Lithium ion secondary battery

Abstract

The present application provides 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 occluding and releasing lithium ions, the negative electrode layer containing a negative electrode active material capable of occluding and releasing lithium ions, and the electrolyte layer containing a positive electrode active material capable of occluding and releasing lithium ions. The negative electrode layer contains an Ag element, an Sn element, and a Li element, and the molar ratio (Sn / Ag) of the Sn element to the Ag element contained in the negative electrode layer is 0.09-0.17.

Description

Technical Field

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

[0002] Various techniques have been proposed regarding a lithium ion secondary battery in which a negative electrode includes a metal layer as disclosed in Japanese Patent Application Laid-Open No. 2021-068706. Summary of the invention

[0003] 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 as charge and discharge are repeated.

[0004] The present disclosure has been made in view of the above-mentioned actual situation, and a main object of the present disclosure is to provide a lithium ion secondary battery capable of suppressing a decrease in reversible capacity.

[0005] That is, the present disclosure includes the following aspects.

[0006] <1> A lithium ion secondary battery utilizing 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 located between the positive electrode layer and the negative electrode layer, the positive electrode layer comprising a positive electrode active material capable of absorbing and releasing lithium ions, the negative electrode layer comprising an Ag element, a Sn element, and a Li element, and a molar ratio (Sn / Ag) of the Sn element contained in the negative electrode layer to the Ag element is greater than 0.09 and less than 0.17.

[0007] <2> A lithium-ion secondary battery according to <1>, wherein the lithium-ion secondary battery has a negative electrode collector on the side of the negative electrode layer opposite to the electrolyte layer, and 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 Sn element in the second area of ​​the negative electrode layer is greater than the content of the Sn element in the first area.

[0008] <3> The lithium ion secondary battery according to <1> or <2>, wherein a Li composition ratio of the Li—Ag alloy produced in the negative electrode layer when the lithium ion secondary battery is fully charged is 94 mol % to 97 mol %.

[0009] <4> The lithium ion secondary battery according to any one of <1> to <3>, wherein the electrolyte layer is a solid electrolyte layer containing a sulfide-based solid electrolyte.

[0010] <5> A lithium-ion secondary battery utilizing 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 located between the positive electrode layer and the negative electrode layer, the positive electrode layer comprising a positive electrode active material capable of absorbing and releasing lithium ions, the negative electrode layer comprising, in order from the electrolyte layer side, a metal Sn layer containing a single substance of Sn and a metal Ag layer containing a single substance of Ag, the molar ratio of the Sn element contained in the negative electrode layer to the Ag element (Sn / Ag) being greater than 0.09 and less than 0.17.

[0011] The lithium ion secondary battery of the present disclosure can suppress a decrease in reversible capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like numerals represent like parts, and in which:

[0013] Figure 1 1 is a schematic cross-sectional view showing an example of a lithium-ion secondary battery before initial charging during manufacture of the present disclosure;

[0014] Figure 2 is a schematic cross-sectional view showing an example of a lithium-ion secondary battery of the present disclosure when fully charged after initial charging;

[0015] Figure 3 is a graph showing the relationship between the Li composition in the Li-Ag alloy layer and the resistance of the laminated battery cell after the initial charge and discharge;

[0016] Figure 4 is a graph showing the relationship between the reversible capacity at 25° C. of each laminated battery cell after charge and discharge cycles of Examples 1 to 2 and Comparative Examples 1 to 2;

[0017] Figure 5 (1) secondary electron image, (2) S element mapping, (3) Ag element mapping, (4) Sn element mapping, (5) Ni element mapping, and (6) O element mapping in the SEM-EDX mapping of the solid electrolyte layer-negative electrode cross section after the initial charge of Example 2; and

[0018] Figure 6 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) Ag element mapping, (4) Sn element mapping, (5) Ni element mapping, and (6) O element mapping. DETAILED DESCRIPTION

[0019] The following describes the implementation of the present disclosure. Furthermore, matters necessary for the implementation of the present disclosure other than those specifically mentioned in this specification can be understood as design matters based on the prior art in the field by those skilled in the art. For example, the above-mentioned necessary matters are the general structure and manufacturing process of lithium-ion secondary batteries that are not the characteristics of the present disclosure. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field.

