WO2014007357A1 - Lithium composite metal oxide, positive electrode active substance, positive electrode, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

A lithium composite metal oxide containing Mn, Ni, Li, and Co, and fulfilling formulas (a) and (b): (a) The ratio (I_BMn/I_AMn) between the intensity (I_AMn) of a first proximity peak (A_Mn) and the intensity (IB_Mn) of a second proximity peak (B_Mn) is 0.5-1.2, in a radial distribution function obtained from an EXAFS spectrum at the K absorption end of Mn; and (b) the ratio (I_BNi/I_ANi) between the intensity (IA_Ni) of a first proximity peak (A_Ni) and the intensity (I_BNi) of a second proximity peak is 1.0-1.7, in a radial distribution function obtained from an EXAFS spectrum at the K absorption end of Ni.

Description

Lithium composite metal oxide, positive electrode active material, positive electrode and non-aqueous electrolyte secondary battery

The present invention relates to a lithium composite metal oxide, a positive electrode active material, a positive electrode, and a nonaqueous electrolyte secondary battery.

Lithium composite metal oxide is used as a positive electrode active material in nonaqueous electrolyte secondary batteries such as lithium secondary batteries. Lithium secondary batteries have already been put into practical use as small power sources for mobile phones and notebook computers, and are also being applied to medium and large power sources for automobiles and power storage.
LiCoO ₂ is most widely used as a positive electrode active material in commercially available lithium secondary batteries. However, since Co is expensive, lithium composite metal oxidation in which the content of Co is lower than that of LiCoO ₂ is used. Things are being researched. Among these, lithium composite metal oxides containing Ni and Mn are considered promising. For example, a lithium composite metal oxide having a composition formula of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is known.
In order to provide a further inexpensive non-aqueous electrolyte secondary battery, it is effective to further reduce the ratio of Co in the composition formula. However, for example, LiNi _0.5 Mn _0.5 O ₂ that does not contain Co has a lower capacity than LiNi _1/3 Co _1/3 Mn _1/3 O _2. Then, it is known that a capacity | capacitance will become relatively low (patent document 1). From the above, even if a positive electrode active material in which the Co ratio is reduced to at least 10% or less with respect to all transition metals is used, a lithium composite metal oxide useful for a non-aqueous electrolyte secondary battery with a high capacity is obtained. It has been demanded.
Under such circumstances, various methods for obtaining a lithium composite metal oxide useful for a non-aqueous electrolyte secondary battery exhibiting a high capacity have been studied. For example, in a layered lithium composite metal oxide containing Mn, Ni and Li, by controlling the oxidation state of Mn and Ni, a lithium composite metal oxide suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery and It has been proposed (Patent Document 2).
In addition, in the lithium composite metal oxide, by specifying the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement, the generation of the disorder phase present in this oxide is suppressed. A method for controlling the structure of a lithium composite metal oxide has been proposed, and thus a lithium metal composite oxide suitable for a high-capacity nonaqueous electrolyte secondary battery has been obtained (Patent Document 3).

Japanese Patent No. 4594605 Japanese Patent No. 4259847 Japanese Patent No. 4877660

As described above, in a lithium composite metal oxide with reduced Co, a high-capacity non-aqueous electrolyte can be obtained by a method for controlling an oxidation state or a method for controlling an average crystal structure obtained by X-ray diffraction measurement. Studies have been made to obtain lithium metal composite oxides suitable for secondary batteries. However, a method for obtaining a lithium metal composite oxide suitable for a high-capacity nonaqueous electrolyte secondary battery by controlling the local structure at the atomic level has not yet been sufficiently studied.
The present invention has been made in view of such circumstances. By controlling the local structure at the atomic level, a lithium composite metal oxide useful for a non-aqueous electrolyte secondary battery exhibiting a higher capacity than before is obtained. The purpose is to provide. It is another object of the present invention to provide a positive electrode active material, a positive electrode, and a nonaqueous electrolyte secondary battery using such a lithium composite metal oxide.
In order to solve the above problems, one embodiment of the present invention is a lithium composite metal oxide containing Mn, Ni, Li, and Co, which satisfies the following (a) and (b): is there.
(A) In a radial distribution function obtained by Fourier transform of a wide-range X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of Mn in the lithium composite metal oxide, 1.5% by oxygen atoms bonded to Mn atoms is obtained. when the first proximity peak _{a Mn} of intensity _I AMn near the intensity of the second closest peak _{B Mn} around 2.5Å by metal atoms near the next Mn atoms of the oxygen atoms bonded to Mn atoms was _{I BMn} , _IBMn / _IAMn is 0.5 or more and 1.2 or less.
(B) In the radial distribution function obtained by Fourier transforming the EXAFS spectrum at the K absorption edge of Ni in the lithium composite metal oxide, the first proximity peak A _Ni near 1.5Å due to oxygen atoms bonded to Ni atoms. the intensity _I ANi, when the next on the intensity of the second closest peak around 2.5Å by metal atoms near the Ni atom bonded oxygen atom to Ni atom was _{I BNi,} the _I BNi _/ I _ANi, 1. It is 0 or more and 1.7 or less.
In one embodiment of the present invention, when the amount (mol) of _Li is A _Li and the amount (mol) of a metal other than _Li is A, A _Li / A is 0.7 or more and 1.4 or less. It is desirable.
In one aspect of the present invention, it is desirable that a product of the I _BMn / I _AMn and the I _BNi / I _ANi is 0.7 or more and 2.0 or less.
In one embodiment of the present invention, it is desirable that the lithium composite metal oxide has a layered structure and is represented by Formula (1).
_{Li 1 + x (Ni 1-} x-y-α-β Mn y Co α M β) O 2 ... (1)
(In the formula (1), −0.3 ≦ x ≦ 0.4, 0.35 ≦ y ≦ 0.7, 0 <α ≦ 0.1, 0 ≦ β <0.1 (where 0 <α + β ≦ 0.1), −0.05 ≦ x + y + α + β <1, and M is selected from the group consisting of Al, Mg, Ti, Ca, Cu, Zn, Fe, Cr, Mo, Si, Sn, Nb and V One or more elements.)
In one aspect of the present invention, the M is preferably Fe.
In one embodiment of the present invention, it is desirable that β = 0.
Another embodiment of the present invention is a positive electrode active material including the above lithium composite metal oxide.
Another embodiment of the present invention is a positive electrode including the above positive electrode active material.
Another embodiment of the present invention is a nonaqueous electrolyte secondary battery including a negative electrode and the positive electrode described above.
In one mode of the present invention, it is desirable to further have a separator arranged between the negative electrode and the positive electrode.
In one aspect of the present invention, the separator is preferably made of a laminated film in which a heat-resistant porous layer and a porous film are laminated.

It is a schematic diagram which shows an example of the nonaqueous electrolyte secondary battery of this embodiment.

DESCRIPTION OF SYMBOLS 1 ... Separator, 2 ... Positive electrode, 3 ... Negative electrode, 4 ... Electrode group, 5 ... Battery can, 6 ... Electrolyte solution, 7 ... Top insulator, 8 ... Sealing body, 10 ... Nonaqueous electrolyte secondary battery, 21 ... Positive electrode lead 31 ... Negative electrode lead

