Method for producing coated active material and coated active material

Abstract

To shorten a time required for production as compared with a case in which a coating active material is produced by a rolling flow coating method.SOLUTION: A manufacturing method of a coated active material includes a first step of obtaining slurry droplets by atomizing a slurry containing an active material and a coating liquid, a second step of air-drying the slurry droplets in heated gas to obtain a precursor, and a third step of firing the precursor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a coated active material and the coated active material. [Background technology]

[0002] Patent Document 1 discloses a method for producing an active material composite (coated active material) by using a tumbling fluidized coating device to spray a specific coating liquid onto the surface of an active material while drying, and then firing the material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6269645 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacturing method disclosed in Patent Document 1, the spraying speed of the coating liquid needs to be slow in order to suppress granulation of the active material, which results in a problem of a longer time required to manufacture the coated active material. [Means for solving the problem]

[0005] As one of the means for solving the above problems, the present application provides: a first step of forming droplets from a slurry containing an active material and a coating liquid to obtain slurry droplets; a second step of drying the slurry droplets in a heated gas stream to obtain a precursor; a third step of calcining the precursor; A method for producing a coated active material, comprising: Disclose.

[0006] In the method of the present disclosure, in the first step, the slurry may be converted into droplets by atomization.

[0007] In the method of the present disclosure, the coating solution may contain a lithium source and a niobium source.

[0008] In the method of the present disclosure, the niobium source may comprise a peroxo complex of niobium.

[0009] In the method of the present disclosure, in the second step, the temperature of the heated gas may be 100° C. or higher.

[0010] The coated active material produced by the method of the present disclosure may have, for example, the following configuration: That is, the coated active material of the present disclosure may have an active material and a coating layer that coats at least a portion of the surface of the active material, and the coating layer may have a plurality of pores. [Effects of the Invention]

[0011] According to the method of the present disclosure, a coated active material can be produced in a short time. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining the method for producing the coated active material. [Figure 2] FIG. 2 is a diagram showing an example of the morphology of slurry droplets. [Figure 3] FIG. 3 is a diagram illustrating one embodiment of the second step. [Figure 4] FIG. 4 is a diagram illustrating another embodiment of the second step. [Figure 5] FIG. 5 is a diagram for explaining the manufacturing method of Comparative Example 1. [Figure 6] FIG. 6 is a diagram illustrating a cross-sectional configuration of the coated active material according to Example 1. As shown in FIG. [Figure 7] FIG. 7 is a diagram illustrating a cross-sectional configuration of the coated active material according to Comparative Example 1. As shown in FIG. [Figure 8]FIG. 8 is a diagram showing the measurement results of the BET specific surface area of ​​the coated active materials according to Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a method for producing a coated active material according to an embodiment will be described in detail with reference to the drawings. Note that the method of the present disclosure is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present disclosure. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions will be omitted.

[0014] 1. Manufacturing method of coated active material As shown in FIG. 1, the method S10 for producing a coated active material of the present disclosure includes a first step S1 of forming droplets from a slurry containing an active material and a coating liquid to obtain slurry droplets, a second step S2 of air-drying the slurry droplets in a heated gas to obtain a precursor, and a third step S3 of calcining the precursor.

[0015] 1.1 First step In the first step, a slurry containing an active material and a coating liquid is formed into droplets to obtain slurry droplets.

[0016] 1.1.1 Active material The active material may be a positive electrode active material or a negative electrode active material. Specific examples of the active material include LiCoO2, LiNi x Co 1-x O2(0 <x<1)、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, hetero-element substituted Li-Mn spinel (LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4, LiMn 1.5 Zn0.5 O4, etc.), lithium titanate (e.g., Li4Ti5O 12 Examples of the active material include lithium-containing oxides such as lithium phosphate (LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4), and various oxide-based active materials other than lithium-containing oxides; Si-based active materials such as Si and Si alloys; carbon-based active materials such as graphite and hard carbon; and metallic lithium and lithium alloys. Among these, a material with a relatively noble charge / discharge potential can be used as the positive electrode active material, and a material with a relatively base charge / discharge potential can be used as the negative electrode active material. In particular, when the active material is a lithium-containing oxide, the method of the present disclosure can be expected to be even more effective. One active material may be used alone, or two or more active materials may be used in combination. The active material may be one used in a sulfide all-solid-state battery.

