KR101649082B1 - Positive electrode active material, production method for same, positive electrode for non-aqueous electrolyte secondary cell, and non-aqueous electrolyte secondary cell - Google Patents

Abstract

An object of the present invention is to provide a positive electrode active material containing lithium manganese phosphate and having a high discharge capacity and high energy density. In the present invention, a part of the surface of the first particles (3) containing lithium iron phosphate is adhered with second particles (5) having a particle diameter smaller than that of the first particles (3) and containing lithium manganese phosphate The particle (1) as a characteristic is used as a positive electrode active material. It is preferable that the particle diameter of the first particle 3 is 100 nm to 10 m and the particle diameter of the second particle 5 is 200 nm or less. It is preferable that at least a part of the surface of the particle 1 is covered with carbon.

Description

TECHNICAL FIELD The present invention relates to a positive electrode active material, a positive electrode active material, a method for producing the same, a positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, a positive electrode active material,

The present invention relates to a lithium transition metal phosphate active material used in a nonaqueous electrolyte secondary battery.

[0002] With the recent mobilization and high functionality of electronic devices, secondary batteries, which are driving power sources, have become one of the most important components. Particularly, the lithium ion secondary battery has a high energy density obtained at high voltages of the positive electrode active material and the negative electrode active material, and thus has occupied the mainstream of the secondary battery in place of the conventional NiCd battery or Ni hydrogen battery. However, Li ion secondary batteries using a combination of a lithium cobalt oxide (LiCoO ₂ ) based active material and a graphite based carbon based negative active material, which are used in current Li ion batteries, The power consumption can not be sufficiently supplied and the required performance can not be satisfied as a portable power source.

In addition, since lithium cobalt oxide uses rare metal cobalt, there are problems in resource constraints, high cost, and price stability. Further, since lithium cobalt oxide releases a large amount of oxygen at a high temperature of 180 DEG C or more, there is a possibility that an explosion may occur during abnormal heat generation or short-circuiting of the battery.

Therefore, it has been found that a phosphorus transition metal lithium having an olivine structure including iron lithium phosphate (LiFePO ₄ ) and manganese phosphate lithium (LiMnPO ₄ ) superior in thermal stability to lithium cobalt oxide is a material satisfying the resource aspect, .

As a method for synthesizing lithium iron phosphate, a method called a solid phase method is known. The outline of the solid phase method is a method in which powders of lithium source, iron source and phosphorus are mixed and subjected to a firing treatment in an inert atmosphere. This method has a problem that if the firing conditions are not well selected, the composition of the product is not as desired and the control of the particle diameter is difficult.

As a method for synthesizing lithium iron phosphate, a hydrothermal synthesis method using hydrothermal synthesis in a liquid phase is also known. The hydrothermal synthesis is carried out in the presence of hot water at a high temperature and a high pressure. A product having a high purity can be obtained at a much lower temperature than the solid phase method. However, the control of the particle diameter is carried out according to the preparation conditions such as the reaction temperature and the time, and the reproducibility of the particle diameter control is insufficient, and it is difficult to control the particle diameter (see Patent Document 1).

A spray pyrolysis method is a method for synthesizing lithium iron phosphate. The spray pyrolysis method generates fine mist from a mixed solution of a carbon-containing compound, a lithium-containing compound, an iron-containing compound, and a phosphorus-containing compound, and thermally decomposes the generated fine mist by heating while flowing it so that a lithium iron phosphate precursor And the resulting fine powder is heated and fired in an inert gas-hydrogen mixed gas atmosphere to produce a lithium iron phosphate powder containing carbon (refer to Patent Document 2).

In addition, the applicants have developed a spray combustion method capable of continuously and massively synthesizing lithium transition metal lithium having a small particle size and uniform spatial distribution of elements, instead of the solid phase method, the hydrothermal synthesis method and the spray pyrolysis method (see Patent Document 3).

Further, attention is focused on lithium manganese phosphate having a high potential of 4.1 V since the potential of lithium iron phosphate is only 3.4 V, while the potential of lithium cobalt oxide is 3.9 V.

However, the surface of lithium manganese phosphate has a problem that the carbon coating due to the carbonization reaction of the organic material is poor. Thus, there has been reported an electrode active material in which the surface of particles made of lithium manganese phosphate is coated with a coating layer containing lithium iron phosphate (see Patent Document 4).

Also, LiCoPO ₄ and LiNiPO ₄ (However, Ni and Co may be substituted by Ni, Co, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, at least one of Ti and Zr other than the element Ni, Mn, Fe, Mg, Cu, Cr, V, Li, Nb, Ti and Zr in the vicinity of the first positive electrode active material such as Li _{1- x} FePO ₄ And x represents a number of 0 or more and less than 1) (refer to Patent Document 5).

Further, a core-shell type positive electrode active material particle is disclosed in which the core particles and the shell layer include an ortho-phosphoric acid compound containing Fe and / or Mn and Li (see Patent Document 6).

Patent Document 1: International Publication No. 2009/131095 Patent Document 2: JP-A-2009-070666 Patent Document 3: International Publication No. 2012/105637 Patent Document 4: JP-A-2011-181375 Patent Document 5: Japanese Patent Application Laid-Open No. 2011-210693 Patent Document 6: International Publication No. 2012/042727

However, since lithium manganese phosphate has a smaller diffusion coefficient of electron conductivity and lithium ion than lithium iron phosphate, and it is difficult to sufficiently coat carbon on the surface, the positive electrode active material using lithium manganese phosphate has a sufficient discharge capacity .

Further, in the electrode active material described in Patent Document 4, in order to solve the problem of carbon coating, the surface of large lithium manganese phosphate particles is coated with lithium iron phosphate. However, since the diffusion coefficient of lithium ions of lithium manganese phosphate is smaller than that of lithium iron phosphate, there is a problem that lithium ion is not intercalated into the center of large lithium manganese phosphate particles during charging and discharging.

It is also known that lithium iron phosphate (LiFe _x Mn _1-x PO ₄ ) in which an iron atom in a lithium iron phosphate crystal is substituted with a manganese atom in the solid phase method or hydrothermal synthesis method is produced, or simply lithium iron phosphate and phosphoric acid By mixing lithium manganese oxide, a lithium transition metal phosphate having an orthorhombic structure using iron and manganese was obtained. However, this phosphorus transition metal lithium is different from the structure in which lithium manganese phosphate particles are attached to the surface of lithium iron phosphate particles as in the present invention.

In addition, the positive electrode active material described in Patent Document 5 does not aim to utilize lithium manganese phosphate, and the second positive electrode active material particles surrounding the first positive electrode active material are lithium iron phosphate. In addition, the positive electrode active material described in Patent Document 5 may be configured not to contain manganese.

