JP5135843B2 - Lithium transition metal composite oxide, positive electrode for lithium secondary battery using the same, and lithium secondary battery using the same - Google Patents

Description

  The present invention resides in a lithium transition metal composite oxide, a positive electrode for a lithium secondary battery using the same, and a lithium secondary battery using the same.

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.
Conventionally, lithium transition metal composite oxides having standard compositions such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ have been used as positive electrode active materials for lithium secondary batteries. Furthermore, from the viewpoint of safety and raw material costs, a technology using a lithium transition metal composite oxide having the same layered structure as LiCoO ₂ or LiNiO ₂ and partially replacing transition metal with manganese or the like, specifically LiNi _1-x Mn _x O _{2 in} which part of nickel sites of LiNiO ₂ is substituted with manganese (where 0 <x <1), LiNi _1-xy Mn in which part of nickel sites is substituted with manganese and cobalt _x Co _y O ₂ (where 0 <x <1, 0 <y <1, 0 <x + y <1) has attracted attention (for example, Patent Documents 1 and 2).

Among the lithium transition metal composite oxides, LiCoO ₂ is one of the materials that have attracted attention as a positive electrode active material, and various techniques have been proposed for this (for example, Patent Document 3). However, LiCoO ₂ has a problem that Co as a raw material is expensive and battery safety is not sufficient.
On the other hand, in recent years, it has been proposed to use lithium nickel manganese cobalt oxide as a positive electrode active material (for example, Patent Document 4). The lithium nickel manganese cobalt oxide can be used as a positive electrode active material that is inexpensive and can improve battery safety due to the small amount of expensive Co used. That is, by using lithium nickel manganese cobalt oxide, there can be obtained a merit in cost that cannot be obtained by the technique of Patent Document 3 and a merit that battery safety is improved.
JP 2003-17052 A JP 2003-45414 A JP-A-10-279315 JP 2003-242976 A

  However, the conventional lithium nickel manganese cobalt oxide has a problem of low output due to high resistance as a battery, and further improvement has been desired. In addition, in the manufacturing method described in Patent Document 4, in order to manufacture lithium nickel manganese cobalt oxide, the precursor manufactured using the coprecipitation method is subjected to heat treatment, so that the process is complicated and the productivity is high. It was not enough and improvement was desired.

As a result of intensive studies in view of the above problems, the present inventors are composed of primary particles and / or secondary particles obtained by agglomerating them, possessing pores inside the secondary particles, and tungsten As a result, the inventors have found that a lithium secondary battery having high characteristics can be obtained.
That is, the gist of the present invention is as follows.
1. A lithium transition metal composite oxide composed of primary particles and / or secondary particles obtained by agglomerating them, wherein the lithium transition metal composite oxide is represented by the following general formula (1), and is a mercury intrusion method: The obtained pore distribution curve of the secondary particles has a main peak top at a pore radius greater than 1 μm and 50 μm or less, and a sub-peak top at a pore radius of 0.08 μm or more and 1 μm or less. , Lithium transition metal composite oxide.

(Chemical formula 1)
Li _x Ni _α Mn _β Co _γ Q _δ W _Y O ₂ (1)
(Wherein Q is at least one element selected from Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca and Mo) 0.2 ≦ α ≦ 0.6, 0.2 ≦ β ≦ 0.6, 0 ≦ γ ≦ 0.5, 0 ≦ δ ≦ 0.1, 0.8 ≦ α + β + γ + δ ≦ 1.2, 0 The number satisfying the relationship of <x ≦ 1.2 and 0 <Y ≦ 0.1 is shown.)
2. ^2. The lithium transition metal composite oxide according to 1, wherein the specific surface area is 0.1 m ² / g or more and 8 m ² / g or less.
3. ^3. The lithium transition metal composite oxide according to 1 or 2 above, wherein the tap density is 0.8 g / cm ³ or more and 3.0 g / cm ³ or less.
4). 4. The lithium transition metal composite oxide according to any one of 1 to 3 above, wherein the median diameter of secondary particles constituting the lithium transition metal composite oxide is 1 μm or more and 20 μm or less.
5. A positive electrode for a lithium secondary battery, comprising the lithium transition metal composite oxide according to any one of 1 to 4 above.
6). 6. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to 5 above, a negative electrode, and an electrolyte.
7). A method for producing a lithium transition metal composite oxide comprising wet pulverizing and mixing raw material compounds in a liquid medium, followed by spray drying and firing, wherein the lithium transition metal composite oxide comprises primary particles and / or In the lithium transition metal composite oxide composed of secondary particles formed by agglomerating the lithium transition metal composite oxide represented by the following general formula (1), the secondary particles obtained by the mercury intrusion method The lithium transition metal composite oxidation is characterized by having a main peak top at a pore radius greater than 1 μm and less than 50 μm and a sub-peak top at a pore radius of 0.08 μm to 1 μm in the pore distribution curve of Manufacturing method.

(Chemical formula 2)
Li _x Ni _α Mn _β Co _γ Q _δ W _Y O ₂ (1)
(Wherein Q is at least one element selected from Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca and Mo) 0.2 ≦ α ≦ 0.6, 0.2 ≦ β ≦ 0.6, 0 ≦ γ ≦ 0.5, 0 ≦ δ ≦ 0.1, 0.8 ≦ α + β + γ + δ ≦ 1.2, 0 The number satisfying the relationship of <x ≦ 1.2 and 0 <Y ≦ 0.1 is shown.)

  According to the present invention, a lithium transition metal composite oxide having high performance (high capacity, high rate characteristics, resistance characteristics, etc.) suitable as a positive electrode material for a lithium secondary battery can be provided at low cost. Furthermore, according to the present invention, a high-performance positive electrode for a lithium secondary battery and a lithium secondary battery can be provided.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention. .
[1. Lithium transition metal composite oxide]
The lithium transition metal composite oxide of the present invention has a form of primary particles and / or secondary particles formed by agglomerating them, and has pores inside the secondary particles and contains tungsten. It consists of particles that do. More specifically, it is a lithium transition metal composite oxide represented by the following general formula (1), and in the pore distribution curve of the secondary particles obtained by the mercury intrusion method, the pore radius is larger than 1 μm and 50 μm. A lithium transition metal composite oxide having a main peak top in the following range and a sub-peak top in a pore radius of 0.08 μm to 1 μm.

(Chemical formula 3)
Li _x Ni _α Mn _β Co _γ Q _δ W _Y O ₂ (1)
(Wherein Q is at least one element selected from Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca and Mo) 0.2 ≦ α ≦ 0.6, 0.2 ≦ β ≦ 0.6, 0 ≦ γ ≦ 0.5, 0 ≦ δ ≦ 0.1, 0.8 ≦ α + β + γ + δ ≦ 1.2, 0 The number satisfying the relationship of <x ≦ 1.2 and 0 <Y ≦ 0.1 is shown.)
Hereinafter, the element represented by the symbol “Q” in the above formula (1) is referred to as “predetermined element”.

