JP2002128526A - Lithium transition metal compound oxide for positive electrode active material for lithium secondary battery and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium-transition metal compound oxide having stable crystal structure and less cycle deterioration, which is used for a positive electrode active material for a lithium secondary battery with good cycle characteristic. SOLUTION: Lithium-transition metal compound oxide is represented by a composition formula Li1+xM1-x-yAlyO2-zFz (M is a kind of element selected among Co, Ni, Mn; 0<=x<=0.2; 0.05<=y<=0.2; 0.01<=z<=0.3) and has a lamellar halite crystal structure and the diffraction peak ratio I003/I104 of 1.7 or more, wherein I003 and I104 are diffraction peak strength at the (003) and (104) sides in X-ray diffraction method using CuKα ray. The lithium-transition metal compound oxide is used for a positive electrode active material for lithium secondary batteries.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for storing and storing lithium.
The present invention relates to a lithium transition metal composite oxide suitable as a positive electrode active material for a lithium secondary battery utilizing a desorption phenomenon, and also relates to a lithium secondary battery using the same.

[0002]

2. Description of the Related Art With the miniaturization of personal computers, video cameras, mobile phones, and the like, in the fields of information-related equipment and communication equipment, lithium secondary batteries are used as power sources for these equipments because of their high energy density. Has been put to practical use and has spread widely. On the other hand, in the field of automobiles, the development of electric vehicles is urgent due to environmental problems and resource problems, and lithium secondary batteries are being studied as power sources for electric vehicles.

[0003] Since lithium secondary batteries are relatively expensive, they are required to have a longer life than other batteries. That is, it is required that the cycle characteristics such that the capacity does not decrease even when charge and discharge are repeated are good. In particular, since the deterioration proceeds further under the high temperature at which the battery reaction is activated, for example, when assuming that the lithium secondary battery is used for an application such as a power supply for an electric vehicle that may be left outdoors, Good cycle characteristics at high temperature is one of the important characteristics required for the lithium secondary battery.

A lithium secondary battery is composed of a positive electrode, a negative electrode, a non-aqueous electrolyte, and the like, and each component has a cause of cycle deterioration. The current lithium secondary battery has a high oxidation-reduction potential and can constitute a 4V-class lithium secondary battery.
₂ , layered rock salt-structured lithium transition metal composite oxides such as LiNiO ₂ are preferably used. In a lithium secondary battery using these lithium transition metal composite oxides as a positive electrode active material, this lithium transition metal composite oxide is used. The cycle deterioration caused by the structural change of the lithium secondary battery is a main factor of the cycle deterioration of the lithium secondary battery.

The layered rock salt structure lithium transition metal composite oxide has a hexagonal crystal structure, and is composed of a layer composed of a transition metal, O
, A layer made of Li, and a layer made of O are repeatedly laminated in this order. In order to suppress the cycle deterioration due to the positive electrode active material, there are many techniques in the lithium transition metal composite oxide in which part of the transition metal element present in the transition metal layer is replaced with another element.

[0006]

According to a number of experiments and studies, although the reason is not clear, the present inventor has proposed that instead of replacing some of the elements present in the transition metal layer with other elements, or in combination therewith. It has been found that by substituting a part of O present in the O layer with F (fluorine) having a high electronegativity, the crystal structure of the lithium transition metal composite oxide can be stabilized.

[0007] However, the present inventor has simply stated that O
At the same time, it was also found that it was not possible to produce a lithium transition metal composite oxide having good crystallinity, that is, a lithium composite oxide having a stabilized crystal structure, in the case where an attempt was made to substitute a part of the compound.

Accordingly, the present inventor has conducted further experiments and studies to replace a part of the transition metal element present in the transition metal layer sandwiched by the O layers with Al having an atomic radius smaller than that of the transition metal element. Thus, a new finding has been obtained that a lithium composite oxide having good crystallinity can be obtained even when a part of O present in the O layer is replaced with F.

The present invention has been made on the basis of such a new finding, and the crystal structure has been stabilized by substituting part of the transition metal with Al and substituting part of O with F. That is, it is an object of the present invention to provide a lithium transition metal composite oxide with less cycle deterioration. Another object of the present invention is to provide a lithium secondary battery having good cycle characteristics by using the lithium transition metal composite oxide as a positive electrode active material.

