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

Abstract

The invention discloses a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium battery, the preparation method comprises the following steps: preparation of a precursor: mixing a lithium source, an iron source, a phosphorus source, a carbon source and an iron chelating agent according to a molar ratio of (1-1.5): (1-1.5): (1-1.5): (0.25-0.5): (0.05-0.10) to obtain the precursor; sintering: performing primary sintering on the obtained precursor to obtain a primary sintered material; dispersing the obtained primary sintered material, and performing secondary sintering on the primary sintered material to obtain a secondary sintered material; and crushing the obtained secondary sintered material to obtain the lithium iron phosphate positive electrode material. The temperature of the secondary sintering is higher than that of the primary sintering. According to the preparation method of the lithium iron phosphate positive electrode material, the lithium iron phosphate positive electrode material has relatively high capacity on the premise of not increasing energy consumption and not reducing the safety of lithium iron phosphate.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium iron phosphate positive electrode material, a preparation method thereof, and a lithium battery. Background Art

[0002] Lithium iron phosphate (LiFePO4) has a good olivine structure, consisting of LiO6 octahedron, FeO6 octahedron and PO4 tetrahedron units. The PO bond in the lithium iron phosphate crystal is stable, difficult to decompose, and has good safety performance. However, during the synthesis of LiFePO4, in the early stage of lithium iron phosphate crystal formation, the binding energy of Fe is lower than that of Li, which will cause Fe to be introduced into the crystal structure from the precursor preferentially over Li, thereby causing Fe-Li antisite defects in the material. Iron-lithium antisite occurs when iron atoms are placed in positions that should be occupied by lithium during the synthesis process, which not only hinders the movement of lithium in the crystal lattice, but also reduces the effective lithium content in the material. In the prior art, in order to solve the problem of lithium iron anti-site, the degree of lithium iron anti-site is suppressed by increasing the synthesis temperature or using anions for doping during the synthesis of lithium iron phosphate; however, the problems existing in the prior art include: 1) high energy consumption and unsuitability for industrialization; 2) due to the nano-sizing of lithium iron phosphate particles, small particles will gradually melt and grow into large particles at high temperatures, resulting in an increase in the primary particle size, an increase in the lithium ion diffusion path, a decrease in the lithium ion diffusion rate, and a reduction in the actual discharge capacity of the lithium iron phosphate; 3) higher temperatures will reduce the cleanliness of the lithium iron phosphate, generate some iron phosphide-like impurities, and reduce the safety of the lithium iron phosphate.

[0003] Therefore, it is very necessary to provide a lithium iron phosphate positive electrode material and a preparation method thereof and a lithium battery that have a higher capacity without increasing energy consumption and reducing the safety of lithium iron phosphate. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for preparing a lithium iron phosphate positive electrode material, a lithium iron phosphate positive electrode material and a lithium battery; the method for preparing the lithium iron phosphate positive electrode material enables the lithium iron phosphate positive electrode material to have a higher capacity without increasing energy consumption and reducing the safety of the lithium iron phosphate.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, comprising the steps of:

[0007] Preparation of a precursor: mixing a lithium source, an iron source, a phosphorus source, a carbon source, and an iron chelating agent in a molar ratio of 1-1.5:1-1.5:1-1.5:0.25-0.5:0.05-0.10 to obtain a precursor;

[0008] Sintering: sintering the obtained precursor once to obtain a primary sintered material; dispersing the obtained primary sintered material, and then sintering the primary sintered material twice to obtain a secondary sintered material; crushing the obtained secondary sintered material to obtain a lithium iron phosphate positive electrode material; the temperature of the secondary sintering is higher than the temperature of the primary sintering.

[0009] The chelating agent is 1,2-dimethyl-3-hydroxypyridin-4(1H)-one.

[0010] Optionally, the primary sintering is performed at a heating rate of 5-8°C / min, heating to 475-490°C, and keeping the temperature for 8-10 hours; the secondary sintering is performed at a heating rate of 3-5°C / min, heating to 775-788°C, and keeping the temperature for 10-12 hours.

[0011] Optionally, the lithium source, the iron source, the phosphorus source, the carbon source and the iron chelating agent are in a molar ratio of 1:1:1:0.25:0.05.

