JP2013089337A - Nonaqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a sufficiently high charge/discharge capacity, by using a sulfur-based positive electrode active material and a non-Li-based negative electrode active material, and to provide a manufacturing method thereof.SOLUTION: The method of manufacturing a nonaqueous electrolyte secondary battery where the reversible capacitance of the negative electrode is equal to or larger than that of a positive electrode by using a sulfur-based positive electrode active material and a non-Li-based negative electrode active material, includes a lithium negative electrode formation step for integrating lithium of a quantity required for charge/discharge of a nonaqueous electrolyte secondary battery, and of a quantity capable of compensating for the initial irreversible capacitance of the negative electrode and the initial irreversible capacitance of the positive electrode with the negative electrode in at least one kind of state selected from metal lithium, LiN and LiCoN.

Description

  The present invention relates to a nonaqueous electrolyte secondary battery using a negative electrode active material containing a sulfur-based positive electrode active material as a positive electrode and a large initial irreversible capacity as a negative electrode, and a method for producing the same.

  As a positive electrode active material of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery or a lithium secondary battery, a material containing a rare metal such as cobalt or nickel is generally used. However, these metals are less circulated and expensive. Compared to these rare metals, the current circulation of sulfur is large, and therefore, a technique using 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 nonaqueous electrolyte 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 non-aqueous electrolyte secondary battery. For this reason, the non-aqueous electrolyte secondary battery using sulfur as the 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 non-aqueous electrolyte secondary battery in which the charge / discharge capacity decreases with repeated charge / discharge is referred to as “cycle characteristic”. The non-aqueous electrolyte secondary battery with a small decrease in charge / discharge capacity is excellent in cycle characteristics, and the non-aqueous electrolyte secondary battery with a large decrease in charge / discharge capacity is inferior in cycle characteristics.

  As a result of intensive studies, the inventors of the present invention have used a positive electrode active material (hereinafter referred to as a sulfur-based positive electrode active material) obtained by heat-treating a mixture of a carbon source compound and sulfur, thereby providing a sulfur electrolyte solution. It was found that elution into the can be suppressed. A carbon source compound is a compound containing carbon (C).

  For example, as disclosed in Patent Document 1, a sulfur-based positive electrode active material is produced by heat treating a mixture of polyacrylonitrile (hereinafter abbreviated as PAN as necessary) and sulfur, which is a kind of carbon source compound. it can. By using the sulfur-based positive electrode active material for the positive electrode, the charge / discharge capacity of the nonaqueous electrolyte secondary battery can be increased, and the cycle characteristics can be improved.

  By the way, it is considered preferable that the negative electrode active material combined with such a sulfur-based positive electrode active material can also increase the capacity of the nonaqueous electrolyte secondary battery and can improve the cycle characteristics. For example, a negative electrode active material containing at least one element selected from the group consisting of silicon (Si), tin (Sn), and carbon (C) satisfies this condition. Hereinafter, these negative electrode active materials are collectively referred to as non-Li-based negative electrode active materials.

  However, on the other hand, since neither the sulfur-based positive electrode active material nor the non-Li-based negative electrode active material contains Li, the amount of Li required for charging / discharging of the non-aqueous electrolyte secondary battery is somehow in the non-aqueous electrolyte secondary. It needs to be added to the battery. Further, non-Li-based negative electrode active materials such as SiO have a large initial irreversible capacity when used as a negative electrode of a lithium ion secondary battery.

  Also, when designing a positive electrode and a negative electrode in a lithium secondary battery and a lithium ion secondary battery, in general, the positive electrode and the negative electrode are set so that the reversible capacity of the negative electrode is slightly larger than the reversible capacity of the positive electrode. (Designed to be a so-called positive electrode regulation type battery). Since the actual capacity of use of the positive and negative electrodes is equal, there is a difference between the reversible capacity and the capacity of use of the negative electrode. In order to increase the battery voltage, which is the potential difference between the positive electrode and the negative electrode, it is preferable to use a low potential region for the negative electrode. In general, the greater the amount of occluded Li, the lower the potential of the negative electrode. For this reason, in order to use an area | region with a low electric potential, it is good to use a negative electrode in the state which has occluded as much Li as possible. Therefore, even when graphite or Si having almost no initial irreversible capacity is used as the negative electrode active material, the negative electrode active material not only simply stores the amount of Li necessary for charging and discharging, but also stores an excessive amount of Li. It is considered that it is preferable to store the maximum amount of Li that can be stored in the negative electrode active material. That is, it is preferable that the negative electrode active material occlude Li, which can compensate for the entire capacity of the negative electrode including the irreversible capacity, regardless of whether there is an initial irreversible capacity.

  As a method of occluding the above-mentioned required amount of Li in a non-aqueous electrolyte secondary battery that does not contain Li in the positive and negative electrodes, it is considered that pre-doping Li into a non-Li negative electrode active material is effective.

  By the way, the above-described sulfur-based positive electrode active material also has a relatively large initial irreversible capacity when used as a positive electrode of a lithium ion secondary battery or a lithium secondary battery. For this reason, it is thought that it is necessary to further supplement Li that compensates for the initial irreversible capacity of the positive electrode. However, as described above, when a non-Li-based negative electrode active material is used, a large amount of Li is required even for the negative electrode. In addition to the Li for the negative electrode, the total amount of Li required to make up for the initial irreversible capacity of the positive electrode is very large. However, it is impossible to pre-dope such a large amount of Li into a non-Li negative electrode active material. This is because it is theoretically impossible to pre-dope Li beyond the total capacity of the negative electrode. For this reason, it has been very difficult to sufficiently increase the charge / discharge capacity of a non-aqueous electrolyte secondary battery using a sulfur-based positive electrode active material and a non-Li-based negative electrode active material.

