JP2013191328A - Nonaqueous electrolyte secondary battery and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics; and a vehicle mounting the nonaqueous electrolyte secondary battery thereon.SOLUTION: Binder obtained by curing alkoxy silyl-group containing resin represented by formula (I) (Ris alkyl, Ris alkyl or alkoxy, and q is an integer of 1 to 100) is used for electrodes.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a vehicle equipped with the non-aqueous electrolyte secondary battery.

  As a positive electrode active material of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a lithium secondary battery, or a sodium ion 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 elemental sulfur as a positive electrode active material is about 6 times the charge / discharge capacity of a lithium ion secondary battery using a lithium cobaltate positive electrode material, which is a general positive electrode material. It is.

  However, in a lithium ion secondary battery using elemental sulfur as the positive electrode active material, a compound of sulfur and lithium is generated during discharge. This compound of sulfur and lithium is soluble in a non-aqueous electrolyte solution (for example, ethylene carbonate, dimethyl carbonate, etc.) of a non-aqueous electrolyte secondary battery. For this reason, the non-aqueous electrolyte secondary battery using elemental 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.

  A decrease in charge / discharge capacity due to repeated charge / discharge is called cycle deterioration. Cycle deterioration is a graph in which charge / discharge is usually repeated under certain conditions, and the relationship between the number of charge / discharge cycles and the capacity of the battery is plotted. Use to evaluate. This non-aqueous electrolyte secondary battery with low cycle deterioration is evaluated as having excellent cycle characteristics, and this non-aqueous electrolyte secondary battery with large cycle deterioration is described as having poor 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.

  In general, the positive electrode and the negative electrode of a nonaqueous electrolyte secondary battery are both produced by the following method. A positive electrode active material or a negative electrode active material and a binder resin are dispersed in a solvent to form a slurry, the slurry is applied onto a metal foil as a current collector, and the solvent in the slurry is removed by drying to form a mixture layer. . The current collector and the mixture layer thereon are compression-molded with a roll press, and the binder resin is cured to produce positive and negative electrode plates.

  As the binder resin in this case, polyvinylidene fluoride (hereinafter abbreviated as “PVdF”) is frequently used for both electrodes. Since this PVdF is a fluorine-based resin, it is difficult for PVdF and the metal current collector to be in close contact with each other. Therefore, when PVdF is used for the binder resin, the active material may fall off from the current collector.

  In recent years, a negative electrode active material having a charge / discharge capacity that greatly exceeds the theoretical capacity of a carbon material has been developed as a negative electrode active material of a lithium ion secondary battery. For example, a material containing a metal that can be alloyed with lithium such as Si or Sn is expected. When a material containing Si or Sn is used for the negative electrode active material, the volume change of Si or Sn due to insertion / extraction of Li during charge / discharge is large. It is difficult to maintain a good binding state with the substance.

  As a result of diligent research, the inventors of the present invention use a specific resin that has not been used as a binder resin for nonaqueous electrolyte secondary battery electrodes, that is, an alkoxysilyl group-containing resin as an electrode binder resin. Thus, it was found that an electrode for a non-aqueous electrolyte secondary battery having excellent cycle characteristics can be provided by suppressing peeling and dropping of the active material from the current collector.

  For example, as disclosed in Patent Document 2, by using an alkoxysilyl group-containing resin as a binder resin for electrodes, the cycle characteristics of a nonaqueous electrolyte secondary battery can be improved.

  Furthermore, the inventors of the present invention include, as disclosed in Patent Document 3, the negative electrode active material includes a lithium inert metal or a lithium inert metal silicide that does not form an intermetallic compound with lithium, and a simple substance of Si. As a result, it was found that the cycle performance was further improved.

  However, in recent years, as the use of nonaqueous electrolyte secondary batteries has expanded, there has been a demand for nonaqueous electrolyte secondary batteries that can provide a larger charge / discharge capacity and have excellent cycle characteristics.

International Publication No. 2010/044437 JP 2009-043678 A JP 2009-259694 A

  The present invention has been made in view of such circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics.

  The nonaqueous electrolyte secondary battery of the present invention that solves the above problems is a nonaqueous electrolyte secondary battery having a positive electrode and a negative electrode, and the positive electrode is a sulfur-based positive electrode containing carbon (C) and sulfur (S). The negative electrode has an active material, and has a negative electrode active material containing a lithium inert metal or a silicide of the lithium inert metal that does not form an intermetallic compound with lithium, and a simple substance of Si. At least one of the above has a binder, and the binder is obtained by curing an alkoxysilyl group-containing resin having a structure represented by the formula (I).

（Ｒ_１は、炭素数１〜８のアルキル基、Ｒ_２は、炭素数１〜８のアルキル基、又はアルコキシ基、ｑは１〜１００の整数）

(R ₁ is an alkyl group having 1 to 8 carbon atoms, R ₂ is an alkyl group having 1 to 8 carbon atoms or an alkoxy group, and q is an integer of 1 to 100)

  The sulfur-based positive electrode active material is a carbon source compound composed of at least one selected from polyacrylonitrile, pitches, polyisoprene, polycyclic aromatic hydrocarbons obtained by condensation of three or more six-membered rings, and plant-based carbon materials It is preferable to use sulfur as a material.

