JP2006273620A - Lithium transition metal complex oxide, its manufacturing method, fired precursor for lithium transition metal complex oxide and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium transition metal complex oxide whose crystallinity is high and which can enhance the cell properties such as initial efficiency, an electric current rate property and the like when used as the positive electrode active material of a lithium secondary battery. <P>SOLUTION: The method for manufacturing the lithium transition metal complex oxide comprises at least a granulating step for a transition metal compound, a mixing step to mix the granulated transition metal compound obtained from the granulating step and a lithium raw material and a firing step to fire the mixture obtained from the mixing step. In the mixing step, the lithium raw material is dissolved and mixed when the granulated transition metal compound is mixed with the lithium raw material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a lithium transition metal composite oxide, a calcined precursor for obtaining a lithium transition metal composite oxide, a lithium transition metal composite oxide obtained by the production method or the calcined precursor, and the lithium transition The present invention relates to a lithium secondary battery using a metal composite oxide.

In recent years, with the reduction in size and weight of portable electronic devices and communication devices, lithium secondary batteries having high output and high energy density have attracted attention as power sources and automobile power sources. As a positive electrode active material of a lithium secondary battery, it is known that a standard composition is preferably a lithium transition metal composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ .
Furthermore, from the viewpoint of safety and raw material cost, LiNi _1-x Mn _x O ₂ , LiNi _1-xy Mn _x Co _{y in} which a part of the transition metal of these lithium transition metal composite oxides is substituted with another transition metal. lithium transition metal composite oxide having the same layered structure as LiCoO ₂ or LiNiO ₂ of O ₂ or the like has attracted attention.

  Many methods are known as a method for producing these lithium transition metal composite oxides. For example, a slurry containing a transition metal-based material such as a nickel material, a cobalt material, or a manganese material, and a small amount of a lithium material as required. Is spray-dried into granulated particles, and a lithium raw material is further dry-mixed so as to have a desired composition ratio, followed by firing (Patent Document 1), a nickel raw material, a cobalt raw material, and a manganese raw material. A method is used in which a composite carbonate obtained by coprecipitation as a carbonate is baked and decarboxylated, and the resulting granulated particles and a lithium raw material are dry mixed and then baked (Patent Document 2).

JP 2003-267732 A Japanese Patent Laid-Open No. 10-134811

  However, in the production methods described in Patent Document 1 and Patent Document 2 described above, since the lithium raw material mixed with the granulated particles obtained by spray drying or coprecipitation is usually mixed in a dry method, The particles and the lithium material are only in point contact with each other. When such a state is used as a firing precursor, there is a possibility that the lithium raw material does not spread throughout the granulated particles during firing, and as a result, segregation is seen in the composition of the lithium transition metal composite oxide after firing. In some cases, the crystallinity of the lithium transition metal composite oxide after firing may be insufficient. Accordingly, when the fired lithium transition metal composite oxide is used as a positive electrode active material of a lithium secondary battery, there is a problem that battery characteristics such as initial efficiency and current rate characteristics become insufficient.

  The present invention has been made in view of the above problems. That is, an object of the present invention is a lithium transition metal composite oxide having high crystallinity and capable of improving battery characteristics such as initial efficiency and current rate characteristics when used as a positive electrode active material of a lithium secondary battery. And a calcining precursor used in the production, and a lithium transition metal composite oxide obtained by the production method or calcining precursor, and lithium lithium using the lithium transition metal composite oxide. The next battery is to provide.

  As a result of intensive studies in view of the above problems, the inventors of the present invention have high crystallinity by dissolving and mixing the lithium raw material when mixing the granulated particles of the transition metal compound and the lithium raw material. The present invention was completed by finding that a lithium transition metal composite oxide capable of improving battery characteristics such as initial efficiency and current rate characteristics when used as a positive electrode active material of a battery can be obtained.

  That is, the gist of the present invention is that the transition metal compound granulation step, the transition metal compound granulation particles obtained by the granulation step and the lithium raw material mixing step, and the mixture obtained by the mixing step In the method for producing a lithium transition metal composite oxide comprising at least a firing step, in mixing the granulated particles of the transition metal compound and the lithium raw material in the mixing step, the lithium raw material is dissolved and mixed. The present invention resides in a method for producing a lithium transition metal complex oxide (claim 1).

  Here, it is preferable to dissolve the lithium raw material with moisture (claim 2).

  In this case, it is preferable to use lithium hydroxide hydrate as the lithium raw material and to heat to a temperature at which the lithium raw material is dissolved in the mixing step.

  In the mixing step, it is also preferable that water be present together (claim 4).

  Another object of the present invention is a precursor for obtaining a lithium transition metal composite oxide by firing, characterized in that the lithium raw material coats the granulated particles of the transition metal compound, It exists in the baking precursor for transition metal complex oxides (Claim 5).

  Further, another gist of the present invention resides in a lithium transition metal composite oxide produced by the above-described method for producing a lithium transition metal composite oxide (claim 6).

  Further, another gist of the present invention resides in a lithium transition metal composite oxide obtained by using the above-mentioned firing precursor for lithium transition metal composite oxide (claim 7).

  Another gist of the present invention is a lithium secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and an organic electrolyte containing a lithium salt as an electrolyte, wherein the positive electrode is the above-mentioned lithium A lithium secondary battery is characterized by containing a transition metal composite oxide.

  According to the method for producing a lithium transition metal composite oxide and the firing precursor for the lithium transition metal composite oxide of the present invention, when used as a positive electrode active material of a lithium secondary battery having high crystallinity, the initial efficiency and current A lithium transition metal composite oxide capable of improving battery characteristics such as rate characteristics can be obtained.

  Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the invention.

