Sulfide solid electrolyte, method for producing sulfide solid electrolyte, positive electrode for power storage element, and power storage element

Abstract

The present invention has a crystal structure according to an aspect of the present invention, and contains: at least one element A selected from the group consisting of a lithium element, a sodium element, and a potassium element; a phosphorus element; at least one element M selected from the group consisting of an aluminum element and a boron element; a nitrogen element; and at least one halogen element. The molar ratio (A / P) of the content of the element A to the content of the phosphorus element is less than 3.74, and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus element is less than 0.33.

Description

Sulfide solid electrolyte, method for producing sulfide solid electrolyte, positive electrode for energy storage element, and energy storage element

[0001] The present invention relates to a sulfide solid electrolyte, a method for producing a sulfide solid electrolyte, a positive electrode for an electric storage device, and an electric storage device.

[0002] Due to their high energy density, lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The lithium ion secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring lithium ions between the electrodes. Furthermore, capacitors such as lithium ion capacitors are also widely used as energy storage elements other than lithium ion secondary batteries.

[0003] In recent years, energy storage elements have been proposed that use a solid electrolyte such as a sulfide solid electrolyte as the nonaqueous electrolyte, instead of a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a liquid such as an organic solvent.

[0004] Patent Document 1 discloses a compound A having a crystalline structure and containing, as constituent elements, one or more divalent elements A, one or more halogen elements X, and a nitrogen element, wherein the divalent element A and the halogen element X are compound A. ０．５ A sulfide solid electrolyte is described in which the hydration energy of X is greater than the hydration energy of LiI.

[0005] International Publication No. 2020 / 045634

[0006] Patent Document 1 describes that the inclusion of nitrogen element in a sulfide solid electrolyte can suppress a hydration reaction with low reversibility. However, the present inventors have found that the inclusion of nitrogen element in a sulfide solid electrolyte can sometimes result in a decrease in oxidation resistance.

[0007] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a sulfide solid electrolyte having high oxidation resistance, a method for producing such a sulfide solid electrolyte, and a positive electrode for an energy storage element and an energy storage element using such a sulfide solid electrolyte.

[0008] A sulfide solid electrolyte according to one aspect of the present invention has a crystalline structure and contains at least one element A selected from the group consisting of lithium, sodium, and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen, and at least one halogen, wherein the molar ratio (A / P) of the content of the element A to the content of the phosphorus is less than 3.74, and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus is less than 0.33.

[0009] A method for producing a sulfide solid electrolyte according to another aspect of the present invention includes treating a composition containing at least one element A selected from the group consisting of lithium, sodium, and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen, and at least one halogen, wherein the molar ratio (A / P) of the content of the element A to the content of the phosphorus is less than 3.74, and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus is less than 0.33.

[0010] A sulfide solid electrolyte according to another aspect of the present invention is produced by the method for producing a sulfide solid electrolyte according to another aspect of the present invention.

[0011] A positive electrode for an energy storage device according to another aspect of the present invention contains the sulfide solid electrolyte according to the aspect of the present invention.

[0012] An electric storage element according to another aspect of the present invention includes the sulfide solid electrolyte according to the aspect of the present invention.

[0013] According to any one aspect of the present invention, it is possible to provide a sulfide solid electrolyte having high oxidation resistance, a method for producing such a sulfide solid electrolyte, and a positive electrode for an energy storage element and an energy storage element using such a sulfide solid electrolyte.

[0014] Fig. 1 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention, and Fig. 2 is a schematic view showing an electricity storage device formed by assembling a plurality of electricity storage elements according to one embodiment of the present invention.

[0015] First, an outline of the sulfide solid electrolyte disclosed in this specification, a method for producing the sulfide solid electrolyte, and a positive electrode for an energy storage element and an energy storage element using such a sulfide solid electrolyte will be described.

[0016] [1] A sulfide solid electrolyte according to one aspect of the present invention has a crystalline structure and contains at least one element A selected from the group consisting of lithium, sodium, and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen, and at least one halogen, wherein the molar ratio (A / P) of the content of the element A to the content of the phosphorus is less than 3.74, and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus is less than 0.33.

[0017] The sulfide solid electrolyte described in [1] above has high oxidation resistance. That is, even when the sulfide solid electrolyte described in [1] above is used in, for example, a positive electrode, the Coulomb efficiency of an energy storage device using the positive electrode or the like is unlikely to decrease. The reason for this effect is unclear, but the following reason is presumed. The sulfide solid electrolyte described in [1] above contains nitrogen and at least one element M selected from the group consisting of aluminum and the like. Therefore, in the sulfide solid electrolyte described in [1] above, the presence of nitrogen and element M is thought to form a highly oxidation-resistant structure. Such a structure may be, for example, a highly oxidation-resistant coating (protective layer) containing nitrogen and element M at crystal grain boundaries, etc. Furthermore, such a structure is thought to be difficult to maintain when the content of at least one element A selected from the group consisting of lithium, sodium, and potassium or nitrogen is excessive. That is, it is presumed that the oxidation resistance of the sulfide solid electrolyte is enhanced when it contains nitrogen element and element M and the molar ratio of the content of element A to the content of phosphorus element (A / P) and the molar ratio of the content of nitrogen element to the content of phosphorus element (N / P) are within the above ranges.

[0018] The presence of a crystalline structure can be confirmed by powder X-ray diffraction measurement. In other words, in the present invention, "having a crystalline structure" means that, in powder X-ray diffraction measurement, peaks derived from the crystalline structure of the solid electrolyte are observed in the X-ray diffraction diagram. The sulfide solid electrolyte described in [1] above may contain an amorphous portion. Powder X-ray diffraction measurement is performed according to the following procedure. An airtight sample holder for X-ray diffraction measurement is filled with the sulfide solid electrolyte powder to be measured under an argon atmosphere with a dew point of -50°C or lower. Powder X-ray diffraction measurement is performed using an X-ray diffractometer (Rigaku's "MiniFlex II"). The radiation source is CuKα radiation, the tube voltage is 30 kV, and the tube current is 15 mA. Diffracted X-rays are passed through a 30 μm-thick Kβ filter and detected with a high-speed one-dimensional detector (model number: D / teX Ultra 2). The sampling width is 0.01°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

[0019] [2] In the sulfide solid electrolyte described in [1] above, the element M may contain an aluminum element.

[0020] [3] In the sulfide solid electrolyte according to the above [1] or [2], the halogen element may include a bromine element or an iodine element.

[0021] [4] The sulfide solid electrolyte according to any one of the above [1] to [3] may be represented by the following formula (1): ａ PM ｂ S ｃ N ｄ X ｅ Y ｆ... (1) In the above formula (1), A is at least one selected from the group consisting of Li, Na, and K. M is at least one selected from the group consisting of Al and B. X is at least one selected from the group consisting of F, Cl, Br, and I. Y is at least one element other than A, P, S, M, N, and X. a, b, c, d, e, and f satisfy the following relationships: 2≦a<3.74, 0.01≦b≦1, 2≦c≦6, 0.01≦d<0.33, 0.01≦e≦1, and 0≦f≦1, respectively.

[0022] The sulfide solid electrolytes described in the above [2] to [4] are preferred embodiments of the present invention, have higher oxidation resistance, and are useful as sulfide solid electrolytes.

[0023] [5] A method for producing a sulfide solid electrolyte according to another aspect of the present invention includes treating a composition containing at least one element A selected from the group consisting of lithium, sodium, and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen, and at least one halogen, wherein the molar ratio (A / P) of the content of the element A to the content of the phosphorus is less than 3.74, and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus is less than 0.33.

[0024] According to the method for producing a sulfide solid electrolyte described in the above [5], a sulfide solid electrolyte having high oxidation resistance can be produced.

[0025] The term "composition" refers to a mixture of two or more compounds or simple substances (hereinafter, compounds and simple substances are collectively referred to as compounds, etc.). The entire composition, i.e., any compound, etc. contained in the composition, may contain element A, phosphorus, element M, nitrogen, and a halogen element. The composition may also contain a compound, etc. that does not contain any of element A, phosphorus, element M, nitrogen, or halogen.

