secondary batteries

Abstract

The present invention is a secondary battery comprising a positive electrode active material layer (15) disposed on the surface of a positive electrode current collector (11"), a negative electrode active material layer (13) disposed on the surface of a negative electrode current collector (11'), and a solid electrolyte layer (17) interposed between the positive electrode active material layer (15) and the negative electrode active material layer (13), wherein: the positive electrode active material layer (15), the solid electrolyte layer (17), or the negative electrode active material layer (13) contains a phosphorus-containing solid electrolyte that includes elemental Li, elemental P, and elemental S; and the secondary battery is configured such that particles of the phosphorus-containing solid electrolyte are bonded to other phosphorus-containing solid electrolyte particles or the like via bonds including one or more selected from the group consisting of -P-O- bonds, -P-S- bonds, and -P-N- bonds, as a result of which the internal resistance of the battery can be reduced.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and there has been active development of non-aqueous electrolyte secondary batteries, such as secondary batteries for driving motors, which hold the key to putting these vehicles into practical use.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium-ion secondary batteries used in mobile phones, laptops, etc. Therefore, lithium secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently widely used liquid-based lithium-ion secondary batteries use flammable organic electrolytes, and these batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, research and development of all-solid-state batteries, such as all-solid-state lithium secondary batteries that use oxide- or sulfide-based solid electrolytes, has been actively pursued. Solid electrolytes are materials primarily composed of ionic conductors that allow ionic conduction in a solid state. Therefore, all-solid-state lithium secondary batteries, unlike conventional liquid-based lithium-ion secondary batteries, do not inherently encounter the various problems associated with flammable organic electrolytes. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density. All-solid-state lithium secondary batteries that use elemental sulfur (S) or sulfide-based materials as the positive electrode active material are promising candidates.

[0006] Incidentally, International Publication No. 2013 / 146916 discloses a technology for improving the high-temperature cycle durability of an all-solid-state secondary battery. Specifically, the publication discloses that in an electrode for an all-solid-state secondary battery, an electrode mixture layer containing a binder, an inorganic solid electrolyte containing sulfur atoms, and an electrode active material is bonded to a current collector via a conductive adhesive layer, the conductive adhesive layer contains a binder for the adhesive layer, which binder is made of conductive particles and a diene-based polymer having a predetermined iodine value and a predetermined diene-based monomer unit content, and the sulfur atoms contained in the inorganic solid electrolyte in the electrode mixture layer are crosslinked with the carbon-carbon double bonds of the diene-based polymer. Summary of the Invention

[0007] However, the inventors' investigations have revealed that even if the technology described in WO 2013 / 146916 is adopted, the internal resistance of the battery may increase in some cases. That is, in the technology disclosed in the publication, when elemental sulfur is used as the electrode active material contained in the electrode mixture layer, the elemental sulfur also participates in the crosslinking reaction. As a result, ionic conduction between sulfur and the solid electrolyte is inhibited, and the internal resistance of the battery increases.

[0008] Therefore, an object of the present invention is to provide a means for reducing the internal resistance of a secondary battery having a solid electrolyte layer.

[0009] According to one embodiment of the present invention, there is provided a secondary battery including a power generating element formed by laminating a positive electrode active material layer, which is disposed on the surface of a positive electrode current collector and contains a positive electrode active material and optionally a first conductive additive; a negative electrode active material layer, which is disposed on the surface of a negative electrode current collector and contains a negative electrode active material and optionally a second conductive additive; a solid electrolyte layer, which is interposed between the positive electrode active material layer and the negative electrode active material layer; and an optionally disposed negative electrode protective layer, which is interposed between the solid electrolyte layer and the negative electrode active material layer. The secondary battery is characterized in that the positive electrode active material layer, the solid electrolyte layer, or the negative electrode active material layer contains a phosphorus-containing solid electrolyte containing Li, P, and S elements, and particles of the phosphorus-containing solid electrolyte are connected to one or more particles selected from the group consisting of other particles of the phosphorus-containing solid electrolyte, the first conductive additive, the second conductive additive, the positive electrode current collector, the negative electrode current collector, the positive electrode active material, the negative electrode active material, and the negative electrode protective layer via bonds including one or more bonds selected from the group consisting of a -P-O- bond, a -PS- bond, and a -P-N- bond. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery, which is one embodiment of the secondary battery according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. [Figure 3] FIG. 3 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. [Figure 4] FIG. 4 is a side view seen from the direction A shown in FIG. [Figure 5] FIG. 5 is a solid-state 31P-NMR spectrum of the positive electrode active material layer of the evaluation cell produced in Comparative Example 1, which will be described later. [Figure 6] FIG. 6 is an enlarged view of the solid-state 31P-NMR spectrum shown in FIG. [Figure 7] FIG. 7 is a solid-state 31P-NMR spectrum of the positive electrode active material layer of the evaluation cell produced in Example 1, which will be described later. [Figure 8]FIG. 8 is an enlarged view of the solid-state 31P-NMR spectrum shown in FIG. [Figure 9] FIG. 9 is a solid-state 31P-NMR spectrum of the positive electrode active material layer of the evaluation cell produced in Example 2, which will be described later. [Figure 10] FIG. 10 is a 1H-NMR spectrum of ethanol. [Figure 11] FIG. 11 is a 1H-NMR spectrum of the positive electrode active material layer of the evaluation cell produced in Comparative Example 2, which will be described later. [Figure 12] FIG. 12 is a 1H-NMR spectrum of the positive electrode active material layer of the evaluation cell produced in Example 2 described below. DETAILED DESCRIPTION OF THE INVENTION

