Lithium secondary battery and method for manufacturing lithium secondary battery

Abstract

The invention relates to a lithium secondary battery and a method for manufacturing the lithium secondary battery. The purpose of the present invention is to provide a lithium secondary battery which uses lithium metal and / or a lithium alloy as a negative electrode active material and which is capable of suppressing an increase in resistance value when the battery generates heat. A lithium secondary battery having 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) containing a lithium metal or a lithium alloy, the metal layer (112) having a thickness of 10-4000 nm, and the metal layer (112) having a first metal that forms an alloy with lithium and a second metal contained in the negative electrode current collector layer (111).

Description

Technical Field

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

[0002] A lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material has a large potential difference between the negative electrode and the positive electrode, and thus can obtain a high output voltage and has a high theoretical capacity density. Therefore, its practical application is expected, and the following lithium secondary batteries are disclosed.

[0003] For example, Patent Document 1 discloses a lithium secondary battery that uses a precipitation-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 foreign metal as a negative electrode active material. When the lithium secondary battery is fully charged, the elemental ratio of lithium element in the alloy is 40.00 atomic % or more and 99.97 atomic % or less. According to Patent Document 1, it is considered that a lithium secondary battery capable of improving the capacity retention rate can be provided.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-103517 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In order to improve the physical properties of a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material, a lithium secondary battery having a specific modified layer on a negative electrode current collector layer is known. However, in the lithium secondary battery having the above-mentioned modified layer, due to the thermal expansion of the modified layer when the lithium secondary battery generates heat, the resistance value may increase.

[0009] Therefore, an object of the present disclosure is 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 when the lithium secondary battery generates heat.

[0010] Means for Solving the Problems

[0011] The present disclosure achieves the above object by adopting the following means.

[0012] <Aspect 1>

[0013] A lithium secondary battery having, in order, 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, 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.

[0014] <Scheme 2>

[0015] The lithium secondary battery according to Scheme 1, wherein the first metal is at least one selected from the group consisting of magnesium, aluminum, silicon, calcium, scandium, titanium, manganese, zinc, gallium, germanium, strontium, yttrium, zirconium, palladium, indium, tin, barium, and gold.

[0016] <Scheme 3>

[0017] A method for manufacturing the lithium secondary battery according to Scheme 1 or 2, comprising the following steps:

[0018] Vapor-depositing the first metal and the second metal on the surface of the negative electrode current collector layer to form the metal layer, thereby obtaining a preliminary negative electrode laminate;

[0019] Stacking the preliminary negative electrode laminate, the electrolyte layer, the positive electrode active material layer that holds lithium, and the positive electrode current collector layer in sequence to obtain a preliminary lithium secondary battery; and

[0020] Performing a charging operation on the preliminary lithium secondary battery so that lithium moving from the positive electrode active material layer precipitates on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium secondary battery.

[0021] Effects of the Invention

[0022] According to the present disclosure, it is possible to suppress an increase in the resistance value during heating of a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material. Description of the Drawings

[0023] Figure 1 A schematic diagram for explaining the lithium secondary battery of the present disclosure.

[0024] Figure 2 A schematic diagram for explaining the manufacturing method of the lithium secondary battery of the present disclosure.

[0025] Description of Reference Numerals

[0026] 100 Lithium secondary battery

[0027] 100a Preliminary lithium secondary battery

[0028] 110 Negative electrode laminate

[0029] 110a Preliminary negative electrode laminate

[0030] 111 Negative electrode current collector layer

[0031] 112 Metal layer

[0032] 113 Negative electrode active material layer

[0033] 120 Electrolyte layer

[0034] 130 Positive electrode laminate

[0035] 131 Positive electrode active material layer

[0036] 132 Positive electrode current collector layer Detailed implementation mode

[0037] The following will explain the implementation modes of the present disclosure in detail. Furthermore, the present disclosure is not limited to the following implementation modes, 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.

[0038] Regarding the present disclosure, "composite material" means a composition that can directly form, or further contain other components to form a positive electrode active material layer, etc. In addition, 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, etc. by coating and drying.

[0039] The lithium secondary battery of the present disclosure can be a liquid battery containing an electrolyte solution as the electrolyte layer, or a solid battery having a solid electrolyte layer as the electrolyte layer. It should be noted that regarding the present disclosure, "solid battery" means a battery that uses at least a solid electrolyte as the electrolyte. Therefore, a solid battery can use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. In addition, the lithium secondary battery of the present disclosure can be an all-solid battery, that is, a battery that uses only a solid electrolyte as the electrolyte.

