WO2013035274A1

WO2013035274A1 - Method for manufacturing positive electrode for non-aqueous electrolyte storage battery, positive electrode for non-aqueous electrolyte storage battery, and non-aqueous electrolyte storage battery

Info

Publication number: WO2013035274A1
Application number: PCT/JP2012/005432
Authority: WO
Inventors: 正孝仲西; 淳一丹羽; 一仁川澄; 中川　敏; 友哉佐藤; 晶小島; 琢寛幸; 境　哲男
Original assignee: 株式会社豊田自動織機; 独立行政法人産業技術総合研究所
Priority date: 2011-09-05
Filing date: 2012-08-29
Publication date: 2013-03-14
Also published as: JP5263557B2; JP2013054957A

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 4^th period metals, 5^th period of metals, 6^th period metals and rare earth elements, and metallic compounds.

Description

Method of manufacturing positive electrode for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

The present invention comprises 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 the non-aqueous electrolyte secondary battery. The present invention relates to a non-aqueous electrolyte secondary battery.

A technology using sulfur as a positive electrode active material for a non-aqueous electrolyte secondary battery is known. As a positive electrode active material of a lithium ion secondary battery, although what contains rare metals, such as cobalt and nickel, is common, these metals have a small amount of circulation, and are expensive. Compared to these rare metals, the current sulfur flow is large. For this reason, sulfur as a positive electrode active material attracts attention. Moreover, when using sulfur as a positive electrode active material of a lithium ion secondary battery, the non-aqueous electrolyte secondary battery with large charging / discharging capacity can be obtained. For example, the charge and discharge capacity of a lithium ion secondary battery using sulfur as a positive electrode active material is about 6 times the charge and discharge capacity of a lithium ion secondary battery using a lithium cobaltate positive electrode material which is a general positive electrode material is there.

However, in a lithium ion secondary battery using elemental sulfur as a positive electrode active material, a compound of sulfur and lithium is formed during discharge. The compound of sulfur and lithium is soluble in the non-aqueous electrolyte solution (for example, ethylene carbonate, dimethyl carbonate, etc.) of the 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 charge and discharge are repeated, the elution of the sulfur into the electrolytic solution gradually deteriorates and the battery capacity decreases. Hereinafter, the characteristics of the lithium ion secondary battery in which the charge and discharge capacity decreases with repetition of charge and discharge are referred to as “cycle characteristics”. The lithium ion secondary battery having a small charge / discharge capacity decrease is a lithium ion secondary battery excellent in cycle characteristics, and the lithium ion secondary battery having a large charge / discharge capacity decrease is a lithium ion secondary battery having poor cycle characteristics.

In order to suppress the elution of sulfur into the electrolytic solution, a positive electrode active material (hereinafter referred to as a sulfur-based positive electrode active material) obtained by heat treatment of a mixture of a carrier and sulfur has been proposed. The term "carrier" as used herein refers to a substance capable of fixing sulfur chemically or physically. That is, the carrier may be chemically bonded to sulfur or may physically hold sulfur. The fixed strength of sulfur by the carrier is not particularly limited.

Patent Document 1 discloses a technique using polysulfide carbon containing carbon and sulfur as main components as a sulfur-based positive electrode active material. The polysulfide carbon is a carrier, that is, one in which sulfur is added to a linear unsaturated polymer. According to Patent Document 1, this sulfur-based positive electrode active material is considered to be able to suppress the decrease in charge / discharge capacity of a lithium ion secondary battery accompanying repetition of charge / discharge. Hereinafter, the characteristics of the lithium ion secondary battery in which the charge and discharge capacity decreases with repetition of charge and discharge are referred to as “cycle characteristics”. The lithium ion secondary battery having a small charge / discharge capacity decrease is a lithium ion secondary battery excellent in cycle characteristics, and the lithium ion secondary battery having a large charge / discharge capacity decrease is a lithium ion secondary battery having poor 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. ). The charge and discharge capacity of a lithium ion secondary battery using this positive electrode active material as a positive electrode is large, and a lithium ion secondary battery using this positive electrode active material as a positive electrode is excellent in cycle characteristics. Moreover, this positive electrode active material can also be used as a positive electrode active material such as a sodium secondary battery.

However, on the other hand, the step of obtaining a sulfur-based positive electrode active material by heat treatment of a carrier such as PAN and sulfur to obtain a sulfur-based positive electrode active material (referred to as a heat treatment step) is relatively high temperature and requires a relatively long time. For this reason, there has been a demand for a manufacturing method capable of more easily manufacturing a sulfur-based positive electrode active material.

Japanese Patent Application Laid-Open No. 2002-154815 WO 2010/044437

The present invention has been made in view of the above-mentioned circumstances, and a manufacturing method by which a positive electrode for a non-aqueous electrolyte secondary battery containing a sulfur-based positive electrode active material can be easily manufactured, and a positive electrode manufactured by this manufacturing method An object of the present invention is to provide a water electrolyte secondary battery.

The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, which solves the above problems, includes a heat treatment step of heating a mixed material containing sulfur (S), a carrier and a compounding material,
The compounding material is characterized by comprising at least one metal or metal compound selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element.
Further, the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, which solves the above problems, is produced by the method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention,
A sulfur-based positive electrode active material containing sulfur (S);
It is characterized by including at least one metal or metal compound selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element.
Further, the non-aqueous electrolyte secondary battery of the present invention for solving the above problems is characterized by including the positive electrode for a non-aqueous electrolyte secondary battery of the present invention as a positive electrode.

