JP7383254B2 - Sulfur active material-containing electrode composition, and electrodes and batteries using the same - Google Patents

Description

The present invention relates to a sulfur active material-containing electrode composition, and an electrode and battery using the same.

In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. In the automobile industry, expectations are high for reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-aqueous batteries such as secondary batteries for motor drives hold the key to their practical application. Electrolyte secondary batteries are actively being developed.

Secondary batteries for motor drives are required to have extremely high output characteristics and high energy compared to consumer lithium ion secondary batteries used in mobile phones, notebook computers, and the like. Therefore, lithium ion secondary batteries, which have the highest theoretical energy of all practical batteries, are attracting attention and are currently being rapidly developed.

Here, lithium ion secondary batteries that are currently in widespread use use a flammable organic electrolyte as an electrolyte. Such liquid-based lithium ion secondary batteries require more stringent safety measures against leakage, short circuits, overcharging, etc. than other batteries.

Therefore, in recent years, research and development on all-solid-state lithium ion secondary batteries using oxide-based or sulfide-based solid electrolytes as electrolytes has been actively conducted. A solid electrolyte is a material mainly composed of an ion conductor capable of ion conduction in a solid state. Therefore, in principle, all-solid-state lithium ion secondary batteries do not suffer from various problems caused by flammable organic electrolytes, unlike conventional liquid-based lithium ion secondary batteries. Furthermore, in general, the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials can significantly improve the output density and energy density of the battery. All-solid-state lithium-ion secondary batteries using elemental sulfur (S) or sulfide-based materials as positive electrode active materials are promising candidates.

As a technique for using an electrode active material containing sulfur in an all-solid-state battery, for example, Patent Document 1 discloses a thin film of sulfur-coated conductive carbon. This material is selected from the group consisting of furnace black, activated carbon, and acetylene black, and the surface of conductive carbon having a predetermined BET specific surface area is coated with a sulfur film having a predetermined thickness. According to Patent Document 1, by using this thin film sulfur-coated conductive carbon as a positive electrode mixture of an all-solid-state battery, the excellent physical properties of sulfur can be utilized to the fullest, and excellent discharge capacity and rate characteristics can be achieved. It is said that it can be done.

JP2014-17240A

However, according to studies conducted by the present inventors, it has been found that even when the thin sulfur-coated conductive carbon disclosed in Patent Document 1 is used, sufficient rate characteristics may not be achieved.

Therefore, an object of the present invention is to provide a means for further improving the rate characteristics of a battery when an electrode active material containing sulfur is used as a positive electrode active material of the battery.

The present inventors conducted extensive studies to solve the above problems. As a result, they discovered that the above problems could be solved by using a porous carbon material exhibiting a predetermined X-ray diffraction pattern as a conductive agent and including it in the positive electrode mixture together with an electrode active material containing sulfur. The invention was completed.

That is, according to one embodiment of the present invention, in the X-ray diffraction spectrum of an electrode active material containing sulfur, a peak derived from the (002) plane of carbon is not observed, or a peak derived from the (002) plane of carbon is observed. A sulfur active material-containing conductive agent containing a porous carbon material having a peak half-width of 5° or more and a peak half-width derived from the (10) plane of carbon of 3.2° or less. An electrode composition is provided.

According to the present invention, due to physical properties such as high specific surface area, excellent electronic conductivity, and high flexibility (elasticity) possessed by the predetermined conductive aid (porous carbon material), the sulfur-based electrode contained in the electrode The characteristics of the active material can be fully utilized. As a result, when an electrode active material containing sulfur is used as a positive electrode active material of a battery, it becomes possible to further improve the rate characteristics of the battery.

1 is a cross-sectional view schematically showing a bipolar all-solid-state lithium ion secondary battery that is an embodiment of the present invention. FIG. 1 is a schematic diagram showing an alumina mold carbon material according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the appearance of a bipolar secondary battery (flat lithium ion secondary battery) according to an embodiment of the present invention. 2 is a graph showing nitrogen adsorption/desorption isotherms of the porous carbon material after mold removal in Production Example 1-1 and the porous carbon material (1-1) obtained after heat treatment. 2 is a graph showing the pore size distribution of the porous carbon material after mold removal in Production Example 1-1 and the porous carbon material (1-1) obtained after heat treatment. This is an XRD pattern showing the results of XRD measurement of the porous carbon material (1-1) obtained in Production Example 1-1. 1 is a TEM photograph of porous carbon material (1-1) obtained in Production Example 1-1. 1 is a TEM photograph of porous carbon material (1-1) obtained in Production Example 1-1. 1 is a graph showing nitrogen adsorption/desorption isotherms before and after applying compressive force to the porous carbon material (1-1) obtained in Production Example 1-1. 2 is a graph showing the nitrogen adsorption/desorption isotherm of the porous carbon material (1-2) obtained in Production Example 1-2. This is an XRD pattern showing the results of XRD measurement of the porous carbon material (2-1) obtained in Production Example 2-1. This is a photograph (magnification: 1000 times, 5000 times, and 20000 times) of the composite particles obtained in Examples 2-1 to 2-3 observed by SEM.

Hereinafter, the embodiments of the present invention described above will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the claims and is not limited only to the following embodiments. Below, we will take as an example a bipolar all-solid-state lithium ion secondary battery, which is a type of secondary battery, and also consider a case where the positive electrode active material is an electrode active material containing sulfur. The invention will be explained by way of example. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

One form of the present invention is an electrode active material containing sulfur, and in an X-ray diffraction spectrum, no peak derived from the (002) plane of carbon is observed, or half of the peak derived from the (002) plane of carbon is observed. A sulfur active material-containing electrode composition comprising a conductive additive containing a porous carbon material having a value width of 5° or more and a half-width of a peak derived from the (10) plane of carbon of 3.2° or less. be. According to the sulfur active material-containing electrode composition according to the present embodiment, the sulfur active material-containing electrode composition is caused by the physical properties such as a high specific surface area, excellent electronic conductivity, and high flexibility (elasticity) that the predetermined conductive agent (porous carbon material) has. Therefore, the characteristics of the sulfur-based electrode active material contained in the electrode can be fully utilized. As a result, when an electrode active material containing sulfur is used as a positive electrode active material of a battery, it becomes possible to further improve the rate characteristics of the battery.

<Bipolar secondary battery>
FIG. 1 is a cross-sectional view schematically showing a bipolar all-solid-state lithium ion secondary battery (bipolar secondary battery) according to an embodiment of the present invention. The bipolar secondary battery 10 shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charging/discharging reaction actually proceeds is sealed inside a laminate film 29 that is a battery exterior body. In the bipolar secondary battery 10 shown in FIG. 1, for example, the positive electrode active material layer 15 or the negative electrode active material layer 13 is formed from the sulfur active material-containing electrode composition according to the present embodiment.

As shown in FIG. 1, the power generation element 21 of the bipolar secondary battery 10 of this embodiment has a positive electrode active material layer 13 electrically coupled to one surface of the current collector 11. It has a plurality of bipolar electrodes 23 each having an electrically coupled negative electrode active material layer 15 formed on its opposite surface. Each bipolar electrode 23 is stacked with the solid electrolyte layer 17 in between to form the power generation element 21 . Note that the solid electrolyte layer 17 has a structure in which a solid electrolyte is formed into layers. At this time, the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23 are arranged to face each other with the solid electrolyte layer 17 in between. , bipolar electrodes 23 and solid electrolyte layers 17 are alternately stacked. That is, the solid electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. has been done. However, the technical scope of the present invention is not limited to bipolar secondary batteries as shown in FIG. It may be.

Adjacent positive electrode active material layer 13 , solid electrolyte layer 17 , and negative electrode active material layer 15 constitute one cell layer 19 . Therefore, it can be said that the bipolar secondary battery 10 has a structure in which the unit cell layers 19 are stacked. Note that the positive electrode active material layer 13 is formed only on one side of the outermost layer current collector 11a on the positive electrode side located at the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed only on one side of the negative electrode side outermost layer current collector 11b located at the outermost layer of the power generation element 21.

Furthermore, in the bipolar secondary battery 10 shown in FIG. 1, a positive electrode current collector plate (positive electrode tab) 25 is arranged adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior body. It is derived from the laminate film 29. On the other hand, a negative electrode current collector plate (negative electrode tab) 27 is arranged adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminate film 29.

Note that the number of times the cell layer 19 is stacked is adjusted depending on the desired voltage. Furthermore, in the bipolar secondary battery 10, if sufficient output can be ensured even if the thickness of the battery is made as thin as possible, the number of times the unit cell layers 19 are stacked may be reduced. In the bipolar secondary battery 10, in order to prevent external impact and environmental deterioration during use, the power generating element 21 is sealed under reduced pressure in a laminate film 29, which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode collector It is preferable to have a structure in which the electric plate 27 is taken out from the laminate film 29.

The main components of the bipolar secondary battery described above will be explained below.

[Current collector]
The current collector has a function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There is no particular restriction on the material constituting the current collector. As the constituent material of the current collector, for example, metal or conductive resin may be used.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a cladding material of nickel and aluminum, a cladding material of copper and aluminum, etc. may be used. Alternatively, it may be a foil whose metal surface is coated with aluminum. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material to the current collector by sputtering, and the like.

