Solid electrolyte and solid battery

Abstract

This solid electrolyte has a first region and a second region having a composition different from that of the first region. The first region contains a compound containing lithium, zirconium, oxygen, halogen, and sulfur. The second region has a composition ratio of sulfur and oxygen of 80 wt% or more when the composition is analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analysis. When this solid electrolyte is X-ray-diffraction-measured using Cu-Kα rays, a first diffraction peak is detected in a diffraction angle range of 28.2 ± 0.4°.

Description

Solid electrolytes and solid-state batteries

[0001] This application claims priority to Japanese Patent Application No. 2024-030938, filed on March 1, 2024, the contents of which are incorporated herein by reference.

[0002] With the remarkable development of electronics technology, portable electronic devices are becoming smaller, lighter, thinner, and more multifunctional. There is also a strong demand for batteries, which serve as the power source for electronic devices, to be smaller, lighter, thinner, more reliable, and safer. Solid-state batteries, which use solid electrolytes, are attracting attention because they are safer than lithium-ion secondary batteries, which use liquid electrolytes.

[0003] The solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a complex hydride-based solid electrolyte, a halide-based solid electrolyte, or the like. ａ E ｂ G ｃ X ｄ The halide-based solid electrolyte has higher atmospheric stability, higher high-voltage resistance, and is more adaptable to various processes than oxide-based solid electrolytes, sulfide-based solid electrolytes, complex hydride-based solid electrolytes, etc.

[0004] WO 2021 / 261558 (A)

[0005] Halide-based solid electrolytes are prone to reductive decomposition, which is an irreversible reaction and is one of the causes of reduced charge-discharge efficiency in solid-state batteries.

[0006] The present disclosure has been made in view of the above problems, and aims to provide a solid electrolyte and a solid battery that have high initial charge / discharge efficiency.

[0007] In order to solve the above problems, the following means are provided.

[0008] A solid electrolyte according to a first aspect has a first region and a second region having a different composition from the first region. The first region contains a compound containing lithium, zirconium, oxygen, a halogen, and sulfur. When the composition of the second region is analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX), the composition ratio of sulfur to oxygen is 80 wt % or more. In X-ray diffraction measurement using Cu-Kα radiation, the solid electrolyte according to the first aspect exhibits a first diffraction peak in a diffraction angle range of 28.2±0.4°.

[0009] In the solid electrolyte according to the above aspect, a second diffraction peak may be detected in a diffraction angle range of 21.2±0.4° by X-ray diffraction measurement using Cu—Kα radiation, and the intensity ratio of the second diffraction peak to the first diffraction peak may be 1.0 or less.

[0010] In the solid electrolyte according to the above aspect, a third diffraction peak may be detected in a diffraction angle range of 22.3±0.4° by X-ray diffraction measurement using Cu—Kα radiation, and the intensity ratio of the third diffraction peak to the first diffraction peak may be 1.0 or less.

[0011] In the solid electrolyte according to the above aspect, a fourth diffraction peak may be detected in a diffraction angle range of 23.0±0.4° by X-ray diffraction measurement using Cu—Kα radiation, and the intensity ratio of the fourth diffraction peak to the first diffraction peak may be 1.0 or less.

[0012] In the solid electrolyte according to the above aspect, a fifth diffraction peak may be detected in a diffraction angle range of 26.7±0.4° by X-ray diffraction measurement using Cu—Kα radiation, and the intensity ratio of the fifth diffraction peak to the first diffraction peak may be 1.0 or less.

[0013] In the solid electrolyte according to the above aspect, a sixth diffraction peak may be detected in a diffraction angle range of 33.6±0.4° by X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of the sixth diffraction peak to the first diffraction peak may be 0.5 or less.

[0014] In the solid electrolyte according to the above embodiment, a seventh diffraction peak may be detected in a diffraction angle range of 32.1±0.4° in X-ray diffraction measurement using Cu—Kα radiation.

[0015] In the solid electrolyte according to the above aspect, the molar ratio of the zirconium to the sulfur in the first region may be 0.1 or more and 10.0 or less.

[0016] In the solid electrolyte according to the above aspect, the molar ratio of the halogen to the zirconium in the first region may be 2.5 or more and 7.5 or less.

[0017] The first region of the solid electrolyte according to the above aspect may have at least one substitution element selected from the group consisting of transition metals other than zirconium, rare earth elements, and alkali rare earth elements, and the content of the substitution element may be 0.3 or less when the total molar amount of the substitution element and the zirconium is 1.0.

[0018] A solid-state battery according to a second aspect includes a positive electrode, a negative electrode, and a solid electrolyte layer, the solid electrolyte layer including the solid electrolyte according to the above aspect.

[0019] The negative electrode of the solid-state battery according to the above aspect may include a negative electrode active material, which is at least one selected from the group consisting of graphite, silicon, tin, and lithium titanate.

