Secondary battery

Abstract

[Problem] To provide a secondary battery in which the decrease in ion conductivity in a solid electrolyte layer is minimized and the growth of dendrites in the solid electrolyte layer is prevented. [Solution] A secondary battery includes a power generating element in which a positive electrode containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode containing a negative electrode active material are sequentially stacked, and the solid electrolyte layer further contains a binder having a Young's modulus of 200 [MPa] or less.

Description

Technical Field

[0001] This invention relates to secondary batteries. Background Technology

[0002] In recent years, there has been an urgent need to reduce carbon dioxide emissions in order to address global warming. In the automotive industry, the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) to reduce carbon dioxide emissions is highly anticipated, and the development of non-aqueous electrolyte secondary batteries, such as those for engine-driven secondary batteries, which are key to their practical application, is actively underway.

[0003] As a secondary battery for engine propulsion, lithium-ion batteries require extremely high power characteristics and high energy density compared to civilian lithium-ion batteries used in mobile phones, laptops, and other devices. Therefore, lithium-ion batteries, which possess the highest theoretical energy density among all existing batteries, are attracting significant attention and are currently under rapid development.

[0004] Here, commonly used lithium-ion secondary batteries typically use flammable organic electrolytes as the electrolyte. In this type of liquid-based lithium-ion secondary battery, safety measures against leakage, short circuits, and overcharging are more stringent than in other batteries.

[0005] Therefore, in recent years, research and development of all-solid-state batteries, such as all-solid-state lithium-ion secondary batteries using oxide-based and sulfide-based solid electrolytes, has been actively underway. Solid electrolytes are materials primarily composed of ion conductors capable of ion conduction in solid states. Therefore, in principle, all-solid-state lithium-ion secondary batteries do not suffer from the various problems caused by flammable organic electrolytes that plagued conventional liquid-based lithium-ion secondary batteries. Furthermore, by using high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials, significant improvements in battery power density and energy density can typically be achieved. All-solid-state lithium-ion secondary batteries using elemental sulfur (S) and sulfide-based materials as positive electrode active materials are promising candidates.

[0006] However, in lithium-ion secondary batteries, the negative electrode potential decreases as charging progresses. If the negative electrode potential drops below 0V (vs. Li / Li+), metallic lithium precipitates in the negative electrode, forming dendritic crystals (this phenomenon is also called lithium electrodeposition). Especially in all-solid-state batteries using metallic lithium or lithium alloys as the negative electrode active material, lithium electrodeposition is essentially the charging reaction itself. Here, if excessive lithium electrodeposition occurs in an all-solid-state battery, the precipitated dendrites can sometimes penetrate the solid electrolyte layer, causing an internal short circuit in the battery.

[0007] To prevent the electrodeposition of metallic lithium in all-solid-state batteries, for example, U.S. Patent No. 2018 / 0342768 discloses a technique of covering solid electrolyte particles constituting a solid electrolyte layer with a polymer film comprising a thermoplastic resin. According to U.S. Patent No. 2018 / 0342768, this configuration improves the mechanical strength and porosity of the solid electrolyte layer and suppresses dendrite growth within the solid electrolyte layer. Summary of the Invention

[0008] The problem the invention aims to solve

[0009] According to U.S. Patent No. 2018 / 0342768, by adopting this configuration, the mechanical strength and porosity of the solid electrolyte layer are improved, and dendrite growth is suppressed.

[0010] However, according to the research of the inventors, it has been determined that even when using the technology described in U.S. Patent No. 2018 / 0342768, sufficient battery performance may not always be obtained, depending on the circumstances. Specifically, it has been determined that depending on the properties of the polymer used, the ionic conductivity in the solid electrolyte layer may decrease, resulting in a reduction in the battery's power characteristics.

[0011] Therefore, the object of the present invention is to provide a solution in which the reduction of ionic conductivity in the solid electrolyte layer is minimized and dendrite growth in the solid electrolyte layer is prevented in a secondary battery having a solid electrolyte layer.

[0012] Solution for solving the problem

[0013] According to one aspect of the present invention, a secondary battery is provided, comprising a power generation element, wherein the power generation element is formed by sequentially stacking a positive electrode containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode containing a negative electrode active material. Furthermore, the secondary battery is characterized in that the aforementioned solid electrolyte layer further comprises a binder having a Young's modulus of 200 MPa or less. Attached Figure Description

[0014] Figure 1 A perspective view showing the appearance of a flat, stacked, all-solid-state lithium-ion secondary battery, which is one embodiment of the secondary battery of the present invention.

[0015] Figure 2 For along Figure 1 The sectional view shown is along line 2-2.

[0016] Figure 3 This is an illustration of the mechanism by which the ionic conductivity of a solid electrolyte layer is improved when using a binder with a low Young's modulus.

[0017] Figure 4 To vary the Young's modulus of the included binder within the range of 1.3 [MPa] to 1300 [MPa], solid electrolyte layers were fabricated and pressurized at a pressure of 300 [MPa]. The cross-sections of the solid electrolyte layers were then observed using a scanning electron microscope (SEM) at atmospheric pressure (secondary electron image and reflected electron image).

[0018] Figure 5 A cross-sectional view of a bipolar all-solid-state lithium-ion secondary battery, which is one embodiment of the secondary battery of the present invention, is shown for illustrative purposes.

[0019] Figure 6 A perspective view of a battery device having a bipolar lithium-ion secondary battery according to an embodiment of the present invention.

[0020] Figure 7 From Figure 6 The side view shown is taken from direction A.

[0021] Figure 8 The graph is a plot of the measured ionic conductivity [S / cm] relative to the Young's modulus [MPa] of the binder for Comparative Examples 4 and 5, and Examples 4 and 7 to 10, in the Example 1 section described later, with the amount of binder added relative to the solid electrolyte being 2% by mass. Detailed Implementation

[0022] Secondary Batteries

[0023] One aspect of the present invention is a secondary battery comprising a power generation element, wherein the power generation element is formed by sequentially stacking a positive electrode containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode containing a negative electrode active material, wherein the aforementioned solid electrolyte layer further comprises a binder having a Young's modulus of 200 MPa or less. According to the secondary battery of the present invention, the decrease in ionic conductivity in the solid electrolyte layer can be minimized, and dendrite growth in the solid electrolyte layer can be prevented.

[0024] The embodiments of this method described above will be explained below with reference to the accompanying drawings. However, the scope of protection of this invention should be determined based on the claims and is not limited to the following embodiments. It should be noted that the dimensions in the drawings are exaggerated for ease of explanation and may sometimes differ from the actual dimensions.

