JP2022115375A - Positive electrode material for electrical device, and positive electrode for electrical device using the same, and electrical device - Google Patents

Abstract

To provide means for further reducing the internal resistance of an electrical device using a positive electrode active material containing sulfur.SOLUTION: In a positive electrode material including a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur, at least a part of the solid electrolyte and at least a part of the positive electrode active material are arranged on the inner surface of a pore so as to be in contact with each other, and as the conductive material, the percentage of the pore volume of pores having a pore diameter in the range of 1 to 4 nm to the pore volume of pores having a pore diameter in the range of 1 to 100 nm is 20% or less.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to a positive electrode material for electrical devices, a positive electrode for electrical devices using the same, and an electrical device.

In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is earnestly desired. In the automobile industry, expectations are gathering for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV). Development of electrolyte secondary batteries has been actively carried out.

Secondary batteries for motor driving are required to have extremely high output characteristics and high energy as compared with consumer lithium secondary batteries used in mobile phones, notebook computers, and the like. Therefore, lithium secondary batteries, which have the highest theoretical energy among all practical batteries, have attracted attention and are being rapidly developed.

Lithium secondary batteries, which are currently widely used, use a combustible organic electrolyte as an electrolyte. Such a liquid-type lithium secondary battery requires stricter safety measures against liquid leakage, short circuit, overcharge, etc. than other batteries.

Therefore, in recent years, extensive research and development has been made on all-solid lithium secondary batteries using oxide-based or sulfide-based solid electrolytes. A solid electrolyte is a material composed mainly of an ionic conductor capable of conducting ions in a solid. Therefore, in the all-solid lithium secondary battery, in principle, various problems due to the combustible organic electrolytic solution do not occur unlike the conventional liquid-type lithium secondary battery. In general, the use of a high-potential, large-capacity positive electrode material and a large-capacity negative electrode material can significantly improve the output density and energy density of the battery. For example, elemental sulfur (S ₈ ) has an extremely large theoretical capacity of about 1670 mAh/g, and has the advantage of being low cost and abundant as a resource.

On the other hand, metallic lithium, which is a negative electrode active material that supplies lithium ions to a positive electrode, is known as a high-capacity negative electrode material that can be used in all-solid-state batteries. However, in an all-solid battery that uses metallic lithium as the negative electrode active material and a sulfide solid electrolyte as the solid electrolyte, the battery characteristics may deteriorate as a result of the reaction between the metallic lithium and the sulfide solid electrolyte. .

Here, in Patent Document 1, for the purpose of coping with such a problem, a composite material containing a conductive agent and an alkali metal sulfide integrated on the surface of the conductive agent is used as a positive electrode material for an all-solid battery. A technique used as According to Patent Document 1, by using a positive electrode material having such a configuration, a positive electrode material and a lithium ion battery having a high theoretical capacity and capable of using a negative electrode active material that does not supply lithium ions to the positive electrode are provided.

International Publication No. 2012/102037 Pamphlet

Here, depending on the application of the secondary battery, it is required that sufficient capacity can be obtained during charging and discharging at a high charging and discharging rate (that is, so-called charging and discharging rate characteristics are sufficient). For example, a secondary battery with insufficient charge/discharge rate characteristics cannot utilize sufficient capacity for rapid charge/discharge. In order to improve the charge/discharge rate characteristics of the secondary battery, it is necessary to reduce the internal resistance of the battery.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide means for further reducing the internal resistance of an electrical device using a positive electrode active material containing sulfur.

The present inventors have made intensive studies to solve the above problems. As a result, in a positive electrode material including a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur, the solid electrolyte and the positive electrode active material are arranged on the inner surfaces of the pores so that they are in contact with each other. The present inventors have found that the above-described problems can be solved by configuring the conductive material so as to have a pore volume profile that is appropriately controlled, and have completed the present invention.

One aspect of the present invention includes a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur, wherein at least part of the solid electrolyte and at least part of the positive electrode active material are in contact with each other. are arranged on the inner surface of the pores, and among the pores, the pore volume of the pores having a pore diameter in the range of 1 to 4 nm, and the pores having a pore diameter in the range of 1 to 100 nm The positive electrode material for electrical devices has a pore volume percentage of 20% or less.

According to the present invention, it is possible to further reduce the internal resistance of an electrical device using a positive electrode active material containing sulfur.

FIG. 1 is a perspective view showing the appearance of a flat laminated all-solid lithium secondary battery that is an embodiment of the present invention. FIG. 2 is a cross-sectional view along line 2-2 shown in FIG. FIG. 3A is a schematic cross-sectional view of a positive electrode material in the prior art. FIG. 3B is a cross-sectional schematic diagram of a positive electrode material according to one embodiment of the present invention. FIG. 4 is a graph of pore size distribution in the pore size range of 1 to 100 nm, measured according to the BJH method, for carbon used in Comparative Examples and Examples described later.

Hereinafter, the above-described embodiments of the present invention will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the claims and is not limited only to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios. Hereinafter, the present invention will be described with reference to an example of a stacked type (internal parallel connection type) all-solid lithium secondary battery, which is one form of a secondary battery. As described above, the solid electrolyte that constitutes the all-solid-state lithium secondary battery is a material mainly composed of an ion conductor capable of conducting ions in a solid state. Therefore, the all-solid-state lithium secondary battery has the advantage that, unlike conventional liquid-type lithium secondary batteries, various problems due to the combustible organic electrolyte do not occur in principle. In general, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials also has the advantage that the output density and energy density of the battery can be greatly improved.

One aspect of the present invention includes a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur, wherein at least part of the solid electrolyte and at least part of the positive electrode active material are in contact with each other. are arranged on the inner surface of the pores, and among the pores, the pore volume of the pores having a pore diameter in the range of 1 to 4 nm, and the pores having a pore diameter in the range of 1 to 100 nm The positive electrode material for electrical devices has a pore volume percentage of 20% or less. According to the positive electrode material for an electrical device according to this embodiment, the internal resistance of the electrical device can be further reduced.

FIG. 1 is a perspective view showing the appearance of a flat laminated all-solid lithium secondary battery that is an embodiment of the present invention. FIG. 2 is a cross-sectional view along line 2-2 shown in FIG. By using a laminate type, the battery can be made compact and have a high capacity. In the present specification, a flat laminated non-bipolar lithium secondary battery (hereinafter also simply referred to as a "laminated battery") shown in FIGS. 1 and 2 will be described in detail as an example. However, when viewed from the electrical connection form (electrode structure) inside the lithium secondary battery according to this embodiment, it can be either a non-bipolar type (internal parallel connection type) battery or a bipolar type (internal series connection type) battery. can also be applied.

