CN117865673A - Garnet-type solid electrolyte and preparation method thereof - Google Patents
Garnet-type solid electrolyte and preparation method thereof Download PDFInfo
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- 239000007784 solid electrolyte Substances 0.000 title claims abstract description 41
- 238000002360 preparation method Methods 0.000 title abstract description 10
- 239000000243 solution Substances 0.000 claims abstract description 85
- 239000002243 precursor Substances 0.000 claims abstract description 81
- 238000000034 method Methods 0.000 claims abstract description 42
- 239000000843 powder Substances 0.000 claims abstract description 40
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 29
- 238000010438 heat treatment Methods 0.000 claims abstract description 27
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000011259 mixed solution Substances 0.000 claims abstract description 26
- 238000002156 mixing Methods 0.000 claims abstract description 20
- 239000012265 solid product Substances 0.000 claims abstract description 20
- 238000003825 pressing Methods 0.000 claims abstract description 19
- 239000002223 garnet Substances 0.000 claims abstract description 9
- 239000000126 substance Substances 0.000 claims abstract description 8
- 238000000227 grinding Methods 0.000 claims abstract description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 22
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 17
- 229910052750 molybdenum Inorganic materials 0.000 claims description 17
- 239000011733 molybdenum Substances 0.000 claims description 17
- 229910052726 zirconium Inorganic materials 0.000 claims description 17
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 16
- 238000000465 moulding Methods 0.000 claims description 15
- 230000008569 process Effects 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- 229910052746 lanthanum Inorganic materials 0.000 claims description 13
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 13
- 229920002153 Hydroxypropyl cellulose Polymers 0.000 claims description 12
- 239000001863 hydroxypropyl cellulose Substances 0.000 claims description 12
- 235000010977 hydroxypropyl cellulose Nutrition 0.000 claims description 12
- 238000010304 firing Methods 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 8
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 6
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 6
- 239000013078 crystal Substances 0.000 abstract description 16
- 238000003980 solgel method Methods 0.000 abstract description 7
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 description 14
- 239000012071 phase Substances 0.000 description 12
- BSDOQSMQCZQLDV-UHFFFAOYSA-N butan-1-olate;zirconium(4+) Chemical group [Zr+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] BSDOQSMQCZQLDV-UHFFFAOYSA-N 0.000 description 7
- 150000002500 ions Chemical class 0.000 description 7
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical group [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 7
- 229910000476 molybdenum oxide Inorganic materials 0.000 description 7
- PQQKPALAQIIWST-UHFFFAOYSA-N oxomolybdenum Chemical group [Mo]=O PQQKPALAQIIWST-UHFFFAOYSA-N 0.000 description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 230000002776 aggregation Effects 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- 230000007062 hydrolysis Effects 0.000 description 4
- 238000006460 hydrolysis reaction Methods 0.000 description 4
- 239000012535 impurity Substances 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- 238000005054 agglomeration Methods 0.000 description 3
- 238000000498 ball milling Methods 0.000 description 3
- 150000001768 cations Chemical class 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000005486 organic electrolyte Substances 0.000 description 3
- 230000001737 promoting effect Effects 0.000 description 3
- 238000010532 solid phase synthesis reaction Methods 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000001453 impedance spectrum Methods 0.000 description 2
- 238000011534 incubation Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011812 mixed powder Substances 0.000 description 2
- MEFBJEMVZONFCJ-UHFFFAOYSA-N molybdate Chemical compound [O-][Mo]([O-])(=O)=O MEFBJEMVZONFCJ-UHFFFAOYSA-N 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- VSZWPYCFIRKVQL-UHFFFAOYSA-N selanylidenegallium;selenium Chemical compound [Se].[Se]=[Ga].[Se]=[Ga] VSZWPYCFIRKVQL-UHFFFAOYSA-N 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 229910001251 solid state electrolyte alloy Inorganic materials 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000004049 embossing Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 239000010416 ion conductor Substances 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical group [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000003801 milling Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 238000011112 process operation Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
Classifications
-
- 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
Abstract
The invention belongs to the field of lithium batteries, and provides a garnet-type solid electrolyte and a preparation method thereof. The chemical formula of the garnet-type solid electrolyte is Li 7‑2x La 3 Zr 2‑x Mo x O 12 X=0.05-0.2, the method comprising (1) formulating solution a, solution B and solution C; (2) Mixing the solution A, the solution B and the solution CObtaining a mixed solution; (3) heating the mixed solution to obtain a solid product; (4) First roasting the solid product to obtain a precursor; (5) grinding the precursor to obtain precursor powder; (6) cold pressing the precursor powder to obtain a molded precursor; (7) Covering the mould pressing precursor with precursor powder, and then performing second roasting to obtain the garnet type solid electrolyte. The invention adopts the sol-gel method to prepare the garnet type solid electrolyte, has low cost and simple operation, and the obtained garnet type solid electrolyte has stable crystal form and higher ionic conductivity.
