Application of graphite-coated Prussian blue in sodium-ion battery cathode materials

Abstract

This invention discloses a graphite-coated Prussian blue and its analogues, their preparation method, and applications, belonging to the field of graphite material preparation technology. The method includes: mixing graphite with one or more of ferric chloride or transition metal chlorides at a mass ratio of 10-0.5, placing the mixture in a reaction apparatus, and purging the apparatus with a protective gas; heating the reaction apparatus to obtain a solid powder; mixing sodium ferrocyanide with the solid powder at a molar mass ratio of 4-1 and adding it to deionized water, with a solid-to-deionized water mass ratio of 1:50-500, and then stirring the reaction for 12-48 hours; filtering the solution after the reaction. This invention uses a protective gas atmosphere to vaporize ferric chloride or transition metal chlorides at high temperature, allowing the ferric chloride or transition metal to be perfectly incorporated into the interlayer spaces of graphite. Then, the sodium ferrocyanide aqueous solution reacts fully with the ferric chloride or transition metal chloride inside the graphite to obtain a graphite structure completely coated with Prussian blue.

Description

Technical Field

[0001] This invention belongs to the field of graphite material preparation technology, specifically relating to the application of graphite-coated Prussian blue in sodium-ion battery cathode materials. Background Technology

[0002] Sodium-ion batteries, due to their advantages such as abundant sodium resources and low cost, have received increasing research and attention as a replacement for lithium-ion batteries in large-scale energy storage applications. Currently, the main materials used in sodium-ion battery systems include transition metal oxides, polyanionic materials, Prussian blue, and its derivatives. Among these, Prussian blue and its derivatives have become a research hotspot for sodium-ion battery cathode materials due to their high specific capacity, ease of synthesis, and low cost.

[0003] The synthesis methods for iron-based Prussian blue are mainly divided into the single-iron source solution method and the dual-iron source coprecipitation method. The single-iron source solution method is unsuitable for large-scale preparation of iron-based Prussian blue due to the potential release of toxic ions from the addition of acid during the preparation process and its low yield. The dual-iron source coprecipitation method is considered a simple method that can be widely applied to the preparation of iron-based Prussian blue. The classic synthesis process of the dual-iron source coprecipitation method involves adding a transition metal salt solution dropwise to a sodium ferrocyanide solution according to a stoichiometric ratio, initiating a precipitation reaction. The resulting precipitate is washed with deionized water and ethanol, and then collected by centrifugation.

[0004] While the dual-iron source co-precipitation method can yield large quantities of Prussian blue at low temperatures, its poor conductivity and side reactions with organic electrolytes at high voltages result in suboptimal cycle performance as a cathode material in sodium-ion batteries. Prussian blue decomposes above 250°C, and traditional carbon coating methods require high-temperature heat treatment, making them unsuitable. Currently, methods to improve the conductivity of Prussian blue using carbon materials primarily involve mechanically mixing Prussian blue with carbon nanotubes, carbon nanofibers, graphene, etc. Hang Chu et al. embedded Prussian blue into a three-dimensional graphene current collector, and this three-dimensional composite structure exhibited high specific capacity and good cycling performance (Nanoscale, 2018, 10, 14697-14704). Jiahuan Luo et al. used freeze-drying and self-rolling of graphene to encapsulate Prussian blue in graphene, which greatly improved the cycling stability and rate performance of Prussian blue (ACS Appl. Mater. Interfaces 2017, 9, 30, 25317–25322). Although the above methods can improve the conductivity of Prussian blue to some extent, none of them achieve complete carbon encapsulation, and the improvement in conductivity and the suppression of side reactions are limited. Summary of the Invention

[0005] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for preparing graphite-coated Prussian blue and its analogues, so as to solve the problem that the existing preparation methods cannot achieve complete carbon coating of Prussian blue.

[0006] To achieve the above objectives, the present invention provides a method for preparing graphite-coated Prussian blue and its analogues, comprising the following steps:

[0007] S1: Mix one or more of ferric chloride or transition metal chloride with graphite at a mass ratio of 10 to 0.5, place the mixture in a reaction apparatus, and fill the reaction apparatus with a protective gas.

[0008] S2: The reaction apparatus is heated to obtain solid powder;

[0009] S3: Mix sodium ferrocyanide or potassium ferrocyanide with solid powder in a molar mass ratio of 4 to 1, add deionized water, and stir to react for 12 to 48 hours.

[0010] S4: The solution obtained in step S3 is washed and filtered to obtain graphite-coated Prussian blue and its analogues.

