Polyanion sodium battery positive electrode material as well as solution spray preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a polyanion sodium battery positive electrode material and a solution spraying preparation method and application thereof. The invention provides a preparation method of a polyanion sodium battery positive electrode material, which comprises the following steps: setting a precursor to be in a solution state, then regulating and controlling the size and pore structure of secondary particles by controlling spray process parameters, and finally sintering to obtain the polyanion sodium battery positive electrode material. The first reversible capacity, the cycling stability and the compaction density of the polyanion positive electrode material prepared by the method are improved, and particularly, the rate capability is remarkably improved compared with that of a control group.

Description

Technical Field

[0001] The present application belongs to the technical field of sodium ion batteries, and more specifically, relates to a polyanion sodium cathode material and a solution spray preparation method and application thereof. Background Art

[0002] Limited by the abundance of lithium in the Earth's crust, lithium-ion batteries struggle to support the growing energy storage market. Sodium-ion batteries, which operate on a similar principle to lithium-ion batteries, offer advantages for large-scale energy storage applications due to their abundant sodium salt reserves and ease of mining. They are expected to find widespread application in new energy vehicles, communication base stations, energy storage, and aerospace.

[0003] Sodium-ion batteries are primarily composed of a positive electrode, a negative electrode, an electrolyte, a separator, and associated components. The positive and negative electrode materials are crucial for the performance of sodium-ion batteries, with the positive electrode material being particularly prominent. While polyanionic cathode materials, such as sodium ferric phosphate pyrophosphate, have attracted widespread attention due to their low cost, environmental friendliness, and excellent structural stability, existing preparation methods for these polyanionic cathode materials, however, have limited electrochemical performance, particularly rate capability, when used. Summary of the Invention

[0004] In response to the defects of the existing technology, the purpose of this application is to provide a polyanion sodium cathode material with excellent rate performance and its solution spray preparation method and application. By specially controlling the precursor to be in a solution state and then regulating the pore structure of the secondary particles during the spray granulation process, a polyanion cathode material with excellent rate performance is finally obtained. This aims to solve the technical problem that the electrochemical performance, especially the rate performance, of the polyanion cathode materials prepared by the existing technology is poor.

[0005] To achieve the above objectives, in a first aspect, the present application provides a method for spraying a solution of a polyanion sodium cathode material, comprising the following steps: (1) mixing powdered ferric phosphate, an acidic organic carbon source with reducing properties, and deionized water, so that the trivalent iron is dissociated under acidic conditions and reduced to divalent iron, which chelates with the carbon source to form a chelate, thereby obtaining a first mixed solution; (2) mixing and stirring the first mixed solution with a phosphorus source, a sodium source, and an additive to react to obtain pyrophosphate ions, thereby obtaining a precursor solution; the additive acts as a dispersant and a surfactant; (3) diluting the precursor solution with deionized water and spray drying to obtain a polyanion sodium cathode material precursor; (4) Sintering the polyanion sodium cathode material precursor in step (3) to obtain the polyanion sodium cathode material.

[0006] Preferably, the phosphorus source is one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate and phosphoric acid; The sodium source is one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium oxalate, sodium chloride, sodium nitrate and sodium citrate; The reducing acidic organic carbon source is one or more of citric acid, sucrose, oxalic acid, maltose, fructose and glucose; The additive is one or more of polyethylene glycol, polyvinyl alcohol, sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate.

[0007] Preferably, the particle size of the powdered iron phosphate is 1 μm or less. Preferably, the mass ratio of the ferric phosphate, carbon source and deionized water in step (1) is (1-10): (2-5): (50-100); The molar ratio of the sodium source to the ferric phosphate is (4-4.1):3, the mass percentage of the sodium source in the precursor solution is 4-5%, and the mass fraction of the additive is 0.5%-5%.

[0008] Preferably, the mixing and stirring time in step (1) is greater than or equal to 4 h, more preferably 4 to 6 h; and / or, The mixing and stirring in step (2) is carried out for 12 to 30 h, at a stirring rate of 600 to 1200 rpm, and at room temperature.

