Integrated preparation method for iron-based phosphate material for positive electrode of secondary battery

Abstract

The present invention discloses an integrated preparation method for an iron-based phosphate material for a positive electrode of a secondary battery, comprising the following steps: adding an iron source and a phosphorus source into an acid solution, mixing and performing a temperature-controlled reaction to prepare a precursor slurry; then adding an alkali metal source and a doping element source into the precursor slurry, and stirring until a uniform mixed slurry is formed; and then subjecting the mixed slurry to mixing and grinding, spray drying, and high-temperature sintering to obtain the iron-based phosphate material for the positive electrode of the secondary battery. The integrated preparation method for the iron-based phosphate material for the positive electrode of the secondary battery according to the present invention has the characteristics of simplified process, high raw material utilization rate, and production process compatibility.

Description

Integrated preparation method of iron-based phosphate material for secondary battery cathode Technical Field

[0001] This invention relates to the field of secondary ion battery technology, specifically to an integrated preparation method for a secondary battery positive electrode iron-based phosphate material. Background Technology

[0002] Against the backdrop of increasingly strained global energy supplies and a continuously deteriorating environmental situation, environmental problems such as air pollution, the intensifying greenhouse effect, frequent acid rain, and nuclear waste disposal are becoming increasingly prominent, posing serious challenges. Therefore, optimizing the energy structure and actively exploring and utilizing renewable and clean energy resources have become core strategic goals for promoting sustainable development.

[0003] In this process, lithium-ion rechargeable batteries have occupied an important position in the new energy field due to their superior performance and have achieved widespread commercialization, especially in portable electronic devices and electric vehicles. This battery system, with its significant advantages such as high energy density and good stability, has become the preferred solution in the current rechargeable battery technology field. However, with the rapid growth in demand for lithium resources, the problem of limited global reserves is becoming increasingly prominent, becoming a new bottleneck restricting the widespread application of lithium-ion batteries. Therefore, developing new, low-cost, and resource-rich battery systems as an alternative energy storage solution is particularly urgent.

[0004] In the periodic table, lithium, sodium, and potassium all belong to Group 1 alkali metals and exhibit similar physicochemical properties. Therefore, the research and development processes and material systems for sodium-ion and potassium-ion batteries can be directly referenced from those for lithium-ion batteries. Furthermore, considering that the abundance of sodium (2.3 wt.%) and potassium (1.5 wt.%) in the Earth's crust far exceeds that of lithium (approximately 0.0065 wt.%), sodium-ion and potassium-ion batteries are potential alternatives to lithium-ion batteries.

[0005] Polyanionic compounds have attracted significant attention in the field of lithium-ion battery energy storage technology due to their remarkable characteristics such as structural stability, long cycle life, high thermal stability, and high operating voltage. Among the many polyanionic cathode materials, iron-based phosphate materials stand out for their performance and have seen rapid industrialization. LiFePO4 with an olivine structure (iron-to-phosphorus ratio of 1) is a typical iron-based phosphate material, exhibiting high voltage, specific capacity, and ionic conductivity, thus making it suitable for use as a cathode material in lithium-ion batteries. In addition, pyrophosphate and composite phosphate materials, such as sodium iron pyrophosphate (Na2FeP2O7, iron-to-phosphorus ratio of 0.5), sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, iron-to-phosphorus ratio of 0.75), and potassium iron phosphate pyrophosphate (K4Fe3(PO4)2P2O7, iron-to-phosphorus ratio of 7.5), are also gradually becoming hot topics in battery material research.

[0006] However, the preparation process of iron-based phosphate materials mainly involves using phosphorus source, ferrous source and oxidant as raw materials. During the reaction, the oxidant converts divalent iron into trivalent iron. The trivalent iron and phosphate ions co-precipitate to generate iron phosphate. Then, pure iron phosphate is obtained through solid-liquid separation. Finally, iron phosphate is mixed with carbon source, metal source, phosphoric acid and other materials to prepare the required iron-based phosphate materials.

[0007] The solid-liquid separation of ferric phosphate in the above method requires cumbersome steps such as filtration, washing, and drying, increasing production energy consumption; the use of hazardous hydrogen peroxide as an oxidant in the synthesis poses a significant safety hazard to industrial production; the generated waste liquid requires subsequent treatment, failing to effectively utilize raw materials and resulting in a large amount of waste during the preparation process, reducing resource utilization efficiency. In subsequent preparation steps of different iron-based phosphate materials, more phosphorus or iron sources need to be introduced during the preparation process to balance the elemental ratio, increasing the cost of process production. Summary of the Invention

[0008] The purpose of this invention is to provide an integrated preparation method for iron-based phosphate materials for secondary battery cathodes, which features simplified process, high raw material utilization, and excellent electrochemical performance.