In addition, the positive electrode active material described in Patent Document 6 essentially contains a metal phosphate such as Me _m P _n O _p , and in each embodiment, the same material is used for the core particles and the shell layer.

The present invention has been made in view of the above problems, and an object thereof is to provide a positive electrode active material containing lithium manganese phosphate and having a high discharge capacity and high energy density.

The inventors of the present invention have found that a positive electrode active material having a high energy density can be obtained by disposing lithium manganese phosphate having a small particle size and a low dislocation density but a high potential on the surface of iron phosphate lithium having excellent electron conductivity and high diffusion coefficient of lithium ion I got it. It has also been found that such a positive electrode active material can be obtained by mixing a precursor of lithium iron phosphate with a precursor of lithium manganese phosphate and then sintering.

That is, the present invention has the following features.

(1) A positive electrode active material, characterized in that at least a part of the surface of a first particle mainly containing lithium iron phosphate is attached with a second particle having a particle diameter smaller than that of the first particle and mainly containing lithium manganese phosphate .

(2) The positive electrode active material according to (1), wherein the first particle has a particle diameter of 100 nm to 10 m and the second particle has a particle diameter of 200 nm or less.

(3) The positive electrode active material according to (1), wherein at least a part of the surface of the first particle and / or the second particle is covered with carbon.

(4) A positive electrode for a nonaqueous electrolyte secondary battery, comprising a current collector and an active material layer comprising the positive electrode active material according to (3), on at least one side of the current collector.

(5) A lithium secondary battery comprising a positive electrode for a nonaqueous electrolyte secondary battery according to (4), a negative electrode capable of intercalating and deintercalating lithium ions, and a separator interposed between the positive electrode and the negative electrode, Wherein the negative electrode and the separator are formed on the surface of the non-aqueous electrolyte.

(6) a step of mixing a third particle which is a precursor of lithium iron phosphate and a fourth particle which is a precursor of lithium manganese lithium having a particle diameter smaller than that of the third particle, and further mixing a carbon source, And a step of firing the positive electrode active material.

(7) The method for producing a positive electrode active material according to (6), wherein a mixing ratio of the third particles and the fourth particles is 60:40 to 90:10 by weight.

(8) The method for producing a positive electrode active material according to (6), wherein the particle diameter of the third particle is 100 nm to 10 m and the particle diameter of the fourth particle is 200 nm or less.

(9) The third particle is prepared by a method of supplying a solution containing lithium, iron and phosphorus into a flame together with a delayed gas and a combustible gas in a misty droplet, 4 particle is prepared by a method of supplying a solution containing lithium, manganese and phosphorus into a flame together with a delayed gas and a combustible gas in the form of mist in the form of mist. The positive electrode active material according to (6) Gt;

(10) The process for producing a positive electrode active material according to (6), wherein the carbon source is at least one of polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose, acetyl cellulose, sucrose and carbon black.

According to the present invention, a positive electrode active material containing lithium manganese phosphate and having a high discharge capacity and high energy density can be provided.

1 is a schematic sectional view showing a particle 1 according to the embodiment;
Fig. 2 is a schematic view of a fine particle production apparatus for producing precursor particles by a spray combustion method according to the present embodiment. Fig.
3 is a schematic cross-sectional view of a nonaqueous electrolyte secondary battery using a positive electrode active material according to this embodiment.
Figs. 4 (a) to 4 (c) are SEM photographs of the pre-fired particles according to Examples. Fig.
Fig. 5 (a) is an HAADF-STEM image of the pre-fired particles of the example, and Figs. 5 (b) to 5 (e) are EDS maps of manganese, iron, oxygen and phosphorus at the same observation sites.
Fig. 6 (a) is an HAADF-STEM image seen from a field of view different from that of Fig. 5 of the preformed particles of the embodiment, and Figs. 6 (b) to 6 (d) are EDS maps of manganese, oxygen and phosphorus at the same observation sites.
FIG. 7 (a) is an HAADF-STEM image of the positive electrode active material after firing in the embodiment, and FIGS. 7 (b) to (e) are EDS maps of manganese, iron, oxygen and phosphorus at the same observation sites.
FIG. 8 (a) is a first charge / discharge curve at 25 ° C. of the lithium ion secondary battery using the positive electrode active material according to the embodiment, and FIG. 8 (b) is a graph of discharge capacity when charge and discharge are repeated at 25 ° C.
9 is a first charge / discharge curve of a lithium ion secondary battery using a positive electrode active material according to an embodiment at 60 ° C.
10 is a first charge / discharge curve of a lithium ion secondary battery using the positive electrode active material according to Comparative Example 1 at 25 ° C.
11 is a first charge / discharge curve of a lithium ion secondary battery using a positive electrode active material according to Comparative Example 2 at 25 ° C.

(particle)

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 is a view showing a particle 1 according to the present embodiment. The particle 1 is a particle formed by attaching the second particle 5 to the surface of the first particle 3. The entire surface of the first particle 3 may be covered by the plurality of second particles 5 and only a part of the surface of the first particle 3 may be covered by the second particles 5. [ The powder in which the particles (1) or a plurality of the particles (1) are gathered can be used as a positive electrode active material of a non-aqueous electrolyte secondary battery.

The first particles 3 are particles mainly containing lithium iron phosphate (LiFePO ₄ ). The first particles (3) preferably have a particle diameter of 100 nm to 10 mu m. If the first particles (3) are smaller than 100 nm, the filling density of the powder does not rise when the electrode is used, and the energy density of the electrode is inferior. If the first particles 3 are larger than 10 mu m, the output density as an electrode is inferior. In order to make the second particles cover the surface of the first particles as in the present invention, the particle diameter of the second particles covering the surface of the first particles must be smaller than the particle diameter of the first particles. If the particle diameter of the second particle is smaller than the particle diameter of the first particle, it is difficult to make the surface of the first particle to have a structure covering the surface of the second particle. In the powder having a large number of particles 1, the average particle diameter of the first particles 3 is preferably 100 nm to 10 m, more preferably 200 nm to 2 m.

The second particles 5 are particles mainly containing lithium manganese phosphate (LiMnPO ₄ ). The second particles (5) preferably have a particle diameter of 200 nm or less. If the second particles (5) are too large, the power dissipation as an electrode is insufficient because lithium is not intercalated into the central portion of the particle. The particle size of the second particles is not particularly limited so as to obtain the effect of the present invention, and the lower limit of the particle size is not particularly specified. However, it is preferably at least 5 nm in view of the fact that it is at least about 5 nm in the limit of the process for producing the precursor and the mixing operation with the first particles. In the powder having a large number of particles 1, the average particle diameter of the second particles 5 is preferably 5 nm to 200 nm, more preferably 10 nm to 100 nm.

