Prussian blue material as well as preparation method and application thereof

Abstract

The invention provides a Prussian blue material as well as a preparation method and application thereof. The Prussian blue material comprises an inner core and a coating layer covering at least part of the surface of the inner core, the inner core comprises a Prussian blue compound; the coating layer comprises a macrocyclic compound, and the macrocyclic compound has a structure as shown in a formula 1 and / or a formula 2. The Prussian blue material provided by the invention is relatively good in conductivity, water absorption resistance, sodium storage capacity and structural stability, and can be applied to a battery, so that the dissolution amount of metal ions of the battery can be reduced, and the service life of the battery can be prolonged. And the specific discharge capacity, the first coulombic efficiency and the cycle performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a Prussian blue material and a preparation method and application thereof. BACKGROUND

[0002] As the positive material of sodium ion batteries, Prussian blue materials have attracted much attention due to their unique structure and chemical properties. They have a MOF-like structure, providing three-dimensional channels that facilitate the rapid insertion and extraction of sodium ions. This structural feature theoretically endows Prussian blue materials with high specific capacity and good ion transport performance. In addition, Prussian blue materials are mainly composed of inexpensive and abundant transition metal elements such as iron and manganese, and have simple preparation process and low cost, which makes them have significant commercialization potential in large-scale energy storage applications.

[0003] However, the Prussian blue materials in the prior art still face some key challenges, which limit their practical application performance in sodium ion batteries. First, the Prussian blue materials have poor electrical conductivity, which will increase the energy loss of the battery during charging and discharging, affecting the cycle stability of the battery. Second, the channel structure of these materials is easy to absorb water, and the existence of crystal water occupies the storage sites of sodium ions, thereby affecting the initial coulombic efficiency and cycle life of the battery. In addition, the Prussian blue materials have poor structural stability, and metal ions may be dissolved during the battery cycle, which will further reduce the cycle performance of the battery. Therefore, it is a technical problem to be solved at the present stage to develop a Prussian blue material with good electrical conductivity, water resistance, sodium storage capacity and structural stability. SUMMARY

[0004] The main purpose of the present application is to provide a Prussian blue material with good electrical conductivity, water resistance, sodium storage capacity and structural stability, which can reduce the dissolution of metal ions in the battery and improve the discharge specific capacity, initial coulombic efficiency and cycle performance of the battery when applied to the battery.

[0005] The present application also provides a preparation method of a Prussian blue material, which can prepare the above-mentioned Prussian blue material and has simple process and low cost.

[0006] The present application also provides a positive electrode sheet comprising the above-mentioned Prussian blue material, so that the positive electrode sheet applied to the battery can reduce the dissolution of metal ions in the battery and improve the discharge specific capacity, initial coulombic efficiency and cycle performance of the battery.

[0007] The application further provides a battery comprising the positive plate, so that the battery has a low metal ion dissolution amount and has a good discharge specific capacity, a first coulomb efficiency and a cycle performance.

[0008] In a first aspect, the application provides a Prussian blue material, comprising a core and a coating layer covering at least part of the surface of the core.

[0009] The core comprises a Prussian blue compound.

[0010] The coating layer comprises a macrocyclic compound, and the macrocyclic compound has a structure shown in Formula 1 and / or Formula 2.

[0011]

[0012] wherein R1, R2, R7, R8 are each independently selected from at least one of a substituted pyridine, an unsubstituted pyridine, a substituted benzene ring, a substituted alkyl, and at least one pyridine or one COOH, and the substituents in the substituted pyridine are selected from at least one of -COOH, -F, -Cl, -Br, and an alkyl, and the substituents in the substituted benzene ring are selected from at least one of -COOH, -F, -Cl, -Br, and an alkyl; R3, R4, R5, R6, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 are each independently selected from at least one of H, F, Cl, and Br; and n is an integer selected from any integer between 0 and 2.

[0013] The Prussian blue material as described above, wherein -COOH in the substituted benzene ring is located at at least one of positions 3, 4, and 5 of the benzene ring.

[0014] The Prussian blue material as described above, wherein the macrocyclic compound comprises at least one of the following compounds:

[0015]

[0016]

[0017] The Prussian blue material as described above, wherein the Prussian blue compound has a chemical composition of Na x Fe y G 1-y [Fe(CN)6]·zH2O, wherein 0

[0018] The coating layer accounts for 3-9% of the mass percentage of the inner core;

[0019] And / or, the average thickness of the coating layer is 10-20nm.

[0020] The specific surface area of the inner core of the Prussian blue type material is ≤3.5m 2 / g;

[0021] And / or, the specific surface area of the Prussian blue type material is 4.2m 2 / g-15m 2 / g.

[0022] The inner core of the Prussian blue type material comprises micropores, and the pore volume of the micropores accounts for 5-20% of the total pore volume of the Prussian blue type material.

