Preparation method of carbon-coated multi-ion gradient co-doped lithium iron phosphate positive electrode material

Abstract

The invention discloses a preparation method of a carbon-coated multi-ion gradient co-doped lithium iron phosphate positive electrode material, which comprises the following steps: dissolving soluble ferrite in water, adjusting pH and oxidizing to obtain an iron source solution A; soluble phosphate is dissolved in water, pH is adjusted, and a phosphorus source solution B is obtained; loading at least two doped ion solutions on the carbonizable porous organic carrier to obtain a doped ion loaded porous organic carrier; under stirring and constant-temperature conditions, synchronously adding the phosphorus source solution B and the doped ion-loaded porous organic carrier into the iron source solution A by adopting a parallel flow progressive increase dropwise adding mode, and carrying out aging reaction after dropwise adding to obtain gradient doped iron phosphate dihydrate slurry; filtering, drying, calcining, cooling, crushing and screening the slurry to obtain a gradient doped iron phosphate precursor; and mixing the precursor with a lithium source and a carbon source, and carrying out high-temperature calcination in an inert atmosphere to obtain the carbon-coated multi-ion gradient co-doped lithium iron phosphate positive electrode material.

Description

Technical Field

[0001] This application relates to the field of battery materials, specifically to a method for preparing a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, is widely used in power batteries and energy storage systems due to its advantages such as high safety, long cycle life, and environmental friendliness. Especially in semi-solid-state battery systems, lithium iron phosphate cathode materials exhibit excellent electrochemical performance and structural stability, making them a research hotspot. Currently, elemental doping modification is one of the important methods to improve the electrochemical performance of lithium iron phosphate.

[0003] In existing technologies, the main challenge in the doping modification of lithium iron phosphate lies in achieving uniform distribution of dopant elements and controlling the gradient. Traditional doping methods, such as solid-phase methods and liquid-phase co-precipitation methods, often result in uneven distribution of dopant elements in the material, failing to form an ideal gradient structure. This uneven distribution limits the doping effect, affects the electronic conductivity and ion diffusion rate of the material, and consequently impacts the rate performance and cycle stability of the battery.

[0004] Achieving a gradient distribution of dopants in lithium iron phosphate is a core technical challenge in the modification of lithium iron phosphate cathode materials. Summary of the Invention

[0005] To address the technical challenge of controlling the gradient distribution of doping elements in lithium iron phosphate, this application provides a method for preparing carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode materials.

[0006] To address the technical challenges of multi-ion gradient distribution and uniform doping, and to improve the structural stability and cycle life of lithium iron phosphate cathode materials, this application provides a method for preparing carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode materials.

[0007] The first aspect of this application provides a method for preparing a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material, comprising the following steps: Soluble ferrous salts are dissolved in water, the pH is adjusted, and the solution is oxidized to obtain iron source solution A. Soluble phosphates are dissolved in water, and the pH is adjusted to obtain phosphorus source solution B; At least two doped ion solutions are loaded onto a carbonizable porous organic support to obtain a porous organic support loaded with doped ions. Under stirring and constant temperature conditions, phosphorus source solution B and porous organic carrier loaded with doped ions were simultaneously added to iron source solution A in a parallel incremental dropwise manner. After dropwise addition, the aging reaction was carried out to obtain gradient doped iron phosphate dihydrate slurry. The slurry was filtered, dried, calcined, cooled, pulverized, and sieved to obtain a gradient-doped iron phosphate precursor. The precursor was mixed with a lithium source and a carbon source and calcined at high temperature under an inert atmosphere to obtain a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material.

