Organic sulfur material, electrode, lithium ion secondary battery, and manufacturing method

Abstract

The present invention provides a novel organic sulfur material capable of improving charge-discharge capacity and cycle characteristics, an electrode including the organic sulfur material, i.e., a positive electrode or a negative electrode, and a lithium ion secondary battery including the electrode. An organic sulfur material obtained by sulfur-modifying an acrylic resin, wherein the acrylic resin is a polymer polymerized from at least one selected from acrylate compounds represented by CH2=C(R 11 )COOR 12 (wherein R 11 is methyl or the like, and R 12 is an alkyl group), or at least one polymer selected from polymers polymerized from at least one selected from the above acrylate compounds and at least one selected from diacrylate compounds represented by CH2=C(R 21 )COO‑Y‑OCO(R 22 )C=CH2(wherein R 21 is the same as or different from R 22 and is methyl or the like, and Y is an alkylene group or the like that may have a substituent selected from a hydroxyl group and an alkyl group).

Description

Technical Field

[0001] The present invention relates to a novel organic sulfur material, an electrode containing the organic sulfur material, a lithium ion secondary battery including the electrode, and methods for manufacturing them. Background Art

[0002] Lithium ion secondary batteries have a large charge and discharge capacity, and are therefore mainly used as batteries for mobile electronic devices. In addition, even as batteries for electric vehicles, the use of lithium ion secondary batteries is increasing, and an improvement in their performance is expected.

[0003] Patent Document 1 describes a positive electrode active material for a lithium ion secondary battery, which is obtained by heating a raw material powder containing sulfur powder and polyacrylonitrile powder in a non-oxidizing atmosphere. In addition, Patent Document 2 attempts to provide a positive electrode active material inexpensively by using industrial rubber.

[0004] On the other hand, there has been a proposal to use materials such as silicon (Si) and tin (Sn), which can store and release more lithium ions, as negative electrode active materials, thereby increasing the battery capacity of lithium ion secondary batteries.

[0005] Prior Art Documents

[0006] [Patent Documents]

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

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

[0009] Problems to be Solved by the Invention

[0010] However, the positive electrode active material of Patent Document 1 has the following problems: the polyacrylonitrile used as the raw material is expensive, and in particular, polyacrylonitrile with stable quality is even more expensive, so it is difficult to provide an inexpensive lithium ion secondary battery. The positive electrode active material of Patent Document 2 still has problems in sufficiently improving the cycle characteristics. The problems with the above-mentioned materials proposed as negative electrode active materials are that, due to the large volume change accompanying the storage and release of lithium ions, the cycle characteristics during repeated charge and discharge are poor. In addition, although carbon materials such as graphite and hard carbon are also used, they have reached their theoretical capacity and it is unlikely to significantly increase the capacity.

[0011] The present invention aims to provide a novel organic sulfur material, an electrode (i.e., a positive electrode or a negative electrode) containing the organic sulfur material, a lithium ion secondary battery including the electrode, and methods for manufacturing them, which can improve the charge and discharge capacity and cycle characteristics of the lithium ion secondary battery.

[0012] Means for Solving the Problems

[0013] After conducting in-depth research to solve the above problems, the inventor of the present invention found that by modifying a specified acrylic resin with sulfur, an organic sulfur material with excellent properties can be obtained. Through further repeated research, the present invention was completed.

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

[0015] [1] An organic sulfur material, which is an organic sulfur material obtained by modifying an acrylic resin with sulfur,

[0016] The acrylic resin is a polymer selected from at least one of the following groups: a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1), or a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2).

[0017] CH2=C(R 11 )COOR 12 (1)

[0018] (Wherein, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.)

[0019] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0020] (Wherein, R 21 is the same as or different from R 22 and is a hydrogen atom or a methyl group, Y is a hydrocarbylene group, and the hydrocarbylene group may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group may have an ether bond formed with an oxygen atom. However, when there are two or more such ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.)

[0021] [2] The organic sulfur material according to the above [1], wherein the modification is carried out by firing in a non-oxidizing atmosphere.

[0022] [3] The organic sulfur material according to the above [1] or [2], wherein R 12R is an alkyl group having 1 to 6 carbon atoms, Y is an alkylene group having 2 to 6 carbon atoms, preferably 2 or 3 carbon atoms. In the alkylene group, the number of substituents is 1 to 4, preferably 1 or 2, and the alkyl group as a substituent has 1 to 4 carbon atoms, preferably 1 carbon atom. The number of ether bonds in the carbon skeleton constituting the alkylene group is 1 to 2, preferably 1 or 2.

[0023] [4] The organic sulfur material according to any one of [1] to [3] above, wherein the particle size of the acrylic resin is 0.1 to 300.0 μm, preferably 1.0 to 270.0 μm, more preferably 1.0 to 200.0 μm, further preferably 1.0 to 100.0 μm, further preferably 1.0 to 50.0 μm, further preferably 1.0 to 20.0 μm, further preferably 1.0 to 15.0 μm.

[0024] [5] The organic sulfur material according to any one of [1] to [4] above, wherein the acrylic resin has a porous structure.

[0025] [6] The organic sulfur material according to any one of [1] to [5] above, wherein in the Raman spectrum measured by Raman spectroscopy, a main peak exists near 1450 cm -1 -1, and peaks also exist near 485 cm -1 -1, near 1250 cm -1 -1, and near 1540 cm -1 -1 in the range of 200 to 1800 cm -1 -1.

[0026] [7] The organic sulfur material according to [6] above, wherein in the Raman spectrum, taking the straight line connecting the intensity at 1000 cm -1 -1 and the intensity at 1800 cm -1 -1 as the baseline, when calculating the difference (I -1 ) between the peak intensity near 1450 cm 1450 -1 and the corresponding baseline intensity and the difference (I -1 ) between the peak intensity near 1540 cm 1540 -1 and the corresponding baseline intensity, the value of I 1450 / I 1540 is in the range of 1 to 4.

[0027] [8] The organic sulfur material according to any one of [1] to [7] above, wherein the sulfur content in the organic sulfur material is 50.0% by mass or more, more preferably 53.0% by mass or more, further preferably 55.0% by mass or more, further preferably 56.0% by mass or more, further preferably 59.0% by mass or more.

[0028] [9] The organic sulfur material according to any one of [1] to [8] above, wherein the acrylic resin is a polymer selected from at least one of the following groups: a group consisting of polymers formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1).

[0029]

[10] An electrode containing the organic sulfur material according to any one of [1] to [9] above.

