JP2007042413A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with excellent safety and high charge-discharge characteristics by preventing a reaction by contact between a positive electrode current collector and a positive electrode active material and by using a positive electrode current collector having small resistance. <P>SOLUTION: In this nonaqueous electrolyte secondary battery provided with a positive electrode having a transition metal oxide as the positive electrode active material, a negative electrode and a nonaqueous electrolyte, a three-layer structure sheet comprising metal M/aluminum/metal M is used in a current collector of the positive electrode, where the metal M contains at least one kind selected from a group comprising nickel, titanium and stainless steel. In the three-layer structure sheet comprising metal M/aluminum/metal M used in the current collector of the positive electrode, the ratio of total thickness of two layers of the metal M to the total thickness is 0.7 or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a positive electrode current collector of a nonaqueous electrolyte secondary battery.

  With the progress of miniaturization, weight reduction, and portability of various electronic devices in recent years, various high performance secondary batteries with high safety and long life have been developed. Among these secondary batteries, a lithium ion battery using lithium cobaltate as a positive electrode active material and a carbon material such as graphite as a negative electrode active material is commercially available as a high energy density secondary battery for mobile phone power supplies, Since then, the use has expanded rapidly.

  In non-aqueous electrolyte secondary batteries such as lithium-ion batteries, the positive electrode current collector must withstand high voltages and currents, be thin and have high mechanical strength, have sufficient conductivity, and be charged and discharged. In order to satisfy this requirement, an aluminum foil has been used as disclosed in Patent Document 1 and Patent Document 2 to satisfy such a requirement.

  Further, Patent Document 3 discloses a technique using stainless steel (austenitic / ferritic duplex stainless steel) as a positive electrode current collector of a non-aqueous electrochemical cell.

  Furthermore, in a non-aqueous electrolyte battery, since the positive electrode package and current collector is a clad material of aluminum and stainless steel, and the positive electrode active material is in contact with aluminum, aluminum can be applied with a positive electrode atmosphere and a high potential. A technique that does not corrode and stainless steel supplements mechanical strength is disclosed in Patent Document 4, and a clad material of aluminum and stainless steel is used for the positive electrode current collector of the organic electrolyte secondary battery, and the positive electrode mixture is made of aluminum. Patent Document 5 discloses a technique for coating both surfaces of stainless steel and stainless steel.

Japanese Patent Publication No. 04-052592 Japanese Patent Publication No. 04-052592 JP 08-222191 A Japanese Patent Laid-Open No. 10-208710 Japanese Utility Model Publication No. 06-070159

In a conventional non-aqueous secondary battery, since a positive electrode mixture (a mixture of a positive electrode active material, a conductive additive, and a binder) is applied onto an aluminum positive electrode current collector, the aluminum and the positive electrode mixture are in contact with each other. I was in a state. When such a non-aqueous secondary battery is in an abnormal state such as an internal short circuit or overcharge and the battery temperature is about 200 ° C. or higher, the electrolytic solution is decomposed and the positive electrode active material lithium cobalt oxide (LiCoO ₂ ) and transition metal oxides such as nickel cobaltate (LiNiO ₂ ) react with aluminum, causing sudden heat generation, and the battery may be heated to fall into a state such as rupture.

  In a non-aqueous electrolyte secondary battery, it is necessary to avoid such an increase in battery temperature. In particular, in a large-sized non-aqueous electrolyte secondary battery having a capacity of 10 Ah or more, a device that does not increase the battery temperature is required. It was.

  Therefore, the present invention was made in the nonaqueous electrolyte secondary battery by discovering that the positive electrode current collector aluminum and the positive electrode active material lithium-containing transition metal oxide are reacting, A non-aqueous electrolyte secondary battery with excellent safety and high-rate charge / discharge characteristics can be obtained by using a positive current collector that has low resistance and prevents reaction due to contact between the positive electrode current collector and the positive electrode active material. It is intended to provide.

  The invention of claim 1 is a non-aqueous electrolyte secondary battery comprising a positive electrode having a transition metal oxide as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte, wherein the current collector of the positive electrode is made of metal M / aluminum / A three-layer structure sheet made of metal M is used, and the metal M is made of at least one selected from the group consisting of nickel, titanium, and stainless steel.

