All-solid-state batteries

Abstract

To provide means enabling an increase in resistance of an all-solid battery to be further suppressed.SOLUTION: An all-solid battery is provided, comprising: a power generation element having a positive electrode in which a positive electrode active material layer including a sulfur-including positive electrode active material and a sulfide solid electrolyte is disposed on the surface of a positive electrode current collector, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a restraining member which restrains the power generation element in the stacking direction, wherein at least a part of the surface of a conductive aid is coated with a coating layer including an iodine compound, and the positive electrode active material layer includes a coating conductive additive having a thickness of the coating layer of 150 nm or more and less than 400 nm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state 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 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 lithium secondary batteries use flammable organic electrolytes, and these liquid-based lithium secondary batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, research and development on all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials primarily composed of ionic conductors capable of ion conduction in a solid state. Therefore, all-solid-state lithium secondary batteries, in principle, do not encounter the various problems associated with flammable organic electrolytes that are common in conventional liquid-based lithium secondary batteries. 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, which use sulfide-based materials as the positive electrode active material and metallic lithium or lithium-containing alloys as the negative electrode active material, are promising candidates.

[0006] In all-solid-state lithium secondary batteries, the positive electrode active material layer contains a conductive additive and a solid electrolyte in addition to the positive electrode active material in order to ensure electronic conductivity and ionic conductivity. However, it is known that when charge and discharge are performed while the conductive additive and the solid electrolyte are in contact with each other, the solid electrolyte decomposes to produce a highly resistive (highly insulating) substance, which increases the resistance of the positive electrode mixture.

[0007] For the purpose of preventing the above-described increase in resistance of the positive electrode mixture, Patent Document 1 discloses a technology in which a coating layer of LiF having a thickness of 5 nm or less is provided on the conductive additive in a positive electrode mixture for an all-solid-state battery containing a positive electrode active material, a solid electrolyte, and a conductive additive. According to the disclosure of Patent Document 1, the conductive additive having such a configuration supplies electrons to the positive electrode active material by the tunneling effect while not supplying electrons to the solid electrolyte, thereby suppressing the reaction between the conductive additive and the solid electrolyte and suppressing the increase in resistance of the positive electrode mixture. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-194955 Summary of the Invention [Problem to be solved by the invention]

[0009] In an all-solid-state battery, a restraining pressure can be applied in the stacking direction of the battery for reasons such as maintaining contact between the layers.

[0010] However, when the present inventors applied a confining pressure to an all-solid-state battery using the positive electrode mixture described in Patent Document 1, they found that an increase in the resistance of the cell could not be sufficiently suppressed in some cases.

[0011] Therefore, an object of the present invention is to provide a means capable of suppressing an increase in resistance of an all-solid-state battery. [Means for solving the problem]

[0012] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by coating the surface of a conductive additive with a coating layer of a specific thickness containing an iodine compound, thereby completing the present invention.

[0013] That is, an all-solid-state battery according to one embodiment of the present invention includes: a coated conductive additive in which at least a portion of the surface of the conductive additive is coated with a coating layer containing an iodine compound, the coating layer having a thickness of 150 nm or more and less than 400 nm; a positive electrode in which a positive electrode active material layer containing a sulfur-containing positive electrode active material and a sulfide solid electrolyte is disposed on the surface of a positive electrode current collector; a negative electrode; and a power generating element having a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a restraining member that restrains the power generating element in the stacking direction. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an all-solid-state battery in which an increase in resistance is suppressed. [Brief explanation of the drawings]

[0015] [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 all-solid-state 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 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. DETAILED DESCRIPTION OF THE INVENTION

[0016] One embodiment of the present invention is an all-solid-state battery comprising: a coated conductive additive in which at least a portion of the surface of the conductive additive is coated with a coating layer containing an iodine compound, the coating layer having a thickness of 150 nm or more and less than 400 nm; a positive electrode in which a positive electrode active material layer containing a sulfur-containing positive electrode active material and a sulfide solid electrolyte is disposed on the surface of a positive electrode current collector; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a restraining member that restrains the power generating element in the stacking direction.