[0025] Figure 1 A perspective view showing the appearance of a flat, stacked, all-solid-state lithium-ion secondary battery, which is one embodiment of the lithium-ion secondary battery of the present invention. Figure 2 For along Figure 1The cross-sectional view shown is along line 2-2. By designing it as a stacked type, the battery can be made compact and have a high capacity. It should be noted that in this specification, examples are listed... Figure 1 and Figure 2 The flat, stacked, non-bipolar lithium-ion secondary battery (hereinafter also referred to as "stacked battery") shown is explained in detail as an example. However, when viewed in terms of the internal electrical connection configuration (electrode structure) of the lithium-ion secondary battery of this type, it can be applied to either non-bipolar (internal parallel connection type) batteries or bipolar (internal series connection type) batteries.

[0026] like Figure 1 As shown, the stacked battery 10a has a rectangular, flat shape, with a negative current collector 25 and a positive current collector 27 extending from its two sides for extracting power. The power generation element 21 is covered by the battery casing material (laminated film 29) of the stacked battery 10a and is thermally fused around its perimeter. The power generation element 21 is sealed while the negative current collector 25 and the positive current collector 27 are extended to the outside.

[0027] It should be noted that the lithium-ion secondary battery of this method is not limited to a stacked, flat shape. The wound lithium-ion secondary battery can be cylindrical, or it can be deformed into a rectangular, flat shape, etc., without particular limitation. For the aforementioned cylindrical shape, the outer shell material can be a laminated film, or a conventional cylindrical can (metal can), etc., without particular limitation. Preferably, the power generation element is housed inside a laminated film containing aluminum. This method achieves weight reduction.

[0028] In addition, regarding Figure 1 There are no particular restrictions on how the current collectors (25, 27) shown are removed. The negative current collector 25 and the positive current collector 27 can be led out from the same side, or the negative current collector 25 and the positive current collector 27 can be divided into multiple parts and removed from different sides, etc., without limitation. Figure 1 As shown in the diagram. Alternatively, in wound lithium-ion batteries, terminals can be formed using, for example, a cylindrical can (metal can), instead of tabs.

[0029] like Figure 2As shown, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generation element 21, which actually performs the charge-discharge reaction, is sealed inside a laminated film 29, which serves as the battery casing material. Here, the power generation element 21 has a structure in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode active material is disposed on both sides of the positive electrode current collector 11'. The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material is disposed on both sides of the negative electrode current collector 11'. Specifically, the positive electrode, the solid electrolyte layer, and the negative electrode are stacked sequentially with one positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 separated by a solid electrolyte layer 17. Thus, the adjacent positive electrode, the solid electrolyte layer, and the negative electrode constitute a single cell layer 19. Therefore, it can be said that... Figure 1 The stacked battery 10a shown has a configuration formed by stacking multiple single cell layers 19 and connecting them in parallel.

[0030] like Figure 2 As shown, the outermost positive current collectors of the two outermost layers of the power generation element 21 are each provided with a positive active material layer 15 on only one side, but active material layers can also be provided on both sides. That is, the current collector with active material layers on both sides can be used directly as the outermost current collector without forming a dedicated outermost current collector with an active material layer on only one side. In addition, depending on the situation, the negative active material layer 13 and the positive active material layer 15 can be used as the negative electrode and the positive electrode respectively without using current collectors (11', 11").

[0031] The negative current collector 11' and the positive current collector 11" are respectively equipped with a negative current collector plate (tab) 25 and a positive current collector plate (tab) 27 that are in contact with each electrode (positive and negative). They have a structure in which they are led out to the outside of the laminated film 29 by being clamped at the end of the laminated film 29, which is used as the battery casing material. The positive current collector plate 27 and the negative current collector plate 25 can also be installed on the positive current collector 11" and the negative current collector 11' of each electrode by means of positive and negative leads (not shown) through ultrasonic welding, resistance welding, etc., as needed.

[0032] The main components of the lithium-ion secondary battery of this method are described below.

[0033] [Current Collector]

[0034] A current collector mediates the movement of electrons from the active material layer of an electrode. There are no particular limitations on the materials used to construct a current collector. Materials such as metals and conductive resins can be used as constituent materials.

[0035] Specifically, as metals, aluminum, nickel, iron, stainless steel, titanium, and copper can be used. In addition to these, cladding materials of nickel and aluminum, copper and aluminum, etc., can be used. Alternatively, a foil formed by coating a metal surface with aluminum can also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, and the adhesion of the sputtered negative electrode active material to the current collector.

[0036] In addition, as a type of conductive resin, examples include resins in which conductive fillers are added to non-conductive polymer materials as needed.

[0037] Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide-imide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl methacrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymer materials can exhibit excellent potential resistance or solvent resistance.

[0038] Conductive fillers can be added to the aforementioned conductive or non-conductive polymer materials as needed. In particular, when the resin, which serves as the substrate for current collectors, is formed solely of non-conductive polymers, conductive fillers are essential to impart conductivity to the resin.

[0039] Conductive fillers can be used without particular restrictions as long as they are conductive materials. For example, metals and conductive carbon can be cited as materials with excellent conductivity, potential resistance, or lithium-ion blocking properties. As for metals, there are no particular restrictions, but it is preferable to include at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or alloys or metal oxides containing these metals. Similarly, as for conductive carbon, there are no particular restrictions. It is preferable to include at least one carbon selected from the group consisting of acetylene black, Vulcan (registered trademark), BLACK PEARL (registered trademark), carbon nanofibers, Ketjenblack (registered trademark), carbon nanotubes, carbon nanohorns, carbon nanospheres, and fullerenes.

[0040] There is no particular limitation on the amount of conductive filler added, as long as it is sufficient to impart sufficient conductivity to the current collector. It is usually 5 to 80% of the total mass of the current collector.

[0041] It should be noted that the current collector can be a single-layer structure formed from a single material, or it can be a stacked structure formed by appropriately combining layers formed from these materials. From the viewpoint of lightweighting the current collector, it is preferable to include at least a conductive resin layer formed from a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between the single-cell layers, a metal layer can be provided in a portion of the current collector. Moreover, as long as the negative electrode active material layer and the positive electrode active material layer described later are themselves conductive and can perform current collection functions, a current collector that is a component different from these electrode active material layers may not be used. In this manner, the negative electrode active material layer described later directly constitutes the negative electrode, and the positive electrode active material layer described later directly constitutes the positive electrode.

[0042] [Solid electrolyte layer]

[0043] In this type of secondary battery, the solid electrolyte layer is sandwiched between the positive electrode active material layer and the negative electrode active material layer, and it is essential to contain a solid electrolyte. There are no particular restrictions on the specific form of the solid electrolyte contained in the solid electrolyte layer. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes, but from the viewpoint of obtaining higher ionic conductivity, sulfide solid electrolytes are preferred.

