JP2023092886A - Positive electrode active material, positive electrode, lithium-ion polymer solid secondary battery, and lithium-ion inorganic all-solid secondary battery - Google Patents

Abstract

To provide a positive electrode active material that makes it possible to construct a lithium-ion solid state secondary battery equipped with a negative electrode containing lithium without safety concerns due to the formation of dendrites, and can manufacture a lithium-ion polymer solid secondary battery and a lithium-ion inorganic all-solid secondary battery that do not require the addition of a large amount of conductive aid and a binder using iron (III) oxide particles with anisotropic shapes that are free from toxicity and resources, a lithium-ion polymer solid secondary battery and a high lithium-ion inorganic all-solid secondary battery including the positive electrode active material.SOLUTION: A positive electrode active material used in a lithium-ion solid state secondary battery including a lithium-containing negative electrode includes iron (III) oxide or heteroelement-substituted iron (III) oxide, and consists of anisotropic iron oxide particles in which the ratio (b/a) of the half-value width b of the diffraction line derived from the plane index 104 plane obtained by X-ray diffraction measurement to the half-value width a of the diffraction line derived from the plane index 110 plane obtained by X-ray diffraction measurement is 2.0 or more.SELECTED DRAWING: None

Description

The present invention relates to a positive electrode active material, a positive electrode, a lithium ion polymer solid secondary battery and a lithium ion inorganic all-solid secondary battery. A lithium ion polymer solid secondary battery using a polymer electrolyte as an electrolyte and a lithium ion inorganic all-solid secondary battery using an inorganic solid electrolyte may be simply called a lithium ion solid secondary battery.

BACKGROUND ART In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been proposed and put into practical use as batteries that are expected to be smaller, lighter, and have higher capacity. A lithium-ion secondary battery is composed of a positive electrode and a negative electrode that are capable of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte.
As the negative electrode active material of the negative electrode material of the lithium ion secondary battery, a carbonaceous material or a metal material such as Si or Sn, or a Li-containing metal oxide, which has the property of reversibly inserting and removing lithium ions, is generally used. . Examples of such Li-containing metal oxides include lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

On the other hand, as the positive electrode of a lithium ion secondary battery, a positive electrode material mixture containing a positive electrode material, a binder and the like is used. Examples of positive electrode active materials include layered oxide lithium cobalt oxide (LCO), ternary layered oxide (NCM) in which cobalt is partially replaced with manganese and nickel, and spinel manganese lithium (LMO), which is a lithium manganate compound. ), lithium iron phosphate (LFP), and lithium iron manganese phosphate (LFMP). Then, the positive electrode of the lithium ion secondary battery is formed by applying this positive electrode material mixture to the surface of a metal foil called an electrode current collector.

A non-aqueous solvent is used for the electrolyte of the lithium ion secondary battery. As the non-aqueous solvent, a positive electrode active material that is oxidized and reduced at a high potential and a negative electrode active material that is oxidized and reduced at a low potential can be used. Thereby, a lithium ion secondary battery having a high voltage can be realized.

Such lithium-ion secondary batteries are lighter and smaller and have higher energy than conventional secondary batteries such as lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Therefore, lithium ion secondary batteries are used not only as small power sources for portable electronic devices such as mobile phones and notebook personal computers, but also as stationary large power sources for emergencies.

In recent years, there has been a demand for improved performance of lithium-ion secondary batteries, and various studies have been made to improve performance. For example, in order to further improve the safety of lithium-ion secondary batteries, all-solid-state batteries using non-volatile polymer electrolyte membranes or inorganic solid electrolytes without using combustible organic solvents as electrolytes, or using ionic liquids Batteries, etc. are being considered. Lithium-ion polymer secondary batteries using polymer electrolyte membranes, among others, are capable of applying a manufacturing process by coating in the same way as batteries using conventional liquid electrolytes, are inexpensive, and have excellent electrical conductivity. It has been actively studied because of its high volatility and ease of thinning. Furthermore, since the polymer electrolyte membrane is in a dense solid state, the formation of acicular metal crystals called dendrites is suppressed in the polymer electrolyte membrane. Therefore, in lithium ion polymer secondary batteries, a lithium metal negative electrode can be used without impairing safety, so a significant increase in capacity can be expected.