[I. Method for producing lithium transition metal composite oxide]
The method for producing a lithium transition metal composite oxide according to the present invention (hereinafter appropriately abbreviated as “the production method of the present invention”) is obtained by a step of granulating a transition metal compound (granulation step) and a granulation step. A process comprising at least a step (mixing step) of mixing the granulated particles of the obtained transition metal compound and a lithium raw material, and a step (firing step) of firing the mixture obtained by the mixing step. In the above, when the granulated particles of the transition metal compound and the lithium raw material are mixed, the lithium raw material is dissolved and mixed.

[Transition metal compounds]
As the transition metal compound, a compound that is known to be used as a raw material for a lithium transition metal composite oxide can be appropriately selected from compounds containing transition metals such as manganese, nickel, and cobalt. . Examples include oxides of transition metals such as manganese, nickel, and cobalt; hydroxides; halides; inorganic acid salts such as carbonates, sulfates, and nitrates; organic acid salts such as acetates. In the following description, a compound containing each transition metal is referred to as “manganese raw material”, “nickel raw material”, “cobalt raw material”, etc. with the metal name.

Specifically, manganese raw materials include manganese oxides such as Mn ₂ O ₃ , MnO ₂ and Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate , Manganese salts such as fatty acid manganese, oxyhydroxides, halides and the like. As Mn ₂ O ₃ , a material prepared by heat-treating a compound such as MnCO ₃ or MnO ₂ may be used. Preferably, oxides such as Mn ₂ O ₃ , Mn ₃ O ₄ and MnO ₂ , hydroxides such as Mn (OH) _{2 and} the like are used.

Examples of the nickel raw material include oxides such as NiO and NiO ₂ ; hydroxides such as Ni (OH) ₂ ; oxyhydroxides such as NiOOH; halides such as NiCl ₂ , NiCO _{3 and the} like. Preferably, an oxide such as NiO or a hydroxide such as Ni (OH) ₂ is used.

Examples of cobalt raw materials include hydroxides such as Co (OH) ₂ ; oxyhydroxides such as CoOOH; oxides such as CoO and Co ₂ O ₃ ; halides such as CoCl ₂ ; Co (NO ₃ ) ₂ .6H Nitrates such as ₂ O; sulfates such as Co (SO ₄ ) ₂ · 7H ₂ O and the like. Preferably, oxides such as Co ₃ O ₄ ; hydroxides such as Co (OH) ₂ ; cobalt oxyhydroxide; cobalt carbonate and the like are used.

[Substituted element materials]
In the production method of the present invention, other elements of the above-mentioned manganese, nickel, and cobalt (hereinafter appropriately referred to as “substitution elements”) may be used depending on the composition of the target lithium transition metal composite oxide.

  Examples of the substitution element include Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, Ca, Sc, Al, and B. Among these, Al, Bi, B, V, Mg, Nb and the like are preferable.

  As a substitution element raw material, a compound known to be used as a raw material for a lithium transition metal composite oxide is appropriately selected from the compounds containing the substitution element described above (hereinafter, referred to as “substitution element raw material” as appropriate). Can be used. Specific examples include oxides, hydroxides, oxyhydroxides, nitrates, carbonates, dicarboxylates, fatty acid salts, and ammonium salts.

[Lithium raw material]
The lithium raw material used in the production method of the present invention is not particularly limited as long as it is a compound containing lithium, but lithium hydrate or anhydrous lithium hydroxide is preferably used.

  When lithium hydroxide hydrate is used, the lithium raw material can be dissolved without adding moisture externally by performing the mixing step described below under conditions that generate moisture from the hydrate. . Examples of the hydrate of lithium hydroxide include lithium hydroxide monohydrate.

  On the other hand, when anhydrous lithium hydroxide is used, no moisture is generated from the lithium compound. Therefore, the lithium raw material can be dissolved by adding water from the outside and coexisting when performing the mixing step described later.

  Further, the lithium raw material used in the production method of the present invention has a median diameter of usually 0.1 μm or more, particularly 0.5 μm or more, and usually 20 μm or less, especially 15 μm or less, more preferably 10 μm or less. Is preferred. Lithium raw materials tend to absorb moisture and carbon dioxide in the air the smaller the median diameter, and the storage stability tends to be poor. On the other hand, if the median diameter of the lithium raw material is too large, the average particle diameter of the obtained lithium transition metal composite oxide is large and the composition tends to be nonuniform, and the lithium transition metal composite oxide was used as the positive electrode active material of the battery. In some cases, battery characteristics such as output characteristics may be deteriorated.

  In the present specification, the “median diameter” of the lithium raw material is a value measured by a laser diffraction / scattering particle size distribution measuring device based on JIS Z 8825-1 at room temperature. As a dispersion medium for measurement, ethanol in which lithium hydroxide is saturated and dissolved in advance is used. By preliminarily dissolving lithium hydroxide in ethanol, it is possible to prevent the lithium raw material from being dissolved in ethanol during the measurement. In the measurement, after adding a lithium raw material to ethanol, a dispersion treatment is performed for 1 minute with an ultrasonic oscillator having an output of 30 W and a frequency of 22.5 kHz, and then used for the measurement. The refractive index used for the measurement is 1.14a000i (real part 1.14, imaginary part 0.00).

[Granulation process]
As the granulation step, for example, a slurry containing a transition metal compound (a manganese raw material, a nickel raw material, a cobalt raw material, and a substitution element raw material used as needed is generically called) is spray-dried. Examples thereof include a method for obtaining granulated particles by spraying (spray drying method) and a method for obtaining granulated particles by precipitation from a solution containing a transition metal compound (coprecipitation method).

  In the following description, a method (spray drying method) for obtaining granulated particles by spray drying a slurry containing the above transition metal compound will be described as an example.

・ Mixing and grinding:
First, the above transition metal compound is mixed and pulverized. The mixing ratio of each element is appropriately adjusted according to the composition of the target lithium transition metal composite oxide.

