Positive electrode active material particles for all-solid-state secondary batteries

Abstract

To provide a positive electrode active material particle for an all-solid secondary battery, which enables the increase in ion conductivity, and which can impart an excellent electrical conductivity and enhance a battery characteristic efficiently while using silicate-based particles as a material.SOLUTION: A positive electrode active material particle for an all-solid secondary battery is composed of a particle based on silicate represented by the following formula (A): LiaMnbFecMxSiO4 (A). Of the particle, the surface is coated at a coverage 30-80% with carbon of 1.0-2.0 in intensity ratio (G / D), which is determined according to Raman spectroscopy.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to positive electrode active material particles for all-solid-state secondary batteries. [Background technology]

[0002] Li7La3Zr2O 12 All-solid-state lithium-ion secondary batteries, which utilize oxide-based solid electrolytes such as 75Li2S·25P2S5 or sulfide-based solid electrolytes such as 75Li2S·25P2S5, are expected to be superior lithium-ion secondary batteries in terms of energy density, structural simplification, and manufacturing cost and productivity, as they do not use flammable materials. In these all-solid-state lithium-ion secondary batteries, various attempts are being made to use different materials to improve battery characteristics.

[0003] For example, Patent Document 1 describes SO4 on the surface. 2- An all-solid-state secondary battery has been disclosed that uses a positive electrode active material which is a metal oxide particle in which anions such as are unevenly distributed, and attempts have been made to suppress the formation of a high-resistance layer at the interface between the positive electrode active material and the solid electrolyte by using the unevenly distributed anions. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-103008 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, silicate particles, which have been conventionally used as materials for lithium-ion secondary batteries and the like, which use electrolytes, are highly promising as high-capacity materials due to two-electron reactions when applied as positive electrode active materials for all-solid-state secondary batteries. However, it is necessary to impart sufficient conductivity to them, as well as to improve ionic conductivity between them and the solid electrolyte.

[0006] However, the technology of using silicate-based particles as a material for a positive electrode active material of an all-solid-state secondary battery is not disclosed in the above patent documents either. In order to sufficiently enhance the battery characteristics in a positive electrode active material for an all-solid-state secondary battery, there is still sufficient room for development to effectively utilize silicate-based particles.

[0007] Therefore, the present invention relates to positive electrode active material particles for an all-solid-state secondary battery that can improve ion conductivity, impart excellent conductivity, and effectively enhance battery characteristics while using silicate-based particles as a material.

Means for Solving the Problems

[0008] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found positive electrode active material particles for an all-solid-state secondary battery that can effectively enhance ion conductivity and impart excellent conductivity by coating the surface of particles with specific carbon at a specific coating rate while using silicate-based particles.

[0009] That is, the present invention provides positive electrode active material particles for an all-solid-state secondary battery composed of silicate-based particles represented by the following formula (A): Li a Mn b Fe c M x SiO4···(A) (In formula (A), M represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V, or Gd. a, b, c, and x satisfy 0 < a ≤ 2.4, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 1.2, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 4.) and carbon having an intensity ratio (G / D) of 1.0 to 2.0 determined by Raman spectroscopy is coated on the surface at a coating rate of 30% to 80%.

Effects of the Invention

[0010] According to the positive electrode active material particles for all-solid-state secondary batteries of the present invention, although composed of silicate-based particles, the ion conductivity between the silicate-based particles and the solid electrolyte is effectively increased, and good conductivity as the positive electrode active material of the all-solid-state secondary battery is also imparted, and an all-solid-state secondary battery having excellent battery characteristics can be realized.

Brief Description of the Drawings

[0011] [Figure 1] It is a TEM photograph of a part of the surface of the positive electrode active material particles A1 obtained in Example 1. The perimeter xm of the surface of the particle not coated with carbon is indicated by a dotted line, and the perimeter xn of the surface of the particle coated with carbon is indicated by a solid line.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. The positive electrode active material particles for all-solid-state secondary batteries of the present invention have the following formula (A): Li a Mn b Fe c M x SiO4···(A) (In formula (A), M represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V or Gd. a, b, c, and x satisfy 0 < a ≤ 2.4, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 1.2, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 4.) and are composed of silicate-based particles represented by carbon having an intensity ratio (G / D) of 1.0 to 2.0 determined by Raman spectroscopy is coated on the surface at a coating rate of 30% to 80%.