[0023] In a second aspect, the present application provides a preparation method of the Prussian blue type material as described above, comprising the following steps:

[0024] The raw material system comprising the Prussian blue type compound and the coating material is subjected to coating treatment to obtain the Prussian blue type material; the coating material comprises a compound having the structure shown in formula 1 and / or a compound having the structure shown in formula 2.

[0025] In a third aspect, the present application provides a positive electrode sheet comprising the Prussian blue type material as described above or the Prussian blue type material prepared according to the preparation method of the Prussian blue type material as described above.

[0026] In a fourth aspect, the present application provides a battery comprising the positive electrode sheet as described above.

[0027] The Prussian blue type material provided by the present application has a coating layer comprising a compound having the structure shown in formula 1 and / or a compound having the structure shown in formula 2, which can improve the conductivity, water absorption resistance, sodium storage capacity and structural stability of the Prussian blue type material, and when applied to a battery, can reduce the dissolution amount of metal ions of the battery, and improve the discharge specific capacity, the first coulombic efficiency and the cycle performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1A schematic structural diagram of a Prussian blue type material provided by the present application is shown in the following figure.

[0030] Figure 2 A TEM image of the Prussian blue type material of Example 1 provided by the present application is shown in the following figure. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] Among the positive electrode materials of sodium-ion batteries, Prussian blue analogues are considered to have the potential for large-scale commercialization due to their unique MOF-like (Metal-Organic Framework) structure. The three-dimensional pore structure of this type of material is conducive to the extraction and intercalation of large-size sodium ions, providing a theoretical specific capacity comparable to that of lithium iron phosphate (about 170 mAh / g). Iron-based Prussian blue is particularly concerned because it combines high capacity, environmentally friendly characteristics and low cost, and exhibits excellent sodium storage performance, making it a promising positive electrode material for sodium-ion batteries.

[0033] However, in practical applications, iron-based Prussian blue faces some technical challenges, which limit its performance and cycle life in sodium-ion batteries. First, the electrical conductivity of iron-based Prussian blue is relatively low, which leads to increased energy loss during charging and discharging, affecting the cycle stability of the battery. Second, the abundant pore structure of the material is easily occupied by crystallization water, affecting the storage and deintercalation of sodium ions, resulting in poor first coulombic efficiency and cycle life of the battery. In addition, the structural stability of iron-based Prussian blue is poor, and defects in the crystal structure and dissolution of metal ions in the electrolyte will cause the material to change structure during charging and discharging, affecting the cycle performance and discharge specific capacity of the battery.

[0034] The present inventors have found that by coating the surface of Prussian blue analogues with a compound having the structure shown in Formula 1 and / or a compound having the structure shown in Formula 2, the electrical conductivity, water absorption resistance, sodium storage capacity and structural stability of the material can be significantly improved, thereby reducing the amount of metal ion dissolution in the battery and improving the specific capacity, first coulombic efficiency and cycle performance of the battery.

[0035] Based on this, in a first aspect, the present application provides a Prussian blue type material, which has the structure shown in the following figure. Figure 1As shown, the core and the coating layer covering at least part of the surface of the core; the core comprises Prussian blue compounds; the coating layer comprises macrocyclic compounds, the macrocyclic compounds have structures shown in formula 1 and / or formula 2:

[0036]

[0037] Wherein, R1, R2, R7, R8 are each independently selected from at least one of substituted pyridine, non-substituted pyridine, substituted benzene ring, substituted alkyl, and at least one pyridine or one COOH, the substituents in the substituted pyridine are selected from at least one of -COOH, -F, -Cl, -Br, alkyl, and the substituents in the substituted benzene ring are selected from at least one of -COOH, -F, -Cl, -Br, alkyl; R3, R4, R5, R6, R9, R10 are each independently selected from at least one of H, F, Cl, Br; n is selected from any integer between 0-2, for example, can be 0, 1, 2. 10 11 12 13 14 15 16

[0038] The Prussian blue material provided by the application, the coating layer comprises compounds having the structure shown in formula 1 and / or compounds having the structure shown in formula 2, which can improve the conductivity, water absorption resistance, sodium storage capacity and structural stability of the Prussian blue material, and when applied to a battery, can reduce the dissolution of metal ions in the battery, and improve the discharge specific capacity, the first coulombic efficiency and the cycle performance of the battery. This is because the compounds having the structure shown in formula 1 and / or the compounds having the structure shown in formula 2 have good conductivity, which helps to form a conductive network and effectively improve the overall conductivity of the material. The conductivity at the pressure point of 15.92 MPa is ≥10 -5 S / cm, and the conductivity at the pressure point of 25.46 MPa is ≥5×10 -5 ​​​​​​​S / cm, reduces the energy loss in the charging and discharging process, and the large conjugate structure can take into account the electron transport and ion storage, thereby improving the cycle performance of the battery. The coating layer can act as a physical barrier to prevent moisture in the environment from entering the pore structure of the material. This barrier effect reduces the adsorption of crystal water, maintains the openness of the pore, and the above compound can reduce the lattice defects of the material, reduce the existence of crystal water, and the rigid molecular skeleton and alkyl structure reduce the water adsorption on the surface of the material. After exposure for 72 hours at a dew point of -20℃, the water content change rate is ≤70%, and after vacuum drying for 24 hours at 150℃, the water content change rate is ≤10%, thereby improving the ion storage and deintercalation efficiency and improving the initial coulombic efficiency and cycle life of the battery. In addition, the above compound can also capture and release sodium ions through the keto-enol tautomerism, thereby improving the sodium storage capacity of the material. At the same time, the pyridine or carboxyl in the substituent group of the above compound can coordinate with the metal ions that are misfit on the surface of the inner core lattice, which can improve the structural stability of the material, reduce the dissolution of metal ions in the electrolyte, thereby improving the discharge specific capacity and cycle performance of the battery; on the other hand, it can also improve the uniformity of the coating layer.

