Modified lithium iron phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the field of positive electrode materials, and particularly relates to a modified lithium iron phosphate positive electrode material and a preparation method and application thereof. The invention provides a preparation method of a modified lithium iron phosphate positive electrode material, which comprises the following steps: (1) mixing a lithium source, an iron source, a phosphorus source, a metal ion dopant, a non-metal ion dopant and a carbon source to prepare precursor slurry; (2) pre-sintering the precursor slurry, adding a fluxing agent, mixing, and carrying out first sintering; adding a metal salt solution for mixing, and performing secondary sintering to obtain a modified lithium iron phosphate positive electrode material; the first sintering comprises the steps of firstly raising the temperature to 550-650 DEG C and sintering for 4-8 hours, and then raising the temperature to 700-900 DEG C and sintering for 8-12 hours. The modified lithium iron phosphate positive electrode material prepared by the invention has high rate capability, cycling stability and specific capacity.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials, and particularly relates to a modified lithium iron phosphate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, and low pollution, and are thus widely used in many fields such as electric vehicles and energy storage power stations; lithium iron phosphate has become a cathode material that has received much attention due to its advantages such as rich raw materials, high safety, and environmental friendliness. However, lithium iron phosphate cathode materials also have defects such as low conductivity and slow lithium ion diffusion rate, resulting in low capacity, low cycle stability, and poor rate performance. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low conductivity and slow lithium ion diffusion rate of lithium iron phosphate cathode materials in the prior art, which lead to low capacity, low cycle stability, and poor rate performance, so as to provide a modified lithium iron phosphate cathode material, a preparation method thereof, and an application thereof.

[0004] For this purpose, the present invention provides the following technical solutions.

[0005] The present invention provides a preparation method of a modified lithium iron phosphate cathode material, comprising the following steps:

[0006] (1) Mix a lithium source, an iron source, a phosphorus source, a metal ion dopant, a non-metal ion dopant, and a carbon source to obtain a precursor slurry;

[0007] (2) Presinter the precursor slurry, add a flux and mix, and perform a first sintering; add a metal salt solution and mix, and perform a second sintering to obtain a modified lithium iron phosphate cathode material;

[0008] The first sintering includes: first heating to 550-650 °C and sintering for 4-8 h, and then heating to 700-900 °C for 8-12 h.

[0009] In an optional embodiment, based on the molar amount of iron element in the iron source, the molar addition amount of the metal element in the metal ion dopant is 1-5%;

[0010] In an optional embodiment, based on the total mass of the lithium source, the iron source, the phosphorus source, the metal ion dopant, and the non-metal ion dopant, the addition amount of the carbon source is 5-15%;

[0011] In an optional embodiment, the molar ratio of the lithium source, the iron source, and the phosphorus source is 1:(0.9-1.1):(0.9-1.1).

[0012] In an alternative embodiment, the metal ion dopant includes at least one of metal nitrates, metal acetates, and tetrabutyl titanate;

[0013] In an alternative embodiment, the non-metal ion dopant includes at least one of fluorides and borides.

[0014] In an alternative embodiment, in step (1), the rotation speed of the mixing is 300 - 500 r / min;

[0015] In an alternative embodiment, the mixing time is 4 - 8 h;

[0016] In an alternative embodiment, ball milling is used for the mixing; preferably, the ball-to-material ratio is (10 - 20):1;

[0017] Ball milling enables the raw materials to be fully mixed and the particles to be refined. The mechanical force chemical action during ball milling is utilized to preliminarily disperse and react the metal ion dopant and the non-metal ion dopant to form a uniform slurry;

[0018] In an alternative embodiment, the mixing further includes adding ethanol;

[0019] Preferably, the ethanol includes anhydrous ethanol;

[0020] In an alternative embodiment, the lithium source includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide;

[0021] In an alternative embodiment, the iron source includes at least one of ferrous oxalate, iron nitrate, iron sulfate, iron phosphate, and iron oxide;

[0022] In an alternative embodiment, the phosphorus source includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and phosphoric acid;

[0023] In an alternative embodiment, the metal nitrate includes at least one of cobalt nitrate, manganese nitrate, and strontium nitrate;

[0024] In an alternative embodiment, the metal acetate includes manganese acetate;

[0025] In an alternative embodiment, the fluoride includes lithium fluoride;

[0026] In an alternative embodiment, the boride includes boric acid;

[0027] In an alternative embodiment, based on the molar amount of phosphorus element in the phosphorus source, the molar addition amount of fluorine and / or boron element in the non-metal ion dopant is 2 - 8%; the non-metal ion dopant is a fluorine- and / or boron-containing substance.