Also, it mainly means that the ratio of the iron phosphate lithium contained in the first particles 3 is 80% by mass or more with respect to the first particles (3). The ratio of lithium phosphate to lithium is preferably 90% by mass or more. The same applies to the ratio of lithium manganese phosphate contained in the second particles (5).

Further, the ratio of the lithium iron phosphate to the lithium transition metal phosphate contained in the first particles (3) is preferably 80 mass% or more, and more preferably 90 mass% or more.

The surface of the particle 1 may be covered with carbon. That is, at least a part of the surface of one or both of the first particles 3 and the second particles 5 constituting the particles 1 may be covered with carbon. By covering with carbon, the electric conductivity of the particle 1 is increased, and a conductive path to the lithium iron phosphate fine particles or the lithium manganese phosphate fine particles is obtained. Thus, when the particles 1 are used for the positive electrode active material, The electrode characteristics are improved.

The weight ratio of lithium iron phosphate to manganese phosphate in the particle (1) is preferably LiFePO ₄ : LiMnPO ₄ = 60:40 to 90:10. Since the particle diameter of the first particles 3 having a large particle diameter is 100 nm to 10 m and the particle diameter of the second particles having a small particle diameter is 200 nm or less, the iron phosphate (LiFePO ₄ ) (LiMnPO ₄ ) of the second particles 5 adhered to the first particles 3 may not be attached to the entire surface of the first particles 3. If a portion of the surface of the first particle 3 is exposed, fine particles including lithium manganese phosphate whose surface is hardly covered with carbon are easily covered with carbon. When the surface of the first particles 3 is exposed, particles containing the first particles 3 directly come into contact with the electrolyte when charging and discharging, so that the particles 1 are brought into contact with the positive electrode active material The electrode characteristics when used are improved.

Further, a part of PO ₄ may be substituted by another anion. For example, the transition metal acid (TiO ₄ ), chromic acid (CrO ₄ ), vanadium acid (VO ₄ , V ₂ O ₇ ), zirconate (ZrO ₄ ), molybdic acid (MoO ₄ , Mo ₇ O ₂₄ ), tungstic acid (WO ₄ ), etc., or by boric acid (BO ₃ ). By substituting a part of the phosphate ions by these anion species, it contributes to suppression and stabilization of crystal structure change due to the repeating of the elimination and insertion of Li ions, thereby improving cycle life. Further, since such anion species are difficult to release oxygen even at high temperatures, they can be safely used because they do not lead to ignition.

(Positive electrode active material)

The powder in which the particles (1) or the plurality of particles (1) are collected can be used as a positive electrode active material used for a positive electrode for a nonaqueous electrolyte secondary battery.

Since the positive electrode active material according to the present embodiment has a lithium manganese phosphate excellent in potential and energy density attached to the surface of iron phosphate lithium having excellent electron conductivity and lithium ion diffusibility, Can be utilized.

(Positive electrode for non-aqueous electrolyte secondary battery)

In order to form the positive electrode for a nonaqueous electrolyte secondary battery by using the positive electrode active material, a conductive auxiliary such as carbon black is added to the positive electrode active material, if necessary, and a conductive additive such as polytetrafluoroethylene, polyvinylidene fluoride, A binder such as a binder, a dispersant such as butadiene rubber, a cellulose derivative other than carboxymethylcellulose, and the like, and adding it to an aqueous solvent or an organic solvent to prepare a slurry; an aluminum alloy foil containing aluminum in an amount of 95 wt% On one side or both sides, and fired to evaporate the solvent. Thereby, a positive electrode for a nonaqueous electrolyte secondary battery having an active material layer containing a positive electrode active material on the current collector is obtained.

At this time, in order to improve the coating property of the slurry, the adhesion between the current collector and the active material layer, and the current collecting property, a secondary particle assembled by a spray drying method using a positive electrode active material and a carbon source and fired may be contained in the slurry. The mass of the assembled secondary particles becomes a large mass of about 0.5 to 20 占 퐉, which improves the slurry applicability and further improves the characteristics and life of the battery electrode. The slurry used in the spray drying method can be used both as an aqueous solvent and as a non-aqueous solvent.

Then, a slurry containing a positive electrode active material is applied on a current collector such as an aluminum alloy foil, and the positive electrode has a current collecting surface roughness of 10 points defined in Japanese Industrial Standard (JIS B 0601-1994) It is preferable that the average roughness Rz is 0.5 mu m or more. The adhesion between the formed active material layer and the current collector is excellent and the electronic conductivity accompanying the insertion and desorption of Li ions and the current collecting ability to the current collector are increased and the cycle life of charging and discharging is improved.

(Non-aqueous electrolyte secondary battery)

In order to obtain a high-capacity secondary battery using the positive electrode of the present embodiment, various materials such as negative electrode, electrolytic solution, separator, battery case and the like using conventionally known negative electrode active material can be used without particular limitation.

Specifically, the nonaqueous electrolyte secondary battery 31 shown in Fig. 3 is exemplified. The positive electrode 33 and the negative electrode 35 are stacked in the order of the separator-negative electrode-separator-positive electrode with the separator 37 interposed therebetween to form the positive electrode 33 Is wound inward so as to constitute a group of electrode plates, which are inserted into the battery can 41. The positive electrode 33 is connected to the positive electrode terminal 47 through the positive electrode lead 43 and the negative electrode 35 is connected to the battery can 41 through the negative electrode lead 45 to connect the non- The chemical energy generated inside can be converted into electric energy and led out to the outside. Then, the electrolyte 39 is filled in the battery can 41 so as to cover the electrode plate group, and then the upper end (opening) of the battery can 41 is formed with the circular lid plate and the positive electrode terminal 47 thereabove, Can be manufactured by mounting the sealing member (49) having the safety valve mechanism therein through an annular insulated gasket.