[0010]

The lithium transition metal composite oxide for a positive electrode active material of a lithium secondary battery according to the present invention has a composition formula of Li _{1 + x} M _1-xy Al _y O _2-z F _z (M is Co , Ni, Mn
0 ≦ x ≦ 0.2; 0.05 ≦ y
≦ 0.2; represented by 0.01 ≦ z ≦ 0.3), the crystal structure is a layered rock salt structure, the intensity I ₀₀₃ of diffraction peaks of (003) plane by X-ray diffraction analysis using a CuKα line (1
04) Intensity ratio I ₀₀₃ / I with the intensity I ₁₀₄ of the diffraction peak of the plane
₁₀₄ is 1.7 or more.

That is, in the present lithium transition metal composite oxide, part of the M atoms present in the transition metal M layer in the layered rock salt structure is partially replaced by Al atoms, and the O atoms present in the O layer are removed.
It is a lithium transition metal composite oxide having high crystallinity in which some of the atoms are replaced with F atoms.

In the lithium transition metal composite oxide, a part of O is substituted by F having a higher electronegativity,
A lithium transition metal composite oxide having an extremely stable crystal structure is obtained. The mere substitution with F deteriorates the crystallinity due to the difference in atomic radius from O or the like. However, in the present lithium transition metal composite oxide, even in the transition metal M layer sandwiched between the O layers, good crystallinity is ensured by substitution with Al having a small atomic radius.

Therefore, the lithium transition metal oxide of the present invention has good crystallinity and an extremely stable crystal structure, whereby the collapse of the crystal structure due to the occlusion and desorption of Li due to the repetition of charge and discharge is suppressed, and the cycle deterioration is small. It becomes a positive electrode active material for lithium secondary batteries. In addition, Al which is a substitution element
Also has a function of improving the thermal stability of the lithium transition metal composite oxide, so that the present lithium transition metal composite oxide is also a positive electrode active material having excellent thermal stability.

Further, a lithium secondary battery of the present invention is characterized in that the above-mentioned lithium transition metal composite oxide of the present invention is used as a positive electrode active material. By using the lithium transition metal composite oxide which is a positive electrode active material with less cycle deterioration, the present lithium secondary battery becomes a lithium secondary battery having good cycle characteristics. The lithium transition metal composite oxide can sufficiently withstand a battery reaction at a high temperature at which the battery reaction is activated, because of its excellent crystal structure stability and the above-described effect of improving the thermal stability of Al. The lithium secondary battery also has good cycle characteristics.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the composition, crystal structure and crystallinity of a lithium transition metal composite oxide for a lithium secondary battery positive electrode active material of the present invention and a lithium secondary battery of the present invention will be described. , Its manufacturing method, and the configuration of the lithium secondary battery will be described in detail.

<Composition of lithium nickel composite oxide>
The lithium transition metal composite oxide of the invention has a composition of Li
_{1 + x}M_1-xyAl_yO_{Two -z}F_z(M is from Co, Ni, Mn
One or more selected; 0 ≦ x ≦ 0.2; 0.05 ≦ y ≦
0.2; 0.01 ≦ z ≦ 0.3).

Depending on the type of the transition metal M, the composition formula Li _{1 + x}
Lithium cobalt composite oxide represented by _{Co 1-xy Al y O 2} -z F z, the lithium nickel composite oxide represented by the composition formula _{Li 1 + x Ni 1-xy} Al y O 2-z F z, Composition formula Li _{1 + x} M
There is a lithium-manganese composite oxide represented by n _1-xy Al _y O _{2 -z} F _z , and the transition metal element M is composed of two or more elements and has a composition formula Li _{1 + x} (Co , N
_{i) 1-xy Al y O} 2-z F z, Li 1 + x (Ni, Mn) 1-xy
Al _y O _2-z F _z , Li _{1 + x} (Mn, Co) _1-xy Al _y O
_{2-z F z, Li 1} + x (Co, Ni, Mn) 1-xy Al y O 2-z
There is one represented by F _z . Note that C in M
The mixing ratio of o, Ni, and Mn can be set arbitrarily.

