Preparation method of Cr-doped composite positive electrode material

Abstract

The invention discloses a preparation method of a Cr-doped composite positive plate, and belongs to the technical field of battery materials. The preparation method comprises the following steps: ball-milling and mixing a sodium source, an iron source, a chromium source, a phosphorus source, oxalic acid and sodium fluoride, carrying out pre-calcination, carrying out secondary ball-milling, carrying out secondary calcination to obtain a Cr-doped composite positive electrode material, grinding and mixing the Cr-doped composite positive electrode material, a conductive material and a binder to obtain slurry, coating a current collector with the slurry, and drying to obtain the positive plate. The conductive material provided by the invention adopts nickel-coated nano superconductive carbon black, and is prepared from nano superconductive carbon black, butyl acrylate, 4-vinylpyridine-nickel and 2, 4, 6-tripropyloxy-1, 3, 5-triazine through water bath, filtration and drying. By adopting the conductive material, the conductivity of the whole electrode can be improved, and the performance of the sodium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a preparation method of a Cr-doped composite cathode material. Background Art

[0002] As a potential alternative to lithium-ion batteries, sodium-ion batteries have broad application prospects in the field of large-scale energy storage. Their advantages lie in the rich reserves and low cost of raw materials, which can alleviate the dilemma of scarce lithium resources. At the same time, they also have multiple performance advantages, such as excellent capacity retention at high and low temperatures, outstanding rate performance, and good safety performance.

[0003] The cathode materials of sodium-ion batteries have a crucial impact on their performance and application fields. These materials not only determine the energy density, power density, and cycle life of the battery but also affect the overall safety and cost.

[0004] CN117660986A discloses a method and system for preparing sodium iron phosphate cathode material by ion exchange. Cut the LiFePO4 electrode sheet, fix it in an electrolytic cell, then put a titanium plate of the same size as the counter electrode, and add sodium electrolyte to submerge the electrode sheet and the titanium plate; set the delithiation voltage until the delithiation specific capacity reaches 160 mAh g-1, then the delithiation is completed. Take out the electrode sheet, wash it repeatedly with distilled water, and dry it to obtain the FePO4 electrode sheet; use FePO4 as the cathode, sodium sheet as the anode, and glass fiber as the separator; assemble the battery with 1M sodium-containing solution as the electrolyte.

[0005] CN114975927B discloses a graphene oxide-sodium iron phosphate composite cathode material and its preparation method, including the following steps: ultrasonically disperse graphene oxide in deionized water to form a graphene oxide dispersion; add sodium salt, iron salt, and phosphorus source to the graphene oxide dispersion, and continuously stir magnetically to obtain a uniformly mixed solution; transfer the uniformly mixed solution to a polytetrafluoroethylene reaction kettle for hydrothermal reaction, and then repeatedly centrifuge and wash the product obtained from the hydrothermal reaction with a solvent, and dry it to obtain a uniformly mixed powder. Place the uniformly mixed powder in a tube furnace for heat treatment to obtain the graphene oxide-sodium iron phosphate composite cathode material.

[0006] CN117446772A provides a method for preparing a carbon-coated titanium-doped composite sodium iron phosphate cathode material by a supercritical method, including: 1) dissolving iron nitrate in preheated deionized water, slowly adding oxalic acid, and maintaining the solution temperature for a certain reaction time; 2) placing the solution obtained in step 1), a titanium source, a carbon source, a sodium source, and a phosphorus source in a high-temperature and high-pressure reaction kettle, adding absolute ethanol, heating and pressurizing the reaction kettle to a certain temperature and pressure to make ethanol form a supercritical state for reaction; 3) subjecting the reaction solution obtained in step 2) to spray drying treatment to obtain a precursor powder; 4) performing high-temperature sintering on the precursor in an inert atmosphere, and then pulverizing to obtain a carbon-coated titanium-doped composite sodium iron phosphate cathode material.

[0007] Although the research on the cathode materials of current sodium-ion batteries is becoming increasingly mature, there are still problems with the cathode materials, such as relatively low specific capacity and low conductivity, which have led to certain limitations in their use in application scenarios that require high energy density and high power output, such as electric vehicles and large-scale energy storage systems. Summary of the Invention

[0008] To solve the problems existing in the background technology, the present invention provides a method for preparing a Cr-doped composite cathode material, including the following steps:

[0009] Step 1: According to mass parts, 18-32 parts of a sodium source, 6-50 parts of an iron source, 5-15 parts of a chromium source, 10-15 parts of a phosphorus source, 2-5 parts of oxalic acid, and 3-5 parts of sodium fluoride are ball-milled at a rotation speed of 400-500 r / min for 8-12 h and mixed evenly, and then vacuum-dried at 60-80 °C for 24-48 h;

