Sulfur-based active material, electrode, nonaqueous electrolyte secondary battery, and manufacturing method

Abstract

To provide a sulfur-based active material for a nonaqueous electrolyte secondary battery, which has a large charge / discharge capacity and excellent cycle characteristics, and which is inexpensive and easy to produce, an electrode containing the sulfur-based active material, a nonaqueous electrolyte secondary battery provided with the electrode, and a method for producing the same. A sulfur-based active material formed by firing a raw material containing (1) a thermally expandable particle having an expansion onset temperature of 150°C or lower, which has a shell containing an acrylic copolymer, and a hydrocarbon enclosed inside the shell, and (2) sulfur.

Description

Technical Field

[0001] The present invention relates to a sulfur-based active material used in an electrode for a non-aqueous electrolyte secondary battery, an electrode containing the sulfur-based active material, a non-aqueous electrolyte secondary battery having the electrode, and a method for manufacturing the same. Background Technology

[0002] Non-aqueous electrolyte secondary batteries, due to their larger charge and discharge capacity, are mainly used in portable electronic products. In addition, their use in electric vehicles is also increasing, thus improvements in their performance are anticipated.

[0003] Patent Document 1 describes a positive electrode active material for lithium-ion secondary batteries obtained by heating a raw material powder containing sulfur powder and polyacrylonitrile powder under a non-oxidizing gas atmosphere. Patent Document 2, on the other hand, describes an invention that provides an inexpensive positive electrode active material using industrial rubber.

[0004] On the other hand, it was proposed that the battery capacity of lithium-ion secondary batteries be increased by using materials such as silicon (Si) and tin (Sn) that can absorb and release more lithium ions as negative electrode active materials.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2010 / 044437

[0008] Patent Document 2: Japanese Patent Application Publication No. 2015-92449 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, the positive electrode active material in Patent Document 1 faces the problem of being difficult to supply cheaply for lithium-ion rechargeable batteries due to the high price of polyacrylonitrile (PAC) used as a raw material, especially the even higher price of PAC with stable quality. The positive electrode active material in Patent Document 2 suffers from insufficiently improved cycle characteristics. The aforementioned materials proposed as negative electrode active materials exhibit poor cycle characteristics during repeated charge-discharge cycles due to significant volume changes with lithium-ion uptake and release. Furthermore, although carbon materials such as graphite and hard carbon are used, their theoretical capacities have been largely reached, making a significant increase in capacity unrealistic.

[0011] The present invention provides a novel sulfur-based active material that can improve the charge-discharge capacity and cycle characteristics of a non-aqueous electrolyte secondary battery, an electrode formed therefrom containing the sulfur-based active material, a non-aqueous electrolyte secondary battery having the electrode, and a method for manufacturing the same.

[0012] Technical solutions to the problem

[0013] The inventors of this invention conducted in-depth discussions and found that the above-mentioned technical problems could be solved by using sulfur-based active substances formed by firing raw materials containing the following substances. After further repeated research, the invention was completed. The above-mentioned substances include: (1) thermally expandable particles with an expansion start temperature of 150°C or less, having a shell formed of an acrylic copolymer, and a hydrocarbon encapsulated inside the shell, and (2) sulfur.

[0014] That is, the present invention relates to,

[0015] [1] A sulfur-based active substance, which is formed by firing a raw material containing the following substances:

[0016] (1) Thermally expandable particles with an expansion initiation temperature of 150°C or less, preferably 70-150°C, having an outer shell containing an acrylic copolymer, and a hydrocarbon encapsulated inside the outer shell, and (2) sulfur.

[0017] [2] The sulfur-based active material as described in [1] above, wherein the firing temperature is 250–550°C, preferably 300–500°C, and more preferably 350–500°C.

[0018] [3] The sulfur-based active substances as described in [1] or [2] above, wherein the acrylic copolymer is a copolymer containing one or more monomer components other than methacrylonitrile as monomer components.

[0019] [4] As described in [3] above, the sulfur-based active material, wherein one or more monomeric components other than the methacrylonitrile are selected from one or more of acrylonitrile and (meth)acrylate.

[0020] [5] The sulfur-based active substance as described in any one of [1] to [4] above, wherein the hydrocarbon is selected from one or more of isobutane, isopentane and isooctane.

[0021] [6] The sulfur-based active material as described in any one of [1] to [5] above, wherein the raw material further comprises (3) a conductive additive.

[0022] [7] As described in [6] above, the sulfur-based active material, wherein the conductive additive is a conductive carbon material.

[0023] [8] As described in any one of [1] to [7] above, the particle size of the thermally expandable particles is 0.1 to 1000 μm, preferably 0.5 to 500 μm, more preferably 1 to 100 μm, and even more preferably 5 to 50 μm.

[0024] [9] An electrode for a non-aqueous electrolyte secondary battery, comprising any one of the sulfur-based active materials described in [1] to [8] above,

[0025]

[10] A non-aqueous electrolyte secondary battery comprising the electrodes described above [9].

[0026]

[11] A manufacturing method for a sulfur-based active substance, the method comprising a step of calcining the following substance:

[0027] (1) A thermally expandable particle with an expansion start temperature of 150°C or less, preferably 70 to 150°C, having an outer shell containing an acrylic copolymer, and a hydrocarbon encapsulated inside the outer shell, and (2) sulfur.

[0028] The effects of the invention

[0029] According to the present invention, a sulfur-based active material for a non-aqueous electrolyte secondary battery with increased charge-discharge capacity and excellent cycle characteristics can be provided inexpensively and easily, as well as an electrode containing the sulfur-based active material, a non-aqueous electrolyte secondary battery having the electrode, and a method for manufacturing the same.

