Preparation method of high entropy sodium vanadium phosphate electrode

Abstract

The present invention relates to the technical field of sodium ion battery positive electrode materials, and discloses a preparation method of a high-entropy sodium vanadium phosphate electrode, comprising the following steps: step 1, adding 2.7g ammonium vanadate and 16.8g oxalic acid to 200mL deionized water, stirring and reacting at 60-120°C for 20-80min; step 2, adding 0.75g ferric nitrate, 0.81g manganese nitrate, 0.80g chromium nitrate, 0.58g cobalt nitrate and 0.49g nickel nitrate dissolved in 100mL deionized water after slight cooling; step 3, adding 8.3g sodium dihydrogen phosphate dissolved in 100mL deionized water after stirring. The present invention adopts a chemical synthesis method to prepare a precursor, and adopts a Joule heat process to prepare a high-entropy metal-doped sodium vanadium phosphate positive electrode material. Compared with the traditional calcination process, this process has the advantages of fast heating rate, low energy consumption, mild reaction conditions, high product purity, good particle size uniformity, and easy control of the ratio of each component, and can achieve continuous preparation.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery positive electrode materials, and in particular to a method for preparing a high-entropy sodium vanadium phosphate electrode. Background Art

[0002] As human production and life continue to escalate in energy demand, the massive consumption of fossil fuels like oil and coal, along with their environmental pollution, has limited the development of the energy sector. Therefore, future energy storage technologies are increasingly oriented towards sustainable and low-cost battery processes. In recent years, the rise of new energy vehicles and energy storage devices has led to excessive lithium resource consumption, necessitating the development of secondary batteries that can replace lithium-ion batteries. Sodium and lithium belong to the same main group of elements, sharing similar physical and chemical properties. However, sodium resources are more abundant and less expensive than lithium. Therefore, sodium-ion batteries are gradually gaining attention and are considered one of the most promising alternatives to lithium-ion batteries.

[0003] NASICON-type Na3V2(PO4)3 has the advantages of high voltage platform, high ion diffusion rate and stable crystal structure, and is one of the candidate materials for future commercial sodium-ion batteries. However, the low intrinsic electronic conductivity and low theoretical specific capacity of Na3V2(PO4)3 cathode materials limit its industrial development. At present, the modification methods of NVP mainly focus on its poor conductivity, mainly in the following three aspects: (1) increasing the electronic conductivity of the material through carbon coating; (2) improving the intrinsic conductivity of the material by metal ion doping; (3) improving the electrochemical performance of the material by preparing a special morphology. Among them, metal doping can not only improve the conductivity of the electrode, but also activate the high voltage platform to meet the energy density requirements of the cathode material. High entropy metal doping can maximize the kinetic transport capacity of the electrode to a certain extent. However, the current traditional preparation methods are not enough to fully utilize the advantages of high entropy metal doped sodium vanadium phosphate, especially for the sodium storage capacity in the low voltage platform area.

[0004] To address the current issues with high-entropy metal-doped sodium vanadium phosphate, a rapid Joule heating method is used to stabilize the cathode structure and increase sodium storage sites, thereby improving the electrochemical performance of the material. High-entropy sodium vanadium phosphate prepared using Joule heating not only has excellent sodium ion diffusion capacity but can also accommodate additional sodium ions, thereby increasing the capacity of the electrode. Furthermore, this rapidly prepared cathode exhibits excellent structural stability, resulting in excellent cycling stability. Summary of the Invention

[0005] The present invention aims to address the limitations of high-entropy metal-doped sodium vanadium phosphate cathode materials for batteries, such as limited sodium ion transport pathways, low intrinsic electronic conductivity, and poor stability, by developing novel strategies for the synthesis and modification of high-entropy sodium vanadium phosphate materials. By treating the powdered precursor with rapid Joule heating, high-entropy metal-doped sodium vanadium phosphate materials are prepared. This simultaneously expands the sodium ion transport pathways and improves the electrical conductivity, thereby enhancing the charge-discharge capacity and cycling stability of high-entropy sodium vanadium phosphate cathode materials.

