A method for preparing zirconium silicon sodium phosphate nano-powder by taking lithium slag as raw material

Abstract

The present application relates to the technical field of comprehensive recycling of industrial solid waste, in particular to a method for preparing zirconium silicate sodium phosphate nano powder by using lithium ore slag as raw material. After removing iron from lithium ore slag by process, aluminum-silicon fine powder is obtained, and sodium superionic conductor zirconium silicate sodium phosphate powder is obtained by solid phase sintering method. The zirconium silicate sodium phosphate powder can be applied to liquid sodium ion battery by diaphragm coating or applied to all-solid-state sodium ion battery by sintering into a sheet. In the process of treating lithium ore slag, the present application realizes the collaborative extraction and full resource utilization of most elements, completely avoids the generation of secondary waste residue, significantly improves the resource benefit and economic benefit, and provides a solution for the green and sustainable development of the secondary battery industry.

Description

Technical Field

[0001] This invention relates to the field of comprehensive recycling technology of industrial solid waste, specifically a method for preparing sodium zirconium silicate nanopowder using lithium slag as raw material. Background Technology

[0002] With the rapid growth of global demand for clean energy and efficient energy storage systems, sodium-ion batteries have attracted widespread attention as a potential alternative technology that is cost-effective, resource-rich, and highly safe. Solid-state electrolytes are one of the key materials for constructing high-safety, high-energy-density all-solid-state sodium-ion batteries. Among them, sodium zirconium silicon phosphate (Na3Zr2Si2PO4) with a NASICON (sodium superionic conductor) structure is particularly important. 12 Sodium ion peroxide (NZSPO) is considered one of the most promising solid electrolyte materials due to its high room-temperature sodium ion conductivity, good chemical stability, and wide electrochemical window.

[0003] Currently, the synthesis of NZSPO powder mainly relies on high-purity chemical raw materials (such as SiO2, ZrO2, Na2CO3, NH4H2PO4, etc.) through high-temperature solid-state methods or sol-gel methods. Although these methods can yield materials with good performance, they suffer from problems such as high raw material costs, high synthesis energy consumption, and complex process flows, which restrict the large-scale industrial application of NZSPO materials and the reduction of sodium-ion battery costs.

[0004] On the other hand, the rapid development of the lithium battery industry has generated a large amount of solid waste—lithium slag. This is the main residue produced after extracting lithium salts from ores such as spodumene and lepidolite. Its main component is aluminosilicate, and it also contains various elements such as lithium, sodium, potassium, iron, calcium, and magnesium that have not been fully recovered. Currently, the main methods of treating lithium slag are low-value stockpiling or simple use as building material raw materials (such as cement admixtures). This not only causes a serious waste of valuable resources such as aluminum and silicon, but also poses environmental risks. Although some studies have attempted to recover residual lithium or extract alumina from lithium slag, they generally suffer from problems such as long processes, poor selectivity, low comprehensive utilization rate, and limited product added value, failing to achieve a key breakthrough in the synergistic high-value utilization of multiple elements in the slag.

[0005] CN121023195A discloses a method for recovering scandium from lithium slag; CN120809755A discloses a lithium-copper composite anode prepared using lithium slag; CN119866954A discloses a method for preparing cat litter using lithium slag; CN116003158A discloses a method for preparing mullite porous ceramics using lithium slag; CN113548673A discloses a method for preparing molecular sieves using lithium slag. These methods recover and utilize lithium slag resources to varying degrees, but the utilization rate is low, and the economic value of the resulting products is not high.

[0006] Therefore, developing an innovative process to convert bulk lithium slag into high-performance NZSPO sodium ion conductor material would simultaneously address two key challenges: providing a high-value-added, fully resource-efficient new path for solid waste disposal in the lithium battery industry, and offering a low-cost, sustainable source of solid electrolyte material for sodium-ion batteries, resulting in significant economic and environmental benefits. The biggest technical bottleneck in the high-value recovery of lithium slag lies in the removal of complex symbiotic impurities (such as aluminum, magnesium, iron, and calcium) from the slag. Deep impurity removal significantly increases reagent consumption and environmental treatment costs, and it is difficult to completely eliminate trace impurities. Furthermore, there are significant batch-to-batch variations in the lithium slag processed, with varying impurity content. When these trace impurities remain in the final product as heterogeneous crystals, they severely block the transport channels of sodium ions in the NZSPO lattice, leading to a sharp decrease in the material's room-temperature ionic conductivity.