Furthermore, examples of the latter resin having electrical conductivity include resins in which a conductive filler is added to a non-conductive polymer material as necessary.

Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide. (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent potential or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin serving as the base material of the current collector consists only of non-conductive polymers, a conductive filler is inevitably required to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a substance that has conductivity. For example, metals, conductive carbon, and the like are examples of materials with excellent conductivity, potential resistance, or lithium ion blocking properties. The metal is not particularly limited, but includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or containing these metals. Preferably, it contains an alloy or a metal oxide. Furthermore, there are no particular limitations on the conductive carbon. Preferably, it is selected from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjenblack (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one kind.

The amount of conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally 5 to 80% by mass based on 100% by mass of the total mass of the current collector. It is.

Note that the current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a resin having conductivity. Further, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector.

[Negative electrode active material layer]
The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but includes carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Furthermore, examples of metal oxides include Nb ₂ O ₅ , Li ₄ Ti ₅ O ₁₂ , and SiO. Further, examples of the metal active material include simple metals such as In, Al, Si, and Sn, and alloys such as TiSi and La ₃ Ni ₂ Sn ₇ . Furthermore, a metal containing Li may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it contains Li, and examples include Li metal and Li-containing alloys. Examples of Li-containing alloys include alloys of Li and at least one of In, Al, Si, and Sn.

In some cases, two or more types of negative electrode active materials may be used together. Note that, of course, negative electrode active materials other than those mentioned above may be used.

Examples of the shape of the negative electrode active material include particulate (spherical, fibrous), thin film, and the like. When the negative electrode active material has a particle shape, the average particle size (D ₅₀ ) is, for example, preferably within the range of 1 nm to 100 μm, more preferably within the range of 10 nm to 50 μm, and even more preferably 100 nm. 20 μm, particularly preferably 1 to 20 μm. Note that in this specification, the value of the average particle diameter (D ₅₀ ) of the active material can be measured by a laser diffraction scattering method.

The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but for example, it is preferably within the range of 40 to 99% by mass, and preferably within the range of 50 to 90% by mass. More preferred.

Preferably, the negative electrode active material layer further includes a solid electrolyte. By including the solid electrolyte in the negative electrode active material layer, the ionic conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, and sulfide solid electrolytes are preferred.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ , LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _4, Li ₃ PS _4, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ - Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-B ₂ S ₃ , Li ₂ S-P ₂ S ₅ -Z _m S _n (where m and n are positive numbers, and Z is either Ge, Zn, or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Examples include Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In). . Note that the description “Li ₂ SP ₂ S ₅ ” means a sulfide solid electrolyte made using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions.

The sulfide solid electrolyte may have, for example, a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. . Examples of the sulfide solid electrolyte having a Li ₃ PS ₄ skeleton include LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS ₄ . Furthermore, examples of the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton include a Li-P-S solid electrolyte (eg, Li ₇ P ₃ S ₁₁ ) called LPS. Further, as the sulfide solid electrolyte, for example, LGPS expressed by Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0<x<1) or the like may be used. Among these, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing the element P, and more preferably the sulfide solid electrolyte is a material containing Li ₂ SP ₂ S ₅ as a main component. Furthermore, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I).

In addition, when the sulfide solid electrolyte is Li ₂ S-P ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is a molar ratio of Li ₂ S:P ₂ S ₅ =50:50 to 100. :0, and particularly preferably Li ₂ S:P ₂ S ₅ =70:30 to 80:20.

Further, the sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method. Note that sulfide glass can be obtained, for example, by performing mechanical milling (ball mill, etc.) on a raw material composition. Further, crystallized sulfide glass can be obtained, for example, by heat-treating sulfide glass at a temperature equal to or higher than the crystallization temperature. Further, the ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25° C.) is preferably 1×10 ⁻⁵ S/cm or more, and 1×10 ⁻⁴ S/cm or more. More preferably, it is at least cm. Note that the ionic conductivity value of the solid electrolyte can be measured by an AC impedance method.

Examples of the oxide solid electrolyte include compounds having a NASICON type structure. Examples of compounds having a NASICON type structure include a compound represented by the general formula Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (0≦x≦2) (LAGP), and a general formula Li _1+x Al _x Ti _{2 -x} (PO ₄ ) ₃ (0≦x≦2) (LATP) and the like. In addition, other examples of oxide solid electrolytes include LiLaTiO (e.g., Li _0.34 La _0.51 TiO ₃ ), LiPON (e.g., Li _2.9 PO _3.3 N _0.46 ), LiLaZrO (e.g. , Li ₇ La ₃ Zr ₂ O ₁₂ ), and the like.

Examples of the shape of the solid electrolyte include particle shapes such as true spheres and ellipsoids, thin film shapes, and the like. When the solid electrolyte has a particle shape, its average particle diameter (D ₅₀ ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle diameter (D ₅₀ ) is preferably 0.01 μm or more, more preferably 0.1 μm or more.

The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60% by mass, more preferably in the range of 10 to 50% by mass.

In addition to the above-described negative electrode active material and solid electrolyte, the negative electrode active material layer may further contain at least one of a conductive additive and a binder.

Examples of conductive aids include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium; alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers); (VGCF), polyacrylonitrile carbon fiber, pitch carbon fiber, rayon carbon fiber, activated carbon fiber, etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark)) , furnace black, channel black, thermal lamp black, etc.), but are not limited to these. Further, a particulate ceramic material or resin material coated with the above metal material by plating or the like can also be used as a conductive aid. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon; , silver, gold, and carbon, and more preferably carbon. These conductive aids may be used alone or in combination of two or more.

The shape of the conductive aid is preferably particulate or fibrous. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, flake, spindle, etc. I don't mind.

The average particle diameter (primary particle diameter) when the conductive additive is in the form of particles is not particularly limited, but from the viewpoint of the electrical characteristics of the battery, it is preferably 0.01 to 10 μm. In addition, in this specification, "particle diameter of a conductive aid" means the maximum distance L among the distances between arbitrary two points on the outline of a conductive aid. The value of the "average particle diameter of the conductive aid" is the particle diameter of particles observed in several to several dozen fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value shall be adopted.

When the negative electrode active material layer contains a conductive additive, the content of the conductive additive in the negative electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass based on the total mass of the negative electrode active material layer. , more preferably 2 to 8% by weight, and still more preferably 4 to 7% by weight. Within this range, it becomes possible to form a stronger electron conduction path in the negative electrode active material layer, and it is possible to effectively contribute to improving battery characteristics.

On the other hand, the binder is not particularly limited, but examples include the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, Polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and hydrogenated products thereof , thermoplastic polymers such as styrene/isoprene/styrene block copolymers and their hydrogenated products, tetrafluoroethylene/hexafluoropropylene copolymers (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymers (PFA) , fluororesins such as ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride- Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber ( Examples include vinylidene fluoride-based fluororubbers such as VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), and epoxy resins. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferred.

The thickness of the negative electrode active material layer varies depending on the structure of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[Cathode active material layer]
The positive electrode active material layer contains a positive electrode active material containing sulfur. The type of positive electrode active material containing sulfur is not particularly limited, but in addition to elemental sulfur (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds may be used. Any material may be used as long as it can release lithium ions during discharge and occlude lithium ions during discharge. Examples of the organic sulfur compound include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compound described in International Publication No. 2010/044437 pamphlet, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polysulfide carbon, and the like. Among these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, and sulfur-modified polyacrylonitrile is particularly preferred. As the disulfide compound, those having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group are more preferable. Here, the sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, which is obtained by mixing sulfur powder and polyacrylonitrile and heating the mixture under an inert gas or reduced pressure. The estimated structure can be found, for example, in Chem. Mater. As shown in 2011, 23, 5024-5028, polyacrylonitrile is ring-closed to become polycyclic, and at least a part of S is bonded to C. The compound described in this document has strong peak signals near 1330 cm ^-1 and 1560 cm ^-1 in the Raman spectrum, and peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 , and 929 cm ^-1 do. On the other hand, inorganic sulfur compounds are preferable because of their excellent stability, and specifically, sulfur element (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S, MoS ₂ , MoS ₃ , and the like. Among these, S, S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , FeS ₂ and MoS ₂ are preferred, elemental sulfur (S), S-carbon composite, TiS 2 and FeS 2 are more preferred, and elemental sulfur (S), S-carbon composite, TiS ₂ and FeS ₂ are more preferred; S) is particularly preferred. Here, the S-carbon composite includes sulfur powder and a carbon material, and is in a composite state by subjecting them to heat treatment or mechanical mixing. In more detail, sulfur is distributed on the surface and within the pores of carbon materials, sulfur and carbon materials are uniformly dispersed at the nano level, and they aggregate to form particles, fine sulfur This is a state in which carbon material is distributed on the surface or inside of the powder, or a state in which a plurality of these states are combined.

