WO2019078563A1 - Sagger for firing lithium secondary battery positive electrode active material and method for manufacturing same - Google Patents

Abstract

The present invention provides a sagger for firing a lithium secondary battery positive electrode active material, wherein the sagger includes 70 to 99.5 at.% of MgO and 0.5 to 30 at.% of Al2O3 and has a porosity of 10 % or less. According to the present invention, the sagger has increased strength and thermal shock resistance in comparison with a conventional sagger and has a lowered reactivity with lithium, and thus is not broken even after being fired repeatedly 100 times or more. Considering that a conventional sagger is broken after being firing about 30 times, the sagger according to the present invention has a durability at least 3 times higher than the conventional sagger.

Description

LITHIUM SECONDARY BATTERY CORE ACTIVATING MATERIAL AND METHOD FOR MANUFACTURING THE SAME

The present invention relates to the improvement of the lifetime of a fireproof container for firing a cathode active material of a lithium secondary battery using a material which has low reactivity with lithium and has high strength and thermal shock resistance compared to existing commercial fireplaces.

Smart phones, laptops and other portable electronic devices, and recently, eco-friendly automobiles such as hybrid and electric vehicles have been developed and become popular. The performance of electronic devices and electric vehicles is closely related to the capacity and efficiency of a battery. Accordingly, development of a high performance lithium secondary battery having excellent stability and high energy density has been competitive.

The cathode active material used for the lithium secondary battery is composed of Li, Co, Mn, Ni, etc., and the raw material is buried in a fireproof container and fired at 400 to 1000 ° C. At this time, the Li and Co compounds are melted and penetrate into the pores of the inner wall and react with the constituents to cause cracking and peeling. The quality of the cathode material is deteriorated by the reactant in the peeled inner shell, and when the inner shell is broken due to cracking, the cathode material may deteriorate in performance when it is introduced into a subsequent process.

Conventional intumescent shells have been developed in such a way that less reactive material is coated on the surface of the inner shell or the thermal shock resistance of the inner shell itself is increased. However, it is disadvantageous that mass production is difficult due to the complication of coating or peeling occurs due to a difference in thermal expansion coefficient from the inner wall material. There is a problem in that it only reacts with the cathode active material in a degree of reducing the degree of the reaction.

An object of the present invention is to improve the service life of a firebox, which is a plastic container of a lithium ion battery cathode active material.

In order to achieve the above object, the present invention provides a lithium secondary battery for cathode active material, which comprises 70 to 99.5 at.% Of MgO and 0.5 to 30 at.% Of Al2O3, and has a porosity of 10% I will provide my wallet.

In one embodiment, the strength of the inner shell may be greater than or equal to 600 MPa.

In addition, the present invention includes a step of mixing a MgO powder and an Al 2 O 3 powder to prepare a mixed powder, molding the mixed powder into a predetermined shape to produce a molded body, and sintering the molded body at a temperature of 1550 to 1700 ° C And the mixed powder is composed of 70 to 99.5 at.% Of MgO and 0.5 to 30 at.% Of Al2O3. The present invention also provides a method of manufacturing an inner shell for firing a lithium secondary battery cathode active material.

In one embodiment, the MgO powder may be a mixture of two kinds of powders having different average particle diameters.

In one embodiment, the average particle diameter of any one of the two kinds of powders may be 27 to 33 mu m and the average particle diameter of the other one may be 3 to 8 mu m.

In one embodiment, the Al2O3 powder may have an average particle diameter of 0.5 to 10 mu m.

In one embodiment, the average particle size of the MgO powder and the average particle size of the Al2O3 powder may be the same.

In one embodiment, the MgO may be dead burnt MgO or molten MgO.

According to the present invention, the strength and the thermal shock resistance of the existing firefly are increased, and the reactivity with lithium is lowered, so that the firefly is not damaged even after the firing is repeated 100 times or more. In view of the fact that the conventional inner wall is broken at about 30 times of firing, the inner wall according to the present invention has a durability 3 times higher than that of the conventional inner wall.

1 is a conceptual diagram showing a sintering process of a lithium ion battery cathode active material.

Figs. 2A and 2B are photographs of samples used for evaluating the performance of the fireproof glove according to the present invention.

