WO2020194822A1 - 固体電解質及び固体電解質の製造方法 - Google Patents
固体電解質及び固体電解質の製造方法 Download PDFInfo
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- WO2020194822A1 WO2020194822A1 PCT/JP2019/041710 JP2019041710W WO2020194822A1 WO 2020194822 A1 WO2020194822 A1 WO 2020194822A1 JP 2019041710 W JP2019041710 W JP 2019041710W WO 2020194822 A1 WO2020194822 A1 WO 2020194822A1
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- Prior art keywords
- solid electrolyte
- 3lioh
- lioh
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- powder
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- 239000007784 solid electrolyte Substances 0.000 title claims abstract description 102
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 229910052796 boron Inorganic materials 0.000 claims abstract description 31
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000002441 X-ray diffraction Methods 0.000 claims abstract description 22
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Chemical compound [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 claims abstract description 20
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 71
- 239000000843 powder Substances 0.000 claims description 38
- 239000002994 raw material Substances 0.000 claims description 17
- 238000001816 cooling Methods 0.000 claims description 11
- 238000002844 melting Methods 0.000 claims description 9
- 230000008018 melting Effects 0.000 claims description 9
- 238000003701 mechanical milling Methods 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 8
- 229910052717 sulfur Inorganic materials 0.000 claims description 8
- 230000005855 radiation Effects 0.000 claims description 6
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 5
- 238000010298 pulverizing process Methods 0.000 claims description 5
- 239000011593 sulfur Substances 0.000 claims description 5
- 230000002194 synthesizing effect Effects 0.000 claims description 4
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 35
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 35
- 238000003860 storage Methods 0.000 abstract description 3
- 230000007774 longterm Effects 0.000 abstract 1
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 16
- 239000000203 mixture Substances 0.000 description 14
- 239000013078 crystal Substances 0.000 description 10
- 230000007423 decrease Effects 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 238000012423 maintenance Methods 0.000 description 6
- 230000014759 maintenance of location Effects 0.000 description 6
- 239000000155 melt Substances 0.000 description 5
- 239000011812 mixed powder Substances 0.000 description 5
- 238000003825 pressing Methods 0.000 description 5
- 238000007723 die pressing method Methods 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 229910052744 lithium Inorganic materials 0.000 description 4
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000003990 capacitor Substances 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 238000004445 quantitative analysis Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- 101100317222 Borrelia hermsii vsp3 gene Proteins 0.000 description 1
- -1 Li 3 BO 3 Chemical compound 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000011088 calibration curve Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000004993 emission spectroscopy Methods 0.000 description 1
- 238000002847 impedance measurement Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000002354 inductively-coupled plasma atomic emission spectroscopy Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000003801 milling Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000011863 silicon-based powder Substances 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 230000004580 weight loss Effects 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/54—Electrolytes
- H01G11/56—Solid electrolytes, e.g. gels; Additives therein
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D15/00—Lithium compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
- H01M10/0562—Solid materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M12/00—Hybrid cells; Manufacture thereof
- H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0068—Solid electrolytes inorganic
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a solid electrolyte and a method for producing a solid electrolyte.
- Non-Patent Document 1 proposes to use a solidified body obtained by homogeneously melting Li 2 SO 4 and Li OH and then quenching it as a solid electrolyte. In particular, it is said that this solid electrolyte can be used for devices that operate at low temperatures.
- Non-Patent Document 1 cannot be said to have sufficiently high lithium ion conductivity at room temperature. Further, the solid electrolyte of Non-Patent Document 1 has a small temperature dependence of conductivity, and the effect of increasing conductivity due to temperature increase cannot be expected. That is, this solid electrolyte cannot be said to be a material having sufficient lithium ion conductivity from room temperature to high temperature. In response to these problems, the present inventors have obtained the finding that the solid electrolyte represented by 3LiOH ⁇ Li 2 SO 4 exhibits high lithium ion conductivity at 25 ° C. However, it has been found that the material having the above composition alone has another problem that the lithium ion conductivity tends to decrease when the material is held at a high temperature for a long time.
