JP5266861B2 - Method for producing positive electrode active material for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive active material for a lithium secondary battery, in which the particle size of primary particles are large and uniform, most primary particles are surrounded only with spaces, and accordingly, cycle characteristics are high when used as the positive active material; and to provide the manufacturing method of the positive active material. <P>SOLUTION: The positive active material for the secondary battery is represented by compositional formula: Li<SB>x</SB>Ni<SB>1-y-z</SB>Co<SB>y</SB>M<SB>z</SB>O<SB>2</SB>(M is at least one kind of element selected from Mn, Al, Zr, Si, Sr and Mg; x, y, and z are a number satisfying 0.95&le;x&le;1.10, 0.1&le;y&le;0.4, and 0&le;z&le;0.1), and in the positive active material, a median diameter measured with a laser diffraction particle size distribution measuring device is in a range of 2 to 20 &mu;m, the average major axis of primary particle diameter by SEM observation of particle cross section treated with a cross section polisher is in a range of 1 to 10 &mu;m, (the median diameter)/(the average major axis of primary particle diameters of the particle cross sections) is in a rang of 1.0 to 3.0, 5% diameter of volume basis cumulative distribution is median diameter/3 or more, 95% diameter is 3 times or less the median diameter. The manufacturing method of the positive active material of the lithium secondary battery is provided. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery and a method for producing the same. Specifically, the present invention has a primary particle size that is large and uniform, and most of such primary particles are surrounded only by a space. Therefore, when used as a positive electrode active material, cycle characteristics are improved. The present invention relates to a positive electrode active material for a lithium secondary battery that provides an excellent lithium secondary battery and a method for producing the same. Furthermore, this invention relates to the lithium ion secondary battery which has a positive electrode containing the positive electrode active material mentioned above.

  In recent years, cellular phones and notebook personal computers have rapidly spread due to high performance and downsizing, and lithium secondary batteries are widely used as power sources for such small mobile devices because of their high energy density. Has come to be. Furthermore, recently, in order to put it to practical use as a power source in an electric vehicle (EV) or a hybrid electric vehicle (HEV) using both an internal combustion engine and a battery as a power source, the capacity is further increased and the safety is further increased. Various researches are being promoted in order to develop lithium secondary batteries with excellent performance and output characteristics.

One direction of such research is such as lithium manganate (LiMn ₂ O ₄ ) having a spinel structure, hexagonal lithium nickelate (LiNiO ₂ ) and lithium cobaltate (LiCoO ₂ ) having a layered structure. Various studies aiming at improving the performance of a positive electrode active material for lithium secondary batteries made of a lithium composite oxide have been conducted.

  Among these lithium composite oxides, lithium cobaltate has a problem in that the source of cobalt as a raw material is limited, and its stable supply is difficult and is very expensive. On the other hand, lithium manganate has a problem that although the material cost can be kept relatively low, the energy density as high as when lithium cobaltate is used cannot be obtained.

  On the other hand, lithium nickelate is promising because it has abundant nickel raw materials, has better capacity characteristics than the above two, and can achieve the highest energy density. Is being viewed. Furthermore, lithium composite oxides containing various metal atoms such as magnesium, strontium, aluminum, cobalt, manganese, iron, vanadium, etc., together with nickel, have high charge / discharge capacity, high voltage, cycle characteristics, etc. Development has been actively promoted because of its excellent battery characteristics, relatively low cost of nickel raw materials, and stable supply.

  Conventionally, a composite oxide containing lithium nickelate and other metals as described above is generally mixed by dry mixing a nickel salt and a salt of the other metal together with a lithium compound, or wet mixing in an appropriate solvent. Then, after drying, it can be obtained by firing in an oxidizing atmosphere at a temperature of usually 600 to 1000 ° C. for 10 to 30 hours, and pulverizing and classifying as necessary.

  However, lithium secondary batteries using lithium nickelate as a positive electrode active material have been known to be inferior in cycle characteristics and storage stability at high temperatures. It is known that increasing the primary particle size is an effective means (see, for example, Patent Document 1).

  That is, in lithium nickelate, the primary particles are particles close to a single crystal, and these aggregate to form secondary particles. Therefore, when the primary particles expand and contract due to insertion / extraction of lithium accompanying charging / discharging of the lithium secondary battery, that is, volumetric change is unavoidable, and thus charging / discharging of the battery is repeated, From the change in volume of the primary particles, the secondary particles collapse and become finer as the aggregation of the primary particles is released.

  More specifically, primary particles of lithium nickelate expand and contract in the c-axis direction due to insertion and extraction of lithium accompanying charging and discharging of the lithium secondary battery. Looking at two primary particles separated by a grain boundary, the crystal directions are rarely the same, and the crystal directions are usually different. Accordingly, the primary particles of lithium nickelate expand and contract in different directions due to insertion and extraction of lithium, and thus the grain boundaries are distorted, and the secondary particles collapse and become finer.

  In a lithium secondary battery, the positive electrode is formed by mixing lithium nickelate, which is powder, with a positive electrode active material, mixing a conductive material thereto, and binding with a binder. Therefore, as described above, if the secondary particles are collapsed and refined, the portion where electron conduction is not ensured in the positive electrode increases, the internal resistance increases, and the utilization rate as an active material decreases. . That is, this is the cycle deterioration of the lithium secondary battery.

  Further, it is known that it is effective to increase the primary particle size in order to enhance the storage stability of lithium nickelate at high temperatures (see Patent Document 2).

Here, the lithium nickelate having large primary particles can be obtained preferably by firing at a high temperature such as 1000 ° C. In such a high temperature firing, lithium due to volatilization of the raw lithium salt is obtained. There is a strong tendency for defects to occur, and Ni ²⁺ having an ionic radius approximately equal to Li ⁺ is mixed into the vacant site to give a composite oxide having a non-stoichiometric composition. Even if such a complex oxide is used as a positive electrode active material, a lithium secondary battery having high charge / discharge characteristics cannot be obtained. Moreover, baking at a high temperature as described above is not suitable for industrial production conditions.

On the other hand, there is also known a method in which lithium hydroxide is added to a slurry of a basic nickel salt for reaction, the resulting reaction product is spray-dried, and the resulting dried product is press-molded to obtain lithium nickelate. (See Patent Document 2). According to this method, even if the reaction product is baked at a high temperature, volatilization of the raw material lithium salt from the inside of the molded product can be prevented, but the raw material lithium salt near the surface of the molded product is still volatilized. . Therefore, in order to obtain lithium nickelate having high charge / discharge characteristics, it is necessary to make a molded product that is sufficiently large with respect to the surface area of the molded product, and thus this method is not industrially suitable.
Japanese Patent Laid-Open No. 2001-243952 Japanese Patent Laid-Open No. 10-069910

  The present invention has been made in order to solve the above-described problem in lithium nickelate for a positive electrode active material of a lithium secondary battery, and the primary particles have a large and uniform particle size. Therefore, there is provided a positive electrode active material for a lithium secondary battery that provides a lithium secondary battery having excellent cycle characteristics when used as a positive electrode active material, and a method for producing the same. For the purpose. Furthermore, an object of this invention is to provide the lithium ion secondary battery provided with the positive electrode containing the positive electrode active material mentioned above.

