JP2006298699A - Method for manufacturing lithium cobalt composite oxide having large particle size - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium secondary cell containing a lithium cobalt composite oxide having a large volume capacity density, high safety and also excellent charging/discharging cycle durability and to provide its manufacture method. <P>SOLUTION: In the method for manufacturing the lithium cobalt composite oxide expressed by the general formula: Li<SB>p</SB>Co<SB>x</SB>M<SB>y</SB>O<SB>z</SB>F<SB>a</SB>(wherein M is a transition metal element or an alkaline earth metal element other than Al and Co., 0.98≤p≤1.04, 0.970≤x≤1.000, 0≤y≤0.03, 1.9≤z≤2.2, x+y=1 and 0≤a≤0.02), a cobalt oxyhydroxide powder being a cobalt source and having an average particle size of 0.1 to 2.5 μm and a lithium carbonate powder being a lithium source and an M element source powder which is contained, if necessary, are mixed so that a molar ratio of lithium/(Co+M element) may be 0.99-1.04 and the obtained mixture is fired at a firing temperature of 900 to 1,100°C in an oxygen-containing atmosphere. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a lithium cobalt composite oxide having a large particle size suitable for a positive electrode active material for a lithium secondary battery having a large volumetric capacity density, high safety, and excellent charge / discharge cycle durability (hereinafter, It may be referred to as lithium cobaltate).

In recent years, as devices become more portable and cordless, demand for non-aqueous electrolyte secondary batteries such as lithium secondary batteries having a small size, light weight, and high energy density is increasing. As such positive electrode active materials for non-aqueous electrolyte secondary batteries, composite oxides of lithium and transition metals such as LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn ₂ O ₄ , LiMnO ₂ are known. Yes.

Among them, lithium secondary batteries using lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material and carbon such as lithium alloy, graphite, and carbon fiber as a negative electrode can obtain a high voltage of 4V, It is widely used as a battery having a high energy density.

However, in the case of a non-aqueous secondary battery using LiCoO ₂ as a positive electrode active material, further improvement in capacity density per unit volume and safety of the positive electrode layer is desired, and by repeatedly performing a charge / discharge cycle, There have been problems such as deterioration of cycle characteristics in which the battery discharge capacity is gradually reduced, weight capacity density, and the like, and a large decrease in discharge capacity at low temperatures.

  In order to solve some of these problems, cobalt oxyhydroxide powder (trade name “Chemigrade”, Queensland Nickel, Australia) is commercially available as a cobalt source. However, in response to the recent increase in battery performance requirements for further increase in capacity, the positive electrode active material sufficiently satisfies safety, volume capacity density, and weight capacity density although the coating characteristics and cycle characteristics are improved. There is nothing to do.

  On the other hand, the production of lithium cobalt composite oxide by directly lithiating cobalt oxyhydroxide is known from several patent publications. Patent Document 1 discloses that lithium cobaltate having an average particle size of 3.8 to 9.3 μm is produced by performing calcination of lithium at 600 to 700 ° C. using cobalt oxyhydroxide particles. . Patent Document 2 discloses that lithium cobalt oxide having a particle size of 4 to 30 μm is synthesized from secondary particles of cobalt oxyhydroxide in the range of 4 to 30 μm as a raw material.

  Patent Document 3 proposes to synthesize lithium cobalt oxide by lithiation using cobalt oxyhydroxide having an average particle diameter of 10 to 15 μm. Patent Document 4 discloses synthesizing 6 μm lithium cobaltate by lithiation using 6 μm cobalt oxyhydroxide-containing cobalt oxide. Patent Document 5 discloses that 9.6 to 11.5 μm of lithium cobaltate is synthesized by lithiation using cobalt oxyhydroxide having an average particle diameter of 8 to 15 μm.

  Further, Patent Document 6 discloses that lithium cobalt oxide having an average particle diameter of 7 to 9 μm is synthesized by lithiating cobalt oxyhydroxide having an average particle diameter of 0.6 to 8.5 μm. Patent Document 7 discloses that lithium cobaltate having an average particle size of 10 to 15 μm is synthesized by lithiation using cobalt oxyhydroxide having an average particle size of secondary particles of 8 to 15 μm. Yes.

Further, in order to solve the above-mentioned problems relating to battery characteristics, Patent Document 8 proposes to replace 5-35% of Co atoms with W, Mn, Ta, Ti or Nb for improving cycle characteristics. Yes.
In the above-described conventional technology, the lithium secondary battery using the lithium cobalt composite oxide as the positive electrode active material sufficiently satisfies all of the volume capacity density, safety, coating uniformity, cycle characteristics, and low temperature characteristics. Things have not yet been obtained.

JP-A-11-49519 JP-A-11-273678 WO01 / 027032 JP 2002-60225 JP2003-2661 JP2003-104729 JP2004-196603 Japanese Unexamined Patent Publication No. 3-201368

  The present invention relates to a method for producing a lithium cobalt composite oxide, which is a positive electrode active material for a lithium secondary battery having a large volumetric capacity density, high safety, and excellent charge / discharge cycle durability, and produced lithium cobalt It aims at providing the positive electrode for lithium secondary batteries which uses complex oxide, and a lithium secondary battery.

