JP2008117611A - Nonaqueous electrolyte secondary battery, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large size nonaqueous electrolyte secondary battery with excellent floating service life characteristic, with high energy density and excellent safety. <P>SOLUTION: The nonaqueous electrolyte secondary battery is provided with a positive electrode containing a first active substance, a second active substance and a third active substance. The first active substance is a lithium-nickel-cobalt-manganese composite oxide provided with a space group R-3m, the second active substance is a lithium-nickel-cobalt composite oxide provided with the space group R-3m and the third active substance is a lithium-manganese composite oxide provided with a space group Fd-3m. It is characteristic that the content of the first active substance in the positive electrode active substance is 30 to 50 wt.%, the content of the second active substance is 30 to 50 wt.% and the content of the third active substance is 20 to 35 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using three types of positive electrode active materials of lithium / nickel / manganese / cobalt composite oxide, lithium / nickel / cobalt composite oxide, and lithium / manganese composite oxide. .

  Nonaqueous electrolyte secondary batteries have a higher energy density than conventional batteries, and are therefore used as power sources for portable devices such as mobile phones and laptop computers that require mainly downsizing and weight reduction. In non-aqueous electrolyte secondary batteries, negative electrode active materials such as metallic lithium, lithium alloys, carbon materials capable of occluding and releasing lithium, positive electrode active materials are complex oxides of lithium and transition metals, and electrolytes are lithium salts. A non-aqueous electrolyte is used in which is a supporting salt.

  On the other hand, since non-aqueous electrolyte secondary batteries have a high energy density, it is expected that not only power sources for portable devices but also their uses will be diversified. One of them is a large battery used for a power source of an electric vehicle or the like. At present, many researches and developments are being carried out for practical use of a large battery.

Lithium manganate (LiMn ₂ O ₄ ), which has a spinel structure that is superior in thermal stability and cost-effective compared to lithium cobaltate having a layered rock salt structure, is mainly used as the positive electrode active material for large-sized batteries. Has been used.

  However, because large batteries for standby (backup) applications require float life characteristics and high energy density, nickel-cobalt and nickel-cobalt-manganese are used for the positive electrode active material rather than manganese. It is like that.

Patent Document 1 discloses a non-aqueous electrolyte using a lithium composite oxide containing nickel and cobalt represented by the general formula Li _x Co _y Ni _1-y O ₂ (where 0 ≦ y ≦ 1) as a positive electrode active material. A secondary battery is disclosed, and Patent Document 2 discloses _a general formula LiNi _a Co _b Mn _c O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1) as a positive electrode active material. A non-aqueous secondary battery using a lithium nickel cobalt manganese composite oxide having a layered structure represented by the following formula is disclosed. Patent Document 3 discloses a non-aqueous solvent secondary using spinel type LiMn ₂ O ₄ as a positive electrode active material. A battery is disclosed.

Patent Document 4 discloses a technique in which a lithium-nickel-cobalt-manganese composite oxide and a spinel-type lithium-manganese composite oxide are mixed and used as a positive electrode active material of a nonaqueous electrolyte secondary battery. In Reference 5, the positive electrode active material of the nonaqueous electrolyte secondary battery includes a part represented by LiCo _z Ni _1-z O ₂ (0 ≦ z ≦ 1) and a part represented by LiMn ₂ O _4. A technique using the composite particles is disclosed.