[0028] In an alternative embodiment, the carbon source includes at least one of glucose, sucrose, phenolic resin, and carbon black;

[0029] In an alternative embodiment, the flux includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE);

[0030] In an alternative embodiment, the mass ratio of the flux to the pre-sintered product is (0.1 - 1):1.

[0031] In an alternative embodiment, the pre-sintering is carried out under a protective atmosphere;

[0032] In an alternative embodiment, the heating rate of the pre-sintering is 3 - 5 °C / min;

[0033] In an alternative embodiment, the temperature of the pre-sintering is 300 - 400 °C;

[0034] In an alternative embodiment, the time of the pre-sintering is 2 - 4 h;

[0035] In an alternative embodiment, the protective atmosphere includes at least one of argon and nitrogen;

[0036] In an alternative embodiment, the gas flow rate of the protective atmosphere is 50 - 100 mL / min;

[0037] In an alternative embodiment, drying is also included before the pre-sintering;

[0038] Preferably, the temperature of the drying is 80 - 120 °C;

[0039] In an alternative embodiment, the first sintering is carried out under a mixed atmosphere of argon and hydrogen;

[0040] In an alternative embodiment, the heating rate of the first sintering is 2 - 4 °C / min;

[0041] In an alternative embodiment, the volume percentage of hydrogen in the mixed atmosphere is 5 - 10%;

[0042] In an alternative embodiment, the gas flow rate of the mixed atmosphere is 80 - 120 mL / min.

[0043] In an alternative embodiment, the temperature of the second sintering is 400 - 600 °C;

[0044] In an alternative embodiment, the heating rate of the second sintering is 2 - 4 °C / min;

[0045] In an alternative embodiment, the second sintering is carried out in a mixed atmosphere of argon and hydrogen;

[0046] In an alternative embodiment, the volume percentage of hydrogen in the mixed atmosphere is 5 - 10%;

[0047] In an alternative embodiment, the gas flow rate of the mixed atmosphere is 80 - 120 mL / min.

[0048] In an alternative embodiment, the time of the second sintering is 4 - 6 h.

[0049] In an alternative embodiment, spray drying is further included before the second sintering;

[0050] Preferably, the inlet air temperature of the spray drying is 200 - 250 °C;

[0051] Preferably, the outlet air temperature of the spray drying is 80 - 120 °C;

[0052] Preferably, the feeding speed of the spray drying is 70 - 90 Kg / hr;

[0053] In an alternative embodiment, the metal salt solution includes at least one of metal nitrate and metal alkoxide;

[0054] Preferably, the metal nitrate includes at least one of lithium nitrate and iron nitrate;

[0055] Preferably, the metal alkoxide includes at least one of lithium ethoxide, silanolate, and titanate; the silanolate and titanate can be selected conventionally in the art; the silanolate belongs to one of the metal alkoxides because of its similar structural characteristics and chemical properties to the metal alkoxide;

[0056] Preferably, the metal salt solution further includes a solvent;

[0057] Preferably, the solvent includes absolute ethanol;

[0058] In an alternative embodiment, the mass ratio of the product after the first sintering to the metal salt solution is 1:(0.01 - 0.1);

[0059] In an alternative embodiment, the solid content of the metal salt solution is 45 - 60%.

[0060] The present invention also provides a modified lithium iron phosphate cathode material prepared by the above preparation method.

[0061] The present invention also provides an application of the modified lithium iron phosphate cathode material prepared by the above preparation method in a lithium-ion battery.