[0017] Hereinafter, embodiments of the all-solid-state battery according to the present embodiment will be described with reference to the drawings. However, the technical scope of the present invention should be defined based on the description of the claims and is not limited to only the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0018] 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 all-solid-state battery according to the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar all-solid-state 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, in terms of the internal electrical connection configuration (electrode structure) of the all-solid-state lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0019] 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.

[0020] The all-solid-state lithium secondary battery according to this embodiment is not limited to a laminated, flat shape. A wound-type all-solid-state lithium secondary battery may be cylindrical, or may be a cylindrical battery modified into a rectangular, flat shape, and is not particularly limited. The cylindrical battery may use a laminate film or a conventional cylindrical can (metal can) as its exterior material, and is not particularly limited. Preferably, the power generating element is housed inside a laminate film containing aluminum. This configuration can achieve weight reduction.

[0021] Furthermore, there are no particular limitations on how the current collectors (25, 27) shown in Fig. 1 are taken out. The negative current collector 25 and the positive current collector 27 may be taken out from the same side, or the negative current collector 25 and the positive current collector 27 may each be divided into a plurality of pieces and taken out from each side, and so on, and are not limited to what is shown in Fig. 1. Furthermore, in a wound-type all-solid-state lithium secondary battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of tabs.

[0022] 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 an adjacent negative electrode active material layer 13 with a 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, the stacked battery 10a shown in FIG. 2 can also be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. Furthermore, a restraining pressure is applied to the stacked battery 10a in the stacking direction of the power generating element 21 by a restraining member (pressure member) (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0023] As shown in FIG. 2, the outermost positive electrode current collectors located on both outermost layers of the power generating element 21 each have a positive electrode active material layer 15 disposed on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector exclusively for the outermost layer with an active material layer provided on only one side, a current collector having active material layers on both sides may be used as the outermost current collector. In some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and the positive electrode, respectively, without using the current collectors (11', 11")

[0024] 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.

[0025] Fig. 3 is a perspective view of a stacked battery according to one embodiment of the present invention, and Fig. 4 is a side view seen from direction A shown in Fig. 3.

[0026] As shown in FIGS. 3 and 4 , the stacked battery 100 according to this embodiment includes a power generating element 21 sealed in a laminate film 29 as shown in FIGS. 1 and 2 , two metal plates 200 sandwiching 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 in a sandwiched state between the metal plates 200. As a result, the metal plates 200 and the fastening members (bolts 300 and nuts 400) function as restraining members that restrain (apply pressure to) the power generating element 21 in the stacking direction. Note that the restraining members are not particularly limited as long as they are members that can restrain the power generating element 21 in the stacking direction. A typical restraining member is a combination of a plate made of a rigid material, such as the metal plate 200, and the fastening members described above. Furthermore, the fastening members are not limited to the bolts 300 and nuts 400, and may include tension plates or the like that fix the ends of the metal plates 200 so as to restrain the power generating element 21 in the stacking direction.

[0027] 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, 150 MPa or less, preferably 100 MPa or less, more preferably 70 MPa or less, even more preferably 40 MPa or less, and particularly preferably 10 MPa or less.

[0028] The main components of the stacked battery according to this embodiment will be described below.

[0029] [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.

[0030] Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. Other examples include clad materials of nickel and aluminum, and clad materials of copper and aluminum. Furthermore, foils in which aluminum is coated on a metal surface may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector by sputtering.

[0031] Furthermore, examples of the resin having electrical conductivity include resins in which a conductive filler is added to a non-conductive polymer material.

[0032] The current collector may have a single layer structure made of a single material, or may have a laminate structure made of an appropriate combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector includes at least a conductive resin layer made of a resin having electrical conductivity. Furthermore, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector. Furthermore, if the negative electrode active material layer and the positive electrode active material layer described later are electrically conductive and can perform a current collecting function, it is not necessary to use a current collector as a separate member from these electrode active material layers. In such a configuration, the negative electrode active material layer described later constitutes the negative electrode, and the positive electrode active material layer described later constitutes the positive electrode.

