JP2005276597A - Lithium transition metal composite oxide powder for positive active material of lithium secondary battery, positive electrode of lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide lithium transition metal composite oxide powder for a lithium secondary battery, whose maximum particle size is small, excessive atomization is prevented, and having high density and high film forming properties. <P>SOLUTION: The lithium transition metal composite oxide powder for a positive active material of a lithium secondary battery has such characteristics that a ratio of a median diameter A (3-10 μm) of lithium transition metal composite oxide powder dispersed at concentration whose laser beam transmission factor becomes 60-90% in a hexasodiummethaphosphate aqueous solution measured by a laser diffraction method prescribed in JIS Z 8825-1 not applying ultrasonic waves and in a flowing state and a median diameter B (μm) of the powder measured when ultrasonic wave dispersion (output: 30 W and frequency: 22.5 kHz) is applied for 5 minutes is 1≤ median diameter A/median diameter B≤1.50, the maximum particle diameter is ≤40 μm, specific surface area measured by BET process is 0.5-1.5m<SP>2</SP>/g, and tap density is ≥1.55 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material, a lithium secondary battery positive electrode, and a lithium secondary battery. Specifically, a lithium transition metal composite oxide powder for a positive electrode active material of a lithium secondary battery that has a good coating performance and can form a high-density thin film positive electrode active material layer, and the lithium secondary battery The present invention relates to a lithium secondary battery positive electrode using a lithium transition metal composite oxide powder for a positive electrode active material, and a lithium secondary battery including the lithium secondary battery positive electrode.

  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 replaced with Mn, and LiNi _1-x-y Mn _x Co _y O _{2 in} which part of the Ni site is replaced with Mn and Co ( For example, Patent Document 1, Non-Patent Documents 1 to 3).

In a lithium secondary battery, as one means for improving load characteristics, it is conceivable to increase the contact area between the active material surface and the electrolytic solution by making the positive electrode active material fine particles. However, if the lithium transition metal composite oxide powder in which the Ni site is substituted with a large amount of Mn so that Ni and Mn are the same amount is made fine, the filling rate into the positive electrode active material layer is restricted and the battery capacity is restricted. There is a problem of being done. In addition, as the fine particles are made, the powder is made into a paint, and the positive electrode active material layer formed by applying the powder becomes hard and brittle. is there. This tendency is particularly noticeable 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 addition, thinning of the electrode is also progressing to improve the load characteristics of lithium secondary batteries. For this reason, a positive electrode active material with a small maximum particle size that can produce a non-stretching paint when creating a coating film as an active material layer. Substances are also desired. On the other hand, when forming an active material layer using a lithium transition metal composite oxide powder having a small particle size, it is necessary to increase the proportion of the conductive material and the binder in order to ensure conductivity and coating strength. However, in order to increase the battery capacity, it is disadvantageous to increase the conductive material and the binder contained in the positive electrode active material layer. From this point, the positive electrode active material is excessively finely divided. That is not preferable.

  Moreover, in order to densify the finely divided particles, it is necessary to bake at a high temperature, for example, 900 ° C. or higher. These treatments have the disadvantage that the finely divided particles are sintered in an irregular shape, and the effect is to lower in spite of the desire to increase the bulk density in order to improve the coating properties. In particular, in the production of the lithium transition metal composite oxide powder, in the step of granulating the mixed powder of the transition metal compound and then mixing the lithium compound with this granulated powder, the lithium compound is a mixture of these granulated powders. As a result of bridging, the particles tend to sinter.

When sintering of particles occurs by firing, crushing the particles is widely performed. For example, in Patent Document 2, pin mill crushing is performed for the purpose of increasing the discharge retention rate in charge and discharge, but the obtained powder is a powdery material having a particle size of 0.5 to 2.5 μm in weight ratio. A large amount of conductive material is required to obtain a good conductive path with such fine powder (15% of acetylene black is used in the example of Patent Document 2). In addition, the fine particles require a large amount of binder to obtain the strength of the coating film, and it is difficult to increase the density (capacity) of the battery.
JP 2003-17052 A JP 2000-285918 A J. et al. Mater. Chem. 6 (1996) p. 1149 J. et al. Electrochem. Soc. 145 (1998) p. 1113 41st Battery Symposium Proceedings (2000) p. 460

  As described above, the lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery for obtaining good battery characteristics is a particle having a small maximum particle size corresponding to a thin film electrode and is not too fine. In addition, it is necessary that the particles have high density and excellent coating properties, but no lithium transition metal composite oxide powder satisfying these properties has been conventionally provided.

  Accordingly, an object of the present invention is to provide a lithium transition metal composite for a positive electrode active material of a lithium secondary battery that has a small maximum particle size corresponding to a thin film electrode, is not too fine, and has a high density and excellent coating properties. It is to provide oxide powder.

  As a result of intensive studies, the inventors of the present invention have a specific maximum particle size and specific surface area obtained by adding a crushing process under specific conditions optimized after firing in the production process of lithium transition metal composite oxide powder. A lithium transition metal composite oxide powder having a tap density and having a rate of change before and after ultrasonic dispersion performed at the time of particle size distribution measurement within a certain range is an excellent lithium secondary battery positive electrode active material. Thus, the present invention was completed by finding that the positive electrode of the lithium secondary battery produced using this was high density and excellent in coating film performance.