  The sulfur-based positive electrode active material preferably has a carbon skeleton derived from a carbon source compound.

  The lithium inert metal is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, Fe, and Mo.

  The vehicle of the present invention is equipped with the non-aqueous electrolyte secondary battery.

  The nonaqueous electrolyte secondary battery of the present invention has a large charge / discharge capacity and excellent cycle characteristics.

  Since the vehicle of the present invention is equipped with the non-aqueous electrolyte secondary battery, it can be equipped with a battery with excellent cycle characteristics and can be a high-performance vehicle.

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 by manufacture of a sulfur type positive electrode active material. The partial schematic explanatory drawing of the negative electrode of a nonaqueous electrolyte secondary battery is shown. The graph which compares cycling characteristics about the battery using the negative electrode of Test Examples 1-5 is shown. It is explanatory drawing of the laminated structure of a laminate type secondary battery. It is explanatory drawing which looked at FIG. 8a from the top. It is explanatory drawing which looked at FIG. 8a from the side. It is a graph which shows the cycle test result of a laminate type secondary battery.

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

  The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode having a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a lithium inert metal or lithium inert metal that does not form an intermetallic compound with lithium. And a negative electrode having a negative electrode active material containing Si alone.

(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 . Moreover, the particle size of PAN is preferably about 0.5 μm to 50 μm, more preferably about 1 μm 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 near 25 ° was confirmed in the diffraction angle (2θ) range of 20 ° to 30 °. It was done. 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 nonaqueous electrolyte secondary battery of the present invention using sulfur-modified PAN as the positive electrode active material is measured, the same peak as the above peak, or the above peak is the number and the position of the peak top. A slightly different peak is observed.

〔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.

  Sulfur modified pitch can be manufactured by heat-treating sulfur and pitches.

  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.

  FIG. 3 shows the result of X-ray diffraction of the sulfur-modified pitch. As shown in FIG. 3, in the diffraction angle (2θ) range 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 non-aqueous electrolyte secondary battery of the present invention using sulfur-modified pitch as the positive electrode active material was measured, peaks that were the same as these peaks or slightly different in number and peak top position were confirmed. The 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]
As the carbon source compound, polycyclic aromatic hydrocarbons (PAH) other than the above-described pitches may be used.

  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. Examples of carbon source compounds composed of PAHs other than benzene include acenes having a structure in which six or more six-membered rings having a benzene ring structure are connected in a straight chain, and three or more six-membered rings are not linear. It is preferable to use at least one of compounds having a bent structure and sulfur.

  Examples of acenes that are polycyclic aromatic hydrocarbons in which a plurality of aromatic rings share a side and are connected in a straight chain include bicyclic naphthalene, tricyclic anthracene, tetracyclic tetracene, pentacyclic pentacene, 6 There are ring hexacene, 7 ring heptacene, 8 ring octacene, 9 ring nonacene, and 10 or more aromatic rings linked together, 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 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 of the non-aqueous electrolyte secondary battery may deteriorate when used for the positive electrode of the non-aqueous electrolyte secondary battery.

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

  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.

<Heat treatment process>
In order to manufacture the sulfur-based positive electrode active material, a process (heat treatment process) of heating the mixed raw material in which the above-described carbon source compound and sulfur are mixed may be performed. 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. 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.

  For example, when PAN is used as the carbon source compound, the heating temperature is preferably 250 ° C. or higher and 500 ° C. or lower, more preferably 250 ° C. or higher and 400 ° C. or lower, and 300 ° C. or higher and 400 ° C. or lower. Further preferred. 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 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, when sulfur is excessively blended with respect to the carbon source compound, the above-described sulfur electrolyte solution is obtained by removing elemental sulfur from the object to be treated (sulfur-carbon source compound complex) after the heat treatment step. It is possible to suppress the adverse effect of elemental sulfur that the electrolytic solution gradually deteriorates due to elution and the battery capacity decreases. 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.

(Negative electrode active material)
The negative electrode active material contains Si alone. The theoretical capacity of carbon, which is a carbon-based material, is 372 mAhg ^−1, whereas the theoretical capacity of Si, which is a metal that can be alloyed with lithium, is 4200 mAhg ⁻¹ . However, Si has a much larger volume change with lithium insertion / extraction than carbon materials.

  Further, the negative electrode active material contains lithium inert metal or lithium inert metal silicide which does not form an intermetallic compound with lithium other than Si alone. Lithium inert metals or silicides of lithium inert metals are not involved in charge / discharge. Therefore, the stress at the time of expansion | swelling of Si simple substance which occludes lithium is relieve | moderated as the whole active material, and the active material is prevented from cracking or peeling from the current collector.

