AU2011290195B2

AU2011290195B2 - Production method for a composite compound comprising nickel and cobalt

Info

Publication number: AU2011290195B2
Application number: AU2011290195A
Authority: AU
Inventors: Hideto Kano; Takeshi Kawasato; Junko Koyama; Takuya Mihara; Koji Tatsumi; Yukimitsu Wakasugi
Original assignee: AGC Seimi Chemical Ltd
Current assignee: AGC Seimi Chemical Ltd
Priority date: 2010-08-10
Filing date: 2011-08-09
Publication date: 2014-04-10
Anticipated expiration: 2031-08-09
Also published as: WO2012020768A1; JPWO2012020768A1; AU2011290195A1

Abstract

The production method inexpensively provides a composite compound which comprises nickel and cobalt with few impurities, and serves as a precursor for the positive electrode active material of a lithium ion secondary battery. The composite compound is safe, has a high service capacity, has a superior charge/discharge cycle durability and can be used with a wide range of voltages. The production method for a composite compound comprising nickel, cobalt and an M element is characterized in that an aqueous solution or dispersion comprising nickel, cobalt and an M element is obtained by mixing a nickel ammine complex, a cobalt ammine complex and an M element source, and the aqueous solution or dispersion is heated to thermally decompose the nickel ammine complex and cobalt ammine complex and thereby produce a composite compound containing nickel, cobalt and an M element.

Description

1 DESCRIPTION TITLE OF INVENTION: METHOD FOR PRODUCING NICKEL-COBALT-M ELEMENT-CONTAINING COMPOSITE COMPOUND 5 TECHNICAL FIELD The present invention relates to a method for producing a nickel-cobalt-M element-containing composite compound useful as a precursor for a cathode active material for a lithium ion secondary battery, and a process for producing a cathode active material by using the nickel-cobalt-M element-containing composite compound. BACKGROUD ART In recent years, as the portability and cordless tendency of instruments have progressed, a demand for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery which is small in size and light in weight and has a high energy density, has been increasingly high. As a cathode active material for such a non-aqueous electrolyte secondary battery, a composite oxide containing lithium and a transition metal element, such as LiCoO 2 , LiNij/ 3 Co1/ 3 Mn 1

/

3

O

2 , LiNiO 2 , LiNio.BCoo.

2 0 2 , LiMn 2 0 4 or LiMnO 2 , has been known. Among them, a lithium-nickel-cobalt-manganese-containing composite oxide is expected to be a cathode active material for a lithium ion secondary battery for the next generation, since it has a cost merit as containing inexpensive manganese and further is excellent in safety and balance of battery properties. However, good battery properties cannot be obtained by a lithium-nickel-cobalt manganese-containing composite oxide obtained by using a conventional solid-phase method of mixing powders of the respective metal sources, followed by firing. Therefore, it has been proposed to use a nickel-cobalt-manganese coprecipitated hydroxide synthesized by using metal sulfates as raw materials (Patent Documents 1 and 2). Further, for the synthesis of a lithium-nickel-cobalt-manganese-containing composite oxide, it has been proposed to use a nickel-cobalt-manganese coprecipitated carbonate synthesized by using metal sulfates as raw materials (Patent Documents 3 and 4). Further, it has been proposed to thermally decompose a nickel-cobalt ammine complex to prepare a nickel-cobalt-containing composite compound, which is further lithium-modified to prepare a lithium-nickel-cobalt-containing composite compound H:\DYB\Intcnvoven\NRPortbl\DCC\DYB\6036159_l.doc-19/02/2014 2 (Patent Document 5). PRIOR ART DOCUMENTS PATENT DOCUMENTS 5 Patent Document 1: JP-A-2002-201028 Patent Document 2: JP-A-2003-059490 Patent Document 3: US Patent Application Publication No. 2009/0087746 Patent Document 4: US Patent Application Publication No. 2010/0151332 Patent Document 5: JP-A-2001-076728 10 DISCLOSURE OF INVENTION TECHNICAL PROBLEM For the synthesis of a lithium-nickel-cobalt-manganese-containing composite oxide, it has been common to use a coprecipitation method, wherein, as disclosed in 15 Patent Documents 1 to 4, to an aqueous solution of e.g. sulfates having nickel, cobalt and manganese dissolved, an aqueous solution having an alkali such as sodium hydroxide or sodium carbonate dissolved, and an aqueous solution having e.g. ammonium sulfate or ammonium hydroxide dissolved, are dropwise added, while adjusting the pH, to precipitate a coprecipitated hydroxide or a coprecipitated carbonate. However, there has 20 been a problem that if a lithium-nickel-cobalt-manganese-containing composite oxide is prepared by using the obtained coprecipitated hydroxide or carbonate, sodium ions (Na*) or sulfate ions (S042) derived from the raw materials are likely to remain as impurities. In the method to thermally decompose a nickel-cobalt ammine complex as disclosed in Patent Document 5, high pressure steam is blown into a solution containing 25 an ammine complex of nickel and an ammine complex of cobalt, to prepare a cobalt-nickel composite oxide, but the battery performance itself is inadequate, and a further improvement is required. Therefore, it is conceivable to add, in addition to nickel and cobalt, other elements to prepare a composite oxide. However, an ammine complex containing other elements is usually unstable as compared with a cobalt-nickel ammine 30 complex, and no synthesis of such a composite oxide containing other elements has been known. The present invention seeks to provide a method for producing inexpensively a precursor containing nickel, cobalt and M element to be used for production of a cathode active material for a lithium ion secondary battery, which can solve the above-mentioned H:\DYB\Intcovcn\NRPortbj\DCC\DYB\6036159_ 1.doc-19102/2014 3 problem, has a uniform composition, contains little impurities, can be used in a wide range of voltage, has a high discharge capacity and is highly safe and excellent in charge/discharge cycle durability, and a process for producing a cathode active material for a lithium ion secondary battery by using such a precursor. 5 SUMMARY OF THE INVENTION The present inventors have continued a research and have found it may be possible to satisfactorily solve the problem relating to the synthesis of a composite compound which contains, in addition to nickel and cobalt, third element(s), by the 10 invention having the following constructions. (1) A method for producing a nickel-cobalt-M element-containing composite compound represented by the following formula (1), which comprises heating a nickel cobalt-M element-containing aqueous solution or dispersion obtained by mixing a nickel ammine complex, a cobalt ammine complex and an M element source, to thermally 15 decompose the nickel ammine complex and the cobalt ammine complex and thereby form a nickel-cobalt-M element-containing composite compound: NixCOyMzCpOqHr Formula (1) wherein M is at least one member selected from the group consisting of alkaline earth metal elements, aluminum and transition metal elements excluding Co and Ni, 20 0.15x<0.85, 0.05<y 0.85, 0.03<z<0.8, x+y+z=1, 0Lps1.6, 0.9sq<3.1, and 0<r<3.1. (2) The method for producing a nickel-cobalt-M element-containing composite compound according to the above (1), wherein the nickel ammine complex and the cobalt ammine complex are carbonate ammine complexes. (3) The method for producing a nickel-cobalt-M element-containing composite 25 compound according to the above (1) or (2), wherein the nickel-cobalt-M element containing aqueous solution or dispersion is heated at a temperature of from 80 to 250C. (4) The method for producing a nickel-cobalt-M element-containing composite compound according to any one of the above (1) to (3), wherein the heating is carried out by introducing steam at a temperature of from 100 to 2500C to the nickel-cobalt-M 30 element-containing aqueous solution or dispersion. (5) The method for producing a nickel-cobalt-M element-containing composite compound according to any one of the above (1) to (4), wherein the M element source is an ammine complex of M element. (6) The method for producing a nickel-cobalt-M element-containing composite H:\DYB\Untenvoven\NRPortbl\DCC\DYB\6036159_ .doc-19/02/2014 4 compound according to any one of the above (1) to (4), wherein the M element source is particles made of at least one member selected from the group consisting of metal manganese, manganese oxide, trimanganese tetroxide, basic manganese carbonate, manganese carbonate and manganese oxyhydroxide and having an average particle 5 diameter D 5 0 of at most 5 pm. (7) The method for producing a nickel-cobalt-M element-containing composite compound according to any one of the above (1) to (4), wherein the M element source is a carbamate of manganese. (8) The method for producing a nickel-cobalt-M element-containing composite 10 compound according to the above (1) to (4), wherein the M element source is a triethanolamine complex of aluminum. (9) The method for producing a nickel-cobalt-M element-containing composite compound according to any one of the above (1) to (8), wherein the content of sodium is at most 0.01 mass%, and the content of iron is at most 0.002%. 15 (10) The method for producing a nickel-cobalt-M element-containing composite compound according to any one of the above (1) to (9), wherein the nickel-cobalt-M element-containing aqueous solution is subjected to filtration before the heating. (11) A process for producing a cathode active material for a lithium secondary battery, which comprises mixing the nickel-cobalt-M element-containing composite compound 20 obtained by the method as defined in any one of the above (1) to (10), with a lithium compound, followed by firing at from 700 to 1,000 0 C in an oxygen-containing atmosphere. (12) A nickel-cobalt-M element-containing composite compound, when obtained by the method according to the invention. (13) A cathode active material for a lithium secondary battery, when obtained by the 25 process according to the invention. ADVANTAGEOUS EFFECTS OF INVENTION According to the present invention, it may be possible to provide a method for producing inexpensively a precursor containing nickel, cobalt and M element to be used 30 for production of a cathode active material for a lithium ion secondary battery, which has a uniform composition, contains little impurities, can be used in a wide range of voltage, has a high discharge capacity and is highly safe and excellent in charge/discharge cycle durability, and a process for producing a cathode active material for a lithium ion secondary battery by using such a precursor.

