JP2003045425A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion nonaqueous electrolyte secondary battery with high capacity, high charging/discharging characteristics at a low cost. SOLUTION: This nonaqueous electrolyte secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte, and an active material constituting the positive electrode contains at least a manganese containing lithium nickel composite oxide and a lithium cobalt composite oxide, and the manganese containing lithium nickel composite oxide is represented by general composition formula, Li1+x+α Ni(1-x-y+δ)/2 My Mn(1-x-y-δ)/2 O2 (Wherein M is at least one selected from a group comprising Cr, Fe, Co, and Al; 0<=x<=0.05, 0<=y<=0.33, -0.05<=α<=0.05, -0.1<=δ<=0.1).

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 having high capacity, excellent charge / discharge characteristics, and low cost.

[0002]

2. Description of the Related Art LiMn is used as a compound effective for intercalating Li ions in a positive electrode active material of a lithium ion secondary battery which is characterized by a voltage of 4 V class and a high capacity.
₂ O ₄ , LiMnO ₂ , LiCoO ₂ , LiCo _1-x Ni _x O
₂ , LiNiO _{2 and the} like are generally used. Among them, rock salt structure type LiCoO ₂ disclosed in JP-A-55-136131 is particularly excellent in that it gives a high discharge potential of 3.5 V or more to Li and has a high capacity. However, LiCoO ₂ has a problem in cycle performance that the crystal structure deteriorates due to repeated charging and discharging and the discharge characteristics deteriorate, and a cost problem that the manufacturing cost increases due to a small supply amount of the cobalt raw material. Is included.

Therefore, a secondary battery using a spinel structure type Li _x Mn ₂ O ₄ made of manganese as a raw material, which is supplied in a large amount at a low cost, is disclosed in JP-A-3-147276.
And No. 4-123769. Further, JP-A-5-13107 discloses a method in which manganese oxide is mixed with cobalt oxide to be used as a positive electrode active material. However, LiMn ₂ O ₄ has a smaller capacity per volume than LiCoO ₂ , and since discharge occurs in two stages in the high-potential portion and the low-potential portion, the voltage change is not flat but becomes stepwise. Have.

As one of means for solving these problems, Japanese Unexamined Patent Publication No. 8-315860 discloses that only a high potential portion of manganese oxide is prepared by combining with a high capacity negative electrode active material, for example, a composite oxide containing tin. Batteries using the are proposed. However, the capacity per volume is small, and the spinel structure type L that discharge is divided into a high potential part and a low potential part.
As long as iMn ₂ O ₄ is used, it is difficult to increase the capacity.

Lithium cobalt composite oxide (LiCoO
₂ ) has a large capacity per volume, but it is 4
It is thermally unstable due to the presence of valent cobalt and decomposes with heat generation. Further, since the lithium nickel composite oxide (LiNiO ₂ ) is charged at a lower voltage than the lithium cobalt composite oxide, it shows a higher capacity than the lithium cobalt composite oxide when compared at the same end voltage. However, it has been reported that thermal stability of nickel is lower than that of the lithium-cobalt composite oxide because it contains tetravalent nickel which is thermally unstable in a charged state.

Therefore, the heat of the lithium nickel composite oxide
Thermal stability in the charging state to improve the thermal stability.
Spinel structure type LiMn containing tetravalent manganese₂O_FourTo
It is made to mix. But that spinel
Structural type of LiMn₂O_FourThe capacity per volume is lithium
The content of LiMn is about 60% of that of the mixed oxide. ₂
O_FourThe capacity per volume of the positive electrode active material mixed with
descend. This reduces the content of lithium in the active material
It can be explained from this.

That is, the volumetric capacity (mAh / cm ³ ) of the mixed positive electrode active material is (LiMn ₂ O ₄ volumetric capacity) × α / 100 + (LiNiO ₂ volumetric capacity) × (100 -Α) / 100. Therefore, for example, the capacity per volume of LiNiO ₂ is 180 mAh / g per mass, and its true density is 4.9 g / c.
Since it is m ^3, it is about 882 mAh / cm ³ . The capacity per volume of LiMn ₂ O ₄ is about 490 mAh.
/ Cm ³ (= 120 mAh / g × 4.08 g / cm ³ ). When the positive electrode active material is composed of 70 mass% LiMn ₂ O ₄ and 30 mass% LiNiO ₂ , the capacity per volume is about 608 mAh / cm ³ . This capacity is equal to that of LiCo, which is currently widely used as a positive electrode active material.
It is extremely low as compared with the capacity of O ₂ which is 787 mAh / cm ³ .

