JP2023119150A - All-solid battery and method of manufacturing activated all-solid battery - Google Patents

Abstract

To provide means enabling an all-solid battery to function, the all-solid battery comprising a carbon-containing layer at a negative electrode side and using a lithium-free positive electrode active material as positive electrode active material.SOLUTION: An all-solid battery is provided, having: a negative electrode active material layer that includes at least one kind of negative electrode active material selected from a group consisting of metallic lithium and lithium-containing alloys; a positive electrode active material layer that includes lithium-free positive electrode active material; a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer; and a carbon-containing layer that is interposed between the negative electrode active material layer and the solid electrolyte layer, and includes carbon material that can occlude lithium. In the all-solid battery, the positive electrode active material layer further includes a lithium-containing positive electrode active material, and a capacity [mAh] of the lithium-containing positive electrode active material is equal to or more than that of the carbon material.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to an all-solid-state battery and a method for manufacturing an activated all-solid-state battery.

In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is earnestly desired. In the automotive industry, expectations are high for the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV) to reduce carbon dioxide emissions. Batteries are being actively developed.

Secondary batteries for motor driving are required to have extremely high output characteristics and high energy compared to 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 conventional liquid-type lithium secondary batteries. 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. A promising candidate is an all-solid lithium secondary battery that uses a sulfide-based material as a positive electrode active material and metallic lithium or a lithium-containing alloy as a negative electrode active material.

By the way, in a lithium secondary battery, the negative electrode potential decreases as the charging progresses. When the negative electrode potential drops below 0 V (vs. Li/Li ⁺ ), metallic lithium precipitates and dendrites (dendritic crystals) precipitate on the negative electrode (this phenomenon is also referred to as metallic lithium electrodeposition). When the electrodeposition of metallic lithium occurs, there is a problem that the deposited dendrite penetrates the solid electrolyte layer and causes an internal short circuit of the battery.

For the purpose of suppressing the formation of dendrites, for example, in Patent Document 1, a negative electrode current collector, a negative electrode active material layer containing carbon black, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector are laminated. An all-solid-state battery is disclosed. When the all-solid-state battery is charged, a metal layer containing lithium is deposited between the negative electrode current collector and the negative electrode active material layer. The negative electrode active material layer may function as a protective layer for the metal layer and may inhibit the deposition and growth of dendrites.

Further, Patent Literature 1 discloses a charging method for an all-solid-state battery characterized by charging beyond the charge capacity of the negative electrode active material layer (that is, overcharging the negative electrode active material layer). According to this charging method, lithium is occluded in the negative electrode active material layer at the initial stage of charging. Lithium is deposited between and forms a metal layer.

U.S. Patent Application Publication No. 2019/0157723

According to the technique described in Patent Document 1, a lithium-containing positive electrode active material is used as a positive electrode active material in manufacturing an all-solid-state battery.

On the other hand, since lithium-containing positive electrode active materials are expensive, there is a demand to manufacture all-solid-state batteries using low-cost lithium-free positive electrode active materials. When adopting a positive electrode using a positive electrode active material that does not contain lithium, it is conceivable to use metal lithium or a lithium-containing alloy as the negative electrode active material and start the initial battery operation from discharging.

However, as a result of investigation by the present inventors, it has been found that the method of starting from discharge as described above causes a problem that an overvoltage is generated and the battery does not function.

Accordingly, an object of the present invention is to provide means capable of operating a battery in an all-solid-state battery that includes a carbon-containing layer on the negative electrode side and uses a positive electrode active material that does not contain lithium as a positive electrode active material.

The present inventors have made intensive studies to solve the above problems. As a result, in addition to the lithium-free positive electrode active material, a lithium-containing positive electrode active material that absorbs lithium in an amount equal to or greater than the amount of lithium that can be absorbed in the carbon-containing layer is used to form the positive electrode active material layer. , found that the above problems could be solved, and completed the present invention.