[0009] This invention can be achieved through the following technical solutions:

[0010] This invention discloses an integrated preparation method for iron-based phosphate material for secondary battery cathodes, comprising the following steps: adding an iron source and a phosphorus source to an acid solution and mixing and reacting at a controlled temperature to prepare a precursor slurry; then adding an alkali metal source and a dopant source to the precursor slurry and stirring until a uniform mixed slurry is formed; then mixing and grinding the mixed slurry, spray drying, and high-temperature sintering to obtain the iron-based phosphate material for secondary battery cathodes.

[0011] In the integrated preparation method of iron-based phosphate electrode material described in this invention, the preparation of iron phosphate slurry does not require cumbersome solid-liquid separation, washing and drying steps, and the subsequent preparation of iron-based phosphate material does not require secondary "iron supplementation" or "sodium supplementation", which greatly simplifies the preparation process, realizes the integrated and efficient preparation of multiple battery materials, improves production efficiency, improves raw material utilization, simplifies waste liquid treatment steps, and significantly reduces production energy consumption and cost.

[0012] Furthermore, the chemical formula of this iron-based phosphate active material is X. a Fe b M c (PO4) d (P2O7) eWherein, 0 < a < 5, 0 < b < 4, 0 ≤ c ≤ 0.06, 0 ≤ d < 4, 0 ≤ e < 4 and d and e are not simultaneously 0, alkali metal X is one or more of sodium, lithium, and potassium, and dopant element M is one or more of transition metals manganese, titanium, vanadium, nickel, magnesium, and copper. During the synthesis process, various active materials for secondary ion batteries can be prepared in an integrated manner by feeding materials according to the proportions of X, Fe, M, and P elements in the target product. In this invention, the value of c is less than or equal to 0.06, which can avoid iron vacancy defects, excessive doping of other elements leading to a reduction in the number of redox atoms in the crystal lattice, excessive lattice distortion, and consequently narrowing of sodium ion channels. Introducing dopant elements to replace part of the divalent Fe element can further improve the electronic conductivity of the material, improve the electrochemical activity of the material, and thus improve the specific capacity and rate performance of the material.

[0013] Furthermore, the particle size D50 of the ground slurry is 0.1–1.5 μm, and the grinding method is one or more of sand milling, high-energy ball milling, and planetary ball milling. Smaller particle size can shorten the diffusion path of ions and increase the diffusion rate of ions, thereby improving the electrochemical performance of the material. When the particle size is too fine, the fine particles in the product are prone to agglomeration and adhesion, which in turn reduces the electrochemical performance of the material.

[0014] Furthermore, the spray drying temperature of the slurry is 100-260℃. The spray drying temperature directly affects the structure and purity of the material. As the temperature increases, the crystallinity of the iron-based phosphate material increases, and the morphology and particle size distribution become more uniform. However, excessively high temperatures can lead to particle agglomeration, impure crystal phases, or structural defects.

[0015] Furthermore, the high-temperature sintering temperature is 400–800℃, the time is 4–15 h, and the protective atmosphere is one or more of nitrogen and argon. If the sintering temperature is too low or the time is too short, it will lead to insufficient crystal transformation, impure crystal phase, and uneven particle size distribution; if the sintering temperature is too high or the time is too long, it will lead to crystal agglomeration, lattice distortion, and reduced electrochemical performance of the material.

[0016] Furthermore, the temperature of the temperature-controlled reaction is 70-180℃, the reaction time is 3-8 h, and the temperature-controlled reaction method is high-temperature reflux and / or hydrothermal method. When the temperature is too low, the diffusion rate of ions in the solution is slow, which is not conducive to crystal formation; as the temperature increases, the ion diffusion rate accelerates, the contact area increases, and the growth of iron phosphate crystals is accelerated; when the temperature is too high, the particle collision frequency will increase, and agglomerates will easily form.

[0017] Furthermore, the pH of the acid solution is 0.1–1.5, and the acid solution is an inorganic acid solution and / or an organic acid solution. The inorganic acid solution is phosphoric acid, and the organic acid solution is one or more of citric acid, ascorbic acid, formic acid, acetic acid, oxalic acid, salicylic acid, and tartaric acid. When the pH is too low, the system viscosity is high, the dispersibility is poor, and the crystals are prone to agglomeration, resulting in an increase in the particle size of ferric phosphate. When the pH is too high, the acidity of the system is insufficient, leading to incomplete reaction.

