JP2020205149A - Method for cleaning and processing sulfur-based active material - Google Patents

Abstract

To provide a method of manufacturing an electrode for a non-aqueous electrolyte secondary battery, which exhibits battery performance regardless of a type of a current collector.SOLUTION: Disclosed is a method of manufacturing an electrode for a non-aqueous electrolyte secondary battery, which includes the steps of: performing cleaning and processing on a sulfur-based active material with water or an aqueous solution whose pH is six or more; and applying the slurry obtained by mixing the cleaned and processed sulfur-based active material and water to a current collector.SELECTED DRAWING: None

Description

The present invention relates to a method for cleaning a sulfur-based active material and a method for manufacturing an electrode for a non-aqueous electrolyte secondary battery using the cleaned sulfur-based active material.

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 a method for manufacturing an electrode for a non-aqueous electrolyte secondary battery that exhibits battery performance regardless of the type of current collector.

As a result of diligent studies, the present inventors can adjust the pH of the slurry applied to the electrode to near neutral by cleaning the sulfur-based active material with water or an aqueous solution having a pH of 6 or more, and collect electricity. We have found that a non-aqueous electrolyte secondary battery having a large charge / discharge capacity and excellent cycle characteristics can be manufactured regardless of the type of body, and completed the present invention.

That is, the present invention
[1] A cleaning treatment method comprising cleaning a sulfur-based active material with water or an aqueous solution having a pH of 6 or higher.
[2] The washing treatment method according to [1], wherein the sulfur-based active material is washed with an alkaline aqueous solution having a pH greater than 7, and then further washed with water.
[3] The production method according to [1] or [2], wherein the sulfur-based active material is an organic sulfur-based active material.
[4] A sulfur-based active material washed by the washing treatment method according to any one of [1] to [3].
[5] Electrodes for non-aqueous electrolyte secondary batteries prepared using the sulfur-based active material according to [4].
[6] Non-including a step of washing the sulfur-based active material with water or an aqueous solution having a pH of 6 or more, and a step of applying a slurry of the washed sulfur-based active material and water to the current collector. Manufacturing method of electrodes for water electrolyte secondary batteries,
[7] The manufacturing method according to [6], wherein the current collector is an aluminum-based current collector.
[8] A non-aqueous electrolyte secondary battery provided with an electrode manufactured by the manufacturing method described in [6] or [7].
[9] The non-aqueous electrolyte secondary battery according to [8], wherein the non-aqueous electrolyte secondary battery is a lithium ion secondary battery.
[10] The present invention relates to an electric device having the non-aqueous electrolyte secondary battery according to [8] or [9].

According to 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 cleaning treatment method 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 and Ketjen black.

The higher the total sulfur content in the sulfur-based active material, the better the cycle characteristics of the non-aqueous electrolyte secondary battery tend 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 can be remarkably improved by the cleaning treatment described later.

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 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. The carbon-sulfur composite obtained by firing a raw material in which a porous carbon material and sulfur are mixed 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 vulcanizable 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.

From the viewpoint of charge / discharge capacity and cycle characteristics, the blending amount of the vulcanization accelerator is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, based on 100 parts by mass of the vulcanizable organic compound. 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.

As the conductive carbon material, a carbon material having a graphite structure is preferable. As such a carbon material, for example, a material having a condensed aromatic ring structure such as carbon black, graphite, carbon nanotube (CNT), carbon fiber (CF), graphene, and fullerene can be used. As the conductive carbon material, one kind or two or more kinds can be used. Of these, carbon black is preferable because it is inexpensive and has excellent dispersibility. Further, a small amount of CNT, graphene or the like may be used in combination with carbon black. With such a combined system, it is possible to further improve the cycle characteristics of the non-aqueous electrolyte secondary battery without significantly increasing the cost. The combined amount of CNT and graphene is preferably 8 to 12% by mass of the total amount of the conductive carbon material.

From the viewpoint of charge / discharge capacity and cycle characteristics, the blending amount of the conductive carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass with respect to 100 parts by mass of the vulcanizable organic compound. On the other hand, the blending amount is preferably 50 parts by mass or less, more preferably 30 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.