[0033] [Cathode active material layer] The positive electrode active material layer essentially contains a positive electrode active material containing sulfur, a sulfide solid electrolyte, and a coating conductive additive.

[0034] (Cathode active material containing sulfur) The type of sulfur-containing cathode active material is not particularly limited, but includes elemental sulfur (S), lithium sulfide (LiS), and particles or thin films of organic or inorganic sulfur compounds. Any material can be used as long as it utilizes the sulfur redox reaction to release lithium ions during charging and absorb lithium ions during discharging. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitriles, sulfur-modified polyisoprenes, rubeanic acid (dithiooxamide), and polycarbonates, as exemplified by the compounds described in International Publication No. 2010 / 044437. Meanwhile, inorganic sulfur compounds are preferred due to their excellent stability. Specific examples include elemental sulfur (S), lithium sulfide (LiS), S-carbon composites, TiS, TiS, TiS, NiS, NiS, CuS, FeS, LiS, MoS, MoS, MnS, MnS, CoS, and CoS. Among these, S, lithium sulfide (LiS), S-carbon composite, TiS, TiS, TiS, TiS, FeS, and MoS are preferred, and elemental sulfur (S) and lithium sulfide (LiS), TiS, and FeS are more preferred, with elemental sulfur (S) and lithium sulfide (LiS) being particularly preferred from the viewpoint of high capacity. Note that elemental sulfur (S) may be α-sulfur, β-sulfur, or γ-sulfur having an S structure.

[0035] The positive electrode active material layer may further contain a sulfur-free positive electrode active material 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; and LiNi 0.5 Mn 1.5 Examples 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] In some cases, two or more kinds of positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used. However, the content of the sulfur-containing positive electrode active material in 100% by mass of the total amount of the positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[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 %, for example.

[0038] (Sulfide solid electrolyte) 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.

[0039] The sulfide solid electrolyte may, for example, have a Li3PS4 framework, a Li4P2S7 framework, or a Li4P2S6 framework. Examples of the sulfide solid electrolyte having a Li3PS4 framework include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Further, examples of the sulfide solid electrolyte having a Li4P2S7 framework include a Li-P-S-based solid electrolyte called LPS (for example, Li7P3S 11 ). Further, as the sulfide solid electrolyte, for example, LGPS represented by Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1) may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and more preferably a material mainly composed of Li2S-P2S5. Further, examples of the sulfide solid electrolyte containing a halogen include an argyrodite-type solid electrolyte (Li6PS5X (X is Cl, Br, or I)), which is also a material that can be preferably used.

[0040] Further, 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. Further, the crystallized sulfide glass can be obtained, for example, by performing heat treatment on the sulfide glass at a temperature above the crystallization temperature. 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.

[0041] The positive electrode active material layer may further contain a solid electrolyte other than the sulfide solid electrolyte. Examples of the solid electrolyte other than the sulfide solid electrolyte include oxide solid electrolytes. Specific examples of oxide solid electrolytes include those represented by the general formula Li 1+x Al x Ge 2-x Compounds (LAGP) represented by (PO4)3 (0≦x≦2), general formula Li 1+x Al x Ti 2-x Examples of the oxide solid electrolyte include compounds having a NASICON structure, such as a compound (LATP) represented by (PO4)3 (0≦x≦2). Other specific examples of oxide solid electrolytes include LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0042] In some cases, two or more solid electrolytes may be used in combination. Of course, solid electrolytes other than those mentioned above may also be used. However, the content of the sulfide solid electrolyte in the positive electrode active material layer relative to the total amount (100% by mass) of the solid electrolytes is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0043] The content of the sulfide solid electrolyte in the positive electrode active material layer is not particularly limited, but is preferably within a range of 1 to 60 mass %, more preferably within a range of 10 to 50 mass %, and even more preferably within a range of 15 to 40 mass %.

