Chlorine and tungsten co-doped sodium vanadium phosphate positive electrode material and preparation method thereof

Abstract

The application provides a sodium vanadium phosphate positive electrode material co-doped with chlorine and tungsten cations and a preparation method thereof, and belongs to the technical field of energy materials. 4+ The V site is doped with ions, and the Cl ‑ The (PO4) site is doped with ions 3‑ The chemical formula of the positive electrode material is Na 3‑ x V 2‑x W x (PO4) 3‑y Cl 3y / C, wherein x=0.05, 0.1, 0.15, and y=0.09, 0.12, 0.15; the application uses ammonium metavanadate, sodium acetate and ammonium dihydrogen phosphate as raw materials, tungsten disulfide and sodium chloride as doping sources, and citric acid monohydrate as a chelating agent, and the sodium vanadium phosphate electrode material co-doped with chlorine and tungsten cations is prepared through a solution gel method, so that the electronic conductivity is improved, the rate performance and the cycle stability are increased, and the material has a good application prospect in a sodium ion battery positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a sodium-ion battery positive electrode material modified by cation and anion doping and a preparation method thereof. BACKGROUND

[0002] Currently, fossil energy (including oil, coal and natural gas) is consumed in large quantities. Due to the limited reserves of fossil energy, the increasing demand and uncontrolled exploitation will accelerate the depletion of fossil energy. At the same time, environmental problems such as soil pollution, greenhouse effect and the like also occur. Therefore, it is urgent to explore new energy systems. As an electrochemical energy storage device, lithium-ion batteries have the advantages of high working voltage and long cycle life. At present, advanced lithium-ion battery technology has been applied to many mobile electronic devices and electric vehicles. However, due to the relative shortage of lithium sources, uneven distribution and price increase, the application and development of lithium-ion batteries are limited. In order to alleviate these problems, many studies have focused on new alternative energy systems. Sodium-ion batteries are considered to be the most suitable alternative to lithium-ion batteries. Sodium-ion batteries have received extensive attention in recent years in the storage and conversion of renewable energy. Compared with the commercialized lithium-ion battery, it has the following characteristics: (1) similar working principle. In the charging and discharging process of sodium-ion batteries, sodium ions are reversibly inserted / extracted between the cathode and the anode, so it is called a "rocking chair" battery. Sodium ions repeatedly migrate between the positive electrode and the negative electrode to achieve energy storage and release. The whole process is very similar to the charging and discharging process of lithium-ion batteries. (2) Sodium and lithium belong to the same main group and have similar chemical and physical properties. Lithium and sodium ions can be reversibly inserted and extracted into electrode materials with similar structures. (3) Low cost of sodium resources. The reserves of sodium resources on earth are much higher than those of lithium, and lithium is widely distributed in seawater. Sodium resources are abundant and cheap. In this sense, the low-cost characteristics of sodium-ion batteries make them more promising in large-scale energy storage.

[0003] As a kind of polyanion compound, sodium vanadium phosphate (Na3V2(PO4)3, NVP) has a unique three-dimensional NASICON structure, which can promote the rapid migration of Na + . With the advantages of structural stability, high working voltage and high capacity, it is considered to be one of the most promising sodium-ion battery cathode materials. However, the high Na + diffusion capacity of NVP is accompanied by a larger bulk structure and poor electronic conductivity, which leads to poor electrochemical performance in terms of rate performance and cycle stability, thereby hindering its practical application. By carbon-coating, sodium vanadium phosphate / carbon composite materials are prepared to improve the electronic conductivity of the materials, thereby improving the electrochemical activity of sodium vanadium phosphate; by doping ions, the structural stability of the material is improved, the ion diffusion channel is expanded, and the ionic conductivity is improved, thereby improving the electrochemical performance of the material.

