JP2016110799A - Cathode active material, cathode, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material capable of realizing a nonaqueous electrolyte secondary battery excellent both in cycle characteristics and high-speed charge-discharge characteristics even when used in conditions of more severe temperatures and charge/discharge current than that of a conventional ones.SOLUTION: A cathode active material for a nonaqueous electrolyte secondary battery is obtained by passing through at least of steps a. and b., the step a is for mixing a cathode active material precursor and an oxo acid, and the step b is for burning a mixture obtained in the step a (in the step a, a superficial area R(m) of the cathode active material precursor, a density A(g/cm) in the oxo acid, and the weight x(g) of the oxo acid fill the following mathematical formula: 1≥10x/AR>0).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material, a positive electrode including the positive electrode active material, and a nonaqueous electrolyte secondary battery including the positive electrode.

With the recent development of electronic technology and increasing interest in environmental technology, various electrochemical devices are used. In particular, there are many demands for energy saving, and the expectation for an electricity storage device that can contribute to this is increasing.
Lithium ion secondary batteries, which are representative examples of power storage devices and also representative examples of non-aqueous electrolyte secondary batteries, have been used mainly as rechargeable batteries for portable devices. However, in recent years, batteries for hybrid vehicles and electric vehicles have been used. The use as is expected.

  However, when a lithium ion secondary battery is used in an automotive application, the operating temperature and charge / discharge conditions are severer than when used for a conventional portable device. Therefore, in order to function well as a secondary battery even under such severe conditions, the lithium ion secondary battery is required to further improve battery characteristics such as cycle characteristics and high-speed charge / discharge characteristics.

With the aim of improving these characteristics, techniques described in Patent Documents 1 to 3 have been proposed. In an example of Patent Document 1, it is described that AlPO ₄ is coated on a positive electrode active material. Patent Document 2 describes that at least one of sulfur (S), phosphorus (P), and fluorine (F) is aggregated on the surface of the positive electrode active material.

  Patent Document 3 describes a method for producing a positive electrode active material in which an aqueous medium is removed from a mixture obtained by mixing a lithium-containing composite oxide powder and an aqueous solution containing boron and / or phosphorus, and further fired. Yes.

JP 2003-7299 A JP 2011-82133 A International Publication No. 2006/085588

  However, none of the conventional techniques including those described in Patent Documents 1 to 3 satisfy both the cycle characteristics and the high-speed charge / discharge characteristics.

For example, in Patent Document 1, since the conductive by the use of poor AlPO ₄ in the lithium ion conductivity is a problem such as a decrease, it is insufficient as an effect. This technique is intended to improve durability by dissolving a part of a metal element such as aluminum contained in a coating material in a positive electrode active material. Although the effect can be seen, there is a problem that if the amount of solid solution is small, the cycle characteristics under high temperature or high charge voltage cannot be improved sufficiently, and if the amount of solid solution is large, the charge / discharge capacity decreases. Is produced.

  Patent Document 2 is not preferable because the compound added causes decomposition of the electrolyte and gas generation, or the compound covers the electrode surface and impairs conductivity. It is insufficient to satisfy the durability in the case where the temperature and charge / discharge conditions are severer than those conventionally used, such as for automobiles.

  Furthermore, in patent document 3, although generation | occurrence | production of gas is suppressed, the improvement of cycling characteristics and a high-speed charge / discharge characteristic is inadequate.

  The present invention has been made in view of the above circumstances. A positive electrode active material capable of realizing a non-aqueous electrolyte secondary battery excellent in both cycle characteristics and high-speed charge / discharge characteristics even when used under conditions and charge / discharge conditions that are severer than before, such as automotive applications, It aims at providing the positive electrode containing this positive electrode active material, and a nonaqueous electrolyte secondary battery provided with this positive electrode.

The present inventors have conducted intensive research to solve the above problems. as a result,
When the positive electrode active material is prepared, the above problem is solved when the positive electrode active material precursor and a specific amount (volume) of oxo acid with respect to the surface area R of the precursor are mixed and fired. As a result, the present invention has been completed.

That is, the present invention is as follows.
[1] At least the following steps a. And b. ;
a. Mixing a positive electrode active material precursor and an oxo acid; and b. Step a. A step of firing the mixture obtained in step {wherein the step a. The surface area R (m ² ) of the positive electrode active material precursor, the density A (g / cm ³ ) of the oxo acid, and the mass x (g) of the oxo acid are expressed by the following formula:
1 ≧ 10x / AR> 0
Satisfy the relationship. }
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein
[2] The positive electrode active material according to [1], wherein the positive electrode active material precursor is a compound containing at least one transition metal atom.

[3] The oxo acid includes an oxo acid containing one or more elements selected from the group consisting of boron (B), phosphorus (P), and sulfur (S) [1] or [2] The positive electrode active material described in 1.
[4] The positive electrode active material according to any one of [1] to [3], wherein the oxo acid includes phosphoric acid.
[5] A positive electrode comprising the positive electrode active material according to any one of [1] to [4].
[6] A nonaqueous electrolyte secondary battery comprising at least the positive electrode according to [5], a negative electrode, a nonaqueous electrolyte, and an exterior body.

  According to the present invention, a non-aqueous electrolyte secondary battery that is excellent in both cycle characteristics and high-speed charge / discharge characteristics even when used under severer temperature and charge / discharge conditions than in the past, such as automotive applications, is realized. A possible positive electrode active material, a positive electrode including the positive electrode active material, and a non-aqueous electrolyte secondary battery including the positive electrode can be provided.

It is sectional drawing which shows roughly an example of the nonaqueous electrolyte secondary battery in this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be implemented with appropriate modifications within the scope of the gist.

