Lithium secondary battery, and method for producing lithium secondary battery

Abstract

To provide a lithium secondary battery in which a lithium metal and / or a lithium alloy is used as a negative electrode active material and in which the increase of a resistance value in heat generation of the battery can be suppressed.SOLUTION: A lithium secondary battery includes a negative electrode current collector layer 111, a metal layer 112, a negative electrode active material layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132, in this order. The negative electrode active material layer 113 contains a lithium metal or a lithium alloy, the thickness of the metal layer 112 is 10 nm to 4,000 nm, and the metal layer 112 has a first metal that is taken with lithium to form an alloy, and a second metal contained in the negative electrode current collector layer 111.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Lithium secondary batteries using lithium metal and / or lithium alloy as a negative electrode active material are expected to be put into practical use because they can obtain a high output voltage due to the large potential difference between the negative electrode and the positive electrode and have a high theoretical capacity density. The following lithium secondary batteries have been disclosed.

[0003] For example, Patent Document 1 discloses a lithium secondary battery that utilizes the deposition-dissolution reaction of lithium metal as a reaction of the negative electrode. The negative electrode includes a negative electrode layer, and the negative electrode layer includes an alloy of the lithium metal and a different metal as a negative electrode active material. When the lithium secondary battery is fully charged, the elemental ratio of lithium elements in the alloy is 40.00 atomic% or more and 99.97 atomic% or less. According to Patent Document 1, it is said that a lithium secondary battery capable of improving the capacity retention rate can be provided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A lithium secondary battery having a specific modified layer on a negative electrode current collector layer is known in order to improve the physical properties of a lithium secondary battery using lithium metal and / or lithium alloy as a negative electrode active material. However, in the lithium secondary battery having the above modified layer, when the lithium secondary battery generates heat, the resistance value may increase due to the thermal expansion of the above modified layer.

[0006] Therefore, the present disclosure aims to provide a lithium secondary battery that uses lithium metal and / or a lithium alloy as a negative electrode active material and can suppress an increase in the resistance value during heat generation of the lithium secondary battery.

Means for Solving the Problems

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

[0008] 〈Aspect 1〉 A lithium secondary battery having a negative electrode current collector layer, a metal layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order, wherein the negative electrode active material layer contains lithium metal or a lithium alloy, the thickness of the metal layer is 10 nm to 4000 nm, and the metal layer has a first metal that forms an alloy with lithium and a second metal contained in the negative electrode current collector layer. Lithium secondary battery. 〈Aspect 2〉 The lithium secondary battery according to Aspect 1, wherein the first metal is at least one selected from magnesium, aluminum, silicon, calcium, scandium, titanium, manganese, zinc, gallium, germanium, strontium, yttrium, zirconium, palladium, indium, tin, barium, and gold. 〈Aspect 3〉 A method for manufacturing a lithium secondary battery according to Aspect 1 or 2, including the following steps: Forming the metal layer by depositing the first metal and the second metal on the surface of the negative electrode current collector layer to obtain a preliminary negative electrode laminate, Stacking the preliminary negative electrode laminate, 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, Performing a charging operation on the preliminary lithium secondary battery to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium secondary battery.

Advantages of the Invention

[0009] According to the present disclosure, an increase in the resistance value during heat generation of a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

[0012] Regarding the present disclosure, “composite material” means a composition that can form a positive electrode active material layer or the like as it is or by further containing other components. Also, regarding the present disclosure, “composite material slurry” means a slurry that contains a dispersion medium in addition to the “composite material” and can form a positive electrode active material layer or the like by coating and drying.

[0013] The lithium secondary battery of the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer, or may be a solid battery having a solid electrolyte layer as an electrolyte layer. Note that, regarding the present disclosure, “solid battery” means a battery that uses at least a solid electrolyte as an electrolyte. Therefore, a solid battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. Also, the lithium secondary battery of the present disclosure may be an all-solid battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0014] "Lithium Secondary Battery" The lithium secondary battery of the present disclosure has a negative electrode current collector layer, a metal layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order, wherein the negative electrode active material layer contains lithium metal or a lithium alloy, the thickness of the metal layer is 10 nm to 4000 nm, and the metal layer has a first metal that forms an alloy with lithium and a second metal contained in the negative electrode current collector layer.

