Sulfide solid electrolyte material

Abstract

Provided is a solid sulfide electrolyte material having a lithium ion conductivity approximately equal to or exceeding that of LGPS.　The solid sulfide electrolyte material has a composition of Li9.54[Si1-δMδ]1.74P1.44S11.1Br0.3O0.6, Li9.54[Si1-δMδ]1.74P1.44S11.7Br0.3, Li9.714[Si1-δM'δ]1.74P1.44S11.1Br0.3O0.6, or Li9.714[Si1-δM'δ]1.74P1.44S11.7Br0.3, where M is Ge, Sn, or Ti; M' is B or Al; when M is Ge, 0≤δ≤0.5; when M is Sn, 0≤δ≤0.4; when M is Ti, 0≤δ≤0.1; when M' is B, 0≤δ≤0.1; and when M' is Al, 0≤δ≤0.1.

Description

Technical Field

[0001] The present invention relates to a novel sulfide solid electrolyte material.

Background Art

[0002] With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones in recent years, the development of batteries used as their power sources has been emphasized. Also, in the automotive industry and the like, the development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles has been underway. Currently, among various batteries, lithium batteries are attracting attention from the viewpoint of high energy density.

[0003] Currently commercially available lithium batteries use an electrolyte containing a flammable organic solvent, so it is necessary to install a safety device for suppressing the temperature rise during short circuit and to improve the structure and materials for preventing short circuit. On the other hand, a lithium battery in which the electrolyte is changed to a solid electrolyte layer and the battery is fully solidified does not use a flammable organic solvent in the battery, so the safety device can be simplified and it is considered to be excellent in manufacturing cost and productivity. However, currently, the fully solidified lithium battery has a lower energy density than the liquid-based battery.

[0004] As a solid electrolyte material used for all-solid lithium batteries, sulfide solid electrolyte materials are known. For example, Li-P-S-based sulfide solid electrolytes have been reported (see, for example, Non-Patent Documents 1 to 5). However, the ionic conductivity of the reported crystalline sulfides is about 10 -7 ~10 -4 Scm -2 and the high energy density of all-solid lithium batteries has not been fully achieved.

[0005] Non-Patent Document 6 shows a high ionic conductivity comparable to that of an electrolyte of 1.2×10 -2 Scm -1 for Li 10 GeP2S 12(In the following, it may be referred to as "LGPS-based sulfide solid electrolyte", "LGPS", etc.) has been reported. However, the search for materials other than LGPS has continued, and such novel solid electrolytes are naturally expected to have an ionic conductivity almost equal to or higher than that of LGPS.)

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Non-Patent Document 10

Non-Patent Document 11

Non-Patent Document 12

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the above problems, the present invention aims to provide a sulfide solid electrolyte material having a lithium ion conductivity substantially equal to or higher than that of LGPS.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention provides the following means.

[0009] [1] Li 9.54 [Si 1-δ M δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Or, Li 9.54 [Si 1-δ M δ 1.74 P 1.44 S 11.7 Br 0.3 Or, Li 9.714 [Si 1-δ M’ δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Or, Li 9.714 [Si 1-δ M’ δ 1.74 P 1.44 S 11.7 Br 0.3 having the composition of, where M is Ge, Sn or Ti, and M’ is either B or Al, when M is Ge, 0 ≦ δ ≦ 0.5, when M is Sn, 0 ≦ δ ≦ 0.4, when M is Ti, 0 ≦ δ ≦ 0.1, when M’ is B, 0 ≦ δ ≦ 0.1, when M’ is Al, 0 ≦ δ ≦ 0.1, a sulfide solid electrolyte material. [2] Li 9.54 Si 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.9 Ge 0.1 1.74 P 1.44 S 11.1 Br​​​​​0.3 O 0.6 Li 9.54 [Si 0.8 Ge 0.2 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.7 Ge 0.3 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.6 Ge 0.4 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.5 Ge 0.5 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.9 Sn 0.1 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.8 Sn 0.2 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.7 Sn 0.3 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.6 Sn 0.4 ​​​​​​​​1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Li 9.54 [Si 0.9 Ti 0.1 1.74 P 1.44 S 11.7 Br 0.3 Li 9.714 [Si 0.9 B 0.1 1.74 P 1.44 S 11.7 Br 0.3 Li 9.714 [Si 0.9 Al 0.1 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 The sulfide solid electrolyte material according to [1], having any one of the compositions. [3] Li 9.54 [Si 0.6 Ge 0.4 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 The sulfide solid electrolyte material according to [1] or [2], having the composition. [4] The sulfide solid electrolyte material according to any one of [1] to [3], having a lithium ion conductivity of 3.2 × 10 -2 S / cm or more. [5] The sulfide solid electrolyte material according to any one of [1] to [4], having peaks at positions of 2θ = 12.33 ± 0.04°, 14.34 ± 0.03°, 17.32 ± 0.08°, 20.11 ± 0.07°, 20.33 ± 0.04°, 23.45 ± 0.11°, 23.84 ± 0.05°, 26.83 ± 0.07°, 28.90 ± 0.05°, 29.46 ± 0.22°, 31.52 ± 0.05°, 33.19 ± 0.06° in X-ray diffraction measurement using CuKα rays. ​​​​[6]It includes a cubic unit cell with the space group of P42 / nmc(137), wherein the unit cell i) Li(2)[S / Br / O]6 octahedra, ii) Si(1) / M(1) / P(1)[S / Br / O]4 tetrahedra, iii) Si(2) / P(2)[S / Br / O]4 tetrahedra, iv) Li(4)[S / Br / O]6 octahedra, v) includes Li(1), Li(3a), and Li(3b) sites, wherein the i) Li(2)[S / Br / O]6 octahedra and the ii) Si(1) / M(1) / P(1)[S / Br / O]4 tetrahedra form a one-dimensional framework structure, wherein the iii) Si(2) / P(2)[S / Br / O]4 tetrahedra are located between the i) Li(2)[S / Br / O]6 octahedra and are connected by vertex (corner) sharing to form a three-dimensional framework structure, wherein the iv) Li(4)[S / Br / O]6 octahedra are connected to the iii) Si(2) / P(2)[S / Br / O]4 tetrahedra by edge sharing, and the Li atoms at the v) Li(1), Li(3a), and Li(3b) sites can move along the c-axis, i.e., the