[0030] In the specification of this invention, "cycle characteristics" refers to the characteristic that the charge and discharge capacity of a secondary battery is maintained despite repeated charging and discharging. Therefore, compared to secondary batteries with a large decrease in charge and discharge capacity due to repeated charging and discharging, and a low capacity retention rate, the cycle characteristics of a secondary battery are poor, while secondary batteries with a small decrease in charge and discharge capacity and a high capacity retention rate are excellent. Attached Figure Description

[0031] Figure 1 This is a schematic cross-sectional view of the reaction apparatus used in the manufacture of sulfur-based reactive substances.

[0032] Figure 2 This is a graph showing the results of Raman spectroscopy analysis of the sulfur-based active substances obtained in Example 1. Detailed Implementation

[0033] The structure of this invention will be described in detail below. However, the following description is for illustrative purposes only, and the technical scope of this invention is not limited to the scope of this description. Furthermore, in the description of numerical ranges, the upper and lower limits referred to by "above," "below," and "~" can be arbitrarily combined, and the values ​​in the embodiments can be set as these upper and lower limits. It should be noted that when a numerical range is determined according to "~", unless otherwise specified, it means including the values ​​at both ends.

[0034] One embodiment of the present invention is a sulfur-based active material formed by firing a substance comprising: (1) a thermally expandable particle with an expansion initiation temperature of 150°C or less, having an outer shell comprising an acrylic copolymer and a hydrocarbon encapsulated inside the outer shell, and (2) sulfur.

[0035] While not wishing to be bound by theory, the following reasons can be considered for obtaining sulfur-based active materials with large charge / discharge capacity and excellent cycle characteristics in this invention. Specifically, when calcining a raw material containing thermally expandable particles and sulfur, the aforementioned thermally expandable particles have an outer shell containing an acrylic copolymer and hydrocarbons encapsulated within it, and have a specified expansion initiation temperature. As the temperature of the thermally expandable particles rises due to heating, the outer shell first softens, and simultaneously the encapsulated hydrocarbons begin to vaporize, thereby increasing the internal pressure and initiating expansion. At the start of this expansion, if the sulfur is in a liquid state, it moves along with the expansion of the thermally expandable particles, resulting in good dispersion of sulfur and uniform contact between the sulfur and the outer shell of the thermally expandable particles. In this invention, the expansion initiation temperature of the thermally expandable particles is below 150°C; therefore, at the start of expansion, the sulfur is in a liquid state rather than an amorphous (rubber-like) state, thus it is believed that uniform contact between the sulfur and the outer shell of the thermally expandable particles, as described above, can be achieved.

[0036] As the temperature gradually increases, the internal pressure rises due to the hydrocarbon gas, causing the outer shell of the thermally expanding particles to become thinner. The well-dispersed sulfur then further promotes the modification of the outer shell. It is believed that through the above process, the outer shell is uniformly and fully modified by sulfur, resulting in sulfur-based active materials with large charge / discharge capacity and excellent cycle characteristics.

[0037] The preferred firing temperature is 250–550°C.

[0038] The aforementioned acrylic copolymers are preferably copolymers containing one or more monomer components other than methacrylonitrile as monomer components.

[0039] The monomer component other than the aforementioned methacrylonitrile preferably includes one or more selected from acrylonitrile and (meth)acrylate.

[0040] The hydrocarbons mentioned above are preferably selected from one or more of isobutane, isopentane and isooctane.

[0041] The above-mentioned raw materials preferably further include (3) conductive additives.

[0042] The conductive additives mentioned above are preferably conductive carbon materials.

[0043] The particle size of the aforementioned thermally expandable particles is preferably 0.1–1000 μm.

[0044] Other embodiments of the present invention are electrodes for non-aqueous electrolyte secondary batteries containing the above-mentioned sulfur-based active materials.

[0045] Other embodiments of the present invention are non-aqueous electrolyte secondary batteries having the electrodes described above.

[0046] Another embodiment of the present invention is a manufacturing method for a sulfur-based active substance, which includes a step of firing a raw material comprising expandable particles having a thermal expansion start temperature of 150°C or less and sulfur, wherein the thermal expansion particles have an outer shell comprising an acrylic copolymer and a hydrocarbon encapsulated inside the outer shell.

[0047] <Sulfur-based active substances>

[0048] The sulfur-based active material of this embodiment is a substance formed by calcining the following raw materials, which include: (1) thermally expandable particles with an expansion initiation temperature of 150°C or less, having an outer shell containing an acrylic copolymer and a hydrocarbon encapsulated inside the outer shell, and (2) sulfur. The above raw materials may further include (3) a conductive additive. In addition, the above raw materials may further include (4) a vulcanization accelerator.

[0049] (Particles with thermal expansion)

[0050] The thermally expandable particles of this embodiment are preferably used if their expansion initiation temperature is below 150°C and they have an outer shell comprising an acrylic copolymer and a hydrocarbon encapsulated within the outer shell. The expansion initiation temperature of the thermally expandable particles refers to the temperature at which the particle begins to expand, determined by the force relationship between the gradually softening strength of the outer shell and the gradually increasing gas pressure of the encapsulated hydrocarbon as the ambient temperature rises. In this invention, the expansion initiation temperature is considered to be below 150°C. As described above, sulfur makes the modification of the outer shell of the thermally expandable particles more uniform, thereby achieving the effects of this invention. It should be noted that the lower limit of this expansion initiation temperature is not particularly limited, but is generally above 70°C.

[0051] Here, an acrylic copolymer refers to a copolymer containing at least one acrylic monomer and composed of two or more monomer components. In this case, the copolymerization ratio of the acrylic monomer is preferably 50% or more, more preferably greater than 50%.

