JP5660730B2 - Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery using a carbon compound as a raw material, a method for producing the same, and a non-aqueous electrolyte secondary battery.

  A lithium secondary battery and a lithium ion secondary battery, which are types of non-aqueous electrolyte secondary batteries, are batteries having a large charge / discharge capacity, and are mainly used as batteries for portable electronic devices. Lithium ion secondary batteries are also expected as batteries for electric vehicles.

  As a positive electrode active material of a lithium ion secondary battery, a technique using sulfur is known. By using sulfur as the positive electrode active material, the charge / discharge capacity of the lithium ion secondary battery can be increased.

  However, in a lithium ion secondary battery using elemental sulfur as the positive electrode active material, a compound of sulfur and lithium is generated during discharge. This compound of sulfur and lithium is soluble in a non-aqueous electrolyte solution (for example, ethylene carbonate, dimethyl carbonate, etc.) of a lithium ion secondary battery. For this reason, a lithium ion secondary battery using sulfur as a positive electrode active material has a problem that, when charging and discharging are repeated, it gradually deteriorates due to elution of sulfur into the electrolytic solution, and the battery capacity decreases. Hereinafter, the characteristic of the lithium ion secondary battery in which the charge / discharge capacity decreases with repeated charge / discharge is referred to as “cycle characteristic”. The lithium ion secondary battery having a small decrease in charge / discharge capacity is a lithium ion secondary battery having excellent cycle characteristics, and the lithium ion secondary battery having a large decrease in charge / discharge capacity is a lithium ion secondary battery having inferior cycle characteristics.

  Therefore, it has been proposed to use a sulfur-modified compound obtained by modifying a carbon compound with elemental sulfur as a positive electrode active material (Patent Document 1). However, since the sulfur-modified compound contains sulfur having a large battery capacity, the battery capacity is large, but the potential is low. Therefore, the inventor has eagerly pursued and decided to develop a positive electrode active material having a high potential.

  In the development stage, we investigated whether the potential of the carbon compound could be increased by introducing various elements into the carbon compound. As described in Patent Documents 2 to 6, fluorine is considered as an introduced element, and it has been proposed to use fluorinated carbon as an electrode active material. Patent Document 7 discloses a method of fluorinating a carbonaceous material by electrolytic decomposition in the presence of hydrogen fluoride. Since fluorine is an element having a strong electric affinity, the carbon material into which fluorine is introduced is considered to have a high potential.

  However, it cannot be said that a fluorinated carbon compound has sufficient performance as a positive electrode active material even if the battery capacity is low and the potential is high.

WO2010 / 044437 JP-A-63-024555 JP 2002-289195 A Japanese Patent Laid-Open No. 2004-265677 Special table 2010-521784 gazette JP 2009-512133 A JP 59-078913

  The present invention has been made in view of such circumstances, and an object thereof is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery having a high battery capacity and high potential, a method for producing the same, and a non-aqueous electrolyte secondary battery.

  (1) The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized by comprising a sulfur-fluorine-introducing compound obtained by introducing sulfur (S) and fluorine (F) into a carbon compound.

  Inclusion of sulfur in the positive electrode active material increases the charge / discharge capacity. In addition, since fluorine has a high electron affinity, the potential of the positive electrode active material can be increased by including fluorine in the positive electrode active material. Sulfur and fluorine are introduced into the carbon compound. For this reason, sulfur or fluorine binds to or adheres to the carbon compound, and elution into the electrolytic solution is suppressed. For this reason, the cycling characteristics of a battery can be improved.

  As described above, a sulfur-fluorine-introducing compound obtained by introducing sulfur and fluorine into a carbon compound can increase the electric capacity of the positive electrode active material, increase the potential, and improve the energy density.

  (2) In the positive electrode active material for a non-aqueous electrolyte secondary battery, the sulfur-fluorine-introducing compound is obtained by modifying the carbon compound with sulfur to form a sulfur-modified product, and then modifying the sulfur-modified portion in the sulfur-modified product. It is preferable to introduce fluorine while leaving at least a part.

  Since fluorine has a strong electron affinity, by introducing fluorine into the sulfur-modified product, the potential of the sulfur-modified product can be increased, the energy density can be improved, and the output voltage can be improved. . Moreover, a part of sulfur remains in the sulfur fluorine introducing compound. For this reason, the high battery capacity which is the characteristic of sulfur itself can be exhibited.

  In addition, after the carbon compound is modified with sulfur, fluorine is introduced while leaving the sulfur-modified portion, so that it can be fluorinated while maintaining a part of the chemical structure of the sulfur-modified portion. Therefore, the sulfur fluorine-introducing compound can maintain at least a part of the chemical structure in the sulfur-modified compound disclosed in Patent Document 1, can exhibit a high battery capacity, and is patented by fluorination. The potential can be made higher than that in Document 1.

  (3) In the positive electrode active material for a nonaqueous electrolyte secondary battery, the carbon compound is at least one selected from polyacrylonitrile, pitches, and polycyclic aromatic hydrocarbons formed by condensation of three or more six-membered rings. Preferably it consists of.

  Since these carbon compounds capture sulfur stably, elution into the electrolyte can be effectively suppressed and cycle characteristics can be improved.

  (4) In the positive electrode active material for a non-aqueous electrolyte secondary battery, the carbon compound is preferably generated from a plant material.

  Since plant materials can also capture sulfur stably, cycle characteristics can be improved. Moreover, since plant raw materials can be obtained at low cost, the production cost can be kept low.

  (5) A non-aqueous electrolyte secondary battery of the present invention includes the positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode active material, and an electrolytic solution. For this reason, battery capacity and an output voltage can be made high.

  (6) The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery includes a sulfur-modified product obtained by modifying the carbon compound with sulfur to bring a fluorinating agent into contact with the sulfur-modified product. The sulfur-modified product is obtained by introducing fluorine into the sulfur-modified product while leaving at least a part of the sulfur-modified portion modified with sulfur.

  Since the positive electrode active material for a non-aqueous electrolyte secondary battery is composed of a sulfur-fluorine-introducing compound containing sulfur and fluorine, the capacity is high and the potential is high. For this reason, the battery capacity and energy density of the nonaqueous electrolyte secondary battery can be increased by using the positive electrode active material for a nonaqueous electrolyte secondary battery.

  (7) In the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, the fluorinating agent is preferably composed of at least one of anhydrous hydrogen fluoride and fluorine gas.

  In this case, the fluorine-modified agent can be modified with fluorine while leaving at least a part of the sulfur-modified portion of the sulfur-modified product simply by contacting the fluorine-modified agent with the sulfur-modified product. For this reason, manufacture of a positive electrode active material can be simplified.

  (8) In the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, the sulfur-modified product includes a mixing step in which a carbon compound and sulfur are mixed to form a mixed raw material, and a heat treatment step in which the mixed raw material is heated. It is preferable to obtain by performing.

  In this case, the carbon compound can be modified with sulfur.

  According to the positive electrode active material for a nonaqueous electrolyte secondary battery and the method for producing the same and the nonaqueous electrolyte secondary battery of the present invention, a sulfur fluorine-introducing compound obtained by introducing sulfur and fluorine into a carbon compound is used as the positive electrode active material. ing. For this reason, battery capacity and potential can be increased.

