Patent Description:
Nonaqueous electrolyte secondary batteries typified by lithium-ion nonaqueous electrolyte secondary batteries are, because of the high energy density, heavily used in electronic devices such as personal computers and communication terminals, and automobiles. The nonaqueous electrolyte secondary battery typically including an electrode assembly with a pair of electrically isolated electrodes and a nonaqueous electrolyte interposed between the electrodes is configured for charge-discharge through ion transfer between the both electrodes.

In recent years, for the purpose of improving the safety of nonaqueous electrolyte secondary batteries, an all-solid-state battery is proposed in which a sulfide solid electrolyte or the like is used as a nonaqueous electrolyte instead of a liquid electrolyte such as an organic solvent (see Patent Document <NUM>).

A sulfide solid electrolyte that contains Li, P, S, and N and has a composition represented by the general formula XLi<NUM>S-25P<NUM>S<NUM>-YLi<NUM>N (<NUM> ≤ Y ≤ <NUM>, <NUM> ≤ X + Y ≤ <NUM>), which is a crystalline material, is disclosed as an example of a sulfide solid electrolyte. (see Patent Document <NUM>).

As sulfide solid electrolytes, 70Li<NUM>S·30P<NUM>S<NUM> glass ceramics and 60Li<NUM>S·25P<NUM>S<NUM>·10Li<NUM>N glass ceramics are reported to show high ion conductivities of <NUM>-<NUM> S/cm or more. (Non-Patent Document <NUM>).

The first principle calculation has clearly demonstrated that such sulfide solid electrolytes essentially have low oxidation resistance and reduction resistance. (Non-Patent Document <NUM>).

The present invention has been made based on the foregoing circumstances, and an object of the present invention is to provide a sulfide solid electrolyte with reduction resistance improved, and an all-solid-state battery including the sulfide solid electrolyte.

According to claim <NUM>, an aspect of the present invention is a sulfide solid electrolyte comprising at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprising N, and having a crystalline structure, wherein the crystalline structure includes a crystalline structure that has a crystal phase of Li<NUM>P<NUM>S<NUM>, Li<NUM>P<NUM>S<NUM>, or β-Li<NUM>PS<NUM>, or a first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKα line.

Described and not claimed per se is a sulfide solid electrolyte that contains Al and N and that has a crystalline structure.

The sulfide solid electrolyte according to an aspect of the present invention makes it possible to provide a sulfide solid electrolyte with reduction resistance improved.

Described and not claimed per se is a sulfide solid electrolyte that contains at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and N and has a crystalline structure.

The present inventors have focused attention on the fact that a nitride containing any of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V (hereinafter, also referred to as an element M), which are difficult to apply as a solid electrolyte because of the low ion conductivity, shows high reduction resistance. Then, the inventors have considered that the sulfide solid electrolyte containing therein the nitrogen element (N) and the element M allows the reduction resistance of the sulfide solid electrolyte to be improved, and achieved the present invention.

The sulfide solid electrolyte contains at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprises N and has a crystalline structure, as defined in claim <NUM>, thereby making it possible to provide a sulfide solid electrolyte with reduction resistance improved. It is to be noted that the element M may be Al in the sulfide solid electrolyte. The reason therefor is not clear, but the following reason is presumed. When the sulfide solid electrolyte containing the element M and N is exposed to a reducing atmosphere, a film with high reduction resistance, containing a nitride of the element M, a lithium nitride of the element M, or the like, is presumed to be formed on the surface or interface of the sulfide solid electrolyte. For this reason, the reduction resistance of the sulfide solid electrolyte is presumed to be improved.

The all-solid-state battery including the sulfide solid electrolyte can be provided as an all-solid-state battery with a first coulombic efficiency improved. The reason therefor is not clear, but the following reason is presumed. The sulfide solid electrolyte has high reduction resistance, although a common sulfide solid electrolyte is known to be likely to be reductively decomposed, and an all-solid-state battery including such a sulfide solid electrolyte is thus known to show a large quantity of electricity for reductive decomposition. For this reason, the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte can be improved.

Furthermore, the sulfide solid electrolyte contains N, thereby causing S to be replaced with N that is smaller in ionic radius, and reducing the crystal lattice volume. Thus, the increased space for lithium ion movements allows the ion conductivity to be improved. As a result, the first coulombic efficiency of the all-solid-state battery can be improved while maintaining good ion conductivity.

The element M in the sulfide solid electrolyte is at least one element selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, as defined in claim <NUM>. These elements are elements that are clarified by the first principle calculation in that a lithium nitride containing the element M has high reduction resistance (see Non-Patent Document <NPL>))). Among these elements, Al, B, and Si are preferable because of the low costs, and of the manufacturing costs that can be reduced.

As defined in claim <NUM>, the crystalline structure includes a crystalline structure that has a crystal phase of Li<NUM>P<NUM>S<NUM>, Li<NUM>P<NUM>S<NUM>, or β-Li<NUM>PS<NUM>, or a first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKα line. This makes it possible to increase the ion conductivity at <NUM>.

The first crystalline structure preferably includes a specific crystalline structure A that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM> ° ± <NUM>° in the X-ray diffraction measurement, or a specific crystalline structure B that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM> ° ± <NUM>° and has no diffraction peak at <NUM>° ± <NUM>° in the X-ray diffraction measurement. The configuration mentioned above makes it possible to further increase the ion conductivity at <NUM>.

In the case where the sulfide solid electrolyte contains Li, P, S, N, and at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, from the viewpoint of reduction resistance, the content ratio of the Li to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio. The content ratios of the Li and N in the sulfide solid electrolyte fall within the ranges mentioned above, thereby further improving the reduction resistance, and making it possible to further increase the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte. It is to be noted that the element M may be Al in the sulfide solid electrolyte.

In the sulfide solid electrolyte, the content ratio of the Li to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio. The content ratios of the Li and N in the sulfide solid electrolyte fall within the ranges mentioned above, thereby allowing the reduction resistance, the atmospheric stability, and the ion conductivity at <NUM> to be improved at the same time.

The sulfide solid electrolyte preferably has a composition represented by the general formula (<NUM> - z)(yLi<NUM>S·(<NUM> - y)P<NUM>S<NUM>)·zLiαMβN (where <NUM> < z ≤ <NUM>, <NUM> ≤ y ≤ <NUM>, α and β represent numerical values that provide stoichiometric ratios depending on the type of the element M). The sulfide solid electrolyte has a composition represented by the general formula mentioned above, thereby further improving the reduction resistance, and making it possible to further increase the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte.

The sulfide solid electrolyte may further contain Ge. Even with such a sulfide solid electrolyte, the effect of the present invention can be enjoyed.

In the case where the sulfide solid electrolyte contains Ge, the sulfide solid electrolyte preferably includes a structure that has a crystal phase of Li<NUM>GeP<NUM>S<NUM>.

In addition, in the case where the sulfide solid electrolyte contains Li, P, S, N, and Ge, and the element M, and has a crystal phase of Li<NUM>GeP<NUM>S<NUM>, the content ratio of the Li to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio. In addition, the content ratio of the Li to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio.

In the case where the sulfide solid electrolyte contains Ge, the sulfide solid electrolyte preferably has a composition represented by the general formula (<NUM> - z)Li<NUM>GeP<NUM>S<NUM>·zLiαMβN (where <NUM> < z ≤ <NUM>, α and β represent numerical values that provide stoichiometric ratios depending on the type of the element M). Above all, in the general formula mentioned above, z particularly preferably satisfies <NUM> < z ≤ <NUM>.

The ion conductivity of the sulfide solid electrolyte at <NUM> is preferably <NUM> × <NUM>-<NUM> S/cm or more. The configuration mentioned above allows the high rate discharge performance of the all-solid-state battery including the sulfide solid electrolyte to be improved.

It is to be noted that the ion conductivity of the sulfide solid electrolyte at <NUM> is determined from measurement of the alternating-current impedance by the following method. Under an argon atmosphere with a dew point of -<NUM> or lower, <NUM> of the sample powder is put into a powder molder of <NUM> in inner diameter, and then subjected to uniaxial pressing at a pressure of <NUM> MPa or less per sample area with the use of a hydraulic press. After pressure release, a SUS316L powder is put as a current collector onto the upper and lower surfaces of the sample, and then subjected to uniaxial pressing at a pressure of <NUM> MPa per pellet area for <NUM> minutes, thereby providing a pellet for ion conductivity measurement. This pellet for ion conductivity measurement is inserted into an HS cell from Hohsen Corp. to measure the alternating-current impedance. The measurement conditions are an applied voltage amplitude of <NUM> mV, a frequency range of <NUM> to <NUM>, and a measurement temperature of <NUM>.

The all-solid-state battery according to another aspect of the present invention is an all-solid-state battery including a negative electrode layer, a solid electrolyte layer, and a positive electrode layer, where the negative electrode layer, the solid electrolyte layer, the positive electrode layer, or a combination thereof contains the sulfide solid electrolyte.

In the all-solid-state battery according to another aspect of the present invention according to claim <NUM>, the first coulombic efficiency is excellent because the negative electrode layer, the solid electrolyte layer, the positive electrode layer, or a combination thereof contains the sulfide solid electrolyte. The sulfide solid electrolyte has excellent reduction resistance, and the negative electrode layer and/or the solid electrolyte layer thus preferably contain the sulfide solid electrolyte. The configuration mentioned above makes the effect of the present invention much greater.

Hereinafter, embodiments of the sulfide solid electrolyte and all-solid-state battery according to the present invention will be described in detail.