[0013] Thus, by coating the surface of the positive electrode active material particles for all-solid-state secondary batteries with carbon having a specific intensity ratio (G / D) in Raman spectroscopy, the ionic conductivity between such carbon and the solid electrolyte can be effectively increased, and good conductivity can also be imparted as the positive electrode active material of the all-solid-state secondary battery. Further, by coating such carbon at a specific ratio on the surface of the positive electrode active material particles for all-solid-state secondary batteries, the ionic conductivity between the positive electrode active material particles and the solid electrolyte can be effectively increased. By having such a structure, it becomes possible to obtain an all-solid-state secondary battery that exhibits excellent battery characteristics while using silicate-based particles as a material.

[0014] The silicate-based particles (hereinafter, also referred to as silicate-based particles (A)) constituting the positive electrode active material particles for all-solid-state secondary batteries of the present invention are represented by the following formula (A): Li a Mn b Fe c M x SiO4···(A) (In formula (A), M represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V or Gd. a, b, c, and x satisfy 0 < a ≤ 2.4, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 1.2, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 4.) They are particles having an olivine-type structure containing at least either manganese or iron, and are represented by the above formula. The positive electrode active material particles for all-solid-state secondary batteries of the present invention are particles in which such silicate-based particles (A) are aggregated or agglomerated as so-called primary particles to form secondary particles.

[0015] Among them, from the viewpoint of ensuring good conductivity, M in the above formula (A) is preferably Co, Zr, Al, Zn or V, more preferably Zr. Also, b in the above formula (A) is preferably 0.1 ≤ b ≤ 0.9, more preferably 0.2 ≤ b ≤ 0.8, and even more preferably 0.3 ≤ b ≤ 0.7.

[0016] The silicate particle (A) represented by the above formula (A) is, specifically, Li2Mn 0.45 Fe 0.45 Co 0.1 SiO4, Li2Mn 0.54 Fe 0.36 Al 0.066 SiO4, Li2Mn 0.45 Fe 0.45 Zn 0.1 SiO4, Li2Mn 0.54 Fe 0.36 V 0.066 SiO4, Li2Mn 0.66 Fe 0.28 Zr 0.03 SiO4, Li2Mn 0.658 Fe 0.282 Zr 0.02 SiO4, Li 2.2 Mn 0.594 Fe 0.252 Zr 0.027 SiO4, Li 1.2 Mn 0.294 Fe 0.392 Zr 0.042 Examples include SiO4, among others, Li2Mn 0.66 Fe 0.28 Zr 0.03 SiO4, Li2Mn 0.658 Fe 0.282 Zr 0.02 SiO4, Li 2.2 Mn 0.594 Fe 0.252 Zr 0.027 SiO4, or Li 1.2 Mn 0.294 Fe 0.392 Zr 0.042 SiO4 is preferred.

[0017] As described later, the average particle size of the silicate particles (A) is preferably 10 nm to 200 nm, more preferably 20 nm to 180 nm, and even more preferably 50 nm to 150 nm, from the viewpoint of ensuring a specific coverage rate on the surface of the positive electrode active material particles for all-solid-state secondary batteries, and from the viewpoint of effectively improving battery characteristics, the carbon that shows a specific value in the intensity ratio (G / D) determined by Raman spectroscopy. Here, "average particle size" in silicate particles (A) refers to the average particle size of 100 silicate particles (A) when observing positive electrode active material particles for all-solid-state secondary batteries, whose surfaces are coated with carbon, using SEM.

[0018] The surface of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is coated with carbon having an intensity ratio (G / D) of 1.0 to 2.0, as determined by Raman spectroscopy. By coating the surface of the particles with carbon exhibiting such a specific intensity ratio (G / D), the ionic conductivity between the carbon and the solid electrolyte can be effectively enhanced, which greatly contributes to imparting excellent conductivity as a positive electrode active material for an all-solid-state secondary battery.

[0019] Specifically, the carbon coating on the surface of the positive electrode active material particles for all-solid-state secondary batteries effectively enhances the ionic conductivity between the carbon and the solid electrolyte. In the Raman spectrum obtained by Raman spectroscopy, the G band (peak position: 1360 cm⁻¹) is present. -1 (Nearby) and D-band (Peak position: 1580cm) -1 The intensity ratio (G / D) with respect to the surrounding area is 1.0 to 2.0, preferably 1.1 to 1.9, more preferably 1.2 to 1.8, and even more preferably 1.3 to 1.7. Furthermore, this intensity ratio (G / D) can be measured by the method described in the examples.

[0020] The above carbon is coated on the surface of the positive electrode active material particles for the all-solid-state secondary battery of the present invention with a coverage rate of 30% to 80%. By having such a coverage rate, carbon exhibiting a specific intensity ratio (G / D) is appropriately unevenly distributed or scattered on the surface and in the gaps of the positive electrode active material particles for the all-solid-state secondary battery formed by silicate particles (A), thereby effectively increasing the ionic conductivity between carbon and the solid electrolyte.

