Nickel-doped porous spherical carbon-coated sodium ferric phosphate composite material as well as preparation method and application thereof

Abstract

The invention relates to the field of sodium ion batteries, in particular to a nickel-doped porous spherical carbon-coated sodium ferric phosphate composite material as well as a preparation method and application thereof. The nickel-doped porous spherical carbon-coated sodium ferric phosphate composite material comprises a central layer and a carbon coating layer, the carbon coating layer is a nickel-doped carbon layer, and a nickel element is doped in crystal lattices of Na4Fe3 (PO4) 2P2O7 in a form of replacing an iron site; the conductivity and sodium ion diffusion kinetics are improved from the interior of a bulk phase through Ni doping, a uniform Ni-doped carbon coating layer constructs a high-speed electron transport network outside particles, internal and external synergism is achieved, and the rate performance and low-temperature performance of the material are remarkably improved. Crystallization, carbonization and nickel doping are completed in one step at low temperature, damage of high temperature to the material structure is avoided, meanwhile, close coupling of a carbon layer and an active substance is achieved, limitation of traditional step-by-step treatment is broken through, and the method has remarkable industrial advantages.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, its preparation method, and its application. Background Technology

[0002] Na4Fe3(PO4)2P2O7 (NFPP) has become an ideal candidate cathode material for sodium-ion batteries due to its cost advantage as an iron-based material, stable three-dimensional framework structure, and high theoretical capacity. However, its low intrinsic electronic conductivity and slow ion diffusion rate severely limit its electrochemical performance, especially in applications under high-rate and low-temperature conditions. Currently, strategies to improve NFPP performance mainly include carbon coating and element doping. Carbon coating typically employs a high-temperature solid-state method (>700℃) to physically mix the NFPP precursor with a carbon source such as sucrose and then sinter it. This method suffers from problems such as uneven coating, high energy consumption, and easy particle growth. Element doping (such as Mg...) 2+ Mn 2+ While it can improve conductivity to some extent, the effect is limited, and achieving a uniform and effective combination of dopant elements and carbon coating remains a major challenge. Existing technologies typically treat doping and coating as two separate processes, which are complex and make it difficult to achieve uniform modification at the molecular level.

[0003] Therefore, developing a preparation process that can simultaneously achieve uniform nickel doping and coating, with controllable morphology and low-temperature efficiency is crucial for overcoming the performance bottleneck of NFPP materials and promoting their industrial application. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, its preparation method, and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention is to provide a nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, comprising: a central layer and a carbon coating layer; wherein the central layer is composed of primary nanoparticles, and the carbon coating layer is a nickel-doped carbon layer, wherein nickel is doped into the crystal lattice of Na4Fe3(PO4)2P2O7 in the form of replacing iron sites.

[0007] A second aspect of the present invention is to provide a method for preparing the above-mentioned nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, comprising the steps of:

[0008] S1, Na4Fe according to stoichiometric ratio 3-x Ni x(PO4)2P2O7 is prepared by weighing iron, sodium, phosphorus and nickel sources, dissolving them in a solvent to obtain precursor solution A;

[0009] S2. The conductive polymer monomer and oxidant are added to the precursor solution A, and an in-situ polymerization reaction is carried out at low temperature to obtain the precursor solution B.

[0010] S3. Add the biomass carbon source to the precursor solution B, stir evenly, and then spray dry to obtain porous microsphere precursor powder.

[0011] S4. The precursor powder is sintered to obtain the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material.

[0012] Preferably, in step S1, the nickel source includes at least one of nickel acetate, nickel nitrate, and nickel chloride; the doping amount x of the nickel source is in the range of 0. <x≤0.2。

[0013] Preferably, in step S2, the conductive polymer monomer includes at least one of pyrrole and aniline; and the oxidant is ammonium persulfate.

[0014] Preferably, in step S3, the biomass carbon source includes at least one of citric acid and ascorbic acid.

[0015] Preferably, in step S3, the inlet temperature of the spray drying process is 180-250°C and the outlet temperature is 90-120°C.

[0016] Preferably, in step S4, the sintering process includes: pre-sintering at 300-400°C under an inert atmosphere, followed by heating to 550-650°C and holding for 6-12 hours.

[0017] A third aspect of the present invention is to provide the application of the above-described nickel-doped porous spherical carbon-coated sodium iron phosphate composite material or the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material prepared by the above-described preparation method in sodium-ion batteries.

[0018] Preferably, the sodium-ion battery comprises: a positive electrode and a negative electrode; the active material of the positive electrode comprises the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material as described in claim 1 or the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material prepared by any one of claims 2-7.

[0019] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0020] (1) The present invention improves the conductivity and sodium ion diffusion kinetics from the bulk phase through Ni doping, while the uniform Ni-doped carbon coating layer constructs a high-speed electron transport network on the outside of the particles. The internal and external synergy significantly improves the rate performance and low-temperature performance of the material.