[0017] The shape of the active material is not particularly limited as long as it can be formed into droplets from the slurry. For example, the active material may be particulate. The active material particles may be solid or hollow. The active material particles may be primary particles or secondary particles formed by agglomeration of multiple primary particles. The average particle size (D50) of the active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. The average particle size D50 is the particle size (median size) at 50% of the cumulative value in a volume-based particle size distribution determined by a laser diffraction / scattering method.

[0018] 1.1.2 Coating liquid The coating liquid forms a coating layer that exhibits a predetermined function on the surface of the active material after air drying and baking, which will be described later. The coating layer may have the function of suppressing an increase in interfacial resistance between the active material and other materials, for example. The type of coating liquid can be selected depending on the type of active material to be coated and the desired function.

[0019] When a layer made of an oxide containing lithium and an element A other than lithium is formed on the surface of an active material, the coating solution may contain a lithium source and an A source. Specific examples of element A include at least one selected from the group consisting of B, C, Al, Si, P, S, Ti, Zr, Nb, Mo, Ta, and W. For example, when a lithium niobate layer is formed on the surface of an active material, the coating solution may contain a lithium source and a niobium source. The coating solution may contain lithium ions as the lithium source. For example, a coating solution containing lithium ions as the lithium source may be obtained by dissolving a lithium compound such as LiOH, LiNO3, or Li2SO4 in a solvent. Alternatively, the coating solution may contain a lithium alkoxide as the lithium source. Furthermore, the coating solution may contain a niobium peroxo complex as the niobium source. Alternatively, the coating solution may contain a niobium alkoxide as the niobium source. The molar ratio of the lithium source to the niobium source contained in the coating solution is not particularly limited, and may be, for example, Li:Nb=1:1. The following are examples of (i) a coating solution containing a lithium ion and a peroxo complex of niobium, and (ii) a coating solution containing an alkoxide of lithium and an alkoxide of niobium.

[0020] (i) Coating solution containing lithium ions and a peroxo complex of niobium The coating solution may be obtained by preparing a transparent solution using, for example, hydrogen peroxide, niobic acid, and aqueous ammonia, and then adding a lithium compound to the transparent solution. 3- ) has the following structural formula, for example:

[0021] [ka]

[0022] (ii) Coating solution containing lithium alkoxide and niobium alkoxide The coating solution may be prepared by dissolving ethoxylithium powder in a solvent, followed by adding a predetermined amount of pentaethoxyniobium to the solution. In this case, examples of the solvent include dehydrated ethanol, dehydrated propanol, and dehydrated butanol.

[0023] The type of coating layer formed on the surface of the active material is not limited to a layer made of an oxide containing lithium and an element A other than lithium. The method of the present disclosure can be used when modifying or coating the surface of an active material with some kind of substance. For example, the method of the present disclosure can be used when coating the surface of a positive or negative electrode active material with a transition metal oxide to increase output power and extend life, or when combining a solid electrolyte, such as a sulfide, with the surface of an active material to increase the output power of an all-solid-state battery. However, the method of the present disclosure is believed to be particularly effective when forming a layer made of an oxide containing lithium and an element A other than lithium on the surface of the active material.

[0024] 1.1.3 Slurry The term "slurry" refers to a suspension or suspension containing an active material and a coating liquid, and may be any suspension having sufficient fluidity to be formed into droplets. In the method of the present disclosure, the slurry may be fluid enough to be formed into droplets using, for example, a spray nozzle or a rotary atomizer. The slurry may contain any solid or liquid component in addition to the active material and coating liquid described above.

[0025] The solid content concentration at which dropletization is possible varies depending on the type of active material, the type of coating liquid, and the conditions for dropletization (the type of device used for dropletization). The solid content concentration of the slurry is not particularly limited and may be, for example, 1 vol% or more, 5 vol% or more, 10 vol% or more, 20 vol% or more, 25 vol% or more, 30 vol% or more, 35 vol% or more, 40 vol% or more, 45 vol% or more, or 50 vol% or more, or 70 vol% or less, 65 vol% or less, 60 vol% or less, 55 vol% or less, 50 vol% or less, 45 vol% or less, 40 vol% or less, or 35 vol% or less. From the viewpoint of more easily obtaining slurry droplets, the solid content concentration of the slurry may be 40 vol% or less.

