JP2023119152A - All-solid battery - Google Patents

Abstract

To provide means enabling suppression of short-circuiting at an end portion of a power generation element of an all-solid battery.SOLUTION: An all-solid battery is provided, comprising a power generation element in which a negative electrode active material layer, a solid electrolyte layer, a carbon-containing layer, and a positive electrode active material layer are sequentially laminated. In the all-solid battery, when seeing the power generation element in a plan view, the positive electrode active material layer is comprised of: a center portion that includes both lithium-free positive electrode active material and lithium-containing positive electrode active material; and an outer peripheral edge portion that includes the lithium-free positive electrode active material and arbitrarily includes the lithium-containing positive electrode active material. A capacity [mAh] of the lithium-containing positive electrode active material included in the center portion of the positive electrode active material layer is equal to or more than that of carbon material included in a region overlapped with the center portion of the positive electrode active material layer, of the carbon-containing layer. A capacity [mAh] of the lithium-containing positive electrode active material included in the outer peripheral edge portion of the positive electrode active material layer is less than that of carbon material included in a region overlapped with the outer peripheral edge portion of the positive electrode active material layer, of the carbon-containing layer.SELECTED DRAWING: Figure 4

Description

The present invention relates to all-solid-state batteries.

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.

Conventionally, as one type of all-solid-state lithium secondary battery, there is known a so-called lithium deposition type battery in which lithium metal is deposited on a negative electrode current collector in the charging process (see, for example, Patent Document 1). In the charging process of such a lithium deposition type all-solid lithium secondary battery, lithium metal is deposited between the solid electrolyte layer and the negative electrode current collector. In Patent Document 1, a fine particle layer (carbon-containing layer) containing fine particles such as amorphous carbon (for example, carbon black) is provided between a negative electrode current collector and a solid electrolyte layer, which constitute power generation elements of a lithium secondary battery. Techniques for placement are disclosed. According to Patent Document 1, with such a structure, when lithium metal is deposited between the fine particle layer and the negative electrode current collector during charging, the fine particle layer serves as a protective layer for the lithium metal layer. In addition, as a result of suppressing the growth of dendrites from the lithium metal layer, the short circuit of the lithium secondary battery and the resulting decrease in capacity can be prevented.

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

However, according to the studies of the present inventors, it has been found that even if the technique described in Patent Document 1 is used, there are still cases where it is not possible to prevent a short circuit at the end of the power generation element.

Accordingly, an object of the present invention is to provide a means capable of suppressing a short circuit at the end of a power generation element of an all-solid-state battery.

The present inventors have made intensive studies to solve the above problems. In the process, during the initial charge in which lithium moves from the positive electrode side to the negative electrode side, lithium is occluded by the carbon material contained in the carbon-containing layer interposed between the negative electrode current collector and the solid electrolyte layer. The inventors have found that the carbon-containing layer is imparted with lithium conductivity. Based on this knowledge, by arranging a lithium-containing positive electrode active material containing lithium in an amount sufficient to impart lithium conductivity to the carbon-containing layer only in the central portion of the positive electrode active material layer, the power generation element can be obtained in a plan view. At this time, sufficient lithium conductivity is imparted only to the region of the carbon-containing layer that overlaps the center portion of the positive electrode active material layer (the center portion of the carbon-containing layer). On the other hand, the lithium conductivity of the other region (peripheral edge of the carbon-containing layer) remains low. As a result of suppressing the charge/discharge reaction at the ends of the power generation element, the present inventors have found that the above problems can be solved, and have 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, a lithium-free positive electrode active material, and a lithium-containing positive electrode active material. A positive electrode active material layer containing a substance, a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer, and a lithium-absorbing material interposed between the negative electrode active material layer and the solid electrolyte layer A power generating element having a carbon-containing layer comprising a carbon material is provided. When the power generation element is viewed from above, the positive electrode active material layer includes a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and the lithium-free positive electrode active material, and an outer peripheral portion that optionally contains the lithium-containing positive electrode active material; and the capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer The capacity [mAh] of the carbon material contained in the containing layer overlapping with the central portion of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer [ mAh] is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping the outer peripheral edge of the positive electrode active material layer.

