JP6511965B2 - Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same. The present invention also relates to a non-aqueous electrolyte secondary battery using the positive electrode active material for the non-aqueous electrolyte secondary battery.

  In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, development of a small and lightweight secondary battery having high energy density is strongly desired. Further, development of a high-power secondary battery as a battery for a motor drive power source, in particular, a power source for transportation equipment such as an electric vehicle, is strongly desired. As a secondary battery satisfying these requirements, there is a lithium ion secondary battery which is a non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution and the like, and an active material capable of desorbing and inserting lithium is used as a material of the negative electrode and the positive electrode.

  With regard to non-aqueous electrolyte secondary batteries, research and development are currently actively conducted, and in particular, non-aqueous electrolyte secondary batteries using layered or spinel lithium transition metal composite oxide particles as a positive electrode active material are: Since a high voltage of 4V class can be obtained, practical use is advanced as a secondary battery having a high energy density.

Lithium cobalt composite oxide (LiCoO ₂ ) particles relatively easy to synthesize at present, lithium nickel composite oxide using nickel cheaper than cobalt (LiNiO ₂ ) as a positive electrode material of such a non-aqueous electrolyte secondary battery ) Particles, lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles, lithium manganese composite oxide (LiMn ₂ O ₄ ) particles using manganese, lithium nickel manganese composite oxide Lithium transition metal complex oxide particles such as lithium (LiNi _0.5 Mn _0.5 O ₂ ) particles have been proposed.

  Among these, lithium-nickel composite oxide particles show a charge / discharge capacity larger than lithium-cobalt composite oxide particles, and are noted as a positive electrode active material capable of producing a secondary battery having a relatively low cost and high energy density. I'm collecting. On the other hand, the lithium nickel composite oxide particles have a problem that the stability of the crystal structure is lower than that of the lithium cobalt composite oxide particles, and the cycle characteristics and the high temperature stability are inferior.

  To solve this problem, part of the nickel constituting the lithium-nickel composite oxide particles is replaced with a transition metal element such as cobalt, manganese or iron, or a different metal element such as aluminum, magnesium, vanadium or tin. It is common practice to improve the stability of the crystal structure by Among these metallic elements, cobalt is known to be effective in preventing phase transition and aluminum is effective in stabilizing the crystal structure. However, it is known that aluminum inhibits the densification of nickel composite hydroxide particles when it is intended to obtain a precursor of lithium nickel composite oxide particles containing aluminum by coprecipitation reaction. In addition, when the precursor contains a plurality of different elements (metal elements other than nickel, cobalt and manganese), when the addition amount becomes excessive due to the difference in the salt formation behavior for each element, the particle shape Changes. Therefore, when such lithium-nickel composite oxide particles are used as a positive electrode active material, the packing property is significantly reduced, and the reduction of the charge and discharge capacity of the secondary battery can not be avoided. For this reason, development of the lithium nickel complex oxide particle which improved stability of crystal structure, without impairing charge and discharge capacity is desired.

For example, in JP 2010-24083 A, reaction vessels are connected in a two-stage cascade, and first, an aqueous solution containing a nickel compound and a cobalt compound, an aqueous solution of sodium hydroxide, and ammonium ions are supplied to the first reaction vessel. The raw material solution consisting of the aqueous solution containing the body is supplied separately and simultaneously for reaction to form nickel-cobalt composite hydroxide particles, and then the nickel-cobalt composite hydroxide particles are formed in the second reaction vessel. An aqueous solution of sodium aluminate and an aqueous solution of sulfuric acid are supplied and reacted while being fed to continuously carry out the general formula (1): Ni _{1 -x} Co _x (OH) ₂ (wherein x is 0. 0). A hydroxylated aluminum having a coating layer consisting of aluminum and containing 0.1% by mass to 5% by mass of aluminum with respect to the total amount Method of manufacturing a hexafluorophosphate coated-nickel-cobalt composite hydroxide particles.

  According to such a production method, it is possible to easily control the particle shape without being affected by aluminum during the coprecipitation reaction, and obtain high-density, nearly spherical nickel-cobalt composite hydroxide particles. be able to. In addition, when the aluminum hydroxide-coated nickel cobalt composite hydroxide particles are fired, aluminum can be uniformly diffused in the particles, so even when the addition amount is a very small amount, crystals can be obtained. It is possible to improve the stability of the structure. However, in this manufacturing method, it is difficult to secure a specific surface area of the lithium nickel composite oxide particles sufficiently because the ratio of coarse particles is large, and when the secondary battery is configured, the output characteristics may be significantly reduced. There is.

On the other hand, according to WO 2011/122448, after nickel-cobalt composite hydroxide particles are formed by crystallization reaction in which the Ni solubility is adjusted to 25 mass ppm to 100 mass ppm, they are obtained by coating with aluminum hydroxide. General formula: (Ni _1-xy Co _x Al _y ) _1-z M _z (OH) ₂ (0.05 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0.1, 0 ≦ z ≦ 0 And M is at least one metal element selected from Mg, Fe, Cu, Zn, and Ga), and the (101) plane half width by X-ray diffraction is 0.45 ° to 0 Aluminum hydroxide coated nickel cobalt composite hydroxide particles, which are at 8 °, are described.

By using this aluminum hydroxide-coated nickel-cobalt composite hydroxide particle as a precursor, the general formula: Li _w (Ni _{1 -xy} Co _x Al _y ) _{1 -z} M _z O ₂ (0.98 ≦ w ≦ 1) .10, 0.05 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.05, provided that M is at least selected from Mg, Fe, Cu, Zn and Ga. A lithium-nickel composite oxide particle comprising a secondary particle obtained by aggregating primary particles represented by one kind of metal element) and having a (003) plane crystallite diameter of 1200 Å to 1600 Å determined by X-ray diffraction and Scherrer equation A positive electrode active material comprising In this positive electrode active material, since the primary particles are appropriately large and the pores between the primary particles can be enlarged, it is possible to sufficiently secure the penetration path of the electrolytic solution. Therefore, it is considered that the output characteristics can be improved by configuring the secondary battery using this positive electrode active material. However, this technique is intended to improve the output characteristics mainly in a low temperature environment, not to improve the cycle characteristics and high temperature stability.

JP, 2010-24083, A WO 2011/122448

  In view of the above problems, the present invention suppresses the decrease in output characteristics and simultaneously improves the charge / discharge capacity, the cycle characteristics and the high temperature stability, and a positive electrode active material for a non-aqueous electrolyte secondary battery and a precursor thereof, , It aims at providing these manufacturing methods. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery using such a positive electrode active material for a non-aqueous electrolyte secondary battery.

The magnesium-coated nickel-cobalt composite hydroxide particles of the present invention have a general formula: Ni ₁ -xyz Co _x Al _y Mg _z (OH) ₂ (where 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ Magnesium-coated nickel cobalt composite hydroxide particles represented by 0.06, 0.01 ≦ z ≦ 0.03 and coated with a coating comprising magnesium or a magnesium compound,
It consists of secondary particles of solid structure formed by aggregation of multiple primary particles,
The average particle diameter of the secondary particles is 10.0Myuemu～14.5Myuemu, and a tap density of 1.4 g / ml or more, and a specific surface area of 10m ² / g~25m ² / g,
It is characterized by

  It is preferable that the thickness of the said film is 0.001 micrometer-0.01 micrometer.

  The primary particles are preferably in the form of a rectangular parallelepiped and have an average particle diameter in the range of 0.01 μm to 0.1 μm.