<Cleaning treatment of sulfur-based active material>
(Washing process)
The cleaning treatment method for the sulfur-based active material is not particularly limited, and examples thereof include immersion cleaning, jet cleaning, bubbling cleaning, stirring cleaning, vacuum cleaning, ultrasonic cleaning, and heat cleaning. Further, by combining a plurality of these cleaning methods, it is possible to perform a cleaning treatment on the sulfur-based active material more effectively and in a short time. For example, Japanese Patent Application Laid-Open No. 2008-142617 reports that impurities adhering to the powder surface can be exfoliated and discharged to the outside of the cleaning system together with the cleaning liquid by synergizing with liquid fluidization by vibration and bubbling. ing.

(Cleaning liquid)
Water or an aqueous solution having a pH of 6 or more can be used as the cleaning liquid, and among them, if an alkaline aqueous solution having a pH greater than 7 is used, an effective cleaning treatment can be performed with the sulfur-based active material in a short time. When an alkaline aqueous solution is used, as the alkaline agent to be used, a metal salt whose aqueous solution is alkaline in the metal elements belonging to Group 1 or Group 2 can be used. For example, in the case of Group 1 metals, lithium hydroxide, lithium carbonate, lithium hydrogen carbonate, lithium acetate, lithium oxalate, lithium phosphate, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, sodium acetate, sodium oxalate , Sodium phosphate, potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, potassium acetate, potassium oxalate, potassium phosphate, rubidium hydroxide, rubidium carbonate, rubidium hydrogen carbonate, rubidium acetate, rubidium oxalate, rubidium phosphate, water Cesium oxide, cesium carbonate, cesium hydrogen carbonate, cesium acetate, cesium oxalate, cesium phosphate, and for Group 2 metals, berylium hydroxide, beryllium carbonate, berylium hydrogencarbonate, beryllium acetate, beryllium oxalate, phosphorus Berylium acid, magnesium hydroxide, magnesium carbonate, magnesium hydrogencarbonate, magnesium acetate, magnesium oxalate, magnesium phosphate, calcium hydroxide, calcium carbonate, calcium hydrogencarbonate, calcium acetate, calcium oxalate, calcium phosphate, strontium hydroxide, carbonic acid Examples thereof include strontium, strontium hydrogen carbonate, strontium acetate, strontium oxalate, strontium phosphate, barium hydroxide, barium carbonate, barium hydrogen carbonate, barium acetate, barium oxalate, barium phosphate and the like. Pure water is preferably used as the solvent for the cleaning liquid, but if the sulfur-based active material has hydrophobicity, a surfactant or the like may be added to the water as a cleaning aid, or a hydrophilic solvent such as alcohol and water may be used. By using a mixture of the above as a solvent, a more effective cleaning treatment can be applied to the sulfur-based active material. Alternatively, even if pure water is used as the solvent for the cleaning liquid, it is effective by adsorbing the surfactant to the sulfur-based active material and performing a hydrophilic treatment to make the surface of the sulfur-based active material hydrophilic before the cleaning step. Cleaning treatment can be performed.

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.

(Washing process after washing)
If the electrode is manufactured with the by-products generated by the cleaning treatment adhering to the surface of the sulfur-based active material, it may adversely affect the battery performance of the sulfur-based active material. Therefore, after cleaning, it is preferable to perform a water washing treatment in which by-products adhering to the sulfur-based active material are washed away with pure water. The method for washing the by-product with water is also not particularly limited, and examples thereof include immersion washing, jet cleaning, bubbling cleaning, stirring cleaning, vacuum cleaning, ultrasonic cleaning, and heat cleaning. Further, by combining a plurality of these cleaning methods, the water washing treatment can be performed effectively and in a short time.

(Solid-liquid separation process)
The method for solid-liquid separation of the sulfur-based active material and the cleaning liquid after the completion of cleaning is not particularly limited, and examples thereof include filtration, pressure filtration (filter press), vacuum filtration, centrifugation, and decantation. After the solid-liquid separation, the residual liquid may be replenished with a cleaning liquid and the cleaning treatment may be performed again. By repeating cleaning and solid-liquid separation in this way, a more effective cleaning treatment can be applied to the sulfur-based active material.