[0062] The technical solution of the present invention has the following advantages:

[0063] 1. The preparation method of the modified lithium iron phosphate cathode material provided by the present invention includes the following steps: mixing a lithium source, an iron source, a phosphorus source, a metal ion dopant, a non-metal ion dopant, and a carbon source to obtain a precursor slurry; (2) pre-sintering the precursor slurry, adding a flux and mixing, and performing the first sintering; adding a metal salt solution and mixing, and performing the second sintering to obtain the modified lithium iron phosphate cathode material; the first sintering includes: first heating to 550-650 °C and sintering for 4-8 h, and then heating to 700-900 °C and sintering for 8-12 h. The modified lithium iron phosphate cathode material provided by the present invention has excellent rate performance and cycle stability, and a high specific capacity. During the pre-sintering process, the lithium iron phosphate crystal structure is initially formed, metal ions and non-metal ions enter the lattice to occupy positions, and part of the carbon source pyrolyzes to form a carbon skeleton prototype, improving the electron conduction path of the material; in the first sintering, first sinter at 550-650 °C for 6-8 h, through sufficient time and a stable temperature environment, make the overall temperature of the intermediate product tend to be consistent, which not only enables the subsequent chemical reaction to be fully completed, but also generates single-phase lithium oxide and crystal grains, improving the crystallinity; then heating to 700-900 °C and sintering for 8-12 h allows the crystal to further grow and perfect, and repair the lattice defects. The metal ion doping effectively regulates the lattice parameters and improves the conductivity in the lithium iron phosphate cathode material; the non-metal ion doping broadens the lithium ion transmission channel, thereby increasing the lithium ion diffusion rate; and a uniform carbon coating layer is formed outside the lithium iron phosphate cathode material, enhancing the conductivity and structural stability of the cathode material.

[0064] Adding a metal salt solution and mixing, and performing the second sintering to form a metal oxide coating layer can further improve the specific capacity and cycle stability of the lithium iron phosphate cathode material, and also enhance the structural stability of the cathode material, reducing the volume expansion and contraction of the cathode material during charge and discharge, thereby reducing the pulverization phenomenon of the material; the doping elements (metal ions and non-metal ions), the carbon coating layer and the metal oxide coating layer in the modified lithium iron phosphate cathode material provided by the present invention have good synergistic effects. The doping elements can improve the energy density and charge-discharge rate of the prepared battery; the three act on each other, further enhancing the electrochemical performance and structural stability of the modified lithium iron phosphate cathode material, thereby greatly improving the battery capacity, cycle stability and rate performance, especially the electrical performance during high-current charge and discharge, extending the battery life, and meeting the requirements of high-power and long-life lithium-ion batteries.

[0065] Mixing the pre-sintered product doped with metal ions and non-metal ions with a flux can achieve effective sintering of the lithium iron phosphate cathode material at a lower temperature, saving energy and reducing costs while promoting crystal growth and forming a crystal structure with fine particle size and dense structure at a lower temperature, thereby improving the electrochemical performance and structural stability of the modified lithium iron phosphate cathode material. Detailed implementation manners

[0066] The following embodiments are provided to better understand the present invention further. They are not limited to the best implementation manner, and do not constitute a limitation on the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0067] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0068] Example 1

[0069] This example provides a preparation method of a modified lithium iron phosphate cathode material, including the following steps:

[0070] (1) Mix 0.95 mol of lithium carbonate, 1 mol of ferrous oxalate, 1 mol of ammonium dihydrogen phosphate, 0.02 mol of manganese acetate, 0.03 mol of tetrabutyl titanate, 0.05 mol of lithium fluoride and glucose at 400 r / min for 7 h. Based on the total mass of lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate, manganese acetate, tetrabutyl titanate and lithium fluoride, the addition amount of glucose is 8%; dry in a vacuum drying oven at 120 °C, place it in a tubular furnace under argon (argon flow rate 80 mL / min), and heat up to 400 °C at a rate of 3 °C / min for pre-sintering for 3 h to obtain a pre-sintered product;

[0071] (2) Grind and mix the pre-sintered product and the flux (PVDF) according to a mass ratio of 1:0.5, press into a mold, place it in a tubular furnace under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 10%), and the gas flow rate of the mixed atmosphere is 100 mL / min; first heat up to 550 °C at a rate of 2 °C / min for sintering for 4 h, and then heat up to 800 °C for sintering for 10 h;

[0072] (3) Add a metal salt solution (tetraethyl titanate, with anhydrous ethanol as the solvent). The inlet temperature of spray drying is 220 °C, and the outlet temperature is 80 °C; the feeding rate of spray drying is 80 Kg / hr; under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 10%), the gas flow rate of the mixed atmosphere is 100 mL / min, and it is sintered at 600 °C for 6 h while heating up at 2 °C / min to obtain the modified lithium iron phosphate cathode material. The mass ratio of the product after the first sintering to the metal salt solution is 1:0.05, and the solid content of the metal salt solution is 50%.

