Lithium secondary battery and method for manufacturing lithium secondary battery

Abstract

The purpose of the present disclosure is to provide a lithium secondary battery which uses a lithium metal and / or a lithium alloy as a negative electrode active material, and which is capable of improving the capacity retention rate and reducing the resistance value. The lithium secondary battery has a negative electrode current collector layer (111), a negative electrode active material layer (112), an inorganic porous 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 (112) contains lithium metal or a lithium alloy, and the inorganic porous layer (113) contains a metal compound containing at least one metal element selected from the group consisting of calcium, barium, lanthanum, and cerium.

Description

Technical Field

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

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

[0003] For example, Patent Document 1 discloses a lithium secondary battery that 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 different metal as a negative electrode active material. At full charge of the lithium secondary battery, 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 Document 1: Japanese Unexamined Patent Application Publication No. 2023-103517 Summary of the Invention

[0006] A lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material is expected to have excellent battery characteristics, but in fact, its capacity retention rate is small and its resistance value is also high, and its characteristics are not sufficient. Therefore, such a lithium secondary battery has room for improvement in terms of capacity retention rate and resistance value.

[0007] 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, can improve the capacity retention rate, and can reduce the resistance value.

[0008] The present disclosure achieves the above object by the following means.

[0009] <Mode 1>

[0010] A lithium secondary battery sequentially includes a negative electrode current collector layer, a negative electrode active material layer, an inorganic porous layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0011] The negative electrode active material layer contains lithium metal or a lithium alloy, and

[0012] The inorganic porous layer contains a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0013] <Mode 2>

[0014] The lithium secondary battery according to Method 1, the thickness of the inorganic porous layer is 10 nm to 100 μm.

[0015] <Method 3>

[0016] The lithium secondary battery according to Method 1 or 2, the metal compound is selected from metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, and combinations thereof.

[0017] <Method 4>

[0018] A method for manufacturing a lithium secondary battery according to any one of Methods 1 to 3, comprising the following steps: immersing the negative electrode current collector layer in a solution containing the metal element and lithium, and forming the negative electrode active material layer and the inorganic porous layer on the surface of the negative electrode current collector layer by an electrolytic reaction.

[0019] According to the present disclosure, it is possible to improve the capacity retention rate of a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material, and to reduce the resistance value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram for explaining the lithium secondary battery of the present disclosure.

[0021] Figure 2 is a schematic diagram for explaining the manufacturing method of the lithium secondary battery of the present disclosure.

[0022] DESCRIPTION OF THE REFERENCE NUMERALS

[0023] 100 Lithium secondary battery

[0024] 110 Negative electrode laminate

[0025] 111 Negative electrode current collector layer

[0026] 112 Negative electrode active material layer

[0027] 113 Inorganic porous layer

[0028] 120 Electrolyte layer

[0029] 130 Positive electrode laminate

[0030] 131 Positive electrode active material layer

[0031] 132 Positive electrode current collector layer DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present disclosure will be described in detail. Furthermore, 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 redundant descriptions are omitted.

[0033] In the present disclosure, the "binder" refers to a composition that can form the positive electrode active material layer as it is or by further containing other components. In addition, in the present disclosure, the "binder slurry" refers to a slurry that contains a dispersion medium in addition to the "binder" and can form the positive electrode active material layer or the like by coating and drying.

[0034] The lithium secondary battery of the present disclosure can be a liquid system battery containing an electrolyte as the electrolyte layer, or a solid battery having a solid electrolyte layer as the electrolyte layer. Furthermore, in the present disclosure, a "solid battery" refers to a battery that uses at least a solid electrolyte as the electrolyte. Therefore, a solid battery can also 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 also be an all-solid battery, that is, a battery that uses only a solid electrolyte as the electrolyte.

[0035] "Lithium Secondary Battery"

[0036] The lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector layer, a negative electrode active material layer, an inorganic porous layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0037] The above negative electrode active material layer contains lithium metal or a lithium alloy, and

[0038] The above inorganic porous layer contains a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0039] According to the present disclosure, it is possible to improve the capacity retention rate of a lithium secondary battery using lithium metal and / or a lithium alloy as the negative electrode active material, and to reduce the resistance value.

