JP5263557B2 - Method for producing positive electrode for nonaqueous electrolyte secondary battery, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

Disclosed are: a method of manufacture whereby a non-aqueous electrolyte storage battery containing a sulphur-based positive electrode active substance can easily be manufactured; and a positive electrode and non-aqueous electrolyte storage battery manufactured by this method. In the method of manufacture of the non-aqueous electrolyte storage battery positive electrode, there is provided a step of heat processing in which a mixed raw material containing sulphur (S), a carrier and a blending agent is heated. As the blending agent, there may be employed material containing at least one type of metal selected from the group consisting of 4th period metals, 5th period of metals, 6th period metals and rare earth elements, and metallic compounds.

Description

  The present invention includes a method for producing a positive electrode for a non-aqueous electrolyte secondary battery containing a sulfur-based positive electrode active material, a positive electrode for a non-aqueous electrolyte secondary battery produced by this method, and a positive electrode for this non-aqueous electrolyte secondary battery. The present invention relates to a non-aqueous electrolyte secondary battery.

  As a positive electrode active material for a non-aqueous electrolyte secondary battery, a technique using sulfur is known. As a positive electrode active material of a lithium ion secondary battery, a material containing a rare metal such as cobalt or nickel is generally used. However, these metals have a small amount of circulation and are expensive. Compared to these rare metals, the current sulfur circulation is large. For this reason, sulfur as a positive electrode active material has attracted attention. Moreover, when using sulfur as a positive electrode active material of a lithium ion secondary battery, a nonaqueous electrolyte secondary battery having a large charge / discharge capacity can be obtained. For example, the charge / discharge capacity of a lithium ion secondary battery using sulfur as a positive electrode active material is approximately six times the charge / discharge capacity of a lithium ion secondary battery using a lithium cobaltate positive electrode material, which is a common positive electrode material. is there.

  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.

  In order to suppress elution of sulfur into the electrolyte, a positive electrode active material (hereinafter referred to as a sulfur-based positive electrode active material) obtained by heat-treating a mixture of a carrier and sulfur has been proposed. The carrier in the present specification refers to a substance that can fix sulfur chemically or physically. That is, the carrier may be chemically bonded to sulfur or physically hold sulfur. The fixing strength of sulfur by the support is not particularly limited.

  Patent Document 1 introduces a technique using polysulfide carbon containing carbon and sulfur as main constituent elements as a sulfur-based positive electrode active material. This polysulfide carbon is obtained by adding sulfur to a carrier, that is, a linear unsaturated polymer. According to Patent Document 1, this sulfur-based positive electrode active material can suppress a decrease in charge / discharge capacity of a lithium ion secondary battery due to repeated charge / discharge. 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.

  In addition, the inventors of the present invention invented a sulfur-based positive electrode active material obtained by heat-treating a mixture of polyacrylonitrile (hereinafter abbreviated as PAN if necessary) and sulfur (see, for example, Patent Document 2). ). The charge / discharge capacity of a lithium ion secondary battery using this positive electrode active material for the positive electrode is large, and the lithium ion secondary battery using this positive electrode active material for the positive electrode is excellent in cycle characteristics. Moreover, this positive electrode active material can be used also as positive electrode active materials, such as a sodium secondary battery.

  However, on the other hand, a process of obtaining a sulfur-based positive electrode active material by heat treating a carrier such as PAN and sulfur (referred to as a heat treatment process) is relatively high temperature and requires a relatively long time. For this reason, the manufacturing method which can manufacture a sulfur type positive electrode active material more easily was desired.

JP 2002-154815 A International Publication No. 2010/044437

  This invention is made | formed in view of the said situation, the manufacturing method which can manufacture easily the positive electrode for nonaqueous electrolyte secondary batteries containing a sulfur type positive electrode active material, the positive electrode manufactured by this manufacturing method, and non- An object is to provide a water electrolyte secondary battery.

The method for producing a non-aqueous electrolyte secondary battery of the present invention that solves the above problems includes a heat treatment step of heating a mixed raw material containing sulfur, a carrier and a compounding material at a temperature at which sulfur melts ,
The carrier contains carbon (C), and is at least one selected from polyacrylonitrile, pitch-based carriers, acenes, and plant-based carriers.
The compounding material is at least one selected from iron oxide, iron chloride, and titanium .

Moreover, the positive electrode for a nonaqueous electrolyte secondary battery of the present invention that solves the above problems is manufactured by the method for manufacturing a positive electrode for a nonaqueous electrolyte secondary battery of the present invention,
It includes a sulfur-based positive electrode active material containing sulfur (S) and carbon (C), and a metal or metal compound containing iron (Fe) or titanium (Ti) .

