Sulfide solid electrolyte, method for producing sulfide solid electrolyte, and electric storage element

Abstract

To provide a highly moisture-resistant sulfide solid electrolyte, a production method for the sulfide solid electrolyte, and an electric storage element incorporating the sulfide solid electrolyte.SOLUTION: A sulfide solid electrolyte according to one aspect of the present invention has a crystal structure and contains at least one element X selected from the group consisting of fluorine, chlorine, and bromine elements; an iodine element; a nitrogen element; and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium elements, wherein a molar ratio (X / I) of a content of the element X to a content of the iodine element is more than 0 and 1.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sulfide solid electrolyte, a method for producing a sulfide solid electrolyte, and an energy storage device. [Background technology]

[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 solid electrolytes such as sulfide solid electrolytes as the nonaqueous electrolyte, instead of nonaqueous electrolyte solutions in which an electrolyte salt is dissolved in a liquid such as an organic solvent. Patent Document 1 describes one sulfide solid electrolyte, which contains Li, A (A is at least one of P, Si, Ge, Al, and B), X (X is a halogen), and S, is a glass ceramic, and has peaks at 2θ=20.2° and 23.6° in X-ray diffraction measurement using CuKα radiation. Patent Document 2 also describes a sulfide solid electrolyte having a crystalline structure and containing P, S, N, element A, element X, and element M as constituent elements (A represents at least one element selected from the group consisting of Li, Na, and K. X represents at least one element selected from the group consisting of Cl, Br, and I. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-016423 [Patent Document 2] International Publication No. 2020 / 045634 Summary of the Invention [Problem to be solved by the invention]

[0005] The sulfide solid electrolyte has the disadvantages of being poor in moisture resistance and easily reacting with water in the atmosphere, and therefore, even when the sulfide solid electrolyte is left in a dry air atmosphere with a low moisture content, the sulfide solid electrolyte is likely to react with the trace amount of water contained in the dry air and thereby decrease in ionic conductivity.

[0006] 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 moisture resistance, a method for producing such a sulfide solid electrolyte, and an energy storage element using such a sulfide solid electrolyte. [Means for solving the problem]

[0007] A sulfide solid electrolyte according to one aspect of the present invention has a crystalline structure and contains at least one element X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, and the molar ratio (X / I) of the content of the element X to the content of the iodine is greater than 0 and not greater than 1.0.

[0008] 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 X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, wherein the molar ratio (X / I) of the element X to the iodine is greater than 0 and not greater than 1.0.

[0009] 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. [Effects of the Invention]

[0010] According to any one aspect of the present invention, it is possible to provide a sulfide solid electrolyte having high moisture resistance, a method for producing such a sulfide solid electrolyte, and an energy storage element using such a sulfide solid electrolyte. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery, which is one embodiment of the energy storage element of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an energy storage device configured by assembling a plurality of energy storage elements according to one embodiment of the present invention. [Figure 3] FIG. 3 is an X-ray diffraction diagram of each of the sulfide solid electrolytes of Examples 1 and 2 and Comparative Examples 1 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an outline of the sulfide solid electrolyte, the method for producing the sulfide solid electrolyte, and the energy storage element disclosed in this specification will be described.

[0013] [1] A sulfide solid electrolyte according to one aspect of the present invention has a crystalline structure and contains at least one element X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, wherein the molar ratio (X / I) of the content of the element X to the content of the iodine is greater than 0 and not greater than 1.0.

[0014] The sulfide solid electrolyte described in [1] above has high moisture resistance. That is, the sulfide solid electrolyte described in [1] above is less likely to experience a decrease in ionic conductivity, even when left in an air atmosphere, for example. The reason for this effect is unclear, but the following reason is presumed. The sulfide solid electrolyte described in [1] above contains at least one element X selected from the group consisting of fluorine, chlorine, and bromine, and iodine. Therefore, the sulfide solid electrolyte described in [1] above has, for example, a portion derived from LiX (X is F, Cl, or Br) and a portion derived from LiI. The portion derived from LiI has lower hydration energy than the portion derived from LiX, and is thought to be more susceptible to hydration reaction. In the sulfide solid electrolyte described in [1] above, the molar content of iodine is higher than that of element X, and, for example, the portion derived from LiI is higher than the portion derived from LiX. Therefore, when the sulfide solid electrolyte described in [1] above is left in, for example, an air atmosphere containing moisture, it is presumed that the LiI-derived portion on the surface of the sulfide solid electrolyte undergoes preferential hydration, thereby suppressing hydration within the sulfide solid electrolyte, i.e., deterioration. It is also believed that a similar effect can be achieved even when the sulfide solid electrolyte described in [1] above does not have a portion derived from LiI and a portion derived from LiX, because iodine or a compound thereof is more susceptible to hydration than element X or a compound thereof. Furthermore, when the sulfide solid electrolyte contains iodine but not element X, i.e., when there is a portion derived from LiI but no portion derived from LiX, it is believed that the hydration reaction is significant, which makes the ionic conductivity of the sulfide solid electrolyte more likely to decrease, i.e., the moisture resistance is low. Furthermore, in the sulfide solid electrolyte described in [1] above, the sulfide solid electrolyte further contains a nitrogen element and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, which is also thought to contribute to the high moisture resistance.The reason for this is presumably that the nitrogen element itself has an effect of suppressing the hydration reaction, the element M has an effect of suppressing the release of the nitrogen element from the system during the production process of the sulfide solid electrolyte, and the nitrogen element remains sufficiently throughout the sulfide solid electrolyte described in the above [1], etc. Note that the sulfide solid electrolyte described in the above [1] is not limited to sulfide solid electrolytes using, for example, LiI, LiX, etc. as raw materials.

