CN102509789A - Method for preparing positive material fluorine-doped sodium vanadium phosphate of sodium-containing lithium ion battery - Google Patents

Abstract

The invention relates to a preparation method of a lithium-ion battery positive electrode material containing sodium, specifically preparing Na ₃ V ₂ (PO ₄ ) _3-x/3 F _x (0≤x≤6 )Material. Disperse the sodium source, vanadium source, phosphorus source and fluorine source, as well as the reducing and conductive carbon source in a certain amount of liquid dispersion medium, and perform high-speed ball milling on the mixed material to make it mechanically activated; after mechanical activation The material is roasted at 450°C-1000°C for 1-72h under the protection of an inert or reducing atmosphere, and the product is obtained after cooling. The lithium ion battery positive electrode material Na ₃ V ₂ (PO ₄ ) _3-x/3 F _x prepared by this method has good electrochemical performance. The process involved in the invention is simple and convenient, easy to control, low in cost and environment-friendly, simplifies the synthesis process, and facilitates the realization of large-scale production.

Description

A method for preparing sodium-containing lithium-ion battery positive electrode material doped with fluorine-doped sodium vanadium phosphate

technical field

The invention relates to a method for preparing a positive electrode material of a sodium-containing lithium ion battery, that is, a method for preparing a sodium-containing lithium ion battery positive electrode material by a one-step high-temperature solid-phase method assisted by mechanical activation, which belongs to the preparation of new energy materials technology field.

Background technique

With the continuous development of the lithium-ion battery industry, especially the rise of electric vehicles, the market demand for lithium-ion batteries is constantly increasing, which brings a strong demand for lithium resources. However, at present, lithium resources are mostly stored in salt lakes, and extracting lithium from salt lakes is still a high-cost process, which has become a bottleneck restricting the rapid development of the lithium-ion battery industry. If we can consider replacing lithium with other cheaper elements, it will break the shackles of lithium resources on the lithium-ion battery industry and bring huge benefits to the country and society.

Fluorine-doped vanadium phosphate sodium salt is a polyanionic material, which was first used as anode material for sodium-ion batteries. Due to the stability of its crystal structure, it has a longer cycle life compared with other cathode materials for sodium-ion batteries. However, people's understanding of sodium-ion battery systems is not as sound as that of lithium-ion battery systems. Considering that the sodium-ion battery has the same principle as the lithium-ion battery, people try to apply the cathode material of the sodium-ion battery to the lithium-ion battery.

In 2005, J. Baker and others first proposed the concept of hybrid lithium-ion battery. They used Na ₃ V ₂ (PO ₄ ) ₂ F ₃ as the positive electrode, organic liquid containing LiPF ₆ as the electrolyte, and graphite as the negative electrode. Hybrid lithium-ion battery, found that the system not only can work stably, but also exhibits good electrochemical performance, its initial reversible specific capacity reaches 120mAh·g ^-1 , cycled 100 times at 0.5C rate, and the specific capacity retention rate is about 96%. In 2010, Jiangqing Zhao and others also did similar research on hybrid lithium-ion batteries, and also obtained good results. In order to ensure that the valence state of vanadium in the material is +3, they used a two-step method to prepare the material, that is, the VPO ₄ precursor was first prepared, and the high-valence vanadium was reduced to +3 valence, which was fixed in VPO ₄ . Then VPO ₄ reacts with NaF to synthesize the final product. With this synthesis method, the process flow is longer, the operation steps are more, and the energy consumption is larger.

According to patent CN101369661A, a sol-gel method is adopted to prepare carbon-coated sodium vanadium fluorophosphate material Na ₃ V ₂ (PO ₄ ) ₂ F ₃ /C in one step. Using this synthesis method, although it is a one-step synthesis, due to the sol-gel processing, the raw materials are required to be soluble, and the one-time raw material input should not be too large, the operation is inconvenient, and a large amount of organic matter is decomposed to cause waste of resources. and environmental pollution, the cost is higher, and it is difficult to realize large-scale production.