[0018] Furthermore, a carbon source is added to the mixed slurry, with the amount of carbon source added being 5-15% of the mass of the mixed slurry. The carbon source is an inorganic carbon source and / or an organic carbon source. The inorganic carbon source is one or more of carbon black, carbon fiber, graphene, graphite, and carbon nanotubes, while the organic carbon source is one or more of glucose, sucrose, isopropanol, starch, citric acid, maltose, formic acid, acetic acid, oxalic acid, and polyethylene glycol. Introducing a carbon source can form a carbon coating layer on the surface of the iron-based phosphate material, increasing the conductivity between particles and constructing an effective electron transport channel for the iron-based phosphate material, thereby improving the electrochemical performance of the material. However, excessive introduction of carbon source will lead to a decrease in the relative content of active substances, thus affecting the performance of the final product.

[0019] Furthermore, the iron source is one or more of the following: iron oxide, iron hydroxy oxide, iron hydroxide, iron(II,III) oxide, iron carbonate, iron oxalate, iron chloride, iron acetate, and iron citrate.

[0020] Furthermore, the phosphorus source is an inorganic phosphorus source and / or an organic phosphorus source. The inorganic phosphorus source is one or more of phosphoric acid, pyrophosphate, ammonium pyrophosphate, sodium pyrophosphate, metaphosphoric acid, etc., and the organic phosphorus source is one or more of 4-(dimethylamino)triphenylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, diethyl(hydroxymethyl) phosphate, ethylenediaminetetramethylidene phosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyethylidene diphosphonic acid, 2-hydroxyphosphonoacetic acid, and polyaminopolyethermethylene phosphonic acid.

[0021] Furthermore, the alkali metal source is a sodium source, a lithium source, and / or a potassium source. The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, sodium oxalate, and sodium pyrophosphate. The lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium citrate. The potassium source is one or more of potassium carbonate, potassium hydroxide, and potassium oxalate.

[0022] Another aspect of the present invention is to protect a secondary battery positive electrode iron-based phosphate material, which is prepared by the above-described preparation method.

[0023] This invention provides an integrated preparation method for iron-based phosphate material for secondary battery cathodes, which has the following beneficial effects:

[0024] First, the process is simplified. The present invention uses an integrated preparation technology for iron-based phosphate electrode materials to prepare a variety of active materials for secondary ion batteries. This method simplifies the preparation process and effectively avoids the solid-liquid separation, washing and drying steps in the preparation of iron phosphate.

[0025] Secondly, it boasts high material utilization. The precursor slurry preparation process avoids solid-liquid separation steps and generates no waste liquid, waste gas, or waste residue. By reducing intermediate steps, it effectively improves reactant utilization, enabling green industrial production. When using this precursor slurry to prepare various battery materials, there is no need to add additional phosphorus and iron sources, significantly reducing production energy consumption and costs.

[0026] Third, the integrated preparation method of iron-based phosphate material for secondary battery cathode provided by this invention exhibits high production process compatibility without changing the process route. It is suitable for the preparation process of various ion secondary battery active materials, without the need to add additional equipment and process routes, and has good industrialization prospects. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0028] This invention discloses an integrated preparation method for iron-based phosphate material for secondary battery cathodes, comprising the following steps: adding an iron source and a phosphorus source to an acid solution and mixing and reacting at a controlled temperature to prepare a precursor slurry; then adding an alkali metal source and a dopant source to the precursor slurry and stirring until a uniform mixed slurry is formed; then mixing and grinding the mixed slurry, spray drying, and high-temperature sintering to obtain the iron-based phosphate material for secondary battery cathodes.

[0029] Furthermore, the chemical formula of this iron-based phosphate active material is X. a Fe b M c (PO4) d (P2O7) e Wherein, 0 < a < 5, 0 < b < 4, 0 ≤ c ≤ 0.06, 0 ≤ d < 4, 0 ≤ e < 4 and d and e are not both 0, the alkali metal X is one or more of sodium, lithium, and potassium, and the doping element M is one or more of transition metals manganese, titanium, vanadium, nickel, magnesium, and copper.

[0030] Furthermore, the particle size D50 of the ground slurry is 0.1 to 1.5 μm, and the grinding method is one or more of sand milling, high-energy ball milling, and planetary ball milling.

[0031] Furthermore, the spray drying temperature of the slurry is 100-260℃.

