Solid electrolyte and secondary battery

Abstract

The present invention improves charge and discharge characteristics while improving water resistance. Provided is a solid electrolyte having a composition formula represented by LixSn1-wZwSy, wherein Z is an element including at least Si, and the relationships 3.0≤x≤5.0, 3.0≤y≤5.0, and 0<w<0.25 are satisfied.

Description

Solid electrolytes and secondary batteries

[0001] The present disclosure relates to a solid electrolyte and a secondary battery.

[0002] In Non-Patent Document 1, the composition formula is Li ４ SnS ４ A solid electrolyte is described in which

[0003] Inorganic Chemistry, 2018, Vol 57, No. 16, p. 9925-9930

[0004] The solid electrolyte disclosed in Non-Patent Document 1 has excellent water resistance, but there is a possibility that the charge / discharge characteristics may be deteriorated.

[0005] The present disclosure has been made in view of the above, and aims to improve charge / discharge characteristics while improving water resistance.

[0006] The solid electrolyte according to one embodiment has a composition formula of Li ｘ Sn １－ｗ Z ｗ S ｙ Z contains at least Si and satisfies 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w<0.25.

[0007] The solid electrolyte according to another embodiment has a composition formula of Li ｘ Sn １－ｗ Z ｗ S ｙ Z contains at least Si, and satisfies 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w / (1−w)<0.33.

[0008] A secondary battery according to one embodiment includes a positive electrode, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer containing the solid electrolyte.

[0009] A secondary battery according to another embodiment includes a positive electrode, a negative electrode including a particulate negative electrode active material and the solid electrolyte, and an electrolyte layer.

[0010] According to the present invention, it is possible to improve the charge / discharge characteristics while improving the water resistance.

[0011] FIG. 1 is a schematic cross-sectional view showing an example of a battery according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing an example of a battery according to a second embodiment. FIG. 3 is a schematic cross-sectional view showing an example of a battery according to a first modified example of the second embodiment. FIG. 4 is a schematic cross-sectional view showing an example of a battery according to a second modified example of the second embodiment. FIG. 5 is a schematic cross-sectional view showing an example of a battery according to a third embodiment.

[0012] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to these embodiments.

[0013] First Embodiment FIG. 1 is a schematic cross-sectional view showing an example of a battery according to a first embodiment. The battery 1 in the first embodiment is an all-solid-state battery in which the electrolyte is solid, and is a lithium-ion secondary battery. As shown in FIG. 1, the battery 1 includes a protective layer 10, a positive electrode 20, a negative electrode 30, and an electrolyte layer 40. In the example of FIG. 1, the battery 1 has a structure in which the sheet-like positive electrode 20, the negative electrode 30, and the electrolyte layer 40 are stacked.

[0014] In the drawings showing this embodiment, the Z direction refers to the stacking direction of the positive electrode 20, the negative electrode 30, and the electrolyte layer 40, the X direction refers to a direction perpendicular to the Z direction and parallel to the cross section of FIG. 1, and the Y direction refers to a direction perpendicular to the X direction and the Z direction. In addition, in describing this embodiment, one of the X directions may be referred to as the +X direction and the other as the −X direction. Similarly, one of the Z directions may be referred to as the +Z direction and the other as the −Z direction.

[0015] The protective layer 10 is a layer provided to physically and chemically protect the battery 1. In plan view in the Z direction, the protective layer 10 is provided so as to overlap the stack of the positive electrode 20, the negative electrode 30, and the electrolyte layer 40, and in the example of Fig. 1, the protective layer 10 is provided on both sides in the Z direction of the stack of the positive electrode 20, the negative electrode 30, and the electrolyte layer 40. The material of the protective layer 10 is not particularly limited as long as it is an insulator, and examples thereof include resin, glass, and ceramics.

[0016] The positive electrode 20 includes a positive electrode current collector layer 21 and a positive electrode active material layer 22 .

[0017] The positive electrode current collector layer 21 is a conductive layer. In the example of FIG. 1 , the end face of the positive electrode current collector layer 21 in the +X direction is exposed and can be connected to the outside. That is, the end face of the positive electrode current collector layer 21 in the +X direction serves as the positive electrode of the battery 1. The material of the positive electrode current collector layer 21 is not particularly limited as long as it is conductive, and examples thereof include metal materials such as silver, palladium, gold, platinum, aluminum, copper, and nickel, and carbon materials.

[0018] The positive electrode active material layer 22 is a layer containing a positive electrode active material. The positive electrode active material layer 22 is laminated on the positive electrode current collector layer 21. The positive electrode active material is not particularly limited, and examples thereof include at least one selected from the group consisting of a lithium-containing phosphate compound having a Nasicon structure, a lithium-containing phosphate compound having an olivine structure, a lithium-containing layered oxide, and a lithium-containing oxide having a spinel structure. An example of a lithium-containing phosphate compound having a Nasicon structure is Li ３ V ２ (P.O. ４ ) ３ Examples of lithium-containing phosphate compounds having an olivine structure include Li ３ Fe ２ (P.O. ４ ) ３ , LiMnPO ４ An example of a lithium-containing layered oxide is LiCoO ２ , LiCo １／３ Ni １／３ Mn １／３ O ２ An example of a lithium-containing oxide having a spinel structure is LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ etc.