[0020] In the present disclosure, a lithium ion secondary battery is provided, which is a lithium ion secondary battery using the precipitation-dissolution reaction of metallic lithium. 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 an Ag element, a Sn element, and a Li element, and the molar ratio (Sn / Ag) of the Sn element contained in the negative electrode layer to the Ag element is greater than 0.09 and less than 0.17.

[0021] In the present disclosure, the increase in the resistance of the negative electrode layer at the end of discharge can be suppressed, and the reduction in charge and discharge efficiency can be suppressed. Since Sn has a low melting point, the adhesion between the electrolyte layer and the negative electrode layer becomes high, and the reduction in charge and discharge efficiency can be suppressed.

[0022] In the present disclosure, by forming a Li-Sn layer between the electrolyte layer and the Li-Ag layer when Li is inserted into the negative electrode layer, the negative electrode layer can be prevented from peeling off from the electrolyte layer. Compared with the case where there is no Li-Ag layer and the case where the Li-Ag layer is used, at the end of discharge, the resistance of the lithium ion secondary battery can be reduced, the reversible capacity can be increased, and the charge and discharge efficiency can be improved.

[0023] When Sn is mixed, the melting point becomes lower than that of Ag alone, the adhesion between the electrolyte layer and the negative electrode layer becomes higher, and separation of the negative electrode layer from the electrolyte layer can be suppressed.

[0024] The lithium ion secondary battery disclosed herein utilizes the precipitation-dissolution reaction of metallic lithium and includes a positive electrode layer, a negative electrode layer, and an electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0025] In the present disclosure, the negative electrode refers to a negative electrode including a negative electrode layer.

[0026] In the present disclosure, when a lithium-ion secondary battery is fully charged, it means when the state of charge (SOC) of the lithium-ion secondary battery is 100%. SOC represents the ratio of the charge capacity of the battery to the fully charged capacity, and the fully charged capacity is SOC100%. SOC can be estimated, for example, based on the open circuit voltage (OCV) of the lithium-ion secondary battery.

[0027] negative electrode

[0028] The negative electrode includes a negative electrode layer and optionally includes a negative electrode current collector.

[0029] Negative electrode collector

[0030] The material of the negative electrode current collector may be a material that is not alloyed with Li, for example, SUS, copper, and nickel. As the form of the negative electrode current collector, for example, foil and plate can be mentioned. The top view shape of the negative electrode current collector is not particularly limited, for example, a circular shape, an elliptical shape, a rectangular shape, and an arbitrary polygonal shape can be mentioned. In addition, the thickness of the negative electrode current collector varies depending on the shape, for example, it can be in the range of 1 μm-50 μm, or in the range of 5 μm-20 μm.

[0031] Negative electrode layer

[0032] The negative electrode layer contains Ag element, Sn element and Li element. The negative electrode layer may contain a metal Sn layer containing a single substance of Sn and a metal Ag layer containing a single substance of Ag in sequence from the electrolyte layer side before the initial charge of the lithium ion secondary battery. The negative electrode layer may contain a Li-Sn alloy layer and a Li-Ag alloy layer containing a Li-Ag alloy in sequence from the electrolyte layer side after the initial charge of the lithium ion secondary battery. The negative electrode layer may also contain no Ag-C complex. That is, the carbon content of the negative electrode layer may be 0% by mass.

[0033] The molar ratio of the Sn element to the Ag element (Sn / Ag) contained in the negative electrode layer may be 0.09 or more and 0.17 or less.

[0034] When the stacking plane of the negative electrode layer and the negative electrode layer is divided into two equal parts in parallel, 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 Sn element in the second area of ​​the negative electrode layer can be greater than the content of the Sn element in the first area. Parallel can also be approximately parallel. Approximately parallel can be within the range of 0°-10°. The stacking direction of the negative electrode layer is the thickness direction of the negative electrode layer.

[0035] The comparison of the contents of the above two regions in the negative electrode layer can be performed, for example, using SEM-EDX, to map the elements from the electrolyte layer to the negative electrode collector as the field of view for observation, 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 states such as after the initial charge and when fully charged. The comparison of the contents is not limited to this, and in addition to SEM-EDX, XPS and TOF-SIMS can also be used.