Contents of the invention

The purpose of the present invention is to overcome and avoid the shortcomings and deficiencies of the prior art, to provide a simple, easy-to-control condition, enhanced reactivity, and the synthesized product has excellent electrochemical properties, a sodium-containing lithium-ion battery positive electrode doped with fluorine The preparation method of sodium vanadium phosphate material.

The positive electrode material for sodium-containing lithium ion batteries prepared by the method has the characteristics of stable electrochemical performance, good rate performance, good safety performance, etc., and can be used to prepare power batteries meeting the needs of electric tools.

The present invention adopts the following process steps to realize the object of the invention.

Method of the present invention comprises the following steps:

(1) Mechanical activation

According to the molar ratio Na:V:P:F=3:2:(3-x/3):x (wherein 0≤x≤6), weigh the sodium vanadium phosphate (Na ₃ V ₂ (PO ₄ ) _3-x/3 F _x ) The raw materials of sodium source, vanadium source, phosphorus source and fluorine source are mixed with carbon sources that account for 10% to 30% of the total weight of raw materials and play a role in reducing and conducting electricity; the mixed raw materials Disperse in the liquid phase dispersion medium, and mechanically activate by ball milling for 5-48 hours;

(2) High temperature solid phase reaction

Place the mechanically activated material under the protection of an inert or reducing atmosphere, bake it at 450-1000°C for 1-72 hours, and finally cool it to room temperature to obtain the Na ₃ V ₂ (PO ₄ ) _3-x/3 F _x positive electrode Material.

In the present invention, it is preferred that the ball milling time of the step 1) is 5-24 hours.

The mechanical activation is carried out in a high-speed ball mill, the preferred rotating speed of the ball mill is 500-1200 rpm, and the ball/material ratio is 8-10:1.

The step 2) is preferably performed at a heating rate of 2-3° C./min.

The preferred calcination temperature in the step 2) is 500-900°C.

Preferred versions of the present invention also include:

The sodium source is one or more of sodium nitrate, sodium acetate, sodium bicarbonate, sodium fluoride, sodium carbonate and sodium hydroxide; the vanadium source is vanadium sulfide, vanadium trioxide, trichloro One or more of vanadyl, vanadium pentoxide and ammonium metavanadate; the phosphorus source is one or more of diammonium hydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, phosphorus pentoxide and sodium phosphate species; the fluorine source is one or more of hydrofluoric acid, ammonium fluoride and sodium fluoride; the carbon source is white sugar, polyacrylamide, glucose, polyvinyl alcohol, sucrose and starch one or several.

The liquid dispersion medium is one or more of ethylene glycol, deionized water, ethanol, butanol and butanediol.

The inert atmosphere is one of nitrogen and argon; the reducing atmosphere is N ₂ /H ₂ mixed gas, N ₂ : H ₂ =6:4, 7:3, 8:2, 9: 1. The flow rate is 10-1000mL/min.

The mechanical activation assisted one-step high-temperature solid-phase method proposed by the present invention is simple and easy to operate, and the conditions are easy to control; mechanical activation can fully mix the reactants and enhance the reactivity, thereby promoting the solid-phase reaction to be carried out more easily; the synthesized product has excellent Electrochemical performance; at the same time, the synthesis process is simple, the production cost is low, the environmental pollution is small, and it is convenient to realize large-scale production.

