JP2007084410A - Method for producing lithium cobalt composite oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium cobalt composite oxide for a lithium secondary battery positive electrode having high safety and excellent charging-discharging cycle characteristics even when used under high voltage and a high volume capacity density at the positive electrode. <P>SOLUTION: The general formula of the lithium cobalt composite oxide is denoted as Li<SB>a</SB>Co<SB>1-b</SB>M<SB>b</SB>O<SB>2</SB>(wherein, M is at least an element selected from the group consisting of a transition metal element except Co, Al and an alkaline-earth metal element; 0.9≤a≤1.2; and 0<b≤0.03). The method for producing the lithium cobalt composite oxide comprises a step to obtain an M-containing cobalt mixture powder by impregnating a cobalt compound powder with an M-containing aqueous solution in which an M-containing compound is dissolved, followed by drying, a step to obtain a raw material mixture powder by mixing the cobalt mixture powder and a lithium compound powder and water and a step to fire the raw material mixture powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention can be used even under high voltage, has a large volume capacity density, high safety, and excellent charge / discharge cycle characteristics. Lithium cobalt used as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium secondary batteries The present invention relates to a method for producing a composite oxide, a positive electrode for a lithium secondary battery including the produced lithium cobalt composite oxide, and a lithium secondary battery.

In recent years, with the rapid development of information-related equipment and communication equipment such as personal computers and mobile phones, there has been an increasing demand for non-aqueous electrolyte secondary batteries such as lithium secondary batteries that are small, lightweight and have high energy density. Yes. 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 and LiMn ₂ O ₄ are known. ing.

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

For example lithium cobalt oxide has been proposed a tap density of particle size in Patent Document 1 are mixed with different particle is and the press density is 1.8 g / cm ³ is 3.5~4.0g / cm ^3. Patent Document 2 discloses a positive electrode active material represented by Li _a Co _1-b Mn _b O _d (0 <a <1.3, 0 <b ≦ 0.15, 1.8 <d <2.2). Proposed.

However, while further improvement of battery characteristics such as volume capacity density, safety, and charge / discharge cycle characteristics is desired, improvement of these battery characteristics under high voltage use is desired, but all of these are fully satisfied at the same time. Nothing has been obtained. For example, in Patent Document 1, the packing density of the positive electrode is improved, but the volume capacity density is not sufficient and the charge / discharge cycle characteristics are also insufficient. Further, Patent Document 2 can be used under a high voltage of 4.5 V, and the charge / discharge cycle characteristics and volume capacity density are somewhat improved, but it is still insufficient.
JP 2004-182564 A JP 2004-356034 A

  According to the present invention, the lithium cobalt composite oxide contains at least one element selected from the group consisting of a transition metal element other than Co, Al, and an alkaline earth metal element (hereinafter referred to as M element). For producing a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery having a high volume capacity density by improving chargeability of the positive electrode and improving chargeability of the positive electrode, and manufactured lithium cobalt composite oxidation It is an object of the present invention to provide a positive electrode for a lithium secondary battery and a lithium secondary battery.

  The inventor conducted intensive studies to achieve the above object, and attempted to produce a lithium cobalt composite oxide for a lithium secondary battery positive electrode having the above characteristics as follows. That is, a cobalt compound powder having a high sphericity and a high filling capacity is used as a cobalt raw material, and the cobalt compound powder having a high sphericity is impregnated with an M element-containing aqueous solution as an M element source and dried. An attempt was made to produce a lithium cobalt composite oxide by firing a powder mixture of a cobalt mixture powder containing M element and a lithium compound powder. However, it has been found that the charge / discharge cycle characteristics of the lithium secondary battery using the lithium cobalt composite oxide produced as described above as the positive electrode active material are significantly reduced.

  Therefore, when further research was continued, in the above manufacturing process, water was added to the raw material mixed powder obtained by mixing the cobalt mixture powder and the lithium compound powder, and the water content in the raw material mixture powder was preferably set to a specific amount. Thus, it has been found that the positive electrode of the obtained lithium cobalt composite oxide has high safety and excellent charge / discharge cycle characteristics, has an improved volume capacity density, and can achieve the desired performance.