Description
Technical Field
The invention relates to the field of lithium batteries, in particular to a garnet type solid electrolyte and a preparation method thereof.
Background
Since the last nineties of lithium ion batteries were commercialized, they have played an increasingly important role in the fields of consumer electronics and energy storage systems, and there is also a need for lithium ion batteries with higher energy density, higher operating voltage, higher energy density, longer cycle life, and smaller self-discharge rate. At present, the traditional lithium ion battery adopts organic electrolyte as electrolyte, and the organic electrolyte can volatilize, dry and leak in the use process, and has the safety problems of inflammability and explosiveness. The solid electrolyte can effectively solve the potential safety hazard of organic electrolyte, and can also enable the use of metallic lithium as a negative electrode.
Garnet-type solid state electrolytes (LLZO) have received a lot of attention because of their advantages of higher ionic conductivity, wider electrochemical window, and good chemical and electrochemical stability to lithium metal anodes. However, LLZO exhibits structural and stoichiometric instability in a humid environment, resulting in a large interfacial resistance between LLZO and metallic lithium, thereby reducing its ionic conductivity.
Thus, the current garnet-type solid electrolyte and the preparation method thereof have yet to be improved.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the related art to some extent.
In one aspect, the present invention provides a method of preparing a garnet-type solid electrolyte having a chemistryLi is 7-2x La 3 Zr 2-x Mo x O 12 X=0.05-0.2, the method comprising the steps of:
(1) Preparing a solution A, a solution B and a solution C, wherein,
mixing a lithium source, a lanthanum source and water to obtain a solution A,
mixing a zirconium source, hydroxypropyl cellulose and ethanol to obtain a solution B,
mixing a molybdenum source and ammonia water to form a solution C;
(2) Mixing the solution A, the solution B and the solution C to obtain a mixed solution;
(3) Heating the mixed solution to remove water and ethanol therein and obtain a solid product;
(4) First roasting the solid product to obtain a precursor;
(5) Grinding the precursor to obtain precursor powder;
(6) Cold pressing the precursor powder to form a molded precursor;
(7) Covering the mould pressing precursor with precursor powder, and then performing second roasting to obtain the garnet type solid electrolyte.
The method synthesizes the Mo-doped garnet type solid electrolyte Li by adopting a sol-gel method 7- 2x La 3 Zr 2-x Mo x O 12 And (LLZOM), the lithium source, the lanthanum source, the zirconium source and the molybdenum source are uniformly mixed in the preparation process, and the synthesized LLZMO is less in impurity phase, so that the production process is simplified. Meanwhile, compared with a solid phase method, the sol-gel method greatly reduces the mixing time and reduces the requirements on cold pressing pressure and pressure maintaining time in the cold pressing treatment process. In addition, the LLZMO is formed by doping Mo element with low cost, so that the cost is reduced, and the obtained LLZMO can keep a stable crystal form in humid air, so that the LLZMO can keep higher ionic conductivity.
According to the embodiment of the invention, the dosages of the lithium source, the lanthanum source, the zirconium source and the molybdenum source are calculated as the molar ratio of Li to La to Zr to Mo to be y to 3 to (2-x) to x, wherein y and (7-2 x) satisfy the following relation: y/(7-2 x) is less than or equal to 1.06 and less than or equal to 1.12. Thus, volatilization of lithium during the high temperature firing process can be compensated.