[0052] As for the acrylic copolymer, in its relationship with the encapsulated hydrocarbon, under the expansion mechanism described above, there are no particular limitations as long as the specified expansion start temperature is met. As a preferred example, acrylic monomers containing methacrylonitrile can be listed as acrylic monomers. In this case, the acrylic copolymer can be a homopolymer of methacrylonitrile (polymethacrylonitrile), a copolymer containing one or more monomer components other than methacrylonitrile, or a copolymer containing one or more monomer components other than methacrylonitrile.

[0053] As a monomer component other than methacrylonitrile, known (meth)acrylic acid monomers such as acrylonitrile, (meth)acrylic acid, (meth)acrylate, and (meth)acrylamide can preferably be used. Among these, one or more selected from acrylonitrile and (meth)acrylate are preferred. Here, alkyl (meth)acrylates can be listed as (meth)acrylates. Furthermore, as "alkyl" in this context, alkyl groups having 1 to 6 carbon atoms can be listed, preferably alkyl groups having 1 to 4 carbon atoms, wherein methyl is preferred. It should be noted that in this specification, "(meth)acrylic acid" means "acrylic acid" or "methacrylic acid".

[0054] As a monomer component other than methacrylonitrile, it is more preferably selected from one or more of acrylonitrile and methyl methacrylate, and even more preferably acrylonitrile and methyl methacrylate.

[0055] In addition to methacrylonitrile, conjugated diene compounds such as butadiene and isobutene can also be used as monomer components.

[0056] In the copolymer, the copolymerization ratio of methacrylonitrile is typically 1–99%, preferably 10–95%, more preferably 20–90%, and even more preferably 30–80%.

[0057] The weight-average molecular weight (Mw) of the polymer is preferably 1,000 to 1,000,000, more preferably 10,000 to 300,000. Furthermore, Mw can be obtained by conversion from standard polystyrene based on the value determined using gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).

[0058] Furthermore, the thermally expandable particles can be manufactured based on the methods described in Japanese Patent Publication No. 42-26524, Japanese Patent Application Publication No. 60-19033, and Japanese Patent No. 6370219. Specifically, for example, they can be manufactured by performing the following steps: a step of preparing an aqueous dispersion comprising the monomer components of the above example, a hydrocarbon, and a dispersion stabilizer used to maintain dispersion, and a step of polymerizing the monomer.

[0059] In addition, commercially available thermal expansion particles, such as those manufactured by Fillite Co., Ltd., Matsumoto Yushi Pharmaceutical Co., Ltd., Kureha Chemical Industry Co., Ltd., and Sekisui Chemical Industry Co., Ltd., can be used as the thermal expansion particles involved.

[0060] The boiling point of a hydrocarbon is the temperature below the softening point of the outer shell of a thermally expandable particle. It is not particularly limited to any substance whose thermally expandable particles reach a specified expansion initiation temperature under the expansion mechanism described above. The boiling point of this hydrocarbon is typically -20°C to 120°C, preferably 0°C to 100°C, and more preferably 20°C to 80°C. Specific examples of hydrocarbons include, for instance, saturated or unsaturated aliphatic hydrocarbons with 2 to 10 carbon atoms; preferably saturated or unsaturated aliphatic hydrocarbons with 3 to 8 carbon atoms; more preferably butane, isobutane, isobutene, pentane, isopentane, neopentane, cyclopentane, hexane, neohexane, cyclohexane, heptane, octane, and isooctane; and even more preferably isobutane, isopentane, and isooctane. These hydrocarbons may be used individually or in combination of two or more.

[0061] The hydrocarbon content in the thermally expandable particles is preferably 1 to 70% by mass, more preferably 3 to 40% by mass, and even more preferably 5 to 20% by mass.

[0062] The average particle size (D) of thermally expandable particles before expansion 50 The average particle size (D) is preferably 0.1–1000 μm, more preferably 0.5–500 μm, even more preferably 1–100 μm, and still more preferably 5–50 μm. In this invention, the average particle size (D) is... 50 The determination was performed using laser diffraction / scattering method with a volume reference.

[0063] The outer shell of the thermally expandable particles may contain polymerization catalysts and polymerization initiators such as magnesium hydroxide, in addition to acrylic copolymers. The content of the acrylic copolymer relative to the outer shell of the thermally expandable particles is preferably 80% by mass or more, more preferably 85% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0064] The thickness of the outer shell of the thermally expandable particles is not particularly limited as long as the expansion start temperature of the thermally expandable particles is below the specified temperature. It can vary depending on the type of acrylic copolymer constituting the outer shell, the type of hydrocarbon encapsulated inside, etc., but it is usually around 2 to 15 μm.

[0065] (sulfur)

[0066] As sulfur, any substance selected from powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, etc., can be used. Among these, precipitated sulfur or colloidal sulfur is preferred. From the viewpoint of charge-discharge capacity and cycle characteristics, the amount of sulfur mixed is preferably 250 parts by mass or more, more preferably 300 parts by mass or more, relative to 100 parts by mass of thermally expandable particles. On the other hand, there is no particular upper limit to the amount of sulfur mixed, but from the perspective of charge-discharge capacity saturation and cost disadvantages, it is preferably 1500 parts by mass or less, more preferably 1000 parts by mass or less.

[0067] (Conductive additive)

[0068] There are no particular limitations on the conductive additives; commonly used conductive additives in the art can be appropriately used, such as vapor-grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), graphite, and other conductive carbon materials. From the viewpoint of capacity density, input / output power characteristics, and conductivity, acetylene black (AB) or Ketjen black (KB) is preferred. These conductive additives can be used alone or in combination of two or more.

