Lithium sulfur battery, and method for manufacturing a lithium sulfur battery

Abstract

To provide a lithium sulfur battery which can suppress short circuits in association with discharges or charges and can obtain a high battery capacity.SOLUTION: A lithium sulfur battery 100 includes: a positive electrode layer 110; a first solid electrolyte layer 210; a second solid electrolyte layer 220; and a negative electrode layer 310 in that order. The first solid electrolyte layer 210 includes a sulfide solid electrolyte. The second solid electrolyte layer 220 includes a polymer electrolyte and / or a gel electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to lithium-sulfur batteries and methods for manufacturing lithium-sulfur batteries. [Background technology]

[0002] Lithium-sulfur batteries are batteries that use sulfur as the positive electrode active material, and because sulfur has a high theoretical capacity, they are attracting attention as next-generation batteries. In liquid-type lithium-sulfur batteries, capacity degradation occurs due to the leaching of lithium polysulfide into the electrolyte, so solid-state lithium-sulfur batteries containing a solid electrolyte layer have been developed, and the following solid-state lithium-sulfur batteries are known.

[0003] For example, Patent Document 1 discloses an all-solid-state battery having a first electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a second electrode layer in that order, wherein the first solid electrolyte layer has a first surface, the second solid electrolyte layer has a second surface in contact with the first surface, and the maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface satisfy the following predetermined relationship. According to the all-solid-state battery of Patent Document 1, even if a crack occurs in one of the first solid electrolyte layer and the second solid electrolyte layer, the propagation of the crack to the other layer is easily suppressed, and excellent short-circuit resistance is easily ensured. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-009988 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The solid electrolyte layer containing a sulfide solid electrolyte has excellent properties as a solid electrolyte layer, but it cannot follow the expansion and contraction accompanying charge and discharge of the sulfur-containing positive electrode layer, cracks may occur in the solid electrolyte layer, and there is a risk of short circuit due to this. Also, if a solid electrolyte layer that follows expansion and contraction is used to prevent short circuit, there is a risk that the capacity will be significantly reduced. Therefore, further improvement of the solid electrolyte layer in a lithium-sulfur battery is required.

[0006] Therefore, an object of the present disclosure is to provide a lithium-sulfur battery that can suppress short circuit accompanying charge and discharge and can obtain a high battery capacity.

Means for Solving the Problems

[0007] The present disclosure achieves the above object by the following means.

[0008] <Aspect 1> A lithium-sulfur battery, The lithium-sulfur battery has a positive electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a negative electrode layer in this order, The first solid electrolyte layer contains a sulfide solid electrolyte, and The second solid electrolyte layer contains a polymer electrolyte and / or a gel electrolyte, Lithium-sulfur battery. <Aspect 2> The negative electrode layer has a negative electrode current collector layer, and Lithium ions that have moved from the positive electrode layer during charging are deposited as metallic lithium between the second solid electrolyte layer and the negative electrode current collector layer, The lithium-sulfur battery according to Aspect 1. <Aspect 3> The lithium-sulfur battery according to Aspect 1 or 2, wherein the second solid electrolyte layer contains a polymer electrolyte. <Aspect 4> The lithium-sulfur battery according to any one of Aspects 1 to 3, wherein the polymer electrolyte contains polyethylene oxide. <Aspect 5> A method for manufacturing a lithium-sulfur battery according to any one of Aspects 1 to 4, including the following steps: A preliminary positive electrode layer containing sulfur, and a sulfide containing a phosphorus element and a sulfur element, the first solid electrolyte layer, the second solid electrolyte layer, and the negative electrode layer are laminated in this order to form a preliminary laminate. By performing a discharging operation on the preliminary laminate, a part of sulfur in the preliminary positive electrode layer and a sulfide containing a phosphorus element and a sulfur element are reacted with lithium to generate a sulfide solid electrolyte, thereby forming the positive electrode layer.

Advantages of the Invention

[0009] According to the lithium-sulfur battery of the present disclosure, short circuits associated with charge and discharge can be suppressed, and a high battery capacity can be obtained.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining the lithium-sulfur battery of the present disclosure.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure. Also, in the description of the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0012] The lithium-sulfur battery of the present disclosure is a solid battery having a solid electrolyte layer as an electrolyte layer. Regarding the present disclosure, the "solid battery" means a battery using at least a solid electrolyte as an electrolyte. Therefore, the solid battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte.

[0013] In this disclosure, “compound mixture” means a composition that can constitute a positive electrode (negative electrode) layer or a solid electrolyte layer, either as is or by further containing other components. In this disclosure, “compound mixture slurry” means a slurry that contains a dispersion medium in addition to the “compound mixture,” and can be applied and dried to form a positive electrode (negative electrode) layer or a solid electrolyte layer.