It is a graph showing the result of having carried out X-ray diffraction of sulfur modification polyacrylonitrile. It is a graph showing the result of having performed a Raman spectrum analysis of sulfur-modified polyacrylonitrile. It is explanatory drawing which represents typically the reaction apparatus used with the manufacturing method of the sulfur modified polyacrylonitrile of an Example.

(Positive electrode active material for non-aqueous electrolyte secondary battery)
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention comprises a sulfur-fluorine-introducing compound obtained by introducing sulfur and fluorine into a carbon compound. The sulfur-fluorine-introducing compound is preferably obtained by modifying a carbon compound with sulfur to obtain a sulfur-modified product and then modifying it with fluorine while leaving at least a part of the sulfur-modified portion in the sulfur-modified product.

  What is produced | generated from a plant raw material can be used for a carbon compound. The plant raw material may be, for example, at least one selected from coffee beans, tea leaves, sugar cane, corns, fruits, cereals, potatoes, straws, and rice husks.

  As the carbon compound, those using at least one selected from [1] polyacrylonitrile, [2] pitches, and [3] polycyclic aromatic hydrocarbons formed by condensation of three or more six-membered rings are preferably used. . The sulfur-fluorine-introducing compound obtained by modifying these carbon compounds with sulfur and then modifying with fluorine includes, for example, a carbon skeleton derived from any of the carbon compounds described above, sulfur (S) bonded to the carbon skeleton, and It is composed of fluorine (F).

  Hereinafter, a sulfur-modified product obtained by modifying a carbon compound with sulfur and a sulfur-fluorine-introducing compound obtained by introducing fluorine into the sulfur-modified product will be described.

A. Sulfur modified product The sulfur modified product is obtained by modifying a carbon compound with sulfur. Here, the modification means that sulfur is chemically bonded to or coordinated with the carbon compound, or that sulfur is bonded to the carbon compound to change the structure of the carbon compound.

  A sulfur-modified product using polyacrylonitrile as a carbon compound is called sulfur-modified PAN. A sulfur-modified product using pitches as a carbon compound is called sulfur-modified pitch. A sulfur-modified product using a polycyclic aromatic hydrocarbon formed by condensation of three or more six-membered rings as a carbon compound is called sulfur-modified PAH.

[1] Sulfur modified PAN
The sulfur-modified PAN is the same as that disclosed in Patent Document 1 above. Polyacrylonitrile (PAN) as a material for sulfur-modified PAN is preferably in the form of powder and preferably has a mass average molecular weight of about 1 × 10 ^{4 to} 3 × 10 ⁵ . Further, the particle size of PAN is preferably about 0.5 to 50 μm, more preferably about 1 to 10 μm, when observed with an electron microscope. If the molecular weight and particle size of PAN are within these ranges, the contact area between PAN and sulfur can be increased, and PAN and sulfur can be reacted with high reliability. For this reason, the elution of sulfur to the electrolytic solution can be more reliably suppressed.

  By using sulfur-modified PAN as the positive electrode active material of the non-aqueous electrolyte secondary battery, the high capacity inherent in sulfur can be maintained, and the elution of sulfur into the electrolyte is suppressed, so the cycle characteristics are greatly improved. . This is probably because sulfur does not exist as a simple substance in the sulfur-modified PAN, but exists in a stable state combined with PAN. In the method for producing a positive electrode active material disclosed in Patent Document 1, sulfur is heat-treated together with PAN. When PAN is heated, it is considered that PAN is three-dimensionally cross-linked and closed while forming a condensed ring (mainly a six-membered ring). For this reason, it is considered that sulfur is present in the sulfur-modified PAN in a state of being bonded to the PAN that has progressed in the ring closure. By combining PAN and sulfur, elution of sulfur into the electrolyte can be suppressed, and cycle characteristics can be improved.

  Sulfur used for sulfur-modified PAN is preferably in the form of a powder, like PAN. Although it does not specifically limit about the particle size of sulfur, when classified using a sieve, those that do not pass through a sieve with a sieve opening of 40 μm and are within a size range that passes through a 150 μm sieve are preferable, It is more preferable that the mesh size does not pass through a 40 μm sieve and is within a size range that passes through a 100 μm sieve.

  The compounding ratio of the PAN powder and sulfur powder used for the sulfur-modified PAN is not particularly limited, but is preferably 1: 0.5 to 1:10 by mass ratio, and 1: 0.5 to 1: 7. More preferably, it is 1: 2 to 1: 5.

  Sulfur-modified PAN can be produced by the following method.

  A mixed raw material in which PAN powder and sulfur powder are mixed is heated (heat treatment step). What is necessary is just to mix a mixing raw material with common mixing apparatuses, such as a mortar and a ball mill. As the mixed raw material, a material obtained by simply mixing sulfur and PAN may be used. For example, the mixed raw material may be formed into a pellet shape. The mixed raw material may be composed only of PAN and sulfur, or may be blended with a general material (such as a conductive aid) that can be blended with the positive electrode active material. The same applies to other positive electrode active materials described later.

  By heating the mixed raw material in the heat treatment step, sulfur and PAN contained in the mixed raw material are combined. The heat treatment step may be performed in a closed system or an open system, but in order to suppress the dissipation of sulfur vapor, it is preferably performed in a closed system. In addition, the atmosphere in which the heat treatment step is performed is not particularly limited, but it is preferably performed in an atmosphere that does not hinder the binding of PAN and sulfur (for example, an atmosphere containing no hydrogen or a non-oxidizing atmosphere). For example, when hydrogen is present in the atmosphere, sulfur in the reaction system reacts with hydrogen to form hydrogen sulfide, so that sulfur in the reaction system may be lost. Further, it is considered that by performing heat treatment in a non-oxidizing atmosphere, vapor-state sulfur reacts with PAN simultaneously with the PAN ring-closing reaction, and PAN modified with sulfur is obtained. The non-oxidizing atmosphere referred to here includes a reduced pressure state in which the oxygen concentration is low enough not to cause an oxidation reaction, an inert gas atmosphere such as nitrogen or argon, a sulfur gas atmosphere, and the like.

  There is no particular limitation on the specific method for creating a non-oxidizing atmosphere in a sealed state. For example, the mixed raw material is placed in a container that is kept tight enough not to dissipate sulfur vapor, and the inside of the container is decompressed. Alternatively, heating may be performed in an inert gas atmosphere. In addition, the mixed raw material may be heated in a vacuum packaged state with a material that does not easily react with sulfur vapor (for example, an aluminum laminate film). In this case, in order to prevent the packaging material from being damaged by the generated sulfur vapor, for example, the packaged raw material is put in a pressure vessel such as an autoclave containing water and heated, and the generated steam is added from the outside of the packaging material. It is preferable to press. According to this method, since pressure is applied by water vapor from the outside of the packaging material, the packaging material is prevented from being swollen and damaged by sulfur vapor.

  What is necessary is just to set suitably the heating time of the mixed raw material in a heat processing process according to heating temperature, and it does not specifically limit it. The preferable heating temperature mentioned above should just be a temperature which the coupling | bonding of sulfur and PAN advances, and a conductive material does not change in quality. Specifically, the heating temperature is preferably 250 to 500 ° C., more preferably 250 to 400 ° C., and further preferably 250 to 300 ° C.

