JP3806262B2 - Method for producing lithium-containing composite oxide for positive electrode active material of lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lithium-containing composite oxide for a positive electrode active material for a lithium secondary battery, and more specifically, a lithium secondary battery positive electrode having improved crystallinity by specifying a mixing condition of a cobalt compound and a lithium compound. The present invention relates to a method for producing a lithium-containing composite oxide for an active material.
[0002]
[Prior art]
Conventionally, lithium cobalt oxide (LiCoO ₂ ) has been used as a positive electrode active material for lithium secondary batteries. Recently, studies are also being conducted on the use of lithium-containing composite oxides obtained by adding a third component to lithium cobaltate as a positive electrode active material for lithium secondary batteries.
[0003]
This lithium cobaltate is synthesized by mixing and firing a cobalt salt and a lithium salt. In addition, the lithium-containing composite oxide to which the third component is added includes a cobalt-containing salt obtained by partially substituting cobalt obtained by coprecipitation of a salt containing the element of the third component and a cobalt salt with other elements. It is synthesized in the same way.
[0004]
When synthesizing the above-described lithium cobaltate, usually the above-mentioned cobalt-containing salt and lithium salt are used as powders, and these powders are mixed by a mixing means such as a ball mill, drum mixer, nauter mixer, etc. A method of firing is used. However, conventionally, when the cobalt-containing salt and the lithium salt are mixed as described above, if the particle size of the raw lithium salt is large, the lithium salt and the cobalt-containing salt are locally unevenly distributed in the mixed powder. As a result, there was a problem that uniform mixing was not possible. When such a non-uniformly distributed portion exists, the synthesis reaction becomes insufficient, and there is a disadvantage that a cobalt-rich phase such as cobalt oxide or a lithium-rich phase is formed in the lithium-containing composite oxide after firing. .
[0005]
As a countermeasure for this, Japanese Patent Application Laid-Open No. 7-262994 discloses a manufacturing method in which the rate of temperature rise and the oxygen concentration are finely limited. Although this method can suppress the free cobalt oxide to a low concentration, it requires a high oxygen concentration at the time of firing, so a firing furnace having a specific structure is necessary, and the equipment becomes expensive. There is a point.
[0006]
Further, it has been proposed to use a lithium salt fine powder having a small particle size as a countermeasure for preventing formation of a portion in which the lithium compound and the cobalt-containing salt are unevenly distributed. However, conventionally, when the fine lithium salt fine powder is used, the lithium salt is agglomerated during the mixing, and as a result, the above-mentioned problem that the lithium salt and the cobalt-containing salt are unevenly distributed can be solved. There wasn't. Such a decrease in the uniformity of the crystal phase in the lithium-containing composite oxide is a serious problem because the battery capacity is reduced when the lithium-containing composite oxide is used as a positive electrode active material for a lithium secondary battery.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a lithium-containing composite oxide having high crystal phase uniformity and useful as a positive electrode active material for a lithium secondary battery.
[0008]
[Means for Solving the Problems]
The above object of the present invention is solved by providing a method for producing the lithium-containing composite oxide of the present invention. That is, in this invention, the manufacturing method of the lithium containing complex oxide for lithium secondary battery positive electrode active materials represented by following formula (1) synthesize | combined by baking the mixture containing a cobalt compound and a lithium compound. The lithium-containing composite oxide for a positive electrode active material for a lithium secondary battery is characterized in that the water content of the lithium compound at the time of mixing the cobalt compound and the lithium compound is 0.15 to 5% by weight. A method is provided (wherein x is a real number from 0.9 to 1.1, y is a real number from 0 to 0.9, and M is Ni, Mn, Fe, V And one or more elements selected from the group consisting of Cr, Al, Mg, Ti, Y, Ce, Nb, Zr, Si, and Ca.
[0009]
[Chemical 2]
[0010]
In the production method of the present invention, the cobalt compound is cobalt oxide (Co ₃ O ₄ , Co ₂ O ₃ or a mixture thereof), cobalt hydroxide (Co (OH) ₂ ), cobalt oxyhydroxide (CoOOH). And one or more selected from the group consisting of compounds containing cobalt carbonate (CoCO ₃ ), and the lithium compound is preferably selected from the group consisting of lithium carbonate and lithium hydroxide.
[0011]
Furthermore, in the manufacturing method of this invention, it is preferable that the said lithium compound is 1-10 micrometers in weight average particle diameter.
Moreover, in the manufacturing method of this invention, it is preferable to bake the said mixture at 850-1000 degreeC in air | atmosphere.
[0012]
Furthermore, in the manufacturing method of this invention, it is preferable to make baking time into 10 to 50 hours.
