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

Abstract

A sulfide solid electrolyte according to one aspect of the present invention has diffraction peaks in an X-ray diffraction pattern using Cu Kα rays at diffraction angles 2θ in the ranges of 20.15° ± 0.50°, 20.37° ± 0.50°, and 29.55° ± 0.50°, and contains carbon.

Description

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

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

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. Non-aqueous electrolyte secondary batteries generally include an electrode assembly having a pair of electrodes and a separator, a non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous electrolyte, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. Other non-aqueous electrolyte storage elements besides non-aqueous electrolyte secondary batteries include capacitors such as lithium ion capacitors and electric double layer capacitors.

[0003] In recent years, energy storage elements have been proposed that use solid electrolytes such as sulfide solid electrolytes as the non-aqueous electrolyte, instead of non-aqueous electrolyte solutions in which an electrolyte salt is dissolved in a liquid such as an organic solvent. As one of the sulfide solid electrolytes, Patent Document 1 describes a sulfide solid electrolyte that 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 1 specifically describes xLiI·(100−x)(0.75Li ２ S 0.25P ２ S ５ A sulfide solid electrolyte having a composition represented by the formula:

[0004] JP 2013-016423 A

[0005] In energy storage elements, heat generation and the like may occur due to use in a normally unexpected manner. For this reason, energy storage elements using a nonaqueous electrolyte often use a porous resin sheet with a shutdown function as the separator. In this specification, the shutdown function refers to a function that forcibly stops or suppresses charging and discharging of the energy storage element when the temperature inside the energy storage element rises, thereby preventing or suppressing further temperature rise. In the case of an energy storage element using a porous resin sheet as the separator, the resin constituting the separator melts as the temperature rises and blocks the pores in the separator, thereby blocking ionic conduction between the two electrodes and stopping or suppressing charging and discharging.

[0006] Solid electrolytes are generally non-flammable or flame-retardant, and therefore have advantages such as higher heat resistance compared to non-aqueous electrolytes. It is desirable to develop energy storage elements using such solid electrolytes that also have a good shutdown function.

[0007] An object of the present invention is to provide a sulfide solid electrolyte having a shutdown function, a material and a production method for producing such a sulfide solid electrolyte, 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 diffraction peaks in the diffraction angle 2θ range of 20.15° ± 0.50°, the diffraction angle 2θ range of 20.37° ± 0.50°, and the diffraction angle 2θ range of 29.55° ± 0.50° in an X-ray diffraction diagram using CuKα rays, and contains carbon element.

[0009] A sulfide solid electrolyte material according to another aspect of the present invention is a material used in the production of a sulfide solid electrolyte, and contains at least one element selected from the group consisting of lithium, sodium, and potassium, carbon, phosphorus, and sulfur.

[0010] A method for producing a sulfide solid electrolyte according to another aspect of the present invention includes heat treating the sulfide solid electrolyte material according to the aspect of the present invention in a temperature range of 180°C or higher and 220°C or lower.

[0011] 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.

[0012] According to any one aspect of the present invention, it is possible to provide a sulfide solid electrolyte having a shutdown function, a material and a production method for producing such a sulfide solid electrolyte, and an energy storage element using such a sulfide solid electrolyte.

[0013] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery that is one embodiment of the energy storage element of the present invention. 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. FIG. 3 is an X-ray diffraction diagram of each of the sulfide solid electrolytes of Examples 1-2, 2, 3-2, and 4-2. FIG. 4 is an X-ray diffraction diagram of each of the sulfide solid electrolytes of Comparative Examples 3 and 4. FIG. 5 is an X-ray diffraction diagram of each of the sulfide solid electrolytes of Comparative Examples 5-1, 5-2, and 6. FIG. 6 is a DSC (differential scanning calorimetry) curve of each of the sulfide solid electrolyte materials of Examples 1, 3, and 4 and Comparative Example 5.

[0014] First, an outline of the sulfide solid electrolyte, the material for the sulfide solid electrolyte, the method for producing the sulfide solid electrolyte, and the energy storage element disclosed in this specification will be described.

[0015] [1] A sulfide solid electrolyte according to one aspect of the present invention has diffraction peaks in the diffraction angle 2θ range of 20.15° ± 0.50°, the diffraction angle 2θ range of 20.37° ± 0.50°, and the diffraction angle 2θ range of 29.55° ± 0.50° in an X-ray diffraction diagram using CuKα rays, and contains carbon element.

[0016] The sulfide solid electrolyte described in [1] above has a shutdown function (a function of forcibly stopping or suppressing charging and discharging of the energy storage element when the temperature inside the energy storage element rises, and preventing or suppressing further temperature rise). The reason for this effect is unclear, but the following reason is presumed. By incorporating carbon element into the material used to produce the sulfide solid electrolyte (sulfide solid electrolyte material), a LGPS-type crystal structure is precipitated that has diffraction peaks in the diffraction angle 2θ range of 20.15°±0.50°, the diffraction angle 2θ range of 20.37°±0.50°, and the diffraction angle 2θ range of 29.55°±0.50° in an X-ray diffraction diagram using CuKα rays, thereby obtaining a sulfide solid electrolyte with sufficient ionic conductivity. On the other hand, when the above-mentioned materials containing carbon and sulfide solid electrolytes obtained by heat-treating the above-mentioned materials at relatively low temperatures are subjected to heat treatment at temperatures exceeding 220 °C, a low ion conduction phase (LICP) having diffraction peaks in the range of a diffraction angle 2θ of 21.00 ° ± 0.50 ° and a diffraction angle 2θ of 28.00 ° ± 0.50 ° in the X-ray diffraction pattern precipitates, resulting in a decrease in ionic conductivity. The sulfide solid electrolyte described in [1] above has an LGPS-type crystal structure, and therefore has sufficient ionic conductivity under normal temperature conditions (e.g., -20 °C or higher and 100 °C or lower). However, when the temperature rises above 220 °C, the ionic conductivity decreases due to the precipitation of LICP. For this reason, it is presumed that the sulfide solid electrolyte described in [1] above exhibits a shutdown function as the temperature rises above 220 °C. Furthermore, in the sulfide solid electrolyte described in [1] above, an LGPS-type crystal structure is precipitated by heat treatment at a relatively low temperature, which has the advantage of high productivity.

