JP6371508B2 - Positive electrode active material for lithium ion secondary battery and method for producing the same, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing the positive electrode active material, a positive electrode for a lithium ion secondary battery containing the positive electrode active material, and a lithium ion secondary battery.

In recent years, the demand for secondary batteries has increased rapidly. Among them, lithium ion secondary batteries have a high voltage and a high energy density, and are attracting particular attention. The characteristics of the lithium ion secondary battery are strongly influenced by the positive electrode material, particularly the positive electrode active material. Conventionally, lithium-containing composite oxides such as lithium cobaltate (LiCoO ₂ ) have been known as positive electrode active materials for lithium ion secondary batteries. Improvements such as discharge characteristics, cycle characteristics, high rate characteristics, and stability at high temperatures are demanded.

  One of the problems of the lithium ion secondary battery is a problem in cycle characteristics that the cycle life is rapidly reduced by repeated charge and discharge. This problem becomes more serious at high temperatures. This is because the crystal structure of the positive electrode active material becomes unstable at high temperatures, elution of transition metals such as Co and release of oxygen (O) occurs, and the electrolyte decomposes due to moisture and other effects inside the battery. As a result, the positive electrode active material deteriorates, the internal resistance of the battery increases, and the like.

As a method for improving the cycle characteristics of a lithium ion secondary battery with respect to such a problem, a method of coating a lithium-containing composite oxide with metal oxide nanoparticles is known (for example, see Patent Document 1). ). However, in this method, since the oxidation resistance of the metal oxide forming the coating is not sufficient when a high potential of 4.3 V (vs. Li ⁺ / Li) or higher is applied, the cycle characteristics are sufficiently improved. Could not be obtained.
Moreover, the coating method is a wet method, and after the lithium-containing composite oxide is coated, a cleaning process and a firing process are required. Therefore, it is difficult to reduce the manufacturing process and manufacturing cost.

  It is also known that a lithium-containing composite oxide is coated with a rare earth fluoride (see, for example, Patent Document 2). However, this method has a problem that the rate characteristics are deteriorated and the discharge voltage is lowered particularly at a high rate because the surface of the lithium-containing composite oxide as the positive electrode active material has a highly insulating fluoride coating. It was.

US Pat. No. 7,608,332 JP 2000-353524 A

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a positive electrode active material from which a lithium ion secondary battery excellent in battery characteristics, particularly cycle characteristics and rate characteristics can be obtained.
Moreover, it aims at providing the method of manufacturing the positive electrode active material for lithium ion secondary batteries excellent in the said battery characteristic simply and at low cost.

  The positive electrode active material for lithium ion secondary batteries of the present invention (hereinafter referred to as the present active material) contains one or more transition metal elements selected from Ni, Co, and Mn and Li, and the content of Li is A lithium-containing composite oxide having a molar ratio of 0.95 times or more with respect to the total content of the transition metal elements, and a metal oxide supported on at least a part of the surface of the lithium-containing composite oxide. The metal oxide is characterized in that a part of O is substituted with a halogen element.

  The method for producing a positive electrode active material for a lithium ion secondary battery of the present invention (hereinafter referred to as the present production method) contains one or more transition metal elements selected from Ni, Co, and Mn and Li, A lithium-containing composite oxide having a molar ratio of 0.95 times or more with respect to the total content of the transition metal elements, and a metal oxide in which a part of O is substituted with a halogen element (hereinafter, halogen) It is characterized by having a dry mixing step of mixing with a substituted metal oxide).

  The positive electrode for a lithium ion secondary battery of the present invention (hereinafter referred to as a positive electrode) has a positive electrode active material layer containing a conductive material, a binder, and the active material on a positive electrode current collector.

  The lithium ion secondary battery (hereinafter referred to as the present battery) of the present invention includes a negative electrode, a separator, a nonaqueous electrolyte, and a present positive electrode.

  In the present invention, “supported on the surface” means that the halogen-substituted metal oxide is present on the surface of the lithium-containing composite oxide by being chemically or physically adsorbed and covers the surface. Say.

  If the positive electrode active material of the present invention is used, a lithium ion secondary battery excellent in cycle characteristics and rate characteristics can be obtained. In particular, a lithium ion secondary battery excellent in cycle characteristics and rate characteristics under high voltage charging can be obtained.

  In addition, according to the method for producing a positive electrode active material of the present invention, a halogen-substituted metal oxide can be supported on the surface of the lithium-containing composite oxide, and a cleaning process or a firing process is not required after the support. Therefore, the cost can be reduced by reducing the number of steps. In addition, it is possible to prevent the lithium-containing composite oxide from being deteriorated due to the structural change of the lithium-containing composite oxide due to heating in the firing step or the presence of moisture.

It is a scanning electron microscope (SEM) photograph of the positive electrode active material (2) of an Example. It is a SEM photograph of the positive electrode active material (3) of an Example. It is a SEM photograph of the positive electrode active material (3) of an Example, (a) is a SEM photograph of the cross section of a positive electrode active material, (b) is a SEM photograph which expanded a part of (a). It is a SEM photograph of the positive electrode active material (7) of an Example. It is an X-ray-diffraction (XRD) spectrum of the metal oxide used in Example 3 of the Example in which some O is substituted with F.

  Hereinafter, modes for carrying out the present invention will be described. In the present specification, the description “Li” indicates that the element is not Li but a Li element unless otherwise specified. The same applies to the notation of other elements.

<Positive electrode active material>
This active material comprises a halogen-substituted metal oxide supported on at least a part of the surface of the lithium-containing composite oxide.

In this active material, it can be confirmed by the following method that the halogen-substituted metal oxide is supported on a part of the surface of the lithium-containing composite oxide.
By observing the surface or cross section of the positive electrode active material with a scanning electron microscope (SEM), it can be seen that materials having different compositions are supported on the surface of the lithium-containing composite oxide. Moreover, the element of the material which exists on the surface is known by conducting an elemental analysis on the surface or cross section of the positive electrode active material with an X-ray microanalyzer (EPMA). At this time, if the cross section of the positive electrode active material is element-mapped by EPMA, it can be seen that the surface contains more halogen elements than the center of the positive electrode active material. From the above elemental analysis, it can be seen that a material containing a halogen element is present on the surface of the lithium-containing composite oxide. Note that the center of the positive electrode active material refers to a point having the maximum average distance from the surface.

  Furthermore, by identifying the crystal structure by analysis by X-ray diffraction (XRD), it can be confirmed that the material containing a halogen element is a halogen-substituted metal oxide. Further, it can be confirmed that the positive electrode active material has both the lithium-containing composite oxide and the halogen-substituted metal oxide.

It is considered that when a metal oxide is present on the surface of the lithium-containing composite oxide, the conductivity and lithium ion diffusibility of the lithium-containing composite oxide surface are improved and rate characteristics are improved. In addition, contact between the lithium-containing composite oxide surface and the electrolytic solution can be reduced. Thereby, it is thought that elution of the transition metal etc. from the lithium containing complex oxide surface to electrolyte solution can be suppressed, and the fall of the discharge capacity and discharge voltage at the time of repeating a charging / discharging cycle can be suppressed. Furthermore, the metal oxide supported on the surface of the lithium-containing composite oxide of the active material has high oxidation resistance and high voltage (4. Durability is high even under 3 V (voltage of vs. Li ⁺ / Li) charge. Therefore, it is considered that the rate characteristics at a high voltage can be improved, and the decrease in the discharge capacity and the discharge voltage when the charge / discharge cycle is repeated can be suppressed.

