Sodium ferric phosphate pyrophosphate-carbon composite material and preparation method thereof, sodium ion battery and electric equipment
A sodium iron pyrophosphate-carbon composite material was prepared by spray drying and sintering a mixture of inexpensive iron powder and organic acid. This method solved the problems of high cost and complicated process, improved electronic conductivity and electrochemical performance, and is suitable for sodium-ion batteries.
Patent Information
- Application Number
- CN202511322811.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-16
- Publication Date
- 2025-12-12
AI Technical Summary
Existing sodium iron pyrophosphate materials are expensive, have complicated sintering processes that hinder industrial production, and have low electronic conductivity and insufficient electrochemical performance.
A sodium iron pyrophosphate-carbon composite material was prepared by mixing inexpensive iron powder and organic acid, followed by spray drying and segmented sintering. The chelating effect of the organic acid was used to form a uniform carbon source coating, which optimized the electronic structure and simplified the process.
It reduces production costs, improves electronic conductivity and electrochemical performance, and has high material density, making it suitable for large-scale industrial applications.
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Figure CN121107394A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of sodium ion batteries, in particular to a sodium iron phosphate pyrophosphate-carbon composite material, a preparation method thereof, a sodium ion battery and an electric equipment. BACKGROUND
[0002] Compared with lithium ion batteries, sodium ion batteries have the advantages of abundant raw material resources, uniform distribution, high safety, good low-temperature performance, etc., so they have become a new energy storage device researched and developed by researchers and major enterprises in recent years. Among them, sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7) has become one of the popular materials for energy storage due to its low cost, extremely low volume expansion (≈4%), excellent structural stability, and excellent cycle performance. However, due to the inherent low electronic conductivity and low energy density of the polyanion body, it is usually modified by carbon coating, morphology control and other means to improve the electrochemical performance of the material.
[0003] However, in the prior art, the raw materials such as iron source are expensive and have high cost, and the sintering process is complicated and needs to be sintered multiple times, which increases the production cost of industrialization.
[0004] Therefore, there is an urgent need to provide a preparation method of a sodium iron phosphate pyrophosphate and C composite material to solve the above problems. SUMMARY
[0005] The purpose of the present application is to provide a sodium iron phosphate pyrophosphate-carbon composite material, a preparation method thereof, a sodium ion battery and an electric equipment to solve the above problems.
[0006] To achieve the above purpose, the first aspect of the present application provides a preparation method of a sodium iron phosphate pyrophosphate-carbon composite material, comprising: mixing an organic acid, iron powder, a sodium source, a phosphorus source and a solvent to obtain a slurry, and spray drying the slurry to obtain a precursor; pre-sintering and sintering the precursor under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate-carbon composite material.
[0007] Optionally, the preparation method of the sodium iron phosphate pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. The organic acid includes at least one of oxalic acid, citric acid, formic acid, malonic acid, gluconic acid, lactic acid, succinic acid, lauric acid, tartaric acid, salicylic acid and phthalic acid; B. The sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium oxalate, sodium acetate, sodium pyrophosphate and disodium pyrophosphate, and hydrates thereof; C. the phosphorus source comprises at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, disodium pyrophosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and hydrates thereof; D. the particle size of the iron powder is 100-3000 mesh; E. the solvent comprises water.
[0008] Optionally, the preparation method of the sodium iron phosphate pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. the organic acid comprises oxalic acid and citric acid; the molar ratio of the oxalic acid to the citric acid is 2:1; B. the molar ratio of the organic acid, the iron powder, the sodium source, the phosphorus source, and the solvent is 2-6:2.95-3.05:3.95-4.05:3.95-4.05; C. the ratio of the volume of the solvent to the molar amount of the iron powder is 200-350 mL:20-40 mmol.
[0009] Optionally, the mixing comprises: first mixing and first heating of the organic acid, the solvent, and the iron powder to obtain a first mixture; second mixing and second heating of the first mixture, the sodium source, and the phosphorus source.