[0012] Optionally, the lithium source includes one or more of lithium nitrate, lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate, lithium trifluoromethanesulfonate or lithium oxalate.

[0013] Optionally, the iron source includes one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric phosphate or ferric citrate.

[0014] Optionally, the phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or lithium dihydrogen phosphate.

[0015] Optionally, the carbon source includes one or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl butyral, polyvinyl alcohol, polyacrylonitrile, starch or cellulose.

[0016] In a second aspect, the present invention provides a lithium iron phosphate positive electrode material, which is prepared using the above-mentioned method for preparing the lithium iron phosphate positive electrode material.

[0017] In a third aspect, the present invention provides a lithium battery comprising the lithium iron phosphate positive electrode material as described above.

[0018] The beneficial effects produced by the present invention include at least:

[0019] In the preparation method of the lithium iron phosphate positive electrode material described in the present invention, an iron chelating agent with a strong force on iron is introduced in the early stage of lithium iron phosphate crystal synthesis, so that during the preparation process of the lithium iron phosphate positive electrode material, the iron chelating agent preferentially chelates trivalent iron lithium ions, preventing iron from entering the crystal structure first and then aligning lithium iron anti-position; the iron chelating agent is mixed with the lithium source, iron source, carbon source and phosphorus source before sintering, and compared with the existing technology, there is no need to further increase the sintering temperature; thereby ensuring that the binding energy of iron is improved, lithium iron anti-position is effectively suppressed, and the effective content of lithium is increased in the early stage of lithium iron phosphate crystal synthesis without increasing energy consumption and reducing the safety of the lithium iron phosphate positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a schematic diagram showing the action principle of the iron chelating agent on iron ions in the present invention.

[0021] Figure 2 0.1C charge and discharge curves of LFP-DFP / C and LFP / C. DETAILED DESCRIPTION

[0022] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may 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 comprehensive understanding of the present disclosure.

[0023] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0024] It should be noted that, unless otherwise specified, the raw materials used in the present invention can be sourced from suppliers known in the art, or can be prepared by known methods.

[0025] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, comprising the steps of:

[0026] Preparation of a precursor: mixing a lithium source, an iron source, a phosphorus source, a carbon source, and an iron chelating agent at a molar ratio of 1-1.5:1-1.5:1-1.5:0.25-0.5:0.05-0.10 to obtain a precursor; wherein the mixing method is ball milling;

[0027] sintering: the obtained precursor is subjected to primary sintering to obtain primary sintered material; the obtained primary sintered material is dispersed and then subjected to secondary sintering to obtain secondary sintered material; the obtained secondary sintered material is crushed to obtain lithium iron phosphate positive electrode material; the temperature of the secondary sintering is higher than that of the primary sintering.

[0028] In the preparation method of the lithium iron phosphate positive electrode material, the iron chelating agent with a larger force on iron is introduced in the early stage of lithium iron phosphate crystal synthesis, so that the iron chelating agent preferentially chelates trivalent iron lithium in the preparation process of the lithium iron phosphate positive electrode material, thereby avoiding the iron from entering the crystal structure first and then the lithium iron anti-position; the iron chelating agent is mixed with the lithium source, the iron source, the carbon source and the phosphorus source before sintering, without the need for further increase in sintering temperature compared with the prior art; thereby ensuring that the binding energy of iron is improved, the lithium iron anti-position is effectively inhibited, the effective content of lithium is improved, and the discharge capacity of lithium iron phosphate is improved without increasing energy consumption and reducing the safety of lithium iron phosphate positive electrode material.

[0029] The chelating agent is 1,2-dimethyl-3-hydroxypyridin-4(1H)-one, which is deferiprone, and its chemical formula is C9H12N2O2.

[0030] The primary sintering is performed at a temperature rising speed of 5-8℃ / min, the temperature is raised to 475-490℃, and the temperature is kept for 8-10 hours; the secondary sintering is performed at a temperature rising speed of 3-5℃ / min, the temperature is raised to 775-788℃, and the temperature is kept for 10-12 hours. In the present application, the two-stage sintering method is adopted, the primary sintering is performed at a lower temperature, the obtained primary sintered material is dispersed, and then the secondary sintering is performed at a higher temperature, thereby ensuring the uniformity of the particles of the finally obtained lithium iron phosphate positive electrode material powder, avoiding the formation of particles with large particle size in the sintering process, shortening the diffusion path of lithium ions, improving the diffusion rate of lithium ions, and increasing the discharge capacity of lithium iron phosphate.