The secondary battery using the positive electrode according to the present embodiment has high capacity and good electrode characteristics. However, when a non-aqueous solvent containing fluorine is used or added to an electrolyte using a non-aqueous solvent constituting the secondary battery, The capacity is not sufficiently lowered and the life span is prolonged. For example, particularly in the case of using a negative electrode containing a high-capacity negative electrode active material of silicon type, in order to suppress large expansion and contraction due to dope and dedoping of Li ions, it is preferable to use a nonaqueous solvent containing fluorine in the electrolyte or fluorine as a substituent It is preferable to use an electrolytic solution. The fluorine-containing solvent relaxes the volumetric expansion of the silicon-based coating film due to the alloying with Li ions during charging, especially during the first charging treatment, so that the capacity decrease due to charge and discharge can be suppressed. As the fluorine-containing non-aqueous solvent, fluorinated ethylene carbonate, fluorinated chain-type carbonate, or the like can be used. Mono-tetra-fluoroethylene carbonate (4-fluoro-1,3-dioxolane-2-one, FEC) is used for the fluorinated ethylene carbonate, methyl 2,2,2-trifluoroethyl carbonate , Ethyl 2,2,2-trifluoroethyl carbonate, and the like, which can be used singly or in combination as an additive to an electrolytic solution. Since the fluorine group is easy to bond with silicon and is strong, it is considered that the fluorine group can stabilize the coating even when expanded due to the filling alloy with Li ions, thereby contributing to suppression of expansion.

(Method for producing particles according to the present embodiment)

The particles according to the present embodiment are obtained by mixing a third particle, which is a precursor of lithium iron phosphate, and a fourth particle, which is a precursor of lithium manganese phosphate, and then firing the mixture.

When it is used as a positive electrode active material, it is preferable to coat the surfaces of the particles with carbon. Thus, the positive electrode active material according to the present embodiment is obtained by mixing the third particles and the fourth particles with a carbon source and then firing.

The third and fourth particles are precursor particles of lithium iron phosphate and precursor particles of lithium manganese phosphate respectively synthesized by a spray combustion method such as a flame hydrolysis method or a thermal oxidation method.

(Method for producing precursor particles by spray combustion)

(Preparation of Precursor Particles)

An example of a production apparatus for producing precursor particles by a spray combustion method is shown in Fig. The reaction vessel of the apparatus for producing fine particles 11 shown in Fig. 2 has a structure in which a particulate compounding nozzle 13 is arranged in a vessel and a combustible gas 23, a retarding gas 25 and a raw- Is supplied to the flames. And an exhaust pipe (27) for exhausting produced fine particles and reaction products to the other, and the precursor particles (17) in the exhaust gas are recovered by the particulate recovery filter (15).

The spray combustion method is a method in which a constituent material is fed into a flame together with a retarding gas and a combustible gas by a method of supplying a raw material gas such as chloride or a method of supplying a raw material liquid or a raw material solution through a vaporizer, This is a method for obtaining a target substance. As a spray combustion method, a vapor-phase axial deposition (VAD) method or the like is a suitable example. The temperature of the flame varies depending on the mixing ratio of the flammable gas and the retarding gas and the addition ratio of the constituent materials, but is usually between 1000 and 3000 캜, particularly preferably between 1500 and 2500 캜, Is more preferable. If the flame temperature is low, there is a possibility that the particulates may go out of the flame before the reaction in the flame is completed. In addition, if the flame temperature is high, the crystallinity of the produced fine particles becomes too high, which is likely to be undesirable for the positive electrode active material although it is stable in the subsequent firing step.

In addition, the flame hydrolysis method is a method in which a constituent material is hydrolyzed in a flame. In the flame hydrolysis method, an oxyhydrogen flame is generally used as a flame. Hydrogen gas is supplied as a combustible gas, oxygen gas is supplied as a delayed gas, and raw materials of a positive electrode active material and flame raw materials (oxygen gas and hydrogen gas) are simultaneously supplied from a nozzle to synthesize a target material. In the flame hydrolysis method, fine particles of a target material composed of minute nanoscale, mainly amorphous, can be obtained in an atmosphere filled with an inert gas.

In addition, the thermal oxidation method is a method in which a constituent material is thermally oxidized in a flame. In thermal oxidation processes, hydrocarbon flames are commonly used as flames. A target material is synthesized by simultaneously supplying a constituent material and a flame raw material (for example, propane gas and oxygen gas) from a nozzle to a flame source to which a hydrocarbon gas is supplied as a combustible gas and a flame source to which air is supplied as a delayed gas. Examples of the hydrocarbon-based gas include paraffinic hydrocarbon gases such as methane, ethane, propane and butane, and olefinic hydrocarbon gases such as ethylene, propylene and butylene.

(Constituent material for obtaining precursor particles)

The constituent materials for obtaining the precursor particles of the present embodiment are a lithium source, a transition metal source, and a phosphorus source. When the raw material is a solid, it is supplied in powder form, dispersed in a liquid, or dissolved in a solvent to form a solution, which is supplied to the flame through a vaporizer. In the case where the raw material is a liquid, vaporization may be performed by raising the vapor pressure by heating or by pressure reduction and bubbling before the supply nozzle, in addition to the vaporization through the vaporizer. Particularly, it is preferable to supply a mixed solution of a lithium source, a transition metal source, and a phosphorus into a mist droplet having a diameter of 20 m or less.

Examples of the lithium source include lithium inorganic acid salts such as lithium chloride, lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium bromide, lithium phosphate and lithium sulfate, lithium organic acid salts such as lithium oxalate, lithium acetate and lithium naphthenate, An organic lithium compound such as lithium? -Diketonato compound, lithium oxide, lithium peroxide, or the like can be used. However, naphthenic acid is mainly a mixture of different carboxylic acids mixed with a plurality of acidic substances in petroleum, and the main component is a carboxylic acid compound of cyclopentane and cyclohexane.

In the case of obtaining the third particles as the precursor, ferric chloride, iron oxalate, iron acetate, ferrous sulfate, iron nitrate, iron hydroxide, iron 2-ethylhexanoate and iron naphthenate may be used as the transition metal source . Further, organic metal salts of iron such as stearic acid, dimethyldithiocarbamic acid, acetylacetonate, oleic acid, linoleic acid and linolenic acid, iron oxide and the like are also used depending on the conditions.

In the case of obtaining the fourth particles as the precursor, examples of the transition metal source include manganese chloride, manganese oxalate, manganese acrate, manganese sulfate, manganese nitrate, manganese hydroxide, manganese oxyhydroxide, manganese 2-ethylhexanoate, manganese naphthenate, . Organic metal salts of manganese such as stearic acid, dimethyldithiocarbamic acid, acetylacetonate, oleic acid, linoleic acid and linolenic acid, and manganese oxide are also used depending on the conditions.

Examples of the precursor include phosphorous acid such as phosphorous acid such as phosphorous acid, orthophosphoric acid and metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogenphosphate and ammonium dihydrogenphosphate, various phosphates or pyrophosphates such as ammonium phosphate and sodium phosphate, 1-iron and the like can be used as the transition metal (transition metal).