[0001] direction, A sulfide solid electrolyte material according to any one of [1] to [5], having a crystal structure.

Advantages of the Invention

[0010] A sulfide solid electrolyte material according to an embodiment of the present invention is a novel electrolyte material and can have a lithium ion conductivity substantially equivalent to or higher than that of LGPS. Further, a sulfide solid electrolyte material according to an embodiment of the present invention is also excellent in thermal stability. Therefore, by using the sulfide solid electrolyte material of this embodiment as a battery material or the like, a battery or the like having a high ion conductivity can be obtained. In particular, by using the sulfide solid electrolyte material as an electrolyte for an electrode, it is also possible to form a thick film of the electrode up to about 1 mm.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 9

Mode for Carrying Out the Invention

[0012] Hereinafter, the sulfide solid electrolyte material of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0013] First, the sulfide solid electrolyte material of the present invention will be described. The inventors of the present invention 10 GeP2S 12 (LGPS-based sulfide solid electrolyte), by substituting anions and cations in an appropriate ratio, it has been found that a sulfide solid electrolyte material having a lithium ion conductivity substantially equivalent to or higher than that of LGPS can be obtained. Specifically, regarding the possibility of expanding the bottleneck of the Li ion path by substituting ionic sites in the solid electrolyte with isovalent elements having a large ionic radius, such as Br or I atoms. On the other hand, since such substitution is too large to occupy the ionic sites in the crystal structure, the possibility of simultaneously introducing elements with a small ionic radius, such as O atoms, to balance the volume of the ionic sites was examined. Furthermore, since the cation species is considered to be closely related to the bottleneck of the LGPS-type electrolyte, in addition to anion substitution, the simultaneous substitution of cations was examined. As a result of these examinations, the present invention was completed.

[0014] (Composition) The sulfide solid electrolyte material according to the present invention is Li9.54 [Si 1-δ M δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Or, Li 9.54 [Si 1-δ M δ 1.74 P 1.44 S 11.7 Br 0.3 Or, Li 9.714 [Si 1-δ M’ δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 Or, Li 9.714 [Si 1-δ M’ δ 1.74 P 1.44 S 11.7 Br 0.3 has a composition of where M is Ge, Sn or Ti, and M’ is either B or Al, when M is Ge, 0 ≦ δ ≦ 0.5, when M is Sn, 0 ≦ δ ≦ 0.4, when M is Ti, 0 ≦ δ ≦ 0.1, when M’ is B, 0 ≦ δ ≦ 0.1, when M’ is Al, 0 ≦ δ ≦ 0.1.

[0015] The inventors derived from the LGPS-based sulfide solid electrolyte and have a high ionic conductivity of 2.5×10 -2 Scm -1 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 ​​​​Based on (LSiPSCl), first, attempts were made for multi-anion substitution with halogen and oxygen, and further, Si atoms were partially replaced with Ge or Sn atoms. Figure 1 shows the X-ray diffraction spectra when the ratio of replacing Si atoms with Ge or Sn atoms was varied. Figure 1(A) shows Li 9.54 [Si 1-δ Ge δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 (0 ≤ δ ≤ 1), and Figure 1(B) shows Li 9.54 [Si 1-δ Sn δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 (0 ≤ δ ≤ 0.6). The main phase is indexed to the space group P42 / nmc(137). On the right side of each of Figure 1(A) and (B), an enlarged pattern near 29.5° is shown to indicate the peak shift of each group. Using the XRD data, the ratio (phase purity) of the crystal phases contained was determined by Rietveld analysis. In a typical example, the phase purity of the LGPS type is determined as the mass ratio of the LGPS type phase to all the compounds identified by Rietveld analysis. The results are shown in Table 1. Also, in Figure 4, the lattice constants calculated from the synchrotron X-ray diffraction data are shown. In the LGPS type LSiMδPSBrO phase, as the amount of Ge / Sn (related to δ) increases, the unit cell volume increases, confirming that Si is replaced by Ge or Sn. From this, the solid solubility limit in these LGPS type phases may be determined. Furthermore, in Figure 6, the conductivity (in the compressed powder state with grain boundary resistance at room temperature) of a series of single-phase LSiMδPSBrO samples is shown, and the conductivity of some of them exceeds 10 mScm -1 . In addition, for LSiGe 0.4 PSBrO, when the in-crystal conductivity was evaluated at t (crystal structure index) = 17.2, which is an approximate value at which the phase purity and conductivity reach the maximum values, LSiGe 0.4 ​​PSBrO has a confirmed in-crystal conductivity of 10 mS cm -1 or higher.

