JP7118851B2 - Method for manufacturing positive electrode active material for all-solid-state lithium-ion battery, and method for manufacturing all-solid-state lithium-ion battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material for an all-solid lithium ion battery and a method for producing an all-solid lithium ion battery.

Lithium-ion batteries currently in use employ layered compound LiMeO ₂ (Me is a cation selected to have +III valence on average and always contains a redox cation), spinel compound LiMeQO ₄ (Q is a cation selected to have a +IV valence on average), an olivine compound LiX1X2O ₄ (X1 is a cation selected to have a +II valence and always contains a redox cation, and X2 has a +V valence Selected cations) and fluorite-type compounds such as Li ₅ MeO ₄ are used.

However, in the case of lithium-ion batteries, most of the electrolytes are organic compounds, and even if flame-retardant compounds are used, the risk of fire cannot be completely eliminated. As an alternative candidate for such a liquid-type lithium ion battery (hereinafter also referred to as a liquid-type LIB), an all-solid-state lithium-ion battery (hereinafter also referred to as an all-solid-state LIB) with a solid electrolyte has been attracting attention in recent years (Patent Document 1 etc). Among them, all-solid-state lithium ion batteries in which sulfides such as Li ₂ SP ₂ S ₅ and lithium halide are added as solid electrolytes are becoming mainstream.

Japanese Patent No. 5971109

In all-solid-state LIBs, the possibility of unexpected battery combustion is significantly lower than that of liquid-based LIBs, but on the other hand, it has the disadvantage that it is difficult to extract current. Alternatively, techniques have been developed such as mixing about 20 to 30% of the solid electrolyte into the positive electrode, and coating the surface of the positive electrode active material particles with Li—Nb oxide.

This Li—Nb oxide coating can extract lithium ions from the positive electrode active material or insert lithium ions into the positive electrode active material by forming a buffer layer between the positive electrode active material and the solid electrolyte. It is an epoch-making technology in that it has become easy to do. However, in the investigations made so far, the coating is mainly applied to solid particles, and it is difficult to apply to particles having a high specific surface area such as hollow particles. The reasons for this are (1) In most coating methods, a liquid organic substance obtained by mixing lithium alkoxide and niobium alkoxide is prepared and coated using a tumbling flow device or the like. (2) the positive electrode active material and the solid electrolyte are in close contact with each other when mixed with the solid electrolyte due to the coating being caught by the small particles; blocking contact, and the like.

On the other hand, in the case of liquid LIBs, there has been an increasing number of investigations into positive electrode active materials having a large specific surface area, such as hollow particles, mainly for HEVs. In the case of liquid LIB, it is not particularly necessary to coat with Li—Nb oxide, and the electrolyte easily penetrates into the electrodes by techniques such as vacuum impregnation, so many approaches related to high output have been made. . However, in the case of an all-solid LIB, it is necessary to coat it with a Li--Nb oxide, and the electrolyte does not permeate. Therefore, in order for the inventors to produce a positive electrode active material with a large specific surface area, a tumbling flow method, which is a known general Li—Nb oxide coating method, and a method of gradually adding the coating raw material were investigated. However, although uniform Li-Nb oxide coating may be possible in some cases, the process is not suitable for mass production because the condition setting is complicated, a long residence time is required, and a high degree of skill is required. Instead of these methods, a simpler method of coating Li—Nb oxide on the positive electrode active material has been demanded.

Now consider the effect of particle size on uniform coating. Small particle size particles originally have a high specific surface area, and the particle surface does not have much unevenness in relation to the particle size. For example, it is often possible to obtain a uniform coating relatively easily by making some changes in manufacturing conditions such as the amount of solvent. However, when it is attempted to obtain a material having a large particle size and a high specific surface area, the Li—Nb oxide coating raw material does not penetrate into the deepest part of the concave portion even if it takes a considerably long time, and remains separated from the core particle. A Li—Nb oxide was sometimes formed (hereinafter referred to as “single Li—Nb oxide”). If this is fired as it is, for example, the single Li-Nb oxide will easily crack due to the impact during pulverization with a pulverizer, etc., and it will fly into the bag filter as it is, for example, in an air current. In some cases, the deepest portion of the concave portion is left uncoated. However, in applications where both capacity and output are required, such as EVs (electric vehicles) and forklifts, a positive electrode active material with a large particle size is required from the viewpoint of capacity, and a positive electrode active material with a high specific surface area is required from the point of output. was sought.

