Method for preparing pyrochlore oxyfluoride solid electrolyte by one-step solid phase method

Abstract

The invention relates to a method for preparing a pyrochlore oxyfluoride solid electrolyte by a one-step solid phase method, which comprises the following steps: uniformly mixing lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5) and lithium fluoride (LiF), and carrying out high-temperature one-time sintering under protective gas to synthesize a Li2-xLa (1 + x) / 3Nb2O6F (LLNOF solid electrolyte material. The synthesis route is optimized, a single fluorine source is used, and the types of raw materials are reduced; according to the method, secondary sintering is not needed, the pure-phase electrolyte powder can be obtained by adopting one-step sintering synthesis, the steps are simple, the efficiency is high, the cost is reduced, and the resource consumption is reduced. According to the obtained LLNOF electrolyte material powder, the synthesis temperature ranges from 900 DEG C to 1100 DEG C, heating to 1100 DEG C or above is not needed, the requirement for heating equipment is low, large-scale mass production can be conducted, the sample yield is large, and energy consumption is low. Required synthesis equipment is simple and easy to obtain, and the ionic conductivity is good. The lithium ion conductor with high conductivity and stability in air is synthesized through a one-step method.

Description

Technical Field

[0001] The invention relates to a solid electrolyte and a preparation method thereof, and in particular to a method for preparing a pyrochlore-type oxyfluoride solid electrolyte by a one-step solid-phase method. Background Art

[0002] The development of lithium-ion batteries that combine high safety with high energy density has been a research hotspot in the energy sector in recent years. Solid-state batteries that utilize solid electrolytes instead of separators and electrolytes not only effectively address safety concerns but also enhance energy density and cycle life. As the core material of solid-state batteries, the ionic conductivity and chemical / electrochemical stability of electrolyte materials are crucial for the development and process selection of solid-state batteries. Therefore, the development of solid-state electrolytes with high ionic conductivity is of great significance.

[0003] Sulfide-based solid electrolyte Li 10 GeP2S 12 (LGPS) has a conductivity of up to 12mS / cm at room temperature, which is comparable to or even higher than that of electrolytes. Since then, research on sulfide-based solid electrolytes has been widely carried out, and a variety of high-conductivity electrolyte materials have been obtained, such as Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (25mS / cm), Li 10.35 [Sn 0.27 Si 1.08 ]P 1.65 S 12 (11mS / cm), and Li 9.54 [Si 0.6 Ge 0.4 ] 1.74 P 1.44 S 11.1 Br 0.3 O 0.6 (32mS / cm). Using Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3The all-solid-state battery as the electrolyte exhibits an excellent cycle performance of about 72% when cycled at a high charge and discharge current density of 18C at 373K. However, sulfide-type electrolytes easily react with moisture in the air to generate toxic hydrogen sulfide (H2S) gas, which places higher requirements on industrial processing and production and requires expensive supporting facilities; and the electrochemical window of sulfide electrolytes is narrow. Although the ionic conductivity of oxide-based solid electrolytes is lower than that of sulfide-based electrolytes, they have high stability in the air and do not produce toxic H2S, so they have also received widespread attention. For example, some oxide-based solid electrolytes with higher ionic conductivity have been developed, such as perovskite-type Li 1-3x La x TiO3(1.0mS / cm), Sr 0.458 Li 0.384 Ti 0.3 Ta 0.7 O3 (1.9mS / cm), and garnet-type Li7La3Zr2O 12 (0.5mS / cm) and doping systems based thereon.

[0004] However, the ionic conductivity of the above electrolytes is still not high enough (≤10 -3 S / cm level). Therefore, in order to realize all-solid-state batteries with safety, excellent cycle performance and high-speed charge and discharge capabilities, it is necessary to develop solid electrolytes with both high ionic conductivity and stability in air. Rutile compound AM2O6F, where A is a low-valent cation with a large ionic radius, such as alkaline earth metals and rare earth ions, and M is a high-valent cation, such as Nb 5+ The structure contains two anionic sites: the 48f site is occupied by an anion that forms a bond with the A and M cations; the 8b site is occupied by the F - ions occupy these F - The ions do not form bonds with the M cations, but instead form a tetracoordinate structure with the A cations. The F ions and A cations are located inside the large hexagonal tunnels formed by the corner-sharing connections of the MO6 octahedrons. These tunnels intersect in the

[110] ,

[101] , and

[011] directions, potentially forming three-dimensional ion conduction channels. Among the reported materials of this type, LiSrNb2O6F can only achieve a 1.08×10 - 3 The ionic conductivity of rutile compounds is mS / cm. This conductivity is still several orders of magnitude lower than that of oxide superionic conductors. Therefore, rutile compounds have not received widespread attention as lithium ion conductors.

