CN116525962A - Method for precisely preparing cubic lithium-rich garnet structure solid electrolyte - Google Patents
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 39
- 239000007784 solid electrolyte Substances 0.000 title claims abstract description 39
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 29
- 239000002223 garnet Substances 0.000 title claims abstract description 26
- 238000006243 chemical reaction Methods 0.000 claims abstract description 16
- 238000002360 preparation method Methods 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims abstract description 13
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 20
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 20
- 238000005245 sintering Methods 0.000 claims description 18
- 239000000843 powder Substances 0.000 claims description 15
- 238000000498 ball milling Methods 0.000 claims description 9
- 238000000227 grinding Methods 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 7
- 238000001354 calcination Methods 0.000 claims description 5
- 238000002156 mixing Methods 0.000 claims description 5
- 229910005191 Ga 2 O 3 Inorganic materials 0.000 claims description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 4
- 229910052593 corundum Inorganic materials 0.000 claims description 4
- 239000010431 corundum Substances 0.000 claims description 4
- -1 la 2 O 3 Inorganic materials 0.000 claims description 4
- 239000011268 mixed slurry Substances 0.000 claims description 4
- 239000002994 raw material Substances 0.000 claims description 4
- 239000002002 slurry Substances 0.000 claims description 4
- 229910002076 stabilized zirconia Inorganic materials 0.000 claims description 4
- 238000009475 tablet pressing Methods 0.000 claims 1
- 239000000543 intermediate Substances 0.000 abstract description 63
- 239000012071 phase Substances 0.000 abstract description 45
- 239000000919 ceramic Substances 0.000 abstract description 22
- 230000008569 process Effects 0.000 abstract description 14
- 238000010532 solid phase synthesis reaction Methods 0.000 abstract description 7
- 229910021525 ceramic electrolyte Inorganic materials 0.000 abstract description 4
- 230000005540 biological transmission Effects 0.000 abstract description 3
- 239000007806 chemical reaction intermediate Substances 0.000 abstract description 2
- 239000007787 solid Substances 0.000 abstract description 2
- 230000002194 synthesizing effect Effects 0.000 abstract description 2
- 239000013078 crystal Substances 0.000 description 11
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 8
- 150000002500 ions Chemical class 0.000 description 8
- 229910001416 lithium ion Inorganic materials 0.000 description 8
- 230000037427 ion transport Effects 0.000 description 6
- 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 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000000354 decomposition reaction Methods 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 230000002829 reductive effect Effects 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 239000007790 solid phase Substances 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 229910052727 yttrium Inorganic materials 0.000 description 3
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
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- 239000012535 impurity Substances 0.000 description 2
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- 230000014759 maintenance of location Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
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- 150000003839 salts Chemical class 0.000 description 2
- 238000003746 solid phase reaction Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000000024 high-resolution transmission electron micrograph Methods 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000012705 liquid precursor Substances 0.000 description 1
- 238000006138 lithiation reaction Methods 0.000 description 1
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- 229910052574 oxide ceramic Inorganic materials 0.000 description 1
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- 239000005518 polymer electrolyte Substances 0.000 description 1
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- 239000011343 solid material Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000007704 wet chemistry method Methods 0.000 description 1
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- H—ELECTRICITY
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- 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
- H01M10/058—Construction or manufacture
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- 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
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- 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
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- 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
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- H01M2300/0068—Solid electrolytes inorganic
- H01M2300/0071—Oxides
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Abstract
A method for precisely synthesizing a cubic lithium-rich garnet structure solid electrolyte belongs to the technical field of solid batteries. The invention is based on different intermediates for preparing solid electrolyte with cubic phase compact garnet structure by high temperature solid phase method, and evaluates the influence of reaction intermediates on the phase composition, ion transmission performance and electrochemical performance of the obtained ceramic wafer. Under the condition of ensuring the consistency of other experimental conditions, the intermediate with four different phase components is obtained by adjusting the excess percentage content of lithium and the first reaction temperature in the initial feeding process. The result shows that the composition is cubic LGLZO+10.99% La 2 Zr 2 O 7 Is easier to obtain pure and compact cubic phase LGLZO ceramic electrolyte sheet by the traditional high temperature solid phase method, and endows the LGLZO ceramic electrolyte sheet with high ionic conductivity and low activationCan be used. The invention lays a foundation for the subsequent large-scale commercial preparation of the solid electrolyte with the low-cost high-performance cubic phase compact garnet structure.