[0026] 1.1.4 Slurry dropletization The phrase "dropletizing" the slurry means that the slurry containing the active material and the coating liquid is converted into particles containing the active material and the coating liquid.

[0027] In the first step, the method for forming droplets from the slurry containing the active material and the coating liquid is not particularly limited. For example, the method for forming droplets from the slurry containing the active material and the coating liquid by spraying can be used. When spraying the slurry, a spray nozzle can be used. Methods for spraying the slurry using a spray nozzle include, but are not limited to, a pressurized nozzle method and a two-fluid nozzle method.

[0028] When the slurry is sprayed using a spray nozzle, the nozzle diameter is not particularly limited. The nozzle diameter may be, for example, 0.1 mm or more or 1 mm or more, or 10 mm or less or 1 mm or less. The spraying speed of the slurry (the supply speed of the slurry to the spray nozzle) is also not particularly limited. The spraying speed may be, for example, 0.1 g / sec or more or 1 g / sec or more, or 5 g / sec or less or 0.5 g / sec or less. The spraying speed may be adjusted depending on the viscosity and solids concentration of the slurry, the nozzle dimensions, etc.

[0029] In addition to the above-described method of spraying the slurry using a spray nozzle, another example of a method for forming droplets from the slurry is to supply a slurry containing an active material and a coating liquid onto a rotating disk at a constant speed and form droplets by centrifugal force. Even in this case, the supply rate of the slurry may be, for example, 0.1 g / sec or more or 1 g / sec or more, or 5 g / sec or less or 0.5 g / sec or less, and the supply rate may be adjusted depending on the viscosity, solids concentration, etc. of the slurry, the nozzle dimensions, etc. Alternatively, a method of forming droplets by applying a high voltage to the surface of the slurry containing the active material and the coating liquid may also be employed.

[0030] In the method of the present disclosure, for example, a spray dryer may be used to form droplets from the slurry (first step) and to dry the slurry by flash drying (second step). The type of spray dryer is not particularly limited, and examples include the above-mentioned type using a spray nozzle and a type using a rotating disk.

[0031] 1.1.5 Slurry droplets "Slurry droplets" are particles of a slurry containing an active material and a coating liquid. The size of the slurry droplets is not particularly limited. The diameter (sphere-equivalent diameter) of the slurry droplets may be, for example, 0.5 μm or more or 5 μm or more, or 5000 μm or less or 1000 μm or less. The diameter of the slurry droplets can be measured, for example, using a two-dimensional image obtained by capturing an image of the slurry droplets, or can be measured using a laser diffraction particle size distribution analyzer. Alternatively, the droplet diameter can be estimated from the operating conditions of the device that forms the slurry droplets.

[0032] In the method of the present disclosure, one slurry droplet may contain, for example, one active material particle and a coating liquid attached thereto, or may contain a plurality of active material particles (particle groups) and a coating liquid attached thereto. An example of the form of the slurry droplet is shown below.

[0033] As shown in FIG. 2(a), the slurry droplet 11 may include one active material particle 11a and a coating liquid 11b attached thereto, and the coating liquid 11b may cover the entire surface of the active material particle 11a.

[0034] As shown in FIG. 2(b), the slurry droplet 21 may include one active material particle 21a and a coating liquid 21b attached thereto, and the coating liquid 21b may cover a portion of the surface of the active material particle 21a.

[0035] 2(c), the slurry droplets 31 may contain a plurality of active material particles 31a and a coating liquid 31b attached thereto. The coating liquid 31b may coat the entirety or a portion of the active material particles 31a.

[0036] 1.2 Second step In the second step, the slurry droplets obtained in the first step are dried in a heated gas stream to obtain a precursor. The term "precursor" refers to a precursor of the target coated active material, and refers to the state before the firing treatment in the third step described below. In the second step, for example, as shown in FIG. 3, the slurry droplets 11 may be dried in a stream to obtain a precursor 12 in which a layer 11c containing a component derived from the coating liquid is formed on the surface of the active material 11a.