[0011] As a further improvement of the present invention, step S5 is also included:

[0012] The powder after cleaning and filtration is then vacuum dried.

[0013] As a further improvement of the present invention, in step S5, the vacuum drying temperature is 80~120℃ and the drying time is 20~24h. After vacuum drying, the powder is also cooled to room temperature.

[0014] As a further improvement of the present invention, the transition metal chloride in step S1 includes one or more of the chlorides of Fe, Co, Mn, Ni or Cu.

[0015] As a further improvement of the present invention, the heating temperature in step S2 is 300~600℃ and the heating time is 12~48h.

[0016] As a further improvement of the present invention, in step S4, deionized water is used for cleaning and filtration, and the cleaning and filtration are performed 3 times or more.

[0017] As a further improvement of the present invention, after cleaning and filtering with deionized water in step S4, the method further includes cleaning and filtering with anhydrous ethanol, and cleaning and filtering with anhydrous ethanol three or more times.

[0018] As a further improvement of the present invention, in step S3, the mass ratio of the solid powder to deionized water is 1:50~500, and the stirring time is 12~48h.

[0019] This application also includes a graphite-coated Prussian blue and its analogue, which is prepared by the above-described method for preparing graphite-coated Prussian blue and its analogue.

[0020] This application also includes the application of graphite-coated Prussian blue and its analogues in sodium-ion battery cathode materials.

[0021] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0022] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include:

[0023] (1) The method for preparing graphite-coated Prussian blue and its analogues of the present invention involves vaporizing ferric chloride or transition metal chloride at high temperature under a protective gas atmosphere, so that ferric chloride or transition metal is perfectly incorporated into the interlayer gaps of graphite. Then, during the contact process between sodium ferrocyanide or potassium ferrocyanide aqueous solution and graphite, some sodium ferrocyanide or potassium ferrocyanide first reacts with ferric chloride or transition metal chloride to generate Prussian blue and increase the interlayer gaps of graphite. This allows sodium ferrocyanide or potassium ferrocyanide to continue reacting with ferric chloride or transition metal chloride in subsequent reactions to generate Prussian blue in graphite, thereby obtaining a graphite structure completely coated with Prussian blue.

[0024] (2) The method for preparing graphite-coated Prussian blue and its analogues of the present invention involves vaporizing and expanding ferric chloride or transition metal chloride at high temperature, thereby generating high temperature and high pressure in a closed reaction device, and then filling the graphite interlayer gaps with the vaporized ferric chloride or transition metal chloride, thus perfectly filling the graphite interlayer gaps with ferric chloride or transition metal chloride.

[0025] (3) The method for preparing graphite-coated Prussian blue and its analogues of the present invention removes ferric chloride or transition metal chloride by washing with deionized water and then washes with anhydrous ethanol to accelerate the drying rate of the powder and improve the yield efficiency of graphite-coated Prussian blue and its analogues.

[0026] (4) The preparation method of this invention adopts a solution method, which is simple, non-toxic, harmless, has high yield, and is suitable for large-scale production. Simultaneously, the prepared graphite-coated Prussian blue and its analogues have fine particles, which, when applied to the positive electrode of sodium-ion batteries, have advantages such as good cycle life and high rate capability. The graphite-coated Prussian blue material in this application not only greatly improves the conductivity of Prussian blue, helping to maximize its capacity and improve cycle rate performance, but the graphite coating also reduces the contact between Prussian blue and the electrolyte, inhibiting the occurrence of side reactions. Attached Figure Description

[0027] Figure 1 This is the XRD pattern of graphite-coated Prussian blue and its analogues in Embodiment 1 of the present invention;

[0028] Figure 2 This is the Raman spectrum of graphite-coated Prussian blue and its analogues in Embodiment 1 of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of graphite-coated Prussian blue and its analogues in Embodiment 1 of the present invention;

[0030] Figure 4 This is a transmission electron microscope image of graphite-coated Prussian blue and its analogues in Embodiment 1 of the present invention;

[0031] Figure 5 This is the first charge-discharge curve obtained by applying graphite-coated Prussian blue and its analogues to a sodium-ion battery in Example 1 of this invention.