[0010] Optionally, the temperature of the first heating and the second heating is independently 50-90°C, the time of the first heating and the second heating is independently 0.5-24h, and the stirring speed of the first heating and the second heating is independently 600-2000 rpm.
[0011] Optionally, the inlet air temperature of the spray drying is 180-240°C, the outlet air temperature is 80-110°C, the feeding speed is 1-3 L / h, and the atomizer speed is 20000-35000 rpm.
[0012] Optionally, the preparation method of the sodium iron phosphate pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. the temperature of the pre-sintering is 300-400°C, and the time is 2-6h; B. the temperature of the sintering is 400-600°C, the heating rate is 2-10°C / min, and the holding time is 2-15h.
[0013] The second aspect of the present application provides a sodium iron phosphate pyrophosphate-carbon composite material, which is prepared by the preparation method of the sodium iron phosphate pyrophosphate-carbon composite material.
[0014] The third aspect of the present application provides a sodium ion battery comprising the sodium iron phosphate pyrophosphate-carbon composite material.
[0015] The fourth aspect of the present application provides an electric device comprising the sodium ion battery.
[0016] Compared with the prior art, the beneficial effects of the present application include: The preparation method of the sodium iron phosphate pyrophosphate-carbon composite material provided by the present application improves the simple process synthesis means of the raw material iron source of the sodium iron phosphate pyrophosphate material with cost-advantageous iron powder and organic acid, and simultaneously utilizes the chelation effect of the organic acid on ferrous ions to form a homogeneous and carbon-rich organic iron source in coordination with each other, taking the iron source as a primary crystal nucleus, and the carbon source carried by the iron source can be coated on the inner surface of the sodium iron phosphate pyrophosphate crystal nucleus in situ, thereby optimizing the electronic structure, enhancing the electronic conductivity of the material, and further improving the electrochemical performance of the material. The preparation method adopts one-step spray drying and one-step segmented sintering, and has the advantages of simple preparation process and operation, high efficiency and energy saving, high process repeatability, safety and environmental protection, controllable cost, excellent electrochemical performance, and suitability for large-scale industrial production and application.
[0017] The sodium iron phosphate pyrophosphate-carbon composite material provided by the present application has complete spherical particles, and the sizes of the spherical particles are filled with each other, so that the material has a high compaction density and can obtain a higher volume / mass energy density of the battery cell.
[0018] The sodium ion battery and the electric device provided by the present application have low cost and excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS
[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.
[0020] Figure 1 The 0.2C first circle charge-discharge curve diagram of the button-type sodium ion battery provided for Example 1 is shown in the following figure: Figure 2 The cycle test diagram of the button-type sodium ion battery provided for Example 1 is shown in the following figure. DETAILED DESCRIPTION
[0021] Firstly, the scheme provided by the present application is explained in more detail as follows: The first aspect of the present application provides a preparation method of a sodium iron phosphate pyrophosphate-carbon composite material, comprising: The organic acid, iron powder, sodium source, phosphorus source and solvent are mixed to obtain a slurry, and the slurry is spray dried to obtain a precursor; It should be noted that the iron powder is used for oxidation to obtain ferrous iron, in order to achieve better coating effect, the replacement reaction of low-cost organic acid and iron source generates divalent iron organic iron source, and the organic acid has strong complexing ability, which can effectively chelate divalent iron ions, the two effects are mutually coordinated and coordinated with each other, forming a homogeneous and carbon-rich organic iron source, taking the iron source as the original crystal nucleus, the carbon source carried by the iron source can be coated in the inner surface of the sodium iron pyrophosphate crystal nucleus in situ, thereby optimizing the electronic structure and enhancing the electronic conductivity of the material; It should be noted that the scheme of the present application ingeniously avoids the sanding process, which can save energy and increase efficiency; and the spray drying is used to control the morphology of the precursor and the finished material, control it to be spherical or spherical, and different particle sizes of spherical particles fill each other, so as to achieve higher compaction density; The precursor is pre-sintered and sintered under an inert atmosphere to obtain a sodium iron pyrophosphate-carbon composite material.
