JP2001185143A - Secondary battery using non-aqueous electrolyte and its battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery using a non-aqueous electrolyte and having high capacity and high safety. SOLUTION: In using a positive electrode active material consisting of a mixture of a lithium nickel-based composite oxide and a lithium manganese double oxide for the battery using the non-aqueous electrolyte, part of the lithium nickel-based composite oxide is replaced with fluorine, boron or niobium. This obtains the positive electrode active material formed by uniformly mixing the two components with each other. In addition, safety is secured even if its capacity is increased increasing the ratio of the lithium nickel-based double oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved positive electrode material.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and VTRs have been reduced in size and demand has increased, there has been a demand for higher capacity secondary batteries which are power sources for these electronic devices. In addition, air pollution due to exhaust gas from automobiles has become a social problem, and it is expected that lightweight and high-performance secondary batteries will be used as power supplies for electric vehicles. As such a secondary battery, a nonaqueous electrolyte secondary battery in which a LiCoO ₂ positive electrode is combined with a carbon negative electrode has been developed and is currently used in large quantities.

However, LiCoO ₂ , which is a positive electrode material of the secondary battery, is expensive because it contains Co, and is limited in resources.
LiNi _1-x Co _x O ₂ in which a portion of the ₂ and Ni substituted with Co,
Alternatively, metal oxide compounds such as LiMn ₂ O ₄ have been proposed, and research is being actively conducted.

[0004] In particular, the positive electrode using the above-mentioned Ni-containing active material can increase the energy density as compared with the case where a conventional Co-based positive electrode material is used. The feature is that the cost can be reduced and the capacitance characteristics are improved. However,
Since Ni-based active materials are easily decomposed at high temperatures, if this is used as a positive electrode material, the battery temperature will rise if an external short circuit occurs due to external pressure or drop when the battery is in a charged state. When the electrode active material itself is decomposed, the electrode and the electrolyte react excessively, causing thermal runaway (generation of heat and release of gas), which may cause an explosion.

[0005] In order to compensate for the above drawbacks, there has been proposed a method using a mixture of two kinds of lithium manganese oxide which is not easily decomposed even at a high temperature and has high safety, with a Ni-based active material such as LiNiO ₂ . However, in order to ensure safety in this battery, the content of lithium manganese oxide in the mixture needs to be 25% or more,
Lithium manganese oxide can be used as the Co-based positive electrode active material or N
As compared with the i-type positive electrode active material, the discharge capacity is low and the bulk density is low. As a result, there is a problem that the energy density of the battery is significantly reduced. Further, a mixture of two Ni-based active materials in which a part of the Ni-based active material is substituted with Al or the like is also known (JP-A-10-92430), but it is still insufficient to satisfy safety and high capacity. there were.

[0006]

As described above, by mixing a nickel-based active material with lithium manganese oxide and lithium cobalt oxide, the safety of the positive electrode material can be improved. However, there is a problem that the energy density is lowered.

The present invention has been made in view of such a problem, and has as its object to provide a battery having a high energy density while improving the safety of a positive electrode material.

[0008]

A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode having an active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte sandwiched between both electrodes. In the nonaqueous electrolyte secondary battery provided, the positive electrode is a first positive electrode active material in which part of a lithium nickel composite oxide is replaced with at least one selected from the group consisting of boron, niobium, and fluorine, and a spinel-type positive electrode. A mixture with a second positive electrode active material made of lithium manganese oxide is provided.

The inventors of the present invention have made prototypes of batteries using a mixture of various lithium nickel oxides and lithium manganese oxides as a positive electrode material, and have compared the effects on battery characteristics. As a result, they have found that when a part of lithium nickel oxide is replaced by fluorine, boron or niobium, safety can be maintained even by adding a small amount of lithium manganese oxide. That is, by reducing the amount of lithium manganese oxide added, it has become possible to obtain a nonaqueous electrolyte secondary battery capable of maintaining safety even when the electrode capacity is increased.