[0006] The present invention is implemented by the following technical solution: a method for preparing a high entropy sodium vanadium phosphate electrode comprises the following steps:

[0007] Step 1: Add 2.7 g of ammonium vanadate and 16.8 g of oxalic acid to 200 mL of deionized water, stir and react at 60-120° C. for 20-80 minutes;

[0008] Step 2: After cooling slightly, add 0.75 g of ferric nitrate, 0.81 g of manganese nitrate, 0.80 g of chromium nitrate, 0.58 g of cobalt nitrate, and 0.49 g of nickel nitrate dissolved in 100 mL of deionized water;

[0009] Step 3: After stirring, 8.3 g of sodium dihydrogen phosphate dissolved in 100 mL of deionized water was added, and then the solution was evaporated by magnetic stirring and then ground to obtain a precursor powder;

[0010] Step 4: subjecting the precursor powder to rapid Joule heating to obtain an improved high-entropy metal-doped sodium vanadium phosphate sodium ion battery cathode material powder;

[0011] Step 5: Prepare a slurry in the ratio of 70:20:10 of the prepared high-entropy metal-doped sodium vanadium phosphate powder: conductive carbon black: binder, grind it thoroughly in an agate mortar, apply it, dry it, and cut it into discs with a diameter of 14 mm to obtain the high-entropy sodium vanadium phosphate electrode sheet.

[0012] Preferably, the high-valent vanadium source may be any one of sodium vanadate, sodium metavanadate, ammonium metavanadate, and vanadium pentoxide, or a combination of at least two thereof.

[0013] Preferably, the phosphorus source can be any one of phosphoric acid, sodium phosphate, sodium metaphosphate or sodium dihydrogen phosphate, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of phosphoric acid and sodium phosphate, and a combination of sodium phosphate and sodium dihydrogen phosphate.

[0014] Preferably, in step 3, the suspension is obtained by stirring on a magnetic stirrer for 8-12 hours; and the molar ratio of ammonium vanadate, oxalic acid, sodium dihydrogen phosphate, ferric nitrate, manganese nitrate, chromium nitrate, cobalt nitrate and nickel nitrate is 0.75:4:3:0.1:0.1:0.1:0.1:0.1.

[0015] Preferably, the rapid Joule heating is set to have a current of 50A-70A and a time of 10-120s.

[0016] Preferably, in step 5, the electrode coating thickness is 10-30 μm.

[0017] A sodium ion battery is assembled using a high-entropy sodium vanadium phosphate electrode sheet as a positive electrode, a metal sodium sheet as a negative electrode, and a glass fiber as a separator. The specification is GF / D and a 1 mol / L sodium perchlorate solution as an electrolyte.

[0018] The preparation method for a high-entropy sodium vanadium phosphate battery includes the following steps: placing the positive electrode shell, positive electrode sheet, and separator in this order in a glove box filled with argon atmosphere, followed by adding an appropriate amount of electrolyte, sodium sheet, stainless steel gasket, spring, and negative electrode shell. The battery is then compressed and sealed using a packaging machine.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention utilizes chemical synthesis to prepare the precursor and Joule heating to produce a high-entropy metal-doped sodium vanadium phosphate cathode material. Compared to traditional calcination, this process utilizes rapid Joule heating, which not only accelerates heating but also reduces energy consumption. This process also offers the advantages of mild reaction conditions, high product purity, good particle size uniformity, and easy control of the ratios of the components, allowing for continuous production.

[0021] 2. The high-entropy metal-doped sodium vanadium phosphate cathode material prepared by the present invention simultaneously achieves the expansion of sodium ion transport channels and the improvement of conductivity, thereby improving the charge and discharge specific capacity and cycle stability of the high-entropy metal-doped sodium vanadium phosphate cathode material, providing new ideas and solutions for the further commercial application of sodium-ion batteries in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the X-ray diffraction (XRD) pattern of the high-entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention.

[0023] Figure 2 This is a comparison diagram of cyclic voltammetry (CV) curves of sodium ion batteries prepared with the high-entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention at a scan rate of 0.1 mVs-1.

[0024] Figure 3 It is a charge and discharge curve diagram of a sodium ion battery using a high entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention at a rate of 0.2C.

[0025] Figure 4 This is a cycle performance diagram of a sodium ion battery using the high-entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention at a 1C rate.

[0026] Figure 5 This is a cycle performance diagram of a sodium ion battery using the high-entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention at a 5C rate.