[0015] The presence of a crystalline structure can be confirmed by powder X-ray diffraction measurement. Specifically, "having a crystalline structure" means that peaks attributable to the crystalline structure of the solid electrolyte are observed in the X-ray diffraction pattern in powder X-ray diffraction measurement. The sulfide solid electrolyte described in [1] above may contain an amorphous portion. Powder X-ray diffraction measurement is performed as follows: The sulfide solid electrolyte powder to be measured is filled into an airtight X-ray diffraction sample holder under an argon atmosphere with a dew point of -50°C or less. Powder X-ray diffraction measurement is performed using an X-ray diffractometer (MiniFlex II, manufactured by Rigaku). The radiation source is CuKα radiation, the tube voltage is 30 kV, and the tube current is 15 mA. The diffracted X-rays are passed through a 30 μm-thick Kβ filter and detected by 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.

[0016] [2] In the sulfide solid electrolyte described in [1] above, the element X may include a bromine element.

[0017] The sulfide solid electrolyte described in [2] above has higher moisture resistance.

[0018] [3] The sulfide solid electrolyte according to the above [1] or [2] may further contain at least one element A selected from the group consisting of lithium, sodium, and potassium.

[0019] [4] The sulfide solid electrolyte according to any one of [1] to [3] above may further contain phosphorus element.

[0020] The sulfide solid electrolytes described in the above [3] and [4] are preferred embodiments of the present invention, have higher moisture resistance, and are useful as sulfide solid electrolytes.

[0021] [5] The sulfide solid electrolyte according to any one of [1] to [4] above may have diffraction peaks in a range of a diffraction angle 2θ of 19.9°±0.5° and a diffraction angle 2θ of 29.3°±0.5° in an X-ray diffraction pattern using CuKα radiation.

[0022] In an X-ray diffraction diagram using CuKα radiation, a specific crystal structure having diffraction peaks in the diffraction angle 2θ range of 19.9°±0.5° and the diffraction angle 2θ range of 29.3°±0.5° is known to be a high ion conduction phase (HICP). Therefore, the sulfide solid electrolyte described in [5] above can be said to have formed an HICP, and can exhibit good ionic conductivity. The "X-ray diffraction diagram using CuKα radiation" is obtained by the powder X-ray diffraction measurement described above.

[0023] [6] In the sulfide solid electrolyte according to any one of [1] to [5] above, the molar ratio (X / I) may be 0.1 or more and 1.0 or less.

[0024] [7] The sulfide solid electrolyte according to any one of the above [1] to [6] may be represented by the following formula (1): A a PM b S c N d X e I f Y g ···(1) In the above formula (1), A is at least one element selected from the group consisting of Li, Na, and K. M is at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, Zr, and Ti. X is at least one element selected from the group consisting of F, Cl, and Br. Y is at least one element other than A, P, S, M, N, X, and I. a, b, c, d, e, f, and g satisfy 2≦a≦7, 0.01≦b≦1, 2≦c≦6, 0.01≦d≦2, 0.01≦e≦1, 0.01≦f≦1, and 0≦g≦1 (with the proviso that 0.01≦e / f≦1.0), respectively.

[0025] The sulfide solid electrolytes described in the above [6] and [7] are also suitable embodiments of the present invention, and are useful as sulfide solid electrolytes with higher moisture resistance.

[0026] [8] 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 X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, wherein the molar ratio (X / I) of the element X to the iodine is greater than 0 and less than or equal to 1.0.

[0027] According to the method for producing a sulfide solid electrolyte described in [8] above, a sulfide solid electrolyte having high moisture resistance can be produced.

[0028] 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 X, iodine, nitrogen, and element M. The composition may also contain a compound, etc. that does not contain any of element X, iodine, nitrogen, or element M.

[0029] [9] An electric storage device according to another aspect of the present invention contains the sulfide solid electrolyte according to any one of the above [1] to [7].

[0030] The energy storage element described in [9] above uses a sulfide solid electrolyte that is highly moisture resistant, and therefore exhibits good energy storage element performance.

[0031] Hereinafter, a sulfide solid electrolyte, a method for manufacturing a sulfide solid electrolyte, 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.

[0032] <Sulfide solid electrolyte> (crystal structure) A sulfide solid electrolyte according to one embodiment of the present invention has a crystalline structure. The sulfide solid electrolyte preferably contains HICP as a crystalline structure. That is, the sulfide solid electrolyte preferably has diffraction peaks in the range of a diffraction angle 2θ of 19.9°±0.5° and a diffraction angle 2θ of 29.3°±0.5° in an X-ray diffraction pattern using CuKα radiation. When the sulfide solid electrolyte has peaks derived from HICP, it can exhibit good ionic conductivity.

[0033] 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, Li7P3S 11 , Thio-LISICON system, etc. The sulfide solid electrolyte may have an amorphous portion.