- the present inventors have stated that by further adding boron to the solid electrolyte identified as 3LiOH / Li 2 SO 4 , the decrease in lithium ion conductivity can be significantly suppressed even after being held at a high temperature for a long time. I got the knowledge of.
- an object of the present invention is to provide a 3LiOH ⁇ Li 2 SO 4 based solid electrolyte capable of significantly suppressing a decrease in lithium ion conductivity even after being held at a high temperature for a long time.
- a solid electrolyte that is identified as 3LiOH ⁇ Li 2 SO 4 by X-ray diffraction, wherein the solid electrolyte further contains boron.
- a method for producing the solid electrolyte comprises a step of forming a solidified body by melting and cooling a raw material containing LiOH, Li 2 SO 4 and Li 3 BO 3 .
- a method for producing a solid electrolyte comprises a step of synthesizing a solid electrolyte powder by mixing and pulverizing a powder containing LiOH, Li 2 SO 4 and Li 3 BO 3 by mechanical milling.
- the solid electrolyte according to the present invention is a solid electrolyte identified as 3LiOH ⁇ Li 2 SO 4 by X-ray diffraction. And this solid electrolyte further contains boron. 3LiOH ⁇ Li 2 SO 4 by causing further contains boron in solid electrolyte identified as can significantly suppress a decrease in lithium ion conductivity even after holding at a high temperature for a long time. That is, as described above, the present inventors have obtained the finding that the solid electrolyte represented by 3LiOH ⁇ Li 2 SO 4 exhibits high lithium ion conductivity at 25 ° C.
- the above composition alone has another problem that the lithium ion conductivity tends to decrease when the lithium ion conductivity is held at a high temperature for a long time.
- it is possible to solve the above problem further be contained boron solid electrolyte identified as 3LiOH ⁇ Li 2 SO 4.
- the mechanism by which the ionic conductivity maintenance rate can be improved by the inclusion of boron is not clear, but according to X-ray diffraction measurement, the diffraction peak of 3LiOH / Li 2 SO 4 is slightly shifted to the higher angle side by the inclusion of boron. since that boron is incorporated into one of the sites of the crystal structure of 3LiOH ⁇ Li 2 SO 4, it is presumed that to improve the stability against the temperature of the crystal structure.
- the solid electrolyte according to the present invention is preferably used for a power storage element such as a lithium ion secondary battery and a capacitor, and particularly preferably used for a lithium ion secondary battery.
- the lithium ion secondary battery may be an all-solid-state battery (for example, an all-solid-state lithium-ion secondary battery).
- the lithium ion secondary battery may be a liquid battery (for example, a lithium air battery) in which a solid electrolyte is used as a separator and an electrolytic solution is provided between the separator and the counter electrode.
- the solid electrolyte according to the present invention is a solid electrolyte identified as 3LiOH ⁇ Li 2 SO 4 by X-ray diffraction. That is, the solid electrolyte contains 3LiOH ⁇ Li 2 SO 4 as the main phase. Whether or not the solid electrolyte contains 3 LiOH / Li 2 SO 4 can be confirmed by identifying the X-ray diffraction pattern using 032-0598 of the ICDD database.
- “3LiOH / Li 2 SO 4 " refers to a crystal structure that can be regarded as the same as that of 3LiOH / Li 2 SO 4, and the crystal composition does not necessarily have to be the same as that of 3LiOH / Li 2 SO 4 .
- the solid electrolyte is a main phase in addition 3LiOH ⁇ Li 2 SO 4, may be included heterophase.
- the heterogeneous phase may contain a plurality of elements selected from Li, O, H, S and B, or may consist only of a plurality of elements selected from Li, O, H, S and B. It may be.
