Secondary battery

Abstract

With regard to this secondary battery that uses a solid electrolyte, the present disclosure provides a means capable of suppressing an increase in internal resistance in a case where the confining pressure of the secondary battery is low.　The present disclosure relates to a secondary battery comprising a power generation element having: a positive electrode active material layer containing a positive electrode active material; a negative electrode active material layer containing a negative electrode active material; and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. In the secondary battery, at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer includes an electrolyte composite of: a first inorganic solid electrolyte; a polymer solid electrolyte containing an ion conductive polymer and an alkali metal salt; and a second inorganic solid electrolyte.

Description

secondary battery

[0001] This invention relates to a secondary battery.

[0002] In recent years, research and development on all-solid-state batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of ion conduction in a solid state. Therefore, all-solid-state batteries have the advantage of not, in principle, occurring in the way that conventional liquid-based batteries using non-aqueous electrolytes are caused by flammable organic electrolytes.

[0003] In such all-solid-state batteries, it is preferable that they exhibit excellent performance in various aspects, similar to conventional non-aqueous electrolyte secondary batteries. For example, Japanese Patent Application Publication No. 2011-187370 discloses a technique in which the anion portions of the first solid electrolyte material and the second solid electrolyte material are the same in the electrode active material layer of an all-solid-state secondary battery, and an electron-ion mixed conductor is used for the first solid electrolyte material. According to this document, by adopting the above configuration, it is possible to effectively suppress the increase in resistance at the interface between the active material and the solid electrolyte material.

[0004] However, our own investigations have revealed that even when using the techniques described in the above-mentioned literature, reducing the confinement pressure of the secondary battery can significantly increase the internal resistance of the secondary battery during charging and discharging.

[0005] Therefore, the present invention aims to provide a means for suppressing the increase in internal resistance when the confinement pressure of a secondary battery using a solid electrolyte is small.

[0006] The inventors of the present invention conducted diligent studies to solve the above problems. As a result, they found that the above problems could be solved by including, in addition to an inorganic solid electrolyte, an electrolyte composite of a polymer solid electrolyte containing an ion-conducting polymer and an alkali metal salt and an inorganic solid electrolyte in at least one of the electrode active material layer, solid electrolyte layer, and negative electrode active material layer that constitute the power generation element of a secondary battery, and thus completed the present invention.

[0007] One embodiment of the present invention relates to a secondary battery comprising a power generation element having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. The secondary battery is characterized in that at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer contains a first inorganic solid electrolyte and an electrolyte composite comprising a polymer solid electrolyte containing an ion-conducting polymer and an alkali metal salt and a second inorganic solid electrolyte.

[0008] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (stacked secondary battery) according to one embodiment of the present invention. Figure 2 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. Figure 3 is a side view taken from direction A shown in Figure 2.

[0009] One embodiment of the present invention is a secondary battery comprising a power generation element having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, wherein at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer contains a first inorganic solid electrolyte and an electrolyte composite of a polymer solid electrolyte containing an ion-conducting polymer and an alkali metal salt and a second inorganic solid electrolyte. Such a secondary battery can suppress an increase in the internal resistance of the battery even when the battery's confinement pressure is small.

[0010] Embodiments of the present invention will be described below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery"), which is one embodiment of the present invention. Figure 1 shows a cross-section of the stacked secondary battery during charging. The stacked secondary battery 10a shown in Figure 1 has a structure in which a substantially rectangular power generation element 21, where the charge and discharge reaction actually proceeds, is sealed inside a laminate film 29, which is the battery casing. Here, the power generation element 21 has a configuration in which a negative electrode, a solid electrolyte layer 17 containing a solid electrolyte, and a positive electrode are stacked.

[0012] The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are stacked. Furthermore, a negative electrode intermediate layer 14 is arranged so as to be in contact with the negative electrode active material layer 13 and the solid electrolyte layer 17, respectively.

[0013] The positive electrode has a structure in which a positive electrode active material layer 15 is arranged on the surface of the positive electrode current collector 11''. As a result, the negative electrode current collector 11'', the negative electrode active material layer 13, the negative electrode intermediate layer 14, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11'' constitute a single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel.

[0014] In this embodiment, the positive electrode active material layer 15 consists of a positive electrode active material (lithium transition metal composite oxide), a binder (polytetrafluoroethylene (PTFE)), a conductive additive (carbon nanofiber (CNF)), and an inorganic solid electrolyte (Li ６ PS ５ In addition to Cl, an inorganic solid electrolyte (Li) is formed by a polymer solid electrolyte consisting of an ion-conducting polymer (polyacrylonitrile (PAN)) and an alkali metal salt (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)). ６ PS ５ It further contains an electrolyte complex in which the surface of Cl particles is coated.

[0015] The negative electrode current collector 11' and the positive electrode current collector 11'' are each fitted with a negative electrode current collector plate 25 and a positive electrode current collector plate 27, which are electrically connected to the respective electrodes (negative and positive electrodes), and are structured to be sandwiched between the edges of the laminate film 29 and led out to the outside of the laminate film 29. In the stacked secondary battery 10a, a restraining pressure is applied in the stacking direction of the power generation elements 21 by a pressurizing member. As a result, the volume of the power generation elements 21 is kept constant.

[0016] The main components of the secondary battery according to this embodiment will be described below.

[0017] [Current Collector] The current collector has the function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials that make up the current collector. For example, metals or conductive resins can be used as the constituent materials of the current collector.

[0018] The current collector may be a single-layer structure made of a single material, or it may be a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between single cell layers, a metal layer may be provided on a part of the current collector. Moreover, if the negative electrode active material layer and positive electrode active material layer described later are conductive and can perform the current collecting function on their own, it is not necessary to use a current collector as a separate component from these electrode active material layers. In such a configuration, the negative electrode active material layer described later will directly constitute the negative electrode, and the positive electrode active material layer described later will directly constitute the positive electrode.

[0019] [Negative Electrode Active Material Layer] The negative electrode active material layer 13 contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but examples include carbon materials, metal oxides, and metal active materials. In addition, a lithium-containing metal may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples include lithium metal and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li and at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. The negative electrode active material preferably contains lithium metal or a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably lithium metal or a lithium-containing alloy.

[0020] Furthermore, when lithium metal or a lithium-containing alloy is used as the negative electrode active material, the secondary battery according to this embodiment may be a so-called lithium deposition type, in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during the charging process. Therefore, in such an embodiment, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during complete discharge, but in some cases, a negative electrode active material layer consisting of a certain amount of lithium metal may be present during complete discharge.

[0021] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 100% by mass, and may be in the range of 50 to 90% by mass.