[0013]
Moreover, the above mixture is preferably pulverized and mixed after being fired at 300 ° C. to 800 ° C., and is preferably fired at 850 ° C. to 1000 ° C., since the uniformity is improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing a lithium composite oxide for a positive electrode active material of a lithium secondary battery according to the present invention comprises mixing a cobalt compound and a lithium compound at a water content of 0.15 to 5% by weight and firing the mixture. A lithium composite oxide represented by the formula (1) is produced.
[0015]
The lithium-containing composite oxide of the present invention may or may not contain the third component (M) other than lithium and cobalt, and y in the above formula (1) is in the range of 0 to 0.9. Is preferred. M as the third component added when y is not 0 is selected from the group consisting of Ni, Mn, Fe, V, Cr, Al, Mg, Ti, Y, Ce, Nb, Zr, Si, and Ca. One or more elements are preferred, and Ni and Mn are particularly preferably used in the present invention. M may consist of a plurality of components, in which case y is the sum of the added amounts of the plurality of M components.
[0016]
A lithium secondary battery using a lithium composite oxide in which the third component M is made of Ni as a positive electrode active material is preferable because a high battery capacity can be achieved. In addition, a lithium secondary battery using a lithium composite oxide whose third component M is Mn as a positive electrode active material maintains the battery characteristics, and the cost of the lithium composite oxide is low because the price of the Mn raw material is low. It is preferable because it can be lowered. Moreover, a cobalt compound can also be used in mixture of 2 or more types of compounds. However, the cobalt compound is particularly preferably used as a single compound from the viewpoint of workability.
[0017]
Examples of the cobalt compound in the present invention include cobalt oxide, cobalt hydroxide (Co (OH) ₂ ), cobalt oxyhydroxide (CoOOH), and cobalt carbonate (CoCO ₃ ) made of Co ₃ O ₄ , Co ₂ O ₃ or a mixture thereof. ) -Containing compounds. When y is not 0, M as the third component is preferably added to the mixture containing the cobalt compound and the lithium compound before firing as an oxide, hydroxide, carbonate, or the like. In order to improve the uniformity, it is preferable to pre-coprecipitate, for example, a cobalt compound and a compound containing the third component to prepare a solid solution with high uniformity of cobalt and M, and then mix the lithium compound. .
[0018]
Moreover, as said lithium compound, lithium carbonate or lithium hydroxide is preferable. Also, two or more lithium compounds can be mixed and used. However, from the viewpoint of workability, the above-described lithium compound is particularly preferably used as a single compound.
[0019]
In the present invention, it is preferable to add the above-described lithium compound as fine powder as fine as possible in terms of improving discharge characteristics. In this case, the weight average particle size of the lithium compound fine powder is preferably 1 to 10 μm, and particularly preferably 2 to 7 μm in order to improve battery characteristics such as discharge characteristics. When the lithium compound fine powder exceeds 10 μm, it is not preferable because the lithium compound as a raw material remains in the lithium-containing composite oxide produced and the uniformity of the crystal phase is lowered. On the other hand, if the thickness is less than 1 μm, workability deteriorates, which is not preferable. In the present invention, the weight average particle size is the particle size at which the cumulative curve is 50% when the particle size distribution is determined on a mass basis and the cumulative curve is determined with the total mass being 100% (Chemical Engineering Handbook). “Revised 5th edition” edited by Chemical Industry Association, pages 220-221).
[0020]
Conventionally, even when a lithium compound having such a weight average particle diameter is used, the lithium compound and the cobalt compound cannot be mixed uniformly, and the discharge characteristics of the lithium secondary battery are deteriorated. It was not obtained. As a result of diligent study, the present inventors have formed an aggregate when the lithium compound fine powder used is mixed, and this aggregation of the lithium compound is one of the reasons that a sufficient uniform crystal phase cannot be obtained. I found out.
[0021]
Various means for suppressing such aggregation during mixing of the lithium compound are conceivable. However, as a result of intensive studies, the present inventors have remarkably improved the aggregation of the lithium compound by adding moisture to the lithium compound. The inventors have found that the present invention has been achieved. At this time, the water content of the lithium compound is preferably 0.15 to 5% by weight in the lithium compound. When the water content of the lithium compound is less than 0.15% by weight, salt aggregation cannot be sufficiently suppressed, and cobalt oxide or the like remains in the lithium-containing composite oxide after firing, which is not preferable. On the other hand, if the water content exceeds 5% by weight, the stickiness of the salt at the time of mixing increases, and the workability decreases, which is not preferable. The water content described above is particularly preferably 0.3 to 1.0% by weight.
