Lithium iron phosphate positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application discloses a lithium iron phosphate positive electrode material and a preparation method and lithium ion battery thereof. Metal ions are doped into the lithium iron phosphate crystal lattice, so that the crystal lattice parameters are optimized, the electron conductivity and lithium ion diffusion rate are improved, and the rate performance of the material is improved. A carbon source forms a carbon coating layer in the sintering process, so that the conductivity of the material is further improved, and particle agglomeration is inhibited. The prepared MOF-based interface modifier is grafted with epoxy groups and phosphonate groups on the MOF surface through amino-olefin addition and Michael addition reaction. The channel structure of the MOF can effectively adsorb harmful products such as HF generated by electrolyte decomposition, so as to reduce the interface side reaction. The phosphonate groups form a coordination bond with metal ions on the positive electrode surface, so that the interface bonding force is enhanced, the structure collapse caused by Li+ deintercalation is inhibited, and the cycle stability of the material is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium iron phosphate cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is a lithium-ion battery cathode material with an olivine-type structure. Due to its advantages such as high thermal stability, good safety, low cost, and environmental friendliness, it is widely used in electric vehicles, energy storage systems, and portable electronic devices.

[0003] However, LiFePO4 materials have the following inherent defects that limit their application in high-performance lithium-ion batteries:

[0004] Low electronic conductivity: The electronic conductivity of LiFePO4 is approximately 10⁻⁶. -9 The S / cm ratio is much lower than other cathode materials, such as ternary materials (LiNi). 1-x-γ Co x Mn γ O2) and LiCoO2, etc. This low conductivity causes a significant decrease in battery capacity during high-rate discharge, limiting its performance in high-power applications.

[0005] Lithium-ion diffusion rate is slow: Lithium ions in LiFePO4 mainly diffuse one-dimensionally along the (010) crystal plane, and its diffusion coefficient is low, approximately 10. -14 ~10 -16 cm 2 / s. This one-dimensional diffusion path limits the migration rate of lithium ions, affecting the rate performance and low-temperature performance of the material.

[0006] To overcome the above-mentioned shortcomings, researchers have proposed several modification strategies, including:

[0007] Nanostructuring: By reducing the size of LiFePO4 particles to the nanoscale, the specific surface area of ​​the material is increased, shortening the migration paths of lithium ions and electrons, thereby improving the electrochemical performance of the material. However, nanostructuring may lead to a decrease in the tap density of the material, affecting the energy density of the battery.

[0008] Carbon coating: A layer of conductive carbon material, such as graphite or carbon black, is coated onto the surface of LiFePO4 particles to form a conductive network and improve electronic conductivity. Carbon coating can also inhibit particle growth, maintain the nanoscale size of the particles, and further improve the rate performance and cycle stability of the material. For example, invention application CN119297254A discloses a carbon-coated lithium iron phosphate, its preparation method, and a lithium battery.

[0009] Elemental doping: Introducing small amounts of metal ions (such as Mg) into the LiFePO4 crystal structure. 2+ Al 3+ Mn 2+ Doping with substances such as Mg can improve the electronic structure of materials, enhance electronic conductivity, stabilize crystal structure, and improve electrochemical performance. For example, doping with Mg... 2+ Or Al 3+ This can improve the electronic conductivity and structural stability of materials, thereby enhancing the high-temperature performance and cycle life of batteries. For example, the invention application with publication number CN119976780A discloses lithium iron phosphate cathode materials, their preparation methods, cathode sheets, and lithium-ion batteries, in which the metal doping source is disclosed to be selected from one or more of titanium, magnesium, aluminum, vanadium, and strontium sources.

[0010] Although the aforementioned modification methods have improved the performance of LiFePO4 to some extent, some problems remain, such as complex preparation processes, increased costs, and poor material consistency. Therefore, developing a simple, controllable, and low-cost doping modification method to further enhance the conductivity and structural stability of LiFePO4 is of significant research importance and application value. Summary of the Invention

[0011] To address the aforementioned shortcomings in existing technologies, this invention provides a lithium iron phosphate cathode material, its preparation method, and a lithium-ion battery. By improving the conductivity and structural stability of the LiFePO4 cathode material, this invention aims to solve problems such as poor conductivity and short cycle life in existing technologies, enhance the overall performance of the material, and meet the application requirements of high-performance lithium-ion batteries.

