JP2003068302A - Positive material for secondary lithium ion battery and secondary lithium ion battery having positive pole made of positive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive material that can increase the charging and discharging capacity of a secondary lithium ion battery and can improve the charging and discharging cycle characteristics thereof. SOLUTION: The positive material comprises an oxide having reverse fluorite crystal structure including lithium and at least two kinds of cation other than lithium. At least one kind of the cation other than lithium is a transition metal shown by general formula Lix Mey Mz O4-a Aa (Me is at least a kind of transition metal, M a cation other than lithium and transition metal, A an anion other than oxygen, 3<=x<=7, 0.5<=y<=3, 0<=z<=2, 0<=a<=1 and 4<x+y+z<=8).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode material for a lithium ion secondary battery and a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, a secondary battery has become one of the essential components as a power source for portable electronic equipment such as mobile phones, PDAs and notebook computers, and information communication equipment. In the field of such portable electronic devices and the like, there is a demand for higher capacity secondary batteries due to higher performance of hard disks and long-term driving of liquid crystal display backlights.

On the other hand, using a non-aqueous electrolyte,
High capacity lithium-ion secondary battery used for battery reaction
Note that it can be expected to be made more compact, and it is even lighter.
Is being watched. As a positive electrode material for lithium-ion secondary batteries
In general, lithium cobalt oxide (LiCoO_Two)etc
Layered oxides and lithium manganate (LiMn
_TwoO _Four) Represented by
ing. These LiCoO _TwoAnd LiMn_TwoO_FourIs
The discharge potential develops about 4 V on the basis of metallic Li. Well
The discharge capacity per unit weight of the positive electrode material is LiMn._TwoO
_FourAnd its theoretical value is about 145 mAh / g, LiCoO_Twoso
Has a theoretical value of about 270 mAh / g, but reversibly
The available capacity is about 150 mAh / g.

By the way, these spinel type composite oxides
The lithium-ion secondary battery has a higher capacity than the positive electrode material.
As a positive electrode material expected to be quantified, Li₆C
oO _Four, Li₅FeO_Four, Li₆MnO_FourSuch as lithium
Inverted Fluorite-Type Crystal Structure Containing Alkali and One Transition Metal Element
Oxide with Solid State Ioni
cs, 122, 59, (1999).
It This material has a discharge potential of about 2 to 3 V based on metallic Li.
Of high power and a large amount of Li in the material,
A large amount, that is, discharge capacity can be taken out.

The inverse fluorite crystal structure is a structure in which a cation having a positive charge enters a tetrahedral site of a face-centered cubic lattice composed of anions having a negative charge. That is, it is composed of four anions per unit cell,
And up to 8 cation atoms can enter. Examples of the oxide having an inverted fluorite type crystal structure include Li ₂ O and Na
Alkali metal oxides such as ₂ O and K ₂ O are known, but in the oxide having an inverted fluorite crystal structure used as the positive electrode material of the above lithium ion secondary battery, oxygen is used as an anion and oxygen is used as a cation. It mainly has Li, and further Mn in order to compensate desorption and insertion of Li during charge and discharge,
It contains Co or Fe.

A reaction formula when a positive electrode containing a positive electrode material made of an oxide having such an inverted fluorite type crystal structure is formed and charged and discharged is shown below by taking Li ₆ CoO ₄ as an example. That is, the reaction at the positive electrode during charging / discharging is such that Li constituting a cation is desorbed during charging and Li is inserted during discharging. At this time, the oxidation number of Co, that is, the valence changes from the law of charge neutrality. Li ₆ CoO ₄ = Li _6-α CoO ₄ + Li _α

However, such a positive electrode material composed of an oxide having an inverted fluorite type crystal structure in the related art can increase the charge / discharge capacity of a lithium ion secondary battery. There is a problem in terms of cycle deterioration in which charge and discharge capacity is reduced by repeating discharge. That is,
In the case of the conventional positive electrode material made of an oxide having an inverted fluorite type crystal structure, the charge / discharge capacity is relatively sharply reduced by repeated charge / discharge, so it is necessary to reduce cycle deterioration and improve charge / discharge cycle characteristics. .

[0007] Here, the cycle deterioration is L due to charging and discharging.
By repeating the desorption and insertion of i, the expansion and contraction of the crystal lattice is repeated to cause a change in the crystal structure, that is, a phase change, and the amount of Li that can be desorbed and inserted reversibly decreases gradually. Therefore, in order to improve the charge / discharge cycle characteristics, L which is desorbed / inserted in order to prevent the phase change of the crystal structure.
It is possible to limit the amount of i, but L to be detached / inserted
Limiting the amount of i is nothing but limiting the charge / discharge capacity, and such a method cannot be adopted.

An object of the present invention is to increase the charge / discharge capacity of a lithium ion secondary battery and improve the charge / discharge cycle characteristics.

[0009]

The positive electrode material for a lithium ion secondary battery of the present invention comprises Li and at least two kinds of Li.
Of an oxide having an inverted fluorite crystal structure containing a cation other than Li, and at least 1 of cations other than Li
The above problem is solved by adopting a constitution in which the seed is a transition metal element.

Further, the general formula Li _x Me _y M _z O _4-a A
_a (however, Me is at least one kind of transition metal element, M is a cation other than Li and a transition metal, A is an anion other than oxygen, and 3 ≦ x ≦ 7, 0.5 ≦ y ≦ 3, 0 ≦ z ≦ 2,0
≦ a ≦ 1 and 4 <x + y + z ≦ 8).

Further, the lithium ion secondary battery is constructed such that the positive electrode contains any one of the above positive electrode materials.