(Drying process)
The method of drying the sulfur-based active material after solid-liquid separation is not particularly limited, and examples thereof include heat drying, hot air drying, vacuum drying, far infrared drying, spray drying (spray drying), and vibration fluidized bed drying. ..

(Crushing process)
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.

<Electrode configuration>
The positive electrode and the negative electrode according to the present embodiment can have the same structure as a general non-aqueous electrolyte storage device. For example, the electrode for a non-aqueous electrolyte secondary battery according to the present embodiment can be produced by applying an electrode material in which a sulfur-based active material, a conductive auxiliary agent, a binder, and a solvent are mixed to a current collector. 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. Further, since the carbon non-woven fabric made of carbon having a high degree of graphitization and / or the current collector made of carbon woven fabric does not contain hydrogen and has low reactivity with sulfur, it can be used as a current collector for sulfur-based active materials. Suitable. Examples of the raw material of the carbon fiber having a high degree of graphitization include various pitches (that is, by-products of petroleum, coal, coal tar, etc.) and polyacrylonitrile fiber (PAN) which are the materials of the carbon fiber.

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 deteriorated when the electrode is manufactured using an uncleaned sulfur-based active material. When the sulfur-based active material is subjected to the cleaning treatment according to the present embodiment, 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.

(Conductive aid)
Examples of the conductive auxiliary agent include vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), graphite and the like. One of these may be used, or two or more of them may be used in combination. From the viewpoint of capacitance density, input / output characteristics, and conductivity, acetylene black (AB) or Ketjen black (KB) is preferable.

(solvent)
As the solvent of the slurry, it is preferable to use water because if an organic solvent is used, the sulfur component that contributes to the charge / discharge reaction may be eluted from the sulfur-based active material, which may lead to a decrease in the capacity of the active material.

(Binder)
As a binder, styrene-butadiene rubber (SBR), water-soluble polyimide (PI), water-soluble polyamide-imide (PAI), carboxymethyl cellulose (CMC), methacrylic resin (PMA), polyethylene oxide (PMA), which have high affinity with water, are used. PEO) and the like are exemplified.

(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.

The electrode according to the present embodiment is mixed with, for example, a sulfur-based active material, a conductive auxiliary agent, a binder, and a solvent and sufficiently kneaded to prepare a uniform slurry, and then the slurry is applied to a current collector. It is formed by drying. The blending ratio of each of the above components is not particularly limited, but for example, 5 to 50 parts by mass of the conductive additive, 10 to 50 parts by mass of the binder, and an appropriate amount of solvent can be blended with 100 parts by mass of the sulfur-based active material. ..

<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, it is preferable to use a thin-walled, microporous or non-woven film made of, for example, polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass or the like.

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.)

[Example 1]
<Manufacturing process of sulfur-based active material>
(Preparation of raw material compound)
Raw materials by kneading organic compounds, sulfur, conductive carbon materials, and vulcanization accelerators 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 vulcanization reaction is contained in the exhaust gas, it is neutralized with the aqueous sodium hydroxide solution and removed from the exhaust gas.

(Baking process)
In the firing step, first, the raw material compound 2 is housed in the bottom of the reaction vessel 3, and Ar (argon) gas is continuously supplied from the gas supply system at a flow rate of 80 mL / min for 30 minutes from the start of supply. Later, 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 55.3%, and the hydrogen content was determined. As a result of calculation, it was 0.23%.

<Sulfur-based active material cleaning process>
Before the cleaning treatment, the following steps were carried out in order to make the sulfur-based active material hydrophilic. A magnetic stirrer (As One Corporation) was added to a mixed solution of 5 mL of a dispersant aqueous solution (Triton X-100 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)) and 300 mL of pure water, and 10 g of a sulfur-based active material was added. The mixture was stirred at 300 rpm for 1 hour using CHP-170DR) manufactured by CHP-170DR. Then, vacuum filtration was performed using a suction filter and an aspirator (MDA-015 manufactured by ULVAC Co., Ltd.) to remove the solvent to obtain a hydrophilized sulfur-based active material. The pure water used was manufactured by Millipore MilliQ-Gradient A-10 manufactured by Merck Group.

