JP2008013405A - Lithium-nickel-manganese-cobalt multiple oxide, method for producing the same, and application of the multiple oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-nickel-manganese-cobalt multiple oxide used as a positive-electrode active material of an Li-secondary battery, which maintains battery performances, especially discharge capacity and discharge capacity maintenance ratio even when the filling density (pressed density) is increased. <P>SOLUTION: The lithium-nickel-manganese-cobalt multiple oxide, which has press density of 3.3-4.5 g/cm<SP>3</SP>and in which the ratio of particles each having a particle diameter of ≤10 μm is 10-70 vol% in the particle size distribution based on volume, is used as the positive-electrode active material. A preferable lithium-nickel-manganese-cobalt multiple oxide is expressed by following formula: Li<SB>1+a</SB>Ni<SB>b</SB>Mn<SB>c</SB>Co<SB>d</SB>M<SB>e</SB>O<SB>2</SB>(wherein, M is a metal other than Ni, Mn, Co and Li; a+b+c+d+e=1; 0<a≤0.2; 0.2≤b/(b+c+d)≤0.4; 0.2≤c/(b+c+d)≤0.4; 0<d/(b+c+d)≤0.4; and 0≤e≤0.1), and has a BET specific surface area of 0.05-1.0 m<SP>2</SP>/g. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium-nickel-manganese-cobalt composite oxide used for a positive electrode active material for a lithium secondary battery, a method for producing the same, and a use thereof.

In recent years, mobile phones, notebook computers, AV equipment, and the like have been miniaturized and improved in performance, and lithium ion secondary batteries are used as power sources thereof. As a positive electrode material of the secondary battery, LiCoO ₂ having a high filling property and a high capacity is mainly used. For example, in the press bulk density (hereinafter referred to as the press density) when pressed with a tap bulk density that is an index of filling property and a pressure of ² t / cm ₂ , the tap bulk density is about 2.9 g / cm ^{3 in} LiCoO ₂ . The press density was about 3.5 g / cm ³ , that is, a high filling bulk density of 70% of the true density.

Conventionally used LiCoO ₂ for secondary batteries has little decrease in electric capacity at high filling, for example, a high capacity of 150 mAh / g in a charge / discharge test under the condition of 32 mA / g, 4.3-2.5V. Has been achieved. However, LiCoO ₂ has a problem of safety in its discharge characteristics in repeated charge and discharge, and it is indispensable to provide a corresponding safety circuit, and since Co is a rare metal as a main component, cost and resources are low. There was a problem in terms. So by using the positive electrode material for other secondary batteries, it has been attempted to fill the high density positive electrode material per unit volume in order to increase the capacity, in many cases LiCoO ₂ parallel high filling of achieving In addition, even when high filling was possible with a specific composition, the battery performance was lowered due to a decrease in the surface area of the positive electrode material.

For example, a layered structure of LiNi _0.5 Mn _0.5 O ₂ has been proposed as a material that may satisfy high energy density, safety, and cost (Non-Patent Document 1). However, it is difficult for the positive electrode material to satisfy both filling properties and battery performance, and further improvement is required to be used as an alternative to LiCoO ₂ .

As an improvement, a positive electrode material doped with an element other than Ni and Mn has been proposed. However, the positive electrode material shown therein has a filling bulk density at a tap density of 1.4 to 2.8 g / cm ³ , and it was described that a higher filling density has a problem of capacity reduction and is not preferable. (For example, patent document 1).

On the other hand, in a Li—Ni—Co—Mn based composite oxide, 2.3 to 3.2 g / cm ³ is proposed as a range of press density as a composite oxide mixed with a Li raw material. It has been reported up to 09 g / cm ³ (for example, Patent Document 2).

However, these positive electrode materials, more than 3.1 g / cm ³ comparable to LiCoO _2, not that matter LiCoO ₂ moderate 3.3 g / cm ³ and high filling property in a high capacity to exceed is achieved It was.

Further, in the conventional high-filling positive electrode material, for example, a positive electrode active material composed of composite oxide particles containing Li and at least one transition element selected from the group consisting of Co, Ni, Mn and Fe, and its tap density In which 2.9 g / cm ³ or more is proposed. (For example, see Patent Document 3)
However, in this document, although a high capacity can be expected, there is no description of a specific example of high filling of a Li-Ni-Co-Mn based composite oxide that has not been achieved so far, and further, A method for achieving the filling property is a method in which the shape of the oxide particles is spherical and / or elliptical, and there is a problem that the contact area between the particles is small and the internal resistance tends to be high.

