Sulfide solid electrolyte material and battery using the same

Abstract

To provide a sulfide solid electrolyte material high in ion conductivity and less in generation amount of hydrogen sulfide.SOLUTION: The sulfide solid electrolyte material (10) contains phosphorus and sulfur. In a spectrum obtained by a 31 P-NMR measurement of the sulfide solid electrolyte material (10), a peak appeared in a range of 87.5 ppm to 88.5 ppm is defined as a first peak, a peak appeared in a range of 84.2 ppm to 85.2 ppm in the spectrum is defined as a second peak, 0.00926≤x≤0.37 is satisfied when a ratio between integrated intensity of the first peak and integrated intensity of the second peak is represented by x:1-x.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a sulfide solid electrolyte material and a battery using the same. [Background technology]

[0002] A lithium secondary battery comprises a positive electrode, a negative electrode, and an electrolyte layer disposed between them. The electrolyte layer contains a non-aqueous electrolyte or a solid electrolyte. Because widely used electrolytes are flammable, lithium secondary batteries using electrolytes require a system to ensure safety. Because solid electrolytes are non-flammable, the system can be simplified. Batteries using solid electrolytes are called all-solid-state batteries.

[0003] Solid electrolytes can be broadly divided into organic solid electrolytes and inorganic solid electrolytes. The former are also called polymer solid electrolytes. The ionic conductivity of organic solid electrolytes at room temperature is 10 -6 Since the conductivity of organic solid electrolytes is about 1 / 2 S / cm, it is difficult to operate all-solid-state batteries using organic solid electrolytes at room temperature. The latter includes oxide solid electrolytes and sulfide solid electrolytes.

[0004] Patent Document 1 discloses that the crystallinity of the sulfide solid electrolyte is 20% or more and 99% or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-27554 Summary of the Invention [Problem to be solved by the invention]

[0006] A sulfide solid electrolyte has a problem in that it easily generates harmful hydrogen sulfide. One aspect of the present disclosure provides a sulfide solid electrolyte material that has high ionic conductivity and generates a small amount of hydrogen sulfide. [Means for solving the problem]

[0007] A sulfide solid electrolyte material according to one embodiment of the present disclosure contains phosphorus and sulfur. 31 In a spectrum obtained by P-NMR measurement, a peak appearing in the range of 87.5 ppm to 88.5 ppm is defined as a first peak, and a peak appearing in the spectrum at 84.2 ppm to 85.2 ppm is defined as a second peak, and when the ratio of the integrated intensity of the first peak to the integrated intensity of the second peak is expressed as x:1-x, the ratio satisfies 0.00926≦x≦0.37. Note that comprehensive or specific aspects of the present disclosure may be realized as a material, a battery, an apparatus, a system, a method, or any combination thereof. [Effects of the Invention]

[0008] According to the sulfide solid electrolyte material according to one embodiment of the present disclosure, it is possible to reduce the amount of hydrogen sulfide generated while increasing ionic conductivity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of a battery according to a second embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of an electrolyte layer according to a modified example. [Figure 3] FIG. 3 is a graph showing the respective content ratios of P2S7 crystals, PS4 crystals, and PS4 glass in the sulfide solid electrolyte materials of Comparative Examples 3 and 4. [Figure 4] FIG. 4 is a graph showing the relationship between the content ratio x of PS4 crystals, ionic conductivity, and the amount of hydrogen sulfide generated. [Figure 5] FIG. 5 is a graph showing the NMR spectra of Examples 1 and 2 and Comparative Examples 1, 2, and 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) Sulfide solid electrolyte materials containing phosphorus (P) and sulfur (S) as constituent elements have various forms such as PS4 crystal, PS4 glass, P2S6 crystal, P2S6 glass, P2S7 crystal, and P2S7 glass. Therefore, phosphorus and sulfur form multiple PS bonds in sulfide solid electrolyte materials. 31 The bonding state of these PS bonds can be identified by P-NMR measurement. For example, PS4 glass has a peak near 84.7 ppm. PS4 crystals have a peak near 88.0 ppm. P2S7 crystals have a peak near 90.5 ppm. P2S6 glass has a peak near 108 ppm. The higher the crystal ratio, the higher the ionic conductivity of the sulfide solid electrolyte material. Note that the term "near" used herein refers to a range of ±0.5 ppm from the center peak. For example, PS4 glass has a peak near 84.7 ppm, which means that the peak is within the range of 84.2 ppm to 85.2 ppm. PS4 crystals have a peak near 88.0 ppm, which means that the peak is within the range of 87.5 ppm to 88.5 ppm.

[0011] After extensive research, the inventors discovered that the ratio of PS4 crystals to PS4 glass is closely related to the generation of hydrogen sulfide, and discovered a sulfide solid electrolyte material that has high ionic conductivity and generates little hydrogen sulfide by adjusting the ratio of PS4 crystals to PS4 glass.