H:\DYBUnTenoven\NRortbl\DCC\DYB\6036159I.doc-19/02/2014 5 The reason as to why the nickel-cobalt-M element-containing composite compound represented by the above formula (1) provided by the present invention, exhibits such excellent properties as the precursor for a cathode active material for a lithium ion secondary battery, is not necessarily clearly understood, but is considered to 5 be substantially as follows. In a coprecipitation method to carry out neutralization by using metal sulfates, metal chlorides, etc., as raw materials, it is difficult, as mentioned above, to clean off sulfate ions (S02) and chlorine ions (CI) being anions of salts used as the raw materials, and sodium ions (Na*) contained in the alkali to be used for the neutralization, and these 10 ions are likely to remain as impurities in the cathode active material. Whereas, in a method of thermally decomposing an aqueous solution of ammine complexes, like in the present invention, ammonia or carbon dioxide gas other than raw material elements will be discharged out of the system, and impurities will not remain in the cathode active material. 15 In the coprecipitation method to carry out neutralization by using metal sulfates, metal chlorides, etc., as raw materials, in a case where a plurality of elements are to be precipitated, their optimum pHs or temperatures are delicately different from one another, and thus, a concentration gradient of elements is likely to be caused inside of particles. Whereas, in the thermal decomposition of the aqueous ammine complex solution, all 20 elements are simultaneously precipitated by directly introducing steam of at least the decomposition temperature, and consequently, the elements inside the particles will be uniformly present. Accordingly, it is considered that in the nickel-cobalt-M element-containing composite compound provided by the present invention, the content of impurities such as 25 sulfate radicals, chlorine, sodium, iron, etc., is extremely small, and a cathode active material obtainable by using such a composite compound can exhibit excellent battery performance. BRIEF DESCRIPTION OF DRAWINGS 30 Fig. 1 is a SEM image of the nickel-cobalt-manganese composite compound obtained in Example 1. Fig. 2 is a chart of XRD spectrum of the nickel-cobalt-manganese composite compound obtained in Example 1. Fig. 3 is a chart of XRD spectrum of the nickel-cobalt-manganese composite H:\DlYB\Intenoven\NRPoribl\DCC\DYB\6036159_ Ldoc-19/02/2014 5A hydroxide obtained in Example 5. DESCRIPTION OF EMBODIMENTS In the present invention, an ammine complex is meant for a complex having, as a 5 ligand, an amine such as ammonia. One having a various organic amine as the amine is also referred to as an ammine complex. The ligand of the ammine complex is preferably at least one member selected from the group consisting of ammonia (NH 3 ), an aliphatic derivative of ammonia, a diamine, pyridine, aniline, dipyridyl and 6 phenanthroline. Among them, at least one member selected from the group consisting of ammonia (NH 3 ), triethanolamine, pyridine, aniline, dipyridyl and phenanthroline, is more preferred. Among them, ammonia (NH 3 ) is particularly preferred. Further, the ligand may include a ligand of other than an ammine complex, such as aqua (OH 2 ), 5 carbonato (C0 3 2 -), cyano (CN-) or hydroxo (OH~). The number of ammonia to be coordinated may be at least one and may be two or more. In a case where the central metal is +3-valent, it is preferably one having a small number of ammonia coordinated to the central metal and having carbonato as the ligand. Specifically, it is more preferably [Me"'(NH 3

)

5

(CO

3 )]*, [Me.'(NH 3

)

4

(CO

2

)

2 1 or [Me'"(NH 3

)

3

(CO

3

)

3

]

3 -. In such a case, while the solubility of Co which is +3-valent and stable, becomes high, Me tends to be unstable, such being undesirable, and therefore, an inert atmosphere is preferred to prevent oxidation of the central metal Me. Specifically, a nitrogen gas atmosphere is preferred, and it is more preferred to use one having oxygen and carbon dioxide gas removed by bubbling nitrogen gas in water, also at the time of preparing the aqueous solution. Raw materials for the nickel ammine complex and the cobalt ammine complex to be used in the present invention, are not particularly limited, but, among them, a metal, a hydroxide, a carbonate, an oxyhydroxide or an oxide is preferred, and a metal, a hydroxide, a carbonate or an oxyhydroxide is more preferred. Specifically, the nickel source is preferably metal nickel, nickel oxide, nickel hydroxide, nickel carbonate, basic nickel carbonate or nickel oxyhydroxide. The cobalt source is preferably metal cobalt, cobalt oxide, cobalt hydroxide, cobalt carbonate or cobalt oxyhydroxide. Aqueous ammonia or the like is added to these nickel and cobalt sources, followed by stirring, and ammonium carbonate or the like is further added, followed by stirring at from 20 to 60 0 C for from 30 minutes to 12 hours, to prepare an aqueous solution containing a nickel ammine complex and a cobalt ammine complex. Raw materials for the M element source to be used in the present invention are not particularly limited. Among them, an ammine complex, a metal, a hydroxide, a carbonate, an oxyhydroxide or an oxide is preferred; an ammine complex, a metal, a carbonate, an oxyhydroxide or an oxide is more preferred; and an ammine complex is particularly preferred. In the present invention, the nickel-cobalt-M element-containing aqueous solution or dispersion is not necessarily required to have all components dissolved and some components may be dispersed, and thus, it includes a suspension or a solution in a colloidal form. Particularly in a case where the M element source is a metal, a hydroxide, a carbonate, an oxyhydroxide or an oxide which is hardly soluble in water, it 7 is preferred to use the M element source in the form of fine particles and heat an aqueous dispersion having the M element source dispersed, to thermally decompose the nickel ammine complex and the cobalt ammine complex. It is particularly preferred that the M element source is water-soluble. When the 5 M element source is in the form of an aqueous solution, nickel, cobalt and M element are dispersed very uniformly, whereby the battery properties tend to be improved. In a case where the M element source is insoluble or hardly soluble in water, a nickel-cobalt M element-containing aqueous dispersion which contains the M element source in the form of fine particles, may be heated to thermally decompose the nickel ammine complex and the cobalt ammine complex and thereby prepare a nickel-cobalt-M element-containing composite compound. A water-soluble M element source may be obtained by adding aqueous ammonia, ammonium carbamate, triethanolamine or the like to a M element raw material, followed by stirring at from 0 to 600C for from 30 minutes to 12 hours and adding e.g. ammonium carbonate or the like to prepare an aqueous solution of an ammine complex. When the M element source is an ammine complex, nickel, cobalt and M element will be dispersed very uniformly, whereby the battery performance tends to be improved, such being desirable. As the amine source to be used to form such an ammine complex, liquid ammonia, aqueous ammonia, ammonium carbonate or ammonium bicarbonate may be used. Further, at least one member selected from the group consisting of an aliphatic derivative of ammonia, a diamine, pyridine, aniline, dipyridyl and phenanthroline, may also be preferably used. Among them, aqueous ammonia is particularly preferred when the costs are taken into account. Further, it is preferred that carbonato (C03) is contained as a ligand of the ammine complex, and the carbonate source is not particularly limited, however, liquid carbon dioxide is particularly preferred. The above mentioned ammonium carbonate is a compound which is formally represented by a chemical formula (NH 4