Description of drawings

Fig. 1: The X-ray diffraction (XRD) spectrum of Na ₃ V ₂ (PO ₄ ) ₂ F ₃ /C material prepared in Example 1;

Figure 2: The charge-discharge rate curve of the Na ₃ V ₂ (PO ₄ ) ₂ F ₃ /C material prepared in Example 1;

Figure 3: The initial charge and discharge curve of the Na ₃ V ₂ (PO ₄ ) ₃ /C material prepared in Example 2;

Fig. 4: the scanning electron microscope (SEM) pattern of the Na ₃ V ₂ (PO ₄ ) ₃ /C material prepared in Example 2;

Figure 5: The initial charge and discharge curve at 0.5C of the Na ₃ V ₂ (PO ₄ ) _2.5 F _1.5 /C material prepared in Example 3;

Figure 6: 5C rate cycle curve of Na ₃ V ₂ (PO ₄ ) _2.5 F _1.5 /C material prepared in Example 3;

Fig. 7: Cycle curves of Na ₃ V ₂ (PO ₄ ) _1.5 F _4.5 /C materials prepared in Example 4 at different rates.

Detailed ways

The present invention will be further described below in conjunction with the examples, and the following examples are intended to illustrate the present invention, rather than to further limit the present invention.

Example 1:

0.052mol vanadium pentoxide, 0.156mol ammonium fluoride, 0.156mol sodium bicarbonate, 0.104mol ammonium dihydrogen phosphate and 6g glucose were mixed and dispersed in ethanol, placed in a ball mill, and mechanically Activation for 8h. The mechanically activated material was calcined at 600°C for 24 hours under the protection of argon, and the product Na ₃ V ₂ (PO ₄ ) ₂ F ₃ /C was obtained after cooling. The X-ray diffraction analysis of the resulting product is shown in Figure 1, analysis shows that the product prepared by this formula also has a small amount of Na ₃ V ₂ (PO ₄ ) ₃ heterophase, and there is no carbon peak in the collection of spectra, which shows that glucose is in the High temperature is decomposed into amorphous carbon. The obtained product was assembled into an experimental button battery, and the electrochemical performance of charge and discharge was tested. The test results showed that the first discharge specific capacity of the material at the rate of 0.5C, 1C, 2C, 5C, and 10C was 107mAh·g ^{- 1} , 105.8mAh·g ^-1 , 102.9mAh·g ^-1 , 97.9mAh·g ^-1 , 90.4mAh·g ^-1 , the discharge specific capacity retention rate from 0.5C to 10C is 84.5%, and at 4.2V and There are two constant voltage platforms near the 3.7V voltage. The first charge and discharge curves of the material at each rate are shown in Figure 2.

Example 2:

0.052mol vanadium pentoxide, 0.156mol ammonium dihydrogen phosphate, 0.156mol sodium hydroxide and 6g glucose were mixed and dispersed in ethanol, placed in a ball mill, and mechanically activated at 800 rpm for 8 hours. The mechanically activated material was calcined at 900°C for 8 hours under the protection of argon, and the product Na ₃ V ₂ (PO ₄ ) ₃ /C was obtained after cooling. The SEM analysis of the material is shown in Figure 3, and the analysis shows that the particle size of the product is about 1 μm. The obtained product was assembled into an experimental button battery, and its charge-discharge electrochemical performance was tested at a rate of 0.1C. The test results showed that the first discharge specific capacity was 109mAh·g ^-1 , and a constant voltage appeared near the voltage of 3.7V. Platform, there is no obvious constant voltage platform near the 4.2V voltage. The first charge and discharge curve of the material at 0.1C is shown in Figure 4.

Example 3:

0.052mol vanadium pentoxide, 0.13mol ammonium dihydrogen phosphate, 0.156mol sodium hydroxide, 0.075mol ammonium fluoride and 6g glucose were mixed and dispersed in ethanol, placed in a ball mill, and mechanically Activate for 10h. The mechanically activated material was calcined at 700°C for 12 hours under the protection of argon, and the product Na ₃ V ₂ (PO ₄ ) _2.5 F _1.5 /C was obtained after cooling. The obtained product was assembled into an experimental button battery, and the electrochemical performance of the material was tested. The results showed that the material material not only appeared a constant voltage platform near a voltage of 3.7V, but also appeared a constant voltage platform near a voltage of 4.2V. The first charge-discharge curve of the material at a rate of 0.5C is shown in Figure 5, and the cycle curve of the material at a rate of 5C is shown in Figure 6.