According to the production method of the present invention, it is possible to produce a positive electrode for a non-aqueous electrolyte secondary battery containing a sulfur-based positive electrode active material in a relatively short time and at a relatively low temperature. Further, the non-aqueous electrolyte secondary battery provided with the positive electrode for a non-aqueous electrolyte secondary battery obtained by the production method of the present invention has a large capacity even if the positive electrode is produced under the condition that the reaction hardly occurs. And it is excellent in battery characteristics.

It is a graph showing the result of X-ray diffraction of sulfur modified polyacrylonitrile. It is a graph showing the result of having carried out the Raman spectrum analysis of sulfur modified polyacrylonitrile. It is a graph showing the result of X-ray diffraction of sulfur-modified pitch. It is a graph showing the result of having carried out Raman spectrum analysis of sulfur denaturation pitch. It is explanatory drawing which represents typically the reaction apparatus used by 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 and Example 2 and Comparative Example 1; 15 is a graph showing the discharge rate characteristics (charge-discharge curve) of the lithium ion secondary battery of Example 3. 15 is a graph showing the discharge rate characteristics (cycle characteristics) of the lithium ion secondary battery of Example 3. 15 is a graph showing the discharge rate characteristics (cycle characteristics) of the lithium ion secondary battery of Example 4. FIG. 18 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-blender composite used for the positive electrode of Example 3. FIG. FIG. 18 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-blender composite used for the positive electrode of Example 4. FIG. It is a graph showing the result of having carried out the X-ray diffraction of the sulfur system positive electrode active material used for the positive electrode of comparative example 1.

The method for producing a positive electrode for a non-aqueous 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 (the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, hereinafter abbreviated as the positive electrode of the present invention) produced by the production method of the present invention may or may not contain a compounding material. That is, in the production method of the present invention, the compounding material may be removed after obtaining the sulfur-based positive electrode active material. The non-aqueous electrolyte secondary battery of the present invention is a battery using the positive electrode of the present invention.

The sulfur-based positive electrode active material is, for example, those disclosed in the above-mentioned Patent Document 1 (using polysulfide carbon as a carrier) and those disclosed in Patent Document 2 (using PAN as a carrier) Or any other carrier may be used. For example, as a carrier, a pitch-based carrier, which will be described later, a polycyclic aromatic hydrocarbon formed by condensation of three or more six-membered rings (hereinafter abbreviated as PAH if necessary), a plant-based carrier or the like is used. It is good. The sulfur-based positive electrode active material using PAN as a carrier is hereinafter referred to as sulfur-modified PAN. A sulfur-based positive electrode active material using a pitch-based carrier as a carrier is called a sulfur-modified pitch. The sulfur-based positive electrode active material using PAH as a carrier is called sulfur-modified PAH.

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 the reaction for fixing sulfur to a carrier by using a compounding material. Also, sulfur can be fixed to the support even under conditions that are not suitable for chemical reactions, such as at relatively low temperatures.
(Method of manufacturing non-aqueous electrolyte secondary battery positive electrode)
<Compounding material>

As a compounding material, at least one metal or metal compound selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element can be used. These metals or metal compounds promote any chemical reaction in fixing sulfur to the carrier. 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 carrier. Such a compounding material may be any of the above-described various metals or compounds thereof (oxides, chlorides, etc.), and may be sulfides or non-sulfurized. That is, even in the case of a sulfide compounding material, it is only necessary to accelerate the reaction in which sulfur is fixed to the carrier. In addition, after the unsulfided compounding material reacts with sulfur to become sulfide, it may promote the reaction in which the sulfur is fixed to the carrier.

In the production method of the present invention, a compounding material is blended to accelerate the reaction in which sulfur is fixed to the carrier. For this reason, the sulfur-based positive electrode active material obtained by the production method of the present invention may or may not contain a compounding material. For example, in the production method of the present invention, using a plate-like or net-like easily removable aggregate-like compounding material, removing the compounding material after the simple substance reacts with sulfur, a sulfur-based material containing no compounding material The positive electrode active material can be manufactured.

The fourth period metal, the fifth period metal, and the sixth period metal in the present specification are according to the periodic table. For example, the fourth period metal refers to a metal included in the fourth period 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 compounds of these metals (excluding sulfides).

The compounding ratio of the carrier to the compounding material is preferably 10: 0.05 to 10: 5 in mass ratio, and more preferably 10: 1 to 10: 3. If the compounding amount of the compounding material is too large, the amount of the positive electrode active material with respect to the whole of the positive electrode will be too small. As described above, in order to remove the compounding material after the reaction of sulfur and the carrier, the compounding material is preferably not in the form of powder but in the form of an aggregate such as 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 the form of powder. The compounding material preferably has a particle diameter of 0.01 to 100 μm, more preferably 0.1 to 50 μm, and still more preferably 0.1 to 20 μm, as measured using an electron microscope or the like.
<Carrier>
[PAN]

When PAN is used as the carrier, the high capacity inherent to sulfur can be maintained, and the elution of sulfur into the electrolytic solution can be suppressed, whereby the cycle characteristics are greatly improved. This is considered to be due to the fact that sulfur is not present as a single substance in the sulfur-based positive electrode active material but is present in a stable state fixed by bonding with PAN or the like. In the method of producing a sulfur-based positive electrode active material disclosed in Patent Document 2, sulfur is heat-treated together with PAN. When PAN is heated, it is believed that PAN bridges three-dimensionally and forms a condensed ring (mainly a six-membered ring) while closing the ring. Therefore, it is considered that sulfur is present in the sulfur-based positive electrode active material in a state of being bonded to PAN in which ring closure has progressed. For this reason, sulfur-modified PAN has a carbon skeleton derived from PAN. By combining PAN with sulfur, elution of sulfur into the electrolyte can be suppressed, and cycle characteristics can be improved.