)

2

CO

3 , but as an available reagent, it is usually a mixture of ammonium hydrogencarbonate (NH 4

.HCO

3 ) and ammonium carbamate (NH 2 COONH4). In the present invention, M element is at least one element selected from the group consisting of alkaline earth metal elements, aluminum and transition metal elements excluding Co and Ni. Here, the above transition metal elements are meant for transition metal elements of Group 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 of the Periodic Table. It is particularly preferred that M element is selected from the group consisting of Mn, Al, Mg, Zr, Ti and Hf. Further, from the viewpoint of the discharge capacity, safety, charge/discharge cycle durability, etc., M element is more preferably at least one 8 element selected from the group consisting of Mn, Al and Mg, further preferably Mn or Al, particularly preferably Mn. When M element is manganese, iron (Fe) contained in a large amount as an impurity in manganese can easily be filtered off. Iron is known as an impurity which adversely affects the battery properties, and by a conventional 5 coprecipitation method, iron is contained in manganese raw material in such a large amount that purification is difficult. On the other hand, in the method of the present invention, trivalent iron Fe(Ill) will not substantially form an ammine complex and therefore can be removed by filtration of the aqueous solution of the ammine complex. The manganese raw material to be used in a case where M element contains Mn, o is preferably at least one member selected from the group consisting of metal manganese, manganese oxide (MnO), manganese dioxide (MnO 2 ), manganese sesquioxide (Mn 2 0), trimanganese tetraoxide (Mn 3

O

4 ), basic manganese carbonate, manganese carbonate and manganese oxyhdroxide, more preferably at least one member selected from the group consisting of metal manganese, manganese oxide, 5 trimanganese tetraoxide, basic manganese carbonate, manganese carbonate and manganese oxyhydroxide, further preferably manganese oxide, trimanganese tetraoxide, basic manganese carbonate, manganese carbonate or manganese oxyhydroxide. From the viewpoint of the solubility, a combination of basic nickel carbonate as the nickel source, cobalt hydroxide as the cobalt source and metal manganese as the manganese source, is particularly preferred. Further, the raw material is preferably one which contains no impurities and has a high solubility. Further, a metal is preferably used in the form of a powder, since the reactivity is thereby high. Particularly in a case where M element contains manganese, it is preferred to use an ammine complex of manganese in order to improve the stability of manganese ions, and as the ammine complex of manganese, it is more preferred to use manganese carbamate being a complex of ammonium manganate. Manganese carbamate may be prepared by dissolving metal manganese or manganese oxide (MnO) in a solution having ammonium carbonate dissolved in concentrated aqueous ammonia. In order to stabilize the manganese carbamate complex, [CO 3

]/[NH

3 ] (molar ratio) i.e. the ratio of the number of moles of [CO3] to the number of moles of [NH 3 ] in the nickel-cobalt-M element-containing aqueous solution, is preferably within a range of from 0.03 to 0.12, more preferably from 0.05 to 0.09. The value of [CO 3

]/[NH

3 ] is obtainable by calculation from the charged amounts. The stability of the ammine complexes decreases in the order of nickel, cobalt and manganese. Therefore, in a case where M element contains manganese, it is 9 preferred to take a step of preparing an ammine complex of manganese, and then, mixing thereto a nickel ammine complex and a cobalt ammine complex separately prepared. As a ligand to form an ammine complex by stabilizing manganese, pyridine 2-methanol, ethanediamine or ethylenediamine may, for example, be preferred. In a case where M element is Al, the material for Al is not particularly limited, but metal aluminum or aluminum hydroxide is preferred. Aluminum is hardly soluble in excess ammonia, and therefore, it is preferred that an aqueous solution of a triethanolamine complex which forms a stable complex in the aqueous solution, is prepared, and then mixed with a nickel ammine complex solution and a cobalt ammine complex solution. In a case where M element is Al, it is preferred to form an ammine complex of [M"'(NH 3

)

6

]

3 +. In a case where M element is Mg, it is preferred to form an ammine complex of

[M"(NH

3

)

6

]

2 * which is present stably, whereby it is possible to obtain a decomposition product having a uniform composition. Ammonia and carbon dioxide gas released at the time of heating the nickel-cobalt M element-containing aqueous solution or dispersion, can easily be recovered and utilized. Further, impurities remaining in the precipitated substance are basically ammonia and carbon dioxide gas only. Therefore, only a simple solid-liquid separation process is required, and an elaborate cleaning process as required in a coprecipitation method using metal sulfates as raw materials, is not necessary. In the coprecipitation method using metal sulfates as raw materials, NaSO 4 and (NH 4

)

2

SO

4 formed as byproducts by neutralization, and water required for washing with water, are consumed, and further a waste liquid is required to be treated to render it harmless, which requires a substantial cost. In contrast with the coprecipitation method using metal sulfates as raw materials, in the method of the present invention, no byproducts will be formed, and a raw material such as ammonia can be recycled, and no treatment of a waste liquid is required, and thus, it is an environmentally friendly, inexpensive and very efficient process. The molar ratio of elements of nickel (x)-cobalt (y)-M (z) contained in the nickel cobalt-M element-containing aqueous solution or dispersion is preferably adjusted to be the molar ratio of x, y and z contained in the above formula (1). Further, the concentration of the nickel ammine complex contained in the nickel-cobalt-M element containing aqueous solution or dispersion is, by mass%, preferably from 2 to 7%, more preferably from 3 to 6%. Further, the concentration of the cobalt ammine complex is, by mass%, preferably from 2 to 7%, more preferably from 3 to 6%. Further, the concentration of the M element source is, by mass%, preferably from 1 to 6%, more 10 preferably from 2 to 5%. Further, the total mass% of the nickel ammine complex, the cobalt ammine complex and the M element source contained in the nickel-cobalt-M element-containing aqueous solution or dispersion, is preferably from 5 to 10%. Further, the concentration of the metal elements contained in the nickel-cobalt-M 5 element-containing aqueous solution or dispersion is preferably from 1 to 10 mass%, more preferably from 3 to 6 mass%. In a case where the M element source is insoluble or hardly soluble in water, the average particle diameter D 50 of the M element source contained in the nickel-cobalt-M element-containing aqueous dispersion is preferably at most 10 pm, more preferably at ) most 8 pm, further preferably at most 5 pm, particularly preferably at most 2 pm. If D 50 exceeds 10 pm, particles obtainable after the heating will have a core-shell structure having a concentration gradient in the composition in the particles, and a nickel-cobalt M element-containing composite compound wherein M element is non-uniform, tends to be obtainable. As D 5 o is small, a uniform composition is obtainable, but as the size becomes small, the production cost increases, and therefore, in consideration of the balance with the battery properties, the average particle diameter D 5 o of the compound of M element is preferably at least 0.01 pm, more preferably at least 0.1 pm, further preferably at least 0.5 pm. In the present invention, the average particle diameter D 50 means a volumetric basis cumulative 50% diameter (D 5 o) which is a particle diameter at a point of 50% in a cumulative curve of particle size distribution obtained by volumetric basis and having the entire volume to be 100%. Further, in the present invention, the average particle diameter D 50 may also be referred to as D 50 . Further, D 10 means a volumetric basis cumulative 10% diameter, and D 90 means a volumetric basis cumulative 90% diameter. The particle size distribution can be obtained from the frequency distribution measured by a laser scattering particle size distribution measuring apparatus and a cumulative volume distribution curve. The measurement of the particle diameter is carried out by thoroughly dispersing particles in an aqueous medium by e.g. ultrasonic wave treatment and measuring the particle size distribution (for example, using e.g. MICROTRAC HRA (X-100), manufactured by NIKKISO CO., LTD.). Further, in a case where particles to be measured are secondary particles, such an average particle diameter D 50 is a volume average particle diameter with respect to the secondary particles having primary particles agglomerated one another, and in a case where particles are composed solely of primary particles, the average particle diameter D 50 is an average particle diameter with respect to the primary particles. Further, the nickel-cobalt-M element-containing composite compound obtainable 11 by the present invention, is preferably a compound containing at least one member selected from the group consisting of a hydroxy group, a carbonate group and an OOH group, more preferably a compound containing both a hydroxy group and a carbonate group, or a compound containing an OOH group. The composition of the nickel-cobalt-M element-containing composite compound obtainable by the present invention is represented by the following formula (1). NixCoyMzCpOqHr Formula (1) wherein 0.1<x<0.85, 0.05<y 0.85, 0.03<z<0.8, 0p 1.6, 0.9 q 3.1, Or 3.1, provided that x+y+z=1. Here, x, y and z are, respectively, preferably 0.3<x<0.85, 0.05 y:0.5 and 0.03.z0.7, more preferably 0.3<x<0.75, 0.05<y 0.3 and 0.03<z<0.6. When x, y and z are within the above ranges, it is possible to increase inexpensive nickel by reducing the amount of expensive cobalt, and a nickel-cobalt-M element-containing composite compound can be obtained inexpensively, such being desirable. NixCoyMzCpOqHr is preferably NixCOyMz(CO 3 )a(OH)b or NixCoyMzOOH. Here, O a 1, O<b<2, and 1<a+b. NixCoyMzOOH is one embodiment wherein the average valency of Ni, Co and Mn is 3. In NixCoyMz(CO 3 )a(OH)b, an embodiment wherein the average valency of Ni, Co and Mn is 2, is a combination of a and b which satisfies ax2+b=2. There may be a combination of a and b, which is not an integer. In the case of an integer, a=1 and b=0, or a=0 and b=2. An embodiment of a case where the average valency of Ni, Co and Mn is 3, is a combination of a and b, which satisfies ax2+b=3. There may be a combination of a and b, which is not an integer. As a specific example, a=1 and b=1, or a=0.5 and b=2. Depending upon the conditions for the thermal decomposition reaction and whether or not M is susceptible to oxidation, the numerical values for a and b or whether or not the composition will be NixCoyMzOOH, will be determined. In a case where the thermal decomposition conditions are vigorous, e.g. the thermal decomposition is carried out at a higher temperature, the proportion of carbonate groups decreases, and the proportion of hydroxy groups increases. In a case where M is contained in a large amount and M is susceptible to oxidation, the average valency of Ni, Co and Mn will be a valency of more than bivalent and at most trivalent. Further, in a case where it is reacted with a lithium compound, and the obtainable lithium-nickel-cobalt-M element-containing composite oxide is used as a cathode active material, the proportion of M element is preferably large, whereby the material will be inexpensive and highly safe and will have a high discharge capacity.