ADVANTAGE OF THE INVENTION According to this invention, the short circuit in the edge part of the electric power generation element of an all-solid-state battery can be suppressed.

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 plan view of a positive electrode active material layer included in a stacked battery according to one embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to an embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view showing a state after initial charge of a single cell layer included in a stacked battery according to an embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view showing a positive electrode active material layer included in a layered battery according to one embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view showing a positive electrode active material layer included in a layered battery according to another embodiment of the present invention. FIG. 8 is an enlarged cross-sectional view showing a positive electrode active material layer included in a layered battery according to still another embodiment of the present invention. FIG. 9 is an enlarged cross-sectional view showing a positive electrode active material layer included in a layered battery according to still another embodiment of the present invention. FIG. 10 is a graph showing charge/discharge curves of test cells. FIG. 11 is a graph showing a charge curve in measuring the capacity of carbon materials. FIG. 12 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to another embodiment of the present invention. FIG. 13 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to still another embodiment of the present invention. FIG. 14 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to still another embodiment of the present invention. FIG. 15 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to still another embodiment of 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, a lithium-free positive electrode active material, and a lithium-containing positive electrode active material. A positive electrode active material layer containing a substance, a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer, and a lithium-absorbing material interposed between the negative electrode active material layer and the solid electrolyte layer A power generating element having a carbon-containing layer comprising a carbon material is provided. When the power generation element is viewed from above, the positive electrode active material layer includes a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and the lithium-free positive electrode active material, and an outer peripheral portion that optionally contains the lithium-containing positive electrode active material; and the capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer The capacity [mAh] of the carbon material contained in the containing layer overlapping with the central portion of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer [ mAh] is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping the outer peripheral edge of the positive electrode active material layer.

Hereinafter, the present embodiment 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 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.

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.

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 configuration in which a positive electrode, a solid electrolyte layer 17, a carbon-containing layer 14, 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 laminate of the carbon-containing layer 14 and the negative electrode active material layer 13 adjacent thereto face each other with the solid electrolyte layer 17 interposed therebetween. , the solid electrolyte layer 17, the carbon-containing layer 14 and the negative electrode are laminated in this order, whereby the adjacent positive electrode, the solid electrolyte layer 17, the carbon-containing layer 14 and the negative electrode constitute one cell layer 19. 2 can be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. Constraining pressure (not shown) is applied by a member in the stacking direction of the power generating element 21. Therefore, the volume of the power generating element 21 is kept constant.

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).

FIG. 3 is a plan view of a positive electrode active material layer included in a stacked battery according to one embodiment of the present invention. As shown in FIG. 3, in the present embodiment, the positive electrode active material layer 15 includes a central portion 15a and an outer peripheral edge portion 15b (excluding the central portion 15a from the positive electrode active material layer 15) when the power generation element 21 is viewed from above. square-shaped area).

FIG. 4 is an enlarged cross-sectional view showing a state before initial charging of a single cell layer included in a stacked battery according to an embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view showing the state after the first charge of the single cell layer included in the stacked battery according to one embodiment of the present invention. In FIGS. 4 and 5, gray portions in the positive electrode active material layer and the carbon-containing layer indicate the presence of lithium. In the state before the initial charge shown in FIG. ), and the outer peripheral edge portion 15b of the positive electrode active material layer 15 contains a non-lithium-containing positive electrode active material and does not contain a lithium-containing positive electrode active material. Then, the capacity [mAh] of the lithium-containing positive electrode active material is the carbon material ("Δ" shown) is greater than or equal to the capacity [mAh]. When the battery having the configuration shown in FIG. 4 is charged, as shown in FIG. 5, lithium is occluded in the carbon material contained in the region 14a of the carbon-containing layer 14 (lithium is released) when the power generation element is viewed from above. The lithium-containing positive electrode active material is indicated by "○", and the lithium-occluded carbon material is indicated by gray "△")). Thereby, the region 14a becomes lithium conductive. On the other hand, the other region (peripheral edge portion of the carbon-containing layer) 14b in the carbon-containing layer 14 does not overlap with the central portion 15a of the positive electrode active material layer (outer peripheral edge portion 15b of the positive electrode active material layer (lithium-free positive electrode active material layer). containing a substance and not containing a lithium-containing positive electrode active material), lithium is not occluded by the carbon material. Thus, the lithium conductivity in region 14b is low and lithium migration is impeded in this region. This suppresses the charge-discharge reaction in the region overlapping the outer edge portion 15b of the positive electrode active material layer 15, thereby preventing a short circuit at the end portion of the power generation element 21. FIG.

