Lithium metal secondary battery

Abstract

To provide a lithium metal secondary battery in which resistance can be reduced and reversible capacity can be increased.SOLUTION: A lithium metal secondary battery includes a negative electrode current collector layer 110, a composite alloy layer 120, a lithium metal layer 121, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150, in this order, and the composite alloy layer 120 contains a combination of a lithium-gallium alloy and a lithium-tin alloy and / or a lithium-indium alloy.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to lithium metal secondary batteries. [Background technology]

[0002] Lithium metal secondary batteries use lithium metal, which has a high ionization tendency among metals, as the negative electrode active material. Lithium metal secondary batteries have a large potential difference between the negative electrode and the positive electrode, a high output voltage can be obtained, and a high theoretical capacity density, so that their practical use is expected, and the following lithium metal secondary batteries have been disclosed.

[0003] For example, Patent Document 1 discloses a lithium metal secondary battery having a solid electrolyte layer between a positive electrode and a negative electrode, the negative electrode having a negative electrode current collector and a protective layer, the protective layer containing a metal capable of being alloyed with lithium, and having a volumetric capacity density of 1000 mAh / L or more. According to the lithium metal secondary battery of Patent Document 1, it is said that durability can be improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-035226 A Summary of the Invention [Problem to be solved by the invention]

[0005] Although lithium metal secondary batteries are expected to have excellent battery characteristics, in reality, they have high resistance and small reversible capacity, so there is room for improvement in terms of resistance and reversible capacity.

[0006] Therefore, an object of the present disclosure is to provide a lithium metal secondary battery that can reduce resistance and increase reversible capacity. [Means for solving the problem]

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

[0008] <Aspect 1> A negative electrode current collector layer, a composite alloy layer, a lithium metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer, in this order; The composite alloy layer comprises a combination of a lithium-gallium alloy and a lithium-tin alloy and / or a lithium-indium alloy; Lithium metal secondary battery. <Aspect 2> the composite alloy layer comprises a lithium-gallium alloy and a lithium-tin alloy; and The atomic ratio of gallium to the total of gallium and tin in the composite alloy layer is 10 to 90 atomic %. 2. The lithium metal secondary battery of embodiment 1. <Aspect 3> the composite alloy layer comprises a lithium-gallium alloy and a lithium-indium alloy; and The atomic ratio of gallium to the total of gallium and indium in the composite alloy layer is 10 to 45 atomic %. 3. The lithium metal secondary battery according to claim 1 or 2. Effect of the Invention

[0009] The lithium metal secondary battery of the present disclosure can reduce resistance and increase reversible capacity. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating a lithium metal secondary battery of the present disclosure. [Diagram 2]FIG. 2 shows a surface SEM image of the composite metal layer A3 of Example 3, and an image showing the results of EDX mapping analysis by surface SEM-EDX for each element (FIG. 2(A) is a surface SEM image, (B) is a superposition of the elements oxygen (O), iron (Fe), nickel (Ni), gallium (Ga), and tin (Sn), (C) is oxygen (O), (D) is iron (Fe), (E) is nickel (Ni), (F) is gallium (Ga), and (G) is tin (Sn)). [Diagram 3] FIG. 3 shows images of the lithium metal secondary battery D3 of Example 3, showing the results of EDX mapping analysis by cross-sectional SEM-EDX for each element (FIG. 3(A) superposition of the elements sulfur (S), oxygen (O), iron (Fe), nickel (Ni), gallium (Ga), and tin (Sn); FIG. 3(B) sulfur (S); FIG. 3(C) oxygen (O); FIG. 3(D) iron (Fe); FIG. 3(E) nickel (Ni); FIG. 3(F) gallium (Ga); and FIG. 3(G) tin (Sn)). [Figure 4] FIG. 4 shows cross-sectional SEM images of the lithium metal secondary battery D3 of Example 3 (FIG. 4(A) is a cross-sectional SEM image, FIG. 4(B) is a schematic diagram of the cross-sectional structure). [Diagram 5] FIG. 5 shows images of the composite metal layer A7 of Example 7, including a surface SEM image and the results of EDX mapping analysis by surface SEM-EDX, for each element (FIG. 5(A) is a surface SEM image, (B) is a superposition of the elements oxygen (O), gallium (Ga), and indium (In), (C) is oxygen (O), (D) is gallium (Ga), and (E) is indium (In)). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the 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. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions will be omitted.