[0073] Example 2

[0074] This example provides a method for preparing a modified lithium iron phosphate cathode material, which includes the following steps:

[0075] (1) Mix 1.05 mol of lithium carbonate, 1 mol of ferrous oxalate, 1 mol of ammonium dihydrogen phosphate, 0.009 mol of manganese acetate, 0.018 mol of tetrabutyl titanate, 0.045 mol of lithium fluoride, and glucose at 300 r / min for 4 h. Based on the total mass of lithium carbonate, ferrous oxalate, ammonium dihydrogen phosphate, manganese acetate, tetrabutyl titanate, and lithium fluoride, the addition amount of glucose is 12%; dry it in a vacuum drying oven at 80 °C, place it in a tubular furnace under argon (argon flow rate 50 mL / min), and heat it up to 400 °C at 5 °C / min for pre-sintering for 2 h to obtain a pre-sintered product;

[0076] (2) Grind and mix the pre-sintered product and the flux (PVDF) according to a mass ratio of 1:0.5, press it into a mold, place it in a tubular furnace under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 10%); the gas flow rate of the mixed atmosphere is 120 mL / min; first heat it up to 650 °C at 3 °C / min for sintering for 8 h, and then heat it up to 900 °C for sintering for 12 h;

[0077] (3) Add a metal salt solution (tetraethyl titanate, with anhydrous ethanol as the solvent). The inlet temperature of spray drying is 220 °C, and the outlet temperature is 80 °C; the feeding rate of spray drying is 80 Kg / hr. Under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 10%), the gas flow rate of the mixed atmosphere is 100 mL / min, and it is sintered at 600 °C for 5 h while heating up at 3 °C / min to obtain the modified lithium iron phosphate cathode material. The mass ratio of the product after the first sintering to the metal salt solution is 1:0.01, and the solid content of the metal salt solution is 50%.

[0078] Example 3

[0079] This example provides a method for preparing a modified lithium iron phosphate cathode material, which includes the following steps:

[0080] (1) Mix 0.95 mol of lithium acetate, 1 mol of iron nitrate, 1 mol of potassium dihydrogen phosphate, 0.01 mol of manganese nitrate, 0.08 mol of boric acid and sucrose at 350 r / min for 6 h. Based on the total mass of lithium acetate, iron nitrate, potassium dihydrogen phosphate, manganese nitrate and boric acid, the addition amount of sucrose is 5%; Dry it in a vacuum drying oven at 100 °C, place it in a tube furnace under argon (argon flow rate 100 mL / min), and heat it to 400 °C at a rate of 4 °C / min for pre-sintering for 3 h to obtain a pre-sintered product;

[0081] (2) Grind and mix the pre-sintered product and the flux (PVDF) according to a mass ratio of 1:0.5, press it into a mold, place it in a tube furnace under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 5%); The gas flow rate of the mixed atmosphere is 80 mL / min; First heat it to 600 °C at a rate of 4 °C / min and sinter for 7 h, then heat it to 900 °C and sinter for 11 h;

[0082] (3) Add a metal salt solution (lithium ethoxide, the solvent is absolute ethanol), the inlet air temperature of spray drying is 210 °C, and the outlet air temperature is 90 °C; The feeding speed of spray drying is 75 Kg / hr, under a mixed atmosphere of argon and hydrogen (the volume ratio of hydrogen is 10%), the gas flow rate of the mixed atmosphere is 100 mL / min, and heat it to 500 °C at a rate of 2 °C / min and sinter for 5 h to obtain a modified lithium iron phosphate cathode material. The mass ratio of the product after the first sintering to the metal salt solution is 1:0.1, and the solid content of the metal salt solution is 50%.

[0083] Comparative Example 1

[0084] This comparative example provides a preparation method of a lithium iron phosphate cathode material. Compared with Example 1, the difference is only that step (3) is not carried out.