Main constituent members of the all-solid-state 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, the decrease in energy density can be suppressed.

[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 particles such as a spherical shape and an ellipsoidal shape, and a thin film shape. When the solid electrolyte is particulate, its 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 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]
In the all-solid-state battery according to this embodiment, the positive electrode active material layer essentially contains 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 preferred. 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 particulate, 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.

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 100% 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, when the power generation element is viewed from above, the positive electrode active material layer has a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and the lithium-free positive electrode active material. and a peripheral edge portion optionally containing a lithium-containing positive electrode active material; and the capacity [mAh] of the lithium-containing positive electrode active material contained in the center portion of the positive electrode active material layer The capacity [mAh] of the carbon material contained in the region overlapping the center portion of the positive electrode active material layer of the layer is equal to or greater than the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer. It is characterized in that it is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps the outer peripheral edge of the positive electrode active material layer. With such a structure, sufficient lithium conductivity is imparted to the carbon-containing layer (the central portion of the carbon-containing layer) in the region overlapping the central portion of the positive electrode active material layer. On the other hand, the lithium conductivity of the other region (peripheral edge of the carbon-containing layer) remains low. As a result, the charge/discharge reaction at the ends of the power generation element of the all-solid-state battery is suppressed, and short circuits at the ends are less likely to occur. Note that the outer peripheral portion may contain a lithium-containing positive electrode active material as long as it is less than the capacity [mAh] of the carbon material contained in the region overlapping the outer peripheral portion of the positive electrode active material layer of the carbon-containing layer. However, from the viewpoint of further suppressing short circuits at the ends of the power generation element, the outer peripheral edge preferably does not contain the lithium-containing positive electrode active material.

In this specification, the “central portion” and the “peripheral edge portion” of the positive electrode active material layer refer to the case where the outer peripheral portion does not contain the lithium-containing positive electrode active material, and the case where the outer peripheral portion contains the lithium-containing positive electrode active material. Each case is determined by the following methods. That is, when the lithium-containing positive electrode active material is not contained in the outer peripheral portion, energy dispersive X-ray spectroscopy (EDX) is performed on an observation image of the positive electrode active material layer in the plane direction with a scanning electron microscope (SEM). Elemental mapping of lithium can be performed using this method, and the count number of lithium elements can be used as an index for determination. More specifically, the boundary between the central portion and the outer peripheral portion is defined as the point where the lithium element is first observed inward from the outer peripheral edge of the positive electrode active material layer. Then, the area surrounded by the boundary (including the boundary) is determined as the "central part", and the area other than this is determined as the "peripheral edge part". On the other hand, when the lithium-containing positive electrode active material is included in the outer peripheral portion of the positive electrode active material layer, the all-solid-state battery according to the present embodiment is charged for the first time. As a result, lithium is released from the lithium-containing positive electrode active material present in the central portion and the outer peripheral portion of the positive electrode active material layer, and lithium is absorbed into the carbon-containing layer. Here, 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 center of the positive electrode active material layer is included in the region overlapping the center of the positive electrode active material layer of the carbon-containing layer. The capacity [mAh] of the carbon material contained in the positive electrode active material layer is greater than or equal to the capacity [mAh] of the carbon material contained in the positive electrode active material layer, whereas the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer is is less than the capacity [mAh] of the carbon material contained in the region overlapping with . For this reason, the carbon material contained in the carbon-containing layer in the region overlapping with the central portion of the positive electrode active material layer absorbs lithium up to the upper limit amount that can be absorbed by the initial charge, and thus absorbs more lithium. Can not. On the other hand, the carbon material contained in the carbon-containing layer in the region overlapping with the outer peripheral portion of the positive electrode active material layer does not occlude lithium up to the upper limit of the amount of lithium that can be occluded even during the initial charge, so it is possible to occlude more lithium. It is possible. Therefore, by confirming whether or not the carbon material contained in the carbon-containing layer can further occlude lithium after the initial charge, the positive electrode active material layer at the corresponding position is either the outer peripheral portion or the central portion. You can judge whether