[0044] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are positive numbers, and Z is any one of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (Where x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In.) It should be noted that the description of "Li2S-P2S5" refers to a sulfide solid electrolyte made using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0045] Sulfide solid electrolytes can, for example, have a Li3PS4 backbone, a Li4P2S7 backbone, or a Li4P2S6 backbone. As sulfide solid electrolytes with a Li3PS4 backbone, examples include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Additionally, as sulfide solid electrolytes with a Li4P2S7 backbone, examples include the Li-P-S-based solid electrolyte called LPS (e.g., Li7P3S 11 ). Additionally, as sulfide solid electrolytes, for example, Li (4-x) Ge (1-x) P x S4 (where 0 < x < 1), such as LGPS, can be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is more preferably a material with Li2S-P2S5 as the main component. Furthermore, the sulfide solid electrolyte can contain halogens (F, Cl, Br, I). As sulfide solid electrolytes containing halogens, examples include thiogermanate solid electrolytes (Li6PS5Cl, LiPS5Br), which are also materials that can be preferably used.

[0046] Additionally, when the sulfide solid electrolyte is of the Li2S-P2S5 system, the ratio of Li2S to P2S5 is preferably in the range of 50:50 to 100:0 in terms of molar ratio, and among them, Li2S:P2S5 = 70:30 to 80:20 is preferred.

[0047] Additionally, the sulfide solid electrolyte can be a sulfide glass, a crystalline sulfide glass, or a crystalline material obtained by a solid-phase method. It should be noted that sulfide glass can be obtained, for example, by mechanically grinding a raw material composition (using a ball mill, etc.). Additionally, crystalline sulfide glass can be obtained, for example, by heat-treating sulfide glass at a temperature above the crystallization temperature. Additionally, the ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is preferably 1×10 -5 S / cm or more, and more preferably 1×10 -4 S / cm or more. It should be noted that the value of the ionic conductivity of the solid electrolyte can be measured by an alternating current impedance method.

[0048] As oxide solid electrolytes, examples include compounds having a NASICON-type structure, etc. As an example of a compound having a NASICON-type structure, a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≤ x ≤ 2) (LAGP), the general formula Li1+x Al x Ti 2-x Compounds such as (LATP) with (PO4)3 (0≤x≤2) can be cited. Other examples of oxide solid electrolytes include LiLaTiO2 (e.g., Li...). 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 LiLaZrO (e.g., Li7La3Zr2O) 12 )wait.

[0049] Examples of solid electrolyte shapes include spherical, ellipsoidal, and other particle shapes, as well as thin film shapes. When a solid electrolyte is in particle shape, its average particle size (D) 50 There is no particular limitation, but 40 μm or less is preferred, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size (D) 50 Preferably, the micrometer size is 0.01 μm or larger, and more preferably, 0.1 μm or larger.

[0050] In this secondary battery, in addition to the aforementioned solid electrolyte, the solid electrolyte layer also contains a binder. Furthermore, this binder is characterized by having a Young's modulus of 200 MPa or less. "Young's modulus," also known as the longitudinal elastic coefficient, is a constant proportional to strain and stress in the coaxial direction within the elastic range for which Hooke's law applies. In this specification, the Young's modulus value of the binder is a value measured using the nanoindentation method described in the examples section below. When the binder contained in the solid electrolyte layer contains a Young's modulus of 200 MPa or less, even with the addition of a binder to the solid electrolyte layer, the decrease in ionic conductivity in the solid electrolyte layer can be sufficiently suppressed. This is presumably because, as... Figure 3 As shown, when a low Young's modulus binder is incorporated into the solid electrolyte layer, by applying pressure during the manufacture of the solid electrolyte layer or during operation of the secondary battery, the binder present between the solid electrolyte particles is extruded and moves into the pores, allowing the solid electrolyte particles to directly contact each other. In contrast, even when a high Young's modulus binder is incorporated into the solid electrolyte layer, the aforementioned phenomenon does not occur, and no improvement in ionic conductivity is obtained. Experimental results demonstrating this fact are shown below. Figure 4 . Figure 4To vary the Young's modulus of the included binder within the range of 1.3 [MPa] to 1300 [MPa], solid electrolyte layers were fabricated, pressurized at 300 [MPa], and then the cross-sections of these solid electrolyte layers were observed using a scanning electron microscope (SEM) at atmospheric pressure, resulting in photographs (secondary electron images and reflected electron images). Based on... Figure 4 The microscopic images shown demonstrate that as the Young's modulus of the binder contained in the solid electrolyte layer decreases, the binder penetrates into the pores between the solid electrolyte particles under pressure, resulting in direct contact between the solid electrolyte particles. It should be noted that even with a binder of low Young's modulus, dendrite growth in the solid electrolyte layer can be prevented by including such a binder in the solid electrolyte layer. In conventional technologies, binders with high Young's modulus are added to prevent dendrite growth, thus inevitably leading to a decrease in the ionic conductivity of the solid electrolyte layer. However, according to the present invention, the decrease in the ionic conductivity of the solid electrolyte layer can be minimized, and dendrite growth in the solid electrolyte layer can be prevented. It should be noted that binders used in secondary batteries can also be cured by crystallization or the like through heat treatment. However, since the binder of the present invention has a Young's modulus of 200 [MPa] or less, it is not cured by crystallization or the like (preferably, it does not crystallize).

[0051] Here, there are no particular restrictions on the specific chemical structure of the adhesive having a Young's modulus of 200 MPa or less, and adhesives with conventionally known chemical structures can be used. As an example, for adhesives having a Young's modulus of 200 MPa or less, from the viewpoint of easily achieving a low Young's modulus, it is preferable to include one or more of the following: acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF) (including compounds obtained by replacing hydrogen atoms with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyethylene carbonate (PEC), and polyethylene oxide (PEO), and more preferably, polyvinylidene fluoride (PVdF) or styrene-butadiene rubber (SBR). It should be noted that even with adhesives having the same chemical structure, the value of the Young's modulus can be controlled by adjusting its composition, degree of polymerization, crosslinking density, etc. In this type of secondary battery, the solid electrolyte layer only needs to contain a binder with a Young's modulus of 200 MPa or less. From the viewpoint of improving the ionic conductivity of the solid electrolyte layer, the lower the Young's modulus of the binder, the better. For example, the Young's modulus of the binder is preferably 100 MPa or less, more preferably 50 MPa or less, further preferably 20 MPa or less, even more preferably 7 MPa or less, particularly preferably 3 MPa or less, and most preferably 1 MPa or less. In addition, there is no particular limitation on the lower limit value of the Young's modulus of the binder, for example, it is 0.1 MPa or more.