[0021] The carbon coverage on the surface of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is 30% to 80%, preferably 34% or more and less than 80%, more preferably 38% to 70%, and even more preferably 42% or more and less than 50%, from the viewpoint of effectively increasing the ionic conductivity between carbon and the solid electrolyte.

[0022] In this invention, the "carbon coverage (%)" on the surface of the positive electrode active material particles for all-solid-state secondary batteries refers to the value obtained by the following method. Specifically, as shown in Figure 1, first, the surface is observed in a field of view 1 of the positive electrode active material particles for all-solid-state secondary batteries by electron microscope observation using a TEM, and the surface of the positive electrode active material particles for all-solid-state secondary batteries that are not coated with carbon and the surface of the positive electrode active material particles for all-solid-state secondary batteries that are coated with carbon are identified. Next, the "circumference xm of the surface of the positive electrode active material particles for all-solid-state secondary batteries that are not coated with carbon" and the "circumference xn of the surface of the positive electrode active material particles for all-solid-state secondary batteries that are coated with carbon" are measured in the field of view, and xm and xn are added together to obtain the "total circumference xA of the surface of the positive electrode active material particles for all-solid-state secondary batteries". The values ​​obtained, "total circumferential length xA of the surface of the positive electrode active material particles for all-solid-state secondary batteries" and "circumferential length xn of the surface of the carbon-coated positive electrode active material particles for all-solid-state secondary batteries," are introduced into the following formula (B) to calculate the carbon coverage rate (%) in one field of view. The values ​​obtained over 50 fields of view are then averaged to obtain the carbon coverage rate (%) on the surface of the positive electrode active material particles for all-solid-state secondary batteries. In TEM electron microscope observation, the limit for determining whether or not carbon is coated on the surface of the positive electrode active material particles for all-solid-state secondary batteries is set to 1 nm. Carbon coverage (%) =[(Circumference xn of the surface of the carbon-coated positive electrode active material particles for all-solid-state secondary batteries) / (Total surface length of positive electrode active material particles for all-solid-state secondary batteries x A) × 100···(B)

[0023] The carbon coating on the surface of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is obtained by carbonizing one or more carbon materials selected from sugars, and then coating the surface with this carbon. While carbonizing one or more carbon materials selected from sugars (also referred to as "carbon coating agent X" as described later), one or more carbon materials selected from polyols, amines, and amides other than sugars (also referred to as "carbon coating inhibitor Y" as described later) are interposed, thereby coating the surface of the positive electrode active material particles for the all-solid-state secondary battery with a specific coating rate while having a specific strength ratio (G / D). Furthermore, the carbon coating on the surface of the positive electrode active material particles for all-solid-state secondary batteries is derived from one or more carbon materials selected from sugars, while one or more carbon materials selected from polyols, amines, and amides other than sugars do not remain on the positive electrode active material particles for all-solid-state secondary batteries.

[0024] Specifically, examples of carbon materials selected from sugars include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch, dextrin, and cellulose; and one or more nanofibers of polysaccharides such as cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, and chitosan nanofibers. In particular, cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers are preferred from the viewpoint of effectively enhancing the ionic conductivity between carbon and the solid electrolyte, and from the viewpoint of providing good conductivity.

[0025] The carbon content in the positive electrode active material particles for all-solid-state secondary batteries of the present invention corresponds to the carbon content obtained by carbonizing the above-mentioned carbon material, and is preferably 0.5% to 8% by mass, more preferably 0.8% to 6% by mass, and more preferably 1.1% to 5% by mass in the positive electrode active material particles for all-solid-state secondary batteries of the present invention.

[0026] Furthermore, the carbon contained in the positive electrode active material particles for all-solid-state secondary batteries includes carbon formed from the carbon material inherent in some of the positive electrode active material particles for all-solid-state secondary batteries (such as carbon that coats the silicate-based particles (A) but is not exposed on the surface of the positive electrode active material particles for solid-state secondary batteries), and is equivalent to the amount of carbon formed from the carbon material present on the surface of the positive electrode active material particles for all-solid-state secondary batteries, i.e., the amount of carbon material on an atomic basis, which can be determined by measurement using a carbon-sulfur analyzer.

[0027] The average particle size of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is preferably 5 μm to 20 μm, more preferably 7 μm to 18 μm, and even more preferably 9 μm to 16 μm. Here, the "average particle size" in the positive electrode active material particles for all-solid-state secondary batteries refers to the D particle size distribution obtained by the volume-based particle size distribution method based on laser diffraction and scattering. 50 This value represents the particle size (median diameter) at a cumulative 50% level.

