Sodium Deficiency Na 2-2x Ca x FePO4F@C composite material and preparation and application thereof

Abstract

The application belongs to the field of electrode materials, and particularly relates to a sodium-deficient Na 2‑2x Ca x FePO4F@C composite material, which is a sodium-deficient Na 2‑2x Ca x FePO4F composite material, wherein x is 0

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a sodium-ion battery positive electrode active material. BACKGROUND

[0002] Lithium-ion batteries have rapidly occupied the portable electronic product market and gradually expanded to the field of electric vehicles due to their high energy density, excellent stability and long service life. However, due to the low reserves and uneven distribution of lithium resources in the earth's crust, the large-scale popularization and application of lithium-ion batteries are limited. In the field of power storage, the application of lithium-ion batteries is restricted to a certain extent.

[0003] Sodium and lithium belong to the same main group and have some similar physical and chemical properties, but the radius of sodium element is larger, so many materials and construction theories suitable for lithium-ion batteries are difficult to apply in the field of sodium-ion batteries. Therefore, lithium-ion batteries have been widely used, while sodium-ion batteries have not been widely used. This is the main reason why lithium-ion batteries have been widely used while sodium-ion batteries have not been widely used.

[0004] In order to promote the progress of sodium-ion battery technology, developing positive electrode materials with excellent performance is an effective entry point. Among them, iron-based composite phosphate has a significant cost advantage because of the wide existence of Fe element on the earth and low cost of raw materials, so it is particularly prominent in sodium-ion electrode materials and becomes one of the most promising sodium-ion battery positive electrode materials.

[0005] However, the conductivity of iron-based composite phosphate is generally poor, especially sodium iron fluorophosphate with a layered structure, which has higher requirements for conductivity. Therefore, the prior art provides some carbon-coated solutions, for example: the Chinese patent document with publication number CN105810902A discloses a method for preparing nano-carbon coated sodium ferrous fluorophosphate by solvothermal method. The Chinese patent document with publication number CN115304047A discloses a preparation method of atomic-level in-situ carbon-coated sodium ferrous fluorophosphate composite material, which specifically discloses that a homogeneous solution containing iron source, phosphorus source, fluorine source, sodium source and polyhydric alcohol is heat-treated at a temperature of 250-300℃ for 12-48h, and then solid-liquid separation is performed to obtain a precursor; the polyhydric alcohol contains two or more alcohol hydroxyl groups, and the total carbon number is 2-6; the molar ratio of polyhydric alcohol to iron in the iron source is 8-12:1; the precursor is calcined at a temperature of 500-750℃ under a protective atmosphere to obtain the material.

[0006] Although the prior art can improve the conductivity of sodium iron fluorophosphate well, and can improve the performance of the material to a certain extent, for some specific application scenarios, such as fast charging performance and low temperature performance, the improvement of conductivity is far from enough, and the improvement effect on fast charging performance and low temperature performance is limited. Fast charging performance and low temperature performance involve the rapid movement of sodium ions in the material. Widening the transmission channel of sodium ions and providing sodium defects of sodium ion jumping sites are the key to improve the diffusion rate of sodium ions. SUMMARY

[0007] In view of the deficiencies of the existing sodium iron fluorophosphate@C material, the present application provides a sodium defect Na 2- 2x Ca x The FePO4F@C composite material (also referred to as a composite material or a new material in the present application) aims to construct a sodium vacancy structure and widen the sodium ion channel, thereby improving the fast charging performance and low temperature performance of the material.

[0008] The second object of the present application is to provide the sodium defect Na 2-2x Ca x The preparation method of the FePO4F@C composite material aims to prepare the new material with excellent performance.

[0009] The third object of the present application is to provide the Na 2-2x Ca x The application of the FePO4F@C composite material, and a sodium ion battery, a positive electrode and a positive electrode material added with the material.

[0010] A sodium defect Na 2-2x Ca x FePO4F@C composite material, which is a carbon layer coated sodium defect Na 2-2x Ca x FePO4F composite material, wherein x is 0

[0011] The present application provides a brand new chemical formula material, which replaces the Na lattice by Ca adaptation, and constructs a new material with Na defect characteristics. The present application research shows that the new material can significantly improve the fast charging performance and low temperature cycle performance based on the new mechanism of Ca-induced Na defect.

