Rare earth oxide modified ferric sodium pyrophosphate positive electrode material and preparation method and application thereof

Abstract

The invention relates to a rare earth oxide modified ferric phosphate pyrophosphate sodium positive electrode material and a preparation method and application thereof. The positive electrode material comprises a rare earth element surface doped ferric phosphate pyrophosphate sodium / carbon base material and a rare earth oxide coating layer coating the surface of the base material, the rare earth element is one of La, Ce, Pr, Y, Nd, Eu, Tb, Sm, Gd and Er, and the rare earth oxide is doped rare earth element oxide; through the structural design of the positive electrode material, the surface of the sodium ferric phosphate pyrophosphate material is coated with the carbon layer and then is coated with the rare earth oxide, so that the conductivity and the stability of the sodium ferric phosphate pyrophosphate positive electrode material can be effectively improved, and the sodium ferric phosphate pyrophosphate positive electrode material has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and more specifically to a rare earth oxide-modified sodium iron phosphate pyrophosphate positive electrode material, a preparation method thereof and an application thereof. Background Art

[0002] Sodium iron pyrophosphate (Na4Fe3(PO4)2(P2O7)) has attracted attention in the research of sodium-ion batteries due to its abundant resources, low cost and environmental friendliness. As a positive electrode material for sodium-ion batteries, it has high cycle stability and good electrochemical performance. This type of material belongs to the NASICON structure, which provides a three-dimensional ion channel structure, which is conducive to the rapid migration of sodium ions and further improves the rate performance of the battery. However, the electrical conductivity of phosphate positive electrode materials is low, which limits their performance under fast charge and discharge conditions. Therefore, it is necessary to improve their electronic and ionic conductivity through material surface modification (such as carbon coating or doping with other elements).

[0003] Research shows that the properties of sodium iron pyrophosphate enable it to provide a stable discharge platform at around 2.5V, but its electrochemical performance can be further optimized through different synthesis and modification methods. For example, incorporating carbon materials such as graphene or carbon nanotubes into sodium iron pyrophosphate can significantly improve the conductivity of the material and enhance its cycle life. In addition, doping with other metals such as titanium or vanadium has also been shown to improve the stability and conductivity of sodium iron pyrophosphate to a certain extent, and reduce irreversible capacity loss, thereby extending the service life of the battery.

[0004] However, the effect of carbon coating modification is limited. In addition, the cost of both coating and doping is too high and the operation is more complicated. Therefore, a multi-effect modification method is sought to improve the surface conductivity and stability of sodium iron pyrophosphate positive electrode materials so that they can meet the high energy density and high power requirements of practical applications. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material, which can effectively improve the conductivity and stability of the sodium iron phosphate pyrophosphate material, so that it has excellent electrochemical properties.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A rare earth oxide modified sodium ferric phosphate pyrophosphate positive electrode material, the positive electrode material comprises a sodium ferric phosphate pyrophosphate / carbon matrix material doped with a rare earth element on the surface and a rare earth oxide coating layer coated on the surface thereof; the rare earth element is one of La, Ce, Pr, Y, Nd, Eu, Tb, Sm, Gd, and Er, and the rare earth oxide is an oxide of the doped rare earth element.

[0008] The present invention firstly carbon-coates the sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2(P2O7)) cathode material, because carbon materials are cheap and the coating can improve the surface electronic and ionic conductivity of sodium iron phosphate pyrophosphate; and the rare earth oxide coating layer on the surface of the base material can significantly accumulate electrons on the surface of the material, which is beneficial to the subsequent ion insertion and extraction reaction, and ultimately improves its fast charging capability. In addition, compared with the problems of insufficient structural stability of carbon coating itself, no obvious improvement in material conductivity, and inability to stabilize the bulk material, large-radius rare earth elements doped in the sodium sites on the surface of the active material can inhibit lattice collapse during long cycles, and have significant advantages in stability, electronic and ionic conductivity.

[0009] In some embodiments, the rare earth oxide content in the positive electrode material is 0.1%-5% of the total mass, for example 0.1%, 1%, 2%, 3%, 4%, 5%, etc., and the corresponding coating thickness is 5-500nm, for example 5nm, 100nm, 200nm, 300nm, 400nm, 500nm, etc. The coating layer of specific thickness can significantly improve the electronic and ionic conductivity and stability of the surface of the positive electrode material, thereby improving the rate performance and cycle life of the battery.