An all-solid-state battery according to one embodiment of the present invention includes a negative electrode active material layer containing at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys, and a positive electrode active material containing a lithium-free positive electrode active material. a layer, a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer, and a carbon-containing layer interposed between the negative electrode active material layer and the solid electrolyte layer and containing a carbon material capable of absorbing lithium. have. The positive electrode active material layer further includes a lithium-containing positive electrode active material, and the capacity of the lithium-containing positive electrode active material is equal to or greater than the capacity of the carbon material.

According to the present invention, during the initial charge, lithium is released from the lithium-containing positive electrode active material and absorbed by the carbon material in the carbon-containing layer, thereby imparting sufficient lithium conductivity to the carbon-containing layer to allow the battery to function. be done. During subsequent discharge, lithium released from the negative electrode active material passes through the carbon-containing layer and the solid electrolyte layer and is absorbed into the non-lithium-containing positive electrode active material. As a result, an all-solid battery having a carbon-containing layer on the negative electrode side and using a lithium-free positive electrode active material as a positive electrode active material can function.

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 is a graph showing charge-discharge curves of test cells. FIG. 4 is a graph showing a charge curve for measuring the capacity of carbon materials.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, 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. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

An all-solid-state battery according to one embodiment of the present invention includes a negative electrode active material layer containing at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys, and a positive electrode active material containing a lithium-free positive electrode active material. a layer, a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer, and a carbon-containing layer interposed between the negative electrode active material layer and the solid electrolyte layer and containing a carbon material capable of absorbing lithium. have. The positive electrode active material layer further includes a lithium-containing positive electrode active material, and the capacity of the lithium-containing positive electrode active material is equal to or greater than the capacity of the carbon material.

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, the flat laminated, non-bipolar, all-solid-state lithium secondary battery (hereinafter also simply referred to as "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.

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.

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 are arranged on both sides of a positive electrode current collector 11″. The negative electrode has negative electrode active material layers 13 containing a negative electrode active material arranged on both surfaces of the negative electrode current collector 11′. One positive electrode active material layer 15 and the adjacent negative electrode active material layer 13 face each other with the solid electrolyte layer 17 interposed therebetween, and the positive electrode, the solid electrolyte layer, and the negative electrode are arranged in this structure. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode form one single cell layer 19. Therefore, the stacked battery 10a shown in FIG. 2, lithium is occluded between the negative electrode active material layer 13 and the solid electrolyte layer 17. A carbon-containing layer 14 is provided which comprises a possible carbon material.

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 the current collector exclusively for the outermost layer having the 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 all-solid lithium secondary battery according to the present 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, 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 active material layer]
In the all-solid-state battery according to this embodiment, the negative electrode active material layer essentially contains at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys. Examples of lithium-containing alloys include, but are not particularly limited to, alloys of Li and at least one of In, Al, Si, Sn, Mg, Au, Ag and Zn. 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 as long as they essentially contain metallic lithium or a lithium-containing alloy.

An all-solid-state battery according to a preferred embodiment is a so-called lithium deposition type battery in which metallic lithium is deposited on a negative electrode current collector during charging. In this case, the layer composed of metallic lithium deposited on the negative electrode current collector during the charging process becomes the negative electrode active material layer. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. Although the negative electrode active material layer does not have to exist at the time of complete discharge, depending on the case, a certain amount of the negative electrode active material layer made of metallic lithium may be arranged at the time of complete discharge.

An all-solid-state battery according to another preferred embodiment has a negative electrode in which a layer made of a lithium-containing alloy is arranged as a negative electrode active material layer on a negative electrode current collector. In this case, as the charging process progresses, lithium is absorbed into the lithium-containing alloy, thereby increasing the thickness of the negative electrode active material layer. As the discharging process progresses, lithium is released from the lithium-containing alloy. The thickness of the negative electrode active material layer is reduced.

The thickness of the negative electrode active material layer at the time of full charge varies depending on the configuration of the intended all-solid-state battery, but is preferably in the range of 0.1 to 1000 μm, for example.

