Lithium-based polyanion particles for secondary battery positive electrode active material and method for producing the same

Abstract

To provide lithium-based polyanion particles for a secondary battery positive electrode active material which can effectively suppress side reactions during charge-discharge cycles of lithium-ion secondary batteries and effectively improve the cycle characteristics of the lithium-ion secondary batteries, and a method for manufacturing the same.SOLUTION: Lithium-based polyanion particles for a secondary battery positive electrode active material are expressed by the following formula (A): LiaMnbFecMxPO4 (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0<a≤1.2, 0≤b≤1.2, 0≤c≤1.2, 0≤x≤0.3, and b+c≠0, and a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.), carbon derived from cellulose nanofibers is carried thereon, and the void volume thereof is increased from the surface to the center. The pore volume in a pore diameter range of 2 nm to 150 nm ranges from 0.01 cm3 / g to 0.15 cm3 / g.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to lithium-based polyanion particles for a positive electrode active material of a secondary battery exhibiting good cycle characteristics and a method for producing the same.

Background Art

[0002] Secondary batteries such as lithium-ion secondary batteries are used in a wide range of fields such as mobile phones, digital cameras, notebook PCs, hybrid vehicles, and electric vehicles. As a positive electrode material for such lithium-ion secondary batteries, lithium-based polyanion particles such as LiMn x Fe 1-x PO 4 are regarded as promising. On the other hand, since lithium-based polyanion particles have low conductivity and still need improvement to sufficiently enhance the battery characteristics in the obtained lithium-ion secondary battery, various developments have been made conventionally.

[0003] For example, Patent Document 1 discloses an electrode material that is an aggregate of electrode active materials (such as Li a A x M y PO 4 etc.) coated with a specific carbonaceous film. By using an ionic organic substance as a carbon source, the growth and sintering of the electrode active material particles are suppressed, and the cycle characteristics are improved. Further, Patent Document 2 discloses composite particles containing a carbon material such as a fibrous carbon material or a chain-like carbon material and a lithium-containing phosphate (such as LiMn x Fe 1-x PO 4 etc.) and having pores leading to the outside of the composite particles starting from the carbon material. Attempts have been made to improve the rate characteristics of the battery and enhance the cycle characteristics and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the electrode active material described in Patent Document 1 and the composite particles described in Patent Document 2 have surface properties that tend to cause side reactions during the charge and discharge cycles of a lithium-ion secondary battery. Therefore, there is still room for improvement to sufficiently enhance the cycle characteristics.

[0006] Accordingly, an object of the present invention is to provide a lithium-based polyanion particle for a positive electrode active material of a secondary battery and a method for producing the same, which can effectively suppress side reactions during the charge and discharge cycles of a lithium-ion secondary battery and effectively improve the cycle characteristics of the lithium-ion secondary battery.

Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that cycle characteristics can be effectively enhanced in a resulting lithium-ion secondary battery if specific lithium-based polyanion particles having an increasing void volume from the surface toward the center are used.

[0008] That is, the present invention provides the following formula (A): Li a Mn b Fe c M x PO 4 ···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3.) It is a lithium-based polyanion particle represented by , in which carbon derived from cellulose nanofibers is supported, and the void volume increases from the surface toward the center, The pore volume in the pore diameter range of 2 nm to 150 nm is 0.01 cm 3 / g to 0.15 cm 3 / g, and it provides lithium-based polyanion particles for a positive electrode active material of a secondary battery.

[0009] Further, the present invention includes the following steps (I) to (V): (I) After adding a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water a, or after obtaining slurry water a' by mixing lithium phosphate particles, a metal compound containing a manganese compound and / or an iron compound, and water, subjecting it to a hydrothermal reaction to obtain preliminary particles i (II) After adding the obtained preliminary particles i, cellulose nanofibers, and water to obtain slurry water b, subjecting it to spray drying to obtain granulated bodies ii (III) Firing the obtained granulated bodies ii to obtain a composite iii (IV) After adding the obtained composite iii, a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, a wetting agent, and water to obtain slurry water c, drying to obtain a composite iv (V) Firing the obtained composite iv is provided, The manufacturing method of the above lithium-based polyanion particles for a positive electrode active material of a secondary battery, wherein the addition amount of the wetting agent in step (IV) is 0.01 part by mass to 2.5 parts by mass with respect to 100 parts by mass of the composite iii.

Effects of the Invention

[0010] If it is the lithium-based polyanion particles for a positive electrode active material of the present invention, since it has a surface property capable of effectively suppressing side reactions during charge and discharge cycles of a lithium-ion secondary battery, it is possible to realize a positive electrode material capable of effectively improving the cycle characteristics of a lithium-ion secondary battery.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. The lithium-based polyanion particles for a positive electrode active material of a secondary battery of the present invention are represented by the following formula (A): Li a Mn b Fe c M x PO 4 ···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3.) It is a lithium-based polyanion particle represented by the formula, in which carbon derived from cellulose nanofibers is supported, and the void volume increases from the surface toward the center, and the pore volume in the pore diameter range of 2 nm to 150 nm is 0.01 cm 3 / g to 0.15 cm 3 / g.

[0013] That is, the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention are such that carbon derived from cellulose nanofibers is firmly supported, the void volume increases from the surface toward the center, and as shown by having a specific pore volume in the above specific pore diameter range, the particles are those in which the density gradually decreases from the vicinity of the surface toward the vicinity of the center, that is, particles having a surface with a higher density than the center. Thus, in the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention, the primary particles constituting such particles carry carbon derived from cellulose nanofibers, and as they approach the surface of the lithium-based polyanion particles for the positive electrode active material of the secondary battery corresponding to the secondary particles, they aggregate densely and the voids are reduced. Therefore, they have a surface property that can effectively suppress side reactions during charge and discharge cycles of the lithium-ion secondary battery, and are considered to effectively improve the cycle characteristics of the lithium-ion secondary battery.

