JP2020050554A - Composite particle - Google Patents

Abstract

To provide a new LiFeO-related material.SOLUTION: The present invention provides a composite particle containing LiFeOand carbon. In the composite particle, in a Raman spectrum obtained by analyzing the composite particle with a Raman spectrophotometer, a half-value width of G-Band is 30 cmor less.SELECTED DRAWING: None

Description

The present invention relates to Li ₅ FeO ₄ used for a positive electrode material of a lithium ion secondary battery and the like.

  Lithium ion secondary batteries are small and have large capacities, and are therefore used as batteries for various devices such as mobile phones and notebook computers. A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte 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 a positive electrode active material of a 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 upon charging, and is used as a lithium ion supply agent to supplement the irreversible capacity of the negative electrode, and as an additive for the positive electrode. It is also known to be used in applications.

For example, Patent Literature 1 specifically describes a lithium ion secondary battery including a positive electrode using LiMn ₂ O ₄ and Li ₅ FeO ₄ at a mass ratio of 95: 5, and Li ₅ FeO ₄ It is described that the addition can compensate for the initial capacity loss of the negative electrode active material.

Patent Literature 2 discloses a lithium ion secondary battery including only Li ₅ FeO ₄ as a positive electrode active material, and a lithium ion secondary battery including Li ₅ FeO ₄ and a metal oxide containing no Li as a positive electrode active material. Is specifically described.

Patent Literature 3 specifically describes a lithium ion secondary battery including a positive electrode using LiCoO ₂ and Li ₅ FeO ₄ at a mass ratio of 91: 9 to 97: 3 as a positive electrode active material. _It is described that the initial charging capacity could be improved by adding ₅ FeO ₄ .

Patent Literature 4 describes that Li ₅ FeO ₄ is added to a positive electrode active material layer as a positive electrode additive that generates gas at the time of initial charging. It is described that holes can be formed.

JP 2007-287446 A JP 2012-99316 A JP 2014-157563 A International Publication No. WO 2014/118834

  In recent years, the industry has been demanding lithium-ion secondary batteries with excellent battery characteristics and excellent materials for manufacturing lithium-ion secondary batteries, and new technologies for realizing them have been demanded. I have.

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

The present inventors _have, was examined for Li 5 FeO _4, battery having a Li 5 FeO ₄ has been finding a phenomenon that does not express sufficiently capacity. The present inventors have presumed 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, the surface of the Li 5 FeO ₄ to produce a carbon coating _Li 5 FeO ₄ that was covered with carbon film, and stored. As a result, they found that the carbon-coated Li ₅ FeO ₄ may be deteriorated depending on storage conditions. Specifically, the carbon-coated Li ₅ FeO ₄ stored in the atmosphere may absorb moisture. The moisture-absorbed carbon-coated Li ₅ FeO ₄ may be degraded by a reaction with water.

The present inventor tried to produce carbon-coated Li ₅ FeO ₄ under various conditions in order to suppress the deterioration due to the storage, and aimed to produce composite particles containing Li ₅ FeO ₄ and carbon. The inventor of the present invention has conducted further intensive studies and completed the present invention.

Composite particles of the present invention,
Li ₅ FeO ₄ and carbon,
In the Raman spectrum obtained by analyzing the composite particles with a Raman spectrophotometer, the half-width of G-Band is 30 cm ^-1 or less.

  The composite particle of the present invention is one in which deterioration due to storage is suppressed.

5 is an SEM image of the composite particles of Example 1 in Evaluation Example 1. 9 is an X-ray diffraction chart of the composite particles of Example 1 in Evaluation Example 2, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2. 11 is a Raman spectrum of the composite particles of Example 1 in Evaluation Example 6, the carbon-coated Li ₅ FeO ₄ of Comparative Example 1, the composite particles of Comparative Example 2, and graphite. 13 is a graph showing the change over time of the mass of the composite particles of Example 1 in Evaluation Example 7, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2.

  Hereinafter, embodiments for implementing the present invention will be described. Unless otherwise specified, the numerical range “ab” described in this specification includes the lower limit a and the upper limit b. A numerical range can be formed by arbitrarily combining these upper and lower limits and the numerical values listed in the examples. Further, numerical values arbitrarily selected from within these numerical ranges can be set as new upper and lower numerical values.

The composite particle of the present invention is a composite particle containing Li ₅ FeO ₄ and carbon. From a different point of view, the composite particles of the present invention may be referred to as particles in which a phase of Li ₅ FeO _{4 and} a phase of carbon are composited.
Hereinafter, if necessary, the phase of _Li 5 FeO ₄ contained in the composite particles of the present invention referred to as _Li 5 FeO ₄ phase, referred to as carbon phase phase carbon.
The Li ₅ FeO ₄ phase is a part mainly involved in the battery reaction, but relatively poor in conductivity, and the carbon phase is a part which plays a role of supplementing the conductivity of the Li ₅ FeO ₄ phase by its excellent conductivity. It can be said that there is.