[0022] The negative electrode active material layer may further contain an inorganic solid electrolyte as needed. The inclusion of an inorganic solid electrolyte in the negative electrode active material layer can improve its ionic conductivity. Examples of inorganic solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes. In this specification, a solid electrolyte refers to a material mainly composed of an ionic conductor capable of ion conduction in a solid state, and in particular, a lithium ion conductivity of 1 × 10⁻¹⁶ at room temperature (25°C). －５ This refers to a material with a lithium ion conductivity of S / cm or higher, and this lithium ion conductivity is preferably 1 × 10⁻⁶. －４It is S / cm or more. Here, the value of ionic conductivity can be measured by the AC impedance method.

[0023] The inorganic solid electrolyte preferably is a sulfide solid electrolyte containing an S element, more preferably is a sulfide solid electrolyte containing Li element, M element and S element, from the viewpoint of showing excellent lithium ion conductivity and being more able to follow the volume change of the electrode active material accompanying charge and discharge. The M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl and I, and even more preferably is a sulfide solid electrolyte containing S element, Li element and P element.

[0024] The sulfide solid electrolyte may have a ３ PS ４ skeleton, and may have a ４ P ２ S ７ skeleton, and may have a ４ P ２ S ６ skeleton. The sulfide solid electrolyte having a ３ PS ４ skeleton includes, for example, LiI-Li ３ PS ４ , LiI-LiBr-Li ３ PS ４ , Li ３ PS ４ . Further, the sulfide solid electrolyte having a ４ P ２ S ７ skeleton includes, for example, a Li-P-S-based solid electrolyte called LPS. Further, as the sulfide solid electrolyte, for example, Li （４－ｘ） Ge （１－ｘ） P ｘ S ４ (where x satisfies 0 < x < 1), such as LGPS, may be used. More specifically, for example, LPS (Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ , Li ３．２ P ０．９６S, Li ３．２５ Ge ０．２５ P ０．７５ S ４ , or Li １０ GeP ２ S １２ These are some examples. ２ S-P ２ S ５ The description of " is Li ２ S and P ２ S ５ This refers to a sulfide solid electrolyte made using a raw material composition containing the above, and the same applies to other descriptions.

[0025] Furthermore, as a preferred embodiment of the solid electrolyte, Li ａ MZ ｂ Ha ｃ A solid electrolyte represented by the following compositional formula is an example: [In this case, M is at least one element selected from the group consisting of Na, K, and elements that exist as divalent to pentavalent cations in the crystal structure; Z is at least one element selected from the group consisting of elements that exist as divalent anions in the crystal structure; Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and a, b, and c satisfy the relationships 5 ≤ ​​a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2, respectively], where it is preferable that M is P (phosphorus) and Z is S (sulfur).

[0026] In particular, sulfide solid electrolytes have high ionic conductivity and low bulk modulus, and therefore can follow the volume change of the electrode active material during charging and discharging. From this viewpoint, the solid electrolyte represented by the above composition formula, LPS (Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ Li ３．２ P ０．９６ S and Li ３ PS ４ It is preferable to select from the group consisting of the above, and more preferably to select from the solid electrolyte represented by the above composition formula.

[0027] Examples of inorganic solid electrolyte shapes include spherical, ellipsoidal, and other particulate forms, as well as thin films. When the inorganic solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size (D50) is preferably 0.01 μm or more, and more preferably 0.1 μm or more. The inorganic solid electrolyte content 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.

[0028] The negative electrode active material layer may further contain, in addition to the negative electrode active material and inorganic solid electrolyte described above, at least one of a binder and a conductive additive. Examples of binders include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC). Examples of conductive additives include fibrous conductive additives and particulate conductive additives. Examples of fibrous conductive additives include carbon fibers such as carbon nanotubes, carbon nanohorns, carbon nanofibers, carbon nanofilaments, carbon fibrils, and vapor-grown carbon fibers. Examples of particulate conductive additives are not particularly limited and include carbon powders such as acetylene black, Ketjen black (furnace black), channel black, and thermal black.

[0029] The thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably in the range of 0.1 to 1,000 μm, and more preferably 40 to 100 μm.

[0030] [Negative Electrode Intermediate Layer] In the case of a secondary battery according to this embodiment that is of the lithium deposition type in which lithium metal or lithium-containing alloy as a negative electrode active material is deposited on the negative electrode current collector 11' during the charging process, it is preferable that the power generation element includes a negative electrode intermediate layer containing a lithium-reactive material between the negative electrode active material layer and the solid electrolyte layer. Examples of lithium-reactive materials include materials that can intercept and deintercept lithium ions during charging and metals that can alloy with lithium during charging. The presence of such a negative electrode intermediate layer suppresses the growth of dendrites from the lithium metal layer (negative electrode active material layer) when lithium metal is deposited between the negative electrode intermediate layer and the negative electrode current collector during charging, thereby preventing short circuits in the battery and the resulting decrease in capacity.

[0031] While there are no particular limitations on the material capable of intercalating and deintercalating lithium ions, carbon materials are preferred. Specific examples of carbon materials include carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNTs), graphite, and hard carbon. Among these, carbon black is preferred, and it is more preferable that it be at least one selected from the group consisting of acetylene black, Ketjenblack®, furnace black, channel black, and thermal lamp black.

[0032] Examples of metals that can be alloyed with lithium include In, Al, Si, Sn, Mg, Au, Ag, and Zn. Among these, In, Si, Sn, and Ag are preferred, with Ag being more preferred.

[0033] The lithium-reactive material may be used alone or in combination of two or more types. As a form of using two or more types in combination, a preferred embodiment is to use a material capable of intercalating and deintercalating lithium ions in combination with a metal capable of alloying with lithium. This ensures sufficient strength and lithium-ion conductivity of the negative electrode intermediate layer. More specifically, it is preferable to use nanoparticles made of In, Si, Sn, and Ag in combination with carbon black, and more preferably to use nanoparticles made of Ag in combination with carbon black. When using a material capable of intercalating and deintercalating lithium ions in combination with a metal capable of alloying with lithium, the mixing ratio (mass ratio) of these materials is not particularly limited, but the ratio of material capable of intercalating and deintercalating lithium ions to metal capable of alloying with lithium is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1.

[0034] The content of lithium-reactive material in the negative electrode intermediate layer (referring to the total content of two or more materials when used in combination; the same applies hereinafter) is not particularly limited, but is preferably in the range of 50 to 100% by mass, more preferably in the range of 70 to 100% by mass, even more preferably in the range of 85 to 100% by mass, and particularly preferably in the range of 90 to 99% by mass.

[0035] The negative electrode intermediate layer may consist solely of lithium-reactive material if a self-supporting film can be fabricated using only lithium-reactive material, but may also contain a binder as needed. The type of binder is not particularly limited, and any known binder in the art can be used as appropriate; one example is described above.

[0036] The binder content in the negative electrode intermediate layer is not particularly limited, but is preferably in the range of 1 to 15% by mass, and more preferably in the range of 5 to 10% by mass. If the binder content is 1% by mass or more, a negative electrode intermediate layer with sufficient strength can be formed. If the binder content is 15% by mass or less, a negative electrode intermediate layer with sufficient lithium ion conductivity can be formed.