[0040] Specifically, for example Figure 1 As shown, the lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector layer 111, a negative electrode active material layer 112, an inorganic porous layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132. The inorganic porous layer 113 contains at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0041] Although not limited by theory, it is speculated that the inorganic porous layer is formed of an inorganic substance to form a porous layer, so it has high mechanical strength and electron insulation, can suppress the decomposition of the electrolyte and the destruction of the solid electrolyte interphase (SEI), and thus the capacity retention rate is improved. In addition, oxides of metal elements such as lanthanum are known as oxide solid electrolytes. It is speculated that due to their high lithium conductivity, the lithium carrier concentration is increased at the interface between the inorganic porous layer and the negative electrode active material layer, reducing the battery resistance. Moreover, it is speculated that by forming a porous shape, the diffusion of the electrolyte into the inorganic porous layer is promoted, making it easier to reach the negative electrode active material, thereby reducing the battery resistance.

[0042] <Configuration of Lithium Secondary Battery>

[0043] The lithium secondary battery of the present disclosure sequentially includes a negative electrode current collector layer, a negative electrode active material layer, an inorganic porous layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0044] <Negative Electrode Current Collector Layer>

[0045] The material for the negative electrode current collector layer is not particularly limited, and a material generally used as the negative electrode current collector of a lithium secondary battery can be appropriately adopted. Examples of the material for the negative electrode current collector layer include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or a carbon sheet, etc., but are not limited to this case. In particular, from the viewpoints of ensuring reducibility resistance and not easily alloying with lithium, 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 a carbon sheet. For the purpose of adjusting resistance, etc., the negative electrode current collector layer may also have a certain coating on its surface.

[0046] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, or a mesh shape, etc. Among them, a foil shape is preferred.

[0047] The thickness of the negative electrode current collector layer is not particularly limited, and it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0048] <Negative Electrode Active Material Layer>

[0049] In the lithium secondary battery of the present disclosure, the negative electrode active material layer contains lithium metal or a lithium alloy.

[0050] Here, when the "negative electrode active material layer" contains lithium metal, in the charged state, there is a layer of lithium metal as the "negative electrode active material layer", and in the discharged state, the lithium metal moves to the positive electrode active material layer in the form of lithium ions, and sometimes the layer of lithium metal as the "negative electrode active material layer" may disappear. Similarly, when the "negative electrode active material layer" contains a lithium alloy, in the charged state, there is a layer of lithium alloy as the "negative electrode active material layer", and in the discharged state, the lithium in the lithium alloy moves to the positive electrode active material layer in the form of lithium ions, and sometimes instead of the lithium alloy as the "negative electrode active material layer", there is a layer of a metal from which lithium has been removed from the lithium alloy.

[0051] The negative electrode active material layer contains at least lithium metal or a lithium alloy as the negative electrode active material, and may optionally contain a conductive additive, a binder, a solid electrolyte, etc. The negative electrode active material layer may also contain various other additives. The content of each of the negative electrode active material, the conductive additive, 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, based on the total (total solid components) of the negative electrode active material layer being 100% by mass, the content of the negative 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.

[0052] (Negative electrode active material)

[0053] As the negative electrode active material, at least lithium metal or a lithium alloy is used as described above. There is no particular limitation on the lithium alloy, and it is sufficient that it is a material that can be alloyed with lithium and occlude and release lithium ions. For example, silicon alloy-based negative electrode active materials, tin alloy-based active materials, etc. can be cited, but it is not limited to these cases. Silicon alloy-based negative electrode active materials include silicon, silicon oxides, silicon carbides, silicon nitrides, or solid solutions thereof. In addition, the silicon alloy-based negative electrode active material may contain metal elements other than silicon, 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 oxides, tin nitrides, or solid solutions thereof. In addition, the tin alloy-based negative electrode active material may contain metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0054] In addition, the negative electrode active material layer may also contain a negative electrode active material other than lithium metal or a lithium alloy. There is no particular limitation on the negative electrode active material other than lithium metal and lithium alloy, and carbon materials, etc. can be cited. As the carbon material, for example, hard carbon, soft carbon, graphite, etc. can be cited, but it is not limited to these cases.

[0055] The proportion of lithium metal or lithium alloy contained in the negative electrode active material layer is not particularly limited, and relative to the negative electrode active material layer, it may also 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.

[0056] (Binder)

[0057] There is no particular limitation on the binder. 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 thereto. The binder is not particularly limited, and only 1 type can be used alone, or 2 or more types can be used in combination.