[0015] According to the present disclosure, it is possible to suppress an increase in the resistance value during heat generation of a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material.

[0016] Although not limited to theory, when the thickness of the metal layer is within a predetermined range, it is presumed that the influence of thermal expansion of the metal layer can be reduced, peeling of the metal layer can be suppressed, and thereby an increase in the resistance value during heat generation can be suppressed. On the other hand, when the thickness of the metal layer is too large, it is presumed that the metal layer peels off due to the influence of thermal expansion during heat generation, and the resistance value increases.

[0017] FIG. 1 is a schematic diagram showing one aspect of the lithium secondary battery of the present disclosure, but is not limited to this case.

[0018] The lithium secondary battery 100 has a negative electrode current collector layer 111, a metal layer 112, a negative electrode active material layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132 in this order, and the metal layer 112 has a predetermined thickness. With the metal layer 112 having a predetermined thickness, an increase in the resistance value during heat generation of the lithium secondary battery can be suppressed. When the thickness of the metal layer 112 is within a predetermined range, it is presumed that the influence of thermal expansion of the metal layer 112 can be reduced, peeling of the metal layer 112 can be suppressed, and thereby an increase in the resistance value during heat generation can be suppressed. On the other hand, when the thickness of the metal layer 112 is too large, it is presumed that the metal layer 112 peels off due to the influence of thermal expansion during heat generation, and the resistance value increases.

[0019] <Configuration of Lithium Secondary Battery> The lithium secondary battery of the present disclosure has a negative electrode current collector layer, a metal layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0020] <Negative Electrode Current Collector Layer> The material used for the negative electrode current collector layer is not particularly limited, but a material generally used as the negative electrode current collector of a lithium secondary battery can be appropriately adopted. Examples of the material 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 viewpoints 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 coating layer on its surface for the purpose of adjusting resistance or the like.

[0021] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, or a mesh shape. Among these, a foil shape is preferable.

[0022] The thickness of the negative electrode current collector layer is not particularly limited, and it may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0023] <Metal Layer> In the lithium secondary battery of the present disclosure, the metal layer has a first metal that forms an alloy with lithium and a second metal contained in the negative electrode current collector layer. Here, the first metal and the second metal may or may not form an alloy combination.

[0024] (First Metal) The first metal is not particularly limited as long as it forms an alloy with lithium.

[0025] The first metal is not particularly limited, and may be at least one selected from magnesium, aluminum, silicon, calcium, scandium, titanium, manganese, zinc, gallium, germanium, strontium, yttrium, zirconium, palladium, indium, tin, barium, and gold.

[0026] (The second metal) The second metal is not particularly limited as long as it is a metal contained in the negative electrode current collector layer. For example, when copper is used as the negative electrode current collector layer, the second metal is copper.

[0027] For the material used for the negative electrode current collector layer, that is, the metal contained in the negative electrode current collector layer, reference can be made to the description of "〈Negative electrode current collector layer〉" above.

[0028] In the lithium secondary battery of the present disclosure, the thickness of the metal layer is 10 nm to 4000 nm. The thickness of the metal layer may be, for example, 10 nm or more, 100 nm or more, 200 nm or more, or 500 nm or more, and may also be 4000 nm or less, 2000 nm or less, or 1000 nm or less. The thickness of the metal layer can be measured by scanning electron microscope observation (SEM) of the cross-section of the metal layer.

[0029] 〈Negative electrode active material layer〉 In the lithium secondary battery of the present disclosure, the negative electrode active material layer contains lithium metal or a lithium alloy.

[0030] Here, when the "negative electrode active material layer" contains lithium metal, in the charged state, there is a layer of lithium metal as the "negative electrode active material layer", but in the discharged state, the lithium metal moves to the positive electrode active material layer as lithium ions, and the layer of lithium metal as the "negative electrode active material layer" may disappear. Similarly, when the "negative electrode active material layer" contains a lithium alloy, in the charged state, there is a layer of lithium alloy as the "negative electrode active material layer", but in the discharged state, the lithium in the lithium alloy moves to the positive electrode active material layer as lithium ions, and there may be no lithium alloy as the "negative electrode active material layer", but a layer of metal from which lithium has been removed from the lithium alloy.

