A nitrogen-doped sodium-ion battery polyanion positive electrode material and a preparation method thereof

Abstract

The application discloses a kind of nitrogen-doped sodium ion battery polyanion positive electrode materials and preparation method thereof, by chromium doping or replacement nitrogen triphosphoric polymeric vanadium trisodium polyanion positive electrode material, citric acid is dissolved with transition metal in deionized water, V source, Cr source, ascorbic acid and transition metal, Na source and P source are added respectively, while the deionized water solution of 12wt% polyvinylpyrrolidone dissolved, urea is added to mixed solution and is magnetically stirred, evaporates by water, drying, grinding, is formed into tablet by mould pressing;With urea grinding and tabletting by mould are together to the test tube and are vacuum sealed, and are placed in muffle furnace and are kept at high temperature, then are taken out and are naturally cooled to room temperature, obtain the positive electrode material.The application does not need to continuously pass in ammonia in preparation process, and reduces the V source consumption, significantly reduces the manufacturing cost is low and manufacturing equipment is simple, improves safety, and is convenient to implement;The cycle of the material prepared is good, and the specific capacity is high.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery materials, in particular to a nitrogen-doped polyanion positive electrode material for sodium ion batteries and a preparation method thereof. BACKGROUND

[0002] With the increasing attention to renewable energy such as solar and wind energy worldwide, the demand for high-performance electrochemical energy storage and conversion devices is rapidly growing. Although lithium ion batteries have achieved great success in the fields of electric vehicles and portable devices, the high cost and uneven distribution of lithium resources make it difficult to meet the demand of large-scale energy storage systems. Sodium ion batteries are considered as one of the promising energy storage materials due to their high crust abundance and low cost of raw materials.

[0003] The capacity of the positive electrode material is a key factor determining the capacity of the whole battery. In the development of new sodium ion battery positive electrode materials, the strong X-O covalent bond in the polyanion compound makes it have good structural stability and thermodynamic stability, and also shows excellent electrochemical sodium storage performance in electrochemical tests, which has been widely studied by people. Kim et al. first prepared a polycrystalline vanadium trisodium nitride positive electrode material (M.W. Kim, S.J. Kim., Synchrotron powder study of Na3V(PO3)3N, Acta Cryst. (2013). E69, i34 [doi:10.1107 / S1600536813012427]) by thermal nitriding method. Due to the existence of N, strong induction effect is produced, which enhances the electrostatic repulsion between adjacent V atoms, so that higher working voltage can be achieved when sodium is inserted / extracted. This discovery has attracted widespread attention.

[0004] However, the preparation of such materials usually requires continuous ammonia gas during the sintering process, which brings certain danger to production. At the same time, high-valence vanadium ions are toxic to the human body and have high cost, which also brings certain difficulties to commercial application. How to reduce the production danger and replace part or all of vanadium ions with non-toxic and low-cost transition metal ions is the key research direction of the material at present. SUMMARY

[0005] (I) Technical problems solved

[0006] In view of the deficiencies of the prior art, the application provides a nitrogen-doped polyanion positive electrode material for sodium ion batteries and a preparation method thereof. The method can significantly reduce the cost of the material, improve the safety during the preparation and use of the material, and the prepared material has good cycle performance and high specific capacity, is low in manufacturing cost and simple in manufacturing equipment.

[0007] (II) Technical solutions

[0008] To achieve the above object, the present application is realized by the following technical solutions:

[0009] A preparation method of a nitrogen-doped sodium-ion battery polyanion positive electrode material, comprising the following steps:

[0010] Step one, according to the stoichiometric ratio of 1:1 of citric acid and transition metal, citric acid is dissolved in deionized water, V source is added according to the molar ratio of chemical formula, and stirring is carried out in a magnetic stirrer to obtain solution 1;

[0011] Step two, Cr source is added to solution 1 according to the molar ratio of chemical formula, and ascorbic acid and transition metal are added to solution 1 according to the molar ratio of 1:2, and stirring is carried out to obtain solution 2;

[0012] Step three, Na source and P source are added to solution 2 according to the molar ratio of chemical formula, and a deionized water solution containing 12wt% polyvinylpyrrolidone is added dropwise to the mixed solution, and the above mixed solution is subjected to magnetic stirring to obtain solution 3;