As a positive electrode active material for a lithium ion battery using a lithium metal negative electrode, for example, a material composed of iron oxide ultrafine particles having an average particle size in the range of 1 to 10 nm and a distribution width of the particle size in the range of 1 to 10 nm. known (see, for example, Patent Document 1).

JP 2008-204777 A

Iron oxide is known to act as a positive electrode active material when it is pulverized. However, when producing a positive electrode containing iron oxide fine particles as a positive electrode active material, a large amount of a binder and a conductive aid is required, so there is a problem that the battery capacity cannot be increased.

The present inventors have found that in a secondary battery using a dense solid electrolyte such as a lithium ion polymer secondary battery or an inorganic all-solid-state battery, there is no safety concern due to the formation of dendrites, and a lithium secondary battery having a lithium-containing negative electrode It is possible to construct a battery, and by using iron oxide particles with a special shape, it is possible to operate well without adding a large amount of a binder or a conductive agent. Arrived.

The positive electrode active material of the present invention is a positive electrode active material used in a lithium-ion solid state secondary battery having a lithium-containing negative electrode, contains iron (III) oxide or hetero-element-substituted iron (III) oxide, and is subjected to X-ray diffraction measurement. The ratio (b/a) of the half-value width b of the diffraction line derived from the plane index 104 plane obtained by X-ray diffraction measurement to the half-value width a of the diffraction line derived from the plane index 110 plane obtained by X-ray diffraction measurement is 2.0 or more of anisotropic iron oxide particles.

The positive electrode of the present invention contains the positive electrode active material of the present invention.

The lithium ion polymer solid secondary battery of the present invention includes a positive electrode containing the positive electrode active material of the present invention, a negative electrode containing lithium, and an ion conductive polymer electrolyte.

A lithium ion inorganic all-solid secondary battery of the present invention includes a positive electrode containing the positive electrode active material of the present invention, a negative electrode containing lithium, and an inorganic solid electrolyte.

According to the positive electrode active material of the present invention, there is no concern about safety due to the formation of dendrites, and it is possible to construct a lithium ion all-solid secondary battery equipped with a lithium-containing negative electrode, and it is possible to add a large amount of a binder or a conductive aid. An all-solid-state lithium-ion secondary battery that can operate with non-ultrafine iron oxide particles can be produced, which is unnecessary, inexpensive, and poses no toxicity concerns.

According to the positive electrode of the present invention, there is no concern about safety due to the formation of dendrites, and it is possible to construct a lithium ion all-solid secondary battery equipped with a lithium-containing negative electrode. , it is possible to provide an all-solid lithium ion secondary battery that can operate with non-ultrafine particles that do not require the addition of a large amount of binder or conductive aid.

According to the lithium ion polymer solid secondary battery of the present invention, there is no concern about safety due to the formation of dendrites, and it is possible to construct a lithium ion polymer secondary battery equipped with a lithium-containing negative electrode. It is possible to provide a lithium ion polymer secondary battery that can operate with non-ultrafine particles that do not require the addition of a large amount of a binder or a conductive aid.

According to the lithium ion inorganic all-solid secondary battery of the present invention, there is no concern about safety due to the formation of dendrites, and it is possible to construct a lithium ion inorganic all-solid secondary battery comprising a lithium-containing negative electrode, and operate at high temperatures. , an alkali metal-free active material can provide a lithium ion inorganic all-solid secondary battery that can operate with non-ultrafine particles that do not require the addition of a large amount of a binder or a conductive aid.

1 is a diagram showing X-ray diffraction patterns of Examples 1 to 3 and Comparative Examples 1 and 2. FIG. FIG. 3 is a diagram showing discharge curves at the second cycle of Examples 1 to 3 and Comparative Examples 1 and 2;

Embodiments of the positive electrode active material, the positive electrode, the lithium ion polymer solid secondary battery, and the lithium ion inorganic all-solid secondary battery of the present invention will be described.
It should be noted that the present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.

[Positive electrode active material]
The positive electrode active material of this embodiment is used in a lithium ion solid state secondary battery having a lithium-containing negative electrode. The positive electrode active material of the present embodiment contains iron (III) oxide or heteroelement-substituted iron (III) oxide, and the half width a of the diffraction line derived from the plane index 110 plane obtained by X-ray diffraction measurement. The anisotropic iron oxide particles are composed of anisotropic iron oxide particles having a ratio (b/a) of 2 or more of the half width b of the diffraction line derived from the plane index 104 plane obtained by diffraction measurement.
Lithium-ion solid secondary batteries include lithium-ion polymer solid-state secondary batteries and lithium-ion inorganic all-solid secondary batteries.