[0012] This invention first provides a method for preparing lithium iron phosphate cathode material, comprising the following steps:

[0013] S1, Preparation of lithium iron phosphate precursor materials doped with metal ions;

[0014] S2, the lithium iron phosphate precursor material doped with metal ions is coated with a MOF-based interface modifier, wherein the MOF-based interface modifier is a MOF material with epoxy groups and phosphonate groups modified on its surface.

[0015] Preferably, in step S1, the lithium source, iron source, phosphorus source, metal dopant and carbon source are ball-milled and then dispersed in a dispersion medium, and then dried to obtain precursor powder. The precursor powder is then sintered to obtain the lithium iron phosphate precursor material doped with metal ions.

[0016] More preferably, in step S1, by mass, there are 11-15 parts of lithium source, 30-38 parts of iron source, 21-25 parts of phosphorus source, 1-4 parts of metal dopant, and 5-10 parts of carbon source.

[0017] More preferably, in step S1, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate;

[0018] The iron source is at least one of ferrous oxalate or its hydrate, ferrous phosphate, ferrous sulfate, ferrous ammonium sulfate, ferrous chloride, and ferrous nitrate.

[0019] The phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid;

[0020] The doping element in the metal dopant is at least one of magnesium and aluminum;

[0021] The carbon source is at least one of sucrose, glucose, and polyethylene glycol.

[0022] Magnesium can be provided by magnesium acetate or its hydrate, and aluminum can be provided by aluminum nitrate or its hydrate. Based on 1-4 parts of the aforementioned metal dopant, 0.5-2 parts of magnesium acetate or its hydrate and 0.5-2 parts of aluminum nitrate or its hydrate are required.

[0023] Anhydrous ethanol can be used as the dispersion medium. Add all raw materials to a ball mill, along with 80-120 parts of anhydrous ethanol as the dispersion medium. During ball milling, mill at 300-500 rpm for 4-8 hours to ensure uniform mixing and a particle size of D50 ≤ 10 μm. After ball milling, dry the mixture at 80-100℃ for 12-24 hours. During the drying process, use vacuum treatment at a pressure of -0.1 to -0.08 MPa.

[0024] More preferably, the sintering temperature is 600-750℃ and the sintering time is 8-12 hours. Sintering is carried out under an inert atmosphere, such as a nitrogen atmosphere.

[0025] Vacuum drying and nitrogen-protected sintering processes ensure that the raw materials react fully, avoid oxidation, and improve the purity and structural integrity of the product.

[0026] Preferably, in step S2, the mass ratio of the MOF-based interface modifier to the lithium iron phosphate precursor material doped with metal ions is 1:50-100. During mixing, the material is dispersed uniformly in anhydrous ethanol medium using wet ball milling or ultrasonic dispersion, and then dried at 60°C for 5 hours to ensure that the modifier is uniformly coated on the material surface.

[0027] Preferably, in step S2, the MOF-based interface modifier is obtained by grafting epoxy groups onto zirconium aminophthalate MOF (UIO-66-BDC-NH2, CAS: 1260119-00-3) and allyl glycidyl ether (CAS: 106-92-3) via an amino-olefin addition reaction, and then modifying the phosphonate groups with 1,2-vinyl diphosphonic acid (CAS: 6145-31-9) via a Michael addition reaction.

[0028] More preferably, an amino-olefin addition reaction: 10-15 parts by mass of zirconium aminophthalate MOF and 20-30 parts by mass of allyl glycidyl ether are added to 50-80 parts by mass of DMF solvent, and 4-6 wt% of triethylamine is added as a catalyst. The reaction is carried out at 75-80°C for 6-8 hours, so that the amino group of MOF and the double bond of allyl glycidyl ether undergo an addition reaction, and epoxy groups are grafted.

