JP2023064496A - Positive electrode material and secondary battery using the same - Google Patents

Abstract

To provide means for further reducing the internal resistance of a secondary battery using a positive electrode active material including sulfur.SOLUTION: A positive electrode material includes: a conducting porous material; an alkali metal sulfide being a positive electrode active material; and a solid electrolyte. At least a portion of the alkali metal sulfide and at least a portion of the solid electrolyte are arranged in pores of the conducting porous material. The positive electrode material exhibits, in an X-ray diffraction measurement, a peak A derived from the conducting porous material in an area where 2θ is 20° or more and less than 25°and a peak B derived from the alkali metal sulfide and/or the solid electrolyte in an area where 2θ is 25 to 29°. A ratio (A/B) of intensity of the peak A with respect to intensity of the peak B exceeds 0.02.SELECTED DRAWING: None

Description

The present invention relates to a positive electrode material and a secondary battery using the same.

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 in widespread use, 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.

WO2012/102037

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 a secondary battery using a positive electrode active material containing sulfur.

The present inventors have made intensive studies to solve the above problems. As a result, it was found that the above problems could be solved by using a material exhibiting a specific X-ray diffraction spectrum in a positive electrode material containing an alkali metal sulfide and a solid electrolyte in the pores of a conductive porous body. , have completed the present invention.

One embodiment of the present invention is a positive electrode material including a conductive porous body, an alkali metal sulfide as a positive electrode active material, and a solid electrolyte, wherein at least part of the alkali metal sulfide and the solid electrolyte is arranged in the pores of the conductive porous body, and the positive electrode material has a peak A derived from the conductive porous body in the region where 2θ is 20 ° or more and less than 25 ° in X-ray diffraction measurement and a peak B derived from the alkali metal sulfide and/or the solid electrolyte in the region where 2θ is 25 to 29°, and the ratio of the intensity of the peak A to the intensity of the peak B (A/B) is , greater than 0.02.

According to the present invention, in a secondary battery using a positive electrode active material containing sulfur, the internal resistance of the secondary battery 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. FIG. 3(a) is a schematic cross-sectional view of a positive electrode material in the prior art, and FIG. 3(b) is a schematic cross-sectional view of a positive electrode material according to an embodiment of the present invention. FIG.3(c) is a cross-sectional schematic diagram of the positive electrode material produced by mechanical mixing. 4(a) is the XRD spectrum of the positive electrode material produced in Example 4, and FIG. 4(b) is the XRD spectrum of the positive electrode material produced in Comparative Example 2. FIG.

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 embodiment of the present invention is a positive electrode material including a conductive porous body, an alkali metal sulfide as a positive electrode active material, and a solid electrolyte, wherein at least part of the alkali metal sulfide and the solid electrolyte is arranged in the pores of the conductive porous body, and the positive electrode material has a peak A derived from the conductive porous body in the region where 2θ is 20 ° or more and less than 25 ° in X-ray diffraction measurement and a peak B derived from the alkali metal sulfide and/or the solid electrolyte in the region where 2θ is 25 to 29°, and the ratio of the intensity of the peak A to the intensity of the peak B (A/B) is , greater than 0.02. According to the positive electrode material according to this embodiment, the internal resistance of the secondary battery 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, instead of tabs, for example, cylindrical cans (metal cans) may be used to form terminals.

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 a 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.

Moreover, as the resin having conductivity, a resin obtained by adding a conductive filler to a non-conductive polymer material can be used.

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 diameter (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 diameter ( _D50 ) 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, a sulfide solid electrolyte containing the element P is preferable, and a material containing Li ₂ SP ₂ S ₅ as a main component is more preferable. 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 particle shapes such as spherical and ellipsoidal shapes, and thin film shapes. When the solid electrolyte is in the form of particles, the average particle diameter ( _D50 ) 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 ( _D50 ) 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 ( VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene fluororubber (VDF-CTFE fluororubber) and other vinylidene fluoride 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 800 μm or less, more preferably 700 μm or less, More preferably, it is 600 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 according to one embodiment of the present invention. The positive electrode material contains an alkali metal sulfide and a solid electrolyte in the pores of the conductive porous body.