[0034] In a sulfide solid electrolyte according to one embodiment of the present invention, it is preferable that the amount of a low ion conduction phase (LICP) having diffraction peaks in the range of a diffraction angle 2θ of 21.0°±0.5° and in the range of a diffraction angle 2θ of 28.0°±0.5° in an X-ray diffraction pattern using CuKα radiation is relatively small compared to HICP. In such a case, the ionic conductivity of the sulfide solid electrolyte is increased.

[0035] In the sulfide solid electrolyte according to one embodiment of the present invention, in an X-ray diffraction diagram using CuKα radiation, the diffraction peak intensities at diffraction angles 2θ of 21.0°±0.5° and 28.0°±0.5° due to LICP are preferably lower than the diffraction peak intensities at diffraction angles 2θ of 19.9°±0.5° and 29.3°±0.5° due to HICP. Furthermore, in an X-ray diffraction diagram using CuKα radiation, the diffraction peak intensity I at a diffraction angle 2θ of 21.0°±0.5° due to LICP is preferably lower than the diffraction peak intensities at diffraction angles 2θ of 19.9°±0.5° and 29.3°±0.5° due to HICP. L HICP-derived diffraction peak intensity I at a diffraction angle 2θ of 19.9°±0.5° H Intensity ratio I H / I L The lower limit of the intensity ratio I is preferably 1, more preferably 2, and even more preferably 3. H / I L is related to the abundance ratio of HICP and LICP contained in the sulfide solid electrolyte. In other words, the intensity ratio I H / I L The larger the intensity ratio, the smaller the amount of LICP contained in the HICP. H / I L There is no particular upper limit to I. L is 0, the above intensity ratio I H / I L is infinity, which is included in being greater than or equal to 1.

[0036] (composition) A sulfide solid electrolyte according to one embodiment of the present invention contains, as constituent elements, at least one element X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium. The sulfide solid electrolyte also contains sulfur as a constituent element. The sulfide solid electrolyte preferably contains, as a constituent element, at least one element A selected from the group consisting of lithium, sodium, and potassium. The sulfide solid electrolyte preferably contains phosphorus. Each constituent element and the like will be described below.

[0037] The element X is at least one element selected from the group consisting of fluorine, chlorine, and bromine. The element X preferably contains bromine, and is preferably bromine. When the element X contains bromine, moisture resistance and ionic conductivity tend to be improved.

[0038] The lower limit of the molar ratio (X / P) of the content of element X to the content of element phosphorus is preferably 0.01, more preferably 0.1, and even more preferably 0.25. The upper limit of the molar ratio (X / P) is preferably 1, more preferably 0.6, even more preferably 0.4, and even more preferably 0.33. When the molar ratio (X / P) is in the above range, moisture resistance, ionic conductivity, and the like tend to be further improved. The molar ratio (X / P) may be in a range that combines any of the above lower limits with any of the above upper limits.

[0039] The upper limit of the molar ratio (X / I) of the content of element X to the content of element iodine (X / I) is 1.0, or may be 0.9 or 0.8. When the molar ratio (X / I) is equal to or less than the upper limit, moisture resistance can be improved. Furthermore, when the molar ratio (X / I) is equal to or less than the upper limit, ionic conductivity also tends to increase. The lower limit of the molar ratio (X / I) is greater than 0, and may be, for example, 0.01, but is preferably 0.1, more preferably 0.3, and even more preferably 0.5. When the molar ratio (X / I) is equal to or greater than the lower limit, moisture resistance and ionic conductivity tend to increase. The molar ratio (X / I) may be within a range that combines any of the above lower limits with any of the above upper limits.

[0040] The lower limit of the molar ratio (I / P) of the iodine content to the phosphorus content is preferably 0.01, more preferably 0.1, even more preferably 0.3, and even more preferably 0.40. The upper limit of the molar ratio (I / P) is preferably 1, more preferably 0.6, and even more preferably 0.50. When the molar ratio (I / P) is in the above range, moisture resistance, ionic conductivity, and the like tend to be further improved. The molar ratio (I / P) may be within a range that combines any of the above lower limits with any of the above upper limits.

[0041] The lower limit of the molar ratio (N / P) of the nitrogen element content to the phosphorus element content is preferably 0.01, more preferably 0.05, even more preferably 0.1, and even more preferably 0.2. The upper limit of the molar ratio (N / P) is preferably 2, more preferably 1, and even more preferably 0.5. When the molar ratio (N / P) is in the above range, moisture resistance, ionic conductivity, etc. tend to be further improved. The molar ratio (N / P) may be within a range that combines any of the above lower limits with any of the above upper limits.

[0042] The element M is at least one element selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium. The element M preferably includes aluminum, and more preferably is aluminum. The element M is believed to have the effect of suppressing the emission of nitrogen to the outside of the system during the production process of a sulfide solid electrolyte. This is thought to be because, as described in Patent Document 2, for example, when a raw material compound containing nitrogen and element M is used, the nitrogen defect formation energy is large, making it difficult for nitrogen defects to form during the synthesis process, and therefore difficult for nitrogen gas to be generated.

[0043] 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 0.05, and even more preferably 0.1. The upper limit of the molar ratio (M / P) is preferably 1, more preferably 0.5, and even more preferably 0.3. When the molar ratio (M / P) is in the above range, moisture resistance, ionic conductivity, and the like tend to be further improved. The molar ratio (N / P) may be within a range that combines any of the above lower limits with any of the above upper limits.