In this case, since the oxide has an inverted fluorite type crystal structure, the charge / discharge capacity of the lithium ion secondary battery can be increased, and at least one transition metal is used as a cation. By including the element, Li
Suppresses the phase change of the crystal structure due to repeated expansion and contraction of the crystal lattice by compensating for the charge at the time of desorption / insertion and additionally containing at least two kinds of cations including transition metal elements in addition to Li. it can. That is, since the phase change of the crystal structure can be suppressed and the charge / discharge cycle characteristics can be improved without limiting the charge / discharge capacity, the charge / discharge capacity of the lithium ion secondary battery can be increased and the charge / discharge cycle characteristics can be improved.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a positive electrode material for a lithium ion secondary battery, to which the present invention is applied, and a lithium ion secondary battery in which a positive electrode is formed of the positive electrode material will be described with reference to FIGS. Will be described with reference to. FIG. 1 is a schematic diagram showing the structure of an oxide having an inverted fluorite type crystal structure, which is a positive electrode material to which the present invention is applied. FIG. 2 is a partial cross-sectional view showing a schematic configuration of a lithium ion secondary battery in which a positive electrode is formed using a positive electrode material to which the present invention is applied.
FIG. 3 is a partial cross-sectional view showing a schematic configuration of an electrochemical cell for examining the electrochemical characteristics of the positive electrode material.

The positive electrode material for a lithium ion secondary battery of the present invention is an oxide having an inverted fluorite crystal structure, as shown in FIG. The inverted fluorite type crystal structure has a structure in which an anion 1 having a negative charge forming a face-centered cubic lattice and a cation 3 having a positive charge is inserted in a tetrahedral site formed by these anions 1. That is, it is composed of 4 anions 1 per unit cell, and can contain a maximum of 8 atoms of cation 3. In the positive electrode material of the present invention, the anion 1 is mainly composed of oxygen, and the cation 3 is at least one of Li, at least two kinds of cation elements other than Li, and at least two kinds of cations other than Li. Is a transition metal element, or all of a plurality of cations other than Li are composed of a transition metal element. That is, in the conventional positive electrode material made of an oxide having an inverted fluorite type crystal structure, the cation is composed of Li and one kind of transition metal element other than Li, while the inverted fluorite type of the present invention is used. The positive electrode material composed of an oxide having a crystal structure has a cation composed of Li and two or more kinds of cation elements containing one or more kinds of transition metal elements, or a cation of Li and a plurality of transition metal elements. It is composed of.

At least one transition metal element contained as a cation in the positive electrode material composed of an oxide having an inverted fluorite type crystal structure of the present invention becomes an element for charge compensation at the time of desorption / insertion of Li. . Therefore, the transition metal element contained as the cation of the positive electrode material is not particularly limited, but if selected from Mn, Fe, and Co, it is charge-compensated, that the positive electrode material is easy to make, and the transition metal element Among them, it is desirable because it is relatively light.

When the positive electrode material of the present invention made of an oxide having an inverted fluorite crystal structure contains Li and an element having a positive charge other than a transition metal element, the cation other than Li and the transition metal element is Although not particularly limited, it is desirable to select from elements other than alkali metals, because it is considered that elements having an oxidation-reduction potential close to Li can be avoided, and cycle characteristics and charge / discharge reactions can be prevented from being lowered. Furthermore, if the cations other than Li and the transition metal element are selected from the elements having an oxidation number of +3 or less in the positive electrode material, the number of inserted Li is difficult to decrease, and the crystal structure is easily stabilized. It is more desirable because of things.

Like the positive electrode material of the present invention, the cations other than Li in the oxide having an inverted fluorite type crystal structure are composed of plural kinds including transition metal elements, whereby expansion and contraction of the crystal lattice is repeated. A change in crystal structure at the time, that is, a phase change can be suppressed. Furthermore, when a plurality of types of cations other than Li do not participate in charge compensation during charge / discharge, that is, a cation whose oxidation number does not change, such as Al
In the case of a typical element such as, the ionic radius does not change due to a change in the oxidation number, so it is considered that a stronger crystal structure can be formed.

In the reverse fluorite type positive electrode material of the present embodiment, the cation is composed of Li and two or more kinds of cation elements containing one or more kinds of transition metal elements, or the cation is Li and a plurality of transitions. It is composed of a metal element and has a general formula of Li _x Me _y M _z O _4-a A _a (however, Me.
Is at least one transition metal element, M is a cation other than Li and the transition metal, A is an anion other than oxygen, and 3
≦ x ≦ 7, 0.5 ≦ y ≦ 3, 0 ≦ z ≦ 2, 0 ≦ a ≦ 1, and 4 <x + y + z ≦ 8).
Here, the value of x indicates the composition of Li, and when x <3, it is difficult to synthesize an oxide having an inverted fluorite type crystal structure,
When x> 7, the amount of the transition metal element Me required for charge compensation becomes small. Therefore, the range of x is preferably 3 ≦ x ≦ 7.

The value of y indicates the composition of the transition metal element Me. When y <0.5, the required charge / discharge capacity cannot be obtained because the amount of Me required for charge compensation is small, and y> In the case of 3, it becomes difficult to synthesize an oxide having an inverted fluorite crystal structure. Therefore, the range of y is 0.5 ≦ y ≦ 3. The value of z indicates the composition of the cation M other than Li and the transition metal element. When the number of transition metal elements is one, it is necessary to include M, so that z> 0, so that two or more transition metal elements are included. When included, it is not always necessary to include M, so z ≧
It becomes 0. On the other hand, when z> 2, it becomes difficult to synthesize an oxide having an inverted fluorite crystal structure. Therefore, the range of z is 0
It is desirable that ≦ z ≦ 2. Further, the value of a indicates the composition of the anion A other than oxygen constituting the inverted fluorite type crystal structure. When a> 1, it becomes difficult to synthesize an oxide having an inverted fluorite type crystal structure. Therefore, the range of a is 0 ≦
It is desirable that a ≦ 1.

Furthermore, it is desirable that the total composition of Li and cations other than Li constituting the positive electrode material made of an oxide having an inverted fluorite type crystal structure is in the range of 4 <x + y + z ≦ 8. This is because when x + y + z ≦ 4, the inverse fluorite crystal structure cannot be maintained, and when x + y + z> 8, the cation to anion ratio is too large to form the inverse fluorite crystal structure.