[0022] It should be noted that the preparation method of the sodium iron pyrophosphate-carbon composite material provided by the present application not only uses inexpensive micron-sized iron powder and other sodium and phosphorus sources as raw materials, avoids the sanding process, and controls the content of the carbon source carried by the organic iron source itself, so that it can be better coated on the surface of the material, but also uses the spray drying process to control the morphology of the material, which is beneficial to improve the compaction density of the product, reduce the sintering process, and enhance the actual application prospect of the material.
[0023] In some embodiments, the inert gas in the inert atmosphere includes at least one of argon, nitrogen, and helium.
[0024] In some embodiments, the preparation method of the sodium iron pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. The organic acid includes at least one of oxalic acid, citric acid, formic acid, malonic acid, gluconic acid, lactic acid, succinic acid, lauric acid, tartaric acid, salicylic acid, and phthalic acid; B. The sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium oxalate, sodium acetate, sodium pyrophosphate, and disodium pyrophosphate, and hydrates thereof; C. The phosphorus source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, disodium pyrophosphate, ammonium dihydrogen phosphate, and ammonium hydrogen phosphate, and hydrates thereof; D. The particle size of the iron powder is 100-3000 mesh; Optionally, the particle size of the iron powder can be 100 mesh, 500 mesh, 1000 mesh, 1500 mesh, 2000 mesh, 2500 mesh, 3000 mesh, or 100-3000 mesh; E. The solvent includes water.
[0025] In some embodiments, the preparation method of the sodium ferric pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. The organic acid comprises oxalic acid and citric acid; The molar ratio of the oxalic acid and the citric acid is 2:1; It should be noted that when the organic acid comprises oxalic acid and citric acid, the organic acid such as citric acid that can carbonize at high temperature to obtain more carbon is used to dissolve a certain amount of iron powder to obtain an organic carbon source, and then oxalic acid and the like that can easily crack into carbon oxides and other volatile substances at high temperature is used; by controlling the former to precisely control the content of the carbon source of the material, and then using the characteristics of the latter organic acid to inhibit the increase of the carbon content, the effect of precisely regulating the carbon content can be achieved, which can avoid the problem that the material specific capacity cannot be fully played or the conductivity is too poor due to too high or too low carbon content, thereby affecting the electrochemical performance; at the same time, the organic acid such as citric acid also has chelation effect, which can complex the divalent iron ions obtained by dissolution, and the core material-iron source is easy to dissolve and disperse, so as to form a carbon-coated NFPP material with NFPP as the crystal nucleus, which is helpful for synthesizing a high-purity phase; In some embodiments, if only one kind of organic acid (for example, citric acid) is used, although a clear and transparent solution can be obtained, the carbon content will increase sharply; and if only oxalic acid and the like is used, a large amount of ferrous oxalate and the like will be generated, which will cause the synthesized precursor solution to agglomerate and be unevenly dispersed if the sand milling process is not performed, thereby affecting the performance; however, by using organic acids with different characteristics in combination, not only can the problem of too high carbon content be avoided, but also by the oxidation and dissolution of the organic acids and the chelation effect, the demand for directly obtaining a homogenate with uniform dispersion can be met, thereby avoiding the sand milling process; B. The molar ratio of the organic acid, the iron powder, the sodium source and the phosphorus source is 2-6:2.95-3.05:3.95-4.05:3.95-4.05; Optionally, the molar ratio of the organic acid, the iron powder, the sodium source and the phosphorus source is any value between 2:2.95:3.95:3.95, 4:3:4:4, 6:3.05:4.05:4.05 or 2-6:2.95-3.05:3.95-4.05:3.95-4.05; C. The ratio of the volume of the solvent to the molar amount of the iron powder is 200-350 mL:20-40 mmol.
[0026] Optionally, the volume of the solvent and the molar ratio of the iron powder can be 200 mL:20 mmol, 300 mL:30 mmol, 350 mL:40 mmol or any value between 200-350 mL:20-40 mmol.
[0027] In some embodiments, the mixing comprises: mixing the organic acid, the solvent and the iron powder, heating the mixture to obtain a first mixture; In some embodiments, the iron powder is added by a hanging bag suspension method. mixing the first mixture, the sodium source and the phosphorus source, heating the mixture.