The method for producing magnesium-coated nickel-cobalt composite hydroxide particles of the present invention has a general formula: Ni _1-xyz Co _x Al _y Mg _z (OH) ₂ (where 0.05 ≦ x ≦ 0.20, 0.01) A method for producing a magnesium-coated nickel cobalt composite hydroxide particle, which is represented by ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03) and coated with a film comprising magnesium or a magnesium compound,
Nickel, cobalt and aluminum in a reaction aqueous solution in which the temperature is controlled to 45 ° C. to 55 ° C., the liquid temperature 25 ° C. to a pH value of 11 to 12 and the ammonium ion concentration to 8 g / L to 12 g / L in an inert atmosphere. A raw material aqueous solution containing C., to obtain nickel-cobalt composite hydroxide particles by a continuous crystallization method, a crystallization step,
A coating step of obtaining magnesium-coated nickel-cobalt composite hydroxide particles by mixing the slurry containing the nickel-cobalt composite hydroxide particles with a coating solution containing magnesium to form a mixed solution;
And the like.

  It is preferable to adjust the pH value in 25 degreeC of liquid temperature of the said mixed solution to the range of 10-11.

  It is preferable to further include a washing step of washing the nickel-cobalt composite hydroxide particles obtained in the crystallization step before the coating step.

  Preferably, the method further comprises a drying step of heating the aluminum-coated nickel-cobalt composite hydroxide particles to 100 ° C. to 150 ° C. for drying.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a general formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0.05 ≦ x Positive electrode active for nonaqueous electrolyte secondary batteries comprising lithium nickel cobalt composite oxide particles having a layered structure, represented by ≦ 0.20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03) A substance,
It consists of secondary particles of solid structure formed by aggregation of multiple primary particles,
The (003) plane crystallite diameter is 1200 Å to 1600 Å, which is determined from Rietveld analysis by XRD measurement;
Wherein the average particle size of the secondary particles is 11.5Myuemu～14.5Myuemu, there tap density above 2.6 g / ml, and the specific surface area is 0.2m ² /g~0.5m ² / g ,
It is characterized by

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention can be prepared according to the general formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0. 0). Non-aqueous electrolyte secondary battery comprising lithium nickel cobalt composite oxide particles having a layered structure, represented by 05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03) A method of manufacturing a positive electrode active material for
Mixing the magnesium-coated nickel-cobalt composite hydroxide particles and a lithium compound to obtain a lithium mixture;
Firing the lithium mixture at 600 ° C. to 800 ° C. in an oxidizing atmosphere,
And the like.

  It is preferable that the calcination temperature in the said baking process shall be 700 degreeC-770 degreeC.

  It is preferable to further include a heat treatment step of heating the magnesium-coated nickel-cobalt composite hydroxide particles at 600 ° C. to 800 ° C. in an oxidizing atmosphere before the mixing step.

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode active material for non-aqueous electrolyte secondary battery is used as a positive electrode material of the positive electrode. It is characterized by

  According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery capable of simultaneously improving charge / discharge capacity, cycle characteristics and high temperature stability while suppressing a decrease in output characteristics, and a precursor thereof, and production thereof We can provide a way. Further, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery using such a positive electrode active material for a non-aqueous electrolyte secondary battery. For this reason, the industrial significance of the present invention is extremely great.

FIG. 1 is a schematic cross-sectional view of a 2032 type coin battery used for battery evaluation. FIG. 2 is a schematic explanatory view of a measurement example of impedance evaluation and an equivalent circuit used for analysis.

  As a result of intensive studies in view of the above problems, the present inventors added aluminum and magnesium to the positive electrode active material composed of lithium-nickel-cobalt composite oxide particles, and had a crystallite diameter in the range of 1200 Å to 1600 Å. In the secondary battery using this positive electrode active material, the charge / discharge capacity is controlled while controlling the decrease in the output characteristics by controlling the average particle diameter, the tap density and the specific surface area within a specific range. It has been found that the cycle characteristics and high temperature stability can be improved. In addition, such a positive electrode active material is a nickel-cobalt composite hydroxide in which nickel, cobalt and aluminum are uniformly distributed by crystallization reaction under specific conditions, and the average particle diameter, tap density and specific surface area are within predetermined ranges. It was found that particles can be obtained by using, as a precursor, magnesium-coated nickel cobalt composite hydroxide particles in which the nickel cobalt composite hydroxide particles are coated with magnesium or a magnesium compound. The present invention has been completed based on these findings.

1. Magnesium-coated nickel-cobalt composite hydroxide particles 1-1. Magnesium-Coated Nickel-Cobalt Composite Hydroxide Particles (1) Composition Ratio The magnesium-coated nickel-cobalt composite hydroxide particles (hereinafter referred to as “Mg-coated composite hydroxide particles”) of the present invention have a general formula: Ni _1-xyz Co _{x Al y Mg z (OH)} 2 ( although, 0.05 ≦ x ≦ 0.20,0.01 ≦ y ≦ 0.06,0.01 ≦ z ≦ 0.03) represented by. The contents of nickel (Ni), cobalt (Co), aluminum (Al) and magnesium (Mg) and their critical meanings are the same as in the case of the positive electrode active material described later, The description is omitted.

(2) Particle Structure The Mg-coated composite hydroxide particles of the present invention are composed of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles are preferably substantially spherical. Here, the substantially spherical shape includes not only spherical secondary particles but also spherical and elliptical spheres having fine irregularities on the surface.

  In addition, the Mg-coated composite hydroxide particles of the present invention have a structure in which secondary particles of a solid structure in which nickel, cobalt and aluminum are uniformly dispersed are covered with a film made of a magnesium or a magnesium compound. As a result, the particle structure and crystal structure of the positive electrode active material using the Mg-coated composite hydroxide particles as a precursor can be stabilized while suppressing the addition amounts of aluminum and magnesium, and thus the obtained secondary battery It is possible to simultaneously improve the charge / discharge capacity, the cycle characteristics and the high temperature stability while suppressing the deterioration of the output characteristics.

  In such Mg-coated composite hydroxide particles, the thickness of the coating is controlled preferably in the range of 0.001 μm to 0.01 μm, more preferably 0.002 μm to 0.007 μm. If the thickness of the coating is less than 0.001 μm, the coverage of the magnesium or the magnesium compound is too small, so that magnesium may not be uniformly dispersed in the secondary particles in the firing step. On the other hand, when the thickness of the coating film exceeds 0.01 μm, a region where high concentration of magnesium is present is formed on the surface of the positive electrode active material using this Mg-coated composite hydroxide particle as a precursor and its vicinity Since the lithium insertion and desorption reactions are inhibited, the battery performance may be degraded.

  The particle shape of the Mg-coated composite hydroxide particles can be confirmed by observation using a scanning electron microscope (SEM). Further, the particle structure can be confirmed by SEM observation after embedding Mg coated composite hydroxide particles in a resin or the like to make it possible to observe the cross section by cross section polisher processing or the like. Furthermore, the thickness of the peritoneal membrane can be measured by characteristic x-ray spectroscopy (energy dispersive x-ray analysis: EDX).

(3) Shape of Primary Particles and Average Particle Size It is preferable that the primary particles constituting the secondary particles have a rectangular parallelepiped shape. The average particle diameter is preferably in the range of 0.01 μm to 0.1 μm, and more preferably in the range of 0.04 μm to 0.07 μm. When the shape and the average particle size of the primary particles satisfy such conditions, the secondary particles can be made more dense. In the present invention, not only those whose cross-sectional shape is rectangular but also those whose cross-sectional shape is a quadrangle other than rectangular, those whose one surface is a curved surface, etc. Shall be included.

  The shape of the primary particles can be confirmed by observing the secondary particles in a state in which cross-sectional observation is possible, as in the case of the particle structure described above. Further, the average particle diameter of the primary particles can be determined by SEM observation of the particle cross section, measuring the maximum diameter of 20 or more primary particles, and calculating the average value thereof.