Proceedings of the 41st Battery Conference (2000) 460-461 JP 2003-89526 A JP 2003-242976 A JP 2003-17050 A

  New positive electrode active material having high safety in repeated charge / discharge when used as a positive electrode material for a Li secondary battery, high filling property, high battery performance, low cost, and production method thereof, and positive electrode active material thereof Li secondary battery using

As a result of intensive studies on the filling performance and battery performance of the positive electrode material of the secondary battery,
In a composite oxide having lithium, nickel, manganese and cobalt as essential components, which has been known to have a high capacity but has been difficult to achieve a high packing density, the volume-based particle size distribution is 10 μm or less. When the ratio of particles is 10 to 70% by volume, particularly when the ratio of particles of 10 μm or less is 20 to 60% by volume, the press density is 3.1 to 4.5 g / cm ³ , particularly preferably 3 in the same range as LiCoO _2. When a lithium-nickel-manganese-cobalt composite oxide (hereinafter referred to as “composite oxide”) of ³ to 4.5 g / cm ³ is obtained and used as a positive electrode material for a Li secondary battery, The present inventors have found that a Li secondary battery having a high discharge capacity, which is important as battery characteristics, and a high discharge capacity retention rate, can be obtained, and the present invention has been completed.

The composite oxide of the present invention has a press density of 3.3 to 4.5 g / cm ³ and a volume-based particle size distribution in which the proportion of particles of 10 μm or less is 10 to 70% by volume. -Manganese-cobalt composite oxide, in particular, in the composition of 3.4 to 4.5 g / cm ³ by setting the ratio of particles of 10 μm or less to 20 to 60% by volume in the volume-based particle size distribution. It has an unprecedented high filling property. Because of this high press density, it is the first time that this lithium-nickel-manganese-cobalt composite oxide is used as a positive electrode material for a secondary battery. It has been clarified that a Li secondary battery having a high rate can be obtained, and the present invention has been completed.

  By setting it as the said particle size distribution, the particle | grains of 10 micrometers or less are filled in the clearance gap between 10-20 micrometers particle | grains, and a high press density can be obtained.

  Furthermore, although the cause is not necessarily clear, when charging / discharging is performed using this material as a positive electrode, the electrical resistance is reduced by containing particles of 10 μm or less, deterioration during charging / discharging is reduced, and secondary When used as a battery, a high discharge capacity and a high discharge capacity retention rate are obtained.

The press density as used in the field of this invention is a bulk density at the time of pressing with the pressure of ² t / cm <2>, and is the same conditions as the press density currently disclosed by the prior art. Even if the press density of the powder is further pressurized at a high pressure, the value of the packing density is saturated and converges to the same value. Moreover, it is not realistic to apply a higher pressure when actually manufacturing a secondary battery.

The tap bulk density of the composite oxide of the present invention is not particularly limited, but is larger than 2.8 g / cm ³ and not larger than 3.5 g / cm ³ . The tap bulk density of the composite oxide of the present invention is not significantly different from that of the conventional product, but a large difference can be seen by evaluating the press density. The reason why the difference becomes obvious depending on the press density is not clear, but the shape of the composite oxide particles is considered to be one of the causes.

The composite oxide of the present invention is not particularly limited as long as it is a composite oxide having lithium, nickel, manganese and cobalt as essential components, but in particular, the composition represented by the following chemical formula,
_{Li 1 + a Ni b Mn c} Co d M e O 2 ( where, M is Ni, Mn, metal other than Co and Li)
a + b + c + d + e = 1
0 <a ≦ 0.2
0.2 ≦ b / (b + c + d) ≦ 0.4
0.2 ≦ c / (b + c + d) ≦ 0.4
0 <d / (b + c + d) ≦ 0.4
0 ≦ e ≦ 0.1
And it is preferable that it is complex oxide whose BET specific surface area is 0.05-1.0 m < ² > / g.

  A complex oxide having such a composition is likely to have a particularly high capacity when it is highly filled.

  In this chemical formula, M represents a metal other than Ni, Mn, Co, and Li.