[0029] Michael addition reaction: 15-25 parts of 1,2-vinyl diphosphonic acid are introduced, and 2.55-3.5 wt% of organotin is added as a catalyst. The reaction is carried out at 70-80℃ for 7-9 hours to form MOF-phosphonate hybrid.

[0030] After the above two steps of reaction are completed, the product of MOF-based interface modifier is washed with anhydrous ethanol. After washing, it is vacuum dried at 70-80℃ for 10-12 hours.

[0031] The present invention also provides a lithium iron phosphate cathode material prepared by the aforementioned preparation method.

[0032] The present invention also provides a lithium-ion battery using the aforementioned lithium iron phosphate cathode material.

[0033] Beneficial effects of this invention:

[0034] 1. Metal ions (Mg 2+ Al 3+ Doping into the lithium iron phosphate lattice optimizes lattice parameters, improves electronic conductivity and lithium-ion diffusion rate, and enhances the rate performance of the material. Doping improves kinetic performance by optimizing the internal structure and provides interfacial binding sites for MOF modifiers; MOF-based modifiers, in turn, protect the interface and reduce side reactions, consolidating the structural and performance advantages brought by doping. The two form a synergistic mechanism of "internal optimization - external protection," jointly achieving a comprehensive improvement in the rate performance and cycle stability of lithium iron phosphate cathode materials.

[0035] 2. The carbon source forms a carbon coating layer during sintering, which further improves the electrical conductivity of the material and inhibits particle agglomeration.

[0036] 3. The prepared MOF-based interface modifier grafts epoxy groups and phosphonate groups onto the MOF surface through amino-olefin addition and Michael addition reactions. The porous structure of the MOF can effectively adsorb harmful products such as HF generated by electrolyte decomposition, reducing interfacial side reactions. The phosphonate groups form coordination bonds with metal ions on the cathode surface, enhancing interfacial bonding and inhibiting structural collapse caused by Li⁺ deintercalation, thereby significantly improving the cycling stability of the material. Attached Figure Description

[0037] Figure 1 This is an electron microscope image of the lithium iron phosphate precursor material doped with metal ions prepared in Example 2. Detailed Implementation

[0038] Example 1

[0039] (1) Raw material preparation

[0040] Lithium carbonate (Li2CO3): 12g, ferrous oxalate dihydrate (FeC2O4·2H2O): 35g, ammonium dihydrogen phosphate (NH4H2PO4): 22g, magnesium acetate (Mg(CH3COO)2·4H2O): 1.0g, aluminum nitrate (Al(NO3)3·9H2O): 1.0g, sucrose: 7g.

[0041] (2) Preparation of interface modifiers

[0042] The preparation method of the MOF-based interface modifier:

[0043] 1) Amino-olefin addition reaction: 10g zirconium aminophthalate MOF and 20g allyl glycidyl ether were added to 50g DMF solvent, and 4wt% of triethylamine was added as a catalyst. The reaction was carried out at 75℃ for 8 hours to allow the MOF amino group to undergo an addition reaction with the double bond of allyl glycidyl ether, and to graft epoxy groups.

[0044] 2) Michael addition reaction: 15g of 1,2-vinyl diphosphonic acid was introduced, and 2.55wt% of organotin was added as a catalyst. The reaction was carried out at 70℃ for 9 hours to form MOF-phosphonate hybrid.

[0045] 3) Post-processing: After the reaction is complete, the product is washed with ethanol and then dried under vacuum at 70°C for 12 hours to obtain the MOF-based interface modifier.

[0046] (3) Mixing and grinding

[0047] Add the raw material from step (1) above and 100g of anhydrous ethanol to a ball mill, and ball mill at 300rpm for 6h, with a target D50≤10μm.

[0048] (4) Drying treatment

[0049] Vacuum drying at 90℃ for 18 hours (-0.09MPa).

[0050] (5) Sintering treatment

[0051] Nitrogen flow rate 150 mL / min; heating rate 4℃ / min; 700℃; holding temperature for 10 h; naturally cooled to room temperature to obtain the precursor.

