A method for preparing a solid-state electrolyte based on a binary eutectic salt assisted low-temperature sintering

Abstract

The application discloses a method for preparing a solid-state electrolyte based on a binary eutectic salt assisted low-temperature sintering, relates to the field of solid-state electrolytes, and discloses the following steps: mixing and grinding NaOH and NaBr to obtain low-melting-point eutectic salt powder; mixing pre-sintered powder and the eutectic salt powder, grinding and dispersing to obtain mixed powder; loading the mixed powder into a mold for cold sintering; and performing heat treatment on the sample after cold sintering to prepare Na 1+ x Zr2Si x P 3‑x O 12 solid-state electrolyte. The application realizes particle rearrangement and pre-densification by using eutectic salt low-temperature melting, and a solid-state electrolyte with a relative density of more than 97%, a room-temperature ionic conductivity of 4.05*10 ‑3 S·cm ‑1 , and a performance far higher than that of a traditional high-temperature solid-phase method prepared NASICON type solid-state electrolyte is prepared at a sintering temperature of below 1170 DEG C. The method significantly reduces the sintering temperature, avoids sodium element volatilization and heteroion introduction, is simple in process, and is easy to scale up.

Description

Technical Field

[0001] This invention relates to the field of solid electrolytes, and more specifically to a method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering. Background Technology

[0002] Na 1+x Zr2Si x P 3-x O 12 (0≤x≤3, abbreviated as NZSP) type solid electrolytes have high sodium ion conductivity (up to 10 at room temperature). -3 With its excellent thermal and electrochemical stability (on the order of S / cm), sodium-ion batteries are among the most promising key materials in the field of all-solid-state batteries. As sodium-ion batteries rapidly develop in areas such as large-scale energy storage and low-speed electric vehicles, the development of high-performance, low-cost, and scalable NASICON solid-state electrolytes has become a research hotspot. Currently, the conventional preparation method for NASICON-type solid-state electrolytes is high-temperature solid-state sintering. This method typically requires prolonged holding at temperatures above 1250°C (several hours to tens of hours) to promote particle diffusion and densification. However, this method has the following prominent problems in practical applications: First, the high energy consumption process is not conducive to industrial production and cost control; second, sodium is prone to volatilization at high temperatures, leading to deviations in stoichiometry and the formation of impurity phases, thereby reducing ionic conductivity; third, prolonged high-temperature treatment may induce abnormal grain growth and thermal stress cracks, affecting the mechanical and electrochemical properties of the electrolyte.

[0003] To lower the sintering temperature, researchers have explored various low-temperature sintering techniques. Spark plasma sintering (SPS) can rapidly densify at lower temperatures, but the equipment is expensive and difficult to scale up. Cold sintering techniques, developed in recent years, have successfully achieved low-temperature densification of various ceramic materials by applying uniaxial pressure and a transient liquid phase at lower temperatures (typically <400℃). For NASICON-type electrolytes, reports have shown that using water, dilute acid, or low-concentration alkaline solutions as the cold sintering liquid phase yields samples with a relative density >90% at around 300℃. However, aqueous liquid phases can easily lead to Na+ in NASICON. + The leaching of impurities such as Na2CO3 or the formation of other impurities, coupled with the rapid evaporation of water potentially leaving pores, makes it difficult to obtain a completely dense electrolyte free of impurities. Therefore, selecting a suitable liquid medium is a key challenge in applying cold sintering technology to NASICON.

[0004] The use of low-melting-point eutectic salts as sintering aids has been preliminarily explored in the field of oxide ceramics. Eutectic salts have lower melting points than single salts and can form a homogeneous liquid phase at milder temperatures. However, there are currently no reports on the use of NaOH-NaBr binary eutectic salts to assist in the preparation of NASICON-type solid electrolytes. Existing research on sintering aids has mostly focused on single salts or Na / K-containing eutectic systems, lacking research on the behavior of NaOH-NaBr eutectic salts in the NASICON cold sintering process. Therefore, developing a method for preparing NASICON-type solid electrolytes that can significantly reduce sintering temperature, avoid sodium volatilization, prevent the introduction of harmful impurity ions, and has a simple process has significant practical value and technical challenges. Summary of the Invention

[0005] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering.