Thus, the present invention is based on the above novel findings and has the following gist.
(1) In formula _{Li a Co 1-b M b} O 2 ( where, M represents at least one element selected from the group consisting of transition metal elements, Al and alkaline earth metal elements other than Co .0. 9 ≦ a ≦ 1.2, 0 <b ≦ 0.03), wherein the cobalt compound powder is impregnated with an aqueous solution containing M element in which a compound containing M element is dissolved. And obtaining a dried cobalt mixture powder containing M element, mixing a lithium compound powder and water in the cobalt mixture powder to obtain a raw material mixed powder, and firing the raw material mixed powder. A method for producing a lithium cobalt composite oxide.
(2) The production method according to (1), wherein the cobalt compound powder has an average particle diameter (D50) of 15 to 30 μm and an average aspect ratio of 1.0 to 1.27.
(3) The manufacturing method according to (1) or (2), wherein the cobalt compound powder has a tap density of 1.5 to 3.0 g / cm ³ .
(4) The manufacturing method according to any one of (1) to (3), wherein the cobalt compound powder is at least one selected from the group consisting of cobalt oxyhydroxide, cobalt hydroxide, and cobalt oxide.
(5) The first cobalt compound powder having an average particle diameter (D50) of 15 to 30 μm and an average aspect ratio of 1.0 to 1.27, and the average particle diameter (D50). ) Is a mixture with the 2nd cobalt compound powder which has 1-8 micrometers, The manufacturing method in any one of said (1)-(4).
(6) The manufacturing method according to (5), wherein the content of the second cobalt compound powder is 1 to 40% by weight of the total cobalt compound powder.
(7) The production method according to any one of (1) to (6), wherein the M element-containing aqueous solution contains a carboxylic acid having two or more carboxylic acid groups or a carboxylic acid having a carboxylic acid group and a hydroxyl group. .
(8) The manufacturing method in any one of said (1)-(7) whose water content of the said raw material mixed powder obtained at the process of obtaining the said raw material mixed powder is 3.5-30 weight%.
(9) The above (1) to (1), wherein the M element is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, Mg, Ca, Sr, Ba and Al. The production method according to any one of 8).
(10) A lithium secondary battery positive electrode comprising a positive electrode active material, a conductive material, and a binder, wherein the positive electrode active material is produced by the production method according to any one of (1) to (9) above. A positive electrode for a lithium secondary battery, comprising a cobalt composite oxide.
(11) A lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode described in (10) is used as the positive electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium cobalt complex oxide for lithium secondary batteries with a high volume capacity density which can achieve the high safety | security which was useful for a lithium secondary battery, and the outstanding charging / discharging cycling characteristics is manufactured. In addition, the positive electrode using the lithium cobalt composite oxide produced according to the present invention can be used for high voltage applications because the above-described effects are not impaired even under high voltage use.

  In the present invention, the mechanism for obtaining the lithium cobalt composite oxide having the excellent characteristics as described above is not necessarily clear, but is estimated as follows. That is, since the cobalt compound powder having a high sphericity as a cobalt source generally has high fluidity, the element M obtained by impregnating the cobalt compound powder with an aqueous solution containing the above M element-containing aqueous solution and drying it. The fluidity of the cobalt mixture powder containing is also increased. When such a high-fluidity cobalt mixture powder and lithium compound powder are mixed, the two powders are separated due to the difference in specific gravity, and a uniform mixed state cannot be obtained. Therefore, in this case, the components are uniformly distributed. Firing in a mixed state is not possible. On the other hand, in the present invention, by adding water obtained in the above-described process, that is, the fluidity of the raw material mixed powder is reduced, separation due to the specific gravity difference between the cobalt mixture powder and the lithium compound powder can be suppressed, and a uniform mixture can be obtained. It seems to be obtained. Thus, in the present invention, it is considered that excellent results as described above can be obtained because the firing is performed in a state where the cobalt mixture powder and the lithium compound powder are uniformly mixed.

The lithium cobalt composite oxide for a lithium secondary battery positive electrode produced in the present invention is represented by the general formula Li _a Co _1-b M _b O ₂ . In this formula, a satisfies 0.9 ≦ a ≦ 1.2, preferably 0.95 ≦ a ≦ 1.15, and b satisfies 0 <b ≦ 0.03, preferably 0.001. ≦ b ≦ 0.025 is satisfied.

The M element represents at least one element selected from the group consisting of transition metal elements other than Co, Al, and alkaline earth metal elements. Among these, at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, Mg, Ca, Sr, Ba, and Al is preferable. In particular, Ti, Zr, Hf, Mg, or Al is preferable from the viewpoint of capacity development, safety, charge / discharge cycle characteristics, and the like. Further, the positive electrode active material of the present invention can further improve charge / discharge cycle characteristics and safety by adding elemental fluorine to the raw material mixed powder using LiF, MgF ₂ , AlF ₃ or the like.

  The cobalt compound powder, which is a cobalt source in the present invention, has an average aspect ratio of preferably 1.0 to 1.27, more preferably 1.05 to 1.25, and even more so as to have high sphericity. 1.1 to 1.23 is preferred. When the average aspect ratio is not within the above range, the filling property of the obtained positive electrode is lowered. In addition, the average aspect ratio of the particles in the present invention can be obtained by observing a photograph with an SEM (scanning electron microscope). Specifically, 100 to 300 secondary particles are measured with an SEM at a magnification of 500 times. At this time, all secondary particles appearing in the image are set as targets for particle size measurement. The aspect ratio is a value obtained by dividing the longest diameter of each particle by the vertical diameter of the longest diameter, and the average value thereof is the average aspect ratio in the present invention. In the examples, the measurement was performed using image analysis software Macview ver3.5 manufactured by Mountec.