[0011] One aspect of the present invention provides a power generating element including a positive electrode active material layer disposed on the surface of a positive electrode current collector and containing a positive electrode active material and optionally a first conductive additive; a negative electrode active material layer disposed on the surface of a negative electrode current collector and containing a negative electrode active material and optionally a second conductive additive; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer; and an optionally disposed negative electrode protective layer interposed between the solid electrolyte layer and the negative electrode active material layer, wherein the positive electrode active material layer, the solid electrolyte layer, or the negative electrode protective layer is not included. The negative electrode active material layer contains a phosphorus-containing solid electrolyte containing Li, P, and S, and particles of the phosphorus-containing solid electrolyte are connected to one or more particles of the phosphorus-containing solid electrolyte, the first conductive additive, the second conductive additive, the positive electrode current collector, the negative electrode current collector, the positive electrode active material, the negative electrode active material, and the negative electrode protective layer via bonds including one or more bonds selected from the group consisting of a -P-O- bond, a -PS- bond, and a -P-N- bond. The secondary battery according to the present invention can reduce the internal resistance of the battery in a secondary battery having a solid electrolyte layer.

[0012] The above-mentioned embodiments will be described below with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited to the following embodiments. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0013] Fig. 1 is a perspective view showing the appearance of a flat-layered all-solid-state lithium secondary battery, which is one embodiment of the secondary battery according to the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 in Fig. 1. In this specification, the flat-layered non-bipolar lithium secondary battery shown in Figs. 1 and 2 (hereinafter also simply referred to as a "layered battery") will be described in detail as an example. However, the lithium secondary battery according to this embodiment may also be a bipolar (internal series connection type) battery.

[0014] 1, the stacked battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and positive electrode current collector 27 extending to the outside.

[0015] 2, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11". The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 faces the adjacent negative electrode active material layer 13 with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10a shown in FIG. 1 has a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0016] Negative electrode current collector 11′ and positive electrode current collector 11″ are respectively attached with negative electrode current collector (tab) 25 and positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and are structured so as to be sandwiched between the ends of laminate film 29, which is the battery outer casing material, and extended to the outside of laminate film 29. Positive electrode current collector 27 and negative electrode current collector 25 may be attached to positive electrode current collector 11″ and negative electrode current collector 11′ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via positive electrode leads and negative electrode leads (not shown) as necessary.

[0017] The main components of the lithium secondary battery according to this embodiment will be described below.

[0018] [Current collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0019] [Solid electrolyte layer] In the secondary battery according to this embodiment, the solid electrolyte layer is a layer interposed between the positive electrode active material layer and the negative electrode active material layer, and essentially contains a solid electrolyte. There are no particular restrictions on the specific form of the solid electrolyte contained in the solid electrolyte layer. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, but from the viewpoint of obtaining higher ionic conductivity, a sulfide solid electrolyte is preferred.

[0020] 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 Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). The term "LiS-P2S5" refers to a sulfide solid electrolyte obtained using a raw material composition containing LiS and P2S5, and the same applies to other terms.

[0021] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes known as LPS (for example, Li7P3S11 ) can be mentioned. Also, as the sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1), such as LGPS, may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing P element, and more preferably a material mainly composed of Li2S - P2S5. Furthermore, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I). Examples of the sulfide solid electrolyte containing halogen include argyrodite-type solid electrolytes (Li6PS5Cl and LiPS5Br), which are also preferably used materials.

[0022] Also, when the sulfide solid electrolyte is of the Li2S - P2S5 system, the ratio of Li2S and P2S5 is preferably within the range of Li2S:P2S5 = 50:50 to 100:0 in terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0023] Also, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by heat-treating a sulfide glass at a temperature above the crystallization temperature. Also, the ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is preferably, for example, 1×10 -5 S / cm or more, and more preferably 1×10 -4 S / cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by an alternating current impedance method.

[0024] The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably in the range of 10 to 100 mass %, more preferably in the range of 50 to 100 mass %, and even more preferably in the range of 90 to 100 mass %, relative to the total mass of the solid electrolyte layer. The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte.

[0025] The thickness of the solid electrolyte layer varies depending on the configuration of the intended 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 restriction 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.

[0026] [Negative electrode (negative electrode active material layer)] In the secondary battery according to this embodiment, the negative electrode active material layer 13 contains a negative electrode active material. The type of the negative electrode active material is not particularly limited, but examples thereof include a carbon material, a metal oxide, and a metal active material. The negative electrode active material preferably contains a carbon material, metallic lithium, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains a carbon material or metallic lithium.

[0027] The shape of the negative electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the negative electrode active material is particulate, its average particle size (D 50 ) is, for example, 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. In this specification, the average particle diameter (D 50 The value of can be measured by a laser diffraction scattering method.

[0028] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0029] The negative electrode active material layer preferably further contains a solid electrolyte. By including the solid electrolyte in the negative electrode active material layer, the ionic conductivity of the negative electrode active material layer can be improved. There are no particular restrictions on the specific form of the solid electrolyte contained in the negative electrode active material layer, and the exemplary and preferred forms described in the section on the solid electrolyte layer can be similarly adopted. The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60 mass %, more preferably in the range of 10 to 50 mass %.

[0030] In addition to the above-described negative electrode active material and solid electrolyte, the negative electrode active material layer may further contain at least one of a binder and a conductive additive (also referred to as a "second conductive additive" in this specification). The specific form of the binder that may be contained in the negative electrode active material layer is not particularly limited, and conventionally known knowledge may be referred to. Examples of conductive additives include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown 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, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), but are not limited thereto. These conductive additives may be used alone or in combination of two or more.

