Lithium secondary battery and method for manufacturing lithium secondary battery

Abstract

The purpose of the present disclosure is to provide a lithium secondary battery capable of increasing reversible capacity and improving cycle characteristics, and a method for manufacturing the same. The lithium secondary battery has a negative electrode current collector layer (110), a first lithium-tin alloy layer (120), a lithium-magnesium alloy layer (121), an electrolyte layer (130), a positive electrode active material layer (140), and a positive electrode current collector layer (150) in this order. A method for manufacturing a lithium secondary battery includes: obtaining a preliminary lithium secondary battery (200); by performing a charging operation on the preliminary lithium secondary battery (200), (i) tin of the first metal layer (220) is reacted with lithium moved from the positive electrode active material layer (140) to form the lithium-tin alloy layer; and (ii) reacting the magnesium of the second metal layer (221) with the lithium moved from the positive electrode active material layer (140) to form the lithium-magnesium alloy layer.

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery and a method for manufacturing the same. Background Art

[0002] A lithium secondary battery uses lithium metal and / or a lithium alloy having a high ionization tendency in a metal as a negative electrode active material. Since a lithium secondary battery has a large potential difference between a negative electrode and a positive electrode, a high output voltage can be obtained, and it has a high theoretical capacity density. Therefore, its practical application is expected, and the following batteries have been disclosed.

[0003] For example, Patent Document 1 discloses an all-solid-state battery that uses a precipitation-dissolution reaction of metallic lithium as a reaction of a negative electrode. The all-solid-state battery is characterized by including: a positive electrode including a positive electrode layer; a negative electrode including a negative electrode current collector and a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer includes a β single-phase alloy of metallic lithium and metallic magnesium as a negative electrode active material. When the all-solid-state battery is fully charged, the elemental ratio of lithium element in the alloy is 81.80 atomic % or more and 99.97 atomic % or less. According to Patent Document 1, an all-solid-state battery with high charge-discharge efficiency can be provided.

[0004] Patent Document 2 discloses an all-solid-state secondary battery including: a positive electrode layer including a positive electrode active material layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer and including a solid electrolyte. The negative electrode layer includes a negative electrode current collector, a first negative electrode active material layer in contact with the solid electrolyte layer, and a second negative electrode active material layer disposed between the negative electrode current collector and the first negative electrode active material layer. The first negative electrode active material layer includes a first carbon-based negative electrode active material, and the second negative electrode active material layer includes a second carbon-based negative electrode active material. The intensity ratio (I 1 D / I 1 G ) of the D band peak to the G band peak in the Raman spectrum of the first carbon-based negative electrode active material is lower than the intensity ratio (I 2 D / I 2 G ) of the D band peak to the G band peak in the Raman spectrum of the second carbon-based negative electrode active material. According to Patent Document 2, an all-solid-state secondary battery capable of preventing short circuit and having excellent cycle characteristics can be provided.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-184513

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2021-132033

[0009] Problems to be Solved by the Invention

[0010] Although lithium secondary batteries are expected to have excellent battery characteristics, in reality, they have a small reversible capacity and insufficient cycle characteristics. Therefore, there is room for improvement in lithium secondary batteries from the viewpoints of reversible capacity and cycle characteristics. Summary of the Invention

[0011] Therefore, an object of the present disclosure is to provide a lithium secondary battery capable of increasing the reversible capacity and improving the cycle characteristics.

[0012] Means for Solving the Problems

[0013] The present disclosure achieves the above object by the following means.

[0014] <Mode 1>

[0015] A lithium secondary battery sequentially includes a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0016] <Mode 2>

[0017] In the lithium secondary battery according to Mode 1, in a fully charged state, the thickness of the first lithium-tin alloy layer is 0.1 to 15 μm.

[0018] <Mode 3>

[0019] In the lithium secondary battery according to Mode 1 or 2, in a fully charged state, the thickness of the lithium-magnesium alloy layer is 0.1 to 40 μm.

[0020] <Mode 4>

[0021] In the lithium secondary battery according to any one of Modes 1 to 3, it sequentially includes the negative electrode current collector layer, the first lithium-tin alloy layer, the lithium-magnesium alloy layer, a second lithium-tin alloy layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer.

[0022] <Mode 5>

[0023] In the lithium secondary battery according to any one of Modes 1 to 4,

[0024] in a fully charged state,

[0025] the thickness of the first lithium-tin alloy layer is 0.1 to 15 μm, and,

[0026] The thickness of the second lithium-tin alloy layer is 0.1 to 15 μm.

[0027] <Method 6>

[0028] A method for manufacturing a lithium secondary battery according to any one of Methods 1 to 5, including the following steps:

[0029] Stacking the negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer in this order to obtain a preliminary lithium secondary battery; and

[0030] By performing a charging operation on the preliminary lithium secondary battery, (i) reacting tin in the first metal layer with lithium moving from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) reacting magnesium in the second metal layer with lithium moving from the positive electrode active material layer to form the lithium-magnesium alloy layer.

[0031] <Method 7>

[0032] A method for manufacturing a lithium secondary battery according to any one of Methods 1 to 5, including the following steps:

[0033] Stacking the negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the third metal layer containing tin, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer in this order to obtain the preliminary lithium secondary battery; and

[0034] By performing a charging operation on the preliminary lithium secondary battery, (i) reacting tin in the first metal layer with lithium moving from the positive electrode active material layer to form the first lithium-tin alloy layer, (ii) reacting magnesium in the second metal layer with lithium moving from the positive electrode active material layer to form the lithium-magnesium alloy layer, and (iii) reacting tin in the third metal layer with lithium moving from the positive electrode active material layer to form the second lithium-tin alloy layer.