[0009] Preferably, in step (3), the precursor solution is diluted with deionized water, and the volume ratio of the precursor solution to the deionized water for dilution is 1:1-10, more preferably 1:2-5, and even more preferably 1:2.5-3.5.

[0010] Preferably, the spray drying in step (3) is carried out at a drying temperature of 100 to 120°C, a feed rate of 100 to 500 mL / h, and a wind speed of 20 to 40 m / h. 3 / h.

[0011] Preferably, the sintering temperature in step (4) is 250-650° C., and the sintering time is 8-15 hours.

[0012] Further preferably, the sintering in step (4) is specifically: pre-sintering at 250-400°C for 2-5 hours under an inert atmosphere; and then secondary sintering at 500-650°C for 6-10 hours.

[0013] According to another aspect of the present invention, a polyanion sodium cathode material prepared by the preparation method is provided.

[0014] According to another aspect of the present invention, a sodium ion battery is provided, wherein the positive electrode active material thereof comprises the polyanion sodium positive electrode material.

[0015] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: (1) The present invention provides a method for preparing a polyanion sodium cathode material. The method controls the precursor reaction process to obtain a solution of the precursor (primary particles). The size and pore structure of the secondary particles are then regulated by controlling spray process parameters. Finally, the polyanion sodium cathode material of the present invention is prepared by sintering. The polyanion cathode material prepared by the present invention has improved first reversible capacity, cycle stability, and compaction density. In particular, the rate performance is significantly improved compared to the control group.

[0016] (2) The present invention improves the first efficiency, compaction density and cycle stability by regulating the pore size and morphology of the polyanion sodium cathode material. Taking a sodium iron pyrophosphate polyanion cathode material prepared in the preferred embodiment 1 of the present invention as an example, after being assembled into a battery, the first cycle reversible discharge capacity at 0.1 C can reach 122.71 mAh / g, which is close to the theoretical specific capacity of 129 mAh / g, and the first cycle coulomb efficiency is as high as 99.35%. After 500 cycles, the specific capacity is still 119.02 mAh / g, and the capacity retention rate is 96.99%. The discharge specific capacity at 1 C is 108.38 mAh / g, the discharge specific capacity at 2 C is 92.45 mAh / g, the discharge specific capacity at 5 C is 81.59 mAh / g, and the discharge specific capacity at 10 C is 70.24 mAh / g. It can be seen that the material not only has a high first cycle coulomb efficiency and good rate performance, but also has good cycle stability. At the same time, the compacted density of the material was also measured, which was 2.36 g / cm 3 , which is beneficial to improving the energy density of the battery.

[0017] (3) The present invention regulates the material morphology and pore size by controlling the spray process parameters, and applies this control method to the control of the morphology and pore size of polyanion sodium cathode materials. The prepared cathode material has a high compaction density, good rate performance and cycle stability, and the synthesis technology route is simple, and it is easy to industrialize. It will be a good energy storage material and is expected to become a leader in the new generation of energy storage materials, especially in the fields of portable energy storage equipment, new energy vehicles, communication base stations, aerospace, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an X-ray phase analysis diagram of the Na4Fe3(PO4)2P2O7 polyanion sodium cathode material obtained in Example 1 of the present invention; Figure 24 is a SEM image of the polyanion sodium cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention; Figure 3 1 is a charge-discharge curve diagram of the polyanion sodium cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention at a rate of 0.1C; Figure 4 4 is a rate performance diagram of the polyanion sodium cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention; Figure 5 4 is a cycle performance diagram of the polyanion sodium cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 of the present invention; Figure 6 4 is a SEM image of the polyanion sodium cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1 of the present invention and Comparative Example 4; Figure 7 These are photos of the precursor fluids obtained in Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0020] The present invention provides a method for preparing a polyanion sodium cathode material by a solution spraying method, comprising the following steps: (1) mixing powdered ferric phosphate, an acidic organic carbon source with reducing properties, and deionized water, so that the trivalent iron is dissociated under acidic conditions and reduced to divalent iron, which chelates with the carbon source to form a chelate, thereby obtaining a first mixed solution; (2) mixing and stirring the first mixed solution with a phosphorus source, a sodium source, and an additive to react to obtain pyrophosphate ions, thereby obtaining a precursor solution; the additive acts as a dispersant and a surfactant; (3) diluting the precursor solution with deionized water and spray drying to obtain a polyanion sodium cathode material precursor; (4) Sintering the polyanion sodium cathode material precursor in step (3) to obtain the polyanion sodium cathode material.