[0016]

Table 1

[0017] It can be seen from Figure 1 that as the ratio (δ) of elemental substitution increases, the change in the X-ray diffraction spectrum also increases. According to the ratio of crystal phases (phase purity) by Rietveld analysis in Table 1, the following is confirmed. · When substituting with Ge, if the substitution ratio (δ) is 0 ≦ δ ≦ 0.5, the LGPS phase contains 100% by mass. · When substituting with Sn, if the substitution ratio (δ) is 0 ≦ δ ≦ 0.4, the LGPS phase contains 100% by mass. · In the case of δ = 0, it is 9.54 Li 1.74 Si 1.44 P 11.1 S 0.3 O 0.6 and the LGPS phase contains 100% by mass. · When substituting with Ti, it has also been confirmed that if the substitution ratio (δ) is 0 ≦ δ ≦ 0.1, the LGPS phase contains 100% by mass. · When substituting with B, it has also been confirmed that if the substitution ratio (δ) is 0 ≦ δ ≦ 0.1, the LGPS phase contains 100% by mass. · When substituting with Al, it has also been confirmed that if the substitution ratio (δ) is 0 ≦ δ ≦ 0.1, the LGPS phase contains 100% by mass.

[0018] (X-ray diffraction peak) In one embodiment of the present invention, it may be a sulfide solid electrolyte material having peaks at positions of 2θ = 12.33 ± 0.04°, 14.34 ± 0.03°, 17.32 ± 0.08°, 20.11 ± 0.07°, 20.33 ± 0.04°, 23.45 ± 0.11°, 23.84 ± 0.05°, 26.83 ± 0.07°, 28.90 ± 0.05°, 29.46 ± 0.22°, 31.52 ± 0.05°, 33.19 ± 0.06° in X-ray diffraction measurement using CuKα rays. The X-ray diffraction peaks are determined by the crystal structure, and the crystal structure is considered to be related to the ionic conductivity. And, the sulfide solid electrolyte material according to the present embodiment is Li 10 GeP2S 12 (LGPS)-derived, having a high ionic conductivity of 2.5×10 -2 Scm -1 (bulk conductivity), and is based on Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (LSiPSCl). Therefore, in the sulfide solid electrolyte material according to the present embodiment, as described above, the X-ray diffraction peaks are well approximated to those of LGPS and LSiPSCl, and accordingly, the ionic conductivity may be approximately equal to or higher than that of LGPS and LSiPSCl.

[0019] (Ionic conductivity) Generally, in practical applications such as batteries, the higher the ionic conductivity, the more preferable. In one embodiment of the present invention, the ionic conductivity may be 1.2×10 -2 Scm -1 or more, preferably 2.5×10 -2 Scm -1 or more, and more preferably 3.2×10 -2 Scm -1 or more. Here, unless otherwise specified, the ionic conductivity refers to the ionic conductivity of the bulk of the sintered body sample, and is measured using the alternating current (AC) impedance method. The detailed measurement conditions will be described in detail later.

[0020] The following is an example of the measurement results of the bulk ionic conductivity of a sulfide solid electrolyte material according to an embodiment of the present invention. ·Li 9.54 [Si 0.6 Ge 0.4 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 3.2×10 -2 Scm -1

[0021] (Crystal structure) The sulfide solid electrolyte material according to an embodiment of the present invention includes a tetragonal unit cell having a space group of P42 / nmc(137), wherein the unit cell i) Li(2)[S / Br / O]6 octahedra, ii) Si(1) / M(1) / P(1)[S / Br / O]4 tetrahedra, iii) Si(2) / P(2)[S / Br / O]4 tetrahedra, iv) Li(4)[S / Br / O]6 octahedra, v) includes Li(1), Li(3a), and Li(3b) sites, wherein the i) Li(2)[S / Br / O]6 octahedra and the ii) Si(1) / M(1) / P(1)[S / Br / O]4 tetrahedra form a one-dimensional framework structure, the iii) Si(2) / P(2)[S / Br / O]4 tetrahedra are located between the i) Li(2)[S / Br / O]6 octahedra and are connected by vertex (corner) sharing to form a three-dimensional framework structure, the iv) Li(4)[S / Br / O]6 octahedra are connected to the iii) Si(2) / P(2)[S / Br / O]4 tetrahedra by edge sharing, and the Li atoms at the v) Li(1), Li(3a), and Li(3b) sites are capable of moving along the c-axis, i.e., the

[0001] direction. It may have a crystal structure.