The details of this reason are unknown, but
Probably, when the lithium nickel oxide substituted with the predetermined element is used, uniform mixing with the lithium manganese oxide becomes possible, and as a result, it is considered that this is related to the uniformity of the electrode. .

That is, if an internal short circuit of the battery simulated by a nail penetration test occurs at a portion where the electrodes are uneven and lithium nickel oxide is unevenly distributed, local heat generation is still large. It is not possible to completely avoid the possibility that the battery will rupture or ignite due to thermal runaway. In particular, when the content of lithium nickel oxide in the mixture increases, the tendency becomes remarkable. On the other hand, if the electrodes are uniform, even if an internal short circuit occurs in the battery, local heat generation is small, and the battery temperature drops before thermal runaway occurs.
Ignition can be avoided.

The first positive electrode active material is a lithium nickel composite oxide in which oxygen of the lithium nickel composite oxide is partially replaced with fluorine.

Specifically, the chemical formula Li _{1 + x} Ni _1-x-y C
o _y O _2-z F _z (where 0 <x ≦ 5, 0 ≦ y ≦ 0.5,
0 <z <2, (z + 0.05) / 2 ≦ x <(z + 1) /
3, and 0 <x + y ≦ 0.5).

When fluorine is added, the value of x is 0.1
As described above, that is, by making the lithium rich, the battery characteristics can be further improved. Even if part of nickel is partially replaced by cobalt or aluminum, there is no significant effect on its characteristics, and it is acceptable if y is 0.5 or less. In particular, when replacement with cobalt is performed, the charge / discharge efficiency is improved.

The first positive electrode active material may be one in which nickel is partially substituted with boron or niobium.

Specifically, the chemical formula Li _{1 + x} Ni _1-x-y C
_{o y M a O 2-z} F z ( provided that at least one of M is B or Nb, 0 ≦ x ≦ 5,0 < y ≦ 0.5,0 <a <0.
5, 0 ≦ z <2, and 0 <x + y + a ≦ 0.5).

That is, when the lithium nickel composite oxide is replaced with at least one of boron and niobium,
Ni will be replaced. In this system, it is not particularly necessary to make the lithium rich, but it is preferable to partially replace nickel with cobalt, and specifically, it is desirable that y is 0.1 or more. In addition, those in which part of cobalt is replaced by aluminum are also permitted.

It is desirable that the value of a be in the range of 0.01 or more and 0.1 or less. If it is less than 0.01, safety cannot be sufficiently improved, and if it exceeds 0.1, the capacity of the positive electrode may be reduced.

The assembled battery of the present invention comprises a nonaqueous electrolyte, a first positive electrode active material in which a lithium nickel composite oxide is partially substituted with at least one selected from the group consisting of boron, niobium and fluorine, and spinel. Material comprising a mixture containing a second positive electrode active material comprising lithium-manganese oxide, a cathode material comprising a mixture of spinel-type lithium manganese oxide, and an active material capable of absorbing and releasing lithium ions And a plurality of non-aqueous electrolyte secondary batteries each including a negative electrode comprising:

As described above, usually, when lithium nickel composite oxide and lithium manganese oxide are mixed,
Electrodes are likely to be non-uniform. In such a battery, the cycle deterioration rate varies for each battery. As a result, in the case of a battery pack with a plurality of these connected,
A battery that has undergone cycle deterioration enters an overdischarged state. When the battery is overdischarged, the voltage of the battery pack rapidly decreases, and it becomes impossible to operate a device including the battery. Further over-discharge causes problems such as liquid leakage and gas ejection. In the case of using the lithium nickel oxide, uniform mixing with the lithium manganese oxide becomes possible and the electrodes are made uniform, thereby preventing overdischarge of each unit cell in the assembled battery and avoiding the above-described problem. It is possible to do.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to the present invention will be described below with reference to FIG.

