Lithium secondary battery, and method for manufacturing a lithium secondary battery

Abstract

To provide a lithium secondary battery in which a lithium metal and / or a lithium alloy is used as a negative electrode active material and which can be enhanced in a capacity retention rate and reduced in a resistance value.SOLUTION: A lithium secondary battery 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, in this order. The negative electrode active material layer 112 contains a lithium metal or a lithium alloy, and the inorganic porous layer 113 contains a metallic compound containing at least one metal element selected from calcium, barium, lanthanum and cerium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to lithium secondary batteries and methods for manufacturing lithium secondary batteries. [Background technology]

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

[0003] For example, Patent Document 1 discloses a lithium secondary battery that utilizes a lithium metal deposition-dissolution reaction as the reaction of the negative electrode, wherein the negative electrode includes a negative electrode layer, and the negative electrode layer includes an alloy of the lithium metal and a dissimilar metal as the negative electrode active material, and when the lithium secondary battery is fully charged, the elemental ratio of the lithium element in the alloy is 40.00 atomic% or more and 99.97 atomic% or less. According to Patent Document 1, it is possible to provide a lithium secondary battery that can improve the capacity retention rate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-103517 [Overview of the project] [Problems that the invention aims to solve]

[0005] While lithium secondary batteries using lithium metal and / or lithium alloys as the negative electrode active material are expected to have excellent battery characteristics, in reality, their capacity retention rate is low and their resistance is high, meaning their characteristics are still not sufficient. Therefore, there is room for improvement in terms of capacity retention rate and resistance in such lithium secondary batteries.

[0006] Accordingly, 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 capacity retention rate and reduce resistance. Means for Solving the Problem

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

[0008] <Aspect 1> Comprising 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 in this order, the negative electrode active material layer contains lithium metal or a lithium alloy, and the inorganic porous layer contains a metal compound containing at least one metal element selected from the group consisting of calcium, barium, lanthanum, and cerium, a lithium secondary battery. <Aspect 2> The lithium secondary battery according to Aspect 1, wherein the inorganic porous layer has a thickness of 10 nm to 100 µm. <Aspect 3> The lithium secondary battery according to Aspect 1 or 2, 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. <Aspect 4> The method for producing a lithium secondary battery according to any one of Aspects 1 to 3, comprising impregnating the negative electrode current collector layer with a solution containing the metal element and lithium, and forming the negative electrode active material layer and the inorganic porous layer on a surface of the negative electrode current collector layer by an electrolytic reaction. Effect of the Invention

[0009] According to the present disclosure, in a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material, the capacity retention rate can be improved and the resistance can be reduced. Brief Description of the Drawings

[0010] [Figure 1] Figure 1 is a schematic diagram illustrating the lithium secondary battery of this disclosure. [Figure 2] Figure 2 is a schematic diagram illustrating the manufacturing method of the lithium secondary battery of this disclosure. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various ways within the scope of the gist of this disclosure. Furthermore, in the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] In this disclosure, "compound mixture" means a composition that can constitute a positive electrode active material layer, etc., either as is or by further containing other components. In this disclosure, "compound mixture slurry" means a slurry that includes a dispersion medium in addition to the "compound mixture," and can be applied and dried to form a positive electrode active material layer, etc.

[0013] The lithium secondary battery of this disclosure may be a liquid-type battery containing an electrolyte as an electrolyte layer, or it may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. In this disclosure, "solid-state battery" means a battery using at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as its electrolyte. Furthermore, the lithium secondary battery of this disclosure may be an all-solid-state battery, i.e., a battery using only a solid electrolyte as its electrolyte.

[0014] Lithium-ion rechargeable battery The lithium secondary battery disclosed herein is The device comprises 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 in this order. The above negative electrode active material layer contains lithium metal or lithium alloy, and The above-mentioned inorganic porous layer contains a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0015] According to this disclosure, it is possible to improve the capacity retention rate and reduce the resistance value of a lithium secondary battery using lithium metal and / or lithium alloy as the negative electrode active material.

