Reacted all-solid-state battery and method for manufacturing same

Abstract

Provided is a means capable of suppressing an increase in cell resistance in an all-solid-state battery provided with a positive electrode active material layer containing a sulfide solid electrolyte. Provided is a reacted all-solid-state battery provided with an electric power generating element comprising: a positive electrode in which a positive electrode active material layer is disposed on a surface of a positive electrode current collector, the positive electrode active material layer including a positive electrode active material containing a sulfur element and a sulfide solid electrolyte containing a sulfur element, a phosphorus element, and a lithium element; a negative electrode in which a negative electrode active material layer is disposed on a surface of a negative electrode current collector, the negative electrode active material layer including a negative electrode active material containing an alkali metal element; a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a solid electrolyte. In an X-ray photoelectron spectroscopy spectrum for the positive electrode active material layer, the ratio (A / B) of the intensity of the maximum peak A within the range of 163-165 eV to the intensity of the maximum peak B within the range of 161-163 eV is 0.6-1 inclusive.

Description

Reacted all-solid-state battery and method for manufacturing the same

[0001] The present invention relates to a reacted all-solid-state battery and a method for manufacturing the same.

[0002] In recent years, research and development of all-solid-state 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 solids. Therefore, all-solid-state secondary batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes, as occurs with conventional liquid-based secondary batteries using nonaqueous 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 output density and energy density of the battery.

[0003] It is known that all-solid-state secondary batteries using a sulfide-based solid electrolyte (hereinafter also simply referred to as a "sulfide solid electrolyte") experience a significant decrease in performance due to decomposition of the sulfide solid electrolyte when repeatedly charged and discharged. To address this issue, for example, International Publication No. 2013 / 084944 discloses a technique for forming a negative electrode active material layer using a negative electrode active material having a predetermined operating potential, and controlling the potential of the negative electrode active material layer so that it does not fall below the potential at which reductive decomposition of the sulfide solid electrolyte material occurs. International Publication No. 2013 / 084944 claims that this configuration can improve charge and discharge efficiency by preventing reductive decomposition of the sulfide solid electrolyte material in contact with the negative electrode active material.

[0004] However, the inventors have conducted studies and found that in an all-solid-state battery having a positive electrode active material layer containing a sulfide solid electrolyte, even the technology described in WO 2013 / 084944 cannot sufficiently suppress an increase in cell resistance due to repeated charge and discharge, and further improvements have been desired.

[0005] Therefore, an object of the present invention is to provide a means capable of suppressing an increase in cell resistance in an all-solid-state battery having a positive electrode active material layer containing a sulfide solid electrolyte.

[0006] The present inventors conducted extensive research to solve the above-mentioned problems. As a result, they found that an increase in cell resistance can be significantly suppressed by charging an unreacted all-solid-state battery that has not been charged or discharged, the battery including a cathode having a cathode active material layer including a sulfur-containing cathode active material and a sulfide solid electrolyte containing sulfur, phosphorus, and lithium, as an initial reaction. They then analyzed the cathode active material layer of the reacted all-solid-state battery by X-ray photoelectron spectroscopy (XPS) and found that the XPS spectrum showed a predetermined profile, leading to the completion of the present invention.

[0007] That is, one embodiment of the present invention is a reacted all-solid-state battery including a power generating element having: a positive electrode in which a positive electrode active material layer containing a sulfur-containing positive electrode active material and a sulfide solid electrolyte containing sulfur, phosphorus, and lithium are disposed on the surface of a positive electrode current collector; a negative electrode in which a negative electrode active material layer containing an alkali metal element is disposed on the surface of a negative electrode current collector; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein in an X-ray photoelectron spectroscopy spectrum of the positive electrode active material layer, the intensity ratio (A / B) of a maximum peak A in the range of 163 to 165 eV to a maximum peak B in the range of 161 to 163 eV is 0.6 or more and 1 or less.

[0008] Another aspect of the present invention is a method for producing a reacted all-solid-state battery, the method comprising: a power generating element including a positive electrode in which a positive electrode active material layer containing a positive electrode active material containing elemental sulfur and a sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium is disposed on the surface of a positive electrode current collector; a negative electrode in which a negative electrode active material layer containing a negative electrode active material containing an alkali metal element is disposed on the surface of a negative electrode current collector; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, the method comprising a charging step of charging, as an initial reaction, an unreacted all-solid-state battery that has not been charged or discharged.

[0009] Fig. 1 is a perspective view showing the appearance of a flat laminate-type reacted all-solid-state lithium secondary battery according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 shown in Fig. 1. Fig. 3 is an X-ray photoelectron spectroscopy spectrum of the reacted cell for XPS evaluation prepared in Example 1.

