Lithium ion secondary battery

Abstract

The present invention provides a lithium ion secondary battery capable of suppressing a decrease in charge capacity. A lithium ion secondary battery using a precipitation / dissolution reaction of metallic lithium, the lithium ion secondary battery comprising a positive electrode layer, a negative electrode layer, and an electrolyte layer positioned between the positive electrode layer and the negative electrode layer, the positive electrode layer containing a positive electrode active material capable of absorbing and releasing lithium ions, the negative electrode layer containing a negative electrode active material capable of absorbing and releasing lithium ions, and the electrolyte layer containing a positive electrode active material capable of absorbing and releasing lithium ions. The negative electrode layer contains Mg element, In element, Sn element, and Li element.

Description

Technical Field

[0001] The present invention relates to a lithium ion secondary battery. Background Art

[0002] Regarding the lithium ion secondary battery disclosed in Patent Document 1 including a metal layer in the negative electrode, various techniques have been proposed.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-068706

[0006] Patent Document 2: Japanese Patent Application Publication No. 2020-191202 Summary of the invention

[0007] Problems to be solved by the invention

[0008] Conventionally, at the end of discharge of a lithium ion secondary battery, the resistance of the negative electrode layer increases, and therefore, the reversible capacity of the lithium ion secondary battery decreases with repeated charge and discharge.

[0009] The present invention has been made in view of the above-mentioned actual situation, and a main object of the present invention is to provide a lithium ion secondary battery capable of suppressing a decrease in charging capacity.

[0010] Methods used to solve problems

[0011] That is, the present invention includes the following aspects.

[0012] <1> A lithium ion secondary battery is a lithium ion secondary battery that utilizes the precipitation-dissolution reaction of metallic lithium, wherein:

[0013] The lithium-ion secondary battery comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0014] The positive electrode layer contains a positive electrode active material capable of absorbing and releasing lithium ions.

[0015] The negative electrode layer contains Mg element, In element, Sn element and Li element.

[0016] <2> according to <1> In the lithium-ion secondary battery, a molar ratio of Sn element to In element (Sn / In) contained in the negative electrode layer is greater than or equal to 0.5 and less than or equal to 3.8.

[0017] <3> according to <1> or <2> In the lithium-ion secondary battery, the negative electrode layer includes, in order from the electrolyte layer side, a Li-In-Sn alloy layer containing a Li-In-Sn alloy and a Li-Mg alloy layer containing a Li-Mg alloy.

[0018] <4> according to <1> ~ <3> The lithium ion secondary battery according to any one of the preceding claims, wherein

[0019] The lithium ion secondary battery has a negative electrode current collector on the negative electrode layer on the side opposite to the electrolyte layer.

[0020] When the negative electrode layer is divided into two equal parts parallel to the stacking surface of the negative electrode layer, and the area on the negative electrode collector side is set as the first area, and the area on the electrolyte layer side is set as the second area, the content of the In element and the Sn element in the second area of ​​the negative electrode layer is greater than the content of the In element and the Sn element in the first area.

[0021] <5> according to <1> ~ <4> The lithium ion secondary battery described in any one of the above aspects, wherein the electrolyte layer is a solid electrolyte layer containing a sulfide-based solid electrolyte.

[0022] <6> A lithium ion secondary battery is a lithium ion secondary battery that utilizes the precipitation-dissolution reaction of metallic lithium, wherein:

[0023] The lithium-ion secondary battery comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0024] The positive electrode layer contains a positive electrode active material capable of absorbing and releasing lithium ions.

[0025] The negative electrode layer includes, in order from the electrolyte layer side, an In—Sn alloy layer containing an In—Sn alloy and a metal Mg layer containing a single substance of Mg.

[0026] Effects of the Invention

[0027] The lithium ion secondary battery of the present invention can suppress a decrease in charging capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic cross-sectional view showing an example of a lithium ion secondary battery before initial charge during production of the present invention.

[0029] Figure 2 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery of the present invention when fully charged after initial charge.

[0030] Figure 3This is a graph showing the relationship between the Sn composition in the In—Sn alloy and the resistance of the laminated battery after the initial charge and discharge.

[0031] Figure 4 This is a graph showing the relationship between the current density at 25° C. and the charge capacity of each laminated battery after the initial charge and discharge of Examples 1 to 3 and Comparative Examples 1 and 7 to 8.

[0032] Figure 5 This is a graph showing the relationship between the Sn composition in the In—Sn alloy and the 25° C. charge capacity at a 2C rate of a laminated battery after the initial charge and discharge.

[0033] Figure 6 These are the SEM-EDX mappings of the solid electrolyte layer-negative electrode cross section after the initial charge of Example 2: (1) secondary electron image, (2) S element mapping, (3) In element mapping, (4) Sn element mapping, (5) O element mapping, (6) Mg element mapping, and (7) Ni element mapping.

