JP2006278031A - Manufacturing method of cathode material for lithium secondary battery and cathode material for lithium secondary battery as well as cathode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a cathode material for a lithium secondary battery capable of surely making classification treatment in a short time, even for baked powder with clinging properties. <P>SOLUTION: A process of classification treatment is carried out by using a classifying machine sifting out baked powder obtained by mixing, granulating, baking, and shredding raw materials as needed, by pressing down the powder on a mesh screen with a high-speed rotating blade and letting it. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a positive electrode material for a lithium secondary battery, a positive electrode material for a lithium secondary battery, and a positive electrode for a lithium secondary battery and a lithium secondary battery using the same. Specifically, a method for producing a positive electrode material for a lithium secondary battery capable of classifying a fired powder at a high processing speed, a positive electrode material for a lithium secondary battery obtained by the method, and a positive electrode material for this lithium secondary battery The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery.

  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, as a positive electrode active material of a lithium secondary battery, a lithium transition metal composite oxide whose standard composition is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like has been used. Furthermore, from the viewpoint of safety and raw material cost, a lithium transition metal composite oxide having the same layered structure as LiCoO ₂ and LiNiO ₂ and in which a part of the transition metal is substituted with manganese or the like, specifically, LiNiO ₂ Attention has been drawn to LiNi _1-x Mn _x O ₂ in which part of the Ni site is substituted with Mn, and LiNi _1-xy Mn _x Co _y O _{2 in} which part of the Ni site is substituted with Mn and Co (for example, Patent Document 1, Non-Patent Documents 1-3).

JP 2003-17052 A Journal of Materials Chemistry, Vol. 6, 1996, p. 1149 Journal of The Electrochemical Society, Vol. 145, 1998, p. 1113 Proceedings of the 41st Battery Symposium, 2000, p. 460

  In the above-described conventional method for producing a lithium transition metal composite oxide, a vibration sieve is used for classifying powders such as lithium transition metal composite oxide obtained by firing (hereinafter referred to as “fired powder” as appropriate). (Sometimes a ball is also used), and hand sieves have been used.

However, particularly when there is a property of being easily clumped as particles, there is a problem that a sieve or the like is clogged at the time of classification or a lump is easily generated. This tendency is particularly observed in LiNi _1-xy Mn _x Co _y O ₂ where Ni: Mn: Co is (1-yz): y: z (0.05 ≦ y ≦ 0.5, 0.05 ≦ This is remarkable in the lithium transition metal composite oxide powder having a composition in the vicinity of z ≦ 0.5). In such a case, there is a problem that the time required for the classification process becomes long or the classification cannot be performed in some cases.

  From the above background, when the fired powder is classified in the production of a positive electrode material for a lithium secondary battery, the classification process can be performed reliably in a short time even when the fired powder has a tendency to cling. Technology was sought.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a method for producing a positive electrode material for a lithium secondary battery and a lithium secondary battery capable of reliably classifying a fired powder having properties such as being easy to cling in a short time. It is providing the positive electrode material for lithium, and the positive electrode for lithium secondary batteries and lithium secondary battery using the same.

  As a result of intensive studies, the inventors of the present invention have made the powder press against the mesh screen with a blade that rotates at high speed when classifying the fired powder in the production of a positive electrode material for a lithium secondary battery. By classifying using a classifier that sifts through, it is possible to perform classification processing in a short time even for fired powders that are easy to cling, etc., and positive electrodes for lithium secondary batteries efficiently. The inventors have found that a material can be produced and have completed the present invention.

  That is, the gist of the present invention is a method for producing a positive electrode material for a lithium secondary battery, in which raw materials are mixed, granulated, fired, and baked powder obtained by pulverization as necessary. A method for producing a positive electrode material for a lithium secondary battery, comprising a step of classifying using a classifier that screens powder by pressing it against a mesh screen with a blade rotating at high speed, (Claim 1).

Here, it is preferable that the fired powder is a powder having an angle of repose measured by the following measurement method of 50 degrees or more.
[Measurement of repose angle]
(1) A standard sieve is vibrated, and powder is supplied onto a circular table through a funnel. However, the sieve frequency is 3600 times / minute, the sieve vibration width is 2 mm, the sieve time is 4 minutes, and the funnel diameter is 8 mm.
(2) The angle of repose of the powder is measured. However, the measurement is performed using an angle calculation method (least square method) using a semiconductor laser (wavelength 670 nm) displacement sensor, and the minimum reading resolution is 0.1 degree.

（式（II）中、Ｑは、Ｆｅ、Ｃｒ、Ｖ、Ｔｉ、Ｃｕ、Ｇａ、Ｂｉ、Ｓｎ、Ｚｎ、Ｍｇ、Ｇｅ、Ｎｂ、Ｔａ、Ｂｅ、Ｃａ、Ｓｃ、Ａｌ、Ｂ、及びＺｒよりなる群から選択される少なくとも１種の元素を表わし、ｘは、０．７≦ｘ≦１．３の数を表わし、ａは、０．２≦ａ≦０．８の数を表わし、ｂは、０．２≦ｂ≦０．８の数を表わし、ｃは、０．１５≦ｃ≦０．４の数を表わし、ｄは、０≦ｄ≦０．４の数を表わし、但し、ａ＋ｂ＋ｃ＋ｄ＝１であり、δは、−０．１＜δ＜０．１の数を表わす。） Moreover, it is preferable that the said positive electrode material has a composition represented by following formula (II).

(In the formula (II), Q is composed of Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, Ca, Sc, Al, B, and Zr. Represents at least one element selected from the group, x represents a number 0.7 ≦ x ≦ 1.3, a represents a number 0.2 ≦ a ≦ 0.8, and b represents Represents a number of 0.2 ≦ b ≦ 0.8, c represents a number of 0.15 ≦ c ≦ 0.4, d represents a number of 0 ≦ d ≦ 0.4, provided that a + b + c + d = 1 and δ represents a number of −0.1 <δ <0.1.)

  Also, when the tap density (after 1 mm) of the fired powder before the classification treatment is A and the tap density of the positive electrode material after the classification treatment is B, (B / A) ≧ 1.05 (Claim 4).

  Further, when C is the median diameter (after passing through 1 mm) of the fired powder before classification treatment and D is the median diameter of the positive electrode material after classification treatment, (D / C) ≦ 0.8 (Claim 5).

  Another gist of the present invention resides in a positive electrode material for a lithium secondary battery, characterized in that the positive electrode material is manufactured by a method for manufacturing a positive electrode material for a lithium secondary battery.

  Another subject matter of the present invention lies in a positive electrode for a lithium secondary battery, which is a positive electrode used for a lithium secondary battery and contains the above-described positive electrode material for a lithium secondary battery (claim). Item 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. The present invention resides in a lithium secondary battery, which is a positive electrode for a lithium secondary battery.

  According to the method for producing a positive electrode material for a lithium secondary battery of the present invention, it becomes possible to reliably classify a fired powder having properties such as being easy to cling in a short time. The production efficiency of materials can be increased.

  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.

  In the following description, for the convenience of explanation, first, a positive electrode material for a lithium secondary battery obtained by the method for producing a positive electrode material for a lithium secondary battery of the present invention (this will be referred to as “the positive electrode material of the present invention” as appropriate) will be described. Subsequently, a method for producing a positive electrode material for a lithium secondary battery of the present invention (this will be referred to as “the production method of the present invention” as appropriate) will be described.

