JP2014225327A - Nonaqueous electrolyte solar batter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery exhibiting excellent safety, in which undue battery temperature rise can be suppressed even if internal short circuit occurs due to a large foreign matter, e.g., a nail, without compromising with high energy density.SOLUTION: A positive electrode includes a positive electrode collector, and a positive electrode mixture layer formed on the surface thereof. A negative electrode includes a negative electrode collector, and a negative electrode mixture layer formed on the surface thereof. The first layer contains a carbon material, and the second layer contains an inorganic oxide which can occlude and release lithium ions. The ratio of the thickness of the first layer Tand the thickness of the second layer Tis 4-50. In the outer periphery of the electrode group, the positive electrode collector exposed part and the negative electrode collector exposed part face each other over at least one round.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having a preferred electrode plate structure.

  In recent years, there has been a demand for higher energy density for secondary batteries used in electronic devices such as mobile phones and laptop computers and in-vehicle power supplies. From this viewpoint, non-aqueous electrolyte secondary batteries that can increase energy density are widely used. It is popular. The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a non-aqueous electrolyte. Many of the positive electrode, the negative electrode, and the separator are wound to form an electrode group.

  In general, when a short circuit having a relatively low resistance value occurs inside the battery, a large current flows in a concentrated manner at the short circuit point, so that the heat generation of the battery may accelerate and lead to overheating. In order to avoid such a phenomenon in a lithium ion battery having a high energy density, various safety measures are taken from the viewpoint of the battery configuration in addition to the viewpoint of manufacturing.

  In general, a separator having a shutdown function for blocking pores and blocking ionic current due to heat generated when a battery causes an internal short circuit is used. The short-circuit current stops flowing due to the shutdown function, and the heat generation stops. However, when the heat generation in the short-circuited portion is large, the separator is melted before the shutdown functions, thereby causing a melt-down that opens a large hole in the separator. When the positive electrode and the negative electrode are short-circuited due to meltdown, further overheating is caused. In some cases, the battery ignites or smokes, which is very dangerous.

  Therefore, a technique for forming a porous film made of an inorganic oxide filler such as alumina and a water-soluble polymer on an active material layer has been proposed (see Patent Document 1). If the technique of patent document 1 is used, it is thought that the capability to maintain the insulation between positive and negative electrodes is high also in an overheating environment.

  Furthermore, a technique for forming a surface layer made of a lithium titanium composite oxide capable of inserting and extracting lithium on the main negative electrode layer has been proposed (see Patent Document 2).

JP-A-9-147916 JP 2010-97720 A

  However, in the technique of Patent Document 1, since an insulating layer is present on the active material layer, large current charge / discharge characteristics are deteriorated. In particular, when an insulating layer is formed on the negative electrode active material, lithium ion acceptability deteriorates. Battery characteristics deteriorate. On the other hand, in the technique of Patent Document 2, the lithium-titanium composite oxide in the vicinity of the short-circuit point is insulated by discharge to improve safety. Even when the negative electrode having such a configuration is used, a nail or the like is used. In the case of an internal short circuit due to a large foreign substance, the expansion of the short circuit point due to the shrinkage of the separator may proceed before the insulation proceeds sufficiently, leading to overheating. To prevent this, a surface layer with excellent thermal stability Needs to be sufficiently thicker than the main negative electrode layer, and the energy density is lowered. In addition, if the surface layer is too thick, the flexibility of the negative electrode is reduced, and the binder in the main negative electrode layer is likely to migrate in the surface direction, so the binding between the main negative electrode layer and the current collector interface Becomes insufficient, and the active material layer falls off.

In order to solve the conventional problems, the nonaqueous electrolyte secondary battery of the present invention has an electrode group in which a positive electrode and a negative electrode are wound through a separator, and the positive electrode is a positive electrode current collector. And a negative electrode current collector, a first layer formed on the surface of the negative electrode current collector, and the first layer on the first layer. The first layer includes a carbon material, the second layer includes an inorganic solid oxide capable of occluding and releasing lithium ions, and the thickness of the first layer is T _1. and then, when the thickness of the second layer and _{T 2,} the ratio of _{T 1} and _{T 2 (T 1 / T 2} ) is 4 or more and 50 or less, and the positive electrode current collector at the outer periphery of the electrode group That is, the exposed portion and the negative electrode current collector exposed portion face each other over at least one turn.