The present inventor has conducted intensive research to achieve the above-described problems, and has found that the above-described problems can be achieved by an invention having the following configuration.
(1) In formula _{Li p Co x M y O z} F a ( where, M is Al, a transition metal element or an alkaline earth metal element other than Co .0.98 ≦ p ≦ 1.04,0.970 ≦ x ≦ 1.000, 0 ≦ y ≦ 0.03, 1.9 ≦ z ≦ 2.2, x + y = 1, 0 ≦ a ≦ 0.02). A cobalt oxyhydroxide powder having an average particle diameter of 0.1 to 2.5 μm as a cobalt source, a lithium carbonate powder as a lithium source, and an M element source powder contained as necessary. The mixture is mixed so that the molar ratio of (Co + M element) is 0.99 to 1.04, and the resulting mixture is fired at a firing temperature of 900 to 1100 ° C. in an oxygen-containing atmosphere. Method for producing lithium cobalt composite oxide.
(2) The production method of the above (1), wherein the lithium cobalt composite oxide has an average particle size of 12 to 30 μm.
(3) The production method according to the above (1) or (2), wherein the lithium carbonate powder has an average particle diameter of 3 to 50 μm and is fired at a firing temperature of 990 to 1050 ° C. for 4 to 24 hours.
(4) The manufacturing method in any one of said (1)-(3) whose average particle diameter of cobalt oxyhydroxide powder is 0.3-2.2 micrometers.
(5) A group consisting of cobalt hydroxide powder, cobalt oxyhydroxide powder, cobalt carbonate powder and cobalt oxide powder per 100 parts by weight of the powder together with cobalt oxyhydroxide powder having an average particle size of 0.1 to 2.5 μm The manufacturing method in any one of said (1)-(3) using what mixed 30-300 weight part of powder with an average particle diameter of 2-6 micrometers selected from at least 1 sort (s).
(6) The M element source is at least one selected from the group consisting of Al, Mg, Ti, Zr and Mn, and the M element contains 0.0001 to 0.03 in atomic ratio with respect to cobalt. The manufacturing method according to any one of (1) to (5) above.
(7) Cobalt oxyhydroxide powder is impregnated with cobalt oxyhydroxide powder and dried with an aqueous solution of carboxylate containing cobalt and containing two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in the molecule. The production method according to any one of (1) to (6) above.
(8) Cobalt oxyhydroxide powder is impregnated with cobalt oxyhydroxide powder with an aqueous solution of carboxylic acid salt containing M element and containing two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in the molecule; The production method according to any one of (1) to (6), which is dried.
(9) The manufacturing method according to any one of (1) to (8), wherein the press density of the lithium cobalt composite oxide is 3.7 to 4.1 g / cm ³ .
(10) A lithium secondary battery positive electrode including a large particle size lithium cobalt composite oxide produced by the production method according to any one of (1) to (9).
(11) A lithium secondary battery using the positive electrode described in (10) above.

  According to the present invention, a lithium cobalt composite oxide having a large particle size suitable as a positive electrode active material for a lithium secondary battery having a large volumetric capacity density, high safety, and excellent charge / discharge cycle durability is obtained. It is done. It is not always clear why the lithium cobalt composite oxide having a large particle diameter as described above can be obtained and an excellent effect can be obtained by the present invention. However, it is inferred as follows.

  That is, the reactivity of cobalt oxyhydroxide, which is a raw material of the lithium cobalt composite oxide having a large particle diameter of the present invention, is higher than that of cobalt oxide and the like. It has high reactivity and easily grows to a large particle size. At the same time, due to the high reactivity of the cobalt oxyhydroxide, the sintering proceeds densely, so that a dense lithium cobalt composite oxide particle having high density can be obtained for each particle unit.

  Furthermore, in the present invention, when the M element is contained as an additive element, particularly when the M element is used in the form of an aqueous solution, a part of cobalt in the lithium cobalt composite oxide is uniformly and sufficiently formed by the M element. Therefore, a lithium cobalt composite oxide for a lithium secondary battery positive electrode having high safety, excellent charge / discharge cycle durability, and excellent low temperature characteristics can be obtained.

  Furthermore, in the present invention, the cobalt oxyhydroxide powder as a cobalt source is impregnated with an aqueous solution containing a cobalt element and dried, thereby forming primary particles constituting primary particles between the primary particles of the cobalt oxyhydroxide powder. In the meantime, a dry product of a solution containing cobalt is deposited, and a dense cobalt raw material in which voids are filled with cobalt element is obtained. When this dense cobalt raw material is used, the crystal grains are easy to grow, each particle becomes dense and the filling property is improved, and the lithium cobalt composite for a lithium secondary battery positive electrode excellent in volume capacity density and battery performance. It is thought that an oxide is obtained.

Lithium-cobalt composite oxide for a lithium secondary battery positive electrode produced in the present invention is represented by the general formula _{Li p Co x M y O z} F a. In such general formula, M, p, x, y, z and a are defined above. Among these, p, x, y, z and a are preferably as follows. 0.99 ≦ p ≦ 1.03, 0.990 ≦ x ≦ 1.0, 0.0005 ≦ y ≦ 0.02, 1.95 ≦ z ≦ 2.05, x + y = 1, 0.0001 ≦ a ≦ 0.01. Here, when a is larger than 0, a composite oxide in which some of the oxygen atoms are substituted with fluorine atoms is obtained, but in this case, the safety of the obtained positive electrode active material is improved.