[0037] In the method of the present disclosure, "air flow drying" refers to drying the slurry droplets while suspending them in a high-temperature air flow. "Air flow drying" can include not only drying but also additional operations using a dynamic air flow. By continuously applying hot air to the slurry droplets or precursor during air flow drying, a force is continuously applied to the slurry droplets or precursor. Taking advantage of this, for example, the second step may include disintegrating (crushing) the slurry droplets or precursor by air flow drying. Specifically, as shown in FIG. 4(a), when air flow drying the slurry droplets, a single slurry droplet 41 may be crushed into individual active material particles or active material particle groups to obtain multiple slurry droplets 51. Alternatively, as shown in FIG. 4(b), a single aggregated precursor 42 may be crushed into individual active material particles or active material particle groups to obtain multiple precursors 52. In other words, in the method of the present disclosure, even if slurry droplets or precursor granules are generated, the granules can be crushed by flash drying. Therefore, a slurry with a low solids concentration can be used, and the processing speed can be easily increased. In this way, by crushing the slurry droplets or precursor by flash drying in the second step, the production time can be easily shortened and a high-performance coated active material can be easily produced.

[0038] In the second step, the drying and crushing may be performed simultaneously or separately. In the second step, a first airflow drying step in which the drying of the slurry droplets is predominant, and a second airflow drying step in which the crushing of the precursor is predominant may be performed. In addition, the second step may be performed repeatedly.

[0039] In the second step, the temperature of the heated gas may be any temperature that allows the solvent to volatilize from the slurry droplets, and may be, for example, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, 140°C or higher, 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, or 220°C or higher.

[0040] In the second step, the supply amount (flow rate) of the heated gas can be appropriately set in consideration of the size of the apparatus used, the supply amount of the slurry droplets, etc. For example, the flow rate of the heated gas is 0.10 m 3 / min or more, 0.15m 3 / min or more, 0.20m 3 / min or more, 0.25m 3 / min or more, 0.30m 3 / min or more, 0.35m 3 / min or more, 0.40m 3 / min or more, 0.45m 3 / min or more, or 0.50m 3 / min or more, and may be 5.00m 3 / min or less, 4.00m 3 / min or less, 3.00m 3 / min or less, 2.00m 3 / min or less, or 1.00m 3 / min or less.

[0041] In the second step, the supply velocity (flow rate) of the heated gas can also be appropriately set in consideration of the size of the apparatus used, the supply amount of slurry droplets, etc. For example, the flow rate of the heated gas may be 1 m / sec or more or 5 m / sec or more, or 50 m / sec or less or 10 m / sec or less, in at least a part of the system.

[0042] In the second step, the treatment time with the heated gas (drying time) can also be set appropriately taking into consideration the size of the apparatus used, the supply amount of slurry droplets, etc. For example, the treatment time may be 5 seconds or less, or 1 second or less.

[0043] In the second step, a heated gas that is substantially inert to the active material and the coating solution may be used. For example, an oxygen-containing gas such as air, an inert gas such as nitrogen or argon, or dry air with a low dew point may be used. In this case, the dew point may be −10° C. or lower, −50° C. or lower, or −70° C. or lower.

[0044] As a device for performing flash drying, for example, a spray dryer can be used, but is not limited to this.

[0045] 1.3 Third step In the third step, the precursor obtained in the second step is fired, thereby obtaining a coated active material having a coating layer on at least a portion of the surface of the active material.

[0046] The firing device may be, for example, a muffle furnace or a hot plate, but is not limited to these.

[0047] The firing conditions are not particularly limited and can be appropriately set depending on the type of coated active material. The firing conditions for producing a coated active material having a coating layer containing lithium niobate on the surface of a positive electrode active material are exemplified below.

[0048] For example, a precursor is obtained by performing the first and second steps using lithium-containing oxide particles as the positive electrode active material and a solution containing lithium ions and a niobium peroxo complex as the coating liquid. The resulting precursor is calcined to form a coating layer containing lithium niobate on the surface of the lithium-containing oxide, which is the positive electrode active material. In this case, the calcination temperature may be, for example, 100°C or higher, 150°C or higher, 180°C or higher, 200°C or higher, or 230°C or higher, or 350°C or lower, 300°C or lower, or 250°C or lower. The calcination temperature in the third step may be higher than the airflow drying temperature in the second step. The calcination time may be, for example, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, or 6 hours or more, or 20 hours or less, 15 hours or less, or 10 hours or less. The calcination atmosphere may be, for example, an air atmosphere, a vacuum atmosphere, a dry air atmosphere, a nitrogen gas atmosphere, or an argon gas atmosphere.