[0044] (Coating conductive additive) The stacked battery according to this embodiment is characterized in that the cathode active material layer contains a conductive additive, at least a portion of whose surface is coated with a coating layer containing an iodine compound, and the coating layer has a thickness of 150 nm or more and less than 400 nm. By adopting such a configuration, an increase in resistance of the all-solid-state battery can be suppressed.

[0045] As mentioned above, Patent Document 1 discloses a technique for providing a coating layer (coating layer) of LiF with a thickness of 5 nm or less on the conductive additive in a cathode composite for an all-solid-state battery containing a cathode active material, a solid electrolyte, and a conductive additive. However, when confining pressure was applied to an all-solid-state battery using the cathode composite, an increase in cell resistance could not be sufficiently suppressed in some cases. This is thought to be due to the following mechanism. According to the technique described in Patent Document 1, since the coating layer is thin, at 5 nm or less, cracks occur in the coating layer when confining pressure is applied. The conductive additive and the solid electrolyte come into contact at the cracks in the coating layer, and when charge / discharge reactions are performed in this state, a decomposition reaction of the solid electrolyte occurs. The product of the decomposition reaction has high resistance, which increases the cell resistance.

[0046] On the other hand, the coated conductive additive according to the present embodiment uses an iodine compound as the material for the coating layer, and by making the coating layer 150 nm or thicker, cracking of the coating layer is less likely to occur even when a restraining pressure is applied. This suppresses decomposition of the sulfide solid electrolyte and suppresses an increase in resistance due to the generation of reaction products. Furthermore, by making the coating layer less than 400 nm thick, the functionality of the conductive additive can be maintained.

[0047] The content of the coated conductive additive in the positive electrode active material layer is not particularly limited, but is preferably in the range of 1 to 40 mass %, more preferably in the range of 5 to 35 mass %, and even more preferably in the range of 10 to 30 mass %.

[0048] The conductive additive constituting the coated conductive additive is not particularly limited, but examples thereof 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.). Furthermore, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon. It is more preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon. It is even more preferable to include at least one selected from the group consisting of carbon. These conductive additives may be used alone or in combination of two or more.

[0049] The conductive additive is preferably in the form of particles or fibers. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, or spindle shape.

[0050] When the conductive additive is particulate, its average particle size (primary particle size) is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical properties of the battery. In this specification, the "particle size of the conductive additive" refers to the longest distance L between any two points on the contour line of the conductive additive. The value of the "average particle size of the conductive additive" is calculated as the average particle size of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0051] The coating layer contains an iodine compound (excluding the sulfide solid electrolyte described above). The iodine compound is not particularly limited, but preferably contains lithium element in addition to iodine element from the viewpoint of further suppressing the increase in resistance. Specific examples of the iodine compound include lithium iodide (LiI), Li7P2S8I, and Li x PS y Among these, from the viewpoint of further suppressing the increase in resistance, the iodine compound preferably contains lithium iodide, and more preferably the iodine compound is lithium iodide.

[0052] The coating layer may cover at least a portion of the surface of the conductive additive, but from the viewpoint of further suppressing an increase in resistance of the all-solid-state battery, it is preferable that a larger proportion of the surface of the conductive additive is covered by the coating layer. Specifically, the proportion of the area covered by the coating layer to the surface area of ​​the conductive additive is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, still more preferably 90% or more, particularly preferably 95% or more, and most preferably 100%.

[0053] The content of the iodine compound contained in the coating layer is not particularly limited, but the proportion of the content of the iodine compound in the total amount (100% by mass) of the coating layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0054] The thickness of the coating layer is essentially in the range of 150 nm or more and less than 400 nm, preferably in the range of 180 nm or more and 300 nm or less, and more preferably in the range of 200 nm or more and 300 nm or less. When the thickness of the coating layer is within the above range, the increase in resistance of the all-solid-state battery can be further suppressed. In this specification, the thickness of the coating layer is a value measured by the method described in the Examples below.

