Doped iron hydrogen phosphate precursor as well as preparation method and application thereof

Abstract

The invention discloses a doped iron hydrogen phosphate precursor and a preparation method and application thereof.The preparation method of the doped iron hydrogen phosphate precursor comprises the steps that a solution containing a phosphorus source and a solution containing an oxidizing agent are added into a solution containing an iron source and a metal doping source respectively, a reaction is conducted, and a reaction solution is obtained; and adjusting the reaction liquid to be acidic, aging, and carrying out solid-liquid separation to obtain the doped iron hydrogen phosphate precursor. According to the preparation method, the metal doping source is added into the reaction liquid for preparing the iron hydrogen phosphate precursor to prepare the doped iron hydrogen phosphate precursor, so that the distribution uniformity of metal doping ions in the iron hydrogen phosphate precursor is effectively improved, and the problem of relatively poor ion uniformity of the iron hydrogen phosphate precursor prepared by a solid-phase reaction method is effectively solved; the intrinsic electron conductivity of the material and the diffusion rate of sodium ions are further improved, so that the electrochemical performance of the material is favorably improved.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery cathode materials technology, and in particular to a doped iron hydrogen phosphate precursor, its preparation method and application. Background Technology

[0002] Sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7) has the following advantages as a cathode material for sodium-ion batteries: 1) Sodium iron phosphate pyrophosphate material has a three-dimensional sodium ion diffusion path, which can rapidly insert / extract Na+. + 2) Sodium iron phosphate pyrophosphate exhibits minimal volume change during cycling, demonstrating good cycle stability. 3) During charge / discharge, sodium iron phosphate pyrophosphate can reversibly insert and extract three Na atoms. + 4) It has a high theoretical specific capacity; 5) It has a high voltage platform.

[0003] However, sodium iron phosphate pyrophosphate has low electronic conductivity, which severely limits its ability to transport electrons and ions together at high current densities, thus affecting the rate performance, specific capacity, and cycle performance of sodium-ion batteries. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to provide a doped ferric hydrogen phosphate precursor, its preparation method, and its application. This application prepares the doped ferric hydrogen phosphate precursor by adding a metal dopant source to the reaction solution used in preparing the precursor. This effectively improves the uniformity of the distribution of metal dopant ions in the ferric hydrogen phosphate precursor, effectively solving the problem of poor ion uniformity in the solid-state reaction method for preparing the ferric hydrogen phosphate precursor. Furthermore, it improves the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thereby enhancing the electrochemical performance of the material.

[0005] In a first aspect, this application proposes a method for preparing a doped ferric hydrogen phosphate precursor. According to an embodiment of this application, the method includes:

[0006] A solution containing a phosphorus source and a solution containing an oxidant are added to solutions containing an iron source and a metal doping source, respectively, and the reactions are carried out to obtain a reaction solution.

[0007] The reaction solution was adjusted to acidity, aged, and then subjected to solid-liquid separation to obtain a doped ferric hydrogen phosphate precursor.

[0008] According to the method for preparing a doped ferrophosphate precursor according to embodiments of this application, this application introduces a metal dopant source into the ferrophosphate precursor, allowing metal dopant ions to replace part of the iron element to form a doped ferrophosphate precursor, which can effectively improve the intrinsic electronic conductivity and sodium ion diffusion rate of the material. Furthermore, this application prepares the doped ferrophosphate precursor by adding the metal dopant source to the reaction solution used in preparing the ferrophosphate precursor, effectively improving the uniformity of the distribution of metal dopant ions in the ferrophosphate precursor, effectively solving the problem of poor ion uniformity in the solid-state reaction method for preparing ferrophosphate precursors, further improving the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thereby contributing to improved electrochemical performance of the material.

[0009] In addition, the method for preparing the doped ferric hydrogen phosphate precursor according to the above embodiments of this application may also have the following additional technical features:

[0010] In some embodiments of this application, the solution containing a phosphorus source and the solution containing an oxidant are added, respectively and simultaneously, to the solution containing an iron source and a metal dopant source, and reacted to obtain the reaction solution.

[0011] In some embodiments of this application, the solution containing the phosphorus source is added at a rate of 14 g / min to 20 g / min; and / or, the solution containing the oxidant is added at a rate of 7 g / min to 13 g / min.

[0012] In some embodiments of this application, the molar ratio of the metal doping source, the iron source, the phosphorus source and the oxidant is x:(3-x):(3.9~5.4):(0.9~2.1), where 0<x<0.3.

[0013] In some embodiments of this application, the pH of the reaction solution is adjusted to 1.7 to 4.

[0014] In some embodiments of this application, a pH adjuster is used to adjust the reaction solution to acidity, the pH adjuster including at least one of NH3·H2O, ethylenediamine and ethanolamine.

[0015] In some embodiments of this application, the aging time is 0.5h to 3h.

[0016] In some embodiments of this application, the method further includes: washing, drying, and first sintering the solid portion obtained from the solid-liquid separation to obtain the doped ferric hydrogen phosphate precursor.

[0017] In some embodiments of this application, the temperature of the first sintering is 300°C to 400°C, and the time of the first sintering is 0.5h to 2h.

[0018] In some embodiments of this application, the iron source includes at least one of ferrous sulfate, ferrous oxalate, iron powder, iron oxide, and ferric nitrate; and / or, the metal doping source includes at least one of a metal salt of Ni, a metal salt of Co, a metal salt of Mn, a metal salt of Cr, a metal salt of Zr, a metal salt of Nb, a metal salt of Cu, a metal salt of V, a metal salt of Ti, a metal salt of Zn, a metal salt of Al, a metal salt of Ga, and a metal salt of Mg; and / or, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, disodium hydrogen phosphate, and phosphoric acid; and / or, the oxidant includes at least one of H2O2 and ozone.

[0019] In a second aspect, this application proposes a doped ferric hydrogen phosphate precursor. According to embodiments of this application, the doped ferric hydrogen phosphate precursor is prepared by the method described in the above embodiments. This effectively improves the uniformity of metal dopant ion distribution in the ferric hydrogen phosphate precursor, further enhancing the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thereby improving the electrochemical performance of the material.

[0020] In a third aspect of this application, a method for preparing modified sodium iron pyrophosphate is provided. According to embodiments of this application, the method includes:

[0021] The doped ferric hydrogen phosphate precursor was prepared using the methods described in the above embodiments;

[0022] The doped ferric hydrogen phosphate precursor, sodium source, carbon source and solvent are mixed and ball-milled to obtain a precursor solution;

[0023] The precursor solution was dried to obtain precursor powder;

[0024] The precursor powder was subjected to a second sintering under a protective atmosphere to obtain modified sodium iron pyrophosphate.