As shown in FIG. 1, the laminated battery 10a has a rectangular flat shape, and from both sides thereof, a negative electrode collector plate 25 and a positive electrode collector plate 27 for extracting electric power are pulled out. there is The power generation element 21 is wrapped by the battery exterior material (laminate film 29) of the laminated battery 10a, and the periphery thereof is heat-sealed. It is sealed in the pulled out state.

In addition, the lithium secondary battery according to the present embodiment is not limited to a laminated flat shape. The wound type lithium secondary battery may have a cylindrical shape, or may have a rectangular flat shape obtained by deforming such a cylindrical shape. , is not particularly limited. In the case of the above-mentioned cylindrical shape, a laminate film may be used as the exterior material, or a conventional cylindrical can (metal can) may be used, and there is no particular limitation. Preferably, the power generation element is housed inside a laminate film containing aluminum. Weight reduction can be achieved by this configuration.

In addition, there are no particular restrictions on how the collector plates (25, 27) shown in FIG. 1 can be taken out. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be pulled out from the same side, or the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be divided into a plurality of pieces and pulled out from each side. It is not limited to what is shown in FIG. 1, such as good. In a wound type lithium battery, terminals may be formed using, for example, cylindrical cans (metal cans) instead of tabs.

As shown in FIG. 2, the laminate type battery 10a of the present embodiment has a structure in which a flat and substantially rectangular power generation element 21 in which charge/discharge reactions actually progress is sealed inside a laminate film 29 that is a battery exterior material. have Here, the power generation element 21 has a structure in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are arranged on both sides of a positive electrode current collector 11″. The negative electrode contains a negative electrode active material on both sides of a negative electrode current collector 11′. It has a structure in which active material layers 13 are arranged, specifically, one positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 face each other with a solid electrolyte layer 17 interposed therebetween. A positive electrode, a solid electrolyte layer, and a negative electrode are stacked in this order, so that the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one single cell layer 19. Therefore, the stacked battery 10a shown in FIG. It can also be said that a plurality of unit cell layers 19 are stacked to have a configuration in which they are electrically connected in parallel.

As shown in FIG. 2, the outermost negative electrode current collectors positioned on both outermost layers of the power generating element 21 have the negative electrode active material layer 13 only on one side, but the active material layer is provided on both sides. may be That is, a current collector having active material layers on both sides may be used as it is as the current collector for the outermost layer, instead of using a current collector exclusively for the outermost layer having an active material layer on only one side. In some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and the positive electrode, respectively, without using the current collectors (11', 11'').

The negative electrode current collector 11′ and the positive electrode current collector 11″ are attached with a negative electrode current collector plate (tab) 25 and a positive electrode current collector plate (tab) 27, which are electrically connected to the electrodes (positive electrode and negative electrode), respectively. It has a structure in which it is sandwiched between the ends of the laminate film 29, which is the material, and led out of the laminate film 29. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are respectively connected to the positive electrode as necessary. It may be attached to the positive electrode current collector 11″ and the negative electrode current collector 11′ of each electrode by ultrasonic welding, resistance welding, or the like via a lead and a negative electrode lead (not shown).

Main constituent members of the lithium secondary battery according to this embodiment will be described below.

[Current collector]
The current collector has a function of mediating transfer of electrons from the electrode active material layer. There are no particular restrictions on the material that constitutes the current collector. As the constituent material of the current collector, for example, a metal or a conductive resin can be used.

Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or the like may be used. Alternatively, a foil in which a metal surface is coated with aluminum may be used. Among them, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electronic conductivity, battery operating potential, adhesion of the negative electrode active material to the current collector by sputtering, and the like.

The latter resin having conductivity includes a resin obtained by adding a conductive filler to a conductive polymer material or 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), and polyimide. (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA) , polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent electrical potential or solvent resistance.

Conductive fillers may be added to the 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 of only a non-conductive polymer, a conductive filler is inevitably essential in order to impart conductivity to the resin.

Any electrically conductive filler can be used without particular limitation. Examples of materials that are excellent in conductivity, potential resistance, or lithium ion blocking properties include metals and conductive carbon. 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 these metals. It preferably contains alloys or metal oxides. Also, the conductive carbon is not particularly limited. 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.

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

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. Moreover, from the viewpoint of blocking movement of lithium ions between the single cell layers, a metal layer may be provided on a part of the current collector. Furthermore, if the negative electrode active material layer and the positive electrode active material layer to be described later themselves have conductivity and can exhibit a current collecting function, a current collector is used as a member separate from these electrode active material layers. No need. In such a form, the negative electrode active material layer to be described later constitutes the negative electrode as it is, and the positive electrode active material layer to be described later constitutes the positive electrode as it is.

[Negative electrode (negative electrode active material layer)]
In the stacked battery according to the embodiment shown in FIGS. 1 and 2, the negative electrode active material layer 13 contains a negative electrode active material. The types of negative electrode active materials are not particularly limited, but include 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, soft carbon, and the like. Moreover, as a metal _oxide , _Nb2O5 , _{Li4Ti5O12 etc.} are _mentioned , for example. Furthermore, a silicon-based negative electrode active material or a tin-based negative electrode active material may be used. Here, silicon and tin belong to Group 14 elements and are known to be negative electrode active materials capable of greatly improving the capacity of non-aqueous electrolyte secondary batteries. Since these simple substances can occlude and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), they become high-capacity negative electrode active materials. Here, it is preferable to use simple Si as the silicon-based negative electrode active material. Similarly, it is also preferable to use a silicon oxide such as SiO _x (0.3≦x≦1.6) disproportionated into two phases of Si phase and silicon oxide phase. At this time, the range of x is more preferably 0.5≦x≦1.5, and more preferably 0.7≦x≦1.2. Furthermore, an alloy containing silicon (silicon-containing alloy-based negative electrode active material) may be used. On the other hand, examples of negative electrode active materials containing a tin element (tin-based negative electrode active materials) include Sn alone, tin alloys (Cu—Sn alloys, Co—Sn alloys), amorphous tin oxides, tin silicon oxides, and the like. Among these, SnB _0.4 P _0.6 O _3.1 is exemplified as an amorphous tin oxide. SnSiO ₃ is exemplified as tin silicon oxide. A metal containing lithium may also be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is an active material containing lithium, and examples thereof include metallic lithium and lithium-containing alloys. Lithium-containing alloys include, for example, alloys of Li and at least one of In, Al, Si and Sn. In some cases, two or more kinds of negative electrode active materials may be used together. Needless to say, negative electrode active materials other than those described above may be used. The negative electrode active material preferably contains metallic lithium, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains metallic lithium.

