A high-compaction-density lithium iron phosphate material, a preparation method thereof and a lithium ion battery

Abstract

The application discloses a high-compaction-density lithium iron phosphate material and a preparation method and lithium ion battery thereof. The preparation method comprises the following steps: mixing a phosphoric acid source, an iron source, a lithium source, a carbon source and modified cerium oxide, and obtaining a primary lithium iron phosphate material through one-time heat treatment; adding a rate modification additive into the primary lithium iron phosphate material and performing secondary heat treatment to obtain a final lithium iron phosphate material, wherein the rate modification additive is prepared by Diels-Alder cyclization reaction of (E)-3-(thiophene-3-yl) ethyl acrylate and bisindole maleimide. Through the addition of the modified cerium oxide and the rate modification additive, the electrochemical performance is effectively improved.

Description

Technical Field

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

[0002] With the rapid development of renewable energy and the continuous expansion of the electric vehicle market, the demand for high-performance, long-life, and safe lithium-ion batteries is increasing. Lithium iron phosphate (LiFePO4) has become one of the important choices for cathode materials of lithium-ion batteries due to its advantages such as high thermal stability, long cycle life, environmental friendliness, and relatively low cost.

[0003] However, lithium iron phosphate materials have some inherent drawbacks, such as low electronic conductivity and low lithium-ion diffusion rate, resulting in poor rate performance and low-temperature performance. Furthermore, the low packing density and poor compaction properties of lithium iron phosphate particles limit their application in high-energy-density batteries.

[0004] To improve the conductivity and compaction density of lithium iron phosphate (LFP), researchers have employed various methods, such as carbon coating, metal ion doping, and nanostructuring. Among these, doping with rare earth metal oxides, such as cerium oxide (CeO2), is considered an effective modification method. CeO2 possesses excellent electronic conductivity and redox properties, which can improve the electronic conductivity and structural stability of LFP to some extent.

[0005] For example, the invention application with publication number CN119822349A discloses the use of cerium oxide as a dopant in the preparation of lithium iron phosphate cathode materials.

[0006] To address the problems associated with direct cerium oxide doping, cerium oxide has been modified. For example, patent application CN118239460A discloses a method of modifying CeO2 by adding Bi2O3 powder, and then doping it with lithium iron phosphate cathode material. This method improves the lattice matching between CeO2 and lithium hydroxyl iron phosphate, further reduces the size of lithium iron phosphate particles, and thus further increases the compaction density of lithium iron phosphate cathode material. It also enhances the rate performance of lithium iron phosphate cathode material.

[0007] However, existing doping methods have some problems. For example, the dopant has poor dispersibility and is prone to agglomeration in the material, affecting its modification effect; the interfacial bonding between the dopant and the lithium iron phosphate matrix is ​​not strong, causing the dopant to easily fall off during cycling, affecting the long-term stability of the material; in addition, the addition of dopant may introduce impurities, affecting the purity and electrochemical performance of the material.

[0008] Therefore, there is an urgent need to develop a new doping modification method that can effectively improve the dispersibility and interfacial bonding strength of dopants in lithium iron phosphate, enhance the compaction density and electrochemical performance of the material, and meet the application requirements of high energy density lithium-ion batteries. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, this invention provides a high-compact-density lithium iron phosphate material, its preparation method, and a lithium-ion battery. By doping modified cerium oxide and adding rate-modifying additives, the compaction density and electrochemical performance of the material are improved.

[0010] This invention first provides a method for preparing high-density lithium iron phosphate material, comprising the following steps:

[0011] S1, a primary lithium iron phosphate material is obtained by mixing a phosphoric acid source, an iron source, a lithium source, a carbon source and modified cerium oxide, and then performing a single heat treatment.

[0012] S2, a rate modifier is added to the primary lithium iron phosphate material and subjected to a second heat treatment to obtain the final high-density lithium iron phosphate material. The rate modifier is prepared by a Diels-Alder cyclization reaction of (E)-3-(thiophene-3-yl)acrylate and bisindole maleimide.

[0013] Preferably, in step S1, the phosphoric acid source and iron source are iron phosphate; the lithium source is at least one of lithium carbonate and lithium hydroxide; and the carbon source is at least one of glucose, sucrose and citric acid.