According to the present invention, the composition formula Li _x Ni _{1 -yz} Co _y M _z O ₂ (M is at least one element selected from Mn, Al, Zr, Si, Sr and Mg, and x, y and z Is a number satisfying 0.95 ≦ x ≦ 1.10, 0.1 ≦ y ≦ 0.4 and 0 ≦ z ≦ 0.1.) The median diameter measured by a laser diffraction particle size distribution measuring device is in the range of 2 to 20 μm, and the average major axis of the primary particle diameter by SEM observation of the cross section of the particle processed by the cross section polisher is in the range of 1 to 10 μm , (The median diameter) / (average major axis of the primary particle diameter of the particle cross section) is in the range of 1.0 to 3.0, and the 5% diameter of the volume-based cumulative distribution is the median diameter / 3 or more. And a positive electrode for a lithium secondary battery whose 95% diameter is not more than 3 times the median diameter An active material is provided.

Furthermore, according to this invention, the manufacturing method of such a positive electrode active material for lithium secondary batteries is provided. That is, according to the present invention, as the first method,
(A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) Provided is a method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is subjected to secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

According to the present invention, as the second method,
(A) Li / (Co + Ni + M) molar ratio of 1.5 to 5.0 on nickel hydroxide particles containing at least one element M selected from Mg, Mn, Sr, Si, Zr and Al together with cobalt element Mix lithium hydroxide in the range,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) Provided is a method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is subjected to secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

According to the present invention, as a third method,
(A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water to remove excess lithium element,
(D) The fired product contains at least one element M selected from Mg, Mn, Sr, Si, Zr and Al,
(E) There is provided a method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is subjected to secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

  The lithium nickelate according to the present invention has a large primary particle size and is uniform, and most of such primary particles are surrounded only by a space. Therefore, when used as a positive electrode active material, cycle characteristics are obtained. A positive electrode active material for a lithium secondary battery is provided that provides an excellent lithium secondary battery.

  According to the first and second methods of the present invention, nickel hydroxide particles containing cobalt element (and other element M) are mixed with water in a Li / (Co + Ni) molar ratio of 1.5 to 5.0. After lithium oxide is mixed and subjected to primary firing, excess lithium element is washed and removed from the obtained fired product, and the fired product is subjected to secondary firing, thereby having the above-described composition and the above-described particles. A positive electrode active material for a lithium secondary battery having characteristics can be obtained.

  According to the third method of the present invention, lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element at a Li / (Co + Ni) molar ratio in the range of 1.5 to 5.0. After the primary firing, the excess lithium element is washed and removed from the fired product, and then the fired product contains another element M, and this is subjected to secondary firing to similarly have the above-described composition. In addition, a positive electrode active material for a lithium secondary battery having the above-described particle characteristics can be obtained.

The positive electrode active material for a lithium secondary battery according to the present invention has a composition formula Li _x Ni _{1 -yz} Co _y M _z O ₂ (M is at least one element selected from Mn, Al, Zr, Si, Sr and Mg). X, y and z are numbers satisfying 0.95 ≦ x ≦ 1.10, 0.1 ≦ y ≦ 0.4 and 0 ≦ z ≦ 0.1.) A positive electrode active material for a battery, having a median diameter measured by a laser diffraction particle size distribution measuring device in a range of 2 to 20 μm, and an average major axis of primary particle diameters by SEM observation of a cross section of a particle treated with a cross section polisher. In the range of 1 to 10 μm, (the median diameter) / (average major axis of the primary particle diameter of the particle cross section) is in the range of 1.0 to 3.0, and the 5% diameter of the volume-based cumulative distribution is Median diameter / 3 or more and 95% diameter is less than 3 times the median diameter It is.

  In the present invention, primary particles refer to grain boundaries or spaces, or particles surrounded by grain boundaries and spaces, and secondary particles refer to aggregates of the primary particles.

  In the present invention, Co stabilizes the crystal structure of the obtained positive electrode active material for a lithium secondary battery, that is, a lithium composite oxide, and therefore, the lithium secondary oxide using such a lithium composite oxide as a positive electrode active material. According to the battery, cycle deterioration is suppressed. However, in the general formula (I), when the value of y is smaller than 0.1, Co hardly contributes to the stabilization of the crystal structure, and on the other hand, when the value of y exceeds 0.4, The charge / discharge capacity in the obtained lithium secondary battery is reduced. Moreover, since Co is expensive, it is economically disadvantageous to contain it unnecessarily in large amounts. Therefore, according to the present invention, in the general formula (I), the value of y is preferably in the range of 0.1 to 0.4.

  Furthermore, the positive electrode active material for a lithium secondary battery according to the present invention, that is, the lithium composite oxide contains at least one element M selected from Mg, Mn, Sr, Si, Zr and Al in addition to the above Co. You may do it.

  Since all of the elements M stabilize the crystal structure of the obtained lithium composite oxide, cycle deterioration is suppressed according to the lithium secondary battery using such a lithium composite oxide as a positive electrode active material. However, when the amount of the element M in the obtained lithium composite oxide is too large, the charge / discharge capacity of the obtained battery is remarkably reduced, or a large excess of lithium hydroxide is used as a flux and firing is performed twice. Since the growth of particles is also inhibited by the method of the present invention, the value of z in the general formula (I) is preferably 0.1 or less.

According to the present invention, the positive electrode active material for a lithium secondary battery as described above is used as the first method,
(A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) The fired product can be obtained by secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

The positive electrode active material for a lithium secondary battery as described above is also a second method,
(A) Li / (Co + Ni + M) molar ratio of 1.5 to 5.0 on nickel hydroxide particles containing at least one element M selected from Mg, Mn, Sr, Si, Zr and Al together with cobalt element Mix lithium hydroxide in the range,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) The fired product can be obtained by secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

Furthermore, the positive electrode active material for a lithium secondary battery as described above is a third method,
(A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water to remove excess lithium element,
(D) The fired product contains at least one element M selected from Mg, Mn, Sr, Si, Zr and Al,
(E) The fired product can be obtained by secondary firing at 600 to 900 ° C. in an oxidizing atmosphere.