[0020] The positive electrode of the solid-state battery according to the above aspect may include a positive electrode active material. The positive electrode active material may be lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese spinel (LiMn ２ O ４ ), and the general formula: LiNi ｘ Co ｙ Mn ｚ O ２ The composite oxide includes at least one selected from the group consisting of composite metal oxides represented by (x+y+z=1).

[0021] The solid state battery according to the above aspect may have a water content of 5000 ppm or less.

[0022] A solid state battery including the solid electrolyte according to the above embodiment has high initial charge / discharge efficiency.

[0023] 1 is a cross-sectional view of a solid-state battery according to an embodiment of the present invention;

[0024] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0025] "Solid-State Battery" FIG. 1 is a cross-sectional schematic diagram of a solid-state battery 100 according to this embodiment. The solid-state battery 100 shown in FIG. 1 includes a power generating element 40 and an exterior body 50. The exterior body 50 covers the periphery of the power generating element 40. The power generating element 40 is connected to the outside via a pair of terminals 60, 62 connected to the power generating element 40. Although a stacked-type battery is shown in FIG. 1, a wound-type battery may also be used. The solid-state battery 100 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, etc.

[0026] <Power generating element> The power generating element 40 includes a solid electrolyte layer 10, a positive electrode 20, and a negative electrode 30. The power generating element 40 is charged or discharged by the exchange of ions between the positive electrode 20 and the negative electrode 30 via the solid electrolyte layer 10 and the exchange of electrons via an external circuit.

[0027] (Solid Electrolyte Layer) The solid electrolyte layer 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The solid electrolyte layer 10 includes a solid electrolyte that can transfer ions by an externally applied voltage. For example, the solid electrolyte conducts lithium ions and inhibits the transfer of electrons.

[0028] The solid electrolyte layer 10 includes, for example, a halide-based solid electrolyte. In addition to the solid electrolyte, the solid electrolyte layer 10 may include a binder or the like. The binder may be the same as that used in the positive electrode 20 or the negative electrode 30 described below.

[0029] The solid electrolyte includes multiple regions with different compositions. The solid electrolyte has, for example, a first region and a second region. The first region and the second region have different compositions. When the solid electrolyte is measured with a scanning electron microscope (SEM), the boundary between the first region and the second region can be confirmed. For example, the second region is scattered within the plane of the first region.

[0030] The first region includes compounds containing lithium, zirconium, oxygen, halogens, and sulfur. These elements contained in the first region can be confirmed by composition analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). Lithium can be confirmed by electron energy loss spectroscopy (EELS).

[0031] The first region is, for example, Li ａ Zr ｂ G ｃ (SO ３ ) ｄ E ｅ X ｆ ... is expressed as (1).

[0032] a represents the composition ratio of Li in the compound represented by formula (1). In formula (1), a satisfies 0.2≦a<6.0, and preferably satisfies 0.5≦a≦5.0. When the content of Li contained in the compound is appropriate, the ionic conductivity of the solid electrolyte is high.

[0033] b is the composition ratio of Zr in the compound represented by formula (1). Zr is an essential element for forming the skeleton of the compound represented by formula (1). b satisfies 0.2≦b≦2.0, and more preferably 0.4≦b≦1.8.

[0034] In the compound represented by formula (1), G is one or more elements selected from the group consisting of Al, Y, Ta, Nb, In, Sn, Zn, W, Ce, Mg, Ba, Sr, Ca, N, and K. G is an element that forms the skeleton of the compound represented by formula (1), but is not an essential element. G is, for example, a substitution element that substitutes a portion of Zr. When the compound contains G, the potential window of the solid electrolyte becomes wider and the ionic conductivity becomes higher.

[0035] c is the composition ratio of G in the compound represented by formula (1), and c satisfies 0≦c≦0.3, and more preferably 0≦c≦0.2.

[0036] d is the SO in the compound represented by formula (1). ３ The composition ratio is SO ３ The ions are substituted for part of the Zr that forms the framework of the solid electrolyte. ３ ２－ ions and Zr ４＋ The covalent bond between the ions is strong. ３ ２－ The ions are Zr ４＋ This inhibits the reduction of ions, making the solid electrolyte less susceptible to reductive decomposition. ３ ２－ A solid electrolyte containing d has a wide potential window on the reduction side and is difficult to reduce. d satisfies 0.1≦c≦2.0, and more preferably satisfies 0.25≦c≦1.5.

[0037] In the compound represented by formula (1), E is PO ３ , P.O. ４ , S.O. ４ , S ２ O ３ , S ４ O ６ , P.F. ６ , P.O. ２ F ２ , P.O. ３ E is one or more elements selected from the group consisting of F, OH, and O. E is an element that forms the skeleton of the compound represented by formula (1), but is not an essential element. E is, for example, a substitution element that substitutes a part of Zr.

[0038] e is the composition ratio of E in the compound represented by formula (1), and e satisfies 0≦e≦1.0, and more preferably 0≦e≦0.75.

[0039] In the compound represented by formula (1), X is a halide atom. X is an essential atom of the solid electrolyte. X is at least one element selected from the group consisting of Cl, F, Br, and I. X preferably includes Cl. When X having a large ionic radius per valence is contained in the solid electrolyte, lithium ions flow more easily, and the ionic conductivity of the solid electrolyte increases.

