KR101323096B1 - Sagger for synthesizing positive electrode active material of secondary battery and manufacturing method of the same - Google Patents

Abstract

The present invention provides a body composed of a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ and Li ₂ O—Al ₂ O ₃ for surface densification formed on the surface of the body in which the cathode active material of the secondary battery is accommodated. The present invention relates to a saggar for synthesizing a cathode active material of a secondary battery including a -SiO ₂ based glaze layer, and a manufacturing method thereof. According to the present invention, through the surface densification process for the saggar box, it is possible to provide a saggar that can be used for a long time by preventing the breakage of the saggar caused by the diffusion of the saggar, the body of the saggar using a material having a high coefficient of thermal expansion The surface of the fireproof sap can be applied to the glaze having a low coefficient of thermal expansion to form a glaze layer, thereby achieving the effect of improving the strength of the saggar.

Description

Sagger for synthesizing positive electrode active material of secondary battery and manufacturing method of the same}

The present invention relates to a fireproof sap for synthesizing a secondary battery positive electrode active material, and more particularly, to prevent the diffusion of Li ⁺ , the surface of the high sag fireproof sac is formed of a glaze layer, thereby densifying the surface of a secondary cell positive electrode active material. It relates to a shoebox and a method of manufacturing the same.

In recent years, with the rapid development of the communication industry, such as the electronics industry, mobile communication, and information communication, high-performance, high-capacity, and high-density energy storage media have been developed in response to the demand for light and short reduction of electronic devices.

In recent years, the development of high performance lithium secondary batteries having excellent stability and high energy density has been made competitive in various countries.

The sagger for producing a cathode of a lithium secondary battery has a problem in that lithium (Li) or cobalt (Co) included in the cathode raw material is diffused into the saggar when firing the raw material of the positive electrode active material. When lithium (Li) or cobalt (Co) diffuses into the refractory pack and reacts with the components of the refractory pack, the durability of the refractory pack is degraded and its life is shortened.

The main cause of this problem is the concentration gradient between the saggar and the cathode active material. Li ⁺ or Co ^{3 +} is absent in the refractory, while Li ⁺ and Co ^{3 +} concentrations are high in the cathode active material. Therefore, a concentration gradient occurs between the saggar and the cathode active material, and the difference in concentration causes the diffusion of Li ⁺ and Co ^{3 +} .

Due to the diffusion of lithium or cobalt, chemical reactions may occur between the lithium or cobalt and the components of the saggar on the surface of the saggar. As a result, the secondary battery cathode active material may not be able to perform its useful purpose of detachment and insertion of Li ⁺ ions.

In the temperature lowering step after firing in the production of the positive electrode active material, the refractory pack and the fired product are forcibly cooled by a method of injecting air into the furnace.

If the thermal expansion rate of the saggar is high, cracking may occur due to the difference in the degree of shrinkage due to the temperature difference when cooling the saggar.

In addition, separation of the positive electrode active material and the fireproof bag obtained by firing in the properties required for the fireproof bag should be easy. If the anode active material and the saggar have poor peeling properties, the cathode active material and the saggar become entangled with each other. As a result, it is difficult to separate the saggar from the positive electrode active material after firing, which may lower the product yield.

In addition, when synthesizing the positive electrode active material using a material having excellent mechanical and thermal properties as a raw material of the fireproof sap, there may be a problem that the saggar breaks only after 20 to 25 repeated use.

In addition, in the case of the fireproof box used as a material container of the positive electrode active material, the porosity reached about 17%, so that there was a problem of easily broken.

The problem to be solved by the present invention is to provide a fireproof sap formed with a Li ₂ O-Al ₂ O ₃ -SiO ₂ based glaze layer that can densify the surface of the saggar to prevent the diffusion of Li ⁺ and Co ^{3 +} have.

Another problem to be solved by the present invention is to provide a method of manufacturing a fireproof sap for synthesizing a secondary battery cathode active material which can achieve the surface reinforcement effect of the saggar by making the thermal expansion coefficient of the fireproof sap body and the glaze layer is different.

