JP2020205150A - Electrode slurry for non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide an electrode for a non-aqueous electrolyte secondary battery, which exhibits battery performance regardless of a type of a current collector, and also to provide a manufacturing method thereof.SOLUTION: Disclosed is electrode slurry for a non-aqueous electrolyte secondary battery, which contains a sulfur-based active material, a binder, and an aqueous solvent. A method of manufacturing an electrode for the non-aqueous electrolyte secondary battery includes a step of applying the electrode slurry, which is characterized in that pH is three or more and nine or less, to a collector.SELECTED DRAWING: None

Description

The present invention relates to an electrode slurry used for an electrode for a non-aqueous electrolyte secondary battery and an electrode for a non-aqueous electrolyte secondary battery including an electrode coated with the electrode slurry.

In recent years, a technique using sulfur as an active material of a lithium ion secondary battery, which is a kind of non-aqueous electrolyte secondary battery, has attracted attention. Sulfur is not only easier to obtain and cheaper than rare metals, but also can increase the charge / discharge capacity of lithium ion secondary batteries. In addition, sulfur has an advantage that it has lower reactivity than oxygen and has a low risk of ignition and explosion due to overcharging. Further, as a sulfur-based active material capable of suppressing elution of sulfur into the electrolytic solution and improving battery performance as compared with the conventional sulfur-based active material, an active material in which sulfur and a carbon material are combined has been reported ( Patent Documents 1 to 4).

JP-A-2002-154815 International Publication No. 2010/0444437 Japanese Unexamined Patent Publication No. 2012-150933 Japanese Unexamined Patent Publication No. 2015-92449

When preparing a slurry to be applied to an electrode using a sulfur-based active material, if an organic solvent is used as the solvent, the sulfur component that contributes to the charge / discharge reaction may elute, which may lead to a decrease in the capacity of the active material. Is preferably used as a solvent. However, the aqueous slurry of the sulfur-based active material may be acidic due to the influence of acid gas such as hydrogen sulfide generated during firing. Therefore, when an electrode is produced by applying an aqueous slurry of a sulfur-based active material to a current collector that is vulnerable to corrosion, there is a problem that sufficient battery performance is not easily exhibited.

An object of the present invention is to provide an electrode for a non-aqueous electrolyte secondary battery that exhibits battery performance regardless of the type of current collector, and a method for manufacturing the same.

As a result of diligent studies, the present inventors applied a predetermined electrode slurry in which the pH of the slurry was adjusted to near neutrality to the electrodes, so that the charge / discharge capacity was large and the cycle characteristics were large regardless of the type of current collector. The present invention has been completed by finding that it is possible to produce an excellent non-aqueous electrolyte secondary battery.

That is, the present invention
[1] An electrode slurry for a non-aqueous electrolyte secondary battery containing a sulfur-based active material, a binder, and an aqueous solvent, which has a pH of 3 or more and 9 or less.
[2] The sulfur-based active material is contained in an amount of 85% by mass or more with respect to 100% by mass of the solid content contained in the electrode slurry for a non-aqueous electrolyte secondary battery, and the solid content in the electrode slurry for a non-aqueous electrolyte secondary battery. The electrode slurry for a non-aqueous electrolyte secondary battery according to [1], wherein the pH of the electrode slurry is 3 or more and 9 or less when the concentration is 10% by mass or more.
[3] The non-sulfur-based active material according to [1] or [2], wherein the sulfur-based active material is a sulfur-based active material obtained by firing a raw material obtained by firing a raw material obtained by mixing sulfur with an organic compound that can be sulphurized or a carbon material having porosity. Electrode slurry for water electrolyte secondary batteries,
[4] The electrode slurry for a non-aqueous electrolyte secondary battery according to any one of [1] to [3], which further contains an alkaline substance.
[5] The electrode slurry for a non-aqueous electrolyte secondary battery according to [4], wherein the alkaline substance is a hydroxide, an organic acid salt, or an inorganic acid salt of a metal belonging to Group 1 or Group 2.
[6] The electrode slurry for a non-aqueous electrolyte secondary battery according to any one of [1] to [5], which further contains a conductive auxiliary agent.
[7] For a non-aqueous electrolyte secondary battery containing at least an active material layer obtained by drying and solidifying the electrode slurry for a non-aqueous electrolyte secondary battery according to any one of [1] to [6] and a current collector. electrode,
[8] The electrode for a non-aqueous electrolyte secondary battery according to [7], wherein the current collector is an aluminum-based current collector.
[9] A non-aqueous electrolyte secondary battery provided with the electrode for the non-aqueous electrolyte secondary battery according to [8].
[10] The non-aqueous electrolyte secondary battery according to [9], wherein the non-aqueous electrolyte secondary battery is a lithium ion secondary battery.
[11] An electrical device having the non-aqueous electrolyte secondary battery according to [9] or [10].
[12] A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, wherein the manufacturing method includes a step of applying an electrode slurry for a non-aqueous electrolyte secondary battery to a current collector, and the non-aqueous electrolyte secondary battery. A production method, wherein the electrode slurry for use contains a sulfur-based active material, a binder, and an aqueous solvent, and has a pH of 3 or more and 9 or less.
[13] The production method according to [12], wherein the electrode slurry for a non-aqueous electrolyte secondary battery further contains an alkaline substance.

By using the electrode slurry of the present invention, it is possible to manufacture an electrode for a non-aqueous electrolyte secondary battery that exhibits battery performance regardless of the type of current collector.

It is sectional drawing which shows typically the reactor used for the production of the sulfur-based active material. It is a graph which shows the result of Raman spectrum analysis of the sulfur-based active material obtained in Example 1. It is a graph which shows the result of FT-IR spectrum analysis of the sulfur-based active material obtained in Example 1. It is a graph which shows the result of Raman spectrum analysis of the sulfur-based active material obtained in Example 4.