Accordingly, an object of the embodiments of the present invention is to provide a simple method for producing a positive electrode active material for an all-solid-state lithium-ion battery, which is coated with Li—Nb oxide with a large particle size and a high specific surface area.

In one embodiment of the present invention, a transition metal hydroxide composed of nickel, cobalt and manganese and having an average particle diameter D50 of 10 μm or more and a specific surface area of 20 m ² /g or more A step of putting the precursor into a rocking mixer and spraying a niobium oxalate aqueous solution to prepare a precursor powder coated with niobium oxalate; A method for producing a positive electrode active material for an all-solid-state lithium-ion battery, comprising a step of dry-mixing and baking.

A method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to another embodiment of the present invention is a transition metal hydroxide precursor composed of nickel, cobalt, and manganese. The amount ratio is represented by 85 to 90:7 to 9:0 to 7.5 (excluding 0) when the total amount of nickel, cobalt and manganese is 100, and the lithium compound is LiOH.H ₂ O.

In a method for producing a positive electrode active material for an all-solid lithium ion battery according to still another embodiment of the present invention, D90 of LiOH.H ₂ O is 20 μm or less.

In a method for producing a positive electrode active material for an all-solid-state lithium ion battery according to still another embodiment of the present invention, the positive electrode active material has an average particle size D50 of 10 μm or more and a specific surface area of 0.5 m ² /g or more.

Another embodiment of the present invention forms a positive electrode layer using a positive electrode active material for an all-solid lithium ion battery manufactured by the method for manufacturing a positive electrode active material for an all-solid lithium ion battery according to an embodiment of the present invention, A method for manufacturing an all-solid lithium ion battery using the positive electrode layer, the solid electrolyte layer and the negative electrode layer.

According to the embodiments of the present invention, it is possible to provide a simple method for producing a positive electrode active material for an all-solid-state lithium ion battery, which is coated with Li—Nb oxide with a large particle size and a high specific surface area.

(Method for producing positive electrode active material for all-solid-state lithium ion battery)
An aqueous transition metal solution prepared so that the molar ratio of nickel source:cobalt source:manganese source is Ni:Co:Mn=85-90:7-9:0-7.5 (excluding Mn=0) prepare. Sulfates are used as the nickel source, the cobalt source, and the manganese source in the following examples, but they may be a combination of at least one selected from sulfates, nitrates, acetates, and the like.

Next, the transition metal aqueous solution, the sodium hydroxide aqueous solution, and the ammonia water are prepared in separate tanks, and these are put into one reaction tank and reacted by the crystallization method. Subsequently, the reactant was filtered, washed with water and dried to obtain a composition formula: _NiaCobMnc (OH) ₂ [wherein a: _b : _c =85-90:7-9:0-7. 5 (excluding c=0)], an average particle size D50 of 10 μm or more and a specific surface area of 20 m ² /g or more. The average particle size D50 and the specific surface area can be controlled, for example, by the hydroxide production conditions (temperature, pH, atmosphere, etc.) to the extent considered common sense by those skilled in the art.

The average particle size D50 of the precursor powder may be 12 μm or more, 15 μm or more, or 20 μm or more. Also, the average particle size D50 of the precursor powder may be 45 μm or less, 40 μm or less, or 35 μm or less.

The specific surface area of the precursor powder may be 22 m ² /g or more, 25 m ² /g or more, or 30 m ² /g or more. Further, the specific surface area of the precursor powder may be 150 m ² /g or less and 120 m ² /g or less.

Next, the precursor powder and an aqueous niobium oxalate solution containing Nb at a concentration of 63 to 189 g/L were mixed, and the ratio of the total amount of Ni, Co, and Mn to the amount of Nb: (Ni+Co+Mn) : Weigh so that Nb becomes 1:0.0027 to 0.0055. Next, the precursor powder is put into a rocking mixer. Subsequently, the niobium oxalate aqueous solution is sprayed onto the surface of the precursor powder in the rocking mixer at a spraying time of 17 to 35 seconds, a smoothing time of 900 seconds after spraying, a rotation speed of 30 Hz, and a rocking speed of 30 Hz. , to obtain a precursor powder coated with niobium oxalate.