[0035] Advantages of the Invention

[0036] According to the lithium secondary battery of the present disclosure, the reversible capacity can be increased and the cycle characteristics can be improved. Brief Description of the Drawings

[0037] Figure 1 It is a schematic diagram for explaining the lithium secondary battery of the present disclosure.

[0038] Figure 2 It is a schematic diagram for explaining another aspect of the lithium secondary battery of the present disclosure.

[0039] Figure 3It is a schematic diagram for explaining a method of manufacturing a lithium secondary battery according to the present disclosure.

[0040] Figure 4 It is a schematic diagram for explaining another mode of a method of manufacturing a lithium secondary battery according to the present disclosure.

[0041] Figure 5 (A) to Figure 5 (F) are images showing the results of EDX mapping analysis using cross-sectional SEM-EDX for each element of the lithium secondary battery E2 of Example 2 ( Figure 5 (A): Overlap of elements of sulfur (S), oxygen (O), tin (Sn), magnesium (Mg), and nickel (Ni), Figure 5 (B) S, Figure 5 (C) O, Figure 5 (D) Sn, Figure 5 (E) Mg, Figure 5 (F) Ni).

[0042] Figure 6 (A) to Figure 6 (B) are images showing the cross-sectional SEM image of the lithium secondary battery E2 of Example 2 ( Figure 6 (A) Cross-sectional SEM image, Figure 6 (B) Schematic diagram of the cross-sectional structure).

[0043] Explanation of reference numerals

[0044] 100 Lithium secondary battery

[0045] 110 Negative electrode current collector layer

[0046] 120 First lithium-tin alloy layer

[0047] 121 Lithium-magnesium alloy layer

[0048] 122 Second lithium-tin alloy layer

[0049] 130 Electrolyte layer

[0050] 140 Positive electrode active material layer

[0051] 150 Positive electrode current collector layer

[0052] 200 Preliminary lithium secondary battery

[0053] 220 First metal layer

[0054] 221 Second metal layer

[0055] 222 Third metal layer Detailed implementation mode

[0056] Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted 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 reference numerals are assigned to the same elements, and repeated descriptions are omitted.

[0057] Regarding the present disclosure, a "composite material" refers to a composition that can directly or further contain other components to form a positive electrode active material layer and an electrolyte layer. In addition, regarding the present disclosure, a "composite material slurry" refers to a slurry that contains a dispersion medium in addition to the "composite material" and can be coated and dried to form a positive electrode active material layer and an electrolyte layer.

[0058] The lithium secondary battery of the present disclosure can be a liquid battery containing an electrolytic solution as an electrolyte layer, or a solid battery having a solid electrolyte layer as an electrolyte layer. It should be noted that, regarding the present disclosure, a "solid battery" refers to a battery that uses at least a solid electrolyte as an electrolyte. Therefore, a solid battery can also use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. In addition, the lithium secondary battery of the present disclosure can also be an all-solid battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0059] "Lithium Secondary Battery"

[0060] The lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0061] According to the lithium secondary battery of the present disclosure, the reversible capacity can be increased and the cycle characteristics can be improved.

[0062] Specifically, for example, as Figure 1 shown, the lithium secondary battery of the present disclosure has a first lithium-tin alloy layer 120 between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121. It is speculated that through the first lithium-tin alloy layer 120, the peeling at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge can be suppressed, and thus, the reversible capacity can be increased and the cycle characteristics can be improved.

[0063] It should be noted that, as the main reason why the peeling at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 can be suppressed by the first lithium-tin alloy layer 120, although the detailed situation is not clear yet, it can be considered as follows. During discharge, compared with the lithium in the first lithium-tin alloy layer 120, the lithium in the lithium-magnesium alloy layer 121 preferentially undergoes dealloying of lithium from the perspective of the reaction potential. Therefore, the lithium-magnesium alloy layer 121 shrinks significantly. On the other hand, compared with the lithium-magnesium alloy layer 121, the first lithium-tin alloy layer 120 is difficult to undergo a dealloying reaction, so the shrinkage is small. Therefore, it is speculated that the shrinkage of the lithium-magnesium alloy layer 121 can be alleviated by the first lithium-tin alloy layer 120, and thus, the peeling at the above interface can be suppressed.

[0064] 〈Negative electrode current collector layer〉

[0065] The material for the negative electrode current collector layer is not particularly limited, and materials commonly used as the negative electrode current collector of a lithium secondary battery can be appropriately adopted. Examples of the material for the negative electrode current collector layer include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or a carbon sheet, etc., but it is not limited to this case. In particular, from the viewpoints of ensuring reducibility resistance and being difficult to alloy with lithium, etc., the material for the negative electrode current collector layer can contain at least one metal selected from Cu, Ni, and stainless steel, or can be composed of a carbon sheet. For the purpose of adjusting resistance, etc., the negative electrode current collector layer can also have a certain coating on its surface.

[0066] The shape of the negative electrode current collector layer is not particularly limited, and examples include a foil shape, a plate shape, or a mesh shape, etc. Among them, a foil shape is preferred.

[0067] The thickness of the negative electrode current collector layer is not particularly limited, and it can be 0.1 μm or more or 1 μm or more, and can also be 1 mm or less or 100 μm or less.

[0068] 〈First lithium-tin alloy layer〉

[0069] The first lithium-tin alloy layer contains lithium element and tin element, and can also optionally contain other metal elements alloyed with lithium. In the lithium secondary battery of the present disclosure, according to the charge-discharge state, the first and second lithium-tin alloy layers can also be considered to function as the negative electrode active material layer.