Among these, the transition metal element M contains Ni as its central element, and has a composition formula of Li _{1 + x} Ni
_{1-xyw M 'w Al y} O 2-z F z (M' is Co, 1 or more selected from Mn; 0 ≦ w ≦ 0.3) lithium nickel composite oxide represented by the composition formula LiNiO The characteristics of the lithium-nickel composite oxide represented by ₂ are maintained, and they are relatively inexpensive because they do not contain a lot of expensive Co. In addition, since their theoretical capacities are relatively large, these merits are considered. In this case, it is desirable that the lithium nickel composite oxide represented by the above composition formula be used as the positive electrode active material. In addition, since the lithium nickel composite oxide has relatively low thermal stability, the effect of improving thermal stability by substituting with Al is greatly exhibited. Also in that respect, the lithium nickel composite oxide represented by the above composition formula is effective.

Composition formula Li _{1 + x} Ni _1-xyw M ′ _w Al _y O _2-z
In the case of a lithium nickel composite oxide represented by F _z ,
Similarly, the composition formulas Li _{1 + x} Ni _1-xy Al _y O _2-z F
_{z, Li 1 + x Ni 1} -xyw Co w Al y O 2-z F z, Li 1 + x N
_{i 1-xyw Mn w Al y} O 2-z F z, Li 1 + x Ni
_1-xyw (Co, Mn) _w Al _y O _2-z F _z is included. Note that also in this case, Co in M ′,
Similarly, the mixing ratio of Mn can be arbitrarily set.

Further, the above composition formula Li _{1 + x} M _1-xy Al _y O
_2-z F _z is Li _{1 + x} which replaces part of the transition metal M with Li.
M _1-xy Al _y O ₂ -z F _z (x> 0) and LiM _{1 -y} Al _y O ₂ -z F _z in which part of the transition metal M is not replaced with Li are included. I have. Furthermore, it does not exclude unavoidable non-stoichiometric compositions such as the incorporation of impurity elements generated in the manufacturing process, excess or deficiency of each constituent element.

In the following, the composition formula Li _{1 + x} M _1-xy Al _y O _2-z
The composition ratio of the respective constituent elements will be described in F _z. First, the composition ratio of Li, 1 + x, that is, the ratio x in which part of the transition metal M is replaced with Li is set to x ≦ 0.2. When x> 0.2, monovalent L is added to the layer of the transition metal M.
This is because the presence of a large amount of i causes too little Li to be occluded / desorbed due to charge / discharge, resulting in an excessive decrease in the capacity as an active material. As a practical range, it is more preferable that x ≦ 0.1.

Next, the composition ratio of Al, that is, the ratio of Al replacing the transition metal M, in other words, the value of y in the composition formula is
It is assumed that 0.05 ≦ y ≦ 0.2. If y <0.05,
The effect of the substitution is small, and not only is the thermal stability inferior, but also the crystallinity is significantly reduced by substituting a part of O with F. Conversely, when y> 0.2, the capacity as an active material is excessively reduced. As a practical range, it is more desirable that y ≦ 0.1.

The composition ratio of F, that is, the ratio of F replacing O,
In other words, the value of z in the composition formula is 0.01 ≦ z ≦ 0.
3 is assumed. When z <0.01, the effect of substitution is small and the crystal structure cannot be stabilized. Conversely, when z> 0.3, there is a problem that it is difficult to obtain a lithium transition metal composite oxide having good crystallinity. Incidentally, from the viewpoint of improving the cycle characteristics by stabilizing the crystal structure, z ≧ 0.
1 is more desirable, and from the viewpoint of securing a large capacity by maintaining good crystallinity, z ≦ 0.2
Is more desirable.

<Crystal Structure of Lithium Nickel Composite Oxide
And crystallinity> The lithium transition metal composite oxide of the present invention
Has a layered rock salt structure. Layered rock salt structure
Is a crystal structure belonging to a hexagonal system and has a composition formula of LiM
O _TwoIn the case of the normal composition represented by
Layer, O layer, Li layer, O layer
It has a crystal structure in which four layers are repeatedly laminated in this order.
You. However, as described above, the lithium transition gold of the present invention
Group oxides are part of the M atoms present in the M layer.
Is replaced by an Al atom and, in some cases, a Li atom,
Some of the O atoms in the layer consisted of F atoms
It has a structure.

When used as a positive electrode active material of a lithium secondary battery, a powdery material may be used, and the structure of the powder particles is not particularly limited. Generally, fine primary particles close to a single crystal are aggregated to form secondary particles, and the secondary particles are powder particles. Therefore, in the case of the lithium transition metal composite oxide of the present invention, an oxide having such a particle structure may be used.

