JP2022156472A - Positive electrode active material particles for lithium ion secondary battery and method for manufacturing the same - Google Patents

Abstract

To provide positive electrode active material particles for lithium ion secondary batteries that can effectively suppress side reactions during charge/discharge cycles of the 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 represent numerical values satisfying 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, the contents of Mn and Fe increase from the center to the surface, and a pore volume in a pore diameter range of 0.5 nm to 20 nm ranges from 0.005 cm3/g to 0.035 cm3/g.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to positive electrode active material particles for lithium ion secondary batteries exhibiting good cycle characteristics and a method for producing the same.

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. Lithium-based polyanion particles such as LiMn _x Fe _1-x PO ₄ are considered promising as positive electrode materials for such lithium ion secondary batteries because of their high safety and high capacity. On the other hand, lithium-based polyanion particles have low conductivity, and further improvements are still required in order to sufficiently improve the battery characteristics of the resulting lithium-ion secondary battery. Therefore, various developments have been made.

For example, Patent Document ₁ discloses an electrode material that is an aggregate of an electrode active material ₍ such as _{LiaAxMyPO4 )} coated with a specific carbonaceous film, and an ionic organic substance is used as a carbon source. is used to suppress particle growth and sintering of the electrode active material, thereby improving cycle characteristics. Further, in Patent Document 2, a carbon material such as a fibrous carbon material or a chain carbon material and a lithium-containing phosphate (such as LiMn _x Fe _1-x PO ₄ ) are included, and the carbon material is used as a starting point. Composite particles having pores communicating with each other have been disclosed, and attempts have been made to improve the rate characteristics of batteries and improve cycle characteristics and the like.

JP 2020-053291 A JP 2018-139213 A

However, in the electrode active material described in Patent Document 1 and the composite particles described in Patent Document 2, when producing a positive electrode, liquid agents such as solvents and binders used for preparing the mixture layer are easily absorbed, and the mixture is The adhesion strength of the layer to the current collector is likely to decrease, and there is a high possibility that the composite material layer will peel off during charging and discharging cycles of the lithium ion secondary battery, and there is still room for improvement in sufficiently improving the cycle characteristics.

Accordingly, an object of the present invention is to effectively suppress side reactions during charge/discharge cycles of a lithium ion secondary battery and effectively improve the cycle characteristics of the lithium ion secondary battery. The object of the present invention is to provide positive electrode active material particles and a method for producing the same.

Therefore, the present inventors have made intensive studies to solve the above problems. In the following battery, it was found that the cycle characteristics were effectively improved.

That is, the present invention provides the following formula (A):
_{LiaMnbFecMxPO4 ( 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; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
Lithium-based polyanion particles supported by carbon derived from cellulose nanofibers and having an increasing content of Mn and Fe from the center to the surface,
Disclosed is a lithium-based polyanion particle for secondary battery positive electrode active material having a pore volume of 0.005 cm ³ /g to 0.035 cm ³ /g in the pore diameter range of 0.5 nm to 20 nm.

The present invention also provides the following steps (I) to (IV):
(I) Step of mixing a lithium compound, a phosphate compound and water or mixing trilithium phosphate particles and water to obtain preliminary particles i (II) Obtained preliminary particles i and cellulose nanofibers , and after adding water to obtain slurry water a, a step of spray drying to obtain granules ii (III) Step of calcining the obtained granules ii to obtain composite iii (IV ) The obtained composite iii, a metal compound containing a manganese compound and/or an iron compound, a phosphoric acid compound, a wetting agent, and water are added to obtain a slurry water b, which is then subjected to a hydrothermal reaction to obtain a composite obtaining iv;
The amount of the wetting agent added in the step (IV) is 0.01 parts by mass to 4 parts by mass with respect to 100 parts by mass of the composite iii. It provides.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention effectively suppress the absorption of liquid agents such as solvents and binders used for preparing the mixture layer, so that the cycle characteristics of the lithium ion secondary battery are effectively improved. It is possible to realize a positive electrode material that can be improved to

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the cross section which passes through the center of the lithium type polyanion particle for secondary battery positive electrode active materials of this invention.

The present invention will be described in detail below.
The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention have the following formula (A):
_{LiaMnbFecMxPO4 ( 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; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
Lithium-based polyanion particles supported by carbon derived from cellulose nanofibers and having an increasing content of Mn and Fe from the center to the surface,
The pore volume in the pore diameter range of 0.5 nm to 20 nm is 0.005 cm ³ /g to 0.035 cm ³ /g.