In addition, in the claims of Patent Documents 6 to 8, three types of composite oxides of nickel / cobalt / manganese, nickel / cobalt, and spinel manganese are mixed as options for the combination of positive electrode active materials. In any of the examples, no positive electrode example in which these active materials are mixed is described in the examples. Therefore, the characteristics of the non-aqueous secondary battery using the positive electrode active material in which three types of these composite oxides are mixed are unknown.
JP 05-290890 A Japanese Patent Application Laid-Open No. 2003-223887 Japanese Patent Laid-Open No. 04-033249 JP 2004-146363 A Japanese Patent Laid-Open No. 08-50895 JP 2003-282055 A JP 2004-241390 A JP 2005-317512 A

  As non-aqueous secondary batteries increase in size, demands for battery safety are increasing. For example, when a nickel / cobalt-based positive electrode active material was used alone, there was no problem in the overcharge test, but in the nail penetration test (internal short circuit test), smoke and ignition were observed. On the other hand, when the nickel / cobalt / manganese positive electrode active material was used alone, there was no problem in the nail penetration test, but smoke and ignition were seen in the overcharge test. Furthermore, when the spinel-type manganese-based positive electrode active material was used alone, there was no problem with both the nail penetration test and the overcharge test, but the energy density and life characteristics were inferior compared to the nickel-cobalt-based positive electrode active material. There was a problem.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in safety, in particular, a large size (capacity of 4 Ah or more) with excellent float life characteristics, high energy density and excellent safety. ) Non-aqueous electrolyte secondary battery.

  The invention according to claim 1 is a non-aqueous electrolyte secondary battery in which the positive electrode includes a first active material, a second active material, and a third active material, and the first active material has a space group R-3m. A cobalt-manganese composite oxide, a lithium-nickel-cobalt composite oxide in which the second active material has a space group R-3m, and a lithium-manganese composite oxide in which the third active material has a space group Fd-3m. Yes, the content of the first active material in the positive electrode active material is 30 to 50% by weight, the content of the second active material is 30 to 50% by weight, and the content of the third active material is 20 to 35% by weight. %.

According to a second aspect of the invention, in the non-aqueous electrolyte secondary batteries, the composition of the first active material is _{Li x Ni a Co b Mn c} M1 d O 2 ( however, 0.9 ≦ x ≦ 1.0,0. 2 ≦ a ≦ 0.4, 0.2 ≦ b ≦ 0.4, 0.2 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1, a + b + c + d = 1, M1 is at least other than Ni, Co, and Mn one metal), the composition of the second active material is _{Li y Ni e Co f M2 g} O 2 ( however, 0.9 ≦ y ≦ 1.0,0.7 ≦ e ≦ 0.9,0.1 ≦ f ≦ 0.2, 0 ≦ g ≦ 0.1, e + f + g = 1, M2 is at least one metal other than Ni, Co, and Mn), and the composition of the third active material is Li _z Mn _h M3 _i O ₄ ( However, 0.9 ≦ z ≦ 1.0, 1.7 ≦ h ≦ 2.0, 0 ≦ i ≦ 0.2, h + i = 2, M3 is at least one metal other than Ni, Co, and Mn And characterized in that.

  As in the present invention, the positive electrode active material of the nonaqueous electrolyte secondary battery includes three active materials of lithium / nickel / cobalt / manganese composite oxide, lithium / nickel / cobalt composite oxide, and lithium / manganese composite oxide. By mixing and using, a non-aqueous electrolyte secondary battery having excellent float life characteristics, high energy density and excellent safety can be obtained.

  In particular, by limiting the composition of the three types of active materials contained in the positive electrode to the range described in claim 2, a non-aqueous electrolyte secondary battery having both high energy density and safety can be obtained.

  Embodiments of the present invention will be described below. Here, preferred embodiments of the present invention will be described, and the present invention is not limited to the following unless it exceeds the gist of the present invention.

  The present invention provides a non-aqueous electrolyte secondary battery in which a positive electrode includes a first active material, a second active material, and a third active material, and the first active material has a space group R-3m. A manganese composite oxide, a lithium / nickel / cobalt composite oxide in which the second active material has a space group R-3m, and a lithium / manganese composite oxide in which the third active material has a space group Fd-3m. The content of the first active material in the active material is 30 to 50% by weight, the content of the second active material is 30 to 50% by weight, and the content of the third active material is 20 to 35% by weight. It is characterized by that.

