Beta"-al2o3 and n-doped c composite coated na3v2(po4)2f3 electrode material

Abstract

This invention provides a method based on β'' A method for preparing Al2O3 and N-doped C composite-coated Na3V2(PO4)2F3 electrode material. First, citric acid, vanadium pentoxide, ammonium dihydrogen phosphate, and sodium fluoride are sequentially dissolved in deionized water and stirred at 60°C until gel formation occurs. After drying, the resulting powder is placed in a tube furnace and subjected to a two-step heat treatment process to obtain Na3V2(PO4)2F3. Then, Na3V2(PO4)2F3 and dopamine hydrochloride are dispersed in an aqueous solution of tris(hydroxymethyl)aminomethane hydrochloride, stirred, and then... β'' -Al2O3, after stirring for another 23 h, was filtered, dried, and then placed in a tube furnace for heat treatment to finally obtain β'' A Na3V2(PO4)2F3 electrode material was developed by coating Al2O3 and N-doped C. This electrode material is simple to prepare, and sodium-ion half-cells assembled using this material as the positive electrode exhibit ideal capacity performance and stable cycle performance, demonstrating potential application value in sodium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry and new energy materials, specifically relating to a method for preparing Na3V2(PO4)2F3 electrode material based on β”-Al2O3 and N-doped C composite coating. Background Technology

[0002] In recent years, lithium-ion batteries, as highly efficient energy storage devices, have been widely used in numerous fields such as portable electronics, electric vehicles, and energy storage power stations, leading to a significant depletion of lithium resources and rising costs. Therefore, sodium-ion batteries, based on abundant and inexpensive sodium, have once again attracted attention. Sodium-ion batteries operate similarly to lithium-ion batteries and are also known as recyclable "rocking chair batteries," where sodium ions undergo reversible insertion and extraction within the host structure of the positive and negative electrodes during charging and discharging. Sodium-ion batteries can use electrolyte solvents and electrolyte salts with lower decomposition potentials, broadening the range of electrolyte choices. Furthermore, sodium does not alloy with aluminum, allowing sodium-ion batteries to use aluminum foil as the current collector for both the positive and negative electrodes, replacing the more expensive and heavier copper current collector, reducing battery costs and increasing energy density. Therefore, sodium-ion batteries are considered the most promising next-generation rechargeable battery to replace lithium-ion batteries.

[0003] The cathode material is a key factor affecting battery performance. Na3V2(PO4)2F3, with its stable crystal structure, high operating voltage (~3.9V), and high energy density (~500Wh / kg), is considered one of the most promising cathode materials for high-voltage sodium-ion batteries. Na3V2(PO4)2F3 possesses a three-dimensional open framework structure, and the large inter-channel gaps facilitate the rapid migration of sodium ions, resulting in faster diffusion kinetics and higher power density. However, because the [V2O8F3] dioctahedrons in the Na3V2(PO4)2F3 structure are separated by [PO4] tetrahedra, its intrinsic conductivity is relatively low, severely limiting its electrochemical performance. Furthermore, Na3V2(PO4)2F3 requires a high voltage during charge and discharge, making it prone to side reactions between the active material and the electrolyte, thus leading to a decrease in the material's cycle performance. Coating Na3V2(PO4)2F3 with carbon, which has high electronic conductivity, is a common method to address the low electronic conductivity of Na3V2(PO4)2F3 and suppress side reactions. However, if the carbon coating layer is too thin, its effect on improving electronic conductivity and suppressing side reactions is not significant. If the carbon coating layer is too thick, it will hinder sodium ion transport due to the poor sodium ion conductivity of the carbon material. Therefore, even the electrochemical performance of Na3V2(PO4)2F3 electrode materials obtained through carbon coating modification is still not satisfactory. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a Na3V2(PO4)2F3 electrode material based on β”-Al2O3 and N-doped C composite coating. The raw materials involved in the synthesis are citric acid (chelating agent), vanadium pentoxide (vanadium source), ammonium dihydrogen phosphate (phosphorus source), sodium fluoride (fluorine and sodium source), dopamine hydrochloride (carbon source), Tris hydrochloride (buffer solution), and β”-Al2O3 (sodium fast ion conductor).