[0008] This invention achieves efficient sustained release and spatial gradient control of various dopant ions by introducing carbonizable porous organic supports (such as lignin fiber particles). Specifically, the porous organic supports possess high specific surface area and abundant pore structure, enabling them to fully adsorb and store large amounts of metal or non-metal ions in the dopant ion solution. When these dopant-loaded supports are added to the iron source solution A at an increasing rate, the dopant ions in the supports are not released instantaneously, but rather gradually diffuse into the reaction system as the reaction progresses. Due to the physical adsorption and chemical binding of ions by the pore structure and organic framework of the supports, the release rate of dopant ions is effectively controlled. In the parallel incremental dropwise addition reaction, the initial amount of support added is small, resulting in a low concentration of released dopant ions. The core region of the precursor formed by the initial reaction with the iron and phosphorus sources has a low doping degree. As the reaction proceeds, the support addition rate gradually increases, leading to an increase in the concentration of subsequently released dopant ions and a significant increase in the doping degree of the outer layer region of the precursor. Ultimately, a spatial gradient distribution structure of dopant ions is formed, increasing from the inside out. This gradient distribution not only optimizes the material's microstructure but also effectively buffers stress concentration caused by volume changes during charging and discharging, reducing microcracks and structural damage, and significantly improving the material's cycle life and structural stability. Furthermore, the in-situ carbonization of the organic carrier during calcination forms a nano-carbon framework network, further enhancing the material's electronic conductivity and structural integrity. The porous structure remaining inside the main material after carrier decomposition helps increase the material's specific surface area and electrolyte wettability, optimizes lithium-ion diffusion paths, reduces internal resistance, and improves capacity retention at high rates.

[0009] The carbonizable porous organic carrier can be lignin fiber particles, phenolic resin microspheres, polypyrrole spheres, polyaniline spheres, or combinations thereof. These materials possess high specific surface area and abundant pore structure, enabling efficient loading and slow release of various dopant ions, forming a uniformly distributed nano-carbon framework after calcination.

[0010] Furthermore, the specific surface area of ​​the carbonizable porous organic carrier is 20-200 m². 2 / g.

[0011] Specifically, the doped ion is selected from at least two of the following: boron ion, magnesium ion, aluminum ion, manganese ion, titanium ion, zinc ion, sodium ion, potassium ion, calcium ion, sulfur ion, phosphorus ion, fluoride ion, and chloride ion. This method is applicable to various types of doped ions.

[0012] Furthermore, in the described parallel incremental dropping method, the porous organic support is added at a rate of 0.1-5 g / min, and this rate is gradually increased during the dropping process. By controlling the incremental addition of the support, a spatial gradient distribution of dopant ions is achieved, buffering material volume changes and improving structural stability.

[0013] Specifically, the calcination step is carried out at 600-900°C, and the atmosphere can be nitrogen, argon, or a mixture thereof. Different calcination atmospheres and temperatures help to adjust the structure of the carbon skeleton and the crystallinity of the material.

[0014] Furthermore, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium nitrate, and lithium acetate, and the carbon source is selected from one or more of glucose, sucrose, polyvinyl alcohol, caramel, citric acid, pitch, ethanol, and cellulose acetate. This variety of lithium and carbon sources provides flexibility for process optimization and performance control.

[0015] Specifically, the iron source is selected from one or more of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous oxalate, and the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, monoammonium phosphate, phosphoric acid, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

[0016] Furthermore, the mass ratio of the porous organic support loaded with doped ions to the doped ion solution is 1:5 to 1:20. By adjusting the mass ratio, reasonable loading and release of doped ions can be achieved.

[0017] Specifically, the carbon source accounts for 1-10% of the precursor mass. A suitable carbon content helps to form a dense and highly dispersed carbon coating layer, improving the electronic conductivity of the material.

[0018] The present invention has the following beneficial effects: By using a carbonizable porous organic carrier to load doped ions, a gradient distribution and uniform doping of doped ions can be achieved, which significantly improves the structural stability and cycle life of lithium iron phosphate cathode materials.

[0019] The nano-carbon framework network formed by in-situ carbonization effectively improves the electronic conductivity of the material, inhibits particle aggregation, and optimizes rate performance.