[0052] In this type of secondary battery, the solid electrolyte layer only needs to contain a binder with a Young's modulus of 200 MPa or less, and may also contain other binders (i.e., binders with a Young's modulus of more than 200 MPa). There are no particular restrictions on the chemical structure of such binders, and binders known in the past as binders for all-solid-state batteries and non-aqueous electrolyte secondary batteries can be used. Examples of the chemical structures of such adhesives include: polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVdF) (including compounds obtained by replacing hydrogen atoms with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrides, styrene-isoprene-styrene block copolymer and its hydrides, and other thermoplastic polymers such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and ethylene-tetrafluoroethylene copolymer (ETFE). Fluoropolymers such as polyvinyl chloride trifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF); fluororubbers such as vinylidene fluoride-hexafluoropropylene (VDF-HFP), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (VDF-HFP-TFE), vinylidene fluoride-pentafluoropropylene (VDF-PFP), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene (VDF-PFP-TFE), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene (VDF-PFMVE-TFE), and vinylidene fluoride-chlorotrifluoroethylene (VDF-CTFE); and epoxy resins.

[0053] From the viewpoint of fully realizing the effects of the present invention, it is preferable that the binder containing the solid electrolyte layer is mainly composed of a binder having a Young's modulus of 200 MPa or less. That is, the content ratio of the binder having a Young's modulus of 200 MPa or less in 100% by mass of the total amount of binder contained in the solid electrolyte layer is preferably 50% by mass or more. Furthermore, this content ratio is more preferably 70% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass, and most preferably 100% by mass.

[0054] The thickness of the solid electrolyte layer varies depending on the structure of the target lithium-ion secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. On the other hand, there is no particular limitation on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more.

[0055] The content of the binder having a Young's modulus of 200 MPa or less in the solid electrolyte layer is not particularly limited, and is, for example, 1 to 12% by mass. From the viewpoint of improving the flexibility and flexural strength of the solid electrolyte layer, it is preferably 3% by mass or more relative to 100% by mass of the solid electrolyte. Furthermore, from the viewpoint of improving the ionic conductivity of the solid electrolyte layer, it is preferably 3% by mass or more and 5% by mass or less relative to 100% by mass of the solid electrolyte.

[0056] [Negative electrode (negative electrode active material layer)]

[0057] In this type of secondary battery, the negative electrode active material layer 13 contains a negative electrode active material. There are no particular limitations on the type of negative electrode active material; examples include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesophase carbon microspheres (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb₂O₅ and Li₄Ti₅O₅. 12 Furthermore, silicon-based and tin-based anode active materials can also be used. Silicon and tin are known to belong to Group 14 elements and are anode active materials that can significantly improve the capacity of non-aqueous electrolyte secondary batteries. These elements can absorb and release a large amount of charge carriers (lithium ions, etc.) per unit volume (mass), thus becoming high-capacity anode active materials. Here, elemental Si is preferred as a silicon-based anode active material. Similarly, SiO2, which disproportionates into two phases—a Si phase and a silicon oxide phase—is also preferred. x Silicon oxides such as (0.3≤x≤1.6). In this case, the range of x is more preferably 0.5≤x≤1.5, and even more preferably 0.7≤x≤1.2. Furthermore, silicon-containing alloys (silicon alloy-based anode active materials) can also be used. On the other hand, as anode active materials containing tin (tin-based anode active materials), examples include elemental Sn, tin alloys (Cu-Sn alloys, Co-Sn alloys), amorphous tin oxides, and tin-silicon oxides. Among these, SnB is an example of an amorphous tin oxide. 0.4 P 0.6 O 3.1Additionally, SnSiO3 is an example of a tin-silicon oxide. Furthermore, lithium-containing metals can be used as the negative electrode active material. There are no particular limitations on this negative electrode active material as long as it contains lithium; lithium alloys can be used in addition to metallic lithium. Examples of lithium alloys include alloys of Li with at least one of In, Al, Si, and Sn. Depending on the situation, two or more negative electrode active materials can be used together. It should be noted that negative electrode active materials other than those mentioned above can, of course, be used. The negative electrode active material preferably contains metallic lithium, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably containing metallic lithium.

[0058] The shape of the negative electrode active material can be, for example, particulate (spherical, fibrous), or thin film. When the negative electrode active material is in particulate form, its average particle size (D) 50 For example, a particle size range of 1 nm to 100 μm is preferred, a range of 10 nm to 50 μm is more preferred, a range of 100 nm to 20 μm is even more preferred, and a range of 1 nm to 20 μm is particularly preferred. It should be noted that, in this specification, the average particle size (D) of the active material is... 50 The value of can be determined by laser diffraction scattering.

[0059] The content of negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, and more preferably in the range of 50 to 90% by mass.

[0060] The negative electrode active material layer preferably also includes a solid electrolyte. By including a solid electrolyte, the ionic conductivity of the negative electrode active material layer can be improved. There are no particular limitations on the specific type of solid electrolyte contained in the negative electrode active material layer, and the examples and preferred methods described in the solid electrolyte layer section are used in the same way. The content of solid electrolyte in the negative electrode active material layer is preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

[0061] In addition to the aforementioned negative electrode active material and solid electrolyte, the negative electrode active material layer may also contain at least one of a binder and a conductive additive. Here, there are no particular limitations on the specific type of binder that may be included in the negative electrode active material layer; the examples and preferred embodiments described in the section on the solid electrolyte layer are similarly applied. That is, the negative electrode active material layer preferably also contains a binder having a Young's modulus of 200 MPa or less.

[0062] Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-deposited carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNTs), and carbon black (specifically, acetylene black, Ketjenblack (registered trademark), furnace black, channel black, thermal lamp black, etc.). Additionally, granular ceramic materials or materials obtained by coating the aforementioned metal materials around a resin material using methods such as plating can also be used as conductive additives. From the viewpoint of electrical stability, it is preferable that these conductive additives include at least one element selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon; more preferably, at least one element selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon; and even more preferably, at least one type of carbon. These conductive additives can be used alone or in combination of two or more.

[0063] The conductive additive is preferably in granular or fibrous form. When the conductive additive is in granular form, the shape of the granules is not particularly limited and can be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, spindle, etc.

[0064] The thickness of the negative electrode active material layer also varies depending on the composition of the target all-solid-state battery, preferably in the range of 0.1 to 1000 μm.