The composite particle of the present invention has a half-width of G-Band of 30 cm ⁻¹ or less in a Raman spectrum obtained by analyzing the composite particle with a Raman spectrophotometer.

Where the composite particles of the present invention have the above-described carbon phase, the carbon alone has a peak called a G-Band derived from a graphite structure or a dangling bond at 1200 to 1700 m ^-1 in a Raman spectrum. In some cases, a peak referred to as D-Band is detected.
G-Band is detected in the Raman scattering spectrum of the composite particles of the present invention. Therefore, it is presumed that the composite particles of the present invention have a graphite structure in the carbon phase. Further, since the half-width of the G-Band is 30 cm ⁻¹ or less, it is assumed that the carbon phase in the composite particles of the present invention is a phase having relatively high crystallinity.

  As will be described in detail in Examples, it can be said that the composite particles of the present invention have high crystallinity of the carbon phase and are suppressed from being deteriorated by storage.

In the Raman spectroscopy spectrum of the composite particles of the present invention, the half-width of G-Band may be at most 30 cm ⁻¹ , but is preferably at most 25 cm ^−1, more preferably at most 22 cm ^−1. , 20 cm ^-1 or less. In other words, it is preferable that the composite particles of the present invention have higher crystallinity of the carbon phase.

  The composite particle of the present invention may be one in which D-Band is detected in the Raman spectrum. That is, the composite particles of the present invention may have dangling bonds in the carbon phase.

It is considered that the carbon phase having dangling bonds easily reacts with water at the dangling bonds. For this reason, it is considered disadvantageous that there are many dangling bonds in the carbon phase in consideration of suppressing the deterioration of the composite particles due to moisture absorption. However, if the amount is small, the presence of dangling bonds is acceptable. Specifically, the amount of dangling bonds can be defined by the G / D ratio, that is, the ratio of the peak intensity between D-Band and the above-described G-Band. If the G / D ratio is small, it can be considered that there are relatively many dangling bonds in the carbon phase. If the G / D ratio is large, it can be considered that there are relatively few dangling bonds in the carbon phase.
Preferred ranges of the G / D ratio in the composite particles of the present invention include 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, and 3.5 or more.

As described above, the composite particles of the present invention have a Li ₅ FeO ₄ phase and a carbon phase. The Li ₅ FeO ₄ phase and the carbon phase may have any size or any shape. However, if the composite particles of the present invention are used for a positive electrode material of a lithium ion secondary battery, Preferably, a carbon phase is present on the surface of the Li ₅ FeO ₄ phase in the form. As described above, the Li ₅ FeO ₄ phase is mainly involved in the battery reaction, and the carbon phase plays a role of supplementing the conductivity of the Li ₅ FeO ₄ phase.

Carbon phase on the surface of the particulate _Li 5 FeO ₄ phase _may in the range of small particulate than Li 5 FeO _4, may be interspersed throughout the surface of the Li 5 FeO _4, It may be present only on a part of the surface of the Li ₅ FeO ₄ .

  The mass% (Wc) of carbon in the composite particles of the present invention is not particularly limited, but is preferably in the range of 1 ≦ Wc ≦ 10. The more preferable range of the mass of the carbon is 2.0 <Wc ≦ 8.0, 2.5 ≦ Wc ≦ 6.0, 3.0 ≦ Wc ≦ 5.0. Can be mentioned.

BET specific surface area of the composite particles of the present invention is not particularly ^{limited, 0.1~15.0m 2 /g,0.5~10.0m 2 /g,0.7~5.0m 2 /} g, 1. It may be mentioned the range of 0~3.8m ² / g.
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 excessively large, it may react with moisture or carbon dioxide in the air to degrade Li ₅ FeO ₄ or adversely affect the properties of the slurry during the production of the positive electrode.

The composite particles of the present invention are preferably in a powder state. Examples of the powder resistance value of the composite particles of the present invention include 10 ^{−1 to} 5 × 10 ³ Ωcm, 1 to 1 × 10 ³ Ωcm, and 10 to 5 × 10 ² Ωcm.
In addition, the powder resistance value in this specification means a volume resistance value when a load of 4 kN is applied to a measurement sample.

The composite particles of the present invention can be produced by heating Li ₂ CO ₃ , an Fe source, and graphite. Hereinafter, as necessary, a method for producing composite particles including a step of heating Li ₂ CO ₃ , an Fe source, and graphite is referred to as a method for producing composite particles of the present invention or simply a method of producing the present invention. In addition, the step of heating the Li ₂ CO ₃ , the Fe source, and the graphite in the production method of the present invention is referred to as a synthesis step, if necessary.