[0031] The negative electrode active material layer contains at least lithium metal or a lithium alloy as the negative electrode active material, and may further optionally contain a conductive aid, a binder, a solid electrolyte, etc. The negative electrode active material layer may also contain various other additives. The content of each of the negative electrode active material, conductive aid, binder, solid electrolyte, etc. in the negative electrode active material layer may be appropriately determined according to the intended battery performance. For example, taking the whole of the negative electrode active material layer (the whole solid content) as 100% by mass, the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, and may also be 100% by mass or less, or 90% by mass or less.

[0032] (Negative electrode active material) As the negative electrode active material, at least lithium metal or a lithium alloy is used as described above. The lithium alloy is not particularly limited as long as it is a material that can be alloyed with lithium and can occlude and release lithium ions. For example, silicon alloy-based negative electrode active materials, tin alloy-based active materials, etc. can be mentioned, but are not limited to these cases. The silicon alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, or a solid solution thereof. Further, the silicon alloy-based negative electrode active materials can contain metal elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. The tin alloy-based negative electrode active materials include tin, tin oxide, tin nitride, or a solid solution thereof. Further, the tin alloy-based negative electrode active materials can contain metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0033] Further, the negative electrode active material layer may contain a negative electrode active material other than lithium metal or a lithium alloy. The negative electrode active material other than lithium metal or a lithium alloy is not particularly limited, and examples include carbon materials. Examples of the carbon material include, but are not limited to, hard carbon, soft carbon, graphite, etc.

[0034] The proportion of the lithium metal or lithium alloy contained in the negative electrode active material layer is not particularly limited, but may be 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, or 90% by mass to 100% by mass with respect to the negative electrode active material layer.

[0035] (Binder) The binder is not particularly limited. The binder may be a material such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), etc., but is not limited to these. The binder is not particularly limited, and only one kind may be used alone, or two or more kinds may be used in combination.

[0036] (Conductive aid) The conductive aid is not particularly limited. The conductive aid 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 aid may be, for example, particulate or fibrous, and its size is not particularly limited. The conductive aid is not particularly limited, but only one kind may be used alone, or two or more kinds may be used in combination.

[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, etc.

[0038] Examples of the sulfide solid electrolyte include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes, etc. Specific examples of the sulfide solid electrolyte include Li2S-P2S5 systems (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof can be cited, but are not limited thereto.

[0039] Examples of the oxide solid electrolyte include Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x (LiPON), etc. may be mentioned, but are not limited thereto.

[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] The shape of the negative electrode active material is not particularly limited, but may be a common shape as the negative electrode active material of a lithium secondary battery. The negative electrode active material may be, for example, layered or sheet-like. The negative electrode active material may involve lithium precipitation during charging and may involve lithium dissolution during discharging. In this case, the negative electrode active material layer may be a layer made of lithium metal or a lithium alloy.

[0043] The shape of the negative electrode active material layer is not particularly limited, but may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 200 μm or less, 1150 μm or less, or 100 μm or less.

[0044] The negative electrode active material layer can be formed with reference to the description of "《Method for manufacturing a lithium secondary battery》" described later.

[0045] 〈Electrolyte layer〉 〈Electrolyte layer - Solid electrolyte layer〉 The lithium secondary battery of the present disclosure can be a solid battery, that is, it can have a solid electrolyte layer as the electrolyte layer.

[0046] In addition to the solid electrolyte, the solid electrolyte layer may contain a binder or the like as necessary.

[0047] For the solid electrolyte and the binder, reference can be made to the description of "<Negative electrode active material layer>" above.

[0048] The thickness of the solid electrolyte 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.

[0049] 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.

[0050] 〈Electrolyte layer - Separator layer〉 The lithium secondary battery of the present disclosure can be a liquid-based battery, that is, it can have an electrolytic solution as the electrolyte layer, particularly an electrolytic solution held in the separator layer.

[0051] (Electrolytic solution) The electrolytic solution is not particularly limited, but preferably contains a supporting salt and a solvent.

[0052] 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 inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, LiAsF6, etc. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc.

[0053] The solvent used in the electrolyte is not particularly limited, and examples thereof include cyclic carbonates, chain carbonates, and the like. Examples of the cyclic carbonate include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the chain carbonate include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. The electrolyte is not particularly limited, and only one kind may be used alone, or two or more kinds may be used in combination.

