JP6922672B2 - Carbon coated Li5FeO4 - Google Patents

Description

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

Since lithium-ion secondary batteries are small and have a large capacity, they are used as batteries for various devices such as mobile phones and notebook computers. The lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution as main components. The positive electrode has 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 composite oxides are used as the positive electrode active material of the lithium ion secondary battery, and Li ₅ FeO ₄ is known as one of them. It _{is also known that Li 5} FeO ₄ has a small reversible capacity and generates gas during charging, and is used as a lithium ion feeder for supplementing the irreversible capacity of the negative electrode and as an additive for the positive electrode. It is also known to be used in the above applications.

For example, Patent Document 1, LiMn ₂ O ₄ and _Li 5 FeO ₄ and a mass ratio of 95: lithium ion secondary battery comprising a positive electrode using 5 have been specifically _described, the Li 5 FeO ₄ It is stated that the addition was able to compensate for the initial capacity loss of the negative electrode active material.

Patent Document 2 describes 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 containing _{Li 5} FeO _{4 and Li as a positive electrode active material.} However, it 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 as positive electrode active materials at a mass ratio of 91: 9 to 97: 3. _It is described that the initial charge capacity could be improved by adding 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 during the initial charging, and the gas is generated during the initial charging to empty the positive electrode active material layer. It is stated that holes can be formed.

Japanese Unexamined Patent Publication No. 2007-287446 Japanese Unexamined Patent Publication No. 2012-99316 Japanese Unexamined Patent Publication No. 2014-157653 International Publication No. 2014/118834

In recent years, the industrial world has been demanding lithium-ion secondary batteries having excellent battery characteristics and excellent materials for manufacturing lithium-ion secondary batteries, and new technologies for realizing them have been demanded. There is.

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

When the present inventor _{examined Li 5} FeO _4, it was found that _{the battery provided with Li 5} FeO ₄ does not sufficiently develop the capacity. The present inventor presumed that such a phenomenon was due to the low conductivity, that is, the high resistance property of _{Li 5} FeO _{4. 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 was found that the volume may not always be sufficiently expressed.

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 present inventor has found that the 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 inventor has found that.
The present invention has been completed based on such findings of the present inventor.

Carbon-coated _Li 5 FeO ₄ of the present invention _is a carbon-coated _Li 5 FeO ₄ containing a carbon film covering the surface of the the _{Li 5 FeO 4 Li 5 FeO 4} , BET specific surface area 1～12M ² It is characterized in that it is within the range of / g.

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

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

Hereinafter, embodiments for carrying out the present invention will be described. Unless otherwise specified, the numerical range "a to b" described in the present specification includes the lower limit a and the upper limit b in the range. Then, a numerical range can be constructed by arbitrarily combining these upper and lower limit values and the numerical values listed in the examples. Further, a numerical value arbitrarily selected from these numerical values can be set as a new upper limit value or lower limit value.

Carbon-coated _Li 5 FeO ₄ of the present invention _is a carbon-coated _Li 5 FeO ₄ containing a carbon film covering the surface of the the _{Li 5 FeO 4 Li 5 FeO 4} , BET specific surface area 1～12M ² It is characterized in that it is within the range of / g.
When the BET specific surface area is in ^{the range of 1 to 12 m 2} / g, a sufficient capacity (lithium ion emission amount) as a positive electrode material is developed.

In terms of volume, as BET specific surface area of the carbon-coated _Li 5 FeO ₄ of the present invention, preferably in the range of 2 to 10 m ² / g, in the range of 3~7m ² / g is more preferable.
If the BET specific surface area is too small, the capacity may be inferior. On the other hand, if the BET specific surface area is excessive, it may react with water or carbon dioxide in the atmosphere _{to deteriorate Li 5} FeO _4, or may adversely affect the physical characteristics of the slurry during the production of the positive electrode. From the viewpoint of both the capacity and the physical characteristics 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 Li ₅ FeO _{4 particles.} 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, further preferably in the range of 10 nm to 40 nm, and particularly preferably in the range of 15 nm to 35 nm.

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

The carbon-coated Li ₅ FeO ₄ of the present invention is preferably in a powder state. Examples of the powder resistance value of the carbon-coated Li ₅ FeO ₄ of the present invention include 0.5 to 20 Ωcm, 1 to 13 Ωcm, 1.5 to 10 Ω cm, and 2 to 7 Ω cm.
The powder resistance value in the present specification means the volume resistance value when a load of 4 kN is applied to the measurement sample.