[0016] Specifically, as shown in Figure 1, the lithium secondary battery of this disclosure comprises, for example, 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, wherein the inorganic porous layer 113 contains at least one metallic element selected from calcium, barium, lanthanum, and cerium.

[0017] While not limited to theory, it is presumed that the inorganic porous layer, being a porous layer formed from inorganic materials, has high mechanical strength and electronic insulation properties, thereby suppressing the decomposition of the electrolyte and the breakdown of the solid-electrolyte interface (SEI), and thus improving capacity retention. Furthermore, oxides of metallic elements such as lanthanum are known as oxide solid electrolytes and have high lithium conductivity, so it is presumed that increasing the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer will reduce battery resistance. In addition, it is presumed that the porous shape promotes the diffusion of the electrolyte into the inorganic porous layer, making it easier for it to reach the negative electrode active material, thereby reducing battery resistance.

[0018] <Composition of a lithium-ion secondary battery> The lithium secondary battery of this disclosure comprises 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 in this order.

[0019] <Negative electrode current collector layer> The material used for the negative electrode current collector layer is not particularly limited, but materials commonly used for the negative electrode current collector of lithium secondary batteries can be appropriately adopted. Examples of materials used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or carbon sheets. In particular, from the viewpoint of ensuring reduction resistance and being less prone to alloying with lithium, the material used for the negative electrode current collector layer may contain at least one metal selected from Cu, Ni, and stainless steel, or it may be made of a carbon sheet. The negative electrode current collector layer may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc.

[0020] The shape of the negative electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0021] The thickness of the negative electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0022] <Negative electrode active material layer> In the lithium secondary battery of this disclosure, the negative electrode active material layer includes lithium metal or a lithium alloy.

[0023] Here, if the "negative electrode active material layer" contains lithium metal, in the charged state, a layer of lithium metal exists as the "negative electrode active material layer," but in the discharged state, the lithium metal moves as lithium ions to the positive electrode active material layer, and the layer of lithium metal as the "negative electrode active material layer" may cease to exist. Similarly, if the "negative electrode active material layer" contains a lithium alloy, in the charged state, a layer of lithium alloy exists as the "negative electrode active material layer," but in the discharged state, the lithium from the lithium alloy moves as lithium ions to the positive electrode active material layer, and the lithium alloy may cease to exist as the "negative electrode active material layer," instead presenting a layer of metal from which lithium has been removed.

[0024] The negative electrode active material layer contains at least lithium metal or lithium alloy as the negative electrode active material, and may further optionally contain conductive additives, binders, solid electrolytes, etc. The negative electrode active material layer may also contain various other additives. The respective content of the negative electrode active material, conductive additives, binders, solid electrolytes, etc. in the negative electrode active material layer can be appropriately determined according to the desired battery performance. For example, if the total (total solid content) of the negative electrode active material layer is 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, 100% by mass or less, or 90% by mass or less.

[0025] (Negative electrode active material) As described above, at least lithium metal or a lithium alloy is used as the negative electrode active material. The lithium alloy is not particularly limited, but any material that can alloy with lithium and intercalate and release lithium ions is acceptable. Examples include silicon alloy-based negative electrode active materials and tin alloy-based active materials, but the invention is not limited to these cases. Silicon alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, or solid solutions thereof. Silicon alloy-based negative electrode active materials may also contain metallic elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. Tin alloy-based negative electrode active materials include tin, tin oxide, tin nitride, or solid solutions thereof. Tin alloy-based negative electrode active materials may also contain metallic elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0026] Furthermore, the negative electrode active material layer may contain negative electrode active materials other than lithium metal or lithium alloy. Examples of negative electrode active materials other than lithium metal or lithium alloy are not limited to lithium metal or lithium alloy, but include carbon materials. Examples of carbon materials include hard carbon, soft carbon, and graphite, but are not limited to these cases.