FIG. 1 is a schematic view of a cylindrical non-aqueous electrolyte secondary battery viewed from the side, and is a partial cross-sectional view showing a right half surface in a cross-sectional view.

An electrode group 2 is housed in a bottomed cylindrical container 1 also serving as a negative electrode terminal made of, for example, mild steel. The electrode group 2 is configured by spirally winding a laminate in which a positive electrode 3, a separator 4, a negative electrode 5, and a separator 4 are sequentially laminated.

The non-aqueous electrolyte is contained in the container 1. The positive electrode 3 has a structure in which a positive electrode mixture layer made of a positive electrode active material, a conductive agent, and a binder is formed on both surfaces of a positive electrode current collector. On the other hand, the negative electrode 5 has a negative electrode active material on both surfaces of a negative electrode current collector,
It has a structure in which a negative electrode mixture layer made of a conductive agent and a binder is formed. The negative electrode 5 is connected to the container 1 via a negative electrode lead 6. The power generating element is constituted by the electrode group 2 and the non-aqueous electrolyte.

The insulating plate 7 having an opening is placed above the electrode group 2 in the container 1.

A sealing body 11 made of, for example, mild steel and having a circular hole 8 in the center, a circular pressure release hole 9 at a position adjacent to the hole 8, and a liquid injection hole 10 is provided.
Is hermetically attached to the upper end opening by laser welding. For example, a positive electrode terminal 12 made of high chromium steel, a sealing body 11, and a circular hole 8 whose upper and lower ends are inserted so as to protrude from the lower surface of the sealing body 11, and a glass insulation filled in the forming hole 8. Hermetically sealed from the material 13. For example, a positive electrode lead 1 made of aluminum
4 has one end connected to the positive electrode 3 and the other end connected to the positive terminal 1
2 connected. For example, a circular pressure release valve 15 made of mild steel is hermetically attached to the lower surface of the sealing body 11 by laser welding so as to cover the pressure release hole 9. A V-shaped cut groove (not shown) is formed on the upper surface of the pressure release valve, and the groove portion is thinned by the cut groove. The pressure relief hole 9 of the sealing body 11 and the pressure relief valve 15 having the cut groove constitute a safety valve mechanism.

Next, the positive electrode 4, the negative electrode 6, and the non-aqueous electrolyte will be described.

1) Positive Electrode The positive electrode 4 contains a mixture of a first positive electrode active material and a second positive electrode active material.

The first positive electrode active material is a lithium-nickel composite oxide such as a lithium-nickel composite oxide or a composite oxide in which part of the lithium-nickel composite oxide is replaced with cobalt, and fluorine, boron or niobium. It has been replaced by at least one kind.

Specifically, the composition formula Li _{1 + x} Ni _1-x-y C
o _y O _2-z F _z (where 0 <x ≦ 5, 0 <y ≦ 0.5,
0 ≦ z, (z + 0.05) / 2 ≦ x <(z + 1) / 3,
And 0 <x + y ≦ 0.5) or the composition formula Li _{1 + x} N
_{i 1-x-y-a} Co y M a O 2-z ( provided that at least one of M is boron or niobium, 0 ≦ x ≦ 5,0 <a ≦ 0.
5, 0 ≦ z <2 and 0 <y + a ≦ 0.5).

A part of nickel may be replaced with cobalt. However, if the ratio of cobalt is high, that is, if y exceeds 0.5, there is a possibility that the capacity may be reduced. Further, it is desirable that the ratio of fluorine, that is, z be in the range of 0.05 ≦ Z ≦ 0.5. In the case of 0.05 or less, there is a possibility that the effect of substitution with fluorine may not be sufficiently obtained,
If it exceeds 0.5, the capacity may be reduced. In addition, when oxygen is replaced with fluorine, the capacity may be reduced. Therefore, it is desirable to increase the ratio of lithium according to the amount of added fluorine as in the relational expression between x and z.