[0006] The technical solution of the present invention is as follows: A method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering includes the following steps: S1: Mix and grind NaOH powder and NaBr powder to obtain eutectic salt powder; S2: Put Na 1+x Zr2Si x P 3-x O 12 The pre-calcined powder is mixed with the eutectic salt powder, and then ground and dispersed to obtain a mixed powder; S3: Cold sinter the mixed powder; S4: The sample after cold sintering in S3 is then heat-treated to obtain Na. 1+x Zr2Si x P 3-x O 12 Solid electrolyte.

[0007] As a preferred embodiment of the present invention, in step S1, the molar fraction of NaOH in the eutectic salt is 0.7-0.95.

[0008] As a preferred embodiment of the present invention, in step S2, the Na 1+x Zr2Si x P 3-x O 12 The range of x in the equation is 0 ≤ x ≤ 3.

[0009] As a preferred embodiment of the present invention, in step S2, the proportion of the eutectic salt powder is 1-20 wt% of the total mass of the mixed powder.

[0010] As a preferred embodiment of the present invention, in step S3, the mixed powder is loaded into a mold, a uniaxial pressure of 50-500 MPa is applied, the cold sintering temperature range is 250-400℃, and the holding time is 0.5-3h.

[0011] As a preferred embodiment of the present invention, in step S4, the temperature range of the heat treatment is 1000-1170℃, and the holding time is 1-5h.

[0012] This invention discloses a Na 1+x Zr2Si x P 3-x O 12 Solid electrolytes are prepared using any of the methods described above.

[0013] The beneficial effects of this invention are: (1) The method of preparing NASICON-type solid electrolyte based on binary eutectic salt-assisted low-temperature sintering of the present invention is simple and energy-efficient. It reduces the sintering temperature of traditional high-temperature solid-state sintering (>1250℃) to about 1100℃. At the same time, the high-temperature holding time is significantly shortened by cold sintering pre-densification, which effectively reduces energy consumption and production costs.

[0014] (2) This invention employs an anhydrous liquid phase system in which NaOH-NaBr binary eutectic salt is dry-mixed in solid powder form and liquefied in situ by heating, avoiding sodium ion leaching and the formation of impurity phases such as Na2CO3 caused by water, dilute acid, and other liquid phase media in traditional cold sintering. Simultaneously, the cations of the eutectic salt (Na...) + This is consistent with the cation in NASICON's bulk, avoiding the introduction of B by common sintering aids (such as B2O3, Bi2O3, CuO, etc.). 3+ Bi 3+ Cu 2+ Heterogeneous cations disrupt sodium ion transport channels. Furthermore, NaBr in the eutectic salt remains a stable sintering aid during the high-temperature heat treatment stage (1000-1170℃) after cold sintering, continuously promoting grain growth and densification. NaBr can stably segregate at grain boundaries, playing a unique interfacial modification role, improving the grain boundary chemical environment, and reducing grain boundary resistivity.

[0015] (3) The present invention uses a two-step process combining cold sintering (250-400℃) pre-densification and subsequent high-temperature sintering (1000-1170℃). The liquid phase formed by the eutectic salt at low temperature promotes particle rearrangement and dissolution-precipitation, so that the relative density of the sample after cold sintering can reach more than 85%. Subsequent heat treatment effectively avoids abnormal grain growth and thermal stress cracks, and finally achieves densification with a relative density of more than 97%, and the microstructure is uniform and controllable.

[0016] (4) Na prepared using the optimized formula and process parameters of this invention 1+x Zr2Si x P 3-x O 12 Solid electrolyte with an ionic conductivity of up to 4.05 × 10⁻⁶ at room temperature. -3 S·cm -1 The sodium ion transference number is close to 1, while exhibiting excellent density (relative density > 97%) and mechanical strength. The NASICON solid electrolyte prepared by this method has broad industrial application prospects in the field of all-solid-state sodium batteries. Attached Figure Description

[0017] Figure 1 A flowchart for preparing NASICON-type solid electrolytes by low-temperature sintering assisted by binary eutectic salt.

[0018] Figure 2 This is the binary phase diagram of the NaBr-NaOH system.

[0019] Figure 3 Na was prepared using conventional high-temperature sintering (Comparative Example 1) and in Example 8. 3.4 Zr2Si 2.4 P 0.6 O 12 Grain morphology diagrams, where (a): Comparative Example 1 sample, (b): Example 8 sample.