Subsequently, the precursor powder coated with niobium oxalate and the lithium compound are dry-mixed and fired. Specifically, first, the precursor powder coated with niobium oxalate is taken out from the rocking mixer, and LiOH.H ₂ O having a D90 of 20 μm or less is mixed with the precursor powder at a humidity of 40 to 65%. are weighed into one bag so that the material amount ratio Li/(Ni+Co+Mn) is 1.00 to 1.03 in an air atmosphere. Next, the powder obtained by roughly mixing the bag (hereinafter also referred to as "coarsely mixed powder") is put entirely from the bag into a Henschel mixer and dry-mixed at 10 to 30 Hz for 5 to 15 minutes. Here, the D90 of the _{LiOH.H 2} O is ₂₀ μm or less. Lumps may be seen, and if baked in such a state, the positive electrode active material may contain a large amount of Li ₂ CO ₃ and LiOH. This is because it is expected that there will be large variations in performance.

Subsequently, the mixed powder (hereinafter also referred to as “mixed powder”) is filled in an alumina sagger. Next, the firing furnace is filled with oxygen, and the alumina sagger is placed in the firing furnace and fired in an oxygen atmosphere at 350° C. for 2 hours, followed by firing at 490° C. for 8 hours and 750° C. for 4 hours. After cooling this to room temperature, the alumina sagger is taken out from the firing furnace into dry air and crushed by a roll crusher and an ACM pulverizer to obtain a positive electrode active material.

According to the above method, there are no problems such as complicated condition setting, long residence time, or skill required for work, as in the conventional method, and it is a very simple method. A Li—Nb oxide-coated positive electrode active material having a large particle size and a high specific surface area, such as D50 of 10 μm or more and a specific surface area of 0.5 m ² /g or more, can be produced. In the positive electrode active material, the surface of the lithium-nickel-cobalt-manganese composite oxide is uniformly coated with the Li—Nb oxide. By using a rocking mixer, compared to a general tumbling flow method, the Li—Nb raw material is actively pressed by the concave portion of the core particle. -Nb oxide-coated positive electrode active material is produced, and it is presumed that the coating will be uniform.

(Manufacturing method of all-solid-state lithium-ion battery)
A positive electrode layer is formed using a positive electrode active material for an all-solid lithium ion battery manufactured by the method for manufacturing a positive electrode active material for an all-solid lithium ion battery according to an embodiment of the present invention, and a solid electrolyte layer, the positive electrode layer and the negative electrode All-solid-state lithium-ion batteries with the layers can be made.

The following examples are provided for a better understanding of the invention and its advantages, but the invention is not limited to these examples.

(Example 1)
An aqueous transition metal solution, an aqueous sodium hydroxide solution, and an aqueous ammonia prepared at a molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate of 88:9:3 are prepared in separate tanks, and these are added to one reaction tank. The mixture was reacted by a crystallization method, filtered, washed with water and dried to obtain a precursor powder represented by the composition formula: Ni _0.88 Co _0.09 Mn _0.03 (OH) ₂ . The specific surface area of this precursor was measured and found to be 21 m ² /g. Moreover, when the average particle diameter D50 of this precursor was measured, it was 14 μm.

Next, the Ni _0.88 Co _0.09 Mn _0.03 (OH) ₂ precursor powder and a niobium oxalate aqueous solution containing Nb at a concentration of 232 g/L were added to the total amount of Ni, Co and Mn and the amount of Nb. The ratio of (Ni+Co+Mn):Nb was 1:0.0033. Next, the precursor powder was put into a rocking mixer. Subsequently, the niobium oxalate aqueous solution is sprayed onto the surface of the precursor powder in the rocking mixer at a spraying time of 17 seconds, a smoothing time of 15 minutes after spraying, a rotation speed of 30 Hz, and a rocking speed of 30 Hz. Stirred with a mixer for 20 minutes.

