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

Abstract

To provide a lithium secondary battery in which cycle characteristics can be improved while increasing reversible capacity, and a method of producing the same.SOLUTION: A lithium secondary battery includes a negative electrode current collector layer 110, a first lithium-tin alloy layer 120, a lithium-magnesium alloy layer 121, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150, in this order. A method of producing the lithium secondary battery includes the following steps of obtaining a preliminary lithium secondary battery 200, and performing a charging operation of the preliminary lithium secondary battery 200 to: (i) allow tin of a first metal layer 220 to react with lithium migrating from the positive electrode active material layer 140, and thereby form the lithium-tin alloy layer; and (ii) allow magnesium of a second metal layer 221 to react with lithium migrating from the positive electrode active material layer 140, and thereby form the lithium-magnesium alloy layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lithium-ion batteries use lithium metal and / or lithium alloys, which have a high ionization tendency among metals, as the negative electrode active material. Because lithium-ion batteries have a large potential difference between the negative and positive electrodes, can produce a high output voltage, and have a high theoretical capacity density, their practical application is expected, and the following types of batteries have been disclosed.

[0003] For example, Patent Document 1 discloses an all-solid-state battery that utilizes a deposition-dissolution reaction of metallic lithium as the reaction of the negative electrode, comprising a positive electrode including a positive electrode layer, a negative electrode including a negative electrode current collector and a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer contains a β single-phase alloy of metallic lithium and metallic magnesium as the negative electrode active material, and when the all-solid-state battery is fully charged, the elemental ratio of the lithium element in the alloy is 81.80 atomic% or more and 99.97 atomic% or less. According to Patent Document 1, it is possible to provide an all-solid-state battery with high charge-discharge efficiency.

[0004] Patent Document 2 describes a positive electrode layer comprising a positive electrode active material layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer and comprising a solid electrolyte, wherein the negative electrode layer comprises a negative electrode current collector, a first negative electrode active material layer in contact with the solid electrolyte layer, and a second negative electrode active material layer disposed between the negative electrode current collector and the first negative electrode active material layer, wherein the first negative electrode active material layer comprises a first carbon-based negative electrode active material, and the second negative electrode active material layer comprises a second carbon-based negative electrode active material, and the intensity ratio of the D-band peak to the G-band peak in the Raman spectrum of the first carbon-based negative electrode active material is (I 1 D / I 1 G ) is the intensity ratio (I 2 D / I 2 G There is disclosed an all-solid-state secondary battery having a lower self-discharge rate than that of )). According to Patent Document 2, it is said that an all-solid-state secondary battery in which short circuit is prevented and cycle characteristics are excellent can be provided.

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 secondary batteries are expected to have excellent battery characteristics, in reality, their reversible capacity is small and their cycle characteristics are not yet sufficient. Therefore, there is room for improvement in lithium secondary batteries from the viewpoints of reversible capacity and cycle characteristics.

[0007] Therefore, an object of the present disclosure is to provide a lithium secondary battery capable of increasing the reversible capacity and improving the cycle characteristics.

Means for Solving the Problems

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

[0009] <Aspect 1> A lithium secondary battery having a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order. <Aspect 2> The lithium secondary battery according to Aspect 1, wherein the thickness of the first lithium-tin alloy layer in a fully charged state is 0.1 to 15 μm. <Aspect 3> A lithium secondary battery according to embodiment 1 or 2, wherein the thickness of the lithium-magnesium alloy layer is 0.1 to 40 μm when fully charged. <Aspect 4> A lithium secondary battery according to any one of embodiments 1 to 3, comprising the above-mentioned negative electrode current collector layer, the above-mentioned first lithium-tin alloy layer, the above-mentioned lithium-magnesium alloy layer, the second lithium-tin alloy layer, the above-mentioned electrolyte layer, the above-mentioned positive electrode active material layer, and the above-mentioned positive electrode current collector layer in this order. <Aspect 5> When fully charged, The thickness of the first lithium-tin alloy layer described above is 0.1 to 15 μm, and A lithium secondary battery according to any one of embodiments 1 to 4, wherein the thickness of the second lithium-tin alloy layer is 0.1 to 15 μm. <Pattern 6> A method for manufacturing a lithium secondary battery according to any one of embodiments 1 to 5, including the following steps: A spare lithium secondary battery is obtained by stacking the above-mentioned negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, the above-mentioned electrolyte layer, the above-mentioned positive electrode active material layer holding lithium, and the above-mentioned positive electrode current collector layer in this order. By performing a charging operation on the above-mentioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) the magnesium in the second metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer. <Aspect 7> A method for manufacturing a lithium secondary battery according to any one of embodiments 1 to 5, including the following steps: To obtain the above-mentioned spare lithium secondary battery, the negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the third metal layer containing tin, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer are stacked in this order. By performing a charging operation on the above-mentioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the first lithium-tin alloy layer, (ii) the magnesium in the second metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer, and (iii) the tin in the third metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the second lithium-tin alloy layer. [Effects of the Invention]