[0021] (2) The porous spherical structure effectively alleviates the volume stress during the charging and discharging process, and Ni doping stabilizes the crystal structure, giving the material an ultra-long cycle life.

[0022] (3) The present invention completes crystallization, carbonization and nickel doping in one step at low temperature, avoiding the damage to the material structure caused by high temperature, and at the same time realizes the tight coupling between the carbon layer and the active material, breaking through the limitations of traditional step-by-step processing, and has significant industrial advantages.

[0023] (4) In this invention, conductive polymer monomers and oxidants are directly introduced into the precursor solution, and a uniform polymer coating layer is formed on the surface of the active material through in-situ polymerization. Then, a porous spherical structure is constructed by spray drying, which ensures the uniformity and consistency of carbon coating. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0026] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, the steps of which include:

[0029] S1, Na4Fe according to stoichiometric ratio 2.95 Ni 0.05 (PO4)2P2O7 Weigh out FeSO4·7H2O, Na2CO3, NH4H2PO4 and Ni(CH3COO)2·4H2O, dissolve them in deionized water, pass N2 under protection, and stir to dissolve to obtain precursor solution A;

[0030] S2. Under ice-water bath conditions, 0.5 mL of pyrrole monomer was added to the precursor solution A, stirred, and then ammonium persulfate was added dropwise. The reaction was carried out for 4 h to obtain precursor solution B.

[0031] S3. Add 2.5g of citric acid to the precursor solution B, stir at 60°C to form a gel, and then spray dry (inlet 220°C, outlet 110°C) to obtain porous microsphere precursor powder.

[0032] Under S4 and Ar atmospheres, the temperature is increased to 350℃ at 3℃ / min and held for 3 hours, then increased to 600℃ and held for 10 hours. After natural cooling, the final product Ni is obtained. 0.05 -NFPP@NC.

[0033] Example 2

[0034] This embodiment provides another method for preparing nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, the steps of which include:

[0035] S1, Na4Fe according to stoichiometric ratio 2.9 Ni 0.1 (PO4)2P2O7 Weigh out FeSO4·7H2O, Na2CO3, NH4H2PO4 and Ni(NO3)2·6H2O, dissolve them in deionized water, pass in N2 for protection, and stir to dissolve to obtain precursor solution A;

[0036] S2. Under ice-water bath conditions, 0.6 mL of pyrrole monomer was added to the precursor solution A, stirred, and then ammonium persulfate was added dropwise. The reaction was carried out for 4 h to obtain precursor solution B.

[0037] S3. Add 3.0g of citric acid to the precursor solution B, stir at 60°C to form a gel, and then spray dry (inlet 200°C, outlet 100°C) to obtain porous microsphere precursor powder.

[0038] Under S4 and Ar atmospheres, the temperature was increased to 350℃ at 3℃ / min and held for 3 hours, then increased to 580℃ and held for 12 hours. After natural cooling, the final product Ni was obtained. 0.1 -NFPP@NC.

[0039] Comparative Example 1

[0040] This comparative example provides a method for preparing a composite material, the steps of which include:

[0041] (1) Dissolve FeSO4·7H2O, Na2CO3, and NH4H2PO4 in deionized water and stir until dissolved.

[0042] (2) Add sucrose as a carbon source and mix by ball milling.

[0043] (3) Spray drying yields precursor powder.

[0044] (4) Under Ar atmosphere, sinter at 750℃ for 12 hours to obtain NFPP / C.

[0045] Comparative Example 2

[0046] This comparative example provides another method for preparing a composite material, the steps of which include:

[0047] (1) According to the stoichiometric ratio Na4Fe 2.9 Ni 0.1 Weigh out FeSO4·7H2O, Na2CO3, NH4H2PO4 and Ni(NO3)2·6H2O, dissolve them in deionized water, and stir until dissolved.

[0048] (2) Spray drying yields precursor powder.

[0049] (3) Ni was obtained by sintering at 600°C for 10 hours under an Ar atmosphere. 0.05 -NFPP.

[0050] Comparative Example 3

[0051] This comparative example provides another method for preparing a composite material, the steps of which include:

[0052] The sintering process includes: heating to 800℃ at 3℃ / min and holding for 10 hours under an Ar atmosphere, followed by cooling to obtain Ni. 0.05 -NFPP@NC.

[0053] The rest are the same as in Example 1.

[0054] Comparative Example 4

[0055] This comparative example provides another method for preparing a composite material, the steps of which include:

[0056] Ni(CH3COO)2·4H2O was not added; all other aspects were the same as in Example 1.

