Sulfide solid electrolytes and all-solid-state batteries

Abstract

The present invention provides a sulfide solid electrolyte with improved reduction resistance and an all-solid-state battery equipped with the sulfide solid electrolyte. [Solution] The sulfide solid electrolyte contains Al and N and has a crystalline structure. The all-solid-state battery 10, which is a secondary battery, has a negative electrode layer 1 and a positive electrode layer 2 arranged via a solid electrolyte layer 3. The negative electrode layer 1 has a negative electrode base layer 4 and a negative electrode mixture layer 5, with the negative electrode base layer 4 being the outermost layer of the negative electrode layer 1. The positive electrode layer 2 has a positive electrode base layer 7 and a positive electrode mixture layer 6, with the positive electrode base layer 7 being the outermost layer of the positive electrode layer 2. The positive electrode mixture layer 6, solid electrolyte layer 3, negative electrode mixture layer 5 and negative electrode base layer 4 are stacked on the positive electrode base layer 7 in this order, and the initial Coulomb efficiency is excellent because the negative electrode layer 1, solid electrolyte layer 3, positive electrode layer 2, or a combination thereof contains the sulfide solid electrolyte.

Description

[Technical Field]

[0001] This invention relates to a sulfide solid electrolyte and an all-solid-state battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of an electrode body having a pair of electrically isolated electrodes, and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring ions between the two electrodes.

[0003] In recent years, all-solid-state batteries have been proposed that use sulfide solid electrolytes instead of liquid electrolytes such as organic solvents as non-aqueous electrolytes, with the aim of improving the safety of non-aqueous electrolyte secondary batteries (see Patent Document 1).

[0004] As an example of a sulfide solid electrolyte, a crystalline sulfide solid electrolyte is disclosed that contains Li, P, S, and N, has a composition represented by the general formula XLi2S-25P2S5-YLi3N (10≦Y≦15, 67.5≦X+Y≦85), and is a crystalline material. (See Patent Document 2) As sulfide solid electrolytes, 70Li2S·30P2S5 glass ceramics and 60Li2S·25P2S5·10Li3N glass ceramics are used. -3 It has been reported to exhibit high ionic conductivity of S / cm or higher. (Non-patent document 1)

[0005] First-principles calculations have revealed that such sulfide solid electrolytes inherently have low oxidation and reduction resistance. (Non-patent document 2) [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-340257 [Patent Document 2] Japanese Patent Publication No. 2018-041671 [Non-Patent Document 1] Solid State Ionics,177,2721(2006), Solid State Ionics,304,85(2016) [Non-Patent Document 2] ACS Appl.Mater.Interfaces, 7, 23685(2015) [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention has been made based on the circumstances described above, and aims to provide a sulfide solid electrolyte with improved reduction resistance, and an all-solid-state battery equipped with said sulfide solid electrolyte. [Means for solving the problem]

[0008] One aspect of the present invention, made to solve the above problems, is a sulfide solid electrolyte having a crystalline structure, 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 N.

[0009] Another aspect of the present invention is a sulfide solid electrolyte comprising Al and N and having a crystalline structure. [Effects of the Invention]

[0010] According to one or another aspect of the present invention, a sulfide solid electrolyte with improved reduction resistance can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing an all-solid-state battery in one embodiment of the present invention. [Figure 2] These are the X-ray diffraction (XRD) spectra of the sulfide solid electrolytes of the examples and comparative examples. [Figure 3] These are the Raman spectra of the sulfide solid electrolytes of the examples and comparative examples. [Figure 4] This graph shows the ionic conductivity of the sulfide solid electrolytes of the examples and comparative examples at 25°C. [Figure 5] This graph shows the initial charge-discharge performance of all-solid-state batteries in the examples and comparative examples. [Figure 6] This graph shows the amount of hydrogen sulfide generated by the sulfide solid electrolytes in the examples and comparative examples. [Figure 7] This graph shows the amount of hydrogen sulfide generated by the sulfide solid electrolytes in the examples and reference examples. [Figure 8] These are the X-ray diffraction (XRD) spectra of sulfide solid electrolytes in the examples, comparative examples, and reference examples. [Figure 9] These are the dQ / dV curves for all-solid-state batteries in the examples and comparative examples. [Modes for carrying out the invention]

[0012] A sulfide solid electrolyte according to one aspect of the present invention is a sulfide solid electrolyte having a crystalline structure and containing 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.

[0013] The inventors of the present invention focused on the fact that nitrides containing any of Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, or V (hereinafter also referred to as element M), which are difficult to use as solid electrolytes due to their low ionic conductivity, exhibit high reduction resistance. Therefore, they considered that the reduction resistance of sulfide solid electrolytes could be improved by incorporating nitrogen (N) and element M into the sulfide solid electrolyte, leading to the present invention.

[0014] 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 N, and has a crystalline structure, thereby providing a sulfide solid electrolyte with improved reduction resistance. In the above sulfide solid electrolyte, element M may be Al. The reason for this is not clear, but the following reason is presumed: When the sulfide solid electrolyte containing elements M and N is exposed to a reducing atmosphere, it is presumed that a highly reduction-resistant film containing nitrides of element M or lithium nitrides of element M is formed on the surface or interface of the sulfide solid electrolyte. This is presumed to improve the reduction resistance of the sulfide solid electrolyte.

[0015] All-solid-state batteries equipped with this sulfide solid electrolyte can be made into all-solid-state batteries with improved initial Coulomb efficiency. The reason for this is not entirely clear, but the following reason is speculated. General sulfide solid electrolytes are easily reduced and decomposed, and all-solid-state batteries equipped with such sulfide solid electrolytes are known to exhibit a large amount of reduced decomposition electricity. However, this sulfide solid electrolyte has high resistance to reduction. Therefore, the initial Coulomb efficiency of all-solid-state batteries equipped with this sulfide solid electrolyte can be improved. Furthermore, the presence of nitrogen in the sulfide solid electrolyte causes sulfur to be replaced by nitrogen, which has a smaller ionic radius, thus reducing the crystal lattice volume. As a result, the space for lithium ions to move increases, improving ionic conductivity. Consequently, the initial Coulomb efficiency of the all-solid-state battery can be improved while maintaining good ionic conductivity.

[0016] The element M in the above sulfide solid electrolyte can be any element that exhibits high reduction resistance to nitrides. Specifically, it can be 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. These elements have been shown by first-principles calculations to exhibit high reduction resistance to lithium nitrides containing element M (see Non-Patent Literature Adv.Sci., 4, 1600517 (2017)). Among these, Al, B, and Si are preferred because they have low production costs and allow for lower manufacturing costs.

[0017] The above crystal structure is Li7P3S 11 Preferably, the material contains a crystal structure having a crystalline phase of Li4P2S6 or β-Li3PS4, or a first crystal structure having diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5° in X-ray diffraction measurements using CuKα rays. This makes it possible to increase the ionic conductivity at 25°C.

[0018] It is preferable that the above first crystal structure includes a specific crystal structure A having diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, 29.8°±0.5° and 30.9°±0.5° in the above X-ray diffraction measurement, or a specific crystal structure B having diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5° and 29.8°±0.5° and not having a diffraction peak at 30.9°±0.5°. With the above configuration, the ionic conductivity at 25°C can be further increased.

[0019] When the sulfide solid electrolyte contains at least one element M selected from the group consisting of Li, P, S, N, and Al, Si, B, Mg, Zr, Ti, Hf, Ca, Sr, Sc, Ce, Ta, Nb, W, Mo, V, from the viewpoint of reduction resistance, the content ratio of Li to P is preferably 1.64 or more and 4.00 or less in terms of molar ratio, and the content ratio of N to P is preferably 0.02 or more and 1.11 or less in terms of molar ratio. When the content ratios of Li and N in the sulfide solid electrolyte are within the above ranges, the reduction resistance is further improved, and the initial Coulomb efficiency of the all-solid-state battery provided with the sulfide solid electrolyte can be further increased. In the sulfide solid electrolyte, the element M may be Al.

[0020] In the sulfide solid electrolyte, it is more preferable that the content ratio of Li to P is 2.77 or more and 3.38 or less in terms of molar ratio, and the content ratio of N to P is 0.28 or more and 0.65 or less in terms of molar ratio. When the content ratios of Li and N in the sulfide solid electrolyte are within the above ranges, the reduction resistance, the air stability, and the ionic conductivity at 25°C can be simultaneously increased.

[0021] When the sulfide solid electrolyte is (100 - z)(yLi2S·(1 - y)P2S5)·zLi α M β N (where 0 < z ≤ 40, 0.50 ≤ y ≤ 0.75, α and β are numerical values that give the stoichiometric ratio depending on the type of element M), it preferably has a composition represented by the above formula. When the sulfide solid electrolyte has a composition represented by the above general formula, the reduction resistance is further improved, and the initial Coulomb efficiency of the all-solid-state battery provided with the sulfide solid electrolyte can be further increased.

[0022] The sulfide solid electrolyte may further contain Ge. Even such a sulfide solid electrolyte can enjoy the effects of the present invention.

[0023] When the sulfide solid electrolyte contains Ge, the sulfide solid electrolyte is Li 10 GeP2S 12It preferably contains a structure having a crystal phase.