[0044] The lower limit of the molar ratio (S / P) of the sulfur element content to the phosphorus element content is preferably 2, more preferably 3, even more preferably 3.4, and even more preferably 3.7. The upper limit of the molar ratio (S / P) is preferably 6, more preferably 5, even more preferably 4, and even more preferably 4.0. When the molar ratio (S / P) is in the above range, ionic conductivity and the like tend to be further increased. The molar ratio (S / P) may be in a range that combines any of the above lower limits with any of the above upper limits.

[0045] The element A is at least one selected from the group consisting of lithium, sodium, and potassium. The element A preferably includes lithium, and more preferably is lithium.

[0046] The lower limit of the molar ratio (A / P) of the content of element A to the content of element phosphorus is preferably 2, more preferably 3, even more preferably 3.5, and even more preferably 3.8. The upper limit of the molar ratio (A / P) is preferably 7, more preferably 6, even more preferably 5, even more preferably 4, and particularly preferably 4.0. When the molar ratio (A / P) is in the above range, ionic conductivity and the like tend to be further increased. The molar ratio (A / P) may be in a range that combines any of the above lower limits with any of the above upper limits.

[0047] The sulfide solid electrolyte according to one embodiment of the present invention may further contain an element Y other than the element X, iodine, nitrogen, M, sulfur, A, and phosphorus. 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.

[0048] The sulfide solid electrolyte according to one embodiment of the present invention is preferably represented by the following formula (1). A a PM b S c N d X e I f Y g ···(1) In the above formula (1), A is at least one element selected from the group consisting of Li, Na, and K. M is at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, Zr, and Ti. X is at least one element selected from the group consisting of F, Cl, and Br. Y is at least one element other than A, P, S, M, N, X, and I. a, b, c, d, e, f, and g satisfy 2≦a≦7, 0.01≦b≦1, 2≦c≦6, 0.01≦d≦2, 0.01≦e≦1, 0.01≦f≦1, and 0≦g≦1 (with the proviso that 0.01≦e / f≦1.0), respectively.

[0049] When the sulfide solid electrolyte according to one embodiment of the present invention has a composition represented by the above formula (1), it exhibits improved moisture resistance, ionic conductivity, and the like. 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 more preferably is Br. The preferred ranges of a, b, c, d, e, f, and g are the same as the preferred ranges of the molar ratios of the contents 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, the preferred range of f is the same as the preferred range of the molar ratio (I / P) described above, and the preferred range of g is the same as the preferred range of the molar ratio (Y / P) described above. Also, the preferred range of e / f is the same as the preferred range of the molar ratio (X / I) of the content of element X to the content of element iodine described above.

[0050] (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, and even more preferably 4 mS / cm. When the ionic conductivity of the sulfide solid electrolyte at 25°C is equal to or greater than the lower limit, the charge / discharge performance of an energy storage device 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.

[0051] 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 molder 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 at 50 MPa or lower using a hydraulic press. 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 a Hohsen HS cell, 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.

[0052] 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 in any of the positive electrode, separator, negative electrode, and the like of the energy storage device.

[0053] <Method for manufacturing sulfide solid electrolyte> A method for producing a sulfide solid electrolyte according to one embodiment of the present invention includes treating a composition containing at least one element X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, wherein the molar ratio (X / I) of the element X to the iodine is greater than 0 and not greater than 1.0.

[0054] (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 sulfur, element A (at least one element selected from the group consisting of lithium, sodium, and potassium), and phosphorus, in addition to element X, iodine, nitrogen, and element M. The composition is typically a mixture of two or more compounds containing at least one element selected from the group consisting of element X, iodine, nitrogen, element M, sulfur, element A, and phosphorus. It is sufficient that any of the compounds contained in the composition (mixture) contains element X, iodine, nitrogen, element M, sulfur, element A, and phosphorus. Two or more elements selected from element X, iodine, nitrogen, element M, sulfur, element A, and phosphorus may be contained in a single compound. For example, LiS, which will be described later, is an example of a compound containing lithium and sulfur as element A, and PS, which will be described later, is an example of a compound containing phosphorus and sulfur. The composition may contain a compound that does not contain any of the element X, iodine, nitrogen, M, sulfur, A, and phosphorus.

[0055] Examples of compounds containing element X (at least one selected from the group consisting of fluorine, chlorine, and bromine) include compounds of element X with an alkali metal element, sulfur element, phosphorus element, etc., with compounds of an alkali metal element and element X being preferred, compounds of element A and element X being more preferred, and compounds of lithium and element X being even more preferred. Examples of compounds of lithium and element X include LiF, LiCl, and LiBr. One type of compound containing element X may be used alone, or two or more types may be used in combination.

[0056] Examples of compounds containing iodine include compounds of iodine with an alkali metal element, sulfur element, phosphorus element, etc., and are preferably compounds of an alkali metal element and iodine, more preferably compounds of element A and iodine, and even more preferably compounds of lithium and iodine (LiI).The compounds containing iodine may be used alone or in combination of two or more.