The method for producing the carbon-coated Li ₅ FeO ₄ of the present invention will be described.
The method for producing carbon-coated Li ₅ FeO ₄ of the present invention includes a step of preparing _{Li 5} FeO _{4 and a step of coating Li 5} FeO ₄ with carbon.

As a method for preparing _{Li 5} FeO _{4 , commercially available Li 5} FeO _{4 may be purchased, or Li 5} FeO ₄ may be synthesized from the Li source and the Fe source as raw materials.

As a _{method for synthesizing Li 5} FeO ₄ , the Li source and the 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 hydrogencarbonate, and lithium fluoride. Examples of the Fe source include iron alone, iron oxide, iron hydroxide, iron oxyhydroxide, iron sulfate, iron nitrate, and iron chloride. When the composition of the Li source and the Fe source is less than the theoretical amount of oxygen, oxygen may be introduced into the reaction system.
From the viewpoint of product purity, it is preferable to react lithium alone with iron oxide, react lithium oxide with iron oxide alone, or react lithium oxide with iron oxide.

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

As a device for crushing, mixing or integrating the Li source and Fe source before heating, a ball mill, a planetary ball mill, a hybridization system (NHS) and MIRALO of Nara Machinery Co., Ltd., Hosokawa Micron Co., Ltd. Mechanofusion and Nobilta, Theta Composer of Tokuju Kosakusho Co., Ltd. can be mentioned.

The heating temperature is preferably 400 to 1000 ° C, more preferably 450 to 900 ° C, even more preferably 500 to 800 ° C, and particularly preferably 550 to 700 ° C. It has been confirmed by the present inventor _{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 , it is preferable to heat in an atmosphere of an inert gas such as argon, helium, or nitrogen, unless there are special circumstances.

As a _{method for synthesizing Li 5} FeO ₄ , sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide, N, N'-ethylenebis fatty acid amide, fumarate alkyl ester alkali metal salt and hardened oil are used as the Li source and Fe source. It is particularly preferable to synthesize _{Li 5} FeO ₄ after adding an organic additive selected from the above.
By adding the organic additive, it is possible to suppress the coarsening of the particles of _{Li 5} FeO _4. Since the amount of the organic additive added is small and the organic additive is vaporized or decomposed in the reaction system, _{the composition of Li 5} FeO ₄ is not significantly affected.
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 can.
The amount of the organic additive added is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, still more preferably 1 to 3% by mass, based on the total of the Li source and the Fe source.

The sucrose fatty acid ester is an ester produced from sucrose and fatty acid, and is a powdery nonionic surfactant known as a trade name such as Ryoto sugar ester.

As the fatty acid in the sucrose fatty acid ester, fatty acid, fatty acid salt, fatty acid amide, and N, N'-ethylenebis fatty acid amide, saturated or unsaturated fatty acid having 12 to 24 carbon atoms is preferable, and saturated fatty acid having 16 to 20 carbon atoms is preferable. Alternatively, unsaturated fatty acids are more preferable. Examples of the fatty acid include palmitic acid, stearic acid, arachidic acid, palmitoleic acid, oleic acid, linoleic acid, and arachidonic acid.

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 the cation forming the salt in the fatty acid salt, an alkali metal such as lithium or sodium is preferable because it is easily scattered and does not easily contaminate the apparatus.

Specific examples of fatty acid salts include lithium palmitate, lithium stearate, lithium arachidic acid, lithium palmitreate, lithium oleate, lithium linoleate, lithium arachidate, sodium palmitate, sodium stearate, sodium arachidic acid, and palmitic acid. Sodium, sodium oleate, sodium linoleate, sodium arachidic acid, magnesium palmitate, magnesium stearate, magnesium arachidic acid, magnesium palmitreate, magnesium oleate, magnesium linoleate, magnesium arachidic acid, palmitic acid, calcium stearate, arachidic acid Examples thereof include calcium, calcium palmitreate, calcium oleate, calcium linoleate, calcium arachidic acid, zinc palmitate, zinc stearate, zinc arachidic acid, zinc palmitate, zinc oleate, zinc linoleate, and zinc arachidic acid.

Specific examples of the fatty acid amide include palmitate amide, stearate amide, arachidic acid amide, palmitere acid amide, oleic acid amide, linoleic acid amide, and arachidonic acid amide.