[0036] The Li composition ratio of the Li-Ag alloy generated in the negative electrode layer can be greater than 0 mol% and less than 100 mol%, or it can be greater than 30 mol% and less than 99 mol%. When the lithium-ion secondary battery is fully charged, the Li composition ratio of the Li-Ag alloy generated in the negative electrode layer can be greater than 94 mol% and less than 97 mol%. In the Li-Ag alloy layer, the average particle size of the Li-Ag alloy particles can be greater than 0 μm and less than 5 μm. In the negative electrode layer, the volume occupied by the Li-Ag alloy can be greater than 0 vol% and less than 100 vol%, or it can be greater than 5 vol% and less than 80 vol%.

[0037] After the initial charge of the lithium ion secondary battery, the thickness of the Li-Sn layer may be greater than 0 μm and less than 100 μm, and the lower limit may be greater than 0.01 μm or greater than 0.1 μm. The upper limit of the thickness of the Li-Sn layer may be less than 15 μm, less than 0.7 μm, or less than 0.35 μm.

[0038] After the initial charge of the lithium ion secondary battery, the thickness of the Li—Ag 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.

[0039] The metal Ag layer is formed on the negative electrode current collector, for example. The film forming method includes a method of placing Ag particles and pressing, a vapor deposition method, a sputtering method, a PVD method, and an electroplating method. Among them, the vapor deposition method or the sputtering method can be used. The adhesion between the metal Ag layer and the negative electrode current collector is improved, and the increase in the resistance of the negative electrode can be suppressed.

[0040] Regarding the metal Sn layer, the metal Sn layer can also be formed on the negative electrode collector side or the solid electrolyte layer side by the same method as described above. Among them, the film can be formed on the solid electrolyte layer side. By forming the film on the solid electrolyte side, the adhesion between the metal Sn layer and the solid electrolyte layer is improved.

[0041] The thickness of the negative electrode layer is not particularly limited, but may be 30 nm to 50 μm when the lithium ion secondary battery is fully charged after the initial charge.

[0042] Electrolyte layer

[0043] The electrolyte layer may be a liquid electrolyte layer using an electrolyte as an electrolyte, or may be a solid electrolyte layer using a solid electrolyte as an electrolyte. The electrolyte may use a conventionally known electrolyte used in a lithium-ion secondary battery. The solid electrolyte layer contains at least a solid electrolyte. As the solid electrolyte contained in the solid electrolyte layer, a known solid electrolyte that can be used for a solid battery may be appropriately used, and oxide solid electrolytes and sulfide solid electrolytes may be cited. In order to suppress the peeling of the negative electrode layer from the solid electrolyte layer, a relatively soft sulfide solid electrolyte may be used as the solid electrolyte.

[0044] Examples of the sulfide-based solid electrolyte include a solid electrolyte containing a Li element, an M element (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and an S element. In addition, the sulfide-based solid electrolyte may further contain at least one of an O element and a halogen element.

[0045] As sulfide 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 records.

[0046] 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.

[0047] 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.

[0048] The sulfide 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. The crystal state of the sulfide solid electrolyte can be confirmed, for example, by performing powder X-ray diffraction measurement of the sulfide solid electrolyte using CuKα rays.

[0049] Sulfide glass can be obtained by subjecting a raw material composition (for example, a mixture of Li2S and P2S5) to an amorphous treatment, for example, mechanical milling.

[0050] Glass ceramics can be obtained, for example, by heat treating sulfide glass. The heat treatment temperature can be any temperature higher than the crystallization temperature (Tc) observed by thermal analysis of the sulfide glass, and is usually 195°C or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited. The crystallization temperature (Tc) of the sulfide glass can be measured by differential thermal analysis (DTA).

[0051] The heat treatment time is not particularly limited as long as it is a time that can obtain the desired crystallinity of the glass ceramic, and is, for example, in the range of 1 minute to 24 hours, wherein, the range of 1 minute to 10 hours can be cited. The heat treatment method is not particularly limited, and, for example, a method using a sintering furnace can be cited.