[0031] The thickness of the negative electrode active material layer varies depending on the intended configuration of the all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0032] [Negative electrode protective layer] In the secondary battery according to this embodiment, an anode protective layer may be provided between the solid electrolyte layer and the anode active material layer. This anode protective layer is a layer that suppresses a reaction between the anode active material layer and the solid electrolyte. Therefore, by providing the anode protective layer, it is possible to prevent degradation of the solid electrolyte and a decrease in battery capacity caused by a reaction between the anode active material layer and the solid electrolyte without impeding the progress of the battery reaction.

[0033] The material for the anode protective layer is not particularly limited, and various materials capable of exhibiting the above-mentioned functions can be used. One example of a material for the anode protective layer is nanoparticles with lithium ion conductivity. By including nanoparticles in the anode protective layer, a secondary battery with particularly excellent anode protective layer functionality can be provided. Here, "nanoparticles" refers to particles with an average particle diameter on the nanometer (nm) scale. The "average particle diameter" of nanoparticles refers to the 50% cumulative diameter (D50) of the particle diameter (the maximum distance between any two points on the outline of the observed particle) measured by observing the cross section of a layer containing the nanoparticles with a scanning electron microscope (SEM). The average particle diameter of the nanoparticles is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 150 nm or less, particularly preferably 100 nm or less, and most preferably 60 nm or less. In particular, when the average particle diameter of nanoparticles is 60 nm or less, a secondary battery with particularly excellent interlayer reaction suppression effect can be provided. There is no particular lower limit to the average particle size of the nanoparticles, but it is usually 10 nm or more, and preferably 20 nm or more.

[0034] From the viewpoint of particularly excellent function as an anode protective layer, such nanoparticles preferably contain one or more elements selected from the group consisting of carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, and more preferably contain one or more of these elements as simple substances or alloys. When the anode protective layer contains such nanoparticles, the layer may further contain a binder. There are no particular restrictions on the average thickness of the anode protective layer, as long as it is disposed at a thickness that allows the above-mentioned functions to be exhibited. However, if the average thickness of the anode protective layer is too large, it increases the internal resistance, thereby reducing charge / discharge efficiency. For this reason, the average thickness of the anode protective layer is preferably smaller than the average thickness of the solid electrolyte layer. Furthermore, if the average thickness of the anode protective layer is too small, the reaction suppression effect of providing the anode protective layer may not be fully achieved. From these viewpoints, the average thickness of the anode protective layer is preferably 300 nm to 20 μm, more preferably 500 nm to 15 μm, and even more preferably 1 to 10 μm.

[0035] [Cathode active material layer] In the secondary battery according to this embodiment, the positive electrode active material layer 15 contains a positive electrode active material. The specific form of the positive electrode active material is not particularly limited, and conventionally known knowledge may be referred to as appropriate. In particular, the positive electrode active material layer preferably contains a sulfur-containing positive electrode active material. The type of sulfur-containing positive electrode active material is not particularly limited, but examples include elemental sulfur (S), as well as particles or thin films of organic or inorganic sulfur compounds. Any material may be used as long as it utilizes the oxidation-reduction reaction of sulfur to release lithium ions during charging and absorb lithium ions during discharging. The positive electrode active material layer may also contain a sulfur-free positive electrode active material instead of or in addition to the sulfur-containing positive electrode active material. Examples of sulfur-free positive electrode active materials include layered rock salt active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li(Ni-Mn-Co)O2, LiMn2O4, LiNi 0.5 Mn 1.5Examples of oxide active materials include spinel-type active materials such as LiFePO4 and LiMnPO4, olivine-type active materials such as LiFeSiO4 and LiMnSiO4, and Si-containing active materials such as LiFeSiO4 and LiMnSiO4. 12 Examples include:

[0036] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle size (D 50 ) is, for example, 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. In this specification, the average particle diameter (D 50 The value of can be measured by a laser diffraction scattering method.

[0037] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %. The positive electrode active material layer also preferably further contains a solid electrolyte. There are no particular restrictions on the specific form of the solid electrolyte contained in the positive electrode active material layer, and the exemplary and preferred forms described in the section on the solid electrolyte layer may be similarly adopted. The content of the solid electrolyte in the positive electrode active material layer is preferably within the range of 1 to 60 mass %, and more preferably within the range of 10 to 50 mass %. The positive electrode active material layer may also further contain a conductive additive (also referred to as a "first conductive additive" in this specification) and / or a binder.

[0038] [Characteristics of secondary batteries] One feature of the secondary battery according to this embodiment is that the positive electrode active material layer, solid electrolyte layer, or negative electrode active material layer contains a phosphorus-containing solid electrolyte containing Li, P, and S. Another feature is that particles of the phosphorus-containing solid electrolyte are connected to one or more of the following: other particles of the phosphorus-containing solid electrolyte, a first conductive additive that may be included in the positive electrode active material layer, a second conductive additive that may be included in the negative electrode active material layer, a positive electrode current collector, a negative electrode current collector, a positive electrode active material, a negative electrode active material, and a negative electrode protective layer, via bonds including one or more selected from the group consisting of -PO-, -PS-, and -PN- bonds. This configuration effectively reduces the internal resistance of the secondary battery according to this embodiment. This is thought to be due to the presence of such bonds (bridge structures) that suppress peeling between the phosphorus-containing solid electrolyte particles and the members connecting them, and the flexible bonds (bridge structures) that alleviate stress caused by the expansion and contraction of the active material particles.

[0039] There is no particular limitation on the specific form of the phosphorus-containing solid electrolyte containing Li, P, and S elements. However, the phosphorus-containing solid electrolyte contains lithium ions (Li + ) and PS4 as an anion 3- , P2S7 4- or P2S6 3- It is preferable that the solid electrolyte contains the sulfide. Such a phosphorus-containing solid electrolyte can be, for example, the sulfide solid electrolyte described above as a material that can be contained in the solid electrolyte layer. By using such a phosphorus-containing solid electrolyte, it is easy to effectively proceed with the reaction for linking the phosphorus (P) contained in the electrolyte with other components.