Description
Technical Field
The invention belongs to the technical field of solid-state batteries, and particularly relates to a method for accurately synthesizing a cubic lithium-rich garnet structure solid electrolyte.
Background
Lithium ion batteries are one of the most promising energy storage and conversion technologies in modern society, and have been widely applied to portable electronic devices, electric automobiles, hybrid electric automobiles and power grid energy storage. However, commercial lithium ion batteries are currently facing serious safety issues due to the tendency of organic liquid electrolytes to leak, poor thermal stability and flammability. The use of a solid electrolyte instead of a liquid electrolyte will eventually solve this problem and will most likely give a higher energy density to the lithium metal battery. Oxide ceramic solid electrolytes possess advantages, such as high mechanical strength, good thermal stability, and no oxidative/reductive decomposition at high operating potentials, which are not comparable to sulfides and polymer electrolytes. Among the numerous oxide-based lithium ion conductors, cubic-phase lithium-filled garnet has attracted considerable attention by researchers due to its wide electrochemical window, acceptable ion transport properties, and stable (electro) chemistry to lithium anodes.
The cubic lithium-rich garnet structure solid electrolyte is prepared by various ways, and the wet chemical method and the high-temperature solid phase method are the most common. Wet chemistry processes are based on liquid precursors where various metal salts can be mixed with molecular components in the liquid phase. In addition, the method requires low temperature and short time, and does not require batch grinding. The powder obtained by the method has the characteristics of uniform morphology, higher purity and specific surface area, finer grain size, uniform components and the like, but agglomerates are extremely easy to form in the hydrolysis-condensation process, so that the obtained sample structure is unstable. In addition, since the powder grain size is small, a large number of grain boundaries exist in the ceramic-based solid electrolyte thus prepared, and thus the ion conductivity is low. The traditional high temperature solid phase method, also known as a ceramic process, is the most commonly used method for preparing oxide type ceramic solid electrolytes. In a typical process flow, metal salts meeting the stoichiometric ratio are firstly mixed by ball milling technology, then annealing, regrinding and pressing steps are carried out, and finally the garnet ceramic sheet with the relative density of 96% can be obtained, and can be directly used as solid electrolyte after being cut/polished to the required thickness. The high-temperature solid phase method is a non-alternative choice for commercial large-scale preparation of cubic lithium-rich garnet structure solid electrolyte from the aspects of preparation process difficulty, equipment cost and the like.
The crystallization process of the high-temperature solid phase reaction is to realize the inter-diffusion reaction between solid phases through continuous mixing and annealing steps, and the dynamics of the inter-diffusion reaction is controlled by point defects and lattice defects caused by plastic deformation. Thus, solid phase reactions offer more possibilities for preparing new ceramic oxide materials. However, this also causes undesirable but common problems in the preparation process: two or more phases are formed in the high temperature diffusion reaction, which seriously hampers the practical application of the ceramic solid electrolyte, because glass phases formed at grain boundaries may block mobile lithium ion transport. Reducing the sintering temperature and reducing the sintering time are two important synthetic regulatory strategies to reduce the generation of heterogeneous phases. But lower synthesis temperatures tend to result in sigma Li ≈10 -7 S·cm -1 Shorter synthesis times induce incomplete reactions. It appears that all optimization strategies are directed to the final product, studying its phase composition and transformation and the associated electrochemical properties, while little attention is paid to intermediates in the synthesis process. In fact, the composition, morphology, size and even elemental distribution of the intermediate can affect the resulting solid material to a large extent, thereby limiting its chemical and physical properties. However, our understanding of intermediates is far behind its importance.
Disclosure of Invention
The invention aims to provide a method for precisely preparing a cubic lithium-rich garnet structure solid electrolyte, and the ceramic solid electrolyte prepared by the method has good compactness and electrochemical performance.