Next, the following cleaning treatment was performed in an environment of room temperature of 25 ° C. 300 mL of pure water is used as the cleaning liquid, a hydrophilized sulfur-based active material is added thereto, and a magnetic stirrer (CHP-170DR manufactured by AS ONE Corporation) is used as a cleaning machine to perform stirring cleaning at 300 rpm for 1 hour. It was. Then, vacuum filtration was performed using a suction filter and an ejector (MDA-015 manufactured by ULVAC, Inc.) to remove the cleaning liquid. This operation is repeated once again, and after washing a total of two times, the sulfur has been washed by drying at 80 ° C. for 5 hours using a constant temperature dryer (DO-450C manufactured by AS ONE Corporation). Obtained a system active material.

<Manufacturing of lithium ion secondary battery>
[1] Positive electrode The above-mentioned sulfur-based active material, conductive auxiliary agent (acetylene black (Denka black manufactured by Denka Co., Ltd.) / VGCF = 1: 1 mixture), and water-based acrylic resin 92.5: 4: 3. Weigh at a ratio of 5 (mass ratio), put in a container, and stir and mix using a rotation / revolution mixer (ARE-250 manufactured by Shinky Co., Ltd.) while adjusting the viscosity using water as a solvent. A uniform slurry was prepared. An aluminum current collector (thickness 20 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) is coated with a slurry prepared using an applicator and dried at 150 ° C. for 10 hours to obtain a positive electrode for a lithium ion secondary battery. Made.

[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 cleaning treatment step of Example 1, a weak alkaline aqueous solution (pH = 9.6) in which 15 g of sodium sesquicarbonate (manufactured by Showa Kagaku Co., Ltd.) was dissolved in 300 mL of pure water was used instead of 300 mL of pure water as the cleaning liquid. A sulfur-based positive electrode active material was prepared in the same manner as in Example 1 except that the washing was performed twice in total by the same method, and a battery was prepared in the same manner as in Example 1.

[Example 3]
In the cleaning treatment step of Example 1, instead of 300 mL of pure water, a weakly alkaline aqueous solution (pH = 9.6) in which 15 g of sodium sesquicarbonate (manufactured by Showa Kagaku Co., Ltd.) was dissolved in 300 mL of pure water was used. A sulfur-based active material was prepared in the same manner as in Example 1 except that the washing was performed twice in total and then once with 300 mL of pure water, and a battery was prepared in the same manner as in Example 1.

[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 3 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 3. 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 44.2%. 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).

[Comparative Example 1]
A sulfur-based active material was prepared in the same manner as in Example 1 except that the cleaning treatment step was excluded, and a battery was prepared in the same manner as in Example 1.

[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 100 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 sulfur-based active material treated by the cleaning treatment method of the present invention as an 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 sulfur-based active material treated by the cleaning treatment method 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 obtained regardless of the type of current collector. Can be manufactured. 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 (10)

A cleaning treatment method characterized by cleaning a sulfur-based active material with water or an aqueous solution having a pH of 6 or higher. The cleaning treatment method according to claim 1, wherein the sulfur-based active material is washed with an alkaline aqueous solution having a pH greater than 7, and then further washed with water. The production method according to claim 1 or 2, wherein the sulfur-based active material is an organic sulfur-based active material. A sulfur-based active material washed by the washing treatment method according to any one of claims 1 to 3. An electrode for a non-aqueous electrolyte secondary battery produced by using the sulfur-based active material according to claim 4. Non-aqueous electrolyte 2 including a step of washing the sulfur-based active material with water or an aqueous solution having a pH of 6 or more, and a step of applying a slurry of the washed sulfur-based active material and water to the current collector. Method for manufacturing electrodes for next batteries. The manufacturing method according to claim 6, wherein the current collector is an aluminum-based current collector. A non-aqueous electrolyte secondary battery provided with an electrode manufactured by the manufacturing method according to claim 6 or 7. The non-aqueous electrolyte secondary battery according to claim 8, 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 8 or 9.