WO2019093094A1 - Carbon-coated li5feo4 - Google Patents

Abstract

The present invention provides a novel Li5FeO4-related material. A carbon-coated Li5FeO4 which contains Li5FeO4 and a carbon film that covers the surface of the Li5FeO4, and which is characterized in that the BET specific surface area thereof is within the range of 1-12 m2/g.

Description

Carbon-coated Li5FeO4

The present invention relates to carbon-coated Li ₅ FeO ₄ used as a positive electrode material or the like of a lithium ion secondary battery.

Lithium ion secondary batteries are small in size and large in capacity, and thus are used as batteries of various devices such as mobile phones and laptop computers. The lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte as main components. The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector and containing a positive electrode active material.

It is known that various lithium metal complex oxides are used as a positive electrode active material of a lithium ion secondary battery, and Li ₅ FeO ₄ is known as one of them. In addition, Li ₅ FeO ₄ is also known to have a small reversible capacity and to generate a gas during charging, and it is used as a lithium ion supply agent for compensating the irreversible capacity of the negative electrode, or as an additive for the positive electrode It is also known to be used in

For example, Patent Document 1 specifically describes a lithium ion secondary battery having a positive electrode using LiMn ₂ O ₄ and Li ₅ FeO ₄ in a mass ratio of 95: 5, and the lithium ion secondary battery of Li ₅ FeO ₄ It is described that the initial capacity loss of the negative electrode active material could be compensated by the addition.

Patent Document 2 discloses a lithium ion secondary battery having only Li ₅ FeO ₄ as a positive electrode active material, and a lithium ion secondary battery having a metal oxide not containing Li ₅ FeO ₄ and Li as a positive electrode active material. Is specifically described.

Patent Document 3 specifically describes a lithium ion secondary battery having a positive electrode using LiCoO ₂ and Li ₅ FeO ₄ in a mass ratio of 91: 9 to 97: 3 as a positive electrode active material. _It is stated that the initial charge capacity could be improved by the addition of ₅ FeO ₄ .

Patent Document 4 describes that Li ₅ FeO ₄ is added to the positive electrode active material layer as a positive electrode additive that generates gas at the time of initial charge, and the gas generation at the time of initial charge causes empty in the positive electrode active material layer. It is described that the holes can be formed.

JP 2007-287446 A JP 2012-99316 A JP, 2014-157653, A WO 2014/118834

In recent years, the industry demands a lithium ion secondary battery excellent in battery characteristics and an excellent material for producing a lithium ion secondary battery, and a new technology for realizing it is required. There is.

The present invention has been made in view of such circumstances, and an object thereof is to provide a new Li ₅ FeO ₄ related material.

When the present inventor examined about Li ₅ FeO _4, it was found that the battery having Li ₅ FeO ₄ did not exhibit sufficient capacity. The present inventors estimated that such a phenomenon is due to the low conductivity of Li ₅ FeO ₄ , that is, the property of high resistance. _Then, Li 5 purpose of increasing the conductivity of FeO _4, where the produced carbon-coated _Li 5 FeO ₄ to the surface of the Li 5 FeO ₄ was coated with carbon film, and test this, carbon-coated _Li 5 FeO ₄ However, it has been found that even the capacity may not necessarily be expressed sufficiently.

Moreover, carbon deposition of the powder in order to suppress against mixing device or synthesizer in synthesizing the Li ₅ FeO _4, where the addition of the organic additive, the Li ₅ FeO ₄ was synthesized through the addition of the organic additive The inventors have found that carbon-coated Li ₅ FeO ₄ coated with a film has excellent properties. Furthermore, it is related to the specific surface area of the carbon-coated _Li 5 Characteristics of FeO ₄ carbon coated _Li 5 FeO _4, and a specific surface area of the carbon-coated _Li 5 FeO ₄ is influenced by the amount of the organic additive The present inventors have found that.
The present invention has been completed based on the findings of the present inventor.

Carbon-coated _Li 5 FeO ₄ of the present _invention, Li 5 FeO ₄ and the _Li 5 A carbon-coated _Li 5 FeO ₄ containing a carbon film covering a surface of FeO _4, BET specific surface area of 1 ~ 12m ² It is characterized by being within the range of / g.

The carbon-coated Li ₅ FeO ₄ of the present invention exhibits a sufficient capacity as a positive electrode material.

It is a graph which shows the result of evaluation example 2.

Below, the form for implementing this invention is demonstrated. Incidentally, unless otherwise specified, the numerical range “ab” described in the present specification includes the lower limit a and the upper limit b in that range. And a numerical range can be constituted by combining these arbitrarily including the upper limit and lower limit, and the numerical value listed in the example. Furthermore, numerical values arbitrarily selected from these numerical ranges can be used as new upper and lower numerical values.

Carbon-coated _Li 5 FeO ₄ of the present _invention, Li 5 FeO ₄ and the _Li 5 A carbon-coated _Li 5 FeO ₄ containing a carbon film covering a surface of FeO _4, BET specific surface area of 1 ~ 12m ² It is characterized by being within the range of / g.
When the BET specific surface area is in the range of 1 to 12 m ² / g, a capacity (lithium ion release amount) sufficient for a positive electrode material is developed.

From the viewpoint of capacity, the BET specific surface area of the carbon-coated Li ₅ FeO ₄ of the present invention is preferably in the range of 2 to 10 m ² / g, and more preferably in the range of 3 to 7 m ² / g.
If the BET specific surface area is too small, the volume may be poor. On the other hand, if the BET specific surface area is too large, it may react with moisture and carbon dioxide in the air to deteriorate Li ₅ FeO ₄ or adversely affect the physical properties of the slurry during positive electrode production. From the viewpoint of both the volume and the physical properties of the slurry, the BET specific surface area of the carbon-coated Li ₅ FeO ₄ of the present invention is particularly preferably in the range of 2 to 5 m ² / g.