[0019] The material contained in the positive electrode active material layer 22 is not limited to the positive electrode active material, and may also contain a solid electrolyte or a sintering aid, which will be described later. The sintering aid is not particularly limited, and examples thereof include lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide, and phosphorus oxide.

[0020] The negative electrode 30 includes a negative electrode current collector layer 31 and a negative electrode active material layer 32 .

[0021] The negative electrode current collector layer 31 is a conductive layer. In the example of FIG. 1 , the negative electrode current collector layer 31 has an exposed end face in the −X direction that can be connected to the outside. That is, the −X direction end face of the negative electrode current collector layer 31 serves as the negative electrode of the battery 1. The material of the negative electrode current collector layer 31 is a conductive metal and contains at least one metal selected from the group consisting of copper, nickel, and iron. However, the material of the negative electrode current collector layer 31 is not limited to these, and may further contain, for example, at least one metal material such as palladium, gold, platinum, or aluminum, and a carbon material. Furthermore, the negative electrode current collector layer 31 is not limited to being composed of a single layer, and may include multiple layers, such as stainless steel coated with nickel on the negative electrode active material layer 32 side.

[0022] The negative electrode active material layer 32 is a layer containing a negative electrode active material. In the example of FIG. 1 , the negative electrode active material layer 32 is provided in the +Z direction of the negative electrode current collector layer 31.

[0023] The average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ It is preferable that the average charging potential of the negative electrode active material is 1.0 V vs. Li or less. This can improve the output characteristics of the battery. ＋ / Li or less, Li ４ SnS ４ On the other hand, in this embodiment, the first solid electrolyte in contact with the negative electrode active material is Li ４ SnS ４ By using a solid electrolyte in which a part of the Sn contained in the negative electrode active material is replaced with Si or at least one element selected from Si, Al, and Sb, the average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ / Li or less, the charge / discharge characteristics can be improved while suppressing reduction of the solid electrolyte in contact with the negative electrode active material. Here, the average charge potential of the negative electrode active material refers to the average negative electrode potential in a charge curve obtained in a charge test for a half cell using the negative electrode active material to be measured. Here, the average charge potential of the negative electrode active material can be measured by subjecting the half cell to charge measurement under, for example, the following conditions, and measuring the average negative electrode potential from the start of charge to the end of charge in the obtained charge curve. Charge rate: 0.1 C Charging method: CC End-of-charge voltage: 0.03 V

[0024] The negative electrode active material layer 32 contains at least one of carbon (C), tin (Sn), and silicon (Si) as the negative electrode active material. When carbon is used as the negative electrode active material, the negative electrode active material is, for example, graphite or hard carbon, with graphite being preferred. This allows the average charging potential of the negative electrode active material to be 1.0 V vs. Li ＋ / Li or less, and as described above, the negative electrode active material comes into contact with the first solid electrolyte described below, which suppresses reduction of the solid electrolyte in contact with the negative electrode active material, thereby improving charge / discharge characteristics.

[0025] In the first embodiment, the anode active material layer 32 is a film made of anode active material. That is, the anode active material layer 32 is a layer in which the anode active material is continuous from the surface on the −Z direction side (the surface on the anode current collector layer 31 side) to the surface on the +Z direction side (the surface on the electrolyte layer 40 side). In other words, the anode active material layer 32 does not substantially contain components of the electrolyte layer 40 (e.g., solid electrolyte). Examples of the continuous body include a pressure-molded body or sintered compact of only the anode active material, or a film formed by plating, sputtering, vapor deposition, or the like, but may also be a metal foil, a wafer, or the like.

[0026] The electrolyte layer 40 is a layer that does not substantially contain a positive electrode active material or a negative electrode active material, and is a layer provided between the positive electrode 20 and the negative electrode 30. The electrolyte layer 40 contains a solid electrolyte. In the first embodiment, the electrolyte layer 40 is a laminate having a first electrolyte layer 41 and a second electrolyte layer 42.

[0027] The first electrolyte layer 41 is a layer on the negative electrode 30 side of the electrolyte layer 40. In the first embodiment, the first electrolyte layer 41 is made of a first solid electrolyte. That is, the surface of the negative electrode active material of the negative electrode active material layer 32 on the +Z direction side (electrolyte layer 40 side) is coated with the first solid electrolyte. This allows the surface of the negative electrode active material to be covered with the first solid electrolyte, which has high reduction resistance, thereby improving charge / discharge characteristics. Here, whether the surface of the negative electrode active material on the electrolyte layer 40 side is coated with the first solid electrolyte is determined by the following method. First, a cross section of the battery 1 along the stacking direction is observed with a scanning electron microscope (SEM) to identify the interface between the negative electrode active material layer 32 and the electrolyte layer 40. Next, an arbitrary point near the interface on the electrolyte layer 40 side is measured with an energy dispersive X-ray fluorescence spectrometer (EDX). In this case, if a spectrum of an element derived from the first solid electrolyte, such as Si, is observed in the spectrum observed by EDX, it can be determined that the surface of the negative electrode active material on the electrolyte layer 40 side is covered with the first solid electrolyte. Here, the vicinity of the interface on the electrolyte layer 40 side refers to a region up to a surface 300 nm away from the interface in the stacking direction.