[0012] In the present disclosure, a "composite" refers to a composition that can constitute a positive electrode active material layer or an electrolyte layer as it is or by further containing other components, and a "composite slurry" refers to a slurry that contains a dispersion medium in addition to a "composite" and can be applied and dried to form a positive electrode active material layer or an electrolyte layer.

[0013] The lithium metal secondary battery of the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer, or may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. In the present disclosure, a "solid-state battery" means a battery using at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The lithium metal secondary battery of the present disclosure may also be an all-solid-state battery, i.e., a battery using only a solid electrolyte as an electrolyte.

[0014] Lithium metal secondary battery The lithium metal secondary battery of the present disclosure has, in this order, a negative electrode current collector layer, a composite alloy layer, a lithium metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer; and The composite alloy layer includes a combination of a lithium-gallium alloy with a lithium-tin alloy and / or a lithium-indium alloy.

[0015] The lithium metal secondary battery of the present disclosure can reduce resistance and increase reversible capacity.

[0016] In the present disclosure, the composite alloy layer can be formed from a composite metal layer including, but not limited to, a combination of gallium and tin and / or indium. Specifically, the composite metal layer forms a composite such that gallium surrounds tin particles or indium particles, as shown in FIG. 2 and FIG. 5. By performing a charging operation on a lithium metal secondary battery including a composite metal layer, the gallium, tin and / or indium of the composite metal layer react with the lithium that has been transferred from the positive electrode active material layer that holds lithium, and each metal in the composite metal layer is alloyed with lithium, thereby forming a composite alloy layer including a composite of a lithium-gallium alloy and a lithium-tin alloy and / or a lithium-indium alloy.

[0017] Without being limited to theory, specifically, for example, as shown in FIG. 1, a composite alloy layer 120 containing the above-mentioned composite is formed in the vicinity of the negative electrode current collector layer 110, and it is speculated that this suppresses interfacial peeling between the electrolyte layer 130 and the lithium metal layer 121 during lithium desorption, thereby reducing the resistance and increasing the reversible capacity.

[0018] <Configuration of Lithium Metal Secondary Battery> The lithium metal secondary battery of the present disclosure has, in this order, a negative electrode current collector layer, a composite alloy layer, a lithium metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0019] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, but may be any material generally used as a negative electrode current collector for lithium metal secondary batteries. 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 a carbon sheet. In particular, from the viewpoint of ensuring reduction resistance and being difficult to alloy 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 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 the resistance, etc.

[0020] The shape of the negative electrode current collector layer is not particularly limited, but examples thereof include a foil shape, a plate shape, a mesh shape, etc. Among these, a foil shape is preferred.

[0021] 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, and may be 1 mm or less, or 100 μm or less.

[0022] <Composite alloy layer> The composite alloy layer of the lithium metal secondary battery of the present disclosure includes a combination of a lithium-gallium alloy with a lithium-tin alloy and / or a lithium-indium alloy.

[0023] (Composite alloy layer: Lithium-gallium alloy / Lithium-tin alloy layer) The composite alloy layer of the lithium metal secondary battery of the present disclosure may include a lithium-gallium alloy and a lithium-tin alloy.

[0024] The atomic ratio of gallium to the total of gallium and tin in the composite alloy layer is not particularly limited, but may be 10 to 90 atomic %. This atomic ratio is not particularly limited, but may be 5 atomic % or more, 10 atomic % or more, 20 atomic % or more, 30 atomic % or more, 40 atomic % or more, 50 atomic % or more, or 60 atomic % or more, or may be 95 atomic % or less, 90 atomic % or less, 85 atomic % or less, or 80 atomic % or less.

[0025] The composite alloy layer may further contain a metal other than gallium, tin, and lithium. The metal other than gallium, tin, and lithium is not particularly limited, but may be 0 atomic % or more, 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more in the composite alloy layer, and may be 50 atomic % or less, 20 atomic % or less, or 10 atomic % or less.

[0026] (Composite alloy layer: Lithium-gallium alloy / Lithium-indium alloy layer) The composite alloy layer of the lithium metal secondary battery of the present disclosure may include a lithium-gallium alloy and a lithium-indium alloy.