International Publication No. 2010/044437

  The present invention has been made in view of the above circumstances, and provides a non-aqueous electrolyte secondary battery having a sufficiently high charge / discharge capacity using a sulfur-based positive electrode active material and a non-Li-based negative electrode active material, and a method for producing the same. For the purpose.

The manufacturing method of the nonaqueous electrolyte secondary battery of the present invention that solves the above problems is as follows.
A positive electrode having a sulfur-based positive electrode active material containing carbon (C) and sulfur (S);
A negative electrode having a non-Li negative electrode active material containing at least one element selected from the group consisting of silicon (Si), tin (Sn), and carbon (C), and the reversible capacity of the negative electrode is the reversible capacity of the positive electrode A method for producing a non-aqueous electrolyte secondary battery as described above,
An amount of lithium that can compensate for the total capacity of the negative electrode including the initial irreversible capacity and the initial irreversible capacity of the positive electrode is at least one selected from metallic lithium, Li ₃ N, and Li _2.6 Co _0.4 N. And a lithium negative electrode forming step that is integrated with the negative electrode in the above state.

Moreover, the nonaqueous electrolyte secondary battery electrode of the present invention that solves the above problems is manufactured by the method of manufacturing a nonaqueous electrolyte secondary battery of the present invention in which a lithium foil is attached to the surface of the negative electrode in the lithium negative electrode forming step. ,
Lithium carbonate is present on the surface of the negative electrode.

  Hereinafter, the manufacturing method of the nonaqueous electrolyte secondary battery of the present invention is referred to as the manufacturing method of the present invention. The non-aqueous electrolyte secondary battery obtained by the production method of the present invention, that is, the non-aqueous electrolyte secondary battery of the present invention, has an amount of Li that can compensate for the total capacity of the negative electrode including the initial irreversible capacity and the initial irreversible capacity of the positive electrode. including. For this reason, in the nonaqueous electrolyte secondary battery of the present invention, even if an initial irreversible capacity occurs between the positive and negative electrodes, a sufficient amount of Li remains for charging and discharging, so the capacity of the nonaqueous electrolyte secondary battery is the theoretical capacity. There is an advantage that can approach.

  Further, as described above, the total capacity of the negative electrode including the initial irreversible capacity and the total amount of Li that can compensate for the initial irreversible capacity of the positive electrode could not be predoped into the negative electrode at the same time. Therefore, in order to manufacture this type of non-aqueous electrolyte secondary battery using the conventional pre-doping method, at least two steps are required as a step of adding Li to the non-aqueous electrolyte secondary battery. For example, a temporary battery for pre-doping is assembled with a positive electrode using a sulfur-based positive electrode active material and a negative electrode using metal Li, and charging and discharging are performed to supplement the positive electrode with Li for an initial irreversible capacity. After that, a new battery must be manufactured by combining a negative electrode pre-doped with Li, for example, by attaching a metallic Li foil, with this positive electrode. Such a manufacturing method has a problem that it requires a lot of man-hours, is complicated, and has a high manufacturing cost.

According to the manufacturing method of the present invention, the amount of Li that can compensate for the total capacity of the negative electrode including the initial irreversible capacity and the initial irreversible capacity of the positive electrode (that is, Li that moves during charging and discharging, Li that becomes the initial irreversible capacity at the positive and negative electrodes) And the total amount of excess Li for keeping the potential of the negative electrode low) are integrated into the negative electrode during production. At this time, Li is at least one state selected from metallic lithium, Li ₃ N, and Li _2.6 Co _0.4 N. In this nonaqueous electrolyte secondary battery, at the time of initial discharge, discharge is performed between a negative electrode made of at least one selected from metal Li, Li ₃ N and Li _2.6 Co _0.4 N and a positive electrode having a sulfur-based positive electrode active material. And Li is occluded in the positive electrode, and Li for the initial irreversible capacity of the positive electrode is trapped in the positive electrode. Also, in the case of a negative electrode having an initial irreversible capacity when Li is pre-doped from the moment the battery is assembled, Li for the initial irreversible capacity is trapped in the negative electrode. Even if the discharge is started before the pre-doping is completed, the pre-doping of Li to the negative electrode is completed during the first discharge. At the time of initial charge, charging is performed between a positive electrode having a sulfur-based positive electrode active material that has already been stored with Li and a negative electrode having a non-Li-based negative electrode active material that has been pre-doped with Li, and Li is stored in the negative electrode. For this reason, according to the manufacturing method of the present invention, the pre-doping process, which has been considered necessary in the past, can be performed at the first charge / discharge by using substantially two types of negative electrodes. One of these two types of negative electrodes (a negative electrode comprising at least one selected from metallic lithium, Li ₃ N and Li _2.6 Co _0.4 N) disappears during the first discharge, and the other negative electrode (non-Li-based negative electrode) Only the negative electrode with active material) remains. For this reason, it is not necessary to rearrange the positive electrode or the negative electrode after pre-doping as in the conventional manufacturing method. Therefore, according to the production method of the present invention, a nonaqueous electrolyte secondary battery having a sulfur-based positive electrode active material as a positive electrode and a non-Li-based negative electrode active material as a negative electrode can be easily produced.