(4) Average particle diameter of secondary particles The average particle diameter of secondary particles is required to be in the range of 10.0 μm to 14.5 μm, preferably 10.5 μm to 13.5 μm. By controlling the average particle size to such a range, it is possible to control the average particle size of the positive electrode active material having the Mg-coated composite hydroxide particles as a precursor to an appropriate range. On the other hand, when the average particle diameter is less than 10.0 μm, the tap density of the positive electrode active material using this Mg-coated composite hydroxide particle as a precursor becomes small, and the charge and discharge capacity of the secondary battery using this becomes small. It will decrease. In addition, it takes not only a long time to separate the crystallized Mg-coated composite hydroxide particles in solid-liquid separation in the crystallization step to be described later, but the dried Mg-coated composite hydroxide particles are easily scattered. On the other hand, when the average particle diameter exceeds 14.5 μm, the positive electrode active material is coarsened, and the specific surface area is reduced, so that the battery performance such as output characteristics is degraded. In the present invention, the average particle diameter means volume-based average particle diameter (MV), and can be determined from the volume integration value measured by a laser light diffraction scattering particle size analyzer.

(5) Tap Density The tap density of secondary particles is required to be 1.4 g / ml or more, preferably 1.5 g / ml or more. If the tap density is less than 1.4 g / ml, the packing properties of the positive electrode active material using the Mg-coated composite hydroxide particles as a precursor will be low. On the other hand, the upper limit value of the tap density is not particularly limited, but under normal production conditions, it is 3 g / ml or less, preferably 2.8 g / ml or less. In the present invention, tap density means bulk density after tapping sample powder collected in a container 500 times based on JIS Z-2504, and it may be measured using a shaking specific gravity measuring device. it can.

(6) The specific surface area of the specific surface area the secondary particles is preferably from 10m ² / g~25m ² / g, more preferably 10m ² / g~15m ² / g. By controlling the specific surface area within this range, the specific surface area of the cathode active material of the Mg-coated composite hydroxide particles and the precursor suitable range (0.2m ² /g~0.5m ² / g Can be controlled). In the present invention, the specific surface area can be measured by the BET method by nitrogen gas adsorption.

1-2. Method of Producing Magnesium-Coated Nickel-Cobalt Composite Hydroxide Particles The method of producing Mg-coated composite hydroxide particles of the present invention is a method of producing Mg-coated composite hydroxide particles described above,
In an inert atmosphere, at least nickel, cobalt and aluminum in a reaction aqueous solution in which the pH value is controlled to 11 to 12 and the ammonium ion concentration to 8 g / L to 12 g / L at a temperature of 45 ° C. to 55 ° C. A raw material aqueous solution containing C., to obtain nickel-cobalt composite hydroxide particles by a continuous crystallization method, a crystallization step,
Coating step of obtaining magnesium-coated nickel-cobalt composite hydroxide particles by mixing a slurry containing the nickel-cobalt composite hydroxide particles and a coating solution containing magnesium to form a mixed solution;
And the like. In addition, you may add the washing | cleaning process demonstrated below, a drying process, etc. as needed.

(1) Crystallization step The crystallization step is to set the temperature to 45 ° C. to 55 ° C., the liquid temperature 25 ° C. to a pH value of 11 to 12 and the ammonium ion concentration to 8 g / L to 12 g / L in an inert atmosphere. In this step, a raw material aqueous solution containing at least nickel, cobalt and aluminum is supplied to a controlled reaction aqueous solution to obtain nickel-cobalt composite hydroxide particles (hereinafter referred to as “composite hydroxide particles”).

  As described above, usually, in the crystallization reaction in the case where aluminum is excessively present, the densification of the composite hydroxide particles is inhibited. On the other hand, in the present invention, as the crystallization method, the continuous crystallization method is adopted, and by appropriately controlling the addition amount of aluminum and the crystallization conditions, the crystallization of high density composite hydroxide particles is performed. Is possible.

a) Supply aqueous solution [raw material aqueous solution]
As the raw material aqueous solution, it is necessary to use one containing nickel, cobalt and aluminum. The ratio of these metal elements is usually adjusted to be the composition ratio of nickel, cobalt, and aluminum in the target positive electrode active material.

  As sources of metal elements, water-soluble metal compounds, specifically, nitrates, sulfates and chlorides can be used. Among these, from the viewpoint of preventing cost and contamination of halogen, these sulfates can be suitably used as a supply source of nickel and cobalt, and sodium aluminate is preferably used as a supply source of aluminum. be able to.

  Further, the concentration of the raw material aqueous solution is adjusted to preferably 1.0 mol / L to 2.6 mol / L, more preferably 1.5 mol / L to 2.2 mol / L, in total of the metal compounds. If the concentration of the raw material aqueous solution is less than 1.0 mol / L, the amount of the crystallized material per reaction vessel decreases, so the productivity is lowered. On the other hand, when the concentration of the raw material aqueous solution exceeds 2.6 mol / L, since the saturation concentration at normal temperature is exceeded, crystals of each metal compound may be reprecipitated to clog piping and the like.

  The metal compound may not necessarily be supplied to the reaction tank as a raw material aqueous solution. For example, when the crystallization reaction is carried out using a metal compound which reacts upon mixing to form a compound other than the target compound, the concentration of the total solution of all the metal compound aqueous solutions is in the above range. An aqueous solution of metal compound may be prepared and supplied as an aqueous solution of individual metal compounds into the reaction tank at a predetermined ratio.

[Alkaline aqueous solution]
The aqueous alkali solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a common aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction aqueous solution, but is preferably added as an aqueous solution in view of the easiness of pH control. In this case, the concentration of the alkali metal hydroxide aqueous solution is preferably about 20% by mass to 50% by mass.

  The method of supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the reaction aqueous solution does not increase locally and is maintained in a predetermined range. For example, it may be supplied using a pump whose flow rate can be controlled, such as a metering pump, while sufficiently agitating the reaction aqueous solution.

[Aqueous solution containing ammonium ion supplier]
An aqueous solution containing an ammonium ion donor is added to adjust the solubility of metal ions in the aqueous reaction solution. The aqueous solution containing such an ammonium ion supplier is not particularly limited, and, for example, aqueous ammonia or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride can be used.

  In addition, the supply of the aqueous solution containing an ammonium ion supply body can also utilize the pump which can control flow volume similarly to alkaline aqueous solution.

b) Reaction conditions [reaction temperature]
The temperature (reaction temperature) of the reaction aqueous solution needs to be controlled in the range of 45 ° C. to 55 ° C., preferably 47 ° C. to 53 ° C. As described above, the primary particles constituting the composite hydroxide particles of the present invention preferably have a rectangular parallelepiped shape, but if the reaction temperature is less than 45 ° C., the number of apexes, ridges and faces increases. Since the primary particles are in the form of a polyhedron composed of seven or more planes, the tap density is reduced. On the other hand, when the reaction temperature exceeds 55 ° C., the primary particles become flaky and secondary particles having a desired crystal structure and shape can not be obtained.

[PH value]
It is necessary to control the pH value of the reaction aqueous solution in the range of 11 to 12, preferably 11.3 to 11.8 on the basis of a liquid temperature of 25 ° C. When the pH value is less than 11, a part of the crystallized composite hydroxide particles is dissolved, and composite hydroxide particles having a desired composition ratio can not be obtained. On the other hand, when the pH value exceeds 12, the composite hydroxide particles become finer.

[Ammonium ion concentration]
The ammonium ion concentration in the reaction aqueous solution needs to be controlled in the range of 8 g / L to 12 g / L, preferably 9 g / L to 11 g / L. Since the ammonium ion functions as a complexing agent in the reaction aqueous solution, when the ammonium ion concentration is less than 8 g / L, the solubility of the metal ion can not be kept constant, and the reaction aqueous solution becomes easy to gel and shape It becomes difficult to obtain composite hydroxide particles with a uniform particle size. On the other hand, when the ammonium ion concentration exceeds 12 g / L, the solubility of the metal ion becomes too large, and the amount of metal ion remaining in the reaction aqueous solution increases, which causes the composition deviation and the like.