12 Further, when x becomes larger than 0.62, calcination may sometimes be required in the firing step to obtain a lithium-nickel-cobalt-M element-containing composite oxide, however, when x is 0.62 or less, such calcination tends to be not required, and the synthesis can be efficiently carried out. Therefore, it is preferred that 0.42<x<0.62, 0.1< y0.2, and 0.2<z<0.6. Further, the composite compound to be formed by thermal decomposition is different in morphology depending upon the conditions for the thermal decomposition, and it will be a hydroxide, an oxyhydroxide, an oxide, a carbonate or a mixture thereof. As the proportion of oxygen is high and the proportion of hydrogen is low in the composite compound, the oxidation reaction tends to readily proceed in the firing step to obtain a lithium-nickel-cobalt-M element-containing composite oxide, and therefore, it is preferred that 0p 1.5, 1.3<q 3.0, and 0.6<r<2.4. Further, in consideration of the charge/discharge cycle durability, rate characteristics, safety, low free alkali content, etc. of the cathode active material obtainable by lithium-modification of the composite compound, it is preferred that 0.46<x<0.54, 0.166y 0.24, 0.26<z<0.34, provided that x+y+z=1, O p 1.5, 1.9<q<2.4, and 0.9<r<1.4. A specific example of the composite compound represented by the above formula (1) may be at least one member selected from the group consisting of a hydroxide represented by Nio.

5 Coo.

2 Mo.

3

(OH)

2 or Nio.

6 Coo.

2 Mo.

2

(OH)

2 , and oxyhydroxide represented by Ni 0

.

5 Co 0

.

2

M

0

.

3 00H or Nio.

6 Coo.

2 Mo.200H, a basic carbonate represented by Nio.

5 C00o.

2

M.

3

(CO

3 )(OH), Nio.

6 Co.

2 Mo.

2

(CO

3 )(OH), Nio, 5 Co.

2 Mo.

3

(CO

3 )o.

5 (OH) or Nio.

6 Coo.

2 Mo.

2

(CO

3

)

0

.

5 (OH), and a carbonate represented by Nio.

5 Coo.

2 Mo.

3

(CO

3 ) or Nio.

6 C00o.

2

M

0

.

2

(CO

3 ). On the other hand, in consideration of the weight capacity density, safety, production cost, etc. of the cathode active material obtainable by lithium-modification of the composite compound, the content of M element is preferably large, and therefore, x, y and z are, respectively, preferably 0.1<x<0.3, 0.05 y 0.2, and 0.5 5z0.7. An example of the composite compound represented by the above formula (1) may be at least one member selected from the group consisting of a hydroxide represented by Ni 1

/

6 Co 1

/

6

M

4

/(OH)

2 , an oxyhydroxide represented by Ni 1

/

6 Co 1

/

6

M

4

/

6 OOH, a basic carbonate represented by Ni 1

/

6 C01/ 6

M

4

/(CO

3 )(OH) or Ni 1

/

6 C01/ 6

M

4

/(CO

3 )o.

5 (OH), and a carbonate represented by Ni 1

/

6 Co 1

/

6

M

4

/(CO

3 ). In the present invention, the amounts of elements contained in the particles can be analyzed by an ICP analysis (inductively-coupled plasma spectrometry) apparatus. In the present invention, in consideration of the charge/discharge cycle durability, rate characteristics, safety, low free alkali content, etc. of the cathode active material 13 obtainable by lithium-modification of the composite compound, it is preferred that M element is Mn, and x, y and z in NixCOyMzCpOqHr are, respectively, 0.46<x<0.62, 0.15<y 0.22, and 0.16<z<0.33. A more specific composition may be at least one type selected from the group consisting of a hydroxide represented by Nio.

5 Co0.

2 Mno.

3

(OH)

2 5 or Nio.

6 Co0.

2 Mno.

2

(OH)

2 , an oxyhydroxide represented by Nio.

5 Co 0

.

2 Mo.

3 00H or Nio.Coo.

2 Mno.

2 00H, a basic carbonate represented by Nio.

5 Co.

2 Mno.(CO 3 )o.

5 (OH) or Nio.

6 Co.

2 Mno.

2

(CO

3 )o.

5 (OH), Nio.

5 Co.

2 Mno.

3

(CO

3 )(OH) or Nio.

6 Co0.

2 Mn.

2

(CO

3 )(OH), and a carbonate represented by Nio.

5 Co0.

2 Mn.

3

(CO

3 ) or Nio.

6 Co.

2 Mno.

2

(CO

3 ). In consideration of the weight capacity density, safety, production cost, etc. of the o cathode active material obtainable by lithium-modification of the composite compound, it is preferred that M element is Mn, and x, y and z in NixCOyMzCpOqHr are, respectively, 0.1<x<0.3, 0.05<y:0.2, and 0.5<z<0.7. A more specific composition may be at least one type selected from the group consisting of a hydroxide represented by Ni 1

/

6 Co1/ 6 Mn 4

/

6

(OH)

2 , an oxyhydroxide represented by Ni 1

/

6 Co 1

/

6 Mn 4

/

6 00H, a basic 5 carbonate represented by Ni 1 /Co 1 6 /Mn 4

/(CO

3 ) (OH) or Ni 1

/

6 Co1/ 6 Mn 4

/(CO

3 )o.

5 (OH), and a carbonate represented by Ni 1

/

1 6 1

/

6 Mn 4

/(CO

3 ). In the present invention, in consideration of the charge/discharge cycle durability, rate characteristics, weight capacity density, low free alkali content, etc. of the cathode active material obtainable by lithium-modification of the composite compound, it is ) preferred that M element is Al, and x, y and z in NixCOyMzCpOqHr are, respectively, 0.7<x<0.82, 0.05<y0.2, and 0.03<z<0.13. Further, it is more preferred that 0.03<z<0.05. In such a case, from 20 to 80 mol% of Al may be substituted by Mn. A more specific composition may, for example, be a hydroxide represented by Nio.

