Prussian blue positive electrode material and preparation method therefor, and prussian blue positive electrode sheet

Abstract

The invention relates to the technical field of positive electrode materials. Disclosed are a Prussian blue positive electrode material and a preparation method therefor, and a Prussian blue positive electrode sheet. The preparation method for the Prussian blue positive electrode material comprises the following steps: mixing a sodium ferrocyanide solution, a hydrophobic liquid and a surfactant until phase separation does not occur, so as to obtain a precursor microemulsion; adding a transition metal salt solution to the precursor microemulsion, and stirring same, so as obtain a Prussian blue microemulsion; and subjecting the Prussian blue microemulsion to an aging treatment, solid-liquid separation, washing and drying, so as to obtain the Prussian blue positive electrode material. The Prussian blue positive electrode material prepared by using the method is unlikely to absorb water, and has good storage performance and conductivity.

Description

A Prussian blue positive electrode material and its preparation method and Prussian blue positive electrode sheet Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and in particular to a Prussian blue positive electrode material, a preparation method thereof, and a Prussian blue positive electrode sheet. Background Art

[0002] Against the backdrop of rapid technological and industrial development, the world is becoming increasingly reliant on fossil fuels, leading to energy shortages and a continuous increase in carbon emissions, ultimately causing serious environmental problems. Renewable energy, as an important means of overcoming the current difficulties, has led to the emergence of new energy vehicles. With the rapid development of new energy vehicles, the new energy battery industry has also been thrust into the spotlight. Lithium-ion batteries, as an excellent electronic energy storage device, have been widely used in the field of new energy vehicles. However, the reserves of lithium resources in the Earth's crust are very limited, which severely restricts the sustainable development and large-scale application of lithium-ion batteries. In comparison, sodium resources are abundant and inexpensive, and sodium and lithium are in the same main group with similar chemical properties. In summary, sodium-ion batteries have great potential and advantages in sustainable development and large-scale application.

[0003] Sodium-ion batteries are driven by concentration differences. During charging, sodium ions travel through the electrolyte from the positive electrode to the negative electrode. During discharge, sodium ions travel through the electrolyte from the negative electrode to the positive electrode, maintaining a high degree of reversibility. However, Prussian blue cathode materials currently face two major challenges. First, the particle consistency is poor. This is because during the co-precipitation process of synthesizing Prussian blue cathode materials, soluble metal salts react with sodium ferrocyanide and rapidly nucleate and grow. Second, Prussian blue cathode materials easily absorb water during storage, which leads to reduced crystallinity and volume expansion, affecting electrochemical performance and stability.

[0004] Summary of the Invention

[0005] The purpose of this article is to overcome the shortcomings of the above-mentioned prior art and provide a Prussian blue positive electrode material, a preparation method thereof, and a Prussian blue positive electrode sheet; the Prussian blue positive electrode material has good storage stability, is not easy to absorb moisture, and has a small particle size and good electrical properties.

[0006] To achieve the above objectives, the technical solutions adopted in this paper are:

[0007] A method for preparing a Prussian blue positive electrode material, the preparation method comprising the following steps:

[0008] mixing a sodium ferrocyanide solution, a hydrophobic liquid, and a surfactant until no phase separation occurs to obtain a precursor microemulsion;

[0009] adding a transition metal salt solution to the precursor microemulsion and stirring to obtain a Prussian blue microemulsion;

[0010] The Prussian blue microemulsion is subjected to aging treatment, solid-liquid separation, washing, and drying to obtain the Prussian blue positive electrode material.

[0011] In this study, a Prussian blue cathode material was prepared using a microemulsion method. The resulting water-in-oil microemulsion effectively controlled the particle size of the Prussian blue cathode material. Furthermore, the surface of the water-in-oil Prussian blue cathode material was coated with an oil film, which prevented the dried material from absorbing water and exhibited good storage stability.

[0012] In one embodiment, the hydrophobic liquid is at least one of a hydrophobic liquid organic matter and a hydrophobic ionic liquid.