- Examples of the heterogeneous phase include LiOH, Li 2 SO 4 and / or Li 3 BO 3 derived from the raw material. Regarding these heterogeneous phases, it is considered that unreacted raw materials remained when forming 3 LiOH / Li 2 SO 4 , but since they do not contribute to lithium ion conduction, the smaller the amount, the better, except for Li 3 BO 3. desirable.
- a heterogeneous phase containing boron such as Li 3 BO 3
- the solid electrolyte may be composed of a single phase of 3LiOH / Li 2 SO 4 in which boron is dissolved.
- the solid electrolyte of the present invention further contains boron.
- the molar ratio (B / S) of boron B to sulfur S contained in the solid electrolyte is preferably more than 0.002 and less than 1.0, more preferably 0.003 or more and 0.9 or less, still more preferably. It is 0.005 or more and 0.8 or less.
- the absolute value of the lithium ion conductivity may decrease, but if the B / S is within the above range, the content of the unreacted heterogeneous phase containing boron becomes low, so that lithium ion conduction
- the absolute value of the degree can be increased.
- the lower limit is not particularly limited, but is typically 0.08 ° or more, and more typically 0.1 °. That is all.
- the ratio of peak intensities I LiOH near 20.5 °, I LiOH / I LHS is preferably less than 0.234, more preferably 0.230 or less, still more preferably 0.200 or less. If the amount of LiOH is large, the absolute value of the lithium ion conductivity may be lowered, but if it is in the above range, the content of LiOH is low, so that the absolute value of the lithium ion conductivity can be increased.
- the solid electrolyte according to the present invention may be a green compact, but a melt-solidified body (that is, one solidified after heating and melting) is preferable.
- the solid electrolyte of the present invention is produced through a step of forming a solid body by melting and cooling a raw material containing LiOH, Li 2 SO 4 and Li 3 BO 3. be able to.
- the raw material used in this case has a composition represented by xLiOH, Li 2 SO 4 , yLi 3 BO 3 (in the formula, 2.0 ⁇ x ⁇ 4, 0.002 ⁇ y ⁇ 1) for ionic conductivity. It is preferable from the viewpoint, but it is not limited to this as long as the desired characteristics can be obtained (for example, 1.0 ⁇ x ⁇ 4 may be obtained).
- a solidified body is formed by cooling a melt of a raw material containing LiOH, Li 2 SO 4 and Li 3 BO 3 (preferably a raw material having the above composition), and (b) The solidified body can be crushed or mechanically milled to obtain a solid electrolyte powder, and (c) the solid electrolyte powder can be formed, or the solid electrolyte powder can be melted again and then cooled to solidify to form a solid electrolyte. it can.
- the cooling of the melt in the above (a) may be either rapid cooling or slow cooling (for example, furnace cooling).
- the mechanical milling in (b) above can be performed by putting a boulder such as zirconia balls and a solidified body of a solid electrolyte into a zirconia container or the like and pulverizing the mixture according to a known method and conditions.
- the molding in the step (c) can be performed by various methods such as pressing (for example, die pressing and rubber pressing), and is preferably a die pressing.
- the temperature lowering rate at the time of cooling after the solid electrolyte powder is melted again in the step (c) is preferably 10 to 1000 ° C./h, more preferably 10 to 100 ° C./h.
- the present invention can be produced through a step of synthesizing a solid electrolyte powder by mixing and pulverizing a powder containing LiOH, Li 2 SO 4 and Li 3 BO 3 by mechanical milling.
- the powder used in this case is LiOH in a blending ratio that brings about the raw material composition represented by xLiOH ⁇ Li 2 SO 4 ⁇ yLi 3 BO 3 (in the formula, 2.0 ⁇ x ⁇ 4, 0.002 ⁇ y ⁇ 1). It is preferable to include powder, Li 2 SO 4 powder and Li 3 BO 3 powder from the viewpoint of ionic conductivity, but it is not limited to this as long as desired properties can be obtained (for example, even if 1.0 ⁇ x ⁇ 4). Good).