  Moreover, the nonaqueous electrolyte secondary battery of the present invention that solves the above-described problems includes the positive electrode for a nonaqueous electrolyte secondary battery of the present invention as a positive electrode.

  According to the production method of the present invention, a positive electrode for a nonaqueous electrolyte secondary battery containing a sulfur-based positive electrode active material can be produced in a relatively short time and at a relatively low temperature. In addition, the nonaqueous electrolyte secondary battery provided with the positive electrode for a nonaqueous electrolyte secondary battery obtained by the production method of the present invention has a large capacity even if the positive electrode is produced under conditions where reaction does not easily occur. In addition, the battery characteristics are excellent.

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 a graph showing the result of having carried out X-ray diffraction of the sulfur modification pitch. It is a graph showing the result of Raman spectrum analysis of sulfur-modified pitch. It is explanatory drawing which represents typically the reaction apparatus used with the manufacturing method of the positive electrode of an Example. 3 is a graph showing discharge curves of lithium ion secondary batteries of Example 1, Example 2 and Comparative Example 1. FIG. 6 is a graph showing discharge rate characteristics (charge / discharge curves) of the lithium ion secondary battery of Example 3. 6 is a graph showing discharge rate characteristics (cycle characteristics) of the lithium ion secondary battery of Example 3. 6 is a graph showing discharge rate characteristics (cycle characteristics) of the lithium ion secondary battery of Example 4. 4 is a graph showing a result of X-ray diffraction of a sulfur-based positive electrode active material-compound material composite used for the positive electrode of Example 3. It is a graph showing the result of having carried out X-ray diffraction of the sulfur type positive electrode active material-compounding material composite used for the positive electrode of Example 4. FIG. 6 is a graph showing the result of X-ray diffraction of the sulfur-based positive electrode active material used for the positive electrode of Comparative Example 1.

  The method for producing a positive electrode for a nonaqueous electrolyte secondary battery of the present invention (hereinafter referred to as the production method of the present invention) includes a heat treatment step of heating a mixed raw material containing sulfur, a carrier, and a compounding material. The production method of the present invention produces a positive electrode containing at least a sulfur-based positive electrode active material. The positive electrode manufactured by the manufacturing method of the present invention (the positive electrode for a nonaqueous electrolyte secondary battery of the present invention, hereinafter abbreviated as the positive electrode of the present invention) may or may not contain a compounding material. That is, in the manufacturing method of this invention, you may remove a compounding material, after obtaining a sulfur type positive electrode active material. The nonaqueous electrolyte secondary battery of the present invention is a battery using the positive electrode of the present invention.

As the sulfur-based positive electrode active material, for example, the one disclosed in Patent Document 1 (using polysulfide carbon as a carrier) may be used, but in the present invention, it is disclosed in Patent Document 2. (Which uses PAN as a carrier) , a pitch-based carrier described later, a polycyclic aromatic hydrocarbon formed by condensation of three or more six-membered rings (hereinafter abbreviated as PAH as necessary) ), At least one selected from plant carriers . Hereinafter, a sulfur-based positive electrode active material using PAN as a carrier is referred to as sulfur-modified PAN. A sulfur-based positive electrode active material using a pitch-based carrier as a carrier is called sulfur-modified pitch. A sulfur-based positive electrode active material is called sulfur-modified PAH using PAH as a carrier.

  The method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention (hereinafter abbreviated as the production method of the present invention) can improve the speed of reaction for fixing sulfur to a carrier by using a compounding material. In addition, sulfur can be fixed to the support even under conditions that are not suitable for chemical reaction, for example, at a relatively low temperature.

(Method for producing positive electrode for non-aqueous electrolyte secondary battery)
<Combination material>
As the compounding material, it is conceivable to use at least one kind of metal or metal compound selected from the group consisting of the fourth period metal, the fifth period metal, the sixth period metal, and the rare earth element. At least one selected from iron, iron chloride, and titanium is used. The various metals or metal compounds described above promote some chemical reaction when sulfur is fixed to the support. That is, in the production method of the present invention, the compounding material is considered to function as a catalyst for the reaction in which sulfur is fixed to the support. Such a compounding material should just be said various metals or its compound (oxide, chloride, etc.), may be sulfide, and may be unsulfurized. That is, even if it is a compounding material of sulfide, it is only necessary to promote the reaction in which sulfur is fixed to the carrier. Moreover, after the compounding material which is non-sulfide reacts with sulfur to form a sulfide, the reaction in which sulfur is fixed to the carrier may be promoted.