  The method for mixing and pulverizing the transition metal compound is not particularly limited, and it may be performed wet or dry. Examples include a method using a bead mill, a ball mill or the like. The pulverization is preferably performed until the average particle diameter of the pulverized raw material particles is usually 2 μm or less, particularly 1 μm or less, and more preferably 0.5 μm or less. If the average particle size is too large, the reactivity between the raw materials in the firing step may be reduced. However, reducing the particle size more than necessary leads to an increase in the cost of pulverization. Therefore, the average particle size is usually 0.01 μm or more, particularly 0.05 μm or more, and more preferably 0.1 μm or more. .

  Next, the pulverized raw material is mixed with a solvent to form a slurry. Examples of the solvent include organic solvents and aqueous solvents, but water is preferable in terms of cost.

  The slurry concentration is not particularly limited, but it is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and particularly preferably 15% by weight or more. If the slurry concentration is too low, the productivity tends to decrease. On the other hand, the upper limit of the slurry concentration is usually 50% by weight or less, particularly 45% by weight or less, and further 40% by weight or less. If the slurry concentration is too high, the viscosity of the slurry becomes high, and there is a possibility that it cannot be sprayed with a nozzle by spray drying described later.

  Further, the viscosity of the slurry is not particularly limited, but is preferably in the range of usually 100 mPs · s or more, particularly 300 mPs · s or more, and usually 2000 mPs · s or less, particularly 1500 mPs · s or less. If the viscosity of the slurry is too low, clean spherical particles tend to be difficult to form during spray drying described later, and if it is too high, there is a possibility that the nozzle cannot be sprayed.

・ Spraying / drying:
The obtained slurry is spray-dried to obtain granulated particles of transition metal compound (this is referred to as “granulated particles” as appropriate). Spray drying is preferable from the viewpoints of uniformity of the granulated particles to be generated, powder flowability, powder handling performance, and the ability to efficiently form secondary particles. Spray drying may be performed by a known method. For example, it is possible to use a method in which a gas flow and a slurry are caused to flow into the tip of a nozzle so that the slurry is discharged as droplets from the nozzle and brought into contact with a drying gas to quickly dry the droplets.

  The average particle size of the granulated particles obtained by spray drying is usually 50 μm or less, preferably 40 μm or less. However, since it tends to be difficult to obtain a small particle size by spray drying, the lower limit of the average particle size is usually 1 μm or more, especially 3 μm or more.

  In the case of producing granulated particles by the spray drying method, the particle size can be controlled by appropriately selecting the spray format, pressurized gas flow supply rate, slurry supply rate, drying temperature and the like. The dry atmosphere is usually air, but may be an inert atmosphere such as nitrogen. The drying gas is preferably introduced into the spraying device at 80 to 300 ° C. and discharged from the device at 45 to 250 ° C.

[Mixing process]
The obtained granulated particles of the transition metal compound and the above-described lithium raw material are mixed. The mixing method is not particularly limited, but from the viewpoint of the degree of mixing, it is preferable to use a mixer type mixing device in which the blades rotate to mix the powder. Examples of the mixing apparatus include a high speed mixer (Fukae Powtech Co., Ltd.), an axial mixer (Sugiyama Heavy Industries Co., Ltd.), and a Redige mixer (Matsubo Co., Ltd.).

  The mixing ratio of the granulated particles and the lithium raw material is determined by the desired composition of the lithium transition metal composite oxide.

  The atmosphere for mixing is preferably carried out in an inert atmosphere. Specific examples include nitrogen gas, argon gas, decarbonated air gas, and the like.

  In order to obtain the target lithium transition metal composite oxide in the present invention, it is important to dissolve the lithium raw material in this mixing step.

The method for dissolving the lithium raw material is not particularly limited, but examples include the following two types.
(1) Use lithium hydroxide hydrate and heat to a temperature at which the hydrate is liberated.
(2) Use anhydrous lithium hydroxide and add water from the outside to coexist.

・ In the case of (1):
When a hydrate of lithium hydroxide is used as the lithium raw material, mixing is performed under conditions that generate water from the hydrate. Specifically, the lithium raw material can be dissolved by heating to a temperature at which the hydrate is liberated during mixing.

  Although there is no restriction | limiting in particular as long as a lithium raw material melt | dissolves, for example, 60-80 degreeC is mentioned. If necessary, a solvent such as water, methanol, ethanol or the like may be further added to the lithium hydroxide hydrate to dissolve it.

・ In case of (2):
When anhydrous lithium hydroxide is used as the lithium raw material, the lithium raw material can be dissolved by adding water from the outside during mixing to allow it to coexist. Although anhydrous lithium hydroxide can be dissolved by a solvent such as water, methanol, ethanol, etc., it is particularly preferable to dissolve with water from the viewpoint of cost and solubility.

  When anhydrous lithium hydroxide is used, the amount of water added during mixing is not particularly limited, but is usually 1% or more, especially 3% or more, and usually 20% or less, especially 10% or less, based on the weight of the lithium raw material. It is a range. When the amount of moisture is below this range, the lithium raw material is not sufficiently dissolved. On the other hand, if the amount of water exceeds this range, the water will be excessive and mixing will not be successful. Moreover, when there is too much moisture, the shape of the granulated particles may be destroyed by the moisture.

  The method for adding moisture is not particularly limited, but it is preferable to spray the moisture in a mist in the mixing apparatus during mixing of the granulated particles and the lithium raw material. If a predetermined amount of water is added at the same time when the granulated particles and the lithium raw material are charged into the mixing apparatus, the granulated particles are locally collapsed and the lithium raw material is dissolved, so that the mixing cannot be performed well.