[0024] Further, the sulfide solid electrolyte contains Li, P, S, N, Ge, and the above element M, and Li 10 GeP2S 12 When it has a crystal phase, the content ratio of Li to P is preferably 5.01 or more and 5.61 or less in terms of molar ratio, and the content ratio of N to P is preferably 0.0051 or more and 0.41 or less in terms of molar ratio. Further, it is more preferable that the content ratio of Li to P is 5.06 or more and 5.19 or less in terms of molar ratio, and the content ratio of N to P is 0.038 or more and 0.13 or less in terms of molar ratio.

[0025] When the sulfide solid electrolyte contains Ge, it preferably has a composition represented by the general formula (100 - z)Li 10 GeP2S 12 ·zLi α M β N (where 0 < z ≤ 50, α and β are numerical values giving a stoichiometric ratio depending on the type of element M). Among them, in the above general formula, it is particularly preferable that z satisfies 0 < z ≤ 20.

[0026] The ionic conductivity of the sulfide solid electrolyte at 25°C is preferably 1.0×10 -3 S / cm or more. With the above configuration, the high-rate discharge performance of the all-solid-state battery provided with the sulfide solid electrolyte can be improved.

[0027] The ionic conductivity of the sulfide solid electrolyte at 25°C is determined by measuring the AC impedance using the following method. Under an argon atmosphere with a dew point of -50°C or lower, 120 mg of the sample powder is placed in a powder molder with an inner diameter of 10 mm, and then uniaxially press-molded using a hydraulic press at a pressure of 50 MPa or less per sample area. After the pressure is released, SUS316L powder is placed on the top and bottom surfaces of the sample as current collectors, and then uniaxially press-molded for 5 minutes at a pressure of 360 MPa per pellet area to obtain a pellet for ionic conductivity measurement. This pellet for ionic conductivity measurement is inserted into a Hosen HS cell and the AC impedance is measured. The measurement conditions are an applied voltage amplitude of 20 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 25°C.

[0028] Another aspect of the present invention relates to an all-solid-state battery comprising 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.

[0029] In another embodiment of the present invention, the all-solid-state battery has excellent initial Coulomb efficiency because the negative electrode layer, the solid electrolyte layer, the positive electrode layer, or a combination thereof contains the sulfide solid electrolyte. Since the sulfide solid electrolyte has excellent reduction resistance, it is preferable that the negative electrode layer and / or solid electrolyte layer contain the sulfide solid electrolyte. With the above configuration, the effects of the present invention are further enhanced.

[0030] The embodiments of the sulfide solid electrolyte and all-solid-state battery according to the present invention will be described in detail below.

[0031] <Sulfide solid electrolyte> 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 N, and has a crystalline structure. The sulfide solid electrolyte, by containing 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 having a crystalline structure, can improve reduction resistance. The sulfide solid electrolyte can be used in any application requiring ionic conductivity. In particular, the sulfide solid electrolyte is preferably used in lithium all-solid-state batteries. Note that in the above sulfide solid electrolyte, element M may be Al.

[0032] The sulfide solid electrolyte has a crystalline structure. Here, "having a crystalline structure" means that in X-ray diffraction measurements, peaks originating from the crystalline structure of the sulfide solid electrolyte are observed in the X-ray diffraction pattern. The sulfide solid electrolyte may contain amorphous regions. A sulfide solid electrolyte having a crystalline structure can be obtained, for example, by crystallizing an amorphous sulfide solid electrolyte through heat treatment or the like.

[0033] Examples of the crystal structures of the sulfide solid electrolyte include LGPS type, argyrodite type, and Li7P3S. 11 Examples include the Thio-LISICON system. Among these, the crystal structures mentioned above, from the viewpoint of lithium ion conductivity, include the LGPS type, the argyrodite type, and Li7P3S. 11 Li7P3S is preferred because it has high stability with respect to Li. 11More preferably, the first crystal structure has a crystalline phase of Li4P2S6 or β-Li3PS4, or a first crystal structure has diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5° and 29.8°±0.5° in X-ray diffraction measurements using CuKα rays. Among these, the first crystal structure has diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5° and 29.8°±0.5° in X-ray diffraction measurements using CuKα rays, due to its high lithium ion conductivity.

[0034] The first crystal structure described above may include specific crystal structure A, which has diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, 29.8°±0.5° and 30.9°±0.5° in the above X-ray diffraction measurement, or specific crystal structure B, which has diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5° and 29.8°±0.5° and does not have a diffraction peak at 30.9°±0.5°. With the above configuration, the ionic conductivity at 25°C can be increased.

[0035] The diffraction peak in the first crystal structure described above may be within a range of ±0.3° or ±0.1° within the range of 2θ described above.

[0036] The X-ray diffraction measurement using CuKα rays described above is performed according to the following procedure. The solid electrolyte powder to be measured is packed into an airtight X-ray diffraction sample holder under an argon atmosphere with a dew point of -50°C or lower. Powder X-ray diffraction measurement is performed using an X-ray diffractometer (Rigaku's "MiniFlex II"). The radiation source is CuKα rays, the tube voltage is 30kV, and the tube current is 15mA. The diffracted X-rays are passed through a 30μm thick Kβ filter and detected by a high-speed one-dimensional detector (model: D / teX Ultra 2). The sampling width is 0.01°, the scan speed is 5° / min, the diverging slit width is 0.625°, the receiving slit width is 13mm (OPEN), and the scattering slit width is 8mm.

[0037] The above Li7P3S 11 The crystal structure having the crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 17.8°±0.5°, 18.5°±0.5°, 23.7°±0.5°, 29.6°±0.5°, and 30.0°±0.5°.

[0038] Examples of the above LGPS-type sulfide solid electrolyte include Li 10 GeP2S 12 Examples include Li 10 GeP2S 12 The crystal structure having the crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 14.4°±0.5°, 20.1°±0.5°, 20.4°±0.5°, 26.9°±0.5°, 29.5°±0.5°, and 47.3°±0.5°.

[0039] Examples of the above-mentioned argyrodite-type sulfide solid electrolytes include Li6PS5Cl. The crystalline structure of Li6PS5Cl having a crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 15.6°±0.5°, 25.5°±0.5°, 30.0°±0.5°, 31.4°±0.5°, 45.0°±0.5°, and 52.5°±0.5°.

[0040] The crystalline structure having the above-mentioned Li4P2S6 crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ=16.9°±0.5°, 27.1°±0.5°, 32.1°±0.5°, and 32.5°±0.5°.

[0041] The crystal structure having the β-Li3PS4 crystalline phase as described above exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 17.5°±0.5°, 18.1°±0.5°, 29.1°±0.5°, 29.9°±0.5°, and 31.2°±0.5°.

[0042] The sulfide solid electrolyte preferably contains Li, P, S, N, and element M. In this case, from the viewpoint of reduction resistance, the molar ratio of Li to P in the sulfide solid electrolyte is preferably 1.64 to 4.00, more preferably 2.36 to 3.70, and even more preferably 2.60 to 3.40. The molar ratio of N to P is preferably 0.02 to 1.11, more preferably 0.19 to 1.01, even more preferably 0.22 to 0.71, and particularly preferably 0.28 to 0.65. By having the above ranges for the Li and N content in the sulfide solid electrolyte, a sulfide solid electrolyte exhibiting good reduction resistance can be obtained. Furthermore, the initial Coulomb efficiency of an all-solid-state battery equipped with this sulfide solid electrolyte can be increased.

[0043] Furthermore, from the viewpoint of atmospheric stability, it is preferable that the content ratio of Li to P is 2.60 or more and 4.00 or less in molar ratio, the content ratio of N to P is 0.19 or more and 1.11 or less in molar ratio, and it is more preferable that the content ratio of Li to P is 2.77 or more and 3.38 or less in molar ratio, and the content ratio of N to P is 0.28 or more and 0.65 or less in molar ratio. It is also preferable that the element M contains Al. In particular, when the value of y in the general formula is less than 0.75, the so-called bridging sulfur P2S7, which is unstable in the atmosphere, is formed. 4- Because the (S3P-S-PS3) content is reduced and the amount of Li2S, which readily reacts with water, is substantially eliminated, the atmospheric stability of the sulfide solid electrolyte is improved, and the generation of hydrogen sulfide due to the reaction of moisture in the atmosphere with sulfur in the sulfide solid electrolyte can be suppressed.

[0044] In particular, it is preferable that the content ratio of Li to P is 2.77 to 3.38 in molar ratio, and the content ratio of N to P is 0.28 to 0.65 in molar ratio, because this can simultaneously improve reduction resistance, atmospheric stability, and ionic conductivity at 25°C.

[0045] The sulfide solid electrolyte contains Li, P, S, N, Ge, and the above element M, Li10 GeP2S 12 When it has a crystal phase of, from the viewpoint of reduction resistance, the content ratio of Li to P is preferably 5.01 or more and 5.61 or less in molar ratio, and the content ratio of N to P is preferably 0.0051 or more and 0.41 or less in molar ratio. Further, it is more preferable that the content ratio of Li to P is 5.06 or more and 5.19 or less in molar ratio, and the content ratio of N to P is 0.038 or more and 0.13 or less in molar ratio.