(Positive electrode active material)
The positive electrode material of this embodiment contains an alkali metal sulfide as a positive electrode active material. Examples of alkali metal sulfides include lithium sulfide (Li ₂ S), sodium sulfide (Na ₂ S), potassium sulfide (K _{2 S), rubidium sulfide (Rb 2 S} ), cesium sulfide (Cs ₂ S), sulfide Examples include francium (Fr ₂ S), preferably lithium sulfide or sodium sulfide, more preferably lithium sulfide.

The positive electrode material according to the present embodiment may further contain a positive electrode active material (another positive electrode active material) other than the alkali metal sulfide in addition to the alkali metal sulfide.

Other positive electrode active materials are not particularly limited, but examples of positive electrode active materials containing sulfur include elemental sulfur (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and the oxidation-reduction reaction of sulfur. Any material may be used as long as it can be used to release lithium ions during charging and absorb lithium ions during discharging. 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. On _the other hand _{, inorganic} sulfur _compounds are preferable _because of _their excellent _{stability .} , CoS ₂ and other metal sulfides. As the elemental sulfur (S), α sulfur, β sulfur, or γ sulfur having an _S8 structure may be used.

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 ; metal oxide active materials such as olivine- _type active materials such as _{LiFePO4 and LiMnPO4 ;} and Si-containing active materials such as _Li2FeSiO4 and _Li2MnSiO4 . mentioned. In addition, examples of metal oxide active materials other than the above include Li ₄ Ti ₅ O ₁₂ .

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 alkali metal sulfide 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 or more. Yes, more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

From the viewpoint of reducing the resistance, the positive electrode material of the present embodiment preferably does not contain elemental sulfur. The content of elemental sulfur in 100% by mass of the total amount of the positive electrode active material is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and even more preferably. is 2% by mass or more, particularly preferably 1% by mass or less, and most preferably 0% 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 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 particular, it is preferable that the positive electrode active material is Li ₂ S and the solid electrolyte contains lithium (carrier ions contain lithium ions). With such a configuration, the effects of the present invention can be obtained more remarkably.

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. More preferably, the solid electrolyte is a sulfide solid electrolyte containing at least lithium atoms, phosphorus atoms and sulfur atoms. Examples of sulfide solid electrolytes containing lithium atoms, phosphorus atoms, and sulfur atoms include LiI—Li ₂ SP ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ , Li ₂ S _{-P2S5 ,} LiI- _{Li3PS4 , LiI} - _{LiBr - Li3PS4 , Li3PS4 , Li2SP2S5 -} LiI, _Li2SP2S5 - _Li2O , Li ₂ SP ₂ S ₅ —Li ₂ O—LiI, Li ₂ S—SiS ₂ —P ₂ S ₅ —LiI, Li ₂ SP ₂ S ₅ —Z _m S _n (where m and n are is a positive number 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 others, the sulfide solid electrolyte contained in the active material layer is more preferably a material containing Li ₂ SP ₂ S ₅ as a main component. 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 sulfide solid electrolytes have high ionic conductivity, they can effectively contribute to manifestation of the effects of the present invention.

(Conductive porous body)
The positive electrode material according to this embodiment essentially contains a conductive porous body having pores. The specific form of the conductive porous body 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 conventionally known materials can be appropriately employed. From the viewpoint of excellent conductivity and ease of processing, the conductive porous body is preferably a carbon material.

Carbon materials include, for example, activated carbon, Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, carbon black such as lamp black, coke, and natural graphite. , carbon particles (carbon supports) made of artificial graphite and the like. Alternatively, a mold such as ceramics and a carbon raw material such as resin are mixed, fired in an inert atmosphere, and then melted with acid to synthesize a carbon material having a porous structure in which the shape of the mold is transferred. and this may be used as the carbon material. 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.