In the present invention, a cobalt oxyhydroxide powder having an average particle size of 0.1 to 2.5 μm is used as a cobalt source. If the average particle size of the cobalt oxyhydroxide is less than 0.1 μm, the cobalt oxyhydroxide powder becomes bulky and the productivity of the lithium cobalt composite oxide is unfavorable. When the average particle diameter of cobalt oxyhydroxide exceeds 2.5 μm, the particle growth becomes insufficient, and the press density of the lithium cobalt composite oxide is lowered, which is not preferable. The preferable average particle diameter of cobalt oxyhydroxide is 0.3-2.2 micrometers, More preferably, it is 0.5-0.9 micrometers. The specific surface area is preferably ² to 200 m ² / g.

  In the case of lithium cobalt composite oxide particles, the average particle size (D50) in the present invention is a volume average particle size with respect to a secondary particle size obtained by agglomerating and sintering primary particles. In this case, when the particles consist only of primary particles, it means the volume average particle diameter of the primary particles. When the cobalt source particles are aggregated to form secondary particles, the secondary particles of the cobalt source are formed. It means the volume average particle size of the secondary particles. The average particle size is a particle size distribution on a volume basis, and in a cumulative curve with the total volume being 100%, the volume-based cumulative 50% diameter (D50) is the particle size at which the cumulative curve becomes 50%. means. 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 Leeds & Northrup).

  In the present invention, cobalt oxyhydroxide powder, preferably used M element source powder, and lithium carbonate powder are mixed in a lithium / (Co + M element) molar ratio in the range of 0.99 to 1.04. The When the molar ratio of lithium / (Co + M element) is less than 0.99, cobalt oxide is produced as a by-product in lithiation, which is not preferable. When the molar ratio of lithium / (Co + M element) exceeds 1.04, it is not preferable because the charge / discharge cycle durability of the battery is lowered and gas generation due to decomposition of the electrolytic solution easily occurs in the battery. The charge molar ratio of lithium / (Co + M element) is particularly preferably 1.0 to 1.02.

  The lithium cobalt composite oxide having a large particle diameter produced by the present invention is preferably a lithium cobalt composite oxide having an average particle diameter (D50) of 10 μm to 40 μm. If the average particle size of the lithium cobalt composite oxide is less than 10 μm, the press density of the lithium cobalt composite oxide decreases, which is not preferable. When the average particle diameter of the lithium cobalt composite oxide exceeds 40 μm, the positive electrode surface becomes unsmooth, which is not preferable. In particular, the average particle size of the lithium cobalt composite oxide is preferably 12 to 30 μm, and particularly preferably 16 to 25 μm.

  In the present invention, when using a highly reactive cobalt oxyhydroxide having an average particle size of 0.1 to 2.5 μm, preferably 0.3 to 2.2 μm, the average particle size is 2 to 6 μm. And having at least one of cobalt hydroxide powder, cobalt oxyhydroxide powder, cobalt carbonate powder or cobalt oxide powder, the latter is preferably 30 to 300 parts by weight, particularly preferably 70 to 200 parts, per 100 parts by weight of the former. Even when the mixture is used as a cobalt source, a lithium cobalt composite oxide having a large particle size and high packing density can be produced. If the latter mixing ratio exceeds 300 parts by weight, it is difficult to obtain a dense positive electrode having a high press density.

  In the present invention, the M element is a transition metal element other than Al and Co or an alkaline earth metal, and the transition metal element is Group 4, Group 6, Group 7, Group 8, Group 9, Group 9 of the Periodic Table, Represents group 10 and group 11 and group 12 transition metals. Among these, M is preferably at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mn, Mg, Ca, Sr, Ba, and Al. Among these, at least one selected from the group consisting of Ti, Zr, Hf, Mn, Mg, and Al is preferable from the viewpoint of capacity development, safety, cycle durability, and the like.

  In the present invention, the M element consists of Al and Mg, Al and Mg are preferably in an atomic ratio of 1/3 to 3/1, particularly preferably 2/3 to 3/2, and y is preferably 0. 0.005 ≦ y ≦ 0.025, particularly preferably 0.01 ≦ y ≦ 0.02. In such a case, the balance of battery performance, that is, the balance of initial weight capacity density, safety, and charge / discharge cycle stability is particularly preferable. In the present invention, M is composed of Mg and M2 (M2 is at least one element selected from the group consisting of Ti, Zr, Ta, and Nb), and M2 and Mg are preferably in an atomic ratio of 1 / 40 to 2/1, preferably 1/30 to 1/5, and y is preferably 0.005 ≦ y ≦ 0.025, particularly preferably 0.01 ≦ y ≦ 0.02. This is particularly preferable because the battery performance balance, that is, the initial weight capacity density, initial volume capacity density, safety, and charge / discharge cycle stability is well balanced.

  In the present invention, the M element is composed of Zr and Mg, and Zr and Mg are preferably in an atomic ratio of 1/40 to 2/1, preferably 1/30 to 1/5, and y is preferably 0.005. ≦ y ≦ 0.025, particularly preferably 0.01 ≦ y ≦ 0.02. In such a case, the balance of battery performance, that is, the balance of initial weight capacity density, initial volume capacity density, safety, and charge / discharge cycle stability is particularly preferable.