[0046] As the sulfide solid electrolyte, it preferably has a composition represented by the general formula (100−z)(yLi2S·(1−y)P2S5)·zLi α M β N (where 0 < z ≤ 40, 0.50 ≤ y ≤ 0.75). When the sulfide solid electrolyte has a composition represented by the above general formula, the reduction resistance can be further improved. Further, the initial Coulomb efficiency of the all-solid-state battery including the sulfide solid electrolyte can be increased.

[0047] In the above general formula, z is preferably more than 0 and 40 or less, more preferably 1 or more and 30 or less, still more preferably 1 or more and 5 or 10 or more and 30 or less, and even more preferably 1 or more and 5 or 10 or more and 25 or less. When z in the above general formula is in the range of more than 0 and 40 or less, the reduction resistance of the sulfide solid electrolyte can be further improved. When 10 ≤ z ≤ 40, so-called cross-linked sulfur P2S7 4- (S3P - S - PS3) decreases and substantially does not contain Li2S which is easy to react with water, so the air stability of the sulfide solid electrolyte is improved, and the generation of hydrogen sulfide due to the reaction between moisture in the air and S in the sulfide solid electrolyte can be suppressed. When 1 ≤ z ≤ 30, the ionic conductivity at 25°C can be increased more. When 1 ≤ z ≤ 5 or 10 ≤ z ≤ 30, the ionic conductivity at 25°C can be further increased. When 1 ≤ z ≤ 5 or 10 ≤ z ≤ 25, the ionic conductivity at 25°C can be increased even more.

[0048] In the above general formula, y is preferably 0.50 or more and 0.75 or less, and more preferably 0.67 or more and 0.70 or less. When the content ratios of Li2S and P2S5 in the sulfide solid electrolyte are within the above ranges, the ionic conductivity of the sulfide solid electrolyte at 25 °C is improved.

[0049] In the above general formula, α and β are numerical values that give a stoichiometric ratio according to the type of element M. The values of α and β are not particularly limited, but for example, 0.80 ≤ α ≤ 3.0 and 0.10 ≤ β ≤ 1.2 may be used. In particular, when the element M contains Al, α = 1.5 and β = 0.5 may be used.

[0050] When the sulfide solid electrolyte contains Ge, it preferably has a composition represented by the general formula (100 - z)Li 10 GeP2S 12 ·zLi α M β N (where 0 < z ≤ 50, and α and β are numerical values that give a stoichiometric ratio according to the type of element M). For example, when the element M contains Al, the sulfide solid electrolyte preferably has a composition represented by the general formula (100 - z)Li 10 GeP2S 12 ·zLi 3 / 2 Al 1 / 2 N (where 0 < z ≤ 50). When the sulfide solid electrolyte has such a composition, the ionic conductivity at 25 °C can be increased.

[0051] In the above general formula, z is more than 0 and 50 or less, preferably 1 or more and 45 or less, more preferably 3 or more and 35 or less, still more preferably 5 or more and 25 or less, and even more preferably 7 or more and 20 or less. When z in the above general formula is within the above range, the reduction resistance and the ionic conductivity at 25 °C can be further increased.

[0052] In the general formula above, α and β are numerical values ​​that give the stoichiometric ratio depending on the type of element M. The values ​​of α and β are not particularly limited, but for example, they may be 0.80 ≤ α ≤ 3.0 and 0.10 ≤ β ≤ 1.2. In particular, when element M includes Al, α = 1.5 and β = 0.5 may be used.

[0053] The ionic conductivity of the sulfide solid electrolyte at 25°C is 0.4 × 10⁻⁶. -3 Preferably, it is S / cm or higher, and 1.0 × 10 -3 It is more preferably S / cm or higher, and 1.5 × 10 -3 It is even more preferable if the ionic conductivity of the sulfide solid electrolyte at 25°C is the above value. By having the above value, the high-rate discharge performance of the all-solid-state battery equipped with the sulfide solid electrolyte can be improved.

[0054] Thus, the sulfide solid electrolyte can be suitably used as a solid electrolyte in an all-solid-state battery.

[0055] <All-solid-state battery> The all-solid-state battery comprises a negative electrode layer, a solid electrolyte layer, and a positive electrode layer. Figure 1 is a schematic cross-sectional view showing an all-solid-state battery in one embodiment of the present invention. The all-solid-state battery 10, which is a secondary battery, has a negative electrode layer 1 and a positive electrode layer 2 arranged via a solid electrolyte layer 3. The negative electrode layer 1 has a negative electrode substrate layer 4 and a negative electrode mixture layer 5, with the negative electrode substrate layer 4 being the outermost layer of the negative electrode layer 1. The positive electrode layer 2 has a positive electrode substrate layer 7 and a positive electrode mixture layer 6, with the positive electrode substrate layer 7 being the outermost layer of the positive electrode layer 2. In the all-solid-state battery 10 shown in Figure 1, the positive electrode mixture layer 6, solid electrolyte layer 3, negative electrode mixture layer 5, and negative electrode substrate layer 4 are stacked on the positive electrode substrate layer 7 in this order.

[0056] In this all-solid-state battery, the negative electrode layer 1, the solid electrolyte layer 3, the positive electrode layer 2, or a combination thereof, contains the sulfide solid electrolyte. Because the negative electrode layer 1, the solid electrolyte layer 3, the positive electrode layer 2, or a combination thereof, contains the sulfide solid electrolyte, the initial Coulomb efficiency is excellent. Since the sulfide solid electrolyte has excellent reduction resistance, it is preferable that the negative electrode layer 1 and / or the solid electrolyte layer 3 contain the sulfide solid electrolyte. With the above configuration, the effects of the present invention are further enhanced.

[0057] The all-solid-state battery may also use other solid electrolytes in addition to the sulfide solid electrolyte. The other solid electrolyte may be a sulfide solid electrolyte other than the sulfide solid electrolyte, or an oxide solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a pseudo-solid electrolyte.

[0058] Other sulfide solid electrolytes besides the aforementioned sulfide solid electrolytes are preferably those with high Li ion conductivity, such as Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S 2n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li δ XO ε (However, δ and ε are positive numbers, and X is one of P, Si, Ge, B, Al, Ga, or In.) Li 10 GeP2S 12 These are some examples. Among these, Li2S-P2S5 is preferred from the viewpoint of good lithium-ion conductivity, and xLi2S·(100-x)P2S5(70≦x≦80) is more preferred.

[0059] [Negative electrode layer] The negative electrode layer 1 comprises a negative electrode base layer 4 and a negative electrode mixture layer 5 laminated on the surface of the negative electrode base layer 4. The negative electrode layer 1 may have an intermediate layer (not shown) between the negative electrode base layer 4 and the negative electrode mixture layer 5.

[0060] (Negative electrode base material layer) The negative electrode substrate layer 4 is a conductive layer. The material of the negative electrode substrate layer 4 is not limited as long as it is a conductor. For example, 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, indium and alloys containing one or more of these, and stainless steel alloys can be used.

[0061] The lower limit of the average thickness of the negative electrode substrate layer 4 is preferably 3 μm, more preferably 5 μm, and even more preferably 8 μm. The upper limit of the average thickness of the negative electrode substrate layer 4 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By setting the average thickness of the negative electrode substrate layer 4 to be above the lower limit, the strength of the negative electrode substrate layer 4 can be sufficiently increased, so that the negative electrode layer 1 can be formed well. By setting the average thickness of the negative electrode substrate layer 4 to be below the upper limit, the volume of other components can be sufficiently secured.

[0062] (Negative electrode mixture layer) The negative electrode mixture layer 5 can be formed from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a negative electrode mixture or negative electrode composite containing the negative electrode active material and the sulfide solid electrolyte. The negative electrode mixture may optionally contain other solid electrolytes, conductive agents, binders, fillers, and other optional components besides the sulfide solid electrolyte.

[0063] <Negative electrode active material> Typically, materials capable of intercalating and releasing lithium ions are used as the negative electrode active material. Specific negative electrode active materials include, for example, Metals or metalloids such as Si and Sn; Metal oxides or metalloids such as Si oxides and Sn oxides; Polyphosphate compounds; Carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon); Examples include lithium metal composite oxides such as lithium titanate.

[0064] The lower limit of the negative electrode active material content in the negative electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the negative electrode active material content is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, particularly preferably 90% by mass, and may also be 95% by mass. By setting the negative electrode active material content within the above range, the electrical capacity of the all-solid-state battery can be increased.

