Method for preparing non-stoichiometric iron phosphate composite using acidic iron-air battery and positive electrode material for sodium ion battery

Abstract

The present invention discloses a method for preparing a non-stoichiometric iron phosphate composite by using an acidic iron-air battery and a positive electrode material for a sodium ion battery. The iron-air battery comprises a positive electrode, a negative electrode and an electrolyte. The method is characterized in that a porous carbon electrode is used as the positive electrode, an iron electrode is used as the negative electrode, an acidic phosphoric acid source solution containing phosphate and / or pyrophosphate is used as the electrolyte, a flowing oxygen atmosphere and an oxidant are added to the iron-air battery, and a redox reaction is achieved by the operation of the iron-air battery under temperature control conditions to generate a non-stoichiometric iron phosphate precipitate Fe. x H y (PO m ) (3x+y) / (2m‑5) zH2O, wherein the iron-hydrogen ratio x / y is in the range of 0.5-8, x is in the range of 0.6-0.96, y is in the range of 0.12-1.2, z is in the range of 1-4, and m is in the range of 3.5-4. The present invention has the characteristics of controllable process, environmental protection and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and specifically refers to a method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery and a sodium ion battery positive electrode material. Background Art

[0002] With the transformation of the global energy structure and the advancement of sustainable development, the rapid development of new energy, particularly electric vehicles and energy storage systems, has led to a growing demand for high-performance battery materials. Sodium-ion batteries, with their abundant raw materials, low cost, and environmental friendliness, are considered an important complement and potential replacement for lithium-ion batteries, demonstrating great potential in large-scale energy storage and low-cost applications.

[0003] Iron phosphate is an important precursor in the synthesis of sodium-ion battery cathode materials. Its chemical composition and cost are crucial for improving battery performance and reducing production costs. However, existing iron phosphate preparation methods, including electrolysis and chemical precipitation, have the following main problems:

[0004] For example, energy consumption: Traditional methods of preparing iron phosphate, such as electrolysis, require a large amount of electricity, which not only increases production costs but is also not conducive to sustainable development.

[0005] For example, environmental pollution: the chemical precipitation method uses and generates a large amount of chemical reagents and by-products during the preparation process, which may cause pollution to the environment.

[0006] For example, waste of resources: existing technologies fail to effectively utilize raw materials, resulting in a large amount of waste during the preparation process, which reduces the efficiency of resource utilization.

[0007] For example, product purity and consistency: the iron phosphate product obtained by traditional methods has low purity and poor consistency, which directly affects the performance and life of sodium-ion batteries.

[0008] For example, production costs, including high equipment investment, raw material costs, and post-processing expenses, make existing technologies for synthesizing iron phosphate economically inefficient. Furthermore, focusing solely on synthesizing iron phosphate with a high iron-to-phosphorus ratio while ignoring the synthesis of low iron-to-phosphorus ratios or non-stoichiometric iron phosphates is detrimental to promoting industry development and technological iteration.

[0009] Such as battery performance limitations: Due to insufficient purity and morphology control of iron phosphate, the performance of sodium-ion battery positive electrode materials, such as capacity, cycle stability and safety, is limited. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery and a positive electrode material for a sodium ion battery, which has the characteristics of controllable process, green environmental protection and low cost.

[0011] The present invention can be achieved through the following technical solutions:

[0012] The present invention discloses a method for preparing a non-stoichiometric iron phosphate composite by using an acidic iron-air battery. The iron-air battery comprises a positive electrode, a negative electrode and an electrolyte. A porous carbon electrode is used as the positive electrode, an iron electrode is used as the negative electrode, and an acidic phosphoric acid source solution containing phosphate and / or pyrophosphate is used as the electrolyte. A flowing oxygen atmosphere and an oxidant are added to the iron-air battery. Under temperature-controlled conditions, an oxidation-reduction reaction is achieved by the operation of the iron-air battery to generate a non-stoichiometric iron phosphate precipitate Fe. x H y (PO m ) (3x+y) / (2m-5) zH2O, the iron-hydrogen ratio x / y ranges from 0.5 to 8, x ranges from 0.6 to 0.96, y ranges from 0.12 to 1.2, z ranges from 1 to 4, and m ranges from 3.5 to 4.