[0039] Therefore, the Prussian blue material provided by the present application can improve the conductivity, water resistance, sodium storage capacity and structural stability of the Prussian blue material. When applied to a battery, the amount of metal ion dissolved in the battery can be reduced, and the discharge specific capacity, initial coulombic efficiency and cycle performance of the battery can be improved.

[0040] In some embodiments of the present application, in the substituted benzene ring, -COOH is located at at least one of positions 3, 4 and 5 of the benzene ring. It can further coordinate with metal ions that are misfit on the surface of the inner core lattice, thereby improving the structural stability of the material, reducing the dissolution of metal ions in the electrolyte, and thereby improving the discharge specific capacity and cycle performance of the battery.

[0041] It should be noted that in the compound having the structure shown in formula 1 and / or the compound having the structure shown in formula 2, the position of the benzene ring connected to N is position 1, then the ortho position of position 1 is position 2, the meta position of position 1 is position 3 or 5, and the para position of position 1 is position 4.

[0042] In some embodiments of the present application, the macrocyclic compound includes at least one of the following compounds having the structure shown below:

[0043]

[0044]

[0045] In the present application, the compound with the structure shown in formula 1-1 to formula 1-8 can further improve the conductivity, water absorption resistance, sodium storage capacity and structural stability of the Prussian blue material, thereby reducing the dissolution of metal ions in the battery, and improving the specific capacity, the first coulombic efficiency and the cycle performance of the battery.

[0046] In some embodiments of the present application, the chemical composition of the Prussian blue compound is Na x Fe y G 1-y [Fe(CN)6]·zH2O, wherein 0

[0047] For example, x can be 0.1, 0.3, 0.5, 0.7, 1, 1.5, 2 or a range consisting of any two of them; y can be 0.1, 0.3, 0.5, 0.7, 1 or a range consisting of any two of them; z can be 0, 0.1, 0.3, 0.5, 0.7, 1, 2, 3, 4 or a range consisting of any two of them.

[0048] The chemical composition of the Prussian blue compound allows the reversible intercalation and deintercalation of sodium ions, which can provide a high energy density. The structural stability of the compound is high, and the material maintains good structural integrity during multiple charge and discharge cycles, providing excellent cycle life. In addition, the volume change of the material during the intercalation and deintercalation of sodium ions is small, which is beneficial to improve the mechanical stability of the battery. The open framework structure and large pore size allow fast ion diffusion, improve the rate performance of the material, and are suitable for fast charge and discharge.

[0049] In some embodiments of the present application, the mass percentage of the coating layer in the core is 3%-9%, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or a range consisting of any two of them.

[0050] In the present application, the mass percentage of the coating layer in the core is in the above range, which can form an effective conductive network to improve the overall electrical conductivity of the material. And it is sufficient to form a uniform and complete coating layer on the surface of the core, which can prevent moisture and other impurities in the environment from entering the core, maintain the structural integrity and chemical stability of the material. And it does not affect the ion transport and intercalation / deintercalation process, and improves the specific capacity and cycle performance of the battery.

[0051] In some embodiments of the present application, the average thickness of the coating layer is 10nm-20nm, for example, it can be 10nm, 12nm, 14nm, 15nm, 17nm, 19nm, 20nm or a range consisting of any two of them.

[0052] In the present application, the average thickness of the coating layer is in the above range, which is sufficient to form a continuous and uniform coating layer, capable of effectively blocking the moisture and other impurities in the environment from entering the material, and helps to improve the water absorption resistance and chemical stability of the material. And it can provide sufficient conductive path without significantly increasing the resistance of the material. In addition, the appropriate thickness of the coating layer will not affect the transmission of ions. At the same time, the appropriate thickness of the coating layer can effectively buffer the volume change of the core material during charging and discharging, reduce the formation of structural stress and defects, thereby improving the cycle stability and prolonging the battery life.

[0053] In the present application, the average thickness of the coating layer can be tested by transmission electron microscopy (TEM) to measure the thickness of the coating layer at least 10 different positions, and then take the average value.