PAN used as a carrier is preferably in the form of powder, and the mass average molecular weight is preferably about 10 ⁴ to 3 × 10 ⁵ . In addition, the particle diameter of PAN is preferably about 0.5 to 50 μm, more preferably about 1 to 10 μm, as observed by an electron microscope. If the molecular weight and the 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. Therefore, the elution of sulfur into the electrolyte can be suppressed more reliably.

The sulfur used for the sulfur-based positive electrode active material is also preferably in the form of powder. The particle size of sulfur is not particularly limited, but when it is classified using a sieve, one having a size which does not pass through a sieve with a sieve opening of 40 μm and which passes through a 150 μm sieve is preferable. It is more preferable not to pass through a sieve with a sieve opening of 40 μm and in the size range of passing through a 100 μm sieve.

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

Sulfur-modified PAN contains carbon, nitrogen, and sulfur as a result of elemental analysis, and may further contain small amounts of oxygen and hydrogen. In addition, 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 near 25 ° was confirmed in the diffraction angle (2θ) range of 20 ° to 30 °. The For reference, X-ray diffraction measurement was performed using a powder X-ray diffractometer (manufactured by MAC Science, model number: M06XCE) using a CuKα ray. The measurement conditions were: voltage: 40 kV, current: 100 mA, scan rate: 4 ° / min, sampling: 0.02 °, number of integrations: 1 measurement range: diffraction angle (2θ) 10 ° to 60 °.

Furthermore, the mass loss by thermogravimetric analysis at the time of heating sulfur-modified PAN from a room temperature to 900 ° C. at a temperature rising rate 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 loss is recognized from around 120 ° C., and at 200 ° C. or more, a large mass loss due to the disappearance of sulfur is recognized.
That is, in sulfur-modified PAN, it is considered that sulfur is not present as a simple substance, but is present in a state of being bound to a ring-closed PAN.

An example of a 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, A peak is present around 317 cm ^-1 . The peak of the above-mentioned Raman shift is observed at the same position even when the ratio of elemental sulfur to PAN is changed. Therefore, these peaks are characteristic of sulfur-modified PAN. Each peak mentioned above exists in the range of about ± 8 cm ⁻¹ around the peak position mentioned above. In addition, in this specification, a "main peak" refers to the peak which peak height becomes the largest among all the peaks which appeared in the Raman spectrum.

For reference, the above-mentioned Raman shift is measured by RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm ⁻¹ ) manufactured by JASCO Corporation. Note that the peaks of the Raman spectrum may change in number 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 in number or peak top position from the above peak is confirmed Ru.
〔pitch〕

In the present specification, a pitch-based carrier is a solid or semi-solid obtained by distillation of various tars, petroleum and coals, and a synthetic material having the same structure and / or composition as these materials. Refers to the whole. Specific examples of the pitch-based carrier include organic materials obtained by polycondensation of coal pitch, petroleum pitch, mesophase pitch (anisotropic pitch), asphalt, coal tar, coal tar pitch, and condensed polycyclic aromatic hydrocarbon compounds. Synthetic pitch or organic synthetic pitch obtained by polycondensation of a heteroatom-containing fused polycyclic aromatic hydrocarbon compound may, for example, be mentioned. These are known as carbon materials containing fused polycyclic aromatics.

Coal tar, which is a type of pitch-based carrier, is a black viscous oily liquid obtained by high temperature dry distillation (coal dry distillation) 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 roughly classified into those obtained as bottoms when vacuum distillation of petroleum (crude oil) is carried out and those which exist naturally. 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). By thermally processing the isotropic pitch in an inert atmosphere, it is possible to obtain an optically anisotropic pitch (anisotropic pitch, mesophase pitch). Pitch is partially soluble in organic solvents such as benzene, toluene, carbon disulfide and the like.

The pitch-based carrier is a mixture of various compounds and comprises fused polycyclic aromatics as described above. The fused polycyclic aromatic group 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 type of pitch-based carrier, is condensed polycyclic aromatics. The fused polycyclic aromatic ring may contain nitrogen and sulfur in addition to carbon and hydrogen in the ring. Therefore, the main component of coal pitch is considered to be a mixture of a condensed polycyclic aromatic hydrocarbon consisting of only carbon and hydrogen and a heteroaromatic compound containing nitrogen, sulfur and the like in the condensed ring.

Even when using a pitch-based carrier as the carrier, as in the case of using PAN as the carrier, the high capacity originally possessed by sulfur can be maintained and the elution of sulfur into the electrolytic solution can be suppressed, thereby greatly improving cycle characteristics. . This is because sulfur is not incorporated as a single substance in the sulfur-based positive electrode active material, but sulfur is taken in between graphene layers of the pitch-based carrier, or hydrogen contained in a condensed polycyclic aromatic ring is substituted by sulfur It is guessed that it is because it is CS bond.

The particle size of the pitch-based carrier is not particularly limited. Further, when a pitch-based carrier is used as the carrier, the particle size of sulfur is also not particularly limited. The mixing ratio of the pitch-based carrier to the sulfur is also not particularly limited, but the mixing ratio of the pitch-based carrier to the sulfur in the mixed raw material is preferably 1: 0.5 to 1:10 by mass ratio, It is more preferably 1: 1 to 1: 7, particularly preferably 1: 2 to 1: 5.

Sulfur-modified pitch contains multiple types of polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbon (PAH) referred to in the present specification is selected from the group consisting of the various pitch-based carriers described above and the various polycyclic aromatic hydrocarbons contained in the various pitch-based carriers described above. Refers to at least one carbon material.

In addition, sulfur-modified pitch (coal pitch: sulfur = 1: 1, 1: 5, 1:10), single coal pitch and single sulfur were subjected to X-ray diffraction with CuKα ray. The diffraction conditions are the same as the sulfur-modified PAN described above.

