solid electrolyte

Abstract

The solid electrolyte comprises Li, P, S, halogen, and M elements (M represents at least one of silicon (Si), tin (Sn), antimony (Sb), germanium (Ge), and boron (B)), and also comprises a crystalline phase having an agirodite-type crystal structure. The molar ratio of S to the sum of P and M elements, S / (P+M), is 3.5 <S / (P+M)<4.2를 만족시킨다. P에 대한 M 원소의 몰비 M / P가 0<M / P<1을 만족시킨다. P 및 M 원소의 합계에 대한 할로겐(X) 원소의 몰비 X / (P+M)이 0.7<X / (P+M)<3.0을 만족시키는 것이 적합하다.

Description

Technology Field

[0001] The present invention relates to a solid electrolyte. The present invention also relates to an electrode composite comprising a solid electrolyte, a solid electrolyte layer, and a battery. Background Technology

[0002] In recent years, solid electrolytes have attracted attention as alternatives to the liquid electrolytes used in many liquid batteries. Solid-state batteries using solid electrolytes are expected to be commercialized as batteries that possess high safety and high energy density compared to liquid batteries using flammable organic solvents. As solid electrolytes, sulfide solid electrolytes containing, for example, lithium (Li), phosphorus (P), sulfur (S), and halogen elements have been proposed (Patent Documents 1 and 2). Prior art literature

[0003] US2016 / 156064A1WO2020 / 095937A1 The problem to be solved

[0004] However, since sulfide solid electrolytes are materials containing sulfur, there is a possibility that hydrogen sulfide may be generated as sulfur reacts with moisture depending on the environment. Therefore, it is desired to reduce the proportion of sulfur in the solid electrolyte. In the aforementioned patent documents 1 and 2, Li5PS4Cl2 and Li5PS4ClBr are described as sulfide solid electrolytes with a relatively low sulfur content. Regarding Li5PS4Cl2, patent document 1 states that it does not have ionic conductivity, and regarding Li5PS4ClBr, it states that it has ionic conductivity, but the degree is not sufficient.

[0005] Therefore, the objective of the present invention is to provide a solid electrolyte having a predetermined composition and high ion conductivity. means of solving the problem

[0006] The present invention comprises a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, a halogen (X) element, and an M element (M represents at least one of silicon (Si), tin (Sn), antimony (Sb), germanium (Ge), and boron (B), and

[0007] The molar ratio of the sulfur (S) element to the sum of the phosphorus (P) element and the M element, S / (P+M), is 3.5

[0008] The molar ratio M / P of the element M to the element Phosphorus (P) is 0 <M / P<1을 만족시키고,

[0009] The present invention provides a solid electrolyte comprising a crystalline phase having an agirodite-type crystal structure. Brief explanation of the drawing

[0010] Figure 1 is a diagram illustrating a high-temperature X-ray diffraction chart of a solid electrolyte. Figure 2 is a graph showing the relationship between the molar ratio M / P and the ideals A and B included in the solid electrolyte. FIG. 3 is a diagram showing X-ray diffraction charts of solid electrolytes obtained in Examples 1 to 3 and Comparative Examples 1 and 2. Figure 4 is a diagram illustrating the charge and discharge behavior of an all-solid-state battery fabricated using the solid electrolyte obtained in Example 2. Specific details for implementing the invention

[0011] The present invention will be described below based on its preferred embodiments. The solid electrolyte of the present invention is a crystalline compound. A crystalline compound is a material in which diffraction peaks attributable to a crystalline phase are observed when measurements are performed using an X-ray diffraction (XRD) device. It is particularly desirable for the solid electrolyte to include a crystalline phase having an agirodite-type crystal structure, as this can increase the lithium ion conductivity of the solid electrolyte.

[0012] ​An agirodite crystal structure is a crystal structure possessed by a group of compounds derived from a mineral represented by the chemical formula Ag8GeS6. Whether a solid electrolyte has a crystal phase of an agirodite crystal structure can be confirmed by measurements such as XRD. For example, in a diffraction pattern measured by an X-ray diffraction device using CuKα1 rays, the crystal phase of an agirodite crystal structure exhibits characteristic diffraction peaks at 2θ = 15.3°±1.0°, 17.7°±1.0°, 25.2°±1.0°, 30.0°±1.0°, 30.9°±1.0°, and 44.3°±1.0°. In addition, depending on the elemental species constituting the solid electrolyte, in addition to the above diffraction peaks, characteristic diffraction peaks may appear at 2θ=47.2°±1.0°, 51.7°±1.0°, 58.3°±1.0°, 60.7°±1.0°, 61.5°±1.0°, 70.4°±1.0°, and 72.6°±1.0°. Data from PDF No. 00-034-0688 can be used to identify diffraction peaks originating from an agarodite-type crystal structure.