[0070] The thickness of the first lithium-tin alloy layer is not particularly limited, and in the fully charged state, it can also be 0.1 - 15 μm. The thickness of the first lithium-tin alloy layer is not particularly limited, and it can be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and can also be 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0071] The method for forming the first lithium-tin alloy layer can refer to the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0072] 〈Lithium-magnesium alloy layer〉

[0073] The lithium-magnesium alloy layer contains lithium element and magnesium element, and may optionally contain other metal elements alloyed with lithium. This lithium-magnesium alloy layer functions as a negative electrode active material layer in the lithium secondary battery of the present disclosure.

[0074] The thickness of the lithium-magnesium alloy layer is not particularly limited, and may be 0.1 to 40 μm even in a fully charged state. The thickness of the lithium-magnesium alloy layer is not particularly limited, and may be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and may also be 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, or 20 μm or less.

[0075] The method for forming the lithium-magnesium alloy layer can refer to the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0076] 〈Electrolyte layer〉

[0077] 〈Electrolyte layer - Solid electrolyte layer〉

[0078] The lithium secondary battery of the present disclosure can be a solid battery, that is, it has a solid electrolyte layer as the electrolyte layer.

[0079] In addition to the solid electrolyte, the solid electrolyte layer may also contain an adhesive or the like as needed.

[0080] (Solid electrolyte)

[0081] The material of the solid electrolyte is not particularly limited. For example, it can be a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, or the like.

[0082] As examples of the sulfide solid electrolyte, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes can be cited, but are not limited thereto. As examples of specific sulfide solid electrolytes, Li 2 S-P 2 S 5 system (Li 7 P 3 S 11 、Li 3 PS 4 、Li 8 P 2 S 9 etc.), Li 2 S-SiS2 , LiI-Li 2 , S-SiS 2 , LiI-Li 2 , S-P 2 , S 5 , LiI-LiBr-Li 2 , S-P 2 , S 5 , Li 2 , S-P 2 , S 5 , -GeS 2 (Li 13 , GeP 3 , S 16 , Li 10 , GeP 2 , S 12 etc.), LiI-Li 2 , S-P 2 , O 5 , LiI-Li 3 , PO 4 , -P 2 , S 5 , Li 7-x , PS 6-x , Cl x etc.; or combinations thereof, but not limited thereto.

[0083] As examples of oxide solid electrolytes, 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 , PO4-x N x (LiPON) etc., but not limited thereto.

[0084] The sulfide solid electrolyte and the oxide solid electrolyte can be glass or crystallized glass (glass ceramic).

[0085] Examples of the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof, etc., but not limited thereto.

[0086] (Adhesive)

[0087] There is no particular limitation on the adhesive. For example, the adhesive can be materials such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc., but not limited thereto. The adhesive is not particularly limited and can be used alone or in combination of two or more.

[0088] The thickness of the solid electrolyte layer is not particularly limited. For example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0089] The solid electrolyte layer can be easily formed, for example, by dry or wet forming of an electrolyte composite material containing the above solid electrolyte and adhesive, etc.

[0090] 〈Electrolyte layer - Separator layer〉

[0091] The lithium secondary battery of the present disclosure can be a liquid battery, that is, it has an electrolytic solution, especially an electrolytic solution held in the separator layer, as the electrolyte layer.

[0092] (Electrolytic solution)

[0093] The electrolytic solution is not particularly limited and preferably contains an auxiliary salt and a solvent.

[0094] There is no particular limitation on the auxiliary salt (lithium salt) of the electrolytic solution having lithium ion conductivity. Examples include inorganic lithium salts, organic lithium salts, etc. As the inorganic lithium salt, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , etc., but not limited to these cases. As the organic lithium salt, for example, LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO2 ) 2 、LiN(FSO 2 ) 2 、LiC(CF 3 SO 2 ) 3 etc., but not limited to these cases.

[0095] As the solvent for the electrolyte, there is no particular limitation, and cyclic carbonates, chain carbonates, etc. can be cited. As cyclic carbonates, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be cited, but not limited to this case. As chain carbonates, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be cited, but not limited to this case. The electrolyte is not particularly limited, and it can be used alone or in combination of two or more.

[0096] (Separator)

[0097] The separator is not particularly limited, and a separator commonly used as a separator for lithium secondary batteries can be appropriately adopted. As the separator, for example, non-woven fabrics such as polyolefin-based, polyamide-based, and polyimide-based can be used.

[0098] 〈Positive electrode active material layer〉

[0099] The positive electrode active material layer contains at least a positive electrode active material, and may optionally contain a conductive assistant, a solid electrolyte, a binder, etc. The positive electrode active material layer may also contain various other additives. The contents of the positive electrode active material, conductive assistant, binder, etc. in the positive electrode active material layer can be appropriately determined according to the target battery performance. For example, based on the whole of the positive electrode active material layer (the whole solid component) being 100% by mass, the content of the positive electrode active material can be 40% by mass or more, 50% by mass or more, 60% by mass or more, and can also be 100% by mass or less or 90% by mass or less.

[0100] (Positive electrode active material)

[0101] The material of the positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. As the positive electrode active material, for example, it can be lithium cobaltate (LiCoO 2 ), lithium nickelate (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 Coy Al z O 2 )、 composed of Li 1+x Mn 2-x-y M y O 4 (where M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn) represents a composition obtained by substituting foreign elements such as Li-Mn spinel, but is not limited thereto.