  As the lithium inert metal, at least one selected from the group consisting of Ti, Zr, Ni, Cu, Fe, and Mo is preferable, and Mo is particularly preferable. By including a lithium inert metal or a silicide thereof in addition to Si having a low electron conductivity in the active material, the electron conductivity can be further improved in accordance with the effects described above. In the charge / discharge reaction of the active material, it is essential to exchange electrons between the active material and the current collector at the same time as the exchange of lithium ions. Therefore, deterioration of cycle characteristics can be suppressed by improving the electronic conductivity of the active material.

  A composite powder of a lithium inert metal or a lithium inert metal silicide that does not form an intermetallic compound with lithium and Si alone can be produced, for example, by a mechanical alloying method. In this method, it is possible to easily form fine primary particles having a particle size of about 10 to 200 nm. As a specific method, a composite powder which is a target active material is obtained by mixing raw materials composed of a plurality of components and performing mechanical alloying treatment so that the primary particle diameter is about 10 to 200 nm. Can do. It is also possible to obtain a mixture of Si simple substance and a silicide of lithium inert metal using only Si simple substance and lithium inert metal as raw materials. That is, a silicide of a lithium inert metal can be made from Si and a lithium inert metal as raw materials by mechanical alloying treatment. The centrifugal acceleration (input energy) in the mechanical alloying process is preferably about 5 to 20G, and more preferably about 7 to 15G.

  The mechanical alloying process itself may be applied as it is. For example, a composite powder that is a target active material can be obtained by compounding (partial alloying) the raw material mixture while repeating mixing and adhesion by mechanical bonding force. As an apparatus used for the mechanical alloying treatment, a mixer, a disperser, a pulverizer and the like generally used in the powder field can be used as they are. Specific examples include a reiki machine, a ball mill, a vibration mill, an agitator mill, and the like. In particular, in order to reduce the stacking of powders mainly composed of battery active materials existing between networks, it is necessary to efficiently disperse the powders that are overlapped or aggregated during the compositing operation one by one. Therefore, it is desirable to use a mixer that can give a shearing force. The operating conditions of these devices are not particularly limited. Moreover, it can also be set as composite powder by mixing the Si simple substance separately manufactured with said method, and the lithium inert metal or the silicide of a lithium inert metal.

  The mixing ratio of Si simple substance and lithium inert metal or lithium inert metal silicide is such that the molar ratio of Si simple substance and lithium inert metal or lithium inert metal silicide is 1: 1-3: 1 is preferable. Moreover, it is preferable that the amount of silicic acid of a lithium inert metal or a lithium inert metal is 40 mass% or more per 100 mass% of negative electrode active materials.

  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. When these negative electrode active materials are used, substances such as Li and Na that are ionized and moved between the positive electrode and the negative electrode (so-called charge carriers, carriers) are transferred between the positive electrode and the negative electrode. It is not included in either. For this reason, it is preferable that the negative electrode is pre-doped with Li or Na by an electrochemical method, or that a Li source or a Na source (for example, metallic Li) is previously integrated on the surface and / or inside of the negative electrode. The amount of Li integrated or pre-doped into the negative electrode varies depending on the use conditions of the battery such as the type and combination of sulfur-based positive electrode active material, non-Li / Na-based negative electrode active material, electrolyte, 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.

  In the nonaqueous electrolyte secondary battery of the present invention, at least one of the positive electrode and the negative electrode has a binder, and the binder is obtained by curing an alkoxysilyl group-containing resin having a structure represented by the formula (I).

  The structure represented by the formula (I) includes a sol-gel reaction site structure, and the alkoxysilyl group-containing resin is a hybrid of a resin that is an organic material and silica that is an inorganic material. Since the alkoxysilyl group-containing resin is a hybrid of resin and silica, it has good adhesion to any of the current collector, active material, and conductive additive, which are inorganic components. Can be held firmly.

The sol-gel reaction site structure is a structure that contributes to a reaction when performing the sol-gel method. In the sol-gel method, a solution of an inorganic or organometallic salt is used as a starting solution, this solution is converted into a colloidal solution (Sol) by hydrolysis and condensation polymerization reaction, and a solid (Gel) that loses fluidity by further promoting the reaction is obtained. It is a method of forming. In general, the sol-gel method uses a metal alkoxide (a compound represented by M (OR) _x , M is a metal, and R is an alkyl group) as a raw material. The compound represented by M (OR) _x reacts as shown in the following formula (A) by hydrolysis.
nM (OR) _x + nH ₂ O → nM (OH) (OR) _x−1 + nROH (A)

When the reaction shown here is further promoted, it finally becomes M (OH) _x , and when a polycondensation reaction takes place between the two molecules of hydroxide produced here, the reaction occurs as shown in the following formula (B).
M (OH) _x + M (OH) _x → (OH) _x−1 M−O−M (OH) _x−1 + H ₂ O (B)

  At this time, all the OH groups can be polycondensed, and a dehydration condensation polymerization reaction with an organic polymer having an OH group at the terminal is also possible.