- a solid electrolyte For example, in the production of a solid electrolyte, (a) LiOH powder, Li 2 SO 4 powder and Li 3 BO 3 powder are mixed and pulverized by mechanical milling (preferably at a blending ratio that results in the above composition) to synthesize a solid electrolyte powder. , (B) It can be carried out by forming a solid electrolyte powder or by forming a solid electrolyte by heating and melting the solid electrolyte powder and then cooling it. In the mechanical milling in (a) above, according to a known method and conditions, a ball stone such as zirconia balls and LiOH powder, Li 2 SO 4 powder and Li 3 BO 3 powder are put into a container such as a zirconia container and mixed and pulverized.
- a ball stone such as zirconia balls and LiOH powder, Li 2 SO 4 powder and Li 3 BO 3 powder are put into a container such as a zirconia container and mixed and pulverized.
- the molding in the step (b) can be performed by various methods such as pressing (for example, die pressing and rubber pressing), and is preferably a die pressing.
- the cooling rate of cooling after melting of the solid electrolyte powder in the step (b) is preferably 10 to 1000 ° C./h, more preferably 10 to 100 ° C./h.
- Examples 1-3 Preparation of raw material powder Li 2 SO 4 powder (commercially available, purity 99% or more), LiOH powder (commercially available, purity 98% or more), and Li 3 BO 3 (commercially available product, purity 99% or more) are shown.
- the raw material mixed powder was obtained by mixing so as to have the molar ratio shown in 1. These powders were handled in a glove box in an Ar atmosphere with a dew point of ⁇ 50 ° C. or lower, and sufficient care was taken not to cause deterioration such as moisture absorption.
- the solid electrolyte in the ion conductivity measurement cell was measured lithium ion conductivity C 1 in the same manner as described above.
- the conductivity retention rate after holding it at 150 ° C. for 100 hours was asked.
- Quantitative analysis of boron and sulfur was performed on the solid electrolytes obtained in each example. Quantitative analysis was performed on each of boron and sulfur by ICP emission spectroscopy (ICP-AES) and a calibration curve method. Each analytical value of boron and sulfur was converted into the number of moles and calculated as B / S.
- ICP-AES ICP emission spectroscopy
- Examples 4-20 Preparation of raw material powder Li 2 SO 4 powder (commercially available, purity 99% or more), LiOH powder (commercially available, purity 98% or more), and Li 3 BO 3 (commercially available product, purity 99% or more) are shown.
- the raw material mixed powder was obtained by mixing so as to have the molar ratio shown in 1. These powders were handled in a glove box in an Ar atmosphere with a dew point of ⁇ 50 ° C. or lower, and sufficient care was taken not to cause deterioration such as moisture absorption.
- a pellet-shaped solid electrolyte having a diameter of 10 mm was formed by pressing a solid electrolyte powder with a die at a pressure of 250 MPa in a glove box in a molten Ar atmosphere.
- a pellet-shaped solid electrolyte is sandwiched between two stainless steel (SUS) electrodes having a diameter of 10 mm and a thickness of 0.5 mm, a weight of 15 g is placed on the obtained laminate, and the mixture is heated at 400 ° C. for 45 minutes. By doing so, the solid electrolyte was melted. Then, the melt was cooled at 100 ° C./h to form a solidified body.
- SUS stainless steel
- Example 1 to 20 The production conditions and evaluation results of the solid electrolytes of Result Examples 1 to 20 are summarized in Table 1.
- the weight loss is reduced. It is very small, 1% or less, and it is presumed that the compositions of Li, O, H, S and B constituting the solid electrolyte are hardly changed from the composition at the time of preparation.
- Examples 3, 8 and 14 containing no boron have a small ionic conductivity maintenance rate of 75% or less, and as in Example 13, the B / S is 0.002 or more, so that the ionic conductivity maintenance rate is 80% or more. It turned out that it became large. Further, when the ionic conductivity of Examples 4 and 6 after holding at 150 ° C. for 100 hours was compared, it was found that the conductivity was low in Example 4. It is presumed that this is because the content of unreacted heterogeneous phase was high because the amount of Li 3 BO 3 added was large, and it was found that the B / S indicating the amount of boron added was preferably less than 1.0.