[0037] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 10 to 30 μm. When the thickness of the negative electrode intermediate layer is 1 μm or more, the functions of the negative electrode intermediate layer can be fully exhibited. When the thickness of the negative electrode intermediate layer is 50 μm or less, the decrease in energy density can be suppressed.

[0038] [Positive Electrode Active Material Layer] The positive electrode active material layer 15 contains a positive electrode active material. The positive electrode active material is not particularly limited as long as it is a material that can release lithium ions during the charging process of the secondary battery and absorb lithium ions during the discharging process. An example of such a positive electrode active material is one that contains an M1 element and an O element, and the M1 element contains at least one element selected from the group consisting of Li, Mn, Ni, Co, Cr, Fe, and P. An example of such a positive electrode active material is LiCoO ２ LiMnO ２ LiNiO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt type active materials such as LiMn ２ O ４ LiNi ０．５ Mn １．５ O ４ spinel-type active materials such as LiFePO ４ LiMnPO ４ Olivine-type active materials such as Li ２ FeSiO ４ Li ２ MnSiO ４ Examples of Si-containing active materials include the above. Other oxide active materials include, for example, Li ４ Ti ５ O １２ LiVO ２ These are some examples.

[0039] Furthermore, the positive electrode active material may contain sulfur element. The positive electrode active material containing sulfur element is not particularly limited, and examples thereof include sulfur simple substance (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any substance that can release lithium ions during charging and occlude lithium ions during discharging by utilizing the redox reaction of sulfur may be used. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compounds described in WO2010 / 044437 pamphlet, sulfur-modified polyisoprene, rubane acid (dithiooxamide), polysulfurized carbon, and the like. Among them, disulfide compounds, sulfur-modified polyacrylonitrile, and rubane acid are preferable, and sulfur-modified polyacrylonitrile is particularly preferable. As the disulfide compound, those having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group are more preferable. Here, sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms obtained by mixing sulfur powder and polyacrylonitrile and heating under an inert gas or reduced pressure. Its presumed structure is, for example, as shown in Chem. Mater. 2011, 23, 5024-5028, a structure in which polyacrylonitrile is cyclized into a polycyclic form and at least a part of S is bonded to C. The compounds described in this document have strong peak signals at around 1330 cm －１ and 1560 cm －１ in the Raman spectrum, and further, peaks exist at around 307 cm －１ , 379 cm －１ , 472 cm －１ , 929 cm －１ . On the other hand, inorganic sulfur compounds are preferable because of their excellent stability. Specifically, sulfur simple substance (S), Li ２ S, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , MoS ２ , MoS ３ , etc. are included. Among them, S, Li ２S, S-Carbon Composite, TiS ２ TiS ３ TiS ４ FeS ２ and MoS ２ Preferably, elemental sulfur (S), Li ２ S, TiS ２ and FeS ２ From the viewpoint of being more preferable and having a high capacity, elemental sulfur (S) or Li ２ S is particularly preferred. Note that elemental sulfur (S) is S ８ Structural α-sulfur, β-sulfur, or γ-sulfur can be used. During discharge, these elemental sulfurs (S) intercalate lithium ions and exist in the positive electrode active material layer in the form of lithium (poly)sulfides.

[0040] In some cases, two or more positive electrode active materials may be used in combination. Of course, other positive electrode active materials may also be used.

[0041] In a preferred embodiment, the positive electrode active material layer 15 constituting the secondary battery according to this embodiment is, from the viewpoint of output characteristics, a layered rock salt type active material containing lithium and cobalt (for example, Li(Ni-Mn-Co)O) ２ ) or contains a positive electrode active material containing sulfur.

[0042] The shape of the positive electrode active material can be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is in particulate form, its average particle diameter is preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. Here, the "average particle diameter" of the positive electrode active material particles is defined as the 50% cumulative diameter (D50) measured by a laser diffraction / scattering particle size distribution device.

[0043] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but it is preferably more than 50% by mass, more preferably in the range of 50% to 95% by mass, and even more preferably in the range of 60% to 90% by mass, relative to 100% by mass of the total solids contained in the positive electrode active material layer.

[0044] The positive electrode active material layer preferably further contains an inorganic solid electrolyte. The inclusion of an inorganic solid electrolyte in the positive electrode active material layer improves its ionic conductivity. There are no particular restrictions on the specific form of the inorganic solid electrolyte contained in the positive electrode active material layer; the inorganic solid electrolytes and their preferred forms exemplified in the negative electrode active material layer section can be similarly employed. The inorganic solid electrolyte content in the positive electrode active material layer is preferably 1% to 70% by mass, more preferably 5% to 50% by mass, and even more preferably 10% to 30% by mass, based on 100% by mass of the total solid content contained in the positive electrode active material layer. If the inorganic solid electrolyte content in the positive electrode active material layer is within the above range, both the ionic conductivity and energy density of the positive electrode active material layer can be achieved.

[0045] Furthermore, the positive electrode active material layer preferably includes a conductive additive and a binder in addition to the positive electrode active material and inorganic solid electrolyte described above. Examples of conductive additives include fibrous conductive additives and / or particulate conductive additives, and it is more preferable to include both.

[0046] In this specification, "fibrous conductive additive" means a conductive additive having a fiber-like shape. "Fibrous" includes, for example, elongated shapes such as columnar shapes, and is not particularly limited to straight or curved shapes. Furthermore, "fibrous" may be a hollow tube shape as long as it has a fiber-like shape. More specifically, a "fibrous conductive additive" is a conductive additive whose aspect ratio (fiber length / fiber diameter) is 10 to 1000 in the observation image when the cross-section of the positive electrode active material layer is observed using a scanning electron microscope (SEM). The average fiber length of the fibrous conductive additive is preferably 10 μm or more. The average fiber length of the fibrous conductive additive is preferably 10 μm to 100 μm, more preferably 10 μm to 50 μm, even more preferably 10 μm to 40 μm, and particularly preferably 15 μm to 40 μm. By setting the average fiber length of the fibrous conductive additive within this range, the conductivity between positive electrode active materials can be improved, and the cycle durability can be further improved. The fiber length of the fibrous conductive additive can be the average value of several to tens of fiber lengths measured using a transmission electron microscope (TEM) or scanning electron microscope (SEM). The average fiber diameter of the fibrous conductive additive is preferably 1 to 300 nm, and more preferably 1 to 50 nm. The average fiber diameter of the fibrous conductive additive can be the average value of several to tens of fiber diameters measured using a transmission electron microscope (TEM) or scanning electron microscope (SEM). Examples of fibrous conductive additives include carbon nanotubes, carbon nanohorns, carbon nanofibers, carbon nanofilaments, carbon fibrils, and carbon fibers such as vapor-grown carbon fibers. The fibrous conductive additive may be used alone or in combination of two or more types.

