JP5039640B2 - Pot for producing positive electrode active material for lithium ion battery and method for producing the same - Google Patents

Description

  The present invention relates to a mortar for producing a positive electrode active material of a lithium ion battery and a method for producing the same.

  Lithium ion secondary batteries are often used as power sources for portable electronic devices such as mobile phones and notebook personal computers. The positive electrode active material of the lithium ion secondary battery includes a lithium-containing composite oxide (for example, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, lithium manganese cobalt composite oxide, lithium nickel cobalt composite oxide). This positive electrode active material is manufactured by putting raw material powder in a refractory (boiled bowl) and baking it. For example, Patent Literature 1 and Patent Literature 2 disclose a mortar for producing a positive electrode active material.

In Patent Document 1, in order to realize a battery with high safety and a long life, it contains at least one component selected from the group consisting of Al, Si, Ca, Y and Zr and MgO, and MgO matter content of at least 99%, or, Si, Ca, Y, containing at least one component and MgAl ₂ O ₄ spinel is selected from the group consisting of Zr and Hf, the MgAl ₂ O ₄ spinel A sheath for synthesizing a lithium-containing composite oxide for a positive electrode active material formed from a material having a content of 95% or more has been proposed.

  In Patent Document 2, in order to improve the corrosion resistance against lithium, (A) one or more selected from the group consisting of magnesia, zirconia and titania is 3 to 15 wt%, and (B) fused silica is 3 to There has been proposed a mortar composed of a sintered body of a material containing 30 wt% or (A) and (B), the balance being substantially made of magnesia-alumina spinel.

Japanese Patent No. 3552210 JP 2003-165767 A

  The following analysis is given from the perspective of the present invention.

  Select a material that does not allow lithium or cobalt contained in the positive electrode material to diffuse into the material when the positive electrode active material (hereinafter referred to as “positive electrode material”) is fired. There is a need to. When lithium or cobalt diffuses into the mortar and reacts with the components of the mortar, the durability of the mortar deteriorates and its life is shortened.

Therefore, when the contents of magnesia (MgO) and spinel (MgAl ₂ O ₄ ) in the mortar are increased as in the mortar described in Patent Document 1 and Patent Document 2, the corrosion resistance of the mortar against lithium diffusion is increased. Sex is improved.

  However, if the content of magnesia and / or spinel in the sagger is increased, the thermal expansion coefficient of the sagger will increase. For example, the thermal expansion coefficient of the mortar containing 90 wt% or more of magnesia is about 1.4% (room temperature to 1000 ° C.), and the thermal expansion coefficient of the mortar containing 90 wt% or more of spinel is about 0.7% ( Room temperature to 1000 ° C.). Usually, in the temperature lowering step after firing at the time of manufacturing the positive electrode active material, in order to increase the manufacturing efficiency, the temperature in the furnace is lowered by, for example, reducing the furnace temperature by feeding air into the furnace. It is cooling. Therefore, if the thermal expansion coefficient of the mortar is high, cracks will occur in the mortar during the temperature lowering process.

  In addition, it is necessary to select a bowl that has good releasability from the positive electrode active material obtained by firing (not welded to the positive electrode active material by firing) after firing. If the positive electrode active material and the mortar are welded, the peelability is poor and it is difficult to remove the positive electrode active material from the mortar after firing, resulting in a decrease in product yield, as well as a part of the surface of the mortar (with lithium and cobalt). The reaction material with the components of the mortar is attached to the manufactured positive electrode active material, and the positive electrode active material cannot be used as a product.

  An object of the present invention is to provide a mortar for producing a positive electrode active material for a lithium ion battery, which has high corrosion resistance against diffusion of the positive electrode material during firing, has good peelability of the fired product, and has a low coefficient of thermal expansion. Is to provide.

According to a first aspect of the present invention, a mortar for producing a positive electrode active material of a lithium ion battery, wherein spinel is 30% by mass to 70% by mass, cordierite is 15% by mass to 70% by mass, and A mortar containing 0% by mass to 35% by mass (including 0% by mass) of mullite is provided.

  According to a preferred form of the first aspect, the mortar contains 45% to 65% by weight of spinel, 20% to 40% by weight of cordierite, and 5% to 25% by weight of mullite.