  Here, “R-3m” and “Fd-3m” are space groups described in International tables for crystallography Volume A, and “R-3m” is No. No. 166, “Fd-3m” is No. It shall mean 227 space groups.

  In the non-aqueous electrolyte secondary battery of the present invention, the first active material (lithium / nickel / cobalt / manganese composite oxide) having a good balance between energy density and safety can be obtained by mixing and using the above three types of positive electrode active materials. ), A second active material (lithium / nickel / cobalt composite oxide) with high energy density and good life characteristics, and a third active material (lithium / manganese composite oxide) excellent in safety included in the positive electrode As a result, a battery with high energy density and high safety can be obtained.

  When the content of the lithium / nickel / cobalt / manganese composite oxide in the positive electrode active material is less than 30% by weight, the energy density is lowered. On the other hand, when the content exceeds 50% by weight, the overcharge safety is achieved. Becomes worse.

  When the content of lithium / nickel / cobalt composite oxidation in the positive electrode active material is less than 30% by weight, the energy density is low and the life characteristics are deteriorated. On the other hand, when the content exceeds 50% by weight, the nail penetration test is performed. The safety is worse.

  When the content of the lithium-manganese composite oxide in the positive electrode active material is less than 20% by weight, the safety of the battery is slightly inferior. On the other hand, when the content exceeds 35% by weight, the energy density of the battery is slightly reduced. Will do.

  In addition, in the nonaqueous electrolyte secondary battery using the positive electrode including the first active material and the second active material, safety cannot be ensured in the nail penetration test and the overcharge test. In a non-aqueous electrolyte secondary battery using a positive electrode containing an active material, safety cannot be ensured in an overcharge test, and a non-aqueous electrolyte secondary battery using a positive electrode containing a second active material and a third active material is not available. With secondary batteries, safety cannot be ensured in the nail penetration test.

  The lithium / nickel / manganese / cobalt composite oxide of the first active material is represented by the following general formula (1).

LiNi _a Co _b Mn _c M1 _d O ₂ (1)
In the general formula (1), a + b + c + d = 1, and M1 represents at least one metal other than Ni, Co, and Mn. In the lithium / nickel / manganese / cobalt composite oxide represented by the general formula (1), 0.9 ≦ x ≦ 1.0, 0.2 ≦ a ≦ 0.4, 0.2 ≦ b ≦ It is preferable that 0.4, 0.2 ≦ c ≦ 0.4, and 0 ≦ d ≦ 0.1. The substitution metal M1 may contain Li, and in this case, Li is present at sites of Ni, Co, and Mn. As M1, Al, Mg, Cr and the like are preferable because the stability of the crystal is increased.

  Although the nickel content in the first active material depends on the composition of Co, Mn, and M1, it is approximately 12% by weight when a = 0.2 and 24% by weight when a = 0.4. However, when the content of Mn is large, the crystal structure is not the space group R-3m. In the first active material, when the nickel content is less than 12% by weight (a <0.2), sufficient charge / discharge capacity cannot be secured, and the nickel content is less than 24% by weight. When the amount is large (a> 0.4), sufficient safety cannot be ensured in a nail penetration test or the like.

  In addition, in the 1st active material represented by General formula (1), the value of x, a, b, c, and d receives a restriction | limiting so that crystal structure may become space group R-3m.

The lithium / nickel / manganese / cobalt composite oxide of the first active material comprises, in an oxidizing atmosphere, a lithium compound such as lithium hydroxide (LiOH), a nickel compound such as nickel hydroxide (Ni (OH) ₂ ), and water. Manufactured by mixing a cobalt compound such as cobalt oxide (Co (OH) ₂ ) and a manganese compound such as manganese dioxide (MnO ₂ ) in a desired ratio, and heat-treating in the range of 400 ° C. to 900 ° C. .