  Examples of the predetermined element include Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca, and Mo. Furthermore, among these, as the predetermined element, Al, Fe, Mg, Ga, Ti, B, Bi, Nb, Mo and Ca are more preferable, and Al, Mg, B, Bi, Nb and Mo are further preferable. In addition, a predetermined element may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  In the above formula (1), x is a number that satisfies the relationship 0 <x ≦ 1.2. Specifically, x is usually greater than 0, preferably 0.8 or more, and usually 1.2 or less, preferably 1.15 or less. If the value of x is too large, the crystal structure of the positive electrode active material of the present invention may become unstable, or the battery capacity of a lithium secondary battery using the positive electrode active material may be reduced. Moreover, even if the value of x is too small, there is a risk that the battery capacity of a lithium secondary battery using this will also be reduced.

  Further, in the above formula (1), α is a number satisfying the relationship of 0.2 ≦ α ≦ 0.6. Specifically, α is usually 0.2 or more, preferably 0.3 or more, and usually 0.6 or less, preferably 0.5 or less, more preferably 0.43 or less. If the value of α is too large, the lithium transition metal composite oxide of the present invention is similar to that used in the conventional positive electrode active material for lithium secondary batteries mainly composed of Ni, and there are too few pores inside the secondary particles. Since the morphology does not exist, the battery safety of a lithium secondary battery using the same may be lowered. On the other hand, if the value of α is too small, the reduction in density due to the decrease in sinterability becomes significant, and it may be difficult to produce a single-phase lithium transition metal composite oxide.

  In the above formula (1), β is a number satisfying the relationship of 0.2 ≦ β ≦ 0.6. Specifically, β is a number of usually 0.2 or more, preferably 0.3 or more, and usually 0.6 or less, preferably 0.5 or less, more preferably 0.43 or less. If the value of β is too large, there is a risk that the density will be lowered due to the decrease in sinterability and the battery characteristics of a lithium secondary battery using this will become noticeable. On the other hand, if the value of β is too small, the raw material cost increases, which is not preferable as a positive electrode for a lithium secondary battery.

Further, in the above formula (1), γ is a number satisfying the relationship of 0 ≦ γ ≦ 0.5. For more information,
γ is usually a number of 0 or more, preferably 0.1 or more, more preferably 0.2 or more, and usually 0.5 or less, preferably 0.45 or less. In general, since Co is scarce in resources and expensive, it is not preferable that γ is too large.
In the above formula (1), δ is a number satisfying the relationship of 0 ≦ δ ≦ 0.1. Specifically, δ is usually a number of 0 or more, preferably 0.001 or more, and usually 0.1 or less, preferably 0.05 or less. If δ is too large, the capacity of the lithium secondary battery using the positive electrode active material of the present invention may decrease, which is not preferable. When two or more elements are used as the predetermined substitution elements, it is desirable that the total of the predetermined substitution elements used is δ, and the value is within the above range.

In the above formula (1), Y is a number that satisfies the relationship 0 <Y ≦ 0.1. Specifically, Y is usually a number greater than 0, preferably 0.001 or more, and usually 0.1 or less, preferably 0.05 or less. If Y is too large, the capacity of the lithium secondary battery using the positive electrode active material of the present invention may decrease, which is not preferable.
Furthermore, the above α, β, γ and δ satisfy the relationship 0.8 ≦ α + β + γ + δ ≦ 1.2. In the general formula (1), the amount of oxygen may have some non-stoichiometry.

Moreover, the lithium transition metal complex oxide of the present invention has a specific surface area of 0.1 m ² / g or more and 8 m ² / g or less. The specific surface area varies greatly depending on the ratio of Ni, Mn and Co, and the amount of addition of Q and W, more preferably 0.2 m ² / g to 6 m ² / g, and most preferably 0.5 m ² / g. It is 5 m ² / g or less. The specific surface area can be measured with a known BET type powder specific surface area measuring device. In the present invention, an OMS Riken: AMS8000 type automatic powder specific surface area measuring device was used, nitrogen was used as an adsorption gas, and helium was used as a carrier gas. Specifically, the powder sample is heated and deaerated with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the nitrogen / helium mixed gas, and then heated to room temperature with water. The adsorbed nitrogen gas was desorbed, the amount was detected by a heat conduction detector, and the specific surface area of the sample was calculated from this.

Furthermore, the lithium transition metal composite oxide of the present invention has a tap density of 0.8 g / cm ³ or more and 3.0 g / cm ³ or less. Similarly, the tap density varies greatly depending on the ratio of Ni, Mn, Co and the amount of addition of Q and W, but is more preferably 0.9 g / cm ³ or more, and most preferably 1.0 g / cm ³ or less. . Since there is no problem with the higher density, there is no particular upper limit, but it is usually 3.0 g / cm ³ or less. In addition, the tap density measured the powder filling density (tap density) after putting sample powder into a 10 ml glass measuring cylinder and tapping 200 times.

  In the lithium transition metal composite oxide of the present invention, the median diameter of the particles constituting the lithium transition metal composite oxide is 1 μm or more and 20 μm or less. If it is too small, it becomes difficult to handle the powder, and if it is too large, the particles will be too large with respect to the thickness of the electrode when making a positive electrode for a lithium secondary battery. Therefore, it is more preferably 2 μm or more and 15 μm or less, and most preferably 3 μm or more and 10 μm or less. The median diameter was measured by a known laser diffraction / scattering particle size distribution measuring apparatus with the real part 1.60 and the imaginary part 0.10 set as the complex refractive index and the particle diameter reference as the volume reference. is there. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

Here, the pore distribution curve of the secondary particles obtained by the mercury intrusion method will be described in detail below.
The mercury intrusion method is a method for obtaining information such as specific surface area and pore size distribution from the relationship between pressure and the amount of mercury intruded into a pore of a sample such as porous particles while applying pressure. It is.

  Specifically, the container containing the sample is first evacuated and filled with mercury. Mercury has a high surface tension, so mercury does not penetrate into the pores on the sample surface as it is, but when pressure is applied to the mercury and the pressure is increased gradually, the pores increase from the largest to the smallest. Mercury gradually enters the pores. If a change in the mercury liquid level (that is, the amount of mercury intruded into the pores) is detected while the pressure is continuously increased, a mercury intrusion curve representing the relationship between the pressure applied to the mercury and the amount of mercury intruded can be obtained. .