The shape of the active material may be any of a spherical shape, a film shape, a fiber shape, a lump shape, and the like. The active material is preferably spherical from the viewpoint of enhancing the filling property.
The average particle size of the active material is preferably 3 to 30 μm, more preferably 4 to 25 μm, and particularly preferably 5 to 20 μm. If an average particle diameter exists in an above-described range, it can be conveniently used as a positive electrode active material of a lithium ion secondary battery.
The average particle size of the active material is calculated as the average particle size of particles carried by the halogen-substituted metal oxide on a part of the surface of the lithium-containing composite oxide. However, when the average particle size of the halogen-substituted metal oxide is sufficiently smaller than that of the lithium-containing composite oxide, the average particle size of the active material can be regarded as equivalent to the average particle size of the lithium-containing composite oxide. .

The average particle size of the active material is determined based on the volume size, and the volume-based cumulative 50% diameter (hereinafter referred to as this particle size), which is the particle size of 50% in the cumulative curve with the total volume being 100%. The average particle size calculated by the method means the average particle size (1)). The particle size distribution is obtained as a frequency distribution measured by a laser scattering particle size distribution measuring apparatus and a cumulative volume distribution curve. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like, and using, for example, a laser diffraction / scattering particle size distribution measuring device (device name: Partica LA-950VII) manufactured by HORIBA, This can be done by measuring the particle size distribution.
In the present specification, the average particle size of the lithium-containing composite oxide is also the volume-based cumulative 50% size (average particle size (1)) similar to the average particle size of the active material. The diameter is not a volume-based cumulative 50% diameter. The average particle size of the halogen-substituted metal oxide will be described later.

(Manufacture of positive electrode active material)
The production method preferably includes a dry mixing step in which the lithium-containing composite oxide and the halogen-substituted metal oxide are mixed in a dry manner. By the dry mixing process, the halogen-substituted metal oxide can be efficiently supported on the surface of the lithium-containing composite oxide. Furthermore, it is more preferable to have a substitution step for obtaining a halogen-substituted metal oxide before the dry mixing step. Details of the substitution step will be described later.

  Unlike the case where the compound is coated on the lithium-containing composite oxide in the wet process, the dry mixing process can omit the firing and washing processes in the process of supporting the halogen-substituted metal oxide. Therefore, the number of steps can be reduced to reduce the manufacturing cost, and the lithium-containing composite oxide can be prevented from being deteriorated due to the presence of moisture, and the structural change of the lithium-containing composite oxide due to heating in the firing step.

In the dry mixing step, the dry mixing method includes, for example, various dispersers, ball mills, super mixers, Henschel mixers, atomizers, V-type mixers, paint shakers, conical blenders, nauta mixers, SV mixers, drum mixers, shaker mixers. Mixing can be performed using a proshear mixer, a universal mixer, a rocking mixer, a ribbon mixer, a container mixer, and the like. In addition, when mixing on a small scale, a rotation / revolution mixer (for example, manufactured by Thinky, apparatus name: Nertaro Awatori ARE-310) can also be used.
The mixing time is preferably 1 to 60 minutes and more preferably 1 to 30 minutes from the viewpoint of productivity.

  The mixing ratio of the lithium-containing composite oxide and the halogen-substituted metal oxide is preferably 0.01 to 10% by mass ratio of the halogen-substituted metal oxide to the lithium-containing composite oxide from the viewpoint of mixing uniformity. 0.1 to 5% is more preferable.

  This manufacturing method may have another process after the process of mixing a lithium containing complex oxide and a halogen-substituted metal oxide by a dry process. Examples of other processes include an annealing process, a cleaning and drying process, and the like.

  The annealing step is a step of heating the lithium-containing composite oxide having a halogen-substituted metal oxide on the surface. Impurities such as organic substances in the positive electrode active material can be decomposed and removed by having an annealing step, and the binding force between the lithium-containing composite oxide and the halogen-substituted metal oxide supported on the surface is further increased. Can do. The positive electrode active material obtained through this step can further improve battery characteristics. The heating temperature in the annealing step is preferably 350 ° C. or less, and more preferably 100 to 300 ° C.

The cleaning step is a step of bringing a lithium-containing composite oxide having a halogen-substituted metal oxide on the surface into contact with a cleaning liquid. When the cleaning step is included, impurities that cannot be removed by the annealing step can be washed away without impairing the binding force between the lithium-containing composite oxide and the halogen-substituted metal oxide. Therefore, the positive electrode active material obtained through this step can further improve battery characteristics. The cleaning liquid is preferably an organic solvent such as ethanol, a fluorine-based solvent such as hydrochlorofluorocarbon, and water. The organic solvent and the fluorine-based solvent are more preferable because the cleaning liquid can be easily removed after contact.
A drying process can be performed after a washing process. Thereby, the cleaning liquid can be removed. The drying temperature is preferably in the range of 20-80 ° C.

  Hereinafter, the lithium-containing composite oxide used in the active material and the halogen-substituted metal oxide supported on the surface will be described.

(Lithium-containing composite oxide)
The lithium-containing composite oxide contains one or more transition metal elements selected from Ni, Co, and Mn and Li, and the content of Li is 0.001 in terms of molar ratio with respect to the total amount of transition metal elements. More than 95 times.
Examples of other transition metal elements other than Ni, Co, and Mn contained in the lithium-containing composite oxide include Fe, Cr, W, Mo, Zr, V, and Cu. When other transition metal elements are contained, the total amount of transition metal elements described above is the total amount of Ni, Co, Mn and other transition metal elements.
The content of Li is preferably 0.96 to 1.08 times in molar ratio with respect to the total amount of transition metal elements.

As the lithium-containing composite oxide, a compound represented by the following formula (1) or (2) is preferable. As a lithium containing complex oxide, 1 type may be used independently from the compound represented by following formula (1) or (2), and 2 or more types may be used together. The compound represented by the formula (1) is more preferable in terms of excellent cycle characteristics of a battery having a lithium-containing composite oxide.
_{Li a (Ni x Mn y Co} z) Me b O 2 ............ (1)
In formula (1), Me represents a transition metal element other than Ni, Co and Mn. Further, 0.95 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ b ≦ 0.3, and 0.90 ≦ x + y + z + b ≦ 1.05.
Furthermore, since the molar amount of Li is 0.95 times or more with respect to the total molar amount of the transition metal elements, 0.95 ≦ a / (x + y + z + b) is established.

In the formula (1), a is preferably 0.97 ≦ a ≦ 1.06 and 0.98 ≦ a ≦ 1. From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having this lithium-containing composite oxide. 04 is more preferable.
In the formula (1), x is preferably 0.2 ≦ x ≦ 0.9, and 0.3 ≦ x ≦ 0. From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having this lithium-containing composite oxide. 8 is more preferable.
Y in the formula (1) is preferably 0 ≦ y ≦ 0.7, and 0.1 ≦ y ≦ 0.6 from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having the lithium-containing composite oxide. More preferred.
Z in the formula (1) is preferably 0.05 ≦ z ≦ 1.0, preferably 0.1 ≦ z ≦ 1.0, from the viewpoint of excellent cycle characteristics of the lithium ion secondary battery having this lithium-containing composite oxide. Is more preferable.

