A composite sodium iron pyrophosphate cathode material and its preparation method

Abstract

The present invention discloses a method for preparing a composite sodium ferric pyrophosphate cathode material, which relates to the technical field of sodium batteries and includes the following steps: Step S1, preparing a precursor; Step S2, combining it with a carbon source; and Step S3, sintering it. The composite sodium ferric pyrophosphate cathode material disclosed in the present invention has excellent electrochemical performance, good electrical conductivity, strong cycle performance and rate performance, and high initial charge and discharge efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium battery electrode materials, and in particular to a composite sodium iron pyrophosphate positive electrode material and a preparation method thereof. Background Art

[0002] With the increasing depletion of traditional fossil fuels like oil and coal, the development and utilization of new energy sources and the research and development of safe, low-cost energy storage technologies are urgent. Sodium-ion batteries, due to their abundant sodium resources, low cost, and similar operating principles, are widely considered an effective alternative or supplement to lithium-ion batteries. They are a typical high-safety, low-cost energy storage device with great development prospects.

[0003] Cathode materials are a crucial component of sodium-ion batteries, playing a crucial role in improving electrochemical performance, energy density, and overall battery cost. Sodium ferric pyrophosphate (SFP) is an ideal cathode material for sodium-ion batteries due to its low cost, environmental friendliness, excellent structural stability, and long cycle life. However, existing SFP has low electronic conductivity, which limits the material's rate capability. Furthermore, due to the low redox potential of iron, the voltage required during the material's use is low, significantly hindering further improvements in battery energy density.

[0004] In order to solve the above problems, the application publication number CN114050244A discloses a pyrophosphate iron-based sodium ion battery cathode composite material and a preparation method thereof, comprising Na 3.16 Fe 2.42 (P2O7)2 and modified in Na 3.16 Fe 2.42 (P2O7)2 bulk particle surface and embedded Na 3.16 Fe 2.42 The carbon-based material in the (P2O7)2 bulk particles; the mass fraction of the carbon-based material is 1-10%. Different types of carbon-based materials are added to the reactants, and a portion of the carbon-based material is evenly coated on the Na 3.16 Fe 2.42 (P2O7)2 material particles are on the surface, and another part can be embedded into the bulk structure. 3.16 Fe 2.42 The (P2O7)2 particles are connected in series, acting as a bridge for charge transfer, significantly increasing the Na 3.16 Fe 2.42 The conductivity of the (P2O7)2 cathode material itself is high. The synthesis process produces no hazardous waste, resulting in low production costs and suitability for large-scale industrial production. However, the material's rate performance and structural stability still need to be further improved. Summary of the Invention

[0005] The main purpose of the present invention is to solve the above technical problems and provide a composite sodium iron pyrophosphate positive electrode material with good electrochemical performance, good conductivity, strong cycle performance and rate performance, and high initial charge and discharge efficiency, and a preparation method thereof.

[0006] To achieve the above objectives, the present invention provides a method for preparing a composite sodium iron pyrophosphate positive electrode material, comprising the following steps:

[0007] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0008] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0009] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0010] Preferably, the molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurate, tetramethylammonium silicate, and deionized water in step S1 is 2:6:4:(1-2):(0.1-0.3):(0.02-0.04):(0.01-0.03):(28-38).

[0011] Preferably, the doping element salt is at least one of scandium nitrate, molybdenum nitrate, niobium oxalate, and germanium acetate.

[0012] Preferably, the heating rate in step S1 is 8-10°C / min.

[0013] Preferably, the certain temperature in step S1 is 95-105°C.

[0014] Preferably, the stirring speed in step S1 is 300-600 r / min.

[0015] Preferably, the mass ratio of the composite precursor to the carbon source in step S2 is 100:(3-5).

[0016] Preferably, the carbon source in step S2 is at least one of graphene, artificial graphite powder, and carbon nanotubes.

[0017] Preferably, the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0018] Preferably, the ball milling speed in step S2 is 300-500 rpm, and the time is 1-3 hours.

[0019] Preferably, the drying temperature in step S2 is 95-105° C., and the baking is performed until the weight no longer changes.

[0020] Preferably, the sintering in step S3 is specifically as follows: preheating to 350-400°C at a heating rate of 3-5°C / min, keeping warm for 1-3h, and then heating to 600-700°C at a heating rate of 5-8°C / min and sintering for 4-6h.