[0010] <Reacted All-Solid-State Battery> One embodiment of the present invention is a reacted all-solid-state battery including a power generating element having a positive electrode including a cathode active material layer disposed on the surface of a positive electrode current collector, the cathode active material layer including a cathode active material containing elemental sulfur and a sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium; a negative electrode including a negative electrode active material layer disposed on the surface of a negative electrode current collector, the negative electrode including a negative electrode active material layer containing an alkali metal element; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a solid electrolyte, wherein in an X-ray photoelectron spectroscopy spectrum of the positive electrode active material layer, the intensity ratio (A / B) of a maximum peak A in the range of 163 to 165 eV to a maximum peak B in the range of 161 to 163 eV is 0.6 or more and 1 or less. According to this embodiment, an increase in cell resistance can be suppressed in an all-solid-state battery including a cathode active material layer containing a sulfide solid electrolyte.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0012] FIG. 1 is a perspective view showing the appearance of a flat-layered, reacted all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. By adopting a layered structure, the battery can be made compact and have a high capacity. In this specification, a flat-layered, non-bipolar, reacted all-solid-state lithium secondary battery (hereinafter also simply referred to as a "layered battery") shown in FIGS. 1 and 2 will be described in detail as an example. However, when viewed from the perspective of the internal electrical connection configuration (electrode structure) of the reacted all-solid-state 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.

[0013] 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 the positive electrode current collector 27 extending to the outside.

[0014] As shown in Fig. 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 the battery exterior material. Note that Fig. 1 shows a cross section of the stacked secondary battery when fully charged, and therefore, a negative electrode active material layer (lithium metal layer) 13 made of lithium metal is present between the negative electrode current collector 11' and the solid electrolyte layer 17. In addition, a pressure member (not shown) applies a restraining pressure to the stacked secondary battery 10a in the stacking direction of the power generating element 21. This keeps the volume of the power generating element 21 constant.

[0015] Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a positive electrode active material (here, elemental sulfur (S)) and a sulfide solid electrolyte (here, Li ６ P.S. ５ The stacked battery 10a shown in FIG. 2 has a structure in which a positive electrode active material layer 15 containing lithium ion (LiCl) is disposed on each side of a negative electrode current collector 11′. The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material (here, lithium metal) is 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 and an adjacent negative electrode active material layer 13 face each other 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 structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0016] 2, the outermost negative electrode current collectors located on both outermost layers of the power generating element 21 each have a negative electrode active material layer 13 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 with active material layers on both sides may be used as the outermost current collector as is.

[0017] A negative electrode current collector (tab) 25 and a positive electrode current collector (tab) 27 that are electrically connected to the electrodes (positive and negative electrodes) are attached to the negative electrode current collector 11′ and the positive electrode current collector 11″, respectively, and are configured to be sandwiched between the ends of a laminate film 29 that is a battery exterior material and led out of the laminate film 29. The positive electrode current collector 27 and the negative electrode current collector 25 may be attached to the positive electrode current collector 11″ and the negative electrode current collector 11′ of the electrodes by ultrasonic welding, resistance welding, or the like, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary.

[0018] The main components of the all-solid-state battery according to this embodiment will be described below.

[0019] [Current Collector] The current collector (positive electrode current collector, negative electrode 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.

[0020] 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.

[0021] Furthermore, examples of the resin having electrical conductivity include resins in which a conductive filler is added to a non-conductive polymer material.

[0022] 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 include 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.

[0023] [Negative Electrode Active Material Layer] The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited as long as it contains an alkali metal element, but preferably contains lithium metal or a lithium-containing alloy, more preferably lithium metal or a lithium-containing alloy, and even more preferably lithium metal. When the negative electrode active material is lithium metal or a lithium-containing alloy, the reacted all-solid-state battery as an electrical device may be a so-called lithium deposition type in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during charging. That is, in a preferred embodiment of the reacted all-solid-state battery, the negative electrode is one in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during charging. In this form, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. The negative electrode active material layer may not be present during full discharge, but in some cases, a negative electrode active material layer containing a certain amount of lithium metal may be present during full discharge.

[0024] 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.

[0025] The negative electrode active material layer may further contain a solid electrolyte as needed. 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. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, and sulfide solid electrolytes are preferred.

[0026] Examples of sulfide solid electrolytes include LiI-Li２ S - SiS ２ , LiI - Li ２ S - P ２ O ５ , LiI - Li ３ PO ４ - P ２ S ５ , Li ２ S - P ２ S ５ , LiI - Li ３ PS ４ , LiI - LiBr - Li ３ PS ４ , Li ３ PS ４ , Li ２ S - P ２ S ５ - LiI, Li ２ S - P ２ S ５ - Li ２ O, Li ２ S - P ２ S ５ - Li ２ O - LiI, Li ２ S - SiS ２ , Li<X000034>S - SiS ２ - LiI, Li ２ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions.