[I. Positive electrode material for lithium secondary battery]
〔composition〕
The composition of the positive electrode material of the present invention is not particularly limited and can be appropriately selected from those known to function as a positive electrode active material of a lithium secondary battery. Powder is preferred. Preferable examples of the lithium transition metal composite oxide powder include transition metal composite oxide powders using nickel compounds, cobalt compounds, manganese compounds and the like as raw materials. Particularly preferred is a layered nickel manganese cobalt composite oxide powder.

  Specifically, the positive electrode material of the present invention is preferably a lithium transition metal composite oxide having a composition represented by the following formula (I).

前記式（Ｉ）中、ｘは、０．５≦ｘ≦１．３の数を表わし、Ｍは、遷移金属から選ばれる少なくとも１種の元素を表わし、δは、−０．１＜δ＜０．１の数を表わす。

In the formula (I), x represents a number of 0.5 ≦ x ≦ 1.3, M represents at least one element selected from transition metals, and δ represents −0.1 <δ <. Represents a number of 0.1.

  Among these, the positive electrode material of the present invention is more preferably a lithium nickel manganese cobalt composite oxide having a composition represented by the following formula (II). The positive electrode material having the composition represented by the following formula (II) often has a property that is easy to cling, and cannot be classified by a normal method, or even if it can be classified, it takes a very long time. The effect obtained by doing is also great.

（式（II）中、Ｑは、Ｆｅ、Ｃｒ、Ｖ、Ｔｉ、Ｃｕ、Ｇａ、Ｂｉ、Ｓｎ、Ｚｎ、Ｍｇ、Ｇｅ、Ｎｂ、Ｔａ、Ｂｅ、Ｃａ、Ｓｃ、Ａｌ、Ｂ、及びＺｒよりなる群から選択される少なくとも１種の元素を表わし、ｘは、０．７≦ｘ≦１．３の数を表わし、ａは、０．２≦ａ≦０．８の数を表わし、ｂは、０．２≦ｂ≦０．８の数を表わし、ｃは、０．１５≦ｃ≦０．４の数を表わし、ｄは、０≦ｄ≦０．４の数を表わし、但し、ａ＋ｂ＋ｃ＋ｄ＝１であり、δは、−０．１＜δ＜０．１の数を表わす。）

(In the formula (II), Q is composed of Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, Ca, Sc, Al, B, and Zr. Represents at least one element selected from the group, x represents a number 0.7 ≦ x ≦ 1.3, a represents a number 0.2 ≦ a ≦ 0.8, and b represents Represents a number of 0.2 ≦ b ≦ 0.8, c represents a number of 0.15 ≦ c ≦ 0.4, d represents a number of 0 ≦ d ≦ 0.4, provided that a + b + c + d = 1 and δ represents a number of −0.1 <δ <0.1.)

  In the above formula (II), x is a number representing the atomic ratio of lithium, and the range is usually 0.7 ≦ x ≦ 1.3, preferably 0.9 ≦ x ≦ 1.2. is there. If x is too large, the battery capacity of the obtained lithium secondary battery may be reduced.

  In the above formula (II), a is a number representing the atomic ratio of nickel, and the range thereof is usually in the range of 0.2 ≦ a ≦ 0.8, preferably in the range of 0.2 ≦ a ≦ 0.4. is there.

  In the above formula (II), b is a number representing the atomic ratio of manganese, and the range is usually in the range of 0.2 ≦ b ≦ 0.8, preferably in the range of 0.2 ≦ b ≦ 0.4. is there.

  In the above formula (II), c is a number representing the atomic ratio of cobalt, and the range is usually in the range of 0.15 ≦ c ≦ 0.4, preferably in the range of 0.2 ≦ c ≦ 0.4. is there.

  When the values of a and b are above the specified range or the value of c is below the specified value and the proportion of cobalt is relatively small, the single-phase lithium nickel manganese cobalt composite oxide Tends to be difficult to synthesize, leading to a decrease in rate. On the other hand, if the values of a and b are below the specified range, or the value of c is higher than the specified value, and the proportion of cobalt is relatively large, the overall cost increases. .

  The atomic ratio of nickel, manganese, and cobalt is such that Ni / Mn / Co = 1 / in the triangular diagram of Ni, Mn, and Co from the viewpoint that the layered crystal structure exists stably and does not deteriorate the battery characteristics. What exists in the periphery of 1/1 and the line of Ni / Mn = 1/1 and its periphery is preferable.

  Therefore, in the above formula (II), it is preferable that the value of a and the value of b are substantially the same value. Specifically, the value of a / b is usually 0.8 or more, particularly 0.9 or more. Further, it is preferably 0.93 or more, particularly 0.95 or more, and usually 1.2 or less, particularly 1.1 or less, more preferably 1.07 or less, particularly 1.05 or less.

  Furthermore, in the above formula (II), it is preferable that the values of a, b and c are substantially the same number. Specifically, the value of a / c is usually 0.8 or more, particularly 0.9 or more. Further, it is preferably 0.93 or more, particularly 0.95 or more, and usually 1.2 or less, particularly 1.1 or less, more preferably 1.07 or less, and particularly preferably 1.05 or less.

  In addition, for the purpose of stabilizing the crystal structure of the positive electrode material, increasing the capacity, improving safety, improving battery characteristics at high temperatures, etc., some of the nickel, manganese, and cobalt sites may be replaced with other metal elements. It is also possible to perform surface treatment.

  In the above formula (II), Q represents such a substitution element or surface treatment element. Specifically, Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, It is at least one element selected from Ta, Be, Ca, Sc, Al, B and Zr.

  As the substitution element, various elements exemplified above can be used, among which metal elements such as aluminum, magnesium and iron are preferable, and aluminum and magnesium are more preferable. Aluminum and magnesium have the advantage that they can be easily dissolved in the layered lithium nickel manganese cobalt composite oxide to obtain a single phase, and further have high performance battery characteristics as a positive electrode active material for lithium secondary batteries. In particular, there is an advantage that good performance is exhibited with respect to the discharge capacity retention rate when repeated charge / discharge is performed.

  On the other hand, as the surface treatment element, various elements exemplified above can be used, and preferably boron, bismuth, zirconia, silicon and the like can be mentioned. These are not easily dissolved in lithium transition metal composite oxides, promote the growth of primary particles, increase the sintering strength between the primary particles in the secondary particles, and suppress the high activity point. Longer life can be achieved in characteristics.

  In addition, any one of these substitution elements / surface treatment elements Q may be used alone, or a plurality of these may be used in any combination and ratio.

  The atomic ratio d of the substitution element / surface treatment element Q to the total of nickel, manganese, and cobalt is usually 0 or more, and usually 0.4 or less, preferably 0.3 or less, more preferably 0.2 or less. It is. If this substitution ratio is too large, the capacity tends to decrease and the resistance increases when used as a positive electrode active material.

  In the composition of the above formula (II), the amount of oxygen may have some non-stoichiometry. Specifically, in the above formula (II), δ is a number satisfying −0.1 <δ <0.1, preferably −0.05 <δ <0.05, more preferably −0. The range is 025 <δ <0.025. Even if δ is small or large, the stabilization of the crystal structure is disturbed, and there is a possibility that the battery capacity of the obtained lithium secondary battery may be reduced or the battery life may be deteriorated.

[Angle of repose]
The positive electrode material of the present invention preferably has an angle of repose of 50 degrees or more. Here, the “repose angle” is an inclination angle formed between the horizontal plane and a conical sedimentary layer formed by gently dropping the powder from above. The angle of repose is an index representing the adhesive force between the powder particles, and the powder particles having a larger value of the angle of repose have a property of being more cohesive and less fluid, that is, having a tendency to cling.