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

Sulfur-modified pitch is excellent in heat stability. The mass loss by thermogravimetric analysis when the sulfur-modified pitch is heated from room temperature to 550 ° C. at a heating rate of 10 ° C./min 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 decreases gradually from around 170 ° C., and decreases sharply above 200 ° C. Coal pitch also tends not to decrease in mass, and in the vicinity of 250 ° C. to 450 ° C., coal pitch tends to be less likely to decrease in weight than sulfur-modified pitch. At 450 ° C. or higher, the sulfur-modified pitch tends to be less likely to lose mass than coal pitch.

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

In the Raman spectrum shown in FIG. 4, the main peak is present 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 pitch-based carrier is changed, and are peaks characterizing 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, a peak having the same or slightly different number or peak top position from these peaks is confirmed. The Raman spectrum of the sulfur-modified pitch is different from the Raman spectrum of the sulfur-modified PAN.

As a result of elemental analysis of the sulfur-modified pitch, carbon, nitrogen and sulfur were detected. Also, in some cases small amounts of oxygen and hydrogen were detected. Therefore, in addition to C and S, the sulfur-modified pitch contains at least one of nitrogen, oxygen, and a sulfur compound as an impurity.
[PAH]

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

The above-described sulfur-modified PAH has a carbon skeleton derived from at least one kind of polycyclic aromatic hydrocarbon (PAH) formed by condensation of three or more six-membered rings. PAH is a generic term for hydrocarbons in which a hetero ring or a substituted aromatic ring is fused, and includes four-, five-, six-, and seven-membered rings. As a compounding material composed of PAH other than the carrier, acenes having a structure in which a six-membered ring having a benzene ring structure is linked in three or more straight chains, and a six-membered ring having three or more rings are not straight chains It is preferable to use at least one of sulfur and a compound having a bent structure.

Examples of acenes which are polycyclic aromatic hydrocarbons in which a plurality of aromatic rings are linked in a straight chain while sharing a side include naphthalene of 2 rings, anthracene of 3 rings, tetracene of 4 rings, pentacene of 5 rings, 6 There are a hexacene ring, a 7-ring heptacene, an 8-ring octacene, a 9-ring nonacene, and 10 or more aromatic rings linked, and at least one selected from these groups can be used. Among them, those having 3 to 6 rings having high stability are desirable.

In addition, as polycyclic aromatic hydrocarbons having a structure in which three or more six-membered rings are not linear but bent, there are phenanthrene, benzopyrene, chrysene, pyrene, pyrene, picene, perylene, triphenylene, coronene, and more rings than these rings. Some of the above aromatic rings are linked, and at least one selected from these groups can be used. Sulfur-modified PAH can be produced in the same manner as sulfur-modified pitch.

In the heat treatment step, PAH and sulfur are reacted. In this reaction, it is desirable that the amount of sulfur be excessive relative to the amount of PAH to make a positive electrode active material containing sulfur at a high concentration. It is desirable that the temperature of this heat treatment step be performed under the condition that at least a part of PAH and at least a part of sulfur become liquid. By doing so, the contact area between PAH and sulfur can be made sufficiently large, and it is possible to obtain a sulfur-modified PAH which contains sulfur sufficiently and whose desorption of sulfur is suppressed.

There is also a preferable range of the compounding ratio of PAH to sulfur in the mixed material. If the blending amount of sulfur to PAH is too small, sufficient amount of sulfur can not be taken into PAH, and if the blending amount of sulfur to PAH is too large, a large amount of free sulfur (single sulfur) remains in the sulfur modified PAH The reason is to contaminate particularly the electrolyte in the non-aqueous electrolyte secondary battery. The mixing ratio of PAH to sulfur in the mixed raw material is preferably 1: 0.5 to 1:10, more preferably 1: 1 to 1: 7, in terms of mass ratio, PAH: sulfur. Particular preference is given to 1: 2 to 1: 5.

In addition, if the compounding quantity of sulfur with respect to PAH is made excessive, a sufficient amount of sulfur can be easily taken in to PAH in a heat treatment process. And, even if sulfur is mixed with PAH in a necessary amount or more, the adverse effect due to the above-mentioned simple substance sulfur can be suppressed by performing the simple substance sulfur removing process for removing excess simple substance sulfur from the object after the heat treatment process. . Specifically, when the compounding ratio of PAH to sulfur in the mixed raw material is 1: 2 to 1:10 in mass ratio, the object to be treated after the heat treatment step is heated at 200 ° C. to 250 ° C. while reducing pressure. By the (single sulfur removing step), it is possible to suppress an adverse effect due to the remaining single sulfur while incorporating a sufficient amount of sulfur into PAH. When the single sulfur removing step is not performed on the object to be treated after the heat treatment step, the object to be treated may be used as the sulfur-modified PAH as it is. When the single sulfur removing step is performed on the target after the heat treatment step, the target after the single sulfur removing step may be used as the sulfur-modified PAH.

The sulfur-modified PAH is considered to have a structure similar to hexathiapentacene, for example, when pentacene is selected as the starting material PAH, but the structure is not clear. Moreover, the sulfur positive electrode active material using anthracene as PAH has peaks respectively at around 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 is possible to identify in FT-IR spectrum.

Elemental analysis of the sulfur-modified PAH shows that sulfur (S) and carbon (C) account for the majority, and small amounts of oxygen and hydrogen are detected. The composition ratio of sulfur (S) to carbon (C) is desirably contained in the range of 1/5 or more in atomic ratio (S / C). When the amount of sulfur is less than this range, the charge and discharge characteristics may be deteriorated when used for a positive electrode for a non-aqueous electrolyte secondary battery.