[0022] ​Figure 2 schematically illustrates the above crystal structure. In Figure 2, the crystal structure is illustrated from two directions. The left side of Figure 2 shows the crystal structure viewed from the a-axis, that is, the

[0100] direction, and the right side of Figure 2 shows the crystal structure viewed from the c-axis, that is, the

[0001] direction. In the above crystal structure, two types of octahedra and tetrahedra are complexly related to form the crystal structure. Here, as shown on the right side of Figure 2, the lithium atoms at the lithium sites can move along the c-axis, that is, the

[0001] direction. Although not wishing to be bound by a particular theory, it is considered that the above structure realizes high ionic conductivity. Also, the above crystal structure may be related to the X-ray diffraction peaks described above.

[0023] (Thermal stability) The sulfide solid electrolyte material according to an embodiment of the present invention may be thermally stable up to 400°C. This can be shown by differential thermal analysis (DTA profile) and high-temperature X-ray diffraction (HT-XRD) as shown in Figure 5. For the solid solution series of LSiMδPSBrO (Li 9.54 [Si 1-δ M δ 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 ; M = Ge, Sn), taking LSiGe 0.4 PSBrO as the representative phase, DTA profile and HT-XRD were measured to examine the thermal stability of the phase and structure. No signal other than noise was observed in the DTA curve shown in Figure 5(A), indicating that the LSiGe 0.4 PSBrO phase is thermally stable without phase change up to 400°C. In fact, the HT-XRD pattern in Figure 5(B) did not change up to 550°C, which is consistent with the DTA result. The XRD pattern recorded at 650°C is completely different from that at 550°C, indicating that the crystal structure of LSiGe 0.4 PSBrO has changed between 550°C and 650°C. From this, it can be concluded that the sulfide solid electrolyte material according to an embodiment of the present invention is thermally stable up to 400°C. ​

[0024] (Manufacturing method) The sulfide solid electrolyte material according to one embodiment of the present invention can be manufactured by the following means although the manufacturing means is not limited.

[0025] The raw material composition for manufacturing the sulfide solid electrolyte material is not particularly limited as long as the desired sulfide solid electrolyte material can be obtained. An element or compound of Li element, Si element, P element, S element, Ge element, Sn element, B element, Al element, Br element, or O element can be prepared. Preparation in the stoichiometric ratio of the composition is easy, and from the viewpoint of availability, etc., Li2S (>99.9% purity, Mitsuwake Chemical Co., Ltd.), P2S5 (>99% purity, Sigma Aldrich), SiS2 (>99% purity, Mitsuwake Chemical Co., Ltd.), GeS2 (>99.9% purity, Mitsuwake Chemical Co., Ltd.), SnS2 (>99.9% purity, Mitsuwake Chemical Co., Ltd.), LiF (>99% purity, Sigma Aldrich), LiCl (>99% purity, Sigma Aldrich), LiBr (>99% purity, Sigma Aldrich), LiI (>99% purity, Sigma Aldrich), and P2O5 (>99.99% purity, High Purity Chemical Research Institute) etc. may be used. The raw material composition is preferably in powder form in consideration of handling in subsequent processes. Hereinafter, the raw material composition may be referred to as raw material powder.

[0026] The raw material powder is mixed in an appropriate blending amount so that the desired composition is obtained to obtain a precursor powder. The mixing may be manually performed using an agate mortar and an agate pestle. The mixing time may be appropriately adjusted in the range of several seconds to several hours according to the amount to be mixed and the degree of mixing.

[0027] In addition to or instead of manual mixing, mechanical milling may be used for mixing. Mechanical milling is a method of mixing raw material powders while pulverizing them while imparting mechanical energy. Mechanical milling is preferred in that it can mechanically mix a large amount of raw material powders. Compared with manual mixing, mechanical milling can more easily refine the raw material powders and may increase the crystal purity of the product, which is preferable. Examples of such mechanical milling include vibration mills, ball mills, turbo mills, mechanofusion, disk mills, and the like. The conditions for mechanical milling are not particularly limited as long as the raw material powders can be mixed. As typical conditions for a ball mill, the raw material powders may be placed in a ZrO2 pot containing balls having a diameter of about several tens of mm, for example, ZrO2 balls, and then mechanically pulverized in the range of 100 rpm to 2000 rpm for several seconds to several tens of hours using a planetary ball mill pulverizer. Typical conditions for a vibration mill are that the vibration amplitude of the vibration mill may be, for example, in the range of 5 mm to 15 mm, and particularly in the range of 6 mm to 10 mm. The vibration frequency of the vibration mill may be, for example, in the range of 500 rpm to 2000 rpm, and particularly in the range of 1000 rpm to 1800 rpm. The filling rate of the sample in the vibration mill may be, for example, in the range of 1% by volume to 80% by volume, and particularly in the range of 5% by volume to 60% by volume, and especially in the range of 10% by volume to 50% by volume. Also, a vibrator (for example, an alumina vibrator) may be used for the vibration mill. The mixing time may be appropriately adjusted in the range of several seconds to several tens of hours according to the amount to be mixed and the degree of mixing.