[0026] [6] In the method for producing a sulfide solid electrolyte according to the above [5], the composition is A α M βN (where A is the element A described above, M is the element M described above, and α and β are values ​​that give a stoichiometric ratio depending on the type of element M).

[0027] In the method for producing a sulfide solid electrolyte according to the above [6], the composition is A α M β Since the composition contains a compound represented by N, it is possible to suppress the release of nitrogen element from the composition during the production of the sulfide solid electrolyte. This makes it possible to control the content of the nitrogen element in the composition with high precision. In other words, since the composition contains the compound, it is possible to easily control the content of the nitrogen element relative to the content of the phosphorus element so that it falls within the above range, and therefore it is possible to reliably and easily produce a sulfide solid electrolyte with high oxidizing properties.

[0028] [7] A sulfide solid electrolyte according to another aspect of the present invention may be produced by the method for producing a sulfide solid electrolyte according to the above [5] or [6].

[0029] The sulfide solid electrolyte described in the above [7] has high oxidation resistance.

[0030] [8] A positive electrode for an energy storage device according to another aspect of the present invention contains the sulfide solid electrolyte according to any one of [1] to [4] and [7] above.

[0031] The positive electrode for an electric storage device according to the above [8] contains a sulfide solid electrolyte having high oxidation resistance, and therefore the performance of an electric storage device using the positive electrode for an electric storage device according to the above [8] can be improved.

[0032] [9] An energy storage device according to another aspect of the present invention includes the sulfide solid electrolyte according to any one of [1] to [4] and [7] above.

[0033] The energy storage element described in [9] above uses a sulfide solid electrolyte having high oxidation resistance, and therefore can exhibit good energy storage element performance.

[0034] Hereinafter, a sulfide solid electrolyte, a method for manufacturing a sulfide solid electrolyte, a positive electrode for an energy storage element, an energy storage element, a method for manufacturing an energy storage element, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art. In addition, element names may be represented by element symbols.

[0035] <Sulfide solid electrolyte> A sulfide solid electrolyte according to one embodiment of the present invention has a crystalline structure. The sulfide solid electrolyte has a predetermined elemental composition, which will be described later. The sulfide solid electrolyte has high oxidation resistance. The sulfide solid electrolyte typically has lithium ion conductivity, sodium ion conductivity, or potassium ion conductivity. The sulfide solid electrolyte preferably has lithium ion conductivity. The sulfide solid electrolyte can also exhibit high ion conductivity.

[0036] (Crystalline Structure) The sulfide solid electrolyte preferably includes a high ion conduction phase (HICP) as a crystalline structure. HICP is a specific crystalline structure that has diffraction peaks in the diffraction angle 2θ range of 19.9°±0.5° and 29.3°±0.5° in an X-ray diffraction pattern using CuKα radiation. When the sulfide solid electrolyte has a diffraction peak derived from HICP, it can exhibit good ionic conductivity.

[0037] The sulfide solid electrolyte according to one embodiment of the present invention may have a crystal structure other than HICP. Examples of other crystal structures include LGPS type, argyrodite type, Li ７ P ３ S １１ , Thio-LISICON, etc. The sulfide solid electrolyte may have an amorphous portion.

[0038] (Composition) The sulfide solid electrolyte contains at least one element A selected from the group consisting of lithium, sodium, and potassium, at least one element M selected from the group consisting of phosphorus, aluminum, and boron, nitrogen, and at least one halogen element X. The sulfide solid electrolyte also contains sulfur as a constituent element. Each constituent element will be described below.

[0039] The element A is at least one element selected from the group consisting of lithium, sodium, and potassium. The element A preferably includes lithium, and more preferably is lithium.

[0040] The upper limit of the molar ratio (A / P) of the content of element A to the content of element phosphorus is less than 3.74, preferably 3.72, more preferably 3.70, and even more preferably 3.68. The lower limit of the molar ratio (A / P) is preferably 3.00, more preferably 3.20, even more preferably 3.40, and even more preferably 3.60. The molar ratio (A / P) may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits. By setting the molar ratio (A / P) within the above range, oxidation resistance can be improved.

[0041] The element M is at least one selected from the group consisting of aluminum and boron. It is believed that the sulfide solid electrolyte forms a structure with high oxidation resistance by containing the element M together with the nitrogen element. The element M preferably contains aluminum, and more preferably is aluminum.

[0042] The lower limit of the molar ratio (M / P) of the content of element M to the content of element phosphorus is preferably 0.01, more preferably 0.02, and still more preferably 0.03. The upper limit of the molar ratio (M / P) is preferably 0.15, more preferably 0.10, and still more preferably 0.05. By setting the molar ratio (M / P) to the above upper limit or less, the ionic conductivity of the sulfide solid electrolyte can be increased. The molar ratio (M / P) may be within a range that combines any of the above lower limits with any of the above upper limits.

[0043] The upper limit of the molar ratio (N / P) of the nitrogen element content to the phosphorus element content is less than 0.33, preferably 0.30, more preferably 0.25, even more preferably 0.20, even more preferably 0.15, and particularly preferably 0.10. The lower limit of the molar ratio (N / P) is preferably 0.01, more preferably 0.02, even more preferably 0.04, and even more preferably 0.06. The molar ratio (N / P) may be in a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits. By setting the molar ratio (N / P) in the above range, oxidation resistance can be improved. Furthermore, since the portion of the sulfide solid electrolyte that comes into contact with water becomes basic, generation of hydrogen sulfide can be easily suppressed.

[0044] Examples of the halogen element X include a fluorine element, a chlorine element, a bromine element, an iodine element, etc. The halogen element X preferably contains a bromine element or an iodine element, more preferably contains both a bromine element and an iodine element, and further preferably contains a bromine element and an iodine element.

[0045] The lower limit of the molar ratio (X / P) of the content of the halogen element X to the content of the phosphorus element is preferably 5.20, more preferably 0.56, even more preferably 0.60, and even more preferably 0.64. The upper limit of the molar ratio (X / P) is preferably 0.82, more preferably 0.78, even more preferably 0.74, and even more preferably 0.70. The molar ratio (X / P) may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits.

[0046] The molar ratio ((Br+I) / X) of the total content of bromine and iodine to the total content of halogen element X is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. The molar ratio ((Br+I) / X) may be substantially 1.0.

[0047] The lower limit of the molar ratio of the bromine content to the phosphorus content (Br / P) is preferably 0.32, more preferably 0.34, even more preferably 0.36, and even more preferably 0.38. The upper limit of the molar ratio (Br / P) is preferably 0.48, more preferably 0.46, even more preferably 0.44, and even more preferably 0.42. The molar ratio (Br / P) may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits.

[0048] The lower limit of the molar ratio (I / P) of the iodide content to the phosphorus content is preferably 0.20, more preferably 0.22, even more preferably 0.24, and even more preferably 0.26. The upper limit of the molar ratio (I / P) is preferably 0.34, more preferably 0.32, even more preferably 0.30, and even more preferably 0.28. The molar ratio (I / P) may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits.

[0049] The lower limit of the molar ratio (S / P) of the sulfur element content to the phosphorus element content is preferably 3.20, more preferably 3.40, even more preferably 3.60, and even more preferably 3.80. The upper limit of the molar ratio (S / P) is preferably 4.80, more preferably 4.60, even more preferably 4.40, and even more preferably 4.20. The molar ratio (S / P) may be within a range that combines any of the above-mentioned lower limits with any of the above-mentioned upper limits.

[0050] The sulfide solid electrolyte according to one embodiment of the present invention may further contain an element Y other than the element A, phosphorus, element M, nitrogen, halogen element X, and sulfur. Examples of the other element Y include oxygen. However, the molar ratio (Y / P) of the content of the other element Y to the content of phosphorus in the sulfide solid electrolyte may preferably be, for example, 0 or more and 1 or less, and more preferably 0.1 or less, or even 0.01 or less.