The procedure for producing a non-aqueous electrolyte secondary battery including the production of the electrode slurry according to the embodiment of the present invention will be described in detail below. However, the following description is an example for explaining the present invention, and does not mean that the technical scope of the present invention is limited to this description range. In this specification, when the numerical range is indicated by using "~", the numerical values at both ends thereof are included.

<Sulfur-based active material>
The sulfur-based active material according to the present embodiment is not particularly limited as long as it is an active material containing a sulfur element as a component. Specific examples of the sulfur-based active material include compounds containing sulfur elements such as titanium sulfide, molybdenum sulfide, iron sulfide, copper sulfide, nickel sulfide, lithium sulfide, and organic disulfide compounds; sulphurable organic compounds and sulfur. Examples thereof include an organic sulfur-based active material obtained by firing a mixed raw material; a carbon-sulfur composite obtained by firing a raw material in which a porous carbon material and sulfur are mixed.

Examples of sulfideable organic compounds include polybutadiene, polyisoprene, poly (meth) acrylonitrile, polychloroprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, acrylonitrile-butadiene copolymer, and styrene-butadiene. Carbon-carbon such as −styrene copolymer, styrene-isoprene-styrene copolymer, (meth) acrylonitrile- (meth) acrylic acid ester copolymer, methacrylonitrile-acrylonitrile- (meth) acrylic acid ester copolymer, etc. Polymers having an unsaturated bond; higher fatty acids such as stearic acid, linoleic acid, and arachidonic acid (preferably fatty acids having 12 to 22 carbon atoms, more preferably fatty acids having 14 to 20 carbon atoms) and the like can be mentioned. Among them, polybutadiene, a polymer or copolymer containing (meth) acrylonitrile as a monomer component, and a higher fatty acid are preferable, and high cis butadiene and methacrylonitrile having a cis-1,4 bond amount of 90% or more are used as a monomer component. The copolymer containing it is more preferable. The above-mentioned "(meth) acrylic" means "acrylic" or "methacryl".

In the present embodiment, the polymer or copolymer containing (meth) acrylonitrile as a monomer component is contained, and the outer shell containing the polymer or copolymer containing (meth) acrylonitrile as a monomer component contains hydrocarbons. The polymerized particles (hereinafter, may be referred to as "heat-expandable microcapsules") may be used. Examples of such heat-expandable microcapsules include the trade name "Expansel" manufactured by Nippon Phillite Co., Ltd., the trade name "Matsumoto Microsphere" manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Commercially available heat-expandable microcapsules such as "Foam" and "Advancel" manufactured by Sekisui Chemical Co., Ltd. can be used.

Examples of the carbon material having porosity include activated carbon, Ketjen black and the like.

The higher the total sulfur content in the sulfur-based active material, the higher the charge / discharge capacity of the non-aqueous electrolyte secondary battery tends to be. Therefore, the total content of sulfur in the sulfur-based active material by elemental analysis is preferably 50% by mass or more. Further, by firing, hydrogen in the organic compound reacts with sulfur to become hydrogen sulfide, which is reduced from the sulfur-based positive electrode active material. Therefore, the smaller the hydrogen content, the more preferable. Specifically, the hydrogen content by elemental analysis is preferably 1.6% by mass or less, particularly 1.0% by mass or less. If the hydrogen content exceeds this range, the sulfurization reaction is insufficient, and the charge / discharge capacity of the non-aqueous electrolyte secondary battery may not be sufficiently increased.

The organic sulfur-based active material is preferably used in the present embodiment because it can strongly immobilize sulfur in the active material and has a high effect of suppressing a decrease in battery capacity due to a charge / discharge reaction. Further, although the organic sulfur-based active material generates acid gas in the firing step, the charge / discharge capacity and cycle characteristics of the non-aqueous electrolyte secondary battery are remarkably improved by using the electrode slurry according to the present embodiment. be able to.

As the organic sulfur-based active material, a carbon-sulfur structure having a thienoacene structure is particularly preferably used. A non-aqueous electrolyte secondary battery using the carbon-sulfur structure as a positive electrode has a large charge / discharge capacity and excellent cycle characteristics. The carbon-sulfur structure can be produced, for example, according to the method described in Patent Document 4.

The carbon sulfur structure has in the Raman spectrum, around 500 cm ^-1 Raman shift, the peak 1250cm around ^-1, and 1450cm around ^-1. Such spectrum is different from a spectrum called D band, and 1590 cm ^-1 vicinity of G band near 1350 cm ^-1 observed in graphite structure is a 6-membered ring, the literature [Chem. Phys. Chem. 2009, 10 , 3069-3076], the carbon-sulfur structure exhibiting the Raman spectrum described above is of formula (i) because it resembles the spectrum of thienoacen.
It is presumed that the thiophene ring has a long-chain polymer-like thienoacen structure in which the thiophene rings are condensed and linked as represented by.

Further, the carbon-sulfur structure preferably has a hydrogen content of 1.6% by mass or less, particularly 1.0% by mass or less. Further, the FT-IR spectrum, 917Cm around ^-1, 1042Cm around ^-1, 1149Cm around ^-1, 1214Cm around ^-1, 1388Cm around ^-1, 1415Cm around ^-1, and that a peak exists in 1439cm around ^-1 preferable.