[0040] During the development of secondary batteries using solid electrolytes, the inventors attempted to dissolve a phosphorus-containing solid electrolyte in ethanol and impregnate the electrode with the resulting solution. They discovered, by chance, that ethanol reacted with the phosphorus-containing solid electrolyte, substituting the PS bonds in the electrolyte with phosphate ester (PO-CH2-) bonds. Based on this discovery, they confirmed that adding a compound having multiple functional groups (such as the -OH groups of ethanol in the above example) capable of substituting the PS bonds in the electrolyte as an additive could link the electrolyte particles together, thereby achieving the above-described effects. As described above, in the secondary battery according to this embodiment, the phosphorus-containing solid electrolyte particles are connected to other components via bonds containing one or more bonds selected from the group consisting of -PO- bonds, -PS- bonds, and -PN- bonds. Of these, the -PO- bonds are formed by substituting the PS bonds in the phosphorus-containing solid electrolyte with -OH groups in the other components. Furthermore, the -PS- bonds are formed by substituting the PS bonds in the phosphorus-containing solid electrolyte with -SH groups in the other components. Furthermore, the -PN- bond is formed by substituting a PS bond contained in the phosphorus-containing solid electrolyte with an amino group (primary to tertiary amino group, preferably a primary amino group) contained in another component.

[0041] Here, depending on the type of other component connected to the particles of the phosphorus-containing solid electrolyte, various combinations are possible, such as (1) connection between particles of the phosphorus-containing solid electrolyte and other particles of the phosphorus-containing solid electrolyte; (2) connection between particles of the phosphorus-containing solid electrolyte and a first conductive additive or a second conductive additive; (3) connection between particles of the phosphorus-containing solid electrolyte and a positive electrode current collector or a negative electrode current collector; (4) connection between particles of the phosphorus-containing solid electrolyte and a positive electrode active material or a negative electrode active material; and (5) connection between particles of the phosphorus-containing solid electrolyte and a negative electrode protective layer. Among these, the form in which particles of the electrolyte are connected to each other by adding, as an additive, a compound having multiple functional groups capable of substituting the PS bond contained in the phosphorus-containing solid electrolyte, corresponds to the above-mentioned (1). In this embodiment, examples of the "compound having multiple functional groups capable of substituting PS bonds contained in the phosphorus-containing solid electrolyte" added as an additive include polyol compounds such as diols, triols, and tetraols; polythiol compounds such as dithiols, trithiols, and tetrathiols; and polyamine compounds such as diamines, triamines, and tetraamines. Among these, diols, triols, dithiols, trithiols, diamines, and triamines are preferred, and diols, dithiols, and diamines are more preferred. By using polyol compounds such as diols (HO-(divalent organic group)-OH), polythiol compounds such as dithiols (HS-(divalent organic group)-SH), or polyamine compounds such as diamines (e.g., HN-(divalent organic group)-NH) as additives, the PS bonds contained in the phosphorus-containing solid electrolyte are substituted by the -OH groups, -SH groups, or -NH groups contained in these additives. As a result, particles of the phosphorus-containing solid electrolyte are linked to other particles of other phosphorus-containing solid electrolytes via -PO-(divalent organic group)-OP- bonds, -PS-(divalent organic group)-SP- bonds, or -PN-(divalent organic group)-NP- bonds. Among these, the use of a polyol compound such as a diol as an additive is preferred, so that particles of the phosphorus-containing solid electrolyte are linked to other particles of other phosphorus-containing solid electrolytes via -PO-(divalent organic group)-OP- bonds. There are no particular limitations on the "divalent organic group" contained in the various additives described above, and conventionally known knowledge can be used as a reference.Examples of the "divalent organic group" include, for example, a divalent aliphatic hydrocarbon group, a divalent alicyclic hydrocarbon group, or a divalent aromatic hydrocarbon group, which may be substituted. By adopting such a configuration, it is possible to form the secondary battery according to this embodiment using readily available materials as additives while preventing the occurrence of side reactions other than the above-mentioned reactions.

[0042] Examples of the optionally substituted divalent aliphatic hydrocarbon group include an optionally substituted alkylene group. Examples of the optionally substituted divalent alicyclic hydrocarbon group include an optionally substituted cycloalkylene group. Examples of the optionally substituted divalent aromatic hydrocarbon group include an optionally substituted arylene group. Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, and a decylene group. The alkylene group may be substituted, and examples of such substituents include branched structures such as methyl groups and ethyl groups; alkenyl groups; alkynyl groups; aryl groups; heteroaromatic ring groups; alkoxy groups; arylthio groups; tri-substituted silyloxy groups; acyloxy groups; alkoxycarbonyl groups; arylsulfinyl groups; sulfonate ester groups; amino groups; hydroxy groups; cyano groups; nitro groups; and halogen atoms. Furthermore, like a polyoxyalkylene group, a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom may be present between the carbon atoms constituting the alkylene group. Examples of cycloalkylene groups include a cyclopropylene group, a cyclobutylene group, a cyclopentylene group, and a cyclohexylene group. These cycloalkylene groups may be substituted with the same substituents as those described above. Examples of arylene groups include a phenylene group, a naphthylene group, an anthrylene group, a phenanthrylene group, and a fluorenylene group. These arylene groups may be substituted with the same substituents as those described above. Among these, the above-mentioned "divalent organic group" is preferably an optionally substituted aliphatic hydrocarbon group, more preferably an optionally substituted alkylene group, and even more preferably a polyol residue derived from one or more polyols selected from the group consisting of ethanediol, n-butanediol, 1,2,4-n-butanetriol, (poly)ethylene glycol, polycaprolactone diol, and polyethylene-vinyl alcohol copolymer. The term "polyol residue derived from polyol" refers to a group in which two hydroxy groups contained in a polyol have been eliminated.

