A nanometer-scale sodium ferrophosphate-type aluminum-doped sodium ferrophosphate and its preparation method and application

Abstract

The present invention provides a nano-scale sodium ferrophosphate doped with aluminum. 3+ , the sodium iron phosphate is a ferrophosphate nano-ore structure, and the particle size of the sodium iron phosphate is 50-700nm; the present invention also provides a method for preparing nano-scale ferrophosphate nano-ore type aluminum-doped sodium iron phosphate, comprising the following steps: grinding a phosphorus source, a sodium source, an iron source, and an aluminum source to obtain a mixed precursor, and sintering the mixed precursor to obtain a nano-scale ferrophosphate nano-ore type aluminum-doped sodium iron phosphate. The present invention also provides an application of a nano-scale ferrophosphate nano-ore type aluminum-doped sodium iron phosphate as a positive electrode material for preparing a sodium ion battery. The nano-scale ferrophosphate nano-ore type aluminum-doped sodium iron phosphate of the present invention is a positive electrode material for polyanion sodium ion batteries, which improves the electronic conductivity and energy density of sodium iron phosphate by doping, providing a positive electrode material for the next step of preparing a safer, more environmentally friendly, and low-cost sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of new energy sodium ion battery positive electrode materials, and in particular to a nano-scale arborite-type aluminum-doped sodium iron phosphate and a preparation method and application thereof. Background Art

[0002] Driven by the vast demand for secondary energy, the widespread use of lithium salts, particularly in the transportation industry, has led to a sharp rise in lithium prices due to the diverse consumption of lithium and lithium-based chemicals. The price of lithium batteries is now almost entirely determined by lithium scarcity. Furthermore, lithium reserves are insufficient to simultaneously meet the growing industrial development needs of transportation and power grid applications. Given this, sodium, with its extremely high abundance and price advantages, is already used in battery systems. Furthermore, sodium and lithium share similar physical and chemical properties, making sodium-based electrochemical energy storage a significant market for large-scale energy storage and power grid development.

[0003] Currently, sodium-ion cathode materials with promising industrial applications can be divided into three types: layered metal oxides, polyanionic materials, and Prussian blue derivatives. Other companies have already developed and produced sodium-ion batteries, including HiNa's P2 and O3 copper-iron-manganese layered oxide cathode materials, Faradion's O3 / P2 mixed nickel-manganese-magnesium-titanium layered oxide cathode materials, Aquion Energy's manganese-based oxide AHI battery, and Novasis Energy's PBA cathode materials. All have achieved comparable specific capacity and energy retention. In 2019, HiNa successfully installed the world's first 30kW / 100kW hSIB energy storage system.

[0004] Layered metal oxide cathode materials: Na + The phase change during the intercalation and deintercalation process leads to unstable unit cells and easy collapse of the structure, which means that the cycle life of the material is not ideal and the specific capacity degrades rapidly. However, its high energy density and high voltage platform make it a research hotspot in recent years. R&D personnel use inactive metal ions such as Al 3+ etc. serve as the support of the layered structure to ensure the stability of the structure.

[0005] Prussian blue derivative positive electrode materials: From the perspective of electrochemical performance alone, they are a very suitable type of sodium ion battery positive electrode material. However, the use of CN- in the preparation process will cause environmental pollution and will form highly toxic HCN when in contact with acid, limiting practical applications.

[0006] Polyanionic cathode materials: Due to the inductive effect of the polyanionic group and its relatively stable structure, these compounds exhibit high operating potentials. The phosphate group's uniquely stable structure demonstrates excellent rate performance and cycling stability during cycling. However, phosphate-based polyanionic cathode materials also have drawbacks: low electronic conductivity and limited energy density.

[0007] NaFePO4 (NFP) is the phosphate with the highest theoretical specific capacity discovered to date. NFP has two structural phases: olivine and niobate. Although the olivine phase has a theoretical specific capacity of 154 mAh / g, it can only be synthesized via an indirect route and is difficult to synthesize using traditional solid-phase methods. While the niobate structure is thermodynamically more stable, only niobate-type NFP at the nanoparticle level is electrochemically active.

