Preparation method of lithium iron phosphate positive pole piece and lithium iron phosphate positive pole piece
By mixing the conductive agent with the pore-forming agent to fix it into pore-forming particles, and pores are generated by decomposition of the pore-forming agent during the drying process, the problem of poor conductivity of the cathode material of the lithium iron phosphate battery is solved, and the effective dispersion of the conductive agent and the increase of the energy density of the electrode is achieved.
Patent Information
- Application Number
- CN202410702328.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-02
- Publication Date
- 2025-05-30
AI Technical Summary
The positive electrode materials of existing lithium iron phosphate batteries have poor conductivity, especially the lithium iron phosphate material after adding manganese elements is an insulator, which leads to limited application in batteries. At the same time, commonly used conductive agents such as carbon black, graphene and carbon nanotubes are prone to agglomeration during the pulping process and are difficult to effectively disperse, affecting the energy density of the electrode.
By mixing the conductive agent with the pore-forming agent to fix it into pore-forming particles, and mixing it with the lithium iron phosphate positive electrode material to form a positive electrode slurry. During the drying process, gas is generated by decomposition of the pore-forming agent, pores are formed and the conductive agent is further dispersed, thereby forming a conductive network and improving the conductivity of the electrode sheet.
This method effectively solves the problem of agglomeration of conductive agents during pulping, reduces the use of dispersants, increases the proportion and energy density of the battery active ingredients, and improves the rate performance of lithium iron phosphate positive electrode sheets.
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Figure BDA0004871423860000071
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of batteries, and particularly to a method for preparing a lithium iron phosphate positive electrode sheet and a lithium iron phosphate positive electrode sheet. Background Art
[0002] With the large-scale popularization of electric vehicles, the safety performance of electric vehicles has attracted more and more attention from consumers. Therefore, the sales volume of electric vehicles equipped with lithium iron phosphate batteries has increased rapidly. The positive electrode material of lithium iron phosphate batteries is LiFePO4, abbreviated as LFP, which is a positive electrode material with an olivine structure and can reversibly insert and extract lithium ions. Compared with ternary lithium batteries, its raw material sources are wide and cheap, and it does not contain heavy metal elements. The lithium iron phosphate material has a good cycle life because its lattice stability is good, and the insertion and extraction of lithium ions do not significantly affect the lattice structure, and it can be charged and discharged more than 2000 times. However, as a semiconductor material, lithium iron phosphate has poor conductivity, especially lithium iron manganese phosphate material added with manganese element, which belongs to an insulator. Therefore, improving the conductivity of lithium iron phosphate is an important improvement direction for lithium iron phosphate batteries.
[0003] Generally, the conductivity of lithium iron phosphate can be improved by adding a conductive agent or preparing nanoscale lithium iron phosphate. However, the cost of preparing nanoscale lithium iron phosphate is too high, and most conductive agents are prone to agglomeration problems during the pulping process, such as conventional carbon black, graphene, carbon nanotubes, etc. Usually, a large amount of addition or a dispersant is required to meet the use requirements, which will reduce the proportion of active materials and affect the volume energy density of the electrode. Summary of the Invention
[0004] Based on this, it is necessary to provide a method for preparing a lithium iron phosphate positive electrode sheet and a lithium iron phosphate positive electrode sheet.
[0005] The first aspect of the present invention provides a method for preparing a lithium iron phosphate positive electrode sheet, comprising the following steps:
[0006] Mix and fix a conductive agent and a pore-forming agent to form pore-forming particles.
[0007] Mix the pore-forming particles with a lithium iron phosphate positive electrode material and a solvent to form a positive electrode slurry.
[0008] Coat, dry and roll the positive electrode slurry.
[0009] That is, a lithium iron phosphate positive electrode sheet is obtained.
[0010] In the present invention, a conductive agent and a pore-forming agent are mixed and fixed into pore-forming particles. During the drying process, the pore-forming agent decomposes to further disperse the conductive agent, thus eliminating the problem of easy agglomeration of the conductive agent during the pulp-making process. As a result, the use of a dispersant is reduced, the proportion of active components in the battery is increased, and the energy density is improved. The gas generated by the decomposition of the pore-forming agent forms pores in the active material layer of the electrode sheet, which may cause the distance between the positive electrode material particles to increase and thus may break the contact. However, since the conductive agent is also dispersed in the pores during the pore-forming process, a conductive network can be formed between the positive electrode material particles to improve the conductivity of the electrode sheet. The pores can also promote the infiltration of the electrolyte and improve the lithium-ion transport efficiency. Therefore, the lithium iron phosphate positive electrode sheet prepared by the above preparation method has excellent rate performance and energy density.
[0011] Further, the conductive agent is at least one of carbon black, carbon nanotubes, and graphene. These three materials all have a large specific surface area and a small particle size, and are prone to agglomeration. Carbon nanotubes and graphene have better conductivity, but their agglomeration problems limit their applications. In the present invention, the problem of difficult dispersion of these conductive agents in the slurry can be solved by dispersing the conductive agent during the drying process.
[0012] Further, the particle size of the pore-forming particles is 0.5 - 2 μm. The particle size of the pore-forming particles should not be too large, otherwise, too large pores may be formed, affecting the stability of the positive electrode material layer; the particle size of the pore-forming particles should not be too small, otherwise, they are prone to agglomeration themselves, resulting in difficulty in uniformly dispersing them in the positive electrode slurry.
[0013] Further, the mass ratio of the conductive agent to the pore-forming agent in the pore-forming particles is 1:(1 - 5). If the proportion of the pore-forming agent is too low, it is difficult to achieve uniform dispersion of the conductive agent; if the proportion of the conductive agent is too low, more pore-forming agent needs to be used when the amount of the conductive agent remains unchanged, resulting in too many pores and affecting the structural stability of the electrode sheet.
[0014] Further, based on the mass of the lithium iron phosphate material, the mass fraction of the pore-forming particles is 2 - 10%. The proportion of the pore-forming particles should not be too large, otherwise, too high a porosity will be formed, affecting the structure of the electrode sheet; the proportion of the pore-forming particles is too small, which will further limit the amount of the conductive agent used and it is difficult to significantly improve the conductivity of the electrode sheet.
[0015] Further, the pore-forming agent is a carbonate and / or a bicarbonate. Carbonates and bicarbonates have poor stability and are prone to decompose to generate gas during the drying process. Further, the pore-forming agent is sodium bicarbonate. Sodium bicarbonate is weakly alkaline and will not cause the pH of the slurry to rise. At the same time, its decomposition product sodium carbonate can increase the pH of the active material layer and neutralize HF generated during the cycling process.
[0016] Further, the drying step includes: a pre-drying step, a rapid decomposition step, and a final drying step. Further, the temperature in the rapid decomposition step is ≥150°C. Further, the heating method in the drying step is microwave heating. Further, the heating time in the rapid decomposition step is 0.5 - 2 h. Through the pre-drying step, the excess moisture in the battery is removed, causing the slurry to transform into a dense solid-liquid mixture. At this time, most of the moisture has been removed, the particles are in contact with each other to form a fixed framework, and the volume of the slurry layer no longer shrinks. Then, through the rapid decomposition step, the pore-forming agent can be rapidly decomposed, a large number of bubbles are formed on the surface of the pore-forming particles, and the conductive agent is pushed to disperse on the particle surface. In the final drying step, the conductive agent dispersed on the particle surface contacts multiple cathode material particles or conductive agents during the shrinkage of the solvent to form a conductive network.
[0017] In the second aspect of the present invention, a lithium iron phosphate cathode plate is provided, which is prepared by the above preparation method and has good rate performance and energy density. Detailed implementation manners
[0018] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of this application more thorough and comprehensive.
[0019] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.
[0021] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.
[0022] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.
[0023] In this application, the percentage content involved, unless otherwise specified, refers to the mass percentage for solid-liquid mixing and solid-solid mixing, and refers to the volume percentage for liquid-liquid mixing.
[0024] In this application, the percentage concentration involved, unless otherwise specified, refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding the component.
[0025] The temperature parameter in this application, unless otherwise specified, allows both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.
[0026] The "particles" mentioned in this application, or substances with a defined particle size distribution, do not necessarily have a spherical shape and may be irregular. They can be primary particles or secondary particles. The particle size of irregular particles is calculated as the average of their maximum diameter and minimum diameter.
[0027] Example 1
[0028] The lithium iron phosphate cathode material was prepared by a conventional solid-phase method. The conductive agent was selected as carbon black, and the pore-forming agent was sodium bicarbonate. The conductive agent and the pore-forming agent were mixed and granulated according to a mass ratio of 1:4 to form pore-forming particles with a size of 0.5 μm. The cathode material, binder PVDF, and pore-forming particles were mixed according to a mass ratio of 8:1:0.8, and an appropriate amount of NMP was added to make a slurry. Then, it was coated on an aluminum foil and dried using a microwave drying device: the pre-drying step was carried out at 80 °C for 10 h, then the temperature was raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step was cooled to 80 °C for 12 h. After rolling, the lithium iron phosphate cathode sheet could be obtained.
[0029] Example 2
[0030] Using the lithium iron phosphate cathode material prepared in Example 1, carbon nanotubes are selected as the conductive agent, and sodium bicarbonate is used as the pore-forming agent. The conductive agent and the pore-forming agent are mixed and granulated according to a mass ratio of 1:4 to form pore-forming particles with a size of 0.5 μm. The cathode material, binder PVDF, and pore-forming particles are mixed according to a mass ratio of 8:1:0.8, and an appropriate amount of NMP is added to make a slurry, which is then coated on an aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is carried out at 80 °C for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0031] Example 3
[0032] Using the lithium iron phosphate cathode material prepared in Example 1, carbon black is selected as the conductive agent, and sodium bicarbonate is used as the pore-forming agent. The conductive agent and the pore-forming agent are mixed and granulated according to a mass ratio of 1:4 to form pore-forming particles with a size of 1 μm. The cathode material, binder PVDF, and pore-forming particles are mixed according to a mass ratio of 8:1:0.8, and an appropriate amount of NMP is added to make a slurry, which is then coated on an aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is carried out at 80 °C for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0033] Example 4
[0034] Using the lithium iron phosphate cathode material prepared in Example 1, carbon black is selected as the conductive agent, and sodium bicarbonate is used as the pore-forming agent. The conductive agent and the pore-forming agent are mixed and granulated according to a mass ratio of 1:0.5 to form pore-forming particles with a size of 0.5 μm. The cathode material, binder PVDF, and pore-forming particles are mixed according to a mass ratio of 8:1:0.8, and an appropriate amount of NMP is added to make a slurry, which is then coated on an aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is carried out at 80 °C for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0035] Example 5
[0036] Using the lithium iron phosphate cathode material prepared in Example 1, carbon fiber tubes are selected as the conductive agent, and sodium bicarbonate is used as the pore-forming agent. The conductive agent and the pore-forming agent are mixed and granulated according to a mass ratio of 1:4 to form pore-forming particles with a size of 0.5 μm. The cathode material, binder PVDF, and pore-forming particles are mixed according to a mass ratio of 8:1:0.25, and an appropriate amount of NMP is added to make a slurry, which is then coated on aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is cooled to 80 °C and dried for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0037] Comparative Example 1
[0038] Using the lithium iron phosphate cathode material prepared in Example 1, carbon black is selected as the conductive agent. The cathode material, binder PVDF, and conductive agent are mixed according to a mass ratio of 8:1:0.16, and an appropriate amount of NMP is added to make a slurry, which is then coated on aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is cooled to 80 °C and dried for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0039] Comparative Example 2
[0040] Using the lithium iron phosphate cathode material prepared in Example 1, carbon black is selected as the conductive agent, and sodium bicarbonate is used as the pore-forming agent. The cathode material, binder PVDF, conductive agent, and pore-forming agent are mixed according to a mass ratio of 8:1:0.16:0.64, and an appropriate amount of NMP is added to make a slurry, which is then coated on aluminum foil and dried using a microwave drying device: the pre-drying step is carried out at 80 °C for 10 h, then the temperature is raised to 150 °C for the rapid decomposition step for 1 h, and the final drying step is cooled to 80 °C and dried for 12 h. After rolling, the lithium iron phosphate cathode sheet can be obtained.
[0041] The lithium iron phosphate cathode sheets prepared in Examples 1-5 and Comparative Examples 1-2 are respectively assembled into 2025 button cells, and the electrochemical performance tests are carried out at 2.5 - 4.2 V to obtain their charge-discharge capacity and rate performance data.
[0042] Table 1
[0043]
[0044] According to the data in Table 1, the results of Examples 1-5 are all better than those of Comparative Example 1. This is because in the present invention, the conductive agent and the pore-forming agent are pre-mixed and fixed into pore-forming particles, and then the pore-forming particles are mixed and dispersed in the cathode material with the cathode material. And during the drying process, through the rapid decomposition step, the pore-forming agent decomposes rapidly, while generating pores, the dispersion of the conductive agent is completed, so that it is not necessary to use a large amount of dispersant to disperse the conductive agent during the pulping process, while ensuring the rate performance, the energy density is improved. The rate performance and specific capacity of Examples 1-5 are higher than those of Comparative Example 2 because without pre-mixing the conductive agent and the pore-forming agent, the gas generated by the decomposition of the pore-forming agent is difficult to disperse the conductive agent. The rate performance of Example 3 is lower than that of Example 1 because it uses pore-forming particles with a larger particle size, and the pore-forming particles are poorly dispersed in the slurry. Example 4 uses a lower proportion of the pore-forming agent, so the dispersion effect generated by its decomposition is weak and the rate performance is poor. Example 5 uses a lower content of the conductive agent, but due to the dispersion effect of the pore-forming particles, the carbon fiber tube can fully exert its performance, so it still has high performance.
[0045] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope described in this specification.
[0046] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.
Claims
1. A method for preparing a lithium iron phosphate positive electrode sheet, characterized in that: The following steps are involved: The conductive agent and the pore-forming agent are mixed and fixed into pore-forming particles; Mixing the pore-forming particles with a lithium iron phosphate positive electrode material and a solvent to form a positive electrode slurry; The positive electrode slurry is coated, dried and roll-pressed; That is, the lithium iron phosphate positive electrode plate is obtained.
2. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The conductive agent is at least one of carbon black, carbon nanotubes and graphene.
3. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The particle size of the pore-forming particles is 0.5-2 μm.
4. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The mass ratio of the conductive agent to the pore-forming agent in the pore-forming particles is 1:(1-5).
5. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The mass fraction of the pore-forming particles is 2-10% based on the mass of the lithium iron phosphate material.
6. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The pore former is carbonate and / or bicarbonate.
7. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 1, characterized in that: The drying step comprises: a preliminary drying step, a rapid decomposition step and a final drying step.
8. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 5, characterized in that: The temperature of the rapid decomposition step is ≥150°C.
9. The method for preparing a lithium iron phosphate positive electrode sheet according to claim 5, characterized in that: The heating method of the drying step is microwave heating.
10. A lithium iron phosphate positive electrode plate, characterized in that: The method for preparing a lithium iron phosphate positive electrode sheet according to any one of claims 1 to 9 is used for preparation.