The lithium / nickel / manganese / cobalt composite oxide as the first active material can also be produced by a coprecipitation method. In this production method, for example, first, a precursor (Ni _x Co _y (OH) _z ) is prepared from an aqueous solution of nickel hydroxide (Ni (OH) ₂ ) and cobalt hydroxide (Co (OH) ₂ ) by a coprecipitation method. Next, this precursor is mixed with lithium carbonate or lithium hydroxide, which is a lithium source, and fired at a high temperature.

  The lithium / nickel / cobalt composite oxide of the second active material is represented by the following general formula (2).

_{Li y Ni e Co f M2 g} O 2 ····· (2)
In the general formula (2), e + f + g = 1, and M2 represents at least one metal other than Ni, Co, and Mn. In the lithium / nickel / cobalt composite oxide represented by the general formula (2), 0.9 ≦ y ≦ 1.0, 0.7 ≦ e ≦ 0.9, 0.1 ≦ f ≦ 0. 2, 0 ≦ g ≦ 0.1 is preferable. The substitution metal M2 may contain Li. In this case, Li is present at the sites of Ni and Co. M2 is preferably Al, Mg, Cr, or the like because the stability of the crystal is increased.

  The nickel content in the second active material is 42% by weight when e = 0.7, and 54% by weight when e = 0.9, although it depends on the composition of Co and Me. The maximum value of the nickel content is about 60% by weight when f = 0 and g = 0. In the second active material, when the nickel content is less than 42% by weight (e <0.7), the discharge capacity is reduced, and safety during overcharge cannot be ensured. The crystal structure of the second active material represented by the general formula (2) is the space group R-3m.

For example, lithium carbonate (Li ₂ CO ₃ ), nickel nitrate (Ni (NO ₃ ) ₂ ), and cobalt nitrate (Co (NO ₃ )) can be used as the second active material. ₂ ) is mixed so that Li: Ni: Co = 1: 0.8: 0.2 (atomic ratio), and these raw material powders are subjected to high-temperature solid reaction (900 ° C., 24 hours) in the air. By reacting, LiNi _0.8 Co _0.2 O ₂ in which a part of cobalt in the lithium cobalt oxide is substituted with nickel can be synthesized.

  The lithium-manganese composite oxide of the third active material is represented by the following general formula (3).

Li _z Mn _h M3 _i O ₄ (3)
In the general formula (3), z + h + i = 3, and M3 represents at least one metal other than Ni, Co, and Mn. In the lithium / manganese composite oxide represented by the general formula (3), 0.9 ≦ z ≦ 1.0, 1.7 ≦ h ≦ 2.0, and 0 ≦ i ≦ 0.2. Is preferred. The substituted metal M3 may contain Li. In this case, Li is present at the Mn site. M3 preferably contains trivalent stable Al, Cr, and Co from the viewpoint of improving cycle life characteristics and suppressing reduction in output.

  Although the manganese content in the third active material depends on the type and composition of M3, it is 52% by weight when M3 is Al and h = 1.7, and the maximum value is 61% by weight when h = 2.0. .

  In the third active material, when the manganese content is less than 52% by weight (h <1.7), the discharge capacity is reduced and the effect on the safety of the battery is also reduced.

  The crystal structure of the third active material represented by the general formula (3) is the space group Fd-3m.

Next, a method for producing a lithium-manganese composite oxide as the third active material will be described. For example, a lithium-manganese composite oxide represented by the composition formula Li _1.1 Mn _1.8 Al _0.1 O ₄ is lithium hydroxide (LiOH) as a lithium raw material, manganese dioxide (MnO ₂ ) as a manganese raw material, and substitution Aluminum oxide (Al ₂ O ₃ ) is used as a raw material for aluminum, which is a metal. Each raw material is wet-mixed according to the number of moles in the composition formula, and a slurry is molded using a spray drying method. It can be obtained by firing for 12 hours in an electric furnace at a firing temperature of 600 to 900 ° C.