According to a preferred embodiment of the first aspect, in a mortar in which a positive electrode active material of a lithium ion battery is not manufactured, the Al ₂ O ₃ component is 46 mass% to 68 mass%, and the MgO component is 14 mass% to 22 mass%. And 12 mass% to 36 mass% of SiO ₂ component.

According to a preferred form of the first aspect, the mortar is composed of 56% to 67% by mass of the Al ₂ O ₃ component, 14% to 22% by mass of the MgO component, and 15% to 24% of the SiO ₂ component. Contains by mass%.

According to a preferred mode of the first view point, saggers, the thermal expansion coefficient at 25 ° C. to 1000 ° C. it is not more than 0.5%. According to a more preferred embodiment, the coefficient of thermal expansion at 25 ° C. to 1000 ° C. is 0.35% or less.

According to a preferred mode of the first view point, saggers is, _Fe 2 _{O 3} component is more than 0.5 mass%.

According to a preferred mode of the first view point, after calcination housed in a positive electrode active sagger material the unfired material of the lithium ion battery, a surface layer in contact with the material after firing, the raw material It contains more MgO components than when unfired.

According to a second aspect of the present invention, there is provided a method for producing a mortar for producing a positive electrode active material of a lithium ion battery, wherein the mass is 30% by mass to 70% by mass with respect to the total mass of spinel, cordierite and mullite. % Spinel, 15% to 70% by weight cordierite, and 0% to 35% by weight (including 0% by weight) of mullite.

According to the preferred form of the second aspect, the Al ₂ O ₃ component is 46% by mass to 68% with respect to the total component of spinel, cordierite, and mullite in an unmanufactured positive electrode active material of a lithium ion battery. The spinel and cordierite, or the mixture containing spinel, cordierite and mullite is fired so that the mass percent, the MgO component is 14 mass percent to 22 mass percent, and the SiO ₂ component is 12 mass percent to 36 mass percent.

According to the preferable form of the second aspect, the mixture does not contain 5 mass% or more of magnesia alone with respect to the total mass of spinel, cordierite and mullite.

According to a preferred form of the second aspect, the mixture contains 0.5% by mass or less of Fe ₂ O ₃ component with respect to the total component of spinel, cordierite and mullite.

  The present invention has at least one of the following effects.

  The mortar of the present invention has a composition such that the coefficient of thermal expansion does not become higher than the mortar containing 90% or more of magnesia or spinel, and thus suppresses the generation of cracks in the temperature lowering process during the production of the positive electrode active material. be able to.

  In the mortar of the present invention, the raw material of the positive electrode active material is once fired, whereby an MgO component is formed on the surface layer in contact with the raw material. That is, once the raw material of the positive electrode active material is fired, the surface layer of the fired mortar contains more MgO components than the surface layer of the unfired mortar. The MgO-rich surface layer formed by firing the raw material can suppress the diffusion of the raw material (for example, lithium) at the time of firing the raw material and also suppress the reaction with the material of the mortar. Thereby, deterioration of a mortar can be suppressed. Moreover, since only the surface layer of the fired mortar that has been in contact with the raw material contains more MgO component than the other regions, the thermal expansion coefficient of the mortar as a whole does not increase.

  In the mortar of the present invention, since the positive electrode active material and the mortar are not welded by firing, the positive electrode active material can be taken out efficiently, and the productivity of the positive electrode active material can be increased. In addition, since a part of the sagger can be prevented from adhering to the positive electrode active material, the quality of the positive electrode active material can be improved and the yield can be improved.

  The mortar for producing the positive electrode active material of the lithium ion battery of the present invention will be described. The mortar of the present invention is a fired product containing spinel in an amount of 30 mass% to 70 mass%, cordierite in an amount of 15 mass% to 70 mass%, and mullite in an amount of 0 mass% to 35 mass%. Preferably, the mortar of the present invention is a fired product containing spinel in an amount of 40% to 70% by mass, cordierite in an amount of 15% to 55% by mass, and mullite in an amount of 0% to 30% by mass. More preferably, the mortar of the present invention is a fired product containing 45% to 65% by weight of spinel, 20% to 40% by weight of cordierite, and 5% to 25% by weight of mullite. The preferable content was set based on the following examples, depending on the state of the mortar after the production of the positive electrode active material, the ease of production of the positive electrode active material, the properties of the produced positive electrode active material, and the like.