[0014] Lithium-sulfur battery The lithium-sulfur battery disclosed herein is The device has a positive electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a negative electrode layer in this order. The first solid electrolyte layer described above contains a sulfide solid electrolyte, and The second solid electrolyte layer described above includes a polymer electrolyte and / or a gel electrolyte.

[0015] The lithium-sulfur battery of this disclosure can suppress short circuits associated with charging and discharging, and can also achieve a high battery capacity.

[0016] The lithium-sulfur battery of this disclosure specifically includes, for example, a positive electrode layer 110, a first solid electrolyte layer 210 containing a sulfide solid electrolyte, a second solid electrolyte layer 220 containing a polymer electrolyte and / or a gel electrolyte, and a negative electrode layer 310, as shown in Figure 1. During charging and discharging, the positive electrode layer 110 containing sulfur as the positive electrode active material expands and contracts.

[0017] The lithium-sulfur battery of this disclosure has a second solid electrolyte layer comprising a polymer electrolyte and / or a gel electrolyte. Because the second solid electrolyte layer comprises a polymer electrolyte layer and / or a gel electrolyte layer, it is relatively flexible and can follow the expansion and contraction associated with the charging and discharging of the sulfur-containing positive electrode layer, thereby suppressing short circuits.

[0018] Furthermore, the lithium-sulfur battery of this disclosure has a first solid electrolyte layer containing a sulfide solid electrolyte between a positive electrode layer and a second solid electrolyte layer containing a polymer electrolyte and / or a gel electrolyte. Since the first solid electrolyte layer is a sulfide solid electrolyte, it is possible to reduce the barrier to lithium insertion into the positive electrode layer, thereby enabling the lithium-sulfur battery to obtain a high battery capacity.

[0019] <Composition of a lithium-sulfur battery> The lithium sulfur battery of this disclosure has a positive electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a negative electrode layer in this order.

[0020] <Positive electrode layer> The positive electrode layer includes at least a positive electrode active material. During battery charging, lithium ions move from the positive electrode active material to the negative electrode layer via the first solid electrolyte layer and the second solid electrolyte layer. During battery discharge, the lithium in the negative electrode layer is ionized and returned to the positive electrode active material. The positive electrode layer comprises a positive electrode active material layer and an optional positive electrode current collector layer.

[0021] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, but a material commonly used for the positive electrode current collector of lithium-sulfur batteries can be appropriately adopted. Examples of materials used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may also have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector layer may be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0022] The shape of the positive electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0023] The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0024] 〈Positive electrode active material layer〉 The positive electrode active material layer contains at least sulfur as the positive electrode active material, and may further optionally contain a conductive assistant, a binder, a solid electrolyte, etc. The positive electrode active material layer may also contain various additives. The content of each of the positive electrode active material, conductive assistant, binder, solid electrolyte, etc. in the positive electrode active material layer may be appropriately determined according to the intended battery performance. For example, taking the whole of the positive electrode active material layer (the whole solid content) as 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, and may also be 100% by mass or less, or 90% by mass or less.

[0025] (Positive electrode active material) As the positive electrode active material, as described above, at least sulfur is used. Sulfur may be any substance that can function as a positive electrode active material, and may be elemental sulfur or a sulfur compound.

[0026] In addition, the positive electrode active material layer may contain a positive electrode active material other than elemental sulfur and sulfur compounds. Examples of positive electrode active materials other than elemental sulfur and sulfur compounds include various lithium-containing compounds. Lithium-containing compounds include, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), lithium nickel cobalt manganate (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, lithium nickel cobalt aluminate (NCA; LiNi x Co y Al z O2), Li 1+x Mn 2-x-y M y O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element substituted Li-Mn spinel with a composition represented by this, but is not limited thereto.

[0027] The proportion of elemental sulfur and sulfur compounds contained in the positive electrode active material layer is not particularly limited, but may be 50% to 100% by mass, 60% to 100% by mass, 70% to 100% by mass, 80% to 100% by mass, or 90% to 100% by mass relative to the positive electrode active material layer.

[0028] The shape of the positive electrode active material is not particularly limited, as long as it is a shape common for positive electrode active materials in lithium-sulfur batteries. The positive electrode active material may, for example, be particulate. The positive electrode active material may be solid, hollow, have voids, or be porous. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter D of the positive electrode active material 50 For example, it may be 1 nm or more, 5 nm or more, or 10 nm or more, and it may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D 50 This is the particle diameter (median diameter) at 50% of the integrated value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0029] (Conductive additive) The conductive additive is not particularly limited. Examples of conductive additives include, but are not limited to, vapor-deposited carbon fibers (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF). The conductive additive may be particulate or fibrous, and its size is not particularly limited. While the conductive additive is not particularly limited, it may be used alone or in combination of two or more types.

