacity has rapidly increased. Yes.

  Currently, research and development for increasing the capacity of non-aqueous electrolyte secondary batteries is actively conducted, and as one of the means, stacked type positive and negative electrodes using different types of separators are stored in a bag shape. An example is proposed. (For example, refer to Patent Document 1). A multilayer separator using different types of separators having different melting points has been proposed. (For example, see Patent Documents 2 and 3).

Japanese Patent No. 3422284 (page 2-4, Fig. 1) Japanese Patent Laid-Open No. 5-13062 (page 2-4) JP 2002-25526 A (page 2-6)

  A separator that can prevent thermal runaway of a battery when the battery is abnormally heated may cause thermal runaway when the battery is overcharged. Also, a separator that does not cause thermal runaway when overcharged may not prevent thermal runaway of the battery when the battery is abnormally heated. An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can prevent both thermal runaway during abnormal heating and thermal runaway when a battery is overcharged, and has a high capacity and excellent safety.

In a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and two types of separators stacked and further wound to form a non-aqueous electrolyte, the non-aqueous electrolyte secondary battery includes: The first separator having an air permeability of 180 sec / 100 cm ³ or more is used on the outer peripheral side of the negative electrode, and the second separator having an air permeability of 120 sec / 100 cm ³ or less is used on the inner peripheral side of the negative electrode. This is a non-aqueous electrolyte secondary battery.

In the present invention, the first separator having an air permeability of 180 sec / 100 cm ³ or more is disposed on the outer peripheral side of the negative electrode where lithium ions concentrate during charging, and the air permeability is 120 sec / 100 cm ³ or less on the inner peripheral side. By disposing the second separator, no thermal runaway occurs when the battery falls into an overcharged state, and it can prevent thermal runaway of the battery even when heated abnormally. A secondary battery can be provided.

Embodiments of the present invention will be described below.
An embodiment of the present invention is a nonaqueous electrolyte secondary battery including an electrode winding body formed by laminating a positive electrode, a negative electrode, and two types of separators, and further wound, and a nonaqueous electrolytic solution. The electrode winding body uses a first separator having an air permeability of 180 sec / 100 cm ³ or more on the outer peripheral side of the negative electrode, and a second separator having an air permeability of 120 sec / 100 cm ³ or less on the inner peripheral side. It is characterized by being.
The air permeability was measured according to the air permeability test method of JIS P8117.

  Further, when the average thickness of the first separator and the second separator is large, the battery capacity is reduced and the internal resistance is also increased. Therefore, both are preferably 25 μm or less, more preferably 22 μm or less, and further preferably 20 μm or less. . In order to increase the battery capacity and improve the load characteristics, the thinner the separator, the better.However, in order to maintain good mechanical strength, electrolyte retention, short circuit prevention, etc., the average thickness is Both are preferably 8 μm or more.

The air permeability of the first separator is preferably 180 sec / 100 cm ³ or more. And is preferably 400 sec / 100 cm ³ or less, 300 sec / 100 cm ³ or less is more preferable. When the air permeability is too high, the lithium ion conductivity is lowered, so that the function as a battery separator is lowered. When the air permeability is too small, the mechanical strength is lowered. Moreover, since the function as a battery separator will fall when a porosity is too small, and mechanical strength will fall when too large, 60% or less is preferable and 55% or less is more preferable. On the other hand, 30% or more is preferable, and 35% or more is more preferable. If it is this range, a load characteristic can be improved, suppressing an internal short circuit.

Air permeability is preferably 120 sec / 100 cm ³ or less of the second separator, 100 sec / 100 cm ³ or less is more preferable. Moreover, 50 sec / 100 cm < ³ > or more is preferable and 80 sec / 100 cm < ³ > or more is more preferable.

  The porosity is preferably 60% or less, and more preferably 55% or less. On the other hand, 30% or more is preferable and 40% or more is more preferable. If it is this range, a load characteristic can be improved, suppressing an internal short circuit.