When a part of the phosphoric acid of the phosphorus-containing transition metal lithium compound is replaced by another anion, a raw material of a transition metal oxide or boric acid is added as an anion source.

Examples of the metal salt include at least one selected from the group consisting of titanium oxide, atitic acid metal salts such as iron titanate and manganese octanoate, zinc titanate, magnesium titanate, titanate such as barium titanate, vanadium oxide, ammonium metavanadate, chromium oxide, Various borates such as manganese oxide, manganese oxide, manganate, cobaltate, zirconium oxide, zirconate, molybdenum oxide, molybdate, tungsten oxide, tungstate, boric acid or diboron trioxide, sodium metaborate, sodium tetraborate, Can be used according to the desired anion source and synthesis conditions, respectively.

These raw materials are supplied to the same reaction system together with the flame raw materials to synthesize precursor particles. The resulting precursor particles can be recovered by a filter from the exhaust. Further, it may be produced around the mandrel as follows. When a silicon or silicon-based mandrel (also referred to as a syringe bar) is provided in the reactor and a source of lithium, a transition metal source and a source of phosphorus are supplied together with the flame raw material in the oxyhydrogen flame or propane flame blown into the reactor, Particles of nano-order are mainly formed on the surface of the mandrel. The produced fine particles are recovered, and in some cases, impurities and cohesive coarse particles are removed by using a filter or a sieve. The precursor particles thus obtained are composed of fine particles having nanoscale extremely fine particle size and mainly amorphous.

In the spray combustion method as a method for producing precursor particles according to the present embodiment, the precursor particles that can be produced are amorphous and the particle size is small. In the spray combustion method, a large amount of synthesis can be performed in a shorter time than the conventional hydrothermal synthesis method and the solid phase method, and homogeneous precursor particles can be obtained at low cost.

(Characteristics of Precursor Particles Obtained by Spray Combustion)

In the present invention, it is possible to obtain a positive electrode active material by mixing third particles and fourth particles as precursors, mixing them with a reducing agent, and firing them. The precursor in the present embodiment is a material capable of obtaining a crystal of a transition metal phosphate by firing. In particular, the precursor in the present embodiment is iron or manganese having a valence of three and an amorphous. However, when the iron or manganese is mixed with a reducing agent and fired, the valence of iron or manganese changes in two directions from trivalent. The composition of the particles containing the iron phosphate lithium or the manganese phosphate lithium constituting the precursor particles is preferably a composition satisfying the stoichiometric composition but is allowed to deviate from the ideal stoichiometric composition due to the inclusion of impurities or the like in a very small amount.

It is preferable that the spatial distribution of the elements in the fine particles constituting the precursor particles is uniform. In particular, it is preferable that there is no imbalance in the spatial distribution of transition metal and phosphorus in the fine particles. Further, the shape of the precursor particles is substantially spherical, and the average aspect ratio (long diameter / short diameter) of the particles is 1.5 or less, preferably 1.2 or less, more preferably 1.1 or less.

However, the term " substantially spherical " means that the particle shape is not limited to a geometrically rigid spherical shape or an elliptical spherical shape, and even if there is a slight protrusion, the surface of the particle may consist of a substantially smooth curved surface.

When the powdery X-ray diffraction of the precursor particles in the range of 2? = 10 to 60 占 is measured, the diffraction peaks show little or no diffraction peaks and exhibit broad diffraction angles. That is, the precursor particles are composed of polycrystalline microparticles in which the crystallites are small microparticles or small single crystals, or in the microcrystalline form in which amorphous components are present around these microparticles.

In the spray combustion method of the present embodiment, since carbon is burned in the flame, the obtained precursor particles do not contain carbon. Even if a carbon component is mixed, it is very small and is not an amount sufficient to become a conductive auxiliary agent when used in a positive electrode.

(Preparation of positive electrode active material)

A third particle which is a precursor of lithium iron phosphate and a fourth particle which is a precursor of lithium manganese phosphate obtained by a spray combustion method are mixed with a carbon source and then fired in an atmosphere filled with an inert gas to obtain a positive electrode active material. In this case, the mixing ratio of the third particles to the fourth particles is preferably 60:40 to 90:10 by weight, and more preferably 70:30. An amorphous compound or an oxide form mixture contained in the precursor particles is changed into a phosphate type transition metal lithium type crystal form compound mainly having an olivine structure by firing. At this time, the particles may be fused to each other at the time of firing, and may include a mixed crystal phase (LiFe _{1- x} Mn _x PO ₄ (0 <x <1)) near the interface of the particles. By forming the horny surface at the bonding interface of the particles in this way, the lattice strain at the bonding interface can be relaxed, as compared with the case where the bonding interface between the third and fourth particles directly constitutes a dichroic interface, Can be stabilized.

It is preferable that the particle diameter of the third particle is 100 nm to 10 m and the particle diameter of the fourth particle is 200 nm or less. Further, the particle diameter of the fourth particle is smaller than that of the third particle. In order to obtain the effect of the present invention, the particle diameter of the fourth particles is not particularly limited, and the lower limit of the particle diameter is not specifically defined. However, in many cases, the particle size is at least about 5 nm at the limit of the production process of the precursor or the mixing operation with the first particles. In the precursor particles and the positive electrode active material, the particle diameters do not change before and after the firing, and the firing of the precursor does not cause fusion and grain growth, and the particle size can be maintained. In the powder having a large number of third particles, the average particle diameter of the third particles is preferably 100 nm to 10 m, more preferably 200 nm to 2 m. In addition, in the powder having a large number of fourth particles, the average particle size of the fourth particles (5) is preferably 5 nm to 200 nm, more preferably 10 nm to 100 nm.

Further, under an atmosphere filled with an inert gas, it is possible to prevent the carbon source from burning at the time of firing and to prevent the positive electrode active material from being oxidized. As the inert gas, a nitrogen gas, an argon gas, a neon gas, a helium gas, a carbon dioxide gas, or the like can be used. In order to increase the conductivity of the product after the heat treatment, a polyvalent alcohol such as polyvinyl alcohol, a polymer such as polyvinylpyrrolidone, carboxymethylcellulose, acetylcellulose, a saccharide such as sucrose, or an organic compound which is a conductive carbon source such as carbon black, The powder is mixed with the third particles and the fourth particles and fired. Polyvinyl alcohol is particularly preferable because it can serve as a binder of pre-fired precursor particles and can reduce iron or manganese during firing.