[0020] This avoids the problem of residual impurities when using inorganic carriers, improves the purity and electrochemical stability of cathode materials, and reduces the risk of side reactions. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a method for preparing a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material, as provided in this embodiment of the disclosure. Detailed Implementation

[0022] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0023] In some preferred embodiments, the carbonizable porous organic carrier may be selected from lignin fiber particles, phenolic resin microspheres, polypyrrole spheres, or polyaniline spheres, or combinations thereof. The specific surface area of ​​the porous organic carrier may be 10, 20, 100, 150, or 200 m². 2 / g, with a pore size of any one of 5, 10, 20, 30, 40, or 50 nm. The doped ion can be selected from any two or more of boron ions, magnesium ions, aluminum ions, manganese ions, titanium ions, zinc ions, sodium ions, potassium ions, calcium ions, sulfur ions, phosphorus ions, fluoride ions, and chloride ions. The lithium source can be lithium carbonate, lithium hydroxide, lithium chloride, lithium nitrate, or lithium acetate, and the carbon source can be glucose, sucrose, polyvinyl alcohol, caramel, citric acid, asphalt, ethanol, or cellulose acetate. The calcination temperature can be selected between 600, 650, 700, 750, 800, 850, or 900°C, and the calcination atmosphere can be nitrogen, argon, or a mixture thereof.

[0024] like Figure 1 The flowchart shown is a process for preparing a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material according to an embodiment of this scheme. The method includes: Step S101: Dissolve the soluble ferrous salt in water, adjust the pH and oxidize it to obtain iron source solution A; Step S102: Dissolve soluble phosphate in water, adjust the pH, and obtain phosphorus source solution B; Step S103: Load at least two doped ion solutions onto a carbonizable porous organic support to obtain a porous organic support loaded with doped ions. Step S104: Under stirring and constant temperature conditions, the phosphorus source solution B and the porous organic carrier loaded with doped ions are simultaneously added to the iron source solution A in a parallel incremental dropwise manner. After dropwise addition, the mixture is aged to obtain a gradient doped iron phosphate dihydrate slurry. Step S105: The slurry is filtered, dried, calcined, cooled, pulverized and sieved to obtain a gradient-doped iron phosphate precursor; Step S106: Mix the precursor with a lithium source and a carbon source, and calcine at high temperature under an inert atmosphere to obtain a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material.

[0025] Example 1: This example provides a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material and its preparation method.

[0026] Raw materials for preparation: Ferrous sulfate heptahydrate (FeSO4·7H2O): 100g; ammonium dihydrogen phosphate (NH4H2PO4): 50g; boric acid (H3BO3): 2g; magnesium nitrate (Mg(NO3)2·6H2O): 2g; lignin fiber particles (Weijia, average diameter <6mm, specific surface area 20㎡ / g): 10g; hydrogen peroxide (H2O2, 30%): 10mL; ammonia (25%): appropriate amount, used to adjust pH; dilute sulfuric acid (1M): appropriate amount, used to adjust pH; lithium carbonate (Li2CO3): 12g; glucose: 5g.

[0027] Preparation method: Dissolve 100g of ferrous sulfate heptahydrate in 1L of deionized water, adjust the pH to 2.0 by adding dilute sulfuric acid dropwise, slowly add 10mL of hydrogen peroxide, filter to remove impurities, and obtain solution A.

[0028] Dissolve 50g of ammonium dihydrogen phosphate in 500mL of deionized water, and adjust the pH to 4.0 by adding ammonia dropwise to obtain solution B.

[0029] Dissolve 2g of boric acid and 2g of magnesium nitrate in 100mL of deionized water and stir until homogeneous to obtain solution C. Add 10g of lignin fiber particles to solution C, stir and impregnate under normal pressure for 12 hours, then filter and spin dry for later use.

