Prussian white material and preparation method therefor, positive electrode sheet, battery, and electric device
By coating the surface of Prussian white material with a nickel-doped shell and forming a carbide layer, the structural degradation problem of the material during charge and discharge processes was solved, achieving high capacity and excellent cycle stability.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NINGBO RONBAY LITHIUM BATTERY MATERIAL CO LTD
- Filing Date
- 2025-09-30
- Publication Date
- 2026-07-16
AI Technical Summary
Prussian white materials are prone to the Jan Taylor effect during charge and discharge, which leads to particle corrosion and dissolution, intergranular crack formation, increased interfacial impedance and severe degradation of bulk structure, resulting in poor cycle stability.
A nickel-doped manganese-based Prussian white shell is coated onto the surface of pure manganese-based Prussian white material, and a carbonization layer is formed on the shell surface. The crystal structure of the material is stabilized by in-situ carbonization treatment, which suppresses the occurrence of the Jan Taylor phenomenon.
This enhances the overall stability and cycle stability of the material while maintaining high capacity, and improves the sodium ion diffusion rate and the material's conductivity.
Smart Images
Figure CN2025126033_16072026_PF_FP_ABST
Abstract
Description
Prussian white materials and their preparation methods, positive electrode sheets, batteries and electrical devices
[0001] This application claims priority to Chinese Patent Application No. 202510019349.8, filed on January 7, 2025, entitled "Prussian White Material and Preparation Method Thereof, Positive Electrode Sheet, Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application belongs to the field of batteries and relates to a Prussian white material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology
[0003] Prussian white material possesses a three-dimensional framework structure conducive to the migration of large-sized sodium ions and exhibits high specific capacity, making it a relatively ideal cathode material for sodium-ion batteries. However, Prussian white material, rich in manganese, is prone to the Jan Taylor effect during charge and discharge, leading to particle corrosion and dissolution, intergranular crack formation, a continuous increase in interfacial impedance, and severe degradation of the bulk structure, resulting in poor cycle stability. Therefore, improving the cycle stability of Prussian white material is a pressing technical problem to be solved in this field. Summary of the Invention
[0004] This application provides a Prussian white material and its preparation method, a positive electrode, a battery, and an electrical device. The Prussian white material of this application is prepared by coating a pure manganese-based Prussian white material with a manganese-based Prussian white material shell doped with nickel. This stabilizes the crystal structure of the material, thereby suppressing the occurrence of the Jan Taylor phenomenon, enhancing the overall stability of the material, and enabling the material to have both high capacity and excellent cycle stability.
[0005] The first aspect of this application provides a Prussian white material, comprising a core and a first outer shell covering the surface of the core;
[0006] The kernel is composed of Na x Mn[Fe(CN)6] y ·αH₂O, where 1≤x≤1.8, 0.9≤y≤0.99, 0.5≤α≤3;
[0007] The first outer shell is composed of Na. a Mn b Ni 1-b [Fe(CN)6] c ·βH2O, where 1.2≤a≤1.8, 0.8≤b≤0.99, 0.8≤c≤0.995, and 0.5≤β≤3.
[0008] The Prussian white material as described above, wherein the particle size of the core is 1 to 6 μm; and / or, the thickness of the first shell is 1 to 2 μm.
[0009] The Prussian white material described above, wherein the surface of the first outer shell is further covered with a second outer shell, the second outer shell being composed of Na. m Ni[Fe(CN)6] n ·γH2O, where 0.5≤m≤1.9, 0.9≤n≤0.99, and 0.05≤γ≤1.5.
[0010] The Prussian white material as described above, wherein the thickness of the second shell is 50-100 nm.
[0011] The Prussian white material as described above, wherein the outer surface of the Prussian white material is a carbonized layer.
[0012] The Prussian white material described above, wherein the thickness of the carbonized layer is 2–15 nm.
[0013] The Prussian white material as described above, wherein the Prussian white material includes a first outer shell and a carbonized layer located on the surface of the first outer shell, the carbonized layer being formed by carbonizing the first outer shell in situ;
[0014] Alternatively, the Prussian white material may include a second outer shell and a carbonized layer located on the surface of the second outer shell, the carbonized layer being formed by carbonizing the second outer shell in situ.
[0015] The Prussian white material as described above, wherein the in-situ carbonization includes: drying in a forced-air environment at 60–100°C for 4–24 h, followed by vacuum drying at 120–200°C for 16–24 h, and finally vacuum calcination at 205–240°C for 0.5–5 h.
[0016] The Prussian white material as described above, wherein the Ni content in the Prussian white material is 2000-10000 ppm and the Mn content is 15-30 wt%.
[0017] The Prussian white material described above, wherein the Prussian white material satisfies at least one of the following conditions:
[0018] (1) Specific surface area ≥ 4.5m² 2 / g;
[0019] (2) Sodium ion diffusion coefficient ≥ 1.14 × 10 -10 ;
[0020] (3) The D50 particle size is 2-10 μm;
[0021] (4) The mass content difference between carbon and nitrogen is 0.5% to 9.5%;
[0022] (5) Water content ≤1200ppm.