Coating or supporting treatment with carbon is performed in the same firing step together with crystallization of the precursor particles. The baking conditions of the desired crystallinity and particle diameter can be appropriately obtained by combining the temperature of 300 to 900 占 폚 and the treatment time of 0.5 to 10 hours. An excessive heat load due to a high temperature or a long heat treatment may generate a coarse single crystal and should be avoided and the size of the crystallite can be suppressed as small as possible under heating conditions such that a desired crystalline or microcrystalline phosphate- A preferable heat treatment condition is preferable. The temperature of the heat treatment is preferably about 400 to 700 占 폚. In this case, the fourth particles do not need to be adhered to the entire surface of the third particles, and the fourth particles are well coated with carbon because of the existence of exposed portions on the surface of the third particles containing lithium iron phosphate, do.

However, since the obtained positive electrode active material often aggregates in the firing step, fine particles can be formed again by using induction or a ball milling means.

(Effect of the present embodiment)

According to the present embodiment, since the spray combustion method is used, the positive electrode active material can be continuously synthesized on a large scale.

In addition, since the positive electrode active material according to the present embodiment adheres lithium manganese phosphate excellent in electric potential and energy density to the surface of lithium iron phosphate particles having excellent electron conductivity and lithium ion diffusibility, It can be used for charging / discharging reaction.

In addition, since the phosphate transition metal lithium-based positive electrode active material according to the present embodiment has a uniform spatial distribution of the elements, it is possible to secure the movement path of lithium ions and efficiently use the active material constituting the particles.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto at all.

(1-1) Synthesis Example 1

(Manufacture of lithium iron phosphate precursor particles by spray combustion method)

A production apparatus for producing precursor particles by a spray combustion method is shown in Fig. In the reaction vessel of the apparatus shown in Fig. 2, propane gas (C ₃ H ₈ ) is used as the combustible gas, air is used as the delayed gas, and the raw material solution is supplied into the flame from the nozzle 13. And an exhaust pipe for exhausting generated fine particles and reaction products to the other, and the precursor particles 17 in the exhaust gas are recovered by the particulate filter 15. The kind of the raw material supplied to the nozzle and the supply condition were as follows. Further, the raw material solution was supplied into the flame by using an air flow nozzle so that the size of the droplet was 20 占 퐉. The temperature of the flame was about 2000 ° C.

Propane (C ₃ H ₈ ): 1 dm ₃ / min,

Air: 5 dm 3 / min,

Lithium naphthenate (4M solution): 0.025 dm3 / min

C ₁₆ H ₃₀ FeO ₄ (2-ethylhexanoate (II)) (1M solution): 0.1 dm 3 / min

Triethyl phosphonoacetate (1M solution): 0.1 dm 3 / min

A method for producing the precursor particles by the spray combustion method is as follows. First, a predetermined amount of N ₂ gas was supplied to make an inert gas atmosphere in the reaction vessel. Under these conditions, a solution obtained by mixing a lithium source, a copper source and a phosphoric acid source was supplied to the flame together with propane gas and air by means of a non-atomizer (atomizer). Precursor particles, which are a mixture of fine particles of lithium oxide, iron oxide, phosphorous oxide, etc., produced in the flame, and fine particles of a lithium iron phosphate compound, were collected by a particulate recovery filter. The obtained precursor particles are precursor particles a. The average particle diameter of the primary particles of the precursor particle a confirmed by an electron microscope was about 500 nm.

(1-2) Synthesis Example 2 (spray combustion method)

(Preparation of Lithium Manganese Phosphate Precursor Particles by Spray Combustion)

In the same manner as in Synthesis Example 1, propane gas, air and a raw material solution having a predetermined concentration below were fed into a flame by propane gas by a spray combustion method, and the precursor particles b were synthesized by thermal oxidation. The average particle diameter of the primary particles of the precursor particle b confirmed by an electron microscope was about 100 nm.

Propane (C ₃ H ₈ ): 1 dm ₃ / min,

Air: 5 dm 3 / min,

LiCl (4M aqueous solution): 0.025 dm3 / min,

MnSO ₄ .5H ₂ O (1M aqueous solution): 0.1 dm 3 / min,

Triethyl phosphonoacetate (1M solution): 0.1 dm 3 / min,

(2-1) Embodiment

The lithium iron phosphate precursor particles a and b of the precursor particles of lithium manganese phosphate, were mixed with a weight ratio of 70: 30, the polyvinyl alcohol in the mixture after the addition of the powder such that 10wt%, 250 ℃ under N ₂ gas atmosphere. Followed by calcination for 4 hours, followed by baking at 650 DEG C for 8 hours. During the firing, the polyvinyl alcohol is melted and impregnated into the powder, carbonization of the polyvinyl alcohol and reduction of the transition metal occur during the firing, and generation and crystallization of lithium transition metal phosphate occur. The resulting aggregate was pulverized to obtain a positive electrode active material A. The positive electrode active material A is a powder having a large number of particles having lithium manganese phosphate particles adhered around large lithium iron phosphate particles.

(2-2) Comparative Example 1

Using only the precursor particle a of lithium iron phosphate, 10 wt% of polyvinyl alcohol was added to the precursor particle a and mixed, and firing and pulverization were carried out in the same manner as in Example to obtain a positive electrode active material B. The positive electrode active material B is a powder having a large number of lithium iron phosphate particles.

(2-3) Comparative Example 2

Using only precursor particles b of lithium manganese phosphate, polyvinyl alcohol was added in an amount of 10 wt% based on the precursor particles b, and the mixture was sintered and pulverized in the same manner as in Example to obtain a positive electrode active material C. The positive electrode active material C is a powder in which many particles of lithium manganese phosphate are collected.

(2-4) Comparative Example 3

Precursor particles d of lithium cobalt phosphate were obtained by the same spray combustion method as in Synthesis Example 1, except that cobalt (II) 2-ethylhexanoate was used instead of 2-ethylhexanoate (II) in the raw material solution. The average particle diameter of the primary particles of the precursor particle d confirmed by an electron microscope was about 500 nm.

A precursor particle a 'of lithium iron phosphate was obtained by the same spraying method as in Synthesis Example 2 except that iron sulfate was used instead of manganese sulfate as a raw material solution. The average particle diameter of the primary particles of the precursor particle a 'confirmed by an electron microscope was about 100 nm.

The precursor particles d of cobalt phosphate and the precursor particles a 'of iron phosphate having a smaller particle diameter than that of cobalt phosphate were mixed at a weight ratio of 70:30 and then added with polyvinyl alcohol so as to be 10wt% , And the positive electrode active material D was obtained. The positive electrode active material D is a powder in which a small number of particles having small lithium iron phosphate particles adhere around the particles of lithium cobalt phosphate.