[0004] At present, most of the inventions adopt solid phase method to prepare the positive electrode material, but the material composition prepared by the solid phase method is uneven, and the particle size distribution is wide. The sol-gel method is adopted in the present application, which is simple and easy to realize. The sample prepared by the method has small particle size and good uniformity. In addition, single-element doping is often one-sided, and the present application adopts multi-element doping, which not only improves the conductivity of the material, but also enhances the structural stability of the material, prolongs the service life of the battery. Secondly, cation doping can adjust the lattice constant, stabilize the crystal structure, and slow down the volume change of the lattice in the cycle process, but the regulation of the lattice by cation doping is limited, and the lattice stress may not be completely eliminated, while anion and cation co-doping can optimize the lattice structure in a deeper level, reduce the volume expansion amplitude in the cycle, make the structure more stable. And it can increase the uniformity of the diffusion channel and improve the sodium ion migration performance. SUMMARY

[0005] The present application aims to provide a chlorine tungsten anion and cation co-doped sodium vanadium phosphate positive electrode material and a preparation method thereof, which is simple in process. The prepared sodium ion battery positive electrode material has stable structure, expands the ion diffusion channel, improves the electronic conductivity and ionic conductivity, and has good rate performance and cycle stability.

[0006] The present application first provides a chlorine tungsten anion and cation co-doped sodium vanadium phosphate positive electrode material, which is prepared from W 4+ ion-doped V site, Cl - ion-doped (PO4) 3- site, and the chemical formula of the positive electrode material is Na 3-x V 2-x W x (PO4) 3- y Cl 3y / C, wherein x=0.05, 0.1, 0.15, and y=0.09, 0.12, 0.15.

[0007] The present application also provides a preparation method of the above-mentioned sodium ion battery positive electrode material, which is prepared by sol-gel method, comprising the following steps:

[0008] (1) The sodium source, vanadium source, tungsten source, phosphorus source, chlorine source and carbon source are weighed according to the molar ratio and then poured into 60ml deionized water solution, and stirred fully in a 50℃ oil bath for 2-4 hours. After the solution turns blue, the temperature is raised to 90℃ for continuous heating until the deionized water is completely evaporated, and a gel-like substance is formed;

[0009] (2) The gel-like substance formed in step (1) is placed in a drying oven for drying to form a precursor;

[0010] (3) Put the precursor formed in step (2) into an agate mortar and grind, and then put into a tube furnace to calcine under an inert atmosphere to obtain a sodium-ion battery positive electrode material.

[0011] The sodium source is one or more of sodium carbonate, sodium nitrate, sodium acetate, and sodium hydroxide; the vanadium source is ammonium metavanadate; the tungsten source is tungsten disulfide; the phosphorus source is one or two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; the chlorine source is sodium chloride; and the carbon source is one or more of sucrose, glucose, and citric acid monohydrate.

[0012] As a further scheme of the application: the drying temperature in step (2) is 100-180 DEG C.

[0013] As a further scheme of the application: the high-temperature calcination experimental conditions in step (3) are: pre-sintering at 350 DEG C for 3h, and then final sintering at 800 DEG C for 8h, with a heating rate of 3-6 DEG C / min, and the inert atmosphere is nitrogen or argon.

[0014] The application also provides a preparation method of a sodium vanadium phosphate positive electrode sheet doped with sodium and tungsten cations and anions, and the steps include:

[0015] (1) Grinding the active positive electrode material, the conductive additive, and the binder uniformly according to a mass ratio of 7:2:1;

[0016] (2) Adding an appropriate amount of N-methylpyrrolidone to the powder in step (1), and stirring on a magnetic stirrer for 0.5-8h to obtain a slurry;

[0017] (3) Uniformly coating the slurry on an aluminum foil by using a coater, with a thickness of 100-400mu m;

[0018] (4) Drying in a vacuum drying oven at 80-120 DEG C for 8-12h;

[0019] (5) Cutting the sheet into a circular sheet to obtain a battery positive electrode.

[0020] Application of the positive electrode material in a sodium-ion battery.