  In the heat treatment step, sulfur is preferably refluxed. In this case, the mixed raw material may be heated so that a part of the mixed raw material becomes a gas and a part becomes a liquid. In other words, the temperature of the mixed raw material may be a temperature equal to or higher than the temperature at which sulfur is vaporized. Vaporization here refers to the phase change of sulfur from a liquid or solid to a gas, and may be any of boiling, evaporation, and sublimation. For reference, the melting point of α sulfur (orthogonal sulfur, which is the most stable structure near room temperature) is 112.8 ° C., the melting point of β sulfur (monoclinic sulfur) is 119.6 ° C., and γ sulfur (monoclinic sulfur). ) Has a melting point of 106.8 ° C. The boiling point of sulfur is 444.7 ° C. By the way, since the vapor pressure of sulfur is high, generation | occurrence | production of sulfur vapor | steam can also be confirmed visually when the temperature of a mixed raw material will be 150 degreeC or more. Therefore, if the temperature of the mixed raw material is 150 ° C. or higher, sulfur can be refluxed. In addition, what is necessary is just to recirculate | reflux sulfur using the reflux apparatus of a known structure, when recirculating | refluxing sulfur in a heat treatment process.

  Even when the amount of sulfur in the mixed raw material is excessive, a sufficient amount of sulfur can be taken into the PAN in the heat treatment step. For this reason, when adding sulfur excessively with respect to PAN, the bad influence by the elemental sulfur mentioned above can be suppressed by removing elemental sulfur from the to-be-processed body after a heat treatment process. Specifically, when the mixing ratio of PAN and sulfur in the mixed raw material is 1: 2 to 1:10 by mass ratio, the target object after the heat treatment step is heated at 200 ° C. to 250 ° C. while reducing the pressure. (Single element sulfur removal step) By taking a sufficient amount of sulfur into the PAN, it is possible to suppress adverse effects due to the remaining single sulfur. When the single sulfur removal step is not performed on the target object after the heat treatment step, this target object may be used as it is as the sulfur-modified PAN. Moreover, what is necessary is just to use the to-be-processed body after a single sulfur removal process as sulfur modified PAN, when performing the single-piece | unit sulfur removal process to the to-be-processed body after a heat treatment process. The time for the elemental sulfur removal step is not particularly limited, but is preferably about 1 to 6 hours.

  As a result of elemental analysis, sulfur-modified PAN contains carbon, nitrogen, and sulfur, and may contain small amounts of oxygen and hydrogen. Further, as shown in FIG. 1, as a result of X-ray diffraction of sulfur-modified PAN with CuKα rays, only a broad peak having a peak position in the vicinity of 25 ° was confirmed in the diffraction angle (2θ) range of 20-30 °. It was. For reference, X-ray diffraction was measured by X-ray diffraction using CuKα rays with a powder X-ray diffractometer (manufactured by MAC Science, model number: M06XCE). The measurement conditions were voltage: 40 kV, current: 100 mA, scan speed: 4 ° / min, sampling: 0.02 °, number of integrations: 1, measurement range: diffraction angle (2θ) 10 ° -60 °.

  Furthermore, the mass loss by thermogravimetric analysis when sulfur-modified PAN is heated from room temperature to 900 ° C. at a rate of temperature increase of 20 ° C./min is 10% or less at 400 ° C. On the other hand, when a mixture of sulfur powder and PAN powder is heated under the same conditions, a mass decrease is observed from around 120 ° C., and when the temperature is 200 ° C. or higher, a large mass loss due to the disappearance of sulfur is recognized.

  That is, in sulfur-modified PAN, it is considered that sulfur does not exist as a simple substance, but exists in a state of being combined with PAN that has advanced ring closure.

An example of the Raman spectrum of sulfur-modified PAN is shown in FIG. In the Raman spectrum shown in FIG. 2, there are major peak near 1331cm ^-1 of Raman shift, and, 1548cm ^-1 in the range of ^{200cm -1 ~1800cm -1, 939cm -1,} 479cm -1, 381cm -1, There is a peak near 317 cm ⁻¹ . The above-described Raman shift peak is observed at the same position even when the ratio of elemental sulfur to PAN is changed. Thus, these peaks characterize sulfur-modified PAN. Each of the peaks described above exists in a range of approximately ± 8 cm ⁻¹ with the above peak position as the center. In the present specification, the “main peak” refers to a peak having the maximum peak height among all peaks appearing in the Raman spectrum.

For reference, the Raman shift described above is measured by JASCO Corporation RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm ⁻¹ ). Note that the number of Raman spectrum peaks may change or the position of the peak top may be shifted depending on the wavelength of incident light or the difference in resolution. Therefore, when the Raman spectrum of the positive electrode of the present invention using sulfur-modified PAN as the positive electrode active material is measured, the same peak as the above peak, or a peak slightly different from the above peak in number and peak top position is confirmed. The

[2] Sulfur-modified pitch A positive electrode active material using pitches as a carbon compound includes a carbon skeleton derived from pitches and sulfur (S) bonded to the carbon skeleton. Pitches include coal pitch, petroleum pitch, mesophase pitch, asphalt, coal tar, coal tar pitch, organic synthetic pitch obtained by polycondensation of condensed polycyclic aromatic hydrocarbon compounds, and heteroatom-containing condensed polycyclic aromatic carbonization. At least one selected from the group consisting of organic synthetic pitches obtained by polycondensation of hydrogen compounds can be used.

  Coal tar, a kind of pitch, is a black viscous oily liquid obtained by high-temperature carbonization (coal carbonization) of coal. Coal pitch can be obtained by refining and heat treating (polymerizing) coal tar.

  Asphalt is a black-brown to black solid or semi-solid plastic material. Asphalt is broadly classified into what is obtained as a kettle residue when petroleum (crude oil) is distilled under reduced pressure and that which exists in nature. Asphalt is soluble in toluene, carbon disulfide and the like. Petroleum pitch can be obtained by refining and heat treating (polymerizing) asphalt.

  The pitch is usually amorphous and optically isotropic (isotropic pitch). An optically anisotropic pitch (anisotropic pitch, mesophase pitch) can be obtained by heat-treating the isotropic pitch in an inert atmosphere. Pitch is partially soluble in organic solvents such as benzene, toluene, carbon disulfide.

  Pitches are a mixture of various compounds and contain fused polycyclic aromatics as described above. The condensed polycyclic aromatic contained in the pitch may be a single species or a plurality of species. For example, the main component of coal pitch, which is a kind of pitches, is a condensed polycyclic aromatic. The condensed polycyclic aromatic can contain nitrogen and sulfur in addition to carbon and hydrogen in the ring. For this reason, the main component of coal pitch is considered to be a mixture of a condensed polycyclic aromatic hydrocarbon composed only of carbon and hydrogen and a heteroaromatic compound containing nitrogen, sulfur, etc. in the condensed ring.

  A positive electrode active material (sulfur-modified pitch) comprising a carbon skeleton derived from pitches and sulfur (S) bonded to the carbon skeleton can be produced by the same method as the above-described sulfur-modified PAN. When producing a sulfur-modified pitch, in the heat treatment step, at least a part of pitches and at least a part of sulfur are configured to be liquid. In other words, in the heat treatment step, at least a part of the pitches and at least a part of the sulfur are in liquid contact. For this reason, the contact area between pitches and sulfur in the heat treatment step can be made sufficiently large, and a sulfur-modified pitch that contains sulfur sufficiently and suppresses the elimination of sulfur can be obtained. In addition, when sulfur is refluxed in the heat treatment step, the contact frequency between pitches and sulfur can be increased, and a sulfur-modified pitch that further contains sulfur and further suppresses the elimination of sulfur can be obtained. .