  In the non-aqueous electrolyte secondary battery according to a second aspect of the present invention, in the three-layer structure sheet used for the positive electrode current collector, the ratio of the total thickness of the two layers of metal M to the total thickness is 0.7 or less. It is characterized by being.

  In the nonaqueous electrolyte secondary battery of the present invention, a three-layer structure sheet made of metal M / aluminum / metal M is used for the positive electrode current collector, and the metal M is at least one selected from the group consisting of nickel, titanium, and stainless steel. Since it is used as a seed, the positive electrode active material in the positive electrode mixture layer is in contact with only the metal M, and is not in contact with aluminum. Therefore, even when the nonaqueous electrolyte secondary battery is in any abnormal state such as an internal short circuit or overcharge, and the battery temperature rises to a high temperature of about 200 ° C. or higher, the thermite reaction between the positive electrode active material and aluminum is It does not occur and further rapid heat generation can be prevented.

  The present invention is effective for improving the safety of a non-aqueous electrolyte secondary battery, but a large-sized non-aqueous electrolyte secondary battery having a capacity of 10 Ah or more is strongly required to avoid “rupture” or the like. It is particularly effective.

  Further, in the three-layer structure sheet made of metal M / aluminum / metal M used for the positive electrode current collector, the ratio of the total thickness of the two layers of metal M to the total thickness is 0.7 or less. The increase in resistance of the electric current can be within a certain range, and further, the weight and mechanical strength of the positive electrode current collector can be within an appropriate range. As a result, a nonaqueous electrolyte secondary battery excellent in safety and excellent in high rate charge / discharge characteristics can be obtained.

  The present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode having a transition metal oxide as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte, wherein the current collector of the positive electrode is made of metal M / aluminum / metal M. The metal M is made of at least one selected from the group consisting of nickel, titanium, and stainless steel.

  Further, in the non-aqueous electrolyte secondary battery according to the present invention, the ratio of the total thickness of the two layers of metal M to the total thickness in the three-layer structure sheet used for the positive electrode current collector is 0.7 or less. It is characterized by being.

  In the three-layer structure sheet made of metal M / aluminum / metal M that is the positive electrode current collector, the material of the metal M on both sides may be the same or different. Examples thereof include Ni / Al / SUS and Ni / Al / Ti.

  Further, the metal M may be a single material or two or more types of laminates made of different types of materials. Examples thereof include Ni / SUS and Ni / SUS / Ni.

  Aluminum is stable even at a high voltage of about 5 V in a non-aqueous electrolyte, has an appropriate mechanical strength, and has a sufficient electrical conductivity. Therefore, it is used for a positive electrode current collector of a non-aqueous electrolyte secondary battery. Has been.

  However, in a nonaqueous electrolyte secondary battery, when an abnormal state such as an internal short circuit or overcharge occurs, a large current flows and the battery temperature locally rises to a high temperature of 200 ° C. or higher, It has been considered that the liquid solvent is thermally decomposed to generate gas inside the battery, and the pressure of this gas causes the battery to rupture.

  However, in the case of a non-aqueous electrolyte secondary battery using aluminum as the positive electrode current collector, when an internal short circuit or overcharge test is performed, the battery ruptures, etc., are more severe than the electrolyte solvent is expected from thermal decomposition. Confirmed to happen. As a result of examining the cause, it became clear that the reaction between the positive electrode active material and the aluminum current collector occurred in addition to the thermal decomposition of the electrolyte solvent.

  That is, when the temperature inside the battery becomes a high temperature of 200 ° C. or higher for some reason, the positive electrode active material that is an oxide is thermally decomposed, and oxygen is generated together with heat generation. It is considered that this oxygen reacts with the aluminum of the current collector, and the battery temperature rises. An increase in battery temperature may cause gas generation due to vaporization or decomposition of the electrolyte, leading to an increase in battery internal pressure, which may lead to explosion.

The reaction between the positive electrode active material and the aluminum current collector refers to a reaction in which aluminum and a metal oxide undergo an exothermic reaction at a high temperature, the metal oxide is reduced, and aluminum oxide (Al ₂ O ₃ ) is generated. This reaction is a method used for the reduction of metal oxides that are difficult to reduce and the production of iron alloys that do not contain carbon.