[0014] The lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention are represented by the following formula (A): Li a Mn b Fe c M x PO 4 ···(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and represent numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3.) It is represented by.

[0015] That is, the lithium-based polyanion particles for secondary battery positive electrode active materials represented by the above formula (A) are lithium-based polyanion particles for secondary battery positive electrode active materials containing at least manganese (Mn) or iron (Fe) (hereinafter, also referred to as "particles (A)"), and are secondary particles formed by aggregation of primary particles. In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, preferably Mg or Zr. a satisfies 0 < a ≤ 1.2, preferably 0.6 ≤ a ≤ 1.2, more preferably 0.65 ≤ a ≤ 1.15, and still more preferably 0.7 ≤ a ≤ 1.1. b satisfies 0 ≤ b ≤ 1.2, preferably 0.25 ≤ b ≤ 0.8, and more preferably 0.35 ≤ b ≤ 0.8. c satisfies 0 ≤ c ≤ 1.2, preferably 0.2 ≤ c ≤ 0.75, and more preferably 0.2 ≤ c ≤ 0.65. And b and c satisfy b + c ≠ 0. x satisfies 0 ≤ x ≤ 0.3, preferably 0 ≤ x ≤ 0.15, and more preferably 0 ≤ x ≤ 0.1. And a, b, c, and x are numbers that satisfy a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. More specifically, examples of the particles (A) represented by the above formula (A) include, for example, LiMnPO 4 , LiFePO 4 , LiMn 0.8 Fe 0.2 PO 4 , LiMn 0.1 Fe 0.9 PO 4 , LiMn 0.8 Fe 0.1 Mg 0.1 PO 4 , LiMn 0.8 Fe 0.1 Zr 0.05 PO 4 , and the like.

[0016] The lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention are represented by the above formula (A) and are supported by carbon derived from cellulose nanofibers. Such cellulose nanofibers are carbonized to become carbon, which is supported on the surface of the primary particles so as to fill a part of the gaps between the primary particles constituting the particles (A), and is also firmly supported on the surface of the particles (A). Cellulose nanofibers are a skeletal component that accounts for about 50% of all plant cell walls, and are lightweight and high-strength fibers that can be obtained by defibrating plant fibers constituting such cell walls to the nanosize. The fiber diameter of such cellulose nanofibers is 1 nm to 1000 nm, and it also has good dispersibility in water. Further, in the cellulose molecular chains constituting the cellulose nanofibers, a periodic structure is formed by carbon, so that this is carbonized and firmly supported on the particles (A). While the amount of voids increases from the surface toward the center, it is possible to ensure the expression of excellent battery characteristics as a whole of the particles (A).

[0017] In addition, the particles (A) may carry carbon derived from a water-soluble carbon material together with carbon derived from cellulose nanofibers. Such a water-soluble carbon material, like cellulose nanofibers, is carbonized to become carbon, which is carried on the surface of the primary particles so as to fill a part of the gaps between the primary particles constituting the particles (A), and is also firmly carried on the surface of the particles (A). Examples of such water-soluble carbon materials include one or more selected from saccharides, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch and dextrin; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among them, from the viewpoint of enhancing solubility and dispersibility in a solvent and effectively functioning as a carbon material, glucose, fructose, sucrose, and dextrin are preferred, and glucose is more preferred.

[0018] The amount of carbon derived from cellulose nanofibers in terms of atomic conversion, that is, the amount of carbon derived from cellulose nanofibers carried on the particles (A), is preferably 0.8% by mass to 1.4% by mass, more preferably 0.9% by mass to 1.4% by mass, and even more preferably 1.0% by mass to 1.4% by mass in 100% by mass of the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention. The amount of carbon derived from cellulose nanofibers (carrying amount) present in the particles (A) is determined by measurement using a carbon-sulfur analyzer.

[0019] The lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention have a pore volume in the pore diameter range of 2 nm to 150 nm of 0.01 cm 3 / g to 0.15 cm 3 / g, and has a unique shape in which the primary particles constituting the surface of the particles (A) are densely aggregated so as to suppress the adsorption of moisture in the atmosphere into the particles (A). Thus, the lithium-based polyanion particles for a secondary battery positive electrode active material of the present invention have an increased void volume from the surface toward the center, while having a high density as a whole, and effectively suppress the adsorption of moisture in the atmosphere to the particle surface, thereby reducing the amount of O-H groups derived from moisture relative to the amount of C=O groups derived from the particles present on the particle surface, and can have a surface property capable of effectively suppressing side reactions during charge and discharge cycles of a lithium-ion secondary battery.

[0020] The lithium-based polyanion particles for a secondary battery positive electrode active material of the present invention have a pore volume in the pore diameter range of 2 nm to 150 nm of 0.01 cm 3 / g to 0.15 cm 3 / g, preferably 0.01 cm 3 / g to 0.12 cm 3 / g, more preferably 0.01 cm 3 / g to 0.10 cm 3 / g. Note that the pore volume in the pore diameter range of 2 nm to 150 nm means a value measured by a mercury intrusion porosimeter.

[0021] Specifically, as shown in FIG. 1, the lithium-based polyanion particles for a secondary battery positive electrode active material of the present invention are divided into a cross-section X including the center 2 of the lithium-based polyanion particles and a cross-section Y including the surface of the lithium-based polyanion particles with a circle 5 formed by connecting points 4 that bisect the radius 3 of the cross-section 1 passing through the center 2 of the lithium-based polyanion particles as a boundary. When divided in this way, the ratio (x / A) of the true density x of the cross-section X to the true density A of the lithium-based polyanion particles is 0.9 to 0.99, and the ratio (y / A) of the true density y of the cross-section Y to the true density A of the lithium-based polyanion particles is preferably 1.01 to 1.1. Thus, the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention, in cross-section 1, have a higher true density y of the cross-section Y including the surface than the true density x of the cross-section X including the center 2 with respect to the true density A of the lithium-based polyanion particles. As approaching the surface of the lithium-based polyanion particles for the positive electrode active material of the secondary battery, they are densely aggregated and voids are reduced, and they have a surface property that can effectively suppress side reactions during charge and discharge cycles of the lithium-ion secondary battery.