[0020] Figure 4 The traditional high-temperature sintering (Comparative Example 1) and the preparation of Na using Example 8 3.4 Zr2Si 2.4 P 0.6 O 12 The ionic conductivity of the solid electrolyte, where 1: sample of Comparative Example 1, 2: sample of Example 8. Detailed Implementation

[0021] A method for preparing Na based on binary eutectic salt-assisted low-temperature sintering 1+x Zr2Si x P 3-x O 12 For methods involving solid electrolytes, refer to [reference needed]. Figure 1 This includes the following steps: S1: Mix NaOH powder and NaBr powder according to the eutectic molar ratio and grind them evenly to obtain low melting point eutectic salt powder; S2: Put Na 1+x Zr2Si x P 3-x O 12The electrolyte powder and the eutectic salt powder obtained from S1 are ground and dispersed to obtain a mixed powder, wherein the mass of the eutectic salt powder accounts for 1-20 wt% of the total mass of the mixed powder; S3: Load the mixed powder into the mold, apply a uniaxial pressure of 50-500 MPa, cold sintering temperature range of 250-400℃, and holding time of 0.5-3h; S4: The cold-sintered sample is then heat-treated at a temperature ranging from 1000 to 1170°C for 1 to 5 hours to further densify the sample and promote grain growth, ultimately yielding high-density Na. 1+x Zr2Si x P 3-x O 12 Solid electrolyte; As an improvement, the molar fraction of NaOH in the eutectic salt is 0.7-0.95. Since the NaOH-NaBr system has a low eutectic point (approximately 260°C) at a specific molar ratio (approximately 0.82:0.18), see... Figure 2 At this ratio, the mixed salts can completely melt at a lower temperature, providing the maximum amount of transient liquid phase. When the molar ratio deviates from this optimal value, the liquidus temperature of the mixed salts will increase significantly. Under cold sintering conditions of 300℃, the eutectic salt at this ratio may be in a state of "solid-liquid coexistence" or even mostly still in the solid state. The lack of sufficient liquid phase for capillary wetting and particle rearrangement means that the voids between powder particles cannot be effectively filled, leading to a significant decrease in the relative density of the final ceramic. Increased porosity directly cuts off ion transport paths, resulting in a decrease in conductivity. If the addition amount is insufficient: the amount of molten liquid phase is too small to form a complete and continuous liquid phase on the surface of the powder particles. Insufficient capillary driving force makes particle rearrangement difficult. If the addition amount is excessive: excessive alkaline liquid phase will strongly erode the NASICON framework, causing the matrix to deviate from the optimal stoichiometry, and even inducing insulating impurities at grain boundaries, completely destroying the local crystal structure.

[0022] As an improvement, the Na 1+x Zr2Si x P 3-x O 12 The range of values ​​for x is 0 ≤ x ≤ 3.

[0023] This invention employs a low-temperature sintering technology based on binary eutectic salt assistance. By introducing NaOH-NaBr binary eutectic salt as a non-aqueous liquid-phase sintering aid during the cold sintering stage, it achieves Na… 1+x Zr2Si x P 3-x O 12High-efficiency low-temperature sintering of (NZSP) solid electrolytes. This process, operating at temperatures ranging from 250°C to 400°C, utilizes the in-situ liquid phase formed by eutectic salts to achieve initial rearrangement and densification of ceramic particles by applying appropriate pressure and controlling time. Further improvements in density and ionic conductivity are achieved during heat treatment at 1000°C to 1170°C. Compared to the high sintering temperatures (above 1250°C) of traditional solid-state sintering, this method significantly reduces the main sintering temperature by 100-200°C, resulting in substantial energy savings. The core of this method lies in leveraging the anhydrous liquid phase wetting effect of the NaOH-NaBr binary eutectic salt to promote the sliding, rearrangement, and dissolution-precipitation of NZSP powder particles at low temperatures. This avoids the sodium ion leaching and impurity phase formation problems associated with aqueous liquid phases, achieving pre-densification of the green body. Subsequently, heat treatment further optimizes the ceramic microstructure, allowing residual NaBr to stabilize and segregate at grain boundaries, acting as an interface modifier, reducing grain boundary resistance, and ultimately resulting in solid electrolytes with excellent ionic conductivity and density.

[0024] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0025] The performance testing methods used in the following examples are as follows: 1. Relative density Test Method: Archimedes' Displacement Method. The actual bulk density of the sintered ceramic sheet was measured using the Archimedes' displacement method. Considering the potential sensitivity of solid electrolytes to moisture, anhydrous ethanol is often used as the test medium. The dry weight of the sample was recorded before measurement, then it was suspended in anhydrous ethanol to read the suspended weight. After drying the surface, the wet weight was measured. The relative density was obtained by the ratio of the measured bulk density to the theoretical density of the material.