[0010] The lithium secondary battery of this disclosure can improve cycle characteristics while increasing reversible capacity. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram illustrating the lithium secondary battery of this disclosure. [Figure 2] Figure 2 is a schematic diagram illustrating another embodiment of the lithium secondary battery of the present disclosure. [Figure 3] Figure 3 is a schematic diagram illustrating the manufacturing method of the lithium secondary battery of this disclosure. [Figure 4] Figure 4 is a schematic diagram illustrating another embodiment of the method for manufacturing the lithium secondary battery of the present disclosure. [Figure 5] Figure 5 shows the results of EDX mapping analysis by cross-sectional SEM-EDX for lithium secondary battery E2 of Example 2, broken down by element (Figure 5(A) Superposition of elements sulfur (S), oxygen (O), tin (Sn), magnesium (Mg), and nickel (Ni), Figure 5(B) S, Figure 5(C) O, Figure 5(D) Sn, Figure 5(E) Mg, Figure 5(F) Ni). [Figure 6] Figure 6 shows a cross-sectional SEM image of lithium secondary battery E2 of Example 2 (Figure 6(A) Cross-sectional SEM image, Figure 6(B) Schematic diagram of the cross-sectional structure). [Modes for carrying out the invention]

[0012] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various ways within the scope of the gist of this disclosure. Furthermore, in the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0013] In this disclosure, “compound mixture” means a composition that can constitute a positive electrode active material layer or an electrolyte layer, either in itself or by further containing other components. In this disclosure, “compound mixture slurry” means a slurry that includes a dispersion medium in addition to the “compound mixture,” and can be applied and dried to form a positive electrode active material layer or an electrolyte layer.

[0014] The lithium secondary battery of this disclosure may be a liquid-type battery containing an electrolyte as an electrolyte layer, or it may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. In this disclosure, "solid-state battery" means a battery using at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as its electrolyte. Furthermore, the lithium secondary battery of this disclosure may be an all-solid-state battery, i.e., a battery using only a solid electrolyte as its electrolyte.

[0015] Lithium-ion rechargeable battery The lithium secondary battery of this disclosure comprises, in this order, a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer.

[0016] The lithium secondary battery of this disclosure can improve cycle characteristics while increasing reversible capacity.

[0017] Specifically, the lithium secondary battery of this disclosure has, for example, a first lithium-tin alloy layer 120 between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121, as shown in Figure 1. It is presumed that the first lithium-tin alloy layer 120 suppresses delamination at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge, thereby increasing the reversible capacity and improving the cycle characteristics.

[0018] Furthermore, although the details are not clear, the following is considered to be the reason why the first lithium-tin alloy layer 120 can suppress delamination at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121. During discharge, the lithium in the lithium-magnesium alloy layer 121 undergoes dealloying more preferentially than the lithium in the first lithium-tin alloy layer 120 from the perspective of reaction potential, and as a result the lithium-magnesium alloy layer 121 shrinks significantly. On the other hand, the dealloying reaction of the first lithium-tin alloy layer 120 is less likely to proceed compared to the lithium-magnesium alloy layer 121, and therefore shrinks less. It is presumed that the first lithium-tin alloy layer 120 can mitigate the shrinkage of the lithium-magnesium alloy layer 121, thereby suppressing delamination at the interface.

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

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

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

[0022] <First lithium-tin alloy layer> The first lithium-tin alloy layer contains lithium and tin, and may further optionally contain other metallic elements that alloy with lithium. In the lithium secondary battery of this disclosure, these first and second lithium-tin alloy layers may also function as negative electrode active material layers depending on the charge and discharge conditions.

[0023] The thickness of the first lithium-tin alloy layer is not particularly limited, but may be 0.1 to 15 μm in a fully charged state. The thickness of the first lithium-tin alloy layer is not particularly limited, but may be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and may be 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0024] For the method of forming the first lithium-tin alloy layer, please refer to the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0025] <Lithium-magnesium alloy layer> The lithium-magnesium alloy layer contains lithium and magnesium elements, and may further optionally contain other metallic elements that alloy with lithium. This lithium-magnesium alloy layer functions as the negative electrode active material layer in the lithium secondary battery of this disclosure.

[0026] The thickness of the lithium-magnesium alloy layer is not particularly limited, and may be 0.1 to 40 μm in the fully charged state. The thickness of the lithium-magnesium metal layer is not particularly limited, and may be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and may also be 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, or 20 μm or less.

[0027] The method for forming the lithium-magnesium alloy layer can refer to the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0028] 〈Electrolyte layer〉 〈Electrolyte layer - Solid electrolyte layer〉 The lithium secondary battery of the present disclosure can be a solid battery, that is, it can have a solid electrolyte layer as the electrolyte layer.