[0007] In summary, existing technologies lack a systematic method for efficiently and economically converting complex lithium slag directly into high-purity, high-performance NZSPO nanoparticles. This invention aims to overcome these shortcomings by selectively retaining aluminum in the slag, allowing it to enter the Zr or Si / P lattice sites of NZSPO in situ during sintering, significantly improving the bulk ionic conductivity. Furthermore, by measuring the effective components (Si, Al) in the activated slag liquid phase, and adaptively calculating and supplementing missing sodium, zirconium, and phosphorus sources, the target stoichiometry of the NASICON configuration is locked from the precursor stage, completely solving the problem of phase impurity caused by raw material fluctuations and providing a novel resource utilization solution. Summary of the Invention

[0008] In view of the above background, this invention addresses the technical bottlenecks in the existing technology, such as high cost of preparing zirconium silicon sodium phosphate materials, low added value of lithium slag resource utilization, and difficulty in directly synthesizing high-performance ionic conductors from complex solid waste. This invention aims to provide a method for converting lithium slag into high-performance zirconium silicon sodium phosphate nanopowder for sodium-ion batteries. Its core lies in providing an integrated process of "deep impurity removal - synergistic elemental regulation - structure-oriented synthesis." Low-iron aluminum silicon powder is obtained through gradient purification of slag, and this powder is used as the main silicon and aluminum source. Through precise batching, high-temperature sintering, and nano-sizing, aluminum-doped Na3Zr2Si2PO4 suitable for solid electrolytes or cathode additives is finally prepared. 12 This invention provides a low-cost key material solution for sodium-ion batteries, thereby achieving high-value utilization of solid waste. The invention achieves the above objectives through the following technical solutions:

[0009] A method for preparing sodium zirconium silicate phosphate nanopowder using lithium slag as raw material includes the following steps:

[0010] (S1) The lithium slag is subjected to slurry preparation, magnetic separation of slurry, treatment with reducing agent, acid leaching to remove iron, and solid-liquid separation to obtain low iron aluminum silicon powder.

[0011] (S2) The low-iron aluminum silicon powder is wet-mixed with zirconium-containing compounds, sodium-containing compounds and phosphorus-containing compounds, and then dried with solvent to obtain a mixed precursor.

[0012] (S3) The mixed precursors were sintered at high temperature to obtain sodium zirconium silicon phosphate, which was then crushed and ground to obtain sodium zirconium silicon phosphate nanopowder.

[0013] Further, in step (S1), the reducing agent is one of sodium sulfite, ascorbic acid, or sodium thiosulfate; the amount of reducing agent used is 5-10 wt% of the lithium slag mass; the acid leaching to remove iron is carried out by adding phosphoric acid; the phosphoric acid concentration is 1.0-5.0 mol / L, and the ratio of phosphoric acid volume to lithium slag mass is 3-5 mL:1 g.

[0014] Further, in step (S1), the obtained low-iron aluminum silicon powder has an iron content of less than 2.0%, an alumina content of 15-35 wt%, and a silicon dioxide content of 40-65 wt% by mass percentage.

[0015] Further, in step (S2), the zirconium-containing compound is selected from at least one of zirconium hydroxide and zirconium oxide; the sodium-containing compound is selected from at least one of sodium carbonate and sodium hydroxide; and the phosphorus-containing compound is at least one of ammonium dihydrogen phosphate and ammonium hydrogen phosphate.

[0016] Further, in step (S2), the molar ratio of each element in the mixed precursor is controlled as follows: Na:Zr:Al:Si:P=(3.0-3.1):(1.9-2.0):(0.01-0.1):(2.0):1; during wet mixing, additional silicon or aluminum sources are added according to the chemical composition of the product sodium zirconium silicon phosphate to precisely control the molar ratio of silicon to aluminum in the final product; the silicon source is silicon dioxide; the aluminum source is selected from at least one of alumina and aluminum hydroxide.