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 this embodiment, the conductive porous body preferably has pores with a pore diameter in the range of 1 to 100 nm. In addition, 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 among the pores possessed by the conductive porous body is 20% or less. is preferably Thereby, the positive electrode active material and/or the solid electrolyte can be easily retained even inside the pores. Also, in the interior of the pores, on the surface of the positive electrode active material, not only electrons entering and exiting via the conductive porous body but also charge carriers entering and exiting via the solid electrolyte can proceed smoothly. As a result, even around the positive electrode active material located deep in the pores, a three-phase interface where the positive electrode active material, the conductive porous body, and the solid electrolyte coexist is sufficiently formed, and the charge/discharge reaction proceeds sufficiently. sell. As a result, it is believed that the internal resistance of the battery is further reduced. Here, in this specification, the pore size distribution of the conductive porous body is obtained by using the BJH method. From the viewpoint that the effect of reducing the internal resistance is further exhibited, the above percentage value is more preferably 18% or less, still more preferably 15% or less, and even more preferably 12% or less. , particularly preferably 9% or less. 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 porous body (preferably carbon material) is preferably 200 m ² /g or more, more preferably 500 m ² /g or more, and further preferably 800 m ² /g or more. It is preferably 1200 m ² /g or more, particularly preferably 1500 m 2 /g or more, most preferably 1500 m ² /g or more. In addition, the total pore volume of the conductive porous material (preferably carbon material) is preferably 1.0 mL/g or more, more preferably 1.3 mL/g or more, and 1.5 mL/g. It is more preferable that it is above. If the BET specific surface area and the total pore volume of the conductive porous body 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 possible. The BET specific surface area and total pore volume of the conductive porous 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. The total pore volume is determined from the volume of adsorbed _N2 at a relative pressure of 0.96.

The average pore size of the conductive porous material is not particularly limited, but is preferably 50 nm or less, particularly preferably 30 nm or less. If the average pore diameter of the conductive porous body is within these ranges, the active material located away from the pore walls of the sulfur-containing positive electrode active material arranged inside the pores is sufficiently can supply electrons. The value of the average pore diameter of the conductive porous body can be calculated by nitrogen adsorption/desorption measurement, similarly to the case of obtaining the values of the BET specific surface area and the total pore volume.

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

As described above, the positive electrode material according to the present embodiment includes a conductive porous body, a solid electrolyte, and an alkali metal sulfide as a positive electrode active material. A positive electrode active material is placed in the pores of the conductive porous body.

FIG. 3(a) is a schematic cross-sectional view of a positive electrode material 100' in Patent Document 1, which is a prior art. Moreover, FIG.3(b) is a cross-sectional schematic diagram of the positive electrode material 100 which concerns on one Embodiment of this invention. In FIGS. 3(a) and 3(b), a conductive porous body (for example, carbon material) 110 has many pores 110a. Here, in the method described in Patent Document 1, the pores 110 a of the conductive porous body 110 are thermally impregnated with the elemental sulfur 140 that is the raw material of the alkali metal sulfide 120 . Thereafter, elemental sulfur 140 is chemically reacted to form alkali metal sulfide 120 integrated with the surface of conductive porous body 110 . After that, solid electrolyte 130 is added by mechanical mixing to obtain positive electrode material 100 ′ having alkali metal sulfide 120 and solid electrolyte 130 on the surface of conductive porous body 110 . Alternatively, as described in Japanese Unexamined Patent Application Publication No. 2013-80637, a compound serving as a raw material of the solid electrolyte 130 is added and reacted, and the alkali metal sulfide 120 and the solid electrolyte 130 are combined with the conductive porous body 110. A cathode material 100' can be obtained.

However, in the above method, the reaction for converting elemental sulfur 140 into alkali metal sulfide 120 proceeds mainly on the surface of conductive porous body 110 (area outside the pores), and the pores 110a of conductive porous body 110 The elemental sulfur 140 impregnated inside remains unreacted. Since the elemental sulfur 140 is an insulator, the resistance of the electrode increases when using the prior art cathode material 100'.

Moreover, in the above method, since the solid electrolyte 130 or its raw material is added later, it is difficult to introduce the solid electrolyte 130 into the pores 110 a of the conductive porous body 110 . Therefore, in the positive electrode material 100′ shown in FIG. 3A, on the surface of the conductive porous body 110, a reaction occurs in which the alkali metal sulfide 120, which is the positive electrode active material, the solid electrolyte 130, and the conductive porous body 110 coexist. A region is formed, and the electrode reaction proceeds in the vicinity of this region. However, the inside of the pores 110a is not filled with the solid electrolyte 130, and the charging/discharging reaction does not proceed sufficiently. As a result, it is considered that the resistance of the electrode increases.