[0028] The first solid electrolyte is Li ｘ Sn １－ｗ Z ｗ S ｙ Here, 3.0≦x≦5.0 and 3.0≦y≦5.0 are satisfied. By setting the ranges, the crystal structure of the first solid electrolyte can be changed to Li ４ SnS ４Since the structure can be the same as that of the negative electrode, water resistance can be improved. Here, x and y can be obtained by obtaining the molar ratio of lithium (Li) or sulfur (S) to M from the spectral intensity measured by windowless energy dispersive X-ray spectroscopy (Window-Less EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES), or glow discharge optical emission spectrometry (GD-OES) using the electrolyte layer or negative electrode removed from the battery as a sample. Here, when measuring x and y by ICP-OES, the ICP-OES measurement is performed using a sample obtained by extracting the solid electrolyte with water or methanol from the electrolyte layer or negative electrode removed from the battery.

[0029] Composition of the first solid electrolyte: Li ｘ Sn １－ｗ Z ｗ S ｙ In the above, the element Z contains at least silicon (Si). This can improve water resistance and reduction resistance, thereby improving charge-discharge characteristics. It is preferable that Z further contains aluminum (Al). This can further improve charge-discharge characteristics. It is more preferable that Z contains antimony (Sb). This can further improve ionic conductivity. It is even more preferable that Z contains Al and Sb. This can improve ionic conductivity.

[0030] w satisfies 0<w<0.25 and preferably satisfies 0.01≦w≦0.24. Furthermore, w preferably satisfies 0<w≦0.20, more preferably satisfies 0.01≦w≦0.20, and even more preferably satisfies 0.10≦w≦0.20. By setting w within this range, water resistance and reduction resistance can be improved, thereby improving charge / discharge characteristics. w can be obtained by obtaining the molar ratio of Z to Sn from the spectral intensity measured by energy dispersive X-ray spectroscopy (EDX) and calculating from the obtained molar ratio. Furthermore, w can also be measured by comparing a calibration curve measured by secondary ion mass spectrometry (SIMS) or electron probe microanalyzer (EPMA) with a calibration curve obtained by previously measuring a standard sample with a known Sn / Z mixture ratio.

[0031] Preferably, w satisfies 0<w / (1-w)<0.33 and 0.01≦w / (1-w)≦0.32. Furthermore, w preferably satisfies 0<w / (1-w)≦0.25, more preferably 0.01≦w / (1-w)≦0.25, and even more preferably 0.11≦w / (1-w)≦0.25. This improves water resistance and reduction resistance, thereby improving charge / discharge characteristics. Here, w / (1-w) can be said to be the amount of Sn relative to the element Z. Therefore, w / (1-w) can be measured by calculating the molar ratio of element Z to Sn using energy dispersive X-ray fluorescence spectroscopy (EDX), secondary ion mass spectrometry (SIMS), or an electron probe microanalyzer (EPMA).

[0032] The crystal structure of the first solid electrolyte preferably includes a hexagonal or orthorhombic crystal structure. This allows the first solid electrolyte to have improved water resistance. The crystal structure of the first solid electrolyte can be measured by X-ray diffraction (XRD) using the electrolyte layer or the negative electrode removed from the battery as a sample. Here, in the XRD measurement of the first solid electrolyte, the crystal group P6 ３ When a peak attributed to crystal group Pnma is observed, the first solid electrolyte can be said to have a hexagonal crystal structure, and when a peak attributed to crystal group Pnma is observed, the first solid electrolyte can be said to have an orthorhombic crystal structure. The crystal structure of the first solid electrolyte can be measured using a transmission electron microscope (TEM) instead of XRD. In this case, in the electron diffraction image obtained by TEM, the crystal group P6 ３ When peaks attributable to Pmmc and Pnma are observed, it can be said that the first solid electrolyte contains a hexagonal crystal structure and an orthorhombic crystal structure, respectively.

[0033] The thickness of the first electrolyte layer 41 is preferably 100 nm or more, and more preferably 200 nm or more, so that the surface of the negative electrode active material is sufficiently covered with the first solid electrolyte, which has high reduction resistance, thereby improving the charge / discharge characteristics.

[0034] The second electrolyte layer 42 is a layer located on the +Z direction side of the first electrolyte layer 41 and is made of a second solid electrolyte different from the first solid electrolyte. The second solid electrolyte is not particularly limited as long as it is a material through which ions can move. The second solid electrolyte is, for example, Li ６ P.S. ５ Cl, Li ３ P.S. ４ , Li ４ SnS ４ and the like.

[0035] The side reinforcing portions 60 are provided to prevent short circuits in the battery 1. In the example of Fig. 1, the side reinforcing portions 60 are provided on the X-direction and Y-direction end surfaces of the positive electrode 20, the negative electrode 30, and the electrolyte layer 40. The material of the side reinforcing portions 60 is not particularly limited as long as it is an insulator, and examples thereof include resin, glass, and ceramics.

[0036] The negative electrode and battery according to the first embodiment are not limited to those described above. For example, if the negative electrode active material layer contains a conductive material, the negative electrode may not have a negative electrode current collector layer. In this case, the negative electrode active material layer serves as the negative electrode of the battery and can be connected to the outside.

[0037] The battery according to the first embodiment may also be a battery having an exterior body (case). That is, the battery according to the first embodiment may be a battery in which a laminate including the positive electrode 20, the negative electrode 30, and the electrolyte layer 40 is housed in an exterior body made of metal, ceramics, or the like.

