NASICON oxide solid electrolyte for improving cycle performance of battery and preparation method and application of NASICON oxide solid electrolyte

Abstract

The invention belongs to the technical field of solid electrolytes, and relates to an NASICON oxide solid electrolyte for improving the cycle performance of a battery as well as a preparation method and application of the NASICON oxide solid electrolyte. According to the NASICON oxide solid electrolyte, generation of by-products is successfully inhibited through optimization of the preparation method, grain boundary resistance is effectively reduced, the overall performance of the material is improved, and it is worthy of notice that gas (such as NOX) released in the decomposition process forms a sodium-philic interface layer containing NO2 <->, NxOy and N3 <-> on the surface of an electrolyte sheet, so that the performance of the NASICON oxide solid electrolyte is improved. Due to the existence of the components, rapid transmission of sodium ions is greatly promoted, and the interface contact condition between the electrolyte and an electrode is improved, so that not only is the ionic conductivity of the electrolyte improved, but also the critical current density of the electrolyte is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolytes and relates to a NASICON oxide solid electrolyte for improving battery cycle performance, a preparation method and an application thereof. Background Art

[0002] Sodium-ion batteries (Na-ion batteries) are widely considered to be the most promising alternative to lithium-ion batteries for large-scale energy storage applications due to their low raw material costs and the abundance of sodium resources (the Earth's crust contains 2.64%). This type of battery is particularly suitable for electric vehicles and grid-level energy storage systems because they can significantly reduce production costs and alleviate dependence on scarce lithium resources. However, the carbonate organic electrolytes used in traditional Na-ion batteries have some inherent defects, such as flammability, volatility, and poor thermal stability. These problems can easily lead to serious safety hazards such as leakage, combustion, and even explosion.

[0003] In order to solve these problems, all-solid-state sodium batteries based on solid electrolytes have emerged. This type of battery has attracted widespread attention from academia and industry due to its inherent safety and long cycle life. As one of the core components of all-solid-state sodium batteries, NASICON (Na Superionic Conductor) structured solid electrolyte has a unique three-dimensional ion diffusion channel, a wide electrochemical window (>4.5V vs. Na / Na + ), excellent thermal stability, and environmentally friendly properties, making it a hot material system in current research. NASICON can optimize its ion transport properties by adjusting the element doping of the Zr / Si / P sites, thereby further improving the overall performance of the battery.

[0004] While NASICON solid electrolytes offer numerous advantages, existing technologies still have shortcomings. A major challenge lies in the poor interfacial compatibility between NASICON electrolytes and the metallic sodium anode. This means that during the battery's charge and discharge processes, a series of uncontrollable chemical or electrochemical side reactions occur between the electrolyte and the metallic sodium. This not only causes the interfacial impedance to rise rapidly, but also severely impacts the battery's long-term stability and service life.

[0005] A Chinese patent document (CN108695552A) discloses a NASICON-structured sodium-ion solid electrolyte, its preparation method, and a solid-state sodium-ion battery. However, the improvement in its limiting current density is not significant, which means that the electrolyte material may not be able to provide sufficient current density support in application scenarios with high power requirements, limiting its use under conditions requiring fast charging and discharging or high current operation. At the same time, long-term cycling cannot be guaranteed under high current, which may be due to the instability of the interface between the electrolyte and the electrode, changes in the microstructure of the electrolyte itself, or other intrinsic factors.

[0006] A Chinese patent document (CN116799291A) discloses a NASICON-type solid electrolyte, a cathode material, and its preparation method and application. However, its electrical conductivity needs to be further improved. Low electrical conductivity directly limits the battery's charge and discharge efficiency, increases the battery's internal resistance, leads to increased energy loss, and affects the battery's overall performance. This problem is particularly prominent in high-power demand application scenarios, such as electric vehicles and large-scale energy storage systems. Summary of the Invention

[0007] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to propose a NASICON oxide solid electrolyte with excellent sodium interface stability and improved battery cycle performance.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] A NASICON oxide solid electrolyte for improving battery cycle performance, wherein the electrolyte chemical formula is Na 3±i Zr 1.9 Zn 0.1 Si 2+y P 1-y O 12 , where 0≤i<1, 0.1≤y≤0.6.