[0028] The precursor powder is compacted with a pelletizer and then fired into a solid electrolyte material by heating. During this heating, the precursor powder is placed under vacuum or in an inert atmosphere. The operation is not particularly limited as long as it can be heated under vacuum or in an inert atmosphere.

[0029] The heating temperature can be adjusted as appropriate, but may be 100°C or higher and 500°C or lower. The heat-treated product obtained when the heating temperature is outside the above range may not sufficiently contain the sulfide solid electrolyte material having the desired composition or crystal structure. This can be confirmed by X-ray diffraction measurement. More specifically, when the heating temperature is less than 100°C, the reaction does not proceed and a large amount of unreacted substances remain, and a synthetic product with the target composition cannot be obtained. When the heating temperature exceeds 500°C, the yield of the synthetic product with the desired composition may decrease due to thermal decomposition of the synthetic product or formation of unintended compositions. Note that the heating time may be appropriately adjusted according to the heating temperature and the charged amount of the precursor powder. For example, assuming the heating time includes the temperature rising time and the holding time, each time may be in the range of 30 minutes to 48 hours. Also, after the heating is completed, when cooling the obtained heat-treated product to room temperature, natural cooling may be employed, or annealing may be performed.

[0030] Further, the precursor powder may be heated while stirring by rotating the heating container for heating the precursor powder. The container for heating the precursor powder is not particularly limited, but a rotatable one is preferable from the viewpoints of heating efficiency and stirring efficiency. If the heating container has a substantially cylindrical shape, axial rotation in the cylindrical axis direction is easy and preferable. The rotation speed can be appropriately adjusted in consideration of heating efficiency and the like, and may be 1 to 100 rotations / min. If it is less than 1 rotation / min, the effects of improving heating efficiency and stirring efficiency by rotation may not be sufficient. The upper limit of the rotation speed is not particularly limited, but since the effect due to an increase in the rotation speed becomes saturated and the equipment cost increases, 100 rotations / min may be set as the upper limit.

[0031] In the series of steps included in the above manufacturing method, in order to prevent the raw material powder, the precursor powder, and the obtained sulfide solid electrolyte material from deteriorating due to moisture in the air, it is preferable to work in a glove box or the like under an inert gas atmosphere such as argon.

[0032] (X-ray Diffraction Measurement) In this specification, unless otherwise specified, X-ray diffraction measurements are carried out as follows. To identify the crystals contained in the sample to be measured, powder X-ray diffraction measurements were performed using a powder X-ray diffractometer Ulima-IV (manufactured by Rigaku Corporation) and Smart Lab (manufactured by Rigaku Corporation). For the powder X-ray diffraction measurements, Cu-Kα rays with an X-ray wavelength of 1.5418 Å were used. Powder X-ray diffraction measurements were performed at a diffraction angle (2θ) in steps of 0.01° in the range of 10 to 60°. Also, if necessary, synchrotron X-ray diffraction measurements were performed at an X-ray wavelength of 0.5 Å using the BL19B2 beamline of SPring-8. The sample was sealed in a Lindemann glass capillary (inner diameter of about 0.3 mm) under an Ar atmosphere. Diffraction data were collected at 25 °C in steps of 0.01° between 0 and 78°. To improve the accuracy of the structural parameters, the Z-Rietveld program was used. Furthermore, neutron diffraction data were collected using a time-of-flight (TOF) diffractometer (SPICA) installed at the BL09 beamline of the Japan Proton Accelerator Research Complex. The sample was sealed in a vanadium cell (diameter of about 6 mm) equipped with an indium ring. The sample was measured at 4 K and 300 K. To improve the accuracy of the structural parameters, the Z-Rietveld program was used.

[0033] (Ionic Conductivity Measurement) In this specification, unless otherwise specified, ionic conductivity measurements are carried out as follows. Ionic conductivity was measured using the alternating current (AC) impedance method. For the measurement of a compressed powder sample (cold press), a pellet (diameter = 5 mm, thickness 1-2 mm) of a sulfide solid electrolyte material was prepared to a relative density of about 85% under a pressure of 370 MPa and measured at room temperature (25 °C). To evaluate the bulk ionic conductivity, measurements were carried out on the sintered pellets obtained via the hot pressing method between -50 and 60 °C. In the hot pressing method, the sulfide solid electrolyte material was pressed into pellets (diameter = 5 millimeters, thickness 1 - 2 mm) and heated at 400 °C, 370 MPa for 1 hour. Next, a sample of this sulfide solid electrolyte material was sandwiched between stainless steel blocking electrodes. For all impedance measurements, a Bio-Logic VSP-300 instrument was used, applying a voltage amplitude of 10 mV and a frequency range of 1 Hz to 7 MHz.

