Patent Description:
An all solid state battery is a battery including a solid electrolyte layer between a cathode layer and an anode layer, and an advantage thereof is that the simplification of a safety device may be more easily achieved compared to a liquid based battery including a liquid electrolyte containing a flammable organic solvent. As a solid electrolyte used for the all solid state battery, a sulfide solid electrolyte is known.

Patent Literature <NUM> discloses a sulfide solid electrolyte comprising an X element that is one kind or more elements selected from lithium, phosphorous, sulfur and halogen, having an argyrodite type crystal structure, and having a specific composition. Also, Patent Literature <NUM> discloses a sulfide based solid electrolyte for a lithium ion battery having a cubical argyrodite type crystal structure and having a specific composition. Moreover, Patent Literature <NUM> discloses a sulfide solid electrolyte according to the prior art. In addition, Non-Patent Literature <NUM> discloses investigations on Li<NUM>PS<NUM>X.

In order to improve the battery properties, a sulfide solid electrolyte with high ion conductivity has been demanded. The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a sulfide solid electrolyte with high ion conductivity.

In order to achieve the above object, the present invention provides a method for producing a sulfide solid electrolyte, wherein the sulfide solid electrolyte comprises: a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element, and the sulfide solid electrolyte has an argyrodite type crystal phase, in <NUM>P-MAS-NMR, the sulfide solid electrolyte has peak A at <NUM> ppm ± <NUM> ppm and peak B at <NUM> ppm ± <NUM> ppm, and when an area ratio of the peak A is regarded as SA, and an area ratio of the peak B is regarded as SB, a proportion of the SB to the SA, that is SB/SA, is <NUM> or less, and wherein the method comprises a mixing step of obtaining a precursor with a Li<NUM>S residual ratio of <NUM>% or more and <NUM>% or less, by mixing a raw material composition including at least Li<NUM>S, and a burning step of burning the precursor, wherein the method for mixing the raw material composition includes mechanical milling and the burning temperature is between <NUM> and <NUM>.

According to the present invention, since SB/SA is low, a sulfide solid electrolyte with high ion conductivity may be obtained.

In the invention, the sulfide solid electrolyte may further have peak C at <NUM> ppm ± <NUM> ppm, and when an area ratio of the peak C is regarded as SC, a proportion of a total of the SB and the SC to the SA, that is (SB + SC) /SA, may be <NUM> or less.

In the invention, the sulfide solid electrolyte may further have peak D at <NUM> ppm ± <NUM> ppm.

In the invention, the M may include at least P.

In the invention, the sulfide solid electrolyte may further comprise an X element (X is a halogen).

In the invention, the X may include at least Cl.

In the invention, the sulfide solid electrolyte may have a composition represented by Li<NUM>-yPS<NUM>-yXy (y satisfies <NUM> < y ≤ <NUM>).

The present invention also provides a precursor of the above described sulfide solid electrolyte wherein a Li<NUM>S residual ratio is <NUM>% or more and <NUM>% or less.

According to the present invention, since the Li<NUM>S residual ratio is in the specific range, a precursor that enables to obtain a sulfide solid electrolyte with high ion conductivity may be obtained.

An all solid state battery comprising a cathode layer, an anode layer, and a solid electrolyte layer formed between the cathode layer and the anode layer, and at least one of the cathode layer, the anode layer and the solid electrolyte layer may include the above described sulfide solid electrolyte.

An all solid state battery with high output property may be obtained by using the above described sulfide solid electrolyte.

As outlined above, the present invention provides a method for producing the above described sulfide solid electrolyte, the method is characterized by comprising steps of: a mixing step of obtaining a precursor with a Li<NUM>S residual ratio of <NUM>% or more and <NUM>% or less, by mixing a raw material composition including at least Li<NUM>S, and a burning step of burning the precursor.

A sulfide solid electrolyte with high ion conductivity may be obtained by using the precursor wherein the Li<NUM>S residual ratio is in the specific range.

The sulfide solid electrolyte in the present invention exhibits effects such that the ion conductivity is high.

The sulfide solid electrolyte, the precursor of the sulfide solid electrolyte, the all solid state battery and the method for producing the sulfide solid electrolyte in the present invention will be hereinafter described in detail.