The positive electrode active material of the present embodiment is mainly composed of iron (III) oxide or hetero-element-substituted iron (III) oxide.

When the positive electrode active material of the present embodiment is mainly composed of iron (III) oxide substituted with a different element, various metal elements and non-metal elements are appropriately added as dopants for the purpose of improving electronic conductivity, stabilizing the structure, etc. may be included as That is, when the positive electrode active material of the present embodiment is mainly composed of iron (III) oxide substituted with a different element, at least part of the iron element constituting the iron (III) oxide is various metal elements other than iron, , may be substituted with a nonmetallic element.
Examples of metal elements include titanium (Ti), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), and aluminum (Al).
Examples of nonmetallic elements include boron (B), phosphorus (P), arsenic (As), silicon (Si), and the like.

When at least part of the iron element constituting the iron (III) oxide is substituted with various metal elements other than iron or with a non-metallic element, that is, when the hetero-element-substituted iron (III) oxide is substituted with a metal as a dopant When an element or a non-metallic element is included, the content of the dopant is preferably 0.001% by mass or more and 10% by mass or less when the total mass of the hetero-element-substituted iron(III) oxide is 100% by mass. , more preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 1% by mass or less. When the content of the dopant is at least the above lower limit, the effect of improving the electron conductivity and stabilizing the structure can be expected. When the content of the dopant is equal to or less than the above upper limit, it is possible to suppress the problem of capacity reduction and price increase due to an increase in inert elements.

The lower limit of the average particle size of the anisotropic iron oxide particles is preferably 30 nm or more, more preferably 200 nm or more, and even more preferably 0.5 μm or more. The upper limit of the average particle size of the iron oxide particles is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.
When the average particle size of the anisotropic iron oxide particles is less than the above lower limit, additives such as conductive aids and binders are excessively required, which may lead to a decrease in electrode capacity. When the average particle size of the anisotropic iron oxide particles is equal to or less than the upper limit, the particles can be operated satisfactorily as an active material.

Here, the average particle size of the anisotropic iron oxide particles can be measured using a laser diffraction scattering particle size distribution analyzer or the like.

The BET specific surface area of the anisotropic iron oxide particles is preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and even more preferably 60 m ² /g or more. The BET specific surface area of the iron oxide particles is preferably 500 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 200 m ² /g or less.
When the BET specific surface area of the anisotropic iron oxide particles is at least the lower limit, an effect of improving electronic conductivity and stabilizing the structure can be expected. When the BET specific surface area of the anisotropic iron oxide particles is equal to or less than the upper limit, the amount of the binder and the conductive material to be added can be reduced, so that the problem of capacity reduction and price increase can be suppressed.
Here, the BET specific surface area of the anisotropic iron oxide particles can be measured using a gas adsorption method using a gas such as nitrogen.

The anisotropic iron oxide particles have a ratio (b/a) of 2.0 or more, preferably 2.2 or more. The upper limit of the ratio (b/a) is preferably 4.0 or less, more preferably 3.3 or less. When the above ratio (b/a) is less than the above lower limit, the non-ultrafine iron oxide (III) does not exhibit sufficient capacity as a positive electrode active material.

[Method for producing positive electrode active material]
The method for producing the positive electrode active material of this embodiment is not particularly limited. The positive electrode active material of the present embodiment can be produced by appropriately selecting a method such as a wet method or a dry method that provides desired iron oxide particles.
If necessary, wet carbon coating by thermal decomposition of organic matter, or dry or semi-dry carbon composite using an attritor or planetary ball mill and a carbonaceous material may be applied.
Similarly, for lithium ion polymer secondary batteries, an ion-conducting polymer coating may be applied, and for lithium ion inorganic all-solid-state batteries, an inorganic solid electrolyte coating may be formed.

[Lithium ion polymer solid secondary battery]
The lithium ion polymer solid secondary battery of the present embodiment includes a positive electrode for a lithium ion polymer solid secondary battery containing the positive electrode active material of the present embodiment, a negative electrode containing lithium, and a positive electrode for a lithium ion polymer solid secondary battery. and an ionically conductive polymer electrolyte present between the lithium-containing negative electrode.