  As a result of intensive studies by the inventors, when a large current is discharged between current collectors during a short circuit, a potential gradient is generated due to the contribution of liquid resistance in the negative electrode active material layer, so that the discharge reaction easily proceeds from the surface layer side. It was revealed that the current was not substantially discharged from the active material on the current collector side for a second. Therefore, when a current collector short-circuit is provided on the outer periphery of the electrode group, lithium ions are released only on the surface layer side. Therefore, resistance is increased by lithium ion release, represented by lithium titanate on the surface layer side, and insulation is achieved when fully discharged. By disposing a layer containing an inorganic solid oxide exhibiting properties as the second layer, the active material layer can be quickly increased in resistance.

Further, the ratio T ₁ / T ₂ between the thickness T ₁ of the first layer and the thickness T ₂ of the second layer needs to be 4 or more and 50 or less. When T ₁ / T ₂ is less than 4, a battery having a high energy density cannot be obtained, and the binding property between the first layer and the current collector interface tends to be insufficient, and when T ₁ / T ₂ is greater than 50, Insulation at short circuit cannot be obtained. It is preferable that the thickness _{T 2} of the second layer is 1.5μm or more 10μm or less. If T ₁ is smaller than 1.5 μm, the insulating property at the time of short circuit may be impaired, and if T ₁ is larger than 10 μm, it is not preferable in terms of energy density.

  As a result, it is possible to obtain a battery having a high energy density while ensuring sufficient safety against an internal short circuit caused by a large foreign object such as a nail.

  According to the present invention, a nonaqueous electrolyte secondary battery excellent in safety that can suppress an excessive increase in battery temperature even when an internal short circuit occurs due to a large foreign matter such as a nail without impairing a high energy density. Can be obtained.

Sectional drawing of the positive electrode and negative electrode for lithium ion batteries which concern on one Embodiment of this invention 1 is a longitudinal sectional view schematically showing a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

In FIG. 1, the longitudinal cross-sectional conceptual diagram of the negative electrode 6 for nonaqueous electrolyte secondary batteries which concerns on one Embodiment of this invention is shown. The negative electrode 6 includes a first layer 12 formed on the surface of the negative electrode current collector 11 and a second layer 13 laminated on the first layer 12. The first layer 12 includes a carbon material, and the second layer 13 include inorganic solid oxide particles on the thickness of the first layer 12 and _{T 1,} when the thickness of the second layer 13 and _{T 2,} the ratio _T 1 / _{T 2} between _{T 1} and _{T 2,} 4 or more 50 or less. Further, in the negative electrode 6, the negative electrode current collector exposed portion 16 in which neither the first layer 12 nor the second layer 13 is formed on the side that becomes the outer peripheral portion of the electrode group when wound is a length corresponding to one or more rounds of the electrode group. It exists.

  The location and number of the negative electrode lead 6a are not particularly limited as long as the current collector is exposed on both surfaces, but one electrode lead 6a is connected to the outer peripheral portion of the negative electrode 6 in FIG.

  Examples of the carbon material included in the first layer 12 as an active material include carbon materials such as various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, and amorphous carbon. The first layer 12 contains a simple substance such as silicon (Si) or tin (Sn), a silicon compound (for example, a silicon alloy, a solid solution containing silicon) or a tin compound (for example, a tin alloy or a solid solution containing tin). You may go out. The first layer 12 preferably contains a binder. The first layer 12 may include a conductive material.

The active material included in the second layer 13 can be appropriately selected by those skilled in the art from inorganic solid oxides that can occlude and release lithium ions and exhibit insulating properties when released. The content of the inorganic solid oxide contained in the second layer 13 is, for example, 80% by weight or more. The inorganic solid oxide contained in the second layer 13 is particularly preferably lithium titanate having a spinel crystal structure because of reversibility of charge and discharge. Lithium titanate has high acceptability of lithium ions, and it is easy to reduce the diffusion resistance of the electrode. Furthermore, lithium titanate has higher thermal stability than carbon materials. Lithium titanate having a typical spinel crystal structure is represented by the formula: Li ₄ Ti ₅ O ₁₂ . However, the general _{formula: Li x Ti 5-y M} y O 12 + lithium titanate represented by _z may be used as well. Here, M is composed of vanadium, manganese, iron, cobalt, nickel, copper, zinc, aluminum, boron, magnesium, calcium, strontium, barium, zirconium, niobium, molybdenum, tungsten, bismuth, sodium, gallium, and rare earth elements. At least one selected from the group, x is the value of lithium titanate immediately after synthesis or in a fully discharged state, 3 ≦ x ≦ 5, 0.005 ≦ y ≦ 1.5, − 1 ≦ z ≦ 1.

