Lithium secondary battery

Abstract

The invention relates to a lithium secondary battery. The purpose of the present invention is to provide a lithium secondary battery that uses a lithium alloy as a negative electrode active material, and that has improved capacity retention and reduced resistance value. A lithium secondary battery having a negative electrode current collector layer (111), a negative electrode active material layer (112), 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 (112) containing lithium, a first metal element that forms an alloy with the lithium, and a second metal element that forms an alloy with the lithium, the concentration (atomic%) of the first metal element at the electrolyte layer-side surface (112a) is higher than the concentration (atomic%) of the first metal element at the negative electrode current collector layer-side surface (112b), and the concentration (atomic%) of the second metal element at the electrolyte layer-side surface (112a) is lower than the concentration (atomic%) of the second metal element at the negative electrode current collector layer-side surface (112b). The first metal element is selected from the group consisting of tin, germanium, antimony, and bismuth.

Description

Technical Field

[0001] The present disclosure relates to a 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, so a high output voltage can be obtained, and it has a high theoretical capacity density. Therefore, its practical application is expected, and the following lithium secondary batteries have been disclosed.

[0003] For example, Patent Document 1 discloses a lithium secondary battery that uses the precipitation-dissolution reaction of lithium metal as the 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, 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] Regarding a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material, excellent battery characteristics are expected, but in fact, the capacity retention rate is small and the resistance value is also high. Therefore, from the viewpoints of the capacity retention rate and the resistance value, there is still room for improvement in the lithium secondary battery.

[0009] Therefore, an object of the present disclosure is to provide a lithium secondary battery that uses a lithium alloy as a negative electrode active material and has an improved capacity retention rate and a reduced resistance value.

[0010] Means for Solving the Problems

[0011] The present disclosure adopts the following means to achieve the above object.

[0012] <Solution 1>

[0013] A lithium secondary battery having, in order, a negative electrode current collector 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, a first metal element that forms an alloy with lithium, and a second metal element that forms an alloy with lithium, the concentration (atomic %) of the first metal element at the side surface of the electrolyte layer is higher than the concentration (atomic %) of the first metal element at the side surface of the negative electrode current collector layer, the concentration (atomic %) of the second metal element at the side surface of the electrolyte layer is lower than the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer, and the first metal element is selected from tin, germanium, antimony, and bismuth.

[0014] <Scheme 2>

[0015] The lithium secondary battery according to Scheme 1, wherein the first metal element is selected from tin, germanium, and antimony.

[0016] <Scheme 3>

[0017] The lithium secondary battery according to Scheme 1 or 2, wherein the second metal element is at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, silver, barium, lead, iridium, gold, platinum, and bismuth.

[0018] <Scheme 4>

[0019] The lithium secondary battery according to any one of Schemes 1 to 3, which contains an alloy containing the lithium, the first metal element, and the second metal element.

[0020] Effects of the Invention

[0021] According to the present disclosure, the capacity retention rate of a lithium secondary battery using a lithium alloy as a negative electrode active material is increased and the resistance value is decreased. Description of the Drawings

[0022] Figure 1 It is a schematic diagram for explaining the negative electrode active material layer of the lithium secondary battery of the present disclosure.

[0023] Figure 2 It is a schematic diagram for explaining the lithium secondary battery of the present disclosure.

[0024] Description of Reference Numerals

[0025] 100 Lithium secondary battery

[0026] 111 Negative electrode current collector layer

[0027] 112 Negative electrode active material layer

[0028] 112a Side surface of electrolyte layer

[0029] The side surface of the negative electrode current collector layer 112b

[0030] The layer 112c closest to the electrolyte layer

[0031] The layer 112d closest to the negative electrode active material layer

[0032] The electrolyte layer 120

[0033] The positive electrode active material layer 131

[0034] The positive electrode current collector layer 132 DETAILED DESCRIPTION

[0035] The embodiments of the present disclosure will be described in detail below. It should be noted that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure. In addition, in the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

[0036] Regarding the present disclosure, "composite material" means a composition that can directly form a positive electrode active material layer or the like, or further contains other components to form a positive electrode active material layer or the like. 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 or the like by coating and drying.

[0037] 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. Further, 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.

[0038] "Lithium Secondary Battery"

[0039] The lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector 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, a first metal element that forms an alloy with lithium, and a second metal element that forms an alloy with lithium. The concentration (atomic %) of the first metal element at the side surface of the electrolyte layer is higher than the concentration (atomic %) of the first metal element at the side surface of the negative electrode current collector layer. The concentration (atomic %) of the second metal element at the side surface of the electrolyte layer is lower than the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer. The first metal element is selected from tin, germanium, antimony, and bismuth.

