Manufacturing method for all-solid-state lithium secondary battery

Abstract

To provide means for improving input and output characteristics and energy density in an all solid lithium secondary battery including metal lithium as a negative electrode active material.SOLUTION: A manufacturing method for an all solid lithium secondary battery including metal lithium as a negative electrode active material includes the steps of: manufacturing a stack including a solid electrolyte layer containing a solid electrolyte, a positive electrode active material layer containing a positive electrode active material, and a positive electrode current collector on a negative electrode current collector in this order, in which the metal lithium is disposed between the positive electrode active material layer and the positive electrode current collector or in the positive electrode active material layer; and precipitating the metal lithium between the solid electrolyte layer and the negative electrode current collector by performing a charging reaction on the stack. The positive electrode current collector is formed of a material that is not made into alloy with lithium, or a surface that is adjacent to the positive electrode active material layer of the positive electrode current collector is covered with a material that is not made into alloy with lithium.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an all-solid-state lithium secondary battery. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and there has been active development of non-aqueous electrolyte secondary batteries, such as secondary batteries for driving motors, which hold the key to putting these vehicles into practical use.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium secondary batteries used in mobile phones, laptops, etc. Therefore, lithium secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently widely used lithium secondary batteries use flammable organic electrolytes, and these liquid-based lithium secondary batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, research and development of all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials primarily composed of ionic conductors capable of ion conduction in a solid state. Therefore, all-solid-state lithium secondary batteries, in principle, do not encounter the various problems associated with flammable organic electrolytes that are common in conventional liquid-based lithium secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density. For example, elemental sulfur (S8) has an extremely high theoretical capacity of approximately 1670 mAh / g and is advantageously low cost and abundant in resources.

[0006] On the other hand, metallic lithium, which is a negative electrode active material that supplies lithium ions to the positive electrode, is known as a high-capacity negative electrode material that can be used in all-solid-state batteries. However, in all-solid-state batteries that use metallic lithium as the negative electrode active material and a sulfide solid electrolyte as the solid electrolyte, the metallic lithium and the sulfide solid electrolyte may react with each other, resulting in a deterioration in battery performance.

[0007] To address this problem, Patent Document 1 proposes an all-solid-state battery in which an intermediate layer that conducts lithium ions is formed between a negative electrode active material layer using metallic lithium and a solid electrolyte layer containing a sulfide solid electrolyte. According to Patent Document 1, by forming an intermediate layer between the metallic lithium and the solid electrolyte layer, contact between the metallic lithium and the solid electrolyte can be suppressed, and reductive decomposition of the solid electrolyte due to contact with the metallic lithium can be suppressed. As a result, a stable charge / discharge cycle can be obtained. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-125578 Summary of the Invention [Problem to be solved by the invention]

[0009] However, it has been found that although the technology described in Patent Document 1 improves the input / output characteristics of the battery, the placement of the intermediate layer increases the volume of the battery, which can result in a decrease in energy density.

[0010] Therefore, an object of the present invention is to provide a means for improving the input / output characteristics and energy density of an all-solid-state lithium secondary battery using metallic lithium as the negative electrode active material. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by first disposing metallic lithium on the positive electrode side (between the positive electrode current collector and the positive electrode active material layer, or in the positive electrode active material layer) and then depositing metallic lithium on the negative electrode current collector by charging, thereby completing the present invention.

[0012] That is, one aspect of the present invention is a method for producing an all-solid-state lithium secondary battery using metallic lithium as a negative electrode active material, the method including the steps of: preparing a laminate having, on a negative electrode current collector, a solid electrolyte layer containing a solid electrolyte, a positive electrode active material layer containing a positive electrode active material, and a positive electrode current collector in this order, the metallic lithium being disposed between the positive electrode active material layer and the positive electrode current collector or in the positive electrode active material layer; and performing a charging reaction on the laminate to precipitate the metallic lithium between the solid electrolyte layer and the negative electrode current collector, wherein the positive electrode current collector is made of a material that does not alloy with lithium, or a surface of the positive electrode current collector adjacent to the positive electrode active material layer is coated with a material that does not alloy with lithium. [Effects of the Invention]

[0013] According to the production method of the present invention, an all-solid-state lithium secondary battery using metallic lithium as the negative electrode active material can be obtained that has excellent input / output characteristics and energy density. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing a method for producing an all-solid-state lithium secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes the above-described embodiments of the present invention with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. Below, the present invention will be described using a stacked-type (internal parallel connection) all-solid-state lithium secondary battery, which is one type of secondary battery. As described above, the solid electrolyte constituting an all-solid-state lithium secondary battery is a material composed primarily of an ion conductor capable of ion conduction in a solid. Therefore, all-solid-state lithium secondary batteries have the advantage that, in principle, they do not encounter various problems associated with flammable organic electrolytes, as in conventional liquid-based lithium secondary batteries. Furthermore, generally, the use of a high-potential, high-capacity positive electrode material and a high-capacity negative electrode material has the advantage of significantly improving the output density and energy density of the battery.

[0016] FIG. 1 is a perspective view showing the appearance of a flat-layered all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar lithium secondary battery shown in FIGS. 1 and 2 (hereinafter also simply referred to as a "layered battery") will be used as an example for detailed explanation. However, in terms of the internal electrical connection configuration (electrode structure) of the lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0017] 1, the stacked battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and positive electrode current collector 27 extending to the outside.

[0018] The lithium secondary battery according to this embodiment is not limited to a laminated, flat shape. A wound lithium secondary battery may be cylindrical, or may be a cylindrical battery modified into a rectangular, flat shape, and is not particularly limited. The cylindrical battery may use a laminate film or a conventional cylindrical can (metal can) as its exterior material, and is not particularly limited. Preferably, the power generating element is housed inside a laminate film containing aluminum. This configuration can achieve weight reduction.