[0013] A crystalline solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements is known, for example, as described in Patent Document 1 previously explained. The solid electrolyte described in said document has a composition of Li5PS4Cl2. Accordingly, this solid electrolyte has a lower proportion of sulfur elements compared to Li6PS5Cl, a solid electrolyte containing a crystalline phase having an agarodite-type crystal structure. A low proportion of sulfur elements in the solid electrolyte is desirable from the perspective of reducing the reaction between sulfur elements and water, thereby suppressing the generation of hydrogen sulfide. From this perspective, a solid electrolyte having the composition of Li5PS4Cl2 is advantageous. However, the solid electrolyte having the composition of Li5PS4Cl2 has lower lithium ion conductivity compared to the solid electrolyte having the composition of Li6PS5Cl. Therefore, the inventors carefully investigated the improvement of lithium ion conductivity of a solid electrolyte having a crystal phase with an agirodite-type crystal structure and a low proportion of S element. As a result, it was discovered that in a solid electrolyte comprising Li element, P element, S element, and X element, the lithium ion conductivity of the solid electrolyte can be improved by substituting a portion of the P element with another element.

[0014] The present invention is based on the above-described findings, and the solid electrolyte of the present invention comprises a Li element, a P element, an S element, an X element, and an M element. M represents at least one of silicon (Si), tin (Sn), antimony (Sb), germanium (Ge), and boron (B). The M element is used for the purpose of substituting for the P element. Sn, Sb, Ge, and B are PS4 in an agirodite-type crystal structure 3- They have chemical commonality in that they can form units similar to the unit.

[0015] The above-mentioned M element may be used as a single type or in combination of two or more types. As for the M element, using at least one of Si, Sb, and Sn is preferable from the perspective of further enhancing the lithium ion conductivity of the solid electrolyte, and from this perspective, using at least Si is even more preferable.

[0016] The inventors believe that the reason the lithium ion conductivity of a solid electrolyte is improved by substituting a portion of the P element with another element is as follows.

[0017] In a solid electrolyte containing the elements Li, P, S, and X, and also having a crystal phase having an agrodite-type crystal structure, when the proportion of the S element is low (in other words, when the proportion of the X element is high), another crystal phase with lower lithium ion conductivity than the agrodite crystal phase (hereinafter this crystal phase is also referred to as "Anomalous A") is likely to be formed. The presence of Anomalous A can be confirmed by measuring the solid electrolyte with XRD. When Anomalous A is present in the solid electrolyte, a diffraction peak is observed at the position 2θ = 21.3° ± 0.3° on the XRD chart, as shown in FIG. 3. In an agrodite-type crystal structure, no diffraction peak is observed in this angle range. The inventors performed high-temperature XRD measurements on a solid electrolyte containing abnormality A, and surprisingly, as shown in FIG. 1, while an agirodite-type crystal structure was observed at approximately 160°C or higher, it was found that as the temperature was lowered, the agirodite-type crystal structure transitioned to abnormality A. That is, it was found that the agirodite-type crystal structure is the stable phase at approximately 160°C or higher, and abnormality A is the stable phase at approximately 160°C or lower. FIG. 1 is a high-temperature XRD chart for Li5PS4ClBr, a solid electrolyte with a molar ratio X / P of 1.8 or higher.

[0018] Based on the above findings, the inventors investigated how to make the agirodite-type crystal structure, which is stable at about 160°C or higher, stable at room temperature. As a result, it was found that in a solid electrolyte containing Li, P, S, and X elements, when the proportion of S element is reduced (in other words, when the proportion of X element is high), it is effective to substitute some of the P element with M element.

[0019] As described above, in the solid electrolyte of the present invention, the presence ratio of abnormal A is low even when the proportion of S element is reduced due to the substitution of a portion of P element with M element. The presence ratio of abnormal A can be evaluated using the intensity of the diffraction peak attributed to abnormal A in the XRD pattern of the solid electrolyte as a measure. Specifically, I a Set as such, and when the background of the XRD pattern is set to I0, the I for I0 a Of I a The presence ratio of A is low to the extent that / I0 is preferably 1.6 or less. As a result, the solid electrolyte of the present invention has high lithium ion conductivity. In order to make this advantage even more prominent, I a It is more preferable that the value of / I0 be 1.58 or less, and even more preferable that it be 1.56 or less. a The smaller the value of / I0, the more favorable it is for improving lithium ion conductivity, and ideally, it is zero. In addition, the diffraction peak originating from A is observed at positions 27.8±1.0° and 30.8±0.5°, in addition to the position 21.3°±0.3° mentioned above.