[Positive electrode active material]
The positive electrode active material of this embodiment is
At least the following steps a. And b. ;
a. Mixing a positive electrode active material precursor and an oxo acid; and b. Step a. A step of firing the mixture obtained in
{However, the step a. The surface area R (m ² ) of the positive electrode active material precursor, the density A (g / cm ³ ) of the oxo acid, and the mass x (g) of the oxo acid are expressed by the following formula:
1 ≧ 10x / AR> 0
Satisfy the relationship. }
It is obtained through
In this embodiment, the predetermined positive electrode active material is
Li,
It is preferable that it contains at least one transition metal atom. The transition metal atom preferably contains one or more selected from the group consisting of Ni, Mn, and Co, and more preferably contains Mn.

[Positive electrode active material precursor]
The positive electrode active material precursor in the present embodiment is a compound containing at least one transition metal atom, and is mixed with a predetermined amount of oxo acid and then baked to become a predetermined positive electrode active material in the present embodiment. Refers to ingredients. Examples thereof include oxides, carbonates, hydroxides, nitrates, and chlorides containing at least one transition metal atom. The typical element metal (for example, Li) may or may not be included.

  The precursor for producing the positive electrode active material in the present embodiment may have all of the metal atoms that the positive electrode active material has, or a compound that has only some of these metal atoms. There may be. In the latter case, a positive electrode active material having a desired metal atom can be obtained by combining the precursor and the oxo acid together with a compound containing a remaining metal atom and mixing the mixture, and firing the mixture.

As the positive electrode active material precursor, preferably,
(1) Li and at least one transition metal atom;
And (2) one selected from the group consisting of compounds selected from hydroxides, oxides, carbonates, nitrates, and chlorides containing at least one or more transition metal atoms That's it.
In the case of the above (2), it is preferable to combine and mix one or more selected from the group consisting of Li carbonate, nitrate, and chloride together with these precursors and oxo acid for firing. In this case, when determining the surface area (R) of the positive electrode active material precursor for determining the amount of oxo acid to be used, the contribution of the Li compound not containing the transition metal is not included.

  It does not specifically limit as said precursor, A well-known thing can be used. For example, you may use what was synthesize | combined by the following method.

  The carbonate is prepared by dissolving at least one selected from the group consisting of a desired metal hydroxide, carbonate, nitrate, sulfate, hydrochloride, chloride, etc. in an appropriate solvent (for example, water). It is also possible to obtain an aqueous solution by collecting and drying the precipitate produced by dropping the aqueous solution into an aqueous solution containing carbonate ions separately adjusted to alkali. The drying temperature in this case is preferably 250 ° C. or less, more preferably 100 to 200 ° C., and further preferably 120 to 180 ° C. The drying time is preferably 1 hour to 10 hours, more preferably 3 hours to 8 hours.

The oxide can be obtained by mixing and firing at least one selected from the group consisting of a desired metal hydroxide, carbonate, nitrate, sulfate, hydrochloride, chloride, and the like. . As a mixing method, solids may be mixed dynamically or may be mixed by dissolving in a soluble solvent and removing the solvent. The firing temperature is preferably 300 ° C. or higher, more preferably 300 to 1,200 ° C., and still more preferably 400 to 1,000 ° C. The firing time is preferably 1 hour to 10 hours, more preferably 3 hours to 8 hours.
The ambient atmosphere during drying and firing is sufficient in the air.

[Oxo acid]
As the oxo acid used in the present embodiment, an inorganic compound or an organic compound can be used and is not particularly limited. Specific examples thereof include, for example, H ₃ PO ₄ , H ₃ BO ₃ , H ₂ CO ₃ , H ₂ SiO ₃ , HAsO, H ₃ AsO ₃ , H ₃ AsO ₄ , HBrO, HCN, HCNO, HIO, HClO, _{H 2 MoO 4, HN 3,} H 2 N 2 O 2, HSCN, HNO 2, H 3 PO 3, H 4 P 2 O 7, H 5 P 3 O 10, H 2 S, H 2 SO 3, H 2 SO ₄ , H ₂ Se, H ₂ SeO ₃ , H ₂ SiO ₂ (OH) ₂ , H ₂ TeO ₃ , H ₂ TeO ₄ , H ₃ VO ₄ , H ₂ WO ₄ , HAgO, H ₃ AlO ₃ , HCrO ₄ , H ₂ GeO ₃ , HSbO ₂ , H ₃ AuO ₃ , H ₃ GaO _{3 and the} like, and one or more selected from the group consisting of these are preferable. The oxo acid used in the present embodiment preferably contains an oxo acid containing at least one element of boron (B), phosphorus (P), or sulfur (S), more preferably, One or more selected from the group consisting of H ₃ PO ₄ , H ₃ BO ₃ , H ₂ B ₄ O ₇ , and H ₂ SO ₄ . It is more preferable to use an oxo acid containing phosphorus (P), and it is particularly preferable to use H ₃ PO ₄ . By using such an oxo acid, even when used under severe temperature and charge / discharge current conditions, it tends to be a positive electrode active material that is more excellent in both cycle characteristics and high-speed charge / discharge characteristics.

As the density (A) of the oxo acid, in principle, the density in the solid state is used. In the case of an oxo acid in which a solid exists only under specific conditions, for example, at a high pressure or at a very low temperature, the density of lithium oxo acid in the solid state can be substituted. For example, as the density of H ₂ SO _4, the density of Li ₂ SO ₄ can be used.