[0058] (Conductive additive)

[0059] 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 thereto. The conductive additive can also be, for example, particulate or fibrous, and its size is not particularly limited. The conductive additive is not particularly limited, and only 1 type can be used alone, or 2 or more types can be used in combination.

[0060] (Solid electrolyte)

[0061] The material of the solid electrolyte is not particularly limited, and can be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, etc.

[0062] Examples of the sulfide solid electrolyte include sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes, etc., but are not limited thereto. As specific examples of the sulfide solid electrolyte, 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 thereto.

[0063] 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 PO 4-x N x (LiPON), etc., but not limited thereto.

[0064] The sulfide solid electrolyte and the oxide solid electrolyte can be glass or crystallized glass (glass ceramic).

[0065] Examples of the polymer electrolyte include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof, etc., but not limited thereto.

[0066] The shape of the negative electrode active material is not particularly limited and can be a general shape as the negative electrode active material of a lithium secondary battery. The negative electrode active material can also 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 also be a layer composed of lithium metal or lithium alloy.

[0067] 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 planar shape. 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 2 mm or less, 1 mm or less, or 500 μm or less.

[0068] The negative electrode active material layer can be formed with reference to the description in the "Manufacturing Method of Lithium Secondary Battery" described later.

[0069] <Inorganic Porous Layer>

[0070] In the lithium secondary battery of the present disclosure, the inorganic porous layer contains a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0071] The above metal compound may also be selected from metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, and combinations thereof.

[0072] The inorganic porous layer is not particularly limited and can be formed by an electrolytic reaction. The inorganic porous layer may also contain supporting salts such as lithium salts contained in the electrolytic solution for the electrolytic reaction, decomposition products of the solvent, and the like.

[0073] The content of the above metal element in the inorganic porous layer is not particularly limited and may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, and may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less.

[0074] The thickness of the inorganic porous layer may also be 10 nm to 100 μm. From the viewpoints of capacity retention rate and resistance value, the thickness of the inorganic porous layer may be 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, or 50 nm or more, and may be 500000 nm or less, 300000 nm or less, 200000 nm or less, or 100000 nm or less. The thickness of the inorganic porous layer can be measured by observing the cross-section of the inorganic porous layer using a scanning electron microscope (SEM).

[0075] The shape of the pores in the inorganic porous layer is not particularly limited. The porosity of the inorganic porous layer is not particularly limited and may be 10% by volume or more, 20% by volume or more, 30% by volume or more, 40% by volume or more, or 50% by volume or more, and may be 90% by volume or less, 80% by volume or less, 70% by volume or less, 60% by volume or less, or 50% by volume or less. Here, the porosity can be calculated using the apparent density and true density of the inorganic porous layer according to the following calculation formula (porosity (% by volume) = {1 - (apparent density (g / cm 3 )) / true density (g / cm 3 ))} × 100).

[0076] The inorganic porous layer can be formed with reference to the description in "Method for Manufacturing Lithium Secondary Battery" described later.

[0077] <Electrolyte layer>

[0078] <Electrolyte layer - Solid electrolyte layer>

[0079] The lithium secondary battery of the present disclosure may be a solid battery, that is, having a solid electrolyte layer as the electrolyte layer.

[0080] In addition to the solid electrolyte, the solid electrolyte layer may contain a binder or the like as needed.

[0081] Regarding the solid electrolyte and the binder, reference can be made to the description of the "<negative electrode active material layer>" above.

[0082] 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.

[0083] The solid electrolyte layer can be easily formed, for example, by dry or wet forming of an electrolyte mixture containing the above-mentioned solid electrolyte and binder or the like.

[0084] <Electrolyte layer - Separator layer>

[0085] The lithium secondary battery of the present disclosure can be a liquid battery, that is, it has an electrolytic solution, particularly an electrolytic solution held in the separator layer, as the electrolyte layer.

[0086] (Electrolytic solution)

[0087] The electrolytic solution is not particularly limited, but preferably contains a supporting salt and a solvent.

[0088] The supporting salt (lithium salt) of the electrolytic solution having lithium ion conductivity is not particularly limited, and examples thereof include inorganic lithium salts and organic lithium salts. As the inorganic lithium salt, for example, LiPF6, LiBF4, LiClO4, LiAsF6, etc. can be mentioned, but not limited to these cases. As the organic lithium salt, for example, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc. can be mentioned, but not limited to these cases.