  Examples of the positive electrode material having a property that can be easily fixed include a positive electrode material having a composition represented by the formula (II). Among them, the positive electrode material in which a, b, and c in the formula (II) are in the ranges of 0.2 ≦ a ≦ 0.4, 0.2 ≦ b ≦ 0.4, and 0.2 ≦ c ≦ 0.4, respectively. However, it has a property that is particularly easy to cling to.

  Specifically, the repose angle of the positive electrode material of the present invention is usually 50 degrees or more as described above, but it is preferable that the repose angle is in the range of 54 degrees or more, and more preferably 58 degrees or more. If the angle of repose is less than this range, it is difficult to obtain the effect of classification treatment in the production method of the present invention described later. On the other hand, the upper limit is usually 84 degrees or less, preferably 80 degrees or less, and more preferably 70 degrees or less. If the angle of repose exceeds this range, classification may not be possible.

In this specification, the “rest angle” of the positive electrode material is a value measured by the following method (injection method).
[Measurement of repose angle]
(1) A standard sieve is vibrated, and powder is supplied onto a table (usually a circular table) through a funnel. However, the sieve frequency is 3600 times / minute, the sieve vibration width is 2 mm, the sieve time is 4 minutes, and the funnel diameter is 8 mm.
(2) The angle of repose of the powder is measured. However, the measurement is performed using an angle calculation method (least square method) using a semiconductor laser (wavelength 670 nm) displacement sensor, and the minimum reading resolution is 0.1 degree.
Note that any known device can be used as the measuring device. An example is a powder tester (PT-R) manufactured by Hosokawa Micron.

(Particle shape)
The positive electrode material of the present invention may exist as primary crystal particles or secondary particles formed by aggregation of primary crystal particles, but in the present invention, primary crystal particles aggregate to form secondary particles. Are preferred.

[Tap density]
The tap density of the positive electrode material of the present invention (bulk density) is usually 1.55 g / cm ³ or higher, preferably 1.6 g / cm ³ or more, more preferably 1.65 g / cm ³ or more, and most preferably 1.7g / Cm ³ or more, and can be optimized according to the composition ratio and elements contained.

  If the secondary particles of the positive electrode material have many point sinterings and form a tufted or beaded tertiary particle structure, the tap density decreases. If the tap density of the positive electrode material is lower than the above range, the amount of the dispersion medium required at the time of coating is increased, the necessary amount of the conductive material and the binder is increased, and the active material filling rate in the positive electrode active material layer is increased. There is a risk that the battery capacity may be limited.

  As the positive electrode material having a high tap density, for example, a spherical material composed of secondary particles obtained by closely sintering primary particles and having a relatively smooth surface of the secondary particles can be given. Since most of the positive electrode active material layer is usually made of a positive electrode material such as a lithium transition metal composite oxide powder, a high-density positive electrode active material layer is formed by using a positive electrode material having a high tap density as the positive electrode active material. Can be formed.

However, if the tap density of the positive electrode material is too large, the diffusion of lithium ions using the electrolytic solution as a medium in the positive electrode active material layer becomes rate-determining, and the load characteristics may be easily lowered. The upper limit is usually 2.4 g / cm ³ or less, preferably 2.2 g / cm ³ or less.

In this specification, the “tap density” of the positive electrode material refers to a value obtained by the following method.
For example, using a tap denser (KYT-4000) manufactured by Seishin Corporation, about 70 g of the positive electrode material is put into a 100 ml graduated cylinder, the tapping operation is performed with a stroke length of 20 mm, and the number of taps of 3000 times. The volume (V). The tare weight of the graduated cylinder is subtracted from the total weight, the net weight (W) of the powder is measured, and the value calculated by the following formula (A) is defined as the tap density.
Tap density (g / ml) = W (g) / V (ml) (A)

[Median diameter]
The median diameter of the positive electrode material of the present invention is usually in the range of 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more, and usually 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less. When the lower limit is not reached, the tap density is difficult to increase, and when the upper limit is exceeded, the specific surface area becomes small and the contact with the electrolytic solution tends to be poor.

  In this specification, the “median diameter” of the positive electrode material is a value measured by a known laser diffraction / scattering type particle size distribution measuring apparatus 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). In addition, since the aggregation of the positive electrode material is solved when it is dispersed with an ultrasonic oscillator in a solvent, in order to use it as an index of the degree of aggregation, the dispersion treatment with the ultrasonic oscillator is performed after the measurement sample is put into the dispersion medium. Measure without doing it.

[Maximum particle size]
The maximum particle size of the positive electrode material of the present invention is usually 40 μm or less, preferably 35 μm or less. If the maximum particle size exceeds this upper limit, streaks are likely to occur during coating film creation.

  In the present specification, the “maximum particle size” of the positive electrode material 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.

〔Specific surface area〕
The specific surface area (specific surface area of secondary particles) in the BET method of the positive electrode material of the present invention varies greatly depending on the composition ratio and contained elements, but is usually 0.5 m ² / g or more, preferably 0.6 m ² / g or more. More preferably, it is 0.7 m ² / g or more. If the specific surface area is smaller than this lower limit, it means that the primary particle size is large, that is, the rate characteristics and the capacity tend to decrease, which is not preferable. In addition, even if the specific surface area is too large, the amount of the required dispersion medium increases at the time of coating, and the necessary amount of conductive material and binder increases, which limits the filling rate of the active material into the positive electrode plate, and the battery Since the capacity is restricted, it is usually 1.5 m ² / g or less, preferably 1.4 m ² / g or less, more preferably 1.3 m ² / g or less.

  In the present specification, the “specific surface area” of the positive electrode material refers to a value measured by a known BET type powder specific surface area measuring device. Specifically, nitrogen is used as an adsorption gas and helium is used as a carrier gas, and BET one-point measurement is performed by a continuous flow method. First, a powder sample is heated and deaerated with a mixed gas at a temperature of 450 ° C. or lower, and then cooled to liquid nitrogen temperature to adsorb the mixed gas. This is heated to room temperature with water and the adsorbed nitrogen gas is desorbed, the amount is detected by a thermal conductivity detector, and the specific surface area of the sample is calculated therefrom.

[II. Method for producing positive electrode material for lithium secondary battery]
The method for producing a positive electrode material for a lithium secondary battery according to the present invention is obtained by mixing raw materials, granulating, firing, and pulverizing the powder as necessary using a blade that rotates at high speed. It is characterized by comprising a step of classifying using a classifier that sifts by pressing the mesh onto a mesh screen.

  In the following description, the case of producing a lithium transition metal composite oxide powder as a positive electrode material will be described as an example. However, the production method of the present invention is not limited to this example, and the production includes the above-described classification step. If it is a method, it is applicable with respect to the method of manufacturing arbitrary positive electrode materials.

[Outline of production method of lithium transition metal composite oxide powder]
Lithium transition metal composite oxide powder is mixed with raw material compounds containing these metal elements so as to have the same metal element composition as the target lithium transition metal composite oxide, and this raw material mixture is formed into particles. After (granulation), it can be produced by firing, pulverizing and classifying as necessary.

  In addition, as an example of the granulation method, a method (spray drying method) of obtaining a particulate material by spray drying a slurry containing these raw material compounds can be mentioned. In the following description, the case where granulation is performed by this spray drying method will be described as an example. However, the production method of the present invention is not limited to the case where the spray drying method is used, and granulation is performed by other methods. It can also be applied to the case where it is performed.