The sulfur-modified PAH preferably further includes a second sulfur-based positive electrode active material (sulfur-modified PAN). The same applies to the sulfur-modified pitch described above. The heat treatment step in the case where the mixed raw material further contains PAN powder can be performed in the same manner as the method for producing sulfur-modified PAN described above. 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, and about 5 to 60% by mass based on the whole positive electrode active material. It is more preferable that the content be about 10 to 40% by mass.
[Other carriers]

As other carriers preferably used in the production method of the present invention, linear unsaturated polymers as disclosed in the above-mentioned Patent Document 1, plant-based carriers such as coffee beans and seaweed, and sulfur are thermally treated, Or these complexes etc. can be mentioned. In the production method of the present invention, the carrier only needs to be capable of fixing sulfur, and does not necessarily contain carbon (C).

In view of the cycle characteristics and capacity of the non-aqueous electrolyte secondary battery, it is more preferable to use PAN as a carrier. Further, in consideration of the cost, it is more preferable to use a pitch-based carrier. Furthermore, multiple types of the above may be used in combination as a carrier.
(Heat treatment process)

The production method of the present invention comprises a heat treatment step of heating a mixed material obtained by mixing the above-described carrier, sulfur and a compounding material. The mixed material may be mixed by a general mixing device such as a mortar or a ball mill. As the mixed raw material, one obtained by simply mixing sulfur, a carrier and a compounding material may be used, but for example, the mixed raw material may be formed into a pellet 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 facilitated by the formulation. 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, the closed system is preferable. The heat treatment step is not particularly limited as to which atmosphere to carry out, but it is preferable to carry out in an atmosphere which does not prevent the fixation of sulfur on the carrier (for example, an atmosphere containing no hydrogen or a nonoxidizing atmosphere). For example, when hydrogen is present in the atmosphere, sulfur in the reaction system reacts with hydrogen to form hydrogen sulfide, which may result in loss of sulfur in the reaction system. In addition, when PAN is used as a carrier, a sulfur-based positive electrode active material in which sulfur in a vapor state is fixed to PAN and PAN is used as a carrier simultaneously with the ring closure reaction of PAN by heat treatment under a nonoxidizing atmosphere. Is considered to be obtained. The non-oxidative atmosphere referred to here includes a reduced pressure state where the oxygen concentration is low to such an extent that the oxidation reaction does not proceed, an inert gas atmosphere such as nitrogen and argon, a sulfur gas atmosphere and the like.

There is no particular limitation on a specific method for making a non-oxidative atmosphere in a sealed state, for example, the mixed raw material is put in a container in which the sealing property is maintained to the extent that the sulfur vapor does not dissipate, and the pressure in the container is reduced. Alternatively, heating may be performed in an inert gas atmosphere. In addition, you may heat in the state vacuum-packed with the material (for example, aluminum laminate film etc.) which is hard to react with a sulfur raw material. In this case, for example, the packaged raw material is placed in a pressure container such as an autoclave containing water and heated so that the packaging material is not damaged by the generated sulfur vapor, and the generated steam is added from the outside of the packaging material It is preferable to press. According to this method, since the steam is pressurized by steam from the outside of the packaging material, the sulfur vapor prevents the packaging material from being blown and broken.

The heating time of the mixed raw material in the heat treatment step may be appropriately set according to the heating temperature, and is not particularly limited. The above-mentioned preferable heating temperature may be a temperature at which the reaction between sulfur and the carrier proceeds and the compounding material does not deteriorate.

For example, when PAN is used as the carrier, the heating temperature is preferably 250 ° C. to 500 ° C., more preferably 250 ° C. to 400 ° C., and still more preferably 300 ° C. to 400 ° C. . When a pitch-based carrier is used as the carrier, the heating temperature is preferably 200 ° C. or more and 600 ° C. or less, more preferably 300 ° C. or more and 500 ° C. or less, and preferably 350 ° C. or more and 500 ° C. or less More preferable. When a pitch-based carrier is used as the carrier, at least a portion of the pitch-based carrier and at least a portion of the sulfur become liquid in the heat treatment step. In other words, in the heat treatment step, at least a portion of the pitch-based carrier and at least a portion of the sulfur contact in a liquid state. For this reason, the contact area of the pitch-based carrier and sulfur in the heat treatment step is large, the pitch-based carrier and sulfur are sufficiently bonded, and 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 material may be heated so that a part of the mixed material becomes a gas and a part becomes a liquid. In other words, the temperature of the mixed raw material may be a temperature higher than the temperature at which sulfur is vaporized. The term "vaporization" as used herein refers to phase change of sulfur from liquid or solid to gas, which may be boiling, evaporation or sublimation. For reference, the melting point of alpha sulfur (orthogonal sulfur, which is the most stable structure around normal temperature) is 112.8 ° C, the melting point of beta sulfur (monoclinic sulfur) is 119.6 ° C, gamma sulfur (monoclinic sulfur) The melting point of) is 106.8 ° C. The boiling point of sulfur is 444.7.degree. By the way, since the vapor pressure of sulfur is high, when the temperature of the mixed raw material reaches 150 ° C. or more, the generation of sulfur vapor can be visually confirmed. Therefore, if the temperature of the mixed raw material is 150 ° C. or more, sulfur reflux is possible. In addition, what is necessary is just to reflux sulfur using the reflux apparatus of known structure, when refluxing sulfur in a heat treatment process.