  If a complex oxide such as lithium cobaltate is in contact with the aluminum current collector inside the non-aqueous electrolyte secondary battery and this contact part becomes hot due to internal short circuit or overcharge, It is considered that the oxide is thermally decomposed, and the generated oxygen and aluminum react to generate heat more intensely, resulting in a dangerous state such as battery rupture.

Therefore, it is necessary to devise a method in which aluminum that is the positive electrode current collector and the positive electrode active material are not in direct contact with each other. However, when stainless steel is used for the positive electrode current collector, there is a problem that stainless steel has a higher specific gravity and higher resistivity than aluminum. That is, according to the Shinko Stainless Steel website (http://www.ss-shinko.co.jp), the density of stainless steel (SUS304) is 7.93 g / cm ³ and the resistivity is 72 μΩcm. On the other hand, according to the Chemical Handbook, Basics I and II (Revised 4th edition, edited by the Chemical Society of Japan, published in Mar. 1993), the density of aluminum is 2.698 g / cm ³ and the resistivity is 2.6548.

  Thus, when stainless steel is used for the positive electrode current collector, the battery becomes heavier, the energy density is lowered, the internal resistance of the battery is increased, and the high rate charge / discharge characteristics are inferior. there were.

  Therefore, the present invention uses a three-layer structure sheet made of metal M / aluminum / metal M as the positive electrode current collector, and the metal M is at least one selected from the group consisting of nickel, titanium and stainless steel, The layer is applied to the surface of the metal M, and the positive electrode active material is in contact with only the metal M and not with aluminum. With such a configuration, even when the inside of the battery is locally heated, the positive electrode active material does not react with aluminum, and further rapid heat generation can be prevented.

  Aluminum having a thickness of about 20 μm has been used for a positive electrode current collector of a conventional standard nonaqueous electrolyte secondary battery. Then, about the thickness of each part of the three-layer structure sheet | seat which consists of metal M / aluminum / metal M which is a positive electrode electrical power collector of this invention, about the case where nickel, titanium, stainless steel (SUS304) is used for metal M, Consider using density and resistivity (room temperature).

  In a certain battery, when the other conditions are the same, and the thickness of the positive electrode current collector changes, the thickness of the electrode mixture layer that can be stored in the battery changes. The amount of material also changes and the battery capacity changes.

  Therefore, the case where the dimensions (length, width, thickness) of the positive electrode current collector were the same and the thicknesses of the metal M and aluminum were changed was examined here. The basic data used for the calculation are summarized in Table 1.

  Since the dimensions (length, width, thickness) of the positive electrode current collector are the same, the calculation was performed on the 1 cm × 1 cm positive electrode current collector shown in FIG. In FIG. 1, 1 indicates aluminum, and 2 indicates a metal M. Also, as indicated by the arrows, since the current flows in the length direction of the current collector, the resistance in this direction can be calculated as a parallel connection of aluminum and two layers of metal M. Here, the calculation is made for the case where the thickness of the metal M on both sides is equal, but the same calculation is possible when the thickness of the metal M on both sides is different.

  First, the symbols are defined as follows.

r: Specific resistance of metal M (μΩcm)
q: Specific resistance of aluminum (μΩcm). It can be expressed as r = αq.

a: Total thickness of positive electrode current collector (cm)
b: Thickness (cm) of metal M layer (for one layer)
R _A : resistance of the aluminum part of the positive electrode current collector (Ω)
R _M : Resistance for one layer of metal M portion of the positive electrode current collector (Ω)
R _A and R _M are expressed as follows.

R _A = q × (1 / (a-2b)) = r / α (a-2b)
R _M = r × (1 / b) = r / b
Therefore, the resistance R in the arrow direction of the positive electrode current collector shown in FIG. 1 can be calculated as follows.

1 / R = α (a−2b) / r + b / r + b / r
R = r / (α (a−2b) + 2b)
Further, when all are aluminum (b = 0), the resistance R _{0 is as} follows.

R ₀ = r / aα = q / a
Therefore, when the metal M is nickel, titanium, or stainless steel (SUS304), the ratio X (= 2b / a) of the thickness of the metal M to the total thickness of the positive electrode current collector and the positive electrode current collector The relationship with the relative resistance in the length direction (ratio of resistance in the case of using two layers of metal M to the resistance in the case where all is aluminum) was determined.