  Therefore, a sol-gel reaction also occurs when the binder resin is cured. The sol-gel reaction reacts between sol-gel reaction sites, and the sol-gel reaction site also reacts with the OH group of the resin. It is also conceivable that the sol-gel reaction site reacts with the current collector surface. Therefore, the alkoxysilyl group-containing resin can be strongly bound to the current collector and the active material.

When the alkoxysilyl group-containing resin is cured, the formula (II): R ¹ _m SiO _{(4-m) / 2} (m = 0 to 2 integer, R ¹ represents an alkyl group or aryl group having 8 or less carbon atoms) It becomes the alkoxysilyl group containing resin hardened | cured material which has a structure shown by these. The structure represented by the formula (II) is a gelled fine silica site structure (high-order network structure of siloxane bonds). This structure is a structure of an organosilicon polymer composed of a siloxane bond, and is a structure obtained by polycondensation of silanol of the following formula (C).
_{nR m Si (OH) 4-} m → (R m SiO (4-m) / 2) n ···· formula (C)
(R: organic group, m = 1 to 3, n> 1)

  As the resin that is an organic material, bisphenol A type epoxy resin, novolac type epoxy resin, acrylic resin, phenol resin, polyamic acid resin, soluble polyimide resin, polyurethane resin, and polyamideimide resin can be used. These resins and silica can be made into a hybrid having a structure represented by the formula (I) by a sol-gel method, and each alkoxy group-containing silane-modified bisphenol A type epoxy resin, alkoxy group-containing silane-modified novolak type epoxy resin, Alkoxy group-containing silane-modified acrylic resin, alkoxy group-containing silane-modified phenol resin, alkoxy group-containing silane-modified polyamic acid resin, alkoxy group-containing silane-modified soluble polyimide resin, alkoxy group-containing silane-modified polyurethane resin or alkoxy group-containing silane-modified polyamideimide resin It becomes.

  Each of the binder resins can be synthesized by a known technique. For example, when the binder resin is an alkoxy group-containing silane-modified polyamic acid resin, it can be formed by reacting a polyamic acid composed of a carboxylic acid anhydride component and a diamine component as a precursor with an alkoxysilane partial condensate. . The alkoxysilane partial condensate is obtained by partially condensing a hydrolyzable alkoxysilane monomer in the presence of an acid or base catalyst and water. At this time, the alkoxysilane partial condensate may be reacted with an epoxy compound in advance to form an epoxy group-containing alkoxysilane partial condensate and then reacted with a polyamic acid to form an alkoxy group-containing silane-modified polyamic acid resin.

  Moreover, a commercial item can be used suitably for said binder resin. For example, the trade name “COMPOCERAN E” (manufactured by Arakawa Chemical Industries), which is an alkoxy group-containing silane-modified bisphenol A type epoxy resin or an alkoxy group-containing silane-modified novolak type epoxy resin, and the trade name “COMPOCELAN”, which is an alkoxy group-containing silane-modified acrylic resin. AC ”(manufactured by Arakawa Chemical Industries Co., Ltd.), trade name“ Composeran P ”(manufactured by Arakawa Chemical Industries Co., Ltd.) which is an alkoxy group-containing silane-modified phenolic resin, and trade name“ Composeran H800 ”which is an alkoxy group-containing silane-modified polyamic acid resin ( Arakawa Chemical Industries, Ltd.), trade name “Composeran H700” (made by Arakawa Chemical Industries) which is an alkoxy group-containing silane-modified soluble polyimide resin, and trade name “Yuliano U” (Arakawa Chemical Industries, which is an alkoxy group-containing silane-modified polyurethane resin). Or alkoxy group A chromatic silane-modified polyamideimide resin has the trade name "Compoceran H900" (manufactured by Arakawa Chemical Industries, Ltd.) and the like various commercial products.

  The above-mentioned product name “COMPOCERAN E” (manufactured by Arakawa Chemical Industry Co., Ltd.), the product name “COMPOCELAN AC” (manufactured by Arakawa Chemical Industry Co., Ltd.), the product name “COMPOCERAN P” (manufactured by Arakawa Chemical Industries Ltd.), the product name “COMPOCERAN H800” ( The chemical formula of the basic skeleton of Arakawa Chemical Industries, Ltd.) or the trade name “COMPOCERAN H900” (Arakawa Chemical Industries, Ltd.) is shown below.

(Bisphenol A epoxy type trade name "Composeran E")

(Product name of phenol novolac epoxy type “COMPOCERAN E”)

(Product name “Composeran AC”)

(Product name “Composeran P”)

(Product name “Composeran H800”)

(Product name “Composeran H900”)

  The alkoxysilyl group-containing resin cured product includes an alkoxy group-containing silane-modified bisphenol A-type epoxy resin cured product, an alkoxy group-containing silane-modified novolak-type epoxy resin cured product, an alkoxy group-containing silane-modified acrylic resin cured product, and an alkoxy group-containing silane-modified phenol. Any one selected from a cured resin, an alkoxy group-containing silane-modified polyimide resin cured product, an alkoxy group-containing silane-modified polyurethane resin cured product, and an alkoxy group-containing silane-modified polyamideimide resin cured product can be used. This binder corresponds to a cured product of the binder resin described above.