[0027] Figure 6 This is a rate performance diagram of a sodium ion battery using the high-entropy sodium vanadium phosphate-Joule heat positive electrode material prepared by the present invention at 0.5-10C. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0029] The chemical reagents used in the present invention were all analytically pure ammonium vanadate, sodium dihydrogen phosphate, oxalic acid, ferric nitrate, manganese nitrate, chromium nitrate, cobalt nitrate, and nickel nitrate. The purity of the inert gas (argon) used in step 1 was 99.999%. The aluminum foil and diaphragm used in step 2 were purchased from Suzhou Duoduo Chemical Technology Co., Ltd.

[0030] Example 1: A method for preparing a high-entropy sodium vanadium phosphate electrode, comprising the following steps:

[0031] Add 2.7g of ammonium vanadate and 16.8g of oxalic acid to 200mL of deionized water, stir and react at 60-120℃ for 20-80min, and add 0.75g of ferric nitrate, 0.81g of manganese nitrate, 0.80g of chromium nitrate, 0.58g of cobalt nitrate and 0.49g of nickel nitrate dissolved in 100mL of deionized water after cooling slightly. After stirring, add 8.3g of sodium dihydrogen phosphate dissolved in 100mL of deionized water, and then stir and evaporate the solution and grind to obtain a precursor powder. The precursor powder is subjected to rapid Joule heating, which is the improved high entropy metal-doped sodium vanadium phosphate sodium ion battery positive electrode material powder. After the sample is taken out, it is fully ground and washed and centrifuged to remove the influence of impurities. When washing the sample, first place the sample powder in a centrifuge tube, add an appropriate amount of ethanol, and set the speed to 12000r min after ultrasonication. -1 , time 5min, then dried and collected.

[0032] The positive electrode active material, conductive black, and polyvinylidene fluoride (PVDF) were added to a mortar and ground in a mass ratio of 7:2:1 for 20 minutes to achieve uniform grinding. An appropriate amount of N-methylpyrrolidone (NMP) was then added and ground into a uniform slurry. The resulting slurry was then coated on an aluminum foil surface and dried to produce a working electrode. A circular electrode sheet with a diameter of 12 mm was then punched out using a sheet punching machine. The active material loading on the electrode sheet was 1.5-1.7 mg cm⁻².

[0033] Example 2: Assembly of sodium ion batteries: Sodium ion batteries are assembled in a glove box filled with argon atmosphere, wherein the water content is less than 0.01ppm and the oxygen content is less than 0.01ppm. During assembly, the positive electrode sheet prepared in step 2 is placed in the positive battery shell, and a glass fiber diaphragm is placed, and an electrolyte of 1M NaClO4 solution is added dropwise. Then, the sodium sheet, stainless steel gasket, shrapnel, and negative electrode shell are placed in sequence, and finally sealed in the glove box with an air pressure packaging machine. The prepared positive electrode material powder is subjected to phase and purity characterization tests, such as phase analysis by X-ray diffraction method and high-resolution transmission electron microscopy to determine the structure and distribution of each component in the test object. The prepared battery is activated and then subjected to electrochemical performance testing. During activation, the charge and discharge current for the first three cycles is 0.2C, and then the test is performed according to 1C, where the theoretical specific capacity of the 1C rate is 176mAh g -1 The test voltage range is 1.2~4.2V. The cyclic voltammetry curve of the material at a scan rate of 0.1mV / s is as follows Figure 2 As shown, the initial charge and discharge curve of the material at 0.2C current is as follows Figure 3 The cycling performance at 1C and 5C rates is shown in Figure 4 and Figure 5 As shown, the rate performance at 0.5C to 10C is as follows Figure 6 shown.

[0034] Result analysis:

[0035] As attached Figure 1 As shown, X-ray diffraction analysis of the prepared cathode material revealed a one-to-one correspondence between the diffraction peaks obtained and those of the standard sodium vanadium phosphate card (JCPDS No. 53-0018). This indicates that the synthesized new cathode material does not affect the integrity of the crystal structure, and all exhibit a hexagonal NASICON structure free of impurities.

[0036] As attached Figure 2 The figure shows a comparison of the cyclic voltammetry (CV) curves of the high-entropy sodium vanadium phosphate-Joule heat sodium ion battery prepared by the present invention and the high-entropy sodium vanadium phosphate-conventional calcined sodium ion battery at a scan rate of 0.1 mV / s. It can be seen that compared with the traditional calcined material, the high-entropy sodium vanadium phosphate-Joule heat redox peak at around 1.6V is significantly enhanced, indicating that the amount of sodium ions intercalated and deintercalated during the process is increased, thereby improving the charge and discharge capacity of the material.