That is, the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention are formed by firmly supporting carbon derived from cellulose nanofibers and increasing the contents of Mn and Fe from the center toward the surface. , And as the specific pore volume is shown in the specific pore size range, particles in which the abundance of Mn and Fe gradually decreases from the vicinity of the surface to the vicinity of the center, that is, the abundance of Mn and Fe is greater than that in the center Particles with a high surface.
Thus, in the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention, the primary particles constituting such particles support carbon derived from cellulose nanofibers, and the secondary battery positive electrode corresponds to secondary particles. Since Mn and Fe are densely present as they approach the surface of the lithium-based polyanion particles for the active material, they have surface properties that make it difficult to absorb liquid agents such as solvents and binders used in preparing the composite layer, resulting in lithium ion secondary It is believed that this effectively improves the cycle characteristics of the battery.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention have the following formula (A):
_{LiaMnbFecMxPO4 ( 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; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
is represented by

That is, the lithium-based polyanion particles for secondary battery positive electrode active material represented by the formula (A) are lithium-based polyanion particles for secondary battery positive electrode active material containing at least manganese (Mn) or iron (Fe) (hereinafter referred to as Also referred to as "particles (A)"), which are secondary particles formed by agglomeration 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 is 0<a≤1.2, preferably 0.6≤a≤1.2, more preferably 0.65≤a≤1.15, still more preferably 0.7≤ a≤1.1. b is 0≤b≤1.2, preferably 0.25≤b≤0.8, more preferably 0.35≤b≤0.8. c is 0≤c≤1.2, preferably 0.2≤c≤0.75, more preferably 0.2≤c≤0.65. These b and c satisfy b+c≠0. x is 0≤x≤0.3, preferably 0≤x≤0.15, more preferably 0≤x≤0.1. These a, b, c, and x are numbers satisfying a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.
More specifically, the particles ₍ A) represented by the above formula ₍ A) include, for _example , _LiMnPO4 , _LiFePO4 , _{LiMn0.8Fe0.2PO4 , LiMn0.7Fe0.3PO4 , LiMn0.1Fe0.9PO4 , LiMn0.8Fe0.1Mg0.1PO4 , LiMn0.8Fe0.1Zr0.05PO4 , and the like .}

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention are represented by the above formula (A) and carry carbon derived from cellulose nanofibers. Such cellulose nanofibers are carbonized to become carbon, which is supported on the surfaces of the primary particles so as to fill part of the interstices of the primary particles constituting the particles (A), and also on the surfaces of the particles (A). Firmly supported. Cellulose nanofibers are a skeletal component that accounts for about 50% of all plant cell walls, and are lightweight, high-strength fibers that can be obtained by defibrating plant fibers that make up the cell walls to nanosize. Such cellulose nanofibers have a fiber diameter of 1 nm to 1000 nm and have good dispersibility in water. In addition, since the cellulose molecular chains constituting the cellulose nanofibers have a periodic structure of carbon, they are carbonized and firmly supported on the particles (A). Although the abundance of Fe and Fe is reduced, the particles (A) as a whole can ensure the expression of excellent battery characteristics.

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 partially fill the interstices of the primary particles constituting the particles (A), It is also firmly supported on the surface of the particles (A). Examples of such water-soluble carbon materials include one or more selected from sugars, 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; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol and butane. polyols and polyethers such as diols, propanediol, polyvinyl alcohol and glycerin; and organic acids such as citric acid, tartaric acid and ascorbic acid. Among these, glucose, fructose, sucrose, and dextrin are preferred, and glucose is more preferred, from the viewpoint of enhancing solubility and dispersibility in a solvent and effectively functioning as a carbon material.

The atom-equivalent amount of carbon derived from carbonized cellulose nanofibers carried on the particles (A), that is, the amount of carbon derived from cellulose nanofibers carried is the lithium-based positive electrode active material for secondary batteries of the present invention. In 100% by mass of polyanion particles, preferably 0.9% by mass to 1.4% by mass, more preferably 0.8% by mass to 1.3% by mass, still more preferably 0.9% by mass to It is 1.2% by mass.
The atom-equivalent amount (supported amount) of carbon derived from cellulose nanofibers present in the particles (A) is obtained by measurement using a carbon/sulfur analyzer.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention have a pore volume of 0.005 cm ³ /g to 0.035 cm ³ /g in a pore diameter range of 0.5 nm to 20 nm. As described above, the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention constitute the particles (A) in order to have a surface property that makes it difficult to absorb liquid agents such as solvents and binders used for preparing the mixture layer. It has a unique shape in which the primary particles are densely present. Therefore, the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention contain an appropriate amount of Mn and Fe as a whole particle while the amount of Mn and Fe is reduced from the surface toward the center, and are combined. It can have surface properties that make it difficult to absorb liquid agents such as solvents and binders used for preparing the material layer.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention have a particle size of 0.5 nm to 20 nm from the viewpoint of ensuring the expression of excellent battery characteristics. The pore volume in the pore diameter range is 0.005 cm ³ /g to 0.035 cm ³ /g, preferably 0.005 cm ³ /g to 0.030 cm ³ /g, more preferably 0.005 cm ³ /g to 0.025 cm ³ /g.
The pore volume in the pore diameter range of 0.5 nm to 20 nm means the value measured by the BET multipoint method.