[0017] [2] In the sulfide solid electrolyte described in [1] above, the diffraction peaks occur at diffraction angles 2θ of 20.15° ± 0.40°, 20.37° ± 0.40°, and 29.55° ± 0.40°. May also occur.

[0018] [3] In the sulfide solid electrolyte described in [1] or [2] above, all of the diffraction peaks are the diffraction peaks having the largest peak intensity in the X-ray diffraction diagram using CuKα rays. It may be any one of the diffraction peaks having the largest peak intensity to the fifth largest diffraction peak.

[0019] X-ray diffraction patterns using CuKα radiation are obtained by powder X-ray diffraction measurement according to the following procedure. 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 (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 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.

[0020] [4] The sulfide solid electrolyte according to any one of [1] to [3] above may further contain a halogen element.

[0021] [5] In the sulfide solid electrolyte described in [4] above, the halogen element may include at least one of a bromine element and an iodine element.

[0022] [6] The sulfide solid electrolyte according to any one of [1] to [5] above may further contain phosphorus element.

[0023] [7] In the sulfide solid electrolyte described in [6] above, the molar ratio of the carbon element content to the phosphorus element content may be 0.01 or more and 0.30 or less.

[0024] [8] The sulfide solid electrolyte according to any one of [1] to [7] above may further contain at least one selected from the group consisting of lithium, sodium, and potassium.

[0025] Each of the sulfide solid electrolytes described in [2] to [8] above is a suitable embodiment, and has sufficient ionic conductivity and a better shutdown function under normal temperature conditions.

[0026] [9] The sulfide solid electrolyte according to any one of [1] to [8] above may further contain a nitrogen element.

[0027] The sulfide solid electrolyte described in [9] above has a better shutdown function, and is also suitable for, for example, LiC ０．５ Since it can be produced using raw materials such as N, productivity is also higher.

[0028]

[10] In the sulfide solid electrolyte according to any one of [1] to [9] above, in the X-ray diffraction diagram using the CuKα ray, the intensity of the diffraction peak appearing in the range of the diffraction angle 2θ of 29.55° ± 0.50° (I １ The intensity of the diffraction peak (I) appears in the range of 28.00°±0.50° of the diffraction angle 2θ. ２ ) ratio (I ２ / I １ ) may be 1 or less.

[0029]

[11] In the sulfide solid electrolyte described in

[10] above, the diffraction peaks may appear in the diffraction angle 2θ range of 29.55°±0.40° and the diffraction angle 2θ range of 28.00°±0.40°.

[0030] In the sulfide solid electrolytes described in

[10] and

[11] above, the intensity of the diffraction peak (I １ ) the intensity of the diffraction peak due to LICP appearing in the range of the diffraction angle 2θ of 28.00°±0.50° or 28.00°±0.40° (I ２ ) ratio (I ２ / I １ ) is not more than 1. That is, in the sulfide solid electrolytes described in

[10] and

[11] above, the amount of LICP is relatively small compared to the LGPS-type crystal structure having good ionic conductivity, and therefore the sulfide solid electrolytes have excellent ionic conductivity under normal temperature environments.

[0031]

[12] In the sulfide solid electrolyte according to any one of [1] to

[11] above, in the X-ray diffraction diagram using the CuKα ray, the intensity of the diffraction peak appearing in the range of the diffraction angle 2θ of 29.55° ± 0.50° (I １ The intensity of the diffraction peak (I) appears in the range of 18.65°±0.50° of the diffraction angle 2θ. ３ ) ratio (I ３ / I １ ) may be 1 or less.

[0032]

[13] In the sulfide solid electrolyte described in

[12] above, the diffraction peaks may appear in the diffraction angle 2θ range of 29.55° ± 0.40° and the diffraction angle 2θ range of 18.65° ± 0.40°.

[0033] In the sulfide solid electrolytes described in

[12] and

[13] above, the intensity of the diffraction peak (I １ ) to Li ７ P ３ S １１ The intensity of the diffraction peak (I) attributable to the crystalline phase having the structure, which appears in the range of the diffraction angle 2θ of 18.65°±0.50° or 18.65°±0.40° ３ ) ratio (I ３ / I １ ) is 1 or less. That is, in the sulfide solid electrolytes described in the above

[12] and

[13] , Li is ７ P ３ S １１ Since the amount of crystalline phase having such structure is relatively small, the ionic conductivity is excellent under normal temperature conditions.

[0034]

[14] In the sulfide solid electrolyte according to any one of [1] to

[13] above, the ionic conductivity (σ ２５ ) relative to the ionic conductivity (σ') of the sulfide solid electrolyte at 25°C after heat treatment at 230°C for 2 hours. ２５ ) ratio (σ' ２５ / σ２５ ) may be 0.5 or less.

[0035] In the sulfide solid electrolyte described in

[14] above, the ionic conductivity (σ ２５ ) versus the ionic conductivity (σ') of the sulfide solid electrolyte after heat treatment at 230°C for 2 hours. ２５ ) ratio (σ' ２５ / σ ２５ ) is 0.5 or less, and the ionic conductivity decreases significantly with increasing temperature. Therefore, the sulfide solid electrolyte described in

[14] above has a better shutdown function.