  The acid dissociation constant (pKa) of oxo acid is preferably 12.01 or less, more preferably 7.65 or less, and still more preferably 2.12 or less. By treating the positive electrode active material precursor with an oxo acid having a pKa of 12.01 or less, a small amount of transition metal constituting the positive electrode active material precursor is eluted, and the elements constituting the positive electrode active material precursor and the element An intermediate may be formed with an oxo acid. Occurrence of such a phenomenon stabilizes the surface of the obtained positive electrode active material and tends to improve cycle characteristics and the like.

The oxo acid preferably has a melting point in the temperature range below the firing temperature (described later). Since the oxo acid has a melting point in the temperature range below the firing temperature, a uniform reaction proceeds with the positive electrode active material precursor, so that both cycle characteristics and high-speed charge / discharge characteristics tend to be more excellent.
The melting point of oxo acid is preferably 1,000 ° C. or lower, and preferably 300 to 900 ° C.
The melting point of the oxo acid can be detected by a thermal analysis means such as thermogravimetric-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC).

[Method for producing positive electrode active material]
The method for producing a positive electrode active material according to this embodiment is as follows:
a. A step of mixing a positive electrode active material precursor and an oxo acid (mixing step); and b. Step a. The step of firing the mixture obtained in step (firing step)
It is necessary to go through.

(Mixing process)
The mixing step is a step of mixing the positive electrode active material precursor and the oxo acid.
Although it does not specifically limit as a mixing method, For example,
A method in which a positive electrode active material precursor is placed in an aqueous solution or an organic solution containing an oxo acid, and the mixture is stirred and mixed (method 1);
A method of dynamically mixing a positive electrode active material precursor and a solid oxo acid (method 2),
Method of contacting gaseous oxoacid with positive electrode active material precursor by means such as vapor deposition or sputtering (Method 3)
Etc.

  The mixing method in the methods (1) and (2) is not particularly limited, but it is preferable to stir and mix at a strength that does not crush the secondary particles of the positive electrode active material precursor. When the oxo acid is mixed in a solid state, it is preferable to mix the oxo acid with a strength that does not pulverize the secondary particles of the oxo acid and a relatively large force. The apparatus that can be used for stirring and mixing is not particularly limited, and examples thereof include a mixer, a planetary ball mill, a jet mill, and a magnetic stirrer.

  The average particle diameter of the oxo acid used in the case of mixing the oxo acid in the solid state (in the case of the method 2) is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 0.1 to 50 μm. It is. When the average particle size of the solid oxo acid is 0.1 μm or more, the oxo acid and the positive electrode active material precursor tend to be contacted more uniformly. Moreover, when the average particle size of the solid oxo acid is 100 μm or less, battery characteristics such as discharge characteristics tend to be maintained better. The average particle diameter of the solid oxo acid can be measured as a median diameter (d50) in which the large particles and the small particles are equivalent by using a laser diffraction particle size distribution measuring apparatus.

  The mixing of the oxo acid and the positive electrode active material precursor is effective even if it is non-uniform, but it is more preferable that the two are uniformly mixed or contacted before being subjected to the firing step.

  In the case of using an aqueous solution or an organic solution containing oxo acid (in the case of the above method 1), it is preferable to pass through a drying step of removing the solvent from the mixture after the mixing step before firing. The drying method is not particularly limited, but from the viewpoint of uniformly treating the positive electrode active material precursor, it is preferable to gradually remove the solvent by heating or the like after the completion of stirring. Alternatively, the positive electrode active material precursor may be immersed in an aqueous solution or organic solution containing oxo acid, filtered to remove the solvent, and then dried.

The amount of the oxo acid used for the production of the positive electrode active material is such that the surface area R (m ² ) of the positive electrode active material precursor, the density A (g / cm ³ ) of the oxo acid, And the mass of oxo acid x (g) is:
1 ≧ 10x / AR> 0
It is an amount that satisfies the relationship. Furthermore, these values are represented by the following formula:
0.8 ≧ 10x / AR ≧ 0.00001
It is preferable to satisfy the relationship of
0.1 ≧ 10x / AR ≧ 0.0001
It is preferable to satisfy the relationship. Here, when 10x / AR is 0, and when 10x / AR exceeds 1, the cycle characteristics tend to deteriorate. Moreover, when 10x / AR exceeds 1, high-speed charge / discharge characteristics tend to deteriorate. Furthermore, when 10x / AR takes a value in the range of 0.1 to 0.0001, the surface of the positive electrode active material is stabilized and finally obtained by suppressing aggregation of the positive electrode active materials. The resistance as an electrode is reduced, and both cycle characteristics and high-speed charge / discharge characteristics tend to be improved.

Here, the above mathematical formula is a relational expression that defines the ratio of the volume (unit: cm ³ ) of the oxo acid used for the production of the positive electrode active material to the precursor surface area (unit: m ² ). Accordingly, the surface area R of the precursor is calculated in square meters, and the density of the oxo acid is calculated in grams per cubic centimeter.

(Baking process)
After mixing an oxo acid, a positive electrode active material precursor, and optionally a Li compound, a positive electrode active material is obtained through a firing step. Through this firing step, the oxo acid and the positive electrode active material precursor react uniformly, and the cycle characteristics and the like tend to be further improved.