Specifically, as shown in FIG. 1, the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention are obtained by dividing a cross section 1 passing through the center 2 of the lithium-based polyanion particles into two equal halves of the radius 3 of the cross section 1. A circle 5 formed by continuous points 4 is a boundary, and when the cross section X including the center 2 of the lithium-based polyanion particle and the cross section Y including the surface of the lithium-based polyanion particle are divided into two, Mn and Fe in the cross section X The ratio (x/A) between the content x and the content A of Mn and Fe in the lithium-based polyanion particles is 0.85 to 0.99, and the content y of Mn and Fe in the cross section Y and the lithium-based The ratio (y/A) of the content A of Mn and Fe in the polyanion particles is preferably 1.01 to 1.15.
Thus, in the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention, the content A of Mn and Fe in the lithium-based polyanion particles in the cross section 1 is different from the content A of Mn and Fe in the cross section X including the center 2. The content y of Mn and Fe in the cross section Y including the surface is higher than the content x, and Mn and Fe are densely present as it approaches the surface of the lithium-based polyanion particles for secondary battery positive electrode active material, and the mixture It has a surface property that makes it difficult to absorb liquid agents such as solvents and binders used for layer preparation.

The content of Mn and Fe in the lithium-based polyanion particles for secondary battery positive electrode active material is Mn when the total amount of Mn, Fe, and P analyzed by X-ray fluorescence analysis (XRF) is 100% by mass. and the total amount of Fe (% by mass). In addition, the content of Mn and Fe in the cross section X and the cross section Y is 100% by mass of the total amount of Mn, Fe, and P analyzed by an energy dispersive X-ray spectrometer (EDX) of a scanning electron microscope (SEM). Means the total amount (% by mass) of Mn and Fe when .

The ratio (x/A) of the content x of Mn and Fe in the cross section X to the content A of Mn and Fe in the lithium-based polyanion particles is preferably 0.85 to 0.99, more preferably 0. 85 to 0.97, more preferably 0.85 to 0.95. In addition, the ratio (y/A) of the content y of Mn and Fe in the cross section Y to the content A of Mn and Fe in the lithium-based polyanion particles is preferably 1.01 to 1.15, more preferably It is 1.03 to 1.15, more preferably 1.05 to 1.15.

The average particle diameter of the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention is preferably 10 μm to 40 μm, more preferably 10 μm to 35 μm, from the viewpoint of effectively improving the cycle characteristics of the resulting battery. , more preferably 10 μm to 30 μm.
The average particle size means the D ₅₀ value (particle size at cumulative 50% (median diameter)) obtained from a volume-based particle size distribution based on a laser diffraction/scattering method.

The tap density of the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention is such that Mn and Fe are densely present from the center to the surface, but the particles (A) as a whole exhibit excellent battery characteristics. ^From the ^viewpoint of ^{ensuring the} cm ³ to 1.9 g/cm ³ .
The tap density means "tap bulk density" measured by the method specified in JIS R 1628 "Method for measuring bulk density of fine ceramic powder".

The BET specific surface area of the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention is such that the contents of Mn and Fe increase from the center to the surface, but the particles (A) as a whole have excellent battery characteristics. is preferably from 10 m ² /g to 23 m ² /g, more preferably from 10 m ² /g to 20 m ² /g, and even more preferably from 10 m ² /g to 17 m ² /g. be. The BET specific surface area can be measured using, for example, a flow-type automatic specific surface area measuring device (FlowSorb III 2305, manufactured by Shimadzu Corporation) under the conditions of a nitrogen-helium mixed gas containing 30% nitrogen.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention are prepared by the following steps (I) to (IV):
(I) Step of mixing a lithium compound, a phosphate compound and water or mixing trilithium phosphate particles and water to obtain preliminary particles i (II) Obtained preliminary particles i and cellulose nanofibers , and after adding water to obtain slurry water a, a step of spray drying to obtain granules ii (III) Step of calcining the obtained granules ii to obtain composite iii (IV ) The obtained composite iii, a metal compound containing a manganese compound and/or an iron compound, a phosphoric acid compound, a wetting agent, and water are added to obtain a slurry water b, which is then subjected to a hydrothermal reaction to obtain a composite obtaining iv;
It can be obtained by a production method in which the amount of the wetting agent added in step (IV) is 0.01 to 4 parts by mass with respect to 100 parts by mass of composite iii.