[0036] The ionic conductivity of the sulfide solid electrolyte 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 compactor with an inner diameter of 10 mm, and then uniaxially pressed at 10 MPa to 100 MPa using a hydraulic press. If it is difficult to prepare 120 mg of sample powder, the amount of sample powder placed may be less than 120 mg. In this case, a powder compactor with an inner diameter of less than 10 mm may be used. After releasing the pressure, 120 mg of SUS316L powder is placed on the top surface of the sample as a current collector, and then uniaxially pressed again at 10 MPa to 100 MPa using a hydraulic press. The SUS216L powder used has a mesh size of less than 100 mesh / inch. Next, 120 mg of SUS316L powder was placed on the underside 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 was inserted into a Hohsen HS cell, and AC impedance measurements were performed at a predetermined temperature. The results were plotted as a Nyquist plot. For sulfide solid electrolytes with no arc component in the Nyquist plot, the value on the real axis at the measurement point on the highest frequency side was taken as the resistance R. For sulfide solid electrolytes with an arc component in the Nyquist plot, the value on the real axis at the end point on the low frequency side of the arc was taken as the resistance R. The measurement conditions were an applied voltage amplitude of 20 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 25°C. Furthermore, 240 mg of SUS316L powder was placed in a powder molding machine with an inner diameter of 10 mm, and then uniaxially pressed at 360 MPa for 5 minutes using a hydraulic press to obtain a SUS current collector pellet. Thereafter, the thicknesses of the pellet for measuring ionic conductivity and the SUS current collector pellet are measured using a micrometer, and then the thickness of the SUS current collector pellet is subtracted from the thickness of the pellet for measuring ionic conductivity to calculate the sample thickness L of the sulfide solid electrolyte. ２５ (Scm －１ ) is the resistance R (Ω), the thickness L (cm) of the sulfide solid electrolyte sample, and the area A (cm) of the solid electrolyte sample. ２ ) and calculate it by the following formula (A): ２５= L / (RA) ... (A) The two-hour heat treatment at 230°C is carried out for two hours in an argon atmosphere with a dew point of -50°C or lower. The temperature is increased at a rate of 2±1°C / min, and after reaching 230°C, the temperature is maintained at 230°C for two hours. After the two-hour heat treatment is completed, heating is stopped and the sample is allowed to cool naturally to room temperature.

[0037]

[15] The sulfide solid electrolyte according to any one of [1] to

[14] above may be represented by the following formula (1): A ａ C ｂ P.S. ｃ N ｄ X ｅ Y ｆ ... (1) In the above formula (1), A is at least one element selected from the group consisting of Li, Na, and K. X is at least one halogen element. Y is at least one element other than A, C, P, S, N, and X. a, b, c, d, e, and f satisfy 2≦a≦7, 0.01≦b≦0.30, 2≦c≦6, 0≦d≦2, 0≦e≦2, and 0≦f≦1, respectively.

[0038] The sulfide solid electrolyte described in the above

[15] has a better shutdown function and the like.

[0039] The elements contained in the sulfide solid electrolyte are quantified by the following methods. Carbon is quantified by combustion-infrared absorption spectroscopy. Sulfur is quantified by combustion-infrared absorption spectroscopy (CS meter). Halogen is quantified by combustion ion chromatography. Nitrogen is quantified by inert gas fusion-thermal conductivity spectroscopy. Hydrogen and oxygen are quantified by inert gas fusion-infrared absorption spectroscopy. Other elements are quantified by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0040]

[16] A sulfide solid electrolyte material according to another aspect of the present invention is a material used in the production of a sulfide solid electrolyte, and contains at least one element selected from the group consisting of lithium, sodium, and potassium, carbon, phosphorus, and sulfur.

[0041] By using the sulfide solid electrolyte material described in

[16] above, it is possible to produce a sulfide solid electrolyte having a shutdown function (a function of forcibly stopping or suppressing charging and discharging of the energy storage element when the temperature inside the energy storage element rises, and preventing or suppressing a further temperature rise).

[0042]

[17] A method for producing a sulfide solid electrolyte according to another aspect of the present invention includes heat treating the sulfide solid electrolyte material according to the above

[16] in a temperature range of 180°C or higher and 220°C or lower.

[0043] According to the method for producing a sulfide solid electrolyte described in

[17] above, it is possible to produce a sulfide solid electrolyte having a shutdown function (a function of forcibly stopping or suppressing charging and discharging of the energy storage element when the temperature inside the energy storage element rises, and preventing or suppressing a further temperature rise).

[0044]

[18] An energy storage device according to another aspect of the present invention includes the sulfide solid electrolyte according to any one of [1] to

[15] above.

[0045] The energy storage element described in

[18] above uses the sulfide solid electrolyte described in any one of [1] to

[15] above, and therefore can have a shutdown function (a function of forcibly stopping or suppressing charging and discharging of the energy storage element when the temperature inside the energy storage element rises, and preventing or suppressing a further temperature rise).

[0046] Hereinafter, a sulfide solid electrolyte, a sulfide solid electrolyte material, a method for producing 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.

[0047] <Sulfide Solid Electrolyte> (Crystal Structure) A sulfide solid electrolyte according to one embodiment of the present invention has diffraction peaks in the diffraction angle 2θ range of 20.15°±0.50°, the diffraction angle 2θ range of 20.37°±0.50°, and the diffraction angle 2θ range of 29.55°±0.50° in an X-ray diffraction diagram using CuKα radiation. Since the sulfide solid electrolyte has the above-mentioned diffraction peaks, it has a so-called LGPS-type crystal structure. Because the sulfide solid electrolyte has such a crystal structure, it has sufficient ionic conductivity under normal temperature environments. In the X-ray diffraction diagram, the diffraction peaks in the diffraction angle 2θ range of 20.15°±0.50° and the diffraction angle 2θ range of 20.37°±0.50° may appear as a single peak without being separated, but are preferably separated into two peaks. In the X-ray diffraction diagram, it is preferable that all of the diffraction peaks in the range of a diffraction angle 2θ of 20.15°±0.50°, the range of a diffraction angle 2θ of 20.37°±0.50°, and the range of a diffraction angle 2θ of 29.55°±0.50° are any of the diffraction peaks in the range of greatest to fifth greatest peak intensity among the diffraction peaks in the X-ray diffraction diagram.

[0048] The sulfide solid electrolyte according to one embodiment of the present invention may have an amorphous portion, or may have a portion having a crystal structure other than the LGPS-type crystal structure.

[0049] In a sulfide solid electrolyte according to one embodiment of the present invention, it is preferable that the amount of a low ionic conductivity phase (LICP) having diffraction peaks in the range of a diffraction angle 2θ of 21.00°±0.50° and in the range of a diffraction angle 2θ of 28.00°±0.50° in an X-ray diffraction diagram using CuKα radiation is relatively small compared to the amount of a LGPS-type crystal structure. In such a case, the ionic conductivity of the sulfide solid electrolyte under a normal temperature environment is further improved. Specifically, in an X-ray diffraction diagram using CuKα radiation, the intensity (I １ ) the intensity of the diffraction peak appearing in the range of a diffraction angle 2θ of 28.00°±0.50° (I ２ ) ratio (I ２ / I １ ) is preferably 1 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and even more preferably 0.1 or less. ２ / I １ The lower limit of may be 0.