[0021] In some embodiments, the phosphorus source is one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; the sodium source is one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium oxalate, sodium chloride, sodium nitrate, and sodium citrate; the carbon source is one or more of citric acid, sucrose, oxalic acid, maltose, fructose, and glucose; and the additive is one or more of polyethylene glycol, polyvinyl alcohol, sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate. The preferred additive is polyethylene glycol, having a molecular weight of 200 to 2000.

[0022] In some embodiments, the particle size (D 50 ) is 1μm or less. In some embodiments, the mass ratio of the ferric phosphate, carbon source, and deionized water in step (1) is (1-10):(2-5):(50-100); the molar ratio of the sodium source to the ferric phosphate is (4-4.1):3, and the mass percentage of the sodium source in the precursor solution is 4-5%. The mass fraction of the additive in the precursor solution is 0.5%-5%, preferably 0.5%-1.0%.

[0023] The present invention first ball-mills ferric phosphate to 1 micron or less, then mixes it with an acidic organic carbon source aqueous solution with reducing properties, and stirs the mixture under acidic conditions (pH of about 2-3) for a sufficiently long time to precipitate the trivalent iron, which then chelates with the carbon source to form a chelate to obtain a first mixed solution. Then, a water-soluble phosphorus source and a sodium source are mixed into the mixed solution, and an additive that acts as a dispersant and a surfactant is further introduced to adjust the pH of the system to between 6 and 7. During the stirring process, phosphate ions react with dihydrogen phosphate ions to obtain pyrophosphate ions, and the reaction is fully stirred to obtain a reaction precursor in a solution state.

[0024] Experiments have found that the control of the reaction process in steps (1) and (2) is crucial to whether a clear and transparent precursor solution can be obtained. For example, if the reaction time in step (1) is not long enough, a clear and transparent first mixed solution cannot be obtained. If additives such as polyethylene glycol are not introduced in step (2), a clear and transparent precursor solution cannot be obtained. It is speculated that the role of additives such as polyethylene glycol is to destroy the isoelectric point of the colloid, prevent the coagulation and suspension of divalent iron ions or the formation of colloids, reduce the interfacial tension between liquids, and act as a dispersant and surfactant to promote the formation of the solution. At the same time, it also increases the surface charge of the solution, effectively increases the reaction force between liquids, and is more conducive to the formation of a dispersed and uniform solution system. For another example, if the reaction time in step (2) is too short, a clear and transparent precursor solution cannot be obtained either. At the same time, experiments have also found that the concentration of the raw materials prepared in step (2) should not be too low, otherwise it is difficult to obtain a clear and transparent precursor solution, which may be due to the influence of reaction kinetics causing the reaction to be too slow. In order to solve this problem, the present invention obtains a clear and transparent precursor solution under the conditions of ensuring the optimal reaction kinetics of step (2), and then in step (3), the precursor solution obtained in step (2) is diluted by an appropriate multiple to obtain a spray feed liquid of appropriate concentration, which is spray-dried to obtain secondary particles of appropriate size and pore specifications, and then further sintered to obtain the polyanion positive electrode material of the present invention with excellent performance.

[0025] In addition, when the precursor solution obtained in step (2) (referred to as primary particles in the present invention) is spray-dried to obtain secondary particles in step (3), the size and pore size of the secondary particles have a great influence on the electrochemical properties of the final positive electrode material, and different concentrations of the spray feed solution have a great influence on the size and pore size of the secondary particles obtained by spray drying.