[0023] A second aspect of this application provides a method for preparing the Prussian white material as described above, comprising the following steps:
[0024] 1) A mixed solution of soluble divalent manganese salt and sodium ferrocyanide is added to a mixed solution of soluble sodium salt and sodium ferrocyanide at a rate of 1-2 L / h to carry out the first coprecipitation reaction and obtain a first solution including the core.
[0025] 2) Add a mixed solution of soluble divalent manganese salt, soluble divalent nickel salt and sodium ferrocyanide to the first solution to carry out a second coprecipitation reaction, forming a first shell on the surface of the core, to obtain the Prussian white material.
[0026] The preparation method described above, wherein after forming the first outer shell on the surface of the core, further includes adding an aqueous solution of a soluble divalent nickel salt to the reaction solution to carry out a third coprecipitation reaction to form a second outer shell, thereby obtaining the Prussian white material.
[0027] The preparation method described above further includes, after forming the first shell or the second shell, drying the material by blowing at 60-100°C for 4-24 hours, followed by vacuum drying at 120-200°C for 16-24 hours, and finally vacuum calcining at 205-240°C for 0.5-5 hours to form a carbonized layer on the surface of the Prussian white material.
[0028] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive active material layer, wherein the positive active material layer comprises the Prussian white material provided in the first aspect of this application.
[0029] A fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.
[0030] The fifth aspect of this application provides for an electrical device including the battery provided in the fourth aspect of this application.
[0031] The implementation of this application has at least the following advantages:
[0032] The Prussian white material provided in this application stabilizes the crystal structure of the Prussian white material by coating the surface of the pure manganese Prussian white core with a manganese-based Prussian white shell doped with nickel, thereby suppressing the occurrence of the Jan Taylor phenomenon, enhancing the overall stability of the material, and enabling the material to have both high capacity and excellent cycling stability. Attached Figure Description
[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0034] Figure 1 shows a comparison of the appearance of Prussian white materials in Examples 1 to 6, where a is the appearance of the Prussian white cathode material in Example 5, b is the appearance of the Prussian white cathode material in Example 6, c is the appearance of the Prussian white cathode material in Example 1, d is the appearance of the Prussian white cathode material in Example 2, e is the appearance of the Prussian white cathode material in Example 3, and f is the appearance of the Prussian white cathode material in Example 4.
[0035] Figure 2 shows the SEM comparison images of Prussian white materials from Examples 1 to 6, where a is the Prussian white material of Example 5, b is the Prussian white material of Example 6, c is the Prussian white material of Example 1, d is the Prussian white material of Example 2, e is the Prussian white material of Example 3, and f is the Prussian white material of Example 4.
[0036] Figure 3 is a comparison diagram of Prussian white material EDS in Example 5;
[0037] Figure 4 is a comparison of the impedance curves of button cells assembled with Prussian white materials in Examples 2, 3, 5, and 6.
[0038] Figure 5 is a comparison of the XRD characteristic curves of the Prussian white material before and after the outer shell of Example 1 was coated;
[0039] Figure 6 is a comparison of the rate performance of button cells assembled with Prussian white materials in Examples 1-6.
[0040] Figure 7 is a SEM image of the Prussian white material from Example 11. Detailed Implementation
[0041] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0042] Prussian white materials possess a three-dimensional framework structure conducive to the migration of large-sized sodium ions and a high specific capacity, making them a relatively ideal cathode material for sodium-ion batteries. Among them, Mn... 2+ / Mn 3+Valence state changes play a crucial role in improving the charge-discharge capacity of Prussian white materials. High manganese content in Prussian white materials is beneficial for achieving high capacity, but excessively high manganese content can easily lead to the Jan Taylor effect during charge-discharge processes, causing some manganese to convert to Mn. 2+ The form of the substance dissolves in the electrolyte, leading to unstable material structure and poor cycle performance.
[0043] Based on this, the first aspect of this application provides a Prussian white material, including a core and a first outer shell covering the surface of the core;
[0044] The kernel is composed of Na x Mn[Fe(CN)6] y ·αH₂O, where 1≤x≤1.8, 0.9≤y≤0.99, 0.5≤α≤3;
[0045] The first outer shell is composed of Na. a Mn b Ni 1-b [Fe(CN)6] c ·βH2O, where 1.2≤a≤1.8, 0.8≤b≤0.995, 0.8≤c≤0.99, and 0.5≤β≤3.
[0046] This application involves coating a pure manganese Prussian white (MnHCF) core with a first shell of nickel-manganese Prussian white (Mn-NiHCF). The first shell is doped with nickel in the manganese-based Prussian white material, which can stabilize the crystal structure of the Prussian white material, thereby suppressing the occurrence of the Jan Taylor phenomenon, enhancing the overall stability of the material, and enabling the material to have both high capacity and excellent cycling stability.
[0047] Smaller particle size translates to a larger specific surface area and improves reaction kinetics, allowing sodium ions to diffuse more quickly to the active sites. However, excessively small particle size can lead to agglomeration and phase transitions, negatively impacting structural stability. Therefore, the core particle size is controlled to be 1–6 μm. For example, the core particle size can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or any combination thereof.