[0013] Step four, urea and transition metal are added to solution 3 according to the molar ratio of 5:1, and the above solution is continuously subjected to magnetic stirring, and after the water is evaporated, a dry gel precursor is obtained;

[0014] Step five, the dry gel precursor is placed in a vacuum oven and dried overnight, and after drying, a dry gel is obtained, the dry gel is taken out and ground thoroughly to become a powder, and then the powder precursor is pressed into a tablet by a mold to obtain a precursor tablet;

[0015] Step six, urea is ground into a powder, and a urea tablet is obtained by tabletting with a mold;

[0016] Step seven, the precursor tablet in step five and the urea tablet in step six are placed in a test tube and subjected to vacuum sealing treatment;

[0017] Step eight, the test tube subjected to vacuum sealing treatment in step seven is placed in a muffle furnace for high-temperature incubation, and then taken out and naturally cooled to room temperature to obtain the positive electrode material.

[0018] Further, in step one, the temperature of the stirring in the magnetic stirrer is 80℃ constant temperature, and the stirring time is 1.5 hours.

[0019] Further, in step two, the stirring temperature is 80℃, and the stirring time is 15 minutes.

[0020] Further, in step three, the temperature of the magnetic stirring is 80℃, and the stirring time is 15 minutes.

[0021] Further, in step four, the temperature of the magnetic stirring is 80 DEG C.

[0022] Further, in step five, the temperature of drying the xerogel precursor in the vacuum oven overnight is 120 DEG C.

[0023] Further, in step eight, the temperature of high-temperature incubation of the vacuum-sealed test tube in the muffle furnace is 700-750 DEG C, and the incubation time is 24-36 hours.

[0024] Further, the mold is a Ф25mm mold.

[0025] The application also provides a nitrogen-doped sodium-ion battery polyanion positive electrode material prepared by the preparation method, and the structural composition is Na3Cr x V 1-x (PO3)3N, 0.5 <= x <= 1.

[0026] (III) Beneficial effects

[0027] The application provides a nitrogen-doped sodium-ion battery polyanion positive electrode material and a preparation method thereof, and has the following beneficial effects:

[0028] 1. The application provides a chromium-doped or substituted nitrogen polyvanadic trisodium polyanion positive electrode material, which eliminates the process of continuously introducing ammonia gas in the material preparation process, significantly reduces the operation cost, improves the production safety, and is convenient to implement.

[0029] 2. The application reduces the amount of V source, reduces the cost of raw materials, and improves the safety of operation.

[0030] 3. The material prepared by the preparation method has good cycle performance, high specific capacity, low manufacturing cost and simple manufacturing equipment. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The XRD spectrum of the Na3Cr 0.5 V 0.5 (PO3)3N material prepared in Example 1.

[0032] Figure 2 The SEM surface morphology diagram of the Na3Cr 0.5 V 0.5 (PO3)3N material prepared in Example 1.

[0033] Figure 3 The cycle curve of the Na3Cr 0.5 V 0.5 (PO3)3N material prepared in Example 1.

[0034] Figure 4 XRD pattern of Na3Cr(PO3)3N material prepared in Example 2.

[0035] Figure 5 SEM surface morphology of Na3Cr(PO3)3N material prepared in Example 2.

[0036] Figure 6 Cycle curve of Na3Cr(PO3)3N material prepared in Example 2.

[0037] Figure 7 Cycle curve of Na3Cr(PO3)3N material prepared in Example 3. 0.25 V 0.75 Cycle curve of Na3Cr(PO3)3N material prepared in Example 4.

[0038] Figure 8 Cycle curve of Na3Cr(PO3)3N material prepared in Example 4. 0.75 V 0.25 Cycle curve of Na3Cr(PO3)3N material prepared in Example 4. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0040] The present application provides a technical solution: a preparation method of a nitrogen-doped sodium-ion battery polyanion positive electrode material, comprising the following steps:

[0041] Step one, citric acid is dissolved in deionized water according to the stoichiometric ratio of 1:1 of citric acid and transition metal, V source is added according to the molar ratio of the chemical formula, and constant temperature stirring is carried out at 80℃ in a magnetic stirrer for 1.5 hours to obtain solution 1;