[0021] Another object of the present invention is to provide a composite sodium ferric pyrophosphate positive electrode material prepared by the above-mentioned preparation method of the composite sodium ferric pyrophosphate positive electrode material.

[0022] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0023] (1) The preparation method of the composite sodium iron pyrophosphate positive electrode material disclosed in the present invention has a simple process, convenient operation, high preparation efficiency and finished product qualification rate, does not require special equipment, and is suitable for efficient large-scale industrial production.

[0024] (2) The composite sodium iron pyrophosphate positive electrode material disclosed in the present invention uses sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurate, and tetramethylammonium silicate as precursor raw materials, and introduces multiple active ingredients into the positive electrode material at the same time. They cooperate with each other to make the prepared positive electrode material have good electrochemical performance, excellent cycle stability, high specific capacity, operating voltage and energy density; the addition of doping elements, tellurium and silicon can improve the activity of the positive electrode material, improve its electrochemical performance, and thus improve the cycle performance.

[0025] (3) The composite sodium iron pyrophosphate cathode material disclosed in the present invention can further stabilize the cathode material lattice structure by introducing a carbon source and working together with other doped elements, thereby making it have excellent thermochemical properties, stronger cycle performance and rate performance, and a larger reversible charge and discharge capacity. The introduction of these components,

[0026] It has no effect on the main framework structure of the material, but also increases the lattice space gap of the material, which helps Na + The diffusion and migration of ions make up for the low conductivity of polyanions.

[0027] (4) The composite sodium iron pyrophosphate positive electrode material disclosed in the present invention has good specific capacity and rate characteristics and long cycle life through reasonable selection of ball milling and sintering process parameters. DETAILED DESCRIPTION

[0028] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations. Example 1

[0029] A method for preparing a composite sodium iron pyrophosphate positive electrode material comprises the following steps:

[0030] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0031] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0032] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0033] The molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurite, tetramethylammonium silicate, and deionized water in step S1 is 2:6:4:1:0.1:0.02:0.01:28; the doping element salt is scandium nitrate.

[0034] The heating rate in step S1 is 8° C. / min; the certain temperature is 95° C.; and the stirring speed is 300 r / min.

[0035] The mass ratio of the composite precursor and the carbon source in step S2 is 100:3; the carbon source is graphene; the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0036] In step S2, the ball milling speed is 300 rpm and the time is 1 hour; the drying temperature is 95° C. and the drying is carried out until the weight no longer changes.

[0037] The sintering in step S3 is specifically as follows: preheating to 350° C. at a heating rate of 3° C. / min, keeping the temperature for 1 hour, and then heating to 600° C. at a heating rate of 5° C. / min and sintering for 4 hours.

[0038] A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing the composite sodium ferric pyrophosphate positive electrode material. Example 2

[0039] A method for preparing a composite sodium iron pyrophosphate positive electrode material comprises the following steps:

[0040] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0041] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0042] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0043] The molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurate, tetramethylammonium silicate, and deionized water in step S1 is 2:6:4:1.2: 0.15:0.025:0.015:31; the doping element salt is molybdenum nitrate.

[0044] The heating rate in step S1 is 8.5° C. / min; the certain temperature is 98° C.; and the stirring speed is 400 r / min.

[0045] The mass ratio of the composite precursor and the carbon source in step S2 is 100:3.5; the carbon source is graphene; the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0046] In step S2, the ball milling speed is 350 rpm and the time is 1.5 h; the drying temperature is 98° C. and the drying is performed until the weight no longer changes.

[0047] The sintering in step S3 is specifically as follows: preheating to 370°C at a heating rate of 3.5°C / min, keeping the temperature for 1.5 hours, and then heating to 630°C at a heating rate of 6°C / min and sintering for 4.5 hours.

[0048] A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing the composite sodium ferric pyrophosphate positive electrode material. Example 3

[0049] A method for preparing a composite sodium iron pyrophosphate positive electrode material comprises the following steps:

[0050] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0051] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0052] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0053] In step S1, the molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurate, tetramethylammonium silicate, and deionized water is 2:6:4:1.5:0.2:0.03:0.02:33; the doping element salt is niobium oxalate.

[0054] The heating rate in step S1 is 9° C. / min; the certain temperature is 100° C.; and the stirring speed is 450 r / min.