  At least one of the positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery can be produced by the following method. The manufacturing method of an electrode has an application | coating process and a hardening process. The coating process is a process of coating the binder resin and the active material on the surface of the current collector. Moreover, you may apply | coat a conductive support agent together in an application | coating process. The curing step is a step of curing the binder resin and binding the active material to the current collector surface. The binder resin is an alkoxysilyl group-containing resin having a structure represented by the formula (I).

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

  What is necessary is that the binder resin and the active material can be placed on the current collector. As a coating method, a coating method generally used for producing electrodes such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method can be used.

  A conductive additive can be applied to the surface of the current collector together with the active material. The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination as a conductive additive. Can be added. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 20 to 100 parts by mass with respect to 100 parts by mass of the active material.

  The binder resin is used as a binder when these active materials and conductive assistants are applied to the current collector. The binder resin is required to bind the active material and the conductive assistant in as small an amount as possible, and the amount is desirably 0.5% by mass to 50% by mass of the total of the active material, the conductive auxiliary and the binder resin.

  In the coating step, the binder resin and the active material are mixed in advance, and a solvent or the like is added to form a slurry, which is then applied to the current collector. The conductive auxiliary agent may also be applied as a slurry. The coating thickness is preferably 10 μm to 300 μm. In addition, the mixing ratio of the binder resin and the active material is preferably by weight, and the active material: binder resin = 99: 1 to 70:30. The mixing ratio in the case of containing a conductive auxiliary agent is preferably active material: conductive auxiliary agent: binder resin = 98: 1: 1 to 60:20:20.

  The curing step is a step of curing the binder resin that is an alkoxysilyl group-containing resin. The active material is bound to the current collector surface by curing the binder resin. When the conductive assistant is included, the conductive assistant is also bound in the same manner. What is necessary is just to harden | cure binder resin according to the hardening conditions of binder resin to be used. Further, when the binder resin is cured, a sol-gel curing reaction is also caused by the structure represented by the formula (I) of the binder resin. Since the alkoxysilyl group-containing resin in which the sol-gel curing reaction has occurred has a fine gelled silica site structure (high-order network structure of siloxane bonds), it has good adhesion to the active material, the conductive auxiliary agent and the current collector.

  The nonaqueous electrolyte secondary battery of the present invention includes at least constituent elements including a positive electrode, a negative electrode, and an electrolyte. In the nonaqueous electrolyte secondary battery of the present invention, a separator may be provided between the positive electrode and the negative electrode. A separator is used as needed. The separator separates the positive electrode and the negative electrode and holds the non-aqueous electrolyte, and a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used. .

  As the electrolyte, an organic solvent-based electrolytic solution in which an electrolyte is dissolved in an organic solvent called a nonaqueous electrolytic solution, a polymer gel electrolyte composed of a polymer gel containing an electrolytic solution, or the like can be used.

  For example, cyclic esters, chain esters, and ethers can be used as the solvent. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers that can be used include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, and the like.

As the electrolyte dissolved in the solvent, for example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm ³ , particularly about 0.4 to 1.5 mol / dm ³ .

  Moreover, in order to improve the safety | security and storage characteristic of a battery, you may make an non-aqueous electrolyte contain an aromatic compound. As the aromatic compound, benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.

  The polymer gel electrolyte is composed of a polymer gel containing an electrolyte solution. As the polymer gel, it is preferable to use a prepolymer TA210 (polyfunctional acrylate polymer having a polyoxyalkylene chain) that is polymerized with a photopolymerization initiator (for example, IRGACURE 184), and acrylonitrile and methyl acrylate or methacrylic acid. Copolymers may be used.

For example, as an electrolytic solution, 0.5 mol / l to 1.7 mol / l of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate. A solution dissolved at a certain concentration can be used.

  A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, the electrode body is impregnated with a nonaqueous electrolyte solution and the nonaqueous electrolyte secondary Use batteries.

  The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The non-aqueous electrolyte secondary battery of the present invention described above is charged in nighttime power and supplied to a house, factory or office in the daytime, in addition to the fields of mobile devices such as mobile phones and laptop computers, and information-related devices. The battery can be suitably used in the field of stationary and automobiles such as a battery that is charged with a solar battery in the daytime and a battery that is charged at night. For example, if this non-aqueous electrolyte secondary battery is mounted on a vehicle, the non-aqueous electrolyte secondary battery can be used as a power source for an electric vehicle.

[vehicle]
The vehicle of the present invention is equipped with the non-aqueous electrolyte secondary battery. The vehicle of the present invention can be equipped with a non-aqueous electrolyte secondary battery having excellent cycle characteristics, and can be a high-performance vehicle. The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, a forklift, an electric wheelchair, an electric assist. Bicycles and electric motorcycles are examples.