[Baking precursor]
A granulated particle and a lithium raw material are mixed by the above-mentioned method to obtain a calcined precursor.
In the calcined precursor obtained in the production method of the present invention (hereinafter referred to as “the calcined precursor of the present invention” as appropriate), the granulated particles are covered with a lithium raw material. The term “coating” as used herein refers to a state in which the dissolved lithium raw material covers the whole or part of the granulated particle surface. In addition to the state in which a single granulated particle is coated with a lithium raw material, there is also a state in which a lithium raw material is coated over a state in which several granulated particles are collected.

  The median diameter of the calcined precursor is usually 3 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less, although it depends on the granulated particles. If the median diameter is less than this lower limit, it becomes difficult to obtain particles, which is not preferable. On the other hand, if the median diameter exceeds this upper limit, a large number of granulated particles are collected, which may lead to segregation of the composition at the stage after firing.

  The covering state of the granulated particles with the lithium raw material can be evaluated by the surface coverage with respect to the surface area of the granulated particles. The surface coverage of the granulated particles of the present invention is usually 30% or more, preferably 50% or more. If the surface coverage is less than this lower limit, the contact area between the granulated particles and the lithium raw material becomes low, which is not preferable. On the other hand, the higher the surface coverage, the better. When fully coated (coverage 100%), the contact area between the granulated particles and the lithium raw material can be used most effectively. Furthermore, the contact area between the granulated particles and the lithium raw material can be used more effectively when the granulated particles are coated alone than when the granulated particles are collected.

  The coating thickness of the granulated particles from the lithium raw material is usually 0.05 μm or more, preferably 0.1 μm or more, and usually 10 μm or less, preferably 5 μm or less. The coating thickness should be as uniform as possible with respect to the granulated particles.

  In addition, the surface coverage and the coating thickness of the granulated particles by the lithium raw material can be measured by a granulated particle optical microscope, an electron microscope (SEM, TEM), or the like.

  By dissolving the lithium raw material in the mixing process, it is possible to improve the above-mentioned effects (high crystallinity and battery characteristics such as initial efficiency and current rate characteristics when used as a positive electrode active material of a lithium secondary battery. The reason why such a lithium transition metal composite oxide is obtained is not clear, but is presumed as follows.

  That is, by mixing the granulated particles and the lithium raw material in a state where the lithium raw material is dissolved, the resulting calcined precursor is in a state in which the lithium raw material is coated with the granulated particles as described above. The contact area between the granulated particles and the lithium raw material is improved as compared with the case where the particles are not used. By firing in that state, a regular layer structure is formed even when viewed on a fine scale. As a result, the crystallinity that can be confirmed by XRD is improved, and when used as a positive electrode active material of a battery, the battery characteristics are improved. It is considered that an excellent lithium transition metal composite oxide can be obtained.

[Baking process]
The obtained firing precursor is fired to obtain a lithium transition metal composite oxide.

  The firing temperature is usually 500 ° C. or higher, preferably 550 ° C. or higher, and usually 1200 ° C. or lower, preferably 1050 ° C. or lower. If the firing temperature is too low, it is difficult to obtain a layered lithium composite oxide having good crystallinity. If the firing temperature is too high, a phase other than the target layered lithium composite oxide may be formed, or a layered lithium composite oxide having many defects may be formed.

  Further, when raising the temperature from room temperature to the above-mentioned firing temperature, in order to carry out the reaction more uniformly, for example, the temperature is gradually raised at a temperature of 5 ° C. or less per minute, or the temperature rise is temporarily stopped in the middle. It is preferable to keep the temperature constant so that the entire temperature becomes uniform.

  The firing time is usually 1 hour or longer, preferably 2 hours or longer, and usually 100 hours or shorter, preferably 50 hours or shorter. If the firing time is too short, it is difficult to obtain a layered lithium composite oxide having good crystallinity. Conversely, a too long reaction time is industrially meaningless.

  Firing is usually performed in air, but can also be performed in other oxygen-containing gases. In addition, when baking in air, it is preferable to use air from which carbon dioxide has been previously removed.

  In order to obtain a layered lithium composite oxide with few defects, it is preferable to cool slowly after the above-mentioned firing, usually to 600 ° C, particularly to 400 ° C, at a cooling rate of 5 ° C or less per minute. Is preferred.

  The heating device used for firing is not particularly limited as long as the above temperature and atmosphere can be achieved. For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, or the like can be used.

  The lithium transition metal composite oxide obtained by firing is usually pulverized and sieved and used as a positive electrode material for a lithium secondary battery.

[II. Lithium transition metal composite oxide]
〔composition〕
It is known that the composition of a lithium transition metal composite oxide obtained by the production method of the present invention (hereinafter referred to as “the lithium transition metal composite oxide of the present invention” as appropriate) can be used as a positive electrode active material of a lithium secondary battery. The lithium transition metal composite oxide having a hexagonal layered rock salt structure is preferable.

Specifically, the composition represented by the following formula (1) is mentioned.

  In the above formula (1), M represents a metal element that substitutes a part of the sites of Ni and Mn, Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Examples thereof include at least one element selected from Ta, Be, Ca, Sc, Al, B, and Zr.

  In the above formula (1), a, b, c, and d are 0.2 ≦ a ≦ 0.85, 0 ≦ b ≦ 0.8, 0.1 ≦ c ≦ 0.4, and 0 ≦ d ≦, respectively. It represents a number satisfying 0.4 and a + b + c + d = 1. X represents a number satisfying 0.7 ≦ x ≦ 1.3, and δ represents a number satisfying −0.1 <δ <0.1.

  Further, the lithium transition metal composite oxide is a lithium composite oxide containing nickel, cobalt, and aluminum represented by the following formula (2) of the present invention, or nickel, manganese represented by the following formula (3), And lithium composite oxide containing cobalt.

  In the above formula (2), x represents a molar excess amount of Li of the stoichiometric ratio or more, and is usually 0.01 or more, preferably 0.02 or more, usually 0.2 or less, preferably 0.15. Hereinafter, the number is more preferably 0.10 or less. If x is outside this range, the crystal structure may become unstable, or the performance of a lithium secondary battery using the same may be reduced.