[0030]

[11] A lithium ion secondary battery including the electrode according to

[10] above.

[0031]

[12] A method for manufacturing an organic sulfur material, comprising:

[0032] (1) A step of preparing an acrylic resin,

[0033] (2) A step of modifying the acrylic resin with sulfur,

[0034] The acrylic resin is a polymer selected from at least one of the following groups: a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1), or a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2).

[0035] CH2=C(R 11 )COOR 12 (1)

[0036] (wherein, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.)

[0037] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0038] (wherein, R 21 is the same as or different from R 22 and is a hydrogen atom or a methyl group, Y is a hydrocarbon group, the hydrocarbon group may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbon group may have an ether bond formed with an oxygen atom. However, when there are two or more such ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.)

[13] According to the manufacturing method described in

[12] above, wherein the modification is carried out by firing in a non-oxidizing atmosphere.

[0039]

[14] According to the manufacturing method described in

[12] or

[13] above, the amount of sulfur relative to the acrylic resin is: 50 to 1000 parts by mass of sulfur relative to 100 parts by mass of the acrylic resin.

[0040]

[15] According to the manufacturing method described in

[13] above, the firing temperature is 250 to 550 °C.

[0041]

[16] According to the manufacturing method described in any one of

[12] to

[15] above, the particle size of the acrylic resin is 0.1 to 300.0 μm, preferably 1.0 to 270.0 μm, more preferably 1.0 to 200.0 μm, further preferably 1.0 to 100.0 μm, further preferably 1.0 to 50.0 μm, further preferably 1.0 to 20.0 μm, and further preferably 1.0 to 15.0 μm.

[0042]

[17] According to the manufacturing method described in any one of

[12] to

[16] above, the acrylic resin has a porous structure.

[0043]

[18] A method for manufacturing an electrode

[0044] After manufacturing the organic sulfur material by the manufacturing method described in any one of

[12] to

[17] above, the following process is further included: (3) A process of manufacturing an electrode using this organic sulfur material by a conventional method.

[0045]

[19] A method for manufacturing a lithium-ion secondary battery

[0046] After manufacturing the electrode by the manufacturing method described in

[18] above, the following processes are further included:

[0047] (4) A process of manufacturing a lithium-ion secondary battery using this electrode by a conventional method.

[0048] Effects of the Invention

[0049] According to the present invention, a novel organic sulfur material capable of improving charge-discharge capacity and cycle characteristics, an electrode including the organic sulfur material, i.e., a positive electrode or a negative electrode, and a lithium-ion secondary battery including the electrode can be provided.

[0050] In this specification, the "cycle characteristics" refer to the characteristics of maintaining the charge-discharge capacity of the secondary battery despite repeated charge and discharge. Therefore, with the repetition of charge and discharge, a secondary battery with a large decrease in charge-discharge capacity and a low capacity retention rate has poor cycle characteristics, and conversely, a secondary battery with a small decrease in charge-discharge capacity and a high capacity retention rate has excellent cycle characteristics. Brief Description of the Drawings

[0051] ​Figure 1 Schematically shows a cross-sectional view of a reaction apparatus for manufacturing an organic sulfur material in an embodiment of the present invention.

[0052] Figure 2 Under the same horizontal axis (Raman shift (cm -1 )), the Raman spectral curves of the organic sulfur materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are listed side by side to compare their peak positions.

[0053] Figure 3 Regarding each Raman spectral curve in the previous figure, a schematic diagram for grasping the I 1450 / I 1540 value. Here, I 1450 is the difference between the peak intensity near 1450 cm -1 and the corresponding baseline intensity (A in the figure), and I 1540 is the difference between the peak intensity near 1540 cm -1 and the corresponding baseline intensity (B in the figure). In addition, the baseline is a straight line drawn almost horizontally in this figure and is a straight line connecting the intensity at 1000 cm -1 and the intensity at 1800 cm -1 in each curve.

[0054] [Reference Signs]

[0055] 1 Reaction apparatus

[0056] 2 Raw material

[0057] 3 Reaction vessel

[0058] 4 Silicone lid

[0059] 5 Alumina protection tube

[0060] 6 Gas inlet tube

[0061] 7 Gas outlet tube

[0062] 8 Electric furnace

[0063] 9 Thermocouple

[0064] 10 Temperature controller

[0065] 11 Aqueous sodium hydroxide solution

[0066] 12 Capture tank

[0067] A Difference between the peak intensity near 1450 cm -1 and the corresponding baseline intensity

[0068] B Difference between the peak intensity near 1540 cm -1 and the corresponding baseline intensity​​ Detailed implementation mode

[0069] The constitution of the present invention will be described in detail below. In addition, for the numerical ranges described, the upper and lower limit values related to "above", "below", and "~" can be arbitrarily combined values, and the numerical values in the examples can also be the upper and lower limits. In addition, when specifying a numerical range by "~", unless otherwise specified, the values at both ends are also included.

[0070] One embodiment of the present invention is an organic sulfur material obtained by sulfur-modifying an acrylic resin, and the acrylic resin is a polymer selected from at least one of the following groups: a polymer polymerized from at least one selected from the group consisting of acrylate compounds represented by the above formula (1), or a polymer polymerized from at least one selected from the group consisting of acrylate compounds represented by the above formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2).

[0071] Another embodiment of the present invention is an electrode containing the organic material.

[0072] Another embodiment of the present invention is a lithium-ion secondary battery including the electrode.

[0073] Another embodiment of the present invention is a method for manufacturing an organic sulfur material, including:

[0074] (1) A step of preparing an acrylic resin,

[0075] (2) A step of sulfur-modifying the acrylic resin,

[0076] The acrylic resin is a polymer selected from at least one of the following groups: a polymer polymerized from at least one selected from the group consisting of acrylate compounds represented by the above formula (1), or a polymer polymerized from at least one selected from the group consisting of acrylate compounds represented by the above formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2).

[0077] Another embodiment of the present invention is a method for manufacturing an electrode. After manufacturing the organic sulfur material by the above manufacturing method, the following steps are further included:

[0078] (3) A step of using the organic sulfur material to fabricate an electrode by a conventional method.

[0079] Another embodiment of the present invention is a method for manufacturing a lithium-ion secondary battery. After manufacturing the electrode by the above manufacturing method, the following steps are further included:

[0080] (4) A step of using the electrode to fabricate a lithium-ion secondary battery by a conventional method.

[0081] <Acrylic resin>

[0082] In the present invention, the acrylic resin is a polymer selected from at least one of the following groups: a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1), or a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2).