  In the production method of the present invention, since the compounding material is blended in order to promote the reaction in which sulfur is fixed to the carrier, the sulfur-based positive electrode active material obtained by the production method of the present invention may contain the compounding material. However, it does not have to be included. For example, in the production method of the present invention, an aggregate-shaped compounding material that is easy to remove, such as a plate-like or net-like material, is removed after reacting with a simple substance and sulfur, so that the sulfur-based material does not contain a compounding material. A positive electrode active material can be manufactured.

  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. More specifically, Ti, Fe, La, Ce, Pr, Nd, Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, Pb, And at least one selected from the group consisting of these metal compounds (excluding sulfides).

  The mixing ratio of the carrier and the compounding material is preferably 10: 0.05 to 10: 5, more preferably 10: 1 to 10: 3, in terms of mass ratio. This is because if the amount of the compounding material is excessive, the amount of the positive electrode active material relative to the entire positive electrode is excessively small. As described above, in order to remove the compounding material after the reaction between sulfur and the carrier, the compounding material is preferably not in the form of powder but in the form of an aggregate such as a plate or net. On the other hand, in order to disperse the compounding material substantially uniformly in the sulfur-based positive electrode active material, the compounding material is preferably in a powder form. The compounding material preferably has a particle size measured using an electron microscope of 0.01 to 100 μm, more preferably 0.1 to 50 μm, and even more preferably 0.1 to 20 μm.

<Carrier>
[PAN]
When PAN is used as a carrier, the high capacity inherent in sulfur can be maintained, and elution of sulfur into the electrolyte is suppressed, so that the cycle characteristics are greatly improved. This is presumably because sulfur does not exist as a simple substance in the sulfur-based positive electrode active material but exists in a stable state in which it is fixed by bonding with PAN or the like. In the manufacturing method of the sulfur type positive electrode active material currently disclosed by patent document 2, sulfur is heat-processed with PAN. When PAN is heated, it is considered that PAN is three-dimensionally crosslinked to form a condensed ring (mainly a 6-membered ring) and close. For this reason, it is considered that sulfur is present in the sulfur-based positive electrode active material in a state of being combined with 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.

The PAN used as the carrier is preferably in the form of a powder, and preferably has a mass average molecular weight of about 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.

  The sulfur used for the sulfur-based positive electrode active material is also preferably in the form of powder. 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 the sulfur powder used for the sulfur-based positive electrode active material is not particularly limited, but is preferably 1: 0.5 to 1:10 by mass ratio, and 1: 0.5 to 1: 7 is more preferable, and 1: 2 to 1: 5 is even more preferable.

  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 above-described peaks exists in a range of approximately ± 8 cm ⁻¹ with the above-described 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 was measured with RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm ⁻¹ ) manufactured by JASCO Corporation. 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

〔pitch〕
In the present specification, the pitch-based carrier is a solid or semi-solid obtained by distilling various tars, petroleum and coals, and a synthetic material having a structure and / or composition similar to those materials. Refers to general. Specific examples of pitch-based carriers include coal pitch, petroleum pitch, mesophase pitch (anisotropic pitch), asphalt, coal tar, coal tar pitch, and organic obtained by polycondensation of condensed polycyclic aromatic hydrocarbon compounds. Synthetic pitch or organic synthetic pitch obtained by polycondensation of a heteroatom-containing condensed polycyclic aromatic hydrocarbon compound can be used. These are known as carbon materials containing condensed polycyclic aromatics.

  Coal tar, a kind of pitch-based carrier, 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.

  The pitch-based carrier is a mixture of various compounds and contains a condensed polycyclic aromatic as described above. The condensed polycyclic aromatic contained in the pitch-based carrier may be a single species or a plurality of species. For example, the main component of coal pitch, which is a kind of pitch carrier, 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.

  Even when a pitch-based carrier is used as the carrier, the cycle characteristics are greatly improved because the high capacity inherent in sulfur can be maintained and the elution of sulfur into the electrolyte is suppressed, as in the case of using PAN as the carrier. . This is because sulfur is not present as a simple substance in the sulfur-based positive electrode active material, but sulfur is taken in between the graphene layers of the pitch-based carrier, or hydrogen contained in the condensed polycyclic aromatic ring is replaced with sulfur. This is presumed to be due to the CS bond.

  The particle size of the pitch-based carrier is not particularly limited. Moreover, when using a pitch-type support | carrier as a support | carrier, the particle size of sulfur is also not specifically limited. The mixing ratio of the pitch-based carrier and sulfur is not particularly limited, but the mixing ratio of the pitch-based carrier and sulfur in the mixed raw material is preferably 1: 0.5 to 1:10 by mass ratio, The ratio is more preferably 1: 1 to 1: 7, and particularly preferably 1: 2 to 1: 5.