[0012] The sulfide solid electrolyte material according to the first aspect of the present disclosure contains phosphorus and sulfur. 31 In a spectrum obtained by P-NMR measurement, a peak appearing near 88.0 ppm is defined as a first peak, and a peak appearing near 84.7 ppm in the spectrum is defined as a second peak. When the ratio of the integrated intensity of the first peak to the integrated intensity of the second peak is expressed as x:1-x, the ratio satisfies 0.00926≦x≦0.37.

[0013] If x is less than 0.00926, the ionic conductivity is low. If x is greater than 0.37, the amount of hydrogen sulfide generated is large. By satisfying the requirement of 0.00926≦x≦0.37, a sulfide solid electrolyte with high ionic conductivity and low hydrogen sulfide generation can be realized.

[0014] In a second aspect of the present disclosure, for example, the sulfide solid electrolyte material according to the first aspect is a compound substantially consisting of lithium, phosphorus, and sulfur. The sulfide solid electrolyte material containing lithium is useful as an electrolyte for lithium-ion batteries.

[0015] In a third aspect of the present disclosure, for example, the compound composition of the sulfide solid electrolyte material according to the second aspect is Li3PS4. Furthermore, in a fourth aspect of the present disclosure, for example, the sulfide solid electrolyte material according to the first aspect contains Li3PS4. Li3PS4 has high ionic conductivity, enabling high-power batteries. Furthermore, Li3PS4 has excellent reduction stability, allowing low-potential materials such as graphite and metallic lithium to be used as anodes. In this case, batteries with high energy density are easily obtained.

[0016] A battery according to a fifth aspect of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the sulfide solid electrolyte material according to any one of the first to third aspects.

[0017] According to the fifth aspect, since the battery contains a sulfide solid electrolyte material that has high ionic conductivity and generates a small amount of hydrogen sulfide, the output characteristics of the battery can be improved and the amount of hydrogen sulfide generated can be reduced.

[0018] In a sixth aspect of the present disclosure, for example, the electrolyte layer of the battery according to the fourth aspect includes a first electrolyte layer and a second electrolyte layer covered by the first electrolyte layer. The first electrolyte layer includes a larger amount of the sulfide solid electrolyte material than the second electrolyte layer, by mass. According to the fifth aspect, the sulfide solid electrolyte material contained in the first electrolyte layer prevents moisture from penetrating into the second electrolyte layer. This prevents the generation of hydrogen sulfide caused by moisture penetrating into the second electrolyte layer.

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0020] (Embodiment 1) The sulfide solid electrolyte material of this embodiment contains phosphorus and sulfur. 31 In the spectrum obtained by P-NMR measurement, the peak appearing near 88.0 ppm is defined as the first peak, and the peak appearing near 84.7 ppm is defined as the second peak. When the ratio of the integrated intensity of the first peak to the integrated intensity of the second peak is expressed as x:(1-x), the ratio satisfies 0.00926≦x≦0.37. The first peak is a peak attributed to PS4 crystals. The second peak is a peak attributed to PS4 glass. The ratio x / (1-x) of the integrated intensity of the first peak to the integrated intensity of the second peak represents the molar ratio of PS4 crystals to PS4 glass.

[0021] 31 In P-NMR measurements, ammonium phosphate can be used as a reference material that indicates a chemical shift of 0 ppm. In NMR measurements, the magnetic field conditions vary strictly for each measurement, resulting in measurement errors in the chemical shift output. The measurement error is, for example, ±0.5 ppm. In this specification, the terms "around 88.0 ppm" and "around 84.7 ppm" mean "88.0±0.5 ppm" and "84.7±0.5 ppm," respectively.

[0022] The other constituent elements and composition of the sulfide solid electrolyte material of this embodiment are not particularly limited. Examples of sulfide solid electrolyte materials that can be used include Li2S-P2S5 and Li-PS compounds. To these, sulfide compounds such as SiS2, B2S3, GeS2, and Al2S3 may be added, and lithium halides such as LiX (X: F, Cl, Br, and I) may be added. Li2O, MO q , Li p MO q An oxide or a lithium oxide such as (M: P, Si, Ge, B, Al, Ga, In, Fe, or Zn) (p and q: natural numbers) may be added. For example, when LiX is added to Li2S-P2S5, Li2S, P2S5, and LiX are reacted by heat treatment, mechanical milling, or other methods to form a compound. This provides various effects such as improved electrical conductivity, improved chemical stability, and reduced interface resistance.

[0023] The sulfide solid electrolyte material of this embodiment is Li3PS4, Li4P2S6, Li7P3S 11 , Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li6PS5X (X: F, Cl, Br, I), or may be a glass ceramic in which crystal and glass are mixed.

[0024] To derive the ratio between PS4 crystal and PS4 glass, 31 P-NMR measurement is the simplest method. 31The method is not limited to P-NMR measurement. For example, the ratio of PS4 crystals to PS4 glass can be derived by Raman spectroscopy, X-ray diffraction, or a combination of these. The ratio of PS4 crystals to PS4 glass is not dependent on the measurement method. For sulfide solid electrolyte materials with the same composition and structure, the same ratio of PS4 crystals to PS4 glass can be derived even when different measurement methods are used.