[0027] The proportion of lithium metal or lithium alloy contained in the negative electrode active material layer is not particularly limited, but may be 50% to 100% by mass, 60% to 100% by mass, 70% to 100% by mass, 80% to 100% by mass, or 90% to 100% by mass relative to the negative electrode active material layer.

[0028] (Binder) The binder is not particularly limited. The binder may be, for example, 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 may be used alone or in combination of two or more types.

[0029] (Conductive additive) The conductive additive is not particularly limited. Examples of conductive additives include, but are not limited to, vapor-grown carbon fibers (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF). The conductive additive may be particulate or fibrous, and its size is not particularly limited. While the conductive additive is not particularly limited, it may be used alone or in combination of two or more types.

[0030] (solid electrolyte) The material of the solid electrolyte is not particularly limited and may be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte.

[0031] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include the Li2S-P2S5 system (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li13 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 may be mentioned, but the present invention is not limited thereto.

[0032] As examples of oxide solid electrolytes, 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) and the like can be mentioned, but the present invention is not limited thereto.

[0033] The sulfide solid electrolyte and the oxide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0034] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), copolymers of the foregoing, and the like.

[0035] The shape of the negative electrode active material is not particularly limited, but any shape common for negative electrode active materials in lithium secondary batteries is acceptable. The negative electrode active material may be in the form of layers or sheets, for example. The negative electrode active material may involve the deposition of lithium during charging, or the dissolution of lithium during discharge. In this case, the negative electrode active material layer may be a layer made of lithium metal or a lithium alloy.

[0036] The shape of the negative electrode active material layer is not particularly limited, but may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0037] The negative electrode active material layer can be formed by referring to the description in "Method for Manufacturing a Lithium Secondary Battery" below.

[0038] <Inorganic porous layer> In the lithium secondary battery of this disclosure, the inorganic porous layer comprises a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0039] The above metal compound may be selected from the group consisting of metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, and combinations thereof.

[0040] The inorganic porous layer is not particularly limited, but can be formed by an electrolytic reaction. The inorganic porous layer may contain supporting salts such as lithium salts and decomposition products of the solvent contained in the electrolyte used in the electrolytic reaction.

[0041] The content of the above-mentioned metal elements in the inorganic porous layer is not particularly limited, but 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, or 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, or 50% by mass or less.

[0042] The thickness of the inorganic porous layer may be 10 nm to 100 μm. 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 500,000 nm or less, 300,000 nm or less, 200,000 nm or less, or 100,000 nm or less, from the viewpoint of capacity retention and resistance. The thickness of the inorganic porous layer can be measured by scanning electron microscopy (SEM) of the cross-section of the inorganic porous layer.

[0043] 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, but may be 10 vol% or more, 20 vol% or more, 30 vol% or more, 40 vol% or more, or 50 vol% or more, and may be 90 vol% or less, 80 vol% or less, 70 vol% or less, 60 vol% or less, or 50 vol% or less. Here, the porosity can be calculated using the apparent density and true density of the inorganic porous layer from the following formula (porosity (volume %) = {1 - (apparent density (g / cm³) 3 ) / true density(g / cm 3 ))}×100).

[0044] The inorganic porous layer can be formed by referring to the description of "Method for Manufacturing a Lithium Secondary Battery" described later.

[0045] <Electrolyte layer> <Electrolyte layer - solid electrolyte layer> The lithium secondary battery of this disclosure may be a solid battery, that is, it may have a solid electrolyte layer as the electrolyte layer.

[0046] The solid electrolyte layer may contain a binder or other components in addition to the solid electrolyte, as needed.

[0047] For information regarding the solid electrolyte and binder, please refer to the description in "<Negative Electrode Active Material Layer>" above.

[0048] The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0049] The solid electrolyte layer can be easily formed, for example, by molding an electrolyte mixture containing the aforementioned solid electrolyte and binder in a dry or wet manner.

[0050] <Electrolyte layer - Separator layer> The lithium secondary battery of this disclosure may be a liquid-type battery, that is, it may have an electrolyte as an electrolyte layer, particularly an electrolyte held in a separator layer.

