Lithium metal secondary battery, and method for producing lithium metal secondary battery

Abstract

To provide a lithium metal secondary battery in which a capacity retention rate is enhanced and a resistance value is reduced.SOLUTION: A lithium metal secondary battery includes a negative electrode current collector layer 111, a metal layer 112, a negative electrode active material 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 113 contains a lithium metal and a metal particle 114 dispersed in the lithium metal, the metal particle 114 contains a metal element that is taken with lithium to form an alloy, and the area ratio of the metal particle 114 is 1×10-5% to 50% in observation of a cross section of the negative electrode active material layer 113 in a full charge state.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0004] Patent Document 2 discloses a secondary battery including a positive electrode, an electrolyte layer, a negative electrode current collector, and metallic lithium as a negative electrode active material that is deposited between the electrolyte layer and the negative electrode current collector upon charging. A nitride of element M is present between the electrolyte layer and the negative electrode current collector, element M is an element capable of alloying with Li, and the nitride is covalent. According to the secondary battery of Patent Document 2, the coulombic efficiency of the deposition and dissolution reactions of metallic lithium is said to be high.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] While lithium metal secondary batteries are expected to have excellent battery characteristics, in reality, the capacity retention rate is small and the resistance value is high. Therefore, there is room for improvement in lithium metal secondary batteries from the viewpoints of capacity retention rate and resistance value.

[0007] Therefore, an object of the present disclosure is to provide a lithium metal secondary battery with an improved capacity retention rate and a reduced resistance value.

MEANS FOR SOLVING THE PROBLEMS

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

[0009] <Aspect 1> A lithium metal secondary battery having a negative electrode current collector layer, a metal layer, a negative electrode active material 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 and metal particles dispersed in the lithium metal, the metal particles contain a metal element that forms an alloy with lithium, and the area ratio of the metal particles is 1×10 -5 % to 50% when observing the cross section of the negative electrode active material layer in a fully charged state. Lithium metal secondary battery. <Aspect 2> The lithium metal secondary battery according to Aspect 1, wherein the metal layer contains a metal element constituting the metal particles. <Aspect 3> The lithium metal secondary battery according to Aspect 1 or 2, wherein the metal element contains at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth. <Aspect 4> The lithium metal secondary battery according to any one of Aspects 1 to 3, wherein the film thickness of the metal layer is 5 nm to 3000 nm. <Aspect 5> A method for manufacturing a lithium metal secondary battery according to any one of Aspects 1 to 4, including the following steps: Forming the metal layer on the negative electrode current collector layer, and then applying a slurry containing metal particles on the surface of the metal layer to obtain a preliminary negative electrode laminate. Stacking the preliminary negative electrode laminate, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer in this order to obtain a preliminary lithium metal secondary battery. Performing a charging operation on the preliminary lithium metal secondary battery to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium metal secondary battery.

Advantages of the Invention

[0010] According to the present disclosure, the capacity retention rate of the lithium metal secondary battery is improved and the resistance value is reduced.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted 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 the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0013] Regarding the present disclosure, "composite material" means a composition that can form a positive electrode active material layer or the like, either as it is or by further containing other components. Further, regarding the present disclosure, "composite material slurry" means a slurry that contains a dispersion medium in addition to the "composite material" and can thereby form a positive electrode active material layer or the like by coating and drying.

[0014] The lithium metal 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. 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. Further, the lithium metal 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.

[0015] 《Lithium Metal Secondary Battery》 The lithium metal secondary battery of the present disclosure has a negative electrode current collector layer, a metal layer, a negative electrode active material 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 and metal particles dispersed in the lithium metal, the metal particles contain a metal element that forms an alloy with lithium, the area ratio of the metal particles is 1×10 -5 % to 50% when observing the cross-section of the negative electrode active material layer in a fully charged state,

[0016] According to the present disclosure, the capacity retention rate of the lithium metal secondary battery is improved and the resistance value is reduced.

[0017] Although not limited to theory, it is presumed that the metal layer and the metal particles dispersed in the negative electrode active material layer homogenize the nucleation of lithium metal as the negative electrode active material, suppress dendrite lithium, and thereby increase the capacity retention rate. Further, it is presumed that the metal layer and the metal particles dispersed in the negative electrode active material layer reduce the nucleation energy of lithium metal, thereby reducing the resistance value.