[Lithium composite metal oxide]
The lithium composite metal oxide of this embodiment contains Mn, Ni, Li and Co and satisfies the following (a) and (b).
(A) In a radial distribution function obtained by Fourier transform of a wide-range X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of Mn in the lithium composite metal oxide, 1.5% by oxygen atoms bonded to Mn atoms Near first adjacent peak A_MnStrength of I_AMn, The second adjacent peak B around 2.5Å due to the metal atom next to the Mn atom next to the oxygen atom bonded to the Mn atom_MnStrength of I_BMnWhen I_BMn/ I_AMnIs 0.5 or more and 1.2 or less.
(B) In the radial distribution function obtained by Fourier transforming the EXAFS spectrum at the K absorption edge of Ni in the lithium composite metal oxide, the first proximity peak A around 1.5Å due to oxygen atoms bonded to Ni atoms._NiStrength of I_ANi, The intensity of the second adjacent peak in the vicinity of 2.5 に よ る by the metal atom close to the Ni atom next to the oxygen atom bonded to the Ni atom is_BNiWhen I_BNi/ I_ANiIs 1.0 or more and 1.7 or less.
Hereafter, it explains in order.
(EXAFS spectrum)
First, the EXAFS spectrum used for defining the lithium composite metal oxide of this embodiment will be described. The EXAFS spectrum used in the present embodiment is handled in the same manner as a general EXAFS spectrum. The measurement and principle of the EXAFS spectrum are described in, for example, “X-ray absorption spectroscopy—XAFS and its applications” (Toshiaki Ohta (2002)). The principle is as follows.
First, when an X-ray having a specific wavelength is transmitted through a substance to be measured, the intensity of the X-ray irradiated to the substance (incident X-ray intensity: I₀) And the intensity of X-rays transmitted through the substance (transmitted X-ray intensity: I_t), The X-ray absorbance per unit thickness is obtained for the substance to be measured at a specific wavelength.
The wavelength of X-rays irradiating the substance is changed (that is, the energy (eV) of incident X-rays is changed), the X-ray absorbance of each wavelength (each energy) with respect to the X-rays is measured, When an X-ray absorption spectrum is created with the energy of the line (eV) and the y-axis as the X-ray absorbance, it can be seen that there is energy at which the X-ray absorbance rapidly increases. This energy value is called the absorption edge. The absorption edge corresponds to the energy level of the atomic shell of the atoms constituting the material and is unique to each atom. For example, an absorption edge corresponding to the K shell of an atom is called a K absorption edge.
In the X-ray absorption spectrum, a fine vibration structure appearing in an energy side region about 20 to 1000 eV higher than the absorption edge is called a broad X-ray absorption fine structure (EXAFS), and the spectrum is called an EXAFS spectrum. When Fourier transformation is performed on the EXAFS spectrum, a radial distribution function centered on X-ray absorbing atoms (atomic atoms of interest) is obtained. From this radial distribution function, information such as the distance between X-ray absorbing atoms and X-ray scattering atoms (atoms near the X-ray absorbing atoms), the number of X-ray scattering atoms, and the like can be obtained. Can be obtained.
Generally, the intensity of the peak of the radial distribution function is affected by the number of X-ray scattering atoms, but it also affects the isotropy of the interatomic distance between X-ray absorbing atoms and X-ray scattering atoms. Is done. For example, when two X-ray absorbing atoms have substantially the same number of X-ray scattering atoms and the X-ray scattering atoms are recognized to have substantially the same scattering power, the peak of the radial distribution function For those with high intensity, the interatomic distance between the X-ray absorbing atom and the X-ray scattering atom is isotropic with no difference in direction, and the distance distribution between the X-ray absorbing atom and the X-ray scattering atom is small. Means.
Therefore, in the present embodiment, attention is paid to the peak intensity ratio of the radial distribution function obtained at the K absorption edge of Mn and Ni.
In other words, by controlling the intensity ratio of the peak of the radial distribution function within a certain range, the atomic level local structure in the lithium composite metal oxide can be controlled to a specific condition even for samples with different composition ratios. In addition, a lithium composite metal oxide useful for a non-aqueous electrolyte secondary battery exhibiting a higher capacity than before can be obtained.
In the lithium composite metal oxide of this embodiment, the peak due to O (oxygen atom) bonded to the Mn atom in the radial distribution function of the K absorption edge of Mn is the first proximity peak A._MnAnd First proximity peak A_MnPreferably appears in the vicinity of 1.5 to 1.9 to 1.9, more preferably 1.5 to 1.6.
Further, in the lithium composite metal oxide of the present embodiment, in the radial distribution function of the K absorption edge of Mn, an atom X next to Mn atom next to O bonded to Mn atom (where X is Li, Mn , And a peak due to a metal atom such as Ni)._MnAnd Second adjacent peak B_MnPreferably appears in the vicinity of 2.5 mm from 2.44 mm to 2.55 mm, more preferably from 2.46 mm to 2.55 mm. Here, the atom X is bonded to O bonded to the Mn atom.
Furthermore, in the lithium composite metal oxide of this embodiment, in the radial distribution function of the K absorption edge of Ni, the peak due to O bonded to Ni atoms is the first proximity peak A._NiAnd First proximity peak A_NiPreferably appears in the vicinity of 1.5 to 1.9 to 1.9, more preferably 1.5 to 1.6.
In the lithium composite metal oxide of this embodiment, in the radial distribution function of the K absorption edge of Ni, an atom X that is closest to the Ni atom next to O bonded to the Ni atom (where X is Li, Mn , And a peak due to a metal atom such as Ni)._NiAnd Second adjacent peak B_NiPreferably appears in the vicinity of 2.5 mm from 2.44 mm to 2.55 mm, more preferably from 2.46 mm to 2.55 mm. Here, atom X is bonded to O bonded to Ni atom.
The lithium composite metal oxide of this embodiment has a peak intensity ratio of the radial distribution function, that is, I_AMnAnd I_BMnTo the ratio (I_BMn/ I_AMn) And I_ANiAnd I_BNiTo the ratio (I_BNi/ I_ANi) Within a specific range, the local structure at the atomic level is controlled. Such a lithium composite metal oxide of this embodiment is useful for a non-aqueous electrolyte secondary battery that exhibits a higher capacity than before.
The lithium composite metal oxide of the present embodiment has a high isotropy of the interatomic distance between O and X around the Mn atom, and falls within a specific range, and thus has high characteristics as a positive electrode active material. I like this_BMn/ I_AMnThe value of is 0.5 or more and 1.2 or less, preferably 0.6 or more and 1.2 or less, more preferably 0.7 or more and 1.2 or less, and even more preferably 1.0 or more. 1.2 or less, particularly preferably 1.1 or more and 1.2 or less.
In addition, the lithium composite metal oxide of the present embodiment has a high degree of isotropy in the interatomic distance between O and X around the Ni atom, and falls within a specific range, and thus has high characteristics as a positive electrode active material. . I like this_BNi/ I_ANiThe value of is 1.0 or more and 1.7 or less, preferably 1.1 or more and 1.7 or less, more preferably 1.2 or more and 1.7 or less.
These I_BMn/ I_AMnRange of values and I_BNi/ I_ANiThe range of values can be arbitrarily combined.
Furthermore, I_BMn/ I_AMnAnd I_BNi/ I_ANiProduct with (I_BMn/ I_AMn× I_BNi/ I_ANi)) Has both the isotropicity of the interatomic distance between the O and the atom X around the appropriate Mn atom and the isotropicity of the interatomic distance between the O and the atom X around the proper Ni atom. 7 or more and 2.0 or less, preferably 0.9 or more and 2.0 or less, more preferably 1.1 or more and 2.0 or less.
The crystal structure of the lithium composite metal oxide of the present embodiment is preferably a layered structure, more preferably a hexagonal crystal structure or a monoclinic crystal structure.
The hexagonal crystal structure is P3, P3₁, P3₂, R3, P-3, R-3, P312, P321, P3₁12, P3₁21, P3₂12, P3₂21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6₁, P6₅, P6₂, P6₄, P6₃, P-6, P6 / m, P6₃/ M, P622, P6₁22, P6₅22, P6₂22, P6₄22, P6₃22, P6mm, P6cc, P6₃cm, P6₃mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P6₃/ Mcm, P6₃It is classified into any one space group selected from the group consisting of / mmc.
The monoclinic crystal structure is P2, P2.₁, C2, Pm, Pc, Cm, Cc, P2 / m, P2₁/ M, C2 / m, P2 / c, P2₁/ C, C2 / c is classified into any one space group selected from the group consisting of C2 / c.
Among these, since the discharge capacity of the obtained nonaqueous electrolyte secondary battery is increased, the crystal structure of the lithium composite metal oxide is a hexagonal crystal structure classified into the space group R-3m, or C2 / m. A monoclinic crystal structure classified as follows is particularly preferable.
The space group of the lithium composite metal oxide of the present embodiment can be confirmed by the following method.
First, X-ray powder diffraction measurement was performed on a lithium composite metal oxide using CuKα as a radiation source and a diffraction angle 2θ measurement range of 10 ° to 90 °, and then Rietveld analysis was performed based on the results. And determining a crystal structure of the lithium composite metal oxide and a space group in the crystal structure. Rietveld analysis is a technique for analyzing the crystal structure of a material using diffraction peak data (diffraction peak intensity, diffraction angle 2θ) in powder X-ray diffraction measurement of the material, and is a conventionally used technique. (See, for example, “Practice of Powder X-ray Analysis—Introduction to Rietveld Method”, published on February 10, 2002, edited by the Japan Society for Analytical Chemistry X-ray Analysis Research Meeting).
The composition of the lithium composite metal oxide in this embodiment is such that the amount (mol) of Li is A_Li, When the amount (mole) of metal other than Li is A, A_Li/ A may be 0.7 or more and 1.4 or less.
The lithium composite metal oxide in the present embodiment preferably has a layered structure and the composition is represented by the following formula (1).
Li_{1 + x}(Ni_1-x-y-αMn_yCo_αM_β) O₂... (1)
(In the formula (1), −0.3 ≦ x ≦ 0.4, 0.35 ≦ y ≦ 0.7, 0 <α ≦ 0.1, 0 ≦ β <0.1 (where 0 <α + β ≦ 0.1), −0.05 ≦ x + y + α + β <1, and M is selected from the group consisting of Al, Mg, Ti, Ca, Cu, Zn, Fe, Cr, Mo, Si, Sn, Nb and V One or more elements.)
The value of x in the formula (1) is −0.3 ≦ x ≦ 0.4, preferably −0.2 ≦ x ≦ 0.35, more preferably −0.1 ≦ x ≦ 0. .3.
Since the lithium composite metal oxide of the present embodiment has a high discharge capacity at 60 ° C., M is preferably Fe.
The lithium composite metal oxide particles of the present embodiment are used as a core material, and B, Al, Ga, In, Si, Ge, Sn, Mg, and the surface of the core material (lithium composite metal oxide particles) A compound containing one or more atoms selected from the group consisting of transition metals may be attached.
Among the above atoms, at least one selected from the group consisting of B, Al, Mg, Co, Cr, and Mn is preferable, and Al is more preferable because a uniform coating layer can be easily formed.
Examples of such a compound include oxides, fluorides, sulfides, hydroxides, oxyhydroxides, carbonates, nitrates, organic acid salts and mixtures thereof of the above atoms. Of these, oxides, hydroxides, oxyhydroxides or mixtures thereof are preferred.
As the compound to be deposited on the surface of the core material, alumina which is an oxide of Al is preferable.
[Method for producing lithium composite metal oxide]
Next, a method for producing the above-described lithium composite metal oxide will be described.
The method for producing a lithium composite metal oxide according to this embodiment includes the following steps (1) to (5).
(1) A step of obtaining a slurry by bringing an aqueous solution containing Ni ions, Mn ions and Co ions (hereinafter sometimes referred to as “raw material aqueous solution”) into contact with an alkali to form a coprecipitate.
(2) Separating the coprecipitate from the slurry obtained in (1)
(3) A step of mixing the coprecipitate obtained in (2) with a lithium compound.
(4) A step of heating the mixture obtained in (3) at a temperature of 200 ° C. or higher and 500 ° C. or lower in an atmosphere having an oxygen concentration of 5% by volume or higher.
(5) A step of firing the product obtained in (4) (hereinafter sometimes referred to as “calcined product”) at a temperature of 600 ° C. or higher and 950 ° C. or lower in an atmosphere having an oxygen concentration of less than 5% by volume.
Here, the “oxygen concentration” in the step (4) refers to an average oxygen concentration in the heat treatment space when the space (heat treatment space) for heating the mixture is in the range of 200 ° C. or more and 500 ° C. or less. Similarly, the “oxygen concentration” in step (5) refers to the average oxygen concentration in the heat treatment space when the space (heat treatment space) for calcining the calcined product is in the range of 600 ° C. or higher and 950 ° C. or lower.
(Process (1))
In the above step (1), the raw material aqueous solution can be adjusted by dissolving a compound containing Ni, Mn and Co in water. In particular, the raw material aqueous solution is preferably an aqueous solution obtained by dissolving Ni sulfate, Mn sulfate, and Co sulfate in water.
Further, when each raw material containing Ni, Mn and Co is difficult to dissolve in water, for example, when these raw materials are oxides, hydroxides, metal materials, these raw materials are mixed with sulfuric acid. The raw material aqueous solution can be obtained by dissolving in the aqueous solution.
