Iron-based composite phosphate positive electrode material and its manufacturing method, positive electrode sheet, and sodium ion battery

Abstract

The present disclosure relates to the technical field of sodium ion battery materials, and in particular to an iron-based composite phosphate positive electrode material and its manufacturing method, a positive electrode sheet, and a sodium ion battery. The manufacturing method of the iron-based composite phosphate positive electrode material includes the steps of uniformly mixing a sodium source, a phosphorus source, a carbon source, and water, and then mixing with iron phosphate to obtain a first mixed system, grinding the first mixed system to obtain a second mixed system, and drying and sintering the second mixed system, in which the first mixed system contains Na element, Fe element, (PO 4 ) 3- and the total mass of the carbon source is 30% to 40% of the mass of the water, and the viscosity of the second mixture system is 300 Pa.S or more. The above method achieves the solution of solid reactants in the grinding process, obtains uniform reaction function, and can further be dried and sintered to obtain an iron-based composite phosphate negative electrode material that is a uniform-sized nano-spherical particle.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This disclosure claims priority to a Chinese patent application entitled "Iron-based composite phosphate positive electrode material and its manufacturing method, positive electrode sheet and sodium ion battery," filed with the China Patent Office on March 14, 2022, bearing application number CN202210247605.5, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the technical field of sodium-ion battery materials, and in particular to an iron-based composite phosphate positive electrode material and a method for producing the same, a positive electrode sheet, and a sodium-ion battery. [Background technology]

[0003] In recent years, great efforts have been made to develop clean energy sources such as solar energy, wind energy, and water energy. However, these clean energy sources have drawbacks such as high variability, low stability, and intermittent supply, and therefore require integration and conversion into large-scale energy storage devices for rational utilization. Among existing energy storage technologies, secondary batteries are considered to be one of the ideal options for large-scale energy storage technology due to their excellent flexibility and high energy conversion efficiency.

[0004] Lithium-ion batteries have been very successful in the fields of portable electronics and electric vehicles due to their high energy density and good cycling stability, but they cannot meet the requirements for inexpensive large-scale energy storage due to the scarcity and uneven distribution of lithium resources. However, sodium-ion batteries have a similar operating principle to lithium-ion batteries, but their storage capacity is more abundant and more widely distributed.

[0005] Considering the important characteristic that the value cost of large-scale energy storage devices is greater than the energy density, sodium-ion batteries are considered to be one of the potential candidates for large-scale energy storage systems.

[0006] Currently, many cathode materials for sodium-ion batteries have been reported, but only a few have shown good electrochemical performance, such as vanadium-based phosphates, iron-based phosphates, and Prussian blue analogues.

[0007] Furthermore, in the process of commercializing experimental results, these materials have also faced several serious problems, such as the high toxicity and high cost of vanadium-based materials and the structural instability of Prussian blue analogues. Among iron-based phosphates, Na4Fe3(PO4)2P2O7 is low-cost, environmentally friendly, and has a theoretical capacity of 129 mAh g -1 ) and high average operating voltage (3.1V / s.Na + This material is considered to be the most promising cathode material for sodium-ion batteries because it combines all the advantages of iron-based phosphates, including a high solubility in iron (Na) and a low volume expansion coefficient (4% reduction).

[0008] However, the synthesis of Na4Fe3(PO4)2P2O7 uses a water-soluble salt, but this process is expensive, causes serious environmental pollution due to decomposition products, and is not favorable for industrial development considering the production costs of raw materials. Therefore, finding a more economical manufacturing process will be helpful for mass production of Na4Fe3(PO4)2P2O7. Summary of the Invention [Means for solving the problem]

[0009] One objective of the present disclosure is to provide a method for producing an iron-based composite phosphate positive electrode material, in which the viscosity of the solution is controlled using an appropriate solid-liquid ratio to achieve solution of solid reactants in the grinding process, obtain uniform reaction functions, and then dry and sinter to obtain the final product.

[0010] Another object of the present invention is to provide an iron-based composite phosphate positive electrode material produced by the method for producing the iron-based composite phosphate positive electrode material.

[0011] Another object of the present invention is to provide a positive electrode sheet containing the positive electrode material.

[0012] Another object of the present invention is to provide a sodium ion battery including the positive electrode sheet.