[0057] 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 the formula N (where A is the element A, M is the element M, and α and β are values that provide a stoichiometric ratio depending on the type of element M) are more preferred. Examples of such compounds include compounds containing lithium, nitrogen, and M (hereinafter also referred to as Li-MN-containing compounds). The Li-MN-containing compounds can be produced by the following procedure. First, LiN and a nitride of 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 the Li-MN-containing compounds. Note that the method for preparing the Li-MN-containing compounds is not limited to this, and other methods may also be used. For example, the raw materials for the Li-MN-containing compounds may be two or more compounds containing any of lithium, M, and nitrogen. The Li-MN-containing compounds may also be produced by mechanical milling. Industrially produced and commercially available Li-MN-containing compounds may also be prepared.

[0058] As the Li-MN-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 N, Li 5 / 3 Si 1 / 3 N, Li 9 / 5 Si 3 / 10 N, LiMgN, LiHf 0.5 N, Li 1.5 Sc 0.5 N, LiZr 0.5 N, Li 5 / 3 Ti 1 / 3 N, Li 4 / 3 Ta 1 / 3 N, Li 7 / 4 Ta 1 / 4 N, Li 7 / 4 Nb 1 / 4 N, LiC 0.5 Among these, Lithium nitrides such as Li1.5 Al 0.5 N is preferred.

[0059] Examples of other compounds containing a nitrogen element include Li3N, PN, P3N5, S4N4, S2N2, S4N2, etc. One type of compound containing a nitrogen element may be used alone, or two or more types may be mixed and used.

[0060] 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. Examples of other compounds containing element M include oxides of element M, sulfides of element M, nitrides of element M, and alloys of element M and element A. Examples of sulfides of element M include Al2S3 and SiS2. Examples of nitrides of element M include AlN, Si3N4, BN, and Mg3N2. One type of compound containing element M may be used alone, or two or more types may be mixed and used.

[0061] Examples of compounds containing sulfur include Li2S, P2S3, P2S5, Al2S3, MgS, SiS2, and elemental sulfur. Among these, Li2S, P2S3, and P2S5 are preferred, and Li2S and P2S5 are more preferred. One type of compound containing sulfur may be used alone, or two or more types may be used in combination.

[0062] Examples of compounds containing element A include halides of element A (such as the above-mentioned LiF, LiCl, LiBr, and LiI), α M β Compounds represented by N (Li 1.5 Al 0.5 N, etc.), Li2S, Li2O, Li3N, Li2CO3, metallic lithium, Na2S, Na2O, Na3N, Na2CO3, metallic sodium, K2S, K2O, K3N, K2CO3, metallic potassium, etc. 1.5 Al 0.5Preferred are N, LiBr and LiI. The compound containing element A may be used alone or in combination of two or more.

[0063] Examples of compounds containing phosphorus include P2S3, P2S5, P2O5, P3N5, and elemental phosphorus. Among these, P2S3 and P2S5 are preferred, and P2S5 is more preferred. One type of compound containing phosphorus may be used alone, or two or more types may be mixed and used.

[0064] For example, in one embodiment, the composition comprises Li2S, P2S5, and Li 1.5 Al 0.5 It may be a composition containing N, LiBr, and LiI, Li2S, P2S5, and Li 1.5 Al 0.5 It may also be a composition consisting of N, LiBr and LiI.

[0065] In the composition, the molar ratio (X / I) of element X to elemental iodine is 1.0 or less. The preferred contents of each element in the composition are the same as the preferred contents of each element in the sulfide solid electrolyte according to one embodiment of the present invention described above.

[0066] (Processing process) 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 obtaining an intermediate by mechanical milling or the like and then heating the intermediate. However, the method for obtaining the intermediate is not limited to this, and methods other than mechanical milling, such as melt quenching, may also be used.

[0067] 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 container-driven mills, media agitation mills, milling using high-speed rotary grinders, roller mills, jet mills, etc. Examples of container-driven mills include rotary mills, vibration mills, planetary mills, etc. Examples of media agitation mills include attritors, bead mills, etc. Examples of milling using high-speed rotary grinders include hammer mills, pin mills, etc. Among these, container-driven mills are preferred, and planetary mills are particularly preferred.

[0068] The intermediate obtained by mechanical milling or the like may have a crystalline structure, but is preferably a sulfide glass. The term "sulfide glass" refers to a sulfide solid electrolyte containing an amorphous structure. When the intermediate is sulfide glass, a sulfide solid electrolyte containing a low level of unstable crystalline phases such as LiS and in which each element is highly dispersed can be obtained.

[0069] 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 HICP phase. 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 300°C, more preferably 170°C to 280°C, and even more preferably 180°C to 260°C. By setting the heating temperature to above the lower limit, crystallization progresses sufficiently, resulting in a sulfide solid electrolyte with sufficiently high moisture resistance and ionic conductivity. Furthermore, by setting the heating temperature to below the upper limit, precipitation of LICP is suppressed, resulting in a sulfide solid electrolyte with higher ionic conductivity.

[0070] <Energy storage element> An energy storage element according to one embodiment of the present invention contains a 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, which is a secondary battery in which a positive electrode 1 and a negative electrode 2 are arranged with an isolation layer 3 interposed therebetween. 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.