Subsequently, the niobium oxalate-coated precursor powder was taken out from the rocking mixer, and the niobium oxalate-coated precursor powder and LiOH.H ₂ O having a D90 of 20 μm or less were mixed together at a humidity of 60. %, and weighed into one bag so that the material amount ratio Li/(Ni+Co+Mn+Nb) was 1.01. Next, while the bag was inflated, the opening was gripped with a hand to prevent the powder from leaking out, and the non-gripped hand was placed on the bottom of the bag and the bag was shaken with both hands to roughly mix the powders. All of the loosely mixed powders were placed in a Henschel mixer from the bag and mixed at 1500 rpm for 5 minutes.

The mixed powder was then filled into an alumina sagger. Next, the firing furnace is filled with oxygen, the alumina sagger is placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa, held at 350 ° C. for 2 hours, held at 490 ° C. for 8 hours, and further heated. It was heated and held at 750° C. for 4 hours. After cooling this to room temperature at 5° C./min, the alumina sagger was taken out from the firing furnace into dry air and pulverized with a roll crusher and an ACM pulverizer to obtain a positive electrode active material of Example 1. When the specific surface area of the positive electrode active material of Example 1 was measured, it was 0.7 m ² /g. Further, when the particle cross section of the positive electrode active material of Example 1 was observed by EPMA, the surface of the lithium-nickel-cobalt-manganese composite oxide was uniformly coated with Nb, and the lithium-nickel-cobalt-manganese composite oxide was exposed on the particle surface. I never did. Furthermore, when the average particle size D50 of the positive electrode active material of Example 1 was measured, it was 14 μm.

(Comparative example 1)
The same precursor powder as in Example 1 was used, together with LiOH.H ₂ O having a D90 of 20 μm or less, in an air atmosphere with a humidity of 60% so that the substance amount ratio Li/(Ni+Co+Mn+Nb) was 1.01. Weigh into one bag, hold the opening with your hand while the bag is inflated to prevent the powder from leaking out, place your other hand on the bottom of the bag and shake the bag with both hands to mix roughly. did. All of the loosely mixed powders were placed in a Henschel mixer from the bag and mixed at 1500 rpm for 5 minutes, and the mixed powders were filled in an alumina sagger. Oxygen is filled in the firing furnace, the alumina sagger is placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa, held at 350 ° C. for 2 hours, held at 490 ° C. for 8 hours, and further heated. It was held at 750° C. for 4 hours. This was cooled to room temperature at 5°C/min. After cooling, the alumina sagger was taken out from the kiln into dry air and pulverized with a roll crusher and an ACM pulverizer. The pulverized powder was added together with lithium ethoxide and niobium pentaethoxide so that the material amount ratio of (Ni+Co+Mn):LiOC ₂ H ₅ :Nb(OC ₂ H ₅ ) ₅ =1:0.0033:0.0033. Then, both alkoxides were dispersed in ethanol to form a dispersion, and the crushed powder and the dispersion were coated with lithium niobium oxide using a tumbling flow apparatus in a conventional manner for comparison. The positive electrode active material of Example 1 was used. When the specific surface area of the positive electrode active material of Comparative Example 1 was measured, it was 0.9 m ² /g. Further, when the particle cross section of the positive electrode active material of Comparative Example 1 was observed by EPMA, the surface of the lithium-nickel-cobalt-manganese composite oxide was coated with Nb. Many of them were exposed and existed in concave portions on the particle surface. Furthermore, when the average particle diameter D50 of the positive electrode active material of Comparative Example 1 was measured, it was 14 μm.

(Reference example 1)
A positive electrode was prepared in the same manner as in Comparative Example 1 except that the precursor powder used in Example 1 and Comparative Example 1 was replaced with a precursor powder having an average particle diameter D50 of 14 μm and a specific surface area of 6 m ² /g. An active material was produced. When the specific surface area of this positive electrode active material was measured, it was 0.3 m ² /g. When the particle cross section of this positive electrode active material was observed by EPMA, it was found that the surface of the lithium-nickel-cobalt-manganese composite oxide was uniformly coated with Nb and the lithium-nickel-cobalt-manganese composite oxide was exposed on the particle surface. I didn't. Furthermore, when the average particle diameter D50 of the positive electrode active material of Reference Example 1 was measured, it was 14 μm.