That is, the gist of the present invention is as follows.
[1] A lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery, wherein the lithium transition metal composite oxide powder is added to a 0.1 wt% sodium hexametaphosphate aqueous solution by a laser diffraction method based on JIS Z 8825-1. The median diameter (hereinafter referred to as “median diameter A”) measured without applying ultrasonic waves while circulating and flowing a dispersion liquid in which the transition metal composite oxide powder was dispersed at a concentration of 60 to 90% of the laser light transmittance. Is 3 μm or more and 10 μm or less,
The median diameter A and the median diameter of the powder measured when ultrasonic dispersion (output 30 W, frequency 22.5 kHz) was applied for 5 minutes while circulating the dispersion liquid (hereinafter referred to as “median diameter B”). (Μm) ratio is 1 ≦ median diameter A / median diameter B ≦ 1.50,
The maximum particle size is 40 μm or less,
Specific surface area by BET method is 0.5 m ² / g or more, 1.5 m ² / g or less,
A lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery, wherein the tap density is 1.55 g / cm ³ or more.

[2] A lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery according to [1] above, represented by the following general formula (I):
Li _x MO _2-δ (I)
(In the formula (I), x is a number satisfying 0.5 ≦ x ≦ 1.3, M represents at least one element selected from transition metals, and δ is −0.1 <δ <. Represents the number 0.1.)

[3] A lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery according to [2] above, represented by the following general formula (II):
Li _x Ni _a Mn _b Co _c Q _d O _2-δ (II)
(In Formula (II), x is a number of 0.7 ≦ x ≦ 1.3, a is a number of 0.2 ≦ a ≦ 0.8, and b is 0.2 ≦ b ≦ 1.3. Represents a number of 0.8, c represents a number of 0.15 ≦ c ≦ 0.4, Q represents Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Represents at least one element selected from the group consisting of Nb, Ta, Be, Ca, Sc, Al, B and Zr, d represents a number 0 ≦ d ≦ 0.4, and a + b + c + d = 1 , Δ represents a number of −0.1 <δ <0.1.)

[4] In the above [3], a in the general formula (II) represents a number of 0.2 ≦ a ≦ 0.4, b represents a number of 0.2 ≦ b ≦ 0.4, c represents a lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material, wherein 0.2 ≦ c ≦ 0.4.

[5] A lithium secondary battery positive electrode containing at least a positive electrode active material, a binder, and a conductive material, wherein the active material is lithium for a lithium secondary battery positive electrode active material according to any one of the above [1] to [4]. A lithium secondary battery positive electrode characterized by being a transition metal composite oxide powder.

[6] A lithium secondary battery comprising a negative electrode and a positive electrode containing a material capable of inserting and extracting lithium, and an electrolyte containing a lithium salt, wherein the positive electrode is the lithium secondary battery positive electrode of [5] above. A lithium secondary battery characterized by being.

  According to the present invention, a thin film cathode active material layer having high capacity and excellent mechanical properties can be obtained by using a lithium transition metal composite oxide powder for a cathode active material of a lithium secondary battery having high density and excellent coating performance. Thus, a lithium secondary battery positive electrode having excellent load characteristics can be realized.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is limited to the following contents. It is not a thing.

[Physical properties and characteristics of lithium transition metal composite oxide powder for positive electrode active material of lithium secondary battery]
<Median diameter>
The lithium transition metal composite oxide powder of the present invention may exist as primary crystal particles or secondary particles formed by agglomeration of primary crystal particles, but in the present invention, primary crystal particles agglomerate. Those forming secondary particles are preferred.

  The lithium transition metal composite oxide powder of the present invention is obtained by applying laser light to the lithium transition metal composite oxide powder in a 0.1% by weight sodium hexametaphosphate aqueous solution by a laser diffraction method based on JIS Z 8825-1. The median diameter measured without applying ultrasonic waves (hereinafter referred to as “median diameter A”) is 3 μm or more and 10 μm or less while circulating and dispersing the dispersion liquid having a concentration of 60 to 90%. The median diameter A and the median diameter of the powder (hereinafter referred to as “median diameter B”) measured when ultrasonic dispersion (output 30 W, frequency 22.5 kHz) is applied for 5 minutes while circulating the dispersion liquid. ) (Μm) indicates a value of 1 ≦ median diameter A / median diameter B ≦ 1.50.

  This median diameter is measured by a known laser diffraction / scattering type particle size distribution measuring device based on JIS Z 8825-1. In this case, in the ultrasonic dispersion probe built-in type measuring instrument, the built-in probe type (30 W) and the homogenizer dispersion (600 W) are almost the same as described in the catalog “LA-920 catalog” of HORIBA, Ltd. It can be seen that it has a dispersion processing speed and dispersion ability. The dispersion method using an ultrasonic cleaning machine (40 W) is not preferable as an index of dispersion because strong agglomerated particles cannot be completely dispersed. Further, in the case of the built-in probe mold, in the case of alumina fine particles, the dispersion proceeds completely in approximately 1 minute. Therefore, in the present invention, a probe-type laser diffraction / scattering particle size distribution measuring device with a built-in ultrasonic wave is used, and the value after 5 minutes of ultrasonic dispersion, which is considered to be completely loosened, and the state including the aggregated state. The ultrasonic dispersion representing the information is compared with the value of 0 minutes of ultrasonic dispersion which is not performed.