[0012] In the present application, the innovative use of Ca element further cooperates with the control of x, which can construct the Na defect characteristics suitable for sodium ion batteries based on the characteristics of Ca atoms, and further cooperatively improve the performance of the new material.

[0013] In the application, x is 0.005-0.03; preferably 0.01-0.02, and further preferably 0.01-0.015; research shows that, at the preferred ratio, the prepared material can be unexpectedly further improved in fast-charging performance and low-temperature performance.

[0014] In the application, the carbon layer is an amorphous carbon layer.

[0015] Preferably, the sodium defect Na 2-2x Ca x In the FePO4F@C composite material, the content of carbon is 0.5-2.5 wt.%.

[0016] The application also provides the sodium defect Na 2-2x Ca x The preparation method of the FePO4F@C composite material comprises the following steps: wet mixing and spray drying of stoichiometric precursors containing a sodium source, a calcium source, an iron source, a phosphorus source and a fluorine source and a carbon source to obtain a precursor, and then gradient sintering of the precursor.

[0017] The gradient sintering process comprises a first holding process at a temperature of 300-450 DEG C and a second holding process at a temperature of 550-625 DEG C.

[0018] Research shows that, in order to successfully prepare the material, the technical difficulty of constructing the required Na defect phase structure needs to be overcome, and in view of the difficulty in the preparation of the new material, the application finds, through in-depth research, that wet mixing, spraying and gradient sintering of the stoichiometric raw materials can successfully induce the Na defect structure based on Ca, avoid the formation of impurities, and further improve the fast-charging performance and low-temperature performance of the prepared material.

[0019] In the application, as an illustrative embodiment, the sodium source is at least one of at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium dihydrogen phosphate, sodium monohydrogen phosphate and sodium phosphate.

[0020] In the application, as an illustrative embodiment, the calcium source is at least one of calcium oxide, calcium carbonate, calcium nitrate, calcium oxalate, calcium acetate and calcium citrate.

[0021] In the application, as an illustrative embodiment, the iron source is at least one of iron phosphate, ferrous oxalate, ferric nitrate, diiron trioxide and iron powder.

[0022] In the application, as an illustrative embodiment, the phosphorus source is at least one of iron phosphate, sodium phosphate, phosphoric acid, ammonium dihydrogen phosphate and sodium dihydrogen phosphate.

[0023] In the present application, as an exemplary embodiment, the fluorine source is at least one of sodium fluoride and ammonium fluoride.

[0024] In the present application, as an exemplary embodiment, the carbon source is at least one of glucose, sucrose, citric acid, sodium citrate, polyethylene glycol, and polyvinyl alcohol; preferably glucose. Research shows that, under the preferred glucose, the prepared material can unexpectedly further improve the fast-charging performance and low-temperature performance in a synergistic manner.

[0025] Preferably, the carbon source accounts for 1% to 10% of the total weight of the precursor raw material and the carbon source, and further preferably 4% to 6%.

[0026] In the present application, the solvent in the wet mixing is at least one of water, ethanol, and acetone.

[0027] In the present application, the wet mixing method is at least one of wet ball milling and sand milling.

[0028] In the present application, the rotation speed in the wet mixing stage is 1000-3000 rpm.

[0029] In the present application, the wet mixing time is 1-4.5 h.

[0030] In the present application, the solid content in the slurry after wet mixing is 20-50%.

[0031] In the present application, the atmosphere in the gradient sintering stage is a protective atmosphere.

[0032] Preferably, the temperature of the first holding stage is 300-400℃, and more preferably 340-360℃.

[0033] Preferably, the time of the first holding stage is 3-6 h.

[0034] Preferably, the temperature of the second holding stage is 590-610℃.

[0035] Preferably, the time of the second holding stage is 6-12 h.

[0036] The present application also provides a sodium-deficient Na 2-2x Ca x The application of the FePO4F@C composite material as a positive active material for preparing a sodium-ion battery.

[0037] In the present application, based on known processes, materials, equipment, and raw materials, the sodium-deficient Na 2- 2x Ca x FePO4F@C composite material preparation required sodium-ion battery and its positive electrode, positive electrode material and other components and materials.