[0040] According to the present disclosure, the capacity retention rate of a lithium secondary battery using a lithium alloy as a negative electrode active material is increased, and the resistance value is decreased.

[0041] Although the details are not clear, it is considered that the first metal element is easily alloyed with lithium and has a high affinity for the electrolyte. In addition, it is considered that the second metal element is less likely to expand even during charging by combining with the first metal element. Without being limited by theory, it is speculated that the negative electrode active material layer 112 containing the first metal element and the second metal element appropriately arranged specifically suppresses the increase in specific surface area accompanying charge and discharge, whereby the capacity retention rate is increased. In addition, it is speculated that by arranging a large amount of the first metal element that is easily alloyed with lithium on the electrolyte layer side surface 112a, lithium easily enters the negative electrode active material layer 112, whereby the resistance value is decreased. Particularly in a liquid system battery containing an electrolyte, it is speculated that the affinity between the negative electrode active material layer and the electrolyte is increased, and lithium becomes easily dissolved and deposited, whereby the resistance value is decreased.

[0042] Figure 2 A schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but it is not limited to this case.

[0043] The lithium secondary battery 100 sequentially includes a negative electrode current collector layer 111, a negative electrode active material layer 112, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132. The negative electrode active material layer has an electrolyte layer side surface 112a and a negative electrode current collector layer side surface 112b. In addition, the negative electrode active material layer 112 contains lithium, a first metal element, and a second metal element. The concentration of the first metal element at the electrolyte layer side surface 112a is higher than the concentration of the first metal element at the negative electrode current collector layer side surface 112b. In addition, the concentration of the second metal element at the electrolyte layer side surface 112a is lower than the concentration of the second metal element at the negative electrode current collector layer side surface 112b. It is considered that the first metal element is easily alloyed with lithium and has a high affinity for the electrolyte. In addition, it is considered that the second metal element is less likely to expand even during charging by combining with the first metal element. It is speculated that the negative electrode active material layer 112 containing the first metal element and the second metal element appropriately arranged specifically suppresses the increase in specific surface area accompanying charge and discharge, whereby the capacity retention rate is increased. In addition, it is speculated that by arranging a large amount of the first metal element that is easily alloyed with lithium on the electrolyte layer side surface, lithium easily enters the negative electrode active material layer, whereby the resistance value is decreased.

[0044] 〈Configuration of lithium secondary battery〉

[0045] The lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0046] 〈Negative electrode current collector layer〉

[0047] There is no particular limitation on the material for the negative electrode current collector layer, and materials commonly used as the negative electrode current collector of a lithium secondary battery can be appropriately employed. Examples of materials for the negative electrode current collector layer include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or carbon sheets, etc., but it is not limited to such cases. In particular, from the viewpoints of ensuring reducibility resistance and difficulty in alloying with lithium, etc., the material 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 carbon sheets. For the purpose of adjusting resistance, etc., the negative electrode current collector layer may have certain coatings on its surface.

[0048] There is no particular limitation on the shape of the negative electrode current collector layer, and for example, foil shape, plate shape, or sieve mesh shape, etc. can be cited. Among these, foil shape is preferred.

[0049] 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.

[0050] 〈Negative electrode active material layer〉

[0051] In the lithium secondary battery of the present disclosure, the negative electrode active material layer contains lithium, a first metal element that alloys with lithium, and a second metal element that alloys with lithium.

[0052] In the "negative electrode active material layer" in the charged state, there exist layers of the lithium alloy of lithium and the first metal element, and the lithium alloy of lithium and the second metal element as the "negative electrode active material layer". In the discharged state, the lithium in the lithium alloy of lithium and the first metal element, and the lithium in the lithium alloy of lithium and the second metal element move as lithium ions to the positive electrode active material layer. Sometimes, as the "negative electrode active material layer", there may be no layers of the lithium alloy of lithium and the first metal element, and the lithium alloy of lithium and the second metal element, but there may be layers of the first metal element and the second metal element.

[0053] The negative electrode active material layer contains at least a first metal element alloyed with lithium and a second metal element alloyed with lithium as the negative electrode active material, and further optionally may contain a conductive additive, a binder, a solid electrolyte, etc. The negative electrode active material layer may additionally contain various additives. The contents of the negative electrode active material, conductive additive, binder, 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.

[0054] (Negative electrode active material)

[0055] As the negative electrode active material, a first metal element alloyed with lithium and a second metal element alloyed with lithium are used. The first metal element and the second metal element contained in the negative electrode active material layer are different from each other. Herein, the first metal element and the second metal element may or may not be a combination that forms an alloy.