[0043] As described above, by including these additives together with the phosphorus-containing solid electrolyte, particles of the phosphorus-containing solid electrolyte are connected to other particles of other phosphorus-containing solid electrolytes through bonds corresponding to the structure of the additives. Here, there is no particular limitation on the amount of the additives added, but it is preferably 0.1 to 10 mass%, more preferably 0.3 to 5 mass%, and even more preferably 0.5 to 3 mass%, relative to 100 mass% of the content of the phosphorus-containing solid electrolyte in the layer containing the phosphorus-containing solid electrolyte.

[0044] The above has described in detail the above-mentioned type (1) (i.e., a form in which particles of the phosphorus-containing solid electrolyte are connected to each other using an additive). Here, in the above-mentioned type (2), for example, particles of a metal oxide or a carbon material having functional groups such as -OH groups on their surfaces are used as the first or second conductive additive, thereby achieving connection between the particles of the phosphorus-containing solid electrolyte and the first or second conductive additive. Furthermore, in the above-mentioned type (3), particles of the phosphorus-containing solid electrolyte and the positive or negative electrode current collector are achieved by using a metal foil having functional groups such as -OH groups on its surface as the positive or negative electrode current collector. Furthermore, in the above-mentioned type (4), particles of the phosphorus-containing solid electrolyte and the positive or negative electrode active material are achieved by using particles of a metal oxide or a carbon material having functional groups such as -OH groups on its surface as the positive or negative electrode active material. In the above-mentioned type (5), by using particles (preferably nanoparticles) of a metal oxide or a carbon material having a functional group such as an -OH group on the surface as a constituent material of the anode protective layer, it is possible to achieve connection between the particles of the phosphorus-containing solid electrolyte and the anode protective layer.

[0045] In the secondary battery according to the present embodiment, when the particles of the phosphorus-containing solid electrolyte are connected to other members via a -PO- bond, the portion where the particles of the phosphorus-containing solid electrolyte are connected is called a solid 31 When observed by P-NMR, a peak at 70 to 80 ppm originating from a phosphate ester bond (-PO- bond) is observed.1 When observed by H-NMR, it is preferable that a peak at 1 to 2 ppm derived from a methyl group in the alkyl group is not observed, because the presence of this peak means that although the PS bond contained in the phosphorus-containing solid electrolyte is substituted with a -PO- bond, the end of this bond is not connected to any other component, in other words, the presence of the -PO- bond does not contribute to the development of the above-mentioned action and effect.

[0046] Although one embodiment of the secondary battery has been described above, the present invention is not limited to the configuration described in the above embodiment and can be modified as appropriate based on the claims. For example, the secondary battery according to the present invention does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular restriction on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount be such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur.

[0047] The secondary battery according to one embodiment of the present invention described above is preferably in a state where the power generating element is pressurized in the stacking direction during operation. Therefore, the secondary battery according to one embodiment of the present invention preferably further includes a pressure member that presses the power generating element in the stacking direction. FIG. 3 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. FIG. 4 is a side view from direction A shown in FIG. 3. As shown in FIGS. 3 and 4, the stacked secondary battery 100 according to this embodiment includes the power generating element 21 sealed in the laminate film 29 shown in FIG. 1, two metal plates 200 that sandwich the power generating element 21 sealed in the laminate film 29, and bolts 300 and nuts 400 as fastening members. The fastening members (bolts 300 and nuts 400) function to secure the power generating element 21 sealed in the laminate film 29 while sandwiching it between the metal plates 200. Thus, the metal plates 200 and the fastening members (bolts 300 and nuts 400) function as pressure members that pressurize (restrain) the power generating element 21 in the stacking direction. The pressure member is not particularly limited as long as it is a member that can apply pressure to the power generating element 21 in the stacking direction. A typical pressure member is a combination of a plate made of a rigid material, such as the metal plate 200, and the fastening member described above. The fastening member is not limited to the bolts 300 and nuts 400, and may also be a tension plate that fixes the end of the metal plate 200 so as to restrain the power generating element 21 in the stacking direction.

[0048] The lower limit of the load applied to the power generating element 21 (restraint pressure in the stacking direction of the power generating element) is, for example, 0.1 MPa or more, preferably 1 MPa or more, more preferably 3 MPa or more, and even more preferably 5 MPa or more. The upper limit of the restraint pressure in the stacking direction of the power generating element is, for example, 100 MPa or less, preferably 70 MPa or less, more preferably 40 MPa or less, and even more preferably 10 MPa or less. [Example]

[0049] 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. The following operations were carried out in an argon glove box (23°C, moisture content of 0.1 ppm or less, oxygen concentration of 10 ppm or less) with a dew point of -70°C or less.

[0050] Example of preparing an evaluation cell: Effect of adding additives to the positive electrode active material layer [Comparative Example 1] First, 50 parts by mass of sulfur as a positive electrode active material, 30 parts by mass of acetylene black (AB) as a conductive additive, and LPSCl (Li6PS5Cl; Li as a cation) as an argyrodite-type sulfide solid electrolyte were mixed. + Contains PS4 as an anion 3- The mixture was weighed and mixed in an agate mortar, and then further mixed and stirred using a planetary ball mill. 2% by mass of styrene-butadiene rubber (SBR) was added to 100% by mass of the resulting mixed powder, and xylene was added as a solvent to prepare a positive electrode active material slurry. This positive electrode active material slurry was coated on the surface of aluminum foil, which serves as a positive electrode current collector, and dried to form a positive electrode active material layer.