[0049] 2.Coated active material The coated active material produced by the method of the present disclosure comprises an active material and a coating layer that coats at least a portion of the surface of the active material. The thickness of the coating layer is not particularly limited and may be, for example, 0.1 nm or more, 0.5 nm or more, or 1 nm or more, or 500 nm or less, 300 nm or less, 100 nm or less, 50 nm or less, or 20 nm or less. The coating layer may cover 70% or more or 90% or more of the surface of the active material. The coverage of the coating layer on the surface of the active material can be calculated by observing a scanning electron microscope (SEM) image of the cross section of the particle, or by calculating the element ratio on the surface using X-ray photoelectron spectroscopy (XPS).

[0050] The particle diameter (D90) of the coated active material is not particularly limited and may be, for example, 1 nm or more, 10 nm or more, 100 nm or more, 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, or 9 μm or more, or may be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. The particle diameter D90 is the particle diameter at 90% cumulative in a volume-based particle size distribution determined by a laser diffraction / scattering method.

[0051] In the coated active material, the coating layer may have a plurality of pores. The pores may be, for example, cavities, bubbles (voids), or gaps. The shape of each pore is not particularly limited. For example, the cross-sectional shape of each pore may be circular or elliptical. The size of each pore is not particularly limited. For example, when observing the cross-section of the coated active material, the circle-equivalent diameter of the pore may be 10 nm or more and 300 nm or less. The number of pores in the coating layer is also not particularly limited. The position of the pores in the coating layer is also not particularly limited. The pores may be present at the interface between the active material and the coating layer, or may be present within the coating layer. The coating layer may have a plurality of pores contained inside (on the active material side) of its outermost surface (the surface opposite the active material).

[0052] In coated active materials, the coating layer having a plurality of pores can be expected to have the following effects. For example, the coated active material may have better contact with other battery materials, promoting the movement of electrons and ions. Furthermore, the coated active material may exhibit cushioning properties, which may improve the performance of the coated active material when used as an electrode or battery. For example, even when the active material expands during charge and discharge, or when pressure is applied to the coated active material during electrode press processing, the cushioning properties reduce the stress applied to the active material, and cracking of the active material is thought to be suppressed.

[0053] 3. Electrode manufacturing method The coated active material produced by the method of the present disclosure can be used, for example, as an electrode active material for an all-solid-state battery. In this respect, the technology of the present disclosure also has an aspect of being a method for producing an electrode. The method for producing an electrode of the present disclosure includes: Obtaining a coated active material by the method for producing a coated active material according to the present disclosure; Mixing the coated active material with a solid electrolyte to obtain an electrode mixture (mixing step); and The electrode mixture is molded to obtain an electrode (molding step). may also include:

[0054] 3.1 Mixing process In the mixing step, the coated active material and the solid electrolyte are mixed to obtain an electrode mixture. In the mixing step, in addition to the coated active material and the solid electrolyte, a conductive additive and a binder may also be mixed. The content of the coated active material in the electrode mixture is not particularly limited and may be, for example, 40% by mass or more and 99% by mass or less. The coated active material and the solid electrolyte may be mixed in a dry state or in a wet state using an organic solvent (preferably a non-polar solvent).

[0055] The solid electrolyte may be any known solid electrolyte for all-solid-state batteries. For example, a perovskite-type, Nasicon-type, or garnet-type oxide solid electrolyte containing Li and S may be used. The technology of the present disclosure is particularly effective when a sulfide solid electrolyte is used. Specific examples of sulfide solid electrolytes include, but are not limited to, LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4. The solid electrolyte may be amorphous or crystalline. One type of solid electrolyte may be used alone, or two or more types may be mixed and used.

[0056] Specific examples of the conductive additive include, but are not limited to, carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF), as well as metal materials that can withstand the environment in which the all-solid-state lithium ion battery is used. Only one type of conductive additive may be used alone, or two or more types may be mixed and used.

[0057] Specific examples of binders include, but are not limited to, acrylonitrile butadiene rubber (ABR)-based binders, butadiene rubber (BR)-based binders, polyvinylidene fluoride (PVdF)-based binders, styrene butadiene rubber (SBR)-based binders, polytetrafluoroethylene (PTFE)-based binders, etc. Only one type of binder may be used alone, or two or more types may be mixed and used.