[0052] Examples of oxide-based solid electrolytes include materials having a garnet crystal structure and containing Li, La, A (A is at least one of Zr, Nb, Ta, and Al), and O. Examples of oxide-based solid electrolytes include 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.

[0053] The solid electrolyte may be in the form of particles from the viewpoint of good handling properties. 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.

[0054] In the present disclosure, unless otherwise specified, the average particle size of particles is the value of the volume-based median particle size (D50) measured by laser diffraction / scattering particle size distribution measurement. In addition, in the present disclosure, the median particle size (D50) refers to the diameter (volume average diameter) at which the cumulative volume of the particles becomes half (50%) of the total volume when the particles are arranged in order from the smallest particle size.

[0055] The solid electrolyte may be used alone or in combination of two or more. In addition, when two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolytes may be formed into a multilayer structure.

[0056] The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited. The proportion of the solid electrolyte in the solid electrolyte layer is, for example, 50% by mass or more, can be in the range of 60% by mass or more and 100% by mass or less, can be in the range of 70% by mass or more and 100% by mass or less, or can be 100% by mass.

[0057] From the viewpoint of showing plasticity, etc., 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 also be less than 5% by mass.

[0058] The thickness of the solid electrolyte layer is not particularly limited, but is usually 0.1 μm or more and 1 mm or less.

[0059] positive electrode

[0060] The positive electrode includes a positive electrode layer and optionally includes a positive electrode current collector.

[0061] Positive electrode layer

[0062] The positive electrode layer contains a positive electrode active material capable of occluding and releasing lithium ions, and may contain a solid electrolyte, a conductive material, a binder, and the like as optional components.

[0063] 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 / 3O2, LiMnO2, LiMn2O4, LiNiO2, LiVO2, heterogeneous element substituted Li-Mn spinel, lithium titanate, lithium metal phosphate, LiCoN, Li2SiO3, and Li4SiO4. Heterogeneous element substituted Li-Mn spinel, for example, 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 0.5 O4, etc. Lithium titanate is, for example, Li4Ti5O 12 Etc. Examples of lithium metal phosphate include LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4.

[0064] 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). A coating layer containing a Li ion conductive oxide may also be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte can be suppressed.

[0065] Examples of Li ion conductive oxides include LiNbO3, Li4Ti5O 12 and Li3PO4, etc. The thickness of the coating is, for example, greater than 0.1 nm, or greater than 1 nm. On the other hand, the thickness of the coating is, for example, less than 100 nm, or less than 20 nm. The coverage of the coating on the surface of the positive electrode active material is, for example, greater than 70%, or greater than 90%.

[0066] The solid electrolyte may be any solid electrolyte that can be contained in the solid electrolyte layer. The content of the solid electrolyte in the positive electrode layer is not particularly limited, and may be, for example, in the range of 1% to 80% by mass when the total mass of the positive electrode layer is 100% by mass.

[0067] As the conductive material, known conductive materials can be used, for example, carbon materials and metal particles can be mentioned. As the carbon material, for example, acetylene black (AB), furnace black, VGCF, carbon nanotubes and carbon nanofibers can be mentioned. 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 of Ni, Cu, Fe and SUS can be mentioned. The content of the conductive material in the positive electrode layer is not particularly limited.

[0068] Examples of the binder include acrylonitrile butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and styrene butadiene rubber (SBR). The content of the binder in the positive electrode layer is not particularly limited.

[0069] There is no particular limitation on the thickness of the positive electrode layer. The positive electrode layer can be formed by a conventionally known method. For example, the positive electrode active material and other components as required are put into a solvent and stirred to prepare a slurry for the positive electrode layer, which is then coated on one side of a support such as a positive electrode collector and dried to obtain a positive electrode layer. Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone.

[0070] The method of applying the positive electrode layer slurry on one side of the support such as the positive electrode collector is not particularly limited. The method of applying the positive electrode layer slurry on one side of the support such as the positive electrode collector can include a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roller coating method, a gravure coating method and a screen printing method. As a support, a support with self-supporting property can be appropriately selected and used, and is not particularly limited, for example, a metal foil of Cu and Al etc. can be used.