(2-5) Comparative Example 4

Precursor particles e of nickel nickel phosphate were obtained by the same spray combustion method as in Synthesis Example 1, except that nickel (II) 2-ethylhexanoate was used instead of 2-ethylhexanoate (II) in the raw material solution. The average particle diameter of the primary particles of the precursor particle e confirmed by an electron microscope was about 500 nm.

The precursor particles e of nickel lithium phosphate and the precursor particles a 'of iron phosphate having a particle diameter smaller than that of the precursor particles e were mixed at a weight ratio of 70:30, and then polyvinyl alcohol was added so as to be 10wt% of the powder and mixed. , And the positive electrode active material E was obtained. The positive electrode active material E is a powder in which a small amount of lithium iron phosphate particles adhere to the periphery of nickel phosphate lithium particles.

(2-6) Comparative Example 5

A precursor particle f of manganese phosphate lithium phosphate was obtained by the same spray combustion method as in Synthesis Example 1, except that manganese (II) 2-ethylhexanoate was used instead of 2-ethylhexanoate (II) in the raw material solution. The average particle size of the primary particles of the precursor particles f confirmed by an electron microscope was about 500 nm.

The precursor particles f of lithium manganese phosphate and the precursor particles a 'of iron phosphate lithium having a particle diameter smaller than that of the precursor particles f were mixed at a weight ratio of 70:30, and then polyvinyl alcohol was added thereto in an amount of 10 wt% Fired and pulverized in the same manner as in Example to obtain a positive electrode active material F. [ The positive electrode active material F is a powder in which a small number of particles of lithium iron phosphate are adhered around the particles of lithium manganese phosphate.

(3) Evaluation of sample

(3-1) Observation of scanning electron microscope (SEM)

The powders of the examples in which the precursor particles a and the precursor particles b were mixed were observed by SEM. SEM image observation results are shown in Fig.

As shown in Figs. 4 (a) to 4 (c), the particles constituting the powder before firing were particles of about 50 to 200 nm and some coarse particles of 500 nm or more were present.

(3-2) Composition analysis of particles by EDS

Observation of the shape of the particles and compositional analysis of the particles contained in the powder obtained by mixing the precursor particle a and the precursor particle b were carried out by using a scanning transmission electron microscope in accordance with HAADF-STEM (High-Angle-Annular-Dark-Field-Scanning-Transmission (Electron Microscopy: High Angle Scattering Dark Field - Scanning Transmission Electron Microscopy), and EDS analysis (Energy Dispersive Spectroscopy: energy dispersive X-ray analysis). FIG. 5 (a) is an HAADF-STEM image of the pre-fired particles in the embodiment, FIG. 5 (b) is an EDS map of manganese atoms at the same observation point, and FIG. Fig. 5 (d) is an EDS map of oxygen atoms at the same observation point, and Fig. 5 (e) is an EDS map of phosphorus atoms at the same observation point.

In Fig. 5 (a), it can be seen that minute particles are present around particles of about 500 nm in diameter, which are roughly spherical. 5 (b) to 5 (e), iron, oxygen and phosphorus are contained in the substantially spherical particles, but manganese is hardly detected from large particles, and manganese is detected from the fine particles in the lower part of the observation field of view .

6 (a) to 6 (d) are STEM images and EDS maps viewed from fields different from those in Fig. Small particles of about 100 nm in particle size were observed, and no iron was detected in this field, and manganese and phosphorus and oxygen were detected. Elements in each particle are uniformly distributed.

(3-3) Composition analysis of the positive electrode active material after firing by EDS

For the positive electrode active material A of the example after firing, observation of the particle shape and compositional analysis were carried out in the same manner. 7 (a) is an HAADF-STEM image of a positive electrode active material of the embodiment, FIG. 7 (b) is an EDS map of manganese atoms at the same observation site, FIG. 7 (d) is an EDS map of oxygen atoms at the same observation point, and FIG. 7 (e) is an EDS map of phosphorus atoms at the same observation point.

7 (a) to 7 (e), it is understood that the positive electrode active material A of the embodiment has a structure in which lithium manganese phosphate particles having a particle diameter of about 50 to 200 nm are attached to iron phosphate lithium particles having a particle diameter of about 1 m. It can also be seen that the lithium manganese phosphate particles do not cover the entire surface of the lithium iron phosphate particles and some of the surface of the lithium iron phosphate particles is exposed.

(4) Preparation of positive electrodes and secondary batteries for test evaluation using positive electrode active material

To the positive electrode active materials A to F obtained in Examples and Comparative Examples, a conductive auxiliary agent (carbon black) was mixed in an amount of 10% by weight, and the mixture was further mixed for 5 hours using a ball mill in which the inside was replaced with nitrogen. The mixed powder and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 95: 5, N-methyl-2-pyrrolidone (NMP) was added and sufficiently kneaded to obtain a positive electrode slurry.

A positive electrode slurry was applied to an aluminum foil current collector having a thickness of 15 탆 at a coating amount of 50 g / m ² and dried at 120 캜 for 30 minutes. Thereafter, the resultant was rolled to a density of 2.0 g / cm &lt; 3 &gt; by a roll press, and punched into a disc of ² cm &lt; 2 &^gt;

A lithium secondary battery was prepared by dissolving LiPF ₆ in a concentration of 1 M in a mixed solvent obtained by mixing metal lithium in the positive electrode, metal lithium in the negative electrode, and ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1. However, the atmosphere of the dew point was set to -50 ° C or lower. Each pole was used by squeezing it into a rolling can with a collector. Using this positive electrode, negative electrode, electrolyte and separator, a coin-type lithium secondary battery having a diameter of 25 mm and a thickness of 1.6 mm was obtained.

(5) Evaluation of electrode characteristics of positive electrode active material

Next, the electrode characteristics of the positive electrode active material were tested and evaluated by the coin type lithium secondary battery as follows.

(To Li / Li ⁺ ) at which the charging curve is temporarily stopped by the CC-CV method at a current rate of 0.1 C at a test temperature of 25 캜 or 60 캜, The charging was stopped after the temperature was lowered to 0.01C. Thereafter, discharge was performed at a rate of 0.1 C up to 2.5 V (same as above) by the CC method, and the initial charge-discharge capacity was measured. Further, the discharge capacity after repeating charge and discharge was measured, and the capacity retention rate was measured.