[0028] The tap density of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is preferably 0.7 g / cm³, from the viewpoint of exhibiting excellent battery characteristics and ease of handling. 3 ~2.0g / cm 3 More preferably, 0.8 g / cm³ 3 ~1.8g / cm 3 That is the case. Furthermore, tap density, as used below, refers to the "tap bulk density" measured by the method specified in JIS R 1628 "Method for Measuring the Bulk Density of Fine Ceramic Powders".

[0029] From the viewpoint of exhibiting excellent battery characteristics, the conductivity of the positive electrode active material particles for the all-solid-state secondary battery of the present invention is preferably 1.0 × 10⁻⁶. -7 The S / cm or greater, and more preferably 1.0 × 10 -6 The S / cm is approximately 0.1 S / cm, and more preferably 1.0 × 10 -5 The S / cm is approximately 0.01 S / cm.

[0030] The positive electrode active material particles for all-solid-state secondary batteries of the present invention can be obtained, for example, by the following manufacturing method. Specifically, steps (I) to (III): (I) A step in which a lithium compound, a metal compound containing at least a manganese compound and an iron compound, and water are added to obtain slurry water i, and then subjected to a hydrothermal reaction to obtain preliminary particles a. (II) The obtained preliminary particles a, carbon coating agent X, carbon coating inhibitor Y, and water are added to obtain slurry water ii, which is then spray-dried to obtain preliminary particles b. (III) Step of calcining the obtained preliminary particles b Equipped with, The carbon coating agent X is one or more carbon materials selected from sugars, and The present invention relates to a method for producing carbon coating inhibitor Y, in which the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides.

[0031] Step (I) described above involves adding a metal compound containing at least a manganese compound and an iron compound, as well as water, to obtain slurry water i, and then subjecting it to a hydrothermal reaction to obtain preliminary particles a. These preliminary particles a correspond to the primary particles, which are the silicate particles (A) described above. Examples of lithium compounds include hydroxides (e.g., LiOH·H2O, LiOH), carbonates, acetates, and nitrates. Among these, hydroxides are preferred from the viewpoint of improving battery characteristics. Examples of manganese compounds include manganese acetate, manganese sulfate, manganese nitrate, and manganese oxide. Among these, manganese sulfate is preferred from the viewpoint of improving battery performance. Examples of iron compounds include iron acetate, iron nitrate, and iron sulfate. Among these, iron sulfate is preferred from the viewpoint of improving battery performance.

[0032] In addition, metal (M) compounds other than manganese and iron compounds may be used as metal compounds along with these manganese and iron compounds. Furthermore, the amount of lithium compounds, manganese compounds, and iron compounds, including metal compounds, used in slurry water i should be determined as appropriate according to the composition of the target silicate particles (A), and the mixture should be prepared according to a conventional method. Furthermore, antioxidants may be added as needed. Suitable antioxidants include sodium sulfite (Na2SO3), sodium hydrosulfite (Na2S2O4), and aqueous ammonia. The amount of antioxidant added is preferably 0.01 to 1 mole, and more preferably 0.03 to 0.5 moles, per 1 mole of the total amount of the manganese compound, iron compound, and optionally used metal (M) compound.

[0033] The solid content concentration of slurry water i is preferably 5 to 60 parts by mass, more preferably 15 to 60 parts by mass, and even more preferably 30 to 60 parts by mass.

[0034] It is preferable to pre-stir the slurry water i after adding water and before subjecting it to the hydrothermal reaction. The stirring time for the slurry water i is preferably 1 to 60 minutes, more preferably 5 to 30 minutes. The temperature of the slurry water i is preferably 10°C to 40°C, more preferably 15°C to 35°C.

[0035] Next, the obtained slurry water i is subjected to a hydrothermal reaction to obtain preliminary particles a. From the viewpoint of controlling the average particle size of silicate particles (A) within the above range, the hydrothermal reaction is preferably carried out at 100°C to 200°C, and more preferably at 110°C to 160°C. The hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 100°C to 200°C, the pressure at this time is preferably 0.1 MPa to 1.6 MPa, and when the reaction is carried out at 110°C to 160°C, the pressure is preferably 0.15 MPa to 0.6 MPa. From the viewpoint of controlling the average particle size of silicate particles (A) within the above range, the hydrothermal reaction time is preferably 0.5 hours to 12 hours, and more preferably 1 hour to 4 hours. The obtained preliminary particles a should be filtered and then washed with water.

[0036] Step (II) described above involves adding the preliminary particles a obtained in step (I), carbon coating agent X, carbon coating inhibitor Y, and water to obtain slurry water ii, and then subjecting it to spray drying to obtain preliminary particles b.

