JP2003346898A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of battery characteristics after stored under a high temperature. <P>SOLUTION: This nonaqueous electrolyte battery is provided with a positive electrode 5 having a positive electrode active material, a negative electrode 6 having a negative electrode active material, and nonaqueous electrolyte 4 including electrolytic salt. This battery is also characterized in employing a mixture between lithium/nickel complex oxide and lithium/manganese complex oxide for the positive electrode active material and including, at least, LiPF<SB>6</SB>and LiBF<SB>4</SB>for the electrolytic salt. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte and having significantly improved battery characteristics.

[0002]

2. Description of the Related Art In recent years, for example, notebook personal computers, portable telephones, camera-integrated VTRs
(Video tape recorder) and other electronic devices,
The development of lightweight and high energy density secondary batteries is under way. As a secondary battery having a high energy density, for example, there is a lithium ion secondary battery having a higher energy density than a lead battery, a nickel cadmium battery, a nickel metal hydride battery, or the like.

This lithium ion secondary battery uses a negative electrode active material such as a carbonaceous material capable of intercalating lithium ions between layers of a carbon material such as graphite for the negative electrode, and has a stable crystal structure for the positive electrode. And a positive electrode active material such as a lithium-cobalt composite oxide which can increase the battery capacity. In this lithium ion secondary battery, a battery reaction is performed by moving a lithium ion between a negative electrode and a positive electrode by a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent. However, in this lithium ion secondary battery, the lithium
Cobalt composite oxides have the problem of scarce cobalt resources.

In a lithium ion secondary battery, it is possible to use a lithium / nickel composite oxide instead of a lithium / cobalt composite oxide which is scarce in resources as a positive electrode active material. The lithium-nickel composite oxide has a larger battery capacity per unit volume than the lithium-cobalt composite oxide, so that a higher energy density can be obtained. However, the lithium-nickel composite oxide has a relatively unstable crystal structure, and may reduce battery safety.

[0005]

In order to solve the above problems, there has been proposed a lithium ion secondary battery using a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide as a positive electrode active material. . A lithium ion secondary battery using such a positive electrode active material can combine high energy density, which is an advantage of a lithium-nickel composite oxide, and high safety, which is an advantage of a lithium-manganese composite oxide. .

[0006] However, in this lithium ion secondary battery, when stored at a high temperature, a positive electrode having a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide as a positive electrode active material and a non-aqueous electrolyte solution are formed. The non-aqueous electrolyte is oxidatively decomposed and degraded due to the reaction, thereby deteriorating battery characteristics such as a decrease in battery capacity.

Accordingly, the present invention has been proposed in view of such conventional circumstances, and has as its object to provide a nonaqueous electrolyte battery in which deterioration of battery characteristics due to high-temperature storage is prevented.

[0008]

The non-aqueous electrolyte battery according to the present invention prevents deterioration of battery characteristics when stored at a high temperature by incorporating LiBF ₄ as an electrolyte salt in the non-aqueous electrolyte. .

That is, the non-aqueous electrolyte battery according to the present invention
Is a positive electrode active material capable of doping / dedoping lithium.
A positive electrode comprising a positive electrode mixture layer having
Equipped with a negative electrode mixture layer having a undoped negative electrode active material
A negative electrode and a non-aqueous electrolyte containing an electrolyte salt.
When the pole active material is lithium-nickel composite oxide or lithium
Manganese composite oxide, electrolyte salt,
LiPF₆And LiBF ₄At least
It is characterized by.

In this nonaqueous electrolyte battery, the positive electrode active material is
Titanium-nickel composite oxide and lithium-manganese composite
High energy density by using a mixture of oxides
LiP is used as an electrolyte salt while maintaining high safety.
F₆And LiBF₄To make LiPF
₆Efficiently transfer lithium ions, and LiBF ₄
Occurs when the positive electrode reacts with the nonaqueous electrolyte during high-temperature storage.
Reduces deterioration of water electrolyte.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte battery to which the present invention is applied will be described. FIG. 1 shows a configuration example of a lithium ion secondary battery (hereinafter, referred to as a battery) as the nonaqueous electrolyte battery. The battery 1 has a structure in which a battery element 2 serving as a power generation element is sealed inside a casing 3 together with a non-aqueous electrolyte 4.