8 (a) shows the first charge / discharge curve of the lithium ion secondary battery using the positive electrode active material according to the embodiment. The charge was up to 4.5V. In Fig. 8 (a), (a-1) shows a charge curve and (a-2) shows a discharge curve. The value of the horizontal axis of the right end of the discharge curve becomes the discharge capacity. According to Fig. 8 (a), the lithium ion secondary battery according to the embodiment has a first discharge capacity of about 120 mAh / g at 25 캜 and an energy density of 438 Wh / kg. The reaction in the vicinity of 3.5 V in the charging curve (a-1) of FIG. 8 (a) and the reaction in the vicinity of 3.5 V in the discharge curve (a-2) are the charging and discharging reactions of lithium iron phosphate. The reaction in the vicinity of 4.1 V in the charging curve (a-1) of FIG. 8 (a) and the reaction in the vicinity of 3.9 V in the discharge curve (a-2) are charge and discharge reactions of lithium manganese phosphate. That is, it can be seen that the charge-discharge reaction of the positive electrode active material according to the embodiment is performed in two steps.

Fig. 8 (b) shows the transition of the discharge capacity when charging and discharging are repeated. The charge was up to 4.5V. After 100 cycles of charging and discharging, the lithium ion secondary battery using the positive electrode active material according to the embodiment has a discharging capacity of 110 mAh / g, and the capacity retention ratio of 100 cycles is about 92%.

FIG. 9 shows the first charge / discharge curve of the lithium ion secondary battery using the positive electrode active material A according to the embodiment at 60 占 폚. The charge was up to 4.5V. In Fig. 9, (a-1) represents a charge curve and (a-2) represents a discharge curve. The value of the horizontal axis of the right end of the discharge curve becomes the discharge capacity. Referring to FIG. 9, the lithium ion secondary battery according to the embodiment has a first discharge capacity of about 140 mAh / g at 60 占 폚 and an energy density of 520 Wh / kg.

10 shows the first charge / discharge curve of the lithium ion secondary battery using the positive electrode active material B according to Comparative Example 1 at 25 ° C. In this case, the charge was up to 4.5V. 10, (a-1) shows a charging curve, and (a-2) shows a discharging curve. The first discharging capacity of the lithium ion secondary battery using the positive electrode active material of lithium phosphate only according to Comparative Example 1 was about 120 mAh / g at 25 占 폚, which was almost the same value as that of the Example, but the energy density was about 395 Wh / kg. Which is lower than the example.

11 shows the first charge / discharge curve of the lithium ion secondary battery using the positive electrode active material C according to Comparative Example 2 at 25 占 폚. In this case, the charge was up to 4.5V. In Fig. 11, (a-1) shows a charging curve and (a-2) shows a discharging curve. The first discharging capacity of the lithium ion secondary battery using the positive electrode active material of manganese phosphate lithium only as Comparative Example 2 was about 30 mAh / g at 25 캜 and the energy density was about 97 Wh / kg, which was much lower than those of the examples.

The first discharging capacity of the lithium ion secondary battery using the positive electrode active material D in Comparative Example 3 was about 59 mAh / g at 25 캜 and about 217 Wh / kg, which was much lower than that in the Examples. However, in Comparative Example 3, charging was performed up to 4.8 V, in which the charging curve of lithium cobalt phosphate was plasto.

The first discharge capacity of the lithium ion secondary battery using the positive electrode active material E in Comparative Example 4 was about 48 mAh / g at 25 캜 and the energy density was about 168 Wh / kg, which was much lower than that in the Examples. In Comparative Example 4, however, charging was performed up to 5.0 V in which the charging curve of nickel lithium phosphate became a platelet.

The first discharging capacity of the lithium ion secondary battery using the positive electrode active material F in Comparative Example 5 was about 66 mAh / g at 25 캜 and about 235 Wh / kg, which was much lower than that in the Examples. In Comparative Example 4, the charging was performed up to 4.5V.

As described above, the positive electrode for a nonaqueous electrolyte secondary battery in which the positive electrode active material of the present invention is coated on a predetermined current collector is a positive electrode exhibiting excellent charge / discharge characteristics in a rechargeable secondary battery including a lithium ion secondary battery using a nonaqueous electrolyte Can be used. In addition, the spray combustion method, which is a method for producing the precursor particles of the present invention, is excellent in mass productivity and can provide a product at low cost.

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to these examples. It will be understood by those skilled in the art that various changes or modifications can be made within the scope of the technical idea disclosed herein and it is obviously also within the technical scope of the present invention.

1: Particle 3: First particle
5: Second particle 11: Particle production apparatus
13: particulate synthesis nozzle 15: particulate recovery filter
17: precursor particle 21: raw material solution
23: combustible gas 25: retarding gas
27: Exhaust 31: Non-aqueous electrolyte secondary battery
33: Positive electrode 35: Negative electrode
37: Separator 39: Electrolyte
41: battery can 43: positive lead
45: negative electrode lead 47: positive electrode terminal
49: Sealing sphere

Claims (10)

At least a part of the surface of the first particle having a particle diameter of 100 nm to 10 占 퐉 containing lithium iron phosphate,
A second particle having a particle diameter smaller than that of the first particle and having a particle size of 200 nm or less including lithium manganese phosphate is attached,
The weight ratio of lithium iron phosphate to lithium manganese phosphate is 60:40 to 90:10,
And at least a part of the surface of at least one of the first particle and the second particle is covered with carbon. delete delete The whole house,
The active material layer according to any one of claims 1 to 7, wherein the positive electrode active material layer
And a positive electrode for a nonaqueous electrolyte secondary battery. A positive electrode for a nonaqueous electrolyte secondary battery according to claim 4,
A negative electrode capable of intercalating and deintercalating lithium ions,
And a separator disposed between the positive electrode and the negative electrode,
Wherein the positive electrode, the negative electrode and the separator are formed in an electrolyte having lithium ion conductivity. A third particle which is a precursor of lithium iron phosphate and a fourth particle which is a precursor of lithium manganese lithium having a particle diameter smaller than that of the third particle;
Further comprising a step of mixing the carbon source,
Process of firing particles obtained by mixing
Wherein the positive electrode active material is a mixture of the positive active material and the negative active material. The method according to claim 6,
Wherein the mixing ratio of the third particles to the fourth particles is 60:40 to 90:10 by weight. The method according to claim 6,
Wherein the third particles have a particle diameter of 100 nm to 10 占 퐉,
Wherein the particle diameter of the fourth particles is 200 nm or less. The method according to claim 6,
The third particle is prepared by a method of supplying a solution containing lithium, iron and phosphorus into a flame together with a delayed gas and a combustible gas in the form of droplets of mist,
Wherein the fourth particles are prepared by a method of supplying a solution containing lithium, manganese, and phosphorus into a flame together with a delayed gas and a combustible gas in a mist state. The method according to claim 6,
Wherein the carbon source is at least one of polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose, acetyl cellulose, sucrose, and carbon black.

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