[0027] The sulfide solid electrolyte is, for example, Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a skeleton include LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ In addition, Li ４ P ２ S ７ Examples of the sulfide solid electrolyte having a skeleton include a Li-P-S solid electrolyte called LPS (for example, Li ７ P ３ S １１ ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li （４－ｘ） Ge （１－ｘ） P ｘ S ４ (x satisfies 0<x<1), etc. may be used. Among them, a sulfide solid electrolyte containing a P element is preferable, and Li ２ S-P ２ S ５It is more preferable that the sulfide solid electrolyte is a material mainly composed of Li. Furthermore, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). In a preferred embodiment, the sulfide solid electrolyte is a material mainly composed of Li. ６ P.S. ５ X, where X is Cl, Br or I, preferably Cl.

[0028] In addition, the sulfide solid electrolyte is Li ２ S-P ２ S ５ In the case of the system, Li ２ S and P ２ S ５ The ratio of Li is the molar ratio. ２ S:P ２ S ５ = 50:50 to 100:0, and among these, Li ２ S:P ２ S ５ It is preferable that the ratio is 70:30 to 80:20.

[0029] The sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by mechanical milling (ball mill, etc.) a raw material composition. The crystallized sulfide glass can be obtained, for example, by heat treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25°C) is, for example, 1 × 10 －５ S / cm or more, and preferably 1×10 －４ The ionic conductivity of the solid electrolyte can be measured by an AC impedance method.

[0030] Examples of the shape of the solid electrolyte include particle shapes such as spherical and oval spheres, and thin film shapes. When the solid electrolyte is in a particle shape, its average particle diameter (D50) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle diameter (D50) is preferably 0.01 μm or more, more preferably 0.1 μm or more. In this specification, the value of "average particle diameter" is a value calculated as the average particle diameter 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).

[0031] 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 %, and more preferably in the range of 10 to 50 mass %.

[0032] The negative electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the above-mentioned negative electrode active material and solid electrolyte.

[0033] The thickness of the negative electrode active material layer varies depending on the intended configuration of the reacted all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0034] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer, and contains a solid electrolyte.

[0035] The specific form of the solid electrolyte contained in the solid electrolyte layer is not particularly limited, and the solid electrolytes exemplified in the section on the negative electrode active material layer and their preferred forms can be similarly employed. In some cases, a solid electrolyte other than the above-mentioned solid electrolytes may be used in combination.

[0036] The solid electrolyte layer may further contain a binder in addition to the above-mentioned predetermined solid electrolyte.

[0037] The thickness of the solid electrolyte layer varies depending on the configuration of the intended reacted all-solid-state 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 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0038] [Positive Electrode Active Material Layer] In this embodiment, the positive electrode active material layer is characterized by including a positive electrode active material containing elemental sulfur and a sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium.

[0039] The type of positive electrode active material is not particularly limited as long as it contains sulfur element, but elemental sulfur (S) and lithium sulfide (Li ２ In addition to sulfur (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds can be used, and any substance can 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. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbon sulfide, etc., as typified by the compounds described in WO 2010 / 044437. On the other hand, inorganic sulfur compounds are preferred because of their excellent stability, and specific examples thereof include elemental sulfur (S), lithium sulfide (Li ２ S), S-carbon composite, TiS ２ , TiS ３ , TiS4, NiS, NiS ２ , CuS, FeS ２ , Li ２ S, MoS ２ , MoS ３ , MnS, MnS ２ , CoS, CoS ２ Among them, S, lithium sulfide (Li ２ S), S-carbon composite, TiS ２ , TiS ３ , TiS4, FeS ２ and MoS２ is preferred, and elemental sulfur (S) and lithium sulfide (Li ２ S), TiS ２ , and FeS ２ is more preferable, and from the viewpoint of high capacity, elemental sulfur (S) and lithium sulfide (Li ２ S) is particularly preferred. ８ Alpha, beta, or gamma sulfur having the structure may be used.

[0040] The content of the sulfur-containing cathode active material in the cathode active material layer is not particularly limited, but is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less, and particularly preferably 45% by mass or more and 60% by mass or less, relative to 100% by mass of the total mass of the cathode active material layer.