  In the obtained sulfur-modified pitch, it is not clear how sulfur and pitches are bonded, but sulfur is taken in between the graphene layers of the pitches, or condensed polycyclic aromatics. It is presumed that hydrogen contained in the ring is substituted with sulfur to form a C—S bond.

  The temperature in the heat treatment step may be a temperature at which at least a part of pitches and at least a part of sulfur become liquid. In addition, regarding pitches, it is preferable that the temperature is such that the whole becomes a liquid. Further, regarding sulfur, the temperature is preferably such that the whole becomes a liquid, and more preferably a temperature at which a part becomes a gas and the rest becomes a liquid (that is, a temperature at which reflux is possible). The temperature in the heat treatment step is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, and further preferably 350 ° C. or higher. For reference, the softening point of the coal pitch is about 200 to 350 ° C. For this reason, when using coal pitch as pitches, it is preferable to perform a heat treatment process at 350 degreeC or more. Moreover, if it is 350 degreeC or more, also when using pitches other than coal pitch, at least one part of pitches will soften (liquefy).

  By the way, when the temperature in the heat treatment process is excessively high, the pitches may be modified (graphitized). In this case, sulfur cannot be sufficiently taken into pitches. For this reason, it is preferable that the temperature in the heat treatment step is lower than the modification temperature of the pitches. If the temperature in the heat treatment step is 600 ° C. or lower, the modification of pitches can be suppressed. The temperature in the heat treatment step is more preferably 600 ° C. or less, and further preferably 500 ° C. or less. Furthermore, considering the above-mentioned softening of pitches, the temperature in the heat treatment step is preferably 200 ° C. or more and 600 ° C. or less, more preferably 300 ° C. or more and 500 ° C. or less, and 350 ° C. or more and 500 ° C. or less. Is more preferable.

  When sulfur is refluxed in the heat treatment step, the mixed raw material may be heated so that part of the mixed raw material becomes gas and part becomes liquid. In other words, the temperature of the mixed raw material may be a temperature equal to or higher than the temperature at which sulfur is vaporized. Vaporization here refers to the phase change of sulfur from a liquid or solid to a gas, and may be any of boiling, evaporation, and sublimation.

  The heat treatment step is preferably performed in a non-oxidizing atmosphere as in the case of producing sulfur-modified PAN.

  The shape of the pitches and sulfur, the particle size, etc. are not particularly limited. This is because the pitches and sulfur are brought into contact with each other in a liquid state in the heat treatment step, so that the pitches and sulfur are in sufficient contact even when the pitches have a non-uniform or large particle size. The pitches and sulfur in the mixed raw material are preferably uniformly dispersed, but may be non-uniform. The mixed raw material may be composed only of pitches and sulfur, or may be blended with a general material (such as a conductive aid) that can be blended with the positive electrode active material.

  The heating time in the heat treatment step may be appropriately set according to the heating temperature, and is not particularly limited. When heating at the preferable temperature mentioned above, it is preferable to heat about 10 minutes-10 hours, and it is more preferable to heat for 30 minutes-6 hours.

  There is also a preferred range for the mixing ratio of pitches and sulfur in the mixed raw material. If the amount of sulfur added to the pitches is too small, a sufficient amount of sulfur cannot be taken into the pitches. If the amount of sulfur added to the pitches is too large, free sulfur (single sulfur) is contained in the sulfur-modified pitch. This is because a large amount remains to contaminate the electrolytic solution in the nonaqueous electrolyte secondary battery. The mixing ratio of pitches and sulfur in the mixed raw material is preferably 1: 0.5 to 1:10 by mass ratio, more preferably 1: 1 to 1: 7, and 1: 2 A ratio of 1: 5 is particularly preferred.

  Even when the amount of sulfur added to pitches is excessive, a sufficient amount of sulfur can be taken into the pitches in the heat treatment step. For this reason, when adding sulfur excessively with respect to pitches, the single-piece | unit sulfur removal process should just be given to the to-be-processed body after a heat processing process similarly to the manufacturing method of the sulfur modified PAN mentioned above.

When Raman spectroscopy of sulfur-modified pitch obtained by the above production method, there is a major peak in the vicinity of 1557cm ^-1 of Raman shift, and, 1371cm ^-1 in the range of 200cm ^-1 ~1800cm ^-1, 1049cm ^{-1, 994cm -1, 842cm -1, 612cm -1} , 412cm -1, 354cm -1, the peak respectively is present in the vicinity of 314 cm ^-1. Note that the Raman spectrum of sulfur-modified pitch is different from the Raman spectrum of sulfur-modified PAN described above.

  The sulfur-modified pitch preferably further includes sulfur-modified PAN as the second positive electrode active material. By further including this second positive electrode active material, the cycle characteristics are further improved when used in a non-aqueous electrolyte secondary battery. The reason is not clear, but it is considered that sulfur is immobilized because of the large binding force between PAN and sulfur.

  In order to produce a sulfur-modified pitch further containing the second positive electrode active material, the sulfur-modified pitch and the second positive electrode active material (that is, sulfur-modified PAN) can be physically mixed. However, since stability may be a concern, in order to increase the stability, a mixing step of mixing raw materials containing pitches, PAN powder, and sulfur powder to form a mixed raw material, It is desirable to perform a heat treatment step of heating. As the PAN powder, those having a mass average molecular weight in the range of about 10,000 to 300,000 are preferable. Moreover, about the particle size of PAN, when it observes with an electron microscope, what is in the range of about 0.5-50 micrometers is preferable, and what is in the range of about 1-10 micrometers is more preferable.

  As a result of elemental analysis of the sulfur-modified pitch, carbon, nitrogen, and sulfur were detected. In some cases, small amounts of oxygen and hydrogen were detected. Accordingly, the sulfur-modified pitch contains at least one of nitrogen, oxygen, sulfur compounds and the like as impurities in addition to C and S.

[3] Sulfur modified PAH
Sulfur-modified PAH has a carbon skeleton derived from at least one polycyclic aromatic hydrocarbon (PAH) formed by condensation of three or more six-membered rings. PAH is a general term for hydrocarbons condensed with aromatic rings that do not contain heteroatoms or substituents. There are four-membered rings, five-membered rings, six-membered rings, and seven-membered rings. In the invention, among acenes having a structure in which three or more six-membered rings that are benzene rings are connected in a straight chain, and compounds having a structure in which three or more six-membered rings are not straight but bent It is preferable to use at least one kind and sulfur.

  Examples of acenes that are polycyclic aromatic hydrocarbons in which a plurality of aromatic rings share a side and are connected in a straight chain include bicyclic naphthalene, tricyclic anthracene, tetracyclic tetracene, pentacyclic pentacene, 6 There are ring hexacene, 7 ring heptacene, 8 ring octacene, 9 ring nonacene, and 10 or more aromatic rings, and at least one selected from these groups can be used. Among them, those having 3 to 6 rings having high stability are desirable.

  Polycyclic aromatic hydrocarbons having a structure in which three or more six-membered rings are not straight but bent include phenanthrene, benzopyrene, chrysene, pyrene, picene, perylene, triphenylene, coronene, and more rings. There are those in which the above aromatic rings are linked, and at least one selected from these groups can be used.

  Sulfur-modified PAH can be produced by the same method as sulfur-modified pitch.

