A method and system for quantitatively evaluating battery aging mechanism based on macro-micro correlation

Abstract

The application discloses a method and system for quantitatively evaluating battery aging mechanism based on macro-micro correlation, comprising: adopting the external characteristic method and the disintegration physicochemical method to respectively perform full battery macroscopic performance test and half-cell microscopic performance test; respectively performing macro-micro analysis on the internal aging mechanism of the battery; correlating and quantitatively evaluating the macro-micro analysis results to obtain a correlation and quantitative evaluation method; and verifying the correlation and quantitative evaluation method. The battery health state is redefined by dynamics loss, the microscopic XRD test result is combined with the capacity increment curve result obtained by macroscopic test to jointly evaluate the battery aging, the active material loss coupled in the XRD test is stripped out, the loss of active lithium ion is calculated alone, the loss of recyclable lithium ion and the loss of active material are quantitatively calculated by removing the IC curve of dynamics loss, and the results are compared with the results calculated by the dQ / dV-charge capacity curve, so as to verify the method for quantitatively evaluating the battery aging mechanism based on macro-micro correlation.

Description

Technical Field

[0001] This invention relates to a method and system for quantitatively evaluating battery aging mechanisms based on macro-micro correlation, belonging to the field of power battery technology. Background Technology

[0002] As electric vehicle batteries age, they deteriorate and degrade. When battery performance deteriorates, its performance declines, affecting the energy efficiency of the electric vehicle and reducing the driving range per full charge. Furthermore, if the same control strategies or thresholds are applied to aged batteries, their performance may deteriorate more rapidly, significantly shortening their lifespan and increasing safety risks.

[0003] Currently, research on the internal mechanisms of battery degradation mainly focuses on two methods: external characteristic analysis and disassembly-physicochemical analysis. The first method involves conducting a series of performance tests on the battery, using the collected data such as temperature, current, and voltage as a starting point. By exploring the deep correlation between key parameters in this data and battery degradation, a correspondence between characteristic parameters and internal aging is established; thus, the internal aging mechanism of the battery can be determined. Commonly used external characteristic analysis methods include impedance spectroscopy, open-circuit voltage curves, differential voltage curves (DV), and incremental capacity curves (IC).

[0004] The second method involves destructively disassembling the full battery, fabricating half-cells from the positive and negative electrodes for testing and analysis, or investigating the mechanisms causing battery aging through microscopic testing of the electrodes. X-ray diffraction (XRD) is used to observe changes in electrode structure; scanning electron microscopy (SEM) is used to detect changes in the microscopic morphology of materials; and X-ray photoemission spectroscopy (XPS) is used to determine the differences in elemental composition of electrodes and separators before and after cycling. Based on the results of microscopic testing of the battery before and after cycling, the true cause of battery degradation can be determined.

[0005] The former analyzes battery aging mechanisms primarily from a data correlation perspective, but it diagnoses and quantifies capacity degradation mechanisms based on certain assumptions, making it impossible to independently verify the correctness of the results. The latter reveals battery aging mechanisms more qualitatively, but due to battery destruction, continuous experiments are not possible, and current disassembly-physicochemical methods mainly target button half-cells, which differ somewhat from full-cell batteries used in actual engineering applications. Summary of the Invention

[0006] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a method and system for quantitatively evaluating battery aging mechanisms based on macro-micro correlation. This invention performs macro- and micro-level tests on battery performance and analyzes them separately, then correlates and quantitatively evaluates the analysis results to derive a correlation-based quantitative evaluation method.

[0007] Technical solution: A method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation, comprising the following steps:

[0008] S1: The macroscopic performance of the full cell and the microscopic performance of the half cell were tested using the external characteristic method and the disassembly physicochemical method, respectively.

[0009] S101: Perform full-cell macroscopic performance tests on the battery to obtain the relationship between battery capacity, ohmic internal resistance, polarization internal resistance, open-circuit voltage and SOC, battery charge-discharge characteristics at different rates, and remaining capacity at different charge-discharge rates.

[0010] The full battery macroscopic performance test includes capacity calibration test, hybrid power pulse characteristic test, low rate charge and discharge test, constant current charge and discharge test at different rates, and test of the effect of rate on remaining capacity.

[0011] S102: Perform half-cell microscopic performance testing on the battery: After charging the full cells in different health states to full charge using a constant current and constant voltage method, the battery is disassembled; then, samples are taken from the intact negative electrode obtained from the disassembly, and X-ray diffractometer (XRD) is used to observe the changes in the electrode structure.

[0012] S2: Based on the parameters obtained from the full-cell macroscopic performance test and the half-cell microscopic performance test in S1, the internal aging mechanism of the battery is analyzed macroscopically and microscopically respectively. The macroscopic and microscopic analysis results are then correlated and quantitatively evaluated to derive a correlation quantitative evaluation method.

[0013] S201: Macroscopic analysis of the internal aging mechanism of the battery is performed using the open-circuit voltage curve method and the capacity increment curve method, respectively.

[0014] S202: Microscopic analysis of the internal aging mechanism of the battery was performed using X-ray diffraction (XRD).

[0015] S203: Conduct a quantitative evaluation of the correlation based on the macroscopic and microscopic analysis results of S201 and S202;

[0016] S3: Validate the correlation quantitative evaluation method derived from S2.

[0017] This invention uses external characteristic method and disassembly physicochemical method to conduct macroscopic performance tests on full-cell batteries and microscopic performance tests on half-cell batteries. Based on the data obtained from the macroscopic performance tests of full-cell batteries and microscopic performance tests of half-cell batteries, the internal aging mechanism of batteries is analyzed macroscopically and microscopically. The macroscopic and microscopic analysis results are correlated and quantitatively evaluated to derive a correlation quantitative evaluation method. Finally, the correlation quantitative evaluation method is verified.

[0018] Preferably, the specific steps of the capacity calibration test in S101 are as follows:

[0019] If the battery is subjected to multiple charge and discharge tests, and the error in the amount of electricity released in three consecutive tests is less than 2%, then the average amount of electricity released in the three tests is taken as the capacity of the battery in the current state.

[0020] The specific steps for testing the hybrid power pulse characteristics of S101 are as follows:

[0021] High-rate discharge pulses and charging pulses are applied to the battery at two different time intervals. After the pulse ends, a normal-rate current is applied to the battery to release a fixed amount of charge. This cycle is repeated until all the charge in the battery is released. Based on the change in voltage difference of the battery in different pulse phases, its dynamic characteristics in multiple state of charge (SOC) regions are obtained, thereby establishing the relationship between ohmic internal resistance, polarization internal resistance, open-circuit voltage and state of charge (SOC).

[0022] The specific steps of the constant current charge and discharge test at different rates of S101 are as follows: At each rate, a constant current is used to continuously charge and discharge the battery to obtain the charge and discharge characteristics of the battery at different rates.

[0023] The specific steps for the S101 test of the effect of the charge rate on the remaining capacity are as follows: After charging or discharging the battery at different rates to the maximum or minimum cutoff voltage at a constant ambient temperature, the battery is left to stand, and then charged or discharged again to the cutoff voltage at a small current in the small rate charge / discharge test to obtain the remaining capacity under different charge / discharge rates.

[0024] Preferably, the specific steps of the open-circuit voltage curve method in S201 are as follows:

[0025] Calculate the battery capacity ratio CR: Establish an open-circuit voltage curve using charge and discharge data of the battery at C / 20 and below. Then, mark the voltage of the battery after completing the charge or discharge experiment at different rates as the resting voltage at the end of charging (EOC-RCV) or the resting voltage at the end of discharging (EOD-RCV). Based on the obtained resting voltage at the end of charging (EOC-RCV) and the resting voltage at the end of discharging (EOD-RCV), find the state of charge at the end of charging (EOC-SOC) and the state of charge at the end of discharging (EOD-SOC) on the open-circuit voltage curve adjusted under different health conditions.