[0013] In the present invention, due to the different concentrations of phosphate or pyrophosphate under acidic conditions, the Fe 3+ The concentration is also different. Considering the precipitation dissolution equilibrium, the iron-phosphorus ratio of the iron phosphate complex will be different if the proportion of each iron phosphate salt in the precipitate is different.

[0014] Specifically, the reactions that the present invention may involve are as follows:

[0015] Negative electrode reaction: The iron electrode undergoes oxidation reaction at the negative electrode to generate divalent iron ions: Fe → Fe 2+ +2e − ;

[0016] Positive electrode reaction: Oxygen undergoes a reduction reaction on the air electrode and combines with hydrogen ions to form water: O2+4H + +4e − →2H2O;

[0017] Oxidation reaction: The divalent iron is oxidized by the flowing oxygen atmosphere and / or oxidant, 4Fe 2+ +O2+4H + →4Fe 3+ +2H2Oor 2Fe 2+ +H2O2+2H + →2Fe 3+ +2H2O;

[0018] Precipitation reaction: Ferric iron and different phosphate species undergo precipitation reaction. The reaction equation is as follows:

[0019] xH2O+Fe 3+ +PO4 3−→FePO4·xH2O↓;

[0020] xH2O+Fe 3+ +3H2PO4 − →Fe(H2PO4)3·xH2O↓;

[0021] xH2O+2Fe 3+ +3HPO4 2− →Fe2(HPO4)3·xH2O↓;

[0022] 4Fe 3+ +3P2O7 4− →2FeP2O7↓.

[0023] Furthermore, the electrolyte is an acid solution or a phosphate solution with an acid solution added thereto, the acid solution is one or more of phosphoric acid, pyrophosphoric acid, and sulfuric acid, the phosphate solution is one or more of phosphoric acid and pyrophosphate such as sodium dihydrogen phosphate solution, ammonium dihydrogen phosphate solution, and sodium pyrophosphate, the mass concentration of phosphorus in the electrolyte is in the range of 1.0-15wt%, and the pH of the electrolyte is 1-3. In the overall process, the pH of the reaction solution is not adjusted by alkaline solution, but mainly by regulating the working time of the battery and the concentration of the acid solution in the phosphorus source. The higher the concentration of the acid solution, the lower the pH of the solution. At the same time, increasing the phosphorus concentration is beneficial to increasing the ionic conductivity of the solution, which is beneficial to Fe 3+ The combination of the phosphorus source and the prepared phosphorus source, the higher the phosphorus source concentration, the faster the reaction rate of the two, and the greater the compaction density of the prepared product. However, if the concentration is too high, the viscosity of the solution will be too high, which is not conducive to the reaction. The pH of the solution is a key parameter for regulating the preparation of non-stoichiometric iron phosphate materials. The lower the pH of the solution, the more acidic species of phosphoric acid and pyrophosphoric acid in the solution, the lower the iron-hydrogen ratio of the prepared non-stoichiometric iron phosphate, which in turn leads to a lower iron-phosphorus ratio of the prepared non-stoichiometric iron phosphate. The higher the pH of the solution, the more conducive it is to the formation of iron phosphate, the higher the iron-hydrogen ratio of the prepared non-stoichiometric iron phosphate, which in turn leads to a higher iron-phosphorus ratio of the prepared non-stoichiometric iron phosphate. However, when the pH of the solution is too low, the solubility of the precipitate increases, which greatly reduces the production efficiency. When the pH of the solution increases to more than 3, it tends to form iron hydroxide, which introduces impurities into the final product.

[0024] Furthermore, the operating conditions of the battery are: an operating temperature of 30-90 ° C. In the present invention, the working temperature is the key to achieving efficient redox reaction and iron phosphate complex precipitation reaction. The operating temperature affects the rate of chemical reaction inside the battery and the activity of the electrode material, thereby affecting the charge and discharge efficiency and overall performance of the battery. At the same time, the temperature range of 30-90 ° C also takes into account the safe operation requirements of the battery to avoid potential safety risks caused by overheating. The working time is 1-10 hours. The working time of the battery has a direct impact on the concentration of iron ions in the solution and the pH of the solution. The longer the working time, the higher the pH in the solution and the higher the concentration of iron ions in the solution. Then, by regulating the working time of the battery, the iron-phosphorus ratio in the solution is regulated. The longer the working time, the higher the iron-phosphorus ratio in the solution. Therefore, as the working time of the battery increases, it is beneficial to increase the iron-hydrogen ratio of the non-stoichiometric iron phosphate, thereby increasing the iron-phosphorus ratio of the prepared non-stoichiometric iron phosphate.