[0030] (Binder) The binder is not particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc., but is not limited to these. The binder is not particularly limited, and may be used alone or in combination of two or more types.

[0031] (solid electrolyte) The material of the solid electrolyte is not particularly limited and may be a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte, etc.

[0032] For sulfide solid electrolytes, please refer to the description in "<First Solid Electrolyte Layer>" below. Similarly, for polymer electrolytes, please refer to the description in "<Second Solid Electrolyte Layer>" below.

[0033] An example of an oxide solid electrolyte is Li7La3Zr2O 12 Li 7-x La3Zr 1-x Nb x O 12 Li 7-3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x Examples include (LiPON), but are not limited to these.

[0034] The oxide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0035] The shape of the positive electrode active material layer is not particularly limited, but may be, for example, a sheet-like positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0036] The positive electrode layer can be manufactured by applying known methods. For example, the positive electrode active material layer can be easily formed by dry or wet molding of a positive electrode mixture containing the above-mentioned components. The positive electrode active material layer may be formed together with the positive electrode current collector layer, or it may be formed separately from the positive electrode current collector layer.

[0037] <First solid electrolyte layer> In the lithium-sulfur battery of this disclosure, the first solid electrolyte layer includes a sulfide solid electrolyte.

[0038] The first solid electrolyte layer contains a sulfide solid electrolyte and may optionally contain a binder or the like.

[0039] (Sulfide solid electrolyte) Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include the Li2S-P2S5 system (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li 13 GeP3S 16 Li 10 GeP2S 12 etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x Etc.; or combinations thereof, but not limited to these.

[0040] The sulfide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0041] For information on the binder, please refer to the description in "〈Positive Electrode Active Material Layer〉" above.

[0042] The thickness of the first solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0043] The first solid electrolyte layer can be easily formed, for example, by dry or wet molding an electrolyte mixture containing the above-mentioned sulfide solid electrolyte and binder.

[0044] <Second solid electrolyte layer> In the lithium-sulfur battery of this disclosure, the second solid electrolyte layer comprises a polymer electrolyte and / or a gel electrolyte. The second solid electrolyte layer is not particularly limited, but preferably comprises a polymer electrolyte.

[0045] (Polymer electrolyte) A polymer electrolyte is an electrolyte in which the solvent component content is 5% by mass or less. The solvent content may be 3% by mass or less, or 1% by mass or less.

[0046] The polymer electrolyte contains at least a polymer component. Examples of polymer components include, but are not limited to, polyether polymers, polyester polymers, polyamine polymers, and polysulfide polymers. From the viewpoint of mechanical properties such as ionic conductivity and Young's modulus, polyether polymers are preferred.

[0047] The polyether polymer is not particularly limited, but polyethylene oxide is preferred. That is, the polymer electrolyte is not particularly limited, but it is preferable to include polyethylene oxide.

[0048] The polyether polymer is not particularly limited, but it is preferable that the main chain of the repeating units has a polyether structure. Examples of polyether structures include, but are not limited to, polyethylene oxide (PEO) structures and polypropylene oxide (PPO) structures.

[0049] The polyether polymer is not particularly limited, but it is preferable that it has a PEO structure as its main repeating unit. The proportion of the PEO structure may be, for example, 50-100 mol%, 60-100 mol%, 70-100 mol%, 80-100 mol%, or 90-100 mol%. The polyether polymer may also be, for example, a homopolymer or copolymer of an epoxy compound (e.g., ethylene oxide, propylene oxide).

[0050] The polymer may have the following ion-conducting units as polymer components. Examples of ion-conducting units include polyethylene oxide, polypropylene oxide, polymethacrylate, polyacrylic acid, polydimethylsiloxane, polyacrylic acid, polymethacrylate, polyethylene vinyl acetate, polyimide, polyamine, polyamide, polyalkyl carbonate, polynitrile, polyphosphazene, polyolefin, and polydiene.

[0051] The weight-average molecular weight of the polymer component is not particularly limited, but is, for example, between 1,000,000 and 10,000,000. The weight-average molecular weight can be determined by gel permeation chromatography (GPC).