[0050] In the sulfide solid electrolyte according to one embodiment of the present invention, in an X-ray diffraction pattern using CuKα rays, Li has diffraction peaks in the range of a diffraction angle 2θ of 17.80° ± 0.50° and in the range of a diffraction angle 2θ of 18.65° ± 0.50°, etc. ７ P ３ S １１ It is preferable that the amount of the crystalline phase having the structure is relatively small compared to the amount of the LGPS-type crystalline structure. In such a case, the ionic conductivity of the sulfide solid electrolyte under a normal temperature environment is further increased. Specifically, in an X-ray diffraction pattern using CuKα radiation, the intensity (I １ ) the intensity of the diffraction peak appearing in the range of a diffraction angle 2θ of 18.65°±0.50° (I ３ ) ratio (I ３ / I １ ) is preferably 1 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and even more preferably 0.1 or less. ３ / I １ The lower limit of may be 0.

[0051] In an X-ray diffraction pattern using CuKα radiation, each diffraction peak appears within a range of ±0.50° from the median value of the diffraction angle 2θ. Each diffraction peak preferably appears within a range of ±0.40° from the median value of the diffraction angle 2θ, and more preferably within a range of ±0.30°, ±0.20°, or ±0.10°.

[0052] (Composition) A sulfide solid electrolyte according to one embodiment of the present invention contains elemental carbon. The sulfide solid electrolyte has an LGPS-type crystal structure and contains elemental carbon, which reduces ionic conductivity and exhibits a shutdown function when the temperature rises above 220°C, or even above 230°C. The sulfide solid electrolyte contains elemental sulfur as well as elemental carbon. Regarding the composition of the sulfide solid electrolyte, the elements other than elemental carbon and elemental sulfur are not particularly limited as long as the sulfide solid electrolyte can have an LGPS-type crystal structure. Preferably, the sulfide solid electrolyte further contains at least one element selected from the group consisting of lithium, sodium, and potassium (hereinafter also referred to as "element A"), and elemental phosphorus. When the sulfide solid electrolyte further contains such an element, the LGPS-type crystal structure is more easily formed, and ionic conductivity under normal temperature conditions is further enhanced. The element A preferably contains elemental lithium, and more preferably elemental lithium. Below, preferred content ratios of each constituent element based on the content of elemental phosphorus, one of the preferred constituent elements, are described.

[0053] In the sulfide solid electrolyte according to one embodiment of the present invention, the molar ratio (C / P) of the carbon element content to the phosphorus element content is preferably 0.01 or more and 0.30 or less, more preferably 0.03 or more and 0.25 or less, even more preferably 0.05 or more and 0.20 or less, and may be 0.08 or more and 0.15 or less. Having the molar ratio (C / P) in the above range makes it possible to enhance the shutdown function, increase ionic conductivity under normal temperature environments, and the like. Furthermore, having the molar ratio (C / P) in the above range makes it possible to produce the sulfide solid electrolyte by heat treatment, since an LGPS-type crystal structure precipitates at a relatively low temperature during heat treatment, thereby improving productivity.

[0054] In the sulfide solid electrolyte according to one embodiment of the present invention, the molar ratio (S / P) of the sulfur element content to the phosphorus element content is preferably from 2 to 6, more preferably from 3 to 5, even more preferably from 3.5 to 4.5, and may be from 3.8 to 4.0. When the molar ratio (S / P) is in the above range, an LGPS-type crystal structure is easily formed, which makes it possible to enhance the shutdown function and increase ionic conductivity under normal temperature environments.

[0055] In the sulfide solid electrolyte according to one embodiment of the present invention, the molar ratio (A / P) of the content of at least one element A selected from the group consisting of lithium, sodium, and potassium to the content of phosphorus is preferably from 2 to 7, more preferably from 2.5 to 5.0, even more preferably from 3.0 to 4.0, and may be from 3.2 to 3.7. By having the molar ratio (A / P) in the above range, it is possible to increase ionic conductivity under normal temperature environments, etc.

[0056] The sulfide solid electrolyte according to one embodiment of the present invention preferably further contains a nitrogen element. When the sulfide solid electrolyte contains a nitrogen element, the shutdown function is further enhanced, and the moisture resistance (atmospheric stability) can also be improved. In addition, the sulfide solid electrolyte in this form is ０．５ The sulfide solid electrolyte can be produced using raw materials such as N, and therefore has higher productivity. In the sulfide solid electrolyte, the molar ratio of the nitrogen element content to the phosphorus element content (N / P) is preferably 0 or more and 2 or less, more preferably 0.01 or more and 1 or less, further preferably 0.05 or more and 0.6 or less, and may be 0.1 or more and 0.4 or less.

[0057] The sulfide solid electrolyte according to one embodiment of the present invention preferably further contains a halogen element (hereinafter, the halogen element may be referred to as "element X"). Examples of element X include fluorine, chlorine, bromine, and iodine. Element X preferably contains at least one of bromine and iodine, more preferably bromine and iodine, and even more preferably bromine and iodine. When the sulfide solid electrolyte further contains element X, ionic conductivity in a normal temperature environment tends to be increased. In the sulfide solid electrolyte, the molar ratio (X / P) of the content of element X to the content of phosphorus is preferably 0 or more and 2 or less, more preferably 0.01 or more and 1.5 or less, even more preferably 0.1 or more and 1.0 or less, even more preferably 0.2 or more and 0.8 or less, and may be 0.3 or more and 0.6 or less. In the sulfide solid electrolyte, the molar ratio of the bromine content to the phosphorus content (Br / P) is preferably 0.01 to 1, and more preferably 0.2 to 0.5. In the sulfide solid electrolyte, the molar ratio of the iodine content to the phosphorus content (I / P) is preferably 0.01 to 1, and more preferably 0.1 to 0.5.

[0058] The sulfide solid electrolyte according to one embodiment of the present invention may further contain another element Y other than carbon, sulfur, phosphorus, element A (at least one selected from the group consisting of lithium, sodium, and potassium), nitrogen, and halogen elements. Examples of the other element Y include metal elements other than element A, oxygen, boron, and silicon. 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, from 0 to 1, and more preferably 0.1 or less, or even 0.01 or less.