[0054] (Separator) The separator is not particularly limited, and a general separator for a lithium secondary battery can be appropriately employed. As the separator, for example, non-woven fabrics such as polyolefin-based, polyamide-based, and polyimide-based non-woven fabrics can be used.

[0055] 〈Positive electrode active material layer〉 The positive electrode active material layer contains at least a positive electrode active material, and may further optionally contain a conductive assistant, a solid electrolyte, a binder, and the like. The positive electrode active material layer may also contain various additives. The content of each of the positive electrode active material, conductive assistant, binder, etc. in the positive electrode active material layer may be appropriately determined according to the intended battery performance. For example, assuming the total of the positive electrode active material layer (total solid content) is 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, and may also be 100% by mass or less, or 90% by mass or less.

[0056] (Positive electrode active material) The material of the positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. Examples of the positive electrode active material include, but are not limited to, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4), lithium nickel cobalt manganate (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3O2, lithium nickel cobalt aluminum oxide (NCA; LiNi x Co y Al z O2), Li 1+x Mn 2-x-y M y O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn), and may be, but is not limited to, a heteroatom-substituted Li-Mn spinel having such a composition.

[0057] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a substance having lithium ion conduction performance, low reactivity with the positive electrode active material and the solid electrolyte, and capable of maintaining the form of a coating layer that does not flow even when in contact with the active material and the solid electrolyte. Specific examples of the material constituting the coating layer include, but are not limited to, LiNbO3, Li4Ti5O 12 , Li3PO4, etc.

[0058] The shape of the positive electrode active material is not particularly limited as long as it is a general shape as the positive electrode active material of a lithium secondary battery. The positive electrode active material may be, for example, particulate. The positive electrode active material may be primary particles or secondary particles in which a plurality of primary particles are aggregated. The average particle diameter D 50 may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D 50 is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0059] Regarding the solid electrolyte, binder, and conductive assistant, reference can be made to the description of "<Negative electrode active material layer>" above.

[0060] The shape of the positive electrode active material layer is not particularly limited, and for example, a sheet-shaped positive electrode active material layer having a substantially flat surface may be used. 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 also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0061] 〈Positive electrode current collector layer〉 The material used for the positive electrode current collector layer is not particularly limited, and generally used materials for the positive electrode current collector of a lithium secondary battery can be appropriately adopted. Examples of the material used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. Further, the positive electrode current collector layer may have some coating layer on its surface for the purpose of adjusting resistance or the like. Also, the positive electrode current collector layer may be a metal foil or a substrate with the above metal plated or vapor-deposited thereon.

[0062] The shape of the positive electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, or a mesh shape. Among these, a foil shape is preferred.

[0063] The thickness of the positive electrode current collector layer is not particularly limited, and 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.

[0064] The positive electrode active material layer can be manufactured by applying known methods. For example, the positive electrode active material layer can be easily formed by molding a positive electrode mixture containing the above various components in a dry or wet manner. 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.

[0065] 〈Shape, etc. of lithium secondary battery〉 Examples of the shape of the lithium secondary battery include, but are not limited to, coin type, laminate type, cylindrical type, and square type.

[0066] 《Manufacturing method of lithium secondary battery》 The lithium secondary battery of the present disclosure can be manufactured by a manufacturing method including the following steps: Forming the metal layer by depositing the first metal and the second metal on the surface of the negative electrode current collector layer to obtain a preliminary negative electrode laminate; Stacking the preliminary negative electrode laminate, 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; Performing a charging operation on the preliminary lithium secondary battery to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer, thereby forming the negative electrode active material layer and obtaining the lithium secondary battery.

[0067] According to the manufacturing method of the lithium secondary battery of the present disclosure, a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material, which can suppress an increase in resistance value during heat generation, can be manufactured.

[0068] FIG. 2 is a schematic diagram showing one aspect of the manufacturing method of the lithium secondary battery of the present disclosure, but is not limited to this case. The manufacturing method of the lithium secondary battery of the present disclosure will be described with reference to FIGS. 1 and 2.