[0065] <Negative electrode mixture or negative electrode composite> The above-mentioned negative electrode mixture is a mixture produced by mixing the negative electrode active material and the sulfide solid electrolyte using mechanical milling or the like. For example, a mixture of the negative electrode active material and the sulfide solid electrolyte can be obtained by mixing particulate negative electrode active material and particulate sulfide solid electrolyte. Examples of the above-mentioned negative electrode composites include composites having chemical or physical bonds between the negative electrode active material and the sulfide solid electrolyte, and composites in which the negative electrode active material and the sulfide solid electrolyte are mechanically combined. In these composites, the negative electrode active material and the sulfide solid electrolyte are present within a single particle, and examples include those in which the negative electrode active material and the sulfide solid electrolyte form an aggregated state, and those in which a film containing the sulfide solid electrolyte is formed on at least a part of the surface of the negative electrode active material. The above-mentioned negative electrode mixture or negative electrode complex may contain a solid electrolyte other than the sulfide solid electrolyte. The negative electrode active material and the sulfide solid electrolyte contained in the negative electrode mixture constitute a negative electrode mixture or negative electrode complex, thereby improving reduction resistance while maintaining high ionic conductivity, resulting in excellent initial Coulomb efficiency.

[0066] When the negative electrode mixture contains a solid electrolyte, the lower limit of the solid electrolyte content in the negative electrode mixture may be 5% by mass, and 10% by mass is preferred. The upper limit of the solid electrolyte content in the negative electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By setting the solid electrolyte content within the above range, the electrical capacity of the all-solid-state battery can be increased.

[0067] When the negative electrode layer contains the sulfide solid electrolyte, the lower limit of the sulfide solid electrolyte content in the negative electrode mixture may be 5% by mass, and is preferably 10% by mass. The upper limit of the sulfide solid electrolyte content in the negative electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By setting the sulfide solid electrolyte content in the negative electrode mixture within the above range, the initial Coulomb efficiency of the all-solid-state battery can be further improved when the negative electrode layer contains the sulfide solid electrolyte.

[0068] <Other optional ingredients> The conductive agent described above is not particularly limited. Examples of such conductive agents include natural or artificial graphite, furnace black, acetylene black, Ketjen black and other carbon blacks, metals, and conductive ceramics. The conductive agent can be in powder or fibrous form. The content of the conductive agent in the negative electrode mixture can be, for example, 0.5% by mass or more and 30% by mass or less. The negative electrode mixture does not need to contain a conductive agent.

[0069] The above-mentioned binder (binding agent) is not particularly limited. Examples include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide, and polyacrylic acid; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0070] The above-mentioned fillers are not particularly limited. Examples of main components of fillers include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and carbon.

[0071] The lower limit of the average thickness of the negative electrode mixture layer 5 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the negative electrode mixture layer 5 is preferably 1000 μm, more preferably 500 μm, and even more preferably 200 μm. By setting the average thickness of the negative electrode mixture layer 5 to or above the above lower limit, an all-solid-state battery with high energy density can be obtained. By setting the average thickness of the negative electrode mixture layer 5 to or below the above upper limit, an all-solid-state battery with a negative electrode that has excellent high-rate discharge performance and high active material utilization can be obtained.

[0072] (Middle class) The above-mentioned intermediate layer is a coating layer on the surface of the negative electrode substrate layer 4, and by containing conductive particles such as carbon particles, it reduces the contact resistance between the negative electrode substrate layer 4 and the negative electrode mixture layer 5. The composition of the intermediate layer is not particularly limited and can be formed, for example, by a composition containing a resin binder and conductive particles.

[0073] [Positive electrode layer] The positive electrode layer 2 comprises a positive electrode base layer 7 and a positive electrode mixture layer 6 laminated on the surface of the positive electrode base layer 7. Similar to the negative electrode layer 1, the positive electrode layer 2 may have an intermediate layer between the positive electrode base layer 7 and the positive electrode mixture layer 6. This intermediate layer can have the same configuration as the intermediate layer of the negative electrode layer 1.

[0074] (Positive electrode substrate layer) The positive electrode substrate layer 7 can have the same configuration as the negative electrode substrate layer 4. The material of the positive electrode substrate layer 7 is not limited as long as it is a conductor. For example, 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, indium and alloys containing one or more of these, and stainless steel alloys can be used.

[0075] The lower limit of the average thickness of the positive electrode substrate layer 7 is preferably 3 μm, more preferably 5 μm. The upper limit of the average thickness of the positive electrode substrate layer 7 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By setting the average thickness of the positive electrode substrate layer 7 to be above the lower limit, the strength of the positive electrode substrate layer 7 can be sufficiently increased, thereby enabling good formation of the positive electrode layer 2. By setting the average thickness of the positive electrode substrate layer 7 to be below the upper limit, sufficient volume for other components can be secured.

[0076] (Positive electrode mixture layer) The positive electrode mixture layer 6 can be formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture may contain a positive electrode mixture or positive electrode composite containing a positive electrode active material and a solid electrolyte. As the solid electrolyte, a sulfide solid electrolyte may be used, but it is more preferable to use a solid electrolyte with high oxidation resistance. The positive electrode mixture forming the positive electrode mixture layer 6, like the negative electrode mixture, may contain optional components such as a solid electrolyte, conductive agent, binder, and filler as needed. The positive electrode mixture layer may also be in a form that does not contain a solid electrolyte.

[0077] <Cathode active material> As the positive electrode active material contained in the positive electrode mixture layer 6, known materials commonly used in all-solid-state batteries can be used. For example, Li x MeO y (Me represents at least one transition metal) A composite oxide (Li having a layered α-NaFeO2 type crystal structure) x CoO2, Li x KiO2, Li x MnO3, Li x Ni α Co (1-α) O2, Li x Ni α Mn β Co (1-α-β) Li such as O2, which has a spinel-type crystal structure x Mn2O4, Li x Ni α Mn (2-α) O4, etc., Li w Me x (AO y ) zExamples of polyanion compounds represented by (Me represents at least one transition metal, and A represents, for example, P, Si, B, V, etc.) include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one of these compounds may be used alone, or two or more may be used in mixture form.

[0078] Positive electrode active materials include 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, Li-Ba, and compounds other than those represented by the above general formula, such as MnO2, FeO2, TiO2, V2O5, V6O 13 Materials with a redox potential greater than that of the negative electrode material, such as TiS2, can be used.

[0079] The lower limit of the content of positive electrode active material in the positive electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the content of positive electrode active material is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, particularly preferably 90% by mass, and may also be 95% by mass. By setting the content of positive electrode active material within the above range, the electrical capacity of the all-solid-state battery can be increased.

[0080] <Positive electrode mixture or positive electrode composite> The above-mentioned positive electrode mixture is a mixture produced by mixing positive electrode active material and solid electrolyte, etc., using mechanical milling or the like, similar to the case of the negative electrode. For example, a mixture of positive electrode active material and solid electrolyte, etc., can be obtained by mixing particulate positive electrode active material and particulate solid electrolyte, etc. Similar to the case of the negative electrode, the positive electrode composites mentioned above include composites having chemical or physical bonds between the positive electrode active material and the solid electrolyte, and composites in which the positive electrode active material and the solid electrolyte are mechanically combined. The above composites have the positive electrode active material and the solid electrolyte present within a single particle, and examples include those in which the positive electrode active material and the solid electrolyte form an aggregated state, and those in which a film containing the solid electrolyte is formed on at least a part of the surface of the positive electrode active material. The positive electrode active material and solid electrolyte contained in the positive electrode mixture constitute a positive electrode mixture or positive electrode complex, thereby maintaining high ionic conductivity. While a sulfide solid electrolyte may be used as the solid electrolyte, it is more preferable to use a solid electrolyte with high oxidation resistance.

[0081] When the positive electrode mixture contains a solid electrolyte, the lower limit of the solid electrolyte content may be 5% by mass, and 10% by mass is preferred. The upper limit of the solid electrolyte content in the positive electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By setting the solid electrolyte content within the above range, the electrical capacity of the all-solid-state battery can be increased.

[0082] The lower limit of the average thickness of the positive electrode mixture layer 6 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the positive electrode mixture layer 6 is preferably 1000 μm, more preferably 500 μm, and even more preferably 200 μm. By setting the average thickness of the positive electrode mixture layer 6 to be above the lower limit, an all-solid-state battery with high energy density can be obtained. By setting the average thickness of the positive electrode mixture layer 6 to be below the upper limit, an all-solid-state battery with excellent high-rate discharge performance and a negative electrode with high active material utilization can be obtained.

[0083] [Solid electrolyte layer] The solid electrolyte layer 3 contains an electrolyte for the solid electrolyte layer. In addition to the sulfide solid electrolyte described above, other examples of electrolytes for the solid electrolyte layer include oxide solid electrolytes, other sulfide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes. Among these, sulfide solid electrolytes are preferred, and more preferred, from the viewpoint of good ionic conductivity and ease of interface formation. By containing the sulfide solid electrolyte in the solid electrolyte layer 3, the reduction resistance of the solid electrolyte layer is improved while maintaining high ionic conductivity, thereby improving the initial Coulomb efficiency of the all-solid-state battery.

[0084] The electrolyte for the solid electrolyte layer may have a crystalline structure or may be amorphous without a crystalline structure. Oxides such as Li3PO4, halogens, halogen compounds, etc., may be added to the electrolyte for the solid electrolyte layer.

[0085] The lower limit of the average thickness of the solid electrolyte layer 3 is preferably 1 μm, and more preferably 3 μm. The upper limit of the average thickness of the solid electrolyte layer 3 is preferably 50 μm, and more preferably 20 μm. By setting the average thickness of the solid electrolyte layer 3 to be above the lower limit, it becomes possible to reliably insulate the positive electrode and the negative electrode. By setting the average thickness of the solid electrolyte layer 3 to be below the upper limit, it becomes possible to increase the energy density of the all-solid-state battery.