Accurate preparation of cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 The method of (1) comprises the steps ofThe following steps:
(1) LiOH, la 2 O 3 、ZrO 2 And Ga 2 O 3 Mixing according to a stoichiometric ratio x 1.5:2:0.1, wherein x=6.4× (1.1-1.4), namely adding 10-40% excess LiOH in the process to compensate lithium loss in the repeated sintering process;
(2) Adding grinding medium and Yttrium Stabilized Zirconia (YSZ) agate balls into the mixture obtained in the step (1) by using isopropyl alcohol (IPA) as the grinding medium, and performing wet ball milling for 10-15 hours at a rotating speed of 200-500 rpm in a planetary ball mill to obtain uniformly mixed slurry; drying the slurry at 70-90 ℃ for 10-15 h, and calcining at 900-960 ℃ for 4-8 h, wherein chemical reaction is carried out between the oxide raw materials to obtain an intermediate;
(3) Ball milling the intermediate obtained in the step (2) in a planetary ball mill at a rotating speed of 200-500 rpm for 10-15 hours to obtain fine powder; the powder is dried and then pressed into tablets, the diameter of a tablet die is 12-20 mm (different diameter dies can be selected according to requirements), and the tablets are kept at 100-200 MPa for 8-15 min, so that a white thin wafer with smooth surface and no cracks is obtained;
(4) Placing the pressed white thin wafer into a corundum crucible with a cover, covering the surface of the white thin wafer with the powder with the same component obtained in the step (3), and performing secondary sintering in a muffle furnace at 1100-1200 ℃ to obtain the cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 And is denoted as LGLZO.
In the preparation process, lithium loss is unavoidable in the high-temperature sintering process, so that a certain amount of lithium source exceeding the stoichiometric ratio is usually added at the beginning of charging to compensate the loss, and the crystal grain growth and the densification of the ceramic sheet are also facilitated. When the lithium input is excessive, excessive lithium remains after high-temperature sintering, and Li is easy to form 2 O and Li 2 ZrO 3 And the like. The retention of these impurities at the grain boundaries makes the grain boundary strength low, which is not preferable for the solid electrolyte. On the other hand, when the amount of lithium added is too small, a large amount of lithium volatilizes with the high-temperature heat treatmentMesophase La formed during the reaction 2 Zr 2 O 7 And the lithium is difficult to lithiate, a compact glass phase is formed at the crystal boundary, and the lithium ions are not easy to move and are transmitted along the crystal boundary. Based on this, an excess of 10 to 20wt% of LiOH is added to obtain an intermediate to reduce the generation of grain boundary impurities during the subsequent sintering process.
Initial La 2 O 3 And ZrO(s) 2 From ZrO at 750 DEG C 2 Surface evolution to generate La 2 Zr 2 O 7 Formed La 2 Zr 2 O 7 The crystal nucleus is acted to influence the subsequent grain growth process. Li and Ga are gradually incorporated into La after 900 DEG C 2 Zr 2 O 7 Mesophase, LLZO phase begins to develop. When the reaction temperature is continuously increased by 50-60 ℃, other crystal phases are sequentially disappeared, and LLZO becomes the only phase. Thus, the intermediate was obtained at both temperature nodes 900 and 960 ℃ in order to more effectively evaluate the effect of the intermediate on the final ceramic sheet phase composition, ion transport properties, and electrochemical properties.
The invention is based on different intermediates for preparing solid electrolyte with cubic phase compact garnet structure by high temperature solid phase method, and evaluates the influence of reaction intermediates on the phase composition, ion transmission performance and electrochemical performance of the obtained ceramic wafer. Under the condition of ensuring the consistency of other experimental conditions, the lithium excess percentage content and the first reaction temperature in the initial feeding process are regulated to obtain four intermediates with different phase components: cubic phase Li 6.4 Ga 0.2 La 3 Zr 2 O 12 (LGLZO) +13.88% pyrochlore La 2 Zr 2 O 7 (intermediate 1); cubic lglzo+10.99% pyrochlore La 2 Zr 2 O 7 (intermediate 2); tetragonal phase LGLZO (intermediate 3) and pure cubic phase LGLZO (intermediate 4). The result shows that the composition is cubic LGLZO+10.99% La 2 Zr 2 O 7 The intermediate 2 of (2) is easier to obtain pure and compact cubic phase LGLZO ceramic electrolyte sheet by the conventional high temperature solid phase method. The invention lays a foundation for the subsequent large-scale commercial preparation of the solid electrolyte with the low-cost high-performance cubic phase compact garnet structure.
Compared with the prior art, the invention has the beneficial effects that:
the method provided by the invention realizes the accurate preparation of the cubic lithium-rich garnet structure solid electrolyte. The problems of complicated phase types and the like of the final product caused by the inter-diffusion reaction among the solid phases which are difficult to control in the high-temperature preparation process are effectively avoided, the complicated preparation process is simplified, and the large-scale production trial-and-error cost is reduced. On the other hand, the excellent physical properties give the ceramic electrolyte good room temperature ion transport properties, and the ceramic sheet fired at 1200 ℃ via intermediate 2 can achieve high ion conductivity as well as low activation energy.