  As elements of M, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Tl, C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi, Se, Te, F, Cl, Br, I, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd and the like are exemplified. In particular, Mg, Ca, B, Al, In, Si, Ge, Sn, Y, Ti, Zr, V, Nb, Cr, Mo, Fe, and Zn are preferable.

  a satisfies the range of 0 <a ≦ 0.2, preferably 0 <a ≦ 0.1, more preferably 0.005 <a ≦ 0.05, and still more preferably 0.00. 01 ≦ a ≦ 0.04. b and c satisfy the ranges of 0.2 ≦ b / (b + c + d) ≦ 0.4 and 0.2 ≦ c / (b + c + d) ≦ 0.4, respectively, preferably 0.32 ≦ b ≦ 0.34, 0.32 ≦ c ≦ 0.34. d satisfies 0 <d / (b + c + d) ≦ 0.4. In particular, 0.32 ≦ d ≦ 0.34 is preferable. e is in the range of 0 ≦ e ≦ 0.1.

The BET specific surface area of the composite oxide is preferably 0.05 to 1.0 m ² / g. If it is smaller than this range, the battery performance is lowered, and if it is larger, the filling property is lowered. The BET specific surface area is particularly preferably 0.1 to 0.6 m ² / g.

  The shape of the composite oxide of the present invention is preferably a shape that increases the contact area between the particles, for example, a shape having corners, more specifically a polyhedral particle, and in such a shape, the positive electrode of the secondary battery When used as a material, the internal resistance is reduced.

  The composite oxide particles of the present invention are secondary particles composed of primary particles of 0.1 μm or more and less than 2 μm, and the average particle diameter of the secondary particles is preferably 5 to 30 μm. When it is smaller than this range, the filling property is lowered, and when it is larger, the battery performance is lowered.

  In the composite oxide of the present invention, the proportion of particles of 50 μm or more is preferably 5% or less. When the proportion is more than 5%, it is difficult to produce a flat electrode sheet, and the proportion is more preferably 1% or less, and further preferably 0.5% or less. Furthermore, it is preferable that the ratio of particles of 5 μm or less is 5% or less. When the proportion is more than 5%, the filling property is lowered. Therefore, the proportion is more preferably 1% or less, and further preferably 0.5% or less.

  When charging / discharging using the composite oxide of the present invention as a positive electrode material, the inclusion of particles of 10 μm or less reduces electrical resistance, reduces deterioration during charging / discharging, and is used as a positive electrode for secondary batteries. In such a case, a Li secondary battery having a tube having a high discharge capacity and a high discharge capacity maintenance ratio which are not conventionally obtained can be obtained. Conventionally, there has been a so-called trade-off relationship that when the filling property of the positive electrode material is improved, the discharge capacity maintenance rate of the battery is lowered, and when the discharge capacity maintenance rate is improved, the filling property is lowered. The oxide is a material that can satisfy both the filling property and the discharge capacity maintenance rate of the battery.

  Next, the method for producing the composite oxide of the present invention will be described.

  The composite oxide of the present invention is a mixture of a coprecipitation compound containing nickel-manganese-cobalt and a Li compound in which the proportion of particles of 10 μm or less is 10 to 80% by volume in a volume-based particle size distribution, and 800 to Co-precipitation comprising nickel-manganese-cobalt, which can be produced by firing at a temperature of 1100 ° C., and in particular the proportion of particles of 10 μm or less is 30-70% by volume in a volume-based particle size distribution Preference is given to using compounds.

  By making the particle size distribution as described above, the composite oxide of the present invention after being mixed with the Li raw material and calcined can make the proportion of particles of 10 μm or less 10 to 70% by volume in the volume-based particle size distribution. , Particles of 10 μm or less are filled in the gaps between the particles of 10 to 20 μm, and a high press density can be obtained.

  As the particle size distribution method, a method of mixing coprecipitation compounds prepared under different coprecipitation conditions, a method of pulverizing the coprecipitation compound, and a method of mixing the pulverized coprecipitation compound are preferable.

  Furthermore, the ratio of the 10 μm or less particles of the coprecipitated compound is 30 to 70% by volume, and the ratio of the 10 μm or less particles of the composite oxide can be 30 to 60% by volume.

The composite oxide of the present invention is a nickel-manganese-cobalt coprecipitation compound having a BET specific surface area of 0.5 m ² / g or more and less than 10 m ² / g, or nickel-manganese-cobalt-nickel, metals other than manganese and cobalt. It can be produced by mixing a coprecipitation compound (hereinafter referred to as “coprecipitation compound”) and a Li compound and then firing at a temperature of 800 to 1100 ° C.