[0013] In one embodiment, the boiling point of the hydrophobic liquid organic phase is higher than that of water.

[0014] In one embodiment, the hydrophobic liquid organic compound is at least one of n-octane, n-decane, toluene, triglyceride (2-ethylhexanoate), n-hexadecane, and xylene, and the hydrophobic ionic liquid is at least one of 1-propyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate. Using these materials as the hydrophobic liquid allows for the formation of a uniform oil film on the surface of the Prussian blue cathode material.

[0015] In one embodiment, the sodium ferrocyanide solution is prepared by dissolving sodium ferrocyanide in water, and the transition metal salt solution is prepared by dissolving a transition metal salt in water.

[0016] In one embodiment, the molar ratio of the sodium ferrocyanide to the transition metal salt is 1:(1-2); the concentration of the sodium ferrocyanide in the sodium ferrocyanide solution is 0.01-0.5 mol / L, and the concentration of the transition metal salt in the transition metal salt solution is 0.01-0.5 mol / L. The transition metal salt is at least one of a divalent iron salt, a cobalt salt, and a manganese salt. In this embodiment, the amount of transition metal salt introduced needs to be in excess to avoid defects in the prepared particles.

[0017] In one embodiment, the volume ratio of the hydrophobic liquid to the aqueous solution is 100:(5-10), and the aqueous solution is a mixture of the sodium ferrocyanide solution and the transition metal salt solution. In addition, when the precursor microemulsion also contains an auxiliary solution, the aqueous solution is a mixture of the sodium ferrocyanide solution, the transition metal salt solution, and the auxiliary solution; the auxiliary solution is a mixed aqueous solution of an antioxidant and a sodium supplement, the concentration of the antioxidant in the auxiliary solution is 0.01-0.05 mol / L, and the concentration of the sodium supplement in the auxiliary solution is 0.01-0.05 mol / L. The above-mentioned limitation on the volume ratio of the hydrophobic liquid to the aqueous solution can ensure that the oil film formed on the surface of the prepared Prussian blue positive electrode material is uniform and dense, and not easy to absorb moisture.

[0018] In one embodiment, the antioxidant is at least one of sodium citrate, ascorbic acid, and sodium thiosulfate, and the sodium supplement is at least one of sodium chloride, sodium carbonate, sodium acetate, sodium thiosulfate, and sodium citrate.

[0019] In one embodiment, the molar ratio of the sodium supplement to the sodium ferrocyanide is (0.3-1.1):1.

[0020] Adding the above-mentioned antioxidant and sodium supplement can improve the electrical properties of the Prussian blue positive electrode material. When the Prussian blue positive electrode material is used in a positive electrode sheet, its first discharge specific capacity and cycle performance are significantly better.

[0021] In one embodiment, the molar volume ratio of the surfactant to the hydrophobic liquid is 0.3 to 0.5 mol / L. By limiting the ratio of the surfactant to the hydrophobic liquid as described above, a stable Prussian blue microemulsion can be obtained.

[0022] In one embodiment, the surfactant is a lipophilic surfactant, and the lipophilic surfactant includes at least one of octylphenol polyoxyethylene ether, sodium di(2-ethylhexyl) succinate sulfonate (AOT), dodecylphenol polyoxyethylene ether, dodecyl glycidyl ether, ethylene glycol fatty acid ester, and sorbitan sesquioleate.

[0023] In one embodiment, the transition metal salt solution is added to the precursor microemulsion at a rate of 20 to 50 mL / h under a protective atmosphere, selected from nitrogen and helium. Controlling the addition rate of the transition metal salt solution within this range can improve the stability of the Prussian blue microemulsion, prevent excessive reaction with sodium ferrocyanide, and form a more uniformly particle-rich cathode material.

[0024] In one embodiment, the Prussian blue microemulsion is stirred at 60-100° C. for 10-60 minutes and then aged.