The carbon film preferably covers the entire surface of the particles of Li ₅ FeO ₄ . The thickness of the carbon film is preferably in the range of 1 nm to 100 nm, more preferably in the range of 5 nm to 50 nm, still more preferably in the range of 10 nm to 40 nm, and particularly preferably in the range of 15 nm to 35 nm.

As mass% (Wc) of carbon, the range of 1 ≦ Wc ≦ 6 is preferable, the range of 1.1 ≦ Wc ≦ 5.4 is more preferable, and the range of 1.3 ≦ Wc ≦ 4 is more preferable. The range of 1.5 ≦ Wc ≦ 3.5 is more preferable, the range of 1.7 ≦ Wc ≦ 3 is particularly preferable, and the range of 1.9 ≦ Wc ≦ 2.5 is the most preferable.

The carbon-coated Li ₅ FeO ₄ of the present invention is preferably in a powder state. The powder resistance value of the carbon-coated Li ₅ FeO ₄ of the present invention can be, for example, 0.5 to 20 Ωcm, 1 to 13 Ωcm, 1.5 to 10 Ωcm, and 2 to 7 Ωcm.
In addition, the powder resistance value in this specification means the volume resistance value at the time of applying the load of 4 kN to a measurement sample.

The method for producing the carbon-coated Li ₅ FeO ₄ of the present invention will be described.
The method of producing a carbon-coated _Li 5 FeO ₄ of the present invention includes _the steps of preparing a Li 5 FeO _4, and _has a step, which is coated with carbon Li 5 FeO _4.

As a method of preparing Li ₅ FeO ₄ , commercially available Li ₅ FeO ₄ may be purchased, or Li ₅ FeO ₄ may be synthesized using a Li source and an Fe source as raw materials.

As a method of synthesizing Li ₅ FeO ₄ , Li source and Fe source may be reacted under heating conditions for synthesis. Examples of the Li source include lithium alone, lithium oxide, lithium hydroxide, lithium carbonate, lithium hydrogen carbonate and lithium fluoride. Examples of the Fe source include elemental iron, iron oxide, iron hydroxide, iron oxyhydroxide, iron sulfate, iron nitrate and iron chloride. If the composition of the Li source and the Fe source contains less oxygen than the theoretical amount, oxygen may be introduced into the reaction system.
From the viewpoint of the purity of the product, it is preferable to react lithium alone with iron oxide, to react lithium oxide with iron alone, or to react lithium oxide with iron oxide.

It is preferable to grind and mix the Li source and the Fe source before heating. Furthermore, it is preferable to integrate the Li source and the Fe source before heating.

As a device for pulverizing, mixing or integrating Li source and Fe source before heating, a ball mill, a planetary ball mill, a hybridization system (NHS) of Nara Machinery Co., Ltd. and MILARO, Hosokawa Micron Corporation Mechanofusion and Nobilta, and theta composer of Dekushou Works, Ltd.

The heating temperature is preferably 400 to 1000 ° C., more preferably 450 to 900 ° C., still more preferably 500 to 800 ° C., and particularly preferably 550 to 700 ° C. The present inventors have already confirmed that Li ₅ FeO ₄ can be synthesized by heating at 400 ° C. using lithium oxide as the Li source and iron alone as the Fe source.
In the synthesis of Li ₅ FeO ₄ , heating is preferably performed under an inert gas atmosphere such as argon, helium, nitrogen and the like except in special circumstances.

As a synthesis method of Li ₅ FeO ₄ , sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide, N, N'-ethylenebis fatty acid amide, alkali metal salt of fumaric acid alkyl ester and hardened oil are exemplified as Li source and Fe source It is particularly preferable to synthesize Li ₅ FeO ₄ after adding an organic additive selected from
The addition of the organic additive can suppress the coarsening of the particles of Li ₅ FeO ₄ . The amount of the organic additive added is small, and the composition does not significantly affect the composition of Li ₅ FeO ₄ because it is vaporized or decomposed in the reaction system.
Due to the fact that controlling the amount of the organic _additive, because it can control the particle size of the Li 5 FeO _4, BET specific surface area of Li 5 FeO ₄ and carbon-coated _Li 5 FeO ₄ is also controlled by the amount of the organic additive it can.
The addition amount of the organic additive is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and still more preferably 1 to 3% by mass, based on the total of the Li source and the Fe source.

Sucrose fatty acid ester is an ester produced from sucrose and fatty acid, and is a powdered non-ionic surfactant known as a trade name such as Ryoto sugar ester.

As a fatty acid in sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide and N, N'-ethylenebis fatty acid amide, a saturated or unsaturated fatty acid having 12 to 24 carbon atoms is preferable, and a saturated fatty acid having 16 to 20 carbon atoms Or unsaturated fatty acids are more preferred. Further, as the above-mentioned fatty acid, palmitic acid, stearic acid, arachidic acid, palmitoleic acid, oleic acid, linoleic acid and arachidonic acid can be exemplified.

Examples of the cation forming the fatty acid salt include alkali metals such as lithium and sodium, alkaline earth metals such as magnesium and calcium, and zinc. As a cation which forms the salt in a fatty acid salt, alkali metals, such as lithium and sodium, are preferable from the point which is hard to scatter and it is hard to contaminate an apparatus.

Specific examples of fatty acid salts include lithium palmitate, lithium stearate, lithium arachidinate, lithium palmitoleate, lithium oleate, lithium linoleate, lithium arachidonate, sodium palmitate, sodium stearate, sodium arachidinate, palmitoleic acid Sodium oleate, sodium linoleate, sodium arachidonate, magnesium palmitate, magnesium stearate, magnesium arachidinate, magnesium palmitolate, magnesium oleate, magnesium linoleate, magnesium arachidonic acid, palmitic acid, calcium stearate, arachidic acid Calcium, calcium palmitolate, calcium oleate, calcium linoleate, Calcium Rakidon acid, zinc palmitate, zinc stearate, zinc arachidate, palmitoleic acid, zinc oleate, zinc linoleate, can be exemplified arachidonic acid zinc.