[0055] The ratio of the mass of the coating layer to the mass of the conductive additive contained in the coated conductive additive (mass of coating layer / mass of conductive additive) is preferably 0.1 to 1, more preferably 0.2 to 0.8, and even more preferably 0.2 to 0.5. When the ratio of the mass of the coating layer to the mass of the conductive additive is within the above range, an increase in the resistance of the all-solid-state battery can be further suppressed.

[0056] The method for producing the coated conductive assistant is not particularly limited, but an example is a method in which the conductive assistant is impregnated in an iodine compound solution and then the solvent is removed.

[0057] The solvent used for the iodine compound solution is not particularly limited, but from the viewpoints of solubility, operability, safety, etc., alcohols are suitable, and alcohols having 1 to 4 carbon atoms are preferred. Examples of alcohols having 1 to 4 carbon atoms include methanol, ethanol, 1-propanol, 2-propanol, n-butanol, 2-butanol, isobutanol, and tert-butanol. Among these, methanol, ethanol, 1-propanol, and 2-propanol are preferred, methanol and ethanol are more preferred, and ethanol is particularly preferred.

[0058] The concentration of the iodine compound solution is preferably 1 to 200 mg / mL, more preferably 10 to 100 mg / mL. The thickness of the coating layer of the coated conductive assistant can be controlled by adjusting the amount or concentration of the iodine compound solution.

[0059] The specific method for removing the solvent after impregnating the conductive assistant into the iodine compound solution is not particularly limited, but it is preferable to remove the solvent while stirring the dispersion containing the iodine compound solution and the conductive assistant. The solvent is preferably removed under reduced pressure at a temperature of 100°C or less. The solid content after solvent removal can be crushed as needed to obtain the coated conductive assistant.

[0060] The thickness of the positive electrode active material layer varies depending on the intended configuration of the stacked battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0061] [Solid electrolyte layer] The solid electrolyte layer is a layer interposed between the above-mentioned positive electrode active material layer and negative electrode active material layer, and essentially contains a solid electrolyte. The sulfide solid electrolyte and oxide solid electrolyte described in the section on the positive electrode active material layer can be appropriately used as the solid electrolyte contained in the solid electrolyte layer. Among these, it is preferable that the solid electrolyte layer contains a sulfide solid electrolyte. The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte. There are no particular restrictions on the blending amount of each component contained in the solid electrolyte layer, but the blending amount of the binder is preferably 2 to 8 mass % relative to the total amount of the solid electrolyte layer (100 mass %).

[0062] The thickness of the solid electrolyte layer varies depending on the configuration of the intended stacked 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 100 μm or more.

[0063] [Negative electrode active material layer] 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 carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb2O5, Li4Ti5O 12and the like. Furthermore, silicon-based negative electrode active materials and tin-based negative electrode active materials may also be used. Here, silicon and tin belong to the 14th group of elements, and are known to be negative electrode active materials that can significantly improve the capacity of non-aqueous electrolyte secondary batteries. These simple substances can absorb and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), and therefore become high-capacity negative electrode active materials. Here, it is preferable to use Si simple substance as the silicon-based negative electrode active material. Similarly, SiO 2 disproportionated into two phases, an Si phase and a silicon oxide phase, is also used. x It is also preferable to use silicon oxides such as (0.3≦x≦1.6). In this case, the range of x is more preferably 0.5≦x≦1.5, and even more preferably 0.7≦x≦1.2. Furthermore, an alloy containing silicon (silicon-containing alloy-based negative electrode active material) may be used. On the other hand, examples of negative electrode active materials containing tin element (tin-based negative electrode active materials) include simple Sn, tin alloys (Cu—Sn alloy, Co—Sn alloy), amorphous tin oxide, tin silicon oxide, etc. Among these, examples of amorphous tin oxide include SnB 0.4 P 0.6 O 3.1Examples of tin silicon oxides include SnSiO3. A lithium-containing metal may also 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 thereof include lithium metal and lithium-containing alloys. Examples of lithium-containing alloys include, but are not limited to, alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. In some cases, two or more negative electrode active materials may be used in combination. Of course, negative electrode active materials other than those listed above may also be used. The negative electrode active material preferably contains lithium metal, a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains lithium metal or a lithium-containing alloy. When the negative electrode active material contains lithium metal or a lithium-containing alloy, the secondary battery according to this embodiment may be a so-called lithium deposition type in which lithium metal or a lithium-containing alloy is deposited on the negative electrode current collector during charging. In this case, a layer of lithium metal or a lithium-containing alloy deposited on the negative electrode current collector during charging serves as the negative electrode active material layer of the stacked battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases with the progress of charging, and decreases with the progress of discharging. Although the negative electrode active material layer need not be present during full discharge, in some cases, a certain amount of the negative electrode active material layer made of lithium metal or a lithium-containing alloy may be present during full discharge.

