High-specific-capacity sodium ferrovanadium phosphate positive electrode material, preparation method thereof and sodium ion battery

Abstract

The invention discloses a high-specific-capacity sodium ferrovanadium phosphate positive electrode material, a preparation method thereof and a sodium ion battery. Iron acetylacetonate and vanadyl acetylacetonate are adopted as an iron source and a vanadium source, the preparation method is simple, and the synthesized high-sodium positive electrode material has the advantages of high rate capability and high specific capacity by replacing vanadium with iron, and is long in cycle life and good in cycle stability. And the method is of great significance in promoting the application of the sodium-ion battery in the field of large-scale energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and more specifically, relates to a high specific capacity sodium vanadium iron phosphate positive electrode material and a preparation method thereof and a sodium ion battery. Background Art

[0002] Sodium-ion batteries are considered to be ideal for stationary energy storage. Electrode materials are key components of sodium-ion batteries and determine the overall performance and energy density of sodium-ion batteries. Therefore, optimizing the working potential and gravimetric / volumetric capacity of electrode materials remains an important prerequisite for designing competitive sodium-ion batteries. However, Na + With a larger radius Its diffusion kinetics are slow, resulting in large volume changes of electrode materials during the sodiumation / de-sodiumation process. As a result, most sodium-ion battery electrode materials exhibit relatively low energy density and unsatisfactory cyclability. The development of electrode materials with high stability and high capacity is crucial for practical applications.

[0003] The cathode materials of sodium ion batteries are generally divided into Prussian blue analogs, layered metal oxides and polyanionic compounds. Among the many options, polyanionic compounds have been widely studied due to their advantages such as stable structure, thermodynamic stability, adjustable working voltage and high safety. The NASICON structure in phosphate has been widely studied. Its general formula is Na 3 M 2 (PO 4 ) 3 (M = transition metal). One of the most widely studied materials is Na 3 V 2 (PO 4 ) 3 , is a cathode material with great application prospects. Chinese patent CN 110993942A discloses a high-performance sodium-deficient cathode material Na 3.4 □ 0.6 Fe 2+ 0.4 Fe 3+ 0.6 V 3+ (PO 4 ) 3 The positive electrode material has good discharge capacity and cycle performance at low rate performance, but poor high rate performance. Chinese patent CN 112429712A synthesizes Na phosphate with NASICON structure by sol-gel process 4 FeV(PO 4 ) 3 As a positive electrode material for sodium ion batteries, the theoretical capacity is 110 mAh g in the voltage range of 1.8-3.8 V. -1However, the reversible specific capacity of the cathode material is low, only 81.6 mAh g at 5C current density. -1 , and also has the defect of poor high-rate performance.

[0004] Therefore, it is necessary to develop a positive electrode material with good high rate performance and high specific capacity. Summary of the invention

[0005] The present invention aims to provide a high specific capacity sodium ferrovanadium phosphate positive electrode material and a preparation method thereof and a sodium ion battery. 3+ Replace V 3+ , reducing the production cost of positive electrode materials and improving the reversible specific capacity and high rate performance of positive electrode materials.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a high specific capacity sodium vanadium iron phosphate positive electrode material comprises the following steps:

[0008] S1. Weigh sodium hydroxide, iron acetylacetonate, vanadyl acetylacetonate, and phosphoric acid according to a ratio of sodium: vanadium: iron: phosphorus = 4:2-x:x:3, and weigh anhydrous citric acid according to a ratio of carbon: vanadium = 1.5:1, wherein x = 0.2-1;

[0009] S2, dissolving sodium hydroxide, ferric acetylacetonate and vanadyl acetylacetonate in anhydrous ethanol to obtain solution A; dissolving phosphoric acid and citric acid in anhydrous ethanol to obtain solution B; and dripping solution B into solution A under stirring;

[0010] S3. After the addition is completed, dry the powder and grind it; in a nitrogen atmosphere, heat it to 350-400°C and keep it for 3-5 hours, then heat it to 500-700°C and keep it for 3-5 hours to obtain sodium vanadium iron phosphate positive electrode material.

[0011] Further, in step S1, x=0.4-1.

[0012] Furthermore, in step S3, the drying temperature is 80-90° C. and the drying time is 10-14 hours.

[0013] Furthermore, in step S3, the heating rate is 5-10°C / min.

[0014] The positive electrode material prepared by the above preparation method.