  The average particle size of lithium titanate (median diameter in the volume-based particle size distribution: D50) is preferably 0.8 to 30 μm, and more preferably 1 to 20 μm. When the average particle size is included in the above range, the lithium ion acceptability tends to be particularly high. The volume-based particle size distribution of lithium titanate can be measured by, for example, a commercially available laser diffraction particle size distribution measuring apparatus.

BET specific surface area of the lithium titanate is preferably 0.5 to 10 m ² / g, more preferably 2.5~4.5m ² / g. When the specific surface area is within the above range, good lithium ion acceptability is exhibited, and excellent I / O characteristics can be easily obtained even in a low temperature environment.

  The second layer 13 may include a carbon material of 20 parts by weight or less, for example, 1 to 10 parts by weight per 100 parts by weight of the inorganic solid oxide. As the carbon material to be included in the second layer 13, for example, graphite particles, carbon black, and carbon fibers or carbon nanotubes can be used. By including an appropriate amount of the carbon material in the second layer 13, appropriate conductivity can be imparted to the second layer 13.

  The first layer 12 may include 0.5 to 10 parts by weight of a binder per 100 parts by weight of the active material. Similarly, the second layer 13 can include 0.5 to 10 parts by weight of the binder per 100 parts by weight of the inorganic solid oxide. The binder used for the first layer 12 and the second layer 13 may be the same or different. Examples of such a binder include acrylic resin, fluororesin, and diene rubber. Examples of the acrylic resin include polyacrylic acid, polymethacrylic acid, sodium salt of polyacrylic acid, sodium salt of polymethacrylic acid, and acrylic acid-ethylene copolymer. Examples of the fluororesin include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer. As the diene rubber, a styrene-butadiene copolymer (SBR) is preferable.

The first layer 12 may include 0.1 to 5 parts by weight of a thickener per 100 parts by weight of the active material. Similarly, the 2nd layer 13 can contain 0.1-5 weight part thickener per 100 weight part of inorganic solid oxides. The thickeners used for the first layer 12 and the second layer 13 may be the same or different. Such a thickener is preferably a water-soluble polymer such as polyethylene oxide or a cellulose derivative. Cellulose derivatives include, for example, carboxymethylcellulose (CMC), methylcellulose (MC) and cellulose acetate phthalate (CAP).

  Although the lamination | stacking method of the 1st layer 12 and the 2nd layer 13 is not specifically limited, For example, after forming the 1st layer 12 by application | coating and drying, it may laminate | stack on the 1st layer 12 surface, and may be applied and dried. Alternatively, the coating material of the first layer 12 and the coating material of the second layer 13 may be applied simultaneously using a die coater having two or more discharge slits, and then dried.

The ratio _T 1 / _{T 2} of the the thickness _{T 1} of the first layer 12 and the thickness _{T 2} of the second layer 13 is required to be 4 or more and 50 or less. If T ₁ / T ₂ is less than 4, a high energy density battery cannot be obtained, and if T ₁ / T ₂ is greater than 50, insulation at short circuit cannot be obtained. It is preferable that the thickness _{T 2} of the second layer 13 is 1μm or more 10μm or less. If T ₁ is smaller than 1.5 μm, the insulating property at the time of short circuit may be impaired, and if T ₁ is larger than 10 μm, it is not preferable in terms of energy density.

  The negative electrode current collector 11 is preferably a copper foil, a copper alloy foil or a nickel foil. The thickness of the current collector is preferably 5 to 30 μm and more preferably 5 to 15 μm from the viewpoint of productivity and energy density.

  In FIG. 1, the longitudinal cross-sectional conceptual diagram of the positive electrode 5 for nonaqueous electrolyte secondary batteries which concerns on one Embodiment of this invention is shown. The positive electrode 5 includes a positive electrode current collector and a positive electrode mixture layer 14 supported on the positive electrode current collector. Further, the positive electrode current collector exposed portion 15 in which the positive electrode mixture layer 14 is not formed on the side that becomes the outer peripheral portion of the electrode group 9 during winding has a length corresponding to one or more rounds of the electrode group 9. Existing.