[0040] f is the composition ratio of X in the compound represented by formula (1), and f satisfies 2.0≦e≦6.1, and more preferably 2.0≦e≦5.0.

[0041] In the first region, the molar ratio of zirconium to sulfur is preferably 0.1 or more and 10.0 or less. The molar ratio of zirconium to sulfur is the molar ratio of Zr element to S element, and is determined by Zr element / S element. These molar ratios are determined, for example, by area analysis using an electron probe microanalyzer (EPMA). Sulfur (S element) is converted into sulfite ions (SO ３ ２－ When a solid electrolyte contains sulfite ions, the potential window on the reduction side of the solid electrolyte becomes wider. Also, when the ratio of sulfite ions in the solid electrolyte is within an appropriate range, the ionic conductivity of the solid electrolyte increases.

[0042] Furthermore, in the first region, the molar ratio of halogen to zirconium is preferably 2.5 or more and 7.5 or less. The molar ratio of halogen to zirconium is the molar ratio of Zr element to X (halogen) element, and is determined by X element / Zr element. These molar ratios are determined, for example, by area analysis using an electron probe microanalyzer (EPMA). When the halogen is F, the resulting solid electrolyte has sufficiently high ionic conductivity and excellent oxidation resistance. When the halogen is Cl, the resulting solid electrolyte has high ionic conductivity and a good balance of oxidation resistance and reduction resistance. When the halogen is Br, the resulting solid electrolyte has sufficiently high ionic conductivity and a good balance of oxidation resistance and reduction resistance. When the halogen is I, the resulting solid electrolyte has high ionic conductivity.

[0043] In the first region, when the total molar amount of the substitution element and zirconium is 1.0, the content of the substitution element is preferably 0.3 or less. Here, the substitution element is at least one element selected from the group consisting of transition metals other than zirconium, rare earth elements, and alkali rare earth elements. The substitution element is, for example, the above-mentioned G element.

[0044] The second region has a composition ratio of sulfur and oxygen of 80 wt % or more. The composition ratio of these elements can be confirmed by composition analysis using scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). The composition ratio of sulfur and oxygen in the second region is preferably 83 wt % or more, more preferably 85 wt % or more, and even more preferably 90 wt % or more. Although not particularly limited, the composition ratio of sulfur and oxygen in the second region may be 100 wt % or less, 98 wt % or less, or 95 wt % or less. The second region may contain, for example, lithium sulfite (Li ２ SO ３ ) is included.

[0045] The solid electrolyte may include a region other than the first region and the second region. ２ ZrCl ６ etc. may be included.

[0046] In the solid electrolyte according to this embodiment, a first diffraction peak is detected in a diffraction angle 2θ range of 28.2±0.4° in X-ray diffraction measurement using Cu-Kα radiation. The first diffraction peak is preferably detected in a diffraction angle 2θ range of 28.2±0.2°, and more preferably in a diffraction angle 2θ range of 28.2±0.1°. The first diffraction peak is considered to be a diffraction peak due to the second region of the solid electrolyte. A solid electrolyte having the first diffraction peak has high initial charge / discharge efficiency. Here, the ordinal numbers (first, second, etc.) used to distinguish the diffraction peaks are used for literal distinction and are not related to the intensity of each diffraction peak. In other words, the peak with the strongest intensity confirmed by X-ray diffraction measurement is not referred to as the first diffraction peak.

[0047] Furthermore, the X-ray diffraction pattern of the solid electrolyte according to this embodiment using Cu-Kα radiation may have a second diffraction peak in the diffraction angle range of 21.2 ± 0.4°, a third diffraction peak in the diffraction angle range of 22.3 ± 0.4°, a fourth diffraction peak in the diffraction angle range of 23.0 ± 0.4°, a fifth diffraction peak in the diffraction angle range of 26.7 ± 0.4°, a sixth diffraction peak in the diffraction angle range of 33.6 ± 0.4°, or a seventh diffraction peak in the diffraction angle range of 32.1 ± 0.4°. The detection range for each diffraction peak is preferably within a range of ± 0.2° relative to the reference angle, more preferably within a range of ± 0.1°. The second to sixth diffraction peaks are considered to be diffraction peaks attributable to the second region of the solid electrolyte. The seventh diffraction peak is Li ２ ZrCl ６ It is considered that the diffraction peak is due to

[0048] The intensity ratio of the second diffraction peak to the first diffraction peak is preferably 1.0 or less. The intensity ratio of the third diffraction peak to the first diffraction peak is preferably 1.0 or less. The intensity ratio of the fourth diffraction peak to the first diffraction peak is preferably 1.0 or less. The intensity ratio of the fifth diffraction peak to the first diffraction peak is preferably 1.0 or less. The intensity ratio of the sixth diffraction peak to the first diffraction peak is preferably 0.5 or less. Although not particularly limited, the intensity ratio of each diffraction peak to the first diffraction peak may be 0.4 or less, or may be 0.3 or less. Furthermore, although not particularly limited, the intensity ratio of each diffraction peak to the first diffraction peak may be 0.001 or more, 0.01 or more, or 0.1 or more.