  As said 1st and 2nd separator, a nonwoven fabric and a microporous film can be used, for example. As a material of the nonwoven fabric, for example, polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate and the like can be used. As a material for the microporous film, for example, polypropylene, polyethylene, ethylene-propylene copolymer, and the like can be used. Further, the separator is preferably one having sufficient strength and capable of holding a large amount of electrolyte. In order to suppress thermal shrinkage, the separator may be heat-treated at a temperature of about 100 ° C. in advance.

  Moreover, this electrode winding body is formed in a cylindrical shape or a substantially long cylindrical shape, and the electrode winding body can be accommodated in an exterior body made of a metal can. Therefore, the shape of the battery may be either a cylindrical battery or a square battery. Further, there is no problem even in a rectangular battery having a part of R shape and a cylindrical battery having a flat part in part.

As the positive electrode active material used in the present embodiment, in particular but the type is not limited, lithium cobalt oxides of the open circuit voltage during charging and LiCoO ₂ showing a 4V or more based on Li, lithium-manganese oxides such as LiMnO ₂ Lithium-containing composite oxides such as lithium nickel oxides such as LiNiO ₂ , composite oxides having these as basic structures, for example, substitution products with different metal elements, or a mixture of two or more thereof, or Those solid solutions can be used. This can increase the energy density of the battery.

  Further, the positive electrode includes, for example, the positive electrode active material, and optionally includes a conductive auxiliary such as flaky graphite and carbon black, and further, a paste containing a binder is applied onto the positive electrode current collector and dried. It is produced through a step of forming a coating film containing at least a positive electrode active material and a binder on the positive electrode current collector. In preparing the paste containing the positive electrode active material, the binder is preferably used as a solution previously dissolved in a solvent, and the solution is mixed with solid particles such as the positive electrode active material.

  Any material can be used for the negative electrode as long as it can dope (occlude) and dedope (release) lithium ions. In the present invention, a material capable of doping and dedoping such lithium ions is used as the negative electrode. It is called an active material. The type of the negative electrode active material is not particularly limited. For example, graphite, pyrolytic carbons, cokes, glassy carbons, sintered organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, etc. Carbonaceous materials, aluminum, silicon, tin, indium, etc. and lithium alloys, or oxides such as silicon, tin, indium, etc. that can be charged and discharged at a low voltage close to lithium can be used.

  The negative electrode is prepared by applying a paste made of the above negative electrode active material, binder, etc. on the negative electrode current collector and drying, and forming a coating film containing at least the negative electrode active material and the binder on the negative electrode current collector. Is done.

When using a carbonaceous material as a negative electrode active material, what has the following characteristic is preferable. That is, the distance (d ₀₀₂ ) between the (002) planes of the crystal of the carbonaceous material is preferably 0.350 nm or less, more preferably 0.345 nm or less, and further preferably 0.340 nm or less. The crystallite size (Lc) in the c-axis direction is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. Furthermore, the average particle diameter of the carbonaceous material is preferably 10 μm to 30 μm, more preferably 15 μm to 25 μm, and the ratio of the pure carbon component to the whole carbonaceous material is preferably 99.9% by mass or more.

  As the binder used for the positive electrode and the negative electrode, a thermoplastic resin, a polymer having rubber elasticity, a polysaccharide, or the like can be used as one kind or a mixture of two or more kinds. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene propylene terpolymer, ethylene-propylene-diene copolymer, styrene butadiene rubber, polybutadiene, butyl rubber, fluoro rubber, polyethylene oxide, polyvinyl pyrrolidone, poly Epichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, cellulose resin such as carboxymethyl cellulose and hydroxypropyl cellulose, etc. It is done.

  In recent years, binders that use water as a solvent have a greater binding effect than organic solvent-based binders, and can be increased in capacity by increasing the active material ratio of the electrode. In particular, a combination of styrene-butadiene rubber and carboxymethyl cellulose is preferably used.