[0051] The composition of the sulfide solid electrolyte according to one embodiment of the present invention is preferably any of the following: a combination of lithium, phosphorus, M, nitrogen, bromine, and sulfur as the element A; a combination of lithium, phosphorus, M, nitrogen, iodine, and sulfur as the halogen element X; and a combination of lithium, phosphorus, M, nitrogen, bromine, iodine, and sulfur as the halogen element X. Among these, a combination of lithium, phosphorus, M, nitrogen, bromine, iodine, and sulfur as the halogen element X is more preferred. In addition to the above combination of elements, the sulfide solid electrolyte may contain the above-mentioned other element Y as an optional element. In the sulfide solid electrolyte having the above combination of elements, the preferred content of each element is the same as described above.

[0052] The sulfide solid electrolyte according to one embodiment of the present invention is preferably represented by the following formula (1): ａ PM ｂ S ｃ N ｄ X ｅ Y ｆ ... (1) In the above formula (1), A is at least one selected from the group consisting of Li, Na, and K. M is at least one selected from the group consisting of Al and B. X is at least one selected from the group consisting of F, Cl, Br, and I. Y is at least one element other than A, P, S, M, N, and X. a, b, c, d, e, and f satisfy the following relationships: 2≦a<3.74, 0.01≦b≦1, 2≦c≦6, 0.01≦d<0.33, 0.01≦e≦1, and 0≦f≦1, respectively.

[0053] When the sulfide solid electrolyte according to one embodiment of the present invention has a composition represented by the above formula (1), its oxidation resistance is further improved. In the above formula (1), A preferably contains Li, and more preferably is Li. M preferably contains Al, and more preferably is Al. X preferably contains Br and I, and more preferably is Br and I. The preferred ranges of a, b, c, d, e, and f are the same as the preferred ranges of the molar ratios of the content of each element relative to the content of phosphorus element described above. That is, the preferred range of a is the same as the preferred range of the molar ratio (A / P) described above, the preferred range of b is the same as the preferred range of the molar ratio (M / P) described above, the preferred range of c is the same as the preferred range of the molar ratio (S / P) described above, the preferred range of d is the same as the preferred range of the molar ratio (N / P) described above, the preferred range of e is the same as the preferred range of the molar ratio (X / P) described above, and the preferred range of f is the same as the preferred range of the molar ratio (Y / P) described above.

[0054] (Physical properties, uses, etc.) The lower limit of the ionic conductivity at 25°C of the sulfide solid electrolyte according to one embodiment of the present invention is preferably 1 mS / cm, more preferably 2 mS / cm, even more preferably 3 mS / cm, even more preferably 4 mS / cm, and particularly preferably 5 mS / cm or 6 mS / cm. When the ionic conductivity of the sulfide solid electrolyte at 25°C is equal to or greater than the above lower limit, the charge / discharge performance of an energy storage element including the sulfide solid electrolyte can be improved. The upper limit of the ionic conductivity is not particularly limited, but may be, for example, 20 mS / cm or 10 mS / cm.

[0055] The ionic conductivity of a sulfide solid electrolyte according to one embodiment of the present invention is determined by measuring AC impedance using the following method. In an argon atmosphere with a dew point of −50°C or lower, 120 mg of sample powder is placed in a powder molding machine with an inner diameter of 10 mm, and then uniaxially pressed at 50 MPa or lower using a hydraulic press. After releasing the pressure, 120 mg of SUS316L powder is placed on the upper surface of the sample as a current collector, and then uniaxially pressed again using a hydraulic press at 50 MPa or lower. Next, 120 mg of SUS316L powder is placed on the lower surface of the sample as a current collector, and then uniaxially pressed at 360 MPa for 5 minutes to obtain a pellet for ionic conductivity measurement. This pellet for ionic conductivity measurement is inserted into an HS cell manufactured by Hohsen Co., Ltd., and AC impedance measurement is performed at a predetermined temperature. The measurement conditions are an applied voltage amplitude of 20 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 25°C.

[0056] The shape of the sulfide solid electrolyte according to one embodiment of the present invention is not particularly limited and is typically granular, blocky, or the like. The sulfide solid electrolyte can be suitably used as an electrolyte for energy storage devices such as lithium ion secondary batteries, particularly lithium ion energy storage devices. In particular, it can be particularly suitably used as an electrolyte for all-solid-state batteries. The sulfide solid electrolyte can be used for any of the positive electrode, separator, negative electrode, and the like in energy storage devices. As described above, the sulfide solid electrolyte has high oxidation resistance and is therefore suitably used as a sulfide solid electrolyte for positive electrodes.

[0057] <Method for Producing Sulfide Solid Electrolyte> A method for producing a sulfide solid electrolyte according to one embodiment of the present invention comprises treating a composition containing at least one element A selected from the group consisting of lithium, sodium, and potassium, at least one element M selected from the group consisting of phosphorus, aluminum, and boron, nitrogen, and at least one halogen element X. The composition typically also contains sulfur. According to this method for producing a sulfide solid electrolyte, a sulfide solid electrolyte with high oxidation resistance can be produced. The sulfide solid electrolyte produced by this method for producing a sulfide solid electrolyte is the same as the sulfide solid electrolyte according to one embodiment of the present invention described above.

[0058] (Composition) The composition used as a raw material in the method for producing a sulfide solid electrolyte according to one embodiment of the present invention typically contains element A, phosphorus, element M, nitrogen, and halogen element X, as well as element sulfur. The composition is typically a mixture of two or more compounds containing at least one element selected from element A, phosphorus, element M, nitrogen, halogen element X, and sulfur. Any compound contained in the composition (mixture) may contain element A, phosphorus, element M, nitrogen, halogen element X, and sulfur. One compound may contain two or more elements selected from element A, phosphorus, element M, nitrogen, halogen element X, and sulfur. For example, Li, which will be described later, is an example of a compound containing lithium and sulfur as element A. ２ S, P, which will be described later as a compound containing phosphorus and sulfur elements ２ S ５ The composition may contain a compound that does not contain any of the element A, phosphorus, element M, nitrogen, halogen element X, and sulfur.

[0059] In the composition, the molar ratio (A / P) of the content of element A to the content of phosphorus is less than 3.74. Also, the molar ratio (N / P) of the content of nitrogen to the content of phosphorus is less than 0.33. The suitable contents of each element in the composition are the same as the suitable contents of each element in the sulfide solid electrolyte according to one embodiment of the present invention described above.

[0060] Examples of compounds containing phosphorus include P ２ S ３ , P ２ S ５ , P ２ O ５ , P ３ N ５ Among these, P ２ S ３ and P ２ S ５ is preferred, and P ２ S ５ The phosphorus-containing compound may be used alone or in combination of two or more.

[0061] Examples of the compound containing a halogen element X include compounds of the element A, sulfur, phosphorus, etc. with the halogen element X, and a compound of the element A with the halogen element X is preferred, and a compound of lithium with the halogen element X is more preferred. Examples of the compound of lithium with the halogen element X include LiF, LiCl, LiBr, and LiI. One type of compound containing a halogen element X may be used alone, or two or more types may be used in combination.

[0062] As the compound containing a nitrogen element, a compound containing a nitrogen element and an element M is preferred, and A α M β Compounds represented by N (A is the element A described above, M is the element M described above, and α and β are values ​​that give a stoichiometric ratio depending on the type of element M) are more preferred. α M β The compound represented by N can suppress the release of nitrogen element from the composition in the treatment process described below. This is thought to be because, as described in Patent Document 1, for example, when a raw material compound containing nitrogen element and element M is used, the nitrogen defect generation energy is large, making it difficult for nitrogen defects to be generated during the synthesis process and nitrogen gas to be generated. Therefore, it becomes possible to control the content of the nitrogen element in the composition with high precision. That is, when the composition is A α M β By including the compound represented by N, the molar ratio of the nitrogen element content to the phosphorus element content (N / P) can be easily controlled to be within the above range, and therefore a sulfide solid electrolyte with high oxidizing properties can be reliably and easily produced.