[0026] The capacity ratio CR is the ratio of the battery's capacity when charged or discharged at a certain rate to the ΔSOC (state of charge) estimated from the charge / discharge rest voltage obtained through the adjusted open-circuit voltage curve.

[0027]

[0028] In the formula, It refers to the amount of battery power that can be charged or discharged at a certain rate. It is the difference between the state of charge (SOC) inferred from the resting voltage EOC-RCV at the end of charging and the resting voltage EOD-RCV at the end of discharging on the open-circuit voltage curve.

[0029] Calculation and verification of remaining capacity: To determine the remaining capacity of the battery, the state of charge (SOC) needs to be converted into the corresponding capacity. The conversion between SOC and capacity is achieved through formula (2), as shown in the following formula:

[0030]

[0031] In the formula, It is the remaining capacity of the battery after the discharge rate has been affected when the battery is discharged; It is determined by locating the SOC corresponding to the resting voltage at the end of battery discharge on the open circuit voltage curve, i.e., EOD-SOC;

[0032] Determining kinetic losses: After the battery has fully discharged, the EOD-RCV increases due to kinetic losses. These kinetic losses are related to the battery's charge / discharge rate. The capacity loss caused by kinetic losses is quantitatively calculated using the remaining capacity. The calculation formula is as follows:

[0033]

[0034]

[0035] In the formula, This refers to the capacity loss caused by kinetic energy loss in the battery. This is the rated capacity of the new battery; The capacity is due to the existence of dynamic losses;

[0036] Determine the cyclic lithium-ion loss (LLI) and active material loss (LAM): Calculate the magnitude of the cyclic lithium-ion loss and active material loss that are the essential causes of battery aging using formula (5);

[0037]

[0038] In the formula, It is the sum of the loss of cyclic lithium ions and the loss of active materials within the battery; This is the battery capacity in its current healthy state.

[0039] Preferably, the specific steps of the capacity increment curve method in S201 are as follows:

[0040] A capacity increment curve is established based on the capacity and voltage data corresponding to charging rates of C / 20 and below. The order in which these peaks appear during charging can be divided into three peaks: Peak A, Peak B, and Peak C, denoted as Peak A, Peak B, and Peak C, respectively. Electrochemical characteristic analysis of the battery reveals that a larger peak value indicates a faster chemical reaction at that point. If Peak C declines and disappears, the magnitude and shift of Peak B value are attributed to the loss of active material and cyclic lithium ions. If Peak C declines but still exists, the magnitude and shift of Peak B value are attributed to the loss of active material. The remaining amount of active material can be calculated by the change in the position of the trough between Peak B and Peak C values ​​on the dQ / dV - charge curve. Then, the amount of cyclic lithium ions lost can be calculated by subtracting the amount of active material decline from the total capacity decline, or directly based on the decline of Peak C. The specific calculation is as follows:

[0041] Calculations were performed on the active material loss (LAM) and the recyclable lithium-ion loss (LLI):

[0042] Calculate the loss of active material:

[0043]

[0044] In the formula, The new battery exhibits its capacity at the trough between the Peak B and Peak C values. This represents the capacity corresponding to the lowest point between the Peak B and Peak C values ​​of the battery under its current healthy state. It is the loss of active materials in the battery;

[0045] The recyclable lithium-ion loss (LLI) is calculated by subtracting the active material degradation from the total capacity degradation:

[0046]

[0047]

[0048] In the formula, The capacity loss is caused by the loss of active materials; It is the loss of recyclable lithium ions;

[0049] The cyclic lithium-ion loss (LLI) is calculated based on the peak value of the decay, using the following formula:

[0050]

[0051] In the formula, This refers to the capacity corresponding to the Peak C battery. This is the capacity corresponding to Peak C of the battery in its current healthy state.

[0052] In a preferred embodiment, the specific steps of S202 are as follows:

[0053] When the battery is charging, a large number of lithium ions are released, pass through the separator, and embed into the graphite anode. At this time, the metal lithium compounds in the anode are mainly lithium-carbon compounds. When C is sufficient, the amount of embedded lithium ions is approximately equal to the amount of recyclable lithium ions.

[0054] By comparing the diffraction peaks appearing in the XRD patterns of batteries in different aging states with standard patterns, two diffraction peaks with higher intensities were observed as the scanning angle increased from low to high. , Calculate the diffraction intensity and corresponding peak area of ​​the diffraction peaks of the battery;

[0055] After normalizing C, the corresponding Li was calculated from the diffraction peak intensities. + Content, i.e., Li x C:

[0056]

[0057] In the formula, for The diffraction intensity; for The diffraction intensity; The lithium-carbon compound content is calculated based on the diffraction peak intensity.

[0058] The corresponding Li was calculated by calculating the diffraction peak area. + content:

[0059]

[0060] In the formula, for The peak area; for The peak area; The content of lithium-carbon compounds is calculated by the area of ​​diffraction peaks;

[0061] By calculating Li x The decay of C is used to characterize the loss of cyclic lithium ions;

[0062]

[0063] In the formula, It refers to the lithium-carbon compound content of the new battery; It represents the lithium-carbon compound content of the battery in its current healthy state.

[0064] In the preferred embodiment, the specific steps of S203 are as follows:

[0065] The battery aging mechanism was quantitatively evaluated by macro-micro correlation using X-ray diffraction (XRD) testing method, which calibrates the battery health state based on kinetic loss and corrects for active material loss.

[0066] Battery health status calibrated for kinetic loss: The standard battery health status is obtained by charging and discharging the battery at a rate of C / 3. Capacity is inevitably affected by kinetic loss; therefore, the health status needs to be adjusted based on the kinetic loss. The formula for calculating the adjusted battery health status is as follows:

[0067]

[0068] In the formula, It is the capacity ratio of the new battery; It is the capacity ratio of the battery in its current state; This is the battery health state considering kinetic losses;

[0069] X-ray diffraction (XRD) method for correcting active material loss: To account for carbon loss and achieve separate calculation of cyclic lithium-ion loss (LLI), the IC method is used to analyze the XRD test results; the specific calculations are as follows:

[0070]

[0071]

[0072] In the formula, The loss of active material was calculated using the IC curve method; This refers to the lithium-carbon compound content considering the loss of active materials; This refers to the loss of recyclable lithium ions, taking into account the loss of active materials.

[0073] In the preferred embodiment, the specific steps of S3 are as follows:

[0074] Based on the constant current charge-discharge tests at different rates in S101, the IC curves at different rates were obtained, and the influence of the charging rate on the IC curve was derived. The battery impedance variation was analyzed based on the results of the hybrid power pulse characteristic test, and the kinetic loss was calculated based on the relationship between the charging rate and impedance. The modified IC curves were obtained by differentiating the charging voltage and the charged capacity after eliminating kinetic losses. The cyclic lithium-ion loss (LLI) and active material loss (LAM) calculated using the peak area of ​​the modified IC curves were compared with the results obtained in S2 to verify the correlation quantitative evaluation method.

[0075] The cyclic lithium-ion loss (LLI) and active material loss (LAM) can be calculated using the characteristic peak area, as shown in the following formula:

[0076]

[0077]

[0078] In the formula, It is the sum of the peak areas of the new battery Peak B and Peak A; It is the sum of the peak areas of Peak B and Peak A of the battery under its current healthy state; It is the Peak C area of ​​the new battery; It is the area of ​​Peak C under the current healthy state.