[0021] The beneficial effects of the application are:

[0022] (1) The citric acid monohydrate acts as both a chelating agent and a reducing agent, a part of which participates in the reduction reaction, so that V 5+ is reduced to V 3+ , and the remaining part acts as a carbon source to form a conductive carbon layer on the surface of the material, improving the conductivity of the material and thus improving the electrochemical performance of the material. The modified material has good rate performance and cycle stability.

[0023] (2) The radius of chloride ion is large, which will cause lattice expansion after doping into the structure of sodium vanadium phosphate, and thus appropriately increase the lattice parameters of the crystal. The lattice expansion can increase the size of the migration channel of sodium ions, thereby reducing the diffusion energy barrier of sodium ions and improving the diffusion coefficient of sodium ions in the crystal. 4+ is an ion with variable valence, which can participate in redox reactions. Doping W 4+ will form mixed valence states in the crystal, and the electronic conductivity will be enhanced through the charge transfer process. The improvement of conductivity helps to reduce the polarization effect of the electrode, improve the charge and discharge efficiency and rate performance. Doping W 4+ can reduce local defects in the crystal, optimize the structural stability of the crystal during charging and discharging, and prolong the cycle life of the electrode material.

[0024] (3) The particle size of the material prepared in the present application is reduced, the agglomeration phenomenon is reduced, and the specific surface area of the material is improved, so that the electrolyte is better wetted, and the electrochemical performance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the X-ray diffraction (XRD) pattern of the sodium ion battery positive electrode material obtained in Example 2 of the present application;

[0026] Figure 2 is the scanning electron (SEM) morphology diagram of the sodium ion battery positive electrode material obtained in Example 2 of the present application;

[0027] Figure 3 is a comparison diagram of the cycle performance of the target product obtained in Example 2 and Comparative Example 1 of the present application at a 1C rate after 200 cycles;

[0028] Figure 4 is a comparison diagram of the cycle performance of the target product obtained in Example 2 and Comparative Example 1 of the present application at a 5C rate after 500 cycles. DETAILED DESCRIPTION

[0029] In order to make the technical method of the embodiment of the present application more clear, the technical method of the embodiment will be clearly described below. The described embodiment is only a part of the embodiments of the present application, not all the embodiments, and the protection scope of the present application is not limited by the following embodiments.

[0030] Example 1:

[0031] Step 1: Prepare Na 2.95 V 1.95 W 0.05 (PO4) 2.96 Cl 0.12 / C positive electrode material

[0032] (1) The ammonium metavanadate 0.570 g, citric acid monohydrate 1.05 g, ammonium dihydrogen phosphate 0.851 g, sodium acetate 0.963 g, sodium chloride 0.018 g, tungsten disulfide 0.031 g were weighed according to the molar ratio and sequentially added to 60 ml of deionized water, stirred in a 50°C oil bath for 2-3 hours, and then the temperature was adjusted to 90°C for continuous stirring until the solution became a blue gel.

[0033] (2) The gel-like material formed in step (1) was placed in a drying oven at 120°C to dry, forming a precursor;

[0034] (3) The precursor formed in step (2) was ground in an agate mortar and transferred to a crucible, then placed in a tube furnace and sintered under an argon atmosphere, first pre-sintered at 350°C for 3h, and then final sintering at 800°C for 8h, with a heating rate of 5°C / min -1 . After natural cooling to room temperature, the battery anode material was obtained;

[0035] Step 2: Preparation of Na 2.95 V 1.95 W 0.05 (PO4) 2.96 Cl 0.12 / C cathode sheet

[0036] (1) The above prepared anode material, Super P and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1, hand ground to uniform mixing, an appropriate amount of N-methyl pyrrolidone was added, stirred on a magnetic stirrer for 30 min to form a slurry, the slurry was coated on an aluminum foil with a thickness of 100 μm, then placed in a vacuum drying oven at 120°C for 12h to obtain the electrode sheet;

[0037] (2) A 2032 button cell was assembled with metallic sodium as the anode, the entire assembly process was carried out in an argon-filled glove box, the assembly sequence was: anode shell, metallic sodium, glass fiber separator (GF / D), electrolyte (1M NaClO4 in EC:DC = 1:1 vol%), anode sheet (14mm), gasket, spring, anode shell; the charge-discharge cycle test was carried out in a Wuhan Blue Electric Battery Test System, cycled at a current density of 5C (1C = 117.6mA g -1 ) and a voltage range of 2.3-4.2V, the capacity retention rate was 82% after 500 cycles.