Examples of the compound represented by the formula (1) include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _Examples include _0.85 Co _0.10 Al _0.05 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Since a battery having excellent cycle characteristics can be provided, LiCoO ₂ or LiNi _0.5 Co _0.2 Mn _0.3 O ₂ is particularly preferable as the compound represented by the formula (1).

_{Li (Li q Mn u Ni v} Co w) O p ............ (2)
In Formula (2), 0.1 <q <0.7, 0.3 <u <0.85, 0.1 <v <0.5, 0 <w <0.33, 2.1 <p < 2.7, q + u + v + w = 1.
Furthermore, since the molar amount of Li is 0.95 times or more with respect to the total molar amount of the transition metal elements, 0.95 ≦ (1 + q) / (u + v + w) is established.

Q in the formula (2) is preferably 0.1 ≦ q ≦ 0.55, and 0.15 ≦ q ≦ 0. 0 from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having this lithium-containing composite oxide. 45 is more preferred.
From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having this lithium-containing composite oxide, u in Formula (2) is preferably 0.15 ≦ u ≦ 0.5, and 0.2 ≦ u ≦ 0. 5 is more preferable.
W in Formula (2) is preferably 0 <w ≦ 0.3, more preferably 0 <w ≦ 0.28, from the viewpoint of excellent cycle characteristics of a lithium ion secondary battery having this lithium-containing composite oxide.
From the viewpoint of increasing the discharge capacity of the lithium ion secondary battery having this lithium-containing composite oxide, v in the formula (2) is preferably 0.4 ≦ v ≦ 0.77, and 0.4 ≦ v ≦ 0. 72 is more preferred.

As an example of the compound represented by the formula (2),
Li (Li _0.16 Ni _0.17 Co _0.08 Mn _0.59 ) O ₂ , Li (Li _0.17 Ni _0.17 Co _0.17 Mn _0.49 ) O ₂ , Li (Li _0.17 Ni _0.21 Co _0.08 Mn _0.54 ) O ₂ , Li (Li _0.17 Ni _0.14 Co _0.14 Mn _0.55 ) O ₂ , Li (Li _0.18 Ni _0.12 Co _{0 .12} Mn _0.58 ) O ₂ , Li (Li _0.18 Ni _0.16 Co _0.12 Mn _0.54 ) O ₂ , Li (Li _0.20 Ni _0.12 Co _0.08 Mn _0.60 ) O ₂ , Li (Li _0.20 Ni _0.16 Co _0.08 Mn _0.56 ) O ₂ , Li (Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ) O _2, Li ( Li _0.45 Ni _0.20 Co _0.15 M _{0.65) O 2} and the like. Li (Li _0.20 Ni _0.12 Co _0.08 Mn _0.60 ) O ₂ and Li (Li _0.45 Ni _0.20 Co _0.15 Mn _0.65 ) O ₂ are particularly preferred.

  The lithium-containing composite oxide is preferably particulate. The shape of the particles is not particularly limited, such as a spherical shape, a needle shape, or a plate shape. The lithium-containing composite oxide is preferably spherical because the active material can be highly filled.

  The average particle size (1) of the lithium-containing composite oxide is preferably 3 to 30 μm, more preferably 4 to 25 μm, and particularly preferably 5 to 20 μm. In addition, the average particle diameter (1) of the lithium-containing composite oxide is a volume-based cumulative 50% diameter as described above. The volume-based cumulative 50% diameter is calculated by the method described above.

0.1-10 m < ² > / g is preferable and, as for the specific surface area of lithium containing complex oxide, 0.15-5 m < ² > / g is especially preferable. When the specific surface area of the lithium-containing composite oxide is 0.1 to 10 m ² / g, the discharge capacity is high and a dense positive electrode can be formed. In the present invention, the specific surface area is a value measured using an adsorption BET (Brunauer, Emmett, Teller) method using nitrogen gas.

(Method for producing lithium-containing composite oxide)
The method for producing a lithium-containing composite oxide includes a method in which a compound obtained by co-precipitation including a transition metal element and a lithium compound are mixed and fired, a hydrothermal synthesis method, a sol-gel method, a dry mixing method (solid phase method) ), An ion exchange method, a glass crystallization method, or the like can be used as appropriate.

  The method for producing a lithium-containing composite oxide is preferably a method in which a compound containing a transition metal element obtained by a coprecipitation method and a lithium compound are mixed and fired. According to the coprecipitation method, a lithium-containing composite oxide containing a transition metal element uniformly can be obtained. When the transition metal element is uniformly contained in the lithium-containing composite oxide, the discharge capacity of the lithium ion secondary battery using the positive electrode active material having the lithium-containing composite oxide can be increased.

  The coprecipitation method is a technique for depositing a hardly soluble compound (coprecipitate) having a desired composition containing two or more transition metals from a solution containing a metal salt of two or more transition metals. As the coprecipitation method for obtaining the compound used for the production of the lithium-containing composite oxide, specifically, an alkali coprecipitation method and a carbonate coprecipitation method are preferable.

Here, the alkali coprecipitation method means that a transition metal salt aqueous solution and a pH adjusting solution containing a strong alkali are added to a reaction solution and mixed to produce a hydroxide containing a transition metal in the mixture. It is a method to do. Use of a hydroxide obtained by the alkali coprecipitation method is preferable because a positive electrode active material having a high powder density can be obtained.
The carbonate coprecipitation method is a method in which an aqueous transition metal salt solution and an aqueous solution containing a carbonate ion source are added to a reaction solution and mixed to produce a carbonate compound containing a transition metal in the mixed solution. is there. It is preferable to use a carbonate compound obtained by the carbonate coprecipitation method because a porous active material having a high specific surface area can be obtained.

  The pH of the reaction solution in the alkali coprecipitation method is preferably 10-12. The pH adjusting liquid to be added is preferably an aqueous solution containing at least one compound selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide, which are strong alkalis. Furthermore, in order to adjust the solubility of the transition metal salt, an aqueous ammonia solution or an aqueous ammonium sulfate solution may be added to the mixed solution.

  The pH of the reaction solution in the carbonate coprecipitation method is preferably 7-9. The aqueous solution containing a carbonate ion source is preferably an aqueous solution containing at least one compound selected from sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Furthermore, in order to adjust the solubility of the transition metal salt, an aqueous ammonia solution or an aqueous ammonium sulfate solution may be added to the mixed solution.

  As a lithium compound used for manufacture of lithium containing complex oxide, at least 1 sort (s) chosen from lithium carbonate, lithium hydroxide, and lithium nitrate is preferable, and since it is cheap, lithium carbonate is more preferable. Examples of the method of mixing the lithium compound and the coprecipitate include a method using a rocking mixer, a nauta mixer, a spiral mixer, a cutter mill, a V mixer, and the like.