[0079] A system for implementing a method for quantitative evaluation of battery aging mechanisms based on macro-micro correlation includes an offline calibration module and an online estimation module;

[0080] The offline calibration module is used to obtain the IC curve of the battery after removing kinetic loss, and to obtain the characteristic peak area of ​​the IC curve and the offline calibration function between LLI and LAM;

[0081] The online estimation module is used to obtain local IC curves based on measured voltage and current data, obtain the corresponding peak area based on the IC curves, and input the peak area into the offline calibration function to obtain the measured LLI and LAM of the battery.

[0082] In a preferred embodiment, the offline calibration module is used to perform hybrid power pulse characteristic tests and low-rate charge-discharge tests on the battery, analyze the battery impedance change law based on the results obtained from the hybrid power pulse characteristic tests, and calculate the dynamic loss based on the relationship between the charging rate and the impedance.

[0083] The corrected IC curve is obtained by differentiating the charging voltage and the charged capacity after eliminating kinetic losses. The loss of battery active material is obtained based on the peak areas of Peak A and Peak B, and the loss of cyclic lithium ions is calculated based on the peak area decay of Peak C. An offline calibration function between the characteristic peak area and LLI and LAM is established.

[0084] In a preferred embodiment, the online estimation module is used to analyze the current magnitude within the voltage range corresponding to different characteristic peaks of the IC curve based on the measured voltage and current data, and to perform corresponding dynamic corrections based on the corresponding current.

[0085] The local IC curve of the battery is obtained by differentiating the corrected voltage based on the charged capacity; then the characteristic peak area is calculated, and the corresponding peak area is substituted into the offline calibration function relationship, so as to achieve quantitative characterization of the loss of cyclic lithium ions and active materials.

[0086] Beneficial Effects: This invention achieves quantitative characterization of cyclic lithium-ion loss and active material loss by differentiating the Q-V curves under different health states to obtain the dQ / dV-charged capacity curve. It proposes a method for obtaining cyclic lithium-ion loss based on X-ray diffraction (XRD) testing and verifies the characterization results of the capacity increment curve method using XRD test results. Finally, based on the changes in the characteristic peaks of the capacity increment curve, a quantitative calculation method for aging mechanisms is proposed. By redefining the kinetic loss of the battery health state and jointly evaluating battery aging with the capacity increment curve results obtained from microscopic XRD testing and macroscopic testing, the active material loss coupled to XRD testing is separated, enabling separate calculation of active lithium-ion loss. Cyclic lithium-ion loss (LLI) and active material loss (LAM) are quantitatively calculated using the IC curve after removing kinetic loss, and compared with the results calculated from the dQ / dV-charged capacity curve to verify the method of quantitatively evaluating battery aging mechanisms based on macro-micro correlation, thus achieving a macro-micro correlation quantitative evaluation of battery aging mechanisms. Attached Figure Description

[0087] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0088] Figure 1 This is a flowchart of the method of the present invention; Figure 2 Test the voltage and current profiles of the HPPC under operating conditions; Figure 3 The curves showing the relationship between the ohmic internal resistance and SOC of the battery under different health conditions; Figure 4 The image shows the XRD test results. Figure 5 Curves showing the relationship between open-circuit voltage and charged capacity for batteries in different health states; Figure 6 Open-circuit voltage curves for batteries in different health states; Figure 7 Open-circuit voltage curves adjusted for batteries in different health states; Figure 8 This is a schematic diagram for calculating the capacity ratio; Figure 9 This is a comparison between the remaining capacity obtained from the experiment and the remaining capacity obtained from the calculation. Figure 10 To account for the impact of kinetic losses on cyclic lithium-ion loss and active material loss; Figure 11 The QV and IC curves are for charging at C / 25 rate; Figure 12 dQ / dV - charge-capacity curves for batteries in different health states; Figure 13 The loss of cyclic lithium ions under different health conditions; Figure 14 The loss of cyclic lithium ions under different health conditions is calculated by Peak C degradation. Figure 15 Li for batteries in different health states x C Intensity ; Figure 16 Li for batteries in different health states x C Area ; Figure 17 To calculate the sum of LLI and LAM under different health conditions using the open-circuit voltage curve method, (a) the standard definition of SOH is provided; (b) SOH is redefined. Figure 18 LLI and LAM calculated based on IC curves before and after health status adjustment; (a) LLI under standard definition of SOH; (b) LLI under redefining SOH; (c) LAM under standard definition of SOH; (d) LAM under redefining SOH; Figure 19 The sum of LLI and LAM calculated based on IC curves before and after health status adjustment; (a) Standard definition of SOH; (b) Redefinition of SOH; Figure 20 LLI calculated based on XRD before and after health status adjustment; Figure 21 The charge / discharge IC curves of AA batteries at different rates; Figure 22 IC curves for batteries in different health states; Figure 23 The curves showing the relationship between the characteristic parameters of different characteristic peaks and SOH; (a) peak height of the characteristic peak; (b) peak area of ​​the characteristic peak; Figure 24 The battery can cycle to reduce lithium-ion loss and active material loss under different health conditions; Figure 25 The loss of active material is calculated using two different methods. Figure 26 The cyclic lithium-ion loss is calculated using two different methods. Figure 27 This is a quantitative calculation process for aging mechanisms based on capacity increment curves; Figure 28 The curves showing the relationship between the peak areas of Peak B and Peak A and the loss of active material are shown. Figure 29 The curve showing the relationship between the peak area of ​​Peak C and the loss of recyclable lithium ions; Figure 30 To verify the IC curve of the battery; Figure 31 To verify the loss of active materials in batteries under different health conditions; Figure 32 To verify the cyclic lithium-ion loss of the battery under different health conditions; Figure 33 This represents the error of the sum of the cyclic lithium-ion loss and the active material loss calculated by the two methods. Detailed Implementation

[0089] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0090] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0091] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0092] This embodiment uses a lithium iron phosphate battery as an example.

[0093] A method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation includes the following steps:

[0094] S1: The macroscopic performance of the full cell and the microscopic performance of the half cell were tested using the external characteristic method and the disassembly physicochemical method, respectively.

[0095] S101: Perform full-cell macroscopic performance tests on the battery to obtain the relationship between battery capacity, ohmic internal resistance, polarization internal resistance, open-circuit voltage and SOC, battery charge-discharge characteristics at different rates, and remaining capacity at different charge-discharge rates.

[0096] The full battery macroscopic performance test includes capacity calibration test, hybrid power pulse characteristic test, low rate charge and discharge test, constant current charge and discharge test at different rates, and test of the effect of rate on remaining capacity.

[0097] As shown in Table 1, this embodiment takes 12 batteries in different health states as examples and conducts full-cell macroscopic performance tests on batteries numbered 1-8.

[0098] Table 1. Battery serial numbers and their health status

[0099]

[0100] The specific steps of the capacity calibration test are as follows: Perform multiple charge and discharge tests on the battery. If the amount of electricity that the battery can release when it is fully discharged in three consecutive experiments has an error of less than 2% compared with the average amount of electricity released in these three experiments, then the average amount of electricity that can be released in the three tests is taken as the capacity calibration result of the battery in the current state.

[0101] The specific steps for the hybrid power pulse characteristic test are as follows:

[0102] The battery is given high-rate discharge pulses and charging pulses at two different time intervals. After the pulses end, the battery is given a normal rate current to release a fixed amount of charge. This cycle is repeated until all the charge in the battery is released. Figure 2 As shown.

