WO2012147877A1 - Surface-modified lithium-containing compound oxide for positive electrode active substance of lithium ion secondary cell and method for producing same - Google Patents

Abstract

Provided are a surface-modified lithium-containing compound oxide having high stability and excellent rate properties and charge-discharge cycle durability, a method for producing the same, a method for producing a positive electrode for a lithium ion secondary cell, and a method for producing a lithium ion secondary cell. The surface of lithium-containing compound oxide particles is coated with a compound oxide formed from gadolinium and zirconium by impregnating the lithium-containing compound oxide particles with a coating liquid containing gadolinium and zirconium and heat treating the resulting impregnated particles at 250 to 550ºC.

Description

Surface-modified lithium-containing composite oxide for positive electrode active material for lithium ion secondary battery and method for producing the same

The present invention provides a surface-modified lithium-containing composite oxide, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery used for a positive electrode active material for a lithium ion secondary battery that has high safety and excellent rate characteristics and charge / discharge cycle durability. The present invention relates to a secondary battery and a manufacturing method thereof.

In recent years, as devices become more portable and cordless, demands for non-aqueous electrolyte secondary batteries such as lithium secondary batteries that are small, lightweight, and have high energy density are increasing. Examples of the positive electrode active material for the non-aqueous electrolyte secondary battery include LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn _2. A composite oxide of lithium and a transition metal or the like such as O ₄ or LiMnO ₂ (in the present invention, sometimes referred to as a lithium-containing composite oxide) is known.

Among them, a lithium secondary battery using LiCoO ₂ as a positive electrode active material and a lithium alloy and carbon such as graphite and carbon fiber as a negative electrode has a high energy density because a high voltage of 4V is obtained. As widely used.

However, in the case of a non-aqueous secondary battery using LiCoO ₂ as the positive electrode active material, the discharge capacity, the stability to heat during heating (in the present invention, sometimes simply referred to as safety), and the unit volume of the positive electrode layer Further improvement in the capacity density (sometimes simply referred to as volume capacity density in the present invention) is desired, and the battery discharge is caused by the reaction between the positive electrode active material interface and the electrolyte by repeating the charge / discharge cycle. There were problems with charge / discharge cycle durability such as capacity reduction and swelling.

In order to solve these problems, various surface treatments have been conventionally studied. For example, a zirconium cobalt-coated lithium cobalt composite oxide has been proposed by coating zirconium (Zr) on a pre-synthesized LiCoO ₂ using an aqueous zirconyl nitrate solution and then firing at a relatively high temperature of 600 ° C. (See Patent Document 1).

In addition, an oxide represented by a lithium-containing composite oxide or a raw material component and LiLnO ₂ (Ln represents at least one selected from the group consisting of yttrium, scandium, and a trivalent rare earth metal) or a raw material component thereof Has been proposed, which includes a step of granulating or forming a mixture with a binder, and a step of holding the granulated product at 600 to 800 ° C. and further holding at 800 to 1100 ° C. . (See Patent Document 2)
Furthermore, a positive electrode active material characterized by containing at least one kind of rare earth oxide in a lithium-containing composite oxide having a layered structure has been proposed (see Patent Document 3).

JP 2004-175609 A JP 2002-151081 A JP 2005-196992 A

However, in spite of various studies as described above, a lithium-containing composite oxide that satisfies all the characteristics such as discharge capacity, safety, volume capacity density, and charge / discharge cycle durability has not been obtained yet.

For example, Patent Document 1 proposes a lithium cobalt composite oxide obtained by coating a lithium cobalt composite oxide synthesized in advance with an aqueous zirconyl nitrate solution and then firing at 600 ° C., which is a relatively high temperature. However, when a coating treatment is performed using an aqueous solution having a low pH such as an aqueous solution of zirconyl nitrate, the surface of the lithium-containing composite oxide is dissolved and contained in a composite powder such as lithium (Li) or cobalt (Co). Since a part of the element elutes, it is considered that safety is insufficient. In addition, since nitrate is used as a raw material for producing the surface-modified lithium-containing composite oxide, there is a problem that toxic nitrogen oxide gas is produced as a by-product during production.

The method for producing the surface-modified lithium-containing composite oxide described in Patent Document 2 is selected from the group consisting of a lithium-containing composite oxide or a raw material component and LiLnO ₂ (Ln is yttrium, scandium, and a trivalent rare earth metal). A step of granulating or forming an oxide represented by (2) at least one of them and a raw material component thereof together with a binder, holding the granulated product at 600 to 800 ° C., and further firing at 800 to 1100 ° C. It consists of a process to do. However, since LiLnO ₂ is unlikely to be uniformly dispersed on the particle surface of the lithium-containing composite oxide, the surface-modified lithium-containing composite oxide described in Patent Document 2 has rate characteristics, safety, and charge / discharge cycle durability. It is considered that the sex is insufficient.

The surface-modified lithium-containing composite oxide described in Patent Document 3 is characterized in that the lithium-containing composite oxide having a layered structure contains at least one kind of rare earth oxide. A 0.01M gadolinium nitrate aqueous solution was added to a lithium-containing composite oxide synthesized in advance in an atomic ratio of gadolinium (Gd) to nickel (Ni), manganese (Mn), and cobalt (Co) contained in the composite oxide. Add to a range of 0.001% to 10% to form a slurry, pulverize and mix with a planetary ball mill, place in an alumina crucible, and perform second baking at 925 ° C. for 10 hours in air. ing. Since pulverization and mixing are repeated in a mixer and firing is performed at a high temperature, gadolinium nitrate is sintered to gadolinium oxide, and the rare earth oxide is uniformly present on the particle surface of the lithium-containing composite oxide. It will not be in the state. For this reason, it is considered that the surface-modified lithium-containing composite oxide described in Patent Document 3 has insufficient rate characteristics, safety, charge / discharge cycle durability, and the like. In addition, since nitrate is used as a raw material for producing the surface-modified lithium-containing composite oxide, there is a problem that toxic nitrogen oxide gas is produced as a by-product during production.

Accordingly, the present invention provides a surface-modified lithium-containing composite oxide, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing them, which have high safety and excellent rate characteristics and charge / discharge cycle durability. For the purpose of provision.