[0010] As an advantage, the electrolyte chemical formula is Na 3±i Zr 1.9 Zn 0.1 Si 2+y P 1-y O 12 , where 0.4≤i≤0.6, 0.1≤y≤0.3.

[0011] The present invention also provides a method for preparing the NASICON oxide solid electrolyte for improving battery cycle performance, the method comprising the following steps:

[0012] S1. According to the above general formula, the sodium source, phosphorus source, zirconium source, silicon source and zinc source in stoichiometric ratio are weighed respectively, and wet mixed and dried for the first time;

[0013] S2, then high-temperature sintering, and then a second wet mixing and drying to obtain a precursor powder;

[0014] S3. Mixing the precursor powder with a binder solution, isostatically pressing the mixture to form a green body, and then sintering the green body to obtain the NASICON oxide solid electrolyte.

[0015] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, the sodium source is NaNO3; and / or the phosphorus source is at least one of NH4H2PO4, NaH2PO4, Na2HPO4, P2O5; and / or the zirconium source is ZrO2; and / or the silicon source is SiO2; and / or the zinc source is ZnO.

[0016] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, the wet mixing is mechanical ball milling or high-energy ball milling, wherein the ball-to-material ratio during the ball milling process is (2-6):1, the ball milling speed is 200-600 rpm, the ball milling time is 2-12 hours, and the ball milling solvent is at least one of anhydrous ethanol, isopropanol, n-propanol, acetone, and butanol.

[0017] Preferably, the drying comprises vacuum drying or forced air drying, and the drying temperature is 40-90°C.

[0018] In the above-mentioned method for preparing a NASICON oxide solid electrolyte that improves battery cycle performance, step S2 is sintered at a high temperature in a pure oxygen atmosphere at a temperature of 500-1200°C for 2-24 hours. The present invention controls the sintering temperature to 500-1200°C in a pure oxygen environment for 2-24 hours to promote the diffusion of oxygen vacancies and lattice mass transfer, significantly improve the density of the material, and reduce pores and microcracks at the grain boundaries. A pure oxygen environment can accelerate grain growth through a liquid phase sintering mechanism (such as the formation of a Zn-enriched liquid phase), while promoting grain boundary migration and eliminating intergranular pores, thereby forming a dense structure. This directly reduces the grain boundary resistance and enhances the overall ionic conductivity.

[0019] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, the mass ratio of the precursor powder to the binder solution in step S3 is (10-50):1.

[0020] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, the concentration of the binder solution is 1-800 mg / ml, wherein the binder is at least one of polyvinyl alcohol, polyvinyl butyral, polydopamine, and polyacrylic acid.

[0021] The present invention is achieved by mixing the precursor powder with a binder solution in a specific concentration range (1-800 mg / ml) in step S3. These binders form a close physical contact by filling the microscopic gaps between the electrode material and the solid electrolyte. This filling not only reduces the gaps and cracks at the interface, but also significantly reduces the charge transfer impedance, improves the transmission efficiency of electrons and ions, and in the pressing process, the binder makes the electrolyte powder easier to form. It plays the role of a "bridge", helping to form a stronger bond between the particles, ensuring that the shape can be maintained during the pressing process and not prone to breakage or cracking, especially when the isostatic pressing treatment is performed later, the presence of the binder can effectively prevent the body from being broken due to uneven pressure, thereby ensuring the quality and consistency of the green body. This is crucial for the successful implementation of the subsequent sintering process, because high-quality green bodies can be converted into final products with uniform structure and stable performance.

[0022] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, the pressure used in the isostatic pressing in step S3 is 10-700 MPa, and the holding time is 1-320 min.

[0023] In the above-mentioned method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance, step S3 sintering includes a first-stage sintering and a second-stage sintering, wherein the temperature of the first-stage sintering is 550-900°C and the time is 1-4 hours; the temperature of the second-stage sintering is 1100-1300°C and the time is 2-24 hours.