[0018] FIG. 1 is a schematic diagram showing one embodiment of the lithium metal secondary battery of the present disclosure, but is not limited to this case.

[0019] The lithium metal secondary battery 100 is a battery having a negative electrode current collector layer 111, a metal layer 112, a negative electrode active material layer 113, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132 in this order. Metal particles 114 are dispersed in the negative electrode active material layer 113. The metal layer 112 and the metal particles 114 dispersed in the negative electrode active material layer 113 increase the capacity retention rate and decrease the resistance value. Although not limited to theory, it is presumed that the metal layer 112 and the metal particles 114 dispersed in the negative electrode active material layer 113 homogenize the nucleation of lithium metal as the negative electrode active material, suppress dendrite lithium, and thereby increase the capacity retention rate. Further, it is presumed that the metal layer 112 and the metal particles 114 dispersed in the negative electrode active material layer 113 reduce the nucleation energy of lithium metal, thereby reducing the resistance value.

[0020] <Configuration of Lithium Metal Secondary Battery> The lithium metal secondary battery of the present disclosure has a negative electrode current collector layer, a metal layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0021] <Negative Electrode Current Collector Layer> The material used for the negative electrode current collector layer is not particularly limited, but those commonly used as the negative electrode current collector of a lithium metal 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.

[0022] 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 preferred.

[0023] 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.

[0024] 〈Metal layer〉 The metal layer is a layer containing a metal element and may contain the metal element constituting the metal particles described later.

[0025] The metal layer is not particularly limited, and it may contain at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

[0026] The thickness of the metal layer is not particularly limited, and it may be 5 nm to 3000 nm. The thickness of the metal layer can be measured by length measurement using a scanning electron microscope observation (SEM) on the cross-section of the metal layer.

[0027] The metal layer can be formed with reference to the description of "Method for Manufacturing a Lithium Metal Secondary Battery" described later.

[0028] 〈Negative electrode active material layer〉 In the lithium metal secondary battery of the present disclosure, the negative electrode active material layer contains lithium metal and metal particles dispersed in the lithium metal.

[0029] Here, 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.

[0030] The dispersion state of the metal particles dispersed in the negative electrode active material layer is not particularly limited. The metal particles may be, for example, monodispersed or dispersed as aggregates of metal particles. Also, the position of the metal particles may change according to the change in the thickness of the negative electrode active material layer accompanying charge and discharge.

[0031] The negative electrode active material layer contains at least lithium metal as the negative electrode active material and metal particles, 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, taking the whole of the negative electrode active material layer (the whole solid content) as 100% by mass, the content of lithium metal as 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 99% by mass or less, or 90% by mass or less.

[0032] (Negative electrode active material) As the negative electrode active material, at least lithium metal is used as described above. Further, the negative electrode active material layer may contain a negative electrode active material other than lithium metal. The negative electrode active material other than lithium metal 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, etc.

[0033] (Metal particles) The metal particles contain a metal element that alloyizes with lithium.

[0034] The metal element is not particularly limited, and may contain at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

[0035] The area ratio of the metal particles contained in the negative electrode active material layer is 1×10 -5 % to 50% when observing the cross section of the negative electrode active material layer in the fully charged state.

[0036] The area ratio of the metal particles can be obtained by disassembling a lithium metal secondary battery in the fully charged state and performing scanning electron microscope (SEM) observation and elemental mapping by energy dispersive X-ray analysis (EDX) on the cross section of the negative electrode active material layer. Specifically, the area of the observed cross section of the negative electrode active material layer is calculated by measuring the length from the SEM image. Next, the area of the metal particles present in the observed cross section of the negative electrode active material layer is calculated by measuring the length from the SEM image. Then, the area ratio can be obtained by calculating the ratio of the area of the metal particles to the area of the negative electrode active material layer.

[0037] The particle size of the metal particles is not particularly limited. For example, it may be 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 200 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 10 nm or less. The particle size of the metal particles can be measured by scanning electron microscope observation (SEM) of the cross-section of the metal layer.

[0038] (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.

[0039] (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.

[0040] (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.

[0041] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5 systems (Li7P3S 11, such as 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 and the like; or combinations thereof can be mentioned, but are not limited thereto.

[0042] 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., but are not limited thereto.

[0043] Sulfide solid electrolytes and oxide solid electrolytes may be glass or crystallized glass (glass ceramics).