The inventors of the present invention have intensively studied to achieve the above-mentioned problems, and have reached the present invention having the following configuration.
(1) In formula _{Li p N x M y O z} F a ( where, N is the, Co, at least one element selected from the group consisting of Mn and Ni, M is, Co, other than Mn and Ni It is at least one element selected from the group consisting of transition metal elements, Al, Sn, and elements of group 2. 0.9 ≦ p ≦ 1.4, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0 .1, 1.9 ≦ z ≦ 2.1, 0 ≦ a ≦ 0.05) obtained by impregnating a coating liquid containing a gadolinium source and a zirconium source into lithium-containing composite oxide particles. A method for producing a surface-modified lithium-containing composite oxide, wherein the impregnated particles are heat-treated at 250 to 550 ° C. so that the surface layer of the lithium-containing composite oxide particles contains gadolinium / zirconium-containing composite oxide. .
(2) The production method according to the above (1), wherein the coating solution has a pH of 1 to 10.
(3) The production method according to (1) or (2), wherein the gadolinium source is at least one selected from the group consisting of gadolinium acetate, gadolinium carbonate, gadolinium hydroxide, gadolinium sulfate, and gadolinium oxide.
(4) The production method according to any one of (1) to (3), wherein the zirconium source is at least one selected from the group consisting of ammonium zirconium carbonate and ammonium zirconium fluoride.
(5) The lithium-containing composite oxide is impregnated with a coating solution containing 0.01 to 1 mol% of gadolinium and zirconium in total of gadolinium and zirconium, according to any one of the above (1) to (4) Manufacturing method.
(6) The production method according to any one of (1) to (5), wherein the coating liquid contains 0.03 to 0.5 mol% of gadolinium with respect to the lithium-containing composite oxide.
(7) The manufacturing method according to any one of (1) to (6), wherein the coating liquid contains 0.03 to 0.5 mol% of zirconium with respect to the lithium-containing composite oxide.
(8) The production method according to any one of (1) to (7), wherein in the gadolinium / zirconium-containing composite oxide, the molar ratio of zirconium to gadolinium (Zr / Gd) is 0.1 to 10.
(9) The production according to any one of (1) to (8), wherein gadolinium contained in the gadolinium / zirconium-containing composite oxide is 0.03 to 0.5 mol% with respect to the lithium composite oxide. Method.
(10) The production according to any one of (1) to (9), wherein zirconium contained in the gadolinium / zirconium-containing composite oxide is 0.03 to 0.5 mol% with respect to the lithium composite oxide. Method.
(11) The production method according to any one of (1) to (10) above, wherein the heat treatment temperature is 300 to 500 ° C.
(12) A slurry obtained by mixing a positive electrode active material, a conductive agent, a binder and a solvent containing a surface-modified lithium-containing composite oxide obtained by the production method according to any one of (1) to (11) above A method for producing a positive electrode for a lithium ion secondary battery, wherein the solvent is removed by heating after coating the metal foil.
(13) A lithium ion secondary battery characterized by laminating a separator and a negative electrode on a positive electrode obtained by the production method described in (12) above, storing the battery in a battery case, and then injecting an electrolytic solution. Manufacturing method.
(14) In formula _{Li p N x M y O z} F a ( where, N is the, Co, at least one element selected from the group consisting of Mn and Ni, M is, Co, other than Mn and Ni It is at least one element selected from the group consisting of transition metal elements, Al, Sn, and elements of group 2. 0.9 ≦ p ≦ 1.4, 0.9 ≦ x ≦ 2.0, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 4.2, 0 ≦ a ≦ 0.05) The surface layer of the lithium-containing composite oxide particles includes a gadolinium / zirconium-containing composite compound having an amorphous structure. A surface-modified lithium-containing composite oxide.
(15) The surface according to (14), wherein gadolinium and zirconium contained in the surface layer of the particles are in a proportion of 0.01 to 1.00 mol% in total of gadolinium and zirconium with respect to the lithium-containing composite oxide. Modified lithium-containing composite oxide.
(16) A positive electrode for a lithium secondary battery comprising a positive electrode active material, a conductive material, and a binder, wherein the positive electrode active material is the surface-modified lithium-containing composite oxide according to (14) or (15). .
(17) A lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode is the positive electrode according to (16).

According to the present invention, a surface-modified lithium-containing composite oxide having high safety, excellent rate characteristics and charge / discharge cycle durability, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing them. Provided.
The reason why the surface-modified lithium-containing composite oxide obtained by the present invention exhibits excellent characteristics as a positive electrode for a lithium secondary battery as described above is not necessarily clear, but is estimated as follows.
In the surface-modified lithium-containing composite oxide of the present invention, the gadolinium / zirconium-containing composite oxide is uniformly contained in the surface layer of the particles. The gadolinium-zirconium-containing composite oxide according to the present invention is stable against structural changes associated with charge / discharge, and the crystal structure of the lithium-containing composite oxide that accompanies charge / discharge even when a large amount of current flows. Can be prevented from collapsing. In addition, since the contact area between the surface of the lithium-containing composite oxide and the electrolytic solution can be reduced by being uniformly present, decomposition of the electrolytic solution can also be suppressed. The gadolinium / zirconium-containing composite oxide is a heat-stable compound. For this reason, the surface-modified lithium-containing composite oxide of the present invention is considered to have a high safety and to obtain a surface-modified lithium-containing composite oxide having excellent rate characteristics and charge / discharge cycle durability. That is, from the viewpoint of the configuration and effect of the invention, the surface-modified lithium-containing composite oxide described in Patent Documents 1 to 3 is considered to be completely different from the surface-modified lithium-containing composite oxide obtained in the present invention. It is done.

The weight change curve obtained by carrying out TG analysis of the coating liquid obtained in Example 1. FIG. The powder X-ray-diffraction chart of each powder obtained when the coating liquid obtained in Example 1 was heated to 80 degreeC. The powder X-ray diffraction chart of each powder obtained when the coating liquid obtained in Example 1 was heated to 200 degreeC. The powder X-ray diffraction chart of each powder obtained when the coating liquid obtained in Example 1 was heated to 400 degreeC. The powder X-ray diffraction chart of each powder obtained when the coating liquid obtained in Example 1 was heated to 600 degreeC. The powder X-ray diffraction chart of each powder obtained when the coating liquid obtained in Example 1 was heated to 900 degreeC.

The surface-modified lithium-containing composite oxide of the present invention can be obtained by impregnating lithium-containing composite oxide particles serving as a base material with a coating solution containing a gadolinium source and a zirconium source and then performing a heat treatment. Lithium-containing composite oxide is impregnated with the coating solution is represented by the general formula _{Li p N x M y O z} F a.
In the above general formula, p, x, y, z and a are 0.9 ≦ p ≦ 1.4, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2. 0.1, 0 ≦ a ≦ 0.05. Of these, p, x, y, z and a are preferably as follows. 0.93 ≦ p ≦ 1.2, 0.9 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2.1, 0 ≦ a ≦ 0.05. Further, p, x, y, z and a are more preferably as follows. 0.97 ≦ p ≦ 1.1, 0.95 ≦ x ≦ 1.00, 0 ≦ y ≦ 0.05, 1.95 ≦ z ≦ 2.05, 0 ≦ a ≦ 0.01.

When the lithium-containing composite oxide as a base material does not contain fluorine, the discharge capacity tends to be higher than when it contains fluorine, and when the capacity is important, a = 0 is preferable. When the lithium-containing composite oxide of the base material contains fluorine, it becomes a positive electrode active material in which a part of oxygen is substituted with fluorine, and there is a tendency to further improve safety. Is preferably in the range of 0.001 ≦ a ≦ 0.01.
In the above general formula, the N element is at least one element selected from the group consisting of Co, Mn, and Ni. Among these, the N element is preferably Co, Ni, a combination of Co and Ni, a combination of Mn and Ni, or a combination of Co, Ni and Mn, and may be a combination of Co or Co, Ni and Mn. More preferably, Co is particularly preferable.