[0040] "Lithium Secondary Battery"

[0041] The lithium secondary battery of the present disclosure sequentially 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. 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.

[0042] 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 the negative electrode active material.

[0043] It is not limited to theory. It is speculated that when the thickness of the metal layer is within a specified range, the influence of the thermal expansion of the metal layer can be reduced, the peeling of the metal layer can be suppressed, and thus the increase in the resistance value can also be suppressed during heating. On the other hand, it is speculated that when the thickness of the metal layer is too large, due to the influence of thermal expansion during heating, the metal layer peels off and the resistance value increases.

[0044] Figure 1 Fig. is a schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but it is not limited to this case.

[0045] The lithium secondary battery 100 successively 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, and the metal layer 112 has a specified thickness. By using the metal layer 112 having a specified thickness, an increase in the resistance value during heating of the lithium secondary battery can be suppressed. It is speculated that when the thickness of the metal layer 112 is within a specified range, the influence of the thermal expansion of the metal layer 112 can be reduced, the peeling of the metal layer 112 can be suppressed, and thus the increase in the resistance value can also be suppressed during heating. On the other hand, it is speculated that when the thickness of the metal layer 112 is too large, due to the influence of thermal expansion during heating, the metal layer 112 peels off and the resistance value increases.

[0046] 〈Configuration of lithium secondary battery〉

[0047] The lithium secondary battery of the present disclosure successively 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.

[0048] 〈Negative electrode current collector layer〉

[0049] There is no particular limitation on the material used for the negative electrode current collector layer, and a material commonly used as the negative electrode current collector of a lithium secondary battery can be appropriately adopted. As the material used for the negative electrode current collector layer, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or a carbon sheet, etc. can be listed, 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 used for the negative electrode current collector layer may contain at least one metal selected from Cu, Ni, and stainless steel, or may be composed of a carbon sheet. The negative electrode current collector layer may have some coatings on its surface for the purpose of adjusting resistance, etc.

[0050] There is no particular limitation on the shape of the negative electrode current collector layer, and for example, a foil shape, a plate shape, or a sieve mesh shape, etc. can be listed. Among these, a foil shape is preferred.

[0051] There is no particular limitation on the thickness of the negative electrode current collector layer, which may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0052] 〈Metal layer〉

[0053] In the lithium secondary battery of the present disclosure, the metal layer has a first metal and a second metal. The first metal is a metal that forms an alloy with lithium, and the second metal is a metal contained in the negative electrode current collector layer. Among them, the first metal and the second metal may or may not be a combination that forms an alloy.

[0054] (First metal)

[0055] The first metal is not particularly limited as long as it forms an alloy with lithium.

[0056] 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.

[0057] (Second metal)

[0058] 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.

[0059] As the material for the negative electrode current collector layer, that is, the metal contained in the negative electrode current collector layer, the description of the above “〈Negative electrode current collector layer〉” can be referred to.

[0060] 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 can be, for example, 10 nm or more, 100 nm or more, 200 nm or more, or 500 nm or more, and 4000 nm or less, 2000 nm or less, or 1000 nm or less. The thickness of the metal layer can be measured by observing the cross section of the metal layer with a scanning electron microscope (SEM).

[0061] 〈Negative electrode active material layer〉

[0062] In the lithium secondary battery of the present disclosure, the negative electrode active material layer contains lithium metal or a lithium alloy.

[0063] Among them, when the “negative electrode active material layer” contains lithium metal, in the charged state, a layer of lithium metal as the “negative electrode active material layer” exists, and in the discharged state, the lithium metal moves as lithium ions to the positive electrode active material layer, and the layer of lithium metal as the “negative electrode active material layer” sometimes no longer exists. Similarly, when the “negative electrode active material layer” contains a lithium alloy, in the charged state, a layer of the lithium alloy as the “negative electrode active material layer” exists, and in the discharged state, the lithium of the lithium alloy moves as lithium ions to the positive electrode active material layer, and the lithium alloy as the “negative electrode active material layer” sometimes does not exist, and a layer of the metal from which lithium has been removed from the lithium alloy exists.