  As mentioned above, although the nonaqueous electrolyte secondary battery of this invention and embodiment of the vehicle were demonstrated, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

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

(Production of sulfur-modified PAN)
[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 treated after the heat treatment process was evaporated and removed, and a sulfur-modified PAN was obtained as a sulfur-based positive electrode active material that does not contain (or substantially does not contain) elemental sulfur.

(Negative electrode)
FIG. 6 is a partial schematic explanatory view of the negative electrode of the nonaqueous electrolyte secondary battery of the present invention. In one embodiment of the negative electrode, the Si simple substance 12, the lithium inert metal or the lithium inert metal silicide 15 and the conductive additive 13 are bound to the surface of the current collector 11 via the binder resin 14. .

  The binder resin 14 is dispersed between the dispersed Si simple substance 12, the dispersed lithium inert metal or the silicide 15 of the lithium inert metal, the dispersed conductive assistant 13 and the current collector 11. The single body 12, the lithium inert metal or the silicide 15 of the lithium inert metal, the conductive auxiliary agent 13, and the current collector 11 are connected to each other.

  Since FIG. 6 is a schematic diagram, the drawn shape is not accurate. The binder resin 14 is described in powder form in FIG. Further, as shown in FIG. 6, the surface of the current collector 11 is entirely covered with a binder resin 14, a Si simple substance 12, a lithium inert metal or a silicide 15 of a lithium inert metal, and / or a conductive aid 13. Instead, there are gaps between the substances and the surface of the current collector 11.

  A coin-type secondary battery was produced as follows, and a charge / discharge cycle test was performed using the coin-type secondary battery.

<Coin-type secondary battery>
(Preparation of negative electrode)
Table 1 shows the constituent components and mixing ratio of each negative electrode.

As the negative electrode active material, Si alone and lithium inert metal or lithium inert metal silicide were used. In the negative electrode 1, Si powder and iron metal powder were used, in the negative electrode 2 and negative electrode 3, Si powder and MoSi ₂ powder were used, and in the negative electrode 4 and negative electrode 5, only Si powder was used.

Si particles (manufactured by High-Purity Chemical) having a particle diameter of 4 μm or less were prepared as Si powder. Iron particles having a particle diameter of 3 to 5 μm (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were prepared as the iron metal powder. As the MoSi ₂ powder, MoSi ₂ particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) having an average particle diameter of 8 μm were prepared. Moreover, KB (Ketjen Black) manufactured by Ketjen Black International Co., Ltd. was prepared as a conductive additive.

  In the negative electrode 1 to the negative electrode 4, the binder resin is an alkoxy-containing silane-modified polyamic acid resin (manufactured by Arakawa Chemical Industry Co., Ltd., trade name Composeran, product number H850D, solvent composition: N, N-dimethylacetamide (DMAc), 15% cured residue, Viscosity 4100 mPa · s / 25 ° C., silica in the cured residue, 2 wt%) was prepared. The alkoxy-containing silane-modified polyamic acid resin is one of the above-mentioned trade name Composeran H800 series and has the structure shown in [Chemical Formula 6]. In the negative electrode 5, PVdF (made by Kureha) was prepared as a binder resin.

Each active material was mixed in the ratio shown in Table 1. The negative electrode 1 has a mass ratio such that the molar ratio of Si and Fe is Si: Fe = 2: 1. This is the mixing ratio when the mass ratio is 1: 1. The negative electrode 2 was mixed at a mass ratio such that the volume occupied by Si and MoSi ₂ was approximately 1: 1. The negative electrode 3 had a mass ratio such that Si: MoSi ₂ = about 1: 2. The negative electrode 4 and the negative electrode 5 have the same mixing ratio except that the active material is only Si and the binder resin is different.

  For example, in the negative electrode 1, a mixed powder of Si powder 43 wt% and iron powder 42 wt% is put in a paste 10 wt% in which an alkoxy-containing silane-modified polyamic acid resin is dissolved in N-methylpyrrolidone (NMP), and ketjen black (KB) 5 wt% Was added and mixed to prepare a slurry. The other negative electrodes 2 to 5 were also prepared in the same manner.

  After slurry adjustment, the slurry was placed on an electrolytic copper foil having a thickness of 18 μm, and a film was formed on the copper foil using a doctor blade.

After the obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, the current collector made of electrolytic copper foil and the negative electrode layer made of the above composite powder were firmly adhered and bonded by a roll press machine. I let you. This was extracted with a 1 cm ² circular punch, and the negative electrode 1 to the negative electrode 4 were vacuum-dried at 200 ° C. for 3 hours and the negative electrode 5 was 140 ° C. for 3 hours to obtain an electrode having a thickness of 100 μm or less.