  The relative resistance in the length direction of the positive electrode current collector can be calculated from the following equation. The calculation results are shown in Table 2.

R / R ₀ = aα / (α (a-2b) + 2b) = α / (α (1-X) + X)

  FIG. 2 is a diagram showing the relationship between the ratio of the thickness of the metal M to the total thickness and the relative resistance in the length direction of the positive electrode current collector, based on the results of Table 2. In FIG. The symbol □ indicates the relationship when the metal M is nickel, the symbol ▲ indicates the relationship when the metal M is titanium, and the symbol ♦ indicates the relationship when the metal M is stainless steel.

  From FIG. 2, when titanium or stainless steel having a very large specific resistance as compared with aluminum is used as the metal M, the current collector has a ratio of the thickness of the metal M to the total thickness exceeding 0.7. It was found that the resistance of the sudden increase.

Next, when the metal M is nickel, titanium, or stainless steel (SUS304), the ratio X of the thickness of the metal M to the total thickness of the positive electrode current collector (= 2b / a) and the positive electrode current collector The relative weight (the ratio of the weight in the case of using two layers of metal M to the weight in the case of all aluminum) was determined. The symbols were determined as follows, and the weight of the current collector was compared with a value per unit area (1 cm ² ). Table 3 shows the calculation results.

S _A : Aluminum density (g / cm ³ )
S _M : Density of metal M (g / cm ³ )
The weight (W) per unit area (1 cm ² ) of the positive electrode current collector can be obtained from the following equation.

W = (a−2b) S _A + 2bS _M
Further, when all are aluminum (b = 0), the weight W _{0 is as} follows.

W ₀ = aS _A
Therefore, the relative weight of the positive electrode current collector is expressed as follows. Table 3 shows the calculation results.

W / W ₀ = ((a−2b) S _A + 2bS _M ) / aS _A = ((1−X) S _A + X) / S _A

  FIG. 3 is a graph showing the relationship between the ratio of the thickness of the metal M to the total thickness and the relative weight of the positive electrode current collector based on the results in Table 3. In FIG. In the case of nickel, the symbol ▲ indicates the relationship when the metal M is titanium, and the symbol ◆ indicates the relationship when the metal M is stainless steel.

  FIG. 3 shows that the weight of the current collector increases in proportion to the ratio of the thickness of the metal M to the total thickness even when the type of the metal M is different.

  In addition, although said calculation was performed about the case where nickel, titanium, and stainless steel (SUS304) were used for the metal M, in this invention, these metals and alloys are used in combination of 2 or more types. be able to. In this case, the metal M may be two layers.

  Next, in the following specific nonaqueous electrolyte secondary battery, the influence on the internal resistance and weight of the battery when the positive electrode current collector of the present invention was used was examined. As an example of the non-aqueous electrolyte secondary battery, the battery having the components shown in Table 4 was used.

  The internal resistance of this battery at 1 kHz was 26 mΩ.

  Therefore, as the positive electrode current collector, a case where aluminum having a thickness of 20 μm was used and a three-layer laminated sheet of SUS304 (thickness 5 μm) / aluminum (thickness 10 μm) / SUS304 (thickness 5 μm) of the present invention were used. In this case, the weight of the battery and the internal resistance were compared. The results are summarized in Table 5.

  As is apparent from Table 5, in a battery having a capacity of 500 mAh, a three-layer laminated sheet of SUS304 (thickness 5 μm) / aluminum (thickness 10 μm) / SUS304 (thickness 5 μm) is used as the positive electrode current collector instead of aluminum. When using, it was found that the internal resistance of the battery hardly changed and the increase in weight was slight.

  As described above, the present invention was found to be effective for a small non-aqueous electrolyte secondary battery having a capacity of about 500 mAh. However, the weight of the positive electrode current collector is increased compared to the case of aluminum alone. It has been found that the present invention is particularly effective for a relatively large non-aqueous electrolyte secondary battery that does not require weight reduction and is not always moved.