In addition to the sulfur-containing cathode active material, the cathode active material layer may further include a sulfur-free cathode active material. Examples of sulfur-free positive electrode active materials include layered rock salt active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and Li(Ni-Mn-Co)O ₂ , LiMn ₂ O ₄ , LiNi _0. Examples include spinel-type active materials such as ₅ Mn _1.5 O ₄ , olivine-type active materials such as LiFePO ₄ and LiMnPO ₄ , and Si-containing active materials such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ . Further, examples of oxide active materials other than those mentioned above include Li ₄ Ti ₅ O ₁₂ .

In some cases, two or more types of positive electrode active materials may be used together. Note that, of course, positive electrode active materials other than those mentioned above may be used.

Examples of the shape of the positive electrode active material include particulate (spherical, fibrous), thin film, and the like. When the positive electrode active material is in the form of particles, the average particle size (D ₅₀ ) is, for example, preferably within the range of 1 nm to 100 μm, more preferably within the range of 10 nm to 50 μm, and even more preferably 100 nm. 20 μm, particularly preferably 1 to 20 μm. Note that in this specification, the value of the average particle diameter (D ₅₀ ) of the active material can be measured by a laser diffraction scattering method.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but for example, it is preferably within the range of 40 to 99% by mass, and preferably within the range of 50 to 90% by mass. More preferred.

In addition to the above-mentioned "sulfur-containing positive electrode active material", the positive electrode active material layer also essentially contains a predetermined conductive additive. The predetermined conductive additive is a porous carbon material, and in the X-ray diffraction spectrum of the porous carbon material, a peak derived from the (002) plane of carbon is not observed, or a peak derived from the (002) plane of carbon is observed. It is characterized in that the half-width of the peak originating from the (10) plane of carbon is 5° or more, and the half-width of the peak originating from the (10) plane of carbon is 3.2° or less.

Here, the basic skeleton of the predetermined porous carbon material is graphene. In order to improve the oxidation resistance of a carbon material, it is more effective to expose the basal surface, which has higher oxidation resistance, than the edge surface, which has lower oxidation resistance. Furthermore, in order to improve conductivity, it is possible to increase the size of graphene. However, increasing the number of graphene layers reduces the specific surface area. From this point of view, the present inventors considered designing a porous carbon material in which the size of a single graphene sheet is large and the number of laminated layers is small. As a result, in the X-ray diffraction spectrum, the half-width of the peak originating from the (002) plane of carbon and the half-width of the peak originating from the (10) plane are controlled to predetermined values. A carbon material has been achieved (Japanese Patent Application Laid-open No. 2015-164889).

The following Scherrer equation is known as a method for determining the size of crystallites from the line width of powder X-ray diffraction peaks.

In the formula, L is the size of the crystallite, K is the shape factor (constant), λ is the wavelength of the X-ray, β is the half width, and θ is the Bragg angle (1/1 of the diffraction angle 2θ). 2). When comparing certain peaks, since θ is a substantially constant value and K and λ are constants, the crystallite size L is inversely proportional to the half width β.

Therefore, it can be said that the larger the half-width W(002) of the peak of the carbon (002) plane derived from the stacked structure of graphene, the smaller the crystallite size in the stacking direction and the smaller the number of stacked graphene layers. Furthermore, when the porous carbon material is composed of a single layer of graphene without lamination, a diffraction peak derived from the carbon (002) plane does not appear. Furthermore, it is considered that when the abundance ratio of the stacked structure is smaller than that of single layer graphene, the diffraction peak derived from the carbon (002) plane may not be observed. It can be said that the smaller the half-value width W(10) of the peak of the carbon (10) plane derived from in-plane diffraction of single-layer graphene, the larger the crystallites in the plane direction and the larger the size of one layer of graphene.

In the porous carbon material according to the present invention, W(002) is 5° or more and W(10) is 3.2° or less.

Generally, the lower the crystallinity of the carbon material, the larger both W(002) and W(10) tend to be. For this reason, in carbon materials such as various carbon blacks and activated carbons as described in Patent Document 1, if the number of stacked graphene layers is reduced, the size of the graphene also becomes smaller, and the number of stacked graphene layers is small and , it is not easy to obtain a structure with a large graphene layer.

Specifically, if W(002) is smaller than 5°, the number of stacked layers of graphene will not be sufficiently reduced and it will be difficult to increase the specific surface area, and if W(10) is larger than 3.2°, the graphene It is difficult to improve oxidation resistance and conductivity because the size of the metal is not sufficient. Preferably, W(002) is 6° or more.

In order to further exhibit the effects of the present invention, it is preferable that W(01) of the porous carbon material according to this embodiment is 1.2 to 3.2°.

Note that in this specification, W(002)(°) and W(10)(°) are values determined by the method described in Examples described later.

Further, in order to further exhibit the effects of the present invention, the porous carbon material according to the present embodiment has a peak intensity (G) of 2650 cm −1 for the G band peak intensity (G) measured at around 1588 cm ⁻¹ by Raman spectroscopy ^. The ratio (G'/G) of the peak intensity (G') of the G' band measured at ¹ to 2675 cm is preferably 0.4 or more, more preferably 0.6 or more. .

In the Raman scattering spectrum of graphite, a G band originating from stacked layers of graphene is observed around 1590 cm ^-1 , and a G' band originating from the presence of graphene with a small number of stacked layers is observed around 2670 cm ^-1 . The ratio (G'/G) of the G' band peak intensity (G') to the G band peak intensity (G) is about 0.5. On the other hand, it is known that G'/G is approximately 4 in the Raman scattering spectrum of single-layer graphene. As the number of laminated layers increases, G'/G decreases, and with four or more layers, the spectrum becomes almost the same as that of graphite (Nano Lett., 2006, 6, 2667-2673, Physics Reports, 2009, 473, 51-87). Therefore, the value of G'/G is an indicator of the presence of monolayer graphene. It is thought that the closer the value of G'/G is to 4, the smaller the number of laminated layers, the more developed the basal plane, and the structure is closer to single-layer graphene, or the higher the proportion of single-layer graphene contained in the carbon material. .

When the value of G'/G is 0.6 or more, high conductivity, high oxidation resistance, and high specific area due to the graphene sheet with a sufficiently reduced number of stacked layers can be effectively achieved. More preferably, the value of G'/G is 0.7 or more. The upper limit of the value of G'/G is not particularly limited, but is preferably 4 or less.

Further, in a carbon material having a G'/G value of 0.6 or more, the BET specific surface area is preferably 800 to 2600 m ² /g. Within the above range, the effect due to the presence of single-layer graphene with a developed basal plane can be obtained even more significantly.

In this specification, the value of G'/G is determined by the method described in Examples below.

Furthermore, the G' band of graphene is shifted to a lower wave number side than the G' band of highly oriented graphite (HOPG), and the half width of the peak is narrower. Therefore, in the carbon material according to this embodiment, the G' band in the Raman scattering spectrum is preferably shifted to a lower wave number side than the G' band of highly oriented graphite (HOPG). With such a structure, it is considered that the structure is close to that of single-layer graphene, and the effects of the invention can be more significantly obtained.

Hereinafter, one embodiment of the porous carbon material of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited only to the following embodiments.

<Porous carbon material>
The porous carbon material used in this embodiment has both a high specific surface area and high corrosion resistance, exceeding the trade-off relationship between specific surface area and corrosion resistance in conventional carbon materials.

Here, the corrosion resistance of the porous carbon material depends on the amount of edges (ends) of the graphene sheet that can become a starting point for electrochemical corrosion, and the fewer the edges, the higher the corrosion resistance. The amount of edges depends on the mesh size of the graphene sheet, and the larger the mesh size, the smaller the amount of edges. That is, the larger the mesh size, the higher the corrosion resistance of carbon. The present inventors designed a porous carbon material with high crystallinity and high specific surface area, which is composed of several layers or less, preferably 1 to 2 layers, and particularly 1 layer, of graphene sheets with few edges and defects. and synthesized it.

The porous carbon material used as a conductive aid in this embodiment contains carbon as a main component. Here, "containing carbon as a main component" is a concept that includes both "consisting only of carbon" and "consisting essentially of carbon," and may include elements other than carbon. "Substantially composed of carbon" means that at least 80% by weight of the whole, preferably at least 95% by weight of the whole, more preferably at least 98% by weight (upper limit: 100% by weight) of the whole is composed of carbon. means.

Further, the size of the powder of the porous carbon material is not particularly limited. However, when used as a catalyst carrier, the average particle size of the porous carbon material powder ( The average secondary particle diameter) is preferably 5 nm to 10 μm, more preferably 100 nm to 5 μm, and still more preferably 500 nm to 3 μm. Unless otherwise specified, the value of "average particle size of porous carbon material powder" is determined using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and a field of several to several tens of fields. The value calculated as the average value of the particle diameters of the particles observed in the test shall be adopted. Moreover, "particle size" shall mean the maximum distance among the distances passing through the center of the particle and between any two points on the contour line of the particle.

The BET specific surface area of the porous carbon material used in this embodiment is not particularly limited, but is preferably 250 m ² /g or more, more preferably 500 m ² /g or more, and particularly preferably 800 m ² /g or more. It is. If the BET specific surface area of the porous carbon material is 250 m ² /g or more, it can exhibit excellent performance when added as a conductive additive to an electrode composition for forming a battery electrode. The BET specific surface area of the porous carbon material is preferably as large as possible, but it is substantially 2600 m ² /g or less, preferably 2500 m ² /g or less. The BET specific surface area of the porous carbon material can be determined by the BET method from the measurement results of nitrogen adsorption/desorption isotherms.