The powder physical properties such as the filling properties of the target composite oxide are closely related to the powder physical properties after drying of the coprecipitated compound, which is a precursor mixed with the Li raw material, particularly the BET specific surface area. That is, the BET specific surface area after drying coprecipitation compound is less than 0.5 m ² / g or more ^{10 m} 2 / g, a BET specific surface area of the composite oxide obtained is 0.05 to 1.0 m ² / g range And the filling property can be improved.

When the BET specific surface area after drying of the coprecipitated compound is smaller than 0.5 m ² / g, the battery performance when the obtained composite oxide is used as a positive electrode material of a Li secondary battery is reduced, and 10 m ² / g. As described above, the filling property of the composite oxide is lowered. BET specific surface area after drying of coprecipitated compound is preferably 0.5~8m ² / g, particularly 1 to 5 m ² / g are preferred.

  As the coprecipitation compound used in the present invention, it is preferable to use particles having an average particle diameter of 5 to 30 μm in which plate crystals having a width of 0.2 to 3 μm and a thickness of 0.05 to 2 μm are aggregated.

  When the plate-like crystal is larger than the above range, the battery performance when the obtained composite oxide is used for the positive electrode active material of the Li secondary battery is lowered, and when it is smaller, the filling property is lowered.

  The coprecipitation compound used in the present invention is a nickel, manganese and cobalt salt or nickel, manganese, cobalt and nickel, an aqueous solution in which a metal other than manganese and cobalt is dissolved in water and an alkaline aqueous solution are continuously added to the reaction vessel, It is preferable that the coprecipitation compound slurry obtained is obtained by continuously withdrawing from the reaction vessel.

  There is no limitation on the method of continuous addition of the aqueous metal salt solution and the aqueous alkali solution, but a method of adding both solutions separately and continuously, either one is added continuously, and the other is the pH in the reaction chamber. A method of intermittently adding so as to be constant is preferable. This reaction may be performed in one stage, two stages, or divided into three or more stages.

  The type of the salt of the aqueous metal salt solution is not particularly limited, and examples thereof include an aqueous sulfate solution, an aqueous nitrate solution, and an aqueous chloride solution. Particularly when chloride is used, crystal growth of the coprecipitated compound proceeds, It is particularly preferable because a desired BET specific surface area and shape can be obtained. In addition, chloride is preferable from the viewpoint that there is no sulfate radical residue in the case of sulfate and generation of nitrogen oxides in the case of nitrate.

  In the coprecipitation reaction, the pH in the reaction vessel is particularly preferably in the range of 8-10. This is for controlling the degree of supersaturation. If the pH is lower than this range, the degree of supersaturation increases, but there are many uncoprecipitated components, which is not industrial. If the pH is higher than this range, the degree of supersaturation becomes small and crystal growth is poor, which is not preferable.

  Furthermore, it is particularly preferable to set the temperature in the reaction vessel to 40 ° C. or higher. This is also for controlling the degree of supersaturation. If the reaction temperature is low, the degree of supersaturation becomes small and crystal growth is poor.

In the production method of the present invention, it is preferable to coexist ammonia during nickel-manganese-cobalt coprecipitation. Ammonia is preferably used in the form of a salt, and examples thereof include ammonium chloride, ammonium sulfate, and ammonium nitrate. The ammonia is preferably fed with metal ions. The concentration is preferably 0.1 to 5 wt% as NH _{3 in the} coprecipitation slurry, and more preferably 0.2 to 0.5 wt%. When NH ₃ coexists, the solubility of metal ions is increased, the degree of supersaturation is increased, and a coprecipitated compound grows.

  In the production method of the present invention, the coprecipitation reaction is preferably performed in an inert gas atmosphere. Furthermore, in the present invention, since an aqueous solution in which nickel, manganese and cobalt salts are dissolved in water and an alkaline aqueous solution are continuously added to the reaction vessel, the nickel, manganese and cobalt salt aqueous solution and alkaline aqueous solution to be added also contain an inert gas. It is preferable to create an inert atmosphere by aeration.

  The alkali aqueous solution of the present invention is preferably an aqueous solution of an alkali metal hydroxide, and examples thereof include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like.

  The obtained coprecipitated compound may be appropriately filtered, washed and used in the form of a slurry, and if necessary, dried nickel, manganese and cobalt hydroxide and / or oxyhydroxide. You may take out and use as a product powder.

  When drying, it is preferable to carry out at 50 degrees C or less, and it is especially preferable to carry out in inert gas atmosphere.