[0008] At present, there are no reports on the doping and modification of NFP in the field of sodium ion battery research. More research is on the doping of transition metals or inactive metals Al into layered oxide cathode materials. 3+ Mg 2+ et al., the literature reported that Al 3+ The stronger bond with O can become the structural pillar of the layered oxide, maintaining the layered Na + The channel does not collapse, which improves the rate performance and cycle stability. At the same time, it is found that the energy density of the positive electrode material can be increased to a certain extent. Inactive metals are used to support the layered structure, so that the layered structure does not collapse or collapses slightly during the process of Na ion deintercalation to improve the cycle performance. Sodium iron phosphate is a polyanion type, and there are no related reports at present. Because sodium iron phosphate is a polyanion type positive electrode material, only sodium iron phosphate type has electrochemical properties, and it must be nanoscale. It cannot be directly prepared like lithium iron phosphate, and can only be prepared by indirect methods, which limits the application of sodium iron phosphate. In the report on LiFePO4 (LFP), researchers have conducted Fe-doping Al 3+ The work of Al 3+ The doping results in smaller particle size and higher crystallinity, which can improve the conductivity of LFP itself.

[0009] Therefore, it is of great significance to develop a method to improve the electronic conductivity and energy density of NFP by doping to prepare high-performance sodium-ion battery cathode materials, so as to provide cathode materials for the next step of preparing safer, more environmentally friendly and low-cost sodium-ion batteries. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a nano-scale niobate-type aluminum-doped sodium ferric phosphate material that improves the electronic conductivity and energy density of NFP by doping, as well as its preparation method and application.

[0011] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0012] A nano-scale sodium ferrophosphate-type aluminum-doped sodium ferrophosphate, wherein the sodium ferrophosphate is doped with Al 3+ The sodium ferric phosphate has a niobate-type structure, and the particle size of the sodium ferric phosphate is 50-700 nm.

[0013] Preferably, the particle size of the sodium ferric phosphate is 150-450 nm.

[0014] Based on the overall inventive concept, the present invention also provides a method for preparing nano-scale nitrophosphate-type aluminum-doped sodium iron phosphate, comprising the following steps: grinding a phosphorus source, a sodium source, an iron source, and an aluminum source to obtain a mixed precursor, and sintering the mixed precursor to obtain nano-scale nitrophosphate-type aluminum-doped sodium iron phosphate.

[0015] Preferably, the phosphorus source and the sodium source are sodium phosphate, the iron source is a combination of one or more of ferrous oxalate and ferrous acetate, and the aluminum source is a combination of one or more of aluminum hydroxide and aluminum oxide.

[0016] Preferably, the molar ratio of the phosphorus source, sodium source, iron source and aluminum source is 1:1:(1-1.5x):x, wherein the value of x is 0<x<2 / 3. The doping amount of aluminum element in the aluminum source is x in the iron source and the aluminum source, and the relative amount of Fe and Al is fixed at Fe. 1-1.5x Al x , in order to keep the total charge of the Fe sublattice at +2, while also keeping the valence of Fe at +2, the value range of x is 0<x<2 / 3.

[0017] Preferably, the grinding agent used during the grinding is one of acetone, anhydrous ethanol, propanol, and ether. The grinding agent plays an auxiliary lubricating role when the solids are ground together. A volatile agent is selected, so the amount added is not limited.

[0018] Preferably, during the grinding, the grinding medium is 0.3-4.0 mm zirconium balls, and the ball-to-material ratio is (1-10): 1. Zirconium balls are selected as the grinding medium because they have high grinding efficiency, good fluidity, good roundness, smooth surface, good impact resistance and wear resistance, and do not react with the ground material.

[0019] Preferably, the grinding is ball milling, and the ball mill used for the ball milling is a high-energy ball mill, which includes a planetary ball mill and a sand mill. The rotation speed of the ball mill is 200-800 rpm, and the ball milling time is 6-48 hours.