  In the above formula (2), e is usually larger than 0, preferably 0.05 or more, more preferably 0.1 or more, and usually 0.4 or less, preferably 0.3 or less, more preferably The number is 0.2 or less. F is usually 0 or more, preferably 0.02 or more, more preferably 0.04 or more, and usually 0.3 or less, preferably 0.25 or less, more preferably 0.2 or less. It is. If e and f are too small, the chemical stability of the positive electrode active material may be insufficient. If e is too large, the cost increases. If f is too large, the capacity of the battery decreases. There is a risk.

  In the above formula (3), x represents a molar excess amount of Li of the stoichiometric ratio or more, and is usually 0 or more, preferably 0.02 or more, and usually 0.2 or less, preferably 0.15 or less. More preferably, the number is 0.10 or less. If x is outside this range, the crystal structure may become unstable, or the performance of a lithium secondary battery using the same may be reduced.

In the above formula (3), g is usually larger than 0, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.8 or less, preferably 0.7 or less, more preferably The number is 0.5 or less.
h is usually larger than 0, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.6 or less, preferably 0.5 or less, more preferably 0.4 or less. is there.
i is usually 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less. .
However, g + h + i = 1.
If g, h, and i are out of the above ranges, the battery capacity may be reduced.

  In this specification, the composition of the lithium transition metal composite oxide can be measured by a technique such as ICP (Inductively Coupled Plasma) analysis.

[Median diameter]
The median diameter of the lithium transition metal composite oxide of the present invention is usually 20 μm or less, preferably 15 μm or less. If a positive electrode is produced using a lithium transition metal composite oxide whose median diameter exceeds the upper limit as the positive electrode active material, it may cause streaking in the coating process, and the composition may be segregated. On the other hand, the lower limit of the median diameter is usually 1 μm or more, preferably 3 μm or more. If the median diameter is below the lower limit, fine powder may increase and the particles may aggregate.

  In the present specification, the “median diameter” of the lithium transition metal composite oxide is a value measured by a known laser diffraction / scattering particle size distribution analyzer based on JIS Z 8825-1. As a dispersion medium at the time of measurement, a 0.1% by weight sodium hexametaphosphate aqueous solution is used. The refractive index used at the time of measurement is 1.60a010i (real part 1.60, imaginary part 0.10). The lithium transition metal composite oxide particles are agglomerated when dispersed with an ultrasonic oscillator in a dispersion medium. Therefore, in order to use the measurement sample as an index of the degree of aggregation, The measurement is performed without performing a dispersion process using a sound wave oscillator.

[Maximum particle size]
The maximum particle diameter of the lithium transition metal composite oxide of the present invention is usually 40 μm or less, preferably 35 μm or less. If the maximum particle size exceeds this range, striations are likely to occur during coating film creation.

  In the present specification, the “maximum particle size” of the lithium transition metal composite oxide is a value measured by a known laser diffraction / scattering particle size distribution analyzer, as in the case of the “median diameter” described above. The dispersion medium at the time of measurement, the refractive index used at the time of measurement, the point of not performing the dispersion treatment by the ultrasonic oscillator, and the like are the same as in the case of the above-mentioned “median diameter” measurement.

  The lithium transition metal composite oxide of the present invention thus obtained is used as a positive electrode material (positive electrode active material) of a lithium secondary battery.

[III. Positive electrode for lithium secondary battery]
A positive electrode for a lithium secondary battery is usually formed by forming a positive electrode active material layer containing a positive electrode active material, a binder and a conductive agent on a current collector, and the lithium transition metal composite oxide of the present invention has a positive electrode active material. Used as a substance. As the positive electrode active material, the lithium transition metal composite oxide of the present invention may be used alone or in combination of two or more in any combination and ratio. Moreover, you may use combining the 1 type, 2 or more types of lithium transition metal complex oxide of this invention, and 1 type, or 2 or more types of other well-known positive electrode active materials.

  The positive electrode active material layer can be usually obtained by preparing a slurry containing the above-described constituents and applying and drying the slurry on a current collector.

  The proportion of the positive electrode active material in the positive electrode active material layer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and usually 99.9% by weight or less, preferably 99% by weight or less. It is. If the amount of the positive electrode active material is too large, the strength of the positive electrode tends to be insufficient. If the amount is too small, the capacity may be insufficient.

  Examples of the conductive agent used for the positive electrode include natural graphite, artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. The proportion of the conductive agent in the active material layer is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 20% by weight or less. More preferably, it is 10% by weight or less. If the amount of the conductive agent is too large, the capacity may be insufficient, and if the amount is too small, the electrical conductivity may be insufficient.

  Moreover, as a binder used for a positive electrode, besides fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and fluorine rubber, EPDM (ethylene-propylene-diene terpolymer) , SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like. The ratio of the binder in the active material layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less, more preferably. Is 40% by weight or less. If the amount is too large, the capacity may be insufficient. If the amount is too small, the strength may be insufficient.

Moreover, as a solvent used when preparing the slurry for forming a positive electrode active material layer, the organic solvent which melt | dissolves or disperse | distributes a binder normally is used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like can be mentioned. In some cases, a dispersant, a thickener, or the like is added to water and slurried with a latex such as SBR.
The thickness of the positive electrode active material layer is usually about 10 to 200 μm.

  As the material of the current collector used for the positive electrode, metals such as aluminum, stainless steel, nickel-plated steel, etc. are used, and preferably aluminum.

  The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the electrode material.