[0059] The sulfide solid electrolyte according to one embodiment of the present invention is preferably represented by the following formula (1): ａ C ｂ P.S. ｃ N ｄ X ｅ Y ｆ... (1) In the above formula (1), A is at least one element selected from the group consisting of Li, Na, and K. X is at least one halogen element. Y is at least one element other than A, C, P, S, N, and X. a, b, c, d, e, and f satisfy 2≦a≦7, 0.01≦b≦0.30, 2≦c≦6, 0≦d≦2, 0≦e≦2, and 0≦f≦1, respectively.

[0060] When the sulfide solid electrolyte according to one embodiment of the present invention has a composition represented by the above formula (1), the shutdown function and the like are improved. In the above formula (1), A preferably contains Li, and more preferably is Li. X preferably contains at least one of Br and I, more preferably contains Br and I, and even 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 (C / 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.

[0061] (Physical Properties, Applications, etc.) The ionic conductivity (σ) of the sulfide solid electrolyte according to one embodiment of the present invention at 25°C ２５ The lower limit of the ionic conductivity (σ) of the sulfide solid electrolyte at 25°C is preferably 1 mS / cm, more preferably 2 mS / cm, even more preferably 3 mS / cm, and even more preferably 4 mS / cm. ２５ When the ionic conductivity (σ) is equal to or greater than the lower limit, the ionic conductivity is improved under normal temperature conditions, and an energy storage device including the sulfide solid electrolyte can exhibit good charge / discharge performance. ２５ The upper limit of the viscosity is not particularly limited, but may be, for example, 20 mS / cm, or 10 mS / cm.

[0062] Ion conductivity (σ) of a sulfide solid electrolyte at 25°C according to one embodiment of the present invention ２５ ) relative to the ionic conductivity (σ') of the sulfide solid electrolyte at 25°C after heat treatment at 230°C for 2 hours. ２５ ) ratio (σ' ２５ / σ ２５ The upper limit of the ratio (σ') is preferably 0.5, more preferably 0.3, and even more preferably 0.1. ２５ / σ ２５ When the ratio (σ') is equal to or less than the upper limit, the shutdown function of the sulfide solid electrolyte is further enhanced. ２５ / σ ２５ The lower limit of the ionic conductivity (σ') of the sulfide solid electrolyte at 25°C after heat treatment at 230°C for 2 hours may be 0. ２５ The ionic conductivity (σ') is preferably 0 mS / cm or more and less than 1.0 mS / cm, and the upper limit thereof is more preferably 0.7 mS / cm, and even more preferably 0.5 mS / cm. ２５ ) may be 0 mS / cm.

[0063] 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 energy storage devices such as 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.

[0064] <Sulfide Solid Electrolyte Material> A sulfide solid electrolyte material according to one embodiment of the present invention is a material used in the production of a sulfide solid electrolyte. It contains at least one element (element A) selected from the group consisting of lithium, sodium, and potassium, as well as carbon, phosphorus, and sulfur. The sulfide solid electrolyte material preferably further contains at least one of nitrogen and a halogen, and more preferably both nitrogen and a halogen. The sulfide solid electrolyte material is, for example, a mixture of two or more compounds or simple substances (hereinafter also referred to as "compounds, etc.") containing at least one element selected from element A, carbon, phosphorus, sulfur, nitrogen, and a halogen. In this case, any of the compounds, etc. contained in the sulfide solid electrolyte material (mixture) may contain element A, carbon, phosphorus, sulfur, nitrogen, and a halogen. A single compound may contain two or more elements selected from element A, carbon, phosphorus, sulfur, nitrogen, and a halogen. For example, Li, which will be described later, is a compound containing lithium and sulfur, which are the element A. ２ S, P, which will be described later as a compound containing phosphorus and sulfur elements ２ S ５ The sulfide solid electrolyte material may contain a compound that does not contain any of element A, carbon, phosphorus, sulfur, nitrogen, and halogen elements.

[0065] Examples of compounds containing element A include Li ２ S., Li. ２ O, Li ３ N., Li. ２ CO ３ , metallic lithium, LiC ０．５ N, LiX (LiBr, LiI, etc.), Na ２ S, Na ２ O, Na ３ N, Na ２ CO ３ , metallic sodium, NaC ０．５ N, NaX (NaBr, NaI, etc.), K ２ S.K. ２ O.K. ３ N.K. ２ CO３ , metallic potassium, KC ０．５ N, KX (KBr, KI, etc.), etc. Among these, Li ２ S, LiC ０．５ N and LiX are preferred. The compound containing element A may be used alone or in combination of two or more.

[0066] Examples of compounds containing carbon include LiC ０．５ N., Li. ２ CO ３ , C.S. ２ , C ３ N ４ and other organic compounds. Examples of compounds containing carbon include LiC ０．５ N is preferred. ０．５ N also has the effect of suppressing the release of nitrogen elements to the outside of the system during the production process of the sulfide solid electrolyte. ０．５ N can be produced by the following procedure. ３ N and C ３ N ４ The raw material compounds are then mixed in a mortar or the like. Next, the mixed raw material compounds are subjected to mechanical milling to obtain LiC. ０．５ N is produced. ０．５ The means for preparing N is not limited to this, and it may be prepared by other methods. ０．５ N may be prepared by a general solid phase synthesis method. ０．５ An industrially produced and commercially available compound may be prepared as N. The compound containing carbon element may be used alone or in combination of two or more.

[0067] 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 S５ The phosphorus-containing compound 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 , P ２ S ５ , Al ２ S ３ , MgS, SiS ２ , C.S. ２ , 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] Examples of compounds containing nitrogen include Li ３ N, PN, P ３ N ５ , S ４ N ４ , S ２ N ２ , S ４ N ２ , LiC ０．５ N, etc., and LiC ０．５ Preferred is N. The compound containing a nitrogen element may be used alone or in combination of two or more.

[0070] Examples of the compound containing a halogen element include alkali metal halides, sulfur halides, phosphorus halides, and other halides, and alkali metal halides are preferred, with lithium halides (LiX) being more preferred. Examples of the lithium halides include LiF, LiCl, LiBr, and LiI. The compound containing a halogen element may be used alone or in combination of two or more, preferably in combination of two or more.

[0071] For example, in one embodiment, the sulfide solid electrolyte material is Li２ S and P ２ S ５ and LiC ０．５ It may be a mixture of N, LiBr and LiI.