- Example 4 and 6 prepared by the melting method with the same composition as in Examples 1 and 2, the ionic conductivity retention rate is large. Focusing on the half-width of 3LiOH ⁇ Li 2 SO 4 by X-ray diffraction, is presumed to have high crystallinity from the half value width is narrow in Example 4 and 6, are more stable as a crystal large conductivity retention It is presumed that it has become. From the above, the half-width of 3LiOH ⁇ Li 2 SO 4 is considered preferable 0.500 or less.
- Examples 6, 11 and 15 in which LiOH is detected by XRD after holding at 150 ° C. for 100 hours it can be seen that Examples 6 and 11 have higher ionic conductivity than Example 15. Focusing on the peak intensity ratio (I LiOH / I LHS ) by X-ray diffraction, it is presumed that LiOH remains as a heterogeneous phase because the value is large in Example 15, and it is considered that this inhibited ion conduction. Guess. From this, when LiOH is detected as a heterogeneous phase, it is considered that the peak intensity ratio (I LiOH / I LHS ) is preferably 0.234 or less.
- Example 17 has higher ionic conductivity than Example 20. Focusing on the peak intensity ratio (I Li2SO4 / I LHS) by X-ray diffraction, since the value is larger in Example 20, it is presumed that Li 2 SO 4 is left as a heterogeneous phase, which inhibits the ionic conductivity It is presumed that it was done. Therefore, Li 2 SO 4 is the case is detected as heterophase, the peak intensity ratio (I Li2SO4 / I LHS) is considered to preferably less than 1.1.
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Abstract
Description
LiOH、Li2SO4及びLi3BO3を含む原料を溶融して冷却することによって凝固体を形成する工程を含む、固体電解質の製造方法が提供される。
LiOH、Li2SO4及びLi3BO3を含む粉末をメカニカルミリングにより混合粉砕して固体電解質粉末を合成する工程を含む、固体電解質の製造方法が提供される。