A more specific example of the former composite oxide is L
i_1.075Ni_0.755Co_0.17O_1.9F_{0 .1 ,}Li_1.10Ni
_0.74Co_0.16O_1.85F_{0.15 ,}Li_1.075Ni_0.705Co
_0.17Al _0.05O_1.9F_{0.1 ,}Li_1.10Ni_0.72Co_0.16
Nb_0.02O_1.85F_{0.15 ,}And the like.

As the latter composite oxide, LiNi is used.
_0.795Co_0.175B_0.03O₂, LiNi _0.795Co_0.175
Nb_0.03O₂, LiNi_0.725Co_0.17Nb_0.02Al
_0.085O₂And the like.

As the spinel-type lithium manganese oxide as the second positive electrode active material, specifically, Li
_{1 + a} Mn _2-a O ₄ , Li _{1 + a} Mn _2-ab Co _b O ₄ ,
_{Li 1 + a Mn 2-ab} Al b O 4, Li 1 + a Mn 2-ab
_{Fe b O 4, Li 1 +} a Mn 2- ab Mg b O 4, Li
_{1 + a Mn 2-ab Ti} b O 4, Li 1 + a Mn 2-ab Nb
_b O ₄ , Li _{1 + a} Mn _2-ab Ge _b O _{4 and the} like (where a is 0 <a <0.1 and 2> a + b
Is shown).

The mixing ratio of the first positive electrode active material and the second positive electrode active material is preferably about 50:50 to 80:20. If the amount of the first positive electrode active material is too large, a problem may occur in terms of safety, and if the amount is too small, the battery capacity decreases.

The particle size of the first positive electrode active material is determined by a laser diffraction type particle size distribution meter (Microtrac HRA particle size distribution meter).
It is desirable that the value of the cumulative average diameter D _N50 is within the range of 5 μm to ₅₀ μm. The value of the accumulated average diameter D _M50 of the second cathode active material is preferably in the range of 1 to 30 [mu] m. If the ratio is out of this range, the homogeneity in the predetermined region is deteriorated, so that the advantage of using the mixture may be reduced.

The positive electrode 4 is produced by, for example, applying a positive electrode paste obtained by dispersing the mixture, a conductive agent and a binder in an appropriate solvent to one or both sides of a current collector. The coating amount per one side of the positive electrode layer is preferably in the range of 80 g / m ² to 300 g / m ² . With such a configuration, a non-aqueous electrolyte secondary battery having an excellent balance between safety and capacity characteristics and high output characteristics can be obtained. The weight per one side of the positive electrode layer is more preferably from 100 g / m ² to 20 g / m ^2.
0 g / m ² .

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

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene propylene, and an ethylene-propylene-silene copolymer. A polymer (EPDM) or the like can be used. Above all, polyvinylidene fluoride (PVdF) is preferable because of its excellent adhesion to the substrate and binding between active materials.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like are used. The compounding amount of the binder is in the range of 2% by weight to 20% by weight based on 100 parts by weight of the pre-distributed positive electrode active material (100 parts by weight in total when the conductive agent is included). Is preferred.

The amount of the conductive agent is determined by the amount of the positive electrode active material 1
It is preferable that the content is in the range of 0% by weight to 18% by weight based on 00 parts by weight. It is preferable that the compounding amount of the organic solvent is in a range of 65% by weight to 150% by weight based on 100 parts by weight of the positive electrode active material (100 parts by weight in total when the conductive agent is included). .

The current collector has a thickness of 15 μm to 3 μm.
Examples include 5 μm aluminum foil, aluminum mesh, aluminum punched metal, aluminum lath metal, stainless steel foil, titanium foil, and the like. 2) Negative electrode The negative electrode 6 is prepared by suspending and mixing a negative electrode mixture 5b composed of, for example, a negative electrode active material, a conductive agent and a binder in an appropriate solvent, and applying a coating solution to one or both surfaces of a current collector. And dried.