[0056] In the present disclosure, the two metal elements being "different" means that the types of the metal elements are different from each other. It does not mean that the types of the metal elements are the same but only the content ratios are different when forming a lithium alloy, for example. In addition, in the present disclosure, the two metal elements being "the same" means that the types of the metal elements are the same as each other, and thus it also includes the case where the types of the metal elements are the same but only the content ratios are different when forming a lithium alloy, for example.

[0057] (First metal element)

[0058] The first metal element is selected from tin, germanium, antimony, and bismuth. In addition, there is no particular limitation on the first metal element, and from the viewpoints of capacity retention rate and resistance value, it is preferably selected from tin, germanium, and antimony.

[0059] In the lithium secondary battery of the present disclosure, the concentration (atomic %) of the first metal element at the side surface of the electrolyte layer is higher than the concentration (atomic %) of the first metal element at the side surface of the negative electrode current collector layer.

[0060] The concentration (atomic %) of the first metal element at the side surface of the electrolyte layer is the amount (number of atoms) of the first metal element relative to the total amount (number of atoms) of the first metal element and the second metal element at the side surface of the electrolyte layer. Similarly, the concentration (atomic %) of the first metal element at the side surface of the negative electrode current collector layer is the amount (number of atoms) of the first metal element relative to the total amount (number of atoms) of the first metal element and the second metal element at the side surface of the negative electrode current collector layer.

[0061] The concentration of the first metal element can be determined by observing a cross-section of the negative electrode active material layer in the discharged state or a preliminary negative electrode active material layer formed by depositing the first metal element and the second metal element on the surface of the negative electrode current collector layer described later, using a scanning electron microscope (SEM) and elemental mapping based on energy-dispersive X-ray analysis (EDX). In the present disclosure, the "concentration of the first metal element at the electrolyte layer side surface" can be obtained as the concentration of the first metal element in the layer closest to the electrolyte layer when the cross-section of the negative electrode active material layer or the preliminary negative electrode active material layer is divided into 30 equal parts from the electrolyte layer side surface to the negative electrode current collector layer side surface. Similarly, the "concentration of the first metal element at the negative electrode current collector layer side surface" can be obtained as the concentration of the first metal element in the layer closest to the negative electrode current collector layer when the cross-section of the negative electrode active material layer or the preliminary negative electrode active material layer is divided into 30 equal parts from the electrolyte layer side surface to the negative electrode current collector layer side surface.

[0062] The concentration (atomic %) of the first metal element at the electrolyte layer side surface is not particularly limited, and can be 2.0 times or more, 2.5 times or more, 3.0 times or more, or 5.0 times or more the concentration (atomic %) of the first metal element at the negative electrode current collector layer side surface, and can be 1000 times or less, 100 times or less, or 10 times or less.

[0063] Figure 1 It is a schematic diagram of a cross-section showing one embodiment of the lithium secondary battery of the present disclosure, and is a schematic diagram in which the negative electrode active material layer is enlarged, but is not limited to this case.

[0064] The dotted line is a line that divides the cross-section of the negative electrode active material layer 112 into 30 equal parts from the electrolyte layer side surface 112a to the negative electrode current collector layer side surface 112b. In the present disclosure, the concentration of the first metal element at the electrolyte layer side surface 112a can be obtained as the concentration of the first metal element in the layer 112c closest to the electrolyte layer 120. Similarly, the concentration of the first metal element at the negative electrode current collector layer side surface 112b can be obtained as the concentration of the first metal element in the layer 112d closest to the negative electrode current collector layer 111. The concentration of the first metal element in the layer 112c closest to the electrolyte layer 120 is higher than the concentration of the first metal element in the layer 112d closest to the negative electrode current collector layer 111, that is, the concentration (atomic %) of the first metal element at the electrolyte layer side surface 112a is higher than the concentration (atomic %) of the first metal element at the negative electrode current collector layer side surface 112b.

[0065] (Second metal element)

[0066] The second metal element is not particularly limited as long as it is a metal element that alloyizes with lithium.

[0067] There is no particular limitation on the second metal element, and it may be at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, silver, barium, lead, iridium, gold, platinum, and bismuth.

[0068] In the lithium secondary battery of the present disclosure, the concentration (atomic %) of the second metal element at the side surface of the electrolyte layer is lower than the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer.