The alkali used in step (1) includes LiOH (lithium hydroxide), NaOH (sodium hydroxide), KOH (potassium hydroxide), Li₂CO₃(Lithium carbonate), Na₂CO₃(Sodium carbonate), K₂CO₃(Potassium carbonate) and (NH₄)₂CO₃One or more salts selected from the group consisting of (ammonium carbonate) can be mentioned. The alkali used may be an anhydride or a hydrate. An anhydride and a hydrate may be used in combination. In the step (1), it is preferable to use the above aqueous solution of alkali (alkaline aqueous solution). Aqueous ammonia can also be used as the alkaline aqueous solution.
The alkali concentration in the alkaline aqueous solution is preferably about 0.5 to 10 M (mol / L), more preferably about 1 to 8 M. Further, from the viewpoint of production cost, NaOH or KOH is preferable as the alkali to be used. NaOH and KOH may be used in combination.
As a contact method in the step (1), (i) a method in which an aqueous alkaline solution is added and mixed, (ii) a method in which an aqueous raw material solution is added and mixed, (iii) an aqueous raw material solution in water And a method of adding and mixing an alkaline aqueous solution. In mixing, it is preferable to involve stirring.
Of the contact methods in step (1), (ii) a method in which a raw material aqueous solution is added to and mixed with an alkaline aqueous solution is preferable because the change in pH is easily controlled. In the case of this method, the pH of the alkaline aqueous solution tends to decrease as the raw material aqueous solution is added to and mixed with the alkaline aqueous solution, but the pH is adjusted to 9 or higher, preferably 10 or higher. It is preferable to add a raw material aqueous solution. In addition, it is preferable that one or both of the raw material aqueous solution and the alkaline aqueous solution are brought into contact with each other while being kept at a temperature of 40 ° C. or higher and 80 ° C. or lower, whereby a coprecipitate having a more uniform composition can be obtained.
In the step (1), by bringing the raw material aqueous solution into contact with the alkali as described above, a salt containing Ni ions, Mn ions and Co ions is co-precipitated and the co-precipitate salt is dispersed. A slurry can be obtained.
(Process (2))
In step (2), a coprecipitate is obtained from the slurry obtained in step (1). As long as the coprecipitate can be obtained, various methods can be adopted as the method for obtaining the coprecipitate in step (2). However, since the operation is simple, a separation operation for obtaining a solid component such as filtration is performed. Is preferred. The coprecipitate can also be obtained by a method of volatilizing the liquid by heating, such as spray drying of the slurry.
When obtaining a coprecipitate in the step (2), it is preferable that the separated coprecipitate is washed and dried in the step (2). When the alkali remaining in the coprecipitate obtained by washing, Ni sulfate, Mn sulfate, or Co sulfate is used as a raw material, SO is released into the raw material aqueous solution.₄ ^2-The amount of ions can be reduced. It is preferable to reduce these by washing because the amount of the inert flux (described later) can be easily controlled.
In order to efficiently wash the coprecipitate, it is preferable to use water as the washing liquid. If necessary, a water-soluble organic solvent such as alcohol or acetone may be added to the cleaning liquid. Moreover, you may perform washing | cleaning twice or more, for example, after washing with water, it can also wash | clean again with the organic solvent which has the above water solubility.
The drying of the washed coprecipitate can be performed by heat treatment, but may be performed by air drying, vacuum drying, or a combination thereof. When the heat treatment is performed, the heating temperature is preferably 50 to 300 ° C, more preferably about 100 to 200 ° C.
(Process (3))
In step (3), the coprecipitate obtained in step (2) and the lithium compound are mixed to obtain a mixture.
Examples of the lithium compound include one or more salts selected from the group consisting of lithium hydroxide, lithium chloride, lithium nitrate, and lithium carbonate. The lithium compound used may be an anhydride or a hydrate. Moreover, you may use an anhydride and a hydrate together.
Mixing may be either dry mixing or wet mixing, but dry mixing is preferred because of the ease of operation. Examples of the mixing apparatus include stirring and mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, and a ball mill.
(Process (4))
In step (4), the mixture obtained in step (3) is heated at a temperature of 200 ° C. or higher and 500 ° C. or lower, preferably 250 ° C. or higher and 450 ° C. or lower to obtain a calcined product. The heating atmosphere includes a method using air and oxygen or a mixed gas thereof, a method of mixing an inert gas such as nitrogen and argon into the air and oxygen or a mixed gas thereof, and the oxygen concentration is 5 volumes. % Of the atmosphere. A high-capacity lithium composite metal oxide having an intended local structure can be easily obtained, and when the obtained lithium composite metal oxide is used as a positive electrode active material, a high-capacity secondary battery can be obtained. Therefore, the oxygen concentration is preferably 7% by volume to 20% by volume, and more preferably 10% by volume to 20% by volume.
(Process (5))
In step (5), the calcined product obtained in step (4) is fired at a temperature of 650 ° C. to 950 ° C., preferably 650 ° C. to 900 ° C. The firing atmosphere may be an atmosphere in which air, oxygen, nitrogen, argon, or the like is mixed and the oxygen concentration is less than 5% by volume. A high-capacity lithium composite metal oxide having an intended local structure can be easily obtained, and when the obtained lithium composite metal oxide is used as a positive electrode active material, a high-capacity secondary battery can be obtained. Therefore, the oxygen concentration is preferably 0.5% by volume or more and less than 5% by volume, and more preferably 1% by volume or more and 3% by volume or less.
In order to make the composition of the obtained lithium composite metal oxide uniform, the step (4) and the step (5) are continuously performed without lowering the temperature from the heating temperature at the end of the step (4) ( 5) is preferably performed. When performing the step (4) and the step (5) continuously, the oxygen concentration is adjusted to the step (4) while maintaining the temperature at the end of the step (4) or raising the temperature to the firing temperature of the step (5). The oxygen concentration in 4) is changed to the oxygen concentration in step (5). As a method for changing the oxygen concentration, a method of changing the oxygen concentration of the introduced gas is preferably used.
The lithium composite metal oxide of the present embodiment can be produced by such steps (1) to (5).
In addition, in the manufacturing method of this embodiment, although demonstrated as having a process (1)-a process (5), it is not restricted to this. For example, a mixture obtained by mixing a salt containing Ni ions, Mn ions and Co ions with a lithium compound by another method in place of steps (1) to (3) is prepared, and the obtained mixture is It is also possible to manufacture the lithium composite metal oxide of the present embodiment by heating while controlling the oxygen concentration and performing the processing corresponding to the above steps (4) and (5).
The above-mentioned “salt containing Ni ions, Mn ions and Co ions” may be a mixture of a salt containing Ni ions, a salt containing Mn ions, and a salt containing Co ions. As the above-mentioned “another method replacing step (1) to step (3)”, a method of mixing the above-mentioned salt in a solid phase, a slurry obtained by dispersing the above-mentioned salt in a liquid phase, For example, the slurry may be spray-dried and mixed.
Further, in the method for producing a lithium composite metal oxide according to the present embodiment, Ni, Mn and Co need to be contained in the mixture in the step (4). The metal atom may be contained. Examples of other metal atoms include one or more atoms selected from the group consisting of Al, Mg, Ti, Ca, Cu, Zn, Fe, Cr, Mo, Si, Sn, Nb, and V.
Various methods can be adopted as a method of including other metal atoms in the mixture to be heated in step (4). In particular, in the step (1), it is preferable to dissolve a water-soluble salt of another metal in the raw material aqueous solution because other metal atoms are uniformly dispersed in the resulting mixture.
(Inert flux)
In the step (4) and step (5), the mixture and calcined product may contain an inert flux. The inert flux is a salt that does not react with the target composite metal oxide and can be easily separated from the target. The inert flux melts at the heating temperature in step (4) and the firing temperature in step (5) to form a reaction field and promotes a uniform reaction. Therefore, when an inert flux is used, a product having a uniform composition is easily obtained.
As an inert flux, K₂SO₄, Na₂SO₄Sulfate such as K;₂CO₃, Na₂CO₃Carbonates such as: NaCl, KCl, NH₄Chlorides such as Cl; LiF, NaF, KF, NH₄Fluorides such as F; boric acid; Among the above-mentioned inert fluxes, sulfate is preferable because the production process becomes simple. More preferably K₂SO₄It is. Two or more inert fluxes can be used in combination.
When the mixture contains an inert flux, the reactivity at the time of heating the mixture and calcining the calcined product is improved, and thereby it may be possible to adjust the BET specific surface area of the obtained lithium composite metal oxide. is there. When the temperature is the same, the BET specific surface area of the oxide tends to increase as the content of the inert flux increases. Further, when an inert fluxing agent is contained during heating or firing, a uniform reaction can be performed, so that the local structure can be controlled at the atomic level of the lithium composite metal oxide by adjusting the heating atmosphere.
The inert flux may be mixed with the coprecipitate obtained by allowing the coprecipitate obtained by the separation operation in step (2) to contain the above inert flux solution and then drying. .
For example, when Ni sulfate, Mn sulfate, or Co sulfate is used as a raw material in step (1), SO₄ ^2-Ions are liberated. This SO₄ ^2-The ions and metal ions contained in the alkali used for the coprecipitation (for example, K ions when KOH is used as the alkali) remain in the coprecipitate separated in step (2), and the inert flux ( K in the above example₂SO₄) May occur. Therefore, the raw material aqueous solution after the coprecipitation in the step (1) is used as the “inert flux solution”, and the coprecipitate obtained in the step (2) is dried while the raw aqueous solution after the coprecipitation is included. By making it, an inert flux may be mixed with the coprecipitate obtained.
In addition, the inert flux can be added and mixed at the time of mixing the coprecipitate and the lithium compound in the step (3). Since it is easy to control the amount of the inert flux, the method of adding the inert flux in the step (3) is preferable to the method of adding the inert flux in the step (2). When an inert flux is added in step (3), the coprecipitate obtained in step (2) is washed, and the alkali, Ni salt, Mn salt, or Co salt remaining in the coprecipitate is washed. By reducing the amount of the derived anion, the amount of the inert flux can be easily controlled.
The inert flux may remain in the lithium composite metal oxide or may be removed by washing.
From the viewpoint of improving the uniformity of the reaction, the inert flux is a sulfate, and when the mixture or calcined product and the sulfate are mixed, the content of the sulfate in the resulting mixture is the lithium used. It is preferable that it is 0.01 to 400 mass parts with respect to 100 mass parts of compounds. More preferably, it is 0.1 to 10 parts by mass.
Further, the lithium composite metal oxide obtained by the method for producing a lithium composite metal oxide of the present embodiment may be pulverized using a ball mill or a jet mill. It may be possible to adjust the BET specific surface area of the lithium composite metal oxide by grinding. Further, the lithium composite metal oxide obtained by carrying out the steps (1) to (5) may be pulverized, and the steps (4) and (5) may be performed again to perform baking after the pulverization. . Furthermore, you may repeat a grinding | pulverization and baking by process (4), (5) twice or more as needed. Further, the lithium composite metal oxide can be washed or classified as necessary.
The lithium composite metal oxide of the present embodiment is preferably a mixture of primary particles having a particle size of 0.05 μm or more and 1 μm or less and secondary particles having a particle size of 2 μm or more and 100 μm or less formed by aggregation of the primary particles. It consists of. The particle diameters of the primary particles and secondary particles can be measured by observing with SEM.
The size of the secondary particles of the lithium composite metal oxide is preferably in the range of 2 μm to 50 μm, more preferably in the range of 2 μm to 10 μm, and even more preferably in the range of 3 μm to 8 μm. Especially preferably, it is the range of 3.5 micrometers or more and 7 micrometers or less. By these, the capacity | capacitance of the nonaqueous electrolyte secondary battery obtained increases more.
The primary particle size of the lithium composite metal oxide is preferably in the range of 0.08 μm to 0.8 μm, more preferably in the range of 0.10 μm to 0.7 μm, and still more preferably in the range of 0.8. It is in the range of 15 μm or more and 0.7 μm or less, and particularly preferably in the range of 0.2 μm or more and 0.5 μm or less. These increase the discharge capacity at a high current rate of the obtained nonaqueous electrolyte secondary battery.
Also, the average particle diameter of lithium composite metal oxide (D₅₀) Is preferably in the range of 1 μm to 50 μm, more preferably in the range of 1.5 μm to 30 μm, even more preferably in the range of 2 μm to 20 μm, and particularly preferably in the range of 3 μm to 10 μm. It is. Accordingly, the density of the electrode using the lithium composite metal oxide is increased, and a high-capacity nonaqueous electrolyte secondary battery can be obtained.
Average particle size of lithium composite metal oxide (D₅₀) Can be measured by the following method.
<Average particle diameter of lithium composite metal oxide (D₅₀) Measurement>