In this way, by first going through the step (I), preliminary particles i, which are trilithium phosphate particles as nuclei of primary particles constituting the particles (A), are formed in the slurry, or Lithium particles and water are mixed to prepare a slurry containing preliminary particles i, and then through steps (II) to (III), Mn and Mn are produced while supporting carbon derived from cellulose nanofibers around the preliminary particles i. A composite iii in which Fe is moderately present can be obtained. After that, through step (IV), primary particles are formed while allowing Mn and Fe to permeate the interior of composite iii, coupled with the intervention of a wetting agent, and these aggregate to form composite iv. Thus, it is possible to obtain lithium-based polyanion particles for secondary battery positive electrode active material that have surface properties that make it difficult to absorb liquid agents such as solvents and binders used in the preparation of mixture layers of lithium ion secondary batteries.

Step (I) provided in the production method of the present invention is a step of mixing a lithium compound, a phosphate compound and water, or mixing trilithium phosphate particles and water to obtain preliminary particles i.

In step (I), when a lithium compound, a phosphate compound, and water are mixed, examples of the lithium compound include hydroxides (e.g., LiOH.H ₂ O, LiOH), carbonates, sulfates, and acetates. . Among them, hydroxide is preferable.
Phosphoric acid compounds include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Among them, it is preferable to use phosphoric acid, and it is preferable to use it as an aqueous solution having a concentration of 70% by mass to 90% by mass.
In slurry water obtained by mixing a lithium compound, a phosphate compound, and water, the content of the lithium compound with respect to 100 parts by mass of water is preferably 5 parts by mass to 50 parts by mass, more preferably 7 parts by mass to 45 parts by mass.

Furthermore, in the step (I), when phosphoric acid is used as the phosphoric acid compound, it is preferable to add the phosphoric acid dropwise while stirring the slurry water when mixing the phosphoric acid into 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 still more preferably 28 mL/min to 40 mL/min. The stirring time of the slurry water while dropping the phosphoric acid is preferably 0.5 hours to 24 hours, more preferably 3 hours to 12 hours. Furthermore, the stirring speed of the slurry water while dropping the phosphoric acid is preferably 200 rpm to 700 rpm, more preferably 250 rpm to 600 rpm, and still more preferably 300 rpm to 500 rpm.
Further, it is preferable to use phosphoric acid as the phosphoric acid compound, and add the phosphoric acid dropwise while stirring the slurry water when mixing the phosphoric acid. By adding phosphoric acid dropwise to the mixed liquid little by little, the reaction proceeds favorably in the slurry water, and the preliminary particles i are generated while being uniformly dispersed in the slurry water, and the preliminary particles i aggregate unnecessarily. can also be effectively suppressed.
In addition, when stirring the slurry water, it is preferable to further cool the slurry water to a boiling point temperature or lower. Specifically, cooling to 80°C or lower is preferable, and cooling to 20°C to 60°C is more preferable.

The slurry water after mixing the phosphoric acid compound preferably contains 2.7 mol to 3.3 mol, more preferably 2.8 mol to 3.1 mol, of lithium per 1 mol of phosphoric acid. Preferably, the lithium compound and the phosphoric acid compound are used in such amounts.

By purging nitrogen into the slurry water after mixing the phosphoric acid compound, the reaction in the mixed solution is completed, and the trilithium phosphate particles as nuclei of the primary particles constituting the particles (A) can be obtained as a slurry. When the nitrogen is purged, the reaction can proceed with the dissolved oxygen concentration in the slurry water being reduced, and the dissolved oxygen concentration of the obtained slurry containing the complex X is also effectively reduced. Oxidation of the metal salt added in step (IV) described below can be suppressed. Such preliminary particles i are obtained as fine dispersed particles of trilithium phosphate (Li ₃ PO ₄ ).
The obtained preliminary particles i may be isolated by filtering, washing with water and drying, or may be used as a slurry containing the preliminary particles i in the subsequent step (II). Freeze drying and vacuum drying are used as drying means.

When the trilithium phosphate particles and water are mixed in step (I), the preliminary particles i are obtained as a slurry containing them. A slurry containing such preliminary particles i may be used as it is in the subsequent step (II) as the preliminary particles i obtained in step (I).
In this case, the content of the preliminary particles i in the slurry is preferably 3% by mass to 50% by mass, more preferably 5% by mass to 45% by mass.

Step (II) is a step of adding preliminary particles i obtained in step (I), cellulose nanofibers, and water to obtain slurry water a, followed by spray drying to obtain granules ii. be. Here, cellulose nanofibers are used, and through subsequent steps, the cellulose nanofibers are carbonized, and carbon derived from the cellulose nanofibers is supported on the preliminary particles i corresponding to the nuclei of the primary particles constituting the particles (A). be able to.
The cellulose nanofibers that can be used in step (II) are as described above.

The content of the cellulose nanofibers in the slurry water a is preferably 0.5 parts by mass to 5 parts by mass, more preferably 0.5 parts by mass to 100 parts by mass, in terms of the amount of carbonization residue per 100 parts by mass of water. 4.5 parts by mass, more preferably 0.5 to 4.0 parts by mass.