[0025] In this specification, the "ratio of PS4 crystals to PS4 glass" means the ratio between the number of PS bonds forming PS4 crystals (i.e., the number of moles of PS4 crystals) and the number of PS bonds forming PS4 glass (i.e., the number of moles of PS4 glass), and is expressed as "x:1-x".

[0026] The PS4 crystals contained in the sulfide solid electrolyte material may exist as microcrystals with a size of several nanometers, or as domain-like crystals with a size of several hundred nanometers to several micrometers. The PS4 crystals and PS4 glass may be uniformly dispersed within the sulfide solid electrolyte material (e.g., within the particles of the sulfide solid electrolyte material), or may be unevenly distributed.

[0027] In this embodiment, the sulfide solid electrolyte material may be a compound substantially consisting of lithium, phosphorus, and sulfur. A sulfide solid electrolyte material containing lithium is useful as an electrolyte for lithium-ion batteries. The sulfide solid electrolyte material may have the composition Li3PS4. Li3PS4 has high ionic conductivity, enabling high-power batteries. Furthermore, Li3PS4 has excellent reduction stability, allowing low-potential materials such as graphite and metallic lithium to be used as the negative electrode. In this case, a battery with high energy density is easily obtained.

[0028] As used herein, the phrase "consisting essentially of" means excluding other ingredients that alter the essential characteristics of the referenced compound.

[0029] According to the above configuration, a sulfide solid electrolyte material with high ionic conductivity and low generation of hydrogen sulfide can be realized.

[0030] The sulfide solid electrolyte material of this embodiment can be produced by the following method.

[0031] Precursor raw materials containing Li2S, P2S5, Li, P, S, etc. are reacted using methods such as melt quenching and mechanochemical milling. This produces a sulfide solid electrolyte material containing PS4 glass. Heat-treating the resulting glassy sulfide solid electrolyte material promotes PS4 crystallization, resulting in a sulfide solid electrolyte material containing PS4 crystals and PS4 glass. The ratio of PS4 crystals to PS4 glass can be controlled by performing the heat treatment at any temperature and for any time.

[0032] The heat treatment temperature is not particularly limited as long as it is equal to or higher than the crystallization temperature of PS4, and is, for example, 200°C or higher. The higher the heat treatment temperature, the shorter the time required for crystallization to proceed. The upper limit of the heat treatment temperature is also not particularly limited, and is, for example, 400°C. The heat treatment time is also not particularly limited. Crystallization proceeds as the heat treatment time increases. As crystallization proceeds, the ionic conductivity increases. The heat treatment time is, for example, 5 hours or less, and may be 30 minutes or less. The lower limit of the heat treatment time is also not particularly limited, and is, for example, 1 minute.

[0033] However, subsequent heat treatment is not required. For example, by appropriately controlling the heat treatment temperature and quenching rate in the melt quenching method, a sulfide solid electrolyte material in which the ratio of PS4 crystals to PS4 glass is adjusted to a desired ratio can be produced without a subsequent heat treatment step. Similarly, by appropriately controlling the rotation speed and treatment time in the mechanochemical milling method, a sulfide solid electrolyte material in which the ratio of PS4 crystals to PS4 glass is adjusted to a desired ratio can be produced without a subsequent heat treatment step.

[0034] The sulfide solid electrolyte material in this embodiment can also be produced by the following method using an organic solvent.

[0035] Precursor materials containing Li2S, PS2S5, Li, P, and S are reacted in an organic solvent. Examples of suitable organic solvents include tetrahydrofuran, ethyl propionate, methyl propionate, ethyl acetate, N-methylformamide, dimethoxyethane, acetonitrile, and mixtures thereof. The reaction mixture may be heated, vibrated by adding grinding media, or ultrasonically energized. The organic solvent is then removed by drying methods such as heat drying or vacuum drying. As the organic solvent is removed, crystallization progresses, yielding a sulfide solid electrolyte material containing PS4 crystals and PS4 glass. By appropriately selecting the precursor materials, organic solvent, reaction time, reaction temperature, and drying conditions for removing the organic solvent, it is possible to produce a sulfide solid electrolyte material with a desired ratio of PS4 crystals to PS4 glass.

[0036] (Embodiment 2) In the following embodiment 2, the description overlapping with embodiment 1 will be omitted as appropriate. The battery according to embodiment 2 uses the sulfide solid electrolyte material described in embodiment 1.

[0037] As shown in FIG. 1 , a battery 20 according to this embodiment includes a positive electrode 21, a negative electrode 23, and an electrolyte layer 22. The positive electrode 21 includes positive electrode active material particles 24. The positive electrode 21 may further include the sulfide solid electrolyte material 10 described in the first embodiment. The electrolyte layer 22 is disposed between the positive electrode 21 and the negative electrode 23. The electrolyte layer 22 is in contact with both the positive electrode 21 and the negative electrode 23. The electrolyte layer 22 may include the sulfide solid electrolyte material 10. The negative electrode 23 includes negative electrode active material particles 25. The negative electrode 23 may include the sulfide solid electrolyte material 10. The battery 20 is, for example, an all-solid-state lithium secondary battery. By including the sulfide solid electrolyte material 10 described in the first embodiment, the battery 20 according to this embodiment exhibits excellent output characteristics and can also reduce the amount of hydrogen sulfide generated.