As defined in claim <NUM>, the sulfide solid electrolyte contains at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprises N and has a crystalline structure. The sulfide solid electrolyte contains at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprises N and has a crystalline structure, thereby making it possible to improve the reduction resistance. The sulfide solid electrolyte can be used in any application that requires ion conductivity. Above all, the sulfide solid electrolyte is preferably used for a lithium all-solid-state battery. It is to be noted that the element M may be Al in the sulfide solid electrolyte.

The sulfide solid electrolyte has a crystalline structure. The phrase "to have a crystalline structure" herein means that a peak derived from the crystalline structure of the sulfide solid electrolyte is observed in the X-ray diffraction pattern in the X-ray diffraction measurement. The sulfide solid electrolyte may contain an amorphous portion. The sulfide solid electrolyte that has a crystalline structure can be obtained, for example, by crystallizing an amorphous sulfide solid electrolyte through a heat treatment or the like.

Examples of the crystalline structure of the sulfide solid electrolyte include a LGPS type, an argyrodite type, Li<NUM>P<NUM>S<NUM>, and Thio-LISICON series. Among these structures, as the crystalline structure, the LGPS type, the argyrodite type, and Li<NUM>P<NUM>S<NUM> are preferable from the viewpoint of lithium ion conductivity, and among these three structures, Li<NUM>P<NUM>S<NUM> is more preferable because of the high stability to Li. As defined in claim <NUM>, it include a crystalline structure that has a crystal phase of Li<NUM>P<NUM>S<NUM>, Li<NUM>P<NUM>S<NUM> or β-Li<NUM>PS<NUM>, or a first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKα line, and among these structures, the first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKα line is more preferable because of the high lithium ion conductivity.

The first crystalline structure may include a specific crystalline structure A that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM> ° ± <NUM>° in the X-ray diffraction measurement, or a specific crystalline structure B that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM> ° ± <NUM>° and has no diffraction peak at <NUM>° ± <NUM>° in the X-ray diffraction measurement. The configuration mentioned above allows the ion conductivity at <NUM> to be increased.

The diffraction peaks in the first crystalline structure may fall within the above-mentioned ranges of 2θ, further within the ranges of ± <NUM>°, or within the ranges of ± <NUM>°.

The X-ray diffraction measurement with the CuKα line used is made in accordance with the following procedure. The airtight sample holder for X-ray diffraction measurement is filled with the solid electrolyte powder to be subjected to the measurement under an argon atmosphere with a dew point of -<NUM> or lower. Powder X-ray diffraction measurement is made with the use of an X-ray diffractometer ("MiniFlex II" from Rigaku Corporation). With a radiation source of a CuKα line, a tube voltage of <NUM> kV, a tube current of <NUM> mA, the diffracted X-ray is detected by a high-speed one-dimensional detector (model number: D/teX Ultra <NUM>) through a Kβ filter with a thickness of <NUM>. The sampling width is <NUM>°, the scan speed is <NUM>°/min, the divergent slit width is <NUM>°, the light-receiving slit width is <NUM> (OPEN), and the scattering slit width is <NUM>.

The crystalline structure with the crystal phase of Li<NUM>P<NUM>S<NUM> has diffraction peaks at the positions of 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in the X-ray diffraction measurement with the CuKα line used.

Examples of the LGPS-type sulfide solid electrolyte include Li<NUM>GeP<NUM>S<NUM>. The crystalline structure with the crystal phase of Li<NUM>GeP<NUM>S<NUM> has diffraction peaks at the positions of 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in the X-ray diffraction measurement with the CuKα line used.

Examples of the argyrodite-type sulfide solid electrolyte include Li<NUM>PS<NUM>Cl. The crystalline structure with the crystal phase of L<NUM>PS<NUM>Cl has diffraction peaks at the positions of 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM> ° ± <NUM>° in the X-ray diffraction measurement with the CuKα line used.

The crystalline structure with the crystal phase of Li<NUM>P<NUM>S<NUM> has diffraction peaks at positions 2θ = 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in the X-ray diffraction measurement with the CuKα line used.

The crystalline structure with the crystal phase of β-Li<NUM>PS<NUM> has diffraction peaks at the positions of 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in the X-ray diffraction measurement with the CuKα line used.

The sulfide solid electrolyte preferably contains Li, P, S, N, and the element M. In this case, from the viewpoint of reduction resistance, the content ratio of the Li to the above P in the sulfide solid electrolyte is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, further preferably <NUM> or more and <NUM> or less in terms of mole ratio. The content ratio of the N to the P is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, further preferably <NUM> or more and <NUM> or less, particularly preferably <NUM> or more and <NUM> or less. When the content ratios of Li and N in the sulfide solid electrolyte fall within the ranges mentioned above, a sulfide solid electrolyte is obtained, which shows favorable reduction resistance. In addition, the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte can be increased.

Furthermore, from the viewpoint of atmospheric stability, the content ratio of the Li to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the Li to the P is more preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is more preferably <NUM> or more and <NUM> or less in terms of mole ratio. Further, Al is preferably contained as the element M. Thus, particularly in the case where the value of y in the general formula is less than <NUM>, so-called cross-linked sulfur P<NUM>S<NUM><NUM>- (S<NUM>P-S-PS<NUM>), which is unstable in the atmosphere, is reduced, substantially without containing Li<NUM>S, which is likely to react with water, thus improving the atmospheric stability of the sulfide solid electrolyte, and making it possible to inhibit the generation of hydrogen sulfide through the reaction between moisture in the atmosphere and S in the sulfide solid electrolyte.

In particular, the content ratio of the Li to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, whereas the content ratio of the N to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, because the reduction resistance and atmospheric stability, and the ion conductivity at <NUM> can be increased at the same time.

In the case where the sulfide solid electrolyte contains Li, P, S, N, Ge, and the element M mentioned above and has a crystal phase of Li<NUM>GeP<NUM>S<NUM>, from the viewpoint of reduction resistance, the content ratio of the Li to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is preferably <NUM> or more and <NUM> or less in terms of mole ratio. In addition, the content ratio of the Li to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio, and the content ratio of the N to the P is further preferably <NUM> or more and <NUM> or less in terms of mole ratio.

The sulfide solid electrolyte preferably has a composition represented by the general formula (<NUM> - z)(yLi<NUM>S·(<NUM> - y)P<NUM>S<NUM>)·zLiαMβN (where <NUM> < z ≤ <NUM>, <NUM> ≤ y ≤ <NUM>,). The sulfide solid electrolyte has a composition represented by the general formula mentioned above, the reduction resistance can be further improved. In addition, the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte can be further increased.

z in the general formula mentioned above is preferably more than <NUM> and <NUM> or less, more preferably <NUM> or more and <NUM> or less, further preferably <NUM> or more and <NUM> or less or <NUM> or more and <NUM> or less, further preferably <NUM> or more and <NUM> or less or <NUM> or more and <NUM> or less. z in the general formula falls within the range of more than <NUM> and <NUM> or less, thereby allowing the reduction resistance of the sulfide solid electrolyte to be further improved. With <NUM> ≤ z ≤ <NUM>, so-called cross-linked sulfur P<NUM>S<NUM><NUM>-(S<NUM>P-S-PS<NUM>), which is unstable in the atmosphere, is reduced, substantially without containing Li<NUM>S, which is likely to react with water, thus improving the atmospheric stability of the sulfide solid electrolyte, and making it possible to inhibit the generation of hydrogen sulfide through the reaction between moisture in the atmosphere and S in the sulfide solid electrolyte. With <NUM> ≤ z ≤ <NUM>, the ion conductivity at <NUM> can be further increased. With <NUM> ≤ z ≤ <NUM> or <NUM> ≤ z ≤ <NUM>, the ion conductivity at <NUM> can be further increased. With <NUM> ≤ z ≤ <NUM> or <NUM> ≤ z ≤ <NUM>, the ion conductivity at <NUM> can be further increased.

y in the general formula mentioned above is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less. When the content ratios of Li<NUM>S and P<NUM>S<NUM> in the sulfide solid electrolyte falls within the range mentioned above, the ion conductivity of the sulfide solid electrolyte at <NUM> is improved.

α and β in the general formula mentioned above represent numerical values that provide stoichiometric ratios depending on the type of the element M. The values of α and β are not particularly limited, but may be, for example, <NUM> ≤ α ≤ <NUM> and <NUM> ≤ β ≤ <NUM>. In particular, in the case where Al is contained as the element M, the values may be α = <NUM> and β = <NUM>.

In the case where the sulfide solid electrolyte contains Ge, the sulfide solid electrolyte preferably has a composition represented by the general formula (<NUM> - z)Li<NUM>GeP<NUM>S<NUM>·zLiαMβN (where <NUM> < z ≤ <NUM>, α and β represent numerical values that provide stoichiometric ratios depending on the type of the element M). For example, in the case where Al is contained as the element M, the sulfide solid electrolyte preferably has a composition represented by the general formula (<NUM> - z)Li<NUM>GeP<NUM>S<NUM>·zL<NUM>/<NUM>Al<NUM>/<NUM>N (where <NUM> < z ≤ <NUM>). The sulfide solid electrolyte has such a composition, thereby allowing the ion conductivity at <NUM> to be increased.

z in the general formula mentioned above is more than <NUM> and <NUM> or less, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, further preferably <NUM> or more and <NUM> or less, even more preferably <NUM> or more and <NUM> or less. When z in the general formula falls within the range mentioned above, the reduction resistance and the ion conductivity at <NUM> can be further improved.

The ion conductivity of the sulfide solid electrolyte at <NUM> is preferably <NUM> × <NUM>-<NUM> S/cm or more, more preferably <NUM> × <NUM>-<NUM> S/cm or more, further preferably <NUM> × <NUM>-<NUM> S/cm or more. When the ion conductivity of the sulfide solid electrolyte at <NUM> has the value mentioned above, the high rate discharge performance of the all-solid-state battery including the sulfide solid electrolyte can be improved.