The average particle size of the cobalt compound powder in the present invention is preferably 15 to 30 μm, more preferably 17 to 28 μm, and further preferably 18 to 25 μm. The specific surface area is preferably 0.5 to ²⁰⁰ m ² / g, more preferably 1 to 150 m ² / g. The average particle size in the present invention means a cumulative 50% value of the volume particle size distribution obtained by a laser scattering particle size distribution measuring apparatus (for example, using Microtrack HRAX-100 manufactured by Leeds & Northrup). The specific surface area was determined by the BET method.

The tap density of the cobalt compound powder in the present invention is preferably 1.5 to 3.0 g / cm ³ , more preferably 1.6 to 2.8 g / cm ³ , and further preferably 1.7 to 2.7 g / cm ³ . ³ is preferred. The tap density in the present invention is measured by using an automatic tap density measuring device (for example, using a tap denser KYT-4000 manufactured by Seishin Industry Co., Ltd.) and pouring the sample powder into a 100 ml dedicated measuring cylinder. Once the tapping height is set to 2 cm and tapping is performed, the volume of the sample powder is read and the volume of the sample powder transferred to the graduated cylinder can be obtained.

  When the average particle diameter, specific surface area and tap density of the cobalt compound powder in the present invention are not within the above ranges, the filling property of the obtained positive electrode is reduced, large current discharge characteristics, self-discharge characteristics and safety. It is not preferable because the properties may decrease.

  In the present invention, only the cobalt compound powder having the above-mentioned physical properties may be used as the cobalt source. Among the cobalt compound powders having the above-mentioned physical properties, the cobalt compound powder having an average particle size of 15 to 30 μm ( Hereinafter, in the case of using a first cobalt compound powder), in addition to this, it may be used by mixing with a cobalt compound powder having an average particle size of 1 to 8 μm (hereinafter referred to as a second cobalt compound powder). it can. Thereby, the filling property of the positive electrode can be further improved, and the volume capacity density can be improved. The average aspect ratio of the second cobalt compound powder may be within the range of the average aspect ratio of the first cobalt compound powder or may be outside the range.

  When a mixture of the first cobalt compound powder and the second cobalt compound powder is used as the cobalt source, the proportion of the first cobalt compound is preferably 60% by weight or more based on the total cobalt compound powder, 70 weight% or more is preferable. When this ratio is less than 60% by weight, the filling property of the obtained positive electrode may be lowered.

  On the other hand, the ratio of the second cobalt compound powder is preferably 1 to 40% by weight and more preferably 5 to 30% by weight with respect to the total cobalt compound powder. When this ratio is less than 1% by weight, the volume capacity density of the positive electrode is not sufficient, and when it exceeds 40% by weight, the filling property of the obtained positive electrode may be lowered.

  As the first cobalt compound powder or the second cobalt compound powder, cobalt oxides such as cobalt hydroxide and cobalt tetroxide, and cobalt compounds such as cobalt oxyhydroxide can be used.

  In the present invention, since the M element is added in the form of an aqueous solution, the cobalt element in the lithium cobalt composite oxide is very sufficiently and uniformly replaced by the M element. And the lithium containing complex oxide for lithium secondary battery positive electrodes with high safety | security and excellent in charging / discharging cycling characteristics is obtained.

  In the present invention, when the cobalt compound is impregnated with the element M in the form of an aqueous solution, an aqueous solution in which the element M is dissolved is used as the aqueous solution. Among these, an aqueous solution obtained by dissolving a compound containing M element and a carboxylic acid compound having two or more carboxylic acid groups or a carboxylic acid compound having a carboxylic acid group and a hydroxyl group in an aqueous solution is preferable. In addition, in the solution which melt | dissolved the compound containing M element in the aqueous solution of the said carboxylic acid, it is thought that M element forms carboxylate and exists in aqueous solution.

  When a plurality of carboxylic acid groups are present in the carboxylic acid molecule used above, the presence of a hydroxyl group in addition to the carboxylic acid group is preferable because the solubility of the M element in an aqueous solution can be increased. For example, when there is only one carboxylic acid group in the molecule, such as acetic acid and propionic acid, the solubility of the M element is low, which is not preferable. 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. As carbon number of a carboxylic acid group, 2-8 are preferable, and 2-6 are especially suitable. 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, and lactic acid. In particular, citric acid, tartaric acid, and oxalic acid are preferable because they can increase the solubility of cobalt element and M element and are relatively inexpensive. When using a highly acidic carboxylic acid such as oxalic acid, the cobalt compound is easily dissolved if the pH of the aqueous solution is less than 2. Therefore, it is necessary to add a base such as ammonia to adjust the pH to 2-12. preferable.