Meanwhile, already mentioned, the carbon-coated _Li 5 FeO ₄ that the present inventors have _prepared, by together with carbon source comprising particles of Li 5 FeO ₄ from organic material is heated above carbonization temperature of the carbon _source, Li 5 FeO ₄ Is coated with a carbon film by a so-called thermal CVD method. The production method of the present invention is essentially different from the method of producing carbon-coated Li ₅ FeO ₄ by the thermal CVD method.

As a method for synthesizing Li ₅ FeO ₄ , a method is known in which a Li source and an Fe source are reacted under heating conditions to synthesize. Examples of the Li source used for the synthesis of Li ₅ FeO ₄ include simple lithium, lithium oxide, lithium hydroxide, lithium carbonate, lithium hydrogen carbonate, and lithium fluoride. The production method of the present invention uses lithium carbonate as the Li source.

Conventionally, lithium oxide has been mainly used as a Li source for Li ₅ FeO ₄ . However, since lithium oxide is relatively expensive, the present inventor has sought to use a cheaper Li source to provide the composite particles at low cost. The present inventor manufactured composite particles by a method of actually heating a Li source, an Fe source, and graphite using a Li source that is cheaper than lithium oxide. As a result, it has been found that when lithium carbonate is used as the Li source, the above-described deterioration due to storage is greatly suppressed as compared with the case where another Li source is used.
In addition, in the composite particles obtained using lithium carbonate as a Li source, the half-width of G-Band in the Raman spectrum was 30 cm ⁻¹ or less. That is, the production method of the present invention is to produce the composite particles of the present invention in which the deterioration due to storage is suppressed by using lithium carbonate, that is, Li ₂ CO ₃ as the Li source.

Examples of the Fe source, which is a raw material of Li ₅ FeO ₄ , include simple iron, iron oxide, iron hydroxide, iron oxyhydroxide, iron sulfate, iron nitrate, and iron chloride. In the production method of the present invention, the Fe source is not particularly limited, but it is preferable to select iron alone or iron oxide from the viewpoint of the purity of the product.

In the synthesis step, Li ₅ FeO ₄ is synthesized in a reaction system in which graphite is present in addition to the Li ₂ CO ₃ and Fe sources, to produce composite particles having a Li ₅ FeO ₄ phase and a carbon phase.
Since graphite becomes a carbon phase as it is, in the synthesis step of the manufacturing method of the present invention, the Li ₅ FeO ₄ phase is synthesized in contact with the carbon phase, and the carbon phase is attached to the surface of the Li ₅ FeO ₄ particles. It is believed that particles are obtained. That is, in the synthesis step of the production method of the present invention, it is not necessary to carbonize a carbon source such as an organic substance, and in the synthesis step, the Li source, the Fe source, and the graphite may be heated at the synthesis temperature of Li ₅ FeO ₄ .
Since graphite has been used as a conductive additive in the positive electrode of a lithium ion secondary battery, it can be said that graphite is particularly preferable as the carbon phase of the composite particles used in the positive electrode of the lithium ion secondary battery.
Hereinafter, the raw material of the composite particles containing Li ₂ CO ₃ , the Fe source, and the graphite and subjected to the synthesis process as necessary is referred to as a mixed raw material.

By the way, when Li ₂ CO ₃ is used as a Li source, Li ₂ CO ₃ is fixed in a reactor of a heating device for heating a mixed raw material containing Li ₂ CO ₃ , an Fe source and graphite in a synthesis step. In some cases. If the fixation of the Li ₂ CO ₃ occurs, the yield of the composite particles deteriorates.
By adding an organic additive capable of functioning as a lubricant such as a sucrose fatty acid ester or a fatty acid to the mixed raw material, it is possible to suppress the problem of sticking of Li ₂ CO ₃ . Examples of the organic additive include sucrose fatty acid esters, fatty acids, fatty acid salts, fatty acid amides, N, N'-ethylenebisfatty acid amides, alkali metal salts of fumaric acid alkyl esters, and hardened oils.

As described above, the addition of the organic additive not only can suppress the fixation of Li ₂ CO ₃ to the reactor of the heating device, but also has an advantage that the particles of Li ₅ FeO ₄ can be suppressed from becoming coarse.
The amount of the organic additive to be added is in the range of 0.1 to 10% by mass, in the range of 0.5 to 5% by mass, based on the total amount of the mixed raw material including Li ₂ CO ₃ , the Fe source and graphite. Each range of 1 to 3% by mass can be mentioned.

In the synthesis step, as a device for heating a mixed raw material of Li ₂ CO ₃ , an Fe source and graphite, for example, a fluidized-bed reaction furnace, a rotary furnace, a hot-wall type, a cold-wall type, a horizontal type, a vertical type, or the like may be used. A known heating device such as a tunnel furnace, a batch-type firing furnace, and a rotary kiln may be used.