On the other hand, if the content of the lithium nickel composite oxide is increased in order to increase the capacity, the thermal stability will decrease,
It is not possible to increase the content of the lithium nickel composite oxide beyond the predetermined amount.

[0009]

Therefore, in recent years, in order to achieve both the thermal stability of the lithium manganese composite oxide (LiMnO ₂ ) and the high capacity of the lithium nickel composite oxide, the layered structure of the lithium nickel composite oxide has been developed. A general formula Li _{1 + x +} αNi _{(1-x-y +} δ _{) / 2} M _y in which a predetermined amount of nickel is replaced with manganese having high thermal stability while maintaining the crystal structure
Mn _(1-xy- δ _{) / 2} O ₂ (where M is Cr, Fe, Co,
At least one selected from the group consisting of Al and 0
≤x≤0.05, 0≤y≤0.33, -0.05≤α≤0.
05, -0.1 ≤ δ ≤ 0.1) has been studied for use of the manganese-containing lithium nickel composite oxide as the positive electrode active material. Among them, it was found that LiMn _0.5 Ni _0.5 O ₂ containing equal amounts of nickel and manganese is thermally stable and has a high capacity.

On the other hand, in the layered type lithium nickel composite oxide (LiNiO ₂ ), the average valence of nickel is trivalent judging from the composition ratio, but from the X-ray diffraction, the deficient type Li _x Ni _{1- xO} is mixed, and usually divalent nickel is not a little mixed. Both divalent and trivalent nickel can participate in charge and discharge, but their electrode characteristics differ due to the difference in stability of their electronic states. Since divalent nickel has 8 d-electrons and is in a relatively stable state as compared with trivalent nickel having 7 d-electrons, it is difficult to extract electrons. That is, it is considered that the reaction speed is slow and the load characteristics as an electrode are low. In the case of a layered type manganese-containing lithium nickel composite oxide, it is obtained as a single phase when equal amounts of manganese and nickel are present. Therefore, in order to increase the load characteristics, it is sufficient to contain a large amount of trivalent nickel. However, when tetravalent Mn is contained in the crystal, the content of divalent nickel increases, and the load characteristics Will be reduced. Further, this problem is particularly noticeable in the state of the initial stage of charging or the final stage of discharging, that is, when the relative valence of nickel is low. Therefore, it can be estimated that the initial charge / discharge efficiency of the manganese-containing lithium nickel composite oxide is low.

Therefore, as a result of continued studies on this manganese-containing lithium nickel composite oxide, the discharge capacity was about 700 mAh / cm ³ (= 150 mAh / g × 4.
It was found to have a high capacity of 65 g / cm ³ ), but the efficiency at the time of initial charge / discharge was low, and the potential drop was large when a large current was passed, that is, the load characteristics were poor. In order to apply this material to a practical battery, it is necessary to solve the above problems.

Further, the layered type manganese-containing lithium nickel composite oxide in which the nickel sites are regularly replaced with manganese is 3.
It shows an operating potential of 7V or higher, and 170 when charging 4.3V.
It shows a capacity of mAh / g or more, but the discharge capacity is 85% of that.
There is a problem that It is considered that this is due to the lack of stability of charge balance and crystal structure in the crystal of the layered manganese-containing lithium nickel composite oxide.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a high capacity, excellent charge / discharge characteristics, and low cost. To aim.

[0014]

As a result of continuing intensive studies on the positive electrode active material, it was found from the measurement of electric resistance that LiCoO ₂ was superior in electron conductivity to the manganese-containing lithium nickel composite oxide. Further, it is known that LiCoO ₂ having a slightly small amount of lithium has an electron conductivity close to that of a metal, and when combined with a manganese-containing lithium nickel composite oxide, LiCoO ₂ is discharged at the end of discharge of the manganese-containing lithium nickel composite oxide.
Is a lithium-deficient state, which means that it has an electronic conductivity similar to that of a metal.

Therefore, LiCo with small particles and high specific surface area is used.
O₂The manganese-containing lithium nickel with poor load characteristics
Reacted LiC by mixing with complex oxide
oO ₂The electron itself becomes an electron conduction path and the electron conduction in the positive electrode active material.
It has been found that the conductivity can be improved.