[0052] (6) Interface modification

[0053] The interface modifier and the precursor were mixed at a mass ratio of 1:100, ultrasonically dispersed in anhydrous ethanol for 1 h, and dried at 60 °C for 5 h.

[0054] (7) Crushing and sieving

[0055] Airflow pulverization to D50≈1.0μm; sieving to remove large particles.

[0056] Example 2

[0057] (1) Raw material preparation

[0058] Li2CO3: 15g, FeC2O4·2H2O: 30g, NH4H2PO4: 25g, Mg(CH3COO)2·4H2O: 0.5g, Al(NO3)3·9H2O: 0.5g, Glucose: 5g.

[0059] (2) Interface modifiers

[0060] The preparation method of the MOF-based interface modifier:

[0061] 1) Amino-olefin addition reaction: 12g zirconium aminophthalate MOF and 25g allyl glycidyl ether were added to 60g DMF solvent, and 5wt% triethylamine was added as a catalyst. The reaction was carried out at 75℃ for 7 hours to allow the MOF amino group to undergo an addition reaction with the double bond of allyl glycidyl ether, and to graft epoxy groups.

[0062] 2) Michael addition reaction: 20g of 1,2-vinyl diphosphonic acid was introduced, and 3.0wt% organotin was added as a catalyst, accounting for the total mass of the reactants. The reaction was carried out at 75℃ for 8 hours to form MOF-phosphonate hybrid.

[0063] 3) Post-processing: After the reaction was completed, the product was washed with ethanol and then dried under vacuum at 75°C for 11 hours to obtain the MOF-based interface modifier.

[0064] (3) Mixing and grinding

[0065] Add 80g of anhydrous ethanol; ball mill at 300rpm for 8 hours.

[0066] (4) Drying treatment

[0067] Vacuum drying at 80℃ for 24 hours (-0.1MPa).

[0068] (5) Sintering treatment

[0069] Nitrogen flow rate 100 mL / min; heating rate 3℃ / min; 650℃; holding temperature for 8 h; natural cooling to obtain the precursor.

[0070] (6) Interface modification

[0071] The interface modifier and the precursor were mixed at a mass ratio of 1:80; 80g of ethanol was sonicated for 1 hour; and dried at 60℃ for 5 hours.

[0072] (7) Crushing and sieving

[0073] Airflow pulverization to D50≈0.8μm; sieving.

[0074] Figure 1 This is an electron microscope image of the lithium iron phosphate precursor material doped with metal ions prepared in Example 2.

[0075] Example 3

[0076] (1) Raw material preparation

[0077] Li2CO3: 11g, FeC2O4·2H2O: 38g, NH4H2PO4: 21g, Mg(CH3COO)2·4H2O: 2.0g, Al(NO3)3·9H2O: 2.0g, sucrose: 10g.

[0078] (2) Interface modifiers

[0079] The preparation method of the MOF-based interface modifier:

[0080] 1) Amino-olefin addition reaction: 14g zirconium aminophthalate MOF and 25g allyl glycidyl ether were added to 70g DMF solvent, and 5wt% triethylamine was added as a catalyst. The reaction was carried out at 80℃ for 7 hours to allow the MOF amino group to undergo an addition reaction with the double bond of allyl glycidyl ether, and to graft epoxy groups.

[0081] 2) Michael addition reaction: 20g of 1,2-vinyl diphosphonic acid was introduced, and 3.0wt% organotin was added as a catalyst, accounting for the total mass of the reactants. The reaction was carried out at 75℃ for 8 hours to form MOF-phosphonate hybrid.

[0082] 3) Post-processing: After the reaction was completed, the product was washed with ethanol and then dried under vacuum at 75°C for 11 hours to obtain the MOF-based interface modifier.

[0083] (3) Mixing and grinding

[0084] Add 120g of anhydrous ethanol; ball mill at 500rpm for 4 hours.

[0085] (4) Drying treatment

[0086] Vacuum drying at 100℃ for 12 hours (-0.08MPa).