[0038] Furthermore, the second electrolyte layer 42 is not an essential component, and the electrolyte layer 40 does not necessarily have to have the second electrolyte layer 42. That is, the surface of the first electrolyte layer 41 opposite to the negative electrode may be in contact with the positive electrode 20.

[0039] As described above, the solid electrolyte (first solid electrolyte) according to this embodiment has the composition formula Li ｘ Sn １－ｗ Z ｗ S ｙ where Z contains at least Si and satisfies 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w<0.25. This can improve water resistance and reduction resistance, thereby improving charge-discharge characteristics.

[0040] In a preferred embodiment, 0<w≦0.20 is further satisfied, which can improve water resistance and reduction resistance, thereby further improving charge-discharge characteristics.

[0041] In a more desirable embodiment, 0.10≦w≦0.20 is further satisfied, which can improve water resistance and reduction resistance, thereby further improving charge-discharge characteristics.

[0042] The solid electrolyte (first solid electrolyte) according to this embodiment has a composition formula of Li ｘ Sn １－ｗ Z ｗ S ｙwhere Z contains at least Si and satisfies 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w / (1−w)<0.33. This improves water resistance and reduction resistance, thereby improving charge-discharge characteristics.

[0043] In a preferred embodiment, the relationship 0<w / (1-w)≦0.25 is further satisfied, which can improve water resistance and reduction resistance, thereby further improving charge-discharge characteristics.

[0044] In a more desirable embodiment, the relationship 0.11≦w / (1−w)≦0.25 is further satisfied, which can improve water resistance and reduction resistance, thereby further improving charge-discharge characteristics.

[0045] In a preferred embodiment, Z further contains Al, which can improve the charge-discharge characteristics.

[0046] In a preferred embodiment, Z further contains Sb, which can further improve ionic conductivity.

[0047] In a preferred embodiment, Z further contains Al and Sb, which can further improve the charge-discharge characteristics.

[0048] A desirable embodiment is a hexagonal or orthorhombic crystal structure, which allows the first solid electrolyte to have improved water resistance.

[0049] As described above, the secondary battery according to this embodiment includes the positive electrode 20, the negative electrode 30 having the negative electrode active material layer 32 containing the negative electrode active material, and the electrolyte layer 40 containing the solid electrolyte (first solid electrolyte) according to this embodiment. This improves water resistance and reduction resistance, thereby improving charge / discharge characteristics.

[0050] The negative electrode active material layer 32 may also be a film made of a negative electrode active material. In this case, the water resistance and reduction resistance can be improved, and therefore the charge / discharge characteristics can be improved.

[0051] In a preferred embodiment, the surface of the negative electrode active material layer 32 facing the electrolyte layer 40 is coated with a solid electrolyte. This allows the surface of the negative electrode active material to be covered with the first solid electrolyte, which has high reduction resistance, thereby improving the charge / discharge characteristics.

[0052] In a preferred embodiment, the average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ / Li or less. This can improve the output characteristics.

[0053] In a preferred embodiment, the negative electrode active material contains at least one of C, Si, and Sn, which can improve the output characteristics.

[0054] Second Embodiment Fig. 2 is a schematic cross-sectional view showing an example of a battery according to a second embodiment. As shown in Fig. 2, the negative electrode 30A of the battery 1A according to the second embodiment differs from the first embodiment in that the negative electrode active material is particulate and the negative electrode active material layer 32A contains a first solid electrolyte. The second embodiment will be described below with reference to Fig. 2.

[0055] In the present disclosure, when the negative electrode active material is in a particulate form, a plane 30a that passes through the point on the surface of the negative electrode active material particle that is farthest from the surface of the negative electrode current collector layer in the Z direction and that is parallel to the surface of the negative electrode current collector layer is defined as the interface between the negative electrode 30A and the electrolyte layer 40. In the example of FIG. 2 , the interface between the negative electrode 30A and the electrolyte layer 40 corresponds to plane 30a that passes through the point on the surface of the negative electrode active material particle that is furthest in the +Z direction and is parallel to the X and Y directions. That is, in the example of FIG. 2 , the side of the negative electrode active material layer 31 closer to the negative electrode current collector layer 31 than plane 30a is the negative electrode active material layer 32A, and the side of the positive electrode 20 closer to the surface 30a is the electrolyte layer 40.

[0056] In the second embodiment, the anode active material layer 32A includes a particulate anode active material 32a and a first solid electrolyte 32b. Here, "particulate" refers to the anode active material layer not being a continuous film. That is, in the second embodiment, the anode active material particles are intermittently arranged from the surface on the -Z direction side (the surface on the anode current collector layer 31 side) to the surface on the +Z direction side (the surface on the electrolyte layer 40 side).

[0057] In the second embodiment, the surface of the particulate anode active material 32a is coated with a first solid electrolyte 32b. In the example shown in FIG. 2, the first solid electrolyte 32b surrounds the particles of the anode active material 32a. In other words, in the anode active material layer 32A according to the second embodiment, the particles of the anode active material 32a are dispersed in the first solid electrolyte 32b. This allows the surface of the anode active material to be coated with the first solid electrolyte, which has high reduction resistance, thereby improving charge / discharge characteristics. Whether the surface of the particulate anode active material 32a is coated with the first solid electrolyte 32b is determined using the following method. First, a cross section of the battery 1 along the stacking direction is observed using a scanning electron microscope (SEM) to identify the interface between the particulate anode active material 32a and the first solid electrolyte 32b. Next, EDX measurement is performed at an arbitrary point near the interface on the first solid electrolyte 32b side. In this case, if a spectrum of an element derived from the first solid electrolyte, such as Si, is observed in the spectrum observed by EDX, it can be determined that the surface of the particulate negative electrode active material 32 a is coated with the first solid electrolyte 32 b. Here, the vicinity of the interface refers to a region from the interface to a surface 300 nm away in the normal direction to the surface of the particulate negative electrode active material 32 a.