[0024] The present invention adopts a two-stage sintering method as one of the key processes to improve the performance of NASICON oxide solid electrolyte. The first stage sintering is carried out at a temperature of 550 to 900°C and lasts for 1-4 hours. It aims to achieve preliminary bonding between precursor particles at a relatively low temperature to form a uniform microstructure framework. This stage not only effectively removes residual organic matter (such as binders), but also avoids the stress concentration problem that may be caused by too rapid densification at high temperatures, thereby ensuring the integrity and uniformity of the material structure. The subsequent second stage sintering raises the temperature to 1100 to 1300°C and lasts for 2 to 24 hours. Under this higher temperature condition, the grains are fully grown and the material is highly densified. High temperature promotes grain boundary migration and pore closure, significantly reduces microcracks and grain boundary defects inside the material, thereby reducing grain boundary resistance and improving ionic conductivity. Through this two-stage sintering method, not only can the microstructural development of NASICON oxide solid electrolyte be precisely controlled, but also potential structural defects can be minimized, and ultimately a material with both excellent electrochemical properties and mechanical stability is obtained. This method provides important support for the manufacture of high-performance and long-life solid-state sodium-ion batteries.

[0025] The present invention also provides an all-solid-state sodium secondary battery, comprising a positive electrode, a negative electrode and the above-mentioned NASICON oxide solid electrolyte or the NASICON oxide solid electrolyte prepared by the above-mentioned method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The NASICON oxide solid electrolyte of the present invention successfully suppresses the generation of by-products by optimizing the preparation method, effectively reduces the grain boundary resistance, and improves the overall performance of the material. It is worth noting that the gases (such as NOX) released during the decomposition process form NO on the surface of the electrolyte sheet. 2- , NxOy and N 3- The presence of these components greatly promotes the rapid transport of sodium ions and improves the interfacial contact between the electrolyte and the electrode, thereby not only improving the ionic conductivity of the electrolyte but also enhancing its critical current density.

[0028] 2. The NASICON oxide solid electrolyte provided by the present invention exhibits excellent sodium stability and a high critical current density while ensuring high ionic conductivity. This means that the electrolyte can not only maintain high ion transport efficiency in practical applications, but also ensure the safety and stability of the battery during operation. In particular, in application scenarios such as large-scale energy storage systems or electric vehicles that require high-performance batteries, this electrolyte material with both high conductivity and good stability is particularly important.

[0029] 3. The preparation method of the NASICON oxide solid electrolyte provided by the present invention has the characteristics of simple operation and strong practicality, and is particularly suitable for large-scale production. This not only means that the method can effectively reduce production costs and improve production efficiency, but also provides the possibility of improving the performance of the final product. By simplifying the preparation process, more research institutions and enterprises can more easily replicate and apply this technology, thereby promoting the development and commercialization of all-solid-state sodium ion battery technology. In summary, the present invention optimizes the performance of the NASICON oxide solid electrolyte from multiple aspects, providing a solid foundation for achieving efficient, safe and economical energy storage solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Scanning electron microscopy image of oxide solid electrolyte;

[0031] Figure 2 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 X-ray diffraction spectrum of oxide solid electrolyte;

[0032] Figure 3 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 AC impedance spectroscopy of oxide solid electrolytes;

[0033] Figure 4 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Limiting current density curve of sodium||sodium symmetric battery with oxide solid electrolyte;

[0034] Figure 5 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Comparison of electronic conductivity of oxide solid electrolytes;

[0035] Figure 6 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Comparison of activation energies of oxide solid electrolytes;

[0036] Figure 7 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Long cycle curve of sodium||sodium symmetric battery with oxide solid electrolyte;

[0037] Figure 8 is Na in Example 1 of the present invention3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Long cycle curve of all-solid-state battery with oxide solid electrolyte at 1C rate; DETAILED DESCRIPTION

[0038] Below by specific embodiment and accompanying drawing, technical scheme of the present invention is further described explanation, it should be understood that specific embodiment described herein is only for helping to understand the present invention, is not used for specific limitation of the present invention.And accompanying drawing used herein, is only for better illustrating the disclosure of the present invention, does not have limiting effect on protection scope.If no special instructions, the raw materials adopted in the embodiment of the present invention are all raw materials commonly used in this area, and the method adopted in the embodiment is all conventional method in this area.