[0034] Figure 7 The SEM-EDX mapping of the solid electrolyte layer-negative electrode cross section after the first discharge of Example 2 includes: (1) secondary electron image, (2) S element mapping, (3) In element mapping, (4) Sn element mapping, (5) O element mapping, (6) Mg element mapping, and (7) Ni element mapping. DETAILED DESCRIPTION

[0035] The following is a description of the embodiments of the present invention. It should be noted that matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention (for example, the general structure and manufacturing process of lithium-ion secondary batteries that do not characterize the present invention) can be understood as design matters for those skilled in the art based on the prior art in this field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in this field.

[0036] In the present invention, a lithium-ion secondary battery is provided, which is a lithium-ion secondary battery that utilizes the precipitation-dissolution reaction of metallic lithium, wherein the lithium-ion secondary battery comprises a positive electrode layer, a negative electrode layer and an electrolyte layer located between the positive electrode layer and the negative electrode layer, the positive electrode layer contains a positive electrode active material that can absorb and release lithium ions, and the negative electrode layer contains Mg element, In element, Sn element and Li element.

[0037] In the present invention, it is possible to suppress an increase in the resistance of the negative electrode layer at the end of discharge, and to suppress a decrease in the charge and discharge efficiency.

[0038] In the present invention, when Li is inserted into the negative electrode layer, a Li-In-Sn layer is formed between the electrolyte layer and the Li-Mg layer, thereby suppressing the negative electrode layer from peeling off from the electrolyte layer. Compared with the case where there is no Li-Mg layer or the case where a Li-In layer or a Li-Sn layer is used between the electrolyte layer and the Li-Mg layer, the reversible capacity of the lithium-ion secondary battery is increased and the charge and discharge efficiency is improved.

[0039] When In and Sn are mixed, the melting point becomes lower than when Sn is a single substance, the adhesion between the electrolyte layer and the negative electrode layer becomes higher, and the reduction in charge and discharge efficiency can be suppressed.

[0040] The lithium ion secondary battery of the present invention utilizes the precipitation-dissolution reaction of metallic lithium.

[0041] The lithium ion secondary battery includes a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0042] In the present invention, the negative electrode refers to an electrode including a negative electrode layer.

[0043] In the present invention, the fully charged state of a lithium ion secondary battery refers to a state where the state of charge (SOC) of the lithium ion secondary battery is 100%. SOC represents the ratio of the charge capacity of a battery to the full charge capacity, and the full charge capacity is SOC 100%.

[0044] The SOC can be estimated from, for example, the open circuit voltage (OCV: Open Circuit Voltage) of the lithium ion secondary battery.

[0045] [negative electrode]

[0046] The negative electrode includes a negative electrode layer and optionally includes a negative electrode current collector.

[0047] [Negative electrode current collector]

[0048] The material of the negative electrode collector may be a material that is not alloyed with Li, for example, SUS, copper, and nickel. As the form of the negative electrode collector, for example, foil and plate can be listed. The top view shape of the negative electrode collector is not particularly limited, for example, a circle, an ellipse, a rectangle, and any polygon can be listed. In addition, the thickness of the negative electrode collector varies depending on the shape, for example, it can be in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0049] [Negative electrode layer]

[0050] The negative electrode layer contains Mg element, In element, Sn element, and Li element.

[0051] The negative electrode layer may include, in order from the electrolyte layer side, an In—Sn alloy layer containing an In—Sn alloy and a metal Mg layer containing a single substance of Mg before the initial charge of the lithium ion secondary battery.

[0052] The negative electrode layer may include a Li—In—Sn alloy layer containing a Li—In—Sn alloy and a Li—Mg alloy layer containing a Li—Mg alloy in this order from the electrolyte layer side after the initial charge of the lithium ion secondary battery.

[0053] The molar ratio of the total of the In element and the Sn element contained in the negative electrode layer to the Mg element {(In+Sn) / Mg} may be 0.01 or more, or 0.0872 or more. If it is less than 0.01, the In element and the Sn element contained in the negative electrode layer are too little, and the charge capacity is reduced.

[0054] The molar ratio of the Sn element to the In element (Sn / In) contained in the negative electrode layer may be 0.5 or more and 3.8 or less.

[0055] When the negative electrode layer is divided into two equal parts parallel to the stacking surface of the negative electrode layer, and the area on the negative electrode collector side is set as the first area, and the area on the electrolyte layer side is set as the second area, the content of the above-mentioned In element and the above-mentioned Sn element in the second area of ​​the negative electrode layer can be greater than the content of the In element and the Sn element in the first area. Parallel can be approximately parallel. Approximately parallel can be in the range of 0° to 10°. The stacking direction of the negative electrode layer is the thickness direction of the negative electrode layer.

[0056] Regarding the comparison of the contents of the above two regions in the negative electrode layer, for example, SEM-EDX can be used to map the elements from the electrolyte layer to the negative electrode collector as the observation field and compare the contents of the target elements in each region. The comparison of the contents of the above two regions in the negative electrode layer can be implemented for lithium-ion secondary batteries in the state of after the initial charge, when fully charged, etc. The comparison of the contents is not limited to this, and XPS and TOF-SIMS can also be used in addition to SEM-EDX.

