Lithium secondary battery, and method for producing 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 in which capacity retention rate is enhanced, resistance is reduced, and a short circuit can be suppressed.SOLUTION: A lithium secondary battery includes a negative electrode current collector layer 111, a negative electrode active material layer 112, a protective 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 first lithium alloy, and the protective layer 113 contains a second lithium alloy different from the first lithium alloy.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery and a method for manufacturing a 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 have a large potential difference between the negative electrode and the positive electrode, can obtain 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 lithium elements 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] While lithium secondary batteries using lithium metal and / or lithium alloy as the negative electrode active material are expected to have excellent battery characteristics, in reality, the capacity retention rate is small and the resistance value is high. In addition, there is also a risk of short circuit due to the formation of lithium dendrites. Therefore, such lithium secondary batteries have room for improvement in terms of capacity retention rate, resistance value, and short-circuit resistance.

[0006] Therefore, the present disclosure aims to provide a lithium secondary battery that uses lithium metal and / or a lithium alloy as a negative electrode active material, has an improved capacity retention rate, a reduced resistance, and suppressed short circuits.

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, a protective 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 first lithium alloy, and the protective layer contains a second lithium alloy different from the first lithium alloy. Lithium secondary battery. 〈Aspect 2〉 The lithium secondary battery according to Aspect 1, wherein the second lithium alloy contains lithium and at least one metal element selected from the following: Sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth. 〈Aspect 3〉 The lithium secondary battery according to Aspect 1 or 2, wherein the thickness of the protective layer is 5 nm to 10 μm. 〈Aspect 4〉 The lithium secondary battery according to any one of Aspects 1 to 3, wherein the protective layer further has a third lithium alloy, and the third lithium alloy is different from the second lithium alloy. 〈Aspect 5〉 The lithium secondary battery according to any one of Aspects 1 to 4, wherein the third lithium alloy contains lithium and at least one metal element selected from the following: Sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth. <Aspect 6> The negative electrode active material layer contains the first lithium alloy and The lithium secondary battery according to any one of Aspects 1 to 5, wherein the third lithium alloy is the same as the first lithium alloy. <Aspect 7> A method for manufacturing a lithium secondary battery according to any one of Aspects 1 to 6, including the following steps: Forming the negative electrode active material layer on the surface of the negative electrode current collector layer, Forming a protective layer containing the second lithium alloy on the surface of the negative electrode active material layer.

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 is improved, the resistance is reduced, and short circuits are suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes 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. Also, 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 it.

[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, a protective 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 has lithium metal or a first lithium alloy, and the protective layer contains a second lithium alloy different from the first lithium alloy.

[0015] 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 is improved, the resistance is reduced, and short circuit is suppressed.

[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, a protective 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 protective layer 113 contains a second lithium alloy.

[0017] Although not limited to theory, the protective layer 113 is believed to contain a second lithium alloy, which has high lithium ion conductivity and electron conductivity, thereby increasing the capacity retention rate of the lithium secondary battery and decreasing the resistance value. Further, since the negative electrode active material layer also contains lithium metal or a lithium metal alloy and the protective layer and the negative electrode active material layer contain similar materials containing lithium, the interface between the protective layer and the negative electrode active material layer becomes highly adherent, thereby suppressing the precipitation of dendrite lithium that breaks through the protective layer and improving the short circuit resistance.

[0018] On the other hand, when the second lithium alloy is not included in the protective layer, not only does the capacity retention rate and the resistance value deteriorate, but also the energy (transmission energy) for lithium ions to pass through the protective layer and reach the negative electrode active material layer becomes higher than the lithium nucleation energy, thereby predicting the precipitation of lithium dendrites on the protective layer and short circuiting.

[0019] <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, a protective layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0020] <Negative Electrode Current Collector Layer> The material used for the negative electrode current collector layer is not particularly limited, but those generally 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.

[0021] The shape of the negative electrode current collector layer is not particularly limited, and examples thereof include a foil shape, a plate shape, a mesh shape, etc. Among these, a foil shape is preferable.

[0022] The thickness of the negative electrode current collector layer is not particularly limited, but 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.

[0023] 〈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 first lithium alloy. The negative electrode active material layer is not particularly limited, but preferably has a first lithium alloy.

