Lithium secondary battery and method for manufacturing 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] The present disclosure relates to a lithium secondary battery and a method for manufacturing the lithium secondary battery.

Background Art

[0002] Lithium 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 large potential difference between the negative electrode and the positive electrode, a high output voltage, and have a high theoretical capacity density. The following lithium secondary batteries have been disclosed.

[0003] For example, Patent Document 1 discloses a lithium secondary battery that utilizes the deposition-dissolution reaction of lithium metal as 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 the negative electrode active material. 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 said that a lithium secondary battery capable of improving the capacity retention rate can be provided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Lithium secondary batteries using lithium metal and / or lithium alloy as the negative electrode active material are expected to have excellent battery characteristics. However, in reality, the capacity retention rate is small, the resistance value is high, and the characteristics are not yet sufficient. Therefore, such lithium secondary batteries have room for improvement in terms of the capacity retention rate and the resistance value.

[0006] 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.

Means for Solving the Problems

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

[0008] 〈Aspect 1〉 A lithium secondary battery having a negative electrode current collector layer, a 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, wherein 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 calcium, barium, lanthanum, and cerium. Lithium secondary battery. 〈Aspect 2〉 The lithium secondary battery according to Aspect 1, wherein the thickness of the inorganic porous layer is 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〉 A method for manufacturing a lithium secondary battery according to any one of Aspects 1 to 3, including 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.

Advantages of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Mode for Carrying Out the Invention

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

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

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

[0014] 《Lithium Secondary Battery》 The lithium secondary battery of the present disclosure has a negative electrode current collector layer, a 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 calcium, barium, lanthanum, and cerium.

[0015] 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 reduce the resistance value.

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

[0017] Although not limited to theory, since the inorganic porous layer is a porous layer formed from an inorganic substance, it has high mechanical strength and electron insulation, and can suppress the decomposition of the electrolyte and the destruction of the solid - electrolyte interphase (SEI), thereby presumably improving the capacity retention rate. In addition, oxides of metal elements such as lanthanum are known as oxide solid electrolytes and have high lithium conductivity. By increasing the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer, it is presumed that the battery resistance decreases. Furthermore, due to the 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 presumably reducing the battery resistance.

[0018] <Configuration of Lithium Secondary Battery> The lithium secondary battery of the present disclosure has 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, and a material commonly used as the negative electrode current collector of a lithium secondary battery can be appropriately adopted. Examples of the material used for the negative electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, or a carbon sheet. In particular, from the viewpoints of ensuring reduction resistance and being difficult to alloy with lithium, the material used for the negative electrode current collector layer may contain at least one metal selected from Cu, Ni, and stainless steel, or may be made of a carbon sheet. The negative electrode current collector layer may have some coating layer on its surface for the purpose of adjusting resistance or the like.

[0020] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, or a mesh shape. Among these, a foil shape is preferable.

[0021] 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 also be 1 mm or less, or 100 μm or less.

[0022] 〈Negative electrode active material layer〉 In the lithium secondary battery of the present disclosure, the negative electrode active material layer contains lithium metal or a lithium alloy.

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

[0024] The negative electrode active material layer contains at least lithium metal or a lithium alloy as the negative electrode active material, and may further optionally contain a conductive assistant, a binder, a solid electrolyte, etc. The negative electrode active material layer may also contain various other additives. The content of each of the negative electrode active material, conductive assistant, binder, solid electrolyte, etc. in the negative electrode active material layer may be appropriately determined according to the intended battery performance. For example, assuming the total of the negative electrode active material layer (total solid content) 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, and may also be 100% by mass or less, or 90% by mass or less.

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

[0026] In addition, the negative electrode active material layer may contain a negative electrode active material other than lithium metal or a lithium alloy. The negative electrode active material other than lithium metal or a lithium alloy is not particularly limited, and examples include carbon materials. Examples of the carbon material include, but are not limited to, hard carbon, soft carbon, graphite, etc.