[0027] The atomic ratio of gallium to the total of gallium and indium in the composite alloy layer is not particularly limited, but may be 10 to 45 atomic %. This atomic ratio is not particularly limited, but may be 5 atomic % or more, 10 atomic % or more, 15 atomic % or more, 20 atomic % or more, 25 atomic % or more, 30 atomic % or more, 35 atomic % or more, or 40 atomic % or more, or may be 90 atomic % or less, 80 atomic % or less, 70 atomic % or less, 60 atomic % or less, 50 atomic % or less, or 45 atomic % or less.

[0028] The composite alloy layer may further contain a metal other than gallium, indium, and lithium. The metal other than gallium, indium, and lithium is not particularly limited, but may be 0 atomic % or more, 1 atomic % or more, 3 atomic % or more, or 5 atomic % or more in the composite alloy layer, and may be 50 atomic % or less, 20 atomic % or less, or 10 atomic % or less.

[0029] The thickness of the composite alloy layer is not particularly limited, and may be 0.1 μm or more, 0.2 μm or more, 0.5 μm or more, 1.0 μm or more, and may be 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less in a fully charged state.

[0030] The composite alloy layer is not particularly limited, but can be easily formed from a composite metal layer containing a combination of gallium, tin and / or indium. Specifically, by performing a charging operation on a lithium metal secondary battery having a composite metal layer, the gallium, tin and / or indium of the composite metal layer react with the lithium that has moved from the positive electrode active material layer that holds lithium, and each metal in the composite metal layer and lithium are alloyed, thereby forming a composite alloy layer containing a composite of a lithium-gallium alloy, a lithium-tin alloy and / or a lithium-indium alloy.

[0031] The composite metal layer can be easily formed on the negative electrode current collector by, for example, a binary deposition method using an ion plating method, but the method is not limited to this.

[0032] <Lithium metal layer> The lithium metal secondary battery of the present disclosure has a lithium metal layer, which functions as a negative electrode active material layer in the lithium metal secondary battery of the present disclosure.

[0033] Here, since the lithium metal layer functions as a "negative electrode active material layer", in a charged state, a layer of lithium metal exists as a "negative electrode active material layer", but in a discharged state, lithium metal moves to the positive electrode active material layer as lithium ions, and the layer of lithium metal as a "negative electrode active material layer" may no longer exist.

[0034] The shape of the lithium metal layer is not particularly limited, and may be, for example, a sheet-like lithium metal layer having a substantially flat surface. The thickness of the lithium metal layer is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less in a fully charged state.

[0035] <Electrolyte layer> <Electrolyte layer - solid electrolyte layer> The lithium metal secondary battery of the present disclosure can be a solid-state battery, i.e., have a solid electrolyte layer as the electrolyte layer.

[0036] The solid electrolyte layer contains a solid electrolyte, and may contain a binder and the like as necessary.

[0037] (solid electrolyte) The material of the solid electrolyte is not particularly limited, and may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte.

[0038] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li 2 SP 2 S 5 System (Li 7 P 3 S 11 , Li 3 P.S. 4 , Li 8 P 2 S 9 etc.), Li 2 S-SiS 2 , LiI-Li 2 S-SiS 2 , LiI-Li 2 SP 2 S 5 , LiI-LiBr-Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -GeS2 (Li 13 GeP 3 S 16 , Li 10 GeP 2 S 12 etc.), LiI-Li 2 SP 2 O 5 , LiI-Li 3 PO 4 -P 2 S 5 , Li 7-x P.S. 6-x Cl x etc.; or combinations thereof, but are not limited to these.

[0039] An example of an oxide solid electrolyte is Li 7 La 3 Zr 2 O 12 , Li 7-x La 3 Zr 1-x Nb x O 12 , Li 7-3x La 3 Zr 2 Al x O 12 , Li 3x La 2 / 3-x TiO 3 , Li 1+x Al x Ti 2-x (PO 4 ) 3 , Li 1+x Al x Ge 2-x (PO 4 ) 3 , Li 3 PO 4 , or Li 3+x PO 4-x N x (LiPON), but is not limited to these.

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

[0041] Examples of the polymer electrolyte include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0042] (Binder) The binder is not particularly limited. The binder may be, for example, a material such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc., but is not limited thereto. The binder is not particularly limited, but only one type may be used alone, or two or more types may be used in combination.