[0038] The application further provides a positive electrode material of a sodium ion battery, comprising a positive electrode active material, characterized in that the positive electrode active material comprises the sodium defect Na 2-2x Ca x FePO4F@C composite material.

[0039] Preferably, in the positive electrode active material, the sodium defect Na 2-2x Ca x The content of the FePO4F@C composite material is more than 10 wt.%, preferably more than 50 wt.%, and further preferably more than 90 wt.%.

[0040] Preferably, the positive electrode material further comprises a conductive agent and a binder.

[0041] Preferably, in the positive electrode material, the content of the conductive agent and the binder is respectively less than 15 wt.%, preferably 1-10 wt.%, and further can be 3-5 wt.%. In the application, due to the excellent performance of the material, excellent electrochemical performance can also be obtained at a low carbon content.

[0042] The application further provides a positive electrode of a sodium ion battery, comprising a current collector and a positive electrode material compounded on the surface of the current collector, wherein the positive electrode material is the positive electrode material added with the sodium defect Na 2-2x Ca x FePO4F@C composite material.

[0043] The application further provides a sodium ion battery, which adopts the positive electrode as the positive electrode of the application.

[0044] In the application, the sodium ion battery is added with the sodium defect Na 2- 2x Ca x FePO4F@C composite material, and other components and part structures can be conventional.

[0045] Advantages

[0046] 1. The application provides a sodium defect Na 2-2x Ca x FePO4F@C composite material, which has excellent fast charging performance and low temperature performance.

[0047] 2. The application performs wet mixing, spraying and gradient roasting treatment on stoichiometric raw materials, so as to successfully induce the Na defect structure based on Ca, avoid the formation of impurities, and successfully prepare the new material. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 SEM image of the material prepared for Example 1.

[0049] Figure 2 Charge-discharge curve of the material prepared for Example 1. DETAILED DESCRIPTION

[0050] Example 1 - Na 2-2x Ca x FeP04F@C (x = 0.01)

[0051] (1) Sodium bicarbonate (0.98 mol) and calcium acetate (0.01 mol) were added to 1 L of pure water, and mechanical stirring was performed at a stirring rate of 500 rpm for 0.5 h to obtain a homogeneous solution.

[0052] (2) Iron phosphate (1 mol), sodium fluoride (1 mol), and polyethylene glycol 600 (carbon source, which is 5% of the total weight of the total raw materials (total weight of sodium carbonate, calcium acetate, iron phosphate, sodium fluoride, and polyethylene glycol 600)) were added to the above homogeneous solution, and mechanical stirring was performed at a stirring rate of 500 rpm for 0.5 h to obtain a slurry.

[0053] (3) The above slurry was added to a sand mill for wet milling treatment, and the sand mill was set to rotate at 2000 rpm for 3 h to obtain a wet slurry.

[0054] (4) The above wet slurry was subjected to dry processing by spray drying to obtain a dry precursor. The spray drying was performed at a feed rate of 300 ml / h, an inlet temperature of 210°C, an outlet temperature of 99°C, a gas inlet rate of 30 L / h, and dry air as the carrier gas.

[0055] (5) The above precursor was placed in a box furnace, and preheating was performed at a temperature increase rate of 2°C / min to 350°C (marked as T1) under the protection of a nitrogen atmosphere, and then maintained at T1for t1(4 h), and then further heated to T2(600°C) and maintained at T2for t2(10 h) to obtain Na 1.98 Ca 0.01 FeP04F@C composite material.

[0056] Example 2

[0057] Compared with Example 1, the only difference is that x is set to 0.005, that is, the amount of sodium bicarbonate in step (1) is 0.99 mol, and the amount of calcium acetate is 0.005 mol. The other operations and parameters are the same as those of Example 1.

[0058] Example 3

[0059] The difference compared with Example 1 is only that x is set to 0.02, i.e. the amount of sodium bicarbonate in step (1) is 0.96 mol and the amount of calcium acetate is 0.02 mol. The other operations and parameters are the same as in Example 1.

[0060] Example 4

[0061] The difference compared with Example 1 is only that the carbon source used in step (2) is replaced by an equal weight of citric acid.

[0062] Example 5

[0063] The difference compared with Example 1 is only that the carbon source used in step (2) is replaced by an equal weight of sucrose.