  The firing temperature is preferably 400 ° C. or higher and 1,000 ° C. or lower, more preferably 600 ° C. or higher and 900 ° C. or lower, and still more preferably 700 ° C. or higher and 900 ° C. or lower. When the firing temperature is 400 ° C. or higher, the reaction between the oxo acid and the positive electrode active material precursor proceeds, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be further improved. Moreover, when the firing temperature is 1,000 ° C. or lower, the primary particle growth rate is excessively increased, and the crystal particles of the positive electrode active material tend to be further suppressed from becoming too large. In addition, when the firing temperature is 1,000 ° C. or less, the amount of Li deficiency excessively increases and the structural instability tends to be further suppressed. Furthermore, since the firing temperature is 1,000 ° C. or less, element substitution between the site occupied by the Li element and the site occupied by the transition metal can be suppressed, so that the Li conduction path is maintained and the discharge capacity is also increased. Maintained. Due to the above effects, oxygen desorption from the positive electrode active material, deterioration of crystal stability, deterioration of charge / discharge cycle performance, change in composition of the positive electrode active material due to volatilization of Li, and battery due to higher density of positive electrode active material particles It tends to be possible to further suppress the performance degradation. Moreover, when the firing temperature is 700 ° C. or higher and 900 ° C. or lower, both cycle characteristics and high-speed charge / discharge characteristics tend to be further improved.

  The firing time is preferably 1 hour to 8 hours, more preferably 1 to 5 hours, and further preferably 3 to 5 hours. When the firing time is 1 to 8 hours, cycle characteristics and storage characteristics tend to be improved.

  The rate of temperature increase in the firing step is preferably 1 ° C / min to 50 ° C / min, more preferably 1 ° C / min to 20 ° C / min. When the temperature increase rate is 50 ° C./min or less, the oxo acid and the positive electrode active material precursor react more uniformly, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be further improved. Moreover, when the rate of temperature increase is 1 ° C./min or more, cycle characteristics, storage characteristics and the like tend to be further improved.

  The temperature lowering rate in the firing step is preferably 1 ° C./min to 25 ° C./min, more preferably 1 ° C./min to 10 ° C./min. When the temperature lowering rate is 25 ° C./min or less, the resistance of the positive electrode active material surface can be reduced, and the cycle characteristics and the high-speed charge / discharge characteristics tend to be improved. Moreover, when the temperature lowering rate is 1 ° C./min or more, the process time of the firing step is shortened, and the productivity tends to be further improved.

  The atmosphere during firing may be any of an oxidizing atmosphere (for example, in the air) and an inert atmosphere (for example, in nitrogen), and is not particularly limited. However, firing in the atmosphere where both oxygen insertion and desorption can occur on and inside the positive electrode active material is preferred.

[Positive electrode active material]
The specific surface area of the positive electrode active material is preferably 0.1 m ² / g or more and 10.0 m ² / g or less. When the specific surface area of the positive electrode active material is 0.1 m ² / g or more, battery characteristics such as discharge characteristics tend to be more excellent. On the other hand, when the specific surface area of the positive electrode active material is 10.0 m ² / g or less, cycle characteristics and storage characteristics tend to be more excellent.

[Nonaqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery according to the present embodiment includes at least a positive electrode including the positive electrode active material according to the present embodiment, a negative electrode, a nonaqueous electrolyte, and an exterior body. Thus, it is preferable that the positive electrode active material which concerns on this embodiment is for nonaqueous electrolyte secondary batteries. This realizes a non-aqueous electrolyte secondary battery that is excellent in both cycle characteristics and high-speed charge / discharge characteristics even when used under severer temperature and charge / discharge conditions than in the past, such as automotive applications. Can do.

  FIG. 1 is a schematic cross-sectional view showing an example of a nonaqueous electrolyte secondary battery in the present embodiment. A non-aqueous electrolyte secondary battery 100 shown in FIG. 1 includes a separator 110, a positive electrode 120 and a negative electrode 130 that sandwich the separator 110 from both sides, and a positive electrode current collector 140 that sandwiches a laminate thereof (arranged outside the positive electrode). ), A negative electrode current collector 150 (arranged on the outside of the negative electrode), and a battery exterior 160 that accommodates them. A laminate in which the positive electrode 120, the separator 110, and the negative electrode 130 are laminated is impregnated with an electrolytic solution.

[Positive electrode]
The positive electrode according to the present embodiment includes the positive electrode active material according to the present embodiment, and may include a conductive material, a binder, and a current collector as necessary.

  As the conductive material that can be included in the positive electrode, a known material that can conduct electrons can be used, and is not particularly limited. Among these, it is preferable to select from non-graphite carbonaceous materials such as activated carbon, various cokes, carbon black, acetylene black, and graphite. These are used singly or in combination of two or more.

  As the binder that can be included in the positive electrode, a known material that can bind at least two of the positive electrode active material, the conductive material, and the current collector can be used, and is not particularly limited. Among these, as the binder, polyvinylidene fluoride and fluororubber are preferable. A binder is used individually by 1 type or in combination of 2 or more types.

  The current collector that can be included in the positive electrode is not particularly limited, and examples thereof include expanded metal, punched metal, foamed metal, carbon cloth, carbon paper, and the like in addition to metal foil made of aluminum, titanium, stainless steel, and the like. These are used singly or in combination of two or more.

[Negative electrode]
The negative electrode used in the present embodiment preferably includes a negative electrode active material, a binder, and a current collector.

  As the negative electrode active material that can be contained in the negative electrode, a known material that can electrochemically occlude and release lithium ions can be used. Among them, for example, metals, alloys, oxides, nitrides, and the like are preferable in addition to carbon materials such as graphite powder, mesophase carbon fibers, and mesophase microspheres. These are used singly or in combination of two or more.

  The binder that can be included in the negative electrode can be any known material that can bind at least two of the negative electrode active material, the conductive material, and the current collector, and is not particularly limited. Among these, for example, carboxymethylcellulose, styrene-butadiene crosslinked rubber latex, acrylic latex, polyvinylidene fluoride, and the like are preferable. These are used singly or in combination of two or more.