[0048] While a larger first shell thickness can better enhance the cycling stability of the material, it can also significantly affect the material's capacity. To achieve a better balance between cycling stability and capacity, the thickness of the first shell is controlled to be 1–2 μm. For example, the thickness of the first shell is 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or any two of these values.
[0049] In some specific embodiments, the surface of the first outer shell further includes a second outer shell, the second outer shell being composed of Na. m Ni[Fe(CN)6] n ·γH2O, where 0.5≤m≤1.9, 0.9≤n≤0.99, and 0.05≤γ≤1.5.
[0050] The second outer shell is made of pure nickel Prussian white material (Ni-HCF), which has strong inertness and can further improve the cycling stability of the material.
[0051] Understandably, the thickness of the second shell should not be too thick, otherwise it will have a significant adverse effect on the material's capacity. Therefore, the thickness of the second shell is controlled to be 50–100 nm. For example, the thickness of the second shell can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any two of these values.
[0052] In some specific implementations, the outer surface of the Prussian white material is a carbonized layer.
[0053] The carbonized layer on the outer surface, rich in carbon, provides an additional conductive network and sodium ion diffusion pathway, promoting electrolyte penetration and mitigating the poor conductivity and reduced capacity issues caused by inert Ni doping. It also increases the specific surface area and reduces the material's impedance.
[0054] Excessive carbide layer thickness can also affect the material's capacity utilization. Therefore, the thickness of the carbide layer is controlled to be between 2 and 15 nm to ensure the material has both high capacity utilization, specific surface area, and conductivity. For example, the thickness of the carbide layer can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or any range of two values thereof.
[0055] When the Prussian white material of this application comprises only a core and a first shell, the carbonized layer is located on the surface of the first shell and can be formed by carbonizing the first shell in situ.
[0056] When the Prussian white material of this application includes a core, a first shell and a second shell, the carbonized layer is located on the surface of the second shell and can be formed by carbonizing the second shell in situ.
[0057] The carbonized layer formed by in-situ carbonization of the first or second shell has high uniformity and density, with almost no individual carbon particles forming, thus avoiding the formation of conductive dead zones.
[0058] Furthermore, in-situ carbonization includes: drying in a forced-air environment at 60–100°C for 4–24 hours, followed by vacuum drying at 120–200°C for 16–24 hours, and finally vacuum calcination at 205–240°C for 0.5–5 hours.
[0059] The carbonization process is carried out in stages. The temperature difference between each stage is controlled at 40 to 100°C, and each stage uses a staged airflow for drying. The gases used include, but are not limited to, air, nitrogen, and argon, and the gas flow rate can be controlled at 2 to 15 L / h.
[0060] Drying with forced air at 60–100℃ removes adsorbed water from the material surface. Subsequent vacuum drying at 120–200℃ removes interstitial water. Finally, high-temperature treatment under an inert gas flow above 200℃ removes internal crystal water and simultaneously carbonizes the material surface, forming a carbonized layer in situ. By using multi-stage heating under different atmospheres during the drying process, a surface carbonized layer is formed in situ while preventing oxidative decomposition of the surface material. This also removes most of the adsorbed and interstitial water, reducing the material's water content.
[0061] In addition, the nickel in the first and second shells enables the material to have good structural stability, and the material can still avoid decomposition during subsequent in-situ carbonization treatment at high temperatures.
[0062] In some preferred embodiments, the Ni content in the Prussian white material is 2000–10000 ppm, and the Mn content is 15–30 wt%.
[0063] By controlling the Ni and Mn content in the Prussian white material within the above-mentioned range, it is possible to dope the material with a certain amount of Ni to maintain the structural stability of the material, and to maintain a sufficient amount of Mn content to keep the material with high capacity.
[0064] For example, the Ni content in Prussian white material can be any combination of 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm or more, and the Mn content can be any combination of 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, or any combination of the above.
[0065] In some specific embodiments, the Prussian white material of this application satisfies at least one of the following conditions:
[0066] (1) Specific surface area ≥ 4.5m² 2 / g;
[0067] (2) Sodium ion diffusion coefficient ≥ 1.14 × 10 -10 ;
[0068] (3) The D50 particle size is 2-10 μm;
[0069] (4) The mass content difference between carbon and nitrogen is 0.5% to 9.5%;
[0070] (5) Water content ≤1200ppm.
[0071] When the specific surface area of the material is ≥4.5m² 2 / g indicates that the material has more active sites, which is more conducive to the material's capacity utilization. Coating and controlling particle size are important means to achieve high specific surface area. Experimental studies have found that the formation of an outer surface carbonization layer can significantly increase the specific surface area of the material and prevent the occurrence of material agglomeration, making it the preferred method to achieve high surface area.