[0026] 2. Ionic conductivity Test method: Electrochemical impedance spectroscopy (EIS). The sintered ceramic sheet was polished flat on both sides, and a gold (Au) layer was uniformly sputtered onto both surfaces using a vacuum sputtering instrument as an ion-blocking electrode. Electrochemical impedance spectroscopy was performed at room temperature (e.g., 25°C) using an electrochemical workstation. The test frequency range was typically set to 3 MHz to 0.1 Hz, with an AC perturbation voltage amplitude of 10 mV. Total ionic conductivity at room temperature was measured. σ (S·cm) -1 ) Calculated according to formula (1), where L The sample thickness is in cm. S Electrode contact area (cm²) 2R is the bulk resistance (Ω).

[0027] (1).

[0028] 3. Activation energy The prepared blocking electrode sample was placed in a variable-temperature testing device, and AC impedance spectroscopy was performed at specific temperature gradients (e.g., 10°C) within a set temperature range (25°C to 100°C). The total ionic conductivity corresponding to each temperature point was calculated. σ According to the Arrhenius equation... σT =Aexp(- E a / k B T (where A is the pre-exponential factor,) k B Boltzmann's constant, T (where absolute temperature is used), with ln( σ A graph showing the relationship between T and 1000 / T is plotted. A linear fit is performed on the resulting curve, and the activation energy (E) for sodium ion migration within the material is calculated from the slope of the fitted line. a ).

[0029] 4. Grain size Test method: Scanning electron microscopy (SEM) line intercept method. The microstructure of the sintered sample cross-section was observed using field emission scanning electron microscopy (FESEM). After acquiring representative high-magnification fracture microscopic images, the line intercept method was used. Multiple lines were randomly selected using image analysis software such as Nano Measurer, and the number of grains traversed by the lines was counted to calculate the average grain size.

[0030] Example 1 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0031] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0032] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300℃ for 1 hour.

[0033] (4) Heat treatment: The cold-sintered sample is transferred into a muffle furnace, pre-fired powder is embedded in it, and the temperature is raised to 1100℃ at a heating rate of 5℃ / min and held for 4 hours to obtain Na3Zr2Si2PO 12 Solid electrolyte.

[0034] (5) The test results are shown in Table 1.

[0035] Table 1 Performance test results of Example 1

[0036] Example 2 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0037] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 5 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0038] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0039] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 °C at a heating rate of 5 °C / min. The holding time was 4 hours to obtain Na3Zr2Si2PO4. 12 Solid electrolyte.

[0040] (5) The test results are shown in Table 2.

[0041] Table 2 Performance test results of Example 2

[0042] Example 3 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0043] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12The pre-calcined powder was mixed with 20 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0044] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0045] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 °C at a heating rate of 5 °C / min. The holding time was 4 hours to obtain Na3Zr2Si2PO4. 12 Solid electrolyte.

[0046] (5) The test results are shown in Table 3.

[0047] Table 3 Performance test results of Example 3 Example

[0048] A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0049] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0050] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 500 MPa is applied, and cold sintering is carried out at 250 °C for 3 hours.

[0051] (4) Heat treatment: The cold-sintered sample is transferred into a muffle furnace, pre-fired powder is embedded in it, and the temperature is raised to 1100℃ at a heating rate of 5℃ / min and held for 4 hours to obtain Na3Zr2Si2PO 12 Solid electrolyte.

[0052] (5) The test results are shown in Table 4.

[0053] Table 4 Performance test results of Example 4

[0054] Example 5 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0055] (2) Mixed pulping: Na2Zr2SiP2O synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0056] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0057] (4) Heat treatment: The cold-sintered sample is transferred into a muffle furnace, pre-fired powder is embedded in it, and the temperature is raised to 1120℃ at a heating rate of 5℃ / min. The holding time is 4 hours to obtain Na2Zr2SiP2O. 12 Solid electrolyte.

[0058] (5) The test results are shown in Table 5 below.

[0059] Table 5 Performance test results of Example 5

[0060] Example 6 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0061] (2) Mixed pulping: Na synthesized according to stoichiometric ratio 3.5 Zr2Si 2.5 P 0.5 O 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0062] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1.5 hours.

[0063] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1080 °C at a heating rate of 5 °C / min. The holding time was 5 hours to obtain Na. 3.5 Zr2Si 2.5 P 0.5 O 12 Solid electrolyte.