[0025] According to the method for preparing modified sodium iron pyrophosphate according to embodiments of this application, firstly, this application introduces a metal dopant source into the modified sodium iron pyrophosphate, allowing metal dopant ions to replace part of the iron element to form doped sodium iron pyrophosphate, which can effectively improve the intrinsic electronic conductivity and sodium ion diffusion rate of the material. Furthermore, this application prepares the doped ferric hydrogen phosphate precursor by adding the metal dopant source to the reaction solution for preparing the ferric hydrogen phosphate precursor, effectively improving the uniformity of metal dopant ion distribution in the ferric hydrogen phosphate precursor, thereby improving the uniformity of metal dopant ion distribution in sodium iron pyrophosphate, further improving the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thus contributing to improved electrochemical performance of the material.

[0026] Second, this application uses a doped iron hydrogen phosphate precursor M.x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2O x Fe (3-x) (PO4)2P2O7@C, doped iron hydrogen phosphate precursor M x Fe 3-x The Fe / P molar ratio in (HPO4)4·H2O and the modified sodium iron phosphate Na4M pyrophosphate x Fe (3-x) The Fe / P molar ratio in (PO4)2P2O7@C is equal, and Fe or P ions do not need to diffuse into / out of the doped ferric hydrogen phosphate precursor. Therefore, this application uses a doped ferric hydrogen phosphate precursor M... x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2O x Fe (3-x) (PO4)2P2O7@C solves the problem of abundant Maricite-NaFePO4 (Fe / P=1) and Na2FeP2O7 (Fe / P=0.5) impurity phases caused by the diffusion of Fe or P ions into / out of the precursor material, thus improving the charge / discharge specific capacity of the modified sodium iron phosphate pyrophosphate material. Meanwhile, this application utilizes a doped iron hydrogen phosphate precursor M... x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2O x Fe (3-x) In the (PO4)2P2O7@C process, ion diffusion is not required during high-temperature sintering, which further improves the uniformity of metal dopant ion distribution in sodium iron phosphate pyrophosphate.

[0027] In addition, the method for preparing modified sodium iron pyrophosphate according to the above embodiments of this application may also have the following additional technical features:

[0028] In some embodiments of this application, the molar ratio of the doped ferric hydrogen phosphate precursor, the sodium source, and the carbon source is 1:(4-4.5):(0.4-0.6).

[0029] In some embodiments of this application, the precursor solution is spray-dried to obtain the precursor powder.

[0030] In some embodiments of this application, the temperature of the second sintering is 450°C to 600°C, and the time of the second sintering is 8h to 15h.

[0031] In some embodiments of this application, the sodium source includes at least one of sodium dihydrogen phosphate, sodium acetate, sodium pyrophosphate, sodium carbonate, sodium oxalate, and disodium hydrogen phosphate; and / or, the carbon source includes at least one of glucose, ascorbic acid, oxalic acid, citric acid, fructose, and sucrose.

[0032] In a fourth aspect, this application discloses a modified sodium iron phosphate pyrophosphate. According to embodiments of this application, a doped iron hydrogen phosphate precursor is prepared using the method described in the above embodiments. This effectively improves the uniformity of metal dopant ion distribution in the modified sodium iron phosphate pyrophosphate, further enhancing the intrinsic electronic conductivity and sodium ion diffusion rate of the modified sodium iron phosphate pyrophosphate material, thereby improving its electrochemical performance. Simultaneously, the modified sodium iron phosphate pyrophosphate of this application exhibits extremely low contents of Maricite-NaFePO4 (Fe / P = 1) and Na2FeP2O7 (Fe / P = 0.5) impurity phases, with virtually no peaks for these two impurity phases in the XRD pattern, thus improving the charge-discharge specific capacity of the modified sodium iron phosphate pyrophosphate material.

[0033] In a fifth aspect, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer, the positive active material layer being coated on the positive current collector, and the positive active material layer comprising modified sodium iron pyrophosphate prepared by the method described in the above embodiments. This improves the electronic conductivity and sodium ion diffusion rate of the positive electrode sheet, thereby enhancing its electrochemical performance.

[0034] In a sixth aspect, the present invention provides a sodium-ion battery. According to embodiments of the present invention, the sodium-ion battery includes the positive electrode sheet described in the above embodiments, thereby effectively improving the high-rate performance, cycle performance, and specific capacity of the sodium-ion battery.

[0035] In a seventh aspect of the invention, an electrical device is provided. According to an embodiment of the invention, the electrical device has the sodium-ion battery described in the above embodiments. Thus, the electrical device possesses all the advantages of the sodium-ion battery, which will not be repeated here.

[0036] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0037] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0038] Figure 1This is a schematic flowchart of a method for preparing a doped ferric hydrogen phosphate precursor according to an embodiment of this application.

[0039] Figure 2 This is a schematic flowchart of the method for preparing modified sodium iron pyrophosphate according to an embodiment of this application;

[0040] Figure 3 These are the XRD patterns of the cathode materials prepared in Example 5, Comparative Example 1, and Comparative Example 2;

[0041] Figure 4 The Mn prepared in Example 5, Comparative Example 1, and Comparative Example 2 0.02 Ti 0.02 Fe 2.96 Electron micrographs of the precursors of (HPO4)4·H2O, Fe3(HPO4)4·H2O and FePO4·2H2O;

[0042] Figure 5 These are electron microscope images of the cathode materials prepared in Example 5, Comparative Example 1, and Comparative Example 2;

[0043] Figure 6 This is an elemental distribution diagram of the precursor prepared in Example 5;

[0044] Figure 7 This is the elemental distribution diagram of the cathode material prepared in Example 5;

[0045] Figure 8 This is the elemental distribution diagram of the cathode material prepared in Comparative Example 1;

[0046] Figure 9 This is the elemental distribution diagram of the cathode material prepared in Comparative Example 2;

[0047] Figure 10 These are charge-discharge curves of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at 0.1C.

[0048] Figure 11 These are the cycle performance graphs of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at 1C.

[0049] Figure 12 These are discharge specific capacity test graphs of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C. Detailed Implementation

[0050] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0051] In related technologies, solid-state reaction methods (including solid-state ball milling and sand milling) are used to modify sodium iron phosphate pyrophosphate. This method mainly involves grinding and drying iron, sodium, carbon, and dopant sources to form a macroscopically homogeneous mixture, which is then calcined to form sodium iron phosphate pyrophosphate crystals. During high-temperature calcination, metal ions migrate to form sodium iron phosphate pyrophosphate crystals. The inventors discovered that solid-state reaction methods can only achieve micron- or submicron-level mixing of the raw material particles. However, gaps exist between the particles of the dopant, phosphorus, iron, and sodium sources. Furthermore, the calcination temperature of solid-state reaction methods is relatively low (approximately 500℃–600℃). Therefore, it is difficult for metal dopant ions to diffuse uniformly into the sodium iron phosphate pyrophosphate during high-temperature calcination.