The porous carbon material used in this embodiment is not particularly limited as long as it has pores and satisfies the above regulations. Preferably, the structure is such that the graphene sheet with few edges and defects is composed of several layers or less, preferably 1 to 2 layers, particularly 1 layer. The carbon material having such a structure is preferably an alumina template carbon material prepared using alumina nanoparticles as a template. The alumina template carbon material is a porous carbon material that has pores that reflect the shape of the alumina nanoparticles that are the template, and is preferably a porous carbon material that has mesopores. The International Union of Pure and Applied Chemistry (IUPAC) defines pores with a diameter of 2 nm or less as micropores, pores with a diameter of 2 to 50 nm as mesopores, and pores with a diameter of 50 nm or more as macropores. Materials having mesopores are collectively referred to as mesoporous materials.

FIG. 2 schematically shows an example of an alumina mold carbon material. Alumina template carbon material 1 is a porous carbon material obtained using alumina nanoparticles 2 as a template. More specifically, in producing the alumina template carbon material 1, first, as shown in FIG. 2(b), the surface of the alumina nanoparticles 2 is coated with a carbon layer 3 (carbon-coated alumina nanoparticles 4). By subsequently removing only the alumina nanoparticles 2, an alumina template carbon material 1 is obtained (FIG. 2(c)). The alumina template carbon material 1 has mesopores 7 that reflect the structural characteristics of the alumina nanoparticles 2 used as a template.

The alumina template carbon material according to this embodiment is preferably a porous carbon material ( The porous carbon material is particularly preferably a porous carbon material composed of only a defect-free single layer of graphene. The BET specific surface area of the porous carbon material can be sufficiently improved by setting the number of stacked graphene sheets to several layers or less, particularly one layer. Preferably, the average number of laminated layers determined from the BET specific surface area of the mold and the amount of carbon coating is 10 or less (equivalent to a BET specific surface area of the porous carbon material of 263 m ² /g or more), and more preferably 5 or less (525 m 2 /g or more). ² /g or more). In addition, from the viewpoint of sufficiently increasing the mechanical strength of the graphene sheet and preventing the structure of the graphene sheet from collapsing and agglomerating after the mold is removed, which leads to a decrease in the specific surface area, the BET specific surface area of the mold and the carbon coating are It is preferable that the average number of layers determined from the amount is one or more. In addition, it is preferable to have a structure in which graphene sheets with few defects and edges are uniformly formed three-dimensionally along the shape of the mesopores 7. With such a structure, the electrochemistry of the porous carbon material can be improved. Durability against chemical oxidation, etc. can be improved.

The porous carbon material used in this embodiment has an average pore diameter of, for example, 0.5 to 10 nm, preferably 0.7 to 8 nm. If the average pore diameter is within the above range, a porous carbon material (shell-like graphene laminate) can be easily obtained. The average pore diameter can be determined by the method described in Examples below.

The total pore volume of the porous carbon material used in this embodiment is preferably 0.5 cm ³ /g or more, preferably 0.9 cm ³ /g or more, and more preferably 2.5 cm ³ /g or more. It is more preferably 2.6 cm ³ /g or more, particularly preferably 2.7 cm ³ /g or more, and most preferably 2.8 cm ³ /g or more. With such a value, a high specific surface area can be obtained, and a sulfur active material-containing electrode composition that can contribute to improving rate characteristics can be provided. On the other hand, the total pore volume is preferably 5.0 cm ³ /g or less, more preferably 4.0 cm ³ /g or less. With such a value, sufficient mechanical strength can be obtained. Further, the volume occupied by the mesopores is, for example, 0.8 cm ³ /g or more, preferably 1.0 cm ³ /g or more, and more preferably 1.3 cm ³ /g or more. It is preferable in terms of mass transfer that the volume occupied by the mesopores is 0.8 cm ³ /g or more, particularly 1.0 cm ³ /g or more.

The total pore volume of the porous carbon material can be determined from the amount of adsorption at a relative pressure (P/P ₀ ) of 0.96 by measuring a nitrogen adsorption/desorption isotherm. Further, the volume of the micropores can be determined by the DR method, and the volume occupied by the mesopores can be determined from the difference between the total pore volume and the volume of the micropores.

<Method for producing porous carbon material>
Carbon meso-sponge (CMS) , which is a porous carbon material used in this embodiment, includes a first step of preparing carbon-coated alumina nanoparticles by using alumina nanoparticles as a template and coating the template with a carbon layer. , and a second step of dissolving and removing the template to obtain a porous carbon material. By using such a method, a porous carbon material called carbon meso-sponge (CMS) can be obtained. In addition, by heat-treating the CMS obtained in this way at a temperature of about 1800°C, graphene sheets with few edges and defects can be formed into several layers or less, preferably 1 to 2 layers, and especially 1 layer. It is possible to easily obtain a porous carbon material (graphene meso sponge (GMS)) with high crystallinity and high specific surface area, which is composed of the number of laminated layers. Then, a carbon material that has both high oxidation resistance and high specific surface area can be obtained. Note that by using alumina nanoparticles having an average particle size of 5 to 30 nm as the template used in the first step, the total pore volume of the resulting porous carbon material can be controlled within the above-mentioned preferred range. It is possible.

In order to obtain a graphene sheet with a high specific surface area, it is insufficient to simply synthesize graphene in large quantities. This is because graphene is stacked together due to van der Waals forces. In order to prevent stacking, it is necessary to give graphene sheets a three-dimensional structure. However, when methods such as mechanical exfoliation or reduction of graphene oxide are used to prepare graphene, it is difficult to provide a three-dimensional structure. On the other hand, according to the above-mentioned method, by forming graphene on alumina nanoparticles as a template and removing the template, it is possible to efficiently produce carbon mesosponges (CMS) and GMS, which are shell-shaped graphene porous bodies; (Graphene meso sponge) can be produced.

The specific structure and manufacturing method of the predetermined porous carbon material, which is a conductive additive that is essential to the positive electrode active material layer, has been explained above in detail. In addition, like the negative electrode active material layer described above, it may further contain at least one of a solid electrolyte and a binder, if necessary. In particular, when the positive electrode active material layer (and the sulfur active material-containing electrode composition that constitutes it) further contains a solid electrolyte, the ionic conductivity in the active material layer is further improved, contributing to improving the rate characteristics of the battery. It is preferable because it absorbs water. Note that since the specific forms of these materials are the same as those described above, detailed explanations will be omitted here.

Here, in a sulfur active material-containing electrode composition containing a conductive aid made of a porous carbon material according to the present invention together with an electrode active material (sulfur active material) and a solid electrolyte, the electrode active material (sulfur active material) It is preferable that the porous carbon material and the solid electrolyte are contained in the form of composite particles. In this case, the average particle size (average secondary particle size) of the composite particles is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less. It is particularly preferable that There is no particular restriction on the lower limit, but it is preferably 1 μm or more, more preferably 5 μm or more. By including composite particles having such an average particle size, a battery with particularly excellent rate characteristics can be provided. To form such composite particles, a mixture of electrode active material (sulfur active material), porous carbon material, and solid electrolyte, which are the constituent components of the composite particles, is mixed and stirred using a mixing/stirring device such as a planetary ball mill. Mechanical milling can be performed by setting appropriate conditions (rotation speed, processing time).

[Solid electrolyte layer]
The solid electrolyte layer of the bipolar secondary battery according to this embodiment is a layer that contains a solid electrolyte as a main component and is interposed between the above-described positive electrode active material layer and negative electrode active material layer. Since the specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, detailed explanation will be omitted here.

The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably within the range of 10 to 100% by mass, more preferably within the range of 50 to 100% by mass, and within the range of 90 to 100% by mass. It is more preferable that

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. Since the specific form of the binder that can be contained in the solid electrolyte layer is the same as that described above, detailed explanation will be omitted here.

The thickness of the solid electrolyte layer varies depending on the configuration of the intended bipolar secondary battery, but for example, it is preferably within the range of 0.1 to 1000 μm, and preferably within the range of 0.1 to 300 μm. is more preferable.

[Positive current collector plate and negative current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries may be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. Note that the positive electrode current collector plate 27 and the negative electrode current collector plate 25 may use the same material or different materials.

[Positive lead and negative lead]
Further, although not shown, the current collector 11 and the current collecting plates (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As constituent materials for the positive electrode and negative electrode leads, materials used in known lithium ion secondary batteries can be similarly employed. In addition, the parts taken out from the exterior are covered with heat-resistant insulating heat-shrinkable material to prevent them from contacting peripheral equipment or wiring and causing electrical leakage, which may affect products (e.g., automobile parts, especially electronic equipment, etc.). Preferably, it is covered with a tube or the like.