<Manufacturing of sulfur-based active materials>
The sulfur-based active material can be produced by a known method. The organic sulfur-based active material can be produced, for example, by blending sulfur and a vulcanization accelerator and / or a conductive carbon material with a sulfurizable organic compound and firing it by the following method. A carbon-sulfur composite obtained by firing a raw material obtained by mixing a porous carbon material and sulfur can be produced, for example, by the method described in International Publication No. 2016/075916.

As the sulfur, powdered sulfur, insoluble sulfur, precipitated sulfur and the like can be used, but colloidal sulfur is preferable because it is fine particles. From the viewpoint of charge / discharge capacity and cycle characteristics, the amount of sulfur compounded is preferably 250 parts by mass or more, more preferably 300 parts by mass or more, based on 100 parts by mass of the sulfideable organic compound. On the other hand, the upper limit of the amount of sulfur blended is not particularly limited, but 1500 parts by mass or less is preferable, and 1000 parts by mass or less is more preferable, because the charge / discharge capacity is saturated and it is disadvantageous in terms of cost.

When the vulcanization accelerator is blended, the amount used with respect to 100 parts by mass of the sulfurizable organic compound is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, from the viewpoint of charge / discharge capacity and cycle characteristics. On the other hand, the upper limit of the blending amount is not particularly limited, but 250 parts by mass or less is preferable, and 50 parts by mass or less is more preferable, because the charge / discharge capacity is saturated and it is disadvantageous in terms of cost.

The conductive auxiliary agent is not particularly limited, but is conductive such as vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), and graphite. A carbon material can be preferably used. From the viewpoint of capacitance density, input / output characteristics, and conductivity, acetylene black (AB) or Ketjen black (KB) is preferable. These conductive auxiliaries may be used alone or in combination of two or more.

When the conductive auxiliary agent is blended, the amount used with respect to 100 parts by mass of the sulfideable organic compound is preferably 1 part by mass or more, preferably 3 parts by mass or more, and further 5 parts by mass from the viewpoint of charge / discharge capacity and cycle characteristics. preferable. On the other hand, the blending amount is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less. If it exceeds 50 parts by mass, the proportion of the sulfur-containing structure in the sulfur-containing compound is relatively low, so that it tends to be difficult to achieve the purpose of further improving the charge / discharge capacity and cycle characteristics.

Baking is carried out by heating in a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere that does not substantially contain oxygen, and is adopted to suppress oxidative deterioration and excessive thermal decomposition of constituent components. Specifically, the heat treatment is carried out in a quartz tube in an inert gas atmosphere filled with an inert gas such as nitrogen or argon. The firing temperature is preferably 250 ° C. or higher, more preferably 300 ° C. or higher. If the temperature is lower than 250 ° C., the sulfurization reaction is insufficient and the charge / discharge capacity of the target product tends to be low. On the other hand, the firing temperature is preferably 550 ° C. or lower, more preferably 450 ° C. or lower. If the temperature exceeds 550 ° C., the decomposition of the raw material compound increases, and the yield tends to decrease or the charge / discharge capacity tends to decrease.

In the sulfide obtained after calcination, so-called unreacted sulfur such as sulfur sublimated during calcination that has cooled and precipitated remains. Since sulfur is an insulator, it acts as an electrical resistance inside the electrode and may cause deterioration of battery performance. Since unreacted sulfur causes a decrease in cycle characteristics, it is necessary to remove unreacted sulfur. The method for removing unreacted sulfur can be carried out by a method such as vacuum heating drying, warm air drying, solvent washing and the like.

The obtained sulfur-based active material can be pulverized to have a predetermined particle size and classified into particles having a size suitable for manufacturing an electrode. The preferred particle size distribution of the particles obtained by using the laser diffraction type particle size distribution measuring device is about 5 to 25 μm in median diameter.

<Preparation of electrode slurry>
The electrode slurry for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter, may be simply referred to as “electrode slurry”) contains the above-mentioned sulfur-based active material, binder, and aqueous solvent, and has a pH of 3. It is characterized by being 0 or more and 9.0 or less, and preferably contains a conductive auxiliary agent. Further, in order to adjust the pH of the slurry to the above range, it is also preferable to add an alkaline substance.

The method for preparing the electrode slurry is not particularly limited, and for example, solid components such as a sulfur-based active material, a binder, and if necessary, a conductive auxiliary agent and an alkaline substance are dispersed in a solvent to prepare a general electrode slurry. It is prepared by processing with the stirring / mixing device used.

The pH of the electrode slurry is 3.0 or more and 9.0 or less, preferably 6.0 or more and 9.0 or less, and more preferably 6.0 or more and 8.0 or less. The pH of the electrode slurry is preferably 3 or more and 9 or less when the solid content concentration in the slurry is 10% by mass or more.

As used herein, "pH" is an index indicating the concentration of hydrogen ions in an aqueous solution. Here, the pH is a value measured by a desktop pH meter (LAQUAact D-71AC) manufactured by HORIBA, Ltd. The pH can also be measured with an equivalent device.

The method of adjusting the pH of the electrode slurry to the above range is not particularly limited. For example, a method of cleaning the sulfur-based active material obtained after firing with a liquid (preferably water or an alkaline aqueous solution), sulfur-based activity. Examples thereof include a method of heat-treating a substance to remove adsorbed acid gas and the like, and a method of adding an alkaline substance to the electrode slurry to neutralize the substance.

By adding an alkaline substance to the electrode slurry, the acidic component contained in the sulfur-based active material is neutralized by a neutralization reaction, and the pH of the slurry can be adjusted to the above range. According to this method, the pH of the electrode slurry can be adjusted by simply adding an alkaline substance to the electrode slurry without increasing the number of processes from the existing slurry production process.

(Alkaline substance)
As the alkaline substance that can be used in this embodiment, a metal salt or metal oxide belonging to Group 1 or Group 2 is preferably used. The metal salts or metal oxides belonging to Group 1 or Group 2 may be used alone or in combination of two or more.

