Method for coating Prussian blue with conductive hydrophobic layer

Abstract

The invention discloses a method for coating Prussian blue with a conductive hydrophobic layer, and belongs to the field of sodium ion batteries. The method comprises the following steps: uniformly mixing a conductive carbon material with Prussian blue, and adding an aluminate coupling agent; or ball-milling and mixing the conductive carbon material, the Prussian blue and the aluminate coupling agent. The conductive carbon material comprises one or a combination of more of graphene, graphene oxide, redox graphene, graphdiyne, a carbon nanotube CNT, a carbon nanotube glue solution, activated carbon, ketjen black, acetylene black, conductive carbon black SUPER P, graphite, expanded graphite, fullerene and amorphous carbon. The conductive carbon material and the Prussian blue are firmly combined through the hydrophobic aluminate coupling agent, and the aluminate coupling agent forms a molecular-level coating layer on the surfaces of the Prussian blue particles, so that the Prussian blue shows a hydrophobic property. The process is simple and convenient to operate, low in cost and very suitable for being used as a coating process of Prussian blue.

Description

Technical Field

[0001] The present invention is mainly applied to the field of new energy batteries, belongs to the field of sodium ion batteries, and relates to a method for coating Prussian blue with a conductive hydrophobic layer. Background Art

[0002] Nowadays, with the vigorous development of new energy and the extensive use of electronic devices, a low-cost battery is needed to meet the energy storage needs. Sodium-ion batteries can be used as the next generation of battery technology due to their abundant resources and excellent electrochemical performance. The main cathode materials for sodium-ion batteries are transition metal oxides, polyanion compounds, and Prussian blue analogs. Among them, Prussian blue analogs have the advantages of low cost, high energy density, good environmental performance, excellent rate performance and low temperature performance, and are expected to occupy a place in the future sodium-ion battery cathode material market. Therefore, exploring the performance of Prussian blue has become a current research hotspot.

[0003] Prussian blue has a three-dimensional open framework and is generally prepared by coprecipitation. However, due to the fast reaction rate, vacancy defects will be generated, thereby forming coordinated water. The coordinated water will hinder the diffusion of sodium ions during the charge and discharge process, resulting in a low specific capacity. Generally, a complexing agent is added during the reaction to reduce the reaction rate, and low-defect Prussian blue can be prepared. However, to further improve the cycle performance, methods such as doping and coating are required.

[0004] The presence of interstitial water in Prussian blue has a significant impact on its electrochemical performance. How to prevent Prussian blue from absorbing water in the air after drying is an industry problem. Carbon coating can improve the conductivity of Prussian blue, reduce the contact between Prussian blue and air, thereby making Prussian blue less likely to absorb water, improve the air stability of Prussian blue, and facilitate the processing of Prussian blue.

[0005] Since Prussian blue decomposes at high temperatures, it cannot be carbon-coated via a high-temperature solid-phase method. If physical coating is performed via a liquid-phase method, there is generally uneven coating, and many functional coating materials are generally difficult to chemically bond with Prussian blue. During subsequent cleaning treatments, the functional coating materials will fall off. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that Prussian blue has poor conductivity and is easy to absorb water, and to provide a method for coating Prussian blue with a conductive hydrophobic layer. The method comprises mixing Prussian blue and a conductive carbon material uniformly, and then adding a commercial hydrophobic aluminate coupling agent to mix the mixture uniformly, so that the aluminate coupling agent combines the conductive carbon material with the surface of the Prussian blue particles through van der Waals force, thereby achieving uniform coating and completing hydrophobic modification.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for coating Prussian blue with a conductive hydrophobic layer, the method comprising: mixing a conductive carbon material and Prussian blue uniformly, and then adding an aluminate coupling agent; or ball-milling the conductive carbon material, Prussian blue and the aluminate coupling agent. The Prussian blue has the following chemical formula: Na x M A [Fe(CN)6] y ·zH2O,M A It is a transition metal element, 2>x>1.4, 1>y>0.7, 4>z≥0.

[0009] Furthermore, the conductive carbon material includes one or more combinations of graphene, graphene oxide, redox graphene, graphyne, carbon nanotube CNT, carbon nanotube glue, activated carbon, Ketjen black, acetylene black, conductive carbon black SUPERP, graphite, expanded graphite, fullerene, and amorphous carbon.

[0010] Furthermore, the aluminate coupling agent is hydrophobic.

[0011] Furthermore, the added amount of the aluminate coupling agent is 0.1wt.%-5wt.%.

[0012] Furthermore, the mixing process uses a liquid phase system or a solid phase system.

[0013] Furthermore, the liquid phase system uses a non-aqueous solvent.

[0014] Furthermore, the non-aqueous solvent is one or more of ethanol, isopropanol, NMP, glycerol, acetonitrile, acetone, ether, ethyl acetate, NMF, tetrahydrofuran, benzene or carbon tetrachloride.

[0015] Furthermore, the mixed system needs to be heated to dissolve or melt the hydrophobic aluminate coupling agent. It starts to melt at 50°C and completely melts at 80°C.

[0016] A sodium ion battery, wherein the positive electrode material of the sodium ion battery is the composite Prussian blue material prepared by the above method.