"Positive electrode for lithium ion polymer solid secondary battery"
A positive electrode for a lithium ion polymer solid secondary battery includes an electrode current collector made of metal foil and a positive electrode mixture layer formed on the electrode current collector. The positive electrode mixture layer includes the positive electrode active material of this embodiment and an ion-conductive polymer electrolyte. Moreover, the positive electrode material mixture layer may contain a conductive aid such as carbon black and a binder, if necessary.

The content of the positive electrode active material in the positive electrode mixture layer is not particularly limited. It is more preferably 90% by mass or more, and even more preferably 60% by mass or more and 70% by mass or less. If the content of the positive electrode active material is less than the above lower limit, the capacity of the lithium ion polymer secondary battery having a positive electrode for a lithium ion polymer solid secondary battery containing the positive electrode active material will be low. If the content of the positive electrode active material exceeds the above upper limit, ions and electrons cannot sufficiently reach the surface of the active material. Battery capacity decreases.

"Ion-conducting polymer electrolyte"
Widely used ion-conductive polymer electrolytes include, for example, lithium perchlorate, lithium hexafluorophosphate, polyethylene oxide containing Li electrolytes such as Li trifluoride (LiTFSI), modified polyethylene oxide, and polyvinylidene fluoride. known and available as appropriate.

An ion-conductive polymer electrolyte, which is an electrolyte, must be contained in the positive electrode mixture layer, and the content of the ion-conductive polymer electrolyte in the positive electrode mixture layer is not particularly limited. When 100% by mass, it is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and further preferably 30% by mass or more and 40% by mass or less. preferable. When the content of the ion-conductive polymer electrolyte is at least the above lower limit, sufficient ion-conductive pathways are formed on the surface of the positive electrode active material, and no active material that does not contribute to the reaction is generated, resulting in a decrease in battery capacity. can be suppressed. When the content of the ion-conductive polymer electrolyte is equal to or less than the above upper limit, the ion-conductive polymer electrolyte is not wasted, and the proportion of the active material in the electrode does not become too low, resulting in a decrease in battery capacity. can be suppressed.

"Binder"
If the ion conductive polymer electrolyte has adhesiveness, the binder is not necessarily required. As the binding agent, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, or the like is preferably used.

The content of the binder in the positive electrode mixture layer is not particularly limited. It is more preferable to have When the content of the binder is equal to or less than the above upper limit, the binding between the positive electrode mixture layer and the electrode current collector can be sufficiently enhanced. As a result, it is possible to prevent the positive electrode mixture layer from cracking or coming off when the positive electrode mixture layer is compacted and formed. In addition, it is possible to prevent the positive electrode material mixture layer from peeling off from the electrode current collector during the charging and discharging process of the lithium ion polymer secondary battery, thereby preventing the battery capacity and the charging and discharging rate characteristics from deteriorating. When the content of the binder is equal to or less than the above upper limit, the internal resistance of the positive electrode material for a lithium ion polymer solid secondary battery decreases, and the decrease in battery capacity at a high charge/discharge rate can be suppressed.

"Conductivity aid"
The conductive agent is not particularly limited, but for example, acetylene black (AB), ketjen black, particulate carbon such as furnace black, vapor grown carbon fiber (VGCF; Vapor Grown Carbon Fiber), fiber such as carbon nanotube. At least one selected from the group consisting of carbon-like carbon and graphene is used.

Although the content of the conductive agent in the positive electrode mixture layer is not particularly limited, for example, when the total mass of the positive electrode mixture layer is 100% by mass, it is preferably 1% by mass or more and 20% by mass or less. It is more preferably 10% by mass or more, and even more preferably 2% by mass or more and 5% by mass or less. When the content of the conductive aid is at least the above lower limit, the lithium ion polymer secondary battery can be sufficiently operated. If the content of the conductive aid exceeds the above upper limit, it is not only wasteful, but also may lead to falling off of the positive electrode active material due to insufficient binding power and a decrease in capacity.

Since the positive electrode of the present embodiment contains the positive electrode active material of the present embodiment, a lithium ion polymer secondary battery using the positive electrode of the present embodiment has excellent battery capacity.