  The concentration of the M element source in the aqueous solution of the carboxylate used in the present invention is preferably higher because it is necessary to remove the aqueous medium by drying in a later step. However, if the concentration is too high, the viscosity becomes high, the uniform mixing property of the M element is lowered, and the aqueous solution does not easily penetrate into the cobalt compound, so 1 to 30% by weight, particularly 4 to 20% by weight is preferable. preferable.

  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 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 M element source used to form an aqueous solution of a carboxylate containing M element in the present invention includes inorganic salts such as oxides, hydroxides, carbonates and nitrates, acetates and oxalates. In addition, organic salts such as 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 elements and the like may be dissolved from the cobalt compound. In that case, ammonia is added to the aqueous solution to make the aqueous solution have a pH of 2 to 12. It is preferable.

  As a method of impregnating the cobalt compound powder with the M element-containing aqueous solution, it is possible to impregnate the cobalt compound powder by spraying the aqueous solution. Further, the cobalt compound can be introduced into the aqueous solution stored in the 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 the solid content concentration in the slurry in this case, a higher concentration is preferable as long as it is uniformly mixed, but usually the solid / liquid weight ratio is preferably 30/70 to 90/10, particularly preferably 50 /. 50-80 / 20 is preferred. Moreover, when a pressure reduction process is performed in the said slurry state, aqueous solution will osmose | permeate a cobalt compound more and is preferable.

  The removal of the aqueous medium from the impregnated product obtained by impregnating the cobalt compound powder with the M element-containing aqueous solution is preferably by drying at 50 to 200 ° C, particularly preferably at 80 to 120 ° C, usually for 1 to 10 hours. Done. At this time, if a large amount of water remains, a large amount of energy is required to dissipate the water in the firing step, so it is preferable to remove as much as possible. Further, if an excessive amount of moisture remains in the cobalt mixture obtained by drying the impregnated product, the water content of the cobalt mixture changes with time. As a result, it becomes difficult to control the mixing ratio of the lithium compound and the cobalt mixture, and it becomes difficult to obtain the lithium cobalt composite oxide as the final product with a predetermined composition.

  In order to avoid this, it is preferable to remove an excessive amount of water. 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.

  In the present invention, the cobalt element of the lithium cobalt composite oxide can also be contained by impregnating a cobalt compound powder with an aqueous solution in which a cobalt raw material is dissolved, and drying. It is preferable to add cobalt element by this method because the filling property of the obtained positive electrode is further improved and the volume capacity density in an actual battery is improved. When the cobalt compound is impregnated with the aqueous solution in which the cobalt raw material is dissolved, the same impregnation method as in the case of impregnating the cobalt compound powder with the aqueous solution in which the M element is dissolved can be applied. In addition, by dissolving a compound containing M element and a compound containing cobalt element in an aqueous solution to prepare an aqueous solution containing M element and cobalt element, M element is produced in the process of preparing a cobalt mixture powder containing M element. It can also be performed simultaneously with the addition of.

  In the present invention, as described above, when the cobalt element is dissolved in an aqueous solution and added, the addition amount is preferably 0.1 to 20 mol% with respect to the cobalt element contained in the lithium cobalt composite oxide, and 0.3 to 5 mol. % Is preferred.

  If the cobalt element is supplied from an aqueous solution in excess of 20 mol%, the aqueous solution cannot sufficiently penetrate into the powder of the cobalt compound and may precipitate as a finely divided cobalt element, which is not preferable. On the other hand, when the amount is less than 0.1 mol%, the amount of cobalt element added may decrease, which is not preferable.

  In the present invention, in the step of obtaining the raw material mixed powder, the fluidity of the mixed powder is controlled by adding water to adjust the water content of the raw material mixed powder. The preferable water content in the mixed powder for this purpose is preferably 3.5 to 30% by weight. More preferably, it is 4.0-25 weight%, More preferably, it is 4.5-22 weight%. When the water content of the mixed powder is less than 3.5% by weight, the fluidity of the mixed powder becomes high, the lithium raw material and the cobalt mixture in the mixed powder are separated, and a non-uniform lithium cobalt composite oxide is generated, resulting in a discharge capacity. There is a risk of deterioration in charge and charge / discharge cycle characteristics. Further, when the water content of the mixed powder is more than 30% by weight, the water becomes too much, the water and the muddy raw material mixture are separated, and a non-uniform lithium cobalt composite oxide is formed, resulting in a decrease in discharge capacity and charge. It may cause deterioration of discharge cycle characteristics.