[0005] Greenstone-type fluoride oxide solid electrolytes are emerging materials in recent years. With their ultra-high conductivity, wide temperature range stability, and absolute safety, they are expected to become a key material for the industrialization of solid-state batteries. However, the mass production process is immature, the interface treatment cost is high, and quality control is difficult, making large-scale production difficult. At the same time, the preparation of greenstone-type fluoride oxide solid electrolytes currently requires two or more fluorine sources and multiple sintering processes. The materials and processes are complex, the energy consumption is high, and it is not suitable for large-scale industrial applications. In addition, the performance of the finished product is unstable and the yield rate is low. These are all technical problems that need to be solved. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a one-step solid-phase method for preparing a pyrochlore-type fluoride oxide solid electrolyte, which uses a single fluorine source and a one-step sintering step to obtain a pure-phase electrolyte powder. The obtained powder material has uniform particle size, good crystallinity, and good ionic conductivity.

[0007] To achieve the above object, the present invention provides a one-step solid-phase method for preparing a pyrochlore-type oxyfluoride solid electrolyte, comprising:

[0008] S100, drying, drying

[0009] S110, pre-sintering lanthanum oxide (La2O3) at 900°C for 2-6 hours to remove crystal water, preferably at 700-900°C; then cooling, and when the temperature is above 100°C, drying the material in a forced air drying oven at 100-120°C, preferably 105°C, to prevent the material from absorbing water;

[0010] S120, placing lithium carbonate (Li2CO3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) in a 100-120°C forced air drying oven and drying for 10-30 hours to remove water for later use, preferably 24 hours;

[0011] S200 preparation of precursor

[0012] Lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) are weighed in a stoichiometric ratio and mixed uniformly to prepare a precursor;

[0013] The stoichiometric ratio is determined according to the following reaction formula:

[0014] (1-x) / 2*Li2CO3+(1+x) / 6*La2O3+Nb2O5+LiF→Li 2-x La (1+x) / 3 Nb2O6F

[0015] Specifically, it can be:

[0016] (1-x) / 2*Li2CO3+(1+x) / 6*La2O3+Nb2O5+LiF→Li 2-x La (1+x) / 3 Nb2O6F, wherein the value of x ranges from 0 to 1, preferably from 0.1 to 0.8, and may also range from 0 to 0.09, 0.51 to 0.8, etc.

[0017] S300, sintering

[0018] S310, drying the precursor prepared in S200;

[0019] S320, placing the precursor processed in S310 in a covered mortar and performing high-temperature sintering under the protection of an inert atmosphere to form a solid-phase sintering combination;

[0020] S400, fine grinding

[0021] After the S320 sintered powder is crushed and sand-milled to the corresponding particle size, Li 2-x La (1+x) / 3 Nb2O6F (LLNOF) electrolyte material.

[0022] Lithium carbonate (Li2CO3) can be replaced by one or any combination of materials such as lithium hydroxide (LiOH), lithium sulfide (Li2S), lithium phosphate (Li3PO4), anhydrous lithium chloride (LiCl), etc. After replacement, the proportion needs to be redetermined according to the reaction formula.

[0023] Lanthanum oxide can be replaced with one or any combination of lanthanum carbonate (La2(CO3)3), lanthanum nitrate (La(NO3)3), lanthanum hydroxide (La(OH)3), or lanthanum oxide precursors (such as LaOOH). These materials also produce lanthanum oxide upon high-temperature decomposition. After replacement, the ratio needs to be re-determined according to the reaction formula.