[0089] The solvent for the electrolytic solution is not particularly limited, and examples thereof include cyclic carbonates and chain carbonates. As the cyclic carbonate, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be mentioned, but not limited to this case. As the chain carbonate, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be mentioned, but not limited to this case. The electrolytic solution is not particularly limited, and it can be used alone as only one kind, or two or more kinds can be used in combination.

[0090] (Separator)

[0091] The separator is not particularly limited, and a separator generally used as a separator for a lithium secondary battery can be appropriately used. As the separator, for example, non-woven fabrics such as polyolefin-based, polyamide-based, and polyimide-based can be used.

[0092] <Positive electrode active material layer>

[0093] The positive electrode active material layer contains at least a positive electrode active material, and may optionally contain a conductive assistant, a solid electrolyte, a binder, etc. The positive electrode active material layer may also contain various other additives. The contents of the positive electrode active material, the conductive assistant, the binder, etc. in the positive electrode active material layer can be appropriately determined according to the target battery performance. For example, based on the whole of the positive electrode active material layer (the whole solid component) being 100% by mass, the content of the positive electrode active material can be 40% by mass or more, 50% by mass or more, 60% by mass or more, and can be 100% by mass or less or 90% by mass or less.

[0094] (Positive electrode active material)

[0095] The material of the positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. As the positive electrode active material, for example, it can also 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 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 thereto.

[0096] The positive electrode active material is not particularly limited and may also have a coating layer. The coating layer is a layer containing a substance that has lithium ion conductivity, low reactivity with the positive electrode active material and the solid electrolyte, and can maintain the form of the coating layer that does not flow even when in contact with the active material and the solid electrolyte. As specific examples of the material constituting the coating layer, in addition to LiNbO3, Li4Ti5O 12 , Li3PO4, etc. can also be cited, but are not limited thereto.

[0097] The shape of the positive electrode active material is not particularly limited as long as it is a general shape of 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 multiple primary particles. The average particle size D 50 For example, it can be 1 nm or more, 5 nm or more, or 10 nm or more, and can be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Furthermore, the average particle size D 50It is the particle diameter (median diameter) at 50% cumulative value in the volume-based particle size distribution obtained by the laser diffraction / scattering method.

[0098] Regarding the solid electrolyte, binder, and conductive additive, reference can be made to the description of the "<negative electrode active material layer>" above.

[0099] The shape of the positive electrode active material layer is not particularly limited. For example, it can also 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.

[0100] <Positive electrode current collector layer>

[0101] The material for the positive electrode current collector layer is not particularly limited, and materials generally used as the positive electrode current collector of a lithium secondary battery can be appropriately adopted. 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 cited, but it is not limited to this case. In addition, for the purpose of adjusting resistance, etc., the positive electrode current collector layer may have a certain coating on its surface. In addition, the positive electrode current collector layer may also be a layer formed by plating or vapor deposition of the above metals on a metal foil or substrate.

[0102] The shape of the positive electrode current collector layer is not particularly limited. For example, foil-like, plate-like, or mesh-like can be cited. Among them, foil-like is preferred.

[0103] The thickness of the positive electrode current collector layer is not particularly limited. 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.

[0104] The positive electrode active material layer can be manufactured by applying known methods. For example, by dry or wet forming a positive electrode mixture containing the above various components, the positive electrode active material layer can be easily formed. The positive electrode active material layer can be formed together with the positive electrode current collector layer or separately from the positive electrode current collector layer.

[0105] <Shape, etc. of the lithium secondary battery>

[0106] As the shape of the lithium secondary battery, for example, coin type, laminated type, cylindrical type, square type can be cited, but it is not limited to these cases.

[0107] Figure 1 It is a schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but it is not limited to this case.