[Reaction atmosphere]
The atmosphere (reaction atmosphere) in the crystallization step needs to be an inert atmosphere, preferably an oxygen concentration of 2% by volume or less, more preferably 1% by volume or less. That is, it is preferable to use an atmosphere composed of an inert gas such as nitrogen or argon which hardly contains oxygen, and the inert gas is sprayed on the surface of the reaction aqueous solution to completely contact the reaction aqueous solution with oxygen. It is more preferable to shut off. By controlling the reaction atmosphere in the crystallization step to such an inert atmosphere, secondary particles having a high density and a suitable particle diameter can be obtained. On the other hand, in an oxidizing atmosphere, in particular, an atmosphere in which the oxygen concentration exceeds 2% by volume, the primary particles of the composite hydroxide are refined by oxidation, and the charge and discharge capacity of the obtained secondary battery is improved. Can not

c) Stirring speed It is necessary to stir the reaction aqueous solution preferably at 100 rpm to 130 rpm, more preferably at 110 rpm to 120 rpm during the crystallization step. Thereby, substantially spherical secondary particles are obtained. On the other hand, if the stirring speed is less than 100 rpm, there is a possibility that substantially spherical secondary particles can not be obtained due to excessive aggregation of primary particles. On the other hand, when the stirring speed exceeds 130 rpm, the aggregation of the primary particles is suppressed, and there is a possibility that the composite hydroxide particles (secondary particles) become finer.

d) Crystallization Method In the present invention, it is necessary to adopt a continuous crystallization method as a crystallization method from the viewpoint of obtaining a positive electrode active material excellent in packing property. That is, according to the continuous crystallization method, composite hydroxide particles (secondary particles) having a large particle diameter can be efficiently obtained, so that the filling property of the positive electrode active material using this as a precursor can be improved. Is possible. On the other hand, when the batch type crystallization method is adopted, it is difficult to increase the particle diameter of the composite hydroxide particles, and the filling property of the positive electrode active material can not be improved.

e) Recovery Method Recovery of the composite hydroxide particles obtained in the crystallization step can be performed by a known method. For example, the reaction aqueous solution containing the composite hydroxide particles obtained in the crystallization step can be introduced into a filter press or the like and recovered by filtration.

(2) Washing Step The washing step is a step of washing the composite hydroxide particles obtained in the crystallization step to remove residual impurities. Thereby, the crystal structure of the positive electrode active material can be further stabilized.

  The washing method is not particularly limited, and known methods can be used. For example, after washing | cleaning liquid is added and stirred to the composite hydroxide particle obtained at the crystallization process, it can wash | clean by filtering with a filter press etc. At this time, as the washing solution, washing water such as purified water or an aqueous solution of sodium hydroxide can be used. When using sodium hydroxide aqueous solution, it is preferable to make the density | concentration into 5 mass%-10 mass%. The amount of the washing solution used is preferably about 5 times to 15 times the mass of the composite hydroxide particles, and more preferably about 8 times to 12 times. Furthermore, it is preferable to perform washing | cleaning separately in multiple times rather than performing by 1 operation, and it is more preferable to divide in 2 times-about 5 times, and to perform.

(3) Coating step In the coating step, the slurry containing the composite hydroxide particles obtained in the crystallization step and the coating solution containing magnesium are mixed to form a mixed solution, thereby forming the Mg-coated composite hydroxide particles. It is a process to obtain.

  First, an appropriate amount of solvent is added to the composite hydroxide particles obtained in the crystallization step and stirred to slurry the composite hydroxide particles. As the solvent, it is preferable to use pure water such as purified water which does not contain impurities.

  Next, while stirring this slurry, a pH adjuster such as sodium hydroxide is added dropwise as necessary, and the pH value at 25 ° C. is preferably 10 to 11, more preferably 10.3 to 10.7. Adjust to a fixed value in the range of When the pH value is out of this range, a part of nickel, cobalt and aluminum constituting the composite hydroxide particles is eluted, or the coating with magnesium or a magnesium compound is not sufficiently performed, and has a desired composition. In some cases, Mg-coated composite hydroxide particles can not be obtained.

  Subsequently, while stirring the slurry, a solution (coating solution) containing magnesium as a coating material is supplied and mixed. At this time, the supply amount of the coating solution needs to be appropriately adjusted so that the composition of the Mg-coated composite hydroxide particles obtained after the coating step becomes the composition of the target Mg-coated composite hydroxide particles. In addition, it is preferable to use what melt | dissolved water-soluble magnesium salts, such as magnesium sulfate, in purified water as a coating solution, and the thing whose magnesium ion concentration is in the range of 0.1 mol / L-1.0 mol / L. It is more preferred to use In addition, the supply of the coating solution needs to be appropriately adjusted according to the conditions such as the amount of the composite hydroxide particles in the slurry, but it is generally carried out over about 5 minutes to 15 minutes, preferably about 10 minutes. preferable.

  By covering magnesium or a magnesium compound on the surface of the composite hydroxide particles through the above-described coating process, Mg-coated composite hydroxide particles can be obtained. The Mg composite hydroxide particles are recovered by filtration with a filter press or the like. The recovered Mg composite hydroxide particles can be used as a precursor of the positive electrode active material after drying. From the viewpoint of removing excess impurities such as magnesium, it is preferable to use as a precursor of the positive electrode active material after washing and drying by the same method as the washing step described above.

(4) Drying Step The drying step is a step of heating the Mg-coated composite hydroxide particles obtained in the coating step to remove residual water. Thereby, each operation in the heat treatment process and mixing process which are mentioned later can be performed easily.

  The heating temperature (drying temperature) in the drying step is preferably in the range of 100 ° C to 150 ° C. If the drying temperature is less than 100 ° C., it takes a long time to remove the residual water, which deteriorates the productivity. On the other hand, even if the drying temperature exceeds 150 ° C., not only can no further effect be obtained, but also the energy cost increases.

2. Positive electrode active material for non-aqueous electrolyte secondary battery 2-1. Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material for non-aqueous electrolyte secondary battery of the present invention has a general formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03), and from lithium nickel cobalt composite oxide particles having a layered structure Become. This positive electrode active material is composed of secondary particles having a solid structure formed by aggregation of a plurality of primary particles, and the (003) plane crystallite diameter obtained from Rietveld analysis by XRD measurement is 1200 Å to 1600 Å. It is characterized by The average particle diameter of the secondary particles is 11.5Myuemu～14.5Myuemu, there tap density above 2.6 g / ml, and a specific surface area of at 0.2m ² /g~0.5m ² / g It is characterized by

(1) Composition The positive electrode active material of the present invention has a general formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0.05 ≦ x ≦ 0. 20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03). The composition of the positive electrode active material can be determined by ICP emission spectrometry or the like.

  The value of u indicating the lithium (Li) content is in the range of 1.00 to 1.04, preferably 1.01 to 1.03, and more preferably 1.015 to 1.025. When the value of u is less than 1.00, the amount of lithium is insufficient, and metal oxide particles other than the positive electrode active material having a desired composition are formed, and the charge and discharge capacity of the obtained secondary battery is reduced. On the other hand, when the value of u exceeds 1.04, the positive electrode active materials are sintered to each other to reduce the specific surface area, and the charge and discharge capacity similarly decreases.

  Nickel (Ni) is an element that contributes to high potential and high capacity of the secondary battery. The value of (1-xyz) indicating the content of nickel is in the range of 0.75 to 0.93, preferably 0.81 to 0.84. If the value of (1-xyz) is less than 0.75, the charge / discharge capacity of a secondary battery using this positive electrode active material can not be improved. On the other hand, when the value of (1-x-y-z) exceeds 0.93, the contents of cobalt, aluminum and magnesium decrease and it becomes impossible to sufficiently obtain the addition effect.

  Cobalt (Co) is an element that contributes to the improvement of charge and discharge cycle characteristics. The value of x indicating the cobalt content is in the range of 0.05 to 0.20, preferably 0.1 to 0.15. If the value of x is less than 0.05, the crystal structure of this positive electrode active material becomes unstable. On the other hand, when the value of x exceeds 0.20, the charge and discharge capacity of the secondary battery is reduced.