[0047] On the other hand, "particulate conductive additive" refers to a conductive additive having a particle-like shape. Particulate means, for example, spherical, hemispherical, ellipsoidal, short chain, flake-like, cylindrical, polygonal prism-like shapes, and may be linear or curved. Furthermore, particulate means having a particle-like shape, and may be hollow inside. More specifically, "particulate conductive additive" refers to a conductive additive other than the "fibrous conductive additive" described above, in which the aspect ratio (major axis / minor axis) in the observation image when the cross-section of the positive electrode active material layer is observed using a scanning electron microscope (SEM) is less than 10.

[0048] The average primary particle diameter of the particulate conductive additive contained in the positive electrode active material layer is not particularly limited, but is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm, and particularly preferably 30 nm to 50 nm. Similarly, the average secondary particle diameter of the particulate conductive additive contained in the positive electrode active material layer is not particularly limited, but is preferably 0.1 μm to 100 μm, and more preferably 0.5 μm to 30 μm. Within the above ranges, the effects of the present invention can be more significantly obtained. The average primary particle diameter of the particulate conductive additive can be the average value of the particle diameters of several to tens of primary particles measured using a transmission electron microscope (TEM) or scanning electron microscope (SEM). Likewise, the average secondary particle diameter can be the average value of the particle diameters of several to tens of secondary particles measured using a transmission electron microscope (TEM) or scanning electron microscope (SEM). Furthermore, the average aspect ratio of the particulate conductive additive contained in the positive electrode active material layer is preferable as it approaches 1, but is preferably 1 to 5, and more preferably 1 to 2. The average aspect ratio of the particulate conductive additive can be the average value of the aspect ratios of several to tens of particulate conductive additives measured using a scanning electron microscope (SEM) or the like. The particulate conductive additive is not particularly limited and includes carbon powders such as acetylene black, Ketjen black (furnace black), channel black, and thermal black. Among these, acetylene black, Ketjen black (furnace black), channel black, and thermal black are preferably used from the viewpoint of being able to better follow the volume change of the positive electrode active material accompanying charging and discharging. Only one type of particulate conductive additive may be used alone, or two or more types may be used in combination.

[0049] The binder has the function of maintaining the structure of the electrode active material layer by binding the components contained in the electrode active material layer together. While not particularly limited, examples of binders include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), styrene-butadiene rubber (SBR), and carboxymethylcellulose. Among these, PTFE is preferred.

[0050] The binder content in the positive electrode active material layer is not particularly limited, but is preferably in the range of 1 to 15% by mass, more preferably in the range of 1 to 10% by mass, and even more preferably in the range of 1 to 5% by mass, based on 100% by mass of the total solid content contained in the positive electrode active material layer. By having the binder content within the above range, the strength of the positive electrode active material layer can be made more sufficient, and furthermore, the ionic conductivity and electronic conductivity of the positive electrode active material layer can also be made sufficient.

[0051] The thickness of the positive electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably in the range of 0.1 to 1000 μm, and more preferably 40 to 100 μm.

[0052] [Solid Electrolyte Layer] The solid electrolyte layer 17 is interposed between the positive electrode active material layer 15 and the negative electrode active material layer 13, and usually contains an inorganic solid electrolyte. There are no particular restrictions on the specific form of the inorganic solid electrolyte contained in the solid electrolyte layer, and the inorganic solid electrolyte and its preferred form exemplified in the section on the negative electrode active material layer can be used in the same way. In some cases, solid electrolytes other than the inorganic solid electrolyte described above may be used in combination.

[0053] The inorganic solid electrolyte content in the solid electrolyte layer is preferably in the range of 10 to 100% by mass, more preferably in the range of 50 to 100% by mass, and even more preferably in the range of 90 to 100% by mass, relative to the total mass of the solid electrolyte layer. In addition to the inorganic solid electrolyte described above, the solid electrolyte layer may further contain a binder. The thickness of the solid electrolyte layer varies depending on the configuration of the intended secondary battery, but is preferably in the range of 0.1 to 1,000 μm, and more preferably in the range of 10 to 100 μm.

[0054] [Characteristics of the Secondary Battery] The secondary battery according to this embodiment is characterized in that at least one of the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer described above contains an inorganic solid electrolyte (first inorganic solid electrolyte) as mentioned in the description of each component, and in addition contains an electrolyte composite of a polymer solid electrolyte containing an ion-conducting polymer and an alkali metal salt and a second inorganic solid electrolyte. The above characteristics will be described in detail below, but among the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer, the layer containing the first inorganic solid electrolyte and the electrolyte composite will also be referred to as the "specific layer" below. In this specification, an inorganic solid electrolyte contained in the specific layer and not constituting the electrolyte composite will be referred to as the "first inorganic solid electrolyte". Furthermore, an inorganic solid electrolyte that constitutes an electrolyte composite together with the polymer solid electrolyte in the specific layer will be referred to as the "second inorganic solid electrolyte". However, the ordinal numbers themselves do not have any particular meaning.

[0055] As the first and second inorganic solid electrolytes contained in a specific layer, the inorganic solid electrolytes described above in the section on the negative electrode active material layer can be used in the same way. Here, from the viewpoint of further improving the ion conductivity of the specific layer and effectively contributing to the reduction of the internal resistance of the battery, at least one (preferably both) of the first or second inorganic solid electrolyte is Li ａ MZ ｂ Ha ｃ It is preferable that the solid electrolyte is represented by the compositional formula [where M is at least one element selected from the group consisting of Na, K, and elements that exist as divalent to pentavalent cations in the crystal structure; Z is at least one element selected from the group consisting of elements that exist as divalent anions in the crystal structure; Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and a, b, and c satisfy the relationships 5 ≤ ​​a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2, respectively], and it is more preferable that M is P (phosphorus) and Z is S (sulfur).

[0056] (First inorganic solid electrolyte) Here, the first inorganic solid electrolyte contained in a particular layer is selected from among the above compositional formulas, with particular emphasis on excellent ionic conductivity. ａ PS ｂ Ha ｃ [In this case, Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and a, b, and c each satisfy 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2] Preferably, the electrolyte contains an argyrodite-type sulfide solid electrolyte represented by the compositional formula, and among these, it is preferable that a, b, and c each satisfy 5 ≤ a ≤ 6, 4 ≤ b ≤ 5, and 0 < c ≤ 2. A preferred embodiment of such an electrolyte is Li ６ PS ５ Cl and Li ５．５ PS ４．５ Cl １．５ These are some examples.

[0057] The content of the first inorganic solid electrolyte in a particular layer varies greatly depending on whether the particular layer is an electrode active material layer (positive electrode active material layer or negative electrode active material layer) or a solid electrolyte layer, making it difficult to define uniquely. For example, when the particular layer is an electrode active material layer, the content of the first inorganic solid electrolyte in the particular layer is preferably 2 to 20% by mass, more preferably 4 to 17% by mass, even more preferably 5 to 15% by mass, particularly preferably 6 to 13% by mass, and most preferably 7 to 12% by mass, based on 100% by mass of the total amount of the particular layer (electrode active material layer). Also, when the particular layer is a solid electrolyte layer, the content of the first inorganic solid electrolyte in the particular layer is preferably 40 to 90% by mass, more preferably 45 to 90% by mass, even more preferably 55 to 90% by mass, and particularly preferably 65 to 85% by mass, based on 100% by mass of the total amount of the particular layer (solid electrolyte layer).