  As the positive electrode current collector and the negative electrode current collector, for example, a metal foil such as aluminum, copper, nickel, stainless steel, or titanium, an expanded metal, a net, or a foam metal can be used.

  As the positive electrode current collector, a foil mainly composed of aluminum is preferably used, and the purity of the aluminum is desirably 98% by mass or more and 99.9% by mass or less. The thickness of the positive electrode current collector is preferably in the range of 5 μm to 60 μm, and more preferably in the range of 8 μm to 40 μm. The thickness of the positive electrode coating film (positive electrode mixture layer) is preferably in the range of 30 μm to 300 μm, more preferably in the range of 50 μm to 150 μm, per side.

  In addition, a copper foil is generally used as the negative electrode current collector, and an electrolytic copper foil is preferably used among them. The thickness of the negative electrode current collector is preferably in the range of 5 μm to 60 μm, and more preferably in the range of 8 μm to 40 μm. The thickness of the negative electrode coating film (negative electrode mixture layer) is preferably in the range of 30 μm to 300 μm, more preferably in the range of 50 μm to 150 μm, per side.

  In the production of the positive electrode and the negative electrode, as the application method when applying the positive electrode active material-containing paste and the negative electrode active material-containing paste to the current collector, for example, various application methods using an extrusion coater, a reverse roller, a doctor blade, etc. Can be adopted.

  In the non-aqueous electrolyte secondary battery of this embodiment, a liquid electrolyte (hereinafter referred to as “electrolytic solution”) can be used. Specifically, an organic solvent-based nonaqueous electrolytic solution in which a solute is dissolved in an organic solvent is used. The type of the organic solvent is not particularly limited, but it is particularly preferable to use a chain ester as the main solvent. Examples of such chain esters include organic compounds having a COO-bond such as diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl acetate (EA), and methyl propionate (MP). A solvent is mentioned. The fact that this chain ester is the main solvent of the electrolytic solution means that these chain esters occupy more than 50% by volume in the total electrolyte solution, and the chain ester is the total electrolyte solution. It is preferable to occupy 65% by volume or more in the solvent, more preferably 70% by volume or more, and still more preferably 75% by volume or more.

  However, as the solvent of the electrolytic solution, it is preferable to mix and use an ester having a high dielectric constant, for example, an ester having a dielectric constant of 30 or more, in order to improve battery capacity, rather than using only the above-mentioned chain ester. The amount of such a high dielectric constant ester in the total electrolyte solvent is preferably 10% by volume or more, and more preferably 20% by volume or more.

Examples of the ester having a high dielectric constant include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (γ-BL), ethylene glycol sulfite (EGS), and the like. Those having a cyclic structure such as ethylene carbonate and propylene carbonate are preferred, cyclic carbonates are particularly preferred, and ethylene carbonate (EC) is most preferred.

  Examples of the solvent that can be used in addition to the ester having a high dielectric constant include 1,2-dimethoxyethane (1,2-DME), 1,3-dioxolane (1,3-DO), and tetrahydrofuran (THF). , 2-methyl-tetrahydrofuran (2-Me-THF), diethyl ether (DEE) and the like. In addition, amine-based or imide-based organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used.

The solute of the electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 Co 2, Li 2 C 2 F 4 (SO 3 ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCnF _{2n + 1} SO ₃ (n ≧ 2) or the like may be used alone or in combination. In particular, LiPF ₆ and LiC ₄ F ₉ SO ₃ are preferable because of good charge / discharge characteristics. The concentration of the solute in the electrolytic solution is not particularly ^{limited, 0.3mol / dm 3 ~1.7mol / dm} 3, in particular 0.4mol / dm ³ ~1.5mol / dm about ³ are preferred.

  In the present embodiment, a solid or gel electrolyte can be used in addition to the electrolytic solution. Examples of such an electrolyte include inorganic solid electrolytes and organic solid electrolytes mainly composed of polyethylene oxide, polypropylene oxide, or derivatives thereof.