[0057] Before the first charge during the manufacture of a lithium-ion secondary battery, the Sn composition ratio in the In-Sn alloy layer can be greater than 0 mol% and less than 100 mol%, the lower limit can be greater than 20 mol%, and the upper limit can be less than 80 mol%, less than 70 mol%, or less than 60 mol%.

[0058] After the initial charge of the lithium-ion secondary battery, the thickness of the Li-In-Sn layer can be greater than 0 μm and less than 100 μm, the lower limit can be greater than 0.01 μm or greater than 0.1 μm, and the upper limit can be less than 15 μm, less than 0.6 μm, or less than 0.35 μm.

[0059] After the initial charge of the lithium ion secondary battery, the Li composition ratio in the Li—Mg alloy layer may be greater than 0 mol % and less than 100 mol %, the lower limit may be greater than 20 mol %, and the upper limit may be less than 98 mol %.

[0060] After the initial charge of the lithium ion secondary battery, the thickness of the Li—Mg alloy layer may be greater than 0 μm and 100 μm or less, the lower limit may be 0.1 μm or more, and the upper limit may be 40 μm or less.

[0061] The metal Mg layer can be formed on the negative electrode current collector, for example. The film forming method can include a method of placing Mg particles and pressing, a vapor deposition method, a sputtering method, a PVD method, and an electroplating method. Among them, it can be a vapor deposition method or a sputtering method. The adhesion between the metal Mg layer and the negative electrode current collector is improved, and the increase in the resistance of the negative electrode can be suppressed.

[0062] Regarding the In-Sn alloy layer, the In-Sn alloy layer can also be formed on the solid electrolyte layer side or the negative electrode collector side by the same method as described above. Among them, the film can be formed on the negative electrode collector side. By forming the film on the negative electrode collector side, the adhesion between the In-Sn alloy layer and the metal Mg layer becomes good.

[0063] The thickness of the negative electrode layer is not particularly limited, but may be 30 nm to 50 μm at the time of full charge after the initial charge of the lithium ion secondary battery.

[0064] [Electrolyte layer]

[0065] The electrolyte layer may be a liquid electrolyte layer using an electrolytic solution as an electrolyte, or may be a solid electrolyte layer using a solid electrolyte as an electrolyte.

[0066] As the electrolyte solution, a conventionally known electrolyte solution used in lithium ion secondary batteries can be used.

[0067] The solid electrolyte layer contains at least a solid electrolyte.

[0068] As the solid electrolyte contained in the solid electrolyte layer, a known solid electrolyte that can be used in a solid-state battery can be appropriately used, and examples thereof include oxide-based solid electrolytes and sulfide-based solid electrolytes, etc. In order to suppress the peeling of the negative electrode layer from the solid electrolyte layer, a relatively soft sulfide-based solid electrolyte can be used as the solid electrolyte.

[0069] Examples of sulfide-based solid electrolytes include solid electrolytes containing Li element, M element (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In) and S element. In addition, the sulfide-based solid electrolyte may further contain at least one of O element and halogen element.

[0070] As sulfide-based solid electrolytes, for example, Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4 can be cited. It should be noted that the above-mentioned "Li2S-P2S5" refers to a material formed using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0071] In addition, "X" of the above-mentioned LiX represents a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element. The raw material composition containing the above-mentioned LiX may contain one or more LiX. When containing two or more LiX, the mixing ratio of the two or more LiX is not particularly limited.

[0072] The molar ratio of each element in the sulfide-based solid electrolyte can be controlled by adjusting the content of each element in the raw material. In addition, the molar ratio and composition of each element in the sulfide-based solid electrolyte can be measured by, for example, ICP emission spectrometry.

[0073] The sulfide-based solid electrolyte may be sulfide glass, crystallized sulfide glass (glass ceramic), or a crystalline material obtained by subjecting a raw material composition to a solid phase reaction treatment.

[0074] The crystal state of the sulfide-based solid electrolyte can be confirmed by, for example, performing powder X-ray diffraction measurement of the sulfide-based solid electrolyte using CuKα rays.

[0075] Sulfide glass can be obtained by subjecting a raw material composition (for example, a mixture of Li2S and P2S5) to an amorphization treatment. Examples of the amorphization treatment include mechanical grinding.

[0076] Glass ceramics can be obtained, for example, by heat treating sulfide glass.

[0077] The heat treatment temperature may be higher than the crystallization temperature (Tc) of the sulfide glass observed by thermal analysis, and is usually 195° C. or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited.

[0078] The crystallization temperature (Tc) of sulfide glass can be measured by differential thermal analysis (DTA).

[0079] The heat treatment time is not particularly limited as long as it is a time that can obtain the desired crystallinity of the glass ceramics, and is, for example, in the range of 1 minute to 24 hours, and particularly, in the range of 1 minute to 10 hours.