[0054] In some embodiments of the present application, the specific surface area of the core is ≤3.5m 2 / g, for example, it can be 0.1m 2 / g, 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g, 3m 2 / g, 3.5m 2 / g or any two of them.

[0055] In some embodiments, the specific surface area of the Prussian blue material is 4.2m 2 / g-15m 2 / g, for example, it can be 4.2m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 10m 2 / g, 12m 2 / g, 15m 2 / g or any two of them.

[0056] In the present application, the specific surface area of the coated Prussian blue material changes by ≥20% compared to the specific surface area of the core, the increased specific surface area provides more active sites, which is conducive to improving the interfacial reaction between the material and the electrolyte, and can improve the charging and discharging rate and specific capacity of the battery. And it can improve the wettability of the electrolyte, ensure that the electrolyte can more evenly cover the surface of the material, which is conducive to improving the first coulombic efficiency and cycle stability of the battery. It can also provide more channels and paths to promote the rapid transmission and embedding / extraction of ions, which is conducive to improving the dynamic performance and energy efficiency of the battery.

[0057] In some embodiments of the present application, the inner core comprises micropores, and the micropores have a pore volume of 5-20% of the total pore volume of the Prussian blue analogue material, for example, 5%, 7%, 9%, 10%, 12%, 15%, 17%, 20%, or a range consisting of any two of them.

[0058] It can be understood that the micropores refer to pore structures with a pore size of less than 2 nm.

[0059] In the present application, the microporous structure provides more channels and surface area, which helps to improve the transmission rate of ions and the embedding / extraction efficiency. This structure can significantly improve the charging and discharging speed and overall performance of the battery. And the appropriate micropores increase the effective surface area of the material, thereby providing more active sites for electrochemical reactions, which helps to improve the specific capacity of the material and enables the battery to store more energy. In addition, the microporous structure helps to increase the contact area of the material with the electrolyte, improve the wettability of the electrolyte, and help to improve the first coulombic efficiency and cycle stability of the battery. At the same time, the microporous structure can buffer the volume change of the material during charging and discharging, reduce the formation of structural stress and cracks, thereby improving the mechanical stability and cycle life of the material.

[0060] In the present application, the Prussian blue analogue material is a cubic crystal structure.

[0061] In a second aspect, the present application provides a preparation method of the Prussian blue analogue material as described above, comprising the following steps:

[0062] The raw material system comprising the Prussian blue analogue compound and the coating material is subjected to coating treatment to obtain the Prussian blue analogue material; the coating material comprises a compound having the structure shown in Formula 1 and / or a compound having the structure shown in Formula 2.

[0063] In the present application, the Prussian blue analogue compound is subjected to coating treatment by the coating material to obtain the Prussian blue analogue material as described above.

[0064] Specifically, the Prussian blue analogue compound and a certain amount of coating material can be uniformly dispersed in a solvent, for example, acetone, and stirred for a certain period of time to obtain the Prussian blue analogue material with a coating layer. And the Prussian blue analogue material has high conductivity, water absorption resistance, sodium storage capacity, and structural stability. When applied to a battery, it can reduce the dissolution of metal ions in the battery, improve the specific capacity, the first coulombic efficiency, and the cycle performance of the battery.

[0065] In the present application, the preparation method of the Prussian blue analogue compound can be prepared by referring to conventional technical means in the art.

[0066] In one embodiment, the preparation method of the Prussian blue analogue compound can comprise the following steps:

[0067] 1) Dissolve low valence water-soluble salt containing element A, water-soluble salt containing element G and complexing agent into polar solvent to form a first solution; wherein the water-soluble salt includes but is not limited to sulfate, chloride, nitrate, etc.; the polar solvent includes at least one of pure water, methanol, ethanol, N,N-dimethylformamide (DMF). The complexing agent includes at least one of sodium citrate, citric acid, ethylenediamine, acetic acid.

[0068] 2) Dissolve sodium ferricyanide or sodium ferrocyanide and antioxidant into polar solvent in a certain proportion to form a second solution.

[0069] 3) Add a certain amount of auxiliary agent, such as polyvinylpyrrolidone, into the saturated water-soluble sodium salt solution to form a third solution, and the solvent used is consistent with the first and second solutions.

[0070] 4) Blow protective gas into the first, second and third solutions to remove oxygen in the solution system; the protective gas can be nitrogen and / or argon, the same below.

[0071] 5) Under a protective atmosphere, pump equal volumes of the first and second solutions into the third solution at an equal volume rate, and then perform aging, centrifugation, washing, drying and heat treatment to obtain a Prussian blue compound. The solution pumping rate is 10 mL / h-200 L / h; the pumping temperature is consistent with the aging treatment temperature, which can be 40°C-90°C (for methanol and ethanol solvent temperature range is 40°C-50°C); the aging treatment time is 12h-36h; the drying treatment temperature can be 105°C-160°C, and the time can be 12h-24h; the heat treatment temperature can be 200°C-300°C, and the time can be 2h-5h.