[0032] Figure 6 This is the cycle curve obtained by applying graphite-coated Prussian blue and its analogues to a sodium-ion battery in Example 1 of this invention;

[0033] Figure 7 This is the rate curve obtained by applying graphite-coated Prussian blue and its analogues to sodium-ion batteries in Example 1 of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example:

[0036] Please see Figures 1-7 The preferred embodiment of the present invention provides a method for preparing graphite-coated Prussian blue and its analogues, which includes the following steps:

[0037] S1: Mix one or more of ferric chloride or transition metal chloride with graphite at a mass ratio of 10 to 0.5, place the mixture in a reaction apparatus, and fill the reaction apparatus with a protective gas.

[0038] S2: The reaction apparatus is heated to obtain solid powder;

[0039] S3: Mix sodium ferrocyanide or potassium ferrocyanide with solid powder in a molar mass ratio of 4 to 1, add deionized water, and stir to react for 12 to 48 hours.

[0040] S4: The solution obtained in step S3 is washed and filtered to obtain graphite-coated Prussian blue and its analogues.

[0041] The method for preparing graphite-coated Prussian blue and its analogues disclosed in this application involves high-temperature vaporization of ferric chloride or transition metal chlorides under a protective gas atmosphere. This allows the ferric chloride or transition metal to be perfectly incorporated into the interlayer spaces of graphite. Then, an aqueous solution of sodium ferrocyanide or potassium ferrocyanide penetrates the graphite interior and reacts fully with the ferric chloride or transition metal chlorides to obtain a graphite structure completely coated with Prussian blue. The composite material structure prepared using this method exhibits good electrical conductivity, high tap density, and long cycle life when used as a cathode material in sodium-ion batteries, demonstrating significant practical value.

[0042] Specifically, in this application, transition metal chlorides refer to one or more of chlorides such as Fe, Co, Mn, Ni, or Cu. Prussian blue and its analogues are a class of metal-organic frameworks with a simple cubic structure, and their general chemical formula is A2M[M'(CN)6], where A is an alkali metal ion or zeolite water; M / M' is Fe, Co, Mn, Ni, or Cu, etc. In Prussian blue and its analogues, a large space is formed between the metal ion and the -CN- group, which can effectively accommodate alkali metal ions such as Li+, Na+, and K+. Therefore, Prussian blue and its analogues exhibit excellent electrochemical performance in sodium-ion batteries.

[0043] Furthermore, as a preferred embodiment of the present invention, this application also includes step S5: vacuum drying the washed and filtered powder. For the use of graphite-coated Prussian blue and its analogue powders, it is necessary not only to remove excess ferric chloride or transition metal chlorides, but also to dry the product for convenient later use.

[0044] Furthermore, the vacuum drying temperature is between 80 and 120°C, and the drying time is between 20 and 24 hours. This drying temperature and time effectively removes the cleaning liquid remaining from the cleaning and filtration stage. After the vacuum drying is completed, the resulting powder is cooled to room temperature.

[0045] More preferably, in step S2 of this application, the heating temperature is 300~600℃, and the heating time is 12~48h. This application uses an excess of ferric chloride or transition metal chloride, which is vaporized at a high temperature, increasing the internal pressure of the reaction device and forming a high-temperature and high-pressure environment to incorporate ferric chloride or transition metal chloride into the interlayer gaps of graphite.

[0046] Preferably, the reaction apparatus in this application is a stainless steel reactor, and the protective gas is an inert gas, preferably argon.

[0047] Furthermore, as a preferred embodiment of the present invention, deionized water is used for cleaning and filtration in step S4 of this application. The aforementioned ferric chloride or transition metal chloride can be dissolved in deionized water, and excess ferric chloride or transition metal chloride can be removed by using deionized water. Preferably, the number of deionized water cleaning cycles is 3 or more. Under normal circumstances, 3 to 4 cleaning and filtration cycles can remove ferric chloride or transition metal chloride.

[0048] More preferably, after the above-mentioned deionized water washing, anhydrous ethanol can also be used to wash the powder. Anhydrous ethanol has higher volatility than deionized water, which can accelerate the subsequent drying process and increase the preparation efficiency of graphite-coated Prussian blue and its analogues. The number of times the anhydrous ethanol is used for washing is the same as or equivalent to the number of times the deionized water is used for washing and filtration, which is also 3 times or more.

[0049] More preferably, in step S3 of this application, the mass ratio of solid powder to deionized water is 1:50~500, and the stirring reaction time is 12~48h. Then, the aqueous solution of sodium ferrocyanide or potassium ferrocyanide reacts fully with ferric chloride or transition metal chloride inside the graphite to generate Prussian blue and its analogues in the interlayer gaps of the graphite.