[0042] Step two, Cr source is added to solution 1 according to the molar ratio of the chemical formula, and ascorbic acid and transition metal are added to solution 1 according to the molar ratio of 1:2, and stirring is carried out at 80℃ for 15 minutes to obtain solution 2;

[0043] Step three, Na source and P source are added to solution 2 according to the molar ratio of the chemical formula, and a deionized water solution containing 12wt% polyvinylpyrrolidone is added dropwise to the mixed solution, and the above-mentioned mixed solution is magnetically stirred at 80℃ for 15 minutes to obtain solution 3;

[0044] Step four, urea and transition metal are added into solution 3 with a molar ratio of 5:1, and the above solution is continuously stirred at 80°C by magnetic force, and the dry gel precursor is obtained after the evaporation of water;

[0045] Step five, the dry gel precursor is dried in a vacuum oven at 120°C overnight, and the dry gel is obtained after drying, and the dry gel is fully ground to become a powder, and then the powder precursor is tablet-shaped by a Ф 25mm mold to obtain a precursor tablet;

[0046] Step six, the urea is ground into a powder, and the urea tablet is obtained by tablet shaping with a Ф 25mm mold;

[0047] Step seven, the precursor tablet in step five and the urea tablet in step six are placed in a test tube and vacuum sealed;

[0048] Step eight, the test tube vacuum sealed in step seven is placed in a muffle furnace and heated at 700-750°C for 24-36 hours, and then taken out and naturally cooled to room temperature to obtain the positive electrode material.

[0049] The application also provides a nitrogen-doped sodium ion battery polyanion positive electrode material prepared by the above preparation method, and the structural composition is: Na3Cr x V 1-x (PO3)3N, 0.5≤x≤1.

[0050] Here, four examples are described in detail.

[0051] Example 1:

[0052] (1) 5mmol Na3Cr 0.5 V 0.5 (PO3)3N material is prepared, 2.5mmol NH4VO3 is put into 50ml deionized water containing 5mmol citric acid, and stirred at 80°C in a magnetic stirrer for 1.5 hours, so as to reduce 5-valent V to 3-valent, and citric acid acts as a complexing agent.

[0053] (2) 2.5mmol Cr(NO3)3·9H2O is put into the solution prepared in step 1, and 2.5mmol ascorbic acid is added, which has a certain carbon coating effect, and is stirred at 80°C in a magnetic stirrer for 15 minutes.

[0054] (3) 2.5mmol (NaPO3)6 is put into the solution prepared in step 2, and 12%wt polyvinylpyrrolidone is added to disperse the solution, and is stirred at 80°C in a magnetic stirrer for 15 minutes.

[0055] (4) The gel is placed in a vacuum oven at 120°C overnight. The xerogel precursor is taken out and ground thoroughly to make it into a powder. Then the powder precursor is pressed into a tablet using a Ф 25 mm mold.

[0056] (5) The gel is placed in a vacuum oven at 120°C overnight. The xerogel precursor is taken out and ground thoroughly to make it into a powder. Then the powder precursor is pressed into a tablet using a Ф 25 mm mold.

[0057] (5) The gel is placed in a vacuum oven at 120°C overnight. The xerogel precursor is taken out and ground thoroughly to make it into a powder. Then the powder precursor is pressed into a tablet using a Ф 25 mm mold.

[0058] (7) The sealed test tubes are placed in a muffle furnace and heated to 750°C at a rate of 3°C per minute and kept at this temperature for 24 hours. After natural cooling to room temperature, the test tubes are taken out and ground to obtain the positive electrode material Na3Cr 0.5 V 0.5 (PO3)3N.

[0059] The specific results are shown in Table 1. Figures 1-3 .

[0060] Example 2:

[0061] (1) 5 mmol of Na3Cr(PO3)3N material is prepared. 5 mmol of Cr(NO3)3·9H2O is placed in 50 ml of deionized water containing 5 mmol of citric acid and 2.5 mmol of ascorbic acid, and stirred at 80°C in a magnetic stirrer for 15 minutes.

[0062] (2) 2.5 mmol of (NaPO3)6 is placed in the solution prepared in step 1, and 12% wt of polyvinylpyrrolidone is added to disperse the solution, and stirred at 80°C in a magnetic stirrer for 15 minutes.