[0064] 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 additives. The content of each of the negative electrode active material, the conductive aid, the binder, the solid electrolyte, etc. in the negative electrode active material layer can be appropriately determined according to the target battery performance. For example, when the whole of the negative electrode active material layer (the whole solid component) is set to 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 be 100% by mass or less, or 90% by mass or less.

[0065] (Negative electrode active material)

[0066] As the negative electrode active material, as described above, at least lithium metal or a lithium alloy is used. As the lithium alloy, there is no particular limitation 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 cited, and it is not limited to these cases. As the silicon alloy-based negative electrode active material, there are silicon, silicon oxide, silicon carbide, silicon nitride, or a solid solution thereof, etc. In addition, in the silicon alloy-based negative electrode active material, metal elements other than silicon can be contained, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. As the tin alloy-based negative electrode active material, there are tin, tin oxide, tin nitride, or a solid solution thereof, etc. In addition, in the tin alloy-based negative electrode active material, metal elements other than tin can be contained, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0067] In addition, in the negative electrode active material layer, a negative electrode active material other than lithium metal or a lithium alloy may be contained. As the negative electrode active material other than lithium metal and lithium alloy, there is no particular limitation, and carbon materials, etc. can be cited. As the carbon material, for example, hard carbon, soft carbon, graphite, etc. can be cited, and it is not limited to these cases.

[0068] There is no particular limitation on the proportion of the lithium metal or lithium alloy contained in the negative electrode active material layer. Relative to the negative electrode active material layer, it may be 50% by mass to 100%, 60% by mass to 100%, 70% by mass to 100%, 80% by mass to 100%, or 90% by mass to 100%.

[0069] (Binder)

[0070] As the binder, there is no particular limitation. The binder can be, for example, materials such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc., but is not limited to these. There is no particular limitation on the binder, and only one kind can be used alone, or two or more kinds can be used in combination.

[0071] (Conductive additive)

[0072] There is no particular limitation on the conductive additive. 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 to these. The conductive additive can be, for example, particulate or fibrous, and there is no particular limitation on its size. There is no particular limitation on the conductive additive, and only one kind can be used alone, or two or more kinds can be used in combination.

[0073] (Solid electrolyte)

[0074] There is no particular limitation on the material of the solid electrolyte. For example, it can be a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte, etc.

[0075] As examples of the sulfide solid electrolyte, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or thioargentogermanate-type solid electrolytes, etc. can be cited, but are not limited to these. As examples of specific sulfide solid electrolytes, Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof, but are not limited to these.

[0076] As examples of the oxide solid electrolyte, Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7- 3x La3Zr2Al x O12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4- x N x (LiPON), etc., but not limited to these.

[0077] The sulfide solid electrolyte and the oxide solid electrolyte can be glass or crystallized glass (glass ceramic).

[0078] Examples of the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), and their copolymers, etc., but not limited to these.

[0079] There is no particular limitation on the shape of the negative electrode active material, as long as it is a general shape of the negative electrode active material for a lithium secondary battery. The negative electrode active material can be, for example, layered or flaky. The negative electrode active material may precipitate lithium during charging or dissolve lithium during discharging. In this case, the negative electrode active material layer can be a layer composed of lithium metal or a lithium alloy.

[0080] There is no particular limitation on the shape of the negative electrode active material layer. For example, it can be a negative electrode active material layer in the form of a flake with a substantially flat surface. There is no particular limitation on the thickness of the negative electrode active material layer. For example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can be 200 μm or less, 150 μm or less, or 100 μm or less.

[0081] The negative electrode active material layer can be formed with reference to the description in the "Manufacturing Method of Lithium Secondary Battery" described later.

[0082] 〈Electrolyte layer〉

[0083] 〈Electrolyte layer - Solid electrolyte layer〉

[0084] 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.

[0085] In addition to the solid electrolyte, the solid electrolyte layer can contain an adhesive, etc. as needed.

[0086] Regarding the solid electrolyte and the adhesive, reference can be made to the description in the above "〈Negative electrode active material layer〉".

[0087] There is no particular limitation on the thickness of the solid electrolyte layer. For example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can be 2 mm or less, 1 mm or less, or 500 μm or less.

[0088] The solid electrolyte layer can be easily formed, for example, by dry or wet molding of an electrolyte composite material containing the above solid electrolyte and a binder, etc.