[Carbon-containing layer]
The carbon-containing layer is a layer interposed between the negative electrode active material layer and the solid electrolyte layer, and contains a carbon material capable of intercalating lithium.

The carbon material is not particularly limited, but carbon black (specifically, acetylene black, Ketjenblack (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon etc. Among them, carbon black is preferred, and at least one selected from the group consisting of acetylene black, Ketjenblack (registered trademark), furnace black, channel black and thermal lamp black is more preferred.

The content of the carbon material in the carbon-containing layer is not particularly limited, but is preferably in the range of 50 to 100% by mass, more preferably in the range of 70 to 100% by mass, and 90 to 100% by mass. is more preferably within the range of , particularly preferably 95 to 100% by mass.

The carbon-containing layer may consist of only a carbon material as long as a self-supporting film can be produced only from the carbon material, and may contain a binder as necessary. Examples of the binder include, but are not limited to, 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 copolymers and their hydrogenated products, thermoplastic polymers such as styrene/isoprene/styrene block copolymers and their hydrogenated products, tetrafluoroethylene/hexafluoropropylene copolymers (FEP), tetrafluoroethylene・Perfluoroalkyl vinyl ether copolymer (PFA), ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride ( PVF) and other fluororesins, vinylidene fluoride-hexafluoropropylene fluororubbers (VDF-HFP fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubbers (VDF-HFP-TFE fluororubbers) , vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-per Vinylidene fluoride fluororubber such as fluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene fluororubber (VDF-CTFE fluororubber), epoxy resin, carboxymethyl cellulose, and the like. Among them, polyimide, styrene-butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

Although the content of the binder in the carbon-containing layer is not particularly limited, it is preferably in the range of 1 to 10% by mass, more preferably in the range of 2 to 5% by mass. If the content of the binder is 1% by mass or more, a carbon-containing layer having sufficient strength can be formed. If the content of the binder is 10% by mass or less, a decrease in energy density can be suppressed.

The carbon-containing layer preferably does not contain components other than the carbon material and the binder. Therefore, according to one preferred embodiment, the carbon-containing layer consists of only the carbon material, or consists of the carbon material and the binder.

Although the thickness of the carbon-containing layer is not particularly limited, it is preferably in the range of 1 to 50 μm, more preferably in the range of 5 to 40 μm, even more preferably in the range of 10 to 30 μm. . When the thickness of the carbon-containing layer is 1 μm or more, the function of the carbon-containing layer can be fully exhibited. When the thickness of the carbon-containing layer is 50 μm or less, it is possible to suppress a decrease in energy density.

[Solid electrolyte layer]
The solid electrolyte layer is a layer containing a solid electrolyte as a main component and interposed between the negative electrode active material layer and the positive electrode active material layer. The solid electrolyte is not particularly limited, but includes, for example, a sulfide solid electrolyte and an oxide solid electrolyte. From the viewpoint of high ionic conductivity, the solid electrolyte preferably contains a sulfide solid electrolyte.

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 -} LiCl, _{Li2SP2S 5} -LiBr _{, Li2SP2S5} -Li2O _, Li2SP2S5- _Li2O -LiI _{, Li2S - SiS2} , _Li2S - _{SiS2 -} LiI _{, Li2} S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, Li ₂ S—SiS ₂ —B ₂ S ₃ —LiI, Li ₂ S—SiS ₂ —P ₂ S ₅ —LiI, Li ₂ S—B ₂ S ₃ , Li ₂ 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—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 P, Si, Ge, B, Al, Ga or In). 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 is preferably a sulfide solid electrolyte containing the element P, and 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).

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

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

The thickness of the solid electrolyte layer varies depending on the configuration of the target all-solid-state 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]
The positive electrode active material layer contains a positive electrode active material capable of intercalating lithium. In the present invention, the positive electrode active material layer essentially includes a non-lithium-containing positive electrode active material and a lithium-containing positive electrode active material.

(Lithium-free positive electrode active material)
In this specification, the lithium-free positive electrode active material refers to a positive electrode active material that does not contain lithium element. Examples of lithium-free positive electrode active materials include, but are not limited to, transition metal oxides, transition metal fluorides, and sulfur-based positive electrode active materials.