[0055] The mass ratio of the composite precursor and the carbon source in step S2 is 100:4; the carbon source is graphene; the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0056] In step S2, the ball milling speed is 400 rpm and the time is 2 h; the drying temperature is 100° C. and the drying is performed until the weight no longer changes.

[0057] The sintering in step S3 is specifically as follows: preheating to 380°C at a heating rate of 4°C / min, keeping the temperature for 2 hours, and then heating to 650°C at a heating rate of 6.5°C / min and sintering for 5 hours.

[0058] A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing the composite sodium ferric pyrophosphate positive electrode material. Example 4

[0059] A method for preparing a composite sodium iron pyrophosphate positive electrode material comprises the following steps:

[0060] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0061] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0062] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0063] In step S1, the molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurite, tetramethylammonium silicate, and deionized water is 2:6:4:1.8:0.25:0.035:0.025:36; the doping element salt is a mixture of scandium nitrate, molybdenum nitrate, and niobium oxalate in a mass ratio of 1:2:3.

[0064] The heating rate in step S1 is 9.5° C. / min; the certain temperature is 103° C.; and the stirring speed is 550 r / min.

[0065] The mass ratio of the composite precursor and the carbon source in step S2 is 100:4.5; the carbon source is graphene; the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0066] In step S2, the ball milling speed is 450 rpm and the time is 2.5 h; the drying temperature is 103° C. and the drying is performed until the weight no longer changes.

[0067] The sintering in step S3 is specifically as follows: preheating to 390°C at a heating rate of 4.5°C / min, keeping the temperature for 2.5 hours, and then heating to 680°C at a heating rate of 7.5°C / min and sintering for 5.5 hours.

[0068] A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing the composite sodium ferric pyrophosphate positive electrode material. Example 5

[0069] A method for preparing a composite sodium iron pyrophosphate positive electrode material comprises the following steps:

[0070] Step S1, preparation of a precursor: sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the mixture is kept warm until the weight no longer changes, thereby obtaining a composite precursor;

[0071] Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying;

[0072] Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

[0073] The molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurite, tetramethylammonium silicate, and deionized water in step S1 is 2:6:4:2:0.3:0.04:0.03:38; the doping element salt is germanium acetate.

[0074] The heating rate in step S1 is 10° C. / min; the certain temperature is 105° C.; and the stirring speed is 600 r / min.

[0075] The mass ratio of the composite precursor and the carbon source in step S2 is 100:5; the carbon source is graphene; the graphene is a single-layer graphene with a thickness of 0.8-1.2 nm and a diameter of 0.5-5 μm, and is numbered XF001H.

[0076] In step S2, the ball milling speed is 500 rpm and the time is 3 hours; the drying temperature is 105° C. and the drying is carried out until the weight no longer changes.

[0077] The sintering in step S3 is specifically as follows: preheating to 400°C at a heating rate of 5°C / min, keeping the temperature for 3 hours, and then heating to 700°C at a heating rate of 8°C / min and sintering for 6 hours.

[0078] A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing the composite sodium ferric pyrophosphate positive electrode material.

[0079] Comparative Example 1

[0080] The present invention provides a composite sodium iron pyrophosphate positive electrode material, the formula and preparation method of which are similar to those of Example 1, except that sodium tellurate and tetramethylammonium silicate are not added.

[0081] Comparative Example 2

[0082] The present invention provides a composite sodium iron pyrophosphate cathode material, the formula and preparation method of which are similar to those of Example 1, except that no doping element salt and carbon source are added.

[0083] To further illustrate the beneficial technical effects of the composite sodium ferric pyrophosphate cathode materials produced in various embodiments of the present invention, the composite sodium ferric pyrophosphate cathode materials produced in each example were ground and mixed with a conductive agent, Super P, and a binder, PVDF, at a mass ratio of 80:10:10. The materials were then dissolved and dispersed evenly in N-methylpyrrolidone, coated onto aluminum foil, dried, and roll-pressed to form a positive electrode sheet. CR2025 button-type batteries were assembled in a glove box using the positive electrode sheet as the working electrode, a sodium metal sheet as the counter and reference electrodes, 1 mol / L NaPF6 (PC:DEC = 2:3 V:V) as the electrolyte, and a Celgard 2400 separator as the separator.