  For the firing, an electric furnace, a continuous firing furnace, a rotary kiln, or the like can be used. The firing is preferably performed in the air, and particularly preferably performed while supplying air. By supplying air during firing, the transition metal element in the coprecipitate is sufficiently oxidized, the crystallinity can be increased, and the target lithium-containing composite oxide can be obtained.

  The firing temperature is preferably 500 to 1000 ° C, more preferably 600 to 1000 ° C, and particularly preferably 800 to 950 ° C. When the firing temperature is within the above range, a positive electrode active material with high crystallinity can be obtained. The firing time is preferably 4 to 40 hours, and more preferably 4 to 20 hours.

(Halogen-substituted metal oxide)
In this active material, the halogen-substituted metal oxide supported on the surface of the lithium-containing composite oxide is a metal oxide in which a part of O of the metal oxide is substituted with a halogen element.

The presence of the halogen-substituted metal oxide can be confirmed by identifying the crystal structure by XRD analysis. As an example, description will be made using an XRD spectrum (FIG. 5) of a compound in which CeO ₂ is used as a metal oxide and a part of CeO ₂ is substituted with F.
The broken line spectrum in FIG. 5 is the CeO ₂ spectrum.
Spectra of the solid line in FIG. 5 is a spectrum of CeO ₂ after the processing by substituting a part of the O of CeO ₂ to F. A method of replacing with F will be described later.
FIG. 5 shows a peak (2θ = 28 to 29 °) corresponding to the (111) plane of the metal oxide (CeO ₂ ) and a peak (2θ = 47 to 48 °) corresponding to the (220) plane. Further, a peak (2θ = 27 to 28 °) corresponding to the (111) plane of the metal halide (CeF ₃ ) and a peak (2θ = 45 to 46 °) corresponding to the (113) plane are observed. Further, a peak (2θ = 24 to 25 °) corresponding to the (220) plane of the metal halide (CeF ₄ ) and a peak (2θ = 21 to 22 °) corresponding to the (021) plane are observed.

From the solid line in the spectrum of FIG. 5, the CeO ₂ after the processing by substituting a part of the O of CeO ₂ to F, a metal oxide and (CeO ₂₎ and metal halides (CeF ₃ and CeF ₄₎ but It has been shown to coexist. From this, it can be said that F is sufficiently introduced into the crystal structure while maintaining the crystal structure of CeO ₂ , and as a result, a part of O in CeO ₂ is replaced with F.

  Examples of halogen-substituted metal oxides include transition metal oxides substituted with halogen elements, rare-earth element oxides substituted with halogen elements, carbon group oxides substituted with halogen elements, and halogen-substituted metal oxides. Examples thereof include oxides of boron group elements, oxides of alkaline earth elements substituted with halogen elements, oxides of alkali metal elements substituted with halogen elements, and composite metal oxides substituted with halogen elements. Examples of the composite metal oxide include oxides having a perovskite structure and oxides having a spinel structure. The halogen-substituted metal oxide is preferably at least one selected from the aforementioned compounds.

  The halogen-substituted metal oxide is more preferably at least one selected from a transition metal oxide substituted with a halogen element and an oxide of a rare earth element substituted with a halogen element from the viewpoint of excellent rate characteristics. When a positive electrode active material in which these halogen-substituted metal oxides are supported on the surface of a lithium-containing composite oxide, the cycle characteristics and rate characteristics of the lithium ion secondary battery, particularly the cycle characteristics and rate characteristics under high voltage charging Can be improved.

The metal element contained in the halogen-substituted metal oxide is at least one selected from the group consisting of Ti, Ce, La, Y, Zr, V, Nb, Ta, W, Zn, Si, Al, Mg, Li, and K It is preferable that The metal element is more preferably at least one selected from the group consisting of Ti, Ce, La, Zr, and Zn, and particularly preferably at least one selected from the group consisting of Ti, Ce, and Zn. preferable. Since such an oxide of a metal element is electrochemically stable, the active material containing the oxide of the metal element can improve the cycle characteristics of the lithium ion secondary battery. Specific examples of the oxide of the metal element include TiO ₂ , CeO ₂ , ZrO ₂ , Y ₂ O ₅ , V ₂ O ₅ , Ta ₂ O ₅ , WO ₃ , ZnO, SiO ₂ , Al ₂ O ₃ , _MgO, Li _{0.35 La} 0.65 TiO ₃ and the like.

  As the halogen element contained in the halogen-substituted metal oxide, fluorine (F) is preferable because it is easy to handle and has high electronegativity and excellent oxidation resistance.

The substitution ratio of the halogen element in the halogen-substituted metal oxide is preferably 0.05 to 90%.
In the present invention, the substitution ratio is the ratio of the halogen content (unit: mass) in the halogen-substituted metal oxide to the maximum amount (unit: mass) of the halogen element that can be substituted for the metal oxide.
The maximum amount of the halogen element that can be substituted for the metal oxide is the sum of values obtained by multiplying the content (unit: mole) of each metal element contained in the metal oxide by the stable maximum valence of each metal element, It is the value multiplied by the atomic weight of the halogen element. The halogen content in the halogen-substituted metal oxide is a value measured by the method described in the examples.

The substitution ratio of the halogen element is more preferably 0.1 to 85%, and particularly preferably 5 to 80%. When the substitution ratio is 0.05% or more, the effect of containing a halogen element and improving oxidation resistance can be sufficiently enhanced. Moreover, if the substitution ratio is 90% or less, the effect of increasing the conductivity of the lithium-containing composite oxide surface can be sufficiently exhibited.
The substitution ratio of the halogen element can be adjusted by changing the halogen substitution temperature or the halogen gas pressure in the preferred halogen-substituted metal oxide production method described below.

The halogen-substituted metal oxide is preferably in the form of particles. In the halogen-substituted metal oxide, the average particle size calculated from the surface area and true density using the following formula (hereinafter, the average particle size calculated by this method is referred to as average particle size (2)) is preferably 1 to 100 nm. .
Average particle diameter (2) = 6 / ρ · Sw
Note that ρ (unit: g / cm ³ ) is the true density of the halogen-substituted metal oxide. In this specification, the true density is a value measured by a constant volume expansion method. The measured density is a particle density including a space (closed pore) inside the particle not connected to the outside. Since the halogen-substituted metal oxide used in the active material can ignore the volume of closed pores in the particles, the density can be considered as the true density of the halogen-substituted metal oxide. Sw (unit: m ² / g) is a specific surface area of the halogen-substituted metal oxide, and is a value calculated by the BET method using nitrogen gas.
If the average particle diameter (2) of the halogen-substituted metal oxide is in the above range, the halogen-substituted metal oxide can be uniformly present on the surface of the lithium-containing composite oxide. The average particle size (2) is more preferably 5 to 70 nm, and particularly preferably 10 to 60 nm.

The specific surface area of the halogen-substituted metal oxide is preferably 1 to 100 m ² / g. If it exists in this range, when mixing with lithium containing complex oxide and manufacturing a positive electrode active material, it will adhere to the surface of lithium containing complex oxide easily. The specific surface area is more preferably 5~80m ² / g, more preferably 10 to 70 m ² / g. The specific surface area is a value calculated by the BET method using nitrogen gas.