[0058] 3.2 Molding process The electrode mixture may be molded by a dry process or a wet process. The electrode mixture may be molded alone or together with a current collector. Furthermore, the electrode mixture may be integrally molded on the surface of a solid electrolyte layer described later. Examples of the molding process include a process in which a slurry containing the electrode mixture is applied to the surface of a current collector, followed by drying and optionally pressing to produce an electrode, or a process in which a powdered electrode mixture is placed in a mold or the like and dry-pressed to produce an electrode.

[0059] 4. Manufacturing method of all-solid-state batteries The technology of the present disclosure also has an aspect of a method for manufacturing an all-solid-state battery. Obtaining an electrode by the electrode manufacturing method of the present disclosure; laminating the electrode and a solid electrolyte layer; may also include:

[0060] The solid electrolyte layer may be, for example, a layer containing a solid electrolyte and a binder. The types of solid electrolytes and binders are as described above. An all-solid-state battery can be manufactured through obvious processes such as laminating the electrodes and the solid electrolyte layer, connecting terminals to the electrodes, housing the battery in a battery case, and constraining the battery. [Example]

[0061] 1. Examples 1 to 3 1.1 Preparation of coating solution To a container containing 870.4 g of 30% by mass hydrogen peroxide solution, 987.4 g of ion-exchanged water and 44.2 g of niobic acid (Nb2O5·3H2O (Nb2O5 water content 72%)) were added. Next, 87.9 g of 28% by mass ammonia water was added to the container. After the addition of the ammonia water, the contents of the container were thoroughly stirred to obtain a clear solution. Furthermore, 10.1 g of lithium hydroxide·monohydrate (LiOH·H2O) was added to the obtained clear solution to obtain a complex solution containing a niobium peroxo complex and lithium ions as a coating liquid.

[0062] 1.2 Preparation of slurry containing active material and coating liquid LiNi as an active material 1 / 3 Mn 1 / 3 Co 1 / 3 20 g of O2 (manufactured by Nichia Corporation) was placed in a mixer container and added to the coating solution prepared as described above to achieve a predetermined solid content concentration, followed by stirring with a magnetic stirrer. Table 1 below shows the solid content concentration in the coating solution for each active material in each example.

[0063] 1.3 Preparation of the precursor of the coated active material Using a liquid pump, the slurry of each example prepared above was supplied to a spray dryer (Buchi Mini Spray Dryer B-290) at a rate of 0.5 g / sec, whereupon the slurry was converted into droplets (first step) and the slurry droplets were air-dried (second step) to obtain a precursor.

[0064] The operating conditions of the spray dryer are as follows: Intake air temperature: 200℃ Air supply volume: 0.45m 3 / min

[0065] The time required to deliver the slurry to the nozzle in the spray dryer and form droplets (dropletization time in the first step) and the time required for air drying (air drying time in the second step) are shown in Table 1. The air drying time refers to the time from the end of supplying the slurry to the spray nozzle to the end of air drying.

[0066] 1.4 Precursor calcination The precursor was baked at 200° C. for 5 hours using a muffle furnace, and lithium niobate was synthesized on the surface of the active material, thereby obtaining the coated active material according to each example.

[0067] 2. Comparative Example 1 As shown in Figure 5, 2000 g of the coating solution prepared above was applied to a tumbling fluidized bed granulation coating device "MP-01" (manufactured by Powrex Corporation) to coat LiNi as an active material. 1 / 3 Mn 1 / 3Co 1 / 3 The mixture was sprayed onto 1 kg of O2 (manufactured by Nichia Corporation) and dried to obtain a precursor of the coated active material (S11). The obtained precursor was fired under the same conditions as in the above-mentioned Examples (S12), to obtain a coated active material according to Comparative Example 1.

[0068] The operating conditions of the tumbling fluidized bed granulation coating apparatus are as follows: Atmospheric gas: Dry air with a dew point of -65°C or less Intake air temperature: 200℃ Air supply volume: 0.45m 3 / min Rotor speed: 400 rpm Spray rate: 4.4g / min

[0069] 3. Evaluation conditions 3.1 Particle size measurement For each of the coated active materials in the Examples and Comparative Examples, the particle diameter D90 at 90% of the cumulative value in the volume-based particle size distribution was measured using a laser diffraction / scattering measurement device (Aerotrac II manufactured by Microtrac-Bell). The measurement results are shown in Table 1 below.