0.1 g of the lithium composite metal oxide powder to be measured is put into 50 ml of a 0.2 mass% sodium hexametaphosphate aqueous solution to obtain a dispersion in which the powder is dispersed. About the obtained dispersion liquid, a particle size distribution is measured using the master sizer 2000 (laser diffraction scattering particle size distribution measuring apparatus) by Malvern, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the value of the particle size viewed from the fine particle side at the time of 50% accumulation is the average particle size (D₅₀).
The BET specific surface area of the lithium composite metal oxide is preferably 0.1 m²/ G or more 20m²/ G or less, more preferably 0.5 m²/ G or more 15m²/ G or less, even more preferably 1 m²/ G or more 10m²/ G or less, particularly preferably 2 m²/ G or more 8m²/ G or less. These increase the discharge capacity at a high current rate of the obtained nonaqueous electrolyte secondary battery.
The BET specific surface area of the lithium composite metal oxide can be measured by the following method.
<Measurement of BET specific surface area of lithium composite metal oxide>
After 1 g of the lithium composite metal oxide powder to be measured is dried at 150 ° C. for 15 minutes in a nitrogen atmosphere, the measurement is performed using a flow sorb II 2300 manufactured by Micromeritics.
When the lithium composite metal oxide is used as a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery showing a higher capacity than before can be obtained.
[Nonaqueous electrolyte secondary battery]
Next, while explaining the configuration of the nonaqueous electrolyte secondary battery, the positive electrode using the lithium composite metal oxide of the present embodiment as the positive electrode active material of the nonaqueous electrolyte secondary battery, and the nonaqueous electrolyte secondary having the positive electrode The battery will be described.
An example of the non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution.
FIG. 1 is a schematic view showing an example of the nonaqueous electrolyte secondary battery of the present embodiment. The cylindrical nonaqueous electrolyte secondary battery 10 of this embodiment is manufactured as follows.
First, as shown in FIG. 1A, two separators 1 each having a strip shape, a strip-like positive electrode 2 having a positive electrode lead 21 at one end, and a strip-like negative electrode 3 having a negative electrode lead 31 at one end, 2, separator 1, and negative electrode 3 are laminated in this order and wound to form electrode group 4.
Next, as shown in FIG. 1B, after the electrode group 4 and an insulator (not shown) are accommodated in the battery can 5, the bottom of the can is sealed, and the electrode group 4 is impregnated with the electrolytic solution 6, An electrolyte is disposed between the negative electrode 3 and the negative electrode 3. Furthermore, the nonaqueous electrolyte secondary battery 10 can be manufactured by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8.
As the shape of the electrode group 4, for example, a columnar shape in which the cross-sectional shape when the electrode group 4 is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners. Can be mentioned.
In addition, as the shape of the nonaqueous electrolyte secondary battery having such an electrode group 4, a shape defined by IEC 60086 or JIS C 8500, which is a standard for batteries determined by the International Electrotechnical Commission (IEC), should be adopted. Can do. For example, cylindrical shape, square shape, etc. can be mentioned.
Furthermore, the non-aqueous electrolyte secondary battery is not limited to the above-described wound type configuration, and may have a stacked type configuration in which a stacked structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of the laminated nonaqueous electrolyte secondary battery include so-called coin-type batteries, button-type batteries, and paper-type (or sheet-type) batteries.
Hereinafter, each configuration will be described in order.
(Positive electrode)
The positive electrode of the present embodiment can be manufactured by first adjusting a positive electrode mixture containing a positive electrode active material, a conductive material and a binder, and supporting the positive electrode mixture on a positive electrode current collector.
(Positive electrode active material)
The positive electrode active material of the present embodiment has the above-described lithium composite metal oxide. By using the lithium composite metal oxide of this embodiment as a positive electrode active material of a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery exhibiting a high capacity can be obtained.
(Conductive material)
A carbon material can be used as a conductive material included in the positive electrode of the present embodiment. Examples of the carbon material include graphite powder, carbon black (for example, acetylene black), and a fibrous carbon material. Since carbon black is fine and has a large surface area, adding a small amount to the positive electrode mixture can improve the conductivity inside the positive electrode and improve the charge / discharge efficiency and output characteristics. Both the binding force between the positive electrode mixture and the positive electrode current collector and the binding force inside the positive electrode mixture are reduced, which causes an increase in internal resistance.
The proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be lowered.
(binder)
A thermoplastic resin can be used as the binder of the positive electrode of the present embodiment. Examples of the thermoplastic resin include polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. And fluororesins such as copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene.
These thermoplastic resins may be used as a mixture of two or more. By using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the whole positive electrode mixture is 1% by mass or more and 10% by mass or less, and the ratio of the polyolefin resin is 0.1% by mass or more and 2% by mass or less. A positive electrode mixture having both high adhesion to the current collector and high bonding strength inside the positive electrode mixture can be obtained.
(Positive electrode current collector)
As the positive electrode current collector included in the positive electrode of the present embodiment, a band-shaped member made of a metal material such as Al, Ni, stainless steel or the like can be used. Among these, a material that is made of Al and formed into a thin film is preferable because it is easy to process and inexpensive.
Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure-molding the positive electrode mixture on the positive electrode current collector. Further, the positive electrode mixture is made into a paste using an organic solvent, and the obtained positive electrode mixture paste is applied to at least one surface of the positive electrode current collector, dried, pressed and fixed, whereby the positive electrode current collector is bonded to the positive electrode current collector. A mixture may be supported.
When pasting the positive electrode mixture, organic solvents that can be used include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; methyl acetate And amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).
Examples of the method of applying the positive electrode mixture paste to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.
The positive electrode can be manufactured by the methods mentioned above.
(Negative electrode)
The negative electrode included in the nonaqueous electrolyte secondary battery of this embodiment is only required to be able to dope and dedope lithium ions at a lower potential than the positive electrode, and the negative electrode mixture containing the negative electrode active material is supported on the negative electrode current collector. And an electrode composed of the negative electrode active material alone.
(Negative electrode active material)
Examples of the negative electrode active material possessed by the negative electrode include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys that can be doped and dedoped with lithium ions at a lower potential than the positive electrode. It is done.
Examples of carbon materials that can be used as the negative electrode active material include graphites such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound fired bodies.
As an oxide that can be used as a negative electrode active material, SiO₂, SiO etc. formula SiO_x(Wherein x is a positive real number) silicon oxide represented by: TiO₂TiO, formula TiO_x(Where x is a positive real number) titanium oxide; V₂O₅, VO₂Etc. VO_x(Where x is a positive real number) oxide of vanadium; Fe₃O₄, Fe₂O₃FeO and other formulas FeO_x(Where x is a positive real number) iron oxide; SnO₂, SnO etc. formula SnO_x(Where x is a positive real number) tin oxide represented by WO₃, WO₂General formula WO_x(Where x is a positive real number)₄Ti₅O₁₂, LiVO₂And a composite metal oxide containing lithium and titanium or vanadium.
As a sulfide that can be used as a negative electrode active material, Ti₂S₃TiS₂TiS and other formula TiS_x(Where x is a positive real number) titanium sulfide; V₃S₄, VS_2,VS formula VS_x(Where x is a positive real number) Vanadium sulfide; Fe₃S₄, FeS₂FeS and other formulas_x(Where x is a positive real number) iron sulfide; Mo₂S₃, MoS₂Etc. MoS_x(Where x is a positive real number) molybdenum sulfide represented by SnS_2,SnS etc. formula SnS_x(Where x is a positive real number) tin sulfide represented by WS₂Formula WS_x(Where x is a positive real number) tungsten sulfide represented by: Sb₂S₃Etc. SbS_x(Where x is a positive real number) antimony sulfide; Se₅S₃, SeS₂, SeS etc. formula SeS_xSelenium sulfide represented by (where x is a positive real number).
Nitrides that can be used as negative electrode active materials include Li₃N, Li_3-xA_xA lithium-containing nitride such as N (where A is one or both of Ni and Co, and 0 <x <3) can be given.
These carbon materials, oxides, sulfides and nitrides may be used alone or in combination of two or more. These carbon materials, oxides, sulfides and nitrides may be crystalline or amorphous.
Further, examples of the metal that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.
Examples of alloys that can be used as the negative electrode active material include lithium alloys such as Li—Al, Li—Ni, Li—Si, Li—Sn, and Li—Sn—Ni; silicon alloys such as Si—Zn; Sn—Mn and Sn. -Tin alloys such as Co, Sn-Ni, Sn-Cu, Sn-La; Cu₂Sb, La₃Ni₂Sn₇And alloys such as:
These metals and alloys are mainly used alone as electrodes after being processed into a foil shape, for example.
Among the negative electrode active materials, the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (potential flatness is good), the average discharge potential is low, and the capacity retention rate when repeatedly charged and discharged is high. For reasons such as high (good cycle characteristics), a carbon material mainly composed of graphite such as natural graphite or artificial graphite is preferably used. The shape of the carbon material may be any of a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.
The negative electrode mixture may contain a binder as necessary. Examples of the binder include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.
(Negative electrode current collector)
Examples of the negative electrode current collector of the negative electrode include a band-shaped member made of a metal material such as Cu, Ni, and stainless steel. In particular, it is preferable to use Cu as a forming material and process it into a thin film from the viewpoint that it is difficult to make an alloy with lithium and it is easy to process.
As a method of supporting the negative electrode mixture on such a negative electrode current collector, as in the case of the positive electrode, a method using pressure molding, pasting with a solvent, etc., applying to the negative electrode current collector, drying and pressing. The method of crimping is mentioned.
(Separator)
Examples of the separator included in the nonaqueous electrolyte secondary battery of the present embodiment include a porous film, a nonwoven fabric, a woven fabric, and the like made of a material such as a polyolefin resin such as polyethylene and polypropylene, a fluororesin, and a nitrogen-containing aromatic polymer. A material having the following form can be used. Moreover, a separator may be formed by using two or more of these materials, or a separator may be formed by laminating these materials.
Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator should be as thin as possible as long as the mechanical strength is maintained because the volume energy density of the battery is increased and the internal resistance is reduced, preferably about 5 to 200 μm, more preferably about 5 to 40 μm. is there.
The separator preferably has a porous film containing a thermoplastic resin. In a nonaqueous electrolyte secondary battery, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, the current at the short circuit point is interrupted to prevent an excessive current from flowing (shut down). It preferably has a function. Here, the shutdown is performed by overheating the separator at the short-circuit location due to a short circuit, and when the temperature exceeds a presumed operating temperature, the porous film in the separator is softened or melted to close the micropores. And even if the temperature in a battery rises to a certain high temperature after a separator shuts down, it is preferable to maintain the shut-down state, without breaking at the temperature.
Examples of such a separator include a laminated film in which a heat resistant porous layer and a porous film are laminated. By using such a laminated film as a separator, the heat resistance of the secondary battery in this embodiment can be further increased. In the laminated film, the heat resistant porous layer may be laminated on both surfaces of the porous film.
(Laminated film)
Hereinafter, a laminated film in which the heat resistant porous layer and the porous film are laminated to each other will be described.