[0030] Solution A was placed in a 50℃ reactor. Solution B and lignin fiber particles loaded with doped ions were simultaneously added dropwise by a peristaltic pump under stirring. The initial feeding rate was 0.5 g / min, which was increased to 3 g / min later. The addition was carried out for about 3 hours, followed by aging for 2 hours, during which a precipitate was formed.

[0031] The precipitate was collected by filtration, dried under vacuum at 60°C for 12 hours, and then ground and sieved. The dried material was calcined at 700°C in air for 4 hours to obtain a gradient-doped iron phosphate precursor.

[0032] The precursor, lithium carbonate, and glucose were mixed in proportion, ball-milled, placed in a tube furnace, heated to 750°C at 5°C / min under an argon atmosphere, held for 6 hours, and then naturally cooled to obtain carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material.

[0033] Example 2 The difference from Example 1 is that the porous organic carrier used is phenolic resin microspheres (Tianzheng CAS: 9002-89-5, specific surface area 500㎡ / g), while other conditions are the same.

[0034] Example 3 The difference from Example 1 is that the amount of porous organic carrier added is 5g.

[0035] Example 4 The difference from Example 1 is that the mass ratio of the doped ion solution C to the lignin fiber particles is 1:15, while other conditions are the same.

[0036] Example 5 The difference from Example 1 is that the calcination temperature is 800°C, while the other conditions are the same.

[0037] Example 6 The difference from Example 1 is that the rate of adding lignin fiber particles was increased from 0.2 g / min to 1.5 g / min, while other conditions remained the same.

[0038] Example 7 The difference from Example 1 is that the doping ions used are aluminum ions and manganese ions, provided by aluminum sulfate and manganese sulfate respectively (mass ratio 1:1), and the doping mass is the same as in Example 1.

[0039] Example 8 The difference from Example 1 is that the lithium source is lithium hydroxide and the carbon source is sucrose, with the same content as in Example 1.

[0040] Example 9 The difference from Example 1 is that the iron source is ferrous chloride and the phosphorus source is potassium dihydrogen phosphate, with the same content as in Example 1.

[0041] Example 10 The difference from Example 1 is that the porous organic carrier is porous chitosan microspheres (specific surface area of ​​200 m²). 2 / g), other conditions are the same.

[0042] Comparative Example 1 The difference from Example 1 is that in step 3, a porous organic support is not used, and the doped ion solution C is directly added to the reaction system.

[0043] Comparative Example 2 The difference from Example 1 is that the rate at which the lignin fiber particles are added is constant at 2 g / min and is not increased, while other conditions are the same.

[0044] Comparative Example 3 The difference from Example 1 is that the traditional solid-phase doping method is used, and the gradient slow-release carrier is not used.

[0045] Cycle life test: The positive electrode material is assembled into a coin cell and charged and discharged at a 1C rate. The capacity retention rate after 100 cycles is calculated.

[0046] Rate performance test: Charge and discharge at 0.1C and 5C rates, and calculate the discharge capacity at each rate.

[0047] Conductivity testing: The electronic conductivity of the material was determined using the four-probe method.

[0048] Table 1 Performance test results of the examples and comparative examples As shown in Table 1, all embodiments exhibit excellent electronic conductivity, rate performance, and cycle life. Examples 1, 5, and 7 are particularly noteworthy. This invention utilizes a carbonizable porous organic carrier to load dopant ions, achieving a gradient distribution and uniform doping of the dopant ions, significantly improving the structural stability and cycle life of the lithium iron phosphate cathode material. The carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material prepared by this invention retains over 99% of its capacity after 100 cycles, exhibits a discharge capacity of over 132 mAh / g at 5C rate, and achieves an electronic conductivity of 1.12 × 10⁻⁶. -2 The S / cm is above 1.0. This is because the porous organic carrier slow-release dopant ion and incremental addition process used in this invention achieves a spatial gradient distribution of dopant ions, effectively buffering the volume change of the material during charge and discharge, reducing stress concentration and microstructure damage, and improving the structural stability and cycle life of the material; at the same time, the porous organic carrier, which is converted into a conductive agent, not only does not have a negative impact on the performance of the battery, but can also improve the conductivity of the battery.