[0037] As attached Figure 3 As shown in the figure, the first charge and discharge curve at 0.2C. It can be seen from the figure that the material exhibits a typical charge and discharge platform curve unique to sodium ion batteries. The initial discharge capacity of the sodium ion battery after rapid Joule heating can reach 174.6mAh g -1The initial discharge capacity of the sodium ion battery prepared by high entropy sodium vanadium phosphate-traditional calcined cathode material is only 148.5 mAh g -1 .

[0038] As attached Figure 4 As shown, the cycle performance test was carried out at a 1C rate. After 100 cycles, the reversible discharge capacity of high entropy sodium vanadium phosphate-Joule heat increased from 149.4 mAh g -1 Down to 146.2mAh g -1 The capacity retention rate is 97.86%, which reflects the good long-term cycle stability at low current density.

[0039] As attached Figure 5 As shown, the cycle performance test was carried out at a rate of 5C. After 700 cycles, the reversible discharge capacity of high entropy sodium vanadium phosphate-Joule heat increased from 137.5 mAh g -1 Down to 125.0mAh g -1 The capacity retention rate is 90.91%, which reflects the good long-term cycle stability at high current density.

[0040] As attached Figure 6 As shown, the discharge specific capacity of the embodiment at 0.5C, 1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C and 10C rates is 155.39 mAh g -1 、148.49mAh g -1 、144.23mAh g -1 、141.22mAh g -1 、138.83mAh g -1 、136.55mAhg -1 、134.47mAhg -1 、132.52mAh g -1 、130.65mAh g -1 、128.51mAh g -1 and 126.61mAhgg -1 When the current returned to 1C, the capacity returned to 148.06 mAh g -1 The capacity retention rate is 95.27%, which fully demonstrates the excellent rate performance of the modified sodium-ion battery.

[0041] Therefore, it can be seen from the experimental data that the positive electrode material of high-entropy metal doped sodium vanadium phosphate using Joule heat shows good electrochemical performance in terms of charge and discharge specific capacity, cycle performance and rate performance in sodium ion batteries, and has great development prospects.

[0042] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a high entropy sodium vanadium phosphate electrode, characterized in that: The steps include: Step 1: Add 2.7 g of ammonium vanadate and 16.8 g of oxalic acid to 200 mL of deionized water, stir and react at 60-120°C for 20-80 min; Step 2: After cooling slightly, add 0.75 g of ferric nitrate, 0.81 g of manganese nitrate, 0.80 g of chromium nitrate, 0.58 g of cobalt nitrate, and 0.49 g of nickel nitrate dissolved in 100 mL of deionized water; Step 3: After stirring, 8.3 g of sodium dihydrogen phosphate dissolved in 100 mL of deionized water was added, and the solution was evaporated by magnetic stirring and then ground to obtain a precursor powder; Step 4: The precursor powder is subjected to rapid Joule heating with a current of 50 A to 70 A to obtain a high entropy metal-doped sodium vanadium phosphate sodium ion battery positive electrode material powder; the rapid Joule heating is set for 10-120 seconds; Step 5: Prepare a slurry according to the mass ratio of the prepared high-entropy metal-doped sodium vanadium phosphate powder: conductive carbon black: binder = 70:20:10, grind it thoroughly in an agate mortar and apply it, dry it and cut it into discs with a diameter of 14 mm to obtain a high-entropy sodium vanadium phosphate electrode sheet.

2. The method for preparing a high entropy sodium vanadium phosphate electrode according to claim 1, wherein: In step 5, the electrode coating thickness is 10-30 um.

3. A sodium ion battery, comprising a high-entropy sodium vanadium phosphate electrode sheet prepared by the preparation method of claim 1 as a positive electrode, a metallic sodium sheet as a negative electrode, a glass fiber as a separator, with a specification of GF / D, and a 1 mol / L sodium perchlorate solution as an electrolyte.

4. A method for preparing a sodium ion battery according to claim 3, characterized in that: In a glove box filled with argon atmosphere, place the positive electrode shell, positive electrode sheet, and diaphragm in turn, then add appropriate amount of electrolyte, sodium sheet, stainless steel gasket, shrapnel, and negative electrode shell, and then use the start packaging machine to press and package the battery.

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