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

[0028] (Binder) The binder is not particularly limited. The binder may be, for example, a material 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, but only one kind may be used alone, or two or more kinds may be used in combination.

[0029] (Conductive aid) The conductive aid is not particularly limited. The conductive aid may be, for example, vapor-grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc., but is not limited thereto. The conductive aid may be, for example, particulate or fibrous, and its size is not particularly limited. The conductive aid is not particularly limited, but only one kind may be used alone, or two or more kinds may be used in combination.

[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 the sulfide solid electrolyte include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of the sulfide solid electrolyte include Li2S-P2S5 systems (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (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 can be mentioned, but are not limited thereto.

[0032] Examples of oxide solid electrolytes 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. can be mentioned, but are not limited thereto.

[0033] Sulfide solid electrolytes and oxide solid electrolytes may be glass or crystallized glass (glass ceramics).

[0034] Examples of polymer electrolytes include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof etc., but are not limited thereto.

[0035] The shape of the negative electrode active material is not particularly limited, but it may be a common shape as the negative electrode active material of a lithium secondary battery. The negative electrode active material may be, for example, layered or sheet-like. The negative electrode active material may involve the precipitation of lithium during charging, or may involve the dissolution of lithium during discharging. 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 it 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 it may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0037] The negative electrode active material layer can be formed with reference to the description of the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0038] 〈Inorganic Porous Layer〉 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.

[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 a supporting salt such as a lithium salt contained in the electrolytic solution used in the electrolytic reaction, or decomposition products of the solvent.

[0041] The content of the above metal element in the inorganic porous layer is not particularly limited, but it 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 also 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.

[0042] The thickness of the inorganic porous layer may 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 also 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 scanning electron microscope observation (SEM) on 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 it 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 also 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 from the following formula using the apparent density and true density of the inorganic porous layer (porosity (% by volume) = {1 - (apparent density (g / cm 3 )) / true density (g / cm 3 ))} × 100).

[0044] The inorganic porous layer can be formed with reference to the description of "《Method for Manufacturing Lithium Secondary Battery》" described later.

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

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

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

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

[0049] The solid electrolyte layer can be easily formed, for example, by dry or wet molding of an electrolyte composite material containing the above-mentioned solid electrolyte and binder.

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

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

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

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

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

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

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

[0057] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a substance having lithium ion conduction performance, low reactivity with the positive electrode active material and the solid electrolyte, and capable of maintaining the form of the coating layer without flowing even when in contact with the active material and the solid electrolyte. Specific examples of the material constituting the coating layer include, but are not limited to, LiNbO3, Li4Ti5O 12 , Li3PO4, etc.

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

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

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

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

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

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

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

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

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

[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 disposed 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 the resistance value. Since the inorganic porous layer 113 is a porous layer formed of an inorganic substance, it has high mechanical strength and electron insulation, and it is presumed that the decomposition of the electrolyte solution and the destruction of the solid-electrolyte interphase (SEI) can be suppressed, thereby improving the capacity retention rate. In addition, oxides of metal elements such as lanthanum are known as oxide solid electrolytes and have high lithium conductivity. It is presumed that the battery resistance decreases by increasing the lithium carrier concentration at the interface between the inorganic porous layer and the negative electrode active material layer. Furthermore, by forming the inorganic porous layer 113 into a porous shape, the diffusion of the electrolyte solution into the inorganic porous layer is promoted, making it easier to reach the negative electrode active material, and it is presumed that the battery resistance decreases accordingly.

[0068] 《Manufacturing Method of Lithium Secondary Battery》 The manufacturing method of the lithium secondary battery of the present disclosure may include impregnating the negative electrode current collector layer with 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 by an electrolytic reaction.

[0069] According to the manufacturing method of the lithium secondary battery of the present disclosure, a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material can be manufactured, and the lithium secondary battery has an improved capacity retention rate and a reduced resistance value.