[0052] In view of this, in one aspect of this application, a method for preparing a doped ferric hydrogen phosphate precursor is proposed, see Appendix Figure 1 According to embodiments of this application, the method includes: adding a solution containing a phosphorus source and a solution containing an oxidant to a solution containing an iron source and a metal dopant source, respectively, reacting to obtain a reaction solution; adjusting the reaction solution to acidity, aging it, and performing solid-liquid separation to obtain a doped ferric hydrogen phosphate precursor M. x Fe 3-x (HPO4)4·H2O, where M is a metal dopant element.

[0053] According to the method for preparing a doped ferrophosphate precursor according to embodiments of this application, this application introduces a metal dopant source into the ferrophosphate precursor, allowing metal dopant ions to replace part of the iron element to form a doped ferrophosphate precursor, which can effectively improve the intrinsic electronic conductivity and sodium ion diffusion rate of the material. Furthermore, this application prepares the doped ferrophosphate precursor by adding the metal dopant source to the reaction solution used in preparing the ferrophosphate precursor, effectively improving the uniformity of the distribution of metal dopant ions in the ferrophosphate precursor, effectively solving the problem of poor ion uniformity in the solid-state reaction method for preparing ferrophosphate precursors, further improving the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thereby contributing to improved electrochemical performance of the material.

[0054] The following describes the preparation of the doped ferric hydrogen phosphate precursor M proposed in this invention. x Fe 3-x The method of (HPO4)4·H2O is explained in detail below:

[0055] Specifically, see the attached document. Figure 1 The above-mentioned preparation of doped iron hydrogen phosphate precursor M x Fe 3-x The method for (HPO4)4·H2O includes the following steps:

[0056] S100: A solution containing a phosphorus source and a solution containing an oxidant are added to solutions containing an iron source and a metal doping source, respectively, and the reactions are carried out to obtain a reaction solution.

[0057] In this step, a solution containing a phosphorus source and a solution containing an oxidant are added to solutions containing an iron source and a metal dopant source, respectively. The iron source, phosphorus source, metal dopant source and oxidant react together to form a precipitate, resulting in a reaction solution.

[0058] According to some specific embodiments of this application, a solution containing a phosphorus source and a solution containing an oxidant are added separately and simultaneously to a solution containing an iron source and a metal dopant source (e.g., added dropwise to a solution containing an iron source and a metal dopant source respectively and simultaneously). The iron source, phosphorus source, metal dopant source and oxidant react together to form a precipitate. By adding the solution containing a phosphorus source and the solution containing an oxidant separately and simultaneously to the solution containing an iron source and a metal dopant source, it is further beneficial for the iron source, phosphorus source, metal dopant source and oxidant to react together to form a precipitate.

[0059] According to some specific embodiments of this application, the addition rate of the solution containing the phosphorus source is 14 g / min to 20 g / min, for example, 14 g / min, 15 g / min, 16 g / min, 17 g / min, 18 g / min, 19 g / min, 20 g / min, etc.; the addition rate of the solution containing the oxidant is 7 g / min to 13 g / min, for example, 7 g / min, 8 g / min, 9 g / min, 10 g / min, 11 g / min, 12 g / min, 13 g / min, etc. Therefore, by limiting the addition rates of the solution containing the phosphorus source and the solution containing the oxidant to the above ranges, it is further beneficial for the iron source, phosphorus source, metal dopant source, and oxidant to react together to form a precipitate.

[0060] According to some specific embodiments of this application, the molar ratio of the metal dopant source, iron source, phosphorus source and oxidant is x:(3-x):(3.9~5.4):(0.9~2.1), where 0<x<0.3. Thus, by limiting the molar ratio of the metal dopant source, iron source, phosphorus source and oxidant to the above range, it is further beneficial for the iron source, phosphorus source, metal dopant source and oxidant to react together to form a precipitate.

[0061] In the embodiments of this application, the specific type of iron source is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific embodiments, the iron source includes at least one of ferrous sulfate, ferrous oxalate, iron powder, iron oxide, and ferric nitrate.

[0062] In the embodiments of this application, the specific types of metal doping sources are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the metal doping sources include at least one of the following: Ni metal salt, Co metal salt, Mn metal salt, Cr metal salt, Zr metal salt, Nb metal salt, Cu metal salt, V metal salt, Ti metal salt, Zn metal salt, Al metal salt, Ga metal salt, and Mg metal salt.

[0063] In the embodiments of this application, the specific types of phosphorus sources are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, disodium hydrogen phosphate, and phosphoric acid.

[0064] In the embodiments of this application, the specific types of oxidants are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the specific types of oxidants are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the oxidants include at least one of H2O2 and ozone.

[0065] S200: Adjust the reaction solution to acidity, age it, and separate the solid and liquid phases to obtain the doped ferric hydrogen phosphate precursor.

[0066] In this step, the reaction solution is adjusted to acidity and aged to allow the raw materials to further precipitate. Then, solid-liquid separation is performed to separate the precipitate and obtain the doped ferric hydrogen phosphate precursor.

[0067] According to some specific embodiments of this application, the pH of the reaction solution is adjusted to 1.7 to 4. For example, the pH of the reaction solution can be adjusted to 1.7, 2, 2.5, 3, 3.5, 4, etc., which further facilitates the full precipitation of each raw material.

[0068] According to some specific embodiments of this application, a pH adjuster is used to adjust the reaction solution to acidity. In the embodiments of this application, the specific type of pH adjuster is not particularly limited, and those skilled in the art can select one according to actual needs. As some specific embodiments, the pH adjuster includes at least one of NH3·H2O, ethylenediamine, and ethanolamine.

[0069] In the embodiments of this application, the amount of the pH adjuster is not particularly limited, as long as it can adjust the reaction solution to acidity.

[0070] According to some specific embodiments of this application, the aging time is 0.5h to 3h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc., which further facilitates the full formation of precipitates from each raw material.

[0071] According to some specific embodiments of this application, the above method further includes: washing the solid portion obtained from solid-liquid separation to remove impurities from the precipitate surface, drying it, and then performing a first sintering. The purpose of the first sintering is to remove excess water of crystallization from the doped ferric hydrogen phosphate precursor to obtain the doped ferric hydrogen phosphate precursor M. x Fe 3-x (HPO4)4·H2O, M is selected from at least one of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga and Mg, 0 < x < 0.3.