[0063] A α M β The compound represented by N includes a compound containing lithium, nitrogen, and element M (hereinafter also referred to as Li-M-N-containing compound). The Li-M-N-containing compound can be produced by the following procedure. First, Li ３Nitrides of N and element M are prepared and mixed in a mortar or the like. Next, pellets of the mixed raw material compounds are produced. Next, the pellets are heat-treated to produce a Li-M-N-containing compound. Note that the means for preparing the Li-M-N-containing compound is not limited to this, and it may be produced by other methods. For example, the raw material for the Li-M-N-containing compound may be two or more compounds containing any of lithium element, element M, and nitrogen element. The Li-M-N-containing compound may be produced by mechanical milling. An industrially produced and commercially available Li-M-N-containing compound may also be prepared.

[0064] As the Li-M-N-containing compound, a lithium composite nitride of element M is preferably used. Examples of the lithium composite nitride of element M include Li １．５ Al ０．５ N., Li. １．５ B ０．５ The lithium composite nitride may be, for example, a lithium composite nitride having a lithium element content relative to a nitrogen element content of, for example, Li ３ It is less than N, etc. Therefore, from the viewpoint of controlling the molar ratio (A / P) of the content of element A to the content of element phosphorus so as to be within the above range, it is preferable that the composition contains the lithium composite nitride. Furthermore, when the composition contains the lithium composite nitride, it is possible to produce a sulfide solid electrolyte in which the generation of hydrogen sulfide is suppressed. The reason for this is that when the composition contains the lithium composite nitride, the obtained sulfide solid electrolyte can reliably and easily contain a sufficient amount of element nitrogen, and becomes basic at the portion in contact with water, making it difficult for hydrogen sulfide to be generated. Among the above lithium composite nitrides, Li １．５ Al ０．５ N is preferred.

[0065] Other compounds containing nitrogen include, for example, Li ３ N, PN, P ３ N ５ , S ４ N ４ , S ２ N ２ , S ４ N２ The nitrogen-containing compound may be used alone or in combination of two or more.

[0066] As the compound containing element M, a compound containing nitrogen element and element M is preferred, α M β Compounds represented by N are more preferred. Other compounds containing element M include oxides of element M, sulfides of element M, nitrides of element M, and alloys of atoms of element M and lithium atoms. Examples of sulfides of element M include Al ２ S ３ Examples of nitrides of element M include AlN and BN. The compound containing element M may be used alone or in combination of two or more.

[0067] Examples of compounds containing element A include halides of element A (such as the above-mentioned LiF, LiCl, LiBr, and LiI), α M β The compound represented by N (Li １．５ Al ０．５ N etc.), Li ２ S., Li. ２ O, Li ３ N., Li. ２ CO ３ , metallic lithium, Na ２ S, Na ２ O, Na ３ N, Na ２ CO ３ , metallic sodium, K ２ S.K. ２ O.K. ３ N.K. ２ CO ３ , metallic potassium, etc. Among these, Li ２ S., Li. １．５ Al ０．５ N, LiBr and LiI are preferred. The compound containing element A may be used alone or in combination of two or more.

[0068] Examples of compounds containing sulfur include Li ２ S, P ２ S ３ , P２ S ５ , Al ２ S ３ , elemental sulfur, etc. Among these, Li ２ S, P ２ S ３ and P ２ S ５ is preferred, and Li ２ S and P ２ S ５ The sulfur-containing compound may be used alone or in combination of two or more.

[0069] For example, in one embodiment, the composition comprises Li ２ S and P ２ S ５ and Li １．５ Al ０．５ It may be a composition containing N, LiBr, and LiI, ２ S and P ２ S ５ and Li １．５ Al ０．５ It may also be a composition consisting of N, LiBr and LiI.

[0070] (Treatment Step) In a method for producing a sulfide solid electrolyte according to one embodiment of the present invention, the composition is treated to obtain a sulfide solid electrolyte. Examples of the treatment include a method of obtaining an intermediate by mechanical milling or the like and then heating the intermediate. Note that the means for obtaining the intermediate is not limited to this, and methods other than mechanical milling, such as melt quenching, may also be used.

[0071] Mechanical milling may be either dry or wet, but wet milling is preferred because it allows for more uniform mixing of raw material compounds, etc. Examples of mechanical milling include milling using a container-driven mill, a media stirring mill, a high-speed rotary grinder, a roller mill, a jet mill, etc. Examples of container-driven mills include a rotary mill, a vibration mill, a planetary mill, etc. Examples of media stirring mills include an attritor, a bead mill, etc. Examples of high-speed rotary grinders include a hammer mill, a pin mill, etc. Among these, a container-driven mill is preferred, and a planetary mill is particularly preferred.

[0072] The intermediate obtained by mechanical milling or the like may have a crystalline structure, but is preferably a so-called sulfide glass. "Sulfide glass" refers to a sulfide solid electrolyte containing an amorphous structure. When the intermediate is sulfide glass, Li ２ It is possible to obtain a sulfide solid electrolyte in which each element is highly dispersed and there is little low-stability crystalline phase such as S.

[0073] The heating (heat treatment) is performed on an intermediate obtained by mechanical milling or the like. This results in a sulfide solid electrolyte in which at least a portion of the intermediate is crystallized, preferably at least a portion of which is crystallized into the above-mentioned HICP. The heating (heat treatment) may be performed under a reduced pressure atmosphere or an inert gas atmosphere. The heating temperature range is, for example, preferably 150°C to 250°C, more preferably 170°C to 240°C, and even more preferably 180°C to 230°C. By setting the heating temperature to the above lower limit or higher, crystallization progresses sufficiently, and a sulfide solid electrolyte with sufficiently high oxidation resistance is obtained. Furthermore, by setting the heating temperature to the above upper limit or lower, precipitation of a phase with low ionic conductivity (LICP: Low Ion Conduction Phase) is suppressed, and a sulfide solid electrolyte with high ionic conductivity is obtained. LICP has a specific crystal structure that exhibits diffraction peaks in the diffraction angle 2θ ranges of 21.0°±0.5° and 28.0°±0.5° in an X-ray diffraction pattern using CuKα radiation.

[0074] <Positive electrode for energy storage device> A positive electrode for an energy storage device according to one embodiment of the present invention (hereinafter also referred to as "positive electrode") contains the sulfide solid electrolyte according to one embodiment of the present invention. Because the positive electrode contains the sulfide solid electrolyte according to one embodiment of the present invention, which has high oxidation resistance, when used in an energy storage device, the charge / discharge efficiency and the like of the energy storage device can be improved. The positive electrode includes a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer. The positive electrode may have an intermediate layer between the positive electrode substrate and the positive electrode active material layer.

[0075] The positive electrode may be used in combination with a solid electrolyte other than the sulfide solid electrolyte according to one embodiment of the present invention. Examples of the other solid electrolyte include sulfide solid electrolytes other than the sulfide solid electrolyte according to one embodiment of the present invention, oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and quasi-solid electrolytes, with sulfide solid electrolytes being preferred.

[0076] Examples of sulfide solid electrolytes other than the sulfide solid electrolyte according to one embodiment of the present invention include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-P ２ S ５ -Li ３ N., Li. ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Zｍ S ２ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.), Li ６ P.S. ５ Cl, Li １０ GeP ２ S １２ Among them, examples of sulfide solid electrolytes other than the sulfide solid electrolyte according to one embodiment of the present invention include Li ６ P.S. ５ An argyrodite-type solid electrolyte such as Cl can be suitably used.

[0077] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0078] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the energy storage element. The "average thickness" is the average value of thicknesses measured at any five locations (the same applies hereinafter to the average thickness).

[0079] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0080] The positive electrode active material layer includes a positive electrode active material and a sulfide solid electrolyte. The positive electrode active material layer can be formed from a so-called positive electrode mixture including a positive electrode active material and a sulfide solid electrolyte. The positive electrode active material layer may contain a mixture or composite including a positive electrode active material and a sulfide solid electrolyte, etc. The positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, a filler, etc., as needed. One or more of these optional components may not be substantially present in the positive electrode active material layer.