[0019] There are also no particular limitations on how the current collectors (25, 27) shown in Fig. 1 are taken out. The negative current collector 25 and the positive current collector 27 may be taken out from the same side, or the negative current collector 25 and the positive current collector 27 may each be divided into multiple pieces and taken out from each side, and so on, and are not limited to what is shown in Fig. 1. Furthermore, in a wound-type lithium secondary battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of tabs.

[0020] 2, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11". The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 faces the adjacent negative electrode active material layer 13 with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10a shown in FIG. 2 has a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0021] As shown in FIG. 2, the outermost positive electrode current collectors located on both outermost layers of the power generating element 21 each have a positive electrode active material layer 15 disposed on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector exclusively for the outermost layer with an active material layer provided on only one side, a current collector having active material layers on both sides may be used as the outermost current collector. 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")

[0022] Negative electrode current collector 11′ and positive electrode current collector 11″ are respectively attached with negative electrode current collector (tab) 25 and positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and are structured so as to be sandwiched between the ends of laminate film 29, which is the battery outer casing material, and extended to the outside of laminate film 29. Positive electrode current collector 27 and negative electrode current collector 25 may be attached to positive electrode current collector 11″ and negative electrode current collector 11′ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via positive electrode leads and negative electrode leads (not shown) as necessary.

[0023] The main components of the all-solid-state lithium secondary battery obtained by the method according to this embodiment will be described below.

[0024] [Current collector] The current collector functions as a medium for the transfer of electrons from the electrode active material layer, and may be made of, for example, a metal or a conductive resin.

[0025] The current collector may have a single layer structure made of a single material, or may have a laminate structure in which layers made of these materials are appropriately combined.

[0026] In the method of this embodiment, the positive electrode current collector is made of a material that does not alloy with lithium, or the surface of the positive electrode current collector adjacent to the positive electrode active material layer is coated with a material that does not alloy with lithium. If the material is alloyable with lithium, the positive electrode current collector may corrode due to alloying, resulting in a decrease in conductivity. Examples of materials that do not alloy with lithium include metals such as nickel, copper, and stainless steel. Examples of materials coated with a material that does not alloy with lithium include aluminum coated with the above metals and carbon-coated aluminum. Among these, stainless steel, nickel, or carbon-coated aluminum are preferred from the viewpoints of corrosion resistance and high conductivity. The thickness of the positive electrode current collector is not particularly limited, but is, for example, 1 to 1,000 μm.

[0027] The negative electrode current collector may be made of, for example, stainless steel, copper, nickel, etc. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 to 1000 μm.

[0028] [Negative electrode active material layer] In the lithium secondary battery according to the present embodiment, metallic lithium is deposited on the negative electrode current collector by a charging reaction. The layer of metallic lithium deposited on the negative electrode current collector during this charging reaction is the negative electrode active material layer of the lithium secondary battery according to the present embodiment.

[0029] The thickness of the metallic lithium layer as the negative electrode active material layer varies depending on the configuration of the intended secondary battery, but is, for example, within a range of 0.1 to 1000 μm, preferably 1 to 1000 μm, and more preferably 10 to 500 μm during charging.

[0030] [Solid electrolyte layer] In the stacked battery according to the embodiment shown in FIGS. 1 and 2, the solid electrolyte layer is interposed between the above-described positive electrode active material layer and negative electrode active material layer, and is a layer that essentially contains a solid electrolyte.

[0031] The specific form of the solid electrolyte contained in the solid electrolyte layer is not particularly limited. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, but sulfide solid electrolytes are preferred. Since sulfide solid electrolytes are prone to reductive decomposition by metallic lithium, the effects of the present invention can be more significantly achieved.

[0032] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). The term "LiS-P2S5" refers to a sulfide solid electrolyte obtained using a raw material composition containing LiS and P2S5, and the same applies to other terms.

[0033] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes known as LPS (for example, Li7P3S 11 ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li (4-x) Ge (1-x)P x An LGPS or the like represented by S4 (where 0 < x < 1) may be used. Among them, a sulfide solid electrolyte containing P element is preferable, and the sulfide solid electrolyte is more preferably a material mainly composed of Li2S - P2S5. Further, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). In a preferred embodiment, the sulfide solid electrolyte contains Li6PS5X (where X is Cl, Br or I, preferably Cl).

[0034] When the sulfide solid electrolyte is a Li2S - P2S5 system, the ratio of Li2S and P2S5 is preferably within the range of Li2S:P2S5 = 50:50 to 90:10 in terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0035] The sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by heat-treating a sulfide glass at a temperature above the crystallization temperature. The ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, 1×10 -5 S / cm or more is preferable, and 1×10 -4 S / cm or more is more preferable. The value of the ionic conductivity of the solid electrolyte can be measured by an alternating current impedance method. ​​​​​​​​​​​​​​(PO4)3 (0≦x≦2) (LATP) and the like. Another example of an oxide solid electrolyte is LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0037] In a preferred embodiment of the present invention, the proportion of the content of the sulfide solid electrolyte in the total amount (100 mass%) of the solid electrolyte contained in the solid electrolyte layer is, for example, 50 mass% or more, preferably more than 50 mass%, more preferably 70 mass% or more, even more preferably 80 mass% or more, still more preferably 90 mass% or more, particularly preferably 95 mass% or more, and most preferably 100 mass%.

[0038] The shape of the solid electrolyte may be, for example, a particulate shape such as a spherical shape or an oval spherical shape, or a thin film shape. When the solid electrolyte is particulate, its 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. 50 ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0039] The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably in the range of 10 to 100 mass %, more preferably in the range of 50 to 100 mass %, and even more preferably in the range of 90 to 100 mass %, relative to the total mass of the solid electrolyte.

[0040] The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte. The binder is not particularly limited, but examples thereof include the following materials.

