A NaVPO 4 F-C cathode material and its preparation method

Abstract

The present invention relates to the technical field of sodium-ion batteries, and particularly to a NaVPO 4 F-C cathode material and a preparation method thereof. The preparation method includes: (1) mixing a vanadium source, a phosphorus source, an alkanolamine substance and an organic solvent, and then drying to obtain a precursor; the molar ratio of the vanadium source, the phosphorus source and the alkanolamine substance is 3:6:1-10; (2) sintering the precursor in an inert atmosphere to obtain a porous VPO 4 ; (3) mixing a fluoride, the porous VPO 4 and an organic solvent, drying and then sintering in an inert atmosphere to obtain the NaVPO 4 F-C cathode material; the molar ratio of the fluoride to the porous VPO 4 is 1:0.95-1.05. The porous-structured NaVPO 4 F-C cathode material prepared by the present invention can effectively improve the rate performance and conductivity of the cathode material, and further improve the cycle life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and particularly relates to a NaVPO 4 F-C cathode material and a preparation method thereof. Background Art

[0002] In the 21st century, lithium batteries are widely used in many fields such as mobile phones, computers, wearable devices, electric vehicles, two-wheeled bicycles, power tools, street lamps, etc. In recent years, the consumption of lithium resources has shown the characteristics of large usage and fast consumption speed, while the production of lithium cannot meet the growth of consumption. This is because: firstly, lithium resources are limited and mainly exist in the form of spodumene ore and salt lake lithium; secondly, salt lake lithium cannot be extracted in winter.

[0003] In contrast, sodium is widely sourced, rich in reserves, and the sodium reserve is 420 times that of lithium, and the price is much lower than that of lithium. In recent years, sodium ion batteries have received wide attention due to the cost advantage of being 30 - 50% lower than that of lithium ion batteries. Especially in the fields of energy storage, hybrid power, and replacing lead-acid batteries, sodium ion batteries have attractive application prospects.

[0004] Sodium is the second lightest alkali metal and has similar chemical properties to lithium. However, the atomic radius of sodium is 34.2% larger than that of lithium. Therefore, the corresponding sodium compounds of cathode materials such as lithium cobaltate, lithium iron phosphate, ternary materials, and lithium manganate used in lithium ion batteries have poor electrochemical performance, such as low capacity, low discharge voltage, high charging voltage, and low charge-discharge efficiency.

[0005] In recent years, researchers have conducted in-depth research on Na 3 V 2 (PO 4 ) 2 F 3 、Na 3 V 2 (PO 4 ) 2 O 2 F and NaVPO 4 F and other fluorophosphates. The research found that compared with other fluorophosphates, NaVPO 4 F has a relatively high theoretical capacity (143 mAh / g) and a single charge-discharge platform, and has important research value. However, this material has poor conductivity and poor rate performance, resulting in poor final cycling and limiting its wide application. Summary of the Invention

[0006] In view of this, the present invention provides a preparation method of a NaVPO 4 F-C cathode material, including:

[0007] (1) Mix a vanadium source, a phosphorus source, an alkanolamine substance, and an organic solvent, and then dry to obtain a precursor; the molar ratio of the vanadium source, the phosphorus source, and the alkanolamine substance is 3:6:1 to 10;

[0008] (2) Sinter the precursor in an inert atmosphere to obtain porous VPO 4 ;

[0009] (3) Mix a fluoride, the porous VPO 4 and an organic solvent, dry and then sinter in an inert atmosphere to obtain the NaVPO 4 F-C cathode material;

[0010] The molar ratio of the fluoride to the porous VPO 4 is 1:0.95 to 1.05.

[0011] The NaVPO 4 F-C cathode material prepared by the above method of the present invention has a porous structure, which is conducive to the entry and exit of sodium ions from the cathode material and improves the rate performance of the cathode material; at the same time, in-situ carbon coating can be formed during the preparation process to improve the conductivity of the cathode material, thereby improving the cycle life of the battery.

[0012] Specifically, the present invention uses an alkanolamine substance as a complexing agent and a carbon source, synthesizes a precursor by a sol-gel method, and obtains VPO 4 powder after calcination treatment in an inert atmosphere; among them, the alkanolamine substance acts as a reducing agent to reduce V 5+ to V 3+ , and the gas generated during the reduction process can form a porous VPO 4 powder, while the remaining alkanolamine substance will crack and carbonize to form conductive carbon; further, the porous VPO 4 powder and the fluoride are calcined in an inert atmosphere, reducing the sintering time and sintering temperature, and finally forming a NaVPO 4 F-C cathode material with a porous structure.

[0013] As a preferred embodiment of the present invention, the molar ratio of the fluoride to the porous VPO 4 is 1:1.