[0043] The thickness of the 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, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0044] The solid electrolyte layer can be easily formed, for example, by dry or wet molding of an electrolyte composite material containing the above-mentioned solid electrolyte and binder.

[0045] 〈Electrolyte layer - Separator layer〉 The lithium metal secondary battery of the present disclosure can be a liquid battery, that is, have an electrolytic solution as the electrolyte layer, particularly an electrolytic solution held in the separator layer.

[0046] (Electrolytic solution) The electrolytic solution is not particularly limited, but preferably contains a supporting salt and a solvent.

[0047] The supporting salt (lithium salt) of the electrolytic solution having lithium ion conductivity is not particularly limited, and examples include inorganic lithium salts and organic lithium salts. Examples of the inorganic lithium salt include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , etc., but are not limited to these cases. Examples of the organic lithium salt include LiCF 3 SO3 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(FSO 2 ) 2 , LiC(CF 3 SO 2 ) 3 The following are examples, but are not limited to these.

[0048] The solvent used in the electrolytic solution is not particularly limited, but may include cyclic carbonates, chain carbonates, etc. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), but are not limited to, ethylene carbonate (BC), etc. Examples of chain carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), but are not limited to, ethyl methyl carbonate (EMC), etc. Examples of the electrolytic solution are not particularly limited, but may be used alone or in combination of two or more.

[0049] (Separator) The separator is not particularly limited, but may be any suitable separator commonly used in lithium metal secondary batteries, such as polyolefin, polyamide, or polyimide nonwoven fabric.

[0050] <Cathode active material layer> The positive electrode active material layer contains at least a positive electrode active material, and may further contain an optional conductive assistant, a solid electrolyte, a binder, and the like. The positive electrode active material layer may also contain various other additives. The contents of the positive electrode active material, the conductive assistant, the binder, and the like in the positive electrode active material layer may be appropriately determined according to the intended battery performance. For example, 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, or 100% by mass or less, or 90% by mass or less, with the entire positive electrode active material layer (total solid content) being 100% by mass.

[0051] (Cathode active material) The material of the positive electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), Lithium nickel-cobalt-manganese oxide (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O 2 , lithium nickel-cobalt-aluminate (NCA; LiNi x Co y Al z O 2 ), Li 1+x Mn 2-x-y M y O 4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), or the like, but is not limited thereto.

[0052] The positive electrode active material may have a coating layer, but is not particularly limited to this. The coating layer is a layer containing a material that has lithium ion conductivity, is low in reactivity with the positive electrode active material and the solid electrolyte, and can maintain the shape of the coating layer without flowing even when it comes into contact with the active material and the solid electrolyte. Specific examples of materials that constitute the coating layer include LiNbO 3 In addition, Li 4 Ti5 O 12 , Li 3 PO 4 These include, but are not limited to, the following.

[0053] The shape of the positive electrode active material is not particularly limited as long as it is a general shape for a positive electrode active material of a lithium metal secondary battery. The positive electrode active material may be, for example, in a particulate form. The positive electrode active material may be a primary particle, or a secondary particle formed by agglomeration of a plurality of primary particles. The average particle diameter D of the positive electrode active material 50 The average particle size D may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. 50 is the particle size (median size) at an integrated value of 50% in the volume-based particle size distribution determined by a laser diffraction / scattering method.

[0054] (Conductive assistant) The conductive assistant is not particularly limited. The conductive assistant may be, for example, vapor grown carbon fiber (VGCF), acetylene black (AB), Ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc., but is not limited thereto. The conductive assistant may be, for example, particulate or fibrous, and its size is not particularly limited. The conductive assistant is not particularly limited, but may be used alone or in combination of two or more kinds.

[0055] For the solid electrolyte and the binder, the above description of "Electrolyte Layer - Solid Electrolyte Layer" can be referred to.

[0056] The shape of the positive electrode active material layer is not particularly limited, and 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, and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0057] <Positive electrode current collector layer> The material used for the positive electrode collector layer is not particularly limited, but may be any material generally used as a positive electrode collector for lithium metal secondary batteries. Examples of materials used for the positive electrode collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. The positive electrode collector layer may have a coating layer on its surface for the purpose of adjusting resistance, etc. The positive electrode collector layer may be a metal foil or a substrate on which the above metal is plated or vapor-deposited.

