A carbon-coating process method in a synthesis process of a positive electrode material of a prussian blue analogue

Abstract

The application discloses a carbon-coating process method in a positive electrode material synthesis process of a Prussian blue analogue, and belongs to the technical field of sodium ion battery positive electrode materials. The process respectively prepares a ferrous salt mixed solution containing dispersed conductive materials, a sodium ferrocyanide solution and a sodium salt base solution, and the first two are slowly added to the base solution under an inert atmosphere for a coprecipitation reaction, in-situ carbon-coating between layers is realized with grain growth, and the reaction solution is subjected to standing, cleaning, positive pressure filtration and vacuum drying, and then conductive materials are added and ball milled to complete secondary surface coating. The application realizes internal conductive bridging of the grains and efficient conduction between the particles through twice carbon-coating, simultaneously inhibits particle agglomeration, guarantees uniform grain structure, and the prepared material has excellent high-rate charge-discharge performance while retaining capacity, and the process has strong controllability and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of cathode materials for sodium-ion batteries, and particularly to a carbon coating process in the synthesis of a Prussian blue analog cathode material. Background Technology

[0002] Prussian blue analogues (PBAs) have a three-dimensional open framework structure. Due to their abundant elemental reserves, high theoretical specific energy, and low preparation cost, they are cathode materials with great industrialization prospects in energy storage devices such as sodium-ion batteries.

[0003] Currently, the mainstream method for industrial preparation of PBAs is the coprecipitation method. This method is simple to operate and easy to scale up for mass production, but it also has certain technical bottlenecks. Since the reaction takes place in an aqueous solution, water molecules can easily enter the material's crystal lattice to form water of crystallization, which can disrupt the integrity of the crystal lattice and trigger side reactions. Therefore, the product must undergo strict dehydration treatment. However, after dehydration, the inherent conductivity of PBAs will be further deteriorated. PBAs themselves have extremely low electronic conductivity, and the dehydration process can also disrupt internal electron transport pathways, seriously affecting the key electrochemical performance of the battery.

[0004] Existing technologies often use the addition of conductive pastes to improve conductivity. However, conductive agents can only adhere to the particle surface, improving inter-particle conductivity, but cannot penetrate into the particle interior, thus failing to address the problem of insufficient conductivity within the particles. Co-precipitation synthesis of PBAs requires water removal, which results in poor conductivity. Traditional conductive paste modification cannot solve the conductivity defects within the particles, limiting their electrochemical performance and wider industrial applications. Summary of the Invention

[0005] This invention proposes a carbon coating process in the synthesis of Prussian blue analog cathode materials. A conductive material is introduced into the precursor solution during the initial preparation phase of the material synthesis. During the cathode material reaction synthesis, the conductive material accompanies the growth of the material grains, forming an interlayer coating structure. This achieves in-situ coating and bridging of the conductive material within the grains. After the material growth is complete, the solution is stirred, allowed to stand, washed, and finally filtered under positive pressure. During this process, due to the effect of the conductive material, the bonding growth space between cathode material particles is significantly reduced, effectively inhibiting particle aggregation and adhesion, and ensuring a stable and uniform grain structure.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A carbon coating process for synthesizing a Prussian blue analogue cathode material includes the following steps:

[0008] (1) Prepare a mixed solution containing ferrous salt and sodium salt, add conductive material and stir to disperse to obtain solution A;

[0009] (2) Prepare a solution containing sodium ferrocyanide and sodium salt, add a conductive material and stir to disperse, to obtain solution B;

[0010] (3) Prepare a sodium salt solution, add a conductive material and stir to disperse it to obtain solution C;

[0011] (4) Reduce the stirring speed of solutions A and B to 50 r / min-200 r / min, and add solutions A and B dropwise to solution C using a peristaltic pump. The dropwise addition time is 40 min-600 min, and the dropwise addition rate is 0.05 L / min-1 L / min. During the dropwise addition process, maintain an inert atmosphere, which is nitrogen or argon. After the dropwise addition is completed, continue stirring the mixed solution for 0.5 h-12 h, and let it stand for 3 h-12 h. During this process, keep the temperature constant.

[0012] (5) Filter the mixed solution to remove the supernatant, and wash with deionized water 1-3 times. The washing and stirring speed is 200r / min-1000r / min and the stirring time is 10min-60min. After the stirring is stopped during the washing process, filter under positive pressure to obtain the final precipitate, and quickly transfer it to a vacuum oven for heating and drying.