[0058] The battery according to the second embodiment is not limited to the one described above. FIG. 3 is a schematic cross-sectional view showing an example of a battery according to a first modification of the second embodiment. FIG. 4 is a schematic cross-sectional view showing an example of a battery according to a second modification of the second embodiment. The battery according to the second embodiment may be the batteries 1B and 1C shown in FIGS. 3 and 4. In the first modification, the electrolyte layer 40A is a single layer made of the first solid electrolyte. In the second modification, the electrolyte layer 40B is a single layer made of the second solid electrolyte. Even in this case, the charge / discharge characteristics can be improved.

[0059] As described above, the secondary battery according to the second embodiment includes the positive electrode 20, the negative electrode 30A including the particulate negative electrode active material 32a and the solid electrolyte according to the first embodiment (first solid electrolyte 32b), and the electrolyte layer 40. Even in this case, the water resistance and reduction resistance can be improved, thereby improving the charge / discharge characteristics.

[0060] In a preferred embodiment, at least a portion of the surface of the particles of the negative electrode active material 32 a is coated with a solid electrolyte (first solid electrolyte 32 b), which has high reduction resistance, thereby improving charge / discharge characteristics.

[0061] In a preferred embodiment, the average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ / Li or less. This can improve the output characteristics.

[0062] In a preferred embodiment, the negative electrode active material contains at least one of C, Si, and Sn, which can improve the output characteristics.

[0063] 5 is a schematic cross-sectional view showing an example of a battery according to the third embodiment. As shown in Fig. 5, in the anode 30B of the battery 1D according to the third embodiment, the anode active material is particulate, and the anode active material layer 32B includes a first solid electrolyte 32b and a second solid electrolyte 32c, which are different from those of the first embodiment.

[0064] In the third embodiment, the anode active material layer 32B includes a particulate anode active material 32a, a first solid electrolyte 32b, and a second solid electrolyte 32c. In the example of FIG. 5 , the first solid electrolyte 32b coats the particles of the anode active material 32a, and the second solid electrolyte 32c surrounds the particles of the anode active material 32a coated with the first solid electrolyte 32b. In other words, in the anode active material layer 32B according to the third embodiment, the particles of the anode active material 32a coated with the first solid electrolyte 32b are dispersed in the second solid electrolyte 32c. This allows the surface of the anode active material 32a to be covered with the first solid electrolyte 32b, thereby improving charge / discharge characteristics. Here, whether the surface of the particulate anode active material 32a is coated with the first solid electrolyte 32b is determined by the following method. First, a cross section of the battery 1D along the stacking direction is observed using a scanning electron microscope (SEM) to identify the interface between the particulate anode active material 32a and the first solid electrolyte 32b. Next, EDX measurements are performed at any point near the interface on the first solid electrolyte 32b side. In this case, if a spectrum of an element derived from the first solid electrolyte, such as Si, is observed in the EDX spectrum, it can be determined that the surface of the particulate anode active material 32a is coated with the first solid electrolyte 32b. Here, the "near-interface" refers to a region extending from the interface to a surface 300 nm away from the surface of the particulate anode active material 32a in the normal direction. It is sufficient that at least a portion of the surface of the anode active material 32a particles is coated with the first solid electrolyte; more preferably, the entire surface of the anode active material 32a particles is coated with the first solid electrolyte.

[0065] The thickness of the first solid electrolyte 32b covering the particulate negative electrode active material 32a is preferably 100 nm or more, and more preferably 200 nm or more. Here, the thickness of the first solid electrolyte 32b refers to the average length of the first solid electrolyte 32b in the direction normal to the surface of the particles of the negative electrode active material 32a. This allows the surface of the negative electrode active material 32a to be sufficiently covered with the first solid electrolyte 32b, which has high reduction resistance, thereby further improving charge / discharge characteristics.

[0066] In the example of FIG. 5, the electrolyte layer 40A is a single layer made of the second solid electrolyte, but this is merely an example and is not limited to this. For example, the electrolyte layer 40A may be a single layer made of the first solid electrolyte, or a laminate of the first solid electrolyte and the second solid electrolyte.

[0067] Examples of the present embodiment will be described below, but the present embodiment is not limited to the following examples.

[0068] Example 1 The first solid electrolyte according to Example 1 was prepared by the following method. ２ S powder, Sn powder, Si powder, and S powder were weighed and mixed in a molar ratio of 2:0.9:0.1:2. Next, the total amount (g) of the raw material mixture was dissolved in pure water so that the solution concentration was 15 wt %, and the mixture was stirred for 24 hours while heating at 80°C. The resulting mixture was then vacuum dried at 120°C to obtain a precursor powder of the solid electrolyte. The resulting precursor powder was then heated to 200°C at a heating rate of 10°C / min in an inert gas and maintained at that temperature for 3 hours for heat treatment, thereby obtaining a powder of the first solid electrolyte according to Example 1.