[0058] The shape of the positive electrode current collector layer is not particularly limited, but examples thereof include a foil shape, a plate shape, a mesh shape, etc. Among these, a foil shape is preferred.

[0059] 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, and may be 1 mm or less, or 100 μm or less.

[0060] The positive electrode active material layer can be manufactured by applying a known method. For example, the positive electrode active material layer can be easily formed by dry or wet forming a positive electrode mixture containing the above-mentioned various components. The positive electrode active material layer may be formed together with the positive electrode current collector layer, or may be formed separately from the positive electrode current collector layer.

[0061] FIG. 1 is a schematic diagram showing one embodiment of a lithium metal secondary battery of the present disclosure, but is not limited to this embodiment.

[0062] In a discharged state, the lithium metal secondary battery 100 may be a battery in which the negative electrode current collector layer 110, the composite alloy layer 120, the electrolyte layer 130, the positive electrode active material layer 140, and the positive electrode current collector layer 150 are laminated in this order as shown in Fig. 1A, and the lithium metal layer 121 may not be present. In a charged state, the lithium metal secondary battery 100 is a battery in which the negative electrode current collector layer 110, the composite alloy layer 120, the lithium metal layer 121, the electrolyte layer 130, the positive electrode active material layer 140, and the positive electrode current collector layer 150 are laminated in this order as shown in Fig. 1B, and the lithium metal layer 121 is present as the negative electrode active material layer. The composite alloy layer 120 includes a combination of a lithium-gallium alloy and a lithium-tin alloy and / or a lithium-indium alloy. Since the composite alloy layer 120 is formed in the vicinity of the negative electrode current collector layer 110, interfacial peeling between the electrolyte layer 130 and the lithium metal layer 121 during lithium desorption is suppressed, thereby reducing resistance and increasing reversible capacity.

[0063] The lithium metal secondary battery of the present disclosure can be produced, for example, by producing a laminate in which a negative electrode current collector layer, a composite metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are stacked in this order, and then housing this laminate in a laminate film, vacuum sealing, and pressing to produce a spare lithium metal secondary battery. By charging this spare lithium metal secondary battery, the metals contained in the composite metal layer react with and alloy with the lithium that has migrated from the positive electrode active material, thereby forming a composite alloy layer, and a lithium metal secondary battery can be obtained, but is not limited to this case.

[0064] The shape of the lithium metal secondary battery may be, for example, a coin type, a laminate type, a cylindrical type, or a square type, but is not limited to these. EXAMPLES

[0065] The present disclosure will be described in more detail with reference to the following examples, but the scope of the present disclosure is not limited to these examples.

[0066] Example 1 <Preparation of Composite Metal Layer A1> A composite metal layer containing gallium and tin was formed to a thickness of 1.0 μm on a stainless steel (SUS) foil as a negative electrode current collector by binary deposition using an ion plating method, to produce a composite metal layer A1 formed on the SUS foil. At this time, the atomic ratio of gallium to the total of gallium and tin was 10 atomic %. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer A1 was 13 atomic %.

[0067] <Preparation of electrolyte layer B1> A sulfide solid electrolyte (92.6 parts by mass) as a solid electrolyte, a binder (7.4 parts by mass), and an appropriate amount of butyl acetate as a dispersion medium were mixed to prepare an electrolyte mixture slurry. The obtained electrolyte mixture slurry was applied to a release film with a coating gap of 325 μm. Next, the film was temporarily dried at room temperature for 3 hours, and then dried at 165° C. for 1 hour. The coated film after the drying was punched out into two pieces with a diameter of 14.50 mm, stacked so that the coated surfaces faced each other, pressed at 7 tons, and the release film was peeled off to produce a free-standing electrolyte layer B1.

[0068] <Preparation of Positive Electrode Active Material Layer C1> A positive electrode composite slurry was prepared by mixing nickel-cobalt-lithium aluminum oxide (NCA) (84.7 parts by mass) as a positive electrode active material, a sulfide solid electrolyte (13.4 parts by mass) as a solid electrolyte, a binder (0.6 parts by mass), a conductive additive (1.3 parts by mass), and an appropriate amount of butyl butyrate as a dispersion medium. The obtained positive electrode composite slurry was applied to an aluminum (Al) foil as a positive electrode current collector with a coating gap of 225 μm, temporarily dried at 60°C, and finally dried at 165°C for 1 hour to prepare a positive electrode active material layer C1 formed on the Al foil. The design capacity of the positive electrode active material layer C1 was 3.0 mAh / cm 2 The weight is 18.7mg / cm 2 It was decided.