[0017] The beneficial effects of the present invention over the prior art are as follows: the present invention uses a hydrophobic aluminate coupling agent to firmly combine the conductive carbon material with the Prussian blue, and the aluminate coupling agent forms a molecular-level coating layer on the surface of the Prussian blue particles, so that the Prussian blue exhibits a hydrophobic property. The process is simple and convenient to operate, low in cost, and is very suitable as a coating process for Prussian blue. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the SEM image of PB-4. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0020] Embodiment 1:

[0021] (1) Disperse 10 g of Prussian blue product and 1.67 g of CNT glue (solid content 6%) in 60 mL of ethanol.

[0022] (2) Add 0.2 g of a hydrophobic aluminate coupling agent, heat the dispersion system to 60° C., and stir for 1 hour. The hydrophobic aluminate coupling agent was purchased from Nanjing Nengde New Materials Co., Ltd., model ACA-K30.

[0023] (3) The dispersed system was stirred and cooled at room temperature, and the lower precipitate was collected after centrifugation and recorded as PB-1.

[0024] Embodiment 2:

[0025] (1) Disperse 10 g of Prussian blue product and 1.67 g of CNT glue (solid content 6%) in 60 mL of NMP.

[0026] (2) Add 0.2 g of a hydrophobic aluminate coupling agent, heat the dispersion system to 60° C., and stir for 1 hour.

[0027] (3) The dispersed system was stirred and cooled at room temperature, and the lower precipitate was collected after centrifugation and recorded as PB-2.

[0028] Embodiment 3:

[0029] (1) Disperse 10 g of Prussian blue product and 0.1 g of conductive carbon black SUPER P in 60 mL of ethanol.

[0030] (2) Add 0.2 g of a hydrophobic aluminate coupling agent, heat the dispersion system to 60° C., and stir for 1 hour.

[0031] (3) The dispersed system was stirred and cooled at room temperature, and the lower precipitate was collected after centrifugation and recorded as PB-3.

[0032] Embodiment 4:

[0033] (1) 0.2 g of hydrophobic aluminate coupling agent was dispersed in 60 mL of ethanol.

[0034] (2) The dispersion system was heated to 60°C and stirred for 1 hour to dissolve the hydrophobic aluminate coupling agent.

[0035] (3) Disperse 10 g of Prussian blue finished product and 1.67 g of CNT glue (solid content 6%) in 40 mL of ethanol, pour the ethanol solution of aluminate prepared in (1) into the Prussian blue dispersion, stir for 10 min, centrifuge and collect the lower precipitate, which is recorded as PB-4. Figure 1 shown.

[0036] Embodiment 5:

[0037] (1) 3 g of Prussian blue, 0.1 g of CNT powder and 0.06 g of hydrophobic aluminate coupling agent were ball-milled for 8 hours and recorded as PB-5.

[0038] Comparative Example 1:

[0039] (1) Disperse 10 g of Prussian blue in 60 mL of ethanol.

[0040] (2) The dispersion system was heated to 60°C and stirred for 1 hour.

[0041] (3) The dispersed system was stirred and cooled at room temperature, and the lower precipitate was collected after centrifugation and recorded as PB-6.

[0042] Case Is it hydrophobic? Example 1 yes Example 2 yes Example 3 yes Example 4 yes Example 5 yes Comparative Example 1 no

[0043] Conclusion: Compared with comparative example 1, all five examples have hydrophobic properties, and the particles are dispersed and not easy to agglomerate, while comparative example 1 is dispersed in water and does not have hydrophobic properties. Aluminate is coated on the particle surface at the molecular level, so the amount used is very small, and the coating can be completed by adding about 0.1% to 5%. It can be seen from the SEM image of PB-4 that the conductive carbon material CNT is firmly combined with Prussian blue, which makes it have high stability in subsequent processes, and the hydrophobic aluminate coupling agent is low in price and simple to operate, which can achieve low-cost coating of Prussian blue.

Claims

1. A method for coating Prussian blue with a conductive hydrophobic layer, characterized in that: The method comprises: mixing the conductive carbon material and Prussian blue uniformly, and then adding an aluminate coupling agent; or mixing the conductive carbon material, Prussian blue and the aluminate coupling agent by ball milling.

2. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 1, characterized in that: The conductive carbon material includes one or more combinations of graphene, graphene oxide, redox graphene, graphyne, carbon nanotube CNT, carbon nanotube glue, activated carbon, Ketjen black, acetylene black, conductive carbon black SUPER P, graphite, expanded graphite, fullerene, and amorphous carbon.

3. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 1, characterized in that: The aluminate coupling agent is hydrophobic.

4. A method for coating Prussian blue with a conductive hydrophobic layer according to claim 1 or 3, characterized in that: The added amount of the aluminate coupling agent is 0.1wt.%-5wt.%.

5. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 1, characterized in that: The mixing process uses a liquid phase system or a solid phase system.

6. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 5, characterized in that: The liquid phase system uses a non-aqueous solvent.

7. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 6, characterized in that: The non-aqueous solvent is one or more of ethanol, isopropanol, NMP, glycerol, acetonitrile, acetone, ether, ethyl acetate, NMF, tetrahydrofuran, benzene or carbon tetrachloride.

8. The method for coating Prussian blue with a conductive hydrophobic layer according to claim 1, characterized in that: The mixed system needs to be heated to dissolve or melt the hydrophobic aluminate coupling agent.

9. A sodium ion battery, characterized in that: The positive electrode material of the sodium ion battery is a composite Prussian blue material prepared by the method according to any one of claims 1 to 8.

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