[0072] In some embodiments of the present application, the mass ratio of the Prussian blue compound to the coating material is 1:(3%-9%), for example, it can be 1:3%, 1:4%, 1:5%, 1:6%, 1:7%, 1:8%, 1:9% or a range consisting of any two of them.

[0073] By controlling the mass ratio of the Prussian blue compound to the coating material, the thickness of the coating layer can be controlled, which can effectively protect the Prussian blue compound, while not excessively increasing the weight of the material or hindering ion transmission.

[0074] In some embodiments, the coating treatment time is 2h-6h, for example, it can be 2h, 3h, 4h, 5h, 6h or a range consisting of any two of them. Sufficient time is provided to form a uniform and stable coating layer, while maintaining the efficiency and economy of the process.

[0075] In some embodiments of the present application, the raw material system further comprises a complexing agent, and the complexing agent comprises at least one of sodium citrate, citric acid, ethylenediamine, and acetic acid.

[0076] In the present application, the addition of the complexing agent in the raw material system can further improve the coating effect, improve the stability of the coating layer, and further improve the conductivity, water absorption resistance, sodium storage capacity, and structural stability of the Prussian blue material. When applied to a battery, the metal ion dissolution amount of the battery can be reduced, and the discharge specific capacity, the initial coulombic efficiency, and the cycle performance of the battery can be improved.

[0077] In some embodiments of the present application, the coated product obtained by the coating treatment is sequentially subjected to centrifugation, washing, drying, and heat treatment to obtain the Prussian blue material.

[0078] In the present application, the centrifugation and washing steps are beneficial to remove the unreacted substances, solvents, and other impurities remaining in the synthesis process, improve the purity of the material, and thus improve the electrochemical performance and stability of the material.

[0079] The drying step can remove the water in the material and prevent the influence of water on the structure and performance of the material.

[0080] The heat treatment can optimize the crystal structure and pore characteristics of the material, improve its conductivity and ion transport efficiency, and thus improve the overall performance of the battery.

[0081] In some embodiments of the present application, the temperature of the drying treatment is 105-160℃, for example, it can be 105℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, or a range consisting of any two of them; the time is 12-24h, for example, it can be 12h, 15h, 17h, 20h, 22h, 24h, or a range consisting of any two of them.

[0082] In the present application, the temperature and time of the drying treatment can ensure that the water in the material is completely removed, which is beneficial to prevent the negative influence of water on the structure and electrochemical performance of the material. At the same time, the removal of water can also avoid the decomposition or structural change of the material caused by excessively high temperature, and maintain the chemical and physical stability of the material.

[0083] In some embodiments, the temperature of the heat treatment is 200-300℃, for example, it can be 200℃, 220℃, 240℃, 250℃, 270℃, 290℃, 300℃, or a range consisting of any two of them; the time is 2-5h, for example, it can be 2h, 3h, 3.5h, 4h, 5h, or a range consisting of any two of them.

[0084] In the present application, the temperature and time of heat treatment can promote the crystallization of the material, improve the order of the crystal structure, and be beneficial to enhancing the electrochemical performance of the material, including conductivity and ion transmission efficiency. It can also improve the mechanical strength and toughness of the material, and enhance its durability and stress resistance during use.

[0085] The preparation method of the present application has mild conditions, does not require extreme conditions such as high temperature and high pressure, the synthesis equipment is simple, the energy consumption is low, and it is conducive to large-scale industrial production.

[0086] In a third aspect, the present application provides a positive electrode sheet comprising the Prussian blue type material as described above or prepared according to the preparation method of the Prussian blue type material as described above.

[0087] The positive electrode sheet of the present application can be prepared by conventional technical means in the art. Specifically, the Prussian blue type material, the conductive agent and the binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry, and then the positive electrode active layer slurry can be coated on at least one functional surface of the positive electrode current collector, and after drying, the positive electrode sheet of the present application can be obtained.

[0088] The present application does not make special limitation on the specific types of conductive agent and adhesive. The components such as conductive agent and adhesive can be selected from conventional materials in the art. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotube, conductive graphite and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, butadiene styrene rubber and phenylpropyl rubber.

[0089] The present application does not make special limitation on the coating method. Any one of gravure coating, extrusion coating, spraying, screen printing and the like can be used to realize the coating of the positive electrode active layer slurry.

[0090] The positive electrode sheet provided by the present application comprises the Prussian blue type material as described above, and therefore the positive electrode sheet applied to a battery can reduce the dissolution amount of metal ions of the battery, and improve the discharge specific capacity, the first coulombic efficiency and the cycle performance of the battery.

[0091] In a fourth aspect, the present application provides a battery comprising the positive electrode sheet as described above.

[0092] The battery of the present application comprises, in addition to the positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The composition of the negative electrode sheet can refer to conventional negative electrode sheets in the art, and the separator can also use conventional separators in the art, such as PP film and PE film.