8 Coo.

15 Alo.o 5

(OH)

2 or Nio.8Coo.1 5 Alo.o 3 Mno.

02

(OH)

2 . In a case where M element includes magnesium (Mg), Mg is preferably at most 3 mol%, more preferably at most 1 mol%, in all metal elements. When Al or Mg contained in M element is within the above range, the discharge capacity tends to be improved, such being desirable. In a case where the M element source contained in the nickel-cobalt-M element containing aqueous solution is an M element ammine complex, elements contained in the nickel-cobalt-M element-containing aqueous solution are all dissolved, whereby an impurity such as Fe which tends to hardly form an ammine complex can be removed by filtration prior to heating the aqueous solution. Especially in a case where M element is Mn, a Fe impurity which adversely affects the battery properties, is contained in a large amount in many cases, and it is therefore preferred that a nickel-cobalt-M element containing composite compound having a very small amount of such an impurity than 14 ever, is obtainable. In a case where M element contains Mn or Mg, it is preferred to let an ammine complex of [M"(NH 3

)

6

]

2 * form, which will be present stably, whereby a decomposition product having a uniform composition can be obtained. The method for heating the nickel-cobalt-M element-containing aqueous solution or dispersion is not particularly limited, but the heating is carried out preferably at from 80 to 2500C, more preferably at from 100 to 2500C. In order to instantaneously carry out the thermal decomposition at a temperature of at least the thermal decomposition temperature, it is effective and preferred to introduce steam of at least 100 C directly to the nickel-cobalt-M element-containing aqueous solution. The temperature of steam to be introduced is preferably from 100 to 2500C, more preferably from 120 to 1800C, and in order to complete the reaction uniformly in a short time, a temperature of from 150 to 1800C is further preferred. Here, in order to make the temperature of steam to be at least 1300C, it is necessary to prepare an installation which is durable against a high pressure. Further, the pressure in the reactor may be under reduced pressure or elevated pressure, and since the reactivity is improved, the pressure is preferably from 0.03 to 2 MPa, more preferably from 0.1 to 2 MPa, and it is particularly preferred to carry out the heating under a pressure of from 0.2 to 1 MPa. The heating time is preferably from 0.1 to 12 hours, more preferably from 0.5 to 10 hours. A lithium-nickel-cobalt-M element-containing composite oxide obtainable by firing a mixture of the obtained nickel-cobalt-M element-containing composite compound and a lithium compound, tends to receive an influence of the particle size of the nickel cobalt-M element-containing composite compound. Therefore, in order to attain a good balance of the safety and the discharge rate characteristics when the composite oxide is used as a cathode active material, the average particle diameter D 50 of the nickel-cobalt-M element-containing composite compound is preferably within a range of from 2 to 25 pm, more preferably within a range of from 5 to 15 pm, further preferably within a range of from 8 to 12 pm. Further, the specific surface area of the nickel-cobalt-M element-containing composite compound is preferably large in order to increase the reactivity with the lithium compound. At the time of separating the nickel-cobalt-M element-containing composite compound precipitated in the aqueous solution by heating, from the aqueous solution, cleaning to remove impurities is not required, and therefore, the separation method is not particularly limited and may, for example, be vacuum filtration, filter press, belt filter 15 or centrifugal separation. At the time of drying after separating the composite compound, adsorbed moisture may be removed by a compressed air blowing method utilizing a capillary action, in order to reduce the drying load. After separating the nickel-cobalt-M element-containing composite compound 5 from the aqueous solution, drying is not required so long as its handling is possible and the contents of metals contained in the composite compound can be measured. However, drying may be carried out as the case requires. At the time of drying, the drying is carried out preferably at a temperature of from 80 to 1500C, more preferably from 100 to 1500C, whereby the composite compound will be a highly reactive 3 oxyhydroxide, such being desirable. The amount of impurities contained in the nickel-cobalt-M element-containing composite compound to be obtained by the present invention is preferably small. Elements influential over the battery performance may be sodium (Na), sulfur (S) and iron (Fe). The content of sodium is preferably at most 0.01 mass%, more preferably at 5 most 0.008 mass%. On the other hand, the content of sodium may be at least 0.0001 mass%. The content of sulfur is preferably at most 0.07 mass%, more preferably at most 0.04 mass%. On the other hand, the content of sulfur may be at least 0.0001 mass%. The content of iron is preferably at most 0.002 mass%, more preferably at most 0.001 mass%. On the other hand, the content of iron may be at least 0.0001 mass%. The content of chromium is preferably at most 0.0005 mass%. On the other hand, the content of chromium may be at least 0.00001 mass%. Further, the obtained nickel-cobalt-M element-containing composite compound and a lithium compound are mixed and then fired, whereby it is possible to obtain a lithium-nickel-cobalt-M element-containing composite oxide which is useful as a cathode active material for a lithium ion secondary battery. The lithium compound to be used is not particularly limited, but lithium hydroxide or lithium carbonate is preferred, since it is inexpensive, and lithium carbonate is more preferred. As a condition for the firing, an oxygen-containing atmosphere is preferred. Further, it is preferred to carry out the firing under a condition of from 700 to 1,000C. If the firing temperature is lower than 7000C, formation of the lithium-nickel-cobalt-M element-containing composite oxide tends to be inadequate, and impurities are likely to be contained. On the other hand, if the firing temperature exceeds 1,000C, the charge/discharge cycle durability or the discharging capacity tends to decrease. The firing temperature is particularly preferably such that the lower limit is 8500C, and the upper limit is 9700C. Further, the oxygen-containing atmosphere is preferably the atmospheric air, and specifically, the oxygen content in the atmosphere is more preferably from 10 to 40 vol%. The firing 16 time is preferably from 1 to 24 hours, more preferably from 2 to 18 hours, particularly preferably from 4 to 14 hours. With respect to particles of the lithium-nickel-cobalt-M element-containing composite oxide of the present invention, the average particle diameter D 50 is preferably from 2 to 25 pm, more preferably from 5 to 15 pm, further preferably from 8 to 12 pm. Further, the specific surface area is preferably from 0.1 to 1.0 m 2 /g, more preferably from 0.3 to 0.8 m 2 /g. Here, in the present invention, the specific surface area was measured by a BET method in all cases. The pressed density is preferably from 2.9 to 3.4 g/cm 3 , more preferably from 3.0 to 3.4 g/cm 3 , particularly preferably from 3.2 to 3.4 ) g/cm 3 . Here, in the present invention, the pressed density means an apparent density of the powder of the lithium-nickel-cobalt-M element-containing composite oxide when it is pressed under a pressure of 1.0 ton/cm 2 . Further, in the present invention, the amount of free alkali is obtained by dispersing 5 g of the powder of the lithium-nickel-cobalt-M element-containing composite oxide in 50 g of pure water, followed by stirring for 30 minutes and then by filtration to obtain a filtrate, and neutralizing and titrating with a 0.02 mol%/L hydrochloric acid aqueous solution, and from the amount of the hydrochloric acid aqueous solution used until the pH reaches 4.0. In a case where the positive electrode for a lithium secondary battery is to be produced from the lithium-nickel-cobalt-M element-containing composite oxide of the present invention, the powder of such a composite oxide is mixed with a binder material and a carbon type electroconductive material such as acetylene black, graphite or Ketjenblack. As such a binder material, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose or an acrylic resin may, for example, be preferably employed. By using a solvent or a dispersant, the powder of the lithium-nickel-cobalt M element-containing composite oxide of the present invention, the electroconductive material and the binder material are formed into a slurry or a kneaded product, which is then supported on a positive electrode current collector such as an aluminum foil or a stainless steel foil by e.g. coating to form the positive electrode for a lithium secondary battery of the present invention. In a lithium secondary battery wherein the lithium-nickel-cobalt-M element containing composite oxide of the present invention is used as a cathode active material, a film of a porous polyethylene or a porous polypropylene may, for example, be used as a separator. Further, as the solvent for the electrolytic solution of the battery, various solvents may be used, but among them, a carbonate ester is preferred. As such a carbonate ester, each of a cyclic type and a chain type may be used. As the cyclic 17 carbonate ester, propylene carbonate or ethylene carbonate (EC) may, for example, be mentioned. As the chain carbonate ester, dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate or methyl isopropyl carbonate may, for example, be mentioned. In the lithium secondary battery of the present invention, the above carbonate ester may be used alone or two or more of them may be used as mixed. Otherwise, the above carbonate ester may be used as mixed with other solvents. Further, depending upon the material for an anode active material, a chain type carbonate ester and a cyclic type carbonate ester may be used in combination, whereby the discharge properties, the cyclic durability or the charge/discharge efficiency may sometimes be improved. Further, in the lithium secondary battery using the lithium-nickel-cobalt-M element containing composite oxide of the present invention as the cathode active material, a gel polymer electrolyte containing a vinylidene fluoride-hexafluoropropylene copolymer (for example, KYNAR, tradename, manufactured by ELF Atochem) or a vinylidene fluoride-perfluoropropyl vinyl ether copolymer, may be employed. As the solute to be added to the solvent for the electrolyte or to the polymer electrolyte, at least one member of lithium salts is preferably used, wherein e.g. C104, CF 3 SO3-, BF 4 , PF 6 -, AsF 6 ~, SbF 6 -, CF 3