[0069] The concentration (atomic %) of the second metal element at the side surface of the electrolyte layer is the amount (number of atoms) of the second metal element relative to the total amount (number of atoms) of the first metal element and the second metal element at the side surface of the electrolyte layer. Similarly, the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer is the amount (number of atoms) of the second metal element relative to the total amount (number of atoms) of the first metal element and the second metal element at the side surface of the negative electrode current collector layer.

[0070] The concentration of the second metal element can be determined by observing the cross-section of the negative electrode active material layer in the discharged state or the preliminary negative electrode active material layer formed by depositing the first metal element and the second metal element on the negative electrode current collector layer described later using a scanning electron microscope (SEM) and elemental mapping based on energy-dispersive X-ray analysis (EDX). In the present disclosure, the "concentration of the second metal element at the side surface of the electrolyte layer" can be obtained as the concentration of the second metal element in the layer closest to the electrolyte layer when the cross-section of the above negative electrode active material layer or the above preliminary negative electrode active material layer is divided into 30 equal parts from the side surface of the electrolyte layer to the side surface of the negative electrode current collector layer. Similarly, the "concentration of the second metal element at the side surface of the negative electrode current collector layer" can be obtained as the concentration of the second metal element in the layer closest to the negative electrode current collector layer when the cross-section of the above negative electrode active material layer or the above preliminary negative electrode active material layer is divided into 30 equal parts from the side surface of the electrolyte layer to the side surface of the negative electrode current collector layer.

[0071] There is no particular limitation on the concentration (atomic %) of the second metal element at the side surface of the electrolyte layer, and it may be 0.001 times or more, 0.01 times or more, or 0.1 times or more of the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer, and may be 0.2 times or less, 0.3 times or less, 0.4 times or less, or 0.5 times or less.

[0072] In the above Figure 1In the present disclosure, the concentration of the second metal element at the side surface 112a of the electrolyte layer can be determined as the concentration of the second metal element in the layer 112c closest to the electrolyte layer 120. Similarly, the concentration of the second metal element at the side surface 112b of the negative electrode current collector layer can be determined as the concentration of the second metal element in the layer 112d closest to the negative electrode current collector layer 111. The concentration of the second metal element in the layer 112c closest to the electrolyte layer 120 is lower than the concentration of the second metal element in the layer 112d closest to the negative electrode current collector layer 111, that is, the concentration (atomic %) of the second metal element at the side surface 112a of the electrolyte layer is lower than the concentration (atomic %) of the second metal element at the side surface 112b of the negative electrode current collector layer.

[0073] The negative electrode active material layer is not particularly limited and may contain an alloy containing lithium, a first metal element, and a second metal element.

[0074] In addition, the negative electrode active material layer may contain a negative electrode active material other than lithium, the first metal element, the second metal element, and an alloy of lithium, the first metal element, and the second metal element. The negative electrode active material other than lithium, the first metal element, the second metal element, and an alloy of lithium, the first metal element, and the second metal element is not particularly limited, and examples thereof include carbon materials. As the carbon material, for example, hard carbon, soft carbon, graphite, etc. can be mentioned, but it is not limited to these cases.

[0075] The ratio of lithium, the first metal element, the second metal element, and an alloy of lithium, the first metal element, and the second metal element contained in the negative electrode active material layer is not particularly limited, and 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.

[0076] (Binder)

[0077] The binder is not particularly limited. The binder may 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. The binder is not particularly limited, and 1 type may be used alone, or 2 or more types may be used in combination.

[0078] (Conductive additive)

[0079] There are no particular limitations 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 are no particular limitations on its size. There are no particular limitations on the conductive additive, and only one type can be used alone, or two or more types can be used in combination.

[0080] (Solid electrolyte)

[0081] There are no particular limitations on the material of the solid electrolyte. For example, it can be a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, etc.

[0082] Examples of the sulfide solid electrolyte include sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or thiogermanate-type solid electrolytes, etc., but are not limited to these. As examples of specific sulfide solid electrolytes, 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, but are not limited to these.

[0083] 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 , 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 PO4- x N x (LiPON) etc., but not limited to these.

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

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

[0086] The shape of the negative electrode active material is not particularly limited as long as it is a common shape as the negative electrode active material of a lithium secondary battery. The negative electrode active material can be, for example, layered or flaky. The negative electrode active material can be accompanied by the precipitation of lithium during charging or the dissolution of lithium during discharging. In this case, the negative electrode active material layer can be a layer composed of a lithium alloy.

[0087] The shape of the negative electrode active material layer is not particularly limited. For example, it can be a flaky negative electrode active material layer having a substantially flat surface. The thickness of the negative 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 200 μm or less, 150 μm or less, or 100 μm or less.

[0088] The negative electrode active material layer can be formed with reference to the <Method for manufacturing a lithium secondary battery> described later.