  In the present invention, the method for producing the positive electrode is not particularly limited. For example, three kinds of positive electrode active materials prepared in advance are mixed using a ball mill or the like, and the resulting mixture, a binder, and a conductive assistant are used as a paste using a solvent. It can be prepared by applying to a certain metal foil, drying, and adjusting thickness and porosity with a roll press. Moreover, after mixing three types of positive electrode active materials and a binder, a conductive support agent and a solvent can be added and it can be set as a paste. Furthermore, three kinds of positive electrode active materials and a conductive additive are mixed, a mixed solution of a binder and a solvent is separately prepared, and a mixture of the positive electrode active material and the conductive auxiliary is dispersed in the mixed solution. It can also be a paste.

  Carbon black, acetylene black, ketjen black, graphite and the like can be used as the conductive additive used in the positive electrode of the present invention, and a mixture of these may be used. As the conductive assistant, acetylene black is particularly preferable, but is not limited thereto. The weight ratio of the conductive auxiliary is suitably 3 to 5% by weight with respect to the positive electrode mixture weight (the total weight of the positive electrode active material, the conductive auxiliary and the binder).

  Examples of the binder used in the positive electrode of the present invention include polyvinylidene fluoride (PVdF), vinylidene fluoride (VdF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), styrene-butadiene rubber (SBR) and the like. A coalescence is used, including a mixture thereof. Polyvinylidene fluoride is particularly preferable, but is not limited thereto. The weight ratio of the binder is suitably 4 to 8% by weight with respect to the weight of the positive electrode mixture (the sum of the weights of the positive electrode active material, the conductive additive and the binder).

  When producing a positive electrode, a non-aqueous solvent or an aqueous solution can be used as a solvent used when mixing an active material, a binder, and a conductive additive, and N-methyl-2-pyrrolidone ( NMP), dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone (MEK), tetrahydrofuran (THF), and the like can be used. Moreover, you may add a dispersing agent, a thickener, etc. to these.

  As the negative electrode active material in the present invention, metallic lithium, a lithium alloy, or a carbon material capable of detaching and inserting lithium ions can be used. As the carbon material, artificial graphite having a high degree of crystallinity, natural graphite, low crystallinity soot graphitized carbon, non-graphitizable carbon, or the like is used alone or in combination.

  When producing a negative electrode, a negative electrode active material, a binder, and, in some cases, a conductive assistant are made into a paste using a solvent, and this paste is applied to a metal foil as a current collector, dried, and rolled. Can be produced by adjusting the thickness and porosity. As the binder used for the negative electrode, in addition to the same binder used for the positive electrode, carboxymethyl cellulose (CMC), carboxy-modified polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer may be used alone or in combination. it can. Moreover, as a solvent, the same solvent as used when mixing the positive electrode paste can be used, and a dispersant, a thickener, or the like may be added.

  As the current collector substrate of the electrode used in the present invention, iron, copper, nickel, stainless steel (SUS), or aluminum can be used. Examples of the shape include a sheet, a foam, a sintered porous body, and an expanded lattice.

  There is no restriction | limiting in particular as an organic solvent of the electrolyte solution used for this invention, A various material can be used suitably. For example, ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (γ-BL) are used as high dielectric constant solvents, and dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate are used as low viscosity solvents. (DEC) can be used alone or in admixture of two or more.

Moreover, there is no restriction | limiting in particular as a solute of the electrolyte solution used for this invention, A various solute can be used suitably. For example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , or the like can be used alone or in admixture of two or more. Of these, LiPF ₆ is preferably used because of its good ion conductivity. Furthermore, the lithium salt concentration is preferably 0.5 to 2.0 mol / dm ³ .

  In addition, vinylene carbonate (VC), biphenyl, propane sultone, or the like may be added to the electrolyte.

  There is no restriction | limiting in particular as a separator used for this invention, A various material can be used suitably. For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. Among these, polyolefin microporous membranes such as polyethylene and polypropylene microporous membranes, or microporous membranes composed of these are preferred in terms of thickness, membrane strength, membrane resistance, and the like.