[0039] Example 1:

[0040] This embodiment Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The preparation method of the oxide solid electrolyte is as follows:

[0041] S1. Weigh Na₂NO₃, ZrO₂, SiO₂, NH₄H₂PO₄, and ZnO (99%+ purity) in the stoichiometric ratio and place them in an agate ball mill. Add zirconia balls at a ball-to-material ratio of 5:1. Add anhydrous ethanol and mill at 400 rpm for 8 hours. After milling, place the mixture in an air drying oven at 80°C to dry out the solvent.

[0042] S2. The dried powder was ground evenly in an agate mortar and placed in a tube furnace for sintering. The sintering atmosphere was pure oxygen, the sintering temperature was 900 degrees, and the sintering time was 12 hours. The sintered powder was placed in an agate ball mill again, and zirconia balls were added according to the ball-to-material ratio of 5:1. Anhydrous ethanol was added, and the ball milling speed was 400 rpm. The ball milling time was 8 hours. After the ball milling was completed, the mixed material was placed in a blast drying oven at 80°C to dry the solvent and obtain Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O12 Precursor.

[0043] S3. Weigh a certain amount of Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor was mixed with polyvinyl alcohol aqueous solution (concentration of 10 mg / ml) (Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor and polyvinyl alcohol aqueous solution (at a mass ratio of 40:1) were placed in a custom mold and isostatically pressed to form a green body at a pressure of 200 MPa for 5 minutes. The green body was then sintered in a tubular furnace in a two-stage process using pure oxygen. The first stage was at 700°C for one hour, and the second stage was at 1250°C for six hours. After annealing, the resulting high-entropy NASICON oxide solid electrolyte sheet was obtained.

[0044] Figure 1 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Scanning electron microscope image of the oxide solid electrolyte; it can be seen from the figure that the oxide solid electrolyte of the present invention is densely stacked when sintered in an oxygen environment, and the Zn-rich phase formed by sintering promotes sintering densification and grain growth, which is beneficial to the improvement of electrical conductivity.

[0045] Example 2:

[0046] This embodiment Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The preparation method of the oxide solid electrolyte is as follows:

[0047] S1. Weigh Na2CO3, ZrO2, SiO2, NH4H2PO4, and ZnO (99%+ purity) in the stoichiometric ratio and place them in an agate ball mill. Add zirconia balls at a ball-to-material ratio of 5:1. Add anhydrous ethanol and mill at 400 rpm for 8 hours. After milling, place the mixture in an air drying oven at 80°C to dry out the solvent.

[0048] S2. The dried powder was ground evenly in an agate mortar and placed in a tube furnace for sintering. The sintering atmosphere was pure oxygen, the sintering temperature was 900 degrees, and the sintering time was 12 hours. The sintered powder was placed in an agate ball mill again, and zirconia balls were added according to the ball-to-material ratio of 5:1. Anhydrous ethanol was added, and the ball milling speed was 400 rpm. The ball milling time was 8 hours. After the ball milling was completed, the mixed material was placed in a blast drying oven at 80°C to dry the solvent and obtain Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Precursor.

[0049] S3. Weigh a certain amount of Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor was mixed with polyvinyl alcohol aqueous solution (concentration of 10 mg / ml) (Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor and polyvinyl alcohol aqueous solution (at a mass ratio of 40:1) were placed in a custom mold and isostatically pressed to form a green body at a pressure of 200 MPa for 5 minutes. The green body was then sintered in a tubular furnace in a two-stage process using pure oxygen. The first stage was at 700°C for one hour, and the second stage was at 1250°C for six hours. After annealing, the resulting high-entropy NASICON oxide solid electrolyte sheet was obtained.