[0089] 〈Electrolyte layer - separator layer〉

[0090] The lithium secondary battery of the present disclosure can be a liquid-based battery, that is, it can have an electrolytic solution, particularly an electrolytic solution held in the separator layer, as the electrolyte layer.

[0091] (Electrolytic solution)

[0092] There is no particular limitation on the electrolytic solution, and it preferably contains a supporting salt and a solvent.

[0093] As the supporting salt (lithium salt) of the electrolytic solution having lithium ion conductivity, there is no particular limitation, and inorganic lithium salts, organic lithium salts, etc. can be cited. As inorganic lithium salts, for example, LiPF6, LiBF4, LiClO4, LiAsF6, etc. can be cited, but it is not limited to these cases. As organic lithium salts, for example, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc. can be cited, but it is not limited to these cases.

[0094] As the solvent for the electrolytic solution, 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 it is not limited to these cases. As chain carbonates, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be cited, but it is not limited to these cases. There is no particular limitation on the electrolytic solution, and it can be used alone or in combination of two or more.

[0095] (Separator)

[0096] There is no particular limitation on the separator (diaphragm), and a separator commonly used as a separator for a lithium secondary battery can be appropriately adopted. As the separator, for example, non-woven fabrics of polyolefin-based, polyamide-based, polyimide-based, etc. can be used.

[0097] 〈Positive electrode active material layer〉

[0098] The positive electrode active material layer contains at least a positive electrode active material, and may further optionally contain a conductive aid, a solid electrolyte, a binder, etc. In addition to these, the positive electrode active material layer may contain various additives. The contents of the positive electrode active material, the conductive aid, the binder, etc. in the positive electrode active material layer can be appropriately determined according to the target battery performance. For example, when the whole of the positive electrode active material layer (the whole solid component) is set to 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 be 100% by mass or less, or 90% by mass or less.

[0099] (Positive electrode active material)

[0100] Regarding the material of the positive electrode active material, there is no particular limitation as long as it can occlude and release lithium ions. As the positive electrode active material, for example, it can be lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium nickel cobalt manganese oxide (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, lithium nickel cobalt aluminate (NCA; LiNi x Co y Al z O2), and a lithium-manganese spinel substituted with a foreign element having a composition represented by 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), etc., but is not limited to these.

[0101] Although not particularly limited, the positive electrode active material 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 not flowing even when in contact with the active material or the solid electrolyte and capable of maintaining the form of the coating layer. As a specific example of the material constituting the coating layer, in addition to LiNbO3, Li4Ti5O 12 , Li3PO4, etc. can be cited, but are not limited to these.

[0102] Regarding the shape of the positive electrode active material, there is no particular limitation as long as it is a common shape as the positive electrode active material of a lithium secondary battery. The positive electrode active material can be, for example, particulate. The positive electrode active material can be primary particles or secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter D 50 For example, it can be 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 diameter D 50It is the particle diameter (median diameter) at the cumulative value of 50% in the particle size distribution of the volume standard obtained by the laser diffraction / scattering method.

[0103] For the solid electrolyte, binder, and conductive assistant, the descriptions of the above “〈negative electrode active material layer〉” can be referred to.

[0104] The shape of the positive electrode active material layer is not particularly limited. For example, it can be a positive electrode active material layer in the form of a sheet with a substantially flat surface. The thickness of the positive electrode active material 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 be 2 mm or less, 1 mm or less, or 500 μm or less.

[0105] 〈Positive electrode current collector layer〉

[0106] The material used for the positive electrode current collector layer is not particularly limited, and materials commonly used as the positive electrode current collector of a lithium secondary battery can be appropriately used. As the material for the positive electrode current collector layer, for example, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. can be listed, but it is not limited to this case. In addition, the positive electrode current collector layer may have some coatings on its surface for the purpose of adjusting resistance, etc. In addition, the positive electrode current collector layer can be a product obtained by plating or vapor-depositing the above metal on a metal foil or substrate.

[0107] The shape of the positive electrode current collector layer is not particularly limited. For example, foil shape, plate shape, or sieve mesh shape, etc. can be listed. Among these, the foil shape is preferred.

[0108] The thickness of the positive electrode current collector layer is not particularly limited, and can be 0.1 μm or more, or 1 μm or more, and can be 1 mm or less, or 100 μm or less.

[0109] The positive electrode active material layer can be manufactured by a known method. For example, the positive electrode composite material containing the above various components can be formed by dry or wet molding, etc., so that 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 independently of the positive electrode current collector layer.