[0017] Further, in step (S3), the high-temperature sintering specifically involves: heating to 1000°C to 1150°C at a rate of 1-5°C / min in an air atmosphere and holding at that temperature for 4-8 hours; or, under a protective atmosphere, using segmented sintering, first pre-firing at 800-900°C for 2-4 hours to remove volatile components, and then heating to 1050-1200°C for sintering for 4-10 hours.

[0018] Further, in step (S3), the crushing and grinding includes first subjecting the sintered body to jaw crushing and disc grinding to obtain micron-sized coarse powder; then using at least one of high-energy ball milling, air jet milling, or sand milling processes to further process the micron-sized coarse powder into nanoparticles. The particle size of the nanoparticles is 30-300 nm.

[0019] Furthermore, in step (S3), the sodium zirconium silicon phosphate nanoparticles are aluminum-doped materials with a NASICON-type crystal structure and their general chemical formula is Na. 3+x Zr 2-x Al x Si2PO 12 Where 0.01≤x≤0.1; at 25℃, the ionic conductivity of the ceramic sheet formed by pressing and sintering the zirconium silicate nanopowder is not less than 1.0×10⁻⁶. -4 S / cm.

[0020] The nanoparticles obtained by the preparation method of this invention can be used in sodium-ion batteries as solid electrolytes or as ion-conducting additives. Specifically, they can be prepared as solid electrolytes by dry pressing and high-temperature sintering to form dense ceramic sheets; or the nanoparticles can be coated on the surface of a separator and dried to obtain solid electrolytes; or the coating of the positive electrode can contain the sodium zirconium silicon phosphate nanoparticles as ion-conducting additives.

[0021] The present invention achieves the following beneficial effects compared to the prior art:

[0022] This invention utilizes a simple, industrially suitable method to transform bulk lithium ore slag into high-performance NZSPO sodium ion conductor material. It selectively retains aluminum in the slag, allowing it to enter the Zr or Si / P lattice sites of NZSPO in situ during sintering, significantly improving the bulk ion conductivity. Furthermore, the effective components (Si, Al) in the activated slag liquid phase are measured, and missing sodium, zirconium, and phosphorus sources are adaptively calculated and supplemented. By locking the target stoichiometry of the NASICON configuration from the precursor stage, a sodium zirconium silicate nanopowder with beneficial electrochemical performance is obtained, which can be used as a solid electrolyte or ion-conducting additive. Attached Figure Description

[0023] Figure 1 This is an optical photograph of the lithium slag used in the examples;

[0024] Figure 2 This is an optical photograph of the aluminum-doped NZSPO electrolyte after sintering in Example 1;

[0025] Figure 3 This is a scanning electron microscope image of the aluminum-doped NZSPO electrolyte in Example 1;

[0026] Figure 4 The image shows the XRD pattern of the aluminum-doped NZSPO electrolyte in Example 1.

[0027] Figure 5 The image shows the AC impedance spectroscopy of the aluminum-doped NZSPO electrolyte in Example 1.

[0028] Figure 6 The graph shows the cycle performance of a sodium-ion battery with aluminum-doped NZSPO electrolyte in Example 1. Detailed Implementation

[0029] The following will further illustrate the above-described embodiments of the present invention with reference to specific examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention, and all technologies based on the above content of the present invention fall within the scope of the present invention.

[0030] The lithium slag was purchased from Ganfeng Lithium's spodumene slag, with a particle size of 1-5 mm and a moisture content of 10 wt.%. Its composition includes: Na₂O: 1.25 wt.%, MgO: 0.45 wt.%, Al₂O₃: 12.90 wt.%, SiO₂: 57.06 wt.%, P₂O₅: 0.12 wt.%, SO₃: 0.35 wt.%, K₂O: 3.85 wt.%, CaO: 2.15 wt.%, TiO₂: 0.28 wt.%, Cr₂O₃: 0.005 wt.%, MnO: 0.15 wt.%, Fe₂O₃: 10.20 wt.%, NiO: 0.003 wt.%, CuO: 0.008 wt.%, ZnO: 0.015 wt.%, Ga₂O₃: 0.004 wt.%, Rb₂O: 0.25wt.%, SrO: 0.012wt.%, ZrO2: 0.025wt.%, Nb2O5: 0.006wt.%.