In the layered rock salt structure, the transition metal M
Exists in a trivalent form of M ³⁺ . However, particularly in the case of Ni, there is a case where it is mixed into the Li site in a divalent state of M ²⁺ . In this case, the region can be considered as a cubic salt structure microscopically, and this region is generally called a "salt domain". When a part of O atoms present in the O layer is simply replaced with F atoms having a larger atomic radius, M atoms that should be present in the transition metal M layer sandwiched between the O layers are disturbed due to disordered arrangement of atoms. , M ²⁺ and easily mixed into the Li layer, resulting in an increase in rock salt domains. The rock salt domain, in addition to being electrochemically inert itself, inhibits the two-dimensional solid-state diffusion of the Li layer and further impairs the stability of the crystal structure. Therefore, a lithium transition metal composite oxide having good crystallinity without this rock salt domain is required.

In the present technology, CuK is used as a parameter indicating the crystallinity of the layered rock salt structure lithium transition metal composite oxide.
The intensity I ₀₀₃ of the diffraction peak on the (003) plane and the intensity I of the diffraction peak on the (104) plane by X-ray diffraction analysis using α-rays
Adopting intensity ratio I ₀₀₃ / I ₁₀₄ of the _104. The diffraction peak of the (003) plane is specific to the layered rock salt structure, while the diffraction peak of the (104) plane is selected not only from the layered rock salt structure but also from the cubic rock salt structure. Therefore, the larger the intensity ratio I ₀₀₃ / I ₁₀₄ , the smaller the number of rock salt domains and the closer to a single phase of a layered rock salt structure. That is, the crystallinity is improved. In the case of the lithium transition metal composite oxide of the present invention, if this parameter is used, I ₀₀₃ / I ₁₀₄ needs to be 1.7 or more. If it is less than 1.7, the crystallinity is low, and the battery performance such as the cycle characteristics of the lithium secondary battery used as the positive electrode active material is deteriorated.

<Production method of lithium nickel composite oxide> The production method of the lithium transition metal composite oxide of the present invention is not particularly limited. It can be produced by various methods known in the art, for example, a solid phase reaction method, a molten salt method, a precipitation method from an aqueous solution, a spray combustion method and the like.

For example, in the case of manufacturing by a solid phase reaction method, a mixture may be obtained by mixing the respective raw materials serving as a lithium source, a transition metal M source, an aluminum source, and a fluorine source, and the mixture may be fired. .

In this case, LiOH.H ₂ O, Li ₂ CO ₃ , LiNO ₃ or the like is used as a raw material as a lithium source, and CoCO ₃ , CoO, or
Co ₃ O ₄ , Ni (OH) ₂ , NiCO ₃ , Ni (NO ₃ ) _{2
· 6H 2 O, Mn 2 O} 3, MnCO 3, Mn (NO 3) 2 · 6
As a raw material serving as an aluminum source, H ₂ O or the like
(OH) ₃ , Al ₂ O _3, etc., and LiF, AlF _3, etc. can be used as a raw material serving as a fluorine source. When LiF is used, it serves not only as a fluorine source but also as a lithium source.

The mixing ratio of the raw materials may be such that the constituent elements in the mixture have a ratio corresponding to the composition of the lithium transition metal composite oxide to be produced. The method of mixing is not particularly limited, and the mixing may be performed using a mixing device such as a ball mill. Also,
The mixture may be fired in the air or in an oxygen atmosphere, and may be fired at a firing temperature of 700 to 1000 ° C. and a firing time of 5 to 50 hours.

<Structure of Lithium Secondary Battery> The lithium secondary battery of the present invention is a lithium secondary battery using the above-described lithium transition metal composite oxide of the present invention as a positive electrode active material. Is not particularly limited, and may be in accordance with the configuration of a known lithium secondary battery. Further, in the lithium transition metal composite oxide of the present invention, various lithium transition metal composite oxides exist depending on the difference in the composition and the like. In the lithium secondary battery of the present invention, one of them may be used as the positive electrode active material, or two or more thereof may be used in combination.