[0089] <Electrolyte layer>

[0090] <Electrolyte layer - Solid electrolyte layer>

[0091] 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.

[0092] In addition to the solid electrolyte, the solid electrolyte layer can contain an adhesive, etc. as needed.

[0093] Regarding the solid electrolyte and the adhesive, reference can be made to the description in the above "<Negative electrode active material layer>".

[0094] The thickness of the solid electrolyte layer is not particularly limited. For example, it can be 0.1 μm or more, 1 μm or more, or 10 μm or more, and can be 2 mm or less, 1 mm or less, or 500 μm or less.

[0095] The solid electrolyte layer can be easily formed, for example, by dry or wet molding, etc. of an electrolyte composite material containing the above solid electrolyte and adhesive, etc.

[0096] <Electrolyte layer - Separator layer>

[0097] 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 the electrolytic solution held in the separator layer.

[0098] (Electrolytic solution)

[0099] There is no particular limitation on the electrolytic solution, and it preferably contains a supporting salt and a solvent.

[0100] There is no particular limitation on the supporting salt (lithium salt) of the electrolytic solution having lithium ion conductivity, 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.

[0101] There is no particular limitation on the solvent for the electrolytic solution, 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.

[0102] (Separator)

[0103] There is no particular limitation on the separator, 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 such as polyolefin-based, polyamide-based, and polyimide-based can be used.

[0104] 〈Positive electrode active material layer〉

[0105] The positive electrode active material layer contains at least a positive electrode active material, and may further optionally contain a conductive additive, a solid electrolyte, a binder, etc. In addition, the positive electrode active material layer can contain various additives. The contents of the positive electrode active material, the conductive additive, 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 can be 40% by mass or more, 50% by mass or more, 60% by mass or more, and can be 100% by mass or less, or 90% by mass or less.

[0106] (Positive electrode active material)

[0107] 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), a lithium - manganese spinel substituted with a foreign element 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.

[0108] There is no particular limitation on the positive electrode active material, and it may have a coating layer. The coating layer is a layer of a substance having a form of a coating layer that has lithium - ion conductivity, low reactivity with the positive electrode active material and the solid electrolyte, and can maintain non - fluidity even when in contact with the active material or the solid electrolyte. As a specific example of the material constituting the coating layer, in addition to LiNbO3, Li4Ti5O 12 , Li3PO4, etc. can be cited, but it is not limited to these.

[0109] 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 aggregated from multiple primary particles. The average particle diameter D 50 of the positive electrode active material can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and can also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. It should be noted that the average particle diameter D 50 is the particle diameter (median diameter) at the cumulative value of 50% in the volume - based particle size distribution determined by the laser diffraction / scattering method.

[0110] For the solid electrolyte, binder, and conductive additive, reference can be made to the description in the above “〈Negative electrode active material layer〉”.

[0111] There is no particular limitation on the shape of the positive electrode active material layer. For example, it can be a positive electrode active material layer in the form of a sheet having a substantially flat surface. There is no particular limitation on the thickness of the positive 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 2 mm or less, 1 mm or less, or 500 μm or less.

[0112] <Positive current collector layer>

[0113] There is no particular limitation on the material for the positive current collector layer, and materials commonly used as the positive current collector of a lithium secondary battery can be appropriately used. As the material for the positive current collector layer, for example, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. can be cited, but it is not limited to this case. In addition, for the purpose of adjusting resistance, etc., the positive current collector layer may have some coatings on its surface. In addition, the positive current collector layer may be a product obtained by plating or vapor-depositing the above-mentioned metals on a metal foil or substrate.

[0114] There is no particular limitation on the shape of the positive current collector layer. For example, foil shape, plate shape, or sieve mesh shape, etc. can be cited. Among these, the foil shape is preferred.

[0115] There is no particular limitation on the thickness of the positive current collector layer. It can be 0.1 μm or more, or 1 μm or more, and can be 1 mm or less, or 100 μm or less.

[0116] The positive electrode active material layer can be manufactured by applying a known method. For example, by dry or wet molding of the positive electrode composite material containing the above various components, the positive electrode active material layer can be easily molded. The positive electrode active material layer can be molded together with the positive current collector layer, or can be molded independently of the positive current collector layer.

[0117] <Shape, etc. of lithium secondary battery>

[0118] As the shape of the lithium secondary battery, for example, coin type, laminate type, cylindrical type, square type can be cited, but it is not limited to these cases.