As described above, the sulfide solid electrolyte can be suitably used as a solid electrolyte for an all-solid-state battery.

According to claim <NUM>, the all-solid-state battery includes a negative electrode layer, a solid electrolyte layer, and a positive electrode layer, wherein the negative electrode layer, the solid electrolyte layer, the positive electrode layer, or a combination thereof contains the sulfide solid electrolyte as disclosed above. <FIG> is a schematic cross-sectional view illustrating an all-solid-state battery according to an embodiment of the present invention. The all-solid-state battery <NUM>, which serves as a secondary battery, has a negative electrode layer <NUM> and a positive electrode layer <NUM> disposed with a solid electrolyte layer <NUM> interposed therebetween. The negative electrode layer <NUM> has a negative electrode substrate layer <NUM> and a negative composite layer <NUM>, and the negative electrode substrate layer <NUM> serves as the outermost layer of the negative electrode layer <NUM>. The positive electrode layer <NUM> has a positive electrode substrate layer <NUM> and a positive composite layer <NUM>, and the positive electrode substrate layer <NUM> serves as the outermost layer of the positive electrode layer <NUM>. For the all-solid-state battery <NUM> shown in <FIG>, the positive composite layer <NUM>, the solid electrolyte layer <NUM>, the negative composite layer <NUM>, and the negative electrode substrate layer <NUM> are stacked in this order on the positive electrode substrate layer <NUM>.

In the all-solid-state battery, the negative electrode layer <NUM>, the solid electrolyte layer <NUM>, the positive electrode layer <NUM>, or a combination thereof contains the sulfide solid electrolyte. In the all-solid-state battery, the negative electrode layer <NUM>, the solid electrolyte layer <NUM>, the positive electrode layer <NUM>, or a combination thereof contains the sulfide solid electrolyte, and the first coulombic efficiency is thus excellent. Because the sulfide solid electrolyte has excellent reduction resistance, the negative electrode layer <NUM> and/or the solid electrolyte layer <NUM> preferably contain the sulfide solid electrolyte. The configuration mentioned above makes the effect of the present invention much greater.

The all-solid-state battery may be used in combination with other solid electrolytes besides the sulfide solid electrolyte. The other solid electrolytes may be sulfide solid electrolytes other than the sulfide solid electrolyte described above, or may be oxide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, or pseudo solid electrolytes.

The sulfide solid electrolytes other than the sulfide solid electrolyte described above preferably has high Li ion conductivity, and examples thereof can include Li<NUM>S-P<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-LiI, Li<NUM>S-P<NUM>S<NUM>-LiCl, Li<NUM>S-P<NUM>S<NUM>-LiBr, Li<NUM>SP<NUM>S<NUM>-Li<NUM>O, Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O-LiI, Li<NUM>S-P<NUM>S<NUM>-Li<NUM>N, Li<NUM>S-SiS<NUM>, Li<NUM>S-SiS<NUM>-LiI, Li<NUM>S-SiS<NUM>-LiBr, Li<NUM>S-SiS<NUM>-LiCl, Li<NUM>S-SiS<NUM>-B<NUM>S<NUM>-LiI, Li<NUM>S-SiS<NUM>-P<NUM>S<NUM>-LiI, Li<NUM>S-B<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-ZmS2n (where m and n represent positive numbers, Z represents any of Ge, Zn, and Ga), Li<NUM>S-GeS<NUM>, Li<NUM>S-SiS<NUM>-Li<NUM>PO<NUM>, Li<NUM>S-SiS<NUM>-LiδXOε (where δ and ε represent positive numbers, X represents any of P, Si, Ge, B, Al, Ga, and In), and Li<NUM>GeP<NUM>S<NUM>. Among these electrolytes, from the viewpoint of favorable lithium ion conductivity, Li<NUM>S-P<NUM>S<NUM> is preferable, and xLi<NUM>S·(<NUM> - x)P<NUM>S<NUM> (<NUM> ≤ x ≤ <NUM>) is more preferable.

The negative electrode layer <NUM> includes the negative electrode substrate layer <NUM> and the negative composite layer <NUM> stacked on the surface of the negative electrode substrate layer <NUM>. The negative electrode layer <NUM> may have an intermediate layer, not shown, between the negative electrode substrate layer <NUM> and the negative composite layer <NUM>.

The negative electrode substrate layer <NUM> is a layer with conductivity. The material of the negative electrode substrate layer <NUM> is not limited as long as the material is a conductor. Examples of the material can include one or more metals selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, and indium, and alloys containing one or more of these metals, as well as stainless-steel alloys.

The lower limit of the average thickness of the negative electrode substrate layer <NUM> is preferably <NUM>, more preferably <NUM>, further preferably <NUM>. The upper limit of the average thickness of the negative electrode substrate layer <NUM> is preferably <NUM>, more preferably <NUM>, further preferably <NUM>. The average thickness of the negative electrode substrate layer <NUM> is adjusted to be equal to or more than the lower limit mentioned above, thereby allowing the strength of the negative electrode substrate layer <NUM> to be sufficiently increased, and thus allowing the negative electrode layer <NUM> to be favorably formed. The average thickness of the negative electrode substrate layer <NUM> is adjusted to be equal to or less than the upper limit mentioned above, thereby allowing the volumes of other constituent elements to be sufficiently secured.

The negative composite layer <NUM> can be formed from a so-called negative composite including a negative active material. The negative composite may contain a negative electrode mixture or a negative electrode composite containing the negative active material and the sulfide solid electrolyte. The negative composite contains, if necessary, optional components such as a solid electrolyte other than the sulfide solid electrolyte, a conductive agent, a binder, and a filler.

As the negative active material, a material capable of occluding and releasing lithium ions is typically used. Specific negative active materials include:.

The lower limit of the content of the negative active material in the negative composite is preferably <NUM>% by mass, more preferably <NUM>% by mass. The upper limit of the content of the negative active material is preferably <NUM>% by mass, more preferably <NUM>% by mass, further preferably <NUM>% by mass, particularly preferably <NUM>% by mass, and may be <NUM>% by mass. The content of the negative active material falls within the range mentioned above, thereby allowing the electric capacity of the all-solid-state battery to be increased.

The negative electrode mixture is a mixture prepared by mixing the negative active material and the sulfide solid electrolyte by mechanical milling or the like. For example, the mixture of the negative active material and the sulfide solid electrolyte can be obtained by mixing the particulate negative active material and the particulate sulfide solid electrolyte.

Examples of the negative electrode composite include a composite with a chemical or physical bond between the negative active material and the sulfide solid electrolyte, and a composite mechanically formed from the negative active material and the sulfide solid electrolyte. The composite mentioned above has the negative active material and the sulfide solid electrolyte present in one particle, and examples of the composite include an aggregate formed by the negative active material and the sulfide solid electrolyte, and the negative active material with a film containing the sulfide solid electrolyte, formed on at least a part of the surface of the material.

The negative electrode mixture or the negative composite may contain a solid electrolyte other than the sulfide solid electrolyte.

The negative active material and the sulfide solid electrolyte contained in the negative composite constitute the negative electrode mixture or the negative electrode composite, thereby allowing the reduction resistance to be improved while maintaining high ion conductivity, and thus resulting in an excellent first coulombic efficiency.

In the case where the negative composite contains a solid electrolyte, the lower limit of the content of the solid electrolyte in the negative composite may be <NUM>% by mass, and is preferably <NUM>% by mass. The upper limit of the content of the solid electrolyte in the negative composite is preferably <NUM>% by mass, more preferably <NUM>% by mass, further preferably <NUM>% by mass, particularly preferably <NUM>% by mass. The content of the solid electrolyte falls within the range mentioned above, thereby allowing the electric capacity of the all-solid-state battery to be increased.

In the case where the negative electrode layer contains the sulfide solid electrolyte, the lower limit of the content of the sulfide solid electrolyte in the negative composite may be <NUM>% by mass, and is preferably <NUM>% by mass. The upper limit of the content of the sulfide solid electrolyte in the negative composite is preferably <NUM>% by mass, more preferably <NUM>% by mass, further preferably <NUM>% by mass, particularly preferably <NUM>% by mass. The content of the sulfide solid electrolyte in the negative composite falls within the range mentioned above, thereby allowing the first coulombic efficiency of the all-solid-state battery to be further improved in the case where the negative electrode layer contains the sulfide solid electrolyte.

The conductive agent mentioned above is not particularly limited. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. Examples of the form of the conductive agent include powdery and fibrous forms. The content of the conductive agent in the negative composite can be, for example, <NUM>% by mass or more and <NUM>% by mass or less. The negative composite may contain no conductive agent.

The binder (binding agent) mentioned above is not particularly limited. Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide, and polyacrylic acid; elastomers such as an ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, a styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

The filler mentioned above is not particularly limited. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and carbon.

The lower limit of the average thickness of the negative composite layer <NUM> is preferably <NUM>, more preferably <NUM>. The upper limit of the average thickness of the negative composite layer <NUM> is preferably <NUM>, more preferably <NUM>, further preferably <NUM>. The average thickness of the negative composite layer <NUM> is adjusted to be equal to or more than the lower limit mentioned above, thereby making it possible to obtain an all-solid-state battery with a high energy density. The average thickness of the negative composite layer <NUM> is adjusted to be equal to or less than the upper limit mentioned above, thereby making it possible to obtain an all-solid-state battery including a negative electrode that is excellent in high rate discharge performance and high in active material utilization.

The intermediate layer mentioned above, which is a coating layer on the surface of the negative electrode substrate layer <NUM>, includes conductive particles such as carbon particles, thereby reducing the contact resistance between the negative electrode substrate layer <NUM> and the negative composite layer <NUM>. The structure of the intermediate layer is not particularly limited, and can be formed from, for example, a composition containing a resin binder and conductive particles.