[0110] 〈Shape, etc. of lithium secondary battery〉

[0111] As the shape of the lithium secondary battery, for example, coin type, laminated type, cylindrical type, square type can be listed, but it is not limited to these cases.

[0112] 《Manufacturing method of lithium secondary battery》

[0113] The lithium secondary battery of the present disclosure can be manufactured by a manufacturing method including the following steps:

[0114] The first metal and the second metal are vapor-deposited on the surface of the negative electrode current collector layer to form the metal layer, thereby obtaining a preliminary negative electrode laminate;

[0115] The preliminary negative electrode laminate, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer are sequentially laminated to obtain a preliminary lithium secondary battery;

[0116] The preliminary lithium secondary battery is charged, so that lithium moving from the positive electrode active material layer is deposited on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium secondary battery.

[0117] According to the method for manufacturing a 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 and capable of suppressing an increase in resistance value during heat generation can be manufactured.

[0118] Figure 2 FIG. is a schematic diagram showing an embodiment of the method for manufacturing a lithium secondary battery of the present disclosure, but is not limited to this case. Use Figure 1 and Figure 2 , the method for manufacturing a lithium secondary battery of the present disclosure will be described.

[0119] First, on the surface of the negative electrode current collector layer 111, the first metal and the second metal are vapor-deposited to form a metal layer 112 having a predetermined thickness, thereby forming a preliminary negative electrode laminate 110a ( Figure 2 A). Next, a positive electrode composite material is coated on the positive electrode current collector layer 132 by a wet or dry method to form a positive electrode active material layer 131, thereby forming a positive electrode laminate 130. The preliminary negative electrode laminate 110a, the electrolyte layer 120, and the positive electrode laminate 130 are laminated 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. For this preliminary lithium secondary battery 100a, a charging operation is performed to deposit lithium moving from the positive electrode active material layer on the surface of the metal layer 112 to form a negative electrode active material layer 113, thereby forming a lithium secondary battery 100 ( Figure 1 ).

[0120] <Formation of preliminary negative electrode laminate>

[0121] The first metal and the second metal are vapor-deposited on the surface of the negative electrode current collector layer to form a metal layer, whereby a preliminary negative electrode laminate can be formed.

[0122] (Preliminary negative electrode laminate)

[0123] The preliminary negative electrode laminate is not particularly limited and is a laminate in which a negative electrode current collector and a metal layer are sequentially laminated.

[0124] (Formation of metal layer)

[0125] There is no particular limitation on the metal layer, and it can be formed by depositing the first metal and the second metal on the surface of the negative electrode current collector layer by vapor deposition. The thickness of the metal layer can be adjusted by adjusting the conditions of the film formation by vapor deposition.

[0126] 〈Formation of preliminary lithium secondary battery〉

[0127] The preliminary lithium secondary battery can be formed by sequentially laminating a preliminary negative electrode laminate, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer.

[0128] (Preliminary lithium secondary battery)

[0129] There is no particular limitation on the preliminary lithium secondary battery, which 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 sequentially laminated, 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 sequentially laminated.

[0130] 〈Formation of lithium secondary battery〉

[0131] The above-mentioned preliminary lithium secondary battery is subjected to a charging operation, so that lithium moving 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, whereby a lithium secondary battery can be formed.

[0132] (Charging operation)

[0133] As the charging operation, for example, it can be carried out under constant current conditions in the range of a cut-off voltage of 3.3 to 4.2V. There is no particular limitation on the current amount (C rate) in the charging operation, and it can be 0.01C or more, 0.1C or more, 0.5C or more, or 1.0C or more, and can be 2.0C or less, 1.5C or less, 1.2C or less, or 1.0C or less.

[0134] (Formation of negative electrode active material layer)

[0135] There is no particular limitation on the negative electrode active material layer, and it can be formed by subjecting the preliminary lithium secondary battery to a charging operation, discharging lithium from the positive electrode active material holding lithium, and depositing lithium on the metal layer to form a negative electrode active material layer.

[0136] Examples

[0137] 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.

[0138] 《Example 1》

[0139] <Fabrication of a preliminary negative electrode laminate: Formation of a metal layer on a negative electrode current collector layer>

[0140] On one side of a copper (Cu) foil serving as a negative electrode current collector layer, a film of tin (Sn) as a first metal and Cu as a second metal was formed by vapor deposition (co-evaporation) to form a metal layer on the negative electrode current collector layer, and a preliminary negative electrode laminate was fabricated. Among them, the film was formed so that the thickness of the metal layer became 600 nm.

