CN114122311B - Carbon-coated ferrous sodium fluorophosphate active material, preparation method thereof and application thereof in sodium electricity - Google Patents

Carbon-coated ferrous sodium fluorophosphate active material, preparation method thereof and application thereof in sodium electricity Download PDF

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CN114122311B
CN114122311B CN202111423185.3A CN202111423185A CN114122311B CN 114122311 B CN114122311 B CN 114122311B CN 202111423185 A CN202111423185 A CN 202111423185A CN 114122311 B CN114122311 B CN 114122311B
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sodium
positive electrode
active material
fepo
preparation
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CN114122311A (en
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张治安
王旭
赖延清
李劼
李仕豪
李煌旭
盖晓臣
贺亮
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Hunan Nabang New Energy Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/582—Halogenides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly discloses Na 2 FePO 4 The preparation method of the F/C positive electrode active material comprises the following steps: step (1): dispersing ferric phosphate, organic acid sodium, a sodium source and a fluorine source in water for mechanical activation modification to obtain slurry; the organic acid sodium is at least one of dicarboxylic acid sodium, polybasic carboxylic acid sodium and carboxylic acid sodium containing hydroxyl with the carbon number of 2-10; the molar ratio of the ferric phosphate to the organic acid sodium is 2-10:1; step (2): carrying out spray drying treatment on the slurry to obtain a precursor; step (3): calcining the precursor to obtain the Na 2 FePO 4 F/C positive electrode active material. According to the invention, by utilizing the phase characteristics of the ferric phosphate and the organic sodium acid, the homogenization immobilization modification and the spraying means in the water phase are further matched, so that the synergy can be realized, the pure phase is improved, the carbon coating uniformity is improved, and the performance is improved.

Description

Carbon-coated ferrous sodium fluorophosphate active material, preparation method thereof and application thereof in sodium electricity
Technical field:
the invention belongs to the technical field of battery materials, and particularly relates to the technical field of sodium ion battery positive electrode active materials.
The background technology is as follows:
with the large-scale application of lithium ion batteries, sales of global large-scale energy storage systems and electric automobiles are rapidly increased, lithium ion battery demands are rapidly increased, and lithium resource consumption speed is remarkably increased. However, lithium resources are limited in reserves, uneven in distribution and large in price rising, and increasingly short lithium resources have become important factors for restricting green energy development and early realization of double-carbon targets. Therefore, there is an urgent need to develop a battery system similar to a lithium ion battery and compatible in production. Sodium and lithium belong to the same main group, and sodium ions and lithium ions have very similar physicochemical properties. Sodium resources are quite abundant, the price is relatively low, and the distribution is relatively uniform, so that the development of the sodium ion battery has extremely important significance.
The positive electrode material is an important component of the sodium ion battery, and is low in cost, easy to prepare and key in the development of the sodium ion battery. The iron-based sodium ferrous fluorophosphate serving as a very low-cost layered sodium ion battery anode material has a two-dimensional sodium guide structure, good ion deintercalation/intercalation stability, and strong thermal stability due to a strong covalent bond of oxygen atoms in polyanions, so that the iron-based sodium ferrous fluorophosphate serving as a layered sodium ion battery anode material has a wide application prospect.
Nazar et al (Nature Materials,2007, 6:749) have previously proposed Na 2 FePO 4 F material, which is regarded as 3.5V (vs. Li + Li) lithium-sodium hybrid battery positive electrode material. The material has typical stoichiometric composition, and its skeleton structure shows unique lamellar structure, and is dioctahedral [ Fe 2 O 7 F 2 ]The units are formed by coplanar FeO 4 F 2 Regular octahedron is formed by connecting F atoms into a chain shape and is connected with PO 4 Tetrahedral connections form layers with two-dimensional ion channels that are easily diffused. Layered Na 2 FePO 4 F has higher theoretical specific capacity (124 mAh g -1 ) And a stable charge-discharge platform (3.0V), and extremely small volume change (< 4%), and is a sodium ion battery anode material with great commercialization prospect. But Na is 2 FePO 4 F has low electron conductivity and insufficient long-cycle performance, and greatly influences the exertion of electrochemical performance. In addition, the raw material proportion, the synthesis process and the method need to be strictly controlled in the synthesis process, and the material synthesis is easy to generate impurity phase and influenceCapacity exertion and stable circulation.