It is a graph showing the result of having carried out X-ray diffraction of sulfur modified PAN. It is a graph showing the result of the Raman spectrum analysis of sulfur-modified PAN. 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 Example. It is explanatory drawing which represents typically the nonaqueous electrolyte secondary battery of an Example. It is a graph showing the result of the measurement test performed in order to calculate the amount of Li integrated with the negative electrode of the nonaqueous electrolyte secondary battery of an Example. It is a graph showing an example of the result of the measurement test performed in order to calculate the amount of Li integrated with the negative electrode of a nonaqueous electrolyte secondary battery. It is a calibration curve showing the relationship between the film thickness of the Li foil used in the examples and the capacity (mAh / cm ² ) obtained by the Li foil of each film thickness. It is a graph showing the result of the charging / discharging test of the nonaqueous electrolyte secondary battery of an Example. It is a graph showing the result of the charging / discharging test of the nonaqueous electrolyte secondary battery of an Example.

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

(Sulfur-based positive electrode active material)
In the nonaqueous electrolyte secondary battery of the present invention, the sulfur-based positive electrode active material may be, for example, one disclosed in Patent Document 1 (one using PAN as a carbon source compound) or the like. The carbon source compound may be used. For example, as the carbon source compound, pitches described later, polyisoprene, polycyclic aromatic hydrocarbons obtained by condensation of three or more six-membered rings (hereinafter abbreviated as PAH if necessary), and Plant carbon materials such as coffee beans and seaweed may be used. Hereinafter, a sulfur-based positive electrode active material using PAN as a carbon source compound is referred to as sulfur-modified PAN. A sulfur-based positive electrode active material using pitches as a carbon source compound is called sulfur-modified pitch. A sulfur-based positive electrode active material is referred to as sulfur-modified PAH using PAH as a carbon source compound. A material using polyisoprene as a carbon source compound is called sulfur-modified rubber. In any case, the sulfur-based positive electrode active material can be obtained by heat-treating the carbon source compound and sulfur.

<Carbon source compound>
[PAN]
When PAN is used as the carbon source compound, 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 1, sulfur is heat-processed with PAN. When PAN is heated, it is considered that PAN is three-dimensionally cross-linked and closed while forming a condensed ring (mainly a six-membered ring). For this reason, it is considered that sulfur is present in the sulfur-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, it is considered that elution of sulfur into the electrolyte can be suppressed and cycle characteristics can be improved.

The PAN used as the carbon source compound is preferably in a powder form, 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 sulfur powder used for the sulfur-modified PAN is not particularly limited, but is preferably 1: 0.5 to 1:10 by mass ratio, and 1: 0.5 to 1: 7. More preferably, it is 1: 2 to 1: 5.

  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 system means a solid or semi-solid obtained by distilling various tars, petroleum, and coals, and a synthetic material having the same structure and / or composition as these materials. Refers to general. Specifically, as pitches, organic synthesis obtained by polycondensation of coal pitch, petroleum pitch, mesophase pitch (anisotropic pitch), asphalt, coal tar, coal tar pitch, condensed polycyclic aromatic hydrocarbon compounds. Examples include pitch, or organic synthetic pitch obtained by polycondensation of a heteroatom-containing condensed polycyclic aromatic hydrocarbon compound. These are known as carbon materials containing condensed polycyclic aromatics.

  Coal tar, a kind of pitch, is a black viscous oily liquid obtained by high-temperature carbonization (coal carbonization) of coal. Coal pitch can be obtained by refining and heat treating (polymerizing) coal tar. Asphalt is a black-brown to black solid or semi-solid plastic material. Asphalt is broadly classified into what is obtained as a kettle residue when petroleum (crude oil) is distilled under reduced pressure and that which exists in nature. Asphalt is soluble in toluene, carbon disulfide and the like. Petroleum pitch can be obtained by refining and heat treating (polymerizing) asphalt. The pitch is usually amorphous and optically isotropic (isotropic pitch). An optically anisotropic pitch (anisotropic pitch, mesophase pitch) can be obtained by heat-treating the isotropic pitch in an inert atmosphere. Pitch is partially soluble in organic solvents such as benzene, toluene, carbon disulfide.

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

  Even when pitches are used as the carbon source compound, since 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 carbon source compound, cycle characteristics are improved. Greatly improved. This is because sulfur does not exist as a simple substance in the sulfur-based positive electrode active material, but sulfur is taken in between the graphene layers of pitches, or hydrogen contained in the condensed polycyclic aromatic ring is replaced with sulfur. This is presumed to be due to the C—S bond.

  The particle size of the pitches is not particularly limited. When pitches are used as the carbon source compound, the particle size of sulfur is not particularly limited. The mixing ratio of pitches and sulfur is not particularly limited, but the blending ratio of pitches and sulfur in the mixed raw material is preferably 1: 0.5 to 1:10 in terms of mass ratio. More preferably, it is 1-1: 7, and it is especially preferable that it is 1: 2-1: 5.

  The sulfur-modified pitch contains a plurality of types of polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbon (PAH) referred to here is at least one carbon selected from the group consisting of the various pitches described above and the various polycyclic aromatic hydrocarbons contained in the various pitches described above. Refers to 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 pitches is changed, and are peaks that characterize 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 hydrocarbons (PAH) other than the above-described pitches 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 alkynes, there are acenes having a structure in which six or more six-membered rings having a benzene ring structure are linked in a straight chain, and three or more six-membered rings are not straight but bent. It is preferable to use at least one of compounds having a different 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 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, 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%.

  In consideration of the cycle characteristics and capacity of the nonaqueous electrolyte secondary battery, it is more preferable to use PAN as the carbon source compound. In consideration of cost, it is more preferable to use pitches. Furthermore, you may use said multiple types together as a carbon source compound.