[0020] As previously described, in the solid electrolyte of the present invention, the abundance of A is reduced by substituting a portion of the P element with the M element. However, the inventors' investigation revealed that as the amount of substitution of the M element increases, a crystalline phase B, which is different from A, is generated. Specifically, as shown in FIG. 2, the abundance of A decreases with increasing molar ratio M / P, while the abundance of B increases with increasing molar ratio M / P. Like A, B is a phase in which lithium ion conductivity is lower than that of an agarodite-type crystal structure. Therefore, in the solid electrolyte of the present invention, it is advantageous to have a low abundance of B, just as with A. The abundance of B can be evaluated using the intensity of the diffraction peak attributed to B in the XRD pattern of the solid electrolyte as a measure. Specifically, I b Set as such, and when the background of the XRD pattern is set to I0, the I for I0 b Of I b The presence ratio of ideal B is low to the extent that / I0 is preferably 2.5 or less. As a result, the solid electrolyte of the present invention has high lithium ion conductivity. In order to make this advantage even more prominent, I b It is more preferable that the value of / I0 be 2.3 or less, and even more preferable that it be 1.7 or less. b The smaller the value of / I0, the more favorable it is for improving lithium-ion conductivity, and ideally, it is zero.

[0021] As described above, in the solid electrolyte of the present invention, it is advantageous to determine the degree of substitution of a portion of the P element with the M element by considering the existence ratios of A and B shown in FIG. 2. The degree of substitution of the P element with the M element is expressed as the molar ratio of the M element to the P element, M / P, and 0 <M / P<1인 것이, 고체 전해질의 리튬 이온 전도성을 높이는 점에서 유리하다. 이 이점을 한층 현저한 것으로 하는 관점에서, 몰비 M / P는, 0.02 이상 0.80 이하인 것이 바람직하고, 0.06 이상 0.60 이하인 것이 더욱 바람직하고, 0.08 이상 0.30 이하인 것이 한층 바람직하다.

[0022] In the case where two or more M elements are included in the solid electrolyte of the present invention, the number of moles of M in the molar ratio M / P above refers to the total number of moles of all M elements.

[0023] In the solid electrolyte of the present invention, a low ratio of the S element to all constituent elements is desirable from the perspective of suppressing the generation of hydrogen sulfide by reducing the reaction between the S element and moisture. In the case of a solid electrolyte comprising a crystalline phase having an agirodite-type crystal structure, it is appropriate to evaluate the ratio of the S element using the molar ratio of the P element to the S element, i.e., S / P, as a measure. In the present invention, as described above, since a portion of the P element is substituted with the M element, the molar ratio S / P is expressed as S / (P+M). Thus, in the solid electrolyte of the present invention, it is appropriate to evaluate the ratio of the S element based on the molar ratio S / (P+M) of the S element to the sum of the P element and the M element. Furthermore, in the present invention, the molar ratio S / (P+M) is 3.5

[0024] In relation to the molar ratio S / (P+M) described above, it is advantageous for the ratio of the S element to all elements constituting the solid electrolyte of the present invention to be 40 mol% or less in terms of reducing the reaction between the S element and water. In terms of making this advantage even more pronounced, it is preferable that the ratio of the S element be 38 mol% or less, and even more preferable that it be 35 mol% or less. Furthermore, in terms of increasing the lithium ion conductivity of the solid electrolyte, it is preferable that the ratio of the S element be 20 mol% or more, more preferable that it be 25 mol% or more, and even more preferable that it be 30 mol% or more.

[0025] ​In the solid electrolyte of the present invention, it is desirable to appropriately adjust the value of X / P, which is the molar ratio of element X to element P, in order to improve the lithium ion conductivity of the solid electrolyte. In the present invention, as described above, since a portion of element P is substituted with element M, the molar ratio X / P is expressed as X / (P+M). Thus, in the solid electrolyte of the present invention, it is appropriate to adjust the molar ratio X / (P+M) of element X relative to the sum of elements P and M. In this regard, the molar ratio X / (P+M) is 0.7 <X / (P+M)<3.0을 만족시키는 것이, 고체 전해질의 리튬 이온 전도성을 높이는 관점에서 유리하다. 이 이점을 한층 현저한 것으로 하는 관점에서, 몰비 X / (P+M)은 1.0 이상 2.8 이하인 것이 바람직하고, 1.5 이상 2.4 이하인 것이 더욱 바람직하고 1.8 이상 2.2 이하인 것이 한층 바람직하다.