  The sulfur-modified pitch contains a plurality of types of polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbon (PAH) referred to in the present specification is selected from the group consisting of the above-mentioned various pitch-based carriers themselves and the various polycyclic aromatic hydrocarbons contained in the above-mentioned various pitch-based carriers. It refers to at least one carbon material.

  Further, sulfur-modified pitch (coal pitch: sulfur = 1: 1, 1: 5, 1:10), simple coal pitch and simple sulfur were X-ray diffracted by CuKα rays. The diffraction conditions are the same as those of the above sulfur-modified PAN.

  As shown in FIG. 3, in the range of diffraction angle (2θ) of 10 to 60 °, the main peak of elemental sulfur was present at around 22 °, and the main peak of elemental coal pitch was present at around 26 °. The peak of the sulfur-modified pitch with a coal pitch / sulfur mixing ratio of 1: 1 was a single peak and was present at around 26 °. The main peak of sulfur-modified pitch having a blending ratio of coal pitch and sulfur of 1: 5 and sulfur-modified pitch having a blending ratio of coal pitch and sulfur of 1:10 was present at around 22 °.

  Sulfur-modified pitch is excellent in thermal stability. When the sulfur-modified pitch is heated from room temperature to 550 ° C. at a heating rate of 10 ° C./min, the mass reduction by thermogravimetric analysis is about 25% at 550 ° C. For reference, the mass loss of the coal pitch is about 30% at 550 ° C. In the case of elemental sulfur, the mass gradually decreases from around 170 ° C., and rapidly decreases when the temperature exceeds 200 ° C. Coal pitch is also difficult to decrease in mass, and in the vicinity of 250 ° C to 450 ° C, coal pitch tends to be less likely to decrease in mass than sulfur-modified pitch. Above 450 ° C., the mass of sulfur-modified pitch is less likely to be reduced than that of coal pitch.

  An example of the Raman spectrum of sulfur-modified pitch is shown in FIG. For reference, this Raman spectrum was measured under the same conditions as the Raman spectrum of the above-described sulfur-modified PAN.

In the Raman spectrum shown in FIG. 4, there are major peak near 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. These peaks are observed at similar positions even when the ratio of elemental sulfur to the pitch-based support is changed, and are peaks that characterize the sulfur-modified pitch. When the Raman spectrum of the positive electrode of the present invention using sulfur-modified pitch as the positive electrode active material is measured, peaks that are the same as these peaks or slightly different in number and peak top position are confirmed. The Raman spectrum of sulfur-modified pitch is different from the Raman spectrum of sulfur-modified PAN.

  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.

[PAH]
In the production method of the present invention, polycyclic aromatic hydrocarbon (PAH) other than the above-described pitch-based carrier may be used as a compounding material.

  The sulfur-modified PAH described above 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, and includes 4-membered rings, 5-membered rings, 6-membered rings, and 7-membered rings. As a compounding material composed of PAH other than the system carrier, acenes having a structure in which three or more six-membered rings having a benzene ring structure are connected in a straight chain, and a six-membered ring having three or more rings are not linear It is preferable to use at least one of compounds having a bent structure 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, PAH 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 PAH 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 PAH and at least a part of sulfur are liquid. By doing in this way, the contact area between PAH and sulfur can be made sufficiently large, and sulfur-modified PAH containing sulphur and suppressing sulfur desorption can be obtained.

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

  If the amount of sulfur added to PAH is excessive, a sufficient amount of sulfur can be easily taken into PAH in the heat treatment step. And even if it mix | blends sulfur more than necessary with respect to PAH, the bad influence by the above-mentioned simple substance sulfur can be controlled by performing the simple substance sulfur removal process which removes excess simple sulfur from the processed object after a heat treatment process. . Specifically, when the blending ratio of PAH 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 PAH, it is possible to suppress the 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 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 starting material PAH, the sulfur-modified PAH is considered to have a structure similar to hexathiapentacene, but the structure is not clear. Moreover, the sulfur positive electrode active material using anthracene as PAH has peaks in the vicinity of 1056 cm ⁻¹ and 840 cm ^{−1 in} the FT-IR spectrum, which is completely different from the FT-IR spectrum of anthracene. Therefore, 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 degraded when used in a positive electrode for a non-aqueous electrolyte secondary battery.

