sulfide solid electrolytes

Abstract

Provided is a sulfide solid electrolyte that has high ionic conductivity and water resistance and can be handled in a dry room environment. [Solution] The sulfide solid electrolyte contains Li, P and S, and in the Raman spectrum from 200cm -1 to 1000cm -1 obtained by micro-Raman spectroscopy measurement using a laser with a wavelength of 532nm, there are a peak A at 420-10cm 3- derived from PS4 -1 and a peak B at 420+10cm -1 , the ratio I A of the peak intensity I of the peak A to the peak intensity I B of the peak B, that is I B / I A is within the range of 0.5 or more and 1.5 or less, and the ratio I -1 of the peak intensity I of the peak C at 920cm C to the peak intensity I A of the peak A, that is I C / I A is less than 0.05.

Description

[Technical Field]

[0001] This invention relates to a sulfide solid electrolyte that is suitably used in, for example, all-solid-state batteries. [Background technology]

[0002] Currently available lithium-ion batteries use flammable organic electrolytes, necessitating the installation of safety devices to suppress temperature rise during short circuits, as well as structural and material improvements to prevent short circuits. In contrast, all-solid-state lithium-ion batteries use a solid electrolyte material, which simplifies the safety devices associated with flammable organic electrolytes, resulting in superior manufacturing costs and productivity. In addition, they have the potential for further development, such as achieving high voltage and high output by stacking batteries in series in a bipolar configuration within the same cell.

[0003] Suitable solid electrolytes for all-solid-state batteries include sulfide solid electrolytes (glass-based, glass-ceramic-based, LGPS crystal-based, and argyrodite crystal-based) that have high ionic conductivity. Here, as a method for defining sulfide solid electrolytes having high ionic conductivity, Raman spectroscopy is used, for example, as shown in Patent Documents 1 and 2.

[0004] In Patent Document 1, PS4 3- Peak and P2S7 4- P2S6 relative to the peak 4- This specifies the area ratio of the peaks. In Patent Document 2, PS4 3- 1300cm relative to the peak -1 This defines the peak intensity ratio. As described above, in these Patent Documents 1 and 2, sulfide solid electrolytes with low impurities (by-products) and high ionic conductivity are identified by defining the peaks of Raman spectroscopy measurements. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 2021-044106 [Patent Document 2] Japanese Unexamined Patent Publication No. 2022-131400 [Summary of the Invention] [Problem to be Solved by the Invention]

[0006] Meanwhile, sulfide solid electrolytes easily react with moisture in the atmosphere, generate toxic hydrogen sulfide gas, form oxides, and may cause a decrease in ionic conductivity. Even when impurities (by-products) are simply defined as in Patent Documents 1 and 2, hydrogen sulfide may be generated due to reaction with the atmosphere during handling, and the ionic conductivity may decrease. For this reason, conventionally, sulfide solid electrolytes have had to be handled in a glove box maintained in an inert gas atmosphere such as Ar gas, for example.

[0007] The present invention has been made in view of the foregoing circumstances, and an object thereof is to provide a sulfide solid electrolyte that has high ionic conductivity and water resistance, and can be handled in a dry room environment. [Means for Solving the Problem]

[0008] In order to solve the above problem, as a result of intensive studies by the present inventors, it has been found that by pre-substituting oxygen on a part of the surface of a sulfide solid electrolyte, generation of hydrogen sulfide and oxides due to reaction with moisture can be suppressed, and a sulfide solid electrolyte excellent in ionic conductivity and water resistance can be provided. Then, in a Raman spectrum obtained by Raman spectroscopy measurement of a sulfide solid electrolyte, normally PS4 3- -derived peak is at 420 cm -1 It appears in the vicinity, but when a part is oxygen-substituted, a peak derived from a P-S bond (420-10 cm -1 ) and a peak derived from a P-O bond (420+10 cm -1It was found that it splits into two parts. Also, PO4 3- If present, 920cm -1 It was found that a peak occurs at that point.