Examples of metal salts (alkali metal salts) belonging to Group 1 include hydroxides of metals belonging to Group 1, inorganic acid salts of metals belonging to Group 1, and organic acid salts of metals belonging to Group 1. , Inorganic acid salts of metals belonging to Group 1 are preferable.

As the metal constituting the metal salt of the metal salt belonging to Group 1, lithium, sodium, potassium, rubidium and cesium are preferable, lithium, sodium and potassium are more preferable, and lithium is particularly preferable.

Examples of the metal salt belonging to Group 2 include hydroxides of metals belonging to Group 2, inorganic acid salts of metals belonging to Group 2, and organic acid salts of metals belonging to Group 2. The inorganic acid salt of the metal to which it belongs is preferable.

As the metal constituting the metal salt belonging to Group 2, magnesium, calcium and barium are preferable, magnesium and calcium are more preferable, and magnesium is particularly preferable.

Examples of the inorganic acid salt constituting the inorganic acid salt of the metal belonging to Group 1 or Group 2 include carbonate, hydrogen carbonate, phosphate, hydrogen phosphate and the like, and carbonate and carbonate having a small molecular weight. Bicarbonate is preferred.

Examples of the organic acid salt constituting the organic acid salt of the metal belonging to Group 1 or Group 2 include formate, acetate, propionate, oxalate, lactate, citrate, benzoate and the like. Therefore, acetates and formates having a small molecular weight are preferable.

Among the metal salts belonging to the above-mentioned Group 1 or Group 2, alkali metal salts are preferable, and alkali metal inorganic acid salts are more preferable. Further, from the viewpoint of weight energy density, it is preferable that the molecular weight is small.

Preferred specific examples of the above-mentioned metal salts belonging to Group 1 or Group 2 include, for example, sodium carbonate, magnesium carbonate, lithium carbonate, sodium hydrogen carbonate, magnesium hydrogen carbonate, lithium hydrogen carbonate, sodium hydroxide, magnesium hydroxide. , Lithium hydroxide and the like.

Examples of alkaline substances that can be used other than metal salts or metal oxides belonging to Group 1 or Group 2 include basic gases such as ammonia, methylamine and ethylamine, carbon black and the like. Alkaline substances other than metal salts or metal oxides belonging to Group 1 or Group 2 may be used alone or in combination of two or more. Further, it may be used in combination with a metal salt or metal oxide belonging to Group 1 or Group 2.

(Binder)
As the binder, a known binder used for the electrode can be used, but an aqueous binder is preferably used from the viewpoint of affinity with water and reduction of environmental load. Examples of the aqueous binder include hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), acrylic resin, styrene-butadiene rubber (SBR), water-soluble polyimide (PI), and water-soluble polyamide-imide (PAI). ), Methacrylic resin (PMA), polyethylene oxide (PEO), urethane and the like. These binders may be used alone or in combination of two or more.

(Conductive aid)
As the conductive auxiliary agent, a conductive auxiliary agent that can be used in the production of the sulfur-based active material can be similarly used.

(solvent)
In the preparation of the electrode slurry, the solvent used for dispersing the solid components such as the sulfur-based active material, the binder, the conductive additive, and the alkaline substance is preferably a solvent containing water (aqueous solvent), and water is preferable. When an organic solvent other than water is used, the sulfur component that contributes to the charge / discharge reaction elutes from the sulfur-based active material, and the charge / discharge capacity of the battery tends to decrease. Further, an aqueous solvent is preferable from the viewpoint of reducing the environmental load. As long as the effect of the present invention is not impaired (for example, organic solvent other than water is less than 20% by mass), N-methyl-2-pyrrolidone (NMP), N, N-dimethylformaldehyde, lower alcohol, etc. A solvent that is miscible with water may be mixed.

The content of the sulfur-based active material with respect to 100% by mass of the solid components (particularly the sulfur-based active material, the binder, the conductive auxiliary agent, and the alkaline agent; the same applies hereinafter) in the electrode slurry is determined from the viewpoint of improving the energy density of the battery. 85% by mass or more is preferable, 87% by mass or more is more preferable, and 90% by mass or more is further preferable. The upper limit of the content of the sulfur-based active material is not particularly limited, but is preferably 99% by mass or less, more preferably 97% by mass or less, and further preferably 95% by mass or less.

The content of the binder in the electrode slurry with respect to 100% by mass of the solid component is preferably 0.1 to 10.0 parts by mass.

When the conductive auxiliary agent is blended in the electrode slurry, the content with respect to 100% by mass of the solid component is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 8.0% by mass.

The content of an alkaline substance in the electrode slurry with respect to 100% by mass of the solid component varies depending on the valence and molecular weight of the ions of the metal salt used, but from the viewpoint of adjusting the pH of the electrode slurry to 3 or more and 9 or less. , 0.5 to 5.0% by mass is preferable.

<Electrode configuration>
The electrodes (positive electrode and negative electrode) for the non-aqueous electrolyte secondary battery according to the present embodiment can have the same structure as a general non-aqueous electrolyte power storage device. For example, when the electrode slurry according to the present embodiment is used for the electrode, the electrode can be an electrode containing at least an active material layer obtained by drying and solidifying the electrode slurry and a current collector. The active material layer preferably contains the above-mentioned sulfur-based active material and binder, and preferably contains a conductive auxiliary agent and / or an alkaline substance.

The electrode for a non-aqueous electrolyte secondary battery according to the present embodiment can be produced by applying the electrode slurry to a current collector and drying it. As another method, a mixture of a sulfur-based active material, a conductive auxiliary agent, and a binder is kneaded and formed into a film by a mortar or a press machine, and the film-like mixture is crimped to a current collector by a press machine or the like. It can also be produced by.