According to an embodiment of the invention, the concentration of hydroxypropyl cellulose in the solution B is 0.01-0.05g/mL.
According to an embodiment of the present invention, step (2) includes: and (3) dropwise adding the solution A into the solution B under the stirring condition to form a mixed solution AB, and dropwise adding the solution C into the mixed solution AB. Thus, agglomeration of particles due to hydrolysis of the zirconium source in solution B can be reduced, thereby promoting uniform mixing of solution a, solution B and solution C.
According to an embodiment of the present invention, in step (3), the heating is performed under stirring, and the heating temperature is 110 to 130 ℃.
According to an embodiment of the present invention, in step (4), the first firing process includes: heating to 500-600deg.C at a heating rate of 8-12deg.C/min, and maintaining for 1-3h.
According to an embodiment of the present invention, in the step (6), the pressure of the cold pressing is 5-15MPa, and the dwell time is 1-5min.
According to an embodiment of the present invention, in step (7), the second firing process includes: heating to 900-1000 deg.C at a heating rate of 8-12 deg.C/min, and maintaining for 7-11h.
According to an embodiment of the present invention, in step (7), the precursor powder covers the molding precursor with a thickness of 1 to 3mm.
In another aspect of the present invention, the present invention provides a garnet-type solid electrolyte prepared by the above method. The garnet-type solid electrolyte has a cubic phase crystal structure and higher ionic conductivity, and the crystal form is stable in a humid environment.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 shows the X-ray diffraction patterns of LLZMO of examples 1-4;
FIG. 2 shows the X-ray diffraction pattern of LLZMO of example 1;
fig. 3 shows the ac impedance spectrum of LLZMO of example 1.
Detailed Description
Embodiments of the present invention are described in detail below. The embodiments described below are exemplary only for explaining the present invention and are not to be construed as limiting the present invention.
The inventors found that LLZO of the cubic phase is poorly stable in a humid environment, li in the crystal lattice + Is easy to escape to the LLZO surface and generate Li with water in the air + And H + Exchange and at CO 2 Is used for generating Li under the action of (2) 2 CO 3 The wettability of lithium metal and LLZO is deteriorated, and a large interfacial resistance is generated, thereby reducing the ionic conductivity of LLZO. However, by doping with aliovalent cations to occupy the Li and Zr sites in the LLZO crystal, more Li vacancies in the garnet-type solid electrolyte can be made, promoting Li + Thereby stabilizing the crystalline structure of the garnet-type solid electrolyte. Ta 5+ 、Ga 3+ Respectively two common doping cations, ta 5+ Ions can occupy Zr sites, one Ta per doping 5+ Correspondingly reduce one Zr 4+ And Li (lithium) + ；Ga 3+ Ions occupy Zr sites, each doped into one Ga 3+ Three Li are correspondingly reduced + But Ta 5+ 、Ga 3+ The ion doping cost is too high, which is not beneficial to popularization and application of garnet type solid electrolyte.
Accordingly, in one aspect, the present invention provides a method of preparing a garnet-type solid electrolyte having the formula Li 7-2x La 3 Zr 2-x Mo x O 12 X=0.05-0.2, the method comprising the following steps:
(1) Preparing a solution A, a solution B and a solution C, wherein,
mixing a lithium source, a lanthanum source and water to obtain a solution A,
mixing a zirconium source, hydroxypropyl cellulose and ethanol to obtain a solution B,
mixing a molybdenum source and ammonia water to form a solution C;
(2) Mixing the solution A, the solution B and the solution C to obtain a mixed solution;
(3) Heating the mixed solution to remove water and ethanol therein and obtain a solid product;
(4) First roasting the solid product to obtain a precursor;
(5) Grinding the precursor to obtain precursor powder;
(6) Cold pressing the precursor powder to form a molded precursor;
(7) Covering the molding precursor with the precursor powder, and then performing the second baking to obtain the garnet-type solid electrolyte.