  The sulfur-modified PAH desirably further contains a second sulfur-based positive electrode active material (sulfur-modified PAN). The same applies to the above-described sulfur-modified pitch. The heat treatment step in the case of further containing PAN powder in the mixed raw material can be performed in the same manner as the above-described method for producing sulfur-modified PAN. The mixing amount of the second sulfur-based positive electrode active material is not particularly limited, but from the viewpoint of cost, it is preferably about 0 to 80% by mass, preferably about 5 to 60% by mass with respect to the entire positive electrode active material. It is more preferable, and it is still more preferable to set it as about 10-40 mass%.

[Other carriers]
Other carriers preferably used in the production method of the present invention include a linear unsaturated polymer as disclosed in Patent Document 1 described above, a plant carrier such as coffee beans and seaweed, and sulfur heat-treated, Or these composites etc. can be mentioned. In the production method of the present invention, the support only needs to fix sulfur, and does not necessarily contain carbon (C).

  In consideration of the cycle characteristics and capacity of the nonaqueous electrolyte secondary battery, it is more preferable to use PAN as the carrier. In view of cost, it is more preferable to use a pitch-based carrier. Furthermore, you may use said multiple types together as a support | carrier.

(Heat treatment process)
The production method of the present invention includes a heat treatment step of heating a mixed raw material obtained by mixing the above-described carrier, sulfur, and a compounding material. 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, one obtained by simply mixing sulfur, a carrier, and a compounding material may be used. For example, the mixed raw material may be formed into a pellet shape and used.

  By heating the mixed raw material in the heat treatment step, the carrier contained in the mixed raw material reacts with sulfur. This reaction is accelerated by the compounding material. 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. 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 fixation of sulfur to the support (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. In particular, when PAN is used as a carrier, by performing heat treatment in a non-oxidizing atmosphere, a sulfur-based positive electrode active material using PAN as a carrier by fixing vapor-state sulfur to PAN simultaneously with the PAN ring-closing reaction Can be 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 reaction of sulfur and a support | carrier progresses, and a compounding material does not change in quality.

  For example, when PAN is used as the carrier, the heating temperature is preferably 250 to 500 ° C., more preferably 250 to 400 ° C., and even more preferably 300 to 400 ° C. When a pitch-based carrier is used as the carrier, the heating temperature is preferably 200 ° C. or higher and 600 ° C. or lower, more preferably 300 ° C. or higher and 500 ° C. or lower, and 350 ° C. or higher and 500 ° C. or lower. Further preferred. When a pitch-based carrier is used as the carrier, at least a part of the pitch-based carrier and at least a part of sulfur become liquid in the heat treatment step. In other words, in the heat treatment step, at least a part of the pitch-based support and at least a part of sulfur are in liquid contact. For this reason, the contact area between the pitch-based carrier and sulfur in the heat treatment step is large, the pitch-based carrier and sulfur are sufficiently bonded, and the desorption of sulfur from the sulfur-based positive electrode active material is suppressed.

  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 carrier in the heat treatment step. For this reason, when sulfur is excessively added to the carrier, the above-described adverse effect of the elemental sulfur can be obtained by removing the elemental sulfur from the object to be treated (sulfur-based positive electrode active material-carrier complex) after the heat treatment step. Can be suppressed. Specifically, when the mixing ratio of the carrier 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 carrier, 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-based positive electrode active material. Moreover, what is necessary is just to use the to-be-processed body after a single sulfur removal process as a sulfur type positive electrode active material, when performing a single-piece | unit sulfur removal process to the to-be-processed body after a heat treatment process.

(Positive electrode)
The positive electrode of the present invention is manufactured by the manufacturing method of the present invention including the heat treatment step described above, and contains a sulfur-based positive electrode active material and a compounding material. In addition, when the positive electrode of the present invention contains sulfur-modified PAN and / or sulfur-modified pitch as a sulfur-based positive electrode active material, the Raman spectrum of the positive electrode is derived from the peak derived from the above-described sulfur-modified PAN or sulfur-modified pitch. Peaks are observed along with other peaks.

  The positive electrode can have the same structure as that of a general positive electrode for a nonaqueous electrolyte secondary battery except for the positive electrode active material (and, in some cases, a compounding material). For example, the positive electrode of the present invention comprises a positive electrode material in which a mixture of a sulfur-based positive electrode active material and a compounding material (that is, an object to be processed obtained by a heat treatment process), a conductive additive, a binder, and a solvent are mixed. It can produce by apply | coating to. Alternatively, the mixed raw material in which the sulfur powder, the carrier powder, and the compounding material powder are mixed can be heated (a heat treatment step is performed) after filling the positive electrode current collector. According to this method, a mixture of the sulfur-based positive electrode active material and the compounding material can be produced, and at the same time, the mixture and the current collector can be integrated without using a binder. If no binder is used, the amount of the positive electrode active material per positive electrode mass can be increased, and the capacity per positive electrode mass can be improved.