[0069] First, a metal layer 112 having a predetermined thickness is formed on the surface of the negative electrode current collector layer 111 by depositing the first metal and the second metal by a vapor deposition method to form a preliminary negative electrode laminate 110a (FIG. 2A). Next, a positive electrode active material layer 131 is formed by applying a positive electrode composite material wet or dry on the positive electrode current collector layer 132 to form a positive electrode laminate 130, and the preliminary negative electrode laminate 110a, the electrolyte layer 120, and the positive electrode laminate 130 are stacked to form a preliminary lithium secondary battery 100a having a negative electrode current collector layer 111, a metal layer 112, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132 in this order. A charging operation is performed on this preliminary lithium secondary battery 100a to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer 112, thereby forming a negative electrode active material layer 113, and thereby a lithium secondary battery 100 can be formed (FIG. 1).

[0070] <Formation of preliminary negative electrode laminate> A metal layer can be formed by depositing a first metal and a second metal on the surface of the negative electrode current collector layer, thereby forming a preliminary negative electrode laminate.

[0071] (Preliminary negative electrode laminate) The preliminary negative electrode laminate is not particularly limited, but is a laminate in which a negative electrode current collector and a metal layer are laminated in this order.

[0072] (Formation of metal layer) The metal layer is not particularly limited, but can be formed by depositing a first metal and a second metal on the surface of the negative electrode current collector layer by a vapor deposition method. The thickness of the metal layer may be adjusted by adjusting the conditions for film formation by the vapor deposition method.

[0073] <Formation of preliminary lithium secondary battery> A preliminary lithium secondary battery can be formed by laminating a preliminary negative electrode laminate, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer in this order.

[0074] (Preliminary lithium secondary battery) The preliminary lithium secondary battery is not particularly limited, but is a laminate in which a preliminary negative electrode laminate, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in this order, that is, a laminate in which a negative electrode current collector, a metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in this order.

[0075] <Formation of lithium secondary battery> By performing a charging operation on the above-mentioned preliminary lithium secondary battery, lithium that has migrated from the above-mentioned positive electrode active material layer is deposited on the surface of the above-mentioned metal layer to form a negative electrode active material layer, thereby forming a lithium secondary battery.

[0076] (Charging operation) As the charging operation, for example, it can be performed under constant current conditions within a range of a cut-off voltage of 3.3 to 4.2V. The current amount (C rate) in the charging operation is not particularly limited, but it may be 0.01C or more, 0.1C or more, 0.5C or more, or 1.0C or more, and may also be 2.0C or less, 1.5C or less, 1.2C or less, or 1.0C or less.

[0077] (Formation of negative electrode active material layer) The negative electrode active material layer is not particularly limited. However, for a preliminary lithium secondary battery, a charging operation can be performed to release lithium from the positive electrode active material that holds lithium, deposit lithium on the metal layer, and form a negative electrode active material layer.

Example

[0078] 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.

[0079] 《Example 1》 〈Production of preliminary negative electrode laminate: Formation of metal layer on negative electrode current collector layer〉 On one side of a copper (Cu) foil as a negative electrode current collector, tin (Sn) as a first metal and Cu as a second metal were formed into a film by a vapor deposition method (co - evaporation) to form a metal layer on the negative electrode current collector layer, and a preliminary negative electrode laminate was produced. Here, the film was formed so that the thickness of the metal layer was 600 nm.

[0080] 〈Production of positive electrode laminate〉 LiNi as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (84 parts by mass), acetylene black (12 parts by mass) as a conductive assistant, PVdF (4 parts by mass) as a binder, and an appropriate amount of N - methyl - 2 - pyrrolidone (NMP) 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 (Al) foil as a positive electrode current collector and dried to produce a positive electrode laminate in which a positive electrode active material layer was formed on the positive electrode current collector layer.

[0081] <Fabrication of a Preliminary Lithium Secondary Battery> A preliminary negative electrode laminate and a positive electrode laminate were laminated so as to face each other with a polyolefin film (film thickness: 20 μm) as a separator interposed therebetween, and wound in a spiral shape. Terminals were connected to the wound preliminary negative electrode laminate and positive electrode laminate, respectively, housed in a battery case, and 1M LiPF6 ethylene carbonate / dimethyl carbonate (1 / 1 (volume ratio)) as an electrolytic solution was injected and sealed to fabricate a preliminary lithium secondary battery.