Specific examples of transition metal oxides and transition metal fluorides include titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₃ ), tungsten oxide (WO ₃ ), iron fluoride (II) (FeF ₂ ), vanadium oxide ( _V2O5 ), iron oxide ( _FeOx ), manganese dioxide ( _MnO2 ) _, and the like.

Examples of sulfur-based positive electrode active materials include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, which can release lithium ions during charging and absorb lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur. Any substance that can 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. On the other hand, inorganic sulfur compounds are preferable because of their excellent stability. Specifically, sulfur (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , MoS ₂ , MoS ₃ and the like. Among them, S,S-carbon composites, TiS ₂ , TiS ₃ , TiS ₄ , FeS ₂ and MoS ₂ are preferred, and S,S-carbon composites, TiS ₂ and FeS ₂ are more preferred. Here, the S-carbon composite includes a sulfur powder and a carbon material, and is in a composite state by subjecting them to heat treatment or mechanical mixing. More specifically, the state in which sulfur is distributed on the surface and in the pores of the carbon material, the state in which sulfur and the carbon material are uniformly dispersed at the nano level and are aggregated into particles, and the state in which fine sulfur It is a state in which the carbon material is distributed on the surface or inside of the powder, or a state in which a plurality of these states are combined.

In some cases, two or more lithium-free positive electrode active materials may be used in combination. Of course, lithium-free positive electrode active materials other than those described above may also be used.

(Lithium-containing positive electrode active material)
In this specification, the lithium-containing positive electrode active material refers to a positive electrode active material containing lithium element. The lithium-containing positive electrode active material is not particularly limited, but layered rock salts such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , Li(Ni--Mn--Co)O ₂ and Li(Ni--Co--Al)O ₂ type active materials, spinel type active materials such as LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ , olivine type active materials such as LiFePO ₄ and LiMnPO ₄ , Si such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ . Contained active material and the like can be mentioned. As an oxide active material other than the above, for example, Li ₄ Ti ₅ O ₁₂ can be mentioned. Among them, a composite oxide containing lithium and nickel is preferably used, and more preferably Li(Ni—Mn—Co)O ₂ (hereinafter simply referred to as “NMC composite oxide”) or Li(Ni—Co —Al)O ₂ (hereinafter also simply referred to as “NCA composite oxide”) and transition metals partially substituted with other elements are used, and NMC composite oxide is particularly preferably used. NMC composite oxides and NCA composite oxides have a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni and Co are arranged in an orderly manner) atomic layers are alternately stacked via oxygen atomic layers, and the transition metal One Li atom is contained per one atom of M, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

NMC composite oxides and NCA composite oxides also include composite oxides in which a portion of the transition metal element is replaced with another metal element, as described above. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, and Cu. , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, Cr, more preferably Ti, Zr, Al, Mg, or Cr from the viewpoint of improving cycle characteristics. However, other metal elements that can substitute for the transition metal elements of the NCA composite oxide are those other than Al. _{More specifically , LiNi0.8Co0.1Al0.1O2 , LiNi0.8Mn0.1Co0.1O2 , LiNi0.88Mn0.06Co0.06O2 _ _ _ _} and LiNi _0.5 Mn _0.3 Co _0.2 O ₂ and the like.

In some cases, two or more lithium-containing positive electrode active materials may be used in combination. It goes without saying that a lithium-containing positive electrode active material other than the above may be used.

Examples of the shape of the positive electrode active material include particulate (spherical, fibrous), thin film, and the like. When the positive electrode active material is in the form of particles, 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, and still more preferably 100 nm. to 20 μm, particularly preferably 1 to 20 μm.

The content of the positive electrode active material (the total amount of the non-lithium-containing positive electrode active material and the lithium-containing positive electrode active material) in the positive electrode active material layer is not particularly limited, but is, for example, within the range of 40 to 99% by mass. preferably in the range of 50 to 90% by mass.