[0103] The specific test steps are as follows: Let the battery under test rest for 2 hours, then discharge it at a constant current (C / 3) to the cutoff voltage of 2.5V, let it rest for 2 hours, then charge it at a constant current (C / 3) to the cutoff current of 1A, then charge it at a constant voltage (C / 20) to the cutoff current of 1A. Let it rest for 5 hours, then discharge it at a 3C rate for 10 seconds, let it rest for 40 seconds, then charge it at a 3C rate for 10 seconds, let it rest for 40 seconds, then discharge it at a C / 3 rate for 9 minutes, then let it rest for 2 hours. Repeat the 3C charge / discharge cycle and subsequent resting steps 20 times. After exiting the cycle, discharge it at a constant current (C / 3) to the cutoff voltage of 2.5V, then let it rest for 2 hours.

[0104] The ohmic internal resistance of the battery under different states of charge was obtained through HPPC experiments. Figure 3 The figure shows the relationship curves between the battery's ohmic internal resistance and state of charge (SOC) under different health conditions. As can be seen from the figure, the relationship curves between the battery's ohmic internal resistance and SOC are similar under different health conditions. Furthermore, regarding the relationship curves between internal resistance and SOC, as the SOC decreases from 1 to 0.95, the internal resistance also decreases sharply, reaching its minimum value around 0.95. With the decrease in SOC, the change in internal resistance fluctuates somewhat, but the overall change is not significant, and its value increases slightly again towards the end of the discharge process.

[0105] The specific steps of the low-rate charge-discharge test are as follows: the battery is charged and discharged by applying a small current at a C / 25 rate:

[0106] The battery under test was left to stand for 1 hour, then discharged at a constant current of C / 3 to the cutoff voltage of 2.5V, left to stand for 4 hours, then charged at a constant current of C / 25 to the cutoff voltage of 3.65V, left to stand for 4 hours, then discharged at a constant current of C / 25 to the cutoff voltage of 2.5V, left to stand for 4 hours, and then the C / 25 charge-discharge and subsequent standing steps were repeated twice.

[0107] The specific steps of the constant current charge-discharge test at different rates are as follows: The battery is continuously charged and discharged at a constant current at each rate to obtain the charge-discharge characteristics of the battery at different rates. During the test, the battery is charged and discharged at current rates of C / 25, C / 10, C / 5, C / 3, C / 2, 1C, and 2C, respectively. Taking 1C constant current discharge as an example, the specific test steps are as follows:

[0108] The battery under test was left to stand for 1 hour, then discharged at a constant current of C / 3 to the cutoff voltage of 2.5V, and left to stand for 4 hours. After that, it was first charged at a constant current of C / 3 to the cutoff current of 1A, and then charged at a constant voltage of C / 20 to the cutoff current of 1A. It was left to stand for 4 hours, and then discharged at a constant current of 1C to the cutoff voltage of 2.5V. It was left to stand for 4 hours. Then the constant current charging of C / 3, constant voltage charging of C / 20, constant current discharging of 1C and subsequent standing steps were repeated twice.

[0109] The specific steps for testing the effect of charging rate on remaining capacity are as follows: After charging or discharging the battery to its highest or lowest cutoff voltage at different rates under a constant ambient temperature, the battery is left to stand for 4 hours. At this point, the open-circuit voltage of the battery is relatively stable. Then, the battery is charged or discharged again to the cutoff voltage using a small current at a rate of C / 25 to study the remaining capacity under different charge / discharge rates.

[0110] S102: Half-cell microscopic performance test of the battery:

[0111] Batteries numbered 1-4 were charged to full capacity using a constant current and constant voltage method. The batteries were then disassembled, and samples of the intact negative electrode were taken for XRD testing. The scanning angle range was 15-35 degrees, and the scanning speed was 0.013 degrees per step. The test results are as follows: Figure 4 As shown.

[0112] The capacity characteristics, internal resistance characteristics, open-circuit voltage characteristics, and capacity increment curve characteristics of the full cell are analyzed:

[0113] Capacity characteristic analysis: When the battery is discharged at discharge rates of C / 25, C / 10, C / 5, C / 3, C / 2, 1C, and 2C, the total discharge capacity of the battery gradually decreases as the discharge rate gradually increases. Figure 5 As shown.

[0114] Internal resistance characteristic analysis: The ohmic internal resistance of the battery under different states of charge was obtained through HPPC experiments. It was found that the relationship curves between the ohmic internal resistance and SOC of batteries under different health states were similar.

[0115] Open-circuit voltage characteristic analysis: such as Figures 6-7 As shown, the open-circuit voltage versus state of charge curves are presented, based on rated capacity and aged capacity, respectively. Figure 6 As shown, with battery aging and degradation, the OCV-SOC curve shifts to the left. Figure 7 As shown, the open-circuit voltage curves obtained under different health conditions with the aged capacity as a reference show similar trends, with some fluctuations only appearing in the higher and lower SOC ranges.

[0116] Capacity increment curve characteristic analysis: Capacity increment curves of batteries in different health states under charging conditions were obtained. With the increase of aging, the voltage and peak height of the first peak do not change much, while the voltage and peak value of the second and third peaks change more significantly. The peak value of the IC curve gradually decreases, and the voltage value corresponding to the peak point also gradually shifts to the high voltage region.

[0117] Analysis of half-cell characteristics: In the lithium-intercalated state at the negative electrode, XRD testing of the negative electrode sheet produces two diffraction peaks with high diffraction intensity, namely LiC6 and LiC. 12 Among them, the diffraction intensity corresponding to LiC6 decreases as the battery health decreases, while that of LiC... 12 The corresponding diffraction intensity increases as the health status decreases.

[0118] S2: Based on the parameters obtained from the full-cell macroscopic performance test and the half-cell microscopic performance test in S1, the internal aging mechanism of the battery is analyzed macroscopically and microscopically respectively. The macroscopic and microscopic analysis results are then correlated and quantitatively evaluated to derive a correlation quantitative evaluation method.

[0119] S201: Macroscopic analysis of the internal aging mechanism of the battery is performed using the open-circuit voltage curve method and the capacity increment curve method, respectively.

[0120] The specific steps of the open-circuit voltage curve method are as follows:

[0121] like Figure 8 As shown, the capacity ratio CR of the battery is calculated as follows: an open-circuit voltage curve is established using the charge and discharge data of the battery at a rate of C / 20 and below. Then, the voltage of the battery after 4 hours of rest following the completion of the charge or discharge experiment at different rates is marked as the resting voltage at the end of charging (EOC-RCV) or the resting voltage at the end of discharging (EOD-RCV). Based on the obtained resting voltages at the end of charging (EOC-RCV) and discharging (EOD-RCV), the state of charge at the end of charging (EOC-SOC) and the state of charge at the end of discharging (EOD-SOC) are found on the open-circuit voltage curve adjusted under different health conditions.

[0122] The capacity ratio CR is the ratio of the battery's capacity when charged or discharged at a certain rate to the ΔSOC (state of charge) estimated from the charge / discharge rest voltage obtained through the adjusted open-circuit voltage curve.

[0123]

[0124] In the formula, It refers to the amount of battery power that can be charged or discharged at a certain rate. It is the difference between the state of charge (SOC) inferred from the resting voltage EOC-RCV at the end of charging and the resting voltage EOD-RCV at the end of discharging on the open-circuit voltage curve.

[0125] Calculation and verification of remaining capacity: To determine the remaining capacity of the battery, the state of charge (SOC) needs to be converted into the corresponding capacity. The conversion between SOC and capacity is achieved through formula (2), as shown in the following formula:

[0126]

[0127] In the formula, It is the remaining capacity of the battery after the discharge rate has been affected when the battery is discharged; It is determined by locating the SOC corresponding to the resting voltage at the end of battery discharge on the open circuit voltage curve, i.e., EOD-SOC;

[0128] like Figure 9 As shown, the calculated remaining capacity affected by the rate is presented. Additionally, to verify the accuracy of the calculated remaining capacity, the tested remaining capacity is also presented. During the experiment, batteries AA to AAA were discharged to their cutoff voltage at a low rate of C / 25 to obtain the remaining capacity not released due to the rate effect. It can be seen that the tested remaining capacity affected by the rate is basically consistent with the calculated remaining capacity, with a maximum error of 27 mAh.