Therefore, in order to achieve the above object, the non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, and the active material constituting the positive electrode has a general composition formula Li.
_{1 + x +} αNi _{(1-x-y +} δ _{) / 2} M _y Mn _(1-xy- δ _{) / 2} O ₂ (where M is at least one selected from the group consisting of Cr, Fe, Co and Al) Yes, 0 ≦ x ≦ 0.05, 0 ≦ y ≦
0.33, -0.05≤α≤0.05, -0.1≤δ≤0.
It is characterized by containing at least a manganese-containing lithium nickel composite oxide represented by 1) and a lithium cobalt composite oxide.

By this, LiCoO₂And thermal stability
Excellent and high capacity manganese-containing lithium nickel composite acid
LiC by using a mixed positive electrode active material
oO ₂And spinel structure type LiMn₂O_FourMixed positive electrode activity with
It can have a higher capacity than a substance. Also metal
-Deficient lithium cobal with electronic conductivity close to
Improved loading characteristics by mixing oxides
Can be made.

In the non-aqueous electrolyte secondary battery of the present invention, the manganese-containing lithium nickel composite oxide and the lithium cobalt composite oxide have the same structure. As a result, the molar ratio of contained lithium and transition metal (manganese, nickel, cobalt) becomes equal, and the capacity can be increased.

Further, the non-aqueous electrolyte secondary battery of the present invention is characterized in that all transition metal elements in the active material constituting the positive electrode are
In the active material, it is preferable that nickel is 25 to 50 mol%, manganese is 25 to 50 mol%, and cobalt is 50 mol% or less, and the content of nickel is smaller than the sum of the content of manganese and the content of cobalt. .
By setting the content of cobalt to 50 mol% or less with respect to all transition metal elements, the content of cobalt having low thermal stability can be reduced, so that the thermal stability of the positive electrode active material can be improved and expensive cobalt Since the content of can be reduced, the cost can be reduced.

That is, the capacity per unit volume of the positive electrode active material (mA
h / cm ³ ) is [capacity per volume of manganese-containing lithium nickel composite oxide (LiMn _0.5 Ni _0.5 O ₂ )]
× α / 100 + (LiCoO ₂ capacity per volume) ×
It is represented by (100−α) / 100. Therefore, for example, 5
Li nickel nickel composite oxide containing 0 mass% LiCoO ₂ and 50 mass% manganese (LiMn _0.5 Ni _0.5 O ₂ ).
When mixed, the capacity per volume is about 744 mA.
h / g. If the cobalt content is the same, the positive electrode active material of the present invention is LiCoO ₂ and spinel structure type LiMn ₂
The capacity is significantly improved as compared with the positive electrode active material mixed with O ₄ .

Further, even if raising the content of manganese in order to improve safety, when the LiMn _0.5 Ni _0.5 O ₂ of 80% by weight and LiCoO ₂ were mixed 20 mass%, the capacity per the volume It becomes about 717 mAh / g.
In order to obtain the same capacity with a mixed positive electrode active material of spinel structure type LiMn ₂ O ₄ and LiCoO ₂ , about 76% by mass is required.
Of LiCoO ₂ and about 24% by weight of LiMn ₂ O ₄ are required. From this, according to the present invention, the content of manganese can be significantly increased, so that the thermal stability can be improved. In addition, since the content of expensive cobalt can be reduced, the cost of the positive electrode active material can be reduced.

Further, the non-aqueous electrolyte secondary battery of the present invention is characterized in that all transition metal elements in the active material constituting the positive electrode are
Lithium in the active material is preferably 95 to 105 mol%. This makes it possible to realize a non-aqueous electrolyte secondary battery having a large capacity per volume and high thermal stability.

In the non-aqueous electrolyte secondary battery of the present invention, the lithium cobalt composite oxide has the general composition formula Li _x C.
It is represented by oO ₂ , and x is in the range of 0.98 to 1.02.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode and a negative electrode.
An active material comprising a positive electrode and a non-aqueous electrolyte and constituting the positive electrode
Is the general composition formula Li_{1 + x +}αNi_{(1-x-y +}δ_{) / 2}M_yMn
_(1-xy-δ _{) / 2}O₂(However, M is Cr, Fe, Co, Al
At least one selected from the group consisting of 0 ≦ x
≤0.05, 0≤y≤0.33, -0.05≤α≤0.0
5, manganese-containing lithium represented by -0.1≤δ≤0.1)
Um-nickel composite oxide and lithium-cobalt composite oxide
And at least one thing.