Here, assuming that the pore shape is cylindrical, the radius is r, the surface tension of mercury is δ, and the contact angle is θ, the magnitude of the force in the direction of pushing mercury out of the pore is −2πrδ ( cos θ) (if θ> 90 °, this value is positive). Further, since the magnitude of the force in the direction of pushing mercury into the pores under the pressure P is represented by πr ² P, the following formulas (1) and (2) are derived from the balance of these forces.

(Equation 1)
−2πrδ (cos θ) = πr ² P Formula (1)
Pr = −2δ (cos θ) Formula (2)
In the case of mercury, values of surface tension δ = 480 dyn / cm and contact angle θ = 140 ° are generally used. When these values are used, the radius of the pore into which mercury is injected under the pressure P is expressed by the following formula (3).

即ち、水銀に加えた圧力Ｐと水銀が浸入する細孔の半径ｒとの間には相関があることから、得られた水銀圧入曲線に基づいて、試料の細孔半径の大きさとその体積との関係を表す細孔分布曲線を得ることができる。例えば、圧力Ｐを０．１ＭＰａから１００ＭＰａまで変化させると、７５００ｎｍ程度から７．５ｎｍ程度までの範囲の細孔について測定が行える。なお、水銀圧入法による細孔半径の大凡の測定限界は、下限が約３ｎｍ以上、上限が約２００μｍ以上である。

That is, since there is a correlation between the pressure P applied to mercury and the radius r of the pore into which mercury intrudes, the size of the pore radius of the sample and its volume are calculated based on the obtained mercury intrusion curve. A pore distribution curve representing the relationship can be obtained. For example, when the pressure P is changed from 0.1 MPa to 100 MPa, the pores in the range from about 7500 nm to about 7.5 nm can be measured. The approximate limit of measurement of the pore radius by mercury porosimetry is about 3 nm or more for the lower limit and about 200 μm or more for the upper limit.

Measurement by the mercury intrusion method can be performed using an apparatus such as a mercury porosimeter. Specific examples of the mercury porosimeter include an autopore manufactured by Micromeritics, a pore master manufactured by Kantachrome, and the like.
The lithium transition metal composite oxide of the present invention has a main peak top at a pore radius of 1 μm to 50 μm and a pore radius of 0 in the pore distribution curve of the secondary particles obtained by the mercury intrusion method described above. It has a sub-peak top at 0.08 μm or more and 1 μm or less.

In this specification, the “pore distribution curve” means the total pore volume per unit weight (usually 1 g) of pores having a radius equal to or larger than the radius of the pore and the radius of the pore. The value differentiated by the logarithm of is plotted on the vertical axis, and is usually represented as a graph connecting the plotted points.
In the present specification, the “main peak” means the largest peak among the peaks of the pore distribution curve, and usually represents a peak corresponding to the voids between the secondary particles. The “sub peak” means a smaller peak than the main peak of the pore distribution curve. “Peak top” means a point where the coordinate value of the vertical axis takes the largest value in each peak of the pore distribution curve.

  The main peak of the pore distribution curve according to the present invention has a main peak top at a pore radius of 1 μm to 50 μm. The fact that the pore radius is large to some extent means that the secondary particles are formed to a certain extent, and it is necessary to secure the conductive path when using a filling rate of the active material as an electrode or a specific amount of conductive material. It is preferable from the viewpoint. When the pore radius is less than 1 μm, secondary particles are not sufficiently formed. The upper limit of the main peak radius is not particularly limited, but even if it is too large, the secondary particles cannot be contacted with each other and the conductive path is insufficient, so that it is usually 50 μm or less.

  The subpeak included in the pore distribution curve according to the present invention has a subpeak top at a pore radius of 0.08 μm to 1 μm. Having a sub-peak in a pore radius region smaller than the main peak described above usually means having a pore inside the secondary particle. The lithium transition metal composite oxide of the present invention is presumed to have both low-temperature output characteristics and good coating properties by having such voids in the secondary particles. Based on the pore radius of the main peak described above, the sub peak top is usually 1 μm or less, and there is no lower limit. Therefore, it is usually 0.08 μm or more.

WO2002-41419 discloses examples of compositions such as Li _1.04 Ni _0.53 Mn _0.30 Co _0.14 W _0.03 O ₂ , all of which are known and conventional techniques. It is synthesized by some coprecipitation method. When synthesized by the coprecipitation method, pores are not generated inside the secondary particles, that is, in the pore distribution curve of the secondary particles obtained by the mercury intrusion method, there is a subpeak at a pore radius of 0.08 μm to 1 μm. This results in a disadvantageous morphology for the output characteristics. A method for producing a lithium transition metal composite oxide having pores inside secondary particles will be described in detail below.

[2. Production method]
The method for producing a lithium transition metal composite oxide of the present invention (hereinafter referred to as “the production method of the present invention” as appropriate) comprises at least a calcined material comprising a calcined precursor obtained by wet pulverizing and mixing raw material compounds and spray drying. It is preferable to provide the process of baking.
Therefore, usually, the raw material compound containing the elements constituting the lithium transition metal composite oxide of the present invention so that the lithium transition metal composite oxide of the present invention has the same elemental composition as the target lithium transition metal composite oxide The mixture of raw material compounds (hereinafter referred to as “raw material mixture” as appropriate) is formed into a particulate firing precursor by spray drying, and then the firing material containing the firing precursor is fired. Can do.

[2-1. Mixing process]
First, raw material compounds are mixed to prepare a raw material mixture.
The raw material compound is not particularly limited as long as it contains an element constituting the positive electrode active material of the present invention, and any compound can be used as long as the effects of the present invention are not significantly impaired. Usually, oxides, including Li, Ni and Mn, and some or more of elements such as Co and predetermined substitution elements; inorganic salts such as carbonates, sulfates, nitrates, phosphates; halides; organics Various things such as salt can be used in combination. In some cases, B and the predetermined substitution element Q can be separately mixed. In this case, the raw material compound containing B or the substitution predetermined element Q is not necessarily the same as the target positive electrode active material. It is not necessary to mix so that it may become the same elemental composition.

As a compound containing lithium (hereinafter referred to as “lithium compound” as appropriate), usually L
Inorganic lithium salts such as i ₂ CO ₃ and LiNO ₃ ; Lithium hydroxide such as LiOH and LiOH.H ₂ O; Lithium halides such as LiCl and LiI; Inorganic lithium compounds such as Li ₂ O; Alkyl lithium and acetic acid Examples of the lithium compound include organic lithium compounds such as lithium and fatty acid lithium. However, in order to produce a more uniform particle group with less variation in composition among particles, a lithium compound that is hardly soluble in water is preferable. When a water-soluble lithium compound is used, the concentration distribution of lithium and transition metal elements varies from particle to particle due to the rapid precipitation of the dissolved lithium component in the spray drying process after the wet pulverization and mixing process. This causes deterioration of battery characteristics. Examples of the lithium compound that is hardly soluble in water include LiF, Li ₂ CO ₃ , Li ₃ PO ₄ , and Li ₃ AsO ₄ . One lithium compound may be used alone, or two or more lithium compounds may be used in any combination and ratio as long as the effects of the present invention are not significantly impaired as long as they are hardly soluble in water.