[0014] Preferably, in step S1, the phosphoric acid source and iron source are iron phosphate, and by mass, the amounts are: 100 parts iron phosphate, 20-35 parts lithium source, 5-15 parts carbon source, and 0.1-1 parts modified cerium oxide. The particle size of iron phosphate is 1-8 μm.

[0015] Preferably, in step S1, the raw materials are mixed in a solvent and ball-milled to obtain a slurry; the slurry is spray-dried to obtain a precursor powder; the precursor powder is then subjected to a primary lithium iron phosphate material under an inert atmosphere. The primary heat treatment temperature is 600-750℃, and the time is 8-12 hours. The ball milling speed is 300-500 rpm, and the time is 2-6 hours. The solvent is at least one of deionized water and ethanol. The feed temperature for spray drying is 150-200℃, and the discharge temperature is 80-100℃. The inert atmosphere is nitrogen or argon.

[0016] Preferably, in step S1, the modified cerium oxide is Bi2O3-doped CeO2.

[0017] More preferably, by weight, 100 parts of cerium nitrate and 0.5-2 parts of bismuth nitrate are dissolved in water to obtain a mixed solution; the pH is adjusted by adding ammonia water, and co-precipitation is performed; the precipitate is washed, dried, and calcined to obtain Bi2O3-doped CeO2. Cerium nitrate is a hydrate, specifically Ce(NO3)3·6H2O. Bismuth nitrate is a hydrate, specifically Bi(NO3)3·5H2O. The amount of water used is 450-500 parts per 100 parts of cerium nitrate. The pH is adjusted to 10 with ammonia water. During precipitate washing, deionized water and anhydrous ethanol are used alternately until the washing solution is neutral. After washing, the obtained precipitate is dried at 50-60°C for 9-12 hours.

[0018] Preferably, the mass ratio of primary lithium iron phosphate material to rate modifier is 100:1-2.17.

[0019] Preferably, in step S2, during the secondary heat treatment, the mixture is first mixed at 50-60°C for 2-4 hours, and then heat-treated at 500-600°C for 2-4 hours under an inert atmosphere. The inert atmosphere is nitrogen or argon. During the secondary heat treatment, the mixture is first mixed at a lower temperature, which is lower than the glass transition temperature of the additive (approximately 80-100°C) and the phase transition temperature of lithium iron phosphate (greater than 700°C). This avoids premature decomposition of the additive or damage to the material structure. At the same time, the thorough mixing for 2-4 hours ensures that the additive does not agglomerate or segregate in the material, improving the uniformity of dispersion.

[0020] The synthesis method of the rate-modifying additive is as follows: Weigh 18-36 parts by weight of (E)-3-(thiophen-3-yl)ethyl acrylate (CAS: 50266-60-9) and 34-78 parts by weight of bisindolemaleimide (CAS: 113963-68-1), and dissolve them in 280-320 parts by weight of toluene. Add 2%-5% of TS-1 catalyst according to the total mass of the reactants, and react at 70-180℃ for 3-5 hours to complete the Diels-Alder cyclization reaction. After the reaction is completed, remove the toluene by distillation, and then dry under vacuum at 60-70℃ to obtain the rate-modifying additive.

[0021] Diels-Alder cyclization mechanism:

[0022] The reactants are bisindolemaleimide (dienite, containing conjugated double bonds) and (E)-3-(thiophen-3-yl)ethyl acrylate (dienophile, containing double bonds). Under the action of TS-1 catalyst (titanium silicate molecular sieve, providing acidic sites), a six-membered cyclic conjugated product is generated through a [4+2] cycloaddition reaction.

[0023] The present invention further provides a high-density lithium iron phosphate material prepared by the aforementioned preparation method.

[0024] The present invention also provides a lithium-ion battery, wherein the positive electrode material uses the aforementioned high-density lithium iron phosphate material.

[0025] Beneficial effects of this invention:

[0026] 1. By introducing doped cerium oxide into lithium iron phosphate cathode materials, the particle morphology and size distribution of the material can be effectively improved. The addition of dopants promotes uniform particle growth, reduces agglomeration, and makes the particles more tightly packed during compaction, thereby significantly improving the compaction density. High compaction density helps to improve the volumetric energy density of the battery, meeting the application requirements of high-energy-density batteries.