A method for synthesizing the positive electrode material of this embodiment will be described. The positive electrode material of this embodiment can be synthesized by a method similar to a general method for synthesizing an inorganic compound. That is, it can be synthesized by weighing a plurality of raw material compounds so that the desired composition ratios of Li, cations Me and M, and anion A are obtained, and then uniformly mixing and firing. In the compound as a raw material, as the lithium compound, hydroxide, chloride, nitrate and carbonate of lithium can be used. As the compound which is a raw material of the cation M other than Li and the transition metal element, a suitable compound thereof can be used, and examples thereof include oxides, hydroxides, chlorides,
Nitrate, carbonate, sulfate, and organic acid salt can be used.

As a compound as a raw material of the cation Me which is a transition metal element, a suitable oxide of each element,
Hydroxides, chlorides, nitrates, carbonates, sulfates, organic acid salts and the like can be used. For example, when the transition metal element Me is Co, Mn, or Fe, manganese dioxide, γ-MnOOH, manganese carbonate, manganese nitrate, manganese hydroxide, Co ₃ O ₄ , CoO, Fe ₂ O ₃ , and Fe _{3 are used.}
O ₄ or the like can be used. In addition, Li and cation M
Of the raw materials of e and M, it is also possible to use a compound containing two or more elements as a raw material, for example, Co and M.
It is also possible to add an alkaline solution to a weakly acidic solution containing n and precipitate it to obtain a hydroxide raw material.

In the manufacturing process of the positive electrode material, the raw materials may be mixed and fired repeatedly if necessary.
In that case, the mixing conditions and the firing conditions can be appropriately selected. When the manufacturing process is repeated from the mixing of the raw materials to the firing, the raw materials are appropriately added when the mixing step is repeated, and each element contained in the positive electrode material in the final firing step has a desired composition ratio. Can also be The firing temperature varies depending on the raw material used and the stage of the process, but is preferably in the range of 400 ° C to 1200 ° C, and particularly in the final firing process 600 ° C to
It is more desirable to fire at 1000 ° C. for 10 hours or more.

The firing step is performed by firing the mixed raw materials in the atmosphere, a vacuum, an oxygen atmosphere, a hydrogen atmosphere, or an inert gas atmosphere such as nitrogen or a rare gas. However, it is desirable that the final firing step is performed in the air or an inert gas atmosphere. As needed,
It can also be fired in a pressurized atmosphere. It is also possible to use a vapor phase raw material and perform firing in an atmosphere containing these raw material gases.

The positive electrode material obtained by such a manufacturing method is preferably an oxide having a single-phase inverted fluorite type crystal structure without an impurity phase in the X-ray diffraction method. Further, to know the crystal structure of the obtained positive electrode material,
If necessary, crush the positive electrode material in a mortar, etc.
This can be known by performing X-ray diffraction using α as a radiation source. The diffraction rate at the time of performing X-ray diffraction is preferably 0.1 ° / sec or less, more preferably 0.02 ° / sec.

Here, an example of the method for measuring the discharge capacity of the positive electrode material will be described. Here, a case is shown in which an electrochemical cell is created and the electrochemical characteristics of the positive electrode material are measured at a metal Li reference potential. As shown in FIG. 2, the electrochemical cell 5 includes a separator 1 including a test positive electrode 7 formed by using a positive electrode material, a counter electrode 9 using metal Li, and a porous insulating material.
1 and the separator 11, the counter electrode 9, the separator 1
1. Test positive electrode 7 and separator 11 were laminated in this order, sandwiched between two stainless steel plates 13 under pressure, and immersed in an organic electrolyte solution 17 contained in a sealable container 15. It is a thing. In addition, in the container 15,
The reference electrode 19 using metal Li is also suspended so as to be immersed in the organic electrolytic solution 17. Such an electrochemical cell 5 is manufactured in a glove box filled with an inert gas such as argon gas.

The test positive electrode 7 was prepared by mixing 85% by weight of the positive electrode material with 8% by weight of massive graphite as a conductive agent and 2% by weight of acetylene black, and mixing them with 5% by weight of polyvinylidene fluoride (PVDF) as a binder. ) Is dispersed in a solution in which N-methylpyrrolidone (NMP) is dissolved to obtain a positive electrode mixture slurry. This positive electrode mixture slurry is uniformly applied to one surface of an aluminum foil having a thickness of 20 μm and dried. The weight of the positive electrode mixture after drying is 10 to 25 mg / cm ² . Then, it is compression-molded by a roll press machine so that the density of the positive electrode mixture becomes 1.5 to 3.0 g / cm ³ .
After compression molding, a test positive electrode 7 is manufactured by punching into a disk shape having a diameter of 15 mm using a punching metal fitting.

The separator 11 is made of a microporous polypropylene film having a thickness of 25 μm. The test positive electrode 7 is
The positive electrode material is laminated so that the surface on which the positive electrode material is present faces the counter electrode 9 with the separator 11 interposed therebetween. The organic electrolytic solution 17 includes ethylene carbonate (EC) and diethyl carbonate (D
1) as an electrolyte in a mixed solvent having a weight ratio of 30:70.
Using a solution obtained by dissolving LiPF ₆ mol / l corresponds.

The electrochemical characteristics of the positive electrode material can be examined by using the electrochemical cell 5 thus manufactured.
When examining the electrochemical characteristics, a current value equivalent to 0.2C,
It is desirable to measure at a current value of 0.1 C or less.

By the way, in order to know the cycle characteristics of the positive electrode material, charging / discharging may be repeated under appropriate charging / discharging conditions and changes in the electrochemical characteristics thereof may be investigated. For example, it is possible to determine a certain appropriate charge end potential and discharge end potential, and examine the change in the charge capacity and the discharge capacity in the operating potential range. Therefore, when comparing the cycle characteristics of a plurality of positive electrode materials, it is only necessary to compare the reduction amounts of the charge capacity and the discharge capacity in a certain operating potential range. Further, a constant charge capacity per weight of the positive electrode material can be set as the charge termination condition. Generally, in the positive electrode material, the cycle characteristics deteriorate as the charge / discharge capacity, that is, the amount of Li to be desorbed / inserted increases. That is, as the charge / discharge capacity increases, the amount of Li that can be desorbed / inserted decreases faster. Therefore, when comparing the cycle characteristics of multiple positive electrode materials,
It is also possible to determine a constant charge capacity per weight of a certain positive electrode material, and compare the number of cycles in which charging cannot be performed up to the determined charge capacity when charging and discharging are repeated.