[0022]
Firing can be performed in the air or in an oxygen atmosphere. However, firing is preferably performed in the air from the viewpoint of workability and cost reduction of equipment. In this case, the firing temperature is preferably 850 to 1000 ° C., and the firing time is preferably 10 to 50 hours. In the firing, a method of calcining at 300 to 800 ° C. for several hours as a calcination before firing, remixing, and firing under the above-mentioned conditions is also used for the purpose of improving the uniformity of the crystal phase. it can.
[0023]
In the present invention, the function and function by setting the water content at the time of mixing the lithium compound to 0.15 to 5% by weight is considered as follows.
[0024]
In the case of small pulverized lithium compounds having an average particle size of 10 μm or less, the particles are agglomerated due to static electricity, and the lithium compound and cobalt compound are locally uneven in the raw material mixed powder. A new part arises. Further, the electrostatically charged lithium compound adheres to the inner wall of a mixing device such as a ball mill, a drum mixer, and a nauter mixer, for example, and similarly forms a small particle lump. For the two reasons described above, it is practically difficult to uniformly mix the lithium compound having a weight average particle diameter of 10 μm or less and the cobalt compound in a static state.
[0025]
By mixing a lithium compound with a small amount of water as in the present invention, static electricity generated between particles that is a cause of this mixing failure can be suppressed, and generation of aggregated lithium compound small agglomerates caused by static electricity or It is considered that the formation of small agglomerates caused by the lithium compound adhering to the inner wall of the mixing apparatus is prevented, and the effect of preventing the decrease in crystallinity after firing and the remaining of cobalt oxide or the like is produced. Furthermore, when a lithium compound fine powder having a weight average particle size of 10 μm or less is reacted with a cobalt compound, the lithium compound fine powder exhibits extremely high reactivity with the cobalt compound in the synthesis process, and the resulting lithium-containing composite oxide crystal The uniformity can be further increased. If the lithium-containing composite oxide synthesized as a result is used as a positive electrode active material for a lithium secondary battery, battery performance such as a discharge capacity of the lithium secondary battery can be further improved.
[0026]
There are two methods for adding water to the lithium compound: a method in which water remains in the lithium compound in the production stage of the lithium compound, and a method in which water is added to the lithium compound by spraying or the like. Even if it is added to a part of the mixture and mixed only by mixing means such as a stirring mill, moisture can be uniformly added, and a sufficient effect can be obtained. The water content can be measured according to a general dry weight method (see JIS K0068.5. Dry weight method).
[0027]
A method of using the lithium-containing composite oxide in the present invention as a lithium secondary battery positive electrode active material for a lithium secondary battery is exemplified below.
[0028]
80 to 90% by weight of a lithium-containing composite oxide, 5 to 16% by weight of acetylene black as a conductive material, 4 to 15% by weight of polytetrafluoroethylene (hereinafter referred to as PTFE) as a binder, and an organic solvent Is applied to a current collector (eg, foil, net, porous body of aluminum, nickel, stainless steel, etc.) as a paste state, dried, and then pressed at a pressure of 0.5 to ^2.5 t / cm ² After the forming, vacuum drying is performed again to obtain a positive electrode plate.
[0029]
On this positive electrode plate, a negative electrode such as metallic lithium and a separator are laminated, and sealed in an electrolytic solution to obtain a lithium secondary battery. Examples of the electrolytic solution include simple substances or mixtures of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethylene carbonate, and the like. Examples of the electrolyte solute include inorganic lithium salts and organic lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , and CF ₃ SO ₃ Li.
[0030]
【Example】
Examples of the present invention are shown below. Examples 1 to 3 are examples, and example 4 is a comparative example.
The lithium-containing composite oxide for a lithium secondary battery positive electrode active material was produced by the following method.
[0031]
[Example 1]
50 parts by weight of cobalt oxide (Co ₃ O ₄ , weight average particle size 6 μm: the same particle size up to Example 4) and lithium carbonate having a water content of 0.15 wt% (weight average particle size 4 μm: the same particle size up to Example 4) ) 22 parts by weight were mixed with a ball mill so as to be uniform. The obtained mixture was heated at a rate of temperature increase of 2 ° C./min and calcined in the atmosphere at 890 ° C. for 30 hours to obtain LiCoO ₂ .
[Example 2]
The same operation as in Example 1 was performed using 50 parts by weight of cobalt oxide and 22 parts by weight of lithium carbonate having a water content of 0.25% by weight to obtain LiCoO ₂ .
[Example 3]
The same operation as in Example 1 was performed using 50 parts by weight of cobalt oxide and 22 parts by weight of lithium carbonate having a water content of 0.50% by weight to obtain LiCoO ₂ .
[Example 4]
The same operation as in Example 1 was performed using 50 parts by weight of cobalt oxide and 22 parts by weight of anhydrous lithium carbonate to obtain LiCoO ₂ .