[0010] Step 2: Pre-calcine the dried powder in an inert atmosphere, add 1.8-3.4 parts of an organic carbon source to the pre-calcined powder, perform secondary ball-milling, with a ball-milling rotation speed of 400-500 r / min and a ball-milling duration of 4-6 h, mix evenly, then vacuum-dry at 60-80 °C for 12-24 h, and perform secondary calcination in an inert atmosphere to obtain a carbon-coated Cr-doped sodium iron phosphate powder, that is, a Cr-doped composite cathode material;

[0011] Step 3: According to mass fraction, 80-90 parts of the Cr-doped composite cathode material, 5-10 parts of a conductive material, and 5-10 parts of a binder are added, and N-methylpyrrolidone is added for grinding and mixing to obtain a slurry. The slurry is coated on a current collector and heated to 60-120 °C in a vacuum environment, and after complete drying, a cathode sheet is obtained.

[0012] As a further supplement, the sodium source in step 1 is one or more of sodium carbonate, sodium bicarbonate, sodium fluoride, and sodium dihydrogen phosphate.

[0013] As a further supplement, the iron source described in step one is one or more of ferrous gluconate, ferrous oxalate, ferrous chloride, ferrous phosphate, ferrous acetate, ferrous citrate, and ferrous lactate.

[0014] As a further supplement, the chromium source described in step one is one or more of chromium sulfate, chromium acetate, and chromium nitrate.

[0015] As a further supplement, the phosphorus source described in step one is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

[0016] As a further supplement, the organic carbon source described in step two is one or more of glucose, sucrose, and citric acid monohydrate.

[0017] As a further supplement, the pre-calcination temperature described in step two is 350 - 550 °C, and the duration is 2 - 4 h.

[0018] As a further supplement, the secondary calcination temperature described in step two is 500 - 800 °C, and the duration is 5 - 7 h.

[0019] As a further supplement, the conductive material described in step three uses nickel-coated nano-superconducting carbon black, and the preparation method is as follows:

[0020] By weight, 100 - 200 parts of nano-superconducting carbon black, 1200 - 1500 parts of water, 2 - 6 parts of butyl acrylate, 0.03 - 0.3 parts of 4-vinylpyridine-nickel, 0.05 - 0.5 parts of 2,4,6-triallyloxy-1,3,5-triazine, and 2 - 5 parts of potassium peroxide are taken, and then they are placed in a water bath at 60 °C - 80 °C, and the above solution is stirred for 2 - 4 h, filtered, and dried to obtain uniformly dispersed nickel-coated nano-superconducting carbon black.

[0021] As a further supplement, the binder described in step three is one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0022] Reaction mechanism

[0023] 1. Formation of the polybutyl acrylate polymerization layer: First, polybutyl acrylate (PAA), as an anionic polymer, the pyridine-nickel complex is introduced into the PAA polymerization layer, and it may bind to the PAA chain through coordination bonds or electrostatic interactions. This complex can provide an additional electron transfer path in the electrochemical reaction, thereby enhancing the conductivity of the material.

[0024] 2. Polytriazine is a polymer with a highly π-conjugated structure, and it can form a stable protective layer on the surface of nano-superconducting carbon black. This protective layer can not only prevent the aggregation of nanoparticles but also improve its dispersibility and stability in the electrolyte.

[0025] 3. Surface modification of nano-superconducting carbon black: Through the above steps, the surface energy of nano-superconducting carbon black is significantly reduced, forming nano-scale dispersed particles. Due to their high specific surface area and small size effect, these particles can more effectively contact with the chromium-doped sodium iron phosphate cathode material, thereby improving the conductivity of the entire electrode.

[0026] Technical effects

[0027] 1. Improve conductivity: The introduction of pyridine-nickel complex and polytriazine provides more transmission channels for electrons, thus significantly improving the conductivity of the material. This is crucial for energy storage devices such as batteries, as it directly affects the ability to quickly store and release energy.

[0028] 2. Enhance stability: The protective layer of polytriazine can effectively prevent the aggregation and oxidation of nanoparticles, maintaining the long-term stability and cycle life of the material. This is an important consideration for reliability and economy in practical applications.

[0029] 3. Optimize interfacial interaction: Through surface modification, the interfacial interaction between nano-superconducting carbon black and chromium-doped sodium iron phosphate cathode material is optimized, which helps to improve the overall performance of the electrode.