[0027] 2. Doped cerium oxide possesses excellent electronic conductivity and redox properties. Its doping into the lithium iron phosphate crystal structure introduces lattice defects, increases lithium-ion migration channels, and reduces electron and ion migration resistance, thereby improving the material's electronic conductivity and lithium-ion diffusion rate. This plays a crucial role in improving the rate performance and low-temperature performance of lithium iron phosphate.

[0028] 3. The introduction of doped and modified cerium oxide helps stabilize the crystal structure of lithium iron phosphate and suppresses phase transitions and structural collapses that may occur during charging and discharging. Furthermore, the redox properties of cerium oxide can provide a buffering effect during charging and discharging, slowing down volume changes and reducing stress concentration, thereby improving the cycle stability of the material and extending the battery's lifespan.

[0029] 4. Ratio-modifying additives have the following characteristics:

[0030] High electronic conductivity: Conjugated π bonds form continuous electron channels, significantly improving electron mobility;

[0031] Strong interfacial bonding: Polar groups (such as ester groups and imine groups) can form hydrogen bonds or chemical adsorption with hydroxyl groups (-OH) on the surface of LiFePO4, thereby enhancing interfacial bonding;

[0032] Balance between flexibility and rigidity: Aromatic rings provide structural rigidity, while ester side chains provide molecular flexibility, adapting to volume changes in the material during charging and discharging. Attached Figure Description

[0033] Figure 1 The image shown is an electron microscope image of the lithium iron phosphate material prepared in Example 1. Detailed Implementation

[0034] Example 1

[0035] (1) Preparation of doped and modified cerium oxide:

[0036] 100g Ce(NO3)3·6H2O and 1g Bi(NO3)3·5H2O were dissolved in 480g deionized water; the pH was adjusted to 10 with 22% ammonia water, and the mixture was stirred for 35 minutes to co-precipitate; the mixture was then vacuum dried at 60℃ for 10 hours; and finally calcined in air at 580℃ for 4 hours to obtain doped modified cerium oxide.

[0037] (2) Synthesis of rate-modifying additives:

[0038] 27g of (E)-3-(thiophen-3-yl)ethyl acrylate and 51g of bisindole maleimide were dissolved in 300g of toluene; 3% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 120℃ for 4 hours; the mixture was then dried under vacuum at 70℃ for 6 hours to obtain the rate-modified additive.

[0039] (3) Preparation of lithium iron phosphate materials:

[0040] 100g of iron phosphate (5μm particle size, 99.5% purity), 25g of lithium carbonate, 10g of glucose, and 0.5g of doped modified cerium oxide were added to 140g of deionized water and mixed. The mixture was then ball-milled at 400 rpm for 4 hours. The powder was then spray-dried at a feed temperature of 180℃ and a discharge temperature of 90℃ to obtain precursor powder. First heat treatment: The precursor powder was held at 700℃ under a nitrogen atmosphere for 10 hours. Second heat treatment: A rate modifier was added, and the product from the previous step (after the first heat treatment) was mixed with the rate modifier at a mass ratio of 100:1.8. The mixture was stirred at 55℃ for 3 hours and then treated with argon at 600℃ for 2 hours to obtain lithium iron phosphate material.

[0041] Figure 1 The image shown is an electron microscope image of the lithium iron phosphate material prepared in Example 1.

[0042] Example 2

[0043] (1) Preparation of doped and modified cerium oxide:

[0044] 100g Ce(NO3)3·6H2O and 0.5g Bi(NO3)3·5H2O were dissolved in 450g deionized water; the pH was adjusted to 10 with 20% ammonia water, and the mixture was stirred for 30 minutes to co-precipitate; the mixture was dried in a forced-air dryer at 50℃ for 12 hours; and calcined in air at 550℃ for 4 hours to obtain doped modified cerium oxide.

[0045] (2) Synthesis of rate-modifying additives:

[0046] 18g of (E)-3-(thiophen-3-yl)ethyl acrylate and 34g of bisindole maleimide were dissolved in 280g of toluene; 2% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 70℃ for 5 hours; the mixture was then dried under vacuum at 60℃ for 8 hours to obtain the rate-modified additive.