[0069] When a conductive additive is mixed, from the viewpoint of charge / discharge capacity and cycle characteristics, the amount of conductive additive used relative to 100 parts by mass of thermally expandable particles is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. On the other hand, this mixing amount is preferably 50 parts by mass or less, more preferably 30 parts by mass or less. When it is 1 part by mass or more, there is a tendency to easily obtain the effect of adding a conductive additive, and when it is 50 parts by mass or less, the proportion of sulfur-containing structures in sulfur-based active materials can be relatively increased, and there is a tendency to easily achieve the goal of further improving charge / discharge capacity and cycle characteristics.

[0070] (Vulcanization accelerator)

[0071] When using a mixed vulcanization accelerator, from the viewpoint of charge / discharge capacity and cycle characteristics, the amount used is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of thermally expandable particles. Furthermore, on the other hand, there is no particular upper limit to the mixing amount; from the perspective of charge / discharge capacity saturation and unfavorable composition, it is preferably 250 parts by mass or less, more preferably 50 parts by mass or less.

[0072] (Firing)

[0073] The firing of the above-mentioned mixed raw materials is carried out by heating the raw materials in a non-oxidizing gas atmosphere.

[0074] Non-oxidizing gas atmosphere

[0075] A non-oxidizing gas atmosphere refers to a gas atmosphere that does not actually contain oxygen, used to suppress the oxidative degradation of the constituent components and excessive thermal decomposition. Specifically, it refers to an inert gas atmosphere filled with inert gases such as nitrogen and argon, or a sulfur gas atmosphere. Therefore, firing can be carried out, for example, in a quartz tube under an inert gas atmosphere.

[0076] Rate of Heating

[0077] The heating rate is preferably in the range of 50 to 500°C / h. More preferably, it is 100°C / h or higher, and even more preferably 120°C or higher. On the other hand, the heating rate is more preferably 400°C / h or lower, even more preferably 300°C / h or lower, even more preferably 200°C / h or lower, and even more preferably 180°C or lower. With a heating rate within the range described above, it is easier to achieve improvements in charge / discharge capacity and cycle characteristics.

[0078] Firing Temperature and Time

[0079] Firing temperature refers to the temperature at which the raw material is heated after the initial heating phase, and the temperature maintained for a certain period of time to allow for firing. This temperature is preferably in the range of 250–550°C. At temperatures above 250°C, sulfur-based modification is more efficient, and there is a tendency to prevent a decrease in the charge / discharge capacity of the target substance. On the other hand, setting the temperature below 550°C tends to prevent decomposition of the raw material, a decrease in yield, and a decrease in charge / discharge capacity. This temperature is more preferably above 300°C, and more preferably above 350°C. On the other hand, this temperature is more preferably below 500°C, and more preferably below 450°C. The duration of maintaining the firing temperature can be appropriately set according to the type of raw material, the firing temperature, etc., and is preferably 1–6 hours. A duration of 1 hour or more tends to allow for sufficient firing, while a duration of 6 hours or less tends to prevent excessive thermal decomposition of the constituent components.

[0080] Device

[0081] Firing can be achieved through methods such as Figure 1In addition to the aforementioned apparatus, continuous equipment such as a twin-screw extruder can also be used. The advantage of using a continuous equipment is that it allows for the simultaneous mixing, crushing, and blending of calcining raw materials within the equipment, enabling the continuous production of sulfur-based active substances through a series of operations.

[0082] Residue Removal Process

[0083] The sulfides obtained after calcination contain residual unreacted sulfur, such as sulfur that sublimated during calcination and precipitated upon cooling. Since these residues are a major cause of reduced cycle characteristics, they need to be removed as much as possible. Residue removal can be carried out using common methods such as vacuum drying, hot air drying, and solvent washing.

[0084] (Active substances)

[0085] Since the sulfur-based active material obtained above is a micro powder with a median particle size of less than 10 μm, it can be directly used for coating electrodes without further pulverization or classification, but further classification to remove impurities is possible. In normal use, the hydrocarbon inside the hollow particles expands upon heating, and the shell expands accordingly, thus functioning as a foaming agent.

[0086] There is a tendency that the higher the total sulfur content in the sulfur-based active material, the better the cycle characteristics of the non-aqueous electrolyte secondary battery. Therefore, it is preferable that the total sulfur content in the sulfur-based active material, as determined by elemental analysis, is 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more. However, when mixed with conductive carbon materials, even if the sulfur content is reduced to some extent due to the influence of the carbon constituting the conductive carbon material, an improvement in charge / discharge capacity and cycle characteristics can sometimes be expected. In the case described above, the sulfur content can be about 5.0% by mass lower than the sulfur content mentioned above.

[0087] Furthermore, during firing, the hydrogen (H) in the thermally expandable particles reacts with sulfur to form hydrogen sulfide, which must be subtracted from the sulfide. Therefore, the hydrogen content of the sulfur-based active material is preferably 1.6% by mass or less. When the hydrogen content is 1.6% by mass or less, there is a tendency for sufficient firing (sulfur modification). Therefore, at this point, there is a tendency for increased charge / discharge capacity. The hydrogen content is more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less.

[0088] The sulfur-based active material of this embodiment has the following technical features: in Raman spectroscopy, at 200 cm⁻¹... -1 ~1800cm -1 The range is 1530cm -1 Nearby, 1320cm -1 Nearby, 940cm -1Nearby, 470cm -1 Nearby, 370cm -1 Nearby and 310cm -1 There are peaks nearby. Therefore, the main peak is 1320cm. -1 Nearby peaks. The aforementioned peaks, centered on the aforementioned peak locations, can exist within approximately ±8cm. -1 Within the range. Furthermore, the aforementioned Raman shift was measured using a RAMANtouch sensor manufactured by Nanophoton Co., Ltd. (excitation wavelength λ = 532 nm, grating: 1200 gr / mm, resolution: 1.2 cm). -1 It was obtained by measurement.