[0119] <Manufacturing method of lithium secondary battery>

[0120] The lithium secondary battery of the present disclosure can be manufactured by a manufacturing method including the following steps:

[0121] Vapor-deposit a first metal element and a second metal element on the surface of the negative current collector layer to form a preliminary negative electrode active material layer, and obtain a preliminary negative electrode laminate;

[0122] Stack the above-mentioned preliminary negative electrode laminate, electrolyte layer, lithium-holding positive electrode active material layer, and positive current collector layer in sequence to obtain a preliminary lithium secondary battery;

[0123] Perform a charging operation on the above-mentioned preliminary lithium secondary battery, so that lithium moves from the above-mentioned positive electrode active material layer to the preliminary negative electrode active material layer to form a negative electrode active material layer, thereby obtaining a lithium secondary battery.

[0124] (Preliminary negative electrode active material layer)

[0125] The preliminary negative electrode active material layer is not particularly limited and can be formed by vapor-depositing a first metal element and a second metal element on the surface of the negative electrode current collector layer. The concentrations of the first metal element and the second metal element on the electrolyte layer side surface of the preliminary negative electrode active material layer can be adjusted by adjusting the conditions of the vapor-deposition method (co-vapor deposition) of the first metal element and the second metal element, but this is not the only case. Similarly, the concentrations of the first metal element and the second metal element on the negative electrode current collector layer side surface of the preliminary negative electrode active material layer can be adjusted by adjusting the conditions of the vapor-deposition method (co-vapor deposition) of the first metal element and the second metal element, but this is not the only case.

[0126] (Preliminary negative electrode laminate)

[0127] The preliminary negative electrode laminate is not particularly limited and is a laminate in which a negative electrode current collector and a preliminary negative electrode active material layer are laminated in sequence.

[0128] 〈Preliminary lithium secondary battery〉

[0129] The preliminary lithium secondary battery is not particularly limited and 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 sequence, that is, a laminate in which a negative electrode current collector, a preliminary negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in sequence.

[0130] Examples

[0131] 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.

[0132] 《Example 1》

[0133] 〈Production of preliminary negative electrode laminate〉

[0134] On one side of a copper (Cu) foil as a preliminary negative electrode current collector, tin (Sn) as a first metal element and silver (Ag) as a second metal element were formed into a film by a vapor-deposition method (co-vapor deposition) to produce a preliminary negative electrode laminate composed of a negative electrode current collector layer and a preliminary negative electrode active material layer. Among them, the conditions of co-vapor deposition were adjusted and the film was formed such that on the electrolyte layer side surface, the first metal element was 90.1 atomic%, the second metal element was 9.9 atomic%, and on the negative electrode current collector layer side surface, the first metal element was 9.9 atomic%, and the second metal element was 90.1 atomic%.

[0135] Furthermore, the concentration of the metal element is determined by observing a cross-section of the preliminary negative electrode active material layer using a scanning electron microscope (SEM) and performing elemental mapping based on energy-dispersive X-ray analysis (EDX). For the concentration of the first metal element at the side surface of the electrolyte layer, the cross-section of the preliminary negative electrode laminate is divided into 30 equal parts from the side surface of the electrolyte layer to the side surface of the negative electrode current collector layer, and the concentration of the first metal element in the layer closest to the electrolyte layer side is obtained. Similarly, for the concentration of the first metal element at the side surface of the negative electrode current collector layer, the cross-section of the preliminary negative electrode laminate is divided into 30 equal parts from the side surface of the electrolyte layer to the side surface of the negative electrode current collector layer, and the concentration of the first metal element in the layer closest to the negative electrode current collector layer side is obtained. For the second metal element, it is determined in the same manner as the first metal element.

[0136] <Fabrication of the positive electrode laminate>

[0137] LiNi as the 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 paste. Next, the obtained positive electrode composite paste was coated on an aluminum (Al) foil as the 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.

[0138] <Fabrication of the preliminary lithium secondary battery>

[0139] 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) 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, filled with 1 M LiPF6 ethylene carbonate / dimethyl carbonate (1 / 1 (volume ratio)) as an electrolyte, and sealed to fabricate a preliminary lithium secondary battery.

[0140] <Formation and evaluation of the capacity retention rate of the lithium secondary battery>

[0141] For the preliminary lithium secondary battery, within the range of the cut-off voltage of 3.3 to 4.2 V at 25 °C, charge and discharge were carried out for 200 cycles in a constant current (current rate 1C) mode. 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. It should be noted that the capacity retention rate in Table 1 is the relative value when the capacity retention rate of the lithium secondary battery in Comparative Example 1 is set to 1.00. Among them, by performing a charging operation on the preliminary lithium secondary battery, lithium moves from the positive electrode active material layer to the preliminary negative electrode active material layer, forming a negative electrode active material layer containing lithium, a first metal element, and a second metal element, thereby forming a lithium secondary battery.