Specific examples of fatty acid amides include palmitic acid amide, stearic acid amide, arachidic acid amide, palmitoleic acid amide, oleic acid amide, linoleic acid amide and arachidonic acid amide.

Specific examples of N, N'-ethylenebisfatty acid amide include N, N'-ethylenebispalmitic acid amide, N, N'-ethylenebisstearic acid amide, N, N'-ethylenebisarachidic acid amide, N Examples include N, N′-ethylenebispalmitoleic acid amide, N, N′-ethylenebisoleic acid amide, N, N′-ethylenebislinoleic acid amide, and N, N′-ethylenebisarachidonamide.

As the alkyl in the fumaric acid alkyl ester alkali metal salt, an alkyl group having 12 to 24 carbon atoms is preferable, and an alkyl group having 16 to 20 carbon atoms is more preferable. Specific examples of the alkyl group include palmityl, stearyl and arachidyl. As a cation which forms an alkali metal salt, lithium and sodium can be illustrated.

Specific examples of alkali metal salts of fumaric acid alkyl ester include: palmityl lithium fumarate, lithium stearyl fumarate, lithium arachidyl fumarate, palmityl fumarate sodium salt, sodium stearyl fumarate, alakisyl fumarate A sodium salt can be illustrated.

Moreover, as a cation in fatty acid salt and fumaric acid alkyl ester alkali metal salt, lithium is preferable.

As a hydrogenated oil, a powdery hydrogenated hydrogenated oil known as Labri wax (registered trademark) can be exemplified.

The addition of the organic additive can suppress the coarsening of Li ₅ FeO ₄ particles, and furthermore, the reason that the particle size of Li ₅ FeO ₄ can be controlled by controlling the addition amount of the organic additive Is considered to be in the following mechanism.

During heating, the Li source and the Fe source react to synthesize Li ₅ FeO ₄ . Here, in the absence of an organic additive, the synthesized _Li 5 FeO ₄ particles as nuclei, to it is envisioned that additional _Li 5 FeO ₄ synthesis reaction proceeds, also synthesized _Li 5 FeO It is also assumed that _four particles stick together. It is thought that these matters cause the formation of coarse Li ₅ FeO ₄ particles.

On the other hand, in the presence of the organic additive, the organic additive or its vaporized or degraded product contacts the Li source and the Fe source with respect to the synthesized Li ₅ FeO ₄ particles and contacts the other Li ₅ FeO ₄ particles. Suppress. Therefore, it is considered that coarsening of Li ₅ FeO ₄ particles can be suppressed.

The present inventors have created the following technical ideas from the experimental fact that the particle size of Li ₅ FeO ₄ can be controlled by the addition of organic additives.

In a method for producing an inorganic compound, wherein an inorganic compound is synthesized by heating a first solid inorganic raw material and a second solid inorganic raw material different from the first solid inorganic raw material.
Powdered form characterized by adding an organic additive selected from sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide, N, N'-ethylenebis fatty acid amide, fumaric acid alkyl ester alkali metal salt and hardened oil Method for producing inorganic compounds.

In the method of producing an inorganic compound in which the first solid inorganic raw material and the second solid inorganic raw material are heated to synthesize an inorganic compound, particles of the powdery inorganic compound are added according to the mechanism described above by adding an organic additive. It can be said that the size and specific surface area can be controlled. It can be said that the production method of the preceding paragraph is a method of controlling the particle size and specific surface area of the inorganic compound.

The inorganic compound to be synthesized needs to be solid at the synthesis temperature, that is, the above heating temperature. Examples of inorganic compounds to be synthesized include metal oxides and metal nitrides. Further, the synthesis temperature is preferably equal to or higher than the temperature at which the organic additive is vaporized or decomposed.

The first solid inorganic raw material and the second solid inorganic raw material are solid at room temperature, but are preferably solid inorganic substances also at the synthesis temperature of the inorganic compound. In addition, as the first solid inorganic raw material and the second solid inorganic raw material, those which are decomposed at a synthesis temperature or a temperature lower than the synthesis temperature and the resultant solid decomposition product may be used as a raw material of the inorganic compound. For example, a hydrate that is converted to an anhydride by heating, or a hydroxide or a carbonate that is converted to an oxide by heating may be adopted as the first solid inorganic material and the second solid inorganic material.

As the first solid inorganic raw material and the second solid inorganic raw material, elemental metals, alloys, elemental elements, oxides, peroxides, hydroxides, hydrides, halides, borides, cyanides, azides, nitrides , Carbide, carbonate, sulfide, sulfate, sulfite, bisulfite, thiosulfate, nitrate, nitrite, phosphate, ammonium salt, silicate, borate, perhalogenate, hypophosphite Halogenates, halogenates and their hydrates can be exemplified.

A carbon coating process for coating Li ₅ FeO ₄ with carbon will be described.
The presence of the Li ₅ FeO ₄ and a carbon source, by heating at a carbonizing temperature above the temperature of the carbon source, the carbon source is decomposed and carbonized to form a carbon film on the surface of Li ₅ FeO _4. The Li ₅ FeO ₄ to be subjected to the carbon coating step is preferably in the form of a crushed or classified powder.

The carbon source is an organic matter. The organic matter may be solid, liquid or gas. In particular, by using a gaseous organic substance, a uniform carbon film can be formed on the surface of Li ₅ FeO ₄ . The method of forming a carbon film using a gaseous organic substance is an application of a method generally called a thermal CVD method. When the carbon coating step is performed by applying the thermal CVD method, a fluidized bed reactor, a rotary furnace, a tunnel furnace, a batch furnace, a rotary kiln, etc. of a hot wall type, cold wall type, horizontal type, vertical type, etc. And the like may be used.