  The median diameter A / median diameter B (hereinafter referred to as “A / B”) of the median diameter A and the median diameter B indicates the rate of change of the median diameter due to ultrasonic dispersion, and the state in which particles are loosened by ultrasonic irradiation. Is a numerical value.

  When ultrasonic dispersion is not applied, it reflects the appearance of light agglomerates due to entanglement of secondary particles and spot sintering. Therefore, the median diameter A can particularly affect the coating performance. Many. In the present invention, the median diameter A is usually 3 μm or more, preferably 4 μm or more, and usually 10 μm or less, preferably 9 μm or less, more preferably 8 μm or less. If this median particle size A is too small, the conductive path cannot be taken sufficiently and the battery capacity tends to decrease. If a large amount of conductive material is added for the purpose of supplementing it, the battery energy density may decrease, which is not preferable. . On the other hand, if it is too large, the internal resistance tends to increase and it becomes difficult to produce a sufficient output, and the electrode cannot be made thin and the energy density cannot be increased. Therefore, the median diameter A is preferably set in the above range.

  When the lithium transition metal composite oxide powder has a small particle size and the lithium compound is mixed with the previously granulated transition metal compound powder in the production method, the lithium compound is secondary particles as described above. It is particularly important to obtain a lithium transition metal composite oxide powder having the powder physical properties as in the present invention, because it is not preferable because the point sintering between the secondary particles increases.

  The ratio A / B between the median diameter A and the median diameter B is usually 1 or more, 1.5 or less, preferably 1.4 or less, and more preferably 1.3 or less. An A / B smaller than 1 indicates that the particles are aggregated by vibration such as ultrasonic waves, which is not preferable. When A / B is larger than the upper limit in the present invention, it indicates that the degree of particle breakage is large, and that the original particle has a fragile structure. Multiple patterns of destruction can be considered, for example, a pattern in which primary particles peel from secondary particles, a pattern in which secondary particles are partially sintered, or a tertiary particle that is physically entangled is divided into secondary particles. is there. There may also be delamination from tertiary particles to primary particles. In particular, when there are a lot of tertiary particles and the particles are separated into secondary particles by irradiating with ultrasonic waves, A / B shows a large value of 1.5 or more. Such particles may cause deterioration of battery life, capacity reduction due to poor conductive paths, and the like. Further, if the lithium transition metal composite oxide powder particles in the active material slurry continue to be destroyed during the formation of the positive electrode active material layer, the stability of the slurry cannot be maintained, and it is difficult to obtain a clean positive electrode active material layer.

<Maximum particle size>
The maximum particle size of the lithium transition metal composite oxide powder of the present invention is 40 μm or less, and more preferably 35 μm or less. If the maximum particle size exceeds this upper limit, striations are likely to occur during coating film creation.

  The maximum particle size of the lithium transition metal composite oxide powder is measured by a laser diffraction / scattering type particle size distribution measuring device in the same manner as the median size. In this case, the ultrasonic dispersion time is 5 minutes.

<Specific surface area>
The specific surface area (specific surface area of secondary particles) in the BET method of the lithium transition metal composite oxide powder 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. .6m ² / g or more, further preferably 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.

  The specific surface area of the lithium transition metal composite oxide powder is measured by a known BET type powder specific surface area measuring device. Specifically, nitrogen is used for the adsorption gas and helium is used for the carrier gas, and BET one-point measurement by the continuous flow method is performed. First, the 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.

<Tap density>
The tap density of the lithium-transition metal composite oxide powder 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, Most preferably, it is 1.7 g / cm ³ or more, and can be optimized according to the composition ratio and contained elements.

  When the secondary particles of the lithium transition metal composite oxide powder have many point sinterings and form a tufted or beaded tertiary particle structure, the tap density decreases. If the tap density of the lithium transition metal composite oxide powder is below the above lower limit, the amount of the required dispersion medium will increase during coating, and the necessary amount of conductive material and binder will increase. The filling rate of the active material is restricted, and the battery capacity may be restricted.

Examples of the lithium transition metal composite oxide powder having a high tap density include secondary particles in which the primary particles are densely sintered, and the surface of the secondary particles is relatively smooth. Since the positive electrode active material layer is usually made up of a lithium transition metal composite oxide powder, a high density positive electrode active material layer is formed by using a lithium transition metal composite oxide powder having a high tap density. be able to. The tap density is preferably as large as possible, and there is no particular upper limit. However, if the tap density is too large, diffusion of lithium ions using the electrolytic solution in the positive electrode active material layer as a medium becomes rate-determining, and load characteristics may be easily lowered. Usually, it is 2.4 g / cm ³ or less, preferably 2.2 g / cm ³ or less.