In the present invention, the M element is at least one element selected from the group consisting of transition metal elements other than Co, Mn and Ni, Al, Sn and Group 2 elements. Here, the transition metal element represents a transition metal of Group 4, Group 5, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11, and Group 12 of the Periodic Table. Among these, the M element is preferably at least one selected from the group consisting of Al, Ti, Zr, Hf, Nb, Ta, Mg, Sn, and Zn. In particular, from the viewpoint of discharge capacity, safety, charge / discharge cycle durability, etc., the M element is more preferably at least one selected from the group consisting of Al, Ti, Zr, Nb and Mg, and Al, Zr and Particularly preferred is at least one selected from the group consisting of Mg.

When the M element contains Al and Mg, the atomic ratio of Al and Mg is preferably 1/4 to 4/1, particularly preferably 1/3 to 3/1, and y is preferably When 0.005 ≦ y ≦ 0.05, particularly preferably 0.01 ≦ y ≦ 0.035, the balance of battery performance, that is, the balance of discharge capacity, safety, and charge / discharge cycle durability is good. Therefore, it is preferable.

When the M element contains Zr and Mg, the atomic ratio of Zr and Mg is preferably 1/40 to 2/1, particularly preferably 1/30 to 1/5, and y is preferably 0. 0.005 ≦ y ≦ 0.05, and particularly preferably 0.01 ≦ y ≦ 0.035, the balance of battery performance, that is, the balance of discharge capacity, safety, and charge / discharge cycle durability. It is particularly preferable because it is good. On the other hand, since the discharge capacity tends to decrease as the additive amount y of the M element increases, y = 0 is preferable when the discharge capacity is particularly important.

In the present invention, the molar ratio Li / (N + M), which is a value obtained by dividing the molar amount of lithium in the lithium-containing composite oxide by the total molar amount of N element and M element, is 0.97 to 1.10. Preferably, 0.99 to 1.05 is particularly preferable. In this case, the particle growth of the lithium-containing composite oxide by firing is promoted, and higher density particles can be obtained.

The coating liquid preferably contains gadolinium and zirconium in a range of 0.01 to 1.00 mol% in total of gadolinium and zirconium with respect to the lithium-containing composite oxide as a base material, and more preferably 0.04 to 0.50 mol% is more preferable, and 0.07 to 0.15 mol% is particularly preferable. Similarly, the total amount of gadolinium and zirconium contained in the surface layer of the particles is preferably 0.01 to 1.00 mol% of the gadolinium and zirconium with respect to the lithium-containing composite oxide. 50 mol% is more preferable, and 0.07 to 0.15 mol% is particularly preferable.

Further, the coating liquid preferably contains 0.03 to 0.5 mol% of gadolinium with respect to the lithium-containing composite oxide, more preferably 0.05 to 0.3 mol%, and more preferably 0.05 to 0. .25 mol% is particularly preferred. Further, it is preferable that 0.03 to 0.5 mol% of zirconium is contained with respect to the lithium-containing composite oxide, more preferably 0.05 to 0.3 mol%, and more preferably 0.05 to 0.25 mol%. Particularly preferred. Similarly, gadolinium contained in the surface layer of the particles is preferably 0.03 to 0.5 mol%, more preferably 0.05 to 0.3 mol%, and more preferably 0.05 to 0.3 mol% with respect to the lithium-containing composite oxide. 0.25 mol% is particularly preferable. Further, zirconium contained in the surface layer of the particles is preferably 0.03 to 0.5 mol%, more preferably 0.05 to 0.3 mol%, and particularly preferably 0.05 to 0.25 mol%.

The composition of the gadolinium-zirconium-containing composite oxide contained in the surface layer of the surface-modified lithium-containing composite oxide, that is, the gadolinium-zirconium-containing composite oxide present in the surface layer is not particularly limited, but the molar ratio of zirconium to gadolinium (Zr / Gd) is 0.1 to 10 is preferable, 0.3 to 5 is more preferable, and 0.5 to 2 is particularly preferable. In particular, the composition of the gadolinium / zirconium-containing composite oxide contained in the surface layer of the surface-modified lithium-containing composite oxide is preferably represented by the structural formula of Gd ₂ Zr ₂ O ₇ . The gadolinium / zirconium-containing composite oxide preferably has an amorphous structure, that is, an amorphous structure. The surface-modified lithium-containing composite oxide of the present invention preferably has a gadolinium-zirconium-containing composite oxide having an amorphous structure in which the gadolinium source and the zirconium source are decomposed, that is, an amorphous structure, in the surface layer.

The gadolinium-zirconium-containing composite oxide has diffraction peaks at 2θ = 29.5 ± 1.5 ° and 48.5 ± 1.5 ° in the spectrum obtained by powder X-ray diffraction using Cu—Kα rays. In particular, the main peak is preferably 2θ = 29.5 ± 1.5 °. The measurement conditions for powder X-ray diffraction were acceleration voltage of 40 kV or more and current of 40 mA or more.
The gadolinium / zirconium-containing composite oxide may be a mixture containing several types of gadolinium / zirconium-containing composite oxide.

In the surface-modified lithium-containing composite oxide of the present invention, when the gadolinium / zirconium-containing composite oxide contains a total of gadolinium and zirconium with respect to the lithium-containing composite oxide, for example, in a proportion as low as 0.1 mol%, gadolinium Even if a zirconium-containing composite oxide is present, the diffraction peak of the X-ray diffraction spectrum derived from the gadolinium / zirconium-containing composite oxide may not be detected. In this case, it is possible to detect a diffraction peak of the X-ray diffraction spectrum by synthesizing a compound subjected to heat treatment by drying the coating liquid and measuring the X-ray diffraction spectrum.

In the surface-modified lithium-containing composite oxide of the present invention, gadolinium oxide or zirconium oxide may further exist in the surface layer of the lithium-containing composite oxide particles.
As a solvent for the coating solution, an aqueous solution is preferable and water is more preferable from the viewpoints of environmental impact and cost. The aqueous solution means a solution using an aqueous medium as a solvent, that is, a solvent mainly containing water, including water, alcohol, ethylene glycol, glycerin and the like. Of these, a solution containing 80 to 100% by mass of water is preferable.

In the present invention, the lithium-containing composite oxide containing gadolinium / zirconium-containing composite oxide in its surface layer is compared with the conventional solid-phase reaction or when the raw material is added in solution to the lithium-containing composite oxide raw material. Thus, it is considered that the battery characteristics are drastically improved because the gadolinium / zirconium-containing composite oxide can be uniformly attached and exist on the surface layer including the surface of the lithium-containing composite oxide particles.

The gadolinium source used for the preparation of the coating liquid is not particularly limited, but is preferably one selected from the group consisting of gadolinium oxide, gadolinium hydroxide, gadolinium carbonate, gadolinium sulfate, and gadolinium acetate, and gadolinium hydroxide or gadolinium acetate is preferable. More preferably, gadolinium acetate is particularly preferable.

The zirconium source used for the preparation of the coating liquid is not particularly limited, but at least selected from the group consisting of ammonium zirconium carbonate, ammonium zirconium halide, zirconyl chloride, zirconyl nitrate, zirconyl carbonate, basic zirconium carbonate, and potassium zirconium carbonate. One is preferred, ammonium zirconium carbonate or ammonium zirconium fluoride is more preferred, and ammonium zirconium carbonate is particularly preferred. The chemical formula of ammonium zirconium carbonate is represented by (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ]. The chemical formula of zirconium ammonium fluoride is represented by (NH ₄ ) ₂ ZrF ₆ .