[0032] Furthermore, the high-temperature sintering temperature is 400–800℃, the time is 4–15 h, and the protective atmosphere is one or more of nitrogen and argon.

[0033] Furthermore, the temperature of the temperature-controlled reaction is 70-180℃, the reaction time is 3-8 h, and the temperature-controlled reaction method is high-temperature reflux and / or hydrothermal method.

[0034] Furthermore, the pH of the acid solution is 0.1 to 1.5, and the acid solution is an inorganic acid solution and / or an organic acid solution. The inorganic acid solution is phosphoric acid, and the organic acid solution is one or more of citric acid, ascorbic acid, formic acid, acetic acid, oxalic acid, salicylic acid, and tartaric acid.

[0035] Furthermore, a carbon source is added to the mixed slurry, with the amount of carbon source added being 5-15% of the mass of the mixed slurry; the carbon source is an inorganic carbon source and / or an organic carbon source, the inorganic carbon source being one or more of carbon black, carbon fiber, graphene, graphite, and carbon nanotubes, and the organic carbon source being one or more of glucose, sucrose, isopropanol, starch, citric acid, maltose, formic acid, acetic acid, oxalic acid, and polyethylene glycol.

[0036] Furthermore, the iron source is one or more of the following: iron oxide, iron hydroxy oxide, iron hydroxide, iron(II,III) oxide, iron carbonate, iron oxalate, iron chloride, iron acetate, and iron citrate.

[0037] Furthermore, the phosphorus source is an inorganic phosphorus source and / or an organic phosphorus source. The inorganic phosphorus source is one or more of phosphoric acid, pyrophosphate, ammonium pyrophosphate, sodium pyrophosphate, metaphosphoric acid, etc., and the organic phosphorus source is one or more of 4-(dimethylamino)triphenylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, diethyl(hydroxymethyl) phosphate, ethylenediaminetetramethylidene phosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyethylidene diphosphonic acid, 2-hydroxyphosphonoacetic acid, and polyaminopolyethermethylene phosphonic acid.

[0038] Furthermore, the alkali metal source is a sodium source, a lithium source, and / or a potassium source. The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, sodium oxalate, and sodium pyrophosphate. The lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium citrate. The potassium source is one or more of potassium carbonate, potassium hydroxide, and potassium oxalate.

[0039] Example 1

[0040] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0041] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus source, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0042] Example 2

[0043] This embodiment employs an integrated preparation method for secondary battery cathode iron-based phosphate materials to prepare doped sodium iron phosphate pyrophosphate (Na4Fe). 2.8 V 0.2 (PO4)2P2O7), including the following steps:

[0044] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.7:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.65 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus sources, sodium carbonate was added as the sodium source, ammonium metavanadate as the vanadium dopant source, and sucrose and polyethylene glycol as the carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, vanadium, and phosphorus in the sodium, iron, and phosphorus sources was 4:2.8:0.2:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The resulting mixed slurry was spray-dried at an inlet air temperature of 250°C and an outlet air temperature of 120°C to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520°C for 10 h under a nitrogen atmosphere to obtain Na4Fe. 2.8 V 0.2(PO4)2P2O7 material was used. It was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0045] Example 3

[0046] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0047] Using pyrophosphate as the phosphorus source, citric acid as the acidic compound, and ferric hydroxide as the iron source, ferric hydroxide powder was added at an iron-to-phosphorus ratio of 0.75:1. After mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus source, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0048] Example 4

[0049] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0050] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus sources, sodium oxalate was added as the sodium source, and glucose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0051] Example 5

[0052] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0053] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus source, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 10% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0054] Example 6

[0055] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0056] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus sources, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 1.0 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0057] Example 7

[0058] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0059] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus source, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 200℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0060] Example 8

[0061] This embodiment uses an integrated preparation method for secondary battery positive electrode iron-based phosphate materials to prepare sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0062] Phosphoric acid was used as the phosphorus source and an acidic compound, and iron oxide was used as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 0.75 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus source, sodium carbonate was added as the sodium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 600℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0063] Comparative Example 1

[0064] This embodiment uses a stepwise method to prepare the positive electrode active material sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0065] Phosphoric acid was used as the phosphorus source and acidic compound, and iron oxide as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at an iron-to-phosphorus ratio of 0.75:1, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, solid-liquid separation was performed, followed by washing and drying to obtain iron phosphate powder. Using iron phosphate as the iron and phosphorus source, sodium carbonate was added as the sodium source, sucrose and polyethylene glycol as the carbon source, and disodium hydrogen phosphate as a supplementary phosphorus source. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the amount of carbon source added was 5% of the mass of the slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0066] Comparative Example 2