[0069] <Water Resistance Evaluation> The water resistance of the first solid electrolyte according to Example 1 was evaluated by the following method. 100 mg of the obtained first solid electrolyte and a hydrogen sulfide gas sensor were placed in a sealed container with a volume of 1 L and exposed to air with a dew point temperature of −30° C. for 1 hour. At this time, the hydrogen sulfide concentration in the sealed container was measured by reading the measurement value of the hydrogen sulfide sensor.

[0070] <Ionic Conductivity Measurement> The ionic conductivity of the first solid electrolyte according to Example 1 was measured by the following method. 100 mg of the obtained first solid electrolyte was pressed using a ceramic insulating cylinder with a diameter of 10 mm at room temperature and a pressure of 294 MPa to obtain a pellet. Thereafter, an electrochemical impedance spectrum was measured at an amplitude of 10 mV and a frequency of 106 Hz-10 Hz while a pressure of 98 MPa was applied to the pellet. The ionic conductivity of the first solid electrolyte according to Example 1 was calculated from the resistance value obtained from the spectrum and the thickness of the pellet.

[0071] <Charge / Discharge Measurement> A plurality of batteries (first to fourth batteries) having different negative electrode active materials were fabricated using the first solid electrolyte according to Example 1, and charge / discharge measurements were performed.

[0072] In the first battery, a Si film was used as the negative electrode active material. Here, the first battery is an example of the battery according to the first embodiment. The first battery was fabricated by the following method.

[0073] The electrolyte layer of the first battery was prepared by the following method. A zirconia cylinder having a diameter of 10 mm was filled with Li as the second solid electrolyte. ６ P.S. ５ 100 mg of Cl powder is 1 tf / (cm ２ The second electrolyte layer was then compressed at a pressure of 1 tf / (cm ２ The mixture was pressed at a temperature of 100°C (min) to prepare a first electrolyte layer. In this way, an electrolyte layer for the first battery was prepared.

[0074] The negative electrode of the first battery was fabricated by the following method. First, a 13 μm thick Si film was punched out as a negative electrode active material to a diameter of 8 mm so as to have an amount (1.43 mg) corresponding to a theoretical capacity of 6 mAh. The negative electrode active material was placed on the first electrolyte layer side of the electrolyte layer fabricated above, and the negative electrode active material was applied with a current density of 3 tf / (cm ２ The negative electrode active material layer was then pressed at a pressure of 1 / 2 min to form a negative electrode active material layer. Thereafter, a stainless steel foil was attached to the negative electrode active material layer as a negative electrode current collector layer to form a negative electrode.

[0075] The first battery was assembled in the following manner. A counter electrode made of an In—Li alloy was attached to the second electrolyte layer side of the electrolyte layer. Then, a stainless steel foil was attached as a counter electrode current collector, and a current density of 1 tf / (cm ２ The laminate was pressed in the stacking direction at a pressure of 1 / 2 sq. min. Thus, a first battery according to Example 1 was fabricated.

[0076] The first battery was charged and discharged under the following conditions. More specifically, the fabricated battery was charged to an upper limit voltage using the following charge / discharge method and charge / discharge current, and then discharged to a lower limit voltage using the following charge / discharge method and charge / discharge current. Here, 1 C was defined as the theoretical capacity of the first battery, 6 mAh. The initial discharge capacity and charge / discharge efficiency were measured using this. Here, the initial discharge capacity was calculated per 1 g of negative electrode active material. The charge / discharge efficiency was calculated as the ratio of the discharge capacity at the initial discharge to the charge capacity at the initial charge. Charge / discharge method: CC Charge / discharge current: 0.05 C Lower limit voltage: -0.57 V (0.05 V vs. Li ＋ / Li) Upper limit voltage: 0.88V (1.5V vs. Li ＋ / Li)

[0077] The second battery was fabricated in the same manner as the first battery, except that powdered graphite was used as the negative electrode active material instead of the Si film, and charge / discharge measurements were performed. In the negative electrode fabrication process for the second battery, the first solid electrolyte powder according to Example 1 and powdered graphite as the negative electrode active material were weighed out in a volume ratio of 1:1, and kneaded in a mortar to obtain a negative electrode mixture. The fabricated negative electrode mixture was then weighed out so that it contained an amount (16.1 g) of graphite as the negative electrode active material corresponding to a theoretical capacity of 6 mAh. This allowed the theoretical capacity of the first battery to be 6 mAh. The negative electrode mixture was then placed on the first electrolyte layer side of the electrolyte layer fabricated above, and a 3 tf / (cm ２ The negative electrode active material layer was produced by compressing the negative electrode active material at a temperature of 1000 kJ / min. As a result, the surface of the negative electrode active material of the second battery came into contact with the particles of the first solid electrolyte of Example 1. The second battery is an example of the battery according to the second embodiment.

[0078] The third battery was fabricated in the same manner as the second battery, except that powdered Si was used as the negative electrode active material instead of powdered graphite, and charge / discharge measurements were performed. In the negative electrode fabrication process for the third battery, the fabricated negative electrode mixture was weighed so that it contained an amount of Si (1.43 mg) as the negative electrode active material corresponding to a theoretical capacity of 6 mAh.