[0102] The positive electrode active material is not particularly limited and may also have a coating layer. The coating layer is a layer containing a material that has lithium ion conduction performance, low reactivity with the positive electrode active material or the solid electrolyte, and can maintain the shape of the coating layer without flowing even when in contact with the active material or the solid electrolyte. As specific examples of the material constituting the coating layer, in addition to LiNbO 3 , Li 4 Ti 5 O 12 , Li 3 PO 4 etc. are mentioned, but are not limited thereto.

[0103] The shape of the positive electrode active material is not particularly limited as long as it is a shape commonly used as the positive electrode active material of a lithium secondary battery. The positive electrode active material can also be, for example, granular. The positive electrode active material can be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle size D 50 of the positive electrode active material can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and can also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. It should be noted that the average particle size D 50 is the particle size (median particle size) at the cumulative value of 50% in the volume-based particle size distribution obtained by the laser diffraction / scattering method.

[0104] (Conductive additive)

[0105] The conductive additive is not particularly limited. The conductive additive can 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 additive can be, for example, granular or fibrous, and its size is not particularly limited. The conductive additive is not particularly limited and can be used alone or in combination of two or more.

[0106] Regarding the solid electrolyte and the binder, reference can be made to the description in the above “〈Electrolyte layer - Solid electrolyte layer〉”.

[0107] The shape of the positive electrode active material layer is not particularly limited. For example, it may also be a positive electrode active material layer in the form of a sheet having a substantially flat surface. The thickness of the positive electrode active material layer is not particularly limited. For example, it may be 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.

[0108] 〈Positive electrode current collector layer〉

[0109] The material for the positive electrode current collector layer is not particularly limited, and a material generally used as a positive electrode current collector of a lithium secondary battery can be appropriately used. Examples of the material for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In addition, for the purpose of adjusting resistance, etc., the positive electrode current collector layer may have a certain coating on its surface. In addition, the positive electrode current collector layer may also be a layer formed by plating or vapor deposition of the above metals on a metal foil or substrate.

[0110] The shape of the positive electrode current collector layer is not particularly limited. For example, foil shape, plate shape, or mesh shape, etc. can be cited. Among them, foil shape is preferred.

[0111] The thickness of the positive electrode current collector layer is not particularly limited, and it may be 0.1 μm or more or 1 μm or more, and may also be 1 mm or less or 100 μm or less.

[0112] The positive electrode active material layer can be manufactured by applying a known method. For example, by dry or wet forming of the positive electrode composite material containing the above various components, the positive electrode active material layer can be easily formed. The positive electrode active material layer can be formed together with the positive electrode current collector layer, or can be formed separately from the positive electrode current collector layer.

[0113] Examples of the shape of the lithium secondary battery include, but are not limited to, coin type, laminated type, cylindrical type, and square type.

[0114] Figure 1 It is a schematic diagram showing one mode of the lithium secondary battery of the present disclosure, but is not limited to this case.

[0115] The lithium secondary battery 100 is a battery in which a negative electrode current collector layer 110, a first lithium-tin alloy layer 120, a lithium-magnesium alloy layer 121, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are laminated in this order. By the first lithium-tin alloy layer 120 disposed between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121, peeling at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge can be suppressed, and thus, the reversible capacity can be increased and the cycle characteristics can be improved.

[0116] 〈Another mode of the lithium secondary battery〉

[0117] The lithium secondary battery of the present disclosure may also sequentially include a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, a second lithium-tin alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0118] 〈Second lithium-tin alloy layer〉

[0119] The second lithium-tin alloy layer contains lithium and tin elements, and may optionally contain other metal elements alloyed with lithium.

[0120] The thickness of the second lithium-tin alloy layer is not particularly limited, and may be 0.1 to 15 μm even in a fully charged state. The thickness of the second lithium-tin alloy layer is not particularly limited, and may be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and may also be 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0121] The method for forming the second lithium-tin alloy layer may refer to "《Manufacturing method of lithium secondary battery》" described later.

[0122] Regarding the negative electrode current collector, the first lithium-tin alloy layer, the lithium-magnesium alloy layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer, reference may be made to the description in "《Lithium secondary battery》".

[0123] Figure 2 It is a schematic diagram showing one mode of the lithium secondary battery of the present disclosure, but is not limited to this case.

[0124] The lithium secondary battery 100 is a battery in which a negative electrode current collector layer 110, a first lithium-tin alloy layer 120, a lithium-magnesium alloy layer 121, a second lithium-tin alloy layer 122, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are sequentially stacked. By the first lithium-tin alloy layer 120 disposed between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121, peeling at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge can be suppressed. Thus, the reversible capacity can be increased and the cycle characteristics can be improved. Furthermore, by the second lithium-tin alloy layer 122 disposed between the lithium-magnesium alloy layer 121 and the electrolyte layer 130, peeling at the interface between the lithium-magnesium alloy layer 121 and the electrolyte layer 130 during discharge can be suppressed. Thus, the cycle characteristics can be further improved.

[0125] 《Manufacturing method of lithium secondary battery》

[0126] The lithium secondary battery of the present disclosure can be manufactured by a method including the following steps:

[0127] Stack the negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer in this order to obtain a preliminary lithium secondary battery; and

[0128] By performing a charging operation on the above-mentioned preliminary lithium secondary battery, (i) react the tin in the first metal layer with the lithium moving from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) react the magnesium in the second metal layer with the lithium moving from the positive electrode active material layer to form the lithium-magnesium alloy layer.