As a compound containing nickel (hereinafter, referred to as “nickel compound” as appropriate), Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O, fatty acid nickel, nickel halide and the like can be mentioned.
Among these, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O and the like are preferable. Such a nickel compound containing no nitrogen and sulfur is preferable because it does not generate harmful substances such as NOx and SOx in the firing step. Furthermore, Ni (OH) ₂ , NiO, and NiOOH are particularly preferable from the viewpoint of being inexpensively available as industrial raw materials and having high reactivity when firing.

In addition, a nickel compound may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios, unless the effect of this invention is impaired remarkably.
As a compound containing manganese (hereinafter referred to as “manganese compound” as appropriate), Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , MnOOH, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , an organic manganese compound, Examples thereof include manganese hydroxide and manganese halide. Among these, MnOOH, Mn ₂ O ₃ , MnO ₂ , Mn ₃ O _{4 and the} like are preferable. These are preferable because they have a valence close to the manganese oxidation number of the positive electrode active material of the present invention which is the final object.

In addition, a manganese compound may also be used individually by 1 type, and 2 or more types of compounds may be used together by arbitrary combinations and ratios, unless the effect of this invention is impaired remarkably.
As a compound containing cobalt (hereinafter referred to as “cobalt compound” as appropriate), CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (OH) ₂ , CoOOH, Co (NO ₃ ) ₂ .6H ₂ O, CoSO ₄ · _7H 2 O, organic cobalt compounds include cobalt halides. Among these, preferred are CoO, Co ₂ O ₃ , Co ₃ O ₄ , CoOOH, Co (OH) _{2 and the} like.

In addition, a cobalt compound may also be used individually by 1 type, and 2 or more types of compounds may be used together by arbitrary combinations and ratios, unless the effect of this invention is impaired remarkably.
Furthermore, for example, as the compound containing element Q, usually, an inorganic salt or an organic salt may be used.
In addition, the compound containing element Q may also be used individually by 1 type, and 2 or more types of compounds may be used together by arbitrary combinations and ratios, unless the effect of this invention is impaired remarkably.

The mixing method of the raw material compounds is not particularly limited as long as it is at least a wet pulverization mixing method. Moreover, in order to produce a more uniform particle group with small variation in composition among particles, the wet pulverization and mixing treatment preferably has an average particle diameter of the raw material compound slurry of 0.45 μm or less. In a lithium transition metal composite oxide synthesized using a slurry having an average particle size larger than this, the variation in composition among particles becomes large, leading to deterioration of battery characteristics. Therefore, the average particle diameter of the raw material compound slurry is usually 0.45 μm or less, more preferably 0.40 μm or less, and most preferably 0.35 μm or less. The median diameter was measured with a known laser diffraction / scattering particle size distribution measuring device with a refractive index of 1.24 and a particle diameter reference as a volume reference. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

  The solid content concentration of the slurry is appropriately selected between 1 wt% and 50 wt%. If it is too low, the productivity will be lowered, so it is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more. If it is too high, the slurry will be greatly thickened. The amount is usually 50% by weight or less, preferably 40% by weight or less, and more preferably 30% by weight or less.

  In the present invention, when the solid content concentration is increased and the slurry is greatly thickened, a dispersant is added. Conversely, when the viscosity of the slurry is too low, a thickener is added. May be prepared. However, if these additives are added excessively more than necessary, in the firing step described below, sintering or uneven firing may be caused, which may lead to deterioration of battery characteristics. Therefore, in the present invention, it is preferable not to add these additives more than necessary, and a better lithium transition metal composite oxide can be obtained if these additives are not added as much as possible. There are many.

[2-2. Spray drying process]
The obtained raw material mixture is then subjected to a granulation step. In the present invention, granulation is performed by spray drying. By spray drying, a calcined precursor can be obtained as a particulate material of the raw material mixture.
Spray drying is an excellent granulation method in terms of the uniformity of the calcined precursor to be produced, powder flowability, powder handling performance, and the ability to efficiently form secondary particles. There is no restriction | limiting in the specific method of spray drying, It can carry out arbitrarily by a well-known method. For example, when the raw material compound is mixed in a wet process, the raw material compound is usually obtained as a slurry. Therefore, the slurry is liquefied from the nozzle by flowing a gas flow and a raw material mixture slurry into the tip of the nozzle. It is possible to use a method in which droplets are ejected as droplets and contacted with a drying gas to rapidly dry the droplets.

  The conditions for the spray drying are arbitrary as long as the effects of the present invention are not significantly impaired, but the drying gas inlet temperature is usually 80 ° C. or higher and 400 ° C. or lower, more preferably 100 ° C. or higher and 300 ° C. or lower. The gas-liquid ratio calculated from the introduced dry gas (L / min) and the discharged slurry (L / min) is usually 500 or more and 5000 or less, more preferably 1000 or more and 3000 or less.

  Furthermore, the firing precursor obtained by spray drying is a particulate material of a metal composite mixture in which the used raw material compounds coexist. Therefore, when a compound containing each of the elements constituting the positive electrode active material of the present invention (excluding oxygen) is used as a raw material without a shortage, this firing precursor is used as a firing material in the next firing step. Provided. However, the raw material compounds of elements such as B and Bi that have not been added to the wet pulverization and mixing step are dry-mixed at the time of producing this firing precursor.

[2-3. Firing step]
The firing precursor is then subjected to a firing step. The lithium transition metal composite oxide of the present invention can be obtained by firing.
Although the specific method of baking is arbitrary as long as the effect of this invention is not impaired remarkably, it can carry out using apparatuses, such as a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, for example.
In general, firing is divided into three steps: a temperature raising step, a maximum temperature holding step, and a temperature lowering step. Here, the maximum temperature holding process is not necessarily performed once, and may be performed in two or more stages according to the purpose.

Furthermore, you may make it perform the process of performing another process during baking. For example, a temperature raising step, a maximum temperature holding step, and a temperature lowering step, with a crushing step performed to eliminate agglomeration to such an extent that the secondary particles are not destroyed, and a crushing step for crushing to primary particles or finer powder Each step may be repeated twice or more.
Moreover, the conditions at the time of baking are arbitrary unless the effect of this invention is impaired remarkably. However, firing is usually performed under the following conditions.

