Entropy-driven Prussian blue positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery positive electrode materials, in particular to an entropy-driven Prussian blue positive electrode material and a preparation method and application thereof. A chemical general formula of the entropy-driven Prussian blue positive electrode material is NaxM1 [M2 (CN) 6] y.-1-y.nH2O,-represents vacancy caused by deficiency of M2 (CN) 6 in Prussian blue, M1 and M2 are five transition metal elements selected from Fe, Mn, Co, Ni and Cu, and the entropy-driven Prussian blue positive electrode material realizes uniform distribution of multiple transition metal elements through an entropy-driven strategy, the configuration entropy of the entropy-driven Prussian blue positive electrode material is greater than or equal to 1.5 R (R is a gas constant). Through an entropy driving strategy and fine process control, the electrochemical performance and cycling stability of the Prussian blue positive electrode material are remarkably improved, and a new thought and method are provided for research and development of the sodium ion battery positive electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of cathode materials for sodium-ion batteries, and particularly relates to an entropy-driven Prussian blue cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] At present, lithium-ion batteries, as the most commercially developed and widely used energy storage technology, are facing bottlenecks due to the limited reserves of lithium elements in the earth's crust. Since sodium is similar in properties to lithium and sodium resources are abundant, sodium-ion batteries have become a current research hotspot.

[0003] However, due to the deficiencies in the energy density and cycle stability of existing sodium-ion battery cathode materials compared with lithium-ion battery cathode materials, the commercial application prospects of sodium-ion batteries are limited. Therefore, developing new high-performance cathode materials has become the key to improving the performance of sodium-ion batteries and promoting their commercialization.

[0004] The entropy-driven strategy refers to forming a single-phase solid solution with high configurational entropy by introducing multiple transition metal elements, and using the entropy increase effect to stabilize the material structure, reduce the Gibbs free energy, thereby suppressing phase transformation and lattice distortion.

[0005] In recent years, the entropy-driven strategy has demonstrated the ability to improve the energy density and cycle stability in the field of cathode materials, and is expected to electrochemically regulate and optimize sodium-ion battery cathode materials by introducing multiple metal cations.

[0006] The characteristics of entropy-driven materials include: (1) Thermodynamic entropy effect, stabilizing the single-phase structure through high configurational entropy; (2) Lattice distortion effect, multiple elements occupying lattice sites resulting in reduced symmetry; (3) Retarded diffusion effect, slowing down the ion migration rate; (4) 'Cocktail effect', integrating the superior properties of each element.

[0007] The thermodynamic stability of the crystal phase is related to the Gibbs free energy (ΔG_mix). According to the Gibbs-Helmholtz equation, it can be inferred that when the material has a large entropy value, it will spontaneously transform into a single-phase solid solution. Experiments have shown that the temperature required for the transformation of a five-component high-entropy oxide into a single-phase solid solution is lower than that required for the transformation of a four-component medium-entropy oxide into a single-phase solid solution. This proves from the side that entropy-driven materials have thermodynamic stability (entropy stability).

[0008] Since entropy-driven materials have multiple "equivalent" cations, different elements with different atomic radii, coordination environments, and bond energies occupy symmetric sites within the same lattice of the material. Subsequently, the lattice changes from a symmetric regular shape to a distorted one, and there is an asymmetry in the spatial arrangement between adjacent atoms. This lattice distortion caused by the entropy-driven strategy is called the lattice distortion effect of the entropy-driven strategy. This effect can further affect the total free energy of the material by influencing the lattice structure, and then manifest as an impact on properties such as the electrical conductivity, thermal conductivity, and ion transport efficiency of the material. The latter is also known as the retarded diffusion effect of the entropy-driven strategy in kinetics.

[0009] The "cocktail" effect in performance, simply put, is that due to the presence of multiple "equivalent" elements in entropy-driven materials and the significant differences in the properties and performances between different elements, the material can exhibit the effect of combining the advantages of each element in terms of performance. For example, in Prussian blue, iron elements usually exhibit electrochemical activity, and iron-based Prussian blue generally shows a relatively high capacity and poor cycle stability. Nickel is usually an electrochemically inert element in Prussian blue, and nickel-based Prussian blue generally shows a relatively low capacity and good cycle stability. However, nickel-iron binary Prussian blue can retain the high capacity of iron-based Prussian blue and the excellent cycle stability of nickel-based Prussian blue. In addition, the characteristic that entropy-driven materials can accommodate multiple "equivalent" elements simultaneously also gives them a broader functional design space and application prospects, and makes the fine regulation of their properties a reality.

[0010] Currently, in academia and practical commercial applications, the cathode materials for sodium-ion batteries mainly include four categories: Prussian blue, transition metal oxides, polyanion compounds, and organic compounds, each with its own advantages and disadvantages. Among them, as the cathode material for sodium-ion batteries, compared with other materials, Prussian blue usually has the advantages of being non-toxic and harmless, having a simple preparation process, low cost, relatively high reversible sodium storage capacity (the maximum theoretical specific capacity is about 170 mAh / g), large lattice gaps, three-dimensional open frameworks, and stability. It is considered a promising intercalation-type cathode material for sodium-ion batteries. Generally, the co-precipitation method is the preferred method for synthesizing Prussian blue. However, due to the too-fast reaction rate between cyanide and transition metal ions in the co-precipitation method, there will be a large number of vacancies in the lattice of Prussian blue synthesized by this method. These vacancies not only damage the integrity of the material lattice, thereby reducing its sodium storage capacity, structural stability, and electron conduction process, but also provide storage space for interstitial water and crystal water. In addition to reacting with Na +In addition to competing interstitial spaces and increasing the migration energy barrier in the lattice, during the cycling process, water molecules may also escape into the electrolyte and cause side reactions, further affecting the cycling stability and safety of the battery. Moreover, with the development of the times, people's requirements for electrode materials are not only getting higher and higher, but also becoming more and more personalized. Traditional Prussian blue cathode materials can no longer meet the needs. Currently, the commercially successful sodium-ion battery cathode materials are mainly of the layered oxide or polyanion compound type. To meet the needs of the development of the times, it is urgent to develop Prussian blue cathode materials with high capacity, high cycling stability and high controllability. Summary of the Invention