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 is in the form of particles, its average particle size (D ₅₀ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, still more preferably 100 nm. to 20 μm, particularly preferably 1 to 20 μm. In addition, in this specification, the value of the average particle size (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. more preferred.

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

Examples of sulfide solid electrolytes 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 _{- Li3PS4} , LiI _- LiBr _{- Li3PS4 , Li3PS4} , _{Li2SP2S5 - LiI} , _{Li2SP2S5 - Li2O} , _Li2SP 2S5 _- Li2O _- LiI, _{Li2S - SiS2} , Li2S _- SiS2 _- LiI, Li2S _- SiS2 _- LiBr, Li2S _- SiS2-LiCl, _{Li2S - SiS2} -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-B ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (where m, n is a positive number and Z is one of Ge, Zn and Ga), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , 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) and the like. The description of “Li ₂ SP _{2 S 5 ” means a sulfide solid electrolyte 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 sulfide solid electrolytes having a Li ₃ PS ₄ skeleton include LiI--Li ₃ PS ₄ , LiI--LiBr--Li ₃ PS ₄ and Li ₃ PS ₄ . Examples of sulfide solid electrolytes having a Li ₄ P ₂ S ₇ skeleton include Li—P—S solid electrolytes called LPS (eg, Li ₇ P ₃ S ₁₁ ). As the sulfide solid electrolyte, for example, LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (where x satisfies 0<x<1) may be used. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing the element P, and the sulfide solid electrolyte is a material containing Li ₂ SP ₂ S ₅ as a main component. It is more preferable to have Furthermore, the sulfide solid electrolyte may contain halogens (F, Cl, Br, I). _In one preferred embodiment, the sulfide solid electrolyte comprises _Li6PS5X , where X is Cl, Br or I, preferably Cl.

When the sulfide solid electrolyte is Li ₂ S—P ₂ S ₅ system, the molar ratio of Li ₂ S and P ₂ S ₅ is Li ₂ S:P ₂ S ₅ =50:50 to 100. :0, and more preferably Li ₂ S:P ₂ S ₅ =70:30 to 80:20.

The sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method. The sulfide glass can be obtained, for example, by subjecting the raw material composition to mechanical milling (such as a ball mill). 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 (eg, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25° C.) is, for example, preferably 1×10 ⁻⁵ S/cm or more, and 1×10 ⁻⁴ S/cm. cm or more is more preferable. Incidentally, the value of the ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

Examples of oxide solid electrolytes include compounds having a NASICON structure. Examples of compounds having a NASICON structure include compounds represented by the general formula Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (0≦x≦2) (LAGP) and general formula Li _1+x Al _x Ti _{2 -x} (PO ₄ ) ₃ (0≦x≦2) (LATP) and the like. 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 a particle shape such as a spherical shape and an ellipsoidal shape, a thin film shape, and the like. When the solid electrolyte is in the form of particles, the average particle size (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.

The negative electrode active material layer may further contain at least one of a conductive aid and a binder in addition to the negative electrode active material and solid electrolyte described above.

Examples of conductive aids include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys containing these metals, and metal oxides; carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, activated carbon fiber, etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjenblack (registered trademark) , furnace black, channel black, thermal lamp black, etc.), but are not limited thereto. In addition, 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 aids, 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 at least one 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 agent is particulate, the shape of the particles is not particularly limited, and may be powdery, spherical, rod-like, needle-like, plate-like, columnar, amorphous, scaly, spindle-like, or the like. I don't mind.

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

When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass with respect to the total mass of the negative electrode active material layer. , more preferably 2 to 8% by mass, more preferably 4 to 7% by mass. Within such a range, it becomes possible to form a stronger electron conduction path in the negative electrode active material layer, which can effectively contribute to the improvement of battery characteristics.

On the other hand, the binder is not particularly limited, but includes, for example, the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced 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) , ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), fluorine resins such as polyvinyl fluoride (PVF), vinylidene fluoride- Hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber ( vinylidene fluoride fluororubbers such as VDF-PFMVE-TFE fluororubbers), vinylidene fluoride-chlorotrifluoroethylene fluororubbers (VDF-CTFE fluororubbers), and epoxy resins. Among them, polyimide, styrene-butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

Although the thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, it is preferably in the range of, for example, 0.1 to 1000 μm.

[Solid electrolyte layer]
In the laminated battery according to the embodiment shown in FIGS. 1 and 2, the solid electrolyte layer is a layer interposed between the positive electrode active material layer and the negative electrode active material layer and essentially containing a solid electrolyte.

The specific form of the solid electrolyte contained in the solid electrolyte layer is not particularly limited, and the solid electrolytes exemplified in the column of the negative electrode active material layer and their preferred forms can be similarly employed. In some cases, solid electrolytes other than the solid electrolytes described above may be used together.

The solid electrolyte layer may further contain a binder in addition to the predetermined solid electrolyte described above. As for the binder that can be contained in the solid electrolyte layer, the examples and preferred forms described in the column of the negative electrode active material layer can be similarly adopted.

The thickness of the solid electrolyte layer varies depending on the structure of the target lithium secondary battery, but from the viewpoint of improving the volume energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, More preferably, it is 400 μm or less. On the other hand, the lower limit of the thickness of the solid electrolyte layer is not particularly limited, but is preferably 1 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more.

[Positive electrode active material layer]
In the layered battery according to the embodiment shown in FIGS. 1 and 2, the positive electrode active material layer contains the positive electrode material for electrical devices according to one embodiment of the present invention. The positive electrode material for an electric device includes a conductive material having pores, a solid electrolyte, and a sulfur-containing positive electrode active material.