The present invention provides a body composed of a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ and Li ₂ O—Al ₂ O ₃ for surface densification formed on the surface of the body in which the cathode active material of the secondary battery is accommodated. Provides a fireproof shell for synthesizing a cathode active material of a secondary battery including a -SiO ₂ based glaze layer.

The glaze layer is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ It may include 25 to 60% by weight.

The glaze layer may further comprise 0.1 to 10% by weight of MgO.

The glaze layer may further comprise 0.1 to 10% by weight of spinel (MgAl ₂ O ₄ ).

It is preferable that the thermal expansion coefficient of the glaze layer is smaller than the thermal expansion coefficient of the body.

The glaze layer may have a thermal expansion coefficient of 30 × 10 ⁻⁷ to 50 × 10 ⁻⁷ / ° C., and the body may have a thermal expansion coefficient of 40 × 10 ⁻⁷ to 60 × 10 ⁻⁷ / ° C.

Preferably, the density of the glaze layer is greater than the density of the body.

In addition, the present invention comprises the steps of preparing a refractory body consisting of a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ and the secondary battery cathode active material is accommodated, and for the surface densification on the surface of the refractory body Synthesis of a secondary battery positive electrode active material comprising the step of coating the Li ₂ O-Al ₂ O ₃ -SiO _{2 type} glaze and heat-treating the glazed fireproof body body to form a glaze layer on the surface of the fireproof body Provided is a method of manufacturing a fireproof saber.

The glaze is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ It may include 25 to 60% by weight.

The glaze may further comprise 0.1 to 10% by weight of MgO.

The glaze may further comprise 0.1 to 10% by weight of spinel (MgAl ₂ O ₄ ).

The heat treatment is preferably performed at a temperature of 1000 ~ 1300 ℃ in an oxidizing atmosphere.

The thermal expansion coefficient of the glaze layer is less than the coefficient of thermal expansion of the inner hwagap body, the glaze layer is a thermal expansion coefficient in the range ^{30 × 10 -7 ~ 50 × 10} -7 / ℃, the body has a thermal expansion coefficient of 40 × 10 ^{- 7} to 60 × 10 ⁻⁷ / ° C.

Preferably, the density of the glaze layer is greater than the density of the body.

According to the present invention, it is possible to provide a saggar that can be used for a long time by preventing breakage of the saggar caused by the diffusion of Li through the surface densification process for the saggar.

In addition, according to the present invention, the body of the fireproof sap using a material having a high coefficient of thermal expansion, the surface of the fireproof sap can be achieved by applying a glaze having a low coefficient of thermal expansion to form a glaze layer to achieve the effect of improving the strength of the saggar. .

In addition, according to the method of manufacturing a fireproof sap for synthesizing a secondary battery positive electrode active material according to the present invention, it is possible to achieve the surface strengthening effect by the method of heat treatment to the glaze and to easily peel the positive electrode active material from the fireproof sac after synthesis of the secondary battery positive electrode active material. .

1 is a schematic diagram showing a process of synthesizing a cathode active material including LiCoO ₂ using a saggar.
Figure 2 is a schematic diagram showing the configuration of the fireproof pack according to the present invention.
3 is a procedure showing the manufacturing process of the saggar box according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided so that those skilled in the art will be able to fully understand the present invention, and that various modifications may be made without departing from the scope of the present invention. It is not. Wherein like reference numerals refer to like elements throughout.

A battery is a device that converts chemical energy into electrical energy by electrochemical oxidation and reduction reactions. In the battery, the ionization tendency is small according to the direction of oxidation / reduction reaction, so that the reduction reaction occurs as a cathode, and the oxidation reaction is called an anode.