In the present invention, it is preferable that the coating liquid contains a carboxylic acid. The carboxylic acid may be in the form of a compound salt. The carboxylic acid is preferably a carboxylic acid having two or more carboxyl groups, or a total of two or more carboxyl groups and hydroxyl groups or carbonyl groups. Such a carboxylic acid can improve the solubility of the gadolinium source and the zirconium source, and can uniformly disperse gadolinium and zirconium. In particular, by using a carboxylic acid having 2 to 4 carboxyl groups or a carboxylic acid having 1 to 4 hydroxyl groups, the dispersibility of gadolinium and zirconium can be further improved.
When using a highly acidic carboxylic acid, if the pH of the coating solution is less than 1, the base lithium-containing composite oxide tends to dissolve, so a base such as ammonia can be added to adjust the pH to 1 to 10 is preferable, and the pH is more preferably 1 to 9.

Also, the pH of the coating solution can be adjusted by adding a pH adjusting agent and / or an alkaline aqueous solution to the coating solution. As the pH adjuster, ammonia, ammonium bicarbonate or the like can be used. As the alkaline aqueous solution, an aqueous solution of a hydroxide such as sodium hydroxide, potassium hydroxide, or lithium hydroxide can be used.

In the present invention, the coating liquid containing a gadolinium source and a zirconium source may be any of a solution, a suspension in which solid fine particles are dispersed, or a colloidal solution in which solid fine particles are dispersed. In the case of a suspension or colloidal solution, in consideration of stability and dispersibility, the average particle size of the solid fine particles is preferably 3 μm or less, more preferably 1 μm or less, and 0.1 μm or less. Is particularly preferred.

In the coating liquid of the present invention, composite particles composed of a gadolinium source and a zirconium source are preferably dispersed as fine particles. Moreover, the dispersion liquid which the composite particle which consists of a gadolinium source and a zirconium source disperse | distributed to the solution in which the gadolinium source and / or the zirconium source were melt | dissolved may be sufficient.
When preparing a coating solution, it is prepared while heating as necessary. The temperature is preferably 40 ° C to 80 ° C, particularly preferably 50 ° C to 70 ° C. By heating, the gadolinium source and the zirconium source can be uniformly dispersed, and the coating liquid can be stabilized in a short time.

In the present invention, since a small amount of the aqueous medium is desired in the subsequent heat treatment step, the total concentration of the gadolinium source and the zirconium source contained in the coating liquid is preferably as high as possible. However, if the concentration is too high, the viscosity increases, the mixing property with the gadolinium source and the zirconium source decreases, and it becomes difficult for gadolinium and zirconium to be uniformly coated on the particle surface of the lithium-containing composite oxide. 0.01 to 30% by mass is preferable, and 0.1 to 15% by mass is more preferable.

The method of impregnating the coating liquid into the lithium-containing composite oxide is not particularly limited, but means for spraying the coating liquid onto the lithium-containing composite oxide powder to impregnate, or the coating liquid and the lithium-containing composite in a container A means for mixing with an oxide, stirring, and impregnating can be used. Specifically, a spray dryer, a flash dryer, a belt dryer, a Laedige mixer, a thermoprocessor, or a paddle dryer can be used as the means for spraying. As a means for mixing and stirring in a container, a twin screw kneader, an axial mixer, a paddle mixer, a turbulator, a Ladige mixer, or a drum mixer can be used. Further, it is preferable to perform a reduced pressure treatment while impregnating, because the lithium-containing composite oxide impregnated with the coating solution can be simultaneously dried in a short time.

After impregnating the lithium-containing composite oxide powder of the present invention with a coating solution, the resulting impregnated particles can be dried. In this case, the impregnated particles are preferably dried at 15 to 200 ° C., particularly preferably at 50 to 120 ° C., usually for 0.1 to 10 hours. Since the aqueous medium in the impregnated particles is removed in a later heat treatment step, it is not always necessary to completely remove it at this stage, but a large amount of energy is required to remove moisture in the heat treatment step, so it can be done. It is preferable to remove as much as possible.

The heat treatment temperature of the impregnated particles impregnated with the coating liquid of the present invention is 250 to 550 ° C., and 300 to 500 ° C. is particularly preferable. By heat-treating in this temperature range, gadolinium and zirconium are uniformly distributed on the surface layer of lithium-containing composite oxide particles, and surface modified lithium containing excellent battery characteristics such as rate characteristics and charge / discharge cycle durability A composite oxide can be obtained. Further, heat treatment in this temperature range is preferable because the gadolinium / zirconium-containing composite oxide in the surface layer of the particles becomes a compound having an amorphous structure, that is, an amorphous structure. When the heat treatment temperature is lower than 250 ° C., the organic acid used for preparing the coating liquid is not sufficiently decomposed. For example, when the temperature is 200 ° C., the coating liquid raw material is not decomposed from the dried state. It is not preferable. A temperature higher than 550 ° C. is not preferable because a highly crystalline gadolinium / zirconium-containing composite oxide starts to be formed, and the particle surface of the lithium-containing composite oxide cannot be uniformly coated. For example, since a gadolinium-zirconium-containing composite oxide having very high crystallinity is formed and sintered at 900 ° C., it is not preferable because the particle surface of the lithium-containing composite oxide cannot be uniformly coated.
The heat treatment is preferably performed in an oxygen-containing atmosphere, and more specifically in an atmosphere having an oxygen concentration of 10 to 40% by volume. The heat treatment time is preferably 30 minutes or longer, more preferably 1 hour or longer, further preferably 3 hours or longer, more preferably 120 hours or shorter, more preferably 60 hours or shorter, further preferably 30 hours or shorter.

The surface modified lithium-containing composite oxide of the present invention has an average particle diameter D50 of preferably 5 to 30 μm, particularly preferably 8 to 25 μm, and a specific surface area of preferably 0.1 to 0.7 m ² / g, particularly Preferably, the integrated width of (110) plane diffraction peak of 2θ = 66.5 ± 1 ° measured by X-ray diffraction using Cu—Kα as a radiation source is preferably 0.15 to 0.5 m ² / g. It is 0.08 to 0.14 °, particularly preferably 0.08 to 0.12 °.

In the present invention, the average particle size D50 is a particle size distribution at which the particle size distribution is obtained on a volume basis and the cumulative curve is 50% in a cumulative curve with the total volume being 100%. 50% diameter (D50) is meant. The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the particles in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, using Microtrack HRAX-100 manufactured by Nikkiso Co., Ltd.). D10 means a point value at which the cumulative curve becomes 10%, and D90 means a point value at which the cumulative curve becomes 90%.

In the surface-modified lithium-containing composite oxide obtained in the present invention, the average particle diameter D50 means a volume average particle diameter of a secondary particle diameter obtained by agglomerating and sintering primary particles. Means consisting of primary particles only means the volume average particle size of the primary particles.
Further, the press density of the surface modified lithium-containing composite oxide obtained by the present invention is preferably 2.7 ~ 3.4g / cm ^3, more preferably ^{2.8 ~ 3.3g / cm 3, 2.9} ~ 3.3 g / cm ³ is particularly preferred. In the present invention, the press density means the apparent density of the powder when the surface-modified lithium-containing composite oxide powder is pressed at a pressure of 0.3 ton / cm ² . In the surface-modified lithium-containing composite oxide of the present invention, the amount of free alkali is preferably 0.035% by mass or less, more preferably 0.02% by mass or less.