[0037] The carbon coating agent X is one or more carbon materials selected from the above-mentioned sugars, and specifically, the same materials as described above can be used. In particular, from the viewpoint of effectively enhancing the ionic conductivity between carbon and the solid electrolyte, and from the viewpoint of providing good conductivity, it is preferable to use cellulose nanofibers, lignocellulose nanofibers, chitin nanofibers, or chitosan nanofibers.

[0038] The carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides, i.e., one or more carbon materials selected from polyols other than carbon coating agent X, and from amines and amides. In this way, by adding the carbon coating inhibitor Y together with the carbon coating agent X in step (II) and proceeding through the subsequent step (III), the carbon coating inhibitor Y coats a portion of the surface of the positive electrode active material particles for all-solid-state secondary batteries that are formed, while moderately inhibiting the coating by the carbon coating agent X. This allows the carbon intensity ratio (G / D) to be controlled within the above range, and the carbon coating rate on the surface of the positive electrode active material particles for all-solid-state secondary batteries to be controlled within the above range. Furthermore, through the process (III) described later, the carbon coating agent X is carbonized and coats the surface of the positive electrode active material particles for all-solid-state secondary batteries as carbon, while the carbon coating inhibitor Y is burned away and does not remain on the positive electrode active material particles for all-solid-state secondary batteries.

[0039] Examples of polyols other than sugars include polyethylene glycol with a mass-average molecular weight of 1000 or less, polypropylene glycol with a mass-average molecular weight of 2000 or less, which have two hydroxyl groups; and polyether polyols with a mass-average molecular weight of 3000 or less, which have three or more hydroxyl groups. Among these, polyols with a volatilization temperature of 170°C to 400°C are preferred, and more specifically, polyols having two hydroxyl groups such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, butanediol, pentanediol, hexanediol, hexanetriol, heptanediol, heptanetriol, octanediol, octantriol, nonanediol, nonanetriol, decanediol, decanetriol, and dodecanediol; Examples include polyols having three or more hydroxyl groups, such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

[0040] As amines and amides, those with a volatilization temperature of 170°C or higher are preferred. Specifically, examples include aliphatic amines such as diethanolamine and triethanolamine, heterocyclic amines such as imidazole; amides such as formamide and acetamide; polyamides such as polyacrylamide and poly-N-vinylacetamide; and fatty acid amides such as oleamide and stearamide.

[0041] The carbon coating inhibitor Y is preferably ethylene glycol, propylene glycol, glycerin, triethanolamine, or oleic acid amide.

[0042] The order in which the preliminary particles a, carbon coating agent X, carbon coating inhibitor Y, and water are added is not particularly limited. They may be added all at once, or the preliminary particles a and water may be mixed first, followed by the addition of the carbon coating agent X and carbon coating inhibitor Y simultaneously, or the preliminary particles a, water, and carbon coating inhibitor Y may be mixed first, followed by the addition of the carbon coating agent X. However, it is preferable to add them all at once.

[0043] The amount of carbon coating agent X added is preferably 0.5 to 30 parts by mass, more preferably 0.8 to 25 parts by mass, and even more preferably 1.1 to 20 parts by mass, per 100 parts by mass of spare particles a, in terms of the amount added in terms of carbon atoms (the mass of carbon atoms contained in the carbon coating agent X to be added).

[0044] Furthermore, the amount of carbon coating inhibitor Y added is preferably 0.2 to 10, more preferably 0.3 to 9, and even more preferably 0.4 to 5, in terms of the mass ratio (X / Y) of the amount of carbon coating agent X added in terms of carbon atoms to the amount of carbon coating inhibitor Y added, from the viewpoint of controlling the carbon coating rate on the surface of the positive electrode active material particles for all-solid-state secondary batteries within the above range.

[0045] The solid content concentration of slurry water II is preferably 15 to 55 parts by mass, more preferably 20 to 50 parts by mass, and even more preferably 25 to 45 parts by mass.

[0046] It is preferable to pre-stir the slurry water ii after adding water and before subjecting it to spray drying. The stirring time for the slurry water ii is preferably 1 to 60 minutes, more preferably 1 to 30 minutes. The temperature of the slurry water ii is preferably 10°C to 40°C, more preferably 15°C to 35°C.

[0047] Next, the obtained slurry water ii is subjected to spray drying to obtain preliminary particles b. As a result, the preliminary particles y a aggregate or flocculate, and as the process continues through the subsequent step (III), the carbon coating inhibitor Y coats a portion of the surface of the positive electrode active material particles for all-solid-state secondary batteries that are formed, while moderately inhibiting the coating by the carbon coating agent X. This allows the carbon intensity ratio (G / D) to be controlled within the above range, and the carbon coating rate on the surface of the positive electrode active material particles for all-solid-state secondary batteries to be controlled within the above range.