[0072] The sodium ion diffusion coefficient refers to the diffusion rate of sodium ions in Prussian white materials, which can be obtained by electrochemical impedance spectroscopy (EIS) or cyclic voltammetry (CV). The sodium ion diffusion coefficient of the material should be controlled to ≥1.14 × 10⁻⁶. -10 This allows sodium ions to move rapidly within the material, facilitating fast charging and discharging. Controlling particle size, introducing doping with other elements to alter the crystal structure, and coating the material surface with a conductive layer are all important methods to improve the sodium ion diffusion coefficient. Research has found that by setting a carbonization layer on the outer surface of the material, the sodium ion diffusion coefficient can be increased by an order of magnitude while maintaining high capacity and good structural stability, making it the preferred method for achieving a high sodium ion diffusion coefficient.
[0073] Controlling the D50 particle size of the material within the range of 2–10 μm, preferably 5–7 μm, is beneficial for subsequent slurry preparation and electrode coating. Furthermore, the D50 particle size exhibits good uniformity within this range, avoiding localized stress concentration and volume changes, which helps extend the battery's cycle life.
[0074] Specifically, the D50 particle size of the material can be controlled within the above-mentioned range by adjusting the aging time during the preparation process.
[0075] For example, the D50 particle size of the material can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any two of the above values.
[0076] During the carbonization process on a material surface, carbon is deposited, while nitrogen is released as a gas, increasing the difference in the overall carbon and nitrogen content. Studies have shown that controlling the difference in carbon and nitrogen content between 0.5% and 9.5% ensures the material surface remains in a micro-carbonized state, preventing over-carbonization and its resulting reduction in material capacity.
[0077] For example, the difference in mass content of carbon and nitrogen in the material can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, or any two of the above values.
[0078] During the synthesis of Prussian white materials, it is unavoidable that some water of crystallization will form and occupy active sites, reducing the specific capacity and structural stability of the material. Simultaneously, the material itself is highly hygroscopic, with a water content reaching as high as 100,000 ppm under normal conditions. During battery cycling, this water can easily escape and react with the electrolyte, leading to structural collapse and electrolyte failure. Furthermore, surface moisture is prone to oxidation at high temperatures, forming a gray oxide layer that affects the material's electrochemical performance. This application utilizes a staged airflow drying process to effectively remove adsorbed and interstitial water from the material, reducing the overall water content (the sum of adsorbed water, interstitial water, and water of crystallization) to ≤1200 ppm.
[0079] A second aspect of this application provides a method for preparing the Prussian white material as described above, the method comprising the following steps:
[0080] 1) A mixed solution of soluble divalent manganese salt and sodium ferrocyanide is added to a mixed solution of soluble sodium salt and sodium ferrocyanide at a rate of 1 to 2 L / h to carry out a first coprecipitation reaction, thereby obtaining a first solution including the core; for example, the addition rate can be 1 L / h, 1.1 L / h, 1.2 L / h, 1.3 L / h, 1.4 L / h, 1.5 L / h, 1.6 L / h, 1.7 L / h, 1.8 L / h, 1.9 L / h, 2 L / h or any two of the above values.
[0081] 2) Add a mixed solution of soluble divalent manganese salt, soluble divalent nickel salt and sodium ferrocyanide to the first solution to carry out a second coprecipitation reaction, forming a first outer shell on the core surface to obtain Prussian white material.
[0082] Specifically, soluble divalent manganese salts, soluble sodium salts, and soluble divalent nickel salts include, but are not limited to, their chlorides, sulfates, nitrates, and acetates. Specifically, soluble divalent manganese salts can be one or more of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; soluble sodium salts can be one or more of sodium chloride, sodium sulfate, sodium nitrate, and sodium acetate; and soluble divalent nickel salts can be one or more of nickel sulfate, nickel nitrate, nickel acetate, and nickel chloride.
[0083] In some specific embodiments, the conditions for the first coprecipitation reaction are: reaction at 60–80°C and 100–300 rpm for 6–8 hours.
[0084] After the first coprecipitation reaction is completed, the reaction system can be heated to 50-90℃ and aged for a certain period of time in order to control the nucleation particle size of the core.
[0085] In some specific embodiments, the conditions for the second coprecipitation reaction are: reaction at 20–40°C and 100–300 rpm for 4–6 hours.
[0086] Furthermore, after the first outer shell is formed on the surface of the core, the reaction also includes adding an aqueous solution of a soluble divalent nickel salt to the reaction solution to carry out a third coprecipitation reaction, so as to form a second outer shell on the surface of the first outer shell.
[0087] In some specific embodiments, the conditions for the third coprecipitation reaction are: reaction at 20–40°C and 100–300 rpm for 6–8 hours.
[0088] After the third coprecipitation reaction is completed, the material can be kept warm, stirred, and aged for a certain period of time in order to control the overall particle size of the material.
[0089] Specifically, the concentration of the solution added in the first coprecipitation reaction, the second coprecipitation reaction, and the third coprecipitation reaction can be controlled in order to control the particle size of the core and the formation thickness of the first and second shells.
[0090] It should be noted that the first coprecipitation reaction, the second coprecipitation reaction, the third coprecipitation reaction, and the aging process all need to be carried out in an inert gas atmosphere to avoid unnecessary oxidation and hydration, which helps to improve the purity of the material and reduce its water content.