Furthermore, when comparing the cycle characteristics of a plurality of positive electrode materials, the charge termination condition for comparing the cycle characteristics can be specified by both the potential and the charge capacity.
Generally, when charging / discharging is performed with a predetermined charging capacity, the potential at the end of charging rises as the cycle deterioration progresses. When the potential at the end of charging reaches the end-of-charge potential, the charge capacity decreases in subsequent charge / discharge cycles. Therefore, even with such a method, the cycle characteristics of the positive electrode materials can be compared.

The structure of a lithium ion secondary battery having a positive electrode containing the positive electrode material of this embodiment will be described below by taking a cylindrical battery as an example. As shown in FIG. 3, the lithium-ion secondary battery 21 having a positive electrode containing the positive electrode material of the present embodiment includes a positive electrode 23 containing the positive electrode material of the present embodiment and a negative electrode active material that reversibly reacts or inserts Li. The negative electrode 25, a separator 27 that serves as a mechanism for electrically insulating the positive electrode 23 and the negative electrode 25, a nonaqueous electrolyte containing a lithium salt that electrochemically bonds the positive electrode 23 and the negative electrode 25, and the like. The separator 27 has a thickness of 15 to 50 μm
Of a porous insulating film such as a microporous polypropylene film.

The lithium-ion secondary battery 21, which is a cylindrical battery, has a separator 27 between a positive electrode 23 and a negative electrode 25.
The electrode group is manufactured by sandwiching the electrode with a cylindrical shape and wound into a cylindrical shape, and inserted into a cylindrical battery container 29 made of, for example, SUS or aluminum. After inserting the electrode group into the battery container 29, a current collecting tab 31 electrically connected to the negative electrode 25.
Is welded to the bottom surface of the cylindrical battery container 29, and the positive electrode collector tab 33 electrically connected to the positive electrode 23 is welded to the closed lid portion 35 having the positive electrode current terminal. After that, in the battery container 29 with one end opened, in the working space in dry air or an inert gas atmosphere, the EC / DMC mixed solvent is added.
After injecting an electrolyte solution in which 1 mol / liter of LiPF ₆ salt is dissolved, the sealing lid portion 35 is caulked and attached to the battery container 29 via a packing 37 provided at the opening edge portion of the cylindrical battery container 29. The inside of the battery container 29 was sealed to form the lithium-ion secondary battery 21, which is a cylindrical battery. An insulating plate 39 is provided between the electrode group and the bottom surface of the cylindrical battery container 29, or between the electrode group and the sealing lid 35.
41 is provided, and the current collecting tabs 31 and 33 are in a state of penetrating the insulating plates 39 and 41, respectively.

The positive electrode 23 is manufactured as follows. A positive electrode material powder made of an oxide having an inverted fluorite type crystal structure, which is a positive electrode material, and a conductive agent are mixed well. As the conductive agent, it is desirable to use graphite-based or amorphous carbon powder. The mixing ratio of the positive electrode material and the conductive agent is
The weight ratio of the conductive agent to the positive electrode material is preferably 7% to 25%. To this, a solution of polyvinylidene fluoride (PVDF) or the like as a binder dissolved in a solvent such as N-methylpyrrolidone (NMP) is added and mixed to obtain a positive electrode mixture slurry. This positive electrode mixture slurry is applied to an aluminum foil having a thickness of 10 μm to 20 μm, and 8
Dry at a temperature of 0 ° C to 100 ° C. By the same procedure, the positive electrode mixture slurry is applied to the opposite surface of the aluminum foil and dried. After that, compression molding with a roll press machine,
The positive electrode 23 is cut into a predetermined size.

As the negative electrode active material of the negative electrode 25, for example,
Metallic lithium, carbon materials, compounds containing Li,
Alternatively, various materials that can form a compound with Li can be used, but a carbon material that is a material that can form a compound into which Li is inserted is particularly preferable. Carbon materials include graphite-based materials and amorphous carbon materials, but their discharge behavior is slightly different depending on the type of carbon material used for the negative electrode active material. Generally, graphite-based materials are metallic Li
Since a flat discharge potential is shown in the vicinity of 0.1 V as a standard, a lithium ion secondary battery having a stable discharge voltage can be obtained. Further, in general, the potential of the amorphous carbon material continuously changes depending on the depth of discharge, so that a lithium ion secondary battery in which the remaining capacity can be easily detected by the battery voltage can be obtained. Examples of the material capable of forming a compound with Li include metals such as aluminum, tin, silicon, indium, gallium, and magnesium, alloys containing these elements, and metal oxides containing tin, silicon, and the like. Also,
As the negative electrode active material of the negative electrode 25, a metal, an alloy, and a metal oxide, which are materials capable of forming a compound with Li,
It is also possible to use a composite material with a graphite-based or amorphous carbon material, which is a material capable of forming a compound into which Li is inserted.

The negative electrode 25 is manufactured as follows. Here, a carbon material is used as the negative electrode active material.
The negative electrode active material made of this carbon material is used as a binder with PV
A solution prepared by dissolving DF or the like in a solvent such as NMP is added and mixed to obtain a negative electrode mixture slurry. This negative electrode mixture slurry is applied to a copper foil and dried at a temperature of 80 ° C to 100 ° C.
In the same procedure, the negative electrode mixture slurry is applied to the opposite surface of the copper foil and dried. After that, compression molding is carried out by a roll press machine and cut into a predetermined size to prepare a negative electrode. What can be used as the separator 27 is a resin-made porous insulating film such as polyethylene (PE) or polypropylene (PP), a laminate of those resin-made porous insulating films, or a resin-made porous insulating film thereof. It is also possible to use a material film in which an inorganic compound such as alumina is dispersed.