In the laminated film used as the separator of the nonaqueous electrolyte secondary battery of the present embodiment, the heat resistant porous layer is a layer having higher heat resistance than the porous film. The heat resistant porous layer may be formed from an inorganic powder (first heat resistant porous layer), may be formed from a heat resistant resin (second heat resistant porous layer), and includes a heat resistant resin and a filler. (A third heat-resistant porous layer). When the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer can be formed by an easy technique such as coating.
(First heat-resistant porous layer)
When the heat resistant porous layer is formed of an inorganic powder, examples of the inorganic powder used for the heat resistant porous layer include inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, and sulfates. Among these, a powder made of an inorganic substance having low conductivity (insulator) is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, calcium carbonate, or the like. Such inorganic powders may be used alone or in combination of two or more.
Among these inorganic powders, alumina powder is preferable because of its high chemical stability. More preferably, all of the particles constituting the inorganic powder are alumina particles, all of the particles constituting the inorganic powder are alumina particles, and part or all of them are substantially spherical alumina particles. preferable.
(Second heat resistant porous layer)
When the heat resistant porous layer is formed from a heat resistant resin, the heat resistant resin used for the heat resistant porous layer is polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyether ketone, aromatic polyester, polyether. Mention may be made of sulfone and polyetherimide. In order to further increase the heat resistance of the laminated film, polyamide, polyimide, polyamideimide, polyethersulfone and polyetherimide are preferable, and polyamide, polyimide or polyamideimide is more preferable.
More preferably, the heat-resistant resin used for the heat-resistant porous layer is a nitrogen-containing aromatic polymer such as aromatic polyamide (para-oriented aromatic polyamide, meta-oriented aromatic polyamide), aromatic polyimide, aromatic polyamideimide, Aromatic polyamides are preferred, and para-oriented aromatic polyamides (hereinafter sometimes referred to as para-aramids) are particularly preferred because they are easy to produce.
Also, examples of the heat resistant resin include poly-4-methylpentene-1 and a cyclic olefin polymer.
By using these heat resistant resins, the heat resistance of the laminated film used as the separator of the nonaqueous electrolyte secondary battery, that is, the thermal film breaking temperature of the laminated film can be further increased. Among these heat-resistant resins, when a nitrogen-containing aromatic polymer is used, the compatibility with the electrolytic solution, that is, the liquid retention in the heat-resistant porous layer may be improved depending on the polarity in the molecule. The rate of impregnation with the electrolytic solution during the production of the electrolyte secondary battery is also high, and the charge / discharge capacity of the nonaqueous electrolyte secondary battery is further increased.
The thermal film breaking temperature of such a laminated film depends on the type of heat-resistant resin, and is selected and used according to the use scene and purpose of use. More specifically, as the heat-resistant resin, when the nitrogen-containing aromatic polymer is used, the cyclic olefin polymer is about 400 ° C. When using, the thermal film breaking temperature can be controlled to about 300 ° C., respectively. In addition, when the heat resistant porous layer is made of an inorganic powder, the thermal film breaking temperature can be controlled to, for example, 500 ° C. or higher.
The para-aramid is obtained by polycondensation of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4′-biphenylene, It consists essentially of repeating units that are bound together in the opposite orientation, such as 1,5-naphthalene, 2,6-naphthalene, etc., in an orientation that extends coaxially or parallelly. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( Para-aligned or para-oriented such as paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer Examples include para-aramid having a structure according to the type.
The aromatic polyimide is preferably a wholly aromatic polyimide produced by polycondensation of an aromatic dianhydride and a diamine.
Specific examples of the aromatic dianhydride used for the polycondensation include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride, 3,3 ′, 4. 4,4′-benzophenone tetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride. It is done.
Specific examples of diamines used for polycondensation include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone. And 1,5-naphthalenediamine.
Also, as the aromatic polyimide, a polyimide soluble in a solvent can be suitably used. Examples of such a polyimide include a polycondensate polyimide of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine.
Examples of the aromatic polyamideimide include those obtained from polycondensation of aromatic dicarboxylic acid and aromatic diisocyanate, and those obtained from polycondensation of aromatic diacid anhydride and aromatic diisocyanate. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. A specific example of the aromatic dianhydride is trimellitic anhydride. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylene diisocyanate, and m-xylene diisocyanate.
In order to further enhance ion permeability, the thickness of the heat resistant porous layer of the laminated film is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and particularly preferably 1 μm or more and 4 μm or less. . The heat-resistant porous layer has fine pores, and the size (diameter) of the pores is preferably 3 μm or less, more preferably 1 μm or less.
(Third heat-resistant porous layer)
Further, when the heat resistant porous layer is formed including a heat resistant resin and a filler, the same heat resistant resin as that used for the second heat resistant porous layer can be used. As the filler, one or more selected from the group consisting of organic powder, inorganic powder, or a mixture thereof can be used. The particles constituting the filler preferably have an average particle size of 0.01 μm or more and 1 μm or less.
Examples of the organic powder that can be used as the filler include, for example, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, and the like, or two or more types of copolymers; Fluorine resin such as tetrafluoroethylene-6-propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine resin; urea resin; polyolefin resin; polymethacrylate; A powder is mentioned. Such organic powders may be used alone or in combination of two or more. Among these organic powders, PTFE powder is preferred because of its high chemical stability.
Examples of the inorganic powder that can be used as the filler include the same inorganic powder used in the heat-resistant porous layer.
When the heat-resistant porous layer is formed including a heat-resistant resin and a filler, the filler content depends on the specific gravity of the filler material, for example, when all of the particles constituting the filler are alumina particles In addition, when the total mass of the heat resistant porous layer is 100 parts by mass, the mass of the filler is preferably 5 parts by mass or more and 95 parts by mass or less, more preferably 20 parts by mass or more and 95 parts by mass or less, Preferably they are 30 to 90 mass parts. These ranges can be appropriately set depending on the specific gravity of the filler material.
Examples of the shape of the filler include substantially spherical, plate-like, columnar, needle-like, and fiber-like shapes, and any particle can be used. However, since it is easy to form uniform pores, Preferably there is. Examples of the substantially spherical particles include particles having a particle aspect ratio (long particle diameter / short particle diameter) of 1 or more and 1.5 or less. The aspect ratio of the particles can be measured by an electron micrograph.
In the laminated film used as the separator of the nonaqueous electrolyte secondary battery of this embodiment, the porous film preferably has fine pores and has a shutdown function. In this case, the porous film contains a thermoplastic resin.
The size of the micropores in the porous film is preferably 3 μm or less, more preferably 1 μm or less. The porosity of the porous film is preferably 30% to 80% by volume, more preferably 40% to 70% by volume. In a non-aqueous electrolyte secondary battery, when the presumed operating temperature is exceeded, the porous film containing the thermoplastic resin has micropores due to softening or melting of the thermoplastic resin constituting the porous film. Can be occluded.
What is necessary is just to select the thermoplastic resin used for a porous film what does not melt | dissolve in the electrolyte solution in a nonaqueous electrolyte secondary battery. Specific examples include polyolefin resins such as polyethylene and polypropylene, and thermoplastic polyurethane resins, and a mixture of two or more of these may be used.
In order for the separator to soften and shut down at a lower temperature, the porous film preferably contains polyethylene. Examples of the polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and ultra high molecular weight polyethylene having a molecular weight of 1,000,000 or more.
In order to further increase the puncture strength of the porous film, it is preferable that the thermoplastic resin constituting the porous film contains at least ultra high molecular weight polyethylene. In addition, in terms of production of the porous film, the thermoplastic resin may preferably contain a wax made of polyolefin having a low molecular weight (weight average molecular weight of 10,000 or less).
Further, the thickness of the porous film in the laminated film is preferably 3 μm or more and 30 μm or less, more preferably 3 μm or more and 25 μm or less. Moreover, in this embodiment, the thickness of a laminated film becomes like this. Preferably it is 40 micrometers or less, More preferably, it is 30 micrometers or less. Moreover, when the thickness of the heat resistant porous layer is A (μm) and the thickness of the porous film is B (μm), the value of A / B is preferably 0.1 or more and 1 or less.
In the present embodiment, the separator allows the electrolyte to permeate well when the battery is used (during charging / discharging). Or less, more preferably 50 seconds / 100 cc or more and 200 seconds / 100 cc or less.
The porosity of the separator is preferably 30% by volume to 80% by volume, more preferably 40% by volume to 70% by volume. The separator may be a laminate of separators having different porosity.
(Electrolyte)
The electrolyte solution included in the nonaqueous electrolyte secondary battery of this embodiment contains an electrolyte and an organic solvent.
As the electrolyte contained in the electrolyte, LiClO₄, LiPF₆, LiAsF₆, LiSbF₆, LiBF₄, LiCF₃SO₃, LiN (SO₂CF₃)₂, LiN (SO₂C₂F₅)₂, LiN (SO₂CF₃) (COCF₃), Li (C₄F₉SO₃), LiC (SO₂CF₃)₃, Li₂B₁₀Cl₁₀, LiBOB (where BOB is bis (oxalato) borate), lower aliphatic carboxylic acid lithium salt, LiAlCl₄And a mixture of two or more of these may be used. Among them, as an electrolyte, LiPF containing fluorine₆, LiAsF₆, LiSbF₆, LiBF₄, LiCF₃SO₃, LiN (SO₂CF₃)₂And LiC (SO₂CF₃)₃It is preferable to use at least one selected from the group consisting of:
Examples of the organic solvent contained in the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di- Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethyla Amides such as toamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by further introducing a fluoro group into these organic solvents ( One obtained by substituting one or more hydrogen atoms in the organic solvent with fluorine atoms can be used.
It is preferable to use a mixture of two or more of these as the organic solvent. Among them, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate and a mixed solvent of cyclic carbonate and ether are more preferable. As a mixed solvent of cyclic carbonate and acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable. The electrolyte using such a mixed solvent has a wide operating temperature range, hardly deteriorates even when charged and discharged at a high current rate, hardly deteriorates even when used for a long time, and natural graphite as an active material of the negative electrode. Even when a graphite material such as artificial graphite is used, it has the advantage of being hardly decomposable.
Also, as the electrolytic solution, since the safety of the obtained nonaqueous electrolyte secondary battery is increased, LiPF₆It is preferable to use an electrolytic solution containing a lithium salt containing fluorine and an organic solvent having a fluorine substituent. A mixed solvent containing dimethyl carbonate and ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether is capable of capacity even when charging / discharging at a high current rate. Since the maintenance rate is high, it is more preferable.
A solid electrolyte may be used instead of the above electrolyte. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the non-aqueous electrolyte in the high molecular compound can also be used. Li₂S-SiS₂, Li₂S-GeS₂, Li₂SP₂S₅, Li₂SB₂S₃, Li₂S-SiS₂-Li₃PO₄, Li₂S-SiS₂-Li₂SO₄An inorganic solid electrolyte containing a sulfide such as may be used. By using these solid electrolytes, the safety of the nonaqueous electrolyte secondary battery may be further improved.
In the nonaqueous electrolyte secondary battery of this embodiment, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.
Since the above-described positive electrode active material uses the above-described lithium composite metal oxide of the present embodiment, the nonaqueous electrolyte secondary battery using the positive electrode active material can exhibit a higher capacity than before.
Further, since the positive electrode has a positive electrode active material using the above-described lithium composite metal oxide of the present embodiment, the non-aqueous electrolyte secondary battery can exhibit a higher capacity than before.
Furthermore, since the nonaqueous electrolyte secondary battery has the positive electrode described above, it exhibits a higher capacity than before.