At present, the synthesis of ferrous sodium fluorophosphate mainly comprises a solid-phase carbothermic reduction method and a sol-gel method. Mixing sodium source, phosphorus source, iron source, fluorine source and carbon source, wherein the carbon source is mostly organic carbon source, so that the solid phase mixing degree is difficult to be uniform and sufficient, and the carbon is difficult to mix Fe 3+ Completely reduce to Fe 2+ The composite material has heterogeneous phase, the carbon layer is coated unevenly, the morphology and granularity uniformity of the material are not ideal, and the electrochemical performance is difficult to develop. The liquid phase methods such as the sol-gel method and the like have long flow, complicated steps, strict control condition requirements, easy phase impurity existence and to-be-improved circulation stability.
The invention comprises the following steps:
aiming at the problems that the prior carbon-coated ferrous sodium fluorophosphate is easy to generate mixed phase, has poor coating uniformity and the like in the preparation process, the first aim of the invention is to provide Na 2 FePO 4 The preparation method of the F/C positive electrode active material (also called as sodium ferrous phosphate/carbon composite material) aims at reducing the impurity phase of a product, improving the uniformity of carbon coating and improving the electrochemical performance of the material.
A second object of the present invention is to provide Na obtained by the above-mentioned production method 2 FePO 4 F/C positive electrode active material.
A third object of the present invention is to provide the Na 2 FePO 4 The application of the F/C positive electrode active material in sodium ion batteries.
A fourth object of the present invention is to provide a composition comprising the Na 2 FePO 4 Sodium ion battery of F/C positive electrode active material, positive electrode material and positive electrode thereof.
Na (Na) 2 FePO 4 The preparation method of the F/C positive electrode active material comprises the following steps:
step (1): the molar ratio of Na, F and Fe elements is 1.9-2.2:1-1.1:1, dispersing ferric phosphate, organic acid sodium, a sodium source and a fluorine source in water in proportion, and carrying out mechanical activation modification to obtain slurry;
the organic acid sodium is at least one of dicarboxylic acid sodium, polybasic carboxylic acid sodium and carboxylic acid sodium containing hydroxyl with the carbon number of 2-10; the molar ratio of the ferric phosphate to the organic acid sodium is 2-10:1;
step (2): carrying out spray drying treatment on the slurry to obtain a precursor;
step (3): calcining the precursor to obtain the Na 2 FePO 4 F/C positive electrode active material.
In the invention, ferric phosphate is taken as a solid carrier, and is mechanically activated with organic acid sodium, an auxiliary sodium source and a fluorine source in a water system, a carboxyl and hydroxyl active organic layer is chemically modified on the surface of ferric phosphate, and the wetting penetration of sodium and F to the ferric phosphate solid carrier is improved, so that uniform and highly dispersed active microparticles are obtained, further, secondary particles aggregated by the active microparticles are obtained by means of spraying, and the secondary particles are subjected to calcination treatment, so that the efficient reaction of micro-areas can be realized, and the preparation of high-purity phase and atomically thick carbon-coated Na is facilitated 2 FePO 4 F, uniformly forming micronuclei, and tightly contacting the micronuclei to construct a uniform conductive network and a sodium ion transmission channel which penetrate the inside and the outside. The invention can construct high-purity phase and high-homogenization carbon-coated materials based on the combination of raw materials, mechanical activation modification, spraying and pyrolysis means; the material has excellent multiplying power and cycle performance.
According to the invention, by utilizing the phase characteristics of the ferric phosphate and the organic sodium acid, the subsequent micro-area calcination reaction can be realized by further matching with a homogenization immobilization modification and a spraying means in the water phase, so that the phase purity is improved, the uniformly carbon-coated micronuclei are obtained, the uniformity from inside to outside is built, and the atomic-level thin layer penetrates through the conductive network.