  In the present invention, when the M element is composed of Mg, Al, and Zr, the balance of battery performance, that is, the balance of initial weight capacity density, initial volume capacity density, safety, and charge / discharge cycle stability is particularly high. It is particularly preferable because it is good. In this case, the Zr content is preferably 1/2 to 1/20 of the total number of moles of Mg and Al.

  In the present invention, when the M element and / or F is contained, both the M element and F are preferably present on the surface of the lithium cobalt composite oxide particles. The presence of these elements on the surface can improve important battery characteristics such as safety and charge / discharge cycle characteristics without causing a decrease in battery performance when added in a small amount. Whether or not these elements are present on the surface can be determined by performing spectroscopic analysis, for example, XPS analysis, on the positive electrode particles.

The lithium cobalt composite oxide obtained in the present invention preferably has a press density of 3.7 to 4.1 g / cm ³ . In the present invention, the press density means an apparent press density when the lithium cobalt composite oxide particle powder is press-compressed at a pressure of ² t / cm ² . When the press density is smaller than the above range, the electrode density of the positive electrode of the actual battery is lowered and the battery capacity is lowered. On the other hand, when it is large, the discharge characteristics at a large current deteriorate, which is not preferable. In particular, the press density is preferably 3.8 to 4.0 g / cm ³ . Further, the lithium cobalt composite oxide preferably contains 0.02% by mass or less, particularly preferably 0.01% by mass or less, of the remaining alkali content.

  The specific means for producing the lithium cobalt composite oxide in the present invention is not limited, but the following means are preferably used. For example, a mixture containing a cobalt source, a lithium source, an M element source and a fluorine source used as necessary is fired in an oxygen-containing atmosphere. As a cobalt source, in addition to the above-described finely divided cobalt oxyhydroxide, cobalt trioxide, cobalt oxyhydroxide, cobalt hydroxide, cobalt carbonate, and the like are used in combination. Control of physical property values such as particle diameter, particle shape and particle size distribution of the lithium cobalt composite oxide particles to be produced can be achieved especially by controlling the particle diameter, particle shape, particle size distribution and specific surface area of the cobalt source.

A mixture containing a cobalt source, a lithium source, an M element source and a fluorine source is baked at 900 to 1100 ° C., particularly preferably 990 to 1050 ° C. in an oxygen-containing atmosphere for 4 to 24 hours. The obtained fired product is cooled, pulverized and classified to produce lithium cobalt composite oxide particles. As the cobalt source, the above-mentioned fine cobalt oxyhydroxide is used. The lithium carbonate powder as the lithium source preferably has an average particle diameter D50 of 3 to 50 μm and a specific surface area of 0.1 to 10 m ² / g.

  In the present invention, when a fine cobalt oxyhydroxide powder is used as a cobalt source, an aqueous solution containing cobalt element is used, and an aqueous solution containing cobalt element is impregnated into the cobalt oxyhydroxide powder and dried. Preferably used as a source. In this case, a dry product of an aqueous solution containing cobalt element is deposited between the primary particles of the cobalt oxyhydroxide powder or between the primary particles constituting the secondary particles, and the dense oxyhydroxide in which the voids are filled with the cobalt element is deposited. Cobalt powder is obtained. When this cobalt oxyhydroxide powder is used, it is dense with few voids, and furthermore, the cobalt element which is a dried product of the aqueous solution has high reactivity with lithium, so that the crystal grains are easy to grow. There are no voids inside. As a result, each of the particles becomes dense, the filling property is improved, and a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery excellent in volume capacity density and battery performance is obtained.

  In the present invention, the amount of cobalt element supplied from an aqueous solution in which cobalt element is dissolved is preferably 0.1 to 20%, particularly preferably 0.3 to 5% of the cobalt element in the lithium cobalt composite oxide. is there. If cobalt element exceeds 20% and is supplied from an aqueous solution, the aqueous solution cannot sufficiently penetrate into the cobalt element raw material powder, and it is not preferable because it precipitates as finely divided cobalt element. On the other hand, when it is less than 0.1%, the amount of cobalt element added is decreased, which is not preferable.

  Furthermore, in this invention, when M element is further contained as an additional element in lithium cobalt complex oxide, it is preferable to use this M element in the form of aqueous solution. In this case, the cobalt element in the lithium cobalt composite oxide is very sufficiently and uniformly substituted by the M element. Thus, a lithium-containing composite oxide for a lithium secondary battery positive electrode having high safety, excellent charge / discharge cycle durability, and excellent low-temperature characteristics can be obtained.

  In the present invention, when cobalt oxyhydroxide particles are impregnated with cobalt element and, if necessary, M element in the form of an aqueous solution, the aqueous solution includes cobalt element and, if necessary, M element, and An aqueous solution of a carboxylic acid salt containing a total of two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in the molecule is preferably used. In the case of having a plurality of carboxylic acid groups, it is preferable that a hydroxyl group coexists in addition to the carboxylic acid group because the solubility in an aqueous solution of cobalt or M element can be increased. For example, if there is only one carboxylic acid group in the molecule, such as acetic acid and propionic acid, the solubility of cobalt and M elements is low, such being undesirable. In particular, a molecular structure in which 2 to 4 carboxylic acid groups or 1 to 4 hydroxyl groups coexist is preferable because the solubility can be increased. The number of carbon atoms of the carboxylic acid group is preferably 2 to 8, and 2 to 6 is particularly preferable. If the carbon number of the carboxylic acid group is 9 or more, the solubility of the M element decreases, which is not preferable.