[0085] Comparative Example 2

[0086] This comparative example provides a preparation method of a lithium iron phosphate cathode material. Compared with Example 1, the difference is only that in step (2), sintering at 800 °C for 10 h is used to replace sintering at 550 °C for 4 h first and then sintering at 800 °C for 10 h in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a preparation method of a lithium iron phosphate cathode material, including the following steps:

[0089] Mix 0.95 mol of lithium carbonate, 1 mol of iron(II) oxalate, 1 mol of ammonium dihydrogen phosphate, 0.02 mol of manganese(II) acetate, 0.03 mol of tetrabutyl titanate, 0.05 mol of lithium fluoride and glucose at 400 r / min for 7 h. Based on the total mass of lithium carbonate, iron(II) oxalate, ammonium dihydrogen phosphate, manganese(II) acetate, tetrabutyl titanate and lithium fluoride, the mass of glucose is 8%; dry it in a vacuum drying oven at 120 °C, place it in a tube furnace under argon, heat it to 400 °C at a rate of 3 °C / min and pre-sinter for 3 h, then heat it to 550 °C at a rate of 2 °C / min and sinter for 4 h, and then heat it to 800 °C and sinter for 10 h; obtain the lithium iron phosphate cathode material.

[0090] Test Example

[0091] Perform performance tests on the lithium iron phosphate cathode materials prepared in Examples 1 - 3 and Comparative Examples 1 - 3, specifically as follows:

[0092] Electrode sheet assembly: Weigh the lithium iron phosphate cathode material, acetylene black and PVDF-NMP (the mass ratio of PVDF to NMP is 8:100) in a mass ratio of 8:1:1 and place them in a stirring tank, and add an appropriate amount of NMP solution to prepare an electrode slurry with a certain viscosity. Manually coat the slurry evenly on the single-sided carbon-coated aluminum foil with the assistance of a coater with a thickness of 50 μm. Then take out the electrode sheet after drying it in a vacuum oven at 80 °C for 5 h, compact the electrode sheet with a tablet press at a pressure of 5 Mpa, and finally cut it into circular pieces with a diameter of 12 mm with a slicing machine. Select several circular pieces with a mass difference within the range of 0.002 mg and place them in a vacuum drying oven at 120 °C for 12 h for standby assembly.

[0093] Battery assembly: Ultrasonically clean the battery case, gasket and insulating tweezers before assembly. During assembly, assemble in the order of negative electrode case - gasket - electrode sheet (the above circular pieces) - electrolyte - separator - electrolyte - lithium metal sheet - gasket - positive electrode case. After assembly, seal it with a tablet press and age it at room temperature for 12 h, and then test its electrochemical performance.

[0094] (1) 0.5C first-cycle discharge specific capacity test: At room temperature, within a cut-off voltage of 2.0 - 4.5 V, charge once at 0.5C and discharge once at 0.5C; the results are shown in Table 1;

[0095] (2) 1C first-cycle discharge specific capacity test: At room temperature, within a cut-off voltage of 2.0 - 4.5 V, charge once at 1C and discharge once at 1C; the results are shown in Table 1;

[0096] (3) 2C first-cycle discharge specific capacity test: At room temperature, within a cut-off voltage of 2.0 - 4.5 V, charge once at 2C and discharge once at 2C; the results are shown in Table 1;

[0097] (4) 0.5C Capacity Retention Test: At room temperature, within a cut-off voltage range of 2.0 - 4.5V, charge once at 0.5C, discharge once at 0.5C, and cycle 500 times; the results are shown in Table 1.

[0098] (5) 1C Capacity Retention Test: At room temperature, within a cut-off voltage range of 2.0 - 4.5V, charge once at 1C, discharge once at 1C, and cycle 500 times; the results are shown in Table 1.

[0099] (6) 2C Capacity Retention Test: At room temperature, within a cut-off voltage range of 2.0 - 4.5V, charge once at 2C, discharge once at 2C, and cycle 500 times; the results are shown in Table 1.

[0100] Table 1

[0101]

[0102] As can be seen from Table 1, the modified lithium iron phosphate cathode material prepared by the present invention has high rate performance, cycle stability and specific capacity. By comparing Examples 1 - 3 with Comparative Examples 1 - 3, it can be known that the modified lithium iron phosphate cathode material provided by the present invention significantly improves the electrochemical performance and structural stability of the cathode material through the combined action of a special sintering process, doping elements, an external carbon coating layer and a metal oxide layer.

