Residual Value Assessment Method for Decommissioned Power Battery Cell Series Packs

Abstract

This invention provides a method for assessing the residual value of a retired power battery cell series-connected pack. The method includes collecting power battery data and quantifying the basic voltage degradation characteristics of individual cells from three dimensions: short-term static voltage deviation, long-term static voltage deviation, and cell static self-recovery voltage deviation. A fixed-weight linear fusion is performed to obtain a comprehensive degradation index. Then, based on the comprehensive degradation index, the original basic residual value of a single cell under conditions without neighboring interference is constructed. Considering the sequential series arrangement of cells within the power battery pack, and the internal circulating current loss caused by voltage differences between adjacent cells, a cell coupling discount coefficient is constructed for correction, resulting in the residual value of the individual cell after neighboring correction. The individual cell voltage deviation coefficient is calculated, and then an adaptive individual cell weight is obtained. The residual values ​​of the individual cells after neighboring correction are then corrected and summed to obtain the final residual value coefficient of the power battery pack. This invention significantly reduces the cost of the entire residual value detection process.

Description

Technical Field

[0001] This invention belongs to the field of power battery recycling and evaluation technology, specifically involving a method for evaluating the residual value of retired power battery cells connected in series. Background Technology

[0002] Currently, most on-site residual value testing methods for retired series-connected power battery packs only collect the open-circuit voltage of a single cell after a short period of power-off and rest, relying solely on voltage data at a single point in time. Conventional evaluation algorithms generally use a simple calculation method that directly compares the measured voltage with the nominal voltage linearly, making it difficult to distinguish the degree of loss corresponding to the three different degradation causes: ohmic internal resistance aging of the cell, decay of the positive electrode active material, and electrolyte polarization aging. The implicit polarization loss caused by the self-recovery of voltage after long-term rest of the cell often cannot be quantified by single-point voltage data. This inherently limits traditional calculations in breaking down the sources of degradation, easily overlooking the residual value loss caused by the superposition of multiple types of aging, resulting in an incomplete evaluation basis from the data source perspective.

[0003] In the existing conventional calculation logic for the residual value of individual cells in a power battery pack (PACK), the industry generally prefers to directly calculate the arithmetic average of the residual values ​​of all cells to obtain the overall pack result, rarely considering the electrical coupling effects caused by the series structure of the PACK. In actual operating conditions, inconsistent voltages between adjacent cells can create internal circulating currents. Severely degraded cells with high polarization can also continuously drag down the aging of surrounding adjacent cells. This kind of implicit value loss caused by the mutual influence between cells is basically not accounted for in the traditional calculation system. Affected by this factor, the final calculated residual value of the entire pack is generally prone to being higher than the actual residual value of the battery, resulting in an objective deviation between the assessment results and the actual deterioration state.

[0004] Traditional solutions often use fixed, equal weights or simply calculate the residual value of all individual cells using an arithmetic average in the weighted aggregation of the entire battery pack's residual value, without adjusting the weighting ratio based on the overall distribution of cell voltages within the pack. Since power batteries are connected in series, a natural "weakest link" effect exists: severely degraded cells or those with voltages significantly deviating from the average will noticeably lower the overall usable value of the pack. However, older algorithms cannot automatically increase the weight of these weaker cells, failing to objectively reflect the negative impact of degraded cells on the overall pack's residual value. This ultimately leads to significant fluctuations in the evaluation results across different batches of batteries, making it difficult to guarantee the reliability of the calculations. Summary of the Invention

[0005] The problem this invention aims to solve is to achieve accurate assessment of the residual value of retired power battery cells connected in series, and proposes a method for assessing the residual value of retired power battery cells connected in series.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for assessing the residual value of a retired power battery cell series pack includes the following steps:

[0008] S1. Collect the open-circuit voltage of each cell in the power battery pack after 2 hours of rest, and the open-circuit voltage of the same numbered cell after 12 hours of further rest, to obtain the nominal open-circuit voltage of the cell at the factory.

[0009] S2. For the data collected in step S1, firstly remove the distorted abnormal voltage data, and then quantify the basic voltage degradation characteristics of a single cell from three dimensions: short-term static voltage deviation, long-term static voltage deviation, and cell static self-recovery voltage deviation.

[0010] S3. The degradation characteristics of the single cell base voltage obtained in step S2 are linearly fused with fixed weights to obtain a comprehensive degradation index. Then, the original base residual value of a single cell under the condition of no neighboring interference is constructed based on the comprehensive degradation index.

[0011] S4. Considering that the cells inside the power battery pack are arranged in series from end to end, the voltage difference between adjacent cells generates internal circulating current loss. Construct a cell coupling discount factor to correct the original basic residual value obtained in step S3, and obtain the residual value of the single cell after neighborhood correction.

[0012] S5. Based on the three statistical indicators of the cell voltage mean, standard deviation and skewness of the power battery pack, calculate the cell voltage deviation coefficient, and then normalize the cell voltage deviation coefficient by mapping transformation using the natural exponent to obtain the adaptive cell weight. Then, correct and sum the cell residual values ​​obtained in step S4 after neighborhood correction to obtain the final residual value coefficient of the power battery pack.