[0069] <Preparation of spare lithium metal secondary batteries> The composite metal layer A1 was punched out to φ14.50 mm, and the positive electrode active material layer C1 was punched out to φ11.28 mm. Between the composite metal layer A1 and the positive electrode active material layer C1, the electrolyte layer B1 was placed, and a laminate was produced in which the negative electrode collector layer, the composite metal layer A1, the electrolyte layer B1, the positive electrode active material layer C1, and the positive electrode collector layer were laminated in this order. Next, this laminate was placed in a laminate film, vacuum sealed, and isostatically pressed at 392 MPa by cold isostatic pressing to produce a spare lithium metal secondary battery. Here, aluminum (Al) was used for the positive electrode tab, and nickel (Ni) was used for the negative electrode tab.

[0070] Preparation of Lithium Metal Secondary Battery D1 and Electrochemical Evaluation: First Cycle Reversible Capacity The spare lithium metal secondary battery was restrained at 1 MPa using a constant pressure jig with a spring inserted therein so that the restraining pressure was constant. The spare lithium metal secondary battery was then placed in a thermostatic chamber at 60°C and subjected to a constant current (current density: 0.15 mA / cm) at a cutoff voltage range of 4.2 V to 3.0 V at 60°C. 2 , equivalent to 0.05C) - constant voltage (cutoff current density: 0.03mA / cm 2 A charging test was carried out at a current of 0.01 C. The spare lithium metal secondary battery was charged to cause the gallium and tin contained in the composite metal layer A1 to react with the lithium that had migrated from the positive electrode active material layer, and the gallium and tin were alloyed with the lithium to form a composite alloy layer, yielding a lithium metal secondary battery D1. The first cycle reversible capacity of the lithium metal secondary battery D1 was 2.37 mAh / cm 2 It was.

[0071] Electrochemical measurements of lithium metal secondary battery D1: Resistance after the first charge / discharge After the initial charge and discharge at 60°C, the resistance of the lithium metal secondary battery D1 was measured by an AC impedance method. The resistance of the lithium metal secondary battery D1 was 108 Ω cm 2 It was.

[0072] Example 2 <Preparation of Composite Metal Layer A2> A composite metal layer A2 formed on a SUS foil was produced in the same manner as in Example 1, except that the atomic ratio of gallium to the total of gallium and tin was 20 atomic %. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer A2 was 25 atomic %.

[0073] <Preparation of lithium metal secondary battery D2 and electrochemical measurement> Except for using the composite metal layer A2 instead of the composite metal layer A1, a lithium metal secondary battery D2 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D2 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D2 are shown in Table 1.

[0074] Example 3 <Preparation of composite metal layer A3> A composite metal layer A3 formed on a SUS foil was produced in the same manner as in Example 1, except that the atomic ratio of gallium to the total of gallium and tin was 50 atomic %. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer A3 was 44 atomic %.

[0075] <SEM-EDX observation of the surface of the composite metal layer A3> The surface of the composite metal layer A3 was observed with a scanning electron microscope (SEM) at an applied voltage of 5 kV as a secondary electron image, and element mapping was performed by energy dispersive X-ray analysis (EDX).

[0076] <Preparation of lithium metal secondary battery D3 and electrochemical measurement> Except for using the composite metal layer A3 instead of the composite metal layer A1, a lithium metal secondary battery D3 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D3 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D3 are shown in Table 1.

[0077] <Cross-sectional SEM-EDX observation of lithium metal secondary battery D3> A cross section of the charged lithium metal secondary battery D3 was observed with a scanning electron microscope (SEM) at an applied voltage of 5 kV as a secondary electron image, and element mapping was performed by energy dispersive X-ray analysis (EDX).

[0078] Example 4 <Preparation of composite metal layer A4> A composite metal layer A4 formed on a SUS foil was produced in the same manner as in Example 1, except that the atomic ratio of gallium to the total of gallium and tin was 80 atomic %. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer A4 was 75 atomic %.