[0129] According to the manufacturing method of the lithium secondary battery of the present disclosure, a lithium secondary battery capable of increasing the reversible capacity and improving the cycle characteristics can be manufactured.

[0130] 〈First metal layer〉

[0131] The first metal layer contains tin element, and may also optionally contain other metal elements alloyed with lithium.

[0132] The thickness of the first metal layer is not particularly limited, and can be 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, and can also be 0.50 μm or less, 0.40 μm or less, 0.30 μm or less, or 0.2 μm or less.

[0133] Specifically, the first metal layer can be formed, for example, by forming a tin layer on the negative electrode current collector by sputtering method, but is not limited to this case.

[0134] 〈Second metal layer〉

[0135] The second metal layer contains magnesium element, and may also optionally contain other metal elements alloyed with lithium.

[0136] The thickness of the second metal layer is not particularly limited, and can be 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, 0.20 μm or more, and can also be 3.0 μm or less, 2.0 μm or less, 1.0 μm or less, or 0.50 μm or less.

[0137] Specifically, the second metal layer can be formed, for example, by forming a magnesium layer on the first metal layer by sputtering method, but is not limited to this case.

[0138] Regarding the negative electrode current collector, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer, reference can be made to the description in "Lithium Secondary Battery".

[0139] 〈Preliminary lithium secondary battery〉

[0140] The preliminary lithium secondary battery is a laminate formed by sequentially laminating a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer.

[0141] Specifically, the preliminary lithium secondary battery can be easily formed, for example, by laminating a negative electrode current collector, a first metal layer, a second metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in the above order, enclosing the laminate in a laminated film, and performing vacuum sealing and pressurization.

[0142] (Charging operation)

[0143] As the charging operation, for example, it can be performed under constant current-constant voltage conditions within a cut-off voltage range of 4.2V - 3.0V. Through the charging operation, lithium is released from the positive electrode active material holding lithium contained in the positive electrode active material layer, and the lithium moves to the first metal layer and the second metal layer.

[0144] As the current amount (C rate) during the charging operation, there is no particular limitation, and it can be 0.01C or more, 0.02C or more, 0.03C or more, or 0.05C or more, and it can also be 0.20C or less, 0.10C or less, 0.075C or less, or 0.05C or less.

[0145] The temperature during the charging operation is not particularly limited. The temperature during the charging operation can be 0°C or more, 10°C or more, 20°C or more, 30°C or more, 40°C or more, 50°C or more, or 60°C or more, and it can also be 200°C or less, 150°C or less, 120°C or less, 100°C or less, or 80°C or less.

[0146] Figure 3 It is a schematic diagram showing one mode of the preliminary lithium secondary battery in the manufacturing method of the lithium secondary battery of the present disclosure, but is not limited to this case. Using Figure 1 and Figure 3 , the specific method for manufacturing the Figure 3 preliminary lithium secondary battery into the Figure 1 lithium secondary battery will be described, but is not limited to this case.

[0147] Figure 3 The preliminary lithium secondary battery 200 is a laminate formed by sequentially laminating a negative electrode current collector layer 110, a first metal layer 220, a second metal layer 221, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150. By performing a charging operation on the Figure 3 preliminary lithium secondary battery 200, the Figure 1The lithium secondary battery 100. That is, by performing a charging operation on the preliminary lithium secondary battery 200, the tin in the first metal layer 220 reacts with the lithium moving from the positive electrode active material layer 140 to form Figure 1 the first lithium-tin alloy layer 120, and the magnesium in the second metal layer 221 reacts with the lithium moving from the positive electrode active material layer 140 to form Figure 1 the lithium-magnesium alloy layer 121, and the lithium secondary battery 100 can be manufactured.

[0148] 〈Another aspect of the manufacturing method of the lithium secondary battery〉

[0149] The lithium secondary battery of the present disclosure can also be manufactured by a method including the following steps:

[0150] Stacking in sequence a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, a third metal layer containing tin, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer to obtain a preliminary lithium secondary battery; and

[0151] By performing a charging operation on the above-mentioned preliminary lithium secondary battery, (i) the tin in the above-mentioned first metal layer reacts with the lithium moving from the above-mentioned positive electrode active material layer to form the above-mentioned first lithium-tin alloy layer, (ii) the magnesium in the above-mentioned second metal layer reacts with the lithium moving from the above-mentioned positive electrode active material layer to form the above-mentioned lithium-magnesium alloy layer, and (iii) the tin in the above-mentioned third metal layer reacts with the lithium moving from the above-mentioned positive electrode active material layer to form the above-mentioned second lithium-tin alloy layer.

[0152] 〈Third metal layer〉

[0153] The third metal layer contains a tin element and may optionally contain other metal elements alloyed with lithium.

[0154] The thickness of the third metal layer is not particularly limited and may be 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, or may be 0.50 μm or less, 0.40 μm or less, 0.30 μm or less, or 0.2 μm or less.

[0155] Specifically, the third metal layer can be formed, for example, by forming a tin layer on the electrolyte layer by sputtering, but is not limited to this case.

[0156] Regarding the negative electrode current collector, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer, reference can be made to the description in "Lithium Secondary Battery". Regarding the first metal layer and the second metal layer, reference can be made to the description in "The Manufacturing Method of Lithium Secondary Battery".

[0157] The preliminary lithium secondary battery may also stack a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, a third metal layer containing tin, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer in this order.

[0158] Specifically, the preliminary lithium secondary battery can be easily formed, for example, by the following method: Stack the negative electrode current collector, the first metal layer, the second metal layer, the third metal layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer in the above order, house the stacked body in a laminated film, and perform vacuum sealing and pressurization.