[Other sulfur-based positive electrode active materials]
Other sulfur-based positive electrode active materials used for the positive electrode in the non-aqueous electrolyte secondary battery of the present invention include sulfur-modified rubber, heat-treated sulfur and plant materials such as coffee beans and seaweed, or composites thereof. Can be mentioned.

<Combination material>
The positive electrode in the nonaqueous electrolyte secondary battery of the present invention preferably contains a compounding material other than the conductive additive. The compounding material in this specification refers to a material that exhibits high electrical conductivity or that can greatly improve the ionic conductivity of the positive electrode. By including a compounding material in the positive electrode, the electrical conductivity and / or ionic conductivity of the entire positive electrode can be improved, and the discharge rate characteristics of the nonaqueous electrolyte secondary battery can be improved. As a material of the compounding material (compounding material), it is preferable to use a material exhibiting the above function in a sulfide state. This is because even if the sulfur-based positive electrode active material is sulfurized by sulfur, the function of the compounding material is not impaired.

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

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

  The mixing ratio of the sulfur-based positive electrode active material and the compounding material is preferably 10: 0.5 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. 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 0.1 to 100 μm, more preferably 0.1 to 50 μm, and even more preferably 0.1 to 20 μm.

  In addition, as a method for identifying whether or not the sulfur-based positive electrode active material and the compounding material are mixed, the following X-ray diffraction analysis can be used.

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

(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 carbon source compound and sulfur (and, in some cases, 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, a simple mixture of sulfur and a carbon source compound may be used. For example, the mixed raw material may be formed into a pellet shape.

  By heating the mixed raw material in the heat treatment step, the carbon source compound and sulfur contained in the mixed raw material react. Depending on the type of compounding material, this reaction may be promoted 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. In addition, the atmosphere in which the heat treatment step is performed is not particularly limited, but it is preferably performed in an atmosphere that does not hinder the fixation of sulfur to the carbon source compound (for example, an atmosphere not containing 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 carbon source compound, by performing heat treatment in a non-oxidizing atmosphere, sulfur in the vapor state is fixed to PAN simultaneously with the PAN ring-closing reaction, and PAN is used as a carbon source compound. It is considered that a positive electrode active material is obtained. The non-oxidizing atmosphere referred to here includes a reduced pressure state in which the oxygen concentration is low enough not to cause an oxidation reaction, an inert gas atmosphere such as nitrogen or argon, a sulfur gas atmosphere, and the like.

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

  What is necessary is just to set suitably the heating time of the mixed raw material in a heat processing process according to heating temperature, and it does not specifically limit it. The preferable heating temperature mentioned above should just be temperature which reaction of sulfur and a carbon source compound advances. When blending a compounding material, the temperature should be such that the compounding material does not change in quality.

  For example, when PAN is used as the carbon source compound, the heating temperature is preferably 250 to 500 ° C., more preferably 250 to 400 ° C., and even more preferably 300 to 400 ° C. When pitches are used as the carbon source compound, 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. Is more preferable. When pitches are used as the carbon source compound, at least a part of the pitches 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 pitches and at least a part of the sulfur are in liquid contact. For this reason, the contact area between pitches and sulfur in the heat treatment step is large, the pitches 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 recirculation | 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 carbon source compound in the heat treatment step. For this reason, in the case where sulfur is excessively added to the carbon source compound, the above-mentioned adverse effect of the single sulfur is removed by removing the single sulfur from the object to be treated (sulfur-carbon source compound complex) after the heat treatment step. Can be suppressed. Specifically, when the mixing ratio of the carbon source compound and sulfur in the mixed raw material is 1: 2 to 1:10 by mass ratio, the object to be processed after the heat treatment step is at 200 ° C. to 250 ° C. while reducing the pressure. By heating (single sulfur removal step), it is possible to suppress an adverse effect due to the remaining single sulfur while taking a sufficient amount of sulfur into the carbon source compound. 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 in the nonaqueous electrolyte secondary battery of the present invention has the above-described sulfur-based positive electrode active material. When the positive electrode includes sulfur-modified PAN and / or sulfur-modified pitch as the sulfur-based positive electrode active material, the Raman spectrum of the positive electrode includes other peaks derived from the above-described sulfur-modified PAN and peaks derived from the sulfur-modified pitch. Recognized with a peak.

  The positive electrode can have the same configuration 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, a positive electrode can be produced by applying a positive electrode material mixed with a sulfur-based positive electrode active material, a conductive additive, a binder, and a solvent to a current collector. Alternatively, the mixed raw material in which the sulfur powder and the carbon source compound powder are mixed can be heated (a heat treatment step is performed) after filling the positive electrode current collector. According to this method, the mixture and the current collector can be integrated without producing a sulfur-based positive electrode active material and at the same time. 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 the above-mentioned compounding materials function as conductive aids. For this reason, when mix | blending a compounding material, a conductive support agent may become unnecessary.

  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 5 to 100 parts by mass of the conductive additive and about 5 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 non-woven 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.