[0014] As a preferred embodiment of the present invention, the alkanolamine substance is at least one of ethanolamine, diethanolamine, and triethanolamine.

[0015] As a preferred embodiment of the present invention, the vanadium source is at least one of V 2 O 5 or NH 4 VO 3 ;

[0016] and / or, the phosphorus source is NH 4 H 2 PO 4 or (NH 4 ) 2 HPO 4 or at least one of them.

[0017] As a preferred embodiment of the present invention, the organic solvent is at least one of absolute ethanol, acetone, and cyclohexane.

[0018] As a preferred embodiment of the present invention, the drying temperature in step (1) is 50 - 80 °C; and / or, the drying temperature in step (3) is 80 - 120 °C.

[0019] As a preferred embodiment of the present invention, the sintering temperature in step (2) is 600 - 800 °C; and / or, the sintering temperature in step (3) is 500 - 650 °C.

[0020] As a preferred embodiment of the present invention, the sintering time in step (2) is 5 - 12 h; and / or, the sintering time in step (3) is 3 - 8 h.

[0021] As a preferred embodiment of the present invention, in step (1), after mixing the vanadium source, phosphorus source, alkanolamine substance, and organic solvent, wet grinding is carried out at a rotation speed of 10 - 30 r / min, and then drying is performed to obtain a precursor.

[0022] As a preferred embodiment of the present invention, in step (3), after mixing the fluoride, the porous VPO 4 and the organic solvent, wet grinding is carried out at a rotation speed of 10 - 30 r / min, and after drying, sintering is performed in an inert atmosphere to obtain the NaVPO 4 F - C cathode material.

[0023] In the specific implementation process, the wet grinding includes but is not limited to being carried out in a ball mill.

[0024] Preferably, the wet grinding time is 3 - 8 h.

[0025] Preferably, vacuum drying is adopted for drying.

[0026] Preferably, the drying time is 2 - 4 h.

[0027] Preferably, the fluoride is NaF.

[0028] Preferably, the inert atmosphere is an argon atmosphere.

[0029] As a more preferred embodiment of the present invention, the preparation method includes the following steps:

[0030] (1) Mix a vanadium source, a phosphorus source, an alkanolamine substance, and an organic solvent, then wet-mill at a rotation speed of 10 - 30 r / min, and then vacuum-dry at 50 - 80 °C to obtain a precursor; the molar ratio of the vanadium source, the phosphorus source, and the alkanolamine substance is 3:6:1 - 10;

[0031] (2) Sinter the precursor in an inert atmosphere at 600 - 800 °C to obtain porous VPO 4 ;

[0032] (3) Mix a fluoride, the porous VPO 4 and an organic solvent, then wet-mill at a rotation speed of 10 - 30 r / min, then dry at 80 - 120 °C, and then sinter in an inert atmosphere at 500 - 650 °C to obtain the NaVPO 4 F-C cathode material;

[0033] The molar ratio of the fluoride to the porous VPO 4 is 1:0.95 - 1.05.

[0034] Those skilled in the art can further combine the above preferred solutions to obtain other preferred implementation schemes of the preparation method of the NaVPO 4 F-C cathode material in the present invention.

[0035] Furthermore, the present invention provides a cathode material prepared by any of the above implementation schemes.

[0036] Even further, the present invention also provides a battery containing the above cathode material.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The porous-structured NaVPO 4 F-C cathode material prepared by the present invention can effectively improve the rate performance of the cathode material, and at the same time can significantly improve the conductivity of the cathode material, thereby improving the cycle life of the cathode material and the battery. In addition, the preparation method of the present invention is simple and convenient, and is easy to be widely applied on a large scale in the industry. Specific Embodiments

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with specific embodiments. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] For those without specific techniques or conditions indicated in the examples, they are all conventional methods or are carried out according to the techniques or conditions described in the literature in this field, or according to the product instructions. For reagents, instruments, etc. without the manufacturer indicated, they are all conventional products that can be obtained through regular channels.

[0041] Example 1

[0042] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0043] (1) Add V 2 O 5 , NH 4 H 2 PO 4 and triethanolamine into a ball mill in a molar ratio of 30 mol: 60 mol: 12 mol for wet milling. The wet milling time is 5 h, the rotation speed of the ball mill is 15 r / min, and the wet milling organic solvent is cyclohexane;

[0044] (2) Vacuum-dry the substance obtained in (1) at 70 °C for 3 h to obtain a green precursor;

[0045] (3) Sinter the green precursor at 700 °C for 8 h in an argon atmosphere to obtain a black porous VPO 4 powder;

[0046] (4) Add NaF and VPO 4 powder into a ball mill in a molar ratio of 20 mol: 20 mol for wet milling. The wet milling time is 6 h, the rotation speed of the ball mill is 20 r / min, and the wet milling organic solvent is cyclohexane;

[0047] (5) Vacuum-dry the substance prepared in (4) at 100 °C for 2 h; then sinter it at 600 °C for 5 h in an argon atmosphere to obtain a black porous NaVPO 4 F-C cathode material, where carbon accounts for 1.23% of the total weight of the finished product.