[0031] Example 1

[0032] 100.0 g of lithium slag was slurried and magnetically separated, then 5.0 g of sodium sulfite was added for pre-reduction, followed by acid leaching and phosphating with 500 mL of 2.0 mol / L phosphoric acid. After solid-liquid separation, washing, and drying, low-iron aluminum-silicon powder was obtained (X-ray fluorescence spectrometry analysis showed SiO2 80.5 wt%, Al2O3 18.2 wt%, Fe 0.4 wt%). 4.20 g of this powder was used as the total aluminum source and part of the silicon source, and 72.08 g of zirconium oxide, 48.49 g of sodium carbonate, and 34.50 g of ammonium dihydrogen phosphate were added sequentially, with 32.67 g of SiO2 precisely added. The mixture was wet-milled in anhydrous ethanol and dried at 80 °C. The resulting precursor was placed in a muffle furnace and heated to 1100 °C in air at a rate of 3 °C / min, and held for 6 h. The sintered body was subjected to jaw crushing, disc grinding, and 4 hours of high-energy ball milling to finally obtain sodium zirconium silicon phosphate (NZSPO) nanopowder with an aluminum doping content of 0.05%. 3.05 Zr 1.95 Al 0.05 Si2PO 12 The particle size is approximately 300 nm.

[0033] Figures 2 to 4 These are optical photographs, scanning electron microscope (SEM) images, and X-ray diffraction (XRD) patterns of the sodium zirconium silicate (NZSPO) nanoparticles prepared in Example 1, demonstrating that Example 1 successfully processed industrial waste lithium slag ( Figure 1 ) is transformed into macroscopically dense and microscopically uniform aluminum-doped NZSPO solid electrolyte ceramic sheets ( Figure 2 ).from Figure 3The SEM images show that the sintered electrolyte grains are well-developed and densely stacked, effectively eliminating grain boundary pores. Figure 4 The XRD pattern further confirmed that the material exhibits a high-purity NASICON-type crystal structure, indicating that the aluminum element extracted from the slag has been successfully doped in situ without generating obvious insulating byproduct impurity phases.

[0034] Based on this structure, a CR2032 button cell with a standard stainless steel gasket was assembled, and the ionic conductivity of the deep eutectic electrolyte was calculated by AC impedance spectroscopy. Figure 5 Electron impedance spectroscopy (EIS) revealed that the high-purity, high-density microstructure, in synergy with the free sodium ions introduced by aluminum doping, significantly reduced the bulk and grain boundary impedance of the material, resulting in an excellent room-temperature sodium ion conductivity of 2 × 10⁻⁶. -3 S / cm.

[0035] Example 2

[0036] The remaining steps of Example 2 are exactly the same as those of Example 1, except that the aluminum doping amount is adjusted to 0.01, and the target product has the chemical formula Na. 3.01 Zr 1.99 Al 0.01 Si2PO 12 Accordingly, the weighing mass of the corresponding precursor raw materials was strictly adjusted according to the stoichiometric ratio. In the subsequent examples and comparative examples, except for the ratio variables specifically mentioned, the basic process parameters such as the proportion of reducing agent in the raw material pretreatment, the acid leaching concentration, and the heating and holding regimes for high-temperature synthesis were kept the same as in Example 1, and will not be repeated hereafter.

[0037] Example 3

[0038] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.02.

[0039] Example 4

[0040] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.03.

[0041] Example 5

[0042] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.04.

[0043] Example 6

[0044] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.06.

[0045] Example 7

[0046] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.07.

[0047] Example 8

[0048] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.08.

[0049] Example 9

[0050] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.09.

[0051] Example 10

[0052] The rest is the same as in Example 1, except that the amount of aluminum doping is adjusted to 0.10.