[0026] The amount of each element constituting the solid electrolyte, including element S, can be measured, for example, by ICP emission spectroscopy. The aforementioned molar ratios M / P, S / (P+M), and X / (P+M) can be calculated from the results based on the measured amounts of each element.

[0027] Considering the aforementioned molar ratios M / P, S / (P+M), and X / (P+M), the solid electrolyte of the present invention is Li w P 1-x M x S y X z Having a composition represented by [formula] is desirable from the perspective of increasing the lithium ion conductivity of the solid electrolyte.

[0028] In the formula, w represents a number preferably 4.5 or more and 5.5 or less, more preferably 4.7 or more and 5.3 or less, and even more preferably 4.9 or more and 5.1 or less.

[0029] x represents a number preferably 0.05 or more and 0.45 or less, more preferably 0.08 or more and 0.30 or less, and even more preferably 0.09 or more and 0.20 or less.

[0030] y represents a number preferably 3.5 or more and 4.2 or less, more preferably 3.6 or more and 4.15 or less, and even more preferably 3.70 or more and 4.10 or less.

[0031] z represents a number preferably greater than 1.0 and less than or equal to 3.0, more preferably greater than or equal to 1.5 and less than or equal to 2.6, and even more preferably greater than or equal to 1.8 and less than or equal to 2.2.

[0032] In the solid electrolyte of the present invention, the X element may be fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The X element may be one of these elements or a combination of two or more. In the view that an agirodite-type crystal structure is easily formed by solid-state reaction and lithium ion conductivity is increased, the solid electrolyte preferably contains at least Br as the X element, and more preferably contains Br and Cl.

[0033] When a solid electrolyte contains Br and Cl as X elements, it is preferable to set the value of the ratio of Br to the sum of the moles of Br and Cl, i.e., Br / (Br+Cl), to 0.2 or more and 0.8 or less, more preferable to set it to 0.3 or more and 0.7 or less, and even more preferable to set it to 0.4 or more and 0.6 or less.

[0034] The introduction of Br facilitates the formation of an agirodite-type crystal structure, but since Br has a larger ionic radius compared to Cl or S, it is thought that the solid solution capacity of halogens in the agirodite-type crystal structure is reduced. Therefore, as described above, by appropriately adjusting Br / (Br+Cl), it is possible to easily generate an agirodite-type crystal structure while incorporating more halogen elements into the agirodite-type crystal structure. As a result, the lithium ion conductivity of the solid electrolyte can be further enhanced. The increase in the solid solution capacity of halogens in the agirodite-type crystal structure corresponds to a decrease in the occupancy rate of lithium sites within the crystal structure. It is thought that this leads to an improvement in lithium ion conductivity.

[0035] The solid electrolyte of the present invention has lithium ion conductivity in a solid state. The lithium ion conductivity of the solid electrolyte of the present invention is preferably 0.5 mS / cm or higher at room temperature, i.e., 25°C, more preferably 1.0 mS / cm or higher, and even more preferably 1.5 mS / cm or higher. The lithium ion conductivity can be measured using the method described in the examples described below.

[0036] Next, a suitable method for manufacturing the solid electrolyte of the present invention will be described. The solid electrolyte can be synthesized by a solid-state reaction in which a raw material composition is heated and sintered. The above-mentioned raw material composition is a mixture of raw materials containing elements constituting the solid electrolyte, and specifically, a compound containing the element Li, a compound containing the element S, a compound containing the element P, a compound containing the element X, and a compound containing the element M.

[0037] Examples of compounds containing the element Li include lithium compounds such as lithium sulfide (Li2S), lithium oxide (Li2O), and lithium carbonate (Li2CO3), as well as lithium metal elements.

[0038] Examples of compounds containing the element S include phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5). Additionally, as a compound containing the element sulfur (S), the element sulfur (S) itself may be used.

[0039] Examples of compounds containing the element P include phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and phosphorus element.

[0040] Examples of compounds containing element X include one or more elements selected from the group consisting of F, Cl, Br, and I, and one or more elements selected from the group consisting of sodium (Na), lithium (Li), boron (B), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), germanium (Ge), arsenic (As), selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb), and bismuth (Bi), or compounds in which oxygen or sulfur is also bonded to said compounds. More specifically, lithium halides such as LiF, LiCl, LiBr, and LiI; phosphorus halides such as PF3, PF5, PCl3, PCl5, POCl3, PBr3, POBr3, PI3, P2Cl4, and P2I4; and SF2, SF4, SF6, and S2F 10 Examples include sulfur halides such as SCl2, S2Cl2, and S2Br2, sodium halides such as NaI, NaF, NaCl, and NaBr, and boron halides such as BCl3, BBr3, and BI3. These compounds may be used individually or in combination of two or more. Among them, it is preferable to use lithium halide (LiX (where X indicates a halogen)).