The above manganese-containing lithium nickel composite oxide is a lithium manganese composite oxide (LiMnO ₂ ).
Thermal stability of lithium nickel composite oxide (LiNi
In order to achieve both high capacity of O ₂ ), a predetermined amount of nickel is replaced with manganese having high thermal stability while maintaining the layered crystal structure of the lithium nickel composite oxide. The lithium cobalt composite oxide is generally represented by the general formula Li _x CoO ₂ , and x is generally used in the range of 0.98 to 1.02.

The manganese-containing lithium nickel composite oxide and the lithium cobalt composite oxide are obtained by mixing a predetermined amount of a compound containing each element and firing.
Examples of the lithium source include lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate. , Lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide and the like can be used, and among these, lithium carbonate is particularly preferable. Further, examples of the manganese source and the nickel source include compounds in which equal amounts of manganese and nickel are uniformly distributed. Among them, coprecipitated manganese-nickel hydroxide is particularly preferable. As the cobalt source, for example, cobalt carbonate, cobalt hydroxide, cobalt nitrate or the like can be used.

The firing conditions of the above compound are not particularly limited, but it is preferable to fire at 750 to 850 ° C. for 5 to 15 hours. The atmosphere during firing is also not particularly limited, but it is preferably performed in air. When the reaction is carried out in air, the reaction progresses easily, and the layered type manganese-containing lithium nickel composite oxide can be obtained in a state where the content of impurities is small.

The flow rate of air is 0.1 cm ³
/ Min or more is preferable, and 1 cm ³ / min or less is more preferable. If the gas flow rate is low, impurities may remain. Further, in order to suppress the generation of trivalent Mn, the firing is preferably performed twice, and particularly 500 to 8
It is preferable to perform calcination at 00 ° C. and then firing again.
When firing is performed twice, the firing temperature for the second firing is preferably higher than the firing temperature for the first firing. In particular, the firing temperature for the first firing is set to 750 to 800 ° C and the firing temperature for the second firing is set to 800 to 850 ° C. Is preferred.

The manganese-containing lithium nickel used in the present invention
The Kell complex oxide has the general composition formula Li _{1 + x +}αNi_{(1-x-y +}
δ_{) / 2}M_yMn_(1-xy-δ_{) / 2}O₂The compound of the layered type represented by
However, the NiMn part is Cr, Fe, Co or
Can be replaced by another element such as Al. Like that
Examples of such substituted parts are NiCoMn, NiFeM
n, NiAlMn, NiFeCoMn, NiCoAlM
n, NiFeAlMn, NiFeCoAlMn, etc.
To be The above-mentioned substitution element is introduced by firing in the form of an oxide or the like.
It may be added at any time, but a coprecipitated compound containing the above elements may be added.
It is desirable to use it for food. It should be noted that the substitution of the above substitution elements
The amount is in the range of 0 ≦ y ≦ 0.33 in the above general composition formula.
Within, and suppresses the change in valence of manganese
For this reason, it is preferable to introduce a trivalent transition metal element.
Yes.

In constructing the non-aqueous electrolyte secondary battery of the present invention, the positive electrode can be manufactured as follows. First, the above general composition formula Li _{1 + x +} αNi _{(1-x-y +} δ _{) / 2} M _y M
If necessary, an electron conduction aid and a binder are added to the positive electrode active material composed of the manganese-containing lithium nickel composite oxide represented by n _{(1 -xy-} δ _{) / 2} O ₂ and the lithium cobalt composite oxide. . Next, the positive electrode mixture obtained by mixing these is dispersed in a solvent to prepare a positive electrode mixture-containing paste. In this case, the binder may be dissolved in an organic solvent in advance and then mixed with the positive electrode active material or the like. Then, the obtained positive electrode mixture-containing paste is applied to a conductive substrate made of aluminum foil or the like and dried to form a positive electrode mixture layer on the conductive substrate. After that, a positive electrode is produced by performing a step of pressure-molding if necessary. However,
The method for producing the positive electrode is not limited to the above-exemplified method, and another method may be used.