Note that the synthesis step is desirably performed with the mixed raw material in a fluid state. By doing so, the Li ₂ CO ₃ , Fe source and graphite can be uniformly dispersed, Li ₅ FeO ₄ can be efficiently produced, and the carbon phase is uniformly formed on the surface of the Li ₅ FeO ₄ phase. The formed composite particles can be produced. Further, in this case, binding between the composite particles can be suppressed. There are various methods for bringing the mixed raw material into a fluidized state, such as using a fluidized bed, but it is preferable to stir the mixed raw material. For example, if a rotary furnace having a baffle plate inside is used, the mixed raw material remaining on the baffle plate is agitated by falling from a predetermined height as the rotary furnace rotates.

The heating temperature in the synthesis step may be around 730 ° C., which is the synthesis temperature of Li ₅ FeO ₄ using Li ₂ CO ₃ as a raw material. Preferred heating temperatures include 720 ° C, 730 ° C and 740 ° C.

  When the heating temperature is 720 ° C. or higher, preferable ranges of the heating time are 15 hours or longer, 20 hours or longer, more than 24 hours, and 26 hours or longer. When the heating temperature is 730 ° C. or higher, preferred ranges of the heating time are 8 hours or longer, 10 hours or longer, and 13 hours or longer. When the heating temperature is set to 740 ° C. or higher, preferable ranges of the heating time include 6 hours or longer, 8 hours or longer, 10 hours or longer, 12 hours or longer, and 13 hours or longer.

The synthesis step may be performed in an atmosphere of an inert gas such as argon, helium, or nitrogen, or may be performed in an atmosphere of an oxidizing gas. When the synthesis process is performed in an oxidizing gas atmosphere, there is an advantage that synthesis of Li ₅ FeO ₄ can be performed efficiently while suppressing reduction of an Fe source such as Fe ₂ O ₃ or Li ₅ FeO ₄ .

The mixed raw material used as the raw material in the synthesis step may be mixed with Li ₂ CO ₃ and an Fe source in amounts based on the stoichiometric ratio of the synthesis reaction of Li ₅ FeO ₄ . The amount of graphite is not particularly limited, but a preferable range is 0.5% to 4.5% by mass when Li ₅ FeO ₄ produced in the synthesis step is 100% by mass, and 0.5% by mass. Each range of the amount to be from 4% by mass to 4% by mass and the amount to be from 0.5% by mass to 3.5% by mass is exemplified. Alternatively, preferred ranges of the amount of graphite include, in terms of carbon, respective ranges of 0.05 mol to 5 mol, 0.1 mol to ₃ mol, and 0.2 mol to 1 mol based on 1 mol of lithium contained in Li ₂ CO ₃ .

_Li 2 CO ₃ and Fe sources contained in the mixed raw material is preferably previously crushed. If necessary, the graphite may be pulverized. The mixed raw material may be one obtained by simply adding Li ₂ CO ₃ , an Fe source, and graphite, or may be a mixed one, but it is one that is uniformly mixed manually or by using a mixing device. Preferably it is. For example, the mixed raw materials include a ball mill, a planetary ball mill, a hybridization system (NHS) and a mirror (MIRALO) of Nara Machinery Co., Ltd .; Depending on the device, it can be ground, mixed or integrated.

  The composite particles 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 composite particle of the present invention is a positive electrode material for a lithium ion secondary battery, and suitably functions as a lithium ion supply agent at the time of initial charging in a positive electrode of a lithium ion secondary battery. Hereinafter, the positive electrode for a lithium ion secondary battery including the composite particles of the present invention is referred to as “the positive electrode of the present invention”, and the lithium ion secondary battery including the positive electrode of the present invention is referred to as “the lithium ion secondary battery of the present invention”. That.

  In the positive electrode of the present invention, the composite particles of the present invention are preferably added to the positive electrode active material layer in which the positive electrode active material exists. One embodiment of the positive electrode of the present invention includes a positive electrode active material layer including the composite particles of the present invention, and a current collector. The positive electrode active material layer is formed on the current collector. When the composite particle of the present invention is a lithium ion supply agent, the amount of the composite particle 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 electronic conductor for continuously supplying current to the electrodes during discharging or charging of the lithium ion secondary battery. The material of the current collector is not particularly limited as long as the metal 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 And other metal materials. The current collector may be covered 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 on the basis of lithium, it is preferable to use aluminum as the positive electrode current collector.

  Specifically, it is preferable to use a collector made of 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 referred to as 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.

  Specific examples of aluminum or aluminum alloy include, for example, A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, JIS A8079, A8021 and the like. A8000-based alloy (Al-Fe-based).