In the temperature raising step, it is usually desirable to raise the temperature at a rate of temperature rise of 0.1 ° C / min to 5 ° C / min. This is because even if the heating rate is too slow, it takes time and is industrially disadvantageous. However, if the heating rate is too fast, the furnace temperature may not follow the set temperature depending on the furnace.
In the maximum temperature holding step, the firing temperature is usually 500 ° C. or higher, preferably 600 ° C. or higher, more preferably 800 ° C. or higher, and usually 1200 ° C. or lower, preferably 1100 ° C. or lower. If the temperature is too low, a long baking time tends to be required to obtain the positive electrode active material of the present invention having good crystallinity. On the other hand, if the temperature is too high, the positive electrode active material of the present invention is vigorously sintered and the pulverization / disintegration yield after firing is lowered, which may be industrially disadvantageous. Moreover, many defects such as oxygen deficiency are generated in the positive electrode active material of the present invention, leading to a decrease in battery capacity of a lithium secondary battery using the positive electrode active material of the present invention and deterioration due to collapse of the crystal structure due to charge / discharge. There is a fear.

Furthermore, the holding time in the maximum temperature holding step is usually selected from a wide range of 1 hour to 100 hours. Further, if the firing time is too short, it is difficult to obtain the positive electrode active material of the present invention having good crystallinity.
In the temperature lowering step, the temperature is usually decreased at a temperature decreasing rate of 0.1 ° C./min to 10 ° C./min. If it is too slow, it may take time and may be industrially disadvantageous, and if it is too fast, the uniformity of the target product may be insufficient, or the container tends to deteriorate.

Furthermore, various types of air, oxygen, nitrogen, argon, carbon dioxide, etc. can be used as the firing atmosphere, but the powder properties such as tap density vary depending on the firing atmosphere, so that the oxygen concentration of air or the like is 10 vol% to An atmosphere of 80% by volume is preferred. If the oxygen concentration is too high, the bulk density of the resulting lithium transition metal composite oxide may be reduced.
The lithium transition metal composite oxide obtained by firing is appropriately subjected to crushing and / or classification. Although the classification method is not particularly limited, when vibration classification through a mesh with a tapping ball is performed, the shape of the secondary particles may be disrupted, which may cause a large change in particle size distribution, pore distribution, and the like. Therefore, it is considered that a classification method that is not the force of hitting the mesh, for example, a method in which the fired powder on the mesh is pressed through the mesh and a method in which the cylindrical mesh is passed by the centrifugal force of the rotating blades are considered to be more preferable.

[2-4. Other processes]
Further, the above-described method for producing a lithium transition metal oxide of the present invention may include steps other than the above-described mixing (including pulverization), spray drying, and firing, as long as the effects of the present invention are not significantly impaired. .
For example, the obtained lithium transition metal composite oxide of the present invention may be used as it is as the positive electrode active material, or may be used after surface treatment. The surface treatment method is not limited, and any surface treatment can be performed as long as the effects of the present invention are not significantly impaired. Although there are various purposes and effects of the surface treatment, for example, the reactive sites on the surface of the positive electrode active material can be reduced, and elution of metal elements such as manganese can be suppressed. As a method used for this purpose, for example, a method in which a lithium transition metal composite oxide is surface-treated with an organosilicon compound such as a silane coupling agent (see, for example, JP-A-2002-83596) can be mentioned. Moreover, in order to improve the electroconductivity at the time of using as a positive electrode, the method (for example, Unexamined-Japanese-Patent No. 2003-137554) etc. which carry out the composite coating process of a carbon material mechanically etc. are mentioned.

[3. Positive electrode for lithium secondary battery]
The lithium transition metal composite oxide of the present invention described above is used as a positive electrode active material for the positive electrode for a lithium secondary battery of the present invention (hereinafter referred to as “the positive electrode of the present invention” as appropriate).
The positive electrode for a lithium secondary battery of the present invention includes a current collector (positive electrode current collector) and an active material layer (positive electrode active material layer) formed on the current collector. Moreover, as long as the effect of this invention is not impaired significantly, you may provide the other layer and member.

[3-1. Positive electrode current collector]
As a material of the positive electrode current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the current collector for the positive electrode include aluminum, nickel, and stainless steel. Among these, aluminum is preferable as the positive electrode current collector. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.
Furthermore, in order to improve the binding effect between the current collector and the active material layer formed on the surface, it is preferable that the surface of these current collectors is roughened in advance. Surface roughening methods include blasting or rolling with a rough surface roll, surface of the current collector with a wire brush equipped with abrasive cloth paper, grindstone, emery buff, steel wire, etc. with abrasive particles fixed Examples thereof include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.

  Further, the shape of the current collector is also arbitrary. For example, in order to reduce the weight of a lithium secondary battery using the positive electrode of the present invention, that is, to improve the energy density per weight, use a perforated current collector such as an expanded metal or a punching metal. You can also. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when an active material layer is formed on both sides of such a perforated current collector, the active material layer tends to be more difficult to peel off due to the rivet effect of the active material layer through the hole. If the rate is too high, the contact area between the active material layer and the current collector becomes small, so that the adhesive strength may be lowered.

  Further, when a thin film is used as the positive electrode current collector, its thickness is arbitrary, but it is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. If it is too thick, the capacity of the entire lithium secondary battery using the positive electrode of the present invention may be reduced. Conversely, if it is too thin, handling may be difficult.

[3-2. Positive electrode active material layer]
The positive electrode active material layer of the positive electrode of the present invention is a layer configured to contain the positive electrode active material of the present invention, and can have any known configuration as long as it contains the positive electrode active material of the present invention. In addition, the positive electrode active material of this invention contained in this positive electrode active material layer may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.
Moreover, the positive electrode active material layer of the positive electrode of the present invention can be used in combination with any positive electrode active material other than the positive electrode active material of the present invention as long as the effects of the present invention are not significantly impaired. The positive electrode active material used in combination is not limited as long as it can occlude / release lithium ions. For example, transition metal oxides such as Fe, Co, Ni, and Mn, transition metal and lithium Examples thereof include composite oxides and transition metal sulfides. In addition, the positive electrode active materials used in combination may be used alone or in combination of two or more in any combination and ratio. However, it is preferable that the ratio of the positive electrode active material of the present invention is large in the positive electrode active material layer of the positive electrode of the present invention.

