Rolling method of lithium iron phosphate pole piece and application thereof
By measuring the porosity of lithium iron phosphate electrodes and selecting an appropriate rolling process based on the results, the problem of inconsistent compaction density after rolling of lithium iron phosphate electrodes was solved, thus achieving accuracy and comparability in lithium-ion battery testing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 安徽得壹能源科技有限公司
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-19
AI Technical Summary
In the existing technology, the rolling process of lithium iron phosphate electrode sheets cannot achieve a consistent compaction density for different materials after rolling, which affects the accuracy and comparability of lithium-ion battery testing.
By measuring the porosity of unrolled lithium iron phosphate electrode sheets after coating and drying, and comparing the porosity with a preset threshold, different rolling processes were used to process materials that are easy to roll and difficult to roll. Rolling pressures of 70~90kN and 80~100kN were used respectively, and single-pass and double-pass rolling methods were combined to ensure that the electrode sheets achieve a consistent compaction density.
This method achieves a more consistent electrode compaction density after rolling of different lithium iron phosphate materials, eliminating the interference of rolling process differences on electrical performance test results and improving the accuracy and comparability of the tests.
Smart Images
Figure CN122246044A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a rolling method for lithium iron phosphate electrodes and its application. Background Technology
[0002] In lithium-ion battery material development, button cell testing is a crucial method for evaluating the performance of lithium iron phosphate batteries. The electrode rolling process directly affects the compaction density and pore structure of the electrode, thus influencing the test results. To ensure the comparability of test results for different materials, all electrodes must be at the same compaction density level. In existing technologies, when rolling button cells for different lithium iron phosphate materials, uniform rolling parameters are typically used, resulting in inconsistent electrode compaction densities and making it difficult to distinguish the source of capacity differences. Other methods set rolling pressures based on differences in powder compaction density, but powder compaction density only reflects the ideal particle packing state and cannot characterize the actual electrode structure after slurry coating. Even materials with similar powder compaction densities may still exhibit significant differences in electrode compaction density after rolling. All of these methods fail to achieve consistent electrode compaction densities for different materials after rolling, affecting the accuracy and comparability of the tests. Summary of the Invention
[0003] In view of this, the present invention provides a rolling method for lithium iron phosphate electrodes and its application, which solves the problem that it is difficult to obtain consistent electrode compaction density after rolling of different lithium iron phosphate materials.
[0004] In a first aspect, the present invention provides a method for rolling lithium iron phosphate electrode sheets, comprising the following steps: The porosity of lithium iron phosphate electrodes that were coated and dried but not rolled was measured to obtain the electrode porosity. The porosity of the electrode is compared with a preset threshold. When the porosity of the electrode sheet is less than the preset threshold, the electrode sheet is rolled using a first rolling process. When the porosity of the electrode sheet is greater than the preset threshold, the electrode sheet is rolled using a second rolling process.
[0005] Preferably, the porosity determination is performed using the mercury porosimetry method.
[0006] Furthermore, during the mercury intrusion porosimetry test, the upper limit of the test pressure is 20,000 to 30,000 psi.
[0007] Preferably, the preset threshold is 34-37%.
[0008] Preferably, the first rolling process includes: performing a single rolling process with a rolling pressure of 70~90kN; the second rolling process includes: performing a first-direction rolling process with a rolling pressure of 80~100kN, and then performing a second rolling process on the electrode sheet along a second direction perpendicular to the first direction.
[0009] Furthermore, in the first rolling process, the roller feed rate is 10~15mm / s; in the second rolling process, the roller feed rate is 3~8mm / s.
[0010] Preferably, the preparation process of the coated and dried lithium iron phosphate electrode sheet without rolling is as follows: Lithium iron phosphate is mixed with conductive agents and binders to form a slurry; The slurry is applied onto the current collector; After drying, the coated and dried lithium iron phosphate electrode sheet is obtained.
[0011] Furthermore, the solid content of the slurry is 28% to 35%.
[0012] Furthermore, the thickness of the slurry coating is 100~300μm.
[0013] Secondly, the present invention provides an application of the above-mentioned rolling method for lithium iron phosphate electrodes for comparative evaluation of the electrical performance of different lithium iron phosphate materials in button battery testing.
[0014] Compared with the prior art, the present invention has achieved the following beneficial effects: This invention measures the porosity of lithium iron phosphate (LFP) electrodes after coating and drying but before rolling. Based on a comparison of the porosity with a preset threshold, different rolling processes are selected. This allows electrodes with porosities below the threshold (easy to roll) and those above the threshold (difficult to roll) to achieve a more consistent compaction density after appropriate processing. This method abandons the conventional approach of using powder compaction density as the basis for rolling process design. Instead, it directly classifies the electrodes based on their actual structural state after slurry coating, effectively overcoming the problem of significant differences in compaction density after rolling for materials with similar powder compaction densities but different actual processing characteristics. This ensures that different LFP materials are on the same compaction benchmark in coin cell testing, eliminating the interference of rolling process differences on electrical performance test results and improving the accuracy and comparability of the tests. Attached Figure Description
[0015] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.
[0016] Figure 1 This is a schematic flowchart of the rolling method according to Embodiment 1 of the present invention; Figure 2 These are scanning electron microscope images of the A-electrode sheet-R-s1 obtained by rolling in Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the B-electrode sheet-R-s1 obtained by rolling in Embodiment 1 of the present invention. Detailed Implementation
[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0018] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in this invention, are intended to cover non-exclusive inclusion. For example, a method step or electrode structure that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such method steps or electrode structures.
[0019] In this invention, when a parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “3~8” is disclosed, the described range should be interpreted as including ranges “3~6”, “3~7”, “3~5”, “3~5 and 6~8”, “3~7 and 8”, etc. When numerical ranges are described in this invention, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.
[0020] In the research and performance evaluation of lithium iron phosphate (LFP) materials, powder compaction density is a commonly referenced processing performance indicator in the industry. It reflects the ideal packing state of LFP dry powder under rigid pressure and is only related to limited factors such as particle size distribution and particle strength. However, in the actual preparation of lithium-ion battery electrodes, LFP particles need to undergo multiple processes such as liquid-phase slurry preparation, coating, and drying. The particle packing behavior is significantly affected by multiple factors. Specifically, the carbon coating layer on the surface of LFP particles will adsorb binders and conductive agents during slurry preparation, changing the surface energy and dispersion characteristics of the particles. LFP particles with different morphologies (such as spherical, near-spherical, and irregular porous particles) will exhibit completely different flocculation and sedimentation behaviors in the slurry. Even if the packing density is similar in the dry powder state, they will form significantly different electrode packing structures after coating and drying. At the same time, the rheological properties of the slurry, the shear force during the coating process, and the solvent evaporation rate during the drying process will further affect the final initial pore structure of the electrode. This leads to a situation where lithium iron phosphate materials with similar powder compaction densities may still have significant differences in the initial porosity of the resulting electrodes under the same slurry coating process. Existing technologies have not paid attention to the decisive impact of this core difference on the rolling effect and still use powder compaction density as the core basis for rolling process design. Therefore, they cannot solve the problem of inconsistent compaction densities after rolling different materials.
[0021] Based on this, the present invention provides a rolling method for lithium iron phosphate electrode sheets, comprising the following steps: The porosity of lithium iron phosphate electrodes that were coated and dried but not rolled was measured to obtain the electrode porosity. The porosity of the electrode is compared with a preset threshold. When the porosity of the electrode sheet is less than the preset threshold, the electrode sheet is rolled using a first rolling process. When the porosity of the electrode sheet is greater than the preset threshold, the electrode sheet is rolled using a second rolling process.
[0022] In this invention, electrode porosity is a key structural parameter reflecting the proportion of void volume within the electrode. Under the same slurry coating process conditions (such as solid content, coating thickness, drying temperature, etc.), different lithium iron phosphate materials, due to differences in particle morphology, particle size distribution, surface properties, and carbon coating methods, result in different initial electrode packing structures, manifested as differences in porosity. This porosity can comprehensively characterize the actual physical state of the material after slurry coating and is an important basis for predicting subsequent rolling behavior.
[0023] In an optional embodiment of the present invention, the porosity determination is performed using mercury intrusion porosimetry. Mercury intrusion porosimetry is a mature method for testing the pore structure of materials. Its principle is based on the non-wetting property of mercury in most solid materials. External pressure is applied to force mercury into the pores of the material, and the porosity is calculated based on the relationship between the pressure and the volume of mercury intruded. This method can accurately determine the open porosity inside the electrode, and the test results are stable and reliable.
[0024] In an optional embodiment of the present invention, the upper limit of the test pressure during the mercury intrusion porosimetry test is 20,000 to 30,000 psi. The upper limit of the test pressure determines the smallest pore size range that can be measured. If the upper limit of the pressure is too low, some tiny pores may not be filled by mercury, resulting in a lower porosity test result; if the upper limit of the pressure is too high, the requirements for equipment and samples are higher, increasing the test cost. Controlling the upper limit of the test pressure within the range of 20,000 to 30,000 psi can meet the accuracy requirements for porosity testing of lithium iron phosphate electrodes. Preferably, the upper limit of the test pressure is 22,000 to 28,000 psi; more preferably, the upper limit of the test pressure can be 20,000 psi, 22,000 psi, 25,000 psi, 28,000 psi, or 30,000 psi, etc.
[0025] When using the mercury intrusion porosimetry method to test the porosity of electrode sheets in this invention, the following formula is preferably used: ; in, A The area of the electrode sample is denoted as . h 极片 The thickness of the electrode sheet, h 集流体 The thickness of the current collector being coated; V 汞 This refers to the volume of mercury pumped in after the mercury pressure stabilizes.
[0026] In this invention, the preset threshold is a critical porosity value that distinguishes different rolling behaviors. When the electrode porosity is below this threshold, it indicates that the initial structure of the electrode is relatively dense, and the contact between particles is relatively tight, classifying it as an "easy-to-roll" material. When the electrode porosity is above this threshold, it indicates that the initial structure of the electrode is relatively loose, and the gaps between particles are relatively large, classifying it as a "difficult-to-roll" material. Through this comparison step, the complex material processing characteristics can be simplified into a binary classification problem, providing a basis for subsequent matching of standardized processes.
[0027] In an optional embodiment of the present invention, the preset threshold is 34-37%, for example, it can be 34%, 35%, 36%, or 37%; more preferably, it is 34.5-35.5%, and most preferably, it is 35%. Through extensive experiments, the inventors have discovered that the rolling behavior of lithium iron phosphate electrodes exhibits a clear critical inflection point around a porosity of 35%. When the porosity is below this preset threshold, a relatively mild rolling process can effectively achieve densification; when the porosity is above this preset threshold, a more robust rolling process is required to achieve the same compaction effect. Setting the preset threshold to 34-37% allows for accurate differentiation of materials with different processing characteristics.
[0028] If the preset threshold is set too low, some materials that should be classified as easy-to-roll materials may be incorrectly classified as difficult-to-roll materials, leading to over-compression after using the enhanced rolling process. This results in excessively low electrode porosity, particle breakage, obstructed ion transport channels, and deteriorated electrical properties. It may also cause classification boundary shifts, potentially leading to process matching deviations. If the preset threshold is set too high, some materials that should be classified as difficult-to-roll materials may be incorrectly classified as easy-to-roll materials, resulting in insufficient densification after using the mild rolling process. This leads to low electrode compaction density and inconsistent compaction levels between different materials. It may also cause classification boundary shifts, similarly affecting the accuracy of process matching. This invention sets the preset threshold at around 35%, which can accurately distinguish materials with different processing characteristics and avoid process mismatch problems caused by classification errors.
[0029] Based on the above classification results, a rolling process matching the material processing characteristics is adopted to ensure that different materials achieve a consistent compaction density level after rolling.
[0030] In an optional embodiment of the present invention, the first rolling process includes: performing a single rolling process with a rolling pressure of 70-90 kN. For easily rolled materials (porosity below a threshold), the initial structure of the electrode is already relatively dense, and effective compaction can be achieved without excessive rolling pressure. Controlling the rolling pressure within the range of 70-90 kN, for example, 70 kN, 75 kN, 80 kN, 85 kN, or 90 kN, ensures that the electrode reaches the target compaction density while avoiding particle breakage or excessively low porosity due to excessive pressure, thereby ensuring unobstructed electrolyte wetting and lithium-ion transport channels.
[0031] In an optional embodiment of the present invention, the second rolling process includes: rolling the electrode sheet in a first direction with a rolling pressure of 80-100 kN, and then rolling the electrode sheet in a second direction perpendicular to the first direction. For materials that are difficult to roll (porosity higher than the threshold), the initial structure of the electrode sheet is relatively loose, requiring a higher rolling pressure to achieve effective compaction. Controlling the rolling pressure within the range of 80-100 kN can provide sufficient densification driving force. At the same time, using a vertical secondary rolling method can eliminate the directional stress distribution generated during the first rolling process, making the internal stress of the electrode sheet more uniform, avoiding electrode sheet warping or particle breakage caused by stress concentration, thereby achieving a more uniform densification effect. Preferably, the rolling pressure is 85-95 kN; more preferably, the rolling pressure is 85-90 kN.
[0032] In an optional embodiment of the present invention, in the first rolling process, the feed rate of the roller is 10-15 mm / s; in the second rolling process, the feed rate of the roller is 3-8 mm / s. The feed rate affects the application time of pressure on the electrode and the stress distribution. For easily rolled materials, a higher feed rate of 10-15 mm / s is used to improve processing efficiency while ensuring compaction effect; for difficult-to-roll materials, a lower feed rate of 3-8 mm / s is used to allow pressure to be transmitted more fully and evenly to the interior of the electrode, achieving deep densification. Preferably, the feed rate of the first rolling process can be 10 mm / s, 12 mm / s, 13 mm / s, 14 mm / s, or 15 mm / s, etc., more preferably 12-14 mm / s; the feed rate of the second rolling process can be 3 mm / s, 4 mm / s, 5 mm / s, 6 mm / s, 7 mm / s, or 8 mm / s, etc., more preferably 4-6 mm / s.
[0033] In an optional embodiment of the present invention, the preparation process of the coated and dried lithium iron phosphate electrode sheet without rolling is as follows: lithium iron phosphate is mixed with a conductive agent and a binder to form a slurry; the slurry is coated on a current collector; and after drying, the coated and dried lithium iron phosphate electrode sheet is obtained.
[0034] The above preparation process is a routine step in the preparation of lithium iron phosphate electrode sheets. The key is to control the consistency of parameters such as slurry solid content and coating thickness to ensure that the porosity measurement results can truly reflect the material's inherent characteristics rather than process fluctuations.
[0035] In an optional embodiment of the present invention, the mass ratio of lithium iron phosphate, conductive agent, and binder is (85~95):(2~10):(2~10). This ratio range ensures that the electrode has sufficient electronic conductivity and structural integrity, while avoiding problems such as decreased energy density or pore blockage due to excessive conductive agent or binder, or increased internal resistance and powder shedding due to insufficient binder. Preferably, the mass ratio of lithium iron phosphate, conductive agent, and binder can be 85:5:10, 88:5:7, 90:5:5, 91:4:5, 92:3:5, 93:3:4, or 95:3:2, etc. The specific ratio needs to be adjusted according to the actual material characteristics and process conditions to ensure that the electrode performance reaches the optimal level.
[0036] In an optional embodiment of the present invention, the conductive agent includes, but is not limited to, one or more of SP, CNT, VGCF, ECP, rGO, acetylene black, and Carbon ECP. The conductive agent functions to form a conductive network between the active material particles, reducing the internal resistance of the electrode. The aforementioned conductive agents possess excellent conductivity and dispersibility, enabling them to be uniformly distributed within the electrode.
[0037] In an optional embodiment of the present invention, the binder includes, but is not limited to, one or more of PVDF, PAA, PMMA, and PTFE. The binder's function is to firmly bond the active material particles to the current collector and maintain the structural stability of the electrode. The aforementioned binder possesses good bonding performance and electrochemical stability, making it suitable for lithium-ion battery cathode systems.
[0038] In an optional embodiment of the present invention, the solvent is N-methylpyrrolidone (NMP). NMP can effectively dissolve binders such as PVDF to form a homogeneous slurry system.
[0039] In an optional embodiment of the present invention, the prepared slurry is placed in a degassing machine for degassing and dispersion. The degassing process is preferably performed at 600-800 rpm for 30-90 seconds, followed by increasing the speed to 1500-2000 rpm for 10-20 minutes, and repeating the process 2-4 times. This alternating low-speed and high-speed degassing and dispersion process effectively removes air bubbles from the slurry while ensuring that the active materials, conductive agents, and binders are fully and uniformly dispersed, resulting in a slurry with good rheological properties and stability.
[0040] In an optional embodiment of the present invention, a vacuum coater is used to coat the slurry onto the current collector. Vacuum coating can reduce the generation of bubbles during the coating process and improve the coating uniformity. The current collector is aluminum foil, which has good conductivity and mechanical strength and is a commonly used current collector material for lithium iron phosphate cathodes.
[0041] In an optional embodiment of the present invention, the solid content of the slurry is 28% to 35%. The solid content of the slurry affects the initial packing structure and drying behavior of the coated electrode. Too low a solid content may lead to excessive drying shrinkage and electrode cracking; too high a solid content will result in poor slurry fluidity and reduced coating uniformity. Controlling the solid content within the range of 28% to 35% can yield electrodes with uniform structure and reasonable pore distribution, for example, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.
[0042] In an optional embodiment of the present invention, the coating thickness is 100~300μm. The coating thickness affects the unit area mass load and pore structure of the electrode after drying. Too thin a coating thickness may result in insufficient mechanical strength of the electrode; too thick a coating thickness makes drying difficult and may cause cracks. Controlling the coating thickness within the range of 100~200μm yields structurally stable electrodes, such as those with thicknesses of 100μm, 120μm, 140μm, 150μm, 160μm, 180μm, 200μm, 250μm, or 300μm.
[0043] This invention also provides an application of the above-mentioned rolling method for lithium iron phosphate electrodes, used for comparative evaluation of the electrical performance of different lithium iron phosphate materials in button battery testing.
[0044] The different lithium iron phosphate materials described in this invention refer to lithium iron phosphate cathode active materials that exhibit one or more differences in chemical composition, microstructure, preparation process, etc., including but not limited to: lithium iron phosphate samples prepared using different modification schemes during the laboratory research and development stage, lithium iron phosphate products from different production batches during mass production, and commercial lithium iron phosphate products from different suppliers. Specifically, these differences include: differences in elemental doping modification, such as the type, amount, and doping sites of doping elements; differences in carbon coating processes, such as the type of carbon source used, the amount of carbon coating, the uniformity of the carbon layer, and the degree of graphitization of the carbon layer; differences in synthesis and preparation processes, such as different synthesis routes including high-temperature solid-state methods, hydrothermal methods, sol-gel methods, and spray pyrolysis methods, as well as differences in parameters such as sintering temperature, holding time, sintering atmosphere, and precursor preparation process; and differences in particle physical properties, such as particle size distribution, primary / secondary particle size, particle morphology, specific surface area, and particle density. Any of the above differences will cause changes in the stacking behavior of lithium iron phosphate materials during the slurry preparation, coating, and drying processes. Even under the same electrode preparation process, significant differences in the initial pore structure of the electrode will be formed, which in turn leads to the problem of inconsistent final compaction density of the electrode under the same rolling process.
[0045] In the industrialization R&D process of lithium iron phosphate materials, button cell testing is a core testing method that runs through the entire process from laboratory small-scale testing to pilot-scale amplification and mass production batch stability control. It is also the core method for evaluating the performance of various lithium iron phosphate materials. In the laboratory R&D stage, researchers need to benchmark and screen lithium iron phosphate samples prepared with different doping modifications, carbon coating processes, and sintering regimes. Typically, dozens of parallel samples are tested in a single test. The rolling method of this invention can quickly achieve consistent control of the compaction density of all parallel sample electrodes, significantly shortening the testing cycle and avoiding misjudgments in R&D direction due to differences in compaction density. In the mass production batch control stage, batch consistency testing of different batches of lithium iron phosphate products is required. The method of this invention can eliminate interference from electrode processing technology, accurately reflect the fluctuations in the intrinsic properties of materials between batches, and provide precise data support for optimizing the production process. In benchmarking tests of materials from different suppliers, the method of this invention can ensure that all benchmark samples are at the same level of compaction test benchmark. The test results can be directly used for horizontal comparison of material performance, providing a reliable basis for battery manufacturers to select raw materials. Compared with existing technologies, the method of the present invention does not require repeated adjustment of rolling parameters for different materials. Material classification and process matching can be completed by a single porosity test. It is simple to operate, highly adaptable, and can be widely used in various lithium iron phosphate materials for coin cell performance evaluation.
[0046] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.
[0047] Preparation Example In the following examples, the method for preparing lithium iron phosphate electrodes is as follows: Eight different lithium iron phosphate materials (denoted as Sample A, Sample B, Sample C, Sample D, Sample E, Sample F, Sample G, and Sample H) were mixed with SP conductive agent and PVDF binder at a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone (NMP) was added to adjust the slurry solid content to 30%. The mixture was then degassed and dispersed using a degassing machine. The degassing process was repeated three times: 650 rpm for 60 seconds, then increased to 1800 rpm for 15 minutes, to obtain a uniformly dispersed slurry of the coin cell active material. The slurry was then coated onto aluminum foil using a vacuum coater to a thickness of 200 μm. After coating, the foil was dried in a 105℃ forced-air drying oven for 6 hours to obtain unrolled electrode sheets for each material, named A-electrode-UR, B-electrode-UR, C-electrode-UR, D-electrode-UR, E-electrode-UR, F-electrode-UR, G-electrode-UR, and H-electrode-UR, respectively.
[0048] Example 1 This embodiment provides a rolling method for lithium iron phosphate electrode sheets, and the process diagram is shown below. Figure 1 As shown.
[0049] (1) Porosity determination and material classification: Take a portion of the unrolled electrode sheets from each material in the preparation examples, cut them into 1cm × 1cm square samples, and determine the porosity using the mercury porosimetry method according to the national standard GB / T 21650.1-2008. The upper limit of the mercury porosimetry test pressure is 25000 psi. After the mercury pressure stabilizes, record the volume of mercury pumped in. V 汞 Porosity can be calculated using the following formula:
[0050] in, a Let be the side length of the electrode sample. h 极片 The thickness of the electrode sheet, h 铝箔 This refers to the thickness of the aluminum foil.
[0051] The porosities of the electrodes were measured as follows: A electrode - UR 46.1%, B electrode - UR 33.5%, C electrode - UR 34.4%, D electrode - UR 45.1%, E electrode - UR 41.4%, F electrode - UR 31.3%, G electrode - UR 36.6%, and H electrode - UR 38.3%.
[0052] Based on a preset threshold of 35%, the following materials are classified: B-electrode-UR, C-electrode-UR, and F-electrode-UR with a porosity of less than 35% are classified as easy-to-roll materials; A-electrode-UR, D-electrode-UR, E-electrode-UR, G-electrode-UR, and H-electrode-UR with a porosity of greater than 35% are classified as difficult-to-roll materials.
[0053] (2) Roll pressing Take the remaining unrolled electrode sheets and roll them according to the above classification results: The easy-to-roll-press material adopts the first rolling process: the rolling pressure is 75kN, the injection rate is 12mm / s, and the rolled electrode is obtained after a single rolling process, which are respectively denoted as B electrode-R-s1, C electrode-R-s1 and F electrode-R-s1.
[0054] For materials that are difficult to roll, a second rolling process is adopted: the rolling pressure is 85kN, the injection rate is 5mm / s, and after rolling once in the first direction, the electrode is rotated 90° and rolled twice in the vertical direction to obtain the rolled electrode, which is denoted as A electrode-R-s1, D electrode-R-s1, E electrode-R-s1, G electrode-R-s1 and H electrode-R-s1 respectively.
[0055] The scanning electron microscope image of the A-electrode-R-s1 obtained by rolling in this embodiment is as follows: Figure 2 As shown, the scanning electron microscope image of the B electrode sheet-R-s1 obtained by roll pressing is as follows: Figure 3 As shown, although the porosity of electrode A-UR and electrode B-UR differs significantly before rolling, after the differentiated rolling process in this embodiment, the density and pore uniformity of the particles in the electrode are basically the same, and the lithium iron phosphate particles do not show obvious stress breakage.
[0056] Comparative Example 1 This comparative example uses a uniform rolling process to roll different lithium iron phosphate materials.
[0057] Unrolled electrode sheets (A electrode-UR, B electrode-UR, C electrode-UR, D electrode-UR, E electrode-UR, and F electrode-UR) were all processed using a uniform rolling process. The specific rolling process was as follows: the rolling pressure was 80kN, the feed rate was 12mm / s, and after a single rolling pass, the rolled electrode sheets were obtained, which were denoted as A electrode-R-d1, B electrode-R-d1, C electrode-R-d1, D electrode-R-d1, E electrode-R-d1, and F electrode-R-d1, respectively.
[0058] Comparative Example 2 This comparative example sets the roller pressure according to the powder compaction density classification.
[0059] (1) The compacted density of six samples was determined according to the national standard GB / T 44330-2024 "Determination of compacted density of positive electrode material for lithium-ion batteries". The results are as follows: A electrode - UR: 2.37 g / cm³ 3 B-type electrode plate - UR: 2.48g / cm³ 3 C electrode plate - UR: 2.35g / cm 3 D-type electrode plate - UR: 2.36g / cm 3 E-electrode-UR: 2.43g / cm³ 3 F-electrode-UR: 2.45g / cm³ 3 .
[0060] (2) Roll pressing: For powders with a compacted density of less than 2.4 g / cm³ 3 The A-electrode-UR, C-electrode-UR, and D-electrode-UR are processed by a single-pass rolling process of 90kN and 12mm / s to obtain rolled electrodes, which are denoted as A-electrode-R-d2, C-electrode-R-d2, and D-electrode-R-d2, respectively.
[0061] For powders with a compacted density greater than 2.4 g / cm³ 3The B-electrode-UR, E-electrode-UR, and F-electrode-UR are processed by a single-pass rolling process of 75kN and 12mm / s to obtain rolled electrodes, which are denoted as B-electrode-R-d2, E-electrode-R-d2, and F-electrode-R-d2, respectively.
[0062] Comparative Example 3 This comparative example is used to verify the rationality of using 35% porosity as the classification threshold.
[0063] The B-electrode-UR, C-electrode-UR, E-electrode-UR, F-electrode-UR, G-electrode-UR, and H-electrode-UR from Example 1 are arranged in ascending order of porosity as follows: F electrode - UR 31.3%, B electrode - UR 33.5%, C electrode - UR 34.4%, G electrode - UR 36.6%, H electrode - UR 38.3%, E electrode - UR 41.4%.
[0064] The above six types of unrolled electrode sheets were subjected to two sets of rolling processes respectively: Group 1: All were rolled using the first rolling process (easy-to-roll material process) in Example 1, i.e., the rolling pressure was 75kN, the sample feeding rate was 12mm / s, and a single rolling was completed to obtain the rolled electrode sheets, which were respectively denoted as F electrode sheet-R-d3-1, B electrode sheet-R-d3-1, C electrode sheet-R-d3-1, G electrode sheet-R-d3-1, H electrode sheet-R-d3-1, and E electrode sheet-R-d3-1.
[0065] The second group: all were rolled using the second rolling process (difficult-to-roll material process) in Example 1, that is, the rolling pressure was 85kN, the injection rate was 5mm / s, and after rolling once in the first direction, the electrode was rotated 90° and rolled twice in the vertical direction to obtain the rolled electrode, which were respectively denoted as F electrode-R-d3-2, B electrode-R-d3-2, C electrode-R-d3-2, G electrode-R-d3-2, H electrode-R-d3-2, and E electrode-R-d3-2.
[0066] Test case 1. Testing Method (1) Measurement of electrode compaction density: The compaction density of each electrode is calculated using the following formula: ; in, m 极片 Total mass of a unit area; m 集流体 Mass of current collector per unit area; w 活性物质 : Mass fraction of positive electrode active material (lithium iron phosphate) in dry coating;h 极片 : Thickness of the electrode sheet after roll forming; h 集流体 : Current collector thickness.
[0067] (2) Button cell manufacturing The rolled electrode sheets were cut into circular pieces with a diameter matching the button cell casing and placed in a vacuum drying oven at 105°C for 2 hours. The button cells were assembled in a glove box under an argon atmosphere. The electrolyte was a mixed solvent of 1M LiPF6 dissolved in EC:DEC:DMC = 1:1:1 (volume ratio), and the lithium metal sheet was used as the counter electrode.
[0068] (3) Electrical performance test Capacity testing was conducted on an Arbin BT2000 battery tester in the United States, with a charge / discharge voltage range of 2.0~3.75V and charge / discharge rates of 0.1C and 1C, respectively.
[0069] 2. Test Results and Analysis The results of the physical, chemical and electrical performance tests of the electrode sheet after rolling in Example 1 are shown in Table 1.
[0070] Table 1. Physicochemical and electrical properties of the electrode sheet after rolling in Example 1 sample Electrode porosity (%) <![CDATA[The compaction density of the electrode sheet (g / cm 3 )]]> 0.1C discharge specific capacity (mAh / g) First-efficacy (%) 1C discharge specific capacity (mAh / g) A-electrode film-R-s1 27.1 2.34 158.9 99.06 132.0 B-electrode-R-s1 26.5 2.32 158.6 98.63 129.9 C-electrode-R-s1 27.7 2.33 157.5 98.06 127.4 D-Electrode-R-s1 27.1 2.34 158.7 98.77 131.7 E-Electrode-R-s1 27.5 2.36 158.6 98.44 127.6 F-electrode-R-s1 26.9 2.34 158.3 98.72 127.9 G-Plate-R-S1 26.8 2.35 158.8 98.42 128.8 H-electrode-R-s1 27.3 2.35 158.9 98.74 130.4 As shown in Table 1, after rolling eight different lithium iron phosphate materials using the method of Example 1 of this invention, the compaction density of each electrode sheet was concentrated between 2.32 and 2.36 g / cm³. 3 The porosity is concentrated between 26.5% and 27.7%, remaining at a similar level. Under these conditions, the differences in electrical properties can accurately reflect the intrinsic characteristics of each material, eliminating the interference of variations in the rolling process on the test results.
[0071] The test results for Comparative Example 1 (uniform rolling process) are shown in Table 2.
[0072] Table 2. Physicochemical and electrical properties of the electrode sheet after roll pressing in Comparative Example 1 sample Electrode porosity (%) <![CDATA[The tap density of the electrode sheet (g / cm 3 )]]> 0.1C discharge specific capacity (mAh / g) First-efficacy (%) 1C discharge specific capacity (mAh / g) A-electrode-R-d1 33.6 2.21 157.1 97.72 125.0 B-electrode-R-d1 26.2 2.33 158.7 98.53 129.2 C-electrode-R-d1 27.7 2.33 157.9 98.05 127.6 D-Electrode-R-d1 33.7 2.22 157.8 98.39 128.4 E-electrode-R-d1 35.6 2.26 157.3 98.42 125.0 F-electrode-R-d1 26.3 2.36 158.5 98.63 128.1 As shown in Table 2, in Comparative Example 1, after treating different materials using a uniform rolling process (80kN, 12mm / s), the compaction density of the electrode sheets fluctuated significantly, ranging from 2.21 to 2.36 g / cm³. 3 Among them, the compaction densities of electrodes A, D, and E were significantly lower than those of electrodes B, C, and F. This indicates that a uniform process cannot achieve consistent compaction levels for different materials, and the test results make it difficult to distinguish whether the capacity differences stem from intrinsic material properties or process factors.
[0073] The test results of Comparative Example 2 (based on powder compaction density classification roll pressing) are shown in Table 3.
[0074] Table 3. Physicochemical and electrical properties of the electrode sheet after roll pressing in Comparative Example 2 sample Electrode porosity (%) <![CDATA[The compaction density of the electrode sheet (g / cm 3 )]]> 0.1C discharge specific capacity (mAh / g) First-efficacy (%) 1C discharge specific capacity (mAh / g) A-electrode-R-d2 30.3 2.26 157.5 97.94 126.2 B-electrode-R-d2 26.5 2.32 158.6 98.64 129.9 C electrode plate-R-d2 24.1 2.35 155.5 96.07 119.4 D-Electrode-R-d2 30.2 2.27 158.1 98.55 128.8 E-electrode-R-d2 36.7 2.24 157.0 97.91 124.9 F-electrode-R-d2 26.9 2.34 158.3 98.71 127.9 As shown in Table 3, in Comparative Example 2, after roller pressing based on powder compaction density, there were still significant differences in the compaction density of the electrode sheets (2.24~2.35 g / cm³). 3 Among them, the compaction density of electrode A, electrode D, and electrode E is too low, while electrode C has too low porosity (24.1%) due to excessive roller pressure, resulting in severe deterioration of electrical properties. This indicates that powder compaction density cannot accurately characterize the actual processing characteristics of materials after slurry coating, and classification based on this index is difficult to achieve consistent compaction levels for different materials.
[0075] The test results for Comparative Example 3 are shown in Table 4.
[0076] Table 4. Physicochemical and electrical properties of the electrode sheets after roll pressing in Comparative Example 3 sample Electrode porosity (%) <![CDATA[The compaction density of the electrode sheet (g / cm 3 )]]> 0.1C discharge specific capacity (mAh / g) First-efficacy (%) 1C discharge specific capacity (mAh / g) F-electrode-R-d3-1 26.9 2.34 158.3 98.72 127.9 F-electrode-R-d3-2 20.8 2.37 155.3 95.83 110.5 B-electrode-R-d3-1 26.5 2.32 158.6 98.63 129.9 B-electrode-R-d3-2 23.2 2.34 156.1 96.11 116.7 C-electrode-R-d3-1 27.7 2.33 157.5 98.06 127.4 C electrode plate-R-d3-2 27.7 2.34 157.3 98.13 127.3 G-Electrode-R-d3-1 27.0 2.33 158.6 98.44 128.6 G-Electrode-R-d3-2 26.8 2.35 158.8 98.42 128.8 H-electrode-R-d3-1 33.3 2.26 156.7 96.82 124.9 H-electrode-R-d3-2 27.3 2.35 158.9 98.74 130.4 E-electrode-R-d3-1 36.7 2.24 157.0 97.91 124.9 E-electrode-R-d3-2 27.5 2.36 158.6 98.44 127.6 As shown in Table 4, for F-electrodes (31.3%) and B-electrodes (33.5%) with porosities much less than 35%, the electrical performance was good after treatment with the first rolling process (easy rolling process). However, after treatment with the second rolling process (difficult rolling process), a "crushing" phenomenon occurred, and the porosity dropped to 20.8% and 23.2%, respectively, below 25%, resulting in severe deterioration of electrical performance. This is because excessively low porosity makes it difficult for the electrolyte to fully wet the interior of the electrode, obstructing the lithium-ion transport channels and causing a sharp decrease in ionic conductivity. This phenomenon further confirms the importance of controlling the electrode porosity within a reasonable range and also demonstrates that the present invention, through the classification and selection of processes, maintains the electrode porosity within the suitable range of 26% to 28%, exhibiting significant process advantages.
[0077] For H-electrodes (38.3%) and E-electrodes (41.4%) with porosities much greater than 35%, the electrical properties were good after treatment with the second rolling process (difficult rolling process), while the compaction density was low (2.26 g / cm³) after treatment with the first rolling process (easy rolling process). 3 and 2.24 g / cm 3 ), with poor electrical performance.
[0078] For C-type electrodes (34.4%) and G-type electrodes (36.6%) with porosities close to 35%, the performance data of the electrodes after the two rolling processes are similar, indicating that the area around 35% is the critical region.
[0079] The above results verify the rationality of using 35% as the classification threshold in this invention: when the porosity is below this threshold, the material is easy to roll and should be processed using the first rolling process (relatively mild); when the porosity is above this threshold, the material is difficult to roll and should be processed using the second rolling process (reinforced process). This classification method can accurately distinguish materials with different processing characteristics, avoiding over-pressing or under-pressing problems caused by incorrect process selection. This ensures that different lithium iron phosphate materials achieve consistent electrode compaction density levels after rolling, providing a reliable electrode preparation method for comparing and evaluating the electrical performance of different materials in button cell testing.
[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for rolling lithium iron phosphate electrode sheets, characterized in that, Includes the following steps: The porosity of lithium iron phosphate electrodes that were coated and dried but not rolled was measured to obtain the electrode porosity. The porosity of the electrode is compared with a preset threshold. When the porosity of the electrode sheet is less than the preset threshold, the electrode sheet is rolled using a first rolling process. When the porosity of the electrode sheet is greater than the preset threshold, the electrode sheet is rolled using a second rolling process.
2. The rolling method for lithium iron phosphate electrode sheets as described in claim 1, characterized in that, The porosity was determined using the mercury porosimetry method.
3. The rolling method for lithium iron phosphate electrode sheets as described in claim 2, characterized in that, During the mercury intrusion porosimetry test, the upper limit of the test pressure is 20,000 to 30,000 psi.
4. The rolling method for lithium iron phosphate electrode sheets as described in claim 1, characterized in that, The preset threshold is 34-37%.
5. The rolling method for lithium iron phosphate electrode sheets as described in claim 1, characterized in that, The first rolling process includes: performing a single rolling process with a rolling pressure of 70~90kN; the second rolling process includes: performing a first-direction rolling process with a rolling pressure of 80~100kN, and then performing a second rolling process on the electrode sheet along a second direction perpendicular to the first direction.
6. The rolling method for lithium iron phosphate electrode sheets as described in claim 5, characterized in that, In the first rolling process, the roller feed rate is 10~15mm / s; in the second rolling process, the roller feed rate is 3~8mm / s.
7. The rolling method for lithium iron phosphate electrode sheets as described in claim 1, characterized in that, The preparation process of the coated and dried lithium iron phosphate electrode sheet without rolling is as follows: Lithium iron phosphate is mixed with conductive agents and binders to form a slurry; The slurry is applied onto the current collector; After drying, the coated and dried lithium iron phosphate electrode sheet is obtained.
8. The rolling method for lithium iron phosphate electrode sheets as described in claim 7, characterized in that, The solid content of the slurry is 28% to 35%.
9. The rolling method for lithium iron phosphate electrode sheets as described in claim 7, characterized in that, The thickness of the slurry coating is 100~300μm.
10. The application of the rolling method for lithium iron phosphate electrodes as described in any one of claims 1 to 9, characterized in that, Comparative evaluation of the electrical performance of different lithium iron phosphate materials in button cell testing.