[0053] Comparative Example 1

[0054] High-purity reagent-grade chemicals were used as both silicon and aluminum sources to ultimately prepare sodium zirconium silicon phosphate (Na₂SO₄) with an aluminum doping concentration of 0.05%. 3.05 Zr 1.95 Al 0.05 Si2PO 12 Nanoparticles.

[0055] Application examples

[0056] The NZSPO nanopowder from the above examples and comparative examples was used to prepare a solid electrolyte membrane: NZSPO nanopowder and PVDF binder were weighed at a mass ratio of 9:1, added to an appropriate amount of organic solvent, and thoroughly ground or magnetically stirred to obtain a uniform NZSPO coating slurry. The slurry was then uniformly coated onto the surface of the substrate membrane using a doctor blade. Subsequently, it was dried in a forced-air oven at 60°C for 2 hours, and then placed in a vacuum oven at 60°C for 12 hours to thoroughly remove the organic solvent from the coating. After drying, the resulting NZSPO modified membrane was cut to the required size and placed in a glove box for later use.

[0057] The preparation and testing process of sodium-ion batteries is as follows: Nickel-iron-manganese ternary cathode powder, SuperP, and PVDF binder were weighed at a mass ratio of 8:1:1, ground and mixed using a mortar and pestle to obtain a uniform cathode slurry. The slurry was then coated onto the surface of aluminum foil using a scraper, dried in a forced-air oven at 80°C for 2 hours, and then dried in a vacuum oven at 80°C for 12 hours to thoroughly remove organic solvents from the electrode. After drying, the mass of the active material of the electrode was weighed and placed in a glove box for later use. The solid electrolyte membrane prepared in the examples / comparative examples was used to assemble CR2032 button batteries with a nickel-iron-manganese ternary cathode / solid electrolyte membrane / sodium metal anode. Performance testing was conducted using a LAND charge-discharge tester at a test temperature of 25°C, a test voltage range of 2.0-4.0V, and a test rate of 0.5C.

[0058] Ionic conductivity testing: The prepared NZSPO nanopowder was placed in a mold and pressed into a disc under a pressure of 200 MPa. The disc was then sintered in a muffle furnace at 1100 °C for 12 h to obtain a dense NZSPO ceramic disc. Both sides of the ceramic disc were sanded smooth, and its thickness and surface area were accurately measured using a micrometer. A conductive silver paste (or sputtered gold film) was then uniformly coated on both sides of the ceramic disc as a blocking electrode, and the disc was dried and cured in a forced-air oven at 120 °C for 2 h. After drying, the disc was transferred to an argon-filled glove box and assembled into a symmetrical coin cell for later use. Electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation, with the test frequency range set from 1 MHz to 0.1 Hz and the AC voltage amplitude set to 10 mV. The bulk impedance was obtained by fitting a semicircle in the high-frequency region, and its room-temperature ionic conductivity was calculated. The results are shown in Table 1 below.

[0059] Figure 6 In Example 1, aluminum-doped NZSPO nanopowder was used to prepare a solid electrolyte, which was matched with the electrochemical performance of a full cell. A CR2032 coin cell with a nickel-iron-manganese ternary cathode / solid electrolyte membrane / sodium metal anode was assembled, and its cycle performance was tested. The sodium-ion battery assembled using this electrolyte exhibited excellent capacity retention and long-term cycle stability, proving that this NZSPO electrolyte, converted from waste residue, possesses excellent electrochemical window and interfacial compatibility. Table 1 systematically summarizes the ionic conductivity and full-cell cycle performance data of each electrolyte in Examples 1-10 and Comparative Example 1. The results strongly confirm that the NZSPO solid electrolyte provided by this invention, prepared from bulk solid waste lithium slag through in-situ conversion, shows excellent practical application prospects. This material not only greatly reduces the synthesis cost, but its electrochemical performance also successfully matches or even rivals that of similar products prepared from traditional high-purity reagent-grade raw materials, possessing extremely high industrial application value.

