JP2017098196A - Positive electrode active material for nonaqueous electrolyte secondary battery, method for manufacturing the same, and method for manufacturing coating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, by which the gelation of a paste-like composition can be suppressed, and an initial battery performance can be maintained at about the same level as that of conventional lithium nickel composite oxide particles.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery comprises: lithium nickel composite oxide particles, each having a lithium compound layer on at least part of its surface, and a composition given by LiNiCoMMO(where Mand Mrepresent at least one element selected from a group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W; 0.97<t1≤1.10; 0≤x≤0.22; 0≤y≤0.15; 0<z≤0.05). The lithium compound layer comprises a lithium compound including Li and M, has a thickness of 5-500 nm and a concentration gradient such that the concentration of Mlowers in a direction from the outermost surface of the composite oxide particle toward the center thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a method for producing a coating liquid.

  In recent years, with the high performance and rapid spread of mobile phones and notebook computers, there are increasing demands for small size, light weight, and high capacity for secondary batteries used in them. A non-aqueous electrolyte secondary battery represented by a lithium secondary battery has a higher battery voltage and higher energy density than a nickel cadmium battery or a nickel hydride battery, and is rapidly spreading in various fields. Nonaqueous electrolyte secondary batteries are also expected as a power source for driving motors of electric vehicles and hybrid vehicles against the background of recent environmental problems. In particular, a hybrid vehicle requires a high output density as a battery for energy storage, and a non-aqueous electrolyte secondary battery used for this is required to have high discharge characteristics and high cycle stability.

Examples of the positive electrode active material of the non-aqueous electrolyte secondary battery include lithium cobaltate (LiCoO ₂ ) having an α-NaFeO ₂ structure, lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) having a spinel structure. Lithium transition metal composite oxide powders as typified by are mainly used. Synthesis of these positive electrode active materials was generally obtained by mixing lithium compound (Li ₂ CO ₃ , LiOH, etc.) powder and transition metal compound (MnO ₂ , NiO, Co ₃ O ₄ etc.) powder, drying and firing. A method of pulverizing a lithium transition metal oxide into a positive electrode active material has been widely adopted.

However, the positive electrode active material has an electric conductivity of 10 ⁻¹ S / cm ² or more and 10 ⁻⁶ S / cm ² or less, and has a lower electric conductivity than a general conductor. In addition, the electrical conduction and electrical contact between the current collector and the positive electrode active material greatly affect the cycle characteristics and discharge rate characteristics of the battery.

Therefore, in Patent Document 1, in order to improve the discharge capacity and cycle characteristics by reducing the internal resistance of the secondary battery as much as possible, the composition formula Li _a Mn _x Ni _y M _z O ₂ (where M is Co, Al And an organic metal compound containing at least one of Al, Mg, Sn, Ti, Zn, and Zr is added to the lithium transition metal composite oxide represented by Thereafter, a positive electrode active material obtained by performing a heat treatment at a temperature of 400 ° C. or higher and 700 ° C. or lower has been proposed. Thus, the positive electrode active material obtained by high-temperature treatment after adhering the organometallic compound to the surface of the complex oxide particles by mechanical crushing is a complex oxide due to the effect of the additive (organometallic compound). It is described that the particle surface is stabilized and the cycle characteristics are improved.

Further, in Patent Document 2, in order to reduce the surface resistance of LiCoO ₂ (LCO) particles and improve cycle characteristics, Li and Nb alkoxide solutions are sprayed using a tumbling flow apparatus, and LiNbO _{3 is} applied to the LCO particle surfaces by heat treatment. There has been a proposal to form a layer (coating layer). It is described that, due to this effect, the reaction with the electrolyte on the surface of the LCO particles generated during the charge / discharge cycle is suppressed, so that the decrease in charge / discharge capacity from the initial stage can be suppressed.

  In Patent Document 3, in order to stably supply a coating film continuously, a coating liquid sprayed by a tumbling fluidizer and a hydrolysis promoting liquid are separately added, and a hydrolysis reaction is caused immediately after injection to obtain a desired film. A method of forming a Li compound film on the particle surface has been proposed.

JP-A-2005-346955 JP 2012-193940 A JP 2012-148251 A

  However, the composite oxide particles described in Patent Document 1 have reduced Li insertion / detachment due to stabilization of the particle surface, and further reduced initial charge / discharge characteristics due to damage to the particle surface during crushing. There was a problem.

  Further, the composite oxide particles described in Patent Document 2 spray a liquid obtained by mixing an unstable Li alkoxide liquid and an Nb alkoxide liquid as a method of laminating a Li-Nb compound film having a low surface resistance on the particle surface. However, it is not synthesized because it takes a short time to become a Li—Nb compound film in the reaction immediately after film formation, and it becomes a composite compound film separated into Li and Nb during the progress of drying. For example, Li compounds are likely to be altered by moisture present in the outside air, so that once they are altered, the desired properties cannot be obtained. 2) The two types of liquids used are affected by moisture in the outside air. Hydrolysis reaction is likely to occur, and the liquid may produce a cloudy precipitate during the preparation or spraying process. 3) Since the main solvent uses a quick-drying lower alcohol, it is the same as spraying. Dried and solidified easily formed film had a non-uniform, etc. problems in.

  Further, in Patent Document 3 improved so that a film can be formed stably and firmly, instead of using a liquid unstable to moisture and moisture mentioned in Patent Document 2, a lithium aqueous solution and a metal alkoxide solution are separately provided. It is described that a coating film having a desired composition is formed by spraying and causing a hydrolysis reaction within a short time after adhering to the particle surface. 1) Using a metal alkoxide solution alone However, it does not change that the hydrolysis reaction is likely to occur. 2) The liquid is only mixed during spraying and is not microscopically synthesized. Therefore, when sprayed onto the Ni-based core particles, there is a problem that the deterioration is accelerated.

  That is, the conventional method described above is to form a composite compound composed of Li and a transition metal having high ion conductivity in order to improve the surface of particles having high resistance due to deterioration of cycle characteristics, and to perform electrolysis during charge / discharge. In order to suppress the reaction with the liquid, an attempt was made to obtain a coating film having a high barrier property on the particle surface. However, since the film quality is non-uniform with a portion having a high Li concentration, the desired low resistance and barrier properties are insufficient, and cycle characteristics are often not improved.

  Furthermore, the oxide films obtained in Patent Document 1 and Patent Document 2 are not only non-uniform in film thickness, but are easy to cause degranulation and peeling, and are filled because the oxide film has a certain thickness or more locally. Li insertion / extraction at the time of discharge may be reduced, and initial charge / discharge capacity may be deteriorated. In order to avoid these problems, it is required to form the coating film uniformly and thinly. However, since it requires a high level of technology and labor, the process is reversed from an industrial viewpoint.

  The present invention has been made in view of the above problems, and an object thereof is to improve the cycle characteristics and water resistance of a positive electrode active material while maintaining the original battery performance.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention has a lithium compound layer on at least a part of its surface, and the composition is Li _t1 Ni _1-xy Co _x M ¹ _y M ² _z O ₂ (wherein M ¹ and M ² are at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W) 0.97 <t1 ≦ 1.10, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, and 0 <z ≦ 0.05. The lithium compound layer contains a lithium compound containing Li and M ^{2 and} has a thickness of 5 nm to 500 nm in the direction from the outermost surface of the composite oxide particle toward the center, and M ² It has a concentration gradient such that the concentration is low.

Moreover, the lithium compound layer may have a coating layer formed from a lithium compound. Further, the lithium compound layer may have a surface layer portion containing a lithium nickel composite oxide containing at least Li and Ni and a lithium compound. Moreover, the lithium compound layer may have the coating layer and the surface layer portion in this order in the direction from the outermost surface of the composite oxide particle toward the center. The portion other than the lithium compound layer has a composition of Li _t2 Ni _1-xy Co _x M ¹ _y O ₂ (M ¹ in the formula is the same element as M ¹ of the composite oxide composition; 97 ≦ t2 ≦ 1.05, and x and y are the same values as x and y in the composition of the composite oxide. Further, even if 1 g of the positive electrode active material is stirred and mixed in 50 g of pure water kept at 24 ° C. for 10 minutes to obtain a slurry, the slurry is allowed to stand for 30 seconds, and the pH of the aqueous solution obtained is 11.2 or less. Good. Further, the lithium nickel composite oxide particles, M in the composition is _{Li t1 Ni 1-x-y} Co x M y O 2 ( formula, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb And at least one element selected from the group consisting of Mo and W, 0.97 ≦ t1 ≦ 1.05, 0 ≦ x ≦ 0.22, and 0 ≦ y ≦ 0.15. The lithium compound layer may be formed by heat treatment after forming a coating layer precursor containing Li and the M ² on at least a part of the surface of the base material. Lithium compound, a ^{M 2,} wherein for the entire base material, containing in the range of 0.02 to 2.0 wt%, the Li, the range of 0.1 to 1.00 in Li / ^{M 2} molar ratio You may contain in. The positive electrode active material is incorporated into a coin-type battery, charged with a charging potential of 4.1 V, measured by the AC impedance method, and the surface resistance value calculated by fitting calculation from the Nyquist plot is the surface of the base material. When the resistance value is 1, it may be 2 or less. The positive electrode active material has an initial discharge capacity within a range of ± 3% relative to the initial discharge capacity of the base material after being incorporated in a coin-type battery, and is 4.3V-3.0V at a rate of 0.5C. The discharge capacity maintenance rate after 200 cycles may be higher by 10% or more than the initial discharge capacity maintenance rate of the base material.

  The method for producing the coating liquid for surface treatment of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the second aspect of the present invention includes Li alkoxide, Mg, Al, Ca, Ti, V, Cr, Mn, Zr, and Nb. Mixing a metal alkoxide monomer or oligomer thereof containing at least one element selected from the group consisting of Mo and W, a high-boiling alcohol, and a water decomposition inhibitor to obtain a mixed solution, Adding alcohol and moisture to the liquid.