[0029] In addition to the solid electrolyte, the solid electrolyte layer may contain a binder or the like as necessary.

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

[0031] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include 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 xEtc.; or combinations thereof, but not limited to these.

[0032] An example of an oxide solid electrolyte is 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 Examples include (LiPON), but are not limited to these.

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

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

[0035] (Binder) The binder is not particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), etc., but is not limited to these. The binder is not particularly limited, and may be used alone or in combination of two or more types.

[0036] The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0037] The solid electrolyte layer can be easily formed, for example, by molding an electrolyte mixture containing the aforementioned solid electrolyte and binder in a dry or wet manner.

[0038] <Electrolyte layer - Separator layer> The lithium secondary battery of this disclosure may be a liquid-type battery, that is, it may have an electrolyte as an electrolyte layer, particularly an electrolyte held in a separator layer.

[0039] (electrolyte) The electrolyte is not particularly limited, but it preferably contains a supporting salt and a solvent.

[0040] The supporting salt (lithium salt) for the lithium-ion conductive electrolyte is not particularly limited, but examples include inorganic lithium salts and organic lithium salts. Examples of inorganic lithium salts include, but are not limited to, LiPF6, LiBF4, LiClO4, and LiAsF6. Examples of organic lithium salts include, but are not limited to, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0041] The solvent used in the electrolyte is not particularly limited, but examples include cyclic carbonates and linear carbonates. Examples of cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of linear carbonates include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte is not particularly limited, but may be used alone or in combination of two or more types.

[0042] (Separator) The separator is not particularly limited, but any separator commonly used in lithium secondary batteries can be appropriately adopted. For example, nonwoven fabrics such as polyolefin, polyamide, or polyimide can be used as the separator.

[0043] <Cathode active material layer> The positive electrode active material layer contains at least positive electrode active material and may optionally contain conductive additives, solid electrolytes, binders, etc. The positive electrode active material layer may also contain various other additives. The respective content of positive electrode active material, conductive additives, binders, etc. in the positive electrode active material layer can be appropriately determined according to the desired battery performance. For example, if the total (total solid content) of the positive electrode active material layer is taken as 100% by mass, the content of positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 100% by mass or less, or 90% by mass or less.

[0044] (Cathode active material) The material of the positive electrode active material is not particularly limited as long as it is capable of intercalating and releasing lithium ions. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), nickel-cobalt-manganese oxide (NCM), and LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Lithium nickel-cobalt aluminum oxide (NCA; LiNi x Co y Al z O2), Li 1+x Mn 2-x-y M y This may include, but is not limited to, heteroatom-substituted Li-Mn spinel with a composition represented by O4 (where M is one or more metallic elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0045] The positive electrode active material is not particularly limited, but may have a coating layer. The coating layer is a layer containing a material that has lithium ion conductivity, low reactivity with the positive electrode active material and solid electrolyte, and can maintain a coating layer form that does not flow even when in contact with the active material and solid electrolyte. Specific examples of materials constituting the coating layer include LiNbO3 and Li4Ti5O3. 12 Examples include Li3PO4, but are not limited to these.

[0046] The shape of the positive electrode active material is not particularly limited, as long as it is a shape common for positive electrode active materials in lithium secondary batteries. The positive electrode active material may be, for example, particulate. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter D of the positive electrode active material 50 For example, it may be 1 nm or more, 5 nm or more, or 10 nm or more, and it may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D 50 This is the particle diameter (median diameter) at 50% of the integrated value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0047] (Conductive additive) The conductive additive is not particularly limited. Examples of conductive additives include, but are not limited to, vapor-grown carbon fibers (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF). The conductive additive may be particulate or fibrous, and its size is not particularly limited. While the conductive additive is not particularly limited, it may be used alone or in combination of two or more types.

[0048] For information regarding the solid electrolyte and binder, please refer to the description in "〈Electrolyte Layer - Solid Electrolyte Layer〉" above.

[0049] The shape of the positive electrode active material layer is not particularly limited, but may be, for example, a sheet-like positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0050] <Positive electrode current collector layer> The material used for the positive electrode current collector layer is not particularly limited, but a material commonly used for the positive electrode current collector of lithium secondary batteries can be appropriately adopted. Examples of materials used for the positive electrode current collector layer include, but are not limited to, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The positive electrode current collector layer may also have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector layer may be a metal foil or a substrate on which the above metals are plated or vapor-deposited.

[0051] The shape of the positive electrode current collector layer is not particularly limited, but examples include foil-like, plate-like, or mesh-like shapes. Among these, a foil-like shape is preferred.