  In the mortar of the present invention, the spinel is considered to contribute to the corrosion resistance against diffusion of the raw material of the positive electrode active material during firing. Therefore, if the spinel content is less than 30% by mass, it is considered that the corrosion resistance against diffusion of the raw material of the positive electrode active material is lowered. On the other hand, if the spinel content exceeds 70% by mass, the thermal expansion coefficient of the mortar increases and cracks are likely to occur.

In the mortar of the present invention, cordierite is considered to contribute to a decrease in the coefficient of thermal expansion. Therefore, if the cordierite content is less than 15% by mass, the thermal expansion coefficient of the mortar is considered to be high. On the other hand, when the cordierite content exceeds 70% by mass, it is considered that the corrosion resistance against diffusion of the raw material of the positive electrode active material is lowered.

  In the mortar of the present invention, mullite may not be contained, but can also be added as a sintering aid. When mullite is added, it is considered that mullite contributes to high temperature strength and creep resistance so that the bottom of the mortar does not sag when the raw material of the positive electrode active material is added and fired. If the mullite content exceeds 35% by mass, it is considered that the corrosion resistance against the diffusion of the raw material of the positive electrode active material is lowered.

  In addition, the mortar of the present invention can contain materials other than spinel, cordierite and mullite as long as the composition can be maintained, and the content of materials other than spinel, cordierite and mullite is preferably It is preferable to make it 5% by mass or less. For example, in order to suppress an increase in the coefficient of thermal expansion of the mortar, it is preferable that the content of magnesia alone does not exceed 5% by mass with respect to the total mass of spinel, cordierite, and mullite.

Moreover, from the viewpoint of chemical composition, the mortar of the present invention is 46 mass% to 68 mass% Al ₂ O ₃ component, 13 mass% to 22 mass% MgO component, and 12 mass% to SiO ₂ component. A fired product containing 36% by mass may be used. Preferably, the mortar of the present invention contains 52% by mass to 67% by mass of the Al ₂ O ₃ component, 14% by mass to 22% by mass of the MgO component, and 15% by mass to 29% by mass of the SiO ₂ component. More preferably, the mortar of the present invention contains 56% by mass to 67% by mass of the Al ₂ O ₃ component, 14% by mass to 22% by mass of the MgO component, and 15% by mass to 24% by mass of the SiO ₂ component. . The content of components other than these components is preferably 5% by mass or less.

In the mortar of the present invention, the Fe ₂ O ₃ component is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and preferably as small as practically possible. Thereby, it is thought that the corrosion-resistant fall with respect to lithium can be prevented.

  The thermal expansion coefficient at 25 ° C. to 1000 ° C. of the mortar of the present invention is preferably 0.5% or less, more preferably 0.4% or less, still more preferably 0.35% or less, and still more preferably. Is 0.2% or less, more preferably 0.15% or less. Thereby, it is considered that breakage of the mortar in the cooling step after firing the positive electrode active material can be prevented. The thermal expansion coefficient of the mortar is preferably measured according to JIS R2207-3. In particular, it is preferable to measure in a temperature range of 25 ° C to 1000 ° C.

  In the mortar of the present invention, before firing the raw material of the positive electrode active material, each composition is distributed almost uniformly and does not have a region containing more MgO component than the others. However, when the positive electrode active material is accommodated in the mortar of the present invention and baked to produce the positive electrode active material, the surface layer of the mortar in contact with the positive electrode active material has more MgO components than other regions. A containing layer (MgO-rich layer) is formed (see Examples below). This MgO-rich layer is considered to prevent diffusion of the raw material of the positive electrode active material into the mortar during firing and improve the life of the mortar.

  Therefore, in order to prevent the deterioration of the mortar in the firing step and to prevent the mortar from being damaged in the cooling step, the coefficient of thermal expansion at 25 ° C. to 1000 ° C. is 0.5% or less, and the positive electrode active material It is preferable that it is a mortar in which a MgO rich content layer is formed in the surface by baking the raw material of this.