  Although it does not specifically limit as a collector which can be contained in a negative electrode, For example, expanded metal, punch metal, foam metal, carbon cloth, carbon paper etc. other than metal foils, such as copper, nickel, and stainless steel, are mentioned. These are used singly or in combination of two or more.

[Non-aqueous electrolyte]
The nonaqueous electrolyte in the present embodiment preferably contains an electrolyte (salt) and a nonaqueous solvent.
The electrolyte (salt) used for the non-aqueous electrolyte in the present embodiment is not particularly limited, and a conventionally known one can be used. Specific examples thereof include, for example, LiPF ₆ (lithium hexafluorophosphate), LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{2k + 1} [k is an integer of 1 to 8], LiN (SO ₂ C _k F _{2k + 1} ) ₂ [k is an integer of 1 to 8], LiPF _n (C _k F _{2k + 1} ) _6-n [n is an integer of 1 to 5, k is an integer of 1 to 8], LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , Li ₂ B ₁₂ F _b H _12-b [b is an integer of 0 to 3], LiBF _q (C _s F _{2s + 1 4-q} [q is an integer of 1 to 3, s is an integer of 1 to 8], LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiB (C ₃ O ₄ H ₂ ) ₂ , LiPF ₄ (C ₂ O ₂ ), etc. It is. These electrolytes are used singly or in combination of two or more. Among these, LiPF ₆ is preferable from the viewpoint of more effectively and reliably achieving the object of the present invention.

  The non-aqueous solvent used in the non-aqueous electrolyte in the present embodiment is not particularly limited, and a conventionally known one can be used. As the non-aqueous solvent, for example, an aprotic polar solvent is preferable. Specific examples thereof include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, trifluoromethylethylene carbonate, Cyclic carbonates such as fluoroethylene carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-butyrolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, Methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl pro Examples include chain carbonates such as pyr carbonate and methyl trifluoroethyl carbonate; nitriles such as acetonitrile; chain ethers such as dimethyl ether; chain carboxylic acid esters such as methyl propionate; chain ether carbonate compounds such as dimethoxyethane. . These are used singly or in combination of two or more.

  Note that the nonaqueous electrolyte of the present embodiment may be in a liquid form or a solid electrolyte.

〔separator〕
As a separator that can be used in the present embodiment, a conventionally known separator used for a nonaqueous electrolyte secondary battery can be used, and is not particularly limited. The separator in the present embodiment may be any separator as long as it has high ion permeability and electrically isolates the positive electrode and the negative electrode.

  Examples of the separator include a synthetic resin microporous membrane, a nonwoven fabric, papermaking, a porous membrane, and a solid electrolyte film. As the synthetic resin microporous membrane, for example, a microporous membrane made of a polyolefin resin such as polyethylene or polypropylene is preferably used. Examples of the nonwoven fabric, papermaking, and porous membrane include those made of cellulose, aromatic polyamide, fluororesin, polyolefin, and the like. These non-woven fabric, papermaking, and porous film may be composed of a mixture of the above-described resin and one or more inorganic materials such as alumina and silica, or at least a part of the surface of the above-described resin may be You may coat | cover with the inorganic substance.

[Exterior body]
A conventionally well-known thing can be used for the exterior body used for this embodiment, and it does not restrict | limit in particular. Although it does not specifically limit as a material of an exterior body, For example, the laminate film etc. which coat | covered metal, such as stainless steel, iron, and aluminum, and the surface of these metals with resin.

  The non-aqueous electrolyte secondary battery of the present embodiment may have the same configuration as a conventionally known one except that it has the above-described configuration. Examples of the nonaqueous electrolyte secondary battery of the present embodiment include a lithium ion secondary battery and a lithium ion capacitor.

  The non-aqueous electrolyte secondary battery of the present embodiment is excellent in both cycle characteristics and high-speed charge / discharge characteristics even when used under severer temperature and charge / discharge conditions than in the past, such as for automotive applications. Become.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

Example 1
<Synthesis of positive electrode active material>
Nickel sulfate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), manganese sulfate (II) pentahydrate (Wako Pure Chemical Industries, Ltd.) and cobalt sulfate (II) heptahydrate (Wako Pure) Yakuhin Kogyo Co., Ltd.) was dissolved in water at a 1: 1: 1 molar ratio of transition metal elements to prepare a nickel-manganese-cobalt mixed aqueous solution having a total metal ion concentration of 2 mol / L. . This nickel-manganese-cobalt mixed aqueous solution was dropped into 3,000 mL of a 1 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min over 120 minutes. During the dropwise addition, nitrogen aqueous solution was bubbled through the aqueous solution while stirring the aqueous sodium carbonate solution. Precipitates were generated by the above operation. The precipitated substance was collected, washed thoroughly with distilled water, and dried at 100 ° C. for 8 hours. Thereafter, the obtained compound was baked in the atmosphere at 800 ° C. for 1 hour to obtain a nickel-manganese-cobalt compound as a positive electrode active material precursor. About the obtained positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 2.2 m < ² > / g.
Next, the obtained nickel-manganese-cobalt compound and lithium carbonate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of Li: Ni: Mn: Co was 3: 1: 1: 1. Further, H ₃ PO ₄ (melting point: 42.35 ° C., density (A): 1.834 g / cm ³ ) was added at a mass of x (g) such that 10x / AR = 0.1.
After these were dry-mixed for 1 hour, the resulting mixture was fired in the atmosphere at 900 ° C. for 5 hours (temperature increase rate: 10 ° C./min, temperature decrease rate: 10 ° C./min) to obtain a positive electrode active material. It was.