<Coin-type secondary battery production>
(Test Example 1, Test Example 2, Test Example 3, Test Example 4, Test Example 5)
The above-mentioned electrodes (negative electrode 1, negative electrode 2, negative electrode 3, negative electrode 4 and negative electrode 5) were used as the negative electrode, and lithium metal was used as the positive electrode, and 1 mol of LiPF ₆ / ethylene carbonate (EC) + diethyl carbonate ( DEC) (EC: DEC = 1: 1 (volume ratio)) A coin-type model battery (CR2032 type) was produced in a dry room using an electrolytic solution. A coin-type model battery is a model of Test Example 1 to Test Example 5 in which a spacer, a Li foil having a thickness of 500 μm as a counter electrode, a separator (trade name Celgard # 2400 manufactured by Celgard), and an evaluation electrode are sequentially stacked and caulked. A battery was produced.

<Coin-type secondary battery evaluation>
Evaluation of the evaluation electrode in this model battery was performed by the following method. First, the model battery was discharged at a constant current of 0.2 mA until reaching 0 V, and after resting for 5 minutes, it was charged until it reached 2.0 V at a constant current of 0.2 mA. This was made into 1 cycle, charging / discharging was performed repeatedly and the charge capacity was investigated.

  FIG. 7 shows a graph showing the number of cycles and the charge capacity per unit mass of Si for the model batteries of Test Examples 1 to 5. As is clear from FIG. 7, first, in the model batteries of Test Examples 1 to 4, the amount of decrease in the initial charge capacity is smaller than that of the model battery of Test Example 5. In other words, in the model battery of Test Example 5 using the conventional binder resin PVdF, the charge capacity dropped to almost 10% in one cycle test, whereas the binder resin was modified with alkoxy group-containing silane. In the model batteries of Test Examples 1 to 4 using the polyamic acid resin, a charge capacity of about 70 to 80% is maintained. In addition, the charge capacity after 10 cycles of the model battery of Test Example 5 is 0, whereas the charge capacity after 10 cycles is maintained at 50% or more in the model batteries of Test Examples 1 to 4. .

  Further, the model battery of Test Examples 1 to 3 in which Si negative electrode and lithium inert metal or silicide of lithium inert metal are included in the negative electrode active material and the model battery of Test Example 4 in which the negative electrode active material is only Si simple substance. In comparison, it can be seen that in the model batteries of Test Examples 1 to 3, the charging capacity decreases after the 20th cycle compared to the model battery of Test Example 4.

Further, as can be seen from FIG. 7, the method of decreasing the charge capacity of the model batteries of Test Example 2 and Test Example 3 in which the negative electrode active material contains Si alone and MoSi ₂ is gentler than that of the model battery of Test Example 1. . This is probably because MoSi ₂ contained in the negative electrode active materials of Test Example 2 and Test Example 3 is hard. It is considered that the cycle characteristics were further improved by suppressing hard cracking and peeling due to volume expansion of Si accompanying occlusion and release of lithium by hard MoSi ₂ . As can be seen from FIG. 7, the model batteries of Test Example 2 and Test Example 3 differed in the mixing ratio of each component, but there was no significant difference in cycle characteristics.

<Laminated secondary battery>
(Preparation of positive electrode)
Sulfur modified PAN, acetylene black (AB) and polyimide (PI) (manufactured by Arakawa Chemical Co., product number HBI-44B) were weighed so as to be sulfur modified PAN: AB: PI = 75: 15: 10 (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 coated using an applicator on the surface of an aluminum foil (made by Fukuda foil powder industry) with a thickness of 15 μm adjusted to φ0.3 and porosity of 17%, dried at 200 ° C. for 5 hours, and rectangular Cut to the top (40 mm × 80 mm) to obtain a positive electrode.

(Preparation of negative electrode)
As the SiO _x , a powdery material having 0.9 ≦ x ≦ 1.1 and an average particle diameter of 5 μm was used.
SiO _x , Ketjen Black (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 coated on the surface of a 18 μm thick copper foil current collector using an applicator, dried at 200 ° C. for 5 hours, and cut into a rectangle (40 mm × 80 mm) to obtain a negative electrode.

(Production of laminate type secondary battery)
The structure of the laminated secondary battery will be described with reference to FIGS. 8a, 8b, and 8c. FIG. 8a is an explanatory diagram of a laminated configuration of a laminated secondary battery, FIG. 8b is an explanatory diagram of FIG. 8a viewed from above, and FIG. 8c is an explanatory diagram of FIG. 8a viewed from the side. 8 positive electrodes 103 coated on both sides with slurry applied to both sides, 7 negative electrodes 102 coated on both sides, and 2 negative electrodes 102 coated on one side are alternately laminated positive and negative, A separator 104 was sandwiched between the electrodes. As the separator 104, a rectangular sheet (Celgard 2400, 40 mm × 80 mm, thickness 25 μm) of a polypropylene microporous film was used. An aluminum tab 109 is welded to each positive electrode 103, and a nickel tab 108 is welded to each negative electrode 102. Lithium electrodes 101 produced by attaching metallic lithium to a copper mesh with nickel tabs 107 were placed on both sides of the eight laminated electrodes. The lithium electrode 101 and the eight stacked electrodes are collectively referred to as an electrode group. The calculated capacity of this 8-layered electrode is 1A.