  Further, as the high boiling point alcohol, 2methyl-1-butanol, 1 ethoxy-2propanol, or 2-isopropoxyethanol may be used.

  The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to a third aspect of the present invention is described in claim 11 or 12 on the particle surface while rocking the lithium nickel composite oxide particles using a stirrer. Spraying the coating liquid, and drying to form a coating layer precursor on the surface of the particles, followed by heat treatment at 400 ° C. to 700 ° C. in an oxygen atmosphere.

The positive electrode active material of the present invention is suppressed in gelation and has good battery characteristics.
The method for producing a coating liquid of the present invention does not show white turbid precipitation even when left in the atmosphere for one day, and has high stability against hydrolysis, so that a good quality coating film is easily obtained. In addition, handling such as storage of liquid and handling during coating spraying becomes easy. Furthermore, since the amount of the organic substance having poor thermal decomposability can be suppressed, the formed film has increased thermal decomposability, and as a result, carbonation to the particle surface by the carbon dioxide component generated during the heat treatment can be reduced. Further, since the coating liquid obtained by the production method of the present invention does not quickly dry when sprayed on the surface of the lithium composite oxide particles, it can sufficiently penetrate the inside of the particles before being dried and solidified, and When the particles are swung by the coating apparatus, the particles easily spread on the surface of the particles, and the uniformity of the coating film (coating layer precursor) formed using this coating solution is extremely excellent. Moreover, the positive electrode active material using this coating liquid does not hinder the initial battery performance such as the charge / discharge characteristics inherent to the lithium composite oxide particles, and can obtain high cycle characteristics. By using this coating solution for forming a coating film of a positive electrode active material for a non-aqueous electrolyte secondary battery, not only in terms of quality, but also convenience and convenience of work are improved. large.

It is a schematic diagram which shows an example of the positive electrode active material which concerns on embodiment. It is a schematic diagram which shows an example of the manufacturing method of the positive electrode active material which concerns on embodiment. It is a flowchart which shows an example of the manufacturing method of the positive electrode active material which concerns on embodiment. It is a flowchart which shows an example of the manufacturing method of the positive electrode active material which concerns on embodiment. It is a schematic sectional drawing of the coin-type battery used for battery evaluation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Further, in the drawings, in order to make each configuration easy to understand, a part of the structure is emphasized or a part of the structure is simplified, and an actual structure, shape, scale, or the like may be different.

1. FIG. 1 is a schematic diagram showing an example of a positive electrode active material for a nonaqueous electrolyte secondary battery (hereinafter also referred to as “positive electrode active material”) 1 according to the present embodiment. . As shown in FIGS. 1A to 1C, the positive electrode active material 1 is composed of lithium nickel composite oxide particles 2 (hereinafter also referred to as “composite oxide particles”). At least one element selected from the group consisting of Li, Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo, and W (hereinafter also referred to as “M ² ”) on the surface thereof. And a lithium compound layer 3 containing a lithium compound (hereinafter also simply referred to as “Li compound layer 3”), and the other central portion 4. As will be described later, the lithium compound layer 3 is formed by modifying at least a part of the surface of the composite oxide particle (base material 5), and includes a compound containing Li and M ² (hereinafter simply referred to as “lithium compound”). Say). The Li compound layer 3 (at least one of 3a and 3b) improves the ionic conductivity of the surface of the composite oxide particle 2, thereby obtaining a positive electrode active material having a high discharge capacity. In addition, the Li compound layer 3 can maintain the stability of the surface of the composite oxide particle 2, and thereby, a positive electrode active material with improved surface characteristics can be obtained by reducing the increase in surface resistance.

Further, the Li compound layer 3 may have a coating layer 3a as shown in FIGS. 1 (A) and 1 (B). Covering layer 3a is a layer formed of a lithium compound (including Li and M ^2). Further, the Li compound layer 3 may have a surface layer portion 3b as shown in FIGS. The surface layer portion 3b is a portion containing a lithium nickel composite oxide containing at least Li and Ni and a lithium compound (including Li and M2). In addition, the Li compound layer 3 may be formed from the coating layer 3a as shown in FIG. 1 (A), and is directed from the outermost surface of the composite oxide particle 2 to the center as shown in FIG. 1 (B). In the direction, the cover layer 3a and the surface layer portion 3b may be provided in this order, and may be formed from the surface layer portion 3b as shown in FIG. The Li compound layer 3 can be formed in various forms (the coating layer 3a and / or the surface layer portion 3b) by appropriately adjusting the coating amount of the coating liquid described later, heat treatment conditions, and the like.

The composite oxide particle 2 has a total composition of Li _t1 Ni _1-xyz Co _x M ¹ _y M ² _z O ₂ (wherein M ¹ and M ² are Mg, Al, Ca, It is at least one element selected from the group consisting of Ti, V, Cr, Mn, Zr, Nb, Mo and W, 0.97 <t1 ≦ 1.10, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15 and 0 <z ≦ 0.05.) The composition can be measured by ICP emission spectroscopic analysis.

  In the above composition of the composite oxide particle 2, the lower limit of t1 indicating the composition ratio of Li exceeds 0.97, preferably 0.98 or more, and more preferably 1.01 or more. In addition, the amount of Li in the composite oxide particle 2 is preferably detected in excess of the stoichiometric composition. The upper limit of t1 is 1.10 or less, preferably 1.08 or less, and more preferably 1.05 or less.

  In the above composition of the composite oxide particle 2, x indicating the composition ratio of Co is 0 ≦ x ≦ 0.22, from the viewpoint of increasing the capacity and improving the cycle characteristics in the secondary battery using the positive electrode active material 1. Preferably, 0.05 ≦ x ≦ 0.20, and more preferably 0.05 ≦ x ≦ 0.15.

In the composition of the composite oxide particles 2, ^{M 1} is, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb, at least one kind of element selected from the group consisting of Mo and W, From the viewpoint of the thermal stability of the positive electrode active material, it is preferable to contain at least Al. Y representing the composition ratio of M ¹ is 0 ≦ y ≦ 0.15, preferably 0.01 ≦ y ≦ 0.10, and more preferably 0.02 ≦ y ≦ 0.08. y, as will be described later, shows the same value as the composition ratio of the additive metal M ¹ in the preform 6 which is a raw material of the positive electrode active material 1.

In the composition of the composite oxide particle 2, M ² is at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo, and W. M ² may be the same element as M ¹ or a different element. Z representing the composition ratio of M ² is more than 0 and not more than 0.05, preferably 0.0001 ≦ z ≦ 0.02, more preferably 0.0001 ≦ z ≦ 0.01. M ² is included in the Li compound layer 3. M ² is an element derived from an element contained in the coating layer precursor 7 described later.

The amount of M ² contained in the Li compound layer 3 is preferably 0.01 to 2.0% by mass, more preferably 0.03 to 1.0% by mass with respect to 100% by mass of the entire composite oxide particle 2. Range.

  The thickness of the Li compound layer 3 is 5 nm or more and 500 nm or less from the outermost surface of the composite oxide particle 2 in the depth direction. The Li compound layer 3 is formed from the cross-sectional side of the composite oxide particle 2 by TEM-EDS line analysis, SEM-EDS, or TOF-SIMS (time-of-flight secondary ion mass spectrometry: Time-of-Flight Secondary Mass Spectrometry). By measuring each element from the film surface to the particle interface and inside the particle, the thickness of the Li compound layer 3 can be measured by specifying the thickness of the portion having a gradient. Can do.

As will be described later, the Li compound layer 3 is sprayed with a coating solution containing Li and M ² on the surface of the composite oxide particles (base material 5) to form the coating layer precursor 7, and then heat-treated in an oxygen atmosphere. To obtain. As a result, the Li compound layer 3 (the coating layer 3a and / or the surface layer portion 3b) on the surface of the composite oxide particle 2 has a concentration gradient in the direction (depth direction) from the outermost surface of the composite oxide particle 2 toward the center. Thus, M ² is distributed. In addition, M ² has a concentration gradient such that its concentration decreases in the depth direction. The state of this concentration gradient is clarified by measuring each element from the outermost surface of the composite oxide particle to the particle interface and inside the particle by using TEM-EDS line analysis or TOF-SIMS.

As will be described later, the central portion 4 is, for example, a portion of the core material 6 (base material 5) in which Li and M ² contained in the coating layer precursor 7 are not diffused by the heat treatment in the manufacturing process, and the composite oxidation In the physical particle 2, the Li compound layer 3 is not formed. Center 4, the composition is _{Li t2 Ni 1-x-y} Co x M 1 y O 2 (M 1 in the formula is the same element as ^{M 1} of the composition of the composite oxide, 0.97 ≦ t2 ≦ 1.05, x and y are the same values as x and y in the composite oxide composition). This composition is substantially the same as the composition of the base material 5 described later.

  The composite oxide particle 2 has improved ion conductivity on the particle surface by forming the Li compound layer 3 on the surface thereof. The secondary battery using the positive electrode active material 1 composed of the composite oxide particles 2 has a high discharge capacity. In addition, the surface of the positive electrode active material 1 is always kept stable, and in the secondary battery using the positive electrode active material 1, an increase in surface resistance is mitigated and cycle characteristics are improved.

  The positive electrode active material 1 has a positive electrode active material 1 particle surface modification, which suppresses gelation and improves water resistance, suppresses an increase in surface resistance, and improves long-term cycle characteristics over 200 cycles. In order to make it compatible, it is preferable that the organic substance derived from the metal alkoxide in the Li compound layer 3 is thermally decomposed by heat treatment. The heat treatment is preferably performed on the low temperature side in consideration of Li scattering, and in order to cause a reaction between the surface of the core material 6 and the coating layer precursor 7, the heat treatment is performed in a suitable temperature range as described later. can do. The present inventors have found that long-term cycle characteristics are further improved by suppressing the gelation of the paste composition as well as suppressing an increase in surface resistance by appropriate temperature treatment.