[IV. Lithium secondary battery]
The lithium secondary battery of the present invention is a lithium secondary battery including a positive electrode and a negative electrode capable of inserting and extracting lithium, and an organic electrolyte containing a lithium salt as an electrolyte, and the positive electrode is used as a positive electrode active material. It is a positive electrode containing the lithium transition metal composite oxide of the invention (that is, the positive electrode for a lithium secondary battery described in the above section [III. Positive electrode for a lithium secondary battery]).

  As a negative electrode material that can be used in the lithium secondary battery of the present invention, a carbon material is preferably used. Such carbon materials include natural or artificial graphite, petroleum coke, coal coke, petroleum pitch carbide, coal pitch carbide, phenolic resin / crystalline cellulose resin carbide, etc. and partially carbonized. Examples thereof include carbon materials, furnace black, acetylene black, pitch-based carbon fibers, PAN-based carbon fibers, or a mixture of two or more thereof. The negative electrode material is usually formed as an active material layer on a current collector together with a binder and, if necessary, a conductive agent. Moreover, lithium metal itself or lithium alloys, such as a lithium aluminum alloy, can also be used as a negative electrode. Examples of the binder and conductive agent that can be used for the negative electrode are the same as those used for the positive electrode.

The thickness of the active material layer of the negative electrode is usually about 10 to 200 μm. Formation of the active material layer of the negative electrode can be performed according to the method for forming the active material layer of the positive electrode.
As the material for the current collector of the negative electrode, metals such as copper, nickel, stainless steel, nickel-plated steel and the like are usually used, and copper is preferable.

  Examples of the electrolyte that can be used in the lithium secondary battery of the present invention include an electrolytic solution, a polymer solid electrolyte, and a semi-solid electrolyte.

  The electrolyte solution is preferably a non-aqueous electrolyte solution. Examples of the non-aqueous electrolyte include those obtained by dissolving various electrolytic salts in a non-aqueous solvent.

  Examples of the non-aqueous solvent include carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, halogenated hydrocarbons, amines, esters, amides, phosphate ester compounds, and the like. it can. Typical examples of these are propylene carbonate, ethylene carbonate, chloroethylene carbonate, trifluoropropylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 4-dioxane, 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, Sulfolane, methyl sulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl Sulfoxides, trimethyl phosphate, and either alone or two or more kinds of mixed solvents such as triethyl phosphate may be used.

  Among the non-aqueous solvents described above, it is preferable to use a high dielectric constant solvent in order to dissociate the electrolyte. The high dielectric constant solvent means a compound having a relative dielectric constant of about 20 or more at 25 ° C. Among the high dielectric constant solvents, it is preferable that the electrolyte solution contains ethylene carbonate, propylene carbonate, and compounds obtained by substituting hydrogen atoms thereof with other elements such as halogen or alkyl groups.

  When such a high dielectric constant solvent is used, the proportion of the high dielectric constant solvent in the electrolytic solution is usually 20% by weight or more, preferably 30% by weight or more, and more preferably 40% by weight or more. If the content of the high dielectric constant solvent is small, desired battery characteristics may not be obtained.

Any conventionally known electrolytic salt can be used, and LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, LiCH ₃ SO ₃ Li, LiCF ₃ SO ₃ , Examples include lithium salts such as LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , and LiN (SO ₃ CF ₃ ) ₂ .

Additives that produce a good film that enables efficient charge and discharge of lithium ions on the negative electrode surface, such as gases such as CO ₂ , N ₂ O, CO, SO ₂ , polysulfide Sx ²⁻ , vinylene carbonate, catechol carbonate, etc. May be present in the electrolyte at an arbitrary ratio.

  Instead of the electrolytic solution, a polymer solid electrolyte that is a conductor of an alkali metal cation such as lithium ion can be used. Alternatively, the electrolyte solution can be made non-fluidized with a polymer to use a semi-solid electrolyte. In the lithium secondary battery of the present invention, an electrolyte layer can be provided between the positive electrode and the negative electrode using various materials as described above.

  Usually, a separator is provided between the positive electrode and the negative electrode. As the separator, a microporous polymer film is used, and the material is nylon, polyester, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, tetrafluoroethylene, polypropylene, polyethylene, polybutene, etc. The polyolefin-type polymer | macromolecule can be mentioned. Further, a nonwoven fabric filter such as glass fiber, a composite nonwoven fabric filter of glass fiber and polymer fiber, and the like can also be used. The chemical and electrochemical stability of the separator is an important factor, and from this point, the polymer is preferably a polyolefin-based polymer. Preferably there is.

  In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000 or more, more preferably 1,000,000 or more, and most preferably 1,500,000 or more. On the other hand, the upper limit of the molecular weight is preferably 5 million or less, more preferably 4 million or less, and most preferably 3 million or less. This is because if the molecular weight is too large, the pores of the separator may not close when heated because the fluidity is too low.

  The shape of the lithium secondary battery can be appropriately selected from various shapes generally employed according to the application. Examples of the shape include a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, and the like. What is necessary is just to assemble a lithium secondary battery by a well-known method according to the shape of the target battery.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded.

[I. Evaluation methods]
[X-ray diffraction measurement]
<Measurement conditions>
X-ray diffraction measurement was performed under the following conditions to evaluate the crystallinity of the lithium transition metal composite oxide.
・ X-ray source: CuKα ray (CuKα = 1.5418Å)
・ Divergent slit: 1 °
・ Scatter slit: 1 °
・ Reception slit: 0.3mm
・ Step width: 0.02 °

<Peak half width>
Since the peak around 18.8 ° attributed to [003] of the hexagonal layered rock salt structure has the strongest intensity, the half-value width of this peak was compared and used as an index of crystallinity. The smaller the half-value width, the higher the crystallinity.