[0022] Note that the "true density" of the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention means the density calculated using only the volume occupied by the lithium-based polyanion particles themselves for density calculation, excluding the voids present in such particles. Similarly, the true density of cross-section X and the true density of cross-section Y also mean the densities calculated based on the volumes excluding the voids present in each cross-section. Such "true density" is measured by pulverizing the measurement sample so that voids disappear and using the Gay-Lussac type pycnometer method. The voids of the measurement sample are completely degassed and replaced with a liquid, and from the relationship between its mass and volume, it is a value calculated by the following formula (x). True density = {(Wb - Wa) / (Wb - Wa - Wc + Wd)} × density of the solution ··· (x) (In formula (x), Wa is the mass of the pycnometer, Wb is the weight of the pycnometer + measurement sample, Wc is the mass of the pycnometer + measurement sample + solution up to the calibration line, and Wd is the mass of the measurement sample bottle + solution up to the calibration line.) Note that in this specification, as described in the examples, a cross-section passing through the center of the particle with a focused ion beam is cut out as a measurement sample, the voids of the measurement sample are identified by TEM observation and image analysis, and the density measured by excluding these is regarded as the value calculated by the following formula (x). Specifically, among the TEM photographs of the cross-section of the positive electrode active material, cross-sections are cut out for 10 randomly selected particles, binarized at a specific gray level to visualize the inter-particle voids, and from the area ratio, the true density of cross-section X and the true density of cross-section Y of the particle are calculated, and the average value of the 10 particles is obtained.

[0023] The ratio (x / A) of the true density x of cross-section X to the true density A of the lithium-based polyanion particles is 0.9 to 0.99, preferably 0.9 to 0.98, and more preferably 0.9 to 0.97. Also, the ratio (y / A) of the true density y of cross-section Y to the true density A of the lithium-based polyanion particles is 1.01 to 1.1, preferably 1.02 to 1.1, and more preferably 1.03 to 1.1.

[0024] From the viewpoint of effectively improving the cycle characteristics in the resulting battery, the average particle size of the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention is preferably 10 μm to 40 μm, more preferably 12 μm to 40 μm, and even more preferably 14 μm to 40 μm. Note that the average particle size means the D value (particle size at cumulative 50% (median diameter)) obtained from the volume-based particle size distribution based on the laser diffraction / scattering method. 50 value (particle size at cumulative 50% (median diameter)).

[0025] From the viewpoint of ensuring the expression of excellent battery characteristics as a whole for the particles (A), while the tap density of the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention increases in void volume from the surface toward the center, it is preferably 1.0 g / cm 3 ~1.8 g / cm 3 and more preferably 1.1 g / cm 3 ~1.8 g / cm 3 and even more preferably 1.2 g / cm 3 ~1.8 g / cm 3 is. Note that the tap density means the "tap bulk density" measured by the method specified in JIS R 1628 "Method for Measuring Bulk Density of Fine Ceramics Powder".

[0026] From the viewpoint of ensuring the expression of excellent battery characteristics as a whole for the particles (A), while the BET specific surface area of the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention increases in void volume from the surface toward the center, it is preferably 10 m 2 / g to 25 m 2 / g, more preferably 10 m 2 / g to 22 m 2 / g, and more preferably 10 m 2 / g to 20 m 2 / g. The BET specific surface area can be measured, for example, using a flow-type specific surface area automatic measuring device (FlowSorb III 2305, manufactured by Shimadzu Corporation), under the condition of using a nitrogen-helium mixed gas containing 30% nitrogen.

[0027] The lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention include the following steps (I) to (V): (I) After adding a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water a, or after obtaining slurry water a' by mixing lithium phosphate particles, a metal compound containing a manganese compound and / or an iron compound, and water, subjecting to a hydrothermal reaction to obtain preliminary particles i (II) After adding the obtained preliminary particles i, cellulose nanofibers, and water to obtain slurry water b, subjecting to spray drying to obtain granulated bodies ii (III) Firing the obtained granulated bodies ii to obtain a composite iii (IV) After adding the obtained composite iii, a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, a wetting agent, and water to obtain slurry water c, drying to obtain a composite iv (V) Firing the obtained composite iv and can be obtained by a production method in which the addition amount of the wetting agent in step (IV) is 0.01 part by mass to 2.5 parts by mass with respect to 100 parts by mass of the composite iii.

[0028] ​Thus, by going through steps (I) to (III), preliminary particles i corresponding to the primary particles constituting particle (A) and forming the vicinity of the center of particle (A) can be formed, and a composite iii can be obtained by aggregating them while having appropriate voids. Then, by going through steps (IV) to (V), primary particles constituting particle (A) are further densely aggregated around the composite iii, and lithium-based polyanion particles for a positive electrode active material of a secondary battery having a surface property capable of effectively suppressing side reactions during charge and discharge cycles of the lithium-ion secondary battery can be obtained.

[0029] Step (I) included in the production method of the present invention is a step of obtaining preliminary particles i by subjecting to a hydrothermal reaction after adding a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water a, or after obtaining slurry water a' by mixing lithium phosphate particles, a metal compound containing a manganese compound and / or an iron compound, and water.