On the other hand, in the positive electrode material 100 according to one embodiment of the present invention shown in FIG. It is also arranged on the inner surface of the pores 110 a of the conductive porous body 110 . On the surface of the alkali metal sulfide 120 located deep in the pores 110a, not only electrons entering and leaving through the conductive porous body 110 but also charge carriers entering and leaving through the solid electrolyte 130 can proceed smoothly. As a result, even around the alkali metal sulfide 120 located deep in the pores 110a, a three-phase interface where the alkali metal sulfide 120, the conductive porous body 110 and the solid electrolyte 130 coexist is sufficiently formed, and charge/discharge is performed. The reaction can proceed satisfactorily. As a result, the alkali metal sulfide existing inside the pores 110a can also be used as an active material for the electrode reaction, and the internal resistance of the battery can be sufficiently reduced.

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 porous body by using various conventionally known techniques. For example, for an observation image of a cross section of a conductive porous body obtained by a transmission electron microscope (TEM), element mapping derived from each material is performed using energy dispersive X-ray spectroscopy (EDX). Using the count number of elements derived from each material with respect to the count number of elements 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, the positive electrode material according to the present embodiment has a peak A derived from the conductive porous body in the region where 2θ is 20 ° or more and less than 25 ° in X-ray diffraction measurement using CuKα rays of the positive electrode material. A peak B derived from an alkali metal sulfide and / or a solid electrolyte is shown in the region of ~ 29 °, and the ratio (A / B) of the intensity of the peak A to the intensity of the peak B exceeds 0.02. is characterized by

Here, FIG. 4A is a graph showing a spectrum obtained by performing X-ray diffraction measurement using CuKα rays for the positive electrode material powder prepared in Example 4, which will be described later. As shown in FIG. 4(a), the X-ray diffraction spectrum of the positive electrode material according to this embodiment first shows a peak A derived from the conductive porous material in the region where 2θ is 20° or more and less than 25°. Also, peak B derived from alkali metal sulfide and/or solid electrolyte is shown in the region of 25 to 29°. A ratio (A/B) of the intensity of the peak A to the intensity of the peak B exceeds 0.02.

Further, according to the studies of the present inventors, it has been found that if such a positive electrode material is used to form an all-solid lithium secondary battery, the internal resistance of the secondary battery can be further reduced. bottom. Although the mechanism has not been completely clarified, the following mechanism is presumed. That is, the positive electrode material according to the present embodiment is obtained by, for example, dissolving an alkali metal sulfide, which is a positive electrode active material, and a solid electrolyte in a solvent as described later to obtain a solution, and then adding a conductive porous body to the solution. It can be produced by impregnating the conductive porous body with the alkali metal sulfide and the solid electrolyte all at once. In this case, since the alkali metal sulfide and the solid electrolyte are uniformly introduced into the surface and the inside of the pores of the conductive porous body, the surface of the conductive porous body is not excessively covered. Therefore, it is considered that the wide-angle peak A derived from the conductive porous material is clearly observed. It is believed that the uniform introduction of the alkali metal sulfide and the solid electrolyte into the surface and inside of the pores of the conductive porous body increases the reaction area and reduces the resistance.

On the other hand, the positive electrode material can be produced by mechanically mixing the alkali metal sulfide 120, the solid electrolyte 130, and the conductive porous body 110. In Comparative Example 2, in which the positive electrode material was produced by mechanical mixing, FIG. ), A/B is 0.02 or less. In the positive electrode material 100″ produced by mechanical mixing, as shown in FIG. A large amount exists on the surface of the body 110. Therefore, it is considered that the intensity of the wide-angle peak A derived from the conductive porous body in the XRD spectrum is relatively small.And in the case of mechanical mixing, the solid electrolyte in the pores is not introduced, the conduction path of ions becomes insufficient, and it is thought that the resistance cannot be sufficiently reduced.In addition, the solid electrolyte 130 is attenuated or denatured by mechanical mixing, and the attenuation product or denatured product 131 is generated. It is conceivable that the resistance may become high.