[0049] When X-ray diffraction measurement is performed on the solid electrolyte in a completed solid-state battery, the solid electrolyte contained in the solid electrolyte layer or electrode is extracted from the solid-state battery, and the extracted sample is analyzed.

[0050] The solid electrolyte according to this embodiment has excellent reduction resistance. One of the reasons why the solid electrolyte according to this embodiment has high reduction resistance is that SO ３ ２－ ions and Zr４＋ Zr, which is easily reduced and decomposed by interacting with ions ４＋ On the other hand, the reduction resistance of the solid electrolyte is improved. ３ ２－ The mere presence of ions may not necessarily provide sufficient reduction resistance. Although the exact cause is unknown, it is believed that by preparing a solid electrolyte so that the second region is present, the crystallinity of the entire solid electrolyte is increased, improving the reduction resistance of the solid electrolyte. Furthermore, the presence of the second region in the solid electrolyte tends to form a stable SEI film when the solid electrolyte is reductively decomposed. The stable SEI film improves the reduction resistance of the solid electrolyte. The use of the solid electrolyte according to this embodiment can improve the initial charge / discharge efficiency of a solid battery.

[0051] 1, the positive electrode 20 has a plate-shaped (foil-shaped) positive electrode current collector 22 and a positive electrode active material layer 24. The positive electrode active material layer 24 is in contact with at least one surface of the positive electrode current collector 22.

[0052] The positive electrode current collector 22 may be made of any electronically conductive material that is resistant to oxidation during charging and corrosion. The positive electrode current collector 22 may be made of, for example, a metal such as aluminum, stainless steel, nickel, or titanium, or a conductive resin. The positive electrode current collector 22 may be in the form of a powder, foil, punched, or expanded.

[0053] The positive electrode active material layer 24 contains a positive electrode active material, and optionally a solid electrolyte, a binder, and a conductive additive.

[0054] The positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions and insert and extract them (intercalate and deintercalate), and any positive electrode active material used in known solid-state batteries can be used. Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing metal phosphates. The positive electrode active material may contain additives such as Mg and Al.

[0055] The lithium-containing metal oxide is, for example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２), lithium manganese spinel (LiMn ２ O ４ ), and the general formula: LiNi ｘ Co ｙ Mn ｚ O ２ A composite metal oxide represented by (x + y + z = 1), a lithium vanadium compound (LiVOPO ４ , Li ３ V ２ (P.O. ４ ) ３ ), olivine-type LiMPO ４ (wherein M represents at least one selected from Co, Ni, Mn, and Fe), lithium titanate (Li ４ Ti ５ O １２ ) etc.

[0056] The positive electrode active material may not contain lithium. Examples of such a positive electrode active material include lithium-free metal oxides (MnO ２ , V ２ O ５ etc.), lithium-free metal sulfides (MoS ２ etc.), lithium-free fluorides (FeF ３ , V.F. ３ When a positive electrode active material that does not contain lithium is used, the negative electrode is doped with lithium ions in advance, or a negative electrode containing lithium ions is used.

[0057] The solid electrolyte contained in the positive electrode 20 is, for example, the same as the solid electrolyte contained in the solid electrolyte layer 10. When the solid electrolyte contained in the solid electrolyte layer 10, the positive electrode 20, and the negative electrode 30 is the same, the solid battery 100 is easily manufactured. The solid electrolyte contained in the positive electrode 20 may be different from the solid electrolyte contained in the solid electrolyte layer 10, for example.

[0058] The content of the solid electrolyte in the positive electrode active material layer 24 is not particularly limited, but is preferably 1 mass % or more and 50 mass % or less, and more preferably 5 mass % or more and 30 mass % or less, based on the total mass of the positive electrode active material, the solid electrolyte, the conductive additive, and the binder.

[0059] The binder bonds the positive electrode active material, the solid electrolyte, and the conductive additive to one another within the positive electrode active material layer 24, and also firmly bonds the positive electrode active material layer 24 to the positive electrode current collector 22. The positive electrode active material layer 24 preferably contains a binder. The binder preferably has oxidation resistance and good adhesiveness.

[0060] Examples of binders used in the positive electrode active material layer 24 include polyvinylidene fluoride (PVDF) or copolymers thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid (PA) and copolymers thereof, metal ion crosslinked polyacrylic acid (PA) and copolymers thereof, maleic anhydride-grafted polypropylene (PP), maleic anhydride-grafted polyethylene (PE), and mixtures thereof. Among these, PVDF is particularly preferred as the binder.

[0061] The binder content in the positive electrode active material layer 24 is not particularly limited, but is preferably 0.3% by mass to 10% by mass, and more preferably 0.3% by mass to 5% by mass, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder. If the binder content is too small, it tends to be difficult to form a positive electrode 20 with sufficient adhesive strength. Conversely, if the binder content is too high, general binders are electrochemically inactive and do not contribute to discharge capacity, making it difficult to obtain sufficient volume or mass energy density.