[0041] As a compound containing the element M, a sulfide of the element M can be used. If the element M is, for example, silicon, SiS2, etc. can be used. If the element M is, for example, antimony, Sb2S3 and Sb2S5, etc. can be used. If the element M is, for example, tin, SnS2, etc. can be used.

[0042] A raw material composition is prepared by mixing each of the raw materials described above. For mixing, for example, an attritor, a paint shaker, an oil ball mill, a ball mill, a bead mill, a homogenizer, etc., may be used. The amount of each raw material added during mixing is appropriately adjusted to satisfy the composition of the desired solid electrolyte.

[0043] The obtained raw material composition is subjected to calcination to induce a solid-state reaction, and a calcined product containing a crystalline phase having an agarodite-type crystal structure is obtained. For the calcination atmosphere, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere, may be used. From the perspective of lowering the proportion of sulfur elements contained in the solid electrolyte, it is preferable to use an inert gas atmosphere.

[0044] From the perspective of ensuring a solid-state reaction of the raw material composition, the calcination temperature is preferably, for example, 200°C or higher, more preferably 300°C or higher, even more preferably 350°C or higher, and even more preferably 400°C or higher. Meanwhile, considering industrial production feasibility and economic efficiency, the calcination temperature is preferably, for example, 700°C or lower, more preferably 600°C or lower, and even more preferably 550°C or lower.

[0045] The firing time is not critical and is sufficient as long as the time required to obtain a fired product of the desired composition. Specifically, it is desirable for the firing time to be sufficient for the solid-state reaction of the raw material composition to occur. The firing time may be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time may be, for example, 10 hours or less, or 5 hours or less.

[0046] After firing, the fired product may be crushed and pulverized as needed, and also classified as needed. For example, it is preferable to crush or pulverize using a grinder, such as a planetary ball mill, a vibrating mill, or an electric mill, or a kneader.

[0047] The solid electrolyte obtained in this way can be used alone or mixed with other solid electrolytes. The solid electrolyte is D based on the volumetric particle size distribution obtained by measuring by the laser diffraction scattering particle size distribution method. 50 It is preferable that this be between 0.1㎛ and 150㎛. D of the solid electrolyte 50 Since this is 0.1㎛ or larger, the excessive increase in the surface area of ​​the solid electrolyte is suppressed, which can suppress the increase in resistance and also facilitate mixing with the active material. Meanwhile, D of the solid electrolyte 50 Since this is 150 μm or less, the contact area increases when, for example, it is mixed with an active material, and the lithium ion migration resistance in the active material and solid electrolyte can be reduced. In this regard, D of the solid electrolyte 50 It is preferable that the particle size be, for example, 0.3 μm or larger, and particularly preferable that it be 0.5 μm or larger. Meanwhile, D of the solid electrolyte 50 For example, it is preferable that the size be 250㎛ or less, among which it is preferable that the size be 70㎛ or less, and particularly preferable that the size be 50㎛ or less.

[0048] The solid electrolyte of the present invention can be used as a material constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer. Specifically, the solid electrolyte of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. That is, the solid electrolyte can be used in so-called solid batteries. More specifically, it can be used in lithium solid batteries. The lithium solid battery may be a primary battery or a secondary battery. There are no particular restrictions on the shape of the battery, and shapes such as laminate, cylindrical, and prismatic types may be adopted. The term "solid battery" includes not only solid batteries that do not contain any liquid or gel-like substances as an electrolyte, but also embodiments that contain, for example, 50 mass% or less, 30 mass% or less, or 10 mass% or less of a liquid or gel-like substance as an electrolyte.

[0049] When the solid electrolyte of the present invention is included in a solid electrolyte layer, the solid electrolyte layer can be manufactured by, for example, by dropping a slurry consisting of a solid electrolyte, a binder, and a solvent onto a gas phase and cutting it by rubbing with a doctor blade, etc., by bringing the gas and the slurry into contact and then cutting with an air knife, or by forming a film using a screen printing method, etc., and then removing the solvent by heat drying. Alternatively, the solid electrolyte in powder form may be manufactured by compacting it into a powder body using a press, etc., and then processing it appropriately.

[0050] The thickness of the solid electrolyte layer is typically preferably 5㎛ or more and 300㎛ or less in balance with short-circuit prevention and volumetric capacity density, and among them, it is more preferably 10㎛ or more and 100㎛ or less.