[0071] Positive electrode collector

[0072] As the positive electrode collector, a known metal that can be used as a 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 collector, for example, SUS, aluminum, nickel, iron, titanium and carbon can be cited. The form of the positive electrode collector is not particularly limited, and can be various forms such as foil and mesh.

[0073] The lithium ion secondary battery has an outer casing as required to accommodate a positive electrode layer, a negative electrode layer, an electrolyte layer, etc. The material of the outer casing is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

[0074] Examples of the shape of the lithium ion secondary battery include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

[0075] Lithium-ion secondary batteries can be liquid lithium-ion secondary batteries using an electrolyte as an electrolyte, or solid lithium-ion secondary batteries using a solid electrolyte as an electrolyte. As the use of lithium-ion secondary batteries, for example, power sources for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), pure electric vehicles (BEV), gasoline vehicles, diesel vehicles and other vehicles can be cited. Among them, it can also be used as a driving power source for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) or pure electric vehicles (BEV). In addition, lithium-ion secondary batteries can be used as power sources for mobile bodies other than vehicles (such as railways, ships, and airplanes), and can also be used as power sources for electrical products such as information processing devices.

[0076] Figure 1 It is a schematic cross-sectional view showing an example of a lithium ion secondary battery before initial charge during production of the present disclosure.

[0077] 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, a metal Sn layer 40, a metal Ag layer 50, and a negative electrode collector 60 in this order. The negative electrode layer includes a metal Sn alloy layer 40 and a metal Ag layer 50.

[0078] Figure 2 It is a schematic cross-sectional view showing an example of a lithium ion secondary battery of the present disclosure when fully charged after initial charging.

[0079] 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-Sn alloy layer 41, a Li-Ag alloy layer 51, and a negative electrode collector 60. Through the initial charge, the metal Sn layer 40 becomes the Li-Sn alloy layer 41, and the metal Ag layer 50 becomes the Li-Ag alloy layer 51. The negative electrode layer includes the Li-Sn alloy layer 41 and the Li-Ag alloy layer 51. The negative electrode layer may also be in the state of a single Li-Sn-Ag alloy layer in which the Li-Sn alloy layer 41 and the Li-Ag alloy layer 51 are mixed and integrated.

[0080] Example 1 to Example 2

[0081] Cathode production

[0082] Butyl butyrate was used as a solvent. NCA was used as a positive electrode active material. Sulfide solid electrolyte particles (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 at the following mass composition ratio to prepare a positive electrode slurry.

[0083] Mass composition ratio positive electrode active material: solid electrolyte: binder: conductive additive = 84.7: 13.4: 0.6: 1.27

[0084] The prepared positive electrode slurry was coated on Al foil with a coating gap of 225 μm. Then, the coated positive electrode slurry was temporarily dried at 60°C for 3 hours. Then, the temporarily dried positive electrode slurry was formally dried at 165°C for 1 hour. Thus, a unit area weight of 18.7 mg / cm 2 、Design capacity 3.0mAh / cm 2 The obtained positive electrode composite material coated foil was punched out to obtain a positive electrode having a diameter of 11.28 mm.

[0085] Solid electrolyte layer fabrication

[0086] Butyl butyrate was used as a solvent. Sulfide 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.

[0087] Mass composition ratio solid electrolyte: binder = 92.6:7.4

[0088] The prepared solid electrolyte slurry is coated on the release film with a coating gap of 325μm. Then, the coated solid electrolyte slurry is temporarily dried at room temperature for 3 hours. Then, the temporarily dried solid electrolyte slurry is formally dried at 165°C for 1 hour. The dried solid electrolyte coated foil is punched out to obtain two discs with a diameter of 14.5mm. The solid electrolyte coated surfaces of the two discs are overlapped and pressed at 7t. After pressing, the release films of the two discs are peeled off to obtain an independent solid electrolyte layer.

[0089] Negative electrode production

[0090] Ni foil was used as the negative electrode current collector. A metal Ag layer film with a thickness of 0.368 μm in Example 1 and a thickness of 0.735 μm in Example 2 was formed on one side of the negative electrode current collector by sputtering to obtain a metal Ag layer / Ni foil. The obtained metal Ag layer / Ni foil was punched to obtain a metal Ag layer / Ni foil with a diameter of 14.5 mm.