[0072] The preferred contents of each element in the sulfide solid electrolyte material according to one embodiment of the present invention 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.

[0073] <Method for Producing Sulfide Solid Electrolyte> The method for producing a sulfide solid electrolyte according to one embodiment of the present invention is not particularly limited, but a method using the sulfide solid electrolyte material according to one embodiment of the present invention described above is preferred. For example, the method for producing a sulfide solid electrolyte according to one embodiment of the present invention comprises heat-treating the sulfide solid electrolyte material according to one embodiment of the present invention at a temperature range of 180°C or higher and 220°C or lower. The production method may comprise pretreating the sulfide solid electrolyte material before the heat treatment. The sulfide solid electrolyte material according to one embodiment of the present invention may be one that has been subjected to the above-mentioned pretreatment.

[0074] (Pretreatment) Pretreatment of the sulfide solid electrolyte material can be carried out by mechanical milling, melt quenching, etc., with mechanical milling being preferred. An intermediate is obtained through the pretreatment.

[0075] 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.

[0076] The pretreated sulfide solid electrolyte material (the intermediate obtained by the pretreatment) may have a crystalline structure, but is preferably a so-called sulfide glass. The term "sulfide glass" refers to a sulfide solid electrolyte containing an amorphous structure. When the intermediate is a sulfide glass, Li２ 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.

[0077] After the mechanical milling or other treatment, and before the heat treatment, the resulting intermediate may be subjected to a pulverization treatment using, for example, a mill (wet mill or dry mill).

[0078] (Heat Treatment) Heat treatment (heating) may be performed on a non-pretreated sulfide solid electrolyte material, but is preferably performed on a pretreated sulfide solid electrolyte material (an intermediate obtained by pretreatment). The heat treatment may be performed under a reduced pressure atmosphere or an inert gas atmosphere. The heat treatment temperature range is 180°C to 220°C, 185°C to 215°C, or 190°C to 210°C. By setting the heat treatment temperature within the above range, an LGPS-type crystal structure having diffraction peaks in the diffraction angle 2θ range of 20.15°±0.50°, the diffraction angle 2θ range of 20.37°±0.50°, and the diffraction angle 2θ range of 29.55°±0.50° in an X-ray diffraction diagram using CuKα rays is sufficiently precipitated. Furthermore, by setting the heat treatment temperature below the above upper limit, precipitation of LICP can be suppressed. In this way, by carrying out the heat treatment within the above temperature range, it is possible to obtain a sulfide solid electrolyte that has sufficient ion conductivity and a shutdown function under normal temperature conditions.

[0079] <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.

[0080] The energy storage device 10 contains the 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. Because the energy storage device 10 contains the sulfide solid electrolyte according to an embodiment of the present invention, a shutdown function can be exhibited when a temperature rise exceeding 220°C occurs, for example.

[0081] 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 in the energy storage element 10 may contain multiple different types of solid electrolytes, or each layer may contain a different solid electrolyte.

[0082] 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 ２S-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 -Z ｍ 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 １０ GeP ２ S １２ The following can be mentioned:

[0083] (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.

[0084] The positive electrode substrate 4 has electrical conductivity. Whether or not the positive electrode substrate 4 has electrical conductivity is determined by determining whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２The resistance is determined using Ω cm as a threshold value. The material for the positive electrode substrate 4 may be 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 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0085] 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 increasing the energy density per volume of the energy storage element 10. The "average thickness" refers to the average value of thicknesses measured at any five locations (the same applies hereinafter to the average thickness).

[0086] 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.

[0087] 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, and a filler as needed. One or more of these optional components may not be substantially contained in the positive electrode active material layer 5.

[0088] 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[Li ｘ 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 the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The 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 of them may be used in combination.

[0089] 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 5 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. 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).

[0090] 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.

[0091] 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, the discharge capacity of the energy storage element 10 can be increased, for example.

[0092] 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 even more preferably 50% by mass or less in some cases. 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, 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.

[0093] 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 solid electrolyte-containing coating is formed on at least a portion of the surface of the positive electrode active material.

[0094] 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 nanofibers, pitch-based carbon fibers, 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, fibrous, 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. As the conductive agent, a fibrous conductive agent such as fibrous carbon may be used.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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 5 may be 1% by mass or less, or 0.1% by mass or less, and the positive electrode active material layer 5 may be substantially free of filler.

[0100] 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.

[0101] 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, it is possible to obtain an energy storage element 10 having a high energy density. By setting the average thickness of the positive electrode active material layer 5 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10, for example.

[0102] (Negative Electrode) The negative electrode 2 has a negative electrode substrate 7 and a negative electrode active material layer 6 disposed directly on the negative electrode substrate 7 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] "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 availability of a material with stable physical properties.

[0109] "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.

[0110] 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.

[0111] "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.

[0112] "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.

[0113] 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 from, for example, the methods exemplified for the positive electrode. 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.

[0114] 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.

[0115] 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 even more preferably 50% by mass or less in some cases. 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, for example. 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. 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 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.

[0116] 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.

[0117] 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.

[0118] (Isolation Layer) The isolation layer 3 contains a solid electrolyte. 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. From the viewpoint of particularly effectively exhibiting the shutdown function, the isolation layer 3 preferably contains a sulfide solid electrolyte according to an embodiment of the present invention. When the isolation layer 3 uses the sulfide solid electrolyte according to an embodiment of the present invention, the content of the sulfide solid electrolyte according to an 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. When the isolation layer 3 uses the sulfide solid electrolyte according to an embodiment of the present invention, the content of the sulfide solid electrolyte according to an embodiment of the present invention 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.

[0119] The isolation layer 3 contains Li ３ P.O. ４ The positive electrode active material layer 5 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 active material layer 5.

[0120] 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.

[0121] <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.

[0122] 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.

[0123] <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.

[0124] (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.

[0125] (2) Isolation Layer Material Preparation Step 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 sealed under reduced pressure and fired, a liquid-phase method such as solution deposition, a gas-phase method, and firing in an argon atmosphere after mechanical milling.

[0126] (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 a metallic lithium foil or the like.

[0127] (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.

[0128] <Other Embodiments> The sulfide solid electrolyte, sulfide solid electrolyte material, sulfide solid electrolyte manufacturing method, and energy storage element 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.