[0067] This embodiment uses ferric phosphate powder as raw material to prepare sodium ferric phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), including the following steps:

[0068] Commercially available ferric phosphate was used as the iron and phosphorus source, sodium carbonate as the sodium source, sucrose and polyethylene glycol as the carbon source, and disodium hydrogen phosphate as a supplementary phosphorus source. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed slurry. The molar ratio of sodium, iron, and phosphorus in the sodium, iron, and phosphorus sources was 4:3:4, and the carbon source was added at 5% of the slurry mass. The resulting slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃, and the dried powder was collected. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain Na4Fe3(PO4)2P2O7 material. This material was then assembled into a sodium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0069] Comparative Example 3

[0070] This embodiment uses an integrated preparation method for secondary battery cathode iron-based phosphate materials to prepare lithium iron phosphate (LiFePO4), including the following steps:

[0071] Phosphoric acid was used as the phosphorus source and acidic compound, and iron oxide as the iron source. Phosphoric acid was diluted to obtain dilute phosphoric acid. Iron oxide powder was added at a 1:1 iron-to-phosphorus ratio, and after mixing, the mixture was refluxed at 110°C for 3 hours with a stirring rate of 500 rpm. After the reaction, an iron-based phosphate precursor slurry with an iron-to-phosphorus ratio of 1 was obtained. Using the iron-based phosphate precursor slurry as the iron and phosphorus sources, lithium carbonate was added as the lithium source, and sucrose and polyethylene glycol were added as carbon sources. After thorough mixing, the mixture was added to a sand mill and milled at 1200 rpm until the particle size D50 ≤ 0.5 μm, resulting in a uniformly dispersed mixed slurry. The molar ratio of lithium, iron, and phosphorus in the lithium, iron, and phosphorus sources was 1:1:1, and the amount of carbon source added was 5% of the mass of the mixed slurry. The obtained mixed slurry was spray-dried at an inlet air temperature of 250℃ and an outlet air temperature of 120℃ to obtain and collect the dried powder. The spray-dried material was then placed in a tube furnace and sintered at 520℃ for 10 h under a nitrogen atmosphere to obtain LiFePO4 material. This material was then assembled into a lithium-ion battery for electrochemical performance testing. Relevant parameters are shown in Table 1.

[0072] Table 1 Performance Test Results

[0073]

[0074] As can be seen from the test results of Examples 1 and 2 in Table 1, introducing doping elements during the integrated fabrication process can improve the electrochemical performance of the material. Specifically, vanadium doping can increase the operating voltage of iron-based phosphate materials, stabilize the crystal structure, and thus improve the specific capacity and long-cycle stability of the electrode material.

[0075] The test results from Examples 1, 3, and 4 show that changing the raw materials has little impact on the electrochemical performance during the integrated preparation of iron-based phosphate materials. In industrial production, lower-priced raw materials can be selected to reduce production costs.

[0076] The test results from Examples 1 and 5 show that the more carbon source introduced, the lower the relative content of active material, thus affecting electrochemical performance.

[0077] The test results from Examples 1 and 6 show that the smaller the particle size after sand milling, the better the electrochemical performance and the higher the compaction density. This is because a smaller particle size can shorten the diffusion path of ions, increase the diffusion rate of ions, and thus improve the electrochemical performance of the material. Furthermore, a smaller particle size reduces the gaps between particles, allowing them to pack together more tightly under the same pressure, thereby increasing the compaction density.

[0078] The test results from Examples 1 and 7 show that as the spray drying temperature increases, the crystallinity of the iron-based phosphate material increases, the morphology and particle size distribution become more uniform, and the compaction density increases.

[0079] The test results from Examples 1 and 8 show that the higher the sintering temperature and the longer the sintering time, the more severe the aggregation of iron-based phosphate grains, which hinders the effective transport of ions, leading to reduced cycle stability and thus affecting the overall performance and lifespan of the battery.

[0080] Based on the comparative analysis of Example 1 with Comparative Examples 1 and 2, compared to the integrated preparation method, regardless of whether ferric phosphate powder is prepared first as an intermediate product or commercial ferric phosphate is used directly as a raw material, the subsequent preparation process of iron-based phosphate materials requires the replenishment of phosphorus source, increasing production costs. Furthermore, the method of preparing iron-based phosphate materials by first preparing ferric phosphate requires cumbersome steps such as solid-liquid separation, washing, and drying, increasing energy consumption; and it also generates waste liquid, reducing raw material utilization.