[0086] [Manufacturing method for all-solid-state batteries] The method for manufacturing the all-solid-state battery mainly comprises, for example, a sulfide solid electrolyte manufacturing step for producing the sulfide solid electrolyte, a negative electrode mixture manufacturing step, an electrolyte manufacturing step for the solid electrolyte layer, a positive electrode mixture manufacturing step, and a lamination step for laminating the negative electrode layer, the solid electrolyte layer, and the positive electrode layer.

[0087] (Process for producing sulfide solid electrolytes) In this process, for example, the sulfide solid electrolyte is prepared by the following procedure. (1) Nitride (Li 3 / 2 Al 1 / 2 Preparation of N) After mixing Li3N and AlN in a mortar and pestle, they are formed into pellets. Next, heat treatment is performed, Li 3 / 2 Al 1 / 2 N is produced. Note that "Li" is generally used. 3 / 2 Al 1 / 2 "N" is written as "Li3AlN2". (2) Preparation of sulfide solid electrolytes The above Li in a predetermined molar ratio 3 / 2 Al 1 / 2 After mixing N, Li2S, and P2S5 in a mortar or the like, a sulfide solid electrolyte precursor is prepared. Methods for preparing the sulfide solid electrolyte precursor include, for example, mechanical milling and molten-quenching. When preparing a sulfide solid electrolyte, the sulfide solid electrolyte can be produced by first preparing a sulfide solid electrolyte precursor and then heat-treating it at a temperature above the crystallization temperature.

[0088] The crystallization temperature mentioned above can be determined by measurement using a differential scanning thermometer (DSC). For example, Li7P3S 11 To obtain a crystalline structure, the heat treatment temperature is preferably between 250°C and 400°C, and to obtain a β-Li3PS4 crystalline structure, the heat treatment temperature is preferably between 200°C and 400°C. This is because if heat treatment is performed at a high temperature such as 500°C, there is a possibility of a phase transition to the stable phase Li4P2S6. For example, to obtain a first crystalline structure having diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5° in X-ray diffraction measurements using CuKα rays, the heat treatment temperature is preferably between 250°C and 400°C.

[0089] In the above manufacturing process, we described the case of producing a sulfide solid electrolyte containing Al as element M. However, a sulfide solid electrolyte having a crystalline structure can be produced by the same method as described above, containing 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 N. For example, as the nitride in the above manufacturing process, Li 3 / 2 Al1 / 2 Replace N with Li 3 / 2 B 1 / 2 N or Li 5 / 3 Si 1 / 3 N, Li 9 / 5 Si 3 / 10 By using elements such as B and Si and N, a sulfide solid electrolyte containing these elements can be produced. As nitrides that can be used in the above production process, in addition to those described above, LiMgN, LiCaN, LiHf 1 / 2 N, Li 3 / 2 Sc 1 / 2 N, LiZr 1 / 2 N, Li 5 / 3 Ti 1 / 3 N, Li 4 / 3 Ta 1 / 3 N, Li 7 / 4 Ta 1 / 4 N, Li 7 / 4 Nb 1 / 4 N, Li 3 / 2 W 1 / 4 N, Li 7 / 4 V 1 / 4 N etc. can be exemplified.

[0090] Also, in the above production process, a nitride composed of elements M, Li, and N was used as the starting material, but the production method of the sulfide solid electrolyte of this embodiment is not limited to this.

[0091] In the above production process, a Li2S-P2S5-based sulfide solid electrolyte was used as an example, but LGPS-type or argyrodite-type sulfide solid electrolytes can also be produced by a similar production process. For example, in the above production process, Li 3 / 2 Al 1 / 2 N, Li2S, and P2S5 were used, but a Ge-containing LGPS-type sulfide solid electrolyte containing Ge may be produced by further adding a Ge-containing compound such as GeS2. More specifically, after mixing starting materials in a predetermined molar ratio in a mortar or the like, mechanical milling methods, for example, ball milling treatment or vibration milling treatment, etc. are performed to produce a sulfide solid electrolyte precursor. Then, the sulfide solid electrolyte can be produced by heat-treating the precursor at a predetermined temperature or higher. For example, Li 10 GeP2S 12 When preparing a sulfide solid electrolyte having a crystalline structure, the heat treatment temperature is preferably 300°C to 1000°C, more preferably 350°C to 700°C, even more preferably 400°C to 650°C, and particularly preferably 450°C to 600°C. The heat treatment may be carried out under a reduced pressure atmosphere or under an inert gas atmosphere.

[0092] (Negative electrode mixture preparation process) In this step, a negative electrode mixture is prepared for forming the negative electrode layer. If the negative electrode mixture contains a mixture or complex of a negative electrode active material and the sulfide solid electrolyte, this step includes mixing the negative electrode active material and the sulfide solid electrolyte using, for example, a mechanical milling method, to prepare a mixture or complex of the negative electrode active material and the sulfide solid electrolyte.

[0093] (Electrolyte fabrication process for solid electrolyte layer) In this process, the electrolyte for the solid electrolyte layer is prepared. In this process, the electrolyte for the solid electrolyte layer can be obtained by processing a predetermined material by mechanical milling. Alternatively, the electrolyte for the solid electrolyte layer may be prepared by heating the predetermined material for the solid electrolyte layer above its melting temperature using a melt-and-cool method, melting and mixing the two in a predetermined ratio, and then rapidly cooling. Other methods for synthesizing the electrolyte for the solid electrolyte layer include, for example, a solid-phase method of firing under reduced pressure, a liquid-phase method such as dissolution extraction, a gas-phase method (PLD), and firing under an argon atmosphere after mechanical milling. If the electrolyte for the solid electrolyte layer is a sulfide solid electrolyte, the sulfide solid electrolyte preparation process described above is performed in the process for preparing the electrolyte for the solid electrolyte layer.

[0094] (Cathode mixture preparation process) In this process, a positive electrode mixture is prepared for forming the positive electrode layer. There are no particular restrictions on the method for preparing the positive electrode mixture, and it can be appropriately selected according to the purpose. Examples include compression molding of the positive electrode active material, mechanical milling of a predetermined material of the positive electrode mixture, and sputtering of the positive electrode active material using a target material. If the positive electrode mixture contains a mixture or composite of the positive electrode active material and the sulfide solid electrolyte, this process includes mixing the positive electrode active material and the sulfide solid electrolyte using, for example, a mechanical milling method, to prepare a mixture or composite of the positive electrode active material and the sulfide solid electrolyte.

[0095] (Lamination process) In this process, a negative electrode layer having a negative electrode substrate layer and a negative electrode mixture layer, a solid electrolyte layer, and a positive electrode layer having a positive electrode substrate layer and a positive electrode mixture layer are laminated. In this process, the negative electrode layer, solid electrolyte layer, and positive electrode layer may be formed sequentially or in reverse order, and the order of formation of each layer is not particularly limited. The negative electrode layer is formed by pressure molding of the negative electrode substrate and negative electrode mixture, the solid electrolyte layer is formed by pressure molding of the electrolyte for the solid electrolyte layer, and the positive electrode layer is formed by pressure molding of the positive electrode substrate and positive electrode mixture.

[0096] The negative electrode layer, solid electrolyte layer, and positive electrode layer may be laminated by pressure molding the negative electrode substrate, negative electrode mixture, electrolyte for the solid electrolyte layer, positive electrode substrate, and positive electrode mixture at the same time. Alternatively, the positive electrode layer, negative electrode layer, or these layers may be pre-formed and laminated by pressure molding with the solid electrolyte layer.

[0097] [Other embodiments] The present invention is not limited to the embodiments described above, and can be implemented in various modified and improved forms in addition to those described above.

[0098] The configuration of the all-solid-state battery according to the present invention is not particularly limited, and may include other layers other than the negative electrode layer, positive electrode layer, and solid electrolyte layer, such as an intermediate layer or an adhesive layer.

[0099] <Examples> The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0100] [Example 1] The following process results in 99(0.70Li2S·0.30P2S5)·1Li 3 / 2 Al 1 / 2 N was synthesized. Li3N and AlN were weighed in a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 750°C for 1 hour. 3 / 2 Al 1 / 2 N was fabricated. Li was fabricated. 3 / 2 Al 1 / 2 N's main phase was determined by XRD measurement to be Li 3 / 2 Al 1 / 2 We confirmed that it is N. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li3 / 2Al 1 / 2 N was weighed in a molar ratio of 69.3:29.7:1.0 and then mixed in a mortar. This mixed sample was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 45 hours at a rotational speed of 510 rpm using a planetary ball mill (FRITSCH, model number Premium line P-7). Heat treatment was performed for 2 hours to obtain the sulfide solid electrolyte of Example 1. This heat treatment was performed at a temperature above the crystallization temperature but not exceeding 100°C below the crystallization temperature. The crystallization temperature was determined by measuring DSC. DSC measurement was performed under the following conditions: a DSC device (Rigaku, Thermo Plus DSC8230) was used, a sealed SUS pan was used, and the temperature was raised from room temperature to 400°C at a rate of 10°C / min.