[0024] Here, when the “negative electrode active material layer” contains lithium metal, in the charged state, there is a layer of lithium metal as the “negative electrode active material layer”, 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 first lithium alloy, in the charged state, there is a layer of the first lithium alloy as the “negative electrode active material layer”, but in the discharged state, lithium in the first lithium alloy moves to the positive electrode active material layer as lithium ions, and there may be no first lithium alloy as the “negative electrode active material layer”, but a layer of metal or non-metal from which lithium has been removed from the first lithium alloy.

[0025] The negative electrode active material layer contains at least lithium metal or a first lithium alloy as the negative electrode active material, and may further optionally contain a conductive auxiliary agent, a binder, a solid electrolyte, etc. The negative electrode active material layer may also contain various additives. The content of each of the negative electrode active material, conductive auxiliary agent, 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.

[0026] (Negative electrode active material) As the negative electrode active material, at least lithium metal or a first lithium alloy is used as described above.

[0027] (Negative electrode active material - First lithium alloy) The first lithium alloy is not particularly limited as long as it is an alloy of lithium and a metal element alloyed with lithium. The first lithium alloy may be any material capable of occluding and releasing lithium ions, and examples thereof include lithium-aluminum alloy, lithium-magnesium alloy, lithium-silver alloy, and the like.

[0028] In addition, the negative electrode active material layer may contain a negative electrode active material other than lithium metal or the first lithium alloy. The negative electrode active material other than lithium metal and the first lithium alloy is not particularly limited, and examples thereof include carbon materials. Examples of the carbon material include, but are not limited to, hard carbon, soft carbon, graphite, and the like.

[0029] The proportion of lithium metal or the first lithium alloy contained in the negative electrode active material layer is not particularly limited, but 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.

[0030] (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, and only one kind may be used alone, or two or more kinds may be used in combination.

[0031] (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.

[0032] (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, a polymer electrolyte, etc.

[0033] 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 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof can be mentioned, but are not limited thereto.

[0034] Examples of the oxide solid electrolyte include Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li1+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. may be mentioned, but are not limited thereto.

[0035] The sulfide solid electrolyte and the oxide solid electrolyte may be glass or crystallized glass (glass ceramics).

[0036] Examples of the polymer electrolyte include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0037] The shape of the negative electrode active material is not particularly limited, but 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 lithium precipitation during charging or lithium dissolution during discharging. In this case, the negative electrode active material layer may be a layer made of lithium metal or a lithium alloy.

[0038] 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, and may also be 200 μm or less, 1150 μm or less, or 100 μm or less.

[0039] The negative electrode active material layer can be formed with reference to the description of the "Method for Manufacturing a Lithium Secondary Battery" described below.

[0040] 〈Protective Layer〉 In the lithium secondary battery of the present disclosure, the protective layer contains a second lithium alloy different from the first lithium alloy. The protective layer is not particularly limited, and may further contain a third lithium alloy.

[0041] In the present disclosure, two alloys being "different" means that the types of metal elements constituting these alloys are different from each other, and does not mean that the types of metal elements constituting these alloys are the same and only the content ratios are different. Further, in the present disclosure, two alloys being "the same" means that the types of metal elements constituting these alloys are the same as each other. Therefore, it also includes the case where the types of metal elements constituting these alloys are the same and only the content ratios are different.

[0042] The protective layer may further contain a metal or an alloy other than the second lithium alloy and the third lithium alloy. The content ratio of the metal or the alloy other than the second lithium alloy and the third lithium alloy is not particularly limited, but may be 0% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more, or may be 50% by mass or less, 20% by mass or less, or 10% by mass or less, with the total of the protective layer (total solid content) being 100% by mass.

[0043] (The second lithium alloy) The second lithium alloy is not particularly limited as long as it is an alloy of lithium and a metal element that alloyizes with lithium.

[0044] The second lithium alloy may contain lithium and at least one metal element selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

[0045] The content ratio (atomic ratio) of the metal element contained in the second lithium alloy is not particularly limited, but in the second lithium alloy, it may be 10 atomic% or more, 20 atomic% or more, 30 atomic% or more, 40 atomic% or more, 50 atomic% or more, 60 atomic% or more, or 70 atomic% or more, and may also be 90 atomic% or less, 80 atomic% or less, 70 atomic% or less, 60 atomic% or less, 50 atomic% or less, 40 atomic% or less, or 30 atomic% or less.