[0103] Obviously, the above examples are only for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing a modified lithium iron phosphate positive electrode material, characterized in that: The steps include: (1) mixing a lithium source, an iron source, a phosphorus source, a metal ion dopant, a non-metal ion dopant and a carbon source to prepare a precursor slurry; (2) pre-sintering the precursor slurry, adding a flux and mixing, and first sintering; Adding a metal salt solution and mixing, and performing a second sintering to obtain a modified lithium iron phosphate positive electrode material; The first sintering includes: firstly heating the temperature to 550-650° C. and sintering for 4-8 hours, and then heating the temperature to 700-900° C. and sintering for 8-12 hours.

2. The preparation method according to claim 1, characterized in that: In the step (1), the molar amount of the metal element in the metal ion dopant is 1-5% based on the molar amount of the iron element in the iron source; and / or Based on the total mass of the lithium source, iron source, phosphorus source, metal ion dopant and non-metal ion dopant, the amount of the carbon source added is 5-15%; and / or, The molar ratio of the lithium source, the iron source and the phosphorus source is 1:(0.9-1.1):(0.9-1.1); and / or, The metal ion dopant comprises at least one of metal nitrate, metal acetate and tetrabutyl titanate; and / or, The non-metal ion dopant includes at least one of fluoride and boride.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the mixing speed is 300-500 r / min; and / or, The mixing time is 4-8h; and / or, The mixing is performed by ball milling; and / or, The lithium source includes at least one of lithium carbonate, lithium acetate and lithium hydroxide; and / or, The iron source comprises at least one of ferrous oxalate, ferric nitrate, ferric sulfate, ferric phosphate and ferric oxide; and / or, The phosphorus source comprises at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate and phosphoric acid; and / or, The metal nitrate comprises at least one of cobalt nitrate, manganese nitrate and strontium nitrate; and / or, The metal acetate comprises manganese acetate; and / or, the fluoride comprises lithium fluoride; and / or, The boride comprises boric acid; and / or, Based on the molar amount of phosphorus in the phosphorus source, the molar amount of fluorine and / or boron added in the non-metallic ion dopant is 2-8%; and / or, The carbon source comprises at least one of glucose, sucrose, phenolic resin and carbon black; and / or, The flux comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber and polytetrafluoroethylene; and / or, The mass ratio of the flux to the pre-sintered product is (0.1-1):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that The pre-sintering is carried out under a protective atmosphere; Preferably, the heating rate of the pre-sintering is 3-5°C / min; Preferably, the pre-sintering temperature is 300-400°C; Preferably, the pre-sintering time is 2-4h; Preferably, the protective atmosphere comprises at least one of argon and nitrogen; Preferably, the protective atmosphere gas flow rate is 50-100 mL / min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The first sintering is performed in a mixed atmosphere of argon and hydrogen; Preferably, the heating rate of the first sintering is 2-4°C / min; Preferably, the volume proportion of the hydrogen in the mixed atmosphere is 5-10%; Preferably, the mixed atmosphere gas flow rate is 80-120 mL / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The second sintering temperature is 400-600°C; Preferably, the heating rate of the second sintering is 2-4°C / min; Preferably, the second sintering is performed in a mixed atmosphere of argon and hydrogen; Preferably, the second sintering time is 4-6h; Preferably, the volume proportion of the hydrogen in the mixed atmosphere is 5-10%; Preferably, the mixed atmosphere gas flow rate is 80-120 mL / min.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The metal salt solution includes at least one of a metal nitrate and a metal alkoxide; Preferably, the metal nitrate comprises at least one of lithium nitrate and iron nitrate; Preferably, the metal alkoxide comprises at least one of lithium ethoxide, silicon alkoxide and titanium alkoxide; Preferably, the metal salt solution further comprises a solvent; Preferably, the solvent comprises anhydrous ethanol.

8. The preparation method according to any one of claims 1 to 6, characterized in that: The mass ratio of the product after the first sintering to the metal salt solution is 1:(0.01-0.1); and / or, The solid content of the metal salt solution is 45-60%.

9. The modified lithium iron phosphate positive electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the modified lithium iron phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 8 in lithium ion batteries.

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