As the positive electrode active material used in the non-aqueous electrolyte secondary battery of the present invention, an active material conventionally used in non-aqueous electrolyte secondary batteries can be used. For example, the general formula Li _x Me _y A _z O ₂ (where Me is at least one element selected from Ni, Co, and Mn, or a mixture of two or three elements, A is Ni, Co, Metal elements other than Mn, 0 <x ≦ 1.2, 0 ≦ z ≦ 0.5, 0.9 ≦ y + z ≦ 1.1) and lithium composite oxides represented by the general formula Li _a Mn _2-b B _b O ₄ (provided that, B is a metal element other than Mn, 0 <a ≦ 1.2,0 ≦ b ≦ 1) spinel-type lithium manganese complex oxide represented by, and the like alone olivine material or two, A mixture of the above can be used. Specifically, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiVOPO _4, or the like can be used.

  As the negative electrode active material used in the nonaqueous electrolyte secondary battery of the present invention, carbon capable of occluding and releasing lithium (for example, natural graphite, artificial graphite, flake graphite, low crystalline carbon, soft carbon, hard carbon) , Activated carbon), mixed materials obtained by mixing or plating compounds such as silicon and tin that are alloyed with lithium can be used.

  As the electrolyte solution solvent of the non-aqueous electrolyte secondary battery of the present invention, solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, ethyl acetate, methyl propionate, and mixtures thereof A solvent can be used.

As the electrolyte salt of the non-aqueous electrolyte secondary battery of the present _{invention, LiPF 6, LiPF 3 (C} 2 F 5) 3, LiBF 4, LiAsF 6, LiClO 4, LiSCN, LiCF 3 CO2, LiCF 3 SO 3, LiN ( Use salts such as SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) _2, LiN (COCF ₂ CF ₃ ) ₂ , LiB (C ₂ O ₄ ), or a mixture thereof. can do.

  In the nonaqueous electrolyte secondary battery of the present invention, it is desirable to add an additive to the electrolyte. For example, vinylene carbonate and derivatives thereof, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, triazole-based cyclic compounds, fluorine-containing esters, hydrogen fluoride complexes of tetraethylammonium fluoride, or these Or at least one selected from the group consisting of amide group-containing compounds, imino group-containing compounds, and nitrogen-containing compounds.

  As the shape of the power generation element of the nonaqueous electrolyte secondary battery of the present invention, the positive electrode plate and the negative electrode plate are optimally a cylindrical type or a long cylindrical type using a strip electrode, but a shape in which flat plate electrodes are laminated. It is also possible.

  As the shape of the non-aqueous electrolyte secondary battery of the present invention, any conventionally used shape such as a cylindrical shape, a long cylindrical shape, and a rectangular shape can be used. As the battery case, a metal case such as an aluminum alloy, nickel-plated iron or stainless steel, or a laminated case in which a metal such as aluminum and a resin are laminated can be used.

[Example 1 and Comparative Examples 1 and 2]
[Example 1]
A non-aqueous electrolyte secondary battery using a three-layer laminated sheet of SUS304 (5 μm) / aluminum (10 μm) / SUS304 (5 μm) as a positive electrode current collector was produced.

The positive electrode plate was produced as follows. LiCoO ₂ (90 wt%) as an active material, acetylene black (5 wt%) as a conductive material, and polyvinylidene fluoride (PVdF) (5 wt%) as a binder are mixed, and N-methyl- After 2-pyrrolidone (NMP) is added and dispersed to prepare a slurry, the slurry is uniformly applied to both sides of the current collector composed of the above three-layer laminated sheet having a total thickness of 20 μm with a doctor blade and dried. Then, the mixture layer was compression-molded with a roll press so that the thickness of one side of the mixture layer was 40 μm, and a positive electrode plate having a cathode mixture layer (total thickness of 100 μm) on both sides of the current collector was produced. The positive electrode plate had a length of 810 mm and a width of 30 mm, and a mixture layer uncoated portion as a lead mounting portion having a width of 10 mm was provided at one end in the length direction.

  The negative electrode plate was produced as follows. Graphite (92 wt%) and PVdF (8 wt%) as a binder are mixed, NMP is added to the mixture and dispersed to prepare a slurry, and the slurry is made of a copper foil having a thickness of 10 μm. After applying uniformly on both sides with a doctor blade and drying, the mixture layer is compression-molded with a roll press so that the thickness of one side of the mixture layer becomes 45 μm, and the negative electrode mixture layer (total thickness on both sides of the current collector) 100 μm) was prepared. The negative electrode plate had a length of 760 mm and a width of 32 mm, and a mixture layer uncoated portion as a lead attachment portion having a width of 10 mm was provided at one end in the length direction.