[0013] Furthermore, the expressions for calculating the short-time static voltage deviation, long-time static voltage deviation, and cell static self-recovery voltage deviation in step S2 are as follows: ; ; ;

[0014] in, For the first The short-term static relative voltage deviation of the cell characterizes the voltage deviation of the cell from the nominal value after 2 hours of static rest. For the first The relative voltage deviation of a battery cell after long-term rest represents the magnitude of the voltage deviation from the nominal value of the cell after 12 hours of rest. For the first The relative deviation of cell self-recovery after being left undisturbed represents the degree of polarization degradation in which the cell's voltage autonomously recovers after being left undisturbed for a long time. For the first The open-circuit voltage of a single cell after it has been left to stand for 2 hours. This refers to the nominal open-circuit voltage of the battery cell at the factory. For the first The cell will continue to be left to stand for 12 hours until the single-cell open-circuit voltage is measured.

[0015] Furthermore, the specific implementation method of step S3 includes the following steps:

[0016] S3.1. Calculate the overall deterioration index. The calculation formula is as follows:

[0017]

[0018] in, For the first The overall degradation index of the battery cell, This refers to the short-time deviation weighting coefficient; This is the long-term deviation weighting coefficient; This is the self-recovery bias weighting coefficient;

[0019] S3.2. Based on the comprehensive degradation index, a multi-layer nested nonlinear function is used to construct the original basic residual value of a single cell under the condition of no neighboring interference. The calculation formula is as follows:

[0020]

[0021] in, For the first The original basic residual value coefficient of the battery cell. It is the hyperbolic tangent function. This is the natural exponentiation operator.

[0022] Furthermore, the specific implementation method of step S4 includes the following steps:

[0023] S4.1. Grouping two sequentially adjacent cells together, calculate the... Measured voltage difference between cell #1 and adjacent cells ;

[0024] S4.2. For the adjacent cells obtained in step S4.1, average the relative deviation of the static self-recovery for each cell to obtain the first... Average self-recovery deviation of cell #1 and adjacent cells ;

[0025] S4.3. Summarize all adjacent cell voltage difference data, calculate the arithmetic mean, and obtain the average cell voltage difference of the power battery pack. ;

[0026] S4.4. Based on the relative relationship between the measured voltage difference between adjacent cells and the average voltage difference between cells in the power battery pack, a decay function is constructed using the natural exponential function, and the influence weight of each group of adjacent cells is obtained by normalization. The expression is as follows:

[0027]

[0028] in, It is the first The spatial attenuation weighting coefficient between cell number 1 and adjacent cells, where k is any one of the effective cells and n is the total number of effective cells;

[0029] S4.5. Combining the average self-recovery deviation of adjacent cells, the average cell voltage difference of the power battery pack, and the influence weight of each group of adjacent cells, a cell coupling discount coefficient is constructed, expressed as follows:

[0030]

[0031] in, For the first The coupling discount factor between cell number 1 and adjacent cells;

[0032] S4.6. Using the cell coupling discount factor obtained in step S4.5, apply it to the first... The original basic residual value factor of the cell is reduced by discounting, and the hidden losses caused by the contagion of degradation of adjacent cells are deducted to obtain the residual value of the individual cell after neighborhood correction.

[0033] Furthermore, the specific implementation method of step S5 includes the following steps:

[0034] S5.1. Summarize the measured voltages of all valid cells and calculate the arithmetic mean of the measured cell voltages of the power battery pack. ;

[0035] S5.2. Based on the voltage of each cell and The difference is used to quantify the overall discrete fluctuation of the cell voltage in the power battery pack using the standard deviation formula, which is expressed as:

[0036]

[0037] in, This represents the standard deviation of the cell voltage in the power battery pack.

[0038] S5.3. Based on the arithmetic mean of the measured cell voltages of the power battery pack and the standard deviation of the cell voltages of the power battery pack, calculate the cell voltage distribution skewness coefficient of the power battery pack. The expression is:

[0039] ;

[0040] S5.4. Combining the relative mean offset of a single cell with the cell voltage distribution skewness coefficient of the power battery pack, an overall deviation coefficient of the single cell voltage is constructed, expressed as follows:

[0041]

[0042] in, For the first Overall voltage deviation coefficient of cell number;

[0043] Then, after normalizing the individual cell voltage deviation coefficient using a mapping transformation based on the natural exponent, we obtain the first... Adaptive weighting coefficient for battery cell # ;

[0044] S5.5. (The following appears to be a separate, unrelated sentence fragment: "with the first...") The adaptive weighting coefficient of cell number is used to weight and accumulate the residual value of the individual cell after neighborhood correction output in step S4 to obtain the final residual value coefficient of the power battery pack.