[0064] Example 6

[0065] The difference compared with Example 1 is only that the carbon source used in step (2) is 1 wt.% of all raw materials.

[0066] Example 7

[0067] The difference compared with Example 1 is only that the carbon source used in step (2) is 10 wt.% of all raw materials.

[0068] Example 8

[0069] The difference compared with Example 1 is only that in step (5), the temperature is raised to 400°C (marked as T1) at a temperature raising rate of 3°C / min, and then kept for t1 (3h), and then the temperature is continuously raised to T2 (590°C) and kept for t2 (11h).

[0070] Example 9

[0071] The difference compared with Example 1 is only that in step (5), the temperature is raised to 320°C (marked as T1) at a temperature raising rate of 2.5°C / min, and then kept for t1 (5h), and then the temperature is continuously raised to T2 (610°C) and kept for t2 (8h).

[0072] Comparative Example 1

[0073] The difference compared with Example 1 is only that in step (1), lithium acetate is used to replace calcium acetate, and the molar amount of Li element is 2 times that of Ca element.

[0074] Comparative Example 2

[0075] The difference compared with Example 1 is only that in step (1), potassium acetate is used to replace calcium acetate, and the molar amount of K element is 2 times that of Ca element.

[0076] Comparative Example 3

[0077] Comparative Example 1 compared with Example 1, the difference is only in step (1), replace calcium acetate with magnesium acetate, where the molar amount of Mg element is the same as Ca element.

[0078] Comparative Example 2

[0079] Comparative Example 2 compared with Example 1, the difference is only in step (1), replace calcium acetate with barium acetate, where the molar amount of Ba element is the same as Ca element.

[0080] Comparative Example 3

[0081] Comparative Example 3 compared with Example 1, the difference is only in step (1), replace calcium acetate with cesium acetate, where the molar amount of cesium element is twice as much as Ca element.

[0082] Comparative Example 4

[0083] Comparative Example 4 compared with Example 1, the difference is only in step (1), lack of calcium acetate, the missing part is supplemented by 2 times the molar amount of sodium acetate, other operations and parameters are the same as Example 1.

[0084] Comparative Example 5

[0085] Comparative Example 5 compared with Example 1, the difference is only in step (5), using a calcination method, that is, lacking the T1 stage of the holding process, that is, directly heating to 600°C, the total holding time is the same as the total holding time of Example 1, other operations and parameters are the same as Example 1.

[0086] Comparative Example 6

[0087] Comparative Example 6 compared with Example 1, the difference is only in step (2), lack of sodium fluoride, other operations and parameters are the same as Example 1.

[0088] Comparative Example 7

[0089] Comparative Example 7 compared with Example 1, the difference is only in that the temperature of T2 stage is 660°C, and other operations and parameters are the same as Example 1.

[0090] The main steps of the test are:

[0091] (1) Use 2032 type battery shell, the positive electrode is the positive electrode active material prepared in each case (the current collector is aluminum foil, and the active material: conductive carbon: PVDF = 8: 1: 1), the negative electrode is sodium metal, and a glass fiber separator (Whatman Grade GF / D) is used. The electrolyte is 1M NaClO4 (pure PC + 5% FEC) to assemble the battery.

[0092] (2) The standing time is 12 h, and a test rate performance program is set, first 0.1C is used for charging and discharging 5 times, then 1C / 3C / 10C is used for charging rate, and 1C is used for discharging rate to cycle 5 times respectively, and fast charging performance test is carried out. The low temperature performance test is carried out in the low temperature-20℃ environment for 200 times of 1C cycle.

[0093] (3) Sodium defect Na 2-2x Ca x The theoretical specific capacity of the FePO4F@C composite material is 124mAh / g;

[0094] The test results are shown in Table 1:

[0095]

[0096]

[0097] As can be seen from the above, in the sodium defect Na 2-2x Ca x FePO4F@C composite material, based on the preparation method of wet-dry-roasting, the construction of sodium defect can be realized, the sodium ion diffusion kinetics is obviously improved, and the electrochemical performance such as fast charging performance and low temperature performance of the material is effectively improved.