[0072] According to some specific embodiments of this application, the temperature of the first sintering is 300℃~400℃ (e.g., it can be 300℃, 320℃, 340℃, 360℃, 380℃, 400℃, etc.), and the time of the first sintering is 0.5h~2h (e.g., it can be 0.5h, 1h, 1.5h, 2h, etc.). By limiting the temperature and time of the first sintering to the above range, it is possible to further ensure the removal of excess water of crystallization in the doped ferric hydrogen phosphate precursor.

[0073] In a second aspect, this application proposes a doped ferric hydrogen phosphate precursor. According to embodiments of this application, the doped ferric hydrogen phosphate precursor is prepared by the method described in the above embodiments. This effectively improves the uniformity of metal dopant ion distribution in the ferric hydrogen phosphate precursor, further enhancing the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thereby improving the electrochemical performance of the material.

[0074] Specifically, the chemical formula of the above-mentioned doped iron hydrogen phosphate precursor is M. x Fe 3-x (HPO4)4·H2O, M is selected from at least one of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga and Mg, 0 < x < 0.3.

[0075] In a third aspect of this application, a method for preparing modified sodium iron pyrophosphate is provided, see Appendix. Figure 2According to embodiments of this application, the method includes: preparing a doped ferric hydrogen phosphate precursor using the method of the first aspect; mixing the doped ferric hydrogen phosphate precursor, a sodium source, a carbon source, and a solvent, and ball milling the mixture to obtain a precursor solution; drying the precursor solution to obtain a precursor powder; and performing a second sintering on the precursor powder under a protective atmosphere to obtain modified sodium iron phosphate pyrophosphate Na4M. x Fe (3-x) (PO4)2P2O7@C, where M is a metal dopant element.

[0076] According to the method for preparing modified sodium iron pyrophosphate according to the embodiments of this application, firstly, this application introduces a metal doping source into the modified sodium iron pyrophosphate, allowing metal dopant ions to replace part of the iron element to form doped sodium iron pyrophosphate, which can effectively improve the intrinsic electronic conductivity and sodium ion diffusion rate of the material. Furthermore, this application prepares the doped ferric hydrogen phosphate precursor by adding the metal doping source to the reaction solution for preparing the ferric hydrogen phosphate precursor, effectively improving the uniformity of metal dopant ion distribution in the ferric hydrogen phosphate precursor, thereby improving the uniformity of metal dopant ion distribution in sodium iron pyrophosphate, further improving the intrinsic electronic conductivity and sodium ion diffusion rate of the material, thus contributing to improved electrochemical performance. Secondly, this application uses the doped ferric hydrogen phosphate precursor M... x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2O x Fe (3-x) (PO4)2P2O7@C, doped iron hydrogen phosphate precursor M x Fe 3-x The Fe / P molar ratio in (HPO4)4·H2O and the modified sodium iron phosphate Na4M pyrophosphate x Fe (3-x) The Fe / P molar ratio in (PO4)2P2O7@C is equal, and Fe or P ions do not need to diffuse into / out of the doped ferric hydrogen phosphate precursor. Therefore, this application uses a doped ferric hydrogen phosphate precursor M... x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2O x Fe (3-x) (PO4)2P2O7@C solves the problem of abundant Maricite-NaFePO4 (Fe / P=1) and Na2FeP2O7 (Fe / P=0.5) impurity phases caused by the diffusion of Fe or P ions into / out of the precursor material, thus improving the charge / discharge specific capacity of the modified sodium iron phosphate pyrophosphate material. Meanwhile, this application utilizes a doped iron hydrogen phosphate precursor M... x Fe 3-x Preparation of modified sodium iron phosphate (Na4M) by (HPO4)4·H2Ox Fe (3-x) In the (PO4)2P2O7@C process, ion diffusion is not required during high-temperature sintering, which further improves the uniformity of metal dopant ion distribution in sodium iron phosphate pyrophosphate.

[0077] The inventors discovered that if a doped ferrous phosphate precursor is used to prepare modified sodium iron phosphate pyrophosphate (Na4M)... x Fe (3-x) (PO4)2P2O7@C, because the Fe / P molar ratio in the doped ferrous phosphate precursor is approximately 1, while the modified sodium iron phosphate pyrophosphate Na4M x Fe (3-x) The Fe / P molar ratio in (PO4)2P2O7@C is approximately 0.75, therefore Fe or P ions need to diffuse into / out of the ferrous phosphate precursor to form modified sodium iron phosphate pyrophosphate Na4M. x Fe (3-x) (PO4)2P2O7@C. However, during the diffusion of Fe or P ions into / out of the ferrous phosphate precursor, the synthesized modified sodium iron pyrophosphate material is prone to contain a large number of Maricite-NaFePO4 (Fe / P=1) impurity phases and Na2FeP2O7 (Fe / P=0.5) impurity phases. Among them, the Maricite-NaFePO4 impurity phase lacks sodium ion migration channels, which leads to a lower charge-discharge specific capacity of the modified sodium iron pyrophosphate.

[0078] The method for preparing modified sodium iron pyrophosphate proposed in this invention will be described in detail below:

[0079] Specifically, see the attached document. Figure 2 The above method for preparing modified sodium iron pyrophosphate includes the following steps:

[0080] The doped ferric hydrogen phosphate precursor M is prepared using steps S100 to S200 of the first aspect. x Fe 3-x (HPO4)4·H2O, where M is a metal dopant element.

[0081] S300: Mix the doped ferric hydrogen phosphate precursor, sodium source, carbon source and solvent, and ball mill to obtain the precursor solution;

[0082] In this step, the doped ferric hydrogen phosphate precursor, sodium source, carbon source, and solvent are mixed and ball-milled to obtain a precursor solution. The sodium source is used to incorporate the doped ferric hydrogen phosphate precursor M in the subsequent second sintering step. x Fe 3-x Sodium iron phosphate pyrophosphate is formed in (HPO4)4·H2O, and a portion of the carbon source is used to remove Fe from the doped iron hydrogen phosphate precursor.3+ Reduced to Fe 2+ The remaining portion is used to form a carbon coating layer on the surface of sodium iron phosphate pyrophosphate.

[0083] According to some specific embodiments of this application, the molar ratio of the doped iron hydrogen phosphate precursor, sodium source and carbon source is 1:(4 to 4.5):(0.4 to 0.6). By limiting the molar ratio of the doped iron hydrogen phosphate precursor, sodium source and carbon source within the above range, it is possible to ensure the effective formation of carbon-coated doped iron phosphate pyrophosphate material.

[0084] In the embodiments of this application, the specific type of sodium source is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific embodiments, the sodium source includes at least one of sodium dihydrogen phosphate, sodium acetate, sodium pyrophosphate, sodium carbonate, sodium oxalate, and disodium hydrogen phosphate.