[0048] Example 2

[0049] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0050] (1) Add V 2 O 5 , NH 4 H 2 PO 4It was added to a ball mill according to a molar ratio of 30 mol: 60 mol: 30 mol for wet grinding. The wet grinding time was 6 h, the rotation speed of the ball mill was 20 r / min, and the wet grinding organic solvent was absolute ethanol;

[0051] (2) The substance obtained in (1) was vacuum dried at 80 °C for 2.5 h to obtain a green precursor;

[0052] (3) The green precursor was sintered at 650 °C for 10 h under an argon atmosphere to obtain black porous VPO 4 powder;

[0053] (4) NaF and VPO 4 powder were added to a ball mill according to a molar ratio of 25 mol: 25 mol for wet grinding. The wet grinding time was 7 h, the rotation speed of the ball mill was 30 r / min, and the wet grinding organic solvent was absolute ethanol;

[0054] (5) The substance prepared in (4) was vacuum dried at 100 °C for 2 h; then it was sintered at 550 °C for 6 h under an argon atmosphere to obtain black porous NaVPO 4 F-C cathode material, in which carbon accounted for 1.86% of the total weight of the finished product.

[0055] Example 3

[0056] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0057] (1) V 2 O 5 , NH 4 H 2 PO 4 and diethanolamine were added to a ball mill according to a molar ratio of 30 mol: 60 mol: 60 mol for wet grinding. The wet grinding time was 6 h, the rotation speed of the ball mill was 20 r / min, and the wet grinding organic solvent was absolute ethanol;

[0058] (2) The substance obtained in (1) was vacuum dried at 80 °C for 3 h to obtain a green precursor;

[0059] (3) The green precursor was sintered at 800 °C for 9 h under an argon atmosphere to obtain black porous VPO 4 powder;

[0060] (4) NaF and VPO 4 powder were added to a ball mill according to a molar ratio of 23 mol: 23 mol for wet grinding. The wet grinding time was 8 h, the rotation speed of the ball mill was 25 r / min, and the wet grinding organic solvent was absolute ethanol;

[0061] (5) The substance obtained in (4) was dried under vacuum at 100 °C for 2 h; then sintered at 550 °C for 6 h under an argon atmosphere to obtain a black porous NaVPO 4 F-C cathode material, where carbon accounts for 2.32% of the total weight of the finished product.

[0062] Example 4

[0063] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0064] (1) V 2 O 5 , NH 4 H 2 PO 4 and triethanolamine were added to a ball mill according to a molar ratio of 30 mol: 60 mol: 100 mol for wet grinding. The wet grinding time was 5.5 h, the rotational speed of the ball mill was 23 r / min, and the wet grinding organic solvent was anhydrous ethanol;

[0065] (2) The substance obtained in (1) was dried under vacuum at 85 °C for 3.5 h to obtain a green precursor;

[0066] (3) The green precursor was sintered at 780 °C for 9 h under an argon atmosphere to obtain a black porous VPO 4 powder;

[0067] (4) NaF and VPO 4 powder were added to a ball mill according to a molar ratio of 25 mol: 25 mol for wet grinding. The wet grinding time was 7 h, the rotational speed of the ball mill was 28 r / min, and the wet grinding organic solvent was anhydrous ethanol;

[0068] (5) The substance obtained in (4) was dried under vacuum at 100 °C for 2 h; then sintered at 575 °C for 5.5 h under an argon atmosphere to obtain a black porous NaVPO 4 F-C cathode material, where carbon accounts for 7.83% of the total weight of the finished product.

[0069] Example 5

[0070] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0071] (1) V 2 O 5 , NH 4 H 2 PO 4Mix with triethanolamine in a molar ratio of 30 mol:60 mol:12 mol, add them to a ball mill for wet grinding. The wet grinding time is 5 h, the rotation speed of the ball mill is 15 r / min, and the wet grinding organic solvent is cyclohexane;

[0072] (2) Vacuum-dry the substance obtained in (1) at 70 °C for 3 h to obtain a green precursor;

[0073] (3) Sinter the green precursor at 700 °C for 8 h under an argon atmosphere to obtain black porous VPO 4 powder;

[0074] (4) Add NaF and VPO 4 powder in a molar ratio of 19 mol:20 mol to a ball mill for wet grinding. The wet grinding time is 6 h, the rotation speed of the ball mill is 20 r / min, and the wet grinding organic solvent is cyclohexane;

[0075] (5) Vacuum-dry the substance prepared in (4) at 100 °C for 2 h; then sinter it at 600 °C for 5 h under an argon atmosphere to obtain black porous NaVPO 4 F-C cathode material, in which carbon accounts for 1.26% of the total weight of the finished product.