"Manufacturing method of positive electrode for lithium ion polymer solid secondary battery"
A method for producing a positive electrode for a lithium ion polymer solid secondary battery is not particularly limited as long as it is a method capable of forming a positive electrode mixture layer on at least one main surface of an electrode current collector using the positive electrode active material of the present embodiment. Examples of the method for producing the positive electrode include the following methods.
First, a positive electrode material paste is prepared by mixing the positive electrode active material of the present embodiment, an ion-conductive polymer electrolyte, and a solvent. At this time, if necessary, a conductive aid such as carbon black and a binder may be added to the positive electrode material paste in the present embodiment.

"solvent"
The solvent used for the positive electrode material paste containing the positive electrode active material of this embodiment is appropriately selected according to the properties of the binder. By appropriately selecting the solvent, the positive electrode material paste can be easily applied to an object to be applied such as an electrode current collector.
Examples of solvents include water, alcohols, esters, ethers, ketones, amides, glycols and the like.
These solvents may be used singly or in combination of two or more.

The content of the solvent in the positive electrode material paste is desirably as low as possible from the viewpoint of cost, but it may be appropriately determined in consideration of positive electrode formability and coatability.

As a method for mixing the positive electrode active material of the present embodiment, the ion-conductive polymer electrolyte, the solvent, and optionally the conductive aid and the binder, any method that can uniformly mix these components can be used. It is not particularly limited. For example, mixing methods using kneaders such as ball mills, sand mills, planetary mixers, paint shakers and homogenizers can be mentioned.

The positive electrode material paste is applied to at least one main surface of the electrode current collector to form a coating film, and then the coating film is dried to obtain at least one main coating film comprising the mixture of the positive electrode material and the binder. An electrode current collector formed on the surface is obtained. After that, the coating film may be pressure-bonded as needed.

"Negative electrode containing lithium"
Examples of lithium-containing negative electrodes include negative electrode materials such as metal Li, Li alloys, Li ₄ Ti ₅ O ₁₂ , and Si-based materials (Li _4.4 Si).

Since the lithium ion polymer solid secondary battery of the present embodiment includes the positive electrode containing the positive electrode active material of the present embodiment as a positive electrode, the battery capacity is excellent.

[Lithium-ion inorganic all-solid secondary battery]
The lithium ion inorganic all-solid secondary battery of the present embodiment includes a positive electrode for a lithium ion inorganic all-solid secondary battery containing the positive electrode active material of the present embodiment, a negative electrode containing lithium, and a lithium ion inorganic all-solid secondary battery. an inorganic solid electrolyte present between the battery positive electrode and the lithium-containing negative electrode.

"Positive electrode for lithium-ion inorganic all-solid secondary battery"
A positive electrode for a lithium ion inorganic all-solid secondary battery includes an electrode current collector made of a metal foil and a positive electrode mixture layer formed on the electrode current collector. The positive electrode mixture layer includes the positive electrode active material of this embodiment and an inorganic solid electrolyte. Moreover, the positive electrode material mixture layer may contain a conductive aid such as carbon black and a binder, if necessary.

The content of the positive electrode active material in the positive electrode mixture layer is not particularly limited. It is more preferably 90% by mass or more, and even more preferably 60% by mass or more and 70% by mass or less. If the content of the positive electrode active material is less than the above lower limit, the capacity of the lithium ion inorganic all-solid secondary battery comprising the positive electrode for a lithium ion inorganic all-solid secondary battery containing the positive electrode active material will be low. If the content of the positive electrode active material exceeds the above upper limit, ions and electrons cannot sufficiently reach the surface of the active material. The capacity of the solid secondary battery is lowered.

"Inorganic solid electrolyte"
As inorganic solid electrolytes, for example, various oxides such as Li ₇ La ₃ Zr ₂ O ₁₂ and Li—Sn—Si—P—S sulfides are widely known and can be used as appropriate. be.

An inorganic solid electrolyte, which is an electrolyte, must be contained in the positive electrode mixture layer, and the content of the inorganic solid electrolyte in the positive electrode mixture layer is not particularly limited. is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less. When the content of the inorganic solid electrolyte is equal to or higher than the above lower limit, a sufficient ionic conductive path is formed on the surface of the positive electrode active material, no active material that does not contribute to the reaction is generated, and a decrease in battery capacity is suppressed. can. When the content of the inorganic solid electrolyte is equal to or less than the above upper limit, the inorganic solid electrolyte is not wasted, and the proportion of the active material in the electrode does not become too low, so it is possible to suppress a decrease in battery capacity. .