[0058] (Electrolyte Composite) The electrolyte composite is a composite of a polymer solid electrolyte and a second inorganic solid electrolyte, and can be clearly distinguished from an inorganic solid electrolyte that is not composited with the polymer solid electrolyte (first inorganic solid electrolyte) by observation using an electron microscope, etc. In the electrolyte composite, it is preferable that the polymer solid electrolyte is present on the surface of the particles of the second inorganic solid electrolyte. Furthermore, in the electrolyte composite, it is more preferable that the polymer solid electrolyte covers at least a part of the surface of the particles of the second inorganic solid electrolyte. By having a polymer solid electrolyte with appropriate viscoelasticity on the surface of the second inorganic solid electrolyte (preferably covering at least a part of the surface), good contact between the components of a specific layer during charging and discharging of the battery can be ensured, which in turn can suppress the increase in internal resistance when the confinement pressure of the secondary battery is small and contribute to improving the rate characteristics.

[0059] <Second Inorganic Solid Electrolyte> As mentioned above, the second inorganic solid electrolyte constituting the electrolyte complex is also the same inorganic solid electrolyte used in the negative electrode active material layer section, and from the viewpoint of further improving the ion conductivity of a specific layer and effectively contributing to the reduction of the internal resistance of the battery, the second inorganic solid electrolyte is also Li ａ MZ ｂ Ha ｃ It is preferable that the solid electrolyte is represented by the compositional formula [where M is at least one element selected from the group consisting of Na, K, and elements that exist as divalent to pentavalent cations in the crystal structure; Z is at least one element selected from the group consisting of elements that exist as divalent anions in the crystal structure; Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and a, b, and c satisfy the relationships 5 ≤ ​​a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2, respectively], and it is more preferable that M is P (phosphorus) and Z is S (sulfur).

[0060] Here, the second inorganic solid electrolyte contained in a particular layer is stable with respect to the polymer solid electrolyte that constitutes the electrolyte complex, and is also stable with respect to the solvent that is normally used when compounding the inorganic solid electrolyte and the polymer solid electrolyte. From this viewpoint, among the above compositional formulas, Li ａ PS ｂ Ha ｃ [In this case, Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and a, b, and c satisfy 6 ≤ a ≤ 7, 5 ≤ b ≤ 6, and 0 < c ≤ 1, respectively] Preferably, the electrolyte contains an argyrodite-type sulfide solid electrolyte represented by the composition formula. A preferred embodiment of such an electrolyte is Li ６ PS ５ Examples include Cl.

[0061] The polymeric solid electrolyte that constitutes the electrolyte complex together with the second inorganic solid electrolyte contains an ion-conducting polymer and an alkali metal salt.

[0062] <Ion-Conducting Polymers> As ion-conducting polymers included in the polymer solid electrolyte constituting the electrolyte complex, any polymer exhibiting high ion conductivity and high reduction resistance can be used without particular limitations. Examples of ion-conducting polymers include polyalkylene carbonate polymers, polyether polymers, poly(meth)acrylonitrile, and poly(meth)alkylate alkyls. Here, examples of polyalkylene carbonate polymers include polyethylene carbonate, polypropylene carbonate, poly(1,2-dimethylethylene carbonate), polybutene carbonate, polyisobutene carbonate, polypentene carbonate, polyhexene carbonate, polycyclopentene carbonate, polycyclohexene carbonate, polycycloheptene carbonate, polycyclooctene carbonate, and polylimonene carbonate. Furthermore, as polyether polymers, those in which ether bonds are linked in a linear chain are preferred, and those with hydroxyl groups, carboxyl groups, amino groups, etc., being crosslinked may also be used. Specifically, examples include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol dimethyl ester (PEGDME), polyethylene carbonate (PEC), and the like. Among these, from the viewpoint of further exhibiting the effects of the present invention, the ion-conducting polymer preferably contains a polyalkylene carbonate polymer, a polyether polymer, or poly(meth)acrylonitrile, more preferably a polyalkylene carbonate polymer or poly(meth)acrylonitrile, particularly preferably polyethylene carbonate or poly(meth)acrylonitrile, and most preferably poly(meth)acrylonitrile.

[0063] In this specification, the weight-average molecular weight (Mw) of the ion-conducting polymer is preferably 1,000 to 1,000,000, more preferably 2,000 to 800,000, even more preferably 3,000 to 700,000, particularly preferably 4,000 to 600,000, and most preferably 5,000 to 500,000. A value above these lower limits has the advantage of preventing the polymer compound from becoming too fluid, while a value below these upper limits has the advantage of preventing the polymer compound from becoming too rigid. The ion-conducting polymer may be used alone or in combination of two or more types. The weight-average molecular weight (Mw) of the ion-conducting polymer described here shall be the value obtained by gel permeation chromatography (GPC) under the following measurement conditions: GPC measurement conditions Measurement device: HLC-8320GPC (manufactured by Tosoh Corporation) Sample concentration: 0.01% by mass Column: TSKgel GMPWXL Detector: Differential refractometer Eluent: Solution of 10 mM lithium bromide dissolved in N,N-dimethylformamide Flow rate: 1 mL / min Measurement temperature: 40°C Molecular weight conversion: Polyethylene glycol equivalent Sample injection volume: 200 μL.

[0064] The content of the ion-conducting polymer in the electrolyte complex is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, even more preferably 50 to 70% by mass, and particularly preferably 55 to 65% by mass, based on 100% by mass of the total amount of the electrolyte complex.

[0065] <Alkali Metal Salts> As alkali metal salts to be included in the polymer solid electrolyte constituting the electrolyte complex, alkali metal salts conventionally known in the art can be used in the same way. Among them, from the viewpoint of being able to express the effects of the present invention more clearly, the alkali metal salt included in the polymer solid electrolyte is the following general formula (1): ((C ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N －(1) Preferably contains a fluorine-containing sulfonyliimide anion represented by (1) (wherein m and n are each independent integers from 0 to 4). Among such alkali metal salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI) is preferably used as the lithium salt, and LiTFSI is more preferably used. Here, by constructing a polymer solid electrolyte using an alkali metal salt containing a fluorine-containing sulfonyliimide anion represented by general formula (1), the effects of the present invention can be expressed more significantly compared to when other alkali metal salts are used. However, other lithium salts may of course be used, and other lithium salts include, for example, LiClO ４ LiBF ４ LiPF ６ LiAlCl ４ LiSbF ６ , LiSCN, LiCl, LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiB １０ Cl １０ Examples include LiCl, LiBr, and LiI. Furthermore, alkali metal salts containing alkali metals other than lithium (e.g., sodium, potassium, rubidium, etc.) as cations may be used. Note that only one alkali metal salt may be used, or two or more may be used in combination.