[0051] Next, the same LPSCl and SBR as above were mixed in a mass ratio of 98:2, and xylene was added as a solvent to prepare a solid electrolyte slurry. This solid electrolyte slurry was applied to the exposed surface of the positive electrode active material layer prepared above and dried to prepare a solid electrolyte layer.

[0052] The laminate obtained above was cut out so that the coating size of the positive electrode active material layer was 2.5 cm long x 2.0 cm wide. Next, a negative electrode consisting of a lithium-indium metal foil of the same dimensions and a nickel foil as a negative electrode current collector was laminated onto the cut-out laminate, and a predetermined pressure was applied to compress the negative electrode. The lamination was performed so that the solid electrolyte layer and the Li foil were in contact with each other. Then, aluminum and nickel tab leads were welded to the aluminum foil and the nickel foil, respectively. The resulting assembly was sandwiched between aluminum laminate films and sealed to prepare an evaluation cell.

[0053] Comparative Example 2 In preparing the positive electrode active material slurry, 50 parts by mass of sulfur as the positive electrode active material, 29 parts by mass of acetylene black as the conductive additive, and LPSCl (Li7P3S 11 20 parts by mass of the above-mentioned ethanol was weighed and mixed in an agate mortar, and then 1 part by mass of the above-mentioned ethanol was further added as an additive and mixed in the agate mortar. An evaluation cell was produced in the same manner as in Comparative Example 1, except that the mixture was mixed and stirred using a planetary ball mill.

[0054] [Example 1] In preparing the positive electrode active material slurry, 50 parts by mass of sulfur as a positive electrode active material, 29.9 parts by mass of acetylene black as a conductive additive, and LPSCl (Li7P3S 11 20 parts by mass of the above-mentioned ethanol and 20 parts by mass of ethanol were weighed and mixed in an agate mortar, and then 0.1 parts by mass of 1,2-ethanediol was further added as an additive and mixed in the agate mortar. An evaluation cell was produced in the same manner as in Comparative Example 1, except that the mixture was mixed and stirred using a planetary ball mill.

[0055] [Example 2] An evaluation cell was produced in the same manner as in Example 1 above, except that the amounts of acetylene black and ethanediol used were changed to 29 parts by mass and 1 part by mass, respectively.

[0056] [Example 3] An evaluation cell was produced in the same manner as in Example 2 above, except that 1,4-butanediol was used instead of ethanediol.

[0057] [Example 4] An evaluation cell was produced in the same manner as in Example 2 above, except that 1,2,4-butanetriol was used instead of ethanediol.

[0058] [Example 5] An evaluation cell was produced in the same manner as in Example 2 above, except that polyethylene glycol having a molecular weight of 400 was used instead of ethanediol.

[0059] [Example 6] An evaluation cell was produced in the same manner as in Example 2 above, except that polycaprolactone diol having a molecular weight of 530 was used instead of ethanediol.

[0060] [Example 7] An evaluation cell was produced in the same manner as in Example 2 above, except that a polyethylene-vinyl alcohol copolymer having a weight average molecular weight (Mw) of 100,000 was used instead of ethanediol.

[0061] <<Measurement of internal resistance of evaluation cell after charge / discharge treatment>> The internal resistance of the evaluation cells prepared in the above comparative examples and examples was measured after charge and discharge. Specifically, each evaluation cell was sandwiched between two 5 mm thick SUS plates and clamped with a clamping pressure of 1000 kgf / cm. 2The cells were pressurized using a flat press with a hydraulic jack to achieve a constant current of 0.05 C. After one hour of pressurization, the cells were placed in a thermostatic chamber set at 25°C and connected to a charge / discharge device for a charge / discharge test. The charge / discharge capacity was measured. The discharge process consisted of applying a current equivalent to 0.05 C and constant-current, constant-voltage discharge with a lower limit of 0.6 V. This discharge process was continued until the current reached 0.01 C or 40 hours had elapsed since the start of discharge. After discharge, the cells were left for one hour before charging. During the charge process, a current equivalent to 0.05 C was applied until the upper limit voltage reached 2.5 V. After reaching the voltage, the cells were charged until the current reached 0.01 C or 40 hours had elapsed since the start of charge, and then left for one hour. After three discharge-charge cycles, the charged cells were discharged at a constant current to achieve a SOC of 50% and then left for one hour. Thereafter, the amount of voltage drop when a discharge current equivalent to 0.05 C was passed for 10 seconds was measured, and the internal resistance of the battery was calculated from the current value and the amount of voltage drop at that time. The results are shown in Table 1 below. The internal resistance values ​​shown in Table 1 are relative values ​​when the internal resistance value of Comparative Example 1 is set to 100. Table 1 also shows the composition of the positive electrode active material layer, but the composition shown in Table 1 does not include the amount of SBR, which serves as a binder.

[0062] <NMR measurement of the positive electrode active material layer> The evaluation cells prepared in Comparative Example 1, Example 1, and Example 2 were disassembled, and the positive electrode active material layer was taken out. 31 P-NMR measurement and 1 The solid state of the positive electrode active material layer of Comparative Example 1 was measured by H-NMR. 31 The P-NMR spectrum and its enlarged view are shown in Figures 5 and 6, respectively. 31 The P-NMR spectrum and its enlarged view are shown in Figures 7 and 8, respectively. 31 The P-NMR spectrum is shown in Figure 9. 1 The H-NMR spectra of the positive electrode active material layers of Comparative Example 2 and Example 2 are shown in FIG. 1The H-NMR spectra are shown in Figures 11 and 12, respectively.