  The water content of the raw material mixed powder is determined as follows. First, about 1.0000 g of raw material mixed powder to be measured in a constant weighing bottle is weighed in advance, and then dried at 120 ° C. for 2 hours. After drying, the mixture is allowed to cool in a desiccator containing silica gel, and then weighed, and the weight changed before and after drying is measured. The water content is calculated by calculating from the weight of the raw material mixed powder before drying measured in this way and the weight changed before and after the drying of the raw material mixed powder.

  The raw material mixed powder according to the present invention is preferably fired at 800 to 1100 ° C. in an oxygen-containing atmosphere, and preferably fired for 5 to 24 hours. When the firing temperature is lower than 800 ° C., the reaction becomes incomplete, and when it exceeds 1100 ° C., the charge / discharge cycle durability and the initial capacity are lowered. In particular, the firing temperature is preferably 900 to 1050 ° C. The obtained fired product is cooled, pulverized, and classified to produce lithium cobalt composite oxide particles.

The lithium cobalt composite oxide of the present invention thus produced has an average particle size of preferably 15 to 30 μm, more preferably 17 to 28 μm, and a specific surface area of preferably 0.15 to 0.60 m ^2. / G, particularly preferably 0.18 to 0.50 m ² / g. The (110) plane diffraction peak integral width of 2θ = 66.5 ± 1 ° measured by X-ray diffraction using a CuKα radiation source (manufactured by Rigaku Corporation, using RINT2100 type) is preferably 0.09-0. The press density is preferably 3.6 to 4.1 g / cm ³ , and particularly preferably 3.7 to 4.0 g / cm ³ . In addition, the press density in this invention means the apparent press density when a particle powder is press-compressed with the pressure of ² t / cm <2>.

  When the average particle size, specific surface area (110) plane diffraction peak integral width, or press density of the lithium cobalt composite oxide is not within the above range, the positive electrode has insufficient filling properties, large current discharge characteristics, self It is not preferable because discharge characteristics and safety deteriorate.

  The method for obtaining a positive electrode for a lithium secondary battery using the lithium cobalt composite oxide according to the present invention can be carried out according to a conventional method. For example, the positive electrode mixture is formed by mixing the positive electrode active material powder of the present invention with a carbon-based conductive material such as acetylene black, graphite, or ketjen black and a binder. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is used.

  A slurry in which the above positive electrode mixture is dispersed in a dispersion medium such as N-methylpyrrolidone is applied to a positive electrode current collector such as an aluminum foil, dried and press-rolled to form a positive electrode active material layer on the positive electrode current collector Form.

In the lithium secondary battery using the positive electrode active material of the present invention for the positive electrode, the solute of the electrolyte solution is ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , It is preferable to use at least one of lithium salts having CF ₃ CO ₂ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or the like as an anion. In the above electrolyte solution or polymer electrolyte, an electrolyte composed of a lithium salt is preferably added to the solvent or the solvent-containing polymer at a concentration of 0.2 to 2.0 mol / L. If it deviates from this range, the ionic conductivity is lowered and the electrical conductivity of the electrolyte is lowered. More preferably, 0.5 to 1.5 mol / L is selected. For the separator, porous polyethylene or porous polypropylene film is used.

  Further, as the solvent of the electrolyte solution, a carbonate ester is preferable. The carbonate ester can be either cyclic or chain. Examples of cyclic carbonates include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate and the like.

  The carbonate ester may be used alone or in combination of two or more. 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, by adding a vinylidene fluoride-hexafluoropropylene copolymer (for example, Kyner manufactured by Atchem Co.) or a vinylidene fluoride-perfluoropropyl vinyl ether copolymer to these organic solvents, and adding the following solute, the gel polymer electrolyte is added. It is also good.

  The negative electrode active material of a lithium battery using the positive electrode active material of the present invention for the positive electrode is a material that can occlude and release lithium ions. 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, periodic table 14, and group 15 metal are used. The main oxides are listed.

  As the carbon material, those obtained by pyrolyzing organic substances under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scale-like 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.

  There is no restriction | limiting in particular in the shape of the lithium secondary battery which uses the positive electrode active material in this invention. A sheet shape (so-called 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]
4.8 g of magnesium carbonate with a magnesium content of 25.8 wt%, 22.9 g of aluminum lactate with an aluminum content of 18.2 wt%, 3.0 g of an aqueous titanium lactate solution with a titanium content of 8.2 wt% and 39.6 g of citric acid An aqueous solution was prepared by dissolving in 300 grams. The aqueous solution was 867.9 g of cobalt oxyhydroxide having an average aspect ratio of 1.22, a tap density of 2.3 g / cm ³ , an average particle size of 19.3 μm, a specific surface area of 80 m ² / g, and a cobalt content of 61.6 wt%. An impregnation product was obtained by impregnating a cobalt compound mixed with 95.4 g of cobalt oxyhydroxide having a tap density of 0.6 g / cm ³ , an average particle size of 2.8 μm, and a cobalt content of 62.3% by weight. This impregnated product was dried at 80 ° C. for 8 hours to obtain a cobalt mixture. Further, 382.0 g of lithium carbonate having a lithium content of 18.70% by weight was mixed with this cobalt mixture to obtain a raw material mixed powder (water content: 3.3% by weight).