The solid content concentration of the slurry water a is preferably 40% to 70% by mass, more preferably 45% to 70% by mass, still more preferably 50% to 70% by mass.
When the preliminary particles i obtained in the step (I) are used as a slurry, the amount of water added in the step (II) may be appropriately adjusted so that the solid content concentration of the slurry water a is such an amount. good.

After adding the water, it is preferred to pre-stir the slurry water a before subjecting it to spray drying. The stirring time of the slurry water a is preferably 3 minutes to 60 minutes, more preferably 5 minutes to 30 minutes. The temperature of the slurry water a is preferably 10°C to 60°C, more preferably 20°C to 40°C.

The resulting slurry water a is then spray-dried to obtain granules ii. In spray drying, operating conditions may be appropriately set according to the equipment used.
For example, as the treatment conditions with a micro mist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a 4-fluid nozzle, the hot air temperature is preferably 110 ° C. to 300 ° C., and 150 ° C. to 250 ° C. is more preferred. Further, the volume ratio of hot air supply to slurry water supply (hot air supply/slurry water supply) is preferably 500 to 10,000, more preferably 1,000 to 9,000.

Step (III) is a step of firing the granules ii obtained in step (II) to obtain a composite iii. The firing conditions in step (III) are preferably 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 is preferably 0.5 hours to 12 hours, more preferably 1 hour to 6 hours.

In step (IV), the complex iii obtained in step (III), a metal compound containing a manganese compound and/or an iron compound, a phosphoric acid compound, a wetting agent, and water are added to obtain slurry water b. , drying to obtain the composite iv, wherein the amount of the wetting agent added is 0.01 to 4 parts by weight with respect to 100 parts by weight of the composite iii. As a result, Mn and Fe can be densely present around the composite iii, the contents of Mn and Fe can be increased from the center to the surface of the composite iv, and the wetting agent is used in a specific amount. As a result, the primary particles are formed while allowing Mn and Fe to permeate the interior of the composite iii, and dense agglomeration of the primary particles can be effectively promoted.

The same phosphoric acid compound as used in step (I) may be used.
As a metal compound containing a manganese compound and/or an iron compound, a metal (M) compound can be used in addition to the manganese compound and the iron compound.
Manganese compounds that can be used include manganese acetate, manganese nitrate, manganese sulfate, and the like. These may be used individually by 1 type, and may be used in combination of 2 or more types. Among them, manganese sulfate is preferable from the viewpoint of improving battery characteristics.
Iron compounds that can be used include iron acetate, iron nitrate, iron sulfate, and the like. These may be used individually by 1 type, and may be used in combination of 2 or more types. Among them, iron sulfate is preferable from the viewpoint of improving battery characteristics.
Usable metal (M) compounds include sulfates, nitrates, acetates, etc. containing the same metal as M in the above formula (A). Among them, sulfate is preferable from the viewpoint of improving battery characteristics.

The amount of the metal compound containing the manganese compound and/or the iron compound added is preferably 200 parts by mass to 600 parts by mass, more preferably 250 parts by mass to 550 parts by mass, with respect to 100 parts by mass of the composite iii. , and more preferably 300 to 500 parts by mass. The molar ratio of the manganese compound and the iron compound (manganese compound:iron compound) is preferably 80:20 to 20:80, more preferably 80:20 to 30:70, still more preferably 80: 20-35:65.
The amount of the phosphoric acid compound added is preferably 50 parts by mass to 300 parts by mass, more preferably 70 parts by mass to 250 parts by mass, and still more preferably 90 parts by mass to 100 parts by mass of the complex iii. 200 parts by mass.

As the wetting agent, one or more selected from polyetherester amine, polyether phosphate amine, and polyether phosphate may be used. Among them, amine polyether ester acid is preferable from the viewpoint of increasing the content of Mn and Fe from the center toward the surface while effectively promoting dense aggregation of the primary particles.
The amount of the wetting agent added is 0.01 to 4 parts by mass, preferably 0.1 to 4 parts by mass, more preferably 0.5 parts by mass, per 100 parts by mass of the composite iii. parts by mass to 4 parts by mass.
The added wetting agent is burnt out and does not remain in the obtained particles (A) through step (IV) described later.

In the step (IV), the order of addition of the complex iii, the metal compound containing the manganese compound and/or the iron compound, the phosphoric acid compound, the wetting agent, and water is such that the addition of the wetting agent can fully exert its effect, and the From the viewpoint of effectively obtaining particles (A) in which the contents of Mn and Fe increase toward the surface, first a wetting agent and water are added, then the complex iii is added, and then a manganese compound and / or iron It is preferable to add a compound and a phosphoric acid compound to obtain slurry water b.