[0034] (Manufacture of all-solid-state battery) In one embodiment of the present invention, an all-solid-state battery may be manufactured using a sulfide solid electrolyte material. The manufacturing means is not limited, and it is possible to manufacture by known means.

[0035] (Cycle test of all-solid-state battery) The all-solid-state battery can also be subjected to a cycle test to confirm its battery performance. The cycle test is carried out using a Bio-Logic VSP-300 device at voltage ranges of 1.9 - 3.6 V and temperatures of 25, 10, 0, -10 °C. Figure 7 shows the cycle test results of a cell containing a positive electrode composite of 245 mg cm -2 (LNO-coated LCO of 171 mg cm -2 ), where the current density corresponding to a 1C rate is 23.5 mA cm -2 . During the charge-discharge cycle, electrochemical impedance spectroscopy (EIS) is carried out at a state of charge of 25 °C using a Biologic VSP with a frequency range from 10 mHz to 1 MHz and an amplitude voltage of 10 mV.

[0036] In one embodiment of the present invention, a solid-state battery, particularly a positive electrode, may be manufactured using a sulfide solid electrolyte material. The thickness of the positive electrode can be increased and may be 800 μm or more, or 1000 μm or more. The upper limit of the thickness is not particularly limited and can be appropriately adjusted according to size limitations of the battery, etc. Typically, it may be 10 mm or less, 8 mm or less, 6 mm or less, 4 mm or less, 2 mm or less, etc. It has been confirmed that the all-solid-state battery is very useful in that it can be stably operated down to a low temperature of about -10°C through cycle tests of more than 100 days, and in that the positive electrode loading mass can be increased.

Examples

[0037] Hereinafter, the present invention will be described in more detail with reference to examples. Note that the following examples do not limit the present invention.

[0038] As the base sulfide solid electrolyte material, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (LSiPSCl) was selected. First, multi-anion substitution with halogen and oxygen was attempted, and further, Si atoms were partially replaced with Ge or Sn atoms, etc. More specifically, the raw material elements or compounds were weighed in appropriate amounts so as to obtain the desired composition and mixed using a mortar for 15 minutes. Next, each mixture was placed in a ZrO2 pot containing ZrO2 balls (Φ10 mm), and then mechanically pulverized at 380 rpm for 40 hours using a planetary ball mill pulverizer. Next, the pulverized sample was pressed to form a pellet, heated from room temperature to a synthesis temperature of 475°C over 3 hours, maintained at that temperature for 8 hours, and then naturally cooled to 25°C to obtain a composition. The actually attempted compositions are shown in Table 2. For the obtained compositions, XRD analysis was performed, and the mass ratio (phase purity) of the contained phases was determined by Rietveld analysis. Note that only those phases that could be identified were analyzed. Li 9.54 Si 1.74 P 1.44 S 11.4 I 0.3 O0.3 contains an unknown phase, and similarly, Li 9.54 Ge 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 contained the unexplained structure of Li2GeS3. Also, for the obtained composition, the ionic conductivity was measured using the alternating current (AC) impedance method. The obtained phase purity and ionic conductivity (including the resistance components at grain boundaries and electrode interfaces in addition to the bulk) are also shown in Table 2. Also, FIG. 1 is an X-ray diffraction spectrum when the ratio of substituting Si atoms with Ge or Sn atoms is changed.

[0039]

Table 2

[0040] Through the exploration of the above compositions, a novel sulfide solid electrolyte material could be obtained, and in particular, a sulfide solid electrolyte material having a lithium ion conductivity almost equal to or higher than that of LGPS could be obtained.

[0041] Discharge performance in a thick cathode configuration To evaluate the advantages of the sulfide solid electrolyte material according to the present invention, as an electrolyte (catholyte) that wets the positive electrode active material of LiNbO3-coated LiCoO2, Li 9.54 [Si 0.6 Ge 0.4 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 was used to fabricate an all-solid-state battery (LSiGe 0.4 PSBrO cell) having a positive electrode composite material. The weight ratio of the positive electrode active material (LNO-coated LCO) to the electrolyte (catholyte) was 7:3. To assemble the all-solid-state cell for measurement, as the solid electrolyte layer, Li 11.25 P3S 12.75 I 0.75 ​(LPSI) powder (80 mg) was pressed into pellets in an insulator tube (diameter = 10 mm). To avoid limiting the cell capacity on the In-Li negative electrode side, an excessive amount of In foil was used. On the other hand, an all-solid-state battery (LGPS cell) using LGPS as the electrolyte (catholite) of the reference cell was fabricated. LSiGe 0.4 For both the PSBrO cell and the LGPS cell, a thick cathode configuration with 40 mg of cathode composite material was applied. This thickness can be approximately eight times that of a typical laboratory-level all-solid-state cell. Figure 3(a) shows the discharge curves of these cells at a 0.5C rate at various temperatures. At 25 °C, both cells show the same high discharge capacity value of 125 mAhg -1 which is comparable to the theoretical value of 137 mAhg -1 (4.2 V vs Li+ / Li). However, when the operating temperature is gradually decreased, the LGPS cell shows a rapid decrease in discharge capacity compared to the LSiGe -1 PSBrO cell. Specifically, at a low temperature of -10 °C, the LSiGe 0.4 PSBrO cell has a discharge capacity of 70 mAhg 0.4 which is 29% higher than that of the LGPS cell. This significant difference in discharge ability indicates that the increase in the ionic conductivity of the solid electrolyte is important for optimizing the charge transfer in the cathode composite. -1 Also, for the LSiGe 0.4 PSBrO cell, an all-solid-state battery consisting of a thicker cathode composite of 100 mg was fabricated. This corresponds to a high areal capacity loading of 12.2 mAhcm -2 . Figure 3(b) shows the charge / discharge curves of this all-solid-state battery under the operating conditions of a charge / discharge rate of 0.05C / 0.05C (0.61 mAcm -2 ) at 25 °C, and a high discharge capacity of 110 mAhg -1 was obtained. If the cell using the sulfide solid electrolyte material according to the present invention is made into a multi-stack structure, a cell with an even higher energy density is possible.