[0052] The thickness of the positive electrode current collector layer is not particularly limited, but may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0053] The positive electrode active material layer can be manufactured by applying known methods. For example, the positive electrode active material layer can be easily formed by dry or wet molding of a positive electrode mixture containing the above-mentioned components. The positive electrode active material layer may be formed together with the positive electrode current collector layer, or it may be formed separately from the positive electrode current collector layer.

[0054] Lithium-ion batteries can take the form of coin-type, laminate-type, cylindrical, or prismatic batteries, but are not limited to these types.

[0055] Figure 1 is a schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but is not limited to this embodiment.

[0056] The lithium secondary battery 100 is a battery in which a negative electrode current collector layer 110, a first lithium-tin alloy layer 120, a lithium-magnesium alloy layer 121, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are stacked in this order. The first lithium-tin alloy layer 120, which is placed between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121, suppresses delamination of the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge, thereby increasing the reversible capacity and improving the cycle characteristics.

[0057] <Another form of lithium secondary battery> The lithium secondary battery of this disclosure may have a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, a second lithium-tin alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0058] <Second lithium-tin alloy layer> The second lithium-tin alloy layer contains lithium and tin elements, and may further optionally contain other metallic elements that alloy with lithium.

[0059] The thickness of the second lithium-tin alloy layer is not particularly limited, but may be 0.1 to 15 μm in a fully charged state. The thickness of the first lithium-tin alloy layer is not particularly limited, but may be 0.1 μm or more, 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and may be 15 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less.

[0060] For the method of forming the second lithium-tin alloy layer, please refer to the "Method for Manufacturing a Lithium Secondary Battery" described later.

[0061] For details regarding the negative electrode current collector, the first lithium-tin alloy layer, the lithium-magnesium alloy layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer, please refer to the description in "Lithium Secondary Batteries".

[0062] Figure 2 is a schematic diagram showing one embodiment of the lithium secondary battery of the present disclosure, but is not limited to this embodiment.

[0063] The lithium secondary battery 100 is a battery in which a negative electrode current collector layer 110, a first lithium-tin alloy layer 120, a lithium-magnesium alloy layer 121, a second lithium-tin alloy layer 122, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are stacked in this order. The first lithium-tin alloy layer 120, positioned between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121, suppresses delamination at the interface between the negative electrode current collector layer 110 and the lithium-magnesium alloy layer 121 during discharge, thereby increasing the reversible capacity and improving the cycle characteristics. Furthermore, the second lithium-tin alloy layer 122, positioned between the lithium-magnesium alloy layer 121 and the electrolyte layer 130, suppresses delamination at the interface between the lithium-magnesium alloy layer 121 and the electrolyte layer 130 during discharge, thereby further improving the cycle characteristics.

[0064] Manufacturing method for lithium-ion batteries The lithium secondary battery of this disclosure can be manufactured by a method comprising the following steps: A spare lithium secondary battery is obtained by stacking a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer in this order. By performing a charging operation on the above-mentioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) the magnesium in the second metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer.

[0065] According to the lithium secondary battery manufacturing method of this disclosure, it is possible to manufacture a lithium secondary battery that can increase reversible capacity while improving cycle characteristics.

[0066] <First Metal Layer> The first metal layer contains tin and may further optionally contain other metal elements that are alloyed with lithium.

[0067] The thickness of the first metal layer is not particularly limited, but may be 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, or 0.50 μm or less, 0.40 μm or less, 0.30 μm or less, or 0.2 μm or less.

[0068] The first metal layer can be formed, for example, by depositing a tin layer on the negative electrode current collector using a sputtering method, but is not limited to this case.

[0069] <Second Metal Layer> The second metal layer contains magnesium and may optionally contain other metal elements that are alloyed with lithium.

[0070] The thickness of the second metal layer is not particularly limited, but may be 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, 0.20 μm or more, or 3.0 μm or less, 2.0 μm or less, 1.0 μm or less, or 0.50 μm or less.

[0071] The second metal layer can be formed, for example, by depositing a magnesium layer on the first metal layer using a sputtering method, but is not limited to this case.

[0072] For details regarding the negative electrode current collector, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer, please refer to the description under "Lithium Secondary Batteries."

[0073] <Spare lithium secondary battery> A spare lithium secondary battery is a laminate in which a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer are stacked in this order.

[0074] A spare lithium secondary battery can be easily formed by, for example, laminating a negative electrode current collector, a first metal layer, a second metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in the order described above, housing this laminate in a laminate film, vacuum sealing it, and pressing it.

[0075] (charging operation) The charging operation can be performed, for example, under constant current-constant voltage conditions within a cutoff voltage range of 4.2V-3.0V. During the charging operation, lithium is released from the positive electrode active material containing lithium in the positive electrode active material layer, and the lithium moves to the first metal layer and the second metal layer.