[0089] When thermally expandable particles and sulfur are mixed and heated at the specified temperature, a ring-closing reaction occurs, and sulfur enters the acrylic copolymer to form a three-dimensional cross-linked structure. The sulfur-based active material of this embodiment thus obtained suppresses the dissolution of sulfur-based active material into the electrolyte during charge-discharge cycles. Therefore, the cycle characteristics of a non-aqueous electrolyte secondary battery using this sulfur-based active material in the electrode are improved.

[0090] <Electrode>

[0091] The electrodes (positive and negative electrodes) for the non-aqueous electrolyte secondary battery of this embodiment can be manufactured using conventional methods with the aforementioned sulfur-based active material in the form of a binder, conductive additive, solvent, and current collector. Such electrodes for the non-aqueous electrolyte secondary battery can be configured with the same structure as conventional non-aqueous electrolyte energy storage devices.

[0092] Electrodes for non-aqueous electrolyte secondary batteries can be manufactured, for example, by coating an electrode slurry obtained by mixing the above-mentioned sulfur-based active material, binder, conductive additive and solvent onto a current collector.

[0093] Alternatively, as another method, a mixture of sulfur-based active materials, conductive additives, and binders can be kneaded using a mortar and pestle, pressed into a film, and then pressed onto a current collector using a pressing machine.

[0094] These non-aqueous electrolyte secondary battery electrodes are preferably used as electrodes for lithium-ion secondary batteries.

[0095] (Current collector)

[0096] As the current collector, current collectors commonly used as electrodes in lithium-ion secondary batteries can be used. Specific examples of current collectors include, for instance, aluminum-based current collectors such as aluminum foil, aluminum mesh, perforated aluminum sheets, and aluminum expanded sheets; stainless steel-based current collectors such as stainless steel foil, stainless steel mesh, perforated stainless steel sheets, and stainless steel expanded sheets; nickel-based current collectors such as foamed nickel and nickel nonwoven fabrics; copper-based current collectors such as copper foil, copper mesh, perforated copper sheets, and copper expanded sheets; titanium-based current collectors such as titanium foil and titanium mesh; and carbon-based current collectors such as carbon nonwoven fabrics and carbon textiles. Among these, aluminum-based current collectors are preferred from the perspectives of mechanical strength, conductivity, mass density, and cost.

[0097] The shape of the current collector is not particularly limited, and materials such as foil or three-dimensional substrates can be used. When using three-dimensional substrates (foam metal, mesh, fabric, non-woven fabric, stretchable material, etc.), even if there is a lack of adhesive that adheres well to the current collector, there is a tendency to obtain electrodes with high capacity density and good high-rate charge-discharge characteristics.

[0098] (Adhesive)

[0099] As a binder, known binders used in electrodes can be used, but from the viewpoint of water affinity and reduced environmental impact, water-based binders are preferred. Examples of water-based binders include: hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), acrylate resins, styrene-butadiene rubber (SBR), water-soluble polyimide (PI), water-soluble polyamide-imide (PAI), methacrylic acid resins (PMA), polyethylene oxide (PEO), polyurethane, etc. One of these binders can be used alone, or two or more can be used in combination.

[0100] (Conductive additive)

[0101] As a conductive additive, the same conductive additives that can be used in the manufacture of the sulfur-based active materials described above can be used.

[0102] (solvent)

[0103] In the manufacture of electrode paste, an aqueous solvent (water-based solvent), preferably water, is preferred as the solvent used to disperse solid components such as sulfur-based active materials, binders, and conductive additives. When using organic solvents other than water, there is a tendency for sulfur components that contribute to the charge-discharge reaction to dissolve from the sulfur-based active materials, resulting in a decrease in the battery's charge-discharge capacity. Furthermore, from the viewpoint of reducing environmental impact, aqueous solvents are preferred. Additionally, solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformaldehyde, and lower alcohols mixed with water can be used as long as it does not impair the effects of the present invention (e.g., the organic solvent other than water is less than 20% by mass).

[0104] In the electrode paste, relative to 100% by mass of the solid components (especially sulfur-based active materials, binders, and conductive additives, hereinafter the same), the content of sulfur-based active materials is preferably 85% by mass or more, more preferably 87% by mass or more, and even more preferably 90% by mass or more. Furthermore, there is no particular upper limit on the content of sulfur-based active materials, but preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less.

[0105] In the electrode paste, the binder content is preferably 0.1 to 10.0% by mass relative to 100% by mass of the solid components, more preferably 0.5 to 8.0% by mass, even more preferably 1.0 to 6.0% by mass, and particularly preferably 2.0 to 5.0% by mass.

[0106] When a conductive additive is mixed into the electrode paste, the content of the conductive additive relative 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, even more preferably 1.0 to 6.0% by mass, and particularly preferably 2.0 to 5.0% by mass.

[0107] <Non-aqueous electrolyte secondary battery>

[0108] Non-aqueous electrolyte secondary batteries can be manufactured using conventional methods, employing electrodes (positive or negative) as counter electrodes and electrolytes in the non-aqueous electrolyte secondary battery electrodes (as described in this embodiment). In addition to, for example, positive, negative, and electrolyte components, non-aqueous electrolyte secondary batteries may include components such as a separator. The separator exists between the positive and negative electrodes, allowing ion movement between the two electrodes and preventing internal short circuits between them. The non-aqueous electrolyte secondary battery only needs to be a sealed type, and the separator is required to retain the electrolyte.