[Battery exterior body]
As the battery exterior body, a known metal can case can be used, or a bag-shaped case using a laminate film 29 containing aluminum that can cover the power generating element as shown in FIG. 1 can be used. The laminate film may be, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order, but is not limited thereto. A laminate film is desirable from the viewpoint that it has high output and excellent cooling performance, and can be suitably used in batteries for large equipment such as EVs and HEVs. Moreover, the exterior body is more preferably a laminate film containing aluminum because the group pressure applied to the power generation element from the outside can be easily adjusted.

The bipolar secondary battery of this embodiment has a configuration in which a plurality of cell layers are connected in series, and thus has excellent output characteristics at a high rate. Therefore, the bipolar secondary battery of this embodiment is suitably used as a power source for driving EVs and HEVs.

FIG. 3 is a perspective view showing the appearance of a flat lithium ion secondary battery, which is a typical embodiment of a bipolar secondary battery.

As shown in FIG. 3, the flat bipolar secondary battery 50 has a flat rectangular shape, and a positive electrode tab 58 and a negative electrode tab 59 for extracting power are pulled out from both sides of the battery. There is. The power generation element 57 is surrounded by the battery exterior body (laminate film 52) of the bipolar secondary battery 50, and its periphery is heat-sealed, and the power generation element 57 has a positive electrode tab 58 and a negative electrode tab 59 pulled out to the outside. It is sealed in a sealed condition. Here, the power generation element 57 corresponds to the power generation element 21 of the bipolar secondary battery 10 shown in FIG. 3 described above. The power generation element 57 includes a plurality of bipolar electrodes 23 stacked together with a solid electrolyte layer 17 in between.

Note that the above-mentioned lithium ion secondary battery is not limited to a flat, stacked type battery. A wound type lithium ion secondary battery may have a cylindrical shape, or may be a cylindrical battery that has been deformed into a rectangular flat shape. etc., there are no particular restrictions. The above-mentioned cylindrical shape is not particularly limited, and its exterior body may be made of a laminate film or a conventional cylindrical can (metal can). Preferably, the power generation element is packaged with an aluminum laminate film. With this form, weight reduction can be achieved.

Furthermore, there is no particular restriction on how to take out the tabs 58 and 59 shown in FIG. 3. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, the terminals may be formed using, for example, a cylindrical can (metal can) instead of a tab.

[Assembled battery]
A battery pack is made up of multiple batteries connected together. Specifically, it is configured by using at least two or more, serially or parallelly, or both. By connecting them in series or parallel, it becomes possible to freely adjust the capacity and voltage.

A plurality of batteries can be connected in series or in parallel to form a small detachable battery pack. By connecting multiple small, removable batteries in series or in parallel, high-capacity, large-capacity batteries suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density can be used. It is also possible to form a battery pack with an output. How many batteries to connect to make a battery pack, and how many stages of small battery packs to stack to make a large-capacity battery pack depends on the battery capacity of the vehicle (electric vehicle) in which it will be mounted. You can decide according to the output.

When carrying out the charging method according to the present invention on an assembled battery, the charging process can be performed, for example, while measuring the AC impedance of each individual battery (single cell) that constitutes the assembled battery. With such a configuration, the charging process can be performed while separately monitoring the occurrence of electrodeposition in each individual battery (single cell).

[vehicle]
The non-aqueous electrolyte secondary battery of this embodiment maintains its discharge capacity even after long-term use, and has good cycle characteristics. Additionally, it has a high volumetric energy density. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer lifespan than electric and portable electronic device applications. . Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a vehicle power source, for example, as a vehicle drive power source or an auxiliary power source.

Specifically, a battery or a battery pack formed by combining a plurality of batteries can be mounted on the vehicle. According to the present invention, it is possible to configure a long-life battery with excellent long-term reliability and output characteristics, so when such a battery is installed, it is possible to configure a plug-in hybrid electric vehicle with a long EV mileage or an electric vehicle with a long mileage on a single charge. . Batteries or assembled batteries made by combining multiple of these can be used, for example, in the case of automobiles, such as hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.), etc. , two-wheeled vehicles (including motorcycles, and three-wheeled vehicles)) can provide long-life and highly reliable vehicles. However, the application is not limited to automobiles; for example, it can be applied to various power sources for other vehicles, such as trains, and on-board power sources such as uninterruptible power supplies. It is also possible to use it as

By implementing the charging method according to the present invention on a battery (assembled battery) mounted on a vehicle, charging processing is performed under charging conditions where metal lithium electrodeposition is likely to occur, such as during rapid charging, for example. Even so, there is an advantage that it is possible to fully utilize the capacity of the battery while detecting the occurrence of metal lithium electrodeposition with high accuracy.

In the above description, the embodiments of the present invention have been described using a bipolar all-solid-state lithium ion secondary battery as an example, but the type of secondary battery to which the present invention can be applied is not particularly limited. So-called parallel stacked all-solid-state batteries in which cell layers are connected in parallel, and any conventionally known bipolar or non-bipolar (parallel stacked) non-aqueous electrolyte secondary batteries (using electrolyte It is also applicable to batteries).

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the technical scope of the present invention is not limited only to the following examples.

[Example of manufacturing porous carbon material]
<Production Example 1-1: Preparation of porous carbon material (1-1)>
(1) Preparation of carbon-coated alumina nanoparticles by CVD method Alumina nanoparticles (TM300 manufactured by Daimei Kagaku Kogyo Co., Ltd., crystal phase: γ-alumina, average particle size: 7 nm, specific surface area: 220 m ² /g) and spacers of quartz sand (manufactured by Sendai Wako Pure Chemical Industries, Ltd.) at a weight ratio of 3:10 (alumina nanoparticles: quartz sand). At this time, the quartz sand used was one that had been soaked in 1M hydrochloric acid for 12 hours, heated in air at 800° C. for 2 hours in a muffle furnace, and sieved at 180 μm intervals. The mixture of alumina nanoparticles and quartz sand prepared above was placed in a reaction tube (inner diameter 57 mm), and CVD using methane as a carbon source (methane CVD) was performed.

In the methane CVD, the alumina nanoparticles were heated from room temperature to 900°C at a temperature increase rate of 10°C/min under conditions where the flow rate of N ₂ gas was adjusted to 400ml/min, and the temperature was held at 900°C for 30 minutes. Then, using _N2 gas as a carrier gas, 20% by volume of methane based on the total amount of carrier gas and methane was introduced into the reaction tube, and chemical vapor deposition (CVD) treatment was performed at 900°C for 4 hours. went. At this time, the flow rate of methane gas was adjusted to 80 ml/min, and the flow rate of N ₂ gas was adjusted to 320 ml/min. Thereafter, the introduction of methane gas was stopped and the flow rate of N ₂ gas was adjusted to 400 ml/min, and the temperature was maintained at 900° C. for 30 minutes, followed by cooling to obtain carbon-coated alumina nanoparticles.

(2) Dissolving and removing the template Next, the template was removed from the carbon-coated alumina nanoparticles obtained above.

Hydrogen fluoride (HF) was used to remove the carbon-coated alumina nanoparticle template. Carbon-coated alumina nanoparticles and an aqueous HF solution with a concentration of 46% by mass were placed in a Teflon (registered trademark) beaker, and the mixture was kept at room temperature for 6 hours while stirring with a Teflon (registered trademark) stirring bar. After that, it was naturally cooled. The sample was collected by filtration and dried by vacuum heating at 150° C. for 6 hours to obtain a porous carbon material. The porous carbon material obtained at this stage is called carbon meso-sponge (CMS).

(3) Heat treatment of porous carbon material The porous carbon material obtained in (2) above was crushed, several pieces were collected, placed in a graphite container, and set in a high-temperature furnace. The pressure in the high-temperature part was reduced to 10 Pa using an oil pump, and heat treatment was performed while flowing a small amount of Ar to obtain a porous carbon material (1-1) of this production example. As for the heat treatment conditions, the temperature was first raised from room temperature to 1800° C. over 120 minutes. Then, it was heat-treated at 1800° C. for 60 minutes, and then naturally cooled to room temperature. The porous carbon material (1-1) thus obtained is one in which the hydrogen-terminated edges of the CMS are fused by heat treatment at a high temperature of 1800°C, forming a three-dimensional graphene skeleton with higher continuity. This is called graphene mesosponge (GMS).