The battery element 2 has a configuration in which a band-shaped positive electrode 5 and a band-shaped negative electrode 6 are wound in close contact with a separator 7 interposed therebetween.

In the positive electrode 5, a positive electrode mixture layer 9 containing a positive electrode active material is formed on a positive electrode current collector 8. A positive electrode terminal 10 is connected to the positive electrode 5 at a predetermined position on the positive electrode current collector 8 so as to protrude from one end in the width direction of the positive electrode current collector 8. For the positive electrode terminal 10, for example, a strip-shaped metal piece made of aluminum or the like is used.

For the positive electrode 5, a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide is used as a positive electrode active material. Specifically, for example, LiNi
O ₂ , Li _x Ni _y Co _1-y O ₂ (x and y vary depending on the charge / discharge state of the battery, and usually 0 <x <1, 0.7 <y
<1.02. ), Li _x Ni _1-y M _y O
₂ (x and y vary depending on the charge / discharge state of the battery and are usually 0
<X <1, 0.7 <y <1.02, and M is at least one of transition metals. ) And LiMn ₂ O ₄ , L
ixMn2-yM'yO4 (x is 0.9 or more, y is 0 or more and 0.5 or less, and M 'is Fe, Co, Ni, C
u, Zn, Al, Sn, Cr, V, Ti, Mg, Ca,
One or more of Sr, B, Ga, In, Si, and Ge. A mixture with a spinel-type lithium-manganese composite oxide represented by the chemical formula (1) is used.

In the positive electrode 5, the above-mentioned lithium
In a mixture of a nickel composite oxide and a lithium-manganese composite oxide, for example, LiCoO ₂ , Li _x MO ₂ (x is 0.5 or more and 1.1 or less, M is Ni, Mn
At least one of transition metals other than. ) And the like can be contained.

In the positive electrode 5, for example, net-like or foil-like aluminum or the like is used as the positive electrode current collector 8. Positive electrode 5
In the above, as a binder contained in the positive electrode mixture layer 9,
A well-known resin material usually used for this type of nonaqueous electrolyte battery can be used. Specifically, as the binder, for example, polyvinylidene fluoride and the like can be mentioned. Also,
In the positive electrode 5, as the conductive material contained in the positive electrode mixture layer 9, a known material generally used in this type of nonaqueous electrolyte battery can be used. Specifically, examples of the conductive material include carbon black and graphite.

In this positive electrode 5, a lithium-nickel composite oxide and a lithium-manganese composite oxide are used as a positive electrode active material, so that a lithium-nickel composite oxide having a large lithium doping amount improves the battery capacity. At the same time, it acts to suppress generation of acid in the non-aqueous electrolyte 4. In the positive electrode 5, the lithium-manganese composite oxide has a relatively stable crystal structure, so that the safety is improved, and the oxidation reaction of the nonaqueous electrolyte 4 is reduced to thereby reduce the nonaqueous electrolyte. 4 so as to suppress deterioration.

In the negative electrode 6, a negative electrode mixture layer 12 containing a negative electrode active material is formed on a negative electrode current collector 11. Negative electrode 6
The negative electrode terminal 13 is at a predetermined position of the negative electrode current collector 10,
The negative electrode current collector 10 is connected so as to protrude from one end in the width direction. For the negative electrode terminal 13, a strip-shaped metal piece made of, for example, copper or nickel is used.

In the negative electrode 6, the negative electrode active material is a material capable of doping / dedoping lithium, such as a metal capable of forming an alloy with lithium or a compound of this metal. Specifically, for example, chemical formula _{D s E} t _Li u (D is at least one metallic element capable compound with lithium and / or semiconductor elements, E is one metal element other than lithium and D and / or a semiconductor element That is, s is larger than 0, and t and u are 0 or larger.)
SiB 4, SiB ₆ ,
Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , M
_{oSi 2, CoSi 2, NiSi 2} , CaSi 2, Cr
Si ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbS
_{i 2, TaSi 2, VSi 2} , WSi 2, ZnSi 2 , etc., using any one or more of them.