[0101] [Examples 2 to 9] The chemical formula of the sulfide solid electrolyte is (100-z)(0.70Li2S·0.30P2S5)·zLi 3 / 2 Al 1 / 2The sulfide solid electrolytes of Examples 2 to 9 were synthesized in the same manner as in Example 1, except that the value of z in N was changed to 5, 7, 10, 15, 20, 25, 30, and 40.

[0102] [Example 10] Li2S, P2S5, and Li are used as raw materials for sulfide solid electrolytes. 3 / 2 Al 1 / 2 N is Li2S:P2S5:Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Example 10 was synthesized in the same manner as in Example 1, except that the weighing was done so that N = 67.5: 22.5: 10.0 (mol%).

[0103] [Example 11] Li2S, P2S5, and Li are used as raw materials for sulfide solid electrolytes. 3 / 2 Al 1 / 2 N is Li2S:P2S5:Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Example 11 was synthesized in the same manner as in Example 1, except that the weighing was done so that N = 35.0:35.0:30.0 (mol%).

[0104] [Example 12] Li2S, P2S5, and Li are used as raw materials for sulfide solid electrolytes. 3 / 2 Al 1 / 2 N is Li2S:P2S5:Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Example 12 was synthesized in the same manner as in Example 1, except that the weighing was done so that N = 53.6: 26.4: 20.0 (mol%).

[0105] [Example 13] Li2S, P2S5, and Li are used as raw materials for sulfide solid electrolytes. 3 / 2 Al 1 / 2 N is Li2S:P2S5:Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Example 13 was synthesized in the same manner as in Example 1, except that the weighing was done so that N = 50.3: 24.7: 25.0 (mol%).

[0106] [Example 14] Li2S, P2S5, and Li are used as raw materials for sulfide solid electrolytes. 3 / 2 Al 1 / 2 N is Li2S:P2S5:Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Example 14 was synthesized in the same manner as in Example 1, except that the weighing was performed so that N = 46.9: 23.1: 30 (mol%).

[0107] [Examples 15 to 18] Li3N and BN were weighed in a molar ratio of 1.1:1, mixed in a mortar, pelletized, and then heat-treated at 800°C for 10 minutes. 3 / 2 B 1 / 2 N was fabricated. Li was fabricated. 3 / 2 B 1 / 2 N's main phase was determined by XRD measurement to be Li 3 / 2 B 1 / 2 We confirmed that it is N. Next, Li 3 / 2 Al 1 / 2 Instead of N, use the above Li 3 / 2 B 1 / 2 Using N, the composition formula of the sulfide solid electrolyte is (100-z)(0.70Li2S·0.30P2S5)·zLi 3 / 2 B 1 / 2 The sulfide solid electrolytes of Examples 15 to 18 were synthesized in the same manner as in Example 1, except that the value of z in N was changed to 1, 10, 20, and 30. [Examples 19 to 23] Li3N and Si3N4 were weighed in a molar ratio of 5.1:1, mixed in a mortar, pelletized, and then heat-treated at 800°C for 10 minutes. 5 / 3 Si 1 / 3 N was fabricated. Li was fabricated. 5 / 3 Si 1 / 3 N's main phase was determined by XRD measurement to be Li 5 / 3 Si 1 / 3 We confirmed that it is N. Next, Li 3 / 2 Al 1 / 2 Instead of N, the above Li 5 / 3 Si 1 / 3Using N, the composition formula of the sulfide solid electrolyte is (100-z)(0.70Li2S·0.30P2S5)·zLi 5 / 3 Si 1 / 3 The sulfide solid electrolytes of Examples 19 to 23 were synthesized in the same manner as in Example 1, except that the value of z in N was changed to 1.5, 15, 20, 30, and 45.

[0108] [Comparative Example 1] Li is used as a raw material for sulfide solid electrolytes. 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Comparative Example 1 was synthesized in the same manner as in Example 1, except that N was not used.

[0109] [Reference example 1] 75Li2S·25P2S5 (Li3PS4) was synthesized by mechanical milling. In an argon-atmosphere glove box with a dew point of -50°C or lower, Li2S and P2S5, the raw materials for the sulfide solid electrolyte, were weighed in a ratio of Li2S:P2S5 = 75:25 (mol%) and then mixed in an agate mortar. The mixture was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 45 hours at a rotational speed of 510 rpm using a planetary ball mill (FRITSCH, model number Premium line P-7). The sulfide solid electrolyte of Reference Example 1 was obtained by the above process.

[0110] [Reference example 2] Li 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Reference Example 2 was synthesized in the same manner as in Example 1, except that Li3N was used instead of N, and the value of z in the composition formula (100-z)(0.70Li2S·0.30P2S5)·zLi3N of the sulfide solid electrolyte was changed to 20.

[0111] [Example 24] The following process results in 87.6(Li10GeP2S12)·12.4Li 3 / 2 Al 1 / 2 N was synthesized. Li3N and AlN were weighed in a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 750°C for 1 hour. 3 / 2 Al 1 / 2 N was created. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), GeS2 (99.99%, High Purity Chemical Laboratory) and Li 3 / 2 Al 1 / 2 N was weighed in a molar ratio of 5:1:1:0.14 and then mixed in a mortar. This mixed sample was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 40 hours at a rotational speed of 370 rpm using a planetary ball mill (FRITSCH, model number Premium line P-7). Subsequently, it was heat-treated at 550 °C for 8 hours to obtain the sulfide solid electrolyte of Example 24.

[0112] [Examples 25, 26, and 2020] Composition formula of sulfide solid electrolyte (100-z)(Li 10 GeP2S 12 )·zLi 3 / 2 Al 1 / 2 The sulfide solid electrolytes of Example 25, Example 26, and Comparative Example 2 were synthesized in the same manner as in Example 1, except that the value of z in N was changed to 30.2, 42.5, and 60.9. [Comparative Example 3] Li is used as a raw material for sulfide solid electrolytes. 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Comparative Example 3 was synthesized in the same manner as in Example 24, except that N was not used. [Reference example 3] Li is used as a raw material for sulfide solid electrolytes. 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Reference Example 3 was synthesized in the same manner as in Example 24, except that Li2O (99%, High Purity Chemical Laboratory) was used instead of N, and the weighing was performed so that Li2S:P2S5:GeS2:Li2O = 4.86:1:1:0.14 (mol%). [Reference example 4] Li is used as a raw material for sulfide solid electrolytes. 3 / 2 Al 1 / 2 The sulfide solid electrolyte of Reference Example 4 was synthesized in the same manner as in Example 24, except that Al2S3 (98%, Aldrich) was used instead of N, and the weighing was performed so that Li2S:P2S5:GeS2:Al2S3 = 5:1:0.93:0.035 (mol%).

[0113] [evaluation] (1)XRD analysis X-ray diffraction measurements were performed using the following method. Using an airtight X-ray diffraction sample holder, the sulfide solid electrolyte powders of the examples and comparative examples were packed under an argon atmosphere with a dew point of -50°C or lower. Powder X-ray diffraction measurements were performed using an X-ray diffractometer (Rigaku "miniFlex II"). The radiation source was CuKα, the tube voltage was 30kV, and the tube current was 15mA. The diffracted X-rays were passed through a 30μm thick Kβ filter and detected by a high-speed one-dimensional detector (model: D / teX Ultra2). The sampling width was 0.01°, the scan speed was 5° / min, the diverging slit width was 0.625°, the receiving slit width was 13mm (OPEN), and the scattering slit width was 8mm.

[0114] Figure 2 shows the X-ray diffraction (XRD) spectra of Examples 1 to 3, 6, 8, 9, 10, 11 and Comparative Example 1 in the range of 2θ = 10° to 40°. Table 1 shows the crystal structures identified from the XRD spectra of Examples 1 to 23, Comparative Example 1 and Reference Example 2.

[0115] Figure 8 shows the X-ray diffraction (XRD) spectra of Example 24, Comparative Example 3, and Reference Examples 3 and 4 in the range of 2θ = 10° to 60°. Table 2 shows the crystal structures identified from the XRD spectra of Examples 24 to 26, Comparative Examples 2 and 3, and Reference Examples 3 and 4. In Table 2, "Unknown" indicates that a diffraction peak was observed that could not be used to identify the crystal structure.

[0116] (2) Raman spectroscopy The Raman spectrum was measured using the following method. A laser Raman spectrophotometer ("LabRAM HR Revolution" manufactured by Horiba, Ltd.) was used, with an excitation laser wavelength of 532 nm (YAG laser) and a grating of 600 gr / mm, at 100 cm². -1 From 1800cm -1 Raman spectroscopy measurements were performed in the wavenumber range.

[0117] Figure 3 shows the Raman spectra of Examples 2 to 6 and Comparative Example 1. Table 1 shows the molecular structures identified from the Raman spectra of Examples 1 to 23, Comparative Example 1 and Reference Example 2.

[0118] (3) Ionic conductivity (σ) The ionic conductivity (σ) was determined at 25°C by measuring the AC impedance using the method described above with a Bio-Logic VMP-300.