[0085] In the embodiments of this application, the specific types of carbon sources are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific embodiments, the carbon source includes at least one of glucose, ascorbic acid, oxalic acid, citric acid, fructose, and sucrose.

[0086] S400: Dry the precursor solution to obtain precursor powder;

[0087] According to some specific embodiments of this application, the precursor solution can be spray-dried to obtain precursor powder. Spray drying is beneficial for forming precursor powder with uniform particle size distribution, and spray drying is highly efficient.

[0088] Furthermore, the precursor solution was spray-dried at an inlet temperature of 180℃~240℃, an outlet temperature of 100℃~120℃, and a feed rate of 3mL / min~33mL / min to obtain precursor powder, which further facilitates the formation of precursor powder with uniform particle size distribution.

[0089] S500: The precursor powder is subjected to a second sintering under a protective atmosphere to obtain modified sodium iron pyrophosphate.

[0090] In this step, the precursor powder is subjected to a second sintering under a protective atmosphere (e.g., a flowing argon atmosphere), and the sodium source is introduced into the doped ferric hydrogen phosphate precursor M. x Fe 3-x Sodium iron phosphate pyrophosphate is formed in (HPO4)4·H2O, and part of the carbon source will convert Fe in the doped iron hydrogen phosphate precursor. 3+ Reduced to Fe 2+ The remaining portion forms a carbon coating layer on the surface of sodium iron pyrophosphate (carbon coating can effectively improve electron transfer in conductive media), ultimately yielding modified sodium iron pyrophosphate.

[0091] According to some specific embodiments of this application, the temperature of the second sintering is 450°C to 600°C (e.g., 450°C, 470°C, 500°C, 520°C, 550°C, 580°C, 600°C, etc.), and the time of the second sintering is 8h to 15h (e.g., 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.). Thus, by limiting the temperature and time of the second sintering to the above range, it is further possible to ensure the effective formation of carbon-coated doped sodium iron pyrophosphate material.

[0092] In a fourth aspect, this application discloses a modified sodium iron phosphate pyrophosphate. According to embodiments of this application, a doped iron hydrogen phosphate precursor is prepared using the method described in the above embodiments. This effectively improves the uniformity of metal dopant ion distribution in the modified sodium iron phosphate pyrophosphate, further enhancing the intrinsic electronic conductivity and sodium ion diffusion rate of the modified sodium iron phosphate pyrophosphate material, thereby improving its electrochemical performance. Simultaneously, the modified sodium iron phosphate pyrophosphate of this application exhibits extremely low contents of Maricite-NaFePO4 (Fe / P = 1) and Na2FeP2O7 (Fe / P = 0.5) impurity phases, with virtually no peaks for these two impurity phases in the XRD pattern, thus improving the charge-discharge specific capacity of the modified sodium iron phosphate pyrophosphate material.

[0093] Specifically, the chemical formula of the above-mentioned modified sodium iron pyrophosphate is Na4M x Fe (3-x) (PO4)2P2O7@C, where M is selected from at least one of Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Ti, Zn, Al, Ga and Mg, and 0 < x < 0.3.

[0094] In a fifth aspect, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer, the positive active material layer being coated on the positive current collector, and the positive active material layer comprising modified sodium iron pyrophosphate prepared by the method described in the above embodiments. This improves the electronic conductivity and sodium ion diffusion rate of the positive electrode sheet, thereby enhancing its electrochemical performance.

[0095] In a sixth aspect, the present invention provides a sodium-ion battery. According to embodiments of the present invention, the sodium-ion battery includes the positive electrode sheet described in the above embodiments, thereby effectively improving the high-rate performance, cycle performance, and specific capacity of the sodium-ion battery.

[0096] In a seventh aspect of the invention, an electrical device is provided. According to an embodiment of the invention, the electrical device has the sodium-ion battery described in the above embodiments. Thus, the electrical device possesses all the advantages of the sodium-ion battery, which will not be repeated here.

[0097] Specifically, the aforementioned electrical equipment can be, but is not limited to, electric vehicles, electric cars, mobile phones, tablets, laptops, electric toys, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0098] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0099] Example 1

[0100] This embodiment provides a method for preparing modified sodium iron pyrophosphate, including:

[0101] 1) Preparation of doped iron hydrogen phosphate precursor Mn 0.02 Fe 2.98 (HPO4)4·H2O, including the following steps:

[0102] Weigh out the raw materials according to the molar ratio of MnSO4, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.02:2.98:4:1. Dissolve MnSO4 and FeSO4·7H2O in 95 mL of deionized water, NH4H2PO4 in 82 mL of deionized water, and H2O2 in 12 mL of deionized water. Simultaneously, add the NH4H2PO4 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 17.8 g / min, and add the H2O2 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 10.5 g / min.

[0103] Next, NH3·H2O solution was added dropwise at a rate of 1.5 g / min to adjust the pH of the reaction solution to 2.5 and then aged for 1 h.

[0104] Finally, the precursor reaction solution was subjected to pressure filtration, water washing, drying, and sintering at a temperature of 350℃ for 1 hour to obtain Mn. 0.02 Fe 2.98(HPO4)4·H2O precursor.

[0105] 2) Preparation of Na4Mn 0.02 Fe 2.98 (PO4)2P2O7@C material, including the following steps:

[0106] According to CH3COONa, Mn 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12 Weigh out the raw materials with a molar ratio of O6 of 4:1:0.5. Add the above CH3COONa and Mn to 20 mL of deionized water. 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12 O6 was ball-milled at 35 Hz for 1 hour to obtain a precursor solution.

[0107] Next, the precursor solution was spray-dried at an inlet temperature of 220°C, an outlet temperature of 110°C, and a feed rate of 10 mL / min to obtain precursor powder.

[0108] Finally, the precursor powder was placed in a porcelain boat, put into a tube furnace, heated to 500℃ at 5℃ / min under a flowing argon atmosphere, and held for 12 hours. After grinding, Na4Mn was obtained. 0.02 Fe 2.98 (PO4)2P2O7@C material.

[0109] Example 2

[0110] This embodiment prepares a Na4Mg 0.04 Fe 2.96 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0111] 1) Preparation of Mg 0.04 Fe 2.96 (HPO4)4·H2O precursor:

[0112] Weigh out each raw material according to the molar ratio of MgSO4, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.04:2.96:4:1.

[0113] Example 3

[0114] This embodiment prepares a Na4Ti 0.03 Fe 2.97 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0115] 1) Preparation of Ti 0.03 Fe 2.97 (HPO4)4·H2O precursor:

[0116] Weigh each raw material according to the molar ratio of Ti(SO4)2, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.03:2.97:4:1.