  Next, in the present invention, the coprecipitation compound and the Li compound are mixed.

  The Li compound to be used is not particularly limited, and examples thereof include lithium hydroxide and lithium carbonate, and lithium carbonate is particularly preferable from the viewpoint of economy. Moreover, it is preferable that the average particle diameter of lithium carbonate is 10 micrometers or less, and it is more preferable that it is 5 micrometers or less.

  As long as the coprecipitation compound and the Li compound can be mixed uniformly, any method can be applied. Examples of the dry mixing include a tumbling mixing method and a stirring mixing method. Examples of the wet mixing include a method of spray drying after slurry mixing.

  Next, the mixture of the coprecipitation compound and the Li compound is fired to obtain a composite oxide.

  Firing is preferably performed at 800 to 1100 ° C. When the firing temperature is lower than 800 ° C., the crystal growth of the composite oxide is lowered, and the filling property and battery performance are lowered. On the other hand, when the firing temperature is higher than 1000 ° C., crystal growth increases and the filling property is improved, but the battery performance is lowered. The firing temperature is particularly preferably 900 to 1050 ° C.

  In the present invention, it is preferable to wash and dry the composite oxide after firing. Washing with water can remove impurities that adversely affect battery performance. As the water washing, repulp washing in which 5 to 10 times as much water as the sample weight is added and agitated, column washing in which a sample is filled in the column and water is passed, etc. can be suitably used. The end point of washing is preferably 11 or less, more preferably 10 or less, by measuring the pH of the washing solution.

  Drying after washing is preferably 100 to 500 ° C, more preferably 300 to 500 ° C, from which moisture can be sufficiently removed.

  By the method of the present invention, a positive electrode material satisfying unprecedented high press density and high battery performance (high discharge capacity and high discharge capacity retention rate) can be obtained.

  The composite oxide thus obtained is used as a positive electrode active material for a lithium secondary battery.

  Usually, a positive electrode active material and at least a conductive material such as a carbon material, a binder such as polyvinylidene fluoride, and a dispersion medium such as N-methyl-2-pyrrolidone are mixed, applied to a current collector, dried, and pressed. Thus, a positive electrode sheet is obtained.

In the present invention, the density of the positive electrode sheet containing the above-described positive electrode active material for a Li secondary battery, at least a conductive material, and a binder is 2.5 g / cm ³ or more.

  The higher the density, the more the positive electrode active material that can be accommodated in the battery can, and the higher the energy density, that is, the high-performance battery can be produced.

The density is preferably 2.7 g / cm ³ or more, more preferably 3.0 g / cm ³ or more.

  In addition, the content of the conductive material and the binder in the positive electrode sheet of the present invention is preferably 25 wt% or less based on the total weight of the positive electrode active material for Li secondary battery, the conductive material, and the binder, % Or less is more preferable.

  When the content is large, the amount of the positive electrode active material that can be accommodated in the battery can with which the positive electrode sheet becomes bulky decreases, and the energy density of the battery decreases.

Furthermore, the press pressure of the positive electrode sheet electrode for Li secondary batteries is preferably 4 ton / cm ² or less, 3 ton / cm ² or less being more preferred.

  This is because when the pressure is high, the structure of the positive electrode active material for Li secondary battery, the conductive material, and the binder may be destroyed, and the material may not function as the material.

  As the negative electrode active material used in the Li secondary battery of the present invention, metallic lithium and a material capable of occluding and releasing lithium or lithium ions can be used. Examples include lithium metal, lithium / aluminum alloy, lithium / tin alloy, lithium / lead alloy, and carbon materials that can electrochemically insert and desorb lithium ions. A carbon material that can be desorbed is particularly preferable in terms of safety and battery characteristics.

  The electrolyte used in the Li secondary battery of the present invention is not particularly limited. For example, a lithium salt dissolved in an organic solvent such as carbonates, sulfolanes, lactones, ether condyles, or lithium ion conductivity. The solid electrolyte can be used.

  Moreover, there is no restriction | limiting in particular as a separator used with the Li secondary battery of this invention, For example, the microporous film etc. made from polyethylene or a polypropylene can be used.

  When the composite oxide of the present invention has a high press density and is used as a positive electrode of a Li secondary battery, a Li secondary battery exhibiting a high discharge capacity and a high discharge capacity retention rate can be obtained. Exhibits excellent electrochemical performance as an active material.