[0063] (solid 31 P-NMR measurement) The positive electrode active material layer was lightly crushed into powder and sealed in a solid-state NMR sample tube in a glove box under an argon atmosphere. 31 P-NMR spectra were measured. In this case, an 85% by mass aqueous solution of phosphoric acid (0 ppm) was used as a chemical shift standard. The measurement equipment was an Agilent NMR System 400WB. 31 P MAS NMR spectrum measurement was performed under the following measurement conditions: observation frequency 162.13 MHz, MAS spinning speed 14 kHz, pulse width 2 microseconds, waiting time between pulses 190 seconds, and number of accumulations 32.

[0064] ( 1 H-NMR measurement) The positive electrode active material layer was lightly crushed into powder and sealed in an NMR measurement tube in a glove box under an argon atmosphere. 1 H-NMR spectrum was measured. In this case, TSP (sodium [2,2,3,3-D]3-3-(trimethylsilyl)propanoate) (0 ppm) was used as a chemical shift standard. The measurement equipment was a Bruker AVANCE III 600. 1 H NMR spectrum measurement was carried out under the following measurement conditions: observation frequency: 600.13 MHz, number of accumulations: 4.

[0065] [Table 1]

[0066] The results shown in Table 1 show that in Examples 1 to 7, in which a polyol was added as an additive to the positive electrode active material layer, the internal resistance value of the battery was significantly reduced compared to Comparative Example 1, in which no additive was added, and Comparative Example 2, in which a monool (ethanol) was added as an additive.

[0067] Here, as shown in FIGS. 7 to 9, the solid state of the positive electrode active material layers of Examples 1 and 2 31 In the P-NMR spectrum, a peak at 70 to 80 ppm derived from a phosphate ester bond (-PO- bond) was observed. On the other hand, as shown in FIGS. 5 and 6, the solid-state image of the positive electrode active material layer of Comparative Example 1 31 In the P-NMR spectrum, no peaks at 70 to 80 ppm due to phosphate ester bonds (—PO— bonds) were observed. 1 In the H-NMR spectrum, ethanol (Figure 10) 1 The peak at 1 to 2 ppm due to the methyl group in the alkyl group, as observed in the H-NMR spectrum, was not observed. On the other hand, as shown in FIG. 1 In the 1 H-NMR spectrum, this peak at 1 to 2 ppm was observed.

[0068] From these findings, in Examples 1 and 2 to 7, by adding a polyol as an additive to the positive electrode active material layer, it was found that the PS4 3- It is believed that the PS bonds of the anions are replaced by the hydroxyl groups of the polyol, resulting in the solid electrolyte particles being cross-linked via the polyol residues.The formation of such a cross-linked structure is believed to prevent peeling between the solid electrolyte particles and to alleviate the stress caused by the expansion and contraction of the active material particles, thereby preventing an increase in the internal resistance of the battery.

[0069] Example of preparing an evaluation cell: Effect of adding additives to the solid electrolyte layer [Example 8] In preparing the solid electrolyte slurry, LPSCl and 1,2-ethanediol were mixed at a mass ratio of 99:1, and 2 mass% of SBR was added to 100 mass% of the resulting mixed powder, followed by the addition of xylene as a solvent to prepare the solid electrolyte slurry. A test cell was fabricated in the same manner as in Comparative Example 1, except that the solid electrolyte layer was fabricated using this solid electrolyte slurry.

[0070] [Example 9] In preparing the solid electrolyte slurry, LPSCl and 1,2-ethanediol were mixed at a mass ratio of 99:1, and 2 mass% of SBR was added to 100 mass% of the resulting mixed powder, followed by the addition of xylene as a solvent to prepare the solid electrolyte slurry. A test cell was fabricated in the same manner as in Example 2, except that the solid electrolyte layer was fabricated using this solid electrolyte slurry.

[0071] [Example 10] An evaluation cell was produced in the same manner as in Example 8 above, except that 1,4-butanediol was used instead of ethanediol.

[0072] <<Measurement of internal resistance of evaluation cell after charge / discharge treatment>> The internal resistance of the evaluation cells prepared in Examples 8 to 10 was measured after charge-discharge treatment using the same method as above. The results are shown in Table 2 below. Table 2 also shows the results of Comparative Example 1 and Example 2, and the internal resistance values ​​shown in Table 2 are relative values ​​when the internal resistance value of Comparative Example 1 is set to 100. Table 2 also shows the compositions of the positive electrode active material layer and the solid electrolyte layer, but the composition shown in Table 2 does not include the amount of SBR, which serves as a binder.

[0073] [Table 2]

[0074] The results shown in Table 2 show that even when a polyol is added as an additive to the solid electrolyte layer instead of the positive electrode active material layer, an increase in the internal resistance of the battery can be similarly prevented (Examples 8 and 10). It is also shown that adding a polyol as an additive to the solid electrolyte layer in addition to the positive electrode active material layer can further reduce the internal resistance of the battery (Example 9).

[0075] Example of preparing an evaluation cell: Effect of adding additives to the negative electrode active material layer Comparative Example 3 First, the positive electrode active material, lithium-transition metal composite oxide (LiNi 0.5 Mn 0.3 Co 0.2 O2) (NMC) 80 parts by mass, and an argyrodite-type sulfide solid electrolyte, LPSCl (Li6PS5Cl; Li as cation) + Contains PS4 as an anion 3- 15 parts by mass of the powder mixture (containing 15 parts by mass of ethylene black, a conductive additive) and 5 parts by mass of acetylene black were weighed and mixed in a defoaming kneader. 2% by mass of styrene-butadiene rubber (SBR) was added to 100% by mass of the resulting mixed powder, and xylene was added as a solvent to prepare a positive electrode active material slurry. This positive electrode active material slurry was applied to the surface of aluminum foil, which serves as a positive electrode current collector, and dried to form a positive electrode active material layer.