[0026] In some embodiments, the mixing and stirring time in step (1) is greater than or equal to 4 hours to obtain a clear and transparent first mixed solution, and more preferably 4 to 6 hours; the mixing and stirring time in step (2) is 12 to 30 hours, the stirring rate is 600 to 1200 rpm, and the reaction temperature is room temperature (20 to 30°C).

[0027] In some embodiments, the precursor solution in step (3) is diluted with deionized water, and the volume ratio of the precursor solution to the deionized water for dilution is 1:1-10, preferably 1:2-5, and more preferably 1:2.5-3.5.

[0028] In some embodiments, the drying temperature of the spray drying in step (3) (here, the outlet temperature of the spray dryer) is 100-120°C, the feed rate is 100-500 mL / h, and the wind speed is 20-40 m 3 / h, the inlet temperature of the spray dryer is generally 220-240℃.

[0029] In the present invention, the precursor solution obtained by mixing in step (1) is referred to as primary particles, and the particles obtained after spray drying and sintering the precursor solution are referred to as secondary particles. Perhaps due to the poor solubility of iron phosphate, the prior art usually directly spray-dries the precursor suspension containing undissolved particles to prepare the cathode material precursor. The prior art uses spray drying to prepare polyanion cathode materials. The purpose of spray drying is mainly to dry the precursor material. Usually, the spray feed liquid is a suspension containing solid particles. The control of the spray drying process parameters is mainly to control the solvent content. The suspension precursor containing solid particles cannot be controlled by the spray process to control the pore structure of the secondary particles. However, unlike the prior art, the present invention redesigns the type and particle size of the raw materials, especially the powder particle size of iron phosphate, the dosage, the use of additives and the reaction conditions, so that the prepared precursor is in a clear and transparent solution state. During spray drying, the spray process parameters are specifically controlled to adjust the size of the obtained cathode material and the particle pore size, and finally a polyanion cathode material with significantly better performance than other comparative samples is obtained.

[0030] In some embodiments, the sintering temperature in step (4) is 250-650°C, and the sintering time is 8-15 hours. In a more preferred embodiment, the sintering in step (4) is specifically: pre-sintering at 250-400°C for 2-5 hours under an inert atmosphere; followed by a secondary sintering at 500-650°C for 6-10 hours.

[0031] In some embodiments, the inert atmosphere is nitrogen, argon, a nitrogen-hydrogen mixed atmosphere, an argon-hydrogen mixed atmosphere, or a vacuum atmosphere.

[0032] The present invention also provides a sodium polyanion cathode material prepared by the above-mentioned preparation method and a sodium ion battery, wherein the positive electrode active material of the sodium ion battery comprises the sodium polyanion cathode material of the present invention.

[0033] The present invention synthesizes a polyanionic sodium cathode material with controllable morphology and pore size, which can be used as a positive electrode active material for sodium ion batteries. The present invention also provides a sodium ion battery comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode active material comprises Na4Fe3(PO4)2P2O7, a polyanionic cathode material described herein.

[0034] The present invention discloses a method for controlling the morphology and pore size of a polyanion sodium positive electrode material, which is a new technology for improving the first-cycle coulombic efficiency, rate performance and cycle stability of the positive electrode material. The use of this technology can promote the rapid development of my country's electrochemical energy storage technology, and to a large extent can alleviate the problem of lagging development of energy storage batteries caused by the import of lithium resources, shortage and high prices, etc., and is expected to serve as a beneficial supplement to lithium-ion batteries. In the preparation process of the positive electrode material of the present invention, a spherical positive electrode material with uniform pore size distribution of secondary particles obtained by spray drying and sintering a precursor solution is prepared by controlling the morphology and pore size of the sodium positive electrode material. Based on the prepared porous small-particle positive electrode material, not only the sodium ion transmission distance is greatly reduced, but also the compaction density of the material is increased. These measures can effectively solve the problems of low first-cycle coulombic efficiency, poor rate performance and cyclability in the charge and discharge process, and are bound to improve the electrochemical properties of the active material.