According to the method, the LLZO is doped with the Mo element with lower price, and LLZMO is synthesized through a sol-gel method. Specifically, hydroxypropyl cellulose is added in the process of preparing the solution B, aggregation among particles caused by hydrolysis of a zirconium source can be reduced, ammonia water is used as a solvent in the process of preparing the solution C, and the ammonia water can dissolve a molybdenum source to obtain a solution C containing molybdate, so that the solubility of the molybdenum source in water and ethanol is improved; and then the solution A, the solution B and the solution C are mixed to form a mixed solution which is uniformly mixed, so that LLZMO with less impurity phase and stable crystal form can be obtained. Meanwhile, compared with a solid phase method, the sol-gel method greatly reduces the mixing time, and can reduce the requirements of cold pressing pressure and pressure maintaining time in the cold pressing treatment process. In addition, the LLZMO is formed by doping the Mo element with low price, so that the production cost is greatly reduced, and the obtained LLZMO can keep a stable crystal form in humid air, so that the LLZMO can keep higher ionic conductivity and a wider electrochemical window.
In step (1), solution A, solution B and solution C are prepared.
The relative amounts of the lithium source, lanthanum source, zirconium source, molybdenum source may be formulated according to their chemical formulas, preferably the relative amounts of the lithium source are slightly higher than those indicated by their chemical formulas.
In some embodiments, in step (1), the lithium source, lanthanum source, zirconium source, molybdenum source are used in a molar ratio of Li: la: zr: mo of y: 3:2-x:x, wherein y and 7-2x satisfy the following relationship: y/(7-2 x) is less than or equal to 1.06 and less than or equal to 1.12. Thus, in the preparation of LLZMO, when the addition amount of the lithium source satisfies the above-mentioned relational expression, volatilization of lithium in the roasting process can be compensated, and the formation of stoichiometrically stable LLZMO can be promoted.
Optionally, the dosages of the lithium source, the lanthanum source, the zirconium source and the molybdenum source are calculated as y:3: (2-x):x according to the molar ratio of Li to La to Zr to Mo, wherein y and (7-2 x) satisfy the following conditions: y/(7-2 x) =1.1. Thus, the amount of the lithium source can compensate for sublimated Li during sintering 2 O, and LLZMO with stable chemical dosage and crystal form can be obtained, and the LLZMO has less impurity phase.
In some embodiments, the lithium source is lithium carbonate, lithium nitrate, lithium hydroxide.
In some embodiments, the zirconium source is zirconium butoxide, zirconium oxide.
In some embodiments, the lanthanum source is lanthanum nitrate.
In some embodiments, the molybdenum source is molybdenum oxide.
In step (1), a lithium source, a lanthanum source and water are mixed so that the lithium source and the lanthanum source are dissolved in the water to form a solution A.
Optionally, the water is added in an amount that at least completely dissolves the lithium source and the lanthanum source.
In general, in the solution A, the concentration of the lithium source is 0.5 to 2mol/L in terms of lithium (Li), for example, 0.5mol/L, 1mol/L, 2mol/L, etc.
In step (1), a zirconium source, hydroxypropyl cellulose and ethanol are mixed to form a solution B.
Generally, the concentration of the zirconium source in the solution B is 0.03 to 0.09mol/L in terms of zirconium (Zr), for example, 0.03mol/L, 0.06mol/L, 0.09mol/L, etc.
Alternatively, the concentration of hydroxypropyl cellulose in solution B is 0.01-0.05g/mL, e.g., 0.01mol/L, 0.02mol/L, 0.05mol/L, etc. The concentration of hydroxypropyl cellulose in the solution B is controlled within the range, so that agglomeration of particles in the hydrolysis process of the zirconium source can be effectively reduced, and the uniformity of the mixed solution is improved.
In step (1), the molybdenum source and ammonia are mixed so that the molybdenum source is dissolved in the ammonia to form a molybdate-containing solution C.
In general, the concentration of the molybdenum source in the solution C is 0.01 to 0.03mol/L in terms of molybdenum (Mo), for example, 0.01mol/L, 0.015mol/L, 0.03mol/L, etc.