The non-aqueous electrolyte 105 is prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 1 (volume ratio). And prepared. Next, the electrode group was covered with a set of two aluminum laminate films 106, and the nonaqueous electrolyte solution 105 was injected into the bag-shaped portion sealed on the three sides. Thereafter, the remaining one side was sealed to obtain a laminate type secondary battery in which the four sides were hermetically sealed and the electrode group and the nonaqueous electrolyte solution 105 were sealed. In addition, a part of the tab of both electrodes and the tab of the lithium electrode extends to the outside for electrical connection with the outside.

(Pre-doping of laminated secondary battery)
A half cell was fabricated by electrically connecting the lithium electrode and the negative electrode. When an electric current is applied in this state, only the negative electrode can be predoped with lithium. When an electric current is applied to the half-cell, lithium ions supplied from the lithium electrode pass through the positive electrode layer and the apertured current collector and are trapped in the negative electrode. At this time, since the positive electrode is not electrically connected, lithium ions are not trapped by the positive electrode. However, since the positive electrode becomes a resistance when lithium ions pass, it is slowly pre-doped. The pre-doping conditions were a temperature of 25 ° C., a rate of 1/100 C, and a cut-off voltage of 0 CV to 0.01 V.

(Battery characteristics of laminate type secondary battery)
A charge / discharge cycle test was performed using the pre-doped laminated secondary battery. The cycle test conditions are a temperature of 25 ° C., a rate of 0.1 C, and a cutoff voltage: 0.3 V to 3 V. The number of cycles was 70. The cycle test results of the laminate type secondary battery are shown in FIG.

  As can be seen from FIG. 9, even after 50 cycles, the discharge capacity was 600 mAh / g or more, and the cycle test result was good.

  The nonaqueous electrolyte secondary battery of the present invention has a sulfur-based positive electrode active material as a positive electrode active material, a lithium inert metal or lithium inert metal silicide that does not form an intermetallic compound with lithium, Si alone, The binder resin has the alkoxysilyl group-containing resin.

  From the cycle test results of the laminate type secondary battery, it was found that the non-aqueous electrolyte secondary battery using a sulfur-based positive electrode active material as the positive electrode active material has a high capacity and excellent cycle characteristics.

  From the test results of the coin-type model battery, the model batteries of Test Example 1 to Test Example 3 in which the negative electrode active material contains Si alone and lithium inert metal or a silicide of lithium inert metal, the negative electrode active material is only Si simple substance. Compared with the model battery of Test Example 4, the model batteries of Test Examples 1 to 3 showed that the method of decreasing the charge capacity after the 20th cycle was gradual.

  Accordingly, the positive electrode active material has a sulfur-based positive electrode active material, has a negative electrode active material containing lithium inert metal or lithium inert metal silicide that does not form an intermetallic compound with lithium, and Si alone, and a binder. The non-aqueous electrolyte secondary battery of the present invention having the above-mentioned alkoxysilyl group-containing resin in the resin is considered to have an effect of high discharge capacity and excellent cycle characteristics.

  DESCRIPTION OF SYMBOLS 1, Reaction apparatus, 2: Reaction container, 3: Cover, 4: Thermocouple, 5: Gas introduction pipe, 6: Gas discharge pipe, 7: Electric furnace, 11, Current collector, 12, Si simple substance, 13, Conduction Auxiliary, 14, binder resin, 15, lithium inert metal or lithium inert metal silicide, 101, lithium electrode, 102, negative electrode, 103, positive electrode, 104, separator, 105, non-aqueous electrolyte.

Claims (5)

A non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode,
The positive electrode has a sulfur-based positive electrode active material containing carbon (C) and sulfur (S),
The negative electrode has a negative electrode active material containing a lithium inert metal that does not form an intermetallic compound with lithium or a silicide of the lithium inert metal, and Si alone,
At least one of the positive electrode and the negative electrode has a binder,
The non-aqueous electrolyte secondary battery, wherein the binder is obtained by curing an alkoxysilyl group-containing resin having a structure represented by the formula (I).

(R ₁ is an alkyl group having 1 to 8 carbon atoms, R ₂ is an alkyl group having 1 to 8 carbon atoms or an alkoxy group, and q is an integer of 1 to 100) 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;
Sulfur and
The nonaqueous electrolyte secondary battery according to claim 1, comprising:   The non-aqueous electrolyte secondary battery according to claim 2, wherein the sulfur-based positive electrode active material has a carbon skeleton derived from the carbon source compound.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium inert metal is at least one selected from the group consisting of Ti, Zr, Ni, Cu, Fe, and Mo.   The vehicle carrying the nonaqueous electrolyte secondary battery of any one of Claims 1-4.

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