(Current collector)
As the current collector, one generally used as an electrode for a lithium ion secondary battery can be used. Specific examples of the current collector include aluminum-based current collectors such as aluminum foil, aluminum mesh, punching aluminum sheet, and aluminum expand sheet; stainless steel foil, stainless steel mesh, punching stainless steel sheet, stainless steel expand sheet, and the like. Stainless steel current collectors; nickel foam collectors such as nickel foam and nickel non-woven fabrics; copper foil collectors such as copper foil, copper mesh, punching copper sheet, and copper expand sheet; titanium-based collectors such as titanium foil and titanium mesh. Current collector: A carbon-based current collector such as a carbon non-woven material or a carbon woven cloth can be used. Of these, an aluminum-based current collector is preferable from the viewpoints of mechanical strength, conductivity, mass density, cost, and the like.

Aluminum foil is cheaper than other current collectors, has excellent conductivity, and is light in weight, which is very useful because it leads to an improvement in the energy density of the battery. However, since aluminum is an amphoteric metal and corrosion progresses in an acid or alkaline environment, the battery performance is extremely high when the electrode is manufactured using an electrode slurry having a pH of less than 3.0 or a pH of more than 9.0. Getting worse. On the other hand, when the electrode slurry according to the present embodiment is used, sufficient battery performance can be obtained even if an aluminum-based current collector such as an aluminum foil is used as the current collector.

The shape of the current collector is not particularly limited, but for example, a foil-like base material, a three-dimensional base material, or the like can be used. When a three-dimensional base material (foam metal, mesh, woven fabric, non-woven fabric, expand, etc.) is used, an electrode with a high capacitance density can be obtained even with a binder that lacks adhesion to the current collector, and a high rate is obtained. The charge / discharge characteristics also tend to be good.

(Electrode material)
When the sulfur-based active material according to the present embodiment is used for the positive electrode, examples of the negative electrode material include carbon-based materials such as metallic lithium and graphite; silicon-based materials such as silicon thin film and SiO; copper-tin, cobalt-tin and the like. Examples thereof include known negative electrode materials such as tin alloy-based materials. When a lithium-free material such as a carbon-based material, a silicon-based material, or a tin alloy-based material is used as the negative electrode material, a short circuit between the positive and negative electrodes due to dendrite generation can be less likely to occur, and a non-aqueous electrolyte secondary material can be used. The life of the battery can be extended. Among them, a silicon-based material which is a high-capacity negative electrode material is preferable, and a thin-film silicon which can reduce the electrode thickness and is advantageous in terms of capacity per volume is more preferable.

However, when a lithium-free negative electrode material is used in combination with the positive electrode according to the present embodiment, neither the positive electrode nor the negative electrode contains lithium. Therefore, lithium is previously added to either or both of them. It is necessary to process the pre-dope to be inserted.

As a predoping method, a known method can be used. For example, when the negative electrode is doped with lithium, an electrolytic doping method in which a semi-battery is assembled using metallic lithium as a counter electrode and the lithium is electrochemically doped, or in an electrolytic solution with a metallic lithium foil attached to the electrode. Examples thereof include a pasting predoping method in which the electrode is left in the electrode and doped by diffusion of lithium to the electrode. The above-mentioned electrolytic doping method can also be adopted when lithium is pre-doped into the positive electrode.

When the sulfur-based active material according to the present embodiment is used for the negative electrode, the positive electrode material may be, for example, a composite oxide of lithium and a transition metal (particularly, a cobalt-based composite oxide, a nickel-based composite oxide, or a manganese-based composite oxide. , A ternary complex oxidation consisting of three elements of cobalt, nickel and manganese). Further, a lithium transition metal phosphate composite compound having an olivine type crystal structure (particularly lithium iron phosphate, lithium manganese phosphate) and the like can also be used. When the electrode produced by using a lithium-containing transition metal lithium composite oxide-based compound as the active material is used as the positive electrode and the electrode using the electrode slurry according to the present embodiment is used as the negative electrode, the positive electrode is used. Lithium predoping is not always necessary as it contains lithium.

<Electrolyte>
The electrolyte constituting the non-aqueous electrolyte secondary battery may be any liquid or solid having ionic conductivity, and the same electrolyte as that used for known non-aqueous electrolyte secondary batteries can be used, but the output of the battery. From the viewpoint of high characteristics, it is preferable to use an organic solvent in which an alkali metal salt as a supporting electrolyte is dissolved.

Examples of the organic solvent include at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone and acetonitrile. Preferably, ethylene carbonate, propylene carbonate, or a mixed solvent thereof is used.

Examples of the supporting electrolyte include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiI, LiClO _{4, and the} like, and LiPF ₆ is preferable.

The concentration of the supporting electrolyte may be about 0.5 mol / L to 1.7 mol / L. The electrolyte is not limited to liquid. For example, when the non-aqueous electrolyte secondary battery is a lithium polymer secondary battery, the electrolyte may be solid (for example, polymer gel), ionic liquid, molten salt, or the like.

The non-aqueous electrolyte secondary battery may include members such as a separator in addition to the above-mentioned positive electrode, negative electrode, and electrolyte. The separator intervenes between the positive electrode and the negative electrode to allow the movement of ions between the two electrodes, and functions to prevent an internal short circuit between the positive electrode and the negative electrode. If the non-aqueous electrolyte secondary battery is a closed type, the separator is also required to have a function of holding the electrolytic solution.

As the separator, for example, a thin, microporous or non-woven film made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass or the like is preferably used.