[0083] CH2=C(R 11 )COOR 12 (1)

[0084] (wherein, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.)

[0085] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0086] (wherein, R 21 is the same as or different from R 22 and is a hydrogen atom or a methyl group, Y is a hydrocarbon group, the hydrocarbon group may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbon group may have an ether bond formed with an oxygen atom. However, when there are two or more such ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.)

[0087] In formula (1), R 11 is preferably a methyl group, R 12 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and among them, methyl, n-butyl, isobutyl or tert-butyl are preferred. As the compound represented by formula (1), for example, methyl (meth)acrylate, butyl (meth)acrylate, etc. can be mentioned, and methyl methacrylate and butyl methacrylate are more preferred. Here, the "(meth)acrylate" of methyl (meth)acrylate and butyl (meth)acrylate means either "acrylate" or "methacrylate" (the same applies hereinafter). A further preferred example of the compound represented by formula (1) is butyl methacrylate.

[0088] In formula (2), R 21 and R 22They are all preferably methyl. The number of carbon atoms of the alkylene group of Y is preferably 2 to 6, more preferably 2 or 3. The number of substituents of Y is preferably 1 to 4, more preferably 1 or 2. As the substituent of Y, it is preferably one or more substituents selected from the group consisting of a hydroxyl group and an alkyl group having 1 to 4 carbon atoms, and as the alkyl group having 1 to 4 carbon atoms, it is preferably methyl. When the carbon skeleton of Y has an ether bond formed with an oxygen atom, preferably, for example, the part corresponding to -Y-O- is represented by the following formula (3) (however, in formula (3), the substituents of Y are not considered).

[0089] -(CH2) l -(CH2CH2O) m -(CH2CH2CH2O) n - (3)

[0090] (Wherein, l is 0 to 6, m is 0 to 3, and n is 0 to 2. However, l, m, and n are not simultaneously 0.)

[0091] In formula (3), preferably, l is 1, 2, 3, 4, 5, or 6, and m and n are 0; or, m is 1, 2, or 3, and l and n are 0; or, n is 1 or 2, and l and m are 0.

[0092] Examples of the compound represented by formula (2) include, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6 - hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, etc. Among them, ethylene glycol dimethacrylate is preferred.

[0093] Preferred examples of the acrylic resin include homopolymers of (meth)acrylic acid methyl ester, homopolymers of (meth)acrylic acid butyl ester, copolymers of (meth)acrylic acid methyl ester and ethylene glycol di(meth)acrylate, copolymers of (meth)acrylic acid butyl ester and ethylene glycol di(meth)acrylate, etc. Among them, as the acrylic resin, a methacrylic acid - type resin is preferred. More preferred examples of the acrylic resin include copolymers of butyl methacrylate and ethylene glycol dimethacrylate.

[0094] One or more kinds of acrylic resins can be used.

[0095] (Morphology of acrylic resin)

[0096] In the present invention, the acrylic resin is preferably in the form of fine particles. Here, the fine particles refer to particles having a particle size of 300.0 μm or less. The particle size is preferably 270.0 μm or less, more preferably 200.0 μm or less, still more preferably 100.0 μm or less, still more preferably 50.0 μm or less, still more preferably 20.0 μm or less, still more preferably 15.0 μm or less, still more preferably 13.0 μm or less, still more preferably 10.0 μm or less, still more preferably 6.0 μm or less. On the other hand, the lower limit of the particle size is not particularly limited, and is usually, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle size is a value measured by a precision particle size distribution analyzer Multisizer 3 manufactured by Beckman Coulter, Inc.

[0097] The acrylic resin may be spherical fine particles or porous fine particles. When the acrylic resin is porous, its oil absorption amount is preferably 100 ml / 100 g or more, more preferably 110 ml / 100 g or more, still more preferably 120 ml / 100 g or more, still more preferably 130 ml / 100 g or more, still more preferably 140 ml / 100 g or more. The oil absorption amount is a value measured with reference to JIS K 5101-13-2:2004. More specifically, it can be measured by the method in paragraph 0069 of Japanese Patent Laid-Open No. 2017-88501.

[0098] (Weight-average molecular weight (Mw) of the acrylic resin)

[0099] As long as the acrylic resin has the above structure, the Mw is not particularly limited. However, the Mw of the acrylic resin is usually in the range of 2,000 to 1,500,000. The Mw is a value measured by gel permeation chromatography (GPC) (polystyrene calibration).

[0100] (Obtaining or manufacturing of the acrylic resin)

[0101] The acrylic resin can be commercially obtained or manufactured by a conventional method within the knowledge of those skilled in the art. Examples of commercially available acrylic resins include those manufactured by Sekisui Chemical Co., Ltd.

[0102] <Sulfur>

[0103] As sulfur, any of various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, etc. can be used, among which precipitated sulfur and colloidal sulfur are preferred. With respect to 100 parts by mass of the acrylic resin, the addition amount of sulfur is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, further preferably 150 parts by mass or more, further preferably 200 parts by mass or more, and further preferably 250 parts by mass or more. By being 100 parts by mass or more, there is a tendency to improve the charge-discharge capacity and cycle characteristics. On the other hand, for the addition amount of sulfur, there is no particular limitation on the upper limit, but it is usually 1000 parts by mass or less, preferably 750 parts by mass or less, more preferably 500 parts by mass or less, further preferably 400 parts by mass or less, and further preferably 350 parts by mass or less. By being 1000 parts by mass or less, there is a cost-advantageous tendency.

[0104] <Conductive carbon material>

[0105] When modifying the acrylic resin with sulfur, a conductive carbon material can also be added to the acrylic resin in advance. This is because it can improve the conductivity of the organic sulfur material. As such a conductive carbon material, a carbon material having a graphite structure is preferred. As the carbon material, for example, carbon black, acetylene black, Ketjen black, graphite, carbon nanotubes (CNT), carbon fiber (CF), graphene, fullerenes, etc. having a condensed aromatic ring structure can be used. As the conductive carbon material, one kind or two or more kinds can be used.

[0106] Among them, from the viewpoints of low cost and excellent dispersibility, acetylene black, carbon black, and Ketjen black are preferred. In addition, a small amount of CNT, graphene, etc. can be used in combination with acetylene black, carbon black, and Ketjen black. By such combination, the cycle characteristics of the lithium-ion secondary battery can be further improved without significantly increasing the cost. In addition, the combined amount of CNT, graphene, etc. is preferably 8% by mass or more and 12% by mass or less of the total amount of the conductive carbon material.