In the all-solid-state battery according to the present embodiment, the boundary between the central portion and the outer peripheral portion of the positive electrode active material layer is located inside the outer peripheral edge of the positive electrode active material layer. In other words, the “peripheral edge portion” exists along the entire circumference of the outer peripheral edge of the positive electrode active material layer. With such a configuration, short circuits at the ends of the power generation element can be suppressed. Also, since the non-lithium-containing cathode active material is less costly than the lithium-containing cathode active material, the non-lithium-containing cathode active material and a sufficient amount of the lithium-containing cathode active material to impart lithium conductivity to the carbon-containing layer can be used. The cost of the all-solid-state battery can be reduced by configuring the positive electrode active material layer using the material.

There are no particular restrictions on the shape, size, etc. of the central portion and the outer peripheral portion when the power generation element is viewed from above. When the positive electrode active material layer is rectangular, the shape of the central portion when the power generating element is viewed in plan is preferably rectangular, and in this case, the outer peripheral edge portion extends from the positive electrode active material layer to the center. It becomes a square shape without the part. From the viewpoint of improving the energy density of the all-solid-state battery, the size of the central portion of the power generation element when viewed from above is preferably large as long as the outer peripheral portion is large enough to prevent short circuits. Specifically, the ratio of the size of the central portion to the size of the positive electrode active material layer is preferably 0.80 or more and 0.98 or less, more preferably 0.85 or more and 0.98 or less, and 0.85 or more and 0.98 or less. It is more preferably 90 or more and 0.98 or less, and particularly preferably 0.95 or more and 0.98 or less. The width of the outer peripheral portion (the distance from the outer peripheral end of the positive electrode active material layer to the boundary between the central portion and the outer peripheral portion) is also not particularly limited, but is preferably 1 mm or more and 5 cm or less, more preferably 2 mm or more and 3 cm or less, and 5 mm or more. 2 cm or less is more preferable. By setting the width of the outer peripheral portion within the above range, short circuits at the ends of the power generation element can be further suppressed.

In the all-solid-state battery according to this embodiment, the central portion contains both the non-lithium-containing positive electrode active material and the lithium-containing positive electrode active material. Since the positive electrode active material layer has lithium conductivity, the arrangement of the non-lithium-containing positive electrode active material and the lithium-containing positive electrode active material in the stacking direction in the central portion is not limited. FIG. 6 is an enlarged cross-sectional view showing the state of the positive electrode active material layer included in the layered battery according to one embodiment of the present invention before the first charge. In the embodiment of FIG. 6, the lithium-containing positive electrode active material is uniformly present throughout the thickness of the central portion. Other embodiments of the positive electrode active material layer include, for example, the embodiments shown in FIGS. 7 to 9. FIG. In the embodiment of FIG. 7, the lithium-containing positive electrode active material is present only in the half-thickness region on the solid electrolyte layer side of the central portion. In the embodiment of FIG. 8, the lithium-containing positive electrode active material is present only in the half-thickness region on the side opposite to the solid electrolyte layer side of the central portion.