Generally, lithium nickel composite oxide particles have low resistance to water, and lithium is easily eluted from the surface. For example, after adding 1 g of composite oxide particles having a coating layer (composition: Li _1.03 Ni _0.85 Co _0.12 Al _0.03 O ₂ ) in 50 g of pure water maintained at 24 ° C., When stirring and mixing for 10 minutes to prepare a slurry and the slurry is allowed to stand for 30 seconds, the pH of the aqueous solution reaches around 13. This is because when the composite oxide particles are added to pure water, a large amount of lithium is instantly eluted from the particles, and the aqueous solution (slurry) moves to the alkali side. On the other hand, since the positive electrode active material 1 of this embodiment has suppressed moisture absorption and improved water resistance, the mixture is stirred and mixed for 10 minutes in 50 g of pure water in which 1 g of the positive electrode active material 1 is kept at 24 ° C. After obtaining the slurry, the pH of the aqueous solution obtained by allowing the slurry to stand for 30 seconds can be adjusted to 11.2 or less. By maintaining the pH of the slurry at 11.2 or less, the alkaline elution of the paste composition is further suppressed during the production of the positive electrode of the secondary battery, and the gelation of the paste composition is suppressed. For example, 9.5 g of a positive electrode active material, 0.5 g of vinylidene fluoride (PVDF), 5.5 g of N-methyl-2-pyrrolidinone (NMP), and 0.2 g of water for promoting gelation are added and kneaded. Thus, a paste composition (slurry) is prepared, and even if the paste composition is stored at 24 ° C. for 1 to 3 days, it does not gel and can be kept in a fluid slurry. By suppressing the gelation of the paste composition, variations in charge / discharge characteristics due to non-uniformity when applied to the positive electrode current collector are suppressed, and the fluidity of the paste composition deteriorates, resulting in a dense coating film. Occurrence of problems such as lowering of the temperature is suppressed.

2A to 2C are schematic views illustrating an example of a method for producing the positive electrode active material 1. FIG. 2A shows lithium nickel composite oxide particles that serve as the base material 5 of the positive electrode active material 1. Preform 5, the composition is _{Li t2 Ni 1-x-y} Co x M y O 2 ( where M consists of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W It is at least one element selected from the group and is represented by 0.97 ≦ t2 ≦ 1.05, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15).

  In the above composition of the base material 5, t2 indicating the composition ratio of Li is 0.97 ≦ t2 ≦ 1.05, preferably 0.98 ≦ t2 ≦ 1.01, more preferably 0.98 ≦ t2 ≦. 1.00. Here, normally, in order to compensate for Li on the surface of the composite oxide particles deficient due to firing or the like, for example, in the above composition, t2 is set to about 1.01 ≦ t2 ≦ 1.20, and Li is mixed slightly excessively. As a result, high properties can be obtained as a positive electrode active material. However, in the above composition of the base material 5, it is possible to compensate for the missing Li on the surface of the composite oxide particles as the Li compound layer 3 (3 a, 3 b) as described later. Therefore, sufficient battery characteristics can be obtained even with a lower Li amount than usual.

  When the composition ratio of Li in the base material 5 is larger than the stoichiometric composition (for example, t2> 1.05), excess Li is present in the form of LiOH or the like on the surface of the composite oxide particle, so that the atmosphere It may react with moisture, carbon dioxide gas, etc., to cause alteration (carbonation). In order to prevent this, it takes time and labor to produce a positive electrode active material in a dry room. On the other hand, when the composition ratio of Li is t2 ≦ 1.05, the amount of excess Li is reduced, so that the reaction with the atmosphere is relaxed and the handleability is improved. Therefore, it is desirable that the Li composition ratio of the base material 5 is smaller in the excess of Li. On the other hand, when t2 is less than 0.97, sufficient battery characteristics may not be obtained even if the Li compound layer 3 is formed.

Figure 2 (B) shows a composite oxide particles (core material 6) having a coating layer precursor 7 containing Li and M ² on the surface thereof. The core material 6 having the coating layer precursor 7 is sprayed with a coating liquid (including Li and M ² ) described later on the composite oxide particles (base material 5), and the coating layer precursor 7 is applied to the surface thereof. It is obtained by forming. Thereafter, the core material 6 having the coating layer precursor 7 is heat-treated, whereby composite oxide particles 2 having the Li compound layer 3 as shown in FIG. 2C can be obtained.

  The structure of the coating layer precursor 7 can be porous continuously in the depth direction. The coating layer precursor 7 preferably has a coating area measured by cross-sectional observation of a transmission electron microscope of 70% or more and 90% or less with respect to the entire area of the core material 6 surface. When the coating area is in the above range, an even reaction with the surface of the core material 6 can be expected after the heat treatment. Here, the covering area is calculated as a ratio of the covering layer precursor 7 adhering to the outer periphery of the core material 6 in the cross-sectional observation.

  In the case of a composite oxide particle formed on the surface of a film formed from a compound not containing Li, for example, a conventionally used coating layer (oxide film), the oxide film has high insulating properties. The surface resistance of the secondary battery using the active material increases. Due to this influence, the discharge capacity and cycle characteristics of the secondary battery are lowered. In particular, the greater the thickness of the oxide film, the greater the effect. In order to improve this, in the prior art, for example, the composite oxide particles on which the oxide film is formed are heated at a high temperature, and the Li component existing on the surface of the core material and the component of the oxide film (or its precursor) In some cases, Li is diffused in the oxide film by reacting with. However, in this method, since Li is partially lost from the surface of the core material due to the diffusion of Li into the oxide film, it is necessary to preliminarily mix Li in the base material. In addition, a base material containing an excessive amount of Li is liable to deteriorate due to reaction of excessive Li components with moisture in the air during storage or coating treatment. Moreover, in order to prevent this, the handling needs to be performed in a dry room, and the manufacturing process tends to be complicated.

  In addition, since the conventional oxide film has poor conductivity, the film itself may be formed thin in order to avoid an increase in surface resistance. In this case, the thickness of the oxide film is optimally about 3 nm, and at most 10 nm or less is required. Conventionally, in order to improve the conductivity of the oxide film, a device for covering the oxide film so that the thickness of the oxide film is thin and there is no film defect has been performed, but it takes time and effort. In addition, when imparting conductivity to the oxide film to improve conductivity, a method of heat treating at a low temperature to leave a small amount of organic matter that contributes to improving the conductivity in the oxide film is also conceivable. Residual organic substances may adversely affect the cycle test.

  On the other hand, the composite oxide particles 2 of the present embodiment can have a thickness (layer thickness) of the coating layer precursor 7 in the range of 3 nm to 100 nm, for example, in the manufacturing process. In addition, the composite oxide particle 2 can have a lower limit of the thickness of the coating layer precursor 7 of, for example, 10 nm or more, 20 nm or more, and further 30 nm or more. The Li compound layer 3 can be produced. Moreover, the upper limit of the layer thickness of the coating layer precursor 7 is about 100 nm or less. If the film thickness is too large, the amount of thermal decomposition during the heat treatment may be reduced, and an organic residue may be generated in the Li compound layer 3 and the cycle characteristics may not be improved. Moreover, in this case, the heat treatment temperature and the holding time of the reached temperature are increased, which is a disadvantage in terms of cost.

When the composite oxide particles are coated with a coating solution that does not contain Li as in the prior art, it is necessary to cover the excess amount of Li existing on the surface of the composite oxide particles with a necessary amount of M ² component. is there. On the other hand, in the method of the present embodiment, for example, a mixture prepared as a coating solution containing Li and M ² can be sprayed to efficiently form the coating layer precursor 7, and sprayed from the time of normal coating layer formation. The amount can be reduced. The method of the present embodiment, the core material 6 surface by the reaction Li and M ² component than necessary can be suppressed to be a Li insufficient. Moreover, the Li compound layer 3 contains Li derived from the coating layer precursor 7, supplements Li on the surface of the core material 6, and can maintain good battery characteristics. Therefore, when the coating liquid is prepared, the Li / M ² molar ratio is preferably adjusted within the range of 0.1 or more and 1.00 or less. When the Li / M ² molar ratio is in the above range, a highly stable liquid, the coating layer precursor 7 and the Li compound layer 3 are obtained. On the other hand, if the Li / ^{M 2} molar ratio of 1.00 than, excess Li tends to carbonation during pyrolysis. In addition, when the Li / M molar ratio is less than 0.1, the desired characteristics described above cannot be obtained. The Li / M ² molar ratio of the coating liquid is also maintained in the lithium compound in the coating layer precursor 7 and the Li compound layer 3. Therefore, the lithium compound contained in the Li compound layer 3, Li and in Li / ^{M 2} molar ratio can be contained in a range of 0.1 to 1.00. The lithium compound preferably contains M ² in the range of 0.02 mass% or more and 2.0 mass% or less with respect to the entire base material 5.

2. Manufacturing method of coating liquid and positive electrode active material A specific manufacturing method of the coating liquid and positive electrode active material of the present embodiment will be described with reference to FIGS. FIG. 3 is a diagram illustrating an example of a method for producing a coating liquid, and FIG. 4 is a diagram illustrating an example of a method for producing a positive electrode active material.

  In order to form a stable Li compound layer, the present inventor pays attention to a coating solution used for forming a coating layer (precursor), and 1) reacts a Li alkoxide with a metal alkoxide at the coating solution stage to form a Li compound. It was found that 2) using a high-boiling alcohol (for example, an alcohol having a boiling point of 120 ° C. or higher) as a solvent used in the synthesis is effective in solving the problems of the prior art. That is, as a means for suppressing deterioration of surface resistance due to the formation of a coating layer (precursor) and a decrease in Li insertion / extraction during charge / discharge, a film is formed on the surface of the composite oxide particle, As a coating solution for covering with an oxide film, a Li alkoxide and a metal alkoxide solution, which are raw materials, are dissolved in a high boiling point alcohol, and for example, Li alkoxide and a metal alkoxide are synthesized by heating and refluxing over time. In addition, it was found that by causing an alcohol substitution reaction with a high-boiling alcohol, white cloudy precipitation does not occur even if left in the atmosphere for one day. This not only facilitates storage of the liquid and handling during spraying of the coating, but also synthesizes the Li compound by reacting Li alkoxide and metal alkoxide in the liquid in advance, so that a microscopically uniform Li compound can be obtained. A coating layer (precursor) having a very high uniformity of components can be produced.