[0159] Regarding the charging operation, refer to the description in “(Charging Operation)”.

[0160] Figure 4 It is a schematic diagram showing one mode of the preliminary lithium secondary battery in the manufacturing method of the lithium secondary battery of the present disclosure, but is not limited to this case. Using Figure 2 and Figure 4 , for the preliminary lithium secondary battery made of Figure 4 , the specific method for manufacturing the Figure 2 lithium secondary battery will be described, but is not limited to this case.

[0161] Figure 4 The preliminary lithium secondary battery 200 of Figure 4 is a stacked body formed by sequentially stacking a negative electrode current collector layer 110, a first metal layer 220, a second metal layer 221, a third metal layer 222, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150. By performing a charging operation on the Figure 2 preliminary lithium secondary battery 200, the Figure 2 lithium secondary battery 100 of Figure 2 can be manufactured. That is, by performing a charging operation on the preliminary lithium secondary battery 200, the tin in the first metal layer 220 reacts with the lithium moving from the positive electrode active material layer 140 to form the Figure 2 first lithium-tin alloy layer 120, the magnesium in the second metal layer 221 reacts with the lithium moving from the positive electrode active material layer 140 to form the

[0162] [Example]

[0163] The present disclosure will be described in more detail with reference to the examples shown below, but the scope of the present disclosure is not limited to these examples.

[0164] 《Example 1》

[0165] <Manufacture of negative electrode current collector A1 with a first metal layer and a second metal layer>

[0166] On one side of a nickel foil serving as a negative electrode current collector layer, a tin layer was formed to a thickness of 0.1 μm by sputtering to form a first metal layer containing tin on the nickel foil. Next, a magnesium layer was formed to a thickness of 0.2 μm by sputtering on the surface of the first metal layer on the nickel foil to form a second metal layer containing magnesium on the first metal layer, obtaining the negative electrode current collector A1. The negative electrode current collector A1 is a laminate having a negative electrode current collector layer, a first metal layer, and a second metal layer in sequence.

[0167] <Manufacture of electrolyte layer B1>

[0168] A sulfide solid electrolyte (92.6 mass parts) as an electrolyte, a binder (7.4 mass parts), and an appropriate amount of butyl butyrate as a dispersion medium were mixed to prepare an electrolyte composite slurry. The obtained electrolyte composite slurry was coated on a release film with a coating gap of 325 μm, temporarily dried at room temperature for 3 hours, and officially dried at 165 °C for 1 hour. The officially dried coating film was punched out into two pieces with a diameter of φ14.50 mm, the two pieces were overlapped with their respective coating surfaces facing each other, pressed at 7.0 tons, and the release film was peeled off to manufacture an independent electrolyte layer B1.

[0169] <Manufacture of positive electrode active material layer C1>

[0170] Lithium nickel cobalt aluminate (NCA) (84.7 mass parts) as a positive electrode active material, a sulfide solid electrolyte (13.4 mass parts) as a solid electrolyte, a binder (0.6 mass parts), a conductive additive (1.3 mass parts), and an appropriate amount of butyl butyrate as a dispersion medium were mixed to prepare a positive electrode composite slurry. Next, the obtained positive electrode composite slurry was coated on an aluminum foil serving as a positive electrode current collector with a coating gap of 225 μm, temporarily dried at 60 °C, and officially dried at 165 °C for 1 hour to manufacture a positive electrode current collector layer C1 formed on the aluminum foil. The designed capacity of the positive electrode active material layer C1 is 3.0 mAh / cm 2 , and the mass per unit area is 18.7 mg / cm 2 .

[0171] <Manufacture of preliminary lithium secondary battery D1>

[0172] The negative current collector A1 is blanked with a diameter of φ14.50 mm, and the positive active material layer C1 is blanked with a diameter of φ11.28 mm. Then, the negative current collector A1, the electrolyte layer B1, and the positive active material layer C1 are stacked in this order: the negative current collector layer, the first metal layer, the second metal layer, the electrolyte layer, the positive active material layer, and the positive current collector layer. The laminate is housed in a laminated film, vacuum-sealed, and isostatically pressed at 392 MPa by cold isostatic pressing to fabricate a preliminary lithium secondary battery D1. Here, the positive electrode tab is made of aluminum, and the negative electrode tab is made of nickel.

[0173] 〈Fabrication of Lithium Secondary Battery E1〉

[0174] Using a constant-pressure fixture with a spring inserted, the preliminary lithium secondary battery D1 is constrained at 1 MPa to keep the constraint pressure constant. Then, the preliminary lithium secondary battery D1 is left standing in a constant-temperature bath at 60 °C, and within the range of the cut-off voltage of 4.2 V - 3.0 V at 60 °C, a single-cycle constant current (current density: 0.15 mA / cm 2 , equivalent to 0.05 C) - constant voltage (cut-off current density: 0.03 mA / cm 2 , equivalent to 0.01 C) test is carried out. Here, through the charging operation of the constant current - constant voltage test on the preliminary lithium secondary battery D1, the tin in the first metal layer reacts with the lithium moving from the positive active material layer C1 to form a first lithium - tin alloy layer, and the magnesium in the second metal layer reacts with the lithium moving from the positive active material layer C1 to form a lithium - magnesium alloy layer, obtaining the lithium secondary battery E1.