  The shape of the battery of the present invention is not particularly limited, and the present invention is applied to non-aqueous electrolyte secondary batteries of various shapes such as a square, an ellipse, a cylinder, a coin, a button, and a sheet. Is possible.

[Examples 1-6 and Comparative Examples 1-10]
[Example 1]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the first active material, LiNi _0.8 Co _0.15 Al _0.05 O ₂ as the _second active material, and Li _1.1 Mn as the third active material A positive electrode active material mixed using _1.8 Al _0.1 O ₄ in a weight ratio of first active material: second active material: third active material = 40: 40: 20 was used. In addition, acetylene black (AB) was used as the conductive assistant, and polyvinylidene fluoride (PVdF) was used as the binder.

  91% by weight of the positive electrode active material, 3% by weight of AB, and 6% by weight of PVdF were mixed, and N-methyl-2-pyrrolidone (NMP) was added and kneaded to obtain a positive electrode mixture paste. This positive electrode mixture paste was applied to both surfaces of an aluminum foil current collector having a thickness of 20 μm, dried, rolled by a roll press, and a positive electrode plate was prepared by adjusting the thickness of the mixture layer. The obtained positive electrode plate had a width of 65 mm, a length of 2300 mm, and a thickness per one side of the mixture layer of 48 μm.

  92% by weight of graphite and 8% by weight of PVdF as a binder were mixed, and NMP was added and kneaded to obtain a negative electrode mixture paste. This negative electrode mixture paste was applied to both sides of a 15 μm thick copper foil current collector, dried and rolled, and a negative electrode plate was prepared by adjusting the thickness of the mixture layer. The obtained negative electrode plate had a width of 67 mm, a length of 2450 mm, and a thickness per one side of the mixture layer of 40 μm.

  Then, a power generation element is constructed by winding a separator between the positive electrode plate and the negative electrode plate, and after inserting this into the battery case and attaching the lid plate, a nonaqueous electrolyte is injected from the injection hole. Then, the opening was sealed by laser welding to produce a nonaqueous electrolyte secondary battery A of Example 1 having an initial discharge capacity of about 4.5 Ah.

A polyethylene microporous film was used as the separator. As the electrolytic solution, a nonaqueous electrolytic solution in which 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethylene carbonate in a volume ratio of 4: 4: 2 was used. .

  FIG. 1 is a cross-sectional view showing a configuration example of a nonaqueous electrolyte secondary battery according to the present invention. In FIG. 1, 1 is a non-aqueous electrolyte secondary battery (hereinafter simply referred to as “battery”), 2 is a power generation element, 3 is a negative electrode, 4 is a positive electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8 is a safety valve, 9 is a negative electrode terminal, and 10 is a negative electrode lead. The power generation element 2 is obtained by winding a positive electrode 4 and a negative electrode 3 in a flat shape with a separator 5 interposed therebetween. The power generating element 2 is housed in a rectangular battery case 6, and an opening of the battery case 6 is sealed by laser welding a battery lid 7 provided with a safety valve 8 and a negative electrode terminal 9. The negative electrode 3 is connected to the negative electrode terminal 9 via the negative electrode lead 10, and the positive electrode 4 is connected to the inner surface of the battery case 6.

[Example 2]
A battery B of Example 2 was fabricated in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 34:35:30 was used. did.

[Example 3]
A battery C of Example 3 was fabricated in the same manner as in Example 1 except that the positive electrode active material in which the first active material: second active material: third active material was mixed at a weight ratio of 50:30:20 was used. did.

[Example 4]
A battery D of Example 4 was produced in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 30:50:20 was used. did.

[Example 5]
The battery E of Example 5 was fabricated in the same manner as in Example 1 except that the positive electrode active material in which the first active material: second active material: third active material was mixed at a weight ratio of 40:30:30 was used. did.