The positive electrode layer <NUM> includes the positive electrode substrate layer <NUM> and the positive composite layer <NUM> stacked on the surface of the positive electrode substrate layer <NUM>. Like the negative electrode layer <NUM>, the positive electrode layer <NUM> may have an intermediate layer between the positive electrode substrate layer <NUM> and the positive composite layer <NUM>. This intermediate layer may have the same structure as the intermediate layer of the negative electrode layer <NUM>.

The positive electrode substrate layer <NUM> may have the same structure as the negative electrode substrate layer <NUM>. The material of the positive electrode substrate layer <NUM> is not limited as long as the material is a conductor. Examples of the material can include one or more metals selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, and indium, and alloys containing one or more of these metals, as well as stainless-steel alloys.

The lower limit of the average thickness of the positive electrode substrate layer <NUM> is preferably <NUM>, more preferably <NUM>. The upper limit of the average thickness of the positive electrode substrate layer <NUM> is preferably <NUM>, more preferably <NUM>, further preferably <NUM>. The average thickness of the positive electrode substrate layer <NUM> is adjusted to be equal to or more than the lower limit mentioned above, thereby allowing the strength of the positive electrode substrate layer <NUM> to be sufficiently increased, and thus allowing the positive electrode layer <NUM> to be formed favorably. The average thickness of the positive electrode substrate layer <NUM> is adjusted to be equal to or less than the upper limit mentioned above, thereby allowing the volumes of the other constituent elements to be sufficiently secured.

The positive composite layer <NUM> can be formed from a so-called positive composite including a positive active material. The positive composite may contain a positive electrode mixture or a positive electrode composite including a positive active material and a solid electrolyte. As the solid electrolyte, the sulfide solid electrolyte may be used, but it is more preferable to use a solid electrolyte that has high oxidation resistance. Like the negative composite, the positive composite that forms the positive composite layer <NUM> includes optional components such as a solid electrolyte, a conductive agent, a binder, and a filler, if necessary. It is to be noted that the positive composite layer may have a form containing no solid electrolyte.

As the positive active material included in the positive composite layer <NUM>, known materials typically for use in all-solid-state batteries can be used. Examples of the positive active material include composite oxides represented by LixMeOy (Me represents at least one transition metal) (LixCoO<NUM>, LixNiO<NUM>, LixMnO<NUM>, LixNiαCo(<NUM>-α)O<NUM>, LixNiαMnβCo(<NUM>-α-β)O<NUM>, and the like that have a layered α-NaFeO<NUM>-type crystalline structure, and LixMn<NUM>O<NUM>, LixNiαMn(<NUM>-α)O<NUM>, and the like that have a spinel-type crystalline structure), and polyanion compounds represented by LiwMex(AOy)z (Me represents at least one transition metal, and A represents, for example, P, Si, B, V, or the like) (LiFePO<NUM>, LiMnPO<NUM>, LiNiPO<NUM>, LiCoPO<NUM>, L<NUM>V<NUM>(PO<NUM>)<NUM>, Li<NUM>MnSiO<NUM>, Li<NUM>CoPO<NUM>F, and the like) The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive active material layer, one of these compounds may be used alone, or two or more of these compounds may be used in mixture.

Lithium alloys such as Li-Al, Li-In, Li-Sn, Li-Pb, Li-Bi, Li-Ga, Li-Sr, Li-Si, Li-Zn, Li-Cd, Li-Ca, and Li-Ba, and materials that are more electropositive in oxidation-reduction potential than the negative electrode material, other than the compounds represented by the general formulas mentioned above, such as MnO<NUM>, FeO<NUM>, TiO<NUM>, V<NUM>O<NUM>, V<NUM>O<NUM>, and TiS<NUM> can be used as the positive active material.

The lower limit of the content of the positive active material in the positive composite is preferably <NUM>% by mass, more preferably <NUM>% by mass. The upper limit of the content of the positive active material is preferably <NUM>% by mass, more preferably <NUM>% by mass, further preferably <NUM>% by mass, particularly preferably <NUM>% by mass, and may be <NUM>% by mass. The content of the positive active material falls within the range mentioned above, thereby allowing the electric capacity of the all-solid-state battery to be increased.

The positive electrode mixture is a mixture prepared by mixing the positive active material and a solid electrolyte or the like by mechanical milling or the like, as in the case of the negative electrode. For example, the mixture of the positive active material and the solid electrolyte or the like can be obtained by mixing the particulate positive active material and the particulate solid electrolyte or the like.

Examples of the positive electrode composite also include, as in the case of the negative electrode, a composite with a chemical or physical bond between the positive active material and the solid electrolyte or the like, and a composite mechanically formed from the positive active material and the solid electrolyte or the like. The composite mentioned above has the positive active material and the solid electrolyte or the like present in one particle, and examples of the composite include an aggregate formed by the positive active material and the solid electrolyte or the like, and the positive active material with a film containing the solid electrolyte or the like, formed on at least a part of the surface of the material.

The positive active material and the solid electrolyte or the like contained in the positive composite constitute the positive electrode mixture or the positive electrode composite, thereby allowing a high ion conductivity to be maintained. Further, as the solid electrolyte, the sulfide solid electrolyte may be used, but it is more preferable to use a solid electrolyte that has high oxidation resistance.

In the case where the positive composite contains a solid electrolyte, the lower limit of the content of the solid electrolyte may be <NUM>% by mass, and is preferably <NUM>% by mass. The upper limit of the content of the solid electrolyte in the positive composite is preferably <NUM>% by mass, more preferably <NUM>% by mass, further preferably <NUM>% by mass, particularly preferably <NUM>% by mass. The content of the solid electrolyte falls within the range mentioned above, thereby allowing the electric capacity of the all-solid-state battery to be increased.

The lower limit of the average thickness of the positive composite layer <NUM> is preferably <NUM>, more preferably <NUM>. The upper limit of the average thickness of the positive composite layer <NUM> is preferably <NUM>, more preferably <NUM>, further preferably <NUM>. The average thickness of the positive composite layer <NUM> is adjusted to be equal to or more than the lower limit mentioned above, thereby making it possible to obtain an all-solid-state battery with a high energy density. The average thickness of the positive composite layer <NUM> is adjusted to be equal to or less than the upper limit mentioned above, thereby making it possible to obtain an all-solid-state battery including a negative electrode that is excellent in high rate discharge performance and high in active material utilization.

The solid electrolyte layer <NUM> contains an electrolyte for solid electrolyte layers. Examples of the electrolyte for solid electrolyte layers can include oxide solid electrolytes, other sulfide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo solid electrolytes, besides the sulfide solid electrolyte described above. Among these electrolytes, from viewpoints such as favorable ion conductivity and easy interface formation, sulfide solid electrolytes are preferable, and the sulfide solid electrolyte described above is more preferable. The solid electrolyte layer <NUM> contains the sulfide solid electrolyte, thereby causing the solid electrolyte layer to improve the reduction resistance while maintaining a high ion conductivity, and thus the first coulombic efficiency of the all-solid-state battery to be improved.

The electrolyte for solid electrolyte layers may have a crystalline structure, or may be amorphous without having a crystalline structure. Oxides such as Li<NUM>PO<NUM>, halogens, halogen compounds, and the like may be added to the electrolyte for solid electrolyte layers.

The lower limit of the average thickness of the solid electrolyte layer <NUM> is preferably <NUM>, more preferably <NUM>. The upper limit of the average thickness of the solid electrolyte layer <NUM> is preferably <NUM>, more preferably <NUM>. The average thickness of the solid electrolyte layer <NUM> is adjusted to be equal to or more than the lower limit mentioned above, thereby making it possible to reliably insulate the positive electrode and the negative electrode. The average thickness of the solid electrolyte layer <NUM> is adjusted to be equal to or less than the upper limit mentioned above, making it possible to increase the energy density of the all-solid-state battery.

The method for manufacturing the all-solid-state battery mainly includes, for example, a sulfide solid electrolyte preparation step of preparing the sulfide solid electrolyte, a negative composite preparation step, a step of preparing an electrolyte for solid electrolyte layers, a positive composite preparation step, and a stacking step of stacking a negative electrode layer, a solid electrolyte layer, and a positive electrode layer.

In this step, the sulfide solid electrolyte is prepared, for example, in accordance with the following procedure.

Li<NUM>N and AlN are mixed in a mortar or the like, and then pelletized. Next, a heat treatment is performed to prepare Li<NUM>/<NUM>Al<NUM>/<NUM>N. It is to be noted that in general, "Li<NUM>/<NUM>Al<NUM>/<NUM>N" is written as "Li<NUM>AlN<NUM>".

After mixing the above-mentioned Li<NUM>/<NUM>Al<NUM>/<NUM>N, Li<NUM>S, and P<NUM>S<NUM> that have predetermined mole ratios in a mortar or the like, a sulfide solid electrolyte precursor is prepared. As a method for preparing the sulfide solid electrolyte precursor, for example, a mechanical milling method, a melt quenching method, or the like can be used.

In the case of preparing a sulfide solid electrolyte, the sulfide solid electrolyte can be prepared by, after the preparation of the sulfide solid electrolyte precursor, subjecting the precursor to a heat treatment at a crystallization temperature or higher.