The above positive electrode mixture layer will be described in more detail.
Then, in the paste containing the positive electrode mixture applied to the conductive substrate,
Volatile components such as solvent evaporate in the drying process and become a conductive substrate.
The formed positive electrode mixture layer has a general composition formula Li_{1 + x +}αNi
_{(1-x-y +}δ_{) / 2}M_yMn_(1-xy-δ _{) / 2}O₂Manga represented by
-Containing lithium nickel composite oxide and lithium cobalt
Positive electrode active material composed of complex oxides and added as needed
Positive electrode composed of a mixture of a binder and an electron conduction aid
Composed of a mixture. In addition, generally available lithium
The composition of the Baltic complex oxide is Li_xCoO₂(0.98 ≦
x ≦ 1.02).

The negative electrode active material facing the positive electrode may be any one that can be doped or dedoped with lithium ions, and examples of such a negative electrode active material include graphite, pyrolytic carbons, cokes, and the like. Glassy carbons, organic polymer compound fired bodies, mesocarbon microbeads,
Carbon-based materials such as carbon fiber and activated carbon can be used. Also,
Lithium or a lithium-containing compound can also be used as the negative electrode active material. The lithium-containing compounds include lithium alloys and others. Examples of the lithium alloy include lithium-aluminum and lithium-
Examples include alloys of lead, lithium-indium, lithium-gallium, lithium-indium-gallium, and the like. Examples of lithium-containing compounds other than lithium alloys include tin oxides, silicon oxides, nickel-silicon alloys, magnesium-silicon alloys, tungsten oxides, lithium iron composite oxides, and the like. Among these negative electrode active materials, graphite is particularly preferable because it has a large capacity density. Some of the negative electrode active materials do not contain lithium immediately after their production, but when they act as active materials, they are in a state of containing lithium.

The negative electrode can be manufactured as follows. First, if necessary, a binder and the like are added to the negative electrode active material in the same manner as in the case of the positive electrode and mixed to prepare a negative electrode mixture, which is dispersed in a solvent to prepare a negative electrode mixture-containing paste. The binder may be dissolved in a solvent in advance and then mixed with the negative electrode active material and the like. Next, the obtained negative electrode mixture-containing paste is applied to a conductive substrate made of copper foil or the like and dried to form a negative electrode mixture layer on the conductive substrate.
After that, a negative electrode is manufactured through a step of pressure-molding if necessary. However, the method for producing the negative electrode is not limited to the above-exemplified method, and other methods may be used.

The above-mentioned negative electrode mixture layer will also be described in more detail. Volatile components such as a solvent in the negative electrode mixture-containing paste applied to the conductive substrate are evaporated in the drying step to form a negative electrode mixture formed on the conductive substrate. The agent layer is composed of a negative electrode mixture made of a mixture of a negative electrode active material and a binder or the like added as necessary.

Examples of the binder used in the production of the positive electrode and the negative electrode in the present invention include polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, and styrene-butadiene rubber. Examples of the electron conduction aid used for producing the positive electrode include graphite, graphite, acetylene black, carbon black, Ketjen black, carbon fiber, and metal powder and metal fiber.

As the conductive substrate used for producing the positive electrode and the negative electrode, for example, foil made of aluminum, copper, stainless steel, nickel, titanium or alloys thereof, punched metal, expanded metal, net, etc. Although it can be used, an aluminum foil is particularly preferable as the positive electrode conductive substrate, and a copper foil is particularly preferable as the negative electrode conductive substrate.

In the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte is usually a non-aqueous liquid electrolyte (hereinafter,
This is called "electrolyte". Then, as the electrolytic solution, a non-aqueous solvent type electrolytic solution in which an electrolyte salt such as a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent is used.

The non-aqueous solvent used for preparing the above-mentioned electrolytic solution is not particularly limited, but it is suitable to use a chain ester as the main solvent. Examples of such chain ester include chain COO such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, and methyl propionate.
An organic solvent having a bond. The fact that the chain ester is the main solvent of the electrolytic solution means that the chain ester occupies a volume of more than 50% by volume in the total electrolytic solution solvent, and in particular, the chain ester is the entire electrolytic solution. It is preferable to occupy 65% by volume or more of the liquid solvent. As a solvent for the electrolytic solution, it is preferable to use this chain ester as the main solvent because the chain ester is 5% of the total electrolytic solution solvent.
This is because when it exceeds 0% by volume, battery characteristics, especially low temperature characteristics are improved.