[0041] The sulfide solid electrolyte is not particularly limited as long as it contains sulfur, phosphorus, and lithium elements, and the solid electrolytes exemplified in the section on the negative electrode active material layer can be similarly used. ３ P.S. ４ , Li ７ P ３ S １１ , Li （４－ｘ） Ge （１－ｘ） P ｘ S ４ (x satisfies 0<x<1), Li ６ P.S. ５ X (wherein X is Cl, Br or I, preferably Cl), and Li ６ P.S. ５ X (wherein X is Cl, Br or I) is more preferred, Li ６ P.S. ５ It is more preferable that the oxidation reaction product is Cl. In the manufacturing method of the reacted all-solid-state battery described below, charging is performed as the first reaction, and thus an oxidation reaction product can be generated on the surface of the sulfide solid electrolyte. For example, in Examples 1 to 5 described later, the oxidation reaction product is a phosphorus sulfide compound, P ２ S ５The oxidation reaction products can be repeatedly reduced and oxidized reversibly during subsequent discharge and charge, preventing the reductive decomposition of the sulfide solid electrolyte and, as a result, suppressing an increase in cell resistance.

[0042] The content of the sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium in the positive electrode active material layer is not particularly limited, but is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and even more preferably 30% by mass or more and 45% by mass or less, relative to 100% by mass of the total mass of the positive electrode active material layer.

[0043] The positive electrode active material layer may contain a conductive additive to improve the electronic conductivity of the active material layer. Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, and carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.). It is also preferable to use porous carbon as the conductive additive. When using porous carbon, the sulfur utilization efficiency can be further improved by incorporating a sulfur-impregnated carbon composite, in which sulfur is impregnated into the pores of the porous carbon, into the positive electrode active material layer. Examples of porous carbon include activated carbon, Ketjenblack (registered trademark) (highly conductive carbon black), (oil) furnace black, channel black, acetylene black, thermal black, lamp black, and other carbon blacks; and carbon particles (carbon carriers) made of coke, natural graphite, artificial graphite, etc. Alternatively, a conductive porous body having a porous structure in which the shape of the template is transferred may be synthesized by mixing a ceramic or other mold with a carbon raw material such as a resin, firing the mixture in an inert atmosphere, and then dissolving the mold with an acid. In this case, the pore size and pore volume of the resulting conductive porous body can be changed by appropriately adjusting the particle size of the template and the compounding ratio of the carbon raw material.

[0044] The BET specific surface area of ​​the porous carbon is 200 m ２ / g or more, and ２ / g or more is more preferable, and 800m ２ / g or more, and more preferably 1200m ２ / g or more is particularly preferred, and 1500m ２ / g or more is most preferable. The pore volume of the porous carbon is preferably 1.0 mL / g or more, more preferably 1.3 mL / g or more, and even more preferably 1.5 mL / g or more. If the BET specific surface area and pore volume of the porous carbon are values ​​within such ranges, a sufficient number of pores can be maintained, and therefore a sufficient amount of elemental sulfur (S) and / or lithium sulfide (Li ２ The BET specific surface area and pore volume of porous carbon can be measured by nitrogen adsorption / desorption measurement. This nitrogen adsorption / desorption measurement is performed using a BELSORP mini manufactured by Microtrac-Bell Corporation at a temperature of -196°C using a multipoint method. 0.01<P / P ０ The BET specific surface area is determined from the adsorption isotherm in the range of relative pressure <0.05. The pore volume is determined from the adsorption N at a relative pressure of 0.96. ２ Calculate from the volume.

[0045] The content of the conductive additive in the positive electrode active material layer is not particularly limited, but is preferably 1 mass % or more and 30 mass % or less, and more preferably 5 mass % or more and 20 mass % or less, relative to 100 mass % of the total mass of the positive electrode active material layer.

[0046] The reacted all-solid-state battery according to this embodiment is also characterized in that, in the X-ray photoelectron spectroscopy (XPS) spectrum of the positive electrode active material layer, the ratio of the intensity of the maximum peak A in the range of 163 to 165 eV to the maximum peak B in the range of 161 to 163 eV (A / B) is 0.6 or more and 1 or less. Here, the XPS spectrum allows quantitative analysis of each element based on peak intensity, and a maximum peak A that is thought to be derived from -S-S- and -P-S-P- is observed in the range of 163 to 165 eV, and a maximum peak A that is thought to be derived from -S-S- and -P-S-P- is observed in the range of 161 to 163 eV (preferably in the range of 161 eV or more and less than 163 eV) of the sulfide solid electrolyte (Li６ P.S. ５ A maximum peak B, which is thought to be derived from sulfide (Cl), is observed. When the ratio (A / B) of these peak intensities is 0.6 or more and 1 or less, reductive decomposition of the sulfide solid electrolyte is less likely to occur in the reacted all-solid-state battery, and an increase in cell resistance can be suppressed. Since an increase in cell resistance can be further suppressed, the peak intensity ratio (A / B) is preferably 0.64 or more and 1 or less, more preferably 0.71 or more and 1 or less, even more preferably 0.82 or more and 1 or less, and particularly preferably 0.90 or more and 1 or less. Note that, as shown in Examples 1 to 5 described later, it is possible to control the limit voltage (upper limit charging voltage) in the initial charge to within a range of 3 V or less, and to control the charge density in the initial charge to 0.3 mA / cm. ２ By controlling the peak intensity ratio (A / B) within the following range, the value of the peak intensity ratio (A / B) can be made closer to 1.