Next, water was added so that the water content of this raw material mixed powder (water content 3.3 wt%) was 9.6 wt%. Subsequently, the raw material mixed powder (water content 9.6% by weight) added with water thus obtained was mixed again, and then fired at 1000 ° C. for 15 hours in the air. After firing, it was crushed to obtain a positive electrode active material powder. This powder was wet-dissolved and examined by ICP and atomic absorption analysis. As a result, it was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder after baking (positive electrode active material powder), the specific surface area was 0.23 m ² / g, the average particle diameter D50 was 20.6 μm, and the press density was 3.85 g / cm ³ . An X-ray diffraction spectrum was obtained. In powder X-ray diffraction using CuKα ray, the (110) plane diffraction peak integration width at 2θ = 66.5 ± 1 ° was 0.120 °.

The LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ powder thus obtained, acetylene black, and polyvinylidene fluoride powder were mixed at a weight ratio of 90/5/5, N-methylpyrrolidone was added to prepare a slurry, which was coated on one side using a doctor blade on a 20 μm thick aluminum foil. Subsequently, it dried and roll-press-rolled to produce the positive electrode sheet for lithium batteries.

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 in volume ratio (1: 1) containing LiPF ₆ as a solute. Solvents described later). The stainless steel simple sealed cell type lithium battery was assembled in an argon glove box.

  The assembled battery is charged at a load current of 75 mA per gram of positive electrode active material at 25 ° C. to 4.3 V, and discharged to 2.5 V at a load current of 75 mA per gram of positive electrode active material. Asked. Further, the volume capacity density was determined from the density of the electrode layer and the capacity per weight. Further, the charge / discharge cycle test was performed 30 times. As a result, the initial weight capacity density at 25 ° C. was 152 mAh / g, and the capacity retention rate after 30 charge / discharge cycles was 98.3%.

  Furthermore, another similar battery was produced. This battery was charged at 4.3 V for 10 hours, disassembled in an argon glove box, the charged positive electrode sheet was taken out, the positive electrode sheet was washed, punched out to a diameter of 3 mm, and put together with EC into an aluminum capsule. Sealed 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 156 ° C.

  Moreover, the same battery was further produced, and the evaluation at the time of high voltage use was performed as follows. The initial discharge capacity was determined by charging to 4.5 V at a load current of 75 mA / g of the positive electrode active material at 25 ° C. and discharging to 2.5 V at a load current of 75 mA / g of the positive electrode active material. Further, the volume capacity density was determined from the density of the electrode layer and the capacity per weight. Further, the charge / discharge cycle test was performed 50 times. As a result, the initial weight capacity density at 25 ° C. was 181 mAh / g, and the capacity retention rate after 50 charge / discharge cycles was 94.5%.

[Example 2]
Example 1 except that the amount of water added to the raw material mixed powder prepared in Example 1 (water content: 3.3% by weight) was changed so that the water content of the raw material mixed powder added with water was 21.4% by weight. In the same manner as above, a positive electrode active material was synthesized and subjected to composition analysis, physical property measurement, and battery performance test. As a result, the composition was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder after baking (positive electrode active material powder), the specific surface area was 0.24 m ² / g, the average particle diameter was 20.8 μm, and the press density was 3.88 g / cm ³ . The integral width of (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.122 °.

As a result of producing a battery in the same manner as in Example 1 and measuring the battery performance, the initial weight capacity density at 4.3 V charge / discharge at 152 ° C. was 152 mAh / g, and the capacity retention rate after 30 charge / discharge cycles. Was 98.0%. The heat generation starting temperature was 157 ° C.
The initial weight capacity density at 4.5 ° C. charge / discharge at 25 ° C. was 182 mAh / g, and the capacity retention rate after 50 charge / discharge cycles was 94.2%.

[Example 3]
Example 1 except that the amount of water added to the raw material mixed powder prepared in Example 1 (water content: 3.3% by weight) was changed so that the water content of the raw material mixed powder added with water was 5.1% by weight. In the same manner as above, a positive electrode active material was synthesized and subjected to composition analysis, physical property measurement, and battery performance test. As a result, the composition was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder after baking (positive electrode active material powder), the specific surface area was 0.23 m ² / g, the average particle diameter was 20.5 μm, and the press density was 3.84 g / cm ³ . The integrated width of the (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.118 °.