The research of the invention finds that the organic sodium acid phase material is innovatively adopted, under the action of the aqueous solution system and the mechanical action, the organic sodium acid phase material can be used for good chemical anchoring of the ferric phosphate solid carrier and promoting the penetration of Na and F to the ferric phosphate solid carrier, so that homogenized microparticles can be obtained, the subsequent micro-area calcination is facilitated, the construction of the material phase and the carbon coating structure is facilitated, the construction of a conductive network is facilitated, and the electrochemical performance is facilitated.
In the present invention, the organic acid sodium needs to have a polycarboxylic structure and/or a hydroxyl-containing carboxyl structure, and in addition, needs to have a sodium salt phase form, so that the assembly of the microparticles in the aqueous phase system can be realized.
Preferably, the organic acid sodium is at least one of sodium dicarboxylic acid having 2 to 7 carbon atoms, sodium polycarboxylic acid, and sodium carboxylate having a hydroxyl group.
In the invention, the organic acid sodium is at least one of sodium citrate, sodium ascorbate, sodium gluconate and sodium oxalate.
Preferably, the molar ratio of the ferric phosphate to the organic acid sodium is 2-5:1, and more preferably 3-4:1.
Preferably, the fluorine source is capable of ionizing F - Preferably at least one of sodium fluoride and ammonium fluoride.
In the invention, the sodium source is a supplementary sodium source, which can be at least one of sodium bicarbonate, sodium carbonate, sodium acetate and sodium hydroxide.
Preferably, the mechanical activation modification process comprises a ball milling and/or sanding step; preferably comprises ball milling and then sanding;
the rotation speed of the ball milling stage is 100-1000rpm, preferably 400-800rpm; ball milling time is 0.5-2 h;
the rotating speed of the sanding stage is 500-1500 rpm; the sanding time is 0.5-2 h;
preferably, the solids content in the slurry is 30% -70%;
preferably the spray drying process has an inlet temperature of 180-270 ℃ and a spray rate of 20-40ml/min.
Preferably, the calcination treatment process is performed under a protective atmosphere:
preferably, the temperature of the calcination process is 500-700 ℃, preferably 600-650 ℃;
preferably, the calcination process is carried out for a period of time of from 4 to 24 hours, preferably from 8 to 12 hours.
The preferred preparation method of the invention comprises the following steps:
step (1):
organic acid sodium, ferric phosphate, a fluorine source and a sodium source are used as raw materials, and the molar ratio of the four elements is 1.9-2.2 according to Na, F, fe, P: 1-1.1:1:1, weighing reaction raw materials; dissolving ferric phosphate, fluorine source, sodium source and organic acid sodium in water, and stirring to obtain suspension A, wherein the solid content of the suspension is controlled to be 30% -70%. The organic acid sodium is sodium citrate C 6 H 5 Na 3 O 7 Sodium ascorbate C 6 H 7 O 6 Na, sodium gluconate C 6 H 11 NaO 7 Sodium oxalate Na 2 C 2 O 4 At least one of them. The fluorine source is at least one of sodium fluoride and ammonium fluoride. Preferably, the sodium source is at least one of sodium bicarbonate, sodium carbonate, sodium acetate, sodium hydroxide. The molar ratio of the iron phosphate to the organic acid sodium is 0.5-10:1.
step (2): transferring the suspension A obtained in the step (1) into a ball mill, and obtaining a suspension B after ball milling.
Step (3): transferring the suspension obtained in the step (2) into a sand mill, and performing sand milling to obtain a suspension C.
Step (4): and (3) carrying out spray drying on the suspension C obtained in the step (3) to obtain a spherical precursor. In the spraying process, the inlet temperature is 180-270 ℃, and the spraying speed is 20-30 ml/min.
Step (5): calcining the precursor obtained in the step (4) in an inert atmosphere to finally obtain the uniform carbon-coated ferrous sodium fluorophosphate material. The thickness of the carbon layer coated on the surface of the material is 3-10nm. The temperature of the heat treatment is 600-650 ℃. The heat treatment time is 8-12h.
The invention also provides the Na prepared by the preparation method 2 FePO 4 F/C positive electrode active material.