The shape of the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and various shapes such as a cylindrical type, a laminated type, a coin type, and a button type can be used.

Since the non-aqueous electrolyte secondary battery provided with the electrodes according to the present embodiment has a high capacity and excellent cycle characteristics, it can be used in an electric device that can be used as a power source for smartphones, power tools, automobiles, UPS, and the like.

The present invention will be specifically described based on Examples, but the present invention is not limited thereto.

Various chemicals used in Examples and Comparative Examples will be described.
Organic compound 1: High cis butadiene rubber (UBEPOL (registered trademark) BR150L manufactured by Ube Industries, Ltd., cis 1,4 bond content 98% by mass)
Organic compound 2: Stearic acid (reagent manufactured by Tokyo Chemical Industry Co., Ltd.)
Sulfur: Precipitated sulfur made by Tsurumi Chemical Industry Co., Ltd. Conductive carbon material: Acetylene black (Denka black manufactured by Denka Co., Ltd.)
Vulcanization accelerator: Zinc diethyldithiocarbamate (Noxeller (registered trademark) EZ manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)
Binder: Aqueous acrylic resin Conductive reagent: Acetylene black (Denka black manufactured by Denka Co., Ltd.) / VGCF (manufactured by Showa Denko KK) = 1: 1 mixture Alkaline substance 1: Lithium carbonate (Tokyo Chemical Industry Co., Ltd. Reagents)
Alkaline substance 2: Calcium carbonate (reagent manufactured by Tokyo Chemical Industry Co., Ltd.)
Alkaline substance 3: Sodium acetate (Reagent manufactured by Tokyo Chemical Industry Co., Ltd.)

[Example 1]
<Manufacturing process of sulfur-based active material>
(Preparation of raw material compound)
Raw materials are obtained by kneading the organic compound, sulfur, conductive carbon material, and vulcanization accelerator using a kneading test device (Mix Lab manufactured by Moriyama Co., Ltd.) according to the formulation shown in Example 1 of Table 1. The compound was obtained. The obtained raw material compound was finely crushed with a cutter mill and used in a firing step.

(Reactor)
The reactor 1 shown in FIG. 1 was used for firing the raw material compound. The reaction apparatus 1 is a reaction vessel 3 having an outer diameter of 60 mm, an inner diameter of 50 mm, and a height of 300 mm, which is made of bottomed tubular quartz glass for accommodating and firing the raw material compound 2, and an upper opening of the reaction vessel 3. A silicon lid 4 and one alumina protective tube 5 (“Alumina SSA-S” manufactured by Nikkato Co., Ltd., outer diameter 4 mm, inner diameter 2 mm, length 250 mm) that penetrates the lid 4 and two Gas introduction pipe 6 and gas discharge pipe 7 (both are "alumina SSA-S" manufactured by Nikkato Co., Ltd., outer diameter 6 mm, inner diameter 4 mm, length 150 mm), and electricity for heating the reaction vessel 3 from the bottom side. It is equipped with a furnace 8 (rutsubo furnace, opening width φ80 mm, heating height 100 mm).

The alumina protective tube 5 has a length below the lid 4 that reaches the raw material compound 2 housed in the bottom of the reaction vessel 3, and a thermocouple 9 is inserted therein. The alumina protective tube 5 is used as a protective tube for the thermocouple 9. The tip of the thermocouple 9 is inserted into the raw material compound 2 while being protected by the closed tip of the alumina protective tube 5, and functions to measure the temperature of the raw material compound 2. The output of the thermocouple 9 is input to the temperature controller 10 of the electric furnace 8 as shown by the solid arrow in the figure, and the temperature controller 10 heats the electric furnace 8 based on the input from the thermocouple 9. It works to control the temperature.

The lower ends of the gas introduction pipe 6 and the gas discharge pipe 7 are formed so as to protrude 3 mm downward from the lid 4. Further, the upper portion of the reaction vessel 3 protrudes from the electric furnace 8 and is exposed to the outside air. Therefore, the vapor of sulfur generated from the raw material compound by heating the reaction vessel 3 rises above the reaction vessel 3 as shown by the arrow of the alternate long and short dash line in the figure, but is cooled in the middle and becomes droplets. As shown by the broken line arrow, the mixture is dropped and refluxed. Therefore, sulfur in the reaction system does not leak to the outside through the gas discharge pipe 7.

Ar gas is continuously supplied to the gas introduction pipe 6 from a gas supply system (not shown). Further, the gas discharge pipe 7 is connected to a trap tank 12 containing the sodium hydroxide aqueous solution 11. The exhaust gas that is going to go out from the reaction vessel 3 through the gas discharge pipe 7 is once passed through the sodium hydroxide aqueous solution 11 in the trap tank 12 and then discharged to the outside. Therefore, even if hydrogen sulfide gas generated by the sulfurization reaction is contained in the exhaust gas, it is neutralized with the sodium hydroxide aqueous solution and removed from the exhaust gas.

(Baking process)
In the firing step, first, with the raw material compound 2 housed in the bottom of the reaction vessel 3, Ar (argon) gas is continuously supplied from the gas supply system at a flow rate of 80 mL / min, and 30 minutes after the start of supply. , The heating by the electric furnace 8 was started. The heating rate was 150 ° C./h. Then, when the temperature of the raw material compound reached 450 ° C., firing was performed for 2 hours while maintaining 450 ° C. Then, while adjusting the flow rate of Ar gas, the temperature of the reaction product was naturally cooled to 25 ° C. under an Ar gas atmosphere, and then the reaction product was taken out from the reaction vessel 3.