If necessary, various additives may be added to the electrolytic solution in which the electrolyte that electrochemically bonds the positive electrode 23 and the negative electrode 25 is dissolved. The electrolytic solution may be a solution in which a lithium salt is used as an electrolyte and is dissolved in an organic solvent, and the lithium salt moves in the electrolytic solution due to charge and discharge of the battery.
i-ion is supplied, and as a lithium salt, Li
Other than PF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li
BF ₄ , LiAsF ₆ or the like alone or 2
More than one kind can be appropriately used. Examples of the organic solvent include carbonates, esters, ethers, and the like. Besides ethylene carbonate (EC) and dimethyl carbonate (DMC), propylene carbonate, butylene carbonate, diethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ- Butyrolactone or the like can be used as appropriate. In general, 0.1 to 2 mol / liter, preferably 0.7 to 1.5 mol / liter, of the above-mentioned Li salt is dissolved and used in a solvent in which these organic solvents are used alone or in a mixture.

Additives are used as necessary for the purpose of improving the safety of batteries, suppressing side reactions, and improving stability at high temperatures. As additives, sulfur compounds, phosphorus compounds, etc. may be used. The thing which melt | dissolves in the said solvent, the thing which doubles as a solvent, etc. are mentioned.

In order to make the lithium ion secondary battery having the positive electrode containing the positive electrode material of this embodiment into a prismatic battery, the positive electrode 23, the negative electrode 25, and the separator of the lithium ion secondary battery 21 which is a cylindrical battery. Using the positive electrode, the negative electrode, and the separator prepared in the same manner as in No. 27, a square center electrode is wound to form a square electrode group. Similar to the lithium-ion secondary battery 21 which is a cylindrical battery, this prismatic electrode group is housed in a prismatic battery container, and after injecting an electrolytic solution, it is sealed. In the case of a prismatic battery, instead of the wound prismatic electrode group, an electrode group composed of a laminate formed by laminating a separator, a positive electrode, a separator, a negative electrode, and a separator in this order may be used.

When examining the electrochemical characteristics of the positive electrode of the lithium-ion secondary battery prepared in this way, FIG.
An electrochemical cell 25 as shown in can be used. At this time, the lithium ion secondary battery 21 is disassembled in an inert atmosphere such as argon. This disassembly can be performed regardless of the charge / discharge state of the lithium ion secondary battery 21. The positive electrode 23 of the disassembled battery is separated and thoroughly washed with a cleaning liquid, such as dimethyl carbonate,
The cleaning liquid attached to the cleaned positive electrode 23 is sufficiently dried. Then, the total weight and area of the positive electrode 23 are measured. Further, the area of application of the positive electrode mixture is also measured.
Then, the positive electrode 23 is punched into a disk shape having a diameter of 15 mm by using a punching metal fitting. When the positive electrode 23 is one in which the positive electrode mixture is applied on both sides, one side is completely peeled off using a solvent such as NMP or acetone to prepare a single-sided coated test positive electrode. An electrochemical cell 25 is produced using this test positive electrode, and a charge / discharge test is performed in the same manner as described above.

Further, by using the disassembling method of the lithium ion secondary battery 21 as described above, the lithium ion secondary battery 2
The crystal structure of the positive electrode material in the positive electrode 23 of No. 1 can be investigated. Positive electrode 23 in which the battery was disassembled, washed and dried in the same manner as described above
Is punched into a disk shape of 15 mm and measured by an X-ray diffraction method. If necessary, the measurement can be performed without using the X-ray transparent film so as not to contact the atmosphere.

The lithium-ion secondary battery provided with the positive electrode containing the positive electrode material of the present invention has various uses, such as a personal computer, a word processor, a cordless handset, an electronic book player, a mobile phone, a car phone, and a pager (registered trademark). ), Handheld terminals, portable copiers, electronic organizers, calculators, LCD TVs, electronic translators, memory cards, and other portable electronic devices, as well as other devices such as radios, tape recorders, headphone stereos, portable CD players, video movies, and electrics. Power supply for various portable devices such as shavers, portable power tools, transceivers, portable radios, voice input devices, refrigerators, air conditioners, TVs, stereos, water heaters, microwave ovens, dishwashers, dryers, washing machines, lighting It can be used for household appliances such as appliances and toys Furthermore, as an industrial application, the present invention can be applied to various electric vehicles, hybrid vehicles using both a power source such as an internal combustion engine and power from an electric motor, medical equipment, golf carts, power storage systems, elevators, and the like.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 4 shows the composition of transition metal elements and
It is a figure which shows the relationship of the discharge capacity of the 10th cycle. Figure 5
6 and 6 are diagrams showing the relationship between the number of charge / discharge cycles and the battery capacity.
Is. The present invention is not limited to the examples described below.
It is not something that can be done. (Example 1) Consists of an oxide having an inverted fluorite type crystal structure
As the positive electrode material, the general formula Li₅Fe _0.8Mn_0.3O_Four
Positive electrode material 1 represented by Li_4.4Fe_0.9Co_0.4O
_3.9F_0.1Positive electrode material 2 represented by Li_4.7Fe
_0.9Mn_0.1Ni_0.2O_FourPositive electrode material 3, L
i₅Fe_0.6Cu_0.4Ni_0.1O_3.8F_0.2Indicated by
Positive electrode material 4, Li_4.4Fe_0.8Al_0.2O_FourIndicated by
Positive electrode material 5, Li_{Four .6}FeAl_0.1O_3.9F
_0.1Positive electrode material 6 represented by Li_4.8Fe_0.9Zn
_0.2Mg_0.05O_FourPositive electrode material 7 represented by Li_4.6
Fe_0.8Co_0.3Mg_0.2O_3.9F_0.1Indicated by
Positive electrode material 8, Li_4.5FeAl_0.1Mg_{0. 1}O_FourIndicated by
Was synthesized.