In this embodiment, the negative electrode lead is welded to the exposed portion of the negative electrode current collector by resistance welding, ultrasonic welding, or the like, and the cross-sectional area of this negative electrode lead is the resistance when a large current flows. In order to reduce the calorific value, it is preferably 0.1 mm ² or more and 1.0 mm ² or less, more preferably 0.30 mm ² or more and 0.70 mm ² or less. Nickel is generally used as the negative electrode lead material, and copper, titanium, stainless steel, etc. can be used, but at least copper or a copper alloy is used to increase the adhesive strength with the copper foil as the negative electrode current collector. It is desirable to use a metal material that is included as an element. Specifically, for example, a copper alloy such as copper or a copper-nickel alloy, a composite material of copper or a copper alloy and another metal such as nickel or titanium, and the like, for example, a two-layer structure of copper and nickel The clad material is inexpensive and can be suitably used.

  Further, as the positive electrode lead, a metal made of a metal having low electric resistance and capable of withstanding a high potential, such as aluminum, is preferably used.

  The positive and negative electrode leads are preferably attached by methods such as spot welding and ultrasonic welding. In particular, it is desirable to attach the negative electrode lead by ultrasonic welding. In spot welding, if the applied current is increased to increase the adhesive strength, the copper foil tends to have holes, the adhesive strength is reduced, or the weld is likely to be oxidized, which may increase the impedance. Because there is.

  Next, an embodiment when the present invention is used for a square battery will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the nonaqueous electrolyte secondary battery of the present embodiment. FIG. 2 is an enlarged view of a portion A in FIG. FIG. 1 is for explaining the positions where the positive electrode lead 1c and the negative electrode lead 2c are arranged. In the actual electrode winding body 4, as shown in FIG. In addition, the first and second separators 3a and 3b exist, but in FIG. 1, the separator is not shown and is simplified to avoid complication.

  1 and 2, the nonaqueous electrolyte secondary battery of the present embodiment includes a positive electrode 1, a negative electrode 2, a first separator 3a, and a second separator 3b, and the first separator 3a. The second separator 3b is impregnated with an electrolytic solution. The positive electrode 1, the first separator 3 a, the negative electrode 2, and the second separator 3 b are stacked and wound in this order to form the electrode winding body 4.

  The positive electrode 1 is formed by applying a positive electrode mixture layer 1b to both surfaces of a positive electrode current collector 1a. However, the positive electrode 1 located on the outermost surface of the electrode winding body 4 forms the positive electrode mixture layer 1b only on the inner surface of the positive electrode current collector 1a, and the outer surface of the positive electrode current collector 1a is exposed. The exposed positive electrode current collector 1 a is in electrical contact with the inner surface of the exterior body 5. Further, in the vicinity of the end portion of the positive electrode 1 located on the outermost surface of the electrode winding body 4, the positive electrode mixture layer 1 b is not formed on both surfaces of the positive electrode current collector 1 a, and the positive electrode 1 is formed in the vicinity of the end portion of the positive electrode 1. A lead 1c is attached.

  The negative electrode 2 is formed by applying a negative electrode mixture layer 2b on both surfaces of a negative electrode current collector 2a. However, the negative electrode 2 located on the innermost surface of the electrode winding body 4 forms the negative electrode mixture layer 2b only on the inner surface of the negative electrode current collector 2a, and the outer surface of the negative electrode current collector 2a is exposed. Further, in the vicinity of the end of the negative electrode 2 located on the innermost surface of the electrode winding body 4, the negative electrode mixture layer 2 b is not formed on both surfaces of the negative electrode current collector 2 a, and the negative electrode near the end of the negative electrode 2 A lead 2c is attached.