  The tap density is about 50 to 500 times / minute from a position of 1 to 5 cm on a wood table by putting about 8 g of lithium transition metal composite oxide powder in a 10 ml glass graduated cylinder. The volume after tapping is measured and obtained until the volume does not change (usually 200 to 800 times).

<Composition>
The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material of the present invention is preferably represented by the following general formula (I), and particularly preferably represented by the following general formula (II).
Li _x MO _2-δ (I)
(In the formula (I), x is a number satisfying 0.5 ≦ x ≦ 1.3, M represents at least one element selected from transition metals, and δ represents −0.1 <δ <. Represents the number 0.1.)
Li _x Ni _a Mn _b Co _c Q _d O _2-δ (II)
(In Formula (II), x is a number of 0.7 ≦ x ≦ 1.3, a is a number of 0.2 ≦ a ≦ 0.8, and b is 0.2 ≦ b ≦ 1.3. Represents a number of 0.8, c represents a number of 0.15 ≦ c ≦ 0.4, Q represents Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Represents at least one element selected from the group consisting of Nb, Ta, Be, Ca, Sc, Al, B and Zr, d represents a number of 0 ≦ d ≦ 0.4, and a + b + c + d = 1 , Δ represents a number of −0.1 <δ <0.1.)

  Lithium transition metal composite oxide powders are generally produced by spray drying a raw material slurry containing a lithium raw material and a transition metal element compound, and firing the resulting dried particles. As the transition metal oxide, a transition metal such as a nickel compound, a cobalt compound, or a manganese compound is preferably used. Particularly preferred are layered nickel manganese cobalt composite oxide particles.

  The atomic ratio of nickel, manganese, and cobalt is such that the layered crystal structure exists stably and the battery characteristics are not deteriorated. In the Ni, Mn, and Co triangular diagrams, Ni / Mn / Co = 1/1/1. Those present on and around the periphery and the Ni / Mn = 1/1 line are preferred.

  Therefore, in the above general formula (II), it is preferable that the value of a and the value of b are substantially the same value, specifically 0.8 ≦ a / b ≦ 1.2, particularly 0.9 ≦ a. It is preferable that /b≦1.1, further 0.93 ≦ a / b ≦ 1.07, and further 0.95 ≦ a / b ≦ 1.05. It is particularly preferable that a, b and c are substantially the same number, 0.8 ≦ a / c ≦ 1.2, particularly 0.9 ≦ a / c ≦ 1.1, and further 0.93 ≦ a. /C≦1.07, more preferably 0.95 ≦ a / c ≦ 1.05. a, b, c are preferably 0.2 ≦ a ≦ 0.4, 0.2 ≦ b ≦ 0.4, and 0.2 ≦ c ≦ 0.4.

  When the proportion of cobalt is relatively large beyond this range, it becomes difficult to synthesize a single-phase lithium-nickel-manganese-cobalt composite oxide, which tends to decrease the rate. Conversely, the proportion of cobalt is relatively large. This will increase the overall cost.

  Furthermore, in order to stabilize the crystal structure of lithium transition metal composite oxide powder, increase its capacity, improve safety, and improve battery characteristics at high temperatures, some nickel, manganese and cobalt sites may be replaced with other metal elements. Substitution is also possible.

  In the general formula (II), Q represents such a substitution element or surface treatment element, and Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, It is at least one selected from Ca, Sc, Al, B and Zr. Q contributes to stabilizing the crystal structure, increasing the capacity, improving safety, and improving battery characteristics at high temperatures. Although various elements can be used as a substitution element, Preferably metal elements, such as aluminum, magnesium, and iron, can be mentioned. Of these, 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 aluminum and magnesium have high performance as positive electrode active materials for lithium secondary batteries. There is an advantage that good performance is exhibited with respect to good battery characteristics, in particular, a discharge capacity retention rate when repeated charge and discharge is performed. Various elements can be used as the surface treatment element, and boron, bismuth, zirconia, silicon, and the like are preferable. 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.

  A plurality of these substituted metal elements may be used.

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

  In the composition of the general formula (II), the amount of oxygen may have some non-stoichiometry. δ is −0.1 <δ <0.1, more preferably −0.05 <δ <0.05, and particularly preferably −0.025 <δ <0.025. Even if δ is small or large, the stabilization of the crystal structure is disturbed, and there is a risk that the capacity of the battery is reduced and the battery life is deteriorated.

  The atomic ratio x of lithium is preferably 0.9 ≦ x ≦ 1.2. If x is too large, the battery capacity of a lithium secondary battery using the x may be reduced.

[Method for producing lithium transition metal composite oxide powder for positive electrode active material of lithium secondary battery]
Below, the manufacturing method of the lithium transition metal complex oxide powder of this invention is demonstrated. The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material of the present invention is a general lithium transition metal composite oxide powder manufacturing method described below. It can be manufactured by adding improvements.

<Method for producing general 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. Then, it can be manufactured by firing.

  Examples of the raw material compound include oxides; inorganic salts such as carbonates, sulfates, nitrates, and phosphates; halides; organic salts, and the like.