  According to the present invention, as described above, in any of the first, second and third methods, in step (b), nickel hydroxide particles containing cobalt element (and element M) and A mixture with a large excess of lithium hydroxide is calcined. Hereinafter, in the first, second, and third methods, the firing in this step (b) may be referred to as primary firing, and the obtained fired product may be referred to as a primary fired product. The temperature at which the primary firing is performed may be referred to as a primary firing temperature.

  Next, according to the present invention, after the primary firing, the second time in the step (d) in the first and second methods and the step (e) in the third method. Is fired. Hereinafter, the second firing in the step (d) in the first and second methods and the second firing in the step (e) in the third method are referred to as secondary firing, and the obtained fired product is divided into two. Sometimes referred to as the next fired product. In addition, the temperature at which the secondary firing is performed may be referred to as a secondary firing temperature.

  Furthermore, according to the present invention, in any of the first, second and third methods, as step (a), nickel hydroxide particles containing cobalt element (and element M) are added to Li / (Co + Ni (+ M). ) Lithium hydroxide is added at a molar ratio in the range of 1.5 to 5.0, dry mixed, and the resulting mixture is primarily fired. According to the present invention, the lithium hydroxide used in step (a) thus has a Li / (Co + Ni (+ M)) molar ratio of approximately 1, preferably 0.95 to 1.05. Lithium oxide is used to react with nickel hydroxide particles containing cobalt element (and element M) to produce a lithium composite oxide.

  The first important feature of the present invention is that a large excess of lithium hydroxide is used in the step (a) with respect to nickel hydroxide particles containing cobalt element (and element M). Among the lithium hydroxides used in the process, surplus lithium hydroxide that does not participate in the reaction with nickel hydroxide particles containing cobalt element (and element M) is composed of nickel hydroxide particles containing cobalt element (and element M) and hydroxide. During the primary firing of the lithium dry mixture, the melt functions as a flux.

  Thus, according to the present invention, during the primary firing of a dry mixture of nickel hydroxide particles containing cobalt element (and element M) and lithium hydroxide, the reaction product produced is the melting of lithium hydroxide as a flux. Since it is covered with an object, volatilization of the raw material lithium can be prevented even when the primary firing temperature is high.

  The details of the reaction in which a lithium composite oxide is produced from nickel hydroxide particles containing cobalt element (and element M) and lithium hydroxide are not necessarily clear, but in the present invention, cobalt element ( When nickel hydroxide particles containing element M) and lithium hydroxide are primarily fired, the small primary particles of the lithium composite oxide produced by the reaction are brought into contact with each other via a flux, thereby fusing with each other. It is considered that a single primary particle having no grain boundary is formed between the particles, and this is repeatedly generated to grow into a large primary particle.

  That is, according to the present invention, the flux appears to have an effect of promoting the formation of larger primary particles by merging the small primary particles of the lithium composite oxide generated by the reaction. Thus, in order for small primary particles to fuse with each other, they need to be close to each other, but when the amount of flux is too high, the average distance between particles increases and particle growth Is inhibited. On the other hand, when the amount of the flux is too small, the above action as a flux is not sufficient, and as a result, small primary particles do not fuse and grow, and a large number of small primary particles having grain boundaries are generated and agglomerated. Thus, it appears that many secondary particles, which are aggregates of many small primary particles, are generated.

  Furthermore, a certain amount of temperature and time are required for the small primary particles of the lithium composite oxide produced by the reaction to fuse with each other. There is a complementary relationship between this temperature and time. That is, when the temperature is relatively high, the small primary particles are rapidly fused with each other, and accordingly, the particles are expected to fuse and grow in a short time. On the other hand, when the temperature is relatively low, The fusion is slow, and it will take more time for the particles to fuse and grow.

  Therefore, in the method of the present invention, as step (a), the nickel / hydroxide particles containing cobalt element (and element M) have a Li / (Co + Ni (+ M)) molar ratio in the range of 1.5 to 5.0. Therefore, lithium hydroxide is added.

  Next, according to the present invention, a mixture of nickel hydroxide particles containing cobalt element (and element M) obtained in step (a) and lithium hydroxide is 730 to 950 ° C. in an oxidizing atmosphere, preferably Is subjected to primary firing at a temperature of 750 to 900 ° C. to obtain a primary fired product, that is, a lithium composite oxide containing excess lithium element.

  When the primary firing temperature is too low, the primary particles are not sufficiently fused and grown. Therefore, even when the obtained positive electrode active material is used for a lithium secondary battery, cycle deterioration of the battery cannot be sufficiently suppressed. . However, even if the primary firing temperature is too high, for example, when it exceeds 950 ° C., lithium hydroxide is decomposed and does not function as a flux. Therefore, since the primary particles do not fuse and grow, a large number of small primary particles having grain boundaries are formed. Therefore, even when the obtained positive electrode active material is used in a lithium secondary battery, the internal resistance is large, and charge / discharge is performed. The characteristics will be inferior.

  Accordingly, in the present invention, the primary firing time depends on the primary firing temperature. For example, when the firing temperature is set to a high temperature, the mixture has sufficient heat energy while the mixture is heated to the firing temperature. Since they are accumulated, after the mixture is heated to a predetermined firing temperature, the mixture can be sufficiently fired by maintaining the temperature for a short time. Accordingly, the primary firing time may usually range from 0.1 to 120 hours, but is preferably in the range of 0.5 to 96 hours.

  In the present invention, the primary firing is preferably performed in an oxygen atmosphere, but may be performed in air if necessary.

  Further, according to the present invention, as a second important feature, the target lithium is finally baked at a temperature of 600 to 900 ° C., preferably 700 to 800 ° C. in an oxidizing atmosphere. A composite oxide is obtained.

  Even in the secondary firing, when the firing temperature is too low, the lithium element unevenly distributed on the surface of the primary particles cannot be sufficiently diffused into the primary particles as described later. Even if the positive electrode active material obtained is used, a lithium secondary battery having excellent charge / discharge characteristics cannot be obtained. On the other hand, when the secondary firing temperature is too high, primary particles agglomerate in the absence of flux and form grain boundaries between them, so that even with the obtained positive electrode active material, cycle characteristics are excellent. A lithium secondary battery cannot be obtained.

  Similarly, when the secondary firing time is too short, the lithium element unevenly distributed on the surface of the primary particles cannot be sufficiently diffused into the primary particles, while the secondary firing time is too long. Sometimes primary particles agglomerate and form grain boundaries between them, both of which have a detrimental effect on the resulting battery as well as when the secondary firing temperature is too low or high.

  Accordingly, in the present invention, the secondary firing time is usually in the range of 0.1 to 15 hours, and preferably in the range of 0.5 to 10 hours, although it depends on the secondary firing temperature. In the present invention, the secondary firing is preferably performed in an oxygen atmosphere, but may be performed in air as necessary.