[0038] In this embodiment, the positive electrode 21, the negative electrode 23, and the electrolyte layer 22 may each contain the sulfide solid electrolyte material 10. It is desirable that at least the electrolyte layer 22 contains the sulfide solid electrolyte material 10 of the present disclosure. Among the positive electrode 21, the negative electrode 23, and the electrolyte layer 22, the electrolyte layer 22 contains the largest amount of electrolyte material. Therefore, by using the sulfide solid electrolyte material 10 of the present disclosure for the electrolyte layer 22, the amount of hydrogen sulfide generated in the battery 20 can be most efficiently reduced. However, as long as at least one selected from the group consisting of the positive electrode 21, the negative electrode 23, and the electrolyte layer 22 contains the sulfide solid electrolyte material 10, the effect of suppressing hydrogen sulfide generation can be obtained. The positive electrode 21, the negative electrode 23, and the electrolyte layer 22 may each contain a sulfide solid electrolyte material other than the sulfide solid electrolyte material 10 of the present disclosure.

[0039] The shape of the sulfide solid electrolyte material 10 is not particularly limited. The shape of the sulfide solid electrolyte material 10 is, for example, needle-like, scale-like, spherical, or oval-spherical. The sulfide solid electrolyte material 10 may be in the form of particles. When the sulfide solid electrolyte material 10 is in the form of particles (for example, spherical), the median diameter (d50) of the sulfide solid electrolyte material 10 may be 100 μm or less. When the sulfide solid electrolyte material 10 has an appropriate size, it is possible to form a good dispersion state between the sulfide solid electrolyte material 10 and other materials such as an active material and a conductive additive in the positive electrode 21 or the negative electrode 23. When the sulfide solid electrolyte material 10 has an appropriate size, it is possible to sufficiently thin the thickness of the electrolyte layer 22 using the sulfide solid electrolyte material 10. These contribute to improving the discharge characteristics of the battery 20.

[0040] The median diameter of the sulfide solid electrolyte material 10 may be 10 μm or less. With this configuration, the sulfide solid electrolyte material 10 can be better dispersed with other materials such as the active material and the conductive additive.

[0041] The median diameter of the sulfide solid electrolyte material 10 may be smaller than the median diameter of the positive electrode active material particles or the negative electrode active material particles. This configuration allows the sulfide solid electrolyte material 10 and the active material particles to be better dispersed. The lower limit of the median diameter of the sulfide solid electrolyte material 10 is not particularly limited and is, for example, 0.01 μm.

[0042] In this specification, the median particle size means the particle size (d50) corresponding to 50% cumulative volume in the particle size distribution measured by a laser diffraction particle sizer or the like.

[0043] The positive electrode 21 includes a material having the property of absorbing and releasing metal ions. An example of the metal ions is lithium ions. The positive electrode 21 includes, for example, a positive electrode active material (e.g., positive electrode active material particles 24). The positive electrode 21 may include a sulfide solid electrolyte material 10.

[0044] The positive electrode active material may be a lithium-containing transition metal oxide, a lithium-free transition metal oxide, a transition metal fluoride, a polyanion material, a fluorinated polyanion material, a transition metal sulfide, a transition metal oxyfluoride, a transition metal oxysulfide, a transition metal oxynitride, etc. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost of the battery 20 can be reduced and the average discharge voltage of the battery 20 can be increased.

[0045] As the positive electrode active material, at least one selected from Li(NiCoAl)O2 and LiCoO2 may be contained in the positive electrode 21. These transition metal oxides can impart a high energy density to the battery 20.

[0046] The median diameter of the positive electrode active material particles 24 may be 0.1 μm or more and 100 μm or less. When the positive electrode active material particles 24 have an appropriate size, the positive electrode active material particles 24 and the sulfide solid electrolyte material 10 can be well dispersed in the positive electrode 21. Furthermore, lithium ions can be quickly diffused inside the positive electrode active material particles 24, which is advantageous for operating the battery 20 at high output. The median diameter of the positive electrode active material particles 24 may be larger than the median diameter of the particles of the sulfide solid electrolyte material 10. This allows the positive electrode active material particles 24 and the sulfide solid electrolyte material 10 to be well dispersed.

[0047] In the positive electrode 21, the ratio of the volume v of the positive electrode active material particles 24 to the total volume of the positive electrode active material particles 24 and the volume of the sulfide solid electrolyte material 10 is, for example, 30% or more and 95% or less. The ratio of the volume (100-v) of the sulfide solid electrolyte material 10 to the total volume of the positive electrode active material particles 24 and the volume of the sulfide solid electrolyte material 10 is, for example, 5% or more and 70% or less. When the amounts of the positive electrode active material particles 24 and the sulfide solid electrolyte material 10 are appropriately adjusted, the energy density of the battery 20 can be sufficiently ensured and the battery 20 can be operated at high output.