  Next, although this invention is demonstrated with a specific Example, this invention is not limited to these Examples.

  In Examples and Comparative Examples, the particle size distribution measurement is performed using a laser diffraction scattering type particle size distribution measuring device (Microtrack 9320HRA (X100) Nikkiso Co., Ltd.), using methanol as a solvent, putting a sample in methanol, and exceeding 30 seconds. Measurements were made after sonic dispersion.

Example 1
In a reaction vessel having an internal volume of 12 liters, nitrogen bubbling was performed beforehand in 10 liters of pure water, and then nickel chloride, manganese chloride, cobalt chloride and ammonium chloride were added to Ni: Mn: Co: NH 3 = 0.5 mol / kg: 0.5 mol. / Kg: 0.5 mol / kg: 0.45 mol / kg aqueous solution and 3 mol / kg sodium hydroxide aqueous solution were continuously added while maintaining the pH in the reaction vessel at 9, and continuously from the bottom of the reaction vessel The coprecipitation compound slurry was extracted. The reaction temperature was 60 ° C. and the average residence time was 5 hours.

  The extracted coprecipitated compound slurry 20 hours to 40 hours after the start of the reaction was filtered, washed with pure water, and dried at 80 ° C.

The dried coprecipitated compound has a BET specific surface area of 5 m ² / g, and average particles in which plate crystals having a width of 1.0 to 2.0 μm and a thickness of 0.2 to 0.3 μm are aggregated from the SEM observation image. The particle size was 10 to 30 μm, and the proportion of particles of 10 μm or less was 3% by volume in the volume-based particle size distribution.

  The obtained dry coprecipitated compound was pulverized so that the proportion of particles of 10 μm or less was 50% by volume in the volume-based particle size distribution.

  The pulverized and dried coprecipitated compound was stirred and mixed with lithium carbonate and a Henschel mixer, and calcined in an air stream at 940 ° C. for 12 hours to obtain a composite oxide. The obtained composite oxide was made into a 10% slurry with pure water, filtered, and repeatedly washed with water until the pH of the filtrate reached 10.5. Thereafter, drying was performed at 400 ° C. for 6 hours.

The XRD pattern of the obtained composite oxide is a single phase, the composition is Li _1.04 [Ni _0.32 Mn _0.32 Co _0.32 ] O ₂ , S element is not detected, and 2 t / cm ² The press density when pressurized at a pressure of 3.56 g / cm ³ was high, indicating a high filling property. The BET specific surface area was 0.6 m ² / g.

  The amount of element eluted when pure water was added to form a 10 wt% slurry was 70 ppm. The average particle size was 12 μm, and the proportion of particles of 10 μm or less was 40% by volume in the volume-based particle size distribution.

Example 2
A part of the dry coprecipitation compound obtained in Example 1 was pulverized to obtain a pulverized coprecipitate having an average particle size of 0.6 μm.

  The unground dry coprecipitate and the ground coprecipitate were mixed at a weight ratio of unground coprecipitate: ground coprecipitate = 3: 1.

  In the obtained mixed coprecipitated compound, the ratio of particles of 10 μm or less was 22% by volume in the volume-based particle size distribution.

  A sample was prepared under the same conditions as in Example 1 except that this mixed dry coprecipitate was used.

The obtained composite oxide had a single phase XRD pattern, and the proportion of particles of 10 μm or less was 26 vol% in the volume-based particle size distribution. The BET specific surface area was 0.5 m ² / g.

The press density when pressurized at a pressure of ² t / cm ² was 3.43 g / cm ³ , indicating a high filling property.

Example 3
In Example 2, it was manufactured under the same conditions except that the unground dry coprecipitate and the ground coprecipitate were mixed at a weight ratio of unground coprecipitate: ground coprecipitate = 1: 1.

  In the obtained mixed coprecipitated compound, the ratio of particles of 10 μm or less was 41% by volume in the volume-based particle size distribution.

The obtained composite oxide had an XRD pattern of a single phase, and the proportion of particles of 10 μm or less was 35% by volume in the volume-based particle size distribution. The BET specific surface area was 0.6 m ² / g.

When pressed at a pressure of ² t / cm ² , the press density was 3.52 g / cm ³ , indicating high fillability.

Example 4
In Example 2, it was manufactured under the same conditions except that the unground dry coprecipitate and the ground coprecipitate were mixed at a weight ratio of unground coprecipitate: ground coprecipitate = 1: 3.