Examples of the negative electrode active material include those containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions, and those made of metal oxides and light metals. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material that occludes and releases lithium ions include coke, carbon fiber, pyrolysis gas phase carbonaceous material, graphite, fired resin, mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. Can be mentioned. Above all, mesophase pitch-based carbon fibers or mesophase spherical carbon graphitized at 2500 ° C. or higher are preferable because the electrode capacity is increased.

The chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiO ₂ ), molybdenum disulfide (MoS ₂ ), niobium selenide (NbSe ₂ ),
Tin oxide (SnO ₂ ) and the like can be given. When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode increases although the voltage of the secondary battery drops, and the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF),
Ethylene-propylene siene copolymer (EPDM), styrene butadiene rubber (SBR) and the like can be used.

The mixing ratio of the negative electrode material and the binder is preferably in the range of 80 to 98% by weight of the negative electrode material and 2 to 20% by weight of the binder. Particularly, in the state where the negative electrode 5 is manufactured, the carbon material is applied in an amount of 30 to 150 g per one surface.
/ M ² . More preferably, it is 60 to 100 g / m ² .

The current collector has a thickness of 10 μm to 3 μm.
5 μm copper foil, copper mesh, copper punched metal, copper lath metal, stainless steel foil, nickel foil and the like can be used.

As the separator 4, for example, a nonwoven fabric, a microporous polypropylene film, a microporous polyethylene film, a laminated microporous polyethylene-polypropylene film, a porous paper, or the like can be used. 3) Non-aqueous electrolyte The non-aqueous electrolyte according to the present invention has a composition in which an electrolyte is dissolved in a non-aqueous solvent. As the non-aqueous solvent, for example, propylene carbonate (PC), cyclic carbonate such as ethylene carbonate (EC), for example, dimethyl carbonate (DM
C), a chain carbonate such as methyl ethyl carbonate (MEC), diethyl carbonate (DEC), a chain ether such as 1,2-dimethoxy kun (DME), dutoxishkun (DEE), tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), etc.
Ter, fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), sulfolane
At least one selected from sulfur compounds such as (SL) and dimethyl sulfoxide (DMSO) can be used.

Among them, those composed of at least one selected from EC, PC and γ-BL, EC, PC and γ-B
L and at least one selected from L and DMC, MEC, DE
It is desirable to use a mixed solvent comprising at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN.

Further, the above-mentioned lithium ions are stored in the negative electrode.
When using a substance containing a carbonaceous substance to be released, from the viewpoint of improving the cycle life of the secondary battery including the negative electrode, EC, PC and γ-BL, EC and PC and MEC, EC
And PC and DEC, EC and PC and DEE, EC and AN, E
C and MEC, PC and DNC, PC and DEC, or EC
It is desirable to use a mixed solvent consisting of and DEC.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and arsenic hexafluoride (LiAs
F ₆ ), lithium lithium orolometasulfonate (LiCF ₃ S
O ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ )
₂ ] and the like. Among them, Li
It is preferable to use PF ₆ , LiBF ₄ , or LiN (CF ₃ SO ₂ ) ₂ because conductivity and safety are improved.

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 1.5 mol / L.

By adopting such a configuration, a non-aqueous electrolyte secondary battery having high safety and large energy capacity can be obtained. In addition, by connecting a plurality of such non-aqueous electrolyte secondary batteries, an assembled battery having an excellent balance between safety and capacity characteristics and excellent cycle life characteristics can be formed.

In the above-described embodiment, an example in which the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery has been described. The present invention can be similarly applied to an electrode group having a structure in which a laminate formed of a separator is flatly wound and a thin nonaqueous electrolyte secondary battery having a structure in which a nonaqueous electrolyte is housed.

[0057]

EXAMPLES Examples of the present invention will be specifically described below with reference to Tables 1 and 2.

<Preparation of Single Cell> Examples 1 to 3 Li _1.075 Ni _0.755 Co _0.17 as the first positive electrode active material
O _1.9 F _0.1 a _{(DN 50 = 7.5μm), Li} 1. 06 Mn as spinel-type manganese oxide of the second positive electrode active material
_1.94 O _{4 (} DM ₅₀ = 15 μm) was used.