  Aluminum (Al) is an element that contributes to the stabilization of the crystal structure. The value of y indicating the aluminum content is in the range of 0.01 to 0.06, preferably 0.02 to 0.04. If the value of y is less than 0.01, the effect of stabilizing the crystal structure can not be obtained sufficiently. On the other hand, when the value of y exceeds 0.06, densification of the positive electrode active material is inhibited, and the charge and discharge capacity of the secondary battery is reduced.

  Magnesium (Mg) is also an element that contributes to the stabilization of the crystal structure, particularly to the temperature resistance. The value of z indicating the content of magnesium is in the range of 0.01 to 0.03, preferably 0.015 to 0.025. If the value of z is less than 0.01, the above effect can not be obtained sufficiently. On the other hand, when the value of z exceeds 0.03, the charge and discharge capacity of the secondary battery is reduced.

(2) (003) Plane Crystallite Size The positive electrode active material of the present invention has a (003) plane crystallite size of 1200 Å to 1600 Å, preferably 1300 Å to 1600 Å, more preferably 1400 Å to which is determined from Rietveld analysis by XRD measurement. It is in the range of 1600 Å. The positive electrode active material having a (003) plane crystallite diameter in such a range can realize a secondary battery having high crystallinity and excellent charge / discharge capacity and cycle characteristics. On the other hand, when the (003) plane crystallite diameter is less than 1200 Å, the crystallinity of the positive electrode active material is low, and the charge and discharge capacity of the secondary battery using the same decreases. On the other hand, when the (003) plane crystallite diameter exceeds 1600 Å, the specific surface area decreases, and the battery performance such as the output characteristics of the secondary battery decreases.

(3) Particle Structure The positive electrode active material of the present invention is composed of substantially spherical secondary particles formed by aggregating a plurality of primary particles. Moreover, this positive electrode active material is comprised from lithium nickel cobalt complex oxide particle of layered structure, and it shows the same diffraction pattern as lithium nickelate (LiNiO ₂ ) in XRD measurement. That is, the positive electrode active material of the present invention has a crystal structure in which cobalt, aluminum and magnesium are uniformly dissolved in a matrix composed of LiNiO ₂ . Therefore, in the positive electrode active material of the present invention, the stability of the crystal structure can be improved even when the addition of magnesium and aluminum is very small, and when the secondary battery is configured, charge and discharge It is possible to simultaneously improve the capacity, cycle characteristics and high temperature stability.

  The particle shape of the positive electrode active material can be confirmed by observation using a scanning electron microscope (SEM). In addition, the particle structure can be confirmed by SEM observation after embedding the positive electrode active material in a resin or the like and enabling cross-sectional observation by cross-section polisher processing or the like.

(4) Average Particle Size The average particle size of the positive electrode active material (secondary particles) is required to be 11.5 μm to 14.5 μm, preferably 12 μm to 13.5 μm. When the average particle diameter of the positive electrode active material is in such a range, the tap density is also increased, and the charge and discharge capacity of the obtained secondary battery can be increased. On the other hand, when the average particle diameter is less than 11.5 μm, the tap density of the positive electrode active material is lowered, and therefore the charge and discharge capacity can not be increased. On the other hand, when the average particle size exceeds 14.5 μm, the specific surface area of the positive electrode active material is significantly reduced. In the present invention, the average particle diameter means volume-based average particle diameter (MV), and can be determined by a laser light scattering type particle size distribution measuring device.

(5) Tap Density The tap density of the positive electrode active material is required to be 2.5 g / ml or more, preferably 2.6 g / ml or more. If the tap density is less than 2.5 g / ml, the packing property is low, and the charge and discharge capacity of the entire secondary battery can not be improved. On the other hand, the upper limit value of the tap density is not particularly limited, but under normal production conditions, it is 4 g / ml or less, preferably 3.8 g / ml or less. In the present invention, tap density means bulk density after tapping sample powder collected in a container 100 times based on JIS Z-2504, and may be measured using a shaking specific gravity measuring device. it can.

(6) The specific surface area of the specific surface area the cathode active material is preferably 0.2m ² /g~0.5m ² / g, more to be 0.30m ² /g~0.40m ² / g preferable. By controlling the specific surface area to such a range, it is possible to improve the cycle characteristics while securing the output characteristics of the secondary battery using this positive electrode active material. On the other hand, when the specific surface area of the positive electrode active material is less than 0.2 m ² / g, when the secondary battery is configured, the reaction area with the electrolytic solution can not be secured, and the output characteristics significantly decrease. Do. On the other hand, when the specific surface area of the positive electrode active material exceeds 0.5 m ² / g, the reactivity with the electrolytic solution becomes too high, and thus the cycle characteristics can not be sufficiently improved. In the present invention, the specific surface area can be measured by the BET method by nitrogen gas adsorption.

2-2. Method of producing positive electrode active material for non-aqueous electrolyte secondary battery According to the method of producing positive electrode active material for non-aqueous electrolyte secondary battery of the present invention, the above-mentioned Mg-coated composite hydroxide particles and lithium compound are mixed to obtain a lithium mixture And a firing step of firing the lithium mixture at 600 ° C. to 800 ° C. in an oxidizing atmosphere. In addition, you may add the heat treatment process, the 2nd washing | cleaning process, the classification process etc. which are demonstrated below as needed.

(1) Heat Treatment Step In the heat treatment step, the Mg-coated composite hydroxide particles after the covering step or the drying step are put into a cauler or the like made of cordierite and oxidized by heating in an oxidizing atmosphere to obtain heat treated particles. It is a process to obtain. By performing the heat treatment step, it is possible to smoothly progress the synthesis reaction of the positive electrode active material in the firing step, and thus it is possible to obtain a positive electrode active material with more excellent crystallinity. The heat-treated particles include not only Mg-coated composite hydroxide particles from which excess water has been removed in the heat treatment step, but also Mg-coated composite oxide particles converted to oxides by the heat treatment step, or a mixture thereof. included.

  The atmosphere in the heat treatment step is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume or more, and still more preferably in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the Mg-coated composite hydroxide particles may not be sufficiently oxidized.

  The heating temperature (heat treatment temperature) in the heat treatment step is preferably equal to or lower than the firing temperature, and preferably 600 ° C. to 800 ° C., and more preferably 680 ° C. to 720 ° C. If the heat treatment temperature is less than 600 ° C., the Mg-coated composite hydroxide particles may not be sufficiently oxidized. On the other hand, even if the heat treatment temperature exceeds 800 ° C., not only the effect above can not be obtained, but also the energy cost is increased.

  The holding time (heat treatment time) at the heat treatment temperature is not particularly limited but is preferably 1 hour to 10 hours.

  In addition, the furnace used for such a heat treatment process is not limited as long as it can be heated in an oxidizing atmosphere, but an electric furnace or the like without gas generation can be suitably used.

(2) Mixing Step The mixing step is a step of mixing a lithium compound with the Mg-coated composite hydroxide particles or heat-treated particles to obtain a lithium mixture.

  In the mixing step, the ratio (Li / Me) of the number of lithium atoms (Li) to the total number (Me) of metal atoms other than lithium in the lithium mixture, specifically nickel, cobalt, aluminum and magnesium However, it is necessary to mix the lithium compound with the Mg-coated composite hydroxide particles or the heat-treated particles so as to be in the range of 1.00 to 1.04, preferably 1.01 to 1.03. That is, since Li / Me hardly changes before and after the firing step, the Mg-coated composite hydroxide particles or the heat treatment are performed so that Li / Me in the mixing step is approximately the target positive electrode active material Li / Me. It is necessary to mix the particles and the lithium compound.

  The lithium compound used in the mixing step is not particularly limited, but it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate or a mixture thereof, in view of easy availability. In particular, lithium hydroxide or lithium carbonate is preferably used in consideration of ease of handling and stability of quality.

  Further, it is preferable that the Mg-coated composite hydroxide particles or the heat-treated particles and the lithium compound be sufficiently mixed to such an extent that no fine powder is generated. Insufficient mixing may cause variation in Li / Me among individual particles, and sufficient battery characteristics may not be obtained. In addition, a common mixer can be used for mixing. For example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, etc. can be used.