[0060] Table 1 Electrochemical performance of NZSPO nanopowder as a solid electrolyte

[0061]

Claims

1. A method for preparing sodium zirconium silicate phosphate nanopowder using lithium slag as raw material, characterized in that, Includes the following steps: (S1) The lithium slag is subjected to slurry preparation, magnetic separation of slurry, treatment with reducing agent, acid leaching to remove iron, and solid-liquid separation to obtain low iron aluminum silicon powder. (S2) The low-iron aluminum silicon powder is wet-mixed with zirconium-containing compounds, sodium-containing compounds and phosphorus-containing compounds, and then dried with solvent to obtain a mixed precursor. (S3) The mixed precursors were sintered at high temperature to obtain sodium zirconium silicon phosphate, which was then crushed and ground to obtain sodium zirconium silicon phosphate nanopowder.

2. The method according to claim 1, characterized in that, In step (S1), the reducing agent is one of sodium sulfite, ascorbic acid or sodium thiosulfate; the amount of reducing agent used is 5-10 wt% of the lithium slag mass.

3. The method according to claim 1, characterized in that, In step (S1), the iron removal treatment by adding phosphoric acid is carried out; the concentration of phosphoric acid is 1.0-5.0 mol / L, and the volume ratio of phosphoric acid to lithium slag is 3-5 mL: 1 g.

4. The method according to claim 1, characterized in that, In step (S1), the obtained low-iron aluminum silicon powder has an iron content of less than 2.0%, an alumina content of 15-35 wt%, and a silicon dioxide content of 40-65 wt% by mass percentage.

5. The method according to claim 1, characterized in that, In step (S2), the zirconium-containing compound is selected from at least one of zirconium hydroxide and zirconium oxide; the sodium-containing compound is selected from at least one of sodium carbonate and sodium hydroxide; and the phosphorus-containing compound is at least one of ammonium dihydrogen phosphate and ammonium hydrogen phosphate.

6. The method according to claim 1, characterized in that, In step (S2), the molar ratio of each element in the mixed precursor is controlled as follows: Na:Zr:Al:Si:P = (3.0-3.1):(1.9-2.0):(0.01-0.1):(2.0):1; during wet mixing, additional silicon or aluminum sources are added according to the chemical composition of the product sodium zirconium silicon phosphate to precisely control the molar ratio of silicon to aluminum in the final product; the silicon source is silicon dioxide; the aluminum source is selected from at least one of alumina and aluminum hydroxide.

7. The method according to claim 1, characterized in that, In step (S3), the high-temperature sintering specifically involves: heating to 1000°C to 1150°C at a rate of 1-5°C / min in an air atmosphere and holding at that temperature for 4-8 hours; or, under a protective atmosphere, using segmented sintering, first pre-firing at 800-900°C for 2-4 hours to remove volatile components, and then heating to 1050-1200°C for sintering for 4-10 hours.

8. The method according to claim 1, characterized in that, In step (S3), the crushing and grinding includes first subjecting the sintered body to jaw crushing and disc grinding to obtain micron-sized coarse powder; then using at least one of high-energy ball milling, air jet milling or sand milling processes to further process the micron-sized coarse powder into nanoparticles; the particle size of the nanoparticles is 30-300 nm.

9. The method according to claim 1, characterized in that, In step (S3), the general chemical formula of sodium zirconium silicate phosphate nanoparticles is Na. 3+x Zr 2-x Al x Si2PO 12 Where 0.01≤x≤0.1; at 25℃, the ionic conductivity of the ceramic sheet formed by pressing and sintering the zirconium silicate nanopowder is not less than 1.0×10⁻⁶. -4 S / cm.

10. The use of the sodium zirconium silicate nanopowder prepared by the method according to any one of claims 1-9 in sodium-ion batteries, characterized in that, The zirconium silicate sodium nanoparticles are used as a solid electrolyte or as a collected ion-conducting additive. Furthermore, the zirconium silicon sodium phosphate nanoparticles are dry-pressed and sintered at high temperature to form dense ceramic sheets to prepare a solid electrolyte; or the zirconium silicon sodium phosphate nanoparticles are coated on the surface of a separator and dried to obtain a solid electrolyte; or the coating of the positive electrode contains the zirconium silicon sodium phosphate nanoparticles as an ion-conducting additive.

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