[0063] (3) 25 mmol of urea is added to the solution prepared in step 2, and magnetic stirring is continued at a temperature of 80°C, and after the water evaporates, a xerogel precursor is obtained.

[0064] (4) The gel is placed in a vacuum oven at 120°C overnight. The xerogel precursor is taken out and ground thoroughly to make it into a powder. Then the powder precursor is pressed into a tablet using a Ф 25 mm mold.

[0065] (5) The gel is placed in a vacuum oven at 120°C overnight. The xerogel precursor is taken out and ground thoroughly to make it into a powder. Then the powder precursor is pressed into a tablet using a Ф 25 mm mold.

[0066] (6) Put the sealed test tube into the muffle furnace, and heat to 700 degrees Celsius at a heating rate of 3 degrees Celsius per minute, and keep for 24 hours. After natural cooling to room temperature, take out and grind to obtain the positive electrode material Na3Cr(PO3)3N.

[0067] The specific results are referred to Figures 4-6 .

[0068] Example 3:

[0069] (1) Prepare 5 mmol Na3Cr 0.25 V 0.75 (PO3)3N material, put 3.75 mmol of NH4VO3 into 50 ml of deionized water containing 5 mmol of citric acid, and stir at 80 degrees Celsius for 1.5 hours in a magnetic stirrer, so as to reduce the 5-valent V to 3-valent, and the citric acid acts as a complexing agent.

[0070] (2) Put 1.25 mmol of Cr(NO3)3·9H2O into the solution prepared in step 1, and add 2.5 mmol of ascorbic acid to achieve a certain carbon coating effect, and stir at 80 degrees Celsius for 15 minutes in a magnetic stirrer.

[0071] (3) Put 2.5 mmol of (NaPO3)6 into the solution prepared in step 2, and add 12% wt of polyvinylpyrrolidone to disperse the solution, and stir at 80 degrees Celsius for 15 minutes in a magnetic stirrer.

[0072] (4) Add 25 mmol of urea to the solution prepared in step 3, and continue to stir at 80 degrees Celsius in a magnetic stirrer to evaporate the water, and obtain a dry gel precursor.

[0073] (5) Put the gel into a vacuum oven at 120 degrees Celsius and dry overnight, take out the dry gel and grind it into powder, then press the powder precursor into tablets with a Ф25 mm mold.

[0074] (6) Grind the urea particles into powder, and press them into tablets with a Ф25 mm mold. Put 50 mg of the precursor tablet and 30 mg of the urea tablet into the same test tube, and seal the test tube by vacuumizing and sealing with a tube sealing machine. Each time, not less than 6 test tubes should be sealed.

[0075] (7) Put the sealed test tube into the muffle furnace, and heat to 750 degrees Celsius at a heating rate of 3 degrees Celsius per minute, and keep for 24 hours. After natural cooling to room temperature, take out and grind to obtain the positive electrode material Na3Cr 0.25 V 0.75 (PO3)3N.

[0076] The specific results are referred to Figure 7 .

[0077] Example 4:

[0078] (1) Preparation of 5mmol Na3Cr 0.75 V 0.25 (PO3)3N material, 1.25mmol of NH4VO3 was put into 50ml deionized water with 5mmol citric acid, and stirred at 80°C for 1.5 hours in a magnetic stirrer, so as to reduce the 5-valent V to 3-valent, and the citric acid acts as a complexing agent.

[0079] (2) 3.75mmol of Cr(NO3)3·9H2O was put into the solution prepared in step 1, and 2.5mmol of ascorbic acid was added, which had a certain carbon coating effect, and was stirred at 80°C for 15 minutes in a magnetic stirrer.

[0080] (3) 2.5mmol of (NaPO3)6 was put into the solution prepared in step 2, and 12%wt of polyvinylpyrrolidone was added to disperse the solution, and was stirred at 80°C for 15 minutes in a magnetic stirrer.

[0081] (4) 25mmol of urea was added to the solution prepared in step 3, and the magnetic stirring was continued at 80°C, so that the water was evaporated to obtain a dry gel precursor.

[0082] (5) The gel was placed in a vacuum oven at 120°C and dried overnight, and the dry gel was ground into powder, and then the powder precursor was pressed into a tablet with a Ф25mm mold.