Furthermore, the positive electrode active material layer usually contains a binder. This binder is for binding the positive electrode active material and holding it on the current collector.
Any binder can be used as long as the effects of the present invention are not significantly impaired. However, the binder is preferably selected in consideration of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Specific examples include inorganic compounds such as silicate and water glass, and organic compounds such as polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose. In addition, a binder may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  The positive electrode active material layer may contain various auxiliaries and the like. Examples of the auxiliary agent include a conductive agent that increases the conductivity of the electrode. The conductive agent is not particularly limited as long as it is capable of imparting conductivity by mixing an appropriate amount in the active material. For example, carbon powder such as natural graphite, artificial graphite, acetylene black, various metal fibers, foil, etc. Is mentioned. In addition, these adjuvants may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The proportion of the positive electrode active material in the positive electrode active material layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10% by weight or more, preferably 30% by weight or more, and usually 99.9% by weight. Hereinafter, it is preferably 99% by weight or less. If the amount of the positive electrode active material is too large, the strength of the positive electrode of the present invention tends to be insufficient. If the amount is too small, the capacity of the lithium secondary battery using the positive electrode of the present invention may be insufficient.

  Further, when the binder is contained in the positive electrode active material layer, the ratio of the binder in the positive electrode active material layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.1% by weight or more, preferably 1% by weight. In addition, it is usually 60% by weight or less, preferably 40% by weight or less. If the amount of the positive electrode active material is too large, the capacity of the lithium secondary battery using the positive electrode of the present invention may be insufficient. If the amount is too small, the strength of the positive electrode of the present invention may be insufficient.

  Furthermore, when the positive electrode active material layer contains a conductive agent, the proportion of the conductive agent in the positive electrode active material layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.1% by weight or more, preferably 1 It is usually not more than 50% by weight and preferably not more than 10% by weight. If the amount of the conductive agent is too large, the capacity of the lithium secondary battery using the positive electrode of the present invention may be insufficient. If the amount is too small, the electric conductivity of the lithium secondary battery using the positive electrode of the present invention will be poor. May be sufficient.

  The thickness of the positive electrode active material layer of the positive electrode of the present invention is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and usually 200 μm. Hereinafter, it is preferably 150 μm or less, more preferably 100 μm or less. If the positive electrode active material layer is too thin, not only is the uniformity of the positive electrode active material layer difficult to ensure, but the capacity of the lithium secondary battery using the positive electrode of the present invention may be small. On the other hand, if it is too thick, the rate characteristics of the lithium secondary battery using the positive electrode of the present invention may be lowered.

Furthermore, there is no restriction | limiting in the manufacturing method of the positive electrode of this invention, Well-known arbitrary methods can be used if the positive electrode active material layer mentioned above can be formed on a collector. For example, a method of forming the above-described constituent components of the positive electrode active material layer into a sheet shape, and pressure-bonding the same to a current collector; preparing a slurry containing the above-described constituent components, and applying this onto the current collector; The method of drying etc. are mentioned. In addition, the positive electrode 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 positive electrode active material.

  When the positive electrode active material layer is formed by coating and drying, a solvent capable of dissolving or dispersing the constituent components of the positive electrode active material layer can be arbitrarily used as a solvent for preparing the slurry to be applied. . As a specific example, either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, and examples of the organic solvent include N-methylpyrrolidone, tetrahydrofuran, dimethylformamide, and the like. In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

[4. Lithium secondary battery]
The positive electrode of the present invention is suitably used for the lithium secondary battery of the present invention.
The lithium secondary battery of the present invention comprises the positive electrode of the present invention, a negative electrode capable of inserting and extracting lithium, and an electrolyte containing a lithium salt. In addition, other members such as a separator may be provided as appropriate.
[4-1. Positive electrode]
The positive electrode of the present invention described above is used as the positive electrode of the lithium secondary battery of the present invention.
[4-2. Negative electrode]
As the negative electrode, a known negative electrode capable of inserting and extracting lithium can be arbitrarily used. For example, a metal foil such as lithium metal or a lithium alloy such as a lithium-aluminum alloy can be used. Usually, as in the case of the positive electrode, an active material layer (negative electrode) is formed on the current collector (negative electrode current collector). It is preferable to use a negative electrode provided with an active material layer. Similarly to the positive electrode, the negative electrode may include other layers and members as long as the effects of the present invention are not significantly impaired.

[4-2-1. Negative electrode current collector]
As a material of the negative electrode current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the negative electrode current collector include copper, nickel, and stainless steel. Among these, copper is preferable as the current collector for the negative electrode. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.
The negative electrode current collector is also preferably subjected to a roughening treatment in advance, as with the positive electrode current collector.
Further, like the positive electrode, the shape of the current collector is also arbitrary, and a perforated current collector such as expanded metal or punching metal can also be used. Moreover, the preferable thickness when using a thin film as a current collector is the same as that of the positive electrode.

[4-2-2. Negative electrode active material layer]
The negative electrode active material layer is a layer configured to contain a negative electrode active material.
The negative electrode active material is not particularly limited as long as it is a material capable of inserting and extracting lithium ions, and a known negative electrode active material can be arbitrarily used. However, it is usually preferable to use a carbon material as the negative electrode active material. Examples of the carbon material include natural graphite and pyrolytic carbon. In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The negative electrode active material layer usually contains the above-described negative electrode active material, a binder, and various auxiliary agents as necessary, as in the case of the positive electrode active material layer. Specific examples of the binder and auxiliary agent are the same as those for the positive electrode active material layer. Moreover, the manufacturing method is the same as that of the positive electrode active material layer.

[4-3. Electrolyte]
The electrolyte is not particularly limited as long as it is an electrolyte containing a lithium salt, and a known electrolyte can be arbitrarily used. For example, an electrolytic solution, a solid electrolyte, a gel electrolyte, and the like can be mentioned, among which an electrolytic solution is preferable, and a nonaqueous electrolytic solution is more preferable.
Examples of the nonaqueous electrolytic solution include those obtained by dissolving various electrolytic salts in a nonaqueous solvent. Examples of the electrolytic salt include lithium salts such as LiCiO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiBr, and LiCF ₃ SO ₃ . Examples of the non-aqueous solvent include tetrahydrofuran, 1,4-dioxane, dimethylformamide, acetonitrile, benzonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and the like. In addition, each of these electrolytic salts and non-aqueous solvents may be used alone or in combination of two or more in any combination and ratio.