[0047] (3) Preparation of lithium iron phosphate materials:

[0048] 100g of ferric phosphate (particle size 3μm, purity 99.2%), 20g of lithium hydroxide, 5g of sucrose, and 0.1g of doped modified cerium oxide were added to 120g of ethanol and mixed. The mixture was then ball-milled at 300 rpm for 6 hours. The powder was then spray-dried at a feed temperature of 150℃ and a discharge temperature of 80℃ to obtain the precursor powder. A first heat treatment was performed: the precursor powder was held at 600℃ under an argon atmosphere for 12 hours.

[0049] Secondary heat treatment: Add a rate modifier. Mix the product from the previous step (after the first heat treatment) with the rate modifier at a mass ratio of 100:1. Stir at 50°C for 4 hours and then treat with nitrogen at 500°C for 4 hours to obtain lithium iron phosphate material.

[0050] Example 3

[0051] (1) Preparation of doped and modified cerium oxide:

[0052] 100g Ce(NO3)3·6H2O and 2g Bi(NO3)3·5H2O were dissolved in 500g deionized water; the pH was adjusted to 10 with 25% ammonia water, and the mixture was stirred for 40 minutes to carry out co-precipitation; the mixture was then vacuum dried at 55℃ for 9 hours; and calcined in air at 600℃ for 4 hours to obtain doped modified cerium oxide.

[0053] (2) Synthesis of rate-modifying additives:

[0054] 36g of (E)-3-(thiophen-3-yl)ethyl acrylate and 78g of bisindole maleimide were dissolved in 320g of toluene; 5% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 180℃ for 3 hours; the mixture was then dried under vacuum at 70℃ for 5 hours to obtain the rate-modified additive.

[0055] (3) Preparation of lithium iron phosphate materials:

[0056] 100g of iron phosphate (8μm particle size, 99.8% purity), 35g of lithium carbonate, 15g of citric acid, and 1g of doped modified cerium oxide were added to 160g of deionized water and mixed. The mixture was then ball-milled at 500 rpm for 2 hours. After spray drying at 200℃ and 100℃, precursor powder was obtained. First heat treatment: The precursor powder was held at 750℃ under a nitrogen atmosphere for 8 hours. Second heat treatment: A rate modifier was added, and the product from the previous step (after the first heat treatment) was mixed with the rate modifier at a mass ratio of 100:2. The mixture was stirred at 60℃ for 2 hours and then treated with argon at 580℃ for 3 hours to obtain lithium iron phosphate material.

[0057] Example 4

[0058] (1) Preparation of doped and modified cerium oxide:

[0059] 100g Ce(NO3)3·6H2O and 1.5g Bi(NO3)3·5H2O were dissolved in 470g deionized water; the pH was adjusted to 10 with 23% ammonia water, and the mixture was stirred for 38 minutes to carry out co-precipitation; the mixture was then vacuum dried at 58℃ for 11 hours; and finally calcined in air at 560℃ for 4 hours to obtain doped modified cerium oxide.

[0060] (2) Synthesis of rate-modifying additives:

[0061] 22g of (E)-3-(thiophen-3-yl)ethyl acrylate and 45g of bisindole maleimide were dissolved in 290g of toluene; 4% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 150℃ for 3.5 hours; the mixture was then vacuum dried at 65℃ for 7 hours to obtain the rate-modified additive.

[0062] (3) Preparation of lithium iron phosphate materials:

[0063] 100g of iron phosphate (particle size 1μm, purity 99%), 30g of lithium hydroxide, 12g of glucose + 3g of citric acid, and 0.8g of doped modified cerium oxide were added to 130g of ethanol and mixed. The mixture was then ball-milled at 350 rpm for 5 hours. After spray drying at a feed temperature of 170℃ and a discharge temperature of 85℃, precursor powder was obtained. First heat treatment: The precursor powder was held at 650℃ under an argon atmosphere for 9 hours. Second heat treatment: A rate modifier was added, and the product mass from the previous step (after the first heat treatment) was mixed with the rate modifier at a mass ratio of 100:2.17. The mixture was stirred at 58℃ for 2.5 hours and then treated with nitrogen at 550℃ for 3.5 hours to obtain lithium iron phosphate material.