  In the present invention, when the fired product obtained in the previous step is subjected to secondary firing, lithium hydroxide is added to the fired product, and the final obtained fired product, that is, the amount of lithium in the positive electrode active material is appropriately set. You may correct to.

  In the method of the present invention, as described above, after the primary firing of the mixture of nickel hydroxide particles containing cobalt element (and element M) and lithium hydroxide, the obtained fired product may be further subjected to secondary firing. It is essential. Only by primary firing, a lithium secondary battery having excellent cycle characteristics cannot be obtained even if the obtained positive electrode active material is used. That is, even after the primary firing, the obtained fired product is washed with water to remove excess lithium from the fired product, and the fired product has a composition close to the stoichiometric composition. Therefore, even if such a positive electrode active material is used, a lithium secondary battery having excellent cycle characteristics cannot be obtained. However, according to the present invention, secondary firing is performed after the primary firing, so that lithium elements unevenly distributed in the primary particles or on the surface can be uniformly diffused into the primary particles, Thus, it seems that it is possible to obtain a positive electrode active material in which the primary particles have a large and uniform particle size, and most of such primary particles are surrounded only by spaces.

  In the method according to the present invention, the temperature of the subsequent secondary firing may be lower than the temperature of the primary firing, and the time of the subsequent secondary firing is shorter than the time of the primary firing. It's okay. In the secondary firing, in addition to the basic structure of the lithium composite oxide already formed in the primary firing, there should be thermal energy and time for the lithium element to diffuse inside or on the surface of the primary particles. It seems to be because it should be.

  Hereinafter, the first, second and third methods according to the present invention will be described.

  According to the present invention, in the first method, the nickel hydroxide particles containing cobalt element are preferably obtained by adding a sodium hydroxide aqueous solution and an aqueous ammonia solution to an aqueous solution containing nickel sulfate and cobalt sulfate, for example. For example, it may be a mixture of cobalt hydroxide and nickel hydroxide.

  In the first method of the present invention, the mixture obtained in step (a) is first calcined in an oxidizing atmosphere in step (b), and lithium composite oxide containing excess lithium element, that is, primary calcining After obtaining the product, the primary fired product is washed with water in step (c) to remove excess lithium element, and then in step (d), the fired product is secondarily fired in an oxidizing atmosphere. Thus, the target lithium composite oxide containing cobalt element can be obtained.

  According to the present invention, in addition to the cobalt element, the lithium composite oxide containing at least one element M selected from Mg, Mn, Sr, Si, Zr and Al is also produced in the same manner as described above. It can be obtained by the method.

  Also in the second method, the nickel hydroxide particles containing the cobalt element and the element M are preferably, for example, a coprecipitated hydroxide of nickel, cobalt, and the element M. However, for example, the coprecipitated water of nickel and cobalt is used. Oxides and hydroxides of element M, sulfates, carbonates, nitrates, chlorides, oxychlorides (especially when element M is zirconium), sodium silicates (especially when element M is silicon) When element M is aluminum, it may be a mixture of sodium aluminate, and hydroxide, sulfate, carbonate, nitrate, chloride, oxychloride of cobalt hydroxide, nickel hydroxide and element M (Especially when element M is zirconium), sodium silicate (especially when element M is silicon), and sodium aluminate when element M is aluminum It may be. Such a coprecipitated hydroxide of nickel, cobalt, and element M is converted into an aqueous solution containing water-soluble salts of nickel, cobalt, and element M in consideration of the conditions for forming the hydroxides of nickel, cobalt, and element M. It can be obtained by adding an appropriate alkali to react.

  Hereinafter, also in the second method, the target lithium composite oxide can be obtained in the same manner as in the first method described above. That is, in the second method, as the step (a), nickel hydroxide particles containing cobalt and the element M are dry-mixed with a large excess of lithium hydroxide and fired in an oxidizing atmosphere.

  Next, in the second method, in the step (b), the mixture obtained in the step (a) is secondarily fired in an oxidizing atmosphere to obtain a lithium composite oxide containing excess lithium element, Next, in step (c), the obtained fired product is washed with water to remove excess lithium element, and then in step (d), this fired product is secondarily fired in an oxidizing atmosphere, and thus the object is obtained. A lithium composite oxide can be obtained.

  Such a second method is suitable for obtaining a lithium composite oxide containing, for example, magnesium, manganese, strontium, zirconium or silicon elements together with nickel and cobalt elements.

  In both the first and second methods described above, nickel hydroxide particles containing cobalt element (and element M) are primarily fired together with a large excess of lithium hydroxide, and excess lithium element is removed from the resulting primary fired product. After washing and removing with water, secondary firing is performed to obtain the target lithium composite oxide.

  However, according to the present invention, according to the third method, nickel hydroxide particles containing cobalt element are first calcined together with a large excess of lithium hydroxide, and the obtained primary calcined product is washed with water to obtain surplus lithium. After removing the element, the element M can be contained therein, and further subjected to secondary firing to obtain the target lithium composite oxide.

  That is, also in this third method, in step (a), a large excess of lithium hydroxide is dry-mixed with nickel hydroxide particles containing cobalt element, and in step (b), the mixture is placed in an oxidizing atmosphere. After primary firing, a primary fired product containing excess lithium element is obtained. Then, in step (c), the primary fired product is washed with water to remove excess lithium element, and then in step (d), The fired product contains at least one element M selected from Mg, Mn, Sr, Si, Zr and Al. Finally, in step (e), this is finally subjected to secondary firing in an oxidizing atmosphere. Thereby, the target positive electrode active material for lithium secondary batteries can be obtained.

  This third method is suitably used for producing a lithium composite oxide containing, for example, an aluminum element together with nickel and cobalt elements. For example, nickel hydroxide particles containing cobalt element are primarily fired together with a large excess of lithium hydroxide, and the resulting primary fired product is washed with water to remove excess lithium compounds, and then the fired product is used as a slurry. If sodium aluminate is added to the slurry, an acid is added to the slurry to adjust the pH to 6 to 7, aluminum hydroxide is adhered to the fired product, and the fired product is subjected to secondary firing to include aluminum element together with cobalt element. A lithium composite oxide can be obtained.

  As described above, according to the method of the present invention, nickel hydroxide particles containing cobalt element (and element M) are used together with a large excess of lithium hydroxide so that lithium hydroxide functions as a flux while cobalt element (and When a lithium composite oxide is produced by primary firing of a mixture of nickel hydroxide particles containing element M) and lithium hydroxide, the volatilization of the raw material lithium is prevented even in firing at a high temperature such as 900 ° C. Furthermore, by finally subjecting the fired product obtained in the previous step to secondary firing, the positive electrode active for lithium secondary batteries having the desired composition and the desired particle characteristics can be obtained. A substance can be obtained.