  Further, as shown in FIG. 1, it is preferable that the positive electrode current collector exposed portion 15 is also present in the central portion in the longitudinal direction of the positive electrode mixture layer 14 with a length of one or more rounds of the electrode group 9. Here, when the distance between the inner peripheral side end portion and the outer peripheral side end portion of the positive electrode 5 is L, the distance from the inner peripheral side end portion and the outer peripheral side end portion is 2/3 L or less, respectively. It is a range. Compared with the inner and outer peripheral portions of the positive electrode 5 in the longitudinal direction, the central portion has a small contribution to the resistance of the current collector, so that a large current flows easily, and the current collector exposed portion also exists in the central portion. Insulation of the second layer 13 of the negative electrode proceeds more effectively at the time of a short circuit through the conductive foreign matter. The current collector exposed portion at the center of the positive electrode mixture layer 14 may be one side or both sides, but in the case of one side, it is preferably provided on the surface facing the battery case 1 instead of the surface facing the winding center of the electrode group 9. The negative electrode surface facing the current collector exposed portion in the center of the positive electrode mixture layer 14 is not necessarily exposed to the negative electrode current collector 11, but the exposed one is more reliable because a large current flows. preferable.

  The location and number of the positive electrode lead 5a are not particularly limited as long as the current collector is exposed on both surfaces, but one positive electrode lead 5a is connected to the central portion of the positive electrode 5 in FIG.

The positive electrode mixture layer 14 may contain a binder and a conductive agent in addition to the positive electrode active material. A lithium composite metal oxide can be used as the positive electrode active material. Examples of the lithium composite metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O _z , and Li _x Ni _{1. -y M y O z, Li x} Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B). Here, 0 <x ≦ 1.2, 0 <y ≦ 0.9, 2.0 ≦ z ≦ 2.
3. In addition, x value which shows the molar ratio of lithium is a value immediately after active material preparation, and increases / decreases by charging / discharging. In addition, the positive electrode active material may be one in which a part of the metal element in the lithium composite metal oxide is replaced with a different element. Furthermore, the positive electrode active material may be one in which the lithium composite metal oxide is surface-treated with a metal oxide, lithium oxide, or a conductive agent, or the surface of the lithium composite metal oxide is hydrophobized. It may be what was done.

The electrolyte layer having lithium ion conductivity includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The electrolyte layer may include a polyolefin microporous film as a separator. In this case, a nonaqueous solvent in which a lithium salt is dissolved is impregnated in the pores of the microporous film. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). It is not limited to. These may be used alone or in combination of two or more. Examples of the lithium salt include LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiCl, and lithium imide salt. These may be used alone or in combination of two or more.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, an Example does not limit the scope of the present invention.

<Example 1>
(I) Production of negative electrode (first layer)
3 kg of artificial graphite (average particle size 10 μm, BET specific surface area 3 m ² / g), 75 g of BM-400B (dispersion of modified styrene-butadiene rubber having a solid content of 40% by weight) manufactured by Nippon Zeon Co., Ltd., and carboxymethylcellulose 30 g of (CMC) was stirred together with an appropriate amount of water in a double arm kneader to prepare a first negative electrode mixture slurry containing graphite.

The first negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector 11 made of a copper foil having a thickness of 10 μm, dried, and rolled to a total thickness of 140 μm, whereby the first layer 12 was formed. That is, the thickness (T ₁ ) of the first layer 12 was 65 μm per one side of the copper foil, and the density of the first layer 12 was 1.5 g / cm ³ .

(Second layer)
2 kg of lithium titanate having a spinel crystal structure (Li ₄ Ti ₅ O ₁₂ , average particle size 1 μm, BET specific surface area 3 m ² / g), artificial graphite (average particle size 10 μm) 50 g, manufactured by Nippon Zeon Co., Ltd. BM-400B (modified styrene-butadiene rubber dispersion having a solid content of 40% by weight) and 50 g of carboxymethylcellulose (CMC) were stirred together with an appropriate amount of water in a double-arm kneader, and titanic acid. A second negative electrode mixture slurry containing lithium was prepared. The 2nd negative electrode mixture slurry was apply | coated to the surface of the 1st layer provided in both surfaces of copper foil, respectively, it dried and rolled so that total thickness might be 160 micrometers, and the 2nd layer 13 was formed. That is, the thickness (T ₂ ) of the second layer 13 was 10 μm per one side of the copper foil, and the density of the second layer 13 was 2 g / cm ³ .