[0047] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plate (25, 27) 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 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0048] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collector and the current collector plate may be electrically connected via a positive electrode lead or a negative electrode lead. Materials used in known all-solid-state batteries may be similarly used as the constituent materials of the positive electrode and the negative electrode lead. It is preferable that the portion removed from the exterior be covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, causing electrical leakage and affecting products (e.g., automotive parts, particularly electronic devices).

[0049] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element can be used, as shown in Figures 1 and 2 . 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 preferable for the exterior body because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0050] 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 power source for driving EVs and HEVs.

[0051] One embodiment of the reacted all-solid-state battery has been described above, but the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0052] <Method for Manufacturing a Reacted All-Solid-State Battery> The above-mentioned reacted all-solid-state battery includes a power generating element having a predetermined positive electrode, a solid electrolyte layer, and a negative electrode. The battery can be manufactured by charging an unreacted all-solid-state battery that has not been charged or discharged as an initial reaction. That is, a method for manufacturing a reacted all-solid-state battery according to another aspect of the present invention includes a power generating element having a positive electrode including a cathode active material layer containing sulfur and a sulfide solid electrolyte containing sulfur, phosphorus, and lithium, disposed on the surface of a positive electrode current collector; a negative electrode including a negative electrode active material layer containing an alkali metal element, disposed on the surface of a negative electrode current collector; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte. According to this aspect, an increase in cell resistance can be suppressed in an all-solid-state battery including a cathode active material layer containing a sulfide solid electrolyte.

[0053] A person skilled in the art can easily fabricate an unreacted all-solid-state battery having a predetermined power-generating element by appropriately referring to conventionally known methods, and therefore, a description of a specific fabrication method will be omitted here.

[0054] The manufacturing method according to the present embodiment includes a charging step in which an unreacted all-solid-state battery that has not been charged or discharged is charged as an initial reaction. Conventionally, an unreacted all-solid-state battery having a cathode active material layer containing a cathode active material containing elemental sulfur (e.g., elemental sulfur (S)) has been discharged (reduced) as an initial reaction to cause an alkali metal (e.g., lithium) to be absorbed into the cathode active material. During the discharge as the initial reaction, a reduction reaction product (e.g., LiP ７ , Li ３ P ７, lithium phosphides such as LiP) can be produced. The reduction reaction products produce oxidative decomposition products upon subsequent charging, but because this reaction is irreversible, the oxidative decomposition products accumulate on the surface of the sulfide solid electrolyte as the charge-discharge reaction is repeated. This reduces the ionic conductivity of the sulfide solid electrolyte, leading to an increase in cell resistance. On the other hand, the present invention is characterized in that it starts with charging (oxidation), which is a reaction in the opposite direction to conventional methods. This allows the oxidation reaction products (P ２ S ５ The oxidation reaction products can be repeatedly reduced and oxidized reversibly during subsequent discharge and charge, preventing the reductive decomposition of the sulfide solid electrolyte and, as a result, suppressing an increase in cell resistance.

[0055] The upper limit of the charging voltage in the charging step is not particularly limited, but is preferably 4 V vs. Li / Li ＋ It is preferable to set it to 3V vs. Li / Li or less. ＋ By setting the value of the upper limit voltage of charging within the above range, it is possible to suppress oxidative decomposition of the sulfide solid electrolyte due to charging (oxidation) in the high voltage region. The lower limit value of the upper limit voltage of charging is not particularly limited, but it is preferable that the lower limit value be 2.3 V vs. Li / Li. ＋ Preferably, the voltage is 2.5 V vs. Li / Li or more. ＋ More preferably, it is equal to or greater than this.

[0056] The current density in the charging step is not particularly limited, but is preferably 12 mA / cm ２ It is preferable that the current is 1 mA / cm or less. ２ More preferably, it is 0.3 mA / cm or less. ２ It is more preferable that the current is 0.1 mA / cm or less. ２ It is particularly preferable that the current is 0.03 mA / cm or less. ２ By setting the current density value within the above range, the oxidation reaction of the sulfide solid electrolyte in the positive electrode active material layer can proceed uniformly, and as a result, an increase in cell resistance can be further suppressed.