[0013] (6) The heated and dried material is placed into a ball mill and a conductive material is added and ball milled for 0.5h-2h. The mass of the conductive material is 0.5%-5% of the mass of the dried material to obtain a Prussian blue analog cathode material.

[0014] Furthermore, the concentration of ferrous salt in step (1) is 0.1 mol / L-0.5 mol / L.

[0015] Furthermore, in step (2), the concentration of sodium ferrocyanide is 0.1 mol / L-0.5 mol / L.

[0016] Furthermore, in steps (1), (2), and (3), the stirring time of the high-speed stirring is 1-4 hours, the stirring speed is 200 r / min-1000 r / min, and the temperature is 20℃-40℃.

[0017] Furthermore, the concentration of sodium salt in steps (1), (2), and (3) is 0.1 mol / L to 1.0 mol / L, preferably sodium citrate or sodium citrate and sodium sulfate or sodium citrate and sodium chloride.

[0018] Further, the concentration of the conductive material after stirring and dispersing in steps (1), (2), and (3) is 0.4 mg / L-40 mg / L, and the conductive material is preferably at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, Ketjen black, and graphene composite conductive agents.

[0019] Furthermore, in step (5), the temperature of the vacuum oven for heating and drying is set to 90℃-200℃, the relative pressure of the vacuum oven is not higher than -90.0kpa, and the heating and drying time is 24h-48h.

[0020] The beneficial effects of this invention are:

[0021] This invention involves two carbon coating processes. The first is an in-situ internal doping coating during crystal growth, which is an interlayer coating and solves the problem of internal particle conductivity. The second is a surface coating after the material is dried. Furthermore, during the settling process after crystal growth, the presence of conductive materials in the solution significantly reduces interparticle bonding, ensuring monodispersity and crystal structure consistency, and further enhancing interparticle electronic conductivity. This material exhibits excellent high-rate charge / discharge performance while maintaining its capacity.

[0022] Other features and advantages of the present invention will be described in detail in part in the following detailed description. Attached Figure Description

[0023] Figure 1 These are energy efficiency graphs for Examples 1, 2, and 3 and Comparative Example 1 at different scaling factors;

[0024] Figure 2 These are the EIS diagrams of Examples 1 and 2 and the comparative example;

[0025] Figure 3 This is the rate performance diagram for Example 3. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] Example 1

[0028] A carbon coating process for synthesizing a Prussian blue analogue cathode material includes the following steps:

[0029] Prepare a mixed aqueous solution of 0.15 mol / L ferrous sulfate, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution A. Add 15 g of single-walled carbon nanotube slurry (0.4% solid content) and stir at high speed for 1 hour at a stirring speed of 200 r / min and a temperature of 25 °C.

[0030] Prepare a mixed aqueous solution of 0.15 mol / L sodium ferrocyanide, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution B. Add 15 g of single-walled carbon nanotube slurry (0.4% solid content) and stir at high speed for 1 hour at a stirring speed of 200 r / min and a temperature of 25 °C.

[0031] Solution C is a mixed dispersion containing 0.15 mol / L sodium sulfate, 0.225 mol / L sodium citrate, and 1.5 mg / L single-walled carbon nanotube slurry (0.4% solid content). After adding deionized water and stirring until uniformly dispersed, the volume was adjusted to 20 L. The mixture was stirred at high speed (500 rpm) for 1 hour at 25°C.

[0032] Reduce the stirring speed of solutions A and B to 50 r / min, and add solutions A and B to solution C using a peristaltic pump at a dropping rate of 10 L / h for 4 h. Nitrogen gas is used for protection during the dropping process at a flow rate of 250 ml / min. After the dropping is complete, continue stirring solution C for 1 h, then let it stand for 3 h, maintaining a constant temperature throughout this process.

[0033] Solution C was filtered to remove the supernatant, and then washed twice with deionized water. During the washing process, the mixture was stirred at a speed of 200 rpm for 10 minutes. After the final washing and stirring, the mixture was filtered under positive pressure to obtain the final precipitate at a pressure of 0.2 MPa. The precipitate was then quickly transferred to a vacuum oven for heating and drying. The temperature of the vacuum oven was set to 190℃, and the vacuum level was set not to exceed -90.0 kPa. The drying time was 24 hours.

[0034] The heated and dried material was placed in a ball mill, and 60g of conductive carbon black was added. The mixture was ball-milled for 2 hours to obtain the final cathode material.

[0035] Example 2

[0036] A carbon coating process for synthesizing a Prussian blue analogue cathode material includes the following steps:

[0037] Prepare a mixed aqueous solution of 0.15 mol / L ferrous sulfate, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution A. Add 5 g of single-walled carbon nanotube slurry (0.4% solid content) and 20 g of graphene composite conductive agent (4% solid content), and stir at high speed for 2 hours at a stirring speed of 400 r / min and a temperature of 25℃.