  Preferred carboxylic acids used above include citric acid, tartaric acid, succinic acid, malonic acid, malic acid, succinic acid, lactic acid, and particularly citric acid and tartaric acid, succinic acid can increase the solubility of cobalt and M element, This is preferable because it is relatively inexpensive. When using a highly acidic carboxylic acid such as oxalic acid, cobalt oxyhydroxide easily dissolves when the pH of the aqueous solution is less than 2, so that the pH is adjusted to 2 to 12 by adding a base such as ammonia. Is preferred.

  The concentration of the cobalt source and the M element source in the aqueous solution of the carboxylate used in the present invention is preferably higher because the aqueous medium needs to be removed by drying in a later step. However, if the concentration is too high, the viscosity becomes high, the uniform mixing with other element-containing compound powder forming the positive electrode active material is reduced, and the solution is less likely to penetrate into the cobalt oxyhydroxide raw material powder. It is preferably 1 to 30% by weight, particularly 4 to 20% by weight.

  If necessary, the medium for forming the aqueous solution of the carboxylate may contain a polyol having an effect of forming a complex in order to increase the solubility of the cobalt source or the M element source in the aqueous solution. Examples of the polyol include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, butanediol, glycerin and the like. The polyol content is preferably 1 to 20% by weight.

  The cobalt source and M element source used to form an aqueous solution of a carboxylate containing cobalt element and M element source used in the present invention include oxides, hydroxides, carbonates, nitrates, etc. Inorganic salts, organic salts such as acetates, oxalates, and citrates, organometallic chelate complexes, and compounds obtained by stabilizing metal alkoxides with chelates or the like are used. In the present invention, those that are uniformly dissolved in a carboxylic acid aqueous solution are more preferable, and oxides, hydroxides, oxyhydroxides, water-soluble carbonates, nitrates, acetates, oxalates, and citrates are more preferable. preferable. Of these, citrate is preferred because of its high solubility. In addition, since oxalate and citrate aqueous solutions have low pH, cobalt element and the like may be dissolved from the cobalt oxyhydroxide powder. In that case, ammonia is added to the aqueous solution to adjust the pH to 2-12. An aqueous solution is preferred.

  Thus, by impregnating cobalt oxyhydroxide powder with the cobalt-containing carboxylate aqueous solution and drying, the press density of the resulting lithium cobalt composite oxide is further improved, and the volume capacity density in the actual battery is improved. To do. Further, it is more preferable that the carboxylate aqueous solution contains M element in addition to cobalt, since the safety of the battery, charge / discharge cycle durability, large current discharge characteristics, and low temperature discharge characteristics may be improved.

As a method for carrying an aqueous solution of a carboxylate salt on cobalt oxyhydroxide powder, several means are selected depending on the mode, and preferred modes include the following means (A) and (B). Is mentioned.
(A) The cobalt oxyhydroxide powder is impregnated with the aqueous solution of the cobalt oxyhydroxide powder and the above-described carboxylate containing M element, and then the water is removed by drying. Next, the lithium source powder and, if necessary, dry-mixing with a compound containing fluorine, and the dried mixed powder is fired at 900 to 1100 ° C. in an oxygen-containing atmosphere.
(B) Cobalt oxyhydroxide powder is impregnated with cobalt oxyhydroxide powder and the above cobalt-containing aqueous solution of carboxylate containing cobalt. Next, after moisture is removed by drying, the dried mixed powder is mixed with the lithium source powder and then fired at 900 to 1100 ° C. in an oxygen-containing atmosphere.

  As a method of impregnating the cobalt oxyhydroxide powder with the carboxylate aqueous solution in the above means, it is possible to impregnate the powder by spraying the aqueous solution. Alternatively, the cobalt oxyhydroxide powder can be charged into a carboxylate aqueous solution stored in a tank and impregnated by stirring. More preferably, a biaxial screw kneader, an axial mixer, a paddle mixer, a turbulizer, or the like is used, and the impregnation can be performed by sufficiently uniformly mixing so as to form a slurry. As a solid content concentration in the slurry in this case, a higher concentration is preferable as long as it is uniformly mixed. Usually, the solid / liquid weight ratio is 30/70 to 90/10, and particularly preferably 50/50 to 80/20 is preferred. Moreover, it is preferable to perform a reduced pressure treatment in the state of the slurry because the solution penetrates more into the cobalt oxyhydroxide powder.

  The removal of the aqueous medium from the impregnated product obtained above is preferably performed by drying at 50 to 200 ° C., particularly preferably at 80 to 120 ° C., usually for 1 to 10 hours. Since the aqueous medium in the impregnated product is incinerated in the subsequent firing process, it is not always necessary to completely remove it at this stage, but a large amount of energy is required to dissipate moisture in the firing process. It is preferable to remove it. Examples of the method for removing the aqueous medium include a spray dryer, a flash dryer, a belt dryer, a paddle dryer, and a biaxial screw dryer. Among these, a biaxial screw dryer is preferable. Examples of the biaxial screw dryer include a thermoprocessor and a paddle dryer.