The crystallization temperature can be determined by measurement with a differential scanning calorimeter (DSC). For example, in order to obtain a Li<NUM>P<NUM>S<NUM> crystalline structure, the heat treatment temperature is preferably <NUM> or higher and <NUM> or lower, and in order to obtain a β-Li<NUM>PS<NUM> crystalline structure, the heat treatment temperature is preferably <NUM> or higher and <NUM> or lower. This is because a phase transition to Li<NUM>P<NUM>S<NUM>, which is a stable phase, may be caused in the case of a heat treatment at a high temperature such as <NUM>. For example, in order to obtain the first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKα line, the heat treatment temperature is preferably <NUM> or higher and <NUM> or lower.

It is to be noted that while a case of preparing the sulfide solid electrolyte containing Al as the element M has been described in the preparation step mentioned above, a sulfide solid electrolyte that contains at least one element M selected from the group consisting of Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprises N and has a crystalline structure as defined in claim <NUM> can be prepared by the same approach as the preparation step mentioned above. For example, a sulfide solid electrolyte containing elements such as B and Si, and N can be prepared with the use of Li<NUM>/<NUM>B<NUM>/<NUM>N, Li<NUM>/<NUM>Si<NUM>/<NUM>N, Li<NUM>/<NUM>Si<NUM>/<NUM>N, or the like instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N as the nitride in the preparation step mentioned above. Examples of the nitride that can be used in the preparation step mentioned above can further include LiMgN, LiCaN, LiHf<NUM>/<NUM>N, Li<NUM>/<NUM>Sc<NUM>/<NUM>N, LiZr<NUM>/<NUM>N, Li<NUM>/<NUM>Ti<NUM>/<NUM>N, Li<NUM>/<NUM>Ta<NUM>/<NUM>N, Li<NUM>/<NUM>Ta<NUM>/<NUM>N, Li<NUM>/<NUM>Nb<NUM>/<NUM>N, Li<NUM>/<NUM>W<NUM>/<NUM>N, and Li<NUM>/<NUM>V<NUM>/<NUM>N, besides the above-mentioned nitrides.

In addition, the nitride composed of the element M, Li, and N is used as a starting material in the preparation step mentioned above, but the method for producing the sulfide solid electrolyte according to the present embodiment is not limited thereto.

Although the Li<NUM>S-P<NUM>S<NUM>-based sulfide solid electrolyte has been described as an example in the preparation step mentioned above, the sulfide solid electrolyte can be prepared in accordance with a similar preparation step even in the case of an LGPS-type or argyrodite-type sulfide solid electrolyte.

For example, Li<NUM>/<NUM>Al<NUM>/<NUM>N, Li<NUM>S, and P<NUM>S<NUM> are used as starting materials in the preparation step mentioned above, but the solid sulfide electrolyte of a LGPS type containing Ge may be prepared by further adding a Ge-containing compound such as GeS<NUM>.

More specifically, starting materials that have predetermined mole ratios are mixed in a mortar or the like, and then subjected to mechanical milling, for example, a ball-mill treatment or a vibration-mill treatment to prepare a sulfide solid electrolyte precursor. Thereafter, the precursor is subjected to a heat treatment at a predetermined temperature or higher, thereby allowing a sulfide solid electrolyte to be prepared.

For example, in the case of preparing a sulfide solid electrolyte that has a Li<NUM>GeP<NUM>S<NUM> crystalline structure, the heat treatment temperature is preferably <NUM> or higher and <NUM> or lower, more preferably <NUM> or higher and <NUM> or lower, more preferably <NUM> or higher and <NUM> or lower, particularly preferably <NUM> or higher and <NUM> or lower. The heat treatment may be performed under a reduced-pressure atmosphere or under an inert gas atmosphere.

In this step, a negative composite for forming the negative electrode layer is prepared. In the case where the negative composite contains a mixture or a composite including the negative active material and the sulfide solid electrolyte, this step includes, for example, using a mechanical milling method or the like to mix the negative active material and the sulfide solid electrolyte and prepare a mixture or a composite of the negative active material and the sulfide solid electrolyte.

In this step, the electrolyte for solid electrolyte layers for forming the solid electrolyte layer is prepared. In this step, the electrolyte can be obtained through treatment of predetermined materials for the electrolyte for solid electrolyte layers by a mechanical milling method. The electrolyte for solid electrolyte layers may be prepared by heating predetermined materials for the electrolyte for solid electrolyte layers to the melting temperature or higher to melt and mix the both materials at a predetermined ratio and quench the mixture in accordance with a melt quenching method. Other methods for synthesizing the electrolyte for solid electrolyte layers include a solid phase method of sealing under reduced pressure and firing, a liquid phase method such as dissolution-precipitation, a gas phase method (PLD), and firing under an argon atmosphere after mechanical milling. It is to be noted that in the case where the electrolyte for solid electrolyte layers is the sulfide solid electrolyte, the above-mentioned sulfide solid electrolyte preparation step is performed in the step for preparing the electrolyte for solid electrolyte layers.

In this step, a positive composite for forming the positive electrode layer is prepared. The method for preparing the positive composite is not particularly limited, and may be selected appropriately depending on the purpose. Examples of the method include compression molding of the positive active material, mechanical milling treatment of predetermined materials for the positive composite, and sputtering with a target material for the positive active material. In the case where the positive composite contains a mixture or a composite including the positive active material and the sulfide solid electrolyte, this step includes, for example, using a mechanical milling method or the like to mix the positive active material and the sulfide solid electrolyte and prepare a mixture or a composite of the positive active material and the sulfide solid electrolyte.

In this step, the negative electrode layer including the negative electrode substrate layer and the negative composite layer, the solid electrolyte layer, and the positive electrode layer including the positive electrode substrate layer and the positive composite layer are stacked. In this step, the negative electrode layer, the solid electrolyte layer, and the positive electrode layer may be formed in sequence, or vice versa, and the order of forming the respective layers is not particularly limited. The negative electrode layer is formed by pressure molding of the negative electrode substrate and the negative composite, the solid electrolyte layer is formed by pressure molding of the electrolyte for solid electrolyte layers, and the positive electrode layer is formed by pressure molding of the positive electrode substrate and the positive composite.

The negative electrode layer, the solid electrolyte layer, and the positive electrode layer may be stacked by pressure molding of the negative electrode substrate, the negative composite, the electrolyte for solid electrolyte layers, the positive electrode substrate, and the positive composite at the same time. The positive electrode layer, the negative electrode layer, or these layers may be molded in advance, and subjected to pressure molding with the solid electrolyte layer to stack the layers.

The present invention is not to be considered limited to the embodiment mentioned above.

The configuration of the all-solid-state battery according to the present invention is not to be considered particularly limited, and may include other layers such as an intermediate layer and an adhesive layer, besides the negative electrode layer, the positive electrode layer, and the solid electrolyte layer.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not to be considered limited to the following examples.

<NUM>(<NUM>. 70Li<NUM>S·<NUM>. 30P<NUM>S<NUM>)·1Li<NUM>/<NUM>Al<NUM>/<NUM>N was synthesized by the following treatment.

Li<NUM>N and AlN were weighed so as to be <NUM> : <NUM> in terms of mole ratio, mixed in a mortar, and then pelletized. Next, Li<NUM>/<NUM>Al<NUM>/<NUM>N was prepared by heat treatment at <NUM> for <NUM> hour. It was confirmed by XRD measurement that the main phase of the prepared Li<NUM>/<NUM>Al<NUM>/<NUM>N was Li<NUM>/<NUM>Al<NUM>/<NUM>N.

Next, in a glove box in an argon atmosphere with a dew point of - <NUM> or lower, Li<NUM>S (<NUM>%, Aldrich), P<NUM>S<NUM> (<NUM>%, Aldrich), and Li<NUM>/<NUM>Al<NUM>/<NUM>N were weighed so as to be <NUM> : <NUM> : <NUM> in terms of mole ratio, and then mixed in a mortar. This mixed sample was put in a hermetically sealed <NUM> zirconia pot containing <NUM> of zirconia balls with a diameter of <NUM>. The sample was subjected to milling for <NUM> hours at a revolution speed of <NUM> rpm with a planetary ball mill (from FRITSCH, model number: Premium line P-<NUM>). The milled sample was subjected to a heat treatment for <NUM> hours to obtain a sulfide solid electrolyte according to Example <NUM>. This heat treatment was performed at a temperature that was equal to or higher than the crystallization temperature and not <NUM> higher than the crystallization temperature. The crystallization temperature was determined by measuring the DSC. The DSC measurement was made under the following conditions. More specifically, the temperature was raised from room temperature to <NUM> at <NUM>/min with the use of a DSC device (Thermo Plus DSC8230 from Rigaku Corporation) and a hermetically sealed pan made of SUS.

Sulfide solid electrolytes according to Examples <NUM> to <NUM> were synthesized similarly to Example <NUM> except that the value of z in the compositional formula (<NUM> - z)(<NUM>. 70Li<NUM>S·<NUM>. 30P<NUM>S<NUM>)·zLi<NUM>/<NUM>Al<NUM>/<NUM>N of the sulfide solid electrolyte was changed to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

A sulfide solid electrolyte according to Example <NUM> was synthesized similarly to Example <NUM> except that Li<NUM>S, P<NUM>S<NUM>, and Li<NUM>/<NUM>Al<NUM>/<NUM>N were weighed as raw materials for the sulfide solid electrolyte so as to be Li<NUM>S : P<NUM>S<NUM> : Li<NUM>/<NUM>Al<NUM>/<NUM>N = <NUM> : <NUM> : <NUM> (mol%).

A sulfide solid electrolyte according to Example <NUM> was synthesized similarly to Example <NUM> except that Li<NUM>S, P<NUM>S<NUM>, and Li<NUM>/<NUM>Al<NUM>/<NUM>N were weighed as raw materials for the sulfide solid electrolyte so as to be Li<NUM>S : P<NUM>S<NUM> : Li<NUM>/<NUM>Al<NUM>/<NUM>N = <NUM>: <NUM> : <NUM> (mol%).