Another classification method is divided into primary battery and secondary battery according to the reusability of the battery by recharging. Primary batteries include manganese batteries, alkaline batteries, silver oxide batteries, lithium primary batteries, and the like, and these primary batteries are small electronic devices whose main uses are small. Rechargeable batteries include lead acid batteries, Ni-Cd, Ni-MH (metal hydrogen), and lithium secondary batteries. In particular, after the successful commercialization of lithium secondary battery, it is widely used in the mobile communication field, and the rapid development of portable electronic devices, power supply for HEV (Hybrid electric vehicle) and battery power storage, mainly in camcorders, cameras, cellular phones and computers. The importance is greatly increased.

Early lithium secondary batteries used lithium metal as a negative electrode. Lithium metal has a low standard reduction potential, and thus high electromotive force can be obtained when used as a cathode. However, during charging and discharging, as the lithium metal repeats deposition and dissolution, a non-moving film is formed and dissolution of lithium metal occurs nonuniformly. In addition, safety problems such as a decrease in capacity, an increase in surface area, and shorts due to dendrite formation occurring during high current charge and discharge occur.

Due to these shortcomings, development of a lithium secondary battery using a carbon material using an insertion and desorption reaction of lithium ions as a negative electrode and using a lithium metal oxide as a positive electrode instead of lithium metal has been in progress. The characteristics of the positive electrode among the positive electrode, the negative electrode, the electrolyte, and the separator, which are components of the lithium secondary battery, have a great influence on the performance of the entire battery.

The positive electrode used in the lithium secondary battery satisfies conditions such as high energy density, reversibility during charging and discharging, and chemical stability to the electrolyte, and there is a very large irreversible capacity due to structural collapse due to large volume expansion when Li ⁺ enters. . The volume change of the main lattice due to the insertion and desorption of Li ⁺ should be accommodated.

Among these cathode materials, a lithium secondary battery using LiCoO ₂ having a layered structure as a cathode active material and carbon as a cathode active material has been commercialized. However, LiCoO ₂ has structural instability, and thus has a limitation of being applied to the positive electrode active material due to the problem that the limit capacity is as low as 150mAh / g and the price increase due to the limit of the reserve of the cobalt compound.

LiNiO _2, LiFePO _4, LiNi _⅓ in an effort to overcome the disadvantages of the LiCoO ₂ Mn ₂ O _⅓ Co _⅓ And lithium transition metal oxides such as LiNi _1-y Co _y O ₂ have been studied as representative cathode active materials.

The voltage of a lithium secondary battery is determined by the type of cathode active material used. LiCoO ₂ oxide, which is currently commercialized, has a nominal voltage of 3.8 V when carbon is used as a cathode. Therefore, conventional Nicard (Ni / Cd), It has a high energy density of more than three times that of a nickel hydride (Ni / MH) battery. Based on this, it is used as a mobile power source for all portable electronic devices such as personal digital assistants (PDA), multimedia players (MP3 (Media player3), PMP (portable multimedia player), notebook PCs, etc. Increasingly, the high power density characteristics of lithium secondary batteries have been improved and improved, and are being applied as power tools, electric bicycles (EBs), and hybrid vehicle (HEV) power sources.

LiCoO ₂ cathode active material, which is currently commercially available and used universally, exhibits a nominal voltage of 3.8V and is reversibly inserted and desorbed of lithium. It is easy to synthesize, has excellent life characteristics, and exhibits high structural reversibility. . Accordingly, in the present invention, LiCoO ₂ will be described as a basic component of the positive electrode active material. However, the scope of the present invention is not limited to the cathode active material made of LiCoO ₂ .

For example, as the cathode active material, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiFePO ₄ , LiNi _⅓ Mn _⅓ Co _⅓ O ₂ And LiNi _{1 - y} Co _y O ₂ , V ₂ O ₅ , and the synthesis methods include sputtering, pulsed laser deposition, electron beam evaporation, and electrostatic spray deposition. (electrostatic spray deposition). Since all oxides except V ₂ O ₅ contain Li ⁺ ions, controlling desorption and insertion of Li ⁺ becomes a factor that determines the characteristics of the lithium secondary battery.