本発明による固体電解質は、X線回折により3LiOH・Li2SO4と同定される固体電解質である。そして、この固体電解質はホウ素をさらに含む。3LiOH・Li2SO4と同定される固体電解質にホウ素をさらに含有させることで、高温で長時間保持した後においてもリチウムイオン伝導度の低下を有意に抑制することができる。すなわち、前述したとおり、本発明者らは、3LiOH・Li2SO4で表される固体電解質が25℃において高いリチウムイオン伝導度を呈するとの知見を得ている。しかしながら、上記組成のみでは高温で長時間保持した場合にリチウムイオン伝導度が低下しやすいとの別の問題があることが分かってきた。この点、3LiOH・Li2SO4と同定される固体電解質にホウ素をさらに含有させることで上記問題を解決することができる。ホウ素の含有によりイオン伝導度維持率を向上できるメカニズムは定かではないが、X線回折測定によると、ホウ素を含有させることにより、3LiOH・Li2SO4の回折ピークがわずかに高角側にシフトしていることから、ホウ素は3LiOH・Li2SO4の結晶構造のサイトのいずれかに取り込まれ、結晶構造の温度に対する安定性を向上させているものと推察される。
本発明の好ましい態様によれば、本発明の固体電解質は、LiOH、Li2SO4及びLi3BO3を含む原料を溶融して冷却することによって凝固体を形成する工程を経て製造することができる。この場合に用いる原料はxLiOH・Li2SO4・yLi3BO3(式中、2.0≦x≦4、0.002≦y≦1)で表される組成を有するのがイオン伝導度の観点から好ましいが、所望の特性が得られるかぎりこれに限定されない(例えば1.0≦x≦4であってもよい)。例えば、固体電解質の製造は、(a)LiOH、Li2SO4及びLi3BO3を含む原料(好ましくは上記組成の原料)の溶融物を冷却することによって凝固体を形成し、(b)凝固体を粉砕又はメカニカルミリングすることによって固体電解質粉末とし、(c)固体電解質粉末を成形すること又は固体電解質粉末を再度溶融後冷却して固化することによって固体電解質を形成することにより行うことができる。上記(a)における溶融物の冷却は急冷又は徐冷(例えば炉冷)のいずれでもよい。上記(b)におけるメカニカルミリングは、公知の手法及び条件に従い、ジルコニア容器等にジルコニアボール等の玉石と固体電解質の凝固体を投入して粉砕することにより行うことができる。上記(c)工程における成形は、プレス(例えば金型プレス、ラバープレス)等の様々な手法により行うことができ、好ましくは金型プレスである。上記(c)工程における固体電解質粉末の再度の溶融後の冷却時の降温速度は10~1000℃/hであるのが好ましく、より好ましくは10~100℃/hである。
(1)原料粉末の準備
Li2SO4粉末(市販品、純度99%以上)、LiOH粉末(市販品、純度98%以上)、及びLi3BO3(市販品、純度99%以上)を表1に示されるモル比となるように混合して原料混合粉末を得た。これらの粉末は、露点-50℃以下のAr雰囲気中のグローブボックス中で取り扱い、吸湿等の変質が起こらないように十分に注意した。
Ar雰囲気中のグローブボックス内で、45mlのジルコニアポットに原料混合粉末及び10個のジルコニアボール(直径10mm)を投入し、ジルコニアポットを完全に密閉した。このジルコニアポットを遊星型ボールミル機に取り付け、回転数400rpmで50時間メカニカルミリングを行って、固体電解質粉末を合成した。
得られた固体電解質粉末を750MPaの圧力で金型プレスして、直径10mm及び厚さ0.5mmのペレット状の固体電解質を形成した。
得られた固体電解質に対して以下の評価を行った。
固体電解質をX線回折装置(XRD、X線源:CuKα線)で分析することによりX線回折パターンを得た。なお、金属Si粉を内部標準として添加して2θ位置を合わせた。得られたX線回折パターンとICDDデータベースの032-0598とを対比することによって、3LiOH・Li2SO4結晶相の同定を行い、3LiOH・Li2SO4の有無を判定した。また、上記得られたXRDプロファイルに基づき、3LiOH・Li2SO4と同定される2θ=18.4°付近のピークの半値幅を算出した。さらに、3LiOH・Li2SO4と同定される2θ=18.4°付近のピーク強度ILHSに対する、LiOHと同定される2θ=20.5°付近のピーク強度ILiOHの比(ILiOH/ILHS)を算出した。同様に、3LiOH・Li2SO4と同定される2θ=18.4°付近のピーク強度ILHSに対する、Li2SO4と同定される2θ=22.2°付近のピーク強度ILi2SO4の比(ILi2SO4/ILHS)を算出した。結果は表1に示されるとおりであった。