[0080] The method of heat treatment is not particularly limited, and an example thereof includes a method using a sintering furnace.

[0081] As oxide-based solid electrolytes, for example, substances having a garnet-type crystal structure containing Li element, La element, A element (A is at least one of Zr, Nb, Ta and Al) and O element can be listed. As oxide-based solid electrolytes, for example, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 、Li7La3Zr2O 12 、Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4 and Li 3+x PO 4-x N x (1≤x≤3) etc.

[0082] From the viewpoint of good handling properties, the solid electrolyte may be in the form of particles.

[0083] The average particle size (D50) of the solid electrolyte particles is not particularly limited, but the lower limit may be 0.5 μm or more and the upper limit may be 2 μm or less.

[0084] In the present invention, the average particle size of the particles is the value of the median diameter (D50) measured by the laser diffraction scattering particle size distribution measurement unless otherwise specified. In addition, in the present invention, the median diameter (D50) refers to the diameter (volume average diameter) at which the cumulative volume of the particles reaches half (50%) of the total volume when the particles are arranged in order from the particles with the smallest particle size.

[0085] The solid electrolyte may be used alone or in combination of two or more. In the case of using two or more solid electrolytes, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure.

[0086] The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, and may be, for example, 50% by mass or more, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, or 100% by mass.

[0087] From the viewpoint of showing plasticity, the solid electrolyte layer may also contain a binder. As such a binder, the material exemplified as the binder used in the positive electrode layer described later can be exemplified. However, in order to easily achieve high output, from the viewpoints of preventing excessive aggregation of the solid electrolyte and being able to form a solid electrolyte layer with a uniformly dispersed solid electrolyte, the binder contained in the solid electrolyte layer may be less than 5% by mass.

[0088] The thickness of the solid electrolyte layer is not particularly limited, but is usually 0.1 μm or more and 1 mm or less.

[0089] [positive electrode]

[0090] The positive electrode includes a positive electrode layer and optionally includes a positive electrode current collector.

[0091] [Positive electrode layer]

[0092] The positive electrode layer contains a positive electrode active material capable of absorbing and releasing lithium ions, and may contain a solid electrolyte, a conductive material, a binder, and the like as optional components.

[0093] The positive electrode active material may contain the Li element before the initial charge of the lithium ion secondary battery. Examples of the positive electrode active material include lithium nickel cobalt aluminum oxide (NCA), LiCoO2, LiNi x Co 1-x O2(0 <x<1)、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, LiMn2O4, LiNiO2, LiVO2, different types of element substitution Li-Mn spinel, lithium titanate, lithium metal phosphate, LiCoN, Li2SiO3 and Li4SiO4, etc. Different types of element substitution Li-Mn spinel, such as LiMn 1.5 Ni 0.5 O4、LiMn 1.5 Al 0.5 O4、LiMn 1.5 Mg 0.5 O4、LiMn 1.5 Co 0.5 O4、LiMn 1.5 Fe 0.5 O4 and LiMn 1.5 Zn 0.5O4, etc. Lithium titanate is, for example, Li4Ti5O 12 Etc. Examples of lithium metal phosphates include LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4.

[0094] The shape of the positive electrode active material is not particularly limited, and may be in the form of particles (positive electrode active material particles).

[0095] A coating layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material because the reaction between the positive electrode active material and the solid electrolyte can be suppressed.

[0096] Examples of Li ion conductive oxides include LiNbO3, Li4Ti5O 12 and Li3PO4, etc. The thickness of the coating is, for example, 0.1 nm or more, or 1 nm or more. On the other hand, the thickness of the coating is, for example, 100 nm or less, or 20 nm or less. The coverage of the coating on the surface of the positive electrode active material is, for example, 70% or more, or 90% or more.

[0097] Examples of the solid electrolyte include those that can be contained in the above-mentioned solid electrolyte layer.

[0098] The content of the solid electrolyte in the positive electrode layer is not particularly limited, and can be, for example, within a range of 1% by mass to 80% by mass when the total mass of the positive electrode layer is 100% by mass.

[0099] As the conductive material, known conductive materials can be used, for example, carbon materials and metal particles can be listed. As the carbon material, for example, acetylene black (AB), furnace black, VGCF, carbon nanotubes and carbon nanofibers can be listed. Among them, from the viewpoint of electronic conductivity, it can be at least one selected from the group consisting of VGCF, carbon nanotubes and carbon nanofibers. As metal particles, particles such as Ni, Cu, Fe and SUS can be listed.

[0100] The content of the conductive material in the positive electrode layer is not particularly limited.

[0101] Examples of the binder include acrylonitrile butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), etc. The content of the binder in the positive electrode layer is not particularly limited.

[0102] The thickness of the positive electrode layer is not particularly limited.

[0103] The positive electrode layer can be formed by a conventionally known method.

[0104] For example, a positive electrode active material and other components as needed are added to a solvent and stirred to prepare a positive electrode layer slurry, which is then applied onto one side of a support such as a positive electrode current collector and dried to obtain a positive electrode layer.