Drawings
Fig. 1: intermediates 1, 2 and cubic Li 7 La 3 Zr 2 O 12 Pyrochlore La 2 Zr 2 O 7 Standard diffraction curve vs. graph (a); intermediate 3, 4 and cubic Li 7 La 3 Zr 2 O 12 Tetragonal Li 7 La 3 Zr 2 O 12 Standard diffraction curve vs. graph (b);
fig. 2: SEM images (a-d) of intermediates 1-4;
fig. 3: sintering behavior curve of intermediate 1 (a) and intermediate 2 (b) at 1100-1200 ℃;
fig. 4: sintering behavior curve of intermediate 3 (c) and intermediate 4 (d) at 1100-1200 ℃;
fig. 5: li obtained by sintering intermediate 2 at 1200 DEG C 6.4 Ga 0.2 La 3 Zr 2 O 12 SEM images of surface (a) and cross section (b) of the ceramic sample; li obtained from HRTEM 6.4 Ga 0.2 La 3 Zr 2 O 12 A profile of (422) crystal plane (c) and (400) crystal plane (d) and surface-related elements of the ceramic sample;
fig. 6: cubic lithium-rich garnet-structured solid electrolyte Li obtained under the condition of the invention 6.4 Ga 0.2 La 3 Zr 2 O 12 Impedance spectrum (a); an Arrhenius plot (b) of total ion conductivity thereof;
FIG. 1 shows the temperatures at 900℃and 960℃being differentAt the node, 10wt% and 20wt% excess LiOH were added to sinter for 6h to obtain XRD pattern. It is evident that the addition of a 10% by weight excess of LiOH at 900℃for 6 hours resulted in the formation of a cubic LGLZO phase, but at the same time a significant amount of pyrochlore La was observed 2 Zr 2 O 7 (intermediate 1). While the reaction temperature remained the same, the percentage of LiOH excess increased to 20wt%, although the XRD pattern showed still cubic LGLZO phase with La 2 Zr 2 O 7 Coexisting with, but ascribed to La 2 Zr 2 O 7 The intensity of the diffraction peak was reduced (intermediate 2). In view of the two phases contained in both intermediates 1 and 2, we calculated the relative amounts of the phases in the mixed intermediate using the K-value method. By neutralizing the squares LGLZO and La with respect to intermediate 1 2 Zr 2 O 7 Integral operation is carried out on the strongest phase peak, la 2 Zr 2 O 7 The mass fraction of the phase was 13.88%. With the increase of lithium content in the feeding process, the intermediate phase La 2 Zr 2 O 7 The lithiation degree is improved, la in intermediate 2 2 Zr 2 O 7 The mass fraction of the phase was reduced to 10.99%. When the reaction temperature was raised to 960 ℃, tetragonal phase LGLZO was obtained with 10wt% lioh excess (intermediate 3). As the amount of LiOH excess increased to 20%, the other crystalline phases all disappeared, and cubic LGLZO became the only dominant phase (intermediate 4).
Four obtained intermediates were observed by SEM, as shown in fig. 2. The four intermediates are all white smooth powder. Obviously, at the same temperature, the number of large-size grains is increased with the increase of the lithium content. When the lithium content is unchanged, the number of large-sized grains increases with an increase in temperature. The larger crystal grains mean that the fewer crystal boundaries are in the ceramic sheet after sintering molding, which is more favorable for the transmission of mobile lithium ions in the solid electrolyte. At the same time, the reduction of grain boundaries also means that the ceramic oxide solid electrolyte has an enhanced resistance to attack by water and carbon dioxide in the air, because the sensitivity of grain boundaries is higher than that of grains.
Comparing the sintering difference of four intermediates in the temperature range of 1100-1200 ℃, it can be seen from fig. 3 and fig. 4 that the intermediate 2 is most suitable for preparing pure and compact phase by high temperature solid phase methodCubic lithium-rich garnet-structured solid electrolyte. SEM and HRTEM images of the ceramic samples prepared via intermediate 2 sintering at 1200 ℃ high temperature are shown in fig. 5. Cubic lithium-rich garnet-structured solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 The top-down SEM image presents its flat and dense surface (fig. 5 a). The morphology of the cross-section may be due to intrinsic air instability of the garnet-based solid electrolyte, which is accompanied by non-uniformity of the chemical elements of the cross-section and segregation of the cationic species at the grain boundaries (fig. 5 b). FIGS. 5 (c) to 5 (d) HRTEMAnd->The interplanar spacings respectively correspond to the cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 The (422) and (400) crystal planes. EDS Mapping indicates that the elements in the ceramic solid electrolyte are uniformly distributed. From the above results, it was found that a dense garnet-type ceramic sheet having a cubic Ia3d structure can be obtained by cold-pressing the intermediate 2 into sheets and sintering at a high temperature of 1200 ℃.