[0042] LSiGe 0.4For the PSBrO cell, additional tests were conducted. Except that the positive electrode mixture was loaded with 245 mg / cm² (equivalent to 171 mg / cm² of LNO-coated LCO with an in-plane theoretical capacity of 23.5 mAh / cm² and a thickness of 800 μm), a solid cell was fabricated using the same method as described above. -2 (171 mg / cm² -2 LNO-coated LCO, in-plane theoretical capacity 23.5 mAh / cm² -2 , corresponding to a thickness of 800 μm), a solid cell was fabricated using the same method as described above. Figure 7A shows the discharge curves at a current density of 0.587 mA / cm² (0.025 C rate) in the temperature range from 25 °C to -10 °C. At 25 °C, an areal discharge capacity of 22.7 mAh / cm² was observed with a utilization efficiency of 97% for the input LCO at a cut-off voltage of 4.25 V vs. Li⁺ / Li. The inset in Figure 7A shows the cross-sectional SEM image of the additional tested solid cell (cathode composite pellet with a capacity of 23.5 mAh / cm²). -2 (0.025 C rate) in the temperature range from 25 °C to -10 °C. At 25 °C, an areal discharge capacity of 22.7 mAh / cm² was observed with a utilization efficiency of 97% for the input LCO at a cut-off voltage of 4.25 V vs. Li⁺ / Li. The inset in Figure 7A shows the cross-sectional SEM image of the additional tested solid cell (cathode composite pellet with a capacity of 23.5 mAh / cm²). -2 of the additional tested solid cell (cathode composite pellet with a capacity of 23.5 mAh / cm²). -2 is shown. Figure 7B shows a comparison of the areal discharge capacity between the all-solid-state battery using the sulfide solid electrolyte material according to one embodiment of the present invention and the all-solid-state lithium batteries reported in Non-Patent Documents 7 to 12. The applied current density was 0.2 - 0.68 mA / cm². The areal discharge capacity of this embodiment was the highest value. -2 The areal discharge capacity of this embodiment was the highest value. Figure 7C shows a comparison of the areal discharge capacity (bottom) and discharge capacity retention rate (top) at 25 °C and temperatures below it for this embodiment and those reported in Non-Patent Documents 7 and 9. As the temperature decreased, the areal discharge capacity gradually decreased and the overvoltage increased. This overvoltage is considered to be due to the gradual decrease in the ionic conductivity of LSiGe PSBrO at low temperatures. Nevertheless, in this embodiment, the discharge capacity at -10 °C was 75% of the discharge capacity at 25 °C. Compared with the high-loading all-solid-state batteries reported in Non-Patent Documents 7 and 9, the solid cell according to this embodiment with an increased positive electrode weight had an improved capacity retention rate at low temperatures (Figure 7C). 0.4 PSBrO at low temperatures. Nevertheless, in this embodiment, the discharge capacity at -10 °C was 75% of the discharge capacity at 25 °C. Compared with the high-loading all-solid-state batteries reported in Non-Patent Documents 7 and 9, the solid cell according to this embodiment with an increased positive electrode weight had an improved capacity retention rate at low temperatures (Figure 7C). The sulfide solid electrolyte material of this embodiment has such excellent performance, and it is expected to expand the utilization of all-solid-state lithium batteries under thick electrodes and low-temperature conditions.