[0070] 3.2 Battery output evaluation 3.2.1 Preparation of the positive electrode The coated active material of each Example and Comparative Example 1 and a sulfide solid electrolyte (10LiI-15LiBr-37.5Li3PS4) were weighed out to a volume ratio of 6:4, and these were placed in heptane together with 3 mass% of vapor grown carbon fiber (VGCF) (manufactured by Showa Denko K.K.) as a conductive additive and 0.7 mass% of butadiene rubber (manufactured by JSR Corporation) as a binder. Next, these were mixed to prepare a positive electrode mixture. The prepared positive electrode mixture was thoroughly dispersed using an ultrasonic homogenizer, then coated on aluminum foil and dried at 100°C for 30 minutes. Then, a 1cm diameter sample was placed in a 1cm diameter container. 2 The positive electrode was obtained by punching out a piece of the sheet.

[0071] 3.2.2 Preparation of the negative electrode A negative electrode active material (layered carbon) and a sulfide solid electrolyte (10LiI-15LiBr-37.5Li3PS4) were prepared in a volume ratio of 6:4, and these were placed in heptane together with 1.2 mass% butadiene rubber (manufactured by JSR Corporation) as a binder. Next, these were mixed to prepare a negative electrode mixture. The prepared negative electrode mixture was thoroughly dispersed using an ultrasonic homogenizer, then coated on copper foil and dried at 100°C for 30 minutes. Then, a 1cm diameter sample was prepared. 2 The negative electrode was obtained by punching out the material into a size of 100 mm.

[0072] 3.2.3 Preparation of solid electrolyte layer Inner diameter cross-sectional area 1cm 2 64.8 mg of sulfide solid electrolyte (10LiI-15LiBr-37.5Li3PS4) was placed in the cylindrical ceramic, smoothed, and then pressed at 1 ton to form a solid electrolyte layer.

[0073] 3.2.4 Battery construction The positive electrode prepared above was placed on one side of the solid electrolyte layer, and the negative electrode prepared above was placed on the other side, and pressed at 4.3 tons for 1 minute. Then, a stainless steel rod was inserted between the electrodes, and they were restrained at 1 ton to obtain all-solid-state lithium-ion batteries according to each Example and Comparative Example 1.

[0074] 3.2.5 Output Measurement For the all-solid-state lithium-ion batteries of each Example and Comparative Example 1, the open circuit voltage (OCV) was adjusted to 3.66 V, and then constant power discharge was performed, and the maximum power value that could be discharged in 5 seconds was measured as the battery output. The cutoff voltage was set to 2.5 V. The output of the battery of Comparative Example 1 was set as the reference (1.00), and the output of the batteries of each Example was evaluated relative to this.

[0075] 4. Evaluation Results The evaluation results are shown in Table 1 below. In Table 1, the "total processing time" is the sum of the "processing time for turning the slurry into droplets (spraying time)" and the "processing time for air drying" in Examples 1 to 3, and is the total processing time for drying the active material while spraying the coating liquid onto it in Comparative Example 1. The "total processing speed" is a value obtained by dividing the amount of active material used by the total processing time.

[0076] [Table 1]

[0077] In tumbling fluidized coating, such as in Comparative Example 1, if the spray speed of the coating liquid is high, granules are formed due to liquid bridging. Furthermore, in tumbling fluidized coating, the ability to break down particles during drying is weak, and once granules are formed, they are difficult to disintegrate. Therefore, in tumbling fluidized coating, the spray speed must be slowed to avoid particle granulation. Conventionally, for example, as in Comparative Example 1, 2000 g of coating liquid is delivered at 4.4 g / min, resulting in a delivery time of 444 minutes. In contrast, as shown in Table 1, the manufacturing methods of Examples 1 to 3 enable the production of coated active materials in a shorter time than the manufacturing method of Comparative Example 1. In Examples 1 to 3, even if slurry droplets or precursor granules are produced, the granules can be disintegrated by flash drying. Therefore, a slurry with a low solids concentration can be used, making it easier to increase the processing speed. In other words, processing at higher speeds than the above conditions is also possible. It is also clear that the outputs of all-solid-state lithium-ion batteries using the coated active materials produced in Examples 1 to 3 are comparable to or superior to those of Comparative Example 1. For example, in Examples 1 to 3, as described above, the granules can be crushed by airflow drying, so that coated active materials with small particle sizes can be obtained even when the processing speed is set to high.