(Characterization of porous carbon material)
-Nitrogen adsorption/desorption isotherm measurement Nitrogen adsorption/desorption isotherm measurement was performed at a temperature of -196°C using a high-precision automatic gas/vapor adsorption measurement device (BEL SORP MAX, manufactured by Japan Bell Co., Ltd.). The sample was vacuum dried at 150° C. for 6 hours before measurement. The BET specific surface area of the sample was determined using the BET method using a multi-point method from the nitrogen adsorption isotherm measured in the relative pressure range of 0.1<P/P ₀ <0.30. The pore size distribution was determined by the BJH method. The average pore diameter d was calculated from the BET specific surface area S and the total pore volume V by d=4V/S assuming cylindrical pores.
- Transmission electron microscope (TEM) observation Transmission electron microscope (TEM) observation was performed using a transmission electron microscope JEM-2010 manufactured by JEOL Ltd. at an accelerating voltage of 200 kV. During observation, the acceleration voltage was set at 200 kV. For TEM observation, add a small amount of ethanol to the sample, suspend it by ultrasonication (45 kHz, 30 minutes), and place the suspension on a microgrid (Oken Shoji: Cu150P grid, carbon reinforced, grid pitch 150 μm). A very small amount of the mixture was dropped onto the substrate, and the mixture was dried under vacuum at 50° C. for 2 hours to obtain a sample for TEM observation.
・Measurement of carbon loading (thermogravimetric analysis)
Thermogravimetric analysis was performed using a Shimadzu differential thermal/thermogravimetric simultaneous measurement device (DTG-60/60H). The sample was heated to 100°C at 10°C/min under synthetic air flow (50 cc/min), held for 30 minutes, then heated to 800°C at 5°C/min, held for 1 hour, and then heated to -10°C. /min to 100°C and held for 30 minutes. The amount of carbon supported was determined from the difference in average mass before and after heating to 800°C and holding at 100°C.
・X-ray diffraction measurement (XRD)
X-ray diffraction measurements were carried out using an X-ray diffraction device XRD-6100 manufactured by Shimadzu Corporation, with the sample placed on a silicon non-reflection plate. The radiation source was Cu-Kα, the voltage was 40 kV, and the current was 30 mA.
- Raman spectrometry The Raman scattering spectrum was measured using a laser Raman spectrophotometer NRS-3300FL manufactured by JASCO Corporation. The measurement conditions are as follows. The peak intensity (height) was determined by drawing the baseline and removing the influence of the background.

(Average number of carbon layers on the mold)
The amount of carbon supported on the carbon-coated alumina nanoparticles after the completion of methane CVD in (1) above was determined by TG measurement, and it was found that the amount of carbon supported was calculated based on the total weight of the alumina nanoparticles and the carbon covering them (100% by weight). The average content was 18% by weight.

In addition, from the nitrogen adsorption/desorption isotherm measurement, the BET specific surface area of the heat-treated alumina described in (1) above was determined, and from this value and the value of the carbon loading determined by the TG measurement above, the average number of laminated carbon layers was approximately determined. It was estimated at 1.2.

Note that the average number N (layers) of carbon layers is:
N=W/(S×g)
is required. Here, W is the amount of carbon supported, and is the ratio of the weight of carbon to the weight of alumina (0.30). S is the specific surface area of alumina, and g is the weight per unit area of one graphene sheet (0.000761 g/m ² ).

(BET specific surface area and pore distribution of porous carbon material)
Figure 4 shows the nitrogen adsorption/desorption isotherms of the porous carbon material after the mold removal in (2) above and the porous carbon material (1-1) obtained after the heat treatment in (3) above. .

As shown in FIG. 4, the BET specific surface area of the porous carbon material after removing the template was 1500 m ² /g, which was greater than 230 m ² /g before removing the template.

The porous carbon material (1-1) obtained after the heat treatment in (3) above has a BET specific surface area of 1690 m ² /g, and an average pore diameter of 4.7 nm, as shown in the pore size distribution in FIG. It was confirmed that the material had mesopores.

(XRD measurement of porous carbon material)
FIG. 6 shows the results of XRD measurement of the porous carbon material (1-1) obtained in this production example. As shown in FIG. 6, it was confirmed that the peak derived from alumina disappeared after the template was removed in (2) above. Furthermore, a peak derived from the (002) plane of carbon (near 2θ=25°), a peak derived from the (10) plane (near 2θ=44°), and a peak derived from the (110) plane were observed. Among these, in the porous carbon material (1-1) obtained in this production example, the intensity of the peak derived from the (002) plane of carbon is small, and it is considered that there is almost no lamination. Furthermore, since the peak of the carbon (10) plane was clearly confirmed, it was suggested that a carbon network plane with good crystallinity was formed. In addition, in the porous carbon material (1-1) obtained in this production example, the half width W (002) of the peak originating from the (002) plane of carbon and the half width W (002) of the peak originating from the (10) plane of carbon are The value width values were 7.30° and 2.50°, respectively.

(TEM measurement of porous carbon material)
FIG. 7A and FIG. 7B show TEM photographs of the porous carbon material (1-1) obtained in this production example after performing the heat treatment step (3) above. FIGS. 7A and 7B are photographs taken of different parts of samples prepared at the same time. As shown in FIG. 7A, it can be seen that the porous carbon material (1-1) obtained in this production example has a shell structure composed of one to two layers of graphene sheets.

Further, from the photograph shown on the left side of FIG. 7B, an aggregate of particles with a diameter of about 10 nm could be confirmed, and it was found that the shell-like structure was maintained even after heat treatment at 1800°C. In the high-magnification photo (right), a carbon mesh surface with a clear outline can be seen. The number of laminated layers was 1 to 3 on average in most places, and it is considered that carbon coating was done almost uniformly by CVD. Structures that appeared to be single-layer graphene were also observed in many places (arrows). Therefore, it can be said that by performing heat treatment at 1800° C., the crystallinity of the constituent carbon could be increased while maintaining the shell-like structure.

That is, it can be said that the carbon material prepared in this production example has a relatively high BET specific surface area and has a shell structure composed of one to two layers of uniform graphene sheets. This is considered to be because carbon precipitation progressed more uniformly by performing the CVD treatment using methane as the carbon source. In addition, this is thought to be due to the fact that by performing CVD at a higher temperature of 900° C., the carbon structure was stabilized and a high specific surface area could be maintained even after the mold was removed. Furthermore, it is thought that by using alumina nanoparticles as a template without forming them into pellets, it was possible to suppress a decrease in the specific surface area of the template, and as a result, a carbon material with a high specific surface area was obtained.

(Raman measurement of porous carbon material)
Furthermore, when the Raman scattering spectrum of the porous carbon material (1-1) obtained in this production example was measured, a peak (G band) derived from the skeletal vibration of the graphene sheet appeared around 1590 cm ^-1 . Furthermore, a peak (D band) originating from the defect structure of the graphene sheet appeared near 1355 cm ^-1 . Note that defect structures include edge sites, dangling bonds, and curved parts of graphene, and are contained in large amounts in low-order carbon, but are hardly contained in highly crystalline graphite. Therefore, the D band is not observed in graphite or single-layer graphene.

Furthermore, when focusing on the peak on the high wavenumber side, a G' band was confirmed around 2670 cm ^-1 . The G' band originates from a graphene-like structure with an sp ² hybrid orbital, and can be observed even if there are no defects as long as the crystallinity is good. Here, in the Raman scattering spectrum of single-layer graphene, G'/G is larger than that of HOPG, and the position of the G' band is shifted to the lower wavenumber side. The ratio G'/G of the peak intensity G' of the G' band to the peak intensity G of the G band of the porous carbon material obtained in this production example was 0.97. In this way, the porous carbon material obtained in this production example has a G'/G of 0.6 or more, and the position of the G' band has shifted to the lower wave number side compared to HOPG. The existence of graphene was suggested.

(Measurement of elasticity of porous carbon material)
The elasticity of the porous carbon material (1-1) obtained in this production example was evaluated using conventionally known carbon materials Denka Black (DB; manufactured by Denka Co., Ltd.) and alkali-activated activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd., MSC). -30).

Specifically, each carbon material was placed in a metal jig capable of applying a compressive force, and loading and unloading of a compressive force of 500 MPa was repeated 10 times. Then, before and after that, nitrogen adsorption/desorption isotherms at -196°C were measured using the same method as above. The results are shown in FIG.

As shown in FIG. 8, for Denka Black (DB) and activated carbon, the nitrogen adsorption and desorption isotherms changed after recovery from compressive force loading. This suggests that the structure of these carbon materials is destroyed by the application of compressive force. In contrast, for the porous carbon material (1-1) obtained in this production example, no change in the nitrogen adsorption/desorption isotherm from the initial state was observed even after recovery from the compressive force load. Ta. This shows that the structure of the porous carbon material (1) obtained in this production example is maintained even when compressive force is applied. That is, it can be said that the porous carbon material according to the present invention has high elasticity as a carbon material and can exhibit excellent flexibility. Note that when the bulk modulus of the porous carbon material (1-1) was measured, a value of 0.79 GPa was confirmed.

<Production Example 1-2: Preparation of porous carbon material (1-2)>
Porous carbon material (1-2) was prepared by the same method as in Production Example 1-1 above, except that the chemical vapor deposition (CVD) treatment time in methane CVD was changed from 4 hours to 8 hours. did.

(Characterization of porous carbon material)
-Nitrogen adsorption/desorption isotherm measurement Nitrogen adsorption/desorption isotherm measurement was performed at a temperature of -196°C using a high-precision automatic gas/vapor adsorption measurement device (BEL SORP MAX, manufactured by Japan Bell Co., Ltd.). The sample was vacuum dried at 150° C. for 6 hours before measurement. A graph of the nitrogen adsorption/desorption isotherm obtained in this way is shown in FIG.
・Measurement of carbon loading (thermogravimetric analysis)
Thermogravimetric analysis was performed using a Shimadzu differential thermal/thermogravimetric simultaneous measurement device (DTG-60/60H). The sample was heated to 100°C at 10°C/min under synthetic air flow (50 cc/min), held for 30 minutes, then heated to 800°C at 5°C/min, held for 1 hour, and then heated to -10°C. /min to 100°C and held for 30 minutes. The amount of carbon supported was determined from the difference in average mass before and after heating to 800°C and holding at 100°C. As a result, it was confirmed that the carbon-coated alumina nanoparticles were coated with carbon in an amount of 35% by weight based on the total weight.