The obtained electrode plate was cut into a width of 58 mm and a length of 805 mm, a double-sided current collector exposed portion having a length of 70 mm was provided on the outer peripheral portion, and a lead was welded to the outer peripheral portion to obtain a negative electrode. This negative electrode satisfies T ₁ / T ₂ = 6.5.

(Ii) Production of Positive Electrode 5 3 kg of lithium cobaltate (LiCoO ₂ , average particle size 10 μm), N-methyl-pyrrolidone (hereinafter referred to as NMP (N-methylpyrrolidone)) solution (trade name: PVDF # 1320) containing 12% by weight of PVDF 1 kg, manufactured by Kureha Co., Ltd.), 90 g of acetylene black and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and rolled to a total thickness of 120 μm to form a positive electrode active material layer.

  The obtained electrode plate was cut into a width of 56 mm and a length of 750 mm, a double-sided current collector exposed portion having a length of 57 mm was provided on the outer peripheral portion, and a lead was welded to the center portion to obtain the positive electrode 5.

(Nonaqueous electrolyte)
LiPF ₆ was dissolved at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1: 1. A non-aqueous electrolyte was obtained by adding 3% by weight of vinylene carbonate.

(Battery assembly)
A cylindrical battery as shown in FIG. 2 was produced.

  The positive electrode 5, the negative electrode 6, and the separator 7 were wound with the separator 7 (single layer of polyethylene resin having a thickness of 20 μm) interposed between the positive electrode 5 and the negative electrode 6 manufactured according to the above method. Thereby, the electrode group 9 was produced. After the upper insulating plate 8a and the lower insulating plate 8b were disposed at both ends of the electrode group 9 in the longitudinal direction, the electrode group 9 was housed in a bottomed cylindrical battery case 1 (diameter 18 mm, height 65 mm, inner diameter 17.85 mm). The other end of the positive electrode lead 5 a made of aluminum was connected to the lower surface of the positive electrode terminal, and the other end of the negative electrode lead 6 a made of nickel was connected to the inner bottom surface of the battery case 1. Thereafter, 5.5 g of the non-aqueous electrolyte described above was injected into the battery case 1. A sealing plate 2 that supports the positive electrode terminal was caulked to the opening of the battery case 1 through the gasket 3. Thereby, the battery case 1 was sealed. In this way, a cylindrical non-aqueous electrolyte secondary battery having a design capacity of 2150 mAh was produced. This battery is referred to as the battery of Example 1.

<Example 2>
The thickness T ₂ of the first layer 12 of thickness T ₁ and the second layer 13, except that was 70μm and 2μm, respectively, similarly creates a negative electrode as in Example 1, further manufactured cylindrical nonaqueous electrolyte secondary battery did.

<Example 3>
The thickness T ₂ of the first layer 12 of thickness T ₁ and the second layer 13, except that was 69μm and 5μm respectively, similarly creates a negative electrode as in Example 1, further manufactured cylindrical nonaqueous electrolyte secondary battery did.

<Example 4>
The thickness T ₂ of the first layer 12 of thickness T ₁ and the second layer 13, except that was 67μm and 8μm respectively, similarly creates a negative electrode as in Example 1, further manufactured cylindrical nonaqueous electrolyte secondary battery did.

<Example 5>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 63μm and 15 [mu] m, the length of the negative electrode 6 795Mm, except that the length of 740mm of the positive electrode 5, in the same manner as in Example 1 A cylindrical nonaqueous electrolyte secondary battery was produced.

<Example 6>
The thickness T ₂ of the first layer 12 of thickness T ₁ and the second layer 13, except that was 70μm and 1.5μm, respectively, similarly creates a negative electrode as in Example 1, further cylindrical nonaqueous electrolyte secondary battery Was made.

<Example 7>
A collector exposed portion having a length of 41 mm was provided on the surface facing the battery case 1 when the positive electrode mixture layer 14 was rolled, and a collector exposed portion was also provided on the negative electrode surface facing the exposed portion. Except for the above, a cylindrical nonaqueous electrolyte secondary battery was further produced in the same manner as in Example 6.