In the negative electrode 6, for example, a carbonaceous material capable of doping / dedoping lithium ions can be used in addition to the above-mentioned compounds. Examples of the carbonaceous material include graphites such as artificial graphite and natural graphite, non-graphitizable carbon, pyrolytic carbons, cokes, glassy carbon fibers,
Examples include an organic polymer compound fired body, carbon fiber, activated carbon, carbon blacks and the like, and any one or more of these are used. Further, among these carbonaceous materials, cokes include, for example, pitch coke, needle coke, petroleum coke, and the like, and an organic polymer compound fired body refers to a polymer material such as a phenol resin or a furan resin at a predetermined temperature. And carbonized. These carbonaceous materials can be used as a mixture of one or more of the above compounds. In this case, the carbonaceous material also functions as a conductive material.

In the negative electrode 6, in addition to the above-mentioned compounds and carbonaceous materials, as the negative electrode active material, for example, polymers such as polyacetylene and polypyrrole, and oxides such as iron oxide, ruthenium oxide, molybdenum oxide and tin oxide. It is also possible to use

In the negative electrode 6, for example, net-like or foil-like copper is used as the negative electrode current collector 11. In the negative electrode 6, as the binder contained in the negative electrode mixture layer 12, a known resin material generally used for this type of nonaqueous electrolyte battery can be used. Specifically, as the binder, for example, polyvinylidene fluoride and the like can be mentioned.

In the battery element 2, the separator 7 separates the positive electrode 5 and the negative electrode 6 from each other, and uses a known material that is generally used as an insulating porous film of this type of nonaqueous electrolyte battery. Can be. Specifically, for example, a polymer film such as polypropylene or polyethylene is used. Further, from the relationship between the lithium ion conductivity and the energy density, it is preferable that the thickness of the separator 7 is as thin as possible, and the thickness of the separator 7 is set to 30 μm or less.

The outer can 3 is, for example, a cylindrical container having a bottom.
The bottom surface has a rectangular shape and a flat circular shape. In addition, exterior can 3
Is formed of a conductive metal such as iron, stainless steel, nickel or the like when conducting with the negative electrode 6. Outer can 3
For example, when is formed of iron or the like, its surface is subjected to nickel plating or the like.

As the non-aqueous electrolyte 4, for example, a solution in which an electrolyte salt is dissolved in a non-aqueous solvent or the like is used. As the non-aqueous solvent, for example, a cyclic carbonate compound, a cyclic carbonate compound in which hydrogen is substituted with a halogen group or a halogenated acryl group, a chain carbonate compound, or the like is used. Specifically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3 -Dioxolane, 4 methyl 1,3 dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile,
Examples thereof include propionitrile, anisole, acetate, butyrate, and propionate, and any one or more of these are used. In particular, propylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and dipropyl carbonate are used as the non-aqueous solvent from the viewpoint of voltage stability.

In the non-aqueous electrolyte 4, at least LiPF ₆ and LiBF ₄ are mixed and used as the electrolyte salt. Thus, in the battery 1, LiPF ₆ is used as the electrolyte salt.
By containing LiBF ₄ and LiBF ₄ , LiPF ₆ having high ion conductivity acts to transfer lithium ions properly and acts to obtain a high battery capacity. In the battery 1, the LiBF ₄ contained in the electrolyte salt is prevented from decomposing due to the reaction between the positive electrode 5 and the non-aqueous electrolyte 4 when the battery is stored at a high temperature. It acts to prevent the capacity from decreasing.

In the non-aqueous electrolyte 4, the above-described LiP
F₆And LiBF₄In addition, as an electrolyte salt, for example, Li
ClO₄, LiAsF₆, LiB (C₆H₅)₄, Li
CF ₃SO₃, LiCH₃SO₃, LiN (CF₃SO
₂)₂, LiSbF₆, LiClO₄, LiCl, Li
Br or the like.
PF₆And LiBF₄Can also be used by mixing
You.