[0044] Examples of polymer electrolytes include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof, etc., but are not limited thereto.

[0045] 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 metal secondary battery. The negative electrode active material may be, for example, in a layered or sheet-like form. The negative electrode active material may involve lithium deposition during charging, or may involve lithium dissolution during discharging. In this case, the negative electrode active material layer may be a layer made of lithium metal.

[0046] 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 200 μm or less, 1150 μm or less, or 100 μm or less.

[0047] The negative electrode active material layer can be formed with reference to the description of the "Method for Manufacturing a Lithium Metal Secondary Battery" described later.

[0048] <Electrolyte layer> <Electrolyte layer - Solid electrolyte layer> The lithium metal secondary battery of the present disclosure can be a solid battery, that is, it can have a solid electrolyte layer as the electrolyte layer.

[0049] In addition to the solid electrolyte, the solid electrolyte layer may contain a binder or the like as necessary.

[0050] The thickness of the solid electrolyte 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.

[0051] 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 or the like.

[0052] <Electrolyte layer - Separator layer> The lithium metal 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 a separator layer.

[0053] (Electrolyte solution) The electrolyte solution is not particularly limited, but preferably contains a supporting salt and a solvent.

[0054] The supporting salt (lithium salt) of the electrolyte solution 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.

[0055] The solvent used in the electrolyte solution 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 solution is not particularly limited, and only one kind may be used alone, or two or more kinds may be used in combination.

[0056] (Separator) The separator is not particularly limited, and a general separator for a lithium metal 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.

[0057] 〈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, etc. 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, 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.

[0058] (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 cobaltate (LiCoO2), lithium nickelate (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 having a composition represented by these, but not limited thereto.

[0059] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a material 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 not limited thereto.

[0060] The shape of the positive electrode active material is not particularly limited as long as it is a common shape for the positive electrode active material of a lithium metal 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 50% of the integrated value in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0061] Regarding the solid electrolyte, binder, and conductive assistant, reference can be made to the description of "<Negative electrode active material layer>" above.

[0062] The shape of the positive electrode active material layer is not particularly limited, and for example, a sheet-shaped positive electrode active material layer having a substantially flat surface may be used. The thickness of the positive electrode active material 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.

[0063] 〈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 metal 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 with the above metal plated or vapor-deposited thereon.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 〈Shape of the lithium metal secondary battery〉 Examples of the shape of the lithium metal secondary battery include, but are not limited to, coin type, laminate type, cylindrical type, and square type.

[0068] 《Manufacturing method of the lithium metal secondary battery》 The lithium metal secondary battery of the present disclosure can be manufactured by a manufacturing method including the following steps: Forming a metal layer on the negative electrode current collector layer, and then applying a slurry containing metal particles on the surface of the metal layer to obtain a preliminary negative electrode laminate. Stacking the above preliminary negative electrode laminate, electrolyte layer, positive electrode active material layer holding lithium, and positive electrode current collector layer in this order to obtain a preliminary lithium metal secondary battery. By performing a charging operation on the above preliminary lithium metal secondary battery, lithium that has migrated from the above positive electrode active material layer is deposited on the surface of the metal layer to form the above negative electrode active material layer, thereby obtaining the above lithium metal secondary battery.

[0069] According to the manufacturing method of the lithium metal secondary battery of the present disclosure, a lithium metal secondary battery with an improved capacity retention rate and a reduced resistance value can be manufactured.

[0070] FIG. 2 is a schematic diagram showing one aspect of the manufacturing method of the lithium metal secondary battery of the present disclosure, but is not limited to this case. The manufacturing method of the lithium metal secondary battery of the present disclosure will be described with reference to FIGS. 1 and 2.

[0071] First, a metal element is deposited on the surface of the negative electrode current collector layer 111 by a vapor deposition method to form a metal layer 112 (FIG. 2A). Next, a slurry containing metal particles is applied to the surface of the metal layer 112 to form a metal layer 112 coated with metal particles 114, thereby forming a preliminary negative electrode laminate 110a (FIG. 2B). Next, a positive electrode active material layer 131 is formed by applying a positive electrode composite material to the positive electrode current collector layer 132 wet or dry to form a positive electrode laminate 130, and the preliminary negative electrode laminate 110a, the electrolyte layer 120, and the positive electrode laminate 130 are laminated to form a preliminary lithium metal secondary battery 100a having a negative electrode current collector layer 111, a metal layer 112 coated with metal particles 114, an electrolyte layer 120, a positive electrode active material layer 131, and a positive electrode current collector layer 132 in this order. A charging operation is performed on this preliminary lithium metal secondary battery 100a to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer 112, thereby forming a negative electrode active material layer 113, and thereby, a lithium metal secondary battery 100 can be formed (FIG. 1). In the process of depositing lithium on the surface of the metal layer 112 by the charging operation, the metal particles 114 applied to the surface of the metal layer 112 diffuse and disperse into the lithium metal layer as the negative electrode active material layer 113 (FIG. 1).