[0010] In some embodiments, the mass content of carbon in the sodium iron pyrophosphate / carbon matrix material is 0.5-5%, such as 0.5%, 1%, 2%, 3%, 4%, 5%, etc.

[0011] The present invention also provides a method for preparing the rare earth oxide-modified sodium iron phosphate pyrophosphate positive electrode material, the method comprising the following steps:

[0012] S1. Weigh a sodium source, an iron source, a phosphorus source, a carbon source and a rare earth source according to chemical measurements, add them into deionized water and stir evenly to obtain a mixed slurry;

[0013] S2. After the mixed slurry is placed in a spray dryer for spray drying, the temperature is first raised to 300-400° C. for sintering in an inert atmosphere, and then the temperature is raised to 500-600° C. for secondary sintering to obtain a rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material.

[0014] In some embodiments, the sodium source is at least one of sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium acetate, and sodium citrate.

[0015] In some embodiments, the iron source is at least one of ferroferric oxide, ferric oxide, ferric chloride, ferrous oxalate, ferrous oxalate, ferrous sulfate, and ammonium ferrous sulfate.

[0016] In some embodiments, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0017] In some embodiments, the carbon source is at least one of sucrose, soluble starch, cellulose, glucose, and ascorbic acid.

[0018] In some embodiments, the rare earth source is one of yttrium oxide, cerium oxide, lanthanum oxide, praseodymium oxide, rubidium oxide, samarium oxide, europium oxide, gadolinium oxide, and terbium oxide.

[0019] In some embodiments, in step S1, the raw materials are mixed and then uniformly mixed by ball milling, the ball milling speed is 300-800 r / min, and the ball milling time is 3-12 h.

[0020] In some embodiments, in step S2, the inlet air temperature of the spray drying is 140-250°C, the outlet air temperature is 80-160°C, the nozzle diameter is 0.5-2.8 mm, the air source is compressed air, and it is preheated to 70-260°C before entering the spray gun. The spray feed flow rate is 500-5000mL / h.

[0021] In some embodiments, in step S2, the inert atmosphere is one of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere.

[0022] The present invention also provides a positive electrode, which includes the positive electrode material of any of the above embodiments or the positive electrode material obtained by the preparation method of any of the above embodiments.

[0023] The present invention also provides an electrochemical energy storage device, comprising the above-mentioned positive electrode; specifically, the electrochemical energy storage device comprises a sodium ion battery, a sodium ion capacitor, etc.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention performs rare earth oxide modification on the surface of sodium iron phosphate pyrophosphate / carbon material to achieve rare earth oxide-coated sodium iron phosphate pyrophosphate / carbon positive electrode material, so that the obtained positive electrode material exhibits excellent electrochemical performance. On the one hand, rare earth oxide coating on the base material can cause the accumulation of electrons, which is conducive to the subsequent ion embedding and extraction reactions, and improves the high-rate performance of the material; on the other hand, rare earths will be doped into the surface lattice of the sodium iron phosphate pyrophosphate bulk material in small amounts, partially replacing the sodium sites on the surface to form a solid surface, resisting lattice collapse under long cycles, and significantly improving the stability of the sodium iron phosphate pyrophosphate material during the cycle. The positive electrode material obtained by the structural design of the present invention has excellent cycle stability, electronic and ionic conductivity.

[0026] The preparation method of the present invention has low cost, simple process and obvious modification effect, which is helpful to promote the industrialization and application of iron-based sodium phosphate ion positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM image of the cerium oxide modified sodium iron phosphate pyrophosphate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0028] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] Example 1

[0031] A method for preparing a cerium oxide modified sodium iron phosphate pyrophosphate positive electrode material comprises the following steps:

[0032] S1. Add 485 g of sodium dihydrogen phosphate, 450 g of ferrous oxalate dihydrate, 90 g of citric acid, 18 g of thiourea, and 20 g of cerium oxide into 3 L of deionized water, stir in a ball mill, and stir at a speed of 600 rpm for 5 h to obtain a slurry;

[0033] S2, the slurry is transported to the spray dryer through a peristaltic pump, the air inlet temperature is 180°C, the air outlet temperature is 100°C, the air source is compressed air, the nozzle diameter is 2.0mm, and it is preheated at 150°C before entering the spray gun. The feed rate is 3500ml / h to obtain dry precursor particles;

[0034] S3. Place the precursor particles in a tubular furnace, heat them to 400°C at a rate of 5°C / min in a nitrogen atmosphere, sinter them for 3 hours, and then heat them to 600°C at a rate of 5°C / min for a second sintering for 5 hours to obtain a cerium oxide-coated sodium iron phosphate pyrophosphate positive electrode material.