[0117] Example 4

[0118] This embodiment prepares a Na4Mn 0.02 Mg 0.02 Fe 2.96 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0119] 1) Preparation of Mn 0.02 Mg 0.02 Fe 2.96 (HPO4)4·H2O precursor:

[0120] Weigh out each raw material according to the molar ratio of MnSO4, MgSO4, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.02:0.02:2.96:4:1.

[0121] Example 5

[0122] This embodiment prepares a Na4Mn 0.02 Ti 0.02 Fe 2.96 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0123] 1) Preparation of Mn 0.02 Ti 0.02 Fe 2.96 (HPO4)4·H2O precursor:

[0124] Weigh out each raw material according to the molar ratio of MnSO4, Ti(SO4)2, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.02:0.02:2.96:4:1.

[0125] Example 6

[0126] This embodiment prepares a Na4Mn 0.02 Fe 2.98 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0127] 1) Preparation of Mn 0.02 Fe2.98 (HPO4)4·H2O precursor:

[0128] Weigh out the raw materials according to the molar ratio of MnSO4, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.02:2.98:4.5:1.5. Dissolve MnSO4 and FeSO4·7H2O in 95 mL of deionized water, NH4H2PO4 in 82 mL of deionized water, and H2O2 in 12 mL of deionized water. Simultaneously, add the NH4H2PO4 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 17.8 g / min, and add the H2O2 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 10.5 g / min.

[0129] Next, NH3·H2O solution was added dropwise at a rate of 1.5 g / min to adjust the pH of the reaction solution to 1.8 and then aged for 1 h.

[0130] Example 7

[0131] This embodiment prepares a Na4Mn 0.02 Fe 2.98 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0132] 1) Preparation of Mn 0.02 Fe 2.98 (HPO4)4·H2O precursor:

[0133] Weigh out the raw materials according to the molar ratio of MnSO4, FeSO4·7H2O, NH4H2PO4, and H2O2 of 0.02:2.98:5.2:2. Dissolve MnSO4 and FeSO4·7H2O in 95 mL of deionized water, NH4H2PO4 in 82 mL of deionized water, and H2O2 in 12 mL of deionized water. Simultaneously, add the NH4H2PO4 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 17.8 g / min, and add the H2O2 solution dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 10.5 g / min.

[0134] Next, NH3·H2O solution was added dropwise at a rate of 1.5 g / min to adjust the pH of the reaction solution to 3.5 and then aged for 3 h.

[0135] Example 8

[0136] This embodiment prepares a Na4Mn 0.02 Fe 2.98The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0137] 2) Preparation of Na4Mn 0.02 Fe 2.98 (PO4)2P2O7@C material, including the following steps:

[0138] According to CH3COONa, Mn 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12 The molar ratio of O6 is 4.2:1:0.4. Weigh out all raw materials. Add the above CH3COONa and Mn to 20 mL of deionized water. 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12 O6 was ball-milled at 35 Hz for 1 hour to obtain a precursor solution.

[0139] Next, the precursor solution was spray-dried at an inlet temperature of 220°C, an outlet temperature of 110°C, and a feed rate of 10 mL / min to obtain precursor powder.

[0140] Finally, the precursor powder was placed in a porcelain boat, put into a tube furnace, heated to 450℃ at 5℃ / min under a flowing argon atmosphere, and held for 15h. After grinding, Na4Mn was obtained. 0.02 Fe 2.98 (PO4)2P2O7@C material.

[0141] Example 9

[0142] This embodiment prepares a Na4Mn 0.02 Fe 2.98 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0143] 2) Preparation of Na4Mn 0.02 Fe 2.98 (PO4)2P2O7@C material, including the following steps:

[0144] According to CH3COONa, Mn 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12 The molar ratio of O6 is 4.5:1:0.6. Weigh out all raw materials. Add the above CH3COONa and Mn to 20 mL of deionized water. 0.02 Fe 2.98 (HPO4)4·H2O precursor and C6H 12O6 was ball-milled at 35 Hz for 1 hour to obtain a precursor solution.

[0145] Next, the precursor solution was spray-dried at an inlet temperature of 220°C, an outlet temperature of 110°C, and a feed rate of 10 mL / min to obtain precursor powder.

[0146] Finally, the precursor powder was placed in a porcelain boat, put into a tube furnace, heated to 600℃ at 5℃ / min under a flowing argon atmosphere, and held for 8 hours. After grinding, Na4Mn was obtained. 0.02 Fe 2.98 (PO4)2P2O7@C material.

[0147] Example 10

[0148] This embodiment prepares a Na4Mn 0.02 Fe 2.98 The (PO4)2P2O7@C material is prepared using a method that is basically the same as that in Example 1, with the only difference being:

[0149] 1) Preparation of Mn 0.02 Fe 2.98 (HPO4)4·H2O precursor:

[0150] First, NH4H2PO4 solution was added dropwise to a mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 17.8 g / min. Then, H2O2 solution was added dropwise to the mixed solution of MnSO4 and FeSO4·7H2O at a dropping rate of 10.5 g / min.

[0151] Comparative Example 1

[0152] This comparative example provides an A-Na4Mn 0.02 Ti 0.02 Fe 2.96 Preparation of (PO4)2P2O7@C material: (Solid-phase mixing was performed using undoped Fe3(HPO4)4·H2O and a dopant source, and the difference in ion distribution was compared with the final product of Example 5).

[0153] First, add CH3COONa, MnSO4, Ti(SO4)2, Fe3(HPO4)4·H2O and C6H to the deionized water. 12 O6 was ball-milled in a high-speed ball mill to obtain a precursor solution. The precursor solution was then spray-dried to obtain a precursor powder. Finally, the precursor powder was placed in a ceramic boat, placed in a tube furnace, and sintered under a flowing argon atmosphere. After grinding, A-Na4Mn was obtained. 0.02 Ti 0.02 Fe 2.96 (PO4)2P2O7@C sample.

[0154] Comparative Example 2

[0155] This comparative example provides a FePO4 precursor (provided by Hunan Yacheng New Energy Co., Ltd.), and its preparation method is as follows: CH3COONa, NaH2PO4, MnSO4, Ti(SO4)2, FePO4·2H2O and C6H are added to deionized water. 12 O6 was ball-milled in a high-speed ball mill to obtain a precursor solution. The precursor solution was then spray-dried to obtain a precursor powder.

[0156] Then, the precursor powder was placed in a porcelain boat, put into a tube furnace, sintered under a flowing argon atmosphere, and ground to obtain B-Na4Mn. 0.02 Ti 0.02 Fe 2.96 (PO4)2P2O7@C sample.