[0079] The fourth battery was fabricated in the same manner as the second battery, except that powdered Sn was used as the negative electrode active material instead of powdered graphite, and charge / discharge measurements were performed. In the negative electrode fabrication process for the third battery, the fabricated negative electrode mixture was weighed so that it contained an amount (6 mg) of Sn as the negative electrode active material corresponding to a theoretical capacity of 6 mAh.

[0080] (Example 2) In Example 2, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, and S powder were weighed and mixed in a molar ratio of 2:0.85:0.15:2.

[0081] (Example 3) In Example 3, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, and S powder were weighed and mixed in a molar ratio of 2:0.8:0.2:2.

[0082] (Example 4) In Example 4, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, Al powder, and S powder were weighed and mixed in a molar ratio of 1.925:0.85:0.1:0.05:1.975.

[0083] (Example 5) In Example 5, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, Al powder, and S powder were weighed and mixed in a molar ratio of 1.85:0.85:0.05:0.1:1.95.

[0084] (Example 6) In Example 6, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, Sb powder, and S powder were weighed and mixed in a molar ratio of 1.975:0.85:0.05:0.1:2.025.

[0085] (Example 7) In Example 7, Li was used as a raw material. ２The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, Sb powder, and S powder were weighed and mixed in a molar ratio of 1.95:0.85:0.1:0.05:2.05.

[0086] (Example 8) In Example 8, Li was used as a raw material. ２ A first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, Al powder, Sb powder, and S powder were weighed and mixed in a molar ratio of 1.9:0.85:0.05:0.05:0.05:2.

[0087] (Comparative Example 1) In Comparative Example 1, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, and S powder were weighed and mixed in a molar ratio of 2:1:2.

[0088] (Comparative Example 2) In Comparative Example 2, Li was used as a raw material. ２ The first solid electrolyte was prepared and measured in the same manner as in Example 1, except that S powder, Sn powder, Si powder, and S powder were weighed and mixed in a molar ratio of 2:0.75:0.25:2.

[0089] Table 1 shows the compositions of the first solid electrolytes according to Examples 1 to 8 and Comparative Examples 1 and 2, as well as the measurement results.

[0090]

[0091] As shown in Table 1, in the water resistance test, the hydrogen sulfide gas sensors in Examples 1 to 8 and Comparative Examples 1 and 2 continued to show values ​​below the lower measurement limit of 0.1 ppm. Therefore, it is clear that the first solid electrolytes in Examples 1 to 8, like the first solid electrolytes in Comparative Examples 1 and 2, have sufficient water resistance.

[0092] As shown in Table 1, in Examples 1 to 8 where 0<w<0.25, the initial discharge capacity and charge / discharge efficiency were improved compared to Comparative Example 1 where w=0 and Comparative Example 2 where w=0.25. This shows that satisfying 0<w<0.25 can improve the charge / discharge characteristics.

[0093] As shown in Table 1, in Examples 1 to 8 where 0<w≦0.20, the initial discharge capacity and charge / discharge efficiency were improved compared to Comparative Example 1 where w=0 and Comparative Example 2 where w>0.20. This shows that satisfying 0<w≦0.20 can improve the charge / discharge characteristics.

[0094] As shown in Table 1, in Examples 1 to 8 where 0<w / (1-w)<0.33, the initial discharge capacity and charge / discharge efficiency were improved compared to Comparative Example 1 where w / (1-w)=0 and Comparative Example 2 where w / (1-w)=0.33. This shows that satisfying 0<w / (1-w)<0.33 can improve charge / discharge characteristics.

[0095] As shown in Table 1, in Examples 1 to 8 where 0<w / (1-w)≦0.25, the initial discharge capacity and charge / discharge efficiency were improved compared to Comparative Example 1 where w / (1-w)=0 and Comparative Example 2 where w / (1-w)>0.25. This shows that satisfying 0<w / (1-w)≦0.25 can improve the charge / discharge characteristics.

[0096] As shown in Table 1, in Examples 1 to 8 where 0.11≦w / (1−w)≦0.25, the initial discharge capacity and charge / discharge efficiency were improved compared to Comparative Example 1 where w / (1−w)<0.11 and Comparative Example 2 where w / (1−w)>0.25. This shows that satisfying 0.11≦w / (1−w)≦0.25 can improve charge / discharge characteristics.

[0097] As shown in Table 1, in Examples 4, 5, and 8 in which Al was further added, the ionic conductivity was improved compared to Example 2 in which the Sn composition ratio (1-w) was 85 mol%, the same as in Examples 4 and 5, and no Al was added. This shows that the addition of Al can improve ionic conductivity.

[0098] As shown in Table 1, in Examples 6 and 7 in which Sb was further added, the ionic conductivity was improved compared to Example 2 in which Sn was not added and the composition ratio (1-w) was 85 mol%, the same as in Examples 6 and 7. This shows that the addition of Sb can improve the ionic conductivity without reducing the initial discharge capacity.

[0099] As shown in Table 1, Example 8, in which Al and Sb were further added, had an improved initial discharge capacity compared to Examples 4 and 5, in which Al was added but Sb was not. This shows that the addition of Al and Sb can improve ionic conductivity while suppressing the decrease in initial discharge capacity due to the addition of Al.

[0100] The above-described embodiments are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present disclosure.