[0052] The polymer electrolyte may be a single polymer component used alone, or a combination of two or more polymer components. Furthermore, the polymer electrolyte may be a crosslinked polymer electrolyte in which the polymer components are crosslinked, or an uncrosslinked polymer electrolyte in which the polymer components are not crosslinked.

[0053] The polymer electrolyte may contain a supporting salt (lithium salt). The supporting salt (lithium salt) is not particularly limited, but examples include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, and LiAsF6. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. For example, if the polymer electrolyte has EO units (C2H5O units), the amount of EO units per mole of supporting salt is not particularly limited, but may be 5 moles or more, 10 moles or more, or 15 moles or more, or 40 moles or less, or 30 moles or less.

[0054] (Gel electrolyte) Gel electrolytes contain an electrolyte solution in addition to a polymer electrolyte.

[0055] (electrolyte) The electrolyte is not particularly limited, but it is preferable that it contains a supporting salt and a solvent. For the supporting salt, refer to the description in "(polymer electrolyte)" above.

[0056] The solvent used in the electrolyte is not particularly limited, but examples include cyclic carbonates and linear carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Examples of solvents include, but are not limited to, acetates such as methyl acetate and ethyl acetate, and ethers such as 2-methyltetrahydrofuran. Examples of solvents include, but are not limited to, γ-butyllactone, sulfolane, N-methylpyrrolidone (NMP), and 1,3-dimethyl-2-imidazolidinone (DMI). The solvent may also be water.

[0057] The thickness of the second solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0058] The second solid electrolyte layer can be easily formed, for example, by dissolving the above-mentioned polymer electrolyte and / or gel electrolyte, and supporting salts, etc., in a solvent and molding it from a second solid electrolyte layer precursor solution containing the above-mentioned components.

[0059] <Negative electrode layer> The negative electrode layer may consist only of a negative electrode current collector layer, or it may comprise both a negative electrode active material layer and a negative electrode current collector layer. During battery charging, lithium ions that have moved from the positive electrode may receive electrons and be deposited as metallic lithium between the second solid electrolyte layer and the negative electrode current collector layer. Alternatively, lithium ions that have moved from the positive electrode during battery charging may receive electrons and be retained in the negative electrode active material of the negative electrode active material layer. During battery discharge, the lithium in the negative electrode layer is ionized and returned to the positive electrode layer.

[0060] <Negative electrode active material layer> The negative electrode active material layer contains at least negative electrode active material and may optionally contain conductive additives, binders, and solid electrolytes. The negative electrode active material layer may also contain various other additives. The respective content of negative electrode active material, conductive additives, binders, and solid electrolytes in the negative electrode active material layer can be appropriately determined according to the desired battery performance. For example, with the total (total solid content) of the negative electrode active material layer being 100% by mass, the content of negative electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or it may be 100% by mass or less, or 90% by mass or less.

[0061] (Negative electrode active material) As the negative electrode active material, various materials can be used whose potential for intercalating and releasing lithium ions (charge / discharge potential) is lower than that of the positive electrode active material described above. The material of the negative electrode active material is not particularly limited and may be metallic lithium, or any material capable of intercalating and releasing metallic ions such as lithium ions. Examples of materials capable of intercalating and releasing metallic ions such as lithium ions include, but are not limited to, alloy-based negative electrode active materials or carbon materials. Among these, the material of the negative electrode active material is not particularly limited, but metallic lithium is preferred.

[0062] The alloy-based anode active material is not particularly limited and includes, for example, Si alloy-based anode active materials or Sn alloy-based anode active materials. Si alloy-based anode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, or solid solutions thereof. Si alloy-based anode active materials may also contain metallic elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. Sn alloy-based anode active materials include tin, tin oxide, tin nitride, or solid solutions thereof. Sn alloy-based anode active materials may also contain metallic elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0063] The carbon material is not particularly limited and examples include hard carbon, soft carbon, and graphite.

[0064] The shape of the negative electrode active material is not particularly limited, but any shape common to negative electrode active materials in lithium-sulfur batteries is acceptable. The negative electrode active material may be in the form of a sheet, or it may be in the form of parts. The negative electrode active material may involve the deposition of lithium during charging, or the dissolution of lithium during discharging. In this case, the negative electrode active material layer may be a layer made of metallic lithium or a lithium alloy (for example, metallic lithium foil or lithium alloy foil).

[0065] The conductive additives, binders, and solid electrolytes that may be included in the negative electrode active material layer can be found by referring to the description in "Positive Electrode Active Material Layer" above.