It should be noted that even in the positive electrode material according to the prior art such as Patent Document 1, the alkali metal sulfide and the solid electrolyte tend to exist in large amounts on the surface of the conductive porous body 110 . Therefore, the intensity of the wide-angle peak A derived from the conductive porous material in the XRD spectrum becomes relatively small, and the above specific A/B value is not obtained.

The above A/B is preferably 0.03 or more, more preferably 0.10 or more, and still more preferably 0.20 or more. Within this range, the effects of the present invention can be obtained more remarkably. On the other hand, the upper limit of A/B is not particularly limited, but is, for example, 100 or less, preferably 10 or less, and more preferably 1 or less. The value of A/B is determined, for example, in the manufacturing process of simultaneously impregnating the conductive porous body with the alkali metal sulfide, which is the positive electrode active material, and the solid electrolyte, as described later. It can be controlled by adjusting the charging ratio of the porous body. Here, the intensity of peak A and peak B refers to the peak height minus the baseline. Moreover, when two or more peaks having a predetermined attribution are observed in the predetermined region, the height of the highest peak is taken as the peak intensity.

The positive electrode material of this embodiment preferably does not have a peak derived from elemental sulfur in the X-ray diffraction spectrum.

Although the mass ratio of the alkali metal sulfide and the solid electrolyte in the positive electrode material of this embodiment is not particularly limited, it is, for example, alkali metal sulfide:solid electrolyte=1:99 to 99:1. The above mass ratio is preferably alkali metal sulfide:solid electrolyte=50:50 to 1:99, more preferably 1:1 to 1:20. Within the above range, a high-performance battery can be obtained because a sufficient amount of the positive electrode active material can be secured. In addition, it is preferable because the ion conductivity of the positive electrode material can be ensured, and an ion-conducting network is sufficiently formed even in the pores. Furthermore, it is preferable because decomposition of the solid electrolyte due to too much solid electrolyte is unlikely to occur.

The positive electrode material of the present embodiment preferably has a pore filling rate of 50% or more, preferably 80% or more, defined as the ratio of the volume occupied by the positive electrode active material and the solid electrolyte to the total pore volume of the conductive porous body. It is preferably 100% or more. Within the above range, the effects of the present invention can be obtained more remarkably. Although the upper limit of the pore filling rate is not particularly limited, it is, for example, 200% or less, preferably 170% or less. The pore filling rate can be obtained by the method described in Examples.

According to a preferred embodiment of the present invention, the mass ratio of alkali metal sulfide and solid electrolyte is alkali metal sulfide:solid electrolyte=1:1 to 1:5, and the pore filling rate is 100% or more. . This configuration is preferable because an ion-conducting network is sufficiently formed even in the pores. Furthermore, it is preferable because decomposition of the solid electrolyte due to too much solid electrolyte is unlikely to occur. It is also preferable from the viewpoint of energy density.

In the positive electrode material of the present embodiment, the mass ratio between the alkali metal sulfide and the conductive porous material is not particularly limited. , preferably 1-4. Within the above range, the effects of the present invention can be obtained more remarkably.

The method for producing the positive electrode material according to the present embodiment having the configuration as described above is not particularly limited. impregnating a flexible porous body. As a result, the conductive porous body can be impregnated with the alkali metal sulfide and the solid electrolyte in a uniformly mixed state. Therefore, the alkali metal sulfide and the solid electrolyte are uniformly mixed both on the surface and in the pores of the conductive porous body, and the reaction area can be increased. An example of such a manufacturing method will be briefly described below.

First, a solution is prepared by dissolving an alkali metal sulfide and a solid electrolyte in a solvent capable of dissolving both of them.

In the present specification, the expression that a certain solid content is soluble in a certain solvent means that the solubility of the solid content in the solvent at 25° C. under normal pressure is 0.1 g/100 g solvent or more. The phrase “capable of dissolving both the metal sulfide and the solid electrolyte” means that the respective solubilities of the metal sulfide and the solid electrolyte separately dissolved in a solvent are within the above range.