As the organic substance, those which can be pyrolyzed and carbonized by heating are used, and examples thereof include saturated aliphatic hydrocarbons such as methane, ethane, propane, butane, isobutane, pentane, hexane, heptane and octane, ethylene, propylene and acetylene Unsaturated aliphatic hydrocarbons, alcohols such as methanol, ethanol, propanol and butanol, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, benzoic acid, salicylic acid, nitrobenzene, chlorobenzene, chlorobenzene, indene, Aromatic hydrocarbons such as benzofuran, pyridine, anthracene, phenanthrene, esters such as ethyl acetate, butyl acetate, amyl acetate, carbohydrates such as sucrose, organic acids such as citric acid, polyfluorinated One or a mixture selected from a resin, such as vinylidene, and the like.
In view of ease of decomposition, boiling point and purity of carbon film, the organic substance is preferably a saturated aliphatic hydrocarbon having 5 to 18 carbon atoms, more preferably a saturated aliphatic hydrocarbon having 5 to 12 carbon atoms, and having carbon atoms More preferred are 5 to 8 saturated aliphatic hydrocarbons.

It is desirable that the carbon coating process be performed with Li ₅ FeO ₄ in a fluidized state. In this way, the entire surface of Li ₅ FeO ₄ can be brought into contact with the organic matter, a more uniform carbon film can be formed, and binding between carbon-coated Li ₅ FeO ₄ particles is suppressed. It can also be done. There are various methods such as using a fluidized bed to make Li ₅ FeO ₄ in a fluid state, but it is preferable to contact Li ₅ FeO ₄ with an organic substance while stirring. For example, if a rotary furnace having a baffle inside is used, Li ₅ FeO ₄ remaining on the baffle is agitated as it falls from a predetermined height with the rotation of the rotary furnace, and contacts with organic matter at that time. Since a carbon film is formed, a more uniform carbon film can be formed on the whole of Li ₅ FeO ₄ .

The temperature of the carbon coating step is preferably in the range of 650 to 800 ° C., more preferably in the range of 700 to 780 ° C., and still more preferably in the range of 720 to 760 ° C. Also, the carbon coating step is preferably performed under an inert gas atmosphere such as argon, helium, nitrogen and the like.

The carbon-coated Li ₅ FeO ₄ of the present invention can function as a positive electrode active material, as a lithium ion supply agent, or as various additives. In particular, the carbon-coated Li ₅ FeO ₄ of the present invention is a positive electrode material for lithium ion secondary batteries, and suitably functions as a lithium ion supply agent at the time of initial charge in a positive electrode of a lithium ion secondary battery. Hereinafter, the positive electrode for a lithium ion secondary battery having the carbon-coated Li ₅ FeO ₄ of the present invention is referred to as “the positive electrode of the present invention”, and a lithium ion secondary battery having the positive electrode of the present invention is referred to as “the lithium ion of the present invention It is called a secondary battery.

In the positive electrode of the present invention, the carbon-coated Li ₅ FeO ₄ of the present invention is preferably added to the positive electrode active material layer in which the positive electrode active material is present. One aspect of the positive electrode of the present invention comprises a positive electrode active material layer containing the carbon-coated Li ₅ FeO ₄ of the present invention, and a current collector. The positive electrode active material layer is formed on the current collector. When the carbon-coated Li ₅ FeO _{4 of the} present invention is a lithium ion supply agent, the amount of the carbon-coated Li ₅ FeO ₄ of the present invention in the positive electrode active material layer may be determined according to the irreversible capacity of the negative electrode.

The current collector refers to a chemically inert electron conductor for keeping current flowing to the electrode during discharge or charge of the lithium ion secondary battery. The material of the current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. The material of the current collector is at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Etc. can be exemplified. The current collector may be coated with a known protective layer. What processed the surface of a collector by a well-known method may be used as a collector.

When the potential of the positive electrode is set to 4 V or more based on lithium, it is preferable to use aluminum as a current collector for the positive electrode.

Specifically, it is preferable to use an aluminum or an aluminum alloy as the positive electrode current collector. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is called an aluminum alloy. Examples of aluminum alloys include Al-Cu, Al-Mn, Al-Fe, Al-Si, Al-Mg, Al-Mg-Si, and Al-Zn-Mg.

As aluminum or aluminum alloy, specifically, for example, A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys such as JIS A3003 and A3004 (Al-Mn series), JIS A8079, A8021 etc. A 8000 series alloys (Al-Fe series).

The current collector can take the form of a foil, a sheet, a film, a line, a rod, a mesh or the like. Therefore, as the current collector, for example, metal foils such as copper foil, nickel foil, aluminum foil, and stainless steel foil can be suitably used. When the current collector is in the form of a foil, a sheet or a film, the thickness is preferably in the range of 1 μm to 100 μm.

The positive electrode active material layer preferably contains a known positive electrode active material in addition to the carbon-coated Li ₅ FeO ₄ of the present invention.
As a positive electrode active material, a general formula of layered rock salt structure: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Lithium mixed metal oxide represented by at least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, and 1.7 ≦ f ≦ 3), Li _a Ni _b Co _c Al _d D _e O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, u, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, at least one element selected from V, lithium mixed metal oxide represented by 1.7 ≦ f ≦ 3), Li ₂ MnO ₃ can be mentioned. In addition, as a positive electrode active material, a metal oxide of spinel structure such as LiMn ₂ O ₄ , a solid solution composed of a mixture of a metal oxide of spinel structure and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ M is selected from at least one of Co, Ni, Mn, and Fe), and the like. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as a positive electrode active material may have the above composition formula as a basic composition, and one obtained by replacing the metal element contained in the basic composition with another metal element can also be used. Further, as the positive electrode active material, one not containing charge carriers (for example, lithium ions contributing to charge and discharge) may be used. For example, elemental sulfur, compounds in which sulfur and carbon are complexed, metal sulfides such as TiS ₂ , oxides such as V ₂ O ₅ , MnO ₂ , polyaniline and anthraquinone, and compounds containing these aromatic groups in the chemical structure, conjugated Conjugated materials such as acetic acid-based organic materials and other known materials can also be used. Furthermore, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl or the like may be adopted as the positive electrode active material. In the case of using a positive electrode active material containing no charge carrier such as lithium, the charge carrier needs to be previously added to the positive electrode and / or the negative electrode by a known method. The charge carrier may be added in the form of ions or may be added in the form of non ions such as metals. For example, when the charge carrier is lithium, a lithium foil may be attached to the positive electrode and / or the negative electrode to be integrated.