(Negative electrode)
As the negative electrode active material, a material containing at least one element selected from the group consisting of silicon (Si), tin (Sn), and carbon (C) (that is, a non-Li-based negative electrode active material) can be used. Specifically, hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), Si, SiO _x , Sn, tin alloy (Cu—Sn alloy, Co—Sn alloy, etc.), etc. are preferably used. can, more preferably Si, _SiO x, Sn, tin alloy (Cu-Sn alloy, Co-Sn alloy) or the like can be used. These negative electrode active materials have a large capacity and are excellent as a negative electrode active material combined with a sulfur-based positive electrode active material. On the other hand, SiO _x or the like has a large initial irreversible capacity generated during the first charge / discharge. The negative electrode in the nonaqueous electrolyte secondary battery of the present invention can be produced by a known method in the same manner as the positive electrode using these negative electrode active materials. For example, a negative electrode can be produced by applying a negative electrode material in which a negative electrode active material, a buffer (such as graphite), a conductive additive, a binder, and a solvent are mixed to a current collector. In particular, SiO _x (x is about 0.3 ≦ x ≦ 1.6) is known as a negative electrode active material having a large capacity and capable of imparting excellent cycle characteristics to a nonaqueous electrolyte secondary battery. It can be preferably used.

  If x is less than the lower limit, the Si ratio increases, so that the volume change during charging / discharging becomes too large and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. For this reason, x is preferably in the range of 0.5 ≦ x ≦ 1.5, and more preferably in the range of 0.7 ≦ x ≦ 1.2.

SiO _x is preferably in the form of particles, and the particle size is not particularly limited. In addition, SiO _x may be primary particles or secondary particles. Furthermore, it is desirable that the SiO _x has an average particle size in the range of 1 μm to 10 μm. When the average particle size is larger than 10 μm, the charge / discharge characteristics of the nonaqueous electrolyte secondary battery may be deteriorated. In addition, if the average particle size is smaller than 1 μm, the particles may agglomerate into coarse particles during the manufacture of the electrode, and the charge / discharge characteristics of the non-aqueous electrolyte secondary battery may be similarly reduced. In addition, the average particle diameter here refers to the mass average particle diameter in the particle size distribution measurement by a laser beam diffraction method.

In the non-aqueous electrolyte secondary battery of the present invention, the negative electrode before the first charge / discharge has an amount of Li necessary for charge / discharge of the non-aqueous electrolyte secondary battery, and an amount of Li () that can supplement the initial irreversible capacity of the positive and negative electrodes. In other words, an amount of Li that irreversibly binds to the positive electrode active material or the negative electrode active material during initial charge / discharge, and excess Li for suppressing the potential of the negative electrode are metal Li, Li ₃ N, and Li _2. They are integrated in at least one state selected from ₆ Co _0.4 N. For example, foil-like or powder-like metal Li may be integrated by mounting on the surface of the negative electrode, bonding, or the like, or these may be mixed into the negative electrode material and integrated within the negative electrode. Furthermore, those obtained by subjecting these materials to some surface treatment may be used. For example, a lithium carbonate (Li ₂ CO ₃ ) film is formed on the surface of the Li foil for the purpose of preventing the reaction between oxygen and Li.

Metals Li, Li ₃ N and Li _2.6 Co _0.4 N may be used alone or in combination of two or more. In any case, at the first discharge, Li integrated on the surface and / or inside of the negative electrode or Li pre-doped on the negative electrode functions as a counter electrode of the positive electrode having the sulfur-based positive electrode active material.

  Moreover, when using what also functions as negative electrode active materials, such as carbon, as a collector of a negative electrode, it is good to add further the amount of Li required for charging / discharging of a collector to a negative electrode.

In addition, when Li foil is integrated with the negative electrode, Li ₂ CO ₃ remains on the negative electrode surface even after charge and discharge. Since the amount of Li ₂ CO ₃ is small, it does not hinder charging / discharging of the non-aqueous electrolyte secondary battery, and the presence of Li ₂ CO ₃ determines that Li foil is used for the non-aqueous electrolyte secondary battery. You can also

  The amount of Li integrated into the negative electrode varies depending on the use conditions of the battery such as the sulfur-based positive electrode active material, non-Li-based negative electrode active material, electrolyte solution, and the like, and voltage. For this reason, what is necessary is just to measure or calculate suitably according to the structure of the battery to manufacture.

<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 and the nonaqueous electrolyte secondary battery of the present invention will be specifically described.

(Example)
[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. 0.4 g of sulfur powder and 0.1 g of PAN 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 process, the elemental sulfur remaining in the object to be processed after the heat treatment process was evaporated and removed, and a sulfur-based positive electrode active material not including (or substantially not including) elemental sulfur was obtained.

<Preparation of nonaqueous electrolyte secondary battery>
[1] Positive electrode Sulfur-modified PAN, KB, and PI were weighed so that sulfur-modified PAN: KB: PI = 60: 20: 20 (mass ratio). These materials were stirred and mixed using a rotating and rotating mixer (ARE-250 made by Sinky) while adjusting the viscosity using N-methyl-2-pyrrolidone (battery grade made by Kishida Chemical) as a dispersant. A slurry was prepared.

  The obtained slurry was applied to the surface of a carbon nonwoven fabric (carbon paper TGP-H-030 manufactured by Toray Industries, Inc.) having a thickness of 120 μm using an applicator and dried at 200 ° C. for 5 hours to obtain a positive electrode. The amount of sulfur-modified PAN contained in this positive electrode was 13.46 mg.

  The structure of the obtained positive electrode will be described with reference to FIG. FIG. 6 is an explanatory diagram showing a configuration of an electrode group 100 of a laminate cell, which will be described in detail later, and the positive electrode manufactured by the above procedure corresponds to the electrode 110 of FIG. The electrode 110 includes a sheet-like current collector 112 made of carbon paper, and a positive electrode active material layer 111 formed on the surface of the current collector 112. The current collector 112 includes a rectangular (16 mm × 22 mm) application part 112a and a joint part 112b extending from a corner of the application part 112a. The slurry adjusted by the above procedure is applied to one surface of the application part 112a, and the positive electrode active material layer 111 is formed.