Figs. 3A to 3C are SEM photographs of an inner fire wall according to the present invention.

FIG. 4 is a photograph of a conventional inner fire coat after being repeatedly fired 30 times.

FIG. 5 is a photograph of the inner fire coat according to the present invention taken after firing 100 times.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals are used to designate identical or similar elements, and redundant description thereof will be omitted. The suffix " module " and " part " for the components used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role. In the following description of the embodiments of the present invention, a detailed description of related arts will be omitted when it is determined that the gist of the embodiments disclosed herein may be blurred. In addition, it should be noted that the attached drawings are only for easy understanding of the embodiments disclosed in the present specification, and should not be construed as limiting the technical idea disclosed in the present specification by the attached drawings.

It is also to be understood that when an element such as a layer, region or substrate is referred to as being present on another element "on," it is understood that it may be directly on the other element or there may be an intermediate element in between There will be.

Before describing the inner shell for firing the cathode active material of the lithium secondary battery according to the present invention, the inner shell for firing the cathode active material of the lithium secondary battery will be described.

Referring to FIG. 1, the lithium secondary battery cathode active material is composed of a mixture of Li and at least one of Co, Ni, Mn, and Fe. The mixture is calcined in an inner shell to prepare a cathode active material of a lithium secondary battery.

During the calcination of the mixture, a chemical reaction between lithium and the inner shell may occur. When a chemical reaction occurs between lithium and the inner shell, the inner shell is peeled off, making it impossible to reuse.

Conventionally, in order to prevent lithium from reacting with the inner shell, the composition of the inner shell was composed of a mixture of Al ₂ O ₃ (main component), SiO ₂ , and MgO. However, there is a problem in that the inner fire coat is peeled off at about 30 times of firing and can not be reused anymore.

In order to solve the above-mentioned problems, the present invention provides an inner shell composed of 70 to 99.5 at.% MgO and 0.5 to 30 at.% Al ₂ O ₃ .

MgO is a major constituent of the fire coat according to the present invention. Since MgO has a very low reactivity with Li, it is possible to prevent the firefly and lithium from reacting during repeated firing.

When the entire inner shell is made of MgO, the reactivity to Li can be minimized, but the sintering temperature becomes very high, which makes it difficult to control the porosity. Accordingly, the MgO contained in the inner protective layer according to the present invention is 70 to 99.5 at.%. The other components of the inner furnace are made of Al ₂ O ₃ .

Al ₂ O ₃ serves to facilitate the porosity control by lowering the sintering temperature for the manufacture of fireproofing. Specifically, Al ₂ O ₃ is added in an amount of 0.5 to 30 at.%. When the content of Al ₂ O ₃ is less than 0.5 at.%, The effect of lowering the sintering temperature is insufficient. When the content of Al ₂ O ₃ is more than 30 at.%, The reactivity with Li is increased and the lifetime of the inner shell decreases.

In this specification, MgO and Al ₂ O ₃ of at.% Being based on the total of the number of MgO and Al ₂ O ₃ by mole. Additives such as binders can be added in the manufacture of fireproofs, but they are not included in the finished fireproofing because they are all removed during the sintering process.

On the other hand, SiC, cordierite, mullite and the like may be further added to control the sintering temperature and increase the thermal expansion coefficient and strength. Specifically, based on the entire inner wallet, 0at. More than 20at. % Or less of spinel, 0at. More than 10at. % Or less of cordierite, 0at. More than 10at. % Mullite, 0at. % 5at. % Or less of SiC. However, the additives are not essential.

Meanwhile, the MgO powder dispersion prepared by the atmospheric oxidation method can be applied to the surface of the inner shell to be dense. However, the coating layer formed in this manner is not essential.

When 0.5 to 30 at.% Of Al 2 O 3 is added, the sintering temperature for producing an inner protective layer is 1550 to 1700 ° C. It is easy to control the porosity at the sintering temperature.

On the other hand, the porosity of the inner shell according to the present invention is preferably 10% or less. The lower the porosity of the inner shell, the lower the amount of lithium penetrated through the shell. In order to allow the cathode active material to be fired more than 100 times, the porosity of the inner shell must be 10% or less. The average size of the pores is preferably 10 탆 or less.