[0081] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. Examples of the positive electrode active material include α-NaFeO ２ Examples of suitable lithium transition metal composite oxides include those having a α-type crystal structure, those having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. ２ As the lithium transition metal composite oxide having a crystalline structure, for example, Li[Li ｘ Ni （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Co （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Liｘ Co （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Mn （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), Li[Li ｘ Ni γ Co β Al （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li ｘ Mn ２ O ４ , Li ｘ Ni γ Mn （２－γ） O ４ Examples of polyanion compounds include LiFePO ４ , LiMnPO ４ , LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２ CoPO ４ Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. These materials have a surface that is not covered with other materials (e.g., LiNbO ３ In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0082] The positive electrode active material is preferably a lithium transition metal composite oxide, more preferably a lithium transition metal composite oxide containing at least one of nickel, cobalt, and manganese, even more preferably a lithium transition metal composite oxide containing at least two of nickel, cobalt, and manganese, and even more preferably a lithium transition metal composite oxide containing nickel, cobalt, and manganese. This lithium transition metal composite oxide is α-NaFeO ２ It is preferable that the lithium transition metal composite oxide has a crystalline structure of the type 1. By using such a lithium transition metal composite oxide, it is possible to increase the energy density.

[0083] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above-mentioned lower limit or more, the positive electrode active material is easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above-mentioned upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0084] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0085] The content of the positive electrode active material in the positive electrode active material layer is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 90% by mass or less, and even more preferably 50% by mass or more and 85% by mass or less, with the lower limit being 60% by mass, and even more preferably 70% by mass. By setting the content of the positive electrode active material within the above range, it is possible to increase the discharge capacity of the energy storage element, etc.

[0086] The content of all solid electrolytes in the positive electrode active material layer is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less. The content of the sulfide solid electrolyte according to one embodiment of the present invention relative to all solid electrolytes in the positive electrode active material layer is preferably 5% by mass or more and 100% by mass or less, more preferably 10% by mass or more and 100% by mass or less, and even more preferably 20% by mass or more and 100% by mass or less. By setting the content of the solid electrolyte within the above range, it is possible to increase the discharge capacity of the energy storage element, etc.

[0087] Examples of the composite of a positive electrode active material and a solid electrolyte or the like include a composite in which the positive electrode active material and the solid electrolyte or the like are chemically or physically bonded, and a composite in which the positive electrode active material and the solid electrolyte or the like are mechanically combined. The composite may be one in which the positive electrode active material and the solid electrolyte or the like are present within a single particle, and examples thereof include one in which the positive electrode active material and the solid electrolyte or the like form an aggregated state, and one in which a coating containing the solid electrolyte or the like is formed on at least a portion of the surface of the positive electrode active material.

[0088] A composite (composite particle) in which at least a portion of the surface of a particle of a positive electrode active material is coated with a sulfide solid electrolyte according to one embodiment of the present invention is also a suitable aspect of the present invention. By coating at least a portion of the surface of the particle of a positive electrode active material with a sulfide solid electrolyte according to one embodiment of the present invention, good ionic conductivity can be exhibited. Furthermore, the sulfide solid electrolyte according to one embodiment of the present invention has good oxidation resistance, making it particularly useful as a solid electrolyte for coating a positive electrode active material. The content of the sulfide solid electrolyte in the composite is, for example, preferably 1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 10% by mass or less. The content of the composite in the positive electrode active material layer is, for example, preferably 60% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less, and even more preferably 75% by mass or more and 85% by mass or less.

[0089] The composite (composite particles) can be produced, for example, by mixing a particulate or powdered positive electrode active material and a solid electrolyte while applying impact, compression, and shear forces. In this case, components other than the positive electrode active material and the solid electrolyte may be further mixed to form the composite. This composite process can be performed, for example, using an apparatus equipped with an impeller (also referred to as a rotating blade or impeller). Specifically, the process is a mechanical kneading process in which an impeller in a container is rotated to apply impact, compression, and shear forces to the mixture of the positive electrode active material and the solid electrolyte between the impeller and the wall of the container. The process can be performed either dry or wet. The positive electrode active material and the solid electrolyte may be mixed in advance before performing the process using the apparatus equipped with the impeller. Alternatively, the positive electrode active material and the solid electrolyte may be separately introduced into the apparatus equipped with the impeller.

[0090] The positive electrode active material layer may include the composite (composite particles), another solid electrolyte, a conductive agent, and a binder. In such a configuration, the solid electrolyte constituting the composite and the other solid electrolyte may both be the sulfide solid electrolyte according to one embodiment of the present invention. Furthermore, the other solid electrolyte may be a solid electrolyte other than the sulfide solid electrolyte according to one embodiment of the present invention. For example, the other solid electrolyte may suitably be a sulfide solid electrolyte other than the sulfide solid electrolyte according to one embodiment of the present invention exemplified above.

[0091] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, conductive ceramics, etc. Examples of carbon materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes, fullerenes, etc. The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. Furthermore, these materials may be used in combination. For example, a composite material of carbon black and carbon nanotubes may be used.

[0092] The content of the conductive agent in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 6% by mass or less, and the upper limit of the content of the conductive agent may be 5%, 4%, or 3% by mass. By setting the content of the conductive agent within the above range, the energy density of the energy storage element can be increased.

[0093] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0094] The content of the binder in the positive electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass, and the upper limit of the binder content may be 5%, 4%, or 3% by mass. By setting the binder content within the above range, the positive electrode active material can be stably maintained.

[0095] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. In one embodiment of the present invention, the content of the thickener in the positive electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, or the positive electrode active material layer may be substantially free of thickener.

[0096] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. In one embodiment of the present invention, the content of the filler in the positive electrode active material layer may be 1% by mass or less, or 0.1% by mass or less, and the positive electrode active material layer may be substantially free of filler.

[0097] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0098] The average thickness of the positive electrode active material layer is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the positive electrode active material layer to the above lower limit or more, a storage element having a high energy density can be obtained. By setting the average thickness of the positive electrode active material layer to the above upper limit or less, it is possible to achieve miniaturization of the storage element.

[0099] <Electricity Storage Element> An energy storage element according to one embodiment of the present invention contains the sulfide solid electrolyte according to one embodiment of the present invention. An all-solid-state battery will be specifically described below as an energy storage element according to one embodiment of the present invention. The energy storage element 10 of FIG. 1 is an all-solid-state battery, and is a secondary battery in which a positive electrode 1 and a negative electrode 2 are arranged with an isolation layer 3 between them. The positive electrode 1 has a positive electrode substrate 4 and a positive electrode active material layer 5, with the positive electrode substrate 4 being the outermost layer of the positive electrode 1. The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6, with the negative electrode substrate 7 being the outermost layer of the negative electrode 2. In the energy storage element 10 shown in FIG. 1 , the negative electrode active material layer 6, the isolation layer 3, the positive electrode active material layer 5, and the positive electrode substrate 4 are stacked in this order on the negative electrode substrate 7.

[0100] The energy storage element 10 contains a sulfide solid electrolyte according to an embodiment of the present invention in at least one of the positive electrode 1, the negative electrode 2, and the separator 3. More specifically, the sulfide solid electrolyte according to an embodiment of the present invention is contained in at least one of the positive electrode active material layer 5, the negative electrode active material layer 6, and the separator 3. When the positive electrode 1 contains the sulfide solid electrolyte according to an embodiment of the present invention, the positive electrode 1 is a positive electrode for an energy storage element according to an embodiment of the present invention. Because the energy storage element 10 uses a sulfide solid electrolyte that is highly resistant to oxidation, it is possible to improve the performance of the energy storage element, such as charge / discharge efficiency and capacity retention rate.

[0101] The energy storage element 10 may use a solid electrolyte other than the sulfide solid electrolyte according to one embodiment of the present invention. Examples of the other solid electrolyte include those exemplified in the description of the positive electrode for the energy storage element according to one embodiment of the present invention, and a sulfide solid electrolyte is preferred. Furthermore, a single layer in the energy storage element 10 may contain multiple different types of solid electrolytes, or each layer may contain a different solid electrolyte.