[0119] For Examples 24 to 26, Comparative Examples 2 and 3, and Reference Examples 3 and 4, the ionic conductivity was also measured at temperatures of -30°C, -20°C, -10°C, 0°C, and 50°C, and the activation energy was calculated using the Arrhenius equation.

[0120] Figure 4 shows the ionic conductivity at 25°C for Examples 1 to 9 and Comparative Example 1, and Table 1 shows the ionic conductivity at 25°C for Examples 1 to 23, Comparative Example 1 and Reference Example 2.

[0121] Table 2 shows the ionic conductivity and activation energy at 25°C for Examples 24 to 26, Comparative Examples 2 and 3, and Reference Examples 3 and 4.

[0122] (4) Initial Coulomb efficiency and charge / discharge performance (4-1) Preparation of positive electrode active material A LiNbO3 precursor solution was prepared by dissolving metallic Li in super-dehydrated ethanol, followed by dissolving niobethoxide (Nb(OC2H5)5). Using a rolling flow coating apparatus (FD-MP-01F) manufactured by Powrec, LiNi 0.8 Co 0.15 Al 0.05O2(NCA) particles were coated with a LiNbO3 precursor. LiNbO3-coated NCA was prepared by heat-treating the LiNbO3-coated NCA at 350°C for 1 hour. This LiNbO3-coated NCA was used as the cathode active material.

[0123] (4-2) Fabrication of all-solid-state battery cells (Li-NCA half cells) LiNbO3-coated NCA and the sulfide solid electrolyte (Li3PS4) from Reference Example 1 were weighed in a ratio of LiNbO3-coated NCA:Li3PS4 = 70:30 (mass%) and then mixed in an agate mortar. The sulfide solid electrolyte from Example 1 was placed into a powder molding machine with an inner diameter of 10 mm and then pressure-molded using a hydraulic press. After the pressure was released, the NCA-Li3PS4 mixed powder was placed on one side of the solid electrolyte layer from Example 1 and pressure-molded at 360 MPa per sample area for 5 minutes. After the pressure was released, a metallic Li foil was bonded to the opposite side of the sulfide solid electrolyte layer from Example 1 and pressure-molded to obtain a laminate of the positive electrode mixture layer, the sulfide solid electrolyte layer from Example 1, and the metallic Li foil. This laminate was sealed under reduced pressure in an aluminum laminate cell and compressed using a stainless steel plate to obtain an all-solid-state battery cell (Li-NCA half cell).

[0124] Except for replacing the sulfide solid electrolyte of Example 1 with the sulfide solid electrolyte of Examples 2, 4, and Comparative Example 1, the same procedure as in Example 1 was followed to obtain all-solid-state battery cells (Li-NCA half cells) equipped with the sulfide solid electrolytes of Examples 2, 4, and Comparative Example 1.

[0125] (4-3) Charge and Discharge Test The above-mentioned all-solid-state battery cell (Li-NCA half-cell) was subjected to charge-discharge tests under the following conditions. The charge-discharge tests were performed in a constant temperature chamber at 50°C. Charging was performed using constant current constant voltage (CCCV) charging with a charging current of 0.125 mA / cm² and a maximum charging voltage of 4.35 V. Charging was terminated when the charging current reached 0.0625 mA / cm². Discharging was performed using constant current (CC) discharge with a discharge current of 0.125 mA / cm² and a discharge termination voltage of 2.85 V. The rest period between charging and discharging was set to 30 minutes. The percentage of the initial discharge capacity relative to the initial charge amount was calculated as the "initial Coulomb efficiency (%)".

[0126] Figure 5 shows the initial charge-discharge performance of Example 1, Example 2, Example 4, and Comparative Example 1. Table 1 shows the initial Coulomb efficiency (%) of Example 1, Example 2, Example 4, and Comparative Example 1.

[0127] (5) Reduction resistance of sulfide solid electrolytes (5-1) Evaluation test using cells for evaluating resistance to reduction In a glove box with an argon atmosphere and a dew point of -50°C or lower, the sulfide solid electrolyte of Example 1 and SUS316L powder were weighed in a mass ratio of 1:4 and then mixed in an agate mortar. The sulfide solid electrolyte (Li3PS4) of Reference Example 1 was placed into a powder molding machine with an inner diameter of 10 mm and then pressure-molded using a hydraulic press. After the pressure was released, the mixed powder of the SUS316 powder and the sulfide solid electrolyte powder of Example 1 was placed on one side of the Li3PS4 layer and pressure-molded at 360 MPa for 5 minutes. After the pressure was released, a metallic Li foil was bonded to the opposite side of the Li3PS4 layer and pressure-molded to obtain a laminate of the sulfide solid electrolyte mixture layer of Example 1, the Li3PS4 layer, and the metallic Li foil. This laminate was sealed under reduced pressure in an aluminum laminate cell and compressed using a stainless steel plate to obtain a cell for evaluating reduction resistance, in which the sulfide solid electrolyte mixture layer of Example 1 was used as the working electrode and metallic Li foil as the counter electrode. The charging test conditions were: measurement temperature 50°C, constant current constant voltage (CCCV) charging, and charging current 0.1 mA / cm². 2The minimum charging potential was set to 0.01V, and the total charging time was set to 100 hours. Here, the reaction in which the sulfide solid electrolyte mixture layer of Example 1 is reduced is defined as "charging". The amount of electricity charged 20 hours after the start of charging was defined as the reductive decomposition capacity (mAh / g) of the sulfide solid electrolyte after 20 hours. Since the SUS316L powder is stable at a potential of 0V vs. Li / Li+, the only redox species is the sulfide solid electrolyte. Therefore, the amount of electricity flowing through this evaluation cell represents the amount of reductive decomposition of the sulfide solid electrolyte. The reduction resistance of the sulfide solid electrolytes in Examples 2, 4, 8 to 17, 19, 20, 22 and Comparative Example 1 was evaluated using a similar procedure.

[0128] Table 1 shows the reductive decomposition capacity of the sulfide solid electrolytes in Examples 1, 2, 4, 8 to 17, 19, 20, 22 and Comparative Example 1 20 hours after the start of charging.

[0129] (5-2) Evaluation test using all-solid-state battery cells (Li-Gr half-cells) The sulfide solid electrolytes of Examples 24 to 26, Comparative Examples 2 and 3, and Reference Examples 3 and 4 were evaluated for their reduction resistance using the procedure described below.

[0130] Graphite particles (Gr) and the sulfide solid electrolyte (Li) from Example 24 10.21 GeP2Al 0.07 S 12 N 0.14 ) to, Gr:Li 10.21 GeP2Al 0.07 S 12 N 0.14 After weighing the mixture to a ratio of 60:40 (mass%), it was mixed in an agate mortar. Li3PS4 was placed into a powder molder with an inner diameter of 10 mm, and then pressure molded using a hydraulic press. After releasing the pressure, Gr-Li was added to one side of the Li3PS4 layer. 10.21 GeP2Al 0.07 S 12 N 0.14The mixed powder was added and pressure molded. After the pressure was released, a metallic Li foil was bonded to the opposite side of the Li3PS4 layer and pressure molded to obtain a laminate of the sulfide solid electrolyte mixture layer, the Li3PS4 solid electrolyte layer, and the metallic Li foil of Example 24. This laminate was sealed under reduced pressure in an aluminum laminate cell and compressed using a stainless steel plate to obtain an all-solid-state battery cell (Li-Gr half cell) in which the sulfide solid electrolyte mixture layer of Example 24 was the working electrode and the metallic Li foil was the counter electrode.

[0131] Except for replacing the sulfide solid electrolyte of Example 24 with the sulfide solid electrolyte of Examples 25, 26, and Comparative Example 3, the same procedure as in Example 24 was followed to obtain all-solid-state battery cells (Li-Gr half-cells) equipped with the sulfide solid electrolytes of Examples 25, 26, and Comparative Example 3.

[0132] The above-mentioned all-solid-state battery cell (Li-Gr half-cell) underwent a discharge test (lithiation of Gr) under the following conditions. The discharge test was performed in a constant temperature bath at 50°C. The discharge current was 0.125 mA / cm². 2 Then, constant current (CC) discharge was performed. A graph (dQ / dV curve) showing the relationship between the differential value dQ / dV, obtained by differentiating the discharge capacity Q with respect to voltage V, and the voltage V was plotted.

[0133] Figure 9 shows the dQ / dV curves for Examples 24 to 26 and Comparative Example 3. Table 2 shows the dQ / dV = -100mAhg for Examples 24 to 26 and Comparative Example 3. -1 V -1 The voltage V value at this point is shown. Furthermore, from Figure 9, it can be seen that the change in dQ / dV is large around 0.4V. The lithiation potential of Gr is approximately 0.1V vs Li / Li + Therefore, the change in dQ / dV around 0.4V is presumed to be due to the reductive decomposition of the sulfide solid electrolyte. Consequently, the dQ / dV of the all-solid-state battery cell (Li-Gr half cell) in this embodiment is -100mAhg -1 V -1 A shift in the voltage V value towards the negative side indicates that the reduction decomposition potential of the sulfide solid electrolyte has shifted towards the negative side, i.e., its resistance to reduction has improved.