[0091] Furthermore, after forming the first or second outer shell, the process further includes drying the material in a forced-air dryer at 60–100°C for 4–24 hours, followed by vacuum drying at 120–200°C for 16–24 hours, and finally vacuum calcining at 205–240°C for 0.5–5 hours. This process aims to remove adsorbed water and interstitial water from the material synthesis process while forming a carbonized layer on the surface of the Prussian white material, thereby reducing the water content of the material.
[0092] A third aspect of this application provides a positive electrode sheet, including a positive current collector and a positive active material layer, wherein the positive active material layer includes the Prussian white material provided in the first aspect of this application.
[0093] Since the positive electrode of this application includes the aforementioned Prussian white material which combines high capacity and structural stability, the positive electrode can also achieve both high capacity and good structural stability during application.
[0094] This application does not impose any particular limitation on the positional relationship between the positive current collector and the positive active material layer. The positive active material can be directly disposed on one or both sides of the positive current collector, or other functional layers or base coatings can be included between the positive current collector and the positive active material layer.
[0095] In addition to the aforementioned positive electrode material, the positive electrode active material layer of this application also includes components such as conductive agents and binders. Both the conductive agent and the binder can be selected from substances conventionally used in the art. Specifically, the conductive agent can be selected from one or more of conductive carbon black, acetylene black, Ketjen black, and carbon nanofibers, and the binder can be selected from one or more of PVDF, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, and styrene-butadiene rubber.
[0096] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, which can be prepared using conventional methods in the art. For example, Prussian white material, conductive agent and binder are dispersed in a solvent in a certain proportion to obtain a slurry, and then the slurry is coated on at least one surface of the positive electrode current collector. After drying, slitting and rolling, the positive electrode sheet can be obtained.
[0097] A fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.
[0098] Because this battery includes positive electrode plates that combine high capacity and structural stability, it also exhibits high capacity utilization, cycle stability, and rate performance during charging and discharging.
[0099] In addition to the aforementioned positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator, forming a conventional battery structure. The compositions of the negative electrode, electrolyte, and separator can all refer to conventional compositions in the art, and will not be elaborated upon here.
[0100] The battery of this application can be prepared by referring to conventional methods in the art. For example, after stacking the positive electrode, separator and negative electrode in sequence, the battery cell is obtained by stacking or winding process, and then the battery of this application can be obtained by baking, liquid injection, formation and packaging.
[0101] The fifth aspect of this application provides an electrical device including the battery provided in the fourth aspect of this application. This application does not specifically limit the type of electrical device; it can be any electrical device including the battery, including but not limited to mobile phones, portable devices, laptops, electric bicycles, electric cars, electric toys, energy storage devices, lighting equipment, cameras, etc.
[0102] The following detailed description, in conjunction with specific embodiments, further illustrates the Prussian white material provided in this application and its applications.
[0103] Example 1
[0104] This embodiment provides a Prussian white material, the preparation method of which includes the following steps:
[0105] 1) Under a nitrogen atmosphere, 15 L of a mixed solution of 1 mol / L manganese sulfate and 0.5 mol / L sodium ferrocyanide was pumped into 10 L of a bottom solution containing 0.1 mol / L sodium sulfate and 0.002 mol / L sodium ferrocyanide at a rate of 1.875 L / h, and stirred at a constant temperature of 25 °C for 8 h.
[0106] The temperature was then raised to 55°C and aged for 8 hours with stirring at 300 rpm. After the temperature was lowered to 25°C, 2.5 L of a mixed solution of manganese sulfate (0.9 mol / L) and nickel sulfate (0.45 mol / L) with a concentration ratio of 2:1 and 4 L of a 0.413 mol / L sodium ferrocyanide solution were pumped into the aged solution, with continuous stirring throughout the process.
[0107] An additional 2.15 L of 0.028 mol / L nickel sulfate solution was pumped into the solution, and the mixture was aged for 8 hours at a constant temperature of 25°C and a stirring speed of 200 rpm to increase the D50 particle size to 5 μm, thus obtaining the Prussian white material precursor solution.
[0108] 2) The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor. The precursor was dried in a forced-air dryer at 80°C for 24 hours, then dried in a vacuum dryer at 180°C for 24 hours. Finally, the temperature was raised to 240°C and calcined in a vacuum for 0.5 hours to obtain the Prussian white material.
[0109] During the vacuum drying process, nitrogen is added every 30 minutes and then the vacuum is evacuated again.
[0110] The core of Prussian white material is composed of Na.1.543 Mn[Fe(CN)6] 0.907 ·1.57H2O, the first outer shell is composed of Na 1.687 Mn 0.991 Ni 0.009 [Fe(CN)6] 0.922 ·1.46H2O, the second shell is composed of Na 1.831 Ni[Fe(CN)6] 0.94 ·1.33H2O.
[0111] Example 2
[0112] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that in Example 1, except that step 2) is as follows:
[0113] The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor. The precursor was dried in a forced-air dryer at 100°C for 4 hours, then dried in a vacuum at 200°C for 24 hours. Finally, the temperature was increased to 240°C and calcined in a vacuum for 1 hour to obtain the Prussian white material. During the vacuum drying process, nitrogen was added every 30 minutes and then the vacuum was evacuated again.