[0072] <Formation of preliminary negative electrode laminate> The preliminary negative electrode laminate can be formed by forming a metal layer on the negative electrode current collector layer and then applying a slurry containing metal particles to the surface of the metal layer.

[0073] (Preliminary negative electrode laminate) The preliminary negative electrode laminate is not particularly limited, but is a laminate in which a negative electrode current collector and a metal layer coated with metal particles are laminated in this order.

[0074] (Formation of metal layer) The metal layer is not particularly limited, but can be formed by depositing a metal element on the surface of the negative electrode current collector layer by a vapor deposition method.

[0075] (Application of slurry containing metal particles) The slurry containing metal particles is not particularly limited, but can be prepared by mixing a powder of a metal element, a binder, and an appropriate amount of a dispersion medium. The method for applying this slurry containing metal particles is not particularly limited, but it can be applied to the surface of the metal layer using a known application method. Here, as the binder, for example, polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc. can be used. Also, as the dispersion medium, for example, N-methyl-2-pyrrolidone (NMP), etc. can be used.

[0076] 〈Formation of a preliminary lithium metal secondary battery〉 The preliminary lithium metal secondary battery can be formed by laminating a preliminary negative electrode laminate, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer in this order.

[0077] (Preliminary lithium metal secondary battery) The preliminary lithium metal secondary battery is not particularly limited, but is a laminate in which a preliminary negative electrode laminate, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in this order, that is, a laminate in which a negative electrode current collector and a metal layer coated with metal particles, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer are laminated in this order.

[0078] 〈Formation of a lithium metal secondary battery〉 By performing a charging operation on the preliminary lithium metal secondary battery, lithium that has migrated from the positive electrode active material layer is deposited on the surface of the metal layer to form a negative electrode active material layer, thereby forming a lithium metal secondary battery.

[0079] (Charging operation) As the charging operation, for example, it can be performed under constant current conditions in the range of a cut-off voltage of 3.3 to 4.2V. The current amount (C rate) in the charging operation is not particularly limited, but may be 0.01C or more, 0.1C or more, 0.5C or more, or 1.0C or more, and may also be 2.0C or less, 1.5C or less, 1.2C or less, or 1.0C or less.

[0080] (Formation of negative electrode active material layer) The negative electrode active material layer is not particularly limited. However, in a preliminary lithium metal secondary battery, a charging operation is performed to release lithium from the positive electrode active material holding lithium, deposit lithium on the metal layer, and form a negative electrode active material layer. At this time, metal particles are coated on the surface of the metal layer, and as lithium is deposited, the metal particles diffuse into the lithium metal layer, thereby forming a negative electrode active material layer in which the metal particles are dispersed.

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 preliminary negative electrode laminate〉 Tin (Sn) was deposited on one side of a copper (Cu) foil as a negative electrode current collector by vapor deposition to form a metal layer on the Cu foil. The thickness of the metal layer was 600 nm. Next, Sn powder as metal particles, which is the same metal element as the metal layer, polyvinylidene fluoride (PVdF), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a slurry containing a metal element. Then, this slurry containing a metal element was coated on the metal layer and vacuum dried at 80 °C to fabricate a preliminary negative electrode laminate.

[0083] 〈Fabrication of positive electrode laminate〉 LiNi as a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (84 parts by mass), acetylene black (12 parts by mass) as a conductive assistant, PVdF (4 parts by mass) as a binder, and an appropriate amount of NMP as a dispersion medium were mixed to prepare a positive electrode composite slurry. Then, the obtained positive electrode composite slurry was coated on an aluminum (Al) foil as a positive electrode current collector and dried to fabricate a positive electrode laminate in which a positive electrode active material layer was formed on the positive electrode current collector layer.