[0105] Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone.

[0106] The method for coating the positive electrode layer slurry on one side of a support such as a positive electrode current collector is not particularly limited, and examples thereof include doctor blade method, metal mask printing method, electrostatic coating method, dip coating method, spraying method, roll coating method, gravure coating method and screen printing method.

[0107] As the support, any self-supporting support may be appropriately selected and used without particular limitation, and for example, metal foil of Cu, Al, or the like may be used.

[0108] [Positive electrode collector]

[0109] As the positive electrode current collector, a known metal that can be used as a current collector of a lithium ion secondary battery can be used. As such a metal, a metal material containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge and In can be exemplified. As the positive electrode current collector, for example, SUS, aluminum, nickel, iron, titanium and carbon can be listed.

[0110] The form of the positive electrode current collector is not particularly limited, and it can be in various forms such as a foil form and a mesh form.

[0111] The lithium-ion secondary battery may include an outer casing that houses a positive electrode layer, a negative electrode layer, an electrolyte layer, and the like, as necessary.

[0112] The material of the outer casing is not particularly limited as long as it is a material stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resins.

[0113] Examples of the shape of the lithium ion secondary battery include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

[0114] The lithium ion secondary battery can be a liquid lithium ion secondary battery using an electrolyte as an electrolyte, or a solid lithium ion secondary battery using a solid electrolyte as an electrolyte. As the purpose of the lithium ion secondary battery, for example, the power supply of vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (BEV), gasoline vehicles, and diesel vehicles can be listed. Among them, it can be used for the driving power supply of hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) or electric vehicles (BEV). In addition, the lithium ion secondary battery can be used as a power supply for mobile bodies (such as trains, ships, and airplanes) other than vehicles, and can also be used as a power supply for electrical products such as information processing devices.

[0115] Figure 1 This is a schematic cross-sectional view showing an example of a lithium ion secondary battery before initial charge during production of the present invention.

[0116] like Figure 1 As shown, the lithium ion secondary battery 100 before the initial charge includes a positive electrode collector 10, a positive electrode layer 20, an electrolyte layer 30, an In-Sn alloy layer 40, a metal Mg layer 50, and a negative electrode collector 60 in this order. The negative electrode layer includes the In-Sn alloy layer 40 and the metal Mg layer 50.

[0117] Figure 2 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery of the present invention when fully charged after initial charge.

[0118] like Figure 2 As shown, the lithium ion secondary battery 200 after the initial charge sequentially comprises a positive electrode collector 10, a positive electrode layer 20, an electrolyte layer 30, a Li-In-Sn alloy layer 41, a Li-Mg alloy layer 51, and a negative electrode collector 60. By the initial charge, the In-Sn alloy layer 40 is changed into a Li-In-Sn alloy layer 41, and the metal Mg layer 50 is changed into a Li-Mg alloy layer 51. The negative electrode layer includes the Li-In-Sn alloy layer 41 and the Li-Mg alloy layer 51.

[0119] Example

[0120] (Examples 1 to 3)

[0121] [Positive electrode production]

[0122] Butyl butyrate was used as a solvent. NCA was used as a positive electrode active material. Particles of a sulfide-based solid electrolyte (average particle size: 2.0 μm) were used as a solid electrolyte. Al foil was used as a positive electrode collector. The positive electrode active material, solid electrolyte, binder, and conductive additive were mixed in a solvent according to the following mass composition ratio to prepare a positive electrode slurry.

[0123] Mass composition ratio positive electrode active material: solid electrolyte: binder: conductive additive = 84.7: 13.4: 0.6: 1.27

[0124] The prepared positive electrode slurry was coated on Al foil with a coating gap of 225 μm. Then, the coated positive electrode slurry was pre-dried at 60°C for 3 hours. Then, the pre-dried positive electrode slurry was mainly dried at 165°C for 1 hour. Thus, the unit area weight of 18.7 mg / cm 2 、Design capacity is 3.0mAh / cm 2 The obtained positive electrode composite material coated foil was punched out to obtain a positive electrode with a diameter of 11.28 mm.

[0125] [Solid electrolyte layer production]

[0126] Butyl butyrate was used as a solvent. Sulfide-based solid electrolyte particles (average particle size: 2.0 μm) were used as solid electrolytes. Solid electrolytes and binders were mixed in a solvent at the following mass composition ratio to prepare solid electrolyte slurry.

[0127] Mass composition ratio solid electrolyte: binder = 92.6:7.4

[0128] The prepared solid electrolyte slurry was coated on the release film with a coating gap of 325 μm. Then, the coated solid electrolyte slurry was pre-dried at room temperature for 3 hours. Then, the pre-dried solid electrolyte slurry was mainly dried at 165°C for 1 hour. The dried solid electrolyte coated foil was punched out to obtain two discs with a diameter of 14.5 mm. The solid electrolyte coated surfaces of the two discs were overlapped and pressed at 7t. After pressing, the release films of the two discs were peeled off to obtain independent solid electrolyte layers.