[0024] Niobium pentoxide (Nb2O5) can be replaced with one or any combination of NH4NbO3, Nb(OC2H5)5, Nb(OH)5, niobium oxalate (Nb2(C2O4)5·xH2O), etc. After replacement, the ratio needs to be re-determined according to the reaction formula.

[0025] As a further improvement of the present invention, in S100, the purity of lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) is not less than 99.5%.

[0026] As a further improvement of the present invention, in S100, lanthanum oxide (La2O3) needs to be sintered at a high temperature to remove crystal water, the temperature is 700-900°C, the heating rate is 5-10°C / minute, and the holding time is 2-6 hours; to prevent the material from absorbing water again; after sintering is completed and the furnace is cooled to 100°C or above, it must be immediately transferred to a drying oven and baked at 100-120°C in the drying oven for standby use, and the baking temperature is preferably 105°C;

[0027] As a further improvement of the present invention, in S100, materials such as lithium carbonate (Li2CO3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) need to be dried at 100-120°C for more than 24 hours to remove water before use. The drying temperature is preferably 105°C.

[0028] As a further improvement of the present invention, in S200, the electronic scale used for weighing has an accuracy of 0.001-0.0001.

[0029] As a further improvement of the present invention, in S200, the materials are added in the following order: light powder (such as Li2CO3) → medium powder (such as LiF) → heavy powder (such as Nb2O5) → La2O3, so as to reduce the material stratification phenomenon.

[0030] As a further improvement of the present invention, in S200, the mixing can be carried out by ball milling, V-type mixer / double cone mixer, high-speed shear mixer (ribbon type, plowshare type), spray drying assisted mixing method, pneumatic mixing (fluidized bed mixing), etc.

[0031] As a further improvement of the present invention, in S200, direct dry mixing can be used for mixing, but the mixing effect of this method is not as good as wet mixing. Alternatively, lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) can be weighed in a stoichiometric ratio, and then a liquid that can be volatilized by heating is added. The mixture is then wet-milled and mixed until uniform, and then heated and dried to obtain a precursor. Specifically, the solid content is 20%-50%, and spray drying is performed, with an inlet temperature of 150-200°C and an outlet temperature of 50-100°C. The liquid can be isopropyl alcohol, ethanol, methanol, etc.

[0032] As a further improvement of the present invention, in S300, the sintering temperature is 900-1100°C, the heating rate is 1-5°C / min, preferably 3-5°C / min; the sintering time is 2-6 hours; and after sintering, the furnace is naturally cooled.

[0033] As a further improvement of the present invention, in S300, the sintering protective atmosphere is an inert gas such as nitrogen or argon to ensure stable composition and prevent fluorine volatilization and oxidation pollution; the airflow needs to cover the entire sintering area, with a temperature difference of ≤±5°C (to avoid local atmosphere imbalance leading to composition segregation); the flow rate is adjusted according to the furnace volume, according to the formula: Q=V×N / t, where:

[0034] Q: gas flow rate (L / min);

[0035] V: effective volume of furnace (L);

[0036] N: number of ventilations (usually 3 to 10 times / minute);

[0037] t: time (minutes);

[0038] For example, if the muffle furnace volume is 5L and the target air exchange rate is 5 times / minute, then Q = 5 × 5 = 25L / min. The preferred flow rate is 0.5 to 5L / min.

[0039] As a further improvement of the present invention, S300 needs to be equipped with precise control equipment, including a mass flow controller (MFC): accuracy of ±1% FS, multi-channel independent control (such as N2 and argon branch input); a pressure feedback system: real-time monitoring of the furnace pressure, adjusting the outlet valve opening through the PID algorithm, and maintaining the set positive pressure (±2Pa fluctuation).

[0040] As a further improvement of the present invention, in S300, oxygen probes (ZrO2 sensors) are respectively installed in the low-temperature zone / high-temperature zone of the muffle furnace to adjust the gas flow rate through real-time feedback.

[0041] As a further improvement of the present invention, S400 further includes screening to remove iron: after mixing, the mixture is passed through a 200-mesh sieve, and a magnetic separator is used to remove iron impurities introduced by grinding ball wear.

[0042] As a further improvement of the present invention, in S400, when the amount of the synthetic material is amplified, geometric similarity amplification is required (eg, keeping the filling rate of the ball mill and the speed / critical speed ratio unchanged).