[0084] <Fabrication of a Preliminary Lithium Metal Secondary Battery> A preliminary negative electrode laminate and a positive electrode laminate were laminated so as 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 connected to the wound preliminary negative electrode laminate and positive electrode laminate, respectively, housed in a battery case, and 1 M LiPF6 ethylene carbonate / dimethyl carbonate (1 / 1, volume ratio) as an electrolytic solution was injected and sealed to fabricate a preliminary lithium metal secondary battery.

[0085] <Formation of a Lithium Metal Secondary Battery and Evaluation of the Capacity Retention Rate> The preliminary lithium metal 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 4.2 V. 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. The capacity retention rate in Table 1 is a relative value when the capacity retention rate of the lithium metal secondary battery of Comparative Example 1 is set to 1.00. Here, by performing a charging operation on the preliminary lithium metal secondary battery, lithium that has migrated from the positive electrode active material layer is deposited on the metal layer, forming a lithium metal layer as the negative electrode active material layer, thereby forming a lithium metal secondary battery.

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

[0087] <Area Ratio of Metal Particles in the Negative Electrode Active Material Layer> A lithium metal secondary battery in a fully charged state was disassembled, and the negative electrode active material layer was recovered. Next, the cross-section of the negative electrode active material layer was observed by a scanning electron microscope (SEM) and elemental mapping by energy dispersive X-ray analysis (EDX) was performed to calculate the area ratio of metal particles to the negative electrode active material layer. The area ratio of metal particles to the negative electrode active material layer was 1%.

[0088] 《Comparative Example 1》 A Cu foil as a negative electrode current collector having no metal layer was used as a preliminary negative electrode laminate.

[0089] 〈Fabrication of Lithium Metal Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value〉 Using only the preliminary negative electrode laminate of the Cu foil of Comparative Example 1, a lithium metal secondary battery was fabricated in the same manner as in Example 1. Since it does not contain metal particles, the area ratio of metal particles to the negative electrode active material layer was 0%. The capacity retention rate and resistance value of the lithium metal 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 metal secondary battery of Comparative Example 1 are shown as relative values with 1.00 as the reference.

[0090] 《Examples 2 to 8, Comparative Examples 2 and 3 (Effect of Area Ratio of Metal Particles)》 〈Fabrication of Preliminary Negative Electrode Laminate〉 A preliminary negative electrode laminate was fabricated in the same manner as in Example 1, except that the coating amount of the paste containing Sn as metal particles was adjusted respectively.

[0091] 〈Fabrication of Lithium Metal Secondary Battery, Evaluation of Capacity Retention Rate, and Evaluation of Resistance Value〉 Using the preliminary negative electrode laminates fabricated in Examples 2 to 8 and Comparative Examples 2 and 3, a lithium metal secondary battery was fabricated in the same manner as in Example 1. The area ratio of metal particles to the negative electrode active material layer was as shown in Table 2. The capacity retention rate and resistance value of the lithium metal secondary batteries in Examples 2 to 8 and Comparative Examples 2 and 3 were evaluated in the same manner as in Example 1. Each result was as shown in Table 1.

[0092]

Table 1

[0093] The lithium metal secondary battery having a metal layer and containing lithium metal and metal particles dispersed in the lithium metal in the negative electrode active material layer had an increased capacity retention rate and a decreased resistance value as compared with the lithium metal secondary battery of Comparative Example 1. Among them, the lithium metal secondary battery provided with a negative electrode active material layer having an area ratio of metal particles to the negative electrode active material layer of 1×10 -5 ~50% had a significantly improved capacity retention rate and resistance value as compared with the lithium metal secondary battery of Comparative Example 1.

[0094] When a metal layer is provided and a predetermined amount of metal particles are dispersed in the negative electrode active material layer, it is presumed that the nucleation of lithium metal is homogenized and dendrite lithium is suppressed, thereby increasing the capacity retention rate. Also, it is presumed that the nucleation energy is reduced by the predetermined amount of metal particles, thereby reducing the resistance value.

[0095] 《Examples 9 to 13 (Effect of the film thickness of the metal layer)》 〈Preparation of the preliminary negative electrode laminate〉 A preliminary negative electrode laminate was prepared in the same manner as in Example 1, except that the film thickness of the metal layer was set to the film thickness shown in Table 2 by adjusting the time for forming Sn by vapor deposition.