[0129] [Negative electrode production]

[0130] Ni foil is used as the negative electrode collector. A metal Mg layer with a thickness of 1.0 μm is formed by vapor deposition on one side of the negative electrode collector to obtain a metal Mg layer / Ni foil. An In-Sn alloy layer with a thickness of 0.1 μm is formed by binary vapor deposition on the metal Mg layer of the metal Mg layer / Ni foil by ion plating to produce an In-Sn alloy layer / metal Mg layer / Ni foil. The obtained In-Sn alloy layer / metal Mg layer / Ni foil is punched out to obtain a negative electrode with a diameter of 14.5 mm. Regarding the target composition (mol%) of the In-Sn alloy, Example 1 is 67:33, Example 2 is 50:50, and Example 3 is 20:80. Regarding the actual composition (mol%) of the In-Sn alloy, Example 1 is 66:34, Example 2 is 53:47, and Example 3 is 21:79.

[0131] [Battery production]

[0132] Al was used as the positive electrode tab and Ni was used as the negative electrode tab.

[0133] The solid electrolyte layer is arranged between the positive electrode and the negative electrode to obtain a laminate. The positive electrode tab is installed on the positive electrode, and the negative electrode tab is installed on the negative electrode. Then, the laminate is contained in a laminate film, and the laminate is sealed after the laminate film is vacuumed. The sealed laminate is isostatically pressed at 392MPa using CIP (cold isostatic pressing) to make a laminated battery (sometimes referred to as a battery). In a manner that the constraint pressure is constant regardless of how the volume of the laminated battery changes, a constant pressure fixture with a spring inserted is used to constrain the laminated battery produced at 1MPa.

[0134] (Comparative Example 1)

[0135] In Comparative Example 1, a laminated battery was produced in the same manner as in Example 1 except that the metal Mg layer / Ni foil was used as the negative electrode.

[0136] (Comparative Example 2)

[0137] In Comparative Example 2, a laminated battery was produced in the same manner as in Example 1 except that a metal In layer with a thickness of 0.1 μm was formed on the negative electrode collector by vapor deposition without using a metal Mg layer and the metal In layer / Ni foil was used as the negative electrode.

[0138] (Comparative Example 3)

[0139] In Comparative Example 3, a laminated battery was produced in the same manner as in Example 1 except that a metal Sn layer with a thickness of 0.1 μm was formed on the negative electrode collector by vapor deposition without using a metal Mg layer and the metal Sn layer / Ni foil was used as the negative electrode.

[0140] (Comparative Examples 4 to 6)

[0141] In Comparative Examples 4 to 6, a 0.1 μm thick In-Sn alloy layer was formed on the prepared solid electrolyte layer by binary evaporation by ion plating without using a metal Mg layer, and the In-Sn alloy layer / Ni foil was used as the negative electrode. Laminated cells were prepared in the same manner as in Example 1. The actual composition (mol%) of the In-Sn alloy was 62:38 for Comparative Example 4, 49:51 for Comparative Example 5, and 38:62 for Comparative Example 6.

[0142] (Comparative Example 7)

[0143] In Comparative Example 7, a laminated battery was produced in the same manner as in Example 1 except that a 0.1 μm thick In layer was formed by sputtering on the produced solid electrolyte layer and metal In layer / metal Mg layer / Ni foil was used as the negative electrode.

[0144] (Comparative Example 8)

[0145] In Comparative Example 8, a laminated battery was produced in the same manner as in Example 1 except that a 0.1 μm-thick Sn layer was formed by sputtering on the produced solid electrolyte layer and the metal Sn layer / metal Mg layer / Ni foil was used as the negative electrode.

[0146] [In-Sn / Mg molar ratio]

[0147] The molar ratio {(In+Sn) / Mg} of the total of the In element and the Sn element contained in the negative electrode layer to the Mg element was calculated for the negative electrode layers of Examples 1 to 3 and Comparative Examples 7 to 8. The results are shown in Table 1.

[0148] [First charge and discharge]

[0149] The initial charge and discharge of each laminated battery produced in Examples 1 to 3 and Comparative Examples 1 to 8 was performed at 60° C. under the following conditions.

[0150] At a current density of 0.15 mA / cm 2 The battery was charged at a constant current of 4.2 V at a rate of 0.05 C, and then charged at a constant voltage to a current density of 0.03 mA / cm 2 , 0.01C rate.

[0151] At a current density of 0.15 mA / cm 2 The battery was discharged at a constant current of 3.0 V at a rate of 0.05 C, and then discharged at a constant voltage of 0.03 mA / cm 2 , 0.01C rate.

[0152] [Resistance after initial charge and discharge]

[0153] The resistance (Ω·cm) of each laminated battery after the first charge and discharge of Examples 1 to 3 and Comparative Examples 1 and 7 to 8 was measured by the AC impedance method when a predetermined current was passed at a predetermined voltage for 1 second. 2 ). The results are shown in Table 1.