(Positive electrode active material containing sulfur)
The type of the positive electrode active material containing sulfur is not particularly limited, but examples thereof include elemental sulfur (S) and particles or thin films of organic sulfur compounds or inorganic sulfur compounds. Any material may be used as long as it can release lithium ions at times and absorb lithium ions at the time of discharge. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile represented by compounds described in WO 2010/044437, 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 group, or a thioamide group are more preferable. Here, sulfur-modified polyacrylonitrile is sulfur-atom-containing modified polyacrylonitrile obtained by mixing sulfur powder and polyacrylonitrile and heating the mixture under an inert gas or under reduced pressure. Its putative structure is described, for example, in Chem. Mater. 2011, 23, 5024-5028, polyacrylonitrile is ring-closed to form a polycyclic structure, and at least 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 further peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 and 929 cm ^-1 . do. On the other hand, inorganic sulfur compounds are preferred because of their excellent stability, and specific examples include elemental sulfur (S), TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S and MoS ₂ . , MoS ₃ , MnS, MnS ₂ , CoS, CoS ₂ and the like. Among them, S, S-carbon composites, TiS ₂ , TiS ₃ , TiS ₄ , FeS ₂ and MoS ₂ are preferred, and elemental sulfur (S), TiS ₂ and FeS ₂ are more preferred, from the viewpoint of high capacity. Elemental sulfur (S) is particularly preferred. As the elemental sulfur (S), α sulfur, β sulfur, or γ sulfur having an _S8 structure may be used.

The positive electrode material according to this embodiment may further include a sulfur-free positive electrode active material in addition to the sulfur-containing positive electrode active material. Examples of positive electrode active materials containing no sulfur include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , Li(Ni--Mn--Co)O ₂ , LiMn ₂ O ₄ , LiNi 0.5 _{. spinel -} type active materials such as _5Mn1.5O4 ; olivine _- type active materials such as _LiFePO4 and _LiMnPO4 ; and Si _- containing active materials such as _Li2FeSiO4 and _Li2MnSiO4 . As an oxide active material other than the above, for example, Li ₄ Ti ₅ O ₁₂ can be mentioned.

In some cases, two or more positive electrode active materials may be used together. It goes without saying that positive electrode active materials other than those described above may be used. However, the ratio of the content of the sulfur-containing positive electrode active material to 100% by mass of the total amount of the positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass. more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

(solid electrolyte)
The positive electrode material according to this embodiment essentially contains a solid electrolyte. The specific form of the solid electrolyte contained in the positive electrode material according to this embodiment is not particularly limited, and the solid electrolytes and their preferred forms exemplified in the column of the negative electrode active material layer can be similarly employed. In some cases, solid electrolytes other than the solid electrolytes described above may be used together.

Among others, the solid electrolyte contained in the positive electrode material according to the present embodiment is preferably a sulfide solid electrolyte. In another preferred embodiment, the solid electrolyte contained in the solid electrolyte layer contains alkali metal atoms. Alkali metals that can be contained in the solid electrolyte include Li, Na, and K. Among them, Li is preferable because of its excellent ion conductivity. In yet another preferred embodiment, the solid electrolyte contained in the positive electrode material contains alkali metal atoms (eg Li, Na or K; preferably Li) and phosphorus and/or boron atoms. Sulfide solid electrolytes containing such alkali metal atoms and phosphorus atoms and/or boron atoms include, for example, LiI-Li ₂ SP ₂ O ₅ and 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 -LiI, Li ₂ SP ₂ S ₅ -Li2O, _{Li2SP2S5 -} Li2O _- LiI, Li2S _{- SiS2 - B2S3 -} LiI, _{Li2S - SiS2 - P2S5 -} LiI, Li2 S—B ₂ S ₃ , Li ₂ SP ₂ S ₅ —Z _m S _n (where m and n are positive numbers and Z is one of Ge, Zn and Ga), Li ₂ S—SiS ₂ —Li ₃ PO ₄ and the like. Examples of sulfide solid electrolytes having a Li ₄ P ₂ S ₇ skeleton include Li—P—S solid electrolytes called LPS (eg, Li ₇ P ₃ S ₁₁ ). Further, for example, LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (where x satisfies 0<x<1) may be used. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing phosphorus atoms, and the sulfide solid electrolyte is a material containing Li ₂ SP ₂ S ₅ as a main component. It is more preferable to have Furthermore, the sulfide solid electrolyte may contain halogens (F, Cl, Br, I). _In one preferred embodiment, the sulfide solid electrolyte comprises _Li6PS5X , where X is Cl, Br or I, preferably Cl. Since these solid electrolytes have high ionic conductivity, they can effectively contribute to manifestation of the effects of the present invention.

(Conductive material)
The positive electrode material according to this embodiment essentially contains a conductive material having pores. The specific form of the conductive material contained in the positive electrode material according to the present embodiment is not particularly limited as long as it is a conductive material having pores and has a predetermined pore volume profile described later. A conventionally known material can be appropriately adopted. The conductive material having pores is preferably a carbon material from the viewpoints of excellent conductivity, ease of processing, and ease of designing a desired pore distribution.

Examples of carbon materials having pores include activated carbon, Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, carbon black such as lamp black, Examples thereof include carbon particles (carbon carriers) made of coke, natural graphite, artificial graphite, and the like. In addition, it is preferable that the main component of the carbon material is carbon. Here, "mainly composed of carbon" means containing carbon atoms as the main component, and is a concept that includes both consisting only of carbon atoms and consisting essentially of carbon atoms. The phrase “substantially composed of carbon atoms” means that 2 to 3% by mass or less of impurities can be mixed.

In the positive electrode material according to the present embodiment, among the pores possessed by the conductive material having pores, the pores having a pore diameter in the range of 1 to 100 nm are included in the pore volume of the pores having a pore diameter in the range of 1 to 4 nm. One of the characteristics is that the ratio of (mesopores) to the pore volume is 20% or less. This feature, expressed qualitatively, means that the proportion of the pore volume occupied by pores with relatively small pore diameters is small. Here, in the present specification, the pore size distribution (value of pore volume) of mesopores of the conductive material is obtained by using the BJH method. "BJH method" is an abbreviation of "Barrett-Joyner-Halenda method", and is a method for determining the pore size distribution of mesopores (pore size 1 to 100 nm). The total adsorption amount is represented by the sum of the multi-layer adsorption amount and the capillary condensation amount. Among them, capillary condensation is a phenomenon that usually occurs in extremely small pores, but in mesopore regions with large pore diameters, capillary condensation is thought to occur in the intermolecular voids left after the multi-layer adsorption layer is completed. The pore distribution of mesopores is analyzed from the thickness of the polymolecular adsorption layer when condensation occurs. For details of the BJH method, see E.I. P. Barrett, L.; G. Joyner andP. P. Halenda, J.; Am. chem. Soc. , 73, 373 (1951). In addition, from the viewpoint that the effect of reducing internal resistance is further exhibited, the above percentage value is preferably 18% or less, more preferably 15% or less, still more preferably 12% or less, especially Preferably it is 9%. On the other hand, the lower limit of the above percentage is not particularly limited, but is, for example, 3% or more.