  In the heat treatment step, the polycyclic aromatic hydrocarbon and sulfur are reacted. In this reaction, it is desirable to react with the amount of sulfur being excessive with respect to the amount of polycyclic aromatic hydrocarbons to obtain a positive electrode active material containing sulfur at a high concentration. It is desirable that the temperature of the heat treatment step be such that at least a part of the polycyclic aromatic hydrocarbon and at least a part of sulfur are liquid. By doing so, it is possible to obtain a sulfur-modified PAH in which the contact area between the polycyclic aromatic hydrocarbon and sulfur can be sufficiently increased, sulfur is sufficiently contained, and sulfur desorption is suppressed.

  There is a preferable range for the blending ratio of the polycyclic aromatic hydrocarbon and sulfur in the mixed raw material. If the amount of sulfur in the polycyclic aromatic hydrocarbon is too small, a sufficient amount of sulfur cannot be taken into the polycyclic aromatic hydrocarbon, and if the amount of sulfur in the polycyclic aromatic hydrocarbon is excessive, sulfur modification This is because a large amount of free sulfur (single sulfur) remains in the PAH and contaminates the electrolyte solution in the non-aqueous electrolyte secondary battery. The blending ratio of the polycyclic aromatic hydrocarbon and sulfur in the mixed raw material is preferably 1: 0.5 to 1:10 of polycyclic aromatic hydrocarbon: sulfur in a mass ratio, and 1: 1 to 1 : 7 is more preferable, and 1: 2 to 1: 5 is particularly preferable.

  If the amount of sulfur added to the polycyclic aromatic hydrocarbon is excessive, a sufficient amount of sulfur can be easily taken into the polycyclic aromatic hydrocarbon in the heat treatment step. And even if it mix | blends sulfur more than necessary with respect to polycyclic aromatic hydrocarbon, by performing the simple substance sulfur removal process which removes excess simple sulfur from the to-be-processed object after a heat treatment process, the simple substance sulfur mentioned above The adverse effect by can be suppressed. Specifically, when the mixing ratio of the polycyclic aromatic hydrocarbon and sulfur in the mixed raw material is 1: 2 to 1:10 by mass ratio, the object to be treated after the heat treatment step is 200 ° C. to By heating at 250 ° C. (single sulfur removal step), a sufficient amount of sulfur can be taken into the polycyclic aromatic hydrocarbon, and adverse effects due to the remaining simple sulfur can be suppressed. When the single sulfur removal step is not performed on the target object after the heat treatment step, this target object may be used as it is as the sulfur-modified PAH. Moreover, what is necessary is just to use the to-be-processed body after a simple sulfur removal process as sulfur modified PAH, when performing the simple substance sulfur removal process to the to-be-processed body after a heat treatment process.

For example, when pentacene is selected as the polycyclic aromatic hydrocarbon which is a starting material, the sulfur-modified PAH is considered to have a structure similar to hexathiapentacene, but the structure is not clear. In addition, the sulfur positive electrode active material using anthracene as the polycyclic aromatic hydrocarbon has peaks in the vicinity of 1056 cm ⁻¹ and 840 cm ^{−1 in} the FT-IR spectrum, and the FT-IR spectrum of anthracene. Since it is completely different from FT, it can be identified by FT-IR spectrum.

  When elemental analysis of sulfur-modified PAH is performed, sulfur (S) and carbon (C) occupy most, and small amounts of oxygen and hydrogen are detected. It is desirable that the composition ratio of sulfur (S) and carbon (C) is included in the range of 1/5 or more in terms of atomic ratio (S / C). If the amount of sulfur is less than this range, the charge / discharge characteristics may be deteriorated when used as a positive electrode active material for a non-aqueous electrolyte secondary battery.

  It is desirable that the sulfur-modified PAH further includes a second positive electrode active material (sulfur-modified PAN) as in the case of using the polyisoprene described above. The mixing amount, production method, and the like are the same as in the case of sulfur-modified polyisoprene.

B. Sulfur Fluorine Introducing Compound The sulfur fluorine introducing compound is a compound in which fluorine is introduced while leaving at least a part of the sulfur-modified portion in the sulfur-modified product. Here, the sulfur-modified part refers to a part in which sulfur is modified into a carbon compound. The sulfur-modified portion is, for example, a portion where sulfur is chemically bonded or coordinated to the carbon compound by introduction of sulfur, or a portion where the chemical structure of the carbon compound is changed by introduction of sulfur.

  “Introducing fluorine” means binding or coordination of fluorine to the sulfur-modified product. There may or may not be a change in the chemical or steric structure of the sulfur-modified product.

  The sulfur-fluorine-introducing compound has a carbon compound as a basic structure, and in addition to sulfur, fluorine is also a constituent element. The sulfur fluorine-introducing compound contains sulfur, so that the battery capacity is increased, and the potential is increased by containing fluorine having a high electron affinity. Therefore, the positive electrode active material made of such a sulfur fluorine-introducing compound has a high battery capacity and potential, and is excellent in cycle characteristics.

  In introducing fluorine into the sulfur-modified product, for example, the sulfur-modified product is brought into contact with a fluorinating agent. In this case, it is considered that fluorine in the fluorinating agent substitutes for sulfur in the sulfur-modified portion of the sulfur-modified product and bonds to carbon.

  Fluorine may be uniformly introduced into the sulfur fluorine-introducing compound, but fluorine may be partially introduced. For example, when the sulfur fluorine-introducing compound is in the form of particles, fluorine may be uniformly introduced into the entire particle, or fluorine may be unevenly distributed on the particle surface.

  The composition ratio of fluorine (F) and carbon (C) in the sulfur fluorine-introducing compound is preferably 1/100 or more and 150/100 or less in terms of atomic ratio (F / C). If the fluorine composition ratio is too small, the potential of the sulfur fluorine-introducing compound does not increase, and if the fluorine composition ratio is too large, the sulfur content in the sulfur-fluorine introducing compound is relatively reduced, and the battery capacity is reduced. There is a fear.

  The composition ratio of sulfur (S) and carbon (C) in the sulfur fluorine-introducing compound is preferably 1/100 or more and 150/100 or less in terms of atomic ratio (S / C). If the sulfur composition ratio is too small, the battery capacity of the sulfur fluorine-introducing compound is lowered, and if the sulfur composition ratio is too large, the fluorine content in the sulfur-fluorine introducing compound is relatively reduced, There is a possibility that the potential cannot be increased.

As the fluorinating agent for introducing fluorine into the sulfur-modified product, anhydrous hydrogen fluoride (HF) or fluorine gas (F ₂ ) is preferably used.

  When fluorine gas is used as the fluorinating agent, for example, a sulfur-modified product is arranged in the fluorine gas. In the reaction between the fluorine gas and the sulfur-modified product, it is only necessary to replace part of the sulfur in the sulfur-modified product with fluorine, so it is better to avoid the reaction in an extreme environment. For example, the reaction between the sulfur-modified product and the fluorine gas may be performed at a temperature of −40 ° C. or more and room temperature (about 25 ° C.) or less. If the reaction temperature is too low, the reaction is difficult to occur, and if the reaction temperature is too high, all sulfur in the sulfur-modified product may be substituted with fluorine.

  The produced sulfur fluorine-introducing compound is used as a positive electrode active material for a non-aqueous electrolyte secondary battery.