[0005] Al₂O₃ has many polymorphs, more than 10 known, but mainly three crystal forms: α-Al₂O₃, β-Al₂O₃, and γ-Al₂O₃. Different crystal forms of Al₂O₃ have different properties due to their different structures. The technical solution of this invention uses Na₂β-Al₂O₃ (commonly referred to as β₻-Al₂O₃), an electrolyte material for sodium-sulfur batteries, with the chemical formula Na₂O·5.33Al₂O₃, space group R-3m, and cell parameters of...

[0006] Due to the excellent adhesion and film-forming properties of dopamine, dopamine is uniformly attached to the surface of Na3V2(PO4)2F3 particles and polymerizes. After a period of dopamine polymerization, β"-Al2O3 nanoparticles are adsorbed by the good adhesion of dopamine. Finally, the polymerized dopamine is pyrolyzed by high-temperature calcination to obtain a Na3V2(PO4)2F3 electrode material with a uniform three-layer coating of N-doped C / β"-Al2O3 / N-doped C. Compared to traditional C coating and composite coating of C with other crystalline Al2O3, this invention achieves a perfect combination of high electronic conductivity and high ionic conductivity through a three-layer coating of N-doped C / β"-Al2O3 / N-doped C obtained from β"-Al2O3 and dopamine with excellent film-forming properties. Furthermore, the three-layer coating can more effectively suppress side reactions between the active material and the electrolyte, stabilize the material structure, and improve the material's cycle stability. In addition, the N-doped C obtained from the pyrolysis of polymerized dopamine can generate edge defects, improving the adsorption and storage of sodium ions, thereby increasing capacity. In particular, the synergistic modification of N-doped C and β"-Al2O3 reduces the polarization of Na3V2(PO4)2F3 at high rates, effectively improving the rate performance of Na3V2(PO4)2F3. Using it as the cathode of a sodium-ion battery exhibits high capacity and excellent rate and cycle performance, demonstrating significant potential application value.

[0007] The specific preparation method is as follows:

[0008] S1. Citric acid and vanadium pentoxide were dissolved in deionized water in sequence. After stirring for a period of time, ammonium dihydrogen phosphate and sodium fluoride were added. Stirring was continued at 60°C until gel formation. After drying, the resulting powder was placed in a tube furnace and subjected to a two-step heat treatment process to obtain Na3V2(PO4)2F3.

[0009] S2. The Na3V2(PO4)2F3 prepared in S1 and dopamine hydrochloride were dispersed in Tris hydrochloride aqueous solution, and the pH was adjusted. After stirring for a period of time, β”-Al2O3 was added, and after stirring for a period of time, the mixture was filtered, dried, and then placed in a tube furnace for heat treatment. Finally, the β”-Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material was obtained.

[0010] Preferably, in step S1, the molar mass ratio of citric acid, vanadium pentoxide, ammonium dihydrogen phosphate, and sodium fluoride is 0.3–1.5:1:2:3; citric acid, vanadium pentoxide, ammonium dihydrogen phosphate, and sodium fluoride are dissolved in deionized water sequentially; and the stirring time is 0.2–0.8 h.

[0011] Preferably, in step S1, the two-step heat treatment process involves sintering at 200–400°C for 3–5 hours in nitrogen or argon, followed by sintering at 400–800°C for 6–10 hours.

[0012] Preferably, in step S2, the amount of dopamine hydrochloride added is 8-12 wt.% of the mass of Na3V2(PO4)2F3 taken. The concentration of the Tris hydrochloride aqueous solution is 0.8-1.2 g / L; the adjusted pH value is 8-9; and the amount of β”-Al2O3 added is 0.2-1.0 wt.%.

[0013] Preferably, in step S2, the stirring period is 0.5 to 1.5 hours; the continued stirring period is 14 to 23 hours; and the second heat treatment is sintering at 500 to 700°C in nitrogen or argon for 7 to 9 hours.

[0014] The electrode material based on β”-Al2O3 and N-doped C composite coating of Na3V2(PO4)2F3 and its preparation method described in this invention have the following characteristics:

[0015] (1) The experimental process is simple and easy to operate. Simply mix NVPF, β”-Al2O3 and dopamine evenly and sinter at a certain temperature to obtain β”-Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material.