<Peak intensity ratio>
Since the reflection corresponding to [003] does not appear in the hexagonal layered rock salt type crystal structure, the smaller the peak near 18.8 ° attributed to [003] of this hexagonal layered rock salt structure, When the rate of mixing of the crystal phase is large and battery evaluation is performed using such a lithium transition metal composite oxide as a positive electrode material for a lithium ion secondary battery, the capacity becomes small (Japanese Patent Laid-Open No. 6-96769). See the official gazette). Therefore, in order to quantitatively compare the peak intensity of [003], the intensity ratio ([003] / [104]) with the peak near 44.6 ° attributed to [104] where the intensity change is small. The mixing ratio of rock salt type crystal phase was compared. A larger value of the intensity ratio ([003] / [104]) serves as an index for decreasing the mixing ratio of the rock salt type crystal phase. As a result, it is considered that the battery characteristics are also improved.

[Battery characteristics measurement]
<Initial efficiency / rate evaluation>
(I) Battery production:
75 parts by weight of the lithium transition metal composite oxide obtained in Examples and Comparative Examples, 20 parts by weight of acetylene black and 5 parts by weight of polytetrafluoroethylene powder were sufficiently mixed in a mortar, and a thin sheet was punched into 9 mmφ. It was. This was pressure-bonded to an aluminum expanded metal to form a positive electrode.

As the negative electrode, metallic lithium having a diameter of 12 mm and a thickness of 1 mm was used.
An electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate and diethyl carbonate in a weight ratio of 3: 7 so as to be 1 mol / liter.

  In the positive electrode can, the above-described positive electrode soaked with the above-described electrolyte solution and then a separator made of a porous polyethylene film soaked with the above-described electrolyte solution were placed, and then a polypropylene gasket was placed and pressed. Further, the above negative electrode and spacer were put, and finally a negative electrode can was covered and sealed to prepare a coin type battery (lithium secondary battery) for evaluation.

(Ii) Measurement of initial efficiency:
The battery for evaluation produced as described above was charged and discharged in a voltage range of 3.0 V to 4.2 V as measurement conditions.

The initial charge capacity (mAh / g) and initial discharge capacity (mAh / g) per unit weight of the positive electrode active material when the charge / discharge test was conducted at a current density of 0.2 mA / cm ² both during charging and discharging. It was measured. Those ratios were calculated in percentage ({(initial discharge capacity) / (initial charge capacity)} × 100), and the obtained value was defined as the initial efficiency.

(Iii) Rate assessment:
Charging time 0.2 mA / cm ^2, when carrying out the charge and discharge test at a current density during discharge 11 mA / cm ^2, the initial discharge capacity per electrode active material unit weight (mAh / g) was measured and this value Used as an index for rate evaluation.

<Resistance evaluation>
(I) Battery production:
75 parts by weight of the lithium transition metal composite oxide obtained in Examples and Comparative Examples, 20 parts by weight of acetylene black, and 5 parts by weight of polytetrafluoroethylene powder were sufficiently mixed in a mortar to make a thin sheet into 12 mmφ. Punched out. This was pressure-bonded to an aluminum expanded metal to form a positive electrode.

92.5 parts by weight of graphite powder having a particle size of about 8 to 10 μm and 7.5 parts by weight of polyvinylidene fluoride were mixed, and N-methylpyrrolidone was added thereto to form a slurry. This slurry was applied to one side of a copper foil and dried. This was punched out to 12 mmφ and further pressed at 0.5 ton / cm ² to obtain a negative electrode.

Ethylene carbonate was dissolved in a mixed solvent of diethyl carbonate in a weight ratio of 3: 7 so that lithium hexafluorophosphate (LiPF ₆ ) was 1 mol / liter to prepare an electrolytic solution.

  In the positive electrode can, the above-mentioned positive electrode immersed in the above electrolytic solution, and then a separator made of a porous polyethylene film immersed in the above electrolytic solution were placed, and a polypropylene gasket was placed and pressed. Furthermore, the negative electrode and the spacer soaked with the electrolytic solution were put, and finally the negative electrode can was covered and sealed to prepare a coin-type battery for evaluation (lithium secondary battery).

(Ii) Room temperature resistance evaluation:
The room temperature resistance was evaluated before and after the following “(iii) cycle load test”.
After charging at a constant current of 1/3 C to 4.1 V at a temperature of 25 ° C., charging was performed at a constant current of 1/3 C with a lower limit voltage of 3.0 V, and the charging depth was adjusted to 40%. This coin battery was discharged at 1/4 C for 10 seconds. The current value (I) at the time of discharge, OCV (Open Circuit Voltage) ₁ immediately before the discharge, and OCV ₂ after the discharge were measured. The difference between OCV ₁ and OCV ₂ was ΔV, and the resistance (R) was calculated from the following equation.

(Iii) Cycle load test:
First, charging and discharging were performed for 2 cycles at 25 ° C. with a constant current of 0.2 C, a charge upper limit voltage of 4.1 V, and a discharge lower limit power source of 3.0 V. Next, at 60 ° C., charging / discharging was repeated 100 cycles at a constant current of 1 C, a charging upper limit voltage of 4.1 V, and a discharging lower limit voltage of 3.0 V. Here, “1C” represents a current value for discharging the reference capacity of the battery in one hour.

[II. Preparation and analysis of lithium transition metal composite oxide]
[Example 1]
Ni (OH) ₂ , Co (OH) ₂ , and Mn ₃ O ₄ are mixed at a molar ratio of Ni: Co: Mn = 0.33: 0.33: 0.33, and water is added thereto. In addition, a slurry having a solid concentration of 15% by weight was prepared. While this slurry was stirred, it was pulverized using a circulating medium agitation type wet pulverizer until the average particle size of the solid content in the slurry became 0.2 μm or less. This slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 10 μm. Air was used as the drying gas, and the drying gas inlet temperature was 140 ° C.