(Positive electrode for non-aqueous electrolyte secondary battery)
The positive electrode in the nonaqueous electrolyte secondary battery of the present invention can have the same structure as a general positive electrode for a nonaqueous electrolyte secondary battery. For example, a positive electrode can be manufactured by applying a positive electrode material in which a positive electrode active material, a conductive additive, a binder, and a solvent are mixed to a current collector.

  As a conductive support agent, the above-mentioned sulfur fluorine introduction | transduction compound is contained as a vapor grown carbon fiber (Vapor Carbon Carbon: VGCF), carbon powder, and a carbon black positive electrode active material. Examples of the positive electrode include other than the positive electrode active material (CB), acetylene black (AB), ketjen black (KB), graphite, fine metal powders stable at the positive electrode potential such as aluminum and titanium.

  As binders, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethylcellulose (CMC), polyvinyl chloride (PVC) ), Methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP) and the like.

  Examples of the solvent include N-methyl-2-pyrrolidone, N, N-dimethylformaldehyde, alcohol, water and the like. These conductive assistants, binders and solvents may be used as a mixture of plural kinds. The blending amount of these materials is not particularly limited. For example, it is preferable to blend about 20 to 100 parts by mass of the conductive additive and about 10 to 20 parts by mass of the binder with respect to 100 parts by mass of the positive electrode active material. As another method, a mixture of the above positive electrode active material, the above-described conductive additive and binder is kneaded with a mortar or a press machine to form a film, and the film mixture is formed into a current collector with a press machine or the like. The positive electrode for nonaqueous electrolyte secondary batteries can also be manufactured by crimping | bonding.

  What is necessary is just to use what is generally used for the positive electrode for nonaqueous electrolyte secondary batteries as a collector. For example, current collectors include aluminum foil, aluminum mesh, punched aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel nonwoven fabric, copper foil, copper mesh Punching copper sheet, copper expanded sheet, titanium foil, titanium mesh, carbon paper (nonwoven fabric / woven fabric) and the like are exemplified. Among these, a carbon paper current collector made of carbon having a high graphitization degree is suitable as a current collector for a positive electrode active material because it does not contain hydrogen and has low reactivity with sulfur and fluorine. As a raw material for carbon fiber having a high degree of graphitization, various pitches (that is, by-products such as petroleum, coal, coal tar, etc.), PAN fibers, etc., which are carbon fiber materials can be used.

  The non-aqueous electrolyte secondary battery of the present invention preferably contains a conductive material in the positive electrode. The conductive material refers to a material that exhibits high electrical conductivity or that can greatly improve the ionic conductivity of the positive electrode. By including a conductive material in the positive electrode, the electrical conductivity and / or ionic conductivity of the entire positive electrode can be improved, and the discharge rate characteristics of the nonaqueous electrolyte secondary battery can be improved. As the material for the conductive material (conductive material), it is preferable to use a material that exhibits the above function in the state of sulfide. This is because the function of the conductive material is not impaired even if it is sulfided by sulfur as a raw material of the positive electrode active material.

  As the conductive material, at least one metal selected from the group consisting of a fourth periodic metal, a fifth periodic metal, a sixth periodic metal, and a rare earth element, or a sulfide thereof can be used. In addition, the 4th periodic metal, the 5th periodic metal, and the 6th periodic metal as used in this specification are based on a periodic table. For example, the fourth periodic metal refers to a metal included in the fourth periodic element in the periodic table. The conductive material is preferably one that exhibits high electrical conductivity in the state of sulfide or that can greatly improve the ionic conductivity of the positive electrode. For example, Ti, Fe, La, Ce, Pr, Nd Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, Pb, or a sulfide thereof is preferable. . In the positive electrode, the conductive material consists of both the metal and its sulfide, or consists only of the metal sulfide. These conductive material materials preferably contain a large amount of sulfide, and more preferably consist only of sulfide. By blending the metal into the positive electrode in a sulfide state, the conductive material and the positive electrode active material containing sulfur can be easily combined, and the conductive material and the positive electrode active material are dispersed substantially uniformly. Further, by using sulfide as the conductive material, there is an advantage that the ratio of the metal and sulfur in the conductive material can be easily controlled within a desired range.

Specifically, as a conductive material having high electrical conductivity and / or ion conductivity (more specifically, lithium ion conductivity, sodium ion conductivity), TiS ₂ , FeS ₂ , Me ₂ S ₃ (wherein Me is a kind selected from Ti, La, Ce, Pr, Nd and Sm), MeS (wherein Me is a kind selected from Ti, La, Ce, Pr, Nd and Sm), Me ₃ S ₄ (wherein Me is a kind selected from Ti, La, Ce, Pr, Nd, Sm), Me _x S _y (wherein Me is Ti, Fe, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, and Pb, and x and y are arbitrary integers. In this case, as the conductive material, Ti, Fe, La, Ce, Pr, Nd, Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, What is necessary is just to use at least 1 type chosen from Pb as it is or in the state of sulfide like said conductive material. By using these conductive material materials, the electrical conductivity and / or ionic conductivity of the entire positive electrode can be improved, and the discharge rate characteristics of the nonaqueous electrolyte secondary battery can be improved. In view of the raw material cost, ease of procurement, and the amount of resources, TiS _z (wherein z is 0.1 to 2) is more preferably used, and TiS ₂ is particularly preferably used.

  The compounding ratio of the positive electrode active material and the conductive material is preferably 10: 0.5 to 10: 5, and more preferably 10: 1 to 10: 3, in terms of mass ratio. This is because if the blending amount of the conductive material is excessive, the amount of the positive electrode active material relative to the entire positive electrode is excessively small. In order to disperse the conductive material in the positive electrode active material substantially uniformly, the conductive material is preferably in the form of powder. The conductive material preferably has a particle size measured with an electron microscope or the like of 0.1 to 100 μm, more preferably 0.1 to 50 μm, and even more preferably 0.1 to 20 μm.

  In addition, in order to identify mixing of a positive electrode active material and a conductive material, it can carry out by X-ray diffraction analysis as follows.

The main diffraction peak positions of La ₂ S ₃ by the ASTM card are 24.7, 25.1, 26.9, 33.5, 37.2, 42.8 °, and the like. The main diffraction peak positions of TiS ₂ are 15.5, 34.2, 44.1, 53.9 °, and the like. The main diffraction peak positions of Ti are 35.1, 38.4, 40.2, 53.0 °, and the like. The main diffraction peak positions of MoS ₂ are 14.4, 32.7, 33.5, 35.9, 39.6, 44.2, 49.8, 56.0, 58.4 °, and the like. The main diffraction peak positions of Fe are 44.7, 65.0, 82.3 °, and the like. In the positive electrode active material using PAN, a broad single peak is recognized around 25 ° in the diffraction angle (2θ) range of 20 to 30 °. On the other hand, in the positive electrode active material-conductive material composite containing the conductive material, a peak derived from the conductive material appears. For example, when La ₂ S ₃ is used as the conductive material, La ₂ S ₃ peaks appear in the vicinity of 24.7, 25.1, 33.5, and 37.2 °. This peak can be confirmed using the La ₂ S ₃ as conductive material (i.e. the positive electrode contains La ₂ S ₃ as conductive material). Further, when TiS ₂ was used as the conductive material, almost no peak was confirmed. When Ti is used as the conductive material, Ti peaks appear in the vicinity of 35.1, 38.4, 40.2, and 53.0 °. From this peak, it can be confirmed that Ti was used as the conductive material. As described above, when TiS ₂ is used as the conductive material, its presence cannot be confirmed by X-ray diffraction. However, if other analysis methods such as ICP elemental analysis or fluorescent X-ray analysis are used, Ti is not detected. Since it can be detected, the addition of TiS ₂ can be estimated even when no peak is confirmed by X-ray diffraction. Further, when MoS ₂ is used as the conductive material, it is around 14.4, 32.7, 33.5, 35.9, 39.6, 44.2, 49.8, 56.0, 58.4 °. The peak of MoS ₂ appears. This peak can be confirmed with MoS ₂ as a conductive material (i.e. the positive electrode contains MoS ₂ as conductive material). When Fe is used as the conductive material, FeS ₂ peaks appear in the vicinity of 28.5, 33.0, 37.1, 40.8, 47.4, 56.3, and 59.0 °. From this peak, it can be confirmed that Fe is used as the conductive material (that is, the positive electrode contains at least one of FeS, FeS ₂ , and Fe ₂ S ₃ as the conductive material).