[0084] At room temperature, charge the battery at a constant current of 0.5C to 3.9V, then switch to constant voltage charging at 3.9V. Stop charging when the charging current drops below 0.05C. Wait for 10 minutes, then discharge the battery at a constant current of 0.5C to 2.0V. Record the discharge capacity. Repeat this process five times, taking the average. Repeat the charging process, then discharge the battery at currents of 1C, 2C, and 3C to 2.0V, recording the discharge capacity. Repeat the test five times at different discharge rates, taking the average. Calculate the percentage of the 3C discharge capacity to the 0.5C discharge capacity.

[0085] At room temperature, the battery was charged at a constant current of 0.5C to 3.9V, then switched to a constant voltage charge of 3.9V. Charging was terminated when the charging current fell below 0.05C. The battery was allowed to rest for 10 minutes, then discharged at a constant current of 0.5C to 2.0V. The battery was allowed to rest for 10 minutes. This step was repeated for 300 cycles. The discharge capacity was recorded at each discharge, and the percentage of the 300th discharge capacity to the first discharge capacity was calculated.

[0086] Charge and discharge were performed at room temperature in the voltage range of 1.0 to 4.2 V and the current density of 0.1 C, and the first charge and discharge efficiency was recorded.

[0087] Table 1

[0088] project First charge and discharge efficiency (%) Rate performance (3C / 0.5C) Capacity retention after 300 cycles (%) Example 1 95.16 96.5 96.8 Example 2 95.35 96.9 97.5 Example 3 95.56 97.6 98.0 Example 4 96.84 97.9 98.6 Example 5 96.97 98.3 99.0 Comparative Example 1 94.39 95.9 95.3 Comparative Example 2 91.74 92.8 91.1

[0089] As can be seen from Table 1, the sodium ion battery using the composite sodium iron pyrophosphate positive electrode material disclosed in the embodiment of the present invention has better electrochemical performance, rate performance and cycle performance than the comparative example product; the addition of sodium tellurate, tetramethylammonium silicate, doping element salt and carbon source is beneficial to improving the above performance.

[0090] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite sodium iron pyrophosphate positive electrode material, characterized in that: The steps include: Step S1, Preparing a Precursor: Sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, a doping element salt, sodium tellurate, and tetramethylammonium silicate are dispersed in deionized water, stirred evenly, and heated while stirring. After heating to a certain temperature, the temperature is maintained until the weight no longer changes, thereby obtaining a composite precursor; the doping element salt is at least one of scandium nitrate, molybdenum nitrate, niobium oxalate, and germanium acetate; Step S2, compounding with a carbon source: mixing the composite precursor with a carbon source, ball milling the resulting mixture, and drying; Step S3, sintering: placing the precursor compounded with the carbon source in a high-purity nitrogen atmosphere for sintering to obtain a composite sodium iron pyrophosphate positive electrode material.

2. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, wherein: The molar ratio of sodium pyrophosphate, ferrous oxalate, ammonium dihydrogen phosphate, citric acid, doping element salt, sodium tellurate, tetramethylammonium silicate, and deionized water in step S1 is 2:6:4:(1-2):(0.1-0.3):(0.02-0.04):(0.01-0.03):(28-38).

3. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, wherein: The heating rate in step S1 is 8-10°C / min; the certain temperature is 95-105°C; and the stirring speed is 300-600r / min.

4. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, wherein: The mass ratio of the composite precursor to the carbon source in step S2 is 100:(3-5).

5. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, wherein: The carbon source in step S2 is at least one of graphene, artificial graphite powder, and carbon nanotubes; the graphene is single-layer graphene with a thickness of 0.8-1.2 nm, a diameter of 0.5-5 μm, and is numbered XF001H.

6. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, characterized in that: The ball milling speed in step S2 is 300-500 rpm, and the time is 1-3 hours.

7. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, characterized in that: The drying temperature in step S2 is 95-105° C., and the drying is performed until the weight no longer changes.

8. The method for preparing the composite sodium iron pyrophosphate positive electrode material according to claim 1, characterized in that: The sintering in step S3 is specifically as follows: preheating to 350-400°C at a heating rate of 3-5°C / min, keeping the temperature for 1-3 hours, and then heating to 600-700°C at a heating rate of 5-8°C / min and sintering for 4-6 hours.

9. A composite sodium ferric pyrophosphate positive electrode material prepared by the method for preparing a composite sodium ferric pyrophosphate positive electrode material according to any one of claims 1 to 8.