Thus, the lithium composite oxide as the positive electrode active material for a lithium secondary battery according to the present invention obtained by the method of the present invention has a composition formula Li _x Ni _{1 -yz} Co _y M _z O ₂ (M is Mn, It is at least one element selected from Al, Zr, Si, Sr and Mg, and x, y and z are 0.95 ≦ x ≦ 1.10, 0.1 ≦ y ≦ 0.4 and 0 ≦ z ≦. And a cross section of a particle treated with a cross section polisher, having a median diameter measured by a laser diffraction particle size distribution measuring device in the range of 2 to 20 μm. The average major axis of the primary particle diameter by SEM observation (hereinafter referred to as “CP treated section”) is in the range of 1 to 10 μm, and (the median diameter) / (the average major axis of the primary particle diameter of the particle section) is 1. In the range of .0 to 3.0, The 5% diameter of the volume-based cumulative distribution has a median diameter / 3 or more, and the 95% diameter has a particle size characteristic that is 3 times or less the median diameter.

  In general, in order to improve the cycle characteristics of a lithium secondary battery, it is effective to increase the particle size of the primary particles constituting the positive electrode active material, but if too large particles are present in the positive electrode active material, In a secondary battery, there is a possibility of breaking through the separator and causing a short circuit. On the other hand, the presence of too small primary particles causes deterioration of cycle characteristics. Therefore, in the present invention, the median diameter of the positive electrode active material is set in the range of 2 to 20 μm.

  In the present invention, as the primary particle size of the obtained lithium composite oxide, the primary particle size is measured by SEM observation of the CP-treated cross section of the primary particle. When a nickel composite oxide is produced, even when the secondary particles are composed of large primary particles, it is compared with the inside of the secondary particles according to the SEM image of the CP-treated cross section of the secondary particles. Small primary particles exist, and the average major axis of such primary particles has a size of 1 μm or less. In such a case, such small primary particles cause cycle deterioration. It is.

  Therefore, in the present invention, the average major axis of the primary particle diameter by SEM observation of the CP-treated section of the lithium composite oxide is in the range of 1 to 10 μm, preferably 1.5 to 8 μm.

  As the number of primary particles forming the secondary particles increases, the value of (median diameter) / (average major axis of primary particle diameter of particle cross section) increases and exceeds 3.0. On the other hand, according to the present invention, the value of (median diameter) / (average major diameter of primary particle diameter of particle cross section) is in the range of 1.0 to 3.0, and thus the lithium composite according to the present invention. The oxide has a large primary particle size and is uniform, and most of such primary particles are surrounded only by a space. Therefore, when used as a positive electrode active material, lithium has excellent cycle characteristics. Give a secondary battery. Of course, in the positive electrode active material according to the method of the present invention, there are also primary particles surrounded by grain boundaries or spaces, but the ratio is small.

  The lithium secondary battery according to the present invention comprises a positive electrode containing the positive electrode active material described above. For example, the above-described positive electrode active material is mixed with a conductive agent, a binder, a filler, and the like, kneaded to form a mixture, and a positive electrode is formed using the mixture to manufacture a battery. More specifically, for example, the positive electrode active material described above is used as a mixture, and this is applied to a positive electrode current collector made of, for example, a stainless mesh, pressure-bonded, and heated and dried under reduced pressure to obtain a positive electrode. However, if necessary, the mixture may be pressure-molded into an appropriate shape such as a disk, and heat treated under vacuum as necessary to form a positive electrode. The positive electrode thus formed is combined with other battery elements to constitute a lithium secondary battery.

  The lithium secondary battery according to the present invention only needs to include a positive electrode containing the positive electrode active material as described above, and other configurations may be the same as those of conventionally known lithium secondary batteries. For example, the above-described positive electrode active material is mixed with a conductive agent, a binder, a filler, and the like, kneaded to form a mixture, and a positive electrode is formed using the mixture to manufacture a battery. More specifically, for example, the positive electrode active material described above is used as a mixture, and this is applied to a positive electrode current collector made of, for example, a stainless mesh, pressure-bonded, and heated and dried under reduced pressure to obtain a positive electrode. However, if necessary, the mixture may be pressure-molded into an appropriate shape such as a disk, and heat treated under vacuum as necessary to form a positive electrode.

  The positive electrode thus formed is combined with other battery elements to constitute a lithium secondary battery. That is, the lithium secondary battery according to the present invention has a positive electrode and a negative electrode, and these are accommodated in a battery container facing each other through a separator impregnated with a non-aqueous electrolyte. The positive electrode is connected to the lead wire for the positive electrode through the positive electrode current collector, and the negative electrode is connected to the lead wire for the negative electrode through the negative electrode current collector. Energy is taken out from the positive lead wire and the negative lead wire as electric energy.

  The conductive agent is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the lithium secondary battery. Accordingly, examples of the conductive agent include conductive polymer materials such as natural graphite, artificial graphite, carbon black, ketjen black, carbon fiber, metal powder, metal fiber, and polyphenylene. These may be used alone or in combination of two or more. Although the compounding quantity of a electrically conductive agent is not specifically limited, Usually, it is the range of 1-50 weight% in the said mixture, Preferably, it is the range of 2-30 weight%.

  The binder is not particularly limited, and for example, starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene , Ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and the like. These may be used alone or in combination of two or more. The blending amount of the binder is not particularly limited, but usually in the above mixture, the range of 1 to 50% by weight is preferable, and the range of 2 to 30% by weight is particularly preferable.

  The said filler is mix | blended with a mixture as needed. As a filler, if it is a fibrous material which does not raise | generate a chemical change in a lithium secondary battery, it will not specifically limit, The conventionally known thing is used suitably. Accordingly, examples of such a filler include polyolefin resin fibers such as polypropylene resin and polyethylene resin, glass fibers, and carbon fibers. The blending amount of the filler is not particularly limited, but is usually in the range of 0 to 30% by weight in the above mixture.

  In the lithium secondary battery according to the present invention, the negative electrode material is not particularly limited as long as it is conventionally used in a lithium secondary battery. For example, in addition to metal lithium and lithium alloy, lithium Examples thereof include carbon materials that can occlude and release ions.

  The positive electrode and the negative electrode are usually formed on a current collector. Although it does not specifically limit as this electrical power collector, Usually, stainless steel, its mesh, etc. are used.

In addition, the non-aqueous electrolyte solution may be any conventionally known one. For example, carbonates such as ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, Lithium perchlorate (LiClO ₄ ) or lithium hexafluorophosphate in organic solvents such as sulfolanes, lactones, ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, etc. there may be mentioned those obtained by dissolving dissociable lithium salts (LiPF ₆₎ or the like. As the separator, for example, a porous film made of a polyolefin resin such as polyethylene or polypropylene is used, but the separator is not limited thereto.