[0129] Determining kinetic losses: After the battery has fully discharged, the EOD-RCV increases due to kinetic losses. These kinetic losses are related to the battery's charge / discharge rate. The capacity loss caused by kinetic losses is quantitatively calculated using the remaining capacity. The calculation formula is as follows:

[0130]

[0131]

[0132] In the formula, This refers to the capacity loss caused by kinetic energy loss in the battery. This is the rated capacity of the new battery; The capacity is due to the existence of dynamic losses;

[0133] Determine the cyclic lithium-ion loss (LLI) and active material loss (LAM): Calculate the magnitude of the cyclic lithium-ion loss and active material loss that are the essential causes of battery aging using formula (5);

[0134]

[0135] In the formula, It is the sum of the loss of cyclic lithium ions and the loss of active materials within the battery; This is the battery capacity in its current healthy state.

[0136] like Figure 10 As shown, after considering kinetic losses, the cyclic lithium-ion losses and active material losses calculated using different scaling factors are basically the same, and generally exhibit a linear relationship.

[0137] The specific steps of the capacity increment curve method are as follows:

[0138] Electrochemical characteristic analysis of the battery revealed that after lithium ions are extracted from the positive electrode, they pass through the electrolyte and separator before being embedded in graphite. The analysis also identified five peak stages that graphite undergoes during the transformation into lithium-carbon compounds. The larger the peak value of the characteristic peak, the faster the chemical reaction at that point; compared with the other three characteristic peaks, as well as The characteristic peaks are relatively weak, and the lithium iron phosphate cathode corresponds to two stages: the single-phase solid solution region (I) at both ends and the pseudo-binary Li. x FePO4-Li 1-y The phase transition stage (II) of FePO4. The dQ / dV peak of the lithium iron phosphate full cell corresponds precisely to the convolution effect between the pseudo-binary phase transition stage of the positive electrode and the five reaction stages of the graphite in the negative electrode.

[0139] like Figure 11 As shown, three relatively clear characteristic peaks can be observed on the battery's capacity increment curve. The capacity increment curve is constructed using capacity and voltage data corresponding to charging at rates of C / 20 and below. Based on their order of appearance during charging, from left to right, they can be divided into three peaks: Peak A, Peak B, and Peak C, denoted as Peak A, Peak B, and Peak C, respectively. For the positive electrode, its voltage plateau includes both Peak A and Peak B, while Peak A also exists at the negative electrode. In the region, Peak B is also located at the negative pole. Voltage position. That is, the area to the left of the positive voltage plateau of the battery and the area to the right of the negative voltage plateau. The convolution at the location corresponding to the peak forms Peak A. Similarly, the critical center of the battery's positive electrode voltage plateau coincides with the negative electrode. The corresponding location undergoes convolution, resulting in Peak B. Peak C, on the other hand, is the region where the voltage slowly increases from the high-voltage position at the positive electrode to the region at the negative electrode. It is formed by convolution at the corresponding positions.

[0140] like Figure 12 The figure shows the charging dQ / dV - charge input curves for batteries in different health states, with a factor of C / 25. Considering that the internal resistance of the lithium iron phosphate battery changes during charging, causing a shift in the characteristic peak of the IC curve, the horizontal axis is transformed into charge input when investigating the internal aging mechanism of the battery. Figure 12 As shown, the ability of lithium ions to intercalate into graphite deteriorates towards the end of charging, resulting in a significant weakening of Peak C strength. This degradation is primarily attributed to the loss of recyclable lithium ions. Peak B exhibits a slight decline in peak height; considering that Peak C does not disappear, its degradation is mainly attributed to the loss of active material.

[0141] If Peak C declines and disappears, the changes in the size and shift of Peak B are attributed to the loss of active material and cyclic lithium ions. If Peak C declines but still exists, the changes in the size and shift of Peak B are attributed to the loss of active material. The remaining amount of active material can be calculated by the change in the position of the trough between the Peak B and Peak C peaks on the dQ / dV - charge curve. Then, the amount of cyclic lithium ions lost can be calculated by subtracting the amount of active material loss from the total capacity decline, or directly based on the decline of Peak C. The specific calculations are as follows:

[0142] Calculations were performed on the active material loss (LAM) and the recyclable lithium-ion loss (LLI):

[0143] The remaining amount of active material is calculated by varying the position of the trough between the Peak B and Peak C values ​​in the dQ / dV-charge capacity curve. Then, the loss of active material is calculated.

[0144]

[0145] In the formula, The new battery exhibits capacity corresponding to the trough between Peak B and Peak C. This represents the capacity corresponding to the trough between Peak B and Peak C in the battery's current healthy state. It is the loss of active materials in the battery;

[0146] The recyclable lithium-ion loss (LLI) is calculated by subtracting the active material degradation from the total capacity degradation:

[0147]

[0148]

[0149] In the formula, The capacity loss is caused by the loss of active materials; It is the loss of recyclable lithium ions;

[0150] like Figure 13 As shown, the loss of cyclic lithium ions increases continuously as the battery health decreases, and there is a relatively good functional relationship between the two.

[0151] The cyclic lithium-ion loss (LLI) is calculated based on the peak value of the decay, using the following formula:

[0152]

[0153] In the formula, This refers to the capacity corresponding to the Peak C battery. This is the capacity corresponding to Peak C of the battery in its current healthy state.

[0154] like Figure 14 The figure shows the calculated loss of recyclable lithium ions, compared with... Figure 13 and Figure 14 It can be observed that the cyclic lithium-ion losses calculated using these two methods are almost equal, with a maximum absolute error of 0.17%.

[0155] S202: Microscopic analysis of the internal aging mechanism of the battery was performed using X-ray diffraction (XRD).

[0156] During battery charging, a large number of lithium ions are released, pass through the separator, and embed into the graphite anode; at this time, the metal lithium compound in the anode is mainly lithium-carbon (LiC). x The compound, when C is sufficient, has an intercalated amount of lithium ions that is approximately equal to the amount of recyclable lithium ions.

[0157] By comparing the diffraction peaks appearing on the XRD patterns of batteries in different aging states with standard patterns, the diffraction peaks of LiC were determined. x The corresponding characteristic peaks, in this embodiment, the diffraction peaks of the battery are mainly LiC6 and LiC. 12 The corresponding diffraction peaks; scanning from low to high angles will produce two diffraction peaks with higher diffraction intensities, respectively. , Calculate the diffraction intensity and corresponding peak area of ​​the diffraction peaks of the battery;

[0158] After normalizing C, the corresponding Li was calculated from the diffraction peak intensities. + Content, i.e., Li x C:

[0159]

[0160] In the formula, for The diffraction intensity; for The diffraction intensity; The lithium-carbon compound content is calculated based on the diffraction peak intensity.

[0161] The corresponding Li was calculated by calculating the diffraction peak area. + content:

[0162]

[0163] In the formula, for The peak area; for The peak area; The content of lithium-carbon compounds is calculated by the area of ​​diffraction peaks.

[0164] By calculating Li x The decay of C is used to characterize the loss of cyclic lithium ions;

[0165]

[0166] In the formula, It refers to the lithium-carbon compound content of the new battery; It represents the lithium-carbon compound content of the battery in its current healthy state.

[0167] Formulas (11) and (12) can be used to determine the different aging states of LiC6 and LiC batteries. 12 The diffraction intensity and peak area of ​​the characteristic peaks were used to calculate the corresponding lithium-carbon compound content, as shown in the following results. Figure 15 and Figure 16 As shown, it can be seen that with battery degradation, the calculated Li diffraction intensity and diffraction peak area decrease. x C generally exhibits a linear decline.