[0078] 5. Structure and properties of coated active materials 5.1 SEM observation FIG. 6 schematically shows the cross-sectional structure of the coated active material according to Example 1. FIG. 7 also shows the cross-sectional structure of the coated active material according to Comparative Example 1. FIGS. 6 and 7 are abstracted cross-sectional SEM images of the coated active materials according to Example 1 and Comparative Example 1, respectively. As shown in FIG. 6, the coated active material according to Example 1 had an active material and a coating layer covering at least a portion of the surface of the active material, and the coating layer had a plurality of pores. The pores were present at the interface between the active material and the coating layer and inside the coating layer. In contrast, as shown in FIG. 7, no pores were observed in the coating layer of the coated active material according to Comparative Example 1. In the coated active material according to Example 1, the plurality of pores included pores with an elliptical or circular cross-sectional shape. Furthermore, when the cross-section of the coated active material according to Example 1 was observed, the coating layer contained a plurality of pores having a pore diameter (circle-equivalent diameter) of 10 nm to 300 nm. In addition, in the coated active material according to Example 1, the coating layer had a thickness of 0.1 nm or more and 300 nm or less, and covered 70% or more of the surface of the active material.

[0079] In Example 1, the rapid drying characteristic of the spray dryer causes the desorption of components contained in the slurry (coating solution and active material) and the formation of a film to occur almost simultaneously. In other words, the shape of the film changes significantly due to the physical forces applied during component desorption, and the film solidifies while retaining this influence. This is thought to be the reason for the formation of multiple voids in the coating layer, as described above. This phenomenon is thought to occur in the same way even if the type of coating solution contained in the slurry is changed, but is expected to occur more predominantly when a low-boiling-point solvent (a solvent that evaporates rapidly during the drying process), such as water, is used.

[0080] When a plurality of pores are present in the coating layer as in the above examples, it is expected that the contact with other battery materials will be improved, electron and ion conduction will be promoted, and the coating layer will have cushioning properties, which will improve battery performance, etc. For example, even when the active material expands during charge and discharge, or when pressure is applied to the coated active material during electrode press processing, etc., the above-mentioned cushioning properties will reduce the stress applied to the active material, and cracking of the active material will be suppressed.

[0081] 5.2 BET specific surface area Fig. 8 shows the measurement results of the BET specific surface area of ​​the coated active materials according to Example 1 and Comparative Example 1. As shown in Fig. 8, the BET specific surface area of ​​the coated active material according to Example 1 is larger than the BET specific surface area of ​​the coated active material according to Comparative Example 1. As described above, it is believed that the coated active material according to Example 1 has a larger specific surface area due to the formation of pores and voids in the coating layer caused by rapid drying using a spray dryer. [Explanation of symbols]

[0082] 11a, 21a, 31a active material 11b, 21b, 31b coating liquid 11, 21, 31, 41, 51 Slurry droplets 42, 52 precursors

Claims

1. A first step of spraying a slurry containing an active material and a coating liquid using a spray nozzle to form droplets of the slurry, thereby obtaining slurry droplets; a second step of drying the slurry droplets in a heated gas stream to obtain a precursor; a third step of calcining the precursor to obtain a coated active material having a coating layer on at least a portion of the surface of the active material; Including, In the second step, the hot air serving as the heated gas is continuously applied to the slurry droplets and the precursor by the air flow drying, thereby disintegrating one or both of the slurry droplets and the precursor; In the second step, the flow rate of the heated gas is 0.10 m 3 / min or more and 5.00 m 3 / min or less; In the second step, the temperature of the heated gas is 180° C. or higher, The coating layer contains a plurality of pores having a pore diameter of 10 nm or more and 300 nm or less. Method for producing coated active material.

2. the coating solution contains a lithium source and a niobium source; The method of claim 1.

3. the niobium source comprises a peroxo complex of niobium; The method of claim 2.

4. The solid content concentration of the slurry is 40 vol% or less. The method according to any one of claims 1 to 3.

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