[0109] (The electrode that serves as the counter electrode)

[0110] When the sulfur-based active material of this embodiment is used as the positive electrode, the negative electrode, which serves as the counter electrode, can be made of known negative electrode materials such as lithium metal, carbon-based materials such as graphite, silicon thin films, SiO, and tin alloys such as copper-tin and cobalt-tin. When lithium-free materials are used in the negative electrode, such as carbon materials, silicon materials, and tin alloys, short circuits between the positive and negative electrodes due to dendrite formation are less likely to occur, thus extending the lifespan of the non-aqueous electrolyte secondary battery. Among these, high-capacity silicon-based materials as negative electrode materials are preferred, and thin-film silicon, which allows for thinner electrode thickness and has advantages in capacity per unit volume, is more preferred.

[0111] When the lithium-free negative electrode material is used in combination with the positive electrode of this embodiment, since neither the positive nor the negative electrode contains lithium, it is preferable to pre-dope the positive and negative electrodes by inserting lithium into either or both.

[0112] As a predoping method, known methods can be used. For example, when doping lithium in the negative electrode, an electrochemical doping method can be used, where lithium metal is used as the counter electrode to form a half-cell, or an attachment predoping method can be used, where lithium metal foil is attached to the electrode and placed in an electrolyte, allowing doping to occur through lithium diffusion into the electrode. Furthermore, the aforementioned electrochemical doping method can also be used when predoping lithium in the positive electrode.

[0113] When the sulfur-based active material of this embodiment is used as the negative electrode, the positive electrode, which serves as the counter electrode, can also be used, for example, composite oxides of lithium and transition metals (especially cobalt-based composite oxides, nickel-based composite oxides, manganese-based composite oxides, and ternary composite oxides formed by cobalt / nickel / manganese). Furthermore, lithium transition metal phosphates with an olivine-type crystal structure (especially lithium iron phosphate and lithium manganese phosphate) can also be used. Additionally, when an electrode prepared using a lithium-containing transition metal lithium composite oxide compound as the active material is used as the positive electrode, and an electrode using the electrode slurry of this embodiment is used as the negative electrode, and these are combined, since the positive electrode contains lithium, lithium pre-doping treatment for lithium insertion is not necessarily required.

[0114] (electrolytes)

[0115] As the electrolyte constituting a non-aqueous electrolyte secondary battery, any liquid or solid with ionic conductivity can be used. The same electrolyte used in known non-aqueous electrolyte secondary batteries can be used. From the viewpoint of high battery output power characteristics, it is preferable to use an electrolyte obtained by dissolving an alkali metal salt as a supporting electrolyte in an organic solvent.

[0116] As an organic solvent, examples include at least one non-aqueous solvent selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, acetonitrile, etc. Preferably, ethylene carbonate, propylene carbonate, or mixtures thereof are preferred.

[0117] Examples of supporting electrolytes include LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, and LiClO4, with LiPF6 being the preferred choice.

[0118] The recommended electrolyte concentration is approximately 0.5 mol / L to 1.7 mol / L. Furthermore, the electrolyte is not limited to a liquid state. For example, in the case of a non-aqueous electrolyte secondary battery, specifically a lithium-ion secondary battery, the electrolyte can be solid (e.g., a polymer gel), ionic liquid, molten salt, etc.

[0119] (Diaphragm)

[0120] Preferred membranes for use include, for example, thin and microporous or nonwoven membranes made of materials such as polyethylene, polypropylene, polyacrylonitrile, aromatic polyamide, polyimide, cellulose, and glass.

[0121] (Battery shape)

[0122] The shape of the non-aqueous electrolyte secondary battery in this embodiment is not particularly limited, and it can be various shapes such as cylindrical, stacked, coin-shaped, and button-shaped.

[0123] (Uses of batteries)

[0124] The non-aqueous electrolyte secondary battery equipped with the electrodes of this embodiment has high capacity and excellent cycle characteristics, and therefore can be used as a power source for electrical devices such as smartphones, power tools, motor vehicles, and UPS.

[0125] [Example]

[0126] The invention is described in detail based on the embodiments, but the invention is not limited to these embodiments.

[0127] The various chemicals used in the examples and comparative examples are described.

[0128] Particle 1: Expensl 980-120-Du (manufactured by Fillite Co., Ltd., Japan; thermally expandable particles containing 2,2,4-trimethylpentane encapsulated inside a shell formed of a copolymer of methacrylonitrile, acrylonitrile, and methyl methacrylate; expansion start temperature: 158–173°C; particle size: 25–40 μm)

[0129] Particle 2: Expensl 920-40-Du (manufactured by Fillite Co., Ltd., Japan; thermally expandable particles containing isopentane inside a copolymer of methacrylonitrile, acrylonitrile, and methyl methacrylate; expansion start temperature: 123–133°C; particle size: 10–16 μm)

[0130] Particle 3: Matsumoto Microsphere (registered trademark) FN-180SS (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.; containing thermally expandable hydrocarbon particles inside an acrylic copolymer shell; expansion start temperature: 135-150°C; particle size: 15-25 μm)

[0131] Particle 4: Matsumoto Microsphere (registered trademark) FN-100S (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.; contains thermally expandable hydrocarbon particles inside an acrylic copolymer shell; expansion start temperature: 125-135°C; particle size: 10-20 μm)

[0132] Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0133] <Example 1>

[0134] (Preparation of raw materials)

[0135] According to the formula in Table 1, particles 1 and sulfur are mixed in a mixer to obtain the raw material for calcination (calcination raw material).