Na prepared by the preparation method 2 FePO 4 F/C positive electrode active material coated with homogenized thin layer carbon (e.g. 3-10 nm) Na 2 FePO 4 F, the microparticles are in close contact with each other. The material has uniform microparticle size, uniform atomic-level carbon layer coating, and intimate contact of microparticles, and can be used for constructionForming a uniform carbon network from inside to outside. The preparation method can endow the material with a special microstructure, and the material prepared by the preparation method has better multiplying power and cycle performance.
The Na of the invention 2 FePO 4 The F/C positive electrode active material is applied to be used as a positive electrode active material of a sodium ion battery;
preferably, the positive electrode slurry of the sodium ion battery is prepared by compounding the positive electrode slurry with a conductive agent and a binder;
preferably, the positive electrode slurry is compounded on a current collector to prepare the positive electrode of the sodium ion battery;
for preferred applications, the positive electrode is used in the assembly of sodium ion batteries.
The application of the invention is not to adopt Na of the invention 2 FePO 4 Other material types, structural components, and preparation methods may be known in addition to the F/C positive electrode active material as the positive electrode active material.
The invention also provides a sodium ion battery anode material which comprises Na prepared by the preparation method 2 FePO 4 The F/C positive electrode active material also comprises a conductive agent and a binder;
the conductive agent can be a material with conductive property which is known in the industry; for example, at least one of acetylene black, ketjen black, and conductive graphite.
Preferably, the percentage of the conductive agent is 5 to 10wt.%.
The binder may be a material known in the industry that can be used to adhere the positive electrode components to each other; for example, it may be at least one of PVDF, PTFE, CMC +SBR and PAA.
Preferably, the percentage of binder is 5 to 10wt.%.
The invention also provides a sodium ion battery anode, which comprises a current collector and the anode material;
preferably, the current collector is at least one of metal aluminum foil, metal copper foil, composite aluminum foil and the like.
In the invention, the content of the positive electrode material in the positive electrode can be adjusted based on the use requirement.
In the present invention, the positive electrode can be prepared based on existing means such as a solvent slurry coating method.
The invention also provides a sodium ion battery which comprises the Na prepared by the preparation method 2 FePO 4 F/C positive electrode active material. Preferably equipped with a positive electrode according to the present invention.
The sodium ion battery of the present invention may have any known components and materials except that the positive electrode thereof contains the positive electrode active material of the present invention.
The invention has the following remarkable characteristics:
(1) The invention utilizes ferric phosphate, organic acid sodium, sodium source and fluorine source to carry out mechanical microencapsulation modification in water, and further cooperates with spraying and calcining means to realize micro-area reaction, thus being beneficial to improving Na 2 FePO 4 F phase purity, constructing a layered microstructure, and being beneficial to obtaining a uniform thin carbon coating layer, and in addition, each microparticle is contacted with each other, so that a uniform ion and electron conductive network from inside to outside is constructed. The invention can obtain the material which is favorable for transporting Na ions with large radius and has excellent multiplying power and cycle stability based on the phase of the material and the combination of mechanical activation modification, spraying and roasting processes.
(2) The method has the advantages of simple raw materials, simple operation and capability of bringing better product performance, and can realize industrial production which is difficult to realize in industry.
(3) The method has the advantages of low cost, large-scale production, environmental friendliness, simple operation and short flow, and has excellent industrial application prospect.
Description of the drawings:
FIG. 1 is an X-ray diffraction pattern of the active material prepared in example 1;
FIG. 2 is an SEM image of the active material prepared in example 1;
FIG. 3 is a graph showing the cycle performance of the material prepared in example 1;
FIG. 4 is an X-ray diffraction pattern of the product obtained in comparative example 1;
FIG. 5 is a graph showing the cycle performance of the material prepared in comparative example 1;
Detailed Description
Example 1
(1) Iron phosphate, sodium fluoride and sodium citrate are used as raw materials, wherein the iron phosphate: sodium citrate = 3:1, at a molar ratio of Na, F, fe, P four elements of 2:1:1:1: 170Kg of reaction raw materials are weighed, the raw materials are dissolved in 220L of water, and suspension A is obtained through stirring, wherein the solid content of the suspension is controlled to be 50%.