When the lithium transition metal composite oxide of the present invention is used as a positive electrode active material, the positive electrode can be formed, for example, by binding the lithium transition metal composite oxide with a binder. The configuration and manufacturing method are not particularly limited. What is necessary is just to follow the already known structure and manufacturing method. More specifically, first, a lithium transition metal composite oxide of the present invention, a conductive material, and a binder are mixed,
A solvent for dispersing these is added to prepare a paste-like positive electrode mixture. Next, this positive electrode mixture is applied to the surface of a positive electrode current collector such as an aluminum foil by a coating machine or the like,
What is necessary is just to dry and form a positive electrode mixture of only solid content in the form of a layer. Thereafter, if necessary, the active material density may be increased by performing compression using a compressor such as a roll press. The positive electrode in this form is in a sheet shape, and may be cut into a size suitable for a battery to be manufactured and used for manufacturing a battery.

The conductive material is used to secure the electrical conductivity of the positive electrode, and one or a mixture of two or more powdered carbon materials such as carbon black, acetylene black and graphite is used. be able to. The binding agent plays a role of binding the active material particles and the conductive material particles, and may be a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. . Further, as a solvent for dispersing, N-methyl-2-
Organic solvents such as pyrrolidone can be used. In addition,
The mixing ratio of the active material, the conductive material, and the binder (only solid content) in the positive electrode mixture is 2 to 20 parts by weight of the conductive material, 100 parts by weight of the positive electrode active material, and the positive electrode binder in weight ratio. The amount may be 1 to 20 parts by weight, and the amount of the solvent added may be an appropriate amount according to the characteristics of the coating machine or the like.

The negative electrode opposed to the positive electrode is formed by sheet-like or sheet-like metal lithium, a lithium alloy, or the like, or by pressing the sheet-like or sheet-like thing to a current collector net made of nickel, stainless steel, or the like. It may be formed. However, in consideration of dendrite precipitation and the like, a negative electrode using a carbon material capable of inserting and extracting lithium as an active material can be used in order to obtain a lithium secondary battery having excellent safety. As carbon materials that can be used,
Examples include natural or artificial graphites, fired organic compounds such as phenolic resins, and powdered materials such as coke. In this case, the binder is mixed with the negative electrode active material, and a suitable solvent is added thereto to form a paste-like negative electrode mixture on a surface of a metal foil current collector of copper or the like, followed by drying. When the carbon material is used as the negative electrode active material, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder and the N-
An organic solvent such as methyl-2-pyrrolidone can be used.

In the lithium secondary battery of the present invention, a general rechargeable battery is used.
Like the rechargeable lithium battery, in addition to the positive and negative electrodes,
A separator sandwiched between the negative electrodes, a non-aqueous electrolyte, etc.
It is a component. The separator separates the positive and negative electrodes and
Holds the lysate, polyethylene, polypropylene
A thin microporous film such as ren can be used. Also non-water
Electrolyte solution is prepared by dissolving lithium salt as electrolyte in organic solvent.
Aprotic organic solvent
Medium, for example, ethylene carbonate, propylene carbonate
Dimethyl carbonate, diethyl carbonate,
Ethyl methyl carbonate, γ-butyrolactone, acetyl
Tonitrile, 1,2-dimethoxyethane, tetrahydro
One or more of furan, dioxolan, methylene chloride, etc.
Two or more of these mixed solvents can be used. Ma
The electrolyte to be dissolved is LiI, LiCl
O_Four, LiAsF₆, LiBF_Four, LiPF₆, LiN (C
F_ThreeSO_Two) _TwoAnd the like.

In place of the separator and the non-aqueous electrolyte, a polymer solid electrolyte using a high molecular weight polymer such as polyethylene oxide and a lithium salt such as LiClO ₄ or LiN (CF ₃ SO ₂ ) ₂ is used. In addition, the above non-aqueous electrolyte can be converted to polyacrylonitrile (P
A gel electrolyte trapped in a solid polymer matrix such as AN) can also be used.

The lithium secondary battery of the present invention configured as described above can have various shapes such as a cylindrical type, a stacked type, and a coin type. Regardless of the shape used, a positive electrode and a negative electrode are sandwiched between separators and laminated to form an electrode body, and a current collecting lead or the like extends from each electrode to the positive electrode terminal and the negative electrode terminal leading to the outside. The electrode body is sealed in a battery case together with the non-aqueous electrolyte to complete the battery.

