A method of heat-induced conversion to prepare a prussian blue analog composite material and its potassium storage application

Abstract

The application discloses a method for preparing a Prussian blue analog composite material by using a heat-induced in-situ transformation strategy. The method refines Prussian blue analog crystal grains by introducing a layered MXene and using a directional freezing method, and the morphology of the synthesized composite material MXene@PBA@NSC is that Prussian blue nanocubes with a size of about 70nm are embedded in nitrogen-sulfur doped porous carbon and layered MXene. The unique structure has remarkable advantages, wherein the nanoscale Prussian blue analog significantly shortens the transmission distance of potassium ions, promotes the fast reaction kinetics, and meanwhile, the solid carbon skeleton and MXene nanosheet improve the structural stability of the electrode, prevent the aggregation of active Prussian blue analog particles, and significantly improve the rate performance of the potassium ion battery. In addition, the MXene@PBA@NSC composite structure provides a rich active interface, strengthens the charge transfer, and improves the potassium storage capacity. Benefited from the advantages, the MXene@PBA@NSC negative electrode shows excellent rate characteristics and long cycle stability, and fully demonstrates the possibility as a negative electrode material of a potassium ion battery. The application provides an efficient synthesis route for the synthesis of the Prussian blue analog.

Description

Technical Field

[0001] This invention belongs to the field of chemical energy materials. It proposes a thermally induced in-situ conversion strategy to synthesize Prussian blue analogues, while simultaneously achieving co-coating of layered MXene and nitrogen- and sulfur-doped porous carbon. This is of great significance for the development of potassium-ion batteries and other related energy storage devices. Background Technology

[0002] With the rapid growth in market demand for portable electronic devices, the design and development of low-cost, high-performance, environmentally friendly, and resource-rich rechargeable batteries is crucial. Potassium-ion batteries have emerged as a competitive alternative to lithium-ion batteries due to the potential cost advantages and good redox potential of potassium compounds. However, compared to Li... + In comparison, the larger K + High lattice strain is generated during the insertion / extraction process, leading to increased potential hysteresis and sluggish ion transport kinetics. Therefore, it is imperative to design and fabricate innovative electrode materials with cost advantages, minimal strain, and fast transport kinetics, which is crucial for achieving reversible storage of large amounts of potassium ions.

[0003] Prussian blue analogues (PBAs) have attracted widespread attention as host materials for reversible insertion / extraction of alkali ions due to their tunable elemental composition and open-framework structure, demonstrating their potential application as anode materials for potassium-ion batteries. However, a critical problem with PBAs as anode materials for potassium-ion batteries is their low intrinsic conductivity, which makes it difficult to achieve high capacity at high current densities. In particular, when a large number of potassium ions are inserted / extracted, severe volume changes can lead to pulverization of the anode material. To alleviate the problem of poor conductivity, two typical approaches have been widely accepted. The first is to shrink the electrode material to the nanoscale. In this case, using nanoscale PBAs can shorten the ion transport distance, enhance reaction kinetics, and improve the utilization rate and structural stability of active materials within the electrode material. The second effective strategy is to construct hybrid electrodes. Encapsulating nanoscale Prussian blue analogues in a conductive matrix is ​​expected to synergistically improve potassium storage performance. Therefore, there is an urgent need to develop small-sized Prussian blue analogue-conductive matrix composites with excellent cycle stability. However, this strategy still faces challenges that need to be addressed. Traditional synthesis methods for PBA composites require multiple steps, namely, first synthesizing pure PBAs through co-precipitation / hydrothermal methods, and then combining them with conductive materials through other methods. There is a lack of a one-step method for synthesizing composite structures.

[0004] Therefore, this invention proposes a one-step thermally induced in-situ conversion method to synthesize a Prussian blue analogue composite material for use as a potassium-ion battery anode. Furthermore, layered MXene is introduced, supplemented by a directional freezing method to refine the grain size, while simultaneously achieving complete coating of the Prussian blue analogue. MXene and the nitrogen-sulfur co-doped carbon framework significantly improve the structural stability of the electrode and prevent the aggregation of active PBA particles. At the same time, the nanoscale PBA synthesized by thermally induced in-situ conversion significantly shortens the potassium ion transport distance, promoting rapid reaction kinetics. In addition, the MXene@PBA@NSC composite material provides abundant active interfaces, enhances charge transfer, and improves potassium storage capacity, showing great potential in practical energy storage devices. Summary of the Invention

[0005] The purpose of this invention is to propose a universal synthetic route for Prussian blue analogues and embed them in a nitrogen-sulfur co-doped porous carbon framework to construct a high-performance potassium-ion battery anode material.