  The current collector may be in the form of a foil, a sheet, a film, a line, a bar, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of a foil, sheet, or 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 composite particles 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, A lithium composite metal oxide represented by at least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, 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 . 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 (wherein M is selected from at least one of Co, Ni, Mn, and Fe). 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 of the metal oxides used as the positive electrode active material may have the above composition formula as the basic composition, and those obtained by replacing the metal element contained in the basic composition with another metal element can also be used. In addition, as the positive electrode active material, a material that does not include a charge carrier (for example, lithium ions that contribute to charge and discharge) may be used. For example, elemental sulfur, a compound of sulfur and carbon, a metal sulfide such as TiS ₂ , an oxide such as V ₂ O ₅ and MnO ₂ , a compound containing polyaniline and anthraquinone and their aromatics in the chemical structure, a conjugated compound Conjugated materials such as acetic acid-based organic materials and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, and phenoxyl may be employed as the positive electrode active material. When a positive electrode active material containing no 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 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 for integration.

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 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 the group consisting of 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, 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 and V, 1.7 ≦ f It is preferable to employ a lithium composite metal oxide represented by ≦ 3).

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

Specific positive electrode active material _can be exemplified by _{LiFePO 4, Li 2 FeSiO 4,} LiCoPO 4, Li 2 CoPO 4, Li 2 MnPO 4, Li 2 MnSiO 4, Li 2 CoPO 4 F. As another specific positive electrode active material _can be exemplified by Li ₂ MnO 3 -LiCoO _2.

  The positive electrode active material layer preferably contains a binder and a conductive auxiliary. As the binder and the conductive auxiliary contained in the positive electrode active material layer, those described for the negative electrode described below may be appropriately employed.

  The lithium ion secondary battery of the present invention specifically includes 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 may contain additives such as a binder and a conductive auxiliary as needed. 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 a charge carrier can be used. Therefore, there is no particular limitation as long as it is a simple substance, an alloy or a compound capable of inserting and extracting a charge carrier such as lithium ions. For example, as a negative electrode active material, Li, a group 14 element such as carbon, silicon, germanium and tin; a group 13 element such as aluminum and indium; a group 12 element such as zinc and cadmium; a group 15 element such as antimony and bismuth; And an alkaline earth metal such as calcium, and a group 11 element such as silver and gold may be used alone. Examples of alloys or compounds, Ag-Sn alloy, Cu-Sn alloy, Co-Sn tin based materials such as alloys, carbon-based materials such as various graphite, _SiO x to disproportionation to silicon simple substance and silicon dioxide ( 0.3.ltoreq.x.ltoreq.1.6), a simple substance of silicon, or a composite of a combination of 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 = Co , Ni, Cu) may be used. One or more of these materials can be used as the negative electrode active material.

In view of the possibility of increasing the capacity, graphite, a Si-containing material, and a Sn-containing material can be given as preferred negative electrode active materials. In particular, when a Si-containing material in which the presence of an irreversible capacity is an important problem is adopted as the negative electrode active material, the effect of Li ₅ FeO ₄ contained in the composite particles of the present invention as a lithium ion supply agent is remarkably exhibited. Is done.

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 store and release lithium ions, and changes its volume as the secondary battery is charged and discharged. The silicon oxide phase has a smaller volume change due to charge and discharge than the Si phase. That is, SiO _x as the negative electrode active material realizes a high capacity by the Si phase, and suppresses a volume change of the whole negative electrode active material by having the silicon oxide phase. If x is less than the lower limit, the ratio of Si becomes excessively large, so that the volume change during charging and discharging becomes too large, and the cycle characteristics of the secondary battery deteriorate. On the other hand, if x exceeds the upper limit, 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-described SiO _x , it is considered that an alloying reaction occurs between lithium and silicon in the Si phase during charging and discharging of the lithium ion secondary battery. And it is thought that this alloying reaction contributes to the charge and discharge of the lithium ion secondary battery. It is also considered that the Sn-containing material described later can be similarly charged and discharged by an alloying reaction between 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. Examples of the amorphous tin oxide include SnB _0.4 P _0.6 O _3.1, and examples of the tin silicon oxide include 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. Due to the composite, the structure of silicon and / or tin is particularly stable, and the durability of the negative electrode is improved. The combination 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 employed. The graphite may be natural graphite or artificial graphite.

  Specific examples of the Si-containing material include a silicon material disclosed in WO 2014/080608 (hereinafter, simply referred to as “silicon material”).

The silicon material has a structure in which a plurality of plate-like silicon bodies are stacked 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.

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

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

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

  Preferably, the silicon material includes amorphous silicon and / or silicon crystallites. In particular, in the plate-like 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, 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 Scherrer's formula using the half-value width of the diffraction peak of the Si (111) plane in the obtained X-ray diffraction chart by performing X-ray diffraction measurement on the silicon material. .

