Prussian blue analogues with core-shell structure, their preparation methods, and sodium-ion secondary batteries containing them

Abstract

This application relates to a Prussian blue analogue with a core-shell structure, which has a core and a coating layer covering the core. Among them, the chemical formula of the core is as follows in Formula 1, Na x P[R(CN)6] δ ·zH2O Formula 1 where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10. The chemical formula of the coating layer is as follows in Formula 2, A y L[M(CN)6] α ·wH2O Formula 2 where A is an alkali metal or alkaline earth metal element other than sodium, L and M are each independently selected from at least one of transition metal elements, 0

Description

Technical Field

[0001] This application relates to the field of sodium-ion secondary batteries, and more particularly to a Prussian blue analogue with a core-shell structure, a method for preparing the Prussian blue analogue with the core-shell structure, a sodium-ion secondary battery containing the analogue, a battery module, a battery pack, and an electrical device. Background Technology

[0002] In recent years, with the gradual development and application of lithium-ion batteries from portable electronic devices to high-power electric vehicles, large-scale energy storage power stations, and smart grids, the demand for lithium-ion batteries has been increasing. However, limited lithium resources restrict the sustainable development of lithium-ion batteries. Sodium, which belongs to the same group as lithium, has similar chemical properties and is abundant. Therefore, sodium-ion batteries, which work on a similar principle to lithium-ion batteries, are currently being developed, with the expectation that they will serve as an important supplement to lithium-ion batteries in large-scale energy storage applications.

[0003] As a cathode material for sodium-ion secondary batteries, Prussian blue analogues (hereinafter sometimes referred to as PBA) exhibit significant advantages in specific capacity and ion transport due to their unique open-framework crystal structure. The chemical formula of PBA is typically written as Na. x PR(CN)6 (P and R are transition metal elements such as Fe, Co, Ni, and Mn). The transition metal ions P and R, along with -C≡N-, arrange themselves in a PC≡NR configuration to form a three-dimensional cubic framework structure. The transition metal atoms P and R are located at the vertices of the face-centered cubic structure and are connected by -C≡N- atoms located on the edges. Its theoretical specific capacity is close to 170 mAh / g, and its voltage plateau is between 3 and 3.5 V. Simultaneously, the size of the cubic pores is relatively large.

[0004] The directional passage is relatively wide. It is highly conducive to the rapid migration of alkali metal ions with large ionic radii.

[0005] However, existing PBA materials are prone to gradual degradation of electrochemical performance during long-term storage. Therefore, although PBA materials possess a series of commercially viable advantages such as high capacity, high voltage plateau, fast sodium-ion transport channels, low cost, and simple preparation, their difficulty in long-term storage hinders industrial applications. If the degradation of the electrochemical performance of PBA materials during long-term storage can be suppressed, their electrochemical performance and stability could be significantly improved, thereby greatly promoting the application of PBA in sodium-ion secondary batteries.

[0006] Therefore, providing a Prussian blue analogue that is stable during long-term storage is of great significance in the field of sodium-ion secondary batteries. Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] This application is made in view of the above problems, and its purpose is to provide a Prussian blue analogue as a cathode material for sodium-ion secondary batteries. This Prussian blue analogue is not easily deteriorated even after long-term storage, and can still maintain excellent electrochemical properties such as cycling performance, and is suitable for industrial application in sodium-ion secondary batteries.

[0009] The inventors of this application have found through extensive research that the deterioration of the electrochemical properties of PBA materials may be related to the water absorption of PBA materials. There has been a technology in the past to dehydrate PBA materials by vacuum heating. For example, vacuum drying and dehydration of MnFe-PBA at 100 °C for 30 h under a high vacuum of 15 mTorr can reduce the water content of MnFe-PBA to as low as 0.5 wt% (0.08 H2O / f.u.) (Journal of the American Chemical Society, 2015, 137(7): 2658-2664). However, such a dehydration process is time-consuming and costly. Moreover, PBA materials are prone to water absorption. Even if water molecules are removed by high-temperature vacuum, the dehydrated PBA materials are very easy to absorb water again when stored in air, resulting in rapid decay of their electrochemical properties, especially cycling performance, and sodium deposition may occur during charge-discharge cycles.

[0010] Technical solutions for solving the problem

[0011] To achieve the above object, a first aspect of this application provides a Prussian blue analogue having a core-shell structure, which has a core and a coating layer covering the core. Among them,

[0012] The chemical formula of the core is the following formula 1,

[0013] Na x P[R(CN)6] δ ·zH2O Formula 1

[0014] Where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10,

[0015] The chemical formula of the coating layer is the following formula 2,

[0016] A y L[M(CN)6] α ·wH2O Formula 2 [[ID=З7]]

[0017] Where A is an alkali metal or alkaline earth metal element other than sodium, and L and M are each independently selected from at least one of transition metal elements, 0 < y ≤ 2, 0 < α ≤ 1 and 0 ≤ w ≤ 10.

[0018] By using chemical composition A y L[M(CN)6] α A Prussian blue analogue is used as a shell to coat the surface of a sodium-containing Prussian blue analogue. This shell effectively prevents water molecules from entering the core-shell structure, making the PBA material less hygroscopic. This significantly improves the storage stability of the PBA material at room temperature and pressure, substantially reducing the manufacturing cost of subsequent cell layers while enhancing the structural stability of the PBA material, meeting the requirements of sodium-ion secondary batteries. Furthermore, the preparation cost of this core-shell structure PBA material is low.

[0019] In any embodiment, P, R, L, and M are each independently selected from at least one of Fe, Mn, Ni, Co, Cu, and Zn. Therefore, using these transition metal ions ensures the structural integrity of the PBA material while maintaining good electrochemical performance such as electrochemical capacity.

[0020] In any embodiment, A is selected from at least one of Li, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba, and optionally from at least one of K, Rb, Cs, Mg, and Ca, for example, from at least one of K, Rb, and Cs. Thus, by selecting the above-mentioned ion as the A ion, a good blocking effect is achieved on the transport of water molecules.

[0021] In any embodiment, in Formula 1, 0.7 ≤ δ ≤ 1; and / or, in Formulas 1 and 2, x and y are each independently 0.5–2, optionally x and y are each independently 1.5–2. The electrochemical capacity of the material can be improved by selecting high δ and / or x and / or y values.

[0022] In any embodiment, the thickness of the coating layer is less than 100 nm, optionally less than 60 nm, more preferably less than 50 nm, optionally in the range of 5 nm to 40 nm, and even more preferably in the range of 10 nm to 20 nm. If the thickness of the coating layer is within the above-mentioned range, the water barrier effect is sufficient, the electrochemical capacity of the material is not easily reduced, and it is also conducive to the rapid transport of sodium ions.

[0023] In any embodiment, the coating amount is 10% by weight or less, optionally 1% to 5% by weight. If the coating amount is within the above range, the water barrier effect is sufficient, the electrochemical capacity of the material is not easily reduced, and it is also conducive to the rapid transport of sodium ions.

[0024] In any embodiment, the particle size of the Prussian blue analogue is from 100 nm to 50 μm. By selecting the above particle size range, it is helpful to maintain good ion-electron transport properties of the material.

[0025] The second aspect of the present application provides a method for preparing a Prussian blue analogue with a core-shell structure, the method comprising the following steps:

[0026] 1) Add Prussian blue analogue particles to solvent 1 and disperse to obtain a suspension. The chemical formula of the Prussian blue analogue particles is Formula 1 below,

[0027] Na x P[R(CN)6] δ ·zH2O Formula 1

[0028] where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10;

[0029] 2) Dissolve a soluble salt containing transition metal element L in solvent 2 to form solution c;

[0030] 3) Dissolve a soluble salt containing an alkali metal or alkaline earth metal element A other than sodium and a soluble transition metal cyanide complex containing transition metal element M in solvent 3 to form solution d;

[0031] 4) Under stirring, drop solutions c and d into the suspension obtained in step 1), and filter the suspension to obtain a precipitate;

[0032] 5) Wash and dry the precipitate obtained in step 4) to obtain a Prussian blue analogue with a core-shell structure. The Prussian blue analogue with a core-shell structure has a core and a coating layer covering the core. The core is the Prussian blue analogue particles, and the chemical formula of the coating layer is Formula 2 below,

[0033] A y L[M(CN)6] α ·wH2O Formula 2

[0034] where A is an alkali metal or alkaline earth metal element other than sodium, L and M are each independently selected from at least one of transition metal elements, 0 < y ≤ 2, 0 < α ≤ 1 and 0 ≤ w ≤ 10.

[0035] Through the above preparation method, a coating layer with chemical composition A y L[M(CN)6] αUsing a Prussian blue analogue as the outer shell, the method produces a shell that uniformly and completely encapsulates the sodium-containing Prussian blue analogue particles. This effectively prevents water molecules from entering the core-shell structure, making the PBA material less hygroscopic and significantly improving its storage stability at room temperature and pressure, while also enhancing its structural stability. Furthermore, this method is inexpensive.

[0036] In any embodiment, the Prussian blue analog particles in step 1) are prepared by a method comprising the following steps:

[0037] i) Dissolve a soluble salt containing P (a transition metal element) and a slow-release agent containing Na in water to prepare solution a;

[0038] ii) Dissolve the soluble transition metal cyano complex containing R as a transition metal element in water to prepare solution b;

[0039] iii) While stirring, add solution a dropwise to solution b. After the addition is complete, allow the mixture to age, filter, and obtain the precipitate; and

[0040] iv) Wash and dry the precipitate obtained in step iii) to obtain Prussian blue analogue particles.

[0041] The above method helps to prepare structurally stable Prussian blue analog particles.

[0042] In any embodiment, the Na-containing sustained-release agent in step i) is at least one selected from sodium citrate, sodium ascorbate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate. Selecting the above-mentioned sustained-release agent helps to obtain a more uniform coating layer.

[0043] In any embodiment, the soluble transition metal cyano complex in step ii) is sodium divalent transition metal cyanide.

[0044] In any embodiment, in step iii), the solution is maintained at a temperature range of 20°C to 120°C, optionally 70°C to 90°C, and optionally 80°C. By controlling the temperature of the solution within the above range, a better coating morphology can be obtained.

[0045] In any embodiment, the solvents 1, 2, and 3 in steps 1), 2), and 3) may be the same or different, and each is independently selected from at least one of deionized water and an organic solvent. Optionally, the organic solvent is selected from at least one of alcohols, ketones, and halogenated hydrocarbons, and optionally from at least one of methanol, glycerol, acetone, and ethanol. By selecting the above solvents, a uniform coating layer can be easily obtained and the electrochemical capacity of the PBA material can be ensured.

[0046] In any embodiment, the soluble transition metal cyano complex in step 3) is sodium divalent transition metal cyanide.

[0047] In any embodiment, in step 4), the dropping rates of solution c and solution d are each independently within the range of 0.1 ml / min to 10 ml / min, optionally within the range of 0.1 ml / min to 5 ml / min, for example, within the range of 0.1 ml / min to 2 ml / min; or in step 4), the reaction system is maintained at a temperature range of 20°C to 120°C, optionally within the temperature range of 70°C to 90°C, optionally maintained at 80°C. By controlling the dropping rate or temperature within the above ranges, a better coating morphology can be obtained.

[0048] A third aspect of this application provides a sodium-ion secondary battery comprising a Prussian blue analogue with a core-shell structure as described in the first aspect of this application or a Prussian blue analogue with a core-shell structure obtained by the method described in the second aspect of this application.

[0049] A fourth aspect of this application provides a battery module that includes the sodium-ion secondary battery of the third aspect of this application.

[0050] The fifth aspect of this application provides a battery pack that includes the battery module of the fourth aspect of this application.

[0051] A sixth aspect of this application provides an electrical device comprising one or more selected from the sodium-ion secondary battery of the third aspect of this application, the battery module of the fourth aspect of this application, or the battery pack of the fifth aspect of this application. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0053] Figure 1 The XRD patterns are of the PBA materials prepared in Examples 1-4 and Comparative Example 1 of this application.

[0054] Figure 2 The SEM and EDS spectra of the PBA material prepared in Example 1 of this application are shown.

[0055] Figure 3 Thermogravimetric analysis (TGA) spectra of water content in the PBA materials prepared in Example 1 and Comparative Example 1 of this application.

[0056] Figure 4 The graph shows the change in water content over time in humid air for the PBA materials prepared in Example 1 and Comparative Example 1 of this application.

[0057] Figure 5 The graph shows the long-term cycle performance of sodium-ion secondary batteries when the PBA materials prepared in the embodiments and comparative examples of this application are used as positive electrode active materials in sodium-ion secondary batteries, with a charge-discharge current density of 150 mA / g.

[0058] Figure 6 The rate curves of the sodium-ion secondary batteries are obtained when the PBA materials prepared in Example 1 and Comparative Example 1 of this application are used as positive electrode active materials in sodium-ion secondary batteries, and the sodium-ion secondary batteries are charged at different current densities and discharged at a rate of 0.33C.

[0059] Figure 7 The K element distribution map is obtained by performing elemental analysis on the cross-section of the PBA material in Example 1 using transmission electron microscopy (TEM) and energy dispersive spectroscopy.

[0060] Figure 8 Photographs of positive electrode sheets prepared using PBA materials from Comparative Example 1 and Example 1 after 400 charge-discharge cycles.

[0061] Figure 9 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0062] Figure 10 yes Figure 9 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0063] Figure 11 This is a schematic diagram of a battery module according to one embodiment of this application.

[0064] Figure 12 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0065] Figure 13 yes Figure 12 An exploded view of a battery pack according to one embodiment of this application is shown.

[0066] Figure 14 This is a schematic diagram of an electrical device using a secondary battery according to an embodiment of this application.

[0067] Explanation of reference numerals in the attached figures:

[0068] 1 battery pack

[0069] 2 upper box

[0070] 3 lower cabinets

[0071] 4 battery modules

[0072] 5 Secondary battery

[0073] 51 Housing

[0074] 52 Electrode assembly

[0075] 53 Cover plate Specific embodiments

[0076] For the sake of brevity, this application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each separately disclosed point or single numerical value by itself can serve as a lower limit or an upper limit and be combined with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0077] Prussian blue analogues with a core-shell structure

[0078] The Prussian blue analogue having a core-shell structure of this application has a core and a coating layer covering the core, wherein

[0079] The chemical formula of the core is Formula 1 below,

[0080] Na x P[R(CN)6] δ ·zH2O Formula 1

[0081] wherein P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10,

[0082] The chemical formula of the coating layer is Formula 2 below,

[0083] A y L[M(CN)6] α ·wH2O Formula 2

[0084] wherein A is an alkali metal or alkaline earth metal element other than sodium, L and M are each independently selected from at least one of transition metal elements, 0 < y ≤ 2, 0 < α ≤ 1 and 0 ≤ w ≤ 10.

[0085] Without wishing to be limited to any theory, it is believed that modifying the surface of PBA with alkali metal or alkaline earth metal ions having a large ionic radius causes the large-radius ions to occupy positions where crystal water might originally exist, reducing the crystal water in the lattice structure. Thus, the resulting core-shell structured Prussian blue analogue has fewer structural defects and a complete crystal structure, which can improve its electrochemical properties such as reversible specific capacity, cycling performance, etc. And, using a chemical composition A yL[M(CN)6] α Prussian blue analogues as shells for Na x P[R(CN)6] δ Using Prussian blue analogues as the core for surface coating is beneficial for obtaining a uniform core-shell structure, while the outer shell has a chemical composition A. y L[M(CN)6] α The Prussian blue analogue coats the entire surface of the core, effectively preventing water molecules from entering, thus making the material less prone to water absorption and greatly improving its storage stability.

[0086] In some embodiments, the transition metal elements P, R, L, and M are each independently selected from Fe, Mn, Ni, Co, Cu, and Zn. For example, the transition metal elements P, R, L, and M are each independently selected from Fe and Mn. By selecting these transition metal ions, the material can possess the desired electrochemical performance and electrochemical capacity while ensuring structural integrity.

[0087] In some embodiments, the alkali metal or alkaline earth metal element A is selected from at least one of Li, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. For example, A is selected from at least one of K, Rb, Cs, Mg, and Ca. In some embodiments, A is selected from at least one of K, Rb, and Cs. By appropriately selecting the alkali metal or alkaline earth metal element A, a good barrier effect is achieved against the transport of water molecules, which is beneficial for achieving a better reduction in the water absorption of Prussian blue analogues.

[0088] In some embodiments, δ in Equation 1 satisfies 0.7 ≤ δ ≤ 1. By selecting the numerical range of δ, the Prussian blue analogue can have a larger capacity and a more stable structure when used as the positive electrode material of a sodium-ion secondary battery.

[0089] In some embodiments, in Formulas 1 and 2, x and y are each independently, for example, in the range of 0.5-2, or for example, in the range of 1.5-2. By appropriately selecting the numerical ranges of x and y, the Prussian blue analogue can have a large capacity when used as the positive electrode material of a sodium-ion secondary battery.

[0090] In some embodiments, the thickness of the coating layer is less than 100 nm, for example, less than 60 nm or less than 50 nm. For example, the thickness of the coating layer can be 5 nm-40 nm, such as 10 nm-20 nm. The inventors have found that when the thickness of the coating layer is within the given range, it is possible to improve the water resistance and electrochemical performance of the PBA material while ensuring that the PBA material has a high capacity when used as a positive electrode active material.

[0091] In some embodiments, the coating amount is less than 10% by weight, for example, 1% to 5% by weight. The coating amount is defined as the ratio of the mass of the coating layer to the total mass of the entire core-shell structure particle. When the coating amount is within the given range, it is possible to improve the water resistance and electrochemical performance of PBA materials while ensuring that PBA has a high capacity when used as a positive electrode active material.

[0092] In this application, the thickness of the coating layer can be tested using equipment and methods known in the art. As an example, the thickness and uniformity can be measured using focused ion beam (FIB) combined with transmission electron microscopy (TEM).

[0093] In this application, the coating thickness can be tested using equipment and methods known in the art. As an example, it can be measured using an inductively coupled plasma spectrometer (ICP).

[0094] In some embodiments, the particle size of the Prussian blue analogue is from 100 nm to 50 μm, for example, from 200 nm to 30 μm. By controlling the particle size of the Prussian blue analogue within the above range, it is beneficial to obtain a uniform coating layer and a smaller coating layer thickness, thereby maintaining good ion and electron transport properties of the material.

[0095] In this application, the particle size of Prussian blue analogues can be tested using equipment and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma300) can be used, referring to JY / T010-1996, to obtain scanning electron microscope (SEM) images of Prussian blue analogues and read the particle size (i.e., the distance between the two farthest points on the particle) in the test area.

[0096] In some embodiments, the specific surface area of ​​the Prussian blue analogue is 1-20 m². 2 / g, for example, 5-18m 2 / g.

[0097] In this application, the specific surface area of ​​Prussian blue analogues can be tested using equipment and methods known in the art. For example, according to the national standard GB / T 19587-2004, after determining the amount of gas adsorbed on the solid surface under different relative pressures at a constant low temperature, the amount of monolayer adsorption of the sample is obtained based on the Brownnor-Etter-Taylor (BET) multilayer adsorption theory and its formula, thereby calculating the specific surface area of ​​the solid.

[0098] Preparation method of Prussian blue analogues with core-shell structure

[0099] This application also provides a method for preparing a Prussian blue analog with a core-shell structure, the method comprising the following steps:

[0100] 1) Add Prussian blue analogue particles to Solvent 1 to obtain a suspension by dispersion. The chemical formula of the Prussian blue analogue particles is as follows: Formula 1

[0101] Na x P[R(CN)6] δ ·zH2O Formula 1

[0102] where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10;

[0103] 2) Dissolve a soluble salt containing transition metal element L in Solvent 2 to prepare Solution c;

[0104] 3) Dissolve a soluble salt containing an alkali metal or alkaline earth metal element A other than sodium and a soluble transition metal cyanide complex containing transition metal element M in Solvent 3 to prepare Solution d;

[0105] 4) Under stirring, drop Solutions c and d into the suspension obtained in step 1), and filter the suspension to obtain a precipitate;

[0106] 5) Wash and dry the precipitate obtained in step 4) to obtain a Prussian blue analogue with a core-shell structure. The Prussian blue analogue with a core-shell structure has a core and a coating layer covering the core. The core is the Prussian blue analogue particles, and the chemical formula of the coating layer is as follows: Formula 2

[0107] A y L[M(CN)6] α ·wH2O Formula 2

[0108] where A is an alkali metal or alkaline earth metal element other than sodium, L and M are each independently selected from at least one of transition metal elements, 0 < y ≤ 2, 0 < α ≤ 1 and 0 ≤ w ≤ 10.

[0109] The descriptions and definitions of P, R, A, L, M, x, y, δ, α, z, and w in the above "Prussian blue analogue with a core-shell structure" section also apply to the method of this application.

[0110] The solvents used in steps 1), 2), and 3) can be the same or different, and can be commonly used solvents in the art, and can be selected by those skilled in the art according to actual needs. In some embodiments, the solvents used in steps 1), 2), and 3) are each independently selected from at least one of deionized water and organic solvents, such as at least one of deionized water, alcohols, ketones, and halogenated hydrocarbons. In some embodiments, the solvents used in steps 1), 2), and 3) are each independently selected from at least one of deionized water, methanol, glycerol, acetone, and ethanol. When the solvent is selected from deionized water, methanol, glycerol, acetone, and ethanol, a uniform coating layer can be easily obtained even when the coating layer thickness is <20 nm and the coating amount is <5% by weight, which can achieve a reversible specific capacity comparable to that of PBA materials without a coating layer while ensuring low water absorption of the material.

[0111] The dispersion in step 1) can be carried out in an appropriate manner by those skilled in the art. In some embodiments, dispersion is aided by ultrasonication and stirring in step 1).

[0112] In some embodiments, a slow-release agent may be added during the preparation of solution c in step 2). When a slow-release agent is added, for example, the molar ratio of the transition metal element L to the slow-release agent is 1:0.1-10. In some embodiments, the molar ratio of the transition metal element L to the slow-release agent is 1:1-7, for example 1:1-5, or for example 1:3. By adding an appropriate amount of slow-release agent, the uniformity of the coating layer can be controlled, resulting in a more uniform coating layer.

[0113] In this application, the sustained-release agent is a chelating agent whose anion has the effect of complexing with transition metal ions, so that the transition metal ions do not exist alone in the solution, or it is a sodium-containing compound that easily dissociates into sodium ions in the solution.

[0114] In some embodiments, the sustained-release agent in step 2) is at least one selected from sodium citrate, sodium ascorbate, disodium EDTA, tetrasodium EDTA, sodium chloride, sodium sulfate, and sodium acetate. By selecting the above-mentioned sustained-release agent, a more uniform coating layer can be obtained by controlling the reaction rate. The concentration of the sustained-release agent in the solution is, for example, in the range of 0.01 mol / L to 10 mol / L.

[0115] There are no particular restrictions on the anion of the soluble salt containing the transition metal element L in step 2), as long as the salt is soluble. In some embodiments, the soluble salt containing the transition metal element L in step 2) is a divalent sulfate, nitrate, chloride, or salt of a weak acid, such as oxalate. Its concentration in solution is, for example, in the range of 0.01 mol / L to 1 mol / L.

[0116] There are no particular restrictions on the anion of the soluble salt containing an alkali metal or alkaline earth metal element A other than sodium in step 3), as long as the salt is soluble. In some embodiments, the soluble salt containing an alkali metal or alkaline earth metal element A other than sodium in step 3) is a sulfate, nitrate, chloride, or salt of a weak acid. Its concentration in the solution is, for example, in the range of 0.001 mol / L to 1 mol / L.

[0117] In some embodiments, the soluble transition metal cyano complex in step 3) is sodium divalent transition metal cyanide. Its concentration in solution is, for example, in the range of 0.01 mol / L to 1 mol / L.

[0118] In some embodiments, after all solutions c and d have been added in step 4), the reaction system is stirred for 0.01 h to 48 h, for example, 12 h.

[0119] In some embodiments, in step 4), the reaction system is maintained in a temperature range of 20°C to 120°C, for example, 70°C to 90°C, or for example, maintained at 80°C. By controlling the temperature of the reaction system within the above range, the uniformity of the coating layer can be controlled, resulting in a better coating layer morphology.

[0120] In some embodiments, in step 4), the dropping rate of each solution is independently within the range of 0.1 ml / min to 10 ml / min, optionally within the range of 0.1 ml / min to 5 ml / min, for example, within the range of 0.1 ml / min to 2 ml / min. By controlling the dropping rate of the solution within the above range, the uniformity of the coating layer can be controlled, and a better coating layer morphology can be obtained.

[0121] In some implementations, in step 4), the stirring rate is in the range of 200 rpm to 1200 rpm.

[0122] The drying in step 5) can be performed by a person skilled in the art using an appropriate drying method. In some embodiments, in step 5), the drying is performed by vacuum drying, for example at a temperature in the range of 0-300°C, such as 150°C; the vacuum degree is, for example, 10-15 mTorr.

[0123] In some embodiments, the Prussian blue analog particles in step 1) are prepared by a method comprising the following steps:

[0124] i) Dissolve a soluble salt containing P (a transition metal element) and a slow-release agent containing Na in water to prepare solution a;

[0125] ii) Dissolve the soluble transition metal cyano complex containing R as a transition metal element in water to prepare solution b;

[0126] iii) While stirring, add solution a dropwise to solution b. After the addition is complete, let it age, filter, and obtain the precipitate.

[0127] iv) Wash and dry the precipitate obtained in step iii) to obtain Prussian blue analogue particles.

[0128] The PBA material prepared by this method has fewer defects and a higher sodium content, which helps to obtain structurally stable materials.

[0129] In some embodiments, in step i), the molar ratio of the transition metal element P to the slow-release agent is 1:0.1-10. In some embodiments, the molar ratio of the transition metal element P to the slow-release agent is 1:1-5, for example, 1:3.2. By controlling the molar ratio within the above range, the uniformity of the coating layer can be controlled, and a better coating layer morphology can be obtained.

[0130] There are no particular restrictions on the anion of the soluble salt containing the transition metal element P in step i), as long as the salt is soluble. In some embodiments, the soluble salt containing the transition metal element P in step i) is a divalent sulfate, nitrate, chloride, or salt of a weak acid, such as oxalate. Its concentration in solution is, for example, in the range of 0.01 mol / L to 1 mol / L.

[0131] In some embodiments, the Na-containing sustained-release agent in step i) is at least one selected from sodium citrate, sodium ascorbate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate. By selecting the above-mentioned sustained-release agent, a more uniform coating layer can be obtained by controlling the reaction rate. The concentration of the sustained-release agent in the solution is, for example, in the range of 0.01 mol / L to 10 mol / L.

[0132] In some embodiments, in step ii), a protective gas is introduced into the container holding solution b to protect the transition metal element from oxidation. The protective gas may be a suitable inert gas selected by those skilled in the art. In some embodiments, in step ii), the protective gas is at least one of N2, Ar, and He.

[0133] In some embodiments, a soluble sodium salt may be added during the preparation of solution b in step ii). For example, the soluble sodium salt may be at least one selected from sodium citrate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate. When a soluble sodium salt is added, for example, the molar ratio of the soluble transition metal cyano complex containing the transition metal element R to the soluble sodium salt is 1:0.1-100. The concentration of the soluble sodium salt in the solution is, for example, in the range of 0.01 mol / L to 10 mol / L. By adding the soluble sodium salt, the sodium source can be replenished and the morphology of the nuclei can be adjusted.

[0134] In some embodiments, the soluble transition metal cyano complex in step ii) is sodium divalent transition metal cyanide. Its concentration in solution is, for example, in the range of 0.01 mol / L to 1 mol / L.

[0135] In some embodiments, in step iii), the stirring rate is in the range of 200 rpm to 1200 rpm.

[0136] In some embodiments, in step iii), the solution is maintained in a temperature range of 20°C to 120°C, for example, 70°C to 90°C, or for example, maintained at 80°C. By controlling the temperature of the solution within the above range, the uniformity of the coating layer can be controlled, resulting in a better coating layer morphology.

[0137] In some embodiments, in step iii), solution a is added dropwise at a rate of 0.1 ml / min to 10 ml / min, for example, at a rate of 1 ml / min. By controlling the dropwise rate of the solution within the above range, the uniformity of the coating layer can be controlled, resulting in a better coating layer morphology.

[0138] In some embodiments, in step iii), aging is carried out for 0.01 h to 48 h, for example, 12 h, and aging can be carried out, for example, with stirring.

[0139] The washing in step iv) can be performed by a person skilled in the art using an appropriate solvent. In some embodiments, the washing in step iv) can be performed using a mixture of deionized water and ethanol, ethanol, or acetone, and can be performed once or multiple times.

[0140] The drying in step iv) can be performed by a person skilled in the art using an appropriate drying method. In some embodiments, the drying in step iv) is performed by vacuum drying, for example at a temperature in the range of 0-300°C, such as 150°C; the vacuum degree is, for example, 10-15 mTorr.

[0141] Positive electrode sheet

[0142] This application also provides a positive electrode for a sodium-ion secondary battery, the positive electrode comprising a positive current collector and a Prussian blue analog of the first aspect of this application having a core-shell structure disposed on the current collector, or a Prussian blue analog of the second aspect of this application having a core-shell structure prepared by the method of the second aspect of this application.

[0143] At least one surface of the positive current collector is provided with a positive electrode film layer, the positive electrode film layer including a Prussian blue analogue with a core-shell structure according to the first aspect of this application.

[0144] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0145] In some embodiments, the positive electrode current collector can be a conventional metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (e.g., aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As an example, the positive electrode current collector can be aluminum foil, such as a 5-30 μm carbon-coated aluminum foil.

[0146] The positive electrode film may optionally include a conductive agent. However, there is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used for the positive electrode film may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In this application, the positive electrode sheet can be prepared according to methods known in the art. As an example, the positive active material, conductive agent and binder of this application can be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.

[0148] In some embodiments, the positive electrode sheet is coated on the current collector with: 70-90 parts by weight of a Prussian blue analogue having a core-shell structure, 1-20 parts by weight of a conductive agent, and 1-10 parts by weight of a binder.

[0149] Sodium-ion secondary batteries

[0150] This application also provides a sodium-ion secondary battery, which includes the above-mentioned positive electrode plate.

[0151] Typically, a sodium-ion secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0152] [Negative electrode plate]

[0153] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0154] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0155] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (e.g., aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymeric material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0156] In the secondary battery of this application, the negative electrode film layer typically comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0157] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] As an example, the adhesive may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0159] Other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0160] As an example, the negative electrode active material may be selected from one or more of carbon materials, alloy materials, transition metal oxides and sulfides, phosphorus-based materials, and titanate materials. For instance, examples of negative electrode active materials include soft carbon, hard carbon, silicon-based materials, and tin-based materials. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0161] In some embodiments, the negative electrode sheet can be directly made of sodium metal or sodium metal alloy sheet.

[0162] [Electrolytes]

[0163] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0164] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0165] The electrolyte may include an electrolyte salt and a solvent. As an example, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). As an example, the electrolyte salt may be NaClO4, NaPF6, or NaFSI (sodium bis(fluorosulfonyl)imide), etc.

[0166] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0167] [Isolation membrane]

[0168] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0169] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0170] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0171] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0172] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0173] In some implementations, refer to Figure 10 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0174] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0175] Figure 11 This is battery module 4, used as an example. (See reference...) Figure 11 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0176] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0177] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0178] Figure 12 and Figure 13 This is battery pack 1 as an example. (See reference...) Figure 12 and Figure 13 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0179] In addition, this application also provides an electrical device, which includes one or more of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0180] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0181] Figure 14 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0182] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0183] Example

[0184] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. The following, in conjunction with embodiments, further illustrates the beneficial effects of this application.

[0185] Performance testing methods

[0186] 1. Water absorption test

[0187] (1) Experimental Method 1

[0188] 1g of PBA material prepared in each embodiment and comparative example was placed in a humid air atmosphere with a relative humidity of 70%, and weighed every three hours after 15min, 30min, 60min, 180min, and 180min. Let the mass of each weighed sample be m, then the water absorption rate = (m-1) / 1*100%. The calculated water absorption rate was plotted against time. Figure 4 The curves showing the water absorption of the core-shell structured PBA materials prepared in Example 1 and Comparative Example 1 as a function of time are shown.

[0189] (2) Test Method 2

[0190] 1g of PBA material prepared in each embodiment and comparative example was placed in a humid air atmosphere with a relative humidity of 70% for 48 hours. After storage, the samples were subjected to thermogravimetric analysis (TGA) under a 99.99% pure N2 atmosphere with a heating rate of 10℃ / min and a temperature range of 0-300℃ to quantitatively determine the water content. The quantitative determination of water content was performed as follows: the initial weight and the weight at 300℃ were extracted through TGA, and the difference between the two was divided by the initial weight to obtain the water content. The water content test results of the PBA materials in each embodiment and comparative example are listed in Tables 1-10 below. Furthermore, the change in water content of the PBA materials prepared in Example 1 and Comparative Example 1 with temperature in the TGA test is expressed as follows: Figure 3 middle.

[0191] 2. Battery performance test

[0192] (1) Preparation of positive and negative electrode plates

[0193] The positive electrode sheet was prepared by the following method: PBA material (positive electrode active material), conductive agent Ketjen black (KB), and binder polyvinylidene fluoride (PVDF) prepared in each example and comparative example were added to N-methylpyrrolidone (NMP), and the mixture was stirred by rotor for 1-3 hours to form a slurry. The slurry was coated onto a current collector Al foil with a coating thickness of 200-300 μm. The slurry was dried in a vacuum drying oven at 90-110℃ for 10-15 hours, and then allowed to cool naturally to room temperature to obtain the positive electrode sheet. The mass ratio of the substances used was: positive electrode active material: conductive agent Ketjen black: binder polyvinylidene fluoride = 7:2:1, with 28 g of active material added for every 20-40 g of NMP.

[0194] The negative electrode sheet is prepared by the following method: Commercial hard carbon negative electrode material (negative electrode active material) of Type I / II / III purchased from Kuraray, Japan, conductive carbon black (CB), and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP), and the mixture is stirred by rotor for 1-3 hours to form a slurry. The slurry is coated onto the current collector Al foil. The coating amount is determined according to the absolute capacity of the positive electrode. The ratio of negative electrode absolute capacity to positive electrode absolute capacity is 1.16, where absolute capacity (mAh) = first discharge reversible specific capacity (mAh / g) * total weight of active material (g). The method for measuring reversible specific capacity is described below. The material is dried in a vacuum drying oven at 90-110℃ for 10-15 hours, and then allowed to cool naturally to room temperature to obtain the positive electrode sheet. The mass ratio of the materials used is: negative electrode active material: conductive carbon black (CB): binder polyvinylidene fluoride = 9:0.4:0.6, with 28g of active material added for every 20-40g of NMP.

[0195] (2) Preparation of sodium-ion secondary batteries

[0196] Sodium-ion coin cell half-cells are prepared by the following method: The positive electrode sheet prepared according to the above method is cut into sheets with a diameter of 14-16 mm using a cutting machine. A glass fiber separator is used, metallic sodium is used as the negative electrode, an electrolyte is added, and the cells are assembled into CR 2032 coin cells in a glove box filled with argon atmosphere. The electrolyte is a solution containing NaClO4 and FEC (fluoroethylene carbonate), wherein the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, the concentration of NaClO4 is 1M, and the mass of FEC is 2% of the solution mass.

[0197] Sodium-ion coin cells are prepared by the following method: the positive and negative electrode sheets prepared according to method (1) above are cut into electrode sheets with diameters of 14 and 16 mm respectively using a cutting machine. A glass fiber separator is used, an electrolyte is added, and the cells are assembled into CR 2032 coin cells in a glove box filled with argon atmosphere. The electrolyte is a solution containing NaClO4 and FEC (fluoroethylene carbonate), wherein the solvent is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, the concentration of NaClO4 is 1M, and the mass of FEC is 2% of the mass of the solution.

[0198] (3) Battery performance test

[0199] [Reversible Capacity]

[0200] Sodium-ion coin cells were charged and discharged at a current density of 20 mA / g within the 2.5-4.0V range and at room temperature of 25°C. The capacity of the cells during the charge and discharge process was recorded, and the reversible specific capacity was obtained by dividing the capacity by the mass of the positive electrode active material. The results of the first discharge reversible specific capacity test of the secondary cells prepared with PBA materials in each example and comparative example are listed in Tables 1-10 below.

[0201] [Long-term cycling performance]

[0202] The prepared sodium-ion coin cell was charged and discharged at 150 mA / g at 45°C, and the capacity value of each charge and discharge cycle was recorded. Using the first charge and discharge capacity value as 100%, the percentage of the initial capacity value for each subsequent charge and discharge cycle was calculated. This percentage was then plotted against the number of cycles. Figure 5 middle.

[0203] [Short-term charging rate]

[0204] Sodium-ion coin cells were charged at different current densities and discharged at a rate of 0.33C. The capacity value was recorded for each discharge, and the capacity retention rate was calculated. The current density and capacity retention rate were plotted to obtain the rate curves of the cells. The rate curves of the cells prepared using the PBA material of Example 1 and Comparative Example 1 are shown in [the graph / image / image]. Figure 6 middle.

[0205] 3. Coating thickness measurement

[0206] The PBA material sample was subjected to ion beam shearing using a focused ion beam (FIB) to expose the cross-section of the material. The sample with the exposed cross-section was then vacuum-transferred into a transmission electron microscope (TEM) testing device. Elemental analysis of the cross-section was performed using an energy dispersive spectroscopy (EDS) instrument to determine the location and uniformity of the K element distribution. Figure 7TEM images of the PBA material of Example 1 obtained using the method described above are shown. Tables 1-2 show the coating thicknesses of the PBA materials of Examples 1-7 measured using the method described above.

[0207] Example 1:

[0208] Weigh out 19.3624 g of sodium ferrocyanide decahydrate, 35.292 g of sodium citrate monohydrate, and 7.9164 g of manganese chloride tetrahydrate. Add the sodium ferrocyanide decahydrate to 100 ml of deionized water and stir for 30 min to form solution b. Add the manganese chloride tetrahydrate and sodium citrate monohydrate to 100 ml of deionized water and stir for 30 min to form solution a. Stir until homogeneous and then add the solution a dropwise to solution b at a rate of 1 ml / min. After the addition is complete, stir for 24 h at a stirring rate of 400 rpm and a temperature of 80 °C to form a suspension.

[0209] The solid material in the suspension was filtered through a Buchner funnel and washed three times with deionized water until no residual sodium salt or transition metal ions remained in the product. The obtained material was then vacuum-dried at 120°C for 24 hours with a relative vacuum of <-0.1 MPa to obtain 10 g of Prussian blue analog particles Na2MnFe(CN)6.

[0210] The obtained Prussian blue analogue particles were added to 100 ml of deionized water and ultrasonically dispersed for 10 min to form a suspension. 0.9681 g of sodium ferrocyanide decahydrate, 0.745 g of potassium chloride, and 0.3958 g of manganese chloride tetrahydrate were weighed. The sodium ferrocyanide decahydrate and potassium chloride were added to 10 ml of deionized water and stirred for 30 min to form solution d. Manganese chloride tetrahydrate was added to 10 ml of deionized water and stirred for 30 min to form solution c. After thorough mixing, solutions c and d were added dropwise to the suspension at a rate of 0.2 ml / min. After the addition was complete, stirring and aging continued for 12 h. The stirring rate was 400 rpm, and the temperature was 80 °C.

[0211] The solid material in the suspension was filtered through a Buchner funnel and washed three times with deionized water until no residual sodium, potassium, or transition metal ions remained in the product. The obtained material was then vacuum-dried at 120°C for 24 hours at a relative vacuum of <-0.1 MPa to obtain a Prussian blue analog with a core-shell structure. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology. Microscopic morphology SEM and elemental distribution EDS are shown below. Figure 2 As shown.

[0212] Example 2:

[0213] Except that 1.21 g of rubidium chloride was used instead of 0.745 g of potassium chloride in the preparation of solution d, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was Rb₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0214] Example 3:

[0215] Except that 1.68 g of cesium chloride was used instead of 0.745 g of potassium chloride in the preparation of solution d, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was Cs₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0216] Example 4:

[0217] Except that 0.43 g of lithium chloride was used instead of 0.745 g of potassium chloride in the preparation of solution d, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was Li₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0218] Table 1

[0219]

[0220] Example 5:

[0221] Except for preparing solution d using 1.9362 g of sodium ferrocyanide decahydrate, 1.49 g of potassium chloride, and 20 ml of deionized water, and preparing solution c using 0.7916 g of manganese chloride tetrahydrate and 20 ml of deionized water, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0222] Example 6:

[0223] Except for preparing solution d using 0.3973 g of sodium ferrocyanide decahydrate, 0.30 g of potassium chloride, and 4 ml of deionized water, and preparing solution c using 0.1583 g of manganese chloride tetrahydrate and 4 ml of deionized water, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0224] Example 7:

[0225] Except for preparing solution d using 0.19362 g of sodium ferrocyanide decahydrate, 0.15 g of potassium chloride, and 1 ml of deionized water, and preparing solution c using 0.07916 g of manganese chloride tetrahydrate and 1 ml of deionized water, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0226] Table 2

[0227]

[0228] Example 8:

[0229] 10g of the finished Prussian blue analogue particles Na2MnFe(CN)6, prepared according to the method described in the Journal of The Electrochemical Society, 163(9)A2117-A2123(2016), were added to 100ml of deionized water and ultrasonically dispersed for 10min to form a suspension. 1.9362g of sodium ferrocyanide decahydrate, 1.49g of potassium chloride, and 0.7916g of manganese chloride tetrahydrate were weighed. The sodium ferrocyanide decahydrate and potassium chloride were added to 20ml of deionized water and stirred for 30min to form solution d. The manganese chloride tetrahydrate was added to 20ml of deionized water and stirred for 30min to form solution c. After thorough mixing, solutions c and d were added dropwise to the suspension at a rate of 0.2ml / min. After the addition was complete, stirring and aging continued for 12h at a stirring rate of 400 rpm and a temperature of 80℃.

[0230] The solid material in the suspension was filtered through a Buchner funnel and washed three times with deionized water until no residual sodium, potassium, or transition metal ions remained in the product. The obtained material was then vacuum-dried at 120°C for 24 hours at a relative vacuum of <-0.1 MPa to obtain a Prussian blue analog with a core-shell structure. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0231] Table 3

[0232]

[0233] Example 9:

[0234] Except for using 100 ml of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol 7:3) instead of 100 ml of deionized water to prepare suspensions of solutions b, a, and Prussian blue analog particles, respectively, and using 20 ml of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol 7:3) instead of 20 ml of deionized water to prepare solution d, and using 20 ml of ethanol instead of 20 ml of deionized water to prepare solution c, the Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 5. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆.

[0235] Table 4

[0236]

[0237] Example 10:

[0238] Except for the addition of 3.529 g of sodium citrate monohydrate in the preparation of solution c, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0239] Table 5

[0240]

[0241] Example 11:

[0242] Except that 7.125 g of manganese chloride tetrahydrate was used instead of 7.9164 g of manganese chloride tetrahydrate in the preparation of solution a, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1, resulting in a Prussian blue analog with a core-shell structure. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a small cubic morphology with distinct edges.

[0243] Example 12:

[0244] Except that 70.584 g of sodium citrate monohydrate was used instead of 35.292 g of sodium citrate monohydrate in the preparation of solution a, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0245] Example 13:

[0246] Except for using 42.161 g of tetrasodium ethylenediaminetetraacetate instead of 35.292 g of sodium citrate monohydrate, and using 7.125 g of manganese chloride tetrahydrate instead of 7.9164 g of manganese chloride tetrahydrate to prepare solution a, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 1. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0247] Table 6

[0248]

[0249] Example 14:

[0250] Except for the addition of 35g of sodium chloride in the preparation of solution b, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 11. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000 nm and exhibited a spherical morphology.

[0251] Example 15:

[0252] Except that 35g of sodium chloride was added during the preparation of solution b, and the dropping rate of solution a was 10ml / min, a Prussian blue analog with a core-shell structure was prepared in the same manner as in Example 11. A Prussian blue analog with a core-shell structure was obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. This Prussian blue analog had a particle size of 500-1000nm and exhibited a small, angular cubic morphology.

[0253] Table 7

[0254]

[0255] Example 16:

[0256] Except that the temperature during the stirring and aging process after the addition of solutions c and d was completed was 40°C, the Prussian blue analogue with a core-shell structure was prepared in the same manner as in Example 1. The resulting Prussian blue analogue had a core-shell structure, with a shell of K₂MnFe(CN)₆ and a core of Na₂MnFe(CN)₆. This Prussian blue analogue had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0257] Example 17:

[0258] Except that the temperature during the stirring and aging process after the addition of solutions c and d was completed was 110°C, Prussian blue analogs with a core-shell structure were prepared in the same manner as in Example 1. Prussian blue analogs with a core-shell structure were obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. These Prussian blue analogs had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0259] Table 8

[0260]

[0261] Example 18:

[0262] Except that the dropping rate for solutions c and d was 2 ml / min, Prussian blue analogs with a core-shell structure were prepared in the same manner as in Example 1. Prussian blue analogs with a core-shell structure were obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. These Prussian blue analogs had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0263] Example 19:

[0264] Except that the dropping rate for solutions c and d was 5 ml / min, Prussian blue analogs with a core-shell structure were prepared in the same manner as in Example 1. Prussian blue analogs with a core-shell structure were obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. These Prussian blue analogs had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0265] Example 20:

[0266] Except that the dropping rate for solutions c and d was 8 ml / min, Prussian blue analogs with a core-shell structure were prepared in the same manner as in Example 1. Prussian blue analogs with a core-shell structure were obtained. The outer shell was K₂MnFe(CN)₆, and the core was Na₂MnFe(CN)₆. These Prussian blue analogs had a particle size of 500-1000 nm and exhibited a small, angular cubic morphology.

[0267] Table 9

[0268]

[0269] Comparative Example 1:

[0270] Prussian blue analog particles were prepared in the same manner as in Example 1 using 19.3624 g of sodium ferrocyanide decahydrate, 35.292 g of sodium citrate monohydrate, and 7.9164 g of manganese chloride tetrahydrate, but without the steps of coating the shell with solutions c and d. 10 g of Prussian blue analog particles Na2MnFe(CN)6 were obtained, with a particle size of 500-1000 nm and a small cubic morphology with distinct edges.

[0271] Comparative Example 2:

[0272] 10g of Prussian blue analog particles Na2MnFe(CN)6 without a shell were prepared using 19.3624g of sodium ferrocyanide decahydrate, 35.292g of sodium citrate monohydrate and 7.9164g of manganese chloride tetrahydrate in the same manner as in Example 1. The particles had a diameter of 500-1000nm and were small cubic in shape with sharp edges.

[0273] 0.5 mol dopamine hydrochloride was placed in a beaker, dissolved in 4 L of deionized water and 210 mL of concentrated hydrochloric acid, and then diluted to volume with a 5 L volumetric flask to obtain a dopamine solution with a molar concentration of 0.1 mol / L. 10 g of the prepared Na₂MnFe(CN)₆ sample was placed in a container, 100 mL of deionized water was added, and the mixture was ultrasonically dispersed to obtain a suspension. 20 mL of the dopamine solution and 0.25 g of sodium alginate were placed in a container, dissolved in 100 mL of deionized water, and then mixed evenly with the Na₂MnFe(CN)₆ suspension. The mixture was allowed to stand at room temperature for 24 h. The solution was then washed three times with water and three times with alcohol, and dried to obtain the polydopamine-coated Na₂MnFe(CN)₆ material.

[0274] Table 10

[0275]

[0276] As can be seen from Tables 1 to 10, the water absorption rate of the core-shell structured PBA materials in Examples 1-20 is significantly lower than that in Comparative Examples 1 and 2. Furthermore, the reversible specific capacity of the materials in Examples 1-20 is similar to that of Comparative Examples 1 and 2. For example, the reversible specific capacity of the secondary battery prepared using the PBA material of Example 1 during the first charge / discharge was 155.2 mAh / g and 150.9 mAh / g, respectively. That is, the effect of the outer shell coating on the reversible specific capacity of the material is within an acceptable range.

[0277] Meanwhile, characterization of the long-term cycling and short-term charge rate performance of the PBA materials in each embodiment and comparative example revealed that the coated materials in each embodiment exhibited significantly superior performance in terms of rate and cycling performance, especially in high-temperature cycling at 45°C. The secondary battery prepared using the PBA material of Example 1 maintained over 85% capacity retention after 500 cycles at a current density of 150 mA / g. Figure 5 It can be seen that the long-term cycling performance of the PBA materials in Examples 1-20 is superior to that in Comparative Example 1. Figure 6 It can be seen that the short-term charging rate of the PBA material in Example 1 is also significantly better than that of Comparative Example 1.

[0278] Depend on Figure 7 As can be seen, in the PBA material prepared in Example 1, K atoms are uniformly distributed on the core surface of the PBA particles, and the coating layer thickness is between 15-20 nm, approximately 19 nm.

[0279] in addition, Figure 8 The images show positive electrode sheets prepared using PBA materials from Comparative Example 1 and Example 1 after 400 charge-discharge cycles. It can be seen that the PBA material in Comparative Example 1 exhibits white spots due to sodium deposition, which leads to a deterioration in the electrochemical performance of the PBA material. In contrast, the PBA material in Example 1 does not exhibit white spots.

[0280] Although this application has been described with reference to embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A Prussian blue analogue with core-shell structure for sodium-ion battery cathode material, characterized in that, has a core and a coating layer coating the core, wherein, a chemical formula of the core is the following formula 1, Na2P[R(CN)6] δ Formula 1 wherein the P, R are each independently selected from at least one of Fe, Mn, Ni, Co, Cu and Zn, 0 < δ ≤ 1, a chemical formula of the coating layer is the following formula 2, A2L[M(CN)6] α Formula 2 wherein the A is selected from at least one of K, Rb, Cs, the L, M are each independently selected from at least one of Fe, Mn, Ni, Co, Cu and Zn, 0 < α ≤ 1; a thickness of the coating layer is 3 nm-20 nm.

2. The Prussian blue analog with core-shell structure according to claim 1, wherein, in the formula 1, the 0.7 ≤ δ ≤ 1.

3. The Prussian blue analog with core-shell structure according to claim 1, wherein, a coating amount of the coating layer is 10 wt% or less.

4. The Prussian blue analog with a core-shell structure according to any one of claims 1 to 3, characterized in that a particle size of the Prussian blue analog is 100 nm to 50 μm.

5. A method for preparing a Prussian blue analog with core-shell structure, comprising the following steps: 1) adding Prussian blue analog particles into a solvent 1 to obtain a suspension, the Prussian blue analog particles having a chemical formula of the following formula 1, wherein the P, R are each independently selected from at least one of Fe, Mn, Ni, Co, Cu and Zn, 0 < δ ≤ 1; Na2P[R(CN)6] δ Formula 1 2) dissolving a soluble salt containing a transition metal element L in a solvent 2 to prepare a solution c; 3) dissolving a soluble salt containing an element A and a soluble transition metal cyanide complex containing an element M in a solvent 3 to prepare a solution d; the A is selected from at least one of K, Rb, Cs; the M is selected from at least one of Fe, Mn, Ni, Co, Cu and Zn; 4) under stirring, dropping the solutions c and d into the suspension obtained in step 1), filtering the suspension to obtain a precipitate; and 5) washing and drying the precipitate obtained in step 4) to obtain the Prussian blue analog with core-shell structure, the Prussian blue analog with core-shell structure having a core and a coating layer coating the core, the core being the Prussian blue analog particles, a chemical formula of the coating layer being the following formula 2, wherein the A is selected from at least one of K, Rb, Cs, the L, M are each independently selected from at least one of Fe, Mn, Ni, Co, Cu and Zn, 0 < α ≤ 1. A2L[M(CN)6] α Formula 2 6. The method according to claim 5, wherein the Prussian blue analog particles in step 1) are prepared by a method comprising the following steps: i) dissolving a soluble salt containing P as a transition metal element and a buffer containing Na in water to prepare a solution a; ii) dissolving a soluble transition metal cyanide complex containing R as a transition metal element in water to prepare a solution b; iii) under stirring, dropping the solution a into the solution b, aging after the dropping is completed, filtering to obtain a precipitate; and iv) washing and drying the precipitate obtained in step iii) to obtain the Prussian blue analog particles.

7. The method according to claim 6, wherein ​ ​ ​ The Na-containing slow release agent in the step i) is at least one selected from the group consisting of sodium citrate, sodium ascorbate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate.

8. The method of claim 6, wherein, The soluble transition metal cyano complex in the step ii) is divalent transition metal sodium cyanide.

9. The method of claim 6, wherein, In the step iii), the solution is maintained at a temperature range of 20-120 °C.

10. The method of any one of claims 5-9, wherein, The solvents 1, 2, and 3 in the steps 1), 2), and 3), respectively, can be the same or different, and each is independently selected from at least one of deionized water and an organic solvent selected from at least one of an alcohol, a ketone, and a halogenated hydrocarbon.

11. The method of any one of claims 5-9, wherein, The soluble transition metal cyano complex in the step 3) is divalent transition metal sodium cyanide.

12. The method of any one of claims 5-9, wherein, In the step 4), the dropping speed of the solution c and the solution d is independently in the range of 0.1-10 ml / min; or In the step 4), the reaction system is maintained at a temperature range of 20-120 °C.

13. A sodium-ion secondary battery, characterized by, It comprises the Prussian blue analog with core-shell structure of any one of claims 1-4 or the Prussian blue analog with core-shell structure obtained by the method of any one of claims 5-12.

14. A battery module, characterized by It comprises the sodium-ion secondary battery of claim 13.

15. A battery pack, characterized by It comprises the battery module of claim 14.

16. An electrical device, comprising: It comprises one selected from the group consisting of the sodium-ion secondary battery of claim 13, the battery module of claim 14, or the battery pack of claim 15.

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