[0066] The alkali metal salt content in the electrolyte complex is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, even more preferably 30 to 50% by mass, and particularly preferably 35 to 45% by mass, based on 100% by mass of the total amount of the electrolyte complex.

[0067] The polymer solid electrolyte constituting the electrolyte complex is composed of SiO2, in order to further improve ionic conductivity. ２ , TiO ２ , ZrO ２Nanofillers of metal oxides such as the above may be included. However, it is preferable that the polymer solid electrolyte constituting the electrolyte complex mainly consists of an ion-conducting polymer and an alkali metal salt. Specifically, the ratio of the total mass of the ion-conducting polymer and the alkali metal salt to 100% by mass of the total amount of the polymer solid electrolyte constituting the electrolyte complex is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, even more preferably 98 to 100% by mass, particularly preferably 99 to 100% by mass, and most preferably 100% by mass.

[0068] There are no particular restrictions on the content of the electrolyte complex in a particular layer. However, from the viewpoint of more clearly exhibiting the effects of the present invention, the content of the electrolyte complex in a particular layer is preferably 10 to 50% by mass, more preferably 10 to 40% by mass, even more preferably 10 to 30% by mass, and particularly preferably 10 to 20% by mass, based on 100% by mass of the total of the first inorganic solid electrolyte and the electrolyte complex.

[0069] The content of the second inorganic solid electrolyte in a particular layer also varies greatly depending on whether the particular layer is an electrode active material layer (positive electrode active material layer or negative electrode active material layer) or a solid electrolyte layer, making it difficult to define uniquely. For example, when the particular layer is an electrode active material layer, the content of the second inorganic solid electrolyte in that particular layer is preferably 2 to 15% by mass, more preferably 4 to 12% by mass, and even more preferably 6 to 10% by mass, based on 100% by mass of the total amount of the particular layer (electrode active material layer). Furthermore, when the particular layer is a solid electrolyte layer, the content of the second inorganic solid electrolyte in that particular layer is preferably 5 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 5 to 20% by mass, based on 100% by mass of the total amount of the particular layer (solid electrolyte layer).

[0070] The secondary battery according to this embodiment, having the configuration described above, exhibits the remarkable effect of suppressing the increase in the internal resistance of the battery even when the confinement pressure of the battery is low. Although the mechanism by which this effect is achieved is not fully understood, the following mechanism is hypothesized. That is, if the solid electrolyte contained in a particular layer is only an inorganic solid electrolyte, the contact state between the components of that particular layer may deteriorate as the charging and discharging of the secondary battery progresses. Even if such a phenomenon occurs, if the confinement pressure applied in the stacking direction of the power generation elements constituting the secondary battery is large, the contact state between the components will not deteriorate significantly. On the other hand, if the above confinement pressure decreases, the contact state between the components deteriorates, and contact loss occurs (this phenomenon is particularly pronounced when the particular layer is an electrode active material layer). With the secondary battery according to this embodiment, even if the contact state between the components of a particular layer deteriorates when the confinement pressure of the secondary battery is low, the polymer solid electrolyte constituting the electrolyte composite acts to suppress the deterioration of the contact state. As a result, with the secondary battery according to this embodiment, it is possible to suppress the increase in internal resistance even when the confinement pressure of the secondary battery is low. It should be noted that the above mechanism is based on speculation, and the accuracy of this mechanism does not affect the technical scope of the present invention. Furthermore, for the reasons stated above, the specific layer is preferably an electrode active material layer (positive electrode active material layer or negative electrode active material layer) that expands and contracts significantly during battery charging and discharging, and is particularly preferably a positive electrode active material layer. In other words, it is preferable that the electrode active material layer (positive electrode active material layer or negative electrode active material layer) contains the electrolyte complex described above, and it is particularly preferable that the positive electrode active material layer contains the electrolyte complex.

[0071] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material, or different materials may be used.

[0072] [Positive and Negative Leads] Although not shown in the diagram, the current collectors (11', 11") and the current collector plates (25, 27) may be electrically connected via positive and negative leads. The materials used for the positive and negative leads may be the same as those used in known secondary batteries. It is preferable to cover the parts that are removed from the casing with heat-resistant insulating heat shrink tubing or the like to prevent leakage current from coming into contact with peripheral equipment or wiring and affecting the product (for example, automotive parts, especially electronic equipment).

[0073] [Battery casing material] As the battery casing material, known metal can cases can be used, or, as shown in Figure 1, a bag-shaped case made of aluminum-containing laminate film 29 that can cover the power generation elements can be used. For example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order can be used, but there are no limitations to these. Laminate film is preferable from the viewpoint of being able to increase output power and have excellent cooling performance, and can be suitably used for batteries in large equipment for EVs and HEVs. Furthermore, since the group pressure applied to the power generation elements from the outside can be easily adjusted, an aluminum-containing laminate film is more preferable for the casing.

[0074] The stacked secondary battery according to this embodiment has a configuration in which multiple single cell layers are connected in parallel, resulting in high capacity and excellent cycle durability. Therefore, the stacked secondary battery according to this embodiment is suitable for use as a power source for EVs and HEVs.

[0075] Although one embodiment of a secondary battery has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and can be modified as appropriate based on the description of the claims.

[0076] For example, one type of battery to which the secondary battery according to the present invention is applied is a bipolar battery, which includes a bipolar electrode having a positive electrode active material layer electrically coupled to one side of a current collector and a negative electrode active material layer electrically coupled to the opposite side of the current collector.

[0077] Furthermore, the secondary battery according to this embodiment does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte solution). There are no particular restrictions on the amount of liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolyte solution) does not occur. As the liquid electrolyte (electrolyte solution), a solution having the form of a conventionally known lithium salt dissolved in a conventionally known organic solvent is used. The liquid electrolyte (electrolyte solution) may further contain additives other than the organic solvent and lithium salt. These additives may be used individually or in combination of two or more. Also, the amount of additives used in the electrolyte can be adjusted as appropriate.

[0078] [Pressurizing Member] As described above, in the secondary battery according to this embodiment, a restraining pressure is applied to the stacking direction of the power generation elements by a pressurizing member. Figure 2 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. Figure 3 is a side view taken from direction A shown in Figure 2.

[0079] As shown in Figures 2 and 3, the stacked secondary battery 100 according to this embodiment includes a power generation element 21 sealed in a laminate film 29 as shown in Figure 1, two metal plates 200 that sandwich the power generation element 21 sealed in the laminate film 29, and a bolt 300 and a nut 400 as fastening members. These fastening members (bolt 300 and nut 400) have the function of fixing the metal plates 200 in a state where they are sandwiching the power generation element 21 sealed in the laminate film 29. As a result, the metal plates 200 and the fastening members (bolt 300 and nut 400) function as pressurizing members that pressurize (restrain) the power generation element 21 in its stacking direction. Note that the pressurizing members are not particularly limited as long as they are members that can pressurize the power generation element 21 in its stacking direction. Typically, a combination of a plate made of a rigid material such as the metal plate 200 and the fastening members described above is used as the pressurizing members. Furthermore, regarding the fastening members, not only bolts 300 and nuts 400 may be used, but also tension plates that fix the ends of the metal plates 200 so as to restrain the power generation element 21 in its stacking direction.