Examples of the compound containing lithium 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; Li ₂ O and the like Examples thereof include inorganic lithium compounds, organic lithium compounds such as alkyl lithium 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. In addition, there is an advantage that no harmful substances such as SOx are generated. If desired, two or more lithium compounds may be used in combination.

In the case where a Li raw material is mixed and fired later in a transition metal compound powder having a desired metal ratio in advance, it is preferable to use LiOH or LiOH.H ₂ O. In this case, the particle diameter of the lithium raw material is usually 500 μm or less, preferably 100 μm or less, preferably an average particle diameter in order to increase the mixing property with the dried product obtained by spray drying and to improve battery performance. Preferably it is 50 micrometers or less, Most preferably, it is 20 micrometers or less. On the other hand, those having a too small particle size have an average particle size of usually 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.2 μm or more, and most preferably 0 because the stability in the air is low. .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.

As the compound containing nickel, 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. Among these, compounds containing no nitrogen and sulfur, such as Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, NiC ₂ O ₄ .2H ₂ O, NOx And harmful substances such as SOx are not generated. 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 compounds may be used in combination.

Examples of the compound containing manganese 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. Can be mentioned. 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. If desired, two or more manganese compounds may be used in combination.

Examples of the cobalt-containing compound 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, an organic cobalt compound, Examples thereof include cobalt halides. 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 compounds may be used in combination.

  Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, Ca, Sc, Al, B represented by Q in the general formula (II) In general, an inorganic salt or an organic salt may be used as a raw material compound such as Zr.

  In principle, the mixing ratio of these raw materials may be the composition of the target lithium transition metal composite oxide, but lithium, boron, bismuth, etc. may volatilize during firing. Is formulated considering the volatilization amount.

  The method for mixing the raw materials is not particularly limited, and may be wet or dry. For example, a method using an apparatus such as a ball mill, a vibration mill, or a bead mill can be used. 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.

  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 is used as an index. 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 usually subjected to a drying process. The method is not particularly limited, but spray drying is preferable from the viewpoints of uniformity of the generated particulate matter, powder flowability, powder handling performance, and formation of secondary particles efficiently. 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 materials are wet-mixed, the lithium-containing compound, the boron-containing compound, and the bismuth-containing compound may be wet-mixed together with other raw materials, or other raw materials may be wet-mixed- These may be mixed in a dry manner with a spray-dried product. For example, a raw material other than a lithium compound is wet-mixed and then spray-dried to form a particulate material, and then the lithium compound is dry-mixed and subjected to firing to obtain a target lithium transition metal composite oxide. Thus, it is also possible to subject the raw materials not added during the wet mixing process to dry mixing with the spray-dried particulate matter and subject to firing. That is, as a timing for adding one or more of a lithium source, a boron source and a bismuth source, for example, (1) When weighing raw materials,
(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
Any of the above-described steps may be used.

  The particulate matter thus obtained is then fired to obtain a lithium transition metal composite oxide powder in which primary particles are sintered to form secondary particles.

  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. In addition, the second maximum temperature holding part is not necessarily limited to one time, and two or more stages may be included depending on the purpose, so that aggregation is eliminated to the extent that secondary particles are not destroyed. The temperature raising, maximum temperature holding, and temperature lowering steps may be repeated twice or more with a crushing step meaning or a crushing step meaning crushing to primary particles or even fine powder.

  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. If the temperature is too low, it tends to require a long firing time in order to obtain a lithium transition metal composite oxide having good crystallinity. On the other hand, if the temperature is too high, the lithium transition metal composite oxide is vigorously sintered and fired. The resulting pulverization / pulverization yield is poor, resulting in industrial disadvantages, or the production of lithium transition metal composite oxides with many defects such as oxygen vacancies. The lithium transition metal composite oxides are used as positive electrode active materials. Since the battery capacity of the lithium secondary battery may be reduced or deteriorate due to the collapse of the crystal structure due to charge / discharge, it is usually 1200 ° C. or lower, preferably 1100 ° C. or lower.

  The holding time at the maximum temperature holding portion is usually selected from a wide range of 1 hour to 100 hours. 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 general formula (I), the bulk density such as the tap density of the obtained powder varies depending on the firing atmosphere, so the atmosphere during firing includes oxygen concentration such as air. An atmosphere of 10 to 80% by volume is preferable, and an atmosphere having an oxygen concentration of 10 to 50% by volume is more 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.

  The lithium transition metal composite oxide powder may be used as it is as a lithium secondary battery positive electrode active material, or may be used after surface treatment. Although there are various purposes and effects of the surface treatment, for example, the reactive site on the surface of the positive electrode active material is reduced, and elution of metal elements such as Mn 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, for example.

<Production method for obtaining lithium transition metal composite oxide powder of the present invention>
In order to produce the lithium transition metal composite oxide powder for the positive electrode active material of the lithium secondary battery of the present invention that satisfies the specific physical properties described above, for example, the lithium transition metal composite oxide powder obtained by the firing is used. And a method of crushing under optimized conditions.