[0045] The beneficial effects of this invention are:

[0046] This invention discloses a method for assessing the residual value of retired power battery cells in series. It collects cell voltages at two differentiated resting time points (2 hours and 12 hours), and uses these two sets of measured voltages to extract three types of dimensionless deviation indicators characterizing different aging mechanisms. The original residual value of each cell is then calculated using a fixed-weight fusion and nested nonlinear function approach. Compared to traditional methods that rely solely on linear calculations based on a single voltage reading, this method can capture three different types of cell degradation losses from various dimensions, improving the completeness of data sources and degradation characterization. It alleviates, to some extent, the problem of one-sided degradation assessment caused by single-sample data, making the calculation logic of the basic residual value of a single cell more consistent with the objective laws of multi-path aging of cells. This method reduces the hardware and software investment costs for residual value testing of retired power batteries, eliminating the need for large-scale testing equipment and reducing destructive disassembly of the battery pack. This significantly reduces the overall cost of residual value testing while improving reliability compared to traditional methods.

[0047] This invention discloses a method for evaluating the residual value of retired power battery cells in series. It adds a series neighborhood coupling discount correction calculation step, sequentially calculating the voltage difference between adjacent cells, the average polarization deviation of adjacent cells, the average voltage difference of the entire string, and the spatial attenuation weight. A discount coefficient is generated by comprehensively considering two types of influencing factors: voltage difference degradation and neighborhood polarization degradation. This quantifies the additional residual value deduction caused by the contagion of degradation between adjacent cells from a computational perspective. This design fills the gap in traditional algorithms that lack a discount term for mutual losses between series cells. The residual value of a single cell after neighborhood correction better adapts to the actual physical law of accelerated aging due to mutual interference between cells in a series-connected battery pack, and moderately improves the problem of traditional algorithms easily overestimating the residual value of a single cell.

[0048] This invention discloses a method for assessing the residual value of retired power battery cells in series. It introduces three statistical parameters—mean voltage, standard deviation, and distribution skewness—to construct a single-cell deviation coefficient. Dynamic adaptive weights are generated using exponential normalization; the more significant the deviation of the cell voltage from the overall distribution and the higher the degree of degradation, the higher the corresponding weight is automatically calculated. Compared to traditional algorithms with fixed average weights, this weighting method aligns with the degradation characteristics of power batteries, reasonably amplifying the impact of weaker cells on the overall residual value of the pack. It effectively improves the assessment bias caused by fixed weight allocation and can significantly enhance the stability of residual value calculation results for different batches of batteries. The unified quantitative calculation formula facilitates the establishment of a standardized residual value assessment system in the recycling industry, contributing to the standardized implementation of power battery recycling. Attached Figure Description

[0049] Figure 1 This is a flowchart of a method for evaluating the residual value of a retired power battery cell series pack, as described in this invention. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0051] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0052] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 Detailed explanation is as follows:

[0053] Example 1:

[0054] A method for assessing the residual value of a retired power battery cell series pack includes the following steps:

[0055] S1. Collect the open-circuit voltage of each cell in the power battery pack after 2 hours of rest, and the open-circuit voltage of the same numbered cell after 12 hours of further rest, to obtain the nominal open-circuit voltage of the cell at the factory.

[0056] Furthermore, For the first The open-circuit voltage of a single cell after it has been left to stand for 2 hours, in volts; Data acquisition method: After the power battery pack (PACK) has been powered off and left to stand for 2 hours, each cell is connected in series via a wiring harness and measured point by point in the field using a high-precision digital multimeter. Represents the cell number. , This represents the total number of cells that are effectively connected in series within the PACK. For the first The open-circuit voltage of cell No. 1 after it has been left to stand for 12 hours, in V; Data acquisition method: Completed. After data acquisition, the PACK is kept in a static state. After 10 hours, the open circuit voltage of the corresponding cell is retested using a multimeter of the same specification and the same connection point, and each cell is matched with its original cell number. This refers to the nominal open-circuit voltage of the battery cell, in volts (V). It is obtained by retrieving the original manufacturer's specifications for the battery cell and the technical file of the battery pack's BOM. This is a fixed constant for the same model of battery cell and does not require on-site measurement.

[0057] S2. For the data collected in step S1, firstly remove the distorted abnormal voltage data, and then quantify the basic voltage degradation characteristics of a single cell from three dimensions: short-term static voltage deviation, long-term static voltage deviation, and cell static self-recovery voltage deviation.

[0058] Furthermore, distorted and abnormal voltage data caused by cell open circuits or internal short circuits during on-site data collection were removed, and valid cell data conforming to physical laws were retained after removal; all collected data were then processed. , To determine validity, data for cells with severely abnormal voltage or that are already faulty are discarded, and only valid cells that meet the threshold conditions are retained for all subsequent calculations. Valid cell selection criteria: ;in, This is the threshold for judging abnormal cell voltage. Cells with voltage values ​​below this threshold are considered physically failed and are directly removed from all subsequent calculations. After this step is completed, the valid cell number sequence is selected to determine the total number of cells to be included in the final calculation. .