[Example 6]
A battery F of Example 6 was fabricated in the same manner as in Example 1 except that the positive electrode active material in which the first active material: second active material: third active material was mixed at a weight ratio of 30:40:30 was used. did.

[Comparative Example 1]
A battery G of Comparative Example 1 was produced in the same manner as in Example 1 except that the first active material was used alone as the positive electrode active material.

[Comparative Example 2]
A battery H of Comparative Example 2 was produced in the same manner as in Example 1 except that the second active material was used alone as the positive electrode active material.

[Comparative Example 3]
A battery I of Comparative Example 3 was produced in the same manner as in Example 1 except that the third active material was used alone as the positive electrode active material.

[Comparative Example 4]
A battery J of Comparative Example 4 was produced in the same manner as in Example 1 except that the positive electrode active material in which the first active material: second active material was mixed at a weight ratio of 50:50 was used.

[Comparative Example 5]
A battery K of Comparative Example 5 was fabricated in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 45:45:10 was used. did.

[Comparative Example 6]
A battery L of Comparative Example 6 was produced in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 30:30:40 was used. did.

[Comparative Example 7]
A battery M of Comparative Example 7 was fabricated in the same manner as in Example 1 except that the positive electrode active material in which the first active material: second active material: third active material was mixed at a weight ratio of 10:40:50 was used. did.

[Comparative Example 8]
A battery N of Comparative Example 8 was fabricated in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 20:60:20 was used. did.

[Comparative Example 9]
A battery O of Comparative Example 9 was produced in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 50:20:30 was used. did.

[Comparative Example 10]
A battery P of Comparative Example 10 was produced in the same manner as in Example 1 except that a positive electrode active material in which a first active material: second active material: third active material was mixed at a weight ratio of 20:50:30 was used. did.

  The mixing ratios of the positive electrode active materials of the batteries A to P produced in Examples 1 to 6 and Comparative Examples 1 to 10 are summarized in Table 1.

[Characteristic measurement]
With respect to the batteries A to F of Examples 1 to 6 and the batteries G to P of Comparative Examples 1 to 10, float life characteristics were measured, and a nail penetration test and an overcharge test were performed. Each test condition was as follows.

(1) Float life characteristics After each battery was fabricated, it was charged to 4.1 V at 2 A constant current at 25 ° C., and further to 4.1 V constant voltage for a total of 5 hours, and then discharged to 2.75 V at 4 A constant current. The discharge capacity at this time was defined as “initial discharge capacity”. Next, each battery was put in a thermostat having a temperature of 45 ° C., and float charging at a charging voltage of 4.10 V was continued for 12 months. Thereafter, the battery was taken out from the thermostat, cooled to 25 ° C., and discharged to 2.75 V at a constant current of 4 A. The discharge capacity at this time was defined as “discharge capacity after float life test”. Then, “capacity retention” was obtained. The “capacity holding ratio” is the ratio (%) of “discharge capacity after float life test” to “initial discharge capacity”.

(2) Nail penetration test After making each battery, after charging to 4.1V at 2A constant current at 25 ° C, and further charging for 3 hours at 4.1V constant voltage, then the company) Japan Storage Battery Industry Association In accordance with the nail penetration test method described in “Guidelines for Safety Evaluation of Lithium Secondary Batteries (SBA G101)”, a nail penetration test is performed in which a nail with a diameter of 2.5 mm is inserted until it penetrates the battery. The state of was observed.

The results of the nail penetration test were classified into three ranks: “no change or valve operation”, “with smoke”, “with smoke and fire”. “No change or valve operation” indicates that the battery only generates heat or the safety valve is activated after nail penetration, and “Smoke generation” indicates that gas is emitted from the battery in addition to heat generation or leakage. Further, “with smoke and ignition” represents a state in which gas is ejected from the battery and a flame is emitted from the battery, and represents a dangerous state in this order.
(3) Overcharge test After each battery was manufactured, it was overcharged to 12 V at 4 A constant current at room temperature, and the state of the battery at that time was observed. As in the case of the nail penetration test, the overcharge test results were classified into three ranks: “no change or valve operation”, “with smoke”, and “with smoke and fire”.