The non-aqueous electrolyte 4 contains LiBF ₄ as an electrolyte salt in a range of 0.01 mol / L or more and 0.1 mol / L or less. When LiBF ₄ is contained in the non-aqueous electrolyte 4 in an amount of less than 0.01 mol / liter, the battery 1 contains too little LiBF ₄ in the non-aqueous electrolyte 4, and thus is stored at a high temperature. It is difficult to suppress the decomposition of the non-aqueous electrolyte 4. On the other hand, LiBF ₄ was added to the non-aqueous electrolyte 4 in an amount of 0.1.
When the content is more than 1 mol / liter, in the battery 1, the LiBF ₄ contained in the nonaqueous electrolyte ₄ is too large,
During charging and storage at high temperatures, a film of the boron compound is formed on the surface of the negative electrode 6. For this reason, in the battery 1, the negative electrode 6
Since the boron compound film formed on the surface hinders the movement of lithium ions, the battery characteristics deteriorate, such as a decrease in battery capacity.

Therefore, in the battery 1, LiBF ₄ is added to the non-aqueous electrolyte _{4 in an amount} of not less than 0.01 mol / liter and 0.1 mol / L.
By being contained in a range of 1 mol / liter or less,
Decomposition of the non-aqueous electrolyte 4 during storage at a high temperature can be suppressed, and the formation of a boron compound film on the surface of the negative electrode 6 can be prevented.

The battery 1 configured as described above is manufactured as follows. First, the positive electrode 5 is manufactured. When preparing the positive electrode 5, a positive electrode mixture coating liquid containing a positive electrode active material containing at least a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide, a conductive material, and a binder is prepared. Then, the positive electrode mixture coating liquid is uniformly applied on both main surfaces of a positive electrode current collector 8 made of, for example, aluminum foil, dried, and then compressed to form a positive electrode mixture layer 9. The positive electrode terminal 10 is cut into dimensions and attached to a predetermined position by, for example, ultrasonic welding. Thus, the long positive electrode 5 is manufactured.

Next, the negative electrode 6 is manufactured. When producing the negative electrode 6, a negative electrode mixture coating liquid containing a negative electrode active material and a binder is prepared, and the negative electrode mixture coating liquid is coated on both main surfaces of the negative electrode current collector 11 made of, for example, copper foil or the like. After applying evenly on top and drying,
The negative electrode mixture layer 12 is formed by compression, cut into a predetermined size, and the negative electrode terminal 13 is attached to a predetermined position by, for example, ultrasonic welding or the like. Thus, the long negative electrode 6 is manufactured.

Next, the positive electrode 5 and the negative electrode 6 obtained as described above are laminated with a long separator 7 interposed therebetween, and the battery element 2 is manufactured by winding many times. At this time, the battery element 2 has a configuration in which the positive electrode terminal 10 protrudes from one end surface in the width direction of the separator 8 and the negative electrode terminal 13 protrudes from the other end surface.

Next, the insulating plates 14 are provided on both end faces of the battery element 2.
a and 14b are installed, and the battery element 2 is housed in an iron outer can 3 having nickel plating or the like on the inside. Then, in order to collect the current of the negative electrode 6, the portion of the negative electrode terminal 13 protruding from the battery element 2 is welded to the bottom of the outer can 3 or the like. Thus, the outer can 3 is electrically connected to the negative electrode 6 and serves as an external negative electrode of the battery 1. Further, in order to collect the current of the positive electrode 5, a portion of the positive electrode terminal 10 protruding from the battery element 2 is welded to the current interrupting thin plate 15 to electrically connect with the battery lid 16 via the current interrupting thin plate 15. Connect to The current interrupting thin plate 15 interrupts the current in accordance with the internal pressure of the battery. As a result, the battery lid 16 conducts the positive electrode 5 and becomes an external positive electrode of the battery 1.

Next, the nonaqueous electrolytic solution 4 is injected into the outer can 3 containing the battery element 2. This non-aqueous electrolyte 4
Is prepared by dissolving an electrolyte salt containing at least LiPF ₆ and LiBF ₄ in a non-aqueous solvent. Next, the battery cover 16 is fixed by caulking the opening of the outer can 3 via the insulating gasket 17 coated with asphalt, and the cylindrical battery 1 is manufactured.

In this battery 1, the battery element 2
A center pin 18 serving as a shaft or the like when winding the battery is provided, and a safety valve 19 for releasing gas inside the battery when the pressure inside the battery becomes higher than a predetermined value, and a temperature rise inside the battery. PTC (positive t) to prevent
An emperature coefficient (element) 20 is provided.