[0025] Furthermore, the flowing oxygen atmosphere can be oxygen and / or air. A flow meter or mass flow controller is used to precisely control the gas flow entering the cell based on the cell's power requirements and reaction efficiency to optimize the electrode reaction. The gas flow rate needs to be determined based on the cell's power requirements and electrode reaction kinetics to ensure sufficient oxygen supply while avoiding unnecessary energy loss due to excessive flow rates. Specifically, the flow rate of the flowing oxygen atmosphere is 0.1 L / min to 1.0 L / min.

[0026] Furthermore, the iron electrode is an iron sheet, iron plate, foamed iron or iron alloy to optimize electrochemical performance and structural stability; the porous carbon electrode is a porous graphite sheet, carbon paper, carbon cloth or carbon nanotubes.

[0027] Furthermore, the positive and negative electrodes are electrically connected through wires made of the above materials, and the wires are made of copper, silver or tinned copper. The wires are made of materials with good electrical conductivity and chemical stability to ensure efficient electron transmission and corrosion resistance. The wires are designed as a multi-strand twisted structure to improve flexibility and mechanical strength and reduce the risk of damage during battery assembly and operation. The connection between the wires and the electrodes is achieved by welding, crimping or bolting to ensure the reliability and long-term stability of the electrical connection. There should be an appropriate insulation layer on the outside of the wires to prevent electrical safety problems caused by short circuits or accidental contact.

[0028] Furthermore, the iron-air battery features an air inlet at the iron electrode for delivering a flowing oxygen atmosphere, and a liquid inlet at the porous electrode for adding an oxidant. The flowing oxygen atmosphere and / or oxidant oxidizes the ferrous iron. Furthermore, oxygen at the air electrode is reduced to hydrogen peroxide, which acts as an oxidant for the ferrous iron.

[0029] Furthermore, the carrier container of the iron-air battery is a plastic container or a metal container. The plastic container is made of polytetrafluoroethylene, polypropylene, polyvinyl chloride, or polyetheretherketone, while the metal container is made of stainless steel or titanium alloy. All of these materials are acid-resistant and corrosion-resistant, have good sealing properties, and are temperature-tolerant, ensuring that they will not chemically react or degrade during long-term use in acidic environments.

[0030] Furthermore, non-stoichiometric iron phosphate Fe x H y (PO m ) (3x+y) / (2m-5) After zH2O separation, an aging treatment is performed. The aging treatment conditions are: an aging temperature of 30-90°C to promote the stabilization of the precipitate in the solution and the growth of particles. Within the aging temperature range of 30-90°C, the precipitate can obtain better stability and sedimentation performance, facilitating subsequent separation and washing; the aging time is 2-5 hours. Specifically, the solid-liquid separation method includes but is not limited to one or more of sedimentation, filtration, suction filtration, centrifugation, and filter press. Finally, Fe x H y (PO m ) (3x+y) / (2m-5) For the convenience of general formula expression, 3x + y = 3. Based on testing of the product's iron-to-hydrogen ratio, the iron-to-hydrogen ratio x / y ranges from 0.5 to 8, with x ranging from 0.6 to 0.96, y ranging from 0.12 to 1.2, z ranging from 1 to 4, and m ranging from 3.5 to 4. The heating process and the presence of pyrophosphate in the raw materials easily introduce pyrophosphate into the final product, so m ranges from 3.5 to 4. The iron-to-phosphorus ratio of the non-stoichiometric acid ferric phosphate and non-stoichiometric ferric phosphate material is 0.6 to 0.9.

[0031] Another aspect of the present invention is to provide a sodium ion battery positive electrode material, which uses the non-stoichiometric iron phosphate composite prepared above as a phosphorus source and / or iron source. For example, the composite is used as the phosphorus and iron source, and is sintered with a sodium source and a carbon source at high temperature to obtain a polyanionic composite sodium iron phosphate. The sodium source can be one or more of sodium carbonate, sodium dihydrogen phosphate, or sodium nitrate, and the carbon source can be one or more of citric acid, sucrose, glucose, starch, or PEG. Sintering under a protective atmosphere tends to form a carbon-coated composite sodium iron phosphate positive electrode material.