The BET specific surface area of the conductive material (preferably carbon material) having pores is preferably 200 m ² /g or more, more preferably 500 m ² /g or more, and 800 m ² /g or more. is more preferable, 1200 m ² /g or more is particularly preferable, and 1500 m ² /g or more is most preferable. In addition, the total pore volume of the conductive material (preferably carbon material) having pores is preferably 1.0 mL/g or more, more preferably 1.3 mL/g or more, and 1.5 mL. /g or more is more preferable. If the BET specific surface area and the total pore volume of the conductive material are values within such ranges, a sufficient amount of pores can be retained, and a sufficient amount of the positive electrode active material can be retained. becomes. The BET specific surface area and total pore volume of the conductive material can be measured by nitrogen adsorption/desorption measurement. This nitrogen adsorption/desorption measurement is performed using BELSORP mini manufactured by Microtrac Bell Co., Ltd. at a temperature of -196°C by a multipoint method. The BET specific surface area is obtained from the adsorption isotherm in the relative pressure range of 0.01<P/P ₀ <0.05. Also, the pore volume is determined from the volume of adsorbed _N2 at a relative pressure of 0.96.

Although the average pore diameter of the conductive material is not particularly limited, it is preferably 50 nm or less, particularly preferably 30 nm or less. If the average pore diameter of the conductive material is a value within these ranges, electrons can be transferred sufficiently to the active material located away from the pore walls in the positive electrode active material containing sulfur arranged inside the pores. can supply. The value of the average pore diameter of the conductive material can be calculated by nitrogen adsorption/desorption measurement in the same manner as the values of the BET specific surface area and pore volume.

The average particle size (primary particle size) when the conductive material is particulate is not particularly limited, but is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm. , 0.5 to 10 μm. As for the definition of the "particle size of the conductive material" and the method for measuring the "average particle size of the conductive material", the same method as described above for the conductive aid is employed.

As described above, the positive electrode material according to the present embodiment includes a conductive material having pores, a solid electrolyte, and a sulfur-containing positive electrode active material. and substances are arranged on the inner surfaces of the pores of the conductive material so as to be in contact with each other.

FIG. 3A is a schematic cross-sectional view of a cathode material 100' in the prior art. Moreover, FIG. 3B is a cross-sectional schematic diagram of the positive electrode material 100 which concerns on one Embodiment of this invention. In FIGS. 3A and 3B, a carbon material (for example, activated carbon) 110, which is a conductive material, has a large number of pores 110a. The pores 110a are filled with sulfur 120, which is a positive electrode active material. This positive electrode active material (sulfur) 120 is also arranged on the surface of the carbon material (activated carbon) 110 . _Here , in the _positive electrode material 100' according to the prior art shown in FIG. there is _On the other hand, in the _positive electrode material 100 according to one embodiment of the present invention shown in FIG. It is arranged not only on the surface but also on the inner surface of the pores of the carbon material (porous carbon) 110 . More specifically, a continuous phase composed of a positive electrode active material (sulfur) 120 is filled inside the pores 110a, and a solid electrolyte 130 is arranged as a dispersed phase in the continuous phase. As a result, at least part of the solid electrolyte arranged on the inner surface of the pores and at least part of the positive electrode active material (sulfur) similarly arranged inside the pores are in contact with each other. In addition, among the pores possessed by the conductive material, the percentage of the pore volume of pores having a pore diameter in the range of 1 to 4 nm to the pore volume of pores having a pore diameter in the range of 1 to 100 nm is controlled to 20% or less. It is Here, it is possible to confirm whether or not the positive electrode active material and the solid electrolyte are arranged inside the pores of the conductive material using various conventionally known techniques. For example, an observation image of a cross section of a conductive material by a transmission electron microscope (TEM) is subjected to element mapping derived from each material using energy dispersive X-ray spectroscopy (EDX), and the obtained element map and all elements Using the count number of elements derived from each material with respect to the count number as an index, it is possible to confirm the arrangement form of each material. For example, when the solid electrolyte contains phosphorus atoms and/or boron atoms, if there is no possibility that the phosphorus atoms and/or boron atoms are derived from other materials, the above elements for phosphorus and/or boron It is possible to obtain a map and confirm the arrangement form of the solid electrolyte from its distribution. It is also possible to confirm the arrangement of the solid electrolyte from the ratio of the counts of phosphorus and/or boron to the counts of all elements in EDX. In addition, when confirming the arrangement form of the solid electrolyte using the count number of elements derived only from the solid electrolyte as an index in EDX, the ratio of the count number of elements derived only from the solid electrolyte to the count number of all elements in EDX If the value is 0.10 or more, it can be determined that the solid electrolyte is arranged inside the pores of the conductive material. Moreover, the value of the ratio is preferably 0.15 or more, more preferably 0.20 or more, still more preferably 0.26 or more, and particularly preferably 0.35 or more. As this value is larger, it means that more solid electrolyte is arranged on the inner surface of the pores of the conductive material. can be expressed more prominently. The preferred upper limit of the ratio is not particularly limited, but a preferred upper limit is 0.50 or less, more preferably 0.45 or less.

According to the positive electrode material according to the present embodiment having the above configuration, in an electrical device such as an all-solid lithium secondary battery using a positive electrode active material containing sulfur, the internal resistance of the electrical device can be further reduced. becomes possible. Although the mechanism by which such excellent effects are exhibited by the configuration according to the present embodiment is not completely clear, the following mechanism is presumed. That is, in order for the charge-discharge reaction to proceed in the positive electrode active material containing sulfur, it is necessary that electrons and charge carriers such as lithium ions enter and leave the surface of the positive electrode active material smoothly. Here, when the positive electrode active material (sulfur) 120 is held inside the pores 110a of the conductive material such as the carbon material 110 as in the positive electrode material 100′ shown in FIG. On the surface of the positive electrode active material (sulfur) 120, electrons can move in and out smoothly to some extent via the conductive material. However, since the solid electrolyte 130 is not arranged inside the pores 110a, charge carriers such as lithium ions enter and exit smoothly on the surface of the positive electrode active material (sulfur) 120 located deep in the pores 110a. do not do. As a result, the charge/discharge reaction does not proceed sufficiently in the positive electrode active material (sulfur) 120 located deep in the pores 110a, causing problems such as an increase in internal resistance and a decrease in charge/discharge rate characteristics.