The solid content concentration of the slurry water b is preferably 5% by mass to 50% by mass, more preferably 8% by mass to 45% by mass, and still more preferably 10% by mass to 40% by mass.
The other conditions for stirring the slurry water b before being subjected to the hydrothermal reaction are the same as the conditions for stirring the slurry water a before being subjected to spray drying in step (II), and may be selected as appropriate. good.

Next, in step (IV), the resulting slurry water b is subjected to a hydrothermal reaction to obtain complex iv. The hydrothermal reaction may be performed at 100°C or higher, preferably from 130°C to 200°C. The hydrothermal reaction is preferably carried out in a pressure vessel, and 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 the reaction is carried out at 140°C to 160°C. The pressure when carrying out is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 to 48 hours, more preferably 0.2 to 24 hours.
The obtained complex iv is isolated by filtering, washing with water, and drying to obtain the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention. Freeze drying and vacuum drying are used as drying means.

The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention are materials used as a positive electrode active material for lithium ion secondary batteries. Specifically, for example, the lithium-based polyanion particles for secondary battery positive electrode active material of the present invention, acetylene black, Ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, etc. are kneaded to prepare a positive electrode slurry. After that, it is applied to a current collector and then press-molded to produce a positive electrode. The lithium-based polyanion particles for secondary battery positive electrode active material of the present invention have a higher Mn and Fe content in the surface than in the center, and the solvent, binder, etc. used for preparing the composite layer of the lithium ion secondary battery. Since it has a surface property that makes it difficult to absorb liquid agents, it exhibits excellent adhesion strength of the mixture layer to the current collector, and effectively suppresses peeling of the mixture layer during charge-discharge cycles of the resulting lithium-ion secondary battery. , the cycle characteristics can be effectively improved.

As a lithium ion secondary battery to which the positive electrode obtained using the lithium-based polyanion particles for a secondary battery positive electrode active material of the present invention can be applied, a positive electrode, a negative electrode, an electrolytic solution and a separator, or a positive electrode, a negative electrode and a solid electrolyte are used. It is not particularly limited as long as it is an essential configuration.

Here, as for the negative electrode, as long as it can absorb lithium ions during charging and release lithium ions during discharging, the material composition is not particularly limited, and a known material composition can be used. For example, lithium metal, graphite, silicon-based (Si, SiOx), lithium titanate, carbon materials such as amorphous carbon, and the like can be used. It is preferable to use an electrode made of an intercalate material capable of electrochemically intercalating and deintercalating 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 can be used.

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 that is usually used in the electrolyte of a lithium ion secondary battery, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones. , oxolane compounds and the like can be used.

The type of supporting salt is not particularly limited, but inorganic salts selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , 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 )(SO ₂ C ₄ F ₉ ), and derivatives of said organic salts. is preferably at least one of

The separator serves to electrically insulate the positive electrode and the negative electrode and retain the electrolyte. For example, a porous synthetic resin film, particularly a porous film of polyolefin polymer (polyethylene, polypropylene) may be used.

The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. _{For example , La0.51Li0.34TiO2.94 , Li1.3Al0.3Ti1.7 ( PO4 ) 3 , Li7La3Zr2O12 , 50Li4SiO4.50Li3BO3 , Li2.9PO3.3N0.46 , Li3.6Si _ _ 0.6P0.4O4 , Li1.07Al0.69Ti1.46 ( PO4 ) 3 , Li1.5Al0.5Ge1.5 ( PO4 ) 3 , Li10GeP2S12 , Li3.25Ge0.25P0.75S4 , 30Li2S . _ 26B2S3.44LiI , 63Li2S.36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 70Li2S.30P2S5 , 50Li2S.50GeS2 , Li7P _ _ _ _ _ 3} S ₁₁ and Li _3.25 P _0.95 S ₄ may be used.

The shape of the lithium-ion secondary battery having the above configuration is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, a square shape, or an irregular shape enclosed in a laminated outer package. .

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.
The amount of carbon converted to atoms (supported amount) and the average particle size of the obtained lithium-based polyanion particles were measured by the following methods.

<<Atom equivalent amount of carbon (supported amount)>>
Using a carbon/sulfur analyzer (EMIA-220V2, manufactured by Horiba Ltd.), the atomic equivalent amount of carbon (supported amount) of the obtained lithium-based polyanion particles was measured.

《Average particle diameter》
The particle size distribution of the resulting lithium-based polyanion particles was measured using a laser diffraction device (Microtrac MT3000II, manufactured by MicrotracBEL) to determine the average particle size ( _D50 ).