<Preparation of nonaqueous electrolyte secondary battery>
(1) Production of Positive Electrode The positive electrode active material obtained as described above, graphite powder (manufactured by TIMCAL, KS-6) and acetylene black powder (manufactured by Denki Kagaku Kogyo Co., HS-100) as a conductive additive. ) And a polyvinylidene fluoride solution (manufactured by Kureha, L # 7208) as a binder at a mass ratio of 80: 5: 5: 10 as a solid content ratio. N-methyl-2-pyrrolidone as a dispersion solvent was added to the obtained mixture so as to have a solid content of 35% by mass, and further mixed to prepare a slurry. This slurry was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a disk shape with a diameter of 16 mm to obtain a positive electrode.

(2) Production of negative electrode Graphite powder (OMAC1.2H / SS, Osaka Gas Chemical Co., Ltd.) and graphite powder (TIMCAL, SFG6) as the negative electrode active material, styrene butadiene rubber (SBR) and carboxymethylcellulose aqueous solution as binder Were mixed at a solid mass ratio of 90: 10: 1.5: 1.8. The obtained mixture was added to water as a dispersion solvent so as to have a solid content concentration of 45% by mass to prepare a slurry. This slurry was applied to one side of a 18 μm thick copper foil, the solvent was removed by drying, and then rolled with a roll press. The negative electrode was obtained by punching the rolled product into a disk shape having a diameter of 16 mm.

(3) Preparation of non-aqueous electrolyte In a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2, LiPF ₆ was dissolved to a concentration of 1 mol / L. An electrolytic solution that was a water electrolyte was obtained.

(4) Production of battery The positive electrode and the negative electrode produced as described above are superimposed on both sides of a separator (film thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm) made of polyethylene microporous film. The laminated body was inserted into a stainless steel disk type battery case (exterior body). Here, 0.5 mL of the electrolytic solution was injected, and the laminate was immersed in the electrolytic solution, and then the battery case was sealed to prepare a nonaqueous electrolyte secondary battery.

<Battery evaluation>
(1) Initial charging / discharging The obtained non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “battery”) is accommodated in a thermostatic bath (manufactured by Futaba Kagaku Co., Ltd., thermostatic bath PLM-73S) set at 25 ° C. The battery was connected to a charge / discharge device (ASKA Electronics Co., Ltd., charge / discharge device ACD-01). Next, this battery was charged at a constant current of 0.05 C, reached 4.2 V, charged at a constant voltage of 4.2 V for 2 hours, and further discharged to 3.0 V at a constant current of 0.2 C.
Note that 1C is a current value at which the battery is discharged in one hour.

(2) High-speed charge / discharge test The battery after the initial charge / discharge is accommodated in a thermostat (manufactured by Futaba Kagaku Co., Ltd., thermostat PLM-73S) set at 25 ° C., and a charge / discharge device (manufactured by Asuka Electronics Co., Ltd.) It connected to charging / discharging apparatus ACD-01). Next, this battery was charged with a constant current of 1/3 C, reached 4.2 V, charged with a constant voltage of 4.2 V for 1 hour, and further discharged to 3.0 V with a constant current of 1/3 C. . Subsequently, the battery was charged with a constant current of 1/3 C, reached 4.2 V, charged with a constant voltage of 4.2 V for 1 hour, and further discharged to 3.0 V with a constant current of 5 C. Subsequently, the battery was charged with a constant current of 1 / 3C, reached 4.2V, charged with a constant voltage of 4.2V for 1 hour, and further discharged to 3.0V with a constant current of 10C. .
At this time, based on the discharge capacity when discharged to 3.0 V with a constant current of 1/3 C, the discharge capacity retention rate when discharged to 3.0 V with a constant current of 5 C was examined. The results are shown in Table 1.

(3) Cycle test The battery after the initial charging / discharging is housed in a thermostat set at 50 ° C. (manufactured by Futaba Kagaku Co., Ltd., thermostatic bath PLM-73S), and a charge / discharge device (manufactured by Asuka Electronics Co., Ltd., charge / discharge). Connected to device ACD-01). Next, this battery was charged to 4.2 V with a constant current of 1 C, reached 4.2 V, charged for 1 hour with a constant voltage of 4.2 V, and further discharged to 3.0 V with a constant current of 1 C. . When this series of charge / discharge cycles was repeated as one cycle, the discharge capacity retention rate at the 100th cycle was examined based on the discharge capacity at the first cycle. The results are shown in Table 1.

Examples 2 to 5 and Comparative Example 1
In <Synthesis of positive electrode active material> in Example 1 above, the amount of H ₃ PO ₄ added (x (g)) is the mass x (g) such that the value of 10x / AR becomes the value shown in Table 1. A positive electrode active material was synthesized in the same manner as in Example 1 except that the non-aqueous electrolyte secondary battery was produced using the positive electrode active material, and evaluated. The results are shown in Table 1.

Example 6
<Synthesis of positive electrode active material>
Nickel sulfate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), manganese sulfate (II) pentahydrate (Wako Pure Chemical Industries, Ltd.) and cobalt sulfate (II) heptahydrate (Wako Pure) Yakuhin Kogyo Co., Ltd.) was dissolved in water at a 1: 1: 1 molar ratio of transition metal elements to prepare a nickel-manganese-cobalt mixed aqueous solution having a total metal ion concentration of 2 mol / L. . This nickel-manganese-cobalt mixed aqueous solution was dropped into 3,000 mL of a 1 mol / L sodium carbonate aqueous solution heated to 70 ° C. at an addition rate of 12.5 mL / min over 120 minutes. In addition, at the time of dripping, nitrogen of the flow volume of 200 mL / min was bubbled into this aqueous solution, stirring sodium carbonate aqueous solution. This produced a precipitated material. The precipitated substance was collected, washed thoroughly with distilled water, and dried at 100 ° C. for 8 hours to obtain a nickel-manganese-cobalt compound.