In some embodiments, step (2) comprises: and (3) dropwise adding the solution A into the solution B under the stirring condition to form a mixed solution AB, and dropwise adding the solution C into the mixed solution AB. Thus, agglomeration of particles due to hydrolysis of the zirconium source in solution B can be reduced, and uniform mixing of solution a, solution B, and solution C can be further promoted.
In step (3), water and ethanol may be removed by evaporation by heating the mixed solution to obtain a solid product.
In some embodiments, the heating is by: heating while stirring on a magnetic stirrer to evaporate the solvent in the mixed solution to obtain a solid product.
Alternatively, the temperature of the heating is 110-130 ℃, e.g., 110 ℃, 120 ℃, 130 ℃, etc.
In the step (4), the solid product is subjected to a first roasting to remove organic matters in the solid product as much as possible, thereby obtaining a precursor.
Optionally, before the first roasting of the solid product, further comprises: the solid product is subjected to a first grinding to obtain a solid product in the form of a powder. In general, the Dv50 of the solid product can be controlled to 50 to 70 μm, for example, 50 μm, 60 μm, 70 μm, etc., by milling with a ball mill.
Optionally, the first firing is performed in a muffle furnace.
Optionally, the first firing has a temperature rise rate of 8-12 ℃/min, such as 8 ℃/min, 10 ℃/min, 12 ℃/min, and the like.
Alternatively, the firing temperature is 500-600 ℃, e.g., 500 ℃, 550 ℃, 600 ℃, etc.,
alternatively, the incubation time is 1-3 hours, such as 1 hour, 2 hours, 3 hours, etc.
In step (5), the precursor is milled to obtain a precursor powder.
In some embodiments, the precursor is milled such that it forms a Dv50 of 50-70 μm, e.g., 50 μm, 60 μm, 70 μm, etc. Thus, LLZMO is preferably obtained in all compactibility in the subsequent second sintering.
In step (6), the precursor powder is cold pressed to obtain a molded precursor.
In some embodiments, the pressure of the cold pressing is 5-15MPa, e.g., 5MPa, 10MPa, 15MPa, etc. The dwell time is 1-5min, such as 1min, 3min, 5min, etc. Thereby facilitating the formation of a uniform phase structure by subsequent calcination.
Typically, the shape of the molded precursor includes a cylindrical shape, a square shape, or a special shape. In some embodiments, the embossing precursor is square, optionally with a length, width and thickness of (10-12) x (2-3) mm.
In the step (7), the precursor powder (namely, the mother powder) is used for covering the molding precursor, and then the second roasting is carried out. On the one hand, unreacted substances in the precursor can be further reacted through second roasting, and on the other hand, crystal grains in the LLZMO can be tightly combined, so that the compactness of the LLZMO is improved.
Optionally, the second firing has a ramp rate of 8-12 ℃/min, such as 8 ℃/min, 10 ℃/min, 12 ℃/min, and the like.
Optionally, the firing temperature is 900-1000 ℃, such as 900 ℃, 950 ℃, 1000 ℃, etc.,
alternatively, the incubation time is 7-11 hours, e.g., 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, etc.
In some embodiments, the precursor powder over-mold precursor has a thickness of 1-3mm, e.g., 1mm, 2mm, 3mm, etc., which refers to the thickness formed by covering the end surface distal from the bottom of the crucible with precursor powder.
By controlling the thickness of the precursor powder for covering the molding precursor, the loss of Li in the process of burning the molding precursor is compensated, and meanwhile, the consumption of the precursor powder is reduced, so that the cost in the LLZMO preparation process is saved.
It will be appreciated that the precursor powder prepared in step (5) comprises the following two modes of use: one is to form the molding precursor of step (6), and the other is to use as a master powder to cover the molding precursor in step (7). In order to improve the production efficiency, it is preferable that the amount of the precursor powder prepared in step (5) is not less than the amount of the molding precursor prepared in step (6) and the amount of the precursor powder used as the master powder in step (7).