  As described above, the positive electrode may contain a compounding material. The content ratio between the sulfur-based positive electrode active material and the compounding material in the positive electrode is preferably 10: 0.01 to 10: 5, more preferably 10: 0.1 to 10: 2 in terms of mass ratio. .

  Examples of the conductive assistant include vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, positive electrodes such as aluminum and titanium. Examples thereof include fine metal powders stable in potential. Some types of compounding materials function as conductive aids. For this reason, it may not be necessary to add a conductive additive.

  As the binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), carboxymethylcellulose (CMC), polychlorinated Examples include vinyl (PVC), methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), and polypropylene (PP).

  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 sulfur-based positive electrode active material. As another method, a mixture of the sulfur-based positive electrode active material of the present invention, the above-described conductive additive and binder is kneaded with a mortar or a press machine to form a film, and the film-like mixture is collected with a press machine or the like. The positive electrode for a non-aqueous electrolyte secondary battery of the present invention can also be produced by pressure bonding to an electric body.

  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 Examples thereof include a punching copper sheet, a copper expanded sheet, a titanium foil, a titanium mesh, a carbon nonwoven fabric, and a carbon woven fabric. Among these, the carbon non-woven fabric / woven fabric current collector made of carbon having a high degree of graphitization is suitable as a current collector for a sulfur-based positive electrode active material because it does not contain hydrogen and has low reactivity with sulfur. 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.

(Non-aqueous electrolyte secondary battery)
Hereinafter, the configuration of the nonaqueous electrolyte secondary battery of the present invention will be described. The positive electrode is as described above.

<Negative electrode>
As the negative electrode material, a known carbon-based material such as lithium metal or graphite, a silicon-based material such as a silicon thin film, or an alloy-based material such as copper-tin or cobalt-tin can be used. When the non-aqueous electrolyte secondary battery is a lithium ion secondary battery, as the negative electrode material, a material that does not contain lithium, such as a carbon-based material, a silicon-based material, an alloy-based material, etc., among the negative electrode materials described above is used. In this case, it is advantageous in that it is difficult to cause a short circuit between the positive and negative electrodes due to the generation of dendrites. However, when these negative electrode materials not containing lithium are used in combination with the positive electrode of the present invention, neither the positive electrode nor the negative electrode contains lithium. For this reason, a lithium pre-doping process in which lithium is inserted in advance into either one or both of the negative electrode and the positive electrode is necessary. The lithium pre-doping method may be a known method. For example, when lithium is doped into the negative electrode, a half-cell is assembled using metallic lithium as the counter electrode, and lithium is inserted by an electrolytic doping method in which lithium is electrochemically doped, or a metallic lithium foil is attached to the electrode After that, there is a method in which lithium is inserted by a pasting pre-doping method in which it is left in an electrolytic solution and doped using diffusion of lithium to the electrode. Also, when the positive electrode is predoped with lithium, the above-described electrolytic doping method can be used. The same applies to sodium.

  As the negative electrode material that does not contain lithium, a silicon-based material that is a high-capacity negative electrode material is particularly preferable, and among these, thin-film silicon that is advantageous in terms of capacity per volume due to thin electrode thickness is more preferable.

<Electrolyte>
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, gamma-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. The concentration of the electrolyte may be about 0.5 mol / l to 1.7 mol / l. The electrolyte is not limited to liquid. For example, when the non-aqueous electrolyte secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (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 production method of the present invention, the positive electrode of the present invention, and the nonaqueous electrolyte secondary battery of the present invention will be specifically described.

Example 1
[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. As a blending material, Fe ₂ O ₃ having a particle size of 50 μm or less when classified using a sieve was prepared.

  0.4 g of sulfur powder, 0.1 g of PAN powder and 0.01 g of compounding material powder were mixed and pulverized in a mortar to obtain a mixed raw material.

[2] Apparatus As shown in FIG. 5, 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), inert It has a gas pipe 50, a gas tank 51 containing an inert 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 inert gas pipe 50 was connected to the gas introduction pipe 5. The inert gas pipe 50 was connected to a gas tank 51 containing an inert 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 the inert gas at this time was 100 ml / min. Ten minutes after the start of introduction of the inert gas, heating of the mixed raw material 9 in the reaction vessel 2 was started while continuing the introduction of the inert gas. The temperature rising rate at this time was 5 ° C./min. Gas was generated when the mixed raw material 9 reached about 200 ° C. The heating was stopped when the mixed raw material 9 reached 300 ° C. Thereafter, the temperature of the mixed raw material 9 was maintained at 300 ° C. for 3 hours. Therefore, in this heat treatment step, the mixed raw material 9 was heated to 300 ° 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.