[0064] (5) The test results are shown in Table 6.

[0065] Table 6 Performance test results of Example 6

[0066] Example 7 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0067] (2) Mixed pulping: Na synthesized according to stoichiometric ratio 3.8 Zr2Si 2.8 P 0.2 O 12 The pre-calcined powder was mixed with 8 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0068] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 400 MPa is applied, and cold sintering is carried out at 280 °C for 2 hours.

[0069] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1050 °C at a heating rate of 5 °C / min. The holding time was 2 hours to obtain Na. 3.8 Zr2Si 2.8 P 0.2 O 12 Solid electrolyte.

[0070] (5) The test results are shown in Table 7.

[0071] Table 7 Performance test results of Example 7

[0072] Example 8 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.82:0.18 and grind them evenly to obtain low melting point eutectic salt powder.

[0073] (2) Mixed pulping: Na synthesized according to stoichiometric ratio 3.4 Zr2Si 2.4 P 0.6 O 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0074] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0075] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 °C at a heating rate of 5 °C / min. The holding time was 4 hours to obtain Na. 3.4 Zr2Si 2.4 P 0.6 O 12 Solid electrolyte.

[0076] (5) The test results are shown in Table 8.

[0077] Table 8 Performance test results of Example 8

[0078] Example 9 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.85:0.15 and grind them evenly to obtain low melting point eutectic salt powder.

[0079] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0080] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0081] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 °C at a heating rate of 5 °C / min. The holding time was 4 hours to obtain Na3Zr2Si2PO4. 12 Solid electrolyte.

[0082] (5) The test results are shown in Table 9.

[0083] Table 9 Performance test results of Example 9

[0084] Example 10 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.75:0.25 and grind them evenly to obtain low melting point eutectic salt powder.

[0085] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0086] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0087] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 °C at a heating rate of 5 °C / min. The holding time was 4 hours to obtain Na3Zr2Si2PO4. 12 Solid electrolyte.

[0088] (5) The test results are shown in Table 10.

[0089] Table 10 Performance test results of Example 10

[0090] Example 11 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.95:0.05 and grind them evenly to obtain low melting point eutectic salt powder.

[0091] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0092] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0093] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was buried inside, and the temperature was raised to 1100℃ at a heating rate of 5℃ / min and held for 4 hours to obtain Na3Zr2Si2PO 12 Solid electrolyte.

[0094] (5) The test results are shown in Table 11.

[0095] Table 11 Performance test results of Example 11

[0096] Example 12 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.85:0.15 and grind them evenly to obtain low melting point eutectic salt powder.

[0097] (2) Mixed pulping: Na synthesized according to stoichiometric ratio 3.4 Zr2Si 2.4 P 0.6 O 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0098] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0099] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 ℃ at a heating rate of 5 ℃ / min, and held for 4 hours to obtain Na. 3.4 Zr2Si 2.4 P 0.6 O 12 Solid electrolyte.

[0100] (5) The test results are shown in Table 12.

[0101] Table 12 Performance test results of Example 12

[0102] Comparative Example 1 Traditional high-temperature sintering preparation of Na 3.4 Zr2Si 2.4 P 0.6 O 12 The solid electrolyte method includes the following process steps: (1) Put Na 3.4 Zr2Si 2.4 P 0.6 O 12 The pre-fired powder was directly dry-pressed and sintered at 1250℃ for 12 hours.

[0103] (2) The test results are shown in Table 13.

[0104] Table 13 Performance test results of Comparative Example 1

[0105] Comparative Example 2 Preparation of Na3Zr2Si2PO without eutectic salt 12 The solid electrolyte method includes the following process steps: (1) Without adding any eutectic salt, pure Na3Zr2Si2PO4 12 The powder was cold-sintered at 300℃ and 300 MPa for 1 hour, and then heat-treated at 1100℃ for 4 hours to obtain Na3Zr2Si2PO4. 12 Solid electrolyte.

[0106] (2) The test results are shown in Table 14.

[0107] Table 14 Performance test results of Comparative Example 2

[0108] Comparative Example 3 A method for preparing NZSP solid electrolyte based on binary eutectic salt-assisted low-temperature sintering, the process steps of which include: (1) Preparation of eutectic salt: Mix NaOH powder and NaBr powder at a molar ratio of 0.5:0.5 and grind them evenly to obtain low melting point eutectic salt powder.