[0015] A sodium ion battery comprises the above-mentioned positive electrode material.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The positive electrode material preparation method of the present invention is simple. Ferrous acetylacetonate and vanadium acetylacetonate are selected as the iron source and vanadium source respectively. The organic salt is dissolved in ethanol, and the carbon-containing functional group is sintered to form a carbon coating layer. Dropwise addition of the solution is conducive to forming sodium vanadium iron phosphate with better performance, which can improve the specific capacity of the positive electrode material, and iron replaces vanadium to reduce the cost. The positive electrode material of the present invention has a specific capacity of 94.9mAh g under the condition of 5C current density. -1 At 20C current density, the specific capacity is 79.3 mAh g -1 , having good high rate performance. In the sodium iron phosphate positive electrode material prepared by the present invention, sodium ions occupy more Na2 positions, thereby increasing the capacity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the SEM image of the positive electrode material prepared in Example 1.

[0019] Figure 2 The XRD patterns of the positive electrode materials prepared in Examples 1-3.

[0020] Figure 3 This is a test diagram of the charge and discharge performance of the positive electrode material prepared in Example 1 of the present invention.

[0021] Figure 4 This is a test chart of the charge and discharge performance of the positive electrode material prepared in Comparative Example 1 of the present invention.

[0022] Figure 5 This is a test chart of the charge and discharge performance of the positive electrode material prepared in Comparative Example 2 of the present invention.

[0023] Figure 6 This is a test diagram of the charge and discharge performance of the positive electrode material prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0024] To make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with embodiment, but the embodiments of the present invention are not limited thereto. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by the technicians belonging to the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. It should be noted that, unless otherwise specified, the reagents used in the present embodiment, etc. are all common commercial products.

[0025] Example 1

[0026] Preparation of Sodium Ferrovanadium Phosphate by Sol-Gel Method 4 VFe(PO 4 ) 3) A sodium ion battery positive electrode material, comprising the following steps:

[0027] 1) Ferrous acetylacetonate (C 15 H 21 FeO 6 ), phosphoric acid (H 3 PO 4 ), sodium hydroxide (NaOH), anhydrous citric acid (C 6 H 8 O 7 ), Vanadyl acetylacetonate (C 10 H 14 O 5 V) in a molar ratio of 1:3:4:0.5:1;

[0028] 2) The powder obtained in step 1) except phosphoric acid and citric acid is slowly added to a 100 mL beaker (containing a magnetic stirrer) in sequence, and then 50 mL of anhydrous ethanol is added thereto as a solvent to form a solution A; phosphoric acid and citric acid are added to a 100 mL beaker, and 10 mL of anhydrous ethanol is added as a solvent to form a solution B; the beaker containing the magnetic stirrer is placed on a stirrer and stirred for 12 hours, and then solution B is added dropwise;

[0029] 3) transferring the suspension obtained in step 2) to a forced air drying oven, and then drying at 80° C. for 24 hours to obtain a completely dry solid powder, which was then ground in an agate mortar for 30 minutes;

[0030] 4) The powder obtained in step 3) is placed in a tubular furnace filled with nitrogen, and is ventilated at room temperature for one hour, and then calcined by heating to 400°C at a rate of 5°C / min and keeping the temperature for 4 hours, and then heating to 650°C and keeping the temperature for 5 hours to obtain sodium vanadium iron phosphate polyanion positive electrode material.

[0031] Example 2

[0032] Compared with Example 1, the difference is that the molar ratio of ferric acetylacetonate to vanadyl acetylacetonate is 0.8:1.2.

[0033] Example 3

[0034] Compared with Example 1, the difference is that the molar ratio of ferric acetylacetonate to vanadyl acetylacetonate is 0.6:1.4.

[0035] Figure 1 The morphology of the positive electrode material synthesized in Example 1 is shown, and the particle size of the prepared material is about 100 nm. Figure 2 The XRD spectra of the positive electrode materials prepared in Examples 1-3 illustrate that the materials synthesized in Examples 1-3 are consistent with the standard card PDF#00-040-0019 (Na8 Fe 4 (PO 4 ) 6 ) matches, the space group is There is a small amount of Na x FePO 4 Miscellaneous, typical crystal structure is Na 4 V 2-x Fe x (PO 4 ) 3 , by MO 6 (M=Fe, V) octahedron and PO 4 The tetrahedra are connected by corner sharing, providing two types of occupied sites for Na with different oxygen environments. + ions (Na1 and Na2), more Na2 occupies, which is beneficial to the improvement of capacity.

[0036] Comparative Example 1

[0037] Compared with Example 1, the difference is that iron is not doped.