Specific examples of the N, N'-ethylenebis fatty acid amide include N, N'-ethylenebispalmitic acid amide, N, N'-ethylenebisstearic acid amide, N, N'-ethylenebisarachidic acid amide, N. , N'-ethylene bispalmitoleic acid amide, N, N'-ethylene bisoleic acid amide, N, N'-ethylene bislinoleic acid amide, N, N'-ethylene bisarachidonic acid amide can be exemplified.

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 arachidil. Examples of the cation forming the alkali metal salt include lithium and sodium.

Specific examples of the alkyl ester alkali metal salt fumarate include palmityl lithium fumarate, stearyl fumarate, lithium arachidyl fumarate, palmityl sodium fumarate, stearyl fumarate, and arachidyl fumarate. An example is a sodium salt.

Lithium is preferable as the cation in the fatty acid salt and the alkyl metal fumaric acid ester alkali metal salt.

Examples of the hydrogenated oil include powdered hydrogenated hydrogenated oil known as love wax (registered trademark) and the like.

The addition of the organic additive, Li ₅ FeO ₄ particles can be prevented from coarsening, furthermore, the reason for a more in controlling the amount of the organic additive, can control the particle size of the Li ₅ FeO ₄ Is considered to be due to the following mechanism.

At the time of 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 the _{four particles stick to each other.} It is considered that these matters cause the formation of _{coarse Li 5} FeO _{4 particles.}

On the other hand, in the presence of an organic additive, an organic additive or gas products or degradation products, the contact of the contact or other _Li 5 FeO ₄ particles Li source and Fe sources for synthesized _Li 5 FeO ₄ particles Suppress. Therefore, it is considered that the coarsening of _{Li 5} FeO _{4 particles can be suppressed.}

The present inventor created the following technical idea from the experimental fact that the particle size of _{Li 5} FeO ₄ can be controlled by adding an organic additive.

In a method for producing an inorganic compound in which 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 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, fumarate alkyl ester alkali metal salt and cured oil. Method for producing inorganic compounds.

In the method for producing an inorganic compound in which an inorganic compound is synthesized by heating a first solid inorganic raw material and a second solid inorganic raw material, by adding an organic additive, powdery inorganic compound particles are formed according to the mechanism described above. It can be said that the size and specific surface area can be controlled. It can be said that the production method in the previous paragraph is a method for 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 heating temperature. Examples of the inorganic compound to be synthesized include metal oxides and metal nitrides. The synthesis temperature is preferably equal to or higher than the temperature at which the organic additive vaporizes or decomposes.

The first solid inorganic raw material and the second solid inorganic raw material are solid at room temperature, but each is preferably a solid inorganic material even at the synthesis temperature of the inorganic compound. Further, the first solid inorganic raw material and the second solid inorganic raw material may be those which are decomposed at a synthetic temperature or lower and the solid decomposition product becomes a raw material of an inorganic compound. For example, a hydrate that becomes an anhydride by heating, a hydroxide or a carbonate that becomes an oxide by heating may be adopted as the first solid inorganic raw material and the second solid inorganic raw material.

The first solid inorganic raw material and the second solid inorganic raw material include metal alone, alloy, element alone, oxide, peroxide, hydroxide, hydride, halide, boride, cyanide, azide, and nitride. , Carbide, carbonate, sulfide, sulfate, sulfite, dihydrosulfate, thiosulfate, nitrate, nitrite, phosphate, ammonium salt, silicate, borate, perhalogenate, hypophalus Phosphates, halides, and hydrates thereof can be exemplified.

The _{carbon coating step of coating Li 5} FeO ₄ with carbon will be described.
In _{the coexistence of Li 5} FeO ₄ and the carbon source, by heating at a temperature equal to or higher than the carbonization 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 used in the carbon coating step is preferably in a crushed or classified powder state.

The carbon source is organic matter. Organic substances include solids, liquids, and gases. In particular, by using an organic substance in a gaseous state, a uniform carbon film can be formed on the surface of _{Li 5} FeO _4. The method of forming a carbon film using an organic substance in a gaseous state is an application of a method generally called a thermal CVD method. When the carbon coating process is performed by applying the thermal CVD method, hot wall type, cold wall type, horizontal type, vertical type, etc., flow layer reactor, rotary furnace, tunnel furnace, batch type firing furnace, rotary kiln A known CVD apparatus such as the above may be used.