The raw materials are lithium hydroxide (LiOH), lithium fluoride (LiF), iron oxide (Fe ₂ O ₃ ), manganese oxide (MnO), cobalt oxide (CoO), copper oxide (Cu ₂ O), and oxidation. Nickel (NiO), zinc oxide (Z
nO), magnesium oxide (MgO), and aluminum hydroxide (Al (OH) ₃ ) were used. These raw materials were weighed so as to have a predetermined metal element ratio and anion ratio, and then dry-mixed at room temperature for 30 minutes by a raider machine to obtain a starting raw material powder. Place this in an alumina box and place in argon for 900
The positive electrode materials 1 to 9 were obtained by firing at 15 ° C. for 15 hours.

The electrochemical characteristics of the obtained positive electrode materials 1 to 9 were examined by the following procedure. Positive electrode materials 1 to 9 85% by weight of positive electrode material, 8% by weight of massive graphite as a conductive agent and 2% by weight of acetylene black were mixed and mixed, and 5% by weight of PVDF was dissolved in NMP as a binder in advance. The mixed solution was dispersed to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was uniformly applied to one surface of an aluminum foil having a thickness of 20 μm, dried, and then compression-molded by a roll press machine so that the density of the positive electrode mixture was 2.0 g / cm ³ . After compression molding, this was punched into a disk shape having a diameter of 15 mm using a punching metal to prepare a test positive electrode containing any of the positive electrode materials 1 to 9.

Using these test positive electrodes, an electrochemical cell 25 using metal Li for the counter electrode 9 and the reference electrode 19 as shown in FIG. 2 was prepared, and a cycle test was conducted in which charging and discharging were repeated. The charging / discharging current was 0.1 mA / cm ² . The test was conducted under two conditions of charge termination conditions: a potential of 4.0 V on the basis of metal Li and a constant capacity charge of 210 mAh / g per weight of the positive electrode material. That is, charging ends when either one of the potential and the capacity is reached. The discharge termination condition is
It was determined that the potential of 1.5 V was reached on the basis of metallic Li. Table 1 shows the charge capacity and discharge capacity per weight of the positive electrode material after 10 cycles.

[0047]

[Table 1] The charge capacity and the discharge capacity per weight of the positive electrode material after 10 cycles were 198 mAh / g and 1 for the positive electrode material 1, respectively.
89 mAh / g, 141 mAh / g and 1 for positive electrode material 2
34 mAh / g, positive electrode material 3 with 168 mAh / g and 1
60 mAh / g, 172 mAh / g and 1 for positive electrode material 4
63 mAh / g, positive electrode material 5 has 128 mAh / g and 1
21 mAh / g, 143 mAh / g and 1 for positive electrode material 6
35 mAh / g, 162 mAh / g and 1 for positive electrode material 7
55 mAh / g, 148 mAh / g and 1 for positive electrode material 8
41 mAh / g, positive electrode material 9 has 135 mAh / g and 1
It was 29 mAh / g. As a positive electrode material composed of an oxide having an inverse fluorite crystal structure (Example 2) Example 2, the general formula Li ₆ Mn
Positive electrode material 1 represented by _0.8 Ni _0.1 O _3.8 F _{0.2
0, Li 5. 9 Mn 0.7 Co} 0.2 Zn 0.1 O 3.9 F
Cathode material 11 indicated by _0.1, Li _{5 .8} MnMg
Positive electrode material 12 represented by _0.1 O ₄ , Li _5.85 Mn
Positive electrode material 13 represented by _0.9 Cu _0.1 Al _0.05 O ₄
Was synthesized in the same manner as in Example 1, and each positive electrode material 10 to 1 was synthesized.
A test positive electrode including any one of 3 was prepared.

Implementation was carried out on the obtained positive electrode materials 10 to 13.
The same charge / discharge test as in Example 1 was performed. 10 cycles in Table 1
The charge capacity and the discharge capacity per unit weight of the positive electrode material are shown.
Charge capacity and discharge per positive electrode material weight at 10 cycles
The capacity is 123 mAh / g and 1 for the positive electrode material 10, respectively.
16 mAh / g, 134 mAh / g for positive electrode material 12 and
125 mAh / g, 120 mAh / g for positive electrode material 12
114 mAh / g, positive electrode material 13 has 128 mAh / g
And 119 mAh / g. (Example 3) As Example 3, it has an inverted fluorite type crystal structure.
As a positive electrode material made of an oxide, the general formula Li_5.8Co
Zn_0.1O_FourPositive electrode material 14 represented by Li₆Co
_0.9Cu _0.1Zn_0.05O_FourPositive electrode material 1
5, Li_5.75Co_1.1Al_{0.0 5}O_FourPositive indicated by
Polar material 16, Li_5.95Co_0.9Mg_0.1O_3.95F
_{0.0 5}Positive electrode material 17 represented by Li₆Co_0.4Ni
_0.1Mg_0.5O_FourPositive electrode material 18 represented by Li_5.6C
o_0.8Al_0.1Mg_0.2O_3.9F_0.1Positive indicated by
Pole material 19 was synthesized. At this time, the same person as in Example 1
Synthesis was performed by the method, but the firing conditions were argon atmosphere.
The temperature was 750 ° C. for 15 hours.

Implementation was carried out on the obtained positive electrode materials 14 to 19.
The same charge / discharge test as in Example 1 was performed. 10 cycles in Table 1
The charge capacity and the discharge capacity per unit weight of the positive electrode material are shown.
Charge capacity and discharge per positive electrode material weight at 10 cycles
The capacity of the positive electrode material 14 is 138 mAh / g and 1 respectively.
30 mAh / g, 137 mAh / g for positive electrode material 15 and
130 mAh / g, 140 mAh / g for positive electrode material 16
And 132 mAh / g, positive electrode material 17 has 152 mAh / g
And 145 mAh / g, the positive electrode material 18 has 119 mAh / g.
g and 112 mAh / g, positive electrode material 19 has 148 mAh
/ G and 129 mAh / g. (Example 4) As Example 4, it has an inverted fluorite type crystal structure.
As a positive electrode material made of an oxide, the general formula Li_5.6Cu
_1.8Ni_0.2O_FourPositive electrode material 20 represented by Li_5.4
Cu _TwoZn_0.1O_3.7F_0.03Positive electrode material 21, Li
_4.9Cu_2.8Al_0.1O_FourA positive electrode material 22 represented by
Li_6.3Cu_1.4Mg_0.1O_3.9F_0.1Indicated by
The positive electrode material 23 was synthesized. At this time, the same as in the first embodiment
Although the synthesis was performed by the method, the firing conditions were argon atmosphere.
The temperature was 800 ° C. in air for 15 hours.