Even when the blending 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 the sulfur is excessively compounded to the carrier, the above-described adverse effect of the single sulfur is caused by removing the single 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 compounding ratio of the carrier to sulfur in the mixed raw material is 1: 2 to 1:10 in mass ratio, the object to be treated after the heat treatment step is heated at 200 ° C. to 250 ° C. while reducing pressure. By the (single sulfur removing step), it is possible to suppress an adverse effect due to the remaining single sulfur while capturing a sufficient amount of sulfur in the carrier. When the single sulfur removing step is not performed on the object to be treated after the heat treatment step, the object to be treated may be used as it is as a sulfur-based positive electrode active material. When the single sulfur removing step is performed on the target after the heat treatment step, the target after the single sulfur removing step may be used as the sulfur-based positive electrode active material.
(Positive electrode)

The positive electrode of the present invention is manufactured by the manufacturing method of the present invention including the above-described heat treatment step, and contains a sulfur-based positive electrode active material and a compounding material. In the case where 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 aforementioned sulfur-modified PAN-derived peak or sulfur-modified pitch Peaks are observed with other peaks.

The positive electrode can have the same structure as a general positive electrode for a non-aqueous electrolyte secondary battery, except for the positive electrode active material (and the compounding material in some cases). For example, the positive electrode of the present invention can be obtained by using 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 treated obtained by the heat treatment step), a conductive additive, a binder, and a solvent is mixed. It can be produced by applying to Alternatively, the mixed raw material in which the sulfur powder, the carrier powder and the compounding material powder are mixed can be filled in the current collector for the positive electrode and then heated (performing a heat treatment step). According to this method, a mixture of the sulfur-based positive electrode active material and the compounding material can be manufactured, and at the same time, the mixture and the current collector can be integrated without using a binder. If a binder is not used, the amount of positive electrode active material per positive electrode mass can be increased, and the capacity per positive electrode mass can be improved.

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

As a conductive support agent, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, positive electrode such as aluminum or titanium For example, fine powders of metals stable at potentials are exemplified. In addition, depending on the kind of compounding material, there is also one that functions as a conductive aid. For this reason, it may not be necessary to blend the conductive aid.

As a binder, polyvinylidene fluoride (PolyVinylidene DiFluoride: PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamidoimide (PAI), carboxymethylcellulose (CMC), polychlorinated Examples include vinyl (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 aids, binders and solvents may be used in combination of two or more. Although the compounding amount of these materials is not particularly limited, for example, it is preferable to mix about 20 to 100 parts by mass of the conductive aid 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. Further, as another method, a mixture of the sulfur-based positive electrode active material of the present invention and the above-mentioned conductive additive and binder is kneaded with a mortar or press and made into a film, and the film-like mixture is collected with a press 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 a current collector.

What is generally used for the positive electrode for nonaqueous electrolyte secondary batteries may be used as a collector. For example, as a current collector, aluminum foil, aluminum mesh, punching aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punching stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel non-woven fabric, copper foil, copper mesh , A punched copper sheet, a copper expanded sheet, a titanium foil, a titanium mesh, a carbon non-woven fabric, a carbon woven fabric and the like. Among them, a carbon nonwoven 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 of carbon fiber having a high degree of graphitization, various kinds of pitch (that is, by-products such as petroleum, coal, coal tar, etc.), PAN fiber, etc. can be used as a material of carbon fiber.
(Non-aqueous electrolyte secondary battery)
Hereinafter, the configuration of the non-aqueous electrolyte secondary battery of the present invention will be described. The positive electrode is as described above.
<Negative electrode>

As the negative electrode active material, it is possible to use a known metal-based material such as metal lithium and graphite, and an element capable of inserting and extracting lithium and capable of alloying with lithium and / or a compound containing the element. In this case, the charge carrier is lithium, and the non-aqueous electrolyte secondary battery of the present invention is a lithium secondary battery, or a lithium ion secondary battery, or a lithium polymer secondary battery. As other negative electrode active materials, metallic sodium, an element capable of storing and releasing sodium ions and capable of alloying with sodium, and / or a compound containing the element can also be used. In this case, the charge carrier is sodium, and the non-aqueous electrolyte secondary battery of the present invention is a sodium secondary battery, or a sodium ion secondary battery, or a sodium polymer secondary battery.

The above-mentioned elements capable of alloying reaction with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, It is preferably at least one selected from the group consisting of Ge, Sn, Pb, Sb, and Bi. Among these, silicon (Si) or tin (Sn) is particularly preferable. The elemental compound having an element capable of alloying reaction with lithium described above is preferably a silicon compound or a tin compound. The silicon compound is preferably SiO _x (0.5 ≦ x ≦ 1.5). Since silicon has a large theoretical capacity and a large volume change at the time of charge and discharge, it is possible to reduce the volume change by using it in the compound state (that is, SiO _x ).

As the tin compound, for example, a tin alloy (Cu-Sn alloy, Co-Sn alloy, etc.), a tin alloy (Cu-Sn alloy, Co-Sn alloy, etc.), etc. are preferably used. In addition, silicon-based materials such as silicon thin films, and alloy-based materials such as copper-tin and cobalt-tin can be preferably used. When the charge carrier is sodium, hard carbon or soft carbon or a tin compound is preferably used as the negative electrode active material.

When using a material not containing lithium, for example, a carbon-based material, a silicon-based material, an alloy-based material or the like among the above-described negative electrode materials as the negative electrode active material, it is difficult to cause a short circuit between positive and negative electrodes Is advantageous. However, when using the negative electrode using these negative electrode active materials in combination with the positive electrode of the present invention, a material involved in charge and discharge by ionizing and moving between the positive electrode and the negative electrode, such as Li and Na. (So-called charge carriers) are not included in either the positive electrode or the negative electrode. For this reason, it is necessary to pre-dope the charge carrier in advance into one or both of the negative electrode and the positive electrode. The charge carrier pre-doping method may be a known method. For example, when lithium, which is a type of charge carrier, is doped to the negative electrode, it is possible to use an electrolytic doping method in which metal lithium is used as a counter electrode to form a half cell and lithium is doped to the negative electrode electrochemically. Alternatively, it is also possible to use a bonding pre-doping method in which a lithium metal foil attached to an electrode is left in an electrolytic solution and lithium diffusion is used to dope lithium into the negative electrode. In addition, the above-described electrolytic doping method can be used also in the case of pre-doping lithium to the positive electrode. The same is true for sodium.