[0107] With respect to 100 parts by mass of the acrylic resin, the addition amount of the conductive carbon material is preferably 5 parts by mass or more, more preferably 10 parts by mass or more. When the addition amount is 5 parts by mass or more, there is a tendency to easily achieve the purpose of further improving the charge-discharge capacity and cycle characteristics. On the other hand, the addition amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less. By being 50 parts by mass or less, the proportion of the sulfur-containing structure in the organic sulfur material will not decrease relatively, and there is a tendency to easily achieve the purpose of further improving the charge-discharge capacity and cycle characteristics.

[0108] <Other materials>

[0109] When the acrylic resin is modified with sulfur, other materials commonly used in the field can also be added to the acrylic resin in advance as needed.

[0110] <Manufacture of Organic Sulfur Materials>

[0111] In the present invention, the organic sulfur material can be manufactured by modifying a specified acrylic resin with sulfur.

[0112] (Preparation of Raw Materials)

[0113] During modification, it is desirable to thoroughly mix the acrylic resin and sulfur in advance. When a conductive carbon material or the like is added to the acrylic resin in advance, these additives are also mixed together. This mixing can be carried out by a conventional method. For example, it can be carried out using a high-speed stirrer or the like. On the other hand, the acrylic resin, sulfur, and additives as required can be in a state formed into granules.

[0114] (Non-Oxidizing Atmosphere)

[0115] It is preferable to carry out the modification in a non-oxidizing atmosphere. A non-oxidizing atmosphere refers to an atmosphere substantially free of oxygen and is used to suppress the oxidative degradation and excessive thermal decomposition of the constituent components. Specifically, it refers to an inert gas atmosphere such as nitrogen or argon, a sulfur gas atmosphere, etc. Therefore, the modification can be carried out, for example, in a quartz tube under an inert gas atmosphere.

[0116] (Method of Modification)

[0117] The sulfur modification of the acrylic resin can be carried out by a conventional method. For example, it can be carried out by firing the acrylic resin and sulfur. The firing can be carried out by a conventional method. For example, it can be carried out by heating the firing raw materials (including the acrylic resin, sulfur, and additives as required) at a specified heating rate until a specified temperature is reached, maintaining at this specified temperature for a specified time, and then naturally cooling.

[0118] [Heating Rate]

[0119] This heating rate is preferably, for example, in the range of 50 to 500 °C / h. This heating rate is more preferably 100 °C / h or more. On the other hand, this heating rate is more preferably 400 °C / h or less, further preferably 300 °C / h or less, and further preferably 200 °C / h or less. By the heating rate being within this range, there is a tendency to easily achieve the purpose of improving the charge-discharge capacity and cycle characteristics.

[0120] [Firing Temperature and Time]

[0121] The firing temperature refers to the temperature after the firing raw material has completed the temperature rise, and it is the temperature maintained for a certain period of time to fire the firing raw material. This temperature is preferably in the range of 250 to 550 °C. By being above 250 °C, there is a tendency to avoid insufficient vulcanization reaction and prevent the charge-discharge capacity of the target from decreasing. On the other hand, by being below 550 °C, there is a tendency to prevent the decomposition of the firing raw material, the decrease in yield, and the decrease in charge-discharge capacity. This temperature is more preferably above 300 °C, further preferably above 350 °C. On the other hand, it is more preferably below 500 °C, and more preferably below 450 °C. The time maintained at the firing temperature can be appropriately set according to the type of the firing raw material, the firing temperature, etc., and is preferably, for example, 1 to 6 hours. By being above 1 hour, there is a tendency to fully carry out firing, and by being below 6 hours, there is a tendency to prevent excessive thermal decomposition of the constituent components.

[0122] [Apparatus]

[0123] Firing can be carried out by Figure 1 the apparatus shown, or can also be carried out using a continuous apparatus such as a twin-screw extruder. When using a continuous apparatus, in this apparatus, while kneading, pulverizing, and mixing the firing raw material, firing is carried out, which has the advantage of being able to continuously manufacture the organic sulfur material through a series of operations.

[0124] (Residue removal process)

[0125] In the processed product obtained after firing, unreacted sulfur such as sulfur precipitated by cooling the sublimated sulfur during firing remains. These residues are the main cause of the decline in cycle characteristics, so it is preferable to remove these residues as much as possible. The removal of residues can be carried out by conventional methods such as vacuum heating drying, warm air drying, and solvent cleaning.

[0126] (Pulverization and classification)

[0127] The obtained organic sulfur material is pulverized to a specified particle size and classified, and particles of a size suitable for manufacturing an electrode can be obtained. As the preferred particle size distribution of the particles, the median particle size is about 5 to 40 μm. In addition, in the firing method using a twin-screw extruder described above, through the shear during kneading, the organic sulfur material can be pulverized while manufacturing the organic sulfur material.

[0128] [Organic sulfur material]

[0129] The main components of the organic sulfur material thus obtained are carbon and sulfur, and those with a higher sulfur content tend to have improved charge-discharge capacity and cycling characteristics. Therefore, it is preferable that the sulfur content is as high as possible. Generally, as the preferred range of the sulfur content, it is 50.0 mass% or more, more preferably 53.0 mass% or more, further preferably 55.0 mass% or more, further preferably 56.0 mass% or more, and further preferably 59.0 mass% or more in the organic sulfur material. However, when a conductive carbon material is added, due to the influence of the carbon constituting the conductive carbon material, even if the sulfur content is slightly lower, an effect of improving the charge-discharge capacity and cycling characteristics can be expected. In this case, the sulfur content can be about 5.0 mass% lower than the above sulfur content. The total of the carbon content and the sulfur content in the organic sulfur material is preferably 90 mass% or more, more preferably 92 mass% or more, and further preferably 94 mass% or more.

[0130] In addition, through firing, hydrogen (H) in the acrylic resin reacts with sulfur and becomes hydrogen sulfide, which is reduced from the sulfide. Therefore, the hydrogen content of the organic sulfur material is preferably 1.8 mass% or less, and further preferably 1.6 mass% or less. When it is 1.8 mass% or less, there is a tendency for firing (sulfidation reaction) to be sufficient, and further, when it is 1.6 mass% or less, there is a tendency for firing (sulfidation reaction) to be more sufficient. Therefore, at this time, there is a tendency for the charge-discharge capacity to increase. The hydrogen content is more preferably 1.0 mass% or less, and further preferably 0.5 mass% or less. In the specification, the content of an element is measured by elemental analysis according to a conventional method.