The granulated particles obtained by spray drying and the pulverized product of LiOH.H ₂ O are weighed so that Li: (Ni + Co + Mn) = 1.05: 1, mixed for 30 minutes with a mixer-type mixer, and mixed powder Got. At this time, the temperature in the mixed system was kept at 70 ° C. (± 10 ° C.). This mixed powder was calcined at 990 ° C. for 15 hours in an air atmosphere, crushed with a mortar, and then sieved with an m sieve having a sieve size of 45 μm to obtain a lithium transition metal composite oxide.

As a result of analyzing the composition of the lithium transition metal composite oxide of Example 1 by the ICP method, the composition was almost as prepared.
Moreover, the X-ray diffraction analysis was implemented about the lithium transition metal complex oxide of Example 1 with the above-mentioned method. The results are shown in Table 1 below.
Moreover, using the lithium transition metal composite oxide of Example 1, a coin-type cell battery for evaluation was produced by the above-described method, and the battery was evaluated. The results are shown in Table 2 below.

[Comparative Example 1]
Ni (OH) ₂ , Co (OH) ₂ , and Mn ₃ O ₄ are mixed at a molar ratio of Ni: Co: Mn = 0.33: 0.33: 0.33, and water is added thereto. In addition, a slurry having a solid concentration of 15% by weight was prepared. While this slurry was stirred, it was pulverized using a circulating medium agitation type wet pulverizer until the average particle size of the solid content in the slurry became 0.2 μm or less. This slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 10 μm. Air was used as the drying gas, and the drying gas inlet temperature was 140 ° C.

  The granulated particles obtained by spray drying and the pulverized product of anhydrous LiOH were weighed so that Li: (Ni + Co + Mn) = 1.05: 1, and mixed for 30 minutes with a mixer-type mixer to obtain mixed powder. . At this time, the temperature in the mixed system was maintained at 25 ° C. (± 5 ° C.). This mixed powder was calcined at 990 ° C. for 15 hours in an air atmosphere, crushed with a mortar, and then sieved with an m sieve having a sieve size of 45 μm to obtain a lithium transition metal composite oxide. This is the lithium transition metal composite oxide of Comparative Example 1.

As a result of analyzing the composition of the lithium transition metal composite oxide of Comparative Example 1 by the ICP method, the composition was almost as prepared.
Moreover, about the lithium transition metal complex oxide of the comparative example 1, X-ray diffraction analysis was implemented with the above-mentioned method. The results are shown in Table 1 below.
Moreover, the coin type cell battery for evaluation was produced by the above-mentioned method using the lithium transition metal complex oxide of Comparative Example 1, and the battery was evaluated. The results are shown in Table 2 below.

[III. Evaluation of analysis results of lithium transition metal composite oxides]
[Results of X-ray diffraction measurement]

  From Table 1 above, the lithium transition metal composite oxide of Example 1 has a smaller [003] peak half-value width and higher crystallinity than the lithium transition metal composite oxide of Comparative Example 1. I understand.

  Further, the lithium transition metal composite oxide of Example 1 has a larger value of [003] / [104] strength ratio than the lithium transition metal composite oxide of Comparative Example 1, and the mixing ratio of the rock salt type crystal phase is larger. It turns out that it is smaller.

  From the above results, when the lithium transition metal composite oxide of Example 1 is used as a positive electrode material of a lithium secondary battery, the battery characteristics obtained are better than the lithium transition metal composite oxide of Comparative Example 1. It is thought that it becomes.

[Battery characteristics measurement results]

From the above Table-2, the lithium secondary battery using the lithium transition metal composite oxide of Example 1 is higher in initial efficiency and larger than the lithium secondary battery using the lithium transition metal composite oxide of Comparative Example 1. The discharge capacity at a current (11 mA / cm ² ) was high, and the resistance increase ratio before and after the cycle test was low. Therefore, the lithium secondary battery using the lithium transition metal composite oxide of Example 1 had better battery characteristics overall.

  From the above results, when the granulated particles of the transition metal compound and the lithium raw material are mixed, the contact area between the granulated particles of the transition metal compound and the lithium raw material is improved by dissolving and mixing the lithium raw material. As a result, it was found that a lithium transition metal composite oxide having high crystallinity after firing was obtained, and by using it as a positive electrode active material of a lithium secondary battery, excellent battery characteristics were exhibited.

  The application of the present invention is not particularly limited, and can be suitably used in various fields such as an electronic device in which a lithium secondary battery is used.

Claims (8)

At least a granulation step of the transition metal compound, a mixing step of the granulated particles of the transition metal compound obtained by the granulation step and the lithium raw material, and a firing step of the mixture obtained by the mixing step, In the method for producing a lithium transition metal composite oxide,
In the mixing step, when the granulated particles of the transition metal compound and the lithium raw material are mixed, the lithium raw material is dissolved and mixed. 2. The method for producing a lithium transition metal composite oxide according to claim 1, wherein the lithium raw material is dissolved by moisture. 3. The method for producing a lithium transition metal composite oxide according to claim 2, wherein the lithium raw material is a hydrate of lithium hydroxide, and is heated to a temperature at which the lithium raw material is dissolved in the mixing step. 3. The method for producing a lithium transition metal composite oxide according to claim 2, wherein moisture is allowed to coexist in the mixing step. A precursor for obtaining a lithium transition metal composite oxide by firing,
A calcined precursor for a lithium transition metal composite oxide, wherein the granulated particles of a transition metal compound are coated with a lithium raw material. It manufactures with the manufacturing method of the lithium transition metal complex oxide as described in any one of Claims 1-4, The lithium transition metal complex oxide characterized by the above-mentioned. A lithium transition metal composite oxide obtained by using the firing precursor for lithium transition metal composite oxide according to claim 5. A lithium secondary battery comprising a positive and negative electrodes capable of inserting and extracting lithium, and an organic electrolyte containing a lithium salt as an electrolyte,
A lithium secondary battery, wherein the positive electrode contains the lithium transition metal composite oxide according to claim 6 or 7.