(3) Firing Step The firing step is a step of firing the lithium mixture obtained in the mixing step at 600 ° C. to 800 ° C. in an oxidizing atmosphere to synthesize a positive electrode active material. The furnace used in the firing step is not particularly limited as long as the lithium mixture can be fired in an oxidizing atmosphere, and either a batch-type or a continuous-type furnace can be used.

  The firing atmosphere is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume or more, and still more preferably in the atmosphere or in an oxygen stream. When the firing atmosphere is a non-oxidizing atmosphere, the synthesis reaction of the positive electrode active material can not sufficiently proceed, and the crystallinity of the positive electrode active material is lowered.

  The calcination temperature needs to be 600 ° C. to 800 ° C., preferably 700 ° C. to 770 ° C. If the calcination temperature is less than 600 ° C., lithium does not diffuse sufficiently, and excess lithium, unreacted Mg-coated composite hydroxide particles or heat-treated particles remain, or the (003) plane crystallite of the obtained positive electrode active material The diameter can not be made more than 1200 Å. On the other hand, when the firing temperature exceeds 800 ° C., the positive electrode active materials are vigorously sintered to cause abnormal grain growth, and the (003) plane crystallite diameter exceeds 1600 Å.

  The holding time (baking time) at the baking temperature is preferably 8 hours to 15 hours, and more preferably 10 hours to 12 hours. If the firing time is less than 8 hours, synthesis of the positive electrode active material may not proceed sufficiently. On the other hand, when the firing time exceeds 15 hours, the productivity may be significantly deteriorated.

  In the positive electrode active material after the firing step, aggregation or slight sintering may occur. In such a case, it is preferable to crush an aggregate or a sintered body of the positive electrode active material. By this, the average particle diameter and particle size distribution of the positive electrode active material can be adjusted to a suitable range. In addition, with crushing, mechanical energy is injected into an aggregate consisting of a plurality of secondary particles generated by sintering necking between secondary particles at the time of firing, and the secondary particles themselves are hardly destroyed. Separated to mean the operation of loosening the aggregates.

  As a method of crushing, known means can be used, and for example, a pin mill, a hammer mill or the like can be used. At this time, it is preferable to adjust the crushing power to an appropriate range so as not to destroy the secondary particles.

(4) Classification Step In the method for producing a positive electrode active material of the present invention, the obtained positive electrode active material may be classified after the firing step. Thereby, a positive electrode active material having a narrow particle size distribution can be obtained, and the cycle characteristics of the secondary battery can be further improved. In addition, the classification method can utilize a well-known technique, without being restrict | limited in particular. For example, a method of classification using a sieve with an opening corresponding to the target average particle diameter can be used.

3. Nonaqueous Electrolyte Secondary Battery The nonaqueous electrolyte secondary battery of the present invention is provided with the same components as a general nonaqueous electrolyte secondary battery, such as a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte solution. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is applied to various modifications and improvements based on the embodiments described herein. It is also possible.

(1) Component Members a) Positive Electrode The positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the present invention is used, for example, to manufacture a positive electrode for a non-aqueous electrolyte secondary battery as follows.

  First, a conductive material and a binder are mixed with the powdery positive electrode active material obtained according to the present invention, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and these are kneaded to combine positive electrodes. Make a material paste. At that time, the mixing ratio of each in the positive electrode mixture paste is also an important factor that determines the performance of the non-aqueous electrolyte secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass to 95 parts by mass as in the positive electrode of a general non-aqueous electrolyte secondary battery The content of the material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

  The obtained positive electrode mixture paste is applied, for example, on the surface of a current collector made of aluminum foil, and dried to disperse the solvent. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-like positive electrode can be produced. This positive electrode can be cut into an appropriate size according to the intended battery and used for battery fabrication. However, the method of producing the positive electrode is not limited to the above-described example, and other methods may be used.

  The conductive material is added to provide the electrode with appropriate conductivity. As the conductive material, it is possible to use, for example, graphite (natural graphite, artificial graphite, expanded graphite and the like), and carbon black based materials such as acetylene black and ketjen black.

  The binder plays a role of holding the positive electrode active material particles, and for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, poly Acrylic acid or the like can be used.

  In addition, if necessary, a positive electrode active material, a conductive material, and activated carbon can be dispersed, and a solvent that dissolves the binder can be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Moreover, in order to increase electric double layer capacity, activated carbon can also be added to the positive electrode mixture.

b) Anode A negative electrode mixture is prepared by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium metal, lithium alloy or the like, or lithium ion and adding an appropriate solvent to form a negative electrode composite material , Applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density if necessary.

  Examples of negative electrode active materials include lithium-containing substances such as metal lithium and lithium alloys, natural graphite capable of absorbing and desorbing lithium ions, organic compound sintered bodies such as artificial graphite and phenol resin, and carbon substances such as coke. Powders can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the positive electrode, and as a solvent for dispersing the active material and the binder, an organic compound such as N-methyl-2-pyrrolidone A solvent can be used.

c) Separator The separator is disposed between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte. As such a separator, for example, a thin film such as polyethylene or polypropylene and a film having many fine pores can be used, but there is no particular limitation as long as it has the above-mentioned function.

d) Nonaqueous Electrolyte Nonaqueous electrolyte is obtained by dissolving a lithium salt as a support salt in an organic solvent.

  As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, and further tetrahydrofuran, 2-methyltetrahydrofuran And one or a mixture of two or more selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. it can.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used.

  Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(2) Nonaqueous Electrolyte Secondary Battery The nonaqueous electrolyte secondary battery of the present invention, which is composed of the above positive electrode, negative electrode, separator, and nonaqueous electrolyte, may be formed into various shapes such as cylindrical or laminated type. it can.

  In any of the shapes, the positive electrode and the negative electrode are stacked via a separator to form an electrode body, which is impregnated with a non-aqueous electrolytic solution, and the positive electrode current collector and the positive electrode terminal connected to the outside. After connecting between the negative electrode current collector and the negative electrode terminal communicating with the outside using a current collection lead or the like, the battery case is sealed to complete the non-aqueous electrolyte secondary battery.

(3) Characteristics of Nonaqueous Electrolyte Secondary Battery As described above, the nonaqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material, so charge / discharge capacity, cycle characteristics and high temperature It can be evaluated that the stability is excellent.

For example, when a 2032 type coin battery as shown in FIG. 1 is configured using the positive electrode active material of the present invention, the initial discharge capacity is 187 mAh / g or more, preferably 188 mAh / g or more, and more preferably 190 mAh / g. It can be more than g. Further, in the case of the 2032 type coin battery was stored for 3 weeks under 60 ° C. environment percentage C ₃ / C ₀ of the discharge capacity C ₃ after storage for 3 weeks to the initial discharge capacity C ₀ 84.0% or more, It is preferably 85.0% or more, more preferably 88.0% or more. Furthermore, the 200 cycle capacity retention rate can be 93% or more, preferably 94% or more, and more preferably 95% or more.

(4) Applications Since the non-aqueous electrolyte secondary battery of the present invention is excellent in charge and discharge capacity and cycle characteristics as described above, it is suitable as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) is there. In addition, such a non-aqueous electrolyte secondary battery of the present invention can be miniaturized and can simplify an expensive protective circuit, so that the transportation equipment which is restricted by the mounting space, in particular, the electricity can be reduced. It can also be suitably used as a power source for automobiles.

  Hereinafter, the present invention will be specifically described using examples and comparative examples.

Example 1
a) Preparation of Mg-Coated Composite Hydroxide Particles After the composite hydroxide particles are crystallized by a continuous crystallization method, the Mg-coated composite hydroxide particles are coated by covering the composite hydroxide particles with magnesium. Manufactured.