[0101] The present invention can also take the following forms: (1) A composition formula of Li ｘ Sn １－ｗ Z ｗ S ｙ (2) A solid electrolyte according to (1), which further satisfies 0<w<0.20. (3) A solid electrolyte according to (2), which further satisfies 0.10<w<0.20. (4) A solid electrolyte according to (3), which further satisfies 0.10<w<0.20. (5) A solid electrolyte according to (4), which further satisfies 0.10<w<0.20. (6) A solid electrolyte according to (4), which further satisfies 0.10<w<0.20. (7) A solid electrolyte according to (4), which further satisfies 0.10<w<0.20. ｘ Sn １－ｗ Z ｗ S ｙ(5) A solid electrolyte represented by the formula (1), wherein Z contains at least Si and satisfies 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w / (1−w)<0.33. (5) A solid electrolyte according to (4), which further satisfies 0<w / (1−w)≦0.25. (6) A solid electrolyte according to (5), which further satisfies 0.11≦w / (1−w)≦0.25. (7) A solid electrolyte according to any one of (1) to (6), wherein Z further contains Al. (8) A solid electrolyte according to any one of (1) to (6), wherein Z further contains Sb. (9) A solid electrolyte according to any one of (1) to (6), wherein Z further contains Al and Sb. (10) A solid electrolyte according to any one of (1) to (9), which has a hexagonal or orthorhombic crystal structure. (11) A secondary battery comprising: a positive electrode; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and an electrolyte layer containing the solid electrolyte according to any one of (1) to (10). (12) The secondary battery according to (11), wherein the negative electrode active material layer is a film made of a negative electrode active material. (13) The secondary battery according to (12), wherein a surface of the negative electrode active material layer facing the electrolyte layer is coated with the solid electrolyte. (14) The average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ (15) The secondary battery according to any one of (11) to (14), wherein the negative electrode active material contains at least one of C, Si, and Sn. (16) A secondary battery comprising: a positive electrode; a negative electrode containing a particulate negative electrode active material and the solid electrolyte according to any one of (1) to (10); and an electrolyte layer. (17) The secondary battery according to (16), wherein at least a portion of the surface of particles of the negative electrode active material is coated with the solid electrolyte. (18) The negative electrode active material has an average charging potential of 1.0 V vs Li ＋ (19) The secondary battery according to any one of (16) to (18), wherein the negative electrode active material contains at least one of C, Si, and Sn.

[0102] REFERENCE SIGNS LIST 1, 1A to 1D Battery 10 Protective layer 20 Positive electrode 21 Positive electrode current collector layer 22 Positive electrode active material layer 30, 30A, 30B Negative electrode 31 Negative electrode current collector layer 32, 32A, 32B Negative electrode active material layer 32a Negative electrode active material 32b First solid electrolyte 32c Second solid electrolyte 40, 40A, 40B Electrolyte layer 41 First electrolyte layer 42 Second electrolyte layer 60 Side reinforcing portion

Claims

1. The formula is Li ｘ Sn １－ｗ Z ｗ S ｙ wherein Z contains at least Si, and 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w<0.25 are satisfied.

2. The solid electrolyte according to claim 1, further satisfying 0<w≦0.

20.

3. The solid electrolyte according to claim 2, further satisfying 0.10≦w≦0.

20.

4. The formula is Li ｘ Sn １－ｗ Z ｗ S ｙ wherein Z contains at least Si, and 3.0≦x≦5.0, 3.0≦y≦5.0, and 0<w / (1−w)<0.33 are satisfied.

5. The solid electrolyte according to claim 4, further satisfying 0<w / (1-w)≦0.

25.

6. The solid electrolyte according to claim 5, further satisfying 0.11≦w / (1−w)≦0.

25.

7. The solid electrolyte according to any one of claims 1 to 6, wherein Z further contains Al.

8. A solid electrolyte according to any one of claims 1 to 6, wherein Z further contains Sb.

9. The solid electrolyte according to any one of claims 1 to 6, wherein Z further includes Al and Sb.

10. The solid electrolyte of any one of claims 1 to 9, comprising a hexagonal or orthorhombic crystal structure.

11. A secondary battery comprising: a positive electrode; a negative electrode having a negative electrode active material layer containing a negative electrode active material; and an electrolyte layer containing the solid electrolyte according to any one of claims 1 to 10.

12. The secondary battery according to claim 11, wherein the negative electrode active material layer is a film made of a negative electrode active material.

13. The secondary battery according to claim 12, wherein the surface of the negative electrode active material layer facing the electrolyte layer is coated with the solid electrolyte.

14. The average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ The secondary battery according to claim 11 , wherein the Cr content is 0.15 / Li or less.

15. The secondary battery according to any one of claims 11 to 14, wherein the negative electrode active material contains at least one of C, Si, and Sn.

16. A secondary battery comprising: a positive electrode; a negative electrode containing a particulate negative electrode active material and the solid electrolyte according to any one of claims 1 to 10; and an electrolyte layer.

17. The secondary battery according to claim 16, wherein at least a portion of the surface of the particles of the negative electrode active material is coated with the solid electrolyte.

18. The average charging potential of the negative electrode active material is 1.0 V vs. Li ＋ The secondary battery according to claim 16 or 17, wherein the Li / Li ratio is 0.1:1 or less.

19. The secondary battery according to any one of claims 16 to 18, wherein the negative electrode active material contains at least one of C, Si, and Sn.