[0065] [Positive electrode active material layer]

[0066] In this type of secondary battery, the positive electrode active material layer 15 contains a positive electrode active material. There are no particular limitations on the specific design of the positive electrode active material, and conventionally known methods can be appropriately referenced. Preferably, the positive electrode active material layer contains a sulfur-containing positive electrode active material. There are no particular limitations on the type of sulfur-containing positive electrode active material; in addition to elemental sulfur (S), particles or films of organic or inorganic sulfur compounds can be used, as long as the material utilizes the redox reaction of sulfur, releases lithium ions during charging, and stores lithium ions during discharging. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile (represented by compounds described in International Publication No. 2010 / 044437), sulfur-modified polyisoprene, erythrine (dithiooxamide), and polysulfide carbon. Disulfide compounds, sulfur-modified polyacrylonitrile, and erythrine are preferred, with sulfur-modified polyacrylonitrile being particularly preferred. As a disulfide compound, a dithiobiuret derivative, or a compound having a thiourea group, a thioisocyanate group, or a thioamide group is more preferred. Here, sulfur-modified polyacrylonitrile refers to a modified polyacrylonitrile containing sulfur atoms, obtained by mixing sulfur powder with polyacrylonitrile and heating under an inactive gas or reduced pressure. Its proposed structure, for example as shown in Chem. Mater. 2011, 23, 5024-5028, is a polycyclic structure with a closed ring of polyacrylonitrile, where at least a portion of the sulfur is bonded to the carbon atom. The compound described in this literature exhibits a Raman spectrum at 1330 cm⁻¹. -1 and 1560cm -1 There is a strong peak signal nearby, and further, at 307 cm⁻¹ -1 379cm -1 472cm -1 929cm -1 A peak exists nearby. On the other hand, inorganic sulfur compounds exhibit excellent stability and are therefore preferred. Specifically, examples include elemental sulfur (S), S-carbon mixtures, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS2, and MoS3. Among these, S, S-carbon mixtures, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, elemental sulfur (S), S-carbon mixtures, TiS2, and FeS2 are more preferred, and elemental sulfur (S) is particularly preferred. Here, an S-carbon mixture refers to a state in which sulfur powder and carbon material are combined by heat treatment or mechanical mixing. More specifically, it refers to a state in which sulfur is distributed on the surface and within the pores of the carbon material; a state in which sulfur and carbon material are uniformly dispersed at the nanoscale and aggregated into particles; a state in which carbon material is distributed on the surface and within the fine sulfur powder; or a state obtained by combining multiple of these states.

[0067] The positive electrode active material layer can contain sulfur-free positive electrode active materials to replace sulfur-containing positive electrode active materials, or it can contain sulfur-free positive electrode active materials in addition to sulfur-containing positive electrode active materials. Examples of sulfur-free positive electrode active materials include layered rock salt type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li(Ni-Mn-Co)O2, as well as LiMn2O4 and LiNi... 0.5 Mn 1.5 Spinel-type active materials such as O4, olivine-type active materials such as LiFePO4 and LiMnPO4, and Si-containing active materials such as Li2FeSiO4 and Li2MnSiO4 are also examples. In addition, as oxide active materials other than those mentioned above, Li4Ti5O can be cited as an example. 12 .

[0068] Depending on the circumstances, two or more positive electrode active materials can be used in combination. It should be noted that positive electrode active materials other than those mentioned above can also be used.

[0069] The shape of the positive electrode active material can be, for example, particulate (spherical, fibrous), or thin film. When the positive electrode active material is particulate, its average particle size (D) 50 For example, a particle size range of 1 nm to 100 μm is preferred, a range of 10 nm to 50 μm is more preferred, a range of 100 nm to 20 μm is even more preferred, and a range of 1 nm to 20 μm is particularly preferred. It should be noted that, in this specification, the average particle size (D) of the active material is... 50 The value of ) can be determined by laser diffraction scattering.

[0070] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 40-99% by mass, more preferably in the range of 50-90% by mass. It should be noted that the positive electrode active material layer may also contain conductive additives and / or binders, and the specific embodiments and preferred methods for these can be described in the section on the negative electrode active material layer. That is, the positive electrode active material layer also preferably contains a binder having a Young's modulus of 200 MPa or less.

[0071] [Positive current collector and negative current collector]

[0072] There are no particular limitations on the materials used to construct the current collectors (25, 27), and conventionally known highly conductive materials can be used as current collectors for secondary batteries. Preferred materials for the current collectors include, for example, aluminum, copper, titanium, nickel, stainless steel (SUS), and their alloys. From the viewpoints of lightweight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. It should be noted that the positive current collector 27 and the negative current collector 25 can be made of the same material or different materials.

[0073] [Positive lead and negative lead]

[0074] Furthermore, although the illustration is omitted, an electrical connection can be made between the current collectors (11, 12) and the current collector plates (25, 27) using positive and negative leads. The materials used in lithium-ion secondary batteries can be the same as those used in the positive and negative leads. It should be noted that the portion removed from the casing is preferably covered with heat-resistant and insulating heat-shrink tubing or the like to prevent contact with external equipment, wiring, etc., which could lead to leakage and damage to the product (e.g., automotive parts, especially electronic devices).

[0075] [Battery casing material]

[0076] As for the battery casing material, known metal can casings can be used; alternatively, materials such as... Figure 1 and Figure 2 The illustration shows a bag-shaped casing using a laminated film 29 containing aluminum to cover the power generation element. This laminated film can be, for example, a three-layer structure consisting of PP, aluminum, and nylon stacked sequentially, but is not limited thereto. From the viewpoint of high power output, excellent cooling performance, and suitability for large-scale motor batteries used in EVs and HEVs, a laminated film containing aluminum is ideal. Furthermore, from the perspective of easily adjusting the overall pressure applied to the power generation element from the outside, the casing is more preferably a laminated film containing aluminum.

[0077] Figure 1 and Figure 2 The stacked battery 10a of the illustrated embodiment has a high capacity and excellent cycle durability due to its structure consisting of multiple single-cell layers connected in parallel. Therefore, the stacked battery of this embodiment is suitable for use as a power source for driving EVs and HEVs.

[0078] The above describes one embodiment of a lithium-ion secondary battery, but the present invention is not limited to the configuration described in the above embodiment and may be appropriately modified based on the claims.

[0079] For example, as a type of battery to which the present invention is applicable, a bipolar battery comprising a bipolar electrode is also mentioned, the bipolar electrode having: a positive active material layer electrically connected to one side of a current collector, and a negative active material layer electrically connected to the opposite side of the current collector.