(Non-aqueous electrolyte secondary battery)
Hereinafter, the structure of the nonaqueous electrolyte secondary battery using the above-described positive electrode active material for the positive electrode will be described. The positive electrode is as described above.

[Negative electrode]
As the negative electrode active material for the non-aqueous electrolyte secondary battery of the present invention, metallic lithium or metallic sodium can be used. When metallic lithium is used for the negative electrode active material, the nonaqueous electrolyte secondary battery of the present invention is a lithium secondary battery. When metallic sodium is used for the negative electrode active material, the nonaqueous electrolyte secondary battery of the present invention is a sodium secondary battery (so-called sodium sulfur battery).

  As the current collector for the negative electrode, aluminum foil, aluminum mesh, punched aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, stainless steel expanded sheet, nickel foam, nickel non-woven fabric, copper foil, Examples include copper mesh, punched copper sheet, copper expanded sheet, titanium foil, titanium mesh, carbon paper (nonwoven fabric / woven fabric) and the like.

〔Electrolytes〕
As the electrolyte used for the nonaqueous electrolyte secondary battery, an electrolyte obtained by dissolving an alkali metal salt as an electrolyte in an organic solvent can be used. As the organic solvent, it is preferable to use at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, isopropyl methyl carbonate, vinylene carbonate, γ-butyrolactone, and acetonitrile. . As the electrolyte, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiI, LiClO ₄ or the like can be used when lithium is used as the negative electrode active material. When sodium is used as the negative electrode active material, it is selected from NaPF ₆ , NaBF ₄ , NaClO ₄ , NaAsF ₆ , NaSbF ₆ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower fatty acid sodium salt, NaAlCl _{4 and the} like. One kind or a plurality of kinds can be used. Among them, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , NaPF ₆ , NaBF ₄ , NaAsF ₆ , NaSbF ₆ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) _{2 and the} like contain fluorine (F). Therefore, it is preferably used. The concentration of the electrolyte may be about 0.5 mol / L to 1.7 mol / L. Note that the electrolyte is not limited to liquid, and may be solid (for example, a polymer gel).

[Others]
The nonaqueous electrolyte secondary battery may include a member such as a separator in addition to the above-described negative electrode, positive electrode, and electrolyte. The separator is interposed between the positive electrode and the negative electrode, allows ions to move between the positive electrode and the negative electrode, and prevents an internal short circuit between the positive electrode and the negative electrode. If the non-aqueous electrolyte secondary battery is a sealed type, the separator is also required to have a function of holding an electrolytic solution. As the separator, it is preferable to use a thin, microporous or non-woven membrane made of polyethylene, polypropylene, PAN, aramid, polyimide, cellulose, glass or the like. The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and can be various shapes such as a cylindrical shape, a stacked shape, and a coin shape.

  Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be specifically described.

Example 1
The nonaqueous electrolyte secondary battery of Example 1 is a lithium secondary battery. The nonaqueous electrolyte secondary battery of Example 1 was produced as follows.

[1] Mixed raw material A sulfur powder having a particle size of 50 μm or less when classified using a sieve was prepared. A PAN powder having a particle size in the range of 0.2 μm to 2 μm when prepared with an electron microscope was prepared. 5 parts by mass of sulfur powder and 1 part by mass of PAN powder were mixed and pulverized in a mortar to obtain a mixed raw material.

[2] Apparatus As shown in FIG. 3, the reaction apparatus 1 includes a reaction vessel 2, a lid 3, a thermocouple 4, an alumina protective tube 40, two alumina tubes (gas introduction tube 5, gas discharge tube 6), argon gas It has a pipe 50, a gas tank 51 containing argon gas, a trap pipe 60, a trap tank 62 containing a sodium hydroxide aqueous solution 61, an electric furnace 7, and a temperature controller 70 connected to the electric furnace.

  As the reaction vessel 2, a bottomed cylindrical glass tube (made of quartz glass) was used. In the heat treatment step described later, the mixed raw material 9 was accommodated in the reaction vessel 2. The opening of the reaction vessel 2 was closed with a glass lid 3 having three through holes. An alumina protective tube 40 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) accommodating the thermocouple 4 was attached to one of the through holes. A gas introduction pipe 5 (alumina SSA-S, manufactured by Nikkato Corporation) was attached to the other one of the through holes. A gas exhaust pipe 6 (alumina SSA-S, manufactured by Nikkato Corporation) was attached to the remaining one of the through holes. The reaction vessel 2 had an outer diameter of 60 mm, an inner diameter of 50 mm, and a length of 300 mm. The alumina protective tube 40 had an outer diameter of 4 mm, an inner diameter of 2 mm, and a length of 250 mm. The gas introduction pipe 5 and the gas discharge pipe 6 had an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 150 mm. The tips of the gas introduction pipe 5 and the gas discharge pipe 6 were exposed to the outside of the lid 3 (inside the reaction vessel 2). The length of this exposed portion was 3 mm. The tips of the gas introduction pipe 5 and the gas discharge pipe 6 become approximately 100 ° C. or less in a heat treatment process described later. For this reason, the sulfur vapor generated in the heat treatment step does not flow out of the gas introduction pipe 5 and the gas discharge pipe 6 but is returned (refluxed) to the reaction vessel 2.

  The tip of the thermocouple 4 placed in the alumina protective tube 40 indirectly measured the temperature of the mixed raw material 9 in the reaction vessel 2. The temperature measured by the thermocouple 4 was fed back to the temperature controller 70 of the electric furnace 7.

  An argon gas pipe 50 was connected to the gas introduction pipe 5. The argon gas pipe 50 was connected to a gas tank 51 containing argon gas. One end of a trap pipe 60 was connected to the gas discharge pipe 6. The other end of the trap pipe 60 was inserted into the sodium hydroxide aqueous solution 61 in the trap tank 62. The trap pipe 60 and the trap tank 62 are traps for hydrogen sulfide gas generated in a heat treatment process to be described later.