[0006] In a first aspect, an embodiment of the present invention provides an MXene@PBA@NSC composite material, comprising MXene and nitrogen-sulfur co-doped porous carbon, and nano-sized Prussian blue analogue cubic particles, wherein the Prussian blue analogue nanocubes are uniformly encapsulated by an MXene and nitrogen-sulfur co-doped porous carbon network, and the size of the Prussian blue analogue nanocubes is approximately 70 nm.

[0007] Secondly, an embodiment of the present invention provides a method for preparing MXene@PBA@NSC composite material, comprising the following steps: (1) Add methylcellulose, sodium bicarbonate, metal salt and thiourea to deionized water and stir evenly to form a mixed system. In addition, layered MXene is introduced and ultrasonically dispersed evenly. (2) The mixture was placed in liquid nitrogen for directional freezing, and the resulting solid phase was collected and freeze-dried to form a biomineralization precursor. This biomineralization precursor was carbonized in a tube furnace, and after washing away the template and drying, MXene@PBA@NSC was obtained.

[0008] Preferably, in step (1), the metal salt is any one, two or more of iron salt, cobalt salt, nickel salt, manganese salt, and copper salt, and the type of metal salt is nitrate, chloride, sulfate, or acetate.

[0009] Preferably, in step (1), the ratio of methylcellulose to metal salt is 10:1 to 0.5:1, and the ratio of sodium bicarbonate to thiourea is 20:0 to 0:20.

[0010] Preferably, in step (1), the amount of layered MXene used is 0-500 mg.

[0011] Preferably, in step (2), the carbonization temperature is 600-1200 degrees Celsius; the carbonization holding time is 0-10 hours; and the carbonization atmosphere is nitrogen or argon.

[0012] Thirdly, the present invention provides a potassium-ion battery anode material prepared using the MXene@PBA@NSC composite material described in the second aspect.

[0013] Fourth aspect: The present invention provides a hybrid potassium-ion capacitor, wherein the potassium-ion battery electrode material described in the third aspect is used as the negative electrode and activated carbon is used as the positive electrode.

[0014] This invention provides a readily synthesizable MXene@PBA@NSC composite material for use as a potassium-ion battery anode. The advantage of this invention lies in the one-step high-temperature synthesis of a Prussian blue analog composite material. Utilizing nanoscale Prussian blue analogs with an open-framework structure as host materials for reversible potassium ion insertion / extraction, the nanoscale PBA significantly shortens the potassium ion transport distance, promoting rapid reaction kinetics. Simultaneously, the coating of MXene and nitrogen-sulfur co-doped porous carbon frameworks improves the stability of the electrode structure and prevents the aggregation of active PBA particles. Furthermore, the MXene@PBA@NSC composite material provides abundant active interfaces, greatly enhancing charge transfer and improving potassium storage capacity. Thanks to these advantages, the MXene@PBA@NSC anode exhibits excellent rate characteristics and superior long-cycle stability, demonstrating its application potential as a potassium-ion battery anode material. This invention features a simple and economical process, synthesizing the Prussian blue analog composite material in a one-step high-temperature process via thermally induced in-situ conversion, meeting the requirements of simplified synthesis. Attached Figure Description

[0015] Figure 1 The X-ray diffraction pattern of the sample prepared in Example 1.

[0016] Figure 2 The X-ray diffraction pattern of the sample prepared in Example 2.

[0017] Figure 3 The image shown is a scanning electron microscope (SEM) image of the sample prepared in Example 1.

[0018] Figure 4 The image shown is a scanning electron microscope image of the sample prepared in Example 2.

[0019] Figure 5 The image shown is a transmission electron microscope (TEM) image of the sample prepared in Example 1.

[0020] Figure 6 The image shown is a transmission electron microscope (TEM) image of the sample prepared in Example 2.

[0021] Figure 7 The nitrogen adsorption-desorption curves are for the samples prepared in Examples 1 and 2.

[0022] Figure 8 Rate performance diagrams of the samples prepared in Examples 1 and 2 as negative electrodes of potassium-ion batteries.

[0023] Figure 9 The image shows the long-cycle performance of the sample prepared in Example 1 as the negative electrode of a potassium-ion battery.