[0041] Thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated products, styrene-isoprene-styrene block copolymer and its hydrogenated products, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene Examples of such fluororesins include ethylene-chlorotrifluoroethylene copolymer (ECTFE) and polyvinyl fluoride (PVF), vinylidene fluoride-based fluororubbers such as vinylidene fluoride-hexafluoropropylene-based fluororubbers (VDF-HFP-based fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-HFP-TFE-based fluororubbers), vinylidene fluoride-pentafluoropropylene-based fluororubbers (VDF-PFP-based fluororubbers), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

[0042] The thickness of the solid electrolyte layer varies depending on the configuration of the intended all-solid-state lithium secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 1000 μm or less, more preferably 700 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0043] [Cathode active material layer] 1 and 2, the positive electrode active material layer contains a positive electrode active material. The positive electrode active material is not particularly limited, but from the viewpoint of increasing the output density and energy density of the battery, it is preferable to use a positive electrode active material containing sulfur.

[0044] (Cathode active material containing sulfur) The type of sulfur-containing positive electrode active material is not particularly limited, but includes elemental sulfur (S) and lithium sulfide (LiS), as well as particles or thin films of organic or inorganic sulfur compounds. Any material can be used as long as it utilizes the sulfur redox reaction to release lithium ions during charging and absorb lithium ions during discharging. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitriles, sulfur-modified polyisoprenes, rubeanic acid (dithiooxamide), and polycarbonate sulfide, as exemplified by the compounds described in International Publication No. 2010 / 044437. Among these, disulfide compounds, sulfur-modified polyacrylonitriles, and rubeanic acid are preferred, with sulfur-modified polyacrylonitrile being particularly preferred. Disulfide compounds containing dithiobiurea derivatives, thiourea groups, thioisocyanates, or thioamide groups are more preferred. Here, sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, obtained by mixing sulfur powder with polyacrylonitrile and heating the mixture under an inert gas or under reduced pressure. Its estimated structure is, for example, as shown in Chem. Mater. 2011, 23, 5024-5028, in which polyacrylonitrile is ring-closed to form a polycyclic ring, and at least a part of S is bonded to C. The compound described in this document has a peak at 1330 cm in the Raman spectrum. -1 and 1560cm -1 There is a strong peak signal near 307 cm -1 , 379cm -1 , 472cm -1 , 929cm -1There is a peak around 1000 kJ / cm. On the other hand, inorganic sulfur compounds are preferred due to their excellent stability. Specific examples include elemental sulfur (S), Li2S, S-carbon composite, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS2, MoS3, MnS, MnS2, CoS, CoS2, and the like. Among these, elemental sulfur (S), Li2S, S-carbon composite, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, with elemental sulfur (S), Li2S, TiS2, and FeS2 being more preferred. Elemental sulfur (S) is particularly preferred from the viewpoint of high capacity and discharge starting characteristics. As elemental sulfur (S), α-sulfur, β-sulfur, or γ-sulfur having an S8 structure can be used.

[0045] The positive electrode active material layer may contain a sulfur-free positive electrode active material. Furthermore, in addition to the sulfur-containing positive electrode active material, the positive electrode active material may further contain a sulfur-free positive electrode active material. Examples of sulfur-free positive electrode active materials include layered rock salt active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li(Ni-Mn-Co)O2; LiMn2O4; and LiNi 0.5 Mn 1.5 Examples of oxide active materials include spinel-type active materials such as O4, olivine-type active materials such as LiFePO4 and LiMnPO4, and Si-containing active materials such as Li2FeSiO4 and Li2MnSiO4. Examples of oxide active materials other than those mentioned above include V2O5 and Li4Ti5O 12 Examples include:

[0046] In some cases, two or more kinds of positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used. However, the content of the sulfur-containing positive electrode active material relative to the total amount (100% by mass) of the positive electrode active material is, for example, 50% by mass or more, preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0047] (cathode material) In a preferred embodiment of the present invention, the positive electrode active material layer preferably contains a positive electrode material in which a sulfur-containing positive electrode active material and a solid electrolyte such as a sulfide solid electrolyte are supported in the pores of a conductive material having pores.

[0048] The specific form of the conductive material is not particularly limited, and conventionally known materials can be appropriately used. From the viewpoints of excellent conductivity, ease of processing, and ease of designing a desired pore distribution, the conductive material is preferably a carbon material. In particular, the conductive material is more preferably a (porous) carbon material having pores, from the viewpoint of being able to form more reaction regions (three-phase interfaces), but a conductive material other than a carbon material may also be used.

[0049] Examples of carbon materials having micropores include activated carbon, Ketjen Black (registered trademark; highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, and other carbon blacks; and carbon particles (carbon supports) made of coke, natural graphite, artificial graphite, and the like. Preferably, the carbon material is primarily composed of carbon. Here, "mainly composed of carbon" refers to carbon atoms being the primary component, and encompasses both carbon atoms alone and carbon atoms essentially. "Substantially composed of carbon atoms" means that impurities of approximately 2 to 3% by mass or less can be present.

[0050] The BET specific surface area of ​​the porous conductive material (preferably a carbon material) is 200 m 2 / g or more is preferable, and 500m 2 / g or more is more preferable, and 800m 2 / g or more is more preferable, and 1200m 2 / g or more is particularly preferred, and 1500m 2It is most preferable that it is / g or more. Further, the pore volume of the conductive material having pores (preferably a carbon material) is preferably 1.0 mL / g or more, more preferably 1.3 mL / g or more, and even more preferably 1.5 mL / g or more. If the BET specific surface area and pore volume of the conductive material are within such ranges, a sufficient amount of pores can be retained, and as a result, a sufficient amount of the positive electrode active material can be retained. Note that the values of the BET specific surface area and pore volume of the conductive material can be measured by nitrogen adsorption / desorption measurement. This nitrogen adsorption / desorption measurement is performed using BELSORP mini manufactured by MicrotracBEL Corporation at a temperature of -196°C by the multi-point method. The BET specific surface area is determined from the adsorption isotherm in the relative pressure range of 0.01 < P / P0 < 0.05. The pore volume is determined from the volume of adsorbed N2 at a relative pressure of 0.96.