[0059] Furthermore, the expressions for calculating the short-time static voltage deviation, long-time static voltage deviation, and cell static self-recovery voltage deviation in step S2 are as follows: ; ; ;

[0060] in, For the first The short-term static relative voltage deviation of the cell characterizes the voltage deviation of the cell from the nominal value after 2 hours of static rest. For the first The relative voltage deviation of a battery cell after long-term rest represents the magnitude of the voltage deviation from the nominal value of the cell after 12 hours of rest. For the first The relative deviation of cell self-recovery after being left undisturbed represents the degree of polarization degradation in which the cell's voltage autonomously recovers after being left undisturbed for a long time. For the first The open-circuit voltage of a single cell after it has been left to stand for 2 hours. This refers to the nominal open-circuit voltage of the battery cell at the factory. For the first The cell will continue to be left to stand for 12 hours until the single-cell open-circuit voltage is measured.

[0061] Furthermore, this step breaks through the limitations of traditional methods that rely solely on voltage over a single duration to calculate degradation by breaking down the layers of deviation. It decomposes the sources of cell degradation from three static storage dimensions and refines the degradation characterization indicators. The output of this step is... , , A complete set of parameters for all battery cells with the correct cell number.

[0062] S3. The degradation characteristics of the single cell base voltage obtained in step S2 are linearly fused with fixed weights to obtain a comprehensive degradation index. Then, the original base residual value of a single cell under the condition of no neighboring interference is constructed based on the comprehensive degradation index.

[0063] Furthermore, short-time voltage deviation, long-time voltage deviation, and self-recovery deviation of the battery cell correspond to three different mechanisms of internal aging loss. These three types of loss are coupled and superimposed to jointly cause the original residual value decay of a single battery cell. This step linearly integrates the three sets of deviations with fixed weights to obtain a comprehensive degradation index. Then, a composite nonlinear formula with nested natural square root and hyperbolic tangent functions is used to constrain the residual value change law. Based on the comprehensive degradation index, the original residual value of a single battery cell under the condition of no neighboring interference is calculated, realizing the quantification of the single-cell residual value under the coupling of multiple degradation factors. The first step integrates the three types of deviations to obtain the comprehensive degradation index, and the second step uses the degradation index to nonlinearly solve for the original residual value of a single battery cell.

[0064] Furthermore, the specific implementation method of step S3 includes the following steps:

[0065] S3.1. Calculate the overall deterioration index. The calculation formula is as follows:

[0066]

[0067] in, For the first The overall degradation index of the battery cell, This refers to the short-time deviation weighting coefficient; This is the long-term deviation weighting coefficient; This is the self-recovery bias weighting coefficient;

[0068] Furthermore, the overall degradation quantification values ​​of the individual cells after integrating the three types of voltage deviations; A fixed value of 0.4 represents the percentage of short-time voltage deviation that affects cell degradation. A fixed value of 0.4 represents the percentage of the impact of long-term voltage deviation on cell degradation; A fixed value of 0.2 represents the proportion of the impact of self-recovery voltage deviation on cell degradation, satisfying the requirement... .

[0069] S3.2. Based on the comprehensive degradation index, a multi-layer nested nonlinear function is used to construct the original basic residual value of a single cell under the condition of no neighboring interference. The calculation formula is as follows:

[0070]

[0071] in, For the first The original basic residual value coefficient of the battery cell. It is the hyperbolic tangent function. This is the natural exponentiation operator. value range The closer the value is to 1, the more complete the original residual value of the battery cell is, indicating that there is no degradation or loss.

[0072] Furthermore, based on the comprehensive degradation index obtained in the previous step, a residual value calculation formula is constructed using multi-layered nested nonlinear functions. The hyperbolic tangent amplifies the degradation effect caused by polarization deviation, and the natural exponent constrains the gradual decay of the residual value as degradation increases. A composite nonlinear function is used to achieve coupled and linked calculation of the three types of degradation indices, which, unlike the conventional linear ratio algorithm, accurately reflects the objective physical law of accelerated residual value decay after intensified polarization degradation. The output of this step is the original residual value of the entire cell. Original measured voltage , Data set.

[0073] S4. Considering that the cells inside the power battery pack are arranged in series from end to end, the voltage difference between adjacent cells generates internal circulating current loss. Construct a cell coupling discount factor to correct the original basic residual value obtained in step S3, and obtain the residual value of the single cell after neighborhood correction.

[0074] Furthermore, the cells inside the PACK are arranged in series from end to end. The voltage difference between adjacent cells will generate internal circulating current loss. Severely degraded cells with large polarization will continuously drag down the surrounding adjacent cells through series electrical coupling, accelerating their aging. This step also introduces the instantaneous voltage difference factor of adjacent cells and the neighborhood average polarization degradation factor. First, a position attenuation weight is generated based on the voltage difference distribution of cells in the whole string. Then, the two types of degradation factors are weighted and coupled to generate a single-cell discount factor. The discount factor is used to deduct and correct the original residual value obtained in the second step, quantifying the additional residual value loss caused by the contagion of neighborhood degradation.