  The purpose of pulverizing lithium transition metal composite oxide powders obtained by firing is to lightly break the tertiary particles in a bunch of vines and a daisy chain structure by gentle sintering (point sintering). A large amount of secondary particles are present. Therefore, crushing that is too strong leads to the destruction of the secondary particles, resulting in deterioration of the coating performance when manufacturing the positive electrode, and crushing that is too weak cannot increase the tap density because the tertiary particles are not loosened. Moreover, even if the mortar crushing is the same, if the crushing time is short, the tertiary particle structure cannot be made into secondary particles.

  The crushing method for obtaining the lithium transition metal composite oxide powder having the specific physical properties in the present invention is not particularly limited. For example, a method capable of optimized crushing that is not too strong, specifically, It can be achieved by using a mortar crush, a vibrating sieve with a tapping ball, a pin mill, etc. under optimum conditions. For example, the degree of crushing can be controlled by adjusting the processing time and rotational speed of a vibrating sieve, a pin mill, etc. according to the sintering strength of the particles.

The crushing conditions for realizing the powder physical properties of the lithium transition metal composite oxide powder of the present invention depend on the sintering strength of the sintered powder, but more specifically, as follows. Examples of such conditions are given as examples.
(1) In mortar crushing, 100g is treated for about 10 to 60 minutes. In this mortar crushing, the whole is ground evenly so that there is no visible coarse powder.
(2) For pin mill crushing, it is processed for about 1 to 60 minutes per kg at a rotation speed of about 1000 to 6000 rpm. The treatment time largely depends on the fluidity of the powder, and even if the residence time is adjusted, the degree of crushing does not change.
(3) When crushing with a vibrating sieve, use a magnetic sieve shaker (eg MRK-RETSCH (Mitamura Riken Kogyo-Lecce) Sieve Shaker) and put ceramic balls such as zirconia beads and alumina beads into the sieve. Then, it is applied for 1 to 3 hours with a continuous amplitude of 2 mm.

  After crushing in this way, classification is performed with a mesh sieve having an opening of 20 to 300 μm as necessary.

[Positive electrode of lithium secondary battery of the present invention]
A lithium secondary battery positive electrode is usually formed by forming a positive electrode active material layer containing a lithium transition metal composite oxide powder, a binder, and a conductive material on a current collector. In the present invention, the above-described lithium transition metal composite oxide powder of the present invention is used as the positive electrode active material.

  The lithium secondary battery positive electrode of the present invention is a sheet obtained by dry mixing the lithium transition metal composite oxide powder of the present invention, a binder and a conductive material, and a thickener as necessary. The positive electrode current collector is bonded to the positive electrode current collector, or these materials are dissolved or dispersed in a dispersion medium to form a slurry (coating liquid), which is applied to the positive electrode current collector and dried to form a sheet. Produced by forming a layer on a current collector. 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 lithium transition metal composite oxide powder of the present invention can be dissolved or dispersed in an appropriate dispersion medium together with a coating performance, that is, a binder, a conductive material, and other additives, depending on the specific powder characteristics. When a coating solution is prepared and applied to a positive electrode current collector and dried to form a positive electrode active material layer, the handling property of the coating solution, coating performance, smoothness of the formed coating film, film strength, thin film Since the lithium secondary battery positive electrode of the present invention is excellent in film formability and density with the current collector, the positive electrode active material layer is formed on the positive electrode current collector by application and drying of such a coating solution. Is preferably formed.

  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.

[Lithium secondary battery of the present invention]
The lithium secondary battery of this invention has the lithium secondary battery positive electrode of this invention, the negative electrode which can occlude / release lithium, and the electrolyte containing lithium salt.

  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.

Further, 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, 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 not more than 0 and 0.5 or less, the peak half width of _{P a} is 26cm ^-1 or less, especially 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 alone and lithium aluminum alloys. 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 for 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 (non-aqueous 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, the organic electrolyte is added with a gas such as CO ₂ , N ₂ O, CO, SO ₂ , or polysulfide S _x ²⁻ that forms a good coating that enables efficient charge / 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 blocked 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 restrict | limited to a following example, unless the summary is exceeded.

  When the lithium transition metal composite oxide powder of the present invention is a wet coated positive electrode obtained by applying a slurry of the lithium transition metal composite oxide powder together with a binder and a conductive material to a current collector as described above. It has the characteristics of excellent smoothness of the coated surface, excellent film strength, and excellent adhesion to the current collector. Therefore, for the lithium transition metal composite oxide powders produced in the following examples and comparative examples, the smoothness, strength, and peel resistance from the current collector of the wet-coated positive electrode using the powder are examined by the following method. As a result, the coating properties were evaluated.