[0030] In summary, by introducing polybutyl acrylate polymer layer, pyridine-nickel complex and polytriazine on the surface of nano-superconducting carbon black, not only the surface energy is reduced, achieving nano-scale dispersion, but also the conductivity of chromium-doped sodium iron phosphate cathode material is significantly improved, which is of great significance for enhancing the performance of energy storage devices such as batteries. Specific implementation manners

[0031] The essential features and remarkable effects of the present invention can be reflected from the following embodiments, but they do not limit the present invention in any way. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the present invention. The present invention will be further described below through specific implementation manners.

[0032] Example 1

[0033] A preparation method of a Cr-doped composite cathode material, comprising the following steps:

[0034] Step 1: According to mass fraction, 18 g of sodium fluoride, 6 g of ferrous chloride, 5 g of chromium acetate, 10 g of phosphoric acid, 2 g of oxalic acid, and 3 g of sodium fluoride are ball-milled at a speed of 400 r / min for 8 h, mixed evenly, and then vacuum-dried at 60 °C for 24 h;

[0035] Step 2: Pre-calcine the dried powder in an inert atmosphere. Add 1.8 g of glucose to the pre-calcined powder, conduct secondary ball milling at a ball milling speed of 400 r / min for 4 h. After mixing evenly, dry it in vacuum at 60 °C for 12 h, and then conduct secondary calcination in an inert atmosphere to obtain the Cr-doped composite cathode material;

[0036] Step 3: According to the mass fraction, 80 g of the Cr-doped composite cathode material, 5 g of the conductive material, and 5 g of polyvinylidene fluoride are added, and N-methylpyrrolidone is added for grinding and mixing to obtain a slurry. Coat the slurry on the current collector and heat it to 60 °C in a vacuum environment. After complete drying, obtain the positive electrode sheet.

[0037] The pre-calcination temperature described in Step 2 is 350 °C and the duration is 2 h.

[0038] The secondary calcination temperature described in Step 2 is 500 °C and the duration is 5 h.

[0039] The conductive material described in Step 3 uses nickel-coated nano-superconducting carbon black, and the preparation method is as follows:

[0040] By weight, 100 g of nano-superconducting carbon black, 1200 g of water, 2 g of butyl acrylate, 0.03 g of 4-vinylpyridine-nickel, 0.05 g of 2,4,6-triallyloxy-1,3,5-triazine, and 2 g of potassium peroxide are placed in a water bath at 60 °C, and the above solution is stirred for 2 h, filtered, and dried to obtain uniformly dispersed nickel-coated nano-superconducting carbon black.

[0041] Example 2

[0042] A preparation method of a Cr-doped composite cathode material, comprising the following steps:

[0043] Step 1: According to the mass fraction, 25 g of sodium carbonate, 28 g of ferrous acetate, 10 g of chromium sulfate, 12 g of ammonium dihydrogen phosphate, 3 g of oxalic acid, and 4 g of sodium fluoride are ball milled at a speed of 450 r / min for 9 h. After mixing evenly, dry it in vacuum at 70 °C for 28 h;

[0044] Step 2: Pre-calcine the dried powder in an inert atmosphere. Add 2.4 g of sucrose to the pre-calcined powder, conduct secondary ball milling at a ball milling speed of 450 r / min for 5 h. After mixing evenly, dry it in vacuum at 70 °C for 16 h, and then conduct secondary calcination in an inert atmosphere to obtain carbon-coated Cr-doped sodium iron phosphate powder, that is, the Cr-doped composite cathode material;

[0045] Step 3: According to the mass fraction, 85 g of Cr-doped composite cathode material, 7 g of conductive material, and 8 g of polytetrafluoroethylene are added to N-methylpyrrolidone and ground and mixed to obtain a slurry. The slurry is coated on a current collector and heated to 80 °C in a vacuum environment. After complete drying, a positive electrode sheet is obtained.

[0046] The pre-calcination temperature described in Step 2 is 400 °C, and the duration is 3 h.

[0047] The secondary calcination temperature described in Step 2 is 600 °C, and the duration is 6 h.

[0048] The conductive material described in Step 3 uses nickel-coated nano-superconducting carbon black, and the preparation method is as follows:

[0049] By weight, 150 g of nano-superconducting carbon black, 1300 g of water, 4 g of butyl acrylate, 0.1 g of 4-vinylpyridine-nickel, 0.2 g of 2,4,6-triallyloxy-1,3,5-triazine, and 3 g of potassium peroxide are placed in a 70 °C water bath, and the above solution is stirred for 3 h, filtered, and dried to obtain uniformly dispersed nickel-coated nano-superconducting carbon black.