  Furthermore, when the coating layer precursor is formed on the surface of the composite oxide particle, the sprayed coating liquid does not quickly dry, so that it can sufficiently penetrate into the particles before being dried and solidified, and the coating layer precursor. Is spread on the surface of the composite oxide particles when the particles are swung by the coating apparatus, and the uniformity of the film tends to be improved. Accordingly, it is possible to provide a coating liquid used for a positive electrode active material that can obtain high cycle characteristics without impairing initial battery performance such as charge / discharge characteristics inherent to lithium nickel composite oxide, and a simple manufacturing method thereof. .

As shown in FIG. 3, the coating liquid is selected from the group consisting of lithium alkoxide (Li alkoxide) and M ² (ie, Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W). and obtaining the alkoxide (M ² alkoxide) and are mixed with a high boiling alcohol and a hydrolysis inhibitor mixture containing at least one element) of the adding solvent and water to the mixture, Can be manufactured (step S1). Further, as shown in FIG. 4, the coating liquid is sprayed on the surface of the base material to form the coating layer precursor 7 (step S2), and the core material 6 after the formation of the coating layer precursor 7 is heat-treated. (Step S3), the coating layer precursor 7 and the surface of the core material 6 are reacted to obtain the composite oxide particle 2 having the Li compound layer 3. Details of each step will be described below.

As shown in FIG. 3, the method for producing the coating liquid is as follows: first, Li alkoxide, a monomer of M ² alkoxide or an oligomer thereof (“metal M alkoxide” in FIG. 3), a high-boiling alcohol, a hydrolysis inhibitor, Are mixed to obtain a mixed solution (step S1-1).

  The Li alkoxide is not particularly limited, and a known one can be used. The Li alkoxide can be produced, for example, by adding Li metal to an alcohol solvent so as to have an arbitrary concentration and heating and dissolving in an inert gas. As the Li alkoxide species, for example, -ethoxide, -methoxide, -isopropoxide, -butoxide monomer or oligomer thereof can be used. A commercially available Li alkoxide may be used. As commercially available products, lithium methoxide and lithium ethoxide are readily available.

Li alkoxide is highly hydrolyzable, and when working in the atmosphere, a cloudy precipitate may be generated instantaneously due to the humidity of the outside air. This is because the Li alkoxide is hydrolyzed and passes through a hydroxide product, and is carbonated by carbon dioxide gas in the outside air to generate an insoluble component, and a cloudy precipitate is generated by the insoluble component. In order to suppress this, the Li alkoxide is preferably handled in an inert gas atmosphere until the synthesis (reaction) with the M ² alkoxide is completed. The synthesis (reaction) of Li alkoxide and M ² alkoxide can be performed, for example, in a glove box under an inert gas atmosphere or in an environment where an inert gas is flowed into a synthesis container.

As the M ² alkoxide, in addition to -ethoxide and -methoxide, monomers of alkoxide such as -isopropoxide and -butoxide, or oligomers thereof can be used. Since this M ² alkoxide reacts remarkably with water like the Li alkoxide, the basic handling is preferably carried out in an inert gas atmosphere like the Li alkoxide.

The M ² alkoxide is not particularly limited as long as it causes a hydrolysis reaction by adding water, and a known one can be used. As the M ² alkoxide monomer, for example, monomers composed of -ethoxide, -methoxide, -isopropoxide, and -butoxide can be used. Of these, lithium methoxide, lithium ethoxide, lithium isopropoxide, lithium butoxide, magnesium methoxide, magnesium ethoxide, magnesium isopropoxide, aluminum ethoxide, aluminum isopropoxide, aluminum butoxide, calcium methoxy are preferable. Calcium ethoxide, titanium isopropoxide, titanium butoxide, vanadium methoxide, vanadium ethoxide, vanadium isopropoxide, vanadium butoxide, chromium methoxide, chromium ethoxide, chromium isopropoxide, chromium butoxide, manganese methoxide, Manganese ethoxide, manganese isopropoxide, manganese butoxide, zirconium ethoxide, zirconium isoprop Kishido, zirconium butoxide, niobium ethoxide, niobium isopropoxide, Niobubutokishido, molybdenum ethoxide, molybdenum isopropoxide, molybdenum butoxide, tungsten ethoxide, tungsten isopropoxide, can be used a monomer consisting of tungsten butoxide. Even oligomers obtained from these monomers can be used as long as they can be dispersed and dissolved in an alcohol solvent described later.

  As the high boiling point alcohol, those having a boiling point higher than that of 1-butanol (117 ° C.) can be used, and examples thereof include those having a boiling point of 120 ° C. or higher. The high boiling alcohol preferably has a boiling point of about 130 ° C. or higher and 150 ° C. or lower. When the boiling point is within this range, it is easier to obtain an effect and it is easy to handle. Examples of the high boiling point alcohol include 2-methyl-1-butanol (boiling point: 128 ° C.), 1 ethoxy-2-propanol (boiling point: 132 ° C.), 2-isopropoxyethanol (boiling point: 144 ° C.), and the like.

Generally, in order to increase the water resistance of a metal alkoxide, a chelating agent (for example, acetylacetone) is added to a solution containing the metal alkoxide to modify the metal alkoxide. By adding a chelating agent, the metal alkoxide is chelated. Since the chelated metal alkoxide is partially modified with a chelate ring, the hydrolysis reaction is suppressed. It is known that a solution containing a chelated metal alkoxide has high water resistance and storage stability as a yellow stable solution. However, if the hydrolysis reaction of the metal alkoxide is suppressed only by chelation, it is necessary to add a large amount of chelating agent, and the stability of the metal alkoxide increases by the added amount, but on the other hand, the surface of the composite oxide particle There was a problem that the adhesion when sprayed on the surface deteriorates or does not dissolve in the lower alcohol. In addition, when a large amount of acetylacetone is added as a chelating agent, acetylacetone is partially pyrolyzed and burned at around 300 ° C. during heat treatment, so that CO ₂ is generated, and the surface of the composite oxide particle is carbonated, causing discharge. There was a problem that the characteristics deteriorated.

Conventionally, when preparing a solution containing M ² alkoxide, the above-mentioned problem has been addressed by limiting the amount of chelating agent added to the amount of chelating one or two functional groups of the alkoxide. . However, since Li alkoxide is difficult to be chelated, it is necessary to add a large amount of chelating agent when the hydrolysis is suppressed only by the chelating agent. For this reason, the above problems are particularly likely to occur, and there has been a demand for a method for stabilizing a metal alkoxide, which replaces the conventional method of adding only a chelating agent.

In this embodiment, after dissolving Li alkoxide, a hydrolysis inhibitor (including a chelating agent) and M ² alkoxide in a high-boiling alcohol, the mixture is refluxed to prepare a mixed solution, whereby the functional group of the alkoxide is converted to alcohol. Simultaneously with the substitution reaction, the liquid can be stabilized by synthesizing two kinds of alkoxides. Li and M ² alkoxides can be dissolved in various solvents other than high-boiling alcohols. For example, when dissolved only in lower alcohols, the properties thereof do not change and an unstable state that is easily hydrolyzed is present. Continue.

For example, a mixed solution is produced by adding Li alkoxide (for example, Li methoxide) into a high-boiling point alcohol (for example, 2-methyl-1-butanol), refluxing for 1 hr, and chelating one functional group with acetylacetone. The M ² alkoxide (for example, Al isopropoxide) that has been converted is further added and refluxed again for 1 hr to obtain a synthesis solution. At this time, if Al isopropoxide is directly added to a solution in which Li methoxide is dissolved, white turbidity may occur due to the influence of the pH of Li ions. For this reason, it is preferable to employ a method in which Al isopropoxide is chelated by one functional group and then charged into the Li solution. If the addition amount of the chelating agent is an amount that can chelate the Al alkoxide, the influence on Li is small. The reflux time can be about 0.3 to 4 hours, preferably about 0.5 to 2 hours.

  High-boiling point alcohol is usually more thermally decomposable than high-boiling point organic solvents such as chelating agents, and decomposes on the low temperature side, so the battery by carbonation of the composite oxide particle surface due to the coating liquid containing high-boiling point alcohol. There is little effect on the characteristics. For example, the thermal decomposition temperature of acetylacetone is around 280 ° C., but high-boiling alcohol can be thermally decomposed at 200 ° C. or lower.

In addition, high-boiling point alcohol has not only high thermal decomposability, but also high-boiling point alcohol (solvent) itself exhibits hydrophobicity. By converting this property to alkoxide, the stability of Li and M ² alkoxide itself to water can be improved. The property can be further modified. If an alcohol having a boiling point that is too high is used, it takes time to circulate, and therefore, the upper limit of the boiling point of the high boiling alcohol is 120 ° C. or higher, preferably 130 ° C. higher than 1-butanol (117 ° C.). A temperature of from about 150 ° C. to about 150 ° C. is easy to obtain an effect and easy to handle.

Li alkoxide, M ² alkoxide, a mixed solution obtained by mixing the system under the above high boiling alcohols and hydrolysis inhibitor, stability is increased, be placed if standing about 1 day to 2 days in air No cloudy precipitation occurs. The mixed solution can also contain a solvent other than the high-boiling point alcohol as long as the above-described effects of the high-boiling point alcohol are not impaired. For example, the mixed alcohol is a lower alcohol or a higher alcohol having 5 or more carbon atoms that is a hydrophobic solvent. And acetates. In the case of higher alcohols or acetates having 5 or more carbon atoms, it is preferably added in an amount of 10% by mass or less based on the entire mixture. However, these solvents have a strong odor of their own and an irritating odor from the decomposition gas, and problems are likely to occur in exhaust gas treatment. The mixed solution does not use toluene, THF, methyl cellosolve, ethyl cellosolve or the like that is generally used as a solvent. This is because these solvents are highly harmful and have a high risk of spray drying.