The positive electrode materials 20 to 23 thus obtained were subjected to the same charge and discharge test as in Example 1. Table 1 shows the charge capacity and discharge capacity per weight of the positive electrode material after 10 cycles.
The charge capacity and the discharge capacity per weight of the positive electrode material after 10 cycles were 125 mAh / g and 1 for the positive electrode material 20, respectively.
20 mAh / g, 130 mAh / g and 123 mAh / g for cathode material 21, 135 mAh / g and 128 mAh / g for cathode material 22, 120 mAh / g for cathode material 23
And 115 mAh / g. As a positive electrode material composed of an oxide having an inverse fluorite crystal structure (Comparative Example 1) Comparative Example 1, the general formula Li ₆ Co
A positive electrode material 24 represented by _0.3 Ni _0.1 Mg _0.6 O ₄ was synthesized in the same manner as in Example 3. In the positive electrode material 24, the composition y of the transition metal element is y <0.5.

The same charge and discharge test as in Example 1 was conducted on the positive electrode material of the obtained positive electrode material 24. Table 1 shows the charge capacity and discharge capacity per weight of the positive electrode material after 10 cycles. The charge capacity and discharge capacity per positive electrode material weight of the positive electrode material 24 after 10 cycles were 98 mAh / g and 93 mAh / g, respectively. (Comparative Example 2) As Comparative Example 2, as a positive electrode material made of an oxide having an inverted fluorite crystal structure, a general formula Li _4.6 Cu was used.
_The positive electrode material represented by _3.1 Al _0.1 O ₄ was synthesized in the same manner as in Example 4. Here, since the composition y of the transition metal element was y> 3, the obtained material was a mixture of an inverted fluorite type crystal phase and a red copper steel type crystal phase. Therefore, a charge / discharge test was not performed because a single phase product was not obtained. Comparative Example 3 As Comparative Example 3, a positive electrode material 25 represented by the general formula Li ₆ CoO ₄ was synthesized in the same manner as in Example 3 as a positive electrode material made of an oxide having an inverted fluorite type crystal structure. The positive electrode material 25 contains only one kind of cation other than Li.

The obtained positive electrode material 25 was subjected to the same charge / discharge test as in Example 1. Table 1 shows the charge capacity and discharge capacity per weight of the positive electrode material after 10 cycles. The charge capacity and discharge capacity of the positive electrode material 25 per 10 cycles of the positive electrode material 25 were 90 mAh / g and 88 mA, respectively.
It was h / g. (Comparative Example 4) As Comparative Example 4, a positive electrode material 26 represented by the general formula Li ₅ FeO ₄ and a positive electrode material 27 represented by Li ₆ MnO ₄ were used as the positive electrode material made of an oxide having an inverted fluorite crystal structure. Synthesis was carried out in the same manner as in Example 1. The positive electrode materials 26 and 27 contain only one kind of cation other than Li.

The positive electrode materials 26 and 27 thus obtained were subjected to the same charge / discharge test as in Example 1. Table 1 shows the charge capacity and discharge capacity per weight of the positive electrode material after 10 cycles.
The charge capacity and the discharge capacity per 10 cycles of the positive electrode material were 110 mAh / g and 98 mAh / g for the positive electrode material 26 and 39 mAh / g and 34 mAh / g for the positive electrode material 27, respectively.

Examples 1 to 4 and Comparative Examples 1 and 3 as described above.
The relationship between the transition metal composition y of the positive electrode material and the discharge capacity at the 10th cycle in Nos. 4 and 4 is shown in FIG. Comparing the results of Examples 1 to 4 and Comparative Examples 1, 3 and 4 shown in Table 1 and FIG. 4, positive electrode materials 1 to 9 in Example 1, positive electrode materials 10 to 13 in Example 2, and Positive Electrode Material 14 to 19 in Example 3 and Positive Electrode Material 20 in Example 4
23 to 23, the positive electrode material 24 in Comparative Example 1, the positive electrode material 25 in Comparative Example 3, and the Comparative Example 4
In comparison with the positive electrode materials 26 and 27 in No. 3, the charge capacity and the discharge capacity are higher and the cycle property is excellent. Therefore,
A positive electrode material comprising an oxide having an inverted fluorite crystal structure containing Li and at least two kinds of cations other than Li, and at least one kind of cations other than Li is a transition metal element is lithium. The charge / discharge capacity of the ion secondary battery can be increased and the charge / discharge cycle characteristics can be improved.

Further, the composition y of the transition metal element is y <0.
5, the discharge capacity was small, and when y> 3, an impurity phase was generated. Therefore, the general formula Li _x Me _y M _z O _4-a A _a
, The composition y of the transition metal element Me is 0.5 ≦
It is desirable that y ≦ 3 in order to increase the charge / discharge capacity of the lithium ion secondary battery and improve the charge / discharge cycle characteristics. (Example 5) In Example 5, the positive electrode material 1 produced in Example 1 was used to produce a lithium-ion secondary battery 21, which was a cylindrical battery as shown in FIG. The positive electrode 23 includes a positive electrode material, a graphite-based conductive material, and acetylene black in a weight ratio of 90 :.
Mix 500 g at a ratio of 8: 2, add 325 g of PVDF solution diluted to 7% with NMP, stir this with a mixer to prepare a positive electrode mixture slurry, and use a transfer type coating machine to roll it. It was prepared by continuous coating and drying on a 20 μm thick aluminum foil wound on the aluminum foil, applying it to both sides of the aluminum foil, cutting it to a predetermined length and width, and then roll pressing it with a linear pressure of 250 kg / cm. . A collector tab 33 made of aluminum for connecting to a current terminal and extracting a current was attached to the positive electrode 23 by spot welding.