[0048] The thickness of the positive electrode 21 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 21 is appropriately adjusted, the energy density of the battery 20 can be sufficiently ensured, and the battery 20 can be operated at high power.

[0049] The electrolyte layer 22 is a layer containing the sulfide solid electrolyte material 10 of the present disclosure. The electrolyte layer 22 may contain, in addition to the sulfide solid electrolyte material 10, a second sulfide solid electrolyte material different from the sulfide solid electrolyte material 10. In this case, the sulfide solid electrolyte material 10 and the second sulfide solid electrolyte material may be uniformly dispersed in the electrolyte layer 22. The second sulfide solid electrolyte material may have, for example, a composition different from that of the sulfide solid electrolyte material 10. The second sulfide solid electrolyte material may have a structure different from that of the sulfide solid electrolyte material 10. For example, the ratio of PS4 crystal to PS4 glass may be different between the sulfide solid electrolyte material 10 and the second sulfide solid electrolyte material.

[0050] The thickness of the electrolyte layer 22 may be 1 μm or more and 500 μm or less. When the thickness of the electrolyte layer 22 is appropriately adjusted, a short circuit between the positive electrode 21 and the negative electrode 23 can be reliably prevented, and the battery 20 can be operated at high power.

[0051] The battery 20 may include an electrolyte layer 28 shown in FIG. 2 instead of the electrolyte layer 22. The electrolyte layer 28 has a first electrolyte layer 26 and a second electrolyte layer 27. The second electrolyte layer 27 is covered by the first electrolyte layer 26. More specifically, the second electrolyte layer 27 is enveloped by the first electrolyte layer 26. The two main surfaces of the electrolyte layer 28 are formed by the first electrolyte layer 26. However, a portion of the second electrolyte layer 27 may appear on the surface of the electrolyte layer 28. The "main surface" means the surface having the largest area.

[0052] The first electrolyte layer 26 is a layer containing the sulfide solid electrolyte material 10 of the present disclosure. The second electrolyte layer 27 may contain the sulfide solid electrolyte material 10, may contain a second sulfide solid electrolyte material, or may contain both. The first electrolyte layer 26 may contain more sulfide solid electrolyte material 10 than the second electrolyte layer 27 on a mass basis.

[0053] According to the electrolyte layer 28 shown in FIG. 2 , the first electrolyte layer 26 is positioned around the second electrolyte layer 27, and the second electrolyte layer 27 is protected by the first electrolyte layer 26. The sulfide solid electrolyte material 10 contained in the first electrolyte layer 26 prevents moisture from penetrating into the second electrolyte layer 27. This prevents the generation of hydrogen sulfide caused by moisture penetrating into the second electrolyte layer 27. For the second electrolyte layer 27, an electrolyte material that is likely to generate hydrogen sulfide but has higher ionic conductivity can be used. This allows the ionic conductivity of the battery 20 to be further increased.

[0054] The negative electrode 23 includes a material capable of absorbing and releasing metal ions. An example of the metal ions is lithium ions. The negative electrode 23 includes, for example, a negative electrode active material (e.g., a negative electrode active material particles 25). The negative electrode 23 may include a sulfide solid electrolyte material 10.

[0055] Examples of the negative electrode active material that can be used include metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metal material may be a single metal or an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, at least one selected from the group consisting of silicon (Si), tin (Sn), silicon compounds, and tin compounds can be suitably used as the negative electrode active material.

[0056] The median diameter of the negative electrode active material particles 25 may be 0.1 μm or more and 100 μm or less. When the negative electrode active material particles 25 have an appropriate size, the negative electrode active material particles 25 and the sulfide solid electrolyte material 10 can be well dispersed. Furthermore, lithium ions can be quickly diffused inside the negative electrode active material particles 25, which is advantageous for operating the battery 20 at high output. The median diameter of the negative electrode active material particles 25 may be larger than the median diameter of the particles of the sulfide solid electrolyte material 10. This allows the negative electrode active material particles 25 and the sulfide solid electrolyte material 10 to be well dispersed.

[0057] In the negative electrode 23, the ratio of the volume V of the negative electrode active material particles 25 to the total volume of the negative electrode active material particles 25 and the sulfide solid electrolyte material 10 is, for example, 30% or more and 95% or less. The ratio of the volume (100-V) of the sulfide solid electrolyte material 10 to the total volume of the negative electrode active material particles 25 and the sulfide solid electrolyte material 10 is, for example, 5% or more and 70% or less. When the amounts of the negative electrode active material particles 25 and the sulfide solid electrolyte material 10 are appropriately adjusted, the energy density of the battery 20 can be sufficiently ensured and the battery 20 can be operated at high output.