[0154] Figure 3 This is a graph showing the relationship between the Sn composition in the In—Sn alloy and the resistance of the laminated battery after the initial charge and discharge.

[0155] The resistance of each laminated battery of Examples 1 to 3 after the initial charge and discharge decreases in the order of Example 3, Example 2, and Example 1, and the resistance of the battery at the end of discharge is suppressed compared with Comparative Example 7 using In single substance as the second layer of the negative electrode layer and Comparative Example 8 using Sn single substance as the second layer of the negative electrode layer.

[0156] It can be inferred that the negative electrode in the production of Examples 1 to 3 becomes a mixture of various In-Sn alloys such as InSn4, InSn, and In3Sn. Therefore, it can be inferred that when Li is inserted into the negative electrode layer by charging the battery, the increase in the melting point of the In-Sn alloy from Sn is reduced due to the alloying of Li and the In-Sn alloy, and the resistance of the battery is reduced.

[0157] [25℃ charging capacity]

[0158] Under the following conditions, the current density during discharge is 0.15 mA / cm 2 The charge capacity (mAh / cm2) of each laminated battery after the initial charge and discharge of Examples 1 to 3, Comparative Examples 1, 7 to 8 was measured at 25°C at a rate of 0.05C, with only the current density during charging changed for each cycle. 2 ).

[0159] At a current density of 6.0 mA / cm 2 The battery was charged at a constant current of 2C to a voltage of 4.2V, and the charge capacity was measured. The results are shown in Table 1.

[0160] Figure 4 This is a graph showing the relationship between the current density at 25° C. and the charge capacity of each laminated battery after the initial charge and discharge of Examples 1 to 3 and Comparative Examples 1 and 7 to 8.

[0161] about Figure 4 As shown in the 25° C. charge capacity, an increase in the charge capacity at each C rate was observed in Examples 1 to 3 compared with Comparative Examples 1 and 7 to 8.

[0162] As shown in Table 1, in each of the laminated batteries of Examples 1 to 3 after the initial charge and discharge, the adhesion between the electrolyte layer and the negative electrode layer was improved, and thus short circuiting was prevented during charging at a 2C rate.

[0163] Figure 5 This is a graph showing the relationship between the Sn composition in the In—Sn alloy and the 25° C. charge capacity at a 2C rate of a laminated battery after the initial charge and discharge.

[0164] Figure 5 The charge capacity of each laminated battery of Examples 1 to 3 at the 2C rate shown in Table 1 increases in the order of Example 3, Example 1, and Example 2.

[0165] The reason why the In-rich composition in the Li—In—Sn alloy shows a higher charge capacity than the Sn-rich composition is generally considered to be that the activation energy of the lithium ion conduction path of the Li—In alloy is lower than that of the Li—Sn alloy.

[0166] [Table 1]

[0167]

[0168] [Reversible capacity after 20 cycles]

[0169] The reversible capacity (mAh / cm2) after 20 cycles of each laminated battery of Examples 1 to 3 and Comparative Examples 1 to 8 after the initial charge and discharge was measured at 25°C under the following conditions: 2 ).

[0170] At a current density of 0.60 mA / cm 2 The battery was charged at a constant current of 4.2 V at a rate of 0.2 C, and then charged at a constant voltage to a current density of 0.03 mA / cm 2 , 0.01C rate.

[0171] At a current density of 0.60 mA / cm 2 The battery was discharged at a constant current of 0.10 V and 0.2 C rate to a voltage of 3.0 V. The above charge and discharge were repeated 20 times, and the reversible capacity (discharge capacity) after 20 cycles was measured. The results are shown in Table 2.

[0172] As shown in Table 2, the reversible capacity after 20 cycles is less different between Examples 1 to 3, with Example 2 having the largest reversible capacity. Compared with Comparative Example 7 using In simple substance as the second layer of the negative electrode layer and Comparative Example 8 using Sn simple substance as the second layer of the negative electrode layer, improvements in reversible capacity are observed in Examples 1 to 3.

[0173] [Table 2]

[0174]

[0175] [SEM-EDX measurement]

[0176] The cross section of the solid electrolyte layer-negative electrode (Li-In-Sn alloy layer / Li-Mg alloy layer / Ni foil) of the laminated battery of Example 2 after the initial charge was subjected to SEM observation using secondary electron imaging and EDX mapping at an applied voltage of 5 kV.

[0177] Figure 6These are the SEM-EDX mappings of the solid electrolyte layer-negative electrode cross section after the initial charge of Example 2: (1) secondary electron image, (2) S element mapping, (3) In element mapping, (4) Sn element mapping, (5) O element mapping, (6) Mg element mapping, and (7) Ni element mapping.

[0178] The cross section of the solid electrolyte layer-negative electrode (Li-In-Sn alloy layer / Li-Mg alloy layer / Ni foil) after the first discharge of the laminated battery of Example 2 was observed by SEM observation using secondary electron imaging and EDX mapping at an applied voltage of 5 kV.