However, in order to improve the battery capacity, an ester having a high dielectric constant (an ester having a dielectric constant of 30 or more) is mixed with the chain ester as compared with the case where the electrolytic solution solvent is composed of only the chain ester. It is preferable to use. When such an ester having a high dielectric constant is 10% by volume or more in the entire electrolytic solution solvent, the capacity is clearly improved, and the ester having a high dielectric constant is 20% by volume or more in the entire electrolytic solution solvent. In this case, the capacity can be more clearly improved. However, when the volume occupied by the ester having a high dielectric constant in the entire electrolyte solution solvent is too large, the discharge characteristics of the battery tend to be deteriorated. As described above, it is preferably 10% by volume or more, more preferably 20% by volume or more, and 40% by volume or less.

Examples of the ester having a high dielectric constant include ethylene carbonate, propylene carbonate,
Examples thereof include butylene carbonate, γ-butyrolactone, and ethylene glycol sulfite, and those having a cyclic structure such as ethylene carbonate and propylene carbonate are particularly preferable, and cyclic carbonate is particularly preferable, and ethylene carbonate is most preferable.

Examples of the solvent that can be used in combination with the ester having a high dielectric constant include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, and 2
-Methyl-tetrahydrofuran, diethyl ether and the like. In addition, amine-based or imide-based organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used.

As an electrolyte salt such as a lithium salt to be dissolved in a non-aqueous solvent for preparing the above-mentioned electrolytic solution, for example, L
iPF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiCF
₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC ₄ F _{2n + 1} SO ₃
(N ≧ 2) and the like may be used alone or in combination of two or more. LiPF ₆ , LiC ₄ F ₉ SO _{3, and the} like are particularly preferable because they have high electric conductivity and good charge and discharge characteristics. The concentration of the electrolyte salt such as the lithium salt in the electrolytic solution is not particularly limited, but is preferably 0.3 to 1.7 mol / dm ³ , particularly 0.4 to 1.5 mol / dm ³ .

Further, in the present invention, a gel polymer electrolyte, a solid electrolyte or the like may be used in addition to the above-mentioned electrolytic solution. The gel polymer electrolyte corresponds to a gel of the electrolytic solution with a gelling agent. In the gelation, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or a copolymer thereof, a polyfunctional monomer which is polymerized by irradiation with an actinic ray such as an ultraviolet ray or an electron beam, for example, pentaerythritol. Tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, dipentaerythritol hexaacrylate and other tetrafunctional or higher acrylates and the same tetrafunctional or higher functional methacrylates are used. . However, in the case of a monomer, the monomer itself does not gelate the electrolytic solution, but a polymer obtained by polymerizing the above monomer acts as a gelling agent.

When the electrolytic solution is gelled using the polyfunctional monomer as described above, if necessary, for example, benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides, Acetophenones, thioxanthones, anthraquinones and the like can be used, and further alkylamines, aminoesters and the like can be used as a sensitizer for the polymerization initiator.

On the other hand, as the solid electrolyte, either an inorganic solid electrolyte or an organic solid electrolyte can be used.

In the present invention, as the separator, for example, a microporous resin film, a non-woven fabric or the like is preferably used. Examples of the microporous resin film include microporous polyethylene film, microporous polypropylene film, microporous ethylene-propylene copolymer film and the like. Examples of the non-woven fabric include polypropylene non-woven fabric, polyethylene non-woven fabric, polyethylene terephthalate non-woven fabric, polybutylene terephthalate non-woven fabric and the like.

In the non-aqueous electrolyte secondary battery of the present invention, when an electrolytic solution is used as the electrolyte, the microporous resin film or nonwoven fabric exemplified above is used as a separator in a normal state, but a gel polymer electrolyte is used. When used, the non-woven fabric or the like used as a support for the gel polymer electrolyte may also serve as a separator. Further, when a solid electrolyte is used as the electrolyte, the solid electrolyte may also serve as a separator.

When an electrolytic solution is used as the electrolyte,
When a battery is assembled, the electrolytic solution is injected into the battery case after inserting the electrode group into the battery case.When using a gel polymer electrolyte, the gel polymer electrolyte is held in advance on the electrode or the support. You may stay.

[0050]

EXAMPLES The present invention will be described below based on examples. However, the present invention is not limited to only those examples.

Example 1 A manganese-containing lithium nickel composite oxide (LiMn _0.5 Ni _0.5 O ₂ ) was synthesized by the following method. As the manganese source and the nickel source, compounds in which equal amounts of manganese and nickel are evenly distributed can be used. Among them, manganese-nickel hydroxide co-precipitated with manganese and nickel was used. First, manganese nickel hydroxide and lithium carbonate were mixed at a ratio of 2: 1 in a mortar and baked in air at 900 ° C. for 12 hours,
The powder was pulverized again in a mortar to obtain a powder of LiMn _0.5 Ni _0.5 O ₂ . Next, cobalt hydroxide and lithium carbonate were mixed at a ratio of 2: 1 and baked in air at 900 ° C. for 12 hours to obtain a lithium cobalt composite oxide (LiCoO ₂ ).