[0013] In order to achieve the above objectives of the present disclosure, the following technical solutions are particularly adopted: The present disclosure provides a method for producing an iron-based composite phosphate cathode material, the method comprising: a step of uniformly mixing a sodium source, a phosphorus source, a carbon source, and water, and then mixing the mixture with iron phosphate to obtain a first mixed system; and a step of grinding the first mixed system to obtain a second mixed system, which is then dried and sintered; In the first mixture system, Na element, Fe element, (PO4) 3- The total mass of the carbon source is 30% to 40% of the mass of the water, and the viscosity of the second mixture system is 300 Pa.S or more.

[0014] Optionally, the sodium source comprises at least one of sodium acetate, sodium nitrate, sodium oxalate, sodium citrate, and sodium phosphate.

[0015] Optionally, the phosphorus source comprises at least one of sodium dihydrogen phosphate, sodium phosphate, and phosphoric acid.

[0016] Optionally, the carbon source comprises at least one of citric acid, glucose, sucrose, and polyethylene glycol.

[0017] Alternatively, the molar ratio of the phosphorus source, sodium source and carbon source is 1:(2.8-3.2):(1-10).

[0018] Optionally, the molar ratio of Fe to P in the iron phosphate is 0.97-1.

[0019] Optionally, the iron phosphate comprises micron-scale particles and / or nano-scale aggregates.

[0020] Optionally, in the second mixture system, the particle size D90 of said iron phosphate is 0.05 to 0.15 μm.

[0021] Optionally, the viscosity of the second mixture system is 300 to 400 Pa.S.

[0022] Optionally, the drying comprises spray drying.

[0023] Optionally, the drying temperature is 80 to 120° C., and the drying time is 5 to 10 hours.

[0024] Optionally, the sintering step includes carrying out a first sintering process at a temperature of 290 to 310°C, and then carrying out a second sintering process at a temperature of 550 to 600°C.

[0025] Optionally, the duration of the first sintering treatment is 3 to 5 hours, and the duration of the second sintering treatment is 10 to 12 hours.

[0026] Optionally, the temperature increase rate is 2 to 5° C. / min.

[0027] The iron-based composite phosphate positive electrode material is manufactured by the method for manufacturing the iron-based composite phosphate positive electrode material.

[0028] Optionally, the iron-based composite phosphate positive electrode material is a spherical particle with a particle size of 100-200 nm.

[0029] The present disclosure further provides a positive electrode sheet comprising the positive electrode material.

[0030] The present disclosure further provides a sodium ion battery including the positive electrode sheet. [Effects of the Invention]

[0031] Compared with the prior art, the beneficial effects of the present disclosure are as follows: (1) This disclosure uses an appropriate solid-liquid ratio to control the viscosity of the solution, thereby achieving a solution of solid reactants during the polishing process, resulting in a uniform reaction function. The resulting material is then dried and sintered to obtain an iron-based composite phosphate cathode material. The material is comprised of nanospherical particles with uniform particle sizes of 100-200 nm and has excellent electrochemical performance.

[0032] (2) The iron-based composite phosphate positive electrode material prepared in this disclosure can be applied to sodium-ion batteries, which can further improve the cycle performance and safety performance of the batteries. [Brief explanation of the drawings]

[0033] In order to more clearly describe the specific embodiments of the present disclosure or the technical solutions of the prior art, the following briefly introduces drawings necessary for describing the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present disclosure, and those skilled in the art can obtain other drawings based on these drawings without any creative efforts. [Figure 1] 1 is a scanning electron microscope photograph (SEM image) of the iron-based composite phosphate positive electrode material obtained in Example 1 of the present disclosure. [Figure 2] 1 is a graph showing the charge and discharge curves of a battery manufactured using the iron-based composite phosphate positive electrode material obtained in Example 1 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to examples. However, those skilled in the art should understand that the following examples are only for illustrating the present disclosure and should not be considered to limit the scope of the present disclosure. If no specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer will be followed. Reagents or equipment for which no manufacturer is specified are all conventional products available on the market.

[0035] According to one aspect of the present disclosure, a method for producing an iron-based composite phosphate cathode material according to the present disclosure includes: a step of uniformly mixing a sodium source, a phosphorus source, a carbon source, and water, and then mixing the mixture with iron phosphate to obtain a first mixed system; and a step of grinding the first mixed system to obtain a second mixed system, which is then dried and sintered; In the first mixture system, Na element, Fe element, (PO4) 3- The total mass of the carbon source is 30% to 40% of the mass of the water, and the viscosity of the second mixture system is 300 Pa.S or more.