[0032] The present invention provides a method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery and a positive electrode material for a sodium ion battery, which has the following beneficial effects:

[0033] First, the process is controllable. By finely controlling the reaction temperature, gas flow rate (0.1-1.0 L / min) and reaction time (1-10 hours), the pH of the final solution and the concentration of trivalent iron in the solution are affected to regulate the iron phosphate complex Fe. x H y (PO m ) (3x+y) / (2m-5) ·ZH2O parameters such as iron-phosphorus ratio, particle size, and compacted density;

[0034] Second, it is green and environmentally friendly. The preparation of iron phosphate using an acidic iron-air battery is based on the principle of a primary cell. The reaction is directly carried out inside the battery through an electrochemical method, converting chemical energy into electrical energy without injecting additional energy, reducing the need for external energy input, achieving solution oxidation of iron, and ultimately achieving precipitation of the iron phosphate complex, thereby improving the overall energy efficiency of the preparation of iron phosphate.

[0035] Third, it is low-cost and uses a combination of air electrode and iron electrode, as well as a suitable electrolyte solution, to achieve efficient electrochemical reaction; the dried iron phosphate complex is used as a precursor of sodium iron phosphate pyrophosphate, the positive electrode material for sodium ion batteries, which greatly reduces the production cost, while the positive electrode material exhibits excellent electrochemical properties. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below with reference to embodiments.

[0037] The present invention discloses a method for preparing a non-stoichiometric iron phosphate composite by using an acidic iron-air battery. The iron-air battery comprises a positive electrode, a negative electrode and an electrolyte. A porous carbon electrode is used as the positive electrode, an iron electrode is used as the negative electrode, and an acidic phosphoric acid source solution containing phosphate and / or pyrophosphate is used as the electrolyte. A flowing oxygen atmosphere and an oxidant are added to the iron-air battery. Under temperature-controlled conditions, an oxidation-reduction reaction is achieved by the operation of the iron-air battery to generate a non-stoichiometric iron phosphate precipitate Fe. x H y (PO m ) (3x+y) / (2m-5) zH2O, wherein the iron-hydrogen ratio x / y is in the range of 0.5-8, x is in the range of 0.6-0.96, y is in the range of 0.12-1.2, z is in the range of 1-4, and m is in the range of 3.5-4.

[0038] Furthermore, the electrolyte is an acid solution or a phosphate solution to which an acid solution is added, the acid solution is one or more of phosphoric acid, pyrophosphoric acid, and sulfuric acid, the phosphate solution is one or more of phosphoric acid and pyrophosphate such as sodium dihydrogen phosphate solution, ammonium dihydrogen phosphate solution, and sodium pyrophosphate, the mass concentration range of phosphorus element in the electrolyte is 1.0-15wt%, and the pH of the electrolyte is 1-3.

[0039] Furthermore, the working conditions of the battery are: working temperature is 30-90°C; working time is 1-10h.

[0040] Furthermore, the flowing oxygen atmosphere is oxygen and / or air, and the flow rate of the flowing oxygen atmosphere is 0.1 L / min-1.0 L / min.

[0041] Furthermore, the iron electrode is an iron sheet, an iron plate, foamed iron or an iron alloy, and the porous carbon electrode is a porous graphite sheet, carbon paper, carbon cloth or carbon nanotube.

[0042] Furthermore, the positive electrode and the negative electrode are electrically connected via a wire, and the wire is made of copper, silver or tinned copper.

[0043] Furthermore, the iron electrode of the iron-air battery is provided with an air inlet for delivering a flowing oxygen atmosphere, and the porous electrode is provided with a liquid inlet for adding an oxidant.

[0044] Furthermore, the carrier container of the iron-air battery is a plastic container or a metal container, the plastic container is made of polytetrafluoroethylene, polypropylene, polyvinyl chloride or polyetheretherketone, and the metal container is made of stainless steel or titanium alloy.

[0045] Furthermore, non-stoichiometric iron phosphate precipitation of Fe x H y (PO m ) (3x+y) / (2m-5) After zH2O separation, an aging treatment is performed. The aging conditions are: aging temperature 30-90°C; aging time 2-5h.