The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive aid, and a binder, if necessary. Since the specific forms of the solid electrolyte and the binder are the same as those described above, detailed description thereof is omitted here.

The conductive aid is not particularly limited, but for example, metals such as aluminum, stainless steel (SUS), silver, gold, copper, titanium, alloys or metal oxides containing these metals; carbon fiber (specifically, Vapor grown carbon fiber (VGCF), polyacrylonitrile carbon fiber, pitch carbon fiber, rayon carbon fiber, activated carbon fiber, etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.), but are not limited 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 positive electrode active material layer contains a conductive aid, the content of the conductive aid in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass with respect to the total weight of the positive electrode active material layer. , more preferably 2 to 8% by mass, more preferably 4 to 7% by mass. Within such a range, it is possible to form a stronger electron conduction path in the positive electrode active material layer, which can effectively contribute to the improvement of battery characteristics.

In the all-solid-state battery according to the present embodiment, the capacity [mAh] of the lithium-containing positive electrode active material contained in the positive electrode active material layer described above is equal to or greater than the capacity [mAh] of the carbon material contained in the carbon-containing layer described above. Also has characteristics. The present inventors have found from the following experimental results that the carbon-containing layer is provided with sufficient lithium conductivity to allow the battery to function during the initial charge (the carbon-containing layer is activated) by having the above configuration, As a result, it was found that the battery can be made to function.

<<Preparation of test cell>>
First, a lithium symmetrical cell was produced as a test cell. More specifically, positive electrode current collector (SUS foil), metallic lithium, solid electrolyte layer (Li ₆ PS ₅ Cl), carbon-containing layer (U.S. Patent Application Publication No. 2019/0157723, paragraphs "0136" to " 0138” using furnace black as a carbon material), metal lithium, and a negative electrode current collector (SUS foil) were laminated in this order. Then, it is sandwiched between a positive electrode current collector (made of SUS) and a negative electrode current collector (made of SUS), and sealed under a pressure of 20 MPa using a pressurized container that can block the outside air, and a test cell is formed. made.

《Charging and discharging test》
Next, the test cell was subjected to a charge/discharge test by the following method. In addition, the measurement was performed in a constant temperature constant temperature bath set at 25°C. The charging/discharging conditions are as follows.

[Voltage range] -2.0 to 2.0V
[Charging process] 0.2 mA/cm ²
[Discharge process] 0.2 mA/cm ²
[Termination conditions] Current capacity 6.0 mAh/cm ² .

FIG. 3 is a graph showing charge-discharge curves of test cells. When charging was performed as the first operation, as shown in FIG. 3, charging and subsequent discharging could be performed. It was found that when discharging was performed as the first operation, as shown in FIG. 3, the overvoltage increased and the battery did not function.

From the above results, in an all-solid-state battery with a carbon-containing layer on the negative electrode side, the lithium released from the positive electrode active material during the initial charge is occluded by the carbon material in the carbon-containing layer, so that the battery functions. was suggested to be expressed. For this reason, even in an all-solid-state battery containing a lithium-free positive electrode active material as a positive electrode active material, the positive electrode active material contains a lithium-containing positive electrode active material having a capacity greater than or equal to the capacity of the carbon material contained in the carbon-containing layer, It can be seen that the battery can be made to function by performing an initial charge equal to or greater than the capacity of the carbon material.