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

[0052] The supporting salt (lithium salt) for the lithium-ion conductive electrolyte is not particularly limited, but examples include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, and LiAsF6. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

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

[0054] (Separator) The separator is not particularly limited, but any separator commonly used in lithium secondary batteries can be appropriately adopted. For example, nonwoven fabrics such as polyolefin, polyamide, or polyimide can be used as the separator.

[0055] <Cathode active material layer> The positive electrode active material layer contains at least positive electrode active material and may optionally contain conductive additives, solid electrolytes, binders, etc. The positive electrode active material layer may also contain various other additives. The respective content of positive electrode active material, conductive additives, binders, etc. in the positive electrode active material layer can be appropriately determined according to the desired battery performance. For example, if the total (total solid content) of the positive electrode active material layer is taken as 100% by mass, the content of positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 100% by mass or less, or 90% by mass or less.

[0056] (Cathode active material) The material of the positive electrode active material is not particularly limited as long as it is capable of intercalating and releasing lithium ions. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), nickel-cobalt-manganese oxide (NCM), and LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3O2, Lithium nickel-cobalt aluminum oxide (NCA; LiNi x Co y Al z O2), Li 1+x Mn 2-x-y M y This may include, but is not limited to, heteroatom-substituted Li-Mn spinel with a composition represented by O4 (where M is one or more metallic elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0057] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a material that has lithium ion conductivity, low reactivity with the positive electrode active material and solid electrolyte, and can maintain a coating layer form that does not flow even when in contact with the active material and solid electrolyte. Specific examples of materials constituting the coating layer include LiNbO3 and Li4Ti5O3. 12 Examples include Li3PO4, but are not limited to these.

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

[0059] For information regarding the solid electrolyte, binder, and conductive additive, please refer to the description in "<Negative Electrode Active Material Layer>" above.

[0060] The shape of the positive electrode active material layer is not particularly limited, but may be, for example, a sheet-like positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0061] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, but a material commonly used for the positive electrode current collector of lithium secondary batteries can be appropriately adopted. Examples of materials used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may also have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector layer may be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

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

[0063] The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0064] The positive electrode active material layer can be manufactured by applying known methods. For example, the positive electrode active material layer can be easily formed by dry or wet molding of a positive electrode mixture containing the above-mentioned components. The positive electrode active material layer may be formed together with the positive electrode current collector layer, or it may be formed separately from the positive electrode current collector layer.

[0065] <Shape of lithium-ion secondary batteries, etc.> Lithium-ion batteries can take the form of coin-type, laminate-type, cylindrical, or prismatic batteries, but are not limited to these types.

[0066] Figure 1 is a schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but is not limited to this embodiment.

[0067] The lithium secondary battery 100 is a battery having 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 inorganic porous layer 113, positioned between the negative electrode active material layer 112 and the electrolyte layer 120, can improve the capacity retention rate of the lithium secondary battery and reduce its resistance. Since the inorganic porous layer 113 is a porous layer formed from inorganic material, it has high mechanical strength and electronic insulation properties, which suppresses the decomposition of the electrolyte and the breakdown of the solid-electrolyte interface (SEI), thereby improving the capacity retention rate. In addition, oxides of metallic elements such as lanthanum are known as oxide solid electrolytes, and they have high lithium conductivity. It is presumed that increasing the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer reduces the battery resistance. Furthermore, by making the inorganic porous layer 113 porous, the diffusion of the electrolyte into the inorganic porous layer is promoted, making it easier for it to reach the negative electrode active material, which is presumed to reduce the battery resistance.

[0068] Manufacturing method for lithium-ion batteries The method for manufacturing a lithium secondary battery according to this disclosure may include impregnating a negative electrode current collector layer with a solution containing the above-mentioned 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 by an electrolytic reaction.

[0069] According to the method for manufacturing a lithium secondary battery of this disclosure, a lithium secondary battery can be manufactured that uses lithium metal and / or a lithium alloy as the negative electrode active material, and has improved capacity retention and reduced resistance.