[0038] Comparative Example 1:

[0039] The sodium ion battery anode material of molecular formula Na3V2(PO4)3 / C was prepared in the same way as Example 1, and the preparation process of the electrode sheet, battery assembly and test process were the same as Example 1.

[0040] Example 2:

[0041] Step 1: Preparation of Na 2.9 V 1.9 W 0.1 (PO4) 2.96 Cl 0.12 / C cathode material by sol-gel method

[0042] (1) 0.556 g of ammonium metavanadate, 1.05 g of citric acid monohydrate, 0.851 g of ammonium dihydrogen phosphate, 0.987 g of sodium acetate, 0.018 g of sodium chloride, and 0.062 g of tungsten disulfide were weighed according to the molar ratio and sequentially added to 60 ml of deionized water. Stirring was carried out in a 50°C oil bath for 2-3 hours. After the solution turned blue, the temperature was adjusted to 90°C and stirring was continued until the solution turned into a blue gel.

[0043] (2) The gel-like substance formed in step (1) was placed in a drying oven at 120°C to dry and form a precursor;

[0044] (3) The precursor formed in step (2) was ground in a marver mortar and transferred to a crucible, which was then placed in a tube furnace for sintering under an argon atmosphere. Pre-sintering was carried out at 350°C for 3h, followed by final sintering at 800°C for 8h, with a heating rate of 5°C / min -1 . After natural cooling to room temperature, the battery cathode material was obtained;

[0045] Step 2: Preparation of Na 2.9 V 1.9 W 0.1 (PO4) 2.96 Cl 0.12 / C cathode sheet, the preparation process was the same as Example 1. The charge-discharge cycle test was carried out in Wuhan LanDian battery test system.

[0046] Figure 1 The XRD image of the target product obtained in Example 2. As can be seen from the figure, the XRD results show that all the characteristic peaks indicate the R-3C space group, which is consistent with the characteristic structure of NVP. It can be considered that the introduction of elements does not destroy the crystal composition.

[0047] Figure 2 The SEM image of the target product obtained in Example 2. The sample particle size is small, which is beneficial to the penetration of electrolyte.

[0048] Figure 3 The cycle stability curve of the cathode material described in Example 2 under a current density of 1C (1C = 117.6mA g -1 ) for 200 cycles. As can be seen from the figure, the material applied in sodium ion battery has a high discharge specific capacity of 98.1mAg -1It can still reach 89.5mAg after 200 cycles. -1 The capacity retention rate is as high as 91.2%.

[0049] Figure 4 The cathode material described in Example 2 was subjected to a temperature of 5C (1C = 117.6 mAg). -1 The cycling stability curves after 500 cycles at the specified current density and within the voltage range of 2.3-4.2V show a capacity retention of 93.1% after 500 cycles. This is because the incorporation of cations and anions expands the ion diffusion path, reduces particle size, increases specific surface area, and improves electronic conductivity, thereby enhancing the electrochemical performance and cycling stability of the material.

[0050] Example 3:

[0051] Step 1: Preparation of Na by sol-gel method 2.85 V 1.85 W 0.15 (PO4) 2.96 Cl 0.12 / C cathode material

[0052] (1) Weigh out the following components according to the molar ratio: 0.541 g ammonium metavanadate, 1.05 g citric acid monohydrate, 0.851 g ammonium dihydrogen phosphate, 0.929 g sodium acetate, 0.018 g sodium chloride, and tungsten disulfide.

[0053] Add 0.093g to 60ml of deionized water and stir in an oil bath at 50℃ for 2-3 hours. Once the solution turns blue, adjust the temperature to 90℃ and continue stirring until the solution turns into a blue gel.