[0079] <Preparation of lithium metal secondary battery D4 and electrochemical measurement> Except for using the composite metal layer A4 instead of the composite metal layer A1, a lithium metal secondary battery D4 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D4 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D4 are shown in Table 1.

[0080] Comparative Example 1 <Preparation of composite metal layer a1> A composite metal layer a1 formed on a SUS foil was produced in the same manner as in Example 1, except that the atomic ratio of gallium to the total of gallium and tin was 0 atomic %, i.e., it was produced using only tin. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer a1 was 0 atomic %.

[0081] <Preparation of lithium metal secondary battery d1 and electrochemical measurement> Except for using a composite metal layer a1 instead of the composite metal layer A1, a lithium metal secondary battery d1 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery d1 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery d1 are shown in Table 1.

[0082] Comparative Example 2 <Preparation of composite metal layer a2> A composite metal layer a2 formed on a SUS foil was produced in the same manner as in Example 1, except that the atomic ratio of gallium to the total of gallium and tin was 100 atomic %, i.e., it was produced using only gallium. The atomic ratio of gallium to the total of gallium and tin in the obtained composite metal layer a2 was 100 atomic %.

[0083] <Preparation of lithium metal secondary battery d2 and electrochemical measurement> Except for using the composite metal layer a2 instead of the composite metal layer A1, a lithium metal secondary battery d2 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery d2 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery d2 are shown in Table 1.

[0084] Table 1 shows the evaluation results of electrochemical measurements for Examples 1 to 4 and Comparative Examples 1 and 2.

[0085] [Table 1]

[0086] Surface SEM-EDX observation of composite metal layer A3 showed that gallium surrounded tin particles to form a complex. Cross-sectional SEM-EDX of lithium metal secondary battery D3 showed that lithium-gallium and lithium-tin composite metal layers were formed in the vicinity of the negative electrode current collector layer during lithium insertion during the first charge.

[0087] In Examples 1 to 4, the first cycle reversible capacity at 60° C. was the highest (2.50 mAh / cm ) for the lithium metal secondary battery D4 having a composite alloy layer containing a lithium-gallium alloy and a lithium-tin alloy formed from the composite metal layer A4 (Example 4). 2) was shown. When the composite metal layers A2 and A3 (Examples 2 and 3) were used, an improvement in the first cycle reversible capacity was observed compared to simple tin or simple gallium. Furthermore, with regard to the resistance after the first charge / discharge at 60°C, the lithium metal secondary batteries D1 to D4 having composite alloy layers formed from the composite metal layers A1 to A4 had lower resistance than the lithium metal secondary batteries d1 and d2 having composite alloy layers formed from the composite metals a1 and a2 of simple tin or simple gallium.

[0088] It is presumed that the composite alloy layer formed from a composite metal layer containing a complex formed in such a way that tin particles are surrounded by gallium is formed in the vicinity of the negative electrode current collector layer, thereby suppressing interfacial peeling between the electrolyte layer and the lithium metal layer when lithium is released, thereby reducing the resistance and increasing the reversible capacity.

[0089] Example 5 <Preparation of composite metal layer A5> A composite metal layer containing gallium and indium was formed to a thickness of 1.0 μm on a stainless steel (SUS) foil as a negative electrode current collector by binary deposition using an ion plating method, to produce a composite metal layer A5 formed on the SUS foil. At this time, the atomic ratio of gallium to the total of gallium and indium was 10 atomic %. The atomic ratio of gallium to the total of gallium and indium in the obtained composite metal layer A5 was 15 atomic %.

[0090] <Preparation of lithium metal secondary battery D5 and electrochemical measurement> Except for using the composite metal layer A5 instead of the composite metal layer A1, a lithium metal secondary battery D5 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D5 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D5 are shown in Table 2.

[0091] Example 6 <Preparation of composite metal layer A6> A composite metal layer A6 formed on a SUS foil was produced in the same manner as in Example 5, except that the atomic ratio of gallium to the total of gallium and indium was 20 atomic %. The atomic ratio of gallium to the total of gallium and indium in the obtained composite metal layer A6 was 25 atomic %.

[0092] <Preparation of lithium metal secondary battery D6 and electrochemical measurement> Except for using a composite metal layer A6 instead of the composite metal layer A1, a lithium metal secondary battery D6 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D6 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D6 are shown in Table 2.