[0131] Preferably, in the Raman spectrum measured by Raman spectroscopy, the organic sulfur material has a main peak near 1450 cm -1 and, in the range of 200 - 1800 cm -1 , there are also peaks near 485 cm -1 , near 1250 cm -1 , and near 1540 cm -1 . In this regard, the Raman spectra of Examples 1 and 2, and Comparative Examples 1 and 2 are shown in Figure 2 . In addition, in the peak positions of the Raman spectrum, "near" means allowing an error of ±50 cm -1 , especially ±30 cm -1 .

[0132] In addition, preferably, in the Raman spectrum of the organic sulfur material, using the straight line connecting the intensity at 1000 cm -1 and the intensity at 1800 cm -1 as the baseline, calculate the difference (I 1450 ) between the peak intensity near 1450 cm -1 and the corresponding baseline intensity and the difference between the peak intensity near 1540 cm -1The difference between the intensity of the nearby peak and the corresponding baseline intensity (I 1540 ) When, I 1450 / I 1540 The value is in the range of 1 to 4. In order to grasp this on the graph, Figure 3 The I of Examples 1 and 7 and Comparative Examples 1 and 2 is shown 1450 / I 1540 The value of. Figure 3 The value of A / B shown is I 1450 / I 1540 The value of.

[0133] For Examples 1 and 7 and Comparative Examples 1 and 2, if I is calculated 1450 / I 1540 The value is as shown in Table 1 below.

[0134] [Table 1]

[0135]

[0136] From the viewpoint of the effects of the present invention, I 1450 / I 1540 The value is more preferably 1.20 or more, further preferably 1.40 or more, further preferably 1.50 or more, further preferably 2.00 or more, and further preferably 2.50 or more. On the other hand, the value is preferably 3.80 or less, more preferably 3.60 or less, further preferably 3.50 or less, and further preferably 3.20 or less.

[0137] In the present invention, the Raman spectrum can be measured using RMP-320 manufactured by JASCO Corporation (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm -1 ).

[0138] <Lithium ion secondary battery>

[0139] The organic sulfur material of the present invention can be used as an electrode active material of a lithium ion secondary battery, that is, a positive electrode active material or a negative electrode active material. That is, in addition to using this organic sulfur material, a lithium secondary battery electrode can be manufactured in the same manner as when manufacturing an electrode for a general lithium ion secondary battery, and in addition to using this lithium ion secondary battery electrode, a lithium ion secondary battery can be manufactured in the same manner as when manufacturing a general lithium ion secondary battery. The lithium ion secondary battery thus manufactured has a large charge-discharge capacity and good cycle characteristics.

[0140] 1. When the organic sulfur material is used as the positive electrode active material

[0141] The lithium-ion secondary battery of the present invention can be fabricated in a conventional manner using components such as a positive electrode containing the above-mentioned organic sulfur material (positive electrode active material), a negative electrode, an electrolyte, and a separator as required.

[0142] (Positive electrode)

[0143] The positive electrode for a lithium-ion secondary battery can be fabricated in the same manner as a general positive electrode for a lithium-ion secondary battery, except that the above-mentioned organic sulfur material is used as the positive electrode active material. For example, the positive electrode can be fabricated by the following method: mixing particulate organic sulfur material with a conductive additive, a binder, and a solvent to prepare a paste-like positive electrode material, coating the positive electrode material on a current collector, and then drying it. Additionally, as another method, the positive electrode can also be fabricated by other methods: for example, co-kneading the organic sulfur material with a conductive additive, a binder, and a small amount of solvent using a mortar or the like, forming it into a film shape, and then pressing it onto a current collector using a press or the like.

[0144] [Conductive additive]

[0145] Examples of the conductive additive include, for example, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), Ketjen black (KB), graphite, or fine metal powders of aluminum, titanium, etc. that are stable at the positive electrode potential. These conductive additives can be used singly or in combination of two or more.

[0146] [Binder]

[0147] Examples of the binder include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, polymethyl methacrylate (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. These binders can be used singly or in combination of two or more.

[0148] [Solvent]

[0149] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformamide, ethanol, hexane, water, etc. These solvents can be used singly or in combination of two or more.

[0150] [Addition amount]

[0151] The addition amount of these materials constituting the positive electrode is not particularly limited. Preferably, for example, relative to 100 parts by mass of the organic sulfur material, 2 to 100 parts by mass of a conductive additive, 2 to 50 parts by mass of a binder, and an appropriate amount of a solvent are added.

[0152] [Current collector]

[0153] As the current collector, a current collector commonly used in the positive electrode of a lithium-ion secondary battery can be used. For example, as the current collector, examples include current collectors formed of aluminum foil, aluminum mesh, perforated aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, perforated stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel non-woven fabric, copper foil, copper mesh, perforated copper sheet, copper expanded sheet, titanium foil, titanium mesh, carbon non-woven fabric, carbon woven fabric, etc. Among them, a current collector formed of a carbon non-woven fabric or carbon woven fabric composed of carbon with a high degree of graphitization is suitable as the current collector when the organic sulfur material of the present invention is used as the positive electrode active material because it contains no hydrogen and has a low reactivity with sulfur. As the raw material of the carbon fiber with a high degree of graphitization, various pitches (i.e., by-products of petroleum, coal, coal tar, etc.) or polyacrylonitrile fiber (PAN) etc. that are used as carbon fiber materials can be used. The current collector can be used in combination of two or more kinds in addition to using one kind.

[0154] (Negative electrode)

[0155] As the negative electrode material, known carbon-based materials such as metallic lithium and graphite, silicon-based materials such as silicon thin films, and alloy materials such as copper-tin and cobalt-tin can be used. As the negative electrode material, using a lithium-free material, for example, when using a carbon-based material, a silicon-based material, an alloy material, etc. among the above-mentioned negative electrode materials, it is advantageous in that it is difficult to cause a short circuit between the positive and negative electrodes due to the generation of dendritic crystals. Among them, when these lithium-free negative electrode materials are used in combination with the positive electrode of the present invention, neither the positive electrode nor the negative electrode contains lithium. Therefore, it is necessary to perform a lithium pre-doping treatment of pre-inserting lithium into either the negative electrode or the positive electrode, or both. As the lithium pre-doping method, a known method can be used. For example, when doping lithium into the negative electrode, a method of inserting lithium by an electrolytic doping method of electrochemically doping lithium by using metallic lithium as the counter electrode to form a half-cell; a method of attaching a metallic lithium foil to the electrode and then placing it in the electrolyte solution, and inserting lithium by an attached pre-doping method of diffusing lithium into the electrode. In addition, when pre-doping lithium into the positive electrode, the above-mentioned electrolytic doping method can also be used. As the lithium-free negative electrode material, a silicon-based material which is a high-capacity negative electrode material is particularly preferably used, and among them, a thin-film silicon with a thin electrode thickness and advantageous in terms of unit volume capacity is more preferably used.