[0071] The energy storage device 10 contains a sulfide solid electrolyte according to one embodiment of the present invention in at least one of the positive electrode 1, the negative electrode 2, and the separator 3. More specifically, at least one of the positive electrode active material layer 5, the negative electrode active material layer 6, and the separator 3 contains a sulfide solid electrolyte according to one embodiment of the present invention.

[0072] The energy storage element 10 may also 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 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 pseudo-solid electrolytes, with sulfide solid electrolytes being preferred. Furthermore, a single layer of the energy storage element 10 may contain multiple different types of solid electrolytes, or each layer may contain a different solid electrolyte.

[0073] Examples of sulfide solid electrolytes other than the sulfide solid electrolyte according to one embodiment of the present invention include LiS-P2S5, LiS-P2S5-LiI, LiS-P2S5-LiCl, LiS-P2S5-LiBr, LiS-P2S5-Li2O, LiS-P2S5-Li2O-LiI, LiS-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S 2n (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.) Li 10 GeP2S 12 The following can be mentioned:

[0074] (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. The positive electrode 1 may have an intermediate layer between the positive electrode substrate 4 and the positive electrode active material layer 5.

[0075] The positive electrode substrate 4 has electrical conductivity. Whether or not the positive electrode substrate 4 has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 -2The threshold value is Ω·cm. The material for the positive electrode substrate 4 is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate 4 include foil, vapor deposition film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred for the positive electrode substrate 4. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0076] The average thickness of the positive electrode substrate 4 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 4 within the above range, the strength of the positive electrode substrate 4 can be increased while also increasing the energy density per volume of the energy storage device 10. The "average thickness" refers to the average value of thicknesses measured at any five positions (the same applies hereinafter to the average thickness).

[0077] The intermediate layer is a layer disposed between the positive electrode substrate 4 and the positive electrode active material layer 5. The intermediate layer contains a conductive agent such as carbon particles, thereby reducing the contact resistance between the positive electrode substrate 4 and the positive electrode active material layer 5. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0078] The positive electrode active material layer 5 contains a positive electrode active material. The positive electrode active material layer 5 can be formed from a so-called positive electrode mixture containing the positive electrode active material. The positive electrode active material layer 5 may contain a mixture or composite containing a positive electrode active material and a solid electrolyte or the like. The positive electrode active material layer 5 contains 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 contained in the positive electrode active material layer 5.

[0079] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(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) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel-type crystal structures include Li x Mn2O4, Li x Ni γ Mn (2-γ)Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. 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. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer 5, one of these materials may be used alone, or two or more may be used in combination.

[0080] 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 lower limit or more, the positive electrode active material is made easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer 5 is improved. 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. The "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).

[0081] 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.

[0082] The content of the positive electrode active material in the positive electrode active material layer 5 is preferably 10% by mass or more and 95% by mass or less, with the lower limit being 30% by mass, and more preferably 50% by mass. By setting the content of the positive electrode active material within this range, it is possible to increase the discharge capacity of the energy storage element 10, for example.

[0083] When the positive electrode active material layer 5 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 is 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 device 10, for example. When the positive electrode active material layer 5 uses a sulfide solid electrolyte according to one embodiment of the present invention, the content of the sulfide solid electrolyte according to one embodiment of the present invention relative to the total solid electrolyte in the positive electrode active material layer 5 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. When the positive electrode active material layer 5 uses a sulfide solid electrolyte according to one embodiment of the present invention, the content of the sulfide solid electrolyte according to one embodiment of the present invention in the positive electrode active material layer 5 is preferably 5% by mass or more and 90% by mass or less, and more preferably 20% by mass or more and 70% by mass or less.

[0084] The mixture of the positive electrode active material and the solid electrolyte is a mixture prepared by mixing the positive electrode active material and the solid electrolyte by mechanical milling or the like. For example, the mixture of the positive electrode active material and the solid electrolyte can be obtained by mixing a particulate positive electrode active material with a particulate solid electrolyte. Examples of the composite of the positive electrode active material and the solid electrolyte include a composite in which the positive electrode active material and the solid electrolyte are chemically or physically bonded, and a composite in which the positive electrode active material and the solid electrolyte are mechanically combined. The composite is a composite in which the positive electrode active material and the solid electrolyte are present within a single particle, such as a composite in which the positive electrode active material and the solid electrolyte are in an aggregated state, or a composite in which a coating containing the solid electrolyte is formed on at least a portion of the surface of the positive electrode active material.

[0085] The conductive agent is not particularly limited as long as it is a material having 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.

[0086] The content of the conductive agent in the positive electrode active material layer 5 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 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 10 can be increased.

[0087] 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.

[0088] The content of the binder in the positive electrode active material layer 5 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.

[0089] 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 5 may be 1% by mass or less, or 0.1% by mass or less, or the positive electrode active material layer 5 may be substantially free of thickener.

[0090] 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 aluminosilicate; 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 filler content in the positive electrode active material layer 5 may be 1% by mass or less, or 0.1% by mass or less, or may be substantially filler-free.

[0091] The positive electrode active material layer 5 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.

[0092] The average thickness of the positive electrode active material layer 5 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 5 to be equal to or greater than the above lower limit, a storage element having a high energy density can be obtained. By setting the average thickness of the positive electrode active material layer 5 to be equal to or less than the above upper limit, the size of the storage element 10 can be reduced.