[0082] <Formation of a Lithium Secondary Battery and Evaluation of Capacity Retention Rate> The preliminary lithium secondary battery was charged and discharged 200 cycles at 25°C in a constant current (current rate: 1C) mode within a cut-off voltage range of 3.3 to 4.2V. The capacities at the first cycle and the 200th cycle were measured, and the capacity retention rate (capacity retention rate = (capacity at the 200th cycle) / (capacity at the first cycle) × 100) was calculated. The results of the capacity retention rate are shown in Table 1. Note that the capacity retention rate in Table 1 is a relative value when the capacity retention rate of the lithium secondary battery of Comparative Example 1 is set to 1.00. Here, by performing a charging operation on the preliminary lithium secondary battery, lithium that has migrated from the positive electrode active material layer is deposited on the metal layer, forming a lithium metal layer as the negative electrode active material layer, thereby forming a lithium secondary battery.

[0083] <Evaluation of Resistance Value of Lithium Secondary Battery at 70°C> The lithium secondary battery was adjusted so that the open circuit voltage became 3.70V. Next, at 70°C, it was discharged for 8 seconds at a current rate of 5C, the voltage drop (ΔV) was measured, and the resistance value of the lithium secondary battery (resistance value = ΔV / current value of 5C) was calculated. The results of the resistance value are shown in Table 1. Note that the resistance value in Table 1 is a relative value when the resistance value of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0084] <Evaluation of Short Circuit Current of Lithium Secondary Battery> The lithium secondary battery was subjected to constant current charging (current rate 1 / 3C) with a charging upper limit voltage of 3.5V, rested for 10 minutes, and the voltage was boosted to 4.5V. Subsequently, it was rested for 10 minutes from the time when the voltage was boosted to 4.5V, and the integrated value of the current amount flowing during that period was obtained. Table 1 shows the results of the short-circuit current. Note that the short-circuit current in Table 1 is the relative value when the short-circuit current of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0085] 〈Evaluation of Discharge Capacity of Lithium Secondary Battery after Vibration Durability〉 The lithium secondary battery was charged to 4.2V at a constant current (current rate 1C). Subsequently, the charged lithium secondary battery was fixed to a horizontal and vertical vibration test device, and a load of 1 million times was applied in each of the x, y, and z directions at an acceleration of 20G and a vibration frequency of 45Hz or less. Thereafter, the loaded lithium secondary battery was discharged to 3.0V at a constant current (current rate 1C), and the discharge capacity was obtained. Table 1 shows the results of the discharge capacity after the durability test. Note that the discharge capacity after the durability test in Table 1 is the relative value when the discharge capacity after the durability test of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0086] 《Comparative Example 1》 〈Preparation of Preliminary Negative Electrode Laminate〉 A metal layer was not formed on the negative electrode current collector layer, and a Cu foil as the negative electrode current collector was used as the preliminary negative electrode laminate.

[0087] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value at 70°C, Evaluation of Discharge Capacity after Vibration Durability, and Evaluation of Short-Circuit Current〉 Using a Cu foil without a formed metal layer, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate, resistance value (70°C), discharge capacity after the durability test, and short-circuit current of the lithium secondary battery were evaluated in the same manner as in Example 1. In the examples and comparative examples of this specification, the relative values are shown with the capacity retention rate and the discharge capacity after the durability test of the lithium secondary battery of Comparative Example 1 set to 1.00.

[0088] 《Examples 2 to 6 and Comparative Examples 2 and 3 (Effect of Thickness of Metal Layer)》 <Preparation of Preliminary Negative Electrode Laminate: Formation of Metal Layer on Negative Electrode Current Collector Layer> A preliminary negative electrode laminate was prepared in the same manner as in Example 1, except that the vapor deposition conditions were adjusted so that the thickness of the metal layer was the thickness shown in Table 1.

[0089] <Preparation of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value at 70 °C, Evaluation of Discharge Capacity after Vibration Durability, and Evaluation of Short-Circuit Current> Using the preliminary negative electrode laminates prepared in Examples 2 to 6 and Comparative Examples 2 and 3, lithium secondary batteries were prepared in the same manner as in Example 1. The capacity retention rate, resistance value (70 °C), discharge capacity after durability test, and short-circuit current of the lithium secondary batteries in Examples 2 to 6 and Comparative Examples 2 and 3 were evaluated in the same manner as in Example 1. The respective results were as shown in Table 1.