[0175] 〈Electrochemical Measurement of Lithium Secondary Battery E1〉

[0176] The lithium secondary battery E1 is left standing in a constant-temperature bath at 25 °C, and within the range of the cut-off voltage of 4.2 V - 3.0 V at 25 °C, a 20-cycle constant current (current density: 0.15 mA / cm 2 , equivalent to 0.05 C) - constant voltage (cut-off current density: 0.03 mA / cm 2 , equivalent to 0.01 C) test is implemented. The initial reversible capacity of the lithium secondary battery E1 at 25 °C is 2.82 mAh / cm 2 , and the reversible capacity after 20 cycles at 25 °C is 1.46 mAh / cm 2 .

[0177] 〈Example 2〉

[0178] 〈Fabrication of Electrolyte Layer B2 with a Third Metal Layer〉

[0179] A sulfide solid electrolyte (92.6 parts by mass) as an electrolyte, a binder (7.4 parts by mass), and an appropriate amount of butyl butyrate as a dispersion medium were mixed to prepare an electrolyte composite slurry. The obtained electrolyte composite slurry was coated on a release film with a coating gap of 325 μm, temporarily dried at room temperature for 3 hours, and then officially dried at 165 °C for 1 hour. Two sheets of the officially dried coating film were punched out with a diameter of φ14.50 mm, and the two sheets were overlapped with their respective coating surfaces facing each other, pressed at 7.0 tons, and the release film was peeled off to obtain an independent electrolyte layer. Subsequently, a tin layer was formed on one side of the independent electrolyte layer by sputtering to a thickness of 0.1 μm to form a third metal layer containing tin on the electrolyte layer, and an electrolyte layer B2 was fabricated.

[0180] 〈Fabrication of Preliminary Lithium Secondary Battery D2〉

[0181] Using the electrolyte layer B2 instead of the electrolyte layer B1, the negative electrode current collector layer, the first metal layer, the second metal layer, the third metal layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer were stacked in this order, and the negative electrode current collector A1, the electrolyte layer B2, and the positive electrode active material layer C1 were fabricated in the same manner as in Example 1 to obtain a preliminary lithium secondary battery D2.

[0182] 〈Fabrication of Lithium Secondary Battery E2〉

[0183] A constant pressure fixture with a spring inserted was used to constrain the preliminary lithium secondary battery D2 at 1 MPa to keep the constraint pressure constant. Subsequently, the preliminary lithium secondary battery D2 was placed in a constant temperature bath at 60 °C, and a constant current (current density: 0.15 mA / cm 2 , corresponding to 0.05 C)-constant voltage (cut-off current density: 0.03 mA / cm 2 , corresponding to 0.01 C) test was conducted within the range of the cut-off voltage from 4.2 V to 3.0 V at 60 °C. Here, through the charging operation of the constant current-constant voltage test, the tin in the first metal layer reacted with the lithium moving from the positive electrode active material layer C1 to form a first lithium-tin alloy layer, the magnesium in the second metal layer reacted with the lithium moving from the positive electrode active material layer C1 to form a lithium-magnesium alloy layer, and the tin in the third metal layer reacted with the lithium moving from the positive electrode active material layer C1 to form a second lithium-tin alloy layer, resulting in a lithium secondary battery E2.

[0184] 〈SEM-EDX Measurement of Lithium Secondary Battery E2〉

[0185] For the cross-section of the lithium secondary battery E2 after the first charge at 60 °C, a scanning electron microscope (SEM) observation in the secondary electron image and elemental mapping using energy dispersive X-ray analysis (EDX) were performed at an applied voltage of 5 kV. Figure 5Shows the results of EDX mapping analysis of the lithium secondary battery E2. Figure 6 Shows the cross-sectional SEM image of the lithium secondary battery E2 and a schematic diagram of the cross-sectional structure. According to SEM-EDX observations, it was confirmed that after the first charge of the lithium secondary battery E2, the negative electrode current collector layer 110, the first lithium-tin alloy layer 120, the lithium-magnesium alloy layer 121, the second lithium-tin alloy layer 122, and the electrolyte layer 130 were stacked in sequence.

[0186] 〈Electrochemical measurement of lithium secondary battery E2〉

[0187] The electrochemical measurement of the lithium secondary battery E2 was carried out using the same method as in Example 1. The initial reversible capacity of the lithium secondary battery E2 at 25 °C and the reversible capacity after 20 cycles at 25 °C are shown in Table 1.

[0188] 《Comparative Example 1》

[0189] 〈Fabrication of negative electrode current collector A2 with a second metal layer〉

[0190] On one side of a nickel foil serving as the negative electrode current collector layer, a magnesium layer was formed to a thickness of 0.2 μm by sputtering to form a second metal layer containing magnesium on the nickel foil, obtaining the negative electrode current collector A2. The negative electrode current collector A2 is a laminate having a negative electrode current collector layer and a second metal layer in sequence.

[0191] 〈Fabrication of preliminary lithium secondary battery d1〉

[0192] Using the negative electrode current collector A2 instead of the negative electrode current collector A1, the negative electrode current collector A2, the electrolyte layer B1, and the positive electrode active material layer C1 were stacked in the order of the negative electrode current collector layer, the second metal layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer, and a preliminary lithium secondary battery d1 was fabricated using the same method as in Example 1.

[0193] 〈Fabrication and electrochemical measurement of lithium secondary battery e1〉

[0194] Except for using the preliminary lithium secondary battery d1 instead of the preliminary lithium secondary battery D1, a lithium secondary battery e1 was fabricated using the same method as in Example 1. The electrochemical measurement of the lithium secondary battery e1 was carried out using the same method as in Example 1. The initial reversible capacity of the lithium secondary battery e1 at 25 °C and the reversible capacity after 20 cycles at 25 °C are shown in Table 1.