The positive electrode active material is 90% by mass of LiMn _0.5.
A mixture of Ni _0.5 O ₂ and 10 mass% LiCoO ₂ was used. 90% by mass of this positive electrode active material, 5% by mass of carbon black as an electron conduction aid, and 5% by mass of polyvinylidene fluoride as a van inder were mixed and dispersed with n-methylpyrrolidone to form a coating film, and a predetermined size was obtained. What was cut out was used as the positive electrode. For evaluation as a battery, a coin-shaped model cell was prepared using lithium metal as a counter electrode. A porous polyethylene sheet was used as the separator, and the electrolytic solution was a mixture of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 3 and 1.2 mol / dm ³ of LiPF ₆ dissolved therein. Was used.

Example 2 As the positive electrode active material, 80% by mass of LiMn _0.5 Ni _0.5 O ₂ and 20% by mass of LiCoO _{2 were used.}
A positive electrode was produced in the same manner as in Example 1 except that a mixture of was used, and battery evaluation was performed in the same manner as in Example 1.

Example 3 As the positive electrode active material, 70% by mass of LiMn _0.5 Ni _0.5 O ₂ and 30% by mass of LiCoO _{2 were used.}
A positive electrode was produced in the same manner as in Example 1 except that a mixture of was used, and battery evaluation was performed in the same manner as in Example 1.

Example 4 As a positive electrode active material, 60% by mass of LiMn _0.5 Ni _0.5 O ₂ and 40% by mass of LiCoO _{2 were used.}
A positive electrode was produced in the same manner as in Example 1 except that a mixture of was used, and battery evaluation was performed in the same manner as in Example 1.

Example 5 As a positive electrode active material, 50% by mass of LiMn _0.5 Ni _0.5 O ₂ and 50% by mass of LiCoO _{2 were used.}
A positive electrode was produced in the same manner as in Example 1 except that a mixture of was used, and battery evaluation was performed in the same manner as in Example 1.

Comparative Example 1 LiMn was used as the positive electrode active material.
_A positive electrode was produced in the same manner as in Example 1 except that only _0.5 Ni _0.5 O ₂ was used, and battery evaluation was performed in the same manner as in Example 1.

(Comparative Example 2) Electrolytic manganese dioxide and lithium carbonate were mixed at a ratio of 4: 1 and the mixture was mixed with air at 900 ° C for 1 hour.
After firing for 2 hours, a spinel structure type lithium manganese composite oxide represented by LiMn ₂ O ₄ was synthesized. Then, the lithium manganese composite oxide was added in an amount of 50% by mass in Example 1.
A battery was evaluated in the same manner as in Example 1 except that a mixture of the lithium cobalt composite oxide LiCoO ₂ synthesized in 50% by mass was used as the positive electrode active material, and a positive electrode was prepared in the same manner as in Example 1. I went.

Comparative Example 3 As the positive electrode active material, 70% by mass of LiMn _0.5 Ni _0.5 O ₂ and 30% by mass of LiCo _{0.2 were used.}
A positive electrode was produced in the same manner as in Example 1 except that a mixture of Ni _0.8 O ₂ was used, and battery evaluation was performed in the same manner as in Example 1.

Table 1 shows the contents (molar ratio) of Li, Mn, Ni and Co in the positive electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 3.

[0061]

[Table 1]

Table 2 also shows Examples 1-5 and Comparative Examples 1-3.
The initial charging / discharging efficiency, the initial discharging capacity, the average potential at the time of discharging 50% of the discharging capacity at a current density of 0.5 mA / cm ² , and the load characteristics were shown.

[0063]

[Table 2]

As is clear from Table 2, Examples 1 to 5 of the present invention are superior to Comparative Example 1 in all of the initial charge / discharge efficiency, initial discharge capacity, average potential and load characteristics. .