FIG. 6 (a) shows a cubic lithium-rich garnet-structured solid electrolyte Li prepared by the method of the present invention 6.4 Ga 0.2 La 3 Zr 2 O 12 Complex impedance spectrum. The capacitive tails appearing in the low frequency impedance plot indicate that the investigated material is ion conducting in nature. Furthermore, the high frequency portion of the impedance plot does not exhibit two distinct semicircles, which means that it is difficult to distinguish the bulk phase from the grain boundary impedance. In order to present conductivity results in the temperature range studied (room temperature to 180 ℃), the total (bulk + grain boundary) ionic conductivity was uniformly considered. Here use sigma ion The lithium ion transport capacity in the ceramic solid electrolyte was calculated by =l/RS, where R (Ω) is the total impedance obtained by EIS fitting, and L and S represent the thickness and area of the ceramic sheet, respectively. In the present invention, intermediate 2 is sintered at 1200 ℃ to obtain cubic Li 6.4 Ga 0.2 La 3 Zr 2 O 12 The maximum room temperature total ion conductivity is 8.8X10 -4 S·cm -1 . As the temperature increases, the ion migration rate in the solid ion conductor increases, and the semicircle in the Nyquist plot gradually decreases, and disappears at 60 ℃ and above. From the Arrhenius plot shown in FIG. 6 (b), the activation energy was 0.314eV.
Detailed Description
Example 1: preparation of cubic garnet-structured solid electrolyte via intermediates 1 and 2
(1) LiOH, la 2 O 3 、ZrO 2 And Ga 2 O 3 Mixing according to a stoichiometric ratio x 1.5:2:0.1, wherein x=6.4x1.1 is used for preparing an intermediate 1, and x=6.4x1.2 is used for preparing an intermediate 2;
(2) Adding grinding medium and Yttrium Stabilized Zirconia (YSZ) agate balls into the mixture obtained in the step (1) by using isopropyl alcohol (IPA) as grinding medium, and performing wet ball milling for 12 hours at a rotating speed of 350rpm in a planetary ball mill to obtain uniformly mixed slurry; drying the slurry at 80 ℃ for 12 hours, and calcining at 900 ℃ for 6 hours, wherein chemical reaction is carried out between oxide raw materials to obtain an intermediate 1 and an intermediate 2;
(3) Respectively carrying out wet ball milling on the intermediate 1 and the intermediate 2 obtained in the step (2) in a planetary ball mill at a rotating speed of 350rpm for 12 hours to obtain fine-grained powder; drying the powder, tabletting, wherein the diameter of a tabletting mould is 15mm, and keeping the tabletting mould for 10min under 150MPa to obtain a white thin disc with smooth surface and no cracks;
(4) Placing the pressed white thin wafer into a corundum crucible with a cover, covering the surface of the white thin wafer with the powder with the same component obtained in the step (3), and performing secondary sintering in a muffle furnace at 1100-1200 ℃ to obtain the cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 And is denoted as LGLZO.
As shown in fig. 3, for the phase consisting of cubic LGLZO and 13.88% La 2 Zr 2 O 7 Intermediate 1, which was composed, was sintered at 1100 ℃ for 12 hours to obtain a pure cubic LGLZO phase. When in opposition toThe temperature was raised to 1150℃and pyrochlore La was observed in the XRD pattern 2 Zr 2 O 7 A diffraction peak associated therewith. This indicates that the cubic LGLZO formed via intermediate 1 undergoes a decomposition reaction at 1150 ℃ to form pyrochlore La as a by-product 2 Zr 2 O 7 . La formed by decomposition at high temperature 2 Zr 2 O 7 The retention at the grain boundaries may be an obstacle to grain boundary conduction during lithium ion transport. Intermediate 2, which has a similar composition to intermediate 1, is sintered at 1100-1200 ℃ to obtain three ceramic samples which are also assigned to the cubic system Ia3d space group. But is different in that La is not observed in the corresponding XRD diffraction pattern 2 Zr 2 O 7 Correlation peaks, which indicate the absence of La in the sinter molded sample 2 Zr 2 O 7 Residual, or residual amounts that are too small to be detected by XRD.