From the point of being excellent in high capacity and durability, etc., a general formula of layered rock salt structure as a positive electrode active material: Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, At least one element selected from Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, and represented by 1.7 ≦ f ≦ 3) lithium mixed metal oxide that, _{or, Li a Ni b Co c Al} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Nb, Mg, Ta, Ti, La, Zr, Cu, C at least one element selected from a, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f It is preferable to adopt a lithium mixed metal oxide represented by ≦ 3).

As a positive electrode active material, Li _x Mn _2-y A _y O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga, and so on) from the viewpoint of high capacity and excellent durability And at least one element selected from Ge, and at least one metal element selected from transition metal elements such as Ni, etc. 0 <x ≦ 2.2, 0 ≦ y ≦ 1) can be exemplified. As the range of the value of x, 0.5 ≦ x ≦ 1.8, 0.7 ≦ x ≦ 1.5, 0.9 ≦ x ≦ 1.2 can be exemplified, and as the range of the value of y, 0 ≦ y ≦ 0.8 and 0 ≦ y ≦ 0.6 can be exemplified. As a specific compound of spinel structure, LiMn ₂ O ₄ and LiMn _1.5 Ni _0.5 O ₄ can be exemplified.

Specific examples of the positive electrode active material include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. As another specific positive electrode active material, Li ₂ MnO ₃ -LiCoO ₂ can be exemplified.

The positive electrode active material layer preferably contains a binder and a conductive auxiliary. What is demonstrated by the below-mentioned negative electrode may be suitably employ | adopted suitably as a binder and a conductive support agent contained in a positive electrode active material layer.

Specifically, the lithium ion secondary battery of the present invention comprises the positive electrode of the present invention, a negative electrode, an electrolytic solution, and a separator. The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer contains a negative electrode active material, and, if necessary, also contains a binder and a conductive additive. The current collector of the negative electrode may be appropriately selected from those described for the positive electrode of the present invention.

As the negative electrode active material, a material capable of inserting and extracting charge carriers can be used. Therefore, there is no particular limitation as long as it is a single body, an alloy or a compound capable of storing and releasing a charge carrier such as lithium ion. For example, Li as a negative electrode active material, a Group 14 element such as carbon, silicon, germanium, tin, a Group 13 element such as aluminum or indium, a Group 12 element such as zinc or cadmium, a Group 15 element such as antimony or bismuth, magnesium And alkaline earth metals such as calcium, and Group 11 elements such as silver and gold may be used alone. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based materials such as various types of graphite, and SiO _x (disproportionate into silicon simple substance and silicon dioxide) Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), a simple substance of silicon, or a composite obtained by combining a silicon-based material and a carbon-based material. As the negative electrode active material, an oxide such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ or Li _3-x M _x N (M = A nitride represented by Co, Ni, Cu) may be employed. One or more of these can be used as the negative electrode active material.

Graphite, a Si-containing material, and a Sn-containing material can be mentioned as a preferable negative electrode active material from the point of possibility of high capacity formation. In particular, when a Si-containing material in which the presence of irreversible capacity is an important problem is employed as the negative electrode active material, the effect of the carbon-coated Li ₅ FeO ₄ of the present invention as a lithium ion supply agent is remarkably exhibited.

As specific examples of the Si-containing material, it is possible to exemplify Si alone or SiO _x (0.3 ≦ x ≦ 1.6) disproportionated into two phases of the Si phase and the silicon oxide phase. The Si phase in SiO _x can occlude and release lithium ions, and changes in volume as the secondary battery charges and discharges. The silicon oxide phase has less change in volume due to charge and discharge as compared to the Si phase. That is, SiO _x as the negative electrode active material realizes a high capacity by the Si phase, and suppresses the volume change of the whole negative electrode active material by having the silicon oxide phase. When x is less than the lower limit value, the ratio of Si becomes excessive, so that the volume change during charge and discharge becomes too large, and the cycle characteristics of the secondary battery deteriorate. On the other hand, when x exceeds the upper limit value, the Si ratio becomes too small and the energy density decreases. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and still more preferably 0.7 ≦ x ≦ 1.2.

In addition, in the above-mentioned SiO _x , it is thought that the alloying reaction by lithium of silicon and silicon of Si phase arises at the time of charge and discharge of a lithium ion secondary battery. And it is thought that this alloying reaction contributes to charge and discharge of a lithium ion secondary battery. It is thought that it can be charged / discharged similarly by the alloying reaction of tin and lithium about the Sn containing material mentioned later.

As specific examples of the Sn-containing material, a simple substance of Sn, a tin alloy such as Cu-Sn or Co-Sn, an amorphous tin oxide, or a tin silicon oxide can be exemplified. The amorphous tin oxide can be exemplified by SnB _0.4 P _0.6 O _3.1 , and the tin silicon oxide can be exemplified by SnSiO ₃ .

The Si-containing material and the Sn-containing material are preferably combined with a carbon material to form a negative electrode active material. The complexing stabilizes the structure of silicon and / or tin, and improves the durability of the negative electrode. The compounding may be performed by a known method. Graphite, hard carbon, soft carbon or the like may be employed as the carbon material used for the complexation. The graphite may be natural graphite or artificial graphite.