FIG. 1 shows Example 1 and Example 3 and Comparative Example 1
² shows a discharge curve at a current density of 0.5 mA / cm ² of the battery. Comparing the average potentials at 50% discharge of the discharge capacity in Table 2, it can be seen that the average potential increases as the content of LiCoO ₂ increases, and approaches the potential of LiCoO ₂ . Comparing Example 3 with Comparative Example 1, a potential increase of about 80 mV could be observed. According to the present invention, it is found that the discharge potential shape and the potential thereof can be intentionally controlled by mixing the positive electrode active materials having different working potentials with the working potential that is uniquely determined by the material originally constituted.

Further, as is clear from Table 2, LiCo
The initial discharge capacity and the initial charge / discharge efficiency gradually improved as the O ₂ content increased. The initial charge / discharge efficiency of Comparative Example 1 containing no LiCoO ₂ was 84%, but improved to 87% in Example 3 and 89% in Example 5, and as a result, the initial discharge capacity could be improved. It was this is,
This is because the initial charge / discharge efficiency of LiCoO ₂ is as high as 96%.

The load characteristics shown in Table 2 are the current density of 0.5.
Current density 4mA / c based on the discharge capacity at mA / cm ²
It was expressed by the ratio of the discharge capacity at m ² . The load characteristic of Comparative Example 1 is 84.8%. In comparison with this, in Examples 1 to 5 containing LiCoO ₂ , improvement in load characteristics was observed. Moreover, since it depends on the content of LiCoO ₂ , LiCoO having high electron conductivity as expected.
It is considered that the presence of the _two powders in the electrode forms an electron conduction path.

To increase the discharge capacity, as shown in Comparative Example 3, LiCo _0.2 N showing a discharge capacity of 180 mAh / g or more.
i _0.8 O ₂ may be mixed, and for example, the positive electrode active material of Comparative Example 3 exhibits a discharge capacity of 159 mAh / g. However, the load characteristics do not improve. Further, in Comparative Example 3, the content of thermally unstable Ni is about 60% of all transition metal elements.
Therefore, there is concern that the thermal stability may decrease.

When a spinel structure type lithium manganese composite oxide is used as in Comparative Example 2, the load characteristics are
Although thermal stability and cost reduction can be realized, the initial discharge capacity is significantly reduced. In order to realize high capacity, high load characteristics, thermal stability, and low cost, a positive electrode active material obtained by combining the manganese-containing lithium nickel composite oxide and the lithium cobalt composite oxide used in the present invention is used. Use is essential.

As described above, in the present invention, expensive LiCo
It is possible to propose a low-cost material by reducing the amount of cobalt in the positive electrode active material while having an electrode characteristic close to that of O ₂ .

[0071]

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a non-aqueous electrolyte secondary battery having high capacity, excellent charge / discharge characteristics, and low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the discharge capacity and the positive electrode potential of an example of the present invention and a comparative example.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4G048 AA04 AB01 AB05 AC06 AE05                 5H029 AJ01 AJ02 AJ14 AK03 AL06                       AL07 AL11 AL12 AM02 AM05                       AM07 AM11 AM15 EJ04 EJ12                       HJ01 HJ02                 5H050 AA01 AA02 AA19 BA15 CA07                       CB03 CB07 CB08 CB11 EA10                       EA23 EA24 HA01 HA02

Claims (5)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the active material constituting the positive electrode has a general composition formula Li _{1 + x +} αNi _{(1-x-y +} δ _{). / 2} M _y Mn
_(1-xy- δ _{) / 2} O ₂ (where M is Cr, Fe, Co, Al
At least one selected from the group consisting of 0 ≦ x
≤0.05, 0≤y≤0.33, -0.05≤α≤0.0
5, a non-aqueous electrolyte secondary battery containing at least a manganese-containing lithium nickel composite oxide represented by −0.1 ≦ δ ≦ 0.1) and a lithium cobalt composite oxide. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the manganese-containing lithium nickel composite oxide and the lithium cobalt composite oxide have the same structure. 3. Nickel in the active material is 25 to 5 relative to all transition metal elements in the active material constituting the positive electrode.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of nickel is 0 mol%, the content of manganese is 25 to 50 mol%, the content of cobalt is 50 mol% or less, and the content of the nickel is smaller than the sum of the content of the manganese and the content of the cobalt. 4. Lithium in the active material is 95 to 10 with respect to all transition metal elements in the active material forming the positive electrode.
It is 5 mol%, The non-aqueous electrolyte secondary battery according to claim 1. 5. The lithium cobalt composite oxide is represented by a general composition formula Li _x CoO ₂ , and x is 0.98 to 1.0.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, which is in the range of 2.