[0046] (The third lithium alloy) The third lithium alloy is not particularly limited as long as it is an alloy of lithium and a metal element alloyed with lithium.

[0047] The third lithium alloy may contain lithium and at least one metal element selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

[0048] The third lithium alloy is not particularly limited, but from the viewpoints of capacity retention rate and resistance value, it is preferably the same as the first lithium alloy.

[0049] The content ratio (atomic ratio) of the metal element contained in the third lithium alloy is not particularly limited, but in the third lithium alloy, it may be 10 atomic% or more, 20 atomic% or more, 30 atomic% or more, 40 atomic% or more, 50 atomic% or more, 60 atomic% or more, or 70 atomic% or more, and may also be 90 atomic% or less, 80 atomic% or less, 70 atomic% or less, 60 atomic% or less, 50 atomic% or less, 40 atomic% or less, or 30 atomic% or less.

[0050] The thickness of the protective layer is not particularly limited, and may be, for example, 5 nm to 10,000 nm (10 μm). The thickness of the protective layer is not particularly limited, and may be 5 nm or more, 10 nm or more, 100 nm or more, or 500 nm or more, and may also be 10 μm (10,000 nm) or less, 5 μm (5,000 nm) or less, 1 μm (1,000 nm) or less, or 500 nm or less. The thickness of the protective layer can be measured by scanning electron microscope observation (SEM) of the cross-section of the protective layer.

[0051] The protective layer can be formed with reference to the description of "《Method for manufacturing a lithium secondary battery》" described later.

[0052] 〈Electrolyte layer〉 〈Electrolyte layer - Solid electrolyte layer〉 The lithium secondary battery of the present disclosure can be a solid battery, that is, can have a solid electrolyte layer as the electrolyte layer.

[0053] In addition to the solid electrolyte, the solid electrolyte layer may contain a binder or the like as necessary.

[0054] Regarding the solid electrolyte and the binder, reference can be made to the description of the above "〈Negative electrode active material layer〉".

[0055] The thickness of the solid electrolyte layer is not particularly limited, and 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.

[0056] The solid electrolyte layer can be easily formed, for example, by dry or wet forming of an electrolyte composite material containing the above-mentioned solid electrolyte and binder.

[0057] 〈Electrolyte layer - Separator layer〉 The lithium secondary battery of the present disclosure can be a liquid-based battery, that is, can have an electrolytic solution, particularly an electrolytic solution held in a separator layer, as the electrolyte layer.

[0058] (Electrolytic solution) The electrolyte is not particularly limited, but preferably contains a supporting salt and a solvent.

[0059] The supporting salt (lithium salt) of the electrolyte having lithium ion conductivity is not particularly limited, and examples thereof 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.

[0060] The solvent used in the electrolyte is not particularly limited, and examples thereof include cyclic carbonates and chain carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of chain carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. The electrolyte is not particularly limited, and only one kind may be used alone, or two or more kinds may be used in combination.

[0061] (Separator) The separator is not particularly limited, and a general separator for a lithium secondary battery can be appropriately adopted. As the separator, for example, non-woven fabrics such as polyolefin-based, polyamide-based, and polyimide-based can be used.

[0062] 〈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 intended battery performance. For example, taking the whole of the positive electrode active material layer (the whole solid content) as 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.

[0063] (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 lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), lithium nickel cobalt manganate (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, lithium nickel cobalt aluminate (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), such as hetero-element substituted Li-Mn spinel with a composition represented by this, but is not limited thereto.

[0064] 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, in addition to LiNbO3, Li4Ti5O 12 , Li3PO4, etc., but are not limited thereto.

[0065] The shape of the positive electrode active material is not particularly limited as long as it is a common 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 formed by aggregation of a plurality of primary particles. The average particle diameter D of the positive electrode active material 50 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. Note that the average particle diameter D 50 is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0066] Regarding the solid electrolyte, binder, and conductive assistant, reference can be made to the description of "<Negative electrode active material layer>" above.