In addition, in the all-solid-state battery according to the present embodiment, the thickness of the central portion of the positive electrode active material layer and the thickness of the outer peripheral portion may be the same or different, as shown in FIGS. may be When the thickness of the central portion and the thickness of the outer peripheral portion are different, for example, as shown in FIG. 9, there is an embodiment in which the central portion is relatively thick and the outer peripheral portion is relatively thin. be done. However, it is preferable that the thickness of the central portion and the thickness of the outer peripheral portion are close to each other from the viewpoint of applying a uniform pressure in the surface direction when applying the confining pressure in the stacking direction of the power generating element. More specifically, the ratio of the thickness of the outer peripheral portion of the positive electrode active material layer to the thickness of the central portion of the positive electrode active material layer is preferably 0.90 or more and 1.10 or less, and is preferably 0.95 or more. It is more preferably 1.05 or less, further preferably 0.98 or more and 1.02 or less, and particularly preferably 1.00. In this specification, the thickness of the central portion means a value calculated as an arithmetic mean value of the thicknesses measured at several to several tens of different locations. The same applies to the thickness of the outer peripheral edge.

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 center of the positive electrode active material layer is included in the region overlapping the center of the positive electrode active material layer of the carbon-containing layer. A region where the capacity [mAh] of the carbon material is equal to or greater than the capacity [mAh] of the carbon material and the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer overlaps with the outer peripheral portion of the positive electrode active material layer of the carbon-containing layer. It is also characterized by being less than the capacity [mAh] of the carbon material contained in. The inventors of the present invention have found from the following experimental results that the carbon-containing layer is provided with lithium conductivity sufficient for 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. 10 is a graph showing charge/discharge curves of test cells. When charging was performed as the first operation, as shown in FIG. 10, charging and subsequent discharging could be performed. When discharging was performed as the first operation, as shown in FIG. 10, it was found that 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.

By applying the above knowledge, it becomes possible to control the lithium conductivity of the carbon-containing layer at the corresponding position when the power generating element is viewed from above, depending on the amount of the lithium-containing positive electrode active material in the positive electrode active material layer. Therefore, the capacity [mAh] of the lithium-containing positive electrode active material contained in the center of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the region overlapping the center of the positive electrode active material layer of the carbon-containing layer. and the capacity [mAh] of the lithium-containing positive electrode active material included in the outer peripheral portion of the positive electrode active material layer is the capacity of the carbon material included in the region where the carbon-containing layer overlaps the outer peripheral portion of the positive electrode active material layer [ By controlling the arrangement of the lithium-containing positive electrode active material in the positive electrode active material layer so as to be less than mAh], the lithium conductivity in the central portion of the carbon-containing layer is sufficiently high, while the lithium in the outer peripheral portion It becomes possible to keep the conductivity low. As a result, charge-discharge reactions at the ends of the power generation element of the all-solid-state battery are suppressed, and short circuits at the ends are less likely to occur.

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. The mass [g] of the lithium-containing positive electrode active material contained in the portion to be measured (the central portion or the outer peripheral portion of the positive electrode active material layer) and the mass [g] of the lithium-containing positive electrode active material used in the half cell are If different, the value [mAh/g] obtained by dividing the capacity [mAh] of the lithium-containing positive electrode active material used in the half-cell by the mass [g] of the lithium-containing positive electrode active material used in the half-cell is included in the part to be measured. By multiplying the mass [g] of the lithium-containing positive electrode active material contained in the measurement target, the capacity [mAh] of the lithium-containing positive electrode active material contained in the measurement target portion 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. 11 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. 11, 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 part to be measured (the central part or the outer peripheral part of the carbon-containing layer) is different from the mass [g] of the carbon material used for the half-cell, By multiplying the value [mAh/g] obtained by dividing the capacity [mAh] of the carbon material used in the half cell by the mass [g] of the carbon material used in the half cell by the mass [g] of the carbon material contained in the part to be measured, It is possible to obtain the capacity [mAh] of the carbon material contained in the site to be measured.

The capacity [mAh] of the lithium-containing positive electrode active material contained in the center of the positive electrode active material layer with respect to the capacity [mAh] of the carbon material contained in the center of the carbon-containing layer (the capacity of the lithium-containing positive electrode active material [mAh] / carbon The ratio of the capacity [mAh]) of the materials is essentially 1 or more, and from the viewpoint of improving energy density and reducing costs, it is preferably 1 to 2, more preferably 1 to 1.5, and still more preferably. is between 1 and 1.2.