[0031] The lithium source includes one or more of lithium nitrate, lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate, lithium trifluoromethanesulfonate or lithium oxalate;

[0032] The iron source includes one or more of iron nitrate, iron chloride, iron sulfate, iron phosphate or citric acid iron;

[0033] The phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or lithium dihydrogen phosphate;

[0034] The carbon source includes one or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl butyral, polyvinyl alcohol, polyacrylonitrile, starch or cellulose.

[0035] In a second aspect, the present application provides a lithium iron phosphate positive electrode material, which is prepared using the above-mentioned method for preparing the lithium iron phosphate positive electrode material.

[0036] In a third aspect, the present application provides a lithium battery, which includes the lithium iron phosphate positive electrode material as described above. Specifically, the lithium battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator, wherein the positive electrode plate is prepared using the lithium iron phosphate positive electrode material as described above. Specifically, the method for making the lithium battery includes the steps of: stirring and mixing the obtained lithium iron phosphate positive electrode material with a conductive agent and an adhesive to obtain a positive electrode slurry; coating the positive electrode slurry on a positive electrode collector to obtain a positive electrode plate; the positive electrode collector includes aluminum foil; and then drying the obtained positive electrode plate under vacuum, and assembling the dried positive electrode plate with metal, separator and electrolyte to obtain a lithium battery.

[0037] Example 1:

[0038] Lithium nitrate, ferric nitrate, ammonium dihydrogen phosphate, glucose, and deferiprone are ball-milled and mixed in a molar ratio of 1:1:1:0.25:0.05 to obtain a precursor; the obtained precursor is then placed in a tube furnace for sintering, and the temperature is increased to 475-490°C at a heating rate of 5-8°C / min during the first sintering, and kept warm for 8-10 hours to obtain a primary sintered material; the obtained primary sintered material is dispersed, and the evenly dispersed primary sintered material is placed in a tube furnace again for a secondary sintering, and the temperature is increased to 775-788°C at a heating rate of 3-5°C / min during the second sintering, and kept warm for 10-12 hours to obtain a secondary sintered material; the obtained secondary sintered material is crushed to obtain a lithium iron phosphate positive electrode material, which is recorded as LFP-DFP / C.

[0039] Comparative Example 1:

[0040] Compared with Example 1, the difference in Comparative Example 1 is that no iron chelating agent is added to the precursor. Lithium nitrate, ferric nitrate, ammonium dihydrogen phosphate, and glucose are ball-milled in a molar ratio of 1:1:1:0.25 to obtain a precursor; the obtained precursor is then placed in a tube furnace for sintering, and the temperature is increased to 475-490°C at a heating rate of 5-8°C / min during the first sintering, and kept warm for 8-10 hours to obtain a primary sintered material; the obtained primary sintered material is dispersed, and the evenly dispersed primary sintered material is placed in a tube furnace again for secondary sintering, and the temperature is increased to 775-788°C at a heating rate of 3-5°C / min during the second sintering, and kept warm for 10-12 hours to obtain a secondary sintered material; the obtained secondary sintered material is crushed to obtain a lithium iron phosphate positive electrode material, recorded as LFP / C.

[0041] Test example:

[0042] The lithium iron phosphate positive electrode materials prepared in Example 1 and Comparative Example 1 were respectively assembled into CR2016 button batteries; and the prepared CR2016 button batteries were subjected to charge and discharge tests.

[0043] Specifically, the steps include:

[0044] Preparation of pole pieces: LFP / C and LFP-DFP / C were respectively ground evenly with a binder (PVDF, 99.9%) and conductive carbon black in a mass ratio of 8:1:1, and N-methylpyrrolidone was added as a solvent to grind evenly. Then, they were evenly coated on aluminum foil and vacuum dried in a vacuum drying oven at 120°C for 12 hours. The copper foil coated with the mixture was taken out and a punching machine was used to punch out discs with a diameter of 10 mm for the assembly of button batteries.