[0067] The shape of the positive electrode active material layer is not particularly limited, but may be, for example, 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, but 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.

[0068] 〈Positive electrode current collector layer〉 The material used for the positive electrode current collector layer is not particularly limited, but a common material as 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 Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc., but are not limited to this case. Further, the positive electrode current collector layer may have some coating layer on its surface for the purpose of adjusting resistance or the like. Also, the positive electrode current collector layer may be a metal foil or a substrate on which the above metal is plated or vapor-deposited.

[0069] 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.

[0070] The thickness of the positive electrode current collector layer is not particularly limited, but it may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0071] 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.

[0072] 〈Shape, etc. of the 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.

[0073] FIG. 1 is a schematic diagram showing one aspect of the lithium secondary battery of the present disclosure, but is not limited to this case.

[0074] The lithium secondary battery 100 is a battery having a negative electrode current collector layer 111, a negative electrode active material layer 112, a protective 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 protective layer 113 disposed between the negative electrode active material layer 112 and the electrolyte layer 120 improves the capacity retention rate of the lithium secondary battery, reduces the resistance, and suppresses short circuits. The protective layer 113 contains a second lithium alloy and has high lithium ion conductivity and electron conductivity, thereby increasing the capacity retention rate of the lithium secondary battery 100 and decreasing the resistance value. Furthermore, since the negative electrode active material layer 112 also contains lithium metal or a lithium metal alloy and the protective layer 113 and the negative electrode active material layer 112 contain similar materials containing lithium, the interface between the protective layer 113 and the negative electrode active material layer 112 becomes highly adherent, thereby suppressing the precipitation of dendrite lithium that breaks through the protective layer 113 and improving the short circuit resistance.

[0075] 《Manufacturing method of lithium secondary battery》 The lithium secondary battery of the present disclosure can be manufactured by a manufacturing method including the following steps: forming the negative electrode active material layer on the surface of the negative electrode current collector layer; forming a protective layer containing the second lithium alloy on the surface of the negative electrode active material layer.

[0076] According to the method for manufacturing a lithium secondary battery of the present disclosure, a lithium secondary battery using lithium metal and / or a lithium alloy as a negative electrode active material can be manufactured, which has an improved capacity retention rate, a reduced resistance, and suppressed short circuit.

[0077] <Formation of Negative Electrode Active Material Layer> The negative electrode active material layer is not particularly limited, but a lithium metal or a first lithium alloy can be formed into a film on the surface of the negative electrode current collector layer by a vapor deposition method.

[0078] <Formation of Protective Layer> The protective layer is not particularly limited, but a second lithium alloy can be formed into a film on the surface of the negative electrode active material layer by a vapor deposition method, and a second lithium alloy and a third lithium alloy can also be simultaneously formed into a film by a vapor deposition method.

[0079] 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 of the present disclosure will be described with reference to FIGS. 1 and 2.

[0080] First, a lithium metal or a first lithium alloy is deposited on the surface of the negative electrode current collector layer 111 by a vapor deposition method to form a negative electrode active material layer 112 (FIG. 2A). Next, a second lithium alloy is deposited on the surface of the negative electrode active material layer 112 by a vapor deposition method to form a protective layer 113, and a negative electrode laminate 110 in which the negative electrode current collector layer 111, the negative electrode active material layer 112, and the protective layer 113 are laminated in this order can be formed (FIG. 2B). Next, a positive electrode active material layer 131 can be formed by applying a positive electrode composite material wet or dry on the positive electrode current collector layer 132 to form a positive electrode laminate 130 (FIG. 2C). Then, the negative electrode laminate 110, the electrolyte layer 120, and the positive electrode laminate 130 are laminated to form a lithium secondary battery 100 shown in FIG. 1 having a negative electrode current collector layer 111, a negative electrode active material layer 112, a protective layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132 in this order.

Example

[0081] 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.

[0082] 《Example 1》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer and protective layer on negative electrode current collector layer〉 Lithium (Li) metal was deposited on one side of a copper (Cu) foil as a negative electrode current collector layer by a vapor deposition method to form a negative electrode active material layer. Next, a lithium-tin (Li-Sn) alloy as a second lithium alloy was deposited on the surface of the negative electrode active material layer by a vapor deposition method to form a protective layer, and a negative electrode laminate was obtained. The negative electrode laminate is a laminate in which a negative electrode current collector layer, a negative electrode active material layer, and a protective layer are laminated in this order, and the thickness of the protective layer was 500 nm.