The sulfide solid electrolyte in the present invention comprises a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element. Further, the sulfide solid electrolyte has an argyrodite type crystal phase. Also, in <NUM>P-MAS-NMR, the sulfide solid electrolyte has peak A at <NUM> ppm ± <NUM> ppm and peak B at <NUM> ppm ± <NUM> ppm, and when an area ratio of the peak A is regarded as SA, and an area ratio of the peak B is regarded as SB, a proportion of the SB to the SA, that is SB/SA, is the specific value or less.

According to the present invention, since SB/SA is low, a sulfide solid electrolyte with high ion conductivity may be obtained. As described later, peak A is a peak deriving from the argyrodite type crystal phase, and peak B is a peak deriving from an amorphous phase related to the argyrodite type crystal phase.

Here, as a method for synthesizing a sulfide solid electrolyte having the argyrodite type crystal phase, a method wherein a sulfide glass is produced by milling a raw material composition, and then, the sulfide glass is burned, is conventionally know.

From the detailed investigation by the present inventor regarding the relationship between the amorphous property of a sulfide glass and the ion conductivity of a sulfide solid electrolyte obtained by burning the sulfide glass, it was found out that, when the amorphous property of the sulfide glass is too high, the amorphous phase tends to remain in the obtained sulfide solid electrolyte so that the ion conductivity is not sufficiently improved. Similarly, it was found out that, when the amorphous property of the sulfide glass is too low, uniform solid-phase reaction hardly occurs during burning so that an argyrodite type crystal phase with high ion conductivity is hardly deposited. So, by producing a precursor by moderately amorphizing the raw material composition and burning the precursor, a sulfide solid electrolyte with little remaining amorphous phase could be obtained. As described above, in the present invention, since SB/SA is low, a sulfide solid electrolyte with high ion conductivity may be obtained.

Patent Literature <NUM>, for example, discloses in Example thereof that mechanical milling was carried out under conditions of <NUM> rpm for <NUM> hours. As described in the later described Comparative Example <NUM>, it was suggested that SB/SA was high since Li<NUM>S residual ratio was low and the amorphization was progressed. Also, Patent Literature <NUM>, for example, discloses in Example thereof that a crushing and mixing was carried out for <NUM> hours with a ball mill; however, since the rotation speed of the ball mill is not known, it is difficult to compare directly. Also, although Patent Literature <NUM> discloses in [<NUM>] "therefore, pulverization and mixing to the extent that crystallinity of the raw material powders can be maintained is desirable", it is difficult to compare quantitatively, since it is not clear whether "crystallinity of the raw material powders" indicates the crystallinity of the all raw material powders, or the crystallinity of a part of the raw material powder. In the first place, an object of Patent Literature <NUM> is to prevent sulfur defects at the time of calcination, and the object is different from that of the present invention.

The sulfide solid electrolyte in the present invention comprises a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element. The sulfide solid electrolyte may further comprise an X element (X is a halogen).

The sulfide solid electrolyte has an argyrodite type crystal phase. The argyrodite type crystal phase in the sulfide solid electrolyte may be confirmed by an X-ray diffraction (XRD) measurement. The sulfide solid electrolyte preferably has a peak at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in an X-ray diffraction (XRD) measurement using a CuKα ray. These peaks are typical peaks of the argyrodite type crystal phase. The sulfide solid electrolyte preferably has the argyrodite type crystal phase as a main phase.

The sulfide solid electrolyte has peak A at <NUM> ppm ± <NUM> ppm and peak B at <NUM> ppm ± <NUM> ppm in <NUM>P-MAS-NMR. Peak A is a peak deriving from the argyrodite type crystal phase, and peak B is a peak deriving from an amorphous phase related to the argyrodite type crystal phase. Also, when an area ratio of the peak A is regarded as SA, and an area ratio of the peak B is regarded as SB, a proportion of the SB to the SA, that is SB/SA, is preferably low. The reason is because the ion conductivity of the crystal phase is higher than the amorphous phase. SB/SA is usually <NUM> or less. Meanwhile, SB/SA may be <NUM>, and may be more than <NUM>. In the latter case, SB/SA may be <NUM> or more.

SA is preferably high. SA is, for example, <NUM>% or more, may be <NUM>% or more, and may be <NUM>% or more. Meanwhile, SA is, for example, <NUM>% or less, and may be <NUM>% or less. SB is preferably low. SB is, for example, <NUM>% or less, and may be <NUM>% or less. Meanwhile, SB may be <NUM>%, and may be more than <NUM>%. In the latter case, SB may be <NUM>% or more.