[0080] As described above, the effects of the present invention are particularly pronounced when the constraining pressure applied in the stacking direction of the power generation element 21 constituting the secondary battery is small. From this viewpoint, the load applied to the power generation element 21 (constraining pressure in the stacking direction of the power generation element) is preferably 10 MPa or less. That is, the secondary battery according to this embodiment is preferably operated with the positive electrode active material layer pressurized with a constraining pressure of 10 MPa or less in the stacking direction of the power generation element. The constraining pressure is more preferably 5 MPa or less, even more preferably 3 MPa or less, even more preferably 1 MPa or less, and particularly preferably 0.5 MPa or less. On the other hand, there is no particular limit to the lower limit of the constraining pressure, but it is preferably 0.11 MPa or more.

[0081] Furthermore, the following embodiments are also included in the scope of the present invention: a secondary battery according to claim 1 having the features of claim 2; a secondary battery according to claim 2 having the features of claim 3; a secondary battery according to any one of claims 1 to 3 having the features of claim 4; a secondary battery according to any one of claims 1 to 4 having the features of claim 5; a secondary battery according to claim 5 having the features of claim 6; a secondary battery according to claim 6 having the features of claim 7; a secondary battery according to claim 5 having the features of claim 8; a secondary battery according to any one of claims 1 to 8 having the features of claim 9; a secondary battery according to any one of claims 1 to 9 having the features of claim 10; a secondary battery according to any one of claims 1 to 10 having the features of claim 11.

[0082] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following examples, the instruments and devices used inside the glove box were thoroughly dried beforehand.

[0083] 《Preparation of Test Cells》 [Example 1] (Preparation of Electrolyte Composite) 0.36 g of polyacrylonitrile (PAN) (manufactured by Sigma Aldrich), an ion-conducting polymer, 0.24 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a lithium salt (manufactured by Kishida Chemical Co., Ltd.), and a second inorganic solid electrolyte, an argyrodite-type sulfide solid electrolyte (Li ６ PS ５ 2.4 g of Cl (average particle size (D50) = 0.2 μm) was weighed. These were added to 27.0 g of solvent (acetonitrile), and the mixture was stirred to obtain a dispersion. The obtained dispersion was dried at atmospheric pressure and 60°C, and then vacuum-dried at 45°C overnight to obtain an electrolyte composite in which the surface of the inorganic solid electrolyte particles was coated with a polymer solid electrolyte (containing an ion-conducting polymer and a lithium salt).

[0084] (Preparation of solid electrolyte mixture) The first inorganic solid electrolyte is an argyrodite-type sulfide solid electrolyte (Li ６ PS ５Cl (average particle size (D50) = 0.2 μm) and the electrolyte complex prepared above were weighed in a 50:50 mass ratio and mixed using an agate mortar to prepare a solid electrolyte mixture. The electrolyte complex accounted for 50% by mass of the total amount of the obtained solid electrolyte mixture.

[0085] (Fabrication of the positive electrode active material layer) The positive electrode active material is an NMC composite oxide (LiNi) ０．８ Mn ０．１ Co ０．１ O ２ A solid electrolyte mixture prepared above was prepared, along with carbon nanofiber (CNF) (manufactured by Resonaq Corporation, VGCF®, aspect ratio: 60, average fiber diameter: approximately 150 nm, average fiber length: approximately 9 μm), which is a fibrous conductive additive, and polytetrafluoroethylene (PTFE), which is a binder capable of fibrillation. In a glove box with an argon atmosphere and a dew point of -68°C or lower, predetermined amounts of the positive electrode active material, solid electrolyte mixture, and conductive additive prepared above were kneaded using an agate mortar to obtain a homogeneous mixture. Next, a predetermined amount of PTFE was added to the mixture and kneaded further using an agate mortar to obtain a solvent-free dry powder composition (mixture for positive electrode formation). The appearance of the mixture obtained in this way resembled udon noodle dough. The mixing ratio of each component in the mixture was 81.3:14.4:2.9:1.4 (mass ratio of positive electrode active material: solid electrolyte mixture: fibrous conductive additive: binder).

[0086] After confirming that the PTFE had fibrillated and become fibrous through kneading, the resulting powder composition (mixture for cathode formation) was supplied to the powder inlet set in a roll press machine. The powder composition was then rolled using the roll press machine to form it into a sheet.

[0087] Next, the sheet was punched out into a 19 mm square rectangular shape so that one pair of opposite sides was parallel to the direction of rolling by the roll press machine. After that, it was pressed using a cold isostatic press (CIP) to obtain the positive electrode active material layer.

[0088] (Preparation of the solid electrolyte layer) In a glove box with an argon atmosphere and a dew point of -68°C or lower, an inorganic solid electrolyte, an argyrodite-type sulfide solid electrolyte (Li ６ PS ５ An inorganic solid electrolyte slurry was prepared by mixing 95 parts by mass of chlorine (Cl) with a binder solution (5 parts by mass of styrene-butadiene rubber (SBR), which is the binder, dissolved in an appropriate amount of mesitylene, which is the solvent). The obtained inorganic solid electrolyte slurry was coated onto the surface of a stainless steel foil, which was used as a support, using an applicator and dried. After that, it was punched out into a 25 mm square rectangular shape and then pressed by cold isostatic pressing (CIP) to obtain a solid electrolyte layer with a thickness of 40 μm.

[0089] (Preparation of the negative electrode intermediate layer) Silver nanoparticles and carbon black nanoparticles were weighed in a mass ratio of 1:3 and mixed. Five parts by mass of the resulting mixture was added to a binder solution (0.5 parts by mass of styrene-butadiene rubber (SBR), which is the binder, dissolved in an appropriate amount of mesitylene, which is the solvent) and mixed to prepare a negative electrode intermediate layer slurry. The obtained negative electrode intermediate layer slurry was coated onto the surface of a stainless steel foil, which is to be used as the negative electrode current collector, using an applicator and dried. After that, it was punched out into a 21 mm square rectangular shape and then pressed using a cold isostatic press (CIP) to obtain a negative electrode intermediate layer with a thickness of 10 μm.

[0090] (Preparation of test cell) The positive electrode active material layer prepared above was placed on top of an aluminum foil (19 mm square rectangular shape), which served as the positive electrode current collector. Then, the solid electrolyte layer formed on the foil surface prepared above was placed on the exposed surface of the positive electrode active material layer, with the exposed surface of the solid electrolyte layer facing the positive electrode active material layer, and transferred by cold isotropic pressing (CIP), and the stainless steel foil support was peeled off. After that, the negative electrode intermediate layer formed on the stainless steel foil surface prepared above was placed on top, with the exposed surface of the negative electrode intermediate layer facing the solid electrolyte layer, and pressurized by cold isotropic pressing (CIP) to prepare the test cell of this embodiment (lithium deposition type all-solid-state lithium secondary battery).