[0050] Example 3:

[0051] This embodiment Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The preparation method of the oxide solid electrolyte is as follows:

[0052] S1. Weigh NaOH, ZrO2, SiO2, NH4H2PO4, and ZnO (99%+ purity) in the stoichiometric ratio and place them in an agate ball mill. Add zirconia balls at a ball-to-material ratio of 5:1. Add anhydrous ethanol and mill at 400 rpm for 8 hours. After milling, place the mixture in an air drying oven at 80°C to dry out the solvent.

[0053] S2. The dried powder was ground evenly in an agate mortar and placed in a tube furnace for sintering. The sintering atmosphere was pure oxygen, the sintering temperature was 900 degrees, and the sintering time was 12 hours. The sintered powder was placed in an agate ball mill again, and zirconia balls were added according to the ball-to-material ratio of 5:1. Anhydrous ethanol was added, and the ball milling speed was 400 rpm. The ball milling time was 8 hours. After the ball milling was completed, the mixed material was placed in a blast drying oven at 80°C to dry the solvent and obtain Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Precursor.

[0054] S3. Weigh a certain amount of Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor was mixed with polyvinyl alcohol aqueous solution (concentration of 10 mg / ml) (Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The precursor and polyvinyl alcohol aqueous solution (at a mass ratio of 40:1) were placed in a custom mold and isostatically pressed to form a green body at a pressure of 200 MPa for 5 minutes. The green body was then sintered in a tubular furnace in a two-stage process using pure oxygen. The first stage was at 700°C for one hour, and the second stage was at 1250°C for six hours. After annealing, the resulting high-entropy NASICON oxide solid electrolyte sheet was obtained.

[0055] Example 3:

[0056] The only difference from Example 1 is that the sodium source is Na2CO3 and Na2NO3 in a mass ratio of 1:1.

[0057] Example 4:

[0058] The only difference from Example 1 is that the sodium source is NaOH and NaNO3 in a mass ratio of 1:1.

[0059] Example 5:

[0060] The only difference from Example 1 is that the high-temperature sintering treatment in step S2 is not performed. After the first wet mixing and drying, the binder solution is directly mixed and the green body is formed after isostatic pressing.

[0061] Example 6:

[0062] The only difference from Example 1 is that no polyvinyl alcohol aqueous solution is added in step S3.

[0063] Example 7:

[0064] The only difference from Example 1 is that step S3 only performs the first sintering process.

[0065] Example 8:

[0066] The only difference from Example 1 is that step S3 only performs the second sintering process.

[0067] Comparative Example 1:

[0068] The only difference from Example 1 is that the chemical formula of the oxide solid electrolyte is Na2Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 .

[0069] Comparative Example 2:

[0070] The only difference from Example 1 is that the chemical formula of the oxide solid electrolyte is Na 3.5 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 .

[0071] Comparative Example 3:

[0072] The only difference from Example 1 is that the chemical formula of the oxide solid electrolyte is Na 3.4 Zr 1.9 Zn 0.1 Si 2.9 P 0.1 O 12 .

[0073] Comparative Example 4:

[0074] The only difference from Example 1 is that the chemical formula of the oxide solid electrolyte is Na 3.4 Zr 1.9 Zn 0.1 Si2PO 12

[0075] Gold was plated on both sides of the oxide solid electrolyte sheets prepared in Examples 1-8 and Comparative Examples 1-4 by ion sputtering, and their room temperature ionic conductivity was tested.

[0076] Symmetrical batteries were assembled using metallic sodium as the symmetrical electrode and the oxide solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-4 as the electrolyte layer. Cyclic tests were performed using a BlueDian CT2001A battery testing system, and the limiting current density was tested at 60°C.

[0077] Gold was plated on both sides of the oxide solid electrolyte sheets prepared in Examples 1-8 and Comparative Examples 1-4 by ion sputtering, and their room temperature electronic conductivity was tested.