[0035] In some embodiments, the specific implementation process is as follows: a certain amount of deionized water is added to a three-necked flask, and a certain amount of FePO4 powder ball-milled to 1 micron or less and a carbon source containing citric acid are added in sequence under magnetic stirring. Then, NaH2PO4, NaHCO3, and PEG-200 are added. The reaction is carried out at room temperature for a certain period of time to obtain a precursor solution of the positive electrode material for a sodium ion battery. This precursor is then diluted with deionized water in a certain proportion and spray-dried under certain conditions. The dried precursor is then placed in a box furnace and sintered at different temperatures in an inert atmosphere to obtain the positive electrode material for a sodium ion battery. The preparation method of the present invention has a simple synthesis process and is easy to industrialize.

[0036] The present invention also provides a method for regulating the morphology and porosity of battery positive electrode materials. By controlling the porosity, morphology and particle size of the positive electrode active material, the sodium ion transmission distance is shortened, thereby improving the rate performance and long-cycle stability. Spherical positive electrode materials with good dispersion performance and uniform particle size are synthesized, which is more conducive to the subsequent assembly of batteries, not only improving the compaction density of the material, but also improving the electrochemical performance of the positive electrode material.

[0037] The porous spherical polyanion sodium cathode material prepared by the present invention has the advantages of simple synthesis technology route, low cost, high compaction density, high initial charge and discharge efficiency, good safety, good rate performance and can be applied to aqueous solution system.

[0038] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0039] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0040] The process parameters in the following examples where no specific conditions are specified are generally based on conventional conditions.

[0041] The following are examples: Example 1 A method for preparing a polyanion sodium cathode material, comprising the following steps: (1) First, ball mill FePO4 for 4 hours to make the powder particle size 1 micron (D 50 ), 4.52 g of finely ground FePO4 was added to 78.06 g of deionized water and 73.50 g of citric acid C6H8O, and the mixture was stirred for 4 hours to precipitate the ferric iron and reduce it to ferrous iron, which then reacted with the citric acid to form a chelate solution with a pH of about 3, thereby obtaining a first mixed solution; (2) Add 1.20 g of NaH2PO4, 2.52 g of NaHCO3, and 0.60 g of PEG-200 to the first mixed solution. The mixture is stirred magnetically at 600 rpm for 18 h, and the pH is 6 to obtain a uniformly mixed precursor solution. Figure 7 As shown ( Figure 7 Content embodiment 1); (3) The mixed solution after the reaction in step (1) was diluted with 3 times of deionized water (the dilution ratio was 3:1, and the deionized water used for dilution was 3 times of the precursor solution). The spray drying conditions were adjusted to control the outlet temperature at 100 °C, the feed rate was 200 ml / h, and the wind speed was 30 m 3 / h, spraying to obtain the cathode precursor of sodium ion battery; (4) The cathode precursor prepared in step (2) was placed in a vacuum box furnace and pre-sintered at 300 °C for 3 h, and then secondary sintered at 600 °C for 8 h to obtain Na4Fe3(PO4)2P2O7 cathode material.

[0042] Other conditions were the same as those in Example 1, except that the amounts of FePO4·2H2O were adjusted to 1.51 g, 3.02 g, and 6.04 g, respectively, to obtain Examples 2, 3, and 4.

[0043] Other conditions were the same as those in Example 1, except that 0.60 g of PEG-200 was replaced with 0.30 g of PEG-200 and 0.30 g of polyvinyl alcohol, to obtain Example 5.

[0044] Other conditions were the same as those in Example 1, except that the carbon source, citric acid, was changed to glucose, to obtain Example 6.

[0045] Other conditions are the same as those in Example 1, except that NaH2PO4 is replaced by Na2HPO4 to obtain Example 7.

[0046] Other conditions are the same as those in Example 1, except that NaHCO 3 is replaced by Na 2 CO 3 to obtain Example 8.

[0047] Comparative Example 1 A method for controlling the pore size of a polyanion sodium cathode material and its application, the specific steps are as follows: (1), (2), and (4) are the same as in Example 1.