[0038] Prepare a mixed aqueous solution of 0.15 mol / L sodium ferrocyanide, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution B. Add 5 g of single-walled carbon nanotube slurry (0.4% solid content) and 20 g of graphene composite conductive agent (4% solid content), and stir at high speed for 2 hours at a stirring speed of 400 r / min and a temperature of 25℃.

[0039] Solution C is a mixed dispersion containing 0.225 mol / L sodium citrate, 0.15 mol / L sodium sulfate, 0.5 mg / L single-walled carbon nanotube slurry (0.4% solid content), and 20 mg / L graphene composite conductive agent (4% solid content). After adding deionized water and stirring to disperse evenly, the volume was adjusted to 20 L. The mixture was stirred at high speed for 2 hours at a stirring speed of 500 r / min and at a temperature of 25℃.

[0040] Reduce the stirring speed of solutions A and B to 50 r / min, and add solutions A and B to solution C using a peristaltic pump at a dropping rate of 10 L / h for 4 h. Nitrogen gas is used for protection during the dropping process at a flow rate of 250 ml / min. After the dropping is complete, continue stirring solution C for 1 h, then let it stand for 3 h, maintaining a constant temperature throughout this process.

[0041] Solution C was filtered to remove the supernatant, and then washed three times with deionized water. During the washing process, the mixture was stirred at 200 rpm for 10 minutes. After the final washing and stirring, the mixture was filtered under positive pressure to obtain the final precipitate at 0.2 MPa. The precipitate was then quickly transferred to a vacuum oven for drying. The oven temperature was set to 190°C, and the vacuum level was set not to exceed -90.0 kPa. The drying time was 24 hours.

[0042] The heated and dried material was placed in a ball mill, and 60g of conductive carbon black was added. The mixture was ball-milled for 2 hours to obtain the final cathode material.

[0043] Example 3

[0044] A carbon coating process for synthesizing a Prussian blue analogue cathode material includes the following steps:

[0045] Prepare a mixed aqueous solution of 0.15 mol / L ferrous chloride, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium chloride. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution A. Add 30 g of graphene composite conductive agent (4% solid content) and stir at high speed for 2 hours at a stirring speed of 400 r / min and a temperature of 25 °C.

[0046] Prepare a mixed aqueous solution of 0.15 mol / L sodium ferrocyanide, 0.225 mol / L sodium citrate, and 0.15 mol / L sodium chloride. Add deionized water, stir to dissolve, and bring the volume to 40 L to obtain solution B. Add 30 g of graphene composite conductive agent (4% solid content) and stir at high speed for 2 hours at a stirring speed of 400 r / min and a temperature of 25 °C.

[0047] Solution C is a mixed dispersion containing 0.15 mol / L sodium chloride, 0.225 mol / L sodium citrate, and 30 mg / L graphene composite conductive agent (4% solid content). After adding deionized water and stirring to disperse evenly, the volume is adjusted to 20 L. The mixture is stirred at high speed for 2 hours at a stirring speed of 500 r / min and at a temperature of 25 °C.

[0048] Reduce the stirring speed of solutions A and B to 50 r / min, and add solutions A and B to solution C using a peristaltic pump at a dropping rate of 10 L / h for 4 h. Nitrogen gas is used for protection during the dropping process at a flow rate of 250 ml / min. After the dropping is complete, continue stirring solution C for 1 h, then let it stand for 3 h, maintaining a constant temperature throughout this process.

[0049] Solution C was filtered to remove the supernatant, and then washed three times with deionized water. During the washing process, the mixture was stirred at 200 rpm for 10 minutes. After the final washing and stirring, the mixture was filtered under positive pressure to obtain the final precipitate at 0.2 MPa. The precipitate was then quickly transferred to a vacuum oven for drying. The oven temperature was set to 190°C, and the vacuum level was set not to exceed -90.0 kPa. The drying time was 24 hours.

[0050] The heated and dried material was placed in a ball mill, and 60g of conductive carbon black was added. The mixture was ball-milled for 2 hours to obtain the final cathode material.

[0051] Comparative Example

[0052] A carbon coating process for synthesizing a Prussian blue analogue cathode material includes the following steps:

[0053] Prepare a mixed aqueous solution of 0.15 mol / L ferrous sulfate, 0.225 mol / L sodium citrate and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve and then bring the volume to 40 L. This is solution A. Stir for 1 hour at a stirring speed of 200 r / min and at a temperature of 25℃.