Electrochemical reactions in the material involve the movement of electrons. The electrochemical potential is different depending on the inherent properties of the material.

Lithium metal has high atomic density (6.941 g / mol) and low density (0.54 g / cm 3), and has a high energy density because the standard reduction potential value is the lowest group of materials on earth. Considering capacity and weight, it has the highest charge of 3,861 mAh / g and 2,062 mAh / l. However, due to its thermodynamic activity, it is very active in aqueous solution and uses molten salt or organic solvent as an electrolyte. However, lithium metal not only forms a dendritic phase on the surface as charging and discharging proceeds, but also shortens battery life because it reacts with an organic solvent. If the dendritic phase continues to grow, it reaches the surface of the positive electrode material. When the dendritic phase of Li reaches the surface, an internal short circuit occurs, causing a risk of ignition.

Efforts have been made to replace Li metal with Li ⁺ ions because of the activity of Li metal, and the cathode used is carbon. When using carbon as the negative electrode of a lithium secondary battery Li ⁺ ions during charging and discharging of the Li ⁺ is to enable the free movement between the graphite forms a crystal structure of the hexagonal layer. As such, when carbon is used instead of lithium metal as a negative electrode, deformation of lithium metal generated when lithium metal is used as a negative electrode does not occur, and the service life of the negative electrode is extended. In addition, there is no risk of ignition because dendritic growth does not occur.

A battery using lithium transition metal oxide as a cathode material and graphite as a cathode material is also called a lithium ion battery. Charging and discharging at the anode means that guest ions are reversibly inserted and desorbed into the crystal structure of the host material. When the lithium ion battery is charged, a charging current flows in the external circuit, and lithium ions are inserted by moving from the positive electrode to the negative electrode through the electrolyte. On discharge, a phenomenon in which lithium ions inserted into the negative electrode detaches occurs. Along with the detachment phenomenon, Li ⁺ ions return to the tetrahedral or octahedral sites of LiMO ₂ (M represents a metal).

Based on the above reaction, when LiCoO ₂ is used as the positive electrode material and graphite is used as the negative electrode active material, the reaction formula can be summarized as follows. Formula 1, Formulas 2 to 3 are chemical formulas representing the positive electrode, the negative electrode, and the entire reaction, respectively.

[Formula 1]

_{LiCoO 2 ↔ Li 1 - x CoO} 2 + xLi + + xe -

(2)

_{^{xLi + + xe - + C 6}} ↔ Li x C 6

(3)

LiCoO ₂ + C ₆ ↔ Li _{1 - x} CoO ₂ + Li _x C ₆

In a lithium secondary battery, Li ⁺ ions move between an anode and a cathode through an electrolyte due to a potential difference between different active materials, and electrons move through an external circuit of the battery. When the movement of lithium is irreversible, it is called a primary battery, and when it is reversible, it is called a secondary battery. Since the reaction described above is for the secondary battery, it is a reversible reaction.

In the cathode material for a lithium secondary battery, an oxide of a transition metal is mainly used because insertion and desorption of lithium ions must be possible. Although Li ⁺ ions are small in size, transition metal oxides having a layered structure or a tunneling structure are suitable for easy attachment and detachment of Li ⁺ ions.

In order to use it as a cathode active material of a lithium secondary battery, it has to have a high energy density and reversibility at the time of charging and discharging. It is structurally stable and should not be destroyed even if there is detachment and adhesion of Li ⁺ ions. In addition, the positive electrode active material should have high electrical conductivity of the material itself, and should not be dissolved in an organic solvent as an electrolyte because of its high chemical stability. As the cathode active material for a lithium secondary battery that satisfies the above conditions, such as V ₅ O ₁₃ , TiS ₂ , LiV ₃ O, and the like, for low voltage having an operating voltage near 2V, and LiNiO ₂ , LiCoO ₂ , LiNi _{1 - y} Co _y O ₂ , For example, LiFePO ₄ has a high voltage for which the operating voltage is about 4V. This electrode material also has a layered structure or a three-dimensional framework structure that is easy to insert and detach lithium ions. The cost of manufacturing is also low, and it does not cause environmental pollution problems.