[Raw compound]
Examples of the raw material compound include a compound containing lithium (hereinafter referred to as “lithium raw material” as appropriate), a compound containing a transition metal (hereinafter referred to as “transition metal compound” as appropriate), and a target lithium transition metal. Depending on the composition of the composite oxide, other elements of manganese, nickel, and cobalt (hereinafter referred to as “substitution element” as appropriate) may be used.

・ Lithium raw material:
Examples of lithium raw materials include inorganic lithium salts such as Li ₂ CO ₃ and LiNO ₃ ; lithium hydroxides such as LiOH and LiOH · H ₂ O; lithium halides such as LiCl and LiI; inorganic lithium compounds such as Li ₂ O And organic lithium compounds such as alkyllithium and fatty acid lithium. Among these, Li ₂ CO ₃ , LiNO ₃ , LiOH, LiOH · H ₂ O, and Li acetate are preferable. Further, in the case of mixing raw materials by the wet method, LiOH, LiOH · H ₂ O is preferably used. LiOH and LiOH.H ₂ O are water-soluble, and when the dispersion medium is water, they not only dissolve and improve the uniformity of the raw material mixture, but also contain no nitrogen and sulfur. There is also an advantage that no harmful substances such as _x and SO _x are generated. If desired, two or more lithium raw materials may be used in combination.

In addition, when a lithium raw material is mixed with the transition metal compound powder having a desired metal ratio in advance and fired, it is preferable to use LiOH or LiOH.H ₂ O as the lithium raw material. In this case, the average particle diameter of the lithium raw material is usually 500 μm or less, preferably 100 μm or less, more preferably 50 μm, in order to improve the mixing property with the dried product obtained by spray drying and to improve battery performance. Hereinafter, it is most preferably 20 μm or less. On the other hand, those having a too small particle size have low stability in the atmosphere, so the average particle size of the lithium raw material is usually 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.2 μm or more, and most preferably. Is 0.5 μm or more. Although there is no restriction | limiting in particular in the mixing method, It is preferable to use the powder mixing apparatus generally used for industrial use. The mixing composition ratio of the powder to be mixed is appropriately selected according to the composition of the target lithium transition metal composite oxide.

・ 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.

Nickel raw materials include Ni (OH) ₂ , NiO, NiOOH, 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 halogen And the like. Of these, compounds containing no nitrogen and sulfur, such as Ni (OH) ₂ , NiO, NiOOH, and NiC ₂ O ₄ .2H ₂ O, are preferable because they do not generate harmful substances such as NO _x and SO _x in the firing step. Ni (OH) ₂ , NiO, and NiOOH are particularly preferable from the viewpoint that they can be obtained at low cost as industrial raw materials and have high reactivity when firing. If desired, two or more nickel raw materials may be used in combination.

Examples of the manganese raw material include Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , MnOOH, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , an organic manganese compound, manganese hydroxide, manganese halide, and the like. it can. Among these manganese compounds, Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ are preferable because they have a valence close to the manganese oxidation number of the composite oxide that is the final target product. Two or more manganese raw materials may be used together if desired.

Cobalt raw materials include 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, cobalt halides. Etc. Among these cobalt compounds, CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (OH) ₂ and CoOOH are preferable. If desired, two or more cobalt raw materials may be used in combination.

  Further, when the substitution element / surface treatment element Q is used in the general formula (II), an inorganic salt or an organic salt of the substitution element / surface treatment element Q may be used as the raw material compound.

・ Combination ratio:
In principle, the blending ratio of these raw material compounds may be determined according to the composition of the target lithium transition metal composite oxide. However, since lithium, boron, bismuth and the like may volatilize during firing, in this case, the blending amount of the lithium raw material, boron raw material, bismuth raw material and the like is determined in consideration of the volatilization amount.

[Granulation process]
First, the above raw material compounds are mixed. The mixing method is not particularly limited, and may be wet or dry. Examples include a method using an apparatus such as a ball mill, a vibration mill, and a bead mill. A water-soluble raw material such as lithium hydroxide may be mixed with other solid raw materials as an aqueous solution. Wet mixing is preferable because more uniform mixing is possible and the reactivity of the mixture can be increased in the firing step described below.

  The mixing time varies depending on the mixing method and scale, but it is sufficient that the raw materials are uniformly mixed at the particle level. For example, in a ball mill (wet or dry type), usually about 1 hour to 2 days, and in a bead mill (wet continuous method) The residence time is usually about 0.1 to 24 hours.

  As the degree of pulverization, the particle diameter of the raw material particles after pulverization serves as an index, but the average particle diameter is usually 2 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. When the average particle size is too large, the reactivity in the firing step is lowered. In addition, in the case of wet mixing, the sphericity of the dry powder in spray drying described later tends to decrease, and the final powder filling density tends to decrease. This tendency becomes particularly remarkable when trying to produce granulated particles having an average particle diameter of 50 μm or less. It should be noted that making particles smaller than necessary leads to an increase in pulverization cost, so that the average particle size is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.1 μm or more. That's fine.

  In the case of wet mixing, it is then subjected to a drying process. Here, the case of using spray drying is described, but according to spray drying, the uniformity of the particulate matter to be produced, powder flowability, powder handling performance, and the viewpoint of being able to efficiently form secondary particles, etc. To preferred. Spray drying may be performed by a known method. For example, it is possible to use a method in which a gas flow and slurry are caused to flow into the tip of the nozzle so that the slurry is ejected as droplets from the nozzle and brought into contact with a drying gas to quickly dry the droplets.

  The average particle diameter of the particulate matter is preferably 50 μm or less, more preferably 40 μm or less. However, since it tends to be difficult to obtain a too small particle size, it is usually 4 μm or more, preferably 5 μm or more. In the case of producing a particulate material by the spray drying method, the particle size can be controlled by appropriately selecting the spray format, the pressurized gas flow supply rate, the slurry supply rate, the drying temperature, and the like.

  In addition, when the raw material compound is wet mixed, the lithium raw material, boron raw material, bismuth raw material, etc. may be wet mixed together with other raw material compounds, or other raw material compounds may be wet mixed-spray dried. These may be mixed dry.

  For example, a raw material compound other than a lithium raw material is wet-mixed, and then spray-dried to form a particulate material, and then a lithium raw material is dry-mixed and subjected to firing to obtain a target lithium transition metal composite oxide. As described above, the raw material compound not added during the wet mixing process can be dry mixed with the particulate matter obtained by spray drying and subjected to firing.

That is, as a timing for mixing lithium raw material, boron raw material, bismuth raw material, etc. with other raw material compounds, for example,
(1) When weighing raw material compounds,
(2) To slurry during wet mixing,
(3) To the slurry after wet mixing,
(4) To slurry before spray drying,
(5) To dry powder after spray drying
(6) To dry powder before firing
However, it may be mixed at any time as described above.

  In addition, a lithium raw material, a boron raw material, a bismuth raw material, etc. may be mixed at the same time with respect to each of other raw material compounds, or may be divided into a plurality of times and mixed at different times.

[Baking process]
By firing the particulate matter thus obtained, a fired powder can be obtained.

  For firing, for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like can be used. Firing is usually divided into three parts: temperature rise, maximum temperature hold, and temperature drop. Further, the second maximum temperature holding portion is not necessarily limited to one time, and two or more steps may be included depending on the purpose.