  Next, the positive electrode plate and the negative electrode plate produced as described above are laminated in the order of negative electrode, separator, positive electrode, and separator through a separator made of a microporous polypropylene film having a length of 1700 mm, a width of 33 mm, and a thickness of 30 μm. After that, it was wound many times to obtain a wound power generation element.

The wound power generation element was housed in a rectangular aluminum battery case. The aluminum positive electrode lead of the wound power generation element was led out from the positive electrode current collector and connected to the positive electrode terminal insulated from the battery lid, and the copper negative electrode lead was led out from the negative electrode current collector and connected to the battery can. Then, in this battery can 2 of ethylene carbonate (EC) dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC): 4: 4 electrolyte was dissolved in a mixed solvent of LiPF ₆ at a rate of 1 mol / l Injected.

  Next, the battery lid and the battery case are laser welded to fix the battery lid, maintain the airtightness in the battery, and when discharged at 25 ° C. and a current of 500 mA, the discharge capacity at the first cycle is about 500 mAh. The long cylindrical nonaqueous electrolyte secondary battery (thickness 5 mm, width 34 mm, height 50 mm) of Example 1 was prepared.

  FIG. 4 shows a schematic cross-sectional structure of the produced square nonaqueous electrolyte secondary battery. In FIG. 4, 3 is a long cylindrical non-aqueous electrolyte secondary battery, 4 is a battery case, 5 is a battery lid, 6 is a negative electrode terminal, and 7 is an insulating member. The battery case 4 and the battery lid 5 are laser welded. The battery case 4 and the battery lid 5 also serve as a positive electrode terminal, and the negative electrode terminal 6 is insulated from the battery lid 5 by an insulating member 7.

[Comparative Example 1]
A long cylindrical nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that an aluminum foil having a thickness of 20 μm was used as the positive electrode current collector.

[Comparative Example 2]
A long cylindrical nonaqueous electrolyte secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that SUS304 foil having a thickness of 20 μm was used as the positive electrode current collector.

[High rate discharge characteristics]
The high rate discharge characteristics of the long cylindrical non-aqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 and 2 were compared. All measurements were performed at 25 ° C. First, each battery was charged to 4.2 V at 100 mA (0.2 CA), and discharged to 3.0 V with the same current. Next, the battery was charged to 4.2 V at 100 mA (0.2 CA) and discharged to 3.0 V with the same current, and the discharge capacity at this time was defined as “low rate discharge capacity”. Further, the battery was charged to 4.2 V at 100 mA (0.2 CA) and discharged to 3.0 V at 1000 mA (2 CA), and the discharge capacity at this time was defined as “high rate discharge capacity”. The ratio of the high rate discharge capacity to the low rate discharge capacity was defined as “high rate / low rate discharge capacity ratio”. The test results are summarized in Table 6.

  From the results of Table 6, the high rate / low rate discharge capacity ratio was 94% or more in the batteries of Example 1 and Comparative Example 1, but 81% in the battery of Comparative Example 2, and the positive electrode current collector Further, it was found that the high rate discharge capacity was slightly reduced in the battery of Comparative Example 2 using SUS304. This is presumably because the resistance of the positive electrode current collector (SUS304) used in the battery of Comparative Example 2 is larger than the resistance of the positive electrode current collector of Example 1 or Comparative Example 1.

[Overcharge test]
The overcharge characteristics of the long cylindrical nonaqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 and 2 were measured. The measurement was carried out by charging 10 batteries each at a constant current of up to 12 V at a current of 1 A (2 CA) at 40 ° C., followed by charging at a constant voltage of 12 V, and observing the state of the batteries. . The test results are summarized in Table 7.

  From the results in Table 7, the batteries of Example 1 and Comparative Example 2 of the present invention were extremely safe and did not smoke or rupture even when the valve was activated. On the other hand, in the batteries of Comparative Example 1 using aluminum for the positive electrode current collector, the operation of the safety valves was confirmed in all, and ignition was observed in 6 out of 10 batteries.

[Examples 2 to 7]
[Example 2]
The long cylindrical nonaqueous electrolyte secondary battery of Example 2 is the same as Example 1 except that a SUS304 (4 μm) / aluminum (12 μm) / SUS304 (4 μm) three-layer laminated sheet is used as the positive electrode current collector. Was made.