Claims

1. A sodium deficient Na 2-2x Ca x FePO4F@C composite material characterized in that, Na for carbon layer-coated sodium defects 2- 2x Ca x Composite of FePO4F, wherein x is 0.005-0.03; The carbon layer is an amorphous carbon layer. The sodium defect Na 2-2x Ca x In the FeP04F@C composite, the content of carbon is 0.5-2.5 wt.%.

2. The sodium deficient Na 2-2x Ca x FePO4F@C composite material characterized in that, The x is 0.01-0.

02.

3. The sodium deficient Na 2-2x Ca x FePO4F@C composite material, characterized in that, The x is 0.01-0.

015.

4. A sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The stoichiometric ratio of the precursor raw materials containing a sodium source, a Ca source, an iron source, a phosphorus source, and a fluorine source and a carbon source are mixed wetly, and then spray dried to obtain a precursor, and then the precursor is gradient sintered to obtain the product. The gradient sintering process includes a first holding process at a temperature of 300-450 ℃ and a second holding process at a temperature of 550-625 ℃.

5. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The sodium source is at least one of at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium citrate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium phosphate.

6. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The Ca source is at least one of calcium oxide, calcium carbonate, calcium nitrate, calcium oxalate, calcium acetate, and calcium citrate.

7. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The iron source is at least one of iron phosphate, ferrous oxalate, ferric nitrate, diiron trioxide, and iron powder.

8. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The phosphorus source is at least one of iron phosphate, sodium phosphate, phosphoric acid, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate.

9. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The fluorine source is at least one of sodium fluoride and ammonium fluoride.

10. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The carbon source is at least one of glucose, sucrose, citric acid, sodium citrate, polyethylene glycol, and polyvinyl alcohol.

11. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The percentage of the carbon source in the total weight of the precursor raw materials and the carbon source is 1%-10%.

12. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The solvent in the wet mixing is at least one of water, ethanol, and acetone.

13. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The wet mixing method is at least one of wet ball milling and sand milling.

14. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The rotation speed in the wet mixing stage is 1000-3000 rpm.

15. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The wet mixing time is 1-4.5 h.

16. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The solid content in the slurry after wet mixing is 20%-50%.

17. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The atmosphere in the gradient sintering stage is a protective atmosphere.

18. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The first holding time is 3-6 h.

19. The sodium deficient Na 2-2x Ca x A method for preparing a FePO4F@C composite material, characterized in that, The second holding time is 6-12 h.

20. A sodium deficient Na 2-2x Ca x FePO4F@C composite material or a sodium deficient Na 2-2x Ca x Use of a FePO4F@C composite material, characterized in that, The product is used as a positive electrode active material for preparing a sodium ion battery.

21. A cathode material for a sodium-ion battery, comprising a cathode active material, characterized in that, The positive electrode active material contains the sodium-deficient Na 2-2x Ca x FePO4F@C composite or the sodium-deficient Na 2-2x Ca x FePO4F@C composite.

22. The positive electrode material of the sodium-ion battery of claim 21, wherein, The positive electrode active material, wherein the sodium defect Na 2-2x Ca x The content of the FePO4F@C composite is more than 10 wt.%.

23. The positive electrode material of the sodium-ion battery of claim 22, wherein, In the positive electrode active material, the sodium defect Na 2-2x Ca x The content of the FePO4F@C composite material is above 50 wt.%.

24. The positive electrode material of the sodium-ion battery of claim 23, wherein, The positive electrode active material, wherein the sodium defect Na 2-2x Ca x The content of the FePO4F@C composite material is 90 wt.% or more.

25. The cathode material for sodium-ion batteries of claim 21, wherein, The positive electrode material further contains a conductive agent and a binder.

26. The cathode material of the sodium-ion battery of claim 25, wherein, In the positive electrode material, the content of the conductive agent and the binder is less than 15 wt.%, and the balance is the positive electrode active material.

27. The positive electrode material of the sodium-ion battery of claim 26, wherein, In the positive electrode material, the content of the conductive agent and the binder is 1-10 wt.%, and the balance is the positive electrode active material.

28. A cathode for a sodium-ion battery, comprising a current collector and a cathode material complexed on a surface thereof, characterized in that, The positive electrode material is the positive electrode material of any one of claims 21-27.

29. A sodium-ion battery, characterized in that, The positive electrode is the positive electrode of claim 28.

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