Li<NUM>N and BN were weighed so as to be <NUM> : <NUM> in terms of mole ratio, mixed in a mortar, then pelletized, and then subjected to a heat treatment at <NUM> for <NUM> minutes to prepare Li<NUM>/<NUM>B<NUM>/<NUM>N. It was confirmed by XRD measurement that the main phase of the prepared Li<NUM>/<NUM>B<NUM>/<NUM>N was Li<NUM>/<NUM>B<NUM>/<NUM>N.

Next, sulfide solid electrolytes according to Examples <NUM> to <NUM> were synthesized similarly to Example <NUM> except that the Li<NUM>/<NUM>B<NUM>/<NUM>N was used instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N and that the value of z in the compositional formula (<NUM> - z)(<NUM>. 70Li<NUM>S·<NUM>. 30P<NUM>S<NUM>)·zLi<NUM>/<NUM>B<NUM>/<NUM>N of the sulfide solid electrolyte was changed to <NUM>, <NUM>, <NUM>, and <NUM>.

Li<NUM>N and Si<NUM>N<NUM> were weighed so as to be <NUM> : <NUM> in terms of mole ratio, mixed in a mortar, then pelletized, and then subjected to a heat treatment at <NUM> for <NUM> minutes to prepare Li<NUM>/<NUM>Si<NUM>/<NUM>N. It was confirmed by XRD measurement that the main phase of the prepared Li<NUM>/<NUM>Si<NUM>/<NUM>N was Li<NUM>/<NUM>Si<NUM>/<NUM>N.

Sulfide solid electrolytes according to Examples <NUM> to <NUM> were synthesized similarly to Example <NUM> except that the Li<NUM>/<NUM>Si<NUM>/<NUM>N was used instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N and that the value of z in the compositional formula (<NUM> - z)(<NUM>. 70Li<NUM>S·<NUM>. 30P<NUM>S<NUM>)·zLi<NUM>/<NUM>Si<NUM>/<NUM>N of the sulfide solid electrolyte was changed to <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

A sulfide solid electrolyte according to Comparative Example <NUM> was synthesized similarly Example <NUM> except that Li<NUM>/<NUM>Al<NUM>/<NUM>N was not used as a raw material for the sulfide solid electrolyte.

75Li<NUM>S·25P<NUM>S<NUM>(Li<NUM>PS<NUM>) were synthesized by a mechanical milling method. In a glove box in an argon atmosphere with a dew point of -<NUM> or lower, Li<NUM>S and P<NUM>S<NUM> as raw materials for the sulfide solid electrolyte were weighed so as to be Li<NUM>S : P<NUM>S<NUM> = <NUM> : <NUM> (mol%), and then mixed in an agate mortar. This mixture was put in a hermetically sealed <NUM> zirconia pot containing <NUM> of zirconia balls with a diameter of <NUM>. The sample was subjected to milling for <NUM> hours at a revolution speed of <NUM> rpm with a planetary ball mill (from FRITSCH, model number: Premium line P-<NUM>). The sulfide solid electrolyte according to Reference Example <NUM> was obtained by the treatment mentioned above.

A sulfide solid electrolyte according to Reference Example <NUM> was synthesized similarly to Example <NUM> except that the Li<NUM>N was used instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N and that the value of z in the compositional formula (<NUM> - <NUM>)(<NUM>. 70Li<NUM>S·<NUM>. 30P<NUM>S<NUM>)·zLi<NUM>N of the sulfide solid electrolyte was changed to <NUM>.

<NUM>(Li<NUM>GeP<NUM>S<NUM>)·<NUM>. 4Li<NUM>/<NUM>Al<NUM>/<NUM>N was synthesized by the following treatment.

Li<NUM>N and AlN were weighed so as to be <NUM> : <NUM> in terms of mole ratio, mixed in a mortar, and then pelletized. Next, Li<NUM>/<NUM>Al<NUM>/<NUM>N was prepared by heat treatment at <NUM> for <NUM> hour.

Next, in a glove box in an argon atmosphere with a dew point of - <NUM> or lower, Li<NUM>S (<NUM>%, Aldrich), P<NUM>S<NUM> (<NUM>%, Aldrich), GeS<NUM> (<NUM>%, Kojundo Chemical Laboratory Co. ), and Li<NUM>/<NUM>Al<NUM>/<NUM>N were weighed so as to be <NUM> : <NUM> : <NUM> : <NUM> in terms of mole ratio, and then mixed in a mortar. This mixed sample was put in a hermetically sealed <NUM> zirconia pot containing <NUM> of zirconia balls with a diameter of <NUM>. The sample was subjected to milling for <NUM> hours at a revolution speed of <NUM> rpm with a planetary ball mill (from FRITSCH, model number: Premium line P-<NUM>). Thereafter, the milled sample was subjected to a heat treatment at <NUM> for <NUM> hours to obtain a sulfide solid electrolyte according to Reference Example <NUM>.

Sulfide solid electrolytes according to Reference Example <NUM>, Reference Example <NUM>, and Comparative Example <NUM> were synthesized similarly to Example <NUM> except that the value of z in the compositional formula (<NUM> - z)(Li<NUM>GeP<NUM>S<NUM>)·zLi<NUM>/<NUM>Al<NUM>/<NUM>N of the sulfide solid electrolyte was changed to <NUM>, <NUM>, and <NUM>.

A sulfide solid electrolyte according to Comparative Example <NUM> was synthesized similarly Reference Example <NUM> except that Li<NUM>/<NUM>Al<NUM>/<NUM>N was not used as a raw material for the sulfide solid electrolyte.

A sulfide solid electrolyte according to Reference Example <NUM> was synthesized similarly Reference Example <NUM> except for using Li<NUM>O (<NUM>%, Kojundo Chemical Laboratory Co. ) as a raw material for the sulfide solid electrolyte instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N, and weighing so as to be Li<NUM>S : P<NUM>S<NUM> : GeS<NUM> : Li<NUM>O = <NUM> : <NUM> : <NUM> : <NUM> (mol%).

A sulfide solid electrolyte according to Reference Example <NUM> was synthesized similarly Reference Example <NUM> except for using Al<NUM>S<NUM> (<NUM>%, Aldrich) as a raw material for the sulfide solid electrolyte instead of Li<NUM>/<NUM>Al<NUM>/<NUM>N, and weighing so as to be Li<NUM>S : P<NUM>S<NUM> : GeS<NUM> : Al<NUM>S<NUM> = <NUM> : <NUM> : <NUM> : <NUM> (mol%).

X-ray diffraction measurement was made by the following method. With the use of airtight sample holder for X-ray diffraction measurement, the sulfide solid electrolyte powders according to the examples and comparative examples were packed under an argon atmosphere with a dew point of -<NUM> or lower. Powder X-ray diffraction measurement was made with the use of an X-ray diffractometer ("miniFlex II" from Rigaku Corporation). The radiation source was a CuKα line, the tube voltage was <NUM> kV, the tube current was <NUM> mA, and diffracted X-rays were detected by a high-speed one-dimensional detector (model number: D/teX Ultra <NUM>) through a Kβ filter with a thickness of <NUM>. The sampling width was <NUM>°, the scan speed was <NUM>°/min, the divergent slit width was <NUM>°, the light receiving slit width was <NUM> (OPEN), and the scattering slit width was <NUM>.

<FIG> shows the X-ray diffraction (XRD) spectra of Examples <NUM> to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and Comparative Example <NUM> in the range of 2θ = <NUM>° to <NUM>°. Table <NUM> shows the crystalline structures identified from the XRD spectra of Examples <NUM> to <NUM>, Comparative Example <NUM>, and Reference Example <NUM>.

<FIG> shows the X-ray diffraction (XRD) spectra of Reference Example <NUM>, Comparative Example <NUM>, and Reference Examples <NUM> and <NUM> in the range of 2θ = <NUM>° to <NUM>°. Table <NUM> shows the crystalline structures identified from the XRD spectra of References Examples <NUM> to <NUM>, Comparative Examples <NUM> and <NUM>, and Reference Examples <NUM> and <NUM>. It is to be noted that, "Unknown" in Table <NUM> indicates that a diffraction peak from which any crystalline structure failed to be identified was observed.

Raman spectra were measured by the following method. With the use of a laser Raman spectrophotometer ("LabRAM HR Revolution" manufactured by Horiba, Ltd. ), Raman spectrometry was performed in the wave number range of <NUM>-<NUM> to <NUM>-<NUM> under the conditions of excitation laser wavelength: <NUM> (YAG laser) and grating <NUM> gr/mm.

<FIG> shows the Raman spectra of Examples <NUM> to <NUM> and Comparative Example <NUM>. Table <NUM> shows the molecular structures identified from the Raman spectra of Examples <NUM> to <NUM>, Comparative Example <NUM>, and Reference Example <NUM>.

For the ion conductivity (σ), the ion conductivity at <NUM> was determined by measuring the alternating-current impedance with the use of "VMP-<NUM>" from (Bio-Logic) in accordance with the method described above.

It is to be noted that for Reference Examples <NUM> to <NUM>, Comparative Examples <NUM> and <NUM>, and Reference Examples <NUM> and <NUM>, the ion conductivity was also measured at each temperature of -<NUM>, -<NUM>, -<NUM>, <NUM>, and <NUM>, and the activation energy was calculated by the Arrhenius equation.

<FIG> shows the ion conductivity at <NUM> for Examples <NUM> to <NUM> and Comparative Example <NUM>, and Table <NUM> shows the ion conductivity at <NUM> for Examples <NUM> to <NUM>, Comparative Example <NUM>, and Reference Example <NUM>.