Organic substances that can be thermally decomposed and carbonized by heating are used, for example, saturated aliphatic hydrocarbons such as methane, ethane, propane, butane, isobutane, pentane, hexane, heptane, and octane, ethylene, propylene, acetylene, and the like. Unsaturated aliphatic hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, benzoic acid, salicylic acid, nitrobenzene, chlorbenzene, inden, A type selected from aromatic hydrocarbons such as benzofuran, pyridine, anthracene, and phenanthrene, esters such as ethyl acetate, butyl acetate, and amyl acetate, carbohydrates such as sucrose, organic acids such as citric acid, and resins such as vinylidene fluoride. Alternatively, a mixture may be mentioned.
Considering the ease of decomposition, the boiling point, and the purity of the carbon film, as the organic substance, a saturated aliphatic hydrocarbon having 5 to 18 carbon atoms is preferable, a saturated aliphatic hydrocarbon having 5 to 12 carbon atoms is more preferable, and a saturated aliphatic hydrocarbon having 5 to 12 carbon atoms is more preferable. 5-8 saturated aliphatic hydrocarbons are more preferred.

It is desirable that the carbon coating step _{be carried out with Li 5} FeO _{4 in a fluid state.} By doing so, _{the entire surface of Li 5} FeO ₄ can be brought into contact with organic substances, a more uniform carbon film can be formed, and the binding of _{carbon-coated Li 5} FeO _{4 particles is suppressed.} You can also do it. There are various methods for bringing Li ₅ FeO ₄ into a fluidized state, such as using a fluidized bed, but _{it is preferable to bring Li 5} FeO ₄ into contact with an organic substance while stirring. For example, if a rotary furnace having a baffle plate inside is used, Li ₅ FeO ₄ staying on the baffle plate is agitated by falling from a predetermined height as the rotary furnace rotates, and at that time, it comes into contact with organic substances. Since the carbon film is formed, a more uniform carbon film can be formed over the entire _{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 even more preferably in the range of 720 to 760 ° C. Further, the carbon coating step is preferably carried out in an atmosphere of an inert gas such as argon, helium or nitrogen.

The carbon-coated Li ₅ FeO ₄ of the present invention can function as a positive electrode active material, as a lithium ion feeder, or as various additives. In particular, the carbon-coated Li ₅ FeO ₄ of the present invention is a positive electrode material for a lithium ion secondary battery, and functions suitably as a lithium ion feeder at the time of initial charging in the positive electrode of a lithium ion secondary battery. Hereinafter, the positive electrode for a lithium ion secondary battery provided with the carbon-coated Li ₅ FeO ₄ of the present invention is referred to as "the positive electrode of the present invention", and the lithium ion secondary battery provided with the positive electrode of the present invention is referred to as "the lithium ion of the present invention". It is called "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 includes 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 feeder, the blending 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.

A current collector is a chemically inert electron conductor that keeps current flowing through the electrodes during the discharge or charging of a 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. As the material of the current collector, 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. Metallic materials such as, etc. can be exemplified. The current collector may be coated with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

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

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

Further, as aluminum or an aluminum alloy, specifically, for example, A1000 series alloys such as JIS A1085 and A1N30 (pure aluminum series), A3000 series alloys such as JIS A3003 and A3004 (Al-Mn series), JIS A8079, A8021 and the like. A8000 series alloy (Al—Fe series) can be mentioned.

The current collector can take the form of foil, sheet, film, linear, rod, mesh or the like. Therefore, as the current collector, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be preferably used. When the current collector is in the form of a foil, a sheet, or a film, the thickness thereof 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 the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} 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, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, _{Li a} Ni, a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3), which is at least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V. _{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, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, Examples _{thereof include Li 2 MnO 3} , a lithium composite metal oxide represented by at least one element selected from P and V, 1.7 ≦ f ≦ 3). Further, as the positive electrode active material, _{a metal oxide having a spinel structure such as LiMn 2} O ₄ , a solid solution composed of a mixture of a metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (in the formula). 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 the positive electrode active material may have the above composition formula as the basic composition, and those in which the metal element contained in the basic composition is replaced with another metal element can also be used. Further, as the positive electrode active material, a material that does not contain a charge carrier (for example, lithium ions that contribute to charging / discharging) may be used. For example, elemental sulfur, compounds complexed with sulfur and carbon, metal sulfides such as TiS _2, oxides such as V 2 _{O 5,} MnO _2, polyaniline and anthraquinone and compounds containing these aromatic in chemical structure, conjugated double Conjugated materials such as acetic acid-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galbinoxyl, phenoxyl and the like may be adopted as the positive electrode active material. When a positive electrode active material that does not contain a charge carrier such as lithium is used, it is necessary to add a charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or may be added in a non-ionic state such as a metal. For example, when the charge carrier is lithium, a lithium foil may be attached to the positive electrode and / or the negative electrode to integrate them.