[0058] The thickness of the negative electrode 23 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 23 is appropriately adjusted, the energy density of the battery 20 can be sufficiently ensured, and the battery 20 can be operated at high power.

[0059] At least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain a second sulfide solid electrolyte material different from the sulfide solid electrolyte material 10 for the purpose of increasing ion conductivity. Examples of the second sulfide solid electrolyte material include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These sulfide materials include LiX (X: F, Cl, Br, I), LiO, MO q , Li p MO q (M: P, Si, Ge, B, Al, Ga, In, Fe or Zn) (p, q: natural numbers) or the like may be added.

[0060] At least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain an oxide solid electrolyte for the purpose of enhancing ion conductivity. Examples of oxide solid electrolytes include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its element substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 LISICON-type solid electrolytes, such as Li4SiO4, LiGeO4 and their elemental substitution products, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as Li3N and its H-substituted products, Li3PO4 and its N-substituted products, and the like, can be used.

[0061] To enhance ion conductivity, at least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain a halide solid electrolyte. Examples of the halide solid electrolyte that can be used include Li3InBr6, Li3InCl6, Li2FeCl4, Li2CrCl4, and Li3OCl.

[0062] To enhance ion conductivity, at least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain a complex hydride solid electrolyte. Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0063] At least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain an organic polymer solid electrolyte to enhance ionic conductivity. A compound of a polymer compound and a lithium salt may be used as the organic polymer solid electrolyte. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt, thereby further enhancing ionic conductivity. Examples of the lithium salt that may be used include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0064] At least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain a nonaqueous electrolyte solution, a gel electrolyte, or an ionic liquid for the purpose of facilitating the exchange of lithium ions and improving the output characteristics of the battery.

[0065] The nonaqueous electrolyte contains a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent. Examples of the nonaqueous solvent include cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, and fluorine-containing solvents. Examples of cyclic carbonate ester solvents include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonate ester solvents include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ether solvents include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic ester solvents include γ-butyrolactone. Examples of chain ester solvents include methyl acetate. Examples of fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, fluorodimethylene carbonate, etc. As the nonaqueous solvent, one nonaqueous solvent selected from these may be used alone, or a mixture of two or more nonaqueous solvents selected from these may be used.

[0066] The non-aqueous electrolyte may contain at least one fluorine-containing solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. Examples of the lithium salt that may be used include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF) , LiN(SOCF) (SOCF), and LiC(SOCF). A single lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 to 2 mol / L.

[0067] The gel electrolyte may be a polymer material impregnated with a non-aqueous electrolyte, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0068] The cations constituting the ionic liquid may be aliphatic chain quaternary salts such as tetraalkylammonium and tetraalkylphosphonium, aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, and piperidiniums, and nitrogen-containing heterocyclic aromatic cations such as pyridiniums and imidazoliums. The anions constituting the ionic liquid may be PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , C(SO2CF3)3 - The ionic liquid may contain a lithium salt.

[0069] To improve adhesion between particles, at least one selected from the positive electrode 21, the negative electrode 23, the electrolyte layer 22, the first electrolyte layer 26, and the second electrolyte layer 27 may contain a binder. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can also be used as binders. Mixtures of two or more materials selected from the above materials can also be used as binders.

[0070] At least one selected from the positive electrode 21 and the negative electrode 23 may contain a conductive additive for the purpose of increasing electronic conductivity.

[0071] Examples of the conductive aid that can be used include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black and ketjen black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride and aluminum powder, conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene.

[0072] The shape of the conductive additive is not particularly limited. The conductive additive may be, for example, needle-like, scale-like, spherical, or oval-spherical. The conductive additive may also be in the form of particles.

[0073] The positive electrode active material particles 24 and the negative electrode active material particles 25 may be coated with a coating material in order to reduce interfacial resistance. Only a portion of the surface of the positive electrode active material particles 24 may be coated with the coating material, or the entire surface of the positive electrode active material particles 24 may be coated with the coating material. Similarly, only a portion of the surface of the negative electrode active material particles 25 may be coated with the coating material, or the entire surface of the negative electrode active material particles 25 may be coated with the coating material.

[0074] The coating material may be a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte. The coating material may be an oxide solid electrolyte. The oxide solid electrolyte has excellent high potential stability. By using the oxide solid electrolyte as the coating material, the charge / discharge efficiency of the battery 20 is improved.

[0075] Oxide solid electrolytes that can be used as coating materials include Li-Nb-O compounds such as LiNbO3, Li-BO compounds such as LiBO2 and Li3BO3, Li-Al-O compounds such as LiAlO2, Li-Si-O compounds such as Li4SiO4, Li2SO4, and Li4Ti5O. 12 Li-Ti-O compounds such as Li2ZrO3, Li-Zr-O compounds such as Li2MoO3, Li-VO compounds such as LiV2O5, and Li-WO compounds such as Li2WO4. [Example]

[0076] Example 1 In an argon glove box with an Ar atmosphere and a dew point of -60°C or less, Li2S powder and P2S5 powder were weighed out to a molar ratio of Li2S:P2S5 = 75:25. These were then placed in a mortar and crushed and mixed. The mixture was milled for 10 hours at 510 rpm using a planetary ball mill to obtain a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 15 minutes. This yielded Li2S-P2S5 powder, a glass-ceramic sulfide solid electrolyte material. The sulfide solid electrolyte material of Example 1 had a composition of Li3PS4.