[0048] In spray drying, the operating conditions should be set appropriately depending on the equipment used. For example, in a micro-mist dryer equipped with four fluid nozzles (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.), the processing conditions are preferably such that the hot air temperature is 110°C to 300°C, and more preferably 150°C to 250°C. In addition, the ratio of the hot air supply amount to the slurry water supply amount (hot air supply amount / slurry water supply amount) is preferably 1000 to 10000, and more preferably 2000 to 9000.

[0049] Step (III) described above is a step of firing the preliminary particles a obtained in step (II). This allows the carbon coating inhibitor Y to coat a portion of the surface of the formed positive electrode active material particles for all-solid-state secondary batteries, while moderately inhibiting the coating by the carbon coating agent X, thereby controlling the carbon intensity ratio (G / D) on the surface within the above range, and obtaining positive electrode active material particles for all-solid-state secondary batteries in which the carbon coating rate is controlled within the above range. Furthermore, through this process (III), the carbon coating agent X is carbonized and coats the surface of the positive electrode active material particles for all-solid-state secondary batteries as carbon, while the carbon coating inhibitor Y is burned away and does not remain on the positive electrode active material particles for all-solid-state secondary batteries.

[0050] The firing conditions for step (III) are preferably in a reducing atmosphere or an inert atmosphere, the firing temperature is preferably 500°C to 750°C, more preferably 550°C to 725°C, and even more preferably 600°C to 700°C, from the viewpoint of effectively controlling the carbon intensity ratio (G / D) and coverage within the above range, and the firing time is preferably 0.4 hours to 8 hours, more preferably 0.6 hours to 4 hours, and even more preferably 0.8 hours to 2 hours.

[0051] The all-solid-state secondary battery to which the positive electrode active material particles for all-solid-state secondary batteries of the present invention can be appropriately applied is not particularly limited as long as it has a positive electrode, a negative electrode, and a solid electrolyte as essential components, and a laminate is formed in which a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer are stacked in that order.

[0052] Here, the negative electrode is not particularly limited in its material composition as long as it can absorb lithium ions during charging and release them during discharging; known material compositions can be used. For example, lithium metal, graphite, silicon-based (Si, SiO x ), or carbon materials such as lithium titanate or amorphous carbon. And it is preferable to use electrodes formed of an intercalate material that can electrochemically intercalate and release lithium ions, particularly carbon materials. Furthermore, two or more of the above negative electrode materials may be used in combination, for example, a combination of graphite and silicon can be used.

[0053] The solid electrolyte can be any material that electrically insulates the positive and negative electrodes and exhibits high lithium-ion conductivity, and many types can be used, including the same material as the solid electrolyte (B) described above. For example, in the case of an oxide system, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 90Li3BO3-10Li2SO4, Li7La3Zr2O 12 Li 0.34 La0.51 TiO 2.94 etc. are preferable. In the case of sulfide-based materials, Li 10 GeP2S 12 、Li 9.54 Su 1.74 P 1.44 S 11.7 C l0.3 、Li 3.25 Ge[[ID=二十]] 0.25 P 0.75 S4, Li6PS5Cl, 50Li2S - 17P2S5 - 33LiBH4, 70Li2S - 30P2S5, Li7P3S 11 、Li 3.25 P 0.95 S4 etc. are preferable.

[0054] The shape of the all-solid-state secondary battery having the above configuration is not particularly limited, and it may be various shapes such as coin type, cylindrical type, rectangular type, or an irregular shape enclosed in a laminated exterior body.

Examples

[0055] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Regarding each physical property, measurement and calculation were performed using the following methods. Examples 3 and 4 are for reference only.

[0056] 《Measurement of average particle size》 The average particle size of the silicate-based particles (A) was measured as the average value (nm) by extracting 100 silicate-based particles (A) when observing the positive electrode active material particles for the all-solid-state secondary battery obtained using SEM (JSM-7001F, manufactured by JEOL Ltd.). The average particle size of the positive electrode active material particles for the all-solid-state secondary battery was determined by obtaining the particle size distribution using a laser diffraction device (Microtrac MT3000II, manufactured by MicrotracBEL), and the D 50 value (μm) was measured (particle permeability: permeation, particle shape: non-spherical, particle refractive index: 1.52, solvent: ethanol, solvent refractive index: 1.36).

[0057] 《Carbon content of positive electrode active material particles for all-solid-state secondary battery》 The carbon content of each cathode active material particle obtained was measured using a carbon-sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.).