[0045] Battery Assembly: Coin-cell batteries were assembled in a glove box with oxygen and water concentrations below 1 ppm. A disc of aluminum foil with active material served as the negative electrode, a lithium sheet served as the positive electrode, a porous polypropylene membrane served as the separator, and a 1 M lithium hexafluorophosphate solution (1:1:1 ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate) served as the electrolyte. The battery was sealed with a sealing machine to prevent leakage and allowed to rest for 12 hours before testing.

[0046] Charge and Discharge Test: Using the BlueDian Battery Test System, the material's electrochemical properties, such as reversible capacity, coulombic efficiency, and cycling stability, are characterized when used as a lithium-ion battery cathode material. Test conditions: Constant current at a 0.1C rate until the voltage reaches 3.75V, followed by constant voltage charge until the current reaches 50µA. At a 0.1C rate, constant current discharge is performed to 2V.

[0047] The test results are as follows Figure 2 As shown, curve L1 is a 0.1C charge curve of a lithium battery made of the material of Example 1, curve L2 is a 0.1C discharge curve of a lithium battery made of the material of Example 1, curve L3 is a 0.1C charge curve of a lithium battery made of the material of Comparative Example 1, and curve L4 is a 0.1C discharge curve of a lithium battery made of the material of Comparative Example 1. It can be seen that, whether charging or discharging, the lithium iron phosphate particles with the addition of deferiprone (DFP) are larger than the lithium iron phosphate particles without deferiprone (DFP). The specific data are shown in Table 1; it can be seen that the 0.1C charge gram capacity LFP-DFP / C is 2.83mAh / g higher than LFP / C, and the 0.1C discharge gram capacity is 2.2mAh / g higher. It can be proved that the addition of DFP increases the charge and discharge gram capacity, and it also proves that the addition of the iron chelator deferiprone can inhibit the iron-lithium anti-position.

[0048] type 0.1C charging capacity (mAh / g) 0.1C discharge capacity (mAh / g) LFP-DTPMP / C 166.03 160.2 LFP / C 163.2 158

[0049] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, 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.

[0050] The above embodiments merely represent preferred embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a lithium iron phosphate positive electrode material, characterized in that: Including steps: Preparation of a precursor: mixing a lithium source, an iron source, a phosphorus source, a carbon source, and an iron chelating agent in a molar ratio of 1-1.5:1-1.5:1-1.5:0.25-0.5:0.05-0.10 to obtain a precursor; Sintering: sintering the obtained precursor once to obtain a primary sintered material; dispersing the obtained primary sintered material, and then sintering the primary sintered material twice to obtain a secondary sintered material; crushing the obtained secondary sintered material to obtain a lithium iron phosphate positive electrode material; the temperature of the secondary sintering is higher than the temperature of the primary sintering.

2. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, characterized in that: The chelating agent is 1,2-dimethyl-3-hydroxypyridin-4(1H)-one.

3. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, characterized in that: The primary sintering is carried out at a heating rate of 5-8°C / min, heating to 475-490°C, and keeping the temperature for 8-10 hours; the secondary sintering is carried out at a heating rate of 3-5°C / min, heating to 775-788°C, and keeping the temperature for 10-12 hours.

4. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the lithium source, the iron source, the phosphorus source, the carbon source and the iron chelating agent is 1:1:1:0.25:0.

05.

5. The method for preparing the lithium iron phosphate positive electrode material according to claim 1, characterized in that: The lithium source includes one or more of lithium nitrate, lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate, lithium trifluoromethanesulfonate or lithium oxalate.

6. The method for preparing a lithium iron phosphate cathode material according to claim 1, wherein: The iron source includes one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric phosphate or ferric citrate.

7. The method for preparing a lithium iron phosphate cathode material according to claim 1, wherein: The phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid or lithium dihydrogen phosphate.

8. The method for preparing a lithium iron phosphate cathode material according to claim 1, wherein: The carbon source includes one or more of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl butyral, polyvinyl alcohol, polyacrylonitrile, starch or cellulose.

9. A lithium iron phosphate positive electrode material, characterized in that: The lithium iron phosphate positive electrode material is prepared by the preparation method of the lithium iron phosphate positive electrode material according to any one of claims 1 to 8.

10. A lithium battery, characterized in that: The lithium battery comprises the lithium iron phosphate positive electrode material as claimed in claim 9.

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