[0075] Furthermore, the specific implementation method of step S4 includes the following steps:

[0076] S4.1. Grouping two sequentially adjacent cells together, calculate the... Measured voltage difference between cell #1 and adjacent cells ;

[0077]

[0078] in, It is the first No. 1 battery cell and subsequent... The measured voltage difference between adjacent cells, in volts (V). This is for absolute value operations.

[0079] S4.2. For the adjacent cells obtained in step S4.1, average the relative deviation of the static self-recovery for each cell to obtain the first... Average self-recovery deviation of cell #1 and adjacent cells ;

[0080]

[0081] in, It is the first , The average self-recovery deviation of adjacent cells is dimensionless and characterizes the overall polarization degradation level of adjacent paired cells.

[0082] S4.3. Summarize all adjacent cell voltage difference data, calculate the arithmetic mean, and obtain the average cell voltage difference of the power battery pack. ;

[0083]

[0084] The unit V is used as the reference value for the total pack differential pressure. The total number of effective battery cells;

[0085] S4.4. Based on the relative relationship between the measured voltage difference between adjacent cells and the average voltage difference between cells in the power battery pack, a decay function is constructed using the natural exponential function, and the influence weight of each group of adjacent cells is obtained by normalization. The expression is as follows:

[0086]

[0087] in, It is the first The spatial attenuation weighting coefficient between cell number and adjacent cells, where k is any one of the effective cells and n is the total number of effective cells; based on the relative relationship between the single-group voltage difference and the average voltage difference of the entire string, an attenuation function is constructed using the natural exponent, and the influence weight of each group of adjacent cells is obtained by normalization. The smaller the voltage difference and the better the cell condition, the higher the corresponding weight ratio. All weights are summed and fixed at 1, and the smaller the voltage difference, the higher the corresponding weight value. Used to avoid errors caused by a denominator of zero.

[0088] S4.5. Combining the average self-recovery deviation of adjacent cells, the average cell voltage difference of the power battery pack, and the influence weight of each group of adjacent cells, a cell coupling discount coefficient is constructed, expressed as follows:

[0089]

[0090] in, For the first The coupling discount factor between cell #1 and adjacent cells is calculated by assigning 50% weights to the differential voltage degradation term and the neighborhood polarization degradation term, respectively, and then summing them after applying numerical constraints using hyperbolic tangent and exponential functions. The final result is the discount ratio coefficient corresponding to the drag from surrounding degradation on a single cell. A larger coefficient indicates a greater residual value loss due to the drag from adjacent degraded cells. The pressure difference degradation term and polarization degradation term are equally weighted to balance the conversion ratio of the two types of neighborhood losses;

[0091] S4.6. Using the cell coupling discount factor obtained in step S4.5, apply it to the first... The original basic residual value factor of the cell is reduced by discounting, and the hidden losses caused by the contagion of degradation of adjacent cells are deducted to obtain the residual value of the individual cell after neighborhood correction.

[0092]

[0093] in, It is the first after neighborhood degradation correction The residual value coefficient of cell number 1 is dimensionless; the last cell has no adjacent cells, so its neighborhood discount coefficient is 0, and it is not affected by series circulating current and its residual value is not deducted. This step adds a neighborhood polarization degradation coupling term, which supplements the residual value loss caused by polarization contagion on the basis of traditional series voltage difference discount, and improves the quantitative calculation logic of mutual losses between series cells. Output the corrected residual value of all cells. Measured voltage of individual units Data set.

[0094] S5. Based on the three statistical indicators of the cell voltage mean, standard deviation and skewness of the power battery pack, calculate the cell voltage deviation coefficient, and then normalize the cell voltage deviation coefficient by mapping transformation using the natural exponent to obtain the adaptive cell weight. Then, correct and sum the cell residual values ​​obtained in step S4 after neighborhood correction to obtain the final residual value coefficient of the power battery pack.

[0095] The residual value of a whole pack of series-connected cells is constrained by the "weakest link" effect. The more a cell deviates from the overall average voltage, the greater its negative impact on the overall residual value of the pack. This step relies on three statistical indicators—mean voltage, standard deviation, and skewness—to quantify the discrete distribution characteristics of cell voltage. Based on the degree of deviation of each cell from the overall voltage distribution, a weighting coefficient is dynamically and adaptively generated. Cells with higher deviations in deterioration are assigned higher weights. Finally, the weighted sum is used to obtain the overall residual value coefficient of the pack, avoiding the defect of overestimating the residual value of the whole pack by the traditional arithmetic mean algorithm.

[0096] Furthermore, the specific implementation method of step S5 includes the following steps:

[0097] S5.1. Summarize the measured voltages of all valid cells and calculate the arithmetic mean of the measured cell voltages of the power battery pack. ;

[0098]

[0099] S5.2. Based on the voltage of each cell and The difference is used to quantify the overall discrete fluctuation of the cell voltage in the power battery pack using the standard deviation formula, which is expressed as:

[0100]

[0101] in, This represents the standard deviation of the cell voltage in the power battery pack.