[0036] This disclosure uses an appropriate solid-liquid ratio to control the viscosity of the solution, thereby achieving a solution of solid reactants during the polishing process and achieving uniform reaction functionality. This is then dried and sintered to obtain an iron-based composite phosphate Na4Fe3(PO4)2P2O7 cathode material, which consists of nanospherical particles with a uniform particle size of 100-200 nm.

[0037] In one embodiment, the first mixture system contains Na element, Fe element, (PO4) 3- The total mass of (phosphate) and carbon source is 30% to 40% of the mass of the water, specifically including, but not limited to, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, or 39%.

[0038] In one embodiment, the viscosity of the second mixture system is 300 Pa.S or more, specifically 310 Pa.S or more. . In one embodiment, the viscosity of the second mixture system is 300 to 500 Pa.S.

[0039] The term "polishing" refers to a method of finely dispersing particles by mechanical force, such as sanding, where the sanding medium includes at least one of sandstone, glass beads, zirconia beads, and zirconium silicate beads.

[0040] In one embodiment, the sodium source comprises at least one of sodium acetate, sodium nitrate, sodium oxalate, sodium citrate, and sodium phosphate.

[0041] In one embodiment, the phosphorus source comprises at least one of sodium dihydrogen phosphate, sodium phosphate, and phosphoric acid.

[0042] In one embodiment, the carbon source comprises at least one of citric acid, glucose, sucrose, and polyethylene glycol.

[0043] In one embodiment, the molar ratio of the phosphorus source, the sodium source, and the carbon source is 1:(2.8 to 3.2):(1 to 10).

[0044] In one embodiment, the molar ratio of the phosphorus source, sodium source, and carbon source is 1:3:1, 1:3:2, 1:3:3, 1:3:4, 1:3:5, 1:3:6, 1:3:7, or 1:3:10.

[0045] In one embodiment, the molar ratio of Fe to P in the iron phosphate is 0.97 to 1. For example, it may be 0.98 or 0.99.

[0046] In one embodiment, the iron phosphate is a crystalline or amorphous particle. The iron phosphate comprises micron-scale particles and / or nano-scale aggregates. The preferred type is the nano-scale aggregates.

[0047] In one embodiment, the iron phosphate micron-scale particles have a particle size of 1-20 μm, including but not limited to, 2 μm, 3 μm, 5 μm, 6 μm, 7 μm, 10 μm, 11 μm, 13 μm, 15 μm, 17 μm, or 20 μm.In one embodiment, the iron phosphate micron-scale particles have a particle size of 20-200 nm, including but not limited to, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 70 nm, 80 nm, 100 nm, 120 nm, 150 nm, 170 nm, 180 nm, and 200 nm.

[0048] In one embodiment, the particle size D90 of the iron phosphate in the second mixture system is 0.05 to 0.15 μm.

[0049] In one embodiment, the particle size D90 of the iron phosphate is 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.11 μm, 0.12 μm, 0.13 μm, 0.14 μm, or 0.15 μm.

[0050] In one embodiment, the drying comprises spray drying.

[0051] In one embodiment, the drying temperature is 80 to 120°C, and the drying time is 5 to 10 hours. In one embodiment, the drying temperature is 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, or 115°C. The drying time is 6 hours, 7 hours, 8 hours, 9 hours, or 9.5 hours.

[0052] In one embodiment, the sintering includes performing a first sintering process at a temperature of 290 to 310°C, and then performing a second sintering process at a temperature of 550 to 600°C. In one embodiment, the temperature of the first sintering process is 292°C, 295°C, 298°C, 300°C, 302°C, 305°C, or 309°C. In one embodiment, the temperature of the second sintering process includes, but is not limited to, 555°C, 560°C, 565°C, 570°C, 575°C, 580°C, 585°C, 590°C, 595°C, or 600°C.

[0053] In one embodiment, the first sintering treatment time is 3 to 5 hours, and the second sintering treatment time is 10 to 12 hours. In one embodiment, the first sintering treatment time includes, but is not limited to, 3 hours, 3.5 hours, 4 hours, or 4.5 hours. The second sintering treatment time includes, but is not limited to, 10.5 hours, 11 hours, or 11.5 hours.

[0054] The temperature rise rate is selectable between 2 and 5°C / min, for example, 2.5°C / min, 3°C / min, 4°C / min, or 4.5°C / min.

[0055] In one embodiment, the sintering is carried out under a protective gas condition, such as nitrogen, an inert gas, or the like, such as argon, neon, or the like.

[0056] In the present disclosure, the above sintering conditions result in iron-based composite phosphate cathode materials with better electrochemical performance.