(2) Transferring the suspension A obtained in the step (1) into a ball mill, and ball-milling at 500rpm for 1h to obtain a suspension B.
(3) Transferring the suspension obtained in the step (2) into a sand mill, and performing sand milling for 1h at 1200rpm to obtain a suspension C.
(4) Transferring the suspension C obtained in the step (3) into a spray drying tower, setting the inlet temperature to 270 ℃, and obtaining the spherical precursor at the spraying rate of 25 ml/min.
(5) And (3) heating the precursor obtained in the step (4) to 600 ℃ at a speed of 4 ℃/min under argon atmosphere, and preserving heat for 8 hours to finally obtain about 100Kg of uniform carbon-coated ferrous sodium fluorophosphate material.
Example 2
The difference compared with example 1 is that the sodium citrate in step (1) is replaced by sodium ascorbate, the proportion of sodium element is regulated by sodium bicarbonate, and other steps and parameters are the same as in example 1.
Example 3
The difference compared with example 1 is that the sodium citrate in step (1) is replaced by sodium gluconate, the proportion of sodium element is regulated by sodium bicarbonate, and other steps and parameters are the same as in example 1.
Example 4
The only difference compared to example 1 is that the sodium fluoride in step (1) is changed to ammonium fluoride, the remaining sodium source is supplemented by sodium bicarbonate in the system, and other steps and parameters are the same as in example 1.
Example 5
The difference compared with example 1 is only that the ball milling rotation speed in the step (4) is changed from 500rpm to 400rpm, and other steps and parameters are the same as in example 1.
Example 6
The only difference compared to example 1 is that the molar ratio of iron phosphate to sodium citrate is 4:1. the remaining sodium is supplemented by sodium bicarbonate in the system.
Example 7
The difference compared with example 1 is that the roasting temperature in the step (5) is 500 ℃ and the temperature is kept for 20 hours.
Example 8
The difference compared with example 1 is that the roasting temperature in the step (5) is 700 ℃ and the temperature is kept for 4 hours.
Comparative example 1
The difference compared with example 1 is that the sodium citrate of the organic acid sodium in step (1) is replaced by citric acid, the other sodium is supplemented by sodium bicarbonate, and the other steps and parameters are the same as in example 1.
Comparative example 2
The only difference compared to example 2 is that the sodium ascorbate of step (1) is changed to ascorbic acid, the other sodium is supplemented by sodium bicarbonate, and the other steps are unchanged.
Comparative example 3
The only difference compared to example 1 is that step (4) is to change spray drying to ordinary 80 ℃ drying to obtain precursor powder, and the other steps and parameters are unchanged.
Comparative example 4
The only difference compared to example 1 is that the incubation temperature in step (5) is changed from 600℃to 400℃with the other steps unchanged.
Comparative example 5
The difference compared to example 1 is only that the incubation temperature in step (5) is changed from 600 ℃ to 800 ℃ and the other steps are unchanged.
Comparative example 6
The only difference compared to example 1 is that ethanol is used instead of the water, and other operations and parameters are the same as in example 1.
Comparative example 7
The only difference compared to example 1 is that citric acid is used instead of sodium citrate, ethanol is used instead of the water, sodium hydroxide is used for supplementation, and other operations and parameters are the same as in example 1.
Comparative example 8
The difference compared with example 1 is that the ball milling and sand milling of steps (2) and (3) were not performed, but stirring was conducted for 2 hours.
Comparative example 9
The only difference compared to example 2 is that sodium caproate is used instead of sodium ascorbate, and other operations and steps are the same as in example 2.