Moreover, even if a positive electrode active material is produced using the mortar of the present invention, the mortar and the positive electrode active material are not welded by firing, and the positive electrode active material can be easily taken out from the mortar. For example, the fired product can be easily removed from the mortar simply by turning over the mortar (with the opening facing downward). The reason for this is that LiAlO ₂ and LiAlSiO ₄ produced by the reaction of a part of the surface of the mortar and the raw material of the positive electrode active material are scattered on the surface of the MgO-rich layer (see the following examples). It is considered that the substance enhances the peelability between the mortar and the fired product. Therefore, according to the mortar of the present invention, the productivity of the positive electrode active material can be increased. In addition, since the positive electrode active material which is a product does not partially adhere to the mortar by peeling off the welding, the purity of the positive electrode active material can be increased and the yield can be improved. Furthermore, since the peeling of the mortar is suppressed, the life of the mortar can be improved.

  The shape and dimensions of the mortar of the present invention are not particularly limited, and any suitable form can be selected as long as the raw material for the positive electrode active material can be accommodated and fired.

Next, the manufacturing method of the mortar of this invention is demonstrated. The mortar of the present invention is obtained by firing a blended mixture so as to obtain an mortar having the above composition. For example, the mortar of the present invention is 30% by mass to 70% by mass of spinel, 15% by mass to 70% by mass of cordierite, and 0% by mass to 35% by mass with respect to the total mass of spinel, cordierite and mullite. The mixture containing% mullite is fired. Speaking of the composition of chemical components, the Al ₂ O ₃ component is 46 mass% to 68 mass%, the MgO component is 13 mass% to 22 mass%, and the SiO ₂ component with respect to the total components of spinel, cordierite and mullite. Is fired to contain spinel and cordierite, or a mixture containing spinel, cordierite and mullite. When adding magnesia alone to the mixture, the content is preferably 5% by mass or less, but it is more preferable not to add magnesia alone to the mixture. This is to prevent an increase in the coefficient of thermal expansion due to containing magnesia alone.

  A molding aid (binder) can be added to the ceramic mixture. For example, as an additive for the water-soluble resin, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, polyvinyl alcohol, polycarboxylate, polysaccharide and the like can be used. Here, “polysaccharide” refers to a polymer compound (usually having a polymerization degree of 10 or more) in which monosaccharides (monosaccharides and derivatives thereof) are polyglycosylated. Of such polysaccharides, either homopolysaccharides or heteropolysaccharides can be used. Specifically, agar, dextrin, agarose, carrageenan, xanthan gum, curdlan, konjac powder and the like can be used. These are preferably those that gel easily when the suspension or solution is heated (gelling agent), and agar powder and dextrin are particularly preferred. One or more selected from these materials can be used as a molding aid. The addition amount of the molding aid is not particularly limited, and can be adjusted as appropriate.

  Next, the mixture of the mortar raw materials is molded (for example, pressure molding using a friction press or the like) and dried (for example, naturally dried), and then fired. The firing temperature and time can be set appropriately as appropriate. For example, firing can be performed at 1300 ° C. to 1420 ° C., preferably 1330 ° C. to 1380 ° C. for several hours, preferably 2 hours to 5 hours. In order to prevent the decomposition of cordierite, the firing temperature is set to 1420 ° C. or lower.

Next, the effect | action of this invention at the time of manufacturing the positive electrode active material of a lithium ion battery using the mortar of this invention is demonstrated. When the raw material of the positive electrode active material (for example, lithium-containing compound) is accommodated in the mortar of the present invention and fired, the spinel and cordierite in the mortar react with the lithium-containing compound, and the mortar, the positive electrode active material raw material, It is considered that MgO is formed on the contact surface (surface layer) (see Examples below). For example, when lithium cobaltate (LiCoO ₂ ) is produced as the positive electrode active material, a mixture of lithium carbonate (Li ₂ CO ₃ ) and cobalt oxide (Co ₃ O ₄ ) can be used as the raw material, for example. It is considered that the MgO-rich layer formed on the surface of the mortar functions as a barrier, prevents the diffusion of lithium into the mortar, and contributes to maintaining the corrosion resistance of the mortar.