  In the temperature raising portion, the temperature in the furnace is usually raised at a temperature raising rate of 1 to 5 ° C./min. Even if this rate of temperature rise is too slow, it takes time and is industrially disadvantageous. However, if it is too fast, the furnace temperature does not follow the set temperature depending on the furnace.

  In the maximum temperature holding portion, 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, it tends to require a long firing time in order to obtain a lithium transition metal composite oxide with good crystallinity. On the other hand, if the temperature is too high, the lithium transition metal composite oxide will violently sinter. Resulting in the production of a lithium transition metal composite oxide with poor pulverization / disintegration yield after firing, which is industrially disadvantageous, or has many defects such as oxygen vacancies. In a lithium secondary battery used as an active material, there is a risk of deterioration due to a decrease in battery capacity or a collapse of the crystal structure due to charge / discharge.

  The holding time (baking time) at the maximum temperature holding portion is usually selected from a wide range of 1 hour or more and 100 hours or less. If the firing time is too short, it is difficult to obtain a lithium transition metal composite oxide powder with good crystallinity.

  In the temperature lowering portion, the temperature in the furnace is usually decreased at a temperature decreasing rate of 0.1 to 5 ° C./min. Even if this rate of temperature decrease is too slow, it takes time and is industrially disadvantageous. If it is too fast, the uniformity of the target product tends to be lacking or the container tends to deteriorate.

  In the lithium transition metal composite oxide represented by the above general formula (I), the bulk density such as the tap density of the obtained powder varies depending on the firing atmosphere. Therefore, the atmosphere during firing usually has an oxygen concentration of 10 volumes. % Or more, preferably 15% by volume or more, and usually 80% by volume or less, particularly 50% by volume or less is preferable. If the oxygen concentration is too high, the bulk density of the resulting lithium transition metal composite oxide may be reduced. If the oxygen concentration is too low, a lithium transition metal composite oxide having many defects such as oxygen vacancies is generated. Specifically, an air atmosphere or the like is preferable.

[Preliminary crushing process]
A lithium transition metal composite oxide powder is obtained by the firing step. This lithium transition metal composite oxide powder may be used as it is in the classification step described later, but if necessary, it may be crushed under optimized conditions and then used in the classification step described later. This crushing is referred to as “preliminary crushing” in order to distinguish it from crushing performed in the classification step described later.

  There are no particular restrictions on the pre-crushing method, but, for example, a method that enables optimized crushing that is not too strong, specifically, mesh screening, mortar crushing, vibrating sieve with tapping balls, pin mill, etc. are optimal. This can be achieved by using it under various conditions. For example, the degree of pulverization can be controlled by adjusting the processing time of the vibrating sieve and the rotation speed in accordance with the sintering strength of the particles.

[Baking powder]
In the present specification, the “fired powder” refers to a lithium transition metal composite oxide powder obtained by firing, or a powder obtained by pre-pulverization when pre-pulverizing it. Say. In other words, the powder is in a state of being subjected to a classification process described later.

  The fired powder is a secondary particle formed by aggregation of primary crystal particles of lithium transition metal composite oxide, and the secondary particles are gently sintered (point-sintered) to form a tuft of grapes. Some of the particles are in the form of tertiary particles with a daisy-chain structure.

-Tap density of the fired powder:
The tap density of the fired powder is usually 1 g / cm ³ or more, preferably 1.2 g / cm ³ or more, more preferably 1.4 g / cm ³ or more, and usually 2 g / cm ³ or less, preferably 1.8 g. / Cm ³ or less. Below this lower limit, the required amount of dispersion medium increases during coating, the required amount of conductive material and binder increases, the filling rate of the active material into the positive electrode active material layer is restricted, and the battery capacity May be constrained. The tap density is preferably as large as possible, and there is no particular upper limit. However, if the tap density is too large, the diffusion of lithium ions using the electrolytic solution in the positive electrode active material layer as a medium becomes rate-determining, and the load characteristics are likely to deteriorate.

  In addition, the measurement of the tap density of a baked powder is the above-mentioned [I. This is carried out in the same manner as the method for measuring the tap density of the positive electrode material described in the section “Positive electrode material for lithium secondary battery”. However, in the case of a fired powder, in order to accurately measure the tap density, the measurement is performed after passing through a 1 mm mesh.

-Median particle size of the calcined powder:
The median particle size of the fired powder is usually in the range of 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more, and usually 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less. If the median particle size of the calcined powder is below this range, the tap density of the obtained positive electrode material is difficult to increase. On the other hand, if it exceeds this range, the specific surface area of the obtained positive electrode material becomes small and contact with the electrolyte solution is reduced. It tends to get worse.

  The measurement of the median diameter of the calcined powder is performed by the above-mentioned [I. The measurement is performed in the same manner as the method for measuring the median diameter of the positive electrode material described in the section of “Positive electrode material for lithium secondary battery”. However, in order to accurately measure the median diameter of the fired powder, the measurement is performed after passing through a 1 mm mesh.

・ Repose angle of the calcined powder:
The angle of repose of the fired powder is usually 50 ° or more, preferably 54 ° or more, more preferably 58 ° or more, and usually 84 ° or less, preferably 80 ° or less, more preferably 70 ° or less. If the angle of repose of the fired powder is less than this range, it is difficult to obtain the effect of the classification step described later. On the other hand, if the angle of repose of the fired powder exceeds this range, classification may not be possible.

  The angle of repose of the fired powder was measured by the above-mentioned [I. This is carried out in the same manner as the method for measuring the angle of repose of the positive electrode material described in the section “Positive electrode material for lithium secondary battery”. However, in order to accurately measure the angle of repose of the fired powder, the measurement is performed after passing through a 1 mm mesh.

・ Specific surface area of calcined powder:
The specific surface area (specific surface area of secondary particles) of the calcined powder in the BET method varies greatly depending on the composition ratio and contained elements, but is usually in the range of 0.5 m ² / g or more, preferably 0.6 m ² / g or more. It is. If the specific surface area is smaller than this lower limit, the primary particle size is increased, and the rate characteristics and the capacity tend to decrease, which is not preferable. On the other hand, even if the specific surface area is too large, the amount of dispersion medium required for coating is increased, the necessary amount of conductive material and binder is increased, and the filling rate of the active material to the positive electrode plate is restricted, so that the battery Since the capacity is limited, the upper limit is usually 1.5 m ² / g or less, preferably 1.4 m ² / g or less. In order to accurately measure the specific surface area of the fired powder, it is measured after passing through a 1 mm mesh.

  In addition, the measurement of the specific surface area of a baked powder is the above-mentioned [I. The measurement is performed in the same manner as the method for measuring the specific surface area of the positive electrode material described in the section of “Positive electrode material for lithium secondary battery”. However, in order to accurately measure the specific surface area of the fired powder, the measurement is performed after passing through a 1 mm mesh.

[Classification process]
In the production method of the present invention, this classification step is performed using a classifier that sifts the powder by pressing it against the mesh screen with a blade rotating at high speed.

・ Classifier:
Various characteristics of the classifier are as follows, for example.

  The mesh screen has a diameter of usually 50 mm or more and 750 mm or less, and a length of usually 100 mm or more and 500 mm or less.

The effective area of the mesh screen is usually 300 cm ² or more and 10000 cm ² or less.

  As the mesh of the mesh screen, one having a mesh opening of 45 μm, 38 μm, 30 μm, or the like is used.

  The rotation speed of the rotor (blade rotation speed) is usually 100 rpm or more and 2000 rpm or less.