[0043] As a further improvement of the present invention, in S200, the value of x can be selected as follows:

[0044] x = 0.1, finished product: Li 1.9 La 0.367 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.45:0.1835:1:1.

[0045] x=0.15, finished product: Li 1.8 5La0.383 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.425:0.192:1:1.

[0046] x = 0.2, finished product: Li 1.8 La 0.4 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.4:0.2:1:1.

[0047] x = 0.25, finished product: Li 1.75 La 0.417 The molar mass ratio of Nb2O6F, lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), and lithium fluoride (LiF) is 0.375:0.2085:1:1.

[0048] x = 0.3, finished product: Li 1.7 La 0.433 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.35:0.208:1:1.

[0049] x=0.35, finished product: Li 1.65 La 0.45 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.325:0.225:1:1.

[0050] x=0.40,finished product: Li 1.6 La 0.467 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.3:0.2335:1:1.

[0051] x=0.45, finished product: Li 1.55 La 0.45 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.275:0.2445:1:1.

[0052] x=0.50, finished product: Li 1.5 La0.45 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.325:0.225:1:1.

[0053] x=0.55, finished product: Li 1.45 La 0.516 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.225:0.258:1:1.

[0054] x=0.60, finished product: Li 1.4 La 0.533 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.2:0.267:1:1.

[0055] x = 0.65, finished product: Li 1.35 La 0.55 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.175:0.275:1:1.

[0056] x=0.60, finished product: Li 1.4 La 0.533 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.2:0.267:1:1.

[0057] x = 0.65, finished product: Li 1.35 La 0.55 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.175:0.275:1:1.

[0058] x=0.70, finished product: Li 1.3 La 0.567 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.15:0.2835:1:1.

[0059] x=0.75,finished product: Li 1.25La 0.45 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.125:0.225:1:1.

[0060] x=0.80, finished product: Li 1.2 La 0.6 Nb2O6F, raw material ratio: lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), lithium fluoride (LiF) molar mass ratio is 0.1:0.3:1:1.

[0061] The beneficial effects of the invention are:

[0062] 1. The present invention optimizes the synthesis route, using a single fluorine source, reducing the number of raw materials. A pure electrolyte powder can be obtained by a single-step sintering synthesis without the need for secondary sintering. This simple and efficient process reduces costs and resource consumption. In the prior art, multiple sintering steps are generally used, and lanthanum fluoride needs to be added during the sintering process. This increases the number of raw materials (this application uses a single fluorine source) and also increases costs.

[0063] 2. Li obtained by the present invention 2-x La (1+x) / 3 Nb2O6F (LLNOF) electrolyte material powders are synthesized at a temperature of 900-1100°C. Without the need for heating above 1100°C, the heating equipment requirements are low, allowing for large-scale mass production, high sample yields, and significantly reduced energy consumption. The required synthesis equipment is readily available, and the resulting material exhibits uniform particle size, good crystallinity, and excellent ionic conductivity.

[0064] 3. This invention innovatively synthesizes a lithium ion conductor with high conductivity and stability in air through a one-step method, creating a class of oxyfluoride superionic conductors with a pyrochlore structure. 1.25 La 0.58 Nb2O6F has a total ionic conductivity of ≥3.5mS / cm, exceeding that of all existing oxide-based electrolyte materials. This fluorite-based structure offers high compositional flexibility, similar to perovskite structures, and its ionic conductivity is expected to be further improved through element substitution, as observed in other solid-state electrolytes. By optimizing the material composition, non-sulfide solid-state electrolytes are also expected to achieve lithium-ion conductivity comparable to that of liquid electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a photo of the precursor slurry prepared in Example 1 S200;

[0066] Figure 2is the Li obtained in Example 1 1.25 La 0.58 X-ray powder diffraction pattern of Nb2O6F;

[0067] Figure 3 is the Li obtained in Example 1 1.25 La 0.58 SEM image of Nb2O6F;

[0068] Figure 4 is the Li obtained in Example 1 1.25 La 0.58 EIS diagram of Nb2O6F;

[0069] Figure 5 is the Li obtained in Example 2 1.25 La 0.58 EIS diagram of Nb2O6F;

[0070] Figure 6 is the Li obtained in Example 3 1.25 La 0.58 X-ray powder diffraction pattern of Nb2O6F;

[0071] Figure 7 is the Li obtained in Example 3 1.25 La 0.58 EIS diagram of Nb2O6F. DETAILED DESCRIPTION

[0072] The technical solutions in the embodiments of the invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the invention.