In the battery 1 manufactured as described above, lithium-nickel composite oxide and lithium-nickel
By using the mixture with the manganese composite oxide, the lithium-nickel composite oxide in the mixture increases the battery capacity and further suppresses the generation of acid in the non-aqueous electrolyte 4. Deterioration of composite oxide due to high temperature storage is suppressed. In addition, in the battery 1, the lithium-manganese composite oxide having a stable crystal structure used for the positive electrode active material improves safety and reduces the oxidation reaction of the non-aqueous electrolyte 4 to reduce the non-aqueous electrolyte 4. Control the deterioration of
Suppress deterioration of battery characteristics.

In this battery 1, LiBF was used as the electrolyte salt.
₄ since the positive electrode 5 and the non-aqueous electrolyte solution 4 at a high temperature storage by containing the suppressed degradation of the non-aqueous electrolyte solution 4 which occurs in response was excellent with no reduction of the battery capacity when it is high-temperature storage High temperature storage characteristics can be obtained.

Therefore, the battery 1 has high energy density, high safety, and excellent high-temperature storage characteristics. In the above example, the battery 1 using the non-aqueous electrolyte 4 is described. However, the present invention is not limited to this, and instead of the non-aqueous electrolyte 4, for example, a solid polymer electrolyte, a gel electrolyte, or the like is used. The present invention is also applicable to a non-aqueous electrolyte battery using the solid electrolyte.

The solid polymer electrolyte comprises, for example, the above-mentioned electrolyte salt containing at least LiPF ₆ and LiBF ₄ , and a polymer compound which is imparted with ionic conductivity by containing this electrolyte salt. As the polymer compound used for the polymer solid electrolyte, for example, silicon, polyether-modified siloxane, polyacryl, polyacrylonitrile,
Acrylonitrile-butadiene rubber, polyacrylonitrile-butadiene styrene rubber, acrylonitrile-chloride polyethylene-propylene-diene-styrene resin, acrylonitrile-chloride Vinyl resin, acrylonitrile-methacrylate resin,
An ether-based polymer such as an acrylonitrile-acrylate resin and a crosslinked product of polyethylene oxide may be used, and any one or a mixture of these may be used.

As the polymer compound used for the polymer solid electrolyte, for example, acrylonitrile, vinyl acetate, methyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, itaconic acid, methyl acrylate, hydroxide A copolymer obtained by copolymerizing any one or more of ethyl acrylate, acrylamide, vinyl chloride, and vinylidene fluoride; poly (vinylidene fluoride); poly (vinylidene fluoride-co-hexafluoropropylene); Fluorinated polymers such as (vinylidenefluoride-co-tetrafluoroethylene) and poly (vinylidenefluoride-co-trifluoroethylene) are also included, and any one or a mixture of these may be used.

The gel electrolyte is composed of the nonaqueous electrolyte 4 described above.
And a matrix polymer that absorbs and gels the non-aqueous electrolyte 4. As the matrix polymer used for the gel electrolyte, for example, among the above-mentioned polymer compounds, any of the above-mentioned polymer compounds that absorb the non-aqueous electrolyte solution 4 to be gelled can be used. Specifically, examples of the matrix polymer include fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene), and ethers such as poly (ethylene oxide) and cross-linked products thereof. And high-molecular-weight polymers, poly (acrylonitrile) and the like, and any one or a mixture of these may be used. In particular, it is preferable to use a fluoropolymer having good oxidation-reduction stability as the matrix polymer.

In the above-described embodiment, the cylindrical battery 1 has been described as an example. However, the present invention is not limited to this. For example, coin type, square type, button type, etc.
The present invention is also applicable to nonaqueous electrolyte batteries having various shapes and sizes, such as a battery using a metal container or the like as an exterior material, a thin type, or a battery using a laminate film or the like as an exterior material.

[0043]

EXAMPLES Examples and comparative examples in which a lithium ion secondary battery was actually manufactured as a nonaqueous electrolyte battery to which the present invention was applied will be described.