  First, purified water is supplied into the reaction vessel, the temperature is adjusted to 50 ° C. while stirring at a stirring speed of 120 rpm, and nitrogen gas is introduced, and an inert atmosphere having an oxygen concentration of 0.7% by volume or less did. In this state, an aqueous solution containing nickel sulfate and cobalt sulfate and an aqueous solution of sodium aluminate were supplied by a pump at a constant flow rate into the reaction vessel. At this time, the aqueous solution of sodium hydroxide and aqueous ammonia should be properly adjusted so that the pH value of the aqueous solution (reaction aqueous solution) in the reaction tank at a liquid temperature of 25 ° C. is maintained at 11.6 and the ammonium ion concentration is 10 g / L. The mixture was supplied to crystallize composite hydroxide particles. Thereafter, the reaction aqueous solution containing the composite hydroxide particles overflowed from the reaction tank was charged into a filter press, and pressure filtration was performed to recover the composite hydroxide particles (crystallization step).

  To this composite hydroxide particle, add 10 times its mass of a 6 mass% aqueous solution of sodium hydroxide, stir and put it into a filter press again, and then feed 10 times the mass of the composite hydroxide particle into purified water. The composite hydroxide particles were washed by pressure filtration (washing step).

  The washed composite hydroxide particles were dispersed in purified water to form a slurry, and a 6% by mass aqueous solution of sodium hydroxide was added so that the pH value of the slurry would be 10.5. In this state, while stirring the slurry, a 0.2 mol / L aqueous solution of magnesium sulfate is supplied over 10 minutes at 100 mL / min to precipitate magnesium on the surface of the composite hydroxide particles, thereby covering the Mg coating. Composite hydroxide particles were obtained. Thereafter, the Mg-coated composite hydroxide particles, together with the slurry, were charged into a filter press, purified water was fed, and washed and filtered (coating step). Subsequently, the Mg-coated composite hydroxide particles were placed in a dryer and heated at 120 ° C. to obtain powdered Mg-coated composite hydroxide particles (drying step).

b) Evaluation of Mg-coated composite hydroxide particles [Composition]
As a result of ICP emission spectroscopy, it was confirmed that this Mg-coated composite hydroxide particle is represented by the general formula: Ni _0.80 Co _0.15 Al _0.04 Mg _0.01 (OH) ₂ .

Particle structure
As a result of observation using SEM (manufactured by Hitachi, Ltd., S-4700), the Mg-coated composite hydroxide particles may be composed of substantially spherical secondary particles formed by aggregation of rectangular primary particles. confirmed. Subsequently, the Mg-coated composite hydroxide particles were embedded in a resin, cross-section polishing was performed to obtain a cross-sectional viewable state, and SEM observation was similarly performed, and as a result, it was confirmed that a solid structure was provided. . Moreover, it was confirmed that the average particle diameter of the primary particles constituting the Mg-coated composite hydroxide particles is 0.08 μm.

  Furthermore, as a result of characteristic X-ray spectroscopy analysis of the particle cross section, in the Mg-coated composite hydroxide particles, the core composed of nickel, cobalt and aluminum was coated with a coating composed of magnesium hydroxide having a thickness of 0.002 μm. It was confirmed to be a thing.

[Average particle size of secondary particles, tap density and specific surface area]
Laser light diffraction / scattering particle size analyzer (Microtrac, manufactured by Nikkiso Co., Ltd.), shaking specific gravity measuring device (KRS-409, manufactured by Kuragaku Scientific Instruments Mfg. Co., Ltd.) As a result of measurement, it was confirmed that the Mg-coated composite hydroxide particles had an average particle diameter of 11 μm, a tap density of 1.6 g / ml, and a specific surface area of 12 m ² / g.

c) Preparation of Positive Electrode Active Material Powdered Mg-coated composite hydroxide particles were placed in a cordierite bowl and heated at 700 ° C. for 10 hours to obtain heat treated particles (heat treatment step). After cooling to room temperature, the heat-treated particles and lithium hydroxide were mixed such that Li / Me = 1.02 to obtain a lithium mixture (mixing step). The lithium mixture was placed in a cordierite bowl and heated at 730 ° C. for 12 hours in an oxygen atmosphere to synthesize a positive electrode active material (baking step). Finally, this positive electrode active material was classified with a sieve of 38 μm openings (classification step).

c) Evaluation of positive electrode active material [Composition]
As a result of ICP emission spectroscopy, it was confirmed that this positive electrode active material is represented by the general formula: Li _1.02 Ni _0.80 Co _0.15 Al _0.04 Mg _0.01 O ₂ .

Particle structure
As a result of SEM observation, it was confirmed that this positive electrode active material is composed of substantially spherical secondary particles formed by aggregation of rectangular primary particles. Subsequently, the positive electrode active material was embedded in a resin, cross-section polishing was performed to make it possible to observe a cross section, and as a result of similar SEM observation, it was confirmed that it had a solid structure.

Moreover, as a result of powder X-ray diffraction measurement, this positive electrode active material is composed only of the crystal structure similar to LiNiO _2, and cobalt, aluminum and magnesium are uniformly dissolved in this crystal structure. That was confirmed.

[Crystallite diameter]
As a result of Riefeld analysis by XRD measurement using an X-ray diffractometer (manufactured by PANalytical, X'Pert3 powder), it was confirmed that the (003) plane crystallite diameter of this positive electrode active material is 1439 Å.

[Average particle size, tap density and specific surface area]
The average particle diameter of this positive electrode active material is 12.8 μm, and the tap density is 2.63 g / ml, as measured by a laser light diffraction / scattering type particle size analyzer, a shaking specific gravity meter and a nitrogen adsorption type BET method measuring instrument. The specific surface area was confirmed to be 0.31 m ² / g.

d) Preparation and evaluation of secondary battery [Evaluation of initial discharge capacity]
Using this positive electrode active material, a 2032 type coin battery 1 as shown in FIG. 1 was produced. First, 85% by mass of the above-mentioned positive electrode active material, 10% by mass of acetylene black and 5% by mass of PVDF are weighed and mixed, and then an appropriate amount of NMP (n-methylpyrrolidone) is added to form a paste did. The positive electrode mixture paste is applied onto an aluminum foil so that the surface density of the dried positive electrode active material is 7 mg / cm ² , vacuum dried at 120 ° C., and then punched into a disk shape having a diameter of 13 mm. Thus, the positive electrode 3a was produced. An equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using carbon as the negative electrode 3 b and 1 M LiClO ₄ as the supporting salt is used as the electrolytic solution, and the dew point is controlled to −80 ° C. The 2032 type coin battery 1 was assembled in the Ar atmosphere glove box.

After production of the 2032 type coin battery 1, it is left for about 24 hours, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density to the positive electrode is 0.1 mA / cm ² and the cutoff voltage is 4.3 V The charge and discharge test was performed to measure the discharge capacity when the battery was discharged until the cut-off voltage became 3.0 V after 1 hour of rest, and the initial discharge capacity was determined. At this time, a multi-channel voltage / current generator (R6741A, manufactured by Advantest Corporation) was used for measurement of the initial discharge capacity. As a result, it was confirmed that the initial discharge capacity was 190.0 mAh / g. Moreover, it was confirmed that the initial discharge capacity (initial efficiency) with respect to the initial charge capacity is 88.2%.

[Evaluation of cycle characteristics]
A 2032 type coin battery 1 was assembled in the same manner except that lithium metal was used for the negative electrode. After preparation, the initial discharge capacity was measured in the same manner. Subsequently, the current density to the positive electrode is set to 0.1 mA / cm ² , charging is performed until the cutoff voltage is 4.3 V, and after one hour of rest, discharging is performed until the cutoff voltage becomes 3.0 V. The discharge capacity after repetition was measured. As a result, it was confirmed that the 200th cycle discharge capacity (200 cycle capacity maintenance ratio) with respect to the initial discharge capacity was 95%.