[0066] The shape of the negative electrode active material layer is not particularly limited, but may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0067] <Negative electrode current collector> The material used for the negative electrode current collector layer is not particularly limited, but a material commonly used for the negative electrode current collector of lithium-sulfur batteries can be appropriately adopted. Examples of materials used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or carbon sheets. In particular, from the viewpoint of ensuring reduction resistance and being less prone to alloying with lithium, the material used for the negative electrode current collector layer may contain at least one metal selected from Cu, Ni, and stainless steel, or it may be made of a carbon sheet. The negative electrode current collector layer may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc.

[0068] The shape of the negative electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0069] The thickness of the negative electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0070] The negative electrode layer can be manufactured by applying known methods. For example, the negative electrode active material layer can be easily formed by dry or wet molding of a negative electrode mixture containing the above-mentioned components. The negative electrode active material layer may be molded together with the negative electrode current collector layer, or it may be molded separately from the negative electrode current collector layer.

[0071] Figure 1 is a schematic diagram showing one embodiment of the lithium-sulfur battery of the present disclosure, but is not limited to this embodiment.

[0072] The lithium-sulfur battery 100 in Figure 1 has a structure in which a positive electrode layer 110, a first solid electrolyte layer 210, a second solid electrolyte layer 220, and a negative electrode layer 310 are stacked. The positive electrode layer 110 contains sulfur, and the first solid electrolyte layer 210 contains a sulfide solid electrolyte. The second solid electrolyte layer 220 contains a polymer electrolyte and / or a gel electrolyte. Because the second solid electrolyte layer contains a polymer electrolyte and / or a gel electrolyte, it is relatively flexible and can follow the expansion and contraction associated with the charging and discharging of the sulfur-containing positive electrode layer, thereby suppressing short circuits. Furthermore, because the first solid electrolyte contains a sulfide solid electrolyte, the barrier to lithium insertion into the positive electrode layer can be reduced, thereby enabling the lithium-sulfur battery to obtain a high battery capacity.

[0073] Manufacturing method for lithium-sulfur batteries The lithium-sulfur battery of this disclosure can be manufactured by a manufacturing method that includes the following steps. A preliminary laminate is formed by stacking a preliminary positive electrode layer containing sulfur and a sulfide containing phosphorus and sulfur, the first solid electrolyte layer, the second solid electrolyte layer, and the negative electrode layer in this order. By performing a discharge operation on the above-mentioned pre-laminate, a portion of the sulfur in the pre-positive electrode layer, as well as sulfides containing phosphorus and sulfur elements, are reacted with lithium to produce a sulfide solid electrolyte, thereby forming the positive electrode layer.

[0074] <Formation of pre-layers> This may also include forming a pre-laminate by stacking a pre-positive electrode layer containing sulfur and a sulfide containing phosphorus and sulfur, the first solid electrolyte layer, the second solid electrolyte layer, and the negative electrode layer in this order.

[0075] <Reserve positive electrode layer> The preliminary cathode layer contains sulfur, as well as sulfides containing phosphorus and sulfur elements.

[0076] (Sulfides containing phosphorus and sulfur elements) The sulfide contains at least phosphorus and sulfur. The pre-positive electrode layer may contain only sulfides containing phosphorus and sulfur, or it may further contain sulfides containing other elements (e.g., Ge, Sn, Si, B, or Al) and sulfur. In the latter case, it is preferable that the pre-positive electrode layer contains sulfides containing phosphorus and sulfur as the main sulfide components.

[0077] The sulfide preferably contains an ortho structure of the phosphorus element. Examples of the ortho structure of the phosphorus element include, but are not limited to, the PS4 structure. The sulfide may also contain an ortho structure of the M element (where M is, for example, Ge, Sn, Si, B, or Al). Examples of the ortho structure of the M element include, but are not limited to, the GeS4 structure, SnS4 structure, SiS4 structure, BS3 structure, AlS3 structure, etc. On the other hand, the sulfide may also contain a sulfide of the phosphorus element (e.g., P2S5). Furthermore, the sulfide may contain a sulfide of the M element (M x S y ) may have ) where x and y are integers that give electrical neutrality with S depending on the type of M. sulfide (M x S yExamples of such materials include GeS2, SnS2, SiS2, B2S3, and Al2S3, but are not limited to these cases.

[0078] The sulfur element in the sulfide may have a chemical bond (SS bond) with elemental sulfur or sulfur compound used as the positive electrode active material. In particular, it is preferable that the sulfur element in the ortho structure has a chemical bond (SS bond) with elemental sulfur used as the positive electrode active material.