[0051] The solid electrolyte of the present invention is used in all active materials to form an electrode composite. The proportion of the solid electrolyte in the electrode composite is typically 10 mass% or more and 50 mass% or less. The electrode composite may include other materials such as a conductive aid or a binder as needed. A positive electrode layer and a negative electrode layer can be produced by mixing the electrode composite with a solvent to produce a paste, applying it onto a current collector such as an aluminum foil, and drying it.

[0052] As the positive electrode material constituting the positive electrode layer, a positive electrode material currently used as a positive electrode active material for lithium-ion batteries can be appropriately used. Examples include positive electrode active materials containing lithium, specifically spinel-type lithium transition metal oxides and lithium metal oxides having a layered structure. By using a high-voltage positive electrode material as the positive electrode material, an improvement in energy density can be achieved. In addition to the positive electrode active material, the positive electrode material may include a conductive material or other materials.

[0053] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material for lithium-ion batteries can be appropriately used. The solid electrolyte of the present invention is electrochemically stable and has a shallow potential comparable to lithium metal or lithium metal (approx. 0.1V vs. Li +Carbon-based materials such as graphite, artificial graphite, natural graphite, and hard carbon, which are materials that are charged and discharged with (Li), can be used as negative electrode materials. This can significantly improve the energy density of the solid-state battery. In addition, silicon or tin, which are promising materials for high capacity, can be used as active materials. In batteries using a conventional electrolyte, the deterioration of battery characteristics is significant due to the reaction between the electrolyte and the active material during charging and discharging, and the occurrence of corrosion on the surface of the active material. In contrast to this, if the solid electrolyte of the present invention is used instead of the electrolyte and silicon or tin is used as the negative electrode active material, the aforementioned corrosion reaction does not occur, thereby improving the durability of the battery. Regarding the negative electrode material, a conductive material may be included in addition to the negative electrode active material, or other materials may be included.

[0054] It comprises Li, P, S, X, and M elements (M represents at least one of Si, Sn, Sb, Ge, and B), and the molar ratio of S element to the sum of P and M elements, S / (P+M), is 3.5 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 There is a solid electrolyte represented as such. This solid electrolyte has an LGPS-type crystal structure, as described in Kato, Y. et al. High-power all-solid-state batteries using sulfide superionic conductor. Nat. Ener. 1, 1630 (2016). Furthermore, it has been reported that this solid electrolyte lacks low-potential stability, and in the negative electrode layer of an all-solid-state battery using said solid electrolyte, Li5Ti5O with an operating potential of about 1.5 V (vs Li) 12 ​It is being used. In contrast, the solid electrolyte of the present invention has an agirodite-type crystal structure, so reversible charging and discharging is possible even when using a negative electrode active material such as graphite operating at 0-0.5 (vs Li). This is also clear from Figure 4, which will be described later.

[0055] Examples

[0056] The present invention will be explained in more detail below by way of examples. However, the scope of the present invention is not limited to these examples.

[0057] [Example 1]

[0058] (1) Preparation of raw material composition

[0059] To achieve the composition shown in Table 1 below, lithium sulfide (Li2S) powder, phosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, and silicon sulfide (SiS2) powder were each weighed to a total of 5g. A slurry was prepared by adding 10g of heptane to these powders. This slurry was placed in a zirconia container with a volume of 80mL and set in a planetary ball mill (Fritsch P-5). ZrO2 balls with a diameter of 5mm were used as the grinding media. The ball mill was operated at 100rpm, and the mixture was ground over 10 hours. A 15-minute rest period was added at 1-hour intervals. The solvent was removed by vacuum drying the obtained slurry at room temperature. In this way, the raw material composition was obtained.

[0060] (2) Sintering

[0061] A calcined product was obtained by calcining the raw material composition. Calcination was carried out using a tubular electric furnace. During calcination, 100% pure nitrogen gas was circulated inside the electric furnace. The calcination temperature was set to 600°C and calcination was carried out over 4 hours.

[0062] (4) Fine grinding

[0063] The calcined material was ground using a mortar and pestle and sieved through a 250 μm mesh to obtain a ground powder. This powder was finely ground using a planetary ball mill. ZrO2 balls with a diameter of 5 mm were used as the grinding media. Heptane was used as the solvent. The ball mill was operated at 100 rpm, and grinding was carried out over 3 hours. The solvent was removed by vacuum drying the obtained slurry at room temperature. In this way, the powder of the target solid electrolyte was obtained.