Hereinafter, based on an Example, this invention is demonstrated more concretely. However, the present invention is not limited only to the following examples.
A non-aqueous electrolyte secondary battery having the same structure as that shown in FIGS. 1 and 2 was produced as follows.

  92 parts by mass of lithium cobaltate, 3 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride were mixed with a planetary mixer using N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture-containing paint. The obtained positive electrode mixture-containing paint is intermittently applied onto a current collector made of an aluminum foil having a thickness of 20 μm by a blade coater, dried, subjected to a pressing step, cut into a predetermined size, and a sheet-like positive electrode Got. In addition, an aluminum lead was attached to the positive electrode by ultrasonic welding.

Next, as an anode, high-density artificial graphite (d ₀₀₂ : 0.336 nm, Lc: 100 nm) 97.5 parts by mass, carboxymethylcellulose aqueous solution (concentration 1% by mass, viscosity 1500 mPa · s to 5000 mPa · s) 1.5 mass A 1 part by weight of styrene-butadiene rubber was mixed with a planetary mixer using ion-exchanged water having a specific conductivity of 2.0 × 10 ⁵ Ω / cm or more as a solvent to prepare a water-based negative electrode mixture-containing paint. The obtained water-based negative electrode mixture-containing paint was intermittently applied onto a 15 μm thick copper foil with a blade coater, dried, subjected to a pressing step, and then cut into a predetermined size to obtain a sheet-like negative electrode. Further, a lead made of a clad material of copper and nickel was attached to the negative electrode by ultrasonic welding.

Next, a polyethylene microporous membrane separator having an average thickness of 20 μm, an air permeability of 180 sec / 100 cm ³ and a porosity of 40% as a first separator, and an average thickness of 22 μm and an air permeability of 80 sec / second as a second separator. A polyethylene microporous membrane separator having 100 cm ³ and a porosity of 50% was prepared. Further, the positive electrode, the first separator, the negative electrode, and the second separator are laminated in this order, the first separator is located on the outer peripheral side of the negative electrode, and the inner peripheral side of the negative electrode is It wound so that the 2nd separator might be located, and produced the substantially long cylindrical electrode winding object.

As the non-aqueous electrolyte, a liquid non-aqueous electrolyte was prepared by dissolving LiPF _{6 in} a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 2 to a concentration of 1 mol / dm ³ .

  Then, the electrode winding body is inserted into an exterior body made of a rectangular aluminum can, the end of the positive electrode lead is welded to the lid portion, the end of the negative electrode lead is welded to the output terminal of the negative electrode, and the nonaqueous electrolyte is removed. After the injection, the outer package was sealed to produce an 800 mAh non-aqueous electrolyte secondary battery. In this non-aqueous electrolyte secondary battery, the inner surface of the outer package and the current collector made of the aluminum foil on the outermost surface of the positive electrode are brought into electrical contact by direct contact.

A polyethylene microporous membrane separator having an average thickness of 20 μm, an air permeability of 180 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 20 μm and an air permeability of 120 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 300 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 22 μm and an air permeability of 80 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 300 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 20 μm and an air permeability of 120 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 400 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 22 μm and an air permeability of 80 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 400 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 20 μm and an air permeability of 120 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.
(Comparative Example 1)

The same procedure as in Example 1 was used except that a polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 80 sec / 100 cm ³ , and a porosity of 50% was used as the first separator and the second separator. A non-aqueous electrolyte secondary battery was produced.
(Comparative Example 2)

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 80 sec / 100 cm ³ and a porosity of 50% is used for the first separator, and an average thickness of 20 μm and an air permeability of 120 sec / A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 50% was used.
(Comparative Example 3)

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 80 sec / 100 cm ³ and a porosity of 50% is used for the first separator, and an average thickness of 20 μm and an air permeability of 180 sec / A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 40% was used.
(Comparative Example 4)

Example 1 was used except that a polyethylene microporous membrane separator having an average thickness of 20 μm, an air permeability of 180 sec / 100 cm ³ , and a porosity of 40% was used as the first separator and the second separator. A non-aqueous electrolyte secondary battery was produced.
(Comparative Example 5)

A polyethylene microporous membrane separator having an average thickness of 22 μm, an air permeability of 400 sec / 100 cm ³ and a porosity of 40% is used for the first separator, and an average thickness of 20 μm and an air permeability of 180 sec / A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1 except that a polyethylene microporous membrane separator having a porosity of 100 cm ³ and a porosity of 40% was used.