[0168] S203: Conduct a quantitative evaluation of the correlation based on the macroscopic and microscopic analysis results of S201 and S202;

[0169] The battery aging mechanism was quantitatively evaluated by macro-micro correlation using X-ray diffraction (XRD) testing method, which calibrates the battery health state based on kinetic loss and corrects for active material loss.

[0170] Battery health status calibrated for kinetic loss: The standard battery health status is obtained by charging and discharging the battery at a rate of C / 3. The capacity is inevitably affected by kinetic loss; therefore, the health status needs to be adjusted according to the kinetic loss. To avoid the influence of kinetic loss on the health status, a newly defined battery health status is calculated using formula (13). Figure 17 The figure shows the sum of cyclic lithium-ion loss and active material loss of AA-8 batteries at different charge / discharge rates, calculated using the open-circuit voltage curve method before and after adjusting the battery health status. It can be seen that the relationship between the battery health status and LLI and LAM is consistent both before and after the health status adjustment. The formula for calculating the adjusted battery health status is:

[0171]

[0172] In the formula, It is the capacity ratio of the new battery; It is the capacity ratio of the battery in its current state; This is the battery health state considering kinetic losses;

[0173] like Figure 18 The figure shows the cyclic lithium-ion loss and active material loss calculated from the IC curve before and after health status adjustment. It can be seen that the functional relationship between cyclic lithium-ion loss and health status calculated using the IC curve method is better after health status adjustment compared to before; while the relationship between active material loss and health status remains basically consistent before and after health status adjustment.

[0174] To verify the accuracy of the calculated cyclic lithium-ion loss and active material loss using the IC curve method, such as... Figure 19 The figure shows the sum of cyclic lithium-ion loss and active material loss calculated by IC curve method before and after health status adjustment. It can be seen that the sum of cyclic lithium-ion loss and active material loss is basically linear with the health status, whether before or after health status adjustment, proving that the cyclic lithium-ion loss and active material loss calculated by IC curve method are correct.

[0175] X-ray diffraction (XRD) method for correcting active material loss: To account for carbon loss and achieve separate calculation of cyclic lithium-ion loss (LLI), the IC method is used to analyze the XRD test results; the specific calculations are as follows:

[0176]

[0177]

[0178] In the formula, The loss of active material was calculated using the IC curve method; This refers to the lithium-carbon compound content considering the loss of active materials; This refers to the loss of recyclable lithium ions, taking into account the loss of active materials.

[0179] like Figure 20 As shown, when characterizing the loss of cyclic lithium ions using XRD analysis, the loss is determined by Li... x The relationship between cyclic lithium-ion loss and health status is obtained after removing the influence of negative electrode active material loss when calculating Li content. For example... Figure 18 (b) and Figure 20 The comparison shows that the cyclic lithium-ion loss calculated by removing the influence of active material loss in the XRD test analysis method is almost equal to the cyclic lithium-ion loss calculated by the IC curve method, which also proves the correctness of the IC curve method and the XRD test analysis method.

[0180] S3: Validate the quantitative evaluation method of correlation derived in S2:

[0181] Based on the constant current charge-discharge tests at different rates in S101, the IC curves at different rates were obtained, and the influence of the rate on the IC curves was derived:

[0182] like Figure 21 The image shows a comparison of the IC curves of the test battery at charge / discharge rates of C / 25, C / 10, C / 5, C / 3, C / 2, 1C, and 2C. The IC curves show that as the charge rate increases, the peak position shifts significantly due to the polarization effect. When the battery is charging, the IC curve shifts towards higher voltage; when the battery is discharging, the IC curve shifts towards lower voltage. Furthermore, as the charging or discharging current increases, the characteristic peaks of the IC curve broaden, but the extent of this broadening varies for different characteristic peaks. During charging, except for the 2C rate, the dQ / dV peak intensity approaches zero when the cutoff voltage is reached at all other rates.

[0183] Using the IC curve at C / 25 rate as the research object, the internal aging mechanism of batteries No. 1 to No. 8 is characterized. Figure 22The image shows the IC curves of batteries in different health states, with a rate of C / 25. It can be seen that the peak voltages corresponding to Peak C, Peak B, and Peak A do not shift significantly; the peak height of Peak A does not change much, the peak height of Peak B decreases only slightly, and the peak height of Peak C gradually decreases as the health state deteriorates. (Extraction) Figure 22 The peak height and peak area of ​​different characteristic peaks are as follows: Figure 23 As shown in the figure, the peak height and peak area of ​​the different peaks generally follow the same trend. Since Peak C, although degraded due to battery aging, still exists, the degradation of Peak A and Peak B can be attributed to the loss of active materials, while the degradation of Peak C can be attributed to the loss of cyclic lithium ions. Since the area of ​​the envelope between the characteristic peaks of the IC curve and the voltage represents the amount of charge the battery receives within the corresponding voltage range, the loss of active materials can be calculated based on the peak area degradation of Peak A and Peak B. Then, the loss of cyclic lithium ions can be characterized by subtracting the active material loss from the total capacity degradation or by the peak area degradation of Peak C.

[0184] The loss of cyclic lithium ions and the loss of active materials can be calculated using the characteristic peak area, as shown in the following formula:

[0185]

[0186]

[0187] In the formula, It is the sum of the peak areas of the new battery Peak B and Peak A; It is the sum of the peak areas of Peak B and Peak A of the battery under its current healthy state; It is the Peak C area of ​​the new battery; It is the area of ​​Peak C under the current healthy state.

[0188] like Figure 18 and Figure 24 The comparison shows that the relationships between active material loss and cyclic lithium-ion loss calculated using traditional IC curves and dQ / dV-charge capacity curves are very similar to those between the active material loss and the health state. The graph shows that the loss of active material increases continuously as the health state declines. Before reaching 80% of the health state, the loss of active material is relatively small and its contribution to capacity decay is not significant; at this point, the loss of cyclic lithium-ions generally exhibits a linear trend.

[0189] To more intuitively illustrate the difference between active material loss and cyclic lithium-ion loss calculated using traditional IC curves and dQ / dV-charge capacity curves, the results calculated by the two methods are compared. The results are as follows: Figures 25-26 As shown, the active material loss and cyclic lithium-ion loss calculated by these two methods are basically the same, with the maximum absolute error of the calculated LLI and LAM being only 0.04%.

[0190] In the offline calibration module, the battery is first subjected to hybrid power pulse characteristic testing and low-rate charge-discharge testing. Based on the hybrid power pulse characteristic test results, the battery impedance change pattern is analyzed, and the kinetic loss is calculated based on the relationship between charging rate and impedance. Furthermore, the corrected IC curve is obtained by differentiating the charging voltage and charged capacity data after eliminating kinetic loss. The voltage change caused by the kinetic resistance experienced by the battery during charging can be expressed as:

[0191]

[0192] In the formula, It is a voltage deviation caused by dynamic resistance; Indicates the charging current; It is the battery impedance.

[0193] After calculating the kinetic losses experienced by the battery, the battery charging voltage can be corrected using the following formula:

[0194]

[0195] The loss of battery active material is calculated based on the peak area decay of Peak A and Peak B, and the loss of cyclic lithium ions is calculated based on the peak area decay of Peak C, thus establishing an offline calibration function between the characteristic peak area and LLI and LAM. To verify the accuracy of the function, a fully charged full cell is disassembled, and the resulting negative electrode is subjected to XRD testing; then, the diffraction peak intensity is calculated to determine the lithium-carbon compound content, and further, the loss of cyclic lithium ions inside the battery is calculated.