Example 1 In Example 1, first, a positive electrode was manufactured. When producing the positive electrode, a mixture was obtained by mixing 60 parts by weight of the lithium-nickel composite oxide and 40 overlapping parts of the lithium-manganese composite oxide. And
The mixture obtained as described above was used as a positive electrode active material in 9
2 parts by weight, 5 parts by weight of graphite as a conductive material,
3 parts by weight of polyvinylidene fluoride (hereinafter, referred to as PVdF) as a binder were uniformly dispersed in N-methyl-2-pyrrolidone (hereinafter, referred to as NMP) to prepare a positive electrode mixture coating solution. . Next, this positive electrode mixture coating liquid is uniformly applied on a 20 μm-thick aluminum foil serving as a positive electrode current collector, dried, and then compressed by a roll press to form a positive electrode mixture layer, and a predetermined size is formed. A positive electrode terminal made of aluminum was attached to the positive electrode current collector by ultrasonic welding. Thus, a long positive electrode was produced.

Next, a negative electrode was manufactured. When preparing the negative electrode, 92 parts by weight of graphite as a negative electrode active material and 8 parts by weight of PVdF as a binder were uniformly dispersed in NMP to prepare a negative electrode mixture coating liquid. Then, the negative electrode mixture coating liquid is uniformly applied on a 15 μm-thick copper foil serving as a negative electrode current collector, dried, and then compressed by a roll press to form a negative electrode mixture layer and cut into predetermined dimensions. Then, a negative electrode terminal made of nickel was attached to the negative electrode current collector by ultrasonic welding. Thus, a long negative electrode was produced.

Next, to produce a battery element, a laminate was formed between the positive electrode and the negative electrode obtained as described above, with a separator made of a porous polyethylene film having a thickness of 25 μm interposed therebetween. It was wound many times. Thus, a battery element was manufactured. At this time, the positive electrode terminal was led out from one end face of the obtained battery element, and the negative electrode terminal was led out from the other end face.

Next, the positive electrode terminal derived from the produced battery element was welded to a battery lid, the negative electrode terminal was welded to an outer can having nickel plating on iron, and the battery element was housed in the outer can.

Next, a mixed solvent of ethylene carbonate, propylene carbonate, and dimethyl carbonate in a volume mixing ratio of 1: 2: 7 was added with 1.2 mol / liter of LiPF ₆ as an electrolyte salt. Thus, a non-aqueous electrolyte solution was prepared. Further, in this non-aqueous electrolyte, LiBF ₄ was dissolved as an electrolyte salt so as to contain 0.01 mol / L.

Next, LiPF ₆ and LiPF _{6 were used} as electrolyte salts.
A non-aqueous electrolyte containing BF ₄ is injected into the outer can, and the battery lid is pressed into the opening of the outer can via an asphalt-coated insulating gasket and the opening of the outer can is swaged to form a battery cover. Was firmly fixed.

As described above, φ18 mm, height 65 m
m of a cylindrical lithium-ion secondary battery. In the following description, a lithium ion secondary battery is simply referred to as a battery for convenience.

[0051] <Example 2> In Example 2, the non-aqueous electrolyte, except that LiBF ₄ was allowed to contain 0.05 mol / l, the battery was fabricated in the same manner as in Example 1.

Example 3 In Example 3, a battery was fabricated in the same manner as in Example 1 except that the nonaqueous electrolyte contained 0.1 mol / L of LiBF ₄ .

Example 4 In Example 4, when manufacturing a positive electrode, 90 parts by weight of a lithium-nickel composite oxide and 1 part of a lithium-manganese composite oxide were used as a positive electrode active material.
A positive electrode was manufactured using a mixture obtained by mixing the superposed portion with the zero overlapping portion. Then, a battery was fabricated in the same manner as in Example 2 except that this positive electrode was used.

Example 5 In Example 5, when preparing a positive electrode, 10 parts by weight of a lithium-nickel composite oxide and 9 parts of a lithium-manganese composite oxide were used as a positive electrode active material.
A positive electrode was manufactured using a mixture obtained by mixing the superposed portion with the zero overlapping portion. Then, a battery was fabricated in the same manner as in Example 2 except that this positive electrode was used.

Comparative Example 1 In Comparative Example 1, a battery was manufactured in the same manner as in Example 1 except that LiBF ₄ was not contained in the nonaqueous electrolyte.

Comparative Example 2 In Comparative Example 2, a battery was produced in the same manner as in Example 1 except that the nonaqueous electrolyte contained 0.15 mol / L of LiBF ₄ .