Examples of such solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, glycerin, capryl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol, and linolyl alcohol. Ethers such as diethyl ether, tetrahydrofuran, 1,4-dioxane and 1,3-dioxolane; Alcohols are preferred because they have high solubility in alkali metal sulfides and solid electrolytes and are less likely to decompose.

The solvent preferably has a water content of 0.2% by mass or less. When the water content is 0.2% by mass or less, it is possible to prevent the water in the solvent from reacting with the alkali metal sulfide and the solid electrolyte and decomposing them. More preferably, the water content in the solvent is 0.1% by mass or less, still more preferably 0.05% by mass or less, even more preferably 0.02% by mass or less, and even more preferably 0.02% by mass or less. 01% by mass or less, more preferably 0.005% by mass or less, particularly preferably 0.002% by mass or less, and most preferably 0.001% by mass or less. The water content in the solvent can be measured, for example, by Karl Fischer coulometric titration.

There are no particular restrictions on the route through which the solvent with a low water content is obtained. If a product with a low moisture content is available on the market, you may purchase it and use it, or after purchasing a commercially available product with a relatively high moisture content, check the moisture content of the product yourself. You may reduce and use it. Techniques for reducing the water content of the solvent are also not particularly limited, and conventionally known knowledge can be referred to as appropriate. Examples thereof include drying by heating, drying under reduced pressure, drying with a desiccant (eg, silica gel or sodium sulfate), and distillation.

Next, the conductive porous material is dispersed in the resulting solution to obtain a dispersion. The solvent is then removed while stirring the dispersion, preferably under reduced pressure. Thereafter, heat treatment is preferably performed at a temperature of, for example, 60 to 250° C., preferably 150 to 180° C., for 1 to 120 hours, preferably 1 to 10 hours, preferably under reduced pressure. As a result, a positive electrode material, which is a composite material in which the positive electrode active material is arranged (filled) together with the solid electrolyte inside the pores of the conductive porous body, can be obtained.

The step of preparing a solution in which an alkali metal sulfide and a solid electrolyte are dissolved in a solvent capable of dissolving both of them, and the step of dispersing a conductive porous body in the above solution to obtain a dispersion are dew point controlled. It is preferable to carry out in an inert gas atmosphere.

The steps of preparing a solution in which an alkali metal sulfide and a solid electrolyte are dissolved in a solvent capable of dissolving both of them, dispersing the conductive porous body in the solution to obtain a dispersion, and removing the solvent. The process is preferably carried out at a temperature of 70°C or less, more preferably at a temperature of 20-50°C. As a result, the decomposition of the solid electrolyte is suppressed, and the effect of reducing the resistance is high.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited. more preferred. The content value is calculated based on the mass of only the positive electrode active material excluding the conductive porous body 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.

Although the thickness of the positive 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.

[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]
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

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>>
[Example 1]
(Preparation of positive electrode material)
In an argon atmosphere glove box with a dew point of −68° C. or less, 0.167 g of lithium sulfide (Li ₂ S), which is a positive electrode active material, and 1.667 g of a sulfide solid electrolyte (Li ₆ PS ₅ Cl, manufactured by Ampcera) were added. In addition to 40 mL of ultra-dehydrated ethanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., water content of 0.001% by mass or less), the mixture was stirred until solid particles disappeared to dissolve the positive electrode active material and the solid electrolyte in ethanol. . To the resulting solution, 0.167 g of a conductive porous carbon powder (Knobel (registered trademark) P (3) 010, manufactured by Toyo Tanso Co., Ltd.) was added and stirred well to add porous carbon to the solution. The powder was well dispersed. The container containing the dispersion of the porous carbon powder was connected to a vacuum apparatus, and the pressure in the container was reduced to 1 Pa or less by an oil rotary pump while stirring the dispersion in the container with a magnetic stirrer. Since the solvent ethanol volatilized under reduced pressure, the ethanol was removed over time, and the conductive porous body impregnated with the positive electrode active material and the solid electrolyte remained in the container. After ethanol was removed under reduced pressure in this manner, the material was heated to 180° C. under reduced pressure and subjected to heat treatment for 3 hours to prepare a positive electrode material.