[0114] Example 3
[0115] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that in Example 1, except that step 2) is as follows:
[0116] The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor. The precursor was dried in a forced-air dryer at 60°C for 24 hours, then dried in a vacuum at 120°C for 24 hours. Finally, the temperature was increased to 240°C and calcined in a vacuum for 2.5 hours to obtain the Prussian white material. During the vacuum drying process, nitrogen was added every 30 minutes and then the vacuum was evacuated again.
[0117] Example 4
[0118] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that in Example 1, except that step 2) is as follows:
[0119] The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor. The precursor was dried in a forced-air dryer at 80°C for 24 hours, then dried in a vacuum at 200°C for 16 hours, and finally calcined in a vacuum at 205°C for 5 hours to obtain the Prussian white material. During the vacuum drying process, nitrogen was added every 30 minutes and then the vacuum was evacuated again.
[0120] Example 5
[0121] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that in Example 1, except that step 2) is as follows:
[0122] The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor, which was then dried in air at 80°C for 24 hours to obtain the Prussian white material.
[0123] Example 6
[0124] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that in Example 1, except that step 2) is as follows:
[0125] The Prussian white material precursor solution was filtered to obtain the Prussian white material precursor, which was then dried in a vacuum environment at 170°C for 24 hours to obtain the Prussian white material.
[0126] Example 7
[0127] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that: step 1) omits the additional pumping of 2.15L of 0.028mol / L nickel sulfate solution, and step 2) omits the vacuum calcination at 240℃ for 0.5h.
[0128] Example 8
[0129] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that step 2) omits the vacuum calcination at 240°C for 0.5 h.
[0130] Example 9
[0131] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that in step 2), it is calcined in vacuum at 240°C for 24 hours.
[0132] Example 10
[0133] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that step 1) omits the additional pumping of 2.15L of 0.028mol / L nickel sulfate solution.
[0134] Example 11
[0135] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that step 2) is as follows: the Prussian white material precursor solution is filtered to obtain the Prussian white material precursor, and Ketjen black (0.5% of the mass of Prussian white) is ball-milled and mixed with the Prussian white material precursor at 1000 rpm to obtain the Prussian white material.
[0136] Example 12
[0137] This embodiment provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that the concentration of the additional 2.15 L nickel sulfate solution pumped in step 1) is replaced with 0.04 mol / L, and the vacuum calcination at 240 °C for 0.5 h in step 2) is omitted. The core composition of the Prussian white material is Na. 1.543 Mn[Fe(CN)6] 0.907 ·1.57H2O, the first outer shell is composed of Na 1.687 Mn 0.991 Ni 0.009 [Fe(CN)6] 0.922 ·1.46H2O, the second shell is composed of Na 1.401 Ni[Fe(CN)6] 0.96 ·1.12H2O.
[0138] Comparative Example 1
[0139] This comparative example provides a Prussian white material, the preparation method of which is basically the same as that of Example 1, except that the reaction is stopped after the first aging of 8 hours, the material is filtered and dried at room temperature to obtain the Prussian white material.
[0140] Comparative Example 2
[0141] This comparative example provides a Prussian white material, the preparation method of which is basically the same as that of Example 1. The difference is that after the first aging for 8 hours, 2.15 L of 0.028 mol / L nickel sulfate solution is pumped in for a second aging for 8 hours. The material is then filtered and dried at room temperature to obtain the Prussian white material.
[0142] Comparative Example 3
[0143] This comparative example provides a Prussian white material, the preparation method of which includes the following steps:
[0144] 1) Under a nitrogen atmosphere, 15 L of a mixed solution of 1 mol / L manganese sulfate and 0.5 mol / L sodium ferrocyanide was pumped into 10 L of a base solution containing 0.1 mol / L sodium sulfate and 0.002 mol / L sodium ferrocyanide at a rate of 1.875 L / h, and stirred at a constant temperature of 25 °C for 8 h; then the temperature was raised to 55 °C and aged for 8 h at a stirring speed of 300 rpm to obtain the aged solution.
[0145] 2) The aged solution was filtered to obtain the Prussian white material precursor. The precursor was dried in a forced-air dryer at 80°C for 24 hours, then dried in a vacuum dryer at 180°C for 24 hours. Finally, the temperature was raised to 240°C and calcined in a vacuum for 0.5 hours to obtain the Prussian white material.
[0146] During the vacuum drying process, nitrogen is added every 30 minutes and then the vacuum is evacuated again.
[0147] Test case
[0148] I. The following parameters were tested on the Prussian white materials prepared in the above examples and comparative examples:
[0149] 1. Visual inspection
[0150] Figure 1 shows a comparison of the appearance of Prussian white materials in Examples 1 to 6. In the figures, a and b are the appearance of Prussian white cathode materials in Examples 5 and 6, respectively. The materials in Examples 5 and 6 are yellowish in color and have severe agglomeration, indicating that there is a severe micro-oxidation phenomenon. In the figures, c, d, e, and f are the appearance of Prussian white cathode materials in Examples 1 to 4, respectively. The materials in Examples 1 to 4 are white in color and have good dispersibility with no obvious agglomeration phenomenon.