As a negative electrode material not containing lithium, particularly, a silicon-based material which is a high capacity negative electrode material is preferable, and among them, thin film silicon which has a thin electrode thickness and which is advantageous in capacity per volume is more preferable.
<Electrolyte>

As an electrolyte used for a non-aqueous electrolyte secondary battery, what melt | dissolved the alkali metal salt which is a supporting electrolyte (supporting salt) 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. When the charge carrier is lithium, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiI, LiClO ₄ or the like can be used as the supporting electrolyte. 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, in the form of a polymer gel). When the charge carrier is Na, sodium salts such as NaPF ₆ , NaBF ₄ , NaAsF ₆ , NaCF ₃ SO ₃ , NaI, NaClO ₄ can be used as the electrolyte.
<Others>

The non-aqueous electrolyte secondary battery may include members 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 movement of ions 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 closed type, the separator is also required to have a function of holding the electrolytic solution. As the separator, it is preferable to use a thin, microporous or non-woven membrane made of polyethylene, polypropylene, PAN, aramid, polyimide, cellulose, glass or the like. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, and a coin shape can be used.

Hereinafter, the manufacturing method of the present invention, the positive electrode of the present invention, and the non-aqueous electrolyte secondary battery of the present invention will be specifically described.
Example 1
[1] Mixed raw materials

A sulfur powder having a particle size of 50 μm or less was prepared when classified using a sieve. As a PAN powder, one having a particle diameter in the range of 0.2 μm to 2 μm as prepared by an electron microscope was prepared. As a compounding 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 crushed in a mortar to obtain a mixed material.
[2] Device

As shown in FIG. 5, the reactor 1 includes a reaction vessel 2, a lid 3, a thermocouple 4, an alumina protective pipe 40, two alumina pipes (a gas introduction pipe 5 and a gas discharge pipe 6), an inert gas pipe 50, It has a gas tank 51 containing an inert gas, a trap pipe 60, a trap tank 62 containing an aqueous sodium hydroxide 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. The mixed raw material 9 was accommodated in the reaction container 2 in the heat treatment process mentioned later. The opening of the reaction vessel 2 was closed by a glass lid 3 having three through holes. An alumina protective tube 40 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) containing a thermocouple 4 was attached to one of the through holes. A gas introduction pipe 5 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) was attached to the other one of the through holes. A gas exhaust pipe 6 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) 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 (in 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 almost 100 ° C. or less in the heat treatment step described later. For this reason, the sulfur vapor generated in the heat treatment step does not flow out from the gas introduction pipe 5 and the gas discharge pipe 6 and 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 of hydrogen sulfide gas generated in a heat treatment process described later.
[3] Heat treatment process

The reaction vessel 2 containing the mixed raw material 9 was housed in an electric furnace 7 (crucible furnace, opening width φ 80 mm, heating height 100 mm). At this time, argon was introduced into the reaction vessel 2 through the gas introduction pipe 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 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. When the mixed material 9 reached about 200 ° C., gas was generated. 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, the mixed raw material 9 was heated to 300 degreeC in this heat treatment process. 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] Single Sulfur Removal Step In order to remove single sulfur (free sulfur) remaining on the object to be treated after the heat treatment step, the following steps were carried out.

The object to be treated after the heat treatment step was crushed in a mortar. 0.15 g of the crushed material was placed in a glass tube oven and heated at 250 ° C. for 3 hours with vacuum suction. The temperature rising temperature at this time was 10 ° C./min. By this step, the single sulfur remaining on the object to be treated after the heat treatment step is evaporated and removed, and a sulfur-based positive electrode active material-compounding material composite containing (or substantially free of) single sulfur is obtained.
<Fabrication of lithium ion secondary battery>
[1] Positive electrode

A mixture of 3 mg of a sulfur-based positive electrode active material-compounding material composite, 2.7 mg of acetylene black and 0.3 mg of polytetrafluoroethylene (PTFE) is kneaded in an agate mortar until it becomes a film while adding an appropriate amount of ethanol. , A film-like positive electrode material was obtained. The whole amount of the positive electrode material was pressure-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 a lithium ion secondary battery of Example 1 was obtained. The compounding material in this positive electrode was Fe ₂ O ₃ , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the compounding material was 100: 6.
[2] Negative Electrode As a negative electrode, metal lithium foil (disk-shaped 14 mm in diameter and 500 μm thick, made of Honjo Metal) was used.
[3] Electrolyte

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

The coin battery was produced using the positive electrode and negative electrode which were obtained by [1] and [2]. More specifically, in a dry room, a separator (Celgard 2400, 25 μm thick polypropylene microporous membrane) and a glass non-woven filter (440 μm thick, ADVANTEC, GA 100) between the positive electrode and the negative electrode in a dry room The electrode battery was used as an electrode battery. The electrode battery was housed in a battery case (CR2032 type coin battery member manufactured by Takasen Co., Ltd.) consisting of a stainless steel container. The electrolytic solution obtained in [3] was injected into the battery case. The battery case was sealed with a caulking machine to obtain the lithium ion secondary battery of Example 1.
(Example 2)