Since the surface-modified lithium-containing composite oxide of the present invention contains gadolinium and zirconium in the particle surface layer, the contact area between the lithium-containing composite oxide and the electrolytic solution is reduced, and atoms such as cobalt are charged during charging and discharging. Elution into the electrolyte can be suppressed. This can be quantitatively evaluated by measuring the amount of free alkali representing the amount of alkali eluted from the lithium-containing composite oxide. This numerical value of the free alkali amount indicates that the surface-modified lithium-containing composite oxide of the present invention is excellent in safety and charge / discharge cycle durability. In the present invention, the amount of free alkali is determined by dispersing 5 g of the surface-modified lithium-containing composite oxide powder in 50 g of pure water and stirring for 30 minutes, and then filtering the filtrate obtained by filtration to 0.02 mol% / liter. It is obtained from a hydrochloric acid aqueous solution used by potentiometric titration with an aqueous hydrochloric acid solution until the pH reaches 4.0. In the present invention, the amount of free alkali is sometimes simply referred to as alkali amount.

When manufacturing a positive electrode for a lithium secondary battery from a surface-modified lithium-containing composite oxide, the surface-modified lithium-containing composite oxide powder is bonded to a carbon-based conductive material such as acetylene black, graphite, or ketjen black. It is formed by mixing materials. For the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is preferably used. The surface-modified lithium-containing composite oxide powder, conductive material and binder according to the present invention are made into a slurry or a kneaded product using a solvent or a dispersion medium. This is supported on a positive electrode current collector such as an aluminum foil or a stainless steel foil by coating or the like to produce a positive electrode for a lithium secondary battery.

In the lithium secondary battery using the surface-modified lithium-containing composite oxide of the present invention as the positive electrode active material, a porous polyethylene film, a porous polypropylene film, or the like is used as the separator. In addition, various solvents can be used as the solvent for the battery electrolyte, and among these, carbonates are preferred. The carbonate ester can be either cyclic or chain. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate, methyl isopropyl carbonate, and the like.

In the present invention, the above carbonate esters can be used alone or in admixture of two or more. Moreover, you may mix and use with another solvent. Further, depending on the material of the negative electrode active material, when a chain carbonate ester and a cyclic carbonate ester are used in combination, discharge characteristics, charge / discharge cycle durability, and charge / discharge efficiency may be improved.

Further, in the lithium secondary battery using the surface-modified lithium-containing composite oxide according to the present invention as a positive electrode active material, a vinylidene fluoride-hexafluoropropylene copolymer (for example, trade name Kyner manufactured by Atchem Co.) or vinylidene fluoride is used. -It may be a gel polymer electrolyte containing a perfluoropropyl vinyl ether copolymer. Solutes added to the electrolyte or polymer electrolyte include ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ CO ₂ ⁻ , (CF ₃ Any one or more of lithium salts having SO ₂ ) ₂ N ^— or the like as an anion is preferably used. It is preferable to add at a concentration of 0.2 to 2.0 mol / l (liter) with respect to the electrolytic solution or polymer electrolyte comprising the lithium salt. If it deviates from this range, the ionic conductivity is lowered and the electrical conductivity of the electrolyte is lowered. Of these, 0.5 to 1.5 mol / l is particularly preferable.

In the lithium battery using the surface-modified lithium-containing composite oxide according to the present invention as the positive electrode active material, a material capable of inserting and extracting lithium ions is used as the negative electrode active material. The material for forming the negative electrode active material is not particularly limited. For example, lithium metal, lithium alloy, carbon material, carbon compound, silicon carbide compound, silicon oxide compound, titanium sulfide, boron carbide compound, or periodic table 14 or group 15 Examples include oxides mainly composed of metals. As the carbon material, those obtained by pyrolyzing an organic substance under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, flake graphite, and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used. Stainless steel or the like is used as the negative electrode current collector. Such a negative electrode is preferably produced by kneading the active material with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector, drying, and pressing.

The shape of the lithium battery using the lithium-containing composite oxide of the present invention as the positive electrode active material is not particularly limited. A sheet shape, a film shape, a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[Example 1] (Example)
An aqueous solution prepared by dissolving 1.91 g of magnesium carbonate, 20.68 g of aluminum maleate having an Al content of 2.65% by mass, and 7.76 g of citric acid monohydrate in 23.12 g of water had a zirconium content of 14.5 g. An aqueous solution obtained by mixing 1.28 g of a mass% zirconium ammonium carbonate aqueous solution and 195.33 g of cobalt oxyhydroxide having a cobalt content of 60.0 mass% and an average particle diameter of 13 μm were added and mixed. The obtained mixture was dried in a constant temperature bath at 80 ° C., 79.17 g of lithium carbonate having a lithium content of 18.7% by mass was mixed in a mortar, calcined at 990 ° C. for 14 hours in an oxygen-containing atmosphere, and then crushed. _Thus , a lithium-containing composite oxide powder having a composition of Li _1.02 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.98 O ₂ was obtained.

0.42 g of gadolinium acetate was dissolved in 68.92 g of water, and then mixed with 0.66 g of an aqueous solution of ammonium zirconium carbonate (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ] having a zirconium content of 14.1% by mass. As a result, a coating solution having a pH of 6.0 was prepared. By this mixing, the color of the aqueous solution changed from colorless and transparent to milky white. The coating liquid was added to and mixed with 200 g of the lithium-containing composite oxide powder. Gadolinium was 0.05 mol% and zirconium was 0.05 mol% with respect to the lithium-containing composite oxide. The mixture was heated with stirring and dried at 120 ° C. for 4 hours to obtain gadolinium-zirconium impregnated particles in which all the gadolinium and zirconium in the added coating solution were impregnated in the lithium-containing composite oxide.

Further, the obtained gadolinium-zirconium impregnated particles were heat-treated at 400 ° C. for 12 hours in an oxygen-containing atmosphere, and then crushed to obtain an average particle diameter D50 of 14.2 μm, D10 of 8.4 μm, and D90 of 22.1 μm. A surface-modified lithium-containing composite oxide powder having a specific surface area of 0.29 m ² / g determined by the BET method was obtained. The press density of this powder was 2.99 g / cm ³ . The alkali amount of the obtained surface-modified lithium-containing composite oxide was 0.013% by mass.

Also, using RINT 2100 type manufactured by Rigaku Corporation, using Cu-Kα line, acceleration voltage 40KV, current 40mA, scan range 15-75 °, sampling width 0.020, scan speed 2.000 ° / min, The X-ray diffraction spectrum of the obtained surface-modified lithium-containing composite oxide was measured with a divergence slit of 1 °, a divergence length limiting slit of 10 mm, a scattering slit of 1 °, and a light receiving slit of 0.15 mm. From the spectrum chart obtained by this measurement, a peak derived from the lithium-containing composite oxide was confirmed.