[0064] Comparative Example 1

[0065] (1) Preparation of doped and modified cerium oxide:

[0066] 100g Ce(NO3)3·6H2O and 1g Bi(NO3)3·5H2O were dissolved in 480g deionized water; the pH was adjusted to 10 with 22% ammonia water, and the mixture was stirred for 35 minutes to co-precipitate; the mixture was then vacuum dried at 60℃ for 10 hours; and finally calcined in air at 580℃ for 4 hours to obtain doped modified cerium oxide.

[0067] (2) Preparation of lithium iron phosphate materials:

[0068] 100g of iron phosphate (5μm particle size, 99.5% purity), 25g of lithium carbonate, 10g of glucose, and 0.5g of doped and modified cerium oxide were added to 140g of deionized water and mixed. The mixture was then ball-milled at 400 rpm for 4 hours. The powder was then spray-dried at a feed temperature of 180℃ and a discharge temperature of 90℃ to obtain the precursor powder. Heat treatment was performed at 700℃ under a nitrogen atmosphere for 10 hours to obtain lithium iron phosphate material.

[0069] Comparative Example 2

[0070] (1) Preparation of doped and modified cerium oxide:

[0071] 100g Ce(NO3)3·6H2O and 1g Bi(NO3)3·5H2O were dissolved in 480g deionized water; the pH was adjusted to 10 with 22% ammonia water, and the mixture was stirred for 35 minutes to co-precipitate; the mixture was then vacuum dried at 60℃ for 10 hours; and finally calcined in air at 580℃ for 4 hours to obtain doped modified cerium oxide.

[0072] (2) Synthesis of rate-modifying additives:

[0073] 51g of bisindolemaleimide was dissolved in 300g of toluene; 3% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 120℃ for 4 hours; the mixture was then vacuum dried at 70℃ for 6 hours to obtain a rate-modifying additive.

[0074] (3) Preparation of lithium iron phosphate materials:

[0075] 100g of iron phosphate (5μm particle size, 99.5% purity), 25g of lithium carbonate, 10g of glucose, and 0.5g of doped modified cerium oxide were added to 140g of deionized water and mixed. The mixture was then ball-milled at 400 rpm for 4 hours. After spray drying at a feed temperature of 180℃ and a discharge temperature of 90℃, precursor powder was obtained. First heat treatment: The precursor powder was held at 700℃ under a nitrogen atmosphere for 10 hours. Second heat treatment: A rate modifier was added, and the product mass from the previous step (after the first heat treatment) was mixed with the rate modifier at a mass ratio of 100:1.8. The mixture was stirred at 55℃ for 3 hours and then treated with argon at 600℃ for 2 hours to obtain lithium iron phosphate material.

[0076] Comparative Example 3

[0077] (1) Preparation of doped and modified cerium oxide:

[0078] 100g Ce(NO3)3·6H2O and 1g Bi(NO3)3·5H2O were dissolved in 480g deionized water; the pH was adjusted to 10 with 22% ammonia water, and the mixture was stirred for 35 minutes to co-precipitate; the mixture was then vacuum dried at 60℃ for 10 hours; and finally calcined in air at 580℃ for 4 hours to obtain doped modified cerium oxide.

[0079] (2) Synthesis of rate-modifying additives:

[0080] 27g of (E)-3-(thiophen-3-yl)ethyl acrylate was dissolved in 300g of toluene; 3% (by mass percentage) of TS-1 catalyst was added, and the mixture was reacted at 120℃ for 4 hours; the mixture was then vacuum dried at 70℃ for 6 hours to obtain the rate-modified additive.

[0081] (3) Preparation of lithium iron phosphate materials:

[0082] 100g of iron phosphate (5μm particle size, 99.5% purity), 25g of lithium carbonate, 10g of glucose, and 0.5g of doped modified cerium oxide were added to 140g of deionized water and mixed. The mixture was then ball-milled at 400 rpm for 4 hours. The powder was then spray-dried at a feed temperature of 180℃ and a discharge temperature of 90℃ to obtain precursor powder. First heat treatment: The precursor powder was held at 700℃ under a nitrogen atmosphere for 10 hours. Second heat treatment: A rate modifier was added, and the product from the previous step (after the first heat treatment) was mixed with the rate modifier at a mass ratio of 100:1.8. The mixture was stirred at 55℃ for 3 hours and then treated with argon at 600℃ for 2 hours to obtain lithium iron phosphate material.