[0142] 〈Evaluation of the resistance value of the lithium secondary battery〉

[0143] The lithium secondary battery was adjusted so that the open circuit voltage became 3.70 V. Next, at -10 °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 value are shown in Table 1. It should be noted that the resistance value in Table 1 is the relative value when the resistance value of the lithium secondary battery in Comparative Example 1 is set to 1.00.

[0144] 《Comparative Example 1》

[0145] 〈Fabrication of the preliminary negative electrode laminate〉

[0146] On one side of a Cu foil serving as a preliminary negative electrode current collector, Sn serving as a first metal element was formed into a film by vapor deposition, and a preliminary negative electrode laminate composed of a negative electrode current collector layer and a preliminary negative electrode active material layer was fabricated.

[0147] 〈Fabrication of the lithium secondary battery, evaluation of the capacity retention rate, evaluation of the resistance value〉

[0148] A lithium secondary battery was fabricated using a preliminary negative electrode laminate composed only of a first metal element by the same method as in Example 1. For the capacity retention rate and resistance value of the lithium secondary battery, evaluation was carried out by the same method as in Example 1. In the examples and comparative examples in this specification, they are expressed as relative values when the capacity retention rate and resistance value of the lithium secondary battery in Comparative Example 1 are set to 1.00.

[0149] 《Comparative Example 2》

[0150] 〈Fabrication of the preliminary negative electrode laminate〉

[0151] On one side of a Cu foil serving as a preliminary negative electrode current collector, Ag as a second metal element was formed into a film by vapor deposition, and a preliminary negative electrode laminate composed of a negative electrode current collector layer and a preliminary negative electrode active material layer was fabricated.

[0152] 《Comparative Example 3》

[0153] 〈Fabrication of Preliminary Negative Electrode Laminate〉

[0154] On one side of a Cu foil serving as a preliminary negative electrode current collector, Sn as a first metal element and Ag as a second metal element were formed into a film by vapor deposition (co-evaporation) in a manner to form an alloy, and a preliminary negative electrode laminate composed of a negative electrode current collector layer and a preliminary negative electrode active material layer was fabricated.

[0155] 《Examples 2 to 4, Comparative Example 4》

[0156] 〈Fabrication of Preliminary Negative Electrode Laminate〉

[0157] A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that the metals listed in Table 1 were used as the first metal element.

[0158] 《Example 5》

[0159] 〈Fabrication of Preliminary Negative Electrode Laminate〉

[0160] On one side of a Cu foil serving as a preliminary negative electrode current collector, tin (Sn) as a first metal element and silver (Ag) as a second metal element were formed into a film by vapor deposition (co-evaporation). Next, Sn as a first metal element and Ag as a second metal element were formed into a film by vapor deposition (co-evaporation) in a manner to form an alloy. Then, tin (Sn) as a first metal element and silver (Ag) as a second metal element were formed into a film by vapor deposition (co-evaporation), and a preliminary negative electrode laminate composed of a negative electrode current collector layer and a preliminary negative electrode active material layer was fabricated. Among them, the co-evaporation conditions were adjusted for film formation such that on the electrolyte layer side surface, the first metal element was 90.1 atomic %, the second metal element was 9.9 atomic %, and on the negative electrode current collector layer side surface, the first metal element was 9.9 atomic %, and the second metal element was 90.1 atomic %.

[0161] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value〉

[0162] Using the preliminary negative electrode laminates fabricated in Examples 2 to 5 and Comparative Examples 2 to 4, lithium secondary batteries were fabricated in the same manner as in Example 1. For the capacity retention rates and resistance values of the lithium secondary batteries in Examples 2 to 5 and Comparative Examples 2 to 4, evaluation was carried out in the same manner as in Example 1. The respective results are shown in Table 1.

[0163]

Table 1

[0164]

[0165] In lithium secondary batteries (Examples 1 to 5) including a negative electrode active material layer having Sn, germanium (Ge), antimony (Sb), or bismuth (Bi) as a first metal element and Ag as a second metal element, compared with lithium secondary batteries including a negative electrode active material layer having only Sn as a first metal element or only Ag as a second metal element, the capacity retention rate increases and the resistance value decreases. Among them, in the batteries including a negative electrode active material layer having Sn, Ge, or Sb (Examples 1 to 3, 5) as a first metal element, the capacity retention rate and the resistance value are good. In a lithium secondary battery (Example 5) in which a tin-silver alloy, which is an alloy of a first metal element and a second metal element, is further included in the negative electrode active material layer, the capacity retention rate and the resistance value are particularly good.