[0108] The lithium secondary battery 100 is a battery having, in order, a negative electrode current collector layer 111, a negative electrode active material layer 112, an inorganic porous layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132. Through the inorganic porous layer 113 disposed between the negative electrode active material layer 112 and the electrolyte layer 120, the capacity retention rate of the lithium secondary battery can be improved and the resistance value can be reduced. It is speculated that the inorganic porous layer 113 is a porous layer formed of an inorganic substance, so it has high mechanical strength and electron insulation, can suppress the decomposition of the electrolyte and the destruction of the Solid Electrolyte Interphase (SEI), and thus the capacity retention rate is improved. In addition, oxides of metal elements such as lanthanum are known as oxide solid electrolytes. It is speculated that due to their high lithium conductivity, the lithium carrier concentration is increased at the interface between the inorganic porous layer and the negative electrode active material layer, and thus the battery resistance decreases. Moreover, it is speculated that by making the inorganic porous layer 113 porous, the diffusion of the electrolyte into the inorganic porous layer is promoted, and it becomes easier to reach the negative electrode active material, and thus the battery resistance decreases.

[0109] "Manufacturing Method of Lithium Secondary Battery"

[0110] The manufacturing method of the lithium secondary battery of the present disclosure may also include the following steps: dipping the negative electrode current collector layer in a solution containing the above metal element and lithium, and forming a negative electrode active material layer and an inorganic porous layer on the surface of the negative electrode current collector layer through an electrolytic reaction.

[0111] According to the manufacturing method of the lithium secondary battery of the present disclosure, a lithium secondary battery using lithium metal and / or a lithium alloy as the negative electrode active material can be manufactured, and the capacity retention rate of the lithium secondary battery is improved and the resistance value is reduced.

[0112] (Solution for electrolytic reaction)

[0113] In the manufacturing method of the lithium secondary battery of the present disclosure, the solution for electrolytic reaction is not particularly limited, and a solution in which a compound containing lithium and a compound of at least one metal element selected from calcium, barium, lanthanum, and cerium are dissolved in a solvent may also be used.

[0114] The solvent is not particularly limited, and examples thereof include cyclic carbonates and chain carbonates. As cyclic carbonates, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be cited, but it is not limited to this case. As chain carbonates, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be cited, but it is not limited to this case. The electrolyte is not particularly limited, and only 1 type can be used alone, or 2 or more types can be used in combination.

[0115] The compound containing lithium is not particularly limited, and examples thereof include LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc., but are not limited to these cases.

[0116] The compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium is not particularly limited, and examples thereof include Ca[N(CF3SO2)2]2, Ba[N(CF3SO2)2]2, La[N(CF3SO2)2]3, Ce[N(CF3SO2)2]3, etc., but are not limited to these cases.

[0117] (Electrolysis reaction)

[0118] The electrolysis reaction is not particularly limited, and cyclic voltammetry can be used with the negative electrode current collector as the working electrode. As the conditions for cyclic voltammetry, for example, a potential of 0 to 0.3 V and a scan rate of 1 mV / s can be cited, and the thickness of the inorganic porous layer can also be adjusted according to the number of cycles.

[0119] The compound containing at least one of the metal elements selected from calcium, barium, lanthanum, and cerium contained in the solvent is not particularly limited, and metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, etc. can also be formed by electrolysis reaction.

[0120] Figure 2 It is a schematic diagram showing one mode of the manufacturing method of the lithium secondary battery of the present disclosure, but is not limited to this case. Use Figure 1 and Figure 2 to illustrate the manufacturing method of the lithium secondary battery.

[0121] First, Figure 2 The negative electrode current collector layer 111 shown in (A) is immersed in a solution containing lithium and at least one metal element selected from calcium, barium, lanthanum, and cerium, and an electrolysis reaction is carried out. The electrolysis reaction can be carried out, for example, by cyclic voltammetry. After the electrolysis reaction, as shown in Figure 2 (B), a negative electrode active material layer 112 and an inorganic porous layer 113 are sequentially formed on the surface of the negative electrode current collector layer 111, and a negative electrode laminate 110 in which the negative electrode current collector layer 111, the negative electrode active material layer 112, and the inorganic porous layer 113 are sequentially laminated can be obtained. Then, on the positive electrode current collector layer 132, a positive electrode mixture is coated by a wet or dry method, whereby a positive electrode active material layer 131 is formed, and Figure 2The positive electrode laminate 130 shown in (C). Thereafter, by laminating the negative electrode laminate 110, the electrolyte layer 120, and the positive electrode laminate 130, a lithium secondary battery 100 can be formed that sequentially has a negative electrode current collector layer 111, a negative electrode active material layer 112, an inorganic porous layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132. Figure 1 The lithium secondary battery 100 shown.