[0048] (3) The mixed solution after the reaction in step (1) is placed in a 120°C oven and dried to obtain a sodium ion battery positive electrode precursor.

[0049] Comparative Example 2 Steps (1), (2), and (4) are the same as in Example 1.

[0050] (3) The mixed solution after the reaction in step (1) was diluted with 3 times of deionized water (the dilution ratio was 3:1, and the deionized water used for dilution was 3 times of the precursor solution). The spray drying conditions were adjusted to control the outlet temperature at 100 °C, the feed rate was 400 ml / h, and the wind speed was 30 m 3 / h, spraying to obtain the positive electrode precursor of sodium ion battery.

[0051] Comparative Example 3 (1) Same as Example 1; (2) The mixed solution after the reaction in step (1) was diluted with 1 times deionized water (dilution ratio of 1:1), and the spray drying conditions were adjusted to control the outlet temperature at 100 ° C, the feed rate at 200 ml / h, and the wind speed at 30 m 3 / h, spraying to obtain the cathode precursor of sodium ion battery; (3) Same as Example 1.

[0052] Comparative Example 4 The FePO4 was ball-milled for 4 hours to obtain a powder particle size of 1 μm (D 50 ), 4.52 g of finely ground FePO4·2H2O was added to 78.06 g of deionized water and 73.50 g of citric acid C6H8O, followed by 1.20 g of NaH2PO4, 2.52 g of NaHCO3, and 0.60 g of PEG-200. The mixture was stirred magnetically at 600 rpm for 2 h to obtain a turbid precursor sample as shown in FIG. Figure 7 As shown ( Figure 7 Comparative Example 4). The turbid precursor was processed according to the operation method of step (3) and step (4) of Example 1 to prepare the positive electrode material sample of Comparative Example 4.

[0053] Comparative Example 5 Comparative Example 5 The rest is the same as Example 1, except that the amount of PEG-200 added in step (2) is 0.1 g, and the precursor obtained is as follows Figure 7 (Content Comparative Example 5) shown.

[0054] Comparative Example 6 The rest is the same as Example 1, except that PEG-200 is not added in step (2), the pH of the system is 4-5, and the obtained precursor is as follows Figure 7 As shown in (Comparative Example 6), a clear and transparent precursor solution cannot be obtained, and the test shows that it has the Tyndall effect and is a colloid.

[0055] The photos of the precursor samples prepared in Example 1, Comparative Example 4, Comparative Example 5 and Comparative Example 6 are shown in Figure 7 It can be seen that the precursor solution obtained in Example 1 is clear and transparent, while in Comparative Example 4, steps (1) and (2) are combined and the reaction time is too short. Although polyethylene glycol is introduced in Comparative Example 5, the amount added is insufficient. In Comparative Example 6, polyethylene glycol is not introduced in step (2), resulting in the obtained precursor sample being a turbid suspension or a colloid.

[0056] The sodium ion battery positive electrode material Na4Fe3(PO4)2P2O7 prepared in Example 1 was placed on an X-ray diffractometer, and the X-ray diffraction phase analysis of the sodium ion battery positive electrode material Na4Fe3(PO4)2P2O7 was obtained. Figure 1 Content. It can be seen in 2 Peaks appeared at 15.91°, 16.73°, 19.35°, 23.93°, 36.91°, 39.25°, 42.68° and 48.56°, which are consistent with the characteristic peaks of Na4Fe3(PO4)2P2O7, indicating that Na4Fe3(PO4)2P2O7 positive electrode material was prepared by this method.

[0057] The other preparation steps of Comparative Examples 1, 2, 3 and 4 are the same as those of Example 1, except that in Comparative Example 1, the spray drying of the precursor in Example 1 is replaced by oven drying, and in Comparative Example 2, the spray drying feed rate is increased from 200 ml / h to 400 ml / h; in Comparative Example 3, the mixed solution obtained in step (1) is diluted with 1 time of deionized water instead of 3 times of deionized water; in Comparative Example 4, steps (1) and (2) are combined and the reaction time is too short, and a turbid suspension precursor is used to prepare the positive electrode material. Figure 6The figures are a comparison of the morphologies of the positive electrode materials prepared in Example 1 and Comparative Example 4, respectively.