[4-4. Separator]
Usually, a separator is interposed between the positive electrode and the negative electrode in order to prevent a short circuit. The material and shape of the separator are not particularly limited, and any separator can be used as long as the effects of the present invention are not significantly impaired. However, the separator is stable with respect to the above non-aqueous electrolyte, has excellent liquid retention, and has an electrode. Those that can reliably prevent short-circuiting between them are preferable.
Examples of the separator include a microporous polymer film made of a polymer such as polytetrafluoroethylene, polyethylene, polypropylene, and polyester, a non-woven filter such as glass fiber, and a composite non-woven filter made of glass fiber and polymer fiber. Can be mentioned.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, In the range which does not deviate from the summary of this invention, it can change arbitrarily and can implement.
Example 1
Li ₂ CO ₃ , Ni (OH) ₂ , Mn ₃ O ₄ , CoOOH, WO ₃ are changed to Li: Ni: Mn: Co = 1.05: 0.33: 0.33: 0.33: 0.005 (mol) Ratio) and pure water was added thereto to prepare a slurry having a solid concentration of 18% by weight. After pulverizing using a circulating medium agitation type wet pulverizer until the average particle size of the solid content in the slurry is 0.3 μm, spray drying is performed using a two-fluid nozzle type spray dryer, and the average particle size is about A 6 μm particulate lithium transition metal composite oxide precursor was obtained.

  About 10 g of the powder obtained as described above is placed in an alumina crucible having a diameter of about 5 cm, and placed in an atmosphere firing furnace that can be fired while circulating air and nitrogen, and air at a flow rate of 1 L / min is circulated. The temperature was increased to a maximum temperature of 1000 ° C. at a rate of temperature increase of 3.3 ° C./min, held at 1000 ° C. for 6 hours, and then decreased at a rate of temperature decrease of 3.3 ° C./min. Lithium transition metal composite oxide was obtained.

This lithium nickel manganese composite oxide was confirmed to be a single phase having a layered structure by a powder X-ray diffraction pattern. In addition, the powder X-ray diffraction pattern was performed with the following apparatus and conditions.
[Powder X-ray diffraction measurement device] PANalytical PW1700
[Measurement conditions] X-ray output: 40 kV, 30 mA, scanning axis: θ / 2θ
Scanning range (2θ): 10.0-90.0 °
Measurement mode: Continuous
Reading width: 0.05 °, scanning speed: 3.0 ° / min.
Slit: DS 1 °, SS 1 °, RS 0.2mm
The median diameter was 5.2 μm. The median diameter is determined by a laser diffraction / scattering type particle size distribution measuring device, a real part 1.60 and an imaginary part 0.10 are set as a complex refractive index, and a 0.1% by weight sodium hexametaphosphate aqueous solution is used as a dispersion medium. The measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

About 5 g of the obtained lithium transition metal composite oxide was put in a 10 ml glass graduated cylinder, and the powder packing density (tap density) after tapping 200 times was measured. As a result, it was 1.1 g / cm ³ .
The BET specific surface area of this composite oxide was 1.8 m ² / g as a result of measurement using “AMS8000 type fully automatic powder specific surface area measuring device” manufactured by Okura Riken.
As a result of obtaining a pore distribution curve by a mercury intrusion method for the obtained lithium transition metal composite oxide, the main peak top was 1.2 μm and the sub peak top was 0.5 μm.
A lithium secondary battery was produced using the obtained lithium nickel manganese composite oxide and evaluated. The results are shown in Table-1.

Comparative Example 1
LiOH, NiO, Mn ₃ O ₄ , and CoOOH were mixed so that Li: Ni: Mn: Co = 0.05: 0.33: 0.33: 0.33 (molar ratio), and pure water was added thereto. In addition, a slurry having a solid content of 18% by weight was prepared. After pulverizing using a circulating medium agitation type wet pulverizer until the average particle size of the solid content in the slurry is 0.3 μm, spray drying is performed using a two-fluid nozzle type spray dryer, and the average particle size is about A 6 μm particulate lithium transition metal composite oxide precursor was obtained. LiOH having a median diameter of about 3 μm was mixed with the obtained precursor so that Li: (Ni + Mn + Co) = 1: 1, and fired in the same manner as in Example 1 to obtain a lithium transition metal composite oxide. It was. The average particle size was 5.5 μm, the tap density was 1.6 g / cm ³ , and the specific surface area was 0.9 m ² / g. As a result of obtaining a pore distribution curve by mercury porosimetry, the main peak top was 1.2 μm, and the sub peak top was 0.2 μm.

Comparative Example 2
A composition similar to that of Example 1 was synthesized by a coprecipitation method. Ni (Mn: Co = 0.33: 0.33: 0.33) is obtained from Ni (NO ₃ ) ₂ .6H ₂ O, Mn (NO ₃ ) ₂ .6H ₂ O, Co (NO ₃ ) ₂ .6H ₂ O. (Molar ratio) was weighed, and pure water was added to prepare a 2 mol / l solution. A 5.4 mol / l aqueous NaOH solution was gradually added thereto to obtain a coprecipitated hydroxide having a molar ratio composition in which Ni, Mn and Co were almost charged. The obtained coprecipitated hydroxide was sufficiently washed and dried, and LiOH having a median diameter of about 3 μm and WO ₃ were changed to Li: Ni: Mn: Co: W = 1.05: 0.33: 0.33: 0.33. : 0.005 (molar ratio) was mixed and fired in the same manner as in Example 1 to obtain a lithium transition metal composite oxide. The average particle size was 6.5 μm, the tap density was 2.3 g / cm ³ , and the specific surface area was 0.7 m ² / g. Further, as a result of obtaining a pore distribution curve by a mercury intrusion method, the main peak top was 1.2 μm and there was no sub peak.
A lithium secondary battery was prepared using the obtained lithium nickel manganese composite oxide, and evaluated with the following capacity.

<Example of battery evaluation test>
A. Production of positive electrode, capacity confirmation and rate test The lithium transition metal composite oxide obtained in Example 1 and Comparative Examples 1 to 6 was 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene powder 5% by weight. The weighed ones were thoroughly mixed in a mortar, and the ones made into thin sheets were punched out using 9 mmφ and 12 mmφ punches. At this time, the total weight was adjusted to about 8 mg and about 18 mg, respectively. This was crimped to Al expanded metal to obtain a positive electrode.

The positive electrode punched out to 9 mmφ was used as a test electrode, and a coin cell was assembled using Li metal as a counter electrode. This is followed by a constant current charge of 0.2 mA / cm ² , that is, a reaction for releasing lithium ions from the positive electrode at an upper limit of 4.2 V, and then a constant current discharge of 0.2 mA / cm ² , that is, occlusion of lithium ions in the positive electrode. The initial charge capacity per unit weight of the positive electrode active material when the reaction is performed at the lower limit of 3.0 V is Qs (C) [mAh / g], the initial discharge capacity is Qs (D) [mAh / g], and then the current value The constant current discharge capacity of ₁₁ mA / cm ² was set to Qs ₁₁ (D) [mAh / g], and the numerical values were compared.