Although the high boiling point alcohol can be used as the total solvent of the coating solution, it is preferably used only when modifying the alkoxide from the viewpoint of the price of the high boiling point alcohol and the drying rate. Specifically, as described above, it can be used when mixing Li alkoxide and M ² alkoxide. The obtained liquid mixture can be diluted to a low concentration using a solvent such as a lower alcohol so that it can be easily sprayed. As a solvent for dilution, a lower alcohol that is easily miscible with a high-boiling alcohol is preferable. Examples of the lower alcohol include ethanol and 2-propanol. The high boiling point alcohol is preferably contained in the mixed solution in the range of 10% to 40%.

The coating liquid can easily control the hydrolysis reaction by adding a high-boiling point alcohol or a chelating agent to the raw materials Li and M ² alkoxide, and performing an alcohol exchange reaction or chelation. This is performed in order to improve the adsorptivity to the particle surface by introducing a hydrolyzable group (hydroxyl group) by forming a partially hydrolyzed oligomer of a part of the functional group of the metal alkoxide. When a chelating agent is used as the hydrolysis inhibitor, the chelating agent is preferably at least one selected from aminocarboxylic acids, salts thereof, or diketones. Among these, acetylacetone is more preferable. As other chelating agents, known ethyl acetoacetate, nitrilotriacetic acid, methylglycine diacetic acid, dicarboxymethylglutamic acid, L-aspartic acid and the like, or salts thereof can be substituted, but acetylacetone having excellent thermal decomposability is used. preferable. For example, among the four functional groups (butoxy group) of zirconium tetrabutoxide, the stability is greatly improved by modifying it by adding the same number of moles of acetylacetone to compensate for one or more functional groups. Is done.

In order to perform a sufficient modification reaction at the time of chelation, for example, an alkoxide monomer is dissolved in a lower alcohol such as 2-propanol to prepare a solution having a concentration of 60% by mass or less, and a chelating agent such as acetylacetone is contained therein. Is gradually added, followed by heating at 20 ° C. or higher and 100 ° C. or lower and 0.5 hour or longer and 4 hours or shorter, to obtain a chelating solution of M ² alkoxide monomer. Such an operation promotes the modification reaction and increases the stability to water.

Furthermore, it is preferable to add water for hydrolysis to the mixed solution in addition to a solvent such as a lower alcohol. The addition of water is intended to be added in order to partially hydrolyze Li and a metal M ² alkoxide, is highly effective idea in addition 10-30% relative alkoxide weight. Since alkoxide is not adsorbed on the particle surface unless it is partially hydrolyzed, moisture is necessary. Alkoxide is adsorbed by causing hydrogen bonds with hydroxyl groups on the particle surface by hydrolysis of a part of functional groups, and by repeating this, a three-dimensional deposit is formed to form a film. For this reason, it is only necessary to add an amount of water sufficient to hydrolyze a part of the functional group that is not chelated or hydrophobized, and adding more than this will affect the particles themselves and cause deterioration. There is also. If the amount of water is an appropriate amount, it is consumed during the hydrolysis reaction, so there is no effect on the particles. Furthermore, if the Li alkoxide and the transition metal alkoxide are not completely synthesized, one of the alkoxides is actively hydrolyzed by the added water, resulting in cloudy precipitation.

  In the partial hydrolysis reaction, it is preferable to add 5% by mass to 50% by mass, preferably 15% by mass to 30% by mass of water with respect to 100% by mass of the metal alkoxide, and after adding water. Further heating is performed to complete the partial hydrolysis reaction. If the water content exceeds 50% by mass, hydrolysis proceeds too rapidly and gelation tends to occur, and if it is 5% by mass or less, the hydrolysis amount is small and the effect is poor.

  As shown in FIG. 4, the base material 5 made of composite oxide particles is coated by spraying the coating liquid obtained by the above-described method, and the core material 6 having the coating layer precursor 7 formed on the surface is obtained. (Step S2), and then heat treatment (Step S3). Hereinafter, each step will be described.

(Formation of coating layer precursor)
The coating layer precursor is formed by mixing or spraying the coating liquid and the base material 5 to deposit the precursor fine particles contained in the coating liquid on the surface of the core material 6.

The lithium nickel composite oxide particles used as the base material 5 have a general formula Li _t Ni _1-xy Co _x M _y O ₂ (where M is Mg, Al, Ca, etc.) in order to improve battery characteristics. , Ti, V, Cr, Mn, Zr, Nb, Mo and W, at least one element selected from the group consisting of 0.97 ≦ t ≦ 1.05, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15) is preferably used. Such composite oxide particles have a property of being liable to elute lithium, although the excess of Li is small but still sensitive to moisture. In addition, the composite oxide particles 2 in which the lithium compound layer 3 is formed using the coating liquid of the present embodiment suppresses gelation of the paste composition by suppressing elution of lithium by moisture, and two When used as a positive electrode for a secondary battery, the initial discharge amount is not lowered, and high cycle characteristics are obtained over the long term.

The amount of M ² when coated by spraying is adjusted to be in the range of 0.01 to 2.0% by mass with respect to 100% by mass of the entire core material in the analysis. If the amount of the precursor fine particles is too small, a sufficient amount of the reaction layer may not be generated when the surface layer is formed.

  Any coating method may be used as long as the surface of the base material 5 can be uniformly coated. For example, a method of forming a film by spraying the coating liquid while allowing the base material particles to flow as in a rolling flow device is more preferable. However, if the coating liquid according to the present invention is used, slight fluctuation of the particles may occur. Uniform coating can be easily performed if possible simple functions and spraying and drying.

  Any method may be used for stirring as long as the particles are not crushed, crushed, or damaged by impact, and a simple apparatus can be used. Other than the rolling flow device, a horizontal drum type stirring container such as a type in which the container itself in which particles are put rotates or a type in which a stirring blade is required inside the container is preferable. The stirring may be performed so long as the particles are oscillated. If the drum-type 50 L stirring vessel is used, the operation can be performed at a low speed of 100 rpm or less, so that damage to the particles is reduced.

  A spray nozzle is used for spraying. A single fluid nozzle may be used, but the coating uniformity is inferior because the mist diameter is large and the spray rate cannot be controlled in a small amount with respect to the capacity of a small apparatus of 20 L to 50 L. The mist diameter is preferably a fine spray consisting of several μm, and from this point, a two-fluid nozzle utilizing gas pressure is preferred. The spraying is controlled by the spraying amount and the spraying speed. For example, if the apparatus capacity is 20 L to 50 L, the spraying amount is sprayed on the particles being stirred at a spraying amount of about 3 to 50 g / min and the spraying speed 0.2 to 3 L / min. be able to.

  Drying after the coating of the coating layer precursor is performed by heating the outside of the device container, and it is preferable to dry at 40 to 100 ° C. at the actual temperature. There is also a method of introducing hot air inside, but there are methods of heating the outside of the container because it becomes difficult to recover the alcohol solvent by blowing air and the filter provided at the exhaust port becomes clogged easily due to the rising of particles. Applied. The outside of the container is heated by providing a hot wire heater, a dryer, and a temperature control jacket. When the alcohol solvent is recovered, alcohol vapor generated during drying can be recovered by providing a vacuum recovery device having a cold trap at the exhaust port, a dust collector with a box containing activated carbon adsorbent, or the like. Since the solvent used in the present invention contains a high-boiling point alcohol, it is difficult to dry and the spraying speed is relatively fast. Therefore, the actual temperature setting is particularly preferably 60 to 90 ° C. If the actual temperature is too low, the sprayed liquid is agitated without being dried, and therefore, the occurrence of agglomeration due to adhesion between powders, adhesion to the apparatus wall surface and agitation blades, and the uniformity of the film is greatly reduced. On the other hand, when it is dried at a high temperature exceeding 110 ° C., the solvent is volatilized too early, and the peeling of the film and the uniformity of the film are lowered.

  Drying is performed by volatilization of the solvent by heating during processing (drying during processing), and as a result, particles in a free-flowing state are obtained. However, organic substances, solvents, and moisture in the film may not be completely removed only by drying the treatment. Therefore, it is preferable to dry the particles taken out from the coating apparatus again in a vacuum. When the drying temperature is set to 110 to 150 ° C., the residue in the film can be removed. When the drying temperature exceeds 200 ° C., the core material particles tend to deteriorate. The drying time is preferably 1 to 24 hours. If the drying time is less than 1 hour, drying may be insufficient. If the drying time exceeds 24 hours, productivity decreases.

(Heat treatment)
The heat treatment is a step in which the coating layer precursor 7 is heat-treated to cause a reaction with the surface of the core material 6 (step S3). The coating layer precursor 7 formed on the surface of the core material 6 described above is firmly bound (bonded) to the surface of the core material 6 by heat treatment at 250 ° C. or higher and 300 ° C. or lower, and most of the existing in the film is unnecessary. As a result, a film close to an oxide is formed, and the film quality is improved. Further, the lithium compound layer 3 (covering layer 3a, surface layer portion 3b) formed by heat treatment at a high temperature is stronger than the covering layer precursor 7 and improves water resistance and further suppresses gelation. Increases the effect. At the stage of heat treatment at 300 ° C. or lower, no significant reaction has occurred in the coating film at the interface of the core material 6. On the other hand, since the coating layer 3a obtained at this stage is an oxide, the initial discharge capacity tends to decrease due to the deterioration of the surface resistance. In order to avoid this, in the conventional technique, it was necessary to make a coating layer as thin as about 5 nm so as not to prevent insertion and release of Li during charging and discharging. The conventional coating layer is thin and increases uniformity, thereby maintaining a balance between the initial charge capacity and water resistance and suppressing defects in the film (occurrence of voids due to decomposition of organic matter) caused by the thinness. However, on the other hand, in the manufacturing process, it was necessary to treat the coating solution with a dilute solution over time. Since the coating liquid used in the present embodiment contains Li, Li is lost from the core material 6 even when it is subjected to high temperature treatment, and the amount of Li does not decrease. The heat treatment temperature is preferably 400 ° C. or higher and 700 ° C. or lower. If it exceeds 700 ° C., the volatilization of Li starts, which may cause a reduction in discharge capacity. If the temperature is lower than 400 ° C., the cycle characteristics may not be improved because organic substances cannot be removed or the reaction of the coating film is not sufficient.