[0011] Aiming at the problems of vacancies, interstitial water, low capacity, poor structural stability and reaction kinetics faced by Prussian blue cathode materials for sodium-ion batteries, this application provides an entropy-driven Prussian blue cathode material, its preparation method and application. By utilizing the highly controllable characteristics of Prussian blue, an entropy-driven strategy is introduced to construct an entropy-driven structure. At the same time, the co-precipitation process is precisely controlled to evenly distribute five elements of iron, manganese, cobalt, nickel and copper in the lattice, construct an entropy-driven structure, reduce the number of vacancies and promote diffusion kinetics, and improve the resistance to stress during cycling, thereby obtaining a sodium-ion cathode material with a low number of vacancies and both high capacity and high cycling stability. Specifically, this application improves the co-precipitation method by means of optimizing measures such as comprehensively adding additional sodium salts, adding additional reaction sites (solution A), adding surfactants, controlling the reaction temperature, introducing protective gases, adding antioxidants, and using disodium citrate as a chelating agent. Using ferrous sulfate heptahydrate, manganese sulfate monohydrate, cobalt sulfate heptahydrate, nickel sulfate hexahydrate, copper sulfate pentahydrate as transition metal ion sources and sodium ferrocyanide as a carbon / nitrogen source, an entropy-driven Prussian blue with a low number of vacancies and both high capacity and high cycling stability is prepared for sodium storage in the cathode of sodium-ion batteries.

[0012] In the first aspect, this application provides an entropy-driven Prussian blue cathode material, adopting the following technical solution: An entropy-driven Prussian blue cathode material, whose chemical general formula is Na x M1[M2(CN)6] y ·□ 1-y ·nH2O, where □ represents the vacancy in Prussian blue caused by the absence of M2(CN)6, M1 and M2 are five transition metal elements selected from Fe, Mn, Co, Ni, Cu, and the entropy-driven Prussian blue cathode material realizes the uniform distribution of multiple transition metal elements through the entropy-driven strategy, and the configurational entropy of the entropy-driven Prussian blue cathode material ≥ 1.5R (R is the gas constant).

[0013] By adopting the above technical solution, the uniform distribution of various transition metal elements is achieved through the entropy-driven strategy, reducing the defects and inhomogeneity inside the material. This uniform distribution helps to improve the structural stability of the material, thereby reducing the risk of stress concentration and material rupture during the cycling process. The entropy-driven structure helps to improve the diffusion kinetics of sodium ions inside the material. This means that the migration speed of sodium ions is faster during charge and discharge, thus improving the charge-discharge efficiency and power performance of the battery. By precisely controlling the co-precipitation process, the number of vacancies caused by the absence of M2(CN)6 is reduced. The lower number of vacancies helps to improve the specific capacity and cycling stability of the material. The entropy-driven structure improves the stress resistance of the material during the cycling process, reducing the attenuation of material performance caused by stress. This helps to maintain the long-term stability of the battery. Due to the improved uniformity and stability of the material, the material can provide a higher specific capacity at a higher current density. This is of great significance for improving the energy density of the battery. In summary, the entropy-driven Prussian blue cathode material realizes the improvement of material performance while maintaining good cycling stability and high specific capacity through the entropy-driven strategy and precise preparation method, providing new ideas and methods for the development of cathode materials for sodium-ion batteries.

[0014] Preferably, after the entropy-driven Prussian blue cathode material is cycled 2000 times at a current density of 1.3 A / g, the specific capacity retention rate ≥ 82%, and the Coulomb efficiency ≥ 99.9%.

[0015] In a second aspect, the present application provides a preparation method for an entropy-driven Prussian blue cathode material, adopting the following technical solution: As a general technical concept, the present application also provides the preparation method for the above entropy-driven Prussian blue cathode material, including the following steps: S31. Dissolve the surfactant and sodium chloride in deionized water to form solution A; S32. Dissolve sodium ferrocyanide in deionized water to form solution B; S33. After dissolving the chelating agent in deionized water, sequentially add the antioxidant and transition metal sulfate and stir evenly until completely dissolved to obtain solution C; S34. Under the protection of an inert gas, dropwise add solutions B and C into solution A in an ice bath, control the reaction temperature at 0-5 °C, and stir for 3-5 hours; S35. After standing and aging for 12 h, centrifuge and wash three times alternately with ethanol and deionized water, and then dry in a vacuum oven at 60 °C for 10-15 h to obtain the entropy-driven Prussian blue cathode material.

[0016] By adopting the above technical solution, the preparation of solution A: Dissolve the surfactant and sodium chloride in deionized water to form solution A. The surfactant helps to improve the uniformity and dispersibility of the solution, while sodium chloride serves as a sodium ion source to provide the necessary sodium ions for subsequent electrochemical reactions. The preparation of solution B: Dissolve sodium ferrocyanide in deionized water to form solution B. Sodium ferrocyanide serves as a carbon / nitrogen source to provide the necessary atoms for constructing the lattice structure of Prussian blue. The preparation of solution C: After dissolving the chelating agent in deionized water, successively add the antioxidant and transition metal sulfate and stir evenly until completely dissolved to obtain solution C. The chelating agent helps to stabilize the transition metal ions and prevent them from being oxidized or precipitated in subsequent reactions. The antioxidant protects the material from oxidation during the preparation process. The transition metal sulfate provides a variety of transition metal ion sources, and its uniform distribution is achieved through the entropy-driven strategy. Control of the reaction process: Under the protection of an inert gas, slowly add solutions B and C dropwise to solution A in an ice bath, control the reaction temperature at 0 - 5 °C, and stir for 3 - 5 hours. The key to this step lies in precisely controlling the reaction conditions to ensure the uniform distribution of transition metal ions and the structural stability of the material. At the same time, the low-temperature reaction helps to reduce the occurrence of side reactions and improve the purity and performance of the material. Aging and washing: After standing and aging for 12 hours, centrifuge and wash three times alternately with ethanol and deionized water. This step helps to remove impurities and unreacted raw materials that may be generated during the reaction, while maintaining the structure and performance of the material. Drying: Dry in a vacuum oven at 60 °C for 20 - 28 hours. The drying process ensures that the moisture content of the material is controlled at a low level while maintaining the structural integrity of the material. Through the synergistic effect of the above steps, the prepared entropy-driven Prussian blue cathode material has a low number of vacancies and high cycle stability. At the same time, through the entropy-driven strategy, the uniform distribution of multiple transition metal elements is achieved, reducing the problem of poor stress resistance of the material during the cycling process and improving the electrochemical performance of the material.