[0057] From the viewpoint of uniformly progressing the oxidation reaction of the sulfide solid electrolyte in the positive electrode active material layer, the cell temperature in the charging step is preferably controlled within a range of 10°C or higher and 70°C or lower, more preferably within a range of 20°C or higher and 60°C or lower, and even more preferably within a range of 25°C or higher and 40°C or lower.

[0058] After the charging step as the initial reaction, one discharge may be carried out, or discharge and charge may be repeated about 1 to 10 times, if necessary.

[0059] The following embodiments are also included within the scope of the present invention: a reacted all-solid-state battery according to claim 1 having the features of claim 2; a reacted all-solid-state battery according to claim 1 or 2 having the features of claim 3; a reacted all-solid-state battery according to any one of claims 1 to 3 having the features of claim 4; a method for manufacturing a reacted all-solid-state battery according to claim 5 having the features of claim 6; a method for manufacturing a reacted all-solid-state battery according to claim 6 having the features of claim 7; a method for manufacturing a reacted all-solid-state battery according to any one of claims 5 to 7 having the features of claim 8; and a method for manufacturing a reacted all-solid-state battery according to claim 8 having the features of claim 9.

[0060] 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.

[0061] <Preparation of Positive Electrode Mixture> In a glove box in an argon atmosphere with a dew point of −68° C. or less, 40 g of zirconia balls with a diameter of 5 mm, 0.100 g of sulfur (manufactured by Aldrich Corporation) as a positive electrode active material, 0.020 g of Ketjenblack (registered trademark) EC600JD (manufactured by Lion Specialty Chemicals) as a conductive additive, and Li ６ P.S. ５0.080 g of CI (Ampcera) was placed in a 45 mL zirconia container and processed for 6 hours at 370 rpm in a planetary ball mill (Premium line P-7, Fritsch GmbH). A powder of a positive electrode mixture was obtained by milling. The composition of the positive electrode mixture was sulfur:conductive additive:sulfide solid electrolyte = 50:10:40 (mass ratio).

[0062] <Preparation of Unreacted Cell (Unreacted All-Solid-State Lithium Secondary Battery)> The unreacted cell was prepared in a glove box with an argon atmosphere at a dew point of −68° C. or less. A stainless steel cylindrical convex punch (10 mm diameter, also serving as a negative electrode current collector) was inserted into one side of a cylindrical tube jig manufactured by Macor (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and a sulfide solid electrolyte, Li, was inserted from the top of the cylindrical tube jig. ６ P.S. ５ 80 mg of Cl (manufactured by Ampcera) was placed inside. Then, another stainless steel cylindrical convex punch was inserted to sandwich the sulfide solid electrolyte, and a solid electrolyte layer with a diameter of 10 mm and a thickness of approximately 0.6 mm was formed in the cylindrical tube jig by pressing for 3 minutes at a pressure of 75 MPa using a hydraulic press. Next, the cylindrical convex punch inserted from above was temporarily removed, and 7.5 mg of the positive electrode mixture prepared above was placed on one side of the solid electrolyte layer in the cylindrical tube. A cylindrical convex punch (also serving as a positive electrode current collector) was inserted from above again and pressed for 3 minutes at a pressure of 300 MPa. A positive electrode active material layer with a diameter of 10 mm and a thickness of approximately 0.06 mm was formed on one side of the solid electrolyte layer. Next, the lower cylindrical convex punch (which also served as the 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 the negative electrode. The cylindrical tube jig was inserted from the bottom so that the indium foil was positioned on the solid electrolyte layer side, and the cylindrical convex punch was inserted again. Pressing was performed for 3 minutes at a pressure of 75 MPa to form a lithium-indium negative electrode. In this way, an unreacted cell (unreacted all-solid-state lithium secondary battery) 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.

[0063] <Preparation of Reacted Cell (Reacted All-Solid-State Lithium Secondary Battery)> The unreacted cell prepared above was subjected to an initial reaction (charge reaction or discharge reaction) and subsequent charge / discharge reactions by the following method to prepare a reacted cell (reacted all-solid-state lithium secondary battery). The initial reaction (charge reaction or discharge reaction) and subsequent charge reaction, as well as evaluation of charge / discharge characteristics, were performed using a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a constant temperature bath set at 25°C.

[0064] [Comparative Example 1] A battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.3 mA / cm ２ A constant current discharge was performed at a current density of 0.01 mA / cm to a cell voltage of 0.5 V, followed by a 2.5 V constant current / constant voltage charge and a 0.5 V constant current / constant voltage discharge at the same current density. ２ Then, the current was set to 0.6 mA / cm ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this comparative example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this comparative example.