The atmosphere during the heat treatment is preferably oxygen gas. When heat treatment is performed by introducing air gas, the discharge capacity may decrease due to moisture or CO ₂ gas mixed in the gas. By using pure oxygen gas as the atmosphere during the heat treatment, organic substances can be decomposed smoothly.

  Residues contained in the lithium compound layer 3 can be detected mainly by analyzing carbon. The control of the carbon content is performed according to the conditions during the heat treatment, and is suppressed by controlling the amount of the mixture introduced into the furnace used for the heat treatment, the heat treatment temperature, the flow rate of oxygen gas supplied to the furnace, and the temperature rising rate. be able to.

As a condition for heat-treating the core material 6 having the coating layer precursor 7, the value obtained by the following formula (1) is preferably 60.0 (g / min) or more and 434.8 (g / min) or less. More preferably, it is in the range of 100 (g / min) to 217 (g / min).
[Mixture amount (g) / furnace volume (L)] × oxygen gas introduction amount (L / min) (1)
By carrying out in these ranges, the carbon content of the positive electrode active material is 0.01 to 0.2% by mass with respect to 100% by mass of the entire positive electrode active material, and the water content is 0.01 to 0.15. A film quality of mass% can be obtained. If the treatment temperature is 300 ° C. or lower, the effect can be obtained sufficiently even if the oxygen gas flow rate is suppressed. However, when performed at a high temperature, the LiNiO ₂ -based positive electrode active material causes Li scattering and oxygen deficiency. In order to avoid this, it is necessary to flow a large amount of oxygen gas. Thereby, the residual amount of organic matter can be further reduced.

  By controlling the heat treatment conditions within the above range, the carbon content of the coating film can be reduced. In addition, if it is in the range of the said conditions, the same effect can be acquired by changing arbitrarily the ratio of the furnace internal volume, the processing amount of a mixture, and oxygen gas flow rate.

  For example, a mixture of 1000 g to 2000 g filled in an alumina container is put into a heat treatment furnace having a volume of 50 L, and pure oxygen gas is introduced at 3 L / min to 10 L / min (gas pressure 0.1 MPa), The temperature is raised from 3 ° C./min to 20 ° C./min, preferably from 5 ° C./min to 10 ° C./min, from 300 ° C. to 700 ° C. from 0.5 hours to 5 hours, preferably from 400 ° C. to 600 ° C. By maintaining at 0.5 ° C. or lower for 0.5 hour or longer and 2 hours or shorter, a higher performance positive electrode active material can be obtained.

  When the temperature dependency of the initial discharge capacity is also investigated, even if the heat treatment temperature is 300 ° C., the surface resistance does not increase significantly due to the effect of Li content, and therefore the initial discharge capacity does not tend to decrease greatly. When the temperature is 400 ° C. or higher, the core material 6 and the coating layer 3a start to react, and mutual diffusion with the core material is performed, whereby the Li compound layer 3 is generated as the surface layer portion 3b on the particle surface. In parallel with this, the surface resistance is close to that when uncoated, and the initial discharge capacity is recovered. On the other hand, since water resistance is improved, there is no problem of gelation.

  Whether or not organic substances are removed can be determined by measuring the amount of TC by ICP analysis. The amount of C at this time includes not only organic substances but also those produced by carbonation. The remaining amount of C is preferably 0.03% by mass or less with respect to the entire composite oxide particles, and if more than this is included, the properties are affected.

  The generation of the surface layer 3b can be confirmed using TEM, TEM-EDS, TOF-SIMS, SEM-EDS, and ICP analysis. For example, when a coating solution containing Li—Nb—O is coated on the surface of the base material 5 so as to be 30 nm and the concentration gradient is analyzed in the depth direction by changing the heat treatment temperature, a high concentration of Nb is mainly obtained at 300 ° C. However, when the temperature reaches 600 ° C., the coating layer 3a decreases and reaches 100 nm from the surface of the composite oxide particle 2 in the depth direction. 50% of the Nb element is detected at the position. As a result, the increase in surface resistance observed at 300 ° C. is restored to 600 ° C., and the discharge capacity is improved as in the case of uncoated. On the other hand, when the heat treatment temperature exceeds 700 ° C., the diffusion of Nb further spreads, and the Nb element becomes 10% or less at a position of 500 nm in the depth direction from the surface of the composite oxide particle 2. Thereby, the surface layer effect is weakened, and the improvement effect on water resistance and cycle characteristics is lowered. Therefore, it is important that the constituent elements present as the coating film are diffused into the core material 6 and remain (stay) in the vicinity of the surface layer of the core material 6 at a constant high concentration.

  The heat treatment time is preferably 0.5 hours or more and 5 hours or less, more preferably 0.5 hours or more and 2 hours or less, after raising the temperature to the predetermined temperature. Thereby, it is possible to sufficiently adhere to the surface of the composite oxide particle 2 and remove an unnecessary organic solvent. If the heat treatment time is less than 0.5 hour, the organic solvent may remain. In addition, when the heat treatment time exceeds 5 hours at high temperature, oxygen deficiency from the base material 5 particles tends to occur, and the initial discharge capacity may be reduced. The atmosphere during the heat treatment is preferably a pure oxygen atmosphere so that the surface of the core material 6 or the composite oxide particles 2 is not reduced.

  As the electric furnace to be heat-treated, it is particularly preferable to use a muffle furnace. By constantly circulating gas in a state where pure oxygen is filled in the furnace, an oxygen-deficient state due to decomposition of organic substances or the like does not occur during the heat treatment, and the core The material particle surface layer can be brought into a sound oxidation state.

  The above-described coating method of the surface of the composite oxide particles can be applied to almost all positive electrode active materials. In addition to the lithium nickel composite oxide as a base material used as a raw material, for example, lithium cobalt composite oxidation Particles made of an oxide, lithium nickel cobalt manganese composite oxide, lithium manganese composite oxide, or the like can be used. Further, the particle size distribution of the obtained positive electrode active material is maintained substantially the same before and after coating. Therefore, the average particle diameter of the base material 5 before coating may be the same as that of the positive electrode active material 1 to be finally obtained, preferably 3 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less. More preferred. Here, the average particle diameter is a median diameter (d50), and can be measured by a particle size distribution measuring apparatus based on a laser diffraction / scattering method.

2. Non-aqueous electrolyte secondary battery An example of the non-aqueous electrolyte secondary battery of the present embodiment will be described in detail below for each component. The non-aqueous electrolyte secondary battery is composed of components such as a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and the above-described positive electrode active material of the present invention is used for the positive electrode, like a general lithium ion secondary battery. It is what. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery according to this embodiment includes various modifications and improvements based on the knowledge of those skilled in the art including the following embodiment. Can be implemented. Moreover, the use of the nonaqueous electrolyte secondary battery according to the present embodiment is not particularly limited.

(Positive electrode)
The positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described. The powdered positive electrode active material of the present invention, a conductive material, and a binder are mixed, and if necessary, a target solvent such as activated carbon and viscosity adjustment is added, and this is kneaded and mixed with a positive electrode mixture paste ( A paste-like composition) is prepared. The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery.

  When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass, respectively, as in the case of the positive electrode of a general lithium secondary battery. It is desirable that the content is 1 to 20% by mass and the content of the binder is 1 to 20% by mass.

  The obtained positive electrode mixture paste (paste-like composition) is applied to the surface of a current collector made of, for example, aluminum foil, and dried to scatter the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production. However, the manufacturing method of the positive electrode is not limited to the above-described examples, and may depend on other methods.

  In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used. Examples of binders (binders) include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as ethylene propylene diene rubber, polypropylene, and polyethylene, styrene butadiene, and cellulose resins. Polyacrylic acid or the like can be used.

  If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphosphoamide, etc. can be used as the solvent. . Moreover, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(Negative electrode)
For the negative electrode, metallic lithium, lithium alloy, or the like, and a negative electrode mixture made by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, and adding a suitable solvent, such as copper The metal foil current collector is coated, dried, and compressed to increase the electrode density as necessary.
Examples of the negative electrode active material include a fired organic compound such as natural graphite, artificial graphite, and a phenol resin, a powdery carbon material such as coke, and an oxide such as lithium / titanium oxide (Li ₄ Ti ₅ O ₁₂ ). Materials can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride can be used as in the case of the positive electrode, and the active material and the solvent for dispersing the binder include N-methyl-2-pyrrolidone. Organic solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many fine holes can be used.

(Non-aqueous electrolyte)
The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.
As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used.
Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(Battery shape and configuration)
The shape of the lithium secondary battery according to the present invention composed of the positive electrode, negative electrode, separator, and non-aqueous electrolyte described above can be various, such as a cylindrical type and a laminated type.
In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolyte solution. The positive electrode current collector and the positive electrode terminal that communicates with the outside, and the negative electrode current collector and the negative electrode terminal that communicates with the outside are connected using a current collecting lead or the like. The battery having the above configuration can be sealed in a battery case (container) to complete the battery.

EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited at all by these Examples. In addition, each evaluation in the Example of this invention was implemented with the following method.
(Evaluation method)
1. Various physical properties of positive electrode active material (1) Reaction of coating layer precursor by heat treatment and measurement of diffusion state of constituent elements Put the coated particles in a φ16 mm mold and compact it at 4 MPa. The concentration distribution in the depth direction was determined with TOF-SIMS (PHI TOFII manufactured by ULVAC-PHI, Inc., attached with a cesium sputtering gun).
(2) Coating layer composition The composition was determined by ICP analysis.
(3) Water resistance evaluation of positive electrode active material Water resistance was evaluated by adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C and stirring, and measuring the pH after 10 minutes.
(4) Gelation Evaluation Gelation evaluation was performed using 9.5 g of a positive electrode active material, 0.5 g of vinylidene fluoride (PVDF) as a binder, 5.5 g of N-methyl-2-pyrrolidinone (NMP) as a solvent, and water 0 .2 g was made into a slurry by a self-rotating kneading machine, and then statically stored at 24 ° C. for 4 days, and the gelation state was confirmed by visual observation.
(5) Preservability of the mixed solution The Li-M ² metal mixed solution was left in the atmosphere of 24 ° C x 60% RH for 1 day to evaluate whether there was a cloudy precipitate.

2. Battery manufacturing and battery characteristics evaluation (Battery manufacturing)
For the evaluation of the positive electrode active material, a 2032 type coin battery CBA (hereinafter referred to as a coin type battery) shown in FIG. 5 was used. As shown in FIG. 5, the coin-type battery includes a case CA and an electrode EL accommodated in the case CA. The case CA has a positive electrode can PC that is hollow and open at one end, and a negative electrode can NC that is disposed at the opening of the positive electrode can PEL. When the negative electrode can NC is disposed at the opening of the positive electrode can PC. A space for accommodating the electrode EL is formed between the negative electrode can NC and the positive electrode can PC.

  The electrode EL is composed of a positive electrode PE, a separator SE, and a negative electrode NE, and is stacked so as to be arranged in this order. The positive electrode PE is in contact with the inner surface of the positive electrode can PC, and the negative electrode NE is in contact with the inner surface of the negative electrode can NC. Thus, it is accommodated in the case CA. The case CA includes a gasket GA, and relative movement is fixed by the gasket GA so that the positive electrode can PC and the negative electrode can NC are kept in a non-contact state. Further, the gasket GA also has a function of sealing the gap between the positive electrode can PC and the negative electrode can NC so as to block the inside and outside of the case CA in an airtight and liquidtight manner.

The coin-type battery was manufactured as follows.
First, 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) are mixed, and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. A positive electrode PE was prepared. The produced positive electrode PE was dried at 120 ° C. for 12 hours in a vacuum dryer. Using the positive electrode PE, the negative electrode NE, the separator SE, and the electrolytic solution, the above-described coin-type battery was fabricated in an Ar atmosphere glove box in which the dew point was controlled at −80 ° C. As the negative electrode NE, a negative electrode sheet in which graphite powder with an average particle diameter of about 20 μm punched into a disk shape with a diameter of 14 mm and polyvinylidene fluoride were applied to a copper foil was used. As the separator SE, a polyethylene porous film having a film thickness of 25 μm was used. As the electrolytic solution, an equivalent mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte was used.

(Evaluation of battery characteristics)
The initial discharge capacity, the positive electrode resistance and the cycle characteristics showing the performance of the manufactured coin-type battery were evaluated as follows.
The initial discharge capacity is about 24 hours after the coin-type battery is manufactured, then charged at 0.05 C to a cut-off voltage of 4.3 V, discharged after 1 hour of rest and discharged to a cut-off voltage of 3.0 V Was defined as the initial discharge capacity.

  The positive electrode resistance was evaluated by the AC impedance method. That is, a coin-type battery was charged at a charging potential of 4.1 V, and measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain a Nyquist plot. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacity, and the characteristic curve indicating the positive electrode resistance and its capacity, the fitting calculation was performed using an equivalent circuit based on this Nyquist plot, and the positive resistance The value (Ω) was calculated.

Cycle characteristics evaluation was made after leaving a coin-type battery for about 24 hours, charging to a cutoff voltage of 4.3 V at 0.5 C, and after discharging for 1 hour, discharging to a cutoff voltage of 3.0 V. This was repeated 200 times as one cycle. As an evaluation method at this time, the capacity maintenance ratio is obtained. The discharge capacity obtained in the first cycle is defined as 100%, and is expressed by the following formula.
Capacity maintenance ratio (%) = [discharge capacity at the 200th cycle / discharge capacity at the first cycle] × 100

Example 1
(Preparation of lithium nickel composite oxide powder)
Lithium nickel composite oxide powder obtained by a known technique was used as a base material. That is, it is expressed as Li _0.99 Ni _0.82 Co _0.15 Al _0.03 O ₂ by mixing nickel oxide powder containing Ni and Co and Al and lithium hydroxide and firing. Lithium nickel composite oxide powder was obtained. This lithium nickel composite oxide powder had an average particle diameter D50 of 11.9 μm and a specific surface area of 0.41 m ² / g.

(Preparation of Li-Ti mixed solution)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. In this, 5 ml of methanol and 0.057 g (0.0015 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added, followed by dissolution while introducing Ar gas to obtain a Li solution. In another container, 10 ml of 2-propanol and 1.5 g (0.0052 mol) of Ti isopropoxide (manufactured by Kanto Chemical) were added, and 0.3 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred, and the Ti solution was stirred. Obtained. Next, 30 ml of 2-methyl-1-butanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the Li solution, and the Ti solution was added thereto, and refluxed for 1 hour while introducing Ar gas to obtain a mixed solution a. . When the obtained mixed solution a was returned to room temperature, a transparent yellow mixed solution b could be produced. A part of this mixed liquid b was taken out, and when hydrolyzability was confirmed immediately after dropping one drop of water, no cloudy precipitation was produced and a transparent liquid was maintained.
(Preparation of coating solution)
100 ml of 2-propanol for dilution and 0.15 g of water for partial hydrolysis were added to the mixed solution b to obtain a coating solution in which lithium and titanium reacted (synthesized).

(Formation of surface layer)
Separately, 600 g of the base material is used, and stirring and drying are alternately repeated using a rocking mixer (manufactured by Aichi Electric Co., Ltd.) with a dryer at an actual temperature of 60 ° C., and the total amount of the above coating liquid is sprayed over 160 minutes to form a coating layer precursor. A core material having (coating film) was obtained. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. 200 g of this dried product was heated up to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min using a 30 L muffle furnace, and held for 0.5 hour to obtain a positive electrode active material Got. Tables 1 and 2 show the evaluation results and the like of the positive electrode active material.

(Example 2)
(Preparation of Li-Al mixed liquid)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 5 ml of methanol and 0.019 g (0.0005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas.
In another container, 1.02 g (0.005 mol) of Al isopropoxide (manufactured by Kanto Chemical) was dissolved in 10 ml of 2-propanol, and 0.4 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred. Next, 30 ml of 2-methyl-1-butanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the produced Li solution, and the produced Al solution was added thereto, and refluxed for 1 hour while introducing Ar gas. When the liquid was returned to room temperature, a transparent yellow synthetic liquid (mixed liquid) could be produced. A part of this synthetic solution was taken out, and when hydrolyzability was confirmed after dropping one drop of water, white turbid precipitation did not occur and a transparent solution was maintained.
(Preparation of coating solution)
To the synthesis solution, 100 ml of 2-propanol for dilution and 0.1 g of water for partial hydrolysis were added to obtain a coating solution in which lithium and aluminum were synthesized.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used, and stirring and drying were alternately repeated while using a rocking mixer (manufactured by Aichi Electric) at an actual temperature of 50 ° C. with a dryer, and the coating liquid prepared in Example 4 was applied for 160 minutes. The entire amount was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain the positive electrode active material. Obtained. Tables 1 and 2 show the evaluation results and the like of the positive electrode active material.

(Example 3)
(Preparation of Li-Nb mixed solution)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol and 0.056 g (0.0015 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas.
In another container, 1.59 g (0.005 mol) of Nb ethoxide (manufactured by Wako Pure Chemical Industries) was dissolved in 10 ml of 2-propanol, and 0.3 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred. Next, 30 ml of 2-methyl-1-butanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the produced Li solution, and the produced Nb solution was added thereto, and refluxed for 1 hour while introducing Ar gas. When the liquid was returned to room temperature, a transparent yellow synthetic liquid could be produced. A part of this synthetic solution was taken out, and when hydrolyzability was confirmed after dropping one drop of water, white turbid precipitation did not occur and a transparent solution was maintained.
(Preparation of coating solution)
Into the synthesis solution, 100 ml of 2-propanol for dilution and 0.15 g of water for partial hydrolysis were added to obtain a coating solution in which lithium and niobium were synthesized.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used, and stirring and drying were alternately repeated while using a rocking mixer (manufactured by Aichi Electric) at an actual temperature of 50 ° C. with a dryer, and the coating prepared in Example 6 was applied for 160 minutes. The whole liquid was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain the positive electrode active material. Obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

Example 4
(Preparation of Li-Mo mixture)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol and 0.056 g (0.0015 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas.
In another container, 1.60 g (0.005 mol) of Mo ethoxide (manufactured by Wako Pure Chemical Industries) was dissolved in 10 ml of 2-propanol, and 0.4 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred. Next, 30 ml of 1 ethoxy-2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the prepared Li solution, and the prepared Mo solution was added thereto, and refluxed for 1 hour while introducing Ar gas. When the liquid was returned to room temperature, a transparent yellow synthetic liquid could be produced. A part of this synthetic solution was taken out and one drop of water was dropped to confirm the hydrolyzability. As a result, white turbid precipitation did not occur and a transparent solution was maintained.
(Preparation of coating solution)
To the synthesis solution, 100 ml of 2-propanol for dilution and 0.15 g of water for partial hydrolysis were added to obtain a coating solution in which lithium and molybdenum were synthesized.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 is used, and stirring and drying are alternately repeated while using a rocking mixer (manufactured by Aichi Electric) at an actual temperature of 50 ° C. with a dryer, and the coating prepared in Example 8 is applied over 160 minutes. The whole liquid was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain the positive electrode active material. Obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Example 5)
(Preparation of Li-Ti-Mg mixed solution)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 15 ml of methanol, 0.11 g (0.003 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries) and 0.06 g (0.0007 mol) of Mg methoxide were added to this, and then dissolved while introducing Ar gas. It was.
In another container, 2.5 g (0.0087 mol) of Ti isopropoxide (manufactured by Kanto Chemical) was added to 10 ml of 2-propanol, and then 0.5 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred. Next, 30 ml of 2-methyl-1-butanol (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the produced Li—Mg solution, and the produced Ti solution was added thereto and refluxed for 1 hour while introducing Ar gas. When the liquid was returned to room temperature, a transparent yellow synthetic liquid could be produced. A part of this synthetic solution was taken out, and when hydrolyzability was confirmed after dropping one drop of water, white turbid precipitation did not occur and a transparent solution was maintained.
(Preparation of coating solution)
Into the synthesis solution, 100 ml of 2-propanol for dilution and 0.15 g of water for partial hydrolysis were added to obtain a coating solution in which lithium and titanium were synthesized.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used and stirred for 40 minutes while stirring at an actual temperature of 60 ° C. and an air flow rate of 0.3 m ³ / hour using a rolling fluidizer (manufactured by POWREC Co., Ltd., MP-01). Then, the entire coating liquid produced in Example 10 was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain a positive electrode active material. Obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 1)
(Li preparation)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol and 0.19 g (0.005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas. When this Li solution was stirred in addition to 140 ml of 2-propanol for dilution, the operation was stopped because white turbidity occurred with the passage of time and a precipitate was observed at the bottom of the container.