[0077] <Example 2> A sulfide solid electrolyte material of Example 2 was obtained in the same manner as in Example 1, except that the heat treatment time was changed to 30 minutes.

[0078] <Comparative Example 1> A sulfide solid electrolyte material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the heat treatment was not carried out.

[0079] <Comparative Example 2> A sulfide solid electrolyte material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the heat treatment time was changed to 5 minutes.

[0080] <Comparative Example 3> A sulfide solid electrolyte material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the heat treatment time was changed to 120 minutes.

[0081] <Comparative Example 4> The sulfide solid electrolyte material of Comparative Example 3 was exposed to the atmosphere at approximately 23°C and a relative humidity of approximately 50% for 60 minutes, thereby obtaining the sulfide solid electrolyte material of Comparative Example 4. After exposure, the sulfide solid electrolyte material was stored in an argon glove box in an Ar atmosphere with a dew point of -60°C or lower.

[0082] [ 31 P-NMR measurement] Using the sulfide solid electrolyte materials of Example 1, Example 2, and Comparative Examples 1 to 4,31 P-NMR measurements were performed. The sample rotation speed was 20 kHz, the measurement integration count was 32, and the relaxation time was 30 seconds. Ammonium phosphate was used as a reference material, indicating a chemical shift of 0 ppm. The integrated intensity of each peak in the resulting spectrum was calculated by fitting. From the integrated intensity of each peak, the abundance ratio (unit: mol%) of each crystal and glass was determined, assuming the entire sulfide solid electrolyte material to be 100 mol%. Furthermore, the ratio of the integrated intensity of the peak attributed to PS4 crystals to the integrated intensity of the peak attributed to PS4 glass was defined as x:(1-x), and the PS4 crystal content ratio x (PS4 crystal ratio) was calculated. "PS4 crystal content ratio x" represents the PS4 crystal content in moles, assuming the sum of the PS4 crystal content and the PS4 glass content is "1."

[0083] [Measurement of ionic conductivity] The ionic conductivities of the sulfide solid electrolyte materials of Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the following method.

[0084] 80 mg of sulfide solid electrolyte material was placed in an insulating outer cylinder and pressure-molded at 360 MPa to obtain an electrolyte layer. The thickness of the electrolyte layer was measured using a vernier caliper. Next, metal In foil (200 μm thick) was placed on each of the upper and lower surfaces of the electrolyte layer. The metal In foil and electrolyte layer were pressure-molded at 80 MPa to produce a laminate consisting of the metal In foil, electrolyte layer, and metal In foil. Next, stainless steel current collectors were placed on each of the upper and lower surfaces of the laminate. Current collector leads were attached to each current collector. Finally, the insulating outer cylinder was sealed with an insulating ferrule to isolate the interior of the insulating outer cylinder from the outside air. In this way, an electrochemical cell for measuring ionic conductivity was produced.

[0085] The electrochemical cell was placed in a thermostatic chamber at 25°C. Resistance measurements were performed using the AC impedance method under conditions of a voltage amplitude of ±10 mV and a measurement frequency of 0.01 Hz to 1 MHz. Ionic conductivity was calculated using the measured resistance value, the area of ​​the electrodes, and the thickness of the electrolyte layer.

[0086] [Measurement of hydrogen sulfide generation] The amounts of hydrogen sulfide generated from the sulfide solid electrolyte materials of Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the following method.

[0087] 80 mg of sulfide solid electrolyte material was weighed out in an argon glove box with an Ar atmosphere at a dew point of -60°C or less. The weighed sulfide solid electrolyte material was placed in a powder molding die with an inner diameter of 9.5 mm and pressure-molded at a pressure of 360 MPa. After molding, pellets of the sulfide solid electrolyte material were removed from the powder molding die and placed in a sealable glass container. The glass container was placed in a thermostatic chamber with a humidified atmosphere at a temperature of 25°C and a relative humidity of 50%, and the interior of the glass container was replaced with a humidified atmosphere. The glass container was then sealed, and the pellets were exposed to the humidified atmosphere for 10 minutes. The amount of hydrogen sulfide inside the glass container 10 minutes after sealing the glass container was measured using a portable gas monitor (Riken Keiki Co., Ltd., GX-2012). The amount of hydrogen sulfide was divided by the weight of the pellets (80 mg) to determine the amount of hydrogen sulfide generated per unit weight (cm 3 / g) was derived.

[0088] Regarding the sulfide solid electrolyte materials of Comparative Examples 3 and 4 31 The P-NMR measurement results are shown in Table 1. The graph in Figure 3 shows the values ​​in Table 1.