[2] Negative electrode As the SiO _x , a powdery material having 0.3 ≦ x ≦ 1.6 and an average particle size of 5 μm was used.

The above-mentioned SiO _x , KB, and PI were weighed so as to be SiO _x : KB: PI = 80: 5: 15 (mass ratio). While adding N-methyl-2-pyrrolidone (battery grade manufactured by Kishida Chemical) as a dispersant to these materials and adjusting the viscosity, stirring and mixing were performed using a rotation and revolution mixer (ARE-250 manufactured by Sinky), A uniform slurry was produced.

The obtained slurry was applied to the surface of a 120 μm thick carbon non-woven fabric (carbon paper TGP-H-030 manufactured by Toray Industries, Inc.) using an applicator and dried at 200 ° C. for 5 hours to obtain a negative electrode. The amount of SiO _x contained in this negative electrode was 10.05 mg.

  The structure of the obtained negative electrode is demonstrated using FIG. The negative electrode corresponds to the electrode 120 in FIG. The electrode 120 includes a sheet-like current collector 122 made of carbon paper, and a negative electrode active material layer 121 formed on the surface of the current collector 122. The current collector 122 includes a rectangular (16 mm × 22 mm) application part 122a and a joint part 122b extending from a corner of the application part 122a. The slurry adjusted by the above procedure is applied to one surface of the application part 122a to form the negative electrode active material layer 121. Current collector leads 141 and 142 are welded to the joint 112b of the current collector 112 and the joint 122b of the current collector 122, respectively.

A Li foil (metal Li) having a thickness of 50 μm was placed on the surface of the negative electrode. The Li foil is subjected to surface treatment to suppress reaction with oxygen. For this reason, lithium carbonate (Li ₂ CO ₃ ) exists on the surface of the Li foil.

  A method of calculating the amount of Li foil used here (that is, the amount of Li integrated with the negative electrode) will be described below.

<Calculation of lithium amount>
[Measurement test]
The same thing as the positive electrode and negative electrode of an Example was prepared, and charge / discharge capacity (reversible capacity) and initial irreversible capacity were measured about this positive electrode and negative electrode. Specifically, a laminate cell for measuring the charge / discharge capacity and the initial irreversible capacity of the positive electrode was prepared using the positive electrode of the example and Li foil (counter electrode). Moreover, the laminate cell for measuring the charging / discharging capacity | capacitance and initial irreversible capacity | capacitance of a negative electrode using the negative electrode of Example and Li foil (counter electrode) was produced. In addition, the laminate cell was produced in the same procedure as the nonaqueous electrolyte secondary battery of the Example mentioned later.

  Each laminate cell was subjected to a charge / discharge test at room temperature (30 ° C.). Specifically, with respect to the laminate cell using the positive electrode and Li foil (counter electrode) of Example, the battery was charged to 0.1 V at 0.1 C and then discharged to 3.0 V at 0.1 C. . This was repeated as 2 cycles. In addition, regarding the laminate cell using the negative electrode and the Li foil (counter electrode) of Example, the battery was charged to 0.1 V at 0.1 C, and then discharged to 1.0 V at 0.1 C. Two cycles were repeated as one cycle. The results are shown in FIG.

As shown in FIG. 7, the initial discharge capacity of the positive electrode is about 830 mAh / g, and among these, the charge / discharge capacity (reversible capacity) of the positive electrode is about 600 mAh / g (2.29 mAh / cm ² for this electrode), The initial irreversible capacity was about 230 mAh / g (0.88 mAh / cm ² for this electrode). On the other hand, the initial charge capacity of the negative electrode is about 2700 mAh / g (7.7143 mAh / cm ² for this electrode), and the charge / discharge capacity (reversible capacity) of the negative electrode is 1500 mAh / g (4.28 mAh / cm for this electrode). ² ), the initial irreversible capacity of the negative electrode was about 1200 mAh / g (3.43 mAh / cm ² for this electrode). The charge / discharge capacity of the positive electrode refers to the charge / discharge capacity after the initial charge, and the initial irreversible capacity of the positive electrode refers to the difference between the initial discharge capacity and the initial charge capacity. The negative electrode charge / discharge capacity refers to the charge / discharge capacity after the initial discharge, and the negative electrode initial irreversible capacity refers to the difference between the initial charge capacity and the initial discharge capacity. For reference, in this battery, the utilization factor of the negative electrode was designed to be 66% of the charge / discharge capacity of the negative electrode, and the utilization factor of the positive electrode was designed to be 90% of the charge / discharge capacity of the positive electrode. Therefore, the use area of the negative electrode in this battery is 1000 mAh / g corresponding to 66% of the charge / discharge capacity (1500 mAh / g) of the negative electrode, and the use area of the positive electrode is 90% of the charge / discharge capacity (600 mAh / g) of the positive electrode. Is 540 mAh / g. The utilization factor may be appropriately designed in consideration of the cycle life of the nonaqueous electrolyte secondary battery, the battery voltage balance, and the like.