[0151] 2. SEM
[0152] Figure 2 shows the SEM comparison images of Prussian white materials in Examples 1 to 6. In the figure, a and b are Prussian white materials in Examples 5 and 6, respectively, and c to f are Prussian white materials in Examples 1 to 4, respectively. As can be seen from Figure 2, high-temperature micro-carbonization does not destroy the cubic morphological structure of Prussian white itself, and the outer layer has morphological extension and expansion, corresponding to a multi-layer shell structure.
[0153] Figure 7 is a SEM image of the Prussian white material of Example 11. As can be seen from Figure 7, the Kojen black in Example 11 is dispersed on the surface of the Prussian white material and does not coat the Prussian white material.
[0154] 3. EDS
[0155] Figure 3 shows the EDS comparison diagram of Prussian white material in Example 5, that is, the elemental composition of Prussian white after different temperature changes. In Figure 3, a, b, c, and d are the elemental distribution of the material after 120℃-12h, 170℃-12h, 230℃-1h (after 170℃-12h treatment), and 230℃-2.5h (after 170℃-12h treatment), respectively. It can be found that the mass ratio of carbon and nitrogen elements is basically unchanged before 170℃, while only after the high temperature treatment of 230℃ does a significant difference appear, corresponding to the decomposition of Prussian white on the surface and the formation of an amorphous carbon layer.
[0156] 4. Specific surface area
[0157] Test method: The test was conducted using the BET method, and the test results are shown in Table 1.
[0158] 5. Sodium ion diffusion coefficient
[0159] Test method: The results were obtained by electrochemical GITT test, and the results are shown in Table 1.
[0160] 6. Impedance curve
[0161] Test method: The impedance curve of the coin cell was tested using an electrochemical workstation.
[0162] Figure 4 is a comparison of the impedance curves of coin cells assembled from Prussian white materials in Examples 2, 3, 5, and 6. Analysis of Figure 4 shows that the amorphous carbon layer formed after carbonization facilitates ion transport and improves the material's conductivity, resulting in the lowest battery impedance in Example 3.
[0163] 7. XRD
[0164] Test method: XRD patterns of materials were tested using an X-ray diffractometer. Figure 5 is a comparison of the XRD characteristic curves of Prussian white material before and after the outer shell coating in Example 1. It can be analyzed from Figure 5 that after the first and second layers of nickel-containing outer shell coating, the original single peak corresponding to the pure Mn core gradually splits into a double peak of Mn-Ni composite phase.
[0165] 8. Core particle size, first shell thickness, second shell thickness, and carbonized layer thickness: The core particle size, first shell thickness, second shell thickness, and carbonized layer thickness were characterized using field emission transmission electron microscopy (Talos F200X, Thermo Fisher Scientific, USA). Anhydrous ethanol was used to disperse the powder samples, and the accelerating voltage was 60 kV. The test results are shown in Table 1.
[0166] 9. Ni and Mn content: After 200 cycles, the battery was disassembled, and the separator and positive and negative electrode surfaces were washed with 50ml of pure water. The washing solution was filtered to remove residue and then sent to ICP-MS for testing. The content of metal elements in the filtrate was tested. The test results are shown in Table 1.
[0167] 10. D50 particle size: The D50 particle size of Prussian white material was tested using a laser particle size analyzer. The test results are shown in Table 1.
[0168] 11. Water content: The water content of Prussian white material was tested using a cassette moisture analyzer. The test results are shown in Table 1.
[0169] 12. C and N elements: C is mainly tested by a carbon-sulfur analyzer, while N is calculated by EDS and chemical composition ratio.
[0170] II. The Prussian white cathode materials from the above embodiments and comparative examples were assembled into coin cells. Specifically, the following method was used: Prussian white, conductive carbon, and PVDF were mixed in a mass ratio of 86:7:7, and NMP was added to prepare a slurry. This slurry was then uniformly coated onto aluminum foil, dried at 120°C for 12 hours, and then cut into 1.131 cm pieces.2 The discs are used to assemble coin cells with sodium plates as the counter electrode.
[0171] The following performance tests were performed on the obtained button cells.
[0172] 1. Ratio performance
[0173] Test method: The coin cells assembled with Prussian white cathode materials from the above examples and comparative examples were subjected to charge-discharge tests at currents of 0.1, 0.2, 0.5, 1, and 2C (1C = 150mAh / g). The test results are shown in Table 1.
[0174] Figure 6 is a comparison of the rate performance of the Prussian white materials of Examples 1 to 6 after being assembled into button cells. As can be seen from Figure 6, Example 3 after micro-carbonization coating has the highest capacity at different current densities and the slowest capacity decay at different current ratios.
[0175] 2. Cyclic Performance: Under 25℃ conditions, the capacitor was charged at a constant current rate of 1C to 4.25V, then charged at a constant voltage of 4.25V to a current rate of 0.5C, and then discharged at a discharge rate of 1C to 2V. This charge-discharge cycle was repeated 200 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 200th cycle were measured. 200 The capacity retention rate after 200 cycles is Q = Q 200 / Q1*100%.