[0028] In some embodiments, the first heating and the second heating are independently at a temperature of 50-90℃, a time of 0.5-24h, and a stirring speed of 600-2000 rpm.
[0029] Alternatively, the first heating and the second heating are independently at a temperature of 50℃, 60℃, 70℃, 80℃, 90℃, or any value between 50-90℃, a time of 0.5h, 1h, 2h, 6h, 10h, 14h, 18h, 20h, 24h, or any value between 0.5-24h, and a stirring speed of 600rpm, 1000rpm, 1500rpm, 2000rpm, or any value between 600-2000rpm.
[0030] In some embodiments, the stirring method comprises magnetic stirring or mechanical stirring.
[0031] In some embodiments, the spray drying is at an inlet temperature of 180-240℃, an outlet temperature of 80-110℃, a feed rate of 1-3 L / h, and an atomizer speed of 20000-35000 rpm.
[0032] Alternatively, the spray drying is at an inlet temperature of 180℃, 200℃, 220℃, 240℃, or any value between 180-240℃, an outlet temperature of 80℃, 90℃, 100℃, 110℃, or any value between 80-110℃, a feed rate of 1L / h, 2 L / h, 3 L / h, or any value between 1-3 L / h, and an atomizer speed of 20000 rpm, 25000 rpm, 30000 rpm, 35000 rpm, or any value between 20000-35000 rpm.
[0033] In some embodiments, the method for preparing the sodium iron phosphate pyrophosphate-carbon composite material satisfies at least one of the following conditions: A. the pre-sintering temperature is 300-400℃, and the time is 2-6 h; Optionally, the temperature of the pre-sintering can be 300℃, 350℃, 400℃, or any value between 300-400℃, and the time can be 2h, 3h, 4h, 5h, 6h, or any value between 2-6h. It should be noted that the pre-sintering can remove the volatile gas generated by the pyrolysis of the organic acid by slow removal, reduce the generation of pores, reduce the porosity, and thus improve the overall density of the material, thereby improving the compaction density; at the same time, the pre-sintering also has the effect of improving the uniformity of the particles and controlling the abnormal growth of the grains, thereby obtaining a relatively small and uniform grain structure and improving the electrochemical performance of the material. B. The sintering temperature is 400-600℃, the heating rate is 2-10 ℃ / min, and the holding time is 2-15 h.
[0034] Optionally, the sintering temperature can be 400℃, 500℃, 600℃, or any value between 400-600℃, the heating rate can be any value between 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, or 2-10 ℃ / min, and the holding time can be 2h, 5h, 10h, 15h, or any value between 2-15h.
[0035] The second aspect of the present application provides a sodium iron phosphate pyrophosphate-carbon composite material, which is prepared by the preparation method of the sodium iron phosphate pyrophosphate-carbon composite material.
[0036] The third aspect of the present application provides a sodium ion battery comprising the sodium iron phosphate pyrophosphate-carbon composite material.
[0037] The fourth aspect of the present application provides an electric device comprising the sodium ion battery.
[0038] Optionally, the electric device can be, but is not limited to, a mobile device, an electric vehicle, an electric ship, an electric aircraft, an electric train and a satellite, an energy storage system, etc.; wherein the mobile device can include, but is not limited to, at least one of a mobile phone, a notebook computer, etc.; the electric vehicle can include, but is not limited to, at least one of a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.
[0039] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.