"Binder"
If the inorganic solid electrolyte has adhesiveness, the binder is not necessarily required. As the binding agent, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, or the like is preferably used.

The content of the binder in the positive electrode mixture layer is not particularly limited. It is more preferable to have When the content of the binder is equal to or less than the above upper limit, the binding between the positive electrode mixture layer and the electrode current collector can be sufficiently enhanced. As a result, it is possible to prevent the positive electrode mixture layer from cracking or coming off when the positive electrode mixture layer is compacted and formed. In addition, it is possible to suppress the separation of the positive electrode material mixture layer from the electrode current collector during the charging and discharging process of the lithium ion inorganic all-solid state, thereby suppressing the deterioration of the battery capacity and the charging and discharging rate. When the content of the binder is equal to or less than the above upper limit, the internal resistance of the positive electrode material for a lithium ion inorganic all-solid secondary battery decreases, and the decrease in battery capacity at a high charge/discharge rate can be suppressed.

"Conductivity aid"
The conductive agent is not particularly limited, but for example, acetylene black (AB), ketjen black, particulate carbon such as furnace black, vapor grown carbon fiber (VGCF; Vapor Grown Carbon Fiber), fiber such as carbon nanotube. At least one selected from the group consisting of carbon-like carbon and graphene is used.

Although the content of the conductive agent in the positive electrode mixture layer is not particularly limited, for example, when the total mass of the positive electrode mixture layer is 100% by mass, it is preferably 1% by mass or more and 20% by mass or less. It is more preferably 10% by mass or more, and even more preferably 2% by mass or more and 5% by mass or less. When the content of the conductive aid is at least the above lower limit, it is possible to sufficiently operate the lithium ion inorganic all-solid secondary battery. If the content of the conductive aid exceeds the above upper limit, it is not only wasteful, but also may lead to falling off of the positive electrode active material due to insufficient binding power and a decrease in capacity.

"Manufacturing method of positive electrode for lithium ion inorganic all-solid secondary battery"
The method for producing a positive electrode for a lithium ion inorganic all-solid secondary battery is not particularly limited as long as it is a method capable of forming a positive electrode mixture layer on at least one main surface of an electrode current collector using the positive electrode active material of the present embodiment. . Examples of the method for producing the positive electrode include the following methods.
First, a positive electrode material paste is prepared by mixing the positive electrode active material of the present embodiment, an inorganic solid electrolyte, and a solvent. At this time, if necessary, a conductive aid such as carbon black and a binder may be added to the positive electrode material paste in the present embodiment.

"solvent"
The solvent used for the positive electrode material paste containing the positive electrode active material of this embodiment is appropriately selected according to the properties of the binder. By appropriately selecting the solvent, the positive electrode material paste can be easily applied to an object to be applied such as an electrode current collector.
Examples of solvents include water, alcohols, esters, ethers, ketones, amides, glycols and the like.
These solvents may be used singly or in combination of two or more.

The content of the solvent in the positive electrode material paste is desirably as low as possible from the viewpoint of cost, but it may be appropriately determined in consideration of positive electrode formability and coatability.

The method for mixing the positive electrode active material of the present embodiment, the inorganic solid electrolyte, the solvent, and optionally the conductive aid and the binder is particularly limited as long as it can uniformly mix these components. not. For example, mixing methods using kneaders such as ball mills, sand mills, planetary mixers, paint shakers and homogenizers can be mentioned.

The positive electrode material paste is applied to at least one main surface of the electrode current collector to form a coating film, and then the coating film is dried to obtain at least one main coating film comprising the mixture of the positive electrode material and the binder. An electrode current collector formed on the surface is obtained. After that, the coating film may be pressure-bonded as needed.

"Negative electrode containing lithium"
Examples of lithium-containing negative electrodes include negative electrode materials such as metal Li, Li alloys, Li ₄ Ti ₅ O ₁₂ , and Si-based materials (Li _4.4 Si).

Since the lithium ion inorganic all-solid secondary battery of the present embodiment includes the positive electrode containing the positive electrode active material of the present embodiment as a positive electrode, it has excellent battery capacity.