[0030] When using slurry water a in step (I), examples of the lithium compound include hydroxides (e.g., LiOH·H 2 O, LiOH), carbonates, sulfates, and acetates. Among them, hydroxides are preferred. As the metal compound containing a manganese compound and / or an iron compound, in addition to manganese compounds and iron compounds, a metal (M) compound can be used. Examples of the manganese compound that can be used include manganese acetate, manganese nitrate, manganese sulfate, etc. These may be used alone or in combination of two or more. Among them, manganese sulfate is preferred from the viewpoint of enhancing battery characteristics. Examples of the iron compound that can be used include iron acetate, iron nitrate, iron sulfate, etc. These may be used alone or in combination of two or more. Among them, iron sulfate is preferred from the viewpoint of enhancing battery characteristics. Examples of the metal (M) compound that can be used include sulfates and nitrates containing a metal synonymous with M in the above formula (A). Examples of the phosphoric acid compound include orthophosphoric acid (H 3 PO4 , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc. Among these, it is preferable to use phosphoric acid, and it is preferable to use it as an aqueous solution with a concentration of 70% to 90% by mass.

[0031] In step (I), when preparing slurry water a, the order of adding the lithium compound, the manganese compound and / or iron compound-containing metal compound, the phosphoric acid compound, and water is not particularly limited. After adding the lithium compound, the phosphoric acid compound, and water, the manganese compound and / or iron compound may be added, or these lithium compound, manganese compound and / or iron compound-containing metal compound, phosphoric acid compound, and water may be added all at once. The content of the lithium compound in the slurry water a obtained by mixing the lithium compound, the manganese compound and / or iron compound-containing metal compound, the phosphoric acid compound, and water is preferably 5 parts by mass to 50 parts by mass, more preferably 7 parts by mass to 45 parts by mass, per 100 parts by mass of water. For example, in step (I), when using phosphoric acid as the phosphoric acid compound, it is preferable to add phosphoric acid to the slurry water obtained by adding the lithium compound and water, and then add the manganese compound and / or iron compound to obtain slurry water a. At this time, it is preferable to stir the slurry water in advance before adding the phosphoric acid compound. The stirring time of such slurry water is preferably 1 minute to 15 minutes, more preferably 3 minutes to 10 minutes. Also, the temperature of the slurry water is preferably 20°C to 90°C, more preferably 20°C to 70°C.

[0032] When further adding phosphoric acid, it is preferable to dropwise add phosphoric acid while stirring the slurry water. The dropping rate of phosphoric acid into the slurry water is preferably 15 mL / min to 50 mL / min, more preferably 20 mL / min to 45 mL / min, and even more preferably 28 mL / min to 40 mL / min. Also, the stirring time of the slurry water while dropping phosphoric acid is preferably 0.5 hour to 24 hours, more preferably 3 hours to 12 hours. Further, the stirring speed of the slurry water while dropping phosphoric acid is preferably 200 rpm to 700 rpm, more preferably 250 rpm to 600 rpm, and even more preferably 300 rpm to 500 rpm. When stirring the slurry water, it is preferable to further cool it to a temperature below the boiling point temperature of the slurry water. Specifically, it is preferably cooled to 80°C or lower, and more preferably cooled to 20°C to 60°C.

[0033] The slurry water after mixing the phosphoric acid compound preferably contains 2.7 moles to 3.3 moles of lithium per 1 mole of phosphoric acid, and more preferably contains 2.8 moles to 3.1 moles. The above lithium compound and phosphoric acid compound may be used so as to obtain such an amount.

[0034] By purging nitrogen into the slurry water after mixing the phosphoric acid compound, the reaction in such slurry water is completed to obtain precursor particles i' which are precursors of particles (A) as a slurry. When nitrogen is purged, the reaction can proceed in a state where the dissolved oxygen concentration in the slurry water is reduced, and the dissolved oxygen concentration of the slurry water containing the obtained precursor particles i' is also effectively reduced, so that the oxidation of the metal compound to be added next can be suppressed. In the slurry water containing such precursor particles i', the precursor of particles (A) is triliium phosphate (Li 3 PO 4 ) which exists as fine dispersed particles.

[0035] Next, a manganese compound and an iron compound may be added to the slurry water. The molar ratio of the manganese compound and the iron compound used (manganese compound: iron compound) is preferably from 80:20 to 20:80, more preferably from 80:20 to 30:70, and still more preferably from 80:20 to 35:65. Further, the total addition amount of these metal compounds is preferably from 0.99 mol to 1.01 mol, more preferably from 0.995 mol to 1.005 mol, per 1 mol of phosphate ions contained in the slurry water a.

[0036] In the preparation of the slurry water a, when a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, and water are added all at once, these lithium compound, a manganese compound and / or an iron compound-containing metal compound, a phosphoric acid compound, and water may have the above-described quantitative relationship, and it is not necessarily required that lithium phosphate (Li 3 PO 4 ) as a precursor of the particle (A) is present in the slurry water a.

[0037] When using the slurry water a' in the step (I), a metal compound containing a manganese compound and an iron compound may be added to the slurry water obtained by mixing lithium phosphate particles and water. The content of lithium phosphate particles in the slurry water a' is preferably from 7% by mass to 60% by mass, more preferably from 9% by mass to 50% by mass. The molar ratio of the manganese compound and the iron compound used and the total addition amount of the metal compound are the same as above.

[0038] The order of addition of the manganese compound, the iron compound, and the metal (M) compound is not particularly limited. Further, an antioxidant may be added as necessary when adding these metal compounds. Examples of such an antioxidant include sodium sulfite (Na 2 SO 3 ), sodium hydrosulfite (Na 2 S 2 O 4) Ammonia water or the like can be used. The addition amount of the antioxidant is preferably 0.01 mol to 1 mol, more preferably 0.03 mol to 0.5 mol, based on 1 mol of the total of the manganese compound, the iron compound, and the metal (M) compound used as necessary.