[0079] In the pre-positive electrode layer, the molar ratio of phosphorus to sulfur (phosphorus / sulfur) is not particularly limited, but may be 0.03 or higher, 0.06 or higher, 0.09 or higher, or 0.12 or higher, or 0.50 or lower, 0.30 or lower, or 0.27 or lower. The denominator of the molar ratio (phosphorus / sulfur) represents the total amount of sulfur contained in the pre-positive electrode layer. In this disclosure, since both the positive electrode active material and the sulfide contain sulfur, it is the total amount of sulfur from both.

[0080] (Lithium element in the preliminary electrode layer) The pre-positive electrode layer does not need to contain substantially no lithium. "Substantially no lithium" means that the proportion of lithium to all elements in the pre-positive electrode layer is 20 mol% or less. The proportion of lithium may be 15 mol% or less, 10 mol% or less, 5 mol% or less, or 1 mol% or less.

[0081] Positive electrode composites containing a solid electrolyte with lithium are known. For example, when a solid electrolyte using Li2S as a raw material is used, batteries using such a positive electrode composite in the positive electrode layer tend to have a lower capacity due to the low water resistance of Li2S. In contrast, in the manufacturing method of the lithium-sulfur battery of this disclosure, if the preliminary positive electrode layer substantially does not contain lithium (e.g., Li2S), the decrease in the capacity of the lithium-sulfur battery can be suppressed.

[0082] For the first solid electrolyte layer, the second solid electrolyte layer, and the negative electrode layer, please refer to the description in "<Construction of a Lithium-Sulfur Battery>" above.

[0083] The method for forming the pre-laminate is not particularly limited, but specifically, for example, a first solid electrolyte layer is placed on top of a pre-positive electrode layer and pressed to obtain a laminate of the pre-positive electrode layer and the first solid electrolyte layer. Then, a second solid electrolyte layer and a negative electrode layer are laminated on top of the first solid electrolyte layer of this laminate in that order, the positive and negative electrode terminals are connected, and the laminate is sealed with a laminating film.

[0084] <Formation of the positive electrode layer> The method for manufacturing a lithium-sulfur battery according to this disclosure may include performing a discharge operation on the pre-layer to react a portion of the sulfur in the pre-positive electrode layer, as well as a sulfide containing phosphorus and sulfur elements, with lithium to produce a sulfide solid electrolyte, thereby forming the positive electrode layer.

[0085] (discharge operation) The discharge operation is not particularly limited, but can be performed in a temperature environment of 60°C or higher. The temperature environment may be 80°C or higher, or 100°C or higher, or 200°C or lower. Normally, the discharge operation is performed on the pre-laminate when the surface temperature of the pre-laminate is the same as the ambient temperature.

[0086] The discharge rate in the discharge operation is not particularly limited, but may be, for example, 0.01C or higher, 0.05C or higher, or 0.10C or higher, or it may be 0.50C or lower, or 0.33C or lower.

[0087] When performing the discharge operation, the pre-electrode stack may be restrained, and the pre-electrode layer may be restrained at, for example, 1 MPa, but is not limited to this case.

[0088] It is preferable that sulfides act as ion conduction paths during charging and discharging. During discharge, lithium ions are conducted from the negative electrode layer to the pre-positive electrode layer via the second solid electrolyte and the first solid electrolyte. Upon reaching the pre-positive electrode layer, lithium ions react with the positive electrode active material. If sulfides are not present in the pre-positive electrode layer, the ion conductivity of the discharge product of sulfur as the positive electrode active material (e.g., Li2S) is low, resulting in insufficient ion conduction paths within the pre-positive electrode layer and hindering the discharge reaction. On the other hand, if sulfides are present in the pre-positive electrode layer, even if the ion conductivity of the discharge product of sulfur as the positive electrode active material (e.g., Li2S) is low, the sulfides ensure ion conduction paths within the pre-positive electrode layer, allowing the discharge reaction to proceed more easily. [Examples]

[0089] The present disclosure will be further described with reference to the following embodiments, but the scope of the present disclosure is not limited to these embodiments.

[0090] Example 1 <Preparation of a preliminary cathode layer> Sulfur (S) (42 parts by mass) as the positive electrode active material, phosphorus pentasulfide (P2S5) (23 parts by mass) as a sulfide containing phosphorus and sulfur elements, and vapor-grown carbon fiber (VGCF) (35 parts by mass) as a conductive additive were mixed using a ball mill. The resulting mixed powder was placed in a polypropylene (PP) container, and a 5% by mass mesitylene solution of a styrene-based binder and mesitylene were added. The mixture was dispersed for 30 seconds using an ultrasonic dispersion device (UH-50, manufactured by SMT Corporation), and then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to prepare a preliminary positive electrode slurry. The obtained preliminary positive electrode slurry was then applied to an aluminum (Al) foil, which served as the positive electrode current collector, using an applicator and the blade method until the basis weight was 7.6 mg / cm². 2 The material was prepared and coated, air-dried, and then dried on a hot plate heated to 100°C for 30 minutes to obtain a preliminary positive electrode layer formed on the Al foil.