CO

2 or (CF 3

SO

2

)

2 N- is anion. The lithium salt as the solute is added at a concentration of preferably from 0.2 to 2.0 mol/L (liter) to the solvent for the electrolyte or to the polymer electrolyte. If the concentration departs from this range, ionic conductivity will decrease, and the electrical conductivity of the electrolyte will decrease. Particularly preferably, it is from 0.5 to 1.5 mol/L. In the lithium secondary battery using the lithium-nickel-cobalt-M element containing composite oxide of the present invention as the cathode active material, as the anode active material, a material which can occlude and discharge lithium ions may be used. The material to form such an anode active material is not particularly limited, however, lithium metal, a lithium alloy, a carbon material, an oxide comprising, as a main component, a metal of Group 14 or 15 of the Periodic Table, a carbon compound, a silicon carbide compound, a silicon oxide compound, titanium sulfide or a boron carbide compound may, for example, be mentioned. As the carbon material, one having an organic material thermally decomposed under various thermal decomposition conditions, artificial graphite, natural graphite, soil graphite, exfoliated graphite or flake graphite, may, for example, be used. Further, as the oxide, a compound comprising tin oxide as a main component may be used. As the negative electrode current collector, a copper foil or a nickel foil may, for example, be used. The negative electrode may be 18 produced preferably by kneading the active material with an organic solvent to form a slurry, which is applied to a metal foil current collector, followed by drying and pressing. The shape of the lithium secondary battery using the lithium-nickel-cobalt-M element-containing composite oxide of the present invention as the cathode active 5 material is not particularly limited. A sheet, film, folding, winding type cylinder with bottom or button shape is selected for use depending upon the particular purpose. EXAMPLES Now, the present invention will be described in further detail with reference to o Examples. However, the present invention is by no means restricted to such specific Examples. In the following, Examples 1 to 4 are Working Examples of the present invention, and Example 5 is a Comparative Example. [Example 1] 1,062.71 g of 25% aqueous ammonia was added to 66.70 g of basic nickel 5 carbonate, 18.59 g of cobalt hydroxide and 16.48 g of metal manganese powder (average particle diameter: 5 pm), and 197.37 g of ion-exchanged water deaerated by bubbling with nitrogen gas for 2 hours, was added, followed by stirring, during which 81.68 g of ammonium carbonate was added, followed by stirring at 250C for 2 hours in a nitrogen gas stream. ) The obtained nickel-cobalt-manganese ammine aqueous solution was subjected to filtration to remove an undissolved component, and then, to the ammine aqueous solution, steam at about 1350C under 0.3 MPa was directly introduced and reacted for 30 minutes to obtain a nickel-cobalt-manganese-containing composite compound. This nickel-cobalt-manganese-containing composite compound was subjected to filtration and then dried at 100 C for 2 hours to obtain a powder of the nickel-cobalt manganese-containing composite compound. The obtained composite compound had an average particle diameter D 50 of 13.1 pm, and based on the total of nickel-cobalt and manganese contained in this composite compound, the ratio of the respective elements was Ni:Co:Mn=5:2:3 by molar ratio. Nickel, cobalt and manganese contained in this composite compound were 42.8 mass% in total. The composition of this composite compound was Nio.

5 Coo.

2 Mno.

3

(CO

3 )(OH). With respect to the obtained nickel-cobalt-manganese-containing composite compound, the amount of impurities was analyzed by ICP analysis and summarized in Table 1. A scanning electron microscopic (hereinafter referred to as SEM) image of this composite compound is shown in Fig. 1. Further, with respect to the obtained composite compound, the powder X-ray 19 diffraction spectrum (which may be referred to as XRD spectrum in the present invention) was measured by using RINT2200V manufactured by Rigaku under conditions of an accelerating voltage of 40 KV and an accelerating current of 40 mA. Here, as the ray source, Cu-Ka-ray was used. The spectrum chart is shown in Fig. 2 5 100.0 g of the obtained nickel-cobalt-manganese-containing composite compound and 28.4 g of lithium carbonate having a lithium content of 18.7 mass% were mixed and fired at 9600C for 14 hours in the atmospheric air, followed by pulverization to obtain a powder of a lithium-nickel-cobalt-manganese-containing composite oxide represented by Li1.

015 [Nio.

5 Coo.

2 Mno.

3 ]o.

985 0 2 . 0 The obtained composite oxide had an average particle diameter D 50 of 11.9 pm,

D

10 of 4.1 pm, D 90 of 19.7 pm and a specific surface area of 0.35 m 2 /g. This composite oxide had a pressed density of 2.99 g/cm 3 and a free alkali amount of 0.43 mol%. The obtained lithium-nickel-cobalt-manganese-containing composite oxide, acetylene black and polyvinylidene fluoride powder were mixed in a mass ratio of 90/5/5, 5 and N-methylpyrrolidone was added to prepare a slurry, which was applied on one side of an aluminum foil having a thickness of 20 pm by means of a doctor blade and dried and roll-pressed twice to prepare a positive electrode sheet for a lithium battery. And, using one punched out from the positive electrode sheet as a positive electrode, using a metal lithium foil having a thickness of 500 pm as a negative electrode, using a nickel foil of 20 pm as a negative electrode current collector, using a porous polypropylene having a thickness of 25 pm as a separator and using a solution of LiPF/EC+DEC (1:1) having a concentration of 1M (it means a mixed solution of EC and DEC in a weight ratio of 1:1 wherein LiPF 6 is the solute, the same applies to solvents mentioned hereinafter) as an electrolytic solution, two simplified sealed cell type lithium batteries made of stainless steel were assembled in an argon globe box. One battery was charged up to 4.3 V at a load current of 75 mA per 1 g of the cathode active material at 250C, and discharged down to 2.5 V at a load current of 75 mA per 1 g of the cathode active material, whereby the first time charge/discharge capacity density (which may be referred to as the initial weight capacity density in this specification) was obtained. Then, the battery was charged up to 4.3 V at a load current of 75 mA and discharged down to 2.5 V at a load current of 113 mA, whereby the discharge capacity was obtained. Further, with this battery, the charge/discharge cycle test was sequentially carried out 30 times whereby the discharge capacity was obtained. As a result, the initial weight capacity density of the cathode active material between 2.5 and 4.3 V at 250C was 173 mAh/g. Further, the high load capacity retention obtained from the discharge capacity at the time of discharging at a high load 20 of 113 mA relating to the discharge rate properties, was 89.3%. Further, the capacity retention after 30 times of the charge/discharge cycle was 95.1%. [Example 2] To 182 g of 28% aqueous ammonia, 219 g of ion-exchanged water was added, 5 and further, 78.5 g of ammonium bicarbonate was added and dissolved with stirring. To this solution, 50.0 g of basic nickel-carbonate and 14.2 g of cobalt hydroxide were added at room temperature and stirred for 2 hours. After the dissolution, an undissolved component was removed by pressure filtration to obtain a nickel-cobalt ammine solution. To the obtained nickel-cobalt ammine aqueous solution, 26.5 g of 3 fine particulate manganese carbonate having an average particle diameter of 0.8 pm was added and stirred to prepare a nickel-cobalt-manganese carbonate suspension. Into a 1 L reactor, 300 ml of ion-exchanged water was put and heated to 1 00 0 C with stirring. Then, to this reactor, the above suspension was dropwise added over a period of 2 hours. Generated vapor was distilled off without recycling. After 5 completion of the dropwise addition of the suspension, heating and distilling were continued for 30 minutes. After cooling, the reaction solution was subjected to filtration and washing, and then, the solid content was dried at 100 C for 12 hours to obtain a nickel-cobalt-manganese-containing composite compound. With respect to the obtained nickel-cobalt-manganese-containing composite compound, the amount of impurities was analyzed by ICP analysis and summarized in Table 1. The obtained composite compound had an average particle diameter D50 of 6.8 pm, and based on the total of nickel, cobalt and manganese contained in this composite compound, the ratio of the respective elements was Ni:Co:Mn=5:2:3 by molar ratio. Further, nickel, cobalt and manganese contained in this composite compound were 47.2 mass% in total, and the compositional ratio of this composite compound was Nio.