Further, regarding the powder of the surface-modified lithium-containing composite oxide, in the powder X-ray diffraction using CuKα ray, the diffraction peak integral width of (110) plane at 2θ = 66.5 ± 1 ° was 0.111 °. .
The above surface-modified lithium-containing composite oxide powder, acetylene black, and polyvinylidene fluoride powder are mixed at a mass ratio of 90/5/5, and N-methylpyrrolidone is added to prepare a slurry. One side coating was performed on a 20 μm aluminum foil using a doctor blade. The positive electrode sheet for lithium batteries was produced by drying and performing roll press rolling 5 times.

Then, the one obtained by punching out the positive electrode sheet is used for the positive electrode, a metal lithium foil having a thickness of 500 μm is used for the negative electrode, stainless steel is used for the negative electrode current collector, and a porous polypropylene having a thickness of 25 μm is used for the separator. Furthermore, the electrolyte solution means a LiPF ₆ / EC + DEC (1: 1) solution having a concentration of 1 M (meaning a mixed solution of EC and DEC in volume ratio (1: 1) containing LiPF ₆ as a solute. Solvents described later are also this). 3), three stainless steel simple sealed cell type lithium batteries were assembled in an argon glove box.

For one of the above three batteries, the battery was charged to 4.5 V with a load current of 180 mA / g of the positive electrode active material at 25 ° C. and then discharged to 2.75 V with a load current of 18 mA / g of the positive electrode active material. The discharge capacity per gram of the positive electrode active material was determined. Subsequently, 1 g of the positive electrode active material is discharged to 2.75 V at a high load current of 270 mA, and the discharge capacity (hereinafter sometimes referred to as high rate capacity) and discharge average potential (hereinafter referred to as high rate average potential). Asked). As a result, the high rate capacity was 164 mAh / g, and the high rate average potential was 3.96V.

One of the three batteries is charged to 4.5 V with a load current of 75 mA / g of the positive electrode active material at 25 ° C. and discharged to 2.75 V with a load current of 75 mA / g of the positive electrode active material. The initial discharge capacity (hereinafter sometimes referred to as initial discharge capacity) was determined, and the battery was subsequently subjected to 50 charge / discharge cycle tests. As a result, the 4.5V initial discharge capacity was 178 mAh / g, the initial charge / discharge efficiency was 91.2%, the initial discharge average potential was 4.03 V, and the capacity retention rate after 50 charge / discharge cycles was 83 The average potential during discharge was 3.94 V (hereinafter may be referred to as initial discharge capacity, initial charge / discharge efficiency, initial average potential, capacity retention rate, and average potential, respectively).

The other battery was charged at 4.4 V for 10 hours, disassembled in an argon glove box, taken out from the charged positive electrode sheet, washed out, then punched out to a diameter of 3 mm, together with EC. The container was sealed in an aluminum capsule and heated at a rate of 5 ° C./min with a scanning differential calorimeter to measure the heat generation start temperature. As a result, the heat generation start temperature of the heat generation curve of the 4.4V charged product was 147 ° C.

Separately, FIG. 1 shows a weight change curve obtained by measuring the weight change of the above coating solution by TG analysis. As can be seen from FIG. 1, the weight greatly changes between 100 ° C. and 400 ° C., and the gadolinium source and the zirconium source are decomposed before being heated to 400 ° C.

Furthermore, the powder X-ray diffraction of the powder obtained when said coating liquid was heated at 80 degreeC, 200 degreeC, 400 degreeC, 600 degreeC, and 900 degreeC was measured, respectively. The obtained spectrum charts are shown in FIGS. FIG. 3 shows that broad peaks appear at 2θ = 29.5 ° and 2θ = 48.5 ° at 200 ° C., suggesting the formation of gadolinium-zirconium-containing composite oxides. In addition, it is inferred that the decomposition of the gadolinium source and the zirconium source is insufficient. On the other hand, from FIG. 5, at 600 ° C., in addition to the peaks near 2θ = 29.5 ° and 2θ = 48.5 °, peaks can be confirmed near 2θ = 58.2 °. It was found that a gadolinium / zirconium-containing composite oxide was formed. Therefore, it is considered from FIG. 4 that the powder obtained by firing at 400 ° C. has a gadolinium source and a zirconium source decomposed and has an amorphous structure, that is, an amorphous structure. Further, from FIG. 6, the powder X-ray diffraction spectrum chart of the powder obtained when heated to 900 ° C. coincided with the powder X-ray diffraction spectrum chart of Gd ₂ Zr ₂ O ₇ .

[Example 2] (Example)
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the gadolinium-zirconium impregnated particles was changed from 400 ° C to 300 ° C. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 14.0 μm, D10 was 8.4 μm, D90 was 21.9 μm, and the specific surface area determined by the BET method was 0.28 m ² / g. Moreover, the alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.014% by mass, and the press density was 3.01 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.099 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 162 mAh / g, and the high rate average potential was 3.96V.
The initial discharge capacity was 181 mAh / g, the initial charge / discharge efficiency was 92.4%, the initial average potential was 4.03 V, the capacity retention rate was 78.7%, and the average potential was 3.86 V. Moreover, the heat generation start temperature was 144 degreeC.

[Example 3] (Example)
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the gadolinium-zirconium impregnated particles was changed from 400 ° C. to 500 ° C. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 13.8 μm, D10 was 8.2 μm, D90 was 21.7 μm, and the specific surface area determined by the BET method was 0.21 m ² / g. Moreover, the alkali amount of the obtained powder of the surface modified lithium-containing composite oxide was 0.012% by mass, and the press density was 3.02 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.104 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 164 mAh / g, and the high rate average potential was 3.96V.
The initial discharge capacity was 179 mAh / g, the initial charge / discharge efficiency was 91.2%, the initial average potential was 4.03 V, the capacity retention rate was 76.0%, and the average potential was 3.90 V. The heat generation starting temperature was 145 ° C.

[Example 4] (Example)
1.25 g of gadolinium acetate and zirconium ammonium carbonate (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ] aqueous solution 1 having a zirconium content of 14.1% by mass with respect to 200 g of the lithium-containing composite oxide powder 1 Example 1 except that .99 g was mixed with 66.76 g of water as a pH 6.0 coating solution, the gadolinium coating amount on the base material was 0.25 mol%, and the zirconium coating amount was 0.25 mol%. Similarly, a surface-modified lithium-containing composite oxide was synthesized. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 14.2 μm, D10 was 8.2 μm, D90 was 23.2 μm, and the specific surface area determined by the BET method was 0.15 m ² / g. The alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.011% by mass, and the press density was 2.96 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.105 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 160 mAh / g, and the high rate average potential was 3.97V.
The initial discharge capacity was 173 mAh / g, the initial charge / discharge efficiency was 91.5%, the initial average potential was 4.03 V, the capacity retention rate was 89.8%, and the average potential was 4.00 V. Moreover, the heat generation start temperature was 144 degreeC.

[Example 5] (Example)
A pH of 6.35 g of gadolinium acetate and 3.32 g of an ammonium zirconium carbonate (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ] aqueous solution having a zirconium content of 14.1% by mass mixed with 65.43 g of water. 1 coating solution was prepared. The coating liquid was added to and mixed with 200 g of the lithium-containing composite oxide powder, and the coating amount of gadolinium was 0.15 mol% and the coating amount of zirconium was 0.25 mol%. Similarly, a surface-modified lithium-containing composite oxide was synthesized. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 13.9 μm, D10 was 8.3 μm, D90 was 22.0 μm, and the specific surface area determined by the BET method was 0.43 m ² / g. The alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.010% by mass, and the press density was 2.93 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.105 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 162 mAh / g, and the high rate average potential was 3.97V.
The initial discharge capacity was 175 mAh / g, the initial charge / discharge efficiency was 90.6%, the initial average potential was 4.03 V, the capacity retention rate was 86.9%, and the average potential was 3.96 V. Moreover, the heat generation start temperature was 144 degreeC.