[0051] The average pore diameter of the conductive material is not particularly limited, but is preferably 50 nm or less, and particularly preferably 30 nm or less. If the average pore diameter of the conductive material is within these ranges, electrons can be sufficiently supplied to the active material existing at a position far from the pore wall among the positive electrode active materials containing sulfur disposed inside the pores. Note that the value of the average pore diameter of the conductive material can be calculated by nitrogen adsorption / desorption measurement in the same manner as when obtaining the values of the BET specific surface area and pore volume.

[0052] When the conductive material is in a particulate form, the average particle diameter (primary particle diameter) is not particularly limited, but is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm, and even more preferably 0.5 to 10 μm. In this specification, the "particle diameter of the conductive material" means the maximum distance L among the distances between any two points on the contour line of the conductive material. As the value of the "average particle diameter of the conductive material", the value calculated as the average value of the particle diameters of the particles observed in several to several tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) shall be adopted.

[0053] In the cathode material, the specific form of the sulfur-containing cathode active material is the same as above, and the specific form of the solid electrolyte is the same as above.

[0054] In the positive electrode material, the mass ratio of the conductive material to the positive electrode active material is not particularly limited, but may be, for example, conductive material:positive electrode active material=1:1 to 1:10.

[0055] By using a positive electrode material having the above-described structure, a three-phase interface where the positive electrode active material, the conductive material, and the solid electrolyte coexist is sufficiently formed not only on the surface of the conductive material but also inside the pores, allowing the charge / discharge reaction to proceed sufficiently. As a result, the internal resistance of the battery is sufficiently reduced, and the charge / discharge rate characteristics are thought to be significantly improved. In addition, the capacity characteristics and cycle durability can be improved.

[0056] As an example of a method for producing a cathode material having the above configuration, first, a solution is prepared by dissolving a solid electrolyte in an organic solvent, and then a conductive material is dispersed therein to obtain a dispersion. Next, after removing the solvent, the mixture is heat-treated at a temperature of approximately 150 to 600°C for approximately 1 to 5 hours. This results in a conductive material in which the pores of the conductive material are impregnated with the solid electrolyte. The resulting conductive material is then dry-mixed with a cathode active material containing sulfur, and then heat-treated for approximately 1 to 5 hours at a temperature at which the cathode active material is in a molten state. This melts the cathode active material and penetrates into the pores of the conductive material, resulting in a composite material in which the cathode active material and the solid electrolyte are disposed (filled) within the pores of the conductive material. While the composite material thus obtained may be used as a cathode material as is, it is preferable to further add a solid electrolyte to the composite material, mix it, and process it in an apparatus such as a ball mill, as necessary, to obtain a cathode material.

[0057] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 35 to 99 mass %, more preferably in the range of 40 to 90 mass %, for example. Note that this content value is calculated based on the mass of only the positive electrode active material excluding the conductive material and solid electrolyte.

[0058] The positive electrode active material layer may further contain a conductive additive (one that does not hold the positive electrode active material or solid electrolyte inside the pores) and / or a binder. Examples of the conductive additive include the above-mentioned carbon materials having pores, as well as carbon materials without pores, such as graphene, carbon nanotubes, carbon nanofibers, carbon nanohorns, and fullerenes.

[0059] Similarly, the positive electrode active material layer preferably contains a solid electrolyte, more preferably a sulfide solid electrolyte. Even when using a positive electrode material in which a sulfur-containing positive electrode active material and a solid electrolyte such as a sulfide solid electrolyte are supported within the pores of the above-mentioned porous conductive material, it is preferable to further contain a solid electrolyte in addition to the positive electrode material, and it is particularly preferable to further contain a sulfide solid electrolyte. In this case, although not particularly limited, it is preferable to adjust the positive electrode active material layer so that, for example, 10 to 100 parts by mass of the solid electrolyte and 10 to 100 parts by mass of the conductive material are contained per 100 parts by mass of the positive electrode active material. Specific and preferred forms of the solid electrolyte, such as the sulfide solid electrolyte, can be similarly adopted as those described in the solid electrolyte layer section above.

[0060] The thickness of the positive electrode active material layer is not particularly limited, but is within the range of 10 to 1000 μm, for example.

[0061] [Manufacturing method of all-solid-state lithium secondary battery] One aspect of the present invention is a method for producing an all-solid-state lithium secondary battery using metallic lithium as a negative electrode active material, the method including the steps of: preparing a laminate having, on a negative electrode current collector, a solid electrolyte layer containing a solid electrolyte, a positive electrode active material layer containing a positive electrode active material, and a positive electrode current collector in this order, the metallic lithium being disposed between the positive electrode active material layer and the positive electrode current collector or in the positive electrode active material layer; and performing a charging reaction on the laminate to precipitate the metallic lithium between the solid electrolyte layer and the negative electrode current collector, wherein the positive electrode current collector is made of a material that does not alloy with lithium, or a surface of the positive electrode current collector adjacent to the positive electrode active material layer is coated with a material that does not alloy with lithium.

[0062] Batteries using metallic lithium as the anode are expected to have high energy density due to their high specific capacity and low reduction potential relative to the standard hydrogen electrode. However, batteries using metallic lithium as the anode have the problem of being prone to short-circuiting during charging. This problem tends to be particularly pronounced in batteries using sulfur-containing cathode active materials.