(Production of halogen-substituted metal oxides)
The method for producing a halogen-substituted metal oxide preferably includes a substitution step of treating the metal oxide to substitute a part of O with a halogen element (hereinafter abbreviated as halogen substitution). The halogen substitution is preferable because the substitution ratio of the halogen element in the halogen-substituted metal oxide can be adjusted to a desired range. The halogen substitution method is a dry method in which a gas containing a halogen element (hereinafter also referred to as a halogen-containing gas) is brought into contact with a metal oxide, or a liquid compound containing a halogen element (hereinafter also referred to as a halogen-containing liquid) and a metal. And a wet method in which an oxide is brought into contact. From the viewpoint of easy handling and adjustment of the content of the halogen element, the halogen substitution method is more preferably a dry method using a halogen-containing gas.

  When halogen substitution is performed using a halogen-containing gas, the treatment temperature is preferably -20 to 350 ° C. When the treatment temperature is within the above range, a halogen element can be introduced into the crystal structure while maintaining the crystal structure of the metal oxide. From the viewpoint of increasing the reaction rate between the halogen element and the metal oxide and facilitating introduction of the halogen element in the plane of the crystal structure, the halogen substitution temperature is more preferably 0 ° C. or higher. In order to maintain the crystal structure of the metal oxide by controlling the content of the halogen element, the halogen substitution temperature is more preferably set to 150 ° C. or lower.

When halogen substitution is performed using a halogen-containing gas, the halogen-containing gas may be used alone or a mixture of a halogen-containing gas and an inert gas such as nitrogen (N ₂ ) gas may be used. Good. When mixing with an inert gas, the mixing ratio of the halogen-containing gas and the inert gas is preferably a volume ratio, and the halogen-containing gas / inert gas is preferably in the range of 50/50 to 99/1.

  Furthermore, when halogen substitution is performed using a halogen-containing gas, the halogen substitution is preferably performed using a highly airtight container. The pressure in the container is preferably 0 to 1 MPaG (gauge pressure), more preferably 0.0001 to 0.2 MPaG, from the viewpoint of increasing the reaction rate of the halogen-containing gas. The treatment time is preferably 1 minute to 1 day, and more preferably 1 to 8 hours.

  The halogen-containing gas used for the halogen substitution in the dry process and the halogen-containing liquid used for the halogen substitution in the wet process often have high erosion with respect to metals and the like. Therefore, it is preferable that the halogen substitution reaction tank has its inner wall and internal equipment made of a material having corrosion resistance to the halogen-containing gas or halogen-containing liquid. In addition, it is preferable that this constituent material is a material that does not generate gaseous impurities in the treatment process or does not become impurities even when a gaseous substance is generated.

  Specific examples of the inner wall of the halogenated reaction tank include stainless steel (for example, SUS316), alloys such as Monel, Inconel and Hastelloy, glasses such as synthetic quartz glass, calcium fluoride, nickel fluoride, etc. Metal halides, polytetrafluoroethylene, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymers, perhalogenated resins such as polychlorotrifluoroethylene can be suitably used.

In the method for producing a halogen-substituted metal oxide, the halogen element is preferably F as described above. In the case where part of O of the metal oxide is substituted with F (hereinafter referred to as fluorine substitution), compounds containing F include HF (hydrogen fluoride), F ₂ (fluorine gas), ClF ₃ , IF ₅ , Fluorine-containing gases such as BF ₃ , NF ₃ , PF ₅ , SiF ₄ , and SF ₆ , fluorine-containing organic compounds such as hydrofluorocarbon and hydrochlorofluorocarbon, metal fluorides such as LiF and NiF ₂ , polytetrafluoroethylene, Examples thereof include fluororesins such as polyvinylidene fluoride. It is preferable to use a fluorine-containing gas in that impurities in the fluorine-containing metal oxide obtained by fluorine substitution can be reduced. Among the above-mentioned fluorine-containing gases, it is more preferable to use one or more selected from F ₂ , ClF ₃ , and NF ₃ , and it is particularly preferable to use F ₂ .

When the fluorine-containing gas is used, as described above, the fluorine-containing gas may be used alone, or a fluorine-containing gas and an inert gas such as N ₂ gas may be mixed and used. The fluorine substitution temperature is preferably -20 to 350 ° C. When the processing temperature is low, F is selectively introduced into the surface of the edge of the crystal structure. In addition, when the treatment temperature is high, the reaction rate increases and the reaction selectivity decreases, but the crystal structure of the metal oxide may be broken. Since the reaction rate is high and F is reacted with an in-plane metal having a crystal structure to obtain a covalently bonded fluorinated metal (MF) _n , the fluorine substitution temperature is more preferably from 0 to 150 ° C., and from 100 to 150 ° C is particularly preferred.

  As described above, the fact that a metal oxide in which part of O is substituted with F by fluorine substitution can be confirmed by identifying the crystal structure of the metal oxide substituted with fluorine by XRD analysis. In other words, the fluorine-substituted metal oxide can be confirmed by identifying the metal oxide, the simple substance of the metal fluoride, and the peak attributed to the metal fluoride other than the metal fluoride in the XRD spectrum.

<Lithium ion secondary battery>
A lithium ion secondary battery contains a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte.

(Positive electrode)
The positive electrode has a positive electrode active material layer containing the present positive electrode active material and a positive electrode current collector. The positive electrode active material layer includes a conductive material and a binder in addition to the positive electrode active material, and may include other components such as a thickener as necessary.

Examples of the conductive material include carbon black such as acetylene black, graphite, and ketjen black. A conductive material may be used individually by 1 type, and may use 2 or more types together.
Examples of the binder include fluorine-based resins (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyolefins (polyethylene, polypropylene, etc.), and polymers having unsaturated bonds (styrene-butadiene rubber, isoprene rubber, butadiene rubber, etc.), Examples include acrylic acid polymers (acrylic acid copolymers, methacrylic acid copolymers, etc.). A binder may be used individually by 1 type and may use 2 or more types together.
Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and polyvinylpyrrolidone. A thickener may be used individually by 1 type and may use 2 or more types together.
Examples of the positive electrode current collector include an aluminum foil and a stainless steel foil.

(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer.
Examples of the negative electrode current collector include metal foils such as nickel foil and copper foil.
The negative electrode active material is a material that can occlude and release lithium or lithium.
The negative electrode active material is a material that can occlude and release lithium or lithium. Examples of the negative electrode active material include lithium alloys, lithium compounds, carbon materials, periodic table 14, group 15, oxides such as ruthenium, molybdenum, tungsten, titanium, silicon carbide compounds, silicon oxide compounds, titanium sulfide, boron carbide compounds. Etc. can be used.

  Carbon materials used for the negative electrode active material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon And carbon blacks. Examples of the cokes include pitch coke, needle coke, and petroleum coke. Examples of the fired organic polymer compound include those obtained by firing and carbonizing a phenol resin, a furan resin, or the like at an appropriate temperature.

  The negative electrode for a lithium ion secondary battery is obtained, for example, by preparing a slurry by mixing a negative electrode active material with an organic solvent, applying the prepared slurry to a negative electrode current collector, drying, and pressing.