  In the obtained mixed coprecipitated compound, the proportion of particles of 10 μm or less was 60% by volume in the volume-based particle size distribution.

Further, the obtained composite oxide had a single phase XRD pattern, and the proportion of particles of 10 μm or less was 58% by volume in the volume-based particle size distribution. The BET specific surface area was 0.8 m ² / g.

The press density when pressurized with a pressure of ² t / cm ² was 3.47 g / cm ³ , indicating a high filling property.

Example 5
In Example 2, all were manufactured on the same conditions except having used only this pulverization coprecipitate.

  In the obtained mixed coprecipitated compound, the proportion of particles of 10 μm or less was 79% by volume in the volume-based particle size distribution.

The obtained composite oxide had a single phase XRD pattern, and the proportion of particles of 10 μm or less in the volume-based particle size distribution was 69% by volume. The BET specific surface area was 1.0 m ² / g.

The press density when pressed with a pressure of ² t / cm ² was 3.31 g / cm ³ .

Comparative Example 1
In Example 1, samples were prepared under the same conditions except that the obtained dry coprecipitated compound was used without being pulverized.

The dried coprecipitated compound has a BET specific surface area of 5 m ² / g, and average particles in which plate crystals having a width of 1.0 to 2.0 μm and a thickness of 0.2 to 0.3 μm are aggregated from the SEM observation image. The particle size was 10 to 30 μm, and the proportion of particles of 10 μm or less was 3% by volume in the volume-based particle size distribution.

The XRD pattern of the obtained composite oxide is a single phase, the composition is Li _1.04 [Ni _0.32 Mn _0.32 Co _0.32 ] O ₂ , S element is not detected, and 2 t / cm ² The press density when pressed at a pressure of 3.28 g / cm ³ was low, and the fillability was low. The BET specific surface area was 0.3 m ² / g, and the tap bulk density was 2.4 g / cm ³ .

  The amount of element eluted when pure water was added to form a 10 wt% slurry was 70 ppm.

  The average particle size was 17 μm, and the proportion of particles of 10 μm or less was 5% by volume in the volume-based particle size distribution.

Comparative Example 2
In Comparative Example 1, samples were prepared under the same conditions except that the firing conditions were 1000 ° C. and 12 hours.

When the obtained composite oxide was pressed at a pressure of ² t / cm ² , the press density was 3.48 g / cm ³ and the filling property was high. The BET specific surface area was 0.3 m ² / g, and the tap bulk density was 2.5 g / cm ³ .

Further, the average particle diameter was 19 μm, and in the volume-based particle size distribution, the proportion of particles of 10 μm or less was 1% by volume.
[Battery evaluation test]
Initial discharge capacity and strong discharge characteristics The positive electrode materials obtained in the examples and comparative examples were mixed at a ratio of 2: 1 by weight with a mixture of polytetrafluoroethylene and acetylene black (trade name: TAB-2) as a conductive agent. And formed into a pellet on a mesh (manufactured by SUS316) at a pressure of 1 ton / cm ² , and then dried under reduced pressure at 150 ° C. to prepare a battery positive electrode. Electrolysis in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / dm ^{3 in} the obtained battery positive electrode, a negative electrode composed of a lithium metal foil (thickness 0.2 mm), and a mixed solvent of ethylene carbonate and diethyl carbonate A CR2032-type coin cell was constructed using the liquid.

Using this battery, the battery voltage was charged and discharged 30 times with a constant current between 4.5 V and 2.5 V, and cycle characteristics were evaluated. The ratio of the 30th average discharge voltage to the first average discharge voltage was determined as the discharge voltage. The ratio of the 30th discharge capacity to the first discharge capacity was defined as the discharge capacity maintenance ratio. The current density was 0.75 mA / cm ² and the temperature was 23 ° C. The initial discharge capacity, discharge voltage maintenance rate, and discharge capacity maintenance rate are shown in Table 1 below.

この表から本願発明の実施例においては、高いプレス密度、高い放電容量、且つ、高い放電容量維持率が得られた。

From this table, in the examples of the present invention, a high press density, a high discharge capacity, and a high discharge capacity retention rate were obtained.

Further, in FIG. 1, when the ratio of particles of 10 μm or less in the volume-based particle size distribution of the lithium-nickel-manganese-cobalt composite oxides of Examples 1 to 5 and Comparative Example 1 is pressurized at a pressure of ² t / cm ^2. The relationship of the press density of is shown.