[0129] 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.

[0130] 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.

[0131] [Example 1-1] A sulfide solid electrolyte of Example 1-1 satisfying the composition ratio shown in Table 1 was synthesized by the following process. ２ ) ３ By heat treating at 550°C for 3 hours, C ３ N ４ This step was carried out under a nitrogen atmosphere. ３ N and C ３ N ４The components were weighed out so that the molar ratio was 2:1, and mixed in a mortar. 0.50 g of the resulting mixture was placed in a sealed 80 mL zirconia pot containing 50 g of zirconia balls with a diameter of 4 mm. These steps were carried out in an argon atmosphere with a dew point of -50°C or less. The mixture was treated in a planetary ball mill (manufactured by FRITSCH, model number Premium line PL-7) at an orbital rotation speed of 190 rpm for 150 hours to obtain LiC. ０．５ Li N was prepared in a glove box with an argon atmosphere at a dew point of −50°C or less. ２ S (99.98%, Aldrich), P ２ S ５ (99%, Aldrich), LiC ０．５ N, LiBr (99.999%, manufactured by Aldrich), and LiI (99.999%, manufactured by Aldrich) were weighed to a molar ratio of 53.28: 18.72: 8.00: 12.00: 8.00, and then mixed in a mortar to prepare a sulfide solid electrolyte material containing lithium, carbon, phosphorus, sulfur, nitrogen, bromine, and iodine as constituent elements. The sulfide solid electrolyte material was placed in a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. A mechanical milling treatment (pretreatment) 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 (pretreated sulfide solid electrolyte material) was heat-treated at 185° C. for 2 hours to obtain the sulfide solid electrolyte of Example 1-1.

[0132] [Examples 1-2 to 4-2, Comparative Examples 1-1 to 9] The sulfide solid electrolytes of Examples 1-2 to 4-2 and Comparative Examples 1-1 to 9 were obtained in the same manner as in Example 1-1, except that the compounds used as raw materials and the amounts (molar ratios) thereof were adjusted to make the composition ratios of the sulfide solid electrolyte material and the resulting sulfide solid electrolyte as shown in Table 1, and the heat treatment temperature (HT) was set as shown in Table 1. In Table 1 and the following description, carbon element and its substitute element are represented by element M. In Comparative Examples 5-1, 5-2, and 6, Li was used as a raw material. ２ S (99.98%, Aldrich), P２ S ５ (99%, Aldrich) and GeS ２ (99.99%, manufactured by Kojundo Chemical Co., Ltd.) was used to obtain a sulfide solid electrolyte material and a sulfide solid electrolyte. ０．５ Replace N with Li １．５ Al ０．５ In Comparative Example 8, LiC ０．５ Replace N with Li １．５ B ０．５ In Comparative Example 9, LiC ０．５ Replace N with Li ５／３ Si １／３ N was used.

[0133] With respect to the constituent elements of each sulfide solid electrolyte of Examples and Comparative Examples, the molar ratio of the lithium element content to the phosphorus element content (Li / P), the type of element M (carbon element, germanium element, aluminum element, boron element or silicon element) and the molar ratio of the element M content to the phosphorus element content (M / P), the molar ratio of the sulfur element content to the phosphorus element content (S / P), the molar ratio of the nitrogen element content to the phosphorus element content (N / P), the molar ratio of the bromine element content to the phosphorus element content (Br / P), and the molar ratio of the iodine element content to the phosphorus element content (I / P) are shown in Table 1. Note that in each sulfide solid electrolyte of Examples and Comparative Examples, elements other than phosphorus element, lithium element, element M (carbon element, germanium element, aluminum element, boron element or silicon element), sulfur element, nitrogen element, bromine element and iodine element are considered to be substantially not contained. That is, for example, the composition formula of the sulfide solid electrolyte of Example 1-1 is Li ３．４９ C ０．１１ P.S. ３．９２ N ０．２１ Br ０．３２ I ０．２１ is.

[0134] (X-ray Diffraction Measurement) For each of the sulfide solid electrolytes of Examples and Comparative Examples, powder X-ray diffraction measurement was performed using the method described above to obtain X-ray diffraction patterns. Figure 3 shows the X-ray diffraction patterns of the sulfide solid electrolytes of Examples 1-2, 2, 3-2, and 4-2. Figure 4 shows the X-ray diffraction patterns of the sulfide solid electrolytes of Comparative Examples 3 and 4. For reference, Figure 4 also shows the X-ray diffraction patterns of Li ３ P.S. ４ 5 shows the X-ray diffraction patterns of the sulfide solid electrolytes of Comparative Examples 5-1, 5-2, and 6. In the X-ray diffraction patterns of the sulfide solid electrolytes of Examples 1-1 to 4-2 and Comparative Examples 3 and 4, the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 29.55°±0.50° (I １ The intensity of the diffraction peak (I) that appeared in the range of the diffraction angle 2θ of 28.00°±0.50° ２ ) ratio (I ２ / I １ The results are shown in Table 1.

[0135] [Evaluation] (Measurement of Ionic Conductivity) The ionic conductivity (σ) of each sulfide solid electrolyte at 25°C of the examples and comparative examples was measured. ２５ ) was determined by measuring AC impedance using a Bio-Logic VMP-300 in accordance with the above-described method. The measurement results are shown in Table 1.

[0136] (DSC Measurement) The sulfide solid electrolyte material used in Examples 1-1, 1-2 and Comparative Example 1 (after mechanical milling, the same applies hereinafter) (Example 1), the sulfide solid electrolyte material used in Examples 3-1, 3-2 and Comparative Example 3 (Example 3), the sulfide solid electrolyte material used in Examples 4-1, 4-2 and Comparative Example 4 (Example 4) and the sulfide solid electrolyte material used in Comparative Examples 5-1 and 5-2 (Comparative Example 5) were subjected to DSC (differential scanning calorimetry) measurement by the following method. Using a DSC device (manufactured by Rigaku Corporation, Thermo Plus DSC8230), each sulfide solid electrolyte material was sealed in a SUS sealed pan and heated from room temperature to 350 ° C. at a heating rate of 10 ° C. / min. The obtained DSC curve is shown in FIG.