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

From the viewpoint of high capacity and excellent durability, Li _x Mn _{2-y Ay} O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga) having a spinel structure as a positive electrode active material. , At least one element selected from Ge, and at least one metal element selected from transition metal elements such as Ni. 0 <x ≦ 2.2, 0 ≦ y ≦ 1) can be exemplified. Examples of the range of x values include 0.5 ≦ x ≦ 1.8, 0.7 ≦ x ≦ 1.5, and 0.9 ≦ x ≦ 1.2, and the range of y values is 0. Examples thereof include ≦ y ≦ 0.8 and 0 ≦ y ≦ 0.6. Examples of specific spinel-structured compounds include LiMn ₂ O ₄ and Limn _1.5 Ni _0.5 O _4.

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 agent. As the binder and the conductive auxiliary agent contained in the positive electrode active material layer, those described in the negative electrode described later may be appropriately and appropriately adopted.

Specifically, the lithium ion secondary battery of the present invention includes the positive electrode, the negative electrode, the electrolytic solution, and the separator of the present invention. 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. The current collector of the negative electrode may be appropriately selected from those described in the positive electrode of the present invention.

As the negative electrode active material, a material capable of occluding and releasing charge carriers can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy or compound capable of occluding and releasing a charge carrier such as lithium ion. For example, Li, Group 14 elements such as carbon, silicon, germanium, and tin, Group 13 elements such as aluminum and indium, Group 12 elements such as zinc and cadmium, Group 15 elements such as antimony and bismuth, and magnesium as negative electrode active materials. , Alkaline earth metals such as calcium, and Group 11 elements such as silver and gold may be used alone. Specific examples of alloys or compounds include tin-based materials such as Ag-Sn alloys, Cu-Sn alloys, and Co-Sn alloys, carbon-based materials such as various graphites, and SiO _{x that disproportionates to elemental silicon and silicon dioxide.} Examples thereof include a silicon-based material such as 0.3 ≦ x ≦ 1.6), a simple substance of silicon, or a composite of a silicon-based material and a carbon-based material. Further, the negative electrode active material is 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 adopted. One or more of these can be used as the negative electrode active material.

From the viewpoint of the possibility of increasing the capacity, graphite, Si-containing material, and Sn-containing material can be mentioned as preferable negative electrode active materials. In particular, when a Si-containing material in which the existence of an irreversible capacity is an important issue is used as the negative electrode active material, _{the effect of the carbon-coated Li 5} FeO ₄ of the present invention as a lithium ion feeder is remarkably exhibited.

Specific examples of the Si-containing material include Si alone and SiO _x (0.3 ≦ x ≦ 1.6) disproportionated into two phases of a Si phase and a silicon oxide phase. The Si phase in SiO _x can occlude and release lithium ions, and its volume changes with the charging and discharging of the secondary battery. The silicon oxide phase has less volume change due to charging and discharging than 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 entire negative electrode active material by having the silicon oxide phase. If x is less than the lower limit, the ratio of Si becomes excessive, so that the volume change during charging / discharging 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 even more preferably 0.7 ≦ x ≦ 1.2.

In the above-mentioned SiO _x , it is considered that an alloying reaction between lithium and silicon in the Si phase occurs during charging / discharging of the lithium ion secondary battery. It is believed that this alloying reaction contributes to the charging and discharging of the lithium ion secondary battery. Similarly, it is considered that the Sn-containing material described later can be charged and discharged by the alloying reaction of tin and lithium.

Specific examples of the Sn-containing material include Sn alone, tin alloys such as Cu-Sn and Co-Sn, amorphous tin oxide, and tin silicon oxide. _{SnB 0.4} P _0.6 O _3.1 can be exemplified as the amorphous tin oxide, and _{SnSiO 3} can be exemplified as the tin silicon oxide.

The Si-containing material and the Sn-containing material are preferably combined with a carbon material to form a negative electrode active material. Due to the compounding, the structure of silicon and / or tin is particularly stable, and the durability of the negative electrode is improved. The above compounding may be performed by a known method. As the carbon material used for the composite, graphite, hard carbon, soft carbon or the like may be adopted. The graphite may be natural graphite or artificial graphite.