The positive electrode is an active material including Li ⁺ ions, an electrode in which Li ⁺ ions are inserted and reduced into an active material during discharge, and are detached and oxidized from the active material during charging.

Representative cathode active material LiCoO ₂ has a layered rock salt structure (α-NaFeO ₂ ). LiNiO _{2, which} is the same layered rock salt structure, is cheaper than LiCoO ₂ and has a high energy density because Li ⁺ ions have high detachment and insertion reversibility. However, Ni ^{3 +} a There is a part of Ni tend to be incorporated into the Li-digit drawback in the synthesis process since the easily reduced to Ni ^{+ 2.} The reason is that tend to be incorporated similar to the ionic radius of Ni ^{2 +} (0.69Å) and Li ⁺ (0.76Å).

On the other hand, unlike these LiMn ₂ O ₄ having a spinel structure is structurally stable to increase the safety of the battery.

As described above, although lithium metal was initially used, carbon having a hexagonal structure has been replaced with graphite, which is a member element, as a problem such as safety has emerged.

Graphite is similar to the potential of lithium metal and exhibits stable properties with respect to organic solvents. However, unlike lithium metal, since it does not form a dendrite, there is a characteristic that can be used for a long time. In addition, graphite has a capacity characteristic of 372 mAh / g, and when used as a negative electrode active material, there is very little volume change.

When the insertion and desorption of Li ⁺ ions are about 10%, the volume change is small compared to the metal or alloy-based negative electrode active material which shows a volume change of 100 to 300%, and thus can be used for a long time.

One method for producing a positive electrode active material is a solid phase reaction method. This method is produced by mixing the powder of oxide or carbonate using the oxide, carbonate, etc. of each element as a raw material, and baking the powder of oxide or carbonate. Disadvantages of the solid phase reaction method is a large amount of impurities introduced when mixing, there is a problem that the high temperature and the production time is long in the manufacturing.

As another method, sol-gel using metal alkoxide, nitrate, acetate and sulfate, and co-precipitation using sodium hydroxide as a chelating agent There is this.

The sol-gel method using metal alkoxide has a disadvantage that it is difficult to apply to powder synthesis due to the high price of metal alkoxide. Coprecipitation, on the other hand, is economical because it uses metal nitrate, acetate, and sulfate, which are less expensive than metal alkoxide. In the ceramic manufacturing field, coprecipitation method is under development, and this method converts the metal salt into a solvent and then converts the metal salt into a metal hydroxide using sodium hydroxide as a coprecipitant in a solvent in which the metal salt is dissolved to obtain a precipitate, and separates the precipitate to dry and heat-treat it. Through the process, a ceramic powder is obtained.

The fireproof pack according to the present invention will be described with respect to the sol-gel method in the method of preparing the positive electrode active material. However, the scope of the present invention is not limited to this sol-gel method, but includes all manufacturing methods of firing at a high temperature.

Refractory pack for secondary battery positive electrode active material according to the present invention is characterized in that the surface layer is composed of a Li ₂ O-Al ₂ O ₃ -SiO ₂ -based glaze layer. The glaze layer is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ It is preferable to contain 25 to 60 weight%.

When the glaze layer is composed of an oxide containing Li, it is possible to prevent the diffusion of Li ⁺ ions generated during the production of the cathode active material. My hwagap is a sintered body of mullite _{(3Al 2 O 3 · 2SiO 2} ) and Al ₂ O _3, made of a solid solution of the ₂ O ₃ · 2SiO ₂ and 3Al Al ₂ O _3.

1 is a schematic diagram showing a process of synthesizing a cathode active material including LiCoO ₂ using a saggar.