[0083] 〈Fabrication of positive electrode laminate〉 LiNi as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 384 parts by mass of O2, 12 parts by mass of acetylene black as a conductive assistant, 4 parts by mass of PVdF as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersion medium were mixed to prepare a positive electrode composite slurry. Subsequently, the obtained positive electrode composite slurry was coated on an aluminum (Al) foil as a positive electrode current collector and dried to produce a positive electrode laminate in which a positive electrode active material layer was formed on the positive electrode current collector layer.

[0084] <Manufacture of Lithium Secondary Battery> The negative electrode laminate and the positive electrode laminate were laminated so as to face each other with a polyolefin film (film thickness: 20 μm) as a separator and wound in a spiral shape. Terminals were respectively connected to the wound negative electrode laminate and positive electrode laminate, housed in a battery case, and 1M LiPF6 ethylene carbonate (EC) / dimethyl carbonate (DMC) (1 / 1 (volume ratio)) as an electrolytic solution was injected and sealed to manufacture a lithium secondary battery.

[0085] <Evaluation of Capacity Retention Rate of Lithium Secondary Battery> The lithium secondary battery was charged and discharged 200 cycles at 25°C in a constant current (current rate: 1C) mode within a cut-off voltage range of 3.3 to 4.2V. The capacities at the first cycle and the 200th cycle were measured, and the capacity retention rate (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.

[0086] <Evaluation of Resistance Value of Lithium Secondary Battery> The lithium secondary battery was adjusted so that the open circuit voltage became 3.70V. Subsequently, at -10°C, it was discharged at a current rate of 5C for 8 seconds to obtain a voltage drop (ΔV), and the resistance value (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 battery in Comparative Example 1 is set to 1.00.

[0087] <Evaluation of Short Circuit of Lithium Secondary Battery> The lithium secondary battery was subjected to constant current charging (current rate 1 / 3C) with a charging upper limit voltage of 3.5V. Subsequently, it was rested for 10 minutes and the voltage was boosted to 4.5V. Then, it was rested for 10 minutes and the voltage was measured. When the voltage after rest was 3.5V or higher, it was judged that there was no short circuit, and when the voltage after rest was less than 3.5V, it was judged that there was a short circuit. The results of the short circuit are shown in Table 1.

[0088] 《Comparative Example 1》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer on negative electrode current collector layer〉 On one side of a Cu foil as the negative electrode current collector layer, Li metal was deposited by a vapor deposition method to form a negative electrode active material layer, and a negative electrode laminate was fabricated.

[0089] 〈Fabrication of lithium secondary battery, evaluation of capacity retention rate, evaluation of resistance value, and evaluation of short circuit〉 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, resistance value, and short circuit 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 1.00.

[0090] 《Example 2》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer and protective layer on negative electrode current collector layer〉 On one side of a Cu foil as the negative electrode current collector layer, lithium (Li) and aluminum (Al) were deposited by a vapor deposition method (co - vapor deposition) to form a negative electrode active material layer containing a first lithium alloy. Subsequently, on the surface of the negative electrode active material layer, a Li - Sn alloy as a second lithium alloy was deposited by a vapor deposition method to form a protective layer, and a negative electrode laminate was obtained. The negative electrode laminate is a laminate in which the negative electrode current collector layer, the negative electrode active material layer, and the protective layer are laminated in this order, and the thickness of the protective layer was 500 nm.

[0091] 《Examples 3, 4》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer and protective layer on negative electrode current collector layer〉 When forming the negative electrode active material layer, a negative electrode laminate was produced in the same manner as in Example 2, except that magnesium (Mg) (Example 3) or silver (Ag) (Example 4) was used instead of Al.