The sulfide solid electrolyte may further have peak C at <NUM> ppm ± <NUM> ppm, and may not have peak C. When the proportion of the X element included in the sulfide solid electrolyte is high, for example, the peak C tends to appear, although the improvement of the ion conductivity may be expected. When an area ratio of the peak C is regarded as SC, a proportion of a total of the SB and the SC to the SA, that is (SB + SC)/SA, is preferably low. (SB + SC)/SA is, for example, <NUM> or less, and may be <NUM> or less. Meanwhile, (SB + SC)/SA is, for example, <NUM> or more, and may be <NUM> or more. The SC is preferably low. The SC is, for example, <NUM>% or less, and may be <NUM>% or less. Meanwhile, SC may be <NUM>%, and may be more than <NUM>%. In the latter case, SC may be <NUM>% or more.

The sulfide solid electrolyte may further have peak D at <NUM> ppm ± <NUM> ppm, and may not have peak D. When the area ratio of the peak D is regarded as SD, the SD is, for example, <NUM>% or more, and may be <NUM>% or more. Meanwhile, SD is, for example, <NUM>% or less.

The sulfide solid electrolyte in the present invention comprises a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element. The M element may be one kind, and may be two kinds or more. The sulfide solid electrolyte preferably comprises at least P element as the M element. Also, the sulfide solid electrolyte may further comprise an X element (X is a halogen), and may not comprise the X element. Examples of the X element may include a F element, a Cl element, a Br element and an I element. The X element may be one kind, and may be two kinds or more. The sulfide solid electrolyte preferably comprises at least a Cl element as the X element. When the sulfide solid electrolyte comprises two kinds or more of the X element, the proportion of Cl element to all the X elements is, for example, <NUM> mol% or more, may be <NUM> mol% or more, and may be <NUM> mol% or more.

Also, peak A and peak B in <NUM>P-MAS-NMR are caused by the argyrodite type crystal phase. Therefore, the composition of the sulfide solid electrolyte is not particularly limited as long as the composition is able to give such an argyrodite type crystal phase. Examples of the composition of the sulfide solid electrolyte may include Li<NUM>-yPS<NUM>-yXy (y satisfies <NUM> ≤ y ≤ <NUM>). The y may be <NUM>, and may be more than <NUM>. In the latter case, the y may be <NUM> or more, may be <NUM> or more, may be <NUM> or more, and may be <NUM> or more. As the y increases, the ion conductivity of the sulfide solid electrolyte also increases. Meanwhile the y is usually <NUM> or less, may be <NUM> or less, may be <NUM> or less, and may be <NUM> or less. When the y is too high, a crystal phase (different phase) with low ion conductivity is likely to occur.

The ion conductivity of the sulfide solid electrolyte is preferably high. The ion conductivity at <NUM> is, for example, <NUM>/cm or more, may be <NUM>/cm or more, and may be <NUM>/cm or more.

Examples of the shape of the sulfide solid electrolyte may include a granular shape. Also, the average particle size (D<NUM>) of the sulfide solid electrolyte is, for example, <NUM> or more and <NUM> or less. The average particle size (D<NUM>) may be determined from the result of a particle size distribution measurement by a laser diffraction scattering method. A use application of the sulfide solid electrolyte is not particularly limited, and is preferably used for, for example, an all solid state battery.

The precursor of the sulfide solid electrolyte in the present invention is a precursor of the above described sulfide solid electrolyte, and the Li<NUM>S residual ratio thereof is in a specific range.

The constituent element, composition, and other matters of the precursor may be in the same contents as those described in "A. Sulfide solid electrolyte" above; thus, the descriptions herein are omitted.

The Li<NUM>S residual ratio is <NUM>% or more, may be <NUM>% or more. When the Li<NUM>S residual ratio is too low, an amorphous phase is likely to be remained in the sulfide solid electrolyte obtained by burning the precursor. As the result, there is a possibility that the ion conductivity is not sufficiently improved. Meanwhile, the Li<NUM>S residual ratio of the precursor is <NUM>% or less, and may be <NUM>% or less. When the Li<NUM>S residual ratio is too high, uniform solid-phase reaction hardly occurs during burning so that an argyrodite type crystal phase with high ion conductivity is hardly deposited. As the result, there is a possibility that the ion conductivity is not sufficiently improved. A method for calculating the Li<NUM>S residual ratio will be described in Examples described later.