First, the first positive electrode active material and the second positive electrode active material were mixed in a mixing ratio (weight ratio) shown in Table 1 using a planetary ball mill. To 100 parts by weight of the obtained mixture, 3 parts by weight of acetylene black as a conductive agent and 4 parts by weight of flake graphite (artificial graphite) were added and mixed again to prepare a positive electrode mixture. This positive electrode mixture was dispersed in a solution in which 5 parts by weight of polyvinylidene fluoride as a binder was dissolved in N-methyl-2-pyrrolidone to prepare a positive electrode material paste. This was applied to both sides of an aluminum foil as a current collector, dried, and roll-pressed to produce a positive electrode.

[Table 1] For each of the obtained positive electrodes, five arbitrary points were selected, mapping was performed by an X-ray microanalyzer (EPMA), and the distribution state of Ni and Mn was examined. As a result, Ni
Alternatively, no bias was observed in the peak intensity of Mn, and it was confirmed that the lithium nickel oxide and the spinel-type manganese oxide were uniformly distributed.

On the other hand, carbonaceous materials were produced by graphitizing mesophase pitch carbon fibers using mesophase pitch as a raw material.

Subsequently, a mixture of 5 parts by weight of graphite and 5 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the carbonaceous material was dispersed in N-methylpyrrolidone to form a paste, and then the current collector substrate was obtained. The coating was applied to both sides of the copper foil, dried, and roll-pressed to produce a negative electrode.

The positive electrode, the separator made of a porous film made of polyethylene, and the negative electrode were laminated in this order, and then spirally wound so that the negative electrode was located outside, thereby producing an electrode group.

As the electrolytic solution, a solution prepared by dissolving 1 M of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) was used. Then, the electrode group and the electrolytic solution were respectively housed in a stainless steel bottomed cylindrical container, and a cylindrical lithium ion secondary battery (φ
33 mm × 61 mm) were assembled in 20 pieces each.

Examples 4 to 6 First positive electrode active materials differing only in the amount of fluorine substitution from Example 1 (compositions are shown in Table 1) were prepared. These and the same spinel-type manganese oxide as in Example 1 were mixed using a planetary ball mill so that the mixing ratio (weight ratio) was 70:30.

Thereafter, in the same manner as in Example 1, 20 cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) were assembled.

Example 7 As the first positive electrode active material, Li _1.075 Ni _0.705 Co _0.17 A
1 _0.05 O _1.9 F _{0.1 (} DN ₅₀ = 10.5 μm) was used. This and the same spinel-type manganese oxide as in Example 1 were mixed at a compounding ratio (weight ratio) of 7 using a planetary ball mill.
The mixture was mixed at 0:30.

Thereafter, in the same manner as in Example 1, 20 cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) were assembled.

Examples 8 to 10 LiNi _0.795 Co _0.175 Nb was used as the first positive electrode active material.
_0.03 O _{2 (} DN ₅₀ = 14 μm) was used. This lithium nickel oxide and the same spinel-type manganese oxide as in Example 1 were mixed at the compounding ratio (weight ratio) shown in Table 1.

Hereinafter, cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) each having a size of 2
Assembled 0 pieces at a time.

Examples 11 to 12 A first positive electrode active material (composition shown in Table 1) was different from Example 8 only in the Nb substitution amount. These and Example 1
The same spinel-type manganese oxide as in Example 1 was mixed using a planetary ball mill so that the mixing ratio (weight ratio) was 70:30, to obtain a positive electrode active material.

Thereafter, in the same manner as in Example 1, 20 cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) were assembled.

Example 13 LiNi _0.725 Co _0.17 Nb was used as the first positive electrode active material.
_0.02 Al _0.085 O _{2 (} DN ₅₀ = 12 μm) was used. This was mixed with the same spinel-type manganese oxide as in Example 1 using a planetary ball mill so that the blending ratio (weight ratio) was 70:30, to obtain a positive electrode active material.