[0046] Another aspect of the present invention is to protect a sodium ion battery positive electrode material, which uses the non-stoichiometric iron phosphate prepared above as a raw material for a phosphorus source and / or an iron source.

[0047] Example 1

[0048] This embodiment involves using an acidic iron-air battery to prepare a non-stoichiometric iron phosphate composite and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0049] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) for the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) for the negative electrode. Prepare a phosphorus reaction solution with a mass percentage of 5wt% of phosphorus as the electrolyte, and use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0050] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.5.

[0051] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0052] S4. Preparation of a positive electrode for a sodium ion battery: The iron phosphate complex prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0053] Example 2

[0054] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0055] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) for the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) for the negative electrode. Prepare a phosphoric acid solution with a mass percentage of 5wt% of phosphorus as the electrolyte, and use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0056] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 70 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 2.

[0057] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 80°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0058] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0059] Example 3

[0060] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0061] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) as the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) as the negative electrode. Prepare a phosphoric acid solution with a mass percentage of 7wt% of phosphorus as the electrolyte, and use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0062] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.

[0063] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0064] Example 4

[0065] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0066] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) for the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) for the negative electrode. Prepare a phosphoric acid solution with a mass percentage of 5wt% of phosphorus as the electrolyte, and use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0067] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 1 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 2.3.

[0068] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid are then separated by centrifugation, and the product is washed five times with deionized water. The washed material is then dried at 100°C to produce non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0069] Example 5

[0070] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0071] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), carbon paper (size: 10cm x 10cm x 0.1cm) as the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) as the negative electrode. Prepare a phosphoric acid solution with a mass percentage of 5wt% of phosphorus as the electrolyte, and use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0072] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 8 hours. The pH of the solution rises to 2.2.

[0073] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0074] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0075] Example 6

[0076] This embodiment relates to the preparation of non-stoichiometric iron phosphate using an acidic iron-air battery and the use of the non-stoichiometric iron phosphate as a phosphorus source and an iron source to prepare a sodium ion battery positive electrode material. The preparation process includes the following steps: S1, assembling a battery module: using a polytetrafluoroethylene container as an electrolyte solution container (size 12cm x 12cm x 5cm), a porous graphite sheet (size 10cm x 10cm x 0.1cm) as an air electrode, and foam iron (size 10cm x 10cm x 0.1cm) as a negative electrode. A mixed solution of sodium dihydrogen phosphate and sulfuric acid is prepared according to a mass percentage of 5wt% of phosphorus element as an electrolyte, and using copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0077] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.5.

[0078] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid are then separated by centrifugation, and the product is washed five times with deionized water. The washed material is then dried at 100°C to produce non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0079] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0080] Example 7

[0081] This embodiment relates to the preparation of non-stoichiometric iron phosphate using an acidic iron-air battery and the use of the non-stoichiometric iron phosphate as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps: S1, assembling a battery module: using a polytetrafluoroethylene container as an electrolyte solution container (size 12cm x 12cm x 5cm), a carbon cloth (size 10cm x 10cm x 0.1cm) as an air electrode, and an iron sheet (size 10cm x 10cm x 0.1cm) as a negative electrode. A phosphoric acid solution is prepared with a mass percentage of 5wt% of phosphorus as an electrolyte, and a copper wire wrapped with an insulated wire is used to connect the positive and negative electrodes through an ammeter.

[0082] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.5.

[0083] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0084] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0085] Example 8

[0086] This embodiment relates to the preparation of non-stoichiometric iron phosphate using an acidic iron-air battery and the use of the non-stoichiometric iron phosphate as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps: S1, assembling a battery module: using a polytetrafluoroethylene container as an electrolyte solution container (size 12cm x 12cm x 5cm), a carbon cloth (size 10cm x 10cm x 0.1cm) as an air electrode, and an iron sheet (size 10cm x 10cm x 0.1cm) as a negative electrode. A phosphoric acid solution is prepared with a mass percentage of 5wt% of phosphorus as an electrolyte, and a copper wire wrapped with an insulated wire is used to connect the positive and negative electrodes through an ammeter.

[0087] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into the positive electrode with a gas flow rate of 0.5 L / min, add hydrogen peroxide solution dropwise to the negative electrode solution, react for 5 hours, and raise the pH of the solution to 1.5.