[0038] Comparative Example 2

[0039] Compared with Example 1, the iron source is replaced by ferric citrate, the vanadium source is replaced by ammonium metavanadate, and the solution is replaced by deionized water.

[0040] Comparative Example 3

[0041] Compared with Example 1, the difference is that all the raw materials are mixed together and added.

[0042] Performance Testing

[0043] The sodium ferrovanadium phosphate positive electrode material powder prepared in Example 1 and Comparative Examples 1-3 was weighed, mixed and ground with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1 for 30 minutes, and then coated on a carbon-containing aluminum foil, dried, and cut to obtain a positive electrode sheet; a metal sodium sheet was used as a metal negative electrode, a glass fiber (GF / D) was used as a separator, and 1 mol / L sodium perchlorate was dissolved in propylene carbonate and 5% fluoroethylene carbonate solvent as an organic electrolyte, and assembled into a 2032 type sodium ion button battery in an argon-filled glove box. The battery was subjected to a constant current cycle charge and discharge test using a NEWARE battery test system, and the battery test was in the voltage range of 1.5-4.2V.

[0044] Figure 3The sodium vanadium iron phosphate prepared in Example 1 was tested at different current densities of 0.1, 0.5, 1, 2, 5, 10, 15, and 20 C during the charge and discharge process, and the average discharge capacities were 147.1, 118.7, 107.7, 102.3, 94.9, 88.1, 83.4, and 79.3 mAh g, respectively. -1 .

[0045] Figure 4 The sodium vanadium phosphate prepared in Comparative Example 1 was tested at different current densities of 0.1, 0.5, 1, 2, 5, and 10 C during the charge and discharge process, and the average discharge capacity was 88.7, 84.9, 82.6, 79.8, 72.7, and 53.5 mAh g, respectively. -1 At higher rates, the capacity decays to almost 0, which is not as good as the performance of sodium vanadium iron phosphate.

[0046] Figure 5 The sodium vanadium iron phosphate with different raw materials prepared in Comparative Example 2 was tested at different current densities of 0.1, 0.5, 1, 2, 5, 10, 15, and 20C during the charge and discharge process. The average discharge capacities were 151.54, 117.0, 106.0, 97.0, 79.7, 60.8, 46.8, and 37.7 mAh g, respectively. -1 At low rates, the average discharge capacity is comparable to that of the sodium ferrous vanadium phosphate positive electrode material prepared in Example 1, but the discharge capacity decreases significantly at high rates. This may be because the structure of the sodium ferrous vanadium phosphate synthesized by ferric citrate is not as stable as that of ferric acetylacetonate. As shown in the figure, the capacity of iron gradually decreases with the increase of the rate.

[0047] Figure 6 The performance of sodium vanadium iron phosphate prepared by directly mixing all raw materials prepared in Comparative Example 3 is 70.8 mAh g -1 , not as good as the performance of adding raw materials separately 79.3mAh g -1 Good. This may be because the direct mixing leads to uneven coating of citric acid, and the carbon layer formed after firing is also uneven, which leads to reduced conductivity of the material and unsatisfactory capacity.

[0048] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a high specific capacity sodium ferrovanadium phosphate positive electrode material, characterized in that: The steps include: S1. Weigh sodium hydroxide, iron acetylacetonate, vanadyl acetylacetonate, and phosphoric acid according to a ratio of sodium: vanadium: iron: phosphorus = 4:2-x:x:3, and weigh anhydrous citric acid according to a ratio of carbon: vanadium = 1.5:1, wherein x = 0.2-1; S2, dissolving sodium hydroxide, ferric acetylacetonate and vanadyl acetylacetonate in anhydrous ethanol to obtain solution A; dissolving phosphoric acid and citric acid in anhydrous ethanol to obtain solution B; and dripping solution B into solution A under stirring; S3. After the addition is completed, dry the powder and grind it; in a nitrogen atmosphere, heat it to 350-400°C and keep it for 3-5 hours, then heat it to 500-700°C and keep it for 3-5 hours to obtain sodium vanadium iron phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step S1, x=0.4-1.

3. The preparation method according to claim 1, characterized in that: In step S3, the drying temperature is 80-90°C; and the drying time is 10-14h.

4. The preparation method according to claim 1, characterized in that: In step S3, the heating rate is 5-10°C / min.

5. The positive electrode material prepared by the preparation method according to any one of claims 1 to 4.

6. A sodium ion battery, characterized in that: Comprising the positive electrode material as claimed in claim 5.

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