[0063] After investigating the causes, it was found that inorganic coatings such as Li2O and Li2CO3 are formed on the surface of metallic lithium (lithium metal foil) during the battery manufacturing process. These inorganic coatings react with the solid electrolyte, forming a resistive layer with low ionic conductivity on the surface of metallic lithium. This results in uneven current distribution on the surface of metallic lithium, the negative electrode active material, during the battery reaction, which causes lithium to deposit unevenly during charging, leading to the formation of dendrites and making short circuits more likely. This can result in a deterioration of the battery's input / output characteristics.

[0064] To address this problem, Patent Document 1 above employs a method of forming an intermediate layer that conducts lithium ions on the surface of metallic lithium. Forming an intermediate layer between metallic lithium and a solid electrolyte layer can prevent contact between metallic lithium and the solid electrolyte, thereby suppressing reductive decomposition of the solid electrolyte due to contact with metallic lithium.

[0065] As described above, the technology of Patent Document 1 can suppress contact between metallic lithium and the solid electrolyte layer, thereby suppressing side reactions between the inorganic coating on the surface of metallic lithium and the solid electrolyte, thereby obtaining a battery that can be charged and discharged without forming a resistance layer. However, the method described in Patent Document 1 requires the formation of an intermediate layer with a finite thickness between the solid electrolyte layer and metallic lithium, which is the negative electrode active material, which reduces the volumetric energy density of the battery.

[0066] To suppress the formation of inorganic coatings, a method of forming a negative electrode active material layer by vapor deposition of lithium on a solid electrolyte layer is known. However, this method can cause a reaction between the lithium and the solid electrolyte due to the application of thermal energy, potentially creating a resistive layer at the contact surface between the lithium and the solid electrolyte layer. Therefore, even when this method is used, short circuits tend to occur, resulting in poor input / output characteristics. Furthermore, the need for a vacuum state during manufacturing poses a cost issue.

[0067] In contrast, the method of the present invention first places metallic lithium on the positive electrode side (between the positive electrode current collector and the positive electrode active material layer, or in the positive electrode active material layer), and then charges the battery to deposit metallic lithium on the negative electrode current collector, forming a negative electrode active material layer. In other words, the battery manufacturing process does not include a step of contacting metallic lithium (lithium metal foil) with a solid electrolyte layer. Therefore, the inorganic coating on the surface of the metallic lithium does not come into contact with the solid electrolyte, thereby suppressing the formation of a resistance layer. This suppresses uneven lithium deposition during the battery reaction, enabling charge and discharge without short-circuiting. Furthermore, because there is no need to form an intermediate layer between the negative electrode active material layer and the solid electrolyte layer, there is no decrease in energy density due to the increased volume caused by the formation of the intermediate layer.

[0068] FIG. 3 is a schematic diagram showing an outline of a method for producing an all-solid-state lithium secondary battery according to one embodiment of the present invention. As shown in FIG. 3, in the method according to this embodiment, first, a laminate 100 is prepared as a battery precursor. Specifically, an anode current collector 111′, a solid electrolyte layer 117, a cathode active material layer 115, metallic lithium 113′, and a cathode current collector 111″ are laminated in this order to produce the laminate 100. Next, when a charging reaction is performed on this laminate, metallic lithium 113′, which has a low reduction potential, is released as lithium ions and precipitates on the anode current collector 111′, thereby producing an all-solid-state lithium secondary battery 100a having an anode active material layer 113 made of metallic lithium between the solid electrolyte layer 117 and the anode current collector 111′.

[0069] While FIG. 3 shows an example of the laminate 100 in which the metallic lithium 113′ is disposed between the positive electrode active material layer 115 and the positive electrode current collector 111″, the metallic lithium 113′ may be disposed in the positive electrode active material layer 115 (not shown). A specific example of a configuration in which the metallic lithium 113′ is disposed in the positive electrode active material layer 115 is a configuration in which the positive electrode active material layer 115 has a two-layer structure and the metallic lithium 113′ is disposed between the two positive electrode active material layers.

[0070] The method for producing the laminate is not particularly limited as long as it does not include a step of contacting metallic lithium with a solid electrolyte layer (e.g., laminating the metallic lithium and the solid electrolyte layer so that they are in close contact with each other). The laminate can be produced, for example, according to the following production method. First, a powder material of the solid electrolyte is pressed to form a pre-formed solid electrolyte layer. Next, a cathode mixture containing a cathode active material for forming a cathode active material layer, metallic lithium, and a cathode current collector are arranged in this order on one side of the pre-formed solid electrolyte layer, and these materials are pre-formed by sequentially or simultaneously pressing them.

[0071] The metallic lithium disposed between the positive electrode active material layer and the positive electrode current collector may be, for example, a lithium metal foil having a thickness of 0.1 to 1000 μm, preferably 1 to 1000 μm, more preferably 10 to 500 μm. The thickness of the lithium metal foil can be appropriately set depending on the desired thickness of the negative electrode active material.

[0072] Next, a negative electrode current collector is placed on the other surface of the solid electrolyte layer, and pressure is applied again to obtain a laminate in which a positive electrode current collector, metallic lithium, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode current collector are laminated in this order.

[0073] The laminate is preferably produced in an inert gas atmosphere with a controlled dew point, for example, an inert gas atmosphere with a dew point of −60° C. or lower.

[0074] Next, a charging reaction is carried out on the laminate, thereby depositing the metallic lithium between the solid electrolyte layer and the negative electrode current collector. The method for carrying out the charging reaction is not particularly limited, and any known method can be appropriately adopted.

[0075] The conditions for the charging reaction are not particularly limited. The conditions for the charging reaction are not particularly limited and can be set depending on the positive electrode active material used. For example, the charging reaction is not particularly limited, but can be performed at a temperature of 15 to 35°C by constant current charging or constant current / constant voltage charging. The voltage conditions for the charging reaction are also not particularly limited, but for example, if the charge termination voltage is set to about 2.8 to 3.3 V, metallic lithium on the positive electrode side can be effectively deposited on the negative electrode current collector.

