A lithium iron phosphate thick electrode having a porous structure and a method of manufacturing the same

Abstract

The application discloses a kind of porous structure lithium iron phosphate thick electrode and its preparation method, comprising the following steps: (1) polyvinylidene fluoride and polymer are dissolved in first solvent to obtain component 1;(2) the positive electrode material powder is mixed with conductive carbon and then put into a ball mill tank, and ball milling is obtained component 2;(3) component 1 is mixed with component 2, and then stirred uniformly to obtain positive electrode slurry;(4) the positive electrode slurry is evenly coated on aluminum foil, dried to obtain thick electrode sheet;(5) soak in a beaker filled with ethanol to remove polymer components, and dry to obtain porous lithium iron phosphate thick electrode.The full battery constructed by the porous lithium iron phosphate thick electrode has smaller interface impedance, and the prepared full battery can achieve higher specific capacity and rate performance, and at 1.0 C, 200 cycles of cycle life are realized, which shows that the porous structure inside the thick electrode can provide a fast transport channel for lithium ions, improve the ion transport dynamics inside the electrode, and thus achieve better lithium ion battery performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a thick lithium iron phosphate electrode with a porous structure and its preparation method. Background Technology

[0002] With the continued expansion of the portable electronics, grid-scale energy storage systems, and electric vehicle markets, lithium-ion battery technology is facing multiple performance demands: higher energy density, stronger power output, and longer cycle life. Typically, high-load electrodes (i.e., thick electrodes; ≥ 12 mg cm⁻¹) are required. -2 Thick electrodes have become a crucial design strategy for achieving high-energy-density batteries. Their core lies in increasing capacity per unit area and effectively reducing the mass proportion of inactive materials such as current collectors, separators, and encapsulation components at the battery level. However, as electrode thickness increases, its ionic conductivity decreases, leading to severe polarization in the thickness direction, which significantly hinders the practical application of thick electrodes. Therefore, ensuring a uniform reaction interface and continuous electron / ion pathways under high loads has become a key challenge for the industrialization of high-energy-density lithium-ion batteries.

[0003] Studies have shown that introducing an appropriate amount of carbon nanotubes (CNTs) during the fabrication of thick electrodes helps to construct a continuous three-dimensional conductive network, thereby effectively alleviating the problem of ion and electron transport imbalance within the thick electrode. However, adding CNTs reduces the content of active material per unit volume / unit mass, which contradicts the design intention of high energy density in thick electrodes. Furthermore, CNTs are prone to entanglement and aggregation, leading to uneven local current density distribution in thick electrodes, which in turn induces side reactions and continuously consumes electrolyte, ultimately causing capacity decay during long-term cycling. In contrast, constructing a porous structure within the thick electrode provides a rapid transport channel for lithium ions, effectively shortening the ion diffusion path, improving ion transport kinetics within the electrode, and enhancing electrode reaction uniformity and active material utilization. This provides an important research approach and development direction for optimizing lithium-ion battery performance. Summary of the Invention

[0004] Based on this, regarding existing thick electrode materials, how can we ensure the effective transport of ions and electrons inside the thick electrode while avoiding the technical problems of reduced active material content and increased local side reactions? The purpose of this invention is to provide a thick lithium iron phosphate electrode with a porous structure, thereby overcoming the aforementioned technical problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a thick lithium iron phosphate electrode with a porous structure, characterized by comprising the following steps: (1) Polyvinylidene fluoride and polymer are dissolved in a first solvent in proportion and stirred continuously at room temperature to obtain component 1; the polymer is at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, and ethyl acrylate. (2) After mixing the positive electrode material powder with conductive carbon in a certain proportion, put the mixture into a ball mill jar and ball mill it evenly to obtain component 2; (3) After mixing component 1 and component 2, the mixture is stirred continuously at room temperature to obtain a positive electrode slurry; (4) Use a scraper to evenly coat the positive electrode slurry onto the aluminum foil, then place it in a vacuum oven to dry and take it out to obtain a thick electrode sheet; (5) The thick electrode sheet is fully immersed in a beaker filled with ethanol to remove the polymer components, and then placed in a forced-air drying oven to obtain a thick lithium iron phosphate electrode with a porous structure.

[0006] Preferably, the first solvent is selected from at least one of N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and ethylene diether.

[0007] Preferably, the mass ratio of polyvinylidene fluoride to polymer is 1:0.5-3; the stirring time is 30-60 min; and the molecular weight of polyvinylidene fluoride is M. w = 400,000 g mol -1 .

[0008] Preferably, the conductive carbon is selected from at least one of carbon black, Super P, and Ketjen black; the cathode material is at least one of lithium iron phosphate, lithium cobalt oxide, and nickel-cobalt-manganese ternary materials; the mass ratio of cathode material, conductive carbon, and polyvinylidene fluoride is 80:10:10 or 90:5:5; and the ball milling time is 30 to 60 minutes.

[0009] Preferably, the stirring time at room temperature in step (3) is 8 to 12 hours; and the soaking time in step (5) is 24 to 72 hours.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention innovatively uses a polymer as a pore-forming agent. The selected polymer is well soluble in the first solvent. After being uniformly stirred with PVDF, a uniform component 1 can be obtained. When component 1 and component 2 are mixed and stirred, the polymer can be well dispersed in the positive electrode slurry. When the prepared thick electrode is immersed in ethanol, the polymer can be completely dissolved in ethanol without damaging the overall structure of the thick electrode. At the same time, it leaves a rich porous structure in the thick electrode, which is conducive to the full penetration of the electrolyte into the electrode and ensures the rapid conduction of lithium ions in the thick electrode.

[0011] (2) The porous lithium iron phosphate thick electrode of the present invention has a smaller electrolyte contact angle than conventional thick electrodes, indicating that the porous lithium iron phosphate thick electrode prepared by the present invention can achieve better electrolyte wetting. Therefore, the full cell constructed using the porous lithium iron phosphate thick electrode of the present invention has a smaller interfacial impedance. The full cell based on the porous lithium iron phosphate thick electrode can achieve higher specific capacity and rate performance, and achieves 200 cycles at 1.0 C. This indicates that the porous structure inside the thick electrode can provide a fast transport channel for lithium ions, improve the ion transport kinetics inside the electrode, and thus achieve better lithium-ion battery performance. Attached Figure Description

[0012] Figure 1 The images are scanning electron microscope (SEM) images of Example 1 and Comparative Example 1 (left image is Example 1, right image is Comparative Example 1). Figure 2 The diagram shows the contact angle of the electrolyte in Examples 1-3 and Comparative Example 1 (the top left diagram is Example 1, the top right diagram is Example 2, the bottom left diagram is Example 3, and the bottom right diagram is Comparative Example 1). Figure 3 The diagrams show the interface impedance of Examples 1-3 and Comparative Example 1 (the top left diagram is Example 1, the top right diagram is Example 2, the bottom left diagram is Example 3, and the bottom right diagram is Comparative Example 1). Figure 4 The rate performance of lithium iron phosphate batteries in Example 1 and Comparative Example 1 is shown (top left: Example 1, top right: Example 2, bottom left: Example 3, bottom right: Comparative Example 1). Figure 5 The graphs show the cycle performance of lithium iron phosphate batteries in Example 1 and Comparative Example 1 at 1.0 C (top left is Example 1, top right is Example 2, bottom left is Example 3, and bottom right is Comparative Example 1). Detailed Implementation

[0013] The molecular weight of "PVDF" in this invention is M. w = 400,000 g mol -1 .

[0014] In this invention, "porous thick electrode" refers to, for example, Figure 1 The high-load cathode material shown has a rich porous structure.

[0015] Example 1: Fabrication of porous thick electrodes 100 mg of PVDF and 100 mg of polyethylene glycol were mixed in 5 mL of N,N-dimethylformamide at a ratio of 1:1 and stirred at room temperature for 60 min to obtain a homogeneous polymer slurry.

[0016] Lithium iron phosphate (0.8 g) and Ketjen black (0.1 g) were ball-milled for 30 min, and then stirred with a polymer slurry for 8 h to prepare a slurry. The slurry was coated onto aluminum foil using a 400 μm doctor blade and vacuum-dried at 80 °C for 12 h. Subsequently, the electrode was immersed in anhydrous ethanol for 24 h to remove polyethylene glycol, and then dried by forced air for 8 h to obtain a lithium iron phosphate loading of ~18 mg / cm³. -2 Porous thick electrode.

[0017] Example 2: Fabrication of porous thick electrodes 100 mg of PVDF and 100 mg of polyvinylpyrrolidone were mixed in 5 mL of N,N-dimethylformamide at a ratio of 1:1 and stirred at room temperature for 60 min to obtain a homogeneous polymer slurry.

[0018] Lithium iron phosphate (0.8 g) and Ketjen black (0.1 g) were ball-milled and mixed for 30 min, then stirred with a polymer slurry for 8 h to prepare a slurry. The slurry was coated onto aluminum foil using a 400 μm doctor blade and vacuum-dried at 80 °C for 12 h. Subsequently, the electrode was immersed in anhydrous ethanol for 24 h to remove polyvinylpyrrolidone, and then dried by forced air for 8 h to obtain a lithium iron phosphate loading of ~18 mg / cm³. -2 Porous thick electrode.

[0019] Example 3: Fabrication of porous thick electrodes 100 mg of PVDF and 100 mg of polyvinyl alcohol were mixed in 5 mL of N,N-dimethylformamide at a ratio of 1:1 and stirred at room temperature for 60 min to obtain a homogeneous polymer slurry.

[0020] Lithium iron phosphate (0.8 g) and Ketjen black (0.1 g) were ball-milled and mixed for 30 min, then stirred with a polymer slurry for 8 h to prepare a slurry. The slurry was coated onto aluminum foil using a 400 μm doctor blade and vacuum-dried at 80 °C for 12 h. Subsequently, the electrode was immersed in anhydrous ethanol for 24 h to remove polyvinyl alcohol, and then dried by forced air for 8 h to obtain a lithium iron phosphate loading of ~18 mg / cm³. -2 Porous thick electrode.

[0021] Comparative Example 1: Fabrication of Conventional Thick Electrodes 100 mg of PVDF was mixed in 5 mL of N,N-dimethylformamide and stirred at room temperature for 60 min to obtain a homogeneous polymer slurry.

[0022] Lithium iron phosphate (0.8 g) and Ketjen black (0.1 g) were ball-milled and mixed for 30 min, then stirred with a polymer slurry for 8 h to prepare a slurry. The slurry was coated onto aluminum foil using a 400 μm doctor blade and vacuum-dried at 80 °C for 12 h. Subsequently, the electrode was immersed in anhydrous ethanol for 24 h and then dried by forced air for 8 h to obtain a lithium iron phosphate loading of ~18 mg / cm³. -2 Porous thick electrode.

[0023] Performance testing: The electrolyte contact angle and interfacial impedance of the thick electrode were tested.

[0024] The rate performance and cycle performance of lithium iron phosphate batteries using thick electrodes were tested.

[0025] The electrolyte contact angle and interfacial impedance of the obtained thick electrode are shown in Table 1.

[0026] Table 1

[0027] The porous thick electrodes prepared in Example 1 and Comparative Example 1 were assembled into lithium iron phosphate batteries, and their rate performance is shown in Table 2.

[0028] Table 2

[0029]

[0030] Conclusion: The data in Table 1 show that, compared with Comparative Example 1, the thick electrodes prepared in Examples 1-3 have smaller electrolyte contact angles, indicating that porous thick electrodes can ensure better electrolyte wettability.

[0031] Figure 1 The images shown are scanning electron microscope images of Example 1 and Comparative Example 1. It can be seen that after the thick electrode is pore-formed, a clear pore structure can be observed, which can enhance the effective contact between the thick electrode and the electrolyte.

[0032] Figure 2 This is a diagram showing the electrolyte contact angle of a porous thick electrode.

[0033] Figure 3 The impedance diagrams for Examples 1-3 and Comparative Example 1 show that Examples 1-3 have lower impedance compared to Comparative Example 1.

[0034] Figure 4The table shows the rate performance and charge / discharge curves of Examples 1-3 and Comparative Example 1. Combined with the data in Table 1, it can be seen that Examples 1 and 2 have higher discharge specific capacity, indicating that the porous structure is beneficial to the electrolyte dynamics, which can enhance electrode kinetics, improve the utilization rate of lithium iron phosphate active material, and achieve higher battery specific capacity.

[0035] Figure 5 The graphs show the cycling performance of Examples 1-3 and Comparative Example 1 at 1.0 C. It can be seen that Example 1 has a higher specific capacity and more stable cycling performance, indicating that lithium iron phosphate electrodes with a certain porous structure can achieve excellent battery cycling stability.

Claims

1. A thick lithium iron phosphate electrode with a porous structure, characterized in that... It is prepared by the following method: (1) Polyvinylidene fluoride and polymer are dissolved in a first solvent in proportion and stirred continuously at room temperature to obtain component 1; the polymer is at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polymethyl acrylate, polymethyl methacrylate, and ethyl acrylate. (2) After mixing the positive electrode material powder with conductive carbon in a certain proportion, put the mixture into a ball mill jar and ball mill it evenly to obtain component 2; (3) After mixing component 1 and component 2, the mixture is stirred continuously at room temperature to obtain a positive electrode slurry; (4) Use a scraper to evenly coat the positive electrode slurry onto the aluminum foil, then place it in a vacuum oven to dry and take it out to obtain a thick electrode sheet; (5) The thick electrode sheet is fully immersed in a beaker filled with ethanol to remove the polymer components, and then placed in a forced-air drying oven to obtain a thick lithium iron phosphate electrode with a porous structure. The mass ratio of polyvinylidene fluoride to polymer is 1:0.5-3; The stirring time in step (1) is 30–60 min; the molecular weight of the polyvinylidene fluoride is M. w = 400,000g mol -1 ; The soaking time in step (5) is 24 to 72 hours.

2. The thick lithium iron phosphate electrode with a porous structure according to claim 1, characterized in that... The first solvent is selected from at least one of N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and ethylene diether.

3. The thick lithium iron phosphate electrode with a porous structure according to claim 1, characterized in that... The conductive carbon is selected from at least one of carbon black, Super P, and Ketjen black; the positive electrode material is lithium iron phosphate; the mass ratio of the positive electrode material to the conductive carbon to the polyvinylidene fluoride is 80:10:10 or 90:5:5; the ball milling time is 30 to 60 minutes.

4. The thick lithium iron phosphate electrode with a porous structure according to claim 1, characterized in that... The stirring time at room temperature in step (3) is 8 to 12 hours.

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