The obtained nickel-manganese-cobalt compound and lithium carbonate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of Li: Ni: Mn: Co was 3: 1: 1: 1. After these were dry-mixed for 1 hour, the obtained mixture was fired in the atmosphere at 900 ° C. for 5 hours to obtain a positive electrode active material precursor (oxide). About this positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 1.2 m < ² > / g.
Next, H ₃ PO ₄ was added to the positive electrode active material precursor obtained above at a mass of x (g) such that 10x / AR = 0.1.
After these were dry-mixed for 1 hour, the resulting mixture was fired at 800 ° C. for 5 hours in an oxygen atmosphere (temperature increase rate: 10 ° C./min, temperature decrease rate: 10 ° C./min) to obtain a positive electrode active material. Obtained.
A nonaqueous electrolyte secondary battery was prepared and evaluated in the same manner as in Example 1 except that the above positive electrode active material was used. The results are shown in Table 1.

Example 7 and Comparative Examples 2 and 4
In <Synthesis of positive electrode active material> in Example 6 above, the amount of H ₃ PO ₄ added (x (g)) is the mass x (g) such that the value of 10x / AR becomes the value shown in Table 1. A positive electrode active material was synthesized in the same manner as in Example 6, except that the non-aqueous electrolyte secondary battery was produced using the positive electrode active material, and evaluated.
In Comparative Example 2, addition and mixing of H ₃ PO ₄ and subsequent firing were not performed.
The evaluation results are shown in Table 1.

Comparative Example 3
A positive electrode active material was synthesized in the same manner as in Example 6 except that in the above <Synthesis of positive electrode active material> in Example 6 above, H ₃ PO ₄ was added and mixed, and thereafter no firing was performed. A nonaqueous electrolyte secondary battery was fabricated using the active material and evaluated. The results are shown in Table 1.

Examples 8 and 9
In Example 1 <Synthesis of positive electrode active material>, instead of H ₃ PO ₄ as the oxo acid, in Example 8, H ₂ SO ₄ (melting point: 10 ° C., Li ₂ SO ₄ substitute density: 2.221 g) / Cm ³ )
In Example 9, H ₃ BO ₃ (melting point: 169 ° C., density: 1.435 g / cm ³ ),
A positive electrode active material was synthesized in the same manner as in Example 1 except that each was used, and a nonaqueous electrolyte secondary battery was produced and evaluated using the positive electrode active material. The results are shown in Table 1.

Example 10
<Synthesis of positive electrode active material>
Nickel nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), cobalt nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.) and manganese nitrate (II) hexahydrate (Wako Pure) Yakuhin Kogyo Co., Ltd.) is weighed so that the molar ratio of Ni: Co: Mn is 0.175: 0.100: 0.525 so that the total nitrate concentration is 40% by mass. Distilled water was added to the solution to make an aqueous nitrate solution. The obtained aqueous solution was dried at 260 ° C. for 2 hours to remove water, and the obtained powder was recovered. This powder was fired at 800 ° C. for 1 hour to obtain a positive electrode active material precursor. About the obtained positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 6.1 m < ² > / g.

Next, lithium nitrate (Wako Pure Chemical Industries, Ltd.) was added to the precursor obtained above so that the molar ratio of Li: Ni: Co: Mn was 1.2: 0.175: 0.100: 0.525. In addition, H ₃ PO ₄ was further added at a mass of x (g) such that 10x / AR = 0.1.
After these were dry-mixed for 1 hour, the resulting mixture was fired in the atmosphere at 830 ° C. for 5 hours to obtain a positive electrode active material.

<Preparation of nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery (battery) was produced in the same manner as in Example 1 except that the positive electrode active material obtained above was used.
<Battery evaluation>
The charge voltage in the initial charge / discharge is 4.7V,
Battery evaluation was performed in the same manner as in Example 1 except that the charging voltage in the cycle test and the high-speed charging / discharging test was set to 4.5 V, respectively. The results are shown in Table 2.

Comparative Example 5
In Example 10 <Synthesis of positive electrode active material>, except that the amount of H ₃ PO ₄ added (x (g)) was changed to a mass x (g) such that 10x / AR = 1.1. Synthesize | combined the positive electrode active material like Example 10, produced the nonaqueous electrolyte secondary battery using this positive electrode active material, and evaluated. The results are shown in Table 2.

Example 11
<Synthesis of positive electrode active material>
Lithium nitrate (Wako Pure Chemical Industries, Ltd.), nickel nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), cobalt nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), And manganese nitrate (II) hexahydrate (Wako Pure Chemical Industries, Ltd.), the composition ratio of Li: Ni: Co: Mn: is 1.2: 0.175: 0.100: 0 in molar ratio. .525, and distilled water was added so that the concentration as the total amount of nitrate was 40% by mass to obtain a nitrate aqueous solution. The obtained aqueous solution was dried at 260 ° C. for 2 hours to remove water, and the obtained powder was recovered. The powder was heated at 500 ° C. for 8 hours to remove nitric acid. The obtained powder after removal of nitric acid content was once taken out from the container, pulverized and mixed, and then calcined at 830 ° C. for 8 hours to obtain a positive electrode active material precursor. About the obtained positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 4.2 m < ² > / g.