[0076] The current (C rate) in the charging operation is not particularly limited, but may be 0.01C or higher, 0.02C or higher, 0.03C or higher, or 0.05C or higher, and may also be 0.20C or lower, 0.10C or lower, 0.75C or lower, or 0.05C or lower.

[0077] The temperature during charging is not particularly limited. The temperature during charging may be 0°C or higher, 10°C or lower, 20°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, or 60°C or higher, and may be 200°C or lower, 150°C or lower, 120°C or lower, 100°C or lower, or 80°C or lower.

[0078] Figure 3 is a schematic diagram showing one embodiment of a spare lithium secondary battery in the lithium secondary battery manufacturing method of the present disclosure, but is not limited to this case. Using Figures 1 and 3, a specific method for manufacturing the lithium secondary battery shown in Figure 1 from the spare lithium secondary battery shown in Figure 3 will be described, but is not limited to this case.

[0079] The spare lithium secondary battery 200 in Figure 3 is a laminate in which a negative electrode current collector layer 110, a first metal layer 220, a second metal layer 221, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are stacked in this order. By performing a charging operation on the spare lithium secondary battery 200 in Figure 3, the lithium secondary battery 100 in Figure 1 can be manufactured. That is, by performing a charging operation on the spare lithium secondary battery 200, the tin in the first metal layer 220 reacts with the lithium that has moved from the positive electrode active material layer 140 to form the first lithium-tin alloy layer 120 in Figure 1, and the magnesium in the second metal layer 221 reacts with the lithium that has moved from the positive electrode active material layer 140 to form the lithium-magnesium alloy layer 121 in Figure 1, thereby manufacturing the lithium secondary battery 100.

[0080] <Another embodiment of the manufacturing method of lithium secondary batteries> The lithium secondary battery of this disclosure may be manufactured by a method including the following steps: A spare lithium secondary battery is obtained by stacking a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, a third metal layer containing tin, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer in this order. By performing a charging operation on the above-mentioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the lithium-tin alloy layer, (ii) the magnesium in the second metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer, and (iii) the tin in the third metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the lithium-tin alloy layer.

[0081] <The third metallic layer> The third metal layer may contain tin and optionally other metal elements that are alloyed with lithium.

[0082] The thickness of the third metal layer is not particularly limited, but may be 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, 0.10 μm or more, or 0.50 μm or less, 0.40 μm or less, 0.30 μm or less, or 0.2 μm or less.

[0083] The third metal layer can be formed, for example, by depositing a tin layer on the electrolyte layer using a sputtering method, but is not limited to this case.

[0084] For the negative electrode current collector, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer, refer to the description in "Lithium Secondary Batteries." For the first metal layer and the second metal layer, refer to the description in "Method for Manufacturing Lithium Secondary Batteries."

[0085] A spare lithium secondary battery may have the following layers stacked in this order: a negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, a third metal layer containing tin, an electrolyte layer, a positive electrode active material layer holding lithium, and a positive electrode current collector layer.

[0086] A spare lithium secondary battery can be easily formed by, for example, laminating a negative electrode current collector, a first metal layer, a second metal layer, a third metal layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in the order described above, housing this laminate in a laminate film, vacuum sealing it, and pressing it.

[0087] For information on charging procedures, please refer to the description under "(Charging Procedure)".

[0088] Figure 4 is a schematic diagram showing one embodiment of a spare lithium secondary battery in the lithium secondary battery manufacturing method of the present disclosure, but is not limited to this case. Using Figures 2 and 4, a specific method for manufacturing the lithium secondary battery shown in Figure 2 from the spare lithium secondary battery shown in Figure 4 will be described, but is not limited to this case.

[0089] The spare lithium secondary battery 200 in Figure 4 is a laminate in which a negative electrode current collector layer 110, a first metal layer 220, a second metal layer 221, an electrolyte layer 130, a positive electrode active material layer 140, and a positive electrode current collector layer 150 are stacked in this order. By performing a charging operation on the spare lithium secondary battery 200 in Figure 4, the lithium secondary battery 100 in Figure 2 can be manufactured. In other words, by performing a charging operation on the spare lithium secondary battery 200, the tin in the first metal layer 220 is reacted with the lithium that has moved from the positive electrode active material layer 140 to form the first lithium-tin alloy layer 120 shown in Figure 2, the magnesium in the second metal layer 221 is reacted with the lithium that has moved from the positive electrode active material layer 140 to form the lithium-magnesium alloy layer 121 shown in Figure 2, and the tin in the third metal layer 222 is reacted with the lithium that has moved from the positive electrode active material layer 140 to form the second lithium-tin alloy layer 122 shown in Figure 2, thereby manufacturing the lithium secondary battery 100. [Examples]

[0090] The present disclosure will be further described with reference to the following embodiments, but the scope of the present disclosure is not limited to these embodiments.