  The supply rate of the powder is usually 100 g / min or more and 2 kg / min or less.

  Specific device names of the classifier used in the production method of the present invention include, for example, Puffy footer (manufactured by Tsukasa Industries, model number PSF-25 / 50), turbo screener (turbo industry TS125 × 200), and the like. .

・ Change in tap density by classification:
According to the production method of the present invention, the ratio represented by B / A, where A is the tap density (after passing through 1 mm) of the fired powder before classification treatment and B is the tap density of the positive electrode material after classification treatment. Is usually 1.05 or more, preferably 1.07 or more.

  The large value of B / A is that the lithium transition metal composite oxide powder in which the secondary particles have many point-sintered particles by classification and form a tuft-like or bead-like tertiary particle structure. Represents being reduced to the secondary particle level.

  If the value of B / A is below the above range, the tap density of the lithium transition metal composite oxide powder is low, the amount of dispersion medium required for coating is increased, and the necessary amount of conductive material and binder increases. However, the filling rate of the active material into the positive electrode active material layer may be restricted, and the battery capacity may be restricted.

  On the other hand, the higher the B / A value, the better, but it is usually 2 or less.

  Note that the tap density (after passing through 1 mm) A of the baked powder before the classification treatment and the tap density B of the positive electrode material after the classification treatment can both be measured by the method described above.

・ Changes in particle size due to classification:
According to the production method of the present invention, when the median diameter (after passing through 1 mm) of the baked powder before classification treatment is C, and the median diameter of the positive electrode material after classification treatment is D, the ratio represented by D / C Is usually 0.8 or less, preferably 0.7 or less.

  The small value of D / C means that the secondary particles have many point-sintered particles by classification, and lithium transition metal composite oxide powders forming a tufted or beaded tertiary particle structure. Indicates that the body is being reduced to the secondary particle level.

  When the value of D / C exceeds the above range, the tap density of the lithium transition metal composite oxide powder is low, and the amount of the required dispersion medium is increased at the time of coating, and the necessary amount of conductive material and binder is reduced. As a result, the filling rate of the active material into the positive electrode active material layer is restricted, and the battery capacity may be restricted.

  On the other hand, the lower limit of the D / C value is not particularly limited as long as the effect of the present invention is observed, but is usually 0.3 or more.

  The median diameter (after passing through 1 mm) A of the baked powder before classification treatment and the median diameter B of the positive electrode material after classification treatment can be measured by the above-described methods.

The reason why the above-described effects can be obtained by the production method of the present invention:
The reason why the above-described effect (that is, the effect that classification processing can be reliably performed in a short time even when the fired powder has a tendency to cling, etc.) can be obtained by the production method of the present invention is not clear. There is not, but it is guessed as follows.

  That is, the classifier used in the classification process in the production method of the present invention is different from the vibration sieve used in the normal classification process, and sifts by passing the powder against the mesh screen with a blade rotating at high speed. Therefore, classification can be performed while appropriately crushing the secondary particles of the fired powder, and as a result, even if the fired powder has a tendency to cling, etc., the classification process can be performed reliably in a short time. It is speculated that it will be possible.

[III. Positive electrode for lithium secondary battery]
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) contains the above-described positive electrode material of the present invention.

  The positive electrode of the present invention is formed by forming a positive electrode active material layer containing a positive electrode active material, a binder and a conductive material on a current collector, and the positive electrode material of the present invention is used as this positive electrode active material. As the positive electrode active material, one kind of the positive electrode material of the present invention described above may be used alone, or two or more kinds may be used in any combination and ratio. Moreover, you may use combining 1 type, or 2 or more types of positive electrode materials of this invention, and 1 type, or 2 or more types of other well-known positive electrode active materials.

  The positive electrode of the present invention is prepared by pressing a positive electrode active material, a binder, a conductive material, and, if necessary, a thickener or the like mixed in a dry form into a sheet shape, or press-bonding the positive electrode current collector. Manufactured by dissolving or dispersing the material in a dispersion medium and applying it as a slurry (coating liquid) to the positive electrode current collector, drying it to form a sheet, and forming the positive electrode active material layer on the positive electrode current collector Is done. Here, the positive electrode active material layer obtained by coating and drying is preferably consolidated by a vertical press, a roller press or the like in order to increase the packing density of the electrode material.

  The positive electrode material of the present invention is prepared by coating or dissolving in a suitable dispersion medium together with a coating performance, that is, a binder and a conductive material, and other additives, depending on the specific powder characteristics, When this is applied to a positive electrode current collector and dried to form a positive electrode active material layer, the handling property of the coating liquid, the coating performance, the smoothness of the formed coating film, the film strength, the thin film formability, the current collection The positive electrode of the present invention is formed by forming a positive electrode active material layer on a positive electrode current collector, in particular, by coating and drying of such a coating solution because of its excellent density with the body. Is preferred.

  The ratio 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, and usually 99.9% by weight or less, preferably 99% by weight or less. 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 material used for the positive electrode include natural graphite, artificial graphite, acetylene black, ketjen black, needle coke, fullerene, and carbon nanotubes. These may be used alone. You may use 2 or more types together by arbitrary combinations and a ratio.

  The proportion of the conductive material in the positive electrode active material layer is usually 0.1% by weight or more, preferably 1% by weight or more, and usually 10% by weight or less, preferably 8% by weight or less. If the amount of the conductive material is too large, the amount of the positive electrode active material may be relatively small and the capacity may be insufficient. If the amount is too small, the electrical conductivity may be insufficient.

  As the binder used for the positive electrode, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, and other resin polymers, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene) Rubber), fluorine rubber, isoprene rubber, butadiene rubber, rubber polymer such as ethylene / propylene rubber; styrene / butadiene / styrene block copolymer and its hydrogenated product, EPDM (ethylene-propylene-diene terpolymer) ), Thermoplastic elastomeric polymers such as styrene / ethylene / butadiene / ethylene copolymers, styrene / isoprene styrene block copolymers and hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate Soft resinous polymers such as ethylene, vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer Fluorinated polymers such as: polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), etc., and these may be used alone or in any combination of two or more And may be used in combination in a ratio.

  The proportion of the binder in the positive electrode 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 60% by weight or less, preferably 40% by weight or less. It is. When the binder content is low, the positive electrode active material cannot be sufficiently retained, the mechanical strength of the positive electrode is insufficient, and battery performance such as cycle characteristics may be deteriorated. On the other hand, when the binder content is too large, the amount of the positive electrode active material and the amount of the conductive material are relatively decreased, and the battery capacity and conductivity may be lowered.

  Moreover, as a dispersion medium used when preparing the slurry for forming a positive electrode active material layer, what can dissolve or disperse | distribute an active material, a binder, a electrically conductive material, and a thickener is used. The type is not particularly limited, and either an aqueous medium or an organic medium may be used. Examples of the aqueous medium include water and alcohol. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and NN-dimethylaminopropylamine; ethers such as dimethyl ether, ethylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) and dimethyl Examples include amides such as formamide and dimethylacetamide; aprotic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide. In particular, when an aqueous medium is used, it is preferable to add a dispersion medium together with the thickener and make a slurry using a latex such as SBR. In addition, these dispersion media may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  Examples of the material of the positive electrode current collector include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

  Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal in the case of a metal material. A thin film, a carbon cylinder, etc. are mentioned. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the current collector is thin, the strength required for the current collector may be insufficient. Conversely, if it is too thick, it becomes difficult to handle.