[0035] The positive electrode material obtained in this example was tested by scanning electron microscope. The test results are as follows Figure 1 As shown. Figure 1 The positive electrode material obtained in this embodiment obviously has the phenomenon that nano-cerium oxide is coated on the surface of the sodium iron pyrophosphate / carbon matrix material.

[0036] The obtained positive electrode material was subjected to electrochemical performance test, as follows:

[0037] The positive electrode material, conductive agent carbon black: binder PVDF were mixed in a mass ratio of 7:2:1, and after sufficient grinding, an appropriate amount of NMP was added to obtain a uniform slurry. The slurry was coated on an aluminum foil current collector, placed in a vacuum drying oven, dried at 120°C, then taken out and cut into discs; a metallic sodium sheet was used as a counter electrode; 1M NaClO4 / EC:DMC:EMC (1:1:1) was used as an electrolyte, and the electrochemical performance of the button battery was tested after assembly.

[0038] After testing, the positive electrode material obtained in this embodiment has a discharge specific capacity of 91 mAh / g at a voltage of 1.7-4.3 V and a current density of 0.5 C.

[0039] The positive electrode material obtained in this embodiment has a discharge capacity retention rate of 99% after 100 cycles at a voltage of 1.7-4.3V and a current density of 0.5C.

[0040] Comparative Example 1

[0041] A method for preparing a cerium oxide modified sodium iron phosphate pyrophosphate positive electrode material comprises the following steps:

[0042] S1. Add 485 g of sodium dihydrogen phosphate, 450 g of ferrous oxalate dihydrate, 90 g of citric acid, 18 g of thiourea, and 50 g of cerium oxide into 3 L of deionized water, stir in a ball mill, and stir at a speed of 600 rpm for 5 h to obtain a slurry;

[0043] S2. The material is transported to the spray dryer through a peristaltic pump, the inlet air temperature is 180°C, the outlet air temperature is 100°C, the air source is compressed air, the nozzle diameter is 2.0mm, and it is preheated at 150°C before entering the spray gun. The feed rate is 3500ml / h to obtain dry precursor particles;

[0044] S3. Place the precursor particles in a tubular furnace, heat them to 400°C at a rate of 5°C / min in a nitrogen atmosphere, sinter them for 3 hours, and then heat them to 600°C at a rate of 5°C / min for a second sintering for 5 hours to obtain a cerium oxide-coated sodium iron phosphate pyrophosphate positive electrode material.

[0045] After testing, the composite material obtained in this comparative example has a discharge specific capacity of 83 mAh / g at a voltage of 1.7-4.3 V and a current density of 0.5 C.

[0046] The composite material obtained in this comparative example has a discharge capacity retention rate of 95% after 100 cycles at a voltage of 1.7-4.3V and a current density of 0.5C.

[0047] Comparative Example 2

[0048] A cerium oxide modified sodium iron phosphate pyrophosphate positive electrode material and a preparation method thereof, comprising the following steps:

[0049] S1. Add 485 g of sodium dihydrogen phosphate, 450 g of ferrous oxalate dihydrate, 90 g of citric acid, 18 g of thiourea, and 5 g of cerium oxide into 3 L of deionized water, stir in a ball mill, and stir at a speed of 600 rpm for 5 h to obtain a slurry;

[0050] S2. The material is transported to the spray dryer through a peristaltic pump, the inlet air temperature is 180°C, the outlet air temperature is 100°C, the air source is compressed air, the nozzle diameter is 2.0mm, and it is preheated at 150°C before entering the spray gun. The feed rate is 3500ml / h to obtain dry precursor particles;

[0051] S3. Place the precursor particles in a tubular furnace, heat them to 400°C at a rate of 5°C / min in a nitrogen atmosphere, sinter them for 3 hours, and then heat them to 600°C at a rate of 5°C / min for a second sintering for 5 hours to obtain a cerium oxide-coated sodium iron phosphate pyrophosphate positive electrode material.

[0052] After testing, the composite material obtained in this comparative example has a discharge specific capacity of 87 mAh / g at a voltage of 1.7-4.3 V and a current density of 0.5 C.

[0053] The composite material obtained in this comparative example has a discharge capacity retention rate of 92% after 100 cycles at a voltage of 1.7-4.3V and a current density of 0.5C.