[0093] Example 7 <Preparation of composite metal layer A7> A composite metal layer A7 formed on a SUS foil was produced in the same manner as in Example 5, except that the atomic ratio of gallium to the total of gallium and indium was 50 atomic %. The atomic ratio of gallium to the total of gallium and indium in the obtained composite metal layer A7 was 43 atomic %.

[0094] <SEM-EDX observation of the surface of composite metal layer A7> The surface of the composite metal layer A7 was observed with a scanning electron microscope (SEM) at an applied voltage of 5 kV as a secondary electron image, and element mapping was performed by energy dispersive X-ray analysis (EDX).

[0095] <Preparation of lithium metal secondary battery D7 and electrochemical measurement> Except for using a composite metal layer A7 instead of the composite metal layer A1, a lithium metal secondary battery D7 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery D7 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery D7 are shown in Table 2.

[0096] Comparative Example 3 <Preparation of composite metal layer a3> A composite metal layer a3 formed on a SUS foil was produced in the same manner as in Example 5, except that the atomic ratio of gallium to the total of gallium and indium was 0 atomic %, i.e., it was produced using only indium. The atomic ratio of gallium to the total of gallium and indium in the obtained composite metal layer a3 was 0 atomic %.

[0097] <Preparation of lithium metal secondary battery d3 and electrochemical measurement> Except for using a composite metal layer a3 instead of the composite metal layer A1, a lithium metal secondary battery d3 was produced in the same manner as in Example 1. The electrochemical measurement of the lithium metal secondary battery d3 was carried out in the same manner as in Example 1. The first cycle reversible capacity and the resistance after the first charge / discharge of the lithium metal secondary battery d3 are shown in Table 2.

[0098] Table 2 shows the evaluation results of the electrochemical measurements for Examples 5 to 7 and Comparative Examples 2 and 3.

[0099] [Table 2]

[0100] From the surface SEM-EDX observation of the composite metal layer A7, it was confirmed that a composite was formed in which the indium particles were surrounded by the gallium.

[0101] In Examples 5 to 7, the first cycle reversible capacity at 60° C. was the highest (2.41 mAh / cm) for the lithium metal secondary battery D6 having a composite alloy layer containing a lithium-gallium alloy and a lithium-indium alloy formed from the composite metal layer A6 (Example 6). 2 ) was shown. Regarding the resistance after the initial charge and discharge at 60°C, the lithium metal secondary batteries D5 to D7 having composite alloy layers formed from the composite metal layers A5 to A7 had lower resistance than the lithium metal secondary batteries d2 and d3 having composite alloy layers formed from the composite metals a2 and a3 of simple indium and simple gallium.

[0102] It is presumed that the composite alloy layer formed from a composite metal layer containing a complex formed so that indium particles are surrounded by gallium is formed in the vicinity of the negative electrode current collector layer, thereby suppressing interfacial peeling between the electrolyte layer and the lithium metal layer when lithium is released, thereby reducing the resistance and increasing the reversible capacity.

[0103] While preferred embodiments of the lithium metal secondary batteries of the present disclosure have been described, those skilled in the art will recognize that modifications can be made without departing from the scope of the claims. [Explanation of symbols]

[0104] 100 Lithium metal secondary battery 110 Negative electrode current collector layer 120 composite alloy layer 121 Lithium metal layer 130 Electrolyte layer 140 Cathode active material layer 150 Positive electrode current collector layer

Claims

1. A negative electrode current collector layer, a composite alloy layer, a lithium metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer, in this order; The composite alloy layer comprises a combination of a lithium-gallium alloy and a lithium-tin alloy and / or a lithium-indium alloy; Lithium metal secondary battery.

2. the composite alloy layer comprises a lithium-gallium alloy and a lithium-tin alloy; and The atomic ratio of gallium to the total of gallium and tin in the composite alloy layer is 10 to 90 atomic %.

2. The lithium metal secondary battery according to claim 1.

3. the composite alloy layer comprises a lithium-gallium alloy and a lithium-indium alloy; and The atomic ratio of gallium to the total of gallium and indium in the composite alloy layer is 10 to 45 atomic %.

3. The lithium metal secondary battery according to claim 1 or 2.

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