[0070] (Solution used in electrolytic reactions) In the method for manufacturing a lithium secondary battery according to the present disclosure, the solution used in the electrolytic reaction is not particularly limited, but a solvent may be used which contains a lithium-containing compound and a compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium.

[0071] The solvent is not particularly limited, but examples include cyclic carbonates and linear carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte is not particularly limited, but may be used alone or in combination of two or more types.

[0072] Examples of lithium-containing compounds include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0073] Compounds containing at least one metallic element selected from calcium, barium, lanthanum, and cerium are not particularly limited, but include, but are not limited to, Ca[N(CF3SO2)2]2, Ba[N(CF3SO2)2]2, La[N(CF3SO2)2]3, Ce[N(CF3SO2)2]3, etc.

[0074] (Electrolytic reaction) The electrolytic reaction is not particularly limited, but can be carried out by cyclic voltammetry using a negative electrode current collector as the working electrode. Examples of cyclic voltammetry conditions include a potential of 0 to 0.3 V and a scanning speed of 1 mV / s, and the thickness of the inorganic porous layer may be adjusted by the number of cycles.

[0075] Compounds containing at least one metal element selected from calcium, barium, lanthanum, and cerium in the solvent may, by electrolytic reaction, form metal oxides, metal phosphates, metal sulfides, metal carbonates, metal alkoxides, metal hydroxides, etc., although these are not particularly limited.

[0076] Figure 2 is a schematic diagram showing one embodiment of the lithium secondary battery manufacturing method of this disclosure, but is not limited to this embodiment. The manufacturing method of the lithium secondary battery will be explained using Figures 1 and 2.

[0077] First, the negative electrode current collector layer 111 shown in Figure 2A is impregnated with a solution containing lithium and at least one metal element selected from calcium, barium, lanthanum, and cerium, and an electrolytic reaction is carried out. The electrolytic reaction can be carried out, for example, by cyclic voltammetry. After the electrolytic reaction, as shown in Figure 2B, a negative electrode active material layer 112 and an inorganic porous layer 113 are formed on the surface of the negative electrode current collector layer 111 in that order, and a negative electrode laminate 110 can be obtained in which the negative electrode current collector layer 111, negative electrode active material layer 112, and inorganic porous layer 113 are stacked in that order. Next, a positive electrode active material layer 131 can be formed by coating the positive electrode current collector layer 132 with a positive electrode composite material using a wet or dry method, thereby forming the positive electrode laminate 130 shown in Figure 2C. Subsequently, the negative electrode stack 110, the electrolyte layer 120, and the positive electrode stack 130 are stacked to form a lithium secondary battery 100 as shown in Figure 1, having the negative electrode current collector layer 111, the negative electrode active material layer 112, the inorganic porous layer 113, the electrolyte layer 120, the positive electrode active material layer 131, and the positive electrode current collector layer 132 in this order. [Examples]

[0078] The present disclosure will be further described with reference to the following embodiments, but the scope of the present disclosure is not limited to these embodiments.

[0079] Example 1 <Fabrication of anode laminate: Formation of anode active material layer and inorganic porous material on anode current collector layer> A copper (Cu) foil, serving as the negative electrode current collector, and lithium metal were laminated facing each other with a polyolefin film (thickness 20 μm) acting as a separator, and housed in a cell container. Next, an electrolyte consisting of bis(trifluoromethanesulfonyl)imidolithium (LiTFSI), bis(trifluoromethanesulfonyl)imidocalcium (Ca(TFSI)2), ethylene carbonate (EC), and propylene carbonate (PC) was injected into this container, and the cell container was sealed. In this cell container, cyclic voltammetry (potential: 0~0.3V, scanning speed: 1mV / s, termination voltage: 0V) was performed for 20 cycles with the Cu foil as the working electrode and the lithium metal as the counter electrode. During the cyclic voltammetry process, a lithium metal layer and an inorganic porous layer were formed on the Cu foil. Subsequently, the cell container was dismantled, and the Cu foil with the formed lithium metal and inorganic porous layers was recovered and used as the negative electrode laminate. The negative electrode laminate had a negative electrode current collector layer, a negative electrode active material layer, and an inorganic porous layer in that order, and the inorganic porous layer had a thickness of 50 nm.