<Allowance of Other Embodiments> The embodiments of the lithium transition metal composite oxide for a lithium secondary battery positive electrode active material of the present invention and the lithium secondary battery of the present invention have been described above. Is only one embodiment,
The lithium transition metal composite oxide for a positive electrode active material of a lithium secondary battery of the present invention and the lithium secondary battery of the present invention include the above-described embodiment, and various modifications and improvements based on the knowledge of those skilled in the art. It can be implemented in the form of

[0040]

EXAMPLES Based on the above embodiment, a lithium transition metal composite oxide of the present invention was actually manufactured, and one having a composition outside the range of the lithium transition metal composite oxide of the present invention was also manufactured. Then, by comparing these, and comparing lithium secondary batteries using these as a positive electrode active material, the superiority of the lithium transition metal composite oxide of the present invention and the lithium secondary battery of the present invention were confirmed. This will be described below.

<Lithium Transition Metal Composite Oxide of Example>
The present lithium transition metal composite oxide has a composition of Li_1.1
Ni_0.75Mn_0.1Al_{0. 05}O_1.8F_0.2Lithium ni
Is a composite oxide manufactured by solid-state reaction method.
is there. LiOH · H as lithium source_TwoO for nickel
Ni (OH) as source_TwoWith Mn as a manganese source_TwoO_Three
With Al (OH) as the aluminum source_ThreeThe fluorine source
LiF (also used as lithium source)
In a molar ratio of 0.9: 0.75: 0.05: 0.05:
0.2 to obtain a mixture.
The mixture is baked at 900 ° C for 12 hours in an oxygen stream.
Manufactured.

<Lithium Transition Metal Composite Oxide of Comparative Example 1> This lithium transition metal composite oxide is a lithium transition metal composite oxide not substituted with fluorine. This is a lithium nickel composite oxide having a composition of Li _1.1 Ni _0.75 Mn _0.1 Al _0.05 O _2, and is manufactured by a solid-state reaction method. LiOH · H ₂ O as a lithium source, Ni (OH) ₂ as a nickel source, and Mn ₂ O ₃ as a manganese source
And Al (OH) ₃ as an aluminum source, and the respective molar ratios are 1.1: 0.75: 0.05: 0.05.
The mixture was mixed at such a ratio as to obtain a mixture, and the mixture was fired at a temperature of 900 ° C. for 12 hours in an oxygen stream to produce the mixture.

<Lithium Transition Metal Composite Oxidation of Comparative Example 2>
The present lithium transition metal composite oxide is
But the transition metal layer is not replaced with aluminum.
Transition metal composite oxide. Its composition is Li_{1. 1}N
i_0.75Mn_0.15O_1.8F_0.2Lithium nickel composite
It is an oxide and is produced by a solid-phase reaction method. Lichi
LiOH ・ H_TwoO as nickel source
i (OH)_TwoWith Mn as Mn source_TwoO_ThreeWith a fluorine source
And LiF (also used as lithium source)
0.9: 0.75: 0.075: 0.2 in molar ratio
The mixture is mixed in such a ratio to obtain a mixture, and this mixture is
Baked at 900 ° C for 12 hours
Was.

<Lithium Transition Metal Composite Oxide of Comparative Example 3> This lithium transition metal composite oxide is a lithium transition metal composite oxide having neither fluorine substitution nor aluminum substitution. This is a lithium nickel composite oxide having a composition of Li _1.1 Ni _0.75 Mn _0.15 O ₂ , which is manufactured by a solid-state reaction method. LiOH.H ₂ O as lithium source
, Ni (OH) ₂ as a nickel source, and Mn ₂ O ₃ as a manganese source, each having a molar ratio of 1.1: 0.
The mixture was mixed at a ratio of 75: 0.075 to obtain a mixture, and the mixture was baked at a temperature of 900 ° C. for 12 hours in an oxygen stream to produce the mixture.

<Evaluation of Crystallinity by X-ray Diffraction Analysis> Each of the lithium transition metal composite oxides of the above Examples and Comparative Examples was subjected to X-ray diffraction analysis by a powder method using CuKα radiation. As a result, XRD spectra of the lithium transition metal composite oxides of Examples and Comparative Example 1 are shown in FIG. 1, and XRD spectra of the lithium transition metal composite oxides of Comparative Examples 2 and 3 are shown in FIG.