[0141] <Fabrication of a positive electrode laminate>

[0142] 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 additive, 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 serving as a positive electrode current collector and dried to fabricate a positive electrode laminate in which a positive electrode active material layer was formed on the positive electrode current collector layer.

[0143] <Fabrication of a preliminary lithium secondary battery>

[0144] The preliminary negative electrode laminate and the positive electrode laminate were laminated so as to face each other via a polyolefin film (film thickness: 20 μm) serving as a separator and wound into a spiral shape. The wound preliminary negative electrode laminate and positive electrode laminate were respectively connected to terminals, housed in a battery case, and 1 M LiPF6-ethylene carbonate / dimethyl carbonate (1 / 1 (volume ratio)) serving as an electrolyte was injected and sealed to fabricate a preliminary lithium secondary battery.

[0145] <Formation and evaluation of the capacity retention rate of a lithium secondary battery>

[0146] For the preliminary lithium secondary battery, at 25 °C, within the range of a cut-off voltage of 3.3 to 4.2 V, charge and discharge were performed 200 cycles in a constant current (current rate: 1C) manner. The capacities of the first cycle and the 200th cycle were measured, and the capacity retention rate was calculated (capacity retention rate = (capacity of the 200th cycle) / (capacity of the first cycle) × 100). The results of the capacity retention rate are shown in Table 1. Furthermore, 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. Among them, 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 to form a lithium metal layer as a negative electrode active material layer, thereby forming a lithium secondary battery.

[0147] <Evaluation of the resistance value of a lithium secondary battery at 70 °C>

[0148] The lithium secondary battery was adjusted so that the open voltage became 3.70 V. Next, at 70 °C, it was discharged at a current rate of 5C for 8 seconds, the voltage drop (ΔV) was measured, and the resistance value of the lithium secondary battery was calculated (resistance value = ΔV / current value of 5C). The results of the resistance values are shown in Table 1. Incidentally, the resistance values in Table 1 are relative values when the resistance value of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0149] <Evaluation of the short-circuit current of the lithium secondary battery>

[0150] For the lithium secondary battery, the charging upper limit voltage was made 3.5 V, constant current charging (current rate 1 / 3C) was performed, and it was left at rest for 10 minutes, and the voltage was boosted up to 4.5 V. Next, from the moment when the voltage was boosted up to 4.5 V, it was left at rest for 10 minutes, and the cumulative value of the current amount flowing during this period was obtained. The results of the short-circuit current are shown in Table 1. It should be noted that the short-circuit current in Table 1 is a relative value when the short-circuit current of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0151] <Evaluation of the discharge capacity after vibration durability of the lithium secondary battery>

[0152] The lithium secondary battery was charged to 4.2 V at a constant current (current rate 1C). Next, 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 the x, y, and z directions at an acceleration of 20G and a vibration frequency of 45 Hz or less. Then, the lithium secondary battery to which the load was applied was discharged to 3.0 V at a constant current (current rate 1C), and the discharge capacity was obtained. The results of the discharge capacity after the durability test are shown in Table 1. It should be noted that the discharge capacity after the durability test in Table 1 is a relative value when the discharge capacity after the durability test of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0153] <<Comparative Example 1>>

[0154] <Production of the preliminary negative electrode laminate>

[0155] 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.

[0156] <Production of the lithium secondary battery, evaluation of the capacity retention rate, evaluation of the resistance value at 70 °C, evaluation of the discharge capacity after vibration durability, and evaluation of the short-circuit current>

[0157] A lithium secondary battery was fabricated using a Cu foil without a formed metal layer by the same method as in Example 1. For the capacity retention rate, resistance value (70 °C), discharge capacity after the durability test, and short-circuit current of the lithium secondary battery, evaluation was carried out by the same method as in Example 1. In the examples and comparative examples of this specification, the capacity retention rate and discharge capacity after the durability test of the lithium secondary battery of Comparative Example 1 were shown as relative values of 1.00.