[0092] 《Example 5》 〈Fabrication of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Protective Layer on Negative Electrode Current Collector Layer〉 On one side of a Cu foil as the negative electrode current collector layer, a negative electrode active material layer containing a first lithium alloy was formed by a vapor deposition method (co - evaporation) of Li and Al. Next, on the surface of the negative electrode active material layer, an Li - Sn alloy as the second lithium alloy and a lithium - aluminum (Li - Al) alloy as the third lithium alloy were simultaneously formed by a vapor deposition method to form a protective layer, and a negative electrode laminate was obtained. The negative electrode laminate is a laminate in which the negative electrode current collector layer, the negative electrode active material layer, and the protective layer are laminated in this order, and the thickness of the protective layer was 500 nm.

[0093] 《Examples 6 and 7》 〈Fabrication of Negative Electrode Laminate: Formation of Negative Electrode Active Material Layer and Protective Layer on Negative Electrode Current Collector Layer〉 For Example 6, a negative electrode laminate was produced in the same manner as in Example 5, except that Mg was used instead of Al when forming the negative electrode active material layer, and an Li - Mg alloy was used instead of the Li - Al alloy when forming the protective layer. For Example 7, a negative electrode laminate was produced in the same manner as in Example 5, except that Ag was used instead of Al when forming the negative electrode active material layer, and an Li - Ag alloy was used instead of the Li - Al alloy when forming the protective layer.

[0094] 〈Fabrication of Lithium Secondary Battery, Evaluation of Capacity Retention Rate, Evaluation of Resistance Value, and Evaluation of Short Circuit〉 Using the negative electrode laminates fabricated in Examples 2 to 7, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate, resistance value, and short circuit of the lithium secondary battery were evaluated in the same manner as in Example 1. The respective results were as shown in Table 1.

[0095] 《Comparative Example 2》 <Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the protective layer on the negative electrode current collector layer> When forming the protective layer, a negative electrode laminate was fabricated in the same manner as in Example 1, except that a compound containing lithium (Li) and iron (Fe), which is not a lithium alloy, was used instead of the Li-Sn alloy as the second lithium alloy.

[0096] <<Comparative Example 3>> <Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the protective layer on the negative electrode current collector layer> When forming the negative electrode active material layer, a negative electrode laminate was fabricated in the same manner as in Comparative Example 1, except that Li and Ag were deposited by a vapor deposition method (co-evaporation) instead of Li metal.

[0097] <<Comparative Example 4>> <Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the protective layer on the negative electrode current collector layer> When forming the protective layer, a negative electrode laminate was fabricated in the same manner as in Example 4, except that a compound containing lithium (Li) and iron (Fe), which is not a lithium alloy, was used instead of the Li-Sn alloy as the second lithium alloy.

[0098] <Fabrication of the lithium secondary battery, evaluation of the capacity retention rate, evaluation of the resistance value, and evaluation of the short circuit> Using the negative electrode laminates fabricated in Comparative Examples 2 to 4, a lithium secondary battery was fabricated in the same manner as in Example 1. The capacity retention rate, resistance value, and short circuit of the lithium secondary battery were evaluated in the same manner as in Example 1. The respective results were as shown in Table 1.

[0099]

Table 1

[0100] Compared with the lithium secondary batteries without a protective layer (Comparative Examples 1 and 3), the lithium secondary batteries (Examples 1 to 7) having a protective layer containing an Li-Sn alloy as the second lithium alloy had an increased capacity retention rate, a decreased resistance value, and no short circuit occurred. Further, the lithium secondary batteries (Examples 5 to 7) having a protective layer containing the second lithium alloy and the third lithium alloy showed even better capacity retention rate and resistance value. However, the lithium secondary batteries (Comparative Examples 2 and 4) having a protective layer containing a compound containing Li and Fe which is not a lithium alloy had performance equivalent to or slightly deteriorated compared to the batteries without a protective layer.

[0101] The protective layer contains the second lithium alloy, and it is presumed that the lithium ion conductivity and electron conductivity of the protective layer are high, thereby increasing the capacity retention rate and decreasing the resistance value. Further, the negative electrode active material layer also contains lithium metal or a lithium metal alloy, and since the protective layer and the negative electrode active material layer contain similar materials containing lithium, the interface between the protective layer and the negative electrode active material layer becomes highly adherent, thereby suppressing the precipitation of dendrite lithium that breaks through the protective layer and improving the short circuit resistance. On the other hand, when the protective layer does not contain the second lithium alloy (for example, a compound containing Li and Fe), the energy (transmission energy) for lithium ions to pass through the protective layer and reach the negative electrode active material layer becomes higher than the lithium nucleation energy, thereby causing lithium dendrites to precipitate on the protective layer and decreasing the short circuit resistance.