[0091] [Example 2] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte (Li ６ PS５ The test cell for this embodiment (a lithium deposition type all-solid-state lithium secondary battery) was fabricated using the same method as in Example 1 described above, except that the mass ratio of Cl) to the electrolyte composite was changed to 60:40.

[0092] [Example 3] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte (Li ６ PS ５ The test cell for this embodiment (a lithium deposition type all-solid-state lithium secondary battery) was fabricated using the same method as in Example 1 described above, except that the mass ratio of Cl) to the electrolyte composite was changed to 80:20.

[0093] [Example 4] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte (Li ６ PS ５ Except for changing the mass ratio of Cl) to the electrolyte composite to 90:10, the test cell for this embodiment (a lithium deposition type all-solid-state lithium secondary battery) was fabricated using the same method as in Example 1 described above.

[0094] [Example 5] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte is Li ５．５ PS ４．５ Cl １．５ Except for the change made to the above-described Example 3, the test cell of this embodiment (lithium deposition type all-solid-state lithium secondary battery) was fabricated using the same method as in Example 3.

[0095] [Comparative Example 1] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte (Li ６ PS ５ The test cell for this comparative example (a lithium deposition type all-solid-state lithium secondary battery) was prepared using the same method as in Example 1 described above, except that the mass ratio of Cl) to the electrolyte complex was changed to 100:0 (i.e., the electrolyte complex was not used).

[0096] [Comparative Example 2] When preparing a solid electrolyte mixture, the first inorganic solid electrolyte (Li ６ PS ５The test cell for this comparative example (a lithium deposition type all-solid-state lithium secondary battery) was prepared using the same method as in Example 1 described above, except that the mass ratio of Cl) to the electrolyte composite was changed to 0:100 (i.e., the first inorganic solid electrolyte was not used).

[0097] 《Evaluation of Test Cells》 (Measurement of 1C Discharge Capacity) The test cells prepared in the above examples and comparative examples were subjected to charge-discharge tests using a charge-discharge test apparatus (Hokuto Denko Co., Ltd., HJ-SD8) in a constant temperature chamber set to 60°C. Specifically, the test cells were placed in the constant temperature chamber, and after the cell temperature stabilized, constant current constant voltage charging (upper limit voltage 4.3V) was performed at a current density equivalent to 1C, with a cutoff current of 0.01C. After a 30-minute rest period, constant current discharge was performed at the same current density until the cell voltage reached 3.0V. During this time, the above charge-discharge test was performed with the cell confinement pressure set to 0.5MPa. The results are shown in Table 1 below as relative values, with the discharge capacity value of Example 1 set to 100.

[0098] (Measurement of internal resistance increase rate) The internal resistance of the test cells prepared in the above examples and comparative examples was measured using the AC impedance method.

[0099] Specifically, an electrochemical measurement system (model 12608W) manufactured by Solartron was used to measure AC impedance under the conditions of a frequency range of 0.01 Hz to 1 MHz and a voltage amplitude of 10 mV. The internal resistance was then calculated from the arc trajectory that appeared in the Cole-Cole plot obtained from the AC impedance measurement. In this process, the internal resistance was calculated with the cell confinement pressure set to 0.5 MPa and 3.0 MPa, respectively. The percentage of the internal resistance value at a confinement pressure of 0.5 MPa relative to the internal resistance value at a confinement pressure of 3.0 MPa was then calculated as the internal resistance increase rate. The results are shown in Table 1 below.

[0100]

[0101] The results shown in Table 1 demonstrate that the all-solid-state lithium secondary batteries of Examples 1 to 5, which have a positive electrode active material layer with a predetermined configuration according to the present invention, can suppress an increase in internal resistance even when the battery's confinement pressure is low. Furthermore, the all-solid-state lithium secondary batteries according to the present invention also exhibit a high 1C discharge capacity.

[0102] 10a, 100 stacked secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layer, 21 power generation element, 25 negative electrode current collector plate, 27 positive electrode current collector plate, 29 laminate film. 200 metal plate, 300 bolt, 400 nut.

Claims

1. A secondary battery comprising a power generation element having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, wherein at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer contains a first inorganic solid electrolyte and an electrolyte composite of a polymer solid electrolyte containing an ion-conducting polymer and an alkali metal salt and a second inorganic solid electrolyte.

2. The secondary battery according to claim 1, wherein in the electrolyte complex, the polymer solid electrolyte is present on the surface of the particles of the second inorganic solid electrolyte.

3. The secondary battery according to claim 2, wherein in the electrolyte composite, the polymer solid electrolyte covers at least a portion of the surface of the particles of the second inorganic solid electrolyte.

4. The secondary battery according to claim 1, wherein the ion-conducting polymer comprises poly(meth)acrylonitrile.

5. At least one of the first inorganic solid electrolyte or the second inorganic solid electrolyte is Li ａ MZ ｂ Ha ｃ A secondary battery according to claim 1, comprising an argyrodite-type sulfide solid electrolyte represented by the compositional formula [wherein M is at least one element selected from the group consisting of Na, K, and elements existing as divalent to pentavalent cations in the crystal structure; Z is at least one element selected from the group consisting of elements existing as divalent anions in the crystal structure; Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and a, b, and c satisfy the relationships 5 ≤ ​​a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2, respectively].

6. The first inorganic solid electrolyte is Li ａ PS ｂ Ha ｃ The secondary battery according to claim 5, comprising an argyrodite-type sulfide solid electrolyte represented by the compositional formula [wherein Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and a, b, and c satisfy 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 0 < c ≤ 2, respectively].

7. The secondary battery according to claim 6, wherein a, b, and c satisfy 5 ≤ a ≤ 6, 4 ≤ b ≤ 5, and 0 < c ≤ 2, respectively.

8. The second inorganic solid electrolyte is Li ａ PS ｂ Ha ｃ [At this time, Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and a, b, and c satisfy 6 ≤ a ≤ 7, 5 ≤ b ≤ 6, and 0 < c ≤ 1, respectively]. The secondary battery according to claim 5, comprising an alditol-type sulfide solid electrolyte represented by the composition formula of 9. The secondary battery according to claim 1, wherein the content of the electrolyte complex in the layer containing the first inorganic solid electrolyte and the electrolyte complex is 10 to 50% by mass with respect to 100% by mass of the total of the first inorganic solid electrolyte and the electrolyte complex.

10. The secondary battery according to claim 1, wherein the positive electrode active material layer comprises the first inorganic solid electrolyte and the electrolyte composite.

11. The secondary battery according to any one of claims 1 to 10, wherein the power generation elements are operated under a constraining pressure of 10 MPa or less in the stacking direction.

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