[0156] (Electrolyte)

[0157] As the electrolyte used in a lithium ion secondary battery, an electrolyte obtained by dissolving an alkali metal salt of an electrolyte in an organic solvent can be used. As the organic solvent, at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl ether, γ-butyrolactone, and acetonitrile is preferably used. As the electrolyte, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, LiClO4, etc. can be used. The concentration of the electrolyte may be about 0.5 mol / L to 1.7 mol / L. In addition, the electrolyte is not limited to a liquid state. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (for example, a polymer gel state).

[0158] (Separator)

[0159] In addition to the above-mentioned negative electrode, positive electrode, and electrolyte, a lithium ion secondary battery may also include components such as a separator. The separator is interposed between the positive electrode and the negative electrode, allowing ions to move between the positive electrode and the negative electrode while preventing internal short circuits between the positive electrode and the negative electrode. If the lithium ion secondary battery is a sealed type, the separator is also required to have the function of retaining the electrolyte. As the separator, a thin-walled and microporous or non-woven fabric-like film made of materials such as polyethylene, polypropylene, polyacrylonitrile, aromatic polyamide, polyimide, cellulose, and glass is preferably used.

[0160] (Shape)

[0161] The shape of the lithium ion secondary battery is not particularly limited and can be various shapes such as cylindrical, laminated, coin-shaped, and button-shaped.

[0162] 2. When using an organic sulfur material as the negative electrode active material

[0163] The lithium ion secondary battery of the present invention can be manufactured by a conventional method using a negative electrode, a positive electrode, and an electrolyte containing the above-mentioned organic sulfur material (negative electrode active material), and components such as a separator as required.

[0164] (Negative electrode)

[0165] The negative electrode for a lithium ion secondary battery can be manufactured in the same manner as a general negative electrode for a lithium ion secondary battery except for using the above-mentioned organic sulfur material as the negative electrode active material. For example, the negative electrode can be manufactured by the following method: mixing particulate organic sulfur material with a conductive additive, a binder, and a solvent to prepare a paste-like negative electrode material, coating the negative electrode material on a current collector, and then drying it. In addition, as another method, the negative electrode can also be manufactured by other methods: for example, co-kneading the organic sulfur material with a conductive additive, a binder, and a small amount of solvent using a mortar or the like, forming it into a film shape, and then pressing it onto a current collector using a press or the like.

[0166] The conductive additive, binder, and solvent can be the same substances as those used in the above case where the organic sulfur material is used as the positive electrode active material, and the current collector can also be the same substance.

[0167] (Positive electrode)

[0168] As the positive electrode material, there is no particular limitation as long as it is, for example, a transition metal oxide or solid solution oxide containing lithium, or a substance that can electrochemically store and release lithium ions. Examples of the transition metal oxide containing lithium include Li·Co-based composite oxides such as LiCoO2, LiNi x Co y Mn z O2 and other Li·Ni·Co·Mn-based composite oxides, Li·Ni-based composite oxides such as LiNiO2, or Li·Mn-based composite oxides such as LiMn2O4. Examples of the solid solution oxide include Li a Mn x Co y Ni z O2 (1.150 ≤ a ≤ 1.430, 0.450 ≤ x ≤ 0.600, 0.100 ≤ y ≤ 0.150, 0.200 ≤ z ≤ 0.280), LiMn x Co y Ni z O2 (0.300 ≤ x ≤ 0.850, 0.100 ≤ y ≤ 0.300, 0.100 ≤ z ≤ 0.300), LiMn 1.5 Ni 0.5 O4 and the like. These compounds can also be used alone or in combination of multiple kinds.

[0169] Regarding the electrolyte, separator, and the shape of the lithium ion secondary battery, the same materials as those used in the above case where the organic sulfur material is used as the positive electrode active material can also be used.

[0170] [Examples]

[0171] The present invention will be described based on examples, but the present invention is not limited to the examples.

[0172] Hereinafter, various chemicals used in the examples and comparative examples are shown in summary. The various chemicals are refined according to conventional methods as needed.

[0173] [Materials used in the test]

[0174] Acrylic resin 1: Spherical acrylic resin composed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate (Techpolymer MB30X-8 manufactured by Sekisui Chemical Co., Ltd., particle size: 8 μm)

[0175] Acrylic resin 2: Spherical acrylic resin composed of a copolymer of butyl methacrylate and ethylene glycol dimethacrylate (Techpolymer BM30X-8 manufactured by Sekisui Chemical Co., Ltd., particle size: 8 μm)

[0176] Acrylic resin 3: Spherical acrylic resin composed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate (Techpolymer MB30X-20 manufactured by Sekisui Chemical Co., Ltd., particle size: 20 μm)

[0177] Acrylic resin 4: Porous acrylic resin composed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate (Techpolymer MBP-8 manufactured by Sekisui Chemical Co., Ltd., particle size: 8 μm)

[0178] Acrylic resin 5: Spherical acrylic resin composed of a homopolymer of methyl methacrylate (Techpolymer MB-8 manufactured by Sekisui Chemical Co., Ltd., particle size: 8 μm)

[0179] Acrylic resin 6: Spherical acrylic resin composed of a homopolymer of methyl methacrylate (Parapet GF-P manufactured by Kuraray Co., Ltd., particle size: 270 μm)

[0180] Acrylic resin 7: Spherical acrylic resin composed of a copolymer of butyl methacrylate and ethylene glycol dimethacrylate (Techpolymer BM30X-5 manufactured by Sekisui Chemical Co., Ltd., particle size: 5 μm)

[0181] Acrylic resin 8: Spherical acrylic resin composed of a copolymer of methyl methacrylate and ethylene glycol dimethacrylate (Techpolymer MB30X-5 manufactured by Sekisui Chemical Co., Ltd., particle size: 5 μm)

[0182] Acrylic resin 9: Spherical acrylic resin composed of a copolymer of butyl methacrylate and ethylene glycol dimethacrylate (Techpolymer BM30X-12 manufactured by Sekisui Chemical Co., Ltd., particle size: 12 μm)

[0183] Acrylic resin 10: Spherical acrylic resin composed of a copolymer of butyl methacrylate and ethylene glycol dimethacrylate (Gantzpearl GB-15S manufactured by AICA Kogyo Co., Ltd., particle size: 15 μm)

[0184] High-cis BR: High-cis butadiene rubber (BR150L manufactured by Ube Industries, Ltd., cis-1,4 bond content = 98% by mass)

[0185] PAN: Polyacrylonitrile (manufactured by Sigma - Aldrich, particle size: 8 μm)

[0186] Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical Co., Ltd.

[0187] Example 1

[0188] <Production of raw materials>

[0189] According to the formulation in Table 2, the materials were mixed in a stirrer to obtain the raw materials for firing (firing raw materials).

[0190] (Reaction device)

[0191] Used in the firing of the firing raw materials Figure 1 The reaction device 1 shown. The reaction device 1 has: a reaction vessel 3 made of quartz glass in the shape of a bottomed cylinder with an outer diameter of 60 mm, an inner diameter of 50 mm, and a height of 300 mm for accommodating the raw materials 2 for firing; a lid 4 made of silicone for closing the upper opening of the reaction vessel 3; one alumina protection tube 5 (manufactured by NIKKATO Corporation, "Alumina SSA - S", outer diameter 4 mm, inner diameter 2 mm, length 250 mm), two gas inlet tubes 6 and a gas outlet tube 7 (both manufactured by NIKKATO Corporation, "Alumina SSA - S", outer diameter 6 mm, inner diameter 4 mm, length 150 mm) passing through the lid 4; and an electric furnace 8 (crucible furnace) for heating the reaction vessel 3 from the bottom side (opening width Heating height 100 mm).

[0192] The alumina protection tube 5 is formed to have a length that can reach the raw materials 2 installed at the bottom of the reaction vessel 3 from the lid 4, and a thermocouple 9 is inserted inside. The alumina protection tube 5 serves as a protection tube for the thermocouple 9. With the front end of the thermocouple 9 protected by the closed front end of the alumina protection tube 5, the front end of the thermocouple 9 is inserted into the raw materials 2 for measuring the temperature of the raw materials 2. The output of the thermocouple 9 is input to the temperature controller 10 of the electric furnace 8 as shown by the solid - line arrow in the figure, and the temperature controller 10 controls the heating temperature of the electric furnace 8 based on the input from the thermocouple 9.

[0193] The lower ends of the gas inlet pipe 6 and the gas outlet pipe 7 protrude 3 mm downward from the lid 4. Continuously supply Ar (argon) gas to the gas inlet pipe 6 from a gas supply system not shown in the figure. In addition, the gas outlet pipe 7 is connected to a capture tank 12 filled with an aqueous sodium hydroxide solution 11. The exhaust gas that wants to be discharged from the reaction vessel 3 to the outside through the gas outlet pipe 7 will first pass through the aqueous sodium hydroxide solution 11 in the capture tank 12 and then be discharged to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the sulfidation reaction, it will be neutralized with the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0194] (Firing process)

[0195] First, place the raw material 2 at the bottom of the reaction vessel 3. In this state, continuously supply Ar gas at a flow rate of 80 ml / min through the gas supply system. After 30 minutes from the start of the supply, start heating with the electric furnace 8. The heating rate is implemented at 150 °C / h. Then, when the temperature of the raw material reaches the firing temperature (400 °C) in Table 2, while maintaining this firing temperature, carry out firing for 2 hours. Next, while adjusting the flow rate of the Ar gas, allow the temperature of the reaction product in the Ar gas atmosphere to cool naturally to 25 °C, and then take out the product from the reaction vessel 3.

[0196] (Removal of unreacted sulfur)

[0197] To remove the unreacted sulfur (free monomeric sulfur) remaining in the product after the firing process, perform the following process. That is, crush the product with a mortar, place 2 g of the crushed material in a glass tube oven, heat it at 250 °C for 3 hours while performing vacuum extraction, to obtain an organic sulfur material from which the unreacted sulfur has been removed (or only contains a trace amount of unreacted sulfur). The heating rate is 10 °C / min.

[0198] (Classification operation)

[0199] To remove the coarse particles of the fired product, classify it using a 32 μm mesh stainless steel sieve to obtain the organic sulfur material 1.

[0200] (Fabrication of a lithium-ion secondary battery)

[0201] Fabricate a lithium-ion secondary battery as follows.

[0202] (Positive electrode)

[0203] The active material uses an organic sulfur material 1, the conductive additive uses acetylene black, and the binder uses an acrylic resin. They are weighed in a ratio of active material:conductive additive:binder = 90:5:5 (mass %), put into a container, and milliQ water is used as a dispersant. A rotation-revolution mixer (ARE-250 manufactured by THINKY Corporation) is used for stirring and mixing to make a uniform slurry. The prepared slurry is coated on an aluminum foil with a thickness of 20 μm using a coater with a slit width of 60 μm. The electrode compressed by a roll press is heated at 120 °C for 3 hours using a dryer. After drying, it is perforated as The electrode (positive electrode) is obtained. Then, the weight of the electrode is measured, and the amount of the active material in the electrode is calculated according to the above ratio.

[0204] (Negative electrode)

[0205] As the negative electrode, a lithium metal foil (a disk with a diameter of 14 mm and a thickness of 500 μm, manufactured by Motoshiro Metal Co., Ltd.) is used.

[0206] (Electrolyte)

[0207] As the electrolyte, a non-aqueous electrolyte in which LiPF6 is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate is used. Ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:1. The concentration of LiPF6 in the electrolyte is 1.0 mol / l.

[0208] (Lithium-ion secondary battery)

[0209] Using the above positive electrode and negative electrode, a button battery is made. Specifically, in a drying room, a separator (Celgard 24, manufactured by Celgard, a polypropylene microporous membrane with a thickness of 25 μm) and a glass non-woven fabric filter layer (with a thickness of 440 μm, GA100 manufactured by ADVANTEC) are sandwiched between the positive electrode and the negative electrode to make an electrode body battery. The electrode body battery is housed in a battery case made of a stainless steel container (CR2032 type button battery component, manufactured by Hosen Co., Ltd.). The above electrolyte is injected into the battery case. The battery case is sealed with a caulking machine to obtain the lithium-ion secondary battery of Example 1.

[0210] Examples 2 to 15 and Comparative Examples 1 to 2

[0211] Except for appropriately changing according to the formulations and conditions in Tables 2 and 3, the same treatments as in Example 1 are carried out for the production of each firing raw material, organic sulfur material, and lithium-ion secondary battery.

[0212] <Measurement of discharge capacity and capacity retention rate>

[0213] For the button-type lithium-ion secondary batteries fabricated in each of the examples and comparative examples, under the condition of a test temperature of 30°C, charge and discharge were carried out at a current value of 50 mA for the first to ninth times and 250 mA for the tenth to thirtieth times per 1 g of the positive electrode active material. The discharge cut-off voltage was set to 1.0 V, and the charge cut-off voltage was set to 3.0 V. In addition, charge and discharge were repeated, and the battery discharge capacities (mAh) at the 10th and 30th times were observed.

[0214] The discharge capacity (mAh / g) at the second time was taken as the initial capacity. The larger the initial capacity, the more preferably it can be evaluated that the charge and discharge capacity of the lithium-ion secondary battery is larger. In addition, based on the discharge capacity DC 10 (mAh / g) at the 10th time and the discharge capacity DC 30 (mAh / g) at the 30th time, the capacity retention rate (%) was obtained by the following formula (a):

[0215] Capacity retention rate (%) = (DC 30 / DC 10 ) × 100 (a)

[0216] It can be said that, as described above, the higher the capacity retention rate, the more excellent the cycle characteristics of the lithium-ion secondary battery.

[0217] <Elemental analysis>

[0218] Elemental analysis was performed on the organosulfur materials fabricated in the examples and comparative examples.

[0219] For carbon, hydrogen, sulfur, and nitrogen, based on the masses measured by the vario MICRO cube, a fully automatic elemental analyzer manufactured by Elementar, the mass ratios (%) they accounted for in the total amount of the organosulfur material were calculated. The results are shown in Tables 2 and 3.

[0220] <Raman spectroscopy>

[0221] The Raman spectra were measured by the above method. Figure 2 The results of the organosulfur materials of Example 1, 7 and Comparative Examples 1, 2 are shown. In this figure, the Raman spectra are listed side by side with the same horizontal axis (Raman shift (cm -1 )) to compare their peak positions.

[0222] [Table 2]

[0223]

[0224] [Table 3]

[0225]

[0226] As can be seen from Table 2 and Table 3, compared with Comparative Example 1, the Example shows a higher initial capacity (mAh / g), and the capacity retention rate (%) also remains at a high level. Although Comparative Example 2 shows a higher initial capacity and capacity retention rate, it is difficult to provide it at a low cost because expensive polyacrylonitrile is used as a raw material. According to the organic sulfur material of the present invention, a lithium ion secondary battery with a high initial capacity and good capacity retention rate can be provided at a low cost.

Claims

1. An organic sulfur material is an organic sulfur material obtained by sulfur-modifying an acrylic resin. The sulfur content in the organic sulfur material is 50.0% by mass or more. The acrylic resin is a polymer selected from at least one of the following groups: a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2); CH2=C(R 11 )COOR 12 (1) Among them, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group; CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2) wherein R 21 is the same as or different from R 22 and is a hydrogen atom or a methyl group, Y is a lower alkylene group which has at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group or has no substituent, and the carbon skeleton constituting the lower alkylene group has or does not have an ether bond formed with an oxygen atom; however, when there are two or more of such ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

2. The organic sulfur material according to claim 1, wherein The modification is carried out by firing in a non-oxidizing atmosphere.

3. The organic sulfur material according to claim 1 or 2, wherein R 12 is an alkyl group having 1 to 6 carbon atoms, Y is an alkylene group having 2 to 6 carbon atoms, in the alkylene group, the number of substituents is 1 to 4, the number of carbon atoms of the alkyl group as a substituent is 1 to 4, and the number of ether bonds in the carbon skeleton constituting the alkylene group is 1 to 2.

4. The organic sulfur material according to claim 1 or 2, wherein The particle size of the acrylic resin is 0.1 to 300.0 μm.

5. The organic sulfur material according to claim 1 or 2, wherein The acrylic resin has a porous structure.

6. The organic sulfur material according to claim 1 or 2, wherein, In the Raman spectrum measured by Raman spectroscopy analysis, a main peak exists near 1450 cm -1 Moreover, in the range of 200 - 1800 cm -1 peaks also exist near 485 cm -1 , near 1250 cm -1 , and near 1540 cm -1 .

7. The organic sulfur material according to claim 6, wherein In the Raman spectrum, a straight line connecting the intensity at 1000 cm -1 and the intensity at 1800 cm -1 is taken as the baseline, and the difference I -1 between the peak intensity near 1450 cm 1450 and the corresponding baseline intensity and the difference I -1 between the peak intensity near 1540 cm 1540 and the corresponding baseline intensity are calculated. When calculating, the value of I 1450 / I 1540 is in the range of 1 to 4.

8. An electrode contains the organic sulfur material according to any one of claims 1 to 7.

9. A lithium ion secondary battery includes the electrode according to claim 8.

10. A method for manufacturing an organic sulfur material includes: (1) A step of preparing an acrylic resin, (2) A step of sulfur-modifying the acrylic resin, The amount of sulfur relative to the acrylic resin is: 50 to 1000 parts by mass of sulfur relative to 100 parts by mass of the acrylic resin, The acrylic resin is a polymer selected from at least one of the following groups: a polymer formed by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2); CH2=C(R 11 )COOR 12 (1) Among them, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group; CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2) wherein R 21 is the same as or different from R 22 and is a hydrogen atom or a methyl group, Y is a lower alkylene group which has at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group or has no substituent, and the carbon skeleton constituting the lower alkylene group has or has no ether bond formed with an oxygen atom; provided that when there are two or more of such ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

11. The manufacturing method according to claim 10, wherein, The modification is carried out by firing in a non-oxidizing atmosphere.

12. The manufacturing method according to claim 11, wherein, The temperature of the firing is 250 to 550 °C.

13. The manufacturing method according to claim 10 or 11, wherein The particle size of the acrylic resin is 0.1 to 300.0 μm.

14. The manufacturing method according to claim 10 or 11, wherein The acrylic resin has a porous structure.

15. A method for manufacturing an electrode, After manufacturing the organic sulfur material by the manufacturing method according to any one of claims 10 to 14, it further includes the following step: (3) A step of using the organic sulfur material to fabricate an electrode by a conventional method.

16. A method for manufacturing a lithium ion secondary battery, After manufacturing the electrode by the manufacturing method according to claim 15, it further includes the following steps: (4) A step of using the electrode to fabricate a lithium ion secondary battery by a conventional method.

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