[0058] Carbon coverage on the surface of positive electrode active material particles for all-solid-state secondary batteries Using a TEM (JEM-ARM200F, manufactured by JEOL Ltd.), each of the obtained positive electrode active material particles was photographed, and the carbon coverage on the surface of such particles was determined according to the method described above.

[0059] 《Strength ratio (G / D)》 Raman spectroscopy was performed on each of the obtained positive electrode active material particles using a Raman spectrophotometer (NRS-3100, JASCO Corporation) (laser light: 532 nm). Subsequently, 1580 cm⁻¹ was used. -1 Nearby is a G-band peak (with peak intensity set to g1), at 1360 cm. -1 After confirming the peak of the D band nearby (let's call the peak intensity d1), we proceeded to 880 cm. -1 and 1835cm -1 Draw a straight line from these two points, and measure 1580cm along that line. -1 The peak intensity was g2, 1360cm -1 The peak intensity was calculated as d2. Then, the intensity ratio (G / D) was calculated using the values ​​of g1-g2 as the G value and the values ​​of d1-d2 as the D value.

[0060] Conductivity of positive electrode active material particles for all-solid-state secondary batteries The conductivity of the obtained positive electrode active material particles for all-solid-state secondary batteries was measured using a low resistivity meter (MCP-T610, manufactured by Mitsubishi Analytec Co., Ltd.) when a load of 20 kN was applied to 3.0 g of these particles.

[0061] Tap density of positive electrode active material particles for all-solid-state secondary batteries The obtained positive electrode active material particles for all-solid-state secondary batteries were passed through a sieve with a mesh size of 1.0 mm, weighed to an accuracy of 0.1%, and then gently placed into a 100 ml graduated cylinder. Next, the graduated cylinder was tapped 600 times at a rate of 180 taps / minute or less, and the tap density was calculated according to the following formula. Tap density = (Weighed weight) / (Mark on a 100ml graduated cylinder after 600 taps)

[0062] [Example 1] 428 g of LiOH·H2O and 1397 g of Na4SiO4·nH2O were mixed with 5000 mL of ultrapure water. Then, 750 g of FeSO4·7H2O, 651 g of MnSO4·5H2O, and 53 g of Zr(SO4)2·4H2O were added and mixed to obtain slurry water i-1. After subjecting the mixture to a hydrothermal reaction at 160°C for 4 hours, the resulting crystals were filtered and then washed with 12 parts by mass of water per 1 part by mass of crystals. The washed crystals were freeze-dried at -50°C for 12 hours to obtain particle a1 (silicate particle (A)). 1000g of the obtained particle a1 was taken out, and 2L of water, 450g of cellulose nanofiber (Wma-10010, manufactured by Sugino Machine Co., Ltd., fiber diameter 4nm~20nm) (2.0 parts by mass in terms of carbon atoms per 100 parts by mass of particle a1), and 60g of propylene glycol were added all at once (mass ratio of amount of cellulose nanofiber added in terms of carbon atoms / amount of propylene glycol added in terms of carbon atoms (X / Y) = 0.7), and mixed to obtain slurry water ii-1. Slurry water ii-1 was spray-dried (hot air temperature during spray drying 220℃, (amount of hot air supplied) / (amount of slurry water supplied) = 4500) to obtain particle b1, and then calcined at 650℃ for 1 hour under an argon hydrogen atmosphere (hydrogen concentration 3%) to obtain positive electrode active material particle A1. Figure 1 shows a TEM image of the surface of the obtained positive electrode active material particle A1.

[0063] [Example 2] Cathode active material particle A2 was obtained in the same manner as in Example 1, except that 900 g of cellulose nanofiber and 20 g of propylene glycol were added to the separated particle a1 (mass ratio of the amount of cellulose nanofiber added in terms of carbon atoms / the amount of propylene glycol added in terms of carbon atoms (X / Y) = 4.2).

[0064] [Example 3] Cathode active material particle A3 was obtained in the same manner as in Example 1, except that instead of adding 450 g of cellulose nanofiber and 60 g of propylene glycol to the separated particle a1, 250 g of glucose and 400 g of propylene glycol were added (mass ratio of the amount of glucose added in terms of carbon atoms / the amount of propylene glycol added in terms of carbon atoms (X / Y) = 0.6).

[0065] [Example 4] Positive electrode active material particles A4 were obtained in the same manner as in Example 1, except that the obtained particles b1 were calcined at 550°C for 1 hour under an argon-hydrogen atmosphere.

[0066] [Example 5] Cathode active material particles A5 were obtained in the same manner as in Example 1, except that the obtained particles b1 were calcined at 750°C for 1 hour under an argon-hydrogen atmosphere.