[0020] Preferably, the particle size of the mixed precursor is 50-1000 nm.

[0021] Preferably, the sintering is a two-stage temperature-raising sintering, and the two-stage temperature-raising sintering is carried out in an inert gas atmosphere. In the two-stage temperature-raising sintering, the first stage has a heating rate of 1-20°C / min, and the temperature is raised to 200-450°C and kept warm for 1-6 hours; the second stage has a heating rate of 1-20°C / min, and the temperature is raised to 500-800°C and kept warm for 6-18 hours, and finally cooled to room temperature. The principle or idea of ​​two-stage sintering comes from the thermogravimetric analysis of these materials. At 25-200°C, the raw materials lose their crystallization water, at 200-450°C, the iron source and aluminum source decompose into intermediate products, and at 500-800°C, the intermediate products undergo a reaction and crystallize.

[0022] The present invention achieves the preparation of nano-scale niobate-type aluminum-doped sodium ferric phosphate through a two-stage sintering temperature system. First, in the first stage at 200-450°C, the hydrate loses its crystal water, and ferrous oxalate decomposes into ferrous carbonate and carbon monoxide. Then, in the second stage at 550-750°C, the ferrous carbonate reacts with sodium dihydrogen phosphate and aluminum oxide to obtain nano-scale niobate-type aluminum-doped sodium ferric phosphate. The reaction process is as follows:

[0023] (1-1.5x)FeC2O4·2H20+NaH2PO4·2H20+0.5xAl(OH)3→

[0024] NaFe 1-1.5x Al x PO4+(5-1.5x)H20↑+(1-1.5x)CO2↑+(1-1.5x)CO↑

[0025] Based on the overall inventive concept, the present invention also provides an application of nano-scale niobate-type aluminum-doped sodium iron phosphate, wherein the nano-scale niobate-type aluminum-doped sodium iron phosphate is used as a positive electrode material for preparing a sodium ion battery.

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

[0027] 1. The nano-scale sodium ferrophosphate of the nitrophosphate type aluminum-doped sodium ferric phosphate of the present invention is a positive electrode material for polyanion sodium ion batteries. By doping, the electronic conductivity and energy density of sodium ferric phosphate are improved to prepare a high-performance positive electrode material for sodium ion batteries, providing a positive electrode material for the next step of preparing safer, more environmentally friendly and low-cost sodium ion batteries.

[0028] 2. The preparation method of the present invention is simple to operate and low in cost, and realizes the recycling of phosphorus sources after the recycling and treatment of waste lithium batteries; it generates less waste and is economical and environmentally friendly.

[0029] 3. When the nano-scale sodium ferrophosphate-doped aluminum phosphate prepared by the present invention is used as a positive electrode material for preparing sodium ion batteries, Al 3+ Doping can significantly improve the conductivity of sodium iron phosphate and effectively increase the energy density, making it a good choice for high-performance sodium ion battery cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 It is NaFe 1-1.5x Al x XRD patterns of PO4 Examples 2, 3, 4 and the comparative example compared with standard card PDF#29-1216;

[0032] Figure 2 is the particle size distribution diagram of the precursor of Comparative Example 1;

[0033] Figure 3 It is the particle size distribution diagram of the sample of comparative example 1;

[0034] Figure 4 is the particle size distribution diagram of the sample in Example 3;

[0035] Figure 5 1 is the electrochemical impedance spectroscopy diagram of Example 3 and Comparative Example 1;

[0036] Figure 6 1 is the charge-discharge voltage curve of the first and fifth cycles of Comparative Example 1;

[0037] Figure 7 3 are the charge and discharge voltage curves of the first and fifth cycles of Example 3. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0040] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0041] Example 1:

[0042] A method for preparing nano-scale sodium ferrophosphate-type aluminum-doped sodium ferric phosphate comprises: firstly, measuring an appropriate amount of acetone and pouring it into a ball mill; weighing sodium dihydrogen phosphate dihydrate, ferrous oxalate dihydrate and aluminum hydroxide (x is 0.05) in a molar ratio of 1:0.925:0.05 and pouring them into the ball mill; weighing 2.5 times of 0.6-0.8 mm zirconium balls in a ball-to-material ratio of 1:2.5; then adding an appropriate amount of acetone to ensure that the acetone covers the mixture of the powder and the zirconium balls; and then heating the mixture on a planetary ball. The precursor was ball-milled at 450 rpm in a mill for 29 h, the zirconium balls were separated through a 50-mesh sieve, and the acetone was filtered out using organic filter paper to obtain a precursor; the precursor was transferred to a combustion boat and placed in a tubular furnace into which argon gas was introduced in advance, and the temperature was raised to 340°C at a heating rate of 5°C / min, and kept warm for 2.4 h, and then raised to 640°C at the same heating rate, and kept warm for 10 h. Finally, the precursor was naturally cooled to room temperature under the protection of inert gas and taken out to obtain nano-sized sodium phosphate ore-type NaFe 0.925 Al 0.05 PO4.

[0043] Application of nano-scale niobate-type aluminum-doped sodium iron phosphate: A sodium ion battery is prepared using nano-scale niobate-type aluminum-doped sodium iron phosphate as a positive electrode, including metallic sodium as a negative electrode, a glass fiber separator, an organic electrolyte and a positive electrode.

[0044] Example 2:

[0045] A method for preparing nano-scale niobate-type aluminum-doped sodium ferric phosphate comprises: first, measuring an appropriate amount of acetone and pouring it into a ball mill; then weighing sodium dihydrogen phosphate dihydrate, ferrous oxalate dihydrate, and aluminum hydroxide (x = 0.10) in a molar ratio of 1:0.85:0.10 and pouring them into the ball mill; then weighing 3.1 times the amount of 0.6-0.8 mm zirconium balls in a ratio of 1:3.1; and then adding an appropriate amount of acetone to ensure that the acetone covers the mixture of powder and zirconium balls. The mixture is then ball milled in a planetary ball mill at 600 rpm for 18 hours, the zirconium balls are separated through a 50-mesh sieve, and the acetone is filtered out using organic filter paper to obtain a precursor. The precursor was transferred to a combustion boat and placed in a tubular furnace that was pre-filled with argon gas. The temperature was raised to 360°C at a heating rate of 6°C / min and kept at that temperature for 3.4 hours. The temperature was then raised to 660°C at the same heating rate and kept at that temperature for 12 hours. Finally, the precursor was naturally cooled to room temperature under the protection of inert gas and taken out to obtain nano-sized sodium phosphate ore-type NaFe 0.85 Al 0.10 PO4.

[0046] The XRD pattern of the nano-sized sodium ferrophosphate prepared in this embodiment is as follows: Figure 1 , it can be seen that Al 3+ After doping, it matches PDF#29-1216 and is still of the pyrophosphate type. 3+ New diffraction peaks begin to appear at 20-25 degrees after the addition of Al, indicating that Al has effectively entered the lattice.

[0047] Example 3:

[0048] A method for preparing nano-scale niobate-type aluminum-doped sodium ferric phosphate comprises: first, measuring an appropriate amount of acetone and pouring it into a ball mill; then, weighing sodium dihydrogen phosphate dihydrate, ferrous oxalate dihydrate, and aluminum hydroxide (x = 0.20) in a molar ratio of 1:0.70:0.20 and pouring them into the ball mill; then, weighing 3.5 times as many 0.6-0.8 mm zirconium balls in a ratio of 1:3.5; and finally, adding an appropriate amount of acetone to ensure that the acetone covers the mixture of powder and zirconium balls. Subsequently, the mixture is ball milled in a planetary ball mill at 550 rpm for 36 hours, the zirconium balls are separated through a 50-mesh sieve, and the acetone is filtered out using organic filter paper to obtain a precursor. The precursor was transferred to a combustion boat and placed in a tubular furnace that was pre-filled with argon gas. The temperature was raised to 380°C at a heating rate of 7°C / min and kept at that temperature for 2.8 hours. The temperature was then raised to 630°C at the same heating rate and kept at that temperature for 9 hours. Finally, the precursor was naturally cooled to room temperature under the protection of inert gas and taken out to obtain nano-sized sodium phosphate ore-type NaFe 0.70 Al 0.20 PO4. The XRD pattern of the nano-sized sodium ferrophosphate prepared in this embodiment is as follows: Figure 1 , it can be seen that the diffraction peak intensity at 20-25 degrees increases, indicating that Al 3+ The particle size distribution of the nano-sized sodium ferrophosphate prepared in this embodiment is as follows: Figure 4 It can be seen that the particle size distribution is uniform, ranging from 150 to 450 nm. The electrochemical impedance spectroscopy of the nano-sized sodium ferrophosphate prepared in this embodiment is shown in FIG. Figure 5 , it can be seen that Al 3+ After doping, the conductive properties can be effectively improved. The charge and discharge curve of the nano-scale sodium ferrophosphite prepared in this embodiment is as follows: Figure 7 , it can be seen that Al 3+ After doping, as the conductivity improves, the specific capacity increases to 123.63 mAh g -1 .

[0049] Example 4:

[0050] A method for preparing nano-scale niobate-type aluminum-doped sodium ferric phosphate comprises: first, measuring an appropriate amount of acetone and pouring it into a ball mill; then, weighing sodium dihydrogen phosphate dihydrate, ferrous oxalate dihydrate, and aluminum hydroxide (x = 0.30) in a molar ratio of 1:0.55:0.30 and pouring them into the ball mill; then, weighing 3.3 times as many 0.6-0.8 mm zirconium balls in a ratio of 1:3.3; and finally, adding an appropriate amount of acetone to ensure that the acetone covers the mixture of powder and zirconium balls. Subsequently, the mixture is ball milled in a planetary ball mill at 480 rpm for 34 hours, the zirconium balls are separated through a 50-mesh sieve, and the acetone is filtered out using organic filter paper to obtain a precursor. The precursor was transferred to a combustion boat and placed in a tubular furnace that was pre-filled with argon gas. The temperature was raised to 380°C at a heating rate of 8°C / min and kept at that temperature for 4 hours. The temperature was then raised to 580°C at the same heating rate and kept at that temperature for 11 hours. Finally, the precursor was naturally cooled to room temperature under the protection of inert gas and taken out to obtain nano-sized sodium phosphate ore-type NaFe 0.55 Al 0.30 PO4.

[0051] Comparative Example 1:

[0052] A method for preparing nano-scale niobate-type aluminum-doped sodium ferric phosphate comprises: first, measuring an appropriate amount of acetone and pouring it into a ball mill; weighing sodium dihydrogen phosphate dihydrate and ferrous oxalate dihydrate (x is 0.0) in a 1:1 molar ratio; weighing three times the amount of 0.6-0.8 mm zirconium balls in a 1:3 ratio; and then adding an appropriate amount of acetone to ensure that the acetone covers the mixture of powder and zirconium balls. Subsequently, the mixture is ball milled in a planetary ball mill at 500 rpm for 30 hours, the zirconium balls are separated through a 50-mesh sieve, and the acetone is filtered out using organic filter paper to obtain a precursor. The precursor is transferred to a combustion boat and placed in a tube furnace pre-filled with argon gas, and the temperature is initially increased to 350°C at a heating rate of 5°C / min, held at this temperature for 3 hours, then increased to 650°C at the same heating rate, held at this temperature for 10 hours, and finally cooled naturally to room temperature under the protection of an inert gas, to obtain nano-scale niobate-type NaFePO4. The XRD pattern of the nano-sized sodium ferrophosphate prepared in this comparative example is as follows: Figure 1, matching PDF#29-1216, which is a pyroxenite type.