Further, among the pores of the conductive material constituting the positive electrode material, the pore volume of the pores having a pore diameter in the range of 1 to 4 nm is the percentage of the pore volume of the pores having a pore diameter in the range of 1 to 100 nm. If it exceeds 20%, the ratio of pores with relatively small pore diameters increases. Here, since the positive electrode active material containing sulfur has a small molecular size of less than 1 nm, it can penetrate into the pores of the conductive material (carbon material) and be supported. On the other hand, the size of a single molecule of a solid electrolyte is as large as about 2 nm, and depending on the manufacturing method, it may be solvated to further increase the size. As a result, the solid electrolyte cannot penetrate into pores having a pore diameter of about several nanometers. As a result, the charge/discharge reaction does not proceed sufficiently, and problems such as an increase in internal resistance and a decrease in charge/discharge rate characteristics are considered to occur.

On the other hand, as in the positive electrode material 100 shown in FIG. When the percentage of pores with respect to the pore volume is controlled to 20% or less, and the solid electrolyte 130 is held together with the positive electrode active material (sulfur) 120 on the inner surface of the pores 110a of the conductive material such as the carbon material 110, On the surface of the positive electrode active material (sulfur) 120 located deep in the pores 110a, not only electrons entering and leaving through the conductive material but also charge carriers entering and leaving through the solid electrolyte 130 can proceed smoothly. As a result, even around the positive electrode active material (sulfur) 120 located deep in the pores 110a, a three-phase interface where the positive electrode active material, the conductive material, and the solid electrolyte coexist is sufficiently formed, and the charge/discharge reaction is sufficient. can proceed to As a result, it is believed that the internal resistance of the battery is sufficiently reduced and the charge/discharge rate characteristics are greatly improved.

Although the manufacturing method of the positive electrode material according to the present embodiment having the above configuration is not particularly limited, an example of the manufacturing method will be briefly described. As described in the section of Examples described later, first, a conductive material that satisfies the predetermined pore volume profile of the present application is prepared using a conventionally known method. Here, the method for obtaining such a conductive material will be described by taking as an example the case where the conductive material is a carbon material. Bake below. After that, by dissolving the template with acid, a carbon material (conductive material) having a porous structure in which the shape of the template is transferred is obtained. At this time, the pore diameter and pore volume of the obtained carbon material can be changed by appropriately adjusting the particle size of the template and the blending ratio of the carbon raw material.

Next, a solution is prepared by dissolving the solid electrolyte in an organic solvent, and the conductive material is dispersed therein to obtain a dispersion. Then, after removing the solvent, heat treatment is performed at a temperature of about 150 to 250° C. for about 1 to 5 hours. As a result, a conductive material is obtained in which the pores of the conductive material are impregnated with the solid electrolyte. Subsequently, the resulting conductive material is dry-mixed with the positive electrode active material, and heat-treated under the same conditions as above. As a result, the positive electrode active material melts and permeates into the pores of the conductive material to obtain a composite material in which the solid electrolyte and the positive electrode active material are arranged (filled) inside the pores of the conductive material. The composite material thus obtained may be used as it is as a positive electrode material, but a solid electrolyte is further added to the composite material and mixed, and if necessary, treated with an apparatus such as a ball mill to obtain a positive electrode. It is preferable to obtain material.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited. more preferred. Note that this content value is calculated based on the mass of only the positive electrode active material, excluding the conductive material and the solid electrolyte.

In addition, the positive electrode active material layer may further contain a conductive aid (a material that does not retain the positive electrode active material or solid electrolyte inside the pores) and/or a binder. , those described in the column of the negative electrode active material layer described above can be similarly employed. Similarly, the positive electrode active material layer preferably further contains a solid electrolyte, particularly preferably a sulfide solid electrolyte. As for the specific form and preferred form of the solid electrolyte such as the sulfide solid electrolyte, those described in the section of the negative electrode active material layer can be similarly adopted.

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

[Positive lead and negative lead]
Also, although not shown, the current collector and the current collector plate may be electrically connected via a positive lead or a negative lead. Materials used in known lithium secondary batteries can also be employed as the constituent materials of the positive and negative electrode leads. In addition, the parts taken out from the exterior should be heat-shrunk with heat-resistant insulation so that they do not come into contact with peripheral equipment or wiring and cause electric leakage and affect the product (for example, automobile parts, especially electronic equipment, etc.). Covering with a tube or the like is preferred.

[Battery exterior material]
As the battery exterior material, a known metal can case can be used, and as shown in FIGS. 1 and 2, a bag-like case using a laminate film 29 containing aluminum that can cover the power generation element is used. can be The laminated film may be, for example, a laminated 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 is excellent in high power output and cooling performance and can be suitably used for batteries for large equipment for EV and HEV. Moreover, since the group pressure applied to the power generating element from the outside can be easily adjusted, the outer package is more preferably a laminate film containing aluminum.

The stacked battery according to this embodiment has a structure in which a plurality of single cell layers are connected in parallel, so that it has a high capacity and excellent cycle durability. Therefore, the stacked battery according to this embodiment is suitably used as a power source for driving EVs and HEVs.

Although one embodiment of the lithium secondary battery has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be appropriately modified based on the description of the claims. is.

For example, as a type of battery to which the lithium secondary battery according to the present embodiment is applied, a positive electrode active material layer electrically coupled to one surface of the current collector and a positive electrode active material layer electrically coupled to the opposite surface of the current collector. Also included are bipolar batteries that include a bipolar electrode having an attached negative electrode active material layer.

Further, the secondary battery according to this embodiment does not have to be an all-solid-state battery. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). The amount of the liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer is not particularly limited, but the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and the liquid electrolyte (electrolyte solution) does not leak. is preferably the amount of

A liquid electrolyte (electrolytic solution) that can be used has a form in which a lithium salt is dissolved in an organic solvent. Examples of organic solvents used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), and methyl formate. (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). Among them, the organic solvent is preferably a chain carbonate, more preferably diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), from the viewpoint that the rapid charging characteristics and output characteristics can be further improved. It is at least one selected from the group consisting of, more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

Lithium salts include Li(FSO ₂ ) ₂ N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF _{3 SO3} and the like. Among them, the lithium salt is preferably Li(FSO ₂ ) ₂ N (LiFSI) from the viewpoint of battery output and charge/discharge cycle characteristics.