Comparative Example 3 In Comparative Example 3, a positive electrode was prepared using only a lithium-nickel composite oxide as a positive electrode active material when preparing a positive electrode. Then, a battery was fabricated in the same manner as in Example 2 except that this positive electrode was used.

Comparative Example 4 In Comparative Example 4, a positive electrode was produced using only a lithium-manganese composite oxide as a positive electrode active material when producing a positive electrode. Then, a battery was fabricated in the same manner as in Example 2 except that this positive electrode was used.

Then, Examples 1 to 5 produced as described above were used.
With respect to the batteries of Example 5 and Comparative Examples 1 to 4, the discharge capacity retention ratio after high-temperature storage was measured.

Table 1 shows the evaluation results of the discharge capacity retention ratio after high-temperature storage in each of Examples and Comparative Examples.

[0061]

[Table 1]

In each of the examples and comparative examples, the discharge capacity retention rate after high-temperature storage was measured as follows. When measuring the discharge capacity retention rate after high-temperature storage in each of the examples and comparative examples, the batteries of each example and each comparative example were subjected to a constant current constant of 1 C and an upper limit voltage of 4.2 V in a 23 ° C. atmosphere. After performing voltage charging for 2.5 hours, in an atmosphere at 23 ° C.,
A constant current discharge up to 3 V was performed at a current value of 1 C, and an initial discharge capacity was measured. Next, the batteries of each of the examples and the comparative examples were stored in an atmosphere at 85 ° C. for 40 hours, then charged and discharged under the same conditions as the initial charge and discharge, and the discharge capacity after high-temperature storage was measured. The discharge capacity retention rate after high temperature storage is the ratio of the discharge capacity after high temperature storage to the initial discharge capacity measured as described above.

From the evaluation results shown in Table 1, the non-aqueous electrolyte
iBF ₄ is not less than 0.01 mol / l and 0.1 mol /
It can be seen that in Examples 1 to _{3 in} which the content was not more than 1 liter, the discharge capacity retention rate after high-temperature storage was larger than that in Comparative Example 1 in which LiBF ₄ was not contained in the nonaqueous electrolyte. .

In Comparative Example 1, since LiBF ₄ was not contained in the non-aqueous electrolyte, the positive electrode and the non-aqueous electrolyte reacted during storage at a high temperature, whereby the non-aqueous electrolyte was decomposed, and the non-aqueous electrolyte was decomposed. Is deteriorated, so that the battery capacity after high-temperature storage is reduced.

From the evaluation results shown in Table 1, it was found that LiBF ₄ was added to the non-aqueous electrolyte at a concentration of 0.01 mol / L or more and 0.1 mol / L or more.
In Examples 1 to 3 in which the content was not more than mol / liter, the discharge capacity retention ratio after high-temperature storage was higher than that in Comparative Example 2 in which the nonaqueous electrolyte contained 0.15 mol / liter of LiBF _4. Is larger.

In Comparative Example 2, the amount of L contained in the nonaqueous electrolyte was
When the amount of iBF ₄ is too large, the boron compound is formed as a film on the surface of the negative electrode during charge / discharge and storage at a high temperature. Accordingly, in Comparative Example 2, the film of the boron compound formed on the negative electrode surface hinders the movement of lithium ions, so that the battery capacity after high-temperature storage is reduced.

In contrast to these comparative examples, in Examples 1 to 3, LiBF ₄ contained in the nonaqueous electrolyte was 0.01%.
Mol / l or more and 0.1 mol / l or less, and since the content of LiBF ₄ is appropriate, the decomposition of the non-aqueous electrolyte during high-temperature storage is suppressed, and the boron compound Can be prevented from being formed. Therefore, in Examples 1 to 3, it is prevented that the battery capacity after high-temperature storage is reduced, and the discharge capacity retention rate after high-temperature storage is increased.

From the above, when manufacturing a battery, LiBF ₄ was added to the non-aqueous electrolyte at 0.01 mol / L or more.
To be contained in a range of 0.1 mol / liter or less,
It can be seen that it is very effective in producing an excellent battery in which a decrease in battery capacity after storage at a high temperature is prevented.