[0064] [Examples 2 and 3]

[0065] Lithium sulfide powder, phosphorus pentasulfide powder, lithium chloride powder, lithium bromide powder, and silicon sulfide powder were used to have the composition shown in Table 1 below. Except for this, a solid electrolyte powder was obtained in the same manner as in Example 1.

[0066] [Comparative Example 1]

[0067] This comparative example is an example in which element M was not used in the manufacture of the solid electrolyte. Lithium sulfide powder, phosphorus pentasulfide powder, lithium chloride powder, and lithium bromide powder were used to obtain the composition shown in Table 1 below. Except for this, the solid electrolyte powder was obtained in the same manner as in Example 2.

[0068] [Comparative Example 2]

[0069] This comparative example is an example in which an excess amount of element M was used in the manufacture of a solid electrolyte. Lithium sulfide powder, phosphorus pentasulfide powder, lithium chloride powder, lithium bromide powder, and silicon sulfide powder were used to obtain the composition shown in Table 1 below. Except for this, the solid electrolyte powder was obtained in the same manner as in Example 2.

[0070] [Evaluation 1]

[0071] XRD measurements were performed on the solid electrolytes obtained in the examples and comparative examples to determine I a / I0 and I bThe value of / I0 was calculated. The results are shown in Table 1. Figure 3 shows the X-ray diffraction charts of the solid electrolytes obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0072] XRD measurements were performed using the X-ray diffractometer "Smart Lab SE" manufactured by Rigaku Co., Ltd. The measurement conditions were set as follows: no atmospheric exposure, scan axis: 2θ / θ, scan range: 10° or more and 120° or less, step width: 0.02°, and scan speed: 1° / min. The X-ray source was CuKα1. The tube voltage was 40kV and the tube current was 80mA.

[0073] I a / I0 and I b The specific measurement method for the value of / I0 is as follows. For the air-exposure-free cell, a hermetic holder for ASC manufactured by Rigaku Co., Ltd. (A00012149) was used. The hermetic cover was a transparent hermetic film, and the atmosphere was set to Ar.

[0074] The average value of the count at 2θ = 20.5 ± 0.3° was set as the background intensity I0. The maximum value of the count at 2θ = 21.3 ± 0.3° was I a It was set as follows. The maximum value of the count at 2θ=19.4±0.3° is I b This measurement was performed under the condition that I0 is between 250 and 450 counts, and that the agirodite peak observed in the range of 2θ = 30±1.0° is 2000 counts or more.

[0075] [Evaluation 2]

[0076] For the solid electrolytes obtained in the examples and comparative examples, the lithium ion conductivity was measured by the following method.

[0077] Each solid electrolyte was uniaxially pressurized by applying a load of approximately 6 t / cm² in a glove box filled with sufficiently dried argon gas (dew point -60°C or lower) to produce a sample for measuring lithium-ion conductivity consisting of a pellet with a diameter of 10 mm and a thickness of approximately 1 mm to 8 mm. The lithium-ion conductivity was measured using a Solartron 1255B manufactured by Toyo Technica Co., Ltd. The measurement conditions were set to the AC impedance method with a temperature of 25°C, a frequency of 100 Hz to 1 MHz, and an amplitude of 100 mV.

[0078] [Evaluation 3]

[0079] A solid-state battery was fabricated using the solid electrolyte obtained in Example 2 in the negative electrode layer, and the charge / discharge behavior of the solid-state battery was verified by the following method.

[0080] (ingredient)

[0081] As a positive electrode active material, LiNi, a layered compound 0.6 Co 0.2 Mn 0.2 O2(NCM) powder with a coating layer composed of Li-Nb-O was used. Graphite was used as the negative electrode active material. For the positive electrode layer and the separator layer, a general agarodite-type sulfide solid electrolyte was used as the solid electrolyte. For the negative electrode layer, the solid electrolyte obtained in Example 2 was used.

[0082] (Preparation of positive and negative combinations)

[0083] The positive electrode mixture was prepared by mixing powders of the positive electrode active material, solid electrolyte, and conductive aid (acetylene black) in a mass ratio of 60:37:3.

[0084] The negative electrode mixture was prepared by mortar-and-mortar mixing graphite and a solid electrolyte in a mass ratio of 64:36.