[0090]

Table 1

[0091] Assuming that the lithium secondary battery generates heat, the resistance value at 70 °C was evaluated. When the thickness of the metal layer was 10 to 4000 nm, it was suggested that the resistance value at 70 °C of the lithium secondary battery containing the metal layer decreased compared with the lithium secondary battery not containing the metal layer, and the increase in the resistance value during heat generation could be suppressed. Furthermore, the capacity retention rate of the lithium secondary battery containing the above metal layer increased, the discharge capacity after vibration durability increased, and the short-circuit current decreased.

[0092] When the thickness of the metal layer was 10 to 4000 nm, it was presumed that the influence of the thermal expansion of the metal layer could be reduced, the peeling of the metal layer could be suppressed, and thereby the increase in the resistance value even during heat generation could be suppressed. On the other hand, when the thickness of the metal layer was 4500 nm, it was presumed that the metal layer peeled off due to the influence of thermal expansion during heat generation, and the resistance value increased. Also, when the thickness of the metal layer was 1 nm, it was equivalent to the lithium secondary battery of Comparative Example 1 without the metal layer, and no effect of the metal layer was observed.

[0093] 《Examples 7 to 23 (Effect of Metal Contained in Metal Layer)》 〈Fabrication of Preliminary Negative Electrode Laminate: Formation of Metal Layer on Negative Electrode Current Collector Layer〉 A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that the metal described in Table 2 was used as the first metal.

[0094] 《Comparative Example 4》 A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that Cu as the second metal was not used.

[0095] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value at 70°C, Evaluation of Discharge Capacity after Vibration Durability, and Evaluation of Short-Circuit Current〉 Using the preliminary negative electrode laminates fabricated in Examples 7 to 23 and Comparative Example 4, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate, resistance value (70°C), discharge capacity after durability test, and short-circuit current of the lithium secondary batteries in Examples 7 to 23 and Comparative Example 4 were evaluated in the same manner as in Example 1. The respective results were as shown in Table 2.

[0096]

Table 2

[0097] Assuming that the lithium secondary battery generates heat, the resistance value at 70°C was evaluated. It was suggested that a lithium secondary battery having a metal layer containing a metal other than Sn as the first metal, compared with a lithium secondary battery not containing a metal layer, had a decreased resistance value at 70°C and could suppress an increase in the resistance value during heat generation. Furthermore, a lithium secondary battery having a metal layer containing a metal other than Sn had an increased capacity retention rate, an increased discharge capacity after vibration durability, and a decreased short-circuit current. Even when various metals were included as the first metal, when the thickness of the metal layer was 10 to 4000 nm, it was presumed that the influence of the thermal expansion of the metal layer could be reduced, peeling of the metal layer could be suppressed, and thereby an increase in the resistance value during heat generation could also be suppressed.

[0098] Preferred embodiments of the lithium secondary battery and the method for manufacturing the lithium secondary battery according to the present disclosure have been described, but those skilled in the art understand that changes can be made without departing from the scope of the claims.

Explanation of Signs

[0099] 100 Lithium secondary battery 100a Preliminary lithium secondary battery 110 Negative electrode laminate 110a Preliminary negative electrode laminate 111 Negative electrode current collector layer 112 Metal layer 113 Negative electrode active material layer 120 Electrolyte layer 130 Positive electrode laminate 131 Positive electrode active material layer 132 Positive electrode current collector layer

Claims

1. A lithium secondary battery having a negative electrode current collector layer, a metal layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order, wherein the negative electrode active material layer contains lithium metal or a lithium alloy, the thickness of the metal layer is 10 nm to 4000 nm, and the metal layer has a first metal that forms an alloy with lithium and a second metal contained in the negative electrode current collector layer. A lithium secondary battery.

2. The lithium secondary battery according to claim 1, wherein the first metal is at least one selected from magnesium, aluminum, silicon, calcium, scandium, titanium, manganese, zinc, gallium, germanium, strontium, yttrium, zirconium, palladium, indium, tin, barium, and gold.

3. A method for manufacturing the lithium secondary battery according to claim 1 or 2, comprising the following steps: forming the metal layer by depositing the first metal and the second metal on the surface of the negative electrode current collector layer to obtain a preliminary negative electrode laminate; laminating the preliminary negative electrode laminate, 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; performing a charging operation on the preliminary lithium secondary battery to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer, thereby forming the negative electrode active material layer and obtaining the lithium secondary battery.

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