[0134] (6) Evaluation of atmospheric stability To evaluate the chemical stability of sulfide solid electrolytes in air, the amount of hydrogen sulfide generated was measured. In a glove box with an argon atmosphere and a dew point of -50°C or lower, 100 mg of sulfide solid electrolyte powder from the examples and comparative examples was uniaxially compressed for 5 minutes at 360 MPa per sample area using a powder molder with an inner diameter of 10 mm to obtain pellets. The obtained pellets were then placed in a sealed desiccator (effective volume 2100 cm³). 3 The device was placed inside a room with a temperature of 20°C and a relative humidity of approximately 90%, and the amount of hydrogen sulfide generated was measured using a hydrogen sulfide sensor (TPA-5200E). The measurement was terminated when the hydrogen sulfide sensor's detection limit of 50 ppm was reached or when 40 minutes had elapsed. Amount of hydrogen sulfide generated per gram from solid electrolyte V(cm) 3 The values ​​per g are the obtained concentration C (ppm) and the effective volume L (cm³) of the desiccator. 3 The result was obtained using the following formula, with the mass m(g) of the pellets. V(cm 3 / g) = C × L × 10 -6 / m

[0135] Figures 6 and 7 show the atmospheric exposure time (minutes) and hydrogen sulfide generation amount (cm³) for the sulfide solid electrolyte pellets of the above examples and comparative examples. 3 This graph shows the relationship with / g). Figure 6 shows the amount of hydrogen sulfide generated up to 20 minutes of exposure to air in Example 4, Example 6, and Comparative Example 1, while Figure 7 shows the amount of hydrogen sulfide generated up to 40 minutes of exposure to air in Example 6 and Reference Example 1.

[0136] [Table 1]

[0137] As shown in Table 1, the sulfide solid electrolytes of the examples, which contain one of the elements M (Al, B, or Si) and N, and have a crystalline structure, showed suppressed reductive decomposition capacity 20 hours after the start of charging and superior initial Coulombic efficiency compared to the sulfide solid electrolyte of Comparative Example 1. The sulfide solid electrolytes of Examples 1, 2, 4 to 8, 10, 12 to 17, and 19 to 22 also showed good ionic conductivity at 25°C. On the other hand, the sulfide solid electrolyte of Comparative Example 1, which did not contain elements M and N, had good ionic conductivity, but had a large reductive decomposition capacity 20 hours after the start of charging, and poor initial Coulomb efficiency.

[0138] From Table 1, if the molar ratio of Li to P is 2.77 or more and 3.38 or less, and the molar ratio of N to P is 0.28 or more and 0.65 or less, then 10 -3 Scm -1 Since a sulfide solid electrolyte exhibiting the above ionic conductivity and having a structure expected to show good atmospheric stability was obtained, it was confirmed that such a composition of sulfide solid electrolyte is particularly preferable. Furthermore, when the sulfide solid electrolyte contained Al as element M, Li2S did not precipitate even when the content of Li and N was high, such as when the molar ratio of Li to P was 3.40 and the molar ratio of N to P was 0.71. This suggests that the inclusion of Al as element M is particularly preferable.

[0139] As shown in Figure 2, all sulfide solid electrolytes in the examples and comparative examples showed peaks in the XRD spectrum, confirming that they possessed a crystalline structure. Examples 1 and 2 used Li7P3S 11Example 3 had the crystal structure of β-Li3PS4, and Example 11 had the crystal structure of Li4P2S6. The crystal structures of the sulfide solid electrolytes in Examples 4 to 9 were specific crystal structure A, having diffraction peaks at 2θ = 17.9°, 19.1°, 29.1°, 29.8°, and 30.9°. The crystal structure of the sulfide solid electrolyte in Example 10 was confirmed to be specific crystal structure B, having diffraction peaks at 2θ = 17.9°, 19.1°, 29.1°, and 29.8°.

[0140] As shown in the Raman spectrum of Figure 3, the sulfide solid electrolyte of the examples shows that as z increases, i.e., as the nitrogen (N) content increases, the cross-linked sulfur P2S7 4- Originating from Raman shift 406cm -1 The peak in the vicinity has decreased, PS4 3- The Raman shift originated from 423cm. -1 A peak appears in the vicinity. Therefore, the molecular structures obtained by Raman spectroscopy for Examples 1 and 15 in Table 1 are PS4 3- P2S7 4- and P2S6 4- It is presumed to be composed of the following. The molecular structures of Examples 7 to 9, 11 to 14, and 20 to 22, as determined by Raman spectroscopy, are PS4 3- It is presumed to be composed of [the following].

[0141] As shown in Figures 6 and 7, it was confirmed that the amount of hydrogen sulfide generated in Examples 4 and 6 was less than that generated in Comparative Example 1. In particular, Example 6 with z=20 showed a superior inhibitory effect on hydrogen sulfide generation compared to Comparative Example 1 and Reference Example 1. Therefore, it was suggested that this sulfide solid electrolyte not only has high resistance to reduction but also excellent atmospheric stability. The reason why this sulfide-based solid electrolyte has a high inhibitory effect on hydrogen sulfide generation is presumed to be as follows: As shown in the Raman spectrum of Figure 3, the sulfide solid electrolyte of the example shows that as z increases, i.e., as the N content increases, the cross-linked sulfur P2S7 4- Originating from Raman shift 406cm -1The peaks in the vicinity are reduced. Furthermore, in the XRD (X-ray diffraction) spectrum shown in Figure 2, no peaks originating from Li2S appeared in the sulfide solid electrolyte of the example. From these findings, it can be inferred that by increasing the N content of the sulfide solid electrolyte, the so-called cross-linked sulfur P2S7, which is unstable in the atmosphere, is reduced. 4- It is presumed that the reduction in (S3P-S-PS3) and the virtually complete absence of Li2S, which readily reacts with water, will improve the inhibitory effect on hydrogen sulfide generation. Note that Example 6 (z=20) is crosslinked sulfur P2S7 4- The reason why the amount of hydrogen sulfide generated is less than in Reference Example 1, which does not have this feature, is thought to be because the introduction of N into the solid electrolyte structure creates a three-dimensional network, resulting in stronger bonds. It is generally known that introducing N into oxynitride glass, in which some of the O in oxide glass is replaced with N, improves water resistance.

[0142] Comparing Examples 6, 17, 21, and Reference Example 2, where the N content was fixed at z=20 and y=0.70, it can be seen that Li2S precipitated only in Reference Example 2, which does not contain element M. From this, it can be concluded that the precipitation of Li2S can be suppressed by including element M.

[0143] The reason why the presence of element M in the sulfide solid electrolyte can suppress the precipitation of Li2S is thought to be as follows: When Li3N is used as the starting material for a sulfide-based solid electrolyte containing N, Li3N and P2S5 react dramatically, releasing N2 and causing Li2S to precipitate. This is thought to be because the energy for generating N defects in Li3N is small. In contrast, in the present invention, Li α M β Since the N-defect formation energy of N is greater than that of Li3N, the reaction proceeds slowly during the synthesis of sulfide-based solid electrolytes, and it is thought that the release of N2 and the precipitation of Li2S are suppressed. The term "defect generation energy" as used here refers to a parameter calculated using the total energy Eperfect of a crystal structure without defects, the total energy Evacancy of a crystal structure with defects, and the chemical potential μ of the defect atom. This parameter is defined by the following equation. E defect = ( E vacancy + μ) - E perfect

[0144] [Table 2]

[0145] As is clear from Table 2, sulfur-based sulfide solid electrolytes containing Li, P, S, Ge, Al, and N, and having a crystalline structure, exhibited excellent ionic conductivity at 25°C. Also, dQ / dV = -100mAhg -1 V -1 A shift in the voltage V value towards the negative side indicates that the reductive decomposition potential of the sulfide solid electrolyte has shifted towards the negative side, meaning that its resistance to reduction has improved. Therefore, the sulfide solid electrolyte in the example also exhibited excellent resistance to reduction. In particular, the sulfide solid electrolyte of Example 24 was found to exhibit superior ionic conductivity at 25°C compared to the sulfide solid electrolytes of Reference Examples 3 and 4.

[0146] The results above demonstrate that the sulfide solid electrolyte according to the present invention exhibits high reduction resistance and can improve the initial Coulomb efficiency of all-solid-state batteries equipped with the sulfide solid electrolyte. Furthermore, it was shown that the sulfide solid electrolyte according to the present invention can also improve atmospheric stability. [Industrial applicability]

[0147] The all-solid-state battery equipped with a sulfide solid electrolyte according to the present invention exhibits excellent initial Coulomb efficiency and is therefore suitable for use as a lithium-ion all-solid-state battery for, for example, HEVs. [Explanation of Symbols]

[0148] 1. Negative electrode layer 2 Positive electrode layer 3 Solid electrolyte layer 4 Negative electrode base material layer 5. Negative electrode mixture layer 6. Cathode mixture layer 7. Positive electrode substrate layer 10 All-solid-state battery

Claims

[Claim 1] A sulfide solid electrolyte containing Al and N and having a crystalline structure.

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