[0080] <Fabrication of positive electrode stacks> LiNi as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 A cathode composite slurry was prepared by mixing 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. Next, the obtained cathode composite slurry was coated onto an aluminum (Al) foil as a cathode current collector and dried to produce a cathode laminate in which a cathode active material layer was formed on the Al foil.

[0081] <Manufacturing of lithium-ion secondary batteries> A negative electrode laminate and a positive electrode laminate were stacked facing each other with a polyolefin film (thickness 20 μm) acting as a separator, and then wound in a spiral shape. Terminals were connected to the wound negative electrode laminate and positive electrode laminate, respectively, and the assembly was placed in a battery case. 1M LiPF6EC / dimethyl carbonate (DMC) (1 / 1 volume ratio) was injected as the electrolyte, the case was sealed, and a lithium secondary battery was fabricated.

[0082] <Evaluation of the capacity retention rate of lithium secondary batteries> A lithium secondary battery was subjected to 200 charge-discharge cycles at 25°C using a constant current (current rate 1C) method within a cutoff voltage range of 3.3 to 4.2V. The capacity was measured at the 1st and 200th cycles, and the capacity retention rate of the lithium secondary battery (capacity retention rate = (capacity at 200th cycle) / (capacity at 1st cycle) × 100) was calculated. Table 1 shows the results of the capacity retention rate. Note that the capacity retention rates in Table 1 are relative values, with the capacity retention rate of the lithium secondary battery in Comparative Example 1 set to 1.00.

[0083] <Evaluation of the resistance value of lithium secondary batteries> The lithium secondary battery was adjusted to have an open-circuit voltage of 3.70V. Next, it was discharged at -10°C at a current rate of 5C for 8 seconds, and the voltage drop (ΔV) was measured to calculate the resistance of the lithium secondary battery (resistance = ΔV / current value at 5C). Table 1 shows the results for the resistance values. Note that the resistance values ​​in Table 1 are relative values, with the resistance of the lithium secondary battery in Comparative Example 1 set to 1.00.

[0084] Comparative Example 1 <Fabrication of anode laminate: Formation of anode active material layer and inorganic porous material on anode current collector layer> The negative electrode laminate was fabricated in the same manner as in Example 1, except that an electrolyte composed of LiTFSI, EC, and PC was used, i.e., an electrolyte obtained by removing Ca(TFSI)2 from the electrolyte of Example 1.

[0085] <Manufacturing of lithium secondary batteries, evaluation of capacity retention rate, and evaluation of resistance value> A lithium secondary battery was fabricated using the negative electrode laminate prepared in Comparative Example 1, in the same manner as in Example 1. The capacity retention rate and resistance value of the lithium secondary battery were evaluated in the same manner as in Example 1. In the examples and comparative examples of this specification, the capacity retention rate and resistance value of the lithium secondary battery of Comparative Example 1 are shown as relative values ​​with the resistance value set to 1.00.

[0086] Examples 2-4 (Metal elements constituting the inorganic porous layer) <Fabrication of anode laminate: Formation of anode active material layer and inorganic porous material on anode current collector layer> The negative electrode laminate was fabricated 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.

[0087] <Manufacturing of lithium secondary batteries, evaluation of battery capacity retention rate, and evaluation of battery resistance> Lithium secondary batteries were fabricated using the negative electrode stacks prepared in Examples 2-4, in the same manner as in Example 1. The capacity retention rate and resistance values ​​of the lithium secondary batteries in Examples 2-4 were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0088] [Table 1]

[0089] Compared to a lithium secondary battery with an inorganic porous layer that does not contain metal elements (Comparative Example 1), lithium secondary batteries with an inorganic porous layer that incorporates metal elements (Examples 1-4) showed increased capacity retention and decreased resistance.