[0093] (Negative electrode) The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6 disposed on the negative electrode substrate 7 directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode 1, for example.

[0094] 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 and copper alloys are preferred. Examples of the negative electrode substrate 7 include foils, vapor-deposited films, meshes, and porous materials, with foils 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.

[0095] 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, while the energy density per volume of the energy storage device 10 can be increased.

[0096] 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, and a filler 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.

[0097] 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.

[0098] The negative electrode active material can be appropriately selected from known negative electrode active materials. Materials capable of absorbing and releasing lithium ions are typically used as negative electrode active materials for lithium ion secondary batteries. Examples of negative electrode active materials 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; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNbO; 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.

[0099] "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.

[0100] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic 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.

[0101] 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. 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 a negative electrode active material as a working electrode and metallic lithium as a counter electrode is 0.7 V or higher.

[0102] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0103] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0104] 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 negative electrode active material can be easily produced or handled. 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 from the methods exemplified for the positive electrode, for example. 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.

[0105] 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, it is possible to increase the discharge capacity of the energy storage element 10, for example.

[0106] 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 of this range is 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 device 10, for example. When the negative electrode active material layer 6 uses a sulfide solid electrolyte according to one embodiment of the present invention, 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. When the negative electrode active material layer 6 uses a sulfide solid electrolyte according to one embodiment of the present invention, the content of the sulfide solid electrolyte according to one embodiment of the present invention in the negative electrode active material layer 6 is preferably 5% by mass or more and 90% by mass or less, and more preferably 20% by mass or more and 70% by mass or less.

[0107] 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.

[0108] 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 device 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 device 10.

[0109] (isolation layer) The separator 3 contains a solid electrolyte. The content of the solid electrolyte in the separator 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 separator 3, the content of the sulfide solid electrolyte according to one embodiment of the present invention relative to the total solid electrolyte in the separator 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. When the sulfide solid electrolyte according to one embodiment of the present invention is used in the separator 3, the content of the sulfide solid electrolyte according to one embodiment of the present invention in the separator 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.

[0110] The separator 3 may contain optional components such as a phosphate compound such as LiPO, an oxide, a halogen compound, a binder, a thickener, a filler, etc. The optional components such as the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode active material layer 5.

[0111] The average thickness of the separator 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 separator 3 to be equal to or greater than the above lower limit, it is possible to reliably insulate the positive electrode 1 from the negative electrode 2. By setting the average thickness of the separator 3 to be equal to or less than the above upper limit, it is possible to increase the energy density of the energy storage element 10.

[0112] <Electricity storage device> The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising 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, the technology of the present invention may be applied to at least one energy storage element included in the energy storage unit.

[0113] 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 units 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.

[0114] <Method of manufacturing an energy storage element> The method for producing an energy storage device 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 production 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.

[0115] (1) Positive electrode mixture preparation process In this step, a positive electrode mixture for forming a positive electrode (positive electrode active material layer) is usually prepared. The method for preparing the positive electrode mixture is not particularly limited and can be appropriately selected depending on the purpose. For example, the positive electrode mixture 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.

[0116] (2) Preparation of materials for the isolation layer In this step, an isolation layer material for forming an isolation layer is usually prepared. When the energy storage element is an all-solid-state energy storage element, the isolation layer material can be a solid electrolyte. The solid electrolyte as the isolation layer material can be prepared by a conventionally known method. For example, it can be obtained by processing a predetermined material by a mechanical milling method. The isolation layer material may also be prepared by heating a predetermined material to a melting temperature or higher by a melt quenching method, melt-mixing the two at a predetermined ratio, and then quenching. Other methods for synthesizing the isolation layer 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 sintering in an argon atmosphere after mechanical milling.

[0117] (3) Negative electrode mixture preparation process 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 a metallic lithium foil or the like.

[0118] (4)Lamination process In this process, 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 laminated. In this process, 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 laminated by pressure molding the positive electrode substrate, the positive electrode mixture, the separator material, the negative electrode mixture, and the negative electrode substrate at the same time. The positive electrode and the negative electrode may be molded in advance, and then pressure molded and laminated with the separator layer. Each layer may be formed by coating, etc.

[0119] <Other embodiments> The sulfide solid electrolyte, the method for manufacturing a sulfide solid electrolyte, 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.

[0120] 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 bipolar electrodes. 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.

[0121] <Example> 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.

[0122] [Example 1] By the following process, Li 3.86 PAl 0.16 S 3.82 N 0.33 Br 0.36 I 0.36 We synthesized a sulfide solid electrolyte represented by the formula: LiN and AlN were weighed out 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 obtain LiN. 1.5 Al 0.5 N was prepared. 1.5 Al 0.5 X-ray diffraction analysis revealed that the main phase of N is Li. 1.5 Al 0.5 It was confirmed that N. Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li 1.5 Al 0.5 N, LiBr (99.999%, manufactured by Aldrich), and LiI (99.999%, manufactured by Aldrich) were weighed out to a molar ratio of 46.02:17.38:11.36:12.62:12.62, and then mixed in a mortar to prepare a composition containing, as constituent elements, element A: lithium, element A: phosphorus, element M: aluminum, element M: sulfur, element N, element X: bromine, and element X: iodine. The composition was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls, and mechanical milling was carried out for 45 hours at a revolution speed of 510 rpm using a planetary ball mill (FRITSCH, model number Premium line PL-7) to obtain an intermediate. The intermediate was heated (heat treated) at 190°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.