[0102] 《Examples 8 to 25 (Effect of the second lithium alloy contained in the protective layer)》 〈Fabrication of negative electrode laminate: Formation of negative electrode active material layer and protective layer on negative electrode current collector layer〉 When forming the protective layer, a negative electrode laminate was fabricated in the same manner as in Example 4, except that the lithium alloy described in Table 2 was used instead of the Li-Sn alloy as the second lithium alloy.

[0103] 〈Fabrication of lithium secondary battery, evaluation of capacity retention rate, evaluation of resistance value, and evaluation of short circuit〉 Using the negative electrode laminate produced in Examples 8 to 25, a lithium secondary battery was produced in the same manner as in Example 1. The capacity retention rate, resistance value, and short circuit of the lithium secondary battery were evaluated in the same manner as in Example 1. The results were as shown in Table 1.

[0104]

Table 2

[0105] Even in the lithium secondary battery (Examples 8 to 25) provided with a protective layer containing a lithium alloy other than the Li-Sn alloy as the second lithium alloy, the capacity retention rate increased, the resistance decreased, and no short circuit occurred. In the protective layer containing a lithium alloy composed of various metal elements, it is presumed that the lithium ion conductivity and electron conductivity of the protective layer increased, thereby increasing the capacity retention rate and reducing the resistance value.

[0106] 《Examples 26 to 31 (Effect of the thickness of the protective layer)》 〈Fabrication of the negative electrode laminate: Formation of the negative electrode active material layer and the protective layer on the negative electrode current collector layer〉 When forming the protective layer, a negative electrode laminate was produced in the same manner as in Example 4, except that the thickness of the protective layer was the thickness described in Table 3.

[0107] 〈Fabrication of the lithium secondary battery, evaluation of the capacity retention rate, evaluation of the resistance value, and evaluation of the short circuit〉 Using the negative electrode laminate produced in Examples 26 to 31, a lithium secondary battery was produced in the same manner as in Example 1. The capacity retention rate, resistance value, and short circuit of the lithium secondary battery were evaluated in the same manner as in Example 1. The results were as shown in Table 1.

[0108]

Table 3

[0109] In Example 4 and Examples 26 to 31, lithium secondary batteries with a protective layer thickness of 5 nm to 10,000 nm (10 μm) were evaluated. In the wide range where the protective layer thickness is 5 nm to 10,000 nm (10 μm), the capacity retention rate of the lithium secondary battery increased, the resistance value decreased, and no short circuit occurred.

[0110] Although the 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.

Description of Reference Numerals

[0111] 100 Lithium secondary battery 110 Negative electrode laminate 111 Negative electrode current collector layer 112 Negative electrode active material layer 113 Protective layer 120 Electrolyte layer 130 Positive electrode laminate 131 Positive electrode active material layer 132 Positive electrode current collector layer

Claims

1. It has a negative electrode current collector layer, a negative electrode active material layer, a protective 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 first lithium alloy, and the protective layer contains a second lithium alloy different from the first lithium alloy, a lithium secondary battery.

2. The lithium secondary battery according to claim 1, wherein the second lithium alloy contains lithium and at least one metal element selected from the following: Sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

3. The lithium secondary battery according to claim 1, wherein the thickness of the protective layer is 5 nm to 10 μm.

4. The protective layer further has a third lithium alloy, and the third lithium alloy is different from the second lithium alloy, the lithium secondary battery according to claim 1.

5. The lithium secondary battery according to claim 4, wherein the third lithium alloy contains lithium and at least one metal element selected from the following: Sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

6. The negative electrode active material layer has the first lithium alloy, and the third lithium alloy is the same as the first lithium alloy, the lithium secondary battery according to claim 4.

7. A method for manufacturing a lithium secondary battery according to any one of claims 1 to 6, comprising the following steps: forming the negative electrode active material layer on the surface of the negative electrode current collector layer, forming a protective layer containing the second lithium alloy on the surface of the negative electrode active material layer.

Images