Next, the present invention will be described in more detail with reference to examples.
In this example, evaluation of the lithium composite metal oxide (positive electrode active material) and production evaluation of the positive electrode and the lithium secondary battery were performed as follows.
(1) Evaluation of lithium composite metal oxide Composition analysis of lithium composite metal oxide The composition analysis of lithium composite metal oxide was conducted by dissolving the obtained lithium composite metal oxide powder in hydrochloric acid and then using an inductively coupled plasma emission spectrometer (SII Nanotechnology Inc.) Manufactured by SPS3000).
2. Powder X-ray diffraction measurement of lithium composite metal oxide Powder X-ray diffraction measurement of lithium composite metal oxide was performed using a powder X-ray diffractometer (manufactured by Rigaku Corporation, RINT2500TTR, sample horizontal type). A powder X-ray diffraction pattern was obtained by filling the obtained lithium composite metal oxide into a dedicated substrate and measuring using a CuKα ray source in a diffraction angle range of 2θ = 10 ° to 90 °. .
Further, Rietveld analysis of powder X-ray diffraction patterns is performed by an analysis program RIETAN-2000 (see F. Izumi and T. Ikeda, Mater. Sci. Forum, 321-324 (2000) 198), and lithium composite metal oxidation. The space group of the crystal structure of the object was determined.
3. EXAFS measurement and analysis of lithium composite metal oxide (measurement of X-ray absorbance, creation of X-ray absorption spectrum)
The X-ray absorption spectrum of the lithium composite metal oxide is measured using the XAFS measurement device of the beamline 9C (BL-9C), a synchrotron radiation science research facility owned by the Institute for Materials Structure Science of the High Energy Accelerator Research Organization. Absorbance was measured and created using the obtained X-ray absorbance values.
In the measurement of X-ray absorbance, a Si (111) double crystal spectrometer was used. Further, regarding the X-ray absorbance measurement of the wavelength corresponding to the K absorption edge of Mn, detuning was performed at 60% in order to remove high-order terms.
In the measurement of X-ray absorbance, the incident X-ray intensity (I ₀ ) is measured at room temperature using a 17 cm ion chamber using N ₂ as a filling gas, and the transmitted X-ray intensity (I _t ) is measured as a filling gas. It was measured at room temperature using a 31cm ion chamber of using N ₂ as.
The measured energy range and the number of measurement points were 4932 at an equal energy interval from 6040 eV to 7640.5 eV for the K absorption edge of Mn. The K absorption edge of Ni was 5333 points at equal energy intervals from 7834 eV to 9434.5 eV.
The energy calibration is performed using a pre-edge peak (about about X-ray Absorption Near-Edge Structure) spectrum of the obtained K absorption edge when measured using copper alone as a standard sample. The angle of the spectral crystal at 8980 eV) was set to 12.7185 °.
In the measurement of X-ray absorbance, each incident X-ray energy, measured I _0, I _t, the following equation was determined X-ray absorbance.
X-ray absorbance μt = −ln (I ₀ / I _t )
In the above measurement, discrete X-ray absorbance is obtained corresponding to the wavelength of X-rays used for measurement (corresponding to the energy of X-rays used for measurement). The obtained X-ray absorbance was averaged and data interpolated as follows.
First, the X-ray absorbance in the range corresponding to the K absorption edge of Mn was averaged by the following method.
From 6040 eV to 6400 eV: 3 times of adjacent average processing of 21 points From 6400 eV to 6700 eV: 1 time of weighted average processing by 7 points of Savitzky-Golay method From 6700 eV to 7640.5 eV: 5 times of adjacent average processing of 11 points Subsequently, using the average value of the obtained X-ray absorbance, data interpolation was performed at the following data intervals to obtain an X-ray absorption spectrum having the X axis as the X-ray energy and the Y axis as the X absorbance.
6040 eV to 6508 eV: 6.5 eV interval 6508 eV to 6609.5 eV: 0.35 eV interval 6609.5 eV to 6640.5 eV: 1 eV interval 6640.5 eV to 7040.5 eV: 2.5 eV interval 7040.5 eV to 7640. Up to 5 eV: 6 eV interval Further, the X-ray absorbance in the range corresponding to the K absorption edge of Ni was averaged by the following method.
From 7834 eV to 8200 eV: 3 times of adjacent average processing of 21 points From 8200 eV to 8500 eV: 1 time of weighted average processing by 7 points of Savitzky-Golay method From 8500 eV to 9734.5 eV: 5 times of adjacent average processing of 11 points Subsequently, using the average value of the obtained X-ray absorbance, data interpolation was performed at the following data intervals to obtain an X-ray absorption spectrum having the X axis as the X-ray energy and the Y axis as the X absorbance.
From 7834 eV to 8302 eV: 6.5 eV interval From 8302 eV to 8403.5 eV: 0.35 eV interval From 8403.5 eV to 8459.5 eV: 1 eV interval From 8459.5 eV to 8834.5 eV: 2.5 eV interval From 8834.5 eV to 9434. Up to 5 eV: 6 eV interval (creation of EXAFS spectrum)
From the obtained X-ray absorption spectrum, an EXAFS spectrum of the K absorption edge of Mn and the K absorption edge of Ni was obtained as follows. Analysis of the X-ray absorption spectrum obtained above was performed using analysis software (Rigaku Corporation, REX2000).
First, the Mn K absorption edge E ₀ was set to an energy value at which the first-order differential coefficient was maximum in the vicinity of the Mn K absorption edge in the X-ray absorption spectrum. Similarly, the K absorption edge E ₀ of Ni is set to an energy value at which the first-order differential coefficient becomes maximum in the spectrum near the K absorption edge of Ni.
The spectrum background is a spectrum in a lower energy region than the K absorption edge of Mn and the K absorption edge of Ni, and Victory's formula (Aλ ³ −Bλ ⁴ + C; λ is the wavelength of incident X-rays, A, B and C are arbitrary constants) and determined by applying the least square method. The EXAFS spectrum was obtained by subtracting the background value corresponding to this Victreeen equation from the X-ray absorption spectrum.
(Calculation of radial distribution function)
A radial distribution function was obtained from the obtained EXAFS spectrum.
First, regarding the EXAFS spectrum, the absorbance (μ ₀ ) of isolated atoms was estimated by the Spline Smoothing method (smoothing spline method), and the EXAFS function χ (k) was extracted. Note that k is the wave number of photoelectrons defined by 0.5123 × (E−E ₀ ) ^1/2 , and the unit of k is ⁻¹ .
Next, the EXAFS function k ³ χ (k) weighted by k ³ was subjected to Fourier transform in the range of k from 3.0 to 11.85Å ⁻¹ to obtain a radial distribution function.
(2) Production of positive electrode A lithium composite metal oxide (positive electrode active material), a conductive material (acetylene black: graphite = 9: 1 (mass ratio)) and a binder (PVdF) obtained by the production method described later are used as a positive electrode active material. A paste-like positive electrode mixture was prepared by adding and kneading so that the composition of the substance: conductive material: binder = 87: 10: 3 (mass ratio) was obtained. When preparing the positive electrode mixture, N-methyl-2-pyrrolidone was used as the organic solvent.
The obtained positive electrode mixture was applied to a 40 μm thick Al foil serving as a current collector and vacuum dried at 150 ° C. for 8 hours to obtain a positive electrode.
(3) Production of nonaqueous electrolyte secondary battery (coin cell) The following operation was performed in a glove box in an argon atmosphere.
The positive electrode created in “(2) Preparation of positive electrode” is placed on the lower lid of a coin cell (manufactured by Hosen Co., Ltd.) for coin-type battery R2032 with the aluminum foil surface facing downward, and a laminated film separator (polyethylene) is placed thereon. A separator (thickness 16 μm) having a heat-resistant porous layer laminated thereon was placed on the porous film. 300 μl of electrolyte was injected here. The electrolyte used was prepared by dissolving LiPF ₆ in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate to a concentration of 1 mol / l.
Next, using lithium metal as the negative electrode, the lithium metal is placed on the upper side of the laminated film separator, covered with a gasket, and caulked with a non-aqueous electrolyte secondary battery (coin type battery R2032, hereinafter, (Sometimes referred to as a “coin-type battery”).
(4) Charge / Discharge Test Using the coin-type battery created in “(3) Production of Nonaqueous Electrolyte Secondary Battery (Coin Cell)”, a charge / discharge test was performed under the following conditions. The charge capacity and discharge capacity in the charge / discharge test were determined as follows.
<Charge / discharge test conditions>
Test temperature: 25 ° C or 60 ° C
Charging conditions: Maximum charging voltage 4.3V, charging time 10 hours, charging current 0.3 mA / cm ²
Discharge conditions: discharge minimum voltage 2.5V, discharge time 10 hours, discharge current 0.3 mA / cm ²
(Example 1)
1. Production of Lithium Composite Metal Oxide Precursor (Coprecipitate) Nickel sulfate hexahydrate, manganese sulfate monohydrate, and cobalt sulfate heptahydrate have a molar ratio of Ni: Mn: Co of 0.45: 0. .45: 0.10, each was weighed and dissolved in pure water to obtain an aqueous transition metal solution containing Ni ions, Mn ions, Co ions and SO ₄ ^2- ions.
To this transition metal aqueous solution, an aqueous potassium hydroxide solution was added to perform coprecipitation to produce a precipitate, thereby obtaining a slurry. The obtained slurry was subjected to solid-liquid separation, washed with distilled water to obtain a coprecipitate Q ¹ and dried for 8 hours at 100 ° C..
2. Production of lithium composite metal oxide The amount (mol) of Li is 1.3 with respect to the obtained coprecipitate Q ¹ and the total amount (mol) 1 of transition metals contained in the coprecipitate Q ^1. The lithium carbonate weighed in this manner and potassium sulfate as an inert flux were mixed in a mortar to obtain a mixture.
Next, the obtained mixture was placed in an alumina firing container, and the alumina firing container was placed in an electric furnace. The oxygen concentration was adjusted to 8.5% by volume using the air atmosphere originally present in the electric furnace and the introduced nitrogen gas, and heated at 400 ° C. to obtain a calcined product. Further, the oxygen concentration was adjusted to 1% by volume, the mixture was held at 850 ° C. for 6 hours and baked, and cooled to room temperature to obtain a baked product.
The fired product obtained was pulverized and dispersed in distilled water. The supernatant after standing was removed by decantation, filtered, and dried at 300 ° C. for 6 hours to obtain a powdered lithium composite metal oxide A ¹ .
3. The results of composition analysis of ^{A 1} to evaluate the resulting lithium composite metal oxide, Li: Ni: Mn: the molar ratio of Co is 1.03: 0.45: 0.45: was 0.10 .
And by performing powder X-ray diffractometry of A ^1, and a compound of layered structure type. As a result of Rietveld analysis, the crystal structure of A ¹ is hexagonal, which is classified to the space group R-3m.
After obtaining EXAFS spectra of Mn and Ni of A ¹ by the above-described method, a radial distribution function was obtained by Fourier transform. In the radial distribution function of _Mn , the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.53 と and the peak B _Mn of _{2.49 Å} was 1.12.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.56 and the peak B _Ni of 2.49 was 1.69.
_{Furthermore, I BMn / I AMn × I} BNi / I ANi was 1.89.
4). A coin type battery was produced by using a charge-discharge test A ¹ of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., the discharge capacity at 0.2C (mAh / g) was 170. When a discharge test at 60 ° C. was performed, the discharge capacity (mAh / g) at 0.2 C was 178.
(Example 2)
1. Preparation of lithium composite metal oxide precursor (coprecipitate) and manufacture of lithium composite metal oxide Nickel sulfate hexahydrate, manganese sulfate monohydrate, cobalt sulfate heptahydrate, Ni: Mn: Co molar ratio of 0.47: 0.48: except that each weighed so that 0.05 was obtained in the same manner as in example 1, to obtain a coprecipitate ^{Q 2.} Furthermore, except for using a coprecipitate Q ^2, the procedure of Example 1 to obtain a powdered lithium composite metal oxide A ^2.
2. Evaluation of Lithium Composite Metal Oxide The composition of A ² obtained was analyzed. The molar ratio of Li: Ni: Mn: Co was 1.06: 0.49: 0.45: 0.06. .
And by performing powder X-ray diffraction measurement of A ^2, and a compound of layered structure type. As a result of Rietveld analysis, the crystal structure of A ² is a hexagonal, classified to the space group R-3m.
After obtaining EX ² AFS spectra of Mn and Ni of A ² by the above-mentioned method, a radial distribution function was obtained by Fourier transform. In the radial distribution function of _Mn , the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.53 と and the peak B _Mn of _{2.49 Å} was 1.14.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.56 and the peak B _Ni of 2.49 was 1.69.
_{Furthermore, I BMn / I AMn × I} BNi / I ANi was 1.93.
3. A coin type battery was produced by using the charge and discharge test A ² of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., 0.2 C definitive discharge capacity (mAh / g) was 168. When a discharge test at 60 ° C. was performed, the discharge capacity (mAh / g) at 0.2 C was 178.
(Example 3)
1. Preparation of lithium composite metal oxide precursor (coprecipitate) and manufacture of lithium composite metal oxide Nickel sulfate hexahydrate, manganese sulfate monohydrate, cobalt sulfate heptahydrate, Ni: Mn: Co molar ratio of 0.48: 0.49: except that each weighed so that 0.03 was obtained in the same manner as in example 1, to obtain a coprecipitate ^{Q 3.} Furthermore, except for using a coprecipitate Q ^3, the procedure of Example 1 to obtain a powdered lithium composite metal oxide A ^3.
2. The results of composition analysis of ^{A 3} Evaluation resulting lithium composite metal oxide, Li: Ni: Mn: the molar ratio of Co is 1.00: 0.48: 0.49: was 0.03 .
And by performing powder X-ray diffraction measurement of A ^3, it was a compound having a layered structure type. As a result of Rietveld analysis, the crystal structure of A ³ is hexagonal, which is classified to the space group R-3m.
After obtaining the EXAFS spectra of Mn and Ni of ^{A 3} by the method described above to obtain the radial distribution function by applying a Fourier transform. In the Mn radial distribution function, the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.50Å and the peak B _Mn of _2.52Å was 1.15.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.56 and the peak B _Ni of 2.49 was 1.58.
_{Furthermore, I BMn / I AMn × I} BNi / I ANi was 1.82.
3. A coin type battery was produced by using the charge and discharge test A ³ of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., the discharge capacity at 0.2C (mAh / g) was 164. When a discharge test at 60 ° C. was performed, the discharge capacity (mAh / g) at 0.2 C was 175.
(Comparative Example 1)
1. And manufacturing the coprecipitate to Q ¹ lithium composite metal oxide, the total amount (mol) 1 of the transition metal contained in the coprecipitate Q ^1, as the amount of Li (mole) is 1.3 Weighed lithium carbonate and potassium sulfate as an inert flux were mixed in a mortar to obtain a mixture.
Subsequently, the obtained mixture was put into an alumina firing container, and fired by holding at 850 ° C. in an air atmosphere for 6 hours using an electric furnace, and cooled to room temperature to obtain a fired product.
The obtained fired product was pulverized, washed with distilled water by decantation, filtered, and dried at 300 ° C. for 6 hours to obtain a powdered lithium composite metal oxide R ¹ .
2. Evaluation of lithium composite metal oxide The composition of R ¹ obtained was analyzed. The molar ratio of Li: Ni: Mn: Co was 1.18: 0.46: 0.44: 0.10. .
When a powder X-ray diffraction measurement of R ¹ was performed, it was a layered structure type compound. As a result of Rietveld analysis, the crystal structure of R ¹ was hexagonal and was classified into the space group R-3m.
After obtaining EX1 AFS spectra of Mn and Ni of R ¹ by the above method, a radial distribution function was obtained by Fourier transform. In the radial distribution function of _Mn , the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.56 と and the peak B _Mn of _{2.49 ０．９} was 0.96.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.56 and the peak B _Ni of 2.49 was 2.13.
3. A coin type battery was produced by using a charge-discharge test R ¹ of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., the discharge capacity at 0.2C (mAh / g) was 154. When a discharge test at 60 ° C. was performed, the discharge capacity (mAh / g) at 0.2 C was 162.
(Comparative Example 2)
1. Except for using the prepared coprecipitate Q ² of the lithium composite metal oxide, the same operation as in Comparative Example 1 to obtain a powdered lithium composite metal oxide R ^2.
2. The results of composition analysis of the evaluation R ² of the lithium composite metal oxide, Li: Ni: Mn: the molar ratio of Co is 1.16: 0.47: 0.48: was 0.05.
When a powder X-ray diffraction measurement of R ² was performed, it was a layered structure type compound. As a result of Rietveld analysis, the crystal structure of R ² was hexagonal and classified into the space group R-3m.
After obtaining EX ² AFS spectra of Mn and Ni of R ² by the above-described method, a radial distribution function was obtained by Fourier transform. In the Mn radial distribution function, the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.53 Å and the peak B _Mn of _{2.49 Å} was 0.94.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.60 と and the peak B _Ni of 2.49 Å was 2.04.
3. A coin type battery was produced by using a charge-discharge test R ² of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., the discharge capacity at 0.2C (mAh / g) was 149. When a discharge test at 60 ° C. was performed, the discharge capacity (mAh / g) at 0.2 C was 160.
(Comparative Example 3)
1. Except for using the prepared coprecipitate Q ³ of the lithium composite metal oxide, the same operation as in Comparative Example 1 to obtain a powdered lithium composite metal oxide R ^3.
2. Evaluation of Lithium Composite Metal Oxide When the composition analysis of R ³ was performed, the molar ratio of Li: Ni: Mn: Co was 1.10: 0.48: 0.49: 0.03.
When a powder X-ray diffraction measurement of R ³ was performed, it was a layered structure type compound. As a result of Rietveld analysis, the crystal structure of R ³ was hexagonal and was classified into the space group R-3m.
After obtaining EXAFS spectra of Mn and Ni of R ³ by the above method, a radial distribution function was obtained by Fourier transform. In the Mn radial distribution function, the intensity ratio I _BMn / I _AMn of the peak A _Mn of 1.50 Å and the peak B _Mn of _{2.49 Å} was 0.94.
In the Ni radial distribution function, the intensity ratio I _BNi / I _ANi between the peak A _Ni of 1.56 and the peak B _Ni of 2.49 was 2.04.
3. A coin type battery was produced by using a charge-discharge test R ³ of the non-aqueous electrolyte secondary battery was subjected to a discharge test at 25 ° C., the discharge capacity at 0.2C (mAh / g) was 148. When a discharge test at 60 ° C. was performed, the discharge capacity at 0.2 C was 159.
The results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 below.