[0062] The conductive additive improves the electronic conductivity of the positive electrode active material layer 24. Known conductive additives can be used. Examples of the conductive additive include carbon materials such as carbon black, graphite, carbon nanotubes, and graphene; metals such as aluminum, copper, nickel, stainless steel, iron, and amorphous metals; conductive oxides such as ITO; and mixtures thereof. The conductive additive may be in the form of powder or fiber.

[0063] There are no particular limitations on the content of the conductive additive in the positive electrode active material layer 24. When a conductive additive is added, the mass ratio of the conductive additive is preferably 0.5 mass % or more and 20 mass % or less, and more preferably 1 mass % or more and 5 mass % or less, based on the total mass of the positive electrode active material, solid electrolyte, conductive additive, and binder.

[0064] 1 , the negative electrode 30 has a negative electrode current collector 32 and a negative electrode active material layer 34. The negative electrode active material layer 34 is in contact with the negative electrode current collector 32. The negative electrode active material layer 34 is located between the negative electrode current collector 32 and the solid electrolyte layer 10.

[0065] The negative electrode current collector 32 may have any suitable electronic conductivity. The negative electrode current collector 32 may be made of, for example, a metal such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin. The negative electrode current collector 32 may be in the form of a powder, a foil, a punched piece, or an expanded piece.

[0066] The negative electrode active material layer 34 contains a negative electrode active material, and optionally a solid electrolyte, a binder, and a conductive additive.

[0067] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions and insert and extract lithium ions. The negative electrode active material may be any negative electrode active material used in known solid-state batteries. The negative electrode active material layer 34 may contain, for example, lithium metal as the negative electrode active material, or one or more selected from graphite, silicon, tin, and lithium titanate.

[0068] Alternatively, the negative electrode 30 may have only the negative electrode current collector 32, with lithium metal being deposited between the negative electrode current collector 32 and the solid electrolyte layer 10 during charging and dissolving during discharging.

[0069] The solid electrolyte contained in the negative electrode 30 is, for example, the solid electrolyte described above. The solid electrolyte contained in the positive electrode 20 may be, for example, different from the solid electrolyte contained in the solid electrolyte layer 10.

[0070] The binder and conductive additive contained in the negative electrode 30 are the same as the binder and conductive additive contained in the positive electrode 20 .

[0071] The power generating element 40 may contain moisture inside. For example, any one of the solid electrolyte layer 10, the positive electrode 20, and the negative electrode 30 that constitute the power generating element 40 contains moisture. The amount of moisture contained in the power generating element is preferably 5000 ppm or less, and more preferably 600 ppm or less. The amount of moisture contained in the power generating element 40 can be measured by the Karl Fischer method. The moisture amount is the amount of moisture contained in 1.0 g of the power generating element 40. When the power generating element 40 contains water, the particles flow during pressure molding, preventing the occurrence of cracks.

[0072] <Exterior Body> The exterior body 50 houses the power generating element 40 inside. The exterior body 50 prevents moisture and the like from entering from the outside to the inside. As shown in Fig. 1 , the exterior body 50 has a metal foil 52 and a resin layer 54 laminated on each side of the metal foil 52. The exterior body 50 is a metal laminate film in which the metal foil 52 is coated with the resin layer 54 from both sides.

[0073] The metal foil 52 is, for example, aluminum foil or stainless steel foil. The resin layer 54 can be, for example, a resin film such as polypropylene. The materials constituting the inner and outer resin layers 54 may be different. For example, the outer material can be a polymer with a high melting point, such as polyethylene terephthalate (PET) or polyamide (PA), and the inner material can be polyethylene (PE) or polypropylene (PP).

[0074] <Terminals> The terminals 60 and 62 are connected to the negative electrode 30 and the positive electrode 20, respectively. The terminal 62 connected to the positive electrode 20 is a positive electrode terminal, and the terminal 60 connected to the negative electrode 30 is a negative electrode terminal. The terminals 60 and 62 are responsible for electrical connection to the outside. The terminals 60 and 62 are made of a conductive material such as aluminum, nickel, or copper. The connection method may be welding or screw fastening. It is preferable to protect the terminals 60 and 62 with insulating tape to prevent short circuits.

[0075] (Method for Producing Solid Electrolyte) The solid electrolyte of this embodiment is synthesized by mixing raw materials in a predetermined raw material ratio and then using a mechanochemical method. The raw materials are synthesized while being heated.

[0076] The temperature and time settings for synthesis using the mechanochemical method are as follows: Setting 1: Synthesis is performed in a planetary rotary ball mill for 24 hours while heating to 60°C. Setting 2: Synthesis is performed in a planetary rotary ball mill for 48 hours while heating to 45°C. Setting 3: Synthesis is performed in a planetary rotary ball mill for 48 hours while heating to 35°C. The rotation speed of the planetary rotary ball mill in the mechanochemical reaction is 300 rpm for both rotation and revolution. Whether synthesis is performed using the above setting 1, 2, or 3, a solid electrolyte is obtained in which the first and second regions are confirmed.