[0050] Example 3

[0051] A preparation method of a Cr-doped composite cathode material, comprising the following steps:

[0052] Step 1: According to the mass fraction, 28 g of sodium source, 35 g of iron source, 13 g of chromium source, 13 g of phosphorus source, 4 g of oxalic acid, and 4 g of sodium fluoride are ball-milled at a rotation speed of 480 r / min for 11 h, mixed evenly, and then vacuum-dried at 75 °C for 36 h;

[0053] Step 2: The dried powder is pre-calcined in an inert atmosphere. 3.0 g of organic carbon source is added to the pre-calcined powder, and secondary ball-milling is carried out. The ball-milling speed is 480 r / min, and the ball-milling duration is 5 h. After mixing evenly, it is vacuum-dried at 75 °C for 20 h, and then secondary calcination is carried out in an inert atmosphere to obtain carbon-coated Cr-doped sodium iron phosphate powder, that is, the Cr-doped composite cathode material;

[0054] Step 3: According to the mass fraction, 88 parts of Cr-doped composite cathode material, 9 parts of conductive material, and 9 parts of binder are added to N-methylpyrrolidone and ground and mixed to obtain a slurry. The slurry is coated on a current collector and heated to 100 °C in a vacuum environment. After complete drying, a positive electrode sheet is obtained.

[0055] The sodium source described in Step 1 is a mixture of sodium fluoride and sodium dihydrogen phosphate.

[0056] The iron source described in Step 1 is ferrous citrate and ferrous lactate.

[0057] The chromium source described in Step 1 is chromium nitrate.

[0058] The phosphorus sources described in Step 1 are phosphoric acid and sodium dihydrogen phosphate.

[0059] The organic carbon sources described in Step 2 are glucose and citric acid monohydrate.

[0060] The pre-calcination temperature described in Step 2 is 420 °C and the duration is 3 h.

[0061] The secondary calcination temperature described in Step 2 is 700 °C and the duration is 6 h.

[0062] The conductive material described in Step 3 is nickel-coated nano-superconducting carbon black, and the preparation method is as follows:

[0063] By weight, 180 g of nano-superconducting carbon black, 1400 g of water, 5 g of butyl acrylate, 0.2 g of 4-vinylpyridine-nickel, 0.4 g of 2,4,6-triallyloxy-1,3,5-triazine, and 4 g of potassium peroxide are placed in a water bath at 70 °C, and the above solution is stirred for 3 h, filtered, and dried to obtain uniformly dispersed nickel-coated nano-superconducting carbon black.

[0064] Example 4

[0065] A preparation method of a Cr-doped composite cathode material includes the following steps:

[0066] Step 1: According to mass fraction, 32 g of sodium source, 50 g of iron source, 15 g of chromium source, 15 g of phosphorus source, 5 g of oxalic acid, and 5 g of sodium fluoride are ball-milled at a speed of 500 r / min for 12 h, mixed evenly, and then vacuum-dried at 80 °C for 48 h;

[0067] Step 2: The dried powder is pre-calcined in an inert atmosphere. 3.4 g of organic carbon source is added to the pre-calcined powder, and secondary ball-milling is carried out at a ball-milling speed of 500 r / min for 6 h. After mixing evenly, it is vacuum-dried at 80 °C for 24 h and then secondarily calcined in an inert atmosphere to obtain carbon-coated Cr-doped sodium iron phosphate powder, that is, the Cr-doped composite cathode material;

[0068] Step 3: According to mass fraction, 90 parts of the Cr-doped composite cathode material, 10 parts of the conductive material, and 10 parts of the binder are added to N-methylpyrrolidone and ground and mixed to obtain a slurry. The slurry is coated on the current collector and heated to 120 °C in a vacuum environment. After complete drying, a positive electrode sheet is obtained.

[0069] The sodium source described in Step 1 is sodium dihydrogen phosphate.

[0070] The iron source described in Step 1 is ferrous phosphate.

[0071] In Step 1, the chromium source is chromium sulfate and chromium nitrate.

[0072] In Step 1, the phosphorus source is phosphoric acid and sodium dihydrogen phosphate.

[0073] In Step 2, the organic carbon source is citric acid monohydrate.

[0074] In Step 2, the pre-calcination temperature is 550 °C and the duration is 4 h.

[0075] In Step 2, the secondary calcination temperature is 800 °C and the duration is 5 - 7 h.

[0076] In Step 3, the conductive material used is nickel-coated nano-superconducting carbon black, and the preparation method is as follows:

[0077] By weight, 200 g of nano-superconducting carbon black, 1500 g of water, 6 g of butyl acrylate, 0.3 g of 4-vinylpyridine-nickel, 0.5 g of 2,4,6-triallyloxy-1,3,5-triazine, and 5 g of potassium peroxide are taken, and then they are placed in an 80 °C water bath and the above solution is stirred for 4 h, filtered, and dried to obtain uniformly dispersed nickel-coated nano-superconducting carbon black.