[0065] [Example 1] A battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.3 mA / cm ２ At a current density of 4 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This was followed by constant current discharge to 0.5 V at the same current density. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this example.

[0066] [Example 2] The battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.3 mA / cm２ At a current density of 3V, constant current and constant voltage charging was performed with a cutoff current of 0.01mA / cm ２ This was followed by constant current discharge to 0.5 V at the same current density. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this example.

[0067] [Example 3] The battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.3 mA / cm ２ At a current density of 2.3 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This was followed by constant current discharge to 0.5 V at the same current density. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this example.

[0068] [Example 4] The battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 0.03 mA / cm ２ At a current density of 3V, constant current and constant voltage charging was performed with a cutoff current of 0.01mA / cm ２ This was followed by constant current discharge to 0.5 V at the same current density. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this example.

[0069] [Example 5] The battery was placed in a thermostatic chamber, and after the cell temperature became constant, a current of 12 mA / cm ２ At a current density of 3V, constant current and constant voltage charging was performed with a cutoff current of 0.01mA / cm ２ This was followed by constant current discharge to 0.5 V at the same current density. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２ This cycle was repeated three times to prepare a reacted cell for XPS evaluation in this example. Furthermore, this cycle was repeated five times to prepare a reacted cell for direct current resistance (DCR) evaluation in this example.

[0070] <X-ray Photoelectron Spectroscopy (XPS) Measurement> X-ray photoelectron spectroscopy (XPS) measurement was performed on the reacted cells for XPS evaluation prepared in the Examples and Comparative Examples by the following method. The reacted cells for XPS evaluation were disassembled in a glove box in an argon atmosphere with a dew point of −68° C. or lower, and the positive electrode active material layer was crushed to prepare a powdered sample. The powdered sample was fixed to a sample holder using indium foil and introduced into a combined electron spectrometer (ESCA 5800, manufactured by ULVAC-PHI, Inc.) using a transfer vessel without exposing it to the atmosphere, and X-ray photoelectron spectroscopy analysis was performed.

[0071] X-ray source: AlKα ray (1486.6 eV) X-ray output: 25 W 15 kV Detection area: 100 μmφ Detection depth: several nm (take-off angle 45°).

[0072] In the obtained X-ray photoelectron spectroscopy spectrum, the peak intensity ratio (A / B) was calculated from the maximum peak A in the range of 163 to 165 eV and the maximum peak B in the range of 161 to 163 eV. The results are shown in Table 1 below. The X-ray photoelectron spectroscopy spectrum (normalized to 1 as the relative intensity of the maximum peak B in the range of 161 to 163 eV) for the reacted cell for XPS evaluation prepared in Example 1 is shown in FIG. 3.

[0073] <Confirmation of phosphorus sulfide compounds> The presence or absence of phosphorus sulfide compounds was confirmed using X-ray diffraction (XRD) for the reacted cells for XPS evaluation prepared in the Examples and Comparative Examples by the following method. The reacted cells for XPS evaluation were disassembled in a glove box in an argon atmosphere with a dew point of −68°C or less, and the positive electrode active material layer was crushed to prepare a powder sample. Powder X-ray diffraction measurement was performed on this powder sample. The measurement was performed using a SmartLab manufactured by Rigaku Corporation under the following conditions.

[0074] Scan speed (2θ / θ): 2° / min Step width (2θ / θ): 0.02° Radiation source: CuKα: λ=1.5418 Å.

[0075] In the X-ray diffraction spectrum measured for each of the reacted cells for XPS evaluation in Examples 1 to 5, P was observed in the vicinity of 2θ=30 to 33°. ２ S ５ On the other hand, in the X-ray diffraction spectrum measured for the reacted cell for XPS evaluation of Comparative Example 1, a peak due to P was observed in the vicinity of 2θ = 30 to 33°. ２ S ５ From these results, it was found that in each of the reacted cells for XPS evaluation in Examples 1 to 5, the positive electrode active material layer contained a phosphorus sulfide compound, P ２ S ５ It was confirmed that the P ２ S ５ was thought to have been generated during the first charge.