[0176] 3. Specific capacity: At 25℃, charge at a constant current rate of 1C to 4.25V, and then charge at a constant voltage rate of 4.25V to a current rate of 0.1C. The charging capacity at this time is recorded as the specific capacity of the first charge. After resting for 5 minutes, discharge at a constant current rate of 1C to a voltage of 2V. The discharge capacity at this time is recorded as the specific capacity of the first discharge.
[0177] Table 1
[0178] The following conclusions can be drawn from Table 1:
[0179] This application involves coating a pure manganese Prussian white (MnHCF) core with a first shell of nickel-manganese Prussian white (Mn-NiHCF). The first shell is doped with nickel in the manganese-based Prussian white material, which can stabilize the crystal structure of the Prussian white material, thereby suppressing the occurrence of the Jan Taylor phenomenon, enhancing the overall stability of the material, and enabling the material to have both high capacity and excellent cycling stability.
[0180] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.
Claims
1. A Prussian white material, characterized in that, The Prussian white material includes a core and a first outer shell covering the surface of the core; The kernel is composed of Na x Mn[Fe(CN)6] y ·αH2O, Where 1≤x≤1.8, 0.9≤y≤0.99, 0.5≤α≤3; The first outer shell is composed of Na. a Mn b Ni 1-b [Fe(CN)6] c ·βH2O, where 1.2≤a≤1.8, 0.8≤b≤0.995, 0.8≤c≤0.99, and 0.5≤β≤3.
2. The Prussian white material according to claim 1, characterized in that, The core has a particle size of 1 to 6 μm; and / or the first outer shell has a thickness of 1 to 2 μm.
3. The Prussian white material according to claim 1, characterized in that, The surface of the first outer shell is further covered with a second outer shell, the second outer shell being composed of Na. m Ni[Fe(CN)6] n ·γH2O, where 0.5≤m≤1.9, 0.9≤n≤0.99, and 0.05≤γ≤1.
5.
4. The Prussian white material according to claim 3, characterized in that, The thickness of the second outer shell is 50-100 nm.
5. The Prussian white material according to claim 4, characterized in that, The outer surface of the Prussian white material is a carbonized layer.
6. The Prussian white material according to claim 5, characterized in that, The thickness of the carbonized layer is 2–15 nm.
7. The Prussian white material according to claim 5 or 6, characterized in that, The Prussian white material includes the first outer shell and a carbonized layer located on the surface of the first outer shell, the carbonized layer being formed by carbonizing the first outer shell in situ; Alternatively, the Prussian white material may include a second outer shell and a carbonized layer located on the surface of the second outer shell, the carbonized layer being formed by carbonizing the second outer shell in situ.
8. The Prussian white material according to claim 7, characterized in that, The in-situ carbonization includes: drying in a forced air at 60–100°C for 4–24 hours, followed by vacuum drying at 120–200°C for 16–24 hours, and finally vacuum calcination at 205–240°C for 0.5–5 hours.
9. The Prussian white material according to claim 1, characterized in that, The Prussian white material contains 2000–10000 ppm of Ni and 15–30 wt% of Mn.
10. The Prussian white material according to claim 1, characterized in that, The Prussian white material must meet at least one of the following conditions: (1) Specific surface area ≥ 4.5m² 2 / g; (2) Sodium ion diffusion coefficient ≥ 1.14 × 10 -10 ; (3) The D50 particle size is 2-10 μm; (4) The mass content difference between carbon and nitrogen is 0.5% to 9.5%; (5) Water content ≤1200ppm.
11. A method for preparing the Prussian white material according to any one of claims 1-10, characterized in that, Includes the following steps: 1) A mixed solution of soluble divalent manganese salt and sodium ferrocyanide is added to a mixed solution of soluble sodium salt and sodium ferrocyanide at a rate of 1-2 L / h to carry out the first coprecipitation reaction and obtain a first solution including the core. 2) Add a mixed solution of soluble divalent manganese salt, soluble divalent nickel salt and sodium ferrocyanide to the first solution to carry out a second coprecipitation reaction, forming a first shell on the surface of the core, to obtain the Prussian white material.
12. The preparation method according to claim 11, characterized in that, After forming the first outer shell on the surface of the core, the process further includes adding an aqueous solution of soluble divalent nickel salt to the reaction solution to carry out a third coprecipitation reaction, forming a second outer shell, and obtaining the Prussian white material.
13. The preparation method according to claim 12, characterized in that, After forming the first shell or the second shell, the process further includes drying the material by blowing at 60–100°C for 4–24 hours, followed by vacuum drying at 120–200°C for 16–24 hours, and finally vacuum calcining at 205–240°C for 0.5–5 hours to form a carbonized layer on the surface of the Prussian white material.
14. A positive electrode plate, characterized in that, It includes a positive electrode current collector and a positive electrode active material layer, characterized in that the positive electrode active material layer includes the Prussian white material as described in any one of claims 1-10.
15. A battery, characterized in that, Includes the positive electrode sheet as described in claim 14.
16. An electrical appliance, characterized in that, Includes the battery as described in claim 15.