In some specific embodiments, the method of preparing a garnet-type solid electrolyte comprises the following steps:
s1: preparing a solution A, a solution B and a solution C;
s2: solution A was slowly added dropwise to solution B to form a mixture AB. Then the solution C is added into the mixed solution AB by a constant pressure dropping funnel in a dropwise manner to form a mixed solution;
s3: heating the mixed solution to remove water and ethanol therein to obtain a solid product;
s4: grinding and first roasting the solid product in sequence to obtain a precursor;
s5: performing second grinding on the precursor to obtain precursor powder;
s6: cold pressing a portion of the precursor powder to obtain a molded precursor;
s7: and covering the other part of precursor powder with the mould pressing precursor, and then performing second roasting to obtain the garnet-type solid electrolyte.
According to the method disclosed by the invention, the LLZMO is synthesized by using the sol-gel method, the raw materials are mixed more uniformly in the preparation process, the obtained LLZMO has fewer impurities, the gel-gel method almost avoids the complex and time-consuming ball milling mixing process in the solid-phase method preparation process, and meanwhile, the sol-gel method has severe requirements on the cold pressing pressure and the pressure maintaining time. In addition, the method disclosed by the invention is simple in process operation, low in cost and beneficial to industrial production.
In another aspect of the invention, the invention proposes to obtain a garnet-type solid electrolyte prepared by the aforementioned method. The garnet-type solid electrolyte has a cubic phase crystal structure and a high levelIon conductivity, and crystal form stability in a humid environment. Specifically, aliovalent cation Mo 6+ Is doped to occupy Zr 4+ According to the principle of valence conservation, li + Will also correspondingly decrease the concentration of Li + Increase of vacancies to cause Li + In which the occupation of empty sites is in a disordered state, while Li in the cubic structure of garnet-type solid electrolyte + Also in a disordered state, so that the doping of Mo element can stabilize the crystal form of LLZMO. In addition, the doping of Mo can effectively reduce Li on the surface of LLZMO 2 CO 3 Thereby improving the ionic conductivity of LLZMO.
The following description of the present invention is made by way of specific examples, which are given for illustration of the present invention and should not be construed as limiting the scope of the invention. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The hydroxypropyl cellulose used in the examples below was assigned the trade designation m.w10000.
Example 1
According to the chemical formula Li of garnet-type solid electrolyte 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Lithium nitrate, lanthanum nitrate, zirconium butoxide and molybdenum oxide are proportioned according to the mole ratio of Li to La to Zr to Mo of 7.26 to 3 to 1.8 to 0.2.
Dissolving the lithium nitrate and lanthanum nitrate of the ingredients in deionized water to form a solution A, wherein the concentration of Li in the solution A is 1mol/L calculated by lithium (Li);
adding zirconium butoxide and hydroxypropyl cellulose into ethanol to form a solution B, wherein the concentration of Zr in the solution B is 0.06mol/L based on zirconium (Zr); solution B with the concentration of hydroxypropyl cellulose of 0.02 g/mL;
molybdenum oxide was dissolved in aqueous ammonia to form a solution C, wherein the concentration of Mo in the solution C was 0.015mol/L in terms of molybdenum (Mo).
Solution a was slowly added dropwise to solution B with stirring using a constant pressure dropping funnel to form a mixed solution AB. And then the solution C is added into the mixed solution AB by dropping through a constant pressure dropping funnel, so as to form a mixed solution.
Heating the mixed solution on a magnetic heating stirrer while stirring, setting the display temperature of a panel of the magnetic heating stirrer to 120 ℃ and setting the rotating speed to 300r/min until the solvent in the mixed solution is evaporated to dryness, so as to form a solid product.
The solid product was ball milled to a powder with Dv50 of 60 μm, placed in an alumina crucible, heated to 550 ℃ at 10 ℃/min in a muffle furnace and calcined at that temperature for 2h to obtain the precursor.
Ball milling the precursor into precursor powder with Dv50 of 60 mu m;
part of the precursor powder is cold-pressed into a square molding precursor with the width of 10mm multiplied by 12mm multiplied by 2mm, the pressure is controlled to be 10MPa in the cold pressing process, and the time is 3min.