[0102] S5.3. Based on the arithmetic mean of the measured cell voltages of the power battery pack and the standard deviation of the cell voltages of the power battery pack, calculate the cell voltage distribution skewness coefficient of the power battery pack. The expression is:

[0103] ;

[0104] The third-order moment formula is introduced to calculate the voltage distribution skewness, which is used to characterize whether there is asymmetrical offset or concentrated offset of the voltage distribution of the entire battery cell string.

[0105] S5.4. Combining the relative mean offset of a single cell with the cell voltage distribution skewness coefficient of the power battery pack, an overall deviation coefficient of the single cell voltage is constructed, expressed as follows:

[0106]

[0107] in, For the first The overall deviation coefficient of cell voltage; combining the relative mean deviation of a single cell with the voltage skewness characteristics of the entire package, the two indicators are integrated to obtain the comprehensive deviation coefficient of a single cell, which reflects the degree of degradation deviation of the cell relative to the overall distribution.

[0108] Then, after normalizing the individual cell voltage deviation coefficient using a mapping transformation based on the natural exponent, we obtain the first... Adaptive weighting coefficient for battery cell # ;

[0109] ;

[0110] After normalizing the deviation coefficient by mapping it with the natural index, the weight ratio of severely degraded cells is automatically amplified, and the total weight of all cells is fixed at 1.

[0111] S5.5. (The following appears to be a separate, unrelated sentence fragment: "with the first...") The adaptive weighting coefficient of cell number is used to weight and accumulate the residual values ​​of individual cells after neighborhood correction output in step S4 to obtain the final residual value coefficient of the power battery pack. The expression is as follows:

[0112]

[0113] in, It is the final residual value coefficient of the power battery pack, with a value range of... The closer the value is to 1, the higher the overall residual value and integrity of the entire battery pack.

[0114] The application example in this embodiment is illustrated below: The test object in this case is a 12-cell series-connected lithium iron phosphate power battery pack, with the nominal open-circuit voltage of the cells at the factory. Total number of effective battery cells The collected data is shown in Table 1:

[0115] Table 1

[0116]

[0117] The step-by-step practical calculation process is as follows: Calculation of individual three-dimensional voltage deviation parameters: This step involves comparing the measured voltage of each cell twice with the nominal value of 3.2V to calculate the short-time deviation, long-time deviation, and self-recovery deviation. Taking cell #1 as an example, the voltage is 3.18V after 2 hours and 3.19V after 12 hours. The difference between these values ​​and 3.2V, divided by 3.2V, yields a short-time deviation of 0.00625 and a long-time deviation of 0.003125. The difference between the two voltages, divided by 3.2V, gives the self-recovery deviation of 0.003125. This calculation method is applied to all cells from #2 to #12 to calculate the three sets of deviations for each cell. After calculation, it is evident that cells #6 and #9 have the highest deviation values ​​in the group, indicating that these two cells show more pronounced aging than the others. All deviation results in this step are saved as the basis for subsequent calculations.

[0118] 3D degraded coupling, solving for the original residual of a single unit: With a fixed ratio, the short-time deviation weight is 0.4, the long-time deviation weight is 0.4, and the self-recovery deviation weight is 0.2. First, the three deviations are multiplied by their corresponding coefficients and then added together to obtain the comprehensive degradation index. Then, the original residual value of a single cell is obtained by relying on index-based calculations.

[0119] Using the data from cell #1 as a substitute for calculation, a weighted sum is obtained, resulting in a comprehensive degradation index of 0.00437. After calculation, the original residual value of cell #1 is 0.958. After calculating the residual values ​​of all cells, the original residual values ​​of most cells in good condition are concentrated in the range of 0.93 to 0.96. The original residual values ​​of cell #6, which shows more obvious aging, are approximately 0.91, and those of cell #9 are approximately 0.90. All original residual value data of cells are retained and proceed to the third step for neighborhood discount correction.

[0120] Serial neighborhood coupling discount correction, and calculation of the residual value of the unit after correction: The first step is to calculate the voltage difference between adjacent cells: The entire package contains 12 cells connected in series, with cell 1 next to cell 2, cell 2 next to cell 3, and so on up to cell 11 next to cell 12. There are no cells after cell 12, so the voltage difference doesn't need to be calculated. Take the absolute value of the difference between the actual voltages of each pair of adjacent cells after 2 hours. For example, if cell 1 is 3.18V and cell 2 is 3.16V, the voltage difference is 0.02V. Calculate the voltage difference data for adjacent cells 1-11 in this way.

[0121] The second step is to calculate the average polarization deviation of adjacent cells: using the self-recovery deviation calculated in step 1 of the previous step, add the self-recovery deviations of each pair of adjacent cells and divide by 2. For example, if cells 1 and 2 are paired, add their self-recovery deviations and take the average to obtain the average polarization data of this pair of cells. Calculate the average polarization data of all 11 pairs one by one.

[0122] The third step is to calculate the average voltage difference of the entire pack: add up all the 11 adjacent voltage differences calculated earlier, then divide by 11, and finally get the average voltage difference of the entire pack, which is about 0.032V. This value is used as the reference benchmark for the voltage difference of the entire pack.