Thereafter, in the same manner as in Example 1, 20 cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) were assembled.

Example 14 As the first positive electrode active material, LiNi _0.795 Co _0.175 B
_0.03 O _{2 (} DN ₅₀ = 12 μm) was used. This was mixed with the same spinel-type manganese oxide as in Example 1 using a planetary ball mill so that the blending ratio (weight ratio) was 70:30, to obtain a positive electrode active material.

Thereafter, in the same manner as in Example 1, 20 cylindrical lithium ion secondary batteries (φ33 mm × 61 mm) were assembled.

Comparative Examples 1 to 3 LiNi _0.7 Co _0.3 O _{2 (} DN) was used as the first positive electrode active material.
_A positive electrode comprising a lithium-nickel composite oxide and a spinel manganese oxide was produced in the same manner as in Example 1 except that ₅₀ = 10 μm) was used.

With respect to each of the obtained positive electrodes, five arbitrary points were selected, mapping was performed using an X-ray microanalyzer (EPMA), and the distribution state of Ni and Mn was examined. As a result, in each case, a site where the peak of Mn was extremely deviated was observed, and it was confirmed that the peak was not uniform.

Using this electrode as a positive electrode, a cylindrical lithium ion secondary battery (φ33 mm ×
61 mm) were assembled.

<Evaluation of Capacity> First, a capacity confirmation test was carried out for each of the fabricated batteries of Examples 1 to 14 and Comparative Examples 1 to 3.

In the capacity confirmation test, charging was performed up to 4.2 V at 20 ° C. at 1/3 C (the current value when discharging the designed rated capacity in 1 hour was 1 C), and then constant at 4.2 V. The voltage was maintained for a total of 8 hours. The discharge was performed at a constant current of 1 / 5C, and the discharge end voltage was set to 2.7V. The rest time after charging and discharging was 30 minutes, respectively. The obtained discharge capacity was measured as a battery capacity, and is shown in Table 2.

[Table 2] <Safety test> Each battery was charged at a constant current of 1 / 3C until it reached 4.2 V, and then a nail penetration test was performed with the battery charged at a constant voltage for a total of 8 hours. Use a nail with a diameter of 5 mm, penetrate it from the side of the battery, operate the safety valve,
The occurrence rate of batteries in which abnormalities such as rupture and ignition were observed was examined, and the results are shown in Table 2.

As is clear from Table 2, in Examples 1 to 14, no abnormality such as operation of the safety valve, rupture or ignition was observed, and it was confirmed that the safety was excellent. Also, the battery capacity was 4 hours or more in each case, and it was confirmed that the battery was excellent in safety and excellent in capacity characteristics.
On the other hand, although the batteries of Comparative Examples 1 and 3 did not rupture or ignite, the operation of the safety valve was recognized, confirming that the safety was poor.

<Cycle Life Characteristics of Assembled Batteries> For each of the batteries of Examples 1 to 14 and Comparative Examples 1 to 3, capacity selection was performed, and four batteries were connected in series to form an assembled battery. Was prepared.

A cycle test was performed on the assembled battery. Charging is performed at a current value of 20 A at 20 ° C. and 4.2
After the voltage was increased to V, the voltage was maintained at a constant voltage of 4.2 V, and the operation was performed for a total of 5 hours. The discharge was performed at a constant current of 1 C, and the discharge end voltage was 2.7 V. The rest time after charging and discharging was 30 minutes, respectively. Such charge / discharge was repeated, and it was examined whether or not an abnormality such as a sudden voltage drop or a safety valve operation occurred.

As a result, in the assembled batteries of Comparative Examples 1 to 3, the above abnormalities were observed during the cycle test.

On the other hand, in Examples 1 to 14, no abnormality was observed.