When an X-ray diffraction (XRD) measurement using a CuKα ray is carried out, the precursor usually has a peak of Li<NUM>S. Also, the precursor may or may not have a peak of LiX (X is a halogen). Examples of LiX may include LiF, LiCl, LiBr and LiI. Also, the precursor may or may not have a peak of P<NUM>S<NUM>. Incidentally, the precursor does not usually have the argyrodite type crystal phase; however, the argyrodite type crystal phase occurs by burning.

The precursor of the sulfide solid electrolyte is preferably used for obtaining the sulfide solid electrolyte described in "A. Sulfide solid electrolyte" above.

<FIG> is a schematic cross-sectional view showing an example of the all solid state battery. All solid state battery <NUM> shown in <FIG> comprises cathode layer <NUM> including a cathode active material, anode layer <NUM> including an anode active material, solid electrolyte layer <NUM> formed between cathode layer <NUM> and anode layer <NUM>, cathode current collector <NUM> for collecting currents of cathode layer <NUM>, anode current collector <NUM> for collecting currents of anode layer <NUM>, and battery case <NUM> that houses these members. Further, at least one of cathode layer <NUM>, anode layer <NUM> and solid electrolyte layer <NUM> includes the sulfide solid electrolyte described in "A. Sulfide solid electrolyte" above.

The cathode layer is a layer including at least a cathode active material. The cathode layer may include at least one of a solid electrolyte, a conductive material and a binder, in addition to the cathode active material.

Examples of the cathode active material may include an oxide active material. Specific examples of the oxide active material may include rock salt bed type active materials such as LiCoO<NUM>, LiMnO<NUM>, LiNiO<NUM>, LiVO<NUM>, LiNi<NUM>/<NUM>Co<NUM>/<NUM>Mn<NUM>/<NUM>O<NUM>; spinel type active materials such as LiMn<NUM>O<NUM>, and Li(Ni<NUM>Mn<NUM>) O<NUM>; and olivine type active materials such as LiFePO<NUM>, LiMnPO<NUM>, LiNiPO<NUM>, and LiCuPO<NUM>.

The surface of the cathode active material may be coated with a coating layer. The reason therefor is to inhibit the reaction of the cathode active material with the sulfide solid electrolyte. Examples of the material for the coating layer may include Li ion conductive oxides such as LiNbO<NUM>, Li<NUM>PO<NUM>, and LiPON. The average thickness of the coating layer is, for example, <NUM> or more and <NUM> or less, and may be <NUM> or more and <NUM> or less.

The cathode layer preferably includes the above described sulfide solid electrolyte. Also, examples of the conductive material may include a carbon material. Examples of the carbon material may include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB); and fibrous carbon materials such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). Examples of the binder may include fluorine-based binders such as polyvinylidene fluoride (PVDF). The thickness of the cathode layer is, for example, <NUM> or more and <NUM> or less.

The solid electrolyte layer is a layer including at least a solid electrolyte. Also, the solid electrolyte layer may include a binder, in addition to the solid electrolyte. The solid electrolyte and the binder are similar to those described above. The solid electrolyte layer preferably includes the above described sulfide solid electrolyte. The thickness of the solid electrolyte layer is, for example, <NUM> or more and <NUM> or less.

The anode layer is a layer including at least an anode active material. Also, the anode layer may include at least one of a solid electrolyte, a conductive material and a binder, in addition to the anode active material.

Examples of the anode active material may include a metal active material and a carbon active material. Examples of the metal active material may include In, Al, Si, and Sn. Meanwhile, examples of the carbon active material may include mesocarbon microbead (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, and soft carbon.

The solid electrolyte, the conductive material and the binder are similar to those described above. The anode layer preferably includes the above described sulfide solid electrolyte. The thickness of the anode layer is, for example, <NUM> or more and <NUM> or less.

The all solid state battery usually comprises a cathode current collector for collecting currents of the cathode active material and an anode current collector for collecting currents of the anode active material. Examples of the materials for the cathode current collector may include SUS, aluminum, nickel, iron, titanium, and carbon. Meanwhile, examples of the materials for the anode current collector may include SUS, copper, nickel, and carbon. Also, for a battery case, a common battery case such as a battery case made from SUS may be used.