Referring to FIG. 1, Li (CH ₃ COOH) .2H ₂ O and Co (NO ₃ ) ₂ .6H ₂ 0 were dissolved in distilled water at a molar ratio of 1: 1 to 1.5, followed by malic acid (HOOC-CH ₂ CH ( OH) -COOH) to aqueous solution of malic acid with a molar ratio of total metal ion sum of at least 0.75 is made and mixed well with the solution. And pH is adjusted to 4.5-5.5 range, while ammonia water is dripped at 2 cc / min to the said mixed aqueous solution. The mixed aqueous solution is gradually heated to 50-90 ° C., more preferably 70-80 ° C. to form a sol, and then the sol is continuously heated to form a gel precursor. The gel precursor is heat-treated at 400 ° C. or higher for 1 hour or longer in an air atmosphere to prepare a precursor powder, and the precursor powder is calcined at 500 to 900 ° C. for 1 hour or longer in an air atmosphere to obtain a low-temperature and high-temperature LiCoO ₂ powder.

The firing temperature is, for example, a temperature range of 500 to 900 ° C. If the firing temperature is less than 500 ° C., the lithium composite metal compound is less likely to be produced. If the firing temperature is higher than 900 ° C., crystals grow more than necessary or some decomposition occurs, which is not preferable.

When the calcination temperature is reached, Li ⁺ ions and Co ^{3 +} ions become dissociated to diffuse. As shown in FIG. 1, Li (CH ₃ COOH) .2H ₂ O and Co (NO ₃ ) ₂ .6H ₂ 0 were quantified in a molar ratio of 1: 1 to 1.5, mixed with a solution dissolved in distilled water and a malic acid solution. The solution will diffuse toward the low density saggar 20.

There are two known causes of such diffusion. One is the concentration gradient between the saggar and the positive electrode active material, and the other is that the porosity of the saggar 20 is spread because it reaches 15 to 20%.

As a result of diffusion, a solid solution and a reaction layer of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ of Li ⁺ and Co ^{3 +} are formed. As the reaction layer is generated, eventually, the mechanical strength of the saggar 20 is weakened to break the saggar 20.

2 is a schematic view showing the configuration of the saggar box 20 according to the present invention.

Referring to FIG. 2, when the surface layer of the refractory pack 20 is coated with a Li ₂ O—Al ₂ O ₃ —SiO ₂ based glaze, the concentration of Li ⁺ in the glaze layer 30 is dissolved from the cathode active material 10. Since the concentration is higher than the dissociated Li ⁺ concentration, diffusion due to the difference in concentration does not occur. Therefore, no reaction occurs with a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ , which are components of Li ⁺ and the saggar 20.

In addition, since the glaze layer 30 is configured to have a higher density than the body of the saggar 20, diffusion due to the difference in density does not occur.

This is due to the surface densification effect of the glaze layer 30. It is preferable to use Li ₂ O—Al ₂ O ₃ —SiO ₂ -based glaze as the glaze layer 30 for protecting the fireproof sacks 20.

The reason for using the Li ₂ O—Al ₂ O ₃ —SiO ₂ based glaze containing lithium (Li) in the glaze layer 30 is to prevent the diffusion of Li ⁺ as described above.

In particular, in the case of the fireproof sacks 20 according to the present invention, it is preferable to manufacture the following process.

3 is a procedure showing the manufacturing process of the saggar 20 according to the present invention.

Referring to FIG. 3, a fireproof shell body made of a sintered body of mullite (3Al ₂ O ₃ · 2SiO ₂ ) and alumina (Al ₂ O ₃ ) is prepared (S110).