As is clear from FIGS. 1 and 2, it can be confirmed that each lithium transition metal composite oxide has a layered rock salt structure. In the XRD spectrum, 2θ ≒
The peak at 19 ° (θ is the diffraction angle) is the peak on the (003) plane, and the peak at 2θ ≒ 44 ° is the peak on the (104) plane. Table 1 below shows the (0) of each lithium transition metal composite oxide calculated from these spectra.
The intensity ratio I ₀₀₃ / I ₁₀₄ between the intensity I ₀₀₃ of the diffraction peak on the 03) plane and the intensity I ₁₀₄ of the diffraction peak on the (104) plane is shown.

[0047]

[Table 1]

As can be seen from Table 1 above, the fluorine substitution
Lithium transition metal of Comparative Example 1 and Comparative Example 3
The composite oxide has an intensity ratio I₀₀₃/ I₁₀₄Is 2.2
8, 2.18 high value and good crystallinity
Can be heard. Also, fluorine substitution without aluminum substitution
The lithium transition metal composite oxide of Comparative Example 2 in which
Degree ratio I₀₀₃/ I₁₀₄Is low at 1.33 and crystallinity is poor
Is shown. In contrast, aluminum substitution was performed
Lithium transition metal composite of Example in which fluorine substitution was performed on
The oxide has an intensity ratio I₀₀₃/ I₁₀₄Is relatively high at 1.72
It shows a high value. In light of this, aluminum
If substitution is performed, high results are obtained even if fluorine is substituted.
It can be confirmed that the crystallinity can be maintained.

<Preparation of Lithium Secondary Battery> Next, a lithium secondary battery using the lithium-transition metal composite oxide of the above example and Comparative Example 1 as a positive electrode active material was prepared. The positive electrode was prepared by first mixing 70 parts by weight of each lithium transition metal composite oxide serving as a positive electrode active material, 25 parts by weight of carbon black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder, Suitable amount of N-
Methyl-2-pyrrolidone was added to prepare a paste-like positive electrode mixture. Next, this paste-like positive electrode mixture was applied to an aluminum foil current collector and pressurized to make the thickness of the positive electrode mixture 65 μm, and then punched into a disk having a diameter of 15 mmφ to obtain a positive electrode.

For the negative electrode to be opposed, metallic lithium was used as an active material. Metallic lithium was formed into a sheet having a thickness of 400 μm and pressed on a nickel current collector network, and this was 17 m in diameter.
A punched out disk having a diameter of mφ was used as a negative electrode.

As the separator, a microporous polyethylene membrane was used, and the nonaqueous electrolytic solution impregnated in the separator was prepared by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 3:
A solution obtained by dissolving LiPF ₆ at a concentration of 1 M in the mixed solvent mixed in Example 7 was used. The positive electrode and the negative electrode were opposed to each other with a separator interposed therebetween, and a suitable amount of the nonaqueous electrolyte was injected and impregnated. Then, the battery was housed in a coin-type battery case to produce a lithium secondary battery. The lithium secondary battery using the lithium transition metal composite oxide of the example as the positive electrode active material was used as the lithium secondary battery of the example, and Comparative Example 1 was similarly used.
A lithium secondary battery using the lithium transition metal composite oxide of Comparative Example 1 as a positive electrode active material was designated as a lithium secondary battery of Comparative Example 1.

<Charge / Discharge Cycle Test> A charge / discharge cycle test was performed on the lithium secondary batteries of the above Examples and Comparative Example 1. The charge-discharge cycle test was performed in a high-temperature environment of 60 ° C, which is considered to be the maximum practical use temperature of a lithium secondary battery.
After charging to a charge end voltage of 4.3 V with a constant current of 0.2 mA, five cycles of discharging to a discharge end voltage of 3.0 V with a constant current of 0.2 mA are performed, and then charging is performed from the sixth cycle. The discharge current was increased to 0.4 mA, for a total of 5
The charge / discharge of 0 cycle was performed. FIG. 3 shows the discharge capacity per unit weight of the positive electrode active material (active material discharge capacity) in each cycle of the lithium secondary batteries of Example and Comparative Example 1 as a result of the charge / discharge cycle test.

<Evaluation of Cycle Characteristics> As is clear from FIG. 3, the discharge capacity of the lithium secondary battery of Comparative Example 1 continued to decrease greatly after conditioning, and the discharge capacity at the 50th cycle was reduced to the 6th cycle. 8 for the discharge capacity of
It dropped to 3%. On the other hand, in the lithium secondary battery of the embodiment using the lithium-transition metal composite oxide subjected to fluorine substitution as the positive electrode active material, the decrease in the discharge capacity in the charge / discharge cycle after the conditioning is small, The discharge capacity at the 50th cycle relative to the discharge capacity at the eye showed a high value of 93%.