[0043] A cycle test was carried out using the all-solid-state lithium battery with the above-mentioned electrode having a thickness of 800 μm. First, as shown in Fig. 8(A), at 25 °C and a current density of 0.587 mA cm -2 (0.025 C rate), two cycles were performed to confirm that the active material of the positive electrode was sufficiently utilized. Then, the temperature dependence of the battery performance was measured, and the results as shown in Fig. 7 were obtained. After the measurement of the temperature dependence, EIS (electrochemical impedance measurement) was performed in the charged state to investigate the impedance change caused by cycling. Fig. 8(B) shows a comparison between the Nyquist plot obtained from EIS and the Nyquist plot recorded after the first charge. The high-frequency side semi-circle in the range of 100 k~1 kHz corresponding to the electrochemical process of the positive electrode changed from 4.3 Ω (after the first charge) to 4.9 Ω (after the temperature dependence test), and no significant change was observed. This result suggests that LiSiGe 0.4 PSBrO used in the positive electrode electrolyte has not decomposed even after several cycles. Finally, a cycle test was carried out at a rate of 0.025 C, and the results are shown in Fig. 8(C). The discharge capacity retention rate was 92% at the 30th cycle, and during the long-term test period of more than 100 days, LiSiGe 0.4 PSBrO was shown to be dynamically stable at an electrochemical potential of 4.25 V vs. Li+ / Li (3.6 V vs. Li+ / In-Li).

[0044] Furthermore, an all-solid-state lithium battery with an electrode having a thickness of 1 mm (1000 μm) was prepared and confirmed to operate in charge and discharge. Fig. 9 shows the discharge curve of the 1 mm-thick electrode under the conditions of 25 °C and 0.73 mA cm -2 (0.025 C) with a capacity load of 29.3 mAh cm -2 . The utilization efficiency was 90%. Also, the inset in Fig. 9 shows the measurement results of the electrode thickness. Through these examples, it was confirmed that the sulfide solid electrolyte material of this embodiment is applicable to all-solid-state batteries, and is very useful especially in terms of being able to operate at low temperatures and being able to increase the positive electrode loading mass.

Claims

1. Li ９．５４ [Si １－δ M δ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ Or,​ Li ９．７１４ [Si １－δ M’’ δ １．７４ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ Or, Li ９．７１４ [Si １－δ M''' δ １．７４ １．７４ P １．４４ S １１．７ Br ０．３ and has a composition of Here, M is Ge or Sn or Sb, M'' is Al, M''' is B, when M is Ge, 0 ≦ δ ≦ 0.5, when M is Sn, 0 ≦ δ ≦ 0.4, when M'' is Al, δ = 0.1, when M''' is B, δ = 0.1, a sulfide solid electrolyte material.

2. Li ９．５４ Si １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ Li ９．５４ [Si ０．９ Ge ０．１ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．８ Ge ０．２ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．７ Ge ０．３ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．６ Ge ０．４ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．５ Ge ０．５ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．９ Sn ０．１ １．７４ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ Li ９．５４ [Si ０．８ Sn ０．２ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．７ Sn ０．３ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ Li ９．５４ [Si ０．６ Sn ０．４ １．７４ P １．４４ S １１．１ Br ０．３ O0.6​ Li ９．７１４ [Si ０．９ B ０．１ １．７４ １．７４ P １．４４ S １１．７ Br ０．３ Li ９．７１４ [Si ０．９ Al ０．１ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ ​ The sulfide solid electrolyte material according to Claim 1, having any of the compositions.

3. Li ９．５４ [Si ０．６ Ge ０．４ １．７４ １．７４ P １．４４ S １１．１ Br ０．３ O ０．６ The sulfide solid electrolyte material according to claim 1 or 2, having a composition of

4. A sulfide solid electrolyte material according to any one of claims 1 to 3, having a lithium ion conductivity of 3.2 × 10 －２ S / cm or more.

5. The sulfide solid electrolyte material according to any one of Claims 1 to 4, having peaks at positions of 2θ = 12.33 ± 0.04°, 14.34 ± 0.03°, 17.32 ± 0.08°, 20.11 ± 0.07°, 20.33 ± 0.04°, 23.45 ± 0.11°, 23.84 ± 0.05°, 26.83 ± 0.07°, 28.90 ± 0.05°, 29.46 ± 0.22°, 31.52 ± 0.05°, 33.19 ± 0.06° in X-ray diffraction measurement using CuKα rays.

6. P4 ２ including a cubic unit cell having a space group of / nmc(137), The unit cell is Li(2)[S / Br / O] ６ Octahedron, Si(1) / M(1) / P(1) [S / Br / O] ４ tetrahedron Si(2) / P(2)[S / Br / O] ４ tetrahedron Li(4)[S / Br / O] ６ Octahedron, including Li(1), Li(3a), and Li(3b) sites, the Li(2)[S / Br / O] ６ octahedron and the Si(1) / M(1) / P(1)[S / Br / O] ４ tetrahedron form a one-dimensional framework structure, the Si(2) / P(2)[S / Br / O] ４ tetrahedron is located between the Li(2)[S / Br / O] ６ octahedrons, and is connected by vertex (corner) sharing to form a three-dimensional framework structure, The Li(4)[S / Br / O] ６ The octahedron is connected to the Si(2) / P(2)[S / Br / O] tetrahedron by edge sharing, ４ and and the Li atoms at the Li(1), Li(3a), and Li(3b) sites can move along the c-axis, that is, the [001] direction. The sulfide solid electrolyte material according to any one of Claims 1 to 5, having a crystal structure.

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