[0093] The battery of the present application can be prepared by conventional methods in the art. Specifically, the positive electrode sheet, the separator and the negative electrode sheet can be sequentially stacked and then the stacked or wound battery core can be obtained. Then, the battery can be obtained by baking, liquid injection, formation, packaging and other processes.

[0094] The battery of the present application can be a single battery, a battery pack, a battery package or a cylindrical battery formed by connecting single batteries. These batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection or mixed connection including both series and parallel connection, without particular limitation.

[0095] In the present application, the battery can include a sodium-ion battery.

[0096] The technical solutions of the present application will be further described below in combination with specific examples.

[0097] Example 1

[0098] The preparation method of the Prussian blue material in this embodiment includes the following steps:

[0099] 1) 0.1 mol of iron sulfate heptahydrate, 0.02 mol of anhydrous zinc sulfate and 0.5 mol of trisodium citrate were mixed in 1 L of ultrapure water to form a first solution.

[0100] 2) 0.1 mol of sodium ferrocyanide and 0.15 mol of ascorbic acid were mixed in 1 L of ultrapure water to form a second solution.

[0101] 3) 20 g of polyvinylpyrrolidone was added to 2 L of saturated sodium chloride aqueous solution to form a third solution.

[0102] 4) Nitrogen was blown into the first solution, the second solution and the third solution to remove oxygen in the solution system.

[0103] 5) Under a nitrogen atmosphere, equal volumes of the first solution and the second solution were pumped into the third solution at a speed of 200 mL / h, the temperature was kept at 50℃, and the precipitation reaction was carried out under stirring. Then, aging treatment was carried out at 50℃ for 24 h, and the resulting product was washed by centrifugation with ultrapure water and anhydrous ethanol, and dried in an oven at 150℃ for 24 h. Finally, the dried powder was further heat treated at 200℃ for 4 h to obtain the Prussian blue compound Na2Fe 0.833 Zn 0.167 [Fe(CN)6]·3.5H2O.

[0104] 6) 20 g of Prussian blue type compound and 5% of coating material (compound with structure shown in formula 1-1) by mass of Prussian blue type compound were uniformly dispersed in 2 L of acetone solvent, 20 mL of complexing agent ethylenediamine was added, stirred for 3 h, the precipitate was separated by centrifugation and washed with ultrapure water and anhydrous ethanol, and placed in a 150°C oven for drying for 24 h. Finally, the dried powder was further heat treated at 200°C for 4 h to obtain a Prussian blue type material. The Prussian blue type material comprises a core and a coating layer covering at least part of the surface of the core, the core comprises Prussian blue type compound Na2Fe 0.833 Zn 0.167 [Fe(CN)6]·3.5H2O, and the coating layer comprises compound with structure shown in formula 1-1.

[0105] Example 2

[0106] Example 2 and the preparation method of Prussian blue type material of Example 1 are basically the same, except that in step 6), the mass ratio of Prussian blue type compound to coating material is 1:3%.

[0107] Example 3

[0108] Example 3 and the preparation method of Prussian blue type material of Example 1 are basically the same, except that in step 6), the mass ratio of Prussian blue type compound to coating material is 1:7%.

[0109] Example 4

[0110] Example 4 and the preparation method of Prussian blue type material of Example 1 are basically the same, except that in step 6), the mass ratio of Prussian blue type compound to coating material is 1:9%.

[0111] Example 5

[0112] Example 5 and the preparation method of Prussian blue type material of Example 1 are basically the same, except that in step 6), the stirring time (i.e. coating time) is 2 h, the drying treatment temperature is 105°C, the time is 12 h, the heat treatment temperature is 250°C, and the time is 5 h.

[0113] Example 6

[0114] Example 6 and the preparation method of Prussian blue type material of Example 1 are basically the same, except that in step 6), the stirring time (i.e. coating time) is 6 h, the drying treatment temperature is 160°C, the time is 12 h, the heat treatment temperature is 300°C, and the time is 2 h.

[0115] Example 7

[0116] Example 7

[0117] Example 8

[0118] Example 8 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), the coating material is a compound having the structure shown in Formula 1-3.

[0119] Example 9

[0120] Example 9 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), the coating material is a compound having the structure shown in Formula 1-7.

[0121] Example 10

[0122] Example 10 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), the coating material is a compound having the structure shown in Formula 1-5.

[0123] Example 11

[0124] Example 11 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), the coating material is a compound having the structure shown in Formula 1-8.

[0125] Comparative Example 1

[0126] Comparative Example 1 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), the Prussian blue-based compound is not coated, i.e., the Prussian blue-based compound does not include a coating layer on its surface.

[0127] Comparative Example 2

[0128] Comparative Example 2 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), a compound having the structure shown below is used as the coating material, i.e., the benzene ring does not include COOH in its substituent group.