[0091] <Preparation of a sulfide solid electrolyte layer> A sulfide solid electrolyte was obtained by mixing L2S-P2S5 glass ceramics containing lithium iodide (LiI) using a ball mill and firing the mixture. Next, the obtained sulfide solid electrolyte was placed in a PP container, and a 5% by mass heptane solution of a butylene rubber-based binder and heptane were added. The mixture was dispersed for 30 seconds using an ultrasonic dispersion device (UH-50, manufactured by SMT Co., Ltd.), and then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to prepare a sulfide solid electrolyte slurry. The sulfide solid electrolyte slurry was coated onto a PET film using an applicator with a blade method, air-dried, and then dried on a hot plate heated to 100°C for 30 minutes to obtain a coating film formed on the PET film. The coated surfaces of the coating films formed on the PET film were overlapped and pressed with 7 tons of pressure, and then the PET film was peeled off to obtain a sulfide solid electrolyte layer.

[0092] <Fabrication of polymer electrolyte layer> Polyethylene oxide (PEO) and bis(trifluoromethanesulfonyl)imide lithium (LiTFSI) were dissolved in acetonitrile. The molar ratio of C2H5O units (EO units) of polyethylene oxide to lithium (Li) in LiTFSI (EO / Li) was adjusted to EO / Li = 20 / 1. Benzoyl peroxide (BPO) was added to this solution as an initiator at a concentration of 10% by mass relative to the total amount of PEO and LiTFSI. The mixture was stirred until a homogeneous solution was obtained, thus preparing a polymer electrolyte layer precursor solution. Next, the polymer electrolyte layer precursor solution was coated onto a polyethylene terephthalate (PET) film using an applicator via the blade method. The film was dried on a hot plate heated to 100°C for 30 minutes, and then the PET film was peeled off to obtain the polymer electrolyte layer.

[0093] <Preparation of Preliminary Laminate A1> A metallic lithium layer, to be used as the negative electrode layer, was punched out to a diameter of φ13.00 mm. Similarly, the polymer electrolyte layer and the sulfide solid electrolyte layer were punched out to a diameter of φ14.50 mm, and the preliminary positive electrode layer was punched out to a diameter of φ11.28 mm. The sulfide solid electrolyte layer, to be used as the first solid electrolyte layer, was placed on top of the circularly processed preliminary positive electrode layer, and then pressed with 7 tons to obtain a laminate of the preliminary positive electrode layer and the sulfide solid electrolyte layer. On top of the sulfide solid electrolyte layer of this laminate, the polymer electrolyte layer, to be used as the second solid electrolyte layer, and the metallic lithium layer, to be used as the negative electrode layer were laminated in this order, the positive and negative electrode terminals were connected, and it was sealed with a laminate film to obtain preliminary laminate A1.

[0094] <Fabrication and electrochemical evaluation of lithium-sulfur battery B1> The preliminary laminate A1 was restrained with a metal plate at a pressure of 1 MPa. Next, it was placed in a constant temperature bath at 60°C, and a constant current (0.06 mA / cm²) was applied within a cutoff voltage range of 1.2 to 3.1 V. 2 Discharge measurements were performed using the test to obtain lithium-sulfur battery B1. Then, charge measurements were performed under the same constant current conditions. The discharge capacity of lithium-sulfur battery B1 was 6.3 mAh, and the charge capacity was 5.0 mAh, and no short circuit occurred.

[0095] Comparative Example 1 <Fabrication of pre-layer a1, fabrication of lithium-sulfur battery b1, and electrochemical evaluation> A metallic lithium layer was punched out to a diameter of φ13.00 mm to serve as the negative electrode layer. Similarly, a sulfide solid electrolyte layer was punched out to a diameter of φ14.50 mm, and a preliminary positive electrode layer was punched out to a diameter of φ11.28 mm. The circular preliminary positive electrode layer was pressed with a 7-ton press, and the sulfide solid electrolyte layer as the first solid electrolyte layer and the metallic lithium layer as the negative electrode layer were laminated on top of it in that order. The positive and negative electrode terminals were connected, and the assembly was sealed with a laminate film to obtain preliminary laminate a1. Preliminary laminate a1 is a laminate that does not include the polymer electrolyte layer, which is the second solid electrolyte layer, compared to preliminary laminate A1. The electrochemical evaluation of preliminary laminate a1 was performed in the same manner as the electrochemical evaluation of preliminary laminate A1, and lithium sulfur battery b1 was obtained. The discharge capacity of lithium sulfur battery b1 was 6.3 mAh, but the charge capacity could not be obtained due to a short circuit.