[0096] 〈Preparation of the lithium metal secondary battery, evaluation of the capacity retention rate, and evaluation of the resistance value〉 Using the preliminary negative electrode laminates prepared in Examples 9 to 13, a lithium metal secondary battery was prepared in the same manner as in Example 1. Since the coating amount of the paste containing Sn as the metal particles was the same in the preparation of the preliminary negative electrode laminate, the area ratio of the metal particles to the negative electrode active material layer in Examples 9 to 13 was all 1% as in Example 1. The capacity retention rate and resistance value of the lithium metal secondary batteries in Examples 9 to 13 were evaluated in the same manner as in Example 1. The respective results were as shown in Table 2.

[0097]

Table 2

[0098] In Examples 1 and 9 to 13, lithium metal secondary batteries were evaluated in which the area ratio of metal particles in the negative electrode active material layer was 1%, and the thickness of the metal layer was 5 nm to 3000 nm. In the wide range where the thickness of the metal layer was 5 nm to 3000 nm, the capacity retention rate of the lithium metal secondary battery increased and the resistance value decreased as compared with the lithium metal secondary battery of Comparative Example 1.

[0099] 《Examples 14 to 31 (Influence of the material of the metal layer and metal particles) A preliminary negative electrode laminate was produced in the same manner as in Example 1, except that the materials of the metal layer and the metal particles were as described in Table 3.

[0100] 〈Production of lithium metal secondary battery, evaluation of capacity retention rate, and evaluation of resistance value〉 Using the preliminary negative electrode laminates produced in Examples 14 to 31, lithium metal secondary batteries were produced in the same manner as in Example 1. In the production of the preliminary negative electrode laminate, since the coating amount of the paste containing Sn as the metal particles was the same, the area ratio of the metal particles to the negative electrode active material layer in Examples 14 to 31 was all 1% as in Example 1. The capacity retention rate and the resistance value of the lithium metal secondary batteries in Examples 14 to 31 were evaluated in the same manner as in Example 1. The respective results were as shown in Table 3.

[0101]

Table 3

[0102] Even when the materials of the metal layer and the metal particles are other than Sn (Examples 14 to 31), the capacity retention rate increased and the resistance value decreased. Even when various metal elements capable of forming an alloy with lithium are included as the materials of the metal layer and the metal particles, the nucleation of lithium metal is homogenized by the metal layer and the metal particles dispersed in the negative electrode, and dendrite lithium is suppressed, whereby it is presumed that the capacity retention rate was improved. Further, it is presumed that the nucleation energy was decreased by the metal layer and the metal particles, whereby the battery resistance was decreased.

[0103] Although the preferred embodiments of the lithium metal secondary battery and the method for manufacturing the lithium metal 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 Reference Numerals

[0104] 100 Lithium metal secondary battery 100a Preliminary lithium metal secondary battery 110 Negative electrode laminate 110a Preliminary negative electrode laminate 111 Negative electrode current collector layer 112 Metal layer 113 Negative electrode active material layer 114 Metal particles 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 metal layer, a negative electrode active material 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 and metal particles dispersed in the lithium metal, the metal particles contain a metal element that forms an alloy with lithium, When observing the cross-section of the negative electrode active material layer in a fully charged state, the area ratio of the metal particles is 1×10 －５ % to 50%, A lithium metal secondary battery.

2. The lithium metal secondary battery according to Claim 1, wherein the metal layer contains the metal element constituting the metal particles.

3. The lithium metal secondary battery according to Claim 1, wherein the metal element contains at least one selected from sodium, magnesium, aluminum, silicon, calcium, zinc, gallium, germanium, strontium, rhodium, palladium, barium, silver, lead, tin, iridium, gold, platinum, and bismuth.

4. The lithium metal secondary battery according to Claim 1, wherein the film thickness of the metal layer is 5 nm to 3000 nm.

5. A method for manufacturing the lithium metal secondary battery according to any one of Claims 1 to 4, including the following steps: Forming the metal layer on the negative electrode current collector layer, and then applying a slurry containing metal particles on the surface of the metal layer to obtain a preliminary negative electrode laminate; Stacking the preliminary negative electrode laminate, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer in this order to obtain a preliminary lithium metal secondary battery; Performing a charging operation on the preliminary lithium metal secondary battery to deposit lithium that has migrated from the positive electrode active material layer on the surface of the metal layer to form the negative electrode active material layer, thereby obtaining the lithium metal secondary battery.

Images