(Removal of unreacted sulfur)
The following steps were carried out in order to remove unreacted sulfur (elemental sulfur in a free state) remaining in the product after the firing step. That is, the product was crushed in a mortar, 2 g of the crushed product was placed in a glass tube oven, and heated at 250 ° C. for 3 hours while sucking vacuum to remove unreacted sulfur (or a small amount of unreacted). A sulfur-based active material (containing only sulfur) was obtained. The heating rate was 10 ° C./min.

(Raman spectrum analysis)
The obtained sulfur-based active material was subjected to Raman spectrum analysis using a laser Raman microscope RAMAN-11 manufactured by Nanophoton Co., Ltd. under the conditions of excitation wavelength λ = 532 nm, grazing: 600 gr / mm, and resolution: 2 cm ^-1 . (Fig. 2). In FIG. 2, the vertical axis represents the relative intensity and the horizontal axis represents the Raman shift (cm ^-1 ). The resulting sulfur-based active material, around 500 cm ^-1 Raman shift, 1250 cm around ^-1, 1450 cm around ^-1, and 1940Cm ^-1 and peak around exists, this result, a large amount of sulfur in the previous It was confirmed that it is in good agreement with the elemental analysis result that hydrogen is taken in and reduced.

The spectrum of Figure 2 is different from the spectrum, called D band, and 1590 cm ^-1 vicinity of G band near 1350 cm ^-1 observed in graphite structure is a 6-membered ring, the literature [Chem. Phys. Chem 2009 , 10, 3069-3076], the resulting sulfur-based active material was expected to have a thienoacen structure represented by the above formula (i), because it resembles the spectrum of thienoacen. ..

(FT-IR spectrum analysis)
The resulting sulfur-based active material, using a Fourier transform infrared spectrophotometer IRAffinity-1 manufactured by Shimadzu Corporation, resolution: 4 cm ^-1, the number of integrations: 100 times, measuring range 400cm ^-1 ~4000cm ^{- Under} the condition of ¹ , FT-IR spectrum analysis was performed by the diffuse reflection method (Fig. 3). The resulting sulfur-based active material, the FT-IR spectrum, 917Cm around ^-1, 1042Cm around ^-1, 1149Cm around ^-1, 1214Cm around ^-1, 1388Cm around ^-1, 1415Cm around ^-1, and 1439cm around ^-1 There is a peak in, and it was confirmed that this result is in good agreement with the elemental analysis result that a large amount of sulfur was taken in and hydrogen was reduced.

(Elemental analysis)
Using a fully automatic elemental analyzer (vario MICRO cube manufactured by Elemental), the sulfur content in the total amount of the obtained sulfur-based active material was calculated to be 55.5%, and the hydrogen content was determined. As a result of calculation, it was 0.21%.

<Manufacturing of lithium ion secondary battery>
[1] Positive electrode The above sulfur-based active material, aqueous acrylic resin, conductive auxiliary agent (acetylene black (Denka black manufactured by Denka Co., Ltd.) / VGCF = 1: 1 mixture), and lithium carbonate 91.8: 3 Weigh at a ratio of .48: 3.97: 0.76 (mass ratio), put it in a container, and adjust the viscosity using water as the solvent while rotating and revolving mixer (ARE-310 manufactured by Shinky Co., Ltd.). Was stirred and mixed using the above to prepare a uniform slurry. The pH of the slurry was 5.3. After that, the above slurry was applied to an aluminum current collector (thickness 20 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) using a desktop coating machine (PI-1210 manufactured by Tester Industry Co., Ltd.) and an applicator. , Dryed in a glass tube oven (B-555 manufactured by BUCHI) at 150 ° C. for 10 hours to prepare a positive electrode for a lithium ion secondary battery. These are the positive electrode slurry and the positive electrode of Example 1.

[2] Negative electrode As the negative electrode, a metallic lithium foil (a disk shape having a diameter of 14 mm and a thickness of 500 μm, manufactured by Honjo Metal Co., Ltd.) was used.

[3] Electrolyte As the electrolyte, a non-aqueous electrolyte in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. The concentration of LiPF ₆ in the electrolytic solution was 1.0 mol / L.

[4] Batteries Coin batteries were produced using the positive and negative electrodes obtained in [1] and [2]. Specifically, a glass non-woven fabric filter (thickness 440 μm, GA100 manufactured by ADVANTEC) was sandwiched between a positive electrode and a negative electrode in a dry room to form an electrode body battery. This electrode body battery was housed in a battery case (CR2032 type coin battery member manufactured by Hosen Co., Ltd.) made of a stainless steel container. The electrolytic solution obtained in [3] was injected into the battery case. The battery case was sealed with a caulking machine to produce the coin-type lithium ion secondary battery of Example 1.

[Example 2]
In the positive electrode manufacturing step of Example 1, a sulfur-based active material, an aqueous acrylic resin, a conductive auxiliary agent, and lithium carbonate were mixed at a ratio of 91.1: 3.45: 3.94: 1.48 (mass ratio). A battery was produced in the same manner as in Example 1 except that the electrode slurry was produced. The pH of the slurry was 7.5.

[Example 3]
In the positive electrode manufacturing step of Example 1, a sulfur-based active material, an aqueous acrylic resin, a conductive auxiliary agent, and lithium carbonate were mixed at a ratio of 90.4: 3.43: 3.91: 2.25 (mass ratio). A battery was produced in the same manner as in Example 1 except that the electrode slurry was produced. The pH of the slurry was 8.9.