A method of manufacturing the positive electrode of Example 2 except that a mixture of 0.4 g of sulfur powder, 0.1 g of PAN powder, and 0.01 g of compounding material powder was used as a mixed material. Is the same as In the manufacturing method of Example 2, the mass ratio of PAN to the compounding material in the mixed raw material was 1: 0.1. 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 to 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 is used.
(Example 3)

The method of manufacturing the positive electrode of Example 3 uses a mixture of 5 g of sulfur powder, 1 g of PAN powder, and 0.1 g of compounding material powder as a mixed raw material, and Example 1 except for the heating temperature and heating time in the heat treatment step. Is the same as the method of manufacturing the positive electrode of In the manufacturing method of Example 3, the mass ratio of PAN to the compounding material in the mixed raw material was 1: 0.1. 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 to the compounding material was 10: 0.6. In the heat treatment step of Example 3, the heating was stopped when the mixed raw material reached 330 ° C. After heating was stopped, the temperature of the mixed raw material rose to 350 ° C. and then dropped. That is, in the heat treatment step of Example 3, the mixed raw material was heated to 350 ° C. In addition, the heating time in the manufacturing method of Example 3 was about 5 minutes at 350 degreeC. 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 is 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 the compounding material is not used. The positive electrode of the comparative example is the same as the positive electrode of Example 1 except that it does not contain any compounding material. Moreover, 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 4 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 mixed raw material. Is the same as the manufacturing method of In the manufacturing method of Example 4, the mass ratio of PAN to the compounding material in the mixed raw material was 1: 0.1. Further, the content ratio (mass ratio) of the sulfur-based positive electrode active material to the additive (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 is used.
[Battery characteristics]

With respect to the lithium ion secondary batteries of Examples 1 and 2 and Comparative Example 1, charge and discharge were performed. Specifically, each lithium ion secondary battery was repeatedly charged and discharged 10 times at 25 ° C. with a cutoff voltage of 3.0 V to 1.0 V. The 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, the current value per 1 g of the positive electrode active material is changed to 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C,. Did. The cutoff voltage at this time was 3.0 V to 1.0 V. 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 containing the compounding material and the lithium ion secondary battery of Example 2 are the lithium ion secondary batteries of the comparative example not containing the compounding material. It was larger than the battery. This fact indicates that, by performing the heat treatment step in the presence of the compounding material, the reaction between sulfur and PAN proceeds even at a relatively low heating temperature of 300 ° C. (that is, a temperature at which the reaction hardly progresses). I support you.
[Analysis of sulfur-based positive electrode active material by X-ray diffraction]

X-ray diffraction analysis was performed on the sulfur-based positive electrode active material-compounding material composite 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. . As a device, a powder X-ray diffractometer (M06XCE manufactured by MAC Science) was used. Measurement conditions were: CuKα ray, voltage: 40 kV, current: 100 mA, scan rate: 4 ° / min, sampling: 0.02 °, number of integrations: 1 time, diffraction angle (2θ): 10 ° to 60 ° . The diffraction patterns obtained by X-ray diffraction are shown in FIGS.

The main diffraction peak positions of Ti by ASTM card are 35.1, 38.4, 40.2, 53.0 ° and so on. The main diffraction peak positions of TiS ₂ are 15.5, 34.2, 44.1, 53.9 ° and so on. As shown in FIG. 12, in the sulfur-based positive electrode active material (comparative example 1) using PAN as a carrier without compounding the compounding material (Comparative Example 1), the diffraction angle (2θ) is broad at around 25 ° in the range of 20 to 30 °. A single peak is observed. In contrast, in the sulfur-based positive electrode active material-compounding material composite in which the compounding material is compounded, a peak derived from the compounding material appears. For example, as shown in FIG. 10, when Ti is used as a compounding material, a Ti peak appears 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 can not 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 presumed that TiO ₂ etc. is blended as a compounding material even when no peak is 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, it is possible to produce a sulfur-based positive electrode active material that can increase the capacity of a non-aqueous electrolyte secondary battery. The sulfur-based positive electrode active material obtained by the production method of the present invention optionally contains a compounding material. The metal such as iron oxide used as the compounding material is considered to function as a catalyst in at least a part of the reaction in which sulfur is fixed to PAN. In addition, 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, while the sulfur-based material of Example 4 is shown 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 considered that in the production method of Example 3 and the production method of Example 4, the compounding materials that substantially function as a catalyst are different. 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 exhibit comparable capacity and cycle characteristics.

1: Reactor 2: Reaction container 3: Lid 4: Thermocouple 5: Gas inlet pipe 6: Gas outlet pipe 7: Electric furnace

Claims

Including a heat treatment step of heating the mixed raw material containing sulfur (S), a carrier and a compounding material,
The compounding material comprises at least one metal or metal compound selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal, and a rare earth element. A positive electrode for a non-aqueous electrolyte secondary battery Manufacturing method.
The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the carrier contains carbon (C).
The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the carrier is at least one selected from polyacrylonitrile, a pitch carrier, acenes, and a plant carrier.
The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the compounding material is an unsulfided metal or metal compound.
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the compounding material contains at least one metal element selected from the group consisting of iron, titanium, manganese, vanadium, platinum and palladium. Method of manufacturing positive electrode.
The positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the compounding material is at least one selected from the group consisting of iron oxide, iron chloride, titanium oxide, and iron hydroxide. Manufacturing method.
A method of producing a positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6,
A sulfur-based positive electrode active material containing sulfur (S);
At least one metal or metal compound selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element; and a positive electrode for a non-aqueous electrolyte secondary battery.
The positive electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the sulfur-based positive electrode active material contains carbon (C).
The positive electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the metal or the metal compound is unsulfided.
A non-aqueous electrolyte secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 9 as a positive electrode.