As a specific example of the Si-containing material, a silicon material (hereinafter, simply referred to as "silicon material") disclosed in WO 2014/080608 and the like can be mentioned.

The silicon material has a structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction. For example, a silicon material may be reacted with CaSi ₂ and an acid to synthesize a layered silicon compound containing polysilane as a main component, and further, the layered silicon compound may be heated at 300 ° C. or higher to release hydrogen. It is manufactured.

An ideal reaction formula in the case of using hydrogen chloride as an acid is as follows when a method of manufacturing a silicon material is used.
3CaSi ₂ +6 HCl → Si ₆ H ₆ +3 CaCl ₂
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is generally used as a reaction solvent from the viewpoint of removal of by-products and impurities. And, since Si ₆ H ₆ can react with water, in the process of synthesizing the layered silicon compound including the reaction in the upper stage, the layered silicon compound is hardly produced as one containing only Si ₆ H ₆ , and the layered silicon compound is layered The silicon compound is represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from the anion of an acid, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6) Manufactured as In the above chemical formula, unavoidable impurities such as remaining Ca are not taken into consideration. And the silicon material obtained by heating the said layered silicon compound also contains the element derived from the anion of oxygen or an acid.

As described above, the silicon material has a structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction. The plate-like silicon body preferably has a thickness in the range of 10 nm to 100 nm, and more preferably in the range of 20 nm to 50 nm, in order to efficiently store and release charge carriers such as lithium ions. The length in the longitudinal direction of the plate-like silicon body is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has a (longitudinal length) / (thickness) in the range of 2 to 1,000. The layered structure of the plate-like silicon body can be confirmed by observation with a scanning electron microscope or the like. Moreover, this laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

The silicon material preferably includes amorphous silicon and / or silicon crystallites. In particular, in the plate-like silicon body, it is preferable that amorphous silicon be a matrix and silicon crystallites be scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scheller equation using the half width of the diffraction peak of the Si (111) plane of the obtained X-ray diffraction chart by performing X-ray diffraction measurement on the silicon material. .

The amount and size of the plate-like silicon body, amorphous silicon and silicon crystallite contained in the silicon material mainly depend on the heating temperature and heating time. The heating temperature is preferably in the range of 350 ° C. to 950 ° C., and more preferably in the range of 400 ° C. to 900 ° C.

The silicon material may be coated with carbon. Silicon coated with carbon is excellent in conductivity.

The average particle size of the silicon material is preferably in the range of 2 to 7 μm, and more preferably in the range of 2.5 to 6.5 μm. If a silicon material having an average particle size too small is used, it may be difficult to manufacture the negative electrode from the viewpoint of cohesion and wettability. Specifically, in the slurry prepared at the time of negative electrode production, a silicon material having an excessively small average particle size may be aggregated. On the other hand, a lithium ion secondary battery having a negative electrode using a silicon material having an excessively large average particle size may not be able to perform preferable charge and discharge. It is presumed that in silicon materials having an average particle size too large, lithium ions can not sufficiently diffuse into the interior of the silicon materials. The average particle diameter herein means a D ₅₀ in the case of measuring a sample in a conventional laser diffraction particle size distribution analyzer.

As the binder, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resin, carboxymethyl cellulose Known materials such as styrene butadiene rubber may be employed.

In addition, a crosslinked polymer in which a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid as disclosed in WO 2016/063882 is crosslinked with a polyamine such as diamine may be used as a binder.

Examples of the diamine used for the cross-linked polymer include alkylene diamines such as ethylene diamine, propylene diamine and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, bis (4-aminocyclohexyl) methane and the like. Saturated carbocyclic ring diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalene diamine can be mentioned.

The content of the binder in the active material layer is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, still more preferably 2 to 10% by mass, and particularly preferably 3 to 5% by mass. When the amount of the binder is too small, the formability of the electrode decreases, and when the amount of the binder is too large, the energy density of the electrode decreases.

A conductive aid is added to enhance the conductivity of the electrode. Therefore, the conductive additive may be optionally added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive support agent may be any chemically active high electron conductor, and carbon black fine particles such as carbon black, graphite, vapor grown carbon fiber, and various metal particles are exemplified. Ru. Examples of the carbon black include acetylene black, ketjen black (registered trademark), furnace black, channel black and the like. These conductive assistants can be added to the active material layer singly or in combination of two or more. The proportion of the conductive auxiliary in the active material layer is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, still more preferably 2 to 10% by mass, and particularly preferably 2 to 5% by mass. If the amount of the conductive additive is too small, efficient conductive paths can not be formed. If the amount of the conductive additive is too large, the formability of the active material layer deteriorates and the energy density of the electrode decreases.

In order to form an active material layer on the surface of a current collector, current collection can be performed using conventionally known methods such as roll coating, die coating, dip coating, doctor blade method, spray coating, and curtain coating. The active material may be applied to the surface of the body. Specifically, the components of the active material layer and the solvent are mixed to form a slurry, and the slurry is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and water. The dried one may be compressed to increase the electrode density.

In a slurry-like composition for producing a positive electrode active material layer comprising carbon coated Li ₅ FeO ₄ and a solvent for producing a positive electrode active material layer, the blending amount of solid content is in the range of 30 to 90% by mass. Is preferable, and the range of 50 to 75% by mass is more preferable. Here, solid content means components other than the solvent contained in the composition for positive electrode active material layer manufacture.