[Method for evaluating coating properties]
The composition ratio of lithium transition metal composite oxide powder as positive electrode active material / conductive material (acetylene black) / binder (polyvinylidene fluoride) = 90 wt% / 5 wt% / 5 wt%, N-methyl A slurry was prepared using pyrrolidone (hereinafter referred to as NMP) as a dispersion medium. As the polyvinylidene fluoride, one previously dissolved in NMP (PVDF # 1120) was used. The solid content concentration in the slurry was basically 45% by weight, and when it was an active material with high liquid absorption and could not be dispersed with a homogenizer, NMP was added to adjust the solid content concentration. The higher the solid content concentration, the better the drying efficiency. These raw materials were 20 g of active material, and all the materials were weighed in a 100 cm ³ polycup. After lightly mixing with a spatula, the mixture was stirred for 10 minutes at 3000 rpm with a homogenizer having a blade diameter of about 2 cm, and then bubbles were removed under reduced pressure to obtain a slurry for coating. A 20 μm thick Al foil is used as a current collector, and a slurry of about 10 cm × 10 cm with a gap of 450 μm is drawn on the slurry for coating thereon using a doctor blade, dried in an oven at 100 ° C. for 30 minutes, and then formed. The film forming surface of the active material layer (film thickness of about 200 to 350 μm) was visually observed.

  A film with a streaked line that shows an Al underlayer, a grainy protrusion with a height of 50 μm or more, or more than 5 points, or a film that peels off is marked with x, and there is no such abnormality and a smooth surface is obtained. The marked ones were marked with ○.

(Example 1)
NiO, Co (OH) ₂ 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 was added thereto. The solid content in the slurry was wet pulverized to a median diameter of 0.2 μm using a circulating medium stirring wet bead mill while adding the aqueous solution and stirring. This slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a median diameter of about 5 μm and consisting only of nickel raw material, cobalt raw material and manganese raw material. LiOH powder with a median diameter of 3 μm is added to the obtained granulated particles so that the molar ratio of Li is 1.05 with respect to (Ni + Co + Mn), and dry-mixed to obtain a nickel raw material, a cobalt raw material, and a manganese raw material. A mixed powder of granulated particles and lithium raw material was obtained. This mixed powder is charged into an alumina crucible and heated up to a maximum temperature of 950 ° C. at a temperature increase rate of 5 ° C./min while circulating air, held at 950 ° C. for 12 hours, and then cooled at a temperature decrease rate of 5 ° C./min. As a result, a lithium transition metal composite oxide having a substantially charged molar ratio composition was obtained.

  Next, mortar crushing (30 minutes / 100 g) of the obtained powder was carried out, and then passed through a mesh having a mesh size of 45 μm to obtain a lithium transition metal composite oxide powder of the present invention.

  With respect to this lithium transition metal composite oxide powder, the median diameter A, median diameter B, A / B, maximum particle size, BET specific surface area, tap density, and coating property were examined, and the results are shown in Table 1. The coating property test was conducted at a solid content concentration of 48% by weight, and neither striation nor grain was observed. In this example, a lithium transition metal composite oxide powder having a small change rate of the median diameter before and after ultrasonic dispersion, a high tap density, and excellent coating characteristics was obtained.

(Example 2)
A lithium transition metal composite oxide powder was produced in the same manner as in Example 1 except that pin mill crushing was performed instead of mortar crushing, and the evaluation results are shown in Table 1. The pin mill was operated at a rotational speed of 5340 rpm using a high-purity crusher (pin mill HPC-1 type) manufactured by Chuo Kako Kikai Co., Ltd. Also in this example, a lithium transition metal composite oxide powder having a small median diameter change rate before and after ultrasonic dispersion, a high tap density, and excellent coating properties was obtained.

(Example 3)
In Example 2, NiO, Co (OH) ₂ and Mn ₃ O ₄ were weighed so as to have a molar ratio of Ni: Co: Mn = 0.33: 0.33: 0.33. The solid content in the slurry was wet pulverized to a median diameter of 0.2 μm using a circulating medium agitation type wet bead mill while stirring, and the same except that this was subjected to spray drying, firing and crushing Thus, lithium transition metal composite oxide powders were produced, and the evaluation results are shown in Table 1. Also in this example, a lithium transition metal composite oxide powder having a small median diameter change rate before and after ultrasonic dispersion, a high tap density, and excellent coating properties was obtained.

Example 4
In Example 3, lithium transition metal composite oxide powder was obtained in the same manner except that lithium transition metal composite oxide powder and zirconia beads were placed in a vibrating sieve tray and subjected to vibration for 2 hours. The evaluation results are shown in Table 1. Also in this example, a lithium transition metal composite oxide powder having a small median diameter change rate before and after ultrasonic dispersion, a high tap density, and excellent coating properties was obtained.

(Comparative Example 1)
A lithium transition metal composite oxide powder was produced in the same manner except that crushing was not performed in Example 1, and the evaluation results are shown in Table 1. The lithium transition metal composite oxide powder obtained in this comparative example had a large median diameter change rate before and after ultrasonic dispersion and a low tap density. In the coating property test, the homogenizer could not be kneaded at a solid content concentration of 45% by weight, so the test was carried out at a solid content concentration of 47% by weight, but about 10 granular protrusions were observed.

  Since the lithium transition metal composite oxide powder obtained in Comparative Example 1 was not crushed, the tertiary particles could not be broken and remained, and the tap density did not increase. Moreover, since the tap density is low, the liquid absorption amount of the lithium transition metal composite oxide powder is high, and it is necessary to increase the amount of NMP for preparing the coating slurry. For this reason, the formed active material layer film The strength decreased, and the current collector and the active material layer were partially peeled after drying.