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

  The silicon material may be coated with carbon. Silicon materials coated with carbon have excellent 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. When a silicon material having an average particle diameter that is too small is used, it may be difficult to manufacture a negative electrode from the viewpoint of cohesiveness and wettability. Specifically, in a slurry prepared at the time of manufacturing the negative electrode, a silicon material having an average particle diameter that is too small may aggregate. On the other hand, a lithium ion secondary battery including a negative electrode using a silicon material having an average particle diameter that is too large may not be able to suitably charge and discharge. It is presumed that in a silicon material having an excessively large average particle size, lithium ions cannot sufficiently diffuse into the silicon material. In addition, the average particle diameter in this specification means D50 when a sample is measured by a general laser diffraction type particle size distribution analyzer.

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

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

  Examples of the diamine used for 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'-diaminodiphenylether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylenediamine, 2,6-tolylenediamine, xylylenediamine, and naphthalenediamine are exemplified.

  The compounding 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. If the amount of the binder is too small, the moldability of the electrode is reduced, and if the amount of the binder is too large, the energy density of the electrode is reduced.

  The conductive additive is added to increase the conductivity of the electrode. Therefore, the conductive assistant 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 additive may be any chemically inert high electron conductor, and examples thereof include carbon black, graphite, vapor grown carbon fiber (Vapor Grown Carbon Fiber), and various metal particles. You. Examples of the carbon black include acetylene black, Ketjen Black (registered trademark), furnace black, and channel black. These conductive assistants can be used alone or in combination of two or more. The compounding ratio of the conductive assistant 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. If the amount of the conductive assistant is too small, an efficient conductive path cannot be formed, and if the amount of the conductive assistant is too large, the moldability 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 the current collector, the current is collected using 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, and a curtain coating method. The active material may be applied to the surface of the body. Specifically, after the components of the active material layer and the solvent are mixed to form a slurry, 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 product may be compressed to increase the electrode density.

  In the slurry-like composition for producing a positive electrode active material layer comprising the composite particles and the solvent of the present invention for producing a positive electrode active material layer, the solid content is preferably in the range of 30 to 90% by mass. More preferably, it is in the range of 50 to 75% by mass. Here, the solid content means components other than the solvent contained in the composition for producing a positive electrode active material layer.

The compounding amount of the composite particles 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 composite particles of the present invention.
When the composite particles of the present invention are used as a lithium ion supply agent for supplementing lithium ions corresponding to the irreversible capacity of the negative electrode, as the compounding amount of the composite particles of the present invention in the composition for producing a positive electrode active material layer. Can be exemplified in the range of 1 to 10% by mass, the range of 3 to 9% by mass, and the range of 5 to 8% by mass with respect to the solid content.

  The amount of the positive electrode active material in the composition for producing a positive electrode active material layer is, with respect to the solid content, in the range of 80 to 95% by mass, in the range of 83 to 93% by mass, and in the range of 85 to 90% by mass. The range can be exemplified. The amount of the binder in the composition for producing a positive electrode active material layer is 0.5 to 10% by mass, 1 to 5% by mass, and 2 to 4% by mass with respect to the solid content. The range can be exemplified. The amount of the conductive additive in the composition for producing a positive electrode active material layer is 0.5 to 5% by mass, 1 to 4% by mass, and 1 to 3% by mass based on the solid content. The range can be exemplified.

  The separator separates the positive electrode and the negative electrode, and prevents lithium ions from passing through while preventing a short circuit due to contact between the two electrodes. Known separators may be used as the separator, 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, suberin and the like, and porous bodies, nonwoven fabrics and woven fabrics using one or more electrically insulating materials such as ceramics. Further, the separator may have a multilayer structure.

  The electrolyte 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 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 alkyl propionate, dialkyl malonate, and alkyl acetate. Examples of the 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 part or all of the hydrogen in the specific chemical structure of the solvent is substituted with fluorine may be used.

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, a nonaqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate is mixed with a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO ₃ at 0.5 mol /. For example, a solution in which the concentration is from about L to about 1.7 mol / L can be exemplified.

A specific method for manufacturing the lithium ion secondary battery of the present invention will be described.
For example, an electrode body is formed by sandwiching a separator between a positive electrode and a negative electrode. The electrode body may be any of a stacked type in which a positive electrode, a separator, and a negative electrode are stacked, or a wound type in which a stacked body 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 collecting lead or the like, an electrolyte 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 laminate 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 a part of its power source, such as 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. Examples of devices on which a lithium ion secondary battery is mounted include various home appliances, office devices, industrial devices, and the like, other than vehicles, such as personal computers and portable communication devices, which are driven by batteries. Further, the lithium ion secondary battery of the present invention is a wind power generation, a photovoltaic power generation, a hydroelectric power generation, a power storage device and a power smoothing device of a power system, a power supply source for motive power of ships and / or accessories, an aircraft, Power supply for spacecraft and other power supplies and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, The present invention may be applied to a power storage device for temporarily storing power required for charging at a charging station for an electric vehicle or the like.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. The present invention can be implemented in various forms with modifications, improvements, and the like that can be made by those skilled in the art without departing from the gist of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to various specific examples. Note that the present invention is not limited by these specific examples.

