Preparation method of lithium iron phosphate battery positive electrode material

Abstract

The invention relates to the technical field of battery positive electrode materials, and provides a preparation method of a lithium iron phosphate battery positive electrode material, which comprises the following steps: mixing iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride and water, adding a dispersing agent and a carbon source to obtain slurry, and carrying out ball milling, drying, compression molding, roasting and grinding to obtain the lithium iron phosphate battery positive electrode material. According to the technical scheme, the problems of low specific capacity and poor cycle performance of the lithium iron phosphate battery positive electrode material in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, specifically to a method for preparing a lithium iron phosphate battery cathode material. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, has been widely used in new energy vehicles, energy storage power stations, portable electronic devices and other fields due to its outstanding advantages such as high theoretical specific capacity, excellent cycle stability, strong safety, low cost and environmental friendliness. It has become one of the most mature cathode materials for commercial application.

[0003] However, in practical applications, lithium iron phosphate (LFP) materials still face two major technological bottlenecks. Firstly, in the olivine-type crystal structure of LFP, lithium ions must migrate along one-dimensional channels, and the material's electronic conductivity and lithium-ion diffusion coefficient are extremely low. This leads to significant polarization during high-rate charge-discharge processes, making it difficult for the actual specific capacity to approach the theoretical value, resulting in poor rate performance. Secondly, the repeated insertion / extraction of lithium ions during charge-discharge processes causes periodic volume changes in the LFP lattice. Under long-term cycling, this periodic deformation can lead to microcracks or even fractures in the lattice, directly disrupting the integrity of the one-dimensional lithium-ion migration channels and resulting in poor cycle performance. To address these issues, existing technologies involve element doping, introducing metal or non-metal ions to modify the LFP lattice. However, single-element doping has limited effect on improving electrochemical performance. Therefore, a high specific capacity and good cycle performance lithium iron phosphate battery cathode material is urgently needed. Summary of the Invention

[0004] This invention proposes a method for preparing a lithium iron phosphate battery cathode material, which solves the problems of low specific capacity and poor cycle performance of lithium iron phosphate battery cathode materials in related technologies.

[0005] The technical solution of the present invention is as follows: This invention proposes a method for preparing a lithium iron phosphate battery cathode material, comprising the following steps: Iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride and water are mixed, and a dispersant and a carbon source are added to obtain a slurry. The slurry is then ball-milled, dried, pressed into shape, calcined, and ground to obtain the lithium iron phosphate battery cathode material.

[0006] As a further technical solution, the molar ratio of Fe:Li:Ge:Zr:F in the iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide and lithium fluoride is 1:1.05:0.0025:0.0025~0.0175:0.01~0.04.

[0007] As a further technical solution, the rotational speed of the ball mill is 300~400 r / min; The ball milling time is 5-7 hours.

[0008] As a further technical solution, the calcination is carried out in an inert gas; The roasting temperature is 720~750℃; The roasting time is 7-9 hours.

[0009] As a further technical solution, after grinding, the median particle size of the lithium iron phosphate battery cathode material is 2.5~3μm.

[0010] As a further technical solution, the dispersant is polyvinylpyrrolidone and / or polyaspartic acid; Preferably, the dispersant is polyvinylpyrrolidone and polyaspartic acid.

[0011] In this invention, polyvinylpyrrolidone (PVP) is a nonionic polymeric dispersant. The pyrrolidone groups on its molecular chain can be adsorbed onto the surface of iron phosphate, lithium carbonate, and zirconium dioxide powder particles via hydrogen bonds, forming a steric hindrance layer that hinders van der Waals forces between particles, reducing particle aggregation. However, its dispersibility for lithium fluoride is limited. Polyaspartic acid (PAA) is an anionic dispersant. The carboxyl groups on its molecular chain can ionize into negative charges in aqueous solution, causing the surface of lithium fluoride and other powder particles to carry the same negative charge. This further improves the dispersibility of the powder particles through electrostatic repulsion. The combined use of these two dispersants can uniformly disperse the powder particles in an aqueous system, forming a stable slurry with a narrow particle size distribution and good flowability, thereby obtaining a uniformly dense green body. This allows the calcined material to form a uniform porous structure, providing channels for rapid lithium ion migration and thus improving specific capacity.

[0012] As a further technical solution, when the dispersant is polyvinylpyrrolidone and polyaspartic acid, the mass ratio of polyvinylpyrrolidone and polyaspartic acid is 3:1~2.

[0013] As a further technical solution, the number-average molecular weight of the polyvinylpyrrolidone is 5500~10100.

[0014] As a further technical solution, the carbon source includes glucose or sucrose.

[0015] As a further technical solution, the mass of the dispersant is 1wt%~2wt% of the mass of the slurry; The mass of the carbon source is 15wt% to 20wt% of the mass of the slurry.

[0016] In this invention, the specific capacity of lithium iron phosphate cathode material can be further improved by further controlling the number-average molecular weight of polyvinylpyrrolidone.

[0017] The working principle and beneficial effects of this invention are as follows: In this invention, the specific capacity and cycle performance of lithium iron phosphate cathode material are improved by zirconium-germanium-fluorine co-doping modification. Specifically, Ge... 4+ and Zr 4+ Can co-occupy Fe 2+ Lattice sites lower the bond energy of the Fe-O bond, significantly reducing the energy barrier for lithium ion movement within the one-dimensional migration channels of the olivine lattice; F - It can replace part of the O in the crystal lattice 2- This involves creating sites for non-equivalent doping of oxygen sites, forming lithium vacancies that facilitate lithium-ion migration. The synergistic effect of these three factors increases the lithium-ion transference number, ensuring more lithium ions can rapidly participate in electrochemical reactions during charge and discharge. This improves the electrochemical performance of lithium iron phosphate cathode materials, promotes their participation in electrochemical reactions, and further enhances specific capacity. Furthermore, F... - Electronegativity ratio O 2- Larger crystals can stabilize the crystal lattice and improve the cycle life of lithium iron phosphate cathode materials. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In the following examples and comparative examples, the manufacturer of polyvinylpyrrolidone (PVP) was Gongbike New Material Technology (Shanghai) Co., Ltd. Specifically, the PVP with a number average molecular weight of 3500 was designated PVPK12, the PVP with a number average molecular weight of 5500 was designated PVPK15, the PVP with a number average molecular weight of 10100 was designated PVPK17, and the PVP with a number average molecular weight of 32000 was designated PVPK25.

[0020] Example 1 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Ge:Zr:F 1:1.05:0.0025:0.0025:0.01, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 0.26g of germanium dioxide (GeO2), 0.31g of zirconium dioxide (ZrO2), and 0.26g of lithium fluoride (LiF) were weighed. The iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride, and water were mixed, and a dispersant and glucose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content of the slurry was 50%, the mass of the dispersant was 1wt% of the slurry mass, and the mass of glucose was 15wt% of the slurry mass. The mixture was ball-milled at 300 r / min for 6 h, dried, pressed into shape, calcined at 720℃ in a nitrogen environment for 9 h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.5 μm.

[0021] Example 2 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Ge:Zr:F 1:1.05:0.0025:0.0175:0.04, weigh 150.8g of ferric phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 0.26g of germanium dioxide (GeO2), 2.16g of zirconium dioxide (ZrO2), and 1.04g of lithium fluoride (LiF). Mix the ferric phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride, and water. The mixture was combined with a dispersant and sucrose. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500 to obtain a slurry. At this point, the solid content of the slurry was 50%, the mass of the dispersant was 2 wt% of the slurry mass, and the mass of the sucrose was 20 wt% of the slurry mass. The mixture was ball-milled at 350 r / min for 6 h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8 h, and ground to obtain a lithium iron phosphate battery cathode material with a median particle size of 2.8 μm.

[0022] Example 3 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Ge:Zr:F 1:1.05:0.0025:0.0075:0.02, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 0.26g of germanium dioxide (GeO2), 0.92g of zirconium dioxide (ZrO2), and 0.52g of lithium fluoride (LiF) were weighed. The iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride, and water were mixed, and a dispersant and glucose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of glucose was 15wt% of the slurry mass. The mixture was ball-milled at 400 r / min for 5 h, dried, pressed into shape, calcined at 750℃ in a nitrogen environment for 7 h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 3 μm.

[0023] Example 4 The only difference between this embodiment and Example 2 is that the dispersant is polyaspartic acid.

[0024] Example 5 The only difference between this embodiment and Example 2 is that the dispersant is polyvinylpyrrolidone and polyaspartic acid in a mass ratio of 3:1, wherein the number average molecular weight of polyvinylpyrrolidone is 3500.

[0025] Example 6 The only difference between this embodiment and Example 2 is that the dispersant is polyvinylpyrrolidone and polyaspartic acid in a mass ratio of 3:2, wherein the number average molecular weight of polyvinylpyrrolidone is 3500.

[0026] Example 7 The only difference between this embodiment and Example 6 is that the number average molecular weight of polyvinylpyrrolidone is 5500.

[0027] Example 8 The only difference between this embodiment and Example 6 is that the number average molecular weight of polyvinylpyrrolidone is 10,100.

[0028] Example 9 The only difference between this embodiment and Example 6 is that the number average molecular weight of polyvinylpyrrolidone is 32,000.

[0029] Comparative Example 1 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Zr:F 1:1.05:0.0175:0.04, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 2.16g of zirconium dioxide (ZrO2), and 1.04g of lithium fluoride (LiF) were weighed. The iron phosphate, lithium carbonate, zirconium dioxide, lithium fluoride, and water were mixed, and a dispersant and sucrose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of the sucrose was 20wt% of the slurry mass. The mixture was ball-milled at 350r / min for 6h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.8μm.

[0030] Comparative Example 2 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Ge:F 1:1.05:0.0025:0.04, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 0.26g of germanium dioxide (GeO2), and 1.04g of lithium fluoride (LiF) were weighed. The iron phosphate, lithium carbonate, germanium dioxide, lithium fluoride, and water were mixed, and a dispersant and sucrose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of the sucrose was 20wt% of the slurry mass. The mixture was ball-milled at 350r / min for 6h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.8μm.

[0031] Comparative Example 3 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the molar ratio of Fe:Li:Ge:Zr 1:1.05:0.0025:0.0175, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), 0.26g of germanium dioxide (GeO2), and 2.16g of zirconium dioxide (ZrO2) were weighed. The iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, and water were mixed, and a dispersant and sucrose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500, and a slurry was obtained. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of the sucrose was 20wt% of the slurry mass. The mixture was ball-milled at 350 r / min for 6 h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8 h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.8 μm.

[0032] Comparative Example 4 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the Fe:Li:F molar ratio of 1:1.05:0.04, 150.8g of iron phosphate (FePO4), 38.42g of lithium carbonate (Li2CO3), and 1.04g of lithium fluoride (LiF) were weighed. The iron phosphate, lithium carbonate, lithium fluoride, and water were mixed, and a dispersant and glucose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of sucrose was 15wt% of the slurry mass. The mixture was ball-milled at 350r / min for 6h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.8μm.

[0033] Comparative Example 5 A method for preparing a lithium iron phosphate battery cathode material includes the following steps: According to the Fe:Li molar ratio of 1:1.05, 150.8g of iron phosphate (FePO4) and 38.42g of lithium carbonate (Li2CO3) were weighed. The iron phosphate, lithium carbonate and water were mixed, and a dispersant and glucose were added. The dispersant was polyvinylpyrrolidone with a number average molecular weight of 3500. At this time, the solid content in the slurry was 50%, the mass of the dispersant was 2wt% of the slurry mass, and the mass of sucrose was 15wt% of the slurry mass. The mixture was ball-milled at 350r / min for 6h, dried, pressed into shape, calcined at 730℃ in a nitrogen environment for 8h, and ground to obtain lithium iron phosphate battery cathode material with a median particle size of 2.8μm.

[0034] The lithium iron phosphate battery cathode materials prepared in Examples 1-9 and Comparative Examples 1-5 were tested respectively: Battery preparation: The positive electrode material of lithium iron phosphate batteries prepared in Examples 1-9 and Comparative Examples 1-5, the conductive agent carbon black and the binder polyvinylidene fluoride were mixed evenly at a mass ratio of 10:1:1 and coated on aluminum foil. The mixture was dried, rolled and punched to obtain a positive electrode sheet. The lithium metal sheet was used as the negative electrode, 1 mol / L LiPF6 was used as the electrolyte, and polypropylene was used as the separator. The batteries were assembled into button batteries. The specific capacity of the button batteries prepared in Examples 1-9 and Comparative Examples 1-3 at the first charge and discharge at 1C and the specific capacity of the button batteries prepared in Examples 1-3 and Comparative Examples 1-5 after 50 cycles were tested in the voltage range of 2.4-4.0V. The results are shown in Tables 1 and 2.

[0035] Table 1. Specific capacity test results of lithium iron phosphate cathode materials prepared in Examples 1-9 and Comparative Examples 1-5

[0036] Table 2. Cyclic performance test results of lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-5

[0037] By comparing the data of Examples 1-3 and Comparative Examples 1-5 in Tables 1 and 2, the lithium iron phosphate cathode materials prepared by adding zirconium dioxide, germanium dioxide and lithium fluoride in Examples 1-3 have a larger specific capacity at 1C initial charge-discharge and a greater retention rate of specific capacity after 50 1C cycles than those in Comparative Examples 1-5. This indicates that by modifying the lithium iron phosphate cathode material with zirconium, germanium and fluorine co-doping, the specific capacity and cycle performance of the lithium iron phosphate cathode material can be improved.

[0038] By comparing the data of Examples 2 and 4-9 in Table 1, it was found that the lithium iron phosphate cathode materials prepared in Examples 5 and 6, by adding polyvinylpyrrolidone and polyaspartic acid as dispersants, had a larger specific capacity at 1C during the first charge-discharge than those in Examples 2 and 4. This indicates that the specific capacity of lithium iron phosphate cathode materials can be improved by using polyvinylpyrrolidone and polyaspartic acid in combination. By comparing the data of Examples 6-9, it was found that the specific capacity of lithium iron phosphate cathode materials in Examples 7 and 8 could be further improved by further adjusting the number average molecular weight of polyvinylpyrrolidone to 5500-10100.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium iron phosphate battery cathode material, characterized in that, Includes the following steps: Iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, lithium fluoride and water are mixed, and a dispersant and a carbon source are added to obtain a slurry. The slurry is then ball-milled, dried, pressed into shape, calcined, and ground to obtain the lithium iron phosphate battery cathode material.

2. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The molar ratio of Fe:Li:Ge:Zr:F in the iron phosphate, lithium carbonate, germanium dioxide, zirconium dioxide, and lithium fluoride is 1:1.05:0.0025:0.0025~0.0175:0.01~0.

04.

3. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The rotational speed of the ball mill is 300~400 r / min; The ball milling time is 5-7 hours.

4. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The calcination is carried out in an inert gas; The roasting temperature is 720~750℃; The roasting time is 7-9 hours.

5. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The median particle size of the lithium iron phosphate battery cathode material is 2.5~3μm.

6. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The dispersant is polyvinylpyrrolidone and / or polyaspartic acid.

7. The method for preparing a lithium iron phosphate battery cathode material according to claim 6, characterized in that, When the dispersant is polyvinylpyrrolidone and polyaspartic acid, the mass ratio of polyvinylpyrrolidone and polyaspartic acid is 3:1~2.

8. The method for preparing a lithium iron phosphate battery cathode material according to claim 7, characterized in that, The number-average molecular weight of the polyvinylpyrrolidone is 5500~10100.

9. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The carbon source includes glucose or sucrose.

10. The method for preparing a lithium iron phosphate battery cathode material according to claim 1, characterized in that, The mass of the dispersant is 1 wt% to 2 wt% of the mass of the slurry; The mass of the carbon source is 15wt% to 20wt% of the mass of the slurry.

Images