[0053] The particle size distribution of the precursor prepared in this comparative example is as follows Figure 2 The particle size distribution is concentrated around 425nm. The particle size distribution of nano-sized sodium ferrophosphate is as follows: Figure 3 It can be seen that the particle size distribution is uniform, the precursor particle size distribution is between 300-500nm, and the particle size distribution of nano-scale sodium ferrophosphate is between 150-500nm. The electrochemical impedance of the nano-scale sodium ferrophosphate prepared in this comparative example is as follows: Figure 5 It can be seen that Al doping can effectively improve the electrical conductivity. The charge and discharge curve of the nano-sized sodium ferrophosphite prepared in this comparative example is as follows: Figure 6 , showing a specific capacity of 85.32 mAh g -1 .

[0054] Comparative Example 2:

[0055] A method for preparing nano-scale niobate-type aluminum-doped sodium ferric phosphate comprises: first, measuring 25 mL of acetone and pouring it into a ball mill; then weighing sodium dihydrogen phosphate dihydrate, ferrous oxalate dihydrate, and aluminum hydroxide (x = 0.03) in a molar ratio of 1:0.955:0.03 and pouring it into the ball mill; then weighing 2.2 times the amount of 0.6-0.8 mm zirconium balls in a ratio of 1:2.2; and then adding 15-20 mL of acetone, ensuring that the acetone covers the mixture of powder and zirconium balls. The mixture is then ball milled in a planetary ball mill at 590 rpm for 24 hours, the zirconium balls are separated through a 50-mesh sieve, and the acetone is filtered out using organic filter paper to obtain a precursor. The precursor was transferred to a combustion boat and placed in a tubular furnace that was pre-filled with argon gas. The temperature was raised to 370°C at a heating rate of 8°C / min and kept at that temperature for 2.5 hours. The temperature was then raised to 650°C at the same heating rate and kept at that temperature for 10 hours. Finally, the precursor was naturally cooled to room temperature under the protection of inert gas and taken out to obtain nano-sized sodium phosphate ore-type NaFe 0.955 Al 0.03 PO4.

Claims

1. A method for preparing nano-scale sodium ferrophosphate-doped aluminum phosphate, characterized in that: Sodium iron phosphate doped with Al 3+ The sodium ferric phosphate has a niobate-type structure, and the particle size of the sodium ferric phosphate is 150-450 nm; The preparation method comprises the following steps: grinding a phosphorus source, a sodium source, an iron source, and an aluminum source to obtain a mixed precursor, wherein the particle size of the mixed precursor is 50-1000 nm, and sintering the mixed precursor to obtain nano-scale niobate-type aluminum-doped sodium iron phosphate; the aluminum source is a combination of one or more of aluminum hydroxide and aluminum oxide; The phosphorus source, sodium source, iron source, and aluminum source are added in a molar ratio of 1:1:(1-1.5x):x, where x is 0<x<2 / 3; the grinding medium is 0.3-4.0 mm zirconium balls, the ball-to-material ratio is (1-10):1, the grinding speed is 200-800 rpm, and the grinding time is 6-48 hours; The sintering is a two-stage temperature-raising sintering, which is carried out in an inert gas atmosphere. In the two-stage temperature-raising sintering, the first stage has a temperature-raising rate of 1-20°C / min, and the temperature is raised to 340-380°C and kept for 1-6 hours; the second stage has a temperature-raising rate of 1-20°C / min, and the temperature is raised to 580-660°C and kept for 6-18 hours, and finally the temperature is lowered to room temperature.

2. The preparation method according to claim 1, characterized in that The phosphorus source and the sodium source are sodium phosphate, and the iron source is a combination of one or more of ferrous oxalate and ferrous acetate.

3. The preparation method according to claim 1, characterized in that During the grinding, the grinding agent used is one of acetone, anhydrous ethanol, propanol and ether.

4. The preparation method according to claim 1, characterized in that The grinding is ball milling, and the ball mill used for the ball milling is a high-energy ball mill, which includes a planetary ball mill and a sand mill.

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