[Example 4]
In the production process of the sulfur-based active material of Example 3, the sulfur-based active material was produced in the same manner as in Example 1 except that the organic compound 1 was changed to the organic compound 2, and the battery was produced in the same manner as in Example 1. It was. The sulfur content in the total amount of the obtained sulfur-based active material was calculated using a fully automatic elemental analyzer (vario MICRO cube manufactured by Elemental) and found to be 42.2%. Further, the obtained sulfur-based active material was analyzed by Raman spectrum using a laser Raman microscope RAMAN-11 manufactured by Nanophoton Co., Ltd. under the conditions of excitation wavelength λ = 532 nm, grazing: 600 gr / mm, and resolution: 2 cm ^-1. It was a near 500 cm ^-1 Raman shift, 1250 cm around ^-1 and 1450cm peak around ^-1 was present (Figure 4). The pH of the slurry was 7.8.

[Comparative Example 1]
In the positive electrode manufacturing step of Example 1, a sulfur-based active material, a conductive auxiliary agent, and an aqueous acrylic resin were mixed at a ratio of 92.5: 4.00: 3.50 (mass ratio) without using lithium carbonate, and an electrode was used. A battery was produced in the same manner as in Example 1 except that the slurry was produced. The pH of the slurry was 2.3.

[Test method]
<Charge / discharge capacity measurement test>
The coin-type lithium ion secondary batteries produced in each Example and Comparative Example were charged and discharged with a current value corresponding to 50 mA per 1 g of the sulfur-based active material under the condition of a test temperature of 30 ° C. The discharge end voltage was 1.0 V, and the charge end voltage was 3.0 V. Further, charging and discharging were repeated, the discharge capacity (mAh / g) of each time was measured, and the second discharge capacity (mAh / g) was set as the initial capacity. The results are shown in Table 1. It can be evaluated that the larger the initial capacity, the larger the charge / discharge capacity of the lithium ion secondary battery, which is preferable.

Further, the capacity retention rate (%) was calculated from the _second discharge capacity DC ₂ (mAh / g) and the tenth discharge capacity DC ₁₀ (mAh / g) by the following formula. The results are shown in Table 1. It can be said that the larger the capacity retention rate, the better the cycle characteristics of the lithium ion secondary battery.
(Capacity retention rate (%)) = (DC ₁₀ (mAh / g)) / (DC ₂ (mAh / g)) × 100

From the results in Table 1, it can be seen that the lithium ion secondary battery using the electrode slurry of the present invention as the electrode material has significantly improved charge / discharge capacity and cycle characteristics.

As described above, the preferred embodiment of the present invention has been described with reference to the drawings, but various additions, changes or deletions can be made without departing from the spirit of the present invention. Further, although the lithium ion battery has been described as an example in the above embodiment, the present invention can be applied not only to the lithium ion battery but also to other non-aqueous electrolyte secondary batteries such as a sodium ion battery and a potassium ion battery. Therefore, such things are also included in the present invention.

By using the electrode slurry of the present invention as an electrode material, a non-aqueous electrolyte secondary battery having a large charge / discharge capacity and excellent cycle characteristics can be manufactured regardless of the type of current collector. Non-aqueous electrolyte secondary batteries using this electrode are suitably used as a main power source or an auxiliary power source for electric devices such as mobile communication devices, portable electronic devices, electric vehicles, electric bicycles, electric motorcycles, and power storage devices. It is a thing.

1 Reaction device 2 Raw material compound 3 Reaction vessel 4 Silicon lid 5 Alumina protection tube 6 Gas introduction tube 7 Gas discharge tube 8 Electric furnace 9 Thermocouple 10 Temperature controller 11 Sodium hydroxide aqueous solution 12 Trap tank

Claims (13)

An electrode slurry for a non-aqueous electrolyte secondary battery containing a sulfur-based active material, a binder, and an aqueous solvent, the electrode slurry having a pH of 3 or more and 9 or less. The sulfur-based active material is contained in an amount of 85% by mass or more with respect to 100% by mass of the solid content contained in the electrode slurry for the non-aqueous electrolyte secondary battery, and the solid content concentration in the electrode slurry for the non-aqueous electrolyte secondary battery is 10. The electrode slurry for a non-aqueous electrolyte secondary battery according to claim 1, wherein the pH of the electrode slurry is 3 or more and 9 or less when the amount is 3% by mass or more. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the sulfur-based active material is a sulfur-based active material obtained by firing a raw material obtained by firing a sulfur-based organic compound or a raw material obtained by mixing a porous carbon material with sulfur. Electrode slurry. The electrode slurry for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, further containing an alkaline substance. The electrode slurry for a non-aqueous electrolyte secondary battery according to claim 4, wherein the alkaline substance is a hydroxide, an organic acid salt, or an inorganic acid salt of a metal belonging to Group 1 or Group 2. The electrode slurry for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, further containing a conductive auxiliary agent. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, which comprises at least an active material layer obtained by drying and solidifying the electrode slurry for a non-aqueous electrolyte secondary battery, and a current collector. The electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the current collector is an aluminum-based current collector. A non-aqueous electrolyte secondary battery comprising the electrode for the non-aqueous electrolyte secondary battery according to claim 8. The non-aqueous electrolyte secondary battery according to claim 9, wherein the non-aqueous electrolyte secondary battery is a lithium ion secondary battery. An electrical device having a non-aqueous electrolyte secondary battery according to claim 9 or 10. A method for manufacturing electrodes for non-aqueous electrolyte secondary batteries.
The manufacturing method includes a step of applying an electrode slurry for a non-aqueous electrolyte secondary battery to a current collector.
The production method, wherein the electrode slurry for a non-aqueous electrolyte secondary battery contains a sulfur-based active material, a binder, and an aqueous solvent, and has a pH of 3 or more and 9 or less. The production method according to claim 12, wherein the electrode slurry for a non-aqueous electrolyte secondary battery further contains an alkaline substance.