固体電解質のリチウムイオン伝導度を一般的な交流インピーダンス測定を用いて以下のようにして測定した。まず、Ar雰囲気中において、固体電解質を2枚のステンレス鋼(SUS)電極の間に挟み、セル(宝泉株式会社製、コインセルCR2032)に入れて密閉し、イオン伝導度測定用セルを作製した。このイオン伝導度測定用セルを150℃の恒温乾燥器に入れ、交流インピーダンス測定装置(BioLogic社製、VMP3)を用いて交流インピーダンス法によりコンダクタンス(1/r)を測定した。測定した値とリチウムイオン伝導度σ=L/r(1/A)の式に基づき、初期リチウムイオン伝導度C0を算出した。
各例で得られた固体電解質についてホウ素と硫黄の定量分析を行った。ホウ素及び硫黄の各々についてICP発光分光分析法(ICP-AES)にて、検量線法で定量分析を行った。ホウ素及び硫黄の各分析値をモル数に換算し、B/Sとして算出した。
(1)原料粉末の準備
Li2SO4粉末(市販品、純度99%以上)、LiOH粉末(市販品、純度98%以上)、及びLi3BO3(市販品、純度99%以上)を表1に示されるモル比となるように混合して原料混合粉末を得た。これらの粉末は、露点-50℃以下のAr雰囲気中のグローブボックス中で取り扱い、吸湿等の変質が起こらないように十分に注意した。
Ar雰囲気中で原料混合粉末を高純度アルミナ製のるつぼに投入し、このるつぼを電気炉にセットし、430℃で2時間熱処理を行い溶融物を作製した。引き続き、電気炉内にて100℃/hで溶融物を冷却して凝固物を形成した。
得られた凝固物をAr雰囲気中にて乳鉢で粉砕することによって、平均粒径D50が5~50μmの固体電解質粉末を得た。
Ar雰囲気中のグローブボックス内で、固体電解質粉末を250MPaの圧力で金型プレスすることによって、直径10mmのペレット状の固体電解質を形成した。直径10mm、厚さ0.5mmの2枚のステンレス鋼(SUS)電極の間にペレット状の固体電解質を挟み、得られた積層物の上に15gの重しを載せ、400℃で45分加熱することにより固体電解質を溶融させた。その後、100℃/hで溶融物を冷却して凝固体を形成した。
得られた凝固体(固体電解質)に対して例1と同様にして評価を行った。結果は、表1に示されるとおりであった。
例1~20の固体電解質の作製条件及び評価結果を表1にまとめて示す。例1~20において、LiOH、Li2SO4及びLi3BO3を含む原料混合粉末を溶融又はメカニカルミリングして固体電解質を合成する工程や、固体電解質粉末を再度溶融する工程において、重量減は1%以下と非常に小さいものであり、固体電解質を構成するLi、O、H、S及びBの組成は調合時の組成からほとんど変化していないものと推測される。
Claims (8)
- X線回折により3LiOH・Li2SO4と同定される固体電解質であって、前記固体電解質がホウ素をさらに含む、固体電解質。
- 前記固体電解質中に含まれる硫黄Sに対する、前記ホウ素Bのモル比である、B/Sが0.002超1.0未満である、請求項1に記載の固体電解質。
- 前記固体電解質は、CuKαを線源としたX線回折パターンにおける、3LiOH・Li2SO4と同定される2θ=18.4°付近のピークの半値幅が0.500°以下である、請求項1又は2に記載の固体電解質。
- 前記固体電解質は、CuKαを線源としたX線回折パターンにおける、3LiOH・Li2SO4と同定される2θ=18.4°付近のピーク強度ILHSに対する、LiOHと同定される2θ=20.5°付近のピーク強度ILiOHの比である、ILiOH/ILHSが0.234未満である、請求項1~3のいずれか一項に記載の固体電解質。
- 前記固体電解質は、CuKαを線源としたX線回折パターンにおける、3LiOH・Li2SO4と同定される2θ=18.4°付近のピーク強度ILHSに対する、Li2SO4と同定される2θ=22.2°付近のピーク強度ILi2SO4の比である、ILi2SO4/ILHSが1.10未満である、請求項1~4のいずれか一項に記載の固体電解質。
- 前記固体電解質が溶融凝固体である、請求項1~5のいずれか一項に記載の固体電解質。
- 請求項1~6のいずれか一項に記載の固体電解質の製造方法であって、
LiOH、Li2SO4及びLi3BO3を含む原料を溶融して冷却することによって凝固体を形成する工程を含む、固体電解質の製造方法。 - 請求項1~6のいずれか一項に記載の固体電解質の製造方法であって、
LiOH、Li2SO4及びLi3BO3を含む粉末をメカニカルミリングにより混合粉砕して固体電解質粉末を合成する工程を含む、固体電解質の製造方法。
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