[0102] (Positive Electrode) The positive electrode 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5 disposed on the positive electrode substrate 4 directly or via an intermediate layer. In one embodiment of the present invention, the positive electrode 1 is a positive electrode for an energy storage element according to one embodiment of the present invention.

[0103] (Negative Electrode) The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6 disposed directly or via an intermediate layer on the negative electrode substrate 7. The configuration of the intermediate layer is not particularly limited, and can be selected from the configurations exemplified for the positive electrode for an energy storage element according to one embodiment of the present invention, for example.

[0104] The negative electrode substrate 7 is electrically conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys of these metals, and carbonaceous materials are used as the material for the negative electrode substrate 7. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate 7 include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate 7. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0105] The average thickness of the negative electrode substrate 7 is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate 7 within the above range, the strength of the negative electrode substrate 7 can be increased, and the energy density per volume of the energy storage element 10 can be increased.

[0106] The negative electrode active material layer 6 contains a negative electrode active material. The negative electrode active material layer 6 can be formed from a so-called negative electrode mixture containing the negative electrode active material. The negative electrode active material layer 6 may contain a solid electrolyte, or a mixture or composite of the negative electrode active material and the solid electrolyte. The negative electrode active material layer 6 may contain optional components such as a conductive agent, a binder, a thickener, a filler, etc. as needed. The types and suitable contents of these optional components in the negative electrode active material layer 6 are the same as those of the optional components in the positive electrode active material layer 5 described above. One or more of these optional components may not be substantially present in the negative electrode active material layer 6.

[0107] The negative electrode active material layer 6 may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0108] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７ Examples of the material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer 6, one of these materials may be used alone, or two or more may be used in combination.

[0109] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0110] "Non-graphitic carbon" refers to a carbon material that has an average lattice spacing (d ００２ ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0111] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released from the carbonaceous material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode is 0.7 V or higher.

[0112] "Non-graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less.

[0113] "Graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0114] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the negative electrode active material layer 6 is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected, for example, from the methods exemplified for the positive electrode for a storage device according to one embodiment of the present invention. When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer 6 may be in the form of a foil.

[0115] The content of the negative electrode active material in the negative electrode active material layer 6 is preferably 10% by mass or more and 100% by mass or less, more preferably 30% by mass or more and 95% by mass or less, with the lower limit being 50% by mass, and even more preferably 70% by mass. When the negative electrode active material is a metal such as metallic lithium, the lower limit of the content of the negative electrode active material in the negative electrode active material layer 6 may be 95% by mass or 99% by mass. By setting the content of the negative electrode active material within the above range, the discharge capacity of the energy storage element 10 can be increased, for example.

[0116] When the negative electrode active material layer 6 contains a solid electrolyte, the content of the solid electrolyte is preferably 5% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and in some cases the upper limit may be even more preferably 50% by mass. By setting the content of the solid electrolyte within the above range, it is possible to increase the discharge capacity of the energy storage element 10, etc. When the sulfide solid electrolyte according to one embodiment of the present invention is used in the negative electrode active material layer 6, the content of the sulfide solid electrolyte according to one embodiment of the present invention relative to the total solid electrolyte in the negative electrode active material layer 6 is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably substantially 100% by mass.

[0117] The mixture or composite of the negative electrode active material and the solid electrolyte or the like can be the mixture or composite of the above-mentioned positive electrode active material and the solid electrolyte or the like, in which the positive electrode active material is replaced with the negative electrode active material.

[0118] The average thickness of the negative electrode active material layer 6 is preferably 30 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the negative electrode active material layer 6 to be equal to or greater than the above lower limit, it is possible to obtain an energy storage element 10 having a high energy density. By setting the average thickness of the negative electrode active material layer 6 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10.

[0119] (Isolation Layer) The isolation layer 3 contains a solid electrolyte. Examples of the solid electrolyte include those exemplified in the description of the sulfide solid electrolyte according to one embodiment of the present invention and the positive electrode for an energy storage device according to one embodiment of the present invention. The content of the solid electrolyte in the isolation layer 3 is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and sometimes even more preferably substantially 100% by mass. When the sulfide solid electrolyte according to one embodiment of the present invention is used in the isolation layer 3, the content of the sulfide solid electrolyte according to one embodiment of the present invention relative to the total solid electrolyte in the isolation layer 3 is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably substantially 100% by mass.

[0120] The isolation layer 3 contains Li ３ P.O. ４ The cathode may contain optional components such as phosphate compounds, oxides, halogen compounds, binders, thickeners, and fillers. The optional components such as binders, thickeners, and fillers can be selected from the materials exemplified for the positive electrode for an energy storage element according to one embodiment of the present invention.

[0121] The average thickness of the isolation layer 3 is preferably 1 μm or more and 50 μm or less, and more preferably 3 μm or more and 20 μm or less. By setting the average thickness of the isolation layer 3 to be equal to or more than the above-mentioned lower limit, it is possible to reliably insulate the positive electrode 1 from the negative electrode 2. By setting the average thickness of the isolation layer 3 to be equal to or less than the above-mentioned upper limit, it is possible to increase the energy density of the energy storage element 10.

[0122] <Electricity Storage Device> The energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) configured by assembling a plurality of energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, it is sufficient that the technology of the present invention is applied to at least one energy storage element included in the energy storage unit.

[0123] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 10, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more energy storage elements 10, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements 10.

[0124] <Method for manufacturing energy storage element> A method for manufacturing an energy storage element according to one embodiment of the present invention can be performed by a commonly known method, except that the sulfide solid electrolyte according to one embodiment of the present invention is used as part or all of the solid electrolyte. Specifically, the manufacturing method includes, for example, (1) preparing a positive electrode mixture, (2) preparing a separator material, (3) preparing a negative electrode mixture, and (4) stacking a positive electrode, a separator, and a negative electrode. Each step will be described in detail below.

[0125] (1) Positive Electrode Mix Preparation Step In this step, a positive electrode mix for forming a positive electrode (positive electrode active material layer) is usually prepared. The method for preparing the positive electrode mix is ​​not particularly limited and can be appropriately selected depending on the purpose. For example, the positive electrode mix can be prepared by mixing a positive electrode active material with a solid electrolyte using a mechanical milling method or the like. Alternatively, a mixture or composite of a positive electrode active material and a solid electrolyte can be prepared in advance using the above-mentioned method or the like, and the resulting mixture or composite can be mixed with other components.

[0126] (2) Separator Material Preparation Step In this step, an separator material for forming an separator is usually prepared. When the energy storage device is an all-solid-state battery, the separator material can be a solid electrolyte. The separator material can be prepared by a conventionally known method. For example, it can be obtained by processing a predetermined material by mechanical milling. The separator material may also be prepared by a melt-quenching method in which predetermined materials are heated to a melting temperature or higher, melt-mixed in a predetermined ratio, and then quenched. Other methods for synthesizing the separator material include, for example, a solid-phase method in which the material is sintered under reduced pressure, a liquid-phase method such as solution deposition, a gas-phase method, and mechanical milling followed by sintering in an argon atmosphere.

[0127] (3) Negative electrode mixture preparation step In this step, a negative electrode mixture for forming a negative electrode (negative electrode active material layer) is usually prepared. The specific method for preparing the negative electrode mixture is the same as that for the positive electrode mixture. Instead of the negative electrode mixture, the negative electrode active material layer may be formed from lithium foil or the like.

[0128] (4) Stacking Step In this step, for example, a positive electrode having a positive electrode substrate and a positive electrode active material layer, a separator layer, and a negative electrode having a negative electrode substrate and a negative electrode active material layer are stacked. In this step, the positive electrode, separator layer, and negative electrode may be formed sequentially in this order, or vice versa; the order of forming each layer is not particularly limited. For example, the positive electrode is formed by pressure molding a positive electrode substrate and a positive electrode mixture, the separator layer is formed by pressure molding an separator material, and the negative electrode is formed by pressure molding a negative electrode substrate and a negative electrode mixture. The positive electrode, separator layer, and negative electrode may be stacked by pressure molding the positive electrode substrate, positive electrode mixture, separator material, negative electrode mixture, and negative electrode substrate all at once. The positive electrode and negative electrode may be molded in advance, and then pressure molded and stacked with the separator layer. Each layer may be formed by coating or the like.