As a result of producing a battery in the same manner as in Example 1 and measuring the battery performance, the initial weight capacity density at 4.3 V charge / discharge at 25 ° C. was 153 mAh / g, and the capacity retention rate after 30 charge / discharge cycles Was 98.4%. The heat generation starting temperature was 156 ° C.
At 25 ° C., the initial weight capacity density at 4.5 V charge / discharge was 180 mAh / g, and the capacity retention after 50 charge / discharge cycles was 95.0%.

[Example 4]
2.4 g of magnesium carbonate having a magnesium content of 25.8 wt%, 11.4 g of aluminum lactate having an aluminum content of 18.2 wt%, 1.5 g of an aqueous titanium lactate solution having a titanium content of 8.2 wt% and 19.8 g of citric acid were added to water. An aqueous solution was prepared by dissolving in 180 grams. The aqueous solution was added to 482.2 g of cobalt oxyhydroxide having an average aspect ratio of 1.22, a tap density of 2.3 g / cm ³ , an average particle size of 19.3 μm, a specific surface area of 80 m ² / g, and a cobalt content of 61.6 wt%. Impregnation was obtained by impregnation. This impregnated product was dried at 80 ° C. for 8 hours to obtain a cobalt mixture. Further, 191.0 g of lithium carbonate having a lithium content of 18.70% by weight was mixed with this cobalt mixture to obtain a raw material mixed powder (water content: 3.2% by weight).

Next, water was added so that the water content of this raw material mixed powder (water content 3.2 wt%) was 10.0 wt%. Subsequently, the raw material mixed powder (water content 10.0 wt%) to which water thus obtained was added was mixed again, and then fired at 1000 ° C. for 15 hours in the air. After firing, it was crushed to obtain a positive electrode active material powder. This powder was wet-dissolved and examined by ICP and atomic absorption analysis. As a result, it was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder (positive electrode active material powder) after baking, the specific surface area was 0.21 m < ² > / g, the average particle diameter was 21.3 micrometers, and the press density was 3.80 g / cm < ³ >. The integrated width of the (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.118 °.

As a result of producing a battery in the same manner as in Example 1 and measuring the battery performance, the initial weight capacity density at 4.3 V charge / discharge at 25 ° C. was 153 mAh / g, and the capacity retention rate after 30 charge / discharge cycles Was 97.5%. The heat generation starting temperature was 157 ° C.
At 25 ° C., the initial weight capacity density at 4.5 V charge / discharge was 181 mAh / g, and the capacity retention after 50 charge / discharge cycles was 94.3%.

[Example 5] Comparative Example A positive electrode active material was synthesized in the same manner as in Example 4 except that water was not added to the raw material mixed powder (water content: 3.2 wt%) prepared in Example 4, and composition analysis and physical property measurement were performed. In addition, a battery performance test was performed. As a result, the composition was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder after baking (positive electrode active material powder), the specific surface area was 0.18 m ² / g, the average particle size was 23.2 μm, and the press density was 3.89 g / cm ³ . The integrated width of (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.110 °.

As a result of producing a battery in the same manner as in Example 1 and measuring the battery performance, the initial weight capacity density at 4.3 V charge / discharge at 25 ° C. was 153 mAh / g, and the capacity retention rate after 30 charge / discharge cycles Was 92.8%. The heat generation starting temperature was 158 ° C.
The initial weight capacity density at 4.5 V charge / discharge at 25 ° C. was 181 mAh / g, and the capacity retention after 50 charge / discharge cycles was 85.2%.

[Example 6] Comparative Example Cobalt oxyhydroxide 244. having an average aspect ratio of 1.22, a tap density of 2.3 g / cm ³ , an average particle size of 19.3 μm, a specific surface area of 80 m ² / g, and a cobalt content of 61.6 wt%. 4 g and 94.8 g of lithium carbonate having a lithium content of 18.70% by weight were mixed to obtain a raw material mixed powder. The water content of this raw material mixed powder was 5.2% by weight. Composition analysis, physical property measurement, and battery performance test were performed in the same manner as in Example 1 except that this raw material mixed powder was used for baking for 15 hours at 1000 ° C. in the atmosphere. As a result, the composition was LiCoO _2.

About the powder (positive electrode active material powder) after baking, the specific surface area was 0.24 m < ² > / g, the average particle diameter was 21.6 micrometers, and the press density was 3.91 g / cm < ³ >. The integrated width of (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.106 °.

As a result of producing a battery in the same manner as in Example 1 and measuring battery performance, the initial weight capacity density at 4.3 V charge / discharge at 25 ° C. was 161 mAh / g, and the capacity retention rate after 30 charge / discharge cycles Was 94.2%. The heat generation starting temperature was 152 ° C.
The initial weight capacity density at 4.5 ° C. charge / discharge at 25 ° C. was 191 mAh / g, and the capacity retention after 50 charge / discharge cycles was 75.3%.