(Separator)
Examples of the separator include a film made of a microporous polyolefin film typified by polyethylene and polypropylene, polyvinylidene fluoride, and a hexafluoropropylene copolymer.

(Nonaqueous electrolyte)
Examples of the non-aqueous electrolyte include a non-aqueous electrolyte, an inorganic solid electrolyte, and a solid or gel polymer electrolyte in which an electrolyte salt is mixed or dissolved.
Examples of the non-aqueous electrolyte include those prepared by appropriately combining an organic solvent and an electrolyte salt.

  As the organic solvent of the non-aqueous electrolyte, known ones can be employed, for example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, Examples include diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetic acid ester, butyric acid ester, and propionic acid ester. Among these, from the viewpoint of voltage stability, the organic solvent is preferably a cyclic carbonate such as propylene carbonate, or a chain carbonate such as dimethyl carbonate or diethyl carbonate. An organic solvent may be used individually by 1 type, and may use 2 or more types together.

Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide.
Examples of the solid polymer electrolyte include an electrolyte containing an electrolyte salt and a polymer compound that dissolves the electrolyte salt. Examples of the polymer compound that dissolves the electrolyte salt include ether polymer compounds (poly (ethylene oxide), cross-linked poly (ethylene oxide), etc.), poly (methacrylate) ester polymer compounds, and acrylate polymer compounds. Etc.

  The matrix of the gel-like polymer electrolyte may be any matrix that absorbs the non-aqueous electrolyte and gels, and various polymer compounds can be used. Examples of the polymer compound include a fluorine-based polymer compound (poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), etc.), polyacrylonitrile, a copolymer of polyacrylonitrile, an ether-based polymer, and the like. Examples thereof include molecular compounds (polyethylene oxide, polyethylene oxide copolymers, and crosslinked products of the copolymers, and the like). Examples of the monomer copolymerized with polyethylene oxide include methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate.

  As the matrix of the gel electrolyte, a fluorine-based polymer compound is particularly preferable among the polymer compounds from the viewpoint of stability against redox reaction.

As the electrolyte salt, known ones used in lithium ion secondary batteries can be used, and examples thereof include LiClO ₄ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, and the like.

  The lithium ion secondary battery includes a negative electrode, a separator, an electrolyte, and a positive electrode of the present invention, and can be manufactured by a known method. The lithium ion secondary battery has a positive electrode active material having a structure in which a halogen-substituted metal oxide is supported on the surface of a lithium-containing composite oxide and at least a part of the surface is supported by the halogen-substituted metal oxide. Yes. Therefore, the cycle characteristics are excellent, such as a reduction in discharge capacity when the charge / discharge cycle is repeated and a high capacity retention rate. In addition, compared to a lithium ion secondary battery having a positive electrode active material in which a metal oxide is coated on the surface of a lithium-containing composite oxide, oxidation resistance under high voltage charging is high, so under high voltage charging. Excellent cycle characteristics. Furthermore, the rate characteristics are better than those of a lithium ion secondary battery having a positive electrode active material in which a fluoride is coated on the surface of a lithium-containing composite oxide.

  A method of supporting both the metal oxide and the metal fluoride on the surface of the lithium-containing composite oxide is also conceivable. However, it is difficult to uniformly support particles of both of these compounds on the surface of the lithium-containing composite oxide. For this reason, it is estimated that it is difficult to improve the rate characteristic and the cycle characteristic in a well-balanced manner.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to an Example. Examples 1 to 6 are examples of the present invention, and examples 7 to 11 are comparative examples.

<Manufacture of positive electrode active material>
(Example 1)
Particulate TiO ₂ (manufactured by C-I Kasei Co., Ltd., average particle size (2) 36 nm, specific surface area 45 m ² / g) was used as a metal oxide that is a raw material for the halogen-substituted metal oxide. In addition, LiCoO ₂ (manufactured by AGC Seimi Chemical Co., Ltd., average particle size (1) 12 μm) was used as the lithium-containing composite oxide.

The particulate TiO ₂ was packed in a container and introduced into a highly airtight reaction vessel. After evacuating the air in the reaction vessel, F ₂ gas (mixed gas of F ₂ / N ₂ = 80/20 in volume ratio) was introduced at room temperature (20 ° C.) until the pressure reached 0.005 MPaG, This state was maintained for 4 hours. In this way, fluorine substitution of particulate TiO ₂ was performed.

Next, 2 g of the lithium-containing composite oxide and 0.05 g of fluorine-substituted particulate TiO ₂ (hereinafter referred to as “fluorine-substituted TiO ₂ ”) were weighed into a 125 cc container, and a rotating / revolving mixer ( Using a Thinky Co., Ltd. apparatus name: Niwataro Awatori ARE-310), the mixture was rotated and mixed at 2,000 rpm for 2 minutes to obtain a positive electrode active material (1). Table 1 shows the production conditions of the positive electrode active material (1).

(Example 2)
As shown in Table 1, a positive electrode active material (2) was obtained in the same manner as in Example 1 except that the fluorination substitution temperature was changed to 140 ° C.

(Example 3)
As shown in Table 1, particulate CeO ₂ (manufactured by C-I Kasei Co., Ltd., average primary particle size (2) 14 nm, specific surface area 60 m ² / g) is used as the metal oxide, and the fluorine substitution temperature is 140. A positive electrode active material (3) was obtained in the same manner as in Example 1 except that the temperature was changed to ° C.

(Example 4)
As shown in Table 1, particulate ZnO (manufactured by C.I. Kasei Co., Ltd., average particle size (2) 34 nm, specific surface area 30 m ² / g) was used as the metal oxide, and the fluorine substitution temperature was changed to 140 ° C. A positive electrode active material (4) was obtained in the same manner as in Example 1 except that.

(Example 5)
As shown in Table 1, a lithium-containing composite oxide represented by the formula: LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (manufactured by AGC Seimi Chemical Co., Ltd., average particle diameter) (1) A positive electrode active material (5) was obtained in the same manner as in Example 2 except that 6 μm) was used.

(Example 6)
As shown in Table 1, a lithium-containing composite oxide represented by the formula: LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (manufactured by AGC Seimi Chemical Co., Ltd., average particle diameter) (1) A positive electrode active material (6) was obtained in the same manner as in Example 3 except that 6 μm) was used.

(Example 7)
As shown in Table 1, LiCoO ₂ (manufactured by AGC Seimi Chemical Co., Ltd., average particle size (1) 12 μm) was used as it was as the positive electrode active material (7) without performing fluorine substitution.

(Example 8)
As shown in Table 1, TiO ₂ (manufactured by C-I Kasei Co., Ltd., average particle size (2) 36 nm, specific surface area 45 m ² / g) was used as the metal oxide, and no fluorine substitution was performed. Other than that was carried out similarly to Example 1, and obtained the positive electrode active material (8).

(Example 9)
As shown in Table 1, CeO ₂ (manufactured by C-I Kasei Co., Ltd., average particle size (2) 14 nm, specific surface area 60 m ² / g) was used as the metal oxide, and fluorine substitution was not performed. Other than that was carried out similarly to Example 3, and obtained the positive electrode active material (9).