[0024] Figure 10 The charge-discharge curve of the sample prepared in Example 1 as the negative electrode of the mixed potassium ion capacitor is shown. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings. The embodiments described below are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the technical principles of the present invention should be included within the protection scope of the present invention. Example 1

[0026] (1) Preparation of MXene and nitrogen-sulfur-doped carbon-coated Prussian blue analogue composite material: 2 g methylcellulose and 2 g thiourea were added to 100 ml deionized water and stirred until completely dissolved. Then, two different metal salts, 0.3 g ferric nitrate nonahydrate and 0.45 g cobalt nitrate hexahydrate, were added and completely dissolved. 5 g sodium bicarbonate was added and dispersed evenly. Then, 50 mg MXene was added and ultrasonically dispersed for 2 h. The uniformly mixed solution was placed in liquid nitrogen and directionally frozen for 1 h. The resulting solid phase was collected and freeze-dried to form a biomineralization precursor. The precursor was placed in a tube furnace and heated at 3 °C for 1 min under an Ar atmosphere. -1 The temperature was increased to 800 °C and held for 2 h. After cooling to room temperature, the mixture was washed with 2 M HCl and dried to obtain the composite material MXene@CoFe PBA@NSC, which is co-coated with MXene and nitrogen-sulfur-doped porous carbon as a Prussian blue analog.

[0027] (2) Assembly of potassium-ion half-cells: The above-mentioned composite material MXene@CoFe PBA@NSC was mixed with Super P and CMC binder at a mass ratio of 75:15:10. An appropriate amount of solvent (the volume ratio of alcohol to deionized water was 1:3) was added and the mixture was thoroughly ground to form a uniform slurry. This slurry was coated onto copper foil and dried in an oven at 80 °C for 12 h. Then, it was cut into electrode discs using a slicer. The potassium-ion half-cells were assembled in an argon-filled glove box. The electrode discs prepared above were used as the negative electrode, potassium foil as the counter electrode, 1.5 M KFSI as the electrolyte, and glass fiber as the separator.

[0028] (3) Assembly of the mixed potassium ion capacitor: The electrode sheet obtained by three cycles of pre-charge and discharge of the negative electrode prepared in Example 1 (2) was used as the negative electrode of the mixed potassium ion capacitor. Activated carbon, Super P, and CMC binder were mixed at a mass ratio of 75:15:10, and an appropriate amount of solvent (the volume ratio of alcohol to deionized water was 1:3) was added and ground thoroughly to form a uniform slurry. The slurry was coated on aluminum foil, dried in an oven at 80 °C for 12 h, and then cut into electrode discs on a slicer. The electrode sheet prepared above was used as the positive electrode of the mixed potassium ion capacitor. Assembly was carried out in an argon-filled glove box, with 1.5 M KFSI as the electrolyte, glass fiber as the separator, and the mass ratio of MXene@CoFe PBA@NSC and activated carbon being 1:1 to prepare the mixed potassium ion capacitor. Example 2

[0029] The preparation process of the nitrogen-sulfur doped carbon-coated Prussian blue analog composite material is similar to the steps in Example 1 (1), except that MXene is not added, resulting in the nitrogen-sulfur doped carbon-coated Prussian blue analog composite material CoFe PBA@NSC. The assembly method of the potassium ion half-cell is the same as that in Example 1 (2).

[0030] The following describes the morphological characterization and electrochemical performance testing of embodiments of the present invention.

[0031] Figure 1 The X-ray diffraction (XRD) pattern of Example 1 is shown, which proves that the CoFe PBA composite material co-coated with MXene and nitrogen-sulfur-doped carbon was synthesized. The broad peak at 7.3° corresponds to the phase of MXene; a broad camel peak belonging to carbon was observed at around 21.6°, which proves the presence of nitrogen-sulfur-doped carbon; the main diffraction peaks at 17.2°, 24.4°, 34.8° and 39.1° correspond to the (200), (220), (400) and (420) crystal planes of Co3[Fe(CN)6]2‧H2O.

[0032] Figure 2The XRD pattern of Example 2 is shown, which proves that the nitrogen-sulfur-doped carbon-coated CoFe PBA composite material was synthesized. A broad peak belonging to carbon was observed at around 21.6°, which proves the presence of nitrogen-sulfur-doped carbon. The main diffraction peaks at 17.2°, 24.4°, 34.8° and 39.1° correspond to the (200), (220), (400) and (420) crystal planes of Co3[Fe(CN)6]2‧H2O.

[0033] Figure 3 The image shown is a scanning electron microscope (SEM) image of Example 1. The SEM image shows that the MXene@CoFe PBA@NSC composite material exhibits an interconnected layered porous structure. At the same time, no obvious CoFe PBA particles were observed on the surface, indicating that MXene and nitrogen-sulfur-doped carbon have achieved complete encapsulation of CoFe PBA.

[0034] Figure 4 The image shown is a SEM image of Example 2. As can be seen from the image, the nitrogen-sulfur doped carbon layer also completely encapsulates the CoFe PBA particles.

[0035] Figure 5 The image shown is a transmission electron microscope (TEM) image of Example 1. It can be seen from the image that the size of the CoFe PBA particles is about 70 nm, and the CoFe PBA nanocubes are tightly coated in the carbon matrix. The reduction in the size of the CoFe PBA nanocube particles proves that the addition of MXene has the effect of refining the grain size.