[0196] In the online estimation module, the current magnitude corresponding to different characteristic peaks of the IC curve within the voltage range is first analyzed based on the measured voltage and current data. Then, the corresponding kinetic correction is performed based on the corresponding current. Further, the local IC curve of the battery is obtained by differentiating the corrected voltage based on the charged capacity. Then, the area of ​​the characteristic peak is calculated and the corresponding peak area is substituted into the offline calibration function relationship, finally realizing the quantitative characterization of the loss of cyclic lithium ions and active materials.

[0197] To validate the method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation, verification batteries of sizes 9-12 were selected for method testing. The capacity ratio and health status of the verification batteries are shown in Table 2.

[0198] Table 2. Capacity ratio and health status of No. 9-No. 12 batteries

[0199]

[0200] Develop a quantitative calculation system for aging mechanisms based on capacity increment curves, such as... Figure 27 As shown, the functional relationships between the peak area of ​​Peak C and the cyclic lithium-ion loss function, as well as the peak areas of Peak A and Peak B and the loss of active material, were calibrated. Figure 28 and Figure 29 The curves showing the relationship between the peak area of ​​Peak C and the loss of cyclic lithium ions, as well as the curves showing the relationship between the peak areas of Peak A and Peak B and the loss of active material, are presented below. The specific fitting formulas involved are as follows:

[0201]

[0202]

[0203] In the formula, It is the loss of active materials. These are the peak areas of Peak A and Peak B. It is the loss of recyclable active lithium ions. It is the area of ​​Peak C. It is the coefficient of determination.

[0204] like Figure 30 The graph shows the capacity increment curves of verification batteries No. 9 through No. 12, calculated based on battery voltage and charge level. It can be seen from the graph that Peak A and Peak B show slight capacity degradation as the battery degrades, but Peak C shows a larger degradation.

[0205] The peak areas corresponding to the three characteristic peaks are calculated based on the IC curve of the battery, and the peak areas are substituted into formulas (20) and (21). The final results of active material loss and recyclable lithium-ion loss are as follows: Figure 31 and Figure 32 As shown in the figure, overall, both the loss of active materials and the loss of recyclable lithium ions increase with the decline in health status.

[0206] Furthermore, the sum of the active material loss and cyclic lithium-ion loss calculated for the four verification batteries was compared with the battery health degradation calculated using the capacity ratio. The error results of the sum of cyclic lithium-ion loss and active material loss obtained by these two methods are as follows: Figure 33 As shown in the figure. The results show that the sum of cyclic lithium-ion loss and active material loss calculated by the proposed quantitative calculation module of aging mechanism is compared with the battery health state degradation calculated by capacity ratio. The maximum absolute error between the two is 0.42%, which further verifies the accuracy of the proposed quantitative calculation of aging mechanism.

[0207] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0208] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation, characterized in that: Includes the following steps: S1: The macroscopic performance of the full cell and the microscopic performance of the half cell were tested using the external characteristic method and the disassembly physicochemical method, respectively. S101: Perform full-cell macroscopic performance tests on the battery to obtain the relationship between battery capacity, ohmic internal resistance, polarization internal resistance, open-circuit voltage and SOC, battery charge-discharge characteristics at different rates, and remaining capacity at different charge-discharge rates. The full battery macroscopic performance test includes capacity calibration test, hybrid power pulse characteristic test, low rate charge and discharge test, constant current charge and discharge test at different rates, and test of the effect of rate on remaining capacity. S102: Perform half-cell microscopic performance testing on the battery: After charging the full cells in different health states to full charge using a constant current and constant voltage method, the battery is disassembled; then, samples are taken from the intact negative electrode obtained from the disassembly, and X-ray diffractometer (XRD) is used to observe the changes in the electrode structure. S2: Based on the parameters obtained from the full-cell macroscopic performance test and the half-cell microscopic performance test in S1, the internal aging mechanism of the battery is analyzed macroscopically and microscopically respectively. The macroscopic and microscopic analysis results are then correlated and quantitatively evaluated to derive a correlation quantitative evaluation method. S201: Macroscopic analysis of the internal aging mechanism of the battery is performed using the open-circuit voltage curve method and the capacity increment curve method, respectively. S202: Microscopic analysis of the internal aging mechanism of the battery was performed using X-ray diffraction (XRD). S203: Conduct a quantitative evaluation of the correlation based on the macroscopic and microscopic analysis results of S201 and S202; The specific steps of S203 are as follows: The battery aging mechanism was quantitatively evaluated by macro-micro correlation using X-ray diffraction (XRD) testing method, which calibrates the battery health state based on kinetic loss and corrects for active material loss. Battery health status calibrated for kinetic loss: The standard battery health status is obtained by charging and discharging the battery at a rate of C / 3. Capacity is inevitably affected by kinetic loss; therefore, the health status needs to be adjusted based on the kinetic loss. The formula for calculating the adjusted battery health status is as follows: ； In the formula, It is the capacity ratio of the new battery; It is the capacity ratio of the battery in its current state; This is the battery health state considering kinetic losses; X-ray diffraction (XRD) method for correcting active material loss: To account for carbon loss and achieve separate calculation of cyclic lithium-ion loss (LLI), the IC method is used to analyze the XRD test results; the specific calculations are as follows: ； ； In the formula, The loss of active material was calculated using the IC curve method; This refers to the lithium-carbon compound content considering the loss of active materials; This considers the loss of recyclable lithium ions due to the loss of active materials; S3: Validate the correlation quantitative evaluation method derived from S2.

2. The method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation according to claim 1, characterized in that: The specific steps of the capacity calibration test of S101 are as follows: If the battery is subjected to multiple charge and discharge tests, and the error in the amount of electricity released in three consecutive tests is less than 2%, then the average amount of electricity released in the three tests is taken as the capacity of the battery in the current state. The specific steps for testing the hybrid power pulse characteristics of S101 are as follows: High-rate discharge pulses and charging pulses are applied to the battery at two different time intervals. After the pulse ends, a normal rate current is applied to the battery to release a fixed amount of charge. This cycle is repeated until all the charge in the battery is released. Based on the change in voltage difference of the battery in different pulse phases, its dynamic characteristics in multiple state of charge (SOC) regions are obtained, thereby establishing the relationship between ohmic internal resistance, polarization internal resistance, open circuit voltage and state of charge (SOC). The specific steps of the constant current charge and discharge test at different rates of S101 are as follows: At each rate, a constant current is used to continuously charge and discharge the battery to obtain the charge and discharge characteristics of the battery at different rates. The specific steps for the S101 test of the effect of the charge rate on the remaining capacity are as follows: After charging or discharging the battery at different rates to the maximum or minimum cutoff voltage at a constant ambient temperature, the battery is left to stand, and then charged or discharged again to the cutoff voltage at a small current in the small rate charge / discharge test to obtain the remaining capacity under different charge / discharge rates.