[0157] The cathode materials (i.e., modified sodium iron phosphate pyrophosphate) prepared in Example 5, Comparative Example 1, and Comparative Example 2 were characterized by XRD. Figure 3 These are the XRD patterns of the cathode materials prepared in Example 5, Comparative Example 1, and Comparative Example 2; Figure 4 The Mn prepared in Example 5, Comparative Example 1, and Comparative Example 2 0.02 Ti 0.02 Fe 2.96 Electron micrographs of the precursors of (HPO4)4·H2O, Fe3(HPO4)4·H2O and FePO4·2H2O; Figure 5 These are electron microscope images of the cathode materials prepared in Example 5, Comparative Example 1, and Comparative Example 2; Figure 6 This is an elemental distribution diagram of the precursor prepared in Example 5; Figure 7 This is the elemental distribution diagram of the cathode material prepared in Example 5; Figure 8 This is the elemental distribution diagram of the cathode material prepared in Comparative Example 1; Figure 9 This is the elemental distribution diagram of the cathode material prepared in Comparative Example 2.

[0158] Table 1

[0159]

[0160] from Figure 3 As can be seen from the example, Na4Mn in Example 5 0.02 Mg 0.02 Fe 2.96 The XRD pattern diffraction peaks of the (PO4)2P2O7@C material are consistent with the JCPDS data (PDF#01-086-4091), and the crystal structure is a triclinic P-1 type space group. Furthermore, the prepared Na4Mn... 0.02 Mg0.02 Fe 2.96 The (PO4)2P2O7@C material showed no obvious impurity peaks. The impurity peak intensity of NaFePO4 at approximately 34° in Comparative Example 2 was significantly higher than that in Example 5 and Comparative Example 1, indicating that using an iron hydrogen phosphate precursor can reduce the impurity phase content in the material. The impurity peak intensity of Na2FeP2O7 at approximately 12° in Comparative Example 1 was higher than that in Example 5, indicating that ball milling of the dopant source and iron hydrogen phosphate precursor (i.e., using a solid-state reaction method) is not conducive to the transport of dopant ions, leading to uneven ion distribution in the material, thus resulting in a higher Na2FeP2O7 impurity phase content in Comparative Example 1.

[0161] from Figure 4 As can be seen from the data, the Mn prepared in Example 5... 0.02 Ti 0.02 Fe 2.96 The morphologies of the Fe3(HPO4)4·H2O precursors prepared in Comparative Example 1 and Comparative Example 1 are not significantly different, indicating that a small amount of doping did not affect the surface morphology of the precursors. The FePO4·2H2O precursor particles in Comparative Example 2 are significantly larger than those in Example 5 and Comparative Example 1.

[0162] from Figure 5 As can be seen, the morphology of the cathode materials prepared in Example 5 and Comparative Example 1 is not significantly different, indicating that doping occurring during precursor synthesis or the ball milling step does not affect the surface morphology of the cathode material. The primary particles of the cathode material prepared in Comparative Example 2 are significantly smaller than those in Comparative Example 1 and Example 5, indicating that the precursor of the material was ball-milled more thoroughly. However, the cathode material prepared in Comparative Example 2 still has a relatively large amount of impurity phases, indicating that the micron- or submicron-level mixing during ball milling still requires a difficult diffusion process and cannot achieve complete ion homogeneity in the material.

[0163] from Figure 6 As can be seen from Table 1, the Mn prepared in Example 5 0.02 Ti 0.02 Fe 2.96 The relatively uniform elemental distribution of the (HPO4)4·H2O precursor indicates that a uniform doped ion distribution can be achieved in the doped ferric hydrogen phosphate precursor, eliminating the need for a difficult diffusion process during sintering.

[0164] from Figures 7-9It can be seen that the uniformity of Mn and Ti element distribution in the cathode materials prepared in Comparative Examples 1 and 2 is poor. The uniformity of other element distribution in Example 5, Comparative Examples 1, and 2 is comparable. This indicates that adding a dopant source during the ball milling step makes it difficult for dopant ions to diffuse during sintering, resulting in uneven distribution of dopant elements in the cathode material. The comparable uniformity of other element distribution in Comparative Example 2 is due to the uniform element distribution of the FePO4·2H2O precursor itself; the small amount of phosphorus source added later does not cause significant elemental unevenness.

[0165] The electrochemical performance of the cathode materials prepared in Examples 1-10 and Comparative Examples 1-2 was tested according to the following methods:

[0166] (a) The positive electrode materials, conductive agent carbon black and PVDF prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were added to the solvent NMP in a weight ratio of 8:1:1, and then stirred in a vacuum mixer to form a stable and uniform battery slurry. The positive electrode slurry was coated on the current collector aluminum foil and dried at 105°C for 6 hours to obtain the positive electrode sheet.

[0167] (b) Cut a sodium metal sheet of suitable size to serve as the negative electrode sheet;

[0168] (c) Dissolve 1 mol of sodium salt NaPF6 in 1 L of organic solvent (the volume ratio of propylene carbonate and fluoroethylene carbonate is 100:6) to obtain an electrolyte.

[0169] (d) In a glove box under an argon atmosphere, the positive electrode sheet, glass fiber separator and negative electrode sheet prepared in step (a) are alternately stacked and injected with the electrolyte prepared in step (c) to assemble a CR2032 coin cell.

[0170] (e) The above-mentioned button cells were left to stand at 25°C for 12 hours and then tested on a Land-2001A battery testing system. Each cell underwent charge-discharge cycle testing and rate performance testing at 25°C with a current of 1C. The voltage range was 2V-4V. The capacity retention rate after 50 cycles was equal to the ratio of the discharge capacity after 50 cycles to the discharge capacity of the first cycle. The specific capacity of the first cycle discharge was equal to the ratio of the first cycle discharge capacity of the button cell to the weight of the positive electrode material in the battery. The test results are shown in Table 2 and appendix. Figures 10-12 As shown.

[0171] in, Figure 10 These are charge-discharge curves of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at 0.1C. Figure 11 These are the cycle performance graphs of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at 1C. Figure 12These are discharge specific capacity test graphs of the batteries prepared in Example 5, Comparative Example 1, and Comparative Example 2 at discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C.

[0172] Depend on Figure 10 It can be seen that the batteries prepared with the cathode materials prepared in Example 5, Comparative Example 1, and Comparative Example 2 exhibit two discharge plateaus at approximately 2.79V and 3.2V during 0.1C charge-discharge. This indicates that the Na in the batteries... + The insertion / extraction reaction is a single-phase reaction. Comparative Example 2 shows a clear impurity phase NaFePO4 discharge plateau at around 2.67V, which is consistent with the XRD results.