[0054] (2) The gel-like substance formed in step (1) is placed in a drying oven at 120°C and dried to form a precursor;

[0055] (3) The precursor formed in step (2) is ground in an agate mortar and then transferred to a crucible. Subsequently, it is placed in a tube furnace and sintered under an argon atmosphere. The pre-sintering is carried out at 350°C for 3 hours, and then at 800°C for 8 hours. The heating rate is 5°C / min. -1 After naturally cooling to room temperature, the positive electrode material of the battery is obtained.

[0056] Step 2: Preparation of Na 2.85 V 1.85 W 0.15 (PO4) 2.96 Cl 0.12 The / C positive electrode sheet was prepared using the same process as in Example 1. Charge-discharge cycle testing was conducted using the Wuhan Landian Battery Testing System at 5C (1C = 117.6 mAg). -1) current density and 2.3-4.2V voltage range, the capacity retention rate was 85.3% after 200 cycles.

Claims

1. A sodium vanadium phosphate cathode material co-doped with chloro-tungsten cations and anions, characterized in that: The chlorine tungsten cation-anion co-doped sodium vanadium phosphate electrode material is prepared by W 4+ ion-doped V sites, Cl - ion-doped (PO4) 3- sites, and the chemical formula of the positive electrode material is Na 3-x V 2-x W x (PO4) 3-y Cl 3y / C, wherein x = 0.05, 0.1, 0.15, and y = 0.09, 0.12, 0.

15.

2. The preparation method of the chlorotungsten cation-anion co-doped sodium vanadium phosphate positive electrode material according to claim 1, characterized in that, Prepared by sol-gel method, comprising the following steps: (1) A sodium source, a vanadium source, a tungsten source, a phosphorus source, a chlorine source, and a carbon source are weighed according to a molar ratio and then poured into 60 ml of a deionized water solution, and stirred thoroughly in a 50°C oil bath for 2-4 hours. When the solution turns blue, the temperature is raised to 90°C for continued heating until the deionized water is completely evaporated, and a gel-like substance is formed; (2) The gel-like substance formed in step (1) is placed in a drying oven to form a precursor; (3) The precursor formed in step (2) is ground in an agate mortar and then placed in a tube furnace for calcination under an inert atmosphere to obtain a sodium-ion battery cathode material.

3. The preparation method of claim 2, characterized in that: In step (1), the sodium source is one or more of sodium carbonate, sodium nitrate, sodium acetate, and sodium hydroxide; The vanadium source is ammonium metavanadate; The tungsten source is tungsten disulfide; The phosphorus source is one or two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; The chlorine source is sodium chloride; The carbon source is one or more of sucrose, glucose, and citric acid monohydrate.

4. The method of claim 2, wherein: The drying temperature in step (2) is 100-180°C.

5. The method of claim 2, wherein: In step (3), the high-temperature calcination experimental conditions are: pre-sintering at 350°C for 3 hours, and then final sintering at 800°C for 8 hours, with a heating rate of 3-6°C / min and an inert atmosphere of nitrogen or argon.

6. A method of manufacturing a jelly-roll of the sodium vanadium phosphate cathode material of claim 1, The features include the following steps: (1) An active cathode material, a conductive additive, and a binder are ground uniformly according to a mass ratio of 7:2:1; (2) An appropriate amount of N-methylpyrrolidone is added to the powder in step (1), and the mixture is stirred on a magnetic stirrer for 0.5-8 hours to obtain a slurry; (3) The slurry is uniformly coated on an aluminum foil using a coater, with a thickness of 100-400 μm; (4) The coated aluminum foil is dried in a vacuum drying oven at 80-120°C for 8-12 hours; (5) The electrode piece is cut into a round piece to obtain a battery cathode.

7. The method of claim 6, wherein: In step (1), the binder is one or more of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, and sodium alginate, and the conductive agent is one or more of Super P, carbon black, and Ketjen black.

8. Use of the cathode material of claim 1 in a sodium-ion battery.

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