Surface coating is performed on the glaze layer 30 for densification of the surface of the sintered body of mullite (3Al ₂ O ₃ · 2SiO ₂ ) and alumina (Al ₂ O ₃ ) (S120). At this time, Li ₂ O-Al ₂ O ₃ -SiO ₂ based glaze is applied to the surface of the fireproof box body made of a solid solution of Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ to accommodate the secondary battery cathode active material And, the glaze is applied to include the process of heat treatment at 1000 ~ 1300 ℃ fireproof body body. The Li ₂ O-Al ₂ O ₃ -SiO ₂ based glaze is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ It is preferable to contain 25 to 60 weight%. The glaze may further comprise 0.1 to 10% by weight of MgO. In addition, the glaze may further comprise 0.1 to 10% by weight of spinel (MgAl ₂ O ₄ ). When MgO or spinel (MgAl ₂ O ₄ ) is contained in the glaze, there is an advantage of suppressing corrosion of the saggar despite the diffusion of lithium.

The glaze layer 30 formed through the heat treatment is not a problem whether crystalline or amorphous.

The heat treatment temperature of the glaze-resistant refractory pack 20 is preferably 1000 ~ 1300 ℃ (S130). The reason why the heat treatment temperature is higher than the firing temperature of the cathode active material 10, which is 500 to 900 ° C., is to prevent diffusion of Li ⁺ by pyrolysis of LiCoO ₂ through the glaze layer 30 and to prevent the fireproof sacks 20 and the cathode active material ( This is to suppress the reaction of 10). The temperature is set at 1300 ° C. or lower to prevent the production of by-products of reactions other than heat treatment and heat treatment. The heat treatment is preferably performed in an oxidizing atmosphere such as air and oxygen (O ₂ ).

At this time, the thermal expansion coefficient of the glaze layer 30 is preferably smaller than the thermal expansion coefficient of the body of the fireproof box 20. More specifically, the coefficient of thermal expansion of the glaze layer 30 obtained as a result of coating and heat treatment of the Li ₂ O—Al ₂ O ₃ —SiO ₂ based glaze is preferably 30 × 10 ⁻⁷ to 50 × 10 ⁻⁷ / ° C. Do. The coefficient of thermal expansion of the body of the fireproof sacks 20 is about 40 × 10 ⁻⁷ to 60 × 10 ⁻⁷ / ° C., and the coefficient of thermal expansion of the glaze layer 30 is smaller than the thermal expansion coefficient of the body of the saggar sacks 20, thereby enhancing the surface. Will appear.

It is well known that in the case of ceramics, the compressive strength is stronger than the tensile strength. Using this property, if the outside of the saggar 20 (glaze layer 30) is made of a material having a low coefficient of thermal expansion, and the body of the saggar 20 is made of a material having a high coefficient of thermal expansion, a low coefficient of thermal expansion is achieved. The glaze layer 30 has an effect of compressing the body of the fireproof box 20 having a high coefficient of thermal expansion therein. This is called the surface strengthening effect.

The surface strengthening effect is described in detail as follows. It demonstrates taking glass as an example. When the glass plate is heated to a high temperature and then rapidly cooled, a compressive stress is formed on the surface layer and a tensile stress is formed inside. This hardened glass is called tempered glass. Tempered glass is not sensitive to compressive stress, and when tensile force is applied, fracture occurs only when a tensile force greater than the sum of the compressive stress formed in the surface layer and the breaking strength of the glass itself is applied. Therefore, in the case of such tempered glass, the strength is about 4 to 5 times higher than that of ordinary plate glass.

This surface reinforcing effect is to apply to the refractory pack 20 for the secondary battery positive electrode active material according to the present invention. The surface layer of the fireproof sacks 20 is coated with a Li ₂ O-Al ₂ O ₃ -SiO ₂ -based glaze, and the glaze layer 30 formed on the surface of the fireproof sacks 20 has a lower coefficient of thermal expansion than the body. . And if the body of the refractory pack 20 is composed of materials having a higher coefficient of thermal expansion than the glaze layer 30, the refractory pack 20 by the difference in the coefficient of thermal expansion at the synthesis temperature of the positive electrode active material 10 of 500 ~ 900 ℃ The surface layer shows less change in length with increasing temperature than the body of the fireproof sacks 20 having a high coefficient of thermal expansion. The small coefficient of thermal expansion of the glaze layer 30 acts as a compressive stress on the body of the saggar 20. Therefore, since the effect of reinforcing the body of the saggar pack 20 by compressive stress can be said to improve the mechanical properties of the saggar box 20 by the surface reinforcing effect.