[0195] 《Comparative Example 2》

[0196] 〈Fabrication of preliminary lithium secondary battery d2〉

[0197] The negative current collector A2 is used instead of the negative current collector A1, and the electrolyte layer B2 is used instead of the electrolyte layer B1. The negative current collector A2, the electrolyte layer B2, and the positive electrode active material layer C1 are stacked in this order: the negative current collector layer, the second metal layer, the third metal layer, the electrolyte layer, the positive electrode active material layer, and the positive current collector layer. Using the same method as in Example 1, a preliminary lithium secondary battery d2 is fabricated.

[0198] 〈Fabrication and Electrochemical Measurement of Lithium Secondary Battery e2〉

[0199] Except for using the preliminary lithium secondary battery d2 instead of the preliminary lithium secondary battery D1, a lithium secondary battery e2 is fabricated using the same method as in Example 1. The electrochemical measurement of the lithium secondary battery e2 is carried out using the same method as in Example 1. The initial reversible capacity of the lithium secondary battery e2 at 25°C and the reversible capacity after 20 cycles at 25°C are shown in Table 1.

[0200] Table 1 shows the evaluation results of the electrochemical measurements of Example 1, 2 and Comparative Example 1, 2.

[0201] [Table 1]

[0202]

[0203] Compared with the lithium secondary batteries e1 and e2 without the first lithium-tin alloy layer, the lithium secondary batteries E1 and E2 equipped with the first lithium-tin alloy layer have a higher initial reversible capacity at 25°C. It is speculated that this is because, by disposing the first lithium-tin alloy layer between the negative current collector layer and the lithium-magnesium alloy layer, peeling at the interface between the negative current collector layer and the lithium-magnesium alloy layer during discharge can be suppressed, thereby increasing the reversible capacity and cycle characteristics.

[0204] It should be noted that the main reason why the first lithium-tin alloy layer can suppress peeling at the interface between the negative current collector layer / lithium-magnesium alloy layer is considered as follows. During discharge, compared with lithium in the first lithium-tin alloy layer, lithium in the lithium-magnesium alloy layer preferentially undergoes dealloying of lithium from the viewpoint of reaction potential, so the lithium-magnesium alloy layer shrinks significantly. On the other hand, the lithium-tin alloy layer shrinks less than the lithium-magnesium alloy layer, so it is speculated that the shrinkage of the lithium-magnesium alloy layer can be alleviated by the lithium-tin alloy layer, thereby suppressing peeling at the above interface.

[0205] Moreover, even after 20 cycles, the lithium secondary battery E2 equipped with the second lithium-tin alloy layer maintains a reversible capacity of 2.77 mAh / cm 2High capacity. It is presumed that this is because, by disposing a second lithium-tin alloy layer between the lithium-magnesium alloy layer and the electrolyte layer, peeling at the interface between the lithium-magnesium alloy layer and the electrolyte layer during discharge can be suppressed, and thus, the cycle characteristics are improved. It should be noted that it is presumed that the suppression of the above interface peeling by the second lithium-tin alloy layer is the same main reason as the suppression of the interface peeling by the first lithium-tin alloy layer.

[0206] Although preferred embodiments of the lithium secondary battery of the present disclosure have been described, those skilled in the art will understand that changes can be made without departing from the scope of protection of the claims.

Claims

1. A lithium secondary battery, wherein: The lithium secondary battery includes a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

2. The lithium secondary battery according to claim 1, wherein In a fully charged state, the thickness of the first lithium-tin alloy layer is 0.1-15 μm.

3. The lithium secondary battery according to claim 1, wherein In a fully charged state, the thickness of the lithium-magnesium alloy layer is 0.1 to 40 μm.

4. The lithium secondary battery according to claim 1, wherein The lithium secondary battery includes the negative electrode collector layer, the first lithium-tin alloy layer, the lithium-magnesium alloy layer, the second lithium-tin alloy layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode collector layer in this order.

5. The lithium secondary battery according to claim 4, wherein: When fully charged, The thickness of the first lithium-tin alloy layer is 0.1 to 15 μm, and The thickness of the second lithium-tin alloy layer is 0.1-15 μm.

6. A method for manufacturing a lithium secondary battery, wherein: The method for manufacturing a lithium secondary battery is a method for manufacturing a lithium secondary battery according to any one of claims 1 to 5, comprising the following steps: The negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the electrolyte layer, the positive electrode active material layer retaining lithium, and the positive electrode current collector layer are sequentially stacked to obtain a preliminary lithium secondary battery; as well as By charging the prepared lithium secondary battery, (i) the tin of the first metal layer reacts with the lithium moved from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) the magnesium of the second metal layer reacts with the lithium moved from the positive electrode active material layer to form the lithium-magnesium alloy layer.

7. A method for manufacturing a lithium secondary battery, wherein: The method for manufacturing a lithium secondary battery is a method for manufacturing a lithium secondary battery according to claim 4 or 5, comprising the following steps: The negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the third metal layer containing tin, the electrolyte layer, the positive electrode active material layer retaining lithium, and the positive electrode current collector layer are sequentially stacked to obtain a preliminary lithium secondary battery; as well as By charging the prepared lithium secondary battery, (i) the tin of the first metal layer reacts with the lithium moved from the positive electrode active material layer to form the first lithium-tin alloy layer, (ii) the magnesium of the second metal layer reacts with the lithium moved from the positive electrode active material layer to form the lithium-magnesium alloy layer, and (iii) the tin of the third metal layer reacts with the lithium moved from the positive electrode active material layer to form the second lithium-tin alloy layer.

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