  The test results are summarized in Table 2. In Table 2, the symbols ○ in the “nail penetration test” and “overcharge test” columns indicate “no change or valve operation”, “Δ” indicates “smoke”, and “x” indicates “smoke and fire”. Shall.

  From the results of Table 2, three types of positive electrode active materials were mixed, and in the batteries of Examples 1 to 6 in which the mixing ratio was within the scope of the present invention, the capacity retention rate of float life characteristics was excellent at 80% or more, The results of the nail penetration test and the overcharge test showed that there was no “smoke and fire”, and a highly safe battery was obtained.

  On the other hand, the batteries G to I of Comparative Examples 1 to 3 in the case where the positive electrode active material is alone, the battery J of Comparative Example 4 in which two types are mixed, and the comparative example in which three types are mixed but the mixing ratio is outside the scope of the present invention It was found that batteries K and MP of 5, 7 to 10 were “smoke and ignite” in at least one of the nail penetration test and the overcharge test, and the safety was low. In addition, although the battery L of Comparative Example 6 was excellent in safety, since the content of the third active material in the positive electrode active material is as large as 40% by weight, the capacity retention rate of the float life characteristics is similar to that of other batteries. It was small compared.

  Thus, in the non-aqueous electrolyte secondary battery, the positive electrode includes the first active material (lithium / nickel / cobalt / manganese composite oxide having space group R-3m) and the second active material (space group R-3m). A lithium / nickel / cobalt composite oxide) and a third active material (lithium / manganese composite oxide having a space group Fd-3m), and the content of the first active material in the positive electrode active material is 30 to 50 When the content of the second active material is 30 to 50% by weight and the content of the third active material is 20 to 35% by weight, the float life characteristics are excellent, the energy density is high, and the safety is ensured. It was found that a non-aqueous electrolyte secondary battery having excellent properties can be obtained.

Sectional drawing which shows the structural example of the nonaqueous electrolyte secondary battery which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Power generation element 3 Negative electrode 4 Positive electrode 5 Separator 6 Battery case 7 Battery lid 8 Safety valve 9 Negative electrode terminal 10 Negative electrode lead

Claims (2)

The positive electrode includes a first active material, a second active material, and a third active material, and the first active material has a space group R-3m, a lithium / nickel / cobalt / manganese composite oxide, and the second active material has a space. Lithium / nickel / cobalt composite oxide having group R-3m, the third active material is lithium / manganese composite oxide having space group Fd-3m, and the content of the first active material in the positive electrode active material 30 to 50% by weight, the content of the second active material is 30 to 50% by weight, and the content of the third active material is 20 to 35% by weight. The composition of the first active material is _{Li x Ni a Co b Mn c} M1 d O 2 ( however, 0.9 ≦ x ≦ 1.0,0.2 ≦ a ≦ 0.4,0.2 ≦ b ≦ 0. 4, 0.2 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.1, a + b + c + d = 1, M1 is at least one metal other than Ni, Co, and Mn), and the composition of the second active material is Li _y Ni _e Co _f M2 _g O ₂ (however, 0.9 ≦ y ≦ 1.0,0.7 ≦ e ≦ 0.9,0.1 ≦ f ≦ 0.2,0 ≦ g ≦ 0.1, e + f + g = 1, M2 is at least one metal other than Ni, Co, and Mn), and the composition of the third active material is Li _z Mn _h M3 _i O ₄ (where 0.9 ≦ z ≦ 1.0, 1.7 ≦ 2. The non-aqueous battery according to claim 1, wherein h ≦ 2.0, 0 ≦ i ≦ 0.2, z + h + i = 3, and M3 is at least one metal other than Ni, Co, and Mn. Quality secondary battery.

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