[0073] Example 1

[0074] Wet ball milling mixing process

[0075] S100, raw material pretreatment

[0076] S110, La2O3 pre-calcination: heat from room temperature to 900℃ at a heating rate of 5℃ / min, then keep warm for 4h, then cool to 100℃ with the furnace, and transfer to a 105℃ drying oven while hot;

[0077] S120, Li2CO3, Nb2O5, and LiF were dried in a drying oven at 105 °C for 24 h;

[0078] S200, mixing process

[0079] S210, according to the ratio of Li2CO3:La2O3:Nb2O5:LiF=0.125:0.225:1:1 (molar ratio), La2O3, Li2CO3, Nb2O5, and LiF were taken out respectively and mixed evenly;

[0080] Mixing method:

[0081] Add anhydrous ethanol (solid content 30%) and then put it into a ball mill for wet mixing. The ball mill uses a planetary ball mill (made of zirconia) with a zirconia ball-to-material ratio of 4:1.

[0082] Parameters: 400 rpm × 6h, zirconia grinding balls (Φ5mm / Φ10mm=1:1). The prepared intermediate photo is shown in Figure 1 ;

[0083] S220, post-processing:

[0084] The slurry after S210 treatment was dried by spray drying, with an inlet temperature of 180°C.

[0085] The outlet temperature is 80°C, and the precursor is obtained after drying;

[0086] S300, sintering process

[0087] Atmosphere: high-purity N2 (flow rate Q = 1.5 V / min, V = 2 L tube furnace → 3 L / min);

[0088] program:

[0089] The room temperature was raised to 900°C at a rate of 3°C / min, then raised to 1000°C at a rate of 2°C / min, kept at this temperature for 4 h, and then cooled in the furnace;

[0090] Key Controls:

[0091] Oxygen probe real-time monitoring (furnace tail pO2 <10 -15 atm);

[0092] S400, post-processing and characterization

[0093] Crushing and screening: 200 mesh sieve + magnetic separation for iron removal (magnetic field strength 1.2T)

[0094] Combine Figure 2-Figure 4 , the final product performance test results are as follows:

[0095]

[0096]

[0097] Example 2

[0098] Fluidized bed mixing process S100, raw material pretreatment (same as in Example 1)

[0099] S200, mixing process

[0100] Equipment: Fluidized bed mixer (nitrogen protection)

[0101] parameter:

[0102] Air flow rate: 2×minimum fluidization rate (Umf=0.15m / s)→0.3m / s; mixing time: 45min;

[0103] Adding order:

[0104] Light powder Li2CO3 → medium powder LiF → heavy powder Nb2O5 → La2O3; S300, sintering process

[0105] Atmosphere: Ar+5% H2 (reducing atmosphere inhibits oxidation)

[0106] program:

[0107] The room temperature was raised to 1000°C at a rate of (5°C / min) and kept at this temperature for 4 h;

[0108] Airflow Control:

[0109] Partition flow rate: 8V / min before 600℃→2V / min in 1000℃ holding section;

[0110] Micro positive pressure control: +15Pa (PID feedback adjustment);

[0111] S400, post-processing and characterization (same as in Example 1)

[0112] Finished product performance results are shown in Figure 5 EIS diagram of .

[0113] Comparative Example

[0114] Synthetic La 0.58 Li x Nb2O6 oxide precursor

[0115] Step 1: Weigh La2O3, Li2CO3, and Nb2O5 according to the molar ratio, and adjust the Li content to compensate for the ignition loss (add 5–10 mol% Li2CO3):

[0116] The ratio is: La:Nb:Li=0.58:2:(1.25+x)

[0117] The raw materials were placed in a zirconia ball mill, and wet-milled for 12 hours with a small amount of ethanol to obtain a uniform mixed slurry.