[0129]

[0130] Comparative Example 3

[0131] Comparative Example 3 is basically the same as the method for preparing the Prussian blue-based material of Example 1, except that in step 6), poly 3,4-ethylenedioxythiophene (PEDOT) is used as the coating material.

[0132] Test Example:

[0133] 1. Average thickness of coating layer: The thickness of coating layer at 10 different positions can be tested by transmission electron microscopy (TEM), and then the average value is obtained.

[0134] 2. Specific surface area: The specific surface area of Prussian blue analogues is tested by BET static method.

[0135] 3. Pore volume: The adsorption-desorption curve is obtained by using BJH-300 specific surface and pore size analyzer, and the pore volume of different pore sizes is calculated by QSDFT model.

[0136] 4. Mass percentage of coating layer to core: Dimethylacetamide (DMA) is used as a dispersion solvent to disperse Prussian blue analogues (mass m0), and in the presence of acetic acid, 120℃ sealed stirring reaction for 48-72h to completely remove the coating layer on the surface of Prussian blue analogues, followed by washing with volatile solvent, drying and weighing, to obtain the mass of the core m1, the mass of the coating layer (m0-m1), and the mass percentage of the coating layer to the core = (m0-m1) / m1×100%.

[0137] 5. Conductivity: The conductivity of Prussian blue analogues is tested by using MCP-PD51 powder impedance tester, and the pressure points are selected as 15.92MPa and 25.46MPa, respectively.

[0138] 6. Moisture content: The initial moisture content of Prussian blue analogues is tested by using Karl Fischer moisture meter, and then after exposure for 24h, 48h, 72h in turn in the environment with dew point-20℃, the moisture content is tested. After drying for 24h in the vacuum environment at 150℃, the moisture content is tested.

[0139] The moisture content change rate of Prussian blue analogues after exposure for 72h in the environment with dew point-20℃ = (moisture content after exposure for 72h-initial moisture content) / initial moisture content×100%.

[0140] The moisture content change rate of Prussian blue analogues after exposure for 72h in the environment with dew point-20℃ = (moisture content after exposure for 72h-initial moisture content) / initial moisture content×100%.

[0141] 7、Specific capacity, initial coulombic efficiency: at 25℃, under normal pressure (0.1 MPa), the Prussian blue type material of each example and the comparative example was weighed and mixed with acetylene black and polyvinylidene fluoride (PVDF) according to a mass ratio of 90:5:5, and an appropriate amount of N-methyl pyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 15 μm, and after drying, it was baked in a vacuum oven at 80℃ for 10 h. After taking out, it was rolled and cut into a circular positive electrode sheet with a diameter of 14 mm. When assembling the button cell, a polished sodium sheet was used as a negative electrode sheet, and a sodium battery electrolyte (electrolyte: 1 mol / L sodium hexafluorophosphate, solvent: EC / DMC / DEC = v / v / v: 1 / 1 / 1) and a sodium battery composite separator (glass fiber) were assembled into a button cell in an argon-filled glove box.

[0142] 0.1C rate constant current charging to 4.0V, then constant voltage charging to 4.0V at 0.05C, at this time the charging capacity is recorded as the first circle charging specific capacity, then standing for 5 min, and then discharging to 2.0V at 0.1C rate constant current, the discharge capacity at this time is recorded as the first circle discharge specific capacity, and the first circle discharge specific capacity / the first circle charging specific capacity is the initial coulombic efficiency.

[0143] 8、Cycling performance test: at 25℃, 1C charging rate constant current charging to 4.0V, then 0.5C charging rate constant voltage charging to 4.0V, then 1C discharging rate discharging to 2.0V, repeating 300 times of such charging and discharging cycles, measuring the discharge capacity Q1 at the first cycle and the discharge capacity Q300 at the 300th cycle. 300 The capacity retention rate Q = Q300 / Q1x 100% after 300 cycles. 300

[0144] 9、ICP test of transition metal elements in electrolyte after cycling: the electrolyte in the button cell of all examples and comparative examples subjected to the cycling test was taken out, and the iron content therein was measured by inductively coupled plasma spectroscopy (ICP). The spectral line was selected as 238.2 nm, and the observation mode was selected as radial observation.

[0145] Figure 2 The TEM image of the Prussian blue type material of Example 1 provided in the present application.

[0146] Figure 2 The dashed part is the coating layer, and it can be seen that the Prussian blue type material of Example 1 is covered with a coating layer on the surface of the core.

[0147] Table 1

[0148]

[0149] Table 2 ​

[0150]

[0151]

[0152] From Table 1-2, compared with the comparative example, the Prussian blue material provided by the application, the coating layer includes a compound having the structure shown in formula 1 and / or a compound having the structure shown in formula 2, can improve the conductivity, water resistance, sodium storage capacity and structural stability of the Prussian blue material. When applied to a battery, it can reduce the dissolution of metal ions in the battery, and improve the discharge specific capacity, the first coulombic efficiency and the cycle performance of the battery.