In the nonaqueous electrolyte secondary battery of the example, the capacity of the negative electrode is much larger than the capacity of the positive electrode. The initial charge capacity of the negative electrode corresponds to the total capacity of the negative electrode including the initial irreversible capacity. Therefore, in the manufacturing method of the example, the sum of the initial charge capacity of the negative electrode and the initial irreversible capacity of the positive electrode is 8.59 mAh / cm ² (= 4.28 mAh / cm ² +3.43 mAh / cm ² +0.88 mAh / The amount of Li necessary to produce (cm ² ) needs to be integrated with the negative electrode. Moreover, in the nonaqueous electrolyte secondary battery of an Example, the carbon nonwoven fabric is used as a collector of a negative electrode. This carbon nonwoven fabric also functions as a negative electrode active material. Therefore, it is necessary to further integrate the amount of Li necessary for charging and discharging the carbon nonwoven fabric into the negative electrode. That is, in the examples, 9.98 mAh / cm ² (= 4.28 mAh / cm ² +3.43 mAh / cm), which is the sum of the initial charge capacity of the negative electrode, the initial irreversible capacity of the positive electrode, and the charge / discharge capacity of the carbon nonwoven fabric of the negative electrode. ² +0.88 mAh / cm ² +1.39 mAh / cm ² ) is integrated into the negative electrode in an amount necessary to produce Li.

The Li foil is placed on the surface of the negative electrode active material layer 121 shown in FIG. For this reason, the size of the Li foil is the same as the area of the application part 122a to which the negative electrode active material layer 21 is applied. The theoretical capacity of Li is 3862.4 mAh / g (= 96485 × 1 / 3.6 / 6.9939). Here, 96485 is the Faraday constant (96485 C / mol), 1 is the number of reaction electrons (lithium is 1 because Li ⁺ Li ¹⁺ reacts), 3.6 is 3600 seconds / 1000 (the unit is m) Divide by 1000). Since the specific gravity of Li is 0.534 g / cm ³ , the theoretical capacity per Li ³ cm ³ is 2062.5 mAh (= 3862.4 mAh / g × 0.534 g / cm ³ ). Therefore, the capacity per unit area of Li having a thickness of 1 μm is 0.206 mAh (= 2062.5 mAh / 10000). Thus, the relationship between the thickness and capacity of the Li foil is calculated, and the relationship between the film thickness of the Li foil used in the examples and the capacity (mAh / cm ² ) obtained by the Li foil of each film thickness is expressed. A calibration curve (FIG. 9) was created. The area of the Li foil is the same area as the application part 122a. Using this calibration curve, for example, as shown in FIG. 8, when the initial irreversible capacity of the negative electrode is 3 mAh / cm ² , the amount (thickness) of the Li foil that can compensate for the initial irreversible capacity can be calculated. As a result, it can be seen that when the thickness of the Li foil is 15 μm, the initial irreversible capacity of the negative electrode can be compensated. The initial charge capacity of the negative electrode (that is, the total capacity of the negative electrode including the initial irreversible capacity) is 7.71 mAh / cm ² (= 4.28 mAh / cm ² +3.43 mAh / cm ² ) and is required. The Li foil had a thickness of 37.4 μm [= 7.71 mAh / cm ² / (capacity per 1 μm of Li: 0.206 mAh)].

Similarly, as a result of converting the initial irreversible capacity of the positive electrode into the amount per unit area (mAh / cm ² ) of the coated portion 122a, the initial irreversible capacity of the positive electrode was 0.88 mAh / cm ² . Using this value and the calibration curve of FIG. 9, the amount (thickness) of Li foil that can compensate for the initial irreversible capacity of 0.88 mAh / cm ² of the positive electrode was calculated. As a result, the required Li foil was 4.27 μm thick.

Furthermore, the total capacity of the carbon nonwoven fabric was measured, and the required thickness of the Li foil was calculated using the calibration curve of FIG. As a result, the charge / discharge capacity of the carbon nonwoven fabric was 1.39 mAh / cm ² , and the required thickness of the Li foil was 6.75 μm.

From the above calculation, 9.98 mAh / cm ² (= 4.28 mAh / cm ² +3.43 mAh / cm), which is the sum of the total capacity of the negative electrode including the initial irreversible capacity, the initial irreversible capacity of the positive electrode, and the charge / discharge capacity of the carbon nonwoven fabric. ² +0.88 mAh / cm ² +1.39 mAh / cm ² ), the thickness of the Li foil is 48.4 μm [= 9.98 mAh / cm ² / (capacity per 1 μm Li: 0.206 mAh)] I know that there is. Furthermore, considering that lithium carbonate (Li ₂ CO ₃ ) and the like present on the surface of the Li thin film do not contribute to charging and discharging, a 50 μm thick Li thin film slightly thicker than 48.4 μm was used. When the negative electrode has no initial irreversible capacity, the initial irreversible capacity of the negative electrode is zero. In this case, the initial discharge capacity of the negative electrode becomes equal to the reversible capacity of the negative electrode. In any case, the total capacity of the negative electrode is equal to the initial discharge capacity of the negative electrode.

<Production of lithium ion secondary battery>
A laminate cell was produced using the positive electrode and the negative electrode produced by the above procedure. The laminate cell is injected into the laminate film (not shown) that encloses and seals the electrode group 100 in which the positive electrode 110, the negative electrode 120, and the separator 130 shown in FIG. 6 are laminated, and the electrode group 100 is sealed. A non-aqueous electrolyte. The production procedure of the laminate cell will be described with reference to FIG.

  The configuration of the positive electrode 110 and the negative electrode 120 was as described above. As the separator 130, a rectangular sheet (Celgard 2400, 20 mm × 30 mm, thickness 25 μm) of a polypropylene microporous film was used. Stacked in order of the coating portion 112a of the positive electrode active material layer 111, the separator 130, and the coating portion 122a of the negative electrode active material layer 121 so that the negative electrode active material layer 111 and the positive electrode active material layer 121 face each other with the separator 130 interposed therebetween. Then, the electrode group 100 was combined.