[0025] At the same time, this article also discloses a Prussian blue positive electrode material prepared by the method and a Prussian blue positive electrode sheet prepared from the Prussian blue positive electrode material. The preparation method of the Prussian blue positive electrode sheet comprises the following steps:

[0026] (1) sintering the Prussian blue positive electrode material at 500-800° C. for 0.5-5 min to obtain a positive electrode active material;

[0027] (2) The positive electrode active material, the conductive agent, and the binder are prepared into a slurry in a mass ratio of (85-98): (1-5): (2-10), and the slurry is coated on a current collector to obtain the Prussian blue positive electrode sheet.

[0028] In one embodiment, the coating density of the slurry on the current collector is 10 to 50 mg / cm 2 The current collector is one of aluminum foil, titanium mesh, carbon paper, and carbon cloth.

[0029] In one embodiment, in step (1), laser heating is performed with a laser power density of 1 to 10 kW / cm 2 Laser heating and cooling rates are fast, and the Prussian blue cathode material can be quickly sintered by laser heating without significantly affecting the particle size. The oil film on the surface of the material can be quickly removed, and the carbon material obtained by decomposing the oil film can form a carbon network between the particles, which has better conductivity than directly adding a conductive agent to mix.

[0030] Compared with the existing technology, the beneficial effects of this article are:

[0031] In this study, a Prussian blue cathode material was prepared using a microemulsion method. The resulting water-in-oil microemulsion effectively controlled the particle size of the Prussian blue cathode material. Furthermore, the surface of the material obtained using the microemulsion method was coated with an oil film, which prevented the cathode material from absorbing water during storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a flow chart of the preparation of the Prussian blue positive electrode sheet described in this article. DETAILED DESCRIPTION

[0033] To better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained through commercial channels.

[0035] The material information used in the following examples and comparative examples is as follows:

[0036] Antioxidant: Ascorbic acid, commercially available;

[0037] Sodium supplement: sodium citrate, commercially available.

[0038] Example 1

[0039] An embodiment of the Prussian blue positive electrode material described herein, and a method for preparing the Prussian blue positive electrode material described in this embodiment are as follows:

[0040] (1) dissolving sodium ferrocyanide in deionized water to obtain a sodium ferrocyanide solution having a sodium ferrocyanide concentration of 0.1 mol / L; dissolving ferrous chloride in deionized water to obtain a transition metal salt solution having a ferrous chloride concentration of 0.1 mol / L; and dissolving an antioxidant and a sodium supplement in deionized water to obtain an auxiliary agent solution having an antioxidant concentration of 0.01 mol / L and a sodium supplement concentration of 0.05 mol / L;

[0041] (2) 3 mL of sodium ferrocyanide solution, 100 mL of n-decane, 3 mL of the auxiliary solution, and 0.04 mol of AOT were added dropwise and mixed until the two phases were evenly mixed and no phase separation occurred, thereby obtaining a precursor microemulsion;

[0042] (3) continuously stirring the precursor microemulsion, and adding 3 mL of the transition metal salt solution dropwise to the precursor microemulsion at a rate of 30 mL / h in a nitrogen atmosphere. After the addition is complete, stirring is continued for 20 minutes to obtain a Prussian blue microemulsion;

[0043] (4) The Prussian blue microemulsion was continuously stirred at 80° C. in a nitrogen atmosphere for 30 min, then aged, solid-liquid separated, washed with pure water, and dried to obtain the Prussian blue positive electrode material.

[0044] Example 2

[0045] An embodiment of the Prussian blue cathode material described herein is different from Example 1 only in that, in step (3), 4 mL of the transition metal salt solution is added dropwise to the precursor microemulsion.

[0046] Example 3

[0047] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that in step (2), the volume of the sodium ferrocyanide solution and the auxiliary agent solution are 2 mL respectively, and in step (3), the volume of the transition metal salt solution is 4 mL.

[0048] Example 4

[0049] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that in step (2), the volume of the sodium ferrocyanide solution and the auxiliary agent solution are 4 mL respectively, and in step (3), the volume of the transition metal salt solution is 4 mL.