[0088] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid are then separated by centrifugation, and the product is washed five times with deionized water. The washed material is then dried at 100°C to produce non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0089] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0090] Example 9

[0091] This embodiment relates to the preparation of non-stoichiometric iron phosphate using an acidic iron-air battery and the use of the non-stoichiometric iron phosphate as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps: S1, assembling a battery module: using a polytetrafluoroethylene container as an electrolyte solution container (size 12cm x 12cm x 5cm), a porous graphite sheet (size 10cm x 10cm x 0.1cm) as an air electrode, and an iron sheet (size 10cm x 10cm x 0.1cm) as a negative electrode. A mixed solution of phosphoric acid and sodium dihydrogen phosphate is prepared at a mass percentage of 5wt% of phosphorus element as an electrolyte, and using copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0092] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 12 h. The pH of the solution is raised to 3.

[0093] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid are then separated by centrifugation, and the product is washed five times with deionized water. The washed material is then dried at 100°C to produce non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0094] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0095] Example 11

[0096] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0097] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) as the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) as the negative electrode. Prepare a mixed solution of phosphoric acid, pyrophosphoric acid, and sodium ferric pyrophosphate according to a mass percentage of 5wt% of phosphorus as the electrolyte. Use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0098] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.5.

[0099] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0100] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0101] Example 12

[0102] This embodiment involves using an acidic iron-air battery to prepare non-stoichiometric iron phosphate and using it as a phosphorus source and an iron source to prepare a positive electrode material for a sodium ion battery. The preparation process includes the following steps:

[0103] S1. Assemble the battery module: Use a polytetrafluoroethylene container as the electrolyte solution container (size: 12cm x 12cm x 5cm), a porous graphite sheet (size: 10cm x 10cm x 0.1cm) as the air electrode, and foam iron (size: 10cm x 10cm x 0.1cm) as the negative electrode. Prepare a mixed solution of phosphoric acid, sulfuric acid, and ammonium dihydrogen phosphate at a mass percentage of 5wt% of phosphorus as the electrolyte. Use copper wires wrapped with insulated wires to connect the positive and negative electrodes through an ammeter.

[0104] S2. Conduct electrochemical reaction: Start mechanical stirring, set the speed to 600 r / min, set the operating temperature of the battery module to 50 degrees Celsius, introduce air flow into both the negative and positive electrodes at a gas flow rate of 0.5 L / min, and the reaction time is 5 hours. The pH of the solution is raised to 1.5.

[0105] S3. Aging, Solid-Liquid Separation, and Drying: Disconnect the circuit, transfer the contents of the electrolyte solution container to a beaker, and age at 70°C for 4 hours. The solid and liquid components are then separated by centrifugation and washed five times using deionized water. The washed material is then dried at 100°C to obtain non-stoichiometric iron phosphate. The iron-to-hydrogen ratio and iron-to-phosphorus ratio are shown in Table 1.

[0106] S4. Preparation of a positive electrode for a sodium ion battery: The non-stoichiometric iron phosphate prepared in step S3 above was used as an iron-phosphorus source, and other sodium salts and an organic carbon source were mixed as raw materials, and calcined under an inert atmosphere to obtain a sodium iron phosphate pyrophosphate positive electrode. The electrochemical properties of the sodium iron phosphate positive electrode are shown in Table 1.

[0107] Table 1 Performance test results

[0108]

[0109] The present invention first utilizes an acidic iron-air battery to prepare iron phosphate. Based on the principle of a primary battery, chemical energy is converted into electrical energy. No additional energy is required except for the introduction of airflow, thereby achieving solution oxidation of iron and ultimately achieving non-stoichiometric precipitation of iron phosphate, providing a new technical approach for the preparation of iron phosphate.

[0110] The test results in Table 1 show that controlling the reaction temperature, reaction time, airflow rate, and reactant concentrations can adjust the reaction progress, ultimately affecting the pH during precipitation. By flexibly manipulating these parameters, iron phosphates with varying iron-phosphorus ratios can be prepared. Using the prepared low-iron-phosphorus non-stoichiometric iron phosphate as the iron-phosphorus source, sodium iron pyrophosphate (SFP) cathode material with high electrochemical performance can be produced.