Thus, the lithium-transition metal composite oxide having high crystallinity, which has been subjected to aluminum substitution and fluorine substitution, is less deteriorated by repeated charge and discharge, and the effect of the fluorine substitution is sufficiently exhibited. Can be confirmed. Therefore, the lithium secondary battery of the present invention using the lithium transition metal composite oxide of the present invention as the positive electrode active material has good cycle characteristics, and can be a lithium secondary battery having good high-temperature cycle characteristics. You can check.

[0055]

According to the present invention, a layered rock salt-structured lithium transition metal composite oxide is constructed such that a part of the transition metal is substituted by aluminum and a part of oxygen is substituted by fluorine to maintain high crystallinity. Is what you do. The lithium transition metal composite oxide of the present invention having such a structure has a stabilized crystal structure and, when used as a positive electrode active material of a lithium secondary battery, has a small deterioration even by repeated charge and discharge. Become.

Further, the present invention provides a lithium secondary battery using the above-mentioned lithium transition metal composite oxide of the present invention as a positive electrode active material. The lithium secondary battery of the present invention having such a configuration is a lithium secondary battery having good cycle characteristics.

[Brief description of the drawings]

FIG. 1 shows the results of X-ray diffraction analysis performed on lithium-nickel composite oxides substituted with aluminum and substituted with fluorine or not substituted with fluorine, as a result of XRD of lithium-transition metal composite oxides of Examples and Comparative Example 1.
The spectrum is shown.

FIG. 2 shows lithium transition metal composite oxides of Comparative Examples 2 and 3 as a result of X-ray diffraction analysis performed on a lithium-nickel composite oxide not substituted with aluminum and substituted with fluorine or not substituted with fluorine. X
3 shows an RD spectrum.

FIG. 3 shows the results of a charge / discharge cycle test conducted to investigate the effect of fluorine substitution, as a result of Examples and Comparative Examples 1.
4 shows the active material discharge capacity in each cycle of the lithium secondary battery of FIG.

Continued on front page F term (reference) 4G048 AA04 AA06 AC06 AD06 5H029 AJ05 AK03 AK19 AL06 AL07 AL12 AM00 AM02 AM03 AM04 AM05 AM07 AM16 DJ17 HJ02 HJ13 5H050 AA07 BA17 CA08 CA09 FA19 HA02 HA13

Claims (3)

[Claims] 1. A composition formula of Li _{1 + x} M _1-xy Al _y O _2-z F
_z (M is at least one selected from Co, Ni and Mn; 0 ≦
x ≦ 0.2; 0.05 ≦ y ≦ 0.2; 0.01 ≦ z ≦
0.3), the crystal structure is a layered rock salt structure, and C
Lithium having an intensity ratio I ₀₀₃ / I ₁₀₄ between the intensity I ₀₀₃ of the diffraction peak on the (003) plane and the intensity I ₁₀₄ of the diffraction peak on the (104) plane obtained by X-ray diffraction analysis using uKα radiation is 1.7 or more. Lithium transition metal composite oxide for secondary battery positive electrode active material. 2. The M has Ni as its central element.
And the composition formula Li _{1 + x}Ni_1-xywM '_wAl_yO_2-zF
_z(M ′ is at least one selected from Co and Mn; 0 ≦ w ≦
The lithium secondary battery according to claim 1, which is represented by 0.3).
Lithium transition metal composite oxide for positive electrode active material. 3. A composition formula _{Li 1 + x M 1-xy} Al y O 2-z F
_z (M is at least one selected from Co, Ni and Mn; 0 ≦
x ≦ 0.2; 0.05 ≦ y ≦ 0.2; 0.01 ≦ z ≦
0.3), the crystal structure is a layered rock salt structure, and C
Lithium having an intensity ratio I ₀₀₃ / I ₁₀₄ between the intensity I ₀₀₃ of the diffraction peak on the (003) plane and the intensity I ₁₀₄ of the diffraction peak on the (104) plane obtained by X-ray diffraction analysis using uKα radiation is 1.7 or more. A lithium secondary battery using a transition metal composite oxide as a positive electrode active material.