[0123] The fourth step is to calculate the impact weight of each group: the smaller the voltage difference between the cells, the lower the negative impact on the surrounding area and the higher the weight assigned. The weight of each group is calculated by exponential conversion and normalization based on the voltage difference of each group and the overall average voltage difference. The weights of all 11 groups are added together and the result is equal to 1. Among them, the voltage difference between cells 3 and 4 and between cells 10 and 11 is relatively small, and the corresponding weight values ​​are relatively high. The voltage difference between cells 6 and 7 and between cells 9 and 10 is relatively large, and the weights are relatively low.

[0124] The fifth step is to calculate the discount factor for each cell: the loss caused by voltage difference and the loss caused by polarization each account for half of the weight. Combine the weights calculated above to calculate the discount factor. There is no cell interference behind cell No. 12, so the discount factor is directly set to 0. Finally, the discount factors for cells No. 6 and No. 9 are calculated to be 0.042 and 0.048 respectively, which are the two highest values ​​in the whole group.

[0125] Step 6: Correcting the residual value of a single cell: Multiply the original residual value obtained in Step 2 by (1 - discount factor) to obtain the final corrected residual value. Cell #12 has no discount, so its corrected residual value is exactly the same as its original residual value; Cells #6 and #9 have a higher discount factor, so their individual residual values ​​are significantly lower than their original values; the discount factors for the other healthy cells are very small, so their residual values ​​only change slightly.

[0126] Multidimensional statistical adaptive weighting is used to calculate the overall residual value of the PACK: The first step is to calculate the average voltage of the entire pack: add up the actual voltages of all 12 cells measured over 2 hours, divide by 12, and calculate the average voltage of the entire pack to be approximately 3.13392V.

[0127] The second step is to calculate the voltage standard deviation: take the voltage of each individual cell and the difference with 3.143V, square the sum, take the average and then take the square root. Finally, the standard deviation of the entire package voltage is about 0.0255967V. This value shows that the overall voltage dispersion of the cells is not large.

[0128] The third step is to calculate the voltage skewness: Based on the calculation logic of third-order statistics, combined with the deviation of the voltage and average value of each cell, the voltage distribution skewness of the entire package is calculated to be -245.313609.

[0129] The fourth step is to calculate the deviation coefficient of each cell: combining the difference between the voltage and the average value of each cell, and adding the deviation results obtained earlier, the deviation index of each cell is calculated. The deviation coefficients of cells No. 6 and No. 9 are much higher than those of other cells.

[0130] The fifth step is dynamic weight normalization: the greater the deviation of the cell value, the higher the calculation weight assigned after exponential conversion. The sum of the weights of all cells equals 1. After the calculation, the weights of the two degraded cells, No. 6 and No. 9, are significantly higher than those of the ordinary cells.

[0131] Step 6: Summarize the residual value of the entire package: Multiply the corrected residual value of each cell by its corresponding dynamic weight, add all the results together, and finally obtain the overall residual value coefficient of the entire package of approximately 0.7276.

[0132] This case study utilizes retired battery pack data collected from a partner company, strictly adhering to the entire calculation methodology throughout the entire process. No cell disassembly or external equipment for full charge / discharge capacity testing is required. The final calculated residual value coefficient is 0.7276, representing a 72.76% overall cell integrity rate for the entire pack. Subsequent capacity measurements by the recycling company after disassembly largely matched this calculation. The step-by-step calculation process clearly demonstrates that the algorithm reduces the hidden losses caused by the mutual drag of degraded cells through neighborhood discounting, and increases the proportion of degraded cells in the overall pack calculation through dynamic weighting. This effectively avoids the drawbacks of traditional simple averaging algorithms that inflate residual values, and to a certain extent, it is suitable for the actual operational scenarios of rapid grading and non-destructive residual value calculation for battery recycling.

[0133] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0134] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for evaluating the residual value of a retired power battery monomer series pack, characterized in that, Includes the following steps: S1. Collect the open-circuit voltage of each cell in the power battery pack after 2 hours of rest, and the open-circuit voltage of the same numbered cell after 12 hours of further rest, to obtain the nominal open-circuit voltage of the cell at the factory. S2. For the data collected in step S1, firstly remove the distorted abnormal voltage data, and then quantify the basic voltage degradation characteristics of a single cell from three dimensions: short-term static voltage deviation, long-term static voltage deviation, and cell static self-recovery voltage deviation. S3. The degradation characteristics of the single cell base voltage obtained in step S2 are linearly fused with fixed weights to obtain a comprehensive degradation index. Then, the original base residual value of a single cell under the condition of no neighboring interference is constructed based on the comprehensive degradation index. S4. Considering that the cells inside the power battery pack are arranged in series from end to end, the voltage difference between adjacent cells generates internal circulating current loss. Construct a cell coupling discount factor to correct the original basic residual value obtained in step S3, and obtain the residual value of the single cell after neighborhood correction. S5. Based on the three statistical indicators of the cell voltage mean, standard deviation and skewness of the power battery pack, calculate the cell voltage deviation coefficient, and then normalize the cell voltage deviation coefficient by mapping transformation using the natural exponent to obtain the adaptive cell weight. Then, correct and sum the cell residual values ​​obtained in step S4 after neighborhood correction to obtain the final residual value coefficient of the power battery pack.