[0077] (Method for manufacturing a solid-state battery) The positive electrode is manufactured by applying a paste containing a positive electrode active material onto a positive electrode current collector 22 and drying it to form a positive electrode active material layer 24. The above-described solid electrolyte may be added to the paste containing the positive electrode active material.

[0078] Next, the negative electrode 30 is prepared. The negative electrode is manufactured by applying a paste containing a negative electrode active material onto a negative electrode current collector 32 and drying it to form a negative electrode active material layer 34. The above-described solid electrolyte may be added to the paste containing the negative electrode active material.

[0079] The power generating element 40 can be produced, for example, by powder molding. A guide with a hole is placed on the positive electrode 20, and the guide is filled with a solid electrolyte. The surface of the solid electrolyte is then smoothed, and the negative electrode 30 is placed on top of the solid electrolyte. This sandwiches the solid electrolyte between the positive electrode 20 and the negative electrode 30. Pressure is then applied to the positive electrode 20 and the negative electrode 30 to pressure-molde the solid electrolyte. This pressure molding produces a laminate in which the positive electrode 20, solid electrolyte layer 10, and negative electrode 30 are stacked in this order.

[0080] Next, external terminals are welded to the positive electrode current collector 22 of the positive electrode 20 and the negative electrode current collector 32 of the negative electrode 30, which form the laminate, by a known method, to electrically connect the positive electrode current collector 22 or the negative electrode current collector 32 to the external terminals. Thereafter, the laminate connected to the external terminals is housed in an exterior body 50, and the opening of the exterior body 50 is heat-sealed to seal it. Through the above steps, the solid state battery 100 according to this embodiment is obtained.

[0081] The solid-state battery according to this embodiment has a high initial charge-discharge efficiency. When the negative electrode is made of graphite, silicon, tin, or lithium titanate, the reduction potential of the solid-state battery is low, and the solid electrolyte of the solid-state battery is prone to reductive decomposition. The reductive decomposition of the solid electrolyte is an irreversible reaction, and the decomposed solid electrolyte loses its function as a solid electrolyte. Therefore, when the solid electrolyte is reductively decomposed, the charge-discharge efficiency of the solid-state battery decreases. The solid-state battery according to this embodiment uses a specified solid electrolyte with improved reduction resistance, and therefore has a high initial charge-discharge efficiency.

[0082] The above describes the embodiments of the present invention in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention.

[0083] Example 1: In a glove box with a dew point of about -75°C, ZrCl ４ and Li ２ SO ３ The raw material powder was weighed out at a predetermined molar ratio. The raw material powder was placed in a zirconia sealed container for a planetary ball mill, which had previously contained 5 mm diameter zirconia balls. The sealed container was then covered with a lid, which was then screwed onto the container body. The space between the lid and the container was then sealed with polyimide tape. The polyimide tape has the effect of blocking moisture.

[0084] The zirconia sealed container was set in a planetary ball mill. The planetary ball mill was heated to 60°C, and a mechanochemical reaction was allowed to proceed for 24 hours. That is, the conditions for producing the solid electrolyte of Example 1 were the first setting described above. The rotation speed of the planetary ball mill was 300 rpm, the revolution speed was 300 rpm, and the rotation direction and the revolution direction were opposite to each other.

[0085] The solid electrolyte thus prepared was subjected to composition analysis using SEM-EDX to confirm the distribution of elements constituting the solid electrolyte. The solid electrolyte according to Example 1 had a first region containing a compound containing lithium, zirconium, oxygen, a halogen, and sulfur, and the second region had a composition ratio of sulfur to oxygen of 80 wt % or more.

[0086] The solid electrolyte was also subjected to X-ray diffraction measurement using Cu-Kα rays, and the presence or absence of diffraction peaks and their intensity ratios were determined.

[0087] [Measurement of Ionic Conductivity] In a glove box with circulating argon gas at a dew point of about −70° C., the solid electrolyte powder was filled into a pressure molding die and pressure molded under a load of about 30 KN to prepare a measurement cell for ionic conductivity.

[0088] The pressure molding die is composed of a cylinder made of PEEK (polyether ether ketone) with a diameter of 10 mm, and upper and lower punches made of SKD11 material with a diameter of 9.99 mm.

[0089] Next, a 50 mm diameter, 5 mm thick stainless steel disk and a Teflon (registered trademark) disk with four screw holes were prepared, and the pressure molding die was set up as follows: stainless steel disk / Teflon (registered trademark) disk / pressure molding die / Teflon (registered trademark) disk / stainless steel disk. The four screws were tightened with a torque of approximately 3 N m. Screws were inserted into the screw holes on the sides of the upper and lower punches to form external connection terminals.