[0016] (2) The material exhibits good cycle performance. The obtained product contains a sodium-oxygen layer in its β"-Al2O3 structure that allows sodium ions to migrate, and has a high sodium content, resulting in superior sodium ion conductivity unmatched by other Al2O3 crystal forms. Its ionic conductivity at 300℃ and room temperature can reach 0.2–0.4 S cm⁻¹, respectively. -1 and 2×10 -3 S cm -1The β”-Al2O3 and N-doped C composite coating layer can effectively reduce the contact between the substrate and the electrolyte, thereby suppressing side reactions between the active material and the electrolyte and stabilizing the material structure.

[0017] (3) High rate capacity of materials (the introduction of dopamine to improve the electronic conductivity of Na3V2(PO4)2F3, the introduction of β”-Al2O3 to improve the migration rate of sodium ions, and the synergistic modification of the two to reduce the polarization of the active material at high rates, effectively improving the rate performance of Na3V2(PO4)2F3). Attached Figure Description

[0018] Figure 1 The XRD patterns are of the samples prepared in Comparative Example 1, Comparative Example 2, and Example 2.

[0019] Figure 2 For comparison, the sample prepared in Example 1 is shown in (a) charge-discharge performance diagram and (b) cycle performance diagram at 1C; and in (c) charge-discharge performance diagram and (d) cycle performance diagram at 0.5C.

[0020] Figure 3 For comparison, the sample prepared in Example 2 is shown in (a) charge-discharge performance diagram and (b) cycle performance diagram at 1C; and in (c) charge-discharge performance diagram and (d) cycle performance diagram at 0.5C.

[0021] Figure 4 (a) Charge-discharge performance diagram and (b) Cyclic performance diagram of the sample prepared in Comparative Example 3.

[0022] Figure 5 The figures show (a) charge-discharge performance and (b) cycle performance of the sample prepared in Example 1.

[0023] Figure 6 The figures show (a) charge-discharge performance and (b) cycle performance of the sample prepared in Example 2 at 1C; and (c) charge-discharge performance and (d) cycle performance at 0.5C.

[0024] Figure 7 The figures show (a) charge-discharge performance and (b) cycle performance of the sample prepared in Example 3. Detailed Implementation

[0025] The present invention will be further described below with reference to comparative examples and embodiments, and the substantial features and advantages of the present invention will be highlighted through comparison.

[0026] Comparative Example 1

[0027] 12 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. Stirring was continued at 60 °C until gel formation. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), and then calcined at 600 °C for 8 h (N2 atmosphere) to obtain C-coated Na3V2(PO4)2F3 electrode material (denoted as C@NVPF). Figure 1 The XRD pattern of the prepared C@NVPF is shown, and it can be seen that the XRD pattern is consistent with the NVPF (PDF#04-012-2207) card. It was used as a positive electrode material to assemble a sodium-ion half-cell, and its performance at 1C (1C = 128 mA g / g) was observed. -1 Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 109.9 mAh g. -1 ( Figure 2 a) After 100 cycles, the capacity retention rate was 84.8% ( Figure 2 b) The reversible capacity at 0.5C rate is 120.0 mAh g. -1 ( Figure 2 c) After 100 cycles, the capacity retention rate was 70.1%. Figure 2 d).

[0028] Comparative Example 2

[0029] 5 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. The mixture was stirred at 60 °C until gel formation was achieved. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), and then calcined at 600 °C for 8 h (N2 atmosphere) to obtain Na3V2(PO4)2F3. Na3V2(PO4)2F3 and 10 wt.% dopamine hydrochloride were dispersed in a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L. After stirring for 24 h, the mixture was filtered, dried, and placed in a tube furnace again for calcination at 600 °C for 8 h (N2 atmosphere) to obtain N-doped C-coated Na3V2(PO4)2F3 electrode material (denoted as NC@NVPF). Figure 1 The XRD pattern of the prepared NC@NVPF is shown, and it can be seen that the XRD pattern is consistent with the NVPF (PDF#04-012-2207) card. It was used as a positive electrode material to assemble a sodium-ion half-cell, and its performance at 1C (1C = 128 mA g / g) was observed. -1 Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 111.8 mAh g. -1 ( Figure 3 a) After 100 cycles, the capacity retention rate was 90.8% ( Figure 3 b) The reversible capacity at 0.5C rate is 121.6 mAh g. -1 ( Figure 3 c) After 100 cycles, the capacity retention rate was 89.4%. Figure 3 d).