[0123] [Examples 2 and 3, Comparative Examples 1 to 6] The sulfide solid electrolytes of Examples 2 and 3 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that the amounts of raw material compounds used 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.

[0124] [evaluation] (1) Powder X-ray diffraction measurement Using the method described above, powder X-ray diffraction measurements were performed on each of the sulfide solid electrolytes of Examples 1 to 3 and Comparative Examples 1 to 6. The airtight sample holder used for the 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 showed diffraction peaks at a diffraction angle 2θ of 19.9°±0.5° and a diffraction angle 2θ of 29.3°±0.5°, which were attributed to HICP, confirming the presence of a crystalline structure.

[0125] 3 shows the X-ray diffraction patterns of the sulfide solid electrolytes of Examples 1 and 2 and Comparative Examples 1 and 4. The diffraction peaks attributable to HICP are in the range of a diffraction angle 2θ of 19.9°±0.5° and a diffraction angle 2θ of 29.3°±0.5°, confirming the presence of a crystalline structure.

[0126] (2) Ionic conductivity The ionic conductivity (σ) of each sulfide solid electrolyte at 25°C in Examples 1 to 3 and Comparative Examples 1 to 6 25a ) was determined by measuring AC impedance using the method described above using a Bio-Logic VMP-300. The measurement results are shown in Table 1.

[0127] (3) Moisture resistance evaluation The moisture resistance of each sulfide solid electrolyte in Examples 1 to 3 and Comparative Examples 1 to 6 was evaluated by the following procedure. For each sulfide solid electrolyte, the ionic conductivity (σ) at 25°C as described in (2) above was measured. 25a After measuring the ionic conductivity (σ 25b ) was measured in the same manner as in (2) above. The results of these measurements are shown in Table 1. In addition, as an index of moisture resistance, the ionic conductivity (σ 25a ) after being left in a dry air atmosphere (σ 25b ) ratio (σ 25b / σ 25a ) are shown in percentage in Table 1.

[0128] [Table 1]

[0129] As shown in Table 1, the sulfide solid electrolytes of Comparative Examples 1 and 2, in which the molar ratio (X / I) of the content of element X to the content of iodine element exceeds 1.0, Comparative Example 3, which does not contain element X, Comparative Examples 4 and 5, which do not contain element nitrogen and element M, and Comparative Example 6, which does not contain element M, have a ratio (σ 25b / σ 25a ) was less than 80%. In contrast to these, the sulfide solid electrolytes of Examples 1 to 3, in which the molar ratio (X / I) of the content of element X to the content of element iodine was 1.0 or less and which contained element nitrogen and element M, had a ratio (σ 25b / σ 25a ) was 80% or more, and the moisture resistance was high. [Industrial Applicability]

[0130] 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. [Explanation of symbols]

[0131] 1 positive electrode 2 negative electrode 3 isolation layer 4. Positive electrode substrate 5 Cathode 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. It has a crystalline structure, at least one element X selected from the group consisting of fluorine, chlorine, and bromine; Iodine element, Nitrogen element, at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium; Contains A sulfide solid electrolyte in which the molar ratio (X / I) of the content of the element X to the content of the iodine element is greater than 0 and less than or equal to 1.

0.

2. The sulfide solid electrolyte according to claim 1 , wherein the element X includes a bromine element.

3. The sulfide solid electrolyte according to claim 1 or 2, further containing at least one element A selected from the group consisting of lithium element, sodium element, and potassium element.

4. The sulfide solid electrolyte according to claim 1 or 2, further containing elemental phosphorus.

5. 3. The sulfide solid electrolyte according to claim 1 or 2, wherein the sulfide solid electrolyte has diffraction peaks in the range of a diffraction angle 2θ of 19.9 ° ± 0.5 ° and a diffraction angle 2θ of 29.3 ° ± 0.5 ° in an X-ray diffraction diagram using CuKα rays.

6. The sulfide solid electrolyte according to claim 1 or 2, wherein the molar ratio (X / I) is 0.1 or more and 1.0 or less.

7. The sulfide solid electrolyte according to claim 1 or 2, represented by the following formula (1): A ａ PM ｂ S ｃ N ｄ X ｅ I ｆ Y ｇ ・・・(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, Ta, Si, Sc, Mg, Nb, B, Hf, C, Zr, and Ti. X is at least one selected from the group consisting of F, Cl, and Br. Y is at least one element other than A, P, S, M, N, X, and I. a, b, c, d, e, f, and g respectively satisfy 2≦a≦7, 0.01≦b≦1, 2≦c≦6, 0.01≦d≦2, 0.01≦e≦1, 0.01≦f≦1, and 0≦g≦1 (provided that 0.01≦e / f≦1.0).

8. A method for producing a sulfide solid electrolyte, comprising treating a composition containing at least one element X selected from the group consisting of fluorine, chlorine, and bromine, iodine, nitrogen, and at least one element M selected from the group consisting of aluminum, tantalum, silicon, scandium, magnesium, niobium, boron, hafnium, carbon, zirconium, and titanium, wherein a molar ratio (X / I) of the element X to the iodine is greater than 0 and not greater than 1.

0.

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

Images