  Using the batteries of Examples 1 to 6 and Comparative Examples 1 to 5, the battery was charged to 4.2 V at 1 C (800 mA), then charged at 4.2 V for 3 hours, and discharged to 3 V at 0.2 C. The discharge capacity was measured. Further, 10 batteries of each of Examples 1 to 6 and Comparative Examples 1 to 5 were charged to 12 V at 1 C, and the number of batteries whose battery temperature became 135 ° C. or higher due to thermal runaway was examined. The results are shown in Table 1. In Table 1, the number n of batteries having a temperature of 135 ° C. or higher and the total number (10) of test batteries are shown in the form of n / 10.

  Similarly, using the batteries of Examples 1 to 6 and Comparative Examples 1 to 5, the battery was charged to 4.2 V at 1 C (800 mA), then constant voltage charging was performed at 4.2 V for 3 hours, and 3 V at 0.2 C. The discharge capacity was measured and 10 batteries of Examples 1 to 6 and Comparative Examples 1 to 5 were charged to 4.25V at 1C and then charged at 4.25V for 3 hours. It was installed in an oven, heated from room temperature to 150 ° C. at a rate of 5 ° C./min, and then held at 150 ° C. for 3 hours. At that time, the number of batteries whose thermal runaway caused the battery surface temperature to rise to 200 ° C. or higher was examined. The results are shown in Table 1. In Table 1, the number n of batteries having reached 200 ° C. or higher and the total number (10) of test batteries are shown in the form of n / 10.

  As can be seen from Table 1, the batteries of Examples 1 to 6 did not show thermal runaway during 1C12V charging and storage in a 150 ° C. oven. On the other hand, in the batteries of Comparative Examples 1 and 2, when the battery was stored in an oven at 150 ° C., the occurrence of thermal runaway with a battery surface temperature of 200 ° C. or higher was not observed. There was something more than that. The battery of Comparative Example 3 showed thermal runaway in both 1C, 12V charging and storage in an oven at 150 ° C. Further, the batteries of Comparative Examples 4 and 5 did not run out of heat in 1C12V charge, and the battery temperature was 135 ° C. or lower. However, the battery temperature was 200 ° C. or higher due to thermal runaway when stored in a 150 ° C. oven. .

  In the above-described embodiment, the present invention has been described using a square battery, but the same effect can be achieved by using a cylindrical battery.

It is sectional drawing which shows typically the nonaqueous electrolyte secondary battery in embodiment of this invention. It is an enlarged view of the A section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 1b Positive electrode mixture layer 1c Positive electrode lead 2 Negative electrode 2a Negative electrode collector 2b Negative electrode mixture layer 2c Negative electrode lead 3a First separator 3b Second separator 4 Electrode winding body 5 Exterior body

Claims (4)

In a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and two types of separators stacked and further wound to form a non-aqueous electrolyte secondary battery, the electrode roll includes: The first separator having an air permeability of 180 sec / 100 cm ³ or more is used on the outer peripheral side of the negative electrode, and the second separator having an air permeability of 120 sec / 100 cm ³ or less is used on the inner peripheral side. Non-aqueous electrolyte secondary battery.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first separator and the second separator each have an average thickness of 25 μm or less.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the porosity of each of the first separator and the second separator is 60% or less.   The electrode winding body is formed in a cylindrical shape or a substantially long cylindrical shape, and the electrode winding body is housed in an exterior body made of a metal can. Water electrolyte secondary battery.

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