(Comparative example 2)
Instead of the rocking mixer in Example 1, the test was conducted using a vibrating mill. Specifically, the same amount of precursor powder and the same amount of niobium oxalate aqueous solution as in Example 1 were placed in a vibrating mill pot together with alumina media having a diameter of 5 mm, and mixed for 60 minutes. A positive electrode active material was produced in the same manner as in Example 1 using the precursor powder coated with niobium oxalate thus obtained. The specific surface area of this positive electrode active material was 0.8 m ² /g. When the particle cross section of this positive electrode active material was observed by EPMA, it was found that the surface of the lithium-nickel-cobalt-manganese composite oxide was only partially coated with Nb, and the lithium-nickel-cobalt-manganese composite oxide was partially exposed on the particle surface. Was. Furthermore, when the average particle size D50 of the positive electrode active material of Comparative Example 2 was measured, it was 10 μm.

(Reference example 2)
In Example 1, a test was conducted by hand kneading instead of using a rocking mixer. Specifically, the same amount of precursor powder as in Example 1 was placed on a glass surface, and the same amount of niobium oxalate aqueous solution as in Example 1 was gradually dropped from a burette and kneaded using a paint knife. A precursor powder coated with niobium oxide was obtained. This is weighed into one bag together with LiOH·H ₂ O having a D90 of 20 µm or less so that the material amount ratio Li/(Ni + Co + Mn + Nb) is 1.01 in an air atmosphere with a humidity of 60%, and the bag is inflated. The opening was gripped with a hand to prevent the powder from leaking out, and the non-gripped hand was applied to the bottom of the bag and the bag was shaken with both hands to roughly mix. All of the loosely mixed powders were placed in a Henschel mixer from the bag and mixed at 1500 rpm for 5 minutes, and the mixed powders were filled in an alumina sagger. Oxygen is filled in the firing furnace, the alumina sagger is placed in the firing furnace to create an oxygen atmosphere of 0.1 MPa, held at 350 ° C. for 2 hours, held at 490 ° C. for 8 hours, and further heated. It was held at 750° C. for 4 hours. This was cooled to room temperature at 5°C/min. After cooling, the alumina sagger was taken out from the kiln into dry air and pulverized with a roll crusher and an ACM pulverizer to obtain a positive electrode active material of Reference Example 2. When the specific surface area of the positive electrode active material of Reference Example 2 was measured, it was 0.7 m ² /g. When the particle cross section of the positive electrode active material of Reference Example 2 was observed by EPMA, the surface of the lithium-nickel-cobalt-manganese composite oxide was uniformly coated with Nb, and the lithium-nickel-cobalt-manganese composite oxide was exposed on the particle surface. I never was. Furthermore, when the average particle diameter D50 of the positive electrode active material of Reference Example 2 was measured, it was 14 μm.

Claims (5)

A hydroxide precursor which is a transition metal hydroxide composed of nickel, cobalt and manganese and has an average particle size D50 of 10 μm or more and a specific surface area of 20 m ² /g or more is charged into a rocking mixer. and spraying a niobium oxalate aqueous solution to prepare a precursor powder coated with niobium oxalate;
a step of dry-mixing the precursor powder coated with niobium oxalate and a lithium compound and firing the mixture;
A method for producing a positive electrode active material for an all-solid-state lithium ion battery, comprising: When the total material amount of nickel, cobalt and manganese is 100, the material amount ratio of nickel, cobalt and manganese in the transition metal hydroxide precursor composed of nickel, cobalt and manganese is 85 to 90: 7-9: 0-7.5 (excluding 0), and the lithium compound is LiOH.H ₂ O. 3. The method for producing a positive electrode active material for an all-solid lithium ion battery according to claim ₂ , wherein D90 of said LiOH.H2O is 20 [mu]m or less. The method for producing a positive electrode active material for an all-solid lithium ion battery according to any one of claims 1 to 3, wherein the positive electrode active material has an average particle size D50 of 10 µm or more and a specific surface area of 0.5 m ² /g or more. . A positive electrode layer is formed using the positive electrode active material for an all-solid lithium ion battery produced by the method for producing a positive electrode active material for an all-solid lithium ion battery according to any one of claims 1 to 4, and the positive electrode layer , A method for manufacturing an all-solid lithium ion battery using a solid electrolyte layer and a negative electrode layer.