[0086]

As described above, according to the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte secondary battery excellent in safety and excellent in capacity characteristics can be provided. Further, by connecting a plurality of such non-aqueous electrolyte secondary batteries, a battery pack having an excellent balance between safety and capacity characteristics can be formed. Therefore, it is extremely useful not only as a battery for portable equipment but also as a power supply for electric vehicles.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cylindrical non-aqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery container 2 ... Electrode group 3 ... Positive electrode 4 ... Separator 5 ... Negative electrode 6 ... Negative electrode lead 7 ... Insulating plate 8 ... Circular hole 9 ... Pressure Opening hole 10 ・ ・ ・ Injection hole 11 ・ ・ ・ Sealing body 12 ・ ・ ・ Positive electrode terminal 13 ・ ・ ・ Glass insulating material 14 ・ ・ ・ Positive electrode lead 15 ・ ・ ・ Pressure release valve

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideaki Morishima 1 Toshiba-cho, Komukai Toshiba-cho, Saitama-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Yoshinao Tatebayashi Toshiba Komukai-shi, Kawasaki-shi, Kanagawa No. 1 town, Toshiba R & D Center (72) Inventor Yuji Sato, No. 1 Komukai Toshiba Town, Sachi-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba R & D Center (72) Inventor Koichi Kubo, Kawasaki-shi, Kanagawa No. 1, Komukai Toshiba-cho, Ward, Tokyo Toshiba R & D Center (72) Inventor Hideyuki Kanai No. 1, Komukai Toshiba-cho, Kawasaki-shi, Kanagawa, Japan Toshiba R & D Center (72) Inventor Motoki Kanda Kanagawa F-term (reference) in the Toshiba R & D Center, 1st address, Komukai Toshiba-cho, Kawasaki-shi, Kawasaki 5H003 AA02 AA10 BA03 BB05 BC06 5H014 AA01 BB06 EE10 HH01 5H029 AJ03 AJ12 AK03 AL02 AL04 AL06 AL07 AL11 AL12 AM02 AM03 AM04 AM05 AM07 CJ08 DJ17 HJ02

Claims (6)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode having an active material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte sandwiched between both electrodes, wherein the positive electrode comprises lithium nickel Mixture of a first positive electrode active material in which a part of the base composite oxide is substituted with at least one selected from the group consisting of boron, niobium and fluorine, and a second positive electrode active material composed of a spinel-type lithium manganese oxide A non-aqueous electrolyte secondary battery comprising: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first positive electrode active material is a lithium nickel-based composite oxide in which a part of oxygen is replaced by fluorine. 3. The method according to claim 1, wherein the first positive electrode active material has a composition formula of Li _{1 + x}
Ni _1-xy Co _y O _2-z F _z (where 0 <x ≦ 5, 0 ≦
y ≦ 0.5, 0 <z, (z + 0.05) / 2 ≦ x <(z
3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the composite oxide is a composite oxide represented by (+1) / 3 and 0 <x + y ≦ 0.5). 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein said first positive electrode active material is obtained by partially replacing nickel with boron or niobium. 5. The method according to claim 1, wherein the first positive electrode active material has a composition formula Li _{1 + x
Ni 1-x-y-a} Co y M a O 2-z F z ( provided that at least one M is selected from boron or niobium, 0 ≦ x ≦ 0.
5, 0 <y ≦ 0.5, 0 <a ≦ 0.5, 0 ≦ z <2, 0
The non-aqueous electrolyte secondary battery according to claim 4, which is a composite oxide represented by (x + y + a≤0.5). 6. A non-aqueous electrolyte, a first positive electrode active material in which part of a lithium nickel composite oxide is substituted with at least one selected from boron or niobium, and a second positive electrode active material comprising a spinel lithium manganese oxide A plurality of non-aqueous liquids each including a positive electrode made of a mixture containing a positive electrode active material, a positive electrode made of a mixture of spinel-type lithium manganese oxide, and a negative electrode made of an active material capable of inserting and extracting lithium ions. An assembled battery in which electrolyte secondary batteries are connected in series.