[0096] Comparative Example 2 <Fabrication of pre-layer a2, fabrication of lithium-sulfur battery b2, and electrochemical evaluation> A metallic lithium layer was punched out to a diameter of φ13.00 mm to serve as the negative electrode layer. Similarly, a polymer electrolyte layer was punched out to a diameter of φ14.50 mm, and a preliminary positive electrode layer was punched out to a diameter of φ11.28 mm. The circular preliminary positive electrode layer was pressed with a 7-ton press, and a polymer electrolyte layer as the second solid electrolyte layer and a metallic lithium layer as the negative electrode layer were laminated on top of it in that order. The positive and negative electrode terminals were connected, and the assembly was sealed with a laminate film to obtain preliminary laminate a2. Preliminary laminate a2 is a laminate that does not include the sulfide solid electrolyte layer, which is the first solid electrolyte layer, compared to preliminary laminate A1. The electrochemical evaluation of preliminary laminate a2 was performed in the same manner as the electrochemical evaluation of preliminary laminate A1, and a lithium sulfur battery b2 was obtained. The discharge capacity of lithium sulfur battery b2 was 1.3 mAh, the charge capacity was 0.8 mAh, and no short circuits occurred.

[0097] Table 1 shows the electrochemical evaluations of Example 1, Comparative Examples 1 and 2.

[0098] [Table 1]

[0099] Lithium-sulfur battery b1 performed well during the initial discharge measurement, but a short circuit occurred during the subsequent charge measurement. The cause of the short circuit in lithium-sulfur battery b1 is presumed to be that the sulfide solid electrolyte layer could not keep up with the expansion of the sulfur-containing positive electrode layer during the discharge measurement, causing cracks within the layer, which then led to the deposition of lithium during the subsequent charge process.

[0100] Lithium-sulfur battery b2 did not experience a short circuit, but its initial discharge capacity was significantly reduced. This is presumed to be because there was an obstacle to lithium insertion from the polymer electrolyte layer to the sulfur-containing positive electrode layer, preventing sufficient insertion of lithium between the positive electrode active material and the lithium.

[0101] On the other hand, lithium-sulfur battery B1 performed well during the initial discharge measurement, achieving a discharge capacity of 6.3 mAh, and also achieved a charge capacity of 5.0 mAh during the subsequent charge measurement, with no short circuits occurring. From the above, it became clear that by placing a sulfide solid electrolyte between the sulfur-containing positive electrode layer and the polymer electrolyte layer, short circuits associated with charging and discharging can be suppressed, and a high battery capacity can be obtained.

[0102] While preferred embodiments of the lithium-sulfur battery and the method for manufacturing the lithium-sulfur battery are described herein, those skilled in the art will understand that modifications are possible without departing from the claims. [Explanation of Symbols]

[0103] 100-unit lithium-ion sulfur battery 110 Positive electrode layer 210 First solid electrolyte layer 220 Second solid electrolyte layer 310 Negative electrode layer

Claims

1. It is a lithium-sulfur battery, The lithium-sulfur battery has a positive electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a negative electrode layer in this order. The first solid electrolyte layer contains a sulfide solid electrolyte, and The second solid electrolyte layer comprises a polymer electrolyte and / or a gel electrolyte. Lithium-sulfur battery.

2. The negative electrode layer has a negative electrode current collector layer, and The lithium-sulfur battery according to claim 1, wherein lithium ions that have moved from the positive electrode layer during charging are deposited as metallic lithium between the second solid electrolyte layer and the negative electrode current collector layer.

3. The lithium sulfur battery according to claim 1, wherein the second solid electrolyte layer comprises a polymer electrolyte.

4. The lithium sulfur battery according to claim 3, wherein the polymer electrolyte comprises polyethylene oxide.

5. A method for manufacturing a lithium sulfur battery according to any one of claims 1 to 4, comprising the following steps: A pre-laminate is formed by stacking a pre-positive electrode layer containing sulfur and a sulfide containing phosphorus and sulfur, the first solid electrolyte layer, the second solid electrolyte layer, and the negative electrode layer in this order. By performing a discharge operation on the pre-laminate, a portion of the sulfur in the pre-positive electrode layer, as well as sulfides containing phosphorus and sulfur elements, are reacted with lithium to produce a sulfide solid electrolyte, thereby forming the positive electrode layer.

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