  In the present invention, a highly dispersed solid electrolyte containing the lithium salt as described above can be used as an electrolyte that also serves as a separator.

  Such a lithium secondary battery according to the present invention can be suitably used for portable electronic devices such as a notebook computer, a mobile phone, and a video movie, as well as a battery mounted on a mobile body, a household auxiliary power source, etc. Application as a large battery is also possible.

  Hereinafter, the present invention will be described with reference to comparative examples together with examples, but the present invention is not limited to these examples. In the following, the particle size distribution of the obtained positive electrode active material was measured as follows.

(Particle size distribution of positive electrode active material)
Using a laser diffraction particle size distribution analyzer (LA-500 manufactured by Horiba, Ltd.), a volume-based cumulative distribution of 5% diameter (D5), 50% diameter (median diameter or D50) and 95% diameter (D95) ) Was measured.

(Cross-section polisher treatment of positive electrode active material and average major axis of primary particle diameter of the treated cross section)
The positive electrode active material and the resin (epoxy G2) are mixed on the glass plate in the same volume, applied to a silicon plate, vacuum defoamed at 80 ° C. for 10 minutes, and then heated at 120 ° C. for 30 minutes for epoxy resin. Was cured. The cured product containing the positive electrode active material was treated with a cross section polisher SM-09010 manufactured by JEOL Ltd. at an ion acceleration voltage of 4.0 kV for 20 hours to prepare a cross section of the cured product.

  The cross section is observed with a scanning electron microscope (SEM), and five visual fields are randomly selected in which the number of primary particles on the cross section is 10, and the major axis (maximum diameter) is measured for a total of 50 primary particles. The average value was calculated | required and it was set as the average major axis of the primary particle diameter.

(Median diameter / average major axis of primary particle diameter of cross section polished cross section)
It calculated | required by calculation from the said median diameter and the average long diameter of the primary particle diameter of a cross section polisher process cross section.

(Particle characteristics of other positive electrode active materials)
The average major diameter of the primary particle diameter of the median diameter / cross section polisher treated cross section, the median diameter / 3 and the median diameter three times are the results of the above particle size distribution measurement and the average major diameter of the primary particle diameter of the cross section polished cross section. From the calculation.

(Battery characteristics)
1 g of the obtained positive electrode active material, 0.06 g of acetylene black (Denka black granular product manufactured by Denki Kagaku Kogyo Co., Ltd.), a polyvinylidene fluoride solution (KF Polymer L # 1120 manufactured by Kureha Chemical Industry Co., Ltd.) and N-methyl-2 -Pyrrolidone weight ratio 1/1 solution) 1.16 g was mixed and kneaded in a mortar for 2 minutes to obtain a paste. This paste was applied onto a 20 μm thick aluminum foil using a roll coater so that the weight of the active material after drying was 0.01 g / cm ² , vacuum-dried at 120 ° C., and then a disc having a diameter of 1.5 cm. The positive electrode was punched into a shape.

Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate and dimethyl carbonate using 1M lithium hexafluorophosphate as a supporting salt was used as the electrolyte. A model cell was produced in a glove box in an argon atmosphere in which the dew point was controlled at −80 ° C. Charging / discharging was performed at 45 ° C. with a current density of 0.5 mA / cm ^{2 with} respect to the positive electrode and a cut-off voltage of 4.3 to 3.0 V, and the discharge capacity d _{1 at the} first cycle (c) and the discharge at the 100th c The capacity d ₁₀₀ was determined, and the discharge capacity maintenance rate (d ₁₀₀ / d ₁ ) × 100 (%) of the 100th c was determined therefrom.

Example 1
A sodium hydroxide aqueous solution and an aqueous ammonia solution were added dropwise to an aqueous solution of a mixture of nickel sulfate and cobalt sulfate (Ni / Co molar ratio 0.84 / 0.16) at a pH of 12 and a temperature of 40 ° C. The obtained reaction product was filtered, washed with water, and then dried at 120 ° C. to obtain hydroxide particles having a composition of Ni _0.84 Co _0.16 (OH) ₂ .

  Lithium hydroxide monohydrate was added to the hydroxide particles so that the Li / (Ni + Co) molar ratio was 3.33, and a mixer (Fiber Mixer MX-V200 manufactured by Matsushita Electric Industrial Co., Ltd., hereinafter the same). Was dry mixed for 10 minutes. In the following Examples and Comparative Examples, dry mixing was thus performed for 10 minutes using the mixer.

The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium element, and then vacuum-dried at 120 ° C. for 24 hours to obtain a fired product of composition Li _1.00 Ni _0.84 Co _0.16 O _2. Obtained.

The obtained fired product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ .

Example 2
Lithium hydroxide monohydrate was dry-mixed with the hydroxide particles having the composition Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 2.16. Thereafter, in the same manner as in Example 1, a fired product having the composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ was obtained.

The obtained calcined product and lithium hydroxide were mixed so that the Li / (Ni + Co) molar ratio was 1.05, and the resulting calcined product and lithium hydroxide monohydrate mixture was 650 ° C. in an oxygen atmosphere. And a positive electrode active material having the composition formula Li _1.05 Ni _0.84 Co _0.16 O ₂ was obtained.

  FIG. 1 shows a positive electrode active material schematically drawn based on a scanning electron micrograph of a CP-treated cross section of this positive electrode active material. Thus, it is understood that the positive electrode active material according to the present invention is composed of primary particles having a large particle diameter surrounded by a space, and the major axis of the primary particle diameter of the CP-treated cross section is large.

Example 3
Lithium hydroxide monohydrate was added to the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.70, and then dry-type. Mixed.

The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 72 hours in an oxygen atmosphere. The obtained fired product was washed with water, filtered, and this was repeated to sufficiently remove excess lithium element, and then vacuum-dried at 120 ° C. for 24 hours to obtain a fired product having the composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ I got a thing.

The fired product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having a composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 1
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.23. . The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 72 hours in an oxygen atmosphere to obtain a positive electrode active material having a composition formula of Li _1.08 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 2
Lithium hydroxide monohydrate was dry-mixed with the hydroxide particles having the composition Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.07. . The obtained mixture of hydroxide particles and lithium hydroxide was fired at 850 ° C. for 24 hours in an oxygen atmosphere to obtain a positive electrode active material having a composition formula of Li _1.05 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 3
A sodium hydroxide aqueous solution and an aqueous ammonia solution were added dropwise to an aqueous solution of a mixture of nickel sulfate and cobalt sulfate (Ni / Co molar ratio 0.84 / 0.16) at a pH of 12 and a temperature of 40 ° C. The obtained reaction product was filtered and washed with water, and then suspended in water to obtain a slurry of hydroxide particles having a composition of Ni _0.84 Co _0.16 (OH) ₂ having a concentration of 1 mol / L.