In the positive electrode active material layer composition for the preparation, the amount of carbon-coated _Li 5 FeO ₄ of the present invention may be properly determined according to the carbon-coated _Li 5 FeO ₄ applications of the present invention.
In the case of using the carbon-coated Li ₅ FeO ₄ of the present invention as a lithium ion supply agent for compensating lithium ions corresponding to the irreversible capacity of the negative electrode, the carbon coating of the present invention in the composition for producing a positive electrode active material layer The compounding amount of Li ₅ FeO ₄ can be, for example, in the range of 1 to 10% by mass, in the range of 3 to 9% by mass, and in the range of 5 to 8% by mass with respect to the solid content.

Further, the compounding amount of the positive electrode active material in the composition for manufacturing a positive electrode active material layer is within the range of 80 to 95% by mass, within the range of 83 to 93% by mass, 85 to 90% by mass The range can be illustrated. The compounding amount of the binder in the composition for manufacturing a positive electrode active material layer is 0.5 to 10% by mass, 1 to 5% by mass, or 2 to 4% by mass with respect to the solid content. The range can be illustrated. The compounding amount of the conductive aid in the composition for manufacturing a positive electrode active material layer is 0.5 to 5% by mass, 1 to 4% by mass, 1 to 3% by mass with respect to the solid content. The range can be illustrated.

The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass while preventing a short circuit due to the contact of the both electrodes. As the separator, a known one may be employed, and polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, synthetic resin such as polyacrylonitrile, polysaccharide such as cellulose, amylose, fibroin Examples thereof include porous materials, non-woven fabrics, and woven fabrics using one or more kinds of natural polymers such as keratin, lignin and suberin, and electrically insulating materials such as ceramics. In addition, the separator may have a multilayer structure.

The electrolytic solution contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

As the non-aqueous solvent, cyclic carbonate, cyclic ester, chain carbonate, chain ester, ethers and the like can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of cyclic esters include gamma butyrolactone, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, and ethyl methyl carbonate. Examples of chain esters include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and the like. As the ethers, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane can be exemplified. As the non-aqueous solvent, a compound in which part or all of hydrogens in the chemical structure of the above specific solvent is substituted with fluorine may be adopted.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / liter of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ and the like in a nonaqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate A solution dissolved at a concentration of about L to 1.7 mol / L can be exemplified.

The specific manufacturing method of the lithium ion secondary battery of this invention is described.
For example, the positive electrode and the negative electrode sandwich a separator to form an electrode body. The electrode body may be any of a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a laminate of a positive electrode, a separator and a negative electrode is wound. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collection lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. Good.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as cylindrical, square, coin, and laminate types can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle using electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form a battery pack. As an apparatus which mounts a lithium ion secondary battery, various household appliances driven by a battery, such as a personal computer and a mobile communication apparatus, as well as a vehicle, an office apparatus, an industrial apparatus and the like can be mentioned. Furthermore, the lithium ion secondary battery of the present invention can be used in wind power generation, solar power generation, hydroelectric power generation, storage devices and power smoothing devices for electric power systems, power sources for power and / or accessories of ships, etc., aircraft, Power supply source for power of spacecraft and / or accessories, auxiliary power supply for vehicles not using electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charge station etc. for electric vehicles.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. In the range which does not deviate from the summary of the present invention, it can carry out with various forms which gave change, improvement, etc. which a person skilled in the art can make.

Below, various specific examples are shown and this invention is more concretely demonstrated to it. The present invention is not limited by these specific examples.

Example 1
Li ₂ O as a Li source and Fe ₂ O ₃ as an Fe source were weighed so as to have a molar ratio of 5: 1, and charged into a planetary ball mill. Furthermore, lithium stearate, which is an organic additive, was weighed in an amount corresponding to 0.5% by mass with respect to the total amount of Li ₂ O and Fe ₂ O ₃ , and was put into a planetary ball mill. The planetary ball mill was operated at a rotation speed of 800 rpm and a rotation speed of 800 rpm to grind and mix Li ₂ O, Fe ₂ O ₃ and lithium stearate until the diameter of the obtained particles was 10 μm or less.

A mixture of ground and mixed Li ₂ O, Fe ₂ O ₃ and lithium stearate was placed in a rotary kiln type reactor. The mixture was then heated at 600 ° C. for 60 minutes under an argon atmosphere to synthesize Li ₅ FeO ₄ . Subsequently, hexane - in ventilation under argon mixed gas, 700 ° C., subjected to thermal CVD under the conditions of 40 _minutes, Li 5 on the surface of FeO ₄ to form a carbon film, a carbon coating _Li 5 FeO Example 1 ₄ was manufactured.
_{Incidentally,} during the synthesis and production of carbon-coated _Li 5 FeO ₄ of Li 5 FeO ₄ was a rotational state of the rotary kiln type reactor.

90 parts by mass of carbon-coated Li ₅ FeO ₄ of Example 1, 5 parts by mass of acetylene black as a conductive additive, 5 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone Mix to form a slurry. The positive electrode of Example 1 was obtained by preparing an aluminum foil as a current collector, applying a slurry thereto, and drying it.

Lithium foil was prepared and used as a negative electrode. A glass filter (Hoechst Celanese) and celgard 2400 (Polypore Co., Ltd.) which is a single-layer polypropylene were prepared as a separator. Further, an electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which 3 parts by volume of ethylene carbonate, 3 parts by volume of ethyl methyl carbonate and 4 parts by volume of dimethyl carbonate were mixed. In the order of the negative electrode, the glass filter, celgard 2400, and the positive electrode of Example 1, two types of separators were sandwiched between the negative electrode and the positive electrode of Example 1 to form an electrode assembly. The electrode body was housed in a coin-type battery case CR2032 (Housen Co., Ltd.), and an electrolyte was further injected to obtain a sealed coin-type battery. The resultant was used as a lithium ion secondary battery of Example 1.