[0076] Example 6

[0077] This example provides a NaVPO 4 F-C cathode material, and its preparation method is as follows:

[0078] (1) Add V 2 O 5 , NH 4 H 2 PO 4 and triethanolamine in a molar ratio of 30 mol:60 mol:30 mol to a ball mill for wet grinding. The wet grinding time is 6 h, the rotation speed of the ball mill is 20 r / min, and the wet grinding organic solvent is anhydrous ethanol;

[0079] (2) Vacuum-dry the substance obtained in (1) at 80 °C for 2.5 h to obtain a green precursor;

[0080] (3) Sinter the green precursor at 650 °C for 10 h under an argon atmosphere to obtain black porous VPO 4 powder;

[0081] (4) Add NaF and VPO 4 powder in a molar ratio of 26.25 mol:25 mol to a ball mill for wet grinding. The wet grinding time is 7 h, the rotation speed of the ball mill is 30 r / min, and the wet grinding organic solvent is anhydrous ethanol;

[0082] (5) The substance obtained in (4) is vacuum dried at 100 °C for 2 h; then sintered at 550 °C for 6 h under an argon atmosphere to obtain a black porous NaVPO 4 F-C cathode material, where carbon accounts for 1.86% of the total weight of the finished product.

[0083] Comparative example

[0084] This example provides a NaVPO 4 F-C cathode material, and the only difference in its preparation method from Example 1 is that triethanolamine is replaced by glucose. Other conditions remain unchanged.

[0085] Test example

[0086] The cathode materials prepared in the examples and comparative examples are used as the cathode. Among them, the mass percentages of the cathode material, binder PVDF, and conductive agent SP are 94:3:3; sodium metal is used as the anode, 20 μm PP / PE / PP is used as the separator, and NaPF 6 ethylene carbonate (EC) / dimethyl carbonate (DEC) solution is used as the electrolyte, and fluoroethylene carbonate (FEC) is used as the electrolyte additive (the molar ratio of FEC to EC + DMC is 1:20). A battery is assembled in a glove box filled with argon to obtain a half-cell.

[0087] Then charge-discharge tests are carried out (voltage range 2 - 4 V). The results are shown in Table 1.

[0088] Table 1 Charge-discharge performance test of the battery

[0089]

[0090]

[0091] As can be seen from the above table, the battery containing the NaVPO 4 F-C cathode material of the present invention has a 0.2C discharge capacity > 115 mAh / g; the 2C discharge capacity is greater than 105 mAh / g.

[0092] In addition, the cycle life of the half-cell is tested, and the results are shown in Table 2. The cycle life test method is as follows: at 25 °C, the batteries prepared in the examples and comparative examples are charged to 4.2 V at a 0.5C rate and discharged to 2 V at a 0.5C rate, and full charge-discharge cycle tests are carried out until the capacity of the sodium-ion battery is less than 80% of the initial capacity, and the number of cycle turns is recorded. The specific data are shown in Table 2.

[0093] Table 2 Cycle life test

[0094] Project Cycle life (number of cycles) Example 1 1759 Example 2 1836 Example 3 1835 Example 4 2038 Example 5 1538 Example 6 1868 Comparative example 866

[0095] As can be seen from the above table, the number of charge and discharge cycles of the battery containing the NaVPO 4 F-C cathode material is ≥ 1500 times at 0.5C.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of NaVPO 4 F-C cathode material It is characterized in that including: (1) Add V 2 O 5 、NH 4 H 2 PO 4 and triethanolamine into a ball mill in a molar ratio of 30 mol: 60 mol: 100 mol for wet grinding. The wet grinding time is 5.5 h, the rotational speed of the ball mill is 23 r / min, and the wet grinding organic solvent is absolute ethanol; (2) Vacuum-drying the substance obtained in (1) at 85 °C for 3.5 h to obtain a green precursor; (3) The green precursor was sintered at 780 °C for 9 h under an argon atmosphere to obtain black porous VPO 4 powder; (4) Add NaF and VPO 4 powders into a ball mill at a molar ratio of 25 mol:25 mol for wet grinding. The wet grinding time is 7 h, the rotation speed of the ball mill is 28 r / min, and the wet grinding organic solvent is absolute ethanol; (5) Vacuum dry the substance obtained in (4) at 100 °C for 2 h; then sinter it at 575 °C for 5.5 h under an argon atmosphere to obtain a black porous NaVPO 4 F-C cathode material.

2. A cathode material, It is characterized in that it is prepared by the preparation method described in claim 1.

3. A battery, It is characterized in that it contains the cathode material described in claim 2.

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