[Example 7]
1.9 g of magnesium carbonate with a magnesium content of 25.8 wt%, 9.2 g of aluminum lactate with an aluminum content of 18.2 wt%, 1.2 g of an aqueous titanium lactate solution with a titanium content of 8.2 wt% and 15.9 g of citric acid An aqueous solution was prepared by dissolving in 130 g. The aqueous solution was converted to 394.7 g of cobalt oxyhydroxide having an average aspect ratio of 1.31, a tap density of 2.0 g / cm ³ , an average particle size of 12.3 μm, a specific surface area of 100 m ² / g, and a cobalt content of 60.2 wt%. Impregnation was obtained by impregnation. This impregnated product was dried at 80 ° C. for 8 hours to obtain a cobalt mixture. Further, 152.8 g of lithium carbonate having a lithium content of 18.70 wt% was mixed with this cobalt mixture to obtain a raw material mixed powder (water content: 3.0 wt%).

Next, water was added so that the water content of this raw material mixed powder (water content: 3.0% by weight) was 10.8% by weight. Subsequently, the raw material mixed powder (water content 10.8 wt%) to which water thus obtained was added was mixed again, and then fired at 1000 ° C. for 15 hours in the atmosphere. After firing, it was crushed to obtain a positive electrode active material powder. This powder was wet-dissolved and examined by ICP and atomic absorption analysis. As a result, it was LiAl _0.015 Mg _0.005 Ti _0.0005 Co _0.9795 O ₂ .

About the powder after baking (positive electrode active material powder), the specific surface area was 0.37 m ² / g, the average particle size was 13.2 μm, and the press density was 3.58 g / cm ³ . The integrated width of (110) plane diffraction peak at 2θ = 66.5 ± 1 ° in powder X-ray diffraction was 0.121 °.

As a result of producing a battery in the same manner as in Example 1 and measuring the battery performance, the initial weight capacity density at 4.3 V charge / discharge was 154 mAh / g at 25 ° C., and the capacity retention rate after 30 charge / discharge cycles Was 98.6%. The heat generation starting temperature was 157 ° C.
The initial weight capacity density at 4.5 V charge / discharge at 25 ° C. was 188 mAh / g, and the capacity retention after 50 charge / discharge cycles was 95.2%.

  INDUSTRIAL APPLICABILITY According to the present invention, a lithium secondary battery having high safety useful for a lithium secondary battery and excellent charge / discharge cycle characteristics, a large volume capacity density, and can be used for high voltage applications. A positive electrode material is provided.

Claims (11)

General formula Li _a Co _1-b M _b O ₂ (where M represents at least one element selected from the group consisting of transition metal elements other than Co, Al and alkaline earth metal elements. 0.9 ≦ a ≦ 1.2, 0 <b ≦ 0.03), wherein the cobalt compound powder is impregnated with a M element-containing aqueous solution in which a compound containing M element is dissolved and dried. A step of obtaining a cobalt mixture powder containing the element M, a step of obtaining a raw material mixed powder by mixing a lithium compound powder and water with the cobalt mixture powder, and a step of firing the raw material mixed powder. A method for producing a lithium-cobalt composite oxide.   The manufacturing method according to claim 1, wherein the cobalt compound powder has an average particle diameter (D50) of 15 to 30 μm and an average aspect ratio of 1.0 to 1.27. The manufacturing method according to claim 1, wherein the cobalt compound powder has a tap density of 1.5 to 3.0 g / cm ³ .   The manufacturing method according to claim 1, wherein the cobalt compound powder is at least one selected from the group consisting of cobalt oxyhydroxide, cobalt hydroxide, and cobalt oxide.   The cobalt compound powder has an average particle diameter (D50) of 15 to 30 μm, and an average particle diameter (D50) of 1 and a first cobalt compound powder having an average aspect ratio of 1.0 to 1.27. It is a mixture with the 2nd cobalt compound powder which has -8micrometer, The manufacturing method in any one of Claims 1-4.   The production method according to claim 5, wherein the content of the second cobalt compound powder is 1 to 40% by weight of the total cobalt compound powder.   The manufacturing method according to claim 1, wherein the M element-containing aqueous solution contains a carboxylic acid having two or more carboxylic acid groups or a carboxylic acid having a carboxylic acid group and a hydroxyl group.   The manufacturing method according to any one of claims 1 to 7, wherein a water content of the raw material mixed powder obtained in the step of obtaining the raw material mixed powder is 3.5 to 30% by weight.   The element M is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, Mg, Ca, Sr, Ba and Al. The manufacturing method as described.   It is a positive electrode for lithium secondary batteries containing a positive electrode active material, a electrically conductive material, and a binder, Comprising: The said positive electrode active material contains the lithium cobalt complex oxide manufactured by the manufacturing method in any one of Claims 1-9. A positive electrode for a lithium secondary battery.   A lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode according to claim 10 is used as the positive electrode.