[0091] A metal Sn layer having a thickness of 0.1 μm was formed on the solid electrolyte layer by sputtering to produce a solid electrolyte layer / metal Sn layer.

[0092] The obtained solid electrolyte layer / metal Sn layer and metal Ag layer / Ni foil were stacked in this order to obtain a negative electrode (metal Sn layer / metal Ag layer / Ni foil) on the solid electrolyte layer.

[0093] Battery Cell Production

[0094] Al is used as the positive electrode tab and Ni is used as the negative electrode tab.

[0095] The prepared positive electrode, the prepared solid electrolyte layer and the prepared negative electrode are arranged in sequence 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 housed in a laminate film, and the laminate film is vacuumed to seal the laminate. The sealed laminate is isostatically pressed at 392MPa using CIP (cold isostatic pressing) to produce a laminated battery cell (sometimes referred to as a battery cell). A constant pressure fixture with a spring inserted is used to constrain the laminated battery cell to 1MPa so that the constraint pressure is constant regardless of the volume change of the laminated battery cell.

[0096] Comparative Example 1 to Comparative Example 2

[0097] A laminated battery cell was prepared in the same manner as in Example 1 except for the following. In the following, a metal Ag layer / Ni foil was used as the negative electrode, wherein a metal Sn layer was not formed on the solid electrolyte layer, and a metal Ag layer having a thickness of 0.368 μm in Comparative Example 1 and a thickness of 0.735 μm in Comparative Example 2 was formed on one side of the negative electrode current collector by sputtering.

[0098] Sn / Ag molar ratio

[0099] The molar ratio of the Sn element to the Ag element (Sn / Ag) contained in the negative electrode layer was calculated for the negative electrode layers of Examples 1 and 2. The results are shown in Table 1.

[0100] Initial charge and discharge

[0101] Each of the laminated battery cells produced in Examples 1 and 2 and Comparative Examples 1 and 2 was initially charged and discharged at 60° C. under the following conditions.

[0102] 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 of 0.03 mA / cm 2 , 0.01C magnification.

[0103] 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 magnification.

[0104] Resistance after initial charge and discharge

[0105] The resistance (Ω·cm) of each laminated battery cell after the first charge and discharge of Examples 1 to 2 and Comparative Examples 1 to 2 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.

[0106] Figure 3 This is a graph showing the relationship between the Li composition in the Li-Ag alloy layer and the resistance of the laminated battery cell after the first charge and discharge.

[0107] The resistance of each laminated battery cell after the initial charge and discharge of Examples 1 and 2 decreases in the order of Example 2 and Example 1, and the resistance of the battery cell at the end of discharge is lower than that of Comparative Examples 1 and 2 in which Ag alone is used for the negative electrode layer.

[0108] 25℃ reversible capacity after initial charge and discharge at 60℃ and 25℃ reversible capacity after 50 cycles

[0109] The 25°C reversible capacity (mAh / cm2) of each laminated battery cell after the initial charge and discharge of Examples 1 to 2 and Comparative Examples 1 to 2 was measured at 25°C under the following conditions: 2 ) and the reversible capacity at 25℃ after 50 cycles (mAh / cm 2 ).

[0110] At a current density of 0.15 mA / cm 2 The battery was charged at a constant current of 0.05 C until the voltage reached 4.2 V, and then charged at a constant voltage until the current density reached 0.03 mA / cm 2 , 0.01C magnification.

[0111] Then, at a current density of 0.15 mA / cm 2 The battery was discharged at a constant current of 0.05C until the voltage reached 3.0V, and the reversible capacity (discharge capacity) was measured. The above charge and discharge were repeated 50 times, and the reversible capacity after 50 cycles was measured. The results are shown in Table 1.

[0112] Figure 4 This is a graph showing the relationship between the reversible capacity at 25° C. of each laminated battery cell after the charge and discharge cycle of Examples 1 and 2 and Comparative Examples 1 and 2.