Powder X-ray diffraction measurement was performed on the positive electrode material obtained above. SmartLab manufactured by Rigaku Denki Co., Ltd. was used for measurement under the following conditions:
Scan speed (2θ/θ): 2°/min
Step width (2θ/θ): 0.02°
Source: CuKα: λ=1.5418 Å.

In the XRD spectrum of the positive electrode material obtained in this example, a wide-angle peak A derived from carbon in the region where 2θ is 20 ° or more and less than 25 °, and a peak derived from Li ₂ S in the region of 20 to 25 °. B was observed and their intensity ratio (A/B) was 0.25.

Also, the pore filling rate of the positive electrode material obtained above was determined. The pore filling rate is the ratio of the volume of the positive electrode active material and the solid electrolyte to the total pore volume of the conductive porous body, and was estimated from the nitrogen adsorption/desorption measurement and the charging ratio of materials. Nitrogen adsorption and desorption measurements were performed using BELSORP mini manufactured by Microtrac Bell Co., Ltd. at a temperature of -196°C by a multipoint method. The total pore volume was determined from the volume of adsorbed _N2 at a relative pressure of 0.96. Table 1 shows the results.

(Preparation of positive electrode mixture)
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 positive electrode material prepared above, and 0.070 g of a solid electrolyte (Li ₆ PS ₅ Cl manufactured by Ampcera). 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 positive electrode mixture powder.

(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 less.

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 positive electrode mixture prepared above is put on one side of the solid electrolyte layer in the cylindrical tube, and the cylindrical convex punch (positive electrode collector) is again inserted from the upper side. A positive electrode active material layer with a diameter of 10 mm and a thickness of about 0.06 mm was formed on one side of the solid electrolyte layer by inserting a material that also serves as an electric body and pressing for 3 minutes at a pressure of 300 MPa. Next, the lower cylindrical convex punch (which also serves as the negative electrode current collector) is extracted, and as the negative electrode, 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 ( Nilaco Co., Ltd., thickness 0.30 mm), put it from the bottom of the cylindrical tube jig so that the indium foil is located on the side of the solid electrolyte layer, 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 2]
In the preparation of the positive electrode material, all were prepared in the same manner as in Example 1 above, except that 0.174 g of lithium sulfide, 1.739 g of sulfide solid electrolyte, and 0.087 g of porous carbon powder were used. A solid lithium secondary battery was fabricated.

In the XRD spectrum of the cathode material prepared in Example 2, the ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.22.

[Example 3]
In the preparation of the positive electrode material, all were prepared in the same manner as in Example 1 above, except that 0.667 g of lithium sulfide, 1.000 g of sulfide solid electrolyte, and 0.333 g of porous carbon powder were used. A solid lithium secondary battery was fabricated.

In the XRD spectrum of the cathode material prepared in Example 3, the ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.33.

[Example 4]
In the preparation of the positive electrode material, all were prepared in the same manner as in Example 1 above, except that 0.727 g of lithium sulfide, 1.091 g of sulfide solid electrolyte, and 0.182 g of porous carbon powder were changed. A solid lithium secondary battery was fabricated.

The result of measuring the XRD spectrum of the positive electrode material prepared in Example 4 is shown in FIG. 4(a). The ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.20.

[Example 5]
In the preparation of the positive electrode material, all the materials were prepared in the same manner as in Example 1 above, except that 1.000 g of lithium sulfide, 0.500 g of sulfide solid electrolyte, and 0.500 g of porous carbon powder were used. A solid lithium secondary battery was fabricated.

In the XRD spectrum of the cathode material prepared in Example 5, the ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.15.

[Example 6]
In the preparation of the positive electrode material, all were prepared in the same manner as in Example 1 above, except that 1.143 g of lithium sulfide, 0.571 g of sulfide solid electrolyte, and 0.286 g of porous carbon powder were used. A solid lithium secondary battery was fabricated.

In the XRD spectrum of the cathode material prepared in Example 6, the ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.03.