Here, the "capacity of the lithium-containing positive electrode active material" includes a positive electrode active material layer containing the target lithium-containing positive electrode active material, a solid electrolyte, a conductive aid and a binder; a solid electrolyte layer; and metal lithium as a negative electrode. It can also be measured using a so-called half cell. For example, the cell is placed on an evaluation jig capable of ensuring an inert atmosphere while applying an appropriate surface pressure (preferably 100 MPa or less, for example 20 MPa). Then, the cell is connected to a charging and discharging device and charged at a constant current (preferably 1/20 [C], more preferably 1/100 [C]) at 25 ° C. (a constant current is passed from the positive electrode to the negative electrode ) to move lithium from the lithium-containing positive electrode active material to the negative electrode. The behavior of the cell voltage at this time is measured, and the current capacity [mAh] of the lithium-containing positive electrode active material is determined from the behavior. The cut-off voltage varies depending on the type of positive electrode active material, but generally the portion where the half-cell voltage drops steeply is taken as the termination voltage. The product of the time (h) from the start of charging to cutoff and the constant charging current (mA/cm ² ) is the capacity per unit area of the positive electrode active material layer [mAh/cm ² ]. Then, by calculating the product of this value and the area of the positive electrode active material layer, the capacity of the positive electrode active material layer, that is, the capacity [mAh] of the lithium-containing positive electrode active material used in the half cell is obtained. If the mass [g] of the lithium-containing positive electrode active material contained in the all-solid-state battery to be measured is different from the mass [g] of the lithium-containing positive electrode active material used in the half-cell, the lithium-containing positive electrode used in the half-cell The value [mAh/g] obtained by dividing the capacity [mAh] of the active material by the mass [g] of the lithium-containing positive electrode active material used in the half cell is added to the mass of the lithium-containing positive electrode active material [ g], the capacity [mAh] of the lithium-containing positive electrode active material can be obtained.

The “capacity of the carbon material” can be measured using a so-called half cell equipped with metallic lithium as the positive electrode; a solid electrolyte layer; and a negative electrode current collector and a carbon-containing layer containing the target carbon material as the negative electrode. For example, the cell is placed on an evaluation jig capable of ensuring an inert atmosphere while applying an appropriate surface pressure (preferably 40 MPa or less, for example 20 MPa). Then, the cell is connected to a charging/discharging device and charged at a constant current (preferably 0.2 mA/cm ² , more preferably 0.05 mA/cm ² , still more preferably 0.01 mA/cm ² ) at 25°C. Lithium is transferred from the positive electrode to the carbon-containing layer and the negative electrode (a constant current is applied from the positive electrode to the negative electrode). FIG. 4 shows the result of measuring the behavior of the cell voltage at this time. It is known that the standard electrode potential of carbon materials generally changes depending on the degree of lithiation thereof, and the potential is known to be higher than the electrode potential of metallic lithium. Therefore, before the start of charging, the cell voltage shows a negative value. As the charging reaction progresses and the degree of lithiation of the carbon material increases, the standard electrode potential approaches that of metallic lithium, and finally becomes almost the same as the potential of metallic lithium. Saturate. In FIG. 4, lithium is occluded in the carbon material in a region (a) from the start of charging to the point of saturation (the point of time when the slope of the curve becomes 0). Lithium deposits at the negative electrode in region (b) after the saturation point. The product of the time (h) from the start of charging until saturation and the constant charging current (mA/cm ² ) is the capacity per unit area of the carbon-containing layer [mAh/cm ² ]. Then, by calculating the product of this value and the area of the carbon-containing layer, the capacity of the carbon-containing layer, that is, the capacity [mAh] of the carbon material used in the half-cell is obtained. If the mass [g] of the carbon material contained in the all-solid-state battery to be measured is different from the mass [g] of the carbon material used in the half cell, the capacity [mAh] of the carbon material used in the half cell is By multiplying the value [mAh/g] divided by the mass [g] of the carbon material used for the measurement by the mass [g] of the carbon material contained in the all-solid-state battery to be measured, the capacity [mAh] of the carbon material is can ask.

The ratio of the capacity [mAh] of the lithium-containing positive electrode active material to the capacity [mAh] of the carbon material (capacity [mAh] of the lithium-containing positive electrode active material/capacity [mAh] of the carbon material) is essentially 1 or more, and energy It is preferably 1 to 2, more preferably 1 to 1.5, still more preferably 1 to 1.2, from the viewpoint of improving the density and reducing the cost.