[0039] When using the slurry water a', the content of the preliminary particles i' in the slurry water a' obtained by adding the manganese compound, the iron compound, and the metal (M) compound and adding an antioxidant or the like as necessary is preferably 5 to 50% by mass, more preferably 7 to 45% by mass, and still more preferably 9 to 40% by mass.

[0040] Next, in step (I), the obtained preliminary particles i' and the slurry water a or slurry water a' containing a metal compound containing at least a manganese compound and an iron compound are subjected to a hydrothermal reaction to obtain the preliminary particles i. The amount of water used when subjecting to the hydrothermal reaction is preferably 10 mol to 50 mol, more preferably 12.5 mol to 45 mol, based on 1 mol of phosphate ions contained in the slurry water a (or slurry water a'), from the viewpoints of the solubility of the metal compound, the ease of stirring, and the efficiency of synthesis.

[0041] The hydrothermal reaction may be at 100°C or higher, preferably 130°C to 200°C. The hydrothermal reaction is preferably carried out in a pressure-resistant container. When the reaction is carried out at 130°C to 200°C, the pressure at this time is preferably 0.3 MPa to 1.6 MPa, and when the reaction is carried out at 140°C to 160°C, the pressure is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 hour to 48 hours, more preferably 0.2 hour to 24 hours. The obtained preliminary particles i are isolated by washing with water and drying after filtration. Freeze drying or vacuum drying is used as the drying means.

[0042] Step (II) is a step of adding the preliminary particles i obtained in Step (I), cellulose nanofibers, and water to obtain slurry water b, and then subjecting it to spray drying to obtain granulated particles ii. Here, by using cellulose nanofibers and going through subsequent steps, the cellulose nanofibers can be carbonized, corresponding to the primary particles constituting particle (A), and carbon derived from the cellulose nanofibers can be supported on the preliminary particles i constituting the vicinity of the center of particle (A). Note that the cellulose nanofibers that can be used in Step (II) are as described above.

[0043] The content of cellulose nanofibers in slurry water b is preferably 0.8 parts by mass to 1.4 parts by mass, more preferably 0.8 parts by mass to 1.3 parts by mass, and still more preferably 0.8 parts by mass to 1.2 parts by mass in terms of the residue amount after carbonization treatment with respect to 100 parts by mass of water.

[0044] The solid content concentration of slurry water b is preferably 35% by mass to 65% by mass, more preferably 35% by mass to 60% by mass, and still more preferably 35% by mass to 55% by mass.

[0045] After adding water, it is preferable to stir slurry water b in advance before subjecting it to spray drying. The stirring time of such slurry water b is preferably 3 minutes to 60 minutes, more preferably 5 minutes to 30 minutes. Also, the temperature of slurry water b is preferably 10°C to 60°C, more preferably 20°C to 40°C.

[0046] Next, the obtained slurry water b is subjected to spray drying to obtain granulated particles ii. In spray drying, the operating conditions may be set as appropriate according to the apparatus used. For example, as the processing conditions in a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle, the hot air temperature is preferably 110°C to 300°C, more preferably 150°C to 250°C. Also, the volume ratio of the supply amount of hot air to the supply amount of slurry water (supply amount of hot air / supply amount of slurry water) is preferably 500 to 10,000, more preferably 1,000 to 9,000.

[0047] Step (III) is a step of firing the granulated product ii obtained in step (II) to obtain the composite iii. The firing conditions for such step (III) are preferably in a reducing atmosphere or an inert atmosphere, the firing temperature is preferably 500°C to 1,000°C, more preferably 550°C to 900°C, the firing time is preferably 0.5 hour to 12 hours, more preferably 1 hour to 6 hours.

[0048] Step (IV) is a step of adding the composite iii obtained in step (III), a lithium compound, a manganese compound and / or an iron compound-containing metal compound, a phosphoric acid compound, a wetting agent, and water to obtain slurry water c, and then drying to obtain the composite iv. The addition amount of the wetting agent is 0.01 part by mass to 2.5 parts by mass with respect to 100 parts by mass of the composite iii. Thereby, primary particles constituting the particle (A) can be densely present around the composite iii, and by using the wetting agent in a specific amount, the dense aggregation of the primary particles can be effectively promoted.

[0049] As the lithium compound, the manganese compound and / or the iron compound-containing metal compound, and the phosphoric acid compound, those similar to those in step (I) may be used.

[0050] Examples of the wetting agent include one or more selected from polyether ester amine, polyether phosphate ester amine, and polyether phosphate ester. Among them, polyether ester amine is preferable from the viewpoint of effectively promoting the dense aggregation of the primary particles. The addition amount of the wetting agent is 0.01 parts by mass to 2.5 parts by mass, preferably 0.1 parts by mass to 2.0 parts by mass, and more preferably 0.2 parts by mass to 1.5 parts by mass, based on 100 parts by mass of the composite iii. Note that by going through the process (V) described later, the added wetting agent will burn out and will not remain in the obtained particles (A).

[0051] In the process (IV), the content of the lithium compound in the slurry water c obtained by adding the composite iii, the lithium compound, the metal compound containing the manganese compound and / or the iron compound, the phosphoric acid compound, the wetting agent, and water is preferably 1 part by mass to 20 parts by mass, and more preferably 1 part by mass to 15 parts by mass, based on 100 parts by mass of water. Also, the lithium compound added in the process (I) I and the lithium compound added in the process (IV) IV The molar ratio of (lithium compound I / lithium compound IV ) is preferably 4 to 49, more preferably 6 to 45, and even more preferably 8 to 40, from the viewpoint of effectively obtaining the particles (A) in which the void amount increases from the surface toward the center.