Further, from the evaluation results shown in Table 1, it can be seen from Examples 1 to 5 that a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide was used as the positive electrode active material.
It can be seen that, in Comparative Example 3, the discharge capacity retention rate after high-temperature storage was larger than that in Comparative Example 3 in which only the lithium-nickel composite oxide was used as the positive electrode active material.

In Comparative Example 3, although the lithium-nickel composite oxide used as the positive electrode active material increased the battery capacity,
In the charged state, the reactivity with the non-aqueous electrolyte is high, and the capacity after high-temperature storage decreases due to the oxidative decomposition of the non-aqueous electrolyte.

Further, from the evaluation results shown in Table 1, the lithium-nickel composite oxide and lithium
In Examples 1 to 5 using a mixture with a manganese composite oxide, the discharge capacity retention ratio after high-temperature storage was increased as compared with Comparative Example 4 in which the positive electrode active material was only lithium-manganese composite oxide. I understand that

In Comparative Example 4, although the lithium-manganese composite oxide used as the positive electrode active material had relatively low reactivity with the nonaqueous electrolyte, it was affected by the acid contained in the nonaqueous electrolyte during high-temperature storage. The valence of Mn tends to change, and the battery capacity after high-temperature storage decreases.

In contrast to these comparative examples, in Examples 1 to 5, in the mixture of the lithium-nickel composite oxide and the lithium-manganese composite oxide used for the positive electrode active material, the lithium-nickel composite oxide was used. Increases the battery capacity and further suppresses the generation of acid in the non-aqueous electrolyte, thereby suppressing deterioration of the lithium-manganese composite oxide due to high-temperature storage. In Examples 1 to 5, the lithium-manganese composite oxide used for the positive electrode active material reduces the oxidation reaction of the electrolyte. Thereby, in Examples 1 to 5,
The battery capacity after high-temperature storage is prevented from lowering, and the discharge capacity retention rate after high-temperature storage is increased.

As described above, when a battery is manufactured, the use of a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide as a positive electrode active material can reduce the battery capacity after high-temperature storage. It can be seen that the method is very effective in producing an excellent battery in which the occurrence of odor is prevented.

[0075]

As is apparent from the above description, according to the present invention, by using a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide as the positive electrode active material, high energy density and high safety can be obtained. While the nature is being planned,
By including LiBF _{4 in the} electrolyte salt, it is possible to suppress the non-aqueous electrolyte from deteriorating due to the reaction between the positive electrode and the non-aqueous electrolyte during high-temperature storage. Therefore, according to the present invention, it is possible to obtain a non-aqueous electrolyte battery having both high energy density, high safety, and excellent high-temperature storage characteristics without deterioration in battery characteristics due to high-temperature storage.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an internal structure of a lithium ion secondary battery according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 lithium ion secondary battery, 2 battery element, 3 outer can, 4 nonaqueous electrolyte, 5 positive electrode, 6 negative electrode, 7 separator, 8 positive electrode current collector, 9 positive electrode mixture layer, 10 positive electrode terminal, 11 negative electrode current collector Body, 12 negative electrode mixture layer, 13 negative electrode terminal, 14a, 14b insulating plate, 15 current cut-off thin plate, 16 battery cover, 17 insulating gasket, 18 center pin, 19 safety valve, 20 PTC element

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 5H029 AJ04 AK03 AK19 AL02 AL06                       AL12 AL16 AM03 AM07 AM16                       BJ02 BJ14 HJ10                 5H050 AA10 BA16 BA17 BA18 CA08                       CA09 CA29 CB02 CB07 CB12                       CB20 FA05 HA10

Claims (2)

[Claims] 1. A positive electrode including a positive electrode mixture layer having a positive electrode active material capable of doping / undoping lithium, and a negative electrode including a negative electrode mixture layer having a negative electrode active material capable of doping / undoping lithium. A non-aqueous electrolyte containing an electrolyte salt, wherein the positive electrode active material is a mixture of a lithium-nickel composite oxide and a lithium-manganese composite oxide, and the electrolyte salt contains at least LiPF ₆ and LiBF _4. Non-aqueous electrolyte battery. 2. The method according to claim 1, wherein the LiBF _{4 is} mixed with the non-aqueous electrolyte.
2. The non-aqueous electrolyte battery according to claim 1, wherein is contained in a range of 0.01 mol / L or more and 0.1 mol / L or less.