[0058] The scanning electron microscope was used to analyze the Figure 2 Content b) and Comparative Example 1 ( Figure 2 Content a), Comparative Example 2 ( Figure 2 Content c) and Comparative Example 3 ( Figure 2 Content d) The morphology, particle size and pore distribution of the prepared sodium ion battery cathode material are obtained. Figure 2 The SEM images shown ( Figure 2 (The magnification of each content is 10,000 times.) As can be seen from Figure 2b, Example 1 obtained a porous positive electrode material with uniform dispersion, small porosity, regular morphology, and a particle size of 1 to 3 μm. Figure 2 Figure a shows the SEM image of Comparative Example 1. The biggest difference from the other three images is that the cathode material's surface is remarkably smooth, lacking pores. This result is primarily due to the different precursor drying methods, demonstrating that control over spray control is crucial for the formation of pores in the material. Figure 2 Content c is the SEM image of comparative example 2. Compared with example 1, it can be clearly seen that the change in feed rate also affects the formation of secondary particles. The reason for this may be that when the feed rate is increased, the spray gun cannot quickly atomize the material, resulting in an increase in the size of the secondary particles and an increase in porosity. Figure 2 Content d is the SEM image of comparative example 3. The difference from Example 1 is that the dilution ratio with deionized water during spraying is different. When the dilution ratio of deionized water to the mixed liquid is less than 3:1, the secondary particles formed have a large particle size, a large porosity, and a rough surface of the positive electrode material.

[0059] The electrochemical performance of the sodium ion battery positive electrode material Na4Fe3(PO4)2P2O7 prepared in Example 1 was tested. The electrochemical performance of the Na4Fe3(PO4)2P2O7 prepared in Example 1 was tested using a blue light source as the positive electrode active material. Figure 3 The charge and discharge curves of the sodium ion battery positive electrode materials prepared in Example 1 and Comparative Examples 1, 2, 3 and 4 at a rate of 0.1 C are shown. Figure 3It can be clearly seen that the first-cycle discharge capacity of Example 1 is 122.71 mAh / g, and the first-cycle coulomb efficiency is as high as 99.35%. The first-cycle discharge capacity of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 are 101.98 mAh / g, 113.21 mAh / g, 93.64 mAh / g and 80.03 mAh / g, respectively, and the first-cycle coulomb efficiency is not less than 96%. It can be seen that the positive electrode active material prepared in Example 1 has a higher discharge capacity, but the first-cycle coulomb efficiency of this material is relatively high. The more prominent technical advantage of the embodiment of the present invention is that by preparing a porous positive electrode material, the rate performance of the material is improved, fast charging and discharging is achieved, and it is applied to portable fast energy storage, communication base stations, new energy vehicles, etc.

[0060] Figure 4 Figure 2 shows the rate performance of the positive electrode material Na₄Fe₃(PO₄)₂P₂Oₐ obtained from Example 1 of the present invention and Comparative Examples 1, 2, 3, and 4. As can be clearly seen from the figure, the positive electrode material prepared in Example 1 has a discharge capacity of 108.38 mAh / g at a rate of 1 C, 92.45 mAh / g at a rate of 2 C, 81.59 mAh / g at a rate of 5 C, and still 70.24 mAh / g at a rate of 10 C. Comparative Example 2, which has the best rate performance among the comparative examples, has discharge capacities of 90.36 mAh / g, 75.45 mAh / g, 64.26 mAh / g, and 54.25 mAh / g at rates of 1 C, 2 C, 5 C, and 10 C, respectively. This shows that the active material of Example 1 has better rate performance.