[0173] Depend on Figure 11 It can be seen that, after 200 cycles at 1C rate, the discharge specific capacity of Example 5 was 95.22 MmAh / g, and the battery capacity retention rate was 99.91%; the discharge specific capacity of Comparative Example 1 after 200 cycles at 1C rate was 93.22 mAh / g, and the battery capacity retention rate was 99.38%; the discharge specific capacity of Comparative Example 2 after 200 cycles at 1C rate was 84.61 mAh / g, and the battery capacity retention rate was 95.29%. This indicates that the battery prepared from the cathode material of Example 5 has excellent cycle performance.

[0174] Depend on Figure 12 It can be seen that at discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, the discharge specific capacities of Example 5 are 98.7, 98.1, 96.6, 95.3, 93.8 and 91.1 mAh / g, respectively; the discharge specific capacities of Comparative Example 1 are 97.0, 96.5, 95.1, 93.8, 92.1 and 89.2 mAh / g, respectively; and the discharge specific capacities of Comparative Example 2 are 94.5, 93.3, 91.5, 88.8, 86.3 and 84.2 mAh / g, respectively. Example 5 showed a discharge specific capacity of 92.3% at 5C rate and 0.1C rate, Comparative Example 1 showed a discharge specific capacity of 92.0% at 5C rate and 0.1C rate and Comparative Example 2 showed a discharge specific capacity of 89.1% at 5C rate and 0.1C rate. This indicates that the battery prepared from the cathode material prepared in Example 5 has good high-rate performance.

[0175] Table 2

[0176]

[0177] As can be seen from Table 2, compared with Comparative Example 1, the high-rate performance and cycle performance of Examples 1-9 are significantly improved. It can be seen that by adding the metal doping source to the reaction solution for preparing the iron hydrogen phosphate precursor, Examples 1-9 can effectively improve the uniformity of the distribution of metal doping ions in the iron hydrogen phosphate precursor, thereby effectively improving the electrochemical performance of the battery.

[0178] As can be seen from Table 2, compared with Comparative Example 2, the high-rate performance and cycle performance of Examples 1-10 were significantly improved. It can be seen that the modified sodium iron pyrophosphate was prepared by using a doped iron hydrogen phosphate precursor in Examples 1-10, which can effectively improve the electrochemical performance of the battery.

[0179] As can be seen from Table 2, compared with Example 10, the high-rate performance and cycle performance of Example 1 are significantly improved. It can be seen that Example 1, by adding NH4H2PO4 solution and H2O2 solution to the mixed solution of MnSO4 and FeSO4·7H2O respectively and simultaneously, is more conducive to improving the electrochemical performance of the battery.

[0180] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0181] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a doped ferric hydrogen phosphate precursor, characterized in that, include: A solution containing a phosphorus source and a solution containing an oxidant are added to solutions containing an iron source and a metal doping source, respectively, and the reactions are carried out to obtain a reaction solution. The reaction solution was adjusted to acidity, aged, and then subjected to solid-liquid separation to obtain a doped ferric hydrogen phosphate precursor.

2. The method according to claim 1, characterized in that, The solution containing the phosphorus source and the solution containing the oxidant are added separately and simultaneously to the solution containing the iron source and the metal doping source, and the reaction is carried out to obtain the reaction solution.

3. The method according to claim 2, characterized in that, The phosphorus source-containing solution is added at a rate of 14 g / min to 20 g / min; And / or, the solution containing the oxidant is added at a rate of 7 g / min to 13 g / min.

4. The method according to claim 1, characterized in that, The molar ratio of the metal doping source, the iron source, the phosphorus source and the oxidant is x:(3-x):(3.9~5.4):(0.9~2.1), where 0<x<0.

3.

5. The method according to claim 1, characterized in that, Adjust the pH of the reaction solution to 1.7–4.

6. The method according to claim 1, characterized in that, The reaction solution is adjusted to acidity using a pH adjuster, which includes at least one of NH3·H2O, ethylenediamine, and ethanolamine.

7. The method according to claim 1, characterized in that, The aging time is 0.5h to 3h.

8. The method according to any one of claims 1 to 7, characterized in that, Also includes: The solid portion obtained from the solid-liquid separation is washed, dried, and subjected to a first sintering to obtain the doped iron hydrogen phosphate precursor.

9. The method according to claim 8, characterized in that, The first sintering temperature is 300℃~400℃, and the first sintering time is 0.5h~2h.

10. The method according to any one of claims 1 to 7, characterized in that, The iron source includes at least one of ferrous sulfate, ferrous oxalate, iron powder, iron oxide, and ferric nitrate. And / or, the metal doping source includes at least one of the following: Ni metal salt, Co metal salt, Mn metal salt, Cr metal salt, Zr metal salt, Nb metal salt, Cu metal salt, V metal salt, Ti metal salt, Zn metal salt, Al metal salt, Ga metal salt, and Mg metal salt. And / or, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, disodium hydrogen phosphate, and phosphoric acid; And / or, the oxidant includes at least one of H2O2 and ozone.

11. A doped ferric hydrogen phosphate precursor, characterized in that, It is prepared by any one of claims 1 to 10.

12. A method for preparing modified sodium iron pyrophosphate, characterized in that, include: The doped ferric hydrogen phosphate precursor was prepared by any one of claims 1 to 10; The doped ferric hydrogen phosphate precursor, sodium source, carbon source and solvent are mixed and ball-milled to obtain a precursor solution; The precursor solution was dried to obtain precursor powder; The precursor powder was subjected to a second sintering under a protective atmosphere to obtain modified sodium iron pyrophosphate.

13. The method according to claim 12, characterized in that, The molar ratio of the doped ferric hydrogen phosphate precursor, the sodium source, and the carbon source is 1:(4-4.5):(0.4-0.6).

14. The method according to claim 12, characterized in that, The precursor solution is spray-dried to obtain the precursor powder.

15. The method according to any one of claims 12 to 14, characterized in that, The second sintering temperature is 450℃~600℃, and the second sintering time is 8h~15h.

16. The method according to any one of claims 12 to 14, characterized in that, The sodium source includes at least one of sodium dihydrogen phosphate, sodium acetate, sodium pyrophosphate, sodium carbonate, sodium oxalate, and disodium hydrogen phosphate. And / or, the carbon source includes at least one of glucose, ascorbic acid, oxalic acid, citric acid, fructose, and sucrose.

17. A modified sodium iron pyrophosphate, characterized in that, It is prepared by any one of claims 12 to 16.

18. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer is coated on the positive current collector, and the positive active material layer includes modified sodium iron pyrophosphate prepared by any one of the methods described in 12 to 16.

19. A sodium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 18.

20. An electrical appliance, characterized in that, Including the sodium-ion battery of claim 19.

Images