[0113] about Figure 4 As for the reversible capacity at 25° C. shown in FIG. 1 and FIG. 2, compared with Comparative Examples 1 and 2, the reversible capacity maintenance rate is higher even if the number of charge and discharge cycles increases.

[0114] The 25° C. reversible capacity after the initial charge and discharge at 60° C. and the reversible capacity after 50 cycles of each laminated battery cell of Examples 1 to 2 shown in Table 1 increase in the order of Example 2 and Example 1.

[0115] (Table 1)

[0116]

[0117] SEM-EDX determination

[0118] The cross section of the solid electrolyte layer-negative electrode (Li-Sn alloy layer / Li-Ag alloy layer / Ni foil) of the laminated battery cell of Example 2 after the initial charge was subjected to SEM observation and EDX mapping under secondary electron imaging at an applied voltage of 5 kV.

[0119] Figure 5 The SEM-EDX mapping of the solid electrolyte layer-negative electrode cross section after the initial charge of Example 2 includes (1) secondary electron image, (2) S element mapping, (3) Ag element mapping, (4) Sn element mapping, (5) Ni element mapping, and (6) O element mapping.

[0120] The cross section of the solid electrolyte layer-negative electrode (Li-Sn alloy layer / Li-Ag alloy layer / Ni foil) of the laminated battery cell of Example 2 after the initial discharge was subjected to SEM observation and EDX mapping under secondary electron imaging at an applied voltage of 5 kV.

[0121] Figure 6 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) Ag element mapping, (4) Sn element mapping, (5) Ni element mapping, and (6) O element mapping.

[0122] like Figure 5 As shown, 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 Sn content in the region on the electrolyte layer side is greater than that in the region on the negative electrode collector side.

[0123] like Figure 5 As shown, it is known that after the initial charge of the lithium-ion secondary battery, a Li-Sn alloy layer is formed between the solid electrolyte layer and the Li-Ag alloy layer. It has been confirmed that the Li-Ag alloy layer is dispersed in a wide range, a lot of Li reacts with Ag, and the Li-Ag alloy layer acts as a Li reaction layer.

[0124] like Figure 6As shown, it can be seen that at the end of the discharge of the lithium-ion secondary battery, even at the end of the discharge of the lithium-ion secondary battery, a Li-Sn alloy layer is maintained between the solid electrolyte layer and the Li-Ag alloy layer. As a result, the reduction decomposition reaction of the solid electrolyte layer caused by Li can be prevented, and the increase in interface resistance and battery cell resistance can be suppressed. In addition, it is believed that the adhesion between the solid electrolyte layer and the negative electrode layer during discharge when Li is separated from the negative electrode layer, and the adhesion between the Li-Sn alloy layer and the Li-Ag alloy layer are improved. In addition, it is believed that the resistance of the interface between the solid electrolyte layer and the negative electrode layer is reduced, the reversible capacity is increased, and the reduction in reversible capacity accompanying repeated charge and discharge is also suppressed.

Claims

1. A lithium ion secondary battery utilizing 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 capable of absorbing and releasing lithium ions. The negative electrode layer contains Ag, Sn and Li elements. The molar ratio of the Sn element to the Ag element contained in the negative electrode layer, ie, Sn / Ag, is 0.09 or more and 0.17 or less.

2. 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 Sn element in the second area of ​​the negative electrode layer is greater than the content of the Sn element in the first area.

3. The lithium ion secondary battery according to claim 1 or 2, wherein: When the lithium ion secondary battery is fully charged, the Li composition ratio of the Li—Ag alloy generated in the negative electrode layer is 94 mol % or more and 97 mol % or less.

4. The lithium ion secondary battery according to claim 3, wherein: The electrolyte layer is a solid electrolyte layer including a sulfide-based solid electrolyte.

5. A lithium-ion secondary battery utilizing 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 capable of absorbing and releasing lithium ions. The negative electrode layer includes, in order from the electrolyte layer side, a metal Sn layer containing a single substance of Sn and a metal Ag layer containing a single substance of Ag, The molar ratio of the Sn element to the Ag element contained in the negative electrode layer, ie, Sn / Ag, is 0.09 or more and 0.17 or less.

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