  In addition, in the mortar of the present invention, since the coefficient of thermal expansion is lower than that of the mortar containing 90% by mass or more of magnesia or spinel, generation of cracks in the cooling step after firing the positive electrode active material raw material is suppressed. Yes.

Furthermore, when the positive electrode raw material is baked using the mortar of the present invention, it is considered that the Al component and Si component present on the surface of the mortar react with the positive electrode active material raw material to form LiAlO ₂ and LiAlSiO _4. . LiAlO ₂ and LiAlSiO ₄ are formed in a state where they do not penetrate into the inside of the bowl and are fixed to the surface of the bowl. Accordingly, the positive electrode active material which is a fired product and the mortar are not welded, and the LiAlO ₂ and LiAlSiO ₄ adherence are separated from the fired product, and the positive electrode active material can be easily removed from the mortar. It is considered possible.

(Test 1)
A test was conducted to confirm the reactivity of the positive electrode active material (positive electrode raw material) with magnesia, cordierite and mullite. As a raw material of the positive electrode active material, a material in which cobalt oxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were mixed at a ratio of 2: 1 (hereinafter referred to as “positive electrode raw material”) was used. 7.5 g of magnesia powder (MgO) (product having a particle size of 45 μm or less) was added to 7.5 g of this positive electrode raw material, mixed in a mortar, and then put in an alumina crucible and baked. As firing conditions, the temperature was raised from room temperature to 1050 ° C. in 2 hours, held at 1050 ° C. for 8 hours, lowered to 500 ° C. in 6 hours, and then lowered to room temperature in 4 hours. The obtained fired product was subjected to powder X-ray diffraction measurement. Based on the powder X-ray diffraction pattern database of the reference sample, a substance that matched the measurement peak was searched to identify the substance contained in the fired product. FIG. 1 shows the identification result. Similarly, spinel powder (MgAl ₂ O ₄ ) (particle size of 10 μm or less), cordierite powder (Mg ₂ Al ₄ Si ₅ O ₁₈ ) (particle size of 200 μm or less), and mullite powder (Al ₆ Si ₂ O). ₁₃ ) (Products with a particle size of 20 μm or less) were fired under the same conditions as magnesia powder (7.5 g added to 7.5 g of raw material powder), and each was contained in the fired product in the same manner as the magnesia powder test. The substance to be identified was identified. Each identification result is shown in FIGS.

(Result of Test 1: Reactivity between positive electrode material and magnesia)
As a result of firing a mixture of the positive electrode raw material and magnesia (MgO), it was found that magnesia did not react with the positive electrode raw material, as shown in FIG.

(Result of Test 1: Reactivity of positive electrode material and spinel)
As a result of firing the mixture of the positive electrode material and spinel (MgAl ₂ O ₄ ), it was confirmed that a part of the spinel reacted with the positive electrode material and changed to MgO as shown in FIG.

(Result of Test 1: Reactivity of cathode material and cordierite)
As a result of firing a mixture of the positive electrode raw material and cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ), it was confirmed that cordierite reacted with the positive electrode raw material to generate spinel, as shown in FIG. From this reaction test result of the positive electrode material and spinel, this spinel is considered to generate MgO if it further reacts with the positive electrode material.

(Result of Test 1: Reactivity between positive electrode material and mullite)
As a result of firing a mixture of the positive electrode raw material and mullite (Al ₆ Si ₂ O ₁₃ ), it was confirmed that mullite reacted with the positive electrode raw material and mullite was completely decomposed as shown in FIG.

(Consideration of Test 1)
Here, considerations that have led to the present invention from the above-described tests will be described. Magnesia has extremely low reactivity with the positive electrode material and lithium cobalt oxide. However, as described above, the mortar made mainly of magnesia has a high coefficient of thermal expansion, and cracks are likely to occur after firing. In addition to this, magnesia causes a hydration reaction at the time of blending, has a large volume shrinkage at the time of firing, and tends to generate sharpness. Therefore, magnesia is suitable as a raw material for the mortar for firing the positive electrode raw material from the viewpoint of reactivity, but is not suitable as a raw material for the mortar from the viewpoint of thermal shock resistance.