The all solid state battery is preferably an all solid state lithium ion battery. Also, the all solid state battery may be a primary battery, and may be a secondary battery. Among the above, the secondary battery is preferable, so as to be repeatedly charged and discharged, and is useful as, for example, a car-mounted battery. Incidentally, the secondary battery includes the use of a secondary battery as a primary battery (use for the purpose of only one discharge, after charge). Also, examples of the shape of the all solid state battery may include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

<FIG> is a flow chart showing an example of the method for producing the sulfide solid electrolyte in the present invention. In <FIG>, a raw material composition including Li<NUM>S, P<NUM>S<NUM>, and LiX (X is a halogen) is prepared. Next, the raw material composition is mixed by, for example, mechanical milling, and a precursor with Li<NUM>S residual ratio in a specific range is obtained. Next, the obtained precursor is burned. Thereby, the sulfide solid electrolyte described in "A. Sulfide solid electrolyte" above is obtained.

According to the present invention, a sulfide solid electrolyte with high ion conductivity may be obtained by using the precursor wherein the Li<NUM>S residual ratio is in the specific range.

The mixing step is a step of obtaining a precursor with Li<NUM>S residual ratio in the specific range, by mixing a raw material composition including at least Li<NUM>S.

The raw material composition of the sulfide solid electrolyte includes a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element. The raw material composition may further include an X element (X is a halogen). Examples of the raw material including an Li element may include a Li sulfide. The raw material composition usually includes Li<NUM>S as the Li sulfide. Examples of the raw material including the M element may include a sulfide including the M element. Examples of the sulfide including the M element may include P<NUM>S<NUM>, GeS<NUM>, SiS<NUM> and SnS<NUM>. Examples of the raw material including the X element may include a lithium halide. Examples of the lithium halide may include LiF, LiCl, LiBr and LiI. Examples of the raw material including a S element may include the above described sulfides and a simple substance of sulfur.

In the mixing step, the raw material composition is mixed and the precursor wherein the Li<NUM>S residual ratio is in the specific range is obtained. That is, the precursor is obtained by moderately amorphizing the raw material composition by mixing. Examples of a method for mixing the raw material composition include mechanical milling such as ball milling and vibration milling. The mechanical milling may be a dry-type and may be a wet-type; the latter is preferable from the viewpoint of uniform treatment. The kind of the dispersing medium used for the wet-type mechanical milling is not particularly limited.

The various conditions for the mechanical milling are set so as to obtain the desired precursor. When planetary ball milling is used, for example, the raw material mixture and balls for crushing are added, and the treatment is conducted at a specific rotation number for a specific time. The weighing table rotation number of the planetary ball milling is, for example, <NUM> rpm or more. Meanwhile, the weighing table rotation number of the planetary ball milling is, for example, <NUM> rpm or less, and may be <NUM> rpm or less. Also, the treatment time of the planetary ball milling is, for example, <NUM> minutes or more, and may be <NUM> minutes or more. Meanwhile, the treatment time of the planetary ball milling is, for example, <NUM> hours or less, may be <NUM> hours or less, and may be <NUM> hours or less.

The precursor obtained by the mixing step may be in the same contents as those described in "B. Precursor of sulfide solid electrolyte" above; thus, the descriptions herein are omitted.

The burning step is a step of burning the precursor.

The burning temperature is preferably, for example, higher than <NUM>, may be <NUM> or more, and may be <NUM> or more. Meanwhile, the burning temperature is, for example, <NUM> or less. The burning time is, for example, <NUM> hour or more, and may be <NUM> hours or more. Meanwhile, the burning time is, for example, <NUM> hours or less, and may be <NUM> hours or less. Examples of a burning atmosphere may include an inert gas atmosphere and a vacuum.

The sulfide solid electrolyte obtained by the above described steps may be in the same contents as those described in "A. Sulfide solid electrolyte" above; thus, the descriptions herein are omitted.

Incidentally, the present invention is not limited to the embodiments.

A raw material composition (composition: Li<NUM>PS<NUM>Cl<NUM>) was obtained by weighing <NUM> of Li<NUM>S (from Furuuchi Chemical Corporation), <NUM> of P<NUM>S<NUM> (from Aldrich Co. LLC) and <NUM> of LiCl (from Kojundo Chemical Lab. The obtained raw material composition was projected into a zirconia pot (<NUM>) together with zirconia balls of <NUM> diameter, then, <NUM> of dehydrated heptane (from Kanto Chemical Industry Co. ) was projected, and the pot was sealed. The sealed pot was set to a planetary ball milling machine (P-<NUM> from Fritsch Japan Co. , Ltd), mechanically milled for <NUM> hours at <NUM> rpm, and a precursor of a sulfide solid electrolyte was obtained.