[0040] Example 1 The embodiment provides a sodium iron phosphate-pyrophosphate-carbon composite material and a preparation method thereof, and specific steps are as follows: S1: 500 mL of deionized water is used to dissolve 20 mmol of citric acid, and stirring is performed until the solid particles are completely dissolved; then, 60 mmol of iron powder (with a particle size of 300 mesh) is added in an equal amount ratio, and after about 5 hours of reaction, 40 mmol of oxalic acid is weighed, and the mixture is continuously heated at 80℃ and stirred to obtain a uniformly dispersed suspension; S2: 80 mmol of sodium dihydrogen phosphate is weighed according to the stoichiometric ratio, and the mixture is continuously heated and stirred at the same temperature for 30 min to obtain a slurry; S3: the obtained slurry is subjected to spray drying under the conditions that the inlet air temperature is 200℃, the outlet air temperature is 85-100℃, the feeding speed is 1.5 L / h, and the atomizer speed is 30000 rpm, to obtain a precursor; S4: the obtained precursor is pre-sintered in a high-purity Ar atmosphere at a temperature increasing rate of 2℃ / min and a temperature of 300℃ for 3 h; then, one-step sintering is performed at a temperature increasing rate of 3℃ / min and a temperature of 500℃ for 5 h, and after natural cooling, the mixture is uniformly ground to obtain the sodium iron phosphate-pyrophosphate-carbon composite material.
[0041] Example 2 The difference from example 1 is that the addition amounts of citric acid and oxalic acid are 40 mmol and 20 mmol respectively, and other conditions are consistent with those in example 1.
[0042] Example 3 The difference from example 1 is that in the S1 step, 500 mL of deionized water is used to dissolve 20 mmol of gluconic acid, and stirring is performed until the solid particles are completely dissolved; then, 60 mmol of iron powder (with a particle size of 300 mesh) is added in an equal amount ratio, and after about 5 hours of reaction, 40 mmol of formic acid is weighed, and the mixture is continuously heated at 80℃ and stirred to obtain a uniformly dispersed suspension, and other conditions are consistent with those in example 1.
[0043] Example 4 The difference from example 1 is that in the S1 step, 500 mL of deionized water is used to dissolve 60 mmol of citric acid, and stirring is performed until the solid particles are completely dissolved; then, 60 mmol of iron powder is added in an equal amount ratio, and after about 5 hours of reaction, a uniformly dispersed suspension is obtained, and other conditions are consistent with those in example 1.
[0044] Comparative Example 1 The difference from Example 1 is that in the S1 step, 40 mmol of phosphoric acid is taken, and an equal amount of iron powder (60 mmol) is heated and dissolved (80°C), and the reaction is carried out overnight to obtain ferrous phosphate precipitate, then deionized water is added to the solution to reach a volume of 500 mL, 10 mmol of citric acid is added, and the subsequent steps are consistent with Example 1.
[0045] Comparative Example 2 The difference from Example 1 is that in the S1 step, 120 mmol of dilute hydrochloric acid is taken to heat and dissolve (50°C) an equal amount of iron powder (60 mmol) to obtain a ferrous chloride solution, then deionized water is added to the solution to reach a volume of 500 mL, 10 mmol of citric acid is added, and the subsequent steps are consistent with Example 1.
[0046] Comparative Example 3 The difference from Example 1 is that in the S1 step, 500 mL of deionized water is taken to dissolve 60 mmol of ferrous citrate, and the solid particles are stirred until they are completely dissolved to obtain a ferrous citrate solution, and the subsequent steps are consistent with Example 1.
[0047] Comparative Example 4 The difference from Example 1 is that in the S1 step, 500 mL of deionized water is taken to dissolve 60 mmol of ferrous sulfate heptahydrate, and the solid particles are stirred until they are completely dissolved to obtain a ferrous sulfate solution, then 10 mmol of citric acid is added, and the subsequent steps are consistent with Example 1.
[0048] Comparative Example 5 The difference from Example 1 is that the S4 step of pre-sintering is not performed, and a one-step sintering is directly performed at a temperature increasing rate of 3°C / min and a temperature holding time of 500°C for 5 h, and after natural cooling, the obtained sodium iron pyrophosphate-phosphoric acid-carbon composite material is ground uniformly.
[0049] The positive electrode materials prepared in the above examples and comparative examples are assembled into button sodium ion batteries, and the first discharge specific capacity is tested at 0.2C and 5C, and the capacity retention rate is tested at 5C for 100 cycles (1C=129 mA g -1 ), and the specific test results are shown in Table 1, and the test conditions are as follows: temperature 25°C; cut-off voltage 1.7-3.8 V; electrolyte 1M NaPF6EC / DMC (1 / 1)+5% FEC; test system: Xinwei constant temperature test box.