The negative electrode 25 is composed of massive graphite 15 which is a negative electrode material.
To 0 g, 240 g of PVDF solution diluted with NMP to 7% was added, and the mixture was stirred with a mixer to form a negative electrode mixture slurry, which was applied on a copper foil having a thickness of 15 μm in the same manner as the positive electrode 23, and then mixed with the positive electrode 23. It cut similarly and pressed and produced. A nickel foil was attached to the negative electrode 25 as a current collecting tab 31 by spot welding.

The positive electrode 23 and the negative electrode 25 produced in this way,
Then, a 25 μm-thick separator 27 is wound to form an electrode group, the electrode group is inserted into a battery container 29 made of SUS, a current collecting tab 31 on the negative electrode side is welded to the bottom surface of the battery container 29, and a positive electrode current is supplied. The collector tab 33 on the positive electrode side is welded to the closed lid portion 35 having a terminal, and 1 mol / liter of the EC / DMC mixed solvent is added.
After injecting an electrolytic solution in which liter of LiPF ₆ salt is dissolved, the sealing lid 35 is attached to the battery container 2 via the packing 37.
The lithium ion secondary battery 21, which is a cylindrical battery, was formed by caulking it in 9 and sealing it.

A charging / discharging test was conducted by connecting a copper wire to the lithium-ion secondary battery 21, which is a cylindrical battery thus formed. The charging / discharging current is 200 mA, and the charge termination condition is a voltage of 3.9 V and a constant capacity charging of 2000 mAh.
The test was conducted under conditions. That is, charging ends when either the voltage or the capacity is reached. The discharge termination condition was a voltage of 1.5V. As shown in FIG. 5, the lithium-ion secondary battery 21 of the present embodiment shows a change in the charge capacity and the discharge capacity of the battery with the lapse of cycles.
mAh and 1920 mAh were 1770 mAh and 1750 mAh at 10 cycles, respectively. (Comparative Example 5) In Comparative Example 5, a positive electrode 23 was prepared using lithium cobalt oxide (LiCoO ₂ ) which is a commercially available positive electrode material, and a lithium ion secondary battery 21 was prepared in the same manner as in Example 5. The charge / discharge test was performed in the same manner as in Example 5 except that the charge termination condition was a voltage of 4.4 V and a constant capacity charge of 2000 mAh, and the discharge termination condition was 3.0 V. As shown in FIG. 6, the change in the charge capacity and the discharge capacity of the battery according to the cycle of the battery of this comparative example was as follows: the charge capacity and the discharge capacity of the battery at 5 cycles were 680 mAh and 525 mAh, respectively. Example 5
Compared with, the charge and discharge capacities were significantly reduced and the cycle characteristics were inferior.

Therefore, in the lithium ion secondary battery provided with the positive electrode formed by using the positive electrode material according to the present invention as in Example 5, the charge / discharge capacity is increased and the charge / discharge cycle characteristics are improved. it can.

[0060]

According to the present invention, the charge / discharge capacity of a lithium ion secondary battery can be increased and the charge / discharge cycle characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of an oxide having an inverted fluorite type crystal structure, which is a positive electrode material to which the present invention is applied.

FIG. 2 is a partial cross-sectional view showing a schematic configuration of an embodiment of a lithium ion secondary battery in which a positive electrode is formed using a positive electrode material to which the present invention is applied.

FIG. 3 is a partial cross-sectional view showing an example of a schematic configuration of an electrochemical cell for examining electrochemical characteristics of a positive electrode material.

FIG. 4 is a diagram showing the relationship between the composition of a transition metal element and the discharge capacity at the 10th cycle.

FIG. 5 is a diagram showing the relationship between the number of charge / discharge cycles and the battery capacity of a positive electrode material according to an embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the number of charge / discharge cycles and the battery capacity in a comparative example.

[Explanation of symbols]

1 anion 3 cations 5 Electrochemical cell 7 Test positive electrode 9 opposite poles 11, 27 separator 13 Stainless steel plate 15 containers 17 Organic Electrolyte 19 reference pole 21 Lithium-ion secondary battery 23 Positive electrode 25 negative electrode 29 Battery case 31, 33 Current collecting tab 35 Sealing lid

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C01G 51/00 C01G 51/00 A 53/00 53/00 A H01M 4/02 H01M 4/02 C 10 / 40 10/40 Z (72) Inventor Toshi Takeuchi 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Akihiro Goto 7-1 Omika-cho, Hitachi-shi, Ibaraki F-term in Hitachi Research Laboratory, Hitachi, Ltd. (Reference) 4G002 AA06 AA10 AA12 AB01 AD04 AE05 4G047 AA04 AA05 AB01 AC03 4G048 AA04 AA05 AA06 AB05 AC06 AD06 AE05 5H029 AJ03 AJ05 AK03 AL02 BJ C08 AM02 AM14 AM02 AL12 AM08 AL07 AM12 AL02 HJ02 5H050 AA07 AA08 BA17 CA07 CB02 CB07 CB08 CB12 CB29 FA05 GA10 HA02

Claims (3)

[Claims] 1. A lithium comprising an oxide having an inverted fluorite type crystal structure containing Li and at least two kinds of cations other than Li, and at least one kind of the cations other than Li is a transition metal element. Positive electrode material for ion secondary batteries. 2. The general formula Li _x Me _y M _z O _4-a A.
_a (however, Me is at least one kind of transition metal element, M is a cation other than Li and a transition metal, A is an anion other than oxygen, and 3 ≦ x ≦ 7, 0.5 ≦ y ≦ 3, 0 ≦ z ≦ 2,0
The positive electrode material for a lithium ion secondary battery according to claim 1, wherein ≦ a ≦ 1 and 4 <x + y + z ≦ 8). 3. A lithium ion secondary battery, wherein the positive electrode contains the positive electrode material according to claim 1 or 2.