As a specific example of the Si-containing material, a silicon material disclosed in International Publication No. 2014/08608 or the like (hereinafter, simply referred to as “silicon material”) can be mentioned.

The silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. The silicon material undergoes, for example, _{a step of reacting CaSi 2} with an acid to synthesize a layered silicon compound containing polysilane as a main component, and a step of heating the layered silicon compound at 300 ° C. or higher to release hydrogen. It is manufactured.

The ideal reaction formula when hydrogen chloride is used as the acid shows the method for producing the silicon material as follows.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl _{2
Si 6 H 6 → 6Si + 3H} 2 ↑

_{However, in the upper reaction for synthesizing Si 6} H ₆ which is polysilane, water is usually used as the reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, the layered silicon compound is rarely produced as containing only _{Si 6} H ₆ in the step of synthesizing the layered silicon compound including the reaction in the upper stage, and is layered. Silicon compounds are represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a compound. In the above chemical formula, unavoidable impurities such as Ca that may remain are not considered. The silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

As described above, the silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. In order to efficiently occlude and release a charge carrier such as lithium ion, the plate-shaped 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. The length of the plate-shaped silicon body in the longitudinal direction is preferably in the range of 0.1 μm to 50 μm. Further, the plate-shaped silicon body preferably has a (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-shaped silicon body can be confirmed by observation with a scanning electron microscope or the like. Further, this laminated structure is considered to be a remnant of the Si layer in _{the raw material CaSi 2.}

The silicon material preferably contains amorphous silicon and / or silicon crystallites. In particular, in the plate-shaped silicon body, it is preferable that amorphous silicon is used as a matrix and silicon crystallites are 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, further 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 Scherrer's equation using the half width of the diffraction peak on the Si (111) plane of the obtained X-ray diffraction chart obtained by performing X-ray diffraction measurement on the silicon material. ..

The abundance and size of the plate-shaped silicon body, amorphous silicon, and silicon crystallites 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., more preferably in the range of 400 ° C. to 900 ° C.

The silicon material may be coated with carbon. The carbon-coated silicon material has excellent conductivity.

The average particle size of the silicon material is preferably in the range of 2 to 7 μm, 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 a negative electrode from the viewpoint of cohesiveness and wettability. Specifically, in the slurry prepared at the time of manufacturing the negative electrode, the silicon material having an average particle size too small may aggregate. On the other hand, a lithium ion secondary battery provided with a negative electrode using a silicon material having an average particle size too large may not be able to be charged and discharged appropriately. In a silicon material having an average particle size too large, it is presumed that the cause is that lithium ions cannot sufficiently diffuse into the inside of the silicon material. The average particle size in the present specification means D50 when the sample is measured by a general laser diffraction type particle size distribution measuring device.

Examples of the binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins and carboxymethyl cellulose. , A known material such as styrene-butadiene rubber may be used.

Further, a crosslinked polymer obtained by cross-linking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid with a polyamine such as diamine disclosed in International Publication No. 2016/06382 may be used as a binder.

Examples of the diamine used in the crosslinked polymer include alkylenediamines such as ethylenediamine, propylenediamine and hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophoronediamine and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-trizine, 2,4- Examples thereof include aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalene diamine.

The blending ratio of the binder in the active material layer is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, further preferably 2 to 10% by mass, and particularly preferably 3 to 5% by mass. This is because if the amount of the binder is too small, the moldability of the electrode is lowered, and if the amount of the binder is too large, the energy density of the electrode is lowered.

The conductive auxiliary agent is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be arbitrarily 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 auxiliary agent may be a chemically inert electron high conductor, and examples thereof include carbon black, graphite, vaporized carbon fiber (Vapor Grown Carbon Fiber), and various metal particles, which are carbonaceous fine particles. NS. Examples of carbon black include acetylene black, Ketjen black (registered trademark), furnace black, and channel black. These conductive auxiliary agents can be added to the active material layer alone or in combination of two or more. The blending ratio of the conductive auxiliary agent in the active material layer is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, further preferably 2 to 10% by mass, and particularly preferably 2 to 5% by mass. This is because if the amount of the conductive auxiliary agent is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary agent is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

In order to form an active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used to collect electricity. 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 then 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 in order to increase the electrode density.

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

_{The blending amount of the carbon-coated Li 5} FeO ₄ of the present invention in the composition for producing a positive electrode active material layer may be appropriately determined according to the use of the carbon-coated Li ₅ FeO _{4 of the present invention.}
When the carbon-coated Li ₅ FeO ₄ of the present invention is used as a lithium ion feeder for supplementing lithium ions corresponding to the irreversible capacity of the negative electrode, the carbon-coated Li 5 FeO 4 of the present invention in the composition for producing a positive electrode active material layer is used. Examples of the blending amount of Li ₅ FeO ₄ include a range of 1 to 10% by mass, a range of 3 to 9% by mass, and a range of 5 to 8% by mass with respect to the solid content.

The blending amount of the positive electrode active material in the composition for producing the positive electrode active material layer is in the range of 80 to 95% by mass, in the range of 83 to 93% by mass, and 85 to 90% by mass with respect to the solid content. The range can be illustrated. The blending amount of the binder in the composition for producing the positive electrode active material layer is in the range of 0.5 to 10% by mass, in the range of 1 to 5% by mass, and 2 to 4% by mass with respect to the solid content. The range can be exemplified. The blending amount of the conductive auxiliary agent in the composition for producing the positive electrode active material layer is in the range of 0.5 to 5% by mass, in the range of 1 to 4% by mass, and 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 through while preventing a short circuit due to contact between the two electrodes. As the separator, a known one may be adopted, and synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester and polyacrylonitrile, polysaccharides such as cellulose and amylose, and fibroin , Natural polymers such as keratin, lignin, and suberin, porous materials using one or more electrically insulating materials such as ceramics, non-woven fabrics, and woven fabrics. Further, the separator may have a multi-layer structure.

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

As the non-aqueous solvent, cyclic carbonates, cyclic esters, chain carbonates, chain esters, ethers and the like can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, and examples of the cyclic ester include gamma-butyrolactone, 2-methyl-gamma-butyrolactone, acetyl-gamma-butyrolactone, and gamma-valerolactone. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, and ethyl methyl carbonate, and examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, and acetate alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which some or all of the chemical structure of the specific solvent is replaced 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 the electrolytic solution, 0.5 mol / mol of lithium salts such as _{LiClO 4} , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO _{3 is} added to a non-aqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. An example of a solution dissolved at a concentration of about 1.7 mol / L from L can be exemplified.

A specific method for manufacturing the lithium ion secondary battery of the present invention will be described.
For example, the separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a laminated body of a positive electrode, a separator and a negative electrode is wound. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collector 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 a cylindrical type, a square type, a coin type, and a laminated type can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses 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 an assembled battery. In addition to vehicles, devices equipped with lithium-ion secondary batteries include various battery-powered home appliances such as personal computers and mobile communication devices, office devices, and industrial devices. Further, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydraulic power generation, other power storage devices and power smoothing devices for electric power systems, power supply sources for power and / or auxiliary machinery such as ships, aircraft, and so on. Power supply sources for spacecraft and / or auxiliary equipment, auxiliary power sources for vehicles that do not use electricity as power sources, power sources for mobile household robots, power sources for system backup, power sources for uninterruptible power supplies, It may be used as a power storage device that temporarily stores the electric power required for charging in a charging station for an electric vehicle or the like.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. As long as it does not deviate from the gist of the present invention, it can be carried out in various forms with modifications, improvements, etc. that can be made by those skilled in the art.

Hereinafter, the present invention will be described in more detail with reference to various specific examples. The present invention is not limited to 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. Further, 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 charged into a planetary ball mill.} A planetary ball mill was operated at a rotation speed of 800 rpm and a revolution 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 pulverized 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, thermal CVD was performed at 700 ° C. for 40 minutes under the aeration of a hexane-argon mixed gas to form a carbon film on the surface of _{Li 5} FeO _{4 , and the carbon-coated Li 5} FeO of Example 1 was formed. 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 auxiliary agent, 5 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone. It was mixed to obtain a slurry. An aluminum foil was prepared as a current collector, a slurry was applied thereto, and the foil was dried to obtain a positive electrode of Experimental Example 1.

A lithium foil was prepared and used as the negative electrode. As a separator, a glass filter (Hoechst Celanese Co., Ltd.) and a single-layer polypropylene celgard 2400 (Polypore Co., Ltd.) were prepared. _{Further, an electrolytic solution 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 ethylmethyl carbonate and 4 parts by volume of dimethyl carbonate were mixed. Two types of separators were sandwiched between the negative electrode and the positive electrode of Example 1 in the order of the negative electrode, the glass filter, the celgard 2400, and the positive electrode of Example 1 to form an electrode body. This electrode body was housed in a coin-type battery case CR2032 (Hosen Co., Ltd.), and an electrolytic solution was further injected to obtain a sealed coin-type battery. This was used as the lithium ion secondary battery of Example 1.

Further, 6.7 parts by mass of the 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 the positive electrode active material, and Li (Fe _{1) as the positive electrode active material. -X} , Mn _x ) PO ₄ was mixed by 19.3 parts by mass, acetylene black as a conductive auxiliary agent by 2 parts by mass, polyvinylidene fluoride as a binder by 3 parts by mass, and N-methyl-2-pyrrolidone. The slurry had 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 carried out in the same manner as in Example 1 except that the amount of lithium stearate added _{was set to an amount corresponding to 1% by 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 added in the same manner as in Example 1 except that the amount of lithium stearate added _{was set to an amount corresponding to 2% by 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.
_{When an elemental analysis of carbon was performed on the carbon-coated Li 5} FeO _{4 of} Example 3 using a carbon / sulfur analyzer, the amount of carbon was 2.0% by mass. Further, when the volume resistivity value was measured by applying a load of _{4 kN to the carbon-coated Li 5} FeO _{4 of} Example 3 using a powder resistivity measurement system (Mitsubishi Analytech Co., Ltd.). It was 4.3 Ωcm.

(Example 4)
The carbon-coated Li of Example 4 was carried out in the same manner as in Example 1 except that the amount of lithium stearate added _{was set to an amount corresponding to 3% by 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 5)
The carbon-coated Li of Example 5 was carried out in the same manner as in Example 1 except that the amount of lithium stearate added was _{7% by 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 6)
The carbon-coated Li of Example 6 was carried out in the same manner as in Example 1 except that the amount of lithium stearate added was _{10% by 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.

(Comparative Example 1)
_{The carbon-coated Li 5} FeO ₄ , positive electrode, lithium ion secondary battery, and slurry of Comparative Example 1 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 Examples 1 to 6 and Comparative Example 1 was measured by the BET method. Table 1 shows the values of the specific surface area of each carbon-coated Li ₅ FeO _4.

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

From Table 1, the amount of the organic additive added and _{the value of the specific surface area of the carbon-coated Li 5} FeO ₄ are correlated, and as the amount of the organic additive increases, the value of the specific surface area of _{the carbon-coated Li 5} FeO _{4 increases.} You can see that it gets bigger. That is, it can be said that the particle size _{of the carbon-coated Li 5} FeO ₄ decreases as the amount of the organic additive increases.
It can be said that it is possible to control the particle size of the synthesized inorganic compound by adding the organic additive.

Further, from Table 1 and FIG. 1, it can be seen that the charging capacity of each example is remarkably high as compared with Comparative Example 1. _{It can be said that the carbon-coated Li 5} FeO ₄ of the present invention, which has a BET specific surface area in ^{the range of 1 to 12 m 2} / g, is proved to have excellent capacity.

(Evaluation example 3)
The viscosities of the slurries of Examples 1 to 6 and Comparative Example 1 were measured 24 hours after the production in a closed state at room temperature. The viscosity was measured with a Brookfield B-type viscometer DV-II + Pro using a spindle 64 under the conditions of a spindle rotation speed of 20 rpm and room temperature. Table 2 shows the viscosity values 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 of the slurry after 24 hours increases, and the change in viscosity of the slurry with time also increases. From the viewpoint of the stability of the physical properties of the slurry, it can be said that it is preferable that the specific surface area of _{the carbon-coated Li 5} FeO _{4 is small.}
Combining the results of Evaluation Example 2 and Evaluation Example 3, 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)

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, a BET specific surface area in the range of 2~5.4m ² / g Characterized carbon-coated Li ₅ FeO ₄ . BET specific surface area is 2.3 to 5.4 m ² The carbon-coated Li according to claim 1, which is within the range of / g. ₅ FeO ₄ .. A positive electrode comprising the carbon-coated Li ₅ FeO _{4 according to claim 1 or 2.} A lithium ion secondary battery comprising the positive electrode according to claim 3. The carbon-coated Li according to claim 1 or 2. ₅ FeO ₄ Is a method of manufacturing
Lithium stearate is a mixture of lithium oxide as a Li source, iron oxide as an Fe source, and lithium stearate in an amount of 0.1 to 10% by mass based on the total amount of lithium oxide and iron oxide. Carbon-coated Li, including the step of heating above the temperature at which it vaporizes or decomposes ₅ FeO ₄ Manufacturing method.

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