  On the other hand, it was found that MgO was generated from the reaction of spinel and cordierite with the positive electrode material. Therefore, even if the mortar is not formed with magnesia but is formed with spinel and cordierite as the main components, when the positive electrode material is fired, the spinel and cordierite present in the surface layer of the mortar and the positive electrode material are It was considered that a layer containing a large amount of MgO having excellent corrosion resistance (or a layer containing MgO as a main component) was formed on the surface of the mortar. And it was considered that this layer containing a lot of MgO suppresses the reaction between the mortar and the positive electrode material and prevents the mortar from being shortened due to diffusion of lithium and cobalt.

  Furthermore, in addition to not using magnesia, if cordierite is included in the mortar, the thermal expansion coefficient of the mortar can be reduced, and the thermal shock resistance of the mortar can be improved. It was.

(Test 2)
Based on the results of Test 1 above, various mortars with different blending ratios of spinel, cordierite and mullite were prepared without adding magnesia, and durability tests in the production of positive electrode active materials were conducted for each mortar. did.

(Test 2: Production of mortar)
Commercially available sintered spinel, cordierite, and mullite were dry-mixed at a predetermined blending ratio shown in Tables 1 to 5 in total 30 kg, and then 600 g of carboxymethylcellulose was added and further mixed. Next, 4.2 kg of 2% by mass agar was added and kneaded for 30 minutes. The kneaded clay is filled in a mold for mortar and press-molded at a molding pressure of 44.1 MPa using a friction press, and the dimensions and outer shape after firing are 300 mm × 300 mm × 100 mm (height). The product was molded so as to have a box shape with an open top with a side wall thickness of 10 mm and a bottom wall thickness of 15 mm. Next, through a natural drying process and an end face finishing process, the molded product was fired in a tunnel kiln at a maximum temperature of 1350 ° C. for 3 hours.

  About the manufactured mortar, the chemical composition, crystal system, bending strength, thermal expansion coefficient, and porosity were measured. The chemical composition was measured by fluorescent X-ray analysis in accordance with JIS R2216. The crystal system was measured by powder X-ray diffraction. The bending strength was measured according to JIS R2213. The coefficient of thermal expansion was measured from room temperature to 1000 ° C. according to JIS R2207-3. The porosity was measured according to JIS R2205.

(Test 2: Durability test of mortar by production of positive electrode active material)
10 kg of a mixture of lithium carbonate and cobalt oxide mixed at a mass ratio of 2: 1 as a raw material of the positive electrode active material is put into the mortar produced by the above method, and the temperature is raised to 1050 ° C. at 500 ° C./H with a roller hearth kiln. After heating at 1050 ° C. for 8 hours, the temperature in the furnace was lowered by introducing air, and the mortar and the fired product were forcibly cooled. Thereafter, the fired product was taken out from the mortar, and the occurrence of cracks in the mortar and the occurrence of peeling when the fired product was taken out were confirmed. The manufacturing process of this positive electrode active material was carried out until cracks occurred in the mortar, and it was confirmed how many times the firing caused cracks. Tables 1 to 5 show the number of firings in which cracks occurred. In addition, the frequency | count shown to Tables 1-5 is an average value of three samples.

(Test 2: Durability test results)
In Examples 1 to 23, the number of repeated uses exceeded 50 times, but in Comparative Examples 1 to 7, it was less than 50 times. From this, as for the raw material of a mortar, each content rate of spinel, cordierite, and mullite is spinel 30 mass%-70 mass%, cordierite 15 mass%-70 mass%, and mullite 0 mass%-35 mass%. It was found that the durability of the mortar is improved by blending so as to be.

In terms of chemical composition, Al ₂ O ₃ component is 46% by mass to 68% by mass, MgO component is 13% by mass to 22% by mass, and SiO ₂ component is 12% by mass to 36% by mass. It was found that the durability of the mortar improves.