[0036] Figure 6 The image shown is a TEM image of Example 2. It can be seen from the image that the size of the CoFe PBA particles is about 100 nm. Similarly, the Prussian blue analog nanocube particles are completely coated with carbon matrix.

[0037] Figure 7 The figure shows a comparison of nitrogen adsorption-desorption curves for Examples 1 and 2. It can be observed that the specific surface area of ​​the MXene@CoFePBA@NSC composite electrode material is 917 m². 2 g -1 Higher than CoFe PBA@NSC (772 m 2 g -1 This indicates that the introduction of MXene increased the specific surface area of ​​the composite material. Simultaneously, the porous structure of the composite material increased the effective contact area with the electrolyte, mitigating the volume expansion of the electrode material during cycling.

[0038] Figure 8The figure shows a comparison of the rate performance of Examples 1 and 2 in potassium-ion batteries. It can be seen that the specific capacity did not increase significantly at low current density after the introduction of MXene, but the specific capacity of the MXene@CoFe PBA@NSC composite material was significantly improved compared with CoFe PBA@NSC at high current density. This indicates that the capacity contribution of MXene is not significant, but mainly improves the conductivity and stability of the electrode structure, so that MXene@CoFe PBA@NSC exhibits better rate performance.

[0039] Figure 9 The image shows the long-cycle performance test of Example 1 in a potassium-ion battery. It can be seen that the MXene@CoFePBA@NSC electrode material achieves good performance at 5A g. -1 It exhibits excellent long-cycle performance at low current densities, with an average capacity decay of only 0.033% per cycle during 2000 cycles, and still retains 167 mAh g⁻¹ at the end of the cycle. -1 Specific capacity.

[0040] Figure 10 The charge-discharge curves of Example 1 in a potassium-ion hybrid capacitor were shown, tested over a voltage range of 0 to 4.0 V. The MXene@CoFe PBA@NSC / / AC potassium-ion hybrid capacitor was tested at a power density of 345 W / kg. -1 It showed 121 Wh kg at that time -1 High energy density. Even at 8583 W kg -1 At high power densities, this potassium-ion hybrid capacitor can still maintain 61 Wh / kg. -1 Energy density.

[0041] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Many specific details have been set forth in the foregoing description to provide a thorough understanding of the invention; however, the invention may also be practiced in other ways different from those described herein. Therefore, the invention is not limited to the embodiments shown herein, but has the broadest scope corresponding to the principles and novel features disclosed herein.

Claims

1. A method for preparing a Prussian blue analog composite material using a heat-induced in situ transformation strategy, characterized by The steps are as follows: (1) Add methylcellulose, sodium bicarbonate, metal salt and thiourea to deionized water and stir evenly to form a mixed system. In addition, layered MXene is introduced and ultrasonically dispersed evenly. The metal salt is any one, two or more of iron salt, cobalt salt, nickel salt, manganese salt and copper salt. (2) The mixed system is placed in liquid nitrogen for directional freezing, the generated solid phase is collected and freeze-dried to form a biomineralization precursor; this biomineralization precursor is placed in a tube furnace for carbonization, the template is washed away and dried to obtain MXene@PBA@NSC.

2. The method for preparing Prussian blue analogue composite materials according to claim 1, characterized in that: In step (1), the types of metal salts are nitrates, chlorides, sulfates, and acetates.

3. The method for preparing Prussian blue analogue composite materials according to claim 1, characterized in that: In step (1), the ratio of methylcellulose to metal salt is 10:1 to 0.5:1, and the ratio of sodium bicarbonate to thiourea is 20:0 to 0:

20.

4. The method for preparing Prussian blue analogue composite materials according to claim 1, characterized in that: In step (1), the amount of the layered MXene used is 0-500 mg.

5. The method for preparing Prussian blue analogue composite materials according to claim 1, characterized in that: In step (2), the carbonization temperature is 600-1200 degrees Celsius; the carbonization holding time is 0-10 hours; and the carbonization atmosphere is nitrogen or argon.

6. The application of the Prussian blue analog composite material prepared by the method of any one of claims 1-5 in potassium-ion battery electrode materials or mixed potassium-ion capacitor electrode materials.

7. The application according to claim 6, characterized in that... The negative electrode of the potassium-ion battery is made of the Prussian blue analogue composite material, and metallic potassium is used as the counter electrode in the assembly.

8. The application according to claim 6, characterized in that... The negative electrode of the hybrid potassium ion capacitor is made of the Prussian blue analogue composite material, and activated carbon is used as the positive electrode in the assembly.

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