[0057] Detection Examples

[0058] The composite materials obtained in Examples 1-2 and Comparative Examples 1-4 were used as positive electrode active materials to prepare battery positive electrodes. The battery positive electrodes were then assembled into batteries. The prepared battery samples were charged at a constant current of 1.0C to 3.2V at room temperature, then charged at a constant voltage of 3.2V to a cutoff current of 0.05C. The batteries were then discharged at a constant current of 1.0C, and the discharge capacity was recorded as C0. This charge-discharge cycle was repeated 1000 times to obtain the discharge capacity C1000 at the 1000th cycle. The capacity retention rate was calculated as C1500 / C0*100%. The test results are shown in Table 1.

[0059] Table 1

[0060]

[0061] As shown in the table above, the battery prepared from the composite material obtained in Example 1 retained 95.26% of its capacity after 1000 cycles, 83.64% of its capacity under 5C high-rate conditions, and 91.84% of its capacity under -20°C / 0.5C rate conditions. Furthermore, no abnormalities occurred during the cycle, indicating that the present invention can still work normally in low-temperature environments, has a longer service life, and reduces the high-temperature sintering temperature.

[0062] This invention selects Ni 2+ As a dopant ion, its ionic radius is similar to that of Fe. 2+ Similar in structure, it easily enters the crystal lattice and forms Na₄Fe. 3-x Ni x (PO4)2P2O7 solid solution. Ni doping not only effectively broadens the sodium ion migration channels and lowers the migration energy barrier, but also introduces more electron carriers, synergistically improving the ionic and electronic conductivity of the material, which is difficult to achieve with single carbon coating or conventional element doping. In this invention, monomers such as pyrrole and oxidants are directly added to the solution-state precursor, causing them to polymerize on the surface of NFPP precursor particles, forming a uniform polypyrrole coating layer. This coating layer is transformed into a nickel-doped carbon layer during subsequent sintering, and its conductivity is superior to that of ordinary amorphous carbon. Spray drying can instantly evaporate the solvent, forming a porous microsphere morphology with a high specific surface area, which is beneficial for electrolyte wetting and shortens the ion diffusion path. Because the precursors achieve uniform mixing at the molecular level and the presence of the polymer inhibits grain growth, this invention significantly reduces the final sintering temperature to 550-650℃. At this temperature, the crystallization of NFPP, the carbonization of the polymer, and the doping process of nickel ions entering the crystal lattice can be achieved simultaneously, completing the three key steps in one step, greatly simplifying the process and reducing energy consumption.

[0063] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A nickel-doped porous spherical carbon-coated sodium iron phosphate composite material, characterized in that, include: The central layer and the carbon coating layer; wherein the central layer is composed of primary nanoparticles, and the carbon coating layer is a nickel-doped carbon layer, wherein nickel is doped into the Na4Fe3(PO4)2P2O7 lattice in the form of replacing iron sites.

2. A method for preparing nickel-doped porous spherical carbon-coated sodium iron phosphate composite material as described in claim 1, characterized in that the steps... include: S1, Na4Fe according to stoichiometric ratio 3-x Ni x (PO4)2P2O7 is prepared by weighing iron, sodium, phosphorus and nickel sources, dissolving them in a solvent to obtain precursor solution A; S2. The conductive polymer monomer and oxidant are added to the precursor solution A, and an in-situ polymerization reaction is carried out at low temperature to obtain the precursor solution B. S3. Add the biomass carbon source to the precursor solution B, stir evenly, and then spray dry to obtain porous microsphere precursor powder. S4. The precursor powder is sintered to obtain the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material.

3. The preparation method according to claim 2, characterized in that, In step S1, the nickel source includes at least one of nickel acetate, nickel nitrate, and nickel chloride; the doping amount x of the nickel source is in the range of 0. <x≤0.2。 4. The preparation method according to claim 2, characterized in that, In step S2, the conductive polymer monomer includes at least one of pyrrole and aniline; the oxidant is ammonium persulfate.

5. The preparation method according to claim 2, characterized in that, In step S3, the biomass carbon source includes at least one of citric acid and ascorbic acid.

6. The preparation method according to claim 2, characterized in that, In step S3, the inlet temperature of the spray drying process is 180-250℃, and the outlet temperature is 90-120℃.

7. The preparation method according to claim 2, characterized in that, In step S4, the sintering process includes: pre-sintering at 300-400℃ under an inert atmosphere, followed by heating to 550-650℃ and holding for 6-12 hours.

8. The application of a nickel-doped porous spherical carbon-coated sodium iron phosphate composite material as described in claim 1 or a nickel-doped porous spherical carbon-coated sodium iron phosphate composite material prepared by any one of the preparation methods described in claims 2-7 in sodium-ion batteries.

9. The application according to claim 8, characterized in that, The sodium-ion battery includes: a positive electrode and a negative electrode; the active material of the positive electrode includes the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material as described in claim 1 or the nickel-doped porous spherical carbon-coated sodium iron phosphate composite material prepared by any one of claims 2-7.

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