2. The method of claim 1, wherein, The expressions for calculating the short-time static voltage deviation, long-time static voltage deviation, and cell static self-recovery voltage deviation in step S2 are as follows: ； ； ； in, For the first The short-term static relative voltage deviation of the cell characterizes the voltage deviation of the cell from the nominal value after 2 hours of static rest. For the first The relative voltage deviation of a battery cell after long-term rest represents the magnitude of the voltage deviation from the nominal value of the cell after 12 hours of rest. For the first The relative deviation of cell self-recovery after being left undisturbed represents the degree of polarization degradation in which the cell's voltage autonomously recovers after being left undisturbed for a long time. For the first The open-circuit voltage of a single cell after it has been left to stand for 2 hours. This refers to the nominal open-circuit voltage of the battery cell at the factory. For the first The cell will continue to be left to stand for 12 hours until the single-cell open-circuit voltage is measured.

3. The method for assessing the residual value of a retired power battery cell series pack according to claim 2, characterized in that, The specific implementation method of step S3 includes the following steps: S3.

1. Calculate the overall deterioration index. The calculation formula is as follows: in, For the first The overall degradation index of the battery cell, This refers to the short-time deviation weighting coefficient; This is the long-term deviation weighting coefficient; This is the self-recovery bias weighting coefficient; S3.

2. Based on the comprehensive degradation index, a multi-layer nested nonlinear function is used to construct the original basic residual value of a single cell under the condition of no neighboring interference. The calculation formula is as follows: ； in, For the first The original basic residual value coefficient of the battery cell. It is the hyperbolic tangent function. This is the natural exponentiation operator.

4. The method for evaluating the residual value of a retired power battery cell series pack according to claim 3, characterized in that, The specific implementation method of step S4 includes the following steps: S4.

1. Grouping two sequentially adjacent cells together, calculate the... Measured voltage difference between cell #1 and adjacent cells ; S4.

2. For the adjacent cells obtained in step S4.1, average the relative deviation of the static self-recovery for each cell to obtain the first... Average self-recovery deviation of cell #1 and adjacent cells ; S4.

3. Summarize all adjacent cell voltage difference data, calculate the arithmetic mean, and obtain the average cell voltage difference of the power battery pack. ; S4.

4. Based on the relative relationship between the measured voltage difference between adjacent cells and the average voltage difference between cells in the power battery pack, a decay function is constructed using the natural exponential function, and the influence weight of each group of adjacent cells is obtained by normalization. The expression is as follows: ； in, It is the first The spatial attenuation weighting coefficient between cell number 1 and adjacent cells, where k is any one of the effective cells and n is the total number of effective cells; S4.

5. Combining the average self-recovery deviation of adjacent cells, the average cell voltage difference of the power battery pack, and the influence weight of each group of adjacent cells, a cell coupling discount coefficient is constructed, expressed as follows: ； in, For the first The coupling discount factor between cell number 1 and adjacent cells; S4.

6. Using the cell coupling discount factor obtained in step S4.5, apply it to the first... The original basic residual value factor of the cell is reduced by discounting, and the hidden losses caused by the contagion of degradation of adjacent cells are deducted to obtain the residual value of the individual cell after neighborhood correction.

5. The method for evaluating the residual value of a retired power battery cell series pack according to claim 4, characterized in that, The specific implementation method of step S5 includes the following steps: S5.

1. Summarize the measured voltages of all valid cells and calculate the arithmetic mean of the measured cell voltages of the power battery pack. ; S5.

2. Based on the voltage of each cell and The difference is used to quantify the overall discrete fluctuation of the cell voltage in the power battery pack using the standard deviation formula, which is expressed as: ； in, This represents the standard deviation of the cell voltage in the power battery pack. S5.

3. Based on the arithmetic mean of the measured cell voltages of the power battery pack and the standard deviation of the cell voltages of the power battery pack, calculate the cell voltage distribution skewness coefficient of the power battery pack. The expression is: ； S5.

4. Combining the relative mean offset of a single cell with the cell voltage distribution skewness coefficient of the power battery pack, an overall deviation coefficient of the single cell voltage is constructed, expressed as follows: ； in, For the first Overall voltage deviation coefficient of cell number; Then, after normalizing the individual cell voltage deviation coefficient using a mapping transformation based on the natural exponent, we obtain the first... Adaptive weighting coefficient for battery cell # ; S5.

5. (The following appears to be a separate, unrelated sentence fragment: "with the first...") The adaptive weighting coefficient of cell number is used to weight and accumulate the residual value of the individual cell after neighborhood correction output in step S4 to obtain the final residual value coefficient of the power battery pack.

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