Due to the surface reinforcing effect as described above it is possible to prevent the weakening of the mechanical strength caused by the low density of the saggar pack 20 and the resulting damage, repeated use which is a problem that occurs during the manufacturing of the positive electrode active material 10 for secondary batteries It is possible to prevent the damage caused by the degradation and the performance degradation due to the outflow of Li ⁺ ions from the positive electrode active material 10 can be prevented in advance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, This is possible.

10: cathode active material
20: fireproof
30: glaze layer

Claims (14)

A body composed of a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ ; And
Fireproof pack for synthesizing the positive electrode active material of a secondary battery comprising a Li ₂ O-Al ₂ O ₃ -SiO ₂ based glaze layer for surface densification formed on the surface of the body in which the positive electrode active material of the secondary battery is accommodated.
The method of claim 1, wherein the glaze layer is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ Fireproof sacks for secondary battery cathode active material synthesis, characterized in that containing 25 to 60% by weight.
The fireproof sap of claim 2, wherein the glaze layer further comprises 0.1 to 10% by weight of MgO.
According to claim 2, wherein the glaze layer is spinel (MgAl ₂ O ₄ ) Refractory box for synthesizing the secondary battery positive electrode active material, characterized in that it further comprises 0.1 to 10% by weight.
According to claim 1, wherein the thermal expansion coefficient of the glaze layer is smaller than the thermal expansion coefficient of the body, the saggar for synthesizing the positive electrode active material of the secondary battery.
According to claim 5, wherein the glaze layer has a coefficient of thermal expansion of 30 × 10 ^-7 ~ 50 × 10 ^-7 / ℃, the body has a coefficient of thermal expansion of 40 × 10 ^-7 ~ 60 × 10 ^-7 / ℃ range Fireproof sacks for the synthesis of secondary battery positive electrode active material, characterized in that.
The firebox for synthesizing a secondary battery cathode active material according to claim 1, wherein the density of the glaze layer is greater than that of the body.
Preparing a fireproof shell body made of a solid solution of 3Al ₂ O ₃ · 2SiO ₂ and Al ₂ O ₃ and containing a secondary battery cathode active material;
Applying a Li ₂ O—Al ₂ O ₃ —SiO ₂ based glaze to the surface of the refractory body for surface densification; And
A method of manufacturing a fireproof sap for synthesizing a secondary battery positive electrode active material, comprising: forming a glaze layer on a surface of the fireproof sac body by heat-treating the glaze-coated saggar body.
According to claim 8, wherein the glaze is Li ₂ O 10-30% by weight, Al ₂ O ₃ 25-60 wt% and SiO ₂ A method of manufacturing a saggar for synthesizing a secondary battery cathode active material, comprising 25 to 60% by weight.
10. The method of claim 9, wherein the glaze further comprises 0.1 to 10% by weight of MgO.
10. The method of claim 9, wherein the glaze further comprises 0.1 to 10% by weight of spinel (MgAl ₂ O ₄ ).
The method of claim 8, wherein the heat treatment is performed at a temperature of 1000 to 1300 ° C. in an oxidizing atmosphere.
The thermal expansion coefficient of the glaze layer is smaller than the thermal expansion coefficient of the fireproof armor body, wherein the glaze layer has a thermal expansion coefficient in the range of 30 × 10 ^-7 ~ 50 × 10 ^-7 / ℃, the body is thermal expansion A method of manufacturing a saggar for synthesizing a secondary battery cathode active material, characterized in that the coefficient is in the range 40 × 10 ^-7 ~ 60 × 10 ^-7 / ℃.
The method of claim 8, wherein the density of the glaze layer is greater than the density of the body.

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