3. The method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation according to claim 2, characterized in that: The specific steps of the open-circuit voltage curve method of S201 are as follows: Calculate the battery capacity ratio CR: Establish an open-circuit voltage curve using charge and discharge data of the battery at C / 20 and below. Then, mark the voltage of the battery after completing the charge or discharge experiment at different rates as the resting voltage at the end of charging (EOC-RCV) or the resting voltage at the end of discharging (EOD-RCV). Based on the obtained resting voltage at the end of charging (EOC-RCV) and the resting voltage at the end of discharging (EOD-RCV), find the state of charge at the end of charging (EOC-SOC) and the state of charge at the end of discharging (EOD-SOC) on the open-circuit voltage curve adjusted under different health conditions. The capacity ratio CR is the ratio of the battery's capacity when charged or discharged at a certain rate to the ΔSOC (state of charge) estimated from the charge / discharge rest voltage obtained through the adjusted open-circuit voltage curve. ； In the formula, It refers to the amount of battery power that can be charged or discharged at a certain rate. It is the difference between the state of charge (SOC) inferred from the resting voltage EOC-RCV at the end of charging and the resting voltage EOD-RCV at the end of discharging on the open-circuit voltage curve. Calculation and verification of remaining capacity: To determine the remaining capacity of the battery, the state of charge (SOC) needs to be converted into the corresponding capacity. The conversion between SOC and capacity is achieved through formula (2), as shown in the following formula: ； In the formula, It is the remaining capacity of the battery after the discharge rate has been affected when the battery is discharged; It is determined by locating the SOC corresponding to the resting voltage at the end of battery discharge on the open circuit voltage curve, i.e., EOD-SOC; Determining kinetic losses: After the battery has fully discharged, the EOD-RCV increases due to kinetic losses. These kinetic losses are related to the battery's charge / discharge rate. The capacity loss caused by kinetic losses is quantitatively calculated using the remaining capacity. The calculation formula is as follows: ； ； In the formula, This refers to the capacity loss caused by kinetic energy loss in the battery. This is the rated capacity of the new battery; The capacity is due to the existence of dynamic losses; Determine the cyclic lithium-ion loss (LLI) and active material loss (LAM): Calculate the magnitude of the cyclic lithium-ion loss and active material loss that are the essential causes of battery aging using formula (5); ； In the formula, It is the sum of the loss of cyclic lithium ions and the loss of active materials within the battery; This is the battery capacity in its current healthy state.

4. The method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation according to claim 3, characterized in that: The specific steps of the capacity increment curve method in S201 are as follows: A capacity increment curve is established based on the capacity and voltage data corresponding to charging rates of C / 20 and below. The order in which these peaks appear during charging can be divided into three peaks: Peak A, Peak B, and Peak C, denoted as Peak A, Peak B, and Peak C, respectively. Electrochemical characteristic analysis of the battery reveals that the larger the peak value, the faster the chemical reaction at that point. If Peak C declines and disappears, the magnitude and shift of Peak B are attributed to the loss of active material and the loss of cyclic lithium ions. If Peak C declines but still exists, the magnitude and shift of Peak B are attributed to the loss of active material. The remaining amount of active material can be calculated by the change in the position of the trough between Peak B and Peak C values ​​on the dQ / dV - charge curve. Then, the amount of cyclic lithium ion loss can be calculated by subtracting the amount of active material decline from the total capacity decline or directly based on the decline of Peak C. The specific calculation is as follows: Calculations were performed on the active material loss (LAM) and the recyclable lithium-ion loss (LLI): Calculate the loss of active material: ； In the formula, The new battery exhibits its capacity at the trough between the Peak B and Peak C values. This represents the capacity corresponding to the lowest point between the Peak B and Peak C values ​​of the battery under its current healthy state. It is the loss of active materials in the battery; The recyclable lithium-ion loss (LLI) is calculated by subtracting the active material degradation from the total capacity degradation: ； ； In the formula, The capacity loss is caused by the loss of active materials; It is the loss of recyclable lithium ions; The cyclic lithium-ion loss (LLI) is calculated based on the peak value of the decay, using the following formula: ； In the formula, This refers to the capacity corresponding to the Peak C battery. This is the capacity corresponding to Peak C of the battery in its current healthy state.

5. The method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation according to claim 4, characterized in that: The specific steps of S202 are as follows: When the battery is charging, a large number of lithium ions are released, pass through the separator, and embed into the graphite anode. At this time, the metal lithium compounds in the anode are mainly lithium-carbon compounds. When C is sufficient, the amount of embedded lithium ions is approximately equal to the amount of recyclable lithium ions. By comparing the diffraction peaks appearing in the XRD patterns of batteries in different aging states with standard patterns, two diffraction peaks with higher intensities were observed as the scanning angle increased from low to high. , Calculate the diffraction intensity and corresponding peak area of ​​the diffraction peaks of the battery; After normalizing C, the corresponding Li was calculated from the diffraction peak intensities. + Content, i.e., Li x C: ； In the formula, for The diffraction intensity; for The diffraction intensity; The lithium-carbon compound content is calculated based on the diffraction peak intensity. The corresponding Li was calculated by calculating the diffraction peak area. + content: ； In the formula, for The peak area; for The peak area; The content of lithium-carbon compounds is calculated by the area of ​​diffraction peaks; By calculating Li x The decay of C is used to characterize the loss of cyclic lithium ions; ； In the formula, It refers to the lithium-carbon compound content of the new battery; It represents the lithium-carbon compound content of the battery in its current healthy state.

6. The method for quantitatively evaluating battery aging mechanisms based on macro-micro correlation according to claim 5, characterized in that: The specific steps of S3 are as follows: Based on the constant current charge-discharge tests at different rates in S101, the IC curves at different rates were obtained, and the influence of the charging rate on the IC curve was derived. The battery impedance variation was analyzed based on the results of the hybrid power pulse characteristic test, and the kinetic loss was calculated based on the relationship between the charging rate and impedance. The modified IC curves were obtained by differentiating the charging voltage and the charged capacity after eliminating kinetic losses. The cyclic lithium-ion loss (LLI) and active material loss (LAM) calculated using the peak area of ​​the modified IC curves were compared with the results obtained in S2 to verify the correlation quantitative evaluation method. The loss of cyclic lithium ions and the loss of active materials can be calculated using the characteristic peak area, as shown in the following formula: ； ； In the formula, It is the sum of the peak areas of the new battery Peak B and Peak A; It is the sum of the peak areas of Peak B and Peak A of the battery under its current healthy state; It is the Peak C area of ​​the new battery; It is the area of ​​Peak C under the current healthy state.

7. A system for implementing the method for quantitative evaluation of battery aging mechanism based on macro-micro correlation as described in any one of claims 1-6, characterized in that: Includes an offline calibration module and an online estimation module; The offline calibration module is used to obtain the IC curve of the battery after removing kinetic loss, and to obtain the characteristic peak area of ​​the IC curve and the offline calibration function between LLI and LAM; The online estimation module is used to obtain local IC curves based on measured voltage and current data, obtain the corresponding peak area based on the IC curves, and input the peak area into the offline calibration function to obtain the measured LLI and LAM of the battery.

8. The system for implementing the method of quantitative evaluation of battery aging mechanism based on macro-micro correlation according to claim 7, characterized in that: The offline calibration module is used to perform hybrid power pulse characteristic tests and low-rate charge-discharge tests on the battery. Based on the results of the hybrid power pulse characteristic test, the battery impedance change law is analyzed, and the dynamic loss is calculated based on the relationship between the charging rate and the impedance. The corrected IC curve is obtained by differentiating the charging voltage and the charged capacity after eliminating kinetic losses. The loss of active materials in the battery is obtained based on the peak areas of Peak A and Peak B, and the loss of cyclic lithium ions is calculated based on the peak area decay of Peak C. An offline calibration function between the characteristic peak area and LLI and LAM is established.

9. The system for implementing a method for quantitative evaluation of battery aging mechanisms based on macro-micro correlation according to claim 8, characterized in that: The online estimation module is used to analyze the current magnitude within the voltage range corresponding to different characteristic peaks of the IC curve based on the measured voltage and current data, and to make corresponding dynamic corrections based on the corresponding current. The local IC curve of the battery is obtained by differentiating the corrected voltage based on the charged capacity; then the characteristic peak area is calculated, and the corresponding peak area is substituted into the offline calibration function relationship, so as to achieve quantitative characterization of the loss of cyclic lithium ions and active materials.

Images