Example 4:

0.052mol vanadium pentoxide, 0.156mol sodium hydroxide, 0.078mol ammonium dihydrogen phosphate, 0.185mol ammonium fluoride and 6g glucose were mixed and dispersed in ethanol, placed in a ball mill, and mechanically Activate for 10h. The mechanically activated material was calcined at 500°C for 36 hours under the protection of argon, and the product Na ₃ V ₂ (PO ₄ ) _1.5 F _4.5 /C was obtained after cooling. The obtained product was assembled into an experimental button battery, and the charging and discharging electrochemical performance of the material was tested. Figure 6 is the cycle curve of the material. The test results show that: the material is at 0.1C, 0.5C, 1C, 2C, 5C, 10C , the first discharge specific capacity at 0.1C rate are 103.1mAh·g ^-1 , 101.3mAh·g ^-1 , 99.4mAh·g ^-1 , 96.1mAh·g ^-1 , 81.5mAh·g ^-1 , 51.3mAh· g ^-1 , 95.6mAh·g ^-1 ; at different rates, the material shows good cycle stability.

Claims (8)

1. one kind prepares and contains the method that the sodium anode material for lithium-ion batteries is mixed fluorophosphoric acid vanadium sodium, it is characterized in that, comprises following processing step:

1) mechanical activation

Na: V: P: F=3 in molar ratio: 2: (3-x/3): x, 0≤x≤6 wherein take by weighing and are used for preparation and mix fluorophosphoric acid vanadium sodium Na ₃V ₂(PO ₄) _3-x/3F _xThe raw material in sodium source, vanadium source, phosphorus source and fluorine source, mix with the carbon source that plays reduction and electric action that accounts for raw material total weight 10%～30%; Mixed material is scattered in the liquid phase dispersion medium, through ball milling mechanical activation 5～48h;

2) high temperature solid state reaction

Material behind the mechanical activation is placed inertia or reducing atmosphere protection down, be warming up to 450～1000 ℃ of roasting 1～72h, stove is chilled to room temperature, promptly gets.

2. method according to claim 1 is characterized in that, said 1) the step mechanical activation is 5～24h.

3. according to claim 1 or claim 2 method, it is characterized in that: described mechanical activation carries out in high speed ball mill, and drum's speed of rotation is 500～1200 commentaries on classics/min, and ball/material is than being 8～10: 1.

4. method according to claim 1 is characterized in that, described 2) step is that heating rate with 2～3 ℃/min carries out warming temperature.

5. method according to claim 4 is characterized in that, described 2) in the step in 500～900 ℃ of roastings.

6. the method for claim 1, it is characterized in that: described sodium source is one or more in sodium nitrate, sodium acetate, sodium acid carbonate, sodium fluoride, sodium carbonate and the NaOH; Described vanadium source is one or more in vanadic sulfide, vanadium trioxide, vanadium oxytrichloride, vanadic oxide and the ammonium metavanadate; Said phosphorus source is one or more in diammonium hydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, phosphorus pentoxide and the sodium phosphate; Described fluorine source is one or more in hydrofluoric acid, ammonium fluoride and the sodium fluoride; Described carbon source is one or more in white sugar, polyacrylamide, glucose, polyvinyl alcohol, sucrose and the starch.

7. the method for claim 1, it is characterized in that: described liquid phase dispersion medium is one or more in ethylene glycol, deionized water, ethanol, butanols and the butanediol.

8. the method for claim 1 is characterized in that: described inert atmosphere is a kind of in nitrogen and the argon gas; Described reducing atmosphere is N ₂/ H ₂Mist, N ₂: H ₂=6: 4,7: 3,8: 2,9: 1, flow was 10～1000mL/min.

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