Hereinafter, a method of manufacturing an inner protective cap according to the present invention will be described in detail.

First, MgO powder and Al ₂ O ₃ powder are mixed to prepare a mixed powder.

The MgO powder may be a mixture of two powders having different average particle diameters. For example, the two types of powders may be mixed in a ratio of 7: 3, 5: 5, or 3: 7.

In one embodiment, the average particle diameter of any one of the two kinds of powders may be 27 to 33 mu m and the average particle diameter of the other one may be 3 to 8 mu m. Accordingly, the present invention reduces the porosity of the inner shell.

However, the present invention is not limited thereto, and the MgO powder may be composed of one kind of powder. When one type of MgO powder is used, the average particle diameter of the MgO powder may be 2 to 4 占 퐉.

On the other hand, the average particle diameter of the Al ₂ O ₃ powder may be 0.5 to 10 μm. When Al ₂ O ₃ powder having an average particle size of less than 0.5㎛ are difficult to manufacture, the mean particle size of Al ₂ O ₃ powder exceeds 10㎛, there is a problem that the increase in porosity of the hwagap.

Meanwhile, the average particle diameter of the MgO powder and the average particle diameter of the Al ₂ O ₃ powder may be equal to each other.

On the other hand, after the mixed powder of MgO and Al ₂ O ₃ is made of a mixture of the said MgO and Al ₂ O ₃ as a sludge state can be produced in such a way as to evaporate water. Moisture can react with MgO in the sludge state, which can adversely affect the hardness of the fire wall. To prevent MgO from reacting with water, the MgO may be Dead Burnt MgO or fused MgO.

Next, the step of molding the mixed powder into a predetermined shape to produce a molded body is proceeded.

An additive such as a binder may be added during the production of the molded article. The additive to be added in the production of the molded article is a well-known technology, and a detailed description thereof will be omitted. Since the additive is an organic material, it is all removed during the sintering of the fireproof glove, and is no longer left in the finished fireproof glove.

Finally, a step of sintering the shaped body at a temperature of 1550 to 1700 ° C is carried out.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the scope and contents of the present invention are not construed to be limited or limited by the following Examples and Experimental Examples.

Hereinafter, the performance comparison result between the inner fire wall according to the present invention and the conventional inner fire wall will be described.

The components of the inner shell used in the performance comparison experiment (hereinafter, comparative example) consisted of 70 at.% Al ₂ O ₃ , 19 at.% SiO ₂ , 10 at.% MgO and other components.

On the other hand, there are two types of specimen used in the performance comparison experiment described later. Specifically, the specimen includes a circular specimen having a predetermined thickness (FIG. 2A) and a rectangular parallelepiped specimen having an internal space (FIG. 2B). The rectangular parallelepiped-shaped specimen has a shape similar to that of an actual inner shell. In the present specification, a circular specimen is referred to as a coin sample, and a rectangular parallelepiped specimen is referred to as Lab. It is called a scale sample.

The composition of the specimen used in the performance evaluation described below is shown in Table 1 below.

division	Material	Granularity	Sintering temperature	shape
existing	Al 2 O 3 , MgO, SiO 2	About 50㎛	1300 ℃	Coin
Coin-1	+ Al 2 O 3 MgO (100 %) (0%)	MgO powder: 13 占 퐉 (30%) + 50 占 퐉 (70%)	1580 ° C
Coin-2	+ Al 2 O 3 MgO (90 %) (10%)
Coin-3	+ Al 2 O 3 MgO (100 %) (0%)		1680 ° C
Coin-4	+ Al 2 O 3 MgO (95 %) (5%)
Coin-5	+ Al 2 O 3 MgO (90 %) (10%)
Lab Scale-1	+ Al 2 O 3 MgO (90 %) (10%)	MgO and Al 2 O 3 powder: 3 탆	1500 ℃	Cube
Lab Scale-2	+ Al 2 O 3 MgO (90 %) (10%)		1450 ℃
Lab Scale-3	+ Al 2 O 3 MgO (90 %) (10%)		1400 ° C

(1) Strength test

A 3 point bending test was performed on the specimens shown in Table 1. The measurement results are shown in Table 2 below.

division	burglar
existing	77 MPa
Coin-1	138 MPa
Coin-2	420 MPa
Coin-3	270 MPa
Coin-4	450MPa
Coin-5	596 MPa
Lab Scale-1	Currently unmeasurable (estimated to be over 600 MPa)

According to Table 2 above, the strength of the example made with Lab Scale exceeded the measurement limit of the measuring instrument (600 MPa). Comparing the strength of the comparative example with that of the sample Coin-5 having the same composition as Lab Scale 1 to 3, it was confirmed that the intensity of Coin-5 was 7 times or more higher.