  The thickness of the positive electrode active material layer formed on such a current collector is usually 10 μm or more and 200 μm or less.

[IV. Lithium secondary battery]
The lithium secondary battery 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. It is a positive electrode for lithium secondary batteries.

  The negative electrode includes a negative electrode active material, a binder, and a negative electrode active material layer containing a conductive material as necessary, and a metal foil such as a lithium alloy such as lithium metal or lithium-aluminum alloy. Used.

  The negative electrode active material is arbitrary as long as it can electrochemically occlude and release lithium ions, but usually a carbon material that can occlude and release lithium is used in terms of safety.

  Examples of the carbon material include graphite (graphite) such as artificial graphite and natural graphite, and organic pyrolysis products under various pyrolysis conditions. Organic pyrolysis products include coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, carbonized products obtained by oxidizing coal-based or petroleum-based pitch, needle coke, pitch coke, and phenol resin. And carbides such as crystalline cellulose and the like, carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like. Among these, graphite, especially artificial graphite or purified natural graphite produced by subjecting easily graphitizable pitch obtained from various raw materials to high-temperature heat treatment, graphite material containing pitch in these graphite, etc., and various surfaces What processed is preferable. One of these carbon materials may be used alone, or two or more thereof may be used in combination.

  As the graphite material, those in which the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is usually 0.335 nm or more and 0.34 nm or less, and particularly preferably 0.337 nm or less. . The ash content of the graphite material is usually 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, based on the weight of the graphite material. The crystallite size (Lc) of the graphite material determined by X-ray diffraction by the Gakushin method is usually 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. The median diameter of the graphite material determined by the laser diffraction / scattering method is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, particularly preferably 7 μm or more, and usually 100 μm or less, preferably 50 μm or less, more preferably. It is 40 μm or less, particularly preferably 30 μm or less.

The BET specific surface area of the graphite material is usually 0.5 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more, and particularly preferably 1.5 m ² / g. or more, usually 25.0 m ² / g or less, preferably 20.0 m ² / g or less, more preferably 15.0 m ² / g or less, particularly preferably 10.0 m ² / g or less. In Raman spectrum analysis using argon laser beam, the intensity I _A of the peak P _A is detected in the range of 1580～1620Cm ^-1, and intensity I _B of a peak P _B detected in the range of 1350 ^-1 The intensity ratio I _A / I _B is preferably 0 or more and 0.5 or less, and the half width of the peak P _A is preferably 26 cm ⁻¹ or less, particularly preferably 25 cm ⁻¹ or less.

  Examples of the negative electrode active material other than the carbon material include metal oxides such as tin oxide and silicon oxide, and lithium alloys such as lithium simple substance and lithium aluminum alloy. These may be used individually by 1 type, may be used in combination of 2 or more types, and may be used in combination with a carbon material.

  The negative electrode active material layer may be formed in the same manner as the positive electrode active material layer. That is, it can be formed by applying the above-described negative electrode active material and binder, and, if desired, a thickener and a conductive material slurryed with a dispersion medium to a negative electrode current collector and drying. As the dispersion medium, the binder, the conductive material, and the thickener, the same materials as the positive electrode active material can be used.

  Examples of the material of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel; and carbon materials such as carbon cloth and carbon paper. Examples of the shape of the metal material include a metal foil, a metal cylinder, a metal coil, a metal plate, and a metal thin film. Examples of the shape of the carbon material include a carbon plate, a carbon thin film, and a carbon cylinder. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the current collector is thin, the strength required for the current collector may be insufficient. Conversely, if it is too thick, it becomes difficult to handle.

  The thickness of the negative electrode active material layer formed on such a current collector is usually 10 μm or more and 200 μm or less.

  Examples of the electrolyte include organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes, etc. Among these, organic electrolytes (nonaqueous electrolytes) are preferable.

  Any known organic solvent can be used for the organic electrolyte. For example, carbonates such as dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1, Ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane and diethyl ether; ketones such as 4-methyl-2-pentanone; sulfolane compounds such as sulfolane and methyl sulfolane; sulfoxide compounds such as dimethyl sulfoxide Lactones such as γ-butyrolactone; nitriles such as acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile; chlorinated hydrocarbons such as 1,2-dichloroethane; amines Esters, amides such as dimethylformamide; trimethyl phosphate, phosphoric acid ester compounds such as triethyl phosphate. These may be used alone or in combination of two or more.

The organic electrolytic solution preferably contains a high dielectric constant solvent having a relative dielectric constant of 20 or more at 25 ° C. in order to dissociate the electrolyte. Especially, it is preferable to contain the organic solvent which substituted ethylene carbonate, propylene carbonate, and those hydrogen atoms with other elements, such as a halogen, or an alkyl group. The ratio of the electrolyte solution of the high dielectric constant solvent to the whole organic electrolyte solution is usually 20% by weight or more, preferably 30% by weight or more, more preferably 40% by weight or more. In addition to organic electrolytes, CO ₂ , N ₂ O, CO, SO _{2 and} other gases and polysulfide S _x ²⁻ such as polysulfide S _x ²⁻ are added to form a good coating that enables efficient charge and discharge of lithium ions on the negative electrode surface. You may add an agent in arbitrary ratios.

Any conventionally known lithium salt can be used as the solute. Specific examples include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) _2. , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) _{2 and the} like. These solutes may be used alone or in combination of two or more in any combination and ratio.

  The concentration of the lithium salt in the electrolytic solution is usually 0.5 mol / L or more, preferably 0.75 mol / L or more, and 1.5 mol / L or less, preferably 1.25 mol / L or less. Whether the concentration is high or low, the conductivity may decrease, and the battery characteristics may deteriorate.

As the inorganic solid electrolyte used for the organic electrolytic solution, any crystalline or amorphous one known to be used as an electrolyte can be used. Examples of the crystalline inorganic solid electrolyte include LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _{0.5 −3x} RE _{0.5 + x} TiO ₃ (RE = La, Pr, Nd, Sm) and the like. Examples of the amorphous inorganic solid electrolyte include oxide glasses such as 4.9LiI-34.1Li ₂ O-61B ₂ O ₅ and 33.3Li ₂ O-66.7SiO ₂ . Any one of these may be used alone, or two or more may be used in any combination and ratio.

  The secondary battery preferably includes a separator that holds a nonaqueous electrolyte between the positive electrode and the negative electrode in order to prevent a short circuit between the electrodes.

  The material and shape of the separator are arbitrary as long as they are stable with respect to the organic electrolyte used, have excellent liquid retention, and can reliably prevent short-circuiting between electrodes. Examples thereof include microporous films, sheets and nonwoven fabrics made of various polymer materials. Examples of the polymer material include polyolefin polymers such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene. Polyolefin polymers are preferable from the viewpoint of chemical and electrochemical stability, and polyethylene is preferable from the viewpoint of the self-closing temperature of the battery. As the polyethylene, ultra high molecular weight polyethylene excellent in high temperature shape maintenance is preferable. The molecular weight of polyethylene is usually 500,000 or more, preferably 1,000,000 or more, particularly preferably 1.5 million or more, and usually 5 million or less, preferably 4 million or less, particularly preferably 3 million or less. If the molecular weight is small, the shape at high temperature may not be maintained. On the other hand, if the molecular weight is too large, the fluidity is lowered, and the hole of the separator may not be closed during heating.

  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.

  In the following Examples and Comparative Examples, evaluation was performed by classifying the fired powder with various classifiers and examining the processing speed, the tap density before and after the processing, the median diameter, and the like by the following methods.