[0030] Comparative Example 3

[0031] 5 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. The mixture was stirred at 60 °C until a gel formed. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), and then calcined at 600 °C for 8 h (N2 atmosphere) to obtain Na3V2(PO4)2F3. 2F3 and 10 wt.% dopamine hydrochloride were dispersed in a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L. After stirring for 1 h, 0.5 wt.% Al2O3 was added, and stirring was continued for another 23 h. The mixture was then filtered, dried, and placed in a tube furnace for calcination at 600 °C for 8 h (N2 atmosphere) to obtain an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material (denoted as NC@0.5Al2O3@NVPF). This material was used as the positive electrode material to assemble a sodium-ion half-cell at 1C (1C = 128 mA g / L). -1 Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 104.6 mAh g. -1 ( Figure 4 a) After 100 cycles, the capacity retention rate was 93.4% ( Figure 4 b).

[0032] Example 1

[0033] 5 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. The mixture was stirred at 60 °C until a gel formed. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), followed by calcination at 600 °C for 8 h (N2 atmosphere) to obtain Na3V2(PO4)2F3. Na3V2(PO4)2F3 and 10 wt.% dopamine hydrochloride were dispersed in a p In a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L, after stirring for 1 h, 0.2 wt.% β”-Al2O3 was added, and stirring continued for another 23 h. The mixture was then filtered, dried, and placed in a tube furnace for calcination at 600 °C for 8 h (N2 atmosphere) to obtain a β”-Al2O3 and N-doped C composite-coated Na3V2(PO4)2F3 electrode material (denoted as NC@0.2β”-Al2O3@NVPF). This material was used as the positive electrode material to assemble a sodium-ion half-cell at 1 C (1C = 128 mA g / L). -1 Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 115.3 mAh g. -1 ( Figure 5 a) After 100 cycles, the capacity retention rate was 94.2% ( Figure 5 b) shows good electrochemical performance.

[0034] Example 2

[0035] 5 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. The mixture was stirred at 60 °C until a gel formed. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), and then calcined at 600 °C for 8 h (N2 atmosphere) to obtain Na3V2(PO4)2F3. Na3V2(PO4)2F3 and... 10 wt.% dopamine hydrochloride was dispersed in a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L. After stirring for 1 h, 0.5 wt.% β”-Al2O3 was added, and stirring was continued for another 23 h. The mixture was then filtered, dried, and placed in a tube furnace for calcination at 600 °C for 8 h (N2 atmosphere) to obtain a β”-Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material (denoted as NC@0.5β”-Al2O3@NVPF). Figure 1 The XRD pattern of the prepared NC@0.5β”-Al2O3@NVPF is shown, and it can be seen that the XRD pattern is consistent with the NVPF (PDF#04-012-2207) card. It was used as a positive electrode material to assemble a sodium-ion half-cell, and its performance at 1C (1C=128mA g) was observed. -1Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 117.4 mAh g. -1 ( Figure 6 a) After 100 cycles, the capacity retention rate was 97.8% ( Figure 6 b) The reversible capacity at 0.5C rate is 124.9 mAh g. -1 ( Figure 6 c) After 100 cycles, the capacity retention rate was 97.3%. Figure 6 d) shows good electrochemical performance.

[0036] Example 3

[0037] 5 mmol of citric acid and 10 mmol of vanadium pentoxide were dissolved sequentially in 100 mL of deionized water. After stirring for 0.5 h, 20 mmol of ammonium dihydrogen phosphate and 30 mmol of sodium fluoride were added. The mixture was stirred at 60 °C until a gel formed. After drying, the resulting powder was placed in a tube furnace and calcined at 300 °C for 4 h (N2 atmosphere), followed by calcination at 600 °C for 8 h (N2 atmosphere) to obtain Na3V2(PO4)2F3. Na3V2(PO4)2F3 and 10 wt.% dopamine hydrochloride were dispersed in a p In a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L, after stirring for 1 h, 1.0 wt.% β”-Al2O3 was added, and stirring continued for another 23 h. The mixture was then filtered, dried, and placed in a tube furnace for calcination at 600 °C for 8 h (N2 atmosphere) to obtain a β”-Al2O3 and N-doped C composite-coated Na3V2(PO4)2F3 electrode material (denoted as NC@1.0β”-Al2O3@NVPF). This material was used as the positive electrode material to assemble a sodium-ion half-cell at 1 C (1C = 128 mA g / L). -1 Charge-discharge tests were conducted at a certain rate, and the initial discharge specific capacity was 113.0 mAh g. -1 ( Figure 7 a) After 100 cycles, the capacity retention rate was 95.9% ( Figure 7 b) shows good electrochemical performance.