[0017] Preferably, in step S31, the surfactant is at least one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium bromide.

[0018] Preferably, in step S33, the chelating agent is trisodium citrate. Trisodium citrate slows down the coprecipitation rate and promotes uniform nucleation by complexing transition metal ions.

[0019] Preferably, in step S33, the antioxidant is one of L-ascorbic acid, mannitol, sorbitol, and distearyl thiodipropionate.

[0020] Preferably, in step S33, the transition metal sulfate includes ferrous sulfate, manganese sulfate, cobalt sulfate, nickel sulfate, and copper sulfate.

[0021] Preferably, in step S34, the inert gas is argon, and it is introduced for 30 minutes before the reaction to completely remove oxygen.

[0022] In a third aspect, the present application provides an application of an entropy-driven Prussian blue cathode material, adopting the following technical solution: As a general technical concept, the present application also provides the above-mentioned entropy-driven Prussian blue cathode material as a cathode material for use in a sodium-ion battery.

[0023] In summary, the present application includes at least one of the following beneficial technical effects: 1. Entropy-driven structure construction: By introducing an entropy-driven strategy, the transition metal elements are evenly distributed in the lattice of Prussian blue, thereby reducing the number of vacancies. This uniform distribution not only improves the structural stability of the material but also promotes the kinetic performance of the electrochemical reaction.

[0024] 2. Improved cycle stability: Due to the construction of the entropy-driven structure, the material can better resist stress changes during the cycling process, thereby improving the cycle stability of the material. This is crucial for the long life and high reliability of sodium-ion batteries.

[0025] 3. High specific capacity: By optimizing various parameters in the co-precipitation method and adding specific components, the prepared entropy-driven Prussian blue cathode material can provide a specific capacity of about 60 mAh g -1 at a current density of 1.3 A g -1 . This high specific capacity is of great significance for improving the energy density of the battery.

[0026] 4. Achievement of a low vacancy number: By precisely controlling the reaction conditions and material composition, a lower vacancy ratio is achieved while maintaining the electrochemical performance of the material. Materials with a low vacancy number usually have better electrochemical performance and stability.

[0027] 5. Excellent electrochemical performance: After 2000 cycles of cycling tests, the entropy-driven Prussian blue cathode material exhibits a capacity retention rate of 82%, showing good cycle stability and high practical application potential. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments are briefly introduced below: Figure 1 SEM images, TEM images, SAED patterns, and EDS spectra of the entropy-driven Prussian blue cathode material EnD-PBA prepared in Example 1; among them, Figures a) and h) are TEM images of EnD-PBA; Figure i) is the SAED pattern of EnD-PBA; Figure j) is the SEM image of EnD-PBA; Figures b) to g) are the EDS spectra of EnD-PBA.

[0029] Figure 2 XRD patterns, thermogravimetric curves, Fourier transform infrared spectra, and Raman spectra of the entropy-driven Prussian blue cathode materials prepared in Example 1 and Comparative Examples 1-5, where a) is the XRD pattern; b) is the thermogravimetric curve; c) is the Fourier transform infrared spectrum; d) is the Raman spectrum.

[0030] Figure 3 XPS spectrum of the entropy-driven Prussian blue cathode material prepared in Example 1; where a) is the full spectrum; b) is the C1s spectrum; c) is the N1s spectrum; d) is the Na1s spectrum; e) is the Fe2p spectrum; f) is the Mn2p spectrum; g) is the Co2p spectrum; h) is the Ni2p spectrum; i) is the Cu2p spectrum.

[0031] Figure 4 Electrochemical performance diagrams of the entropy-driven Prussian blue cathode materials prepared in Example 1 and Comparative Examples 1-5. a) is the CV curve of EnD-PBA at 0.2 - 1.0 mV / s; b) is the linear relationship between log(v) and log(i) of different redox peaks of EnD-PBA; c) is the schematic diagram of pseudocapacitance contribution of EnD-PBA at 1.0 mV / s (blue area); d) is the percentage of pseudocapacitance contribution rate of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), EnD-PBA(-Cu) at different scan rates; e) is the cycling curve of EnD-PBA at 1.5 A / g. Detailed implementation manners

[0032] The following will describe the implementation schemes of the present application in detail with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] Example 1 Preparation of the entropy-driven Prussian blue cathode material EnD-PBA Take an appropriate three-necked flask, denoted as flask A. Use it to measure 100 mL of deionized water (DI water) and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After PVP-K30 is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0034] Take an appropriate round-bottom flask, denoted as flask B. Use it to measure 50 mL of deionized water and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. Denote this solution as solution B.

[0035] Take an appropriate round-bottom flask, denoted as flask C. Use it to measure 50 mL of deionized water and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After trisodium citrate dihydrate is completely dissolved, sequentially weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O), and add them to flask C sequentially after the above drugs are completely dissolved. Denote this solution as solution C.

[0036] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through a silicone hose, and set and introduce an argon gas path.

[0037] Before starting the reaction, continuously introduce argon gas into the device for 30 minutes to completely expel the air in the device. Subsequently, place flask A in an ice bath environment, control the temperature at 3 °C, turn on the peristaltic pump, slowly drip solution B and solution C into solution A, and at the same time, turn on the constant temperature magnetic stirrer and continuously stir slowly under this condition for 3 h. After stirring is completed, continue to introduce argon gas and let flask C stand for aging for 12 h. After aging is completed, remove the supernatant, centrifuge and wash it three times alternately with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60 °C and dry it for 10 h to obtain a blue powder, named EnD-PBA.

[0038] Example 2: Preparation of Entropy-driven Prussian Blue Cathode Material EnD-PBA Take a suitable three-necked flask, denoted as flask A. Measure 100 mL of deionized water (DI water) with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of sodium dodecylbenzenesulfonate and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After the sodium dodecylbenzenesulfonate is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0039] Take a suitable round-bottom flask, denoted as flask B. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. Denote this solution as solution B.