[Evaluation of high temperature stability]
After assembling the laminate type battery, the initial discharge capacity _C0 was measured in the same manner. Moreover, after storage for three weeks inside incubator maintained at 60 ° C., in the same manner, the discharge capacity was measured C _3. As a result, it was confirmed that C ₃ / C ₀ was 89.3%.

(Example 2)
In the crystallization step, Mg coated composite hydroxide particles, positive electrode active material, and 2032 were prepared in the same manner as in Example 1 except that the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. was adjusted to 11.9 and maintained. Type coin cells were obtained and evaluated. The results are shown in Tables 2 to 4.

(Example 3)
In the crystallization step, Mg coated composite hydroxide particles, positive electrode active material, and 2032 were prepared in the same manner as in Example 1 except that the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. was adjusted to 11.3 and maintained. Type coin cells were obtained and evaluated. The results are shown in Tables 2 to 4.

(Example 4)
In the crystallization step, the Mg-coated composite was prepared in the same manner as in Example 1, except that the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. was 11.9 and the stirring speed was 114 rpm (95% of Example 1). Hydroxide particles, a positive electrode active material, and a 2032 type coin battery were obtained and evaluated. The results are shown in Tables 2 to 4.

(Example 5)
In the coating step, the procedure of Example 1 was repeated except that a 0.6 mol / L aqueous solution of magnesium sulfate was supplied to the slurry over 10 minutes at 100 ml / min, that is, the amount of magnesium added was tripled. The Mg-coated composite hydroxide particles, the positive electrode active material, and the 2032-type coin battery were obtained and evaluated. The results are shown in Tables 2 to 4.

(Example 6)
In the firing step, Mg coated composite hydroxide particles, a positive electrode active material and a 2032 type coin battery were obtained and evaluated in the same manner as in Example 1 except that the firing temperature was set to 700 ° C. Tables 2 to 4 show the results.

(Example 7)
In the firing step, Mg coated composite hydroxide particles, a positive electrode active material and a 2032 type coin battery were obtained and evaluated in the same manner as Example 1 except that the firing temperature was 710 ° C. The results are shown in Tables 2 to 4.

(Example 8)
In the firing step, Mg coated composite hydroxide particles, a positive electrode active material and a 2032 type coin battery were obtained and evaluated in the same manner as in Example 1 except that the firing temperature was set to 760 ° C. The results are shown in Tables 2 to 4.

(Example 9)
In the firing step, Mg coated composite hydroxide particles, a positive electrode active material and a 2032 type coin battery were obtained and evaluated in the same manner as in Example 1 except that the firing temperature was set to 770 ° C. The results are shown in Tables 2 to 4.

(Comparative example 1)
A composite hydroxide particle, a positive electrode active material, and a 2032 type coin battery were produced and evaluated in the same manner as in Example 1 except that the covering step was not performed. These results are shown in Tables 2 to 4.

(Comparative example 2)
In the coating step, in the same manner as in Example 1, except that a 1 mol / L aqueous solution of magnesium sulfate was supplied to the slurry over 10 minutes at 100 ml / min, that is, the amount of magnesium added was five times. The Mg-coated composite hydroxide particles, the positive electrode active material, and the 2032-type coin battery were obtained and evaluated. The results are shown in Tables 2 to 4.

  As described above, since the non-aqueous electrolyte secondary battery of the present invention has high capacity, excellent cycle characteristics and high temperature stability, it can be suitably used as a power source for electric vehicles and the like.

1 2032 type coin battery 2 case 2a positive electrode can 2b negative electrode can 2c gasket 3 electrode 3a positive electrode 3b negative electrode 3c separator

Claims (12)

General formula: Ni _1-xyz Co _x Al _y Mg _z (OH) ₂ (where, 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03) Magnesium-coated nickel-cobalt composite hydroxide particles represented by and coated with a coating comprising magnesium or a magnesium compound,
It consists of secondary particles of solid structure formed by aggregation of multiple primary particles,
The average particle diameter of the secondary particles is 10.0Myuemu～14.5Myuemu, and a tap density of 1.4 g / ml or more, and a specific surface area of 10m ² / g~25m ² / g,
Magnesium coated nickel cobalt composite hydroxide particles.   The magnesium-coated nickel cobalt composite hydroxide particles according to claim 1, wherein the thickness of the coating is 0.001 μm to 0.01 μm.   The aluminum-coated nickel-cobalt composite hydroxide particles according to claim 1 or 2, wherein the primary particles have a rectangular parallelepiped shape and an average particle diameter in the range of 0.01 μm to 0.1 μm. General formula: Ni _1-xyz Co _x Al _y Mg _z (OH) ₂ (where, 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, 0.01 ≦ z ≦ 0.03) And a method of producing magnesium-coated nickel cobalt composite hydroxide particles coated with a coating comprising magnesium or a magnesium compound,
In an inert atmosphere, at least nickel, cobalt and aluminum in a reaction aqueous solution in which the pH value is controlled to 11 to 12 and the ammonium ion concentration to 8 g / L to 12 g / L at a temperature of 45 ° C. to 55 ° C. A raw material aqueous solution containing C., to obtain nickel-cobalt composite hydroxide particles by a continuous crystallization method, a crystallization step,
Coating step of obtaining magnesium-coated nickel-cobalt composite hydroxide particles by mixing the slurry containing the nickel-cobalt composite hydroxide particles and a coating solution containing magnesium to form a mixed solution;
A manufacturing method of magnesium covering nickel cobalt compound hydroxide particles provided with.   The method for producing magnesium-coated nickel-cobalt composite hydroxide particles according to claim 4, wherein the pH value of the mixed solution at a liquid temperature of 25 ° C is adjusted to a range of 10-11.   The method for producing magnesium-coated nickel cobalt composite hydroxide particles according to claim 4 or 5, further comprising a washing step of washing the nickel-cobalt composite hydroxide particles obtained in the crystallization step before the coating step. .   The aluminum-coated nickel cobalt composite hydroxide particles according to any one of claims 4 to 6, further comprising a drying step of heating and drying the aluminum-coated nickel cobalt composite hydroxide particles to 100 ° C to 150 ° C. Production method. General formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium-nickel-cobalt composite oxide particle having a layered structure, represented by 0.01 ≦ z ≦ 0.03),
It consists of secondary particles of solid structure formed by aggregation of multiple primary particles,
The (003) plane crystallite diameter is 1200 Å to 1600 Å, which is determined from Rietveld analysis by XRD measurement;
Has a crystal structure in which cobalt, aluminum and magnesium are uniformly dissolved in a matrix constituted by LiNiO ₂ , and
Wherein the average particle size of the secondary particles is 11.5Myuemu～14.5Myuemu, there tap density above 2.6 g / ml, and the specific surface area is 0.2m ² /g~0.5m ² / g ,
Positive electrode active material for non-aqueous electrolyte secondary batteries. General formula: Li _u Ni _1-xyz Co _x Al _y Mg _z O ₂ (where 1.00 ≦ u ≦ 1.04, 0.05 ≦ x ≦ 0.20, 0.01 ≦ y ≦ 0.06, It is a manufacturing method of the quality of cathode active material for nonaqueous electrolyte secondary batteries which is expressed by 0.01 <= z <= 0.03 and consists of lithium nickel cobalt compound oxide particles of layered structure,
A mixing step of mixing a magnesium-coated nickel cobalt composite hydroxide particle according to any one of claims 1 to 3 and a lithium compound to obtain a lithium mixture,
Firing the lithium mixture at 600 ° C. to 800 ° C. in an oxidizing atmosphere,
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries provided with these.   The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 9 which sets the calcination temperature in the said baking process to 700 degreeC-770 degreeC.   11. The nonaqueous electrolyte electrolyte according to claim 9, further comprising a heat treatment step of heating the magnesium-coated nickel cobalt composite hydroxide particles in an oxidizing atmosphere at 600 ° C. to 800 ° C. before the mixing step. The manufacturing method of the positive electrode active material for subsequent batteries.   A non-aqueous electrolyte secondary comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8 is used as a positive electrode material of the positive electrode. battery.

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