[0067] [Comparative Example 1] Cathode active material particles Z1 were obtained in the same manner as in Example 1, except that instead of adding 450 g of cellulose nanofiber and 60 g of propylene glycol to the separated particles a1, 400 g of cellulose nanofiber and 600 g of propylene glycol were added.

[0068] [Comparative Example 2] Cathode active material particles Z2 were obtained in the same manner as in Example 1, except that instead of adding 450 g of cellulose nanofiber and 60 g of propylene glycol to the separated particles a1, 250 g of glucose was added and propylene glycol was not added.

[0069] [Comparative Example 3] Particle b1 was obtained in the same manner as in Example 1, except that the hot air temperature during spray drying was 350 °C and the value of (hot air supply rate) / (slurry water supply rate) was 12,000. Then, it was calcined at 450 °C for 1 hour in an argon-hydrogen atmosphere to obtain cathode active material particles Z3.

[0070] [Comparative Example 4] Cathode active material particles Z4 were obtained in the same manner as in Example 1, except that the obtained particles b1 were calcined at 900 °C for 1 hour in an argon-hydrogen atmosphere.

[0071] 《Fabrication of All-Solid-State Secondary Battery》 Each of the obtained cathode active material particles and the oxide solid electrolyte Li 1.5 Al 0.5 Ge 1.5 P3O 12 (manufactured by Toyo Seisakusho Co., Ltd., hereinafter referred to as LAGP) and the conductive assistant acetylene black were mixed at a mass ratio of 60:30:10, and further pulverized by a ball mill to prepare a composite powder. The obtained composite powder was put into a pressing jig, and then pressed at 600 °C for 10 hours using a hot press to form a cathode active material layer, and a polyethylene oxide solid electrolyte film containing a lithium salt was laminated on the layer. Next, a lithium foil was used as the anode, and it was attached on the polyethylene oxide solid electrolyte film on the side opposite to the laminated cathode active material layer to fabricate an all-solid-state lithium-ion secondary battery.

[0072] 《Evaluation of Battery Characteristics》 Using the fabricated all-solid-state lithium-ion secondary battery, the discharge capacity was determined when the charging conditions were constant current charging at 16 mA / g (1 C = 320 mA / g) and a cut-off voltage of 5.0 V, and the discharging conditions were constant current discharging at 16 mA / g and a cut-off voltage of 1.5 V. Also, the discharge capacity was determined when the charging conditions were constant current charging at 16 mA / g (1 C = 320 mA / g) and a cut-off voltage of 5.0 V, and the discharging conditions were constant current discharging at 96 mA / g and a cut-off voltage of 1.5 V, and this was used as an index for evaluating the rate characteristics. All charge-discharge tests were carried out at 60 °C. The results are shown in Table 1.

[0073] Table 1

Claims

1. Formula (A) below: Li a Mn b Fe c M x SiO 4 ・・・(A) (In equation (A), M represents Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, Al, Zn, V, or Gd. a, b, c, and x represent numbers that satisfy 0 < a ≤ 2.4, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 1.2, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 4.) It is composed of silicate particles represented by and Positive electrode active material particles for all-solid-state secondary batteries, comprising carbon with an intensity ratio (G / D) of 1.31 to 2.0 determined by Raman spectroscopy, coated on the surface with a coverage rate of 30% to 80%.

2. The positive electrode active material particles for an all-solid-state secondary battery according to claim 1, wherein the average particle size of the silicate-based particles is 10 nm to 200 nm.

3. Positive electrode active material particles for all-solid-state secondary batteries according to claim 1 or 2, wherein the carbon content is 0.5% by mass to 8% by mass.

4. The conductivity is 1.0 × 10⁻⁶. -7 Positive electrode active material particles for all-solid-state secondary batteries according to any one of claims 1 to 3, wherein the S / cm is 1 or higher.

5. The following steps (I) to (III): (I) A step in which a lithium compound is subjected to a hydrothermal reaction to obtain preliminary particles a by adding a metal compound containing at least a manganese compound and an iron compound, and water to obtain a slurry water i, and then subjecting it to a hydrothermal reaction. (II) Adding carbon coating agent X, carbon coating inhibitor Y, and water to the obtained preliminary particles a to obtain slurry water ii, and then subjecting it to spray drying to obtain preliminary particles b. (III) A step of calcining the obtained preliminary particles b. Equipped with, The carbon coating agent X is cellulose nanofiber, lignocellulose nanofiber, chitin nanofiber, or chitosan nanofiber, and A method for producing positive electrode active material particles for all-solid-state secondary batteries according to any one of claims 1 to 4, wherein the carbon coating inhibitor Y is one or more carbon materials selected from polyols other than sugars, amines, and amides.

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