[0080] Figure 5 A cross-sectional view of a bipolar lithium-ion secondary battery (hereinafter also simply referred to as "bipolar secondary battery") as an embodiment of the lithium-ion secondary battery of the present invention is shown for illustrative purposes. Figure 5 The bipolar secondary battery 10b shown has a structure in which a roughly rectangular power generation element 21, in which the actual charging and discharging reaction takes place, is sealed inside a laminated film 29, which serves as the battery casing.

[0081] like Figure 5 As shown, the power generation element 21 of the bipolar secondary battery 10b of this type has: a plurality of bipolar electrodes 23 having a positive electrode active material layer 15 electrically connected to one side of the current collector 11, and a negative electrode active material layer 13 electrically connected to the opposite side of the current collector 11. Each bipolar electrode 23 is stacked with a solid electrolyte layer 17 to form the power generation element 21. It should be noted that the solid electrolyte layer 17 has a structure in which the solid electrolyte is formed in a layered manner. Figure 5 As shown, a solid electrolyte layer 17 is sandwiched between the positive active material layer 15 of a bipolar electrode 23 and the negative active material layer 13 of another bipolar electrode 23 adjacent to the aforementioned bipolar electrode 23.

[0082] The adjacent positive electrode active material layer 15, solid electrolyte layer 17, and negative electrode active material layer 13 constitute a single cell layer 19. Therefore, it can be said that the bipolar secondary battery 10b has a configuration consisting of stacked single cell layers 19. It should be noted that in the outermost current collector 11a located on the outermost positive electrode side of the power generation element 21, the positive electrode active material layer 15 is formed only on one side. In addition, in the outermost current collector 11b located on the outermost negative electrode side of the power generation element 21, the negative electrode active material layer 13 is formed only on one side.

[0083] and then, Figure 5 In the bipolar secondary battery 10b shown, a positive electrode current collector plate (positive electrode tab) 25 is arranged adjacent to the outermost current collector 11a on the positive electrode side, and it is extended and extended from the laminated film 29, which serves as the battery casing. On the other hand, a negative electrode current collector plate (negative electrode tab) 27 is arranged adjacent to the outermost current collector 11b on the negative electrode side, and it is similarly extended and extended from the laminated film 29.

[0084] It should be noted that the number of times the single cell layer 19 is stacked is adjusted according to the desired voltage. Furthermore, in the bipolar secondary battery 10b, if sufficient power can be ensured even with minimal reduction in battery thickness, the number of times the single cell layer 19 is stacked can be reduced. In the bipolar secondary battery 10b, to prevent external impacts and environmental degradation during use, the following structure can be formed: the power generation element 21 is depressurized and sealed into the laminated film 29, which serves as the battery casing, and the positive current collector 27 and the negative current collector 25 are removed and placed outside the laminated film 29.

[0085] Furthermore, the secondary battery of this method does not necessarily have to be entirely solid-state. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There is no particular limitation on the amount of liquid electrolyte (electrolyte) that may be contained in the solid electrolyte layer, but it is preferable to have an amount that maintains the shape of the solid electrolyte layer formed by the solid electrolyte and prevents leakage of the liquid electrolyte (electrolyte).

[0086] The usable liquid electrolyte (electrolyte) has a form in which lithium salts are dissolved in an organic solvent. Examples of usable organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). From the viewpoint of further improving rapid charging characteristics and power characteristics, the organic solvent is preferably a chain carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), methyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and even more preferably selected from methyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0087] Examples of lithium salts include Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3. Among these, Li(FSO2)2N (LiFSI) is preferred from the perspective of battery power and charge-discharge cycle characteristics.

[0088] Liquid electrolytes (electrolytes) may further contain additives in addition to the above-mentioned components. Specific examples of such compounds include ethylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinylene carbonate, 1,2-divinylene carbonate, 1-methyl-1-vinylene carbonate, 1-methyl-2-vinylene carbonate, 1-ethyl-1-vinylene carbonate, 1-ethyl-2-vinylene carbonate, vinylene carbonate, allyl ethylene carbonate, ethyleneoxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloyloxymethyl ethylene carbonate, methacryloyloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propynyl ethylene carbonate, propynyloxymethyl ethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives can be used alone or in combination of two or more. In addition, the amount of additives used in electrolytes can be adjusted appropriately.

[0089] [Battery Device]

[0090] The secondary battery of one aspect of the present invention is preferably pressurized in the stacking direction of the power generation elements during its operation. Therefore, the secondary battery of one aspect of the present invention is preferably used in conjunction with a pressurizing member that pressurizes the power generation elements of the secondary battery in the stacking direction. Therefore, according to another aspect of the present invention, a battery device is also provided, comprising: the secondary battery of one aspect of the present invention described above; and a pressurizing member that pressurizes the power generation elements of the aforementioned secondary battery in the stacking direction.

[0091] Figure 6 A perspective view of a battery device having a bipolar lithium-ion secondary battery according to an embodiment of the present invention. Figure 7 From Figure 6 The side view shown is taken from direction A.

[0092] like Figure 6 As shown, a battery device 100 having a stacked battery 10 according to one aspect of the present invention includes: Figure 1The diagram shows a stacked battery 10; two metal plates 200 clamping the stacked battery 10; and bolts 300 and nuts 400 as fastening members. These fastening members (bolts 300 and nuts 400) function to fix the metal plates 200 in a clamping state of the stacked battery 10. Thus, the metal plates 200 and the fastening members (bolts 300 and nuts 400) function as pressure-applying members that pressurize the power generation elements 21 of the stacked battery 10 in its stacking direction. It should be noted that there are no particular limitations on the pressure-applying members as long as they are capable of pressing the power generation elements 21 of the stacked battery 10 in its stacking direction. Typically, a combination of a plate made of a rigid material, such as the metal plates 200, and the aforementioned fastening members can be used as pressure-applying members. Furthermore, in addition to bolts 300 and nuts 400, tension plates or similar devices that fix the ends of the metal plates 200 by pressing the power generation elements 21 in their stacking direction can also be used as fastening members. It should be noted that there is no particular limitation on the magnitude of the pressurizing pressure applied to the power generation element by the pressurizing member. It can be appropriately determined by considering the desired battery performance. From the viewpoint of the obtained battery performance, in the stacking direction of the power generation element, the pressurizing member preferably applies a pressurizing pressure of 50 to 200 [MPa], and more preferably 80 to 150 [MPa].

[0093] According to this method of battery device, the stacked battery 10 is pressurized in the stacking direction of the power generation element 21 during operation. As a result, even during battery operation, a reference power can be enjoyed. Figure 3 and Figure 4 The advantages of including a binder with a low Young's modulus in the solid electrolyte layer are explained, as it can improve the ionic conductivity of the solid electrolyte layer. This, in turn, can increase the energy density of the secondary battery and improve its power characteristics, making it a preferred option.