[0091] Example 1 <Fabrication of a negative electrode current collector A1 comprising a first metal layer and a second metal layer> A tin layer was deposited on one side of a nickel foil, which was to be used as a negative electrode current collector, to a thickness of 0.1 μm by sputtering, thereby forming a first metal layer containing tin on the nickel foil. Next, a magnesium layer was deposited on the surface of the first metal layer on the nickel foil to a thickness of 0.2 μm by sputtering, thereby forming a second metal layer containing magnesium on the first metal layer, and a negative electrode current collector A1 was obtained. The negative electrode current collector A1 was a laminate having the negative electrode current collector layer, the first metal layer, and the second metal layer in this order.

[0092] <Fabrication of electrolyte layer B1> An electrolyte slurry was prepared by mixing a sulfide solid electrolyte (92.6 parts by mass) as the electrolyte, a binder (7.4 parts by mass), and an appropriate amount of butyl butyrate as a dispersion medium. The obtained electrolyte slurry was coated onto a release film with a coating gap of 325 μm, pre-dried at room temperature for 3 hours, and then fully dried at 165°C for 1 hour. Two φ14.50 mm coated films were punched out after the full drying, and the two films were stacked with their coated surfaces facing each other. They were then pressed at 7.0 tons to remove the release film and create a self-supporting electrolyte layer B1.

[0093] <Fabrication of the positive electrode active material layer C1> A positive electrode mixture slurry was prepared by mixing lithium nickel-cobalt-aluminate (NCA) (84.7 parts by mass) as the positive electrode active material, a sulfide solid electrolyte (13.4 parts by mass) as the solid electrolyte, a binder (0.6 parts by mass), a conductive additive (1.3 parts by mass), and an appropriate amount of butyl butyrate as a dispersion medium. Next, the obtained positive electrode mixture slurry was coated onto aluminum foil, which was to be used as the positive electrode current collector, with a coating gap of 225 μm. The mixture was pre-dried at 60°C and then fully dried at 165°C for 1 hour to produce a positive electrode current collector layer C1 formed on the aluminum foil. The design capacity of the positive electrode active material layer C1 is 3.0 mAh / cm². 2 The estimated amount is 18.7 mg / cm³. 2 That's what I decided.

[0094] <Fabrication of a spare lithium secondary battery D1> The negative electrode current collector A1 was punched out to a diameter of φ14.50 mm, and the positive electrode active material layer C1 was punched out to a diameter of φ11.28 mm. Next, the negative electrode current collector A1, electrolyte layer B1, and positive electrode active material layer C1 were laminated in the following order: negative electrode current collector layer, first metal layer, second metal layer, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer. This laminate was placed inside a laminate film, vacuum sealed, and cold isotropically pressed at 392 MPa to produce a spare lithium secondary battery D1. Aluminum was used for the positive electrode tab and nickel for the negative electrode tab.

[0095] <Fabrication of Lithium-ion secondary battery E1> To ensure a constant restraining pressure, the spare lithium secondary battery D1 was restrained at 1 MPa using a constant pressure jig with a spring inserted. Next, the spare lithium secondary battery D1 was placed in a constant temperature bath at 60°C, and a constant current (current density: 0.15 mA / cm²) was applied within the cutoff voltage range of 4.2 V to 3.0 V at 60°C. 2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2 One cycle of the test (equivalent to 0.01C) was performed. Here, by charging the spare lithium secondary battery D1 with a constant current-constant voltage test, the tin in the first metal layer reacted with the lithium that had moved from the positive electrode active material layer C1 to form the first lithium-tin alloy layer, and the magnesium in the second metal layer reacted with the lithium that had moved from the positive electrode active material layer C1 to form the lithium-magnesium alloy layer, thereby obtaining the lithium secondary battery E1.

[0096] <Electrochemical measurement of lithium secondary battery E1> Lithium secondary battery E1 is placed in a constant temperature bath at 25°C, and at 25°C, a constant current (current density: 0.15 mA / cm²) is maintained within a cutoff voltage range of 4.2V-3.0V. 2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2 A 20-cycle test (equivalent to 0.01C) was conducted. The lithium secondary battery E1 had an initial reversible capacity of 2.82 mAh / cm³ at 25°C. 2 The reversible capacity after 20 cycles at 25°C is 1.46 mAh / cm². 2 That was the case.

[0097] <Example 2> <Fabrication of electrolyte layer B2 with a third metal layer> An electrolyte slurry was prepared by mixing a sulfide solid electrolyte (92.6 parts by mass) as the electrolyte, a binder (7.4 parts by mass), and an appropriate amount of butyl butyrate as a dispersion medium. The obtained electrolyte slurry was coated onto a release film with a coating gap of 325 μm, pre-dried at room temperature for 3 hours, and then fully dried at 165°C for 1 hour. Two φ14.50 mm coated films were punched out after the full drying, and the two films were stacked with their coated surfaces facing each other. They were then pressed at 7.0 tons to peel off the release film and obtain a self-supporting electrolyte layer. Next, a tin layer of 0.1 μm was deposited on one side of the self-supporting electrolyte layer by sputtering, forming a third metal layer containing tin on the electrolyte layer, and thus creating electrolyte layer B2.