[0054] Example 2

[0055] A lanthanum oxide modified sodium iron phosphate pyrophosphate positive electrode material and a preparation method thereof, comprising the following steps:

[0056] S1, add 485g sodium dihydrogen phosphate, 450g ferrous oxalate dihydrate, 90g citric acid, 18g thiourea, 20g lanthanum oxide into 3L deionized water, stir in a ball mill, stir at a speed of 600rpm for 5h to obtain a slurry;

[0057] S2. The material is transported to the spray dryer through a peristaltic pump, the inlet air temperature is 180°C, the outlet air temperature is 100°C, the air source is compressed air, the nozzle diameter is 2.0mm, and it is preheated at 150°C before entering the spray gun. The feed rate is 3500ml / h to obtain dry precursor particles;

[0058] S3. Place the precursor particles in a tubular furnace, heat them to 400°C at a rate of 5°C / min in a nitrogen atmosphere, and sinter them for 3 hours. Then heat them to 600°C at a rate of 5°C / min and sinter them for a second time for 5 hours to obtain the lanthanum oxide-coated sodium iron phosphate pyrophosphate positive electrode material.

[0059] After testing, the composite material obtained in this example has a discharge specific capacity of 88 mAh / g at a voltage of 1.7-4.3 V and a current density of 0.5 C.

[0060] The composite material obtained in this example has a discharge capacity retention rate of 96% after 100 cycles at a voltage of 1.7-4.3 V and a current density of 0.5 C.

[0061] The electrochemical performance test results of the positive electrode materials obtained in Example 1-2 and Comparative Example 1-2 are shown in Table 1.

[0062] Table 1 Electrochemical performance test results of positive electrode materials of Examples 1-2 and Comparative Examples 1-2

[0063]

[0064] The present invention can effectively improve the specific capacity and cycle stability of the sodium iron pyrophosphate material at a specific rate by specifically modifying the coating layer, thereby improving the electrochemical performance of the composite material.

[0065] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0066] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material, characterized in that: The positive electrode material includes a sodium iron phosphate pyrophosphate / carbon matrix material doped with a rare earth element on the surface and a rare earth oxide coating layer coated on the surface of the matrix material; the rare earth element is one of La, Ce, Pr, Y, Nd, Eu, Tb, Sm, Gd, and Er, and the rare earth oxide is an oxide of a doped rare earth element.

2. The rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The content of the rare earth oxide is 0.1%-5% of the mass of the positive electrode material.

3. The rare earth oxide-modified sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The mass content of carbon in the matrix material is 0.5%-5%.

4. The method for preparing the rare earth oxide-modified sodium iron phosphate pyrophosphate positive electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Weigh a sodium source, an iron source, a phosphorus source, a carbon source and a rare earth source according to chemical measurements, add them into deionized water and stir evenly to obtain a mixed slurry; S2. After the mixed slurry is placed in a spray dryer for spray drying, the temperature is first raised to 300-400° C. for sintering in an inert atmosphere, and then the temperature is raised to 500-600° C. for secondary sintering to obtain a rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material.

5. The method for preparing the rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material according to claim 4, characterized in that: In step S2, the inlet air temperature of the spray drying is 140-250°C, the outlet air temperature is 80-160°C, the nozzle diameter is 0.5-2.8mm, the air source is compressed air, and it is preheated to 70-260°C before entering the spray gun. The spray feed flow rate is 500-5000mL / h.

6. The method for preparing the rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material according to claim 4, characterized in that: The sodium source is at least one of sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium acetate, and sodium citrate; and / or, the iron source is at least one of ferroferric oxide, ferric oxide, ferric chloride, ferrous oxalate, ferrous oxalate, ferrous sulfate, and ammonium ferrous sulfate; and / or, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; and / or, the carbon source is at least one of sucrose, soluble starch, cellulose, glucose, and ascorbic acid; and / or, the rare earth source is one of yttrium oxide, cerium oxide, lanthanum oxide, praseodymium oxide, rubidium oxide, samarium oxide, europium oxide, gadolinium oxide, and terbium oxide.

7. The method for preparing the rare earth oxide modified sodium iron phosphate pyrophosphate positive electrode material according to claim 4, characterized in that: In step S1, the raw materials are mixed and then ball-milled to be uniform, the ball-milling speed is 300-800 r / min, and the ball-milling time is 3-12 h.

8. A positive electrode, characterized in that The invention comprises the positive electrode material according to any one of claims 1 to 3 or the positive electrode material obtained by the preparation method according to any one of claims 4 to 7.

9. An electrochemical energy storage device, characterized in that: Comprising the positive electrode as claimed in claim 8.

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