  When producing a positive electrode for a lithium secondary battery using the lithium cobalt composite oxide powder obtained in the present invention, carbon-based conductive materials such as acetylene black, graphite, and Ketchen black are added to the lithium cobalt composite oxide powder. It is formed by mixing a material and a binder. For the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is preferably used. The lithium cobalt composite oxide powder, the conductive material and the binder are made into a slurry or kneaded material using a solvent or a dispersion medium, and this is supported on a positive electrode current collector such as an aluminum foil or a stainless steel foil by coating or the like. A positive electrode plate for a secondary battery is manufactured.

  In the lithium secondary battery using the lithium cobalt composite oxide powder 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. Various solvents can be used as the solvent for the electrolyte solution of the battery, and among them, carbonate ester is preferable. 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 ester include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate, methyl isopropyl carbonate and the like.

  In this invention, the said carbonate ester can be used individually or in mixture of 2 or more types. Moreover, you may mix and use with another solvent. Moreover, 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, cycle durability, and charge / discharge efficiency may be improved.

Further, in the lithium secondary battery using the lithium cobalt composite oxide powder of the present invention as the positive electrode active material, a vinylidene fluoride-hexafluoropropylene copolymer (for example, trade name Kyner manufactured by Atchem Co.) or vinylidene fluoride-par A gel polymer electrolyte containing a fluoropropyl vinyl ether copolymer may be used. Solutes added to the electrolyte solvent 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 electrolyte solvent 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 lithium cobalt composite oxide powder of 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 this negative electrode active material is not particularly limited, but for example, lithium metal, lithium alloy, carbon material, periodic table 14, oxide mainly composed of group 15 metal, carbon compound, silicon carbide compound, silicon oxide compound, Examples thereof include titanium sulfide and boron carbide compounds. 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. As the negative electrode current collector, a copper foil, a nickel foil, or the like is used. 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.

  There is no restriction | limiting in particular in the shape of the lithium battery which uses the lithium cobalt complex oxide powder of this invention for a positive electrode active material. 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. In the following, Examples 1 to 6 are examples of the present invention, and Examples 7 to 8 are comparative examples.

[Example 1]
189 g of cobalt oxyhydroxide powder having an average particle size of 0.7 μm and a specific surface area of 45 m ² / g and 76.6 g of lithium carbonate having an average particle size of 20 μm were mixed at a Li / Co molar ratio of 1.01. And calcined at 950 ° C. for 12 hours. As a result of measuring the particle size distribution of the lithium cobalt composite oxide powder composed of Li _1.005 Co _0.995 O ₂ obtained by crushing the fired product in a water solvent using a laser scattering type particle size distribution measuring device, the average particle size D50 22.7μm, D10 is 11.1μm, D90 is 44.4Myuemu, the specific surface area determined by the BET method form secondary particles primary particles with a number aggregation of 0.25 m ² / g A substantially spherical lithium cobalt composite oxide powder was obtained.

With respect to this lithium-containing composite oxide powder, an X-ray diffraction spectrum was obtained using an X-ray diffractometer (RINT 2100 type, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane at 2θ = 66.5 ± 1 ° was 0.113 °. The press density of this powder was 3.79 g / cm ³ .

The above powder composed of Li _1.005 Co _0.995 O ₂ , acetylene black, and polyvinylidene fluoride powder were mixed at a mass ratio of 90/5/5, and N-methylpyrrolidone was added to prepare a slurry. One side coating was performed on a 20 μm thick aluminum foil using a doctor blade. The positive electrode sheet for lithium batteries was produced by drying and roll press rolling.

Then, the positive electrode sheet is used as a positive electrode, a metal lithium foil having a thickness of 500 μm is used as a negative electrode, a nickel foil is used as a negative electrode current collector, and a porous polypropylene having a thickness of 25 μm is used as a separator. Further, the electrolytic solution used is a LiPF ₆ / EC + DEC (1: 1) solution having a concentration of 1 M (meaning a mixed solution of EC and DEC having a mass ratio (1: 1) of LiPF ₆ as a solute. Solvents described later) In accordance with this, two stainless steel simple sealed cell type lithium batteries were assembled in an argon glove box.

For one battery using an EC + DEC (1: 1) solution as the electrolyte, the battery was charged to 4.3 V at a load current of 75 mA / g of the positive electrode active material at 25 ° C., and loaded at 75 mA / g of the positive electrode active material. The initial discharge capacity was determined by discharging to 2.5 V with current. Moreover, about this battery, the charging / discharging cycle test was done 30 times continuously. As a result, the initial weight capacity density at 25 ° C. and 2.5 to 4.3 V was 161 mAh / g-LiCoO ₂ , and the capacity retention rate after 30 charge / discharge cycles was 94.8%. On the other hand, the remaining battery using the EC + DEC (1: 1) solution as the electrolyte was charged at 4.3 V for 10 hours, disassembled in an argon glove box, and charged positive electrode sheet. The positive electrode sheet was washed, punched out to a diameter of 3 mm, sealed in an aluminum capsule together with EC, 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 4.3V charged product was 161 ° C.