[0061] Figure 5 Figure 2 is a graph showing the cycling stability of the cathode material Na4Fe3(PO4)2P2O7 obtained in Example 1 of the present invention and Comparative Examples 1, 2, 3 and 4 at a rate of 0.1C. Figure 5 It can be seen that the sodium ion battery positive electrode material Na4Fe3 (PO4) 2P2O7 prepared and synthesized in Example 1 has a first-cycle discharge capacity of 122.71 mAh / g at a rate of 0.1C, and the discharge capacity after 500 cycles is still 119.02 mAh / g, with a capacity retention rate of up to 96.99%. For Comparative Example 1, Comparative Example 2 and Comparative Example 3, the capacity retention rates are 58.86%, 90.61% and 80.09% after 200 cycles, respectively. At the same time, it can also be seen from the figure that the discharge capacity of Comparative Example 4 decreases more significantly, and the discharge capacity after only 100 cycles is only 40.02 mAh / g. It can be seen that the porous positive electrode material prepared in Example 1 has better long-cycle stability. Figure 4 and Figure 5The results again demonstrate that the porous material prepared in Example 1 not only has excellent rate performance but also has superior long-cycle stability. Based on this, we can conclude that by controlling the morphology and porosity of the porous material, the rate performance, safety performance, and long-cycle performance of the positive electrode active material can be significantly improved.

[0062] In summary, the pore size control method and application of the polyanion sodium cathode material prepared by the present invention not only have the characteristics of low cost, high specific capacity and good safety, but also have the advantages of good rate performance and cycle stability. Therefore, the new technology provided by the present invention for controlling the morphology and porosity of porous battery materials can be promoted and applied in the field of chemical power sources.

[0063] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a polyanion sodium cathode material by spraying a solution, characterized in that: The steps include: (1) mixing powdered ferric phosphate, an acidic organic carbon source with reducing properties, and deionized water, so that the trivalent iron is dissociated under acidic conditions and reduced to divalent iron, which chelates with the carbon source to form a chelate, thereby obtaining a first mixed solution; (2) mixing and stirring the first mixed solution with a phosphorus source, a sodium source, and an additive to react to obtain pyrophosphate ions, thereby obtaining a precursor solution; the additive acts as a dispersant and a surfactant; (3) diluting the precursor solution with deionized water and spray drying to obtain a polyanion sodium cathode material precursor; (4) Sintering the polyanion sodium cathode material precursor in step (3) to obtain the polyanion sodium cathode material.

2. The preparation method according to claim 1, wherein The phosphorus source is one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate and phosphoric acid; The sodium source is one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium oxalate, sodium chloride, sodium nitrate and sodium citrate; The reducing acidic organic carbon source is one or more of citric acid, sucrose, oxalic acid, maltose, fructose and glucose; The additive is one or more of polyethylene glycol, polyvinyl alcohol, sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate.

3. The preparation method according to claim 1, wherein The particle size of the powdered iron phosphate is 1 μm or less.

4. The preparation method according to claim 1, wherein The mass ratio of the ferric phosphate, carbon source and deionized water in step (1) is (1-10): (2-5): (50-100); The molar ratio of the sodium source to the ferric phosphate is (4-4.1):3, the mass percentage of the sodium source in the precursor solution is 4-5%, and the mass fraction of the additive is 0.5%-5%.

5. The preparation method according to claim 1, wherein The mixing and stirring time in step (1) is greater than or equal to 4 h; and / or, The mixing and stirring in step (2) is carried out for 12 to 30 h, at a stirring rate of 600 to 1200 rpm, and at room temperature.

6. The preparation method according to claim 1, wherein In step (3), the precursor solution is diluted with deionized water, and the volume ratio of the precursor solution to the deionized water for dilution is 1:1 to 10.

7. The preparation method according to claim 1, wherein The spray drying in step (3) is carried out at a drying temperature of 100-120°C, a feed rate of 100-500 mL / h, and a wind speed of 20-40 m 3 / h.

8. The preparation method according to claim 1, wherein The sintering temperature in step (4) is 250-650° C., and the sintering time is 8-15 h.

9. The polyanion sodium cathode material prepared by the preparation method according to any one of claims 1 to 8.

10. A sodium ion battery, characterized in that: The positive electrode active material thereof comprises the polyanion sodium positive electrode material as claimed in claim 9.

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