The liquid electrolyte (electrolytic solution) may further contain additives other than the components described above. Specific examples of such compounds include ethylene carbonate, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2- Divinylethylene carbonate, 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxymethylethylene carbonate, allyloxymethylethylene carbonate, acryloxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1 , 1-dimethyl-2-methylene ethylene carbonate and the like. These additives may be used alone or in combination of two or more. In addition, when the additive is used in the electrolytic solution, the amount used can be appropriately adjusted.

[Assembled battery]
An assembled battery is an object configured by connecting a plurality of batteries. Specifically, at least two or more are used, and serialization or parallelization or both of them are used. By connecting in series and in parallel, it is 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 assembled battery. A plurality of these detachable small battery packs are further connected in series or in parallel to form a large-capacity, large-capacity battery suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density. It is also possible to form assembled batteries (battery modules, battery packs, etc.) with output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery, depends on the battery capacity of the vehicle (electric vehicle) in which it is installed. It should be decided according to the output.

[vehicle]
A battery or an assembled battery formed by combining a plurality of these batteries can be mounted on the vehicle. In the present invention, since a long-life battery with excellent long-term reliability can be configured, a plug-in hybrid electric vehicle with a long EV driving range and an electric vehicle with a long driving range per charge can be configured by mounting such a battery. Batteries or assembled batteries made by combining a plurality of these, for example, in the case of automobiles, hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) , two-wheeled vehicles (motorcycles) and three-wheeled vehicles) will provide a long-lasting and highly reliable automobile. However, the application is not limited to automobiles, for example, it can be applied to various power sources for other vehicles, such as moving bodies such as trains, and power sources for installation such as uninterruptible power supplies. It can also be used as

The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited only to the following examples.

<<Preparation example of test cell>>
[Comparative Example 1]
(Preparation of solid electrolyte-impregnated carbon)
In an argon atmosphere glove box with a dew point of −68° C. or lower, 0.500 g of a sulfide solid electrolyte (Li ₆ PS ₅ Cl, manufactured by Ampcera) was added to 100 mL of super-dehydrated ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). , the solid electrolyte was dissolved in ethanol by stirring until the solution became clear. 1.00 g of carbon (activated carbon, MSC-30, manufactured by Kansai Coke and Chemicals Co., Ltd.) was added to the solid electrolyte ethanol solution thus obtained, and the mixture was thoroughly stirred to sufficiently disperse the carbon in the solution. The container containing the carbon dispersion was connected to a vacuum device, and the inside of the container was evacuated to 1 Pa or less by an oil rotary pump while stirring the carbon dispersion in the container with a magnetic stirrer. Since the solvent ethanol volatilized under reduced pressure, the ethanol was removed over time, and the carbon impregnated with the solid electrolyte remained in the container. After the ethanol was removed under reduced pressure in this way, the solid electrolyte-impregnated carbon was prepared by heating to 180° C. under reduced pressure and performing heat treatment for 3 hours. Regarding the carbon used in this comparative example, E.I. P. Barrett, L.; G. Joyner andP. P. Halenda, J.; Am. chem. Soc. , 73, 373 (1951). The horizontal axis of FIG. 4 is the carbon pore diameter Dp [nm], and the vertical axis is the pore volume Vp [cm ³ /g]. Further, when the percentage of the pore volume of pores with a pore diameter in the range of 1 to 4 nm to the pore volume of pores in the pore diameter range of 1 to 100 nm was calculated, it was 79%.

(Preparation of Sulfur/Solid Electrolyte/Carbon Composites by Thermal Impregnation of Sulfur)
In an argon atmosphere glove box with a dew point of -68 ° C. or less, 2.50 g of sulfur (manufactured by Aldrich) was added to 0.750 g of the solid electrolyte-impregnated carbon prepared above and mixed thoroughly with an agate mortar. The mixture was placed in a sealed pressure-resistant autoclave container and heated at 170° C. for 3 hours to melt sulfur and impregnate the solid electrolyte-impregnated carbon with sulfur. A sulfur/solid electrolyte/carbon composite material was thus prepared.

(Preparation of sulfur-containing positive electrode material)
In an argon atmosphere glove box with a dew point of −68° C. or less, 40 g of 5 mm diameter zirconia balls, 0.130 g of the sulfur/solid electrolyte-impregnated carbon prepared above, and 0.070 g of a solid electrolyte (manufactured by Ampcera, Li6PS5Cl). was placed in a zirconia container with a capacity of 45 mL and treated with a planetary ball mill (Premium line P-7 manufactured by Fritsch) at 370 rpm for 6 hours to obtain a sulfur-containing positive electrode material powder. The composition of the sulfur-containing positive electrode material was sulfur:solid electrolyte:carbon=50:40:10.

In addition, by quantifying the content of the solid electrolyte contained inside the pores of the conductive material (carbon) that constitutes the powder of the sulfur-containing positive electrode material obtained above by EDX mapping, together with sulfur as the positive electrode active material It was confirmed that the solid electrolyte was placed inside the pores of the conductive material (carbon).

(Preparation of test cell (all-solid lithium secondary battery))
The battery was fabricated in a glove box in an argon atmosphere with a dew point of −68° C. or lower.

A SUS cylindrical convex punch (diameter of 10 mm) was inserted into one side of a Macor cylindrical tube jig (inner diameter: 10 mm, outer diameter: 23 mm, height: 20 mm), and a sulfide solid electrolyte ( 80 mg of Li ₆ PS ₅ Cl (manufactured by Ampcera) was added. After that, another SUS cylindrical convex punch is inserted to sandwich the solid electrolyte, and a solid electrolyte layer having a diameter of 10 mm and a thickness of about 0.6 mm is formed into a cylinder by pressing for 3 minutes at a pressure of 75 MPa using a hydraulic press. Formed in a tube jig. Next, the cylindrical convex punch inserted from the upper side is once extracted, 7.5 mg of the sulfur-containing positive electrode mixture prepared above is put on one side of the solid electrolyte layer in the cylindrical tube, and the cylindrical convex punch ( A positive electrode current collector) was inserted and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer with a diameter of 10 mm and a thickness of about 0.06 mm on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch (which also serves as a negative electrode current collector) is extracted, and a lithium foil (manufactured by Nilaco Corporation, thickness 0.20 mm) punched to a diameter of 8 mm and an indium foil (thickness 0.20 mm manufactured by Nilaco) punched to a diameter of 9 mm are used as the negative electrode. Nilaco Co., Ltd., thickness 0.30 mm), put it from the bottom side of the cylindrical tube jig so that the indium foil is located on the solid electrolyte layer side, insert the cylindrical convex punch again, and apply a pressure of 75 MPa. A lithium-indium negative electrode was formed by pressing for 3 minutes at .