[0076] Furthermore, the conditions for discharging after the above-mentioned charging reaction are not particularly limited. For example, the battery can be discharged by constant current discharge at a temperature of 15 to 35° C. The voltage conditions during discharge are also not particularly limited, but the discharge termination voltage can be set to about 0.8 to 1.3 V, for example.

[0077] The above-mentioned charging reaction and subsequent discharging may also serve as the initial charging and discharging treatment of the battery.

[0078] Although not particularly limited, the all-solid-state lithium secondary battery of this embodiment preferably does not contain either lithium oxide or lithium carbonate on the surface of the solid electrolyte layer that contacts metallic lithium. This prevents lithium oxide and lithium carbonate from reacting with the solid electrolyte layer to form a resistive layer. This prevents uneven lithium deposition during charging, resulting in a short circuit, resulting in a battery with excellent charge-discharge characteristics. More preferably, the battery does not contain oxides, nitrides, or carbonates (e.g., Li2CO3, Li3N, LiO2) that may be generated as a result of reactions between metallic lithium and gases such as CO2, N2, and O2, or reaction products of these with the solid electrolyte. The presence of oxides and carbonates, including lithium oxide and lithium carbonate, on the surface of the solid electrolyte layer can be confirmed by, for example, determining the composition of elements present in the material using X-ray photoelectron spectroscopy (XPS, ESCA).

[0079] That is, one aspect of the present invention provides an all-solid-state lithium secondary battery having, on an anode current collector, an anode active material layer composed of metallic lithium, a solid electrolyte layer containing a solid electrolyte, a cathode active material layer containing a cathode active material, and a cathode current collector, in this order, wherein the cathode current collector is made of a material that does not alloy with lithium, or a surface of the cathode current collector adjacent to the cathode active material layer is coated with a material that does not alloy with lithium, and the surface of the solid electrolyte layer that comes into contact with the metallic lithium contains neither lithium oxide nor lithium carbonate.

[0080] Although not particularly limited, the all-solid-state lithium secondary battery of this embodiment preferably has a total content of lithium oxide and lithium carbonate present in the solid electrolyte layer of 1 mass % or less relative to the total amount of the solid electrolyte layer. This prevents the lithium oxide and lithium carbonate from reacting with the solid electrolyte layer to form a resistance layer. This prevents the occurrence of short circuits due to uneven lithium deposition during charging, and a battery with excellent charge / discharge characteristics can be obtained.

[0081] In a preferred embodiment of the present invention, the solid electrolyte layer is made of only a solid electrolyte containing neither oxygen atoms nor carbon atoms, and the surface of the solid electrolyte layer that contacts metallic lithium contains neither oxides nor carbonates. With such a configuration, the effects of the present invention can be more significantly obtained.

[0082] [Positive and negative current collector plates] The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plates. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive current collector plate 27 and the negative current collector plate 25 may be made of the same material or different materials.

[0083] [Positive and negative leads] Although not shown, the current collectors (11′, 11″) may be electrically connected to the current collector plates (25, 27) via positive and negative electrode leads. Materials used in known lithium secondary batteries may be used as the constituent materials of the positive and negative electrode leads. The parts removed from the exterior are preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting products (e.g., automobile parts, particularly electronic devices).

[0084] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power-generating element as shown in Figures 1 and 2 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited to these. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large devices such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable for the exterior body because it allows for easy adjustment of the collective pressure applied to the power-generating element from the outside.

[0085] The stacked battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0086] Although one embodiment of the all-solid-state lithium secondary battery has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0087] For example, the type of battery to which the lithium secondary battery according to the present invention is applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically coupled to one surface of a current collector and a negative electrode active material layer electrically coupled to the opposite surface of the current collector. [Example]

[0088] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, all operations were carried out at room temperature (25°C).

[0089] [Example 1] (Production of test cells (all-solid-state lithium secondary batteries)) The battery was fabricated in a glove box with an argon atmosphere at a dew point of −68° C. or lower.

[0090] (Preparation of solid electrolyte-impregnated carbon) In a glove box with an argon atmosphere and a dew point below -68°C, 0.500 g of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was added to 100 mL of ultra-dehydrated ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and thoroughly stirred to dissolve the solid electrolyte in the ethanol. 1.00 g of carbon (activated carbon, MSC-30, manufactured by Kansai Thermal Chemicals Co., Ltd.) was added to the resulting solid electrolyte ethanol solution and thoroughly stirred to fully disperse the carbon in the solution. The container containing this carbon dispersion was connected to a vacuum device, and the container was evacuated to below 1 Pa using an oil-sealed rotary pump while stirring the carbon dispersion in the container with a magnetic stirrer. Because the solvent ethanol volatilizes under reduced pressure, the ethanol was removed over time, leaving the carbon impregnated with the solid electrolyte in the container. After removing the ethanol under reduced pressure, the container was heated to 180°C under reduced pressure for 3 hours to prepare a solid electrolyte-impregnated carbon.

[0091] (Preparation of sulfur / solid electrolyte / carbon composites by hot impregnation of sulfur) In a glove box with an argon atmosphere at a dew point of -68°C or less, 2.50 g of elemental sulfur (manufactured by Aldrich) was added to 0.750 g of the solid electrolyte-impregnated carbon prepared above and mixed thoroughly in an agate mortar. The mixed powder was then placed in a sealed pressure-resistant autoclave and heated at 170°C for 3 hours to melt the sulfur and impregnate the solid electrolyte-impregnated carbon with sulfur. This produced a sulfur / solid electrolyte / carbon composite.