[0090] The external connection terminal was connected to a potentiostat (VersaSTAT3 manufactured by Princeton Applied Research) equipped with a frequency response analyzer, and the ionic conductivity was measured using an impedance measurement method. Measurement was performed at a measurement frequency range of 1 MHz to 0.1 Hz, an amplitude of 10 mV, and a temperature of 25°C. The ionic conductivity of the solid electrolyte of Example 1 was 0.4 mS / cm.

[0091] [Charge / Discharge Evaluation] Charge / discharge evaluation was carried out for each of the first negative electrode half-cell, the second negative electrode half-cell, the third negative electrode half-cell, and the full cell.

[0092] The first negative electrode half-cell was fabricated as follows: 80 mg of solid electrolyte was pressed at a pressure of 0.6 tons for 1 minute in a glove box. This solid electrolyte was LPSC (Li ６ P.S. ５Cl). Then, 10 mg of a negative electrode composite was added to one side of the pressed solid electrolyte, and the mixture was pressed at a pressure of 0.6 tons for 1 minute, followed by a final pressing at 3 tons for 1 minute. The negative electrode composite contained a negative electrode active material, a solid electrolyte, and a conductive additive in a ratio of 75 parts by mass:20 parts by mass:5 parts by mass. The negative electrode active material was lithium titanate (LTO). The solid electrolyte contained in the negative electrode was the solid electrolyte prepared by the above procedure. The conductive additive was carbon black. Li foil was then placed on the surface of the solid electrolyte opposite the surface on which the negative electrode composite was laminated. These were restrained at 1 Nm using a restraining jig and sealed in an aluminum pouch with terminals. Using this procedure, a negative electrode half cell for charge / discharge evaluation was prepared. This negative electrode half cell contained the above-mentioned solid electrolyte as the solid electrolyte contained in the negative electrode composite.

[0093] The second negative electrode half-cell differs from the first negative electrode half-cell in that the negative electrode active material is graphite, but the other conditions are the same as those of the first negative electrode half-cell.

[0094] The third negative electrode half-cell differs from the first negative electrode half-cell in that the negative electrode active material is silicon, but the other conditions are the same as those of the first negative electrode half-cell.

[0095] The full cell was fabricated using the following procedure. In a glove box, 80 mg of solid electrolyte was filled into a container and pressed at a pressure of 0.6 tons for 1 minute. The solid electrolyte was the solid electrolyte fabricated using the procedure described above. A negative electrode composite was added to one side of the pressed solid electrolyte, and the solid electrolyte was pressed at a pressure of 0.6 tons for 1 minute, followed by a final pressing at 3 tons for 1 minute. The negative electrode composite was the same as that used in the first negative electrode half-cell. Next, a positive electrode composite was added to the side of the pressed solid electrolyte opposite the side on which the negative electrode composite was laminated, and the solid electrolyte was pressed at a pressure of 0.6 tons for 1 minute, followed by a final pressing at 3 tons for 1 minute. The positive electrode composite contained a positive electrode active material, a solid electrolyte, and a conductive additive in a ratio of 60 parts by mass:35 parts by mass:5 parts by mass. The positive electrode active material was lithium cobalt oxide (LiCoO ２) The solid electrolyte contained in the positive electrode was also the solid electrolyte prepared by the above procedure. Carbon black was used as the conductive additive. These were restrained at 3 Nm using a restraining jig and sealed in an aluminum pouch with terminals. Using this procedure, a full cell for charge / discharge evaluation was prepared. This full cell contained the above solid electrolyte in the positive electrode, negative electrode, and solid electrolyte layer.

[0096] The first negative electrode half-cell, the second negative electrode half-cell, the third negative electrode half-cell, and the full cell were used to measure the initial charge-discharge efficiency. The charge-discharge, charge capacity, and discharge capacity in the charge-discharge test were measured using a charge-discharge device BCS805 (trade name; manufactured by Biologic).

[0097] The initial charge-discharge efficiency was calculated using the charge capacity in the first cycle (initial charge capacity) and the discharge capacity in the first cycle (initial discharge capacity) according to the following formula: Initial charge-discharge efficiency (%) = (discharge capacity in the first cycle (mAh) / charge capacity in the first cycle (mAh)) × 100

[0098] The charge / discharge test was performed at 1 V (vs. Li / Li ＋ ) and discharged to 3V (vs. Li / Li ＋ The charge rate and discharge rate were 0.05 C (a current value at which charging or discharging is completed in 20 hours when charging or discharging at a constant current of 1 mA is performed at 25° C.).

[0099] Examples 2 to 63 Examples 2 to 63 differ from Example 1 in that the raw materials used to synthesize the solid electrolyte and the conditions used to synthesize the solid electrolyte by the mechanochemical method were changed. The conditions used to synthesize the solid electrolyte were as follows: First setting: Synthesis was performed in a planetary ball mill for 24 hours while heating to 60°C. Second setting: Synthesis was performed in a planetary ball mill for 48 hours while heating to 45°C. Third setting: Synthesis was performed in a planetary ball mill for 48 hours while heating to 35°C.

[0100] In Examples 2 to 63, similarly to Example 1, the properties of the solid electrolyte and the charge / discharge characteristics were measured.