The obtained precursor was molded into pellets, projected into a carbon coated quartz tube, vacuum sealed, burned at <NUM> for <NUM> hours (temperature increasing rate of <NUM>/min), crushed and mixed in a mortar, and thereby, a sulfide solid electrolyte was obtained.

A precursor of a sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the conditions for the mechanical milling were changed to <NUM> rpm for <NUM> minutes. A sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the obtained precursor was used.

A precursor of a sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the conditions for the mechanical milling were changed to <NUM> rpm for <NUM> hours. A sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the obtained precursor was used.

A precursor of a sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that, instead of the mechanical milling, the raw material composition was mixed in a mortar so as to be even. A sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the obtained precursor was used.

A sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the burning temperature was changed to <NUM> for <NUM> hours.

An X-ray diffraction (XRD) measurement using a CuKα ray was carried out for precursors obtained in Examples <NUM> to <NUM> and Comparative Examples <NUM>, <NUM> and <NUM>. The results are shown in <FIG>. As shown in <FIG>, the peaks of Li<NUM>S were confirmed in Example <NUM> in the vicinity of 2θ = <NUM>° and in the vicinity of 2θ = <NUM>°. Also, in Example <NUM>, the peaks of LiCl were confirmed in the vicinity of 2θ = <NUM>° and in the vicinity of 2θ = <NUM>°. Also, as shown in <FIG> and <FIG>, the peaks of Li<NUM>S and the peaks of LiCl were confirmed also in Examples <NUM> to <NUM>, as similar to Example <NUM>.

Meanwhile, as shown in <FIG>, although the peaks of Li<NUM>S and the peaks of LiCl were confirmed in Comparative Example <NUM>, these peaks were broad compared to the peaks in Examples <NUM> to <NUM>, and it was confirmed that the amorphization has been progressed. Also, as shown in <FIG>, the peaks of Li<NUM>S and the peaks of LiCl were confirmed in Comparative Example <NUM>. Particularly in Comparative Example <NUM>, extremely large peak was confirmed in the vicinity of 2θ = <NUM>°. Also, as shown in <FIG>, it was confirmed that the amorphization has been progressed also in Comparative Example <NUM>, as similar to Comparative Example <NUM>. Also, the intensity of the peak of Li<NUM>S (the peak at 2θ = <NUM>° ± <NUM>°) in Comparative Example <NUM> was regarded as <NUM>%, the intensity of the peak of Li<NUM>S in Examples <NUM> to <NUM> and Comparative Example <NUM> was determined as Li<NUM>S residual ratio. The results are shown in Table <NUM>. Incidentally, the peak of P<NUM>S<NUM> was confirmed in the vicinity of 2θ = <NUM>° in Comparative Example <NUM>. Meanwhile, although the peak of P<NUM>S<NUM> was confirmed in the vicinity of 2θ = <NUM>° also in Example <NUM>, the intensity was decreased.

<NUM>P-MAS-NMR measurement was carried out for the sulfide solid electrolytes obtained in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>. The measuring conditions were as described below.

The results are shown in <FIG>. Incidentally, although the sulfide solid electrolyte is a material whose relaxation time is short, the repetition time is preferably, for example, <NUM> seconds or more. When the repetition time is too short, sufficient relaxation may not be obtained, and the waveform tends to be disturbed. Meanwhile, the repetition time is, for example, <NUM> seconds or less.

As shown in <FIG>, the following peaks A to D were confirmed in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>.

Peak A is a peak deriving from the argyrodite type crystal phase. Peak B is a peak deriving from an amorphous phase related to the argyrodite type crystal phase. Meanwhile, peak C is presumed to be a peak deriving from the crystal phase other than the argyrodite type crystal phase (different phase), and peak D is presumed to be a peak deriving from P-S bonding in the vicinity of the site where Cl is not dissolved in the argyrodite type crystal phase.

In Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM>, only peaks A to D were confirmed and other peak was not confirmed in a range of <NUM> ppm or more and <NUM> ppm or less. In contrast to this, in addition to peaks A to D, peaks E and F were confirmed in Comparative Example <NUM>, in a range of <NUM> ppm or more and <NUM> ppm or less. Also, as shown in <FIG>, the area ratio of peak A to D was determined by carrying out a waveform separation for the obtained NMR chart, by fitting in a state where each peak top is fixed so as to be in the designated range. The results are shown in Table <NUM>.