[0040] Take a suitable round-bottom flask, denoted as flask C. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After the trisodium citrate dihydrate is completely dissolved, weigh 0.25 g of mannitol, 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), and 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O) in sequence, and add them to flask C in sequence after the above drugs are completely dissolved. Denote this solution as solution C.

[0041] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through silicone hoses, and set and introduce an argon gas path.

[0042] Before starting the reaction, argon gas was continuously introduced into the device for 30 minutes to completely expel the air in the device. Subsequently, flask A was placed in an ice bath at 0 °C. The peristaltic pump was turned on, and solutions B and C were slowly dropped into solution A. At the same time, the constant-temperature magnetic stirrer was turned on, and slow stirring was continued under these conditions for 5 h. After stirring was completed, argon gas was continuously introduced, and flask C was allowed to stand for aging for 12 h. After aging was completed, the supernatant was removed, centrifuged, and washed alternately with ethanol and DI water three times to obtain a blue precipitate. The above blue precipitate was dried in a vacuum oven at 60 °C for 15 h to obtain a blue powder, named EnD-PBA.

[0043] Example 3 Preparation of Entropy-Driven Prussian Blue Cathode Material EnD-PBA Take an appropriate three-necked flask, denoted as flask A. Measure 100 mL of deionized water (DI water) with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of cetyltrimethylammonium bromide and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After the cetyltrimethylammonium bromide was completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl was completely dissolved. This solution was denoted as solution A.

[0044] Take an appropriate round-bottom flask, denoted as flask B. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. This solution was denoted as solution B.

[0045] Take an appropriate round-bottom flask, denoted as flask C. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After the trisodium citrate dihydrate was completely dissolved, successively weigh 0.25 g of distearyl thiodipropionate, 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O), and add them to flask C successively after the above drugs were completely dissolved. This solution was denoted as solution C.

[0046] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through silicone hoses, and set up and introduce an argon passage.

[0047] Before starting the reaction, continuously introduce argon into the apparatus for 30 minutes to completely expel the air in the apparatus. Subsequently, place flask A in an ice bath at a controlled temperature of 5 °C, turn on the peristaltic pump, and slowly drip solutions B and C into solution A. At the same time, turn on the thermostatic magnetic stirrer and continuously stir slowly under these conditions for 4 h. After stirring is completed, continue to introduce argon and let flask C stand for aging for 12 h. After aging is completed, remove the supernatant, centrifuge, and wash three times alternately with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60 °C and dry for 13 h to obtain a blue powder, named EnD-PBA.

[0048] Preparation of entropy-driven Prussian blue cathode material EnD-PBA(-Fe) in Comparative Example 1 Take a suitable three-necked flask, denoted as flask A, measure 80 mL of deionized water (DI water) with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After PVP-K30 is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0049] Take a suitable round-bottom flask, denoted as flask B, measure 40 mL of deionized water with it and completely wrap it with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. Denote this solution as solution B.

[0050] Take an appropriate round-bottom flask, denoted as flask C, measure 40 mL of deionized water with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After the trisodium citrate dihydrate is completely dissolved, successively weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O), and add them to flask C successively after the above-mentioned drugs are completely dissolved. Denote this solution as solution C.

[0051] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through a silicone hose, and set and introduce an argon gas path.

[0052] Before starting the reaction, continuously introduce argon gas into the device for 30 minutes to completely exhaust the air in the device. Subsequently, place flask A in an ice bath environment, control the temperature at 3 °C, turn on the peristaltic pump, slowly drip solution B and solution C into solution A, and at the same time, turn on the constant-temperature magnetic stirrer and continuously stir slowly under this condition for 3 h. After the stirring is completed, continue to introduce argon gas and let flask C stand for aging for 12 h. After the aging is completed, remove the supernatant, centrifuge and wash it alternately three times with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60 °C and dry it for 10 h to obtain a blue powder, named EnD-PBA(-Fe).

[0053] Preparation of entropy-driven Prussian blue cathode material EnD-PBA(-Mn) in Comparative Example 2 Take an appropriate three-necked flask, denoted as flask A, measure 80 mL of deionized water (DI water) with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After PVP-K30 is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0054] Take an appropriate round-bottom flask, denoted as flask B. Measure 40 mL of deionized water with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm under normal temperature conditions. Denote this solution as solution B.

[0055] Take an appropriate round-bottom flask, denoted as flask C. Measure 40 mL of deionized water with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm under normal temperature conditions. After the trisodium citrate dihydrate is completely dissolved, weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), and 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O) in sequence, and add them to flask C in sequence after the above-mentioned drugs are completely dissolved. Denote this solution as solution C.

[0056] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through a silicone hose, and set and introduce an argon passage.

[0057] Before starting the reaction, continuously introduce argon into the device for 30 minutes to completely exhaust the air in the device. Subsequently, place flask A in an ice bath environment, control the temperature at 3°C, turn on the peristaltic pump, and slowly drip solution B and solution C into solution A. At the same time, turn on the constant-temperature magnetic stirrer and continuously stir slowly under this condition for 3 h. After the stirring is completed, continue to introduce argon and let flask C stand for aging for 12 h. After the aging is completed, remove the supernatant, centrifuge and wash it three times alternately with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60°C and dry it for 10 h to obtain a blue powder, named EnD-PBA(-Mn).

[0058] Preparation of entropy-driven Prussian blue cathode material EnD-PBA(-Co) in Comparative Example 3 Take an appropriate three-necked flask, denoted as flask A. Measure 100 mL of deionized water (DI water) with it and wrap it completely with aluminum foil to ensure that its interior is completely shielded from light. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After PVP-K30 is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0059] Take an appropriate round-bottom flask, denoted as flask B. Measure 50 mL of deionized water with it and wrap it completely with aluminum foil to ensure that its interior is completely shielded from light. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. Denote this solution as solution B.

[0060] Take an appropriate round-bottom flask, denoted as flask C. Measure 50 mL of deionized water with it and wrap it completely with aluminum foil to ensure that its interior is completely shielded from light. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After trisodium citrate dihydrate is completely dissolved, weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), and 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O) in sequence, and add them to flask C in sequence after the above drugs are completely dissolved. Denote this solution as solution C.

[0061] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through silicone hoses, and set and introduce an argon gas path.

[0062] Before starting the reaction, continuously introduce argon gas into the device for 30 minutes to completely expel the air in the device. Subsequently, place flask A in an ice bath environment, control the temperature at 3 °C, turn on the peristaltic pump, and slowly drip solution B and solution C into solution A. At the same time, turn on the constant-temperature magnetic stirrer and continuously stir slowly under this condition for 3 h. After stirring is completed, continue to introduce argon gas and let flask C stand for aging for 12 h. After aging is completed, remove the supernatant, centrifuge and wash it three times alternately with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60 °C and dry it for 10 h to obtain a blue powder, named EnD-PBA(-Co).

[0063] Preparation of Entropy-driven Prussian Blue Cathode Material EnD-PBA(-Ni) for Comparative Example 4 Take a suitable three-necked flask, denoted as flask A. Measure 100 mL of deionized water (DI water) with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm at room temperature. After PVP-K30 is completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl is completely dissolved. Denote this solution as solution A.

[0064] Take a suitable round-bottom flask, denoted as flask B. Measure 50 mL of deionized water with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm at room temperature. Denote this solution as solution B.

[0065] Take a suitable round-bottom flask, denoted as flask C. Measure 50 mL of deionized water with it and wrap it completely with aluminum foil to ensure complete light shielding inside. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm at room temperature. After trisodium citrate dihydrate is completely dissolved, weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), and 0.2497 g of copper sulfate pentahydrate (CuSO4·5H2O) in sequence, and add them to flask C in sequence after the above drugs are completely dissolved. Denote this solution as solution C.

[0066] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through a silicone hose, and set and introduce an argon passage.

[0067] Before starting the reaction, argon was continuously introduced into the apparatus for 30 minutes to completely expel the air in the apparatus. Subsequently, flask A was placed in an ice bath environment with a controlled temperature of 3 °C. The peristaltic pump was turned on, and solutions B and C were slowly dropped into solution A. At the same time, the constant temperature magnetic stirrer was turned on, and stirring was continuously carried out slowly under these conditions for 3 h. After stirring was completed, argon was continuously introduced and flask C was allowed to stand and age for 12 h. After aging was completed, the supernatant was removed, centrifuged, and washed three times alternately with ethanol and DI water to obtain a blue precipitate. The above blue precipitate was placed in a vacuum oven at 60 °C and dried for 10 h to obtain a blue powder, named EnD-PBA(-Ni).

[0068] Comparative Example 5 Preparation of Entropy-Driven Prussian Blue Cathode Material EnD-PBA(-Cu) Take an appropriate three-necked flask, denoted as flask A. Measure 100 mL of deionized water (DI water) with it and completely wrap it with aluminum foil to ensure that its interior is completely light-shielded. Subsequently, weigh 5 g of polyvinylpyrrolidone K30 (PVP-K30) and dissolve it in the deionized water in flask A by stirring at a speed of 300 rpm under normal temperature conditions. After PVP-K30 was completely dissolved, weigh 10 g of NaCl and add it to the above solution and continue stirring until NaCl was completely dissolved. This solution was denoted as solution A.

[0069] Take an appropriate round-bottom flask, denoted as flask B. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure that its interior is completely light-shielded. Subsequently, weigh 3.6304 g of sodium ferrocyanide decahydrate (Na4Fe(CN)6·10H2O) and dissolve it in the deionized water in flask B by stirring at a speed of 300 rpm under normal temperature conditions. This solution was denoted as solution B.

[0070] Take an appropriate round-bottom flask, denoted as flask C. Measure 50 mL of deionized water with it and completely wrap it with aluminum foil to ensure that its interior is completely light-shielded. Subsequently, weigh 7.3525 g of trisodium citrate dihydrate (C6H5Na3O7·2H2O) and dissolve it in the deionized water in flask C by stirring at a speed of 300 rpm under normal temperature conditions. After trisodium citrate dihydrate was completely dissolved, successively weigh 0.25 g of L-ascorbic acid (C6H8O6), 0.2780 g of ferrous sulfate heptahydrate (FeSO4·7H2O), 0.1690 g of manganese sulfate monohydrate (MnSO4·H2O), 0.2811 g of cobalt sulfate heptahydrate (CoSO4·7H2O), 0.2628 g of nickel sulfate hexahydrate (NiSO4·6H2O), and add them to flask C successively after the above drugs were completely dissolved. This solution was denoted as solution C.

[0071] Connect flasks A, B, and C containing the corresponding solutions to a peristaltic pump through a silica hose, and set and introduce an argon passage.

[0072] Before starting the reaction, continuously introduce argon into the device for 30 minutes to completely expel the air in the device. Subsequently, place flask A in an ice bath environment, control the temperature at 3°C, turn on the peristaltic pump, slowly drip solution B and solution C into solution A, and at the same time, turn on the constant temperature magnetic stirrer and continuously stir slowly under this condition for 3 h. After stirring is completed, continue to introduce argon and let flask C stand for aging for 12 h. After aging is completed, remove the supernatant, centrifuge and wash three times alternately with ethanol and DI water to obtain a blue precipitate. Place the above blue precipitate in a vacuum oven at 60°C and dry for 10 h to obtain a blue powder, named EnD-PBA(-Cu).

[0073] Performance detection test 1. Sampling was carried out on the entropy-driven Prussian blue cathode materials prepared in Example 1 Ratio 1 - Comparative Example 5, and they were analyzed by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, and thermogravimetry (TG) respectively. The test results are as Figure 1 、 Figure 2 and Figure 3 shown.

[0074] 2. Preparation and testing methods of the battery The entropy-driven Prussian blue cathode materials prepared in Example 1 Ratio 1 - Comparative Example 5 were respectively made into electrodes and assembled into coin cells.

[0075] (1) Mix the entropy-driven Prussian blue cathode material, conductive agent Super P activated carbon, and binder polyvinylidene fluoride (PVDF) in a ratio of 7:2:1, and add an appropriate amount of N-methylpyrrolidone (NMP) as a solvent, and uniformly mix in a planetary ball mill at a speed of 4000 Hz to obtain a black slurry with moderate viscosity. Use a four-sided spreader to evenly apply the above slurry on one side of the aluminum foil coated with a carbon layer, and the thickness of the slurry application is 100 μm. Subsequently, place the aluminum foil coated with the slurry in a vacuum oven at 80°C and dry for 10 h. Subsequently, use a coin cell punching machine to cut the above aluminum foil into a positive electrode sheet with a diameter of 12 mm. Use a CR2016 type button cell casing. The specific assembly process is as described below: Using a sodium sheet as the reference electrode and the counter electrode, using a 1M sodium perchlorate (NaClO4) solution with dimethyl carbonate (DMC): ethylene carbonate (EC): propylene carbonate (PC) = 1:1:1 (volume ratio) mixed and adding 5% of vinylene carbonate (FEC) by the total solution volume as the electrolyte, and using glass fiber (Whatman, GF / D) as the separator. The assembly order is the positive electrode case, the positive electrode sheet, dropping 50 μL of the electrolyte, the separator, dropping another 50 μL of the electrolyte, the sodium sheet, the gasket, and the negative electrode case. After assembly, a MSK-110 model button cell sealer produced by Hefei Kejing Materials Technology Co., Ltd. is used to press-seal the obtained button cell. After the assembly and sealing are completed, for the prepared button cell, after standing for 12 h, the electrochemical performance test is carried out.

[0076] Electrochemical test methods Galvanostatic charge-discharge test (GCD) The results of the galvanostatic charge-discharge tests were all measured by a CT-4008 model battery test system produced by Shenzhen Neware Electronic Co., Ltd. By performing galvanostatic charge-discharge tests on the button-type half-cells, test information such as the specific capacity of the electrode material, cycle stability (capacity retention rate), Coulombic efficiency, charge-discharge curves, and plateaus was obtained, and then the electrochemical performance of the electrode material was evaluated.

[0077] Cyclic voltammetry (CV) The cyclic voltammograms were all measured by a CHI-760E model electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd. The test voltage window was 2.0 - 4.2 V, and the system used was a three-electrode system. Specifically, the green clip (working electrode) of the electrochemical workstation was clamped on the working electrode side of the assembled button-type half-cell, and the red clip (counter electrode) and the white clip (reference electrode) were clamped on the other side of the battery. In addition, at different scan rates (0.2 - 1.0 mV / s), different cyclic voltammograms of the same battery were measured, and based on this, the pseudocapacitance effect of the electrode material was studied.

[0078] The test results are as Figure 4 shown.

[0079] Figure 1 SEM images, TEM images, SAED patterns, and EDS maps of the entropy-driven Prussian blue positive electrode material EnD-PBA prepared in Example 1; among them, Figures a) and h) are TEM images of EnD-PBA; Figure i) is the SAED pattern of EnD-PBA; Figure j) is the SEM image of EnD-PBA; Figures b) to g) are the EDS spectra of EnD-PBA.

[0080] From Figure 1It can be seen that from Figures a) and h), the morphology of EnD-PBA is a relatively regular cube and is not significantly distorted due to the entropy-driven strategy. Figures b) to g) show the EDS images of EnD-PBA under a transmission electron microscope. From these images, it can be seen that EnD-PBA contains elements such as Na, Fe, Mn, Co, Ni, and Cu, which is consistent with the element types observed by XPS. Moreover, the above elements are evenly distributed inside the material, proving that EnD-PBA conforms to the characteristics of "multiple transition metal elements" and "even distribution" of entropy-driven materials, thus demonstrating that EnD-PBA is an entropy-driven material (high-entropy material). Figure i) is the SAED image of EnD-PBA, from which it can be seen that EnD-PBA is in a state of single crystal tending to polycrystal. Figure j) is the SEM image of EnD-PBA. From this image, it can be found that there is a serious stacking phenomenon in EnD-PBA.

[0081] Figure 2 XRD spectra, thermogravimetric curves, Fourier infrared spectra, and Raman spectra of the entropy-driven Prussian blue cathode materials prepared in Example 1 and Comparative Examples 1-5. Among them, Figure a) is the XRD spectrum; Figure b) is the thermogravimetric curve; Figure c) is the Fourier infrared spectrum; Figure d) is the Raman spectrum.

[0082] From Figure 2 It can be seen that by comparing the XRD spectra of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu) with the data in the database, it is found that except for EnD-PBA(-Cu), the entropy-driven Prussian blues prepared by this application are all cubic phase structures (Cubic) with the Fm-3m space group, and the crystal structure is consistent with the JCPDS No. 83-2293 PDF card, thus confirming the cubic phase structure. Among them, the diffraction peaks of the above products at 2θ = 17.19°, 24.40°, 34.78°, 39.05°, 42.95°, 50.01°, 53.28°, and 56.41° can correspond to the (200), (220), (400), (420), (422), (440), (600), and (620) crystal planes in the PDF card, respectively. Although the XRD pattern of EnD-PBA(-Cu) is consistent with the JCPDS No. 83-2293 PDF card in terms of peak positions, the diffraction peaks at 24.40°, 39.05°, 50.01°, and 56.41° are significantly split, that is, the original single peak becomes a double peak, proving that the crystal structure of the EnD-PBA(-Cu) material is a rhombohedral phase.

[0083] As can be seen from the intercept points of the curves in Figure b) at 170 °C, the residual masses of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu) are 91.5%, 88.1%, 90.9%, 90%, 88.5%, and 92.2% respectively. Among them, the residual mass of EnD-PBA(-Cu) at 170 °C is the highest, at 92.2%, rather than 91.5% of EnD-PBA, proving that EnD-PBA(-Cu) has a more perfect crystal structure than EnD-PBA. At 270 °C, the residual masses of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu) are 82.1%, 79.5%, 81.9%, 79.2%, 80.2%, and 83.6% respectively. Still, the residual mass of EnD-PBA(-Cu) is the largest, and the residual mass of EnD-PBA is the second largest, once again proving the advantage of the entropy-driven strategy.

[0084] The FT-IR spectra of EnD-PBA and EnD-PBA(-M) are shown in Figure c). The strong absorption peak at 2082.9 cm -1 can be attributed to the stretching vibration of C≡N. The absorption peaks at 1619.7 cm -1 and 3422.6 cm -1 can be attributed to the bending and stretching vibrations of H-O-H and H-O of water molecules. The absorption peak at 588.9 cm -1 can be attributed to the bonding of C≡N with Fe, Mn, Co, Ni, and Cu. Through the characterization test of Fourier transform infrared spectroscopy, it can be proved that there is a large amount of interstitial water and crystal water in EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu). At the same time, the transition metal elements and C≡N do bond, and the Prussian blue framework is indeed established.

[0085] Figure d) shows the Raman spectra of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu). Among them, EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), and EnD-PBA(-Cu) mainly show peaks at 2075 cm -1 and 2101 cm -1At 2442 cm -1 There are three broad peaks at this position, all of which can be attributed to the bonding of C≡N with Fe, Mn, Co, Ni, and Cu. This result is consistent with the FT-IR characterization result, demonstrating a good and uniform binding between the transition metal ions and the Prussian blue framework. In addition, it can be found from the Raman spectrum that the peak position of EnD-PBA shifts to a lower wavenumber compared with other entropy-driven Prussian blues, indicating that the crystal structure of EnD-PBA contains more Fe 2+ , and the average valence state of the transition metal ions inside is lower. This shows from another perspective that the application of the entropy-driven strategy to Prussian blue can endow it with better antioxidant ability, which is beneficial to overcoming its disadvantage of being sensitive to oxygen, providing a useful reference for its preparation and commercial application under conventional conditions.

[0086] Figure 3 XPS spectra of the entropy-driven Prussian blue cathode material prepared in Example 1; among them, a) is the full spectrum; b) is the C1s spectrum; c) is the N1s spectrum; d) is the Na1s spectrum; e) is the Fe2p spectrum; f) is the Mn2p spectrum; g) is the Co2p spectrum; h) is the Ni2p spectrum; i) is the Cu2p spectrum.

[0087] From Figure 3 it can be seen that the XPS spectrum of EnD-PBA was measured by a Kratos AXIS Ultra DLD model X-ray photoelectron spectrometer produced by Kratos, UK. As shown in b), since the material contains C element and it is impossible to calibrate based on the peak at the binding energy of C-C / C=C at 284.8 eV, the peak at the binding energy of C=O at 288.7 eV is used as the calibration reference. a) is the XPS full spectrum of EnD-PBA, from which it can be seen that the sample contains 8 main elements including C, N, Na, Fe, Mn, Co, Ni, and Cu, which is consistent with the results of the TEM elemental distribution images of each element. In addition, according to the full spectrum and subsequent fine spectra, EnD-PBA also contains a certain amount of O element, which may be due to the inevitable exposure of the material to air during centrifugal washing and testing. c) is the high-resolution XPS spectrum of the N1s of the material, where the peaks at the binding energies of 397.8 eV and 402.8 eV correspond to N1s and the oxidized N. The peak at the binding energy of 1072 eV in d) corresponds to Na1s. e) shows the high-resolution XPS spectrum of the Fe2p of the material, where the peaks at the binding energies of 708.7 eV, 713 eV, 715.6 eV, and 721.6 eV correspond to Fe2p 3 / 2 , Fe 3+ , Fe 2+ 's (shake-up) satellite peaks, Fe2p 1 / 2, which proves that the iron element in EnD-PBA coexists in the divalent and trivalent states. The high-resolution XPS spectrum of Mn2p in EnD-PBA is shown in Figure f), where the peaks at the binding energies of 641.8 eV and 653.8 eV correspond to Mn2p 3 / 2 and Mn2p 1 / 2 , which proves that the manganese element in EnD-PBA is divalent. Figure g) is the high-resolution XPS spectrum of Co2p of the material. The peaks at the binding energies of 783 eV and 797.6 eV in the figure correspond to Co2p 3 / 2 and Co2p 1 / 2 , and the peaks at the binding energies of 781.2 eV and 789.1 eV indicate that part of the Co in the EnD-PBA material combines with oxygen to form CoO. The peaks at the binding energies of 786 eV and 803 eV are the (oscillatory) satellite peaks of Co 2+ . The above situation shows that the cobalt element in EnD-PBA is divalent. Figure h) shows the high-resolution XPS spectrum of Ni 2p in EnD-PBA, where the peaks at the binding energies of 856.3 eV and 874.1 eV correspond to Ni2p 3 / 2 and Ni2p 1 / 2 , and the peaks at the binding energies of 858.6 eV and 876.2 eV indicate that part of the nickel element is oxidized to trivalent. The peak at the binding energy of 863 eV is the (oscillatory) satellite peak. The high-resolution XPS spectrum of Cu2p in EnD-PBA is shown in Figure i), where the peaks at the binding energies of 935.2 eV and 955.1 eV correspond to Cu2p 3 / 2 and Cu2p 1 / 2 , the peaks at the binding energies of 944 eV and 964 eV are the (oscillatory) satellite peaks, and the peaks at the binding energies of 933 eV and 952.9 eV prove that a large amount of Cu 2+ in the material is reduced to Cu + , which may be due to the use of excessive L-ascorbic acid during the reaction process.

[0088] Figure 4 are the electrochemical performance diagrams of the entropy-driven Prussian blue cathode materials prepared in Example 1 and Comparative Examples 1-5. Figure a) is the CV curve of EnD-PBA at 0.2-1.0 mV / s, and Figure b) is the linear relationship between log(v) and log(i) of different redox peaks of EnD-PBA; Figure c) is the schematic diagram of the pseudocapacitance contribution of EnD-PBA at 1.0 mV / s (blue area); Figure d) is the percentage of the pseudocapacitance contribution rate of EnD-PBA, EnD-PBA(-Fe), EnD-PBA(-Mn), EnD-PBA(-Co), EnD-PBA(-Ni), EnD-PBA(-Cu) at different scan rates; Figure e) is the cycling curve of EnD-PBA at 1.5 A / g.

[0089] From Figure 4It can be seen that a) the figure clearly shows the CV curves of EnD-PBA at 0.2 - 1.0 mV / s. From this, it can be found that the material has relatively clear symmetric peaks, proving its good cyclic reversibility. b) The figure shows the linear relationship between log(i) and log(v) in EnD-PBA. Among them, the fitted b value of Peak 1 is 0.92, and the fitted b value of Peak 2 is 1.08. This result indicates that the sodium storage mechanism of EnD-PBA is mainly dominated by pseudocapacitive control behavior, but still includes some diffusion control behavior. c) and d) The figures illustrate that the pseudocapacitive contribution fractions of the EnD-PBA material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 78.3%, 81.7%, 87.6%, 89.8%, and 94.8% respectively, indicating that the material mainly stores sodium through pseudocapacitive behavior during charge and discharge, and the pseudocapacitive contribution rate increases with the increase of the sweep rate. The high pseudocapacitive contribution rate stems from the surface redox reaction and rapid ion adsorption / desorption promoted by the entropy-driven strategy. In addition, the pseudocapacitive contribution fractions of the EnD-PBA(-Fe) material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 73.9%, 80.1%, 84.8%, 87.4%, and 92.4% respectively; the pseudocapacitive contribution fractions of the EnD-PBA(-Mn) material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 71.3%, 79.6%, 83.8%, 86.1%, and 91.6% respectively; the pseudocapacitive contribution fractions of the EnD-PBA(-Co) material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 76.7%, 83.2%, 87.9%, 91.5%, and 93.9% respectively; the pseudocapacitive contribution fractions of the EnD-PBA(-Ni) material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 81.2%, 86.1%, 89.7%, 93.1%, and 95.3% respectively; the pseudocapacitive contribution fractions of the EnD-PBA(-Cu) material at sweep rates of 0.2, 0.4, 0.6, 0.8, and 1.0 mV / s are 80.2%, 85.8%, 89.1%, 92.2%, and 95.3% respectively. The cyclic performance of EnD-PBA was tested for 2000 cycles at a current density of 1.3 A / g, and the results are shown in e) the figure. The results show that at this current density, EnD-PBA always maintains a relatively gentle specific capacity decay rate, and its cyclic performance curve can be approximated as a straight line. After 2000 charge-discharge cycles, the capacity of EnD-PBA remains at 50.1 mAh / g, and the capacity retention rate is 82.0%, indicating that the EnD-PBA electrode material has excellent long-cycle performance. In addition, during the entire cycle, the average Coulombic efficiency of EnD-PBA is 99.97%, which also shows that the material has excellent cyclic stability from the side.Comparative Examples 1 - 5: Fe, Mn, Co, Ni, and Cu were respectively missing. By excluding transition metal elements one by one, the necessity of the synergistic effect of multiple elements in the entropy-driven strategy was verified.

[0090] In summary, the prepared entropy-driven Prussian blue cathode material was made into the cathode of a sodium-ion battery. A pure sodium sheet was used as the counter electrode and reference electrode, and a CR2016 coin cell was assembled and subjected to electrochemical measurements. The assembled CR2016 coin cell was subjected to constant current charge-discharge tests and cycling tests on a NEWARE battery tester. The tests showed that the entropy-driven Prussian blue cathode material maintained good cycle stability and high specific capacity, obtained a specific capacity of about 60 mAh g-1 at a current density of 1.3 A g-1, and exhibited a capacity retention rate of 82% after 2000 cycles, indicating that the prepared entropy-driven Prussian blue has great potential and advantages among cathode materials with high specific capacity and good cycle stability, and it can be seen that the entropy-driven strategy is effective in improving the specific capacity and cycle stability of cathode materials.

[0091] The above embodiments are only used to explain the technical solutions of the present application and are not intended to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that the specific implementation manners of the present application can still be modified or equivalently replaced. Any modification and equivalent replacement without departing from the spirit and scope of the present application shall be covered by the protection scope of the present application.

Claims

1. An entropy-driven Prussian blue cathode material, characterized in that, Its chemical general formula is Na x M1[M2(CN)6] y ·□ 1-y ·nH2O, where □ represents the vacancy caused by the absence of M2(CN)6 in Prussian blue, M1 and M2 are five transition metal elements selected from Fe, Mn, Co, Ni, and Cu, and the entropy-driven Prussian blue cathode material realizes the uniform distribution of multiple transition metal elements through an entropy-driven strategy, and the configurational entropy of the entropy-driven Prussian blue cathode material ≥ 1.5R (R is the gas constant).

2. The entropy-driven Prussian blue cathode material according to claim 1, characterized in that After cycling 2000 times at a current density of 1.3 A / g, the specific capacity retention rate of the entropy-driven Prussian blue cathode material is ≥82%, and the Coulombic efficiency is ≥99.9%.

3. A preparation method of the entropy-driven Prussian blue cathode material according to any one of claims 1-2, characterized in that, It includes the following steps: S31: Dissolve the surfactant and sodium chloride in deionized water to form solution A; S32: Dissolve sodium ferrocyanide in deionized water to form solution B; S33: After dissolving the chelating agent in deionized water, successively add the antioxidant and transition metal sulfate and stir evenly until completely dissolved to obtain solution C; S34: Under the protection of inert gas, dropwise add solutions B and C into solution A in an ice bath, control the reaction temperature at 0-5°C, and stir for 3-5 hours; S35: After standing and aging for 12 h, centrifuge and wash three times alternately with ethanol and deionized water, and then dry in a vacuum oven at 60°C for 10-15 h to obtain the entropy-driven Prussian blue cathode material.

4. The preparation method of an entropy-driven Prussian blue cathode material according to claim 3, characterized in that, In step S31, the surfactant is at least one of poly(ethylene glycol) pyrrolidone, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium bromide.

5. The preparation method of an entropy-driven Prussian blue cathode material according to claim 3, wherein In step S33, the chelating agent is trisodium citrate.

6. The preparation method of an entropy-driven Prussian blue cathode material according to claim 3, characterized in that, In step S33, the antioxidant is one of L-ascorbic acid, mannitol, sorbitol, and distearyl thiodipropionate.

7. The preparation method of an entropy-driven Prussian blue cathode material according to claim 3, wherein, In step S33, the transition metal sulfate includes ferrous sulfate, manganese sulfate, cobalt sulfate, nickel sulfate, and copper sulfate.

8. The preparation method of an entropy-driven Prussian blue cathode material according to claim 3, characterized in that, In step S34, the inert gas is argon, and it is introduced for 30 minutes before the reaction to completely remove oxygen.

9. Use of an entropy-driven Prussian blue cathode material as described in any one of claims 1-2, characterized in that, The entropy-driven Prussian blue cathode material is used as a cathode material in a sodium-ion battery.

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