[0009] The present invention is based on the above-mentioned findings, and the sulfide solid electrolyte of embodiment 1 of the present invention contains Li, P, S, and is measured by micro-Raman spectroscopy using a laser with a wavelength of 532 nm at 200 cm². -1 From 1000cm -1 In the Raman spectrum up to PS4 3- Originating from 420-10cm -1 Peak A at 420 + 10 cm -1 There is a peak B in the aforementioned peak A, and the peak intensity I A and the peak intensity I of the aforementioned peak B B Ratio I B / I A The value is within the range of 0.5 to 1.5, and 920cm -1 Peak intensity I of peak C C and the peak intensity I of the aforementioned peak A A Ratio I C / I A It is characterized by being less than 0.05.

[0010] According to the sulfide solid electrolyte of embodiment 1 of the present invention, in the Raman spectrum, PS4 3- Originating from 420-10cm -1 Peak A at 420 + 10 cm -1 There is a peak B in the aforementioned peak A, and the peak intensity I A and the peak intensity I of peak B B Ratio I B / I A Since the ratio is within the range of 0.5 to 1.5, a portion of the surface is replaced with oxygen, which suppresses the generation of hydrogen sulfide and oxides due to reaction with moisture, resulting in excellent water resistance. Also, PO4 3- 920cm derived from -1 Peak intensity I of peak C C and the peak intensity I of the aforementioned peak AA Ratio I C / I A It is said to be less than 0.05, PO4 3- It contains very little structural material and has excellent ionic conductivity. Note PO4 3- 920cm derived from -1 Peak C does not appear in I C / I A It may be 0.00.

[0011] The sulfide solid electrolyte of embodiment 2 of the present invention is characterized in that, in the sulfide solid electrolyte described in embodiment 1 of the present invention, the ionic conductivity after being left for 24 hours in an atmospheric atmosphere with a dew point of -30°C is 2 mS / cm or more. According to the sulfide solid electrolyte of embodiment 2 of the present invention, the ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C is 2 mS / cm or more, which is particularly excellent in water resistance and can be handled particularly stably even in a dry room environment. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a sulfide solid electrolyte that has high ionic conductivity and water resistance and can be handled in a dry room environment. [Brief explanation of the drawing]

[0013] [Figure 1] This is a flow chart showing an example of a method for producing a sulfide solid electrolyte, which is an embodiment of the present invention. [Figure 2] These are the Raman spectra of the sulfide solid electrolytes of the present invention example and comparative example in the examples. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the attached drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified.

[0015] The sulfide solid electrolyte according to this embodiment is a sulfide used, for example, as a solid electrolyte constituting an all-solid-state battery. Sulfide solid electrolyte materials have high ionic conductivity and are non-flammable, making them highly safe, and are therefore applied to electric vehicles and the like.

[0016] In this embodiment, the sulfide solid electrolyte has a composition containing Li, P, and S, and was measured using micro-Raman spectroscopy with a 532 nm laser at 200 cm². -1 From 1000cm -1 In the Raman spectrum up to PS4 3- Originating from 420-10cm -1 Peak A at 420 + 10 cm -1 There is a peak B in the aforementioned peak A, and the peak intensity I A and the peak intensity I of peak B B Ratio I B / I A The range is set to be between 0.5 and 1.5. Furthermore, in the Raman spectrum mentioned above, at 920 cm⁻¹ -1 Peak intensity I of peak C C and the peak intensity I of the aforementioned peak A A Ratio I C / I A It is considered to be less than 0.05.

[0017] In other words, in the sulfide solid electrolyte according to this embodiment, 420-10cm -1 Peak A at 420 + 10 cm -1 There is a peak B in the aforementioned peak A, and the peak intensity I A and the peak intensity I of peak B B Ratio I B / I A Since it is set to be within the range of 0.5 to 1.5, PS4 3- The peak originating from the PS bond (420-10cm) -1 ) and a peak originating from PO bonding (420 + 10 cm) -1It has split into two parts, and a portion of the surface has been replaced by oxygen. Also, PO4 3- 920cm derived from -1 Peak intensity I of peak C C and the peak intensity I of the aforementioned peak A A Ratio I C / I A It is said to be less than 0.05, PO4 3- This means it contains almost no of it.