[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. 0.15 g of the pulverized product was placed in a glass tube oven and heated at 250 ° 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-based positive electrode active material-compounding material composite not containing (or substantially not including) elemental sulfur was obtained.

<Production of lithium ion secondary battery>
[1] Positive electrode A mixture of 3 mg of a sulfur-based positive electrode active material-compounding material complex, 2.7 mg of acetylene black, and 0.3 mg of polytetrafluoroethylene (PTFE) is added into a film in an agate mortar while adding an appropriate amount of ethanol. The film was kneaded until a film-like positive electrode material was obtained. The total amount of the positive electrode material was press-bonded to an aluminum mesh (mesh roughness # 100) punched into a circle having a diameter of 14 mm and vacuum-dried at 120 ° C. for 5 hours. In this step, the positive electrode for the lithium ion secondary battery of Example 1 was obtained. The blend material in this positive electrode is Fe ₂ O _3, the content ratio of sulfur-based positive electrode active material and compounding material (mass ratio) was 100: 6.

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

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

[4] Battery A coin battery was fabricated using the positive electrode and the negative electrode obtained in [1] and [2]. Specifically, in a dry room, a separator (Celgard 2400 made by Celgard, a polypropylene microporous membrane having a thickness of 25 μm) and a glass nonwoven fabric filter (thickness 440 μm, made by ADVANTEC, GA100) are placed between the positive electrode and the negative electrode. To be an electrode body battery. 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 a lithium ion secondary battery of Example 1.

(Example 2)
The manufacturing method of the positive electrode of Example 1 is the same as that of Example 1, except that a mixture of 0.4 g of sulfur powder, 0.1 g of PAN powder, and 0.01 g of the compounding material powder was used as the mixed raw material. Is the same. In the manufacturing method of Example 2, the mass ratio of PAN and compounding material in the mixed raw material was 1: 0.1. Moreover, the compounding material in the positive electrode of Example 2 was FeCl, and the content ratio (mass ratio) of the sulfur-based positive electrode active material and the compounding material was 100: 6. The lithium ion secondary battery of Example 2 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 2 was used.

(Example 3)
The manufacturing method of the positive electrode of Example 3 was the same as that of Example 1 except that a mixture of 5 g of sulfur powder, 1 g of PAN powder, and 0.1 g of the compounding material powder was used as the mixing raw material, and the heating temperature and heating time in the heat treatment step. This is the same as the positive electrode manufacturing method. In the manufacturing method of Example 3, the mass ratio of PAN and compounding material in the mixed raw material was 1: 0.1. Moreover, the compounding material in the positive electrode of Example 3 was Ti, and the content ratio (mass ratio) of the sulfur-based positive electrode active material and the compounding material was 10: 0.6. In the heat treatment step of Example 3, heating was stopped when the mixed raw material reached 330 ° C. After stopping the heating, the temperature of the mixed raw material increased to 350 ° C. and then decreased. That is, in the heat treatment step of Example 3, the mixed raw material was heated to 350 ° C. The heating time in the production method of Example 3 was about 5 minutes at 350 ° C. The lithium ion secondary battery of Example 3 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 3 was used.

(Comparative Example 1)
The manufacturing method of the positive electrode of the comparative example is the same as the manufacturing method of the positive electrode of Example 1 except that no compounding material was used. The positive electrode of the comparative example is the same as the positive electrode of Example 1 except that it does not contain a compounding material. The lithium ion secondary battery of the comparative example is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of the comparative example was used.

Example 4
The positive electrode of Example 3 was manufactured by using TiS ₂ as a compounding material and using a mixture of 5 g of sulfur powder, 1 g of PAN powder, and 0.1 g of compounding material powder as a mixing material. The manufacturing method is the same. In the manufacturing method of Example 4, the mass ratio of PAN and compounding material in the mixed raw material was 1: 0.1. Further, the content ratio (mass ratio) between the sulfur-based positive electrode active material and the compounding material (TiS ₂ ) in the positive electrode of Example 4 was 10: 0.6. The lithium ion secondary battery of Example 4 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 4 was used.

[Battery characteristics]
The lithium ion secondary batteries of Examples 1 and 2 and Comparative Example 1 were charged and discharged. Specifically, each lithium ion secondary battery was repeatedly charged and discharged 10 times at a cutoff voltage of 3.0 V to 1.0 V and 25 ° C. A second discharge curve is shown in FIG.