Example 2: preparation of cubic garnet-structured solid electrolyte via intermediates 3 and 4
(1) LiOH, la 2 O 3 、ZrO 2 And Ga 2 O 3 Mixing according to a stoichiometric ratio x 1.5:2:0.1, wherein x=6.4x1.1 is used for preparing an intermediate 3, and x=6.4x1.2 is used for preparing an intermediate 4;
(2) Adding grinding medium and Yttrium Stabilized Zirconia (YSZ) agate balls into the mixture obtained in the step (1) by using isopropyl alcohol (IPA) as grinding medium, and performing wet ball milling for 12 hours at a rotating speed of 350rpm in a planetary ball mill to obtain uniformly mixed slurry; drying the slurry at 80 ℃ for 12 hours, and calcining at 960 ℃ for 6 hours, wherein chemical reaction is carried out between oxide raw materials to obtain an intermediate 3 and an intermediate 4;
(3) Respectively carrying out wet ball milling on the intermediate 3 and the intermediate 4 obtained in the step (2) in a planetary ball mill at a rotating speed of 350rpm for 12 hours to obtain fine-grained powder; drying the powder, tabletting, wherein the diameter of a tabletting mould is 15mm, and keeping the tabletting mould for 10min under 150MPa to obtain a white thin disc with smooth surface and no cracks;
(4) Placing the pressed white thin wafer into a corundum crucible with a cover, and covering the white thin wafer with the powder with the same composition obtained in the step (3)The surface of the wafer is sintered for the second time in a muffle furnace at 1100-1200 ℃ to obtain the cubic crystal system lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 And is denoted as LGLZO.
As shown in fig. 4, for intermediate 3 composed of tetragonal phase LGLZO, calcination at a high temperature of 1100 ℃ underwent a tetragonal to cubic structure phase transformation. However, garnet phase transformation occurs in a narrow temperature range, and once the temperature is too high, a large amount of lithium is lost to cause cubic phase decomposition. La in XRD spectrum with increasing sintering temperature 2 Zr 2 O 7 The characteristic diffraction peaks are stronger and stronger, meaning that the cubic garnet LGLZO phase is decomposed more and more severely. XRD pattern obtained by sintering intermediate 4 (pure cubic LGLZO phase) at a temperature in the range of 1100-1200 ℃. The long-time high-temperature heat treatment leads the cubic LGLZO to be delithiated and changed back to the pyrochlore La again 2 Zr 2 O 7 . The higher the temperature, the more pronounced the delithiation phenomenon. In view of the above, it is preferable to select a solution for preparing intermediate 2 to produce cubic garnet.
Claims (2)
1. Accurate preparation of cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 The method comprises the following steps:
(1) LiOH, la 2 O 3 、ZrO 2 And Ga 2 O 3 Mixing according to a stoichiometric ratio x of 1.5:2:0.1, wherein x=6.4× (1.1-1.4);
(2) Adding grinding medium and yttrium-stabilized zirconia agate balls into the mixture obtained in the step (1) by using isopropanol as the grinding medium, and performing wet ball milling for 10-15 hours at a rotating speed of 200-500 rpm to obtain uniformly mixed slurry; drying the slurry at 70-90 ℃ for 10-15 h, and calcining at 900-960 ℃ for 4-8 h, wherein chemical reaction is carried out between the oxide raw materials to obtain an intermediate;
(3) Carrying out wet ball milling on the intermediate obtained in the step (2) at a rotating speed of 200-500 rpm for 10-15 h to obtain fine powder; drying the powder and tabletting to obtain a white thin wafer with smooth surface and no cracks;
(4) Placing the pressed white thin wafer into a corundum crucible with a cover, covering the surface of the white thin wafer with the powder with the same component obtained in the step (3), and performing secondary sintering in a muffle furnace at 1100-1200 ℃ to obtain the cubic lithium-rich garnet structure solid electrolyte Li 6.4 Ga 0.2 La 3 Zr 2 O 12 。
2. An accurate preparation of cubic lithium-rich garnet structure solid electrolyte Li according to claim 1 6.4 Ga 0.2 La 3 Zr 2 O 12 Is characterized in that: in the step (3), the diameter of the tablet pressing die is 12-20 mm, and the die is kept at 100-200 MPa for 8-15 min.
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