As described above, since the inner shell according to the present invention has much higher strength than the conventional shell shell, the possibility of breakage during firing of the cathode active material is lowered.

(2) Measurement of porosity

The cross section of each sample was photographed by SEM (see Figs. 3A to 3C), and the ratio of pores in the SEM image was measured. The results of the porosity measurement of each sample are shown in Table 3 below.

division	Porosity
existing	24.5%
Coin-1	37.0%
Coin-2	22.0%
Coin-3	32.0%
Coin-4	24.7%
Coin-5	11.1%
Lab Scale-1	0.1% - 1.5%
Lab Scale-2	4.0%
Lab Scale-3	10.3%

(3) Life evaluation

A cathode material containing lithium was placed on each sample, and then the temperature was raised to 800 ° C at a rate of 10 ° C / min and maintained at 800 ° C for one hour. Thereafter, it was cooled by an air cooling method for 30 minutes or more. The lifetime evaluation was performed under pressure conditions taking into consideration the actual weight of the cathode material. After repeated evaluation of the lifetime described above, changes in the sample were observed. Observation results are shown in Table 4 below.

division	Observation result
existing	5 crack initiation 30 peeling start (Fig. 4)
Coin-1	19 breaks start 36 breaks
Coin-2	Completed 50 times Crack / No peeling
Coin-3	22 crack initiation and break
Coin-4	100 times complete crack / no peeling
Coin-5	100 times complete crack / no peeling
Lab Scale-1	100 times in progress (Fig. 5) No crack / peeling
Lab Scale-2	100 times in progress (50 minute peeling)
Lab Scale-3	During 100 runs (5 microcracks)

Referring to Table 4, it can be seen that the lower the porosity is, the longer the life of the inner shell is, and in order to be reused in the firing process at least 100 times, it can be confirmed that the inner shell has a porosity of at least 10% .

According to the present invention, the strength and the thermal shock resistance of the existing firefly are increased, and the reactivity with lithium is lowered, so that the firefly is not damaged even after the firing is repeated 100 times or more. In view of the fact that the conventional inner wall is broken at about 30 times of firing, the inner wall according to the present invention has a durability 3 times higher than that of the conventional inner wall.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

In addition, the above detailed description should not be construed in all aspects as limiting and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Claims (8)

1. % Of MgO, and 0.5 to 30 at.% Of Al ₂ O ₃ , and having a porosity of 10% or less. The fireproof fireproof material for firing a cathode active material of a lithium secondary battery according to claim 1,
2. The method according to claim 1,

   Wherein the strength of the inner shell is 600 MPa or more.
3. MgO powder and Al ₂ O ₃ powder to prepare a mixed powder;

   Molding the mixed powder into a predetermined shape to produce a molded body; And

   Sintering the shaped body at a temperature of 1550 to 1700 ° C,

   Wherein the mixed powder is composed of 70 to 99.5 at.% Of MgO and 0.5 to 30 at.% Of Al ₂ O ₃ .
4. The method of claim 3,

   Wherein the MgO powder is mixed with two kinds of powders having different average particle diameters.
5. 5. The method of claim 4,

   Wherein the average particle diameter of one of the two types of powders is 27 to 33 占 퐉 and the average particle diameter of the other one is 3 to 8 占 퐉.
6. The method of claim 3,

   Wherein the Al ₂ O ₃ powder has an average particle diameter of 0.5 to 10 μm.
7. The method of claim 3,

   Wherein the average particle diameter of the MgO powder and the average particle diameter of the Al ₂ O ₃ powder are equal to each other.
8. The method of claim 3,

   Wherein the MgO is dead burnt MgO or molten MgO. ≪ RTI ID = 0.0 > 11. < / RTI >

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