To this slurry, a lithium hydroxide aqueous solution having a concentration of 3.5 mol / L was dropped so that the Li / (Ni + Co) molar ratio was 1.07, followed by spray drying. The obtained spray-dried product was press-molded at a pressure of 1000 kg / cm ² for 1 minute, and the obtained molded product was fired at 850 ° C. for 24 hours in an oxygen atmosphere to obtain the composition formula Li _1.07 Ni _0.84 Co _0.16 O ₂ . A positive electrode active material was obtained.

  In the above press molding, 3.0 g of the spray-dried product was molded using a circular mold having a diameter of 20 mm (hereinafter the same).

  As shown in FIG. 2, the positive electrode active material schematically drawn on the basis of a scanning electron micrograph of the cross section of the positive electrode active material treated with CP is surrounded by a grain boundary or a space between the positive electrode active material and the positive electrode active material. It is understood that the secondary particles are aggregates of a large number of primary particles having a small particle diameter.

Comparative Example 4
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.00. . The obtained mixture of hydroxide particles and lithium hydroxide was calcined in an oxygen atmosphere at 850 ° C. for 24 hours to obtain a positive electrode active material having the composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 5
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.23. . The obtained mixture of hydroxide particles and lithium hydroxide was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _1.22 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 6
Lithium hydroxide monohydrate was dry-mixed with the hydroxide particles having the composition Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.07. . The obtained mixture of hydroxide particles and lithium hydroxide was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _1.07 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 7
A lithium hydroxide aqueous solution having a concentration of 3.5 mol / L was added dropwise to the hydroxide particle slurry obtained in Comparative Example 3 so that the Li / (Ni + Co) molar ratio was 1.07, followed by spray drying. It was. The obtained spray-dried product was press-molded at a pressure of 1000 kg / cm ² for 1 minute, and the obtained molded product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain the composition formula Li _1.07 Ni _0.84 Co _0.16 O ₂ . A positive electrode active material was obtained.

Comparative Example 8
Lithium hydroxide monohydrate was added to the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.00, and dry-type. Mixed. The obtained mixture of hydroxide particles and lithium hydroxide was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _1.00 Ni _0.84 Co _0.16 O ₂ .

Example 4
While adding sodium hydroxide aqueous solution and aqueous ammonia solution little by little to an aqueous solution of a mixture of nickel sulfate, cobalt sulfate and magnesium sulfate (Ni / Co / Mg molar ratio 0.79 / 0.16 / 0.05), pH 12 and temperature The reaction was carried out at 40 ° C. The obtained reaction product was filtered and washed with water, and then dried at 120 ° C. to obtain hydroxide particles having a composition of Ni _0.79 Co _0.16 Mg _0.05 (OH) ₂ .

Lithium hydroxide monohydrate was dry mixed with the hydroxide particles so that the Li / (Ni + Co + Mg) molar ratio was 3.29. The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 880 ° C. for 0.5 hour in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium and then vacuum-dried at 120 ° C. for 24 hours to have the composition formula Li _1.00 Ni _0.79 Co _0.16 Mg _0.05 O ₂ A fired product was obtained.

The fired product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having a composition formula of Li _1.00. Ni _0.79 Co _0.16 Mg _0.05 O ₂ .

Example 5
A sodium hydroxide aqueous solution and an aqueous ammonia solution were dropped little by little into an aqueous solution of a mixture of nickel sulfate and cobalt sulfate (Ni / Co molar ratio 0.841 / 0.159), and the mixture was reacted at pH 12 and a temperature of 40 ° C. The obtained reaction product was filtered, washed with water, and then dried at 120 ° C. to obtain hydroxide particles having a composition of Ni _0.841 Co _0.159 (OH) ₂ .

  Strontium hydroxide is added to the hydroxide particles so that the Ni / Co / Sr molar ratio is 0.837 / 0.158 / 0.005, and the Li / (Ni + Co + Sr) molar ratio is 3.33. Lithium hydroxide monohydrate was dry mixed.

The obtained hydroxide particle / strontium hydroxide / lithium hydroxide mixture was calcined at 800 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium and then vacuum-dried at 120 ° C. for 24 hours to have the composition formula Li _1.00 Ni _0.837 Co _0.158 Sr _0.005 O ₂ A fired product was obtained.

The obtained calcined product and lithium hydroxide monohydrate were mixed so that the Li / (Ni + Co + Sr) molar ratio was 1.05, and the resulting calcined product and lithium hydroxide mixture was 700 ° C. in an oxygen atmosphere. _And a positive electrode active material having the composition formula Li _1.05 Ni _0.837 Co _0.158 Sr _0.005 O ₂ was obtained.

Example 6
While adding aqueous sodium hydroxide solution and aqueous ammonia solution little by little to an aqueous solution of a mixture of nickel sulfate, cobalt sulfate and manganese sulfate (Ni / Co / Mn molar ratio 0.79 / 0.16 / 0.05), pH 12 and temperature The reaction was carried out at 40 ° C. The obtained reaction product was filtered, washed with water, and then dried at 120 ° C. to obtain hydroxide particles having a composition of Ni _0.79 Co _0.16 Mn _0.05 (OH) ₂ .

  Lithium hydroxide monohydrate was dry mixed with the hydroxide particles so that the Li / (Ni + Co + Mn) molar ratio was 3.32.

The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium and then vacuum-dried at 120 ° C. for 24 hours to have the composition formula Li _1.00 Ni _0.79 Co _0.16 Mn _0.05 O ₂ A fired product was obtained.

The fired product was fired at 900 ° C. for 1 hour in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _1.00 Ni _0.79 Co _0.16 Mn _0.05 O ₂ .

Example 7
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 3.33. . The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 72 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this process was repeated to sufficiently remove excess lithium and then vacuum-dried at 120 ° C. for 24 hours to obtain a fired product having the composition formula Li _1.01 Ni _0.84 Co _0.16 O ₂ Got.

The fired product is added to water and stirred to form a slurry. To this slurry, sodium aluminate (NaAlO ₂ ) is added so that the Al / (Ni + Co + Al) molar ratio is 0.05, and then sulfuric acid is added. The slurry was neutralized to have a pH of 6-7. The obtained neutralized product was filtered, washed with water, and dried at 120 ° C.

The dried product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _0.97 Ni _0.80 Co _0.15 Al _0.05 O ₂ .