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

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

[0072] The lithium-containing compound is not particularly limited, and examples thereof include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0073] The compound containing at least one metal element selected from calcium, barium, lanthanum, and cerium is not particularly limited, and examples thereof include, but are not limited to, Ca[N(CF3SO2)2]2, Ba[N(CF3SO2)2]2, La[N(CF3SO2)2]3, and Ce[N(CF3SO2)2]3.

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

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

[0076] FIG. 2 is a schematic diagram showing one aspect of the method for manufacturing a lithium secondary battery of the present disclosure, but is not limited to this case. The method for manufacturing a lithium secondary battery will be described with reference to FIGS. 1 and 2.

[0077] First, the negative electrode current collector layer 111 shown in FIG. 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 performed. The electrolytic reaction can be performed, for example, by cyclic voltammetry. After the electrolytic reaction, as shown in FIG. 2B, a negative electrode active material layer 112 and an inorganic porous layer 113 are formed in this order 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 laminated in this order can be obtained. Next, a positive electrode active material layer 131 is formed by coating a positive electrode mixture on the positive electrode current collector layer 132 wet or dry, and a positive electrode laminate 130 shown in FIG. 2C can be formed. Thereafter, the negative electrode laminate 110, the electrolyte layer 120, and the positive electrode laminate 130 are laminated to form the lithium secondary battery 100 shown in FIG. 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.

Example

[0078] The present disclosure will be described in more detail with reference to the examples shown below, but the scope of the present disclosure is not limited to these examples.

[0079] 《Example 1》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer and inorganic porous layer on negative electrode current collector layer〉 A copper (Cu) foil as a negative electrode current collector and lithium metal were laminated to face each other with a polyolefin film (film thickness: 20 μm) as a separator interposed therebetween, and the laminate was housed in a cell container. Next, a electrolytic solution composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), calcium bis(trifluoromethanesulfonyl)imide (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, the Cu foil was used as a working electrode and the lithium metal was used as a counter electrode, and cyclic voltammetry (potential: 0 to 0.3 V, scanning rate: 1 mV / s, end voltage: 0 V) was performed for 20 cycles. During the process of cyclic voltammetry, a lithium metal layer and an inorganic porous layer were formed on the Cu foil. Thereafter, the cell container was disassembled, and the Cu foil on which the lithium metal and the inorganic porous layer were formed was recovered and used as a 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 this order, and had an inorganic porous layer with a thickness of 50 nm.

[0080] <Preparation of the positive electrode laminate> LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (84 parts by mass), acetylene black (12 parts by mass) as a conductive assistant, PVdF (4 parts by mass) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersion medium were mixed to prepare a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry was coated on an aluminum (Al) foil as a positive electrode current collector and dried to prepare a positive electrode laminate in which a positive electrode active material layer was formed on the Al foil.

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

[0082] <Evaluation of Capacity Retention Rate of Lithium Secondary Battery> The lithium secondary battery was charged and discharged 200 cycles at 25°C in the range of a cut-off voltage of 3.3 to 4.2 V by a constant current (current rate 1C) method. The capacities at the first cycle and the 200th cycle were measured, and the capacity retention rate of the lithium secondary battery (capacity retention rate = (capacity at the 200th cycle) / (capacity at the first cycle) × 100) was calculated. The results of the capacity retention rate are shown in Table 1. Note that the capacity retention rate in Table 1 is a relative value when the capacity retention rate of the lithium secondary battery in Comparative Example 1 is set to 1.00.

[0083] <Evaluation of Resistance Value of Lithium Secondary Battery> The lithium secondary battery was adjusted so that the open-circuit voltage was 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 (resistance value = ΔV / current value of 5C) was calculated. The results of the resistance value are shown in Table 1. Note that the resistance value in Table 1 is a relative value when the resistance value of the lithium secondary battery in Comparative Example 1 is set to 1.00.

[0084] <<Comparative Example 1>> <Fabrication of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Inorganic Porous Material on Negative Electrode Current Collector Layer> A negative electrode laminate was fabricated in the same manner as in Example 1, except that an electrolytic solution composed of LiTFSI, EC, and PC, that is, the electrolytic solution of Example 1 excluding Ca(TFSI)2, was used.