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples below, but the present invention is not limited to the following examples.

[Example 1]
"Preparation of iron oxide particles"
An excess amount of sodium hydroxide aqueous solution was added to a 1 mol/L iron (II) sulfate aqueous solution, and the mixture was neutralized to pH 12. Further, the iron was sufficiently oxidized by bubbling air for 24 hours while stirring. The resulting precipitate was washed with water, dried, and then calcined in air at 450° C. for 3 hours to obtain a sample (powder). The obtained sample was pulverized using a ball mill to obtain an electrode active material. The obtained powder was confirmed by XRD measurement to be iron (III) oxide (Fe ₂ O ₃ ) with a hematite structure. The half-value width a of the diffraction line derived from the 110 plane index plane was 0.1893°, and the half-value width b of the diffraction line derived from the 104 plane index plane was 0.6030°. Also, the ratio (b/a) of the half-value width b to the half-value width a was about 3.2.

"Fabrication of lithium-ion polymer solid-state secondary battery"
In N-methyl-2-pyrrolidinone (NMP) as a solvent, the above iron (III) oxide (Fe ₂ O ₃ ) and polyethylene oxide (PEO 20000, average molecular weight 20000 g/ mol), LiTFSI as a lithium salt, and acetylene black (AB) as a conductive aid in a mass ratio of iron oxide (III) (Fe ₂ O ₃ ):PEO20000:LiTFSI:AB=70 in the paste. : 22:6:2, and further mixed so that the total solid content of the paste is 36% by mass, and using a kneader (trade name: Awatori Mixer, manufactured by Thinky Co., Ltd.) under the conditions of revolution 2000 rpm and rotation 1000 rpm After kneading for 15 minutes, a positive electrode material paste (for positive electrode) was prepared.
This positive electrode material paste (for positive electrode) is applied to the surface of a 20 μm thick aluminum foil (electrode current collector) to form a coating film, the coating film is dried, and a positive electrode mixture layer is formed on the surface of the aluminum foil. formed.
After that, the positive electrode mixture layer was pressurized with a linear pressure of 4 kN/100 mm to prepare the positive electrode of Example 1.

An ion ^- conductive polymer film as an electrolyte and a lithium metal as a negative electrode were placed on the positive electrode and pressed under a predetermined pressure.
Next, the battery member was arranged in a CR2032 type coin cell, and a lithium ion polymer solid secondary battery of Example 1 was produced.

[Example 2]
"Preparation of iron oxide particles"
Polyethylene glycol 400 was added to a 1 mol/L iron (III) nitrate aqueous solution so that the amount of Fe ions and —CH ₂ CH ₂ O— units of polyethylene glycol was 1:1, and allowed to stand overnight. . 28% aqueous ammonia was added to the obtained solution for neutralization, and the obtained slurry-like sample was dried using a spray dryer. Furthermore, the obtained dried product was calcined at 500° C. for 2 hours to obtain a sample. At that time, the generated gas was passed through a scrubber using a 10% sodium hydroxide aqueous solution and absorbed and detoxified. The obtained powder was confirmed by XRD measurement to be iron (III) oxide (Fe ₂ O ₃ ) with a hematite structure. The half-value width a of the diffraction line derived from the 110 plane index plane was 0.1632°, and the half-value width b of the diffraction line derived from the 104 plane index plane was 0.5377°. Also, the ratio (b/a) of the half-value width b to the half-value width a was about 3.3.

"Fabrication of lithium-ion polymer solid-state secondary battery"
A lithium ion polymer solid secondary battery of Example 2 was produced in the same manner as in Example 1 except that Fe ₂ O ₃ of Example 2 was used.

[Example 3]
"Preparation of iron oxide particles"
A sample of Example 3 was obtained in the same manner as in Example 2 except that the amount of polyethylene glycol 400 in the aqueous solution was halved (Fe ion: —CH ₂ CH ₂ O— unit substance amount was 2:1). rice field. The obtained powder was confirmed by XRD measurement to be iron (III) oxide (Fe ₂ O ₃ ) with a hematite structure. The half-value width a of the diffraction line derived from the 110 plane index plane was 0.1667°, and the half-value width b of the diffraction line derived from the 104 plane index plane was 0.3734°. Also, the ratio (b/a) of the half-value width b to the half-value width a was about 2.2.