[Comparative Example 1]
In an argon atmosphere glove box with a dew point of −68 ° C. or less, 6.104 g of sulfur (manufactured by Aldrich) and 1.896 g of carbon (manufactured by Kansai Coke and Chemicals Co., Ltd., activated carbon, P (3) 010) are sufficiently added in an agate mortar. After mixing, the mixture was mixed in a planetary ball mill for 15 minutes. The mixed powder was placed in a sealed pressure-resistant autoclave container and heated at 170° C. for 3 hours to melt sulfur and impregnate the carbon with sulfur. A sulfur/carbon composite material was thus obtained.

To the resulting sulfur/carbon composite material, lithium triethylborohydride was added and reacted according to Example 1 of JP-A-2013-80637 to obtain a lithium sulfide/carbon composite. Phosphorus pentasulfide was added to the obtained lithium sulfide/carbon composite and reacted to obtain a positive electrode material.

In the XRD spectrum of the positive electrode material prepared in Comparative Example 1, the ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.01.

[Comparative Example 2]
In an argon atmosphere glove box with a dew point of −68° C. or less, 40 g of 5 mm diameter zirconia balls, 0.667 g of lithium sulfide, 1.000 g of a solid electrolyte (manufactured by Ampcera, Li ₆ PS ₅ Cl), and porous carbon. Powder (Toyo Tanso Co., Ltd., Knobel (registered trademark) P (3) 010) 0.333 g is placed in a zirconia container with a capacity of 45 ml and treated with a planetary ball mill at 370 rpm for 6 hours to obtain lithium sulfide / solid electrolyte / A positive electrode material, which is a carbon mixed powder, was obtained. An all-solid lithium secondary battery was fabricated in the same manner as in Example 1 except for the above.

The result of measuring the XRD spectrum of the positive electrode material prepared in Comparative Example 2 is shown in FIG. 4(b). The ratio of the intensity of peak A to the intensity of peak B (A/B) was 0.02.

<<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)
As a measurement device, Bio-Logic SAS (France), trade name "SP-200" high-performance electrochemical measurement system is used, frequency range 7 MHz to 0.1 Hz, temperature conditions are room temperature, applied voltage 50 mV. Impedance was measured as an electrochemical characteristic under the measurement conditions of . A test cell was installed in a constant temperature bath, and the evaluation was performed after the cell temperature became constant. The results are shown in Table 1 below.

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 an alkali metal sulfide as the positive electrode active material.

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 element,
25 negative electrode current collector,
27 positive current collector,
29 laminate film,
100, 100', 100" positive electrode material,
110 conductive porous body,
110a pores,
120 alkali metal sulfide (positive electrode active material),
130 solid electrolyte,
131 Attenuation products or modifications of solid electrolytes,
140 Sulfur elemental (inert sulfur).

Claims (7)

A positive electrode material comprising a conductive porous body, an alkali metal sulfide as a positive electrode active material, and a solid electrolyte,
At least part of the alkali metal sulfide and at least part of the solid electrolyte are arranged in the pores of the conductive porous body,
In the X-ray diffraction measurement, the positive electrode material has a peak A derived from the conductive porous body in the region where 2θ is 20° or more and less than 25°, and the alkali metal sulfide and / or showing a peak B derived from the solid electrolyte,
A positive electrode material, wherein a ratio (A/B) of the intensity of the peak A to the intensity of the peak B exceeds 0.02. 2. The positive electrode material of claim 1, wherein the alkali metal sulfide is lithium sulfide and the solid electrolyte comprises lithium. 3. The positive electrode material according to claim 1 or 2, wherein the solid electrolyte contains at least P, Li and S. The positive electrode material according to any one of claims 1 to 3, wherein the mass ratio of the alkali metal sulfide and the solid electrolyte is alkali metal sulfide:solid electrolyte = 50:50 to 1:99. The positive electrode material according to any one of claims 1 to 4, wherein the mass ratio of the alkali metal sulfide and the solid electrolyte is alkali metal sulfide:solid electrolyte = 1:1 to 1:20. 6. The method of claims 1 to 5, wherein the mass ratio of the alkali metal sulfide and the solid electrolyte is alkali metal sulfide:solid electrolyte=1:1 to 1:5, and the pore filling rate is 100% or more. A positive electrode material according to any one of claims 1 to 3. A secondary battery comprising the positive electrode material according to any one of claims 1 to 6.

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