[I. Method for evaluating positive electrode material]
[Evaluation method of classification speed]
20 kg of the calcined powder that was crushed (preliminarily crushed) through a mesh with a mesh opening of 1 mm was supplied to the classifier at a rate of 1 kg / min, and classification was performed. While visually observing how powder is discharged through the mesh screen, measure the time until discharge of the fired powder cannot be confirmed, and calculate the value obtained by dividing the supply amount of the fired powder by the processing time. The classification speed was obtained.

[Tap density evaluation method]
[I. It measured using the method described in the column of [tap density] in the positive electrode material for lithium secondary batteries. As a device, a tap denser (KYT-4000) manufactured by Seishin Company was used.

[Evaluation method of median diameter]
[I. It measured using the method described in the column of [Median diameter] in [Positive electrode material for lithium secondary battery]. As an apparatus, LA-920 manufactured by Horiba Seisakusho was used.

[Evaluation method of repose angle]
[I. It measured using the method described in the column of [Angle of repose] in the positive electrode material for lithium secondary batteries. As a device, a powder tester (PT-R) manufactured by Hosokawa Micron was used.

[II. Production and evaluation of cathode material]
[Example 1]
NiO, CoOOH and Mn ₃ O ₄ were weighed so as to have a molar ratio of Ni: Co: Mn = 0.33: 0.33: 0.33, and 0.15 mol / L LiOH aqueous solution was added thereto, While stirring, the solid content in the slurry was wet pulverized to a median diameter of 0.35 μm using a circulating medium stirring type wet bead mill. The obtained slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 7 μm. By adding LiOH powder having a median diameter of 3 μm to the obtained granulated particles so that the molar ratio of Li to (Ni + Co + Mn) is 1.05, dry mixing is performed to prepare nickel raw material, cobalt raw material, and manganese raw material. A mixed powder of grain particles and lithium raw material was obtained. This mixed powder was charged into a ceramic baking pot, and while circulating air, the temperature was raised to a maximum temperature of 945 ° C. at a rate of temperature increase of 5 ° C./min, held at 945 ° C. for 15 hours, and then at a rate of temperature decrease of 5 ° C./min. The temperature was lowered to obtain a fired powder having a substantially charged molar ratio composition.

  Preliminary crushing was performed by passing the fired powder through a mesh having an opening of 1 mm. The angle of repose of the obtained calcined powder after preliminary pulverization was measured and found to be 59 degrees.

  The preliminarily pulverized fired powder was pressed against a mesh screen with a blade rotating at high speed and classified by using a classifier that screened and passed, thereby obtaining a positive electrode material. In addition, as a classifier, a Pukashita (model number PSF-25 / 50) manufactured by TSUKASA INDUSTRIES was used and operated at a rotation speed of 900 rpm. A mesh screen having an opening of 45 μm was used.

Tap density (A) and median diameter (C) were measured for the calcined powder after preliminary pulverization, and the tap density (B) and median diameter (D) of the positive electrode material after classification were measured. Table 1 shows the values of A, B, C, D and B / A, D / C. In this example, the calcined powder could be classified at a rate of 10 kg / hour, and the mesh screen was not clogged and no bulk material was generated. The positive electrode material obtained through the classification was reduced in particle size and the tap density was improved as compared with the fired powder before classification.
The repose angle of the positive electrode material after classification was measured and found to be 60 degrees.

[Example 2]
The pre-ground calcined powder obtained by the same method as in Example 1 was classified using a turbo screener instead of the puffer foot of Example 1. As the turbo screener, TS125 × 200 manufactured by Turbo Kogyo was used and operated at a rotational speed of 1200 rpm.

  Tap density (A) and median diameter (C) were measured for the calcined powder after preliminary pulverization, and the tap density (B) and median diameter (D) of the positive electrode material after classification were measured. Table 1 shows the values of A, B, C, D and B / A, D / C. In this example, the fired powder could be classified at a rate of 60 kg / hour, and no clogging of the mesh screen, generation of bulk material, etc. were observed. As in Example 1, the positive electrode material obtained through the classification had a smaller particle size and improved the tap density compared to the fired powder before classification.

[Comparative Example 1]
The calcined powder after preliminary pulverization obtained by the same method as in Example 1 was classified using a vibrating sieve instead of the Puffer foot of Example 1. As a vibrating sieve, KGOR-500 manufactured by Kowa Industries, Ltd. was used. The evaluation results are shown in Table 1. In this comparative example, the particles of the calcined powder adhered to each other on the sieve to form a lump and could hardly be classified.

  The positive electrode material for a lithium secondary battery obtained by the production method of the present invention is a portable electronic device in which a positive electrode for a lithium secondary battery is formed by forming an active material layer on a current collector together with a binder and a conductive material. It can be used for various lithium secondary battery applications such as devices, communication devices and automobile power sources.

Claims (8)

A method for producing a positive electrode material for a lithium secondary battery, comprising:
A classifier that sifts the powder by mixing the raw materials, granulating, firing, and crushing if necessary, by pressing the powder against the mesh screen with a blade that rotates at high speed. The manufacturing method of the positive electrode material for lithium secondary batteries characterized by including the process of classifying using. 2. The method for producing a positive electrode material for a lithium secondary battery according to claim 1, wherein the fired powder is a powder having an angle of repose of 50 degrees or more measured by the following measurement method.
[Measurement of repose angle]
(1) Vibrate the standard sieve and feed the powder onto the table through the funnel. However, the sieve frequency is 3600 times / minute, the sieve vibration width is 2 mm, the sieve time is 4 minutes, and the funnel diameter is 8 mm.
(2) The angle of repose of the powder is measured. However, the measurement is performed using an angle calculation method (least square method) using a semiconductor laser (wavelength 670 nm) displacement sensor, and the minimum reading resolution is 0.1 degree. The said positive electrode material has a composition represented by following formula (II), The manufacturing method of the positive electrode material for lithium secondary batteries of Claim 1 or Claim 2 characterized by the above-mentioned.

(In the formula (II),
Q is at least one selected from the group consisting of Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, Ca, Sc, Al, B, and Zr. Represents the element of the species,
x represents a number of 0.7 ≦ x ≦ 1.3;
a represents a number of 0.2 ≦ a ≦ 0.8;
b represents a number of 0.2 ≦ b ≦ 0.8;
c represents a number of 0.15 ≦ c ≦ 0.4;
d represents a number 0 ≦ d ≦ 0.4, provided that a + b + c + d = 1;
δ represents a number of −0.1 <δ <0.1. ) A tap density (after passing through 1 mm) of the fired powder before the classification treatment is A,
When the tap density of the positive electrode material after the classification treatment is B,
(B / A)> = 1.05, The manufacturing method of the positive electrode material for lithium secondary batteries as described in any one of Claims 1-3 characterized by the above-mentioned. The median diameter (after passing through 1 mm) of the calcined powder before the classification treatment is C,
When the median diameter of the positive electrode material after the classification treatment is D,
(D / C) <= 0.8, The manufacturing method of the positive electrode material for lithium secondary batteries as described in any one of Claims 1-4 characterized by the above-mentioned. It manufactures with the manufacturing method of the positive electrode material for lithium secondary batteries as described in any one of Claims 1-5, The positive electrode material for lithium secondary batteries characterized by the above-mentioned. A positive electrode used in a lithium secondary battery,
A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 6. 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,
The lithium secondary battery, wherein the positive electrode is a positive electrode for a lithium secondary battery according to claim 7.