  From this figure, it is clear that the press density increases when the ratio of particles of 10 μm or less is in the range of 10 to 70% by volume, and is particularly high in the range of 20 to 60% by volume.

  2 to 7 show graphs representing the volume-based particle size distributions of the lithium-nickel-manganese-cobalt composite oxides of Examples 1 to 5 and Comparative Example 1. FIG.

Relationship between the ratio of particles of 10 μm or less in the volume-based particle size distribution of the lithium-nickel-manganese-cobalt composite oxides of Examples 1 to 5 and Comparative Example 1 and press density when pressed at a pressure of ² t / cm ² It is a graph showing. 2 is a graph showing a volume-based particle size distribution of the lithium-nickel-manganese-cobalt composite oxide of Example 1. FIG. 3 is a graph showing a volume-based particle size distribution of a lithium-nickel-manganese-cobalt composite oxide of Example 2. FIG. 4 is a graph showing a volume-based particle size distribution of a lithium-nickel-manganese-cobalt composite oxide of Example 3. FIG. 6 is a graph showing a volume-based particle size distribution of a lithium-nickel-manganese-cobalt composite oxide of Example 4. 6 is a graph showing a volume-based particle size distribution of a lithium-nickel-manganese-cobalt composite oxide of Example 5. 4 is a graph showing a volume-based particle size distribution of a lithium-nickel-manganese-cobalt composite oxide of Comparative Example 1.

Claims (11)

A lithium-nickel-manganese-cobalt composite oxide having a press density of 3.3 to 4.5 g / cm ³ and a ratio of particles of 10 μm or less in a volume-based particle size distribution of 10 to 70% by volume. 2. The lithium-nickel-manganese-cobalt according to claim 1, wherein the press density is 3.4 to 4.5 g / cm ³ , and the proportion of particles of 10 μm or less is 20 to 60% by volume in a volume-based particle size distribution. Complex oxide. It is a composition represented by the following chemical formula,
_{Li 1 + a Ni b Mn c} Co d M e O 2 ( where, M is Ni, Mn, metal other than Co and Li)
a + b + c + d + e = 1
0 <a ≦ 0.2
0.2 ≦ b / (b + c + d) ≦ 0.4
0.2 ≦ c / (b + c + d) ≦ 0.4
0 <d / (b + c + d) ≦ 0.4
0 ≦ e ≦ 0.1
The lithium-nickel-manganese-cobalt composite oxide according to claim 1 or 2, wherein the BET specific surface area is 0.05 to 1.0 m ² / g. In a volume-based particle size distribution, a coprecipitation compound containing nickel-manganese-cobalt in which the proportion of particles of 10 μm or less is 10 to 80% by volume and a Li compound are mixed and then fired at a temperature of 800 to 1100 ° C. The method for producing a lithium-nickel-manganese-cobalt composite oxide according to claim 1. 5. The lithium-nickel-manganese-cobalt composite oxidation according to claim 4, comprising nickel-manganese-cobalt having a particle size distribution of 10 μm or less in a volume-based particle size distribution of 30 to 70% by volume. Manufacturing method. A coprecipitation compound comprising nickel-manganese-cobalt having a BET specific surface area of 0.5 m ² / g or more and less than 10 m ² / g and a Li compound are mixed and then calcined at a temperature of 800 to 1100 ° C. The method for producing a lithium-nickel-manganese-cobalt composite oxide according to claim 5. 5. The nickel-manganese-cobalt coprecipitation compound is obtained by continuously adding an aqueous solution obtained by dissolving nickel, manganese and cobalt salts in water and an alkaline aqueous solution to the reaction vessel. The method for producing a lithium-nickel-manganese-cobalt composite oxide according to -6. The method for producing a lithium-nickel-manganese-cobalt composite oxide according to claim 7, wherein the aqueous salt solution of nickel, manganese and cobalt is an aqueous chloride solution. The coprecipitation compound comprising nickel-manganese-cobalt and the Li compound are mixed, calcined at a temperature of 800 to 1100 ° C, washed, and dried at 300 to 500 ° C. A method for producing the lithium-nickel-manganese-cobalt composite oxide described in 1. A positive electrode active material for a Li secondary battery comprising the lithium-nickel-manganese-cobalt composite oxide according to claim 1. A Li secondary battery comprising the lithium-nickel-manganese-cobalt composite oxide according to claim 1, wherein the positive electrode active material.

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