[0087] (5) Sintering treatment

[0088] Nitrogen flow rate 200 mL / min; heating rate 5℃ / min; 750℃; holding temperature for 12 h; natural cooling to obtain the precursor.

[0089] (6) Interface modification

[0090] The interface modifier and the precursor were mixed at a mass ratio of 1:60; 120g of ethanol was sonicated for 1 hour; and dried at 60℃ for 5 hours.

[0091] (7) Crushing and sieving

[0092] Airflow pulverization to D50≈2.0μm; sieving to remove coarse particles.

[0093] Example 4

[0094] (1) Raw material preparation

[0095] Li2CO3: 13g, FeC2O4·2H2O: 33g, NH4H2PO4: 23g, Mg(CH3COO)2·4H2O: 1.5g, Al(NO3)3·9H2O: 1.5g, glucose: 6g.

[0096] (2) Interface modifiers

[0097] The preparation method of the MOF-based interface modifier:

[0098] 1) Amino-olefin addition reaction: 15g zirconium aminophthalate MOF and 30g allyl glycidyl ether were added to 80g DMF solvent, and 6wt% of triethylamine was added as a catalyst. The reaction was carried out at 80℃ for 6 hours to allow the MOF amino group to undergo an addition reaction with the double bond of allyl glycidyl ether, and to graft epoxy groups.

[0099] 2) Michael addition reaction: 25g of 1,2-vinyl diphosphonic acid was introduced, and 3.5wt% of organotin as a catalyst was added. The reaction was carried out at 80℃ for 7 hours to form MOF-phosphonate hybrid.

[0100] 3) Post-processing: After the reaction is complete, the product is washed with ethanol and then dried under vacuum at 80°C for 10 hours to obtain the MOF-based interface modifier.

[0101] (3) Mixing and grinding

[0102] Add 100g of anhydrous ethanol; ball mill at 350rpm for 7 hours.

[0103] (4) Drying treatment

[0104] Vacuum drying at 85℃ for 20 hours (-0.09MPa).

[0105] (5) Sintering treatment

[0106] Nitrogen flow rate 120 mL / min; heating rate 3.5℃ / min; 600℃; holding temperature for 9 h; natural cooling to obtain the precursor.

[0107] (6) Interface modification

[0108] The interface modifier and the precursor were mixed at a mass ratio of 1:50; wet milled with 100g of ethanol for 2 hours; and dried at 60℃ for 5 hours.

[0109] (7) Crushing and sieving

[0110] Airflow pulverization to D50≈1.5μm; sieving.

[0111] Comparative Example 1

[0112] (1) Raw material preparation

[0113] Lithium carbonate (Li2CO3): 12g, ferrous oxalate dihydrate (FeC2O4·2H2O): 35g, ammonium dihydrogen phosphate (NH4H2PO4): 22g, magnesium acetate (Mg(CH3COO)2·4H2O): 1.0g, aluminum nitrate (Al(NO3)3·9H2O): 1.0g, sucrose: 7g.

[0114] (2) Mixing and grinding

[0115] Add the raw material from step (1) above and 100g of anhydrous ethanol to a ball mill, and ball mill at 300rpm for 6h, with a target D50≤10μm.

[0116] (3) Drying treatment

[0117] Vacuum drying at 90℃ for 18 hours (-0.09MPa).

[0118] (4) Sintering treatment

[0119] Nitrogen flow rate 150 mL / min; heating rate 4℃ / min; 700℃; hold for 10 h; allow to cool naturally to room temperature.

[0120] (5) Crushing and sieving

[0121] Airflow pulverization to D50≈1.0μm; sieving to remove large particles.

[0122] Comparative Example 2

[0123] (1) Raw material preparation

[0124] Lithium carbonate (Li2CO3): 12g, ferrous oxalate dihydrate (FeC2O4·2H2O): 35g, ammonium dihydrogen phosphate (NH4H2PO4): 22g, magnesium acetate (Mg(CH3COO)2·4H2O): 1.0g, aluminum nitrate (Al(NO3)3·9H2O): 1.0g, sucrose: 7g.