[Example 6] (Example)
A pH of 6.99 g of gadolinium acetate and 1.99 g of an ammonium zirconium carbonate (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ] aqueous solution having a zirconium content of 14.1% by mass mixed with 65.93 g of water. A coating solution of 0 was prepared. The coating solution was added to and mixed with 200 g of the lithium-containing composite oxide powder, and the coating amount of gadolinium was 0.25 mol% and the coating amount of zirconium was 0.15 mol%. Similarly, a surface-modified lithium-containing composite oxide was synthesized. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 13.4 μm, D10 was 7.9 μm, D90 was 21.4 μm, and the specific surface area determined by the BET method was 0.28 m ² / g. The alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.010% by mass, and the press density was 2.93 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.112 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 158 mAh / g, and the high rate average potential was 3.96V.
The initial discharge capacity was 175 mAh / g, the initial charge / discharge efficiency was 90.8%, the initial average potential was 4.02 V, the capacity retention rate was 92.9%, and the average potential was 4.00 V. The heat generation starting temperature was 145 ° C.

[Example 7] (Comparative Example)
Evaluation of the lithium-containing composite oxide powder having a composition of Li _1.02 (Co _0.979 Mg _0.01 Al _0.01 Zr _0.001 ) _0.98 O ₂ which is the base material synthesized in Example 1 did. As a result, the average particle diameter D50 was 13.2 μm, D10 was 7.5 μm, D90 was 21.6 μm, the specific surface area determined by the BET method was 0.24 m ² / g, and the alkali amount was 0.018% by mass. there were.
When the X-ray diffraction spectrum of this lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.101 °. The press density of this powder was 3.09 g / cm ³ .
Regarding the above lithium-containing composite oxide, an electrode and a battery were prepared in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 156 mAh / g, and the high rate average potential was 3.92 V.
The initial discharge capacity was 176 mAh / g, the initial charge / discharge efficiency was 90.7%, the initial average potential was 4.01 V, the capacity retention rate was 28.8%, and the average potential was 3.36 V. The heat generation starting temperature was 143 ° C.

[Example 8] (Comparative example)
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the gadolinium-zirconium impregnated particles was changed from 400 ° C. to 200 ° C. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 14.1 μm, D10 was 8.4 μm, D90 was 22.0 μm, and the specific surface area determined by the BET method was 0.36 m ² / g. Moreover, the alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.017% by mass, and the press density was 2.98 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.104 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 160 mAh / g, and the high rate average potential was 3.95 V.
The initial discharge capacity was 176 mAh / g, the initial charge / discharge efficiency was 91.2%, the initial average potential was 4.02 V, the capacity retention rate was 39.2%, and the average potential was 3.48 V. The heat generation starting temperature was 140 ° C.

[Example 9] (Comparative Example)
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature of the gadolinium-zirconium impregnated particles was changed from 400 ° C to 600 ° C. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 13.9 μm, D10 was 8.4 μm, D90 was 21.7 μm, and the specific surface area determined by the BET method was 0.19 m ² / g. Moreover, the alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.011% by mass, and the press density was 3.04 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.104 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 162 mAh / g, and the high rate average potential was 3.96V.
The initial discharge capacity was 178 mAh / g, the initial charge / discharge efficiency was 91.7%, the initial average potential was 4.02 V, the capacity retention rate was 57.8%, and the average potential was 3.73 V. The heat generation starting temperature was 145 ° C.

[Example 10] (Comparative Example)
To 200 g of the lithium-containing composite oxide powder synthesized in Example 1, a coating solution of pH 5.2 in which 0.46 g of gadolinium nitrate was dissolved in 41.13 g of water was added, and gadolinium was mixed at 0.05 mol%. Drying at 120 ° C. for 4 hours with stirring gave gadolinium-impregnated particles. Further, the obtained gadolinium-impregnated particles were heat-treated at 925 ° C. for 12 hours in an oxygen-containing atmosphere and then pulverized to obtain an average particle diameter D50 of 15.3 μm, D10 of 9.3 μm, and D90 of 23.3 μm. A surface-modified lithium-containing composite oxide powder having a specific surface area of 0.17 m ² / g determined by the BET method was obtained. The alkali amount of the obtained surface-modified lithium-containing composite oxide was 0.014% by mass. The press density of this powder was 3.11 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.093 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 154 mAh / g, and the high rate average potential was 3.95V.
The initial discharge capacity was 176 mAh / g, the initial charge / discharge efficiency was 90.5%, the initial average potential was 4.02 V, the capacity retention rate was 58.4%, and the average potential was 3.67 V. The heat generation start temperature was 142 ° C.

[Example 11] (Comparative Example)
To 200 g of the lithium-containing composite oxide powder synthesized in Example 1, a coating solution having a pH of 5.4 in which 0.93 g of gadolinium nitrate was dissolved in 205.64 g of water was added, and gadolinium was mixed at 0.10 mol%. Drying at 120 ° C. for 4 hours with stirring gave gadolinium-impregnated particles. Further, the obtained gadolinium-impregnated particles were heat-treated at 925 ° C. for 12 hours in an oxygen-containing atmosphere and then crushed to obtain an average particle diameter D50 of 15.1 μm, D10 of 9.3 μm, and D90 of 23.2 μm. A surface-modified lithium-containing composite oxide powder having a specific surface area of 0.16 m ² / g determined by the BET method was obtained. The alkali amount of the obtained surface-modified lithium-containing composite oxide was 0.013% by mass. The press density of this powder was 3.09 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.099 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 159 mAh / g, and the high rate average potential was 3.96V.
The initial discharge capacity was 176 mAh / g, the initial charge / discharge efficiency was 90.4%, the initial average potential was 4.02 V, the capacity retention rate was 71.2%, and the average potential was 3.84 V. Moreover, the heat generation start temperature was 143 ° C.

[Example 12] (Example)
In an aqueous solution in which 1.93 g of magnesium carbonate, 20.87 g of aluminum maleate having an Al content of 2.65% by mass, and 7.74 g of citric acid monohydrate were dissolved in 28.28 g of water, the titanium content was 8.3. An aqueous solution obtained by mixing 1.18 g of a mass% titanium lactate aqueous solution and 196.80 g of cobalt oxyhydroxide having an average particle size of 13 μm and a cobalt content of 60.0 mass% are added and mixed to obtain. The obtained mixture was dried in a constant temperature bath at 80 ° C. This dried mixture and 79.00 g of lithium carbonate having a lithium content of 18.7% by mass were mixed in a mortar, fired at 1010 ° C. for 14 hours in an oxygen-containing atmosphere, and then crushed to obtain Li _1.02 (Co _{0 .979} Mg _0.01 Al _0.01 Ti _0.001 ) _0.98 O ₂ was obtained as a lithium-containing composite oxide powder.
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the lithium-containing composite oxide obtained above was used as a base material. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 19.6 μm, D10 was 11.1 μm, D90 was 33.3 μm, and the specific surface area determined by the BET method was 0.21 m ² / g. Moreover, the alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.016% by mass, and the press density was 3.08 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.105 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 152 mAh / g, and the high rate average potential was 3.98 V.
The initial discharge capacity was 170 mAh / g, the initial charge / discharge efficiency was 89.0%, the initial average potential was 4.02 V, the capacity retention rate was 85.0%, and the average potential was 3.93 V. Moreover, the heat generation start temperature was 142 degreeC.