[0083] (6) The urea particles were ground into powder, and pressed into a tablet with a Ф25mm mold, and 50mg of the precursor tablet and 30mg of the urea tablet were placed in the same test tube, and were sealed by a tube sealing machine, and not less than 6 test tubes were sealed each time.

[0084] (7) The sealed test tubes were placed in a muffle furnace, and were heated to 750°C at a heating rate of 3°C per minute, and were kept for 24 hours, and were naturally cooled to room temperature, and were ground to obtain the positive electrode material Na3Cr 0.75 V 0.25 (PO3)3N.

[0085] The specific results are shown in Table 1. Figure 8 .

[0086] In conclusion, the application provides a chromium-doped or substituted nitrogen triphosphate polycrystalline vanadium trisodium polyanion positive electrode material, which eliminates the process of continuously passing ammonia gas in the material preparation process, significantly reduces the operation cost, improves the production safety, and is convenient to implement. The application reduces the amount of V source, reduces the cost of raw materials, and improves the safety of operation. The material prepared by the preparation method of the application has good cycle performance, high specific capacity, low manufacturing cost and simple manufacturing equipment.

[0087] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0088] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, alternatives, and variations can be made in the embodiments without departing from the principles and spirit of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nitrogen-doped sodium-ion battery polyanion cathode material, characterized in that, The method comprises the following steps: Step one, citric acid is dissolved in deionized water according to the stoichiometric ratio of 1:1 of citric acid and total amount of vanadium V and chromium Cr transition metal ions, V source is added according to the molar ratio of the chemical formula, and stirring is performed in a magnetic stirrer to obtain solution 1; Step two, Cr source is added to solution 1 according to the molar ratio of the chemical formula, and ascorbic acid is added to solution 1 according to the molar ratio of 1:2 of the total amount of transition metal ions, and stirring is performed to obtain solution 2; Step three, Na source and P source are added to solution 2 according to the molar ratio of the chemical formula, and a deionized water solution containing 12wt% polyvinylpyrrolidone is added dropwise to the mixed solution, and the mixed solution is subjected to magnetic stirring to obtain solution 3; Step four, urea is added to solution 3 according to the molar ratio of 5:1 of the total amount of transition metal ions, and the solution is continuously subjected to magnetic stirring, and after water evaporation, a dry gel precursor is obtained; Step five, the dry gel precursor is placed in a vacuum oven for drying overnight, and after drying, a dry gel is obtained, the dry gel is taken out and fully ground to become a powder, and then the powder precursor is pressed into a tablet by using a mold to obtain a precursor tablet; Step six, urea is ground into a powder, and a urea tablet is obtained by pressing the powder into a tablet by using a mold; Step seven, the precursor tablet in step five and the urea tablet in step six are placed in a test tube and subjected to vacuum sealing treatment; Step eight, the test tube subjected to vacuum sealing treatment in step seven is placed in a muffle furnace for high-temperature heat preservation, and then taken out and naturally cooled to room temperature to obtain the positive electrode material.

2. The method of claim 1, wherein the method further comprises: In step one, the temperature of the stirring in the magnetic stirrer is 80 ℃, and the stirring time is 1.5 hours.

3. The method of claim 1, wherein the method further comprises: In step two, the temperature of the stirring is 80 ℃, and the stirring time is 15 minutes.

4. The method of claim 1, wherein the method further comprises: In step three, the temperature of the magnetic stirring is 80 ℃, and the stirring time is 15 minutes.

5. The method of claim 1, wherein the method further comprises: In step four, the temperature of the magnetic stirring is 80 ℃.

6. The method of claim 1, wherein the method further comprises: In step five, the temperature of placing the dry gel precursor in the vacuum oven for drying overnight is 120 ℃.

7. The method of claim 1, wherein the method further comprises: In step eight, the temperature of placing the test tube subjected to vacuum sealing treatment in the muffle furnace for high-temperature heat preservation is 700-750 ℃, and the heat preservation time is 24-36 hours.

8. The method of claim 1, wherein the method further comprises: The mold is a Ф25 mm mold.

9. A nitrogen-doped sodium-ion battery polyanion cathode material, prepared by the method of any one of claims 1-8, having a composition of: Na3V2(PO4)2(N3)2. 0.5≤x≤1.

Images