[0018] In this embodiment, it is preferable that the sulfide solid electrolyte has an ionic conductivity of 3 mS / cm or more. Furthermore, the ionic conductivity is more preferably 4 mS / cm or higher, and even more preferably 5 mS / cm or higher.

[0019] Furthermore, in the sulfide solid electrolyte of this embodiment, it is preferable that the ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C is 2 mS / cm or more. Furthermore, the ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C is more preferably 3 mS / cm or higher, and even more preferably 4 mS / cm or higher.

[0020] Next, an example of a method for producing a sulfide solid electrolyte according to this embodiment will be explained using the flow chart in Figure 1. In this embodiment, as shown in the flow diagram of Figure 1, the process includes a raw material mixing step S01, a primary calcination step S02, a grinding step S03, an oxygen replacement step S04, and a secondary calcination step S05.

[0021] (Raw material mixing process S01) First, raw materials containing each element that makes up the sulfide solid electrolyte are mixed to obtain a mixed raw material. In this embodiment, elemental sulfur is preferably used as the raw material. Furthermore, in order to utilize the solid-liquid reaction between each raw material and liquid sulfur for the production of a sulfide solid electrolyte, an excess of elemental sulfur exceeding the stoichiometric ratio composition of the sulfide solid electrolyte may be added to the mixed raw materials. Furthermore, in order to promote elemental diffusion and chemical reactions in later processes, each raw material and excess elemental sulfur are preferably in the form of a powder (powdered powder, particulate matter, or aggregates of powder and matter), and among these, powder is more preferable.

[0022] Elemental sulfur refers to sulfur that contains no elements other than sulfur, excluding unavoidable impurities. In other descriptions of this embodiment, unless otherwise specified, each raw material may contain unavoidable impurities. Furthermore, the elemental sulfur added may be any of the sulfur allotropes such as α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), or rubbery sulfur, or it may contain multiple allotropes.

[0023] The mixing method in the raw material mixing process S01 is not particularly limited as long as it can uniformly mix each raw material. However, various existing methods include mortars and pestles, general mixers, blenders, ball mills, bead mills, vibratory mills, and V-type mixers. Alternatively, instead of a general mixing process, mechanical milling may be performed using a planetary ball mill, vibratory mill, ball mill, etc.

[0024] Furthermore, if the raw material mixing process S01 contains sulfides or the like, it is preferable to carry out the mixing process in a gaseous atmosphere that does not react with the raw materials. Therefore, it is preferable to carry out the process in an inert atmosphere such as nitrogen, argon, or other noble gases. In addition, it is preferable that the atmospheric gas used does not contain water or oxygen gas. In particular, the water content in the atmospheric gas is preferably 100 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less. By keeping the water content in the atmospheric gas within this range, oxidation due to water is suppressed, making it possible to produce high-quality sulfide solid electrolytes.

[0025] (Primary firing process S02) The mixed raw materials obtained as described above are fired under the following conditions: atmosphere: inert gas atmosphere such as Ar gas, firing temperature: within the range of 300°C to 600°C, and holding time at firing temperature: within the range of 1 hour to 24 hours, to obtain a primary fired body.

[0026] (Grinding process S03) Next, the primary calcined body obtained as described above is pulverized to obtain a raw material powder. Preferably, the average particle size of the pulverized raw material powder is within the range of 1 μm to 100 μm. There are no particular restrictions on the pulverization method; existing methods can be appropriately selected and applied.

[0027] (Oxygen replacement process S04) Next, the raw material powder obtained as described above is kept in an atmospheric environment with a dew point of -30°C for 12 to 48 hours, and a portion of the surface is purged with oxygen.