In addition, 6.7 parts by mass of carbon-coated Li ₅ FeO ₄ of Example 1, 69 parts by mass of LiNi _82/100 Co _15/100 Al _3/100 O ₂ as a positive electrode active material, Li (Fe ₁₎ as a positive electrode active material Mixed 19.3 parts by mass of _-x , Mn _x ) PO ₄ , 2 parts by mass of acetylene black as a conductive additive, 3 parts by mass of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone; The slurry was made to have a solid content of 64% by mass. This was used as the slurry of Example 1.

(Example 2)
The carbon-coated Li of Example 2 was prepared in the same manner as Example 1, except that the amount of lithium stearate added was 1 mass% with respect to the total amount of Li ₂ O and Fe ₂ O _{3. 5} FeO ₄ , positive electrode, lithium ion secondary battery and slurry were manufactured.

(Example 3)
The carbon-coated Li of Example 3 was prepared in the same manner as Example 1, except that the amount of lithium stearate added was 2 mass% with respect to the total amount of Li ₂ O and Fe ₂ O _{3. 5} FeO ₄ , positive electrode, lithium ion secondary battery and slurry were manufactured.
Incidentally, by using the carbon-sulfur analyzer, to the carbon-coated Li ₅ FeO ₄ of Example 3, was subjected to elemental analysis for the carbon, the amount of carbon was 2.0 wt%. In addition, when a load of ₄ kN was applied to the carbon-coated Li ₅ FeO _{4 of} Example 3 using a powder resistivity measurement system (Mitsubishi Analytech Co., Ltd.), the volume resistance value was measured, It was 4.3 Ωcm.

(Example 4)
The carbon-coated Li of Example 4 was prepared in the same manner as Example 1, except that the amount of lithium stearate added was 3% by mass relative to the total amount of Li ₂ O and Fe ₂ O _{3. 5} FeO ₄ , positive electrode, lithium ion secondary battery and slurry were manufactured.

(Example 5)
The carbon-coated Li of Example 5 was prepared in the same manner as Example 1, except that the amount of lithium stearate added was 7% by mass relative to the total amount of Li ₂ O and Fe ₂ O _{3. 5} FeO ₄ , positive electrode, lithium ion secondary battery and slurry were manufactured.

(Example 6)
The carbon-coated Li of Example 6 was prepared in the same manner as Example 1, except that the amount of lithium stearate added was 10% by mass relative to the total amount of Li ₂ O and Fe ₂ O _{3. 5} FeO ₄ , positive electrode, lithium ion secondary battery and slurry were manufactured.

(Comparative example 1)
A carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, a positive electrode, a lithium ion secondary battery, and a slurry were produced in the same manner as in Example 1 except that lithium stearate was not added.

(Evaluation example 1)
The surface area of the carbon-coated Li ₅ FeO ₄ of each of Examples 1 to 6 and Comparative Example 1 was measured by the BET method. The value of the specific surface area of each carbon-coated Li ₅ FeO ₄ is shown in Table 1.

(Evaluation example 2)
Each lithium ion secondary battery was charged to a voltage of 4.4 V at a current of 0.1 mA. The observed charge capacity is shown graphically in FIG. 1 and further in Table 1 together with the results of Evaluation Example 1.

From Table 1, the addition amount of the organic additive and the value of the specific surface area of the carbon-coated Li ₅ FeO ₄ are in correlation, and as the amount of the organic additive increases, the value of the specific surface area of the carbon-coated Li ₅ FeO ₄ is It turns out that it becomes large. That is, it can be said that the particle diameter of the carbon-coated Li ₅ FeO ₄ decreases as the amount of the organic additive increases.
It can be said that the addition of the organic additive can support the control of the particle size of the synthesized inorganic compound.

Further, it is understood from Table 1 and FIG. 1 that the charge capacity of each example is extremely high as compared with Comparative Example 1. It can be said that the carbon-coated Li ₅ FeO ₄ of the present invention having a BET specific surface area in the range of 1 to 12 m ² / g is proved to be excellent in capacity.

(Evaluation example 3)
The viscosity of each of the slurries of Examples 1 to 6 and Comparative Example 1 was measured in a sealed state at room temperature after 24 hours from production. The viscosity was measured with a Brookfield type B viscometer DV-II + Pro using a spindle 64 at a spindle rotational speed of 20 rpm at room temperature. The values of the viscosity are shown in Table 2 together with the results of Evaluation Example 1 and Evaluation Example 2.

From Table 2, it can be said that as the specific surface area of the carbon-coated Li ₅ FeO ₄ increases, the viscosity after 24 hours of the slurry increases, and it can be said that the change with time of the viscosity of the slurry also increases. From the viewpoint of the stability of the physical properties of the slurry, it may be preferable that the specific surface area of the carbon-coated Li ₅ FeO _{4 be} smaller.
When the results of Evaluation Example 2 and Evaluation Example 3 are combined, it can be said that the BET specific surface area of the carbon-coated Li ₅ FeO ₄ of the present invention is particularly preferably in the range of 2 to 5 m ² / g.

Claims (5)

1. A carbon-coated _Li 5 FeO ₄ containing a carbon film covering the surface of the Li ₅ FeO ₄ and the _Li 5 FeO _4, and a BET specific surface area in the range of 1 ~ ^12m 2 / g Carbon coated Li ₅ FeO ₄ .
2. A positive electrode comprising the carbon-coated Li ₅ FeO _{4 according} to claim 1.
3. A lithium ion secondary battery comprising the positive electrode according to claim 2.
4. In a method for producing an inorganic compound, wherein an inorganic compound is synthesized by heating a first solid inorganic raw material and a second solid inorganic raw material different from the first solid inorganic raw material.
   Powdered form characterized by adding an organic additive selected from sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide, N, N'-ethylenebis fatty acid amide, fumaric acid alkyl ester alkali metal salt and hardened oil Method for producing inorganic compounds.
5. The method for producing a powdered inorganic compound according to claim 4, wherein the temperature of the heating is equal to or higher than a temperature at which the organic additive is vaporized or decomposed.

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