[0122] [Examples]

[0123] 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.

[0124] <<Example 1>>

[0125] <Fabrication of negative electrode laminate: Formation of negative electrode active material layer and inorganic porous layer on negative electrode current collector layer>

[0126] A copper (Cu) foil as a negative electrode current collector and lithium metal were laminated so as to face each other with a polyolefin film (film thickness: 20 μm) as a separator therebetween, and the laminate was housed in a unit container. Next, an electrolytic solution composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), calcium bis(trifluoromethylsulfonyl)imide (Ca(TFSI)2), ethylene carbonate (EC), and propylene carbonate (PC) was injected into the container, and the unit container was sealed. Inside the unit container, cyclic voltammetry (potential: 0 to 0.3 V, scan rate: 1 mV / s, termination voltage: 0 V) was performed 20 times with the Cu foil as the working electrode and the lithium metal as the counter electrode. During the cyclic voltammetry, a lithium metal layer and an inorganic porous layer were formed on the Cu foil. Thereafter, the unit container was disassembled, and the Cu foil on which the lithium metal layer and the inorganic porous layer were formed was recovered and used as the negative electrode laminate. The negative electrode laminate sequentially has a negative electrode current collector layer, a negative electrode active material layer, and an inorganic porous layer, and has an inorganic porous layer with a thickness of 50 nm.

[0127] <Fabrication of positive electrode laminate>

[0128] 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 mixture slurry. Next, the obtained positive electrode mixture slurry was applied to an aluminum (Al) foil as a positive electrode current collector and dried to fabricate a positive electrode laminate having a positive electrode active material layer formed on the Al foil.

[0129] <Manufacture of Lithium Secondary Battery>

[0130] The negative electrode laminate and the positive electrode laminate were laminated so as to face each other with a polyolefin film (film thickness: 20 μm) as a separator therebetween, and wound into a spiral shape. Terminals were respectively connected to the wound negative electrode laminate and positive electrode laminate, and they were housed in a battery case. 1 M LiPF6 in EC / dimethyl carbonate (DMC) (1 / 1 (volume ratio)) as an electrolyte was injected, and it was sealed to manufacture a lithium secondary battery.

[0131] <Evaluation of Capacity Retention Rate of Lithium Secondary Battery>

[0132] The lithium secondary battery was charged and discharged 200 times in the range of cut-off voltages of 3.3 to 4.2 V at 25°C 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 of the lithium secondary battery 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.

[0133] <Evaluation of Resistance Value of Lithium Secondary Battery>

[0134] The lithium secondary battery was adjusted to an open-circuit voltage of 3.70 V. Then, 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. Furthermore, the resistance value in Table 1 is a relative value when the resistance value of the lithium secondary battery of Comparative Example 1 is set to 1.00.

[0135] <<Comparative Example 1>>

[0136] <Manufacture of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Inorganic Porous Layer on Negative Electrode Current Collector Layer>

[0137] A negative electrode laminate was manufactured in the same manner as in Example 1, except that an electrolyte composed of LiTFSI, EC, and PC, that is, an electrolyte from which Ca(TFSI)2 was removed from the electrolyte of Example 1, was used.

[0138] <Manufacture, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value of Lithium Secondary Battery>

[0139] Using the negative electrode laminate produced in Comparative Example 1, a lithium secondary battery was produced in the same manner as in Example 1. For the capacity retention rate and resistance value of the lithium secondary battery, evaluation was performed in the same manner as in Example 1. In the examples and comparative examples of this specification, relative values were used with the capacity retention rate and resistance value of the lithium secondary battery of Comparative Example 1 set to 1.00.

[0140] 《Examples 2 to 4 (Metal elements constituting the inorganic porous layer)》

[0141] <Fabrication of the negative electrode laminate: A negative electrode active material layer and an inorganic porous layer were formed on the negative electrode current collector layer>

[0142] A negative electrode laminate was produced in the same manner as in Example 1, except that Ba(TFSI)2, Ce(TFSI)3, or La(TFSI)3 was used instead of Ca(TFSI)2.

[0143] <Fabrication of the lithium secondary battery, evaluation of the capacity retention rate of the battery, and evaluation of the resistance value of the battery>

[0144] Using the negative electrode laminates produced in Examples 2 to 4, lithium secondary batteries were produced in the same manner as in Example 1. For the capacity retention rate and resistance value of the lithium secondary batteries in Examples 2 to 4, evaluation was performed in the same manner as in Example 1. The respective results are shown in Table 1.