(Example 10)
As shown in Table 1, CeF ₃ which is a fluoride was used in place of particulate CeO ₂ substituted with fluorine. Other than that was carried out similarly to Example 1, and obtained the positive electrode material active material (10).

(Example 11)
As shown in Table 1, the lithium-containing composite oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (AGC Seimi Chemical Co., Ltd. average particle size (1) 6 μm) is subjected to fluorine substitution. It used as a positive electrode active material (11) as it was.

<Observation with SEM>
Among the positive electrode active materials (1) to (11) thus obtained, the surface of each of the positive electrode active material (2), the positive electrode active material (3), and the positive electrode active material (7) was subjected to SEM (manufactured by HITACHI) Name: S-4300).
1 is a SEM photograph of the positive electrode active material (2), FIGS. 2 and 3 are positive electrode active materials (3), and FIG. 4 is a SEM photograph of the positive electrode active material (7). FIG. 3A is an SEM photograph of the surface and cross section of the positive electrode active material (3), and FIG. 3B is an enlarged SEM photograph of part of FIG.

From the SEM photograph of FIG. 1, in the positive electrode active material (2), irregularities are observed on the surface of the secondary particles of LiCoO _{2 and} no grain boundary is confirmed.
From the SEM photograph of FIG. 2, in the positive electrode active material (3), irregularities on the particle surface are observed in the secondary particles of LiCoO ₂ , and grain boundaries are confirmed, but are clearer than the grain boundaries seen in FIG. Not. From the SEM photographs of FIGS. 3A and 3B, it can be seen that the compound is supported only on the surface of the LiCoO ₂ particles when the section of LiCoO ₂ of the positive electrode active material (3) is seen.
From the SEM photograph of FIG. 4, in the positive electrode active material (7), no irregularities are observed on the surface of the secondary particles of LiCoO ₂ and grain boundaries are confirmed.

<Measurement of XRD spectrum>
The XRD spectrum of the halogen-substituted metal oxide used in Example 3 was measured with an X-ray diffractometer (manufactured by RIGAKU, device name: SmartLab), and the components were identified by analyzing the crystal structure. The halogen-substituted metal oxide used in Example 3 is particulate CeO ₂ substituted with fluorine (hereinafter referred to as fluorine-substituted CeO ₂ ). The spectrum obtained as a result of the XRD measurement is shown in FIG. In FIG. 5, the XRD spectrum of CeO ₂ is shown for comparison.

As described above, FIG. 5 shows a peak (2θ = 28 to 29 °) corresponding to the (111) plane of the metal oxide (CeO ₂ ) and a peak (2θ = 47 to 48 °) corresponding to the (220) plane. Is seen. Further, a peak (2θ = 27 to 28 °) corresponding to the (111) plane of the metal halide (CeF ₃ ) and a peak (2θ = 45 to 46 °) corresponding to the (113) plane are observed. Further, a peak (2θ = 24 to 25 °) corresponding to the (220) plane of the metal halide (CeF ₄ ) and a peak (2θ = 21 to 22 °) corresponding to the (021) plane are observed.
From the solid line spectrum of FIG. 5, the introduction of F into the crystal structure is sufficiently carried out while maintaining the crystal structure of CeO ₂ , and as a result, a part of O in CeO ₂ is replaced with F to form a metal fluoride. You can see that

<Measurement of fluorine content and specific surface area>
The fluorine content of the fluorine-substituted TiO2 used in Examples 1 and 2 and the fluorine-substituted CeO2 used in Example 3 were measured. Further, the specific surface area was measured by the BET method using a specific surface area measuring device (manufactured by Mountec Co., Ltd., device name: HM model-1208). The results are shown in Table 2.

The fluorine content in the fluorine-substituted metal oxide was measured by the following method. The measurement sample was burned with an automatic combustion apparatus (manufactured by Mitsubishi Chemical Analytech Co., Ltd., apparatus name: AQF-100), and then a combustion gas was collected using a H ₂ O ₂ aqueous solution in which NaOH was dissolved as a collection liquid. And this collection liquid was introduce | transduced into the ion chromatography (The product made by Dionex, apparatus name: DX120, column: AS12A), and the amount of fluorine was quantified. Polytetrafluoroethylene and phosphorus (P) were used as standard samples for correcting the F recovery rate by the internal standard method.
Note that the maximum amount of F that can be substituted for the metal oxide is a value obtained by calculating the molar amount of the metal from the mass of the metal oxide and multiplying the molar amount by the stable maximum valence of the metal and the atomic weight of F. .

  Next, using the positive electrode active materials (1) to (11), a positive electrode was produced as follows. Furthermore, the lithium ion secondary battery was manufactured using the produced positive electrode, respectively.

<Production of positive electrode>
2.05 g of the positive electrode active materials (1) to (11), 0.25 g of acetylene black (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), and 2.07 g of polyvinylidene fluoride (PVDF) are N- A solution dissolved in methylpyrrolidone (NMP) and 4.02 g of NMP are mixed using an autorotation / revolution mixer (Thinky Co., Ltd., apparatus name: Nertaro Awatori ARE-310), each containing a positive electrode active material A slurry was prepared. Next, this slurry was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 20 μm to produce a positive electrode sheet. This positive electrode sheet was rolled twice on a roll press having a gap of 40 μm, punched into a circle having a diameter of 18 mm, and then vacuum-dried at 180 ° C. to obtain a positive electrode.

<Manufacture of lithium ion secondary batteries>
In an Ar glove box, a stainless steel simple sealed cell type battery evaluation cell, the positive electrode obtained above, a separator (manufactured by Celgard, trade name: # 2500), and a negative electrode including a metal lithium foil, The layers were laminated in this order. Next, an electrolyte solution in which LiPF ₆ was dissolved in a mixed solvent of diethylene carbonate and ethylene carbonate (volume ratio 1: 1) so that the concentration was 1 mol / dm ³ was put into a lithium ion secondary battery. . As the negative electrode current collector, a stainless steel plate having an average thickness of 1 mm was used, and a metal lithium foil having an average thickness of 300 μm was formed on the negative electrode current collector to form a negative electrode. The average thickness of the separator was 50 μm (25 μm × 2 sheets).

<Battery evaluation>
The obtained lithium ion secondary battery was charged to 4.3 V at a load current of 37.5 mA per 1 g of the positive electrode active material in the constant current / constant voltage mode, and then 37. The battery was discharged to 2.75 V with a load current of 5 mA (0.25 C).
Next, in examining the rate characteristics, the above charging conditions are fixed, and in the constant current mode, 225 mA (1.5 C), 450 mA (3 C), and 900 mA (9 C) are performed in order of 2.75 V per 1 g of the positive electrode active material. Until discharged. Then, the discharge capacity and the average discharge voltage at 900 mA load current per 1 g of the positive electrode active material were measured. These measurement results are shown in Tables 3 and 4.
Table 3 shows the measurement results for the batteries having positive electrode active materials (1) to (4) and positive electrode active materials (7) to (10) using LiCoO ₂ as the lithium-containing composite oxide. Further, the cathode active material using _LiNi 0.5 _Co 0.2 _Mn 0.3 _{O 2} as a lithium-containing composite oxide (5), the measurement results for the cell having a (6) and a positive electrode active material (11) Table 4 shows.