(Comparative Example 2)
(Preparation of Li liquid with chelating agent added)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol, 0.19 g (0.005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries) and 0.6 g of acetylacetone were added thereto, followed by dissolution while heating at 50 ° C. while introducing Ar gas. . In this Li solution, 140 ml of 2-propanol for dilution was added and stirred to obtain a coating solution. When a drop of water was added to see a partial hydrolysis reaction in a part of the coating solution, a cloudy precipitate was gradually formed. Therefore, the coating solution was used as it was without partial hydrolysis.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used and stirred for 40 minutes while stirring at an actual temperature of 60 ° C. and an air flow rate of 0.3 m ³ / hour using a rolling fluidizer (manufactured by POWREC Co., Ltd., MP-01). Then, the entire coating liquid prepared in Comparative Example 2 was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Many peeled white powders were observed on the surface of the dried product.
Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain a positive electrode active material. Obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 3)
(Preparation of mixed liquid of Li liquid and Al liquid)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol and 0.019 g (0.0005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas.
In another container, 1.02 g (0.005 mol) of Al isopropoxide (manufactured by Kanto Chemical) was dissolved in 10 ml of 2-propanol.
First, the Li solution was added to 130 ml of 2-propanol for dilution and stirred, and then the prepared Al solution was added. The operation was stopped because white turbidity occurred with the passage of time and a precipitate was observed at the bottom of the container.

(Comparative Example 4)
(Preparation of mixed liquid of Li liquid and Nb liquid)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol and 0.019 g (0.0005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries, Ltd.) were added thereto, and then dissolved while introducing Ar gas. In another container, 1.59 g (0.005 mol) of Nb ethoxide (manufactured by Wako Pure Chemical Industries) was dissolved in 10 ml of 2-propanol, and 0.3 g of acetylacetone (manufactured by Kanto Chemical) was added and stirred. First, the Li solution was added to 130 ml of 2-propanol for dilution and stirred, and then the prepared Nb solution was added. No white turbidity was observed even when allowed to stand due to the influence of acetylacetone added to the Nb alkoxide, but when 0.15 g of water for partial hydrolysis was added, it immediately began to become cloudy, so no water was added to the coating solution. Decided to spray on.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used and stirred for 40 minutes while stirring at an actual temperature of 60 ° C. and an air flow rate of 0.3 m 3 / hour using a rolling fluidizer (manufactured by POWREC Co., Ltd., MP-01). The entire coating liquid prepared in Comparative Example 5 was sprayed. On the way, the tip of the spray nozzle that was spraying the liquid began to become cloudy and clogged, and because it became impossible to spray normally, the operation was stopped.

(Comparative Example 5)
(Preparation of mixed liquid of Li liquid and Nb liquid)
A four-neck separable cover was attached to the round bottom separable flask, and a cooler, two separatory funnels, and a gas introduction tube were connected. 10 ml of methanol, 0.019 g (0.0005 mol) of Li methoxide (manufactured by Wako Pure Chemical Industries) and 0.6 g of acetylacetone were added thereto, followed by dissolution at 50 ° C. while introducing Ar gas. In a separate container, 1.59 g of Nb ethoxide (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.5 g of acetylacetone were added to 10 ml of 2-propanol and dissolved, and then stirred at 50 ° C. First, the Li solution was added to 130 ml of 2-propanol for dilution and stirred, and then the prepared Nb solution was added. To this, 0.15 g of water for partial hydrolysis was added to form a coating solution.

(Formation of surface layer)
Separately, 600 g of the base material prepared in Example 1 was used and stirred for 40 minutes while stirring at an actual temperature of 60 ° C. and an air flow rate of 0.3 m ³ / hour using a rolling fluidizer (manufactured by POWREC Co., Ltd., MP-01). Then, the entire coating liquid prepared in Comparative Example 7 was sprayed to obtain a coating film. Further, drying was carried out in a vacuum at 120 ° C. for 1 day. Using a 30 L muffle furnace with a volume of 30 L, the dried product was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 5 L / min, and then held for 0.5 hour to obtain a positive electrode active material. Obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 6)
The base material produced in Example 1 was used as a positive electrode active material in an uncoated and unheated state. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material 2 ... Lithium nickel composite oxide particle 3 ... Lithium compound layer 3a ... Cover layer 3b ... Surface layer part 4 ... Center part 5 ... Base material 6 ... Core material 7 ... Coating Layer precursor CBA ... Coin-type battery CA ... Case PC ... Positive electrode NC ... Negative electrode GA ... Gasket PE ... Positive electrode NE ... Negative electrode SE ... Separator

Claims (13)

At least a part of the surface has a lithium compound layer, and the composition is Li _t1 Ni _1-xy Co _x M ¹ _y M ² _z O ₂ (wherein M ¹ and M ² are Mg, Al, Ca , Ti, V, Cr, Mn, Zr, Nb, Mo and W, at least one element selected from the group consisting of 0.97 <t1 ≦ 1.10, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.05.), And composed of lithium nickel composite oxide particles,
The lithium compound layer contains a lithium compound containing Li and M ^2, has a thickness of 5 nm to 500 nm in a direction from the outermost surface of the composite oxide particle toward the center, and a concentration of M ² Has a concentration gradient such that
A positive electrode active material for a non-aqueous electrolyte secondary battery.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium compound layer has a coating layer formed from the lithium compound.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium compound layer has a surface layer portion containing a lithium nickel composite oxide containing at least Li and Ni and the lithium compound. Positive electrode active material.   The said lithium compound layer has the said coating layer and the said surface layer part in this order in the direction which goes to the center from the outermost surface of the said complex oxide particle, It is any one of Claims 1-3 characterized by the above-mentioned. The positive electrode active material for non-aqueous electrolyte secondary batteries. A portion other than the lithium compound layer composition _{Li t2 Ni 1-x-y} Co x M 1 y O 2 (M 1 in the formula is the same element as ^{M 1} of the composition of the composite oxide, 0 .97 ≦ t2 ≦ 1.05, and x and y are the same values as x and y in the composite oxide composition). The positive electrode active material for nonaqueous electrolyte secondary batteries as described in 2.   After stirring and mixing 1 g of the positive electrode active material in 50 g of pure water kept at 24 ° C. for 10 minutes to obtain a slurry, the pH of the aqueous solution obtained by allowing the slurry to stand for 30 seconds is 11.2 or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5. The lithium nickel composite oxide particles, M in the composition is _{Li t1 Ni 1-x-y} Co x M y O 2 ( formula, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb, And at least one element selected from the group consisting of Mo and W, 0.97 ≦ t1 ≦ 1.05, 0 ≦ x ≦ 0.22, and 0 ≦ y ≦ 0.15. on at least part of the surface of the base material that, after forming the coating layer precursor containing Li and the M ^2, any of claims 1 to 6, characterized in that the lithium compound layer is formed, it by heat treatment A positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. The lithium compound, a ^{M 2,} with respect to entire base material, containing in the range of 0.02 to 2.0 wt%, the Li, the 0.1 to 1.00 in Li / ^{M 2} molar ratio The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein the positive electrode active material is contained within a range.   The positive electrode active material is incorporated into a coin-type battery, charged with a charging potential of 4.1 V, measured by an alternating current impedance method, and a surface resistance value calculated by fitting calculation from a Nyquist plot is a value of the base material. 9. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein when the surface resistance value is 1, it is 2 or less.   The positive electrode active material has an initial discharge capacity within a range of ± 3% relative to the initial discharge capacity of the base material after being incorporated in a coin-type battery, and is 4.3V-3.0V, rate 0.5C. The discharge capacity maintenance rate after 200 cycles is 10% or more higher than the initial discharge capacity maintenance rate of the base material, The positive electrode active for a non-aqueous electrolyte secondary battery according to claim 7 or 8 material.   Li alkoxide, a metal alkoxide monomer containing at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, or an oligomer thereof, A surface of a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: mixing a boiling alcohol and a water decomposition inhibitor to obtain a mixed solution; and adding the alcohol and moisture to the mixed solution. A method for producing a coating liquid for treatment.   The surface of the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 11, wherein the high-boiling alcohol uses 2-methyl-1-butanol, 1 ethoxy-2 propanol, or 2-isopropoxyethanol. A method for producing a coating liquid for treatment. The coating liquid according to claim 11 or 12 is sprayed on the particle surface while rocking the lithium nickel composite oxide particles using a stirrer, and then dried to form a coating layer precursor on the particle surface. Thereafter, a heat treatment is performed at 400 ° C. or higher and 700 ° C. or lower in an oxygen atmosphere, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

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