5 Coo.

2 Mno.

3

(CO

3 )(OH)o.

26 . 85.0 g of the obtained nickel-cobalt-manganese-containing composite compound and 26.6 g of lithium carbonate having a lithium content of 18.7 mass% were mixed and fired at 9600C for 14 hours in the atmospheric air, followed by pulverization to obtain a powder of a lithium-nickel-cobalt-manganese-containing composite oxide represented by Li 1

.

015 [Nio.

5 Coo.

2 Mno.

3 ]o.

985 0 2 . The obtained composite oxide had an average particle diameter D50 of 5.7 pm, D1 0 of 3.5 pm, D90 of 9.6 pm and a specific surface area of 0.52 m 2 /g. This composite oxide had a pressed density of 2.90 g/cm 3 and a free alkali amount of 0.58 mol%. An electrode and a battery were prepared and evaluated in the same manner as 21 in Example 1 except that the positive electrode sheet was one prepared by using the above lithium-nickel-cobalt-manganese-containing composite oxide. As a result, the initial weight capacity density of the cathode active material between 2.5 and 4.3V at 250C was 174 mAh/g. Further, the high load capacity retention obtained from the discharge capacity at the time of discharging at a high load of 113 mA relating to the discharge rate characteristics was 93.2%. Further, the capacity retention after 30 times of the charge/discharge cycle was 95.6%. [Example 3] To 182 g of 28% aqueous ammonia, 219 g of ion-exchanged water was added, and further, 78.5 g of ammonium bicarbonate was added and dissolved with stirring. To this solution, 50.0 g of basic nickel-carbonate and 14.2 g of cobalt hydroxide were added at room temperature and stirred for 2 hours. After the dissolution, an undissolved component was removed by pressure filtration to obtain a nickel-cobalt ammine solution. On the other hand, to 268 g of 28% aqueous ammonia, 34.9 g of ammonium carbonate was added and cooled to 150C with stirring. To this solution, 12.4 g of metal manganese powder having an average particle size of 30 pm was added while cooling so that the inner temperature would not exceed 200C. When almost all was dissolved, pressure filtration was carried out to remove an undissolved component, whereby a manganese carbamate solution was obtained. Into a 1 L reactor, 300 ml of ion-exchanged water was put, and steam at about 1350C under 0.3 MPa was directly introduced with stirring, and after raising the inner temperature to 100 C, the nickel-cobalt ammine solution at a rate of 4.3 g/min and the manganese carbamate solution at a rate of 2.5 g/min were, respectively, continuously supplied and dropwise added to the reactor. Generated vapor was distilled off without recycling. After completion of the dropwise addition of the solution, introduction of the steam was continued for 30 minutes. After cooling, the reaction solution was subjected to filtration and washing, and then, the solid content was dried at 1000C for 12 hours to obtain a nickel-cobalt-manganese-containing composite compound. With respect to the obtained lithium-nickel-cobalt-manganese-containing composite compound, the amount of impurities was analyzed by ICP and summarized in Table 1. The obtained composite compound had an average particle diameter D50 of 18.6 pm, and based on the total of nickel-cobalt and manganese contained in this composite compound, the ratio of the respective elements was Ni:Co:Mn=5:2:3 by molar ratio. Further, nickel, cobalt and manganese contained in this composite compound were 47.0 mass% in total, and the compositional ratio of this composite compound was Nio.

5 Co 0

.

2 Mn.

3

(CO

3

)(OH)

0

.

29

.

22 85.0 g of the obtained nickel-cobalt-manganese-containing composite compound and 26.5 g of lithium carbonate having a lithium content of 18.7 mass% were mixed and fired at 9600C for 14 hours in the atmospheric air, followed by pulverization to obtain a powder of a lithium-nickel-cobalt-manganese-containing composite oxide represented by Li 1

.

015 [Nio.

5 Co0.

2 Mno.

3 ]o.

985 0 2 . The obtained composite oxide had an average particle diameter D50 of 16.2 pm, D10 of 7.6 pm, D90 of 26.8 pm and a specific surface area of 0.32 m 2 /g. This composite oxide had a pressed density of 3.18 g/cm 3 and a free alkali amount of 0.40 mol%. An electrode and a battery were prepared and evaluated in the same manner as in Example 1 except that the positive electrode sheet was one prepared by using the above lithium-nickel-cobalt-manganese-containing composite oxide. As a result, the initial weight capacity density of the cathode active material between 2.5 and 4.3 V at 250C was 173 mAh/g. Further, the high load capacity retention obtained from the discharge capacity at the time of discharging at a high load of 113 mA relating to the discharge rate characteristics, was 90.2%. Further, the capacity retention after 30 times of the charge/discharge cycle was 96.5%. [Example 4] To 182 g of 28% aqueous ammonia, 219 g of ion-exchanged water was added, and further 78.5 g of ammonium bicarbonate was added and dissolved with stirring. To this solution, 50.0 g of basic nickel carbonate and 14.2 g of cobalt hydroxide were added at room temperature and stirred for 2 hours. After the dissolution, an undissolved component was removed by pressure filtration to obtain a nickel-cobalt ammine solution. To the obtained nickel-cobalt ammine aqueous solution, 17.4 g of fine particulate trimanganese tetraoxide having an average particle diameter of 0.6 pm was added and stirred to prepare a nickel-cobalt-trimanganese tetraoxide suspension. Into an autoclave equipped with a stirrer, 300 ml of ion-exchanged water was charged, and steam under 0.3 MPa was introduced with stirring at a constant speed, so that the inner pressure was 0.2 MPa and the inner temperature was 1200C. The nickel-cobalt-trimanganese tetraoxide suspension obtained as described above, was added at a rate of 3 g/min. As the inner pressure increased at the same time as the addition of the suspension, the inner pressure was adjusted to be maintained at 0.2 MPa while discharging the gas to the exterior. After completion of the addition of the suspension, the introduction of steam under 0.3 MPa was continued for 30 minutes, followed by cooling. After the cooling, the reaction solution was subjected to filtration and washing, and then, the solid content was dried at 100*C for 12 hours to obtain a 23 nickel-cobalt-manganese-containing composite compound. With respect to the obtained lithium-nickel-cobalt-manganese-containing composite compound, the amount of impurities was analyzed by ICP analysis and summarized in Table 1. The obtained composite compound had an average particle 5 diameter D50 of 8.2 pm, and based on the total of nickel, cobalt and manganese contained in this composite compound, the ratio of the respective elements was Ni:Co:Mn=5:2:3 by molar ratio. Further, nickel, cobalt and manganese contained in this composite compound were 53.1 mass% in total, and the compositional ratio of this composite compound was Nio.

5 Co 0

.

2 Mno.

3

(CO

3 )o.

7 0 0

.

4 (OH)o.15. 0 75.0 g of the obtained nickel-cobalt-manganese-containing composite compound and 26.4 g of lithium carbonate having a lithium content of 18.7 mass% were mixed and fired at 9600C for 14 hours in the atmospheric air, followed by pulverization to obtain a powder of a lithium-nickel-cobalt-manganese-containing composite oxide represented by Li1., 1 5[Nio.