[0050] Example 5

[0051] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that, in step (2), the content of AOT is 0.05 mol.

[0052] Example 6

[0053] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that, in step (2), the content of AOT is 0.03 mol.

[0054] Example 7

[0055] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that, in step (2), the content of AOT is 0.07 mol.

[0056] Example 8

[0057] An embodiment of the Prussian blue positive electrode material described herein differs from Example 1 only in that the hydrophobic ionic liquid 1-propyl-3-methylimidazolium hexafluorophosphate is used instead of n-decane.

[0058] Example 9

[0059] An embodiment of the Prussian blue cathode material described herein is different from Example 1 only in that the rate of adding the transition metal salt solution dropwise to the precursor microemulsion is 20 mL / h.

[0060] Example 10

[0061] An embodiment of the Prussian blue cathode material described herein is different from Example 1 only in that the rate of adding the transition metal salt solution dropwise to the precursor microemulsion is 50 mL / h.

[0062] Example 11

[0063] An embodiment of the Prussian blue cathode material described herein is different from Example 1 only in that the rate of adding the transition metal salt solution dropwise to the precursor microemulsion is 60 mL / h.

[0064] Example 12

[0065] An embodiment of the Prussian blue positive electrode material described herein is different from Example 1 only in that no auxiliary solution is added in step (2).

[0066] Comparative Example 1

[0067] A Prussian blue positive electrode material, wherein the Prussian blue positive electrode material is different from that of Example 1 only in that n-decane and AOT are not added in step (2).

[0068] Comparative Example 2

[0069] A Prussian blue positive electrode material, wherein the Prussian blue positive electrode material differs from that of Example 1 only in that n-decane is not added in step (2).

[0070] Effect Examples 1-12

[0071] Effect Examples 1 to 12 are the Prussian blue positive electrode sheets described herein, which are prepared from the Prussian blue positive electrode materials described in Examples 1 to 12, respectively. The specific preparation methods are as follows:

[0072] (1) The Prussian blue cathode material was sintered for 2 min at 600 °C using laser heating, with a laser power density of 3 kW / cm 2 , obtaining a positive electrode active material;

[0073] (2) The positive electrode active material, the conductive agent, and the binder are prepared into a slurry in a mass ratio of 90:3:8, and the slurry is coated on the current collector aluminum foil with a coating density of 30 mg / cm 2 , and dried to obtain the Prussian blue positive electrode sheet.

[0074] Effect Comparative Examples 1-2

[0075] Comparative Examples 1-2 are Prussian blue positive electrode sheets prepared from Comparative Examples 1-2, and the preparation method thereof is the same as that of Effective Examples 1-12.

[0076] Performance Testing

[0077] 1. Electrical Performance of Prussian Blue Positive Electrode Sheets: The Prussian blue positive electrode sheets described in Examples 1-12 and Comparative Examples 1-2 were assembled into sodium ion half-cells. Their initial discharge specific capacity at 0.1C and after 200 cycles were measured. The moisture content of the materials was measured using a Karl-Fischer titrator, with a cutoff temperature of 200°C. The test results are shown in Table 1.

[0078] 2. Particle size of Prussian blue cathode material.

[0079] Table 1

[0080] As can be seen from Table 1, the particle size of the Prussian blue cathode material prepared by the method described in this article can be maintained within 100 nm, the particle uniformity is high, and the intrusion of water can be effectively prevented. After 30 days, the moisture content of the product changes little. During the charge and discharge cycle, the initial discharge specific capacity can basically reach more than 140 mAh / g. At the same time, after 200 cycles at a 0.1C rate, it can still basically maintain more than 135 mAh / g, with excellent electrochemical performance.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A method for preparing a Prussian blue positive electrode material, characterized in that: The steps include: The sodium ferrocyanide solution, the hydrophobic liquid, and the surfactant are mixed until no phase separation occurs to obtain a precursor microemulsion; adding a transition metal salt solution into the precursor microemulsion and stirring to obtain a Prussian blue microemulsion; The Prussian blue microemulsion is subjected to aging treatment, solid-liquid separation, washing and drying to obtain the Prussian blue positive electrode material.

2. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The hydrophobic liquid is at least one of a hydrophobic liquid phase organic matter and a hydrophobic ionic liquid; the hydrophobic liquid phase organic matter is at least one of n-octane, n-decane, toluene, triglyceride of isooctanoate, n-hexadecane, and xylene; the hydrophobic ionic liquid is at least one of 1-propyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate.

3. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The sodium ferrocyanide solution is prepared by dissolving sodium ferrocyanide in water, and the transition metal salt solution is prepared by dissolving a transition metal salt in water; the molar ratio of the sodium ferrocyanide to the transition metal salt is 1:(1-2); the concentration of the sodium ferrocyanide in the sodium ferrocyanide solution is 0.01-0.5 mol / L, the concentration of the transition metal salt in the transition metal salt solution is 0.01-0.5 mol / L, and the transition metal salt is at least one of a divalent iron salt, a cobalt salt, and a manganese salt.

4. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The volume ratio of the hydrophobic liquid to the aqueous solution is 100:(5-10), and the aqueous solution is a mixed solution of the sodium ferrocyanide solution and the transition metal salt solution.

5. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The precursor microemulsion also contains an auxiliary agent solution, which is a mixed aqueous solution of an antioxidant and a sodium supplement. The concentration of the antioxidant in the auxiliary agent solution is 0.01-0.05 mol / L, and the concentration of the sodium supplement in the auxiliary agent solution is 0.01-0.05 mol / L.

6. The method for preparing the Prussian blue positive electrode material according to claim 5, characterized in that: The volume ratio of the hydrophobic liquid to the aqueous solution is 100:(5-10), and the aqueous solution is a mixed solution of the sodium ferrocyanide solution, the transition metal salt solution, and the auxiliary agent solution.

7. The method for preparing the Prussian blue positive electrode material according to claim 5, characterized in that: The antioxidant is at least one of sodium citrate, ascorbic acid, and sodium thiosulfate, and the sodium supplement is at least one of sodium chloride, sodium carbonate, sodium acetate, sodium thiosulfate, and sodium citrate.

8. The method for preparing the Prussian blue positive electrode material according to claim 5, characterized in that: The molar ratio of the sodium supplement to the sodium ferrocyanide is (0.3-1.1):

1.

9. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The molar volume ratio of the surfactant to the hydrophobic liquid is 0.3 to 0.5 mol / L.

10. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The surfactant is a lipophilic surfactant, and the lipophilic surfactant includes at least one of octylphenol polyoxyethylene ether, sodium di(2-ethylhexyl) succinate sulfonate, dodecylphenol polyoxyethylene ether, dodecyl glycidyl ether, ethylene glycol fatty acid ester, and sorbitan sesquioleate.

11. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The rate of adding the transition metal salt solution into the precursor microemulsion is 20-50 mL / h, and the adding process is carried out under a protective atmosphere.

12. The method for preparing the Prussian blue positive electrode material according to claim 1, characterized in that: The Prussian blue microemulsion is stirred at 60-100° C. for 10-60 minutes and then subjected to aging treatment.

13. A Prussian blue positive electrode material, characterized in that: Prepared by the method according to any one of claims 1 to 12.

14. A Prussian blue positive electrode sheet, characterized in that: The method is prepared from the Prussian blue positive electrode material as claimed in claim 13, comprising the following steps: Sintering the Prussian blue positive electrode material at 500-800° C. for 0.5-5 min to obtain a positive electrode active material; The positive electrode active material, the conductive agent and the binder are prepared into a slurry in a mass ratio of (85-98): (1-5): (2-10), and the slurry is coated on a current collector to obtain the Prussian blue positive electrode sheet.

15. The Prussian blue positive electrode sheet according to claim 14, characterized in that: The coating density of the slurry on the current collector is 10 to 50 mg / cm 2 .

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