Next, after charging to 4.5 V with a load current of 150 mA per 1 g of the positive electrode active material in the constant current mode, the battery is repeatedly charged and discharged 50 times to 2.75 V with a load current of 150 mA per 1 g of the positive electrode active material in the constant current mode. (Cycle) went. And the capacity | capacitance maintenance factor and voltage maintenance factor after 50 cycles were calculated | required, respectively.
The capacity retention rate (%) after 50 cycles is the ratio (%) of the discharge capacity in the 50th 4.5V charge to the discharge capacity in the first 4.5V charge. The voltage maintenance rate (%) after 50 cycles is the ratio (%) of the average discharge voltage in the 50th 4.5V charge to the average discharge voltage in the first 4.5V charge.

From Table 3 and Table 4, it can be seen that:
Lithium ion secondary batteries having positive electrode active materials (1) to (4) having a halogen-substituted metal oxide supported on the surface of LiCoO ₂ are lithium ion secondary batteries having positive electrode active materials (7) to (9). Compared to the battery, the capacity retention rate after 50 cycles is high. The positive electrode active material (7) is LiCoO ₂ itself, and the positive electrode active materials (8) and (9) are positive electrode active materials in which a metal oxide not containing a halogen element is supported on the surface of LiCoO ₂ . That is, the lithium ion secondary battery having the positive electrode active material of the present invention is excellent in cycle characteristics.

A lithium ion secondary battery having positive electrode active materials (5) and (6) in which a halogen-substituted metal oxide is supported on the surface of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ is LiNi _0. compared to the lithium ion secondary battery having a _.5 Co _0.2 Mn _0.3 O ₂ positive active material is itself (11), a high capacity maintenance rate after 50 cycles. That is, the lithium ion secondary battery having the positive electrode active material of the present invention is excellent in cycle characteristics.

Further, the lithium ion secondary battery having a positive electrode active material (3) a fluorine-substituted CeO ₂ is supported on the surface of LiCoO ₂ is the positive electrode active material CeF ₃ on the surface of LiCoO ₂ is supported (10) Compared with the lithium ion secondary battery which has, the discharge capacity and average discharge voltage in 900 mA load current are high. That is, the lithium ion secondary battery having the positive electrode active material of the present invention is excellent in rate characteristics.

Furthermore, when comparing the lithium ion secondary battery having the positive electrode active material (1) and the positive electrode active material (2) on which the fluorine-substituted TiO ₂ is supported on the surface of LiCoO _2, the positive electrode active material (2) is obtained. The battery has a higher capacity retention rate than the battery having the positive electrode active material (1). Therefore, a lithium ion secondary battery having a positive electrode active material carrying a fluorine-substituted metal oxide having a high fluorine substitution temperature relative to the metal oxide and a high fluorine content in the metal oxide is The capacity retention rate in the charge / discharge cycle is high, that is, the cycle characteristics are improved.

  According to the positive electrode active material of the present invention, it is possible to realize a lithium ion secondary battery that is excellent in rate characteristics, has a high capacity retention rate under high voltage charge / discharge, and is excellent in cycle characteristics.

Claims (15)

Lithium containing one or more transition metal elements selected from Ni, Co and Mn and Li, and the content of Li is 0.95 times or more in molar ratio with respect to the total content of transition metal elements And a metal oxide supported on at least a part of the surface of the lithium-containing composite oxide, wherein the metal oxide is a lithium ion bismuth in which a part of O is substituted with a halogen element. A positive electrode active material for a secondary battery,
In the metal oxide, the ratio of the halogen content (unit: mass) measured by ion chromatography in the metal oxide to the maximum amount of halogen element (unit: mass) that can be substituted is 0.05 to 90%,
In the XRD spectrum, the metal oxide is attributed to a peak attributed to a simple substance of the metal oxide before halogen substitution, to a simple substance of the metal halide (first halide) constituting the metal oxide. And a peak attributed to a second halide other than the first halide, and the metal oxide is contained in a mass ratio with respect to the lithium-containing composite oxide. The positive electrode active material for lithium ion secondary batteries characterized by containing 0.1 to 5% by weight.   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the halogen element is F. The metal oxide includes a transition metal oxide, a rare earth element oxide, a carbon group element oxide, a boron group element oxide, an alkaline earth element oxide, an alkali element oxide, and a composite metal oxide. is at least one selected from the group consisting of object, the positive electrode active material for a lithium ion secondary battery according to claim 1 or 2. The metal oxide is an oxide containing one or more metal elements selected from the group consisting of Ti, Ce, La, Y, V, Nb, Ta, W, Zr, Zn, Si, Al, Mg, Li and K. The positive electrode active material for lithium ion secondary batteries according to any one of claims 1 to 3, wherein the positive electrode active material is a product. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4 , wherein the metal oxide is in the form of particles and has an average particle diameter of 1 to 100 nm. The metal oxide has a specific surface area of 1 to 100 m 2 / ^g, the positive electrode active material for a lithium ion secondary battery according to any one of claims 1-5. The said lithium containing complex oxide is a positive electrode active material for lithium ion secondary batteries of any one of Claims 1-6 which is a compound represented by following formula (1).
_{Li a (Ni x Mn y Co} z) Me b O 2 ............ (1)
(In the formula (1), Me is a transition metal element other than Ni, Mn and Co, 0.95 ≦ a ≦ 1.1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦. 1, 0 ≦ b ≦ 0.3, 0.90 ≦ x + y + z + b ≦ 1.05) 1 or more types of transition metal elements chosen from Ni, Co, and Mn, and Li are contained, The content of said Li is 0.95 times or more by molar ratio with respect to the sum total of content of a transition metal element A dry compound in which a lithium-containing composite oxide is mixed with a metal oxide in which a part of O is substituted with a halogen element, and the metal oxide is supported on at least a part of the surface of the lithium-containing composite oxide. The manufacturing method of the positive electrode active material for lithium ion secondary batteries characterized by having a mixing process. The manufacturing method of the positive electrode active material for lithium ion secondary batteries of Claim 8 which has a substitution process which substitutes a part of O of metal oxide with a halogen element, and obtains a halogen substitution metal oxide. 10. The positive electrode active material for a lithium ion secondary battery according to claim 9 , wherein in the replacing step, a halogen-containing gas and a metal oxide are brought into contact with each other to replace a portion of the metal oxide with a halogen element. Manufacturing method. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 10 , wherein the halogen element is F. Gas containing halogen _{element, HF,} F _{2, ClF} is _{3, IF 5, BF 3,} NF 3, PF 5, SiF 4, and a gas containing one or more selected from SF _6, to claim 10 The manufacturing method of the positive electrode active material for lithium ion secondary batteries of description. In the dry mixing step, the mixing ratio of the portion of O metal oxide has been replaced with a halogen element to the lithium-containing composite oxide, from 0.01 to 10 percent by weight ratio, claim 8 12. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of 12 above. Conductive material, binder, and claims 1-7 positive electrode active positive electrode for a lithium ion secondary battery characterized by having a positive electrode active material layer material containing on the positive electrode current collector according to any one of. A lithium ion secondary battery comprising a negative electrode, a separator, a nonaqueous electrolyte, and the positive electrode according to claim 14 .