[0054] Prepare a mixed aqueous solution of 0.15 mol / L sodium ferrocyanide, 0.225 mol / L sodium citrate and 0.15 mol / L sodium sulfate. Add deionized water, stir to dissolve, and then bring the volume to 40 L. This is solution B. Stir for 1 hour at a stirring speed of 200 r / min and at a temperature of 25 °C.

[0055] Solution C is a mixed aqueous solution containing 0.15 mol / L sodium sulfate and 0.225 mol / L sodium citrate. After adding deionized water and stirring to dissolve, the solution is brought to a final volume of 20 L. The solution is then stirred at high speed for 1 hour at a stirring speed of 500 r / min and at a temperature of 25 °C.

[0056] Reduce the stirring speed of solutions A and B to 50 r / min, and add solutions A and B to solution C using a peristaltic pump at a dropping rate of 10 L / h for 4 h. Nitrogen gas is used for protection during the dropping process at a flow rate of 250 ml / min. After the dropping is complete, continue stirring solution C for 1 h, then let it stand for 3 h, maintaining a constant temperature throughout this process.

[0057] Solution C was filtered to remove the supernatant, and then washed twice with deionized water. During the washing process, the mixture was stirred at 200 rpm for 10 minutes. After the final washing and stirring, the mixture was filtered under positive pressure at 0.2 MPa to obtain the final precipitate. The precipitate was then quickly transferred to a vacuum oven for drying. The oven temperature was set to 190°C, and the vacuum level was set not to exceed -90.0 kPa. The drying time was 24 hours to obtain the final cathode material.

[0058] Figure 1 These are energy efficiency graphs for Examples 1, 2, and 3 and Comparative Example 1 at different scaling factors; Figure 2 These are the EIS diagrams of Examples 1 and 2 and the comparative example; Figure 3 This is the rate performance diagram for Example 3.

[0059] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A carbon coating process for synthesizing a Prussian blue analogue cathode material, characterized in that, The steps include the following: (1) Prepare a mixed solution containing ferrous salt and sodium salt, add conductive material and stir to disperse to obtain solution A; (2) Prepare a solution containing sodium ferrocyanide and sodium salt, add a conductive material and stir to disperse, to obtain solution B; (3) Prepare a sodium salt solution, add a conductive material and stir to disperse, to obtain solution C; (4) Reduce the stirring speed of solutions A and B to 50 r / min-200 r / min, and add solutions A and B dropwise to solution C using a peristaltic pump. The dropwise addition time is 40 min-600 min, and the dropwise addition rate is 0.05 L / min-1 L / min. During the dropwise addition process, maintain an inert atmosphere, which is nitrogen or argon. After the dropwise addition is completed, continue stirring the mixed solution for 0.5 h-12 h, and let it stand for 3 h-12 h. During this process, keep the temperature constant. (5) Filter the mixed solution to remove the supernatant, and wash with deionized water 1-3 times. The washing and stirring speed is 200r / min-1000r / min and the stirring time is 10min-60min. After the stirring is stopped during the washing process, filter under positive pressure to obtain the final precipitate, and quickly transfer it to a vacuum oven for heating and drying. (6) The heated and dried material is placed into a ball mill and a conductive material is added and ball milled for 0.5h-2h. The mass of the conductive material is 0.5%-5% of the mass of the dried material to obtain a Prussian blue analog cathode material.

2. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In step (1), the concentration of ferrous salt is 0.1 mol / L-0.5 mol / L.

3. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In step (2), the concentration of sodium ferrocyanide is 0.1 mol / L-0.5 mol / L.

4. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In steps (1), (2), and (3), the stirring time of the high-speed stirring is 1-4 hours, the stirring speed is 200 r / min-1000 r / min, and the temperature is 20℃-40℃.

5. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In steps (1), (2), and (3), the concentration of sodium salt is 0.1 mol / L to 1.0 mol / L, preferably sodium citrate or sodium citrate and sodium sulfate or sodium citrate and sodium chloride.

6. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In steps (1), (2), and (3), the concentration of the conductive material after stirring and dispersing is 0.4 mg / L to 40 mg / L. The conductive material is preferably at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, Ketjen black, and graphene composite conductive agents.

7. The carbon coating process in the synthesis of a Prussian blue analog cathode material according to claim 1, characterized in that, In step (5), the temperature of the vacuum oven for heating and drying is set to 90℃-200℃, the relative pressure of the vacuum oven is not higher than -90.0kpa, and the heating and drying time is 24h-48h.

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