[0129] <Other Embodiments> The sulfide solid electrolyte, the method for manufacturing a sulfide solid electrolyte, the positive electrode for an energy storage device, and the energy storage device of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0130] For example, the energy storage element according to the present invention may include layers other than the positive electrode, separator, and negative electrode. The present invention can also be applied to an energy storage element including a bipolar electrode. The energy storage element according to the present invention may also include a liquid. Examples of such an energy storage element include an energy storage element in which voids in the positive electrode active material layer 5, separator 3, and negative electrode active material layer 6 of the above-described energy storage element 10 are filled with a nonaqueous electrolyte solution containing an ionic liquid or the like. The energy storage element according to the present invention may be a secondary battery, a capacitor, or the like.

[0131] EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0132] [Example 1] Li was obtained by the following treatment. ３．６７ P.A.I.L. ０．０３ S ３．９５ N ０．０６ Br ０．４０ I ０．２７ A sulfide solid electrolyte represented by the formula: Li ３ N and AlN were weighed to a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Then, the mixture was heat-treated at 750°C for 1 hour to form a pellet. １．５ Al ０．５ N was prepared. １．５ Al ０．５ N is determined by X-ray diffraction measurement to be the main phase of Li. １．５ Al ０．５ It was confirmed that the substance was LiN. ２S (99.98%, Aldrich), P ２ S ５ (99%, Aldrich), Li １．５ Al ０．５ N, LiBr (99.999%, manufactured by Aldrich), and LiI (99.999%, manufactured by Aldrich) were weighed to a molar ratio of 54.1:18.6:2.3:15.0:10.0, and then mixed in a mortar to prepare a composition containing lithium (element A), phosphorus, bromine and iodine (halogen elements), nitrogen, aluminum (element M), and sulfur. The composition was placed in a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. Mechanical milling was performed for 45 hours at an orbital rotation speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line PL-7), to obtain an intermediate. The intermediate was heated (heat treated) at 220 ° C. for 2 hours to obtain the sulfide solid electrolyte of Example 1. The heating temperature was set to be near the crystallization temperature, within ±50°C of the crystallization temperature. The crystallization temperature was determined by taking a portion of the intermediate after mechanical milling and subjecting it to DSC measurement. The DSC measurement was performed under the following conditions: a DSC device (Rigaku Thermo Plus DSC8230) was used, and a sealed SUS pan was used, and the temperature was increased from room temperature to 400°C at a rate of 10°C / min.

[0133] [Examples 2, 4, 5, Comparative Examples 1, 3 to 8] The sulfide solid electrolytes of Examples 2, 4, 5 and Comparative Examples 1, 3 to 8 were obtained in the same manner as in Example 1, except that the amounts of raw material compounds used and the like were adjusted so that the element ratios and composition formulas of the sulfide solid electrolytes were as shown in Table 1, and the heating temperature (HT) was set as shown in Table 1. Each heating temperature was within a range of ±50°C of the crystallization temperature determined in the same manner as in Example 1 above.

[0134] [Example 3] Li was obtained by the following treatment. ３．６７ PB ０．０２ S ３．９７ N ０．０４ Br ０．４０ I ０．２７ A sulfide solid electrolyte represented by the formula: Li ３N and BN were weighed to a molar ratio of 1.1:1, mixed in a mortar, and pelletized. Then, the mixture was heat-treated at 800°C for 10 minutes to form a pellet. １．５ B ０．５ N was prepared. １．５ B ０．５ N is determined by X-ray diffraction measurement to be the main phase of Li. １．５ B ０．５ It was confirmed that the substance was LiN. ２ S (99.98%, Aldrich), P ２ S ５ (99%, Aldrich), Li １．５ B ０．５ N, LiBr (99.999%, manufactured by Aldrich), and LiI (99.999%, manufactured by Aldrich) were weighed to a molar ratio of 54.8: 18.7: 1.5: 15.0: 10.0, and then mixed in a mortar to prepare a composition containing lithium (element A), phosphorus, bromine and iodine (halogen elements), nitrogen, boron (element M), and sulfur. The composition was placed in a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. Mechanical milling was performed for 45 hours at an orbital rotation speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line PL-7), to obtain an intermediate. The intermediate was heated (heat treated) at 180 ° C. for 2 hours to obtain the sulfide solid electrolyte of Example 3. This heating temperature is within the range of ±50° C. of the crystallization temperature determined in the same manner as in Example 1 above.

[0135] [Comparative Example 2] Li was obtained by the following treatment. ３．６７ PSi ０．０１ S ３．９７ N ０．０４ Br ０．４０ I ０．２７ A sulfide solid electrolyte represented by the formula: Li ３ N and Si ３ N ４ The two compounds were weighed out so as to have a molar ratio of 5.1:1, mixed in a mortar, and then pelletized. Then, the mixture was heat-treated at 800°C for 10 minutes to obtain Li １．６７ Si ０．３３N was prepared. １．６７ Si ０．３３ N is determined by X-ray diffraction measurement to be the main phase of Li. １．６７ Si ０．３３ It was confirmed that the substance was LiN. ２ S (99.98%, Aldrich), P ２ S ５ (99%, Aldrich), Li １．６７ Si ０．３３ N, LiBr (99.999%, manufactured by Aldrich), and LiI (99.999%, manufactured by Aldrich) were weighed to a molar ratio of 54.8:18.7:1.5:15.0:10.0, and then mixed in a mortar to prepare a composition containing element A: lithium, phosphorus, bromine and iodine, which are halogen elements, nitrogen, silicon, and sulfur. The composition was placed in a sealed 80 mL zirconia pot containing 160 g of zirconia balls having a diameter of 4 mm. Mechanical milling was performed for 45 hours at an orbital rotation speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line PL-7), to obtain an intermediate. The intermediate was heated (heat treated) at 180 ° C. for 2 hours to obtain the sulfide solid electrolyte of Comparative Example 2. This heating temperature is within the range of ±50° C. of the crystallization temperature determined in the same manner as in Example 1 above.

[0136] [Confirmation of Crystal Structure] Using the method described above, powder X-ray diffraction measurements were performed on each of the sulfide solid electrolytes of Examples 1 to 5 and Comparative Examples 1 to 8. The airtight sample holder for X-ray diffraction measurements was a "General-Purpose Atmosphere Separator" manufactured by Rigaku Corporation. The X-ray diffraction patterns of each of the sulfide solid electrolytes of the Examples and Comparative Examples all had diffraction peaks in the range of 2θ = 19.9° ± 0.5° and 2θ = 29.3° ± 0.5° due to HICP, confirming that they had a crystalline structure.

[0137] [Measurement of Ionic Conductivity] The ionic conductivity (σ) of each of the sulfide solid electrolytes in Examples 1, 2, 4, and 5 and Comparative Examples 1, 3 to 8 at 25°C was measured. ２５The AC impedance of each of the electrodes was measured by the method described above using a Bio-Logic VMP-300. The measurement results are shown in Table 1.

[0138] [Measurement of the Amount of Hydrogen Sulfide Generated] For each of the sulfide solid electrolytes of Example 1 and Comparative Examples 4 and 5, hydrogen sulfide (H ２ The amount of generated CO₂ was measured. A desiccator was placed in a dry box with a dry air atmosphere at a dew point of −35°C. Then, the solid electrolyte powder (500 mg) was placed in a sealed desiccator (effective volume 2300 cm). ３ The amount of hydrogen sulfide generated was measured using a hydrogen sulfide sensor (PGM-1860). The measurement results are shown in Table 1.