The electrical properties of the sodium ferrous fluorophosphate prepared in each example and comparative example were tested:
the main testing steps are as follows:
(1) The positive electrode of 2032 type battery shell is a pole piece of prepared sodium ferrous fluorophosphate, the current collector is aluminum foil, and active substances (materials prepared in examples 1-8 and comparative examples 1-9) are as follows: conductive carbon (acetylene black): pvdf=7: 2:1, the negative electrode is sodium metal, and a fiber diaphragm (model Whatman Grade GF/D) is used for filling a battery, and the electrolyte is 1M NaClO4 (pure PC+5% FEC);
(2) Setting standing time to be 12h, setting a multiplying power charging program, setting multiplying power to be 1C, setting voltage interval to be 2.0V-4.0V, and circulating for 2000 circles;
(3) The theoretical specific capacity of the sodium ferrous fluorophosphate is 124mAh/g;
the test results are shown in table 1:
therefore, the material constructed by the method has better capacity, multiplying power and cycle performance.

Claims (24)

1. Na (Na) 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized by comprising the following steps:
step (1): the molar ratio of Na, F and Fe elements is 1.9-2.2:1-1.1:1, dispersing ferric phosphate, organic acid sodium, a sodium source and a fluorine source in water in proportion, and carrying out mechanical activation modification to obtain slurry;
the organic acid sodium is at least one of dicarboxylic acid sodium, polybasic carboxylic acid sodium and carboxylic acid sodium containing hydroxyl with the carbon number of 2-10; the molar ratio of the ferric phosphate to the organic acid sodium is 0.5-10:1;
step (2): carrying out spray drying treatment on the slurry to obtain a precursor;
step (3): calcining the precursor to obtain the Na 2 FePO 4 F/C positive electrode active material.
2. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the organic sodium acid is at least one of sodium citrate, sodium ascorbate, sodium gluconate and sodium oxalate.
3. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the fluorine source is at least one of sodium fluoride and ammonium fluoride.
4. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the sodium source is at least one of sodium bicarbonate, sodium carbonate, sodium acetate and sodium hydroxide.
5. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the mechanical activation modification process comprises ball milling and/or sand milling steps.
6. Na as claimed in claim 5 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the mechanical activation modification process comprises ball milling and then sand milling.
7. Na as claimed in claim 6 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the rotating speed of the ball milling stage is 100-1000rpm; ball milling time is 0.5-2 h;
the rotating speed of the sanding stage is 500-1500 rpm; the sanding time is 0.5-2 h.
8. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the solid content in the slurry is 30-70%.
9. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the inlet temperature of the spray drying process is 180-270 ℃, and the spray rate is 20-40ml/min.
10. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the calcination treatment process is carried out under a protective atmosphere.
11. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the temperature of the calcination process is 500-700 ℃.
12. Na as claimed in claim 1 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the time of the calcination process is 4-24h.
13. Na as claimed in claim 12 2 FePO 4 The preparation method of the F/C positive electrode active material is characterized in that the time of the calcination process is 8-12h.
14. A claim1-13, and the Na obtained by the preparation method 2 FePO 4 F/C positive electrode active material.
15. The Na of any one of claims 1 to 13 2 FePO 4 The use of an F/C positive electrode active material, characterized in that it is used as a positive electrode active material for sodium ion batteries.
16. The use according to claim 15, wherein the positive electrode slurry of the sodium ion battery is prepared by compounding the positive electrode slurry with a conductive agent and a binder.
17. The use of claim 16, wherein the positive electrode slurry is combined with a current collector to produce a positive electrode of a sodium ion battery.
18. The use of claim 17, wherein the positive electrode is used in the assembly of a sodium ion battery.
19. A positive electrode material for sodium ion battery, comprising Na prepared by the preparation method of any one of claims 1 to 13 2 FePO 4 The F/C positive electrode also comprises a conductive agent and a binder.
20. The positive electrode material of sodium ion battery of claim 19, wherein the conductive agent is at least one of conductive carbon black, acetylene black, ketjen black, and conductive graphite.
21. The positive electrode material of sodium ion battery of claim 19, wherein said binder is at least one of PVDF, PTFE, CMC + SBR and PAA.
22. A positive electrode for a sodium ion battery, comprising a current collector and the positive electrode material of any one of claims 19 to 21.
23. The positive electrode of claim 22, wherein the current collector is at least one of a metal aluminum foil, a metal copper foil, a composite copper foil, and a composite aluminum foil.
24. A sodium ion battery equipped with a positive electrode according to any one of claims 22 to 23.
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