<Production Example 2-1: Preparation of porous carbon material (2-1)>
Using the same method as in Production Example 1-1 above, alumina nanoparticles (TM300 manufactured by Daimei Kagaku Kogyo Co., Ltd., crystal phase: γ-alumina, average particle size: 7 nm, specific surface area: 220 m ² /g) were used as a template. A porous carbon material (2-1) was prepared. In this production example, the amount of carbon supported in the carbon-coated alumina nanoparticles was set to 16% by weight on average by adjusting the conditions when performing methane CVD. Moreover, the average number of stacked carbon layers corresponding to this was estimated to be about 1.0.

(Measurement of various physical properties of porous carbon material)
The BET specific surface area of the porous carbon material (2-1) after removing the template was 1700 m ² /g. Further, the pore volume of the micropores was 0.7 cm ³ /g, the pore volume of the mesopores was 2.1 cm ³ /g, and the total pore volume was 2.8 cm ³ /g. Furthermore, when XRD measurement was performed, it was confirmed that the peak derived from alumina disappeared after the template was removed, as in FIG. 6 ("GMS" shown in FIG. 10). As shown in Figure 10, the intensity of the peak derived from the (002) plane of carbon (near 2θ = 25°) is small and broad, and the intensity of the peak derived from the (10) plane of carbon (near 2θ = 44°) is small and broad. The half width was 3.2° or less. As a result of Raman measurement, it was also confirmed that the ratio (G'/G) of the G' band peak intensity (G') to the G band peak intensity (G) was 0.6 or more.

<Production Example 2-2: Preparation of porous carbon material (2-2)>
Using the same method as in Production Example 1-1 above, alumina nanoparticles (TM100 manufactured by Daimei Kagaku Kogyo Co., Ltd., crystal phase: θ-alumina, average particle size: 14 nm, specific surface area: 120 m ² /g) were used as a template. A porous carbon material (2-2) was prepared. Note that in this production example, the step of "(3) Heat treatment of porous carbon material" was not performed. Therefore, the porous carbon material (2-2) obtained in this production example is carbon meso sponge (CMS). Furthermore, in this production example, the amount of carbon supported in the carbon-coated alumina nanoparticles was set to 13% by weight on average by adjusting the conditions when performing methane CVD. Moreover, the average number of stacked carbon layers corresponding to this was estimated to be about 1.5.

(Measurement of various physical properties of porous carbon material)
The BET specific surface area of the porous carbon material (2-2) after removing the template was 1500 m ² /g. Further, the pore volume of micropores was 2.4 cm ³ /g, the pore volume of mesopores was 1.6 cm ³ /g, and the total pore volume was 4.0 cm ³ /g. Furthermore, when XRD measurement was performed, it was confirmed that the peak derived from alumina disappeared after the template was removed, as in FIG. 6 ("CMS" shown in FIG. 10). As shown in Figure 10, the intensity of the peak derived from the (002) plane of carbon (near 2θ = 25°) is small and broad, and the intensity of the peak derived from the (10) plane of carbon (near 2θ = 44°) is small and broad. The half width was 3.2° or less. As a result of Raman measurement, it was also confirmed that the ratio (G'/G) of the G' band peak intensity (G') to the G band peak intensity (G) was 0.6 or more.

<Production Example 2-3: Preparation of porous carbon material (2-3)>
Using the same method as in Production Example 2-2 above, alumina nanoparticles (TM100 manufactured by Daimei Kagaku Kogyo Co., Ltd., crystal phase: θ-alumina, average particle size: 14 nm, specific surface area: 120 m ² /g) were used as a template. A porous carbon material (2-3) was prepared. Therefore, the porous carbon material (2-3) obtained in this production example is also a carbon meso sponge (CMS). In addition, in this production example, by adjusting the conditions when performing methane CVD, the amount of carbon supported on the carbon-coated alumina nanoparticles was set to 8.8% by weight on average. Moreover, the average number of stacked carbon layers corresponding to this was estimated to be about 2.0.

(Measurement of various physical properties of porous carbon material)
The BET specific surface area of the porous carbon material (2-3) after removing the template was 2300 m ² /g. Further, the pore volume of micropores was 0.8 cm ³ /g, the pore volume of mesopores was 4.5 cm ³ /g, and the total pore volume was 5.3 cm ³ /g. Furthermore, when XRD measurement was performed, it was confirmed that the peak derived from alumina disappeared after the template was removed, similar to FIG. 6. Furthermore, the intensity of the peak (around 2θ = 25°) originating from the (002) plane of carbon is small and broad, and the half-width of the peak (around 2θ = 44°) originating from the (10) plane of carbon is 3. It was less than 2°. As a result of Raman measurement, it was also confirmed that the ratio (G'/G) of the G' band peak intensity (G') to the G band peak intensity (G) was 0.6 or more.

[Manufacturing example of lithium ion secondary battery]
<Example 1-1>
(Preparation of sulfur active material-containing electrode composition (positive electrode mixture))
40 parts by mass of Li ₃ PS ₄ as a solid electrolyte, 50 parts by mass of elemental sulfur (S) as a positive electrode active material, and the porous carbon material obtained in Production Example 1-1 (1-1) as a conductive agent. 1) 10 parts by mass was weighed in a glove box and placed in a zirconia grinding pot (45 mL) of a planetary ball mill (manufactured by Fritsch Japan, P-6). Then, 20,300 parts by mass of zirconia grinding balls (φ5 mm) were added, and the grinding process was then carried out at 280 rpm for 8 hours to prepare a sulfur active material-containing electrode composition (positive electrode mixture). In the obtained sulfur active material-containing electrode composition (positive electrode mixture), the positive electrode active material (sulfur alone), the conductive agent (porous carbon material), and the solid electrolyte form composite particles, and the average particle size of The diameter (average secondary particle diameter) was measured using a scanning electron microscope (SEM) and found to be 15 μm.

(Preparation of battery)
An all-solid-state lithium ion secondary battery was fabricated by making the sulfur active material-containing electrode composition (positive electrode mixture) prepared above face the Li-In electrode as a counter electrode, and interposing a solid electrolyte layer between them. did.

Specifically, 100 mg of solid electrolyte (argyrodite-type sulfide solid electrolyte) was weighed, the weighed solid electrolyte was put into a PET tube, the surface was smoothed, and a pressure of 580 MPa was applied to a fastening jig to remove the solid electrolyte. Electrolyte pellets were prepared. The surface area of the produced solid electrolyte pellet was 0.817 cm ² (pellet diameter φ=1.02 cm). Further, the thickness of the electrolyte layer was measured from the change in thickness before and after fabrication, and was found to be 600 μm.

After that, the fastening jig was removed, a positive electrode mixture and a counter Li-In electrode were placed on both sides of the pellet, and the fastening was performed at 100 MPa using an all-solid battery evaluation cell (manufactured by Hosen Co., Ltd.). An ion secondary battery was created. Note that the basis weight of the positive electrode mixture was 9.6 mg/cm ² . The Li-In electrode used as the negative electrode is a laminate of Li metal foil (diameter 8 mm, thickness 200 μm, manufactured by Honjo Metal Co., Ltd.) and In metal foil (diameter 9 mm, thickness 300 μm, manufactured by Nilaco Co., Ltd.). The Li--In electrode was arranged so that the In metal foil was located on the solid electrolyte layer side.

<Example 1-2>
As a conductive agent contained in the sulfur active material-containing electrode composition (positive electrode mixture), the porous carbon material (1-2) obtained in Production Example 1-2 above was used instead of the porous carbon material (1-1). ) An all-solid lithium ion secondary battery was produced in the same manner as in Example 1-1 above, except that 10 parts by mass was used.

<Comparative example 1-1>
As a conductive additive contained in the sulfur active material-containing electrode composition (positive electrode mixture), Ketjenblack (registered trademark) (manufactured by Lion Specialty Chemicals Co., Ltd., EC600JD) was used instead of the porous carbon material (1-1). ) An all-solid lithium ion secondary battery was produced in the same manner as in Example 1-1 above, except that 10 parts by mass was used.

<Comparative example 1-2>
As a conductive agent contained in the sulfur active material-containing electrode composition (positive electrode mixture), 10 parts by mass of alkali-activated activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd., MSC-30) was used in place of the porous carbon material (1-1). An all-solid-state lithium ion secondary battery was produced by the same method as in Example 1-1 described above, except that the following was used.

[Characteristics evaluation of lithium ion secondary battery]
For each lithium ion secondary battery produced in each of the above Examples and Comparative Examples, evaluation of rate characteristics (measurement of charge capacity and discharge capacity at different rates) was performed according to the following charge/discharge test conditions.

(Charge/discharge test conditions)
1) Charge/discharge tester: HJ0501SM8A (manufactured by Hokuto Denko Co., Ltd.)
2) Charge/discharge conditions [Charging process] 0.5V → 2.5V (constant current/constant voltage mode)
[Discharge process] 2.5V → 0.5V (constant current/constant voltage mode)
3) Constant temperature chamber: PFU-3K (manufactured by ESPEC Co., Ltd.)
4) Evaluation temperature: 300K (27°C).