[0078] Gold was plated on both sides of the oxide solid electrolyte sheets prepared in Examples 1-8 and Comparative Examples 1-4 by ion sputtering, and their ionic conductivity was tested at -20°C to 80°C, and their activation energy was calculated.

[0079] Sodium metal was used as the symmetrical electrode, and the oxide solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-4 were used as the electrolyte layer to assemble a symmetrical battery. Cyclic testing was performed using a Blue Power CT2001A battery testing system. The test conditions were as follows: the battery was heated at 60°C and the current density was 5 mA cm -2 The cycle time can be stabilized.

[0080] An all-solid-state battery was assembled using the oxide solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-4, a Na₃V₂(PO₄)₃ positive electrode, and a metallic sodium negative electrode. The ball-milled Na₃V₂(PO₄)₃ positive electrode, conductive agent SP, and binder PEO were mixed in a mass ratio of 70:20:10. An appropriate amount of acetonitrile was added as a solvent, and an appropriate amount of NaFSI was added as a conductive sodium salt to form a positive electrode slurry. The molar ratio of ether radicals to NaFSI was 14:1. The positive electrode slurry was evenly coated on one side of the NASICON-structured sodium ion solid electrolyte sheet described above and dried at 80°C. The coated electrolyte sheet was transferred to an inert atmosphere glove box, and a metallic sodium sheet was loaded on the other side. The battery was assembled and sealed to obtain a solid-state sodium ion battery. Electrochemical performance testing of the battery was performed using a Blue Power CT2001A battery test system. Charge and discharge voltages ranged from 2.5 to 3.8 V, and the rate was 1C, with constant-rate charge and discharge.

[0081] Table 1: Performance test results of oxide solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-4

[0082]

[0083] Table 2: Battery performance test results of oxide solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-4

[0084]

[0085]

[0086] In the table, / indicates that the result cannot be detected.

[0087] Figure 2 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 X-ray diffraction spectrum of oxide solid electrolyte; As can be seen from the figure, Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The crystalline material contained in the oxide solid electrolyte structure is mainly monoclinic Na3Zr2Si2PO 12 (PDF 84-1200).

[0088] Figure 3 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 AC impedance spectrum of oxide solid electrolyte; compared with Example 2, Na3Zr2Si2PO in Example 1 12 The ionic conductivity of the oxide solid electrolyte is increased by 180%.

[0089] Figure 4 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12The limiting current density curve of sodium||sodium symmetric battery of oxide solid electrolyte; compared with Example 2, Na3Zr2Si2PO in Example 1 12 The oxide solid electrolyte exhibits excellent resistance to sodium dendrites.

[0090] Figure 5 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Comparison of electronic conductivity of oxide solid electrolytes; relative to Example 1, Na in Example 2 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The electronic conductivity of the oxide solid electrolyte is reduced by about 3 times.

[0091] Figure 6 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Comparison of activation energies of oxide solid electrolytes; Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The activation energy of the oxide solid electrolyte is 0.244 eV.

[0092] Figure 7 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Sodium oxide solid electrolyte | | sodium symmetric battery long cycle curve; From the figure, we can see that the Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolytes exhibit excellent stability to sodium.

[0093] Figure 8 is Na in Example 1 of the present invention 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolyte and Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 The long cycle curve of the all-solid-state battery with oxide solid electrolyte at 1C rate; it can be seen from the figure that the Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 Oxide solid electrolytes exhibit excellent electrochemical performance.