[0028] (Secondary firing process S05) In the secondary firing process S05, the raw material powder placed in firing containers such as crucibles and saggars is heated to generate a sulfide solid electrolyte. Regarding the material of the firing container, it is preferable to use a material for the inner wall of the container that does not react easily with molten materials such as elemental sulfur and sulfides, in other words, a material that is resistant to corrosion by sulfidation. Examples include alumina, zirconia, carbon, and silicon carbide.

[0029] The heating temperature in the secondary firing step S05 is preferably 400°C or higher, and more preferably 500°C or higher. On the other hand, the heating temperature is preferably 1000°C or lower, and more preferably 650°C or lower. Furthermore, the holding time at the heating temperature is preferably 30 minutes or more, and more preferably 60 minutes or more. On the other hand, the holding time at the heating temperature is preferably 24 hours or less, and more preferably 6 hours or less.

[0030] In addition, the heat treatment in the secondary firing step S05 is preferably performed in a gas atmosphere that does not react with the mixed raw material, intermediate product or sulfide solid electrolyte. Therefore, it is preferably performed in an inert atmosphere such as nitrogen, argon or other noble gases. In addition, it is preferable that the atmosphere gas used does not contain moisture and oxygen gas. In particular, the moisture content in the atmosphere gas is preferably 100 ppm or less, more preferably 30 ppm or less, and still more preferably 10 ppm or less. By setting the moisture content in the atmosphere gas within this range, reaction with moisture is suppressed, making it possible to produce high-quality sulfide solid electrolytes.

[0031] According to the sulfide solid electrolyte of the present embodiment configured as described above, in a Raman spectrum, PS4 3- -derived 420-10 cm -1 has peak A, 420+10 cm -1 has peak B, the ratio of the peak intensity I of peak A A to the peak intensity I of peak B B , that is I B / I A is within the range of 0.5 or more and 1.5 or less. Therefore, a part of the surface is substituted with oxygen, generation of hydrogen sulfide and oxides due to reaction with moisture can be suppressed, and the sulfide solid electrolyte has excellent water resistance.

[0032] In addition, the ratio of the peak intensity I of peak C at 920 cm 3- derived from PO4 -1 to the peak intensity I of peak A C derived from PS4, that is I A / I C / I A is less than 0.05, so the sulfide solid electrolyte hardly contains a PO4 3- structure and has excellent ionic conductivity. Note that, if PO4 3- is not contained, peak C at 920 cm 3- derived from PO4 -1 does not need to appear.

[0033] In this embodiment, if the sulfide solid electrolyte has an ionic conductivity of 2 mS / cm or more after being left for 24 hours in an atmospheric environment with a dew point of -30°C, it exhibits particularly excellent ionic conductivity and is particularly suitable as a solid electrolyte used in all-solid-state batteries, etc. At the same time, it exhibits particularly excellent water resistance and can be handled particularly stably even in a dry room environment.

[0034] Although one embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. [Examples]

[0035] The verification experiments conducted to confirm the effectiveness of the present invention will be described.

[0036] (Example 1 of the present invention) In an Ar-atmosphere glove box, 1.31 g of Li2S powder, 0.21 g of elemental P powder, 0.28 g of elemental Si powder, and 2.00 g of elemental S powder were weighed and then mixed in an agate mortar for 10 minutes. The mixed raw materials were subjected to primary calcination under conditions of an Ar atmosphere and held at 550°C for 6 hours, and then pulverized to obtain calcined powder. The obtained calcined powder was left for 24 hours in an atmospheric environment with a dew point of -30°C to allow a portion of the surface to oxidize and replace, and then subjected to secondary calcination under conditions of Ar atmosphere and holding at 550°C for 6 hours to obtain the sulfide solid electrolyte of the present invention.