[0057] According to another aspect of the present disclosure, the present disclosure also relates to an iron-based composite phosphate positive electrode material produced by the method for producing the iron-based composite phosphate positive electrode material.

[0058] In one embodiment, the iron-based composite phosphate positive electrode material is a spherical particle having a particle size of 100 to 200 nm, including, but not limited to, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm.

[0059] According to another aspect of the present disclosure, the present disclosure also relates to a positive electrode sheet comprising the positive electrode material.

[0060] According to another aspect of the present disclosure, the present disclosure also relates to a sodium-ion battery including the positive electrode sheet.

[0061] The battery of the present disclosure has excellent cycle performance and safety performance.

[0062] Hereinafter, the present disclosure will be further explained and described in combination with specific examples and comparative examples.

[0063] FIG. 1 is a scanning electron microscope photograph (SEM image) of the iron-based composite phosphate positive electrode material obtained in Example 1 of the present disclosure.

[0064] FIG. 2 is a graph showing the charge and discharge curves of a battery manufactured using the iron-based composite phosphate positive electrode material obtained in Example 1 of the present disclosure.

[0065] Example 1 The method for producing the iron-based composite phosphate positive electrode material includes: The method includes the steps of: adding sodium dihydrogen phosphate, sodium acetate, and citric acid monohydrate to 5 kg of deionized water in a molar ratio of 1:3:2, and continuing to stir until a clear solution is formed; taking a certain proportion of iron phosphate solid and adding it to the clear solution to control the total solid content at 35%, where the iron phosphate is nanoscale aggregates with a particle size of 50-100 nm; sanding the solution to disperse the iron phosphate, gradually increasing the viscosity of the solution until it reaches 300 Pa.S, and stopping the sanding; spray-drying the solution at 95°C for 8 hours, followed by high-temperature calcination in a N2 atmosphere at a heating rate of 2°C / min, maintaining the temperature at 300°C for 5 hours, and then maintaining the temperature at 550°C for 12 hours, and then naturally cooling to obtain an iron-based composite phosphate positive electrode material.

[0066] The results of SEM analysis of the morphology of the material are shown in FIG. 1, which shows that the material is comprised of nano-spherical particles with a uniform particle size of 100 to 200 nm.

[0067] Example 2 The method for producing the iron-based composite phosphate positive electrode material includes: The method includes the steps of: adding sodium dihydrogen phosphate, sodium acetate, and citric acid monohydrate to 5 kg of deionized water in a molar ratio of 1:3:5, and continuing to stir until a clear solution is formed; taking a certain proportion of iron phosphate solid and adding it to the clear solution to control the total solid content at 40%, where the iron phosphate is nanoscale aggregates with a particle size of 20-95 nm; sanding the solution to disperse the iron phosphate, gradually increasing the viscosity of the solution until it reaches 350 Pa.S, and stopping the sanding; spray-drying the solution at 120°C for 10 hours, followed by high-temperature calcination in an inert N2 atmosphere at a heating rate of 5°C / min, maintaining the temperature at 300°C for 4 hours, and then maintaining the temperature at 600°C for 10 hours, and then naturally cooling to obtain an iron-based composite phosphate positive electrode material.

[0068] Example 3 The method for producing the iron-based composite phosphate positive electrode material includes: The method includes the steps of: adding sodium dihydrogen phosphate, sodium acetate, and citric acid monohydrate to 5 kg of deionized water in a molar ratio of 1:3:10, and continuing to stir until a clear solution is formed; taking a certain proportion of iron phosphate solid and adding it to the clear solution to control the total solid content to 30%, where the iron phosphate is nanoscale aggregates with a particle size of 75-95 nm; sanding the solution to disperse the iron phosphate, gradually increasing the viscosity of the solution, and stopping the sanding when the viscosity of the solution reaches 400 Pa.S; spray-drying the solution at 80°C for 6 hours, followed by high-temperature calcination in an inert N2 atmosphere at a heating rate of 2.5°C / min, maintaining the temperature at 290°C for 4.5 hours, and then maintaining the temperature at 585°C for 11 hours, and then naturally cooling to obtain an iron-based composite phosphate positive electrode material.

[0069] Example 4 In the method for producing the iron-based composite phosphate positive electrode material, the sodium source is sodium oxalate, the phosphorus source is sodium phosphate, the carbon sources are glucose and citric acid, and the molar ratio of sodium oxalate, sodium phosphate, glucose and citric acid is 0.5:1:1:2.5, except that the other conditions are the same as in Example 1.