[0098] <Fabrication of a spare lithium secondary battery D2> Instead of electrolyte layer B1, electrolyte layer B2 was used, and the negative electrode current collector A1, electrolyte layer B2, and positive electrode active material layer C1 were stacked in the following order: negative electrode current collector layer, first metal layer, second metal layer, third metal layer, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer. A spare lithium secondary battery D2 was then fabricated in the same manner as in Example 1.

[0099] <Manufacturing of Lithium-ion secondary battery E2> To ensure a constant restraining pressure, the spare lithium secondary battery D2 was restrained at 1 MPa using a constant pressure jig with a spring inserted. Next, the spare lithium secondary battery D2 was placed in a constant temperature bath at 60°C, and a constant current (current density: 0.15 mA / cm²) was applied within a cutoff voltage range of 4.2 V to 3.0 V at 60°C. 2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2A test (equivalent to 0.01C) was performed for one cycle. During the constant current-constant voltage test, the tin in the first metal layer was reacted with the lithium that had moved from the positive electrode active material layer C1 to form the first lithium-tin alloy layer, the magnesium in the second metal layer was reacted with the lithium that had moved from the positive electrode active material layer C1 to form the lithium-magnesium alloy layer, and the tin in the third metal layer was reacted with the lithium that had moved from the positive electrode active material layer C1 to form the second lithium-tin alloy layer, thereby obtaining the lithium secondary battery E2.

[0100] <SEM-EDX measurement of lithium secondary battery E2> The cross-section of lithium secondary battery E2 after initial charging at 60°C was observed using a scanning electron microscope (SEM) to obtain secondary electron images at an applied voltage of 5kV, and elemental mapping was performed using energy-dispersive X-ray spectroscopy (EDX). Figure 5 shows the results of the EDX mapping analysis of lithium secondary battery E2, and Figure 6 shows the cross-sectional SEM image and a schematic diagram of the cross-sectional structure of lithium secondary battery E2. From the SEM-EDX observation, it was confirmed that after initial charging, lithium secondary battery E2 has the following layers stacked in this order: negative electrode current collector layer 110, first lithium-tin alloy layer 120, lithium-magnesium alloy layer 121, second lithium-tin alloy layer 122, and electrolyte layer 130.

[0101] <Electrochemical measurement of lithium secondary battery E2> The electrochemical measurements of lithium secondary battery E2 were performed using the same method as in Example 1. The initial reversible capacity of lithium secondary battery E2 at 25°C and the reversible capacity after 20 cycles at 25°C are shown in Table 1.

[0102] Comparative Example 1 <Fabrication of negative electrode current collector A2 with a second metal layer> A magnesium layer of 0.2 μm was deposited on one side of a nickel foil, which served as the negative electrode current collector, by sputtering, thereby forming a second metal layer containing magnesium on the nickel foil, and a negative electrode current collector A2 was obtained. The negative electrode current collector A2 was a laminate having the negative electrode current collector layer and the second metal layer in that order.

[0103] <Fabrication of a spare lithium secondary battery d1> Instead of negative electrode current collector A1, negative electrode current collector A2 was used, and the negative electrode current collector A2, electrolyte layer B1, and positive electrode active material layer C1 were stacked in the following order: negative electrode current collector layer, second metal layer, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer. A spare lithium secondary battery d1 was then fabricated in the same manner as in Example 1.

[0104] <Fabrication of lithium secondary battery e1 and electrochemical measurement> Lithium secondary battery e1 was fabricated in the same manner as in Example 1, except that a spare lithium secondary battery d1 was used instead of spare lithium secondary battery D1. The electrochemical measurements of lithium secondary battery e1 were performed in the same manner as in Example 1. The initial reversible capacity of lithium secondary battery e1 at 25°C and the reversible capacity after 20 cycles at 25°C are shown in Table 1.

[0105] Comparative Example 2 <Fabrication of spare lithium secondary battery d2> A spare lithium secondary battery d2 was fabricated in the same manner as in Example 1, by using a negative electrode current collector A2 instead of negative electrode current collector A1, and an electrolyte layer B2 instead of electrolyte layer B1, and stacking the negative electrode current collector layer, second metal layer, third metal layer, electrolyte layer, positive electrode active material layer, and positive electrode current collector layer in this order.