(Test 2: Analysis of mortar and fired product after firing)
Next, the surface of the mortar after the production of the positive electrode active material was analyzed. Powder X-ray diffraction pattern of the mortar according to the composition of Example 6 before firing the positive electrode raw material, powder X-ray diffraction pattern of the surface of the mortar where the fired product (positive electrode active material) was in contact after firing the positive electrode raw material, and The powder X-ray diffraction pattern on the surface of the fired product that was in contact with the mortar was measured, and based on the powder X-ray diffraction pattern database of the reference sample, a substance that matched the peak data as the measurement result was searched, and the measurement sample was Each contained substance was identified. The results are shown in FIGS. Moreover, about the mortar which has the composition of Example 4 which baked the positive electrode raw material once, the fracture | rupture surface of the center of the bottom face which has contacted baked material was observed using the scanning electron microscope and the energy dispersive X-ray spectrometer. . FIG. 8 shows the result.

From FIG. 5, it was found that spinel, cordierite, and mullite were contained in the mortar before firing the positive electrode material. On the other hand, from FIG. 6, it was found that the surface of the mortar after firing the positive electrode material contained MgAl ₂ O ₄ (spinel), LiAlO ₂ (lithium aluminate), MgO (magnesium oxide), and LiAlSiO ₄ . . In addition, FIG. 9 shows that a layer containing a large amount of Mg but a small amount of Al and Si is formed in a region having a depth of about 10 μm from the surface of the mortar. From this, it was found that when the positive electrode material was fired using the mortar of the present invention, MgO was generated on the surface, and a layer containing a large amount of MgO was formed. This result agrees with the result of Test 1 shown above that MgO is produced when the spinel and cordierite and the positive electrode material are fired. Therefore, it is understood that the layer containing a large amount of MgO formed by firing the positive electrode raw material prevents the positive electrode raw material from penetrating into the mortar and suppresses the deterioration of the mortar. Furthermore, this MgO layer suppresses the reaction between cordierite or the like and the positive electrode material, thereby suppressing an increase in the coefficient of thermal expansion of the mortar of the present invention and preventing the occurrence of cracks in the mortar in the temperature lowering process. It is understood that.

In addition, according to the mortar of the present invention, it was possible to take out the baked product (positive electrode active material) that was easily baked simply by turning over the mortar (turning the opening downward). That is, the mortar and the fired product were not welded. This is presumed that LiAlO ₂ and LiAlSiO ₄ formed on the surface of the mortar prevent the fired product and the mortar from sticking. FIG. 9 shows a scanning electron micrograph of the surface of the mortar before firing the positive electrode material and a scanning electron micrograph of the surface of the mortar after firing the positive electrode material for the mortar according to Example 4.

From FIG. 7, the surface of the fired product obtained using the mortar of the present invention, which was in direct contact with the mortar, was LiCoO _{2 as the} positive electrode active material and unreacted Co ₃ O _4. Although detected, adhesion of the reaction product of the positive electrode raw material and the mortar to the surface of the fired product was not confirmed. Thus, it was found that a positive electrode active material having no adhesion of impurities can be obtained by using the mortar of the present invention.

(Test 3)
Durability tests were carried out on the koji bowl containing magnesia as the main component by producing a positive electrode active material. The mortar used in the test is a commercial product, and the shape and dimensions thereof are the same as the shape and dimensions of the mortar used in Test 2. The test method is the same as Test 2 except for the mortar used. Table 6 shows the chemical composition and test results as Comparative Example 8. The number of repeated uses shown in Table 6 is the average value of three samples as in Test 2.

  As shown in Table 6, the useable number of magnesia mortars is 15 times, which is less than the number of useable mortars according to Examples 1 to 23 and Comparative Examples 1 to 7 shown in Tables 1 to 5. In particular, it was less than 1/3 of the number of times of use of the mortar of the present invention according to Examples 1 to 23. This is presumably because the magnesia mortar has a high coefficient of thermal expansion, so that cracks are likely to occur in the temperature lowering process.

  The sagger for producing a positive electrode active material of a lithium ion battery and a method for producing the same according to the present invention have been described based on the above embodiment, but are not limited to the above embodiment, and are within the scope of the present invention, and It goes without saying that various modifications, changes and improvements can be included in the above embodiment based on the basic technical idea of the present invention. Further, various combinations, substitutions, or selections of various disclosed elements are possible within the scope of the claims of the present invention.