[0049] Comparative Example 1 did not use a porous organic support; the dopant ions were directly added, resulting in uneven dopant distribution, a significant decrease in electronic conductivity and rate performance, and a reduced cycle life. Comparative Example 2 did not use a incremental doping method, resulting in an indistinct dopant ion distribution gradient and limited performance improvement. Comparative Example 3 used a traditional solid-phase doping method, lacking slow release and gradient control, leading to an inhomogeneous material structure and the worst electrochemical performance.

[0050] In Examples 4 and 6, the lower dopant ion loading ratio or slower dropping rate resulted in a less than ideal doping gradient, leading to slightly lower performance than other examples, but still significantly better than the comparative examples. Examples 7, 8, 9, and 10, using different dopant ions, lithium sources, iron sources, or calcination atmospheres, all exhibited good overall performance, demonstrating the strong process adaptability and flexibility of the present invention. Although porous organic supports with high specific surface areas possess stronger adsorption capacity, excessively high specific surface areas (such as 500 m² in Example 2) can lead to problems. 2 The microporous structure resulting from / g) leads to uncontrolled release rate and uneven spatial distribution of dopant ions, making it difficult to achieve the most ideal gradient doping effect.

[0051] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material, characterized in that, Includes the following steps: Soluble ferrous salts are dissolved in water, the pH is adjusted, and the solution is oxidized to obtain iron source solution A. Soluble phosphates are dissolved in water, and the pH is adjusted to obtain phosphorus source solution B; At least two doped ion solutions are loaded onto a carbonizable porous organic support to obtain a porous organic support loaded with doped ions. Under stirring and constant temperature conditions, phosphorus source solution B and the porous organic carrier loaded with doped ions are simultaneously added to the iron source solution A in a parallel incremental dropwise manner. After dropwise addition, an aging reaction is carried out to obtain gradient doped iron phosphate dihydrate slurry. The slurry was filtered, dried, calcined, cooled, pulverized, and sieved to obtain a gradient-doped iron phosphate precursor. The precursor was mixed with a lithium source and a carbon source and calcined at high temperature under an inert atmosphere to obtain a carbon-coated multi-ion gradient co-doped lithium iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the carbonizable porous organic carrier is 20-200 m². 2 / g.

3. The preparation method according to claim 1, characterized in that, The carbonizable porous organic carrier is lignin fiber particles, phenolic resin microspheres, polypyrrole spheres, polyaniline spheres, or a combination thereof.

4. The preparation method according to claim 1, characterized in that, The doped ions are selected from at least two of the following: boron ions, magnesium ions, aluminum ions, manganese ions, titanium ions, zinc ions, sodium ions, potassium ions, calcium ions, sulfur ions, phosphorus ions, fluorine ions, and chloride ions.

5. The preparation method according to claim 1, characterized in that, In the parallel-flow incremental dripping method, the porous organic carrier is added at a rate of 0.1-5 g / min, and the rate is gradually increased during the dripping process.

6. The preparation method according to claim 1, characterized in that, The calcination step is carried out at 600-900℃ in an atmosphere of nitrogen, argon, or a mixture thereof.

7. The preparation method according to claim 1, characterized in that, The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium nitrate, and lithium acetate, and the carbon source is selected from one or more of glucose, sucrose, polyvinyl alcohol, caramel, citric acid, asphalt, ethanol, and cellulose acetate.

8. The preparation method according to claim 1, characterized in that, The iron source is selected from one or more of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous oxalate, and the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, monoammonium phosphate, phosphoric acid, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

9. The preparation method according to claim 1, characterized in that, The mass ratio of the porous organic carrier loaded with doped ions to the doped ion solution is 1:5 to 1:

20.

10. The preparation method according to claim 1, characterized in that, The carbon source accounts for 1-10% of the mass of the precursor.

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