[0136] (Reaction apparatus)

[0137] Firing and use of raw materials Figure 1 The reaction apparatus 1 is described above. The reaction apparatus 1 comprises: a reaction vessel 3, a bottomed cylindrical quartz glass container 3 with an outer diameter of 60 mm, an inner diameter of 50 mm, and a height of 300 mm, for receiving and firing the raw materials 2; a silicone cap 4 sealing the upper opening of the reaction vessel 3; an alumina protective tube 5 (alumina SSA-S manufactured by Nikkato Co., Ltd., with an outer diameter of 4 mm, an inner diameter of 2 mm, and a length of 250 mm) penetrating the cap 4; two gas inlet pipes 6 and a gas outlet pipe 7 (both alumina SSA-S manufactured by Nikkato Co., Ltd., with an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 150 mm); and an electric furnace 8 (crucible furnace, opening width) for heating the reaction vessel 3 from the bottom side. Heating height 100mm).

[0138] The alumina protective tube 5 is formed to extend from the cover 4 to the bottom of the reaction vessel 3, where the raw material 2 is contained. A thermocouple 9 is inserted inside the tube. The alumina protective tube 5 serves as a protective tube for the thermocouple 9. With the front end of the thermocouple 9 protected by the closed front end of the alumina protective tube 5, it is inserted into the raw material compound 2 to measure its temperature. As shown by the solid arrow in the figure, the output of the thermocouple 9 is input to the temperature controller 10 of the electric furnace 8. Based on the input from the thermocouple 9, the temperature controller 10 controls the heating temperature of the electric furnace 8.

[0139] The lower ends of the gas inlet pipe 6 and the gas outlet pipe 7 are formed to protrude 3mm downward from the cover 4.

[0140] Argon (Ar) gas is continuously supplied to the gas inlet pipe 6 via a gas supply system not shown in the diagram. Furthermore, the gas outlet pipe 7 is connected to a collection tank 12 containing an aqueous sodium hydroxide solution 11. The exhaust gas from the reaction vessel 3, destined for the outside via the gas outlet pipe 7, first passes through the aqueous sodium hydroxide solution 11 in the collection tank 12 before being discharged to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas produced by the sulfidation reaction, this hydrogen sulfide gas can be neutralized by the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0141] (Firing process)

[0142] In the firing process, with the raw material 2 contained at the bottom of the reaction vessel 3, Ar gas is continuously supplied from the gas supply system at a flow rate of 80 mL / min. Thirty minutes after the supply begins, heating based on the electric furnace 8 is initiated, with a heating rate of 150°C / hour. Then, when the raw material temperature reaches 450°C, it is maintained at 450°C for 2 hours of firing. Next, the Ar gas flow rate is adjusted, and the reaction product is allowed to cool naturally to 25°C under the Ar atmosphere before being removed from the reaction vessel 3.

[0143] (Removal of unreacted sulfur)

[0144] To remove residual unreacted sulfur (free elemental sulfur) from the product after the firing process, the following steps are performed: The product is pulverized in a mortar, 2g of the pulverized material is placed in a glass tube furnace, vacuumed, and heated at 250°C for 3 hours to obtain sulfur-based reactive substances with unreacted sulfur removed (or containing only trace amounts of unreacted sulfur). The heating rate is 10°C / minute.

[0145] (Graded operation)

[0146] To remove impurities contained in the calcined product, it was classified using a 32μm stainless steel sieve to obtain sulfur-based active materials. These were used as the sulfur-based active materials in Example 1.

[0147] (Raman spectroscopy analysis)

[0148] The obtained sulfur-based active materials were tested using a RAMANtouch sensor manufactured by Nanophoton Co., Ltd., at an excitation wavelength of λ = 532 nm, a grating of 1200 gr / mm, and a resolution of 1.2 cm. -1 Raman spectroscopy analysis was performed under the following conditions. Figure 2 ).in addition, Figure 2 In the diagram, the vertical axis represents relative strength, and the horizontal axis represents Raman displacement (cm). -1 The obtained sulfur-based active substances were obtained at 200 cm⁻¹. -1 ~1800cm -1 The range is within 1530cm -1 Nearby, 1320cm -1 Nearby, 940cm -1 Nearby, 470cm -1 Nearby, 370cm -1 Nearby and 310cm -1 A peak was observed nearby. 1320cm -1 The nearby peaks are the main peaks.

[0149] (Elemental Analysis)

[0150] Elemental analysis was performed on the obtained sulfur-based active substances. For carbon, hydrogen, and nitrogen, the mass percentage (%) of each element in the total mass of the sulfur-based active substances was calculated based on the mass measured using the vario MICRO cube fully automated elemental analyzer manufactured by Elementar. Additionally, the mass percentage (%) of sulfur in the total mass of the sulfur-based active substances was calculated based on the mass measured using an IonPac AS12A column manufactured by Dionex in a DX-320 ion chromatography system manufactured by Dionex.

[0151] (Preparation of lithium-ion secondary batteries)

[0152] [1] Positive electrode

[0153] Using the aforementioned sulfur-based active material, acetylene black as a conductive additive, and acrylic resin as a binder, the sulfur-based active material, conductive additive, and binder were weighed in a 90:5:5 (mass ratio) ratio and added to a container. MilliQ water was used as a dispersant, and the mixture was stirred and mixed using a rotary mixer (ARE-250 manufactured by Shinki Co., Ltd.) to produce a homogeneous slurry. Using a coater with a 60 μm slit width, the slurry was coated onto a 20 μm thick aluminum foil. The foil was then compressed using a roller press to obtain a positive electrode. This positive electrode was heated at 120°C for 3 hours in a dryer. After drying, it was stamped... The positive electrode for lithium-ion secondary batteries is then obtained. The weight of the positive electrode is then measured, and the amount of active material in the electrode is calculated using the aforementioned ratio.

[0154] [2] Negative electrode

[0155] As the negative electrode, a lithium metal foil (a disc-shaped foil with a diameter of 14 mm and a thickness of 500 μm, manufactured by Honjo Metals Co., Ltd.) is used.