[0050] Among them, the 0.2C first cycle charge-discharge curve of Example 1 is shown in Figure 1 , which shows that the charge-discharge platform is around 3V, and the voltage window is wide, reaching 1.7-3.8V, and the first cycle discharge specific capacity is as high as 100.71 mAh / g, which has a high energy density.
[0051] The cycle test of Example 1 is shown in Table 1, indicating that the retention rate is as high as 99.42% at 5C rate after 100 cycles, and the first cycle specific capacity can reach 88.38 mAh / g, indicating that the cycle stability of the sodium iron pyrophosphate-carbon composite material provided by Example 1 is excellent, and is suitable for application in the field of sodium ion battery energy storage. Figure 2
[0052] Table 1 Electrochemical performance test
[0053] Analysis: From the above results, it can be seen that the electrochemical performance of the positive electrode material of the example is significantly better than that of the comparative example.
[0054] Because the amorphous carbon produced by pyrolysis of citric acid has a relatively rich oxygen-containing functional group on the surface, which is beneficial to the combination of the carbon layer and the bulk material, the carbon layer has good uniformity and high carbon content, while oxalic acid has more oxygen-containing functional groups, but the content of amorphous carbon obtained by carbonization is much lower than that of amorphous carbon produced by citric acid. Therefore, compared with Example 1, the carbon content coated by Example 2 is higher than that of Example 1, so that the non-active carbon content increases, which reduces the overall capacity of the material; Compared with Example 1, Example 3 is similar to Example 1, and gluconic acid (similar to citric acid) can complex with ferrous ions to form [Na-Fe-HPO4] x (C6H 12 O7) y analog, which is also the main contributor of carbon source, while formic acid (similar to oxalic acid) mainly provides additional protons (H + ) to dissolve more iron powder, and contributes less to the carbon source. The proportion of the two organic acids is adjusted, which not only obtains complexed iron source, but also controls the carbon content, which is beneficial to the dispersion of iron source, facilitates the growth of NFPP crystal nucleus, and forms an in-situ carbon coating layer, effectively enhances the conductivity, and helps to generate high-purity phase, so its electrochemical performance is equivalent to that of Example 1; Compared with Example 1, Example 4 uses single citric acid as an organic acid to dissolve Fe powder, compared with Examples 1 and 2, the non-active species (i.e. carbon content) obtained in the subsequent sintering stage increases sharply, which greatly reduces the electrochemical performance of the material; Compared with Example 1, the ferrous phosphate precipitate generated in Comparative Example 1 is directly sprayed, which is easy to cause material agglomeration and uneven dispersion, thereby making the electrochemical performance of the material poor; Compared with Example 1, the ferrous chloride generated by the reaction of the inorganic acid hydrochloric acid and iron powder in Comparative Example 2 will generate various chlorine-containing gas substances in the spraying and calcination process, polluting the environment; in addition, additional carbon sources need to be added, and the inorganic acid fails to form a chelate with the iron source, and the dispersibility is poor, affecting the electrochemical performance; Compared with Example 1, Comparative Example 3 directly uses the organic acid ferrous citrate as the raw material, which meets the requirement of the organic acid iron source, but because the carbon content is much higher than that of the iron source obtained by the combined organic acid with a good proportion, the proportion of non-active species in the bulk material is greatly increased, and the specific capacity is reduced; more importantly, the ready-made organic acid iron source does not have the dual functions of the displacement reaction of acid and iron element and the complexation reaction of ferrous ions and organic acid (the product is: [Na-Fe-HPO4] x (C2O4 / C6H8O7) y complex) generated by the reaction of organic acid and iron powder, and the pyrolysis carbon source cannot uniformly and effectively coat the NFPP bulk material in situ, resulting in a sharp decrease in the rate performance; Compared with Example 1, Comparative Example 4 directly uses the soluble inorganic acid salt ferrous sulfate as the raw material, which will generate sulfur-containing gas substances in the material synthesis process, causing serious pollution to the environment; in addition, mixed phases such as sodium sulfate and sodium iron phosphate may be generated in the pre-sintering stage, and the sodium sulfate and sulfate phases are not completely decomposed in the subsequent high-temperature sintering process, greatly affecting the phase purity, resulting in poor electrochemical performance; Compared with Example 1, Comparative Example 5 lacks a pre-sintering process, which not only leads to a significant increase in material porosity and poor material density, but also causes poor material uniformity and inability to inhibit abnormal grain growth, resulting in a longer sodium ion diffusion channel, making the overall electrochemical performance poor.