[Example 1]
1272 g of LiOH.H ₂ O and 4 L of water were mixed to obtain a slurry. Next, while the resulting slurry is maintained at a temperature of 25° C. and stirred for 3 minutes, 1153 g of an 85% aqueous solution of phosphoric acid is added dropwise at 35 mL/min, and stirred at a speed of 400 rpm for 12 hours to obtain preliminary particles i-1. A slurry containing (Li ₃ PO ₄ ) was obtained. The resulting slurry was filtered, washed with water and dried with hot air at 80° C. for 12 hours to isolate preliminary particles i-1.
1158 g of the obtained preliminary particles i-1 was taken, 3 L of water was added thereto, and then 2114 g of cellulose nanofiber (Celish KY-100G, manufactured by Daicel Finechem, fiber diameter 4 nm to 100 nm) was added, A slurry a1 was obtained. The obtained slurry a1 was dispersed for 2 minutes with an ultrasonic stirrer (T25, manufactured by IKA) to uniformly color the whole, and then a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) was used. Then, it was spray-dried (nozzle air flow rate: 52 L/min, supply air temperature: 180°C) to obtain granules ii-1.

The resulting granules ii-1 were sintered at 650° C. for 30 minutes in an argon-hydrogen atmosphere (hydrogen concentration: 3%) to obtain a composite iii-1. 585 g of the obtained complex iii-1 was taken, and 0.06 g of polyether ester acid amine (Disparlon DA-234, manufactured by Kusumoto Kasei Co., Ltd.) (per 100 parts by mass of complex iii-1, 0.06 g) was added. 01 parts by mass) and 5 L of water, and then 2415 g of MnSO ₄ .5H ₂ O, 1251 g of FeSO ₄ .7H ₂ O, and 1153 g of an 85% aqueous solution of phosphoric acid are added to prepare slurry water b1. Obtained.
Next, the obtained slurry water b1 was charged into an autoclave and hydrothermally reacted at 170° C. for 2 hours. The pressure inside the autoclave was 0.3 MPa. After the hydrothermal reaction, the crystals produced 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 lithium-based polyanion particles (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1 mass %, average particle size: 15 μm).

[Example 2]
Lithium-based polyanion particles ( LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1% by mass, average particle size: 15 μm).

[Example 3]
Lithium-based polyanion particles ( LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1% by mass, average particle size: 14 μm).

[Example 4]
Lithium-based polyanion particles ( LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1% by mass, average particle size: 14 μm).

[Example 5]
Lithium-based polyanion particles (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1% by mass, average particle size: 13 μm).

[Comparative Example 1]
Lithium-based polyanion particles (LiMn _0.7 Fe _0.3 PO ₄ , amount of carbon supported=1.1% by mass, average particle size: 16 μm) were added in the same manner as in Example 1, except that no polyether ester acid amine was added. Obtained.

<<Measurement of pore volume in the pore diameter range of 0.5 nm to 20 nm>>
Using each of the obtained lithium-based polyanion particles, the pore volume (cm ³ /g) in the pore diameter range of 0.5 nm to 20 nm was measured by the BET multipoint method using BELSORP MINI X (manufactured by Shimadzu Corporation). did.
Table 1 shows the results.

<<Ratio (x/A) between the Mn and Fe content x in the cross section X and the Mn and Fe content A in the lithium-based polyanion particles, and the Mn and Fe content y in the cross section Y and the lithium-based polyanion particles Calculation of the ratio (y/A) to the content A of Mn and Fe>>
Using each of the obtained lithium-based polyanion particles, the total amount of Mn and Fe (mass% ) was calculated as A. Also, using each lithium-based polyanion particle obtained, a cross section passing through the center of the particle is cut out with a laser cutter, and the average value in 10 fields of view of 500 nm × 500 nm with SEM-EDX (manufactured by JEOL Ltd., JSM-7900F). x and y were calculated as the total amount (% by mass) of Mn and Fe when the total amount of Mn, Fe, and P analyzed was 100% by mass.
Table 1 shows the results.

<<Evaluation of the presence or absence of impurities>>
Using each of the obtained lithium-based polyanion particles, an X-ray diffraction pattern (D8 ADVANCE manufactured by BRUKER) was used to obtain an X-ray diffraction pattern at 2θ = 10 to 80 °, and then Li at 2θ = 23.8 ° The presence or absence of impurities was evaluated from the presence or absence of peaks derived from ₃ PO ₄ .
Table 1 shows the results.

《Calculation of the amount of adsorbed water》
Using each of the obtained lithium-based polyanion particles, the amount of adsorbed water ( %).
Table 1 shows the results.