[Example 3]
The long cylindrical nonaqueous electrolyte secondary battery of Example 3 is the same as Example 1 except that a SUS304 (6 μm) / aluminum (8 μm) / SUS304 (6 μm) three-layer laminated sheet is used as the positive electrode current collector. Was made.

[Example 4]
The long cylindrical nonaqueous electrolyte secondary battery of Example 4 is the same as Example 1 except that a SUS304 (7 μm) / aluminum (6 μm) / SUS304 (7 μm) three-layer laminated sheet is used as the positive electrode current collector. Was made.

[Example 5]
The long cylindrical nonaqueous electrolyte secondary battery of Example 5 is the same as Example 1 except that a SUS304 (8 μm) / aluminum (4 μm) / SUS304 (8 μm) three-layer laminated sheet is used as the positive electrode current collector. Was made.

[Example 6]
The long cylindrical nonaqueous electrolyte secondary battery of Example 6 is the same as Example 1 except that a nickel (5 μm) / aluminum (10 μm) / nickel (5 μm) three-layer laminated sheet is used as the positive electrode current collector. Was made.

[Example 7]
The long cylindrical nonaqueous electrolyte secondary battery of Example 7 is the same as Example 1 except that a three-layer laminated sheet of titanium (5 μm) / aluminum (10 μm) / titanium (5 μm) is used as the positive electrode current collector. Was made.

[High rate discharge characteristics]
The high rate discharge characteristics of the long cylindrical non-aqueous electrolyte secondary batteries of Examples 2 to 7 were compared. The measurement conditions were the same as in Example 1. The test results are summarized in Table 8.

  From Table 8, the high rate / low rate discharge capacity ratio was 85% or more in the batteries of Examples 2 to 7. However, the high rate / low rate discharge capacity ratio of the battery of Example 5 was slightly smaller than Examples 2-4. This is because the ratio of SUS304 to the thickness of the positive electrode current collector is 70% or less in the batteries of Examples 2 to 4 and 80% in the battery of Example 5, so This is presumably because the resistance of the positive electrode current collector of the battery was considerably larger than the resistance of the positive electrode current collector used in the batteries of Examples 2 to 4.

  Further, when nickel or titanium was used instead of SUS304, no significant change was observed in the high rate / low rate discharge capacity ratio.

[Overcharge test]
For the long cylindrical nonaqueous electrolyte secondary batteries of Examples 2 to 7, overcharge characteristics were measured under the same conditions as in Example 1. As a result, no smoke or ignition was observed in all these batteries.

  From the above results, in the three-layer structure sheet used for the positive electrode current collector, when the ratio of the total thickness of the two layers of metal M to the total thickness is 0.7 or less, high rate discharge characteristics and safety A non-aqueous electrolyte secondary battery excellent in the above can be obtained.

The figure which shows the positive electrode electrical power collector of 1 cm x 1 cm which consists of a three-layer structure sheet | seat which consists of metal M / aluminum / metal M. The figure which shows the relationship between the ratio of the thickness of the metal M with respect to the total thickness, and the relative resistance of the length direction of a positive electrode collector in a three-layer structure sheet | seat positive electrode collector. The figure which shows the relationship between the ratio of the thickness of the metal M with respect to total thickness, and the relative weight of a positive electrode electrical power collector in a three-layer structure sheet | seat positive electrode electrical power collector. The figure which shows schematic sectional structure of the square-shaped non-aqueous electrolyte secondary battery of this invention.

Explanation of symbols

1 Aluminum 2 Metal M
3 Square type nonaqueous electrolyte secondary battery 4 Battery case 5 Battery cover 6 Negative electrode terminal 7 Insulating member

Claims (2)

In a non-aqueous electrolyte secondary battery comprising a positive electrode having a transition metal oxide as a positive electrode active material, a negative electrode, and a non-aqueous electrolyte, the current collector of the positive electrode has a three-layer structure made of metal M / aluminum / metal M A non-aqueous electrolyte secondary battery using a sheet, wherein the metal M is at least one selected from the group consisting of nickel, titanium, and stainless steel. The three-layer structure sheet used for the positive electrode current collector has a ratio of the total thickness of the two layers of the metal M to the total thickness of 0.7 or less. Next battery.

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