[0052] In the process (IV), the addition order of the composite iii, the lithium compound, the metal compound containing the manganese compound and / or the iron compound, the phosphoric acid compound, the wetting agent, and water is preferably to first add the wetting agent and water, then add the composite iii, and then add the lithium compound, the manganese compound and / or the iron compound, and the phosphoric acid compound to obtain the slurry water c, from the viewpoint of fully exerting the effect of adding the wetting agent and effectively obtaining the particles (A) in which the void amount increases from the surface toward the center.

[0053] The obtained slurry water c preferably contains 0.99 mol to 1.01 mol of lithium per 1 mol of phosphoric acid, and more preferably contains 0.995 mol to 1.005 mol of lithium. Also, the solid content concentration of the slurry water c is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 50% by mass, and even more preferably 15% by mass to 45% by mass. In addition, other conditions for obtaining the slurry water c are the same as those in step (I) and may be appropriately selected.

[0054] Next, in step (IV), the obtained slurry water c is dried to obtain the composite iv. Examples of the drying means include vacuum drying, spray drying, box drying, fluidized bed drying, external heat drying, and freeze drying. Among them, vacuum drying is preferred.

[0055] Step (V) is a step of firing the composite iv obtained in step (IV). Thereby, the cellulose nanofibers added in step (II) are carbonized, and particles (A) can be obtained in which the void volume increases from the surface toward the center while being firmly supported. The firing conditions of such step (V) are preferably in a reducing atmosphere or an inert atmosphere. The firing temperature is preferably 500°C to 800°C, more preferably 550°C to 750°C, and the firing time is preferably 1 hour to 20 hours, more preferably 3 hours to 10 hours.

[0056] The lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention are materials used as the positive electrode active material of a lithium-ion secondary battery. Specifically, for example, after kneading the lithium-based polyanion particles for the positive electrode active material of the present invention with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. to prepare a positive electrode slurry, it is coated on a current collector, and then press-molded to produce a positive electrode. If it is the lithium-based polyanion particles for the positive electrode active material of the secondary battery of the present invention, since the density on the surface is higher than that at the center and it has a surface property capable of effectively suppressing side reactions during charge and discharge cycles of a lithium-ion secondary battery, unnecessary moisture adsorption is also effectively suppressed, and the cycle characteristics of the obtained lithium-ion secondary battery can be effectively improved.

[0057] As for the lithium ion secondary battery to which the positive electrode obtained by using the lithium-based polyanion particles for the positive electrode active material of the present invention can be applied, there is no particular limitation as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte as essential components.

[0058] Here, regarding the negative electrode, as long as it can occlude lithium ions during charging and release them during discharging, its material composition is not particularly limited, and a known material composition can be used. For example, carbon materials such as lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, or amorphous carbon can be used. And it is preferable to use an electrode formed of an intercalation material capable of electrochemically occluding and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination. For example, a combination of graphite and silicon-based can be used.

[0059] The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used in the electrolytic solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds, etc. can be used.

[0060] The type of the supporting salt is not particularly limited, but LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 inorganic salts selected from, derivatives of the inorganic salts, LiSO 3 CF 3 , LiC(SO 3 CF 3 )( 2 and LiN(SO 3 CF 3 )( 2 , LiN(SO 2 C 2 F 5 )( 2 and LiN(SO 2 CF 3 )(SO2 C 4 F 9 It is preferably at least one selected from organic salts and derivatives of the organic salts.

[0061] The separator electrically insulates the positive electrode and the negative electrode and serves to hold the electrolyte. For example, a porous synthetic resin film, particularly a porous film of a polyolefin-based polymer (polyethylene, polypropylene) may be used.

[0062] The solid electrolyte electrically insulates the positive electrode and the negative electrode and exhibits high lithium ion conductivity. For example, La 0.51 Li 0.34 TiO 2.94 、Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、50Li 4 SiO 4 ·50Li 3 BO 3 、Li 2.9 PO 3.3 N 0.46 、Li 3.6 Si 0.6 P 0.4 O 4 、Li 1.07 Al 0.69 Ti 1.46 (PO 4 ) 3 、Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 、Li 10 GeP 2 S 12 、Li 3.25 Ge 0.25 P 0.75 S 4 、30Li 2 S·26B 2 S 3 ·44LiI、63Li 2 S·36SiS2 ·1Li 3 PO 4 、57Li 2 S·38SiS 2 ·5Li 4 SiO 4 、70Li 2 S·30P 2 S 5 、50Li 2 S·50GeS 2 、Li 7 P 3 S 11 、Li 3.25 P 0.95 S 4 may be used.

[0063] The shape of the lithium ion secondary battery having the above configuration is not particularly limited, and it may be various shapes such as coin type, cylindrical type, square type, etc., or an irregular shape enclosed in a laminated exterior body.

Examples

[0064] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. The amount (loading amount) of carbon in terms of atoms and the average particle size of the obtained lithium-based polyanion particles were measured by the following methods.

[0065] 《Amount of carbon in terms of atoms (loading amount)》 Using a carbon-sulfur analyzer (EMIA-220V2, manufactured by Horiba, Ltd.), the amount of carbon in terms of atoms (loading amount) of the obtained lithium-based polyanion particles was measured.

[0066] 《Average particle size》 The particle size distribution of the obtained lithium-based polyanion particles was measured using a laser diffraction device (Microtrac MT3000II, manufactured by MicrotracBEL), and the average particle size (D 50 ) was determined.

[0067] [Example 1] LiOH·H 21272 g of O and 4 L of water were mixed to obtain slurry a1. Next, while maintaining the temperature of the obtained slurry a1 at 25°C, 1153 g of an 85% phosphoric acid aqueous solution was dropped at 35 mL / min while stirring for 3 minutes, and then stirred at a speed of 400 rpm for 12 hours to obtain slurry a2 containing Li 3 PO 4 . The obtained slurry a2 was purged with nitrogen to make the dissolved oxygen concentration of slurry a2 0.5 mg / L. Then, with respect to the total amount of slurry a2, 1610 g of MnSO 4 ·5H 2 O and 834 g of FeSO 4 ·7H 2 O were added to obtain slurry a3. The molar ratio (manganese compound: iron compound) of the added MnSO 4 and FeSO 4 was 70:30.