[0078] In Step 3, the binder is sodium carboxymethyl cellulose.

[0079] Comparative Example 1

[0080] In this example, the conductive agent used is common acetylene black, and the rest of the technical solutions are the same as those in Example 1.

[0081] Comparative Example 2

[0082] In this example, in the preparation of the nickel-coated nano-superconducting carbon black used as the conductive agent, 4-vinylpyridine-nickel is not added, and the rest of the technical solutions are the same as those in Example 1.

[0083] Comparative Example 3

[0084] In this example, in the preparation of the nickel-coated nano-superconducting carbon black used as the conductive agent, 2,4,6-triallyloxy-1,3,5-triazine is not added, and the rest of the technical solutions are the same as those in Example 1.

[0085] Testing process: Use a punching machine to punch the positive electrode sheet into a round sheet with a diameter of 12 mm, use metallic sodium as the counter electrode, 1 mol / L NaClO 4 EC + DEC (1:1 vol%) + 5% FEC is used as the electrolyte, the separator is a PP / PE / PP three-layer separator, and it is assembled into a CR2016 type button battery in a glove box, and the electrochemical performance is tested in a voltage window of 1.8 - 4.2 V. The test results are shown in Table 1:

[0086] Table 1

[0087]

[0088] As can be seen from the above specific embodiments, by doping with Cr and using the nickel-coated nano-superconducting carbon black proposed in the present invention, the sodium-ion battery can improve its cycle performance, rate performance, and discharge specific capacity.

[0089] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for preparing a Cr-doped composite positive electrode sheet, the operating steps of which are: Step 1: According to the mass proportions, 18-32 parts of sodium source, 6-50 parts of iron source, 5-15 parts of chromium source, 10-15 parts of phosphorus source, 2-5 parts of oxalic acid, and 3-5 parts of sodium fluoride are ball-milled at a speed of 400-500 r / min for 8-12 hours to mix evenly, and then vacuum-dried at 60-80°C for 24-48 hours; Step 2: pre-calcining the dried powder in an inert atmosphere, adding 1.8-3.4 parts of an organic carbon source to the pre-calcined powder, performing secondary ball milling, the ball milling speed is 400-500r / min, the ball milling time is 4-6h, and after mixing evenly, vacuum drying at 60-80°C for 12-24h, and secondary calcining in an inert atmosphere to obtain carbon-coated Cr-doped sodium iron phosphate powder, that is, Cr-doped composite positive electrode material; Step 3: According to the mass fraction, 80-90 parts of Cr-doped composite positive electrode material, 5-10 parts of conductive material, and 5-10 parts of binder are added into N-methylpyrrolidone for grinding and mixing to obtain slurry, the slurry is coated on the current collector, heated to 60-120°C in a vacuum environment, and the positive electrode sheet is obtained after complete drying.

2. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The sodium source in step 1 is one or more of sodium carbonate, sodium bicarbonate, sodium fluoride, and sodium dihydrogen phosphate.

3. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The iron source in step 1 is one or more of ferrous gluconate, ferrous oxalate, ferrous chloride, ferrous phosphate, ferrous acetate, ferrous citrate, and ferrous lactate.

4. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The chromium source in step 1 is one or more of chromium sulfate, chromium acetate and chromium nitrate.

5. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The phosphorus source in step 1 is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and sodium dihydrogen phosphate.

6. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The organic carbon source in step 2 is one or more of glucose, sucrose and citric acid monohydrate.

7. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The pre-calcination temperature in step 2 is 350-550° C. and the duration is 2-4 hours.

8. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The secondary calcination temperature in step 2 is 500-800° C. and the duration is 5-7 hours.

9. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The conductive material described in step 3 is nickel-coated nano superconducting carbon black, and the preparation method is as follows: By weight, 100-200 parts of nano superconducting carbon black, 1200-1500 parts of water, 2-6 parts of butyl acrylate, 0.03-0.3 parts of 4-vinylpyridine-nickel, 0.05-0.5 parts of 2,4,6-tripropyleneoxy-1,3,5-triazine, and 2-5 parts of potassium peroxide are placed in a 60°C-80°C water bath, the solution is stirred for 2-4 hours, filtered, and dried to obtain uniformly dispersed nickel-coated nano superconducting carbon black.

10. The method for preparing a Cr-doped composite positive electrode sheet according to claim 1, characterized in that: The binder described in step three is one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

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