[0037] (Example 2 of the present invention) In an Ar-atmosphere glove box, 1.31 g of Li2S powder, 0.21 g of elemental P powder, 0.28 g of elemental Si powder, and 2.00 g of elemental S powder were weighed and then mixed in an agate mortar for 10 minutes. The mixed raw materials were subjected to primary calcination under conditions of an Ar atmosphere and held at 550°C for 6 hours, and then pulverized to obtain calcined powder. The obtained calcined powder was left for 24 hours in an atmospheric environment with a dew point of -30°C to allow a portion of the surface to oxidize and replace, and then subjected to secondary calcination under conditions of Ar atmosphere and holding at 400°C for 24 hours to obtain the sulfide solid electrolyte of the present invention.

[0038] (Comparative example) In an Ar-atmosphere glove box, 1.31 g of Li2S powder, 0.68 g of P2S5 powder, and 1.01 g of SiS2 powder were weighed and then mixed for 24 hours at 360 rpm using a ball mill with 10 mmφ tungsten carbide media. The mixed raw material powders were formed into pellets in a glove box under an Ar atmosphere, and the pellets, placed in an alumina firing container, were placed in a furnace and fired under conditions of an Ar atmosphere and 550°C for 6 hours to obtain the comparative example solid electrolyte powder.

[0039] The obtained sulfide solid electrolyte was evaluated using Raman spectroscopy, ionic conductivity, and ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C, as described below. The evaluation results are shown in Table 1.

[0040] <Raman spectroscopy measurement> Raman analysis was performed using a HORIBA XploRa analyzer. The measurement involved a 50x objective lens, a 532nm wavelength laser as the incident light, and a slit width of 0.1mm. The measurement range was 100-1000cm². -1 The exposure time was 30 seconds, and the number of integrations was 3. The obtained Raman spectrum is shown in Figure 2.

[0041] <Ionic conductivity measurement> The sulfide solid electrolyte obtained in the present invention example after secondary calcination, and the sulfide solid electrolyte obtained in the present invention example after secondary calcination, were left for 24 hours in an atmospheric environment with a dew point of -30°C. The AC impedance was measured using a SUS conductivity measurement cell. The measurement was performed by applying a pressure of 500 MPa to a 0.1 g sample and then measuring within a range of 1 Hz to 1 MHz at room temperature of 25°C.

[0042] [Table 1]

[0043] In the comparative example, as shown in Figure 2, PS4 3- -derived 420 cm -1 peak is not split, indicating that part of the PS4 3- is not oxygen-substituted. For this reason, the ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C is greatly reduced, and water resistance is poor.

[0044] In contrast, in the examples of the present invention, PS4 3- -derived 420-10 cm -1 peak A at -1 and peak B at 420+10 cm A exist, and the peak intensity I of peak A B and the peak intensity I of peak B B ratio I A A / I 3- B is within the range of 0.5 or more and 1.5 or less, which shows that part of PS4 is oxygen-substituted. For this reason, high ionic conductivity is maintained after being left for 24 hours in an atmospheric environment with a dew point of -30°C, and water resistance is excellent.

[0045] From the results of the above confirmation experiments, it was confirmed that according to the examples of the present invention, a sulfide solid electrolyte having high ionic conductivity and water resistance and being handleable in a dry room environment can be provided.

Claims

1. It contains Li, P, S, and in the Raman spectrum from 200 cm －１ -1 to 1000 cm －１ -1 obtained by microscopic Raman spectroscopy measurement using a laser with a wavelength of 532 nm, the PS ４ ３－ 4-derived peak A at (420-10) cm －１ -1 and peak B at (420+10) cm －１ -1 exist, and the ratio I Ａ A / I Ｂ B of the peak intensity I Ｂ A of the peak A to the peak intensity I Ａ B of the peak B is within the range of 0.5 or more and 1.5 or less, and the ratio I －１ C / I Ｃ A of the peak intensity I Ａ C of peak C at 920 cm Ｃ -1 to the peak intensity I Ａ A of the peak A is less than 0.

05. A sulfide solid electrolyte characterized in that.

2. The sulfide solid electrolyte according to claim 1, characterized in that the ionic conductivity after being left for 24 hours in an atmospheric environment with a dew point of -30°C is 2 mS / cm or more.

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