[0092] (Preparation of sulfur-containing cathode materials) In a glove box with an argon atmosphere (dew point below -68°C), 40 g of 5 mm diameter zirconia balls, 0.130 g of the sulfur / solid electrolyte-impregnated carbon prepared above, and 0.070 g of solid electrolyte (Ampcera, Li6PS5Cl) were placed in a 45 mL zirconia container and milled at 370 rpm for 6 hours in a planetary ball mill (Fritsch, Premium line P-7) to obtain a powder of sulfur-containing positive electrode material. The composition of the sulfur-containing positive electrode material was sulfur:solid electrolyte:carbon = 50:40:10.

[0093] (Preparation of test cell) A 10 mm diameter stainless steel cylindrical convex punch was inserted into one side of a McCorm cylindrical tube jig (inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and 80 mg of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was placed into the cylindrical tube jig from above. The other SUS cylindrical convex punch was then inserted to sandwich the solid electrolyte, and the tube was pressed at 75 MPa for 3 minutes using a hydraulic press to form a 10 mm diameter, approximately 0.6 mm thick solid electrolyte layer in the cylindrical tube jig.

[0094] Next, the cylindrical convex punch inserted from above was removed, and 7.5 mg of the sulfur-containing positive electrode material prepared above was placed on one side of the solid electrolyte layer inside the cylindrical tube. The cylindrical convex punch was then inserted again from above and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm on one side of the solid electrolyte layer. Next, the cylindrical convex punch inserted from above was removed again, and a lithium foil (manufactured by Honjo Metals Co., Ltd., thickness 0.10 mm) punched to a diameter of 10 mm and a SUS430 foil (thickness 0.010 mm) punched to a diameter of 10 mm as a positive electrode current collector were placed on top of the positive electrode active material layer in this order. Then, the cylindrical convex punch was inserted again from above.

[0095] Next, the lower cylindrical convex punch was removed, and a piece of SUS foil (thickness: 0.010 mm) punched to a diameter of 10 mm was placed into the cylindrical tube jig from the bottom, and the cylindrical convex punch was inserted again, and the jig was then restrained in a metal casing at a pressure equivalent to 100 MPa.

[0096] In this manner, a laminate was obtained in which the negative electrode current collector, the solid electrolyte layer, the positive electrode active material layer, the lithium metal foil, and the positive electrode current collector were laminated in this order.

[0097] Next, the laminate prepared above was charged, and metallic lithium was precipitated between the negative electrode current collector and the solid electrolyte layer. Specifically, the laminate was placed in a constant temperature bath set at 25°C, and after the temperature of the laminate became constant, a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) was used to charge the laminate at a current of 0.1 mA / cm. 2 3.1V constant current constant voltage (CCCV) charging at a current density of 0.05mA / cm 2 The current was cut off at 0.03 C. Then, the battery was discharged at a rate of 0.03 C according to the battery design. In this way, an all-solid-state lithium secondary battery was obtained.

[0098] [Example 2] An all-solid-state lithium secondary battery was produced in the same manner as in Example 1 above, except that in producing the test cell, the positive electrode current collector was changed from SUS430 foil to Ni foil (thickness: 0.020 mm).

[0099] [Example 3] An all-solid-state lithium secondary battery was produced in the same manner as in Example 1 described above, except that in the production of the test cell, the positive electrode current collector was changed from SUS430 foil to carbon-coated aluminum foil (manufactured by Showa Denko K.K., carbon layer thickness: 1 μm, aluminum layer thickness: 20 μm).

[0100] [Comparative Example 1] A sulfur-containing positive electrode material was prepared in the same manner as in Example 1 above.

[0101] A 10 mm diameter stainless steel cylindrical convex punch was inserted into one side of a McCorm cylindrical tube jig (inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and 80 mg of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was placed into the cylindrical tube jig from above. The other SUS cylindrical convex punch was then inserted to sandwich the solid electrolyte, and the tube was pressed at 75 MPa for 3 minutes using a hydraulic press to form a 10 mm diameter, approximately 0.6 mm thick solid electrolyte layer in the cylindrical tube jig.

[0102] Next, the cylindrical convex punch inserted from above was removed, and 7.5 mg of the sulfur-containing positive electrode material prepared above was placed on one side of the solid electrolyte layer inside the cylindrical tube. The cylindrical convex punch was then inserted again from above and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm on one side of the solid electrolyte layer. Next, the cylindrical convex punch inserted from above was removed again, and a SUS430 foil (thickness 0.010 mm) punched to a diameter of 10 mm was placed on top of the positive electrode active material layer. Then, the cylindrical convex punch was inserted again from above.

[0103] Next, the lower cylindrical convex punch was removed, and a lithium metal foil (manufactured by Honjo Metals Co., Ltd., thickness 0.10 mm) punched to a diameter of 10 mm as the negative electrode active material layer and a SUS foil (thickness 0.010 mm) punched to a diameter of 10 mm as the negative electrode current collector were inserted from the bottom of the cylindrical tube jig, and the cylindrical convex punch was inserted again, and the jig was restrained in a metal casing at a pressure equivalent to 100 MPa.

[0104] In this manner, a laminate was obtained in which the negative electrode current collector, lithium metal foil, solid electrolyte layer, positive electrode active material layer, and positive electrode current collector were laminated in this order. Thereafter, charging and discharging were performed in the same manner as in Example 1, and an all-solid-state lithium secondary battery of Comparative Example 1 was obtained.

[0105] Comparative Example 2 In the above Comparative Example 1, a laminate was fabricated by disposing a 0.10 mm thick polyethylene oxide (PEO) film between the lithium metal foil and the solid electrolyte layer. This resulted in a laminate in which the negative electrode current collector, lithium metal foil, polyethylene oxide layer (intermediate layer), solid electrolyte layer, positive electrode active material layer, and positive electrode current collector were laminated in this order. Except for the above, an all-solid-state lithium secondary battery was fabricated using the same method as in Comparative Example 1.

[0106] Comparative Example 3 An all-solid-state lithium secondary battery was produced in the same manner as in Example 1 above, except that in producing the test cell, the positive electrode current collector was changed from SUS430 foil to aluminum foil (thickness 0.020 mm).