[0085] (Fabrication of solid-state battery cells)

[0086] With the lower opening of a ceramic cylinder (opening diameter 10.5 mm, height 18 mm) with upper and lower ends open closed with a SUS electrode, 0.05 g of solid electrolyte was injected into the cylinder. An electrode was mounted on the upper opening, and a solid electrolyte layer was fabricated by uniaxial press forming at approximately 0.8 tf / cm². The upper electrode was temporarily removed, a positive electrode composite was injected onto the solid electrolyte layer, the positive electrode composite was smoothed, and then the upper electrode was remounted. Subsequently, the lower electrode was temporarily removed, and a negative electrode composite was injected onto the solid electrolyte layer. The lower electrode was remounted, and uniaxial press forming was performed at approximately 4.6 tf / cm². Afterward, the upper and lower electrodes were clamped together and constrained by a torque of 4 N·m to fabricate an all-solid-state battery equivalent to 1 mAh. The fabrication process of the all-solid-state battery was carried out in a glove box replaced with dry air having an average dew point of -70°C.

[0087] The all-solid-state battery obtained in this way was loaded into an environment tester maintained at 25°C and connected to a charge / discharge measuring device to evaluate the battery characteristics.

[0088] Charging and discharging of the battery was performed using 1 mA as 1 C. Charging was performed from 0.2 C to 4.5 V using the CC-CV method, and the charging capacity was obtained. Discharging was performed from 0.2 C to 2.5 V using the CC method, and the discharge capacity was obtained. When the solid electrolyte obtained in Example 2 was used in the negative electrode layer, the charge-discharge efficiency (discharge capacity ÷ charge capacity × 100%) was 98.2% in the second cycle and 98.6% in the third cycle, confirming reversible charge-discharge behavior. Figure 4 illustrates the charge-discharge behavior of the all-solid-state battery in the second cycle.

[0089]

[0090] As is evident from the results shown in Table 1, the solid electrolyte obtained in each example contains a proportion of sulfur element almost equivalent to that of the solid electrolyte of the comparative example, yet has higher lithium ion conductivity compared to the solid electrolyte of the comparative example. Industrial applicability

[0091] According to the present invention, a solid electrolyte having a predetermined composition and high lithium ion conductivity is provided.

Claims

Claim 1 It comprises lithium (Li) element, phosphorus (P) element, sulfur (S) element, halogen (X) element, and M element (M represents at least one of silicon (Si), tin (Sn), antimony (Sb), germanium (Ge), and boron (B), and the molar ratio S / (P+M) of the sulfur (S) element to the sum of the phosphorus (P) element and the M element is 3.5 a Let it be, and when the background of the X-ray diffraction pattern is set to I0, the I for said I0 a Of I a Solid electrolyte with / I0 of 1.6 or less.​ Claim 2 It comprises lithium (Li) element, phosphorus (P) element, sulfur (S) element, halogen (X) element, and M element (M represents at least one of silicon (Si), tin (Sn), antimony (Sb), germanium (Ge), and boron (B), and the molar ratio S / (P+M) of the sulfur (S) element to the sum of the phosphorus (P) element and the M element is 3.5 b Let it be, and when the background of the X-ray diffraction pattern is set to I0, the I for said I0 b Of I b Solid electrolyte with / I0 of 2.5 or less.​ Claim 3 In paragraph 2, in the X-ray diffraction pattern measured by an X-ray diffraction device (XRD) using CuKα1 rays, the intensity of peak A observed at the position 2θ = 21.3° ± 0.3° is I a Let it be, and when the background of the X-ray diffraction pattern is set to I0, the I for said I0 a Of I a Solid electrolyte with / I0 of 1.6 or less. Claim 4 In claim 1 or 2, the molar ratio X / (P+M) of the halogen (X) element to the sum of the phosphorus (P) element and the M element is 0.7 <X / (P+M)<3.0을 만족시키는, 고체 전해질. Claim 5 In paragraph 1 or 2, Li w P 1-x M x S y X z A solid electrolyte having a composition represented by (wherein w represents a number greater than or equal to 4.5 and less than or equal to 5.5, x represents a number greater than or equal to 0.05 and less than or equal to 0.45, y represents a number greater than or equal to 3.5 and less than or equal to 4.2, and z represents a number greater than or equal to 1.0 and less than or equal to 3.0). Claim 6 A solid electrolyte according to claim 1 or 2, wherein the halogen (X) element comprises a bromine (Br) element. Claim 7 A solid electrolyte according to claim 1 or 2, wherein the halogen (X) comprises the elements bromine (Br) and chlorine (Cl). Claim 8 A solid electrolyte according to claim 1 or 2, wherein the ratio of the sulfur (S) element to all elements is 40 mol% or less. Claim 9 An electrode composite comprising a solid electrolyte and an active material as described in claim 1 or 2. Claim 10 A solid electrolyte layer containing the solid electrolyte described in paragraph 1 or 2. Claim 11 A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and containing the solid electrolyte described in claim 1 or 2.

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