The method for manufacturing the positive electrode active material layer according to this embodiment is not particularly limited, and a known vapor deposition method or coating method can be appropriately employed. As a specific example of the vapor deposition method, (i) the part forming the outer peripheral edge of the substrate surface is masked, and the lithium-free positive electrode active material and the lithium-containing positive electrode active material are simultaneously or sequentially deposited to form the central part. Form. After that, the surface of the central portion and the region outside the outer edge portion of the positive electrode active material layer are masked, and the masking material on the outer edge portion is removed. Then, a method of forming a peripheral edge portion by vapor-depositing a non-lithium-containing positive electrode active material on the exposed portion of the substrate; A region outside the region is masked, and a non-lithium-containing positive electrode active material is vapor-deposited to form an outer peripheral edge. After that, while masking the surface of the outer peripheral edge, the masking material in the center is removed. Then, a non-lithium-containing positive electrode active material and a lithium-containing positive electrode active material are simultaneously or sequentially deposited on the exposed portion of the substrate to form the central portion. As a specific example of the coating method, (iii) a portion forming the outer peripheral edge of the substrate surface is masked, and a slurry containing a non-lithium-containing positive electrode active material and a lithium-containing positive electrode active material is applied and dried to form a central part. form a part. After that, the surface of the central portion and the region outside the outer edge portion of the positive electrode active material layer are masked, and the masking material on the outer edge portion is removed. Then, a method of applying a slurry containing a non-lithium-containing positive electrode active material to the exposed portion of the substrate and drying it to form an outer peripheral portion; (iv) a portion forming the central portion of the substrate surface and the positive electrode active material layer; A region outside the outer peripheral end portion of is masked, and a slurry containing a non-lithium-containing positive electrode active material is applied and dried to form an outer peripheral edge portion. After that, while masking the surface of the outer peripheral edge, the masking material in the center is removed. Then, there is a method of applying slurry containing a non-lithium-containing positive electrode active material and a lithium-containing positive electrode active material to the exposed portion of the base material and drying it to form the central portion. In the coating methods (iii) and (iv) above, a slurry containing both a lithium-free positive electrode active material and a lithium-containing positive electrode active material was used to form the central portion. A slurry containing only a lithium-free positive electrode active material and a slurry containing only a lithium-containing positive electrode active material as a positive electrode active material may be separately prepared. Then, a slurry containing only a non-lithium-containing positive electrode active material as a positive electrode active material is applied and dried, and then a slurry containing only a lithium-containing positive electrode active material is applied and dried to form a two-layer central portion. Alternatively, a slurry containing only a lithium-containing positive electrode active material as a positive electrode active material is applied and dried, and then a slurry containing only a non-lithium-containing positive electrode active material is applied and dried to form a two-layer core. I do not care.

After the positive electrode active material layer is formed on the base material surface by the above method, the exposed surface of the positive electrode active material layer is superimposed on the solid electrolyte layer and transferred to obtain a laminate of the solid electrolyte layer and the positive electrode active material layer. be able to. Alternatively, the positive electrode active material layer may be formed directly on the solid electrolyte layer instead of the base material. Also in this case, the positive electrode active material layer can be formed by a vapor deposition method or a coating method in the same manner as described above.

Next, the size of each layer constituting the power generation element will be described. In the all-solid-state battery according to the present embodiment, when the power generating element is viewed in plan, the outer peripheral edge of the negative electrode active material layer is (1a) positioned at the same position as the outer peripheral edge of the central portion of the positive electrode active material layer, or , as in the embodiment shown in FIG. 12, (1b) preferably positioned outside the outer peripheral edge of the central portion of the positive electrode active material layer. Among them, the above embodiment (1b) is more preferable. With such a structure, it is possible to prevent a decrease in capacity due to a decrease in the area mainly involved in charging and discharging.