[0050] Furthermore, the present application can use the above preparation method to prepare graphite-coated Prussian blue and its analogues, and apply them to the positive electrode material of sodium-ion batteries, which have the characteristics of good cycle performance and high rate capability.

[0051] In some specific embodiments, the method for preparing graphite-coated Prussian blue includes the following steps:

[0052] S1: Mix ferric chloride or (one or more chlorides of Fe, Co, Mn, Ni, Cu) with graphite at a mass ratio of 10~0.5, place the mixture in a stainless steel reactor, and purge with argon for protection.

[0053] S2: Place the stainless steel reactor from step S1 into a muffle furnace and treat it at 300~600℃ for 12~48h;

[0054] S3: Mix sodium ferrocyanide or potassium ferrocyanide with solid powder in a molar mass ratio of 4 to 1 and add it to deionized water. The mass ratio of solid to deionized water is 1:50 to 500. Then stir and react for 12 to 48 hours.

[0055] S4: Filter the solution from step S3, rinse it three times with deionized water, and then rinse it three times with anhydrous ethanol to obtain graphite-coated Prussian blue and its analogues.

[0056] S5: The product cleaned in step S4 is vacuum dried at a temperature of 80~120℃ for 20~24h, and then cooled to room temperature to obtain graphite-coated Prussian blue powder.

[0057] To better illustrate the preparation method, product, and application of the present invention, the following specific embodiments and comparative examples are provided:

[0058] Example 1:

[0059] S1: Mix 5g of ferric chloride and 0.5g of graphite evenly, place them in a stainless steel reactor, and purge with argon gas for protection.

[0060] S2: Place the reaction vessel from step S1 into a muffle furnace and heat-treat it at 600℃ for 12 hours.

[0061] S3: Add 0.968g of sodium ferrocyanide and 0.1g of the solid powder obtained in step S2 to 53.4g of deionized water, and then stir and react for 12h.

[0062] S4: Filter the solution from step S3, rinse it three times with deionized water, and then rinse it three times with anhydrous ethanol.

[0063] S5: Vacuum dry the product obtained in step S4 at a temperature of 80-120°C for 20 hours, and cool it to room temperature to obtain graphite-coated Prussian blue powder.

[0064] Example 2:

[0065] S1: Mix 5g of ferric chloride and 0.5g of graphite evenly, place them in a stainless steel reactor, and purge with argon gas for protection.

[0066] S2: Place the reaction vessel from step S1 into a muffle furnace and heat-treat it at 300℃ for 48 hours.

[0067] S3: Add 0.968g of potassium ferrocyanide and 0.2g of the solid powder obtained in step S2 to 116.8g of deionized water, and then stir to react for 24h.

[0068] S4: Filter the solution from step S3, rinse it three times with deionized water, and then rinse it three times with anhydrous ethanol.

[0069] S5: Vacuum dry the product obtained in step S4 at a temperature of 80-120°C for 22 hours, and cool it to room temperature to obtain graphite-coated Prussian blue powder.

[0070] Example 3:

[0071] S1: Mix 1g of ferric chloride and 2g of graphite evenly, place them in a stainless steel reactor, and purge with argon gas for protection.

[0072] S2: Place the reaction vessel from step S1 into a muffle furnace and heat-treat it at 600℃ for 48 hours.

[0073] S3: Add 0.968g of sodium ferrocyanide and 0.4g of the solid powder obtained in step S2 to 684g of deionized water, and then stir to react for 48h.

[0074] S4: Filter the solution from step S3, rinse it three times with deionized water, and then rinse it three times with anhydrous ethanol.

[0075] S5: Vacuum dry the product obtained in step S4 at a temperature of 80-120°C for 24 hours, and cool it to room temperature to obtain graphite-coated Prussian blue powder.

[0076] Comparative Example:

[0077] S1: Add 0.968g sodium ferrocyanide, 0.2g ferric chloride and 2g graphite to 116.8g deionized water and stir to react for 24h.

[0078] S2: Filter the solution from step S1, rinse it three times with deionized water, and then rinse it three times with anhydrous ethanol.

[0079] S3: Vacuum dry the product from step S2 at a temperature of 80-120°C for 24 hours, and cool it to room temperature to obtain graphite-coated Prussian blue powder.