As a result of the evaluation, all of the non-aqueous electrolyte secondary batteries using the lithium composite metal oxides of Examples 1 to 3 as the positive electrode active material used the lithium composite metal oxides of Comparative Examples 1 to 3 as the positive electrode active material. A secondary battery having a higher discharge capacity and higher performance than the nonaqueous electrolyte secondary battery was obtained.
Moreover, even if it is the lithium composite metal oxide of Example 3 with the least Co usage-amount among Examples, it discharges rather than the lithium composite metal oxide of Comparative Example 1 with the most Co usage-amount among Comparative Examples. Since a non-aqueous electrolyte secondary battery having a large capacity was obtained, it was found that the performance could be maintained and improved even if the amount of Co used was reduced.
From the above results, it was found that the lithium composite metal oxide of the present invention is useful for a non-aqueous electrolyte secondary battery exhibiting a high capacity. Further, the positive electrode active material using the lithium composite metal oxide of the present invention, the positive electrode is useful for a high-performance non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery of the present invention has a higher capacity than before. It was found that

According to the present invention, it is possible to provide a lithium composite metal oxide useful for a nonaqueous electrolyte secondary battery exhibiting a higher capacity than before. In addition, a positive electrode active material, a positive electrode, and a nonaqueous electrolyte secondary battery using a lithium composite metal oxide can be provided.