The evaluation cell was placed in a constant-temperature bath set at the above evaluation temperature using a charge/discharge tester, and set to constant current/constant voltage mode during the charging process (referring to the process of inserting Li into the evaluation electrode). , and charged from 0.5V to 2.5V at a predetermined constant current. Thereafter, in the discharge process (referring to the Li desorption process from the evaluation electrode), the constant current/constant voltage mode was used, and discharge was performed from 2.5 V to 0.5 V at a predetermined constant current. At this time, rate characteristics were evaluated by performing charging and discharging at constant current rates of 1/30C, 1/20C, and 1/12C, respectively. The results are shown in Table 2 below. Note that the values of charging capacity and discharging capacity shown in Table 2 are relative values when the measured value (capacity) when the rate value is 1/30C in each example or comparative example is set as 100.

From the results shown in Table 2, it can be seen that in Examples 1-1 and 1-2, in which the porous carbon material having predetermined physical properties according to the present invention was blended into the positive electrode mixture as a conductive additive, other conventionally known carbon Compared to Comparative Example 1-1 and Comparative Example 1-2 in which the material was used as a conductive aid, the charge/discharge capacity was maintained at a high rate even under high rate conditions. That is, according to the present invention, it has been shown that when an electrode active material containing sulfur is used as a positive electrode active material of a battery, it is possible to further improve the rate characteristics of the battery. Note that the porous carbon material having predetermined physical properties according to the present invention has a high specific surface area, excellent electronic conductivity, and high flexibility (elasticity). Therefore, it functions as an excellent conductive aid and contributes to improving rate characteristics in electrodes and batteries that contain active materials that expand and contract significantly during charging and discharging, and also contain insulating sulfur. it is conceivable that.

<Example 2-1>
(Preparation of sulfur active material-containing electrode composition (positive electrode mixture))
50 parts by mass of elemental sulfur (S) as a positive electrode active material and 10 parts by mass of the porous carbon material (2-1) obtained in Production Example 2-1 above as a conductive aid were weighed in a glove box. After sealing the container in a pressure- and heat-resistant container (autoclave), the container was kept in a heating furnace at 170 degrees for 6 hours to obtain a sulfur-carbon composite. 40 parts by mass of LiPS ₄ as a solid electrolyte was added thereto at room temperature in a glove box, and the mixture was placed in a zirconia grinding pot (45 mL) of a planetary ball mill (manufactured by Fritsch Japan, P-6). Then, 20,300 parts by mass of zirconia grinding balls (φ5 mm) were added, and the grinding process was then carried out at 280 rpm for 8 hours to prepare a sulfur active material-containing electrode composition (positive electrode mixture). In the obtained sulfur active material-containing electrode composition (positive electrode mixture), the positive electrode active material (sulfur alone), the conductive agent (porous carbon material), and the solid electrolyte form composite particles, and the average particle size of When the diameter (average secondary particle diameter) was measured using a scanning electron microscope, it was 15 μm (lower row of FIG. 11). Note that FIG. 11 is a photograph (magnification: 1000 times, 5000 times, and 20000 times) of the composite particles obtained in Examples 2-1 to 2-3 observed by SEM.

(Preparation of battery)
The sulfur active material-containing electrode composition (positive electrode mixture) prepared above was used, and the entire process was carried out in the same manner as in Example 1-1 above, except that the pressure force of the fastening jig was changed from 580 MPa to 400 MPa. A solid lithium ion secondary battery was fabricated.

<Example 2-2>
Same as Example 2-1 above, except that porous carbon material (2-2) obtained in Production Example (2-2) above was used instead of porous carbon material (2-1). An all-solid-state lithium-ion secondary battery was fabricated using this method. In addition, in the sulfur active material-containing electrode composition (positive electrode mixture) obtained in this example, the positive electrode active material (sulfur alone), the conductive agent (porous carbon material), and the solid electrolyte formed composite particles. When the average particle size (average secondary particle size) was measured using a scanning electron microscope, it was found to be 15 μm (middle row of FIG. 11).

<Example 2-3>
Same as Example 2-1 above, except that porous carbon material (2-3) obtained in Production Example (2-3) above was used instead of porous carbon material (2-1). An all-solid-state lithium-ion secondary battery was fabricated using this method. In addition, in the sulfur active material-containing electrode composition (positive electrode mixture) obtained in this example, the positive electrode active material (sulfur alone), the conductive agent (porous carbon material), and the solid electrolyte formed composite particles. When the average particle size (average secondary particle size) was measured using a scanning electron microscope, it was found to be 15 μm (upper row of FIG. 11).

<Comparative example 2-1>
All solids were prepared by the same method as in Example 2-1 described above, except that alkali-activated activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd., MSC-30) was used in place of the porous carbon material (2-1). A lithium ion secondary battery was manufactured.

[Characteristics evaluation of lithium ion secondary battery]
Regarding each lithium ion secondary battery produced in each of the above-mentioned Examples and Comparative Examples, evaluation of rate characteristics (measurement of charging capacity at different rates) was performed according to the same charging/discharging test conditions as described above. At this time, the evaluation temperature was changed from 300K (27°C) to 353K (80°C). In addition, rate characteristics were evaluated by performing charging and discharging at constant current rates of 0.2C, 0.5C, 1C, and 2C, respectively. The results are shown in Table 3 below. Note that the charging capacity values shown in Table 3 are relative values when the measured value (capacity) when the rate value is 0.2 C in each example or comparative example is set to 100.

From the results shown in Table 3, it can be seen that in Examples 2-1 to 2-3, in which the porous carbon material having predetermined physical properties according to the present invention was blended into the positive electrode mixture as a conductive additive, other conventionally known carbon Compared to Comparative Example 2-1 in which the material was used as a conductive aid, the charging capacity was maintained at a high rate even under high rate conditions. That is, according to the present invention, it has been shown that when an electrode active material containing sulfur is used as a positive electrode active material of a battery, it is possible to further improve the rate characteristics of the battery. Note that the porous carbon material having predetermined physical properties according to the present invention has a high specific surface area, excellent electronic conductivity, and high flexibility (elasticity). Therefore, it functions as an excellent conductive aid and contributes to improving rate characteristics in electrodes and batteries that contain active materials that expand and contract significantly during charging and discharging, and also contain insulating sulfur. it is conceivable that.

1 Alumina mold carbon material,
2 Alumina nanoparticles,
3 carbon layer,
4 carbon-coated alumina nanoparticles,
7 mesopores,
10, 50 bipolar secondary battery,
11 current collector,
11a outermost layer current collector on the positive electrode side,
11b outermost layer current collector on the negative electrode side,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 Power generation element,
23 Bipolar electrode,
25 Positive electrode current collector plate (positive electrode tab),
27 Negative electrode current collector plate (negative electrode tab),
29, 52 laminate film,
58 Positive electrode tab,
59 Negative electrode tab.

Claims (12)

an electrode active material containing sulfur;
In the X-ray diffraction spectrum, either no peak originating from the (002) plane of carbon is observed, or the half-width of the peak originating from the (002) plane of carbon is 5° or more, and the peak originating from the (10) plane of carbon is not observed. A conductive aid containing a carbon meso-sponge whose half width of the derived peak is 3.2° or less;
A sulfur active material-containing electrode composition. The sulfur active material-containing electrode composition according to claim 1, wherein the half width of a peak derived from the (10) plane of carbon in the X-ray diffraction spectrum is in the range of 1.2 to 3.2°. Regarding the carbon meso sponge , the ratio (G') of the G' band peak intensity (G') measured near 2670 cm ^-1 to the G band peak intensity (G) measured near 1590 cm ^-1 by Raman spectroscopy. '/G) is 0.6 or more, the sulfur active material-containing electrode composition according to claim 1 or 2. The sulfur active material-containing electrode composition according to any one of claims 1 to 3 , wherein the carbon meso-sponge has a BET specific surface area of 2300 to 2600 m ² /g. The sulfur active material-containing electrode composition according to any one of claims 1 to 4, wherein the carbon meso-sponge has a total pore volume of more than 4.0 cm ³ /g . The total pore volume of the carbon meso sponge is 5.3 cm. ³ The sulfur active material-containing electrode composition according to any one of claims 1 to 4, wherein the sulfur active material-containing electrode composition is at least /g. The sulfur active material-containing electrode composition according to any one of claims 1 to 6, wherein the pore volume of the mesopores in the carbon mesosponge is larger than the pore volume of the micropores in the carbon mesosponge.. The sulfur active material-containing electrode composition according to any one of claims 1 to 7 , further comprising a solid electrolyte. The sulfur active material-containing electrode composition according to claim 8 , comprising composite particles of the electrode active material, the carbon meso-sponge , and the solid electrolyte, and wherein the composite particles have an average secondary particle diameter of 50 μm or less. . An electrode comprising the sulfur active material-containing electrode composition according to any one of claims 1 to 9 . A battery comprising the electrode according to claim 10 . The battery according to claim 11 , which is an all-solid-state battery.