[0109] (2) Mixed pulping: Na3Zr2Si2PO synthesized according to stoichiometric ratio 12 The pre-calcined powder was mixed with 10 wt% of the above eutectic salt powder, and then ground and dispersed to obtain a mixed powder.

[0110] (3) Cold sintering: The mixed powder is placed in a cemented carbide mold, a uniaxial pressure of 300 MPa is applied, and cold sintering is carried out at 300 °C for 1 hour.

[0111] (4) Heat treatment: The cold-sintered sample was transferred into a muffle furnace, pre-fired powder was embedded in it, and the temperature was raised to 1100 ℃ at a heating rate of 5 ℃ / min. The holding time was 4 hours to obtain Na3Zr2Si2PO 12 Solid electrolyte.

[0112] (5) The test results are shown in Table 15.

[0113] Table 15 Performance test results of Comparative Example 3

[0114] Electron microscopy scans were performed on the cross-sections of the solid electrolyte samples from Comparative Example 1 and Example 8. The results are shown in the figure. Figure 3 ,from Figure 3It is known that traditional high-temperature sintering causes severe element volatilization and abnormal grain growth, which easily induces microcracks and disrupts the ion transport network. In contrast, eutectic salt-assisted low-temperature sintering significantly reduces the mass transfer barrier through the transient liquid phase, achieving high densification while suppressing excessive grain coarsening. Ultimately, it achieves a microstructure with tightly fused grain boundaries and moderate size (fine-grained state), providing an efficient and continuous three-dimensional transport channel for sodium ions.

[0115] Figure 4 This is a comparison graph of the ionic conductivity of the samples from Example 8 and Comparative Example 1. Figure 4 It is evident that, compared to the extremely high grain boundary resistance generated by traditional high-temperature sintering, eutectic salt-assisted low-temperature sintering significantly eliminates the internal grain boundary barrier, resulting in a substantial decrease in the total resistance of the solid electrolyte, thereby achieving a room-temperature ionic conductivity of 1.37 × 10⁻⁶. -3 S·cm -1 Increased to 4.05×10 -3 S·cm -1 .

[0116] In summary, this invention utilizes a binary eutectic salt-assisted low-temperature sintering technique to prepare a high-performance NZSP solid electrolyte. Results show that using a eutectic salt with a NaOH-NaBr eutectic molar ratio of 0.7-0.95, under cold sintering conditions of 250-400℃ and heat treatment conditions of 1000-1170℃, and selecting a eutectic salt with a mass fraction of 1-20 wt%, preliminary densification can be achieved, and the relative density of the green body after cold sintering is higher than 85%. After heat treatment at 1000℃ to 1170℃, the relative density of the ceramic can be further increased to over 97%, and the room temperature ionic conductivity reaches as high as 4.05 × 10⁻⁶. -3 S·cm -1 All of them are superior to samples prepared by traditional solid-state methods.

[0117] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering, characterized in that, Includes the following steps: S1: Mix and grind NaOH powder and NaBr powder to obtain eutectic salt powder; S2: Put Na 1+x Zr2Si x P 3-x O 12 The pre-calcined powder is mixed with the eutectic salt powder, and then ground and dispersed to obtain a mixed powder; S3: Cold sinter the mixed powder; S4: The sample after cold sintering in S3 is then heat-treated to obtain Na. 1+x Zr2Si x P 3-x O 12 Solid electrolyte.

2. The method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering according to claim 1, characterized in that, In step S1, the molar fraction of NaOH in the eutectic salt is 0.7-0.

95.

3. The method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering according to claim 1, characterized in that, In step S2, the Na 1+x Zr2Si x P 3-x O 12 The range of x in the equation is 0 ≤ x ≤ 3.

4. The method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering according to claim 1, characterized in that, In step S2, the eutectic salt powder accounts for 1-20 wt% of the total mass of the mixed powder.

5. The method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering according to claim 1, characterized in that, In step S3, the mixed powder is loaded into a mold, a uniaxial pressure of 50-500 MPa is applied, the cold sintering temperature range is 250-400℃, and the holding time is 0.5-3h.

6. The method for preparing solid electrolytes based on binary eutectic salt-assisted low-temperature sintering according to claim 1, characterized in that, In step S4, the temperature range of the heat treatment is 1000-1170℃, and the holding time is 1-5h.

7. A type of Na 1+x Zr2Si x P 3-x O 12 Solid electrolyte, characterized in that, It is prepared by the method described in any one of claims 1-6.

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