The ion conductivity (<NUM>) of the sulfide solid electrolytes obtained in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was measured. <NUM> of the obtained sulfide solid electrolyte powder was pressed under pressure of <NUM> ton/cm<NUM> with a pelleting press so as to produce a pellet. The resistance of the pellet was determined by an AC impedance method, and the ion conductivity was determined from the thickness of the pellet. The results are shown in Table <NUM>.

As shown in Table <NUM>, the ion conductivity was higher in Examples <NUM> to <NUM>, compared to Comparative Examples <NUM> to <NUM>. The ion conductivity in Examples <NUM> and <NUM> was <NUM>/cm or more, and the ion conductivity was particularly high. Also, in Examples <NUM> to <NUM>, the Li<NUM>S residual ratio in the precursor was <NUM>% or more and <NUM>% or less, higher than Comparative Example <NUM>. As described above, it was confirmed that a sulfide solid electrolyte with high ion conductivity may be obtained by making the Li<NUM>S residual ratio high to an extent.

Also, from the MNR results, it was suggested that the area ratio of peaks A to C and the ion conductivity of the sulfide solid electrolyte were mutually related. Comparing Examples <NUM> to <NUM>, for example, a tendency was suggested that, the higher the area ratio of peak A SA was, the higher the ion conductivity was. Also, comparing Example <NUM> and Comparative Example <NUM>, a tendency was suggested that, the lower the area ratio of peak B SB was, the higher the ion conductivity was, although the area ratios of peak A SA and peak C SC were almost the same. Also, comparing Example <NUM> and Comparative Example <NUM>, a tendency was suggested that, the lower the area ratio of peak C SC was, the higher the ion conductivity was, although the area ratios of peak A SA and peak B SB were almost the same. As described above, the lower SB/SA or (SB + SC) /SA was, the higher the ion conductivity was.

Also, comparing Comparative Example <NUM> (burning temperature <NUM>) and Comparative Example <NUM> (burning temperature <NUM>), the area ratio SA was higher and the area ratio SB was lower in Comparative Example <NUM> than Comparative Example <NUM>. As described above, it was suggested that, in order to make the area ratio SA higher, relatively high burning temperature was preferable. Also, although the mechanical milling conditions in Comparative Example <NUM> (<NUM> rpm, <NUM> hours) were the same as the mechanical milling conditions in Example in Patent Literature <NUM>, the Li<NUM>S residual ratio was low so that it was suggested that SB/SA was high since the amorphization was progressed.

A raw material composition (composition: Li<NUM>PS<NUM>Cl<NUM>) was obtained by weighing <NUM> of Li<NUM>S (from Furuuchi Chemical Corporation), <NUM> of P<NUM>S<NUM> (from Aldrich Co. LLC) and <NUM> of LiCl (from Kojundo Chemical Lab. A sulfide solid electrolyte was obtained in the same manner as in Comparative Example <NUM> except that the obtained raw material composition was used.

<NUM>P-MAS-NMR measurement was carried out for the sulfide solid electrolytes obtained in Reference Examples <NUM> to <NUM>. The measuring conditions were the same as described above. The results are shown in Table <NUM>.

Claim 1:
A method for producing a sulfide solid electrolyte, wherein the sulfide solid electrolyte comprises:
a Li element,
an M element (M is at least one kind of P, Ge, Si and Sn), and
a S element, and
the sulfide solid electrolyte has an argyrodite type crystal phase,
in <NUM>P-MAS-NMR, the sulfide solid electrolyte has
peak A at <NUM> ppm ± <NUM> ppm and
peak B at <NUM> ppm ± <NUM> ppm, and
when an area ratio of the peak A is regarded as SA, and an area ratio of the peak B is regarded as SB, a proportion of the SB to the SA, that is SB/SA, is <NUM> or less, wherein
the measuring conditions of <NUM>P-MAS-NMR are as described in the description, and
wherein the method comprises the steps of:
a mixing step of obtaining a precursor with a Li<NUM>S residual ratio of <NUM>% or more and <NUM>% or less, by mixing a raw material composition including at least Li<NUM>S, and
a burning step of burning the precursor, wherein
the Li<NUM>S residual ratio is determined according to the method disclosed in the description,
the method for mixing the raw material composition includes mechanical milling, and
the burning temperature is between <NUM> and <NUM>.