[0064] 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, the average particle diameter 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.

[0065] 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 mass %, and more preferably in the range of 50 to 90 mass %. When the negative electrode active material contained in the negative electrode active material layer is in a particulate form, the negative electrode active material layer may further contain a solid electrolyte, a conductive additive (including a coated conductive additive), and / or a binder, and specific and preferred forms thereof may be the same as those described in the section on the positive electrode active material layer above.

[0066] The thickness of the negative electrode active material layer (in the case of a lithium deposition type secondary battery, the thickness when fully charged) differs depending on the intended configuration of the stacked battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0067] [Positive and negative current collector plates] The material constituting the current collector plate is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate and the negative electrode current collector plate may be made of the same material or different materials.

[0068] [Positive and negative leads] The current collector and the current collecting plate may be electrically connected via a positive electrode lead or a negative electrode lead. Materials used in known lithium secondary batteries may be used as the constituent materials of the positive electrode and negative electrode leads. It is preferable that the portion removed from the outer casing be covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting the product (e.g., automobile parts, particularly electronic devices).

[0069] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film that can cover the power generating element can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferred for the exterior body because it can easily adjust the collective pressure applied to the power generating element from the outside.

[0070] The stacked battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0071] Although one embodiment of the all-solid-state 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. [Example]

[0072] 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, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0073] <Example of test cell fabrication> [Comparative Example 1] (Preparation of positive electrode material) In a glove box with an argon atmosphere and a dew point of −68°C or lower, 40 g of 5 mm diameter zirconia balls, 0.1 g of sulfur (manufactured by Aldrich Chemicals), 0.08 g of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and 0.02 g of conductive additive (manufactured by Lion Specialty Chemicals Co., Ltd., Ketjenblack (registered trademark) EC600JD, primary particle diameter 34.0 nm) were placed in a 45 mL zirconia container and milled at 370 rpm for 6 hours in a planetary ball mill (manufactured by Fritsch, Premium line P-7) to obtain a powdered positive electrode material.

[0074] (Production of test cells (all-solid-state lithium secondary batteries)) The battery was fabricated in a glove box with an argon atmosphere at a dew point of -68°C or below. A 10mm diameter stainless steel cylindrical punch was inserted into one side of a Macor cylindrical tube jig (inner diameter 10mm, outer diameter 23mm, height 20mm), and 80mg of sulfide solid electrolyte (Li6PS5Cl, manufactured by Ampcera) was placed from the top of the cylindrical tube jig. The other 10mm diameter stainless steel cylindrical punch was then inserted to sandwich the solid electrolyte. The tube was then pressed at 75MPa for 3 minutes using a hydraulic press to form a 10mm diameter, approximately 0.6mm thick solid electrolyte layer in the cylindrical tube jig. Next, the cylindrical convex punch inserted from above was removed, and 7.5 mg of the prepared positive electrode material was placed on one side of the solid electrolyte layer inside the cylindrical tube. A cylindrical convex punch (also serving as a positive electrode current collector) was inserted from above and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch (also serving as a negative electrode current collector) was removed, and a lithium foil (manufactured by Nilaco Corporation, thickness 0.20 mm) punched to a diameter of 8 mm and an indium foil (manufactured by Nilaco Corporation, thickness 0.30 mm) punched to a diameter of 9 mm were stacked as negative electrodes. The cylindrical tube was inserted from the bottom of the jig so that the indium foil was positioned next to the solid electrolyte layer. The cylindrical convex punch was inserted again and the tube was constrained in a metal case at a pressure equivalent to 100 MPa. In this manner, a test cell (all-solid-state lithium secondary battery) of this comparative example was produced, in which the negative electrode current collector (punch), lithium-indium negative electrode, solid electrolyte layer, positive electrode active material layer, and positive electrode current collector (punch) were stacked in this order.