Table <NUM> shows the ionic conductivity at <NUM> and the activation energy for Reference Examples <NUM> to <NUM>, Comparative Examples <NUM> and <NUM>, and Reference Examples <NUM> and <NUM>.

A LiNbO<NUM> precursor solution was prepared by dissolving a metal Li in an ultra-dehydrated ethanol and then dissolving niobium ethoxide (Nb(OC<NUM>H<NUM>)<NUM>) therein. The particle surfaces of LiNi<NUM>Co<NUM>Al<NUM>O<NUM> (NCA) were coated with the LiNbO<NUM> precursor with the use of a rolling flow coating device (FD-MP-01F) from Powrex Corporation. The NCA coated with the LiNbO<NUM> precursor was subjected to a heat treatment at <NUM> for <NUM> hour to prepare a LiNbO<NUM>-coated NCA. This LiNbO<NUM>-coated NCA was used as the positive active material.

The LiNbO<NUM>-coated NCA and the sulfide solid electrolyte (Li<NUM>PS<NUM>) according to Reference Example <NUM> were weighed so as to be LiNbO<NUM>-coated NCA : Li<NUM>PS<NUM> = <NUM> : <NUM> (% by mass), and then mixed in an agate mortar. The sulfide solid electrolyte according to Example <NUM> was put into a powder molder with an inner diameter of <NUM>, and then subjected to pressure molding with the use of a hydraulic press. After releasing the pressure, the NCA-Li<NUM>PS<NUM> mixed powder was put on one side of the solid electrolyte layer according to Example <NUM> and subjected to pressure molding at <NUM> MPa per sample area for <NUM> minutes. After releasing the pressure, metal Li foil was attached to the opposite surface of the sulfide solid electrolyte layer according to Example <NUM> and subjected to pressure molding to obtain a layered product of the positive composite layer, the sulfide solid electrolyte layer according to Example <NUM>, and the metal Li foil. This layered product was encapsulated in an aluminum laminate cell under reduced pressure, and pressed with a stainless steel plate to obtain an all-solid-state battery cell (Li-NCA half-cell).

All-solid-state battery cells (Li-NCA half-cells) including the sulfide solid electrolytes according to Examples <NUM> and <NUM> and Comparative Example <NUM> were obtained by the same operations as in Example <NUM>, except that the sulfide solid electrolyte according to Example <NUM> was changed to the sulfide solid electrolytes according to Examples <NUM> and <NUM> and Comparative Example <NUM>.

The all-solid-state battery cells (Li-NCA half-cells) mentioned above were subjected to a charge-discharge test under the following conditions. The charge-discharge test was performed in a constant-temperature bath at <NUM>. The charge was constant-current constant-voltage (CCCV) charge at a charge current of <NUM> mA/cm<NUM> with a charge upper limit voltage of <NUM> V. The charge cutoff condition was set to allow the charge until the charge current reached <NUM> mA/cm<NUM>. The discharge was constant current (CC) discharge at a discharge current of <NUM> mA/cm<NUM> with an end-of-discharge voltage of <NUM> V. The pause time between the charge and the discharge was set to be <NUM> minutes. The percentage of the first discharge capacity with respect to the first amount of charge in this case was determined as a "first coulombic efficiency (%)".

<FIG> shows the first charge-discharge performance of Example <NUM>, Example <NUM>, Example <NUM>, and Comparative Example <NUM>. Table <NUM> shows the first coulombic efficiencies (%) of Example <NUM>, Example <NUM>, Example <NUM>, and Comparative Example <NUM>.

In a glove box in an argon atmosphere with a dew point of -<NUM> or lower, the sulfide solid electrolyte according to Example <NUM> and a SUS316L powder were weighed so as to be <NUM> : <NUM> in ratio by mass, and then mixed in an agate mortar. The sulfide solid electrolyte (Li<NUM>PS<NUM>) according to Reference Example <NUM> was put into a powder molder with an inner diameter of <NUM>, and then subjected to pressure molding with the use of a hydraulic press. After releasing the pressure, a mixed powder of the SUS316 powder mentioned above and the sulfide solid electrolyte powder according to Example <NUM> was put on one side of the Li<NUM>PS<NUM> layer and subjected to pressure molding at <NUM> MPa for <NUM> minutes. After releasing the pressure, metal Li foil was attached to the opposite surface of the Li<NUM>PS<NUM> layer and subjected to pressure molding to obtain a layered product of the mixture layer of the sulfide solid electrolyte according to Example <NUM>, the Li<NUM>PS<NUM> layer, and metal Li foil.

This layered product was encapsulated in an aluminum laminate cell under reduced pressure, and pressed with a stainless steel plate to obtain a cell for reduction resistance evaluation with the mixture layer of the sulfide solid electrolyte according to Example <NUM> as a working electrode and the metal Li foil as a counter electrode.

The charge test conditions were a measurement temperature of <NUM>, and constant-current constant-voltage (CCCV) charge for the charge, with a charge current of <NUM> mA/cm<NUM>, a charge lower limit potential of <NUM> V, and a total charge time of <NUM> hours. In this regard, the reaction of reducing the mixture layer of the sulfide solid electrolyte according to Example <NUM> is referred to as "charge". The amount of charge after <NUM> hours from the start of the charge was defined as the reductive decomposition capacity (mAh/g) of the sulfide solid electrolyte after <NUM> hours. Since the SUS316L powder is stable at a potential of <NUM> V vs. Li/Li+, the redox species is only the sulfide solid electrolyte. Thus, the amount of electricity flowing through the cell for evaluation means the amount of reductive decomposition of the sulfide solid electrolyte.

The sulfide solid electrolytes according to Examples <NUM>, <NUM>, <NUM> to <NUM>, <NUM>, <NUM>, and <NUM> and Comparative Example <NUM> were evaluated for reduction resistance in accordance with the same procedure.

Table <NUM> shows the reductive decomposition capacities of the sulfide solid electrolytes according to Examples <NUM>, <NUM>, <NUM>, <NUM> to <NUM>, <NUM>, <NUM>, and <NUM> and Comparative Example <NUM> after <NUM> hours from the start of the charge.

The sulfide solid electrolytes according to Reference Examples <NUM> to <NUM>, Comparative Examples <NUM> and <NUM>, and Reference Examples <NUM> and <NUM> were evaluated for reduction resistance in accordance with the following procedure.

Graphite particles (Gr) and the sulfide solid electrolyte (Li<NUM>GeP<NUM>Al<NUM>S<NUM>N<NUM>) according to Reference Example <NUM> were weighed so as to be Gr : Li<NUM>GeP<NUM>Al<NUM>S<NUM>N<NUM> = <NUM> : <NUM> (% by mass), and then mixed in an agate mortar. Li<NUM>PS<NUM> was put into a powder molder with an inner diameter of <NUM>, and then subjected to pressure molding with the use of a hydraulic press. After releasing the pressure, the Gr-Li<NUM>GeP<NUM>Al<NUM>S<NUM>N<NUM> mixed powder was put on one side of the Li<NUM>PS<NUM> layer and subjected to pressure molding. After releasing the pressure, metal Li foil was attached to the opposite surface of the Li<NUM>PS<NUM> layer and subjected to pressure molding to obtain a layered product of the mixture layer of the sulfide solid electrolyte according to Reference Example <NUM>, the Li<NUM>PS<NUM> solid electrolyte layer, and metal Li foil. This layered product was encapsulated in an aluminum laminate cell under reduced pressure, and pressed with a stainless steel plate to obtain an all-solid-state battery cell (Li-Gr half-cell) with the mixture layer of the sulfide solid electrolyte according to Reference Example <NUM> as a working electrode and the metal Li foil as a counter electrode.

All-solid-state battery cells (Li-Gr half-cells) including the sulfide solid electrolytes according to Reference Examples <NUM> and <NUM> and Comparative Example <NUM> were obtained by the same operations as in Reference Example <NUM>, except that the sulfide solid electrolyte according to Reference Example <NUM> was changed to the sulfide solid electrolytes according to Reference Examples <NUM> and <NUM> and Comparative Example <NUM>.

The all-solid-state battery cells (Li-Gr half-cells) mentioned above were subjected to a discharge test (lithiation of Gr) under the following conditions. The discharge test was performed in a constant-temperature bath at <NUM>. The discharge was constant current (CC) discharge with a discharge current of <NUM> mA/cm<NUM>. The discharge capacity Q in this case was plotted on a graph (dQ/dV curve) that shows the relation between the differential value dQ/dV differentiated with respect to the voltage V and the voltage V.

<FIG> shows the dQ/dV curves of Reference Examples <NUM> to <NUM> and Comparative Example <NUM>. Table <NUM> shows the values of the voltage V at dQ/dV = -<NUM> mAhg-<NUM>V-<NUM> for Reference Examples <NUM> to <NUM> and Comparative Example <NUM>. It is to be noted that the large amount of change in dQ/dV around <NUM> V is confirmed from <FIG>. Since the lithiation potential of Gr is about <NUM> V vs Li/Li+, the change in dQ/dV around <NUM>. 4V is presumed to be derived from the reductive decomposition of the sulfide solid electrolyte. Accordingly, the fact that the value of the voltage V at dQ/dV = -<NUM> mAhg-<NUM>V-<NUM> for the all-solid-state battery cell (Li-Gr half-cell) according to the present example is shifted in the electronegative direction means that the reductive decomposition potential of the sulfide solid electrolyte is shifted in the electronegative direction, that is, the reduction resistance improved.