[0125] (2) Preparation of interface modifiers

[0126] The preparation method of the MOF-based interface modifier:

[0127] 1) Amino-olefin addition reaction: 10g zirconium aminophthalate MOF was added to 50g DMF solvent, and 4wt% of triethylamine was added as a catalyst. The reaction was carried out at 75℃ for 8 hours to allow the MOF amino group to undergo an addition reaction with the allyl glycidyl ether double bond and graft epoxy groups.

[0128] 2) Michael addition reaction: 15g of 1,2-vinyl diphosphonic acid was introduced, and 2.55wt% of organotin was added as a catalyst. The reaction was carried out at 70℃ for 9 hours to form MOF-phosphonate hybrid.

[0129] 3) Post-processing: After the reaction is complete, the product is washed with ethanol and then dried under vacuum at 70°C for 12 hours to obtain the MOF-based interface modifier.

[0130] (3) Mixing and grinding

[0131] Add the raw material from step (1) above and 100g of anhydrous ethanol to a ball mill, and ball mill at 300rpm for 6h, with a target D50≤10μm.

[0132] (4) Drying treatment

[0133] Vacuum drying at 90℃ for 18 hours (-0.09MPa).

[0134] (5) Sintering treatment

[0135] Nitrogen flow rate 150 mL / min; heating rate 4℃ / min; 700℃; holding temperature for 10 h; naturally cooled to room temperature to obtain the precursor.

[0136] (6) Interface modification

[0137] The interface modifier and the precursor were mixed at a mass ratio of 1:100, ultrasonically dispersed in anhydrous ethanol for 1 h, and dried at 60 °C for 5 h.

[0138] (7) Crushing and sieving

[0139] Airflow pulverization to D50≈1.0μm; sieving to remove large particles.

[0140] Comparative Example 3

[0141] (1) Raw material preparation

[0142] Lithium carbonate (Li2CO3): 12g, ferrous oxalate dihydrate (FeC2O4·2H2O): 35g, ammonium dihydrogen phosphate (NH4H2PO4): 22g, magnesium acetate (Mg(CH3COO)2·4H2O): 1.0g, aluminum nitrate (Al(NO3)3·9H2O): 1.0g, sucrose: 7g.

[0143] (2) Preparation of interface modifiers

[0144] The preparation method of the MOF-based interface modifier:

[0145] 1) Amino-olefin addition reaction: 10g zirconium aminophthalate MOF and 20g allyl glycidyl ether were added to 50g DMF solvent, and 4wt% of triethylamine was added as a catalyst. The reaction was carried out at 75℃ for 8 hours to allow the MOF amino group to undergo an addition reaction with the double bond of allyl glycidyl ether, and to graft epoxy groups.

[0146] 2) Post-processing: After the reaction was completed, the product was washed with ethanol and then dried under vacuum at 70°C for 12 hours to obtain the MOF-based interface modifier.

[0147] (3) Mixing and grinding

[0148] Add the raw material from step (1) above and 100g of anhydrous ethanol to a ball mill, and ball mill at 300rpm for 6h, with a target D50≤10μm.

[0149] (4) Drying treatment

[0150] Vacuum drying at 90℃ for 18 hours (-0.09MPa).

[0151] (5) Sintering treatment

[0152] Nitrogen flow rate 150 mL / min; heating rate 4℃ / min; 700℃; holding temperature for 10 h; naturally cooled to room temperature to obtain the precursor.

[0153] (6) Interface modification

[0154] The interface modifier and the precursor were mixed at a mass ratio of 1:100, ultrasonically dispersed in anhydrous ethanol for 1 h, and dried at 60 °C for 5 h.

[0155] (7) Crushing and sieving

[0156] Airflow pulverization to D50≈1.0μm; sieving to remove large particles.

[0157] Detection Example 1

[0158] The testing method involved in this invention is as follows:

[0159] 1. Battery assembly

[0160] Positive electrode preparation: Lithium iron phosphate positive electrode material, polyvinylidene fluoride (PVDF) binder, and conductive agent (Super P) are mixed at a mass ratio of 85:10:5, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added to prepare a slurry. The slurry is uniformly coated on aluminum foil, dried, pressed into sheets, and cut into 14mm diameter discs as positive electrodes.