[0158] 《Examples 2 - 6 and Comparative Examples 2, 3 (Effect of Metal Layer Thickness)》

[0159] 〈Fabrication of Preliminary Negative Electrode Laminate: Formation of Metal Layer on Negative Current Collector Layer〉

[0160] A preliminary negative electrode laminate was fabricated by the same method as in Example 1, except that the evaporation conditions were adjusted so that the thickness of the metal layer was the thickness shown in Table 1.

[0161] 〈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〉

[0162] Using the preliminary negative electrode laminates fabricated in Examples 2 - 6 and Comparative Examples 2, 3, a lithium secondary battery was fabricated by the same method as in Example 1. For the capacity retention rate, resistance value (70 °C), discharge capacity after the durability test, and short-circuit current of the lithium secondary batteries in Examples 2 - 6 and Comparative Examples 2, 3, evaluation was carried out by the same method as in Example 1. The respective results are shown in Table 1.

[0163]

Table 1

[0164]

[0165] Assuming a situation where heat generation occurs in the lithium secondary battery, the resistance value at 70 °C was evaluated. When the thickness of the metal layer was 10 - 4000 nm, compared with the lithium secondary battery without a metal layer, the resistance value at 70 °C of the lithium secondary battery containing a metal layer decreased, suggesting that an increase in the resistance value during heat generation can 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.

[0166] It is speculated that when the thickness of the metal layer is 10 to 4000 nm, the influence of the thermal expansion of the metal layer can be reduced, the peeling of the metal layer can be suppressed, and thus the increase in the resistance value can be suppressed even when heated. On the other hand, it is speculated that when the thickness of the metal layer is 4500 nm, due to the influence of thermal expansion during heating, the metal layer peels off and the resistance value increases. In addition, when the thickness of the metal layer is 1 nm, the same effect as that of Comparative Example 1 of the lithium secondary battery without the metal layer is not found.

[0167] 《Examples 7 to 23 (Effect of the Metal Contained in the Metal Layer)》

[0168] 〈Fabrication of the Preliminary Negative Electrode Laminate: Formation of the Metal Layer on the Negative Electrode Current Collector Layer〉

[0169] A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that the metals listed in Table 2 were used as the first metal.

[0170] 《Comparative Example 4》

[0171] 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.

[0172] 〈Fabrication of the Lithium Secondary Battery, Evaluation of the Capacity Retention Rate, Evaluation of the Resistance Value at 70 °C, Evaluation of the Discharge Capacity after Vibration Durability, and Evaluation of the Short-Circuit Current〉

[0173] Using the preliminary negative electrode laminates fabricated in Examples 7 to 23 and Comparative Example 4, lithium secondary batteries were fabricated in the same manner as in Example 1. For the capacity retention rate, resistance value (70 °C), discharge capacity after the durability test, and short-circuit current of the lithium secondary batteries in Examples 7 to 23 and Comparative Example 4, evaluation was performed in the same manner as in Example 1. The respective results are shown in Table 2.

[0174]

Table 2

[0175]

[0176] Suppose a situation where a lithium secondary battery generates heat, and the resistance value at 70 °C was evaluated. Compared with a lithium secondary battery without a metal layer, the lithium secondary battery having a metal layer containing a metal other than Sn as the first metal also has a reduced resistance value at 70 °C, suggesting that an increase in the resistance value during heat generation can be suppressed. Furthermore, the capacity retention rate of the lithium secondary battery having a metal layer containing a metal other than Sn increases, the discharge capacity after vibration durability increases, and the short-circuit current decreases. Even when various metals are included as the first metal, it is presumed that when the thickness of the metal layer is 10 to 4000 nm, the influence of the thermal expansion of the metal layer can be reduced, peeling of the metal layer can be suppressed, and thus an increase in the resistance value during heat generation can also be suppressed.

[0177] The preferred embodiments of the lithium secondary battery and the method for manufacturing a lithium secondary battery of the present disclosure have been described above. Those skilled in the art can understand that modifications can be made without departing from the patent claims.

Claims

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

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. The method for producing a lithium secondary battery according to claim 1 or 2, comprising the following steps: Vapor depositing the first metal and the second metal on the surface of the negative electrode current collector layer to form the metal layer and obtain a preliminary negative electrode laminate; The preliminary negative electrode laminate, the electrolyte layer, the positive electrode active material layer for retaining lithium, and the positive electrode collector layer are sequentially laminated to obtain a preliminary lithium secondary battery; and The preliminary lithium secondary battery is charged so that lithium moved from the positive electrode active material layer is deposited on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium secondary battery.

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