[Example 2]
193.8 g of cobalt oxyhydroxide powder having an average particle size of 2.0 μm and 76.6 g of lithium carbonate having an average particle size of 20 μm were mixed at a Li / Co molar ratio of 1.01, and calcined at 1000 ° C. for 12 hours. Then, the same operation as in Example 1 was performed except that the fired product was crushed to obtain a lithium-containing composite oxide powder composed of Li _1.005 Co _0.995 O ₂ .

The average particle diameter D50 of this powder is 17.9 μm, D10 is 8.5 μm, D90 is 39.6 μm, (110) area width is 0.105 °, specific surface area is 0.31 m ² / g press density is It was 3.77 g / cm ³ . The weight capacity density of the positive electrode using this powder was 161.6 mAh / g, the capacity retention after 30 charge / discharge cycles was 94.7%, and the heat generation starting temperature was 161 ° C.

[Example 3]
1.0 g of magnesium carbonate having a magnesium content of 25.8%, 4.7 g of aluminum lactate having an aluminum content of 17.7%, and 7.9 g of citric acid were dissolved in 60 g of water. This solution was mixed with 186.6 g of cobalt oxyhydroxide having an average particle size of 0.7 μm and dried at 80 ° C. The obtained dry powder and 76.4 g of lithium carbonate having an average particle diameter of 20 μm were mixed at a Li / (Co + Mg + Al) molar ratio of 1.01, and fired at 950 degrees for 12 hours. The fired product was crushed to obtain a lithium-containing composite oxide powder composed of Li _1.005 (Co _0.98 Mg _0.005 Al _0.015 ) _0.995 O ₂ , and the same as in Example 1. The operation was performed.

This powder has an average particle size D50 of 20.9 μm, D10 of 7.1 μm, D90 of 40.0 μm, (110) area width of 0.105 °, specific surface area of 0.29 m ² / g, press density Was 3.91 g / cm ³ . Moreover, the weight capacity density of the positive electrode using this powder was 150.6 mAh / g, the capacity retention after 30 charge / discharge cycles was 98.0%, and the heat generation starting temperature was 166 ° C.

[Example 4]
1.0 g of magnesium carbonate with 25.8% magnesium, 4.7 g of aluminum lactate with 17.7% aluminum, 2.7 g of cobalt carbonate with 44.9% cobalt and 16.6 g of citric acid in water Dissolved in 140 g. This solution was mixed with 184.7 g of cobalt oxyhydroxide having an average particle size of 0.7 μm and dried at 80 ° C. The obtained dried powder and 76.4 g of lithium carbonate of 20 μm were mixed at a Li / (Co + Mg + Al) molar ratio of 1.01, and baked at 950 degrees for 12 hours. The fired product was crushed to obtain a lithium-containing composite oxide powder composed of Li _1.005 (Co _0.98 Mg _0.005 Al _0.015 ) _0.995 O ₂ , and the same as in Example 1. The operation was performed.

This powder has an average particle diameter D50 of 22.2 μm, D10 of 9.6 μm, D90 of 39.3 μm, (110) area width of 0.102 °, specific surface area of 0.28 m ² / g, press density Was 3.98 g / cm ³ . The weight capacity density of the positive electrode using this powder was 151.3 mAh / g, the capacity retention after 30 charge / discharge cycles was 97.8%, and the heat generation start temperature was 165 ° C.

[Example 5]
1.0 g of magnesium carbonate having a magnesium content of 25.8%, 4.7 g of aluminum lactate having an aluminum content of 17.7%, and 7.9 g of citric acid were dissolved in 60 g of water. This solution was mixed with 94.8 g of cobalt oxyhydroxide having an average particle diameter of 3 μm and 93.3 g of cobalt oxyhydroxide having an average particle diameter of 0.7 μm, and dried at 80 ° C. The obtained dry powder and 76.4 g of lithium carbonate having an average particle diameter of 20 μm were mixed at a Li / (Co + Al + Mg) molar ratio of 1.01, and baked at 950 degrees for 12 hours. The fired product was crushed to obtain a lithium-containing composite oxide powder composed of Li _1.005 (Co _0.98 Mg _0.005 Al _0.015 ) _0.995 O ₂ , and the same as in Example 1. The operation was performed.

This powder has an average particle diameter D50 of 20.0 μm, D10 of 8.0 μm, D90 of 32.0 μm, (110) area width of 0.108 °, specific surface area of 0.29 m ² / g, press density Was 3.90 g / cm ³ . The weight capacity density of the positive electrode using this powder was 150.9 mAh / g, the capacity retention rate after 30 charge / discharge cycles was 97.6%, and the heat generation start temperature was 165 ° C.

[Example 6]
1.0 g of magnesium carbonate having a magnesium content of 25.8%, 4.7 g of aluminum lactate having an aluminum content of 17.7%, and 7.9 g of citric acid were dissolved in 60 g of water. This solution was mixed with 100.2 g of cobalt oxyhydroxide having an average particle diameter of 0.7 μm and 94.7 g of cobalt hydroxide having an average particle diameter of 1 μm, and dried at 80 ° C. The obtained dry powder and 76.4 g of lithium carbonate having an average particle diameter of 20 μm were mixed at a Li / (Co + Mg + Al) molar ratio of 1.01, and fired at 950 degrees for 12 hours. The fired product was crushed to obtain a lithium-containing composite oxide powder composed of Li _1.005 (Co _0.98 Mg _0.005 Al _0.015 ) _0.995 O ₂ , and the same as in Example 1. The operation was performed.