[0076] Next, the same LPSCl and SBR were mixed in a mass ratio of 98:2, and xylene was added as a solvent to prepare a solid electrolyte slurry. This solid electrolyte slurry was applied to the exposed surface of the cathode active material layer prepared above and dried to prepare a solid electrolyte layer. The resulting laminate was cut to a size of 2.5 cm long x 2.0 cm wide for the cathode active material layer.

[0077] Separately, 80 parts by weight of graphite (negative electrode active material) and 20 parts by weight of the same LPSCl were weighed and mixed in a degassing kneader. 2% by weight of SBR was added to 100% by weight of the resulting mixed powder, and xylene was added as a solvent to prepare a negative electrode active material slurry. This negative electrode active material slurry was applied to a stainless steel (SUS304) foil (negative electrode current collector) and dried to form a negative electrode active material layer.

[0078] Next, a laminate of the negative electrode active material layer / negative electrode current collector cut to the same dimensions was attached to the exposed surface of the solid electrolyte layer prepared above, and a predetermined pressure was applied to compress the laminate. The attachment was performed so that the solid electrolyte layer, the negative electrode active material layer, and the foil were in contact with each other. Aluminum and nickel tab leads were then welded to the aluminum foil and the stainless steel foil, respectively. The resulting assembly was sandwiched between aluminum laminate films and sealed to prepare an evaluation cell.

[0079] [Example 11] To prepare the negative electrode active material slurry, 80 parts by mass of graphite (the negative electrode active material) and 19 parts by mass of the same LPSCl as above were weighed and mixed in a degassing kneader, and then 1 part by mass of 1,2-ethanediol was added as an additive. 2% by mass of SBR was added to 100% by mass of the resulting mixed powder, and xylene was added as a solvent to prepare a negative electrode active material slurry. An evaluation cell was fabricated in the same manner as in Comparative Example 3, except that the negative electrode active material layer was formed using this negative electrode active material slurry.

[0080] [Example 12] In preparing the positive electrode active material slurry, the positive electrode active material, lithium-transition metal composite oxide (LiNi 0.5 Mn 0.3 Co 0.2 O2) 80 parts by mass, and an argyrodite-type sulfide solid electrolyte, LPSCl (Li6PS5Cl; Li as cation) + Contains PS4 as an anion 3-14 parts by mass of a powder containing acetylene black (containing 14 parts by mass of a conductive additive) and 5 parts by mass of acetylene black were weighed and mixed in a defoaming kneader, and then 1 part by mass of 1,2-ethanediol was added as an additive and mixed. 2% by mass of styrene-butadiene rubber (SBR) was added to 100% by mass of the resulting mixed powder, and xylene was added as a solvent to prepare a positive electrode active material slurry. An evaluation cell was fabricated in the same manner as in Example 11 described above, except that the positive electrode active material layer was formed using this positive electrode active material slurry.

[0081] <<Measurement of internal resistance of evaluation cell after charge / discharge treatment>> The internal resistance of the evaluation cells prepared in Comparative Example 3 and Examples 11 and 12 was measured after charge-discharge treatment using the same method as above. The results are shown in Table 3 below. The internal resistance values ​​shown in Table 3 are relative values ​​when the internal resistance value of Comparative Example 3 is set to 100. Table 3 also shows the compositions of the positive electrode active material layer and the negative electrode active material layer, but the compositions shown in Table 3 do not include the amount of SBR, which serves as a binder.

[0082] [Table 3]

[0083] The results shown in Table 3 show that even in an all-solid-state lithium secondary battery using a lithium-transition metal composite oxide as the positive electrode active material and graphite as the negative electrode active material, if a polyol is added as an additive to the negative electrode active material layer (and further to the positive electrode active material layer) together with the solid electrolyte, an increase in the internal resistance of the battery can be similarly prevented. [Explanation of symbols]

[0084] 10a, 100 stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film, 200 metal plate, 300 volts, 400 Nuts.

Claims

1. a positive electrode active material layer disposed on a surface of a positive electrode current collector and containing a positive electrode active material and optionally a first conductive additive; a negative electrode active material layer disposed on a surface of the negative electrode current collector, the negative electrode active material layer containing a negative electrode active material and optionally a second conductive assistant; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer; an anode protective layer optionally disposed between the solid electrolyte layer and the anode active material layer; a power generating element formed by stacking the a secondary battery in which the positive electrode active material layer, the solid electrolyte layer, or the negative electrode active material layer contains a phosphorus-containing solid electrolyte containing Li, P, and S elements, particles of the phosphorus-containing solid electrolyte are connected to other particles of the phosphorus-containing solid electrolyte via a -P-O-(divalent organic group)-O-P- bond, and the divalent organic group in the -P-O-(divalent organic group)-O-P- bond contains a polyol residue derived from one or more polyols selected from the group consisting of ethanediol, n-butanediol, 1,2,4-n-butanetriol, polycaprolactone diol, and polyethylene-vinyl alcohol copolymer.

2. The phosphorus-containing solid electrolyte contains lithium ions (Li ＋ ) as an anion, and ４ ３－ , P ２ S ７ ４－ or P ２ S ６ ３－ The secondary battery according to claim 1 , comprising:

3. The part where the particles of the phosphorus-containing solid electrolyte are connected is called a solid ３１ When observed by P-NMR, a peak at 70 to 80 ppm due to a phosphate ester bond (-P-O- bond) was observed, and １ 3. The secondary battery according to claim 1, wherein, when observed by H-NMR, a peak at 1 to 2 ppm derived from a methyl group in the alkyl group is not observed.

4. The secondary battery according to any one of claims 1 to 3, which is an all-solid-state lithium secondary battery.

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