[0161] Negative electrode preparation: Lithium metal sheet is used as the negative electrode.

[0162] Electrolyte: 1 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 1:1:1).

[0163] Separator: Celgard 2400 porous polyethylene membrane.

[0164] Battery assembly: Assemble the CR2025 button cells in an argon-protected glove box.

[0165] 2. Electrochemical performance testing

[0166] Specific capacity test: Using a battery testing system, constant current charge and discharge tests are performed at different rates (0.1C, 1C) within a voltage range of 2.5V to 4.2V, and the initial discharge capacity is recorded.

[0167] Cyclic performance test: Charge and discharge cycles were performed at 1C rate, and the capacity retention rate was recorded after 100 cycles.

[0168] High-temperature performance testing: The material's high-temperature cycling stability was evaluated by performing charge-discharge cycles at a rate of 1C at 60°C.

[0169] Table 1 Test Results

[0170]

[0171] In summary, by doping lithium iron phosphate materials with metal ions and adding MOF-based interface modifiers, the specific capacity, cycle stability, and high-temperature performance of the materials are significantly improved, verifying the effectiveness and superiority of the preparation method of this invention.

Claims

1. A method for preparing a lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1, Prepare lithium iron phosphate precursor material doped with metal ions; the doping element is at least one of magnesium and aluminum; S2, the lithium iron phosphate precursor material doped with metal ions is coated with a MOF-based interface modifier, wherein the MOF-based interface modifier is a MOF material with epoxy groups and phosphonate groups modified on its surface. In step S2, the MOF-based interface modifier is made by grafting epoxy groups onto zirconium aminophthalate MOF and allyl glycidyl ether via an amino-olefin addition reaction, and then modifying the phosphonate group with 1,2-vinyl diphosphonic acid via a Michael addition reaction. Amino-olefin addition reaction: By mass, 10-15 parts of zirconium aminophthalate MOF and 20-30 parts of allyl glycidyl ether are added to 50-80 parts of DMF solvent, and 4-6 wt% of triethylamine is added as a catalyst. The reaction is carried out at 75-80℃ for 6-8 hours, so that the double bond of the MOF amino group and the allyl glycidyl ether undergo an addition reaction, and epoxy groups are grafted. Michael addition reaction: 15-25 parts of 1,2-vinyl diphosphonic acid are introduced, and 2.55-3.5 wt% of organotin is added as a catalyst. The reaction is carried out at 70-80℃ for 7-9 hours to form MOF-phosphonate hybrid.

2. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the lithium source, iron source, phosphorus source, metal dopant and carbon source are ball-milled and then dispersed in a dispersion medium. After drying, the precursor powder is obtained, and the precursor powder is sintered to obtain the lithium iron phosphate precursor material doped with metal ions.

3. The method for preparing the lithium iron phosphate cathode material according to claim 2, characterized in that, In step S1, by mass, there are 11-15 parts of lithium source, 30-38 parts of iron source, 21-25 parts of phosphorus source, 1-4 parts of metal dopant, and 5-10 parts of carbon source.

4. The method for preparing the lithium iron phosphate cathode material according to claim 2, characterized in that, In step S1, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium nitrate. The iron source is at least one of ferrous oxalate or its hydrate, ferrous phosphate, ferrous sulfate, ferrous ammonium sulfate, ferrous chloride, and ferrous nitrate. The phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; The carbon source is at least one of sucrose, glucose, and polyethylene glycol.

5. The method for preparing the lithium iron phosphate cathode material according to claim 2, characterized in that, The sintering temperature is 600-750℃, and the sintering time is 8-12h.

6. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the mass ratio of MOF-based interface modifier to lithium iron phosphate precursor material doped with metal ions is 1:50-100.

7. The lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1 to 6.

8. A lithium-ion battery, characterized in that, The lithium iron phosphate cathode material as described in claim 7 is used.

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