<Example 8>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 40μm and 10 [mu] m, the length of the negative electrode 6 1010 mm, except that the thickness of the positive electrode 5 and a length of 950mm of the positive electrode 5 and 90 [mu] m, A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 9>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 48μm and 5 [mu] m, the length of the negative electrode 6 1025Mm, except that the length of 965mm of the positive electrode 5, in the same manner as in Example 8 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Example 10>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 50μm and 1 [mu] m, the length of the negative electrode 6 1040 mm, except that the length of 980mm of the positive electrode 5, in the same manner as in Example 8 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Example 11>
The thickness _{T 2} of the thickness _{T 1} and the second layer 13 of the first layer 12, respectively and 83μm and 20 [mu] m, the length of the negative electrode 6 650 mm, a thickness of the positive electrode 5 and 155μm except that the length 590mm of the positive electrode 5, A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

<Example 12>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 90μm and 10 [mu] m, the length of the negative electrode 6 660 mm, except that the length of 600mm of the positive electrode 5, in the same manner as in Example 11 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Example 13>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 95μm and 2 [mu] m, the length of the negative electrode 6 670 mm, except that the length of 610mm of the positive electrode 5, in the same manner as in Example 11 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Comparative Example 1>
The thickness T ₂ of the first layer 12 of thickness T ₁ and the second layer 13, except that was 70μm and 1μm, respectively, similarly creates a negative electrode as in Example 1, further manufactured cylindrical nonaqueous electrolyte secondary battery did.

<Comparative example 2>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, and 60m and 20μm, respectively, the length of the negative electrode 6 785 mm, except that the length of 730mm of the positive electrode 5, in the same manner as in Example 1 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Comparative Example 3>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 54m and 30 [mu] m, the negative electrode length 770 mm, except that the length of 715mm of the positive electrode 5, in the same manner as in Example 1 Cylindrical Type non-aqueous electrolyte secondary battery was produced.

<Comparative example 4>
A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the second layer 13 was not formed.

<Comparative Example 5>
A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the length of the positive electrode 5 was 693 mm and the current collector exposed portion was not provided on the outer periphery of the positive electrode.

<Comparative Example 6>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 43μm and 15 [mu] m, the length of the negative electrode 6 995Mm, except that the length of 935mm of the positive electrode 5, in the same manner as in Example 8 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Comparative Example 7>
The thickness _{T 2} of the thickness _{T 1} and the second layer 13 of the first layer 12, respectively and 50μm and 0.5 [mu] m, the length of the negative electrode 6 1040 mm, except that the length of 980mm of the positive electrode 5, similarly to Example 8 Thus, a cylindrical non-aqueous electrolyte secondary battery was produced.

<Comparative Example 8>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 80μm and 25 [mu] m, the length of the negative electrode 6 645 mm, except that the length of 585mm of the positive electrode 5, in the same manner as in Example 11 A cylindrical non-aqueous electrolyte secondary battery was produced.

<Comparative Example 9>
The thickness _{T 2} of the first layer 12 of thickness _{T 1} and the second layer 13, respectively and 95μm and 1.5 [mu] m, the length of the negative electrode 6 670 mm, except that the length of 610mm of the positive electrode 5, similarly to Example 11 Thus, a cylindrical non-aqueous electrolyte secondary battery was produced.

(Battery evaluation method)
The batteries of Examples 1 to 13 and Comparative Examples 1 to 9 were subjected to the following nail penetration test and charge / discharge test to evaluate the safety of each battery and the energy density of each battery. In addition, the presence or absence of the negative electrode active material layer in the battery manufacturing process was visually confirmed.

[Nail penetration test]
The batteries of Examples 1 to 13 and Comparative Examples 1 to 9 were charged under the following conditions. Then, in a 70 ° C. environment, an iron nail having a diameter of 2.7 mm was penetrated from the side surface of the charged battery at a speed of 10 mm / second. The same test was performed 5 cells each, and it was confirmed whether or not abnormal overheating occurred. The results are shown in “Number of abnormally overheated batteries” in Table 1.

-Charging conditions-
Constant current charging: Current value 0.5C, end-of-charge voltage 4.3V
Constant voltage charge: Voltage value 4.3V, charge end current 100mA
[Charge / discharge test]
The batteries of Examples 1 to 13 and Comparative Examples 1 to 9 were charged and discharged under the following conditions in a 25 ° C. environment. The energy per cell was determined from the discharge battery capacity and the average discharge voltage, and the energy density was calculated. The results are shown in Table 1.