Claims (11)

1. Lithium composite metal oxide containing Mn, Ni, Li and Co and satisfying the following (a) and (b):
   (A) In a radial distribution function obtained by Fourier transform of a wide-range X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of Mn in the lithium composite metal oxide, 1.5% by oxygen atoms bonded to Mn atoms is obtained. when the first proximity peak _{a Mn} of intensity _I AMn around, the intensity of the second closest peak _{B Mn} around 2.5Å by metal atoms near the next Mn atoms of the oxygen atoms bonded to Mn atoms was _{I BMn IBMn} / _IAMn is 0.5 or more and 1.2 or less,
   (B) In the radial distribution function obtained by Fourier transforming the EXAFS spectrum at the K absorption edge of Ni in the lithium composite metal oxide, the first proximity peak A _Ni near 1.5Å due to oxygen atoms bonded to Ni atoms. the intensity _I ANi, when the next on the intensity of the second closest peak around 2.5Å by metal atoms near the Ni atom bonded oxygen atom to Ni atom was _{I BNi,} the _I BNi _/ I _ANi, 1. It is 0 or more and 1.7 or less.
2. The lithium composite metal according to claim 1, wherein A _Li / A is 0.7 or more and 1.4 or less, where A Li is the amount (mol) of _Li and A is the amount (mol) of a metal other than _Li . Oxides.
3. _3. The lithium mixed metal oxide according to claim 1, wherein a product of the I _BMn / I _AMn and the I _BNi / I _ANi is 0.7 or more and 2.0 or less.
4. The lithium composite metal oxide according to any one of claims 1 to 3, wherein the lithium composite metal oxide has a layered structure and is represented by the formula (1):
   _{Li 1 + x (Ni 1-} x-y-α-β Mn y Co α M β) O 2 ... (1)
   (In the formula (1), −0.3 ≦ x ≦ 0.4, 0.35 ≦ y ≦ 0.7, 0 <α ≦ 0.1, 0 ≦ β <0.1 (where 0 <α + β ≦ 0.1), −0.05 ≦ x + y + α + β <1, and M is selected from the group consisting of Al, Mg, Ti, Ca, Cu, Zn, Fe, Cr, Mo, Si, Sn, Nb and V One or more elements.)
5. The lithium mixed metal oxide according to claim 4, wherein the M is Fe.
6. The lithium composite metal oxide according to claim 4, wherein β = 0.
7. A positive electrode active material comprising the lithium composite metal oxide according to any one of claims 1 to 6.
8. A positive electrode having the positive electrode active material according to claim 7.
9. A nonaqueous electrolyte secondary battery having a negative electrode and the positive electrode according to claim 8.
10. The nonaqueous electrolyte secondary battery according to claim 9, further comprising a separator disposed between the negative electrode and the positive electrode.
11. The non-aqueous electrolyte secondary battery according to claim 10, wherein the separator is a laminated film in which a heat-resistant porous layer and a porous film are laminated.

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