[0118] Drying and pre-sintering: Drying at 80–100°C to remove ethanol;

[0119] The powder was placed in a crucible and sintered at 900°C in air for 6–8 hours;

[0120] After cooling, the powder was taken out and ball-milled again to make it uniform.

[0121] Step 2: Introduce fluorine source (F - ), mixed LiF;

[0122] The above oxide precursor is mixed with LiF in molar ratio so that the final F - Content corresponding to Li 1.25 La 0.58 Nb2O6F composition, with an excess of 1–2 mol% LiF to compensate for burn-off.

[0123] Re-ball milling: ball mill the mixture in ethanol or isopropanol for 12 h to ensure that the LiF is fully dispersed.

[0124] Place the dried mixed powder in a sealed crucible or aluminum fluoride crucible and sinter at 700-750℃ for 4-6 hours.

[0125] The powder prepared in the comparative example was subjected to XRD test, and the results are shown in Figure 6 , it can be clearly seen that the powder synthesized by the two-step method contains unknown impurities.

[0126] See also Figure 7 Furthermore, the powder prepared in the comparative example was sintered into a ceramic sheet using the same preparation method as in Example 1, and an EIS test was performed. The results showed that the ionic conductivity of the ceramic sheet was 1.41×10 -3 S / cm, the performance is far lower than that of Example 1 and Example 2. Specifically, the advantages of Example 1 and Example 2 over the comparative example are as follows:

[0127] 1. One-step sintering replaces traditional multi-step process

[0128] In Examples 1 and 2, pure-phase electrolyte powder can be obtained by "single-step sintering" (e.g., keeping warm at 1000°C for 4h in Example 1), while the comparative example requires "two-step sintering" (first synthesizing the oxide precursor, then introducing LiF for secondary sintering). This application reduces the number of sintering times and process complexity.

[0129] In the comparative example, the secondary sintering requires the additional use of an aluminum fluoride crucible or a sealed container, and excess LiF (1-2 mol%) needs to be compensated to prevent fluorine volatilization. However, the present application avoids complex equipment and raw material waste by using a single fluorine source (LiF) and inert atmosphere control (such as N2 or Ar+H2), and reduces costs by about 30%-50%.

[0130] 2. Significant improvement in ionic conductivity

[0131] Li of Example 1 1.25 La 0.58 The ionic conductivity of Nb2O6F reaches 3.75×10 -3S / cm, the performance of Example 2 after using the fluidized bed mixing process is comparable; while the conductivity of the product synthesized by the two-step method of the comparative example is only 1.41×10 -3 S / cm, the difference is 2.6 times.

[0132] The present invention forms a pyrochlore structure (such as XRD Figure 2 、 5 The three-dimensional ion channel (composed of MO6 octahedrons connected at the same angle) has a higher conduction efficiency, while the comparative example introduces impurities ( Figure 6 ), hindering ion transport.

[0133] 3. Better particle size uniformity and crystallinity

[0134] The powder particle size D50 of Example 1 is 1.45 μm (specification value 1.5±0.2 μm), D90≤3.0 μm, and the specific surface area is 11.3 m 2 / g, narrow particle size distribution and good crystallinity (SEM Figure 3 The comparative example shows regular particles); due to the two-step process, the powder agglomerates and the particle size distribution is uneven, and the specific surface area is reduced to 8.5m 2 / g or less.

[0135] 4. Low junction temperature and low energy consumption

[0136] The sintering temperature in this application is controlled at 900-1100°C (e.g., Example 1, which was sintered at 1000°C), eliminating the need for temperatures above 1100°C. While the secondary sintering temperature in the comparative example is 700-750°C, the total energy consumption for the two-step sintering process is still approximately 60% higher than that of this application. Taking a 10L furnace as an example, the energy consumption for a single sintering cycle in this application is approximately 80kWh, while that in the comparative example is 130kWh.

[0137] 5. Low equipment requirements and suitable for large-scale production

[0138] This application can achieve mass production using an ordinary muffle furnace or a tubular furnace (equipped with a mass flow controller and an oxygen probe), and the equipment cost is about 40% lower than the aluminum fluoride crucible and high-temperature sintering furnace required for the two-step method; and when geometrically similarly scaled up (such as expanding the production capacity by 10 times), the production can be directly scaled up by keeping the ball mill filling rate and speed ratio unchanged, while the comparative example is difficult to linearly scale up due to the complex process.