[Example 13] (Example)
In an aqueous solution in which 1.93 g of magnesium carbonate, 20.87 g of aluminum maleate having an Al content of 2.65% by mass, and 7.74 g of citric acid monohydrate were dissolved in 28.28 g of water, the titanium content was 8.3. An aqueous solution obtained by mixing 1.18 g of a mass% titanium lactate aqueous solution and 196.80 g of cobalt oxyhydroxide having an average particle size of 13 μm and a cobalt content of 60.0 mass% are added and mixed to obtain. The obtained mixture was dried in a constant temperature bath at 80 ° C. This dried mixture, 79.00 g of lithium carbonate having a lithium content of 18.7% by mass, and 0.05 g of lithium fluoride were mixed in a mortar, fired at 1010 ° C. for 14 hours in an oxygen-containing atmosphere, and then crushed. _Thus , a lithium-containing composite oxide powder having a composition of Li _1.02 (Co _0.979 Mg _0.01 Al _0.01 Ti _0.001 ) _0.98 O _0.9995 F _0.001 was obtained.
A surface-modified lithium-containing composite oxide was synthesized in the same manner as in Example 1 except that the lithium-containing composite oxide obtained above was used as a base material. The average particle diameter D50 of this surface-modified lithium-containing composite oxide was 19.3 μm, D10 was 10.5 μm, D90 was 37.6 μm, and the specific surface area determined by the BET method was 0.21 m ² / g. Moreover, the alkali amount of the obtained surface-modified lithium-containing composite oxide powder was 0.014% by mass, and the press density was 3.10 g / cm ³ .
When the X-ray diffraction spectrum of this surface-modified lithium-containing composite oxide powder was measured in the same manner as in Example 1, a peak derived from the lithium-containing composite oxide was confirmed. The integrated width of diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.105 °.
Regarding the surface-modified lithium-containing composite oxide, an electrode and a battery were produced in the same manner as in Example 1 and evaluated. As a result, the high rate capacity was 157 mAh / g, and the high rate average potential was 3.97V.
The initial discharge capacity was 172 mAh / g, the initial charge / discharge efficiency was 89.5%, the initial average potential was 4.03 V, the capacity retention rate was 81.0%, and the average potential was 3.97 V. Moreover, the heat generation start temperature was 142 degreeC.

According to the present invention, a surface-modified lithium-containing composite oxide having high safety and excellent rate characteristics and charge / discharge cycle durability, a positive electrode for lithium ion secondary batteries and the lithium ion including the surface-modified lithium-containing composite oxide Secondary batteries and methods for manufacturing them are provided.
The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-101705 filed on April 28, 2011 are cited here as disclosure of the specification of the present invention. Incorporated.

Claims (17)

Formula _{Li p N x M y O z} F a ( where, N is the, Co, at least one element selected from the group consisting of Mn and Ni, M is, Co, transition metal elements other than Mn and Ni , Al, Sn and at least one element selected from the group consisting of elements of group 2. 0.9 ≦ p ≦ 1.4, 0.9 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 1.9 ≦ z ≦ 2.1, 0 ≦ a ≦ 0.05) impregnated with a coating liquid containing a gadolinium source and a zirconium source into the lithium-containing composite oxide particles, A method for producing a surface-modified lithium-containing composite oxide, characterized in that a gadolinium / zirconium-containing composite oxide is contained in the surface layer of the lithium-containing composite oxide particles by heat treatment at 250 to 550 ° C. The production method according to claim 1, wherein the coating solution has a pH of 1 to 10. The method according to claim 1 or 2, wherein the gadolinium source is at least one selected from the group consisting of gadolinium acetate, gadolinium carbonate, gadolinium hydroxide, gadolinium sulfate, and gadolinium oxide. The method according to any one of claims 1 to 3, wherein the zirconium source is at least one selected from the group consisting of ammonium zirconium carbonate and ammonium zirconium fluoride. The production method according to any one of claims 1 to 4, wherein the lithium-containing composite oxide is impregnated with a coating solution containing 0.01 to 1 mol% gadolinium and zirconium in total of gadolinium and zirconium. 6. The production method according to claim 1, wherein the coating liquid contains 0.03 to 0.5 mol% of gadolinium with respect to the lithium-containing composite oxide. The manufacturing method according to any one of claims 1 to 6, wherein the coating liquid contains 0.03 to 0.5 mol% of zirconium with respect to the lithium-containing composite oxide. The production method according to any one of claims 1 to 7, wherein a molar ratio (Zr / Gd) of zirconium to gadolinium in the gadolinium / zirconium-containing composite oxide is 0.1 to 10. The production method according to any one of claims 1 to 8, wherein gadolinium contained in the gadolinium / zirconium-containing composite oxide is 0.03 to 0.5 mol% with respect to the lithium composite oxide. 10. The production method according to claim 1, wherein zirconium contained in the gadolinium / zirconium-containing composite oxide is 0.03 to 0.5 mol% with respect to the lithium composite oxide. The method according to any one of claims 1 to 10, wherein the heat treatment temperature is 300 to 500 ° C. A positive electrode active material containing a surface-modified lithium-containing composite oxide obtained by the production method according to any one of claims 1 to 11, a conductive agent, a binder and a solvent are mixed, and the resulting slurry is applied to a metal foil. A method for producing a positive electrode for a lithium ion secondary battery, wherein the solvent is removed by heating. A method for producing a lithium ion secondary battery, comprising: laminating a separator and a negative electrode on a positive electrode obtained by the production method according to claim 12 and storing the laminate in a battery case; and then injecting an electrolytic solution. Formula _{Li p N x M y O z} F a ( where, N is the, Co, at least one element selected from the group consisting of Mn and Ni, M is, Co, transition metal elements other than Mn and Ni , Al, Sn and at least one element selected from the group consisting of elements of Group 2. 0.9 ≦ p ≦ 1.4, 0.9 ≦ x ≦ 2.0, 0 ≦ y ≦ 0. 1, 1.9 ≦ z ≦ 4.2, 0 ≦ a ≦ 0.05), wherein the surface layer of the lithium-containing composite oxide particles includes a gadolinium / zirconium-containing composite compound having an amorphous structure. A surface-modified lithium-containing composite oxide. The surface-modified lithium-containing composite according to claim 14, wherein gadolinium and zirconium contained in the surface layer of the particles are in a ratio of 0.01 to 1.00 mol% in total of gadolinium and zirconium with respect to the lithium-containing composite oxide. Oxides. A positive electrode for a lithium secondary battery, comprising a positive electrode active material, a conductive material, and a binder, wherein the positive electrode active material is the surface-modified lithium-containing composite oxide according to claim 14 or 15. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode is the positive electrode according to claim 16.

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