In the all-solid-state battery according to the present embodiment, the capacity [mAh] of the negative electrode active material included in the negative electrode active material layer described above is equal to or greater than the capacity [mAh] of the lithium-free positive electrode active material included in the positive electrode active material layer described above. is preferably With such a configuration, the positive electrode active material can be effectively used, and the energy density can be improved.

Here, the "capacity of the negative electrode active material" can be measured using a so-called half cell provided with a negative electrode active material layer containing metallic lithium as a positive electrode; a solid electrolyte layer; and a target negative electrode active material. For example, the cell is placed on an evaluation jig capable of ensuring an inert atmosphere while applying an appropriate surface pressure (preferably 100 MPa or less, for example 20 MPa). Then, the cell is connected to a charge/discharge device and discharged at a constant current (preferably 1/20 [C], more preferably 1/100 [C]) at 25 ° C. (a constant current flows from the negative electrode to the positive electrode ) to move lithium from the negative electrode active material to the positive electrode. The behavior of the cell voltage at this time is measured, and the current capacity [mAh] of the negative electrode active material is determined from the behavior. The cut-off voltage varies depending on the type of negative electrode active material, but generally the portion where the half-cell voltage drops steeply is taken as the termination voltage. The product of the time (h) from the start of discharge to cutoff and the constant discharge current (mA/cm ² ) is the capacity per unit area of the negative electrode active material layer [mAh/cm ² ]. Then, by calculating the product of this value and the area of the negative electrode active material layer, the capacity of the negative electrode active material layer, that is, the capacity [mAh] of the negative electrode active material used in the half cell is obtained. If the mass [g] of the negative electrode active material contained in the all-solid-state battery to be measured is different from the mass [g] of the negative electrode active material used in the half cell, the capacity [mAh ] divided by the mass [g] of the negative electrode active material used in the half cell [mAh/g], and by multiplying the mass [g] of the negative electrode active material contained in the all-solid-state battery to be measured, the negative electrode active material capacity [mAh] can be obtained.

"Capacity of lithium-free positive electrode active material" refers to a positive electrode active material layer containing a target lithium-free positive electrode active material, a solid electrolyte, a conductive aid, and a binder; a solid electrolyte layer; and metallic lithium as a negative electrode. It can be measured using a so-called half cell. For example, the cell is placed on an evaluation jig capable of ensuring an inert atmosphere while applying an appropriate surface pressure (preferably 100 MPa or less, for example 20 MPa). Then, the cell is connected to a charge/discharge device and discharged at a constant current (preferably 1/20 [C], more preferably 1/100 [C]) at 25 ° C. (a constant current flows from the negative electrode to the positive electrode ) to transfer lithium from the negative electrode to the lithium-free positive electrode active material. The behavior of the cell voltage at this time is measured, and the current capacity [mAh] of the lithium-free positive electrode active material is determined from the behavior. The cut-off voltage varies depending on the type of positive electrode active material, but generally the portion where the half-cell voltage drops steeply is taken as the termination voltage. The product of the time (h) from the start of discharge to cutoff and the constant discharge current (mA/cm ² ) is the capacity per unit area of the positive electrode active material layer [mAh/cm ² ]. Then, by calculating the product of this value and the area of the positive electrode active material layer, the capacity of the positive electrode active material layer, that is, the capacity [mAh] of the lithium-free positive electrode active material used in the half cell is obtained. If the mass [g] of the lithium-free positive electrode active material contained in the all-solid-state battery to be measured is different from the mass [g] of the lithium-free positive electrode active material used in the half cell, the lithium used in the half cell The value [mAh/g] obtained by dividing the capacity [mAh] of the non-containing positive electrode active material by the mass [g] of the lithium-free positive electrode active material used in the half cell is the lithium-free positive electrode contained in the all-solid-state battery to be measured. By multiplying by the mass [g] of the active material, the capacity [mAh] of the lithium-free positive electrode active material can be obtained.

The ratio of the capacity [mAh] of the negative electrode active material to the capacity [mAh] of the lithium-free positive electrode active material (the capacity [mAh] of the negative electrode active material/the capacity [mAh] of the lithium-free positive electrode active material) is preferably 1 or more. From the viewpoint of improving energy density and reducing costs, it is more preferably 1 to 2, still more preferably 1 to 1.5, and particularly preferably 1 to 1.2.