[0153] Compared with Comparative Example 1-3, the conductivity data of Example 1-11 is better than that of Comparative Example 1-3, which shows that the compound having the structure shown in formula 1 and / or the compound having the structure shown in formula 2 has good electron conductivity, which effectively improves the conductivity of the material.

[0154] From the comparison of Example 1-4, it can be seen that as the coating amount increases, the electrical conductivity gradually increases, that is, a thicker coating layer can further improve the conductivity of the material. And as the coating amount increases, the water resistance gradually increases. In addition, as the coating amount increases, the first discharge specific capacity first increases and then decreases, while the cycle capacity retention rate gradually increases, which shows that the compound having the structure shown in formula 1 and / or the compound having the structure shown in formula 2 improves the sodium storage capacity of the material through the keto-enol tautomerism, while improving the structural stability of the material.

[0155] From the comparison of Example 1, Example 7 and Comparative Example 2, it can be seen that as the number of carboxyl groups in the substituent group increases, the iron content in the electrolyte gradually decreases, and the cycle capacity retention rate gradually increases, which shows that the iron dissolution on the surface of the material is an important factor for the capacity decrease of the battery. This is mainly because the carboxyl oxygen coordinates and chelates with the surface defects of the core, especially the iron ions, which can effectively prevent the corrosion of the electrolyte to the material and improve the structural stability.

[0156] Compared with Comparative Example 1-3, the water content change rate of the Prussian blue material of Example 1-11 is ≤10% after vacuum drying at 150℃ for 24h, which shows that the compound having the structure shown in formula 1 and / or the compound having the structure shown in formula 2 can restore the water content of the Prussian blue material to a level close to the initial water content.

[0157] It should be understood that many of the materials and devices exemplified in this disclosure are articles of manufacture (i.e., articles of manufacture) according to this disclosure. The articles of manufacture can be employed as such to provide advantageous results. The articles of manufacture can also be employed in the practice or testing of the present disclosure. The articles of manufacture can also be employed in the practice or testing of other examples of the present disclosure. The articles of manufacture employed as such for realizing the advantageous results described herein, for practicing the instant disclosure, and for practicing other examples of the instant disclosure will vary depending on the specific context.

Claims

1. A Prussian blue material, characterized in that: comprising a core and a coating layer covering at least a portion of a surface of the core; The core includes a Prussian blue compound; The coating layer includes a macrocyclic compound having a structure shown in Formula 1 and / or Formula 2: Wherein, R1, R2, R7, and R8 are each independently selected from at least one of substituted pyridine, unsubstituted pyridine, substituted benzene ring, and substituted alkyl, and contain at least one pyridine or one COOH, the substituent in the substituted pyridine is selected from at least one of -COOH, -F, -Cl, -Br, and alkyl, and the substituent in the substituted benzene ring is selected from at least one of -COOH, -F, -Cl, -Br, and alkyl; R3, R4, R5, R6, R9, R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 Each is independently selected from at least one of H, F, Cl, and Br; and n is selected from any integer between 0 and 2.

2. The Prussian blue material according to claim 1, characterized in that In the substituted benzene ring, -COOH is located at at least one of the 3-position, 4-position, and 5-position of the benzene ring.

3. The Prussian blue material according to claim 1 or 2, characterized in that The macrocyclic compound includes at least one of the compounds shown below:

4. The Prussian blue material according to any one of claims 1 to 3, characterized in that The chemical composition of the Prussian blue compound is Na x Fe y G 1-y [Fe(CN)6]·zH2O, wherein 0<x≤2, 0<y≤1, 0≤z≤4, and G includes at least one of Ni, Mn, Zn, Cu, Al, and Mg.

5. The Prussian blue material according to any one of claims 1 to 4, characterized in that The coating layer accounts for 3% to 9% of the core by mass; And / or, the average thickness of the coating layer is 10nm-20nm.

6. The Prussian blue material according to any one of claims 1 to 5, characterized in that The specific surface area of ​​the core is ≤3.5m 2 / g; And / or, the specific surface area of ​​the Prussian blue material is 4.2m 2 / g-15m 2 / g.

7. The Prussian blue material according to any one of claims 1 to 6, characterized in that The inner core comprises micropores, and the pore volume of the micropores accounts for 5% to 20% of the total pore volume of the Prussian blue material.

8. A method for preparing a Prussian blue material according to any one of claims 1 to 7, characterized in that: The following steps are involved: A raw material system including a Prussian blue compound and a coating material is subjected to coating treatment to obtain the Prussian blue material; the coating material includes a compound having a structure shown in Formula 1 and / or a compound having a structure shown in Formula 2.

9. A positive electrode sheet, characterized in that: The invention relates to a Prussian blue material according to any one of claims 1 to 7 or a Prussian blue material prepared according to the preparation method of the Prussian blue material according to claim 8.

10. A battery, characterized in that: Including the positive electrode sheet according to claim 9.

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