[0089] [Table 1]

[0090] As shown in Table 1, exposing the sulfide solid electrolyte material to the atmosphere reduced the content of PS4 crystals. The decrease in the content of PS4 crystals indicates that the PS4 crystals reacted with moisture in the atmosphere, breaking the PS bonds and generating hydrogen sulfide. On the other hand, the content of P2S7 crystals and PS4 glass did not decrease. These results indicate that PS4 crystals are the main cause of hydrogen sulfide generation. As can be seen from the fact that the content of P2S7 crystals did not decrease, the generation of hydrogen sulfide does not depend on the proportion of crystals in the sulfide solid electrolyte material as a whole, but rather on the proportion of PS4 crystals among the crystals.

[0091] Regarding the sulfide solid electrolyte materials of Example 1, Example 2 and Comparative Examples 1 to 3, 31 The measurement results of the first peak (i.e., PS4 crystal) position, the second peak (i.e., PS4 glass) position, the PS4 crystal content ratio x, the ionic conductivity, and the amount of hydrogen sulfide generated obtained by P-NMR measurement are shown in Table 2. The peak positions of the first and second peaks are shown in Table 2. 31 The spectra obtained by P-NMR measurement were subjected to waveform separation using a Gaussian function. The graph in Figure 4 shows the values ​​in Table 2. Figure 5 shows the NMR spectra of Examples 1 and 2 and Comparative Examples 1, 2, and 3.

[0092] [Table 2]

[0093] As can be seen from the results of Examples 1 and 2 and Comparative Examples 1, 2 and 3, the first and second peaks were located around 88.0 ppm (87.5 ppm or more and 88.5 ppm or less) and around 84.7 ppm (84.2 ppm or more and 85.2 ppm or less), respectively. As can be seen from the results of Examples 1, 2 and Comparative Example 3, the ionic conductivity and the amount of hydrogen sulfide generated increased with an increase in the content ratio x of the PS4 crystal. As can be seen from the results of Comparative Example 1 and Comparative Example 2, when the content ratio x of the PS4 crystal was less than 0.00926, the amount of hydrogen sulfide generated increased by 10 -2 cm3 / g or less, but the ionic conductivity was 4×10 -4 The ionic conductivity was as low as 4×10 S / cm or less. -4 When a battery is fabricated using a sulfide solid electrolyte material with an ionic conductivity of less than 1.5 S / cm, it may be difficult to operate the battery at high power. As can be seen from the results of Comparative Example 3, when the content ratio x of PS4 crystals is greater than 0.37, the ionic conductivity is 4 × 10 -4 Although the amount of hydrogen sulfide generated was higher than 10 S / cm, -2 cm 3 / g. The amount of hydrogen sulfide generated was 10 -2 cm 3 When a sulfide solid electrolyte material with a content of more than 1 / g is used, there is a concern that the sulfide solid electrolyte material will react with trace amounts of moisture in the atmosphere during the battery manufacturing process, resulting in deterioration of the quality of the sulfide solid electrolyte material and a decline in battery performance.When the PS4 crystal content ratio x satisfies 0.00926≦x≦0.37, a sulfide solid electrolyte material with high ionic conductivity and low hydrogen sulfide generation can be obtained. [Industrial Applicability]

[0094] The technology disclosed in this specification is useful, for example, in all-solid-state lithium secondary batteries. [Explanation of symbols]

[0095] 10 Sulfide solid electrolyte materials 20 batteries 21 Positive electrode 22 Electrolyte layer 23 Negative electrode 24 Positive electrode active material particles 25 Negative electrode active material particles 26 1st electrolyte layer 27 Second electrolyte layer

Claims

1. A compound consisting essentially of lithium, phosphorus, and sulfur, Ammonium phosphate was used as an external standard (0 ppm). 31 In a spectrum obtained by P-NMR measurement, a peak appearing in a range of 87.5 ppm or more and 88.5 ppm or less is defined as a first peak, and a peak appearing in the spectrum in a range of 84.2 ppm or more and 85.2 ppm or less is defined as a second peak, and when the ratio of the integrated intensity of the first peak to the integrated intensity of the second peak is expressed as x:1-x, the ratio satisfies 0.00926≦x≦0.

37. Sulfide solid electrolyte material.

2. The composition of the compound is Li 3 P.S. 4 That is, The sulfide solid electrolyte material according to claim 1.

3. The sulfide solid electrolyte material is Li 3 P.S. 4 Including, The sulfide solid electrolyte material according to claim 1.

4. The spectrum is PS 2 O 2 does not have a peak assigned to The sulfide solid electrolyte material according to claim 1.

5. A positive electrode and a negative electrode; an electrolyte layer disposed between the positive electrode and the negative electrode; Equipped with At least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer comprises the sulfide solid electrolyte material according to any one of claims 1 to 4, battery.

6. the electrolyte layer includes a first electrolyte layer and a second electrolyte layer covered by the first electrolyte layer; The first electrolyte layer contains more of the sulfide solid electrolyte material than the second electrolyte layer, on a mass basis. The battery of claim 5.

Images