[0107] The configurations of the batteries fabricated in each example and comparative example are shown in Table 1. In Table 1, the "initial Li metal arrangement" refers to the case where the lithium foil was placed between the positive electrode current collector and the solid electrolyte layer when fabricating the laminate, which is the battery precursor, and is represented as the "positive electrode side," and the case where the lithium foil was placed between the negative electrode current collector and the solid electrolyte layer is represented as the "negative electrode side."

[0108] <<Observation of the cross section of an all-solid-state lithium secondary battery>> When the cross sections of the all-solid-state lithium secondary batteries of Examples 1 to 3 and Comparative Example 3 described above were observed using a scanning electron microscope (SEM) after the charging process, it was confirmed that a layer of metallic lithium was present between the negative electrode current collector and the solid electrolyte layer.

[0109] <<Analysis of the surface of the solid electrolyte layer of an all-solid-state lithium secondary battery>> Furthermore, for the all-solid-state lithium secondary batteries of Examples 1 to 3, the solid electrolyte layers were removed after the charging process, and the surface in contact with metallic lithium was measured by X-ray photoelectron spectroscopy (XPS, ESCA), confirming that no peaks derived from oxygen atoms or carbon atoms were observed. This suggests that no oxides or carbonates were formed on the surface of the solid electrolyte layer in contact with metallic lithium. On the other hand, when a similar measurement was performed on the all-solid-state lithium secondary battery of Comparative Example 1, peaks derived from oxygen atoms and carbon atoms were observed, indicating that oxides or carbonates were formed on the surface of the solid electrolyte layer in contact with metallic lithium.

[0110] <Test cell evaluation> The DC resistance and energy density of the test cells prepared in each of the above examples and comparative examples were evaluated by the following methods. All of the following measurements were carried out using a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a constant temperature bath set at 25°C.

[0111] (Energy density measurement) 0.1mA / cm 2 3.1V constant current constant voltage (CCCV) charging at a current density of 0.05mA / cm 2 The test was performed with a current cutoff of 0.01C. Thereafter, the battery was discharged at a rate of 0.03C according to the battery design, the battery capacity was confirmed, and the energy density was calculated. In this case, the voltage range was 1.1 to 2.5V, the current rate during charge and discharge was 0.05C, and the cutoff current during charge was 0.01C. The energy densities calculated in this manner are shown in Table 1 below as relative values, with the value for Comparative Example 1 set to 100.

[0112] (internal resistance measurement) The capacity value per mass of the positive electrode active material (mAh / g) was calculated from the charge / discharge capacity value obtained after repeating the above charge / discharge cycle 10 times and the mass of the positive electrode active material contained in the positive electrode. Next, the capacity value was calculated by 0.2 mA / cm up to 50% capacity (SOC50%) of 100% of the calculated capacity value. 2A constant current discharge was performed at a current density of 1 C. After a 30-minute rest, discharge was performed for 10 seconds at a discharge rate of 1 C. The direct current resistance (DCR) was calculated from the voltage drop and current value during this discharge according to Ohm's law, and this was used as the internal resistance of the test cell. The results are shown in Table 1 below. The internal resistance (DCR) shown in Table 1 is a relative value when the value in Comparative Example 1 is set to 100.

[0113] [Table 1]

[0114] The results shown in Table 1 demonstrate that, as in Examples 1 to 3, the method of the present invention can improve input / output characteristics without reducing energy density in all-solid-state lithium secondary batteries using metallic lithium as the negative electrode active material. In contrast, when a process of disposing a solid electrolyte layer on metallic lithium is included, as in Comparative Example 1, the internal resistance increases. This is thought to be because an inorganic coating, such as Li2O or Li2CO3, formed on the metallic lithium reacts with the solid electrolyte to form a resistive layer. Furthermore, when an intermediate layer is disposed between the negative electrode active material layer and the solid electrolyte layer, as in Comparative Example 2, the reaction between metallic lithium and the solid electrolyte is suppressed, but the energy density of the battery decreases due to the increased volume of the intermediate layer. Furthermore, when the positive electrode current collector is made of a metal that can be alloyed with lithium, as in Comparative Example 3, the current collector corrodes upon alloying with lithium, reducing its functionality as a current collector, which is thought to increase the internal resistance. [Explanation of symbols]

[0115] 10a, 100a stacked battery, 11', 111' negative electrode current collector, 11”, 111” positive electrode current collector, 13, 113 negative electrode active material layer, 15, 115 positive electrode active material layer, 17, 117 solid electrolyte layer, 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film, 100 laminates, 113' metallic lithium.

Claims

1. A method for producing an all-solid-state lithium secondary battery using metallic lithium as a negative electrode active material, comprising: preparing a laminate having, on an anode current collector, a solid electrolyte layer containing a solid electrolyte, a cathode active material layer containing a cathode active material, and a cathode current collector in this order, wherein the metallic lithium is disposed between the cathode active material layer and the cathode current collector or in the cathode active material layer; and performing a charging reaction on the laminate to deposit the metallic lithium between the solid electrolyte layer and the negative electrode current collector, the positive electrode current collector is made of a material that does not alloy with lithium, or a surface of the positive electrode current collector adjacent to the positive electrode active material layer is coated with a material that does not alloy with lithium.

2. The method according to claim 1 , wherein the solid electrolyte is a sulfide solid electrolyte.

3. The method according to claim 1 or 2, wherein the positive electrode active material is a positive electrode active material containing sulfur.

4. The method according to any one of claims 1 to 3, wherein the positive electrode current collector is made of stainless steel, nickel, or carbon-coated aluminum.

5. A manufacturing method described in any one of claims 1 to 4, wherein the all-solid-state lithium secondary battery does not contain either lithium oxide or lithium carbonate on the surface of the solid electrolyte layer that comes into contact with the metallic lithium.

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