[0139] The comparison between Example 1 and Example 2 and the comparative example is as follows:

[0140]

[0141] Through a one-step solid-phase method, the bottlenecks of "multi-step sintering, dependence on multiple fluorine sources, and high energy consumption" in the preparation of traditional greenstone-type fluoride oxides have been broken through. While ensuring high ionic conductivity (≥3.5×10-3S / cm) and air stability, the process simplification, cost reduction and large-scale production feasibility have been achieved, providing a better technical path for the industrialization of solid-state electrolytes.

[0142] It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should have the common meanings understood by technicians in the field to which this application belongs.

[0143] The above description is merely a preferred embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a pyrochlore-type oxyfluoride solid electrolyte by a one-step solid phase process, characterized in that: The electrolyte material molecular formula is Li 2-x La (1+x) / 3 Nb2O6F(LLNOF); comprising the following steps: S200 preparation of precursor La2O3, Li2CO3, Nb2O5, and LiF were weighed in a stoichiometric ratio and mixed uniformly to prepare a precursor; The stoichiometric ratio is determined according to the following reaction formula: <h2 style=";text-align:left;direction:ltr">(1-x) / 2*Li2CO3+(1+x) / 6*La2O3+Nb2O5+LiF→Li<h2 style=";text-align:left;direction:ltr"> 2-x <h2 style=";text-align:left;direction:ltr"> No<h2 style=";text-align:left;direction:ltr"> (1+x) / 3 <h2 style=";text-align:left;direction:ltr"> Nb2O6F; S300, sintering The precursor is sintered at high temperature and solid-phase sintered to form it.

2. The method according to claim 1, characterized in that In S300, the sintering temperature is 900-1100°C, the heating rate is 1-5°C / min; and the sintering time is 2-6 hours; After sintering is completed, the furnace is cooled naturally.

3. The method according to claim 1, characterized in that In S300, the precursor is sintered under the protection of an inert atmosphere. The airflow needs to cover the entire sintering area, and the temperature difference is ≤±5°C. The flow rate is adjusted according to the furnace volume, and the adjustment formula is: Q=V×N / t.

4. The method according to claim 3, characterized in that The S300 needs to be equipped with precise control equipment, including a mass flow controller (MFC): accuracy of ±1% FS, multi-channel independent control; a pressure feedback system: real-time monitoring of furnace pressure, adjusting the outlet valve opening through the PID algorithm, and maintaining the set positive pressure (±2Pa fluctuation).

5. The method according to any one of claims 1 to 4, characterized in that In S200, La2O3, Li2CO3, Nb2O5, and LiF are weighed according to a stoichiometric ratio, and a liquid that can be volatilized by heating is added, and then mixed evenly to a solid content of 20%-50%; and then dried to obtain a precursor.

6. The method according to any one of claims 1 to 4, characterized in that The S200 also includes: S100, drying, drying S110, heating La2O3 to remove crystallization water; S120. Dry Li2CO3, Nb2O5, and LiF to remove water for later use.

7. The method according to claim 6, characterized in that In S110, the heating rate for removing crystal water from lanthanum oxide is 5-10°C / minute, and the temperature is raised to 700-900°C and maintained for 2-6 hours; then the temperature is cooled, and when the temperature is above 100°C, the lanthanum oxide is placed in a drying oven to keep dry at a drying temperature of 100-120°C.

8. The method according to any one of claims 1 to 4, characterized in that S300 and later also include: S400, fine grinding The S300 sintered powder is crushed and sand-milled into powder; when the amount of the synthetic material is enlarged, geometric similarity enlargement is required.

9. The method according to claim 6, characterized in that The purity of lithium carbonate (Li2CO3), lanthanum oxide (La2O3), niobium pentoxide (Nb2O5), and LiF is not less than 99.5%.

10. The method according to any one of claims 1 to 4, characterized in that In S200, the materials are added in the following order: light powder (Li2CO3) → medium powder (LiF) → heavy powder (Nb2O5) → La2O3 to reduce the material stratification phenomenon.

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