In the all-solid-state battery according to this embodiment, when the power generating element is viewed from above, the outer peripheral edge of the carbon-containing layer is located at the same position as (2a) the outer peripheral edge of the negative electrode active material layer, or As in the embodiment shown (2b), it is preferably located outside the outer peripheral edge of the negative electrode active material layer. Among them, the above embodiment (2b) is more preferable. With such a configuration, the carbon-containing layer acts as a physical barrier, so short circuits at the ends of the power generating element can be further suppressed.

In the all-solid-state battery according to this embodiment, when the power generating element is viewed from above, the outer peripheral edge of the solid electrolyte layer is located at the same position as the outer peripheral edge of the (3a) carbon-containing layer, or is shown in FIG. It is preferably located outside the outer peripheral edge of the (3b) carbon-containing layer as in the embodiment. Above all, the above embodiment (3b) is more preferable. With such a structure, it is possible to prevent a decrease in capacity due to a decrease in the area involved in charging and discharging. With such a configuration, the solid electrolyte layer acts as a physical barrier, so short circuits at the ends of the power generating element can be further suppressed.

In the all-solid-state battery according to the present embodiment, the width of the outer peripheral edge of the positive electrode active material layer when the power generating element is viewed from above is (4a) the thickness of the positive electrode active material layer in the stacking direction of the power generating element and the solid electrolyte layer. or, as in the embodiment shown in FIG. 15, (4b) greater than that sum. Among them, the above embodiment (4b) is more preferable. With such a configuration, the influence of diffusion of lithium in the surface direction of the positive electrode active material layer can be reduced, so that short circuits at the ends of the power generating element can be further suppressed.

[Positive collector plate and negative collector plate]
The material constituting the current collector 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 current collector plate and the negative electrode current collector plate.

[Positive lead and negative lead]
Also, the current collector and the current collector plate may be electrically connected via a positive electrode lead or a negative electrode 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 a bag-like case using a laminated film containing aluminum that can cover the power generation element can also be used. The laminate film may be, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order, but is not limited thereto. A laminate film is desirable from the viewpoint that it 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.

10a laminated battery,
11' negative electrode current collector,
11″ cathode current collector,
13 negative electrode active material layer,
14 carbon-containing layer,
14a central part of the carbon-containing layer,
14b the outer edge of the carbon-containing layer,
15 positive electrode active material layer,
15a central part of the positive electrode active material layer,
15b outer peripheral edge of the 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.

Claims (6)

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 and a lithium-containing 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 with a power generation element having a layer,
When the power generating element is viewed from above, the positive electrode active material layer includes a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and the lithium-free positive electrode active material, and and an outer peripheral portion optionally containing the lithium-containing positive electrode active material,
The capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer is the capacity [mAh] of the carbon material contained in the region where the carbon-containing layer overlaps the central portion of the positive electrode active material layer. ] is greater than or equal to
The capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer is the capacity of the carbon material contained in the region where the carbon-containing layer overlaps the outer peripheral portion of the positive electrode active material layer. An all-solid-state battery that is less than [mAh]. The all-solid-state battery according to claim 1, wherein the outer peripheral portion of said positive electrode active material layer does not contain a lithium-containing positive electrode active material. When the power generating element is viewed from above, the outer peripheral edge of the negative electrode active material layer is positioned at the same position as the outer peripheral edge of the central portion of the positive electrode active material layer, or The all-solid-state battery according to claim 1 or 2, located outside the outer peripheral edge. When the power generating element is viewed from above, the outer peripheral edge of the carbon-containing layer is positioned at the same position as the outer peripheral edge of the negative electrode active material layer, or is positioned outside the outer peripheral edge of the negative electrode active material layer. The all-solid-state battery according to any one of claims 1 to 3. The width of the outer peripheral edge of the positive electrode active material layer when the power generating element is viewed from above is the same as the sum of the thickness of the positive electrode active material layer and the thickness of the solid electrolyte layer in the stacking direction of the power generating element. The all-solid-state battery according to any one of claims 1 to 4, wherein there is or is greater than the sum. 6. The method according to any one of claims 1 to 5, wherein the ratio of the thickness of the outer peripheral portion of the positive electrode active material layer to the thickness of the central portion of the positive electrode active material layer is 0.90 to 1.10. The all-solid-state battery described.