[3] Heat treatment step The reaction vessel 2 containing the mixed raw material 9 was placed in an electric furnace 7 (crucible furnace, opening width φ80 mm, heating height 100 mm). At this time, argon was introduced into the reaction vessel 2 through the gas introduction tube 5. The flow rate of argon gas at this time was 100 ml / min. Ten minutes after the start of the introduction of the argon gas, heating of the mixed raw material 9 in the reaction vessel 2 was started while continuing the introduction of the argon gas. The temperature rising rate at this time was 5 ° C./min. When the mixed raw material 9 reached 100 ° C., the introduction of argon gas was stopped while continuing to heat the mixed raw material 9. Gas was generated when the mixed raw material 9 reached about 200 ° C. The heating was stopped when the mixed raw material 9 reached 360 ° C. After stopping the heating, the temperature of the mixed raw material 9 increased to 400 ° C. and then decreased. Therefore, in this heat treatment step, the mixed raw material 9 was heated to 400 ° C. Thereafter, the mixed raw material 9 was naturally cooled, and when the mixed raw material 9 was cooled to room temperature (about 25 ° C.), the product (that is, the object to be treated after the heat treatment step) was taken out from the reaction vessel 2. The heating time at this time was about 10 minutes at 400 ° C., and sulfur was refluxed.

[4] Elemental sulfur removal step In order to remove elemental sulfur (free sulfur) remaining in the object to be treated after the heat treatment step, the following steps were performed.

  The object to be treated after the heat treatment step was pulverized in a mortar. 2 g of the pulverized product was placed in a glass tube oven and heated at 200 ° C. for 3 hours while being vacuumed. The temperature elevation temperature at this time was 10 ° C./min. By this process, the elemental sulfur remaining in the object to be treated after the heat treatment process was evaporated and removed, and a sulfur-modified PAN not including (or substantially not including) elemental sulfur was obtained.

Elemental analysis of sulfur-modified PAN confirmed the presence of sulfur, carbon, and the like. When the Raman spectrum of sulfur-modified PAN was measured, a peak peculiar to sulfur-modified PAN was observed in the vicinity of 1331 cm ^{−1 of} the Raman shift.

[5] Fluorination step Sulfur-modified PAN was immersed in anhydrous hydrogen fluoride at -30 ° C for 0.2 hours to introduce fluorine.

Elemental analysis of the produced fluorinated modified carbon material revealed the presence of fluorine, sulfur and carbon. Further, when the Raman spectrum was measured, a peak peculiar to sulfur-modified PAN was recognized in the vicinity of 1331 cm ^{−1 of} the Raman shift. This shows that the modified part of sulfur-modified PAN remains even after the introduction of fluorine.

<Production of lithium secondary battery>
[1] Positive electrode 60 parts by mass of the positive electrode active material obtained in the elemental sulfur removal step, 20 parts by mass of ketjen black (KB), 20 parts by mass of polyimide (PI), and N-methyl-2-pyrrolidone (NMP) Were mixed to prepare a slurry.

  On the other hand, a current collector prepared by punching carbon paper (“TGP-H-030” manufactured by Toray Industries, Inc.) to a diameter of 13 mm is prepared, and after filling the slurry, dried at 200 ° C. under reduced pressure for 2 hours to produce a positive electrode. did.

[2] Negative electrode As the negative electrode, a disc-shaped lithium foil formed of metallic lithium with a thickness of about 0.5 mm and a diameter of 13 mm was used.

[3] Electrolytic Solution As the electrolytic solution, a nonaqueous electrolyte in which LiPF ₆ was dissolved in propylene carbonate was used. The concentration of LiPF ₆ in the electrolytic solution was 1.0 mol / L.

[4] Battery A coin battery was manufactured using the positive electrode, the negative electrode and the electrolytic solution obtained in [1], [2] and [3] above. Details sandwiched, within a dry room, and a separator made of polypropylene microporous multi-porous film having a thickness of 25 [mu] m ( "Celgard2400" Celgard Inc.), a glass nonwoven fabric filter having a thickness of 500 [mu] m, the between the positive electrode and the negative electrode Thus, an electrode body battery was obtained. This electrode body battery was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.) made of a stainless steel container. The electrolyte solution obtained in [3] was injected into the battery case. The battery case was sealed with a caulking machine to obtain the nonaqueous electrolyte secondary battery of Example 1.

  The operation of the nonaqueous electrolyte secondary battery of Example 1 was confirmed.

(Example 2)
The nonaqueous electrolyte secondary battery of Example 2 is different in that fluorinated modified anthracene is used as the positive electrode active material instead of fluorinated modified PAN. Hereinafter, a method for producing the fluorinated modified anthracene will be described.

  First, in the mixing step, sulfur powder having an average particle size of 50 μm was mixed with anthracene powder to prepare a mixed raw material. The mixing ratio of anthracene and sulfur in the mixed raw material was such that anthracene was 1 part by mass with respect to 5 parts by mass of sulfur.

  In the heat treatment step, the mixed raw material was subjected to a heat treatment using the same reaction apparatus as in Example 1 and refluxing sulfur under the same conditions.

  In the elemental sulfur removal step, the object to be treated after the heat treatment step was pulverized in a mortar. 2 g of the pulverized product was placed in a glass tube oven and heated at 200 ° C. for 3 hours while being vacuumed. The temperature elevation temperature at this time was 10 ° C./min. By this step, the elemental sulfur remaining in the object to be treated after the heat treatment step was evaporated and removed, and a sulfur-modified anthracene containing no (or almost not including) elemental sulfur was obtained.

  In the fluorination step, anhydrous hydrogen fluoride was used as a fluorinating agent, and fluorine was introduced in the same manner as in Example 1 above for sulfur-modified anthracene. Thereby, fluorinated modified anthracene was obtained.

When elemental analysis was performed on the obtained fluorinated modified anthracene, the presence of fluorine, sulfur, carbon and the like was confirmed. The measured FT-IR spectrum, a near 1056cm ^-1, there are respectively a peak and around 840 cm ^-1, the was quite different from the FT-IR spectrum of the anthracene. This shows that the modified part of sulfur-modified anthracene remains even after the introduction of fluorine.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 using the above fluorinated modified anthracene as the positive electrode active material. The operation of the produced nonaqueous electrolyte secondary battery was confirmed.

1: Reactor 2: Reaction vessel 3: Lid 4: Thermocouple 5: Gas introduction pipe 6: Gas discharge pipe 7: Electric furnace

Claims (7)

  A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a sulfur-fluorine-introducing compound obtained by introducing sulfur (S) and fluorine (F) into a carbon compound.   The sulfur fluorine-introducing compound is obtained by modifying the carbon compound with sulfur to obtain a sulfur-modified product, and then introducing fluorine while leaving at least a part of the sulfur-modified portion modified with sulfur in the sulfur-modified product. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.   3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon compound is composed of at least one selected from polyacrylonitrile, pitches, and polycyclic aromatic hydrocarbons formed by condensation of three or more six-membered rings. 4. Positive electrode active material. A nonaqueous electrolyte secondary battery comprising the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3 , a negative electrode active material, and an electrolytic solution. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 ,
A sulfur-modified product obtained by modifying the carbon compound with sulfur is brought into contact with a fluorinating agent to leave at least a part of the sulfur-modified portion modified with sulfur in the sulfur-modified product. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein fluorine is introduced to obtain the sulfur fluorine-introducing compound. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5 , wherein the fluorinating agent comprises at least one of anhydrous hydrogen fluoride and fluorine gas. The non-aqueous electrolyte secondary battery according to claim 5 or 6 , wherein the sulfur-modified product is obtained by performing a mixing step of mixing a carbon compound and sulfur to form a mixed raw material, and a heat treatment step of heating the mixed raw material. For producing a positive electrode active material for use.

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