[0179] Figure 7 The SEM-EDX mapping of the solid electrolyte layer-negative electrode cross section after the first discharge of Example 2 includes: (1) secondary electron image, (2) S element mapping, (3) In element mapping, (4) Sn element mapping, (5) O element mapping, (6) Mg element mapping, and (7) Ni element mapping.

[0180] like Figure 6 As shown, it can be seen that when the negative electrode layer is divided into two equal parts: the region on the negative electrode collector side and the region on the electrolyte layer side, the content of In and Sn elements in the region on the electrolyte layer side is greater than the content of In and Sn elements in the region on the negative electrode collector side.

[0181] like Figure 6 As shown, it is known that a Li-In-Sn alloy layer is formed between the solid electrolyte layer and the Li-Mg alloy layer. It is confirmed that the Li-Mg alloy layer is widely dispersed, a large amount of Li reacts with Mg, and the Li-Mg alloy layer functions as a Li reaction layer.

[0182] like Figure 7 As shown, it can be seen that even at the end of the discharge of the lithium-ion secondary battery, a Li-In-Sn alloy layer is maintained between the solid electrolyte layer and the Li-Mg alloy layer. Compared with the Li-Mg alloy layer, it is not easy for the Li-In-Sn alloy layer to shrink and peel off the interface due to the potential, so the Li-In-Sn alloy layer functions as an interface layer to maintain the solid-solid interface. Compared with the absence of the Li-In-Sn layer, the reduction and decomposition reaction of the solid electrolyte layer caused by Li can be prevented, and the increase of the interface resistance and the battery resistance can be suppressed. In addition, as the reason why the Li-In-Sn alloy layer is more suitable as a protective layer than the Li-In alloy layer and the Li-Sn alloy layer, it is considered to be the following two points.

[0183] The first point is that the melting point of Li-In-Sn alloy is lower than that of Li-In alloy and Li-Sn alloy. At the same operating temperature, Li-In-Sn alloy is softer than Li-In alloy and Li-Sn alloy. Therefore, the close adhesion between the solid electrolyte layer and the negative electrode layer during discharge when Li is separated from the negative electrode layer, and the close adhesion between the Li-In-Sn alloy layer and the Li-Mg alloy layer are improved, the resistance of the interface between the solid electrolyte layer and the negative electrode layer is reduced, and the charging rate characteristics are improved.

[0184] The second point is that the lithium ion conductivity of the Li—In—Sn alloy is considered to be higher than that of the Li—In alloy and the Li—Sn alloy.

[0185] Explanation of symbols

[0186] 10. Positive electrode collector

[0187] 20 Positive electrode layer

[0188] 30 Electrolyte layer

[0189] 40 In-Sn alloy layer

[0190] 41 Li-In-Sn alloy layer

[0191] 50 Metal Mg layer

[0192] 51 Li-Mg alloy layer

[0193] 60 Negative electrode collector

[0194] 100 Lithium-ion secondary battery

[0195] 200 Lithium-ion secondary battery

Claims

1. A lithium ion secondary battery, which is a lithium ion secondary battery utilizing a precipitation-dissolution reaction of metallic lithium, wherein: The lithium ion secondary battery comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer. The positive electrode layer contains a positive electrode active material capable of absorbing and releasing lithium ions. The negative electrode layer contains Mg element, In element, Sn element and Li element.

2. The lithium ion secondary battery according to claim 1, wherein A molar ratio of Sn element to In element contained in the negative electrode layer, Sn / In, is greater than or equal to 0.5 and less than or equal to 3.

8.

3. The lithium ion secondary battery according to claim 1, wherein The negative electrode layer includes, in order from the electrolyte layer side, a Li—In—Sn alloy layer containing a Li—In—Sn alloy and a Li—Mg alloy layer containing a Li—Mg alloy.

4. The lithium ion secondary battery according to claim 1, wherein The lithium ion secondary battery comprises a negative electrode current collector on the negative electrode layer opposite to the electrolyte layer. When the negative electrode layer is divided into two equal parts parallel to the stacking surface of the negative electrode layer, and the area on the negative electrode collector side is set as the first area, and the area on the electrolyte layer side is set as the second area, the content of the In element and the Sn element in the second area of ​​the negative electrode layer is greater than the content of the In element and the Sn element in the first area.

5. The lithium ion secondary battery according to claim 1, wherein The electrolyte layer is a solid electrolyte layer containing a sulfide-based solid electrolyte.

6. A lithium ion secondary battery, which is a lithium ion secondary battery using a precipitation-dissolution reaction of metallic lithium, wherein: The lithium ion secondary battery comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer. The positive electrode layer contains a positive electrode active material capable of absorbing and releasing lithium ions. The negative electrode layer includes, in order from the electrolyte layer side, an In—Sn alloy layer containing an In—Sn alloy and a metal Mg layer containing a single substance of Mg.

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