[0111] In summary, the present invention has good technical contributions in the following aspects:

[0112] Adjustability: By adjusting the reaction conditions such as pH value, temperature, reaction time, etc., non-stoichiometric iron phosphate with different iron-hydrogen ratios and iron-phosphorus ratios can be prepared. x H y (PO m ) (3x+y) / (2m-5) zH2O, increasing product diversity.

[0113] Improved environmental friendliness: The present invention does not adopt traditional chemical precipitation or electrolysis methods, thus avoiding the use of harmful chemical reagents and energy-intensive processes commonly found in these methods, and reducing negative impacts on the environment.

[0114] Energy Efficiency: Electrochemical reactions are carried out directly within the battery, reducing the need for external energy input and improving the overall energy efficiency of iron phosphate production. Furthermore, battery packs can be connected in series for efficient production and scalability.

[0115] Cost-effectiveness: It uses low-cost raw materials such as iron and phosphoric acid, while simplifying the preparation process and reducing production costs.

[0116] Product purity and consistency: By precisely controlling electrochemical conditions and reaction time, high-purity and consistent iron phosphate products can be obtained, which helps improve the performance of the final product.

[0117] Improved performance of sodium-ion batteries: High-purity non-stoichiometric iron phosphate obtained through solid-liquid separation can be used as a high-quality precursor for sodium-ion battery positive electrode materials, helping to improve battery performance and reduce production costs.

[0118] The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and such obvious alternatives are all within the scope of protection of the present invention.

Claims

1. A method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery, wherein the iron-air battery comprises a positive electrode, a negative electrode, and an electrolyte, characterized in that: A porous carbon electrode is used as the positive electrode and an iron electrode is used as the negative electrode. A flowing oxygen atmosphere and an oxidant are added to the iron-air battery. Under temperature-controlled conditions, the redox reaction is achieved through the operation of the iron-air battery to generate non-stoichiometric iron phosphate precipitation. x H y (PO m ) (3x+y) / (2m-5) zH2O, wherein the iron-hydrogen ratio x / y is in the range of 0.5-8, x is in the range of 0.6-0.96, y is in the range of 0.12-1.2, z is in the range of 1-4, and m is in the range of 3.5-4; The electrolyte is an acid solution or a phosphate solution to which an acid solution is added, wherein the acid solution is one or more of phosphoric acid, pyrophosphoric acid, and sulfuric acid, and the phosphate solution is one or more of phosphoric acid and pyrophosphate such as sodium dihydrogen phosphate solution, ammonium dihydrogen phosphate solution, and sodium pyrophosphate, wherein the mass concentration of phosphorus in the electrolyte is in the range of 1.0-15wt%, and the pH of the electrolyte is 1-3; The working conditions of the battery are: working temperature of 30-90°C; working time of 1-10h; The flowing oxygen atmosphere is oxygen and / or air, and the flow rate of the flowing oxygen atmosphere is 0.1 L / min-1.0 L / min.

2. The method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery according to claim 1, wherein: The iron electrode is an iron sheet, an iron plate, foamed iron or an iron alloy, and the porous carbon electrode is a porous graphite sheet, carbon paper, carbon cloth or carbon nanotube.

3. The method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery according to claim 1, wherein: The positive electrode and the negative electrode are electrically connected via a wire, and the wire is made of copper, silver or tinned copper.

4. The method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery according to claim 1, wherein: An air inlet for conveying a flowing oxygen atmosphere is provided at the iron electrode of the iron-air battery, and a liquid inlet for adding an oxidant is provided at the porous carbon electrode.

5. The method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery according to claim 1, wherein: The carrier container of the iron-air battery is a plastic container or a metal container. The material of the plastic container is polytetrafluoroethylene, polypropylene, polyvinyl chloride or polyetheretherketone, and the material of the metal container is stainless steel or titanium alloy.

6. The method for preparing a non-stoichiometric iron phosphate composite using an acidic iron-air battery according to claim 1, wherein: The non-stoichiometric iron phosphate precipitation Fe x H y (PO m ) (3x+y) / (2m-5) After zH2O separation, an aging treatment is performed. The aging conditions are: aging temperature 30-90°C; aging time 2-5h.

7. A sodium ion battery cathode material, characterized in that: The non-stoichiometric iron phosphate complex prepared according to any one of claims 1 to 6 is used as a raw material for the phosphorus source and / or iron source.

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