[0094] In summary, through Examples 1-8 and Comparative Examples 1-4, it can be seen that sodium nitrate is beneficial to improving the ionic conductivity and limiting current density of the solid electrolyte, and has excellent sodium stability. The long-cycle stability of the all-solid-state sodium secondary battery prepared by further using the oxide solid electrolyte is better. The advantage of sodium nitrate as a sodium source is mainly reflected in its ability to regulate the structure of its decomposition products. Sodium nitrate decomposes into Na2O and nitrogen oxide gas during high-temperature sintering, which promotes the formation of the intermediate phase and optimizes the size of the sodium ion transmission channel, making it closer to the ideal value (about ), thereby improving the sodium ion migration efficiency and making the prepared NASICON electrolyte obtain high conductivity (5.4×10 -3 S / cm). Compared with other sodium sources (such as Na2CO3 or NaOH), sodium nitrate decomposes more thoroughly, reducing the residual impurity phase, thereby improving the purity of the NASICON main phase. The presence of impurity phases usually increases the grain boundary resistance, while NaNO3 inhibits the formation of such by-products through high-temperature reactions. These factors work together to generate NO on the entire electrolyte surface.2- 、N x O y 、N 3- , enhance the interface contact between electrolyte and electrode, thereby increasing the critical current density (CCD: 11.8mA / cm 2 ) and long cycle stability (2400 hours).

[0095] The parts of the embodiment herein that are not exhaustive of the midpoint values ​​of the technical scope claimed for protection by the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope claimed for protection by the present invention; at the same time, in all the embodiments listed or not listed in the solutions of the present invention, each parameter in the same embodiment merely represents an example of its technical solution (i.e., a feasible solution), and there is no strict coordination and limitation relationship between the parameters, wherein the parameters can be replaced with each other without violating the axioms and the claims of the present invention, unless otherwise stated.

[0096] The technical means disclosed in the solutions of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical solutions composed of any combination of the above technical features. The above is a specific embodiment of the present invention. It should be noted that for those skilled in the art, various improvements and modifications can be made without departing from the principles of the present invention, and such improvements and modifications are also considered to be within the scope of protection of the present invention.

[0097] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A NASICON oxide solid electrolyte for improving battery cycle performance, characterized in that: The electrolyte chemical formula is Na 3±i Zr 1.9 Zn 0.1 Si 2+y P 1-y O 12 , where 0≤i<1, 0.25≤y≤0.

5.

2. A method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 1, characterized in that: The method comprises the following steps: S1. Weigh the sodium source, phosphorus source, zirconium source, silicon source and zinc source in stoichiometric proportions according to the general formula of claim 1, perform a first wet mixing and drying; S2, then high-temperature sintering, and then a second wet mixing and drying to obtain a precursor powder; S3. Mixing the precursor powder with a binder solution, isostatically pressing the mixture to form a green body, and then sintering the green body to obtain the NASICON oxide solid electrolyte.

3. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: The sodium source is NaNO3; and / or the phosphorus source is at least one of NH4H2PO4, NaH2PO4, Na2HPO4, P2O5; and / or the zirconium source is ZrO2; and / or the silicon source is SiO2; and / or the zinc source is ZnO.

4. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: The wet mixing is mechanical ball milling or high-energy ball milling, wherein the ball-to-material ratio during the ball milling process is (2-6):1, the ball milling speed is 200-600 rpm, the ball milling time is 2-12 hours, and the ball milling solvent is at least one of anhydrous ethanol, isopropanol, n-propanol, acetone, and butanol.

5. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: Step S2: high temperature sintering in a pure oxygen atmosphere at a temperature of 500-1200° C. for 2-24 hours.

6. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: In step S3, the mass ratio of the precursor powder to the binder solution is (10-50):

1.

7. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2 or 6, characterized in that: The concentration of the binder solution is 1-800 mg / ml, wherein the binder is at least one of polyvinyl alcohol, polyvinyl butyral, polydopamine and polyacrylic acid.

8. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: The pressure used in the isostatic pressing in step S3 is 10-700 MPa, and the holding time is 1-320 min.

9. The method for preparing a NASICON oxide solid electrolyte for improving battery cycle performance according to claim 2, characterized in that: The sintering in step S3 includes a first stage sintering and a second stage sintering, wherein the first stage sintering temperature is 550-900° C. and the time is 1-4 hours; the second stage sintering temperature is 1100-1300° C. and the time is 2-24 hours.

10. An all-solid-state sodium secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the NASICON oxide solid electrolyte according to claim 1 or the NASICON oxide solid electrolyte prepared by the preparation method according to claim 2.

Images