[0083] Detection Example 1

[0084] The testing method involved in this invention is as follows:

[0085] 1) Compacted density test

[0086] Sample preparation: The obtained positive electrode material powder is loaded into a mold and pressed into a cylindrical sample by applying a constant pressure (200 MPa).

[0087] Measurement method: The sample mass was measured using a precision balance, and the diameter and height of the sample were measured using vernier calipers. The volume was then calculated. Compacted density (g / cm³) 3 = Mass / Volume

[0088] 2) Conductivity test

[0089] Sample preparation: The positive electrode material powder is pressed into a circular sheet sample with a thickness of about 1 mm.

[0090] Measurement method: The resistance of the sample is measured using the four-probe method or the two-probe method, and the conductivity (S / cm) is calculated.

[0091] 3) Cyclic performance test

[0092] Battery assembly: The positive electrode material is mixed with a conductive agent and a binder in a mass ratio of 80:10:10, coated onto aluminum foil, dried, compacted, and cut into electrode sheets. These are then assembled with a lithium metal negative electrode, separator, and electrolyte to form a CR2032 coin cell.

[0093] Test conditions: Under constant temperature (25°C), charge-discharge cycle test was performed at a rate of 0.5 C, and the capacity retention rate and coulombic efficiency were recorded.

[0094] 4) Thermal stability test

[0095] Sample preparation: The positive electrode material is taken out in a fully charged state and dried.

[0096] Measurement method: Thermogravimetric analysis (TGA) was used in a nitrogen atmosphere to heat from room temperature to 800°C at a heating rate of 10°C / min, and the mass change and thermal decomposition temperature were recorded.

[0097] Table 1 Test Results

[0098]

[0099] In summary, the rate-modifying additives used in the embodiments effectively improved the various properties of the lithium iron phosphate cathode material, verifying the technical effect of the present invention.

Claims

1. A method for preparing a high tap density lithium iron phosphate material, characterized in that, The method comprises the following steps: S1, mixing a phosphoric acid source, an iron source, a lithium source, a carbon source and modified cerium oxide, and obtaining a primary lithium iron phosphate material through a first heat treatment; the modified cerium oxide is Bi2O3-doped CeO2; S2, adding a rate modification additive to the primary lithium iron phosphate material and performing a second heat treatment to obtain a final high-compactness lithium iron phosphate material, wherein the rate modification additive is prepared by Diels-Alder cyclization reaction of (E)-3-(thiophene-3-yl) ethyl acrylate and bisindole maleimide.

2. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, In step S1, the phosphoric acid source and the iron source are iron phosphate; The lithium source is at least one of lithium carbonate and lithium hydroxide; The carbon source is at least one of glucose, sucrose and citric acid.

3. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, In step S1, the phosphoric acid source and the iron source are iron phosphate, and the iron phosphate is 100 parts, the lithium source is 20-35 parts, the carbon source is 5-15 parts, and the modified cerium oxide is 0.1-1 parts by mass.

4. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, In step S1, each raw material is added to a solvent for mixing, and a slurry is obtained through ball milling; the slurry is spray dried to obtain a precursor powder, and the precursor powder is subjected to a first heat treatment under an inert atmosphere to obtain the primary lithium iron phosphate material; the first heat treatment is performed at a temperature of 600-750°C for 8-12 hours.

5. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, 100 parts of cerium nitrate and 0.5-2 parts of bismuth nitrate are dissolved in water to obtain a mixed solution; co-precipitation is performed by adjusting the pH through the addition of ammonia; after washing and drying, the precipitate is calcined to obtain Bi2O3-doped CeO2.

6. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, The mass ratio of the primary lithium iron phosphate material to the rate modification additive is 100:1-2.

17.

7. The method for preparing high-density lithium iron phosphate material according to claim 1, characterized in that, In step S2, during the second heat treatment, the mixture is first mixed at 50-60°C for 2-4 hours, and then heat treated at 500-600°C for 2-4 hours under an inert atmosphere.

8. The high-compactness lithium iron phosphate material prepared by the preparation method of any one of claims 1-7.

9. A lithium-ion battery, characterized by The positive electrode material uses the high-compactness lithium iron phosphate material of claim 8.

Images