Placing a molding precursor in an alumina crucible, covering the surface of the molding precursor far away from the bottom of the crucible with the rest precursor powder, controlling the thickness of the covering precursor powder to be 2mm, heating to 950 ℃ at a heating rate of 10 ℃/min, roasting at the temperature for 9 hours, and cooling to room temperature along with a furnace after heat preservation is finished to obtain garnet type solid electrolyte Li 6.6 La 3 Zr 1.8 Mo 0.2 O 12 This sample is designated L1.
Example 2
A garnet-type solid electrolyte was prepared as in example 1, except that lithium nitrate, lanthanum nitrate, zirconium butoxide and molybdenum oxide were formulated in a molar ratio of Li: la: zr: mo of 7.37:3:1.85:0.15, thereby obtaining a garnet-type solid electrolyte Li 6.7 La 3 Zr 1.85 Mo 0.15 O 12 This sample was designated L2.
Example 3
Garnet-type solid electrolyte was prepared as in example 1, except that lithium nitrate, lanthanum nitrate, zirconium butoxide and molybdenum oxide were formulated in a molar ratio of Li: la: zr: mo of 7.48:3:1.9:0.1Thereby obtaining garnet-type solid electrolyte Li 6.8 La 3 Zr 1.9 Mo 0.1 O 12 This sample was designated L3.
Example 4
Garnet-type solid electrolyte was prepared as in example 1, except that lithium nitrate, lanthanum nitrate, zirconium butoxide and molybdenum oxide were formulated in a molar ratio of Li: la: zr: mo of 7.59:3:1.95:0.05, thereby obtaining a garnet-type solid electrolyte Li 6.9 La 3 Zr 1.9 Mo 0.1 O 12 This sample was designated L4.
Comparative example 1
Mixing lithium nitrate, lanthanum nitrate, zirconium butoxide and molybdenum oxide according to the mole ratio of Li to La to Zr to Mo of 7.26 to 3 to 1.8 to 0.2, and then mixing and ball milling to form mixed powder with Dv50 of 60 mu m.
The mixed powders were placed in an alumina crucible, heated to 550 ℃ at a heating rate of 10 ℃/min in a muffle furnace and baked at that temperature for 2 hours to obtain a precursor.
The precursor is ball-milled to form precursor powder with Dv50 of 60 mu m, and the precursor powder is divided into two parts, wherein one part is cold-pressed to form a molding precursor with the width and thickness of 10mm multiplied by 2mm, and the pressure is controlled to be 10MPa in the cold-pressing process, and the time is 3min.
And (3) placing the molding precursor in an alumina crucible, covering the molding precursor with another part of precursor powder, controlling the thickness of the covering precursor powder to be 3mm, roasting at 950 ℃ for 9 hours, and cooling to room temperature along with a furnace after heat preservation is finished. Obtaining Li 6.6 La 3 Zr 1.8 Mo 0.2 O 12 This sample was designated as D-L1.
Test case
The garnet-type solid state electrolytes obtained in examples 1 to 4 and comparative example 1 described above were subjected to the following performance test.
1. And (3) phase test: phase analysis was performed on LLZMO using an X-ray diffractometer.
2. Ion conductivity test
Ion conductivity tests were performed on LLZMO (LLZMO-10 day) after 10 days of being placed in humid air (humidity 70%) and LLZMO not being placed in humid air (humidity 70%) at room temperature.
Specific tests were not: the alternating current impedance of LLZMO and LLZMO-10day is tested by using an electrochemical workstation to obtain the impedance value of the solid electrolyte at room temperature, and then the ionic conductivity sigma of the solid electrolyte is calculated by using the following formula.
Ion conductivity:wherein L represents the thickness of the solid electrolyte sheet, in cm, R represents the resistance, in Ω, and S represents the surface area of the solid electrolyte sheet, in cm 2 。
The results of the ion conductivity test are shown in table 1.
TABLE 1
FIG. 1 is an X-ray diffraction pattern of LLZMO obtained in examples 1-4, from which it can be seen that the LLZMO obtained in examples 1-4 has a cubic phase.