[0094] Example

[0095] The present invention will now be described in further detail with reference to the embodiments. However, the scope of protection of the present invention should not be limited to the following embodiments. It should be noted that the following operations were performed inside an argon glove box (23°C, moisture content below 0.1 ppm, oxygen concentration below 10 ppm) with a dew point below -70°C. In addition, the Young's modulus of the adhesives used in the following experimental examples was determined by the following method.

[0096] (Method for determining the Young's modulus of adhesives)

[0097] First, Young's modulus was determined using nanoindentation with a Hysitron Nano Indenter "TI980" as the measuring device. A spherical diamond indenter with a tip radius of 100 μm was used as the measuring indenter. The measurement conditions were set as follows:

[0098] Measurement mode: Load-unloading test

[0099] Maximum indentation depth: 4000nm

[0100] Hold time at maximum load: 0 seconds

[0101] Loading and unloading speeds: 800 nm / s

[0102] During the measurement, the adhesive used to determine the Young's modulus is fixed to the glass substrate with an adhesive, and then secured to the sample stage using a vacuum chuck. Then, under the aforementioned measurement conditions, the relationship between the indentation depth and the indentation load is determined. From the obtained measurements, the relationship between the indentation strain and the average contact pressure (stress-strain curve) is calculated. Based on Hertz's contact theory, the slope of the thus calculated stress-strain curve is used to determine the composite elastic modulus Er at indentation, and the yield contact pressure Py is determined from the yield point. It should be noted that Hertz's contact theory is expressed by the following formula.

[0103] Hertz's contact theory

[0104] P = 4 / 3E r R 1 / 2 h 3 / 2

[0105] In the formula, P is the applied load [mN], and E r R is the composite elastic modulus [GPa], R is the radius of the indenter tip [μm], and h is the indentation depth [nm].

[0106] Then, based on the composite elastic modulus Er obtained above, assuming the Poisson's ratio v of the sample, the Young's modulus is calculated using the following formula. The Young's modulus values ​​for the adhesives used in each experimental example are shown in Table 1 below.

[0107] 1 / E r ={(1-v 2 ) / E}sample+{(1-v1 2 ) / E i Indentation

[0108] In the formula, E is the Young's modulus of the sample (binder) [GPa], v is the Poisson's ratio of the sample (binder) (the ratio of longitudinal strain to transverse strain when a load is applied to the sample (binder)), and E rThis represents the composite elastic modulus [GPa] of the sample (adhesive) calculated above. Additionally, v i E represents the Poisson's ratio of the diamond indenter (set to 0.06). i Let be the Young's modulus of the diamond indenter (set to 1141 [GPa]).

[0109] Example of fabrication of experimental adhesive battery cells

[0110] [Comparative Example 1]

[0111] [Fabrication of the solid electrolyte layer (without binder)]

[0112] A sulfide-based solid electrolyte of silver sulfide type (Li6PS5Cl) was prepared as a lithium-ion conductive solid electrolyte. 100 mg of this solid electrolyte was weighed and placed in a φ10 mm Macor tube, held in place by an aluminum foil (20 μm thick) serving as an electrode. The tube was then uniaxially pressurized at 300–400 MPa at 25 °C to form an adhered battery cell (non-activated battery cell) with a structure of aluminum foil (20 μm) / solid electrolyte layer (600 μm) / aluminum foil (20 μm).

[0113] [Comparative Example 2]

[0114] [Fabrication of the solid electrolyte layer (with binder)]

[0115] As a binder, styrene-butadiene rubber (SBR) with a Young's modulus of 1229 MPa was prepared. Then, a pre-prepared dehydrated 1,3,5-trimethylbenzene solution containing 10.0% by mass of the styrene-butadiene rubber was mixed with the binder at a ratio of 5% by mass to 100% by mass of the same sulfogermanium sulfide-germanium mineral solid electrolyte (Li6PS5Cl) to prepare a primary mixture. Next, an appropriate amount of dehydrated 1,3,5-trimethylbenzene was added to this primary mixture to adjust the viscosity, thereby preparing a secondary mixture. Furthermore, to improve the dispersibility of the mixed powder and the binder, the mixture was placed in a rotary mixer and stirred at 2000 rpm for 4 minutes to prepare an electrolyte coating solution.

[0116] A 20 μm thick aluminum current collector foil was placed on a benchtop applicator, and the electrolyte coating solution prepared above was applied to the aluminum current collector foil using a bar coater with a gap of 230 μm. Afterwards, it was dried on a hot plate at 80°C for 10 minutes, and then vacuum dried at 80°C for 12 hours to form a solid electrolyte layer. The total thickness of the dried solid electrolyte layer was approximately 80 μm.

[0117] The solid electrolyte layer and aluminum current collector foil prepared above are cut into two sheets using a φ10mm punching machine. They are then bonded together with the solid electrolyte layer facing each other. A flatbed press is used to apply uniaxial pressure of 300MPa to the solid electrolyte layer to produce an adhesive battery cell (non-activated battery cell) with the structure of aluminum foil (20μm) / solid electrolyte layer (80μm) / aluminum foil (20μm).

[0118] [Comparative Example 3]

[0119] The amount of binder added was 10% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was made by the same method as in Comparative Example 2 above.

[0120] [Comparative Example 4]

[0121] A styrene-butadiene rubber (SBR) with a Young's modulus of 600 MPa was prepared as the binder. The amount of binder added was 2% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was made by the same method as in Comparative Example 2 above.

[0122] [Comparative Example 5]

[0123] As a binder, polyvinylidene fluoride (PVdF) with a Young's modulus of 1229 [MPa] was prepared. Then, as a solvent to dissolve the PVdF binder, butyl butyrate was used, and the binder was added / mixed in an amount of 2% by mass relative to 100% of the same silver-germanium sulfide solid electrolyte (Li6PS5Cl) as described above. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was prepared by the same method as in Comparative Example 2 described above.

[0124] [Example 1]

[0125] As a binder, styrene-butadiene rubber (SBR) with a Young's modulus of 0.864 [MPa] was prepared. Then, the binder was added / mixed in an amount of 10% by mass relative to 100% by mass of the same sulfogermanium sulfide solid electrolyte (Li6PS5Cl) as described above. Otherwise, the bonded battery cell (non-activated battery cell) of this embodiment was manufactured by the same method as in Comparative Example 2 described above.

[0126] [Example 2]

[0127] The amount of binder added was 5% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was made by the same method as in Example 1 above.

[0128] [Example 3]

[0129] The amount of binder added was 3% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was made by the same method as in Example 1 above.