As described above, a test cell (all-solid lithium secondary) in which the negative electrode current collector (punch), the lithium-indium negative electrode, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector (punch) are laminated in this order battery) was produced.

[Example 1]
In the preparation of the solid electrolyte-impregnated carbon, as the carbon, instead of MSC-30, porous carbon powder (Toyo Tanso Co., Ltd., Knobel (registered trademark) P (3) 010) was used. An all-solid lithium secondary battery was produced in the same manner as in Example 1. Also in this example, it was confirmed that the solid electrolyte was arranged inside the pores of the conductive material (carbon) together with the sulfur that was the positive electrode active material.

Here, regarding the carbon used in this example, E.I. P. Barrett, L.; G. Joyner andP. P. Halenda, J.; Am. chem. Soc. , 73, 373 (1951). Further, when the percentage of the pore volume of pores with a pore diameter in the range of 1 to 4 nm to the pore volume of pores in the pore diameter range of 1 to 100 nm was calculated, it was 9%.

[Example 2]
In the preparation of the solid electrolyte-impregnated carbon, carbon black (Ketjenblack (registered trademark) EC600JD manufactured by Lion Specialty Chemicals Co., Ltd.) was used as the carbon instead of MSC-30. An all-solid lithium secondary battery was produced in the same manner as in Example 1. Also in this example, it was confirmed that the solid electrolyte was arranged inside the pores of the conductive material (carbon) together with the sulfur that was the positive electrode active material.

Here, regarding the carbon used in this example, E.I. P. Barrett, L.; G. Joyner andP. P. Halenda, J.; Am. chem. Soc. , 73, 373 (1951). Further, when the percentage of the pore volume of pores with a pore diameter in the range of 1 to 4 nm to the pore volume of pores in the pore diameter range of 1 to 100 nm was calculated, it was 20%.

<<Evaluation example of test cell>>
The internal resistance values of the test cells produced in each of the above Comparative Examples and Examples were measured by the following method. All of the following measurements were performed using a charge/discharge tester (HJ-SD8, manufactured by Hokuto Denko Co., Ltd.) in a constant temperature bath set at 25°C.

(Measurement of internal resistance)
After the test cell was placed in a constant temperature bath and the cell temperature became constant, constant current discharge was performed at a current density of 0.2 mA/cm ² to a cell voltage of 0.5 V as cell conditioning. A constant current constant voltage charge of 2.5 V was performed at a current density of 0.01 mA/cm ² with a cutoff current set. The capacity value per mass of the positive electrode active material (mAh/g) was calculated from the value of the charge/discharge capacity obtained after repeating this conditioning charge/discharge cycle 10 times and the mass of the positive electrode active material contained in the positive electrode. Then, constant current discharge was performed at a current density of 0.2 mA/cm ² to reach 50% capacity (50% SOC) with respect to 100% of the calculated capacity value. After resting for 30 minutes, discharge is performed at a discharge rate of 1 C for 10 seconds, and from the voltage drop amount and current value at that time, the DC resistance value (DCR) is calculated according to Ohm's law, and the internal resistance value of the test cell. and The results are shown in Table 1 below. The internal resistance value (DCR) shown in Table 1 is a relative value when the value in Comparative Example 1 is set to 1.

From the results shown in Table 1, it can be seen that according to the present invention, the internal resistance can be further reduced in the all-solid lithium secondary battery using the positive electrode active material containing sulfur. In addition, when the internal resistance value of the positive electrode was compared between Example 1 and Example 2, the internal resistance value of Example 1, in which the value of the above percentage (Vp1-4 nm/Vp@1-100 nm) was smaller, was It was reduced to about 80% of Example 2. Therefore, in the present invention, the smaller the value of the above percentage (Vp1-4 nm/Vp@1-100 nm), the better from the viewpoint of reducing the internal resistance.

10a laminated battery,
11' negative electrode current collector,
11″ cathode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 solid electrolyte layer,
19 cell layer,
21 power generation elements,
25 negative electrode current collector,
27 positive current collector,
29 laminate film,
100, 100' cathode material,
110 carbon materials (activated carbon, porous carbon),
110a pores,
120 positive electrode active material (sulfur),
130 solid electrolyte.

Claims (13)

Containing a conductive material having pores, a solid electrolyte, and a positive electrode active material containing sulfur,
At least part of the solid electrolyte and at least part of the positive electrode active material are arranged on the inner surface of the pores so as to be in contact with each other, and
The positive electrode for an electrical device, wherein the percentage of the pore volume of the pores having a pore diameter in the range of 1 to 4 nm to the pore volume of the pores having a pore diameter in the range of 1 to 100 nm is 20% or less. material. 2. The positive electrode material for electrical devices according to claim 1, wherein said percentage is 9% or less. 3. The positive electrode material for an electric device according to claim 1, wherein a continuous phase made of said positive electrode active material is filled inside said pores, and said solid electrolyte is arranged as a dispersed phase in said continuous phase. . 4. Any one of claims 1 to 3, wherein, in an observation image of the cross section of the conductive material obtained by TEM-EDX, the ratio of the count number of the element derived only from the solid electrolyte to the count number of all elements is 0.10 or more. 2. The positive electrode material for electrical devices according to 1 or 2 above. The positive electrode material for electrical devices according to any one of claims 1 to 4, wherein said conductive material is a carbon material. The positive electrode material for electrical devices according to any one of claims 1 to 5, wherein the conductive material has a total pore volume of 1.0 mL/g or more. The positive electrode material for an electrical device according to any one of claims 1 to 6, wherein said conductive material has an average pore size of 50 nm or less. The positive electrode material for electrical devices according to any one of claims 1 to 7, wherein the solid electrolyte is a sulfide solid electrolyte. The positive electrode material for electrical devices according to any one of claims 1 to 8, wherein the solid electrolyte contains alkali metal atoms and phosphorus atoms and/or boron atoms. 10. The positive electrode material for electrical devices according to claim 9, wherein said alkali metal atoms are lithium atoms. A positive electrode for electrical devices, comprising the positive electrode material for electrical devices according to any one of claims 1 to 10. An electrical device comprising the positive electrode for electrical devices according to claim 11 . 13. The electrical device according to claim 12, which is an all-solid lithium secondary battery.

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