《Evaluation of battery characteristics (cycle characteristics)》
Using each lithium-based polyanion particle obtained, a positive electrode for a lithium-ion secondary battery was first produced. Specifically, the obtained particles, Ketjenblack, and polyvinylidene fluoride are mixed at a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone is added and kneaded sufficiently to obtain a positive electrode. A slurry was prepared. The positive electrode slurry was applied to a current collector made of aluminum foil having a thickness of 20 μm using a coating machine, and vacuum-dried at 80° C. for 12 hours. After that, the current collector coated with the positive electrode slurry was pressed at 20 kN using a roll press, and punched into a disk shape of φ14 mm to obtain a positive electrode.
Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched into a diameter of φ15 mm was used as the negative electrode. The electrolytic solution used was obtained by dissolving LiPF ₆ at a concentration of 1 mol/L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7. A polymer porous film was used as the separator. These battery parts were incorporated and housed in an atmosphere with a dew point of -50°C or less by a conventional method to obtain a coin-type secondary battery (CR-2032).
Cycle characteristics were evaluated using the obtained secondary battery. Specifically, a constant current charge at a current density of 170 mA/g and a voltage of 4.5 V and a constant current discharge at a current density of 85 mA/g and a final voltage of 2.0 V are discharged at a current density of 85 mA/g (0.5 CA). asked for capacity. Furthermore, a 100-cycle repeated test was performed under the same charge/discharge conditions, and the capacity retention rate (%) was obtained from the following formula (y). All charge/discharge tests were conducted at 30°C.
Capacity retention rate (%)
= (Discharge capacity after 100 cycles)/(Discharge capacity after 1 cycle) x 100 (y)
Table 1 shows the results.

1: Cross section passing through the center 2 of the lithium-based polyanion particle 2: Center of the lithium-based polyanion particle 3: Radius of the cross section 4: A point that bisects the radius 3 of the cross section 5: A point 4 that bisects the radius 3 of the cross section is continuous circle X: cross section X including the center 2 of the lithium-based polyanion particle
Y: Cross section Y including the surface of the lithium-based polyanion particles

Claims (8)

Formula (A) below:
_{LiaMnbFecMxPO4 ( 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; In addition, a number that satisfies a + (valence of Mn) x b + (valence of Fe) x c + (valence of M) x = 3.)
Lithium-based polyanion particles supported by carbon derived from cellulose nanofibers and having an increasing content of Mn and Fe from the center to the surface,
Lithium-based polyanion particles for secondary battery positive electrode active material having a pore volume of 0.005 cm ³ /g to 0.035 cm ³ /g in a pore diameter range of 0.5 nm to 20 nm. A cross section passing through the center of the lithium-based polyanion particle, with a circle formed by continuously dividing the radius of the cross section into two equal parts, a cross section X including the center of the lithium-based polyanion particle and a cross section including the surface of the lithium-based polyanion particle. When bisected into Y and
The ratio (x/A) of the Mn and Fe content x in the cross section X to the Mn and Fe content A in the lithium-based polyanion particles is 0.85 to 0.99, and the Mn and Fe content in the cross section Y The lithium-based polyanion for a secondary battery positive electrode active material according to claim 1, wherein the ratio (y/A) between the content y and the content A of Mn and Fe in the lithium-based polyanion particles is 1.01 to 1.15. particle. The lithium-based polyanion particles for secondary battery positive electrode active material according to claim 1 or 2, having an average particle size of 10 µm to 40 µm. The secondary according to any one of claims 1 to 3, which has a tap density of 1.0 g/cm ³ to 1.9 g/cm ³ and a BET specific surface area of 10 m ² /g to 23 m ² /g. Lithium-based polyanion particles for battery positive electrode active materials. The lithium-based polyanion particles for secondary battery positive electrode active material according to any one of claims 1 to 4, wherein the amount of carbon derived from cellulose nanofibers is 0.9% by mass to 1.4% by mass. The following steps (I)-(IV):
(I) Step of mixing a lithium compound, a phosphate compound and water or mixing trilithium phosphate particles and water to obtain preliminary particles i (II) Obtained preliminary particles i and cellulose nanofibers , and after adding water to obtain slurry water a, a step of spray drying to obtain granules ii (III) Step of calcining the obtained granules ii to obtain composite iii (IV ) The obtained composite iii, a metal compound containing a manganese compound and/or an iron compound, a phosphoric acid compound, a wetting agent, and water are added to obtain a slurry water b, which is then subjected to a hydrothermal reaction to obtain a composite obtaining iv;
The secondary battery according to any one of claims 1 to 5, wherein the amount of the wetting agent added in step (IV) is 0.01 to 4 parts by mass with respect to 100 parts by mass of composite iii. A method for producing lithium-based polyanion particles for positive electrode active material. 7. The method according to claim 6, wherein in step (IV), the wetting agent and water are first added, then the complex iii is added, and then the manganese compound and/or iron compound and the phosphoric acid compound are added to obtain slurry water b. A method for producing lithium-based polyanion particles for secondary battery positive electrode active material. The lithium-based polyanion for secondary battery positive electrode active material according to claim 6 or 7, wherein the wetting agent is one or more selected from polyetherester amine, polyether phosphate amine, and polyether phosphate. Particle production method.

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