[0139] [Evaluation of Oxidation Resistance] The following measurement cells were prepared using each of the sulfide solid electrolytes of Examples 1 to 5 and Comparative Examples 1 to 8, and square wave voltammetry (SWV) measurements were performed to evaluate oxidation resistance. In an argon atmosphere with a dew point of -50°C or less, 80 mg of sample powder (solid electrolyte to be measured) was placed in a powder molding machine with an inner diameter of 10 mm, and then uniaxially pressed at 50 MPa or less using a hydraulic press. After releasing the pressure, graphite powder was placed on the upper surface of the sample, and then uniaxially pressed at 360 MPa or less using a hydraulic press for 5 minutes. Next, a metal foil consisting of a metal indium foil bonded to a metal lithium foil was placed on the lower surface of the sample, and then uniaxially pressed at 50 MPa or less to obtain a pellet-type measurement cell. This measurement cell was compressed in the stacking direction using a compression jig with a torque of 50 cNm, and SWV measurements were performed under the following measurement conditions. (SWV measurement conditions) Voltage amplitude: 20 mV Relaxation time: 50 ms Step voltage: 1 mV Voltage range: OCV to 4.5 V Measurement temperature: 50°C Measured peak current I ＭＡＸ is shown in Table 1. Peak current I ＭＡＸ When the value of β is small, it can be judged that the oxidation resistance is improved.

[0140] [Fabrication of Energy Storage Element] Energy storage elements were fabricated using the sulfide solid electrolytes of Example 1 and Comparative Examples 4 and 5 in the following manner. ０．５ Co ０．２ Mn０．３ O ２ On the surface of the particle ３ The cathode active material, each sulfide solid electrolyte, and fibrous carbon as a conductive agent were weighed in a predetermined mass ratio. Next, a binder (SBR) and butyl butyrate as a solvent were added to this mixture so that the solid content ratio was 60 mass%, and the mixture was kneaded in a hybrid mixer to obtain a cathode mixture. The obtained cathode mixture was applied to an aluminum foil (average thickness 20 μm) as a cathode substrate using a YBA type baker applicator to obtain a cathode mixture with a basis weight of 15 mg cm. －２ 25mg・cm or more －２ The coating was performed as follows. This was dried in an argon atmosphere dryer set at 100°C, a temperature at which the solvent volatilized, under normal pressure for 20 minutes, and then under reduced pressure for 15 minutes, to form a positive electrode active material layer on the positive electrode substrate. This was punched out into a circle with a diameter of 10 mm to form a positive electrode for evaluation. An all-solid-state battery was produced for each of the above-mentioned positive electrodes. Li was placed in a powder molding machine with an inner diameter of 10 mm as the material for the separator layer. ６ P.S. ５ 80 mg of an argyrodite-type sulfide solid electrolyte represented by Cl was added and pressure-molded using a uniaxial press at room temperature at 100 MPa for several seconds to form an isolation layer. After releasing the pressure, the prepared positive electrode was added to one side of the isolation layer and pressure-molded using a uniaxial press at 160 °C and 400 MPa for 5 minutes. After releasing the pressure, indium foil and lithium foil as a negative electrode and SUS316L foil as a negative electrode substrate were added to the side opposite the bonding surface of the positive electrode and bonded using a uniaxial press at 50 MPa for several seconds at room temperature. The resultant was removed from the ceramic powder molding machine to obtain an energy storage element (all-solid-state battery).

[0141] [Charge / Discharge Test] A charge / discharge test was performed on each of the obtained energy storage devices at 50°C as follows. Constant-current, constant-voltage charging was performed at a current of 0.1 C with a charge cut-off voltage of 3.75 V. The charge was terminated until the current reached 0.025 C. A 10-minute rest period was then provided. Subsequently, a constant-current discharge was performed at a current of 0.1 C with a discharge cut-off voltage of 2.25 V. The ratio of the discharge capacity to the initial charge capacity was determined as the initial charge / discharge efficiency. Next, a charge / discharge cycle test was performed on each of the energy storage devices at 50°C as follows. Constant-current, constant-voltage charging was performed at a current of 0.2 C with a charge cut-off voltage of 3.75 V. The charge was terminated until the current reached 0.05 C. A 10-minute rest period was then provided. Subsequently, a constant-current discharge was performed at a current of 0.2 C with a discharge cut-off voltage of 2.25 V. A 10-minute rest period was then provided. This charge and discharge cycle was repeated 30 times. The ratio of the discharge capacity at the 30th cycle to the discharge capacity at the 1st cycle was calculated as the capacity retention rate. The results of the initial charge and discharge efficiency and the capacity retention rate are shown in Table 1.

[0142]

[0143] As shown in Table 1, the sulfide solid electrolytes of Comparative Examples 1, 2, 5, and 6, which do not contain nitrogen element or element M, Comparative Examples 3 and 4, in which the molar ratio of the content of nitrogen element to the content of phosphorus element (N / P) is 0.33 or more, and Comparative Examples 7 and 8, in which the molar ratio of the content of lithium element (element A) to the content of phosphorus element (A / P) is 3.74 or more, have a peak current I ＭＡＸ In contrast, the sulfide solid electrolytes of Examples 1 to 5, which contained nitrogen and element M, had a molar ratio (N / P) of the nitrogen element content to the phosphorus element content of less than 0.33, and a molar ratio (A / P) of the lithium element content (element A) to the phosphorus element content of less than 3.74, had a peak current I ＭＡＸ Furthermore, the energy storage element using the sulfide solid electrolyte of Example 1, which had high oxidation resistance, had higher initial charge-discharge efficiency and capacity retention rate than the energy storage elements using the sulfide solid electrolytes of Comparative Examples 4 and 5, which had low oxidation resistance.

[0144] The sulfide solid electrolyte according to the present invention is suitably used as a solid electrolyte for an electricity storage element such as an all-solid-state battery.

[0145] REFERENCE SIGNS LIST 1 Positive electrode 2 Negative electrode 3 Separator layer 4 Positive electrode substrate 5 Positive electrode active material layer 6 Negative electrode active material layer 7 Negative electrode substrate 10 Energy storage element (all-solid-state battery) 20 Energy storage unit 30 Energy storage device

Claims

1. A sulfide solid electrolyte having a crystalline structure and containing at least one element A selected from the group consisting of lithium, sodium and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen and at least one halogen element, wherein a molar ratio (A / P) of the content of element A to the content of phosphorus is less than 3.74, and a molar ratio (N / P) of the content of nitrogen element to the content of phosphorus is less than 0.

33.

2. The sulfide solid electrolyte according to claim 1, wherein the element M includes an aluminum element.

3. The sulfide solid electrolyte according to claim 1 or 2, wherein the halogen element includes a bromine element or an iodine element.

4. The sulfide solid electrolyte according to claim 1 or 2, which is represented by the following formula (1): A ａ P.M. ｂ S ｃ N ｄ X ｅ Y ｆ ... (1) In the above formula (1), A is at least one selected from the group consisting of Li, Na, and K. M is at least one selected from the group consisting of Al and B. X is at least one selected from the group consisting of F, Cl, Br, and I. Y is at least one element other than A, P, S, M, N, and X. a, b, c, d, e, and f respectively satisfy 2≦a<3.74, 0.01≦b≦1, 2≦c≦6, 0.01≦d<0.33, 0.01≦e≦1, and 0≦f≦1.

5. A method for producing a sulfide solid electrolyte, comprising processing a composition containing at least one element A selected from the group consisting of lithium, sodium and potassium, phosphorus, at least one element M selected from the group consisting of aluminum and boron, nitrogen and at least one halogen element, wherein the molar ratio (A / P) of the content of the element A to the content of the phosphorus is less than 3.74 and the molar ratio (N / P) of the content of the nitrogen element to the content of the phosphorus is less than 0.

33.

6. The above composition is A α M β The method for producing a sulfide solid electrolyte according to claim 5, comprising the step of:

7. A sulfide solid electrolyte produced by the method for producing a sulfide solid electrolyte according to claim 5 or 6.

8. A positive electrode for a storage element containing the sulfide solid electrolyte according to claim 1 or 2.

9. An electric storage element containing the sulfide solid electrolyte according to claim 1 or 2.

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