[0068] Next, the obtained slurry a3 was put into an autoclave and subjected to a hydrothermal reaction at 150°C for 1 hour. The pressure in the autoclave was 0.2 MPa. After the hydrothermal reaction, the generated crystals were filtered and then washed with 12 parts by mass of water per 1 part by mass of the crystals. The washed crystals were freeze-dried at -50°C for 12 hours to obtain preliminary particles i-1. 1000 g of the obtained preliminary particles i-1 was separated, 1 L of water was added thereto, and then 675 g of cellulose nanofibers (Celish KY-100G, manufactured by Daicel Finechem Ltd., fiber diameter 4 nm to 100 nm) was added to obtain slurry b1. The obtained slurry b1 was dispersed for 2 minutes with an ultrasonic stirrer (T25, manufactured by IKA) to make the whole uniformly colored, and then spray-dried (nozzle air flow rate 55 L / min, supply air temperature 180°C) using a spray-drying apparatus (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain granulated particles ii-1.

[0069] The obtained granule ii-1 was calcined at 700 °C for 60 minutes under a nitrogen atmosphere to obtain a composite iii-1. 707 g of the obtained composite iii-1 was collected, and this was added to a mixed solution containing 0.07 g of polyether ester amine (Disparon DA-234, manufactured by Enomoto Kasei Co., Ltd.) (corresponding to 0.01 part by mass with respect to 100 parts by mass of the composite iii-1) and 0.7 L of water. After that, LiOH·H 2 O 21 g, (CH 3 COO 3 ) 2 Mn·4H 2 O 85.8 g, (CH 3 COO 3 ) 2 Fe 26.1 g, and 57.6 g of an 85% aqueous phosphoric acid solution were added to obtain slurry water c1. Next, the obtained slurry water c1 was dried at 80 °C for 12 hours under vacuum to obtain a composite iv-1. The obtained composite iv-1 was calcined at 700 °C for 5 hours under a nitrogen atmosphere to obtain lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 13 μm).

[0070] [Example 2] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 13 μm) were obtained in the same manner as in Example 1, except that the addition amount of the polyether ester amine was 0.21 g (corresponding to 0.03 part by mass with respect to 100 parts by mass of the composite iii-1).

[0071] [Example 3] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 12 μm) were obtained in the same manner as in Example 1, except that the addition amount of the polyether ester amine was 3.5 g (corresponding to 0.55 part by mass with respect to 100 parts by mass of the composite iii-1).

[0072] [Example 4] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 12 μm) were obtained in the same manner as in Example 1, except that the addition amount of the polyether ester acid amine was 7.0 g (equivalent to 1.1 parts by mass with respect to 100 parts by mass of the composite iii-1).

[0073] [Example 5] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 13 μm) were obtained in the same manner as in Example 1, except that the addition amount of the polyether ester acid amine was 14.0 g (equivalent to 2.2 parts by mass with respect to 100 parts by mass of the composite iii-1).

[0074] [Comparative Example 1] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 15 μm) were obtained in the same manner as in Example 1, except that the polyether ester acid amine was not added.

[0075] [Comparative Example 2] Lithium-based polyanion particles (LiMn 0.7 Fe 0.3 PO 4 , carbon loading = 1.3% by mass, average particle size: 16 μm) were obtained in the same manner as in Example 1, except that the addition amount of the polyether ester acid amine was 21.0 g (equivalent to 3.3 parts by mass with respect to 100 parts by mass of the composite iii-1).

[0076] 《Measurement of Pore Volume in the Pore Size Range of 2 nm to 150 nm》 For each of the obtained lithium-based polyanion particles, measurement was carried out by mercury intrusion porosimetry using a measuring device (AutoPore IV9520, manufactured by Micromeritics). A Model08 (manufactured by Micromeritics) was used as the sample cell, and the surface tension of mercury was determined to be 485 dynes / cm and the contact angle of mercury was 130°. The measurement pressure range was set to 0.1 to 60000 psia. From the peak area of the obtained pore size distribution diagram, the pore volume (cm 3 / g) in the pore size range of 2 nm to 150 nm was determined. The results are shown in Table 1.

[0077] 《Calculation of the ratio (x / A) of the true density x of cross-section X to the true density A of the lithium-based polyanion particles, and the ratio (y / A) of the true density y of cross-section Y to the true density A of the lithium-based polyanion particles》 Using each of the obtained lithium-based polyanion particles, a cross-section passing through the center of the particle was cut out with a laser cutter and calculated according to the above method. The results are shown in Table 1, and a photograph when observing a cross-section passing through the center of the particle cut out with a laser cutter and performing TEM observation using the particles obtained in Example 1 is shown in Figure 2.

[0078] 《Evaluation of the surface properties of the particles》 Using each of the obtained lithium-based polyanion particles, the lithium-based polyanion particles were sandwiched between KBr plates, and the ratio (O-H / C=O) of the peak intensity of the spectrum attributed to the O-H bond to the peak intensity of the spectrum attributed to the C=O bond, which was measured by a Fourier transform infrared spectrophotometer by the KBr plate method, was determined. Note that the spectrum attributed to the O-H bond is due to the water adsorbed on the particle surface, and the spectrum attributed to the C=O bond is due to the particle (A) constituting the particle surface. Therefore, the value of the ratio (O-H / C=O) of these peak intensities serves as an index of the amount of water adsorbed on the particle surface and also as an index of whether or not the surface properties can suppress side reactions during charge and discharge cycles of the resulting battery. The smaller such a value, the more it can be evaluated that the surface properties have the ability to suppress side reactions.