−Charging / discharging conditions−
Constant current charging: Current value 0.5C, end-of-charge voltage 4.2V
Constant voltage charging: Voltage value 4.2V, charging end current 100mA
Constant current discharge: current value 0.5C, final discharge voltage 1.0V

  Hereinafter, the obtained results will be described in detail.

In Examples 1 to 5, 9, 12, and 13, batteries with high energy density were obtained without abnormal overheating during nail penetration and removal of the negative electrode active material layer. In Examples 6 and 10, abnormal overheating during nail penetration occurred in 1 cell out of 5 cells. In Example 6 and Example 10, the thickness T ₂ of the second layer 13 was somewhat thin, average 1.5 μm and 1 μm, respectively, and the location where the first layer, which is the lower layer, was exposed on the surface depending on the location was found. It is considered that the insulation at this point is insufficient and the safety is slightly lowered. On the other hand, in Example 7 in which the current collector exposed portion on one side of the central portion was added to Example 6, no abnormal overheating occurred at the time of nail penetration. This is because insulation of the second layer 13 of the negative electrode proceeds more effectively by short-circuiting the exposed portion of the current collector at the center where the electronic resistance in the longitudinal direction is small, and the insulation by the part where the first layer 12 is exposed partially. This is thought to be due to the ability to cover the decline in sex. In Example 8, the energy density was slightly low. This is presumably because the average discharge voltage was lowered because the thickness T ₂ of the second layer 13 was slightly thicker than the thickness T ₁ of the first layer 12 that was the main negative electrode layer. In Example 11, the negative electrode active material layer was partially removed. This is because the thickness T ₂ of the second layer 13 somewhat thicker average 20 [mu] m, in addition to the flexibility becomes slightly lower, and the migration binder in Shumakekyokuso is toward the surface of the current collector interface formation This is thought to be due to insufficient wearability.

In Comparative Examples 1, 4, 5, 7, and 9, many abnormal overheatings occurred. Comparative Example 1,7,9 are very thin thickness T ₂ of the second layer 13 relative to the thickness T ₁ of the first layer 12, since the surface exposed area many insulating first layer 12 becomes insufficient It is thought that the safety was lowered. In Comparative Example 4, since the second layer 13 was not present, insulation was not obtained and safety was low. In Comparative Example 5, since there is no current collector exposed portion on the outer peripheral portion, it is considered that overheating occurred before the second layer 13 was sufficiently insulated. In Comparative Examples 2, 3, 6 and 8, the safety at the time of nail penetration was high, but the second layer 13 was too thick compared to the first layer 12, so that the energy density decreased and the negative electrode active material layer dropped off. It was.

These results, T ₁ and the ratio T _{1 /} T ₂ and T ₂ is 4 or more and 50 or less, and the positive electrode current collector exposed portion and the negative electrode current collector exposed portion at the outer periphery of the electrode group at least It has been necessary that they face each other over one round, and it was found that T ₂ is preferably 1.5 μm or more and 10 μm or less.

  In the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having excellent safety while preventing a decrease in energy density. Therefore, the present invention is useful as a technology that can be applied not only to a small power source such as a portable electronic device but also to a large power source such as an EV (Electric Vehicle).

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate 9 Electrode group 11 Negative electrode collector 12 1st layer 13 2nd layer 14 Positive electrode mixture layer 15 Positive electrode current collector exposed portion 16 Negative electrode current collector exposed portion

Claims (4)

The positive electrode and the negative electrode have an electrode group formed by winding through a separator,
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector,
The negative electrode includes a negative electrode current collector, a first layer formed on a surface of the negative electrode current collector, and a second layer laminated on the first layer, wherein the first layer includes a carbon material. , said second layer comprises capable of absorbing and releasing inorganic solid oxide lithium ions, the thickness of the first layer and T _1, when the thickness of the second layer and T _2, T ₁ and T ₂ And the ratio is 4 or more and 50 or less, and
A nonaqueous electrolyte secondary battery characterized in that a positive electrode current collector exposed portion and a negative electrode current collector exposed portion face each other over at least one turn in the outer peripheral portion of the electrode group.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the inorganic solid oxide is lithium titanate having a spinel crystal structure. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein a thickness T ₂ of the second layer is 1.5 μm or more and 10 μm or less.   4. The non-aqueous electrolyte 2 according to claim 1, wherein in the positive electrode, a positive electrode current collector exposed portion is provided in a central portion of the positive electrode mixture layer in a longitudinal direction over at least one side. Next battery.