The average particle diameter D50 of this powder is 20.1 μm, D10 is 8.8 μm, D90 is 35.5 μm, (110) area width is 0.110 °, specific surface area is 0.31 m ² / g, press density Was 3.89 g / cm ³ . The weight capacity density of the positive electrode using this powder was 150.1 mAh / g, the capacity retention after 30 charge / discharge cycles was 97.8%, and the heat generation starting temperature was 165 ° C.

Example 7 Comparative Example 192.2 g of cobalt oxyhydroxide powder having an average particle size of 3.0 μm and 75.9 g of lithium carbonate having an average particle size of 20 μm were mixed at a Li / Co molar ratio of 1.01. The same operation as in Example 1 was performed except that the fired product was pulverized at 950 ° C. for 12 hours, and the lithium-containing composite oxide powder composed of Li _1.005 (Co _0.995 O ₂ was obtained. .

The average particle diameter D50 of this powder is 9.4 μm, D10 is 4.3 μm, D90 is 20.1 μm, (110) area width is 0.114 °, specific surface area is 0.39 m ² / g press density is It was 3.53 g / cm ³ . Moreover, the weight capacity density of the positive electrode using this powder was 161.0 mAh / g, the capacity retention after 30 charge / discharge cycles was 94.2%, and the heat generation start temperature was 160 ° C.

Example 8 Comparative Example 192.2 g of cobalt oxyhydroxide powder having an average particle diameter of 16.2 μm and 75.9 g of lithium carbonate having an average particle diameter of 20 μm were mixed at a Li / Co molar ratio of 1.01. The same operation as in Example 1 was performed except that the fired product was pulverized at 950 ° C. for 12 hours to obtain a lithium-containing composite oxide powder composed of Li _1.005 Co _0.995 O ₂ .

The average particle diameter D50 of this powder is 17.4 μm, D10 is 9.4 μm, D90 is 25.0 μm, (110) area width is 0.116 °, specific surface area is 0.26 m ² / g press density is It was 3.57 g / cm ³ . Moreover, the weight capacity density of the positive electrode using this powder was 161.2 mAh / g, the capacity retention after 30 charge / discharge cycles was 93.3%, and the heat generation start temperature was 160 ° C.

  According to the present invention, a positive electrode active material for a lithium secondary battery having a large volumetric capacity density, high safety, excellent uniform coatability, charge / discharge cycle durability, and low temperature characteristics, and lithium using the same A positive electrode for a secondary battery and a lithium secondary battery are provided.

Claims (11)

Formula _{Li p Co x M y O z} F a ( where, M is Al, .0.98 ≦ p ≦ 1.04,0.970 ≦ x ≦ a transition metal element or an alkaline earth metal element other than Co 1.000, 0 ≦ y ≦ 0.03, 1.9 ≦ z ≦ 2.2, x + y = 1, 0 ≦ a ≦ 0.02). Cobalt oxyhydroxide powder having an average particle size of 0.1 to 2.5 μm which is a cobalt source, lithium carbonate powder which is a lithium source, and M element source powder contained as necessary, lithium / (Co + M element) ), And the resulting mixture is fired in an oxygen-containing atmosphere at a firing temperature of 900 to 1100 ° C. Manufacturing method.   The method according to claim 1, wherein the lithium cobalt composite oxide has an average particle size of 12 to 30 μm.   The production method according to claim 1 or 2, wherein the lithium carbonate powder has an average particle size of 3 to 50 µm and is fired at a firing temperature of 990 to 1050 ° C for 4 to 24 hours.   The method according to any one of claims 1 to 3, wherein the cobalt oxyhydroxide powder has an average particle size of 0.3 to 2.2 µm.   Selected from the group consisting of cobalt hydroxide powder, cobalt oxyhydroxide powder, cobalt carbonate powder and cobalt oxide powder per 100 parts by weight of the powder together with cobalt oxyhydroxide powder having an average particle size of 0.1 to 2.5 μm The manufacturing method in any one of Claims 1-3 using what mixed 30-300 weight part of powder with an average particle diameter of 2-6 micrometers at least 1 sort (s).   The M element source is at least one selected from the group consisting of Al, Mg, Ti, Zr and Mn, and the M element is contained in an atomic ratio of 0.0001 to 0.03 with respect to cobalt. Item 6. The production method according to any one of Items 1 to 5.   The cobalt oxyhydroxide powder is impregnated with cobalt oxyhydroxide powder and dried with an aqueous solution of carboxylate containing cobalt and containing two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in the molecule. The manufacturing method according to any one of claims 1 to 6.   Cobalt oxyhydroxide powder impregnated with cobalt oxyhydroxide powder and dried with an aqueous solution of carboxylate containing M element and containing two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in the molecule. The production method according to claim 1. The manufacturing method according to claim 1, wherein the lithium cobalt composite oxide has a press density of 3.7 to 4.1 g / cm ³ .   The lithium secondary battery positive electrode containing the lithium cobalt complex oxide of the large particle size manufactured by the manufacturing method in any one of Claims 1-9.   A lithium secondary battery using the positive electrode according to claim 10.