[0166] It is considered that the first metal element disposed in a large amount on the side surface of the electrolyte layer is likely to alloy with lithium and has a high affinity with the electrolyte solution. In addition, it is considered that the second metal element disposed in a large amount on the side surface of the negative electrode current collector layer is not easily swollen even during charging by combining with the first metal element. It is speculated that the negative electrode active material layer containing appropriately disposed first and second metal elements specifically suppresses the increase in the specific surface area accompanying charge and discharge, thereby increasing the capacity retention rate. In addition, it is speculated that by disposing a large amount of the first metal element, which is likely to alloy with lithium, on the side surface of the electrolyte layer, lithium easily enters the negative electrode active material layer, thereby reducing the resistance value. Furthermore, it is speculated that the affinity between the negative electrode active material layer and the electrolyte solution increases, and lithium is easily dissolved and deposited, thereby reducing the resistance value.

[0167] 《Examples 6 to 13 (Effect of Concentration)》

[0168] 〈Fabrication of Preliminary Negative Electrode Laminate〉

[0169] A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that the co-evaporation conditions were adjusted to obtain the concentrations shown in Table 2.

[0170] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value〉

[0171] Using the preliminary negative electrode laminates fabricated in Examples 6 to 13, lithium secondary batteries were fabricated in the same manner as in Example 1. For the capacity retention rate and the resistance value of the lithium secondary batteries in Examples 6 to 13, evaluation was performed in the same manner as in Example 1. The respective results are shown in Table 2.

[0172]

Table 2

[0173]

[0174] When the concentration (atomic %) of the first metal element at the side surface of the electrolyte layer is higher than the concentration (atomic %) of the first metal element at the side surface of the negative electrode current collector layer, and the concentration (atomic %) of the second metal element at the side surface of the electrolyte layer is lower than the concentration (atomic %) of the second metal element at the side surface of the negative electrode current collector layer, the capacity retention rate increases and the resistance value decreases.

[0175] It is speculated that the negative electrode active material layer containing the first metal element and the second metal element appropriately arranged specifically suppresses the increase in specific surface area associated with charge and discharge, thereby increasing the capacity retention rate. In addition, it is speculated that a large amount of the first metal element that is easily alloyed with lithium is arranged on the side surface of the electrolyte layer, and lithium becomes easily incorporated into the negative electrode active material layer, thereby reducing the resistance value.

[0176] 《Examples 14 to 30 (Effect of the second metal element)》

[0177] 〈Fabrication of the negative electrode laminate〉

[0178] Except for using the metals described in Table 3 as the second metal element, a preliminary negative electrode laminate was fabricated in the same manner as in Example 1.

[0179] 〈Fabrication of the lithium secondary battery, evaluation of the capacity retention rate, evaluation of the resistance value〉

[0180] Using the preliminary negative electrode laminates fabricated in Examples 14 to 30, lithium secondary batteries were fabricated in the same manner as in Example 1. For the capacity retention rate and resistance value of the lithium secondary batteries in Examples 14 to 30, evaluation was carried out in the same manner as in Example 1. The respective results are shown in Table 3.

[0181]

Table 3

[0182]

[0183] Even when a metal other than Ag is used as the second metal element, the capacity retention rate increases and the resistance value decreases. It is speculated that even when the second metal element is various metal elements, by combining with the first metal element, it is not easily swollen due to charging, specifically suppressing the increase in specific surface area associated with charge and discharge, thereby increasing the capacity retention rate.

[0184] The preferred embodiments of the lithium secondary battery of the present disclosure have been described above, but those skilled in the art should 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 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 includes lithium, a first metal element that forms an alloy with lithium, and a second metal element that forms an alloy with lithium. The concentration (atomic %) of the first metal element at the surface on the electrolyte layer side is higher than the concentration (atomic %) of the first metal element at the surface on the negative electrode current collector layer side, The concentration (atomic %) of the second metal element at the surface on the electrolyte layer side is lower than the concentration (atomic %) of the second metal element at the surface on the negative electrode current collector layer side, The first metal element is selected from tin, germanium, antimony and bismuth.

2. The lithium secondary battery according to claim 1, wherein The first metal element is selected from tin, germanium and antimony.

3. The lithium secondary battery according to claim 1 or 2, wherein: The second metal element is at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, silver, barium, lead, iridium, gold, platinum and bismuth. 4 . The lithium secondary battery according to claim 1 , comprising an alloy containing the lithium, the first metal element, and the second metal element.

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