[0101] Comparative Examples 1 to 3 Comparative Examples 1 to 3 differ from Example 1 in that the raw materials used to synthesize the solid electrolyte and the conditions used to synthesize the solid electrolyte by the mechanochemical method were changed. The conditions used to synthesize the solid electrolyte were as follows: Fourth setting: Synthesis was performed using a planetary ball mill at room temperature (25°C) for 24 hours.

[0102] In Comparative Examples 1 to 3, similarly to Example 1, the characteristics of the solid electrolyte and the charge / discharge characteristics were measured.

[0103] The raw materials and synthesis conditions for producing the solid electrolytes of Examples 1 to 63 and Comparative Examples 1 to 3 are summarized in Tables 1 to 3 below.

[0104]

[0105]

[0106]

[0107] The evaluation results of the solid electrolytes of Examples 1 to 63 and Comparative Examples 1 to 3 are summarized in Tables 4 to 6 below.

[0108]

[0109]

[0110]

[0111] The charge-discharge characteristics of Examples 1 to 63 and Comparative Examples 1 to 3 are summarized in Tables 7 to 9 below.

[0112]

[0113]

[0114]

[0115] The charge-discharge characteristics of Examples 1 to 63 were superior to those of Comparative Examples 1 to 3. For example, Example 1 and Comparative Example 1 used the same raw materials for synthesizing the solid electrolyte, but had different charge-discharge characteristics. This is thought to be due to the difference in the state of the solid electrolyte caused by the difference in manufacturing method. Example 1, which had a first region and a second region, had superior charge-discharge characteristics to Comparative Example 1.

[0116] According to the present invention, it is possible to provide a solid electrolyte and a solid battery with high charge / discharge efficiency.

[0117] REFERENCE SIGNS LIST 10 solid electrolyte layer 20 positive electrode 22 positive electrode current collector 24 positive electrode active material layer 30 negative electrode 32 negative electrode current collector 34 negative electrode active material layer 40 power generating element 50 exterior body 52 metal foil 54 resin layer 60, 62 terminal

Claims

1. A solid electrolyte having a first region and a second region having a different composition from the first region, wherein the first region contains a compound containing lithium, zirconium, oxygen, a halogen, and sulfur, and wherein the second region has a sulfur to oxygen ratio of 80 wt % or more when analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX), and wherein a first diffraction peak is detected in a diffraction angle range of 28.2±0.4° when measured by X-ray diffraction using Cu-Kα radiation.

2. The solid electrolyte according to claim 1, wherein a second diffraction peak is detected in a diffraction angle range of 21.2±0.4° in X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of said second diffraction peak to said first diffraction peak is 1.0 or less.

3. The solid electrolyte according to claim 1, wherein a third diffraction peak is detected in a diffraction angle range of 22.3±0.4° in X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of said third diffraction peak to said first diffraction peak is 1.0 or less.

4. The solid electrolyte according to claim 1, wherein a fourth diffraction peak is detected in a diffraction angle range of 23.0±0.4° in X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of the fourth diffraction peak to the first diffraction peak is 1.0 or less.

5. The solid electrolyte according to claim 1, wherein a fifth diffraction peak is detected in a diffraction angle range of 26.7±0.4° in X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of the fifth diffraction peak to the first diffraction peak is 1.0 or less.

6. The solid electrolyte according to claim 1, wherein a sixth diffraction peak is detected in a diffraction angle range of 33.6±0.4° in X-ray diffraction measurement using Cu-Kα radiation, and the intensity ratio of said sixth diffraction peak to said first diffraction peak is 0.5 or less.

7. The solid electrolyte according to claim 1, wherein a seventh diffraction peak is detected in a diffraction angle range of 32.1±0.4° in X-ray diffraction measurement using Cu-Kα radiation.

8. The solid electrolyte according to claim 1, wherein the molar ratio of zirconium to sulfur in the first region is 0.1 or more and 10.0 or less.

9. The solid electrolyte according to claim 1, wherein the molar ratio of said halogen to said zirconium in said first region is 2.5 or more and 7.5 or less.

10. The solid electrolyte according to claim 1, wherein the first region has at least one substitution element selected from the group consisting of transition metals other than zirconium, rare earth elements, and alkali rare earth elements, and the content of the substitution element is 0.3 or less when the total molar amount of the substitution element and the zirconium is 1.

0.

11. A solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer contains the solid electrolyte according to any one of claims 1 to 10.

12. The solid-state battery according to claim 11, wherein the negative electrode contains a negative electrode active material, and the negative electrode active material is at least one selected from the group consisting of graphite, silicon, tin, and lithium titanate.

13. The positive electrode includes a positive electrode active material, and the positive electrode active material is lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese spinel (LiMn ２ O ４ ), and the general formula: LiNi ｘ Co ｙ Mn ｚ O ２ The solid state battery according to claim 11, comprising at least one selected from the group consisting of composite metal oxides represented by (x+y+z=1).

14. The solid-state battery according to claim 11, wherein the water content is 5000 ppm or less.

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