  Further problems, objects, and developments of the present invention will become apparent from the entire disclosure of the present invention including the claims.

The powder X-ray-diffraction pattern of the baking thing of the mixture of the magnesia and positive electrode raw material in Test 1, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern of the baked material of the mixture of the spinel and positive electrode raw material in Test 1, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern of the baked material of the mixture of the cordierite and positive electrode raw material in Test 1, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern of the baked material of the mixture of the mullite and positive electrode raw material in Test 1, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern of the mortar which concerns on the composition of Example 6 before positive electrode raw material baking, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern of the surface of the mortar with which the baked material (positive electrode active material) was in contact after baking of a positive electrode raw material, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. The powder X-ray-diffraction pattern on the surface of the baked product which the mortar contacted, and the peak figure of the substance matched with the peak of this powder X-ray-diffraction pattern. About the mortar which has the composition of Example 4 which baked the positive electrode raw material once, the scanning electron micrograph of the bottom center fracture surface which is in contact with the baked product, and the measurement figure by an energy dispersive X-ray spectrometer. About the mortar concerning Example 4, the scanning electron micrograph of the mortar surface before baking a positive electrode raw material, and the scanning electron micrograph of the mortar surface after positive electrode raw material baking.

Claims (12)

A mortar for producing a positive electrode active material of a lithium ion battery,
A mortar containing 30% to 70% by weight of spinel, 15% to 70% by weight of cordierite, and 0% to 35% (including 0% by weight) of mullite.   The mortar according to claim 1, comprising 45% by mass to 65% by mass of spinel, 20% by mass to 40% by mass of cordierite, and 5% by mass to 25% by mass of mullite. In a non-manufactured mortar, the positive electrode active material of a lithium ion battery
The Al ₂ O ₃ component is contained in 46% by mass to 68% by mass, the MgO component is contained in 14 % by mass to 22% by mass, and the SiO ₂ component is contained in 12% by mass to 36% by mass. The mortar described. The Al ₂ O ₃ component is contained in 56% by mass to 67% by mass, the MgO component is contained in 14% by mass to 22% by mass, and the SiO ₂ component is contained in 15% by mass to 24% by mass. A bowl.   The thermal expansion coefficient in 25 to 1000 degreeC is 0.5% or less, The mortar as described in any one of Claims 1-4 characterized by the above-mentioned.   The mortar according to claim 5, wherein the thermal expansion coefficient at 25 ° C to 1000 ° C is 0.35% or less. Fe ₂ O ₃ component is 0.5 mass% or less, The mortar according to any one of claims 1 to 6 characterized by things.   After the raw material of the positive electrode active material of the lithium ion battery is placed in an unfired mortar and fired, the surface layer that comes into contact with the raw material after firing contains more MgO component than when the raw material is unfired. The mortar according to any one of claims 1 to 7, characterized in that. A method for producing a mortar for producing a positive electrode active material of a lithium ion battery,
30% to 70% by weight of spinel, 15% to 70% by weight of cordierite, and 0% to 35% (including 0% by weight) of mullite based on the total weight of spinel, cordierite and mullite. A method for producing a mortar characterized by firing a mixture containing slag. In a non-manufactured mortar with a positive electrode active material of a lithium ion battery,
46 mass% to 68 mass% of Al ₂ O ₃ component, 14 mass% to 22 mass% of MgO component, and 12 mass% to 36 mass% of SiO ₂ component with respect to the total components of spinel, cordierite and mullite. The method for producing a mortar according to claim 9 , wherein the mixture containing spinel and cordierite or a mixture containing spinel, cordierite and mullite is fired. The said mixture does not contain 5 mass% or more of magnesia single-piece | unit with respect to the total mass of a spinel, a cordierite, and a mullite, The manufacturing method of the mortar according to claim 9 or 10 characterized by the above-mentioned. The method for producing a mortar according to claim 10 or 11 , wherein the mixture contains 0.5% by mass or less of Fe ₂ O ₃ component based on a total component of spinel, cordierite and mullite.