[0055] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.
[0056] Furthermore, to the extent that the terms "comprises", "comprising", "includes", "including" and "has" or any variation thereof are used in the specification and / or claims, these terms are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, includes or has a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, to the extent that the terms "coupled", "coupling", "connected", "connecting" or "connection" are used in the specification and / or claims, these terms are intended to refer to either a direct connection between entities that are in physical or logical contact with each other or an indirect connection through one or more intermediate entities.
Claims
1. A method for preparing a sodium iron pyrophosphate-carbon composite material, characterized in that, include: Organic acid, iron powder, sodium source, phosphorus source and solvent are mixed to obtain slurry, and the slurry is spray dried to obtain precursor; The precursor was pre-sintered and sintered under an inert atmosphere to obtain a sodium iron pyrophosphate-carbon composite material.
2. The method for preparing the sodium iron pyrophosphate-carbon composite material according to claim 1, characterized in that, At least one of the following conditions must be met: A. The organic acid includes at least one of oxalic acid, citric acid, formic acid, malonic acid, gluconic acid, lactic acid, succinic acid, lauric acid, tartaric acid, salicylic acid, and phthalic acid; B. The sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium oxalate, sodium acetate, sodium pyrophosphate, and disodium pyrophosphate and their hydrates; C. The phosphorus source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, disodium pyrophosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and their hydrates; D. The particle size of the iron powder is 100-3000 mesh; E. The solvent includes water.
3. The method for preparing the sodium iron pyrophosphate-carbon composite material according to claim 2, characterized in that, At least one of the following conditions must be met: A. The organic acids include oxalic acid and citric acid; The molar ratio of oxalic acid to citric acid is 2:1; B. The molar ratio of the organic acid and the iron powder, the sodium source and the phosphorus source is 2-6: 2.95-3.05：3.95-4.05：3.95-4.05； C. The volume ratio of the solvent to the molar amount of the iron powder is 200-350 mL: 20-40 mmol.
4. The method for preparing the sodium iron pyrophosphate-carbon composite material according to claim 1, characterized in that, The mixture includes: The organic acid, the solvent, and the iron powder are first mixed and first heated to obtain a first mixture; The first mixture, the sodium source, and the phosphorus source are then subjected to a second mixing and a second heating.
5. The method for preparing the sodium iron pyrophosphate-carbon composite material according to claim 4, characterized in that, The temperatures of the first heating and the second heating are each 50-90℃, the times are each 0.5-24h, and the stirring speeds are each 600-2000 rpm.
6. The method for preparing the sodium iron pyrophosphate-carbon composite material according to claim 1, characterized in that, The spray dryer has an inlet air temperature of 180-240℃, an outlet air temperature of 80-110℃, a feed rate of 1-3 L / h, and an atomizer speed of 20000-35000 rpm.
7. The method for preparing the sodium iron pyrophosphate-carbon composite material according to any one of claims 1-6, characterized in that, At least one of the following conditions must be met: A. The pre-sintering temperature is 300-400℃, and the time is 2-6 h; B. The sintering temperature is 400-600℃, the heating rate is 2-10℃ / min, and the holding time is 2-15 h.
8. A sodium iron pyrophosphate-carbon composite material, characterized in that, It is prepared by the method for preparing sodium iron pyrophosphate-carbon composite material according to any one of claims 1-7.
9. A sodium-ion battery, characterized in that, Including the sodium iron pyrophosphate-carbon composite material as described in claim 8.
10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.