The non-aqueous electrolyte was obtained by dissolving LiPF ₆ at a concentration of 1 mol in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at EC: DEC = 1: 1 (volume ratio). . Next, the electrode group 100 was covered with a set of two laminate films (Tech Barrier HX, manufactured by Mitsubishi Plastics, Inc.), and a nonaqueous electrolyte was injected into a bag-like portion sealed on three sides. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode group 1 and the nonaqueous electrolyte were sealed. Note that some of the current collecting leads 141 and 142 of both poles extend outward for electrical connection with the outside.

<Charge / discharge test>
The laminate cell produced by the above procedure was subjected to a charge / discharge test at room temperature (30 ° C.). In the charge / discharge test, the battery was charged at 0.1 C to 0.8 V, then discharged at 0.1 C to 3.0 V, and this was repeated 5 cycles. The results are shown in FIG. 10 and FIG. In addition, FIG. 10 shows only the result to 1-3 cycles.

  As shown in FIG. 10, the discharge capacity at the first cycle was 769 mAh / g, and the discharge capacity at the second cycle was 535 mAh / g. As described above, the use area of the negative electrode in the non-aqueous electrolyte secondary battery of the example is 1000 mAh / g, and the use area of the positive electrode is 540 mAh / g. The charge / discharge capacity is considered to be about 540 mAh / g. The discharge capacity at the second cycle is 535 mAh / g, which is a value almost coincident with 540 mAh / g. For this reason, it can be said that the nonaqueous electrolyte secondary battery of an Example contains sufficient amount of Li to make up for the initial irreversible capacity of the negative electrode and the positive electrode and to charge and discharge. Moreover, according to the manufacturing method of an Example, it can be said that the nonaqueous electrolyte secondary battery which supplemented the initial irreversible capacity | capacitance of a negative electrode and a positive electrode, and contained sufficient quantity for charging / discharging was able to be manufactured.

  Moreover, as shown in FIG. 11, the nonaqueous electrolyte secondary battery of the Example was also excellent in cycle characteristics.

1: Reaction apparatus 2: Reaction vessel 3: Lid 4: Thermocouple 5: Gas introduction pipe 6: Gas discharge pipe 7: Electric furnace 100: Electrode group 110: Electrode (positive electrode) 112: Current collector 111: Positive electrode active material layer 112a: Applied portion 112b: Bonded portion 120: Electrode (negative electrode) 122: Current collector 121: Negative electrode active material layer 122a: Applied portion 122b: Bonded portion 141, 142: Current collecting lead 130: Separator

Claims (11)

A positive electrode having a sulfur-based positive electrode active material containing carbon (C) and sulfur (S);
A negative electrode having a non-Li negative electrode active material containing at least one element selected from the group consisting of silicon (Si), tin (Sn), and carbon (C), and the reversible capacity of the negative electrode is the reversible capacity of the positive electrode A manufacturing method for manufacturing a non-aqueous electrolyte secondary battery as described above,
An amount of lithium that can compensate for the total capacity of the negative electrode including the initial irreversible capacity and the initial irreversible capacity of the positive electrode is at least one selected from metallic lithium, Li ₃ N, and Li _2.6 Co _0.4 N. The manufacturing method of the nonaqueous electrolyte secondary battery characterized by including the lithium negative electrode formation process integrated with this negative electrode in the state of this. In the lithium negative electrode forming step,
The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium is integrated with the negative electrode in the form of metallic lithium. In the lithium negative electrode forming step,
The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein a lithium foil is attached to the surface of the negative electrode. The sulfur-based positive electrode active material is
A carbon source compound comprising at least one selected from polyacrylonitrile, pitches, polyisoprene, a polycyclic aromatic hydrocarbon formed by condensation of three or more six-membered rings, and a plant-based carbon material;
The manufacturing method of the nonaqueous electrolyte secondary battery as described in any one of Claims 1-3 which uses sulfur as a material. The negative active _{material, SiO x (0.3 ≦ x ≦} 1.6) of silicon oxide represented by claim 1 of the non-aqueous electrolyte secondary battery according to claim 4 Production method.   The method for producing a non-aqueous electrolyte secondary battery according to claim 4, wherein the positive electrode active material has a carbon skeleton derived from the carbon source compound. It is manufactured by the method for manufacturing a nonaqueous electrolyte secondary battery according to any one of claims 3 to 6,
A non-aqueous electrolyte secondary battery, wherein lithium carbonate is present on the surface of the negative electrode. Before the first discharge, the total amount of the negative electrode including the initial irreversible capacity, and the amount of lithium that can compensate for the initial irreversible capacity of the positive electrode is integrated into the negative electrode in the form of metallic lithium,
At the first discharge, the metallic lithium functions as a negative electrode active material,
The nonaqueous electrolyte secondary battery according to claim 7, wherein the non-Li-based negative electrode active material functions as a negative electrode active material after the first charge. The sulfur-based positive electrode active material is
A carbon source compound comprising at least one selected from polyacrylonitrile, pitches, polyisoprene, a polycyclic aromatic hydrocarbon formed by condensation of three or more six-membered rings, and a plant-based carbon material;
The nonaqueous electrolyte secondary battery according to claim 7 or 8, wherein the material is sulfur. The non-aqueous electrolyte secondary battery according to claim 7, wherein the negative electrode active material is made of a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6).   The non-aqueous electrolyte secondary battery according to claim 9 or 10, wherein the positive electrode active material has a carbon skeleton derived from the carbon source compound.

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