[0076] <Measurement of DC Resistance (DCR)> The DC resistance (DCR) of the reacted cells for DC resistance (DCR) evaluation prepared in the Examples and Comparative Examples was measured by the following method. The measurement was carried out using a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) in a constant temperature bath set at 25°C. The battery was placed in the bath, and after the cell temperature became constant, a current of 0.6 mA / cm was applied. ２ At a current density of 2.5 V, constant current and constant voltage charging was performed with a cutoff current of 0.01 mA / cm ２The charge / discharge capacity was set to 0.5 V, and then constant current discharge was performed at the same current density to 0.5 V. The capacity value (mAh / g) per mass of the positive electrode active material was calculated from the charge / discharge capacity value at this time and the mass of the positive electrode active material (sulfur) contained in the positive electrode. Next, the capacity value was calculated as 100% of the capacity value calculated in this way, and the capacity was increased to 50% (SOC50%) by 0.2 mA / cm. ２ After a 30-minute pause, the battery was discharged at a discharge rate of 1 C for 10 seconds, and the direct current resistance (DCR) was calculated from the voltage drop and current value according to Ohm's law. The results are shown in Table 1 below.

[0077]

[0078] As shown in Table 1, according to the present invention, an increase in cell resistance can be suppressed by setting the peak intensity ratio (A / B) in the range of 0.6 to 1 in the X-ray photoelectron spectroscopy spectrum of the positive electrode active material layer. Also, as shown in Table 1, by setting the first reaction after cell assembly to a charging reaction, the peak intensity ratio (A / B) can be controlled to be in the range of 0.6 to 1. Furthermore, the results in Table 1 show that in order to further suppress an increase in cell resistance, the limit voltage (upper limit charging voltage) in the first charge is set to 3 V vs. Li / Li. ＋ The charge density in the first charge is controlled to within the range below 0.3 mA / cm ２ It is also found that it is effective to control the temperature within the following range.

[0079] 10a: laminated 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: single cell layer, 21: power generating element, 25: negative electrode current collector, 27: positive electrode current collector, 29: laminate film.

Claims

1. a positive electrode including a positive electrode active material layer disposed on a surface of a positive electrode current collector, the positive electrode active material layer including a positive electrode active material containing elemental sulfur and a sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium; a negative electrode including a negative electrode active material layer including a negative electrode active material containing an alkali metal element and disposed on the surface of a negative electrode current collector; a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a solid electrolyte; a charging step of charging an unreacted all-solid-state battery that has not been charged or discharged as an initial reaction, The positive electrode active material containing the sulfur element is selected from the group consisting of sulfur element, disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid, polycarbon sulfide, S-carbon composite, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , MoS ２ , MoS ３ , MnS, MnS ２ , CoS and CoS ２ At least one selected from the group consisting of a cathode active material in the cathode active material layer that utilizes a sulfur oxidation-reduction reaction to release lithium ions during charging and absorb lithium ions during discharging.

2. The upper limit of the charging voltage in the charging step is 4 V vs. Li / Li ＋ The method for producing a reacted all-solid-state battery according to claim 1, wherein:

3. The upper limit of the charging voltage in the charging step is 3 V vs. Li / Li ＋ The method for producing a reacted all-solid-state battery according to claim 2, wherein:

4. The current density in the charging step was 12 mA / cm ２ The method for producing a reacted all-solid-state battery according to claim 1 or 2, wherein:

5. The current density in the charging step was 0.3 mA / cm ２ The method for producing a reacted all-solid-state battery according to claim 4, wherein:

6. 2. The method for producing a reacted all-solid-state battery according to claim 1, wherein the positive electrode current collector is made of at least one material selected from aluminum, nickel, iron, stainless steel, titanium, copper, and a conductive resin.

7. Produced by the production method according to claim 1, a positive electrode including a positive electrode active material layer disposed on a surface of a positive electrode current collector, the positive electrode active material layer including a positive electrode active material containing elemental sulfur and a sulfide solid electrolyte containing elemental sulfur, elemental phosphorus, and elemental lithium; a negative electrode including a negative electrode active material layer including a negative electrode active material containing an alkali metal element and disposed on the surface of a negative electrode current collector; a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a solid electrolyte; A reacted all-solid-state battery comprising a power generating element having a reacted all-solid-state battery, in which, in an X-ray photoelectron spectroscopy spectrum of the positive electrode active material layer of the reacted all-solid-state battery, the intensity ratio (A / B) of a maximum peak A in a range of 163 to 165 eV to a maximum peak B in a range of 161 to 163 eV is 0.6 or more and 1 or less.

8. The reacted all-solid-state battery according to claim 7, wherein the negative electrode of the reacted all-solid-state battery is one in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during charging.

9. 8. The reacted all-solid-state battery of claim 7, wherein the positive electrode active material layer of the reacted all-solid-state battery further comprises a phosphorus sulfide compound.

10. The sulfide solid electrolyte of the reacted all-solid-state battery is Li ６ P.S. ５ The reacted all-solid-state battery according to claim 7, wherein X is at least one selected from Cl, Br, or I.