Method for evaluating compaction density of electrode sheet of lithium-ion battery
Patent Information
- Application Number
- PCT/CN2026/089988
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-04-14
- Filing Date
- 2026-04-10
- Publication Date
- 2026-10-22
Smart Images
Figure CN2026089988_22102026_PF_FP_ABST
Abstract
Description
A method for evaluating the compaction density of lithium-ion battery electrodes
[0001] This application claims priority to Chinese Patent Application No. CN202510463147.2, filed on April 14, 2025, entitled "A Method for Evaluating the Compacted Density of Lithium-ion Battery Electrodes", the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application relates to the field of lithium-ion battery technology, and in particular to a method for evaluating the compaction density of lithium-ion battery electrodes. Background Technology
[0003] Lithium-ion batteries, with their high energy density, excellent cycle performance, and rate performance, have become core energy storage devices in mobile communications, new energy vehicles, and grid energy storage. As application scenarios continue to expand, market demands for lithium-ion battery performance are constantly increasing, with improving energy density being particularly crucial.
[0004] Increasing the compaction density of the positive and negative electrode sheets is the most direct way to improve the energy density of lithium-ion batteries. However, optimizing the compaction density of the electrode sheets faces significant technical challenges: if the compaction density is too high, the electrode sheets are prone to breakage during manufacturing, leading to decreased production efficiency and increased costs; if the compaction density is too low, the electrode sheets occupy too much space in the core, reducing the active material loading and thus lowering the battery capacity and energy density. Therefore, how to accurately evaluate the compaction performance of the electrode sheets to balance energy density and processing feasibility has become a pressing technical problem that needs to be solved.
[0005] Currently, the industry's assessment of electrode compaction density mainly relies on empirical design, followed by repeated adjustments based on cell performance or processing characteristics. This method is not only time-consuming and labor-intensive, but also lacks scientific rigor and accuracy, making it difficult to meet the demands of efficient and precise R&D and production.
[0006] Therefore, there is an urgent need to develop an objective, rapid and accurate method for evaluating the compaction density of lithium-ion battery electrodes, in order to guide the optimization of electrode processes and improve battery performance and production efficiency. Summary of the Invention
[0007] This application provides a method for evaluating the compaction density of lithium-ion battery electrodes to improve battery performance and production efficiency.
[0008] In a first aspect, this application provides a method for evaluating the compaction density of lithium-ion battery electrode sheets, comprising the steps of: performing a real-time compaction test on the electrode sheet, wherein the real-time compaction test includes, under constant pressure conditions, gradually decreasing the roll gap distance with a preset length value as a gradient, and recording the electrode sheet thickness data corresponding to each roll gap value in real time; and under constant roll gap conditions, gradually increasing the roll pressure with a preset pressure value as a gradient, and recording the electrode sheet thickness data corresponding to each roll pressure value in real time; obtaining the corresponding compaction density data based on the corresponding electrode sheet thickness data; obtaining a first compaction characteristic curve based on each roll gap value and the compaction density data corresponding to the roll gap value; obtaining a second compaction characteristic curve based on each roll pressure value and the compaction density data corresponding to the roll pressure value; and determining the ultimate compaction density of the electrode sheet based on the first compaction characteristic curve and / or the second compaction characteristic curve.
[0009] By recording the electrode thickness data corresponding to each roll gap value and roll pressure value in real time using the above method, the instantaneous state of the electrode under different compaction conditions can be reflected promptly and accurately. Based on the collected data, a first compaction characteristic curve (the relationship between roll gap and compaction density) and a second compaction characteristic curve (the relationship between roll pressure and compaction density) are plotted. Analysis of these two curves allows for a direct observation of the trend and pattern of electrode compaction density changes with roll gap and roll pressure. When the curve tends to stabilize or an inflection point appears, it corresponds to the electrode's ultimate compaction density. This characteristic curve-based analysis method can more accurately determine the electrode's ultimate compaction density, providing crucial parameter data for battery design and production. Furthermore, by comprehensively analyzing the first and second compaction characteristic curves, the ultimate compaction density of the electrode can be determined more comprehensively and accurately. This comprehensive evaluation method avoids the bias that may arise from single-factor evaluation, improving the accuracy and reliability of determining the ultimate compaction density. This method can complete the evaluation of electrode compaction density in a short time. Compared with traditional evaluation methods, it greatly shortens the evaluation cycle, is not affected by human factors or experience values, and does not require additional testing costs. It can objectively and quickly obtain the ultimate compaction density, thereby timely feeding the evaluation results back to the production process. This allows production personnel to quickly adjust the production process based on the evaluation results, reducing production downtime caused by waiting for evaluation results, and thus improving production efficiency.
[0010] In one possible design, before conducting real-time compaction tests on the electrode sheet, the following steps are included: determining the areal density of the electrode sheet, marking it along the length of the electrode sheet to divide it into multiple test sections along the length of the electrode sheet; providing a roller press and an automatic thickness gauge, and calibrating the roller gap, pressure parameters of the roller press and the automatic thickness gauge.
[0011] The above scheme utilizes areal density, which is the mass per unit area of the electrode sheet, directly affecting its compaction density. Accurate measurement of areal density allows for more precise calculation of the compaction density under different compaction conditions, thus improving the accuracy of the entire evaluation process. Marking along the length of the electrode sheet to divide it into multiple test segments ensures uniform and consistent testing of all parts of the electrode sheet during real-time compaction testing. This segmented testing method avoids uneven testing caused by excessive electrode length, ensuring accurate and reliable compaction density data for each test segment. Segmented testing also improves testing efficiency and reduces the impact of mechanical or human errors on the overall test results. Calibrating the roller gap, pressure parameters, and automatic thickness gauge of the roller press are crucial steps in ensuring the accuracy of test data. The roller gap and pressure parameters of the roller press directly affect the compaction effect of the electrode sheet, while the automatic thickness gauge is a key device for measuring the electrode sheet thickness. Calibrating these devices ensures they accurately reflect the compaction state of the electrode sheet during testing, thereby improving the accuracy and reliability of the test data.
[0012] In one possible design, the corresponding compaction density data is obtained based on the corresponding electrode thickness data, including the following steps: obtaining the average thickness of the electrode based on the electrode thickness data; and calculating the compaction density data based on the average thickness and the areal density.
[0013] By employing the above method, the average thickness of the electrode is obtained based on the electrode thickness data, which more accurately reflects the average thickness of the electrode under different compaction conditions. This averaging process reduces evaluation errors caused by localized uneven thickness of the electrode, thereby improving the accuracy of the evaluation results. Compaction density data is calculated based on the average thickness and areal density, which more precisely reflects the density variation of the electrode under different compaction conditions. Compaction density is the mass per unit volume of the electrode and is a key parameter for evaluating the compaction effect of the electrode. Accurate calculation of compaction density provides a more comprehensive understanding of the electrode's compaction state, offering more accurate parameter data for battery design and production.
[0014] In one possible design, the average thickness of the electrode is obtained based on the electrode thickness data, including: removing abnormal data from the electrode thickness data in the corresponding test section to obtain the effective electrode thickness data, where abnormal data includes the thickness data of the edge thinning area, joint area, or defect point of the electrode; and calculating the average value based on the effective electrode thickness data to obtain the average thickness of the electrode.
[0015] The above method addresses the issue that outlier data, potentially arising from defects or measurement errors during electrode production, significantly impacts the accuracy of the average thickness. Removing these outliers ensures that the average thickness calculation is based on more accurate and reliable data, thereby improving the accuracy of the evaluation results. Averaging the effective electrode thickness data obtained after outlier removal more accurately reflects the average thickness of the electrode under different compaction conditions. This averaging process reduces evaluation errors caused by localized thickness inhomogeneities in the electrode, further enhancing the accuracy of the evaluation results.
[0016] In one possible design, the compaction density data is calculated based on the average thickness and the areal density of the electrode, including: obtaining the compaction density data by dividing the areal density of the electrode by the average thickness of the electrode.
[0017] The above method allows us to obtain the compaction density of the electrode sheet by directly dividing the areal density by the average thickness. This direct calculation method avoids complex mathematical models and algorithms, reduces errors in the calculation process, and thus improves the accuracy of the evaluation results.
[0018] In one possible design, the preset length is 5µm to 10µm, the preset pressure is 10T to 25T, and the length of the test section is 10m to 20m.
[0019] The above scheme presets the length value to 5µm to 10µm, allowing for more precise adjustment of the roll gap. During electrode compaction, smaller changes in roll gap can more accurately reflect changes in electrode thickness, thereby improving the accuracy of compaction density assessment. For example, when the electrode approaches its ultimate compaction density, smaller changes in roll gap can more sensitively capture minute changes in electrode thickness, avoiding assessment errors caused by excessive changes in roll gap.
[0020] The preset pressure value is 10T to 25T, which covers the common pressure range in the electrode compaction process and also meets the requirements of different electrode materials and processes. By gradually increasing the roller pressure within this range, a more comprehensive understanding of the compaction characteristics of the electrode under different pressure conditions can be obtained, thus providing a more reliable basis for determining the ultimate compaction density. For example, for some electrode materials that are difficult to compact, higher pressure values can ensure the reliability of the evaluation results.
[0021] The test section is 10m-20m in length. This length range ensures the representativeness of the test without reducing testing efficiency due to excessive length. A longer test section better reflects the uniformity of the electrode along its length, reducing the impact of local defects or non-uniformity on the test results. Simultaneously, the 10m-20m length range is also feasible in actual production and will not cause excessive interference to the production process.
[0022] In one possible design, a first compaction characteristic curve is obtained based on each roll gap value and the compaction density data corresponding to the roll gap value, including: using the compaction density data as the x-axis and the roll gap value as the y-axis, and fitting the data curve as the first compaction characteristic curve; a second compaction characteristic curve is obtained based on each roll pressure value and the compaction density data corresponding to the roll pressure value, including: using the compaction density data as the x-axis and the roll pressure value as the y-axis, and fitting the data curve as the second compaction characteristic curve.
[0023] By fitting the compaction density data with the corresponding roll gap or roll pressure values using the above method, a smoother and more continuous compaction characteristic curve can be obtained. This data fitting can reduce the impact of measurement errors or data fluctuations, thereby improving the accuracy of the evaluation results. For example, when the electrode is close to its limit compaction density, data fitting can more sensitively capture minute changes in the electrode thickness, avoiding evaluation errors caused by data fluctuations. By analyzing the fitted compaction characteristic curve, the trend and pattern of electrode compaction density with changes in roll gap or pressure can be observed more intuitively.
[0024] In one possible design, determining the ultimate compaction density of the electrode based on a first compaction characteristic curve includes: determining a first inflection point based on the first compaction characteristic curve, and determining the ultimate compaction density of the electrode based on the compaction density value corresponding to the first inflection point, wherein the first inflection point is a point where the slope suddenly increases in the first compaction characteristic curve; determining the ultimate compaction density of the electrode based on a second compaction characteristic curve includes: determining a second inflection point based on the second compaction characteristic curve, and determining the ultimate compaction density of the electrode based on the compaction density value corresponding to the second inflection point, wherein the second inflection point is a point where the slope suddenly increases in the second compaction characteristic curve.
[0025] By analyzing the inflection points of the first and second compaction characteristic curves using the above method, the ultimate compaction density of the electrode can be determined more accurately. Inflection points typically correspond to abrupt changes in electrode compaction density, i.e., the critical point where the electrode transitions from a compactable to an incompressible state. Accurately identifying these inflection points allows for a more precise assessment of the electrode's ultimate compaction density, providing crucial parameter data for battery design and production. A sudden increase in slope indicates a significant change in the curve's slope. Identifying these points allows for more sensitive detection of changes in electrode compaction density, thus improving the accuracy of the assessment results. For example, in the compaction density (PD)-roll gap / pressure curve, an inflection point where the slope suddenly increases reflects the critical state where the electrode transitions from the elastic compression stage to the plastic deformation stage. The PD value corresponding to the sudden increase in slope is the maximum compaction density allowed by the process; exceeding this value can lead to brittle fracture of the electrode or blockage of ion transport channels.
[0026] In one possible design, the method further includes: verifying the result of the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point by comparing the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point.
[0027] The above scheme demonstrates that different testing methods may be affected by various factors. For example, the measurement of the roll gap value may be affected by the equipment accuracy, while the measurement of the roll pressure value may be affected by the accuracy of the pressure sensor. By comparing the results of the two methods, the impact of these measurement errors on the final result can be identified and reduced. The first and second inflection points reflect the limiting states of the electrode under different compaction conditions. The first inflection point (roll gap value) mainly reflects the limiting compaction density of the electrode under changes in physical dimensions, while the second inflection point (roll pressure value) reflects the limiting compaction density under applied external force. By comparing the limiting compaction densities under these two conditions, a more comprehensive understanding of the electrode's compaction characteristics can be obtained. In the battery production process, by comparing and verifying the limiting compaction density, potential deviations in the production process can be identified in a timely manner, and production process parameters can be adjusted promptly. This helps improve the consistency and stability of battery production and reduces battery performance differences caused by inconsistent electrode compaction densities.
[0028] In one possible design, the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point is verified, including: when the error between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point is within a preset range, the ultimate compaction density determined by the first inflection point and / or the ultimate compaction density determined by the second inflection point is determined to be valid; when the error between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point exceeds a preset range, the first inflection point and / or the second inflection point are redefined.
[0029] By setting a preset error range, the validity of the ultimate compaction density determined by the first and second inflection points can be clearly determined. When the error of the ultimate compaction density obtained by the two methods is within the preset range, it indicates that the results of the two methods have high consistency and reliability, thus the result can be determined to be valid. When the error exceeds the preset range, the inflection point is re-determined, which can avoid misjudgment caused by random errors or inaccurate measurements. This verification mechanism can effectively reduce erroneous conclusions caused by data fluctuations or local anomalies, ensuring the accuracy of the evaluation results. Setting a preset error range provides a clear standard for verification, ensuring a unified judgment basis for each evaluation process. This standardized verification process can ensure the repeatability and consistency of test results from different batches and different operators. The clear error range reduces errors caused by human judgment. Operators can directly determine the validity of the result based on the preset range, avoiding interference from subjective factors. By setting a preset error range to verify the ultimate compaction density determined by the first and second inflection points, the accuracy and reliability of the evaluation results can be significantly improved, providing a more scientific basis for the design and production of lithium-ion batteries.
[0030] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more obvious and understandable, specific implementation methods of this application are described below. Attached Figure Description
[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0032] Figure 1 is a flowchart of a method for evaluating the compaction density of lithium-ion battery electrodes according to an embodiment of this application.
[0033] Figure 2 is a flowchart of a method for evaluating the compaction density of lithium-ion battery electrodes according to another embodiment of this application.
[0034] Figure 3 is a correlation curve between the roll gap and the compaction density of the electrode sheet provided in an embodiment of this application.
[0035] Figure 4 is a correlation curve between rolling pressure and electrode compaction density provided in an embodiment of this application. Detailed Implementation
[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0037] Unless otherwise defined, 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 application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.
[0038] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0039] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists, A and B exist simultaneously, or B exists. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.
[0040] The directional terms appearing in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this application. For example, in the description of this application, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0041] Furthermore, the terms "first," "second," etc., in the specification and claims of this application or in the aforementioned drawings are used to distinguish different objects rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.
[0042] In the description of this application, unless otherwise stated, "multiple" means two or more (including two), and similarly, "multiple groups" means two or more (including two groups).
[0043] Accurately assessing the limiting compaction density of electrodes helps battery designers better understand their performance under different compaction conditions. During the battery design phase, the electrode structure and formulation can be optimized based on the limiting compaction density, thereby improving key performance indicators such as energy density, cycle life, and safety. For example, by properly controlling the electrode compaction density, it is possible to reduce the battery's internal resistance and improve its charge / discharge efficiency while maintaining battery capacity.
[0044] As can be seen from the background technology, the current methods used to evaluate the compaction density of battery electrodes lack scientific rigor and accuracy, making it difficult to meet the needs of efficient and precise research and development and production. Therefore, there is a need for a scientific and accurate method to evaluate the compaction density of battery electrodes.
[0045] Analysis revealed that the methods in the relevant technologies include: a. Powder compaction method: the electrode compaction is estimated based on the powder compaction of the positive and negative electrode main materials, and the electrode compaction is equal to the powder compaction plus an empirical value.
[0046] b. Surface density elongation method: By calculating the surface density elongation under different compaction conditions, the electrode compaction is determined using the electrode elongation.
[0047] c. Visual inspection method: The presence of wavy shapes on both sides of the electrode and vertical lines in the middle of the electrode after rolling can be considered as the maximum compaction density of the electrode.
[0048] d. Folding method: Fold the electrode sheets with different compaction densities in half. After folding, the electrode sheets will become translucent or break, reaching the maximum compaction of the electrode sheets.
[0049] e. SEM (Scanning Electron Microscope) method: Cross-sectional scanning of electrodes with different compaction densities is performed, and the maximum compaction of the electrode is reached when the main material particles break down. It can be seen that the above methods for determining electrode compaction density are all based on experience, and then adjusted according to the performance of the battery cell or processing requirements. This method is not only time-consuming and labor-intensive, but also lacks sufficient accuracy.
[0050] In view of this, embodiments of this application provide a method for evaluating the compaction density of lithium-ion battery electrodes. This method involves real-time compaction testing of the electrodes. The real-time compaction test includes, under constant pressure, gradually decreasing the roll gap distance with a preset length value as a gradient, and recording the electrode thickness data corresponding to each roll gap value in real time; and under constant roll gap conditions, gradually increasing the roll pressure with a preset pressure value as a gradient, and recording the electrode thickness data corresponding to each roll pressure value in real time. Real-time recording of the electrode thickness data corresponding to each roll gap value and roll pressure value can reflect the immediate state of the electrode under different compaction conditions in a timely and accurate manner. Based on the collected data, a first compaction characteristic curve (the relationship between roll gap and compaction density) and a second compaction characteristic curve (the relationship between roll pressure and compaction density) are plotted. Analysis of these two curves allows for a direct observation of the trend and pattern of electrode compaction density changes with roll gap and roll pressure. Comprehensive analysis of the first and second compaction characteristic curves enables a more comprehensive, accurate, and objective determination of the electrode's ultimate compaction density, thereby improving production efficiency.
[0051] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.
[0052] Figure 1 is a flowchart of the method for evaluating the compaction density of lithium-ion battery electrodes provided in this embodiment. Referring to Figure 1, the method for evaluating the compaction density of lithium-ion battery electrodes in this embodiment includes:
[0053] Step 1: Perform real-time compaction test on the electrode sheet. The real-time compaction test includes, under constant pressure, gradually decreasing the roll gap with a preset length value as the gradient, and recording the electrode sheet thickness data corresponding to each roll gap value in real time; and under constant roll gap, gradually increasing the roll pressure with a preset pressure value as the gradient, and recording the electrode sheet thickness data corresponding to each roll pressure value in real time.
[0054] Real-time recording of electrode thickness data corresponding to each roll gap value and roll pressure value can reflect the immediate state of the electrode under different compaction conditions in a timely and accurate manner.
[0055] In this embodiment, the preset length value is 5µm to 10µm. This range allows for more precise adjustment of the roll gap. During electrode compaction, a roll gap variation of 5µm to 10µm can more accurately reflect changes in electrode thickness, thereby improving the accuracy of compaction density assessment. For example, when the electrode approaches its ultimate compaction density, a smaller roll gap variation can more sensitively capture minute changes in electrode thickness, avoiding assessment errors caused by excessively large roll gap variations.
[0056] The preset pressure value is 10T to 25T; this range covers the common pressure range in the electrode compaction process and also meets the requirements of different electrode materials and processes. By gradually increasing the roller pressure within this range of 10T to 25T, a more comprehensive understanding of the compaction characteristics of the electrode under different pressure conditions can be obtained, thus providing a more reliable basis for determining the ultimate compaction density. For example, for some electrode materials that are difficult to compact, higher pressure values can ensure the reliability of the evaluation results.
[0057] Figure 2 is a flowchart of the method for evaluating the compaction density of lithium-ion battery electrode sheets provided in this embodiment. Referring to Figure 2, in this embodiment, before performing real-time compaction testing on the electrode sheets, the following steps are also included:
[0058] Step 101: Determine the areal density of the electrode and mark it along the length of the electrode. The markings divide the electrode into multiple test sections along the length of the electrode.
[0059] Understandably, the electrode sheet refers to the original electrode sheet after continuous coating. The electrode sheet should have normal areal density and appearance, meaning it has no obvious defects. Areal density is the mass per unit area of the electrode sheet, and it directly affects the compaction density. By accurately measuring the areal density, the compaction density of the electrode sheet under different compaction conditions can be calculated more precisely, thereby improving the accuracy of the entire evaluation process. The areal density can be pre-calibrated using a weighing method.
[0060] In this embodiment, the electrode sheet is 100m to 600m long, and its width depends on the specifications of the coating machine, ranging from 300mm to 800mm. Marking along the length of the electrode sheet divides it into multiple test sections, ensuring uniform and consistent testing of all parts of the electrode sheet during real-time compaction testing. This segmented testing method avoids uneven testing caused by excessively long electrode sheets, ensuring accurate and reliable compaction density data for each test section. Segmented testing also improves testing efficiency and reduces the impact of mechanical or human errors on the overall test results. Calibrating the roller gap, pressure parameters, and automatic thickness gauge of the roller press are crucial steps in ensuring the accuracy of the test data.
[0061] In this embodiment, the length of the test section can be 10m-20m. This length range ensures the representativeness of the test without reducing testing efficiency due to an excessively long test section. A longer test section can better reflect the uniformity of the electrode along its length, reducing the impact of local defects or non-uniformity on the test results. At the same time, the 10m-20m length range is also feasible in actual production and will not cause excessive interference to the production process.
[0062] Step 102: Provide a roller press and an automatic thickness gauge, and calibrate the roller gap and pressure parameters of the roller press and the automatic thickness gauge.
[0063] The roll gap and pressure parameters of the roller press directly affect the compaction effect of the electrode sheet, while the automatic thickness gauge is a key device for measuring the electrode sheet thickness. By calibrating these devices, it can be ensured that they accurately reflect the compaction state of the electrode sheet during the testing process, thereby improving the accuracy and reliability of the test data.
[0064] Step 2: Obtain the corresponding compaction density data based on the corresponding electrode thickness data.
[0065] The electrode thickness data consists of raw thickness data points measured by an automatic thickness gauge in a single measurement or in real time. It represents a local instantaneous state and may include all measured values such as thinned areas and defect points. Therefore, in this embodiment, obtaining the corresponding compaction density data based on the corresponding electrode thickness data includes the following steps: removing abnormal data from the electrode thickness data in the corresponding test section to obtain effective electrode thickness data; calculating the average value of the electrode thickness based on the effective electrode thickness data to obtain the average thickness of the electrode; and calculating the compaction density data based on the average thickness and areal density.
[0066] Obtaining the average electrode thickness from the electrode thickness data allows for a more accurate reflection of the average thickness under different compaction conditions. This averaging process reduces evaluation errors caused by localized thickness inhomogeneities, thus improving the accuracy of the evaluation results. Calculating the compaction density data from the average thickness and areal density provides a more precise reflection of the electrode's density variation under different compaction conditions. Compaction density is the mass per unit volume of the electrode and is a key parameter for evaluating the compaction effect. Accurate calculation of compaction density allows for a more comprehensive understanding of the electrode's compaction state, providing more accurate parameter data for battery design and production.
[0067] Outlier data includes thickness data from thinned areas at the edges of the electrode, joint areas, or defect points. Outlier data may arise from defects or measurement errors during the electrode manufacturing process, and their presence can significantly affect the accuracy of the average thickness. Removing these outliers ensures that the calculation of the average thickness is based on more accurate and reliable data, thereby improving the accuracy of the evaluation results.
[0068] For example: The automatic thickness gauge measured the electrode thickness data sequence [85, 102, 105, 107, 82] μm in a certain scan (the two sides are the thinned areas).
[0069] The average thickness of the electrode is obtained from the electrode thickness data: after removing abnormal data (such as thinning area, joint area, defect point), only the data of the normal coating area is retained. In the example above, only the average of the middle 3 points is calculated: (102+105+107) / 3≈104.7μm.
[0070] By averaging the effective electrode thickness data obtained after removing outliers, the average thickness of the electrode can be more accurately reflected under different compaction conditions. This averaging process can reduce the evaluation error caused by local unevenness in electrode thickness, thereby improving the accuracy of the evaluation results.
[0071] In this embodiment, the compaction density data is calculated based on the average thickness and the areal density of the electrode sheet, including dividing the areal density of the electrode sheet by the average thickness of the electrode sheet. This direct calculation method avoids complex mathematical models and algorithms, reduces errors in the calculation process, and thus improves the accuracy of the evaluation results.
[0072] Step 3: Obtain the first compaction characteristic curve based on the compaction density data of each roll gap value and the corresponding roll gap value, and obtain the second compaction characteristic curve based on the compaction density data of each roll pressure value and the corresponding roll pressure value.
[0073] Based on the collected data, a first compaction characteristic curve (the relationship between roll gap and compaction density) and a second compaction characteristic curve (the relationship between roll pressure and compaction density) were plotted. Analysis of these two curves allows for a direct observation of the trend and pattern of electrode compaction density changes with roll gap and roll pressure.
[0074] In this embodiment, the first compaction characteristic curve is obtained based on each roll gap value and the compaction density data corresponding to the roll gap value, including: using the compaction density data as the x-axis and the roll gap value as the y-axis, the fitted data curve is the first compaction characteristic curve.
[0075] The second compaction characteristic curve is obtained based on the compaction pressure value and the corresponding compaction density data of each roller pressure value, including: the compaction density data as the x-axis and the roller pressure value as the y-axis, and the fitted data curve is the second compaction characteristic curve.
[0076] In this embodiment, the curve fitting method includes the least squares method or a nonlinear regression algorithm.
[0077] By fitting compaction density data with corresponding roll gap or roll pressure values, a smoother and more continuous compaction characteristic curve can be obtained. This data fitting can reduce the impact of measurement errors or data fluctuations, thereby improving the accuracy of the evaluation results. For example, when the electrode is close to its ultimate compaction density, data fitting can more sensitively capture minute changes in electrode thickness, avoiding evaluation errors caused by data fluctuations. By analyzing the fitted compaction characteristic curve, the trend and pattern of electrode compaction density with changes in roll gap or pressure can be observed more intuitively.
[0078] Step 4: Determine the ultimate compaction density of the electrode based on the first compaction characteristic curve and / or the second compaction characteristic curve.
[0079] In some embodiments, the ultimate compaction density of the electrode can be determined based on a first compaction characteristic curve. This includes the steps of: determining a first inflection point based on the first compaction characteristic curve, and determining the ultimate compaction density of the electrode based on the compaction density value corresponding to the first inflection point. The first inflection point is a point in the first compaction characteristic curve where the slope suddenly increases.
[0080] In some embodiments, the ultimate compaction density of the electrode can be determined based on the second compaction characteristic curve. This includes the steps of: determining a second inflection point based on the second compaction characteristic curve, and determining the ultimate compaction density of the electrode based on the compaction density value corresponding to the second inflection point. The second inflection point is the point where the slope of the second compaction characteristic curve suddenly increases.
[0081] In the compaction density (PD)-roll gap / pressure curve, the inflection point where the slope suddenly increases reflects the critical state where the electrode transitions from the elastic compression stage to the plastic deformation stage. The PD value corresponding to the point of sudden slope increase is the maximum compaction density allowed by the process; exceeding this value will lead to brittle fracture of the electrode or blockage of ion transport channels. Therefore, when the curve tends to be flat or an inflection point appears, it corresponds to the electrode's ultimate compaction density. This characteristic curve-based analysis method can more accurately determine the electrode's ultimate compaction density, providing crucial parameter data for battery design and production.
[0082] By analyzing the inflection points of the first and second compaction characteristic curves, the ultimate compaction density of the electrode can be determined more accurately. Inflection points typically correspond to abrupt changes in the electrode's compaction density, i.e., the critical point where the electrode transitions from a compactable to an incompressible state. Accurately identifying these inflection points allows for a more precise assessment of the electrode's ultimate compaction density, thus providing crucial parameter data for battery design and production.
[0083] A point where the slope suddenly increases indicates a significant change in the curve's slope. Identifying these points allows for more sensitive detection of variations in electrode compaction density, thereby improving the accuracy of assessment results.
[0084] In some embodiments, the ultimate compaction density of the electrode is determined by combining the results of determining the first compaction characteristic curve and the second compaction characteristic curve. By comprehensively analyzing the first and second compaction characteristic curves, the ultimate compaction density of the electrode can be determined more comprehensively and accurately. This comprehensive evaluation method avoids the bias that may arise from single-factor evaluation, improving the accuracy and reliability of determining the ultimate compaction density.
[0085] Figure 3 shows the correlation curve between the roll gap and the electrode compaction density provided in this embodiment. Figure 4 shows the correlation curve between the roll pressure and the electrode compaction density provided in this embodiment. Referring to Figures 3 and 4, it can be seen that the first inflection point (slope abrupt increase point) in the first compaction characteristic curve in Figure 3 is the third to last point, corresponding to a compaction density value of approximately 2.67, meaning the ultimate compaction density determined by the first compaction characteristic curve is 2.67. In contrast, the second inflection point (slope abrupt increase point) in the second compaction characteristic curve in Figure 4 is the third to last point, corresponding to a compaction density value of approximately 2.65, meaning the ultimate compaction density determined by the second compaction characteristic curve is 2.65. The ultimate compaction density values obtained by the two methods are quite close; therefore, either one can be selected as the ultimate compaction density.
[0086] In this embodiment, the working compaction density can be set at 5%-10% before the first inflection point or the second inflection point (e.g., inflection point 1.72 g / cm³). 3 Then the production control is ≤1.65g / cm³. 3 ).
[0087] The above-described method enables the evaluation of electrode compaction density in a shorter time. Compared with traditional evaluation methods, it significantly shortens the evaluation cycle, is not affected by human factors or experience values, and does not require additional testing costs. It can objectively and quickly obtain the ultimate compaction density, thereby providing timely feedback of the evaluation results to the production process. This allows production personnel to quickly adjust the production process based on the evaluation results, reducing production downtime caused by waiting for evaluation results and thus improving production efficiency.
[0088] In this embodiment, considering that different testing methods may be affected by different factors, such as the measurement of roll gap value being affected by equipment accuracy, and the measurement of roll pressure value being affected by pressure sensor accuracy, the results of the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point are verified by comparing the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point.
[0089] By comparing the results of the two methods, the impact of these measurement errors on the final result can be identified and reduced. The first and second inflection points reflect the limiting state of the electrode under different compaction conditions. The first inflection point (roll gap value) mainly reflects the limiting compaction density of the electrode under changes in physical dimensions, while the second inflection point (roll pressure value) reflects the limiting compaction density under applied external force. By comparing the limiting compaction densities under these two conditions, a more comprehensive understanding of the electrode's compaction characteristics can be obtained. In the battery production process, by comparing and verifying the limiting compaction density, potential deviations in the production process can be identified in a timely manner, and production process parameters can be adjusted promptly. This helps improve the consistency and stability of battery production and reduce battery performance differences caused by inconsistent electrode compaction densities.
[0090] In this embodiment, verifying the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point includes: when the error between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point is within a preset range, determining that the ultimate compaction density determined by the first inflection point and / or the ultimate compaction density determined by the second inflection point is valid; when the error between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point exceeds a preset range, re-determining the first inflection point and / or the second inflection point.
[0091] In this embodiment, the preset range of the error can be 0.01-0.1. That is, the difference between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point does not exceed 0.01-0.1.
[0092] In some embodiments, the determination of the ultimate compaction density includes: at the first inflection point and / or the second inflection point (after the point where the slope of the curve suddenly increases), the electrode shows obvious brittle fracture or powdering.
[0093] By setting a preset error range, the validity of the ultimate compaction density determined by the first and second inflection points can be clearly determined. When the error of the ultimate compaction density obtained by the two methods is within the preset range, it indicates that the results of the two methods have high consistency and reliability, thus the result can be determined to be valid. When the error exceeds the preset range, the inflection point is re-determined, which can avoid misjudgment caused by random errors or inaccurate measurements. This verification mechanism can effectively reduce erroneous conclusions caused by data fluctuations or local anomalies, ensuring the accuracy of the evaluation results. Setting a preset error range provides a clear standard for verification, ensuring a unified judgment basis for each evaluation process. This standardized verification process can ensure the repeatability and consistency of test results from different batches and different operators. The clear error range reduces errors caused by human judgment. Operators can directly determine the validity of the result based on the preset range, avoiding interference from subjective factors. By setting a preset error range to verify the ultimate compaction density determined by the first and second inflection points, the accuracy and reliability of the evaluation results can be significantly improved, providing a more scientific basis for the design and production of lithium-ion batteries.
[0094] The method for evaluating the compaction density of lithium-ion battery electrodes provided in this application can accurately obtain the ultimate compaction density and can be directly applied to actual design or production. It does not require additional costs to determine whether the material compaction meets the requirements, is not affected by human factors or experience values, obtains accurate electrode compaction density based on actual measurement data, reduces production line trial and error costs, and improves company efficiency.
[0095] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A method of evaluating lithium-ion battery electrode sheet compaction density, characterized by, Including the following steps: The electrode sheet is subjected to a real-time compaction test, which includes, under constant pressure, gradually reducing the roller gap with a preset length value as a gradient, and recording the electrode sheet thickness data corresponding to each roller gap value in real time. And under constant roll gap conditions, the roll pressure is gradually increased with a preset pressure value as a gradient, and the electrode thickness data corresponding to each roll pressure value is recorded in real time; The corresponding compaction density data is obtained based on the corresponding electrode thickness data; A first compaction characteristic curve is obtained based on each of the roll gap values and the compaction density data corresponding to the roll gap values; a second compaction characteristic curve is obtained based on each of the roll pressure values and the compaction density data corresponding to the roll pressure values. The ultimate compaction density of the electrode is determined based on the first compaction characteristic curve and / or the second compaction characteristic curve.
2. The method of claim 1, wherein, Before performing real-time compaction testing on the electrode sheets, the following steps are also included: The areal density of the electrode is determined, and markings are made along the length of the electrode, which divides the electrode into multiple test segments along the length. Provide a roller press and an automatic thickness gauge, and calibrate the roller gap, pressure parameters of the roller press and the automatic thickness gauge.
3. The method of claim 2, wherein, The step of obtaining the corresponding compaction density data based on the corresponding electrode thickness data includes the following steps: The average thickness of the electrode is obtained based on the electrode thickness data; The compaction density data is calculated based on the average thickness and the areal density.
4. The method of claim 3, wherein, The step of obtaining the average thickness of the electrode based on the electrode thickness data includes: removing abnormal data from the electrode thickness data corresponding to the test section to obtain effective electrode thickness data, wherein the abnormal data includes the thickness data of the edge thinning area, joint area or defect point of the electrode. The average thickness of the electrode is obtained by averaging the effective electrode thickness data.
5. The method of claim 3, wherein, The step of calculating the compaction density data based on the average thickness and the areal density includes: The compaction density data is obtained by dividing the areal density of the electrode by the average thickness of the electrode.
6. The method of claim 2, wherein, The preset length value is 5um to 10um, the preset pressure value is 10T to 25T, and the length of the test section is 10m to 20m.
7. The method of claim 1, wherein, The step of obtaining the first compaction characteristic curve based on each of the roll gap values and the compaction density data corresponding to the roll gap values includes: Using the compaction density data as the x-axis and the roll gap value as the y-axis, the fitted data curve is the first compaction characteristic curve; The step of obtaining the second compaction characteristic curve based on each of the roller pressure values and the compaction density data corresponding to the roller pressure values includes: Using the compaction density data as the x-axis and the roller pressure value as the y-axis, the fitted data curve is the second compaction characteristic curve.
8. The method of claim 1, wherein, Determining the ultimate compaction density of the electrode sheet based on the first compaction characteristic curve includes: The first inflection point is determined based on the first compaction characteristic curve, and the compaction density value corresponding to the first inflection point is determined as the ultimate compaction density of the electrode. The first inflection point is the point where the slope of the first compaction characteristic curve suddenly increases. Determining the ultimate compaction density of the electrode sheet based on the second compaction characteristic curve includes: The second inflection point is determined based on the second compaction characteristic curve, and the compaction density value corresponding to the second inflection point is determined as the ultimate compaction density of the electrode. The second inflection point is the point where the slope of the second compaction characteristic curve suddenly increases.
9. The method of claim 8, wherein, Also includes: The ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point are compared to verify the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point.
10. The method of claim 9, wherein, The verification of the ultimate compaction density determined by the first inflection point or the ultimate compaction density determined by the second inflection point includes: When the error between the ultimate compaction density determined by the first inflection point and the ultimate compaction density determined by the second inflection point is within a preset range, the ultimate compaction density determined by the first inflection point and / or the ultimate compaction density determined by the second inflection point is determined to be valid. When the error between the ultimate compaction density determined by comparing the first inflection point and the ultimate compaction density determined by the second inflection point exceeds a preset range, the first inflection point and / or the second inflection point are re-determined.