FIG. 2 is Li obtained in example 1 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Exposure to humid air (humidity 70%) for ten days (Li) 6.6 La 3 Zr 1.8 Mo 0.2 O 12 -10 day) and X-ray diffraction patterns not exposed to humid air (humidity 70%), from which it can be seen that Li 6.6 La 3 Zr 1.8 Mo 0.2 O 12 10day still maintains the cubic phase crystal structure, and no obvious tetragonal phase and Li are observed in the figure 2 CO 3 Which indicates the occurrence of diffraction peaks of Li prepared by the method of the present invention 6.6 La 3 Zr 1.8 Mo 0.2 O 12 The crystal form is stable in humid air.
FIG. 3 is Li obtained in example 1 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Exposure to humid air (humidity 70%) for ten days (Li) 6.6 La 3 Zr 1.8 Mo 0.2 O 12 -10 day) and an alternating current impedance spectrum not exposed to humid air (humidity 70%) and an ionic conductivity of 1.23×10 was calculated for LLZMO-10day -4 S/cm, li not exposed to humid air 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Is 1.21×10 -4 S/cm, which indicates that Mo doping can effectively reduce Li 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Surface Li 2 CO 3 Thereby promoting Li 6.6 La 3 Zr 1.8 Mo 0.2 O 12 Is a metal ion conductor.
In conclusion, the LLZMO crystal form obtained by the method is stable and has higher ionic conductivity.
In the description of the present specification, reference is made to the description of the terms "some embodiments," "other embodiments," etc., meaning that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (10)
1. A method for preparing garnet-type solid electrolyte, characterized in that the garnet-type solid electrolyte has the chemical formula of Li 7-2x La 3 Zr 2-x Mo x O 12 X=0.05-0.2, the method comprising the steps of:
(1) Preparing a solution A, a solution B and a solution C, wherein,
mixing a lithium source, a lanthanum source and water to obtain a solution A,
mixing a zirconium source, hydroxypropyl cellulose and ethanol to obtain a solution B,
mixing a molybdenum source and ammonia water to form a solution C;
(2) Mixing the solution A, the solution B and the solution C to obtain a mixed solution;
(3) Heating the mixed solution to remove water and ethanol therein and obtain a solid product;
(4) First roasting the solid product to obtain a precursor;
(5) Grinding the precursor to obtain precursor powder;
(6) Cold pressing the precursor powder to obtain a molded precursor;
(7) Covering the mould pressing precursor with precursor powder, and then performing second roasting to obtain the garnet type solid electrolyte.
2. The method according to claim 1, wherein in the step (1), the amounts of the lithium source, the lanthanum source, the zirconium source and the molybdenum source are calculated as the molar ratio of Li to La to Zr to Mo to be y to 3 to (2-x) to x, wherein y and (7-2 x) satisfy the following relation:
1.06≤y/(7-2x)≤1.12。
3. the method according to claim 1 or 2, characterized in that the concentration of hydroxypropyl cellulose in the solution B is 0.01-0.05g/mL.
4. The method according to claim 1 or 2, wherein step (2) comprises:
dropwise adding the solution A into the solution B under the stirring condition to form a mixed solution AB;
and then the solution C is dripped into the mixed solution AB.
5. The method according to claim 1 or 2, wherein in step (3), the heating is performed under stirring, and the heating temperature is 110-130 ℃.
6. The method according to claim 1 or 2, wherein in step (4), the first firing process comprises: heating to 500-600deg.C at a heating rate of 8-12deg.C/min, and maintaining for 1-3h.
7. The method according to claim 1 or 2, wherein in step (6), the cold pressing is performed at a pressure of 5-15MPa and a dwell time of 1-5min.
8. The method according to claim 1 or 2, wherein in step (7), the second firing step comprises heating to 900-1000 ℃ at a heating rate of 8-12 ℃/min and maintaining for 7-11h.
9. The method according to claim 1 or 2, wherein in step (7), the precursor powder covers the molding precursor with a thickness of 1-3mm.
10. A garnet-type solid electrolyte prepared by the method of any one of claims 1 to 9.
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