[0079] "Evaluation of Battery Characteristics (Cycle Characteristics)" Using each of the obtained lithium-based polyanion particles, first, a positive electrode of a lithium-ion secondary battery was fabricated. Specifically, each of the obtained particles, Ketjen black, and polyvinylidene fluoride were mixed at a mixing ratio of 90:5:5 by mass, and N-methyl-2-pyrrolidone was added thereto and kneaded thoroughly to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil with a thickness of 20 μm using a coater, and vacuum drying was performed at 80 °C for 12 hours. Thereafter, the current collector coated with the positive electrode slurry was pressed at 20 kN using a roll press and punched into a disk shape with a diameter of 14 mm to obtain a positive electrode. Next, a coin-type secondary battery was constructed using the above positive electrode. As the negative electrode, a lithium foil punched into a diameter of 15 mm was used. As the electrolytic solution, a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7 was used, and LiPF 6 dissolved at a concentration of 1 mol / L was used. As the separator, a polymer porous film was used. These battery components were incorporated and housed by a conventional method in an atmosphere with a dew point of -50 °C or lower to obtain a coin-type secondary battery (CR-2032). Using the obtained secondary battery, the cycle characteristics were evaluated. Specifically, constant current charging at a current density of 170 mA / g and a voltage of 4.5 V, and constant current discharging at a current density of 85 mA / g and a cut-off voltage of 2.0 V were performed, and the discharge capacity at a current density of 85 mA / g (0.5 CA) was determined. Furthermore, a 100-cycle repetition test under the same charge-discharge conditions was performed, and the capacity retention rate (%) was determined by the following formula (y). Note that all charge-discharge tests were performed at 30 °C. Capacity retention rate (%) =(Discharge capacity after 100 cycles) / (Discharge capacity after 1 cycle)×100 ··· (y) The results are shown in Table 1.

[0080]

Table 1

Explanation of Symbols

[0081] 1: Cross-section passing through the center 2 of the lithium-based polyanion particles 2: Center of the lithium-based polyanion particles 3: Radius of the cross-section 4: Point bisecting the radius 3 of the cross-section 5: Circle formed by the continuous points 4 bisecting the radius 3 of the cross-section X: Cross-section X containing the center 2 of the lithium-based polyanion particles Y: Cross-section Y containing the surface of the lithium-based polyanion particles A: Lithium-based polyanion particles z: Void existing in the lithium-based polyanion particles

Claims

1. The following formula (A): Li a Mn b Fe c M x PO 4 ... (A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. a, b, c, and x satisfy 0 < a ≤ 1.2, 0 ≤ b ≤ 1.2, 0 ≤ c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn) × b + (valence of Fe) × c + (valence of M) × x = 3. The numbers shown satisfy this.) A lithium-based polyanion particle represented by the formula, in which carbon derived from cellulose nanofibers is supported, and the void volume increases from the surface toward the center, The pore volume in the pore diameter range of 2 nm to 150 nm is 0.01 cm 3 / g to 0.15 cm 3 / g, and When a cross-section passing through the center of the lithium-based polyanion particle is divided into two parts, a cross-section X including the center of the lithium-based polyanion particle and a cross-section Y including the surface of the lithium-based polyanion particle, with a circle formed by connecting the points that bisect the radius of the cross-section as the boundary, A lithium-based polyanion particle for a positive electrode active material of a secondary battery, wherein the ratio (x / A) of the true density x of the cross-section X to the true density A of the lithium-based polyanion particle is 0.9 to 0.99, and the ratio (y / A) of the true density y of the cross-section Y to the true density A of the lithium-based polyanion particle is 1.01 to 1.

1.

2. The lithium-based polyanion particle for a positive electrode active material of a secondary battery according to Claim 1, having an average particle size of 10 μm to 40 μm.

3. The tap density is 1.0 g / cm 3 to 1.8 g / cm 3 and the BET specific surface area is 10 m 2 / g to 25 m 2 / g, the lithium-based polyanion particles for a secondary battery cathode active material according to claim 1 or 2.

4. The lithium-based polyanion particle for a positive electrode active material of a secondary battery according to any one of Claims 1 to 3, wherein the supported amount of carbon derived from cellulose nanofibers is 0.8% by mass to 1.4% by mass.

5. The following steps (I) to (V): (I) After adding a metallized compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, and water to obtain slurry water a, or after obtaining slurry water a' by mixing lithium phosphate particles, a metal compound containing a manganese compound and / or an iron compound, and water, and subjecting it to a hydrothermal reaction to obtain preliminary particles i (II) After adding the obtained preliminary particles i, cellulose nanofibers, and water to obtain slurry water b, and subjecting it to spray drying to obtain granulated bodies ii (III) A step of firing the obtained granulated bodies ii to obtain a composite iii (IV) After adding the obtained composite iii, a metal compound containing a lithium compound, a manganese compound and / or an iron compound, a phosphoric acid compound, a wetting agent, and water to obtain slurry water c, and drying to obtain a composite iv (V) A step of firing the obtained composite iv Comprising ​ The method for producing lithium-based polyanion particles for a secondary battery positive electrode active material according to any one of claims 1 to 4, wherein the addition amount of the wetting agent in step (IV) is 0.01 part by mass to 2.5 parts by mass with respect to 100 parts by mass of the composite iii.

6. The method for producing lithium-based polyanion particles for a secondary battery positive electrode active material according to claim 5, wherein in step (IV), first, a wetting agent and water are added, then the composite iii is added, and then a lithium compound, a manganese compound and / or an iron compound, and a phosphoric acid compound are added to obtain slurry water c.

7. The method for producing lithium-based polyanion particles for a secondary battery positive electrode active material according to claim 5 or 6, wherein the wetting agent is one or more selected from polyether ester amine, polyether phosphate ester amine, and polyether phosphate ester.

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