[0032]
LiCoO ₂ synthesized in Examples 1 to 4 was subjected to powder X-ray diffraction (CuKα ray) measurement, residual cobalt oxide content analysis, and battery evaluation. The above measurement, analysis, and battery evaluation were performed as follows. Moreover, the weight average particle diameter in each example was measured by Nikkiso Co., Ltd. Microtrac HRAX-100.
[0033]
[Powder X-ray diffraction (CuKα ray) measurement]
The powder obtained by pulverizing and classifying synthesized LiCoO ₂ was measured by a powder X-ray diffraction method (CuKα ray), and it was confirmed whether a diffraction line near 2θ = 36.5 ° due to residual Co ₃ O ₄ was visually recognized. . The results were evaluated in three stages: presence of diffraction lines, slight presence, and absence. As the X-ray diffractometer, an X-ray diffractometer XD-D1 manufactured by Shimadzu Corporation was used.
[0034]
[Amount analysis of residual cobalt oxide]
A glass filter precisely weighed was prepared, and the weight of the glass filter at this time was defined as w0 (g). About 1 g of synthesized LiCoO ₂ (the weight of LiCoO ₂ at this time is defined as wA (g)) was precisely weighed, added to the FeSO ₄ solution, and stirred at room temperature for 1 hour. Thereafter, the solution was filtered through the above-described glass filter with a constant balance, and the glass filter was dried and allowed to cool at 120 ° C. for 1 hour. The weight of the glass filter at this time was defined as w1 (g). The residual cobalt oxide amount (g) was determined from the following formula (1).
[0035]
[Expression 1]
[0036]
[Battery evaluation]
80 parts by weight of the powder obtained by pulverizing and classifying synthesized LiCoO ₂ , 16 parts by weight of acetylene black and 4 parts by weight of PTFE were mixed, and toluene was added to form a paste. The paste was vacuum-dried, pressed with a pressure of ² t / cm ² to a thickness of 0.15 mm, and cut into a 1.2 cm square to obtain a positive electrode plate. Using this positive electrode plate, a charge / discharge test was conducted using Li metal as a counter electrode assembled in a coin cell. As an electrolytic solution, a solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) was used. The discharge capacity was measured by repeatedly charging and discharging to 0.9V / cm ² to 4.3V and then discharging to 2.5V. The first (1st), 10th (10th), 20th ( 20th) discharge capacity was measured. The obtained results are shown in Table 1.
[0037]
[Table 1]
[0038]
From the results of Table 1, it was found that the amount of remaining cobalt oxide can be suppressed by adding water to lithium carbonate fine powder, mixing and firing, and the crystal phase can be made to be a more uniform phase of lithium cobaltate.
Table 2 shows the battery characteristics measured for Examples 1 to 4.
[0039]
[Table 2]
[0040]
【The invention's effect】
As described above, by providing a method for producing a lithium-containing composite compound that uses a lithium compound having a certain water content when the cobalt compound of the present invention and a lithium compound are mixed, a uniform layer excellent in crystallinity is provided. A lithium-containing composite oxide can be provided. Moreover, a high-performance lithium secondary battery can be provided by using the lithium-containing composite oxide as a positive electrode active material.

Claims (4)

The mixture containing the cobalt compound and the lithium compound, the method for producing a lithium secondary battery positive electrode active material for a lithium-containing composite oxide represented by the following formula (1) which is synthesized by firing, said cobalt compound and containing A method for producing a lithium-containing composite oxide for a positive electrode active material for a lithium secondary battery, comprising mixing the lithium compound having a water content of 0.15 to 5% by weight and a weight average particle diameter of 1 to 10 μm. (In the formula (1), x is a real number of 0.9 to 1.1, y is a real number of 0 to 0.9, and M is Ni, Mn, Fe, V, Cr, Al, One or more elements selected from the group consisting of Mg, Ti, Y, Ce, Nb, Zr, Si, and Ca are shown.
The cobalt compound is composed of cobalt oxide (Co ₃ O ₄ , Co ₂ O ₃ or a mixture thereof), cobalt hydroxide (Co (OH) ₂ ), cobalt oxyhydroxide (CoOOH), and cobalt carbonate (CoCO ₃ ). The lithium-containing composite oxide for a lithium secondary battery positive electrode active material according to claim 1, wherein the lithium compound is one or more selected from the group consisting of lithium carbonate and lithium hydroxide. Manufacturing method. The manufacturing method of the lithium containing complex oxide for lithium secondary battery positive electrode active materials of Claim 1 or 2 which bakes the said mixture at 850-1000 degreeC in air | atmosphere. The method for producing a lithium-containing composite oxide for a lithium secondary battery positive electrode active material according to claim 1, 2, or 3 , wherein the mixture is fired for 10 to 50 hours.