[0156] [3] Non-aqueous electrolytes

[0157] As a non-aqueous electrolyte, an electrolyte solution was used, which was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate. The ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1. The concentration of LiPF6 in the electrolyte solution was 1.0 mol / L.

[0158] [4] Battery

[0159] Using the positive and negative electrodes obtained in [1] and [2], a coin battery was fabricated. Specifically, in a drying chamber, a separator (Celgard 2400, 25 μm thick polypropylene microporous membrane manufactured by Celgard Corporation) and a glass nonwoven fabric membrane (440 μm thick, ADVANTEC GA100 manufactured by ADVANTEC Corporation) were sandwiched between the positive and negative electrodes to form an electrode body battery. This electrode body battery was housed in a battery case (CR2032 type coin battery component, manufactured by Hosen Co., Ltd.) formed by a stainless steel container. The electrolyte obtained in [3] was injected into the battery case. The battery case was sealed with a riveting machine to prepare the coin-type lithium-ion secondary battery of Example 1.

[0160] <Other Embodiments / Comparative Examples>

[0161] Lithium-ion secondary batteries were prepared according to the formulation in Table 1, using the same treatment as in Example 1.

[0162] <Experimental Methods>

[0163] (Charge / discharge capacity test)

[0164] For the coin-shaped lithium-ion secondary batteries manufactured in each embodiment and comparative example, charging and discharging were performed at a test temperature of 30°C, with a current equivalent to 50 mA per 1 g of sulfur-based active material. The discharge termination voltage was 1.0 V, and the charging termination voltage was 3.0 V. Furthermore, the charge-discharge cycle was repeated 30 times, and the discharge capacity (mAh / g) of each cycle was measured, with the discharge capacity (mAh / g) of the second cycle being taken as the initial capacity. The results are shown in Table 1. Additionally, a larger initial capacity indicates a higher charge-discharge capacity for the lithium-ion secondary battery, which is preferable.

[0165] Furthermore, based on the 10th discharge capacity DC10 (mAh / g) and DC discharge capacity at the 30th cycle 30 The capacity retention rate (%) was calculated using the following formula (mAh / g). The results are shown in Table 1. Furthermore, a higher capacity retention rate indicates better cycle characteristics of the lithium-ion secondary battery.

[0166] (Capacity maintenance rate (%)) = (DC) 30 (mAh / g) / (DC) 10 (mAh / g)×100

[0167] [Table 1]

[0168] Table 1

[0169]

[0170] As shown in Table 1, the lithium-ion secondary battery using the sulfur-based active material of the present invention as the electrode material has excellent charge-discharge capacity and cycle characteristics.

[0171] [Industry availability]

[0172] By using the sulfur-based active material of the present invention as an electrode material, non-aqueous electrolyte secondary batteries with large charge-discharge capacity and excellent cycle characteristics can be manufactured inexpensively and easily.

[0173] [Symbol Explanation]

[0174] 1. Reaction apparatus

[0175] 2 Raw materials

[0176] 3. Reaction Vessel

[0177] 4. Lid made of silicone.

[0178] 5. Alumina protective tube

[0179] 6. Gas inlet tube

[0180] 7. Gas exhaust pipe

[0181] 8 Electric Furnace

[0182] 9. Thermocouple

[0183] 10 Temperature Controller

[0184] 11. Sodium hydroxide aqueous solution

[0185] 12 Collection Tanks

Claims

1. A sulfur-based active material for non-aqueous electrolyte secondary batteries, formed by calcining a raw material containing the following substances: (1) Thermally expandable particles with an expansion initiation temperature of 123°C to 150°C, having an outer shell comprising an acrylic copolymer, and a hydrocarbon encapsulated within the outer shell, and (2) Sulfur, The acrylic copolymer is a copolymer comprising methacrylonitrile and one or more monomers selected from acrylonitrile and (meth)acrylates. The hydrocarbon is selected from one or more of isobutane, isopentane, and isooctane. The amount of sulfur added is between 250 and 1500 parts by mass relative to 100 parts by mass of thermally expandable particles. The firing temperature is 250–550°C.

2. The sulfur-based active material for non-aqueous electrolyte secondary batteries as described in claim 1, wherein, The firing temperature is 300–500°C.

3. The sulfur-based active material for non-aqueous electrolyte secondary batteries as described in claim 1 or 2, wherein, The raw material further includes (3) a conductive additive.

4. The sulfur-based active material for non-aqueous electrolyte secondary batteries as described in claim 3, wherein, The conductive additive is a conductive carbon material.

5. The sulfur-based active material for non-aqueous electrolyte secondary batteries as described in any one of claims 1 to 4, wherein, The particle size of the thermally expandable particles is 0.1–1000 μm.

6. An electrode for a non-aqueous electrolyte secondary battery, comprising the sulfur-based active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 5.

7. A non-aqueous electrolyte secondary battery comprising the electrode as described in claim 6.

8. A manufacturing method for a sulfur-based active material for a non-aqueous electrolyte secondary battery, the method comprising a step of calcining the following material: (1) Thermally expandable particles with an expansion initiation temperature of 123°C to 150°C, having an outer shell comprising an acrylic copolymer and a hydrocarbon encapsulated within the outer shell, and (2) Sulfur, The acrylic copolymer is a copolymer comprising methacrylonitrile and one or more monomers selected from acrylonitrile and (meth)acrylates. The hydrocarbon is selected from one or more of isobutane, isopentane, and isooctane. The amount of sulfur added is between 250 and 1500 parts by mass relative to 100 parts by mass of thermally expandable particles. The firing temperature is 250–550°C.

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