  Further, the discharge rate characteristics of the lithium ion secondary batteries of Example 3 and Example 4 were measured. Specifically, for each lithium ion secondary battery, the current value per gram of the positive electrode active material is changed to 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C,. Went. The cut-off voltage at this time was 3.0V to 1.0V. The temperature was 25-30 ° C. The results of the discharge rate characteristic test are shown in FIGS.

  As shown in FIG. 6, the discharge capacities of the lithium ion secondary battery of Example 1 in which the compounding material was blended and the lithium ion secondary battery in Example 2 were the lithium ion secondary battery of the comparative example in which the compounding material was not blended. It was bigger than the battery. This fact is that the heat treatment step is performed in the presence of the compounding material, so that the reaction between sulfur and PAN proceeds even at a relatively low heating temperature of 300 ° C. (that is, the temperature at which the reaction does not proceed easily). Is backed up.

[Analysis of sulfur-based positive electrode active materials by X-ray diffraction]
X-ray diffraction analysis was performed on the sulfur-based positive electrode active material-compounding material complex of Example 3, the sulfur-based positive electrode active material of Comparative Example 1, and the sulfur-based positive electrode active material-additive complex of Example 4. . A powder X-ray diffractometer (manufactured by MAC Science, M06XCE) was used as the apparatus. The measurement conditions were CuKα line, voltage: 40 kV, current: 100 mA, scan speed: 4 ° / min, sampling: 0.02 °, number of integrations: 1, diffraction angle (2θ): 10 ° to 60 °. . Diffraction patterns obtained by X-ray diffraction are shown in FIGS.

The main diffraction peak positions of Ti by the ASTM card are 35.1, 38.4, 40.2, 53.0 °, and the like. The main diffraction peak positions of TiS ₂ are 15.5, 34.2, 44.1, 53.9 °, and the like. As shown in FIG. 12, in the sulfur-based positive electrode active material (Comparative Example 1) using PAN as a carrier without blending the compounding material, the diffraction angle (2θ) is in the range of 20 to 30 ° and is broad at around 25 °. A single peak is observed. On the other hand, in the sulfur-based positive electrode active material-compounding material composite containing the compounding material, a peak derived from the compounding material appears. For example, as shown in FIG. 10, when Ti is used as the compounding 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 a compounding material. As shown in FIG. 11, when TiS ₂ was used as the compounding material, the peak of Ti could not be confirmed even when X-ray diffraction was performed on the sulfur-based positive electrode active material-compounding material complex. Furthermore, although not shown, even when TiO ₂ is used as a compounding material, its presence cannot be confirmed by X-ray diffraction. However, since Ti can be detected by using other analysis methods such as ICP elemental analysis and fluorescent X-ray analysis, it is assumed that TiO ₂ or the like was blended as a blending material even when no peak was confirmed by X-ray diffraction it can.

  From the above results, it can be seen that according to the production method of the present invention, a sulfur-based positive electrode active material capable of increasing the capacity of the nonaqueous electrolyte secondary battery can be produced. The sulfur type positive electrode active material obtained by the manufacturing method of this invention contains a compounding material depending on the case. A metal such as iron oxide used as a compounding material is considered to function as a catalyst in at least a part of the reaction in which sulfur is fixed to PAN. As shown in FIG. 10, the peak of Ti is confirmed in the diffraction pattern of the sulfur-based positive electrode active material-compounding material composite of Example 3, whereas the sulfur-based of Example 4 is used as shown in FIG. The peak of Ti is not confirmed in the diffraction pattern of the positive electrode active material-compounding material composite. For this reason, it is thought that the compounding material substantially functioning as a catalyst differs between the manufacturing method of Example 3 and the manufacturing method of Example 4. However, as shown in FIGS. 8 and 9, the lithium ion secondary battery of Example 3 and the lithium ion secondary battery of Example 4 show comparable capacity and cycle characteristics.

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

Claims (4)

Including a heat treatment step of heating a mixed raw material containing sulfur, a carrier and a compounding material at a temperature at which sulfur is melted ,
The carrier contains carbon (C), and is at least one selected from polyacrylonitrile, pitch-based carriers, acenes, and plant-based carriers.
The method for producing a positive electrode for a non-aqueous electrolyte secondary battery, wherein the compounding material is at least one selected from iron oxide, iron chloride, and titanium . The method for producing a positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the compounding material is at least one selected from iron oxide and iron chloride . It is manufactured by the method for manufacturing a positive electrode for a nonaqueous electrolyte secondary battery according to claim 1,
A non-aqueous electrolyte secondary comprising a sulfur-based positive electrode active material containing sulfur (S) and carbon (C), and a metal or metal compound containing iron (Fe) or titanium (Ti) Battery positive electrode.   A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 3 as a positive electrode.