(Comparative Example 2)
A lithium transition metal composite oxide powder was produced in the same manner as in Example 1 except that crushing was performed with a pneumatic classifier (Turboplex 100ATP type, wheel rotation speed: 10,000 rpm) manufactured by Hosokawa Micron Co., Ltd., and evaluation results Is shown in Table 1. The coating property test was carried out at a solid content concentration of 47% by weight because the homogenizer kneading could not be carried out at a solid content concentration of 45% by weight.

  In Comparative Example 2, since the degree of crushing was too strong, pulverization proceeded and the median diameter B was as small as 1.8 μm. Since the median diameter B was too small, the tap density increased and the smoothness of the film of the active material layer was good, but the coating film strength was weak and the active material layer peeled off from the current collector after drying.

(Comparative Example 3)
A lithium transition metal composite oxide powder was produced in the same manner except that crushing was not performed in Example 3, and the evaluation results are shown in Table 1. The coating property test was carried out at a solid content concentration of 47% by weight because it could not be kneaded at a solid content concentration of 45% by weight.

  In Comparative Example 3, the median diameter change rate before and after the ultrasonic dispersion is large, the tap density is low, and the structure of the tertiary particles by light sintering of the secondary particles is not loosened in advance, so that the maximum particle size is the present invention. The upper limit of was exceeded. And many striations generate | occur | produced in the coating film, and also the granular protrusion was scattered.

(Comparative Example 4)
A lithium transition metal composite oxide powder was produced in the same manner as in Example 3 except that pulverization was performed in a mortar (5 minutes / 100 g), and the evaluation results are shown in Table 1. The coating property test was carried out at a solid content concentration of 47% by weight because it could not be kneaded at a solid content concentration of 45% by weight.

  In Comparative Example 4, the tap density is high as in Comparative Example 3, but because the crushing is too weak, the median diameter change rate before and after the ultrasonic dispersion is large, and the structure of the tertiary particles by light sintering of the secondary particles. As a result, the maximum particle size exceeded the upper limit of the present invention, and the coating film had many striations and was further dotted with granular protrusions.

  The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material of the present invention is formed as a lithium secondary battery positive electrode 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 portable electronic devices, communication devices, and automobile power sources.

Claims (6)

Lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery, wherein the lithium transition metal composite powder is added to a 0.1% by weight sodium hexametaphosphate aqueous solution by a laser diffraction method based on JIS Z 8825-1. The median diameter (hereinafter referred to as “median diameter A”) measured without applying ultrasonic waves while circulating and flowing a dispersion liquid in which oxide powder is dispersed at a concentration of 60 to 90% of laser light transmittance 3 μm or more and 10 μm or less,
The median diameter A and the median diameter of the powder measured when ultrasonic dispersion (output 30 W, frequency 22.5 kHz) is applied for 5 minutes while circulating the dispersion liquid (hereinafter referred to as “median diameter B”). (Μm) ratio is 1 ≦ median diameter A / median diameter B ≦ 1.50,
The maximum particle size is 40 μm or less,
Specific surface area by BET method is 0.5 m ² / g or more, 1.5 m ² / g or less,
A lithium transition metal composite oxide powder for a positive electrode active material for a lithium secondary battery, wherein the tap density is 1.55 g / cm ³ or more. The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material according to claim 1, represented by the following general formula (I):
Li _x MO _2-δ (I)
(In the formula (I), x is a number satisfying 0.5 ≦ x ≦ 1.3, M represents at least one element selected from transition metals, and δ is −0.1 <δ <. Represents the number 0.1.) The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material according to claim 2, represented by the following general formula (II).
Li _x Ni _a Mn _b Co _c Q _d O _2-δ (II)
(In Formula (II), x is a number of 0.7 ≦ x ≦ 1.3, a is a number of 0.2 ≦ a ≦ 0.8, and b is 0.2 ≦ b ≦ 1.3. Represents a number of 0.8, c represents a number of 0.15 ≦ c ≦ 0.4, Q represents Fe, Cr, V, Ti, Cu, Ga, Bi, Sn, Zn, Mg, Ge, Represents at least one element selected from the group consisting of Nb, Ta, Be, Ca, Sc, Al, B and Zr, d represents a number 0 ≦ d ≦ 0.4, and a + b + c + d = 1 , Δ represents a number of −0.1 <δ <0.1.)   In the general formula (II), a represents a number of 0.2 ≦ a ≦ 0.4, b represents a number of 0.2 ≦ b ≦ 0.4, and c represents 0.2 ≦ c. The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode active material according to claim 3, wherein ≦ 0.4.   5. The lithium transition for a lithium secondary battery positive electrode active material according to claim 1, wherein the positive electrode active material includes at least a positive electrode active material, a binder, and a conductive material. A positive electrode for a lithium secondary battery, which is a metal composite oxide powder.   A lithium secondary battery comprising a negative electrode and a positive electrode containing materials capable of inserting and extracting lithium, and an electrolyte containing a lithium salt, wherein the positive electrode is the positive electrode of the lithium secondary battery according to claim 5. A lithium secondary battery characterized by.