[0085] <Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value> Using the negative electrode laminate fabricated in Comparative Example 1, a lithium secondary battery was fabricated 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 in Comparative Example 1 are shown as relative values with 1.00.

[0086] <<Examples 2 to 4 (Metal Element Constituting Inorganic Porous Layer)>> <Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the inorganic porous material on the negative electrode current collector layer> A 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] <Fabrication of the lithium secondary battery, evaluation of the capacity retention rate of the battery, and evaluation of the resistance value of the battery> Using the negative electrode laminates fabricated in Examples 2 to 4, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate and the resistance value of the lithium secondary batteries in Examples 2 to 4 were evaluated in the same manner as in Example 1. Each result was as shown in Table 1.

[0088]

Table 1

[0089] Compared with a lithium secondary battery (Comparative Example 1) having an inorganic porous layer containing no metal element, it was confirmed that 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.

[0090] Since the inorganic porous layer is a porous layer formed from an inorganic substance, it is presumed that its mechanical strength and electrical insulation are high, decomposition of the electrolyte and destruction of the SEI can be suppressed, and thereby the capacity retention rate is improved. In addition, oxides such as lanthanum are known as oxide solid electrolytes and have high lithium conductivity. 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. Furthermore, by making it porous, diffusion of the electrolyte into the inorganic porous layer is promoted, making it easier to reach the negative electrode active material, and thereby it is presumed that the resistance value decreased.

[0091] 《Examples 5 to 11 (Thickness of the inorganic porous layer)》 <Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the inorganic porous material on the negative electrode current collector layer> In Example 4, a negative electrode laminate was produced in the same manner as in Example 4, except that the number of cycles of cyclic voltammetry was adjusted so that the thickness of the inorganic porous layer was as described in Table 2.

[0092] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value〉 Using the negative electrode laminates produced in Examples 5 to 11, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate and resistance value of the lithium secondary batteries in Examples 5 to 11 were evaluated in the same manner as in Example 1. The respective results were as shown in Table 2.

[0093] 《Comparative Example 2 (Film Thickness of Inorganic Porous Layer)》 〈Fabrication of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Inorganic Porous Material on Negative Electrode Current Collector Layer〉 In Comparative Example 1, a negative electrode laminate was produced in the same manner as in Comparative Example 1, except that the number of cycles of cyclic voltammetry was adjusted so that the thickness of the inorganic porous layer was as described in Table 2.

[0094] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value〉 Using the negative electrode laminate produced in Comparative Example 2, a lithium secondary battery was fabricated 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 respective results were as shown in Table 2.

[0095]

Table 2

[0096] In lithium secondary batteries (Comparative Examples 1 and 2) provided with 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 provided with 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 presumed that the inorganic porous layer became a resistance layer, thereby reducing the capacity retention rate. On the other hand, in a lithium secondary battery provided with an inorganic porous layer containing lanthanum as a metal element, even when the film thickness was large compared to 50 nm, the capacity retention rate increased and the resistance value decreased, showing the best capacity retention rate and resistance value at a film thickness of 1000 nm.

[0097] Although preferred embodiments of the lithium secondary battery and the method for manufacturing the lithium secondary battery of the present disclosure have been described, those skilled in the art understand that changes can be made without departing from the scope of the claims.

Explanation of Symbols

[0098] 100 Lithium secondary battery 110 Negative electrode laminate 111 Negative electrode current collector layer 112 Negative electrode active material layer 113 Inorganic porous layer 120 Electrolyte layer 130 Positive electrode laminate 131 Positive electrode active material layer 132 Positive electrode current collector layer

Claims

1. A lithium secondary battery having a negative electrode current collector layer, a 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, wherein 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 calcium, barium, lanthanum, and cerium. A lithium secondary battery.

2. The lithium secondary battery according to claim 1, wherein the thickness of the inorganic porous layer is 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. The method for manufacturing a lithium secondary battery according to any one of claims 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 the surface of the negative electrode current collector layer by an electrolytic reaction.

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