[0090] The inorganic porous layer, being a porous layer formed from inorganic materials, has high mechanical strength and electronic insulation properties, which suppresses the decomposition of the electrolyte and the breakdown of the SEI, thereby improving the capacity retention rate. Furthermore, oxides such as lanthanum are known as oxide solid electrolytes and have high lithium conductivity, so it is presumed that the resistance value decreased by increasing the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer. In addition, the porous shape promotes the diffusion of the electrolyte into the inorganic porous layer, making it easier for it to reach the negative electrode active material, which is presumed to have decreased the resistance value.

[0091] Examples 5-11 (Film thickness of inorganic porous layer) <Fabrication of anode laminate: Formation of anode active material layer and inorganic porous material on anode current collector layer> In Example 4, the negative electrode laminate was fabricated in the same manner as in Example 4, except that the number of cyclic voltammetry cycles was adjusted to set the thickness of the inorganic porous layer as shown in Table 2.

[0092] <Manufacturing of lithium secondary batteries, evaluation of capacity retention rate, and evaluation of resistance value> Lithium secondary batteries were fabricated using the negative electrode stacks prepared in Examples 5-11, in the same manner as in Example 1. The capacity retention rate and resistance values ​​of the lithium secondary batteries in Examples 5-11 were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0093] Comparative Example 2 (Film Thickness of Inorganic Porous Layer) <Fabrication of anode laminate: Formation of anode active material layer and inorganic porous material on anode current collector layer> In Comparative Example 1, the negative electrode laminate was fabricated using the same method as in Comparative Example 1, except that the number of cyclic voltammetry cycles was adjusted to set the thickness of the inorganic porous layer as shown in Table 2.

[0094] <Manufacturing of lithium secondary batteries, evaluation of capacity retention rate, and evaluation of resistance value> A lithium secondary battery was fabricated using the negative electrode laminate prepared in Comparative Example 2, in the same manner as in Example 1. The capacity retention rate and resistance value of the lithium secondary battery in Comparative Example 2 were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0095] [Table 2]

[0096] In lithium secondary batteries equipped with an inorganic porous layer that does not contain metal elements (Comparative Examples 1 and 2), increasing the film thickness of the inorganic porous layer from 50 nm to 1000 nm resulted in a decrease in capacity retention and an increase in resistance. In lithium secondary batteries equipped with an inorganic porous layer that does not contain metal elements, the resistance increased significantly when the film thickness of the inorganic porous layer was 1000 nm, suggesting that the inorganic porous layer acted as a resistive layer, thereby reducing the capacity retention. On the other hand, in lithium secondary batteries equipped with an inorganic porous layer containing lanthanum as a metal element, the capacity retention increased and the resistance decreased even at larger film thicknesses compared to 50 nm, showing the best capacity retention and resistance at a film thickness of 1000 nm.

[0097] While preferred embodiments of the lithium secondary battery and the method for manufacturing the lithium secondary battery are described herein, those skilled in the art will understand that modifications can be made without departing from the scope of the claims. [Explanation of Symbols]

[0098] 100 Lithium-ion rechargeable batteries 110 Negative electrode laminate 111 Negative electrode current collector layer 112 Negative electrode active material layer 113 Inorganic porous layer 120 Electrolyte layer 130 Cathode Stack 131 Cathode active material layer 132 Positive electrode current collector layer

Claims

1. A method for manufacturing a lithium secondary battery, The lithium secondary battery comprises 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 in this order. The negative electrode active material layer comprises lithium metal or lithium alloy, The inorganic porous layer contains a metal compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium, and The process involves impregnating the negative electrode current collector layer with 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. A method for manufacturing lithium-ion batteries.

2. The method for manufacturing a lithium secondary battery according to claim 1, wherein the thickness of the inorganic porous layer is 10 nm to 100 μm.

3. The method for producing a lithium secondary battery according to claim 1 or 2, 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.

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