"Fabrication of lithium-ion polymer solid-state secondary battery"
A lithium ion polymer solid secondary battery of Example 3 was produced in the same manner as in Example 1 except that Fe ₂ O ₃ of Example 3 was used.

[Comparative Example 1]
"Preparation of iron oxide particles"
A sample of Comparative Example 1 was obtained in the same manner as in Example 2, except that polyethylene glycol 400 was not added. The obtained powder was confirmed by XRD measurement to be iron (III) oxide (Fe ₂ O ₃ ) with a hematite structure. The half-value width a of the diffraction line derived from the 110 plane index plane was 0.1759°, and the half-value width b of the diffraction line derived from the 104 plane index plane was 0.1836°. Also, the ratio (b/a) of the half-value width b to the half-value width a was about 1.0.

"Fabrication of lithium-ion polymer solid-state secondary battery"
A lithium ion polymer solid secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the Fe ₂ O ₃ of Comparative Example 1 was used.

[Comparative Example 2]
"Fabrication of lithium-ion polymer solid-state secondary battery"
A thium ion polymer solid secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 using commercially available hematite-type iron oxide (Fujifilm Wako Pure Chemical Reagent Class 1). The half-value width a of the diffraction line derived from the plane index 110 plane of the iron oxide used was 0.1684°, and the half-value width b of the diffraction line derived from the plane index 104 plane was 0.1703°. Also, the ratio (b/a) of the half-value width b to the half-value width a was about 1.0.

[X-ray diffraction measurement]
The X-ray diffraction measurement of the sample was carried out by a powder method using CuKα rays (600 W) using a Malvern Panalytical powder X-diffractometer Aeris. The half-value width of the obtained diffraction line was determined by least-squares fitting with the Pseudo Voigt function using analysis software X'Pert Pro attached to the apparatus. The X-ray diffraction patterns of Examples and Comparative Examples are shown in FIG. are shown in Table 1 together.

[Evaluation of secondary battery]
Using the lithium ion polymer solid secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, a constant current charge/discharge test was performed. The test temperature was 50° C., the measured current was 100 mA/g (per active material weight), and the cutoff voltage was 1V-4V. FIG. 2 shows the discharge curve of the second cycle, and Table 1 shows the discharge capacity of the second cycle and the results of the cycle test (capacity and retention rate after 10-cycle test).

From the results shown in FIG. 2 and Table 1, half of the diffraction line derived from the plane index 104 plane obtained by X-ray diffraction measurement with respect to the half width a of the diffraction line derived from the plane index 110 plane obtained by X-ray diffraction measurement The lithium ion polymer solid secondary batteries of Examples 1 to 3 containing iron oxide particles having a value width b ratio (b/a) of 2 or more as a positive electrode active material are excellent in discharge capacity and capacity retention rate. Do you get it.
On the other hand, the ratio (b/a ) of less than 2 as the positive electrode active material, the lithium ion polymer solid secondary batteries of Comparative Examples 1 and 2 were found to be inferior in discharge capacity and capacity retention rate.

Since the lithium ion polymer solid secondary battery or the lithium ion inorganic all-solid secondary battery using the positive electrode active material of the present invention has excellent battery capacity, the reliability of the lithium ion solid secondary battery, including mobile applications, is high. can make a significant contribution to progress.

Claims (4)

A positive electrode active material used in a lithium ion solid state secondary battery comprising a lithium-containing negative electrode,
containing iron(III) oxide or heteroelement-substituted iron(III) oxide,
The ratio (b/a) of the half-value width b of the diffraction line derived from the plane index 104 plane obtained by X-ray diffraction measurement to the half-value width a of the diffraction line derived from the plane index 110 plane obtained by X-ray diffraction measurement is A positive electrode active material comprising anisotropic iron oxide particles of 2.0 or more. A positive electrode comprising the positive electrode active material according to claim 1 . A lithium ion polymer solid secondary battery comprising a positive electrode containing the positive electrode active material according to claim 1, a negative electrode containing lithium, and an ion conductive polymer electrolyte. A lithium ion inorganic all-solid secondary battery comprising a positive electrode containing the positive electrode active material according to claim 1, a negative electrode containing lithium, and an inorganic solid electrolyte.

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