The amount of hydrogen sulfide generated was measured in order to evaluate the chemical stability of the sulfide solid electrolyte in the atmosphere. In a glove box in an argon atmosphere with a dew point of - <NUM> or lower, <NUM> of the sulfide solid electrolyte powder according to each of the examples and comparative examples was subjected to uniaxial pressing at <NUM> MPa per sample area for <NUM> minutes with the use of a powder molder with an inner diameter of <NUM>, thereby providing pellets. Thereafter, the obtained pellets were placed inside a hermetically sealed desiccator (actual volume: <NUM><NUM>, temperature: <NUM>, relative humidity: about <NUM>%), and the amount of hydrogen sulfide generated was measured with the use of a hydrogen sulfide sensor (TPA-5200E). The measurement was terminated after reaching the detection upper limit <NUM> ppm of the hydrogen sulfide sensor or after a lapse of <NUM> minutes for the measurement time.

The amount V (cm<NUM>/g) of hydrogen sulfide generated from the solid electrolyte per gram was determined from the following formula with the obtained concentration C (ppm), the real volume L (cm<NUM>) of the desiccator, and the mass m (g) of the pellet.

<FIG> and <FIG> are graphs showing the relation between the air exposure time (minutes) and the amount of hydrogen sulfide generated (cm<NUM>/g) for the sulfide solid electrolyte pellets according to the examples and comparative examples mentioned above.

<FIG> shows the amount of hydrogen sulfide generated for the air exposure time up to <NUM> minutes in Example <NUM>, Example <NUM>, and Comparative Example <NUM>, and <FIG> shows the amount of hydrogen sulfide generated for the air exposure time up to <NUM> minutes in Example <NUM> and Reference Example <NUM>.

As shown in Table <NUM>, the sulfide solid electrolytes according to the examples that contain any element of Al, B, or Si as the element M and N and have a crystalline structure are, as compared with the sulfide solid electrolyte according to Comparative Example <NUM>, reduced in the reductive decomposition capacity after <NUM> hours from the start of the charge, and excellent in first coulombic efficiency. The sulfide solid electrolytes according to Example <NUM>, Example <NUM>, Example <NUM> to Example <NUM>, Example <NUM>, Example <NUM> to Example <NUM>, and Example <NUM> to <NUM> are favorable in ion conductivity at <NUM>.

In contrast, the sulfide solid electrolyte according to Comparative Example <NUM> containing no elements M and N is favorable in ion conductivity, but high in the reductive decomposition capacity after <NUM> hours from the start of the charge and inferior in first coulombic efficiency.

From Table <NUM>, because a sulfide solid electrolyte that has a structure expected to show an ion conductivity of <NUM>-<NUM> Scm-<NUM> or more and favorable atmospheric stability is obtained with the content ratio of Li to P being <NUM> or more and <NUM> or less in terms of mole ratio and the content ratio of N to P being <NUM> or more and <NUM> or less in terms of mole ratio, it has been confirmed that it is particularly preferable for the composition of the sulfide solid electrolyte to have such values.

In addition, in the case where the sulfide solid electrolyte contains Al as the element M, there is no precipitation of Li<NUM>S even in the case of the high content ratios of the Li element and N, such as the content ratio of Li to P being <NUM> in terms of mole ratio and the content ratio of N to P being <NUM> in terms of mole ratio. From the foregoing, it has been suggested that it is particularly preferable to include Al as the element M.

As shown in <FIG>, it has been confirmed that the sulfide solid electrolytes according to all of the examples and comparative examples have peaks observed in the XRD spectra, and have crystalline structures. Example <NUM> and Example <NUM> have a crystalline structure of Li<NUM>P<NUM>S<NUM>, Example <NUM> has a crystalline structure of β-Li<NUM>PS<NUM>, and Example <NUM> has a crystalline structure of Li<NUM>P<NUM>S<NUM>. The crystalline structure of the sulfide solid electrolytes according to Examples <NUM> to <NUM> is a specific crystalline structure A that has diffraction peaks at 2θ = <NUM>°, <NUM>°, <NUM>°, <NUM>°, and <NUM>°. It has been confirmed that the crystalline structure of the sulfide solid electrolyte according to Example <NUM> is a specific crystalline structure B that has diffraction peaks at 2θ = <NUM>°, <NUM>°, <NUM>°, and <NUM>°.

As shown by the Raman spectrum of <FIG>, the sulfide solid electrolytes according to the examples undergo a decrease in peak derived from the crosslinked sulfur P<NUM>S<NUM><NUM>- around a Raman shift of <NUM>-<NUM> with increased z, that is, with the increased content of nitrogen (N), causing a peak derived from PS<NUM><NUM>- around a Raman shift of <NUM>-<NUM> to appear. Thus, the molecular structures based on the Raman spectra of Examples <NUM> and <NUM> in Table <NUM> are presumed to be composed of PS<NUM><NUM>-, P<NUM>S<NUM><NUM>-, and P<NUM>S<NUM><NUM>-. The molecular structures based on the Raman spectra of Examples <NUM> to <NUM>, Examples <NUM> to <NUM>, and Examples <NUM> to <NUM> are presumed to be composed of PS<NUM><NUM>-.

As shown in <FIG> and <FIG>, it has been successfully confirmed that the amounts of hydrogen sulfide generated in Examples <NUM> and <NUM> are smaller than the amount of hydrogen sulfide generated in Comparative Example <NUM>. In particular, Example <NUM> with z = <NUM> is superior in the effect of inhibiting the hydrogen sulfide generation as compared with Comparative Example <NUM> and Reference Example <NUM>. Accordingly, it has been suggested that the sulfide solid electrolyte not only has high reduction resistance but also excellent atmospheric stability.

The reason why the sulfide-based solid electrolyte has a highly inhibitory effect on the generation of hydrogen sulfide is presumed as follows. As shown by the Raman spectrum of <FIG>, the sulfide solid electrolytes according to the examples undergo a decrease in peak derived from the crosslinked sulfur P<NUM>S<NUM><NUM>- around a Raman shift of <NUM>-<NUM> with increased z, that is, with the increased content of N. In addition, the sulfide solid electrolytes according to the examples have no appearing peak derived from Li<NUM>S in the XRD (X-ray diffraction) spectra shown in <FIG>. From these facts, the sulfide solid electrolyte with the content of N increased is presumed to reduce so-called cross-linked sulfur P<NUM>S<NUM><NUM>-(S<NUM>P-S-PS<NUM>), which is unstable in the atmosphere, substantially without containing Li<NUM>S, which is likely to react with water, thus making it possible to improve the inhibitory effect on the generation of hydrogen sulfide.

Further, the reason why Example <NUM> (z = <NUM>) has a smaller amount of hydrogen sulfide generated than Reference Example <NUM> without cross-linked sulfur P<NUM>S<NUM><NUM>- is believed to be because the introduction of N into the structure of the solid electrolyte constituted a three-dimensional network, thereby making the bonds stronger. It is generally known that the water resistance is improved by introducing N in oxynitride glass with O of oxide glass partially replaced with N.

The comparison among Example <NUM>, Example <NUM>, Example <NUM>, and Reference Example <NUM> with the content of N fixed with z = <NUM> and y = <NUM> finds the precipitation of Li<NUM>S only in Reference Example <NUM> containing no element M. From the foregoing, the precipitation of Li<NUM>S is considered allowed to be inhibited by containing the element M.

The reason why the precipitation of Li<NUM>S can be inhibited by containing the element M in the sulfide solid electrolyte is considered as follows. In the case of using Li<NUM>N as a starting material for the sulfide-based solid electrolyte containing N, Li<NUM>N and P<NUM>S<NUM> react dramatically to release N<NUM>, thereby resulting in precipitation of Li<NUM>S. This is believed to be because of the low N defect generation energy of Li<NUM>N. In contrast, according to the invention of the present application, because the N defect generation energy of LiαMβN is higher than the N defect generation energy of Li<NUM>N, the reaction is considered to proceed slowly in the process of synthesizing the sulfide-based solid electrolyte, thereby inhibiting the release of N<NUM> and the precipitation of Li<NUM>S.

It is to be noted that the "defect generation energy" herein refers to a value calculated with the use of the total energy Eperfect of a crystalline structure including no defects, the total energy Evacancy of a crystalline structure including defects, and the chemical potential µ of a defective atom, and means a parameter defined by the following formula.

As is clear from Table <NUM>, the sulfur-based sulfide solid electrolytes that contain Li, P, S, Ge, Al, and N and have a crystalline structure are excellent ion conductivity at <NUM>.

In addition, the fact that the value of the voltage V at dQ/dV = -<NUM> mAhg-<NUM>V-<NUM> is shifted in the electronegative direction means that the reductive decomposition potential of the sulfide solid electrolyte is shifted in the electronegative direction, that is, the reduction resistance improved, and the sulfide solid electrolytes according to the examples are also excellent in reduction resistance.

Among the electrolytes, the sulfide solid electrolyte according to Reference Example <NUM> has been found to show an excellent superior ion conductivity at <NUM> as compared with the sulfide solid electrolytes according to Reference Examples <NUM> and <NUM>.

From the foregoing results, it has been demonstrated that the sulfide solid electrolyte according to the present invention, with high reduction resistance, is capable of improving the first coulombic efficiency of the all-solid-state battery including the sulfide solid electrolyte. In addition, it has also been demonstrated that the sulfide solid electrolyte according to the present invention is also capable of improving the atmospheric stability.

Claim 1:
A sulfide solid electrolyte comprising at least one element M selected from the group consisting of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, and V, and comprising N, and having a crystalline structure, wherein the crystalline structure includes a crystalline structure that has a crystal phase of Li<NUM>P<NUM>S<NUM>, Li<NUM>P<NUM>S<NUM>, or β-Li<NUM>PS<NUM>, or a first crystalline structure that has diffraction peaks at 2θ = <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, <NUM>° ± <NUM>°, and <NUM>° ± <NUM>° in X-ray diffraction measurement with a CuKa line.