[0075] Comparative Example 2 (Preparation of coated conductive additive) Lithium iodide was dissolved in ethanol to a concentration of 20 mg / mL. 1.00 g of a conductive additive (Ketjenblack® EC600JD, manufactured by Lion Specialty Chemicals Co., Ltd., primary particle size 34.0 nm) was added to 10 mL of this solution and stirred. The ethanol was then distilled off under reduced pressure to obtain a coated conductive additive having a coating layer made of lithium iodide.

[0076] A test cell for this comparative example was prepared in the same manner as in Comparative Example 1, except that in the above (Preparation of the positive electrode material), 0.02 g of the above coated conductive additive was used instead of the conductive additive that was not coated with lithium iodide.

[0077] [Example 1] In the above (preparation of coated conductive additive), 1.00 g of conductive additive (Ketjenblack (registered trademark) EC600JD, primary particle size 34.0 nm, manufactured by Lion Specialty Chemicals Co., Ltd.) was added to 15 mL of a 20 mg / mL lithium iodide solution and stirred, and the ethanol was distilled off under reduced pressure to obtain a coated conductive additive having a coating layer made of lithium iodide.

[0078] In the above (preparation of positive electrode material), 0.1 g of sulfur (manufactured by Aldrich), 0.08 g of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and 0.02 g of coating conductive additive were treated in a planetary ball mill at 370 rpm for 6 hours in an argon atmosphere glove box with a dew point of −68°C or less, to obtain a powdered positive electrode material.

[0079] Other than this, the test cell of this example was fabricated in the same manner as in Comparative Example 2.

[0080] [Example 2] In the above (Preparation of coated conductive additive), 1.00 g of conductive additive (Ketjenblack (registered trademark) EC600JD, primary particle size 34.0 nm, manufactured by Lion Specialty Chemicals Co., Ltd.) was added to 20 mL of a 20 mg / mL lithium iodide solution and stirred, and the ethanol was distilled off under reduced pressure to obtain a coated conductive additive having a coating layer made of lithium iodide.

[0081] In the above (preparation of positive electrode material), 0.1 g of sulfur (manufactured by Aldrich), 0.08 g of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and 0.02 g of coating conductive additive were treated in a planetary ball mill at 370 rpm for 6 hours in an argon atmosphere glove box with a dew point of −68°C or less, to obtain a powdered positive electrode material.

[0082] Other than this, the test cell of this example was fabricated in the same manner as in Comparative Example 2.

[0083] [Example 3] In the above (preparation of coated conductive additive), 1.00 g of conductive additive (Ketjenblack (registered trademark) EC600JD, primary particle size 34.0 nm, manufactured by Lion Specialty Chemicals Co., Ltd.) was added to 30 mL of 20 mg / mL lithium iodide solution and stirred, and the ethanol was distilled off under reduced pressure to obtain a coated conductive additive having a coating layer made of lithium iodide.

[0084] In the above (preparation of positive electrode material), 0.1 g of sulfur (manufactured by Aldrich), 0.08 g of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and 0.02 g of coated conductive additive were treated in a planetary ball mill at 370 rpm for 6 hours in an argon atmosphere glove box with a dew point of −68°C or less, to obtain a powdered positive electrode material.