Next, H ₃ PO ₄ (density: 1.69 g / ml) was added to the positive electrode active material precursor obtained above at a mass of x (g) such that 10x / AR = 0.1.
After these were dry-mixed for 1 hour, the resulting mixture was fired at 800 ° C. for 5 hours in an oxygen atmosphere (temperature increase rate: 10 ° C./min, temperature decrease rate: 10 ° C./min) to obtain a positive electrode active material. Obtained.

<Preparation of nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery (battery) was produced in the same manner as in Example 1 except that the positive electrode active material obtained above was used.
<Battery evaluation>
The battery evaluation was performed in the same manner as in Example 10. The results are shown in Table 2.

Comparative Example 6
In Example 11 <Synthesis of positive electrode active material>, a positive electrode active material was synthesized in the same manner as in Example 11 except that H ₃ PO ₄ was not added and mixed and baked, and the positive electrode active material was used. A non-aqueous electrolyte secondary battery was prepared and evaluated. The results are shown in Table 2.

Comparative Example 7
In Example 11 <Synthesis of positive electrode active material>, a positive electrode active material was synthesized in the same manner as in Example 11 except that H ₃ PO ₄ was added and mixed, and no subsequent firing was performed. A nonaqueous electrolyte secondary battery was fabricated using the active material and evaluated. The results are shown in Table 2.

Example 12
<Synthesis of positive electrode active material>
Manganese (II) carbonate n hydrate (Wako Pure Chemical Industries, Ltd.) was fired at 800 ° C. for 1 hour in the air to obtain a positive electrode active material precursor. About the obtained positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 2.0 m < ² > / g.
Next, the obtained positive electrode active material precursor and lithium carbonate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of Li: Mn was 1: 2, and further H ₃ PO ₄ was added at 10 × / It was added at a mass of x (g) such that AR = 0.1.
After these were dry-mixed for 1 hour, the resulting mixture was fired at 1,000 ° C. for 5 hours in an oxygen atmosphere (temperature increase rate: 10 ° C./min, temperature decrease rate: 10 ° C./min). Obtained material.

<Preparation of nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery (battery) was produced in the same manner as in Example 1 except that the positive electrode active material obtained above was used.
<Battery evaluation>
The battery evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 8
A positive electrode active material was synthesized in the same manner as in Example 12 except that H ₃ PO ₄ was added at a mass of x (g) such that 10x / AR = 1.1, and this positive electrode active material was used. A non-aqueous electrolyte secondary battery was prepared and evaluated. The results are shown in Table 3.

Example 13
<Synthesis of positive electrode active material>
Lithium carbonate (Wako Pure Chemical Industries, Ltd.) and manganese carbonate (II) n hydrate (Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of Li: Mn was 1: 2. Dry mixed for 1 hour. The obtained mixture was baked at 1,000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material precursor. About this positive electrode active material precursor, the nitrogen adsorption specific surface area measured by BET method using the autosorb-1 by a cantachrome company was 1.8 m < ² > / g.
H ₃ PO ₄ was added to the obtained positive electrode active material precursor at a mass of x (g) such that 10x / AR = 0.1. After these were dry-mixed for 1 hour, the resulting mixture was fired at 800 ° C. for 5 hours in an oxygen atmosphere (temperature increase rate: 10 ° C./min, temperature decrease rate: 10 ° C./min), whereby a positive electrode active material Got.
<Preparation of nonaqueous electrolyte secondary battery>
A nonaqueous electrolyte secondary battery (battery) was produced in the same manner as in Example 1 except that the positive electrode active material obtained above was used.
<Battery evaluation>
The battery evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 9
In <Synthesis of positive electrode active material> in Example 13, a positive electrode active material was synthesized in the same manner as in Example 13 except that H ₃ PO ₄ was not added and mixed and then fired, and the positive electrode active material was used. A non-aqueous electrolyte secondary battery was prepared and evaluated. The results are shown in Table 3.

Comparative Example 10
In Example 13 <Synthesis of positive electrode active material>, a positive electrode active material was synthesized in the same manner as in Example 13 except that H ₃ PO ₄ was added and mixed, and then not fired. A non-aqueous electrolyte secondary battery was fabricated and evaluated. The results are shown in Table 3.

  The nonaqueous electrolyte secondary battery of the present invention can be suitably applied to, for example, various consumer equipment power supplies, automobile power supplies, and the like.

100 Nonaqueous electrolyte secondary battery 110 Separator 120 Positive electrode 130 Negative electrode 140 Positive electrode current collector 150 Negative electrode current collector 160 Battery exterior

Claims (6)

At least the following steps a. And b. ;
a. Mixing a positive electrode active material precursor and an oxo acid; and b. Step a. A step of firing the mixture obtained in step {wherein the step a. The surface area R (m ² ) of the positive electrode active material precursor, the density A (g / cm ³ ) of the oxo acid, and the mass x (g) of the oxo acid are expressed by the following formula:
1 ≧ 10x / AR> 0
Satisfy the relationship. }
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein   The positive electrode active material according to claim 1, wherein the positive electrode active material precursor is a compound containing at least one transition metal.   The positive electrode active according to claim 1 or 2, wherein the oxo acid comprises an oxo acid containing one or more elements selected from the group consisting of boron (B), phosphorus (P), and sulfur (S). material.   The positive electrode active material according to claim 1, wherein the oxo acid includes phosphoric acid.   The positive electrode containing the positive electrode active material of any one of Claims 1-4.   A nonaqueous electrolyte secondary battery comprising at least the positive electrode according to claim 5, a negative electrode, a nonaqueous electrolyte, and an exterior body.

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