5 Co0.

2 Mno.

3 ]o.

985 0 2 . 5 The obtained composite oxide had an average particle diameter D50 of 7.2 Pm, D10 of 3.1 pm, D90 of 14.2 pm and a specific surface area of 0.46 m 2 /g. This composite oxide had a pressed density of 2.92 g/cm 3 and a free alkali amount of 0.55 mol%. An electrode and a battery were prepared and evaluated in the same manner as in Example 1 except that the positive electrode sheet was one prepared by using the above lithium-nickel-cobalt-manganese-containing composite oxide. As a result, the initial weight capacity density of the cathode active material between 2.5 and 4.3 V at 250C was 174 mAh/g. Further, the high load capacity retention obtained from the discharge capacity at the time of discharging at a high load 5 of 113 mA relating to the discharge rate characteristics, was 92.8%. Further, the capacity retention after 30 times of the charge/discharge cycle was 95.8%. [Example 5] A sulfate aqueous solution containing 2.5 mol/L of nickel sulfate, 1.0 mol/L of cobalt sulfate and 1.5 mol/L of manganese sulfate, was prepared and subjected to filtration to obtain a nickel-cobalt-manganese-containing sulfate aqueous solution. Then, into a reaction tank, 500 g of ion-exchanged water was put and stirred at 400 rpm while bubbling with nitrogen gas and maintaining the temperature at 500C. To this ion exchanged water, the above nickel-cobalt-manganese-containing sulfate aqueous solution at 1.2 L/hr and an aqueous ammonia solution at 0.03 L/hr were simultaneously and continuously supplied, and a 18 mol/L sodium hydroxide aqueous solution was supplied so that the pH in the reaction tank was maintained to be 11. The amount of 24 the liquid in the reaction system was adjusted by vacuum filtration through a filter, and after aging at 500C for 24 hours, a coprecipitated slurry was subjected to filtration and washing with water and then dried at 700C to obtain a nickel-cobalt-manganese containing composite hydroxide. 5 With respect to the obtained nickel-cobalt-manganese-containing composite hydroxide, the amount of impurities was analyzed by ICP analysis and summarized in Table 1. The obtained particles of the nickel-cobalt-manganese-containing composite hydroxide were spherical, and their average particle diameter was 12.7 pm. Based on the total of nickel, cobalt and manganese contained in this composite hydroxide, the ) ratio of the respective elements was Ni:Co:Mn=5:2:3 by molar ratio. The composition of this composite hydroxide was Nio.

5 Co0.

2 Mno.

3

(OH)

2 , Further, nickel, cobalt and manganese contained in this composite compound were 61.5 mass% in total. With respect to the obtained composite hydroxide, the XRD spectrum was measured under the same measuring conditions as in Example 1 by using RINT2200V manufactured by Rigaku. The spectrum chart is shown in Fig. 3. 195.59 g of the obtained nickel-cobalt-manganese-containing composite compound and 79.81 g of lithium carbonate having a lithium content of 18.7 mass% were mixed and fired at 9600C for 14 hours in the atmospheric air, followed by pulverization to obtain a powder of substantially spherical lithium-nickel-cobalt manganese-containing composite oxide represented by Li 1 .01 5 [Nio.

5 Coo.

2 Mno.

3 ]o.

985 0 2 . The obtained composite oxide had D 50 of 11.2 pm, D 1 0 of 5.3 pm, D 90 of 19.0 pm and a specific surface area of 0.38 m 2 /g. This powder had a pressed density of 2.97 g/cm 3 and a free alkali amount of 0.48 mol%. An electrode and a battery were prepared and evaluated in the same manner as in Example 1 except that the positive electrode sheet was one prepared by using the above lithium-nickel-cobalt-manganese-containing composite oxide. As a result, the initial weight capacity density of the cathode active material between 2.5 and 4.3 V at 250C was 169 mAh/g. Further, the high load capacity retention obtained from the discharge capacity at the time of discharging at a high load of 113 mA relating to the discharge rate characteristics, was 87.5%. Further, the capacity retention after 30 times of the charge/discharge cycle was 92.8%.

H:\DYB\ntevovcn\NRPortbl\DCC\DYB\6036159_I.doc-19/02/2014 25 [Table 1] Amounts of impurities contained in composite oxide (mass%) Fe S Na Cr Cd Ex. 1 0.0008 0.03 0.008 <0.0005 <0.001 Ex. 2 0.0010 0.03 0.007 <0.0005 <0.001 Ex. 3 0.0004 0.01 0.004 <0.0005 <0.001 Ex. 4 0.0010 0.02 0.006 <0.0005 <0.001 Ex. 5 0.0029 0.10 0.025 0.0010 <0.001 INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide inexpensively a 5 precursor for a cathode active material for a lithium ion secondary battery, which has a uniform composition, contains little impurities, is useful within a wide range of voltage, has a high discharge capacity and is highly safe and excellent in the charge/discharge cycle durability. Further, a process for producing a cathode active material for a lithium secondary battery wherein such a precursor is employed, is provided. They are useful in 10 the field of lithium ion secondary battery, and their applicability in this field is very high. The entire disclosure of Japanese Patent Application No. 2010-179707 filed on August 10, 2010 including specification, claims, drawings and summary is incorporated herein by reference in its entirety. 15 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers 20 or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from 25 it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A method for producing a nickel-cobalt-M element-containing composite compound represented by the following formula (1), which comprises heating a nickel cobalt-M element-containing aqueous solution or dispersion obtained by mixing a nickel ammine complex, a cobalt ammine complex and an M element source, to thermally decompose the nickel ammine complex and the cobalt ammine complex and thereby form a nickel-cobalt-M element-containing composite compound: NixCOyMzCpOqHr Formula (1) wherein M is at least one member selected from the group consisting of alkaline earth ) metal elements, aluminum and transition metal elements excluding Co and Ni, 0.1<x<0.85, 0.05 y 0.85, 0.03<z<0.8, x+y+z=1, O<p 1.6, 0.9<q 3.1, and O<r<3.1.

2. The method for producing a nickel-cobalt-M element-containing composite compound according to Claim 1, wherein the nickel ammine complex and the cobalt ammine complex are carbonate ammine complexes.

3. The method for producing a nickel-cobalt-M element-containing composite compound according to Claim 1 or 2, wherein the nickel-cobalt-M element-containing aqueous solution or dispersion is heated at a temperature of from 80 to 250 0 C.

4. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 3, wherein the heating is carried out by introducing steam at a temperature of from 100 to 250 0 C to the nickel-cobalt-M element containing aqueous solution or dispersion.

5. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 4, wherein the M element source is an ammine complex of M element.

6. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 4, wherein the M element source is particles made of at least one member selected from the group consisting of metal manganese, manganese oxide, trimanganese tetroxide, basic manganese carbonate, manganese carbonate and manganese oxyhydroxide and having an average particle diameter D 50 of at most 5 pm.

7. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 4, wherein the M element source is a carbamate of manganese.

8. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 4, wherein the M element source is a triethanolamine complex of aluminum. H:\DYB\Intenvovcn\NRPortbl\DCC\DYB\6036159_1.doc-24/02/2014 27

9. The method for producing a nickel-cobalt-M element-containing composite compound according to any one of Claims 1 to 8, wherein the content of sodium is at most 0.01 mass%, and the content of iron is at most 0.002%.

10. The method for producing a nickel-cobalt-M element-containing composite 5 compound according to any one of Claims 1 to 9, wherein the nickel-cobalt-M element containing aqueous solution is subjected to filtration before the heating.

11. A method for producing a nickel-cobalt-M element-containing composite compound, substantially as hereinbefore described with reference to any one of the Examples, excluding the Comparative Example, and/or any one of the accompanying 10 drawings.

12. A nickel-cobalt-M element-containing composite compound, when obtained by the method according to any one of Claims 1 to 11.

13. A process for producing a cathode active material for a lithium secondary battery, which comprises mixing the nickel-cobalt-M element-containing composite compound 15 according to claim 12 with a lithium compound, followed by firing at from 700 to 1,000*C in an oxygen-containing atmosphere.

14. A cathode active material for a lithium secondary battery, when obtained by the process according to Claim 13. 20