[0080] Figure 1 The XRD diffraction pattern of the graphite-coated Prussian blue powder obtained in Example 1 of this application shows that the product is pure Prussian blue (NaxFe[Fe(CN)6]). Figure 2 The image shows the Raman spectrum of graphite-coated Prussian blue powder obtained in Example 1 of this application. The two peaks at 1348 cm⁻¹ and 1580 cm⁻¹ represent the D and G peaks of graphite, respectively, and the two peaks at 2094.5 cm⁻¹ and 2132.3 cm⁻¹ are the two peaks of Prussian blue. Figure 3The image shows a scanning electron microscope (SEM) image of graphite-coated Prussian blue obtained in Example 1 of this application. As can be seen from the image, the graphite-coated Prussian blue consists of micron-sized particles, and no fine Prussian blue particles are visible on the outside of the particles, indicating that the Prussian blue particles are embedded in the inner layer of graphite and are completely coated by graphite. Figure 4 The image shows a transmission electron microscope (TEM) image of graphite-coated Prussian blue obtained in Example 1 of this application. As can be seen from the image, the Prussian blue particles are smaller than 50 nm and are completely coated with graphite.

[0081] Meanwhile, the graphite-coated Prussian blue powder obtained in Example 1 of this application was applied to the positive electrode of a sodium-ion battery for testing, and the results were as follows: Figures 5-7 Experimental data. Figure 5 This is the first charge-discharge curve obtained from testing the graphite-coated Prussian blue powder prepared in Example 1 of this application in a sodium-ion battery. The current density in this experiment was 1C = 170 mA / g. As can be seen from the figure, the specific charge capacity of this material is 106 mAh / g, and the specific discharge capacity is 133.6 mAh / g. Figure 6 The graph shows the cycling curve obtained by testing the graphite-coated Prussian blue powder prepared in Example 1 of this application with a sodium-ion battery. As can be seen from the figure, it has excellent cycling performance as a positive electrode material for sodium-ion batteries. At a current density of 1C (170 mA / g), the capacity retention rate is 93% after 300 cycles. Figure 7 The graph shows the rate performance curves obtained by testing the graphite-coated Prussian blue powder prepared in Example 1 with a sodium-ion battery. As can be seen from the figure, the graphite-coated Prussian blue and its analogues prepared in this application have excellent rate performance as positive electrode materials for sodium-ion batteries. The discharge capacity is 114 mAh / g at a current density of 85 mA / g at 0.5C; and the discharge specific capacity is still maintained at about 91 mAh / g at a high current density of 17000 mA / g at 100C, with a retention rate of 80%.

[0082] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of graphite-coated Prussian blue in the cathode material of sodium-ion batteries, characterized in that, The method for preparing graphite-coated Prussian blue includes the following steps: S1: Mix ferric chloride and graphite in a mass ratio of 10~0.5:1, place them in a sealed reaction apparatus, and fill the reaction apparatus with a protective gas. S2: The reaction apparatus is heated at a temperature of 300~600℃ to obtain solid powder; S3: Mix sodium ferrocyanide or potassium ferrocyanide with solid powder in a molar mass ratio of 4~1:1, add deionized water, and stir to react for 12~48h; S4: The solution obtained in step S3 is washed and filtered to obtain graphite-coated Prussian blue, wherein the Prussian blue particles are smaller than 50 nm and are completely coated with graphite.

2. The application of graphite-coated Prussian blue according to claim 1 in the cathode material of sodium-ion batteries, characterized in that, The method for preparing graphite-coated Prussian blue further includes step S5: The powder after cleaning and filtration is then vacuum dried.

3. The application of graphite-coated Prussian blue according to claim 2 in the cathode material of sodium-ion batteries, characterized in that, In step S5, the vacuum drying temperature is 80~120℃ and the drying time is 20~24h. After vacuum drying, the powder is also cooled to room temperature.

4. The application of graphite-coated Prussian blue according to claim 1 in the cathode material of sodium-ion batteries, characterized in that, The heating treatment time in step S2 is 12~48h.

5. The application of graphite-coated Prussian blue according to claim 1 in the cathode material of sodium-ion batteries, characterized in that, In step S4, deionized water is used for cleaning and filtration, and the cleaning and filtration are performed more than 3 times.

6. The application of graphite-coated Prussian blue according to claim 5 in the cathode material of sodium-ion batteries, characterized in that, In step S4, after cleaning and filtering with deionized water, the process further includes cleaning and filtering with anhydrous ethanol, and the anhydrous ethanol is used for cleaning and filtering more than 3 times.

7. The application of graphite-coated Prussian blue according to claim 1 in the cathode material of sodium-ion batteries, characterized in that, In step S3, the mass ratio of the solid powder to deionized water is 1:50~500.

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