B. Production of negative electrode and capacity confirmation Graphite powder (d002 = 3.35Å) having an average particle diameter of about 8 to 10 μm as a negative electrode active material and polyvinylidene fluoride as a binder in a ratio of 92.5: 7.5 by weight And weighed the mixture in an N-methylpyrrolidone solution to obtain a negative electrode mixture slurry. The slurry was applied to one side of a 20 μm thick copper foil, dried to evaporate the solvent, punched to 12 mmφ, and pressed at 0.5 ton / cm 2 to form a negative electrode.
In addition, the negative electrode active material unit weight when the negative electrode was used as a test electrode, a battery cell was assembled using Li metal as a counter electrode, and a test for occluding Li ions in the negative electrode at a constant current of 0.5 mA / cm ² was performed at a lower limit of 0 V. The initial storage capacity per unit was Qf [mAh / g].

C. Assembling the coin cell The battery performance was evaluated using a coin-type cell. That is, a positive electrode is placed on a positive electrode can, a porous polyethylene film having a thickness of 25 μm is placed thereon as a separator, pressed with a polypropylene gasket, a negative electrode is placed, and a spacer for adjusting the thickness is placed. As a water electrolyte solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 in which 1 mol / L lithium hexafluorophosphate (LiPF ₆ ) was dissolved was used as the electrolyte solution. This was added to the battery and sufficiently impregnated, and then the negative electrode can was placed to seal the battery. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material is almost the same.

(Equation 2)
Positive electrode active material weight [g] / Negative electrode active material weight [g] = (Qf [mAh / g] /1.2) / Qs (C) [mAh / g]
It set so that it might become.

D. Room temperature resistance measurement For the obtained coin cell, the conditioning current value I [mA] = {Qs (D) [mAh / g]} represented by the following formula 3 × charge active material weight M [g] / 5 4.1V
In addition, initial conditioning of 2 cycles of charge and discharge is performed with a discharge lower limit voltage of 3.0 V, and the discharge capacity Qs ₂ (D) [mAh per unit weight of positive electrode active material in the second cycle at that time
/ G] was measured.
Subsequently, after sufficiently relaxing the battery in a low temperature atmosphere of −30 ° C., 1 hour rate current value, 1 C [mA] = Qs ₂ (D) [mAh / g] × positive electrode active material weight M [g] Constant current 1 / 3C [m
A] was adjusted to a charging depth of 40%, and then discharging was performed at a constant current of 0.25 C for 10 seconds. At this time, the voltage after 10 seconds of discharge is V [mV], the voltage before discharge is V ₀ [mV], and the difference ΔV [mV] = V [mV] −V ₀ [mV] is calculated. Resistance R [using current 0.25 C [mA]
Ω] = ΔV [mV] /0.25 C [mA]. The smaller the resistance R [Ω], the better the output characteristics at a low temperature and the more advantageous for rapid discharge.

In Table 1, 0.2 mA / cm ² charge / discharge capacity, 11 mA / cm ² discharge capacity, low temperature resistance value of the counter electrode Li of the lithium transition metal composite oxide obtained in Example 1 and Comparative Examples 1 and ² , Main peak top and sub-peak top are shown respectively.
From Table 1, the lithium transition metal composite oxide obtained in the Examples has a low resistance value R and exhibits good low-temperature output characteristics. On the other hand, the lithium transition metal composite oxide obtained in Comparative Example 1 has a sub peak of 0.08 μm or more and 1 μm or less, but does not contain tungsten, so has a high resistance value R and poor low-temperature output characteristics. I understand that. In addition, the lithium transition metal composite oxide obtained in Comparative Example 2 has a sub-peak, that is, a morphology that does not have pores in the secondary particles, which is disadvantageous for the diffusion of lithium ions. The characteristics are bad and the resistance value R is not as good as that of the first embodiment. Therefore, having sufficient pores in the secondary particles and containing tungsten is an important point for obtaining a lithium transition metal composite oxide having excellent battery characteristics, and could not be achieved conventionally. Technology.

Claims (7)

A lithium transition metal composite oxide composed of primary particles and / or secondary particles obtained by agglomerating them, wherein the lithium transition metal composite oxide is represented by the following general formula (1), and is a mercury intrusion method: The obtained pore distribution curve of the secondary particles has a main peak top at a pore radius greater than 1 μm and 50 μm or less, and a sub-peak top at a pore radius of 0.08 μm or more and 1 μm or less. , Lithium transition metal composite oxide. (Chemical formula 1)
Li _x Ni _α Mn _β Co _γ Q _δ W _Y O ₂ (1)
(Wherein Q is at least one element selected from Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca and Mo) 0.2 ≦ α ≦ 0.6, 0.2 ≦ β ≦ 0.6, 0 ≦ γ ≦ 0.5, 0 ≦ δ ≦ 0.1, 0.8 ≦ α + β + γ + δ ≦ 1.2, 0 The number satisfying the relationship of <x ≦ 1.2 and 0 <Y ≦ 0.1 is shown.) The lithium transition metal composite oxide according to claim 1, wherein the specific surface area is 0.1 m ² / g or more and 8 m ² / g or less. The lithium transition metal composite oxide according to claim 1 or 2, wherein the tap density is 0.8 g / cm ³ or more and 3.0 g / cm ³ or less. 4. The lithium transition metal composite oxide according to claim 1, wherein the median diameter of secondary particles constituting the lithium transition metal composite oxide is 1 μm or more and 20 μm or less. 5.   The positive electrode for lithium secondary batteries containing the lithium transition metal complex oxide in any one of Claim 1 to 4.   A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 5, a negative electrode, and an electrolyte. A method for producing a lithium transition metal composite oxide comprising wet pulverizing and mixing raw material compounds in a liquid medium, followed by spray drying and firing, wherein the lithium transition metal composite oxide comprises primary particles and / or In the lithium transition metal composite oxide composed of secondary particles formed by agglomeration, a lithium transition metal composite oxide represented by the following general formula (1),
In the pore distribution curve of the secondary particles obtained by the mercury intrusion method, the main peak top has a pore radius greater than 1 μm and not more than 50 μm, and the sub-peak top has a pore radius of 0.08 μm to 1 μm. A process for producing a lithium transition metal composite oxide, characterized in that
(Chemical formula 2)
Li _x Ni _α Mn _β Co _γ Q _δ W _Y O ₂ (1)
(Wherein Q is at least one element selected from Al, Fe, Ga, Sn, V, Cr, Cu, Zn, Mg, Ti, Ge, B, Bi, Nb, Ta, Mo, Zr, Ca and Mo) 0.2 ≦ α ≦ 0.6, 0.2 ≦ β ≦ 0.6, 0 ≦ γ ≦ 0.5, 0 ≦ δ ≦ 0.1, 0.8 ≦ α + β + γ + δ ≦ 1.2, 0 The number satisfying the relationship of <x ≦ 1.2 and 0 <Y ≦ 0.1 is shown.)