[0106] <Fabrication of lithium secondary battery e2 and electrochemical measurement> Lithium secondary battery e2 was fabricated in the same manner as in Example 1, except that a spare lithium secondary battery d2 was used instead of spare lithium secondary battery D1. Electrochemical measurements of lithium secondary battery e2 were performed in the same manner as in Example 1. The initial reversible capacity of lithium secondary battery e2 at 25°C and the reversible capacity after 20 cycles at 25°C are shown in Table 1.

[0107] Table 1 shows the evaluation results of the electrochemical measurements for Examples 1 and 2 and Comparative Examples 1 and 2.

[0108] [Table 1]

[0109] Lithium secondary batteries E1 and E2, which had the first lithium-tin alloy layer, showed higher initial reversible capacity at 25°C compared to lithium secondary batteries e1 and e2, which did not have the first lithium-tin alloy layer. This is presumed to be because the placement of the first lithium-tin alloy layer between the negative electrode current collector layer and the lithium-magnesium alloy layer suppressed delamination at the interface between the negative electrode current collector layer and the lithium-magnesium alloy layer during discharge, thereby increasing reversible capacity and cycle characteristics.

[0110] Furthermore, the following is considered to be the reason why the first lithium-tin alloy layer was able to suppress delamination at the interface between the negative electrode current collector layer and the lithium-magnesium alloy layer. During discharge, the lithium in the lithium-magnesium alloy layer undergoes dealloying more preferentially than the lithium in the first lithium-tin alloy layer in terms of reaction potential, and as a result the lithium-magnesium alloy layer shrinks significantly. On the other hand, the lithium-tin alloy layer shrinks less than the lithium-magnesium alloy layer, so it is presumed that the lithium-tin alloy layer mitigated the shrinkage of the lithium-magnesium alloy layer, thereby suppressing the delamination at the interface.

[0111] Furthermore, the lithium secondary battery E2, which incorporates a second lithium-tin layer, maintains a reversible capacity of 2.77 mAh / cm² even after 20 cycles. 2 The battery maintained a high capacity. This is presumed to be because the placement of a second lithium-tin layer between the lithium-magnesium layer and the electrolyte layer suppressed delamination at the interface between the lithium-magnesium layer and the electrolyte layer during discharge, thereby improving the cycle characteristics. It is also presumed that the suppression of interfacial delamination by the second lithium-tin alloy layer is due to the same factors as the suppression of interfacial delamination by the first lithium-tin alloy layer.

[0112] While preferred embodiments of the lithium secondary battery of this disclosure have been described, those skilled in the art will understand that modifications are possible without departing from the claims. [Explanation of symbols]

[0113] 100 Lithium-ion rechargeable batteries 110 Negative electrode current collector layer 120 First lithium-tin alloy layer 121 Lithium-magnesium alloy layer 122 Second lithium-tin alloy layer 130 Electrolyte layer 140 Cathode active material layer 150 Positive electrode current collector layer 200 spare lithium-ion batteries 220 First metal layer 221 Second metal layer 222 Third Metal Layer

Claims

1. A lithium secondary battery comprising a negative electrode current collector layer, a first lithium-tin alloy layer, a lithium-magnesium alloy layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

2. The lithium secondary battery according to claim 1, wherein the thickness of the first lithium-tin alloy layer is 0.1 to 15 μm when fully charged.

3. The lithium secondary battery according to claim 1, wherein the thickness of the lithium-magnesium alloy layer is 0.1 to 40 μm when fully charged.

4. A lithium secondary battery according to claim 1, comprising the negative electrode current collector layer, the first lithium-tin alloy layer, the lithium-magnesium alloy layer, the second lithium-tin alloy layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector layer in this order.

5. When fully charged, The thickness of the first lithium-tin alloy layer is 0.1 to 15 μm, and The lithium secondary battery according to claim 4, wherein the thickness of the second lithium-tin alloy layer is 0.1 to 15 μm.

6. A method for manufacturing a lithium secondary battery according to any one of claims 1 to 5, comprising the following steps: To obtain a spare lithium secondary battery, the negative electrode current collector layer, the first metal layer containing tin, the second metal layer containing magnesium, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer are stacked in this order. By performing a charging operation on the aforementioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-tin alloy layer, and (ii) the magnesium in the second metal layer is reacted with the lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer.

7. A method for manufacturing a lithium secondary battery according to claim 4 or 5, comprising the following steps: To obtain a spare lithium secondary battery, the negative electrode current collector layer, a first metal layer containing tin, a second metal layer containing magnesium, a third metal layer containing tin, the electrolyte layer, the positive electrode active material layer holding lithium, and the positive electrode current collector layer are stacked in this order. By performing a charging operation on the aforementioned spare lithium secondary battery, (i) the tin in the first metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the first lithium-tin alloy layer, (ii) the magnesium in the second metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the lithium-magnesium alloy layer, and (iii) the tin in the third metal layer is reacted with lithium that has moved from the positive electrode active material layer to form the second lithium-tin alloy layer.

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