[0038] The self-polymerization time of dopamine hydrochloride affects the thickness of the nitrogen-doped carbon coating. To explore the effect of the thickness of the nitrogen-doped carbon coating on the introduction of β”-Al2O3, we added Examples 4, 5, and 6. The operation steps were the same as in Example 2, and the stirring speed was 300 rpm. The difference was that Na3V2(PO4)2F3 and 10 wt.% dopamine hydrochloride were dispersed in a Tris hydrochloride aqueous solution with a pH of 8.5 and a concentration of 1 g / L, and stirred for 2 h, 5 h, and 10 h, respectively, before adding 0.5 wt.% β”-Al2O3. These were then used as positive electrode materials to assemble sodium-ion half-cells at 1C (1C = 128 mA g). -1Charge-discharge tests were conducted at various rates, and Table 1 summarizes the electrochemical performance of each example as a positive electrode material for sodium-ion batteries. The initial discharge specific capacity of Example 4 was 116.0 mAh g⁻¹. -1 After 100 cycles, the capacity retention rate was 96.6%; the initial discharge specific capacity of Example 5 was 115.9 mAh g. -1 After 100 cycles, the capacity retention rate was 97.2%; the initial discharge specific capacity of Example 6 was 113.2 mAh g. -1 After 100 cycles, the capacity retention rate was 97.1%, demonstrating good electrochemical performance.

[0039] Table 1. Electrochemical performance of each example as a cathode material in sodium-ion batteries.

[0040] Table 1. Electrochemical performance of each example as a cathode material in sodium-ion batteries.

[0041]

Claims

1. A method based on β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... The steps are as follows: S1. Citric acid and vanadium pentoxide are dissolved sequentially in deionized water. After stirring for a period of time, ammonium dihydrogen phosphate and sodium fluoride are added, and stirring is continued until a gel forms. After drying, the resulting powder is placed in a tube furnace and heat-treated to obtain Na3V2(PO4)2F3. The molar mass ratio of citric acid, vanadium pentoxide, ammonium dihydrogen phosphate, and sodium fluoride is 0.3~1.5:1:2:

3. S2. Disperse the Na3V2(PO4)2F3 prepared in S1 and dopamine hydrochloride in an aqueous solution of tris(hydroxymethyl)aminomethane hydrochloride, adjust the pH, stir and mix well, and then add... β'' -Al2O3, after stirring for a period of time, is filtered, dried, and then placed in a tube furnace for heat treatment to finally obtain... β'' -Al2O3 and N-doped C composite coating of Na3V2(PO4)2F3 electrode material, wherein the amount of dopamine hydrochloride added is 8-12% of the mass of the Na3V2(PO4)2F3 taken. β'' The amount of Al2O3 added is 0.2~1.0 wt.%.

2. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... In step S1, citric acid, vanadium pentoxide, ammonium dihydrogen phosphate, and sodium fluoride are dissolved in deionized water in sequence; the stirring time is 0.2~0.8 h.

3. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... In step S1, the heat treatment process involves sintering at 200-400°C for 3-5 hours in nitrogen or argon gas, followed by sintering at 400-800°C for 6-10 hours.

4. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... In step S2, the concentration of the tris(hydroxymethyl)aminomethane hydrochloride aqueous solution is 0.8~1.2 g / L.

5. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... The adjusted pH value is 8-9.

6. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... Add in step S2 β'' -Stir Al2O3 for 14~23 h.

7. A method based on claim 1 β'' A method for preparing an Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material, characterized in that... In step (2), the heat treatment is carried out again by sintering at 500~700℃ for 7~9 h in nitrogen or argon.

8. The preparation method according to any one of claims 1 to 5 yields... β'' -Al2O3 and N-doped C composite coating Na3V2(PO4)2F3 electrode material.

9. The method according to claim 8 β'' Application of Al2O3 and N-doped C composite coated Na3V2(PO4)2F3 electrode material in the preparation of cathode materials for sodium-ion batteries.

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