Example 8
A sodium hydroxide aqueous solution and an aqueous ammonia solution were dropped little by little into an aqueous solution of a mixture of nickel sulfate and cobalt sulfate (Ni / Co molar ratio 0.841 / 0.159), and the mixture was reacted at pH 12 and a temperature of 40 ° C. The obtained reaction product was filtered, washed with water, and then dried at 120 ° C. to obtain hydroxide particles having a composition of Ni _0.841 Co _0.159 (OH) ₂ .

  Sodium metasilicate is added to the hydroxide particles so that the Ni / Co / Si molar ratio is 0.837 / 0.158 / 0.005, and the Li / (Ni + Co + Si) molar ratio is 3.33. Thus, lithium hydroxide monohydrate was dry mixed.

The obtained mixture of hydroxide particles, sodium metasilicate and lithium hydroxide was calcined at 850 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium, followed by vacuum drying at 120 ° C. for 24 hours, and firing having the composition Li _1.00 Ni _0.837 Co _0.158 Si _0.005 O ₂ I got a thing.

This fired product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having a composition formula Li _1.00 Ni _0.837 Co _0.158 Si _0.005 O ₂ .

Example 9
1 L of water was added to 200 g of hydroxide particles having a composition of Ni _0.841 Co _0.159 (OH) ₂ obtained in Example 8 and stirred to obtain a slurry. To this slurry, a zirconium oxychloride aqueous solution having a Zr content of 1% by weight and a 1 mol / L sodium hydroxide aqueous solution were dropped little by little, and reacted at pH 7.5. The reaction was stopped when the / Zr molar ratio reached 0.837 / 0.158 / 0.005.

  The obtained reaction product was filtered, washed with water, and dried at 120 ° C. Lithium hydroxide monohydrate was dry mixed with the obtained dried product so that the Li / (Ni + Co + Zr) molar ratio was 3.33.

The obtained mixture of dried product and lithium hydroxide was calcined at 850 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium, followed by vacuum drying at 120 ° C. for 24 hours, and firing having the composition Li _1.00 Ni _0.837 Co _0.158 Zr _0.005 O ₂ I got a thing.

This fired product was fired at 750 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition Li _1.00 Ni _0.837 Co _0.158 Zr _0.005 O ₂ .

Example 10
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 3.33. . The resulting mixture of hydroxide particles and lithium hydroxide was calcined at 750 ° C. for 1 hour in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium, followed by vacuum drying at 120 ° C. for 24 hours to obtain a fired product having the composition formula Li _0.98 Ni _0.84 Co _0.16 O ₂ Got.

The obtained calcined product and lithium hydroxide monohydrate were mixed so that the Li / (Ni + Co) molar ratio was 1.05, and the obtained calcined product / lithium hydroxide mixture was 750 ° C. in an oxygen atmosphere. and calcined for 1 hour to obtain a cathode active material having a composition formula _{Li 1.05 Ni 0.84 Co 0.16 O 2} .

Comparative Example 9
Lithium hydroxide monohydrate was dry mixed with the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 3.33. . The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 700 ° C. for 72 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium and then vacuum-dried at 120 ° C. for 24 hours to obtain a fired product having the composition formula Li _0.97 Ni _0.84 Co _0.16 O ₂ Got.

The obtained calcined product and lithium hydroxide monohydrate were mixed so that the Li / (Ni + Co) molar ratio was 1.05, and the obtained calcined product / lithium hydroxide mixture was 750 ° C. in an oxygen atmosphere. and calcined 5 hours to obtain a cathode active material having a composition formula _{Li 1.05 Ni 0.84 Co 0.16 O 2} .

Comparative Example 10
Lithium hydroxide monohydrate was added to the hydroxide particles having a composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 so that the Li / (Ni + Co) molar ratio was 1.00, and a mixer was added. Was dry mixed for 10 minutes. The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 1000 ° C. for 24 hours in an oxygen atmosphere to obtain a positive electrode active material having the composition formula Li _0.96 Ni _0.84 Co _0.16 O ₂ .

Comparative Example 11
Lithium hydroxide monohydrate was added to the hydroxide particles having the composition of Ni _0.84 Co _0.16 (OH) ₂ obtained in Example 1 using a mixer so that the Li / (Ni + Co) molar ratio was 3.33. And dry mixed for 10 minutes. The obtained mixture of hydroxide particles and lithium hydroxide was calcined at 850 ° C. for 24 hours in an oxygen atmosphere. The obtained fired product was washed with water and filtered, and this was repeated to sufficiently remove excess lithium, followed by vacuum drying at 120 ° C. for 24 hours to obtain a positive electrode active material having the composition formula Li _1.00 Ni _0.84 Co _0.16 O _2. Obtained material.

  Along with the composition of the lithium composite oxide obtained in the above examples and comparative examples (elements M, x, y and z in the general formula (I)), the average major axis of the primary particles measured on the CP-treated cross section, laser Table 1 shows the particle size characteristics measured by the diffraction particle size distribution measuring apparatus and the cycle characteristics of the obtained lithium secondary battery.

  As is clear from the results shown in Table 1, in the lithium ion secondary battery including the positive electrode containing the positive electrode active material according to the present invention, the discharge capacity at 1c is 140 mAh / g or more, and the discharge capacity at 100c. Although the condition that the maintenance ratio is 90% or more is satisfied, in the lithium ion secondary battery including the positive electrode including the positive electrode active material according to the comparative example, at least one of the above conditions is not satisfied.

It is the schematic diagram drawn based on the operation-type electron micrograph of the cross section which carried out CP process of an example of the particle | grains of the positive electrode active material obtained by the method of this invention. It is the schematic diagram drawn based on the operation-type electron micrograph of the cross section which CP-processed an example of the particle | grains of the positive electrode active material obtained as a comparative example.

Claims (3)

(A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) A method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is secondarily fired at 600 to 900 ° C. in an oxidizing atmosphere. (A) Li / (Co + Ni + M) molar ratio of 1.5 to 5.0 on nickel hydroxide particles containing at least one element M selected from Mg, Mn, Sr, Si, Zr and Al together with cobalt element Mix lithium hydroxide in the range,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water and removing excess lithium element from the fired product,
(D) A method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is secondarily fired at 600 to 900 ° C. in an oxidizing atmosphere. (A) Lithium hydroxide is mixed with nickel hydroxide particles containing cobalt element in the range of Li / (Co + Ni) molar ratio of 1.5 to 5.0,
(B) The obtained mixture is primarily fired at 730 to 950 ° C. in an oxidizing atmosphere,
(C) After washing the obtained fired product with water to remove excess lithium element,
(D) The fired product contains at least one element M selected from Mg, Mn, Sr, Si, Zr and Al,
(E) A method for producing a positive electrode active material for a lithium secondary battery, wherein the fired product is secondarily fired at 600 to 900 ° C. in an oxidizing atmosphere.

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