[0137]

[0138] As shown in Table 1, by heat treating the sulfide solid electrolyte material containing lithium, phosphorus, and sulfur as well as carbon in a temperature range of 180°C to 220°C, the ionic conductivity (σ ２５ The sulfide solid electrolytes of Examples 1-1 to 4-2 each had an ionic conductivity (σ) of more than 1.0 mS / cm. Furthermore, as shown in FIG. 3, the sulfide solid electrolytes of Examples 1-2, 2, 3-2, and 4-2 each had diffraction peaks in the X-ray diffraction pattern at a diffraction angle 2θ of 20.15°±0.50°, a diffraction angle 2θ of 20.37°±0.50°, and a diffraction angle 2θ of 29.55°±0.50°, respectively, confirming that they had an LGPS-type crystal structure. The sulfide solid electrolytes of the other Examples were also confirmed to have a similar crystal structure. Meanwhile, the sulfide solid electrolytes of Comparative Examples 1 to 4, which were obtained by heat-treating a sulfide solid electrolyte material containing lithium, phosphorus, and sulfur as well as carbon at 230°C, each had an ionic conductivity (σ ２５ 4, the sulfide solid electrolytes of Comparative Examples 3 and 4 had a crystal structure of LICP and β-Li ３ P.S. ４ It was confirmed that the sulfide solid electrolytes of Examples 1-1 to 4-2 had a crystal structure of 1-Li. It was also confirmed that the sulfide solid electrolytes of Comparative Examples 1 and 2 had a similar crystal structure. From the above, it can be seen that the sulfide solid electrolytes of Examples 1-1 to 4-2 have good ionic conductivity under normal temperature environments, but when heated to, for example, 230°C, a crystalline structure of LICP and the like precipitates as in Comparative Examples 1 to 4, and the ionic conductivity decreases. In other words, it was confirmed that the sulfide solid electrolytes of Examples 1-1 to 4-2 have a shutdown function that is exhibited as the temperature rises to 230°C. Note that, as shown in FIG. 6, in the DSC curves of the sulfide solid electrolyte materials of Examples 1, 3, and 4 at a heating rate of 10°C / min, LICP and β-Li were present in the range from 230°C to 250°C. ３ P.S. ４ From these results, it can be seen that in the sulfide solid electrolytes of each Example obtained from these sulfide solid electrolyte materials, the exothermic peak resulting from the crystallization of LICP or β-Li was observed within 1 to 2 minutes at the latest after the temperature rose to 230°C. ３ P.S.４ It is believed that a crystal structure such as LGPS precipitates, resulting in a decrease in ionic conductivity. On the other hand, as shown in Table 1 and FIG. 5, in the sulfide solid electrolytes of Comparative Examples 5-1 and 5-2 obtained by heat-treating a sulfide solid electrolyte material composed of lithium, germanium, phosphorus, and sulfur at 250 ° C. or less, the LGPS crystal structure did not precipitate, and the ionic conductivity was low. And, in the sulfide solid electrolyte of Comparative Example 6 obtained by heat-treating a sulfide solid electrolyte material composed of lithium, germanium, phosphorus, and sulfur at 550 ° C., the LGPS crystal structure precipitated, and sufficient ionic conductivity was exhibited. Furthermore, as shown in Table 1, each of the sulfide solid electrolytes of Comparative Examples 7 to 9 obtained by heat-treating a sulfide solid electrolyte material containing aluminum, boron, or silicon as the element M at 230 ° C. had sufficient ionic conductivity. In other words, each of the sulfide solid electrolytes of Comparative Examples 5-1 to 5-9 had good ionic conductivity under normal temperature conditions, and did not precipitate a crystalline structure with low ionic conductivity when heated to 230°C, and did not have the shutdown function that appears as the temperature rises to 230°C.

[0139] 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.

[0140] REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 separator 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 containing carbon element, which has diffraction peaks in the range of a diffraction angle 2θ of 20.15°±0.50°, a diffraction angle 2θ of 20.37°±0.50°, and a diffraction angle 2θ of 29.55°±0.50° in an X-ray diffraction pattern using CuKα rays.

2. The sulfide solid electrolyte according to claim 1, further containing a nitrogen element.

3. The sulfide solid electrolyte according to claim 1 or 2, further containing a halogen element.

4. The sulfide solid electrolyte according to claim 3, wherein the halogen element includes at least one of a bromine element and an iodine element.

5. The sulfide solid electrolyte according to claim 1 or 2, further containing phosphorus element.

6. The sulfide solid electrolyte according to claim 5, wherein the molar ratio of the carbon element content to the phosphorus element content is 0.01 or more and 0.30 or less.

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

8. In the X-ray diffraction pattern using the CuKα ray, the intensity of the diffraction peak appearing in the range of the diffraction angle 2θ of 29.55°±0.50° (I １ The intensity of the diffraction peak (I) appears in the range of 28.00°±0.50° of the diffraction angle 2θ. ２ ) ratio (I ２ / I １ 3. The sulfide solid electrolyte according to claim 1 or claim 2, wherein σ is 1 or less.

9. Ionic conductivity (σ) of the sulfide solid electrolyte at 25°C ２５ ) relative to the ionic conductivity (σ') of the sulfide solid electrolyte at 25°C after heat treatment at 230°C for 2 hours. ２５ ) ratio (σ' ２５ / σ ２５ 3. The sulfide solid electrolyte according to claim 1 or claim 2, wherein the value of (a) is 0.5 or less.

10. The sulfide solid electrolyte according to claim 1 or 2, which is represented by the following formula (1): A ａ C ｂ P.S. ｃ N ｄ X ｅ Y ｆ ... (1) In the above formula (1), A is at least one element selected from the group consisting of Li, Na, and K. X is at least one halogen element. Y is at least one element other than A, C, P, S, N, and X. a, b, c, d, e, and f satisfy 2≦a≦7, 0.01≦b≦0.30, 2≦c≦6, 0≦d≦2, 0≦e≦2, and 0≦f≦1, respectively.

11. A material for a sulfide solid electrolyte, which is used to produce a sulfide solid electrolyte, and contains at least one element selected from the group consisting of lithium, sodium, and potassium, carbon, phosphorus, and sulfur.

12. A method for producing a sulfide solid electrolyte, comprising heat treating the sulfide solid electrolyte material according to claim 11 in a temperature range of 180°C to 220°C.

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

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