[0081] Based on the comparative analysis of Example 1 and Comparative Example 3, the integrated preparation method of the secondary battery cathode iron-based phosphate material has a wide range of applications. Without changing the process flow, only the types of reactants can be changed to prepare other ion-ion battery active materials with high electrochemical performance using the integrated preparation method of this invention. This characteristic makes it suitable for the compatible production needs of different types of secondary ion battery production lines in industrial production, reducing industrial production costs.

[0082] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for the integrated preparation of a positive electrode iron-based phosphate material for secondary batteries, characterized in that Includes the following steps: Iron and phosphorus sources are added to an acid solution and mixed and reacted under controlled temperature to prepare a precursor slurry. Then, an alkali metal source and a dopant source are added to the precursor slurry and stirred until a uniform mixed slurry is formed. The mixed slurry is then mixed, ground, spray-dried, and sintered at high temperature to obtain a secondary battery cathode iron-based phosphate material.

2. The method of claim 1, wherein the method is characterized by: The chemical formula of this iron-based phosphate active material is X. a Fe b Mc(PO4)d(P2O7) e Wherein, 0 < a < 5, 0 < b < 4, 0 ≤ c ≤ 0.06, 0 ≤ d < 4, 0 ≤ e < 4, and d and e are not both 0, the alkali metal X is one or more of sodium, lithium, and potassium, and the doping element M is one or more of transition metals manganese, titanium, vanadium, nickel, magnesium, and copper.

3. The method of claim 1, wherein the method is characterized by: The particle size D50 of the slurry after grinding is 0.1 to 1.5 μm, and the grinding method is one or more of sand milling, high-energy ball milling, and planetary ball milling.

4. The method of claim 1, wherein the method is characterized by: The spray drying temperature of the slurry is 100-260℃.

5. The method of claim 1, wherein the method is characterized by: The high-temperature sintering temperature is 400-800℃, the time is 4-15h, and the protective atmosphere is one or more of nitrogen and argon.

6. The method of claim 1, wherein the method is characterized by: The temperature of the temperature-controlled reaction is 70-180℃, the reaction time is 3-8h, and the temperature-controlled reaction method is high-temperature reflux and / or hydrothermal method.

7. The method of claim 1, wherein the method is characterized by: The pH of the acid solution is 0.1 to 1.

5. The acid solution is an inorganic acid solution and / or an organic acid solution. The inorganic acid solution is phosphoric acid, and the organic acid solution is one or more of the following: citric acid, ascorbic acid, formic acid, acetic acid, oxalic acid, salicylic acid, and tartaric acid.

8. The method of claim 7, wherein the method is characterized by: The mixed slurry also contains a carbon source, the amount of which is 5-15% of the mass of the mixed slurry; the carbon source is an inorganic carbon source and / or an organic carbon source, the inorganic carbon source is one or more of carbon black, carbon fiber, graphene, graphite, and carbon nanotubes, and the organic carbon source is one or more of glucose, sucrose, isopropanol, starch, citric acid, maltose, formic acid, acetic acid, oxalic acid, and polyethylene glycol.

9. The method of claim 1, wherein the method is characterized by: The iron source is one or more of the following: iron oxide, iron hydroxide, iron(II) oxide, iron carbonate, iron oxalate, iron chloride, iron acetate, and iron citrate. The phosphorus source is an inorganic phosphorus source and / or an organic phosphorus source. The inorganic phosphorus source is one or more of phosphoric acid, pyrophosphate, ammonium pyrophosphate, sodium pyrophosphate, metaphosphoric acid, etc., and the organic phosphorus source is one or more of 4-(dimethylamino)triphenylphosphine, aminotrimethylphosphonic acid, hydroxyethylidene diphosphonic acid, diethyl(hydroxymethyl) phosphate, ethylenediaminetetramethylidene phosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxyethylidene diphosphonic acid, 2-hydroxyphosphonoacetic acid, polyaminopolyethermethylene phosphonic acid; The alkali metal source is a sodium source, a lithium source, and / or a potassium source. The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium chloride, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, sodium oxalate, and sodium pyrophosphate. The lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium citrate. The potassium source is one or more of potassium carbonate, potassium hydroxide, and potassium oxalate.

10. A secondary battery positive electrode iron-based phosphate material, characterized by: It is prepared by any one of the preparation methods of claims 1-9.

Images