[0070] Example 5 In the method for producing the iron-based composite phosphate positive electrode material, the sodium source is sodium citrate, the phosphorus source is phosphoric acid, the carbon sources are polyethylene glycol, glucose, and sucrose, and the molar ratio of sodium citrate, phosphoric acid, polyethylene glycol, glucose, and sucrose is 1:1:0.1:1:1.5, except that the other conditions are the same as in Example 1.

[0071] Comparative Example 1 The preparation method of the iron-based composite phosphate cathode material was the same as that in Example 1, except that the total solid content was controlled at 25% and sanding was stopped when the solution viscosity reached 250 Pa.S.

[0072] Comparative Example 2 The preparation method of the iron-based composite phosphate positive electrode material was the same as that in Example 1, except that the total solid content was controlled at 45% and sanding was stopped when the solution viscosity reached 280 Pa.S.

[0073] Experimental example The positive electrode materials of the examples and comparative examples were weighed and mixed with acetylene black and PVDF. The resulting mixture (70:20:10 mass ratio of acetylene black to PVDF) was applied to aluminum foil with a diameter of 19 mm. The aluminum foil was then vacuum dried at 120°C for 12 hours to obtain a positive electrode sheet. Metallic sodium was used as the counter electrode, 1 mol / L NaClO4, ethylene carbonate / diethyl carbonate (volume ratio 1:1) was used as the electrolyte, and Cellgard 2035 was used as the separator. A button battery (model CR2016) was assembled in a glove box. A constant current charge / discharge test of the battery showed a current density of 26 mA / g. The test results are shown in Figure 2, and the reversible specific capacity is 109 mAh / g in the voltage range of 2.0 to 4.3 V.

[0074] The results of performance tests on the initial efficiency and capacity retention rate of the batteries of the examples and comparative examples are shown in Table 1.

[0075] [Table 1]

[0076] As can be seen from Table 1, in this disclosure, by controlling the viscosity of the solution using an appropriate solid-liquid ratio, the solid reactants are dissolved in the grinding process, resulting in a uniform reaction function. After further drying and sintering, the resulting iron-based composite phosphate positive electrode material has excellent initial efficiency and capacity retention. The solid-liquid ratios and solution viscosities of Comparative Examples 1 and 2 are outside the scope of protection of this disclosure, and the resulting positive electrode materials have much lower capacity retention than the positive electrode materials of this application.

[0077] Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present disclosure, and are not intended to limit the same. Although the present disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent substitutions for some or all of the technical features therein, and these modifications or substitutions will not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. a step of uniformly mixing a sodium source, a phosphorus source, a carbon source, and water, and then mixing the mixture with iron phosphate to obtain a first mixed system; and a step of grinding the first mixed system to obtain a second mixed system, which is then dried and sintered; In the first mixture system, the total solids mass content is 30% to 40%, and the viscosity of the second mixture system is 300 Pa.S or more. A method for producing an iron-based composite phosphate cathode material.

2. (1) The sodium source includes at least one of sodium acetate, sodium nitrate, sodium oxalate, sodium citrate, and sodium phosphate; (2) the phosphorus source includes at least one of sodium dihydrogen phosphate, sodium phosphate, and phosphoric acid; (3) The carbon source includes at least one of citric acid, glucose, sucrose, and polyethylene glycol; (4) the molar ratio of the phosphorus source, sodium source, and carbon source is 1:(2.8-3.2):(1-10); At least one of the following conditions is met: A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

3. (1) The molar ratio of Fe to P in the iron phosphate is 0.97 to 1; (2) the iron phosphate comprises micron-scale particles and / or nano-scale aggregates; At least one of the following conditions is met: A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

4. The viscosity of the second mixture system is 300 Pa.S to 400 Pa.S. A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

5. The drying comprises spray drying. A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

6. The drying temperature is 80°C to 120°C, and the drying time is 5 hours to 10 hours. A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

7. The sintering includes performing a first sintering process under conditions of 290°C to 310°C, and then performing a second sintering process by increasing the temperature to 550°C to 600°C. A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

8. The time for the first sintering treatment is 3 hours to 5 hours, and the time for the second sintering treatment is 10 hours to 12 hours. The method for producing the iron-based composite phosphate positive electrode material according to claim 7.

9. The temperature rise rate is 2°C / min to 5°C / min. The method for producing the iron-based composite phosphate positive electrode material according to claim 7.

10. The iron-based composite phosphate positive electrode material is a spherical particle having a particle size of 100 nm to 200 nm. A method for producing the iron-based composite phosphate positive electrode material according to claim 1.

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