[0145] Table 1

[0146]

[0147] It was confirmed that, compared with the lithium secondary battery (Comparative Example 1) having an inorganic porous layer not containing a metal element, the lithium secondary batteries (Examples 1 to 4) having an inorganic porous layer into which a metal element was introduced had an increased capacity retention rate and a decreased resistance value.

[0148] It is speculated that since the inorganic porous layer is a porous layer formed of an inorganic substance, it has high mechanical strength and electron insulation properties, and can suppress the decomposition of the electrolyte and the destruction of the SEI, thereby improving the capacity retention rate. In addition, oxides such as lanthanum are known as oxide solid electrolytes, and it is speculated that they have high lithium conductivity and increase the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer, thereby reducing the resistance value. Moreover, it is speculated that by forming a porous shape, the diffusion of the electrolyte into the inorganic porous layer is promoted, and it easily reaches the negative electrode active material, thereby reducing the resistance value.

[0149] 《Examples 5 to 11 (Film thickness of the inorganic porous layer)》

[0150] <Fabrication of the negative electrode laminate: A negative electrode active material layer and an inorganic porous layer were formed on the negative electrode current collector layer>

[0151] In Example 4, the number of cycles of cyclic voltammetry was adjusted, whereby the thickness of the inorganic porous layer was as shown in Table 2. Except for this, the negative electrode laminate was fabricated in the same manner as in Example 4.

[0152] <Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value>

[0153] Using the negative electrode laminates fabricated in Examples 5 to 11, 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 5 to 11, evaluations were performed in the same manner as in Example 1. The respective results are shown in Table 2.

[0154] <<Comparative Example 2 (Film Thickness of Inorganic Porous Layer)>>

[0155] <Fabrication of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Inorganic Porous Layer on Negative Electrode Current Collector Layer>

[0156] In Comparative Example 1, the number of cycles of cyclic voltammetry was adjusted, whereby the thickness of the inorganic porous layer was as shown in Table 2. Except for this, the negative electrode laminate was fabricated in the same manner as in Comparative Example 1.

[0157] <Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value>

[0158] Using the negative electrode laminate fabricated in Comparative Example 2, a lithium secondary battery was fabricated in the same manner as in Example 1. For the capacity retention rate and resistance value of the lithium secondary battery in Comparative Example 2, evaluations were performed in the same manner as in Example 1. The respective results are shown in Table 2.

[0159] Table 2

[0160]

[0161] In lithium secondary batteries (Comparative Examples 1 and 2) having an inorganic porous layer containing no metal element, when the film thickness of the inorganic porous layer was increased from 50 nm to 1000 nm, the capacity retention rate decreased and the resistance value increased. In a lithium secondary battery having an inorganic porous layer containing no metal element, when the film thickness of the inorganic porous layer was 1000 nm, the resistance value increased significantly. Therefore, it is speculated that the above inorganic porous layer becomes a resistance layer, whereby the capacity retention rate decreases. On the other hand, in a lithium secondary battery having an inorganic porous layer containing lanthanum as a metal element, compared with the case where the film thickness is 50 nm, even when the film thickness is large, the capacity retention rate increases and the resistance value also decreases. The best capacity retention rate and resistance value are exhibited when the film thickness is 1000 nm.

[0162] Although preferred embodiments of the lithium secondary battery and the method for manufacturing the lithium secondary battery of the present disclosure are described, those skilled in the art can understand that changes can be made without departing from the scope of 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 inorganic porous 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, and The inorganic porous layer includes a metal compound containing at least one metal element selected from the group consisting of calcium, barium, lanthanum, and cerium. 2 . The lithium secondary battery according to claim 1 , wherein the inorganic porous layer has a thickness of 10 nm to 100 μm. 3 . The lithium secondary battery according to claim 1 , wherein the metal compound is selected from the group consisting of metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, and combinations thereof.

4. A method for manufacturing a lithium secondary battery according to any one of claims 1 to 3, comprising the following steps: immersing the negative electrode collector layer in a solution containing the metal element and lithium, and forming the negative electrode active material layer and the inorganic porous layer on the surface of the negative electrode collector layer by an electrolytic reaction.

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