[0130] [Example 4]

[0131] The amount of binder added was 2% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this comparative example was made by the same method as in Example 1 above.

[0132] [Example 5]

[0133] As a binder, polyvinylidene fluoride (PVdF) with a Young's modulus of 6.98 [MPa] was prepared. Then, as a solvent to dissolve the PVdF binder, butyl butyrate was used, and the binder was added / mixed in an amount of 10% by mass relative to 100% by mass of the same silver-germanium sulfide solid electrolyte (Li6PS5Cl) as described above. Otherwise, the bonded battery cell (non-activated battery cell) of this embodiment was fabricated by the same method as in Example 1 above.

[0134] [Example 6]

[0135] The amount of binder added is 3% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this embodiment is made by the same method as in Example 5 above.

[0136] [Example 7]

[0137] The amount of binder added is 2% by mass relative to 100% by mass of the solid electrolyte. Otherwise, the adhesive battery cell (non-activated battery cell) of this embodiment is made by the same method as in Example 5 above.

[0138] [Example 8]

[0139] As a binder, polyvinylidene fluoride (PVdF) with a Young's modulus of 42.4 [MPa] was used. Otherwise, the bonded battery cell (non-activated battery cell) of this embodiment was made by the same method as in Example 7 above.

[0140] [Example 9]

[0141] As a binder, polyvinylidene fluoride (PVdF) with a Young's modulus of 1.29 [MPa] was used. Otherwise, the bonded battery cell (non-activated battery cell) of this embodiment was made by the same method as in Example 7 above.

[0142] [Example 10]

[0143] As a binder, polyvinylidene fluoride (PVdF) with a Young's modulus of 200 [MPa] was used. Otherwise, the bonded battery cell (non-activated battery cell) of this embodiment was made by the same method as in Example 7 above.

[0144] Evaluation Examples of Adhesive Battery Cells Used in Experiments

[0145] (Evaluation of effective ionic conductivity)

[0146] For the adherent battery cells (non-activated battery cells) prepared in the above experimental examples, the effective ionic conductivity was determined by electrochemical impedance spectroscopy (EIS). Specifically, a Solartron Model 1260A impedance analyzer was used as the measuring apparatus, and the measurement conditions were set to an amplitude of 10 mV and a frequency of 1 MHz to 0.1 Hz. Furthermore, a pressure of 100 MPa was applied to the stacked direction of the sample during the measurement. The resistance value was obtained from the intercept of the Cole-Cole plot obtained by this EIS measurement with respect to the X-axis (real axis), and the effective ionic conductivity [S / cm] was calculated based on the cross-sectional area and thickness of the sample. The results are shown in Table 1 below. It should be noted that Table 1 also shows the relative value of the effective ionic conductivity of Comparative Example 1 as 100. In addition, for Comparative Examples 4 and 5, where the amount of binder added relative to the solid electrolyte is 2% by mass, and Examples 4 and 7 to 10, the graph obtained by plotting the measured value of ionic conductivity [S / cm] against the Young's modulus [MPa] of the binder is shown below. Figure 8 .

[0147] (Evaluation of the presence or absence of a rupture)

[0148] When the adhered battery cells (non-activated battery cells) prepared in the above embodiments were bent at 90 degrees, the samples were visually examined to determine whether cracking occurred. The results are shown in Table 1 below. It should be noted that in Table 1, cases where cracking occurred are marked as "×" and cases where no cracking occurred are marked as "○".

[0149] [Table 1]

[0150]

[0151] From Table 1 and Figure 8The results show that, according to the various embodiments (the present invention), even with the addition of a binder to the solid electrolyte layer, the decrease in ionic conductivity in the solid electrolyte layer can be sufficiently suppressed. This is presumably because, by applying pressure, the binder (which has a low Young's modulus and is flexible) existing between the solid electrolyte particles is extruded and moves into the pores, allowing the solid electrolyte particles to come into direct contact with each other.

[0152] Furthermore, when comparing the various embodiments, it was determined that a binder addition of 3% by mass or more relative to 100% by mass of the solid electrolyte was preferred, as it prevented cracking in the sample. This is presumably because the softness of the solid electrolyte layer in the sample improves with increasing amounts of the binder (which has a low Young's modulus and is flexible).

[0153] Explanation of reference numerals in the attached figures

[0154] 10. 10a stacked battery

[0155] 10b bipolar battery,

[0156] 11 collectors,

[0157] 11' negative current collector,

[0158] 11” positive current collector,

[0159] 13 negative electrode active material layer,

[0160] 15 positive electrode active material layers

[0161] 17. Solid electrolyte layer

[0162] 19 single-cell layers

[0163] 21 power generation components

[0164] 25 negative current collector,

[0165] 27 Positive current collector,

[0166] 29-layer laminated film

[0167] 100 battery device

[0168] 200 metal sheet

[0169] 300 bolts

[0170] 400 nuts.

Claims

1. A secondary battery comprising a power generation element, The power generation element is a positive electrode containing a positive electrode active material, which is sequentially stacked. Solid electrolyte layer containing solid electrolyte, and It is formed by a negative electrode containing negative electrode active material. The solid electrolyte layer also contains a binder with a Young's modulus of 0.864 MPa or higher and less than 1 MPa, the Young's modulus being determined by nanoindentation. The content of the binder having a Young's modulus of 0.864 MPa or more and less than 1 MPa in the solid electrolyte layer is 3% by mass or more and 5% by mass or less relative to 100% by mass of the solid electrolyte.

2. The secondary battery according to claim 1, wherein, The solid electrolyte includes a sulfide solid electrolyte.

3. The secondary battery according to claim 2, wherein, The sulfide solid electrolyte includes a sulfide-germanium ore type solid electrolyte.

4. The secondary battery according to any one of claims 1 to 3, wherein, The adhesive comprises one or more selected from the group consisting of acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyethylene carbonate (PEC), and polyethylene oxide (PEO).

5. The secondary battery according to any one of claims 1 to 3, wherein, The binder having a Young's modulus of 0.864 MPa or more and less than 1 MPa accounts for 50% or more of the total amount of binder contained in the solid electrolyte layer.

6. The secondary battery according to any one of claims 1 to 3 is an all-solid-state lithium-ion secondary battery.

7. The secondary battery according to any one of claims 1 to 3, wherein, The adhesive comprises styrene-butadiene rubber (SBR) or polyvinylidene fluoride (PVdF).

8. A battery device comprising: The secondary battery according to any one of claims 1 to 7, and A pressurizing component that applies pressure to the power generation elements of the secondary battery along the stacking direction. The pressurizing component applies a pressure of 50MPa to 200MPa to the power generation element.

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