[0085] Other than this, the test cell of this example was fabricated in the same manner as in Comparative Example 2.

[0086] Comparative Example 3 In the above (Preparation of coated conductive additive), 1.00 g of conductive additive (Ketjenblack (registered trademark) EC600JD, primary particle size 34.0 nm, manufactured by Lion Specialty Chemicals Co., Ltd.) was added to 40 mL of a 20 mg / mL lithium iodide solution and stirred, and the ethanol was distilled off under reduced pressure to obtain a coated conductive additive having a coating layer made of lithium iodide.

[0087] In the above (preparation of positive electrode material), 0.1 g of sulfur (manufactured by Aldrich), 0.08 g of sulfide solid electrolyte (manufactured by Ampcera, Li6PS5Cl), and 0.02 g of coating conductive additive were treated in a planetary ball mill at 370 rpm for 6 hours in an argon atmosphere glove box with a dew point of −68°C or less, to obtain a powdered positive electrode material.

[0088] Other than this, the test cell of this comparative example was produced in the same manner as in Comparative Example 2.

[0089] <Observation of the coating layer of the conductive additive> The cathode active material layer of the test cell prepared above was thinned using a focused ion beam processing device (FEI Nova200 NanoLab), and cross-section observation and composition analysis were performed using a TEM-DEX (JEOL JEM-F200). The thickness of the coating layer covering the surface of the conductive additive was determined from cross-sectional images of the particles in several fields of view. The area where I was detected by EDX was considered to be the area covered by the coating layer. The thickness of the coating layer was then measured at 20 different points, and the arithmetic mean value was calculated to determine the thickness of the coating layer. The results are shown in Table 1 below.

[0090] <Measurement of DC resistance (DCR)> The direct current resistance (DCR) of the test cells prepared in each of the above examples and comparative examples was measured using a charge-discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a constant temperature bath set at 25°C.

[0091] First, 0.1mA / cm 2 3.1V constant current constant voltage (CCCV) charging at a current density of 0.05mA / cm 2The charge-discharge cycle was repeated five times, with a current cutoff of 0.05C. The battery was then discharged at a rate of 0.03C according to the battery design. The voltage range was 1.1 to 2.5V, the charge-discharge current rate was 0.05C, and the cutoff current during charging was 0.01C. The capacity value per mass of the positive electrode active material (mAh / g) was calculated from the charge-discharge capacity value obtained after five cycles of the charge-discharge cycle and the mass of the positive electrode active material contained in the positive electrode. The capacity value thus calculated was then reduced to 50% capacity (SOC50%) by 0.2 mA / cm. 2 A constant current discharge was performed at a current density of 1 C. After a 30-minute pause, a discharge was performed for 10 seconds at a discharge rate of 1 C, and the direct current resistance (DCR) was calculated according to Ohm's law from the voltage drop and current value during this discharge. The results are shown in Table 1 below. The direct current resistance (DCR) shown in Table 1 is a relative value when the value for Comparative Example 1 is set to 100. Measurement of the direct current resistance (DCR) for Comparative Example 3 was impossible due to its high resistance.

[0092] [Table 1]

[0093] The results shown in Table 1 show that the present invention can suppress an increase in resistance of an all-solid-state battery.

[0094] In particular, it was shown that Examples 1 and 2, in which the thickness of the coating layer was within the range of 180 nm to 300 nm, were able to maintain an even lower resistance. [Explanation of symbols]

[0095] 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 including a conductive additive, at least a portion of the surface of which is coated with a coating layer containing lithium iodide, the coating layer having a thickness of 193 nm or more and 388 nm or less, a positive electrode active material layer containing sulfur, and a sulfide solid electrolyte, and the positive electrode active material layer is disposed on a surface of a positive electrode current collector; a negative electrode; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a restraining member that restrains the power generating element in a stacking direction.

2. The all-solid-state battery according to claim 1 , wherein the coating layer has a thickness of 200 nm or more and 300 nm or less.

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