[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 laminate film may be, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order, but is not limited thereto. A laminate film is desirable from the viewpoint that it 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.

[Method for manufacturing activated all-solid-state battery]
As described above, in the all-solid-state battery according to the present embodiment, sufficient lithium conductivity is imparted to the carbon-containing layer to make the battery function during the initial charge after battery manufacture (the carbon-containing layer is activated). ). Therefore, according to another aspect of the present invention, the step of manufacturing the all-solid-state battery according to one aspect of the present invention described above (hereinafter also referred to as step 1), and the capacity [mAh of the carbon material in the all-solid-state battery ] A method for manufacturing an activated all-solid-state battery is provided, which includes the step of performing the above initial charging (hereinafter also referred to as step 2). Each step will be described below in order.

(Step 1)
In step 1, the all-solid-state battery according to one embodiment of the present invention described above is manufactured. An all-solid-state battery according to one embodiment of the present invention is formed by sequentially stacking a positive electrode active material layer, a solid electrolyte layer, a carbon-containing layer, and a negative electrode active material layer. A detailed description is omitted here because it can be easily manufactured by referring to it. In addition, a method of making the capacity [mAh] of the lithium-containing positive electrode active material equal to or higher than the capacity [mAh] of the carbon material, or a method of making the capacity [mAh] of the negative electrode active material equal to or higher than the capacity [mAh] of the lithium-free positive electrode active material. For, after obtaining the capacity per unit mass of each material by the above-described method, the blending amount may be appropriately adjusted so that the capacities of these materials contained in the all-solid-state battery have a predetermined relationship.

(Step 2)
In step 2, the all-solid-state battery (all-solid-state battery before charging and discharging) manufactured in step 1 is initially charged to a capacity [mAh] or more of the carbon material. The "capacity of the carbon material" here is the same as defined above. Since the all-solid-state battery manufactured in step 1 contains a lithium-containing positive electrode active material having a capacity equal to or greater than the capacity of the carbon material in the positive electrode active material layer, the SOC (State of Charge) is 100% in the initial charge. By performing the charging operation in such a manner that the all-solid-state battery is charged to the capacity [mAh] or more of the carbon material. The specific method of the initial charge is not particularly limited, but a pressure member is used in the cell to apply a confining pressure preferably in the range of 5 to 100 MPa, more preferably in the range of 5 to 50 MPa in the stacking direction. The charging is performed at a constant current at a temperature preferably within the range of 10 to 60°C, more preferably within the range of 20 to 40°C. The charging rate (C) at this time is preferably as low as possible, specifically, preferably 1/20 [C] or less, more preferably 1/100 [C] or less. Although the lower limit of the charging rate (C) is not particularly limited, it is preferably 1/1000 [C] or more, more preferably 1/500 [C] or more. Note that 1C is a current value at which the battery is fully charged (100% charged) when charged for one hour at that current value.

10a laminated battery,
11' negative electrode current collector,
11″ cathode current collector,
13 negative electrode active material layer,
14 carbon-containing 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.

Claims (3)

a negative electrode active material layer containing at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys;
a positive electrode active material layer comprising a lithium-free positive electrode active material;
a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer; In an all-solid-state battery having a layer,
the positive electrode active material layer further comprises a lithium-containing positive electrode active material;
An all-solid battery, wherein the capacity [mAh] of the lithium-containing positive electrode active material is equal to or greater than the capacity [mAh] of the carbon material. The all-solid-state battery according to claim 1, wherein the capacity [mAh] of the negative electrode active material is equal to or greater than the capacity [mAh] of the non-lithium-containing positive electrode active material. A step of manufacturing the all-solid-state battery according to claim 1 or 2;
A step of initially charging the all-solid-state battery to a capacity [mAh] or more of the carbon material;
A method for manufacturing an activated all-solid-state battery, comprising: