Lithium ion battery slurry stability evaluation method and system

Abstract

The invention discloses a lithium ion battery slurry stability evaluation method and system, and the method comprises the steps: selecting a central electrode and a first group of electrodes to construct a first test circuit; applying a preset constant current between the first group of electrodes, and collecting a first voltage value; calculating to obtain a first resistivity; selecting a second group of electrodes to construct a second test circuit; applying a preset constant current between the second group of electrodes, and collecting a second voltage value between the central electrode and the second group of electrodes; calculating a second resistivity according to the second constant current and the second voltage value; when it is determined that the average value of the first resistivity and the second resistivity is smaller than a preset first judgment threshold value, it is determined that resistivity distribution is uniform; according to a preset sampling time interval, continuously collecting resistivity data of a preset number of times, and calculating a standard deviation of the resistivity data of the preset number of times; and when the standard deviation is determined to be less than a preset second determination threshold, determining that the lithium ion battery slurry is stable. The method is used for improving the accuracy of lithium ion battery slurry stability evaluation.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion battery slurry evaluation, and particularly relates to a lithium ion battery slurry stability evaluation method and system. BACKGROUND

[0002] As an important energy storage device, the performance of a lithium ion battery is directly affected by electrode slurry. In the preparation process of electrode slurry, the stability of the slurry is one of the key factors affecting the performance of the battery. At present, traditional methods such as visual observation and deterioration experiments are commonly used to evaluate the stability of the slurry in industrial production. These methods mainly rely on the experience of the operator, and have the problems of strong subjectivity of the evaluation results, low accuracy, and difficulty in real-time monitoring, which cannot meet the requirements of modern lithium ion battery manufacturing process for slurry stability evaluation.

[0003] In related technologies, a slurry stability evaluation method based on ultrasonic detection can be used. This method emits ultrasonic waves into the slurry, uses the attenuation characteristics of ultrasonic waves in the propagation process to characterize the uniformity and stability of the slurry, and analyzes the changes of the ultrasonic wave signal by computer software to evaluate the state of the slurry. This method not only objectively reflects the stable state of the slurry, but also realizes continuous monitoring, improving the accuracy and efficiency of the evaluation.

[0004] However, since the ultrasonic waves are easily affected by the temperature and bubbles of the slurry during propagation, and the ultrasonic signal is difficult to distinguish the dispersion state of each component in the slurry, the evaluation results can only reflect the overall uniformity of the slurry, and it is difficult to accurately characterize the formation of the conductive network, which to some extent limits the comprehensive evaluation of the conductive performance and stability of the slurry, and reduces the accuracy of the lithium ion battery slurry stability evaluation. SUMMARY

[0005] The application provides a lithium ion battery slurry stability evaluation method and system for improving the accuracy of lithium ion battery slurry stability evaluation.

[0006] In a first aspect, the application provides a lithium ion battery slurry stability evaluation method. In the case of determining that the lithium ion battery slurry is injected into a glass ring test cavity, a first test circuit is constructed by selecting a center electrode of the glass ring test cavity and a first group of electrodes located on one side of the center electrode. The inner wall of the glass ring test cavity is provided with seven conductive electrodes, including one center electrode located at the center and six conductive electrodes distributed along both sides of the center electrode. A predetermined constant current is applied between the first group of electrodes, and a first voltage value between the center electrode and the first group of electrodes is collected. A first resistivity is calculated according to the predetermined constant current and the first voltage value. selecting the center electrode and a second group of electrodes located on the other side of the center electrode to construct a second test circuit; applying a preset constant current between the second group of electrodes, and collecting a second voltage value between the center electrode and the second group of electrodes; calculating a second resistivity according to the preset constant current and the second voltage value; In the case where the average of the first resistivity and the second resistivity is less than a preset first determination threshold, it is determined that the resistivity distribution is uniform; According to the preset sampling time interval, the resistivity data of the preset number of times is continuously collected, and the standard deviation of the resistivity data of the preset number of times is calculated; When it is determined that the standard deviation is less than a preset second determination threshold, it is determined that the lithium ion battery slurry is stable.

[0007] By adopting the above technical scheme, by arranging seven conductive electrodes in the glass circular ring test cavity, and using the center electrode and the two pairs of electrode groups located on both sides of the center electrode to construct test circuits, the resistivity of the slurry at different heights can be measured. When the resistivity ratio measured at two heights is less than a preset threshold, it indicates that the electric field distribution of the slurry in the cavity is uniform, which indicates that the slurry dispersion is good. On this basis, by continuously collecting resistivity data at a preset time interval and calculating the standard deviation, the stability of the slurry can be evaluated. When the standard deviation is less than a preset threshold, it indicates that the electrical properties of the slurry fluctuate less during the test, which proves that the distribution of the slurry components is stable and no obvious stratification or agglomeration phenomenon occurs. This evaluation method directly reflects the uniformity and stability of the slurry through the measurement of electrical parameters, can monitor the dynamic changes of the slurry state in real time, and improves the accuracy of the evaluation of the quality of the slurry.

[0008] In combination with some embodiments of the first aspect, in some embodiments, after determining that the lithium ion battery slurry is stable, the method further comprises: In the first test circuit, a preset constant current is applied in a direction opposite to the direction of the preset constant current, and a third voltage value between the center electrode and the first group of electrodes is collected; calculating a third resistivity according to the preset constant current and the third voltage value; calculating the difference between the first resistivity and the third resistivity to obtain a first difference; In the second test circuit, a preset constant current is applied in a direction opposite to the direction of the preset constant current, and a fourth voltage value between the center electrode and the second group of electrodes is collected; calculating a fourth resistivity according to the preset constant current and the fourth voltage value; calculating the difference between the second resistivity and the fourth resistivity to obtain a second difference; When the first difference value and the second difference value are both less than a preset third determination threshold, and a ratio of the first difference value to the second difference value is within a preset range, it is determined that the lithium ion battery slurry is stable.

[0009] By adopting the technical scheme, the polarization characteristics and the reversibility of the electrical performance of the lithium ion battery slurry under the action of an electric field are evaluated by applying preset constant currents in opposite directions in the first test circuit and the second test circuit respectively and calculating the corresponding resistivity difference values and the ratio thereof. When the conductive material in the slurry is uniformly and stably distributed, the resistivity difference values measured by applying the currents in opposite directions are small, indicating that the slurry will not be obviously polarized and the composition will not be migrated under the action of an electric field. By setting a reasonable third determination threshold and a preset range, the stability of the slurry can be accurately determined, and the decline in the electrochemical performance caused by the uneven distribution or agglomeration of the conductive material in the slurry can be avoided. The bidirectional test method can more comprehensively reflect the intrinsic conductive characteristics of the slurry, reduce the measurement error caused by the electrode polarization effect in the test process, and improve the accuracy and reliability of the stability evaluation of the slurry.

[0010] In combination with some embodiments of the first aspect, in some embodiments, after it is determined that the lithium ion battery slurry is stable, the method further comprises: applying a preset constant current in the direction of the preset constant current in the first test circuit and keeping for a first preset time duration, and recording an initial first resistivity and a steady-state first resistivity; calculating a first change rate of the initial first resistivity and the steady-state first resistivity; applying the preset constant current in the direction opposite to that of the preset constant current in the first test circuit and keeping for the first preset time duration, and recording an initial second resistivity and a steady-state second resistivity; calculating a second change rate of the initial second resistivity and the steady-state second resistivity; applying the preset constant current in the direction of the preset constant current in the second test circuit and keeping for the first preset time duration, and recording an initial third resistivity and a steady-state third resistivity; calculating a third change rate of the initial third resistivity and the steady-state third resistivity; applying the preset constant current in the direction opposite to that of the preset constant current in the second test circuit and keeping for the first preset time duration, and recording an initial fourth resistivity and a steady-state fourth resistivity; calculating a fourth change rate of the initial fourth resistivity and the steady-state fourth resistivity; When a maximum difference among the first change rate, the second change rate, the third change rate and the fourth change rate is less than a preset fourth determination threshold, it is determined that the solid particles in the lithium ion battery slurry are stably distributed.

[0011] By adopting the technical scheme, forward and reverse constant current tests are respectively performed on two test circuits for a certain time length, the initial and steady-state resistivity is recorded and the change rate thereof is calculated, and the distribution state and migration trend of the solid particles in the lithium ion battery slurry can be evaluated. When the solid particles in the slurry are stably distributed, the change rate of the resistivity under the action of the continuous current is small, and the change rates obtained by tests in different directions are close, which indicates that the solid particles will not migrate or agglomerate in a direction under the action of the electric field. By comparing the maximum difference of the change rates of the resistivity obtained by tests in the four directions with the preset fourth determination threshold, the accuracy of characterizing the stability of the distribution of the solid particles in the slurry can be improved.

[0012] In some embodiments in combination with some embodiments of the first aspect, after determining that the lithium ion battery slurry is stable, the method further comprises: arranging the resistivity data of the preset number of times in time sequence to obtain resistivity time sequence data; segmenting the resistivity time sequence data to obtain a plurality of groups of resistivity segmented data; calculating the mean value of each group of resistivity segmented data to obtain a resistivity mean value sequence; calculating the difference between the mean values of adjacent two groups of resistivity segmented data to obtain a resistivity gradient sequence; when the change rate of the resistivity gradient sequence is greater than a preset rate threshold and the maximum gradient value is greater than a preset fifth determination threshold, determining that the lithium ion battery slurry is deteriorated.

[0013] By adopting the technical scheme, the continuously collected resistivity data is subjected to time sequence analysis and segmentation processing, the resistivity mean value sequence and the gradient sequence are calculated, and the change trend of the performance of the lithium ion battery slurry with time can be dynamically monitored. When the slurry is deteriorated, the resistivity of the slurry will present an obvious change trend, which is that the change rate of the resistivity gradient sequence is significantly increased. By setting reasonable preset rate threshold and preset fifth determination threshold, abnormal changes in the performance of the slurry can be found in time. This method based on time sequence data analysis can reflect the dynamic change process of the performance of the slurry in real time, and the accuracy of the quality evaluation of the slurry is improved.

[0014] In some embodiments in combination with some embodiments of the first aspect, segmenting the resistivity time sequence data to obtain a plurality of groups of resistivity segmented data specifically comprises: selecting a preset time length as a segmentation time window; dividing the resistivity time sequence data into a plurality of groups of resistivity time sequence data according to the segmentation time window, each group of resistivity time sequence data containing an equal number of time points; linearly fitting each group of resistivity time sequence data to obtain a fitting slope; deleting the data group with an absolute value of the fitting slope greater than a preset sixth determination threshold to obtain a plurality of groups of resistivity segmented data.

[0015] By adopting the technical solution, the continuous resistivity data is divided into multiple data groups with the same time span by selecting the preset time length as the segmentation time window, so that each group of data can reflect the resistivity change characteristics of the slurry in a specific time period. Linear fitting is performed on each group of data, and the fitting slope is calculated, so that the abnormal data segment with rapid fluctuation of resistivity can be identified. By setting a preset sixth determination threshold and deleting the data group with an absolute value of the fitting slope exceeding the threshold, the abnormal data caused by external interference or measurement error can be filtered out, and the data segment truly reflecting the change of the slurry state is retained, thereby improving the accuracy of subsequent quality change judgment, reducing the interference of noise data on the judgment result, and enabling the system to more accurately identify the actual quality change state of the slurry.

[0016] In combination with some embodiments of the first aspect, in some embodiments, after determining that the lithium ion battery slurry is undergoing downward quality change or upward quality change, the method further comprises: calculating the ratio of adjacent gradient values in the resistivity gradient sequence to obtain a gradient change rate sequence; when the average value of the gradient change rate sequence is greater than a preset seventh determination threshold, determining that the lithium ion battery slurry is undergoing accelerated quality change; when the average value of the gradient change rate sequence is not greater than the preset seventh determination threshold, determining that the lithium ion battery slurry is undergoing uniform quality change.

[0017] By adopting the technical solution, the average value of the gradient change rate sequence is compared with the preset seventh determination threshold, so that it can be determined whether the slurry is in an accelerated quality change state or a uniform quality change state. When the average value of the gradient change rate sequence is greater than the threshold, it indicates that the resistivity change speed is continuously increasing, which means that the interaction between the active material particles in the slurry is gradually enhanced, and the quality change speed is continuously accelerated. When the average value of the gradient change rate sequence is not greater than the threshold, it indicates that the resistivity change speed is basically stable, which means that the active material particles in the slurry have reached a dynamic equilibrium state, and the quality change speed tends to be constant. This quality change state judgment method based on the gradient change rate can more timely find the deterioration trend of the stability of the slurry.

[0018] In combination with some embodiments of the first aspect, in some embodiments, after determining that the lithium ion battery slurry is undergoing accelerated quality change, the method further comprises: sorting the gradient change rate sequence according to the numerical value; calculating the gradient change rate value at the preset percentile in the sorted gradient change rate sequence; determining the quality change degree level of the lithium ion battery slurry according to the interval of the gradient change rate value in the preset quality change degree level table.

[0019] By adopting the technical solution, the gradient change rate sequence is sorted and the gradient change rate value of a specific percentile is calculated, a characteristic value reflecting the change of the slurry metamorphic speed is obtained, the characteristic value is not affected by individual extreme data. Comparing the characteristic value with the interval in the preset metamorphic degree grade table can accurately determine the metamorphic degree grade of the slurry. By establishing the corresponding relationship between the gradient change rate value and the metamorphic degree grade, the system can quantitatively evaluate the metamorphic degree of the slurry, and the accuracy of the slurry stability evaluation is improved.

[0020] In a second aspect, the embodiments of the present application provide a lithium ion battery slurry stability evaluation system, which comprises one or more processors and a memory; the memory is coupled with the one or more processors, and is used to store computer program codes, the computer program codes comprising computer instructions, and the one or more processors invoke the computer instructions to enable the system to perform the method described in the first aspect and any possible implementation manner of the first aspect.

[0021] In a third aspect, the embodiments of the present application provide a computer readable storage medium comprising instructions, which, when executed on a system, cause the system to perform the method described in the first aspect and any possible implementation manner of the first aspect.

[0022] In a fourth aspect, the embodiments of the present application provide a computer program product, which, when executed on a system, causes the system to perform the method described in any possible implementation manner of the first aspect.

[0023] The one or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. The present application provides a lithium ion battery slurry stability evaluation method, by arranging seven conductive electrodes in a glass circular test cavity, and using the central electrode and the two pairs of electrodes located on both sides of the central electrode to construct test circuits, the resistivity of the slurry at different heights can be measured. When the resistivity ratio measured at two heights is less than a preset threshold, it indicates that the electric field distribution of the slurry in the cavity is uniform, which indicates that the slurry dispersion is good. On this basis, by continuously collecting resistivity data at a preset time interval and calculating the standard deviation, the stability of the slurry can be evaluated. When the standard deviation is less than a preset threshold, it indicates that the electrical properties of the slurry fluctuate less during the test, proving that the slurry component distribution is stable and no obvious stratification or agglomeration phenomenon occurs. This evaluation method directly reflects the uniformity and stability of the slurry through the measurement of electrical parameters, can monitor the dynamic changes of the slurry state in real time, and improves the accuracy of the slurry quality evaluation.

[0024] 2. The application provides a lithium ion battery slurry stability evaluation method. A preset constant current is applied in opposite directions in the first test circuit and the second test circuit, respectively, and the corresponding resistivity difference and the ratio thereof are calculated to evaluate the polarization characteristics and the reversibility of the electrical properties of the lithium ion battery slurry under the action of an electric field. When the conductive material in the slurry is uniformly and stably distributed, the resistivity difference measured by applying the current in opposite directions is small, indicating that the slurry will not undergo significant polarization and composition migration under the action of an electric field. By setting a reasonable third determination threshold and a preset range, the stability of the slurry can be accurately determined, and the decline in electrochemical performance caused by uneven distribution or agglomeration of the conductive material in the slurry can be avoided. This bidirectional testing method can more comprehensively reflect the intrinsic conductive properties of the slurry, reduce measurement errors caused by electrode polarization effects during testing, and improve the accuracy and reliability of slurry stability evaluation.

[0025] 3. The application provides a lithium ion battery slurry stability evaluation method. The resistivity data collected continuously is subjected to time series analysis and segmented processing, and by calculating the mean value sequence and the gradient sequence of the resistivity, the change trend of the lithium ion battery slurry performance over time can be dynamically monitored. When the slurry deteriorates, its resistivity will show a significant change trend, which is manifested as a significant increase in the change rate of the resistivity gradient sequence. By setting a reasonable preset rate threshold and a preset fifth determination threshold, abnormal changes in the performance of the slurry can be detected in a timely manner. This method based on time series data analysis can reflect the dynamic change process of the performance of the slurry in real time, improving the accuracy of slurry quality evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a glass circular ring test cavity schematic diagram provided by an embodiment of the application.

[0027] Figure 2 is a flowchart of a lithium ion battery slurry stability evaluation method in an embodiment of the application.

[0028] Figure 3 is a flowchart of an evaluation method based on forward and reverse current testing in an embodiment of the application.

[0029] Figure 4 is a physical device structure schematic diagram of a lithium ion battery slurry stability evaluation system provided by an embodiment of the application. DETAILED DESCRIPTION

[0030] The terminology used in the following embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the embodiments of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include both singular and plural forms, unless the context clearly indicates otherwise. It will be further understood that the terms "and / or", as used in the description of the embodiments of the application, refers to any or all possible combinations of one or more of the associated listed items.

[0031] Hereinafter, the terms "first", "second" are only for the purpose of description, and cannot be understood as implying or suggesting relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features, and in the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise specified.

[0032] Firstly, in combination with Figure 1 A glass ring test cavity is introduced in the embodiments of the present application. There are seven electrodes in the glass ring test cavity, the electrode in the center is the center electrode, three electrodes are evenly distributed on the left side of the center electrode, and three electrodes are also evenly distributed on the right side of the center electrode. The left three electrodes and the center electrode form the first group of electrodes, and the right three electrodes and the center electrode form the second group of electrodes. The center electrode is a current source, the first electrode and the last electrode arranged from left to right are grounded, and the remaining electrodes are voltage sources.

[0033] Next, an embodiment is used to combine Figure 2 A lithium ion battery slurry stability evaluation method in the embodiments of the present application is described: Please refer to Figure 2 A flowchart of a lithium ion battery slurry stability evaluation method in the embodiments of the present application is shown.

[0034] S101, in the case of determining that the lithium ion battery slurry is injected into the glass ring test cavity, the center electrode of the glass ring test cavity and the first group of electrodes on one side of the center electrode are selected to construct a first test circuit; In the case of determining that the lithium ion battery slurry has been injected into the glass ring test cavity, the system selects the center electrode of the glass ring test cavity and the first group of electrodes on one side of the center electrode to construct a first test circuit. The specific schematic diagram of the glass ring test cavity is shown in Figure 1 .

[0035] The system can construct the first test circuit using a mechanical connection method. Specifically, the center electrode is first fixed to the center of the test chamber using threads or clips, ensuring the electrode is vertically inserted into the slurry to an appropriate depth. Then, three adjacent electrodes located on one side of the center electrode are selected as the first group of electrodes. Test leads with spring clips or alligator clips are used to connect the center electrode and the first group of electrodes to the corresponding ports of the measuring instrument. The measuring instrument can be a comprehensive tester with constant current source and voltage measurement functions. Measurements can begin after setting the test parameters via the instrument panel or software interface. Alternatively, the system can construct the first test circuit using an automated testing platform. This platform includes an electrode switching matrix, a programmable constant current source, a digital voltmeter, and a control computer. The electrode switching matrix automatically switches between different electrode combinations via relays or semiconductor switches. The control computer controls the switching matrix to select the center electrode and the first group of electrodes through a preset program, simultaneously controlling the constant current source output and voltmeter measurement, thus automating the construction of the test circuit and the measurement process.

[0036] S102. Apply a first constant current between the first set of electrodes and collect the first voltage value between the center electrode and the first set of electrodes. This step is performed after the first test circuit is constructed. A constant current is applied between the first set of electrodes, and the voltage value between the center electrode and the first set of electrodes is acquired and recorded as the first voltage value. The magnitude of the first constant current can be set according to actual needs and is not limited here.

[0037] The system can apply a constant current between the first set of electrodes using a constant current source. Simultaneously, the system uses a voltmeter to measure the voltage between the center electrode and the first set of electrodes, and records the measurement result as the first voltage value.

[0038] The system can also use a signal generator to produce a constant current signal, amplify it to the required current value through a signal amplifier, and then apply it between the first set of electrodes. Simultaneously, the system uses a data acquisition card to acquire the voltage signal between the center electrode and the first set of electrodes, converts it into a digital quantity, and records it as the first voltage value.

[0039] During low-current testing, noise in the measurement circuit can significantly affect the voltage measurement value, reducing measurement accuracy. To address this issue, the system can filter the acquired voltage signal, for example, using a low-pass filter to remove high-frequency noise and improve signal quality. Furthermore, the system can acquire voltage values ​​multiple times and average them to reduce the impact of random noise.

[0040] S103. Calculate the first resistivity based on the first constant current and the first voltage value; This step involves using a first constant current and a first voltage value to calculate the resistivity of the slurry along a first direction, denoted as the first resistivity. The calculation formula is: First resistivity = First voltage value / First constant current.

[0041] S104. Select the center electrode and the second set of electrodes located on the other side of the center electrode to construct the second test circuit; After completing the measurements of the first test circuit, the system selects a central electrode and a second set of electrodes located on the other side of the central electrode to construct a second test circuit. The second set of electrodes refers to one or more electrodes located on the other side of the central electrode relative to the first set of electrodes; these electrodes are also distributed on the circumference of the annular cavity. The construction method of the second test circuit is similar to that of the first test circuit, but the electrode combination is different. Its purpose is to measure the electrical properties of the slurry in another direction, which will not be elaborated here. By comparing the measurement results in two different directions, the uniformity of the slurry distribution within the test cavity can be evaluated.

[0042] S105. Apply a second constant current between the second set of electrodes and collect the second voltage value between the center electrode and the second set of electrodes. This step is similar to step S102, except that the test circuit and the current and voltage values ​​are different. The system applies a second constant current between the second set of electrodes and collects the voltage value between the center electrode and the second set of electrodes, which is recorded as the second voltage value.

[0043] S106. The second resistivity is calculated based on the second constant current and the second voltage value; This step is similar to step S103, except that the current and voltage values ​​used are different. Based on the second constant current and the second voltage value, the system calculates the resistivity of the slurry along the second direction, denoted as the second resistivity. The calculation formula is: Second resistivity = Second voltage value / Second constant current.

[0044] S107. If the ratio of the first resistivity to the second resistivity is less than a preset first judgment threshold, the resistivity distribution is determined to be uniform. This step determines the uniformity of the electric field distribution in the slurry by comparing the ratio of the first resistivity to the second resistivity with a preset threshold. If the resistivity ratio in both directions is less than the preset first threshold, the electric field distribution in the slurry within the test chamber is considered uniform; otherwise, it is considered non-uniform. The first threshold can be set according to the properties of the slurry and the uniformity requirements; for example, it can be set to 1.2, 1.5, etc., and is not limited here.

[0045] The system can directly calculate the ratio of the first resistivity to the second resistivity, and then compare it with a preset first judgment threshold. If the ratio is less than the threshold, the electric field distribution is determined to be uniform; otherwise, the electric field distribution is determined to be non-uniform.

[0046] The system can also first calculate the difference between the first resistivity and the second resistivity, then calculate the ratio of this difference to either the first resistivity or the second resistivity (whichever is larger), and compare this ratio to a preset percentage threshold. If the ratio is less than the percentage threshold, the electric field distribution is determined to be uniform; otherwise, the electric field distribution is determined to be non-uniform.

[0047] When the slurry has poor conductivity, the resistivity measurement value may fluctuate significantly, leading to inaccurate results from a single comparison. To address this issue, the system can perform multiple resistivity measurements and comparisons, statistically analyze the results, and only determine uniform electric field distribution when the uniformity rate exceeds a preset value (e.g., 80%), thus improving the reliability of the judgment. Furthermore, the system can adapt to slurries with different conductivity properties by adjusting the judgment threshold.

[0048] S108. Collect resistivity data continuously for a preset number of times according to a preset sampling time interval, and calculate the standard deviation of the resistivity data for the preset number of times. This step is to assess the stability of the slurry properties. The system measures the resistivity of the slurry multiple times at preset sampling intervals, obtaining a set of resistivity data. Then, the system calculates the standard deviation of this set of data to evaluate the degree of fluctuation in the slurry properties. The sampling interval and the number of sampling times can be set according to actual needs, such as sampling once every 1 minute for 10 consecutive times; there is no limitation here.

[0049] The system can use a timer to control the sampling interval, performing a resistivity measurement at each sampling time and recording the measured value until a preset number of samples are completed. Then, the system uses the standard deviation formula to calculate the standard deviation of this set of data.

[0050] If the system has a data caching function, the sampling time points for the preset number of times can be set first, and then resistivity measurements can be performed continuously, with the measured values ​​automatically recorded in the cache. When the last sampling time point is reached, the system reads the data from the cache and calculates its standard deviation.

[0051] During prolonged continuous testing, the properties of the slurry may change, leading to significant deviations in later measurement data compared to earlier data, thus affecting the accuracy of the overall evaluation results. To address this issue, the system can monitor data trends while collecting data. When a monotonically increasing or decreasing trend is detected, it indicates a possible change in the slurry properties, requiring immediate cessation of testing and reassessment. Furthermore, the system can divide the sampling time window into multiple segments, calculating the standard deviation of the data within each window. By comparing the standard deviations across different time windows, it can determine whether the stability of the slurry properties has changed.

[0052] S109. When the standard deviation is less than the preset second judgment threshold, the lithium-ion battery slurry is determined to be stable.

[0053] This step determines the stability of the slurry properties by comparing the standard deviation with a preset threshold. If the calculated standard deviation is less than the preset second judgment threshold, the electrical properties of the slurry are considered to have minimal fluctuations during the test, the component distribution of the slurry is stable, and there is no obvious stratification or agglomeration. Conversely, the slurry properties are considered unstable. The second judgment threshold can be set according to the stability requirements of the slurry properties, typically 5% or 10% of the average resistivity of the slurry, etc., and is not limited here.

[0054] In the above embodiments, by arranging seven conductive electrodes in a glass ring test chamber and constructing test circuits using a central electrode and two pairs of electrode groups located on either side of the central electrode, the resistivity of the slurry at different heights can be measured. When the ratio of the resistivity measured at two heights is less than a preset threshold, it indicates that the electric field distribution of the slurry within the chamber is uniform, indicating good slurry dispersion. Based on this, the stability of the slurry can be evaluated by continuously collecting resistivity data at preset time intervals and calculating the standard deviation. When the standard deviation is less than a preset threshold, it indicates that the electrical properties of the slurry fluctuate little during the test, proving that the slurry component distribution is stable and no obvious stratification or agglomeration has occurred. This evaluation method directly reflects the uniformity and stability of the slurry through the measurement of electrical parameters, enabling real-time monitoring of the dynamic changes in the slurry state and improving the accuracy of slurry quality assessment.

[0055] The above embodiments mainly describe the evaluation of the uniformity and stability of lithium-ion battery slurry by resistivity measurements in different directions. To further improve the reliability of the evaluation, this application also provides an evaluation method based on forward and reverse current testing. This method can not only detect the stability of the slurry, but also evaluate the polarization characteristics and solid particle distribution of the slurry under the action of an electric field.

[0056] Please see Figure 3 This is a flowchart illustrating an evaluation method based on forward and reverse current testing in an embodiment of this application.

[0057] S201. In the first test circuit, a preset constant current is applied in a direction opposite to the preset constant current direction, and the third voltage value between the center electrode and the first group of electrodes is collected. In the first test circuit, the system applies a preset constant current in the opposite direction to the preset constant current, and collects the third voltage value between the center electrode and the first set of electrodes. The preset constant current refers to the current value set during the preceding test, which remains constant throughout the test. The opposite current direction means that the current flows in the opposite direction to the previous test; for example, if the current previously flowed from one electrode to another in the first set of electrodes, now the current flows from the other electrode to the first electrode. The third voltage value is the voltage measured between the center electrode and the first set of electrodes under the action of the reverse current. This forward and reverse current testing method can eliminate the influence of factors such as electrode polarization on the measurement results and improve measurement accuracy. The magnitude of the preset constant current can be set according to the conductivity of the slurry and the required testing accuracy; for example, it can be from 0.1mA to 10mA, and is not limited here. The application time of the reverse current can be the same as the forward current, or it can be adjusted according to actual needs, and is not limited here.

[0058] The system can apply reverse current using a bipolar constant current source. The bipolar constant current source has a positive / negative output switching function, and the direction of the output current can be changed via a control signal. Specifically, the system first connects the output terminal of the bipolar constant current source to the first set of electrodes, sets the output current value to a preset constant current value, and then switches the current direction to reverse via the control panel or software interface. Simultaneously, a high-precision digital voltmeter is connected between the center electrode and the first set of electrodes to collect voltage values ​​in real time. Once the current stabilizes, the voltage value at this point is recorded as the third voltage value. The system can also be implemented using a combination of a programmable power supply and a multiplexer. This scheme uses a unipolar programmable constant current source in conjunction with a double-pole double-throw relay to switch the current direction. The normally open and normally closed contacts of the relay are connected to the two electrodes of the first set of electrodes, respectively, and the direction of current flow is changed by controlling the on / off state of the relay. According to a preset program, after completing the forward current test, the control system automatically switches the relay state to reverse the current flow and then collects the corresponding voltage value.

[0059] S202. Calculate the third resistivity based on the preset constant current and the third voltage value; The system calculates the third resistivity based on a preset constant current and a third voltage value. The third resistivity is a parameter characterizing the electrical properties of the slurry under reverse current. The calculation formula is: Third resistivity = Third voltage value / Preset constant current × Geometric factor. The geometric factor is related to the structure of the test chamber and the electrode configuration, and can be determined through theoretical calculation or calibration experiments. The unit of the third resistivity is usually Ω·m or Ω·cm, but is not limited here. The current value used in the calculation should be the absolute value of the actual applied current, regardless of direction.

[0060] The system can obtain the third resistivity through direct calculation. Specifically, the system reads the third voltage value and a preset constant current value from the measuring instrument, divides them to obtain the resistance value, and then multiplies it by a predetermined geometric factor to obtain the third resistivity. The geometric factor can be calculated using finite element simulation software or calibrated using a standard solution with known resistivity. The calculation results can be displayed on the instrument interface and stored in a data file for subsequent analysis. Alternatively, the system can use a lookup table method to quickly calculate the third resistivity. This method pre-establishes a voltage-current-resistivity correspondence table, storing the resistivity values ​​corresponding to different combinations of voltage and current values. During measurement, the system quickly obtains the third resistivity value based on the measured third voltage value and the preset constant current value through table lookup and interpolation. This method is fast and suitable for real-time monitoring applications.

[0061] S203. Calculate the difference between the first resistivity and the third resistivity to obtain the first difference; The system calculates the difference between the first and third resistivity, obtaining the first difference value. The first resistivity is the resistivity value measured under forward current, and the third resistivity is the resistivity value measured under reverse current. The first difference value reflects the degree of difference in the electrical properties of the slurry under forward and reverse current. The calculation formula is: First difference value = |First resistivity - Third resistivity|. The magnitude of the difference value can reflect whether there is a directional structure or polarization phenomenon in the slurry.

[0062] It should be noted that steps S201-S203 and steps S204-S206 are two parts that are not related in terms of timing. They can be executed simultaneously or separately, and there is no limitation here.

[0063] S204. In the second test circuit, a preset constant current is applied in the opposite direction to the preset constant current, and the fourth voltage value between the center electrode and the second set of electrodes is collected. In the second test circuit, a preset constant current is applied in the opposite direction to the preset constant current, and a fourth voltage value is acquired between the center electrode and the second set of electrodes. This step is similar to step S201, but is performed in the second test circuit. The second test circuit includes a center electrode and a second set of electrodes located on the other side of the center electrode. The fourth voltage value is the voltage value measured in the second test circuit under the action of reverse current. By performing forward and reverse current tests in test circuits with different directions, the anisotropy and stability of the slurry can be evaluated more comprehensively. The value of the preset constant current is the same as in step S201 to ensure the consistency of the test conditions, and is not limited here.

[0064] The system can achieve this step by automatically switching the test circuit and current direction. Specifically, the system is equipped with an electrode switching matrix and a bipolar constant current source. The test circuit is first switched to the second test circuit via program control, and then the constant current source is set to output a reverse current. The voltage acquisition module automatically records the voltage value between the center electrode and the second set of electrodes. The entire process can be completed automatically through a preset test sequence without manual intervention. The system can also employ a parallel testing scheme. This scheme uses a multi-channel constant current source and a multi-channel voltage acquisition device, which can simultaneously apply current to multiple test circuits and acquire voltage values. After the second test circuit is connected to an independent test channel, the system can apply a reverse current to the second test circuit and acquire a fourth voltage value while performing other tests, improving testing efficiency.

[0065] S205. Calculate the fourth resistivity based on the preset constant current and the fourth voltage value; The system calculates the fourth resistivity based on a preset constant current and a fourth voltage value. The calculation method for the fourth resistivity is similar to that of the third resistivity, but it uses the fourth voltage value measured in the second test circuit. The formula is: Fourth resistivity = Fourth voltage value / Preset constant current × Geometric factor. Since the electrode configuration of the second test circuit may differ from that of the first test circuit, the geometric factor may need to be redefined. The fourth resistivity also reflects the electrical properties of the slurry, but in different test directions.

[0066] S206. Calculate the difference between the second resistivity and the fourth resistivity to obtain the second difference. The system calculates the difference between the second and fourth resistivity to obtain the second difference value. The second resistivity is the resistivity value measured under forward current in the second test circuit, and the fourth resistivity is the resistivity value measured under reverse current in the same circuit. The calculation method for the second difference is the same as that for the first difference, and the formula is: Second difference value = |Second resistivity - Fourth resistivity|. By comparing the first and second differences, the uniformity and symmetry of the slurry in different directions can be evaluated.

[0067] S207. When both the first difference and the second difference are less than the preset third judgment threshold, and the ratio of the first difference to the second difference is within the preset range, the lithium-ion battery slurry is determined to be stable. When both the first and second differences are less than a preset third threshold, and the ratio of the first to the second difference is within a preset range, the system determines that the lithium-ion battery slurry is stable. The preset third threshold is a standard value used to determine whether the difference between forward and reverse tests is within an acceptable range. It can be set according to the slurry type and quality requirements; for example, it can be set to 5% or 10% of the average resistivity, without limitation here. The preset range refers to the allowable range of the ratio of the first to the second difference, for example, 0.8 to 1.2, indicating that the test differences in the two directions should be similar, without limitation here. This dual judgment condition can more accurately assess the stability and uniformity of the slurry.

[0068] The system can implement this step through a logical judgment procedure. The program first compares the first and second differences with a preset third judgment threshold. If both are less than the threshold, it proceeds to the next judgment step. Then, it calculates the ratio of the first to the second difference and determines whether this ratio is within a preset range. Only when both conditions are met does the system output a judgment result indicating slurry stability. Alternatively, the system can employ a fuzzy logic judgment method. This method converts the difference magnitude and ratio range into fuzzy membership degrees and comprehensively evaluates slurry stability through fuzzy inference rules. This method can handle the uncertainty of the judgment boundary and provide a more reasonable judgment result.

[0069] It should be noted that steps S208-S211 and steps S212-S215 are two parts that are not related in terms of timing. They can be executed simultaneously or separately, and there is no limitation here.

[0070] S208. In the first test circuit, a preset constant current is applied in the direction of a preset constant current and maintained for a first preset duration, and the initial first resistivity and steady-state first resistivity are recorded. In the first test circuit, a preset constant current is applied in the direction of the preset constant current and maintained for a preset duration. The initial first resistivity and the steady-state first resistivity are recorded. The first preset duration refers to the length of time the current is continuously applied, which can be determined based on the time required for the slurry to reach a steady state, for example, 30 seconds to 5 minutes, and is not limited here. The initial first resistivity is the resistivity value measured when the current is first applied, and the steady-state first resistivity is the resistivity value when the system reaches a steady state after the current has been applied for a period of time. By comparing the initial value and the steady-state value, the dynamic response characteristics of the slurry under the action of an electric field can be evaluated.

[0071] The system can achieve this step through continuous data acquisition. Specifically, while applying a constant current, the system continuously acquires voltage values ​​at a fixed sampling frequency (e.g., 1Hz to 10Hz) and calculates the corresponding resistivity in real time. The resistivity of the first sampling point is used as the initial first resistivity. When the resistivity change at multiple consecutive sampling points is less than a preset threshold, the average of the last few sampling points is taken as the steady-state first resistivity. All data is stored in a time-series database for subsequent analysis. The system can also employ a staged acquisition method. This method performs high-frequency sampling in the initial stage of current application (e.g., the first 5 seconds) to accurately capture the initial first resistivity, then reduces the sampling frequency, and increases it again near the first preset duration to ensure accurate acquisition of the steady-state first resistivity. This method can reduce the amount of data while maintaining measurement accuracy.

[0072] When a constant current is applied for an extended period, electrode polarization or slurry electrolysis may occur, affecting the accuracy of resistivity measurements. To address this issue, the system can employ an alternating polarity testing method. Specifically, the system periodically changes the current direction within a first preset time interval, for example, switching every 10 seconds, while maintaining a constant current magnitude. By averaging the measurement results of the positive and negative half-cycles, the influence of polarization can be eliminated, yielding more accurate resistivity change data.

[0073] S209. Calculate the first rate of change of the initial first resistivity and the steady-state first resistivity; The system calculates the initial first resistivity and the first rate of change of the steady-state first resistivity. The first rate of change reflects the degree of resistivity change of the slurry under the influence of an electric field. The calculation formula is: First rate of change = (Steady-state first resistivity - Initial first resistivity) / Initial first resistivity × 100%. A positive rate of change indicates an increase in resistivity, while a negative rate of change indicates a decrease in resistivity. The magnitude of the rate of change can reflect the intensity of dynamic processes such as ion migration and particle rearrangement in the slurry.

[0074] S210. In the first test circuit, a preset constant current is applied in the direction opposite to the preset constant current direction and maintained for a first preset duration, and the initial second resistivity and steady-state second resistivity are recorded. In the first test circuit, a preset constant current is applied in the opposite direction to the preset constant current and maintained for a first preset duration. The initial second resistivity and the steady-state second resistivity are recorded. This step is similar to step S208, but the current direction is reversed. The initial second resistivity is the resistivity value when the reverse current is first applied, and the steady-state second resistivity is the stable value after the reverse current continues to act. By comparing the forward and reverse current tests, the sensitivity of the slurry to the current direction can be evaluated. The first preset duration is the same as in step S208 to ensure consistency of test conditions, and is not limited here.

[0075] The system can achieve this step through an automatic reverse testing program. After completing the forward current test, the program automatically switches the current direction and restarts data acquisition. Acquisition parameters, such as sampling frequency and data processing methods, remain consistent with the forward test. The system monitors resistivity changes in real time, automatically identifies initial and steady-state values, and stores the data. Alternatively, the system can employ a dual-channel synchronous testing scheme. Using a dual-channel constant current source with positive and negative outputs, one channel is used for forward testing, and the other for reverse testing. Through precise timing control, the forward and reverse switching can be completed in a very short time, reducing the impact of slurry state changes on the test results.

[0076] S211. Calculate the second rate of change of the initial second resistivity and the steady-state second resistivity; The system calculates the second rate of change of the initial second resistivity and the steady-state second resistivity. The calculation method for the second rate of change is the same as the first rate of change, and the formula is: Second rate of change = (Steady-state second resistivity - Initial second resistivity) / Initial second resistivity × 100%. The second rate of change reflects the dynamic response characteristics of the slurry under reverse current. By comparing the first and second rates of change, the symmetry of the slurry response can be evaluated.

[0077] S212. In the second test circuit, a preset constant current is applied in the direction of a preset constant current and maintained for a first preset duration, and the initial third resistivity and steady-state third resistivity are recorded.

[0078] In the second test circuit, a preset constant current is applied in the direction of the preset constant current and maintained for a first preset time, recording the initial third resistivity and the steady-state third resistivity. This step extends the test to the second test circuit, evaluating the dynamic response characteristics of the slurry at different spatial locations. The definitions of the initial third resistivity and the steady-state third resistivity are the same as in the previous steps, representing the resistivity values ​​when the current is first applied and when the steady state is reached in the second test circuit, respectively. The first preset time remains unchanged to ensure comparability between different test circuits, and is not limited here.

[0079] This step can be achieved using a multi-circuit parallel testing system. This system is equipped with multiple independent constant current sources and voltage measurement channels, allowing simultaneous testing of multiple test circuits. After the second test circuit is connected, the system applies a constant current according to a preset program and independently acquires the voltage data of that circuit, calculating the resistivity change curve over time. Alternatively, the system can employ a time-division multiplexing testing scheme. Using a single high-precision constant current source and a fast-switching switch, different test circuits are tested alternately using time-division multiplexing. Although not strictly simultaneous testing, the rapid switching allows for the testing of multiple circuits to be completed in a short time, reducing the impact of changes in slurry condition.

[0080] S213. Calculate the initial third resistivity and the third rate of change of the steady-state third resistivity; The system calculates the third rate of change of the initial third resistivity and the steady-state third resistivity. The calculation method is the same as the aforementioned rate of change calculation, and the formula is: Third rate of change = (Steady-state third resistivity - Initial third resistivity) / Initial third resistivity × 100%. The third rate of change reflects the dynamic response characteristics of the slurry at the location of the second test circuit.

[0081] S214. In the second test circuit, a preset constant current is applied in the direction opposite to the preset constant current direction and maintained for a first preset duration. The initial fourth resistivity and the steady-state fourth resistivity are recorded. In the second test circuit, a preset constant current is applied in the opposite direction to the preset constant current and maintained for a first preset duration, recording the initial fourth resistivity and the steady-state fourth resistivity. This step completes the reverse current test of the second test circuit and is compared with step S212. The initial fourth resistivity and the steady-state fourth resistivity represent the initial and steady-state resistivity values ​​under reverse current conditions, respectively. Through comprehensive analysis of the four sets of data, the stability of the slurry can be fully evaluated.

[0082] The system can implement this step through a programmed testing process. The test program automatically completes all test steps in a predetermined sequence, including circuit switching, current direction switching, data acquisition, and storage. The program has a robust exception handling mechanism to ensure the continuity of the testing process and the integrity of the data. Alternatively, the system can employ an intelligent testing scheme. Based on the results of the preceding test steps, the system intelligently adjusts the parameters of the fourth test step, such as adjusting the sampling frequency or test duration according to the rate of change, to achieve better testing results.

[0083] S215. Calculate the initial fourth resistivity and the fourth rate of change of the steady-state fourth resistivity; The system calculates the fourth rate of change for both the initial and steady-state fourth resistivity. The formula is: Fourth rate of change = (Steady-state fourth resistivity - Initial fourth resistivity) / Initial fourth resistivity × 100%. This fourth rate of change calculation completes the calculation of rates of change under all test conditions, providing a data foundation for subsequent comprehensive judgment.

[0084] S216. When the maximum difference between the first rate of change, the second rate of change, the third rate of change, and the fourth rate of change is less than the preset fourth determination threshold, the distribution of solid particles in the lithium-ion battery slurry is determined to be stable.

[0085] When the maximum difference between the first, second, third, and fourth rates of change is less than a preset fourth threshold, the system determines that the solid particle distribution in the lithium-ion battery slurry is stable. The maximum difference refers to the maximum value of the difference between any two of the four rates of change, calculated using the formula: Maximum Difference = max(|rate of change i - rate of change j|), where i, j = 1, 2, 3, 4. The preset fourth threshold is the standard for judging the consistency of the rates of change and can be set according to the slurry type and quality requirements, such as 5% or 10%, without limitation here. When the differences among the four rates of change are all within the allowable range, it indicates that the dynamic response of the slurry at different locations and under different current directions is basically consistent, indicating that the solid particle distribution is uniform and stable.

[0086] The system can achieve this determination using a matrix comparison algorithm. It constructs a 4×4 difference matrix, calculates the difference between each pair of all change rates, and then finds the maximum value in the matrix (excluding diagonal elements). The maximum difference is compared to a preset fourth determination threshold; if it is less than the threshold, a result indicating stable particle distribution is output. The system can also generate a change rate distribution map to visually display the differences in change rates under various test conditions. Alternatively, the system can employ a statistical determination method. It calculates the mean and standard deviation of the four change rates; if the ratio of the standard deviation to the mean is less than a certain threshold (e.g., 0.1), the particle distribution is determined to be stable. This method can more comprehensively assess the dispersion of the change rates.

[0087] In the above embodiments, by applying preset constant currents in opposite directions in the first and second test circuits, and calculating the corresponding resistivity differences and their ratios, the polarization characteristics and reversibility of the electrical performance of the lithium-ion battery slurry under the influence of an electric field are evaluated. When the conductive material in the slurry is uniformly and stably distributed, the resistivity difference measured by applying currents in both directions is small, indicating that the slurry will not undergo significant polarization or component migration under the influence of an electric field. By setting a reasonable third judgment threshold and preset range, the stability of the slurry can be accurately determined, avoiding the decline in electrochemical performance caused by uneven distribution or agglomeration of conductive materials in the slurry. This bidirectional testing method can more comprehensively reflect the intrinsic conductivity characteristics of the slurry, reduce measurement errors caused by electrode polarization effects during the testing process, and improve the accuracy and reliability of slurry stability assessment.

[0088] Furthermore, in another embodiment, after determining that the lithium-ion battery slurry is stable, the method further includes: The resistivity data from a preset number of tests are arranged in chronological order to obtain resistivity time-series data. The resistivity time-series data is segmented to obtain multiple sets of segmented resistivity data, specifically including: Select a preset time length as the segmented time window; divide the resistivity time series data into multiple groups of resistivity time series data according to the segmented time window, with each group of resistivity time series data containing an equal number of time points; perform linear fitting on each group of resistivity time series data to obtain the fitting slope; delete the data groups whose absolute value of the fitting slope is greater than the preset sixth judgment threshold to obtain multiple groups of resistivity segmented data. Calculate the mean value of each group of resistivity segment data to obtain the resistivity mean value sequence; Calculate the difference between the mean values ​​of two adjacent sets of resistivity segment data to obtain the resistivity gradient sequence; When the rate of change of the resistivity gradient sequence is greater than the preset rate threshold and the maximum gradient value is greater than the preset five judgment threshold, it is determined that the lithium-ion battery slurry has deteriorated. Calculate the ratio of adjacent gradient values ​​in the resistivity gradient sequence to obtain the gradient change rate sequence; When the mean of the gradient change rate sequence is greater than the preset seventh judgment threshold, it is determined that the lithium-ion battery slurry has undergone accelerated deterioration. When the mean of the gradient change rate sequence is not greater than the preset seventh judgment threshold, it is determined that the lithium-ion battery slurry has undergone uniform deterioration. Sort the gradient rate of change sequence according to its numerical value; Calculate the gradient rate of change value located at the preset percentile in the sorted gradient rate of change sequence; The degree of degradation of lithium-ion battery slurry is determined based on the range of gradient change rate values ​​in a preset degradation degree level table.

[0089] Specifically, the system arranges the previously collected resistivity data (previously collected a preset number of times) in chronological order of collection time, forming resistivity time-series data. Resistivity time-series data is a sequence of data containing timestamps and corresponding resistivity values, which can be represented as {(t1, ρ1), (t2, ρ2), ..., (tn, ρn)}, where ti represents the i-th sampling time point and ρi represents the corresponding resistivity value. The chronological arrangement ensures that the temporal relationship of the data is preserved, laying the foundation for subsequent time-series analysis. The data can be arranged in ascending or descending order, but ascending order is commonly used, from the earliest data to the latest data; this is not a limitation here. The system can implement this step through database query and sorting functions. Specifically, the system queries the data storage system for all resistivity measurement records within a specified time period. These records contain measurement timestamps, resistivity values, and related test condition parameters. SQL statements or a database API are used to sort the data in ascending order by the timestamp field, obtaining an ordered dataset. The sorted data can be exported as a structured file format, such as CSV or JSON, for subsequent processing. The system can also implement sorting using an in-memory data structure. All resistivity data is read into memory and stored in a dynamic array or linked list structure, with each data node containing a timestamp and resistivity value. Efficient algorithms such as quicksort and mergesort are then used to sort the data, with the timestamp as the sorting key. This method is suitable for scenarios with moderate amounts of data that require frequent access.

[0090] The preset time length refers to the time span covered by each data segment, such as 5 minutes, 10 minutes, or 30 minutes, and is not limited here. The selection of the segmented time window needs to balance data resolution and statistical reliability. A window that is too small may result in too few data points per segment, leading to unstable statistical results; a window that is too large may lose information about local variations. The system can automatically determine the segmented time window based on the sampling frequency. In practice, the system first calculates the average sampling interval of the data, and then calculates an appropriate time window based on the expected number of data points per segment (e.g., 10-20 points). For example, if the sampling interval is 30 seconds and each segment is expected to contain 15 data points, the time window is set to 450 seconds (7.5 minutes). The system can also use an adaptive window selection method. This method analyzes the autocorrelation function of the resistivity data to identify the time scale at which the data correlation significantly decreases, and uses this as the segmented time window. This method can automatically select an appropriate window size based on the characteristics of the data itself.

[0091] The mean resistivity represents the overall resistivity level over a given time period. Meaning reduces the impact of random fluctuations and highlights the main trend. The mean resistivity sequence retains the temporal characteristics of the original data but significantly reduces the number of data points, facilitating trend analysis. The mean can be calculated using methods such as arithmetic mean, weighted average, or truncated average; no specific method is specified here. The system can calculate the mean for each data set using the arithmetic mean. For the i-th data set {ρi1, ρi2, ..., ρin}, the mean ρ̄i = Σρij / n is calculated. The means of all groups are arranged in chronological order to obtain the mean resistivity sequence {ρ̄1, ρ̄2, ..., ρ̄m}. The time stamp corresponding to each mean is the midpoint of that data set. The system can also employ robust statistical methods, such as using the median instead of the mean, or calculating a truncated mean to reduce the impact of outliers. The differences between adjacent terms in the mean resistivity sequence are calculated to obtain a gradient sequence reflecting the resistivity trend. The sign of the gradient value indicates the direction of resistivity increase or decrease, while the absolute value indicates the magnitude of the change. The resistivity gradient sequence can more intuitively demonstrate the dynamic changes in slurry properties. Gradient calculation can employ forward differencing, backward differencing, or central differencing methods, which are not limited here. The system can obtain the gradient sequence through differencing operations. For the resistivity mean sequence {ρ̄1, ρ̄2, ..., ρ̄m}, the gradient gi = ρ̄(i+1) - ρ̄i is calculated, resulting in the gradient sequence {g1, g2, ..., g(m-1)}. For ease of analysis, the gradient values ​​can be normalized and divided by the corresponding time interval to obtain the rate of change per unit time. The system can also use a smoothing differencing method, first smoothing the mean sequence and then calculating the differencing to reduce the impact of noise on gradient estimation.

[0092] The rate of change reflects how fast the gradient sequence changes and can be obtained by calculating the standard deviation or range of the gradient sequence. The maximum gradient value is the maximum absolute value in the gradient sequence. The preset rate threshold and the preset fifth judgment threshold are set according to the slurry type and quality standards. For example, the rate threshold can be set to 0.5 Ω·m / min², and the fifth judgment threshold can be set to 2 Ω·m / min; no specific limit is imposed here. When both conditions are met simultaneously, it indicates that the slurry properties have undergone a significant and accelerated change, and it is judged as deterioration. The system can achieve deterioration judgment through statistical analysis. First, the standard deviation σg of the gradient sequence {g1, g2, ..., g(m-1)} is calculated as the rate of change index, and the maximum absolute value gmax = max(|gi|) in the sequence is found as the maximum gradient value. σg is compared with the preset rate threshold, and gmax is compared with the preset fifth judgment threshold. When σg > rate threshold and gmax > fifth judgment threshold, the system judges that the slurry has deteriorated. The system can also use a dynamic threshold judgment method, adaptively adjusting the judgment threshold based on the statistical characteristics of historical data to improve the accuracy of the judgment.

[0093] The gradient rate of change sequence reflects the dynamic evolution of slurry properties. A ratio greater than 1 indicates accelerated change, while a ratio less than 1 indicates decelerated change. The calculation of the gradient rate of change needs to handle possible zero or near-zero gradient values, but this is not limited here. The system can obtain the gradient rate of change sequence through ratio calculation. For the gradient sequence {g1, g2, ..., g(m-1)}, the rate of change ri = g(i+1) / gi (when gi≠0) is calculated, resulting in the gradient rate of change sequence {r1, r2, ..., r(m-2)}. For cases where gi is close to zero, a small threshold ε can be set; when |gi| < ε, the rate of change at that position is set to 1 or the calculation is skipped. The system can also use the logarithmic rate of change method, calculating ln|g(i+1)| - ln|gi|. This method can better handle cases with a large numerical range and has symmetry.

[0094] A preset seventh threshold defines the criteria for accelerated deterioration. For example, it can be set to 1.2, meaning that an average change rate exceeding 20% ​​is considered accelerated deterioration; no specific limit is set here. Accelerated deterioration means that the rate of deterioration of the slurry properties is continuously increasing, requiring timely measures. The system can make this determination through mean calculation and threshold comparison. The arithmetic mean r̄ = Σri / (m-2) of the gradient change rate sequence {r1, r2, ..., r(m-2)} is calculated, and r̄ is compared with the preset seventh threshold. When r̄ > the seventh threshold, the system determines that the slurry has undergone accelerated deterioration and can calculate an acceleration index (r̄-1) × 100% to quantify the degree of acceleration. The system can also use a weighted average method, assigning higher weight to recent change rates to more sensitively detect the latest acceleration trend.

[0095] When the mean of the gradient rate of change sequence does not exceed the preset seventh judgment threshold, but the slurry has already been determined to have deteriorated, the system classifies it as uniform deterioration. Uniform deterioration indicates that the slurry properties are continuously deteriorating at a relatively constant rate. Although there is no accelerating trend, it still requires attention and control. The determination of uniform deterioration provides guidance for different processing strategies in subsequent quality control. The system can identify uniform deterioration through logical judgment. Under the premise that the slurry has been determined to have deteriorated, if the mean r̄ of the gradient rate of change sequence is less than or equal to the seventh judgment threshold, the system automatically marks the deterioration type as uniform deterioration. The system can also calculate the standard deviation of the rate of change sequence to assess the stability of the uniformity. The smaller the standard deviation, the more stable the deterioration rate. The system can also further subdivide the type of uniform deterioration, such as slow uniform deterioration (r̄ close to 1 but slightly greater than 1) and stagnant deterioration (r̄ close to 1 or slightly less than 1).

[0096] Sorting can be ascending or descending. Usually, ascending sorting is used for ease of calculating percentiles. The sorted sequence can visually display the distribution of the rate of change, helping to identify extreme values and evaluate the overall distribution characteristics. The sorting algorithm can be selected according to the data volume, such as quicksort, mergesort, etc., which is not limited here. The system can implement this step through standard sorting algorithms. Copy the gradient rate of change sequence {r1, r2,..., r(m - 2)} to a new array and use the quicksort algorithm to sort it in ascending order to obtain an ordered sequence {r'1, r'2,..., r'(m - 2)}, where r'1 ≤ r'2 ≤... ≤ r'(m - 2). The original sequence is retained during the sorting process so that the original time order can be traced back when needed. The system can also adopt an index-based sorting method, creating an index array to record the position of each element in the original sequence after sorting, so that logical sorting can be achieved without changing the original data.

[0097] The preset percentile can be 75%, 90%, 95%, etc., indicating that the corresponding percentage of data is less than this value. Percentiles are more robust than the maximum value and can better represent the overall characteristics of the sequence. The selection of the preset percentile can be determined according to the strictness of quality control, which is not limited here. The system can calculate the percentile through linear interpolation. For the sorted sequence {r'1, r'2,..., r'(m - 2)} and the preset percentile p (0 < p < 1), calculate the position index k = p × (m - 2). If k is an integer, the p-th percentile is r'k; if k is not an integer, calculate it through linear interpolation: r_p = r'⌊k⌋+(k - ⌊k⌋)×(r'⌈k⌉ - r'⌊k⌋). The system can also adopt the nearest neighbor method, directly taking the data point closest to the calculated position as the percentile. This method is simple to calculate but has slightly lower accuracy.

[0098] The preset deterioration degree grade table defines the deterioration grades corresponding to different ranges of rate of change values. For example: slight deterioration (1.0 - 1.2), moderate deterioration (1.2 - 1.5), severe deterioration (1.5 - 2.0), extremely severe deterioration (> 2.0), which is not limited here. The grade division provides a clear quality judgment standard for production control. The system can implement grade determination through an interval matching algorithm. The system maintains a grade table data structure, including the upper and lower limits and grade names of each grade. Compare the calculated percentile gradient rate of change value with each interval to determine its belonging interval and output the corresponding deterioration degree grade. The system can also output the relative position of this value within the belonging interval to provide more refined evaluation information. The system can also adopt a fuzzy grade evaluation method, using a membership function near the grade boundary to give the probability of belonging to adjacent two grades, avoiding boundary effects.

[0099] In the above embodiments, time-series analysis and segmented processing are performed on continuously collected resistivity data. By calculating the mean resistivity sequence and gradient sequence, the changing trend of lithium-ion battery slurry performance over time can be dynamically monitored. When the slurry deteriorates, its resistivity will show a significant changing trend, manifested as a significant increase in the rate of change of the resistivity gradient sequence. By setting reasonable preset rate thresholds and preset fifth judgment thresholds, abnormal changes in slurry performance can be detected in a timely manner. This method based on time-series data analysis can reflect the dynamic change process of slurry performance in real time, improving the accuracy of slurry quality assessment.

[0100] The system in the embodiments of this invention is described below from the perspective of hardware processing. Please refer to [link / reference needed]. Figure 4 This is a schematic diagram of the physical device structure of a lithium-ion battery slurry stability evaluation system provided in an embodiment of this application.

[0101] It should be noted that, Figure 4 The structure of the system shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of the present invention.

[0102] like Figure 4 As shown, the system includes a Central Processing Unit (CPU) 301, which can perform various appropriate actions and processes based on a program stored in Read-Only Memory (ROM) 302 or a program loaded from storage portion 308 into Random Access Memory (RAM) 303, such as executing the methods described in the above embodiments. The RAM 303 also stores various programs and data required for system operation. The CPU 301, ROM 302, and RAM 303 are interconnected via a bus 304. An Input / Output (I / O) interface 305 is also connected to the bus 304.

[0103] The following components are connected to I / O interface 305: input section 306 including a camera, infrared sensor, etc.; output section 307 including a liquid crystal display (LCD) and speakers, etc.; storage section 308 including a hard disk, etc.; and communication section 309 including a network interface card such as a LAN (Local Area Network) card and a modem, etc. Communication section 309 performs communication processing via a network such as the Internet. Drive 310 is also connected to I / O interface 305 as needed. Removable media 311, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., are installed on drive 310 as needed so that computer programs read from them can be installed into storage section 308 as needed.

[0104] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing computer programs for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication section 309, and / or installed from removable medium 311. When the computer program is executed by central processing unit (CPU) 301, it performs the various functions defined in the present invention.

[0105] It should be noted that the computer-readable medium shown in the embodiments of the present invention can be a computer-readable signal medium or a computer-readable storage medium, or any combination thereof. A computer-readable storage medium can be, for example,—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), flash memory, optical fiber, portable compact disc read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. In the present invention, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, wherein a computer-readable computer program is carried. The transmitted data signal can take many forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof.

[0106] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. Each block in a flowchart or block diagram may represent a module, segment, or portion of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0107] In another aspect, the present invention also provides a computer-readable storage medium, which may be included in the system described in the above embodiments; or it may exist independently and not assembled into the system. The storage medium carries one or more computer programs that, when executed by a processor of a system, cause the system to implement the methods provided in the above embodiments.

[0108] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. 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 scope of the technical solutions of the embodiments of this application.

[0109] As used in the above embodiments, depending on the context, the term "when..." can be interpreted as "if...", "after...", "in response to determining...", or "in response to detecting...". Similarly, depending on the context, the phrase "when determining..." or "if (the stated condition or event) is interpreted as "if determining...", "in response to determining...", "when (the stated condition or event) is detected", or "in response to detecting (the stated condition or event)".

[0110] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state drive), etc.

[0111] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. This program can be stored in a computer-readable storage medium, and when executed, it can include the processes described in the above method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as ROM or random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A method for evaluating the stability of lithium-ion battery slurry, characterized in that, include: Given that lithium-ion battery slurry is injected into a glass ring test cavity, a first test circuit is constructed by selecting the central electrode of the glass ring test cavity and a first set of electrodes located on one side of the central electrode. The inner wall of the glass ring test cavity is provided with seven conductive electrodes, including a central electrode located in the center and six conductive electrodes distributed along both sides of the central electrode. A preset constant current is applied between the first set of electrodes, and a first voltage value between the center electrode and the first set of electrodes is collected. The first resistivity is calculated based on the preset constant current and the first voltage value; A second test circuit is constructed by selecting the central electrode and a second set of electrodes located on the other side of the central electrode. A preset constant current is applied between the second set of electrodes, and a second voltage value between the center electrode and the second set of electrodes is collected. The second resistivity is calculated based on the preset constant current and the second voltage value; If the average value of the first resistivity and the second resistivity is less than a preset first determination threshold, then the resistivity distribution is determined to be uniform. Resistivity data is continuously collected a preset number of times at a preset sampling time interval, and the standard deviation of the resistivity data for the preset number of times is calculated. When the standard deviation is determined to be less than a preset second determination threshold, the lithium-ion battery slurry is determined to be stable.

2. The method according to claim 1, characterized in that, After determining that the lithium-ion battery slurry is stable, the method further includes: In the first test circuit, the preset constant current is applied in a direction opposite to the preset constant current direction, and the third voltage value between the center electrode and the first group of electrodes is collected. The third resistivity is calculated based on the preset constant current and the third voltage value; Calculate the difference between the first resistivity and the third resistivity to obtain the first difference; In the second test circuit, the preset constant current is applied in a direction opposite to the preset constant current direction, and a fourth voltage value between the center electrode and the second set of electrodes is collected. The fourth resistivity is calculated based on the preset constant current and the fourth voltage value; Calculate the difference between the second resistivity and the fourth resistivity to obtain the second difference; When both the first difference and the second difference are less than a preset third determination threshold, and the ratio of the first difference to the second difference is within a preset range, the lithium-ion battery slurry is determined to be stable.

3. The method according to claim 2, characterized in that, After determining that the lithium-ion battery slurry is stable, the method further includes: In the first test circuit, the preset constant current is applied in the direction of the preset constant current and maintained for a first preset time, and the initial first resistivity and steady-state first resistivity are recorded. Calculate the initial first resistivity and the first rate of change of the steady-state first resistivity; In the first test circuit, the preset constant current is applied in the direction opposite to the preset constant current direction and maintained for the first preset duration, and the initial second resistivity and steady-state second resistivity are recorded. Calculate the second rate of change of the initial second resistivity and the steady-state second resistivity; In the second test circuit, the preset constant current is applied in the direction of the preset constant current and maintained for the first preset duration, and the initial third resistivity and steady-state third resistivity are recorded. Calculate the initial third resistivity and the third rate of change of the steady-state third resistivity; In the second test circuit, the preset constant current is applied in the opposite direction to the preset constant current and maintained for the first preset duration, and the initial fourth resistivity and steady-state fourth resistivity are recorded. Calculate the fourth rate of change of the initial fourth resistivity and the steady-state fourth resistivity; When the maximum difference between the first rate of change, the second rate of change, the third rate of change, and the fourth rate of change is less than a preset fourth determination threshold, the distribution of solid particles in the lithium-ion battery slurry is determined to be stable.

4. The method according to claim 1, characterized in that, After determining that the lithium-ion battery slurry is stable, the method further includes: The resistivity data from the preset number of times are arranged in chronological order to obtain resistivity time-series data; The resistivity time-series data is segmented to obtain multiple sets of resistivity segmented data. Calculate the mean value of each group of resistivity segment data to obtain a resistivity mean value sequence; Calculate the difference between the mean values ​​of two adjacent sets of resistivity segment data to obtain the resistivity gradient sequence; When the rate of change of the resistivity gradient sequence is greater than a preset rate threshold and the maximum gradient value is greater than a preset five-judgment threshold, it is determined that the lithium-ion battery slurry has deteriorated.

5. The method according to claim 4, characterized in that, The step of segmenting the resistivity time-series data to obtain multiple sets of segmented resistivity data specifically includes: Select a preset time length as the segmented time window; The resistivity time series data is divided into multiple groups of resistivity time series data according to the segmented time window, and each group of resistivity time series data contains an equal number of time points. Linear fitting is performed on each set of resistivity time series data to obtain the fitting slope; Delete the data groups whose absolute value of the fitted slope is greater than the preset sixth judgment threshold to obtain multiple sets of resistivity segmented data.

6. The method according to claim 4, characterized in that, After determining that the lithium-ion battery slurry has deteriorated, the method further includes: Calculate the ratio of adjacent gradient values ​​in the resistivity gradient sequence to obtain the gradient change rate sequence; When the mean of the gradient change rate sequence is greater than the preset seventh determination threshold, it is determined that the lithium-ion battery slurry has undergone accelerated deterioration. When the mean of the gradient change rate sequence is not greater than the preset seventh determination threshold, it is determined that the lithium-ion battery slurry has undergone uniform deterioration.

7. The method according to claim 6, characterized in that, After determining that the lithium-ion battery slurry has undergone accelerated deterioration, the method further includes: Sort the gradient rate of change sequence according to its numerical value; Calculate the gradient rate of change value located at the preset percentile in the sorted gradient rate of change sequence; The degree of degradation of the lithium-ion battery slurry is determined based on the range of the gradient change rate value in the preset degradation degree level table.

8. A lithium-ion battery slurry stability evaluation system, characterized in that, The system includes: One or more processors and a memory; the memory is coupled to the one or more processors, the memory being used to store computer program code, the computer program code including computer instructions, the one or more processors invoking the computer instructions to cause the system to perform the method as described in any one of claims 1-7.

9. A computer-readable storage medium comprising instructions, characterized in that, When the instructions are executed on the system, the system performs the method as described in any one of claims 1-7.

10. A computer program product, characterized in that, When the computer program product is run on the system, the system performs the method as described in any one of claims 1-7.

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