(Example 1)
(Synthesis process)
4.138 g (56.0 mmol) of Li ₂ CO ₃ as a Li source, 1.789 g (11.2 mmol) of Fe ₂ O ₃ as an Fe source, and 0.538 g (44.8 mmol in terms of carbon) of graphite were blended. The mixed raw material was charged into a planetary ball mill. Further, lithium stearate, which is an organic additive, was charged into a planetary ball mill in an amount corresponding to 2% by mass based on the total amount of Li ₂ CO ₃ , Fe ₂ O ₃ , graphite and lithium stearate. The planetary ball mill was operated at a rotation speed of 800 rpm and a revolution speed of 800 rpm to produce a composite of the mixed raw material.
The composite of the mixed raw materials was placed in a reactor and heated in a tubular furnace at 720 ° C. for 26 hours in an argon atmosphere to obtain composite particles of Example 1 in the form of particles.
Note that the mixed raw material in Example 1 was mixed with Li ₂ CO ₃ and an Fe source in amounts such that the atomic ratio of Li and Fe was 5: 1. The amount of graphite was adjusted to 0.4 mol in terms of carbon with respect to 1 mol of lithium contained in Li ₂ CO ₃ .

(Comparative Example 1)
(Synthesis process)
3.126 g (104.6 mmol) of Li ₂ O as a Li source and 3.342 g (20.9 mmol) of Fe ₂ O ₃ as a Fe source were put into a planetary ball mill. Further, lithium stearate, which is an organic additive, was weighed in an amount corresponding to 2% by mass based on the total amount of Li ₂ O and Fe ₂ O ₃ and charged into a planetary ball mill. The planetary ball mill was operated at a rotation speed of 800 rpm and a revolution speed of 800 rpm, and the mixed raw material was pulverized and mixed until the obtained particles had a diameter of 10 μm or less.

The pulverized mixed raw material was placed in a rotary kiln-type reactor, and then the mixed raw material was 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 20 minutes under a gaseous mixture of hexane and argon to form a carbon film on the surface of Li ₅ FeO ₄ , and the carbon-coated Li ₅ FeO of Comparative Example 1 was formed. ₄ was produced. During the synthesis of Li ₅ FeO ₄ and carbon-coated Li ₅ FeO ₄ , the rotary kiln type reactor was rotated.

(Comparative Example 2)
3.805 g (158.9 mmol) of LiOH as a Li source, 2.537 g (15.9 mmol) of Fe ₂ O ₃ as an Fe source, and 0.257 g (21.5 mmol in terms of carbon) of graphite were weighed. It was a mixed raw material. The heating temperature and the heating time in the synthesis step were 460 ° C. and 4 hours. Except for this, the composite particles of Comparative Example 2 were obtained in the same manner as in Example 1.
In the mixed raw material in Comparative Example 2, Li source and Fe source were added in such amounts that Li and Fe became 5: 1 in atomic ratio.

(Evaluation Example 1)
The appearance of the composite particles of Example 1 was observed using a scanning electron microscope (Scanning Electron Microscope: SEM). An SEM image of the composite particles of Example 1 is shown in FIG.

As shown in FIG. 1, the composite particles of Example 1 have relatively large particles and many fine particles existing on the surface of the particles. From the composition of the mixed raw material, it is assumed that the relatively large particles in FIG. 1 are Li ₅ FeO ₄ and the fine particles are carbon. In other words, it can be said that the composite particles of Example 1 have a relatively large particulate Li ₅ FeO ₄ phase and a large number of fine particulate carbon phases existing on the surface thereof.

(Evaluation example 2)
The composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2 were subjected to powder X-ray diffraction analysis using a Cu bulb as a radiation source, and analyzed. The obtained X-ray diffraction chart is shown in FIG.

As shown in FIG. 2, it was confirmed that Li ₅ FeO ₄ was generated in each of the composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2. Was done.

(Evaluation example 3)
Using the carbon / sulfur analyzer, elemental analysis was performed on carbon for the composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2. Table 1 shows the results.

(Evaluation example 4)
The specific surface areas of the composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2 were measured by the BET method, and were defined as BET specific surface areas. Table 1 shows the value of the BET specific surface area of each composite particle together with the results of Evaluation Example 3 described above.

(Evaluation example 5)
A load of 4 kN was applied to the composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2 using a powder resistivity measurement system (Mitsubishi Analytech Co., Ltd.). The volume resistance value was measured. The results are shown in Table 1 together with the results of Evaluation Examples 3 and 4.

As shown in Table 1, the composite particles of Example 1 and Comparative Example 2 obtained by reacting a Li source and an Fe source in the presence of graphite were obtained by coating Li ₅ FeO ₄ with carbon by a thermal CVD method. Although the specific surface area was smaller than that of the obtained carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, it was as good as the carbon amount and the conductivity.
From these results, it can be said that the composite particles of Example 1 can be preferably used for the positive electrode of a lithium ion secondary battery, like the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1. It has been confirmed by tests by the present inventors that the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1 can be preferably used for the positive electrode of a lithium ion secondary battery.

(Evaluation Example 6)
The composite particles of Example 1, the carbon-coated Li ₅ FeO ₄ of Comparative Example 1, the composite particles of Comparative Example 2, and graphite were analyzed with a Raman spectrophotometer. The results are shown in FIG.

As shown in FIG. 3 and Table 2, at 1200 to 1700 m ⁻¹ in the Raman spectrum of graphite, a carbon-derived peak called G-Band derived from graphite, and a D-dangling bond derived from dangling bond are included. A peak derived from carbon called Band was detected.

As shown in FIG. 3 and Table 2, in the Raman spectrum of each composite particle of Example 1 and Comparative Example 2, a sharp G-Band having a half width of 40 cm ⁻¹ or less was detected. However, in the Raman spectrum of the carbon-coated Li ₅ FeO ₄ of Comparative Example 1, no sharp G-Band was detected, and only a broad peak having a half width of 88 cm ⁻¹ was detected. Comparing the composite particles of Example 1 and the composite particles of Comparative Example 2, the half-width of G-Band was 19 cm ⁻¹ for the composite particles of Example 1 and 32 cm ⁻¹ for the composite particles of Comparative Example 2. .
Based on this result, the half-width of the G-Band in the composite particles of the present invention can be 30 cm ^-1 or less, and a preferable range of the half-width is 27 cm ^-1 or less, 25 cm ^-1 or less, 22 cm ^-1 or less, Each range of 20 cm ^-1 or less can be mentioned.

  Focusing on D-Band, in the composite particles of Comparative Example 2 using lithium hydroxide as the Li source, clear D-Band was detected in the Raman spectrum. On the other hand, in the composite particles of Example 1 using lithium carbonate as the Li source, the D-Band detected in the Raman spectrum was very small. The G / D ratio obtained by dividing the G-Band peak area by the D-Band peak area was 3.6 for the composite particles of Example 1 and 0.8 for the composite particles of Comparative Example 2. And 1.3 for graphite. Based on this result, the preferable range of the G / D ratio in the composite particles of the present invention is 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, and 3.5 or more. Can be mentioned.

(Evaluation Example 7)
The composite particles of Example 1, the carbon-coated Li ₅ FeO _{4 of} Comparative Example 1, and the composite particles of Comparative Example 2 were allowed to stand in the air at about 23 ° C. and a dew point of about 0 ° C., and their mass changes with time. Was measured. FIG. 4 shows the results.

As shown in FIG. 4, the mass change rate of the composite particles of Example 1 and the composite particles of Comparative Example 2 was smaller than the mass change rate of the carbon-coated Li ₅ FeO ₄ of Comparative Example 1. From these results, the composite particles obtained by reacting the Li source and the Fe source in the presence of graphite were compared with the carbon-coated Li ₅ FeO ₄ obtained by carbon coating Li ₅ FeO ₄ by the thermal CVD method. Therefore, it can be said that even when stored in the atmosphere, it is hard to absorb moisture and hardly deteriorates.

In addition, comparing the composite particles of Example 1 using Li ₂ CO ₃ as the Li source and the composite particles of Comparative Example 2 using lithium hydroxide as the Li source, the mass change rate of the composite particles of Example 1 Was even smaller than the mass change rate of the composite particles of Comparative Example 2. From these results, it can be said that, when Li ₂ CO ₃ is used as the Li source, it is harder to absorb moisture even during storage in the atmosphere and deteriorate more than when LiOH is used. Considering this result and the result of Evaluation Example 6 described above, it can be said that in the composite particles of Example 1 in which the half-width of G-Band is 30 cm ⁻¹ or less, deterioration during storage is suppressed. Furthermore, it can be said that the composite particles of the present invention having a G-Band half-width of 30 cm ^-1 or less are those in which deterioration during storage is suppressed.

Claims (5)

Composite particles containing Li ₅ FeO ₄ and carbon,
A composite particle having a half-width of G-Band of 30 cm ^-1 or less in a Raman spectrum obtained by analyzing the composite particle with a Raman spectrophotometer.   The composite particle according to claim 1, wherein a G / D ratio, which is a ratio of peak intensities of G-Band and D-Band in the Raman spectroscopy